Welding
Handbook
Ninth Edition
Volume 4
MATERIALS AND APPLICATIONS, PART 1
Prepared under the direction of the
Welding Handbook Committee
Annette O’Brien, Editor
Carlos Guzman, Associate Editor
American Welding Society
550 N.W. LeJeune Road
Miami, FL 33126
iii
© 2011 by American Welding Society
All rights reserved
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Library of Congress Control Number: 2001089999
ISBN: 978-0-87171-759-7
The Welding Handbook is the result of the collective effort of many volunteer technical specialists who provide information to assist with the design and application of welding and allied processes.
The information and data presented in the Welding Handbook are intended for informational purposes only. Reasonable
care is exercised in the compilation and publication of the Welding Handbook to ensure the authenticity of the contents.
However, no representation is made as to the accuracy, reliability, or completeness of this information, and an independent
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iv
Printed in the United States of America
PREFACE
This is Volume 4 of the five-volume series in the Ninth Edition of the Welding Handbook. It is Materials and
Applications, Part 1, presented in ten peer-reviewed chapters covering the metallurgical properties of various forms
of ferrous metals and how these properties affect welding. The titles of the chapters in this book, which includes two
applications chapters, indicate the variety of challenges presented to welders, designers, welding engineers, and others
in the welding workplace.
The ability of scientists to examine the microstructures of the metals, identify constituent elements, and determine how
the properties of the metals can be used and controlled during welding is reflected in the updated and expanded
information in this book. Many of the best scientists in the welding industry from university, government or other
research laboratories, metals producing companies, fabricators, consulting firms, and testing facilities have stepped
forward as volunteers to update this volume. These highly regarded experts are recognized on the title pages of their
respective chapters.
Three basic chapters of this volume, Chapter 1, Carbon and Low-Alloy Steels; Chapter 2, High-Alloy Steels; and
Chapter 5, Stainless and Heat-Resistant Steels contain detailed sections on the metallurgy, composition and properties
of steels, and methods of producing high-integrity welds in carbon steels, alloy steels, and stainless steels.
Different sets of welding conditions, challenges, and solutions are presented for the specialized steels represented in
Chapter 3, Coated Steels; Chapter 4, Tool and Die Steels; Chapter 6, Clad and Dissimilar Metals; Chapter 7, Surfacing
Materials; and Chapter 8, Cast Irons. The chapters provide information on the composition, metallurgy, weldability,
and recommended welding procedures for these metals.
Two major applications are included in this volume. Chapter 9, Maintenance and Repair Welding, contains a model
for a systematic approach to the sometimes difficult procedures involved in repair welding. Chapter 10, Underwater
Welding and Cutting, contains critical information on producing strong, durable welds, sometimes under very difficult
welding conditions, for use in the severest of service conditions.
A table of contents of each chapter is outlined on the cover page, along with names and affiliations of contributors of
the updated information. A subject index with cross-references appears at the end of the volume. Appendix A contains
a list of safety standards and publishers. Frequent references are made to the chapters of Ninth Edition Volumes 1, 2,
and 3. To avoid repetition of information published in these volumes, a reference guide is presented in Appendix B.
This book follows three previously published volumes of the Ninth Edition of the Welding Handbook: Volume 1,
Welding Science and Technology, which provides prerequisite information for welding and the welding processes;
Volume 2, Welding Processes, Part 1, which contains the technical details of arc welding and cutting, the gas processes, brazing, and soldering; and Volume 3, Welding Processes, Part 2, which is devoted to the resistance, solid
state, and other welding processes, such as laser beam, electron beam, and ultrasonic welding.
The Welding Handbook Committee welcomes your comments and suggestions. Please address them to the Editor, Welding Handbook, American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126. www.aws.org.
Wangen Lin, Chair
Welding Handbook Committee
Douglas D. Kautz, Chair
Welding Handbook Volume 4 Committee
Annette O’Brien, Editor
Carlos Guzman, Associate Editor
Welding Handbook
xi
CONTENTS
ACKNOWLEDGMENTS ..................................................................................................................................... x
PREFACE ............................................................................................................................................................. xi
REVIEWERS ....................................................................................................................................................... xii
CONTRIBUTORS ............................................................................................................................................. xiii
CHAPTER 1—CARBON AND LOW-ALLOY STEELS ............................................................................... 1
Introduction .......................................................................................................................................................... 2
Welding Classifications.......................................................................................................................................... 2
Fundamentals of Welding Carbon and Low-Alloy Steels ....................................................................................... 3
Common Forms of Weld-Related Cracking in Carbon and Low-Alloy Steels ...................................................... 12
Carbon Steels ...................................................................................................................................................... 23
High-Strength Low-Alloy Steels........................................................................................................................... 41
Quenched and Tempered Steels ........................................................................................................................... 55
Heat-Treatable Low-Alloy Steels ......................................................................................................................... 67
Chromium-Molybdenum Steels ........................................................................................................................... 75
Applications ........................................................................................................................................................ 83
Safe Practices ....................................................................................................................................................... 90
Bibliography ........................................................................................................................................................ 90
Supplementary Reading List ................................................................................................................................ 92
CHAPTER 2—HIGH-ALLOY STEELS ........................................................................................................ 95
Introduction ........................................................................................................................................................ 96
Classification of High-Alloy Steels....................................................................................................................... 96
Precipitation-Hardening Steels............................................................................................................................. 98
Maraging Steels ................................................................................................................................................... 99
Nickel-Cobalt Steels .......................................................................................................................................... 108
Austenitic Manganese Steels .............................................................................................................................. 119
Applications ...................................................................................................................................................... 130
Safe Practices ..................................................................................................................................................... 133
Conclusion ........................................................................................................................................................ 133
Bibliography ...................................................................................................................................................... 134
Supplementary Reading List .............................................................................................................................. 135
CHAPTER 3—COATED STEELS............................................................................................................... 137
Introduction ...................................................................................................................................................... 138
Terneplate.......................................................................................................................................................... 138
Tin-Plated Steel (Tinplate) ................................................................................................................................. 142
Joining Processes for Tinplate............................................................................................................................ 143
Galvanized Steels ............................................................................................................................................... 145
Aluminized Steels .............................................................................................................................................. 186
Chromized Steels ............................................................................................................................................... 193
Other Coated Steels ........................................................................................................................................... 196
Painted Steels..................................................................................................................................................... 207
Applications ...................................................................................................................................................... 209
Safe Practices ..................................................................................................................................................... 216
Bibliography ...................................................................................................................................................... 217
Supplementary Reading List .............................................................................................................................. 218
CHAPTER 4—TOOL AND DIE STEELS .................................................................................................. 221
Introduction ...................................................................................................................................................... 222
Metallurgical Properties .................................................................................................................................... 222
Tool Steel Classifications ................................................................................................................................... 223
Weldability ........................................................................................................................................................ 229
vii
Heat Treatment ..................................................................................................................................................229
Arc Welding of Tool and Die Steels ....................................................................................................................233
Flash Welding and Friction Welding ...................................................................................................................244
Brazing...............................................................................................................................................................244
Tool Steel Welding Applications .........................................................................................................................246
Safe Practices......................................................................................................................................................253
Conclusion .........................................................................................................................................................253
Bibliography.......................................................................................................................................................253
Supplementary Reading List...............................................................................................................................254
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS ............................................................255
Introduction .......................................................................................................................................................256
Martensitic Stainless Steels .................................................................................................................................272
Ferritic Stainless Steels........................................................................................................................................282
Austenitic Stainless Steels ...................................................................................................................................289
Precipitation-Hardening Stainless Steels .............................................................................................................334
Superferritic Stainless Steels................................................................................................................................340
Superaustenitic Stainless Steels ...........................................................................................................................343
Duplex Stainless Steels .......................................................................................................................................351
Brazing and Soldering of Stainless Steels ............................................................................................................369
Thermal Cutting.................................................................................................................................................378
Applications .......................................................................................................................................................380
Safe Practices......................................................................................................................................................385
Bibliography.......................................................................................................................................................386
Supplementary Reading List...............................................................................................................................390
CHAPTER 6—CLAD AND DISSIMILAR METALS..................................................................................393
Introduction .......................................................................................................................................................394
Welding Variables...............................................................................................................................................395
In-Service Properties of Dissimilar-Metal Welds .................................................................................................403
Filler Metals .......................................................................................................................................................405
Welding Process Selection...................................................................................................................................412
Specific Dissimilar Metal Combinations.............................................................................................................413
Welding of Clad Steels........................................................................................................................................432
Applications .......................................................................................................................................................445
Safe Practices......................................................................................................................................................448
Bibliography.......................................................................................................................................................450
Supplementary Reading List...............................................................................................................................450
CHAPTER 7—SURFACING MATERIALS ................................................................................................453
Introduction .......................................................................................................................................................454
Fundamentals.....................................................................................................................................................454
Surfacing Variables.............................................................................................................................................461
Surfacing Processes.............................................................................................................................................469
Base Metals for Hardfacing................................................................................................................................491
Surfacing Metals ................................................................................................................................................498
Applications .......................................................................................................................................................506
Safe Practices......................................................................................................................................................511
Bibliography.......................................................................................................................................................511
Supplementary Reading List...............................................................................................................................512
CHAPTER 8—CAST IRONS .......................................................................................................................513
Introduction .......................................................................................................................................................514
Metallurgy of Cast Irons ....................................................................................................................................515
Properties of Cast Irons......................................................................................................................................519
viii
Welding Variables.............................................................................................................................................. 527
Joining Processes and Filler Metals .................................................................................................................... 535
Other Joining Processes ..................................................................................................................................... 547
Surfacing ........................................................................................................................................................... 551
Applications ...................................................................................................................................................... 553
Safe Practices ..................................................................................................................................................... 561
Conclusion ........................................................................................................................................................ 561
Bibliography ...................................................................................................................................................... 562
Supplementary Reading List .............................................................................................................................. 562
CHAPTER 9—MAINTENANCE AND REPAIR WELDING.................................................................... 565
Introduction ...................................................................................................................................................... 566
Preventive Maintenance and Corrective Repair Welding.................................................................................... 567
Systematic Planning of Repair Welding.............................................................................................................. 567
Documenting the Cause of Failure..................................................................................................................... 574
Codes, Standards, and Specifications ................................................................................................................. 576
Establishing Repair Welding Procedures ............................................................................................................ 583
Repair of Machine Components by Surfacing and Hardfacing .......................................................................... 585
Applications ...................................................................................................................................................... 591
Safe Practices ..................................................................................................................................................... 603
Conclusion ........................................................................................................................................................ 604
Bibliography ...................................................................................................................................................... 607
Supplementary Reading List .............................................................................................................................. 607
CHAPTER 10—UNDERWATER WELDING AND CUTTING................................................................ 609
Introduction ...................................................................................................................................................... 610
Preparation for Underwater Welding ................................................................................................................. 612
Fundamentals of Underwater Welding............................................................................................................... 613
Dry Hyperbaric Welding.................................................................................................................................... 616
Underwater Wet Welding................................................................................................................................... 621
Underwater Thermal Cutting ............................................................................................................................ 649
Qualification of Welding Personnel ................................................................................................................... 655
Underwater Welding Codes and Specifications .................................................................................................. 656
Underwater Weld Inspection.............................................................................................................................. 657
Applications ...................................................................................................................................................... 660
Safe Practices ..................................................................................................................................................... 664
Conclusion ........................................................................................................................................................ 669
Bibliography ...................................................................................................................................................... 670
Supplementary Reading List .............................................................................................................................. 670
APPENDIX A—SAFETY CODES AND OTHER STANDARDS ............................................................ 675
Publishers of Safety Codes and Other Standards ............................................................................................... 677
APPENDIX B—WELDING HANDBOOK REFERENCE GUIDE ........................................................... 679
MAJOR SUBJECT INDEX.......................................................................................................................... 697
Volumes 3 and 4, Eighth Edition ....................................................................................................................... 697
Volumes 1, 2, 3, and 4, Ninth Edition ............................................................................................................... 697
INDEX OF VOLUME 4, NINTH EDITION ............................................................................................... 719
ix
1
AWS WELDING HANDBOOK 9.4
CHAPTER
C H A P T E1 R 9
CARBON AND
LOW-ALLOY
STEELS
Prepared by the
Welding Handbook
Chapter Committee
on Carbon and LowAlloy Steels:
R. W. Warke, Chair
LeTourneau University
W. A. Bruce
DNV Columbus
D. J. Connell
Detroit Edison Co.
S. R. Harris
Northrop Grumman Corp.
M. Kuo
ArcelorMittal
S. J. Norton
BP America, Inc.
Welding Handbook
Volume 4 Committee
Member:
Douglas E. Williams
Consulting Engineer
Contents
Introduction
Welding Classifications
Fundamentals of
Welding Carbon and
Low-Alloy Steels
Common Forms of
Cracking
Carbon Steels
High-Strength
Low-Alloy Steels
Quenched and
Tempered Steels
Heat-Treatable
Low-Alloy Steels
ChromiumMolybdenum Steels
Applications
Safe Practices
Bibliography
Supplementary
Reading List
Photograph courtesy of W. Virginia Dept. of Transportation—High-Performance Steel Bridge over the Ohio River
2
2
3
12
23
41
55
67
75
83
90
90
92
2
AWS WELDING HANDBOOK 9.4
CHAPTER 1
CARBON AND LOWALLOY STEELS
INTRODUCTION
Carbon and low-alloy steels represent over 95% of
the construction and fabrication metals used worldwide. Good mechanical properties over a wide range of
strengths combined with relatively low cost and ease of
fabrication account for the widespread use of these
steels. These attributes make carbon and low-alloy steels
excellent choices for use in appliances, vehicles, bridges,
buildings, machinery, pressure vessels, offshore structures,
railroad equipment, ships, and a wide range of consumer products. The extensive use of these steels means
that welding, brazing, and thermal cutting are essential
processes of continuing importance.
This chapter contains information on steel compositions and properties, weldability considerations, recommended practices and procedures for welding, brazing,
and thermal cutting of carbon and low-alloy steels; and
also provides guidance on how to avoid problems when
welding these steels.1 A section on typical applications
illustrates the scope and the importance of high-integrity
welding of carbon steels and low-alloy steels.
WELDING CLASSIFICATIONS
From a weldability standpoint, carbon and low-alloy
steels can be divided into five groups according to composition, strength, heat-treatment requirements, or high1. At the time of the preparation of this chapter, the referenced codes
and other standards were valid. If a code or other standard is cited
without a date of publication, it is understood that the latest edition
of the document referred to applies. If a code or other standard is
cited with the date of publication, the citation refers to that edition
only, and it is understood that any future revisions or amendments to
the code or standard are not included; however, as codes and standards undergo frequent revision, the reader is encouraged to consult
the most recent edition.
temperature properties. Overlap exists among these groups
due to the use of some steels in more than one heattreated condition. The groups, each of which is discussed
in a section of this chapter, are identified as follows:
1.
2.
3.
4.
5.
Carbon steels,
High-strength low-alloy (HSLA) steels,
Quenched and tempered (Q&T) low-alloy steels,
Heat-treatable low-alloy (HTLA) steels, and
Chromium-molybdenum (Cr-Mo) steels.
Steels in these five groups are available in a variety of
product forms, including sheet, strip, plate, pipe, tubing, forgings, castings and structural shapes. Regardless
of the product form, in order to establish satisfactory
welding procedures, the composition, mechanical properties, and condition of heat treatment must be known,
as weldability is primarily a function of these three factors. Although most steels are used in rolled form, the
same considerations for welding, brazing and thermal
cutting apply also to forgings and castings. However,
with large forgings and castings, consideration should
be given to the effect of size or thickness with respect to
heat input, cooling rate, and restraint. Other factors to
be considered with castings are the effects of residual
elements and localized variations in composition, which
may not occur in wrought steels.
The compositions of carbon steels typically include
weight percentages (wt %) of up to 1.00% carbon, up
to 1.65% manganese, and up to 0.60% silicon. Steels
identified as low-carbon steels contain less than about
0.15% carbon; mild steels contain 0.15% to 0.30%
carbon; medium-carbon steels contain 0.30% to 0.50%
carbon; and high-carbon steels contain 0.50% to
1.00% carbon. Although wrought carbon steels are
most often used in the as-rolled condition, they are
sometimes used in the normalized or annealed condition.
AWS WELDING HANDBOOK 9.4
High-strength low-alloy steels are designed to provide better mechanical properties than conventional
carbon steels. Generally, they are classified according to
mechanical properties rather than chemical compositions. Their minimum yield strengths commonly fall
within the range of 290 megapascals (MPa) to 550 MPa
(40 000 pounds per square inch [40 kips per square
inch {ksi} to 80 ksi]). These steels usually are welded in
the as-rolled, normalized, or precipitation-hardened
condition.
Quenched and tempered steels are a group of carbon
and low-alloy steels that generally are heat treated by
the producer to provide yield strengths in the range of
340 MPa to 1030 MPa (50 ksi to 150 ksi). In addition,
they are designed to be welded in the heat-treated condition. Normally, the weldments receive no postweld heat
treatment (PWHT), unless it is required to achieve dimensional stability or to conform to a construction code.
Many grades of heat-treatable low-alloy steels
exhibit poor weldability. These steels generally have
higher carbon content than high-strength low-alloy or
quenched and tempered steels. Consequently, although
they are capable of higher strengths, they may lack
toughness in the as-welded condition and may be susceptible to cracking in the heat-affected zone (HAZ).
Postweld heat treatment may reduce the risk of cracking and enhance the notch toughness of heat-treatable
low-alloy steel weldments.
Chromium-molybdenum steels are used primarily for
service at elevated temperatures up to about 700°C
(1300°F) to resist creep and corrosion for applications
in power plants, chemical plants, or petroleum refineries. Chromium-molybdenum steels may be welded in
various heat-treated conditions (i.e., annealed, normalized and tempered, or quenched and tempered).
Postweld heat treatment is often required by fabrication
codes to improve ductility, toughness, and corrosion
resistance, and to reduce stresses caused by welding.
FUNDAMENTALS OF WELDING
CARBON AND LOW-ALLOY
STEELS
Carbon steels and low-alloy steels can be welded by
arc, oxyfuel gas, resistance, electron beam, laser beam,
electroslag, and solid-state welding processes. These steels
also can be joined by brazing, soldering, and adhesive
bonding.2 Subsequent sections of this chapter provide
2. Standard welding terms and definitions used in this chapter are from
American Welding Society (AWS) Committee on Definitions and Symbols, 2010, Standard Welding Terms and Definitions, AWS A3.0M/A3.0:
2010, Miami: American Welding Society.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
3
information on the most commonly used joining processes for each of the five steel groups previously described.
METALLURGY AND WELDABILITY
The versatility of steel as an engineering material can
be attributed to the wide variety of microstructures that
can be created through changes in composition and
processing. Understanding the basic properties of these
structures and the effects of changes in chemistry are
essential in designing and fabricating welds that are fit
for their intended purpose.
PHASES AND MICROSTRUCTURES
In metals and other material systems, a phase is considered to be a physically homogeneous and distinct
portion of the system.3 It is bound by compositional
limits, which vary with temperature. The term microstructure is used because virtually all of the geometric
features of the phases and other structures that determine the properties of steels are observable only with
the aid of microscopy. The microstructure of a type of
steel is dependent on the amount of the various alloying
elements that it contains, and also on both its present
temperature and thermal history. The following section
outlines the phases of the iron-iron carbide system, of
which steel is composed, and the microstructures commonly observed in steel.
Ferrite
Pure iron (Fe) at room temperature has a body-centered cubic (BCC) crystal structure. Its unit cell (smallest repeating unit) is a cube with iron atoms at each
corner and one iron atom in the center, as depicted in
Figure 1.1. The atomic packing factor, or volume fraction occupied by atoms, of this structure is 0.68. The
phase of iron exhibiting this structure is called either
alpha (α)-iron or α-ferrite. The shape of its octahedral
interstices gives it very low solubility for carbon, on the
order of 10–5% at room temperature, gradually increasing to a maximum of 0.022% at 727°C (1341°F). At
temperatures below 770°C (1418°F), ferrite is ferromagnetic and thus can be attracted by a magnet, while
at temperatures between 770°C and 910°C (1418°F and
1675°F), it is paramagnetic. The temperature at which
the change in magnetic properties takes place, changing
3. Sinha, A. K., 1989, Ferrous Physical Metallurgy, Boston: Butterworth
Publishers.
4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Source: American Welding Society (AWS), 2008, Welding Inspection Technology, 5th
ed., Miami: American Welding Society.
Figure 1.1—Body-Centered Cubic Unit Cell
AWS WELDING HANDBOOK 9.4
ter. The phase of iron exhibiting this structure is called
gamma (γ)-iron or austenite, and its lattice parameter is
0.359 nm. The changing packing factor between ferrite
and austenite is responsible for a volumetric contraction
when ferrite changes to austenite on heating above
912°C (1674°F). Austenite is paramagnetic. In spite of
closer packing of austenite, the more open shape of its
octahedral interstices makes carbon much more soluble
in austenite than in ferrite. The sudden change in carbon solubility as iron changes from FCC to BCC on
cooling below 912°C (1674°F) is the primary reason
the mechanical properties of steels can be so widely varied, and thus can be “tailored” for specific applications.
Delta Iron
from ferromagnetic to paramagnetic (770°C [1418°F]),
is called the Curie temperature.
In pure iron, the structure reverts to BCC from
1394°C (2541°F) to its melting temperature at 1538°C
(2800°F). This form of iron is referred to as delta (δ)iron or δ-ferrite. The result is another volume change
when the transformation from austenite to δ-iron
occurs, except that in this case it is a volumetric
expansion.
Austenite
Cementite
At temperatures between 912°C and 1394°C (1674°F
and 2541°F), the stable crystal structure of pure iron is
face-centered cubic (FCC). This structure is so named
because its unit cell is a cube with iron atoms at each
corner and in the center of each cube face. An FCC unit
cell is shown in Figure 1.2. The atomic packing factor
for this atom arrangement is 0.74, which represents the
closest possible packing for spheres of uniform diame-
Iron and carbon readily form a metastable intermetallic compound called cementite. It is represented by
the chemical formula Fe3C. Given enough time, cementite will decompose into iron and graphite. However,
once formed, cementite is stable enough to be treated as
an equilibrium phase. Unlike the ferrite and austenite
phases of iron, cementite is noncubic and has an orthorhombic crystal structure. If tested by itself, it exhibits
essentially zero tensile ductility and a Brinell hardness
(HB) of more than 700 HB.4
Iron-Iron Carbide Phase Diagram
Source: American Welding Society (AWS), 2008, Welding Inspection Technology, 5th
ed., Miami: American Welding Society.
Figure 1.2—Face-Centered Cubic Unit Cell
A phase diagram is a graphic representation of the
temperature and composition limits for the various
phases exhibited by a particular material system. The
most common phase diagrams are binary equilibrium
diagrams. For two-component systems, binary equilibrium diagrams represent the phases and also their
respective compositions and mass fractions that are stable at any temperature under steady-state conditions.
Figure 1.3 shows the iron-cementite (Fe-Fe3C) equilibrium phase diagram for steels and cast irons. As noted
in the axis labels, very small changes in the carbon
concentration have a large effect on phase equilibrium.
The effect of carbon on the stability of austenite also is
4. Davis, J. R., ed. 1992, ASM Materials Engineering Dictionary, Materials Park, Ohio: ASM International.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
5
Source: Linnert, G. E., 1994, Welding Metallurgy, Vol. 1, 4th ed., Miami: American Welding Society.
Figure 1.3—Fe-Fe3C Phase Diagram for Steels and Cast Irons
shown in the diagram. Carbon is an austenite stabilizer,
and in sufficient concentration, enables austenite to
remain stable to temperatures well below the equilibrium temperature of austenite in pure iron. The diagram illustrates that over certain ranges of composition
and temperature, it may be possible for two phases to
coexist. For example, the triangular region bounded by
points G, S, and P in the diagram contains a two-phase
region known as the intercritical region, within which
both ferrite and austenite are stable. The line from
Point G to the point labeled S on the A3 line represents
the locus of upper critical temperatures, that is, temperatures above which austenite becomes the only stable phase.
The horizontal line at 727°C (1341°F) is commonly
referred to as the A1 line or lower critical temperature.
The microstructural behavior of steel heated into the
intercritical region can be understood in a practical way
6
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
by considering a steel containing 0.20% carbon and
being held at 780°C (1440°F). Both ferrite and austenite would be present, with all of the ferrite containing
~0.02% carbon and all of the austenite containing
~0.42% carbon. These values correspond to the equilibrium carbon concentrations for ferrite and austenite
at 780°C (1440°F), as indicated by the phase boundary
intersections of a horizontal “tie” line drawn across this
region at 780°C (1440°F). It should be noted that while
the composition of each individual phase varies with
temperature, the overall or “bulk” composition remains
constant at 0.20% carbon.
For a specified composition, the mass fractions of the
two phases present at a given temperature may be calculated using what is referred to as the lever law. The
bulk composition of the steel may be considered as the
fulcrum of a lever, while the horizontal line between the
compositions of the coexisting phases represents the
lever. The amount of each phase present must balance
the lever. In the preceding example, the equilibrium percentage of ferrite in a 0.20% carbon steel being held at
780°C (1440°F) can be expressed as follows:
0.42 – 0.2---------------------------× 100% = 55% ferrite
0.42 – 0.02
(1.1)
Phase Morphologies
Pearlite
Pearlite was named for its mother-of-pearl appearance
when optically observed without sufficient magnification to resolve its microstructural features. It is a lamellar product of austenite decomposition, consisting of
alternating lamellae of ferrite and cementite. Rather
than grains, pearlite forms nodules.7 Each nodule is
composed of colonies of parallel lamellae which have
different orientations from those of adjacent colonies,
as shown in Figure 1.4. When resolved under a microscope, pearlite often resembles the stripes on a zebra.
Very fine pearlite is often difficult to resolve and may
appear as very dark or even black grains. This difficulty
led early metallurgists to identify fine pearlite as a separate phase. Pearlite may form under isothermal, continuous cooling, or directional growth conditions.
Bainite
There are two classic morphologies of bainite in ferrous microstructures: upper bainite and lower bainite.
These two types form over different temperature
ranges; upper bainite forms at higher temperatures than
lower bainite. Upper bainite is often characterized by a
7. See Reference 3.
Phase diagrams such as those shown in Figure 1.3
are made under equilibrium conditions; samples are
heated and cooled at very slow rates, allowing time for
atoms to diffuse and energy barriers to be overcome,
which is required for changing from one phase to
another. While this is useful for determining the transformation temperatures of the equilibrium phases,
welding normally involves dynamic thermal processes.
These rapid thermal processes typically do not allow
enough time for the nucleation and growth of equilibrium phases. When cooling is fast enough, a phase may
continue to exist below its equilibrium transformation
temperature in a phenomenon known as supercooling
or undercooling. When transformations occur as a result
of rapid cooling from elevated temperatures, the cooling
rate has a significant effect on the resulting structure.
It should be noted, as pointed out by both Linnert5
and Samuels,6 that a variety of terms have been used to
identify the same microstructures over the years. While
there have been efforts to arrive at an internationally
accepted terminology, final agreement has not been
reached. The following sections cover some of the morphologies commonly found in steels, using the nomenclature according to Samuels.
5. Linnert, G. E., 1994, Welding Metallurgy, Vol. 1, 4th ed., Miami:
American Welding Society.
6. Samuels, L. E., 1980, Optical Microscopy of Carbon Steels, Materials Park, Ohio: American Society for Metals.
Figure 1.4—Typical Lamellar Appearance
of Pearlite, 1500X Magnification
(before Reduction); Etchant: Picral
AWS WELDING HANDBOOK 9.4
feathery structure of low-carbon ferrite laths in cementite.
It forms at temperatures between 350°C and 550°C
(660°F and 1020°F).8 Lower bainite generally forms
below 350°C (660°F), although carbon content may
influence the temperature at which lower bainite begins
to form. Lower bainite is characterized by a plate-like
morphology. Plates of ferrite are separated by cementite,
as in upper bainite. However, the ferrite plates that form
in lower bainite have carbide precipitates within them. 9
Martensite
Martensite has a body-centered tetragonal (BCT)
crystal structure in iron. This structure is similar to the
BCC crystal structure, except that four of the faces of
the cube are rectangular rather than square. The martensite phase is formed by a martensitic transformation,
which has been defined as the coherent formation of
one phase from another, without change in composition, by a diffusionless, homogeneous lattice shear.10 In
steels, transformation to martensite is achieved by rapid
cooling from an austenitic state. When resolved with
optical microscopy, low- to medium-carbon martensite
appears as a lathy structure, as shown in Figure 1.5.
Martensite can be differentiated from bainite by hard8. See Reference 3.
9. Bhadeshia, H. K. D. H., 2001, Bainite in Steels. 2nd ed., London:
Institute of Materials.
10. See Reference 3.
Figure 1.5—Lath-Type Martensite in a MediumCarbon Steel, As-Quenched, 2% Nital Etched,
500X Magnification (before Reduction)
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
7
ness, with martensite being harder, and by etching, with
martensite etching lighter.11
For a given steel composition, the amount of martensite formed is determined by the degree of austenite
supercooling, which is determined by the cooling or
“quench” rate imposed upon it. Figure 1.6 illustrates
this principle with a continuous cooling transformation
(CCT) diagram for a steel containing 0.76% carbon
and essentially no other alloy content.12 This steel, having a eutectoid carbon content, has perhaps the simplest
transformation behavior of any that might be considered. It should be noted that for this particular composition, 140°C (285°F) per second (as measured at
700°C (1290°F) is the slowest cooling rate that will
produce a fully martensitic microstructure. Similarly,
35°C (95°F) per second is the fastest cooling rate that
will produce a fully pearlitic microstructure. Any cooling rate between these two rates will produce a mixture
of martensite and pearlite. Also, the cooling rate
through a range of temperatures from around 800°C to
500°C (1470°F to 930°F) is crucial to determining the
amount of martensite in the resulting microstructure.
This concept is applied more specifically to the behavior
of the HAZ of steels in the section titled Carbon Equivalent in this chapter.
ALLOYS AND ALLOYING ELEMENTS
Alloys of iron containing up to approximately 1%
carbon are classified as carbon and low-alloy steels.
Carbon has a crucial influence on the mechanical properties of steel: very small changes in carbon contents
can have a significant effect. However, steels are composed not only of iron and carbon, but also contain
residual elements from processing. Steels may also contain other elements intentionally added to produce one
or more desired characteristics.
The addition of even very small amounts of other
elements to a pure metal or to a binary system like FeFe3C can significantly affect its phase equilibria. In general, alloying elements added to steels may be classified
as either austenite stabilizers or ferrite stabilizers. Austenite stabilizers expand the γ-phase field, making austenite stable over a wider range of carbon contents and
temperatures. Ferrite stabilizers shrink the γ-phase field,
promoting the formation of ferrite over a wider range
of compositions and temperatures. Additionally, some
elements significantly impede the kinetics of transformation from one phase to another, particularly the
decomposition of austenite upon cooling below A1.
They do so primarily by inhibiting the diffusion of carbon, thereby increasing the hardenability of a steel. The
11. See Reference 3 and Reference 9.
12. Callister, W. D., 2007, Materials Science and Engineering: an
Introduction, 7th ed., Hoboken, New Jersey: John Wiley & Sons, Inc.
8
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
LIVE GRAPH
AWS WELDING HANDBOOK 9.4
Click here to view
Source: Callister, W. D., 2007, Materials Science and Engineering, an Introduction, 7th ed. Hoboken, New Jersey:
John Wiley & Sons, Inc.
Figure 1.6—Continuous Cooling Transformation Diagram
for Eutectoid (0.76% C) Plain Carbon Steel
common elements found in steels and the reasons for
their presence are discussed in this section.13, 14
Carbon
Carbon has a greater effect on iron than any other
alloying element. It is a potent austenite stabilizer and
forms an interstitial solid solution in austenite. The
solid solubility of carbon in ferrite at room-temperature
is only about 0.008%, so most of the carbon is rejected
13. See Reference 5.
14. For additional information on the effects of deformation and heat
treatment, refer to American Welding Society (AWS) Welding Handbook Committee, Jenney, C. L. and A. O’Brien, eds., 2001, Welding
Science and Technology, Volume 1 of the Welding Handbook, 9th
edition, Chapter 3, pp 121–132. Miami: American Welding Society.
from solution in the form of cementite as the temperature falls below A1 temperature (refer to Figure 1.3). The
maximum attainable hardness for any particular microstructure in a steel is determined almost entirely by the
amount of carbon it contains.
Manganese
Manganese (Mn) is added to virtually all steels
because it has several helpful attributes and is inexpensive compared to most other alloying elements. Manganese combines with sulfur to form manganese sulfide
(MnS) and combines with oxygen to form manganese
oxide (MnO). In molten steel, manganese reduces the
amount of both oxygen and sulfur in the melt by forming these compounds, most of which are removed as
AWS WELDING HANDBOOK 9.4
slag. Manganese that is not consumed in the formation
of MnS may form manganese carbide (Mn3C), which is
optically indistinguishable from cementite. It is a promoter of hardenability (the formation of martensite and
other nonequilibrium structures when cooled from
above the A3 temperature). Manganese refines pearlite
nodules and ferrite grain sizes, which increases the yield
strength of carbon steel. The combination of these
actions by manganese normally brings about an
increase in fracture toughness.
Sulfur
Although sulfur (S) may be added to steels to promote chip formation when machining, it generally is
considered a “tramp” element and held to very low levels (below 0.05%). When present in iron alloys, sulfur
can form iron sulfide (FeS), which has a relatively low
melting point (1200°C [2190°F]) compared to the iron
solidus temperature. The effect of this low-meltingpoint constituent in the manufacture of steel is known
as hot shortness, a loss of ductility at hot-working temperatures. Traditionally, FeS formation has been controlled by the addition of manganese to the melt. The
affinity of manganese for sulfur is greater than that of
iron, thus it reacts and binds with most of the sulfur in
the form of relatively innocuous manganese sulfides
(MnS). The MnS compound has a higher melting temperature and its internal surface-wetting characteristics
are less detrimental than those of FeS.
However, the deleterious effects of sulfur are of even
greater concern from a weldability standpoint, as FeS
can produce solidification cracking and HAZ liquation
cracking in fusion welds. Moreover, the MnS inclusions
formed in the steelmaking process can lead to lamellar
tearing, which is discussed in the section of this chapter
titled Lamellar Tearing. Current techniques for sulfur
control can reliably achieve residual sulfur contents
below 0.005%.
Steels to which sulfur has been intentionally added to
enhance machinability (i.e., with sulfur content of
0.08% up to about 0.35%) are called free-machining
steels and generally should not be welded.
Phosphorus
Very small additions of phosphorus (P) can increase
the strength, hardness, and corrosion resistance of steel.
However, like sulfur, phosphorus is considered a tramp
element. In the solid state, phosphorus forms Fe3P,
which is extremely brittle. The presence of this compound in steel causes cold shortness, the tendency to
crack during cold working. Phosphorus causes a
decrease in fracture toughness of steels designed to be
strengthened by heat treatment. Another problem
caused by phosphorus is segregation during solidifica-
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
9
tion. Phosphorus tends to become enriched in the metal
that solidifies last, and as a weak ferrite former, promotes the formation of ferrite and its rejection of carbon into the surrounding metal. This results in bands in
the microstructure that contain less cementite and more
ferrite. These negative effects are incentives to keep the
phosphorus content to 0.04% or less in most steels.
Silicon
Silicon (Si) is used in the steelmaking process to
remove oxygen from the melt. When silicon is not used
as a killing agent (removing oxygen from molten steel)
it is only a residual element and may be found in trace
amounts (approximately 0.008%). Silicon is a potent
ferrite stabilizer that can prevent the transformation to
austenite altogether if it is present in large enough
quantities. Silicon also promotes the fluidity of molten
steel, which makes it a useful addition in casting and
welding applications.
Copper
Copper (Cu) is a very weak austenite stabilizer, but it
is used in alloying for other purposes. Until the early
1900s, copper was regarded only as a tramp element
responsible for surface checking and hot cracking. This
problem was solved with the addition of nickel. In
modern alloys, the motive for most copper additions is
the significant increase in corrosion resistance imparted by
copper in concentrations above 0.20%. Also, the addition
of about 1.25% copper with an equal amount of nickel
can form precipitates that significantly increase hardness.
Chromium
Chromium (Cr) is a very potent ferrite stabilizer.
Like silicon, sufficient chromium can completely prevent the transformation from ferrite to austenite in
steels. Chromium has a strong effect on the corrosion
resistance of steel, and when present in sufficient quantities, it promotes the formation of a protective oxide
surface film, which is the basis of the stainless steel
alloys. Chromium is also added to maintain the
strength of steel at elevated temperatures and it strongly
increases the hardenability of steel.
Nickel
Nickel (Ni) is a strong austenite stabilizer and is
added to stainless steels to counterbalance the ferritestabilizing effect of chromium. Nickel is completely soluble in FCC iron, and when alloyed with iron in concentrations greater than about 25%, it makes austenite
stable at all temperatures. Nickel also has the unique
ability to increase hardenability while also increasing
10
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
fracture toughness. Nickel has little affinity for oxygen
and carbon and therefore forms no carbides or oxides
when alloyed with iron. As previously mentioned,
nickel is used in some steels with copper as a precipitation-hardening agent.
Molybdenum
Molybdenum (Mo) is a potent ferrite stabilizer. Additions to iron of just 3% will cause the retention of ferrite at all temperatures. Molybdenum readily forms
carbides and increases hardenability. For this purpose,
it is frequently added in concentrations ranging from
0.25% to 0.5%, along with chromium and nickel. In
steels to be used at elevated service temperatures,
molybdenum may be added in amounts from 0.5% to
4% to improve strength and creep resistance. In steels
with low alloy composition, molybdenum is added in
small amounts (0.05% to 0.25%) along with manganese and some nickel to suppress the formation of
pearlite or to produce fine carbide lamellae that reduces
the size of pearlite areas.
Niobium
Niobium (Nb) has a BCC crystal structure and is a
ferrite stabilizer when added to iron. Prior to the standardization of element names, niobium was also known
as columbium. Niobium is added to steels in very small
amounts to form niobium carbide and carbonitride precipitates, which increase strength and inhibit grain
coarsening at temperatures above A3. Niobium carbides
begin to precipitate in steel at about 1200°C (2190°F);
additions of niobium as small as 0.05% can produce a
significant increase in strength. When properly controlled, niobium additions also promote fine ferrite
grain size, which tends to improve toughness. Niobium
is commonly added with vanadium and nitrogen to
form complex niobium and vanadium carbonitrides.
The optimum size and distribution of niobium-based
precipitates and refinement of ferrite grains is achieved
by carefully designed and controlled hot-rolling
sequences. This technology, called thermomechanically
controlled processing (TMCP), and the steels produced
by it, are discussed in the High-Strength Low-Alloy
Steel section of this chapter.
Vanadium
Vanadium (V), like niobium, is a ferrite stabilizer. It
has traditionally been added to steels, especially tool
steels, to promote hardenability. When a sufficient
amount of manganese is present, small additions of
vanadium (0.05% to 0.10%) provide effective strengthening. A benefit of vanadium is the reduced coarsening
of austenite grains when heated above the A3 tempera-
AWS WELDING HANDBOOK 9.4
ture. Vanadium has a strong affinity for nitrogen and a
tendency to form carbides. Strengthening of steels
alloyed with vanadium is achieved by controlled rolling, heat treatment, or a combination of the two.
Aluminum
Aluminum (Al) is a potent ferrite stabilizer; as little
as 1% added to iron will make ferrite stable at all temperatures. It is used primarily in the steelmaking process
to remove oxygen from the melt by forming Al2O3.
Aluminum also has the ability to form aluminum
nitride (AlN) particles, which act to restrict austenite
grain coarsening at temperatures above the A3. A beneficial side effect of the AlN reaction is to counteract the
adverse effects of excess nitrogen on the toughness of
ferrite.
CARBON EQUIVALENT
The heat of welding, thermal cutting, and brazing
causes changes in the microstructure and mechanical
properties in a region of the heated steel that is referred
to as the heat-affected zone (HAZ). The width of this
region and the microstructure(s) it contains depend on
the composition and prior microstructure of the steel,
the peak temperature reached, and the rates of heating
and cooling. This heating-cooling thermal cycle may
result in the formation of martensite in the weld metal
or HAZ, or both.15 The amount of martensite formed
and the resulting hardness of these areas depend on the
carbon and alloy content, the length of time at elevated
temperatures, and the subsequent cooling rate through
a critical temperature range. This range is usually considered to be 800°C to 500°C (1470°F to 930°F), and
the cooling rate through the HAZ is often stated in
terms of the length of time within the range, designated
Δt8–5.16
The overall alloy content of a type of steel determines its hardenability (the minimum cooling rate necessary to produce martensite). However, carbon content
alone determines the maximum attainable hardness of
any martensite that does form. Figure 1.7 shows this
relationship for steels that are 50% and 100% martensite after quenching. High hardness levels increase susceptibility to hydrogen cracking in the weld or HAZ,
thus the degree of hardening is an important consideration in assessing the weldability of a carbon or lowalloy steel. The weldability of steels, particularly resistance to hydrogen cracking, generally decreases with
increasing carbon or martensite in the weld metal or
HAZ, or both.
15. See Reference 3.
16. See Reference 3.
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AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
11
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Although carbon is the most significant alloying element affecting weldability of steels, the effects of other
elements can be estimated by equating them to an
equivalent amount of carbon. Thus, the effect of total
alloy content can be expressed in terms of a carbon
equivalent (CE). An empirical formula that may be used
for judging the risk of underbead cracking in carbon
steels is the following:17
100% MARTENSITE
60
50
50% MARTENSITE
40
30
(1.2)
20
( Mn + Si ) ( Cr + Mo + V ) ( Ni + Cu )
CE = C + ------------------------- + -------------------------------------- + -------------------------6
5
15
10
0
0
0.20
0.40
0.60
0.80
1.00
CARBON, wt %
Figure 1.7—Relationship between Carbon
Content and Maximum Hardness of Steels with
Microstructure of 50% and 100% Martensite
Figure 1.8 shows the general relationships between
carbon steel composition (the carbon equivalent) and
hardness, underbead cracking sensitivity, or weldability
17. American Welding Society (AWS) Committee on Structural Welding,
2010, Structural Welding Code, Steel, AWS D.1.1/D1.1M:2010, Annex I,
Miami: American Welding Society.
LIVE GRAPH
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50
90
500
80
450
70
60
50
40
30
20
MAXIMUM UNDERBEAD HARDNESS, DPH
AVERAGE UNDERBEAD CRACK SENSITIVITY, %
550
40
HARDNESS
400
30
350
300
250
BEND ANGLE
200
10
150
10
0
20
CRACK SENSITIVITY
0.30
0.40
0.50
0.60
0.70
AVERAGE BEND ANGLE AT MAXIMUM LOAD, DEGREES
MAXIMUM HARDNESS, HRC
70
0
0.80
CARBON EQUIVALENT, CE = % C + % Mn/4 + % Si/4
Figure 1.8—Relationship Between Composition and Underbead
Hardness, Crack Sensitivity, and Notched-Weld-Bead Bend Angle for
25 mm (1 in.) Thick C-Mn Steel Plate Welded with E6010 Covered Electrodes
12
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
based on the slow-bend capacity of notched weld-bead
test bars. Generally, steels with low CE values (e.g., 0.2
to 0.3) have excellent weldability; however, the susceptibility to underbead cracking from hydrogen increases
when the CE exceeds 0.40. A steel with only 0.20% C
and 1.60% Mn will have a CE of 0.60, indicating relatively high sensitivity to cracking.
COMMON FORMS OF
WELD-RELATED CRACKING
IN CARBON AND LOWALLOY STEELS
The various types of cracking, including hydrogen
cracking, solidification cracking, liquation cracking,
lamellar tearing, reheat cracking, and fatigue cracking
are discussed in this section. Methods of preventing
cracking also are described.
Surface preparation is standard practice in all welding applications, and is especially important in preventing most types of weld cracking. The presence of
impurities has a very significant effect on the various
cracking mechanisms and thus the quality of welds. Oil,
grease, dirt, rust, metal filings, paint or other coatings
must be cleaned from the surface of the steel in the
region where the weld is to be made. For example, copper residue from tools such as cooling blocks and fixturing should be removed from the surface of the steel
workpiece because copper can be a source of solidification cracking.
HYDROGEN CRACKING
Hydrogen cracking (also known as underbead cracking, cold cracking, or delayed cracking) can occur when
welding carbon and low-alloy steels.18, 19, 20 The potential for hydrogen cracking in the weld metal or heataffected zone, or both, depends on the composition,
hydrogen content, and tensile stress level of these areas.
Hydrogen cracking generally occurs at a temperature
below 150°C (300°F), either immediately on cooling or
after an incubation period of up to 48 hours. Increasing
amounts of diffusible hydrogen, more susceptible (har18. For additional information, refer to Reference 14.
19. See Reference 5.
20. For a definitive work on hydrogen cracking, refer to Bailey, N.,
and F. R. Coe, 1993, Welding Steels Without Hydrogen Cracking,
Edition: 2, illustrated; 1855730146, 9781855730144, Great Abington, Cambridge, UK: Woodhead Publishing.
AWS WELDING HANDBOOK 9.4
der) microstructures or higher tensile stresses, or all
three, increase the likelihood of cracking and shorten
the incubation period. The following sequence describes
the overall process:
1. Water (H2O) or hydrocarbon (HxCx) molecules
dissociate into atomic hydrogen in the welding
arc;
2. Atomic hydrogen readily dissolves into the weld
pool;
3. As the pool solidifies, hydrogen begins diffusing
outward into the surrounding HAZ;
4. As the welded area cools, hydrogen diffusion
slows, especially below about 200°C (390°F);
5. Over time, hydrogen accumulates at regions of
triaxial tensile stress, such as at the weld toe or
weld root at slag inclusions, or at small solidification or liquation cracks; and
6. When (or if) the hydrogen concentration at any
location exceeds a threshold value, as determined by the present stress and microstructure,
cracking begins.
Cracking sometimes occurs in the weld metal, particularly when its yield strength is over 620 MPa (90 ksi).
In general, however, alloy steels are more likely to crack
in the HAZ.
To summarize, hydrogen cracking in welded joints is
associated with the combined presence of the following
four conditions:
1. The presence of atomic (diffusible) hydrogen;
2. A susceptible microstructure, typically but not
necessarily martensitic;
3. A sustained tensile stress at the sensitive location;
and
4. A temperature below 150°C (300°F).
Hydrogen Sources
Molten steel has a high solubility for atomic (diffusible) hydrogen, which may be present due to the dissociation of water vapor or hydrocarbons in the welding
arc. The diffusion rate of atomic hydrogen in steel is
high at or near its melting temperature. Therefore, the
molten weld metal can rapidly pick up atomic hydrogen
from arc plasma. Once in the weld metal, hydrogen
atoms can diffuse rapidly into the HAZ of the base
metal.
There are several possible sources of moisture and
other hydrogenous compounds that can dissociate in
the welding arc and introduce diffusible hydrogen into
the weld metal. Sources include the filler metal, moisture in the electrode covering, welding flux, shielding
gas, or surface contaminants, such as adsorbed mois-
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
ture, hydrated rust, oil, grease, or paint on the filler
metal or base metal. The welding wire or rod may be
contaminated with lubricants used during the wiredrawing operation. In shielded metal arc welding
(SMAW), the primary sources of hydrogen are cellulose
or moisture, or both, in the electrode covering. In submerged arc welding (SAW), the primary source is moisture in the flux. In flux-cored arc welding (FCAW) and
gas-metal arc welding (GMAW) with metal-cored wire,
moisture in the core ingredients is the primary source.
Shielding gases contaminated with humid air or moisture are additional sources of hydrogen.
The American Welding Society standard AWS A4.3
describes methods for measuring the diffusible hydrogen content of welds deposited by shielded metal arc
welding, gas metal arc welding, flux cored arc welding,
and submerged arc welding processes.21 As a result of
standardized testing provided by this specification, a
diffusible hydrogen designator, H16, H8, H4, or H2,
can be attached to the classification of carbon steel and
low-alloy steel filler metals to identify the maximum
diffusible hydrogen limit the filler metal will meet.
The tendency for hydrogen cracking is approximately proportional to the logarithm of the diffusible
hydrogen content of the weld deposit. Accordingly, the
diffusible hydrogen designators in AWS filler metal
specifications are based on a geometric progression of
hydrogen content limits, as shown in Table 1.1.
A low-hydrogen electrode classified with one of these
designators is certified to meet the corresponding
hydrogen limit under the standardized test conditions
specified in AWS A4.3.22
21. American Welding Society (AWS), 2006, Standard Methods for
Determination of the Diffusible Hydrogen Content of Martensitic,
Bainitic, and Ferritic Steel Weld Metal Produced by Arc Welding,
AWS A4.3-93 (R2006), Miami: American Welding Society.
22. See Reference 17 and American Welding Society (AWS), 2008, The
Official Book of D1.1 Interpretations, AWS D1.1-BI:2008, Miami:
American Welding Society.
Table 1.1
Diffusible Hydrogen Limits for Weld Metal
Designator
Diffusible Hydrogen Content,
mL/100g of Deposited Metal
H16
no more than 16
H8
no more than 8
H4
no more than 4
H2
no more than 2
13
Electrodes that resist moisture pickup for extended
time periods under conditions of high atmospheric
humidity are designated with an “R” in the electrode
classification. The AWS standard, Structural Welding
Code—Steel, AWS D1.1/D1.1M:201023 permits longer
exposure times for such electrodes, thus a moistureresistant E7018 low-hydrogen electrode might be designated as E7018-H4R. Similar designations also are
available in alloy combinations. This is an area of active
development in shielded metal arc electrodes; therefore,
recommendations from the manufacturers of electrodes,
in addition to the most recent editions of AWS A5.1 and
A5.5, should be consulted for the latest information.24
Microstructure
Hydrogen is most likely to promote cracking when
the steel has a martensitic microstructure. With this
microstructure and a quantity of hydrogen present, a
tensile stress much lower than the normal cohesive
strength of the metal can initiate a crack. In general, the
stress required to produce a crack in steel is progressively lower as the hydrogen content increases. The susceptibility of martensite to hydrogen cracking is believed
to be due partly to high local transformation stresses.
Bainitic microstructures in steel display a distinctly
lower susceptibility to hydrogen cracking compared to
martensitic microstructures. The local stresses are significantly lower in bainite, even though it may have a
degree of hardness approaching that of any martensite
in the microstructure. A mixture of ferrite and high-carbon martensite or bainite also is quite susceptible to
hydrogen cracking. This microstructure is produced
during cooling from austenite at a rate that is slightly
faster than the critical cooling rate for the steel. Therefore, in the presence of sufficient hydrogen, any localized area with this sort of mixed microstructure will be
susceptible to cracking in the HAZ.
Susceptibility to cracking can be reduced by minimizing the formation of martensite in the weld metal and
HAZ. This is accomplished by controlling the cooling
rate of the weld with either higher preheat temperature
or higher heat input. The cooling rate depends on the
thickness of the workpiece, preheat temperature, and
welding heat input. With some steels, however, a change
in welding procedures that reduces the amount of martensite in the microstructure may result in a detrimental
change in certain mechanical properties of the welded
joint.
23. See Reference 17.
24. Refer to AWS Committee on Filler Metals and Allied Materials,
2004, Specification for Carbon Steel Electrodes for Shielded Metal
Arc Welding, AWS A5.1/A5.1M:2004, and 2006, AWS A5.5/A5.5M:
2006, Specification for Low-Alloy Steel Electrodes for Shielded Metal
Arc Welding, Miami: American Welding Society.
14
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
High-heat-input welds, such as electroslag welds,
also can exhibit hydrogen cracking in the extensive ferrite veining common to the weld metal. In these
instances, high moisture content in the welding flux is
usually the cause of the cracking.
Stresses
Possible sources of stress are phase transformation,
thermal contraction, mechanical restraint, applied
loads, or fabrication sequence. These stresses may be
reduced by preheating, adjusting the welding procedure, or redesigning the weldment or fabrication
sequence to reduce restraint on the joint. The Welding
Handbook, Volume 1, Chapter 3, Heat Flow in Welding; Chapter 5, Design for Welding; and Chapter 7,
Residual Stress and Distortion, can be consulted for
background information on the development of stresses
in weldments and information on weldment design.
Appendix B of this volume provides a reference guide
to the contents of various volumes of the Welding
Handbook.25
25. See Reference 14.
(A)
AWS WELDING HANDBOOK 9.4
Underbead Cracking
The most common occurrence of hydrogen-induced
cracking is in the grain-coarsened HAZ of a steel with a
susceptible microstructure that has not been adequately
preheated. When cracking occurs in this particular location it is often called underbead cracking because of its
proximity to the weld interface, as illustrated in Figure
1.9.
Weld Metal Cracking
Weld metal normally presents fewer problems than
base metal with regard to hydrogen cracking. This is
probably a result of the general use of filler metal with
lower carbon content than the base metal. Nevertheless,
in some cases hydrogen can still cause weld metal cracking to a significant extent. For example, consumables
alloyed to produce weld metal with strength levels
matching those of certain high-strength low-alloy (HSLA)
steels, particularly those designed to meet United States
Navy requirements for ships and submarines, have
resulted in weldments that are more susceptible to
(B)
Figure 1.9—(A) Underbead Crack in a Transverse Metallographic Section
of a Weld in SAE 9310 Steel and (B) SEM Fractograph of the Same Crack
AWS WELDING HANDBOOK 9.4
hydrogen cracking in the weld metal than to hydrogen
cracking in the HAZ. Thus, for these steels, preheating
requirements are dictated by the weld metal rather than
the base metal.
Hydrogen cracking in the weld metal may take several forms. It usually occurs transverse to the weld bead
length and at right angles to the surface. Hydrogen cracks
can occur longitudinally, or also as 45° chevron cracks.
One form of hydrogen-induced cracking that occurs
in weld metal appears as small bright spots on the fractured faces of broken specimens of weld metal. These
spots are called fisheyes. The fisheye usually surrounds
some discontinuity in the metal, such as a gas pocket or
a nonmetallic inclusion, which gives the appearance of
the pupil of an eye.
Conditions that lead to the formation of fisheyes in
weld metal can be minimized by using dry, low-hydrogen
electrodes, by increasing the preheat temperature, or by
applying immediate postweld hydrogen release treatment to the weldment for at least 20 minutes at temperatures ranging from 95°C to 320°C (200°F to 600°F).
The elevated temperature serves to speed the diffusion
of atomic hydrogen away from the weld region. Longer
times or higher temperatures, or both, should be applied
when there is increased hydrogen contamination and
higher alloy content.
Microcracks may be observed in weld metal deposited
by shielded metal arc welding (SMAW) electrodes containing cellulose in the covering, or by low-hydrogen
electrodes that have excessive moisture in the covering.
These microcracks generally are oriented transverse to
the axis of the weld. They are less likely to occur in weld
metal deposited with dry low-hydrogen electrodes. Even
with this precaution, however, weld metal cracking can
occur at higher levels of strength or carbon equivalence.
Methods of Avoiding Hydrogen Cracking
When the carbon content of steel is increased, the
hardness of any martensite formed within its microstructure is also increased. When the alloy content of
steel is increased for greater quench hardenability, the
likelihood and thus the quantity of martensite are consequently increased. Both of these effects tend to reduce
the hydrogen tolerance of steels.
Residual stresses, being limited by yielding, also tend
to increase with yield strength. Susceptibility to hydrogen
cracking increases with increasing residual stress, although
this may also reflect the more susceptible microstructure. For example, carbon steels with an ultimate tensile
strength (UTS) that does not exceed 410 MPa (60 ksi)
can be welded with E6010 or E6011 covered electrodes,
which are characteristically high in hydrogen because the
coverings contain cellulose and 3% to 7% moisture. Conversely, higher-strength quenched and tempered steels
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
15
such as HY-130 must be welded with covered electrodes
that contain no more than 0.1% moisture in the covering. (Refer to Table 1.18 for the chemical composition
of HY-130.) Moisture or hydrogen limits for covered
electrodes vary between these two levels, depending on
the type of steel being welded.
Hydrogen cracking can be controlled by several
means. A welding process or an electrode that produces
minimal diffusible hydrogen can be selected. A combination of welding heat input and thermal treatments
can be used to drive off the hydrogen, or produce a
microstructure that is less sensitive to it. Another alternative is to use joint designs and welding procedures
that minimize restraint and thus minimize residual
stresses.
Welding Process
The amount of diffusible hydrogen produced during
welding can be limited by using an inherently lowhydrogen process such as GMAW. For processes that
employ a flux, such as SMAW, low-hydrogen electrodes
are recommended for the welding of crack-susceptible
steels. However, the moisture content of these electrodes must be maintained below the limits stated in the
applicable filler metal specification.
Electrodes are manufactured for use within acceptable moisture limits consistent with the type of covering
and strength of the weld metal. Low-hydrogen electrodes are packaged in containers that provide the
moisture protection necessary for the type of covering
and the application. These electrodes can be maintained
for many months in these protective containers when
stored at room temperature with the relative humidity
at 50% or less. Unpackaged, they can be stored in electrode-holding ovens for short times. However, if the
containers are removed or damaged and the electrodes
are improperly stored, the coverings may absorb excessive moisture.
Some covered electrodes are designed to resist moisture pickup during exposure to the atmosphere. A standardized absorbed-moisture test is described in
Specification for Carbon Steel Electrodes for Shielded
Metal Arc Welding, AWS A5.1/A5.1M:2004, and Specification for Low-Alloy Steel Electrodes for Shielded
Metal Arc Welding, AWS A5.5/A5.5M:2006.26 As a
result of passing this exposure test of 9 hours at 27°C
(80°F) and 80% relative humidity, electrodes may have
an “R” designator attached to the classification; AWS
A5.1 electrodes may be classified as E7018M to indicate moisture resistance.
The low-hydrogen electrodes (EXX15 and EXX16)
and low-hydrogen iron powder electrodes (EXX18,
26. See Reference 24.
16
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
EXX28, and EXX48) are designed to contain a minimal
amount of moisture in the coverings. The maximum
acceptable moisture level of the filler metal decreases
in proportion to the increase in the strength of the
weld metal. To maintain this low moisture level in the
covering, hermetically sealed containers are mandatory
for electrodes that deposit weld metal with a tensile
strength of 550 MPa (80 ksi) or higher. These containers are optional for electrodes of lower-strength
classifications.27
As previously mentioned, electrodes that have been
exposed to a humid atmosphere for an extended time
may absorb excessive moisture. The moisture content
of electrodes that have been exposed to the atmosphere
should not exceed the limits stated in the appropriate
specification. If there is a possibility that the electrodes
have picked up excessive moisture, they may be reconditioned by baking in an oven. The appropriate time
and temperature for baking should be requested from
the electrode manufacturer. The user should be aware
that the applicable welding code may place limits on
reconditioning. For example, Structural Welding Code—
Steel, AWS D1.1 specifies conditions for baking submerged arc welding flux.28
The hydrogen designators shown in Table 1.1 are
used in AWS specifications to designate the diffusible
hydrogen content of covered carbon steel electrodes
and submerged arc low-alloy steel welding wires and
fluxes. The same hydrogen designators also apply to
other ferritic covered electrodes, submerged arc wires
and fluxes, and flux-cored wires. Although none of the
specifications for austenitic stainless steel and nickel
alloy electrodes contain limits on hydrogen or moisture,
special precautions should be exercised when using
these electrodes to weld high-strength and alloy steels.
Flux-cored electrodes, in particular, should not be used
to weld steels that are sensitive to hydrogen cracking if
the electrodes have been contaminated with moisture or
any other hydrogen-containing substance.
Thermal Treatments
Preheating and postheating at or just above the preheat temperature should be considered when there is a
significant risk of hydrogen cracking in the welded
joint. Preheating involves raising the temperature of the
weldment prior to welding, and maintaining an elevated
27. See Reference 24.
28. Structural Welding Code—Steel, AWS D1.1 (see Reference 17),
requires that flux be baked at 120°C (250°F) for 1 hour if the packaging has been damaged. A 25 mm (1 in.) thick layer of exposed flux in
hoppers and wet flux must be discarded. These procedures should be
followed for all applications.
AWS WELDING HANDBOOK 9.4
interpass temperature during the entire welding operation. Controlling preheat and interpass temperatures
achieves the following conditions:
1. Reduces cooling rates and thus reduces the hardness of heat-affected zones,
2. Increases the rate at which hydrogen diffuses
away from the weld and heat-affected zone, and
3. Reduces residual stresses in and near the weld.
Preheat may be applied to the entire weldment or to
a band of specified width that includes the weld joint.
The selection of preheat temperature and the degree to
which preheat must be applied involves a number of
considerations. In general, preheat temperatures must
increase with increasing carbon equivalent, plate thickness, restraint, and hydrogen levels. Conversely, the use
of high levels of arc energy and low-hydrogen
consumables may permit the use of a lower preheat
temperature. Recommendations for minimum preheat
temperatures for carbon steels and low-alloy steels are
published in a number of documents, including the
standard, Structural Welding Code—Steel, AWS D1.1,
and Bailey et al, Welding Steels without Hydrogen
Cracking.29, 30 These recommendations are discussed for
each type of steel in subsequent sections of this chapter.
Postheating should be performed immediately after
welding, while the weldment is still at the preheat temperature. The postheat temperature may be the same
used for preheating: 95°C to 320°C (200°F to 600°F).
The holding time at postheat temperature depends on
the joint thickness, because the length of the path over
which the hydrogen must diffuse to the surface is a controlling factor.
Weldments of steels that are quenched and tempered
to achieve desired properties require special treatment.
They must be either welded with a low-hydrogen process, or heat treated after welding and prior to the hardening treatment.
It is recommended that steels not be welded if the
steel temperature is below 0°C (32°F). If the temperature of the steel is below 0°C (32°F), it should be heated
to at least 20°C (70°F) prior to welding. Under humid
conditions, the steel should be heated to a higher temperature to drive off any surface moisture.
Limits on Heat-Affected Zone Hardness
The hardness of the heat-affected zone (HAZ) is
often used as an indicator of susceptibility to hydrogen
cracking. A Vickers hardness number of 350 HV is a
29. See Reference 17.
30. Bailey, N. et al, 1993, Welding Steel without Hydrogen Cracking,
Cambridge, England: Abington Publishing.
AWS WELDING HANDBOOK 9.4
widely used value, below which it is generally agreed
that hydrogen cracking is not expected to occur. Both
API 1104 and CSA Z662 indicate that procedures producing HAZ hardness greater than 350 HV should be
evaluated regarding the risk of hydrogen-cracking. 31, 32
They do not indicate that HAZ hardness greater than
350 HV is unacceptable, but neither do they provide
guidance pertaining to how HAZ hardness greater than
350 HV should be evaluated. The Australian standard
AS 2885 prohibits hardness in the HAZ in excess of
350 HV.33 The generally regarded notion that 350 HV
is a hardness level below which hydrogen cracking is
not expected dates back to work in the 1940s for welds
with a diffusible hydrogen content of approximately 16
ml (100 g) of deposited weld metal.34 Nevertheless, the
critical hardness level, or the hardness level below
which hydrogen cracking is not expected, depends on
the hydrogen level typically produced by the welding
process being used, and on the chemical composition
(carbon content or carbon equivalent [CE] level) of the
workpieces. The risk of hydrogen cracking increases as
the hydrogen level increases. Lower limits on hardness
are required when higher hydrogen levels are anticipated. Conversely, closer control of hydrogen level
allows higher hardness to be tolerated. Many modern
low-hydrogen electrodes, such as AWS EXX18, particularly the H4R variety, produce hydrogen levels of less
than 4 ml/100 g in the weld. For this reason, a hardness
limit of 350 HV may be highly conservative for some
in-service welding applications.
While HAZ hardness is often used as an indicator of
cracking susceptibility, the true susceptibility depends
on the microstructures present in the HAZ. A better
indicator of cracking susceptibility might be the volume
fraction of martensite in the HAZ. For a material of a
given chemical composition, HAZ hardness is a good
indicator of the relative amount of martensite present in
the HAZ. However, the hardness of martensite depends
on the carbon level of the material being welded. The
measured hardness in the HAZ of a low-carbon material that consists mostly of martensite may be lower
than the measured hardness in a higher carbon material
with a much lower volume fraction of martensite, yet
the cracking susceptibility in the lower carbon material
might be higher. In other words, materials with lower
31. Canadian Standards Association (CSA), 2003, Oil and Gas Pipeline Systems, Z662, Toronto, Ontario, Canada: CSA International.
32. American Petroleum Institute. 2005. Welding of Pipelines and
Related Facilities. API Standard 1104 (R2010). 20th edition. Washington, D.C.: American Petroleum Institute.
33. Australian Standards (AS) 2002, Pipelines—Gas and Liquid Petroleum, Part 2, AS2885.2-2002, Sidney: Australian Standards.
34. Dearden, J. and H. O’Neill, 1940, A Guide to the Selection and
Welding of Low Alloy Structural Steels, Vol. 3, Institute of Welding
Transactions.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
17
carbon content tend to crack at lower hardness levels.
Conversely, higher hardness can be tolerated when
welding higher carbon content materials.
A HAZ hardness of 350 HV may be overly conservative for some in-service welding applications and not
conservative for others. Acceptance criteria that allow
trade-offs to be made between HAZ hardness, hydrogen level, and chemical composition for welds made
onto in-service pipelines have been proposed.35
Interruption of the Heating Cycle
When a welding procedure employs preheating or
postheating, a question sometimes arises as to whether
the weldment should be allowed to cool to room temperature during or after welding but before final heat
treatment. The effects of interrupting the heating cycle
are both metallurgical and mechanical in nature.
Metallurgical effects involve microstructural changes.
The mechanical effects involve thermal contraction in
the weldment that may produce localized distortion or
high residual stresses. Accordingly, the greatest assurance of successful welding requires the use of continuous
heating without interruption, postweld heat treatment
immediately after completion of welding, or maintenance
of preheat until postweld heat treatment can be performed.
However, operational or economical reasons may prevent carrying out a continuous heating procedure.
Interrupted operations are necessary in some cases
and quite common in many applications. It is difficult
to make general rules for when interruptions are permissible, because many factors must be considered.
Once welding has started, the heating of steels with
high hardenability should not be interrupted unless
appropriate steps are taken to avoid cracking. Procedures for the various types of hardenable steels are discussed in the sections on high-carbon steels and highstrength low-alloy steels.
Interruptions in heating are less desirable if a partially completed weld will be subjected to tensile
stresses when cooled. All welding and postweld heat
treatment should be completed before a weldment is
exposed to any type of loading.
For the heat-affected zone and weld metal, an
increase in workpiece thickness increases both the
restraint on the weld and the rate of cooling from welding temperatures. Accordingly, the weld area is subjected to increasingly high residual stresses.
Once welding has started, it should not be stopped
until the weld has enough strength and rigidity to withstand the residual and applied stresses. For this reason,
35. Bruce, W. A., and M. A. Boring, 2005, Realistic Hardness Limits
for In-Service Welding, Draft Final Report for PRCI Contract No.
GRI-8758, EWI Project No. 46344CAP, Columbus, Ohio: Edison
Welding Institute.
18
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
an interruption of welding generally is not permitted on
heavy sections until some minimum number of weld
passes have been completed, or a specified fraction of
the joint thickness has been welded. When interruptions
are permitted, the weldment must be cooled slowly and
uniformly. Welding should not resume until the weld
area has been reheated uniformly to the specified preheat temperature.
SOLIDIFICATION CRACKING
Solidification cracking is a type of hot cracking that
can occur in carbon steel and low-alloy steel welds
when the weld metal just behind the weld pool is unable
to support the tensile strains that develop as it solidifies.
Liquid films are required for this type of cracking to occur, and as such, solidification cracks normally appear
along grain boundaries (intergranular), although in some
cases may be found along dendrite boundaries within
grains (interdendritic). These liquid films are created by
the segregation of certain elements, especially sulfur or
phosphorus, but also lead, tin, antimony, and arsenic,
which can form low-melting-point compounds. Fracture surfaces of solidification cracks, as shown in Figure
1.10, typically exhibit an “egg-crate” topography when
examined at the high magnification possible in a scanning electron microscope (SEM). These fracture surfaces
are created by the separation of intergranular liquid
films just before completion of solidification.
While solidification cracking can occur in almost any
of the carbon and low-alloy steels, resulfurized freemachining steels and some heat-treated low-alloy steels
are particularly susceptible. Solidification cracks often
are longitudinal cracks along the centerline of the weld
bead. These are often associated with the teardrop
shape of the weld pool that can occur at higher travel
speeds. Weld beads that are undersized, have a concave
profile, or have a high depth-to-width ratio are also
more susceptible. As in all forms of weld cracking, joint
restraint is an important influence.
Manganese and silicon additions tend to reduce the
susceptibility of steel to solidification cracking. Therefore, one precaution to reduce solidification cracking
involves the use of filler metals with a higher manganese or silicon content. However, it should be noted
that this approach becomes less effective with increasing carbon content. Medium- to high-carbon steel
weld metal exhibits a greater tendency toward solidification cracking in spite of elevated manganese or silicon
levels.
(A)
(B)
Figure 1.10—(A) Transverse Metallographic
Section and (B) SEM Fractograph of Solidification
Cracking in an Autogenous Laser Weld
in Carburized SAE 8620 Steel
LIQUATION CRACKING
Cracking along grain boundaries in the heat-affected
zone due to wetting of the boundaries by liquid is called
HAZ liquation cracking. This cracking normally occurs
in the partially melted zone (PMZ) of the HAZ, which
is the region of the HAZ that borders the fusion zone
and in which some localized melting or liquation
occurs. Liquation cracking may be caused by the penetration of the grain boundary by a liquid constituent (a
liquating particle or molten weld metal), or by the formation of liquid at the grain boundary from the segre-
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
(A)
19
(B)
Figure 1.11—SEM Fractographs of Liquation Cracking in the HAZ of a Weld in SAE 1080 Rail Steel
gation of impurity elements to the boundary. In both
cases, the liquid wets the boundary and thus reduces its
strain capacity. Figure 1.11 contains SEM images, at two
different levels of magnification, of a cluster of HAZ
liquation cracks that initiated brittle fracture during
proof testing of a welded joint in a high-carbon steel.
Weld metal liquation cracking is a special type of
HAZ liquation cracking that occurs in the previous
passes of multiple-pass welds as subsequent passes are
made. Liquation cracking in the HAZ is likely to happen in welds that are also susceptible to solidification
cracking.
The risk of liquation cracking in the HAZ can be
reduced by using one or a combination of the following
methods:
1. Welding on base metal with a low impurity content
(e.g., sulfur and phosphorous, but also lead, tin,
antimony, and arsenic) to decrease the likelihood
of impurity segregation to the grain boundaries;
2. Using high-purity filler metals to limit the chances
of low-melting constituents forming in the fusion
zone and penetrating the grain boundaries of the
HAZ;
3. Solution heat treating of the base metal to reduce
the chance of forming liquids around liquating
particles in the HAZ;
4. Selecting a base metal of finer grain size, as
smaller grains provide greater grain boundary
surface area over which impurities and liquid
films can be dispersed; and
5. Reducing the residual stress in the HAZ by using
an undermatching filler metal or a solutionannealed base metal to reduce the chances of liquation cracking.
LAMELLAR TEARING
Shrinkage from groove welds, fillet welds, or combinations of these used in corner joints or T-joints can
result in tensile stresses in the through-thickness direction of the through member. The resulting throughthickness strains must be accommodated by the base
metal that lies within the joint. The magnitude of these
stresses and strains depends on the size of the weld, the
welding procedures used, and the degree of restraint
imposed by the base metal thickness and the joint design.
In steel plate and structural shapes that have been
produced by conventional steelmaking processes, manganese sulfide or oxide-silicate inclusions that have
been flattened and elongated by the rolling process
sometimes occur in clusters around mid-thickness. These
can significantly reduce the through-thickness ductility
of the steel, making it susceptible to lamellar tearing.
This internal tearing progresses in a step-like manner
from one inclusion to another, and may or may not
propagate to exposed surfaces. On an etched cross-section,
20
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
lamellar tearing is evidenced by a step-like or jagged
crack with many of its steps oriented parallel to the plate
surfaces, as shown in Figure 12(A) and (B). Macroscopically,
the fracture surface will appear fibrous or “woody,” as
shown in Figure 12(C), and microscopic examination will
reveal the planar rupturing of the interfaces that once
surrounded the elongated, flattened inclusions.
Figure 1.13 shows three joint designs, (A), (B), and
(C), that may be prone to lamellar tearing, along with
modified joint designs that should improve their resistance to it. There is some evidence that sensitivity to
lamellar tearing is increased by the presence of hydrogen
in the steel.
Following are some approaches to minimizing the
possibility of lamellar tearing:
1. Change the location and design of the welded
joint to minimize through-thickness strains, including selecting fillet welds instead of completepenetration groove welds in T-joints;
2. Reduce the available hydrogen;
3. Butter the surface of the plate with at least two
layers of weld metal prior to making the weld;
4. Use preheat and interpass temperatures of at least
95°C (200°F);
5. Peen the weld beads;
6. Use steel plates especially processed to achieve
improved through-thickness properties (very lowsulfur steels—0.010% maximum) or steels with
rare-earth additions to control the shape of manganese sulfide inclusions);36 and
7. Substitute forgings or castings for plate.
The most reliable methods for avoiding lamellar
tearing are to use alternate materials and the buttering
technique, and if plate is used, to minimize stresses in
the through-thickness direction. It is not possible to
detect lamellar tearing prior to welding since it does not
exist. However, by employing straight-beam ultrasonic
examination, it is relatively easy to detect subsurface
laminations that may be susceptible to lamellar tearing.
Also, a through-thickness tension test (e.g., ASTM
A 770) can be used to determine the susceptibility of a
plate to lamellar tearing. A reduction of area in the
through-thickness direction greater than 20% in the
A 770 test indicates a low likelihood of lamellar tearing.
36. American Association of State Highway and Transportation Officials (AASHTO) and American Welding Society (AWS), 2010, Bridge
Welding Code, AASHTO/AWS D1.5M/D1.5:2010, Miami: American
Welding Society, Subclause 12.4.4.1, Optional Through-Thickness and
Low-Sulfur Requirements.
AWS WELDING HANDBOOK 9.4
(A)
(B)
(C)
Figure 1.12—Lamellar Tearing:
(A) Typical Location, (B) As Shown in a
Longitudinal Metallographic Section, and
(C) Macroscopic Appearance of Fracture Surfaces
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
21
REHEAT CRACKING
Reheat cracking (also called strain-age cracking, strain
relaxation cracking, stress-rupture cracking, or stressrelief cracking) can occur in some low-alloy steels and
Cr-Mo steels during postweld heat treatment or in hightemperature service. Reheat cracks are intergranular and
usually appear in the grain-coarsened region of the
HAZ during postweld heat treatment at stress-relieving
temperatures, especially in thick workpieces where the
combined effects of restraint and residual stress are significant. Dissolution of alloy carbides and nitride particles in the grain-coarsened HAZ during welding is
followed by reprecipitation during postweld stress relief.
This increases the creep resistance of the grains, making
them less able to accommodate the relaxation strains
that result from grain boundary sliding. The magnitude
of these strains is increased by the coarseness of the
grains in this region. Intergranular stresses thus accumulate, particularly at grain-boundary triple points,
which may result in the nucleation and growth of intergranular cracks. There is experimental evidence that the
diffusional segregation of impurity elements such as phosphorus (P), copper (Cu), tin (Sn), arsenic (As), and antimony (Sb) increases the susceptibility of grain boundaries
to reheat cracking by reducing their cohesive strength at
stress-relieving temperatures. It has been reported that
this occurs in Cr-Mo-V steels, in ASTM A 508 Class 2
steel, in ASTM A 514 and A 517 steels, shown in Table
1.2, and in some precipitation-hardened ASTM A 710
HSLA steels.37 (Refer to Chapter 3 of Welding Handbook,
Volume 1, for a review of residual stress development.)38
The occurrence of reheat cracking can be reduced by
several means, as follows:
1. Reducing joint restraint during welding, which
will reduce the overall level of residual stress prior
to stress relieving;
2. Eliminating stress concentrations, such as in fillet
toes;
3. Using multiple-pass welding, which refines the
grains of previous passes; and
4. Using rapid heating and cooling to minimize
time spent in the carbide precipitation range.
FATIGUE CRACKING
Although fatigue cracking in welded steel structures
is primarily a design issue, its prevalence as a cause of
failure justifies mention in this section.
Source: Adapted from ASM International (ASM), ASM Metals Handbook, Vol. 6, Figure
14, Materials Park, Ohio: ASM International, p 652.
Figure 1.13—Weld Joint Designs Prone
to Lamellar Tearing, with Susceptible
and Improved Weld Metal Profiles
37. Steel classifications are published by ASTM International
(ASTM) (formerly American Society for Testing and Materials), 100
Barr Harbor Drive, West Conshohocken, Pennsylvania, 19428-2959.
www.astm.org.
38. See Reference14.
22
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.2
Susceptibility of Ferritic Alloy Steels to Reheat Cracking
Not Susceptible
Borderline
Susceptible
Very Susceptible
C-Mn
A 517J
A 517E
A 517F
1Cr1/2Mo
A 508/1
A 533B
1/2MoB
1/2Cr1/2MoV
5Cr1/2Mo
A 508/3
HY 80
9Cr1Mo
2-1/4Cr1Mo
HY 130
A 517A
A 517B
A 508/2
A 533A
A 508/2
Structural weldments, especially those fabricated
from plate and structural shapes, contain sharp corners
and other abrupt transitions which act as stress concentrators. Unfortunately, these transitions typically (and
often necessarily) coincide with the welded joints, which
add inherently detrimental features that must also be
considered. Although these inherent geometric discontinuities are rarely detrimental to the static or even the
impact properties of most welded structures, they are
often markedly damaging to the long-term integrity of
welded structures in service environments that impose
cyclic stresses.
For a given cyclic nominal stress range (Δσ = σmax –
σmin), the fatigue life of a sound weld is controlled primarily by the local geometry of the weld toe or weld
root, and secondarily by the joint design. Weldinginduced tensile residual stresses may or may not have a
contributing effect, depending on the applied nominal
stress ratio (R = σmin/σmax). Unless R < 0 or R > 1, residual tensile stresses tend to be of little to no consequence.
Other factors, such as the tensile strength, yield
strength, and microstructure of the weld metal, HAZ
and base metal have negligible influence on high-cycle
condition.
Figure 1.14 provides an example of this by demonstrating the absence of a yield strength effect for a particular class of weldments. The effects of geometry
essentially overwhelm all other factors unless steps are
taken to improve the profile of the weld toe by means
such as grinding, peening or remelting, and by ensuring
complete joint penetration to eliminate the crack-like
root geometry of a partial-penetration weld. In many
applications, such measures are cost-prohibitive.
Since weld toe and root geometries are largely
beyond the control of the structural designer, most
design codes for welded steel structures, including AWS
D1.1, specify fatigue design rules based only on joint
design and nominal stress range. To develop such rules,
thousands of fatigue test results obtained from various
joint geometries are assembled and divided into categories for statistical analysis. This produces a series of
discrete performance categories based on test-piece
geometry. The lower-bound stress-life (S-N) curve derived
from each category is typically codified as the basis for
fatigue design. Code users then select the category most
closely matching each joint design and apply the designated S-N curve. This establishes a permissible stress
range for the number of cycles that a joint will be
required to perform in service, thereby guiding designers in the sizing of structural members or welds, or
both. Conversely, a conservative estimate of the life
expectancy of an existing joint can be obtained from
the appropriate S-N curve.
For structures known to contain fatigue cracks, the
fracture toughness of the steel in which the fatigue
cracks are growing determines the most conservative
critical crack size for a given loading condition. The
critical crack size is the size above which a crack or
crack-like flaw becomes unstable, resulting in sudden
brittle failure of the component. By increasing this
value, high-toughness steel can extend the crack growth
portion of the fatigue life of a weldment. However, in
many situations this may produce only a modest
increase, as illustrated in Figure 1.14. In any case, neither high toughness nor high strength can be expected
to provide a significant, reliable improvement in the
overall fatigue performance of as-welded steel structures, as illustrated in Figure 1.15.
In situations where fatigue cracking is expected to be
a problem, the following guidelines may be helpful:
1. Wherever possible, the weldment should be designed with butt joints instead of fillet or T-joints;
2. Placing welded joints at the same locations as
changes in section thickness generally should be
avoided;
3. The workpieces should be carefully fixtured to
minimize joint misalignment;
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
23
Click here to view
Figure 1.14—Absence of Yield Strength Dependence in High-Cycle Fatigue
Performance of Weldments, as Demonstrated by Stress-Life Data
Obtained from Test Geometries with Longitudinal Attachments
4. Undercut, overlap and excessive weld reinforcement should be avoided; and
5. If grinding, peening, or remelting of the weld-toe
is necessary, it should be performed in accordance with established procedures.39
CARBON STEELS
Carbon steels are alloys of iron and carbon in which
carbon usually does not exceed 1.0%, manganese does
not exceed 1.65%, and copper and silicon each do not
exceed 0.60%. Other alloying elements normally are
not present in more than residual amounts. Carbon
steels generally are categorized according to their carbon content, as listed in Table 1.3. The properties and
weldability of these steels depend mainly on carbon
content; other elements have only a limited effect.
39. See Reference 17.
Deoxidation practices in the steelmaking process
affect the characteristics and properties of steel. Thus,
carbon steel can be broadly classified according to various deoxidation practices: rimmed, capped, semikilled,
or killed (deoxidized) steel. The great majority of modern steels are continuously cast steels, fully killed and
aluminum-treated for grain size control.
The Society of Automotive Engineers (SAE) carbon
steels are classified in the 10XX, 11XX, 12XX, and
15XX groups.40 The 10XX group has a maximum of
1.0% manganese; manganese in the 15XX group ranges
from 1.00% to 1.65%. The 11XX resulfurized steels
and the 12XX resulfurized and rephosphorized steels
are designed for improved machinability. Fusion welding is difficult with these materials, however, as they are
notably prone to solidification cracking.
Standards published by ASTM designate carbon steels
on the basis of chemical or mechanical properties, or
40. Society of Automotive Engineers (SAE International) 400 Commonwealth Drive, Warrendale, Pennsylvania, 15096-0001. www.sae.org.
24
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
both, in conjunction with product form and the intended application.41 The ASTM standard A 830 covers
SAE carbon steel plates; ASTM A 576 covers SAE carbon steel bars. Typical ASTM carbon steels used in construction, pressure vessels, and piping are listed in Table
1.4.42, 43
WELDABILITY OF CARBON STEELS
The weldability of a specific type of carbon steel is
determined primarily by the sensitivity of the steel to
hydrogen cracking; although susceptibility to solidification cracking and deoxidization practice also can affect
the weldability of some grades, as previously explained.
Carbon Content
Key:
N f1 = Stress cycles to failure for fatigue crack growth in a
steel with lower fracture toughness
N f2 = Stress cycles to failure for fatigue crack growth in a
steel with higher fracture toughness
A f1 = Critical size of fatigue crack in a steel with lower fracture
toughness
A f2 = Critical size of fatigue crack in a steel with higher fracture
toughness
Source: Bannantine, J. A., J. L. Comer, and J. J. Handrock, 1990, Fundamentals of Metal
Fatigue Analysis, Upper Saddle River, New Jersey: Prentice-Hall.
Figure 1.15—General Behavior of a Growing
Fatigue Crack, Comparing Critical Crack
Sizes for Two Steels with Different
Values of Fracture Toughness
Several points stated in the section titled Fundamentals of Welding Carbon and Low-Alloy Steels bear
repeating in this section, as follows:
1. Sensitivity to hydrogen cracking increases in
proportion to increases in carbon equivalent,
41. See Reference 36.
42. ASTM International (formerly American Society of Testing and
Materials), 2006, Standard Specification for Steel Bars, Carbon, HotWrought, Special Quality, A 576-90b (2006), West Conshohocken,
Pennsylvania: ASTM International.
43. ASTM International (formerly American Society of Testing and
Materials), 2006, Standard Specification for Plates, Carbon Steel,
Structural Quality, Furnished to Chemical Composition Requirements
A 830-06, West Conshohocken, Pennsylvania: ASTM International.
Table 1.3
Classification and Weldability of Carbon Steels
Common Name
Carbon, %
Typical
Hardness
Low-carbon steel
0.15 max.
60 HRB
Special plate and shapes,
sheet, strip, welding
electrodes
Excellent
Mild steel
0.15–0.30
90 HRB
Structural shapes, plate, and
bar
Good
Medium-carbon steel
0.30–0.50
25 HRC
Machine parts and tools
Fair (preheat and postheat
normally required; lowhydrogen welding process
recommended)
High-carbon steel
0.50–1.00
40 HRC
Springs, dies, railroad rail
Poor (low-hydrogen welding
process, preheat, and postheat
required)
Typical Use
Weldability
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
25
Table 1.4
Composition and Strength Requirements of Typical ASTM Carbon Steels
Application
ASTM
Standard
Type or
Grade
Typical Composition Limits, %a
Tensile Strength
C
Si
MPa
ksi
MPa
ksi
Mn
Min. Yield Strength
Structural Steels
Welded buildings, bridges, and
general structural purposes
A 36
—
0.29
0.80–1.20
0.15–0.40
440–550
58–80
250
36
Welded buildings and general
purposes
A 529
50
55
0.27
0.27
1.35
1.35
0.40
0.40
485–690
485–690
70–100
70–100
345
380
50
55
General purpose plate
(improved toughness)
A 573
58
65
70
0.23
0.26
0.28
0.60–0.90
0.85–1.20
0.85–1.20
0.10–0.35
0.15–0.40
0.15–0.40
400–490
450–530
485–620
58–71
65–77
70–90
220
240
290
32
35
42
Pressure Vessel Steels
Plate, low and intermediate
tensile strength
A 285
A
B
C
0.17
0.22
0.28
0.90
0.90
0.90
—
—
—
310–450
345–485
380–515
45–65
50–70
55–75
165
185
205
24
27
30
Plate, manganese-silicon
A 299
—
0.30
0.90–1.40
0.15–0.40
515–655
75–95
275
40
Plate, intermediate and hightemperature service
A 515
60
65
70
0.31
0.33
0.35
0.90
0.90
1.20
0.15–0.40
0.15–0.40
0.15–0.40
415–550
450–585
485–620
60–80
65–85
70–90
220
240
260
32
35
38
Plate, moderate and lowtemperature service
A 516
55
60
65
70
0.26
0.27
0.29
0.31
0.60–1.20
0.85–1.20
0.85–1.20
0.85–1.20
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
380–515
415–550
450–585
485–620
55–75
60–80
65–85
70–90
205
220
240
260
30
32
35
38
Plate, carbon-manganese-silicon
heat-treated
A 537
1b
2c
3c
0.24
0.24
0.24
0.70–1.60
0.70–1.60
0.70–1.60
0.15–0.50
0.15–0.50
0.15–0.50
450–585
515–655
515–655
65–85
75–95
75–95
310
380
345
45
55
50
Piping and Tubing
Welded and seamless pipe,
black and galvanized
A 53
A
B
0.25
0.30
0.95–1.20
0.95–1.20
—
—
330
415
48 min.
60 min.
205
240
30
35
Seamless pipe for hightemperature service
A 106
A
B
C
0.25
0.30
0.35
0.27–0.93
0.29–1.06
0.29–1.06
0.10 min.
0.10 min.
0.10 min.
330
415
485
48 min.
60 min.
70 min.
205
240
275
30
35
40
Structural tubing
A 501
—
0.26
—
—
400
58 min.
250
36
Cast Steels
General use
A 27
60–30
0.30
0.60
0.80
415
60 min.
205
30
Valves and fittings for hightemperature service
A 216
WCA
WCB
WCC
0.25
0.30
0.25
0.70
1.00
1.20
0.60
0.60
0.60
415–585
485–655
485–655
60–85
70–95
70–95
205
250
275
30
36
40
Valves and fittings for lowtemperature service
A 352
LCAc
LCBc
LCCc
0.25
0.30
0.25
0.70
1.00
1.20
0.60
0.60
0.60
415–585
450–620
485–655
60–85
65–90
70–95
205
240
275
30
35
40
a. Single values are maximum unless otherwise noted.
b. Normalized condition.
c. Quenched and tempered (Q&T) condition.
26
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
hydrogen content of the weld metal, and workpiece thickness;
2. Carbon is the alloying element that has the greatest effect on sensitivity to hydrogen cracking;
3. The effects of carbon and other elements on susceptibility to hydrogen cracking can be estimated
using the carbon equivalent formula; and
4. Carbon steels exhibit increasing susceptibility
to hydrogen cracking when the carbon content
exceeds about 0.15%, although steels with less
than 0.15% carbon are not immune to hydrogen
cracking, especially when thick sections are welded
or high residual stresses are present, or both.
Weld Cooling Rates
When welding thick workpieces with an arc welding
process, the weld metal and heat-affected zone can be
hardened significantly because they are quenched by the
large mass of base metal. The cooling rate and the carbon equivalent of the steel are the controlling factors in
determining the degree of hardening. The cooling rate
depends primarily on the following factors: the thickness and joint geometry of the workpiece, the base-metal
temperature before welding commences, and heat input.
Consequently, the use of higher welding current, slower
welding speed (resulting in high heat input), or preheating of the base metal will reduce the cooling rate of the
weld zone. Preheat should be maintained while successive beads are deposited.
With higher carbon content or increased workpiece
thickness, a higher preheat and interpass temperature
should be used to decrease the weld cooling rate and
thus control the weld hardness and minimize the likelihood of cracking.44
In resistance spot welding of carbon steel sheets, the
nugget may be hardened as a result of rapid cooling by
the water-cooled copper alloy electrodes in contact with
the sheet surfaces. Special electronic heat controls can
provide a preheat or postweld heating cycle in the welding schedule to control the cooling rate and hardness of
the nugget.
Free-Machining Steels
Normal sulfur and phosphorus contents in carbon
steels do not promote weld solidification cracking.
However, when large amounts of these elements are
added, as is the case in some free-machining steels, the
steel will have relatively poor weldability because of
solidification cracking in the weld metal. Solidification
44. For a comprehensive preheating guide for steels, refer to Ott, C.
W. and D. J. Snyder, 1987, Suggested Arc-Welding Procedures for
Steels Meeting Standard Specifications, WRC Bulletin 326 (Revised
Bulletin 191), New York: Welding Research Council.
AWS WELDING HANDBOOK 9.4
cracking results from the low-melting constituents
enriched in phosphorus and sulfur at the grain boundaries. The grains may be torn apart by thermal stresses
during solidification. High sulfur content also promotes
porosity in the weld metal.
Lead (Pb) is another element added to some steels to
improve machinability. It is nearly insoluble in steel and
exists as distinct globules. The lead can melt during
welding and volatilize into the weld fumes. Occasionally, lead may cause porosity and embrittlement of steel.
Another concern with lead is its toxic presence in the
welding fumes. This requires special precautions to ensure
good ventilation during welding. (Refer to Appendix A.)
Normally, free-machining steels should not be
welded. If a steel of this type must be welded, lowhydrogen electrodes and low welding current should be
used to limit dilution, porosity, and cracking.
LOW-CARBON STEEL
Steels with less than 0.15% carbon are known as
low-carbon steels. In general, these steels have very low
hardenability and are easily joined by welding. As previously noted, a carbon steel containing 0.15% carbon
is capable of being hardened to 30 Rockwell Hardness
C Scale (HRC) to 40 HRC when cooled at a very high
rate. (Refer to Figure 1.7.) However, this would require
a welding process with high energy density (e.g., EBW,
LBW). For most welding processes, the cooling rate is
too low to allow the heat-affected zone of a weld to
reach this level of hardness.
Rapidly cooled welded joints in steel containing carbon of about 0.10% and higher can develop cracks during severe cold-forming operations because the weld
area is harder than the unaffected base metal. When the
welded joint will be subjected to severe cold-forming
(for example, when using the resistance spot welding
process), the carbon content of the steel should be low;
0.08% carbon is sufficient to develop substantial hardness for resistance spot welds in thin steel sheet. Hardness in spot welds is not a serious problem with these
low-carbon steels, except for some critical applications.
The deoxidation practice used in steelmaking is
another factor that can influence weld metal soundness
in low-carbon steels, particularly with autogenous
welding. Rimmed and capped low-carbon steels are not
deoxidized. When these steels are remelted during welding without the addition of deoxidizers, carbon and
oxygen in the steel react to form carbon monoxide,
which can be entrapped as porosity in weld metal. This
is particularly true at high welding speeds, because the
gas has less time to escape from the weld pool. Weldmetal porosity in these steels can be minimized by adding a filler metal containing sufficient deoxidizers (e.g.,
AWS WELDING HANDBOOK 9.4
aluminum, manganese, or silicon) to scavenge oxygen
from the weld pool.
With gas tungsten arc, plasma arc, or gas metal arc
welding, E70S-2 filler metal should be used because it
contains large amounts of deoxidizers.45 The covering
on shielded metal arc welding electrodes usually contains sufficient deoxidizers for welding rimmed or
capped steels. Special aluminum-containing paints are
available that can be applied to the joint faces to deoxidize the weld metal during autogenous welding. Submerged arc welding of rimmed or capped steel requires
the selection of an electrode and flux combination containing sufficient deoxidizers (e.g., silicon or manganese) to produce a sound weld, especially when high
welding speeds are used.46 Weld metal soundness normally is not a problem with killed, low-carbon steels
when good welding practices are used.
MILD STEEL
Carbon steels containing from about 0.15% to
0.30% carbon are commonly called mild steels. Underbead cracking or lack of toughness in the heat-affected
zone (HAZ) usually is not encountered when welding
mild steels containing no more than 0.20% carbon and
1.0% manganese. These steels can be welded without
preheat, postheat, or special welding procedures when
the joint thickness is less than 25 mm (1 in.) and when
joint restraint is not severe.
As the carbon content increases to about 0.30% and
manganese content increases to about 1.40%, weldability remains good; however, these weldments become
more susceptible to hydrogen cracking due to the
increased hardenability and yield strength. Welding
with a low-hydrogen procedure is recommended. Preheating and control of the interpass temperature also
may be required, particularly when the joint thickness
is greater than 25 mm (1 in.) or when extrinsic joint
restraint is high. If hydrogen cracking still is a problem
with these procedures, hydrogen may be diffused from
the joint either by maintaining the preheat temperature
or by postheating after welding is complete. A temperature of at least 150°C (300°F) usually is effective for
dissipating hydrogen in mild steel weldments. Hold
time will increase in proportion to the thickness of the
weld, typically 2 to 3 hours per 25 mm (1 in.).
Some mild steels are supplied in the normalized or
quenched and tempered condition to provide good
toughness or high-strength properties. Tensile strengths
45. Refer to American Welding Society (AWS), 2005, Specification
for Carbon Steel Electrodes and Rods for Gas Shielded Arc Welding,
AWS A5.18/A5.18M:2005, Miami: American Welding Society.
46. Refer to American Welding Society (AWS), 2007, Specification
for Carbon Steel Electrodes and Fluxes for Submerged Arc Welding,
AWS A5.17/A5.17M-97 (R2007), Miami: American Welding Society.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
27
may range from 450 MPa to 690 MPa (65 ksi to 100 ksi),
depending on the carbon and manganese content and the
heat treatment.
Welding procedures for heat-treated mild steels are
guided to a large extent by a need to have some minimum
toughness in the weld metal, the HAZ, and the unaffected base metal. Precautions should be taken to ensure
that welding is done using low-hydrogen conditions.
Standard procedures are used with shielded metal
arc, submerged arc, and gas metal arc welding because
the cooling rates in the HAZ are sufficiently rapid to
reproduce a microstructure similar to that of the normalized or quenched steel. When the carbon content is
limited to about 0.20%, underbead cracking or lack of
toughness in the HAZ normally is not a problem. This
is true even when very rapid cooling occurs due to the
low input of welding heat. In fact, allowing the HAZ to
cool rapidly may be preferable. Higher welding heat
input or higher preheat and interpass temperatures than
normal, which result in a slower rate of cooling, tend to
increase the grain size and produce coarser pearlite in
the HAZ. These microstructural conditions lead to low
strength and poor toughness.
If the welding process or procedure subjects the
HAZ to prolonged heating, high temperature and slow
cooling (e.g., in electroslag welding), the weldment may
require heat treatment (e.g., normalizing and tempering) to restore good strength and toughness to the
HAZ. When heat treatment of the weldment is not economical or practical, the rate of cooling in the weld
zone must be sufficiently rapid to produce a microstructure of adequate strength and toughness.
In general, heat-treated mild steels can be arc welded
without preheat. However, a preheat should be used
when the metal temperature is below about 10°C (50°F),
and a preheat of about 40°C (100°F) or higher should
be used if the plate thickness is over 25 mm (1 in.) or if
the joint is highly restrained.
Dilution must be considered when selecting a filler
metal to provide specified mechanical properties in the
joint in the selected steel. The mechanical properties of
weld-metal specified in AWS A5 standards apply to
undiluted weld metal.47 The properties of the weld metal
in an actual fabrication may differ from the reported
values because of dilution effects.
Low-alloy steel filler metal may be required to meet
mechanical property requirements for heat-treated mild
steels. However, the weld-metal strength should not
greatly exceed the strength of the base metal. Highstrength weld metal may force a softer HAZ to undergo
excessive localized strain when the joint is subjected to
deformation near room temperature. Under such conditions, fracture may occur prematurely in the HAZ.
47. See Reference 24.
28
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
For a butt joint, a filler metal should be selected that
will provide weld metal with essentially the same
strength as the base metal. For fillet welds, filler metal
of lower strength is sometimes used to provide sufficient ductility to accommodate stress concentrations,
although the weld size may need to be increased. However, a low-strength filler metal should not be used
indiscriminately as a remedy for cracking difficulties.
MEDIUM-CARBON STEEL
A pronounced change in the weldability of carbon
steels takes place over the range of carbon content from
0.30% to 0.50%, which identifies medium-carbon
steel. Steels containing about 0.30% carbon and less
than roughly 1.5% manganese have relatively good
weldability. However, as the carbon content is
increased, welding procedures must be designed to
avoid the formation of large amounts of hard martensite in the heat-affected zone (HAZ). If a steel containing about 0.50% carbon is welded with procedures
commonly used for mild steel, the HAZ is likely to be
quite hard, low in toughness, and susceptible to hydrogen cracking, as shown in Figure 1.16.
Figure 1.16—Severe Hydrogen Cracking through
the HAZ of SAE 1045 Plate 13 mm (1/2 in.) Thick,
Preheated at 24°C (75°F) and Welded with GMAW
AWS WELDING HANDBOOK 9.4
For most applications, medium-carbon steel should
be preheated before welding to control the cooling rate
in the weld metal and HAZ, thereby controlling the formation of martensite. The appropriate preheat temperature depends on the carbon equivalent of the steel, the
joint thicknesses, and the welding procedure. In general, preheat temperature requirements increase with
higher carbon equivalent, greater joint thickness, or
increased hydrogen in the arc. With a carbon equivalent
in the 0.45 to 0.60 range, a preheat temperature in the
range of 95°C to 200°C (200°F to 400°F) is recommended, depending on the welding process and the
joint thickness. Figure 1.17 shows how increasing preheat temperature reduces the amount of martensite
(light-etching phase) formed in the grain-coarsened
HAZ of gas-metal-arc welded SAE 1045 steel plate
13 mm (1/2 in.) thick.
A subcritical stress-relief heat treatment (e.g., 600°C
for 1 h/25 mm [1100°F for 1 h/in.]) is recommended
immediately after welding—especially with thick workpieces, high joint restraint, or service conditions involving impact or dynamic loading.48 When immediate
stress relief is impractical, the welded joint should be
maintained at or slightly above the specified preheat
temperature for 5 min/mm to 7 min/mm (2 h/in. to 3 h/
in.) of joint thickness. This procedure promotes the diffusion of hydrogen from the weld zone and reduces the
possibility of cracking during intermediate handling.
However, it should not be considered a substitute for an
appropriate stress-relief heat treatment. Slow cooling to
room temperature following stress-relief is recommended to avoid introducing new thermal stresses.
Low-hydrogen welding procedures are mandatory
for these steels. The selection of filler metal for arc
welding becomes more critical as the carbon content
increases. Pickup of carbon by dilution from a steel
containing 0.5% carbon usually will result in high
hardness in the weld metal, susceptibility to cracking,
and a tendency for brittle failure. Dilution can be minimized by depositing small weld beads, or by using a
welding procedure that provides shallow penetration,
or by buttering the groove faces prior to fitting.
To limit dilution in a multiple-pass weld, low heat
input generally is recommended for the first few layers.
Higher heat input can be used to complete the joint. It
is good practice to deposit the final weld bead, or
beads, entirely on previously deposited weld metal
without melting any base metal. This practice has the
effect of tempering the heat-affected zones of previously
deposited weld beads, especially those in the base metal.
Optimum tempering is achieved when the heat input of
the second layer is approximately 50% greater than
that used for the first layer against the base metal. How48. See Reference 14 for recommended preheat and stress-relief heat
treatment temperatures for specific steels.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
(A)
(B)
(C)
(D)
29
Figure 1.17—Effect of Preheat Temperature on Grain-Coarsened Microstructure in the
HAZ of Gas Metal Arc Welds in SAE 1045 Steel, 13 mm (1/2 in.) Plate Thickness
ever, postweld heat treatment still is a requirement with
this technique.
Medium-carbon steels are used extensively in the
fabrication of machinery and tools. Often these steels
are selected for their wear resistance rather than high
strength, and workpieces frequently must be heat
treated to meet in-service strength requirements. Welding may be performed before or after final heat treatment; however, the selection of filler metal and welding
procedures must be considered in this context. If welding is performed prior to heat treatment, special care
must be exercised when choosing the filler metal in
order to achieve a good match between weld-metal and
base-metal properties after heat treatment. A low-alloy
filler metal may be required for this purpose. If welding
is to be performed on a previously heat-treated component, extra precautions may be necessary. A hardened
component can impose additional restraint that increases
the likelihood of cracking if a suitable preheat procedure is not used. Also, because the heat of welding will
most likely soften the outlying portions of the HAZ,
(grain-refined or tempered, or both) a reheating treatment of the weldment may be required to restore the
desired properties.
HIGH-CARBON STEEL
The weldability of high-carbon steels is poor because
of the high hardenability and sensitivity to cracking in
the weld metal and heat-affected zones in weldments of
these steels. Low-hydrogen welding procedures must be
used for arc welding. Preheat and interpass temperatures
of 204°C (400°F) and higher are required to retard the
formation of brittle high-carbon martensite in the weld
metal and HAZ. Postweld stress relief is recommended,
particularly for welded joints in thick workpieces. The
stress relieving procedure described previously for mediumcarbon steels should be used.
The selection of an appropriate filler metal depends
on the carbon content of the steel, the weldment design,
and service requirements. Normally, steel filler metals
are not produced with high carbon content. However, a
30
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
low-alloy steel filler metal may be suitable for many
applications. Austenitic stainless steel or nickel-base
filler metals such as E309, E312, or ENiCrFe-3 also
may be used. The effects of dilution of the weld metal
on the response to postweld heat treatment must be
evaluated. Pickup of carbon in an alloy-steel filler metal
may significantly increase the hardenability of the weld
metal. Consequently, the welding procedures should be
designed to minimize dilution.
High-carbon steels are commonly used for applications requiring high hardness or abrasion resistance,
which is imparted by heat treatment. The steel should
be welded in the annealed condition and then heat
treated. Annealing is recommended prior to the repairwelding of broken parts. Successful welding requires
the development and testing of specific welding procedures for each application. Service requirements of the
weldment must be considered when developing these
welding and testing procedures.
WELDING CARBON STEELS
The processes and filler metals used to weld carbon
steels are discussed in this section. Processes include
shielded metal arc welding (SMAW) and the gasshielded arc welding processes: gas metal arc welding
(GMAW), gas tungsten arc welding (GTAW), and
plasma arc welding (PAW). Flux cored arc welding
(FCAW), submerged arc welding (SAW), electroslag
welding (ESW), electrogas welding (EGW), oxyfuel gas
welding (OFW), resistance welding (RW), Electron
beam welding (EBW), laser beam welding (LBW), and
friction welding (FW) are also discussed.
Filler metals used with these processes are classified
by the American Welding Society (AWS) Committee on
Filler Metals and Allied Materials, and specifications
are published by AWS. Carbon steels also may be joined
by several resistance welding and solid state welding
processes. All of these processes are discussed in detail
in Volumes 2 and 3 of the Welding Handbook, Welding
Processes, 9th edition. For additional information on
welding processes, refer to Appendix B, which provides
a resource guide to the various chapters of current
Welding Handbook volumes.49
Shielded Metal Arc Welding
Most carbon steels can be welded with the SMAW
process and covered electrodes, provided that appropriate welding procedures (including preheat, when
required) are used. Covered electrodes are classified
49. American Welding Society (AWS) Welding Handbook Committee,
A. O’Brien, ed., 2004, Welding Processes, Part 1, Volume 2 of Welding
Handbook, 9th ed.; and, 2007, Welding Processes, Part 2, Volume 3
of Welding Handbook, 9th ed., Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
according to the type of covering and also the chemical
composition and mechanical properties of undiluted
weld metal. Carbon steel covered electrodes that produce weld metal with 410 MPa (60 ksi) minimum tensile strength are classified as E60XX; those that
produce 480 MPa (70 ksi) are classified as E70XX.50
A general rule when using SMAW to weld carbon
steel is that the weld metal should slightly overmatch
the strength of the base material. On this basis, the
E60XX classifications are suitable for welding lowcarbon and mild steels, provided the weld metal
strength is adequate. E60XX covered electrodes are not
generally produced with low-hydrogen coverings, and
they should not be used for welding steels that are sensitive to hydrogen cracking.
Type E70XX covered electrodes are produced with
cellulose, titania, and low-hydrogen coverings. Lowhydrogen electrodes should be used when higherstrength welds or low-hydrogen welding conditions, or
both, are required. The low-hydrogen types (E7015,
E7016, E7018, E7028, and E7048) must be handled
and stored under conditions that prevent moisture
pickup in the coating.
Low-alloy steel electrodes, Types E70XX-X through
E130XX-X, which are produced with low-hydrogen and
other coatings, are designed to produce weld metal with
minimum tensile strengths of 480 MPa to 830 MPa
(70 ksi to 120 ksi).51 The carbon content of the deposited
weld metal will be 0.15% or less, depending on the
electrode type. Low-hydrogen electrodes can be selected
from this group to match the tensile strength of a
medium-carbon or high-carbon steel. Again, service
conditions and the design of the structure will determine whether the weld should match the strength or
hardness of the steel. The electrodes must be stored and
used under conditions that prevent moisture pickup by
the coating, as discussed previously.
Gas-Shielded Arc Welding
The gas-shielded arc welding processes include gas
metal arc welding, gas tungsten arc welding, and
plasma arc welding. Carbon and low-alloy steel bare
electrodes and welding rods are available for use with
these processes.52 The electrodes are classified on the
basis of chemical composition and the mechanical
properties of the undiluted weld metal. Minimum tensile strength ranges from 480 MPa to 830 MPa (70 ksi
to 120 ksi). The same considerations apply to the selection of a bare electrode as those for a covered electrode.
50. See Reference 24.
51. See Reference 24 (A5.5/A5.5M:2006).
52. Refer to AWS A5.18/A5.18M:2005 (Reference 46), or American
Welding Society (AWS), 2005, Specification for Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding, AWS A5.28/A5.28M:
2005, Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
Shielding gases commonly used for the gas metal arc
welding of carbon steels are carbon dioxide (CO2),
argon with carbon dioxide, and argon with oxygen.53
The selection of a gas mixture depends primarily on the
electrode composition and the type of metal transfer
desired (i.e., spray, globular, or short-circuiting). Generally, CO2 shielding is suitable for low-carbon and mild
steels. A mixture of argon-oxygen or argon-carbon
dioxide is suitable for all carbon steels and is recommended for use with low-alloy steel electrodes. Weld
metal toughness is improved often, but not always, when
one of these gas mixtures is used.
Argon is the shielding gas typically used with GTAW
and PAW. However, helium-argon mixtures may be
used to provide deeper joint penetration or to permit
faster travel speeds with automated welding.
The low-hydrogen characteristics of gas-shielded arc
welding processes will be compromised if the filler
metal or shielding gas is contaminated. The filler metal
may be contaminated with rust, moisture, oil, grease,
drawing compounds, or other hydrogen-bearing materials. Therefore, proper cleaning, packaging, rust prevention, and storage are important to avoid hydrogeninduced cracking.
The gas delivery system must be leak-tight to prevent
contamination of the shielding gases by moisture or
hydrocarbons, and to prevent aspiration of moist air
into the system. Only welding-grade (i.e., low dew
point) shielding gases should be used.
All GMAW electrodes that meet the same diffusible
hydrogen limits indicated for SMAW electrodes are
identified by the same designators, whether they are
solid or tubular metal-cored. The designator applied to
these electrodes is based on testing in the shielding gas
with which the electrode is classified.
Flux Cored Arc Welding
Flux cored arc welding (FCAW) electrodes consist of
a steel tube surrounding a core of fluxing ingredients
and sometimes alloying elements. They are designed to
deposit either carbon steel or low-alloy steel weld metal.54
Some electrode classifications are self-shielding; other
classifications use carbon dioxide or mixtures of argon
and carbon dioxide for shielding.
53. Refer to American Welding Society (AWS), 2003, Recommended
Practices for Shielding Gases for Welding and Cutting, AWS C5.10/
C5.10M:2003, Miami: American Welding Society.
54. For electrode specifications, refer to American Welding Society
(AWS) Committee on Filler Metals and Allied Materials, 2005, Specification for Carbon Steel Electrodes for Flux Cored Arc Welding,
AWS A5.20/A5.20M:2005; and, 2010, Specification for Low-Alloy
Steel Electrodes for Flux Cored Arc Welding, AWS A5.29/A5.29M:
2010, Miami: American Welding Society.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
31
Flux cored electrodes that meet the same diffusible
hydrogen limits indicated previously for SMAW electrodes are identified by the same hydrogen designators.
Electrodes that meet the lowest hydrogen limits are not
available for all classifications. Users should contact
electrode manufacturers to determine specific availability. It should be noted that flux cored electrodes can
absorb moisture when exposed to high humidity for prolonged time periods. The absorbed moisture can increase
the hydrogen entering the weld metal, resulting in higher
diffusible hydrogen or porosity in some instances. It is
especially important to avoid absorbed moisture when
welding medium-carbon and high-carbon steels. Electrode wire that will remain unused overnight or longer
should be returned to its protective packaging. If wire is
exposed for longer periods of time, the manufacturer
should be consulted regarding probable damage to the
low-hydrogen characteristics and possible reconditioning procedures.55
The operating characteristics of FCAW electrodes
vary with the ingredients in the core and the shielding
gas, if used. In general, the gas-shielded electrodes provide better notch toughness, particularly with argonrich shielding mixtures and a basic slag (i.e., class
EXXT-5). However, some self-shielded electrodes can
provide weld metal with adequate notch toughness for
many low-carbon or mild steel applications.
Carbon steel FCAW electrodes are designed to produce undiluted weld metal with a minimum tensile
strength of 410 MPa or 480 MPa (60 ksi or 70 ksi).
These are suitable for welding low-carbon and mild
steels. Medium-carbon and high-carbon steels can be
welded with these electrodes if the weld metal will have
adequate strength for the application. For weld strength
requirements above 480 MPa (70 ksi), a suitable lowalloy steel FCAW electrode should be used. Electrodes
are available that can deposit undiluted weld metal with
tensile strengths ranging from 410 MPa to 830 MPa
(60 ksi to 120 ksi).
Submerged Arc Welding
Submerged arc welding (SAW) is performed with an
electrode, either solid or metal-cored, and a granular
flux. The flux shields the arc and weld pool from the
atmosphere and modifies the composition and mechanical properties of the weld. Solid-wire electrodes made
of carbon steel and low-alloy steel are classified according to chemical composition. The classification of
metal-cored electrodes made of low-alloy steel is based
on the chemical composition of deposited weld metal
using an appropriate flux.56 Likewise, fluxes are classi55. See Reference 54.
32
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
fied on the basis of the chemical composition and
mechanical properties of weld metal deposited with a
particular type of electrode.
The welding and heat treatment schedules required
for certain applications may produce weld metal with
mechanical properties that differ from those required
by the filler metal specification. In such cases, the
mechanical properties of the weld metal should be
determined by appropriate testing. Weld-metal properties may be determined either in the as-welded condition or after a specified postweld heat treatment.
Carbon steel electrode and flux combinations are
designed to achieve minimum weld-metal tensile
strengths of 410 MPa or 480 MPa (60 ksi or 70 ksi).
These combinations are recommended for welding lowcarbon and mild steels and also for medium-carbon,
high-carbon, and low-alloy steels when high strength is
not required in the weld joint. Combinations of lowalloy steel electrodes and fluxes are recommended for
welding alloy steels of similar composition, or for welding medium- and high-carbon steels when high-strength
joints are needed to meet service requirements.
Response to postweld heat treatment must be considered. As described, flux must be kept clean and dry to
maintain low-hydrogen welding conditions, and it must
be applied at a sufficient depth to provide adequate
shielding. Also, the electrode must be clean and free of
contaminants, as discussed for the gas-shielded arc welding processes.
Submerged arc welding flux and wire combinations
that meet the same diffusible hydrogen limits indicated
for SMAW electrodes are identified by the same hydrogen designators. The welding wire and flux must be
considered together.
Electroslag and Electrogas Welding
Electroslag welding (ESW) and electrogas welding
(EGW) are used primarily for producing single-pass
groove welds in the vertical position. Electroslag welding uses a resistance-heated, slag pool to melt the electrode. This process generally is used for welding steel
plates 32 mm to 305 mm (1.25 in. to 12 in.) in thickness. Electrogas welding is similar to gas metal arc
welding or flux cored arc welding, depending on the
type of electrode. This process is best suited for welding
thick plates over 13 mm (1/2 in.).
These processes are used mostly to weld low-carbon
and mild steels, but medium-carbon steels also may be
welded. Generally, when the weldment requires
postweld heat treatment, an electrode composition
56. See Reference 47, and American Welding Society (AWS) Committee on Filler Metals and Allied Materials, 2007, Specification for
Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding,
AWS A5.23/A5.23M:2007, Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
should be selected that will produce weld metal that
responds satisfactorily to the heat treatment. Dilution
by the base metal must be considered during selection.
Electrodes and fluxes for ESW are classified in a
manner similar to that for submerged arc welding.57
Both solid and metal-cored ESW electrodes can produce
weld metal with a minimum tensile strength of 410 MPa
(60 ksi) or higher, depending on the specific electrodeand-flux combination and the welding conditions. Most
solid electrodes consist of carbon-manganese steels.
Metal-cored electrodes generally deposit low-alloy steel
weld metal.
Solid carbon steel electrodes for electrogas welding
are essentially the same as those used for GMAW. Fluxcored electrodes are designed specifically for use with
this process to deposit low-carbon or low-alloy steel
weld metal.58 Welding may be accomplished using carbon dioxide, argon mixed with carbon dioxide, or
argon mixed with oxygen. One of the carbon steel fluxcored electrode classifications, EGXXT-1, can be used
without shielding gas. Minimum tensile strength requirements for deposited weld metal are the same as for electroslag welding.
Oxyacetylene Welding
Most low-carbon and mild steels can be joined by oxyacetylene welding (OAW), but the process is much slower
than arc welding. The slow heating characteristics of
the process result in rather extensive heating of the
steel. As a result, mechanical properties developed in
the base metal by prior heat treatment or cold working
may be impaired. Conversely, the cooling rate in the
weld zone will be comparatively slow.
Oxyacetylene welding of steel is performed without
flux, and obviously without a shielding gas. Therefore,
the weld metal is not protected from the atmosphere by
a slag or shielding-gas cover, but is protected only by
gases derived from the combustion of the correctly
selected mixture of oxygen and acetylene. Welded joints
are likely to contain discontinuities that are unacceptable for many applications, and the mechanical properties of the weld metal may be inadequate for the
intended service.
Carbon steels containing more than 0.35% carbon
require special precautions when welded with oxyacetylene welding. Preheating with a torch or another heat
source is recommended to retard the cooling rate of the
57. Refer to American Welding Society (AWS) Committee on Filler
Metals and Allied Materials, 2009, Specification for Carbon and
Low-Alloy Steel Electrodes and Fluxes for Electroslag Welding, AWS
A5.25/A5.25M-97 (R2009), Miami: American Welding Society.
58. Refer to American Welding Society (AWS) Committee on Filler
Metals and Related Materials, 2009, Specification for Carbon and
Low-Alloy Steel Electrodes for Electrogas Welding, AWS A5.26/
A5.26M-97 (R2009), Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
weld and heat-affected zone. In some cases, postweld
heat treatment may be needed to refine the grain size of
the weld zone and improve toughness.
Steel welding rods are available for oxyacetylene
welding of carbon steel and low-alloy steels.59 They are
classified on the basis of the minimum tensile strength
of as-deposited weld metal. Type R45 welding rods are
recommended for depositing low-carbon steel weld
metal for general applications. Type R60 welding rods
should be used for steels with tensile strengths in the
range of 340 MPa to 450 MPa (50 ksi to 65 ksi). Type
R65 rods are best for welding either carbon steels or lowalloy steels with tensile strength in the range of 450 MPa
to 520 MPa (65 ksi to 75 ksi). Carbon steel and lowalloy steel welding rods designed for GTAW also can be
used for oxyacetylene welding. If a suitable welding rod
is not available for welding a specific steel, strips
sheared from the base metal may be used as filler metal.
Resistance Welding
Carbon steels can be joined by all of the resistance
welding processes, i.e., resistance spot welding (RSW),
resistance seam welding (RSEW), projection welding
(PW), flash welding (FW) upset welding (UW), high-frequency upset welding (UW-HF), and high-frequency
resistance welding (RSEW-HF). The heating and cooling rates for these processes are very high compared to
those for arc welding. Consequently, the hardenability
and critical cooling rate of the specific steel must be considered when selecting the process and welding procedures.
The weld zone and heat-affected zone are quenched
by a water-cooled copper-alloy electrode bearing onto
the workpieces. The severity of the quench depends on
the length of the heat conduction path, the size of the
electrode contact area, and the duration of quenching.
Quenching is more severe when welding thin sheet with
the resistance spot, seam, or projection processes, and
when flash welding or upset welding with a welding rod
or wire that has a small cross-section. Retracting the
electrodes from the weldment as soon as practical will
reduce the quenching rate. With some processes, such
as resistance seam welding and high-frequency welding,
the weld may be quenched as the electrode is cooled by
water spraying or flooding. If the hardness of the weld
and HAZ is excessive, postheating or tempering while
in the welding machine may reduce the hardness to an
acceptable level. In some cases, it may be appropriate to
heat treat the weldment in auxiliary equipment.
59. Refer to American Welding Society (AWS) Committee on Filler
Metals and Allied Materials, 2007, Specification for Carbon and
Low-Alloy Steel Rods for Oxyfuel Gas Welding, AWS A5.2/A5.2M:
2007, Miami: American Welding Society.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
33
Low-Carbon Steel. Low-carbon steel is readily joined
by all resistance welding processes because these steels
have low hardenability. Resistance welds normally have
adequate ductility for the application. Spot welds and
seam welds in thin sheet steel can have relatively high
hardness when the carbon content exceeds about
0.08%. If this is objectionable, sheet with a nominal
carbon content of 0.08% or less should be specified.
Suggested schedules for resistance welding of lowcarbon steel sheet are provided in the following charts:
Table 1.5 for resistance spot welding, Table 1.6 for
multiple-impulse resistance spot welding, Table 1.7 for
resistance seam welding, and Table 1.8(A) and 1.8(B) for
resistance projection welding.60 Variation from these
conditions will be necessary to adjust for the weldment
design and the configuration of the welding machine.
Suitable welding conditions for a specific application
should be determined by appropriate testing.
Data for the flash welding of carbon steel shapes
are provided in Chapter 3 of the Welding Handbook,
Volume 3, which covers this process (refer to Appendix
B).61 Recommended procedures for high-frequency resistance welding and upset welding should be obtained from
the equipment manufacturer.
Resistance Seam Weldability Lobes. The resistance seam weldability of steel can be quantified by a
weldability lobe. The weldability lobe defines the welding conditions over which a continuous seam weld can
be produced without either damaging the weld integrity
or interrupting the process. The weldability lobe generally is depicted in two dimensions representing effective
combinations of welding speed and welding current. In
three dimensions, this is expanded to include all combinations of welding current, welding speed, and electrode force. The upper limit of the lobe (i.e., excessive
heating of the weld) typically is characterized by surface
eruption, copper-contamination cracking of the steel, or
sticking of the electrodes to the steel. The lower limit of
the lobe (i.e., insufficient weld growth) is defined as the
point where a continuous seam is no longer found.
Weldability lobes are powerful tools for determining
both the process performance of a given application
and the weldability of a specific steel. A wide lobe generally is very tolerant of changes in process conditions,
while a narrow lobe suggests that even small changes in
process conditions will have a significant effect on weld
quality.
To illustrate this approach, the weldability lobes of
typical 0.80 mm (0.032 in.) thick low-carbon steels and
hot-dipped galvanized steels for the most common
60. Appropriate projection designs for steel are discussed in Volume
3 of Welding Handbook, 9th ed., Chapter 2 (see Reference 50). Refer
also to Appendix B of this volume for a list of the contents of current
volumes of the Welding Handbook.
61. See Reference 50.
34
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.5
Suggested Schedules for Resistance Spot Welding of Low-Carbon Steel Sheet
Thicknessa
Electrode
Face Diam.b
Static
Electrode
Force
mm
in.
mm
N
in.
Weld
Time,
Cyclesc
lb
Approx.
Welding
Current
kAd
Minimum Shear Strength When
Base Metal Tensile Strength is:
Approximate
Nugget
Diameter
Minimum
Pitche
Below 70 ksi
(480 MPa)
Above 70 ksi
(480 MPa)
mm
mm
N
N
in.
in.
lb
lb
0.25
0.010
3.30
0.13
890
200
4
4.0
2.54
0.10
6.4
0.25
578
130
801
180
0.53
0.021
4.82
0.19
1334
300
6
6.5
3.30
0.13
9.4
0.37
1423
320
1957
440
0.79
0.031
4.82
0.19
1779
400
8
8.0
4.06
0.16
12.7
0.50
2535
570
3559
800
1.02
0.040
6.35
0.25
2224
500
10
9.5
4.82
0.19
19.1
0.75
4092
920
5338
1200
1.27
0.050
6.35
0.25
2891
650
12
10.5
5.58
0.22
22.1
0.87
6005
1350
—
—
1.57
0.062
6.35
0.25
3559
800
14
12.0
6.35
0.25
25.4
1.00
8229
1850
—
—
1.98
0.078
7.87
0.31
4893
1100
17
14.0
7.36
0.29
31.8
1.25
12 010
2700
—
—
2.39
0.094
7.87
0.31
5783
1300
20
15.5
7.87
0.31
38.0
1.50
15 346
3450
—
—
2.77
0.109
9.65
0.38
7117
1600
23
17.5
8.12
0.32
41.2
1.62
18 460
4150
—
—
3.18
0.125
9.65
0.38
8007
1800
26
19.0
8.38
0.33
44.5
1.75
22 241
5000
—
—
a. Thickness of thinnest outside sheet. Data applicable to a total metal thickness of four times the given thickness. Maximum ratio of two adjacent
thicknesses is 3 to 1.
b. Flat-faced electrode of RWMA Group A, Class 2 copper alloy.
c. Single-impulse, frequency of 60 Hz.
d. Single-phase ac machine.
e. Minimum spacing between adjacent spot welds between two sheets without adjustment of the welding schedule for shunting.
Table 1.6
Suggested Schedules for Multiple-Impulse Resistance Spot Welding of Low-Carbon Steel Sheet
No. of Impulsesc
a.
b.
c.
d.
Static Electrode
Force
Approx.
Nugget
Diameter
Min. Shear
Strength
mm
N
Thicknessa
Electrode Face
Diameterb
mm
in.
mm
in.
N
lb
Single
Spot
3.18
0.125
11.18
0.44
8007
1800
3
4
5
18.0
9.4
0.37
22 241
5000
4.76
0.188
12.70
0.50
8674
1950
6
14
20
19.5
14.2
0.56
44 482
10 000
6.35
0.25
14.22
0.56
9564
2150
12
18
24
21.5
19.1
0.75
66 723
15 000
7.87
0.31
15.74
0.62
10 675
2400
15
23
30
24.0
22.1
0.87
88 964
20 000
Multiple Spot Spacing
51–102 mm 25–51 mm
(2–4 in.)
(1–2 in.)
Approx.
Welding
Current,
kAd
in.
lb
Thinnest of two sheets. Maximum ratio of sheet thickness is 2 to 1.
Flat-faced electrode of RWMA Group A, Class 2 copper alloy.
Heat time is 20 cycles; cool time is 5 cycles (60 Hz).
Single-phase ac machine.
current pulsing condition (3-on/1-off) are shown in Figure 1.18 and Figure 1.19. These lobes were developed
using RWMA Class II electrodes. The width of the circular electrode (wheel) was 11 mm (0.44 in.); the radius
of the electrode face was 13 mm (0.5 in.). The welding
conditions (welding current, electrode force, and welding speed) can be selected for each application using
the weldability lobe approach, which clearly indicates
the robustness of the process at the various welding
conditions.
Mild Steels and Medium-Carbon Steels. When
using resistance welding processes to join mild steels
and medium-carbon steels, it is usually necessary to
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
35
Table 1.7
Suggested Schedules for Resistance Seam Welding of Low-Carbon Steel Sheet
Thicknessa
Electrode
Face Widthb
Static
Electrode Force
Travel Speed
Welds Per
Unit Length
Approx.
Welding
Current,
Cool
Time,
Cyclesc
mm/s
in./min
mm
in.
kAd
mm
in.
mm
in.
N
lb
Heat
Time,
Cyclesc
0.25
0.010
4.82
0.19
1779
400
2
1
33.8
80
381
15
8.0
0.53
0.021
4.82
0.19
2447
550
2
2
31.7
75
305
12
11.0
0.79
0.031
6.35
0.25
3114
700
3
2
30.0
72
254
10
13.0
1.02
0.040
6.35
0.25
4003
900
3
3
28.6
67
228
9
15.0
1.27
0.050
7.87
0.31
4671
1050
4
3
27.5
65
203
8
16.5
1.57
0.062
7.87
0.31
5338
1200
4
4
26.7
63
177
7
17.5
1.98
0.078
9.65
0.38
6672
1500
6
5
23.3
55
152
6
19.0
2.39
0.094
11.18
0.44
7562
1700
7
6
21.2
50
139.7
5.5
20.0
2.77
0.109
12.7
0.50
8674
1950
9
6
20.3
48
127
5
21.0
3.18
0.125
12.7
0.50
9786
2200
11
7
19.1
45
114.3
24.5
22.0
a. Thickness of thinnest outside piece. Data applicable to a total metal thickness of 4 times the given thickness. Maximum ratio of two adjacent thicknesses
is 3 to 1.
b. Flat-faced wheel electrode of RWMA Group A, Class 2 copper alloy.
c. Frequency of 60 Hz
d. Single-phase ac machine.
control the cooling rate from welding temperature or
from a subsequent tempering cycle to prevent excessive
hardness and associated cracking in the weld zone.
With mild steels, postheating with a lower current for
several cycles (60 Hz) may be sufficient to avoid the formation of hard martensite in the weld. Spot welds in
medium-carbon steels can be quenched to martensite
and then tempered by resistance heating to soften the
martensite and improve ductility. Suitable postheat or
quench-and-temper cycles must be established by welding tests. Table 1.9 lists examples of quench-and-temper
cycles for the spot welding of SAE 1020, 1035, and
1045 carbon steel sheet. As expected, the shear strength
of the spot weld increases in proportion to the increase
in the carbon content of the steel.
Normally, low-carbon and medium-carbon steels can
be flash welded without the risk of cracking. Preheat or
postheat is not required, but the application of one or
both can improve ductility in the weld joint. When
using flash welding for small or thin cross sections,
postheating in the welding machine can be used to control weld hardness. The welding machine should be
equipped with appropriate current and time controls to
program a postheat cycle. An alternative is to heat treat
the weldment in a furnace to homogenize the microstructure of the weld zone and provide the required
mechanical properties.
High-Carbon Steel. High-carbon steels are seldom
joined by resistance welding processes because of the
high hardenability of these steels, and because applications and products for these processes are limited. However, the procedures provided for welding low-carbon
and medium-carbon steels are applicable also to highcarbon steels, with appropriate adjustments to accommodate the higher hardenability.
Electron Beam and Laser Beam Welding
Low-carbon steels are readily welded by electron
beam welding (EBW) and laser beam welding (LBW).
The rapid heating and cooling rates associated with
these processes result in weld metal and heat-affected
zones with relatively small grain sizes compared to
those found in arc welds. Also, the heat-affected zone is
much narrower. Fully killed steel is preferred for applications involving these welding processes.
Thickness, t Diam.,
mmd
mm
Height,
mm
Welding Schedule B for
1–3 Projections, per Projectionb
Welding Schedule A for
Single Projectiona
Projection
Min.
Pitch,
mm
Min.
Contact
Overlap,
mm
Welding Schedule C for
3 or More Projections, per Projectionc
Weld Electrode Welding
Shear
Shear
Weld Electrode Welding
Shear
Weld Electrode Welding
Force, Current, Strength, Time,
Force, Current, Strength,
Time,
Force, Current, Strength, Time,
N
N
Cycles
A
A
N
N
N
A
Cyclese
N
Cyclese
0.56
2.29
0.64
9.7
6.4
3
667
4400
1646
6
667
3850
1446
6
356
2900
1290
0.71
2.29
0.64
9.7
6.4
3
867
5500
2224
6
667
4450
1890
8
445
3300
1513
0.94
2.79
0.89
12.7
9.7
3
1068
6600
3114
6
667
5100
2335
11
556
3800
1890
1.09
2.79
0.89
12.7
9.7
5
1468
8000
4715
10
934
6000
3892
15
712
4300
3203
1.25
3.56
0.97
19.1
2.7
8
1779
8800
5783
16
1201
6500
4893
19
979
4600
3892
1.55
3.81
1.07
19.1
12.7
10
2447
10 300
8007
20
1624
7650
7006
25
1468
5400
5449
1.96
4.57
1.22
22.4
12.7
14
3559
11 850
10 787
28
2358
8850
9564
34
2091
6400
7784
2.34
5.33
1.27
26.9
15.8
16
4537
13 150
14 457
32
3025
9750
12 455
42
2713
7200
10 342
2.72
6.10
1.40
31.8
19.1
19
5560
14 100
17 126
38
3692
10 600
15 346
50
3292
8300
12 900
3.12
6.86
1.47
38.1
20.6
22
6672
14 850
21 351
45
4448
11 300
18 683
60
4003
9200
16 014
3.43
7.62
1.58
41.4
22.4
24
7340
15 300
24 465
48
4893
11 850
21 574
66
4448
9900
18 905
a.
b.
c.
d.
AWS WELDING HANDBOOK 9.4
Schedule A is usable for welding more than one projection if current is decreased but excessive weld expulsion may result and power demand will be greater than with Schedules B or C.
Schedule B is usable for welding more than three projections, but some weld expulsion may result and power demand will be greater than with Schedule C.
Schedule C is usable for welding less than three projections with welding current increased approximately 15% and possible objectionable final sheet separation.
For unequal sheet thickness ratios, T/t, up to 3 to 1:
1. The weld time, cycles, should be increased by a factor f t determined by the formula ft = 1.5 (T/t) – 0.5.
2. The welding current per projection should be increased by a factor fc determined by the formula fc = 0.1 (T/t) + 0.9.
e. Frequency of 60 Hz.
36 CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.8(A)
Suggested Schedules for Resistance Projection Welding of Low-Carbon Steel Sheet
(Metric Units)
AWS WELDING HANDBOOK 9.4
Table 1.8(B)
Suggested Schedules for Resistance Projection Welding of Low-Carbon Steel Sheet
(U.S. Customary Units)
Thickness, t Diam.,
in.d
in.
Height,
in.
Min.
Pitch,
in.
Min.
Contact
Overlap,
in.
Welding Schedule C for
3 or More Projections, per Projectionc
Weld Electrode Welding
Shear
Shear
Weld Electrode Weld
Shear
Weld Electrode Welding
Force, Current, Strength, Time,
Force, Current, Strength,
Time,
Force, Current, Strength, Time,
lb
lb
Cycles
A
A
lb
lb
lb
A
Cyclese
lb
Cyclese
0.022
0.090
0.025
0.38
0.25
3
150
4400
370
6
150
3850
325
6
80
2900
290
0.028
0.090
0.025
0.38
0.25
3
195
5500
500
6
150
4450
0.037
0.110
0.035
0.50
0.38
3
240
6600
700
6
150
5100
425
8
100
3300
340
525
11
125
3800
0.043
0.110
0.035
0.50
0.38
5
330
8000
1060
10
210
6000
425
875
15
160
4300
720
0.049
0.140
0.038
0.75
0.50
8
400
8800
1300
16
270
6500
1100
19
220
4600
875
0.061
0.150
0.042
0.75
0.50
10
550
10 300
1800
20
365
7650
1575
25
330
5400
1225
0.077
0.180
0.048
0.88
0.50
14
800
11 850
2425
28
530
8850
2150
34
470
6400
1750
0.092
0.210
0.050
1.06
0.62
16
1020
13 150
3250
32
680
9750
2800
42
610
7200
2325
0.107
0.240
0.055
1.25
0.75
19
1250
14 100
3850
38
830
10 600
3450
50
740
8300
2900
0.123
0.270
0.058
1.50
0.81
22
1500
14 850
4800
45
1000
11 300
4200
60
900
9200
3600
0.135
0.300
0.062
1.63
0.88
24
1650
15 300
5500
48
1100
11 850
4850
66
1000
9900
4250
Schedule A is usable for welding more than one projection if current is decreased, but excessive weld expulsion may result and power demand will be greater than with Schedules B or C.
Schedule B is usable for welding more than three projections, but some weld expulsion may result and power demand will be greater than with Schedule C.
Schedule C is usable for welding less than three projections with welding current increased approximately 15%; objectionable final sheet separation is possible.
For unequal sheet thickness ratios, T/t, up to 3 to 1:
1. The weld time, cycles, should be increased by a factor ft determined by the formula ft = 1.5 (T/t) – 0.5.
2. The welding current per projection should be increased by a factor fc determined by the formula fc = 0.1 (T/t) + 0.9.
e. Frequency of 60 Hz.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
a.
b.
c.
d.
Welding Schedule B for
1–3 Projections, per Projectionb
Welding Schedule A for
Single Projectiona
Projection
37
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
50
CURRENT, kA
45
40
35
30
25
20
15
0
180
600
1
350
0
0
0
F
0
8
300
OR 140
0
0
25 in
CE 1200
00
700
, lb
0 2 , in./m
150
0
5
FO
0
0
1
0
0
D
1
125
00
RC 60
EE
1
0
0
P
0
0
0
S
1
8 5
E, 5000
ec
75
m/s
N
0
,m
50
D
400
E
25
SPE
Figure 1.18—The 3-Dimensional Averaged
Weldability Lobe for Uncoated Steel
Using a 3-On/1-Off Pulsing Schedule
50
45
40
CURRENT, kA
38
35
30
25
20
15
800
1
0
160
350
00
00
FO 14
0 3
5
0
0
2
RC 120
700
200 ./min
150
E,
0
150 ED, in
FO 6000
0
lb 100
125
0
E
1
0
RC
0
P
0
0
S
1
80 5
E, 5000
/sec
75
N
mm
0
,
0
0
5
D
0
4
E
25
SPE
0
800
Figure 1.19—The 3-Dimensional Averaged
Weldability Lobe for Hot-Dipped Galvanized Steel
Using a 3-On/1-Off Pulsing Schedule
AWS WELDING HANDBOOK 9.4
AWS WELDING HANDBOOK 9.4
39
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.9
Typical Resistance Spot Welding Schedules for Medium-Carbon and Low-Alloy Steel Sheet
AISI
No.
Thickness
Electrode
Face
Diameterb
Electrode
Force
mm
mm
N
in.
in.
lb
Approx.
Approx.
Nugget
Weld Quench Temper Welding Temper
Diameter
Time, Time, Time, Current, Current,e
%
mm
in.
Cyclesc Cyclesc Cyclesc
kAd
Minimum
Shear
Strength
Min.
Pitchf
mm
in.
N
lb
1020
1.02 0.040
6.35
0.25
6561 1475
6
17
6
16.0
90
5.84
0.23
25.4
1
6050
1360
1035
1.02 0.040
6.35
0.25
6561 1475
6
20
6
14.2
91
5.58
0.22
25.4
1
6939
1560
1045
1.02 0.040
6.35
0.25
6561 1475
6
24
6
13.8
88
5.33
0.21
25.4
1
8896
2000
4130
1.02 0.040
6.35
0.25
6561 1475
6
18
6
13.0
90
5.58
0.22
25.4
1
9430
2120
4340
0.79 0.031
4.82
0.19
4003
900
4
12
4
8.3
84
4.06
0.16
19.0
0.75
4804
1080
—
1.57 0.062
7.87
0.31
8896 2000
10
45
10
13.9
77
6.85
0.27
38.1
1.50 17 081
3840
—
3.18 0.125 16.00
0.63 24 465 5500
45
240
90
21.8
88
13.97
0.55
63.5
2.50 60 940 13 700
8630
0.79 0.031
4.82
0.19
3559
800
4
12
4
8.7
88
4.06
0.16
19.0
0.75
5427
1220
—
1.57 0.062
7.87
0.31
8007 1800
10
36
10
12.8
83
6.85
0.27
38.1
1.50 18 860
4240
—
3.18 0.125 16.00
0.63 20 017 4500
45
210
90
21.8
84
13.97
0.55
63.5
2.50 58 717 13 200
a.
b.
c.
d.
e.
f.
Two equal thicknesses.
Flat-faced electrode of RWMA Group A, Class 2 copper alloy.
Cycle of 60 Hz.
Single-phase ac machine.
Percentage of welding current with phase-shift heat control.
Minimum pitch between adjacent spot welds without adjustment of the welding schedule for shunting.
Friction Welding
Filler Metals
Low-carbon steels are readily joined by friction welding (FW). Welding conditions are not critical from a
metallurgical standpoint. Medium- and high-carbon
steels can be friction welded, but the welding conditions
must be controlled within narrow ranges. The heating
time for these steels should be relatively long to slow
the cooling rate of the weld.
Carbon steels can be brazed with copper, gold,
nickel, and silver filler metals.62 All silver (BAg) brazing
filler metals are suitable for use with carbon steel. Filler
metals containing nickel usually have better wettability
and are preferred for good joint strength.
The copper (BCu) filler metals are used mainly for
furnace brazing, where preplacement of the workpieces
is needed. The RBCuZn filler metals in rod form generally are used with torch brazing, but they also can be
used with furnace brazing or induction brazing. The
high brazing temperatures tolerated by these filler metals often permit simultaneous brazing and heat-treating
operations.
The nickel (BNi) filler metals are used when their
unique properties are needed for special applications.
Brazing with nickel filler metals normally is done in a
controlled atmosphere.
BRAZING CARBON STEELS
Carbon steels can be joined by virtually all of the
brazing processes. Torch brazing (TB), furnace brazing
(FB), and induction brazing (IB) are commonly used.
Filler metals in the form of continuous wire or strip can
be applied automatically using electro-mechanical wire
feeders. Filler metal in powder form can be blended
with flux and paste-forming ingredients, and automatically applied with pressurized dispensing equipment.
For torch brazing, the heating equipment includes a
standard oxyfuel gas torch. Brazing furnaces can be
either a batch type or a conveyor type, with or without
control of the atmosphere.
62. Refer to American Welding Society (AWS) Committee on Filler
Metals and Allied Materials, 2004, Specification for Filler Metals for
Brazing and Braze Welding, AWS A5.8/A5.8M:2004; and, 2003,
Specification for Fluxes for Brazing and Braze Welding, AWS A5.3192R, Miami: American Welding Society.
40
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Fluxes and Atmospheres
The selection of a proper flux or furnace atmosphere
generally is required when brazing steels depends on the
brazing filler metal. American Welding Society (AWS)
brazing flux Type 3A, 3B, or 4 is suitable for BAg filler
metals. Type 5 flux normally is used with the RBCuZn
filler metals. Fluxes and atmospheres may be used
together. Flux can be used in either paste or powder
form, or it can be combined with the filler metal. In a
face-fed operation, the hand-held filler metal can be
coated with the appropriate flux. In atmosphere brazing, the filler metal is preplaced in or near the joint, and
the assembly is charged into the brazing chamber. Brazing temperature and time must be controlled to ensure
proper melting and flow of the filler metal into the
joint. For more detailed information, refer to Table 12.6
in the Welding Handbook, Volume 2, Chapter 12.63
Joint Clearance
When using a mineral flux, joint clearances in the
range of 0.05 mm to 0.127 mm (0.002 in. to 0.005 in.)
produce the best mechanical properties with most filler
metals. When furnace brazing with a protective atmosphere, light-press fits are preferred for copper and
other filler metals. Filler metals with relatively narrow
melting ranges are required for close-fitting joints. Conversely, filler metals with wide melting ranges have
good bridging characteristics when wide clearances are
involved. Furnace dew point can be used to control the
fluidity of BCu filler metal when brazing joints with
wide joint clearances.
Metallurgical Considerations
The mechanical properties of the heated area in coldworked steel may be impaired as a result of annealing
during brazing. With hot-rolled steel, brazing above the
austenitizing temperature will alter the mechanical
properties of the metal. These changes in properties
may result from decarburization of the steel in some
furnace atmospheres, or a change in grain size, or both.
Original grain size can be restored by subsequent heat
treatment below the remelt temperature of the filler
metal. Loss of carbon through decarburization usually
is unimportant in low-carbon steels. However, in
medium-carbon steels and high-carbon steels, decarburization may lower surface hardness substantially.
The brazing of high-carbon steel is best accomplished prior to or during the hardening operation,
because brazing after hardening will soften the steel.
The hardening temperature for carbon steels normally
63. Refer to Table 12.6 in Chapter 12 of the Welding Handbook,
Volume 2, 9th edition (see Reference 50).
AWS WELDING HANDBOOK 9.4
is in the range of 760°C to 870°C (1400°F to 1600°F).
If brazing is performed prior to the hardening operation, the filler metal must melt well above the hardening
temperature so that the brazed joints will have sufficient strength during that operation. Copper filler metal
is frequently used for this purpose.
At times, the high temperature required for copper
brazing (1090°C to 1150°C [2000°F to 2100°F]) adversely
affects the microstructure of the steel. In such cases, silver
and copper-zinc filler metals with brazing temperatures
in the range of 930°C to 980°C (1700°F to 1800°F) can
be used.
When brazing and hardening operations are combined, a filler metal that solidifies above the austenitizing temperature of the steel generally is used. The
brazement is cooled to below the solidus temperature of
the filler metal and then it is quenched to harden the
steel. Particular attention must be given to the brazement design and the handling procedures, because the
strength of the brazed joint will be very low at the austenitizing temperature. The brazement should be designed
so that the joint is placed in compression rather than
tension during quenching.
THERMAL CUTTING OF CARBON STEELS
Carbon steels are cut or gouged easily by oxyfuel
gas, air-carbon arc, plasma arc, and other thermal cutting processes. Low-carbon steels and mild steels are cut
using standard procedures. With medium- and highcarbon steels, however, significant quench hardening
may occur in the heat-affected zone during cutting. Preheating or postheating, or both, may be necessary for
controlling the hardness of the cut edge to avoid cracking or heat checking.
Preheat temperatures similar to those recommended
for welding with a low-hydrogen process normally are
satisfactory for cutting. The temperature must be nearly
uniform through the workpiece when using oxyfuel gas
cutting. If it is not, the oxidation reaction will proceed
faster in the hotter zone, resulting in a rough cut surface.
The cut surface may be heat treated to relieve
stresses, reduce hardness, or alter the microstructure.
Furnace heating or local torch heating may be suitable.
Air-carbon arc gouging may leave areas of carburized steel on the cut surface when improper cutting procedures are used. These high-carbon areas may result in
excessive hardening of the steel during welding if they
are not removed. When air-carbon arc gouging is performed manually, it is good practice to grind to clean
metal after cutting to remove any carburized areas on
the surface. This procedure normally is not required
with mechanized gouging.
AWS WELDING HANDBOOK 9.4
HIGH-STRENGTH LOW-ALLOY
STEELS
From a metallurgical standpoint, the group of steels
known as high-strength low-alloy (HSLA) or microalloyed steels actually are low-alloy steels, despite the fact
that historically, they have been marketed to industry as
high-end carbon steels. High-strength low-alloy steels
are formulated with small amounts of certain alloying
elements to provide higher strength, better toughness
and weldability, and in some cases, greater resistance to
corrosion in specific environments, than ordinary carbon steels. One of the first HSLA steels was COR-TEN.64
Introduced in the 1930s, COR-TEN has atmospheric
corrosion resistance about five times superior to normal
carbon steel. Modern HSLA steels are tailored to produce specific properties. For instance, some HSLA steels
used in pipelines and pressure vessels are designed to
resist H2S degradation, such as hydrogen-induced stepwise cracking. Conventional HSLA steels are used
mainly in the as-rolled or normalized condition. The
rolling process is integral to the development of final
mechanical properties; however, normalizing or quenching
and tempering may improve toughness in thick sections
or extend the strength ranges of some grades. Also, special rolling practices known as thermomechanically controlled processing (TMCP) have been devised over the
past 25 years. Steels produced by these methods are still in
widespread use, especially in the oil and gas industry. A
separate section of this chapter is devoted to TMCP steels.
In general, HSLA steels are strengthened by a combination of ferrite grain refinement, precipitation hardening and substructural strengthening. Substructural
strengthening occurs as dislocation arrays and ferrite
subgrains interact to raise the yield strength. Because of
these alternative strengthening mechanisms, HSLA
steels do not rely on transformation products such as
pearlite, bainite or martensite for their high strength.
Their low carbon and alloy content, in turn, contribute
to the excellent weldability of most HSLA steels.
The principal microalloy additions in HSLA steels
are niobium and vanadium, added singly or in combination in amounts up to around 0.10%. For some
applications, when thicker sections or higher strengths
are involved, nickel or molybdenum may be used to
complete the alloy formulation. Early HSLA steels often
contained nitrogen added in combination with vanadium; however, this practice has been largely eliminated
due to the detrimental effects of nitrogen on toughness,
particularly in the heat-affected zone. In fact, modern
steels often include titanium in amounts of up to
0.025% in order to combine with residual nitrogen,
64. COR-TEN is a Trademark of United States Steel Corporation.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
41
thereby suppressing grain coarsening in the heataffected zone and improving overall toughness.
Early HSLA steels were often ingot-cast and were
either fully killed or semikilled. The vast majority of
modern steels are continuously cast, which necessitates
the use of fully killed steels. A few mills, especially those
in recently industrialized countries, may still be producing semikilled ingot castings for low-strength applications.
Typical yield strengths of HSLA steels range from
290 MPa to 760 MPa (42 ksi to 110 ksi). Tensile
strengths are in the range of 410 MPa to 830 MPa
(60 ksi to 120 ksi). Apart from higher strength and better toughness, HSLA steels often are produced with
strict control of impurities (e.g., sulfur, phosphorus, and
oxygen) to enhance other properties such as malleability, resistance to lamellar tearing, and notch toughness.
STEELS PRODUCED BY
THERMOMECHANICALLY CONTROLLED
PROCESSING
Since the late 1960s, structural steelmaking practice
has been driven by the demand for better toughness and
strength, combined with leaner alloy content for
improved weldability. Recognition of the importance of
a fine-grained structure for improving both strength
and toughness resulted in the development of controlled
rolling practices, in which the final rolling temperature
is kept within the normalizing range. Ultimately, these
practices evolved into the sophisticated thermomechanically controlled processing used in modern steelmaking. Major advances in weldability, strength, and lowtemperature toughness have resulted.
Classifications
Steels produced by thermomechanically controlled
processing are subdivided into three categories: Types I,
II, and III. As shown in Figure 1.20, Type I and Type II
do not involve accelerated cooling and differ from one
another in one main respect: the temperature range over
which mechanical deformation (thickness reduction) by
rolling is performed. For Type I TMCP steels, rolling is
performed at relatively low temperatures corresponding
to the dual-phase austenite-ferrite region of the continuous cooling transformation (CCT) diagram. By comparison, Type III steels incorporate accelerated cooling over
a limited temperature range after rolling, depending on
the target properties and other mill-to-mill variables.
Compared with control-rolled Type I and Type II
TMCP steels, the accelerated cooling of Type III TMCP
steel improves through-thickness uniformity in grain
size and mechanical properties, especially in thicker
plates (>25 mm [>1 in.]), while maintaining leaner compositions. Figure 1.21 illustrates these properties. The
42
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Structure(s) Present
or Being Formed
RECRYSTALLIZED
(EQUIAXED)
AUSTENITE
AWS WELDING HANDBOOK 9.4
Temperature
Conventional Processing
SLAB REHEAT
SRT
NORMALIZING
NT
Thermomechanically
Controlled Processing
NONRECRYSTALLIZED
(ELONGATED) AUSTENITE
AUSTENITE + FERRITE
Ar3
Ar1
FERRITE + PEARLITE
FERRITE + BAINITE
Key:
SRT = Slab reheating temperature
NT = Normalizing temperature
Ar3 = Upper critical temperature (A3) with downward correction for the austenite supercooling that occurs on cooling (r)
Ar1 = Lower critical temperature (A1) with downward correction for the austenite supercooling that occurs on cooling (r)
r
= Refroidissement
AcC = With accelerated cooling through the intercritical temperature range
Figure 1.20—Definitions of Thermomechanically Controlled Processing of Steels
LIVE GRAPH
LIVE GRAPH
Click here to view
Click here to view
Figure 1.21—Strength Improvements Relative to Carbon Equivalent
optimized chemical composition, especially low carbon
levels, limits the degradation of toughness in the heataffected zone relative to that of the base metal. This
makes it easier to meet stringent HAZ fracture toughness requirements such as those specified for offshore
plate in the American Petroleum Institute (API) publication Recommended Practice for Preproduction Qualifi-
cation for Steel Plates for Offshore Structures, API RP
2Z.65 Weldability, in terms of resistance to hydrogen
cracking in the HAZ, is also enhanced. According to the
65. American Petroleum Institute (API), Recommended Practice for
Preproduction Qualification for Steel Plates for Offshore Structures,
API RP 2Z, Washington, D.C.: American Petroleum Institute.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
International Institute of Welding (IIW) index, the carbon
equivalent (CE) and Pcm of Type III TMCP steels generally are low enough so that preheating is not required.66
The composition parameter Pcm was introduced to
accommodate the evolution of HSLA steels as they were
being introduced in the early 1970s. It was shown that
the conventional CE formula developed by IIW (Equation 1.2 without Si) did not accurately predict the
cracking tendencies of the reduced-carbon grades
among the newer HSLA steels,67 especially those being
utilized in the oil and gas industry for line pipe and
structural plate. Therefore, the following formula was
developed for and applied to these steels:
(1.3)
Si- + Mn
V- + 5B
Pcm = C + ------------- + Cu
-------- + Ni
------- + Cr
------- + Mo
--------- + ----30 20 20 60 20 15 10
Optimum performance in the production of Type III
TMCP steels requires improved cleanliness, inclusion
shape control, decreased centerline segregation, optimized composition, and optimized rolling schedules.
43
The solidification of a continuous-cast strand tends to
produce bands enriched with alloying and impurity elements such as C, Mn, Nb, P and S, especially along the
centerline. This becomes the mid-thickness region in
rolled plate. This alloy segregation is detrimental to
through-thickness ductility and toughness and reduces
resistance to hydrogen cracking. Magnetic stirring was
developed to minimize centerline segregation.
Optimized Composition and Rolling
Schedule
To optimize composition and rolling schedules, the
microalloy content (V, Nb, Ti, B) is carefully balanced
with low levels of interstitial elements (C, N). Rolling
schedules are then designed to achieve the targeted
grain size and microstructure, and thus the desired
properties.
COMPOSITION AND PROPERTIES
Centerline segregation often results from the continuous casting processes widely used in steel production.
Material specifications for most HSLA steels that
are used in the as-rolled or normalized condition are
provided by ASTM International (formerly American
Society for Testing and Materials).68 Specifications for
other HSLA steels appear in SAE Recommended Practice J1392 and in MIL-S-24645A (HSLA-80/100).69
These steels are designed to provide improved strength,
corrosion resistance, or notch toughness compared to
mild steels while retaining good weldability. Niobium,
copper, molybdenum, nickel, titanium, and vanadium
are used in various combinations.
Table 1.10 lists a number of ASTM specifications
covering structural-quality HSLA steels and shows
alloying elements and ranges of tensile-strength. Table
1.11 lists several HSLA steels classified by ASTM for
pressure vessel applications. Tubing and castings with
similar mechanical properties and chemical compositions are covered by other ASTM specifications.
Table 1.12 presents material specifications for HSLA
line pipe provided by the American Petroleum Institute.
Other API specifications cover plate used in the fabrication
of offshore structures. Representative chemical compositions of modern line pipe and plate produced according to
API specifications are shown in Table 1.12. Table 1.13
shows API mechanical specifications for seamless and
welded pipe.
High-strength low-alloy steels are used in pipelines,
buildings, bridges, offshore structures, construction
66. International Institute of Welding (IIW), 90 Rue des Vanesses,
93420 Villepinte, France. http://www.iiw-iis.org.
67. Yurioka, N., 1990, Weldability of Modern High-Strength Steels,
Proceedings of First US-Japan Symposium on Advances in Welding
Metallurgy, AWS/JWS/JWES.
68. See Reference 37.
69. Society of Automotive Engineers (SAE), 2008, Steel, HighStrength, Hot Rolled Sheet and Strip, Cold Rolled Sheet, and Coated
Steel, Recommended Practice J1392, Warrendale, Pennsylvania: Society of Automotive Engineers.
Cleanliness
Cleanliness, or enhanced purity, is a primary attribute
of TMCP steels. Toughness in the heat-affected zone of a
weld is improved by reduced levels of phosphorus and
nitrogen. Low sulfur content improves through-thickness
ductility and resistance to lamellar tearing.
Control of Inclusion Shape
Clusters of manganese-sulfide stringer inclusions that
have been flattened by rolling, often found at midthickness in steel plate, are detrimental to throughthickness ductility and upper-shelf toughness. These
clustered inclusions also reduce the resistance of a steel
to lamellar tearing and hydrogen cracking. In the
TMCP process, the molten steel is treated with calcium
or certain rare earth elements to convert these inclusions to a less detrimental globular shape.
Decreased Centerline Segregation
44
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.10
ASTM Specifications for High-Strength Low-Alloy Structural Steels
Tensile Strength
Minimum
Yield Strength
Other
MPa
ksi
MPa
ksi
—
0.20 min. Cu
435
63
290
42
—
—
—
415
60
290
42
—
—
—
—
450
65
345
50
—
—
—
—
—
380
55
485
70
0.15–
0.40
—
—
—
—
—
515
75
415
60
0.05
0.15–
0.40
—
—
—
—
—
550
80
450
65
0.80– 0.04
1.25
0.05
0.30– 0.40– 0.40
0.65 0.65
—
0.02– 0.25–0.40 Cu
0.10
485
70
345
50
0.20
0.75– 0.04
1.35
0.05
0.15– 0.40– 0.50
0.50 0.70
—
0.01– 0.20–0.40 Cu
0.10
—
—
—
—
C
0.15
0.80– 0.04
1.35
0.05
0.15– 0.30– 0.25–
0.50 0.50 0.50
—
0.01– 0.20–0.50 Cu
0.10
—
—
—
—
K
0.17
0.50– 0.04
1.20
0.05
0.25– 0.40– 0.70
0.50 0.70
0.10
—
0.30–0.50 Cu;
0.005–0.05 Nb
—
—
—
—
A
0.18
1.00– 0.04
1.35
0.05
0.15–
0.50
—
—
—
—
0.05 Nb
435–570
63–83
290
42
C
0.20
65 mm
(2.5 in.)
and
under
1.15– 0.04
1.50
0.05
0.15–
0.50
—
—
—
—
0.01–0.05 Nb 485–620
70–90
345
50
D
0.20
65 mm
(2.5 in.)
and
under
0.70– 0.04
1.60
0.05
0.15– 0.25
0.50
0.25
0.08
485–620
70–90
345
50
E
0.22
65 mm
(2.5 in.)
and
under
1.15– 0.04
1.50
0.05
0.15–
0.50
—
—
—
550–690
80–100
415
60
A
0.07
Class 1,
20 mm
(0.75 in.)
and
under
0.40– 0.025 0.025
0.70
0.35
0.60– 0.70– 0.15–
0.90 1.00 0.25
—
1.00–1.30 Cu;
0.02 min. Nb
620
90
550
80
B
Class 1
0.40– 0.025 0.025
0.65
0.20–
0.35
—
—
1.00–1.30 Cu;
0.02 min. Nb
550
80
485
70
Composition, %a
ASTM Type
Specifior
cation
Grade
C
Mn
P
S
Si
Cr
Ni
Mo
V
A 242
1
0.15
1.00
0.15
0.05
—
—
—
—
A 572
42b
0.21
1.35
0.04
0.05
0.15–
0.40
—
—
50b
0.23
1.35
0.04
0.05
0.15–
0.40
—
55b
0.25
1.35
0.04
0.05
0.15–
0.40
60b
0.26
1.35
0.04
0.05
65b
0.26
1.65
0.04
A
0.19
B
A 588
100 mm
(4 in.)
and
under
A 633
A 710
0.06
a. Single values are maximum unless otherwise noted.
b. These grades may contain niobium, vanadium, or nitrogen.
1.20–
1.50
—
0.35 Cu
0.04– 0.01–0.03 N
0.11
AWS WELDING HANDBOOK 9.4
45
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.11
ASTM Specifications for High-Strength Low-Alloy Steels for Pressure-Vessel Plate
Composition, %*
ASTM
Type
Specifior
cation Grade
C
Mn
A 202
A
0.17
1.05– 0.035 0.035
1.40
B
0.25
A
A 203
A 204
A 225
A 302
P
S
Si
Cr
Tensile Strength
Minimum Yield
Strength
Ni
Mo
V
Other
MPa
ksi
MPa
ksi
0.60– 0.35–
0.90 0.60
—
—
—
—
515–655
75–95
310
45
1.05– 0.035 0.035
1.40
0.60– 0.35–
0.90 0.60
—
—
—
—
585–760
85–110
325
47
0.23
0.80
0.035 0.035
0.15–
0.30
—
2.10–
2.50
—
—
—
450–585
65–85
255
37
B
0.25
0.80
0.035 0.035
0.15–
0.30
—
2.10–
2.50
—
—
—
485–620
70–90
275
40
D
0.20
0.80
0.035 0.035
0.15–
0.30
—
3.25–
3.75
—
—
—
450–585
65–85
255
37
E
0.23
0.80
0.035 0.035
0.15–
0.30
—
3.25–
3.75
—
—
—
480–620
70–90
275
40
F
0.23
0.80
0.035 0.035
0.15–
0.40
—
3.25–
3.75
—
—
—
550–690
515–655
80–100
75–95
380
345
55
50
A
0.25
0.90
0.035 0.040
0.15–
0.30
—
—
0.45–
0.60
—
—
450–585
65–85
255
37
B
0.27
0.90
0.035 0.040
0.15–
0.30
—
—
0.45–
0.60
—
—
485–620
70–90
275
40
C
0.28
0.90
0.035 0.040
0.15–
0.30
—
—
0.45–
0.60
—
—
515–655
75–95
295
43
C
0.25
1.60
0.035 0.040
0.15–
0.40
—
0.40–
0.70
—
0.13–
0.18
—
725–930
105–135
485
70
D
0.20
75 mm
(3 in.)
and under
1.70
0.035 0.040
0.10–
0.50
—
0.40–
0.70
—
0.10–
0.18
—
550–725
80–105
415
60
A
0.25
0.95– 0.035 0.040
1.30
0.15–
0.30
—
—
0.45–
0.60
—
—
515–655
75–95
310
45
B
0.25
1.15– 0.035 0.040
1.50
0.15–
0.30
—
—
0.45–
0.60
—
—
550–690
80–100
345
50
C
0.25
1.15– 0.035 0.040
1.50
0.15–
0.30
—
0.40– 0.45–
0.70 0.60
—
—
550–690
80–100
345
50
D
0.25
1.15– 0.035 0.040
1.50
0.15–
0.30
—
0.70– 0.45–
1.00 0.60
—
—
550–689
80–100
345
50
A 353
—
0.13
0.90
0.15–
0.30
—
8.50–
9.50
—
—
—
690–825 100–120
515
75
A 735
Class
3
0.06
1.20– 0.04
2.20
0.025
0.40
—
—
0.23–
0.47
—
90–110
515
75
A 737
B
0.20
1.15– 0.035 0.030
1.50
0.15–
0.50
—
—
—
—
0.05 Nb
485–620
70–90
345
50
C
0.22
1.15– 0.035 0.030
1.50
0.15–
0.50
—
—
—
0.04–
0.11
0.03 Nb
550–690
80–100
415
60
0.035 0.040
*Single values are maximum unless otherwise noted.
0.20–0.35 Cu; 620–760
0.03–0.09 Nb
46
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.12
API Material Specifications for HSLA Line Pipe
Carbon Equivalent a
% Maximum
Composition, Based Upon Heat and Product Analyses
% Maximum
Steel
Grade
bCb
Si
bMn b
P
S
V
Nb
Ti
Other
CEIIW
Pcm
X52M
0.22
0.45
1.40
0.025
0.015
d
d
d
e
0.43
0.25
X56M
0.22
0.45
1.40
0.025
0.015
d
d
d
e
0.43
0.25
X60M
0.12 f
0.45 f
1.60 f
0.025
0.015
g
g
g
h
0.43
0.25
X65M
0.12 f
0.45 f
1.60 f
0.025
0.015
g
g
g
h
0.43
0.25
X70M
0.12 f
0.45 f
1.70 f
0.025
0.015
g
g
g
h
0.43
0.25
X80M
0.12 f
0.45 f
1.85 f
0.025
0.015
g
g
g
i
0.43 f
0.25
0.10
0.55 f
2.10 f
0.020
0.010
g
g
g
i
—
0.25
X100M
0.10
0.55 f
2.10 f
0.020
0.010
g
g
g
i, j
—
0.25
X120M
0.10
0.55 f
2.10 f
0.020
0.010
g
g
g
i, j
—
0.25
X90M
a. Based on product analysis. For seamless pipe with >20.0 mm (0.787 in.), the carbon equivalent limits shall be as agreed. The CEIIW limits apply if the carbon
composition is greater than 0.12% and the CEPcm limits apply if the carbon composition is less or equal to 0.12%.
b. For each reduction of 0.01% below the specified maximum for carbon, an increase of 0.05% above the specified maximum for manganese is permissible, up
to a maximum of 1.65% for grades >L245 or B, but <L360 or X52; up to a maximum of 1.75% for grades >L360 or X52, but <1.485 or X70; up to a maximum
of 2.00% for grades >L485 or X70, but <L655 or X80; and up to a maximum of 2.2% for grades >L555 or X80.
c. Unless otherwise agreed, the sum of the niobium and vanadium concentrations shall be <0.06%.
d. The sum of the niobium, vanadium, and titanium concentrations shall be <0.15%.
e. Unless otherwise agreed, 0.50% maximum for copper, 0.30% maximum for nickel, 0.30% maximum for chromium, and 0.15% maximum for molybdenum.
f. Unless otherwise agreed.
g. Unless otherwise agreed, the sum of the niobium, vanadium, and titanium concentrations shall be <0.15%.
h. Unless otherwise agreed, 0.50% maximum for copper, 0.50% maximum for nickel, 0.50% maximum for chromium, and 0.50% maximum for molybdenum.
i. Unless otherwise agreed, 0.50% maximum for copper, 1.00% maximum for nickel, 0.50% maximum for chromium, and 0.50% maximum for molybdenum.
j. 0.004% for boron.
Source: Adapted from American Petroleum Institute, 2007, API Specification 5L/ISO 3183, 44th edition.
equipment and machinery, railroad equipment, automobile and truck frames, and ships. Specifications published by ASTM, API, SAE, and those used by the
United States military (MIL) cover chemical compositions and additional testing and procedures relevant to
each application. Supplementary testing may be ordered
by a user for special or critical applications. For example, notch toughness testing may be conducted on components to be used in low-temperature service. Also,
weldability prequalification (API RP2Z) is used to verify the properties of the HAZ in heavy plate intended
for critical components in offshore structures.
As-rolled HSLA steels may have poor or variable
notch toughness unless they are properly processed.
During rolling, the finishing temperature and the
amount of deformation is strictly controlled (i.e., controlled rolling) to achieve the necessary grain refinement.
Additional strength may be obtained by using water to
accelerate the cooling of plate (i.e., Type III TMCP).
Aside from processing, however, enhanced notch toughness requires additional measures such as lowering the
carbon and sulfur contents. For example, the actual carbon contents of modern line pipe steels typically are
well below API allowable limits, as shown in Figure
1.22.
WELDING HIGH-STRENGTH LOW-ALLOY
STEELS
Although many of the newer HSLA steels do exhibit
good to excellent weldability, successful welding of HSLA
steels in general still requires consideration of preheat
and careful control of hydrogen in the welding process.
Guidance pertaining to preheat and hydrogen control
and the variables that affect them are discussed in this
section.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
47
Table 1.13
API Mechanical Specifications for Seamless and Welded Pipe
Weld Seam of
HFW, SAW, and
COW Pipes*
Pipe Body of Seamless and Welded Pipe
Yield Strengtha
R10.5b
MPa (psi)
Tensile Strengha
Rm
MPa (psi)
Ratio a, b, c
R10.5 /Rm
Elongation
Af
%
Tensile Strengthd
Rm
MPa (psi)
Pipe
Grade
Minimum
Maximum
Minimum
Maximum
Maximum
Minimum
Minimum
X52M
360 (52 200)
530 (76 900)
460 (66 700)
760 (110 200)
0.93
f
460 (66 700)
X56M
390 (56 600)
545 (79 000)
490 (71 100)
760 (110 200)
0.93
f
490 (71 100)
X60M
415 (60 200)
565 (81 900)
520 (75 400)
760 (110 200)
0.93
f
520 (75 400)
X65M
450 (65 300)
600 (87 000)
535 (77 600)
760 (110 200)
0.93
f
535 (77 600)
X70M
485 (70 300)
635 (92 100)
570 (82 700)
760 (110 200)
0.93
f
570 (82 700)
X80M
555 (80 500)
705 (102 300)
625 (90 600)
825 (119 700)
0.93
f
625 (90 600)
X90M
625 (90 600)
775 (112 400)
695 (100 800)
915 (132 700)
0.95
f
695 (100 800)
X100M
690 (100 100)
840 (121 800)
760 (110 200)
990 (143 600)
0.97g
f
760 (110 200)
X120M
830 (120 400)
1050 (152 300)
915 (132 700)
1145 (166 100)
0.99g
f
915 (132 700)
*HFW = High-frequency welding
*SAW = Submerged arc welding
*COW = Combination GMAW and SAW; usually the first pass or the first several passes are made with GMAW, then filled and capped with SAW.
a. Based on product analysis. For seamless pipe with >20.0 mm (0.787 in.), the carbon equivalent limits shall be as agreed. The CEIIW limits apply if
the carbon composition is greater than 0.12% and the CEPcm limits apply if the carbon composition is less or equal to 0.12%.
b. For each reduction of 0.01% below the specified maximum for carbon, an increase of 0.05% above the specified maximum for manganese is permissible,
up to a maximum of 1.65% for grades >L245 or B, but <L360 or X52; up to a maximum of 1.75% for grades >L360 or X52, but <1.485 or X70; up to a
maximum of 2.00% for grades >L485 or X70, but <L655 or X80; and up to a maximum of 2.2% for grades >L555 or X80.
c. Unless otherwise agreed, the sum of the niobium and vanadium concentrations shall be <0.06%.
d. The sum of the niobium, vanadium, and titanium concentrations shall be <0.15%.
e. Unless otherwise agreed, 0.50% maximum for copper, 0.30% maximum for nickel, 0.30% maximum for chromium, and 0.15% maximum for
molybdenum.
f. Unless otherwise agreed.
g. Unless otherwise agreed, the sum of the niobium, vanadium, and titanium concentrations shall be <0.15%.
h. Unless otherwise agreed, 0.50% maximum for copper, 0.50% maximum for nickel, 0.50% maximum for chromium, and 0.50% maximum for
molybdenum.
i. Unless otherwise agreed, 0.50% maximum for copper, 1.00% maximum for nickel, 0.50% maximum for chromium, and 0.50% maximum for
molybdenum.
j. 0.004% for boron.
Source: Adapted from American Petroleum Institute, 2007, API Specification 5L/ISO 3183, 44th edition.
Preheat
Preheat requirements, if applicable, depend on the
type and thickness of HSLA steel and also the filler
metal and welding process to be used. The AWS publication, Structural Welding Code—Steel, AWS D1.1
requires preheat for many HSLA steels, depending on
thickness, carbon equivalent, and the welding process
being used. The primary purpose of preheating is to
minimize the risk of hydrogen cracking, as described in
greater detail in the section Avoiding Hydrogen Cracking in this chapter.
The recommended minimum heat input or preheat
and interpass temperature for arc welding a particular
HSLA structural steel should be based on the specific
carbon equivalent (CE) and composition parameter
(Pcm) of the steel. These values can be calculated easily
from steel composition data using Equations 1.2 and
1.3, and applied in accordance with guidance provided
in Annex I of AWS D1.1/D1.1M:2010.70 It contains, for
example, a susceptibility index that was devised as a
guideline to prevent cracking in the heat-affected zone
(HAZ) of structural steels. The index also has been
adopted as a guide for welding pipeline steels:
Susceptibility Index = 12Pcm + log10 H
70. See Reference 17.
(1.4)
48
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Figure 1.22—Trend Toward Reduced Carbon Content with Increasing Strength of Line Pipe
Variable H in Equation 1.4 is the diffusible hydrogen
level in mL/100g of deposited weld metal. This relationship, combined with workpiece thickness and restraint
level, was the basis for the minimum preheat and interpass temperatures shown in Table 1.14 and Table 1.15.
The preheat temperature must be high enough to prevent cracking from restraint of the joint, or the presence
of hydrogen in varying amounts, or both. When welding two different HSLA steels, the higher of the two
preheat temperatures should be used. The base metal on
each side of the joint must be thoroughly preheated to
temperature over a distance equal to the workpiece
thickness or 76 mm (3 in.), whichever is larger. It
should be noted that ASTM A 710 and A 736 (plate),
and A 707 (forgings), are steels that can be quenched
and age-hardened. These HSLA steels normally are
quite low in carbon and have relatively high strength.
The lower carbon content will reduce the calculated CE
and Pcm values; therefore, lower preheat and interpass
temperatures will be required. Care should be exercised, because the weld metal for these specific HSLA
steels may be stronger and subject to hydrogen cracking
problems.
Welding Processes
High-strength low-alloy steels can be welded by all
of the commonly used arc welding processes. Shielded
metal arc, gas metal arc, flux cored arc, and submerged
arc welding are used for most applications. Low-hydrogen practices should be employed with all processes
when carbon equivalents or Pcm values indicate susceptibility to cracking.
High-heat-input welding processes such as electroslag, electrogas, and multiple-wire submerged arc can
be used to weld these steels. However, the advantage of
the use of these processes warrants careful evaluation
when notch toughness in the weld metal and heataffected zone is a requirement.
The HSLA steels also can be joined by resistance
welding processes: spot, seam, projection, upset, or
flash welding. When using resistance spot, seam, or
projection welding, these steels can be welded with current and time settings similar to those used with lowcarbon steel. Higher electrode force may be needed,
however, because of the higher strength of the steel.
Higher upsetting force may be required with flash or
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
49
Table 1.14
Minimum Preheat and Interpass Temperatures for Three Levels of Restraint
Minimum Preheat and Interpass Temperature ( °C)b
Susceptibility Index Grouping
Restraint
Level
Low
Medium
High
Thickness a
mm
A
B
C
D
E
F
G
< 10 <
< 20
< 20
< 20
< 20
60
140
150
> 10–20 incl.
< 20
< 20
20
60
100
140
150
> 20–38 incl.
< 20
< 20
20
80
110
140
150
> 38–75 incl.
20
20
40
95
120
140
150
> 75<
20
20
40
95
120
140
150
< 10<
< 20
< 20
< 20
< 20
70
140
160
> 10–20 incl.
< 20
< 20
20
80
115
145
160
> 20–38 incl.
20
20
75
110
140
150
160
> 38–75 incl.
20
80
110
130
150
150
160
> 75<
95
120
140
150
160
160
160
< 10<
< 20
< 20
20
40
110
150
160
> 10–20 incl.
< 20
20
65
105
140
160
160
> 20–38 incl.
20
85
115
140
150
160
160
> 38–75 incl.
115
130
150
150
160
160
160
> 75<
115
130
150
150
160
160
160
Minimum Preheat and Interpass Temperature ( °F)b
Susceptibility Index Grouping
Restraint
Level
Thickness a
in
A
B
C
D
E
F
G
Low
< 3/8
< 65
< 65
< 65
< 65
140
280
300
3/8–3/4 incl.
< 65
< 65
65
140
210
280
300
> 3/4–1-1/2 incl.
< 65
< 65
65
175
230
280
300
> 1-1/2–3 incl.
65
65
100
200
250
280
300
>3
65
65
100
200
250
280
300
Medium
High
< 3/8
< 65
< 65
< 65
< 65
160
280
320
3/8–3/4 incl.
< 65
< 65
65
175
240
290
320
> 3/4–1-1/2 incl.
< 65
65
165
230
280
300
320
> 1-1/2–3 incl.
65
175
230
265
300
300
320
>3
200
250
280
300
320
320
320
< 3/8
< 65
< 65
< 65
100
230
300
320
3/8–3/4 incl.
< 65
65
150
220
280
320
320
> 3/4–1-1/2 incl.
65
185
240
280
300
320
320
> 1-1/2–3 incl.
240
265
300
300
320
320
320
>3
240
265
300
300
320
320
320
a. Thickness is that of the thicker part welded.
b. “<” indicates that preheat and interpass temperatures lower than the temperature shown may be suitable to avoid hydrogen cracking. Preheat and interpass
temperatures that are both lower than the listed temperature and lower than Table 3.2 (refer to AWS D1.1) shall be qualified by test.
Source: Adapted from American Welding Society (AWS) Structural Welding Code—Steel, AWS D1.1/D1.1M:2010, Annex I, Table I.2, Miami: American Welding Society, p 324.
50
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.15
Susceptibility Index Grouping as a Function of Hydrogen Level and Composition Parameter, Pcm
Susceptibility Index Grouping*
Diffusible Hydrogen,
mL/100g of Deposited Metal
Carbon Equivalent, Pcm
<0.18
<0.23
<0.28
<0.33
<0.38
5
A
B
C
D
E
10
B
C
D
E
F
30
C
D
E
F
G
Note: Susceptibility index values for groupings: A = 3.0; B = 3.1; C = 3.6; D = 4.1 to 4.5; E = 4.6 to 5.0; F = 5.1 to 5.5; G = 5.6 to 7.0.
Source: Adapted from American Welding Society (AWS) Structural Welding Code—Steel, AWS D1.1/D1.1M:2010, Annex I, Table I.1, Miami: American Welding Society, p 324.
upset welding for the same reason, but the other welding variables should be similar to those used for lowcarbon steel. Preheat or postheat cycles may be helpful
during resistance welding of some HSLA steels to avoid
excessive hardening of the weld zone and the heataffected zone.
In general, the welding processes used to join HSLA
steels should be selected with consideration for the
following:
1. Strength requirements of the weld metal;
2. Weld metal behavior during multiple-pass welding (i.e., the tempering effect of each pass on the
previous passes);
3. Toughness requirements; and
4. Propensity for cracking in the weld-metal and
heat-affected zone.
Filler Metals
The considerations governing the choice of filler metals for welding HSLA steels are often very similar to
those for welding structural carbon steels, except that it
is necessary to use low-hydrogen welding practices with
HSLA steels. The amount of hydrogen carried by the
filler metal to the weld pool should be evaluated with
reference to the carbon equivalent (CE) and composition parameter (Pcm), as previously discussed. Generally,
a higher hydrogen potential suggests that a higher preheat value is required.
The lower-carbon HSLA steels, such as some API
grades of line pipe steel (refer to Table 1.12), may allow
the use of cellulosic electrodes (EXX10) to enable a
complete-penetration root pass without internal backing. This may be performed with or without preheat,
depending on the relevant CE or Pcm. However, the
industry standard that governs pipeline fabrication
requires welding procedures to specify a maximum
allowable time interval between the root pass and the
second pass (often called the hot pass), and also between
the second pass and third pass, regardless of base metal CE
or Pcm.71 Moreover, the time interval between the root pass
and the second pass is treated as an essential variable,
to the extent that requalification of the welding procedure is required if this time interval must be exceeded.
The purpose of this requirement is to minimize the possibility of hydrogen cracking.
For normalized HSLA steels that have good notch
toughness, additional consideration must be given to
choosing an arc welding electrode and procedure that
will provide adequate levels of notch toughness in both
the weld metal and the heat-affected zone. Filler metals
are available that can produce weld metal with various
levels of notch toughness for any of the commonly used
arc welding processes. In some cases, the weld metal
composition can be similar to that of the steel. The specific welding parameters used, such as preheat, heat
input, bead sequence, and bead size can have an effect
on the notch toughness of the weld metal and the heataffected zone. If notch toughness in these areas is
required, a welding procedure should be developed,
tested, and then rigorously followed during fabrication
to ensure that satisfactory mechanical properties are
achieved in the welded joint.
Suggested electrodes for arc welding several HSLA
steels for structural and pressure vessel applications are
shown in Tables 1.16(A), (B), and (C).
71. See Reference 32.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
51
Table 1.16(A)
Recommended Base Metal-Filler Metal Combinations for Matching
Electrode Tensile Strengths Nominally of 480 MPa (70 ksi) Minimum
Steels
Yield
Strength
(Minimum
or Range)
Tensile Strength
(Minimum
or Range)
MPa
ksi
MPa
ksi
Electrode
Specificationc
Grade A
255
37
450–585
65–85
Shielded Metal Arc Welding (See AWS A5.1 or A5.5)e
Steel Specification a, b
ASTM A 203
Matching Filler Metals
Grade B
275
40
485–620
70–90
Grade D
255
37
450–585
65–85
E7015, E7016,
Grade E
275
40
480–620
70–90
E7018, E7028
Grade F
345
50
515–655
75–95
Grade A
255
37
450–585
65–85
Grade B
275
40
485–620
70–90
E7015-X, E7016-X,
ASTM A 204
—
290
42
435
Tensile Strength
(Minimum
or Range)
MPa
MPa
ksi
ksi
400
58
490
70
390
57
490
70
390
57
490
70
E7018-X
E7010-Xd
ASTM A 242
Yield
Strength
(Minimum
or Range)
63
Submerged Arc Welding (See AWS A5.17 or A5.23)e
ASTM A 572
Grade 42
290
42
415
60
Grade 50
345
50
450
65
F7XX-EXXX
Grade 55
380
55
485
70
or F7XX-EXX-XX
ASTM A 588
100 mm (4 in.)
and under
345
50
485
70
ASTM A 633
Grade A
290
42
430–570
63–83
Grades C and D 65 mm
(2.5 in.) and under
345
50
485–620
70–90
Grade A, Class 2,
under 50 mm (2 in.)
380
55
450
65
Grade X52M
360–530
52.2–
76.9
460–760
66.7–
110.20
Grade X56M
390–545
56.6–
79.0
490–760
71.1–
110.20
Grade X60M
415–565
60.2–
81.9
520–760
75.4–
110.20
API 5L
58
480–660
70–95
Gas Metal Arc Welding (See AWS A5.18)
ER70S-X
ASTM A 710
400
400
58
480
70
Flux Cored Arc Welding (See AWS A5.20)
E7XT-X (except
-2, -3, -10, -GS)
400
58
480
70
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be used. The lowhydrogen processes shall be subject to the technique requirements applicable to the higher strength group.
b. Match API Standard 2B (fabricated tubes) according to steel used.
c. When welds are to be stress-relieved, the deposited weld metal shall not exceed 0.05% vanadium.
d. Cellulose electrodes for field pipeline welding.
e. Deposited weld metal shall have a minimum impact strength of 27 J (20 ft·lb) at –18°C (0°F) when Charpy V-notch specimens are required.
52
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.16(B)
Recommended Base Metal-Filler Metal Combinations for Matching
Electrode Tensile Strengths Nominally of 550–620 MPa (80–90 ksi) Minimum
Steels
Yield
Strength
(Minimum
or Range)
Tensile Strength
(Minimum
or Range)
MPa
ksi
MPa
ksi
Grade A
310
45
515–655
75–95
Grade B
325
47
585–760
85–110
Steel Specification a, b
ASTM A 202
Matching Filler Metals
Electrode
Specificationc
Yield
Strength
(Minimum
or Range)
Tensile Strength
(Minimum
or Range)
MPa
MPa
ksi
ksi
Shielded Metal Arc Welding (See AWS A5.5)e
E8015-X, E8016-X,
460
67
550
80
ASTM A 204
Grade C
295
43
515–655
75–95
E8018-X
ASTM A 302
Grade A
310
45
515–655
75–95
E8010-Gd
460
67
550
80
Grade B
345
50
550–690
80–100
Grade C
345
50
550–690
80–100
E9010-Gd
530
77
620
90
Grade D
345
50
550–690
80–100
Submerged Arc Welding (See AWS A5.23)e
ASTM A 572
Grade 60
415
60
520
75
Grade 65
450
65
550
80
ASTM A 633
Grade E
65 mm (2.5 in.)
and under
415
60
550–690
80–100
ASTM A 710
Grade A, Class 2,
50 mm (2 in.) and under
415
60
495
72
Grade A, Class 3,
50 mm (2 in.) and under
515
75
585
85
ASTM A 736
Grade A, Class 3,
50 mm (2 in.) and under
515
75
585–725
85–105
ASTM A 737
Grade B
345
50
485–620
70–90
Grade C
415
60
550–690
80–100
Grade X65M
450–600
65.3–
87.0
535–760
77.6–
110.20
Grade X70M
485–635
70.3–
92.1
570–760
82.7–
110.20
F8XX-EXX-XX
68
550–700
80–100
Gas Metal Arc Welding (See AWS A5.28)e
ER80S-X
470
68
550
80
Flux Cored Arc Welding (See AWS A5.29)e
E8XTX-X
API 5L
470
470
68
550–690
80–100
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be used. The lowhydrogen processes shall be subject to the technique requirements applicable to the higher strength group.
b. Match API Standard 2B (fabricated tubes) according to steel used.
c. When welds are to be stress-relieved, the deposited weld metal shall not exceed 0.05% vanadium.
d. Cellulose electrodes for field pipeline welding.
e. Deposited weld metal shall have a minimum impact strength of 27 J (20 ft·lb) at –18°C (0°F) when Charpy V-notch specimens are required.
Next Page
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
53
Table 1.16(C)
Recommended Base Metal-Filler Metal Combinations for Matching
Electrode Tensile Strengths Nominally of 690 MPa (100 ksi) Minimum
Steels
Yield
Strength
(Minimum
or Range)
Tensile Strength
(Minimum
or Range)
MPa
ksi
MPa
ksi
Grade C
485
70
725–930
105–135
Grade D
75 mm (3 in.) and under
415
60
550–725
80–105
Steel Specification a, b
ASTM A 225
Matching Filler Metals
Electrode
Specificationc
550
80
620
90
Grade A, Class 3,
50 mm (2 in.) and under
515
75
585
85
Class 3
515
75
620–760
MPa
MPa
ksi
ksi
600
87
690
100
E10018-X
Submerged Arc Welding (See AWS A5.23)d
F10XX-EXX-XX
ASTM A 735
Tensile Strength
(Minimum
or Range)
Shielded Metal Arc Welding (See AWS A5.5)d
E10015-X, E10016-X,
ASTM A 710 Grade A, Class 1, 20 mm
(0.75 in.) and under
Yield
Strength
(Minimum
or Range)
610
88
690–830 100–120
90–110
Gas Metal Arc Welding (See AWS A5.28)d
API 5Le
X80M
550–
705
80.5–
102.30
625–
825
90.6–
119.70
ER100S-X
610
88
690
100
Flux Cored Arc Welding (See AWS A5.29)d
E10XTX-X
ASTM A 353f
—
515
75
690–825
100–120
610
88
690–830 100–120
Shielded Metal Arc Welding (See AWS A5.4 and A5.11)
E310-XX
—
—
550
80
ENiCrFe-2
—
—
550
80
ENiCrMo-3
—
—
760
110
Gas Metal Arc Welding (See AWS A5.14)
ERNiCr-3
—
—
550
80
ERNiCrFe-6
—
—
550
80
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be used. The lowhydrogen processes shall be subject to the technique requirements applicable to the higher strength group.
b. Match API Standard 2B (fabricated tubes) according to steel used.
c. When welds are to be stress-relieved, the deposited weld metal shall not exceed 0.05% vanadium.
d. Deposited weld metal shall have a minimum impact strength of 27 J (20 ft·lb) at –18°C (0°F) when Charpy V-notch specimens are required.
e. Undermatching cellulose electrodes may be used for root and cap passes for field pipeline welding.
f. Applicable electrodes for welding this steel are only the stainless steel and nickel-alloy electrodes (AWS A5.11 and A5.14) shown in lower right.
Previous Page
54
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.17
Suggested Welding Filler Metals for Exposed Applications of ASTM A 242 and A 588 Steelsa
Shielded Metal Arc Welding
(AWS A5.5)
Submerged Arc Welding
(AWS A5.23)
Gas Metal Arc Welding
(AWS A5.28)
Flux Cored Arc Welding
(AWS A5.29)c
E8016 or 18-Gb, c
F7XX-EXXX-Wc, d
ER80S-Gc
E80T1-W
E8016 or 18-B1c
—
ER80S-B2c, d
E81T1-B1
E8016 or 18-B2c
F7XX-EXXX-B2c, d
ER70S-B2Lc, d
E8XTX-B2
E7015 or 18-B2Lc
—
—
E80T5-B2L
E8016 or 18-C1
F7XX-EXXX-Ni1d
ER80S-Ni1d
EXTX-Ni1
E8016 or 18-C2
F7XX-EXXX-Ni2d
ER80S-Ni2d
EXTX-Ni2
E8016 or 18-C3
F7XX-EXXX-Ni3d
ER80S-Ni3d
E80T5-Ni3
E7018-W2
F7XX-EXXX-Ni4d
—
—
E8018-W2
—
—
—
a. See Figure 3.3, pp 78–93, Structural Welding Code—Steel, AWS D1.1/D1.1M:2010, Miami: American Welding Society.
b. Deposited weld metal shall have the following chemical composition percent: 0.12 C max., 0.50–1.30 Mn, 0.03 P max., 0.04 S max., 0.35–0.80 Si, 0.30–
0.75 Cu, 0.40–0.80 Ni, 0.45–0.70 Cr.
c. Deposited weld metal shall have a minimum Charpy V-notch impact strength of 27.1 J (20 ft·lb) at –18°C (0°F) for bridges.
d. The use of the same type of filler metal having next higher mechanical properties as listed in the AWS specifications is permitted.
The electrodes shown in a particular table (A, B, or
C) generally match the steels shown in that table with
regard to composition and strength. Similar consumables
are available for other welding processes. For ASTM
A 242 and A 588 steels used in the bare, unpainted condition, welding electrodes should be specified that will
provide weld metal with similar corrosion resistance
and color match in the weathered condition. Welding
filler metals are available to provide various weld-metal
compositions for meeting those requirements. Table 1.17
provides suggestions for specific welding consumables
that will provide suitable weld metal for these steels.
ASTM A 353 steels can be welded with nickel or stainless steel electrodes when weld metal with good toughness at cryogenic temperatures is required. However,
consideration must be given to the difference between
the base metal and the austenitic stainless-steel weld
metal with regard to thermal expansion characteristics.
Also, the yield strength of the weld metal is likely to
undermatch that of the base metal. The welded joint
must be capable of withstanding the stresses developed
at the weld interface if it is thermally cycled in service.
Low-alloy steel electrodes are available for electroslag and the electrogas welding of HSLA steels. A flux is
used in combination with an electrode in electroslag
welding. The flux is classified on the basis of the
mechanical properties of weld deposit made with a particular electrode. With both processes, the weld metal is
required to have a tensile strength, as-welded, in the
range of 480 MPa to 620 MPa (70 ksi to 90 ksi) and a
minimum yield strength of 340 MPa (50 ksi).
Postweld Heat Treatment
Weldments in structures of HSLA steels seldom
require postweld stress relief or tempering heat treatment
(PWHT). However, a heat treatment may be necessary
if the weldment must maintain dimensions during
machining, if it is exposed to an environment that can
cause stress-corrosion cracking, or if it requires softening to improve ductility. For proprietary steels, the recommendations of the producer should be followed.
Some fabrication codes require that welded joints or the
entire weldment be heat treated for certain applications.
Caution should be exercised when any heat treatment is
planned for a quenched and tempered or quenched and
aged steel. The postweld heat treatment temperature
should never exceed the temperature used in the tempering or precipitation hardening (aging) process.
The evolution of low-carbon HSLA steels with relatively low hardness in the HAZ has dramatically reduced
the occurrence of hydrogen cracking in the HAZ of
these steels. However, the weld metal produced when
joining these higher strength HSLA steels still must be
considered to be prone to hydrogen cracking. Postweld
hydrogen-release treatments (at temperatures between
95°C to 320°C [200°F to 600°F]) are commonly used to
AWS WELDING HANDBOOK 9.4
prevent hydrogen buildup and subsequent cracking in
higher-strength weld metal.
BRAZING OF HSLA STEELS
High-strength low-alloy steels can be brazed with the
same brazing filler metals, processes and procedures
used for carbon steels. When selecting a brazing process
and a filler metal, the effects of the proposed brazing
cycles on the mechanical properties of the steel must be
considered. Exposure of a steel, especially a heattreated steel, to a particular brazing cycle may alter its
mechanical properties. In most cases, the brazing temperature should be below the lower transformation
temperature of the steel.
THERMAL CUTTING OF HSLA STEELS
Thermal cutting of high-strength low-alloy steels can
be performed using conventional oxyfuel gas, air-carbon arc, plasma arc, and other processes. The procedures are the same as those used for carbon steels,
described previously. Preheating temperatures suggested
for arc welding (refer to Table 1.14). are recommended
also for cutting operations to minimize cracking in the
cut edge.
The cut surface should be clean and free of cracks for
subsequent welding. Oxide or other residue on the surface should be removed mechanically, along with any
cracks which may have formed during cutting.
QUENCHED AND TEMPERED
STEELS
Quenched and tempered steels are designed especially for welded construction and fabrication. Commonly referred to as Q&T steels, they are furnished by
steel producers in the heat-treated condition, with yield
strengths ranging from 340 MPa to 1030 MPa (50 ksi
to 150 ksi) depending on the chemical composition,
thickness, and type of heat treatment. The heat treatment for most of these steels consists of austenitizing,
quenching, and tempering. A few are given a precipitation-hardening (i.e., aging) treatment following hot rolling or some other thermal treatment. Welded structures
fabricated from these steels generally do not need further heat treatment, except for a postweld heat treatment (i.e., stress relief) in special situations.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
55
COMPOSITION AND PROPERTIES
Quenched and tempered steels combine high yield
and tensile strengths with good weldability, notch
toughness, ductility, and corrosion resistance. The various steels in this group can be specified to possess different combinations of these characteristics, depending
on the intended application. The chemical compositions
and strengths of typical Q&T steels are provided in
Table 1.18. Most of those listed are covered by ASTM
specifications; a few steels such as HY-80, HY-100, and
HY130, are covered by military specifications. The
steels listed are produced primarily as plate, although
some of these and other similar steels are produced as
forgings or castings.
Plate designations ASTM A 514 and A 517 and forgings specified as ASTM A 592 are used in a wide range
of applications requiring good notch toughness and
moderate-to-high yield strength (about 690 MPa [100 ksi]).
Typical applications are earth-moving equipment, bridges,
steel mill and mining equipment, communications towers,
and ships.
Steels designated as ASTM A 533 Grade B are used
for nuclear pressure-vessel construction. At its highest
strength level (Class 3), they may be used for thin-wall
or multiple-layer pressure vessels. Steels designated as
ASTM A 537 Class 2 are intended for use in pressure
vessels that require high notch toughness and a minimum yield strength of 410 MPa (60 ksi).
Classes 1 and 2 of ASTM A 543 Type B steel are
modifications of HY-80 and HY-100 steels. These steels
are intended for nuclear reactor vessels and other applications requiring high yield strength and good toughness. HY-80 and HY-100 steels are used in construction
of ships, submarines, and other marine equipment.
HY130 steel is similar to the other two HY steels, but it
has a higher yield strength and better toughness.
The ASTM A 553 steels contain 8% or 9% nickel.
They are essentially Q&T variations of ASTM A 353, a
high-strength low-alloy steel also containing 9% nickel.
The welding considerations are the same for both types
of steels, regardless of heat treatment. Therefore, the
information presented in the previous section for
ASTM A 353 high-strength low-alloy steel is applicable
to A 553 steel.
Steel designated as ASTM A 678 Q&T carbon steel
is similar to ASTM A 537 Class 2 steel, but A 678 is
intended for structural applications that require good
toughness and yield strength of about 410 MPa (60 ksi).
The carbon content of Q&T steels generally does not
exceed 0.22%, which ensures adequate weldability. The
other alloying elements are carefully selected to provide
the most economically favorable heat-treated steel with
the desired properties and acceptable weldability. Table
1.19 shows the heat treatment and the resulting microstructure for selected steels in Table 1.18. Austenitizing
Common
Desig-nation
A 514 or A 517
65 mm (2.5 in.)
and under
A 533, Class 2
A 537, Class 2
65 mm (2.5 in.)
and under
A 543, Class 2
A 678
20–40 mm
(0.75–1.50 in.)
HY-80
HY-100
HY-130
a.
b.
c.
d.
Tensile
Strength
Composition, %a
Ni
Mo
Cu
A
B
0.15–0.21 0.80–1.10 0.035 0.040 0.40–0.80 0.50–0.80
0.12–0.21 0.70–1.00 0.035 0.040 0.20–0.35 0.40–0.65
C
Mn
P
S
Si
Cr
—
—
0.18–0.28
0.15–0.25
—
—
C
D
0.10–0.20 1.10–1.50 0.035 0.040 0.15–0.30
—
0.13–0.20 0.40–0.70 0.035 0.040 0.20–0.35 0.85–1.20
—
—
0.20–0.30
0.15–0.25
E
0.12–0.20 0.40–0.70 0.035 0.040 0.20–0.35 1.40–2.00
—
0.40–0.60
F
0.10–0.20 0.60–1.00 0.035 0.040 0.15–0.35 0.40–0.65 0.70–1.00 0.40–0.60
G
H
0.15–0.21 0.80–1.10 0.035 0.040 0.50–0.90 0.50–0.90
—
0.40–0.60
0.12–0.21 0.95–1.30 0.035 0.040 0.20–0.35 0.40–0.65 0.30–0.70 0.20–0.30
J
K
L
0.12–0.21 0.45–0.70 0.035 0.040 0.20–0.35
—
0.10–0.20 1.10–1.50 0.035 0.040 0.15–0.30
—
0.13–0.20 0.40–0.70 0.035 0.040 0.20–0.35 1.15–1.65
M
N
0.12–0.21 0.45–0.70 0.035 0.040 0.20–0.35
—
1.20–1.50 0.45–0.60
0.15–0.21 0.80–1.10 0.035 0.040 0.40–0.90 0.50–0.80
—
0.25
P
Q
A
B
C
D
2
0.12–0.21 0.45–0.70
0.14–0.21 0.95–1.30
0.25
1.15–1.50
0.25
1.15–1.50
0.25
1.15–1.50
0.25
1.15–1.50
0.24
0.70–1.60
0.035
0.035
0.035
0.035
0.035
0.035
0.035
0.040
0.040
0.040
0.040
0.040
0.040
0.040
0.20–0.35 0.85–1.20 1.20–1.50 0.45–0.60
0.15–0.35 1.00–1.50 1.20–1.50 0.40–0.60
0.15–0.30
—
—
0.45–0.60
0.15–0.30
—
0.40–0.70 0.45–0.60
0.15–0.30
—
0.70–1.00 0.45–0.60
0.15–0.30
—
0.20–0.40 0.45–0.60
0.15–0.30
0.25
0.25
0.08
B
C
1
2
A
B
C
0.23
0.40
0.23
0.40
0.13
0.90
0.13
0.90
0.16
0.90–1.50
0.20
0.70–1.60
0.22
1.00–1.60
0.12–0.18 0.10–0.40
0.12–0.20 0.10–0.40
0.12
0.60–0.90
0.020
0.020
0.035
0.035
0.040
0.040
0.040
0.025
0.025
0.010
0.020
0.020
0.035
0.035
0.050
0.050
0.050
0.025
0.025
0.015
0.20–0.40
0.20–0.40
0.15–0.40
0.15–0.40
0.15–0.50
0.15–0.50
0.20–0.50
0.15–0.35
0.15–0.35
0.15–0.35
—
—
—
1.50–2.00 2.60–4.00c
1.20–1.50 2.25–3.50
—
8.50–9.50
—
7.50–8.50
0.25
0.25
0.25
0.25
0.25
0.25
1.00–1.80 2.00–3.25
1.00–1.80 2.25–3.50
0.40–0.70 4.75–5.25
When a single value is shown, it is a maximum limit.
Vanadium may be substituted for part or all of titanium content on a one-for-one basis.
Limiting values vary with the plate thickness.
When specified.
0.50–0.65
0.45–0.55
0.25–0.40
0.45–0.60
0.45–0.60
—
—
0.08
0.08
0.08
0.20–0.60
0.20–0.60
0.30–0.65
Others
MPa
ksi
Zr, 0.05–0.15; B, 0.0025
A 514
V, 0.03–0.08; Ti, 0.01– 760–895 110–130
0.03; B, 0.0005–0.005
—
B, 0.001–0.005
A 517
0.20–0.40
Ti, 0.004–0.10b;
795–930 115–135
B, 0.0015–0.005
0.20–0.40
Ti, 0.04–0.10b;
B, 0.0015–0.005
0.15–0.50
V, 0.03–0.08;
B, 0.0005–0.006
—
Zr, 0.05–0.15; B, 0.0025
—
V, 0.03–0.08;
B, 0.0005–0.005
—
B, 0.001–0.005
—
B, 0.001–0.005
0.20–0.40
Ti, 0.04–0.10b;
B, 0.0015–0.005
—
B, 0.001–0.005
—
Zr, 0.05–0.15;
B, 0.0005–0.0025
—
B, 0.001–0.005
—
V, 0.03–0.08
—
—
620–795 90–115
—
—
620–795 90–115
—
—
620–795 90–115
—
—
620–795 90–115
0.35
—
550–690 80–100
—
—
—
—
d0.20d
d0.20d
d0.20d
0.25
0.25
—
V, 0.03
V, 0.03
—
—
—
V, 0.03; Ti, 0.02
V, 0.03;Ti, 0.02
V, 0.05–0.10
795–930
795–930
690–825
690–825
485–620
550–690
620–760
—
—
—
115–135
115–135
100–120
100–120
70–90
80–100
90–110
—
—
—
Minimum
Yield Strength
MPa
ksi
A 514
690
100
A 517
690
100
485
485
485
485
415
70
70
70
70
60
690
690
585
585
345
415
485
550
690
895
100
100
85
85
50
60
70
80
100
130
AWS WELDING HANDBOOK 9.4
A 553
Grade
or
Class
56 CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.18
Typical Quenched and Tempered Steels
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
57
Table 1.19
Heat Treatments for Typical Quenched and Tempered Steels
Austenitizing Temperature
Tempering Temperature
Steel
°C
°F
Quenching
Medium
ASTM A 514, A 517
900
1650
Water or oil
620
1150
Bainite and martensite
ASTM A 533, Type B
840
1550
Water
590
1100
Bainite and martensite (thin plate) or ferrite
and bainite (thick plate)
ASTM A 537, Class 2
900
1650
Water
590
1100
Ferrite and bainite, martensite, or all three
ASTM A 543, Type B
900
1650
Water
590
1100
Bainite and martensite
ASTM A 678, Grade C
900
1650
Water
590
1100
Ferrite and bainite, martensite, or all three
HY-80, HY-100
900
1650
Water
650
1200
Bainite and martensite
HY-130
820
1500
Water
540
1000
Bainite and martensite
and tempering temperatures for other Q&T steels may
be obtained from the applicable specification or the
producer of the steel.
METALLURGICAL CONSIDERATIONS
The way in which quenched and tempered (Q&T)
steels respond to heat treatment and welding depends
on the composition and thickness of the steel, as previously described under Fundamentals of Welding Carbon and Low-Alloy Steels in this chapter. In general,
Q&T steels are alloyed to promote the formation of tempered martensite and lower-bainite structures, as shown
in Table 1.19. Some of the microstructural features of
Q&T steels are discussed in this section, using ASTM
A 514 or A 517 steels as an example. These ASTM steels
are frequently specified for high-strength welded structures.
Transformation Behavior
An isothermal transformation diagram for a typical
ASTM A 514 or A 517 steel is shown in Figure 1.23.
The transformation behavior of this steel has several
significant features. One feature is the significant length
of time that passes before transformation of austenite to
pearlite begins after cooling in the temperature range of
about 590°C to 700°C (1100°F to 1300°F). This long
duration precludes the formation of upper bainite, ferrite, and pearlite, unless the cooling rate is very slow.
Thus, the presence of these microstructures and their
consequent lower strength and toughness are avoided.
Other features of Q&T steels are that a moderately
long period of time elapses before transformation to
°C
°F
Microstructure
ferrite, and that upper bainite starts in the temperature
range of about 510°C to 590°C (950°F to 1100°F).
These time and temperature ranges permit the quenching of plates up to at least 50 mm (2 in.) thick with little
or no undesirable transformations. Transformation to
ferrite and upper bainite should be avoided because the
remaining austenite, enriched in carbon, may be retained
or transformed to high-carbon martensite or bainite during cooling to room temperature. If considerable transformation occurs in the temperature range of 510°C to
590°C (950°F to 1100°F) as a result of slow cooling, then
the final microstructure will consist of a heterogeneous
mixture of ferrite, upper bainite, and retained austenite
mixed with high-carbon martensite or bainite. A combination of such soft and hard microconstituents, even when
tempered, will not produce a high level of toughness.
If the steel is cooled at a relatively rapid rate, transformation to lower bainite occurs in a relatively short
period of time at temperatures below 480°C (900°F).
This type of microstructure is essentially homogeneous
and has good toughness, particularly after tempering.
Martensite begins to form at the relatively high temperature of 390°C (740°F), a characteristic that is significant
to the ability of these steels to resist quench cracking. It
is also an important consideration in welding because
the cooling of martensite from this relatively high temperature provides some degree of self-tempering.
Hardenability
The specific chemical composition of a type of steel
essentially defines its hardenability. End-quench hardenability bands for typical heats of Grades B and F of
ASTM A 514 or A 517 are shown in Figure 1.24. The
lower alloy content of Grade B steel is reflected in its
58
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
800
AWS WELDING HANDBOOK 9.4
Ac3 820°C (1507°F)
AUSTENITIZED AT 913°C (1675°F)
ASTM GRAIN SIZE: 6-7
Ac1 714°C (1316°F)
A+F+C
1400
F+C
A+F
AUSTENITE
1200
50% I-T
600
A+F
1000
A+F+C
500
50% I-T
800
Ms 393°C (740°F)
400
TEMPERATURE, °F
TEMPERATURE, °C
700
99% I-T
1 MIN
1 HOUR
1 DAY
1 WEEK
600
5
10
102
103
104
TIME, s
105
106
LIVE GRAPH
Click here to view
Notes: A = Austenite, F = Ferrite, C = Cementite, Ms = Martensite Start Temperature,
I-T = Isothermal Transformation
Figure 1.23—Isothermal Transformation Diagram for a Typical ASTM A 514 or A 517 Steel
lower hardenability, as shown by a more rapid drop in
hardness with increasing distance from the quenched
end of the test specimen. However, the hardenability of
these two steels is similar enough to produce nearly
identical microstructures up to a point slightly more
than 10 mm (0.4 in.) from the quenched end. As a
result, they can be expected to produce similar microstructures in plate thicknesses up to 25 mm (1 in.) when
similarly quenched on both surfaces. Grade F steel may
be used for plate thicknesses exceeding 25 mm (1 in.)
because of its greater hardenability. The hardenability
bands also give an indication of the maximum hardness
that may be expected in the heat-affected zone (HAZ)
of a weld in the as-welded condition.
Tempering Response
The effect of tempering on the hardness and strength
of ASTM A 514 or A 517, Grades B and F, is shown in
Figure 1.25. The change in slope of the hardness curves
for both steels at about 510°C (950°F) is a result of the
secondary hardening effect of vanadium in these steels.
Secondary hardening, which results from the precipita-
tion of fine vanadium carbides, occurs at tempering
temperatures up to about 680°C (1250°F); however, it
is most pronounced in the range of 510°C to 620°C
(950°F to 1150°F).
WELDING QUENCHED AND TEMPERED
STEELS
Quenched and tempered (Q&T) steels are not inherently difficult to weld. However, the desirable mechanical
properties of these steels, specifically high strength and
good toughness, will be developed in welded joints only
by following proper welding procedures.
This section explains how design and welding thermal
cycles affect the serviceability of products fabricated from
Q&T steels.
Joint Design
In addition to good workmanship and adequate
inspection, appropriate joint design is needed to take
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
LIVE GRAPH
DISTANCE FROM QUENCHED END, mm
0
10
20
30
40
Click here to view
50
60
45
GRADE F STEEL
HARDNESS, HRC
40
35
30
25
GRADE B STEEL
20
15
0
0
0.5
1.0
1.5
2.0
2.5
DISTANCE FROM QUENCHED END, in.
Figure 1.24—End Quench Hardenability
Bands for ASTM A 514 or A 517
Grades B and F Steels
LIVE GRAPH
TEMPERING TEMPERATURE, °C
200
300
400
500
600
Click here to view
700
45
GRADE B STEEL
HARDNESS, HRC
40
35
GRADE F STEEL
30
25
20
15
400
600
800
1000
1200
TEMPERING TEMPERATURE, °F
1400
Figure 1.25—Relationship Between Hardness,
Tensile Strength, and Tempering Temperature
for Quench-Hardened ASTM A 514 or
A 517 Grades B and F Steels
59
60
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
advantage of the high strength of quenched and tempered
steels and to optimize the serviceability of weldments made
from them. Abrupt changes in cross section produce stress
concentrations, which are less tolerable in steels with yield
strengths of about 550 MPa (80 ksi) or higher than they
are in low-carbon and mild steels. With higher yield
strengths, welding-induced tensile residual stresses are less
readily accommodated by plastic strain, and stress concentrations are more likely to result in cracking. Poorly
located and poorly contoured welds can contribute
unnecessarily to the severity of a stress concentration.
From the standpoint of stress concentration, groove
welds are preferable to fillet welds. In either case, the
weld metal should blend smoothly with the base metal
at the toe and the root of the weld. For fillet welds, the
leg length should be proportioned so that there is a minimum 120° re-entrant angle. Excessive weld reinforcement should be avoided.
Complete joint penetration (CJP) is desirable in most
cases, therefore joint designs employing V-grooves or Ugrooves are preferred. Bevel-grooves or J-grooves may
be used, but welding procedures must ensure complete
fusion with both groove faces. Double-welded joints
should be used wherever practical.
A significant issue when welding Q&T steels is weld
metal cracking in the root of a thick or otherwise highly
restrained weld. A technique for avoiding this problem
is to use a low-strength electrode (e.g., E7018) to weld
the root pass, which can be later removed by backgouging
for CJP so that the weld joint strength is not affected.
Welded joints in Q&T steels should be designed and
located to provide sufficient access for the performance
of proper welding practices and inspection. Again,
groove welds generally are better than fillet welds for
this purpose, as fillet welds are more difficult to inspect
by radiographic or ultrasonic methods.
Preheat and Interpass Temperature
Preheating is often recommended for quenched and
tempered steels, especially when the joint to be welded
is thick or highly restrained, or both, or when some
other condition is present that may promote cracking.
Table 1.20 shows suggested minimum preheat and
interpass temperatures for welding several ASTM Q&T
steels using low-hydrogen welding practice. The maximum temperature should not exceed the suggested minimum temperature by more than 65°C (150°F), because
the upper limit for acceptable welding heat input
(described in this section under Heat Input) may be
exceeded as a result. Table 1.21 provides the preheat
temperature ranges for HY-80, HY-100, and HY-130
steels for military applications. As with HSLA steels,
minimum preheat and interpass temperatures can vary
with the welding process and heat input rate. If preheating at less than 40°C (100°F) is used, precautions are
necessary to ensure that the surfaces of the workpieces
are free of moisture.
Maximum preheat and interpass temperatures are
often specified. Excessively high values of either can reduce the cooling rate of the reaustenitized heat-affected
zone to an extent that produces ferrite with regions of
high-carbon martensite, or coarse bainite. This type of
microstructure lacks the combination of strength and
toughness needed to meet the service demands for
which Q&T steels are typically selected. In the absence
of specific restrictions on interpass temperature, 190°C
(370°F) can be considered an appropriate maximum for
Table 1.20
Suggested Preheat and Interpass Temperatures for
Arc Welding Typical ASTM Quenched and Tempered Steels
Minimum Preheat and Interpass Temperature*
Thickness Range
A 514/A 517
A 533
A 537
A 543
A 678
mm
in.
°C
°F
°C
°F
°C
°F
°C
°F
°C
°F
Up to 12.7
Up to 0.50
10
50
10
50
10
50
40
100
10
50
14.2 to 19.1
0.56 to 0.75
10
50
40
100
10
50
50
125
40
100
20.6 to 25.4
0.81 to 1.00
50
125
40
100
10
50
65
150
40
100
27.9 to 38.1
1.1 to 1.5
50
125
95
200
40
100
95
200
65
150
40.6 to 50.8
1.6 to 2.0
80
175
95
200
65
150
95
200
65
150
53.3 to 63.5
2.1 to 2.5
80
175
150
300
65
150
150
300
65
150
Over 63.5
Over 2.5
105
225
150
300
105
225
150
300
—
—
*With low-hydrogen welding practices, maximum temperature should not exceed the given value by more than 66°C (150°F).
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
61
Table 1.21
Recommended Preheat and Interpass Temperature Ranges for HY-80, HY-100, and HY-130 Steels
Temperature
Thickness Range
mm
HY-80, HY-100
in.
HY-130
°C
°F
°C
°F
Up to 12.7
Up to 0.5
15–150
60–300
25–65
75–150
13.0–16.00
0.51–0.63
50–150
125–300
25–65
75–150
16.3–22.4
0.64–0.88
50–150
125–300
50–95
125–200
22.6–28.7
0.89–1.13
50–150
125–300
95–135
200–275
29.0–35.1
1.1 –1.38
95–150
200–300
95–135
200–275
Over 35.1
Over 1.38
95–150
200–300
105–150
225–300
not receive the benefits of tempering produced by additional weld passes. The toughness of the HAZ of prior
passes in multiple-pass welds is expected to be significantly better. Nevertheless, in comparing the effects of
the two preheat temperatures 95°C (200°F) and 260°C
(500°F), the higher temperature resulted in significantly
decreased toughness.
Arc Welding Processes
Any of the commonly used arc welding processes—
shielded metal arc welding (SMAW), submerged arc
welding (SAW), gas metal arc welding (GMAW), flux
LIVE GRAPH
TEST TEMPERATURE, °C
–120
–90
–60
–30
0
30
Click here to view
60
ABSORBED ENERGY, J
WELDING HEAT INPUT – 1850 kJ/m (47 kJ/in.)
50
60
40
AS-RECEIVED
BASE METAL
HEAT-AFFECTED ZONE
90°C (200°F) PREHEAT
40
30
20
20
HEAT-AFFECTED
ZONE 260°C
(500°F) PREHEAT
0
–200 –150 –100
–50
0
50
100
150
10
ABSORBED ENERGY, ft·lb
most Q&T steels. Adjacent to the re-austenitized HAZ,
a outlying band of base metal may be softened somewhat
by overtempering. Restoring this region to its original
strength level requires a postweld quench-hardening
heat treatment, although many weldment designs do not
require this and thus it is rarely performed in practice.
The effects of two preheat temperatures on the
toughness of a simulated HAZ in ASTM A 514 or
A 517 steel plate 13 mm (0.5 in.) thick, are illustrated
in Figure 1.26. The curves indicate the toughness of the
grain-coarsened area in the HAZ on a single-pass weld,
or on the final pass of a multiple-pass weld. This area is
considered to be the worst condition, because it does
0
TEST TEMPERATURE, °F
Figure 1.26—Effect of Preheat Temperature on the Charpy V-Notch Toughness of
the Heat-Affected Zone in 13 mm (0.5 in.) Thick ASTM A 514 or A 517 Steel
62
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
cored arc welding (FCAW), and gas tungsten arc welding (GTAW)—can be used to join Q&T steels with minimum yield strengths up to 690 MPa (100 ksi). For
higher-strength steels, the welding process must be considered carefully if yield strength and toughness in service is critical. To weld steels with minimum yield
strengths over 690 MPa (100 ksi), such as HY-130, the
GMAW and GTAW processes are best for achieving a
satisfactory level of notch toughness in the weld metal.
Care should be exercised with manual GTAW on highstrength material, however, since a heat input rate that
depends on welder technique may exhibit greater variability.
The cooling rate of an arc weld usually is sufficiently
rapid under normal conditions so that the resulting
mechanical properties of the HAZ approach those of
the unaffected base metal. A postweld hardening heat
treatment, such as quenching and tempering, usually is
not necessary.
Excessive heat input when welding a Q&T steel can
reduce the strength and toughness of the welded joint.
These reductions can occur in the heat-affected zone or
the weld metal, or both. Welding with a process that
has extremely high heat input (e.g., electroslag or
electrogas welding) results in a slow cooling rate, and
this may require complete quenching and tempering
heat treatment of the welded joint to obtain acceptable
mechanical properties.
Quenched and tempered steels can be joined by electron beam and laser beam welding. The heat input will
be much lower with one of these processes than with
the arc welding processes. In laboratory tests, autogenous
welds in 13 mm (0.5 in.) thick HY-130 steel plate made
with these processes were as strong as the base metal.72
The weld metal and HAZ structures consisted of untempered martensite and bainite, both of which were harder
than the unaffected base metal.
Heat Input
The cooling rates of the weld metal and heat-affected
zone are functions of welding heat input, the temperature of the adjacent base metal, and the joint thickness.
The relative effects of welding heat input and preheat
temperature are the same—the higher the heat input,
the lower is the cooling rate. For a given joint thickness
and preheat temperature, heat input during welding
must not exceed a specific value if the HAZ is to have
an acceptable cooling rate. If the preheat temperature is
increased, the welding heat input must be decreased to
maintain the same cooling rate.
The minimum cooling rate required to produce a
microstructure with suitable mechanical properties will
72. Stoop, J., and E. A. Metzbower, 1978, A Metallurgical Characterization of HY-130 Steel Welds, Welding Journal 57(11): 345-s–353-s.
AWS WELDING HANDBOOK 9.4
vary with the particular steel being welded, and a cooling rate that is sufficiently fast for one type of steel may
be too slow for another. For example, heat input suitable for welding a joint in a particular Q&T steel with
a specific thickness and preheat may be too high for a
similar joint in another Q&T steel with the same thickness and preheat.
Welding heat is dissipated more rapidly into a thick
cross section of steel than into a thin one. For this reason, the maximum heat input can be increased as the
joint thickness increases. Prior to welding a particular
Q&T steel, recommendations should be obtained from
the steel producer concerning its weldability, hardenability, and preheat and heat-input limitations. The following tables are presented in this section to provide
maximum heat input for welding various thicknesses of
Q&T steels:
1. Table 1.22 for ASTM A 514 or A 517, Grade F;
2. Table 1.23 for HY-80, HY-100, and ASTM A 678,
Grade C; and
3. Table 1.24 for HY-130.
The heat input limitations for most Q&T steels are
based on requirements for toughness rather than
strength, because toughness decreases more than
strength as a result of excessive heat input. With a few
Q&T steels, strength is degraded more severely than
toughness, thus the heat input limitations for these
steels would be based on achieving adequate joint
strength. Heat input limitations have not been established for every Q&T steel. However, excessively high
heat input should be avoided as a matter of good welding practice. Heat-input limitations for a particular
Q&T steel may be a specification requirement, as in the
case of HY-80, HY-100, and HY-130 steels used for the
fabrication of naval ships. Welding heat input may be
calculated using the following formula:
60V IHI = --------------s
(1.5)
where
HI = Heat input in Joules per unit length,
V = Arc voltage,
I = Welding current, and
s = Arc travel speed in unit length per minute.
Heat input limitations are applicable to each weld
pass individually and do not apply cumulatively. Also,
they are applicable only to single-arc welding processes.
Multiple-arc processes with the arcs arranged in tandem generally do not provide time for the first weld
bead to cool sufficiently before the trailing arc passes
over it and adds additional heat. Therefore, these pro-
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
63
Table 1.22
Maximum Welding Heat Input for Butt Joints in ASTM A 514 or A 517 Grade F Steel
Maximum Heat Input for Joints at Various Preheatsa
Section Thickness
20°C (70°F)
95°C (200°F)
150°C (300°F)
200°C (400°F)
mm
in.
kJ/mm
kJ/in.
kJ/mm
kJ/in.
kJ/mm
kJ/in.
kJ/mm
kJ/in.
4.8
0.19
1.06
27
0.83
21
0.67
17
0.51
13
6.4
0.25
1.42
36
1.14
29
0.94
24
0.75
19
12.7
0.50
2.76
70
2.20
56
1.85
47
1.57
40
19.1
0.75
4.76
121
3.90
99
3.23
82
2.56
65
25.4
1.0
Note b
6.81
173
4.96
126
3.66
93
175
5.0
127
6.50
165
31.8
1.25
Note b
Note b
38.1
1.5
Note b
Note b
6.89
Note b
50.8
2.0
Note b
Note b
Note b
Note b
a. Heat input limit for intermediate preheat temperatures and thicknesses may be obtained by interpolation. Heat input limit may be increased 25% for fillet
welds.
b. No limit with respect to the heat-affected zone cooling rate with most arc welding processes. Welding processes of high heat input should not be used to
weld these steels.
Table 1.23
Maximum Welding Heat Input for Joints in HY-80,
HY-100, and ASTM A 678 Grade C Steels
Section Thickness
Maximum Heat Input
mm
in.
kJ/mm
kJ/in.
Up to 12.7
Up to 0.50
1.77
45
Over 12.7
Over 0.50
2.17
55
Table 1.24
Maximum Welding Heat Input
for Butt Joints in HY-130 Steel
Maximum Heat Input
Workpiece Thickness*
SMAW
GMAW and GTAW
mm
in.
kJ/mm
kJ/in.
kJ/mm
kJ/in.
9.4–14.2
0.37–0.56
1.57
40
1.38
35
16.0–22.4
0.63–0.88
1.77
45
1.57
40
25.4–35.1
1.0–1.38
1.77
45
1.77
45
38.1–102
1.5–4.0
1.97
50
1.97
50
*Welding thin sections with the SMAW or SMAW process is not recommended.
GTAW is recommended for plate under 9.7 mm (0.38 in.).
cesses should not be used for welding Q&T steels
unless a detailed evaluation proves their suitability.
Welding heat input also has an effect on the mechanical properties of the weld metal. This effect becomes a
concern when welding steels with minimum yield strengths
that are greater than 690 MPa (100 ksi). The heat-input
limitation needed to ensure adequate mechanical properties in the HAZ also limits the size of the weld beads. Large
weld beads characteristically have poor notch toughness.
Moreover, using a weave technique to achieve larger beads
usually requires a slower travel speed along the joint, with
a corresponding increase in heat input that may diminish
strength and toughness.
Good practice for welding Q&T steels is to deposit
many small stringer beads (i.e., without appreciable
transverse oscillation of the electrode). For vertical welding, slight weaving of the electrode for a width equal to
no more than about two electrode diameters usually is
acceptable for SMAW, and up to five electrode diameters for GMAW and FCAW. This technique produces
weld metal with good notch toughness as a result of the
grain-refining and tempering action of succeeding passes.
Filler Metals
Welding electrodes or electrode-flux combinations
are available for arc welding most of the Q&T steels by
the commonly used processes. Suggested filler metals for
typical Q&T steels are listed in Table 1.25. The selection is based on the tensile strength, composition, and
64
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.25
Suggested Filler Metals for Arc Welding Typical Quenched and Tempered Steels
Welding Process
ASTM Specification
or Common Name
Grade or Type
A 514 or A 517
All
—
E1X01X-M
A 533
B
1, 2
E901X-D1
Class
SMAWa
GMAW,b GTAW
SAWc
FCAWd
ER1X0S-1
F1XXX-EXXX-MX
E1X0TX-KX
ER100S-1
F9XX-EXXX-FX
E9XTX-NiX
E901X-M
A 537
—
E9XTX-K2
3
E1101X-M
ER110S-1
F11XX-EXXX-M2
E110TX-XX
2
E801X-CX
ER80X-NiX
F8XX-EXXX-NiX
E8XTX-NiX
F9XX-EXXX-NiX
E9XTX-NiX
F11XX-EXXX-FX
E11XTX-KX
F9XX-EXXX-FX
E9XTX-NiX
F10XX-EXXX-MX
E9XTX-NiX
F11XX-EXXX-MX
E11XTX-KX
E901X-D1
E9018-M
A 543
B
1, 2
E1101X-M
ER110S-1
A 678
C
—
E901X-D1
ER100S-1
ER120S-1
E9018-M
E1001X-D2
E10018-M
HY-80, HY-100
—
—
E1101X-M
ER110S-1
ER120S-1
a. Shielded metal arc welding electrodes with low-hydrogen coverings in AWS A5.5/A5.5M:2006, Specification for Low-Alloy Steel Electrodes for Shielded
Metal Arc Welding Electrodes.
b. Electrodes for gas metal arc or gas tungsten arc welding in AWS A5.28/A5.28M:2005, Specification for Low-Alloy Steel Electrodes and Rods for Gas
Shielded Arc Welding.
c. Submerged arc welding with electrode-flux combinations in AWS A5.23/A5.23M:2007, Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding.
d. Flux cored arc welding electrodes in AWS A5.29/A5.29M:2010, Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding. Classification of
EXXT1 and EXXT5 electrodes is done with CO2 shielding gas. However, Ar-CO2 gas mixtures may be used when recommended by the manufacturer to
improve usability.
notch toughness of the weld metal. Some entries in this
table cover two or more classifications that have similar
characteristics. Classifications other than those listed
may be suitable for some applications.
The selection of the filler metal for a specific Q&T
steel application should be based on a thorough evaluation of expected weld joint properties. In general, the
welding filler metal chosen should deposit weld metal
that has suitable strength and toughness for the application. Specific consideration should be given to the weld
toughness in either the as-welded or postweld heat-treated
condition (assuming postweld heat treatment is required).
Joint efficiency of 100% can be obtained for butt
joints in these steels when proper welding filler metals
and procedures are used. However, filler metals that
deposit weld metal that has strength lower than that of the
base metal often are adequate for welds that are subject
to relatively low stresses. These lower-strength weld met-
als often bring the benefit of greater toughness. Typical
examples are fillet welds stressed in longitudinal shear,
welds carrying secondary stresses, and welds joining a
lower-strength steel to a Q&T steel. Low-strength weld
metal also may be desirable for highly restrained welds
to reduce susceptibility to toe cracking or lamellar tearing in the steel, especially with corner joints and T-joints.
Hydrogen is very detrimental when welding Q&T
steels; a very small quantity may cause hydrogen cracking. Because moisture is a source of hydrogen, the moisture content of covered electrodes must be kept as low
as possible. Proper packaging and handling procedures
can minimize moisture pickup and the need for reconditioning covered electrodes for welding Q&T steels.
Electrodes should be packaged by the manufacturer in
hermetically sealed containers. If the container is damaged, the electrodes should be reconditioned prior to
use or discarded.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.26
Permissible Atmospheric Exposure
of Low-Hydrogen Electrodes
Electrode
Column Aa Hours
Column Bb Hours
E70XX-X
E80XX-X
E90XX-X
E100XX-X
E110XX-X
4 max.
2 max.
1 max.
0.5 max.
0.5 max.
Over 4 to 10 max.
Over 2 to 10 max.
Over 1 to 5 max.
Over 0.5 to 4 max.
Over 0.5 to 4 max.
a. Electrodes exposed to atmosphere for longer periods than shown shall
be redried before use.
b. Electrodes exposed to atmosphere for longer periods than those established by testing shall be redried before use.
The moisture content of a flux covering should not
be allowed to exceed 0.4% when welding Q&T carbon
steels with minimum yield strength up to 480 MPa
(70 ksi), such as ASTM A 537 steels and A 678 steels.
Moisture content should not be allowed to exceed 0.1%
with Q&T low-alloy steels that have minimum yield
strengths of 690 MPa (100 ksi) and above, such as HY130 steel. If the permitted moisture content of the selected
covered electrode exceeds the appropriate limit for the
steel, the electrodes must be reconditioned prior to use,
regardless of the type of packaging.
The maximum time at which electrodes may be
exposed to specific humidity and temperature conditions without exceeding moisture content limits can be
determined by testing or obtained from the electrode
manufacturer. If these data are not available, the maximum exposure time to ambient conditions should not
exceed that listed for the electrode classification in
Table 1.26.73
Covered electrodes should be placed in a holding
oven maintained at 120°C (250°F) or in a low-humidity
storage cabinet immediately after opening the container
or removing them from a reconditioning oven. Electrodes should be removed from the holding oven or
storage cabinet as needed. If the electrodes are exposed
to ambient conditions longer than the approved time,
they should be reconditioned according to the manufacturer’s recommendations and then returned to the holding oven or low-humidity cabinet for storage. Typically
this may be done only once. For this reason, many users
discard rather than recondition overly exposed electrodes. When welding under very humid conditions,
portable holding ovens should be used at the welding
site and the electrodes should be removed individually
73. A test to determine the moisture content of the electrode covering
is described in AWS A5.5/A5.5M:2006, Specification for Low-Alloy
Steel Electrodes for Shielded Metal Arc Welding (see Reference 24).
65
as needed by the welder. Electrodes contaminated by contact with water, paint, oil, grease, or other hydrocarbons should be discarded.
Fluxes for submerged arc welding should be purchased in moisture-resistant packages and stored in a
dry location. Packages should not be opened until the
contents are needed. Immediately after opening, the
flux should be placed in the dispensing system. Excess
flux from opened packages should be stored in a holding oven operating at about 120°C (250°F). Flux from
damaged packages should be either discarded or dried
in an oven at about 260°C (520°F) for at least one hour.
After drying, the flux should be used immediately or
stored in a holding oven. Flux should be discarded if it
was fused during welding or if it has been contaminated
by foreign materials such as water, oil, or grease.
Shielding gases used for gas metal arc, flux cored arc,
or gas tungsten arc welding of Q&T steels should have
a low moisture content, as indicated by a dew point
of –50°C (–60°F) or lower, according to Welding Consumables—Gases and Gas Mixtures for Fusion Welding
and Allied Processes.74
Postweld Heat Treatment
Service experience with structures and pressure vessels, in addition to full-scale laboratory tests, have
shown that postweld stress-relief heat treatment generally is not required to prevent brittle fracture of welded
joints in most Q&T steels. Of the steels listed previously (refer to Table l.18), only welds in ASTM A 533
and A 537 steels usually are stress relieved due to code
provisions when the weld thickness is greater than a
specified amount. With any of the Q&T steels, postweld
stress-relief heat treatment should be used only after it
is ensured that worthwhile benefits can be achieved and
possible detrimental effects can be tolerated.
Stress relief may be desirable for some applications,
under conditions such as the following:
1. The steel has inadequate notch toughness after
cold forming or welding,
2. Dimensional stability must be maintained during
close-tolerance machining, or
3. The steel is susceptible to environmentally-assisted
cracking after cold forming or welding.
The need for postweld stress-relief treatment should
be investigated thoroughly for each application, because
many Q&T steels are designed for service in the as-welded
condition. The mechanical properties of the welded steel
74. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2011, Welding Consumables—Gases and Gas
Mixtures for Fusion Welding and Allied Processes, AWS A5.32M/A5.32:
2011 (ISO 14175:2008 MOD), Miami: American Welding Society.
66
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
or even the weld metal may be adversely affected by a
stress-relief treatment. The alloying elements that contribute most to the high strength and notch toughness
of Q&T steel and weld metal usually are those that
cause adverse effects when the weldment is heat-treated
after welding.
A postweld heat treatment in the temperature range
of 510°C to 650°C (950°F to 1200°F) may decrease the
toughness of the weld metal and the heat-affected zone.
The extent of such impairment depends on the chemical
composition of the weld metal or base metal, the stressrelieving temperature, and the time held at temperature.
The impairment is greater with slow cooling; nevertheless,
most codes that specify postweld heat treatment require
slow cooling through this range (e.g., no more than
280°C/hr [500°F/hr]).
Reheat cracking also can occur when weldments of
many of the high-strength steels are heated above about
510°C (950°F). Intergranular cracking may take place
in the grain-coarsened region of the heat-affected zone
of the weld. The intergranular cracking occurs by stress
rupture, usually in the early stage of the heat treatment.
Susceptibility to cracking increases with increasing weld
restraint and the severity of stress concentrations. Chromium, molybdenum, and vanadium are the major contributors to this type of crack susceptibility, but other
carbide-forming elements contribute to the problem.
The precipitation of carbides during stress relaxation at
elevated temperature alters the delicate balance between
resistance to grain boundary sliding and resistance to
deformation within the coarse grains in the HAZ.
The following procedures may be used alone or in
combination to minimize reheat cracking in steels:
1. Selecting a weld joint design, weld location, and
sequence of assembly that minimize restraint;
2. Ensuring that the weld joint design and contour
will minimize stress concentrations;
3. Providing a weld metal that has lower strength
than that of the HAZ at the heat-treating temperature; and
4. Peening each layer of weld metal to reduce
shrinkage stresses.
If postweld stress relief is required, the temperature
must not exceed that used for tempering the steel. For
example, a temperature about 30°C to 60°C (50°F to
100°F) lower than the tempering temperature is desirable to avoid lowering the strength of the steel.
BRAZING QUENCHED AND TEMPERED
STEELS
Quenched and tempered steels can be brazed using
filler metals, brazing methods, and procedures suitable
AWS WELDING HANDBOOK 9.4
for carbon steels. However, the brazing temperatures
used with filler metals for carbon steels generally exceed
the tempering temperatures of Q&T steels. Consequently, the mechanical properties of the steel would be
impaired by a brazing cycle. Heat treating the brazement by further quenching and tempering would be
necessary to restore mechanical properties.
THERMAL CUTTING OF QUENCHED AND
TEMPERED STEELS
Oxyfuel gas cutting is the preferred means of thermal
cutting Q&T steels; it is accomplished readily whether
performed by hand or machine. Mechanized cutting is
recommended to obtain smoother and more uniform
cut edges for welding. Generally, the cutting conditions
are the same for carbon steels and Q&T steels. If scale
on the steel surface causes erratic cutting action, the
travel speed should be reduced about 10% to 15%, or a
cutting tip of the next larger size should be used. Otherwise, the scale should be removed from the surface by
grinding or sandblasting. Stack cutting of thin plates
should be avoided, because the high heat input tends to
overheat the plate closest to the cutting tip. Plasma arc
cutting also may be used on Q&T steels.
Thermally cut edges of Q&T steels will be hardened
by the cutting operation, but they will remain relatively
tough. These hard edges may be tempered (preferably in
a furnace) to soften them and facilitate machining. The
tempering temperature should be at least 30°C (50°F)
below the original tempering temperature of the steel to
avoid softening. These steels generally can be thermally
cut without preheat. However, the steel temperature
should not be lower than 10°C (50°F) during cutting.
Preheat is recommended when cutting sections greater
than about 100 mm (4 in.) thick. For example, a preheat temperature of 150°C (300°F) is suggested by one
steel manufacturer for ASTM A 514 or A 517 steels.
For cutting the higher carbon steels, such as ASTM
A 533 and A 543, the same preheat temperature recommended for welding is suggested for cutting.
All slag or loose scale from thermal cutting should be
removed before welding. Any area of excessive roughness from the cutting should be smoothed by grinding.
Air carbon arc gouging may be used to remove
welds, portions of welds, or base metal. Proper current,
air pressure, and operating technique must be used to
ensure that any metal liquefied by the arc is removed by
air blast because the resolidified metal will be high in
carbon and can crack. The gouged surface should be
ground to remove any carburized steel. Thermal gouging with the oxyfuel gas process is not recommended
for Q&T steels because of the excessive heat input and
the slow cooling rate inherent with this process. Plasma
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
arc gouging is recommended because it avoids the risks
associated with both oxyfuel gas gouging and carbon
arc gouging.
HEAT-TREATABLE LOW-ALLOY
STEELS
Steels classified as heat-treatable low-alloy (HTLA)
have high hardenability by design, and are thus highly
susceptible to hydrogen cracking in the weld metal and
heat-affected zone. Low-hydrogen welding procedures
must be used with sufficient preheat and interpass temperature to prevent hydrogen cracking.
COMPOSITION AND PROPERTIES
The compositions of several HTLA steels are listed in
Table 1.27. The carbon contents of these steels generally range from about 0.25% to 0.45%, in contrast to
0.10% to 0.25% for the quenched and tempered
(Q&T) low-alloy steels. Heat-treatable low-alloy steels
have sufficient carbon and alloy content to give them
high hardenability, and they can be heat-treated to
higher strength and hardness than the Q&T steels.
The approximate relationship between tempering
temperature and tensile strength for several HTLA
steels is provided in Table 1.28. Adjustment of the tempering temperature to enhance certain desired properties in a weldment can be guided by tension or hardness
testing. A lower tempering temperature promotes higher
strength and hardness, but lower ductility and toughness.
Proper control of sulfur and phosphorus contents is
especially important for HTLA steels. Sulfur increases
susceptibility to solidification cracking of the weld
metal, which is already high due to the elevated carbon
content. Phosphorus increases sensitivity to quench
cracking and to hydrogen cracking, which is already
high due to the high hardenability. The upper limit on
phosphorus and sulfur is 0.025% for SAE alloy steels
made by the electric furnace process. For SAE alloy
steels made by the open-hearth or basic oxygen furnace
processes, the upper limits are 0.035% for sulfur and
0.040% for phosphorus. Sulfur and phosphorus limits
of less than 0.015% each should be specified for HTLA
steels when they are to be heat treated to very high
strength levels (≥1380 MPa [≥200 ksi]). Vacuum-melted
filler metals may be required in some cases.
Table 1.27
Compositions of Typical Heat-Treatable Low-Alloy Steels
Composition, %
Common
Designation
4027
67
C
Mn
Si
Ni
Cr
Mo
V
0.25–0.30
0.70–0.90
0.15–0.35
—
—
0.20–0.30
—
4037
0.35–0.40
0.70–0.90
0.15–0.35
—
—
0.20–0.30
—
4130
0.28–0.33
0.40–0.60
0.15–0.35
—
0.80–1.10
0.15–0.25
—
4135
0.33–0.38
0.70–0.90
0.15–0.35
—
0.80–1.10
0.15–0.25
—
4140
0.38–0.43
0.75–1.00
0.15–0.35
—
0.80–1.10
0.15–0.25
—
4320
0.17–0.22
0.45–0.65
0.15–0.35
1.65–2.00
0.40–0.60
0.20–0.30
—
4340
0.38–0.43
0.60–0.80
0.15–0.35
1.65–2.00
0.70–0.90
0.20–0.30
—
5130
0.28–0.33
0.70–0.90
0.15–0.35
—
0.80–1.10
—
—
5140
0.38–0.43
0.70–0.90
0.15–0.35
—
0.70–0.90
—
—
8630
0.28–0.33
0.70–0.90
0.15–0.35
0.40–0.70
0.40–0.60
0.15–0.25
—
8640
0.38–0.43
0.75–1.00
0.15–0.35
0.40–0.70
0.40–0.60
0.15–0.25
—
8470
0.38–0.43
0.75–1.00
0.15–0.35
0.40–0.70
0.40–0.60
0.20–0.30
—
AMS6434
0.31–0.38
0.60–0.80
0.20–0.35
1.65–2.00
0.65–0.90
0.30–0.40
0.17–0.23
300M
0.40–0.46
0.65–0.90
1.45–1.80
1.65–2.00
0.70–0.95
0.30–0.45
0.05 min.
D-6a
0.42–0.48
0.60–0.80
0.15–0.30
0.40–0.70
0.90–1.20
0.90–1.10
0.05–0.10
68 CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Table 1.28
Approximate Heat-Treating Conditions for Several Heat-Treatable Low-Alloy Steels
Room Temperature Tensile Strength, MPa (ksi)
690
(100)
Common
Designation
Austenitizing
Temperature, °C (°F)
820 to 970
(120 to 140)
Quenching
Medium
970 to 1100
(140 to 160)
1100 to 1240
(160 to 180)
1240 to 1380
(180 to 200)
1380 to 1520
(200 to 220)
1780
(250)
2070
(300)
Approximate Tempering Temperature, °C (°F)
4037
830–855 (1525–1575)
Oil or water
650 (1200)
590 (1100)
495 (925)
—
—
—
—
—
4130
845–885 (1550–1625)
Oil or water
675 (1250)
565 (1050)
495 (925)
455 (850)
385 (725)
—
—
—
—
4135
845–885 (1550–1625)
Oil
—
605 (1125)
550 (1025)
480 (900)
425 (800)
—
—
4140
830–870 (1525–1600)
Oil
700 (1300)
635 (1175)
580 (1075)
510 (950)
455 (850)
385 (725)
—
—
4340
800–845 (1475–1550)
Oil
—
—
635 (1175)
565 (1050)
495 (925)
455 (850)
—
—
8630
845–885 (1550–1625)
Oil or water
660 (1225)
565 (1050)
495 (925)
455 (850)
385 (725)
—
—
—
8735
830–870 (1525–1600)
Oil
—
605 (1125)
550 (1025)
425 (800)
420 (785)
—
—
—
8740
830–870 (1525–1600)
Oil
—
635 (1175)
580 (1075)
510 (950)
455 (850)
385 (725)
—
—
D-6
845–900 (1550–1650)
Air or oil
—
—
—
—
—
540 (1000)
345 (650)
230 (450)
AWS WELDING HANDBOOK 9.4
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
69
1600
AUSTENITIZING TEMPERATURE
800
AUSTENITE
FERRITE
Ae3
700
1400
Ae1
1170°C/h (2100°F/h)
1200
AUSTENITE
500
20°C/h (40°F/h)
1170°C/h
(2100°F/h)
30 000°C/h
(54 000°F/h)
PEARLITE
1000
85°C/h (150°F/h)
800
400
AUSTENITE
BAINITE
600
300
200
AUSTENITE
MARTENSITE
TEMPERATURE, °F
TEMPERATURE, °C
600
400
100
200
A
10
B
102
C
103
104
TRANSFORMATION TIME, s
D
E
105
106
LIVE GRAPH
Click here to view
Note: A = Martensite, B = Martensite Bainite, C = Martensite Ferrite Bainite,
D = Martensite Ferrite Pearlite Bainite, E = Ferrite Pearlite
Figure 1.27—Continuous Cooling Transformation Diagram for SAE 4340 Steel
METALLURGICAL CONSIDERATIONS
The combined carbon and alloy content of HTLA
steels is sufficiently high to promote the formation of
martensite at relatively slow cooling rates; in the
absence of preheat, a martensitic HAZ is essentially
unavoidable. A somewhat extreme example of the high
hardenability of HTLA steels is shown in Figure 1.27
for SAE 4340. High hardenability increases the sensitivity of HTLA steels to hydrogen, thus the likelihood of
hydrogen cracking is significantly higher than that of
other classes of steels (refer to Figure 1.8). Therefore, it
is imperative that welding processes and procedures be
selected to minimize the presence of hydrogen and the
formation of martensite during welding.
The relatively high carbon and alloy content of HTLA
steels also tends to promote solidification cracking in
diluted weld metal. Studies of weld metal composition
based on SAE 4340 steel indicate that its resistance to
solidification cracking can be improved by maintaining the
sum of the sulfur and phosphorus contents below 0.025%.
Improved cracking resistance also can be obtained by
using a filler metal with a lower carbon and alloy content.
These conditions also can be applied to other HTLA steels.
70
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
WELDING HTLA STEELS
Heat-treatable low-alloy steels frequently are welded
in the annealed condition. The entire weldment is then
heat treated to the desired strength or hardness.
Because of their high hardenability, it is necessary to
preheat HTLA steels properly for welding in order to
avoid hydrogen cracking. Controlled preheat and interpass
temperatures are necessary to slow the cooling rate of the
weld enough to prevent excessive hardness in the weld
metal and heat-affected zone. The preferred approach is
to preheat at a temperature high enough to permit the formation of softer bainite instead of hard martensite. A bainitic microstructure in the weld zone and heat-affected zone
will have sufficient toughness to permit handling of the
weldment prior to postweld heat treatment.
In some applications, a practical preheat temperature
may be too low for complete transformation to bainite.
In this case, the weld and HAZ may contain some martensite and retained austenite. Appropriate postweld
operations will be necessary to transform the austenite
to martensite or bainite, depending on the intermediate
processing performed prior to hardening.
Welding variables for HTLA steels, including preheat,
filler metals, postheat, and the selection of welding processes are discussed in this section.
Preheat
The minimum preheat and interpass temperatures
required to prevent cracking in a given steel depend on
the following:
1. Carbon and alloy content,
2. Condition of heat treatment,
3. Workpiece thickness or amount of joint restraint,
and
4. Available hydrogen during welding.
A change in process or procedures to reduce available hydrogen or a decrease in thickness or joint
restraint may permit the use of a lower preheat temperature. Recommended minimum preheat and interpass
temperatures for several SAE low-alloy steels are shown
in Table 1.29.
A complete list of recommended preheat temperatures for each alloy can be found in Welding Research
Council (WRC) Bulletin 191.75
The ideal preheat temperature is about 30°C (50°F)
above the temperature at which martensite begins to
form on cooling, known as the martensite start (Ms)
temperature. Holding at this temperature for a time
after welding will produce a bainitic structure in the
weld metal and heat-affected zone. It also will permit
75. See Reference 45.
AWS WELDING HANDBOOK 9.4
Table 1.29
Recommended Minimum Preheat and Interpass
Temperatures for Several SAE Low-Alloy Steels
Thickness Range
SAE Steel
4027
4037
4130, 5140
4135, 4140
4320, 5130
Minimum Preheat
and Interpass
Temperature*
mm
in.
°C
°F
Up to 13
Up to 0.5
10
50
15–26
0.6–1.0
65
150
27–51
1.1–2.0
120
250
Up to 13
Up to 0.5
40
100
15–26
0.6–1.0
95
200
27–51
1.1–2.0
150
300
Up to 13
Up to 0.5
150
300
15–26
0.6–1.0
200
400
27–51
1.1–2.0
230
450
Up to 13
Up to 0.5
180
350
15–26
0.6–1.0
230
450
500
27–51
1.1–2.0
260
Up to 13
Up to 0.5
95
200
15–26
0.6–1.0
150
300
400
27–51
1.1–2.0
200
4340
Up to 51
Up to 2.0
290
550
8630
Up to 13
Up to 0.5
95
200
15–26
0.6–1.0
120
250
27–51
1.1–2.0
150
300
Up to 13
Up to 0.5
95
200
15–26
0.6–1.0
150
300
27–51
1.1–2.0
180
350
Up to 26
Up to 1.0
150
300
27–51
1.1–2.0
200
400
8640
8740
*Low-hydrogen welding processes only.
dissolved hydrogen to escape from thin sections. At this
preheat temperature, the volumetric expansion that
takes place during transformation will not produce
localized peak stresses that lead to cracking. However,
the Ms temperature of many of the HTLA steels is
above 260°C (500°F).
A preheat temperature of 290°C (550°F) or higher
will contribute to welder discomfort and promote the
formation of a thin oxide layer on the joint faces of the
workpieces. This oxidation may cause unacceptable discontinuities in the weld. Consequently, a welding process that permits the use of a lower preheat temperature
should be used when practical. Otherwise, the welding
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
process and procedures must be designed to minimize
the problems associated with high preheat temperatures. Welding at a preheat temperature below 204°C
(400°F) will require that the hydrogen content be kept
extremely low to prevent cracking. Some low-alloy
steels with high carbon content will require high preheat
and interpass temperatures even with low-hydrogen
welding processes.
When a preheat temperature below the Ms temperature of the steel is used, some austenite will transform
immediately into hard martensite. The balance will
remain unchanged until the temperature is decreased
further toward the martensite finish (Mf) temperature.
Transformation to martensite will increase the risk of
hydrogen cracking. Therefore, the interpass temperature must not fall below the preheat temperature, and
certain postweld treatments must be performed before the
weld is cooled to room temperature. (See the subsequent
section on Postweld Heat Treatment in this chapter.)
Filler Metals
Covered electrodes, bare electrodes and flux cored
electrodes that deposit matching weld metal are available for welding some heat-treatable low-alloy (HTLA)
steels that are quenched and tempered after welding.
These include SAE 4130 and 4340 steels. The electrode
manufacturers should be consulted for recommendations for specific applications, particularly for multiplepass applications in which high joint strength is required
and dilution is limited.
The effect of tempering temperature on the tensile
strength and ductility of weld metal produced in 4130,
4140, and 4340 compositions is shown a Figure 1.28.
LIVE GRAPH
Click here to view
TEMPERING TEMPERATURE, °C
300
200
300
400
500
600
700
2000
WELD METAL ANALYSIS, %
275
C
Mn
Si
Cr
Mo
Ni
1800
250
1600
1500
1400
1300
1200
TENSILE STRENGTH, ksi
TENSILE STRENGTH, MPa
1700
225
TENSILE
STRENGTH
4130
0.21
1.48
0.23
0.54
0.15
1.30
4140
0.40
0.87
0.68
0.72
0.33
–
35
4340
0.37
0.89
0.77
0.71
0.40
1.91
30
25
4140
20
200
4340
ELONGATION
15
175
4130
1100
10
150
1000
900
5
125
4140
800
700
100
300
400
500
600
700
800
900
1000
TEMPERING TEMPERATURE, °F
1100
1200
0
1300
Figure 1.28—Effect of Tempering Temperature on Tensile Strength and
Ductility of 4310, 4140, and 4340 All-Weld-Metal Test Specimens
(Oil-Quenched from 855°C [1575°F] and Tempered for Four Hours)
ELONGATION, %
1900
71
72
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
The weld metal of these compositions responds to
heat treatment in a manner similar to that of the base
metals, as shown in Table 1.28.
Filler metals matching the composition and properties of HTLA steels are available commercially; they
are covered by SAE Aerospace Materials Standards
6457C76 (4130), 6452C77 (4140), and 6456D (4340).78
Typical mechanical properties in various heat-treatment
conditions are listed in Table 1.30.
Electrodes with compositions comparable to the
HTLA base metal but with lower carbon content, may
be suitable for certain applications in which it is acceptable for joint strength to be somewhat lower than basemetal strength. Carbon steel and low-alloy steel, Type
309, Type 312 stainless steel, and nickel alloy (e.g.,
ENiCrFe-3) filler metals also can be used when lower
joint strength is permitted. Lower-strength filler metals
can reduce the risk of cracking in some applications.
Joint strength will depend on the following parameters:
1.
2.
3.
4.
5.
6.
Electrode selection,
Base-metal thickness,
Joint design,
Welding procedure,
Amount and uniformity of dilution, and
Response of the weld metal to postweld heat
treatment.
The welding procedure and expected results should
be evaluated by appropriate tests, including response to
heat treatment. In any case, low-hydrogen electrodes
and filler metals must be used, and they must be kept
dry to avoid hydrogen cracking.
Postweld Heat Treatment
76. Society of Automotive Engineers (SAE), 2010, Steel, Welding
Wire, 0.95Cr-0.20Mo (0.28-0.33C) Vacuum Melted, Environment
Controlled Packaging SAE 4130, SAE Standard AMS6457, Revision
C, Warrendale, Pennsylvania: Society of Automotive Engineers.
77. Society of Automotive Engineers (SAE), 2007, Steel, Welding
Wire, 0.95Cr-0.20Mo (0.38-0.43C), Vacuum Melted, Environment
Controlled Packaging, SAE Standard AMS6452, Revision C, Warrendale, Pennsylvania: Society of Automotive Engineers.
78. Society of Automotive Engineers (SAE International), 2007, Steel,
Welding Wire 0.80Cr-1.8Ni-0.25Mo (0.35-0.40C) (SAE 4340 Mod)
Vacuum Melted, Environment-Controlled Packaging, SAE Standard
AMS6456, Revision D, Warrendale, Pennsylvania: Society of Automotive Engineers.
The heat treatment required immediately after welding of heat-treatable low-alloy steels with an arc welding
process depends on the preheat and interpass temperature, and any subsequent processing prior to hardening.
When the preheat and interpass temperatures are above
the Ms temperature of the steel, the weld must not be
cooled to room temperature until after it is given a thermal treatment to avoid cracking.
If the weldment can be stress-relieved in the range of
590°C to 680°C (1100°F to 1250°F) shortly after weld-
Table 1.30
Typical Mechanical Properties of Heat-Treatable Electrodes
Mechanical Properties
Electrode
Material Types
4130
4140
4340
4340
Ultimate Tensile Strength
Minimum Yield Strength
MPa
MPa
ksi
Charpy Impact Value,
at –18°C (0°F)
ksi
Minimum
Elongation,%
J
ft·lb
860 to 1000
125 to 145
690
100
11.0
64
47
1030 to 1170
150 to 170
830
120
8.0
38
28
1240 to 1380
180 to 200
1000
145
6.0
20
15
860 to 1000
125 to 145
690
100
11.0
64
47
1030 to 1170
150 to 170
830
120
8.0
38
28
15
1240 to 1380
180 to 200
1000
145
6.0
20
1380 to 1520
200 to 220
1100
160
5.0
11
8
1030 to 1170
150 to 170
830
120
8.0
34
25
1240 to 1380
180 to 200
965
140
6.0
16
12
1380 to 1520
200 to 220
1100
160
5.0
11
8
1790 to 1930
260 to 280
1380
200
4.0
8
6
AWS WELDING HANDBOOK 9.4
ing, it should first be allowed to cool from the preheat
temperature to a lower temperature where the transformation of austenite to martensite will be essentially
complete, as indicated by an isothermal transformation
diagram for the steel. Then, without allowing the temperature to fall below 200°C (400°F), the weldment
should be heated to the stress-relieving temperature where
the martensite in the welded joint will be tempered and
softened. After holding the weldment at temperature for
the specified time, typically one hour per inch of thickness, the weldment can be cooled to room temperature
without risk of cracking.
When immediate stress relief after welding is not
practical, the welded joint should be heated from the
preheat temperature to a temperature 30°C to 55°C
(50°F to 100°F) above the Ms temperature of the steel.
Any remaining austenite will transform to a reasonably
ductile bainitic structure after about one hour at temperature; then the weldment can be cooled to room
temperature without risk of cracking.
The weld should be inspected for discontinuities; any
defects should be repaired before final heat treatment.
Repair welding procedures should be the same as those
used for the initial welding.
If required, the completed weldment should be austenitized, then quenched and tempered to achieve the
desired mechanical properties. These procedures are
devised to ensure that all of the austenite transforms to
martensite before the weldment is tempered.
Arc Welding
Arc welding usually is performed on HTLA steels
with a relatively low heat input. High heat input tends
to produce a wide heat-affected zone with enlarged
grain size. It also increases the likelihood of hot cracking in the weld metal and HAZ. Automatic welding is
preferred over manual welding for linear or simple circumferential joints. Automatic operation produces uniform
welds with fewer stops and starts, which frequently give
rise to weld discontinuities. All materials involved in the
welding operation must be clean. This includes the base
metal, welding rods or electrodes, and fixtures. For
example, a problem with porosity and nonmetallic
inclusions in a welded joint in heat-treatable alloy steel
was traced to abrasive grit that remained on ground
faces after joint preparation.
Shielded Metal Arc Welding. Shielded metal arc
welding (SMAW) can be used to weld HTLA steels
using the electrodes described in the previous section on
Filler Metals.
Gas-Shielded Arc Welding. HTLA steels can be
welded by gas tungsten arc welding (GTAW), gas metal
arc welding (GMAW), and flux cored arc welding
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
73
(FCAW). Gas tungsten arc welding is capable of producing welds with the lowest hydrogen content, and is preferred for thin, highly stressed joints. Bare wire having a
composition similar to the base metal may be used for
filler metal with GTAW and GMAW. The carbon, phosphorus, and sulfur contents of the filler metal are generally low to reduce solidification-cracking tendencies and
improve ductility in the weld metal. These processes provide good control of weld-metal composition and cleanliness. Argon, helium, or mixtures of the two may be
used for GTAW. Argon-oxygen or argon-carbon dioxide
mixtures may be used with GMAW. Typical transverse
tensile properties of GTAW and GMAW joints in typical
HTLA steels after heat treatment are listed in Table 1.31.
Electrode selection for FCAW may be limited. Welds
made with this process are comparable to those made
with low-hydrogen covered electrodes. Generally,
argon-carbon dioxide shielding gas mixtures are used,
especially with electrodes 1.58 mm (0.062 in.) diameter
and smaller.
Submerged Arc Welding. Some low-alloy steels can
be welded by the submerged arc welding (SAW) process. The most important part of a submerged arc welding procedure is the selection of a filler metal and a flux
that will produce weld metal with the desired tensile
strength, ductility, and notch-toughness after heat treatment. The recommendations of the manufacturer should
be followed in selecting the optimum combination of flux
and filler metal. Fluxes that produce a neutral or a basic
slag generally produce better mechanical properties. Loss
of carbon from the wire to the deposit is greatest with
acid fluxes and least with basic fluxes, but some carbon
loss should be expected.
Submerged arc or flux cored arc welding normally is
used when a high deposition rate is desired. However,
the weld metal usually has lower toughness than weld
metal deposited by GTAW, particularly after heat treatment to a high strength level. The toughness obtained will
be affected by the characteristics of the slag produced by
the flux.
Flash Welding
The procedure used for the flash welding (FW) of
heat-treatable low-alloy (HTLA) steels is very much like
that used for medium-carbon steels. In some cases, the
welding current is lower and the flashing time is longer
to compensate for the higher electrical resistance of
HTLA steels. Welding procedures should be established
for the particular steel and qualified by suitable tests to
ensure that the required mechanical properties will be
obtained. Preheat and postheat (tempering) are sometimes
recommended to avoid cracking of air-hardening steels
when the flash welding process is used.
74
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.31
Typical Transverse Tensile Properties of Arc Welded
Joints in Low-Alloy Steels After Quenching and Tempering
Welded Joint
Tempering
Temperature
Thickness
Steel
Designation
mm
4130
6.4
Tensile Strength
Yield Strength
Approx. Base
Metal Tensile
Elongation %
Strength
in 50.8 mm
(2 in.)
MPa
ksi
in.
Welding
Process
Filler
Metala
°C
°F
MPa
ksi
MPa
ksi
0.25
GMAW
Note a.1
510
950
1170
170
1140
165
7
1170
170
4140
13
0.50
GMAW
4140
480
900
1300
189
1230
178
8b
1310
190
4340
25
1.0
GMAW
4340
510
950
1310
190
1250
181
11
1310
190
4340
25
1.0
GMAW
Note a.2
510
950
1320
191
1220
177
8
1310
190
4335V
6.4
0.25
GTAW
4340
205
400
1760
255
1530
222
9
1790
260
D6
2.4
0.093
GTAW
Note a.3
315
600
1860
270
1630
237
6b
1900
275
D6
2.4
0.093
GTAW
D6
315
600
1780
258
1500
218
6
1830
265
D6
13
0.50
GTAW
Note a.4
540
1000
1540
224
1430
207
7
1590
230
a. Noted filler metal constituent percentages are as follows:
1. 0.18C, 1.50Mn, 0.44Si, 1.2Ni, 0.34Mo, 0.65Cr
2. 0.25C, 1.17Mn, 0.65Si, 1.8Ni, 0.80Mo, 1.17Cr, 0.21V
3. 0.25C, 0.28Mn, 0.03Si, 1.29Mo, 0.98Cr, 0.56V
4. 0.25C, 0.55Mn, 0.65Si, 0.50Mo, 1.25Cr, 0.30V
b. Elongation in 25.4 mm (1 in.) gauge length.
Resistance Spot Welding
Heat-treatable low-alloy steels can be spot welded
using procedures similar to those for medium-carbon
steels. Application of a tempering cycle in the welding
machine to soften the quench-hardened weld nugget is
strongly recommended. Examples of spot welding
schedules for SAE 4130, 4340, and 8630 low-alloy
steels were shown previously (refer to Table 1.9).
Overlapping spot welds can be made with wheel
electrodes to produce a seam weld. Intermittent travel
should be used, with the workpiece stationary during
the welding and tempering cycle.
A welding schedule is qualified by mechanical testing, metallurgical examination, and hardness tests. The
welds must be free of cracks and other discontinuities
or defects before and after subsequent heat treatments.
Electron Beam Welding
Heat-treatable low-alloy (HTLA) steels can be joined
readily by electron beam welding. This process can produce deep, narrow welds with a narrow HAZ and
lower welding stresses than welds produced with an arc
process. As a result, these steels can be welded with the
electron beam process at room temperature or with
moderate preheat, depending on the alloy composition
and thickness.
Electron beam welds generally solidify with a columnar grain structure, which tends to promote segregation
and subsequent cracking in the weld. Some low-alloy
steels require oscillation of the electron beam to avoid
these problems.
BRAZING HTLA STEELS
Heat-treatable low-alloy steels can be brazed using
processes, procedures, and filler metals commonly used
for carbon steels. When the steel is to be quenched and
tempered to achieve desired properties, brazing and
hardening operations can be combined. The solidus of
the filler metal must be above the austenitizing temperature of the low-alloy steel. The joint is made at normal
brazing temperature. The brazement is then removed
from the heat source to permit the filler metal to solidify. After it cools to the hardening temperature of the
steel, the brazement is uniformly quenched in the
appropriate cooling medium. Finally, the brazement is
tempered to the desired hardness. Proper support must
be provided at high tempering temperatures to avoid
rupturing the brazed joint.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
CHROMIUM-MOLYBDENUM
STEELS
Alloy steels in the chromium-molybdenum group contain 0.5 to 9% chromium and 0.5 to 1% molybdenum.
For most grades, the carbon content does not exceed
0.15%. This composition delivers good weldability and
high hardenability for these alloys. The chromium provides improved oxidation and corrosion resistance, and
the molybdenum increases strength at elevated tempera-
tures. The combination of chromium and molybdenum
also increases resistance to high-temperature hydrogen
attack and to creep. These high-temperature properties
have been further improved by the addition of small
amounts of titanium, vanadium, niobium, and nitrogen.
These steels usually are supplied in either the normalized and tempered or the annealed condition.
Chromium-molybdenum (Cr-Mo) steels are widely
used in the petroleum industry and in elevated-temperature applications such as steam power generating equipment. They are used in various product forms according
to ASTM specifications, as shown in Table 1.32.
Table 1.32
Representative ASTM Specifications for Chromium-Molybdenum Steel Product Forms
Type
1/2Cr-1/2Mo
Forgings
A 182-F2
Tubes
Pipe
Castings
Plate
A 213-T2
A 335-P2
A 356-GR5
A 387-Gr2
—
A 387-Gr12
A 387-Gr11
A 369-FP2
A 426-CP2
1Cr-1/2Mo
A 182-F12
A 213-T12
A 336-F12
A 335-P12
A 369-FP12
A 426-CP12
1-1/4Cr-1/2Mo
2-1/4Cr-1Mo
3Cr-1Mo
5Cr-1/2Mo
F182-F11/F11A
A 199-T11
A 335-P11
A 217-WC6/11
A 336-F11/F11A
A 200-T11
A 369-FP11
A 356-Gr6
A 213-T11
A 426-CP11
A 389-C23
A 182-F22/F22A
A 199-T22
A 335-P22
A 217-WC9
A 336-F22/F22A
A 200-T22
A 369-FP22
A 356-Gr10
A 213-T22
A 426-CP22
A 182-F21
A 199-T21
A 335-P21
A 336-F21/F21A
A 200-T21
A 369-FP21
A 213-T21
A 426-CP21
A 182-F5/F5A
A 199-T5
A 335-P5
A 336-F5/F5A
A 200-T5
A 369-FP5
A 213-T5
A 426-CP5
A 387-Gr22
—
A 387-Gr21
A 217-C5
A 387-Gr5
5Cr-1/2MoSi
—
A 213-T5b
A 335-P5b
5Cr-1/2MoTi
—
A 213-T5c
A 335-P5c
—
—
—
—
7Cr-1/2Mo
A 182-F7
A 199-T7
A 335-P7
—
A 387-Gr7
A 200-T7
A 369-FP7
A 213-T7
A 426-CP7
A 199-T9
A 335-P9
A 217-C12
A 387-Gr9
A 200-T9
A 369-FP9
—
A 387-Gr91
A 426-CP5b
9Cr-1Mo
A 182-F9
A 336-F9
9Cr-1Mo A nd V+Nb+N
A 182-F91
75
A 213-T9
A 426-CP9
A 199-T91
A 335-P91
A 200-T91
A 369-FP91
A 213-T91
76
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Composition and Properties
The nominal chemical compositions of the Cr-Mo
steels are shown in Table 1.33. Some alloys may contain
small additions of nitrogen, niobium, titanium, or vanadium, or increased amounts of carbon or silicon for
specific applications. Some castings or forging alloys
may include up to 0.35% carbon.
Oxidation resistance, elevated temperature strength,
and resistance to sulfide corrosion all increase as the
chromium or molybdenum content is increased. However, the corrosion resistance in high-temperature steam
does not vary significantly when the chromium content
is increased beyond 2.25%.
Recently developed grades with slightly higher chromium content, and grades with tungsten or microalloy
additions (e.g., vanadium, niobium, nitrogen) have
shown improvements in elevated-temperature tensile
and creep strength. For example, piping and tubing
grades such as P/T91, 92, 911, 23, 24, and 122 and
others are specified by ASTM (A 335 for piping and
A 213 for tubing), but not all have been approved for
use by ASME codes. Steels in this group are becoming
known as creep strength enhanced ferritic (CSEF) steels,
and are supplied in the fully martensitic, tempered condition. They are being developed to permit the use of
significantly thinner components than historical Cr-Mo
steels when used in service conditions above 510°C
(950°F). In the years prior to 2010, filler metal compositions and welding procedures were still under development to maximize service life and overall usability.
Cr-Mo steels are relatively hardenable and undergo
the high- and low-temperature metallurgical transformations common to heat-treatable low-alloy steels.
Mechanical properties depend on the heat treatment
condition. The tensile property requirements of the
ASTM specifications for these steels vary with the product form and the type of heat treatment, as summarized
in Table 1.34. Because of the wide range of properties
available for some product forms, the user must be
familiar with the actual specification to which the product was produced. (Refer to Table 1.32.)
When these steels are cooled rapidly from above
their upper critical temperatures, hardness and strength
increase but ductility and toughness are reduced. Since
the carbon content usually is below about 0.15%, they
cannot be quenched to high hardness (refer to Figure
1.8). Therefore, ductility is greater at any given strength
level than when a high-carbon variation is used, as in
some specifications for forgings and castings. Because
of their hardenability, chromium-molybdenum steels
may require further heat treatment to restore toughness,
ductility, or other desired mechanical properties after
being heated above their transformation temperatures,
as will occur during welding or hot-forming operations.
Heat Treatment
The types of heat treatment normally applied in production of chromium-molybdenum (Cr-Mo) steels are
the same as those applied to other hardenable steels.
Table 1.33
Nominal Chemical Composition of Chromium-Molybdenum Steels
Composition, %a
Type
C
Mn
1/2Cr-1/2Mo
0.10–0.20
0.30–0.60
1Cr-1/2Mo
0.15
0.30–0.60
1-1/4Cr-1/2Mo
0.15
0.30–0.60
S
P
Si
Cr
Mo
0.045
0.045
0.10–0.30
0.50–0.80
0.45–0.65
0.045
0.045
0.50
0.80–1.25
0.45–0.65
0.030
0.045
0.50–1.00
1.00–1.50
0.45–0.65
2Cr-1/2Mo
0.15
0.30–0.60
0.030
0.030
0.50
1.65–2.35
0.45–0.65
2-1/4Cr-1Mo
0.15
0.30–0.60
0.030
0.030
0.50
1.90–2.60
0.87–1.13
0.80–1.06
3Cr-1Mo
0.15
0.30–0.60
0.030
0.030
0.50
2.65–3.35
5Cr-1/2Mo
0.15
0.30–0.60
0.030
0.030
0.50
4.00–6.00
0.45–0.65
7Cr-1/2Mo
0.15
0.30–0.60
0.030
0.030
0.50–1.00
6.00–8.00
0.45–0.65
9Cr-1Mo
0.15
0.30–0.60
0.030
0.030
0.25–1.00
8.00–10.00
0.90–1.10
9Cr-1Mob
0.08–0.12
0.30–0.60
0.010
0.020
0.20–0.50
8.00–9.50
0.85–1.05
a. Single values are maximum.
b. Plus 0.18–0.25 V, 0.06–0.10 Nb, and 0.03–0.07 N.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
77
Table 1.34
Representative Minimum Tensile Properties for
Chromium-Molybdenum Steel Products Manufactured to ASTM Specifications
Tensile Strength
Yield Strength
MPa
ksi
MPa
ksi
Elongation,
%
Reduction of
Area, %
Forgings
410 to 590
60 to 85
210 to 450
30 to 65
20 to 22
30 to 50
Tubing
410 to 590
60 to 85
210 to 410
30 to 60
20 to 30
—
Pipe
380 to 620
55 to 90
210 to 410
30 to 60
18 to 20
—
Castings
480 to 620
70 to 90
280 to 410
40 to 60
18 to 20
35 to 45
Plate
380 to 590
55 to 85
210 to 410
30 to 60
18 to 22
40 to 45
Product Form
Heat treatments such as annealing, normalizing and
tempering, quenching and tempering, or tempering only
are used to obtain desired grain size or required
mechanical properties for the application.
A Cr-Mo steel is annealed by heating it to a temperature in the range of 840°C to 910°C (1550°F to 1675°F)
and holding at temperature for 2.36 min/mm (1 h/in.)
of thickness. It is then cooled to 540°C (1000°F) at a
rate of 30°C/h (50°F/h), followed by furnace cooling or
air cooling to room temperature. This procedure produces a relatively soft, ferritic structure throughout the
steel. For normalizing, tempering, or quenching and
tempering treatments, the steel is heated to the same
temperature range of 840°C to 910°C (1550°F to 1675°F),
held at temperature as previously described, and then
continuously cooled to room temperature. Normalizing
requires cooling in still air; however, for thick materials,
it may be necessary to use moving air or even steam.
Quenching requires immersing in oil or spraying with
water. These treatments, which harden the steel and
improve notch toughness, usually are followed by a
tempering operation.
Cr-Mo steels are tempered at temperatures below
their lower critical temperature (approximately 760°C
[1400°F] for an appropriate time). They are then cooled
in still air or in a furnace.
Heat treatment of these steels is used to advantage
when fabricating large, heavy-walled pressure vessels.
These vessels often are constructed from 2-1/4 Cr-1 Mo
steel that has been normalized and tempered or quenched
and tempered. These treatments result in a microstructure
of bainite or low-carbon martensite which has good
ductility. Regardless of the heat treatment given to the
steel, proper control of the tempering treatment is required. The tempering temperature and time at temperature are both important.
METALLURGICAL CONSIDERATIONS
The welding metallurgy of chromium-molybdenum
(Cr-Mo) steels is similar to that of the other hardenable,
low-alloy steels discussed previously. These steels will
harden when quenched from the austenitizing temperature, and they are sensitive to hydrogen cracking. Welding procedures must include the necessary safeguards to
prevent cracking in the weld metal and heat-affected
zone (HAZ). Cracking types include quench cracking
and hydrogen cracking. Appropriate preheat and welding consumables must be selected to avoid cracking. A
postweld heat treatment may be used to improve the
toughness of the weld metal and heat-affected zone.
The carbon content of the base metal and weld metal
and also dilution effects must be taken into account.
Low-hydrogen welding processes and procedures
must be used with Cr-Mo steels. The composition of the
filler metal should be nearly the same as that of the base
metal except for carbon content, which usually is lower
than that of the base metal. If corrosion resistance and
maximum hardness limits are of primary concern, it is
often desirable to select a low-carbon grade of filler
metal. However, higher carbon levels are required when
the weldment is to be normalized and tempered or
quenched and tempered, or when 100% joint efficiency
is required at elevated temperatures. The effect of increasing carbon content on the tensile strength and ductility
of 2-1/4 Cr-1 Mo weld metal is shown in Figure 1.29.
The Cr-Mo steels, like other low-alloy steels, are subject to embrittlement during long-time service at temperatures in the range from 370°C to 590°C (700°F to
1100°F). The degree of embrittlement of the steel is
influenced by chemical composition, exposure temperature, and duration. This condition, which is known as
temper embrittlement, increases the ductile-to-brittle
transformation temperature. Temper embrittlement has
78
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
Click here to view
145
1000
NGTH –
TENSILE STRE
AW
135
800
700
600
500
TENSILE STRENGTH, ksi
TENSILE STRENGTH, MPa
125
115
50
105
RENGTH – SR
TENSILE ST
95
40
30
85
75
20
ELONGATIO
ELONGATION IN 2.54 mm (2 in.), %
900
N – SR
65
ELONGATION – AW
400
55
0.04
0.08
0.12
10
0
0.16
CARBON CONTENT, %
Figure 1.29—Effect of Carbon Content on the Room-Temperature
Tensile Strength and Ductility of 2-1/4 Cr-1Mo Weld Metal
(As-Welded and Postweld Heat Treated at 704°C [1300°F] for One Hour)
been researched most thoroughly for 2-1/4Cr-1Mo steel
operating at about 454°C (850°F), and the principal
reason for this condition appears to be the segregation
of phosphorus, arsenic, antimony, and tin. After hightemperature exposure, room-temperature notch toughness and elongation can be quite low, but they are usually acceptable if the material is heated to 149°C (300°F).
The effects of temper embrittlement can be overcome
by high-temperature subcritical and critical heat treatments. During recent years, step-cooling tests have been
developed to detect steels that are susceptible to temper
embrittlement. In addition, cleaner steels capable of
resisting temper embrittlement have become available.
These facts should be considered when working with
service-exposed Cr-Mo steels.
monly used for carbon steel. They also can be joined by
electroslag, electron beam, laser beam, friction, and
resistance welding. Brazing procedures are similar to
those used for other steels, but the thermal effects of the
brazing cycle on the properties of Cr-Mo steel must be
considered.
WELDING AND BRAZING CHROMIUMMOLYBDENUM STEELS
Preheat
Chromium-molybdenum (Cr-Mo) steels are readily
joined using the welding and brazing processes com-
Joint Design
Joint designs used in Cr-Mo steel weldments should
minimize notch conditions which might contribute to
stress concentration. Sharp corners and rapid changes
in section size are to be avoided. Fit-up for single-pass
welded joints should ensure complete joint penetration
without excessive melt-through.
Preheat is required to prevent cracking when welding
Cr-Mo steels. Recommended minimum preheat temperatures for various thicknesses are listed in Table 1.35.
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
79
Table 1.35
Recommended Minimum Preheat Temperatures for Welding
Chromium-Molybdenum Steels with Covered Low-Hydrogen Electrodes
Thickness
Up to 12.7 mm (0.5 in.)
Steel*
°C
12.7 mm to 25.4 mm (0.5 in. to 1.0 in.)
°F
°C
°F
Over 25.4 mm (1.0 in.)
°C
°F
1/2Cr-1/2Mo
40
100
95
200
150
300
1Cr-1/2Mo
120
250
150
300
150
300
150
300
175
350
175
350
175
350
205
400
205
400
1-1/4Cr-1/2Mo
2Cr-1/2Mo
2-1/4Cr-1Mo
3Cr-1Mo
5Cr-1/2Mo
7Cr-1/2Mo
9Cr-1Mo
9Cr-1Mo V+Nb+N
*Maximum carbon content of 0.15%. For higher carbon content, the preheat temperature should be increased 40°C to 95°C (100°F to 200°F). Lower preheat
temperatures may be used with gas tungsten arc welding.
These temperatures generally increase in proportion to
increases in alloy content and workpiece thickness.
The preheat and interpass temperatures should be
increased if cracking is encountered, particularly if
hydrogen is suspected as the cause. Higher preheat temperatures should be employed when the carbon content
of the steel exceeds 0.15%. If no other data are available, a weldability test (such as the Lehigh or the Tekken
Y-Groove) can be used to establish a minimum preheat
temperature.79 Unless limited by applicable codes and
regulations, lower preheat and interpass temperatures may
be used if the welding heat input is relatively high or the
available hydrogen is very low, as with gas tungsten arc
welding (GTAW).
The method of heating should be one that will provide a uniform temperature along the entire joint length
before welding is started. Also, the width of the heated
area should be sufficient to ensure that the temperature
is nearly uniform through the joint thickness.
Based on industrial experience, some general suggestions can be made regarding the interruption of the
heating cycle during welding of Cr-Mo steels. These
suggestions should not be applied indiscriminately;
rather, they should be interpreted in consideration of
79. Davidson, J. A., P. J. Konkol, and J. F. Slovak, 1989, Addressing
Fracture Toughness and Cracking Susceptibility—a Review, Welding
Research Bulletin 345, New York: Welding Research Council. (Refer
to Lehigh Papers 8 and 9; and Tekken Test, Papers 13 and 14.)
the specific job conditions and the general factors discussed previously.
When welding Cr-Mo base metals containing more
than 2.5% chromium, the preheat temperature should
be maintained until the completion of welding. For
those containing 2.5% Cr or less, the preheat temperature should be maintained until the weld has been completed to at least 1/3 of the workpiece thickness, or at
least 19 mm (3/4 in.) if the section thickness exceeds
57 mm (2-1/4 in.). In the event of an interruption in
welding, the incomplete weld should be covered with
suitable thermal insulation to produce slow cooling
from the preheat temperature. Welding should be
resumed only after the weld joint has been reheated to
the specified minimum preheat temperature.
When the welding consumables, such as covered
electrodes, are a potential source of hydrogen, the completed weld should be cooled slowly to ambient temperature to allow any trapped hydrogen to escape. When
welding heavy or complex shapes, it is good practice to
raise the temperature to approximately 260°C (500°F)
for an hour or more, depending on the thickness. This
is referred to as a dehydrogenation treatment (DHT),
postweld hydrogen bake-out or post bake. This step is
not necessary when the welding consumables are essentially free of hydrogen.
On completion of welding, it is considered acceptable either to proceed immediately to postweld heat
treatment, or to allow slow cooling so that postweld
80
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
heat treatment can be performed at a more convenient
time. It should be noted, however, that in steels with
higher chromium content (5% to 9%), the weld metal
and heat-affected zone are likely to be hard and relatively brittle prior to postweld heat treatment. Externally applied stresses such as lifting-induced bending
should be avoided, as sudden brittle fracture can occur.
A postweld hydrogen bakeout will be of little to no benefit in this instance.
Filler Metals
The filler metal should be a low-hydrogen type and
should have the same nominal composition as the base
metal except for carbon content, which normally is lower
than that of the base metal. Suggested filler metals for
the arc welding of Cr-Mo steels with low-hydrogen cov-
ered electrodes are provided in Table 1.36. Other filler
metals may be acceptable for specific applications.
When several grades of Cr-Mo steels are to be
welded on one job, limiting the number of different
filler metals used will simplify material control. Filler
metal of the same or slightly higher alloy content can be
used for welding several Cr-Mo steels. For example, 11/4Cr-1/2Mo filler metal sometimes can be used for
welding 1/2Cr-1/2Mo, 1Cr-1/2Mo, and 1-1/4Cr-1/2Mo
steels. Similarly, 2-1/4Cr-1Mo filler metal can be used
for 1-1/4Cr-1/2Mo, 2Cr-1/2Mo, 2-1/4Cr-1Mo, and
3Cr-1Mo steels. In any case, each welded joint must
possess the required properties for the intended service
after postweld heat treatment. When service conditions
require resistance to corrosion or oxidation, the characteristics of the filler metal and base metal should be
matched as closely as possible.
Table 1.36
Suggested Welding Consumables for Joining Chromium-Molybdenum Steels
Steel
1/2Cr-1/2Mo
SMAWa
E801X-B1
GTAW,e GMAW
Note f
FCAWh
E7XT5-A1
SAWi
F8XX-EXXX-B1
E8XT1-A1
1Cr-1/2Mo, 1 1/4Cr-1/2Mo
E801X-B2
ER80X-B2
or E701X-B2L
or ER70X-B2L
E8XTX-B2
F8XX-EXXX-B2
or E8XTX-B2L
or F8XX-EXXX-B2H
or E8XTX-B2H
2-1/4Cr-1Mo
E901X-B3
ER90X-B3
E9XTX-B3
or E801X-B3L
or ER80X-B3L
or E9XTX-B3L
F9XX-EXXX-B3
3Cr-1Mo
Note b
Note b
Note b
5Cr-1/2Mo
E502-1Xd
ER502g
E502T-1 or 2
F9XX-EXXX-B6
or E801X-B6
or ER80X-B6
or E6XT5-B6
or F9XX-EXXX-B6H
Note c
Note c
Note c
F9XX-EXXX-B8
or E9XTX-B3H
Note b
or E801X-B6L
7Cr-1/2Mo
E7Cr-1Xd
or E801X-B7
or E801X-B7L
9Cr-1Mo
E505-1Xd
ER505g
E505T-1 or 2
or E801X-B8
or ER80X-B8
or EX15-B8
or E801X-B8L
9Cr-1Mo and V+Nb+N
a.
b.
c.
d.
e.
f.
g.
h.
i.
E901X-B9
or E6XT5-B8L
ER90X-B9
—
F9XX-EXXX-B9
Per AWS A5.5/A5.5M:2006, Specification for Low-Alloy Steel Electrodes for Shielded Metal Arc Welding, unless otherwise indicated.
No matching filler metal; select between 2-1/4Cr-1Mo and 5Cr-1/2Mo.
No matching filler metal; select between 5Cr-1Mo and 9Cr-1/2Mo.
Originally classified per AWS A5.4/A5.4M:2006, Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding.
Per AWS A5.28/A5.28M:2005, Specification for Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding, unless otherwise indicated.
No matching filler metal; consider higher alloy.
Originally classified per AWS A5.9/A5.9M:2006, Specification for Bare Stainless Steel Welding Electrodes and Rods.
Per AWS A5.29/A5.29M:2010, Specification for Low-Alloy Steel Electrodes for Flux Cored Arc Welding (use with CO2 or Ar-CO2 mixture).
Weld metal designation per AWS A5.23/A5.23M:2007, Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding.
AWS WELDING HANDBOOK 9.4
For butt joints, when joining dissimilar Cr-Mo steels
or when joining a carbon steel to a Cr-Mo steel, a filler
metal with a composition similar to the lower-alloy
steel or to an intermediate composition is commonly
used. Normally, the weld metal need not be stronger or
more resistant to creep or corrosion than the loweralloy base metal.
Covered electrodes used to join Cr-Mo steels with
the SMAW process are typically low-hydrogen types, as
shown in Table 1.36. Procedures for storing and handling low-hydrogen covered electrodes were described
previously. However, it should be noted that in some
countries, rutile-coated electrodes are sometimes used for
the lower-alloy Cr-Mo grades. These tend to require
higher preheat temperatures to avoid hydrogen cracking.
The electrode-flux combinations most frequently used
for SAW deposits are 1-1/4Cr-1/2Mo and 2-1/4Cr-1Mo
weld metals. In general, the weld metal is lower in carbon, manganese, and chromium and higher in silicon
than the electrode. The electrode usually contains less
than 0.50% silicon, but the weld metal may contain up
to 0.80% due to fluxing reactions. The carbon content
of the weld metal typically is about 0.07%.
Filler metal should be used whenever Cr-Mo steel is
joined to carbon steel with the GTAW process. Deoxidized welding rod containing at least 0.50% silicon
should be selected to avoid porosity in the weld.
Weld metal with good ductility and good corrosion
resistance can be obtained using a low-carbon-grade of
filler metal. The carbon content of the filler metal may
be 0.05% or less (ER80S-B2L is an example). Postweld
heat treatment (PWHT) sometimes can be omitted for
low-carbon welds in austenitic stainless steel and some
high-nickel alloys, containing 0.5% to 2.25% Cr and
0.5% to 1% Mo. However, since low-carbon electrodes
do not exhibit creep strength equal to that of the base
metal, they should not be used for applications where
the service temperature exceeds 450°C (850°F).
Type 309, such as ENiCrFe-3, are used as filler metals to weld Cr-Mo steels to stainless steels and nickel
alloys. Sometimes they are also employed for minor
repair welding of Cr-Mo steels, or for applications in
which the weldment cannot be given a postweld heat
treatment. Weld metals of stainless steel and high-nickel
alloy have a lower yield strength and better ductility
than as-welded Cr-Mo steels. They are also effective at
absorbing and holding large amounts of diffusible
hydrogen, while being essentially immune to hydrogen
cracking, although low hydrogen welding practices
should still be maintained. Thus, they perform like a
plastic hinge, absorbing most of the strain and thereby
reducing the risk of cracking in the Cr-Mo base metal.
Despite the advantages they provide, austenitic stainless steel filler metals are not satisfactory for Cr-Mo
welded joints that will be subjected to cyclic temperature service, or to service temperatures at which carbon
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
81
migration or sigma formation can take place. During
cyclic temperature service, the coefficient of thermal
expansion (CTE) mismatch between austenitic weld
metal and ferritic Cr-Mo base metal produces cyclic
stresses and thermal fatigue along the weld interface.
This condition can promote early failure, particularly
when aided by carbon migration. To partially compensate for this, some guidelines call for a nickel-base filler
metal, which produces weld metal with a CTE more
closely matched to that of a ferritic steel, for use in service temperatures above 320°C (600°F).
Carbon migration occurs in a Cr-Mo steel when it is
welded with a higher-chromium filler metal and then
subjected to high-temperature service. Carbon diffuses
from the lower-chromium base metal to the higherchromium weld metal and forms chromium carbide
adjacent to the weld interface. This does not seem to be
an issue when combining different grades of Cr-Mo
steels; many welds have been in service for years with
filler metals that have matched the lower chromium
grade in some cases, and in other cases have matched
the higher chromium grade. Only when welding a lower
Cr-Mo steel with an austenitic filler have all the factors
come together to produce early failures in the Cr-Mo
base metal.
Postweld Heat Treatment
Steels containing up to 2.25% Cr and 1% Mo have
sufficient as-welded ductility to meet the requirements
of some codes, particularly when welded with a lowcarbon filler metal (i.e., 0.05% C or lower). However,
the welding procedure specification must be qualified
without postweld heat treatment. For example, welds in
Cr-Mo steel pipe or tubing with a wall thickness under
13 mm (0.5 in.) and a chromium content of 2.25% or
lower can be placed in service as-welded if a proper preheat is used during welding.
Welds in Cr-Mo steels that have higher hardenability
(i.e., containing >3% Cr or >0.15% C) should be
postweld heat-treated regardless of thickness. In addition, this treatment is required for weldments that will
be exposed to certain corrosive environments. Postweld
heat treatment of Cr-Mo steel weldments provides a
tempering effect that reduces hardness and increases
ductility and toughness. It also relieves residual stresses,
drives out hydrogen, and improves resistance to corrosion and stress-corrosion cracking. This is accomplished
by heating the welded joint or the entire weldment to a
temperature just below the lower critical (Ac1). Table 1.37
provides recommended postweld heat treatment ranges
for Cr-Mo steels.
The postweld heat treatment temperature should not
exceed the tempering temperature of normalized and
tempered or quenched and tempered steel. Special service
conditions may require the temperature to be in the low
82
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.37
Recommended Stress-Relief Temperature
Ranges for Chromium-Molybdenum Steels
Temperature Range*
Steel
°C
°F
1/2Cr-1/2Mo
620–700
1150–1300
1Cr-1/2Mo
620–720
1150–1325
680–760
1250–1400
700–760
1300–1400
730–760
1350–1400
1-1/4Cr-1/2Mo
2Cr-1/2Mo
2-1/4Cr-1Mo
3Cr-1Mo
5Cr-1/2Mo
7Cr-1/2Mo
9Cr-1Mo
9Cr-1Mo plus V+N6+N
*Temperature should not exceed the tempering temperature of the steel.
end of the recommended range for high creep strength,
and in the high end of the range for good resistance to
corrosion or to hydrogen embrittlement.
Depending on the requirements of the application, it
may be necessary to normalize and temper a weldment
that is fabricated with a high-heat-input welding process, such as electroslag welding. This will refine the
grain size in the weld metal and heat-affected zone and
thereby improve toughness.
Postweld heat treatments tend to lower the strength
of the base metal, particularly if it is in the normalized
and tempered or the quenched and tempered condition.
The effect is more pronounced with long holding times
at temperature. Welding codes and standards specify
minimum holding time at temperature. In the absence of
other requirements, the time should be about 2.36 min/
mm (1 h/in.) of thickness up to 50 mm (2 in.), then an
additional 0.60 min/mm (15 min/in.) over 50 mm (2 in.),
with one-half hour being the minimum.
For welded joints in piping and tubing, the heating
method and the equipment used should provide uniform heat around the circumference. With local heating
instead of furnace heating, no matter how long the
holding time, there is always a temperature gradient
through the thickness. The thicker the section, the
wider is the heated band required to achieve the desired
temperature at the root of the weld (the internal surface
of the pipe). Therefore, the width of the heated band on
the surface directly under the heat source should be at
least five times that of the thickness. To achieve this
band, it is often necessary to provide wider heating elements and extended insulation. Piping and tubing must
be free of any liquids, and air flow through the system
must be limited as much as possible. The “chimney
effect” of flowing air in a vertical piping system will
make it difficult or impossible to heat the weld root to
the required temperature.
Heating and cooling rates depend on workpiece
thickness, geometry, heating method and insulation.
Code requirements often dictate allowable maximums.
Slow ramp rates are specified to avoid introducing high
stresses resulting from steep temperature gradients. For
many workpieces, including pipe and tube, heating may
be done as rapidly as commercially possible. Once up to
postweld heat treating temperature, any stresses developed during heating will be relaxed during the “soak”
period (the time held at temperature). Cooling rates are
specified to limit the temperature differential in any
direction to 65°C (150°F). Generally, there is no compelling metallurgical reason to limit heating or cooling
rates during postweld heat treating, so there may be situations when relatively rapid values can be specified.
For specific guidance on heat treatment of piping, refer
to Recommended Practices for Local Heating of Welds
in Piping and Tubing, AWS D10.10.80
SPECIAL-PURPOSE WELDS
Two types of special-purpose welds are discussed in
this section: longitudinal seam welds in pipe and welds
involving thick sections.
Tube mills sometimes use the resistance upset welding process to make longitudinal seams in chromiummolybdenum (Cr-Mo) steel pipe and tubing. Strip is
formed by rolling to shape and welded continuously.
The square edges are progressively heated to welding
temperature by resistance heating with a frequency of
60 Hz or higher with alternating current. The hot edges
are forged together by pressure rolls, and any flash produced by the resulting interfacial upset usually is
trimmed off while the seam is still hot. The highly localized heat input and fast cooling rates typical of these
welding operations result in an as-welded microstructure having low ductility. A postweld heat treatment is
required to restore ductility and toughness. This may be
performed in the welding machine if the machine is
designed for this operation, or it may be performed in a
separate procedure.
Joining thick sections of Cr-Mo steels (i.e., 76 mm
[3 in.] or more) can be accomplished by electroslag
welding. Typically, a solid or alloy-cored welding electrode of the same nominal composition as the base
80. American Welding Society (AWS), 2009, Recommended Practices
for Local Heating of Welds in Piping and Tubing, AWS D10.10/
D10.10M:1999 (R2009), Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
metal is used with an appropriate flux designed for electroslag welding. An advantage of this process is that the
large quantity of heat generated during welding preheats the base metal ahead of the weld pool. This large
heat buildup slows cooling and permits hydrogen to
escape. As a result, the weldment can be cooled to room
temperature before it is given a postweld heat treatment. An annealing or normalizing heat treatment is
necessary to refine the grain structure of the weld metal
and heat-affected zone.
APPLICATIONS
It is almost impossible to name an industry, commercial entity, professional endeavor, or household that
does not use products made of carbon steels or lowalloy steels, or benefit from advancements in the science
behind the practical improvements of these steels.
Industries such as automotive, rail transportation,
marine, aircraft and space, communications, power
generation, mining, agriculture, and petroleum are
major participants in the progressive use of carbon and
low-alloy steels. Several examples are discussed in this
section.
WELDING OF HIGH-PERFORMANCE
STEELS FOR BRIDGES
The development of high-performance steels (HPS)
was motivated by the requirements of bridge building:
steel plate with higher strength, higher toughness,
improved weldability and weathering characteristics.
Weathering refers to the ability of the steel to adequately resist atmospheric corrosion, under normal
conditions and without painting, by forming an adherent red-oxide patina. The letter “W” is attached to the
designation of grade numbers of ASTM A 709 and
AASHTO M270 to indicate weathering properties, following the numerals indicating the specified minimum
yield strengths in ksi, i.e., HPS 50W, 70W, and 100W.81
Therefore, welding consumables must be chosen not
only to match yield strength, but also the color of the
base metal.
The composition of the high-performance (HP) steels
resembles the COR-TEN and T-1 grades used in the
past, which were characterized by small additions of
copper and nickel, but the HP steels have lower carbon
equivalents and finer-grained microstructures. These
81. American Association of State Highway and Transportation Officials (AASHTO), 444 N Capitol St. NW, Suite 249, Washington, DC
20001.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
83
properties are the result of improved steelmaking practices, such as sulfide shape control, vacuum degassing,
and continuous casting. Most HP steel can be produced
either by traditional quench and tempered (Q&T) processing or by thermomechanically controlled processing
(TMCP). Both types have excellent uniformity of properties, although the TMCP type sometimes exhibits
anisotropy in the through-thickness direction. From a
reheating standpoint, both types of HP steel are limited
to a maximum temperature of 590°C (1100ºF) for heat
bending or straightening.
High-performance steels are extremely tough and
were designed to meet the most stringent Charpy VNotch (CVN) toughness requirements imposed by
bridge applications. The heat-affected zone (HAZ) of
the welds retains its fine grain size under most normal
heat input conditions and is much tougher than nonHPS plate grades. Also, because of the low hardenability in the HAZ of welds in HP steels, hydrogen cracking
migrates to the fusion zone of the weld. As demonstrated by extensive Tekken Y-groove and gapped beadon-plate testing, the as-solidified structure is typically
harder and thus more susceptible to cracking than the
HAZ when residual tensile stresses and sufficient diffusible hydrogen are present.82 Nevertheless, all other factors being equal, HP steels need less preheating than
regular bridge steels. Sometimes no preheating is necessary. This is reflected in the preheating guidelines provided in Table 1.38.
Traditionally, the shielded metal arc welding (SMAW)
and submerged arc welding (SAW) were the most commonly accepted welding processes for bridge fabrication.
However, the successful use of gas metal arc welding
(GMAW), flux cored arc welding (FCAW) and the narrow-groove mode of electroslag welding (ESW) has
been well documented by performance: crack-free
welds in over 200 HPS bridges built between 1994 and
2004. Recommended welding electrodes or consumables
for HPS 50W, 70W and 100W are listed in the HPS
Manufacturer’s Guide83 and in the AWS D1.584 and
AASHTO85 welding codes for steel bridges. The use of
low-hydrogen welding practices (less than 4 ml/ 100g diffusible hydrogen [H4]) can be expected to eliminate the
need for preheating most joints in up to 2-inch-thick HP
steel plate. Heat input control is also important, and a
range of 40 kJ/in. to 70 kJ/in is optimum for most submerged arc welds.
The higher strength and toughness of HP steels result
in less weight, greater spans, more flexibility of design,
and overall lower costs. Welding HP steels generally
does not require preheating, which contributes to cost
82. See Reference 79.
83. American Iron and Steel Institute, 1140 Connecticut Ave., NW,
Suite 705, Washington, D.C. 20036, www.steel.org.
84. See Reference 36.
85. See Reference 81.
84
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 1.38
Comparison of Preheat Temperatures for Three Levels
of Diffusible Hydrogen in Two Grades of 70W Steel
Diffusible Hydrogen
H4*
H8*
H16*
70W
100°C (210°F)
120°C (250°F)
120°C (250°F)
HPS 70W
20°C (70°F)
40°C (100°F)
65°C (150°F)
AASHTO M270 Grade
*Laboratory measurement of the level of hydrogen in milliliters per 100 grams of deposited weld metal; e.g., H4 = 4 ml per 100 g of diffusible hydrogen in the
weld metal.
Source: Adapted from American Association of State Highway and Transportation Officials (AASHTO), High Performance Steel Manufacturing Guide, Washington, D.C., AASHTO,
Table 2.24.
saving. By 2010, more than 300 high-performance steel
bridges were in service in the United States. An example
is shown in Figure 1.30, the Blennerhassett Island Bridge,
which spans the Ohio River connecting Belpre, Ohio and
Parkersburg, West Virginia via U.S. Highway 50.
PIPELINE WELDING
The principal guide for welding petroleum pipelines
in the United States and many other countries of the
world is API Standard 1104—Welding Pipelines and
Related Facilities, which provides the requirements for
obtaining welded joints of adequate quality for pipelines to accommodate the flow of crude oil and refined
products, and transmission of natural gas.86 These pipelines are constructed from carbon-manganese and
microalloyed steels that conform to API Specification
5L, Specification for Line Pipe, with typical yield
strengths in the range of 290 MPa to 480 MPa (42 ksi
to 70 ksi) and as high as 550 MPa (80 ksi).87
Joints in a pipeline are welded in the field from the
outside only with the pipe in a fixed position, requiring
weld metal to be deposited in all positions. The root
pass is deposited as a stringer bead in the downhill
direction using the shielded metal arc welding (SMAW)
process. The type of electrode generally used is EXX10,
because of its penetration and operating characteristics
in all positions. Deposition of the root bead under the
difficult conditions of field welding calls for great skill;
only the most highly trained welders are entrusted with
this phase of the welding.
The low-hydrogen electrode types (EXX18) have
limited use for the root and hot passes in pipeline con86. See Reference 32.
87. American Pipe Institute (API), 2007, Specification for Line Pipe,
API 5L/ISO 3183, American Petroleum Institute, Washington, D.C.
struction because of poor penetration, the large volume
of viscous slag that hampers the downhill welding technique, and the difficulty encountered in overhead deposition. However, low-hydrogen electrodes are used for
uphill fill and cap passes, and for downhill welding
electrodes such as EXX45 that are being used to some
extent for pipeline construction.
It is important to note that in sections of pipe joined
with groove welds, the root pass is deposited as a relatively small, thin pass, and any movement of the pipe is
likely to crack this bead. Also, the cellulosic covering on
the electrode supplies hydrogen to the heat-affected
zone of the base metal. Therefore, depending on the
carbon equivalent of the base metal and temperature to
which the joint cools after deposition of the root bead,
a distinct risk of underbead cracking can arise. For
these reasons, in modern pipeline welding practice, one
welder makes the root pass, another welder, often called
the hot-pass welder, makes the second weld pass, depositing this layer within five minutes after completion of
the root pass. Other welders, called filler bead welders,
then deposit all of the remaining layers of weld metal
required, except the last. The last layer of the weld,
called the capping pass, also is often entrusted to a
welder of above-average skill to ensure compliance with
code requirements, such as reinforcement height and
undercutting. Pipeline construction requires a team of
highly trained individuals responsible not only for welding the high-strength steel pipeline but also ensuring
that the metallurgical qualities of the steel are maintained.
MECHANIZED GAS METAL ARC WELDING
OF LARGE-DIAMETER, HIGH-STRENGTH
STEEL PIPE
Modern long-distance, large-diameter pipelines are
constructed of high-strength line pipe materials and
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Photograph courtesy of West Virginia Department of Transportation
Figure 1.30—Blennerhassett Bridge over the Ohio River Constructed of High-Performance Steel
welded with the mechanized gas metal arc welding
(GMAW) process. The use of high-strength line pipe
(e.g., API 5L-X80) makes it possible to use pipe with
reduced wall thickness, which lowers the overall material cost and requires less welding. The GMAW mechanized pipe-welding systems typically have built-in
functions that align and clamp the workpieces, and then
deposit the root pass.88 A typical line-up clamp/internal
welding system using multiple welding heads that operate simultaneously is shown in Figure 1.31.
The weld bevel is a narrow-groove preparation,
which further reduces the amount of welding required.
The second and remaining passes are deposited from
the outside using a mechanized GMAW machine (called
a bug by field welding operators) that welds as it travels
along the circumference of the pipe joint. These welding
machines, as shown in Figure 1.32, use a single GMAW
torch and wire feed, although dual torch and tandem
arc systems are also available.
In a “bug and band” technique, a second welding
machine follows, making another pass. The machines
88. Beeson, R., 1999, Pipeline Welding Goes Mechanized, Welding
Journal, 78(11): 37–41.
Source: Welding Journal 78(11): 37–41.
Figure 1.31—Mechanized Gas Metal Arc
Welding Machine is Clamped Into Line
Pipe to Deposit Root Beads Internally
85
86
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Figure 1.32—A Single-Torch GMAW Machine
Travels around the Pipe to Make Exterior Welds
operate on a single band on opposite sides of the pipe in
the downhill direction. A weld in progress is shown in
Figure 1.33.
Completed welds made using mechanized GMAW
systems are typically inspected using automated ultrasonic testing systems. These systems are more effective
than radiographic testing for detecting the discontinuities that typically occur in gas metal arc welds (e.g.,
incomplete fusion), and provide through-thickness sizing information required by the fitness-for-purpose
acceptance criteria.
The low-hydrogen characteristics of the GMAW process make the completed weld resistant to underbead
cracking. When used for long-distance large-diameter
pipelines, the mechanized GMAW systems can result in
improved weld quality, increased productivity, and
reduced overall construction costs. However, the cost of
these systems can be prohibitive for short-distance,
small-diameter pipelines.
ELECTRIC MINING SHOVEL DIPPER BODY
Dipper bodies for electric mining shovels are fabricated from high-strength steels with properties that
meet the severe service requirements of the mining
industry. These steels provide a combination of high
strength, good toughness, and excellent weldability.
The dipper body shown in Figure 1.34 was constructed
from several grades of steel ranging in thickness from
25 mm to 100 mm (1 in. to 4 in.). Many of the com-
Source: Welding Journal 78(11): 37–41.
Figure 1.33—Mechanized Single-Torch GMAW
Machine Used to Deposit External Weld Passes
and Capping Passes for Line Pipe Construction
ponents were made from ASTM A 633 Grade C and
Grade D steel with yield strength of 340 MPa (50 ksi).
A quenched and tempered steel, ASTM A 514, was
used for the dipper and other areas that require high
strength and good abrasion resistance. Other components subject to high stresses were made from ASTM
A 710, a copper-strengthened, precipitation-hardened,
high-strength low-alloy steel.
The flux cored arc welding process (FCAW) was used
to weld the dipper body. Multiple-pass groove welds
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
87
To avoid distortion due to thermal expansion during
day-night cycles, the track was designed with a small gap
ranging from 0.5 mm to 3.8 mm (0.02 in. to 0.15 in.)
between the 10 m (33 ft) lengths of rail. Over the years,
the rail surfaces near these gaps had worn preferentially
about 0.25 mm (0.01 in.) deep. This wear produced
unacceptable shock loadings and vibration in the carriage.
After evaluating the effect of heat input and preheat
on the weld, a welding procedure was developed for
rebuilding the worn surface. The rail was preheated at
temperatures between 200°C and 260°C (400°F and
500°F). Welding procedures included using 4 mm
(0.157 in.) diameter SMAW 0.05C-2.3Cr-1Mo electrodes at 175 A. The interpass temperature was maintained between 200°C and 260°C (400°F and 500°F).
This welding procedure produced welds that exhibited
hardness values between 30 and 40 HRC on the Rockwell
C scale, which was close to the target value of 35 HRC.
SHIP CONSTRUCTION
Figure 1.34—Dipper Body
for Electric Mining Shovel
and fillet welds were deposited using 2.4 mm (3/32 in.)
diameter E70T-5 electrode wire, with CO2 as the shielding gas. Typical welding parameters included welding
currents of 475 A to 580 A, wire feed speeds of 99 mm/s
to 112 mm/s (235 in./min to 265 in./min) and welding
voltages of 32 V to 36 V.
REPAIR WELDING OF A PRECISION RAIL
TRACK
A weld repair procedure was developed for a precision railroad-type track made of 0.75C–0.8Mn rail
steel. The rail initially was level to within 0.1 mm
(0.004 in.) over a length of more than 0.3 km (1000 ft).
The precision of the track was even more challenging in
the context of the massive size of the basin and the carriage, as shown in Figure 1.35.
The USS George H. W. Bush, the tenth and last of the
Nimitz-class aircraft carriers, is shown in Figure 1.36
during construction in dry dock. Superlifts, cranes with
a lifting capacity of up to 925 metric tons (1050 tons)
were used to raise large modules of the ship to be
welded to the rest of the hull. Figure 1.36 shows the
bow of the USS George H. W. Bush being raised into
position.
Welds in HY-100 steel of MIL S 16216 and HSLA100 steel of MIL-S-24645 were used extensively during
construction. HY-100 is a 3% Ni, 1.5% Cr, 0.5% Mo
quenched and tempered low-alloy steel with yield
strength of 690 MPa to 790 MPa (100 ksi to 115 ksi).
HSLA-100 is a low-carbon (maximum 0.07% C), highstrength low-alloy steel used for reduced preheat when
the process and application permit. Nominal analysis is
1.75% Ni, 0.6% Cr, 0.4% Mo, and 1.2% Cu. Welds
joining the modules to hull structure typically are made
with semiautomatic and mechanized flux cored arc welding (FCAW), pulsed gas metal arc welding (GMAW-P)
and mechanized submerged arc welding (SAW).
Arc Gouging
Mechanized air carbon arc gouging was used to prepare carbon steel for welding during the construction of
the USS George H. W. Bush. Both manual and mechanized air carbon arc gouging are widely used for building combat ships because of the need for backgouging
double-sided weld joints to achieve complete joint penetration. Air carbon arc gouging is shown in Figure 1.37.
The Virginia Class attack submarine, USS Virginia, is
shown in Figure 1.38. The sail on this vessel is free of
88
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Figure 1.35—Repair of a Precision Rail Track
Figure 1.36—The Bow Module of the USS George H. W. Bush
is Lifted and Lowered into Position to be Welded to the Hull
AWS WELDING HANDBOOK 9.4
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
Figure 1.37—Mechanized Air Carbon Arc Gouging
Used to Prepare Carbon Steel Welds Aboard the
USS George H. W. Bush Submarine Bow Planes
Figure 1.38—Testing of Welded Retractable Bow Planes
on the USS Virginia During Sea Trials
89
90
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
the fairwater planes found on previous submarine
classes. Welds joining the retractable bow plane system
and penetrations in the pressure hull were made with
the SMAW and semiautomatic GMAW-P processes.
These welds had to be made with careful attention to
bead sequence and placement in order to maintain precise alignment tolerances. The steel used in the pressure
hull is HY-100, MIL-S-16216, a 2.75% Ni, 1.5% Cr,
0.5% Mo quenched and tempered low-alloy steel with
690 MPa to 830 MPa (100 ksi to 120 ksi) yield strength.
SAFE PRACTICES
Chapter 17 of the Welding Handbook, 9th edition,
Volume 1 contains a comprehensive presentation of safe
practices for welding, brazing, soldering, and cutting. It
is intended for reference collectively for the five volumes of the 9th edition; thus, details of these topics are
not fully addressed in this chapter.89
The American National Standards Institute (ANSI)
standard, Safety in Welding, Cutting, and Allied Processes,
ANSI Z49.1, should be consulted before performing
any welding or cutting operation. This standard is published by the American Welding Society and can be
downloaded from the AWS website at http://www.
aws.org.90
Special care may be required when arc welding, cutting, or gouging alloys that contain higher percentages
of chromium, nickel, and manganese, as these common
metals have relatively low permissible exposure limits.
The Material Safety Data Sheet (MSDS) supplied by the
manufacturer of the welding consumable should be
consulted to determine which materials are present in
the consumable and what the required or suggested
exposure limits should be for those materials. Some
consumables may require particular attention.
Proper control of fumes is also required in brazing
operations using filler metals and fluxes. Materials with
low permissible exposure limits other than those previously mentioned may also be contained in these
consumables; the MSDSs should be consulted.
The United States Department of Labor, Occupational Health and Safety Administration publishes mandatory safety procedures and rules in Code of Federal
89. American Welding Society (AWS) Welding Handbook Committee,
2001, Welding Handbook, 9th edition, Welding Science and Technology,
Volume 1, Miami: American Welding Society. Chapter 17.
90. American National Standards Institute (ANSI) Accredited Standards
Committee Z49, 2005, Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1:2005, Miami: American Welding Society. Available
on the Internet at www.aws.org.
AWS WELDING HANDBOOK 9.4
Regulations (CFR) Title 29, CFR 1910.91 Lists of additional safety resources are published in ANSI Z49.1,
Safety in Welding, Cutting, and Allied Processes,
Annexes A, B, and C.
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SUPPLEMENTARY
READING LIST
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Welding Research Council. 76(6).
Dorschu, K. E. 1977. Factors affecting weld metal properties in carbon and low-alloy pressure vessel steels. WRC
bulletin 231. New York: Welding Research Council.
Emmer, L. G., C. D. Clauser, and J. R. Low. 1973. Critical literature review of embrittlement in 2-1/4Cr1Mo steel. WRC bulletin 183. New York: Welding
Research Council.
Guntz, G., et al. 1990. The T91 book. Vallourec Industries, France, 1990.
International Institute of Welding. 1967. Technical report,
Doc. IX-535-67: International Institute of Welding.
Irving, B. 1995. The challenge of welding heat-treatable
alloy steels. Welding journal 74(2): 43–48.
Ito, Y. and K. Bessyo. 1968. Weldability formula of
high strength steels related to heat-affected zone
cracking. Doc. IX-576–68: International Institute of
Welding.
Jubb, J. E. M. 1971. Lamellar tearing. WRC bulletin
168. New York: Welding Research Council.
AWS WELDING HANDBOOK 9.4
Meitzner, C. F. 1975. Stress relief cracking in steel
weldments. WRC bulletin 211. New York: Welding
Research Council.
Shackleton, D. N. 1973. Welding HY-100 and HY-130
steels. Cambridge, England: The Welding Institute. 73(9).
Stout, R. D. 1971. Hardness as an index to the weldability and service performance of steel weldments. WRC
bulletin 168. New York: Welding Research Council.
Stout, R. D. and W. D. Doty. 1978. Weldability of
steels. 3rd ed. S. Epstein. and R. E. Somers, eds. New
York: Welding Research Council.
CHAPTER 1—CARBON AND LOW-ALLOY STEELS
93
Welding Research Council. 1969. Interpretive report on
effect of hydrogen in pressure vessel steels. WRC
bulletin 145. New York: Welding Research Council.
The Welding Institute. 1975. The toughness of weld
heat-affected zones. Cambridge, England: The Welding
Institute.
Yurioka, N. 1994. TMCP steels and their welding. IIW
Document IX-1739-94.
Yurioka, N. and T. Kasuya. 1994. A chart method to
determine necessary preheat in steel welding. IIW
Document II-1230-94.
95
AWS WELDING HANDBOOK 9.4
CHAPTER
C H A P T E2 R 9
Prepared by the
Welding Handbook
Chapter Committee
on High-Alloy Steels:
HIGH-ALLOY
STEELS
D. J. Kotecki, Chair
Damian Kotecki
Welding Consultants
C. V. Robino
Sandia National
Laboratories
T. A. Siewert
National Institute of
Standards and Technology
B. R. Somers
Lehigh Heavy Forge
Welding Handbook
Volume 4 Committee
Member:
W. Lin
Pratt & Whitney
Contents
Photograph courtesy of The Lincoln Electric Company
Introduction
95
Classification of
High-Alloy Steels
96
PrecipitationHardening Steels
98
Maraging Steels
99
Nickel-Cobalt Steels
108
Austenitic
Manganese Steels
119
Applications
130
Safe Practices
133
Conclusion
133
Bibliography
134
Supplementary
Reading List
135
96
AWS WELDING HANDBOOK 9.4
CHAPTER 2
HIGH-ALLOY STEELS
INTRODUCTION
This grouping of alloy steels, because of the combination of high strength and high toughness, is important to many engineering applications and thus is
included in this volume of the Welding Handbook as a
separate chapter. This chapter covers the weldability of
certain selected steel alloys with compositions that
include total alloy additions of more than about 10%.
This chapter does not include stainless steels, chromium-molybdenum steels, 9%-nickel steels, such as
ASTM A 353 and A 553, or tool steels.1, 2, 3
Alloy additions are intended to improve the properties of steels. As a basic example, the tensile strength of
plain carbon steel may be increased simply by raising
the carbon content. However, this approach has several
limitations. Principal limitations to alloy additions are
that plain high-carbon steels have poor weldability and
relatively shallow hardening during rapid cooling. Also,
toughness and ductility are inadequate for many applications, and the range of mechanical properties usually
is severely limited. Nevertheless, many high-strength
carbon steels are used for structural applications in the
quenched-and-tempered condition.
Among the most important criteria for high-strength
steels designed for critical applications is good fracture
toughness at the service temperature. Another is that
the steels have nearly uniform isotropic mechanical prop1. For information on other high-performance alloys, see Chapter 4,
Tool and Die Steels, and Chapter 5, Stainless and Heat-Resisting
Steels, in this volume. Also see Chapter 4, Nickel and Cobalt Alloys in
Volume 3 of the Welding Handbook, 8th ed.
2. At the time of the preparation of this chapter, the referenced codes
and other standards were valid. If a code or other standard is cited
without a date of publication, it is understood that the latest edition
of the document referred to applies. If a code or other standard is
cited with the date of publication, the citation refers to that edition
only, and it is understood that any future revisions or amendments to
the code or standard are not included; however, as codes and standards undergo frequent revision, the reader is encouraged to consult
the most recent edition.
3. Definitions of welding processes and standard welding terms in
this chapter are from American Welding Society (AWS) Committee on
Definitions and Symbols, 2010, Standard Welding Terms and Definitions, AWS A3.0M/A3.0:2010, Miami: American Welding Society.
erties. Relatively few commercial alloy steels meet such
criteria and are often proprietary. The steels discussed
in subsequent sections of this chapter are representative.
Also included in this chapter are sections on the metallurgy of high-alloy precipitation-hardened steels (lowcarbon maraging steels and higher-carbon nickel-cobalt
alloy steels), and austenitic manganese steels. A section
on applications provides detailed descriptions of welding and fabrication procedures for several projects with
high-integrity service requirements. A brief section on
safe practices is presented, deferring to a comprehensive
chapter on health and safety published in Volume 1 of
the Welding Handbook and with references to national
health and safety standards.
CLASSIFICATION OF HIGHALLOY STEELS
Three general classes of high-alloy steels are discussed in this section: maraging steels, nickel-cobalt
alloy steels, and austenitic manganese steels. Designations of the Unified Numbering System (UNS) are used
in this chapter for the nickel-cobalt steels.
Steels in the first two classes, called ultrahighstrength steels, provide tensile and yield strengths significantly higher than those of common low-alloy
steels. Steels in the third class, the austenitic manganese
steels, have unique combinations of high toughness,
high work-hardening capacity, and good resistance to
wear.
The maraging steels generally are 18% nickel by
weight (18 wt%), with very low carbon content. The
alloy designation AF1410 (UNS K92571) in Table 2.1
represents an alloy developed for airframe structural
applications and nominally has 14 weight percent
(wt%) cobalt and 10 wt% nickel. AerMet® 100 Alloy
(UNS K92580) is a similar Ni-Co alloy with slightly
Composition, %
Specification
or UNS Number
Common
Designation
C
Mn
Si
P
—
18Ni (200)
0.03
0.10
0.10
0.01
0.01
MIL-S46850
AMS 6512, or
ASTM A 579 Grade 72
18Ni (250)
0.03
0.10
0.10
0.01
MIL-S46850
AMS 6514
18Ni (300)
0.03
0.10
0.10
MIL-S46850
18 Ni (350)
0.03
0.10
—
18 Ni (cast)
—
—
S
Cr
Ni
Mo
V
Co
Al
Ti
—
17–19
3.0–3.5
—
8–9
0.05–0.15
0.15–0.25
0.01
—
17–19
4.6–5.2
—
7–8.5
0.05–0.15
0.30–0.50
0.01
0.01
—
18–19
4.6–5.2
—
8.5–9.5
0.05–0.15
0.50–0.80
0.10
0.010
0.010
0.50
18–19
4.6–5.2
—
11.5–12.5
0.05–0.15
1.30–1.60
—
—
—
—
17
5
—
10
—
—
AWS WELDING HANDBOOK 9.4
Table 2.1
Composition of Typical High-Alloy Steels
Maraging Steels
Ni-Co Steels
—
AF1410
0.13–0.17
0.10
0.10
0.01
0.01
1.8–2.2
9.5–10.5
0.9–1.1
—
13.5–14.5
—
—
K92580
0.21–0.27
0.10
0.10
0.003
0.002
2.5–3.3
11.0–12.0
1.0–1.3
—
13.3–13.5
—
—
—
HP9-4-20
0.16–0.23
0.20–0.40
0.10
0.01
0.01
0.65–0.85
8.5–9.5
0.9–1.1
0.06–0.12
4.25–4.75
—
—
ASTM A 579 Grade 82
HP9-4-30
0.29–0.34
0.10–0.35
0.20
0.01
0.01
0.9–1.1
7.0–8.0
0.9–1.1
0.06–0.12
4.25–4.75
—
—
AMS 6478, 6532
Austenitic Manganese Steels (ASTM A 128)
—
1.05–1.35
11.0 min.
1.0
0.07
—
—
—
—
—
—
—
—
—
0.9–1.05
11.5–14.0
1.0
0.07
—
—
—
—
—
—
—
—
ASTM A 128 Grade B-2
—
1.05–1.2
11.5–14.0
1.0
0.07
—
—
—
—
—
—
—
—
ASTM A 128 Grade B-3
—
1.12–1.28
11.5–14.0
1.0
0.07
—
—
—
—
—
—
—
—
ASTM A 128 Grade B-4
—
1.2–1.35
11.5–14.0
1.0
0.07
—
—
—
—
—
—
—
—
ASTM A 128 Grade C
—
1.05–1.35
11.5–14.0
1.0
0.07
—
1.5–2.5
—
—
—
—
—
—
ASTM A 128 Grade D
—
0.7–1.3
11.5–14.0
1.0
0.07
—
—
3.0–4.0
—
—
—
—
—
ASTM A 128 Grade E-1
—
0.7–1.3
11.5–14.0
1.0
0.07
—
—
—
0.9–1.2
—
—
—
—
ASTM A 128 Grade E-2
—
1.05–1.45
11.5–14.0
1.0
0.07
—
—
—
1.8–2.1
—
—
—
—
ASTM A 128 Grade F
—
1.05–1.35
6.0–8.0
1.0
0.07
—
—
—
0.9–1.2
—
—
—
—
CHAPTER 2—HIGH-ALLOY STEELS
ASTM A 128 Grade A
ASTM A 128 Grade B-1
97
98
CHAPTER 2—HIGH-ALLOY STEELS
higher nickel content.4 HP9 4-20 (UNS K91472) and
HP9-4-30 (UNS K91283) are high-performance alloys
with nominally 9 wt% nickel, 4 wt% cobalt, and
0.20 wt% and 0.30 wt% of carbon respectively. The
K92571, K92580, and all of the maraging alloys obtain
some strength from age-hardening mechanisms.
The austenitic manganese alloys, also known as
Hadfield manganese steels, are rendered austenitic
because of high manganese content, nominally 12 wt%
to 13 wt%. Although austenitic manganese alloys are not
exceptionally high-strength in the as-cast or annealed
state, they can be significantly work-hardened; this
makes the manganese steels particularly suited for
equipment designed for repetitive impact loading, such
as railroad switch gear.
Ultra-high-strength steels such as the maraging steels
and the Ni-Co alloy steels are formulated for applications requiring yield strength of at least 1240 megapascals (MPa) (180 kips per square inch [ksi]) or tensile
strength of 1380 MPa (200 ksi), and good fracture
toughness. They are used for critical applications
requiring high strength-to-weight ratios, excellent reliability, and consistent response to heat treatment. The
alloying additions to ultra-high-strength steels restrict
the higher temperature and diffusion-driven decomposition of austenite, and permit the formation of tough
martensite during cooling from austenitizing temperatures. Subsequent tempering may lead to secondary
hardening that further increases the strengths of these
steels. Welded joints in ultra-high-strength steels generally require no heat treatment other than stress relief in
certain applications. With specific alloys, the weldment
may be re-aged or quenched and tempered to obtain
desired properties.
Manganese was among the earliest alloying elements
used widely by steel producers. The addition of manganese significantly improves the notch toughness of
carbon steels. Manganese, coupled with low carbon
content and with the addition of strong carbide-forming
elements, achieves superior combinations of strength
and toughness. Later, nonmetallic inclusions were
found to influence the toughness and weldability of
alloy steels. Reducing the amount and type of nonmetallic inclusions by special melting techniques
improved the mechanical properties and resulted in the
production of high-alloy steels with very high levels of
strength.
Adding alloys to manipulate the transformation
characteristics of steels is another way of contributing
to improved strength and toughness. The steel producer
can further improve properties either by heat treatment
after processing or by controlled processing of various
mill forms (billet, plate, rod, and other forms) during
4. AerMet is a registered trademark of CRS Holdings, Inc., a subsidiary
of Carpenter Technology Corporation, www.cartech.com.
AWS WELDING HANDBOOK 9.4
hot working. The precise combinations of alloying,
refining, processing and heat treatment can provide premium-quality high-strength alloy steels, with very low
levels of residual elements that exhibit good fracture
toughness and through-thickness properties.
Ultra-high-strength alloy steels generally are susceptible to embrittlement when a certain level of impurity
elements is exceeded. These elements tend to segregate
during solidification. Fracture commonly takes place
along the prior austenite grain boundaries, where the
impurities tend to concentrate. Temper embrittlement,
for example, can occur in certain steels during or after
tempering if the temperature is held or cooling is
slowed through the range of 565°C to 370°C (1050°F
to 700°F). Special deoxidation practices and refinement
techniques are used to reduce the levels of undesired
residual elements, such as sulfur and phosphorus. In
order to reduce inclusions and impurities to very low
levels (often less than 0.01%), steel producers use a
combination of the following steel melting and refining
techniques: vacuum induction melting, vacuum arc
melting, argon rinsing, vacuum degassing, electroslag
remelting, vacuum arc remelting, and rare-earth treatment. These practices provide reasonable toughness and
ductility at high strength levels while improving properties in the heat-affected zone (HAZ) of the weld. Many
alloy steels can be heat treated to tensile strengths
exceeding 1380 MPa (200 ksi) with moderate ductility.
PRECIPITATION-HARDENING
STEELS
Precipitation-hardening steels as discussed in this
chapter are steels which, after transformation of high
temperature austenite to martensite on cooling, are
capable of forming an extremely fine additional phase
(a precipitate) from the martensite matrix when
reheated to a temperature below, but close to, the temperature at which austenite would reform. When the
precipitate is fine enough to maintain a degree of coherency with the martensite matrix, remarkable strengthening can be achieved over that of the martensite before
precipitation takes place. Precipitation hardening is
often referred to as aging, and the two terms are used
interchangeably in this chapter.
METALLURGY: PRECIPITATION
HARDENING IN HIGH-ALLOY STEELS
Fine carbides, along with intermetallic compounds
and other precipitates, facilitate important mechanisms
in high-alloy steels designed to provide high strength.
AWS WELDING HANDBOOK 9.4
Precipitation hardening (also referred to as age hardening or secondary hardening) can be promoted by one or
more alloying elements such as titanium, molybdenum,
chromium, or aluminum. These elements are dissolved
in the austenite during the initial solution heat treatment, and held in supersaturated solution when subsequently cooled from the solution temperatures. During
an ensuing aging at intermediate temperatures, very
fine, uniformly dispersed submicroscopic precipitates
are formed, which can increase the hardness and
strength of the matrix. This hardening mechanism is
used to advantage in maraging steels and some of the
Ni-Co alloy steels.
The efficacy of the alloy-solute atoms to produce
strengthening by this hardening mechanism depends on
the relative precipitate size and the effect of these precipitates on the atomic structure of the alloy matrix. In
fact, maximum hardening is achieved at a stage just
before actual particles appear in the microstructure of
the matrix of the metal. During aging, the solute atoms
initially diffuse to form zones. The boundaries between
these zones and the matrix generally will be coherent
(i.e., the planes of atoms are continuous from the
matrix through the zones and back into the matrix);
however, there will be some lattice mismatch, leading
to the development of elastic strain fields surrounding
the coherent precipitate zone boundaries. As aging is
allowed to continue, the precipitates and eventually the
boundaries become incoherent (i.e., the planes of atoms
lose continuity at the precipitate-matrix boundary).
Thus, the effectiveness of the strengthening mechanism
initially increases, reaches a peak, and then declines.
This decline in strengthening is termed overaging. The
optimum combination of strength and toughness often
is achieved in a slightly overaged condition.
The precipitation particles in maraging steels usually
are identified as fine intermetallics—Ni3 Mo and Ni3 Ti.
The precipitating particles in the K92571 and K92580
usually are identified as fine M2C carbides, in which the
“M” stands for chromium and molybdenum.
The phenomena of particle growth, particle dissolution, reprecipitation, and pinning of grain boundaries
to prevent grain growth are all related to the presence of
carbides and intermetallic particles. Any or all of these
may occur during the thermal cycle of the weld. The
resulting particle sizes and distribution depend on the
thermodynamic properties of the precipitates, the starting
condition of the alloy being welded, and the actual local
thermal history during and subsequent to welding. Thus,
the resulting distribution of properties in the heat-affected
zone (HAZ) will depend on the initial precipitationhardened condition, the maximum temperature and the
cooling rates occurring in each region of the HAZ as a
result of the weld thermal cycle. Welding procedures
using high heat input will create larger heat-affected
zones and can have unfavorable effects on the resulting
CHAPTER 2—HIGH-ALLOY STEELS
99
properties in the HAZ. For this reason, processes using
lower heat input are often recommended for welding
these high-alloy steels. More detail about the effects
of the interaction of weld thermal cycles and the age
hardening mechanisms is provided in the sections that
follow.
MARAGING STEELS
Maraging steels are a class of iron-nickel alloys that
are strengthened by precipitation of one or more intermetallic compounds in a matrix that essentially is carbon-free martensite. In addition to nickel, these steels
generally contain molybdenum, cobalt, and smaller
amounts of titanium and aluminum.
Table 2.1 includes the composition ranges of five
commercially produced maraging steels. For optimal
properties, the carbon, silicon, manganese, sulfur, and
phosphorus in these steels are deliberately minimized.
METALLURGY
The desirable combination of high strength and
excellent toughness in maraging steels results from the
precipitation hardening of low-carbon martensite. The
principal substitutional alloying elements are nickel,
molybdenum, and cobalt or chromium. The iron-nickel
equilibrium diagram in Figure 2.1 shows a wide twophase region of alpha (ferrite) and gamma (austenite).
Smaller additions of aluminum and titanium also are
commonly made to produce further strengthening
through the formation of precipitates.
In practice, alloys containing about 18% nickel
transform from austenite to body-centered tetragonal
martensite during air cooling over a relatively narrow
temperature range. Transformation back to austenite
on reheating occurs over another narrow, but higher,
temperature range, as shown in Figure 2.2. This behavior permits the aging of the martensite at a temperature
of 480°C (900°F) for several hours without transformation to austenite. However, extended heating at this
temperature eventually will result in transformation
back to austenite as more extensive precipitation removes more and more alloy elements from solid solution.
The typical heat treatment for maraging steels consists of a solution anneal at 815°C (1500°F), followed
by air cooling to ambient temperature and then aging at
480°C (900°F). The annealing temperature must be
high enough to remove residual stresses and to cause
precipitates to go into solution. The cooling rate is not
critical; therefore, martensite formation is similar over a
wide range of section sizes.
100
CHAPTER 2—HIGH-ALLOY STEELS
Click here to view
1800
900
TEMPERATURE, °C
γ
1400
700
1200
600
1000
500
α+γ
800
TEMPERATURE, °F
1600
800
400
α
300
600
400
200
0
0
5
10
15
20
25
30
NICKEL, wt %
Figure 2.1—Iron-Nickel Equilibrium Diagram
LIVE GRAPH
Click here to view
1700
850
ON HEATING
1100
550
250
α
10%
TRANSFORMED
γ
10%
90%
TRANSFORMED
TRANSFORMED
150
α
450
350
900
700
500
300
50
100
0
ON COOLING
–100
0
5
10
15
20
25
NICKEL, wt %
30
35
Figure 2.2—Transformation Temperature
Ranges for Maraging Steels on
Heating and on Cooling
TEMPERATURE, °F
TEMPERATURE, °C
1300
γ
650
The conventional concepts of hardenability are not
applicable to maraging steels. The martensite formed
on cooling is relatively soft (30 Rockwell Hardness, C
scale [HRC]) and consists of low-carbon, iron-nickel
lath martensite. The austenite-to-martensite transformation takes place at fairly low temperatures, about
200°C to 300°C (390°F to 570°F) for most grades.
Fairly intricate machining can be performed while the
workpiece is in the soft (30 HRC) solution-annealed
condition, with very little distortion resulting from subsequent age hardening.
Postweld aging at 480°C (900°F) for three hours to
12 hours causes a significant increase in hardness and
strength. Age hardening results from precipitation of a
metastable Ni3Mo phase. Additional hardening also
results from the precipitation of particles of Ni3Ti.
The role of cobalt is more complex. Neither cobalt
nor cobalt-alloy phases precipitate in the 18Ni maraging alloy system; however, cobalt increases the precipitation of Ni3Mo by limiting molybdenum solubility in
the martensite matrix. Cobalt also raises the temperature at which martensite starts. This permits a fully
martensitic structure to be obtained on cooling with no
need for refrigeration below room temperature.
With extended periods of aging time, there is evidence of precipitation of Fe2Mo. Reversion to austenite
ultimately will occur, causing the steel to soften.
Although overaging usually is avoided, some components may be slightly overaged deliberately to provide
desired properties.
Heat-Affected Zone
1500
90%
TRANSFORMED
750
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
The heat-affected zone (HAZ) of the weld can be
divided into three regions, shown as A, B, and C in
Figure 2.3. Region A, adjacent to the weld interface,
becomes fully austenitic during welding and transforms
to a coarse martensite on cooling. This region is relatively soft in the as-welded condition, but will harden if
re-aged after welding. The next region, B, is a narrow
area characterized by darker etching. During welding,
Region B is reheated to the range of 590°C to 730°C
(1100°F to 1350°F). The microstructure in Region B is
martensite with fine, reverted austenite. Region C is
martensitic and will have been aged to various extents
at temperatures up to 590°C (1100°F). The properties of
Region C, for practical purposes, are relatively unchanged
by welding.
The microhardness across the HAZ of a typical weld
in aged maraging steel, as welded and after re-aging, is
shown in Figure 2.4. The as-welded hardness of Region
A, a coarse low-carbon martensite, decreased to approximately 330 diamond pyramid hardness (DPH) from an
initial base-metal hardness of approximately 570 DPH.
After re-aging, the hardness increased to approximately
that of the precipitation-hardened base metal.
AWS WELDING HANDBOOK 9.4
C
CHAPTER 2—HIGH-ALLOY STEELS
B
A
A
B
101
C
Figure 2.3—Three Regions in the Heat-Affected Zone of a Weld in Maraging Steel (x4)
The adjacent, narrow region, B, is a fine dispersion
of austenite in martensite. The amount of austenite
formed increases with increasing heat input. The austenite in Region B will not harden during subsequent
aging; therefore, the zone will remain softer than the
unaffected base metal. This may not be of practical significance if the zone is narrow, and in most cases the
joint strength will be controlled by the properties of the
weld metal. After welding with a high heat input, joints
in Region B may fail if a relatively large amount of austenite was formed. Therefore, control of heat input to
restrict the width and microstructure of this region is
recommended.
Weld Metal
The weld metal and base metal will have the same
basic structure provided a matching filler metal is used.
Both structures are low-carbon martensite, which hardens during aging. The weld-metal structure, however, is
more complex as areas with composition gradients
move through the phase regions shown in Figure 2.2.
Both single- and multiple-pass welds have small, white
patches of austenite in the matrix of the martensite after
aging. These austenitic patches form when the weld
metal is reheated during subsequent weld passes or during the precipitation-hardening heat treatment. Local
segregation of alloying elements allows austenite to
remain stable down to relatively low temperatures.
Martensitic weld metal containing small patches of austenite is shown in Figure 2.5.
Aged weld metal containing patches of austenite generally will have strength lower than that of aged base
metal. However, in most applications, joint efficiency
exceeding 90% can be obtained.
Cracking
Maraging steels are less sensitive to hydrogen embrittlement than the heat-treated low-alloy steels of the
same strength levels. The low-carbon martensite formed
in the heat-affected zone of the weld on cooling has low
susceptibility to hydrogen-induced cracking. This is
partly because the region close to the weld interface is
relatively soft in the as-welded condition.
The risk of cold cracking also is lessened because of
the pattern of the residual stress field in the weld. The
weld metal is under compressive longitudinal stress
rather than tensile stress because the martensitic transformation occurs at a relatively low temperature. The
stress changes from tension to compression when the
weld metal expands during the phase transformation.
At the same time, the stress in the heat-affected zone
changes from compression to tension.
The potential problem of hot cracking when maraging steels are welded is related primarily to the level of
impurities, although the low levels of manganese in
these steels makes them particularly sensitive to sulfur
embrittlement. Hot cracking can occur with a sulfur
content as low as 0.005% when the joint fitup is poor.
With good fitup, sulfur levels up to 0.010% can be
102
LIVE GRAPH
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Click here to view
DISTANCE FROM WELD INTERFACE, mm
2
4
6
MICROHARDNESS, DPH
600
8
AFTER RE-AGING
AS WELDED
500
tolerated. An example of a hot crack in a fillet weld is
shown in Figure 2.6.
Examination of the fracture surfaces of hot cracks in
welds has revealed inclusions of titanium sulfide that can
liquate during welding and form fissures as the metal
cools. The higher-strength maraging steels, which contain larger amounts of titanium than the lower strength
maraging steels, are more susceptible to hot cracking
and require greater care when welding. In consideration
of the low austenite-to-martensite transformation temperature and the sensitivity to hot cracking, maraging
steels should be welded without preheat, and the interpass temperature should be restricted to 120°C (250°F)
maximum. Control of heat input also is recommended.
400
PROPERTIES OF MARAGING STEEL
300
0
0.1
0.2
0.3
DISTANCE FROM WELD INTERFACE, in.
Figure 2.4—Microhardness of the Heat-Affected
Zone of a Weld in Aged 18Ni (250) Maraging
Steel As-Welded and After Re-Aging
Figure 2.5—Microstructure of Aged Maraging
Steel Weld Metal Showing Small White
Patches of Austenite in Martensite
(x500) (Reduced to 75%)
The excellent combination of material properties justifies the extra expense of maraging steels. While the
physical properties are similar to those of mild steels,
the mechanical properties are superior.
Physical Properties
The physical properties of maraging steel that are pertinent to welding are compared to those of mild steel and
austenitic stainless steel in Table 2.2. Differences between
maraging steels and mild steels are not significant for
Figure 2.6—Hot Crack in Maraging Steel
Weld Metal (x7) (Reduced to 70%)
AWS WELDING HANDBOOK 9.4
103
CHAPTER 2—HIGH-ALLOY STEELS
Table 2.2
Physical Properties of Maraging Steel, Mild Steel, and Austenitic Stainless Steel
Property
Maraging Steel
Mild Steel
Density, Mg/m3 [lb/in.3]
Austenitic Stainless Steel
8.0 (0.29)
7.85 (0.28)
8.0 (0.29)
Coefficient of thermal expansion, μm/(m·K) (μin./[in.·°F])
10.1a (5.6)
12.8b (7.1)
17.8c (9.9)
Thermal conductivity (20°C [68°F]), W/(m·K) (Btu/([t·h·°F])
19.7 (11.4)
52 (30)
15 (8.7)
Electrical resistivity, μΩ·m
0.36–0.7
0.17
0.72
Melting temperature, °C (°F)
1430–1450 (2606–2642)
1520 (2768)
1400–1450 [2552–2642]
a. 24°C to 284°C (75°F to 543°F).
b. 20°C to 300°C (68°F to 572°F).
c. 0°C to 315°C (32°F to 599°F).
most properties, except for thermal conductivity. Heat
loss by conduction during welding is lower with maraging steel, and the significant difference in coefficients of
thermal expansion between maraging steel and austenitic
stainless steel may cause some problems when welding
them together. Maraging steels are magnetic, therefore,
arc blow may be encountered during arc welding operations, particularly if the metal becomes magnetized.
Mechanical Properties
Maraging steels are designed for applications in
which high strength, high toughness, and weldability
are all important considerations. These steels are commonly used for aircraft and aerospace components, and
for nuclear fuel processing components. The low dimensional changes during precipitation hardening also
makes them useful for tooling applications, because the
tool can be machined to size while the steel is in the
annealed condition, then aged to increase strength and
hardness.
The grade designation for a given maraging steel
indicates the nominal yield strength in 1000 pounds
(kip) per square inch (ksi). These steels are used for
applications in which high reliability is paramount.
They are readily welded, usually requiring a precipitation-hardening heat treatment in the range of only
425°C to 510°C (800°F to 950°F) after fabrication.
They also have better toughness than most other alloys
above the 1380 MPa (200 ksi) yield-strength range.
Typical mechanical properties of common grades of
maraging steel are provided in Table 2.3. One of the
notable features of maraging steels is the excellent
combination of toughness and high strength. The
Charpy V-notch impact strength and fracture toughness
properties are more than twice those of conventional
quenched-and-tempered high-strength steels of similar
strength. Toughness, to a great extent, depends on the
purity of the steel.
Table 2.3
Typical Mechanical Properties of Commercial Aged Maraging Steels
ksi
Elongation
in 50.8 mm
(2 in.),
%
Reduction
of Area,
%
MPa m
ksi in.
J
ft·lb
1399
203
10
60
154–242
140–220
47
35
260
1703
247
8
55
121
110
27
20
297
1999
290
7
40
80
73
20
15
2448
355
2399
348
6
25
35–49
32–45
11
8
1551
225
1655
240
8
35
104
95
68
50
Tensile Strength
Yield Strength
Grade*
MPa
ksi
MPa
18Ni (200)
1503
218
18Ni (250)
1793
18Ni (300)
2048
18Ni (350)
Cast 18Ni
*Solution treated at 816°C (1500°F).
Fracture Toughness
Charpy V-Notch
Impact Strength
104
CHAPTER 2—HIGH-ALLOY STEELS
The maximum service temperature for maraging
steels is about 400°C (750°F). Above this temperature,
long-term strength drops rapidly due to overaging.
AWS WELDING HANDBOOK 9.4
Heat input must be limited to avoid hot cracking and
inferior mechanical properties. The effect of the joint
geometry on heat-input requirements also should be
considered. Joint design, weld backing, and clamping
fixtures should be chosen to minimize heat input during
welding.
Welding should be performed under conditions that
limit the depth of fusion, yet provide complete fusion
with the joint faces and with previously deposited weld
beads.
surfaces should be cleaned with lint-free cloths and a
suitable solvent. Vacuum annealing and ultrasonic
cleaning are possible options.
Maintaining the cleanliness of the filler metal
deserves particular emphasis. Wire feed rolls and guides
should be kept clean to avoid contaminating the filler
metal. Shielding gases must be dry and pure. Gas equipment and lines should be clean, free of leaks, and
purged of air and moisture prior to use. (A dark surface
discoloration would indicate poor shielding of the weld
zone.) Cleaned wire should be stored in dry containers
filled with inert gas to avoid contamination.
Each weld bead in a multiple-pass operation should
be cleaned of any surface contamination before depositing the next bead. The use of a clean stainless steel wire
brush or motor-driven metal-cutting tool is recommended.
Filler Metal Selection
Joint Design
The filler metal should have a composition similar to
that of the base metal and should be produced with one
of the vacuum-melting techniques to obtain low levels
of oxygen, nitrogen, and hydrogen. Control of the filler
metal composition is critical. Oxygen and nitrogen
should be below 50 parts per million (ppm), and hydrogen should be below 5 ppm. In particular, carbon and
sulfur must be kept as low as possible. Carbon can form
brittle inclusions that tie up some solid-solution
strengthening alloy additions, and sulfur forms lowmelting sulfide inclusions. Excessive silicon should be
avoided, as it can lower impact properties and increase
the sensitivity to cracking. Titanium content must be
controlled within strict limits. A titanium level that is
too low results in low strength and a tendency for
porosity; a titanium level that is too high can lead to
hot cracking and an increased tendency to re-form austenite in the weld metal. Solid electrodes AMS 6501 can
be specified for welding 18Ni 250 grade and AMS 6463
can be specified for the 18Ni 300 grade.5
Typical joint designs for arc welding the maraging
steels are shown in Figure 2.7. The joint dimensions,
groove angle, or root opening may need to be adjusted
for specific welding processes and applications. The
root of double-welded joints should be mechanically
gouged to sound metal before the second side is welded.
WELDING VARIABLES
Cleanliness
To achieve good toughness at high strength levels in
maraging steel weld metal, impurities must be kept at
very low levels to maintain the purity achieved during
the filler metal manufacturing process. Welding procedures must be designed to ensure that levels of impurities in welds are minimized. Prior to welding, joint
5. Society of Automotive Engineers (SAE) Aerospace Materials Division, Aerospace Materials` Specification (AMS), Steel, Maraging, Welding Wire, 18Ni - 8.0Co - 4.9Mo - 0.40Ti - 0.10Al, Vacuum Induction
Melted, Environment Controlled Packaging, AMS 6501, and Wire, Steel
Welding, 18.5Ni - 8.5Co - 5.2Mo - 0.72Ti - 0.10Al, Vacuum Melted,
Environment Controlled Packaging, AMS 6463, Warrendale, PA: Society
of Automotive Engineers.
Process Selection
The most widely used welding processes for maraging steels are gas tungsten arc welding (GTAW), gas
metal arc welding (GMAW), shielded metal arc welding
(SMAW), submerged arc welding (SAW), and electron
beam welding (EBW). (Volumes 2 and 3 of the Welding
Handbook contain more information about these processes. Refer to Appendix B for chapter content of the
Welding Handbooks.) Toughness is the most important
variable among these processes. The lowest oxygen
content in the weld is produced by GTAW, GMAW, and
EBW, therefore producing the most toughness. Welds
made with SMAW and SAW should be used only when
toughness is a secondary consideration.
Gas Tungsten Arc Welding. The preferred welding
processes for maraging steels are the inert gas-shielded
processes, particularly GTAW. This process allows good
control of heat input and protection of the weld from
oxidation. Conventional joint designs for GTAW are
shown in Figure 2.7.
Typical welding procedures using GTAW are shown
in Table 2.4. These may be used as guides to establish
suitable welding procedures for specific applications.
Joints welded with GTAW have better toughness than
those made by GMAW. This is illustrated in Table 2.5,
which shows a comparison of fracture toughness and
Charpy V-notch impact strengths for the two processes.
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
A to D
105
B to H
60° to 80°
60° to 80°
I to L
G to J
C to F
A to C
E
C to E
15° to 30°
7° to 30°
R1
I to K
L min.
C to E
R2
A to E
A to C
C to F
Note: A = 0 mm (0 in.); B = 1.0 mm (0.04 in.); C = 1.5 mm (0.06 in.); D = 2.0 mm (0.08 in.); E = 2.3 mm (0.09 in.);
F = 3.0 mm (0.12 in.); G = 3.8 mm (0.15 in.); H = 4.1 mm (0.16 in.); I = 13 mm (0.5 in.); J = 15 mm (0.6 in.);
K = 19 mm (0.75 in.); L = 25 mm (1 in.); R1 = 4.6 mm to 7.9 mm (0.18 in. to 0.31 in.); R2 = 6.4 mm (0.25 in.).
Figure 2.7—Typical Joint Designs for Arc Welding Maraging Steels
Weld-metal strength generally is below that of the base
metal (particularly with the higher-strength grades of
maraging steel) as a result of small patches of austenite
that occur in multiple-pass welds. Joint efficiency based
on yield strength can exceed 95% with appropriate
welding procedures. The toughness of gas tungsten arc
welds can match that of the base metal, but the toughness of gas metal arc welds tends to be somewhat lower.
Gas Metal Arc Welding. As described previously,
the properties of maraging steels depend on impurity
levels. In particular, carbon and oxygen levels should be
kept low. The need to minimize contamination presents
a problem if the GMAW process is to be used. In contrast to the welding of carbon steels and low-alloy
steels, where oxidizing shielding gases are often used to
stabilize the arc, maraging steels require an inert environment. Oxygen pickup may result in the formation of
titanium oxide inclusions and a reduction in fracture
toughness; the extent of this effect depends on the size
of the oxide particles (and the effectiveness as nuclei for
micro-void development during deformation). Also,
carbon pickup from shielding mixtures that contain
carbon dioxide could result in embrittlement, due to the
106 CHAPTER 2—HIGH-ALLOY STEELS
Table 2.4
Typical Procedures for Gas Tungsten Arc Welding of Maraging Steels
Welding
Current,
Aa
Travel Speed
Welding Wire
Feed Rateb
Weld
Passes
Arc
Volts,
V
mm/s
in./min
mm/s
in./min
Shielding Gas
Wire
Feed
Joint Thickness
Joint Design
mm
in.
2.0
0.080
Square groove
1
8
150
3.0
7
4.2
10
Argon
Cold
2.0
0.080
0.0
Single-V-groove, 1.0 mm (0.04 in.) root face,
90° groove angle
1
2
8
120
150
4.7
11
—
4.2
—
10
Argon
Cold
12.7
0.5
Single-U-groove, 2.3 mm (0.09 in.) groove radius,
1.5 mm (0.06 in.) root face, 30° groove angle
1
2
3–5
6–12
9–10
100
150
200
225
3.4
8
4.2
4.2
8.5
12.7
10
10
20
30
80% He-20% Ar
Cold
15.2
0.6
Single-U-groove, 4.1 mm (0.16 in.) groove radius,
1.5 mm (0.06 in.) root face, 60° groove angle
1
2–6
11–11.5
265
400
3.8
5.9
9
14
44.9
69.0
106
163
75% He-25% Ar
cHotc
19.0
0.75
Double-U-groove 2.3 mm (0.09 in.) groove radius,
1.5 mm (0.06 in.) root face, 60° groove angle
1–10
10
340–400
50.7–6.30
12–15
25.4–29.6
60–70
Argon
Cold
25.4
1.0
Double-V-groove, 1.5 mm (0.06 in.) root face,
60° groove angle
1–30
10–12
210–230
1.7–2.5
4–6
8.5–10.2
20–24
Argon
Cold
a. Direct current, electrode negative.
b. Welding wire diameter: 1.6 mm (0.06 in.).
c. Hot wire power: 5.5 V to 6 V, 135 A to 170 A, ac.
AWS WELDING HANDBOOK 9.4
AWS WELDING HANDBOOK 9.4
Table 2.5
Typical Mechanical Properties of Arc Welds in Maraging Steel Plate at Room Temperature
Toughness
ASTM Gradea
Process
Variation
Filler Metal
Tensile Strengthb
Yield Strength
MPa
MPa
ksi
ksi
Elongation
in 25.4 mm Reduction
(1 in.),
of Area,
%
%
Approximate
Joint
Efficiency,c
%
Charpy V-Notch
Impact Strength
Fracture Toughness
J
ft·lb
MPa
ksi
Gas Tungsten Arc Welds
A 358
Gr A (200)
Cold wire
Hot wire
18Ni (200)
18Ni (200)
1427–1482
1358–1455
207–215
197–211
1372–1475
1351–1400
199–214
196–203
10–13
9–13
53–60
43–58
90–100
90–95
47–50
—
35–37
—
99–143
145–163
90–130
132–148
Gr B (250)
Cold wire
High-current
18Ni (250)
18Ni (250)
1565–1675
1682
227–243
244
1517–1634
1675
220–237
243
10–13
12–16
44–60
21–28
90–95
97
26–31
—
19–23
—
68–69
77–88
62–63
70–80
Gr C (300)
Cold wire
18Ni (300)
1675
243
1393
202
8
40
75
—
—
65
59
Gas Metal Arc Welds
A 358
Gr A (200)
18Ni (200)
18Ni (200)
1413–1517
1434
205–220
208
1358–1496
1400
197–217
203
6–11
5
34–56
—
90–100
100
23–30
33
17–22
24
84
76
Gr B (250)
Spray
Pulsed spray
18Ni (250)
18Ni (250)
1620–1737
1689
235–252
245
1516–1703
1572
220–247
228
1.5–7 4
7–38
14
83–95
95
9–14
16
7–10
12
77–88
72–83
70–80
65–75
Gr C (300)
Spray
18Ni (300)
1689
245
1600
232
3
13
85
—
—
59
54
a. Plate thickness is 10 mm to 25.4 mm (0.4 in. to 1.0 in.).
b. Welds aged at 482°C (900°F) for 3 hours to 10 hours. Transverse weld tension tests used.
c. Based upon yield strength.
CHAPTER 2—HIGH-ALLOY STEELS
Spray
Pulsed spray
107
108
CHAPTER 2—HIGH-ALLOY STEELS
formation of titanium carbides at the grain boundaries.
Therefore, carbon dioxide should not be added to the
shielding gas, and oxygen should not be deliberately
added to the shielding gas unless it is necessary to stabilize the arc. In that case, oxygen should be limited to a
0.5% addition, beyond which the toughness might be
reduced. It should be noted that significant amounts of
oxygen could be drawn into the arc atmosphere during
gas metal arc welding; thus the quality of the shielding
gas should be maintained through adequate gas flow
and protection from side drafts.
Typical procedures for gas metal arc welding of
maraging steels are provided in Table 2.6. Spray transfer
generally is used with this process, but short-circuiting
transfer or pulsed-spray transfer also are suitable. The
bead shape should be controlled. Welding should be
performed using conditions that limit the depth of
fusion, yet provide complete fusion with the joint faces
and with previously deposited weld beads. Hot cracking in the weld metal of fillet welds is related to the
depth-to-width ratio of the weld bead, and also to the
alloy composition, the root opening, and the degree of
joint restraint. In general, the tendency to hot cracking
is increased with a high depth-to-width ratio (over 0.6)
or a wide root opening, and high joint restraint (i.e.,
increased section thicknesses).
Shielded Metal Arc Welding. The SMAW process
is not widely used to weld maraging steels, although
covered electrodes for these steels have been produced.
The composition of the core wire generally is similar to
that of the base metal, but the titanium content is
increased to account for losses across the arc. The coatings generally are basic carbonates with low levels of
silica. Weld joint strengths matching those of the base
metal have been achieved with the lower-strength
maraging steels, but at the expense of lower weld-metal
toughness.
Submerged Arc Welding. Maraging steels have
been joined with submerged arc welding using an electrode composition similar to that of the base metal but
with higher titanium content to deoxidize the weld
metal. Basic fluxes that do not contain silica appear to
be suitable. Conventional fluxes are not adequate
because the titanium recovery is low and the welds are
crack-sensitive and brittle. A typical basic flux for
maraging steels might be based on aluminum oxide, calcium carbonate, and calcium fluoride.
Double-V-groove joint designs with a root face of
6 millimeters (mm) (0.25 inch [in.]) and double-Ugroove joint designs with a root face of 8 mm (0.31 in.)
have been used for the submerged arc welding of plate
19 mm to 32 mm (0.75 in. to 1.25 in.) thick. Typical
welding conditions that have been used are 500 amperes (A) to 600 A (direct current, electrode positive);
27 arc volts to 30 arc volts; and travel speed of 4.2 mil-
AWS WELDING HANDBOOK 9.4
limeters per second (mm/s) to 5.0 mm/s (10 in./min to
12 in./min), using a 3.2 mm (0.125 in) diameter
electrode.
The strength of submerged arc welds generally
matches those of the maraging steel base metal in the
lower-strength grades, but the weld metal properties of
ductility and toughness are considerably lower than
those achieved with the inert-gas-shielded processes.
The low weld-metal toughness is presumed to be a
result of contamination by oxygen. Submerged arc weld
metal generally has a higher inclusion content than
metal deposited by an inert-gas-shielded welding process.
Attempts to produce multiple-pass welds with the
submerged arc process generally have been unsuccessful
because of cracking in the underlying bead. The cracks
are apparently associated with the high energy input of
the process, but the exact cause is uncertain. The general problems associated with submerged arc welding
(SAW) severely limit its use with maraging steels.
Electron Beam Welding. Electron beam welding
(EBW) in a vacuum is particularly well suited for joining maraging steels because of the clean conditions this
process provides during welding. The low heat input,
narrow heat-affected zone, and low distortion are additional advantages. Table 2.7 shows typical mechanical
properties of an electron-beam weld in maraging steel
plate. In general, the weld metal toughness is below that
of the base metal and, in some cases, below that
achieved with inert-gas-shielded welding.
NICKEL-COBALT STEELS
The nickel–cobalt steels discussed in this chapter,
K91472 (HP-9-4-20), K91283 (HP-9-4-30), K92571
(AF1410), and K92580 are premium alloy steels known
for high strength, fracture toughness, and good weldability. The primary applications for these alloys are in
aerospace and defense structures, including landing
gear, armor plate, gears, dies, fasteners, and bearings.
The nickel-cobalt steels provide an alternative to
maraging steels for achieving ultra-high strength. They
provide this ultra-high strength by virtue of precipitation of extremely fine alloy carbides instead of by
precipitation of intermetallic compounds.
MATERIAL PROPERTIES
Tensile strengths for this class of alloys can range
from approximately 1240 MPa to 1930 MPa (180 ksi
to 280 ksi), with fracture toughness ranging from
over 176 megapascals per square root meter (MPa m )
(160 ksi per square root inch [ksi in. ]) for low strength
Electrode
Diameter
Joint Thickness
mm
in.
Joint Design
12.7
0.50
Single-V-groove, 60°–80° groove angle,
1.5 mm (0.06 in.) root face,
1.5 mm (0.06 in.) root opening
Electrode
Feed Rate
in./min
No. of
Passes
Arc
Volts
Welding
Current
Aa
mm/s
in./min
84–93
200–220
3–5
30–34
290–310
10
4.2
138
325
18
25
125
6–8
2.5–3.4
28
350–375
15–20
6.3–8.4
Type of
Transfer
Shielding
Gas
mm
in.
mm/s
Spray
Argon
1.60
0.062
Short circuiting
Helium
0.89
0.035
Travel Speed
19.0
0.75
Single-U-groove, 45° groove angle,
2.3 mm (0.09 in.) root face,
1.8 mm (0.07 in.) root opening
Spray
Ar+2%O2
1.60
0.062
101
240
b10b
25.4
1.00
Double-V-groove, 60°–80° groove angle,
0.06 in. (1.5 mm) root face,
0.09 in. (2.3 mm) root opening
Spray
Argon
1.60
0.062
84–93
200–220
8
30–34
290–310
10
4.2
Pulsed spray
Ar+0.3%O2
1.14
0.045
76
180
24
70 peak
20 bkgd
140 avg
6
2.5
AWS WELDING HANDBOOK 9.4
Table 2.6
Typical Conditions for Gas Metal Arc Welding of Maraging Steels
a. Direct current, electrode positive.
b. First two passes made by gas tungsten arc welding using same filler metal and argon shielding. Arc volts: 8 to 10. Welding current (DCEN): 160 A to 175 A. Travel speed: 1.7 mm/s to 2.5 mm/s
(4 in./min to 6 in./min).
Table 2.7
Typical Mechanical Properties of Electron Beam Welds in Maraging Steel Plate
Processing
Sequencea
No. of
Passes
Welding
Conditions
Voltage,
kV
Thickness
Mechanical Propertiesb
ksi
Elongation,c
%
Reduction
of Area,
%
Travel Speed
Tensile Strength
Yield Strength
Current,
mA
mm/s
in./min
MPA
ksi
MPa
mm
in.
A 358 Gr A (200)
25.4
1.0
S-A-W
S-A-W-A
S-A-W
S-A-W-A
1
1
2
2
50
50
150
150
400
400
13
13
17
17
4
4
40
40
10
10
1041.1
1365.1
1158.3
1496.1
151.0
198.0
168.0
217.0
1013.5
1351.3
1103.1
1461.6
147.0
196.0
160.0
212.0
7
4
10
7
31
13
32
14
A 358 Gr B (250)
2.54
0.1
7.62
0.3
12.7
0.5
25.4
1.0
S-A-W
S-A-W-A
S-A-W
S-A-W-A
S-A-W
S-A-W-A
S-A-W-A
1
1
1
1
1
1
1
30
30
150
150
150
150
50
65
65
20
20
17
17
320
17
17
25
25
7
7
17
40
40
60
60
17
17
40
1143.1
1891.9
1671.9
1827.1
1303.1
1799.5
1794.0
165.8
274.4
242.5
265.0
189.0
261.0
260.2
1143.1
1867.1
1671.9
1806.4
1247.9
1723.6
1765.7
165.8
270.8
242.5
262.0
181.0
250.0
256.1
2.5
4.1
4
4
8
14
4
21.2
12.7
—
—
30
25
27.8
109
a. S = solution annealed, A = aged, W = welded.
b. All test specimens failed in the weld.
c. Elongation is not a true indication of weld ductility because an electron beam weld is a small portion of the gauge length.
CHAPTER 2—HIGH-ALLOY STEELS
ASTM Grade
110
CHAPTER 2—HIGH-ALLOY STEELS
alloys, to 110 MPa m (100 [ksi in. ) for the higher
strength alloys.
The K91472 and K91283 alloys are considered
quenched-and-tempered alloys; K92571 and K92580
are secondary or precipitation-hardening martensitic
steels. All the alloys in this class exhibit good hardenability. For example, the K91283 alloy can be fully
hardened in section thicknesses up to 150 mm (4 in.)
The K92571 and K92580 alloys can be fully hardened
in even greater thicknesses.
The K91472 and K91283 (HP9-4-20 and HP9-4-30)
alloys originally were produced by vacuum induction
melting/vacuum arc remelting (VIM/VAR), although
they are also produced by electric furnace-argonoxygen-decarburization (EF-AOD) followed by VAR
processing. The K92571 (AF 1410) and K92580 (also
known by the trade name, AerMet® 100) alloys generally are produced by VIM/VAR processing. Due to the
cobalt and nickel contents and complex primary production routes, the nickel-cobalt steels are relatively
expensive. Depending on the specific grade, nickelcobalt steels are available in billet, bar, rod, plate, strip,
and sheet, although due to the required remelting processes, the most commonly available forms are forging
billet, bar, and plate.
Specific base metal and weldment properties, including descriptions of the welding behavior of each of the
alloys, are provided in the subsections that follow. General welding considerations applicable to all nickelcobalt steels are included at the end of the section.
K91472 and K91283 Alloys
The K91472 and K91283 (HP-9-4-20 and HP-9-4-30)
alloys are designed for applications requiring high yield
strength and toughness, combined with good weldability. Grade K91472 steel can develop yield strength of
1240 MPa (180 ksi) and a Charpy V-notch impact
strength of 68 joules (J) (50 pound-force-foot [lbf-ft]) at
room temperature and in plate thicknesses up to
100 mm (4 in.). K91283 steels can be heat treated to a
yield strength of 1380 MPa (200 ksi). K91472 steel has
better weldability, temper resistance, and toughness
than K91283 steel.
Table 2.8 shows typical recommended heat treatments for K91472 and K91283. Refrigeration to below
–73°C (–100°F) after quenching from the austenitizing
temperature transforms the retained austenite to martensite. The response to tempering will be uniform, and
secondary hardening will not be significant. Usually a
double-temper cycle is recommended for both alloys.
Figure 2.8 shows the microstructures of K91472 steel
plate both as-rolled and after a quenching and tempering heat treatment.
AWS WELDING HANDBOOK 9.4
Table 2.8
Heat Treatments for K91472 (HP9-4-20)
and K91283 (HP9-4-30) Alloy Steels
Heat Treatment
Procedure
Normalizing
Hold at 871°C to 927°C (1600°F to 1700°F) for
2.4 min/mm (1 h/in.) of thickness, air cool
Hardening
Hold at 830°C to 857°C (1525°F to 1575°F) for
2.4 min/mm (1 h/in.) of thickness; water or oil
quench; refrigerate to –87°C to –101°C (–125°F to
–150°F) for 1 h; warm to room temperature
Tempering
Hold at 538°C to 579°C (1000°F to 1075°F) for
2 h, air cool; then repeat operation
Softening
Hold at 566°C (1150°F) for 24 h, air cool
Stress relieving
Hold at 538°C (1000°F) for 24 h, air cool
Table 2.9 lists typical mechanical properties for
K91472 and K91283 alloy steels after quenching and
tempering. The higher carbon content of K91283 is
responsible for its higher strength and its lower ductility
and toughness.
The weldability of K91472 alloy steel is considered
excellent, provided that the heat input is not excessive
and the welding process and procedures do not introduce weld metal contamination. Weld metal properties
equivalent to heat-treated base metal can be obtained
with the gas tungsten arc welding (GTAW) process
using the conditions listed in Table 2.10. Mechanized
welding with cold wire feed generally is recommended.
Preheat or postweld heat treatment is not required.
There is less welding information available for K91283,
as it is primarily intended for use in forging applications
that do not require welding.
Table 2.11 shows typical mechanical properties of
K91472 weld metal, as deposited, using GTAW. The
range of weld-metal impact strengths that may be expected
from various heats of K91472 filler metal is shown in
Figure 2.9.
Weldments may be stress relieved at 538°C (1000°F)
without significantly changing the mechanical properties of the weld metal. Toughness and yield strength of
the weld metal tend to increase, while the tensile strength
decreases.
Figure 2.10 shows a cooling transformation diagram
for K91472 alloy steel. The diagram for K91283 steel is
very similar. The diagram for K91472 alloy steel indicates that at slow cooling rates, bainitic structures are
formed. This suggests that the HAZ of a high-heat-input
weld may contain bainite, which can degrade toughness
in the HAZ. Thus, weld schedules with high heat input
generally should be avoided.
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
(A) As Rolled
(B) Heat Treated
Figure 2.8—Microstructures of As-Rolled and Heat-Treated
25.4 mm (1 in.) K91472 (HP9-4-20) Alloy Steel Plate (x500)
Table 2.9
Typical Mechanical Properties of K91472 (HP9-4-20) and K91283 (HP9-4-30) Alloy
Steels at Room Temperature in Quenched and Tempered (552°C [1025°F]) Condition
K91472
K91283
Tensile strength, MPa (ksi)
1413 (205)
1517–1655 (220–240)
Yield strength, MPa (ksi)
1276 (185)
1310–1379 (190–200)
Elongation, %
17a
12–16b
Reduction of area, %
65
35–50
Charpy V-notch impact strength, J (ft·lb)
Fracture toughness, MPa
m (ksi
a. In 25.4 mm (1 in.) gage length.
b. In 4D gage length.
in. )
81 (60)
24–34 (18–25)
—
99–115 (90–105)
111
112
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 2.10
Typical Conditions for Gas Tungsten
Arc Welding of K91472 (HP9-4-20)
K91472
Filler wire diameter, mm (in.)
1.6 (0.062)
Filler wire feed, mm/s (in./min)
8.5–12.7 (20–30)
Shielding gas
Ar
Welding current (dc), A
300–350
Arc voltage, V
10–12
Travel speed, mm/s (in./min)
2.1–4.2 (5–10)
Heat input, kJ/m (kJ/in.)
787–945 (20–24)
Max. interpass temperature, °C (°F)
93 (200)
K92571 Steel
The nickel-cobalt alloy steel K92571 (AF 1410)
exhibits higher strengths than those of the K91472 and
J91283. Typical strengths in the heat-treated condition
for K92571 are tensile strength 1760 MPa (255 ksi),
and yield strength1590 MPa (230 ksi); fracture toughness is in the vicinity of 154 MPa m (140 ksi in. ). It
should be noted that specification-required minimums
are lower than these values. Type K92571 steel provides
very high strength, resistance to stress corrosion cracking, and superior fracture properties. The alloy has
good hot-working and cold-working characteristics and
is readily machined in the overaged condition. This
alloy steel generally is available as bar stock or as billet
stock for forging. The cobalt-nickel content of this alloy
suppresses the transformation of austenite to equilibrium eutectoid phases during cooling. On cooling (usually in air) from austenitizing temperatures, a relatively
soft iron-nickel lath-martensite is formed. During aging
or tempering, a complex series of carbide precipitations
occur that improve strength. However, the reversion of
martensite to austenite at aging temperatures above
540°C (1000°F) reduces strength. Table 2.12 lists typical mechanical properties for a K92571 forging in two
heat-treated conditions.
Like other nickel-cobalt alloy steels, K92571 steel is
best joined by gas tungsten arc or plasma arc welding
using low heat input and multiple-pass weld schedules.
A matching filler metal of high quality, such as those
shown in Table 2.13, generally is recommended. Typical welding procedures for the gas tungsten arc welding
of K92571 are shown in Table 2.14. However, it should
be noted that an understanding of the metallurgical
response of nickel-cobalt alloys to welding thermal
cycles will help in establishing successful welding procedures for these materials. Electron beam welding is also
suitable for K92571. Sources of more detailed descriptions of the metallurgy and welding behavior of this
alloy are provided in the Supplementary Reading List
provided at the end of this chapter.
Table 2.15 shows typical mechanical properties of
weld metal deposited in 16 mm (0.625 in.) K92571
plate using typical GTAW conditions (refer to Table
2.14). Aging the weld metal at 482°C (900°F) for two
hours appears to improve yield strength and toughness.
K92580 Alloy Steel
An important development in the class of nickelcobalt steels is UNS K92580, with the trade name AerMet® 100 Alloy.6 This alloy, also known as AMS 6478
or AMS 6532, is included in the group of secondaryhardening martensitic Ni-Co alloys, and is similar in
many respects to K92571 steel. The welding characteristics of K92580 are also somewhat similar to those of
maraging steels and the precipitation-hardening martensitic stainless steels discussed previously.
6. See Reference 4. AerMet 100 Alloy is also known also as AMS 6478
or AMS 6532. Refer to www.cartech.com.
Table 2.11
Mechanical Properties of K91472 (HP9-4-20) Weld Metal As Deposited by Gas Tungsten Arc Welding
Charpy V-Notch Impact Strength
Base Metal
Thickness
Tensile Strength
Yield Strength
mm
in.
MPa
ksi
MPa
ksi
Elongation,
%
25.4
1.0
1427
207
1282
186
17.0
25.4
1.0
1455
211
1400
203
20.0
50.8
2.0
1441
209
1379
200
18.5
Reduction
of Area,
%
at 21°C (70°F)
at –62°C (–80°F)
J
ft·lb
J
ft·lb
59
85
63
68
50
65
87
64
75
55
60
80
59
77
57
AWS WELDING HANDBOOK 9.4
Click here to view
80
100
80
60
60
40
40
–80 –60 –40 –20
0
20
40
60
TEST TEMPERATURE, °F
Figure 2.9—Charpy V-Notch Impact
Strength Range for As-Deposited
K91472 (HP9-4-20) Steel Weld Metal
Click here to view
1600
800
SL
OW
700
1400
CO
OL
1000
500
BAINITE
800
400
600
300
TEMPERATURE, °F
1200
600
MARTENSITE
200
400
100
200
101
SECONDS 1
MINUTES 10–1
113
Typical mechanical properties for K92580 in the
standard heat-treated condition are provided in Table
2.16. It should be noted that the properties provided in
Table 2.16 represent typical values rather than specification minimums.
The combination of high strength and high toughness
provided by the K92580 alloy is in large part due to very
close control of impurity levels in the alloy. As a result,
welding processes and procedures must maintain this
cleanliness. In addition, high strength and toughness generally require the maintenance of fine microstructural
features; thus, low heat input welding processes are preferred. Because of these considerations, typical welding
processes are cold-wire gas tungsten arc welding (GTAW),
cold-wire plasma arc welding (PAW), or electron beam
welding (EBW). Examples of typical low-heat-input
GTAW and EBW welding parameters are shown in Tables
2.17 and 2.18. Figure 2.11(A) shows a gas tungsten arc
weld and (B) an electron beam weld in K92580 alloy.
LIVE GRAPH
TEMPERATURE, °C
IMPACT STRENGTH, J
20
120
IMPACT STRENGTH, ft·lb
TEST TEMPERATURE, °C
–40
0
–20
–60
CHAPTER 2—HIGH-ALLOY STEELS
LIVE GRAPH
102
103
104
101
1
HOURS 10–1
102
1
9Ni-4Co ULTRAHIGH-STRENGTH STEEL
0.32% C – 0.13% Mn – 0.15% Si – 0.090% P – 0.005% S – 9.05% Ni – 4.07% Co
Figure 2.10—Continuous Cooling Transformation Diagram for K91472 (HP9-4-20) Alloy Steel
114
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 2.12
Typical Tensile and Impact Properties of
K92571 (AF1410) Forging in Several Heat Treated Conditions
Condition
Forging Heat Treat: 899°C (1650°F), 1 h Air Cool + 677°C (1250°F), 8 h Air Cool
899°C (1650°F), 1/2 h Air Cool + 816°C (1500°F),
Specimen Heat Treat 1/2 h Air Cool + (–73°C [–100°F]) + 510°C (950°F), 5 h Air Cool
816°C (1500°F), 1/2 h Air Cool +
(–73°C [–100°F]) + 510°C (950°F), 5 h Air Cool
Ftu – MPa (ksi)
1751 (254)
1765 (256)
Fty – MPa (ksi)
1572 (228)
1634 (237)
Charpy J (ft·lb)
86.8 (64).0
80 (59)
Adapted from Brown, W. F. Jr., ed., Aerospace Structural Metals Handbook, 2000, West Lafayette, Indiana: CINDAS/Purdue University,
Table 2.13
Typical Composition of K92571 (AF1410) Alloy
Steel Wire Produced by Double-Vacuum Melting
Element
Weight Percent
C
Mn
Si
S
P
Ni
Cr
Mo
Co
Al
V
Ti
H
O
N
0.15
less than 0.05
less than 0.01
0.005
0.001
9.82
1.90
1.00
13.76
0.025
less than 0.01
less than 0.01
1 ppm*
52 ppm*
4 ppm*
*Parts per million
Table 2.14
Typical Conditions for Gas Tungsten Arc
Welding of K92571 (AF1410) Alloy Steel Plate
Filler Metal
K91472 (HP9-4-20)
Welding wire diameter, mm (in.)
1.6 (0.062)
Welding wire feed, mm/s (in./min)
8.5–12.7 (20–30)
Shielding gas
Ar
Welding current (dc), A
300–350
Arc voltage, V
10–12
Travel speed, mm/s (in./min)
2.1–4.2 (5–10)
Heat input, kJ/m (kJ/in.)
787–945 (20–24)
Max. interpass temperature, °C (°F)
93 (200)
In general, matching welding wires are used to
ensure high joint-strength efficiency. For thicker sections, GTAW and PAW welds usually are accomplished
by the use of multiple small stringer beads. Although
multiple-pass GTAW and PAW welds with low heat
input have relatively low deposition rates, the inherent
cleanliness and control of the microstructure afforded
by these processes generally outweigh this disadvantage. Clearly, the cleanliness of the vacuum environment and the rapid cooling rates associated with the
EBW process also are advantageous for welding of
K92580 and similar alloys.
For fabrication projects, the weldability of K92580
is quite good. Although the alloy solidifies as austenite,
the impurity levels are low, as mentioned previously;
therefore, hot cracking generally is not encountered.
While the alloy initially solidifies as austenite, it transforms to a low-carbon, Fe-Ni lath martensite upon
cooling to room temperature.
The potential for crater cracking exists, but it can
be controlled by applying suitable dwell time prior to
weld termination, in order to fill the crater. Depending
on mechanical property requirements, K92580 can be
successfully welded in the overaged-annealed, solutiontreated, or fully aged conditions. However, the postweld
heat treatment must be appropriate for each condition,
and a range of weld properties can be developed.
The major features controlling the properties of the
welds in K92580 (and similar materials) relate to the
fact that the as-deposited weld metal generally will be
similar to the solution-annealed wrought alloy (since the
martensitic transformation which occurs on cooling of
the weld significantly alters the as-solidified structure).
Although microstructural changes in the fusion and
heat-affected zones are complex (especially in multiplepass welds) and can have a strong effect on properties,
the heat-affected zone will contain three basic regions: a
reaustenitized region (which subsequently transforms to
fresh martensite on cooling of the weld), a region with a
significant fraction of reverted stable austenite, and an
overaged region. Some considerations regarding service
Next Page
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
115
Table 2.15
Typical Mechanical Properties of K92571 (AF1410)
Weld Metal Deposited by Gas Tungsten Arc Welding
Weld Metal
As-Welded
Aged*
Base Plate
Tensile strength, MPa (ksi)
1538 (223)
1538 (223)
1586 (230)
Yield strength, MPa (ksi)
1393 (202)
1455 (211)
1448 (210)
Elongation in 25.4 mm (1 in.), %
16
16
—
Reduction of area, %
57
63
—
56 (41)
60 (44)
47 (35 min.)
Charpy V-notch impact strength at 0°C (18°F), J (ft·lb)
*Aged at 482°C (900°F) for 2 h and water quenched.
Table 2.16
Typical Mechanical Properties of K92580 Alloy
Yield Strength
MPa
Ultimate Tensile Strength
ksi
MPa
ksi
Elongation,
%
Reduction
of Area,
%
Charpy V-Notch
Impact Energy
Fracture
Toughness KIC*
J
ft·lbs
MPa m
MPa in.
41
30
126
115
34
25
110
100
Longitudinal Orientation
1724
250
1965
285
1724
250
1965
285
14
65
Transverse Orientation
13
55
*Heat treatment 885°C (1625°F) 1 h, air cool, –73°C (–100°F) 1 h, aged 482°C (900°F) 5 h.
Source: Carpenter Technology Corporation.
Table 2.17
Typical Low-Heat Input Welding
Parameters for GTA Welding of 16 mm
(5/8 in.) Thick K92580 Alloy Plate
Parameter
Schedule
Filler metal
Matching
Arc current, A
250
Arc voltage, V
12
Travel speed, mm/sec (ipm)
5.92 (14)
Wire diameter, mm (in.)
1.6 (1/16)
Wire feed rate, mm/sec (ipm)
23.7 (56)
Shielding, 80He/20Ar (l/min)
16.5
Trailing shield, Ar (l/min)
11.8
Heat input, J/mm (kJ/in.)*
402 (10)
Interpass temperature, maximum, °C (°F)
150 (302)
*Assumes an arc efficiency of 0.80.
Source: Carpenter Technology Corporation.
applications, weldability, and properties of K92580 are
provided in succeeding paragraphs.
Properties comparable to the wrought base metal can
be obtained by welding the alloy in the overagedannealed condition, then performing a full-solution
heat treatment and normal aging of the entire weldment. In this case, the microstructure of the welds is
very similar to that of wrought base metal, since solidification segregation and solidification features are
diminished by the solution-heat treatment and subsequent martensitic transformation. From a welding perspective, welding in the overaged condition followed by
full-solution heat treatment may be problematic for
large structures; therefore, the distortions that may
occur during the martensitic transformation and subsequent aging must be considered.
Table 2.19 and Table 2.20 show typical roomtemperature tensile and impact properties of low-heatinput welds made with GTAW in K92580. Typical
properties of electron beam welds in K92580 plate are
shown in Table 2.21 and Table 2.22.
Previous Page
116
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 2.18
Typical EB Welding Parameters for
16 mm (5/8 in.) Thick K92580 Alloy Plate
Parameter
Schedule
Accelerating voltage, kV
100
Beam current, mA
75
Travel speed, mm/s (ipm)
10.2 (24)
Heat input, J/mm (kJ/in.)
740 (18.8)
The welding of K92580 in the solution-treated condition requires a direct postweld aging treatment (generally at 482°C [900°F] for 5 h) to obtain optimum
properties. In this case, the weld metal and unaffected
base metal respond in a similar manner, and similar
strength levels are achieved in these regions. Overall,
the strength of the weldment is controlled primarily by
the overaged region of the HAZ, which does not
respond to the aging treatment. Nevertheless, for lowheat-input welds, transverse tensile strength across the
weld generally approaches that of the base metal, while
the toughness of the weld metal is somewhat lower than
that of the wrought base metal. K92580 displays rela-
(A)
tively little distortion on aging, so distortion from direct
postweld aging will be minimal and similar to that
encountered during normal aging of the wrought alloy.
The welding of the K92580 alloy in the aged condition normally requires a postweld aging treatment to
obtain maximum properties in the weld metal;
postweld aging may not be required if the weld is
located in a low-stress region of the structure. If the
weld is to be aged after welding, consideration must be
given to the fact that some overaging of the base metal
also will occur. However, experience has shown that
postweld aging at 482°C (900°F) for five hours produces only a minimal loss of strength in the base metal.
For postweld aged welds in fully heat-treated (previously aged) plate, joint strength levels are again controlled by the overaged region in the HAZ. From a
distortion perspective, the welding of fully heat-treated
plate followed by direct postweld aging probably will
produce weldments with close to optimum properties
and minimal overall distortion.
WELDING CONSIDERATIONS
For acceptable welds in any high-strength alloy steel,
the mechanical properties of the weld metal must be
approximately equal to those of the base metal. Nickel-
(B)
Source: C. V. Robino, P. M. Novotny, J. R. Michael, and D. A. Englehart, 1999, Fusion Welding of AerMet ® 100 Alloy, Report SAND99-1833, Albuquerque: Sandia National Laboratories.
Figure 2.11—Comparison of Cross Sections of
(A) a Gas Tungsten Arc Weld and (B) an Electron Beam Weld in K92580 Alloy Plate
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
117
Table 2.19
Typical Tensile Properties of a Gas Tungsten Arc Weld in 16 mm (5/8 in.) K92580 Alloy Plate
Yield Strength
Base Metal Condition
Solution-Treated
Aged
Postweld
Heat Treatment
Orientation
As-Welded
Trans
1489
Long
1565
MPa
Tensile Strength
Reduction
of Area,
%
MPa
ksi
Elongation,
%
216
1834
266
13.0
58.6
227
1923
279
14.0
48.1
45.5
ksi
–73°C/1 h + 482°C/5 h
Trans
1765
256
2013
292
11.2
(–163°F/1 h + 900°F/5 h)
Long
1765
256
1971
286
11.0
37.6
As-Welded
Trans
1551
225
1923
279
6.6
21.5
Long
1565
227
1923
279
14.0
48.0
–73°C/1 h + 482°C/5 h
Trans
1730
251
1951
283
7.2
25.0
(–163°F/1 h + 900°F/5 h)
Long
1785
259
2034
295
8.3
28.9
Notes: Results are average of three tests.
Transverse tests sample: base metal, fusion zone, and heat-affected zone.
BM, FZ, and HAZ. Longitudinal tests are all-weld metal.
Table 2.20
Typical Charpy Impact Properties of a
Gas Tungsten Arc Weld in 16 mm (5/8 in.) K92580 Alloy Plate
Base Metal Impact Energy
Base Metal Condition
Solution-Treated
Impact Energy
Postweld
Heat Treatment
J
ft·lb
Notch Location
J
ft·lb
As-Welded
61.2
45.1
Centerline
29.3
21.6
Weld Interface
41.4
30.5
–73°C/1 h + 482°C/5 h
49.2
36.3
Centerline
25.1
18.5
Weld Interface
47.9
35.3
(–163°F/1 h + 900°F/5 h)
Aged
As-Welded
–73°C/1 h + 482°C/5 h
45.0
33.2
48.3
35.6
(–163°F/1 h + 900°F/5 h)
Centerline
29.3
21.6
Weld Interface
59.0
43.5
Centerline
22.2
16.4
Weld Interface
46.5
34.3
Note: Values are averages of three tests per condition.
Table 2.21
Typical Tensile Properties of an Electron Beam Weld in 16 mm (5/8 in.) K92580 Alloy Plate
Yield Strength
Base Metal Condition
Solution-Treated
Aged
Tensile Strength
ksi
Elongation,
%
Reduction
of Area,
%
264
14.3
60.4
1992
289
12.3
55.2
Postweld
Heat Treatment
MPa
ksi
MPa
As-Welded
1351
196
1820
–73°C/1 h + 482°C/5 h
(–163°F/1 h + 900°F/5 h)
1785
259
As-Welded
1606
233
1992
289
12.4
53.3
–73°C/1 h + 482°C/5 h
(–163°F/1 h + 900°F/5 h)
1751
254
1992
289
14.8
60.7
Notes: Results are average of three tests.
Transverse tests sample: base metal, fusion zone, and heat-affected zone.
118
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
Table 2.22
Typical Charpy Impact Properties of an Electron Beam Weld in 16 mm (5/8 in.) K92580 Alloy Plate
Impact Energy
Base Metal Condition
Solution-Treated
Aged
Postweld Heat Treatment
Notch Location
J
ft·lb
As-Welded
Centerline
30.0
22.1
Weld interface
48.8
36.0
–73°C/1 h + 482°C/5 h
Centerline
24.0
17.7
(–163°F/1 h + 900°F/5 h)
Weld interface
39.6
29.2
As-Welded
Centerline
26.7
19.7
Weld interface
37.0
27.3
11.6
–73°C/1 h + 468°C/5 h
Centerline
15.7
(–163°F/1 h + 874°F/5 h)
Weld interface
26.4
19.5
–73°C/1 h + 482°C/5 h
Centerline
25.9
19.1
(–163°F/1 h + 900°F/5 h)
Note: All values are averages of three tests per condition.
cobalt alloys are weldable, with appropriate precautions, although they tend to be more difficult to
machine than typical alloy steels. (Refer to the welding
considerations discussed in the section on maraging
steels.)
The limitation of residual elements in the weld metal
to low levels is necessary for obtaining optimum toughness in the nickel-cobalt alloy steels. (To achieve this
control, vacuum arc remelting as a minimum refining
procedure is often required during processing of wire
stock.) The unique combination of strength and toughness of nickel-cobalt alloy steels can be maintained only
when impurity levels in the weld metal are kept very
low. Therefore, levels of oxygen, hydrogen, nitrogen,
carbon, sulfur, and phosphorus must be controlled not
only by the steel producer, but also by the manufacturer
of the filler metal and the welder.
Careful control of welding conditions is another
requirement for successfully welding ultra-high-strength
alloy steels. Exceptional cleanliness of the filler metal,
the joint area, and the base metal is essential. An important measure of weld metal cleanliness is the total oxygen content. Because of the low level of deoxidizing
elements in these compositions and the necessity for
close control of carbon, it has been found necessary in
some cases to control oxygen content to less than
50 ppm. Welding heat input also must be controlled at
a consistently low level to take advantage of grain
refinement in prior weld beads and to minimize structural degradation of the heat-affected zone. High heat
input welding processes, such as SAW or high heat
input welding parameters, or both, may incur some sacrifice in mechanical properties, but they can be used if
the weld-metal impurities are kept exceptionally low.
Nickel-cobalt alloy steels often are welded in the
heat-treated condition. Postweld heat treatment of single-pass welds may be required with some steels
because of the absence of tempering. Postweld heat
treatment generally is not necessary for the K91472 and
K91283 grades, except for stress relief in special situations. This is because the rapid cooling associated with
low heat input results in minimum deterioration of
properties in the HAZ. For the age-hardening grades
(i.e., K92571 and K92580), direct postweld aging or
full re-heat treatment can be used to restore properties
to levels approaching those of the base metal.
Successful fabrication of these steels is dependent on
the use of low-hydrogen welding techniques and matching filler metals with low impurity levels. The filler
metal generally must be manufactured from selected
melting stock and double refined. An example of the
required cleanliness is provided by the composition of
K92571 welding wire (refer to Table 2.13). Vacuum
induction melting followed by vacuum arc remelting is
required to produce steel of this quality. Solid welding
wire for welding K92571 using AMS 6533 or K91283
using or AMS 6468 can be specified. Solid welding wire
for K92580 is available from the base metal producer.
Shielding gases should be essentially free from oxygen, nitrogen, and hydrogen. Pure dry argon, helium, or
mixtures of both can be used. A gas purity of 99.99%
or more is recommended. The filler rod or wire must be
absolutely clean; no surface debris or lubricant can be
permitted. Similarly, all joints must be thoroughly
cleaned of all traces of cutting fluids, lubricants, oils,
greases, scale, oxide films, and other contaminants.
Most oils fluoresce when viewed under an ultraviolet
light. Thus, a good way to verify that a workpiece has
AWS WELDING HANDBOOK 9.4
been thoroughly degreased is to examine it under ultraviolet light.
Properties in the heat-affected zone and weld metal
are maintained by controlling heat input and interpass
temperature, and by postweld heat-treatment as appropriate. The gas tungsten arc, plasma arc, and electron
beam welding processes can be used to weld these
premium-quality, high-strength alloys and will provide
clean weld metal with suitable mechanical properties.
Laser welding, under suitable shielding conditions is
also feasible, but has not been extensively evaluated for
any of the nickel-cobalt alloy steels. Gas metal arc
welding is not recommended because oxygen levels in
the weld metals seldom fall below 150 ppm with this
process.
Some general guidelines for designing welded joints
in ultra-high-strength steel structures are the following:
1. Forgings and butt joints should be used, and
fillet welds and T-joints should be avoided;
2. Any thermal cut surface should be subsequently
machined or ground back to unaffected metal
before welding;
3. Welded joints should be placed in low-stress
locations with good accessibility for welding and
inspection;
4. Automatic or mechanized welding equipment
should be used to ensure consistent uniform and
stable welding conditions and consistent weldment
properties;
5. Groove welds should be designed to minimize the
amount of filler metal required to fill them; and
6. Careful supervision for welding operations should
be provided.
AUSTENITIC MANGANESE
STEELS
Austenitic manganese steel was originally developed
by Sir Robert Hadfield in 1882 and is sometimes called
Hadfield manganese steel. These steels are extremely
tough, nonmagnetic alloys. The high manganese content
lowers the martensite start (MS) temperature to below
room temperature.
Austenitic manganese steels are characterized by
good strength, ductility, and wear resistance and also
have rapid work-hardening characteristics. They may
have yield strengths of only 345 MPa to 415 MPa
(50 ksi to 60 ksi) in the solution-annealed condition;
however, surface deformation by hammering, rolling, or
any other cold-work process will raise the yield strength
to provide a hard surface with a tough core structure.
CHAPTER 2—HIGH-ALLOY STEELS
119
The manganese content generally ranges from 11%
to 14%, and the carbon content generally ranges from
0.7% to 1.4%. (Refer to Table 2.1 for compositions
specified for castings in ASTM A 128.7) Wrought
compositions generally are similar to cast compositions,
but wrought compositions do not appear in ASTM
specifications, because most are proprietary and apparently there has been little interest on the part of either
the suppliers or the users in the standardization of compositions. In some proprietary compositions, especially
those with carbon content reduced to 0.1% or even
lower, manganese content may be as high as 35%. In
some proprietary compositions, chromium, molybdenum,
nickel, vanadium, copper and titanium may be added
singly or in combinations to provide special properties.
Bismuth has been added to proprietary alloys to enhance machinability, but this occurs at the expense of
weldability.
Austenitic manganese steel is available in the form of
castings, hot-rolled billets, bars and plates. Both castings and rolled products normally are supplied in the
quenched (annealed) condition.
Austenitic manganese steel castings are widely used
in crushing, earthmoving, and material-handling equipment, railroad track, switch gears and frogs (the device
that allows a rail car wheel to cross an intersecting
track), and special applications in which nonmagnetic
properties are important. The nonmagnetic properties
make austenitic manganese steels useful in components
of electromagnets, induction furnaces, and other electrical equipment.
Although austenitic manganese steels have relatively
low yield strength and tensile strength in the as-cast
condition, they have good wear resistance under impact
and abrasion. Examples of applications with severe
impact and abrasion service include gyratory and cone
crusher parts such as concaves, bowl liners and mantles,
jaw crushers, and hammer mill components. The
weight of these parts varies from 45 kilograms (kg) to
13 600 kg (100 pounds [lb] to 30 000 lb).
Wrought austenitic manganese steel ranging in thickness from 3.2 mm to 13 mm (0.125 in. to 0.5 in.) is
widely used for replaceable wear-plates and shoes. It also
is used by railroads for applications such as pedestals
and journals. The primary advantage of work-hardened
austenitic manganese steel in these applications is its
ability to resist metal-to-metal wear without lubrication.
METALLURGY
In the as-cast condition, austenitic manganese steel is
not a single-phase alloy. Depending on composition and
7. ASTM International (ASTM), 2007, Standard Specification for
Steel Castings, Austenitic Manganese, A 128/A 128M-93 (2007), West
Conshohocken, Pennsylvania: ASTM International.
CHAPTER 2—HIGH-ALLOY STEELS
Figure 2.12—Microstructure of As-Cast
Austenitic Manganese Steel (x100)
LIVE GRAPH
Click here to view
2100
1100
AUSTENITE
(SOLID SOLUTION)
1900
1700
900
800
Acm
AUSTENITE
AND
CARBIDES
A1-UPPER
700
600
500
0.3
1500
1300
FERRITE, AUSTENITE,
AND CARBIDES
1100
A1-LOWER
900
F
1000
TEMPERATURE, °
cooling rate, the as-cast microstructure may consist of
austenite with pearlite, austenite with grain boundary
carbides, or austenite with martensite and carbides. The
martensite results when the composition is relatively
lean and the cooling rate is slow enough to permit
extensive carbides to form, thereby removing both carbon and manganese (and other alloy elements such as
chromium or molybdenum, if present) from solid solution and raising the MS temperature to above ambient.
Some castings are usable in the as-cast condition, such
as when the carbides are useful for resisting abrasion,
and the lower ductility and toughness due to the presence of the carbides is not sufficient to make the alloy
unserviceable. An as-cast structure, shown in Figure
2.12, is very brittle; therefore, large castings are cracksensitive until they are heat-treated.
Most austenitic manganese steel castings, and virtually all wrought product forms, are given a solutionannealing heat treatment followed directly by a water
quench to develop optimum toughness, ductility and
work-hardening properties. The appropriate austenitizing (solutioning) temperature depends on both the carbon content and the manganese content, as indicated in
Figure 2.13. The temperature required to dissolve all
the carbides increases with carbon content. The desired
microstructure after austenitizing and quenching is
shown in Figure 2.14. In this condition, the steel is virtually nonmagnetic. Improper quenching, or a cooling
rate that is too slow because of heavy section thickness,
may result in grain boundary carbides, as shown in
Figure 2.15.
Many commercial austenitic manganese steel castings have carbon contents in the range of 1.05% to
1.35% (as shown in Table 2.1) and manganese in the
range of 11.0% to 14.0%. The carbon content normally is kept close to the midpoint of the range, and the
manganese is kept between 12% and 13%. Manganese
content below 12% results in low tensile strength, and
above 13% provides no advantage. A minimum manganese content of 11.5% is recommended for most applications. The maximum content is arbitrary and usually
depends more on production costs than on material
properties. During solidification, segregation within the
microstructure can result in manganese variations of up
to 2% above or below the nominal.
The effect of carbon on yield strength is slight but
distinct. The optimum carbon content is about 1.15%.
Low carbon content helps to avoid the embrittling
effect of carbide precipitation during cooling. For this
reason, filler metals with low carbon content and other
modifications are produced for use in applications
where the normal solution annealing and quenching
heat treatment after welding is impractical.
Silicon is added to the steel mainly for the purpose of
facilitating production. While silicon content generally
does not exceed 1%, it may be increased up to 2% to
AWS WELDING HANDBOOK 9.4
TEMPERATURE, °C
120
FERRITE
AND CARBIDES
0.5
0.7
0.9
1.1
CARBON CONTENT, wt %
1.3
Figure 2.13—Equilibrium Diagram Showing the
Effect of Carbon on the Microstructure
of 12.5% Manganese Steel
AWS WELDING HANDBOOK 9.4
Figure 2.14—Microstructure of Properly
Quenched Austenitic Manganese Steel (x100)
Figure 2.15—Microstructure of Austenitic
Manganese Steel Improperly Quenched
from Austenitizing Temperature (x100)
CHAPTER 2—HIGH-ALLOY STEELS
121
provide a moderate increase in yield strength and
improved resistance to plastic flow under repeated
impact. Silicon in excess of about 2.2% sharply reduces
strength and ductility, and a higher content is not desirable for normal applications.
Phosphide and sulfide inclusions in wrought austenitic manganese steels may contribute to directional
properties. They are relatively harmless in castings, and
sulfur seldom influences the properties of austenitic
manganese steel. The scavenging effect of the manganese results in the formation of manganese sulfide in the
form of innocuous rounded inclusions. Although
ASTM A 128 allows a maximum of 0.07% phosphorus, problems with cracking during fabrication and
repair welding will be fewer if the phosphorus content
of cast or wrought products does not exceed 0.04%. In
welding electrodes the phosphorus content should not
exceed 0.03%, because this element tends to cause hot
cracking in weld metal.
Molybdenum or chromium is added to the steel as an
alloying element to raise the yield strength. The addition of nickel has little effect on the yield strength, but it
stabilizes the austenite and may slightly increase ductility. Bismuth additions can improve machinability, while
titanium in the steel can lower the amount of carbon
dissolved in the austenite by forming stable carbides.
The solution-annealing temperature for ASTM
A 128 castings typically is 1010°C (1850°F) to 1090°C
(2000°F), the temperature range in which all carbides
dissolve to produce essentially 100% austenite. The
time held at this temperature is not critical. Equilibrium
is probably established within 20 minutes to 30 minutes
at temperatures above 1010°C (1850°F), but an added
time allowance is needed for the center of heavy sections to reach the austenitizing temperature. Water
quenching is essential to preventing reprecipitation of
carbides on cooling. Complete avoidance of carbide
formation may be impossible in very heavy section castings because the cooling rate, even under the most
severe conditions of agitated chilled water, may not be
rapid enough to prevent the formation of carbide in the
interior of the casting. As a result, commercially available castings are usually, but not always, limited in
maximum thickness to about 150 mm (6 in.).
If the austenitic manganese steel is properly solution
annealed and quenched, reheating to temperatures
above 595°C (1100°F) for even a very short time, or to
temperatures as low as 315°C (600°F) for a long time,
can cause manganese carbides to precipitate and can
severely embrittle the steel. As a result, the maximum
weldment interpass temperature usually is limited to
260°C (500°F).
Isothermal transformation can occur in quenchannealed steel if it is subsequently heated to a temperature just below the transition temperature at which
pearlite begins to form and carbides precipitate from
CHAPTER 2—HIGH-ALLOY STEELS
MATERIAL PROPERTIES
Austenitic manganese steels can have a range of
physical and mechanical properties. The physical prop-
Click here to view
900
BRITTLE
400
800
700
600
300
DUCTILE
500
400
200
0.1
10
100
1
1000
TIME AT TEMPERATURE, h
REHEATING TEMPERATURE, °F
the austenite. The carbides precipitate at temperatures
from about 538°C to 590°C (1000°F or 1100°F), and
pearlite forms at temperatures from about 538°C to
760°C (1000°F to 1400°F). Transformation generally
starts along the grain boundaries, as shown in Figure
2.16. These transformations result in significant embrittlement as well as significant loss of ductility and reduction of strength.
Figure 2.17 shows the effect on the ductility of austenitic manganese steel of exposure to elevated temperatures. Figure 2.18 shows the relationship between alloy
composition, tensile strength, and elongation with
reheat temperature. Steels with higher carbon or lower
manganese content tend to embrittle at lower temperatures. Hence, alloy segregation during solidification can
have a significant effect during the reheating that
accompanies welding.
To avoid embrittlement during reheating, manganese
steel should not be tempered or stress relieved after
welding. In general, this type of steel should not be
heated above 315°C (600°F), except for very short
durations during welding, unless it will be given a
quench anneal later.
LIVE GRAPH AWS WELDING HANDBOOK 9.4
REHEATING TEMPERATURE, °C
122
Figure 2.17—Effect of Reheating Temperature
and Time on the Ductility of Austenitic
Manganese Steel (1.2%C-13%Mn-0.5%Si) after
Solution-Heat Treatment at 1093°C (2000°F)
for Two Hours and Water Quenching
(Based on Metallographic Examination)
erties do not vary with heat treatment; however,
the mechanical properties, especially ductility, can vary
significantly.
Physical Properties
Typical physical properties of austenitic manganese
steel pertinent to welding are shown in Table 2.23. The
melting temperature can be affected significantly by
carbon and alloy content. In general, higher alloy content and especially higher carbon content correlate with
lower melting temperature. The thermal and electrical
characteristics of this steel are similar to those of other
austenitic steels. The dimensional change expected during heating is about 1.5 times that of mild steel (compare with data in Table 2.2). Thermal conductivity is
about 25% of that of mild steel at room temperature,
and this contributes to heat buildup during welding.
When a strong and tough nonmagnetic metal is required, austenitic manganese steel frequently is specified.
Mechanical Properties
Figure 2.16—Microstructure of Austenitic
Manganese Steel After Quench Annealing and
Reheating at 538°C (1000°F) for Two Hours (x250)
Typical mechanical properties for various types of
austenitic manganese steels are given in Table 2.24. The
outstanding toughness of these steels is shown by the
stress-strain curves in Figure 2.19. The relatively low
yield strength, a characteristic of austenitic manganese
steel, is significant. It is a factor when deformation in
service is not acceptable. If deformation is not critical,
AWS WELDING HANDBOOK 9.4
123
LIVE GRAPH CHAPTER 2—HIGH-ALLOY STEELS
Click here to view
27
250
REHEATING TEMPERATURE, °C
300
350
400
900
13.0% Mn, 1.0 to 1.4% C
850
120
800
750
11.0% Mn, 1.0 to 1.3% C
700
100
650
600
ELONGATION, % IN 50.8 mm (2 in.)
550
TENSILE STRENGTH, ksi
TENSILE STRENGTH, MPa
140
80
60
1.0% C
13.0% Mn
40
1.2% C
11.0% Mn
1.3% C
1.2% C
1.4% C
20
0
80
500
600
700
800
REHEATING TEMPERATURE, °F
Figure 2.18—Relationship Between Composition, Reheat Temperature, Strength,
and Ductility of Austenitic Manganese Steel (25.4 mm [1 in.] Diameter Bars
Solution-Heat Treated, Quenched, and Reheated for 48 Hours at Temperature)
LIVE GRAPH
Property
Value
Density, mg/m3 (lb/in.3)
7.92 (0.286)
Coefficient of thermal expansion,a μm/(m·K)
20.7 (11.5)
(μin./[in.·°F])
Thermal conductivity,b W/(m·K) (Btu/[ft·h·°F])
13.4 (7.75)
Electrical resistivity,b μΩ·m
0.68
Melting temperature, °C (°F)
1396 (2545)
Specific heat,b J/[g·K] (Btu/[lb·°F])
500 (0.12)
a. 0°C to 300°C (32°F to 572°F).
b. Room temperature.
240
1650
1450
1250
1050
850
650
450
250
HEAT-TREATED
CAST MANGANESE
STEEL
200
160
120
HEAT-TREATED
ROLLED MANGANESE
STEEL
80
40
TRUE STRESS, ksi
Table 2.23
Physical Properties of
Austenitic Manganese Steel
TRUE STRESS, MPa
Click here to view
0
0
0.10
0.20
0.30
0.40
STRAIN, UNIT LENGTH/UNIT LENGTH
Figure 2.19—Stress-Strain Characteristics
of Austenitic Manganese Steel
124 CHAPTER 2—HIGH-ALLOY STEELS
Table 2.24
Typical Mechanical Properties of Austenitic Manganese Steel
Diameter (d) or
Thickness (t)
Chemical Compositions, %
Type
C-Mn
C-Mn-Cr
C
Mn
Si
Cr
Ni
Mo
mm
in.
1.0–1.4
11–14
0.2–1.0
—
—
—
25 (d) 1 (d)
1.11
12.7
0.54
—
—
—
Tensile Strength
Yield Strength
Condition*
MPa
ksi
MPa
ksi
Elongation,
%
C,QA
689–999
100–145
345–393
50–57
30–65
Reduction
of Area, Hardness,
%
HB
30–45
185–210
25 (d) 1 (d)
C
448
65
359
52
4
—
—
102 (t) 4 (t)
C,QA
620
90
359
52
25
35
—
203 (t) 8 (t)
C.QA
455
66
324
47
18
25
—
1.1–1.4
11–14
0.2–0.6
—
—
—
25 (d) 1 (d)
R,QA
903–1089 131–158
296–462
43–67
40–63
35–50
170–200
1.1–1.25
12.5–13.5
0.5
1.8–2.1
—
—
25 (d) 1 (d)
C,QA
661–1013
96–147
400–469
58–68
27–59
26–38
205–215
102 (t) 4 (t)
C,QA
565
82
365
53
31
29
—
152 (t) 6 (t)
C,QA
558
81
386
56
20
19
—
25 (d) 1 (d)
C,QA
620–910
90–132
290–338
42–49
40–88
—
150–180
C-Mn-Ni
0.6–0.9
12.4–14.3
0.5–0.9
—
3.4–3.6
—
0.8–0.9
13.9–15.1
0.9–1.3
—
2.8–4.0
—
—
R,QA
924–1006 134–146
317–386
46–56
74–87
45
180
C-Mn-Mo
0.75–1.0
12.1–14.1
0.4–0.6
—
—
1
25 (d) 1 (d)
C,QA
731–944
106–137
345–407
50–59
37–67
30–39
179–207
203 (t) 8 (t)
C,QA
551–917
80–133
290–379
42–55
27–61
26–60
—
1.15
0.72
13
0.5
—
—
—
—
—
1
1
25 (d) 1 (d)
C,QA
827–993
120–144
386–510
56–74
45–53
31–37
202–207
203 (t) 8 (t)
C,QA
524–531
76–77
345–386
50–56
16–33
12–29
—
25 (d) 1 (d)
R,QA
999–1013 145–147
365–372
53–54
60–72
43–49
187
AWS WELDING HANDBOOK 9.4
*C—cast
R—rolled
QA—quench-annealed
12.8–14.3
—
AWS WELDING HANDBOOK 9.4
the low yield strength may be considered as temporary
because it will increase rapidly with deformation.
The mechanical properties of austenitic manganese
steel between –45°C and 200°C (–50°F and 400°F) are
excellent for many applications. However, standard
grades are not recommended for wear applications above
260°C (500°F) because of structural instability. At high
temperatures, these steels may lack the strength and
ductility necessary to withstand the residual stresses of
welding. They are not oxidation resistant (except for
some high-chromium proprietary grades), and creep
properties are poor in comparison with the Cr-Ni austenitic stainless steels.
Ductility tends to increase with temperature until transformation to austenite begins. A hot shortness range,
and a resulting tendency toward hot cracking, starts
between 815°C and 870°C (1500°F and 1600°F) and may
extend to the melting temperature. This behavior must
be considered when establishing welding procedures in
order to avoid hot cracking.
Tensile Properties. Work hardening of austenitic
manganese steel develops approximately the same range
of tensile properties as are produced in other steels by
heat treatment. In a standard tensile test, these steels
exhibit little or no necking. As extension under load
occurs, the strength of separate, favorably oriented
grains increases. As these grains become stronger, other
grains are stretched and hardened progressively. Deformation is practically uniform along the entire reduced
section.
Impact Properties. The impact properties of austenitic manganese steel are high, as evidenced by service
experience and Charpy V-notch impact tests. The
impact strengths of ASTM A 128, Grade B-2 cast steel
are between 122 J and 149 J at –73°C (90 ft·lb and
110 ft·lb at –100°F). The impact strength of Grade D
is reported to be between 102 J and 122 J at –73°C
(75 ft·lb and 90 ft·lb at –100°F).
As-rolled C-Mn-Ni steel bar has an impact strength
of about 270 J 200 (ft·lb) at room temperature and
135 J at –73°C (100 ft·lb at –100°F). The impact
strength at –73°C (–100°F) is increased to about 230 J
(170 ft·lb) by quench annealing.
At all service temperatures experienced in mining,
construction, and rail-track service, cast manganese steel
has outstanding toughness. This is a valuable asset for
service applications operating at sub-zero temperatures.
Standard austenitic manganese steel is reasonably
insensitive to hydrogen-induced embrittlement. Hydrogen does not diffuse appreciably in the austenitic phase,
so hydrogen damage of annealed austenitic manganese
steel is highly unlikely. Considerable hydrogen has been
extracted from standard austenitic manganese steel,
suggesting that up to 6.3 milliliters (ml) per 100 grams
(g) can be accommodated without adverse effects.
CHAPTER 2—HIGH-ALLOY STEELS
125
Work Hardening. Manganese steels have a very high
coefficient of work hardening, exceeding that of austenitic stainless steel. The maximum hardness obtainable is
about 550 Brinell hardness (HB). The work-hardening
properties make the manganese steels particularly suitable
for applications in which repeated impact loading occurs.
Work hardening is attributable in part to the formation of martensite. Austenitic manganese steels with less
than about 0.2% C can work harden through the formation of epsilon martensite (hexagonal close-packed
crystal structure), which is not ferromagnetic. Higher
carbon austenitic manganese steels work-harden through
the formation of alpha martensite, which has a bodycentered tetragonal crystal structure and is ferromagnetic. Ferromagnetism due to martensite may also
be found in a thin skin on heat-treated forgings or
castings when the skin is lower in alloy content than the
nominal alloy content.
Work hardening is produced by deformation, thus
dimensional allowances must be made for the required
work hardening if a work-hardened surface is required
on austenitic manganese steel.
Although the hard layer will vary in depth, depending on the processing, it is always rather shallow. However, any application involving both wear and impact
continually will harden the surface as hardened metal is
worn away.
Some austenitic manganese steel applications do not
promote work hardening before the steel or weldment
is placed into service. Therefore, if a hardened surface is
required immediately, other methods, such as alloying,
heat treatment, and age hardening are employed to
increase hardness. Resistance to flow during cold working is increased as the yield strength is raised. Additions
of vanadium, chromium, silicon, molybdenum, and carbon are all effective in raising yield strength, although
vanadium and chromium may reduce ductility at the same
time.
WELDING PROCEDURES
As discussed previously, the reheating of austenitic
manganese steel may cause the precipitation of carbide
and some transformation of austenite, which significantly reduces ductility. Therefore, these steels should
be welded with a process that results in minimal heat
input and minimal heat buildup. Arc welding with a
consumable electrode generally is used for joining and
surfacing operations.
Oxyacetylene welding (OAW) and gas tungsten arc
welding (GTAW) are not recommended because of characteristic heat buildup in the workpieces during welding.
Submerged arc welding (SAW) is seldom applied to austenitic manganese steels due to heat buildup and a tendency for hot cracking.
126
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
The air carbon arc gouging process is commonly
used for the removal of metal when preparing badly
damaged austenitic manganese steel for weld repair or
buildup, but overheating of the steel must be carefully
avoided. Oxyfuel gas cutting (OFC) can be applied to
austenitic manganese steel, provided that the chromium
content is no higher than about 5%. Cutting austenitic
manganese steel that has a chromium content higher
than 5% makes the slag refractory when using the
oxyfuel gas process, and results in very poor quality of
the cut surface.
Filler Metal Selection
Arc welding electrodes for the deposition of austenitic manganese steel are available as bare wire and, for
shielded metal arc welding, as covered electrodes. The
covered electrodes generally are made with a mild-steel
core wire and with all alloying elements in the coating.
As a result, the coating generally is very thick; consequently, welding in vertical and overhead positions is
difficult (if not impossible in some cases). While uphill
welding may be possible with some small-diameter covered electrodes, it generally should be discouraged
because the wide weave technique necessary for uphill
welding tends to seriously overheat the base metal,
leading to carbide precipitation. Years ago, solid austenitic manganese steel welding wires were available, but
these have largely disappeared, having been superseded
by tubular wires filled with alloying and fluxing ingredients. Most tubular (flux cored) wires for depositing
austenitic manganese steel weld metal are self-shielded,
designed for welding without shielding gas.
Typical electrode classifications for arc deposition of
austenitic manganese steel compositions are provided in
Table 2.25. Other proprietary electrodes also are available. In fact, many manufacturers of austenitic manganese steel filler metals do not classify them according to
AWS A5.13 or AWS A5.21.8
Covered electrodes and flux cored electrodes are
suitable for building up worn components and for joining austenitic manganese steel components. Joining is
most commonly done with high-chromium (often 10%
Cr or more) austenitic manganese steel filler metals
because they have better resistance to hot cracking than
austenitic manganese filler metals with little or no chromium. Austenitic stainless steel filler metals such as
309L, 307 and 18-8 Mn also are often used for joining
austenitic manganese steels because these filler metals,
too, have better resistance to hot cracking in welding
applications than the austenitic manganese steel filler
metals. (18-8 Mn is a composition from ISO 3581
[stainless steel covered electrodes], ISO 14343 [bare
solid stainless steel wires] and ISO 17633 [stainless steel
tubular electrodes]).9
Table 2.26 shows all-weld metal compositions and
Table 2.27 shows as-welded mechanical properties
obtained in a study of a number of commercially available austenitic manganese steel self-shielded FCAW
8. American Welding Society (AWS), Specification for Surfacing Electrodes for Shielded Metal Arc Welding, AWS 5.13; and, Specification
for Bare Electrodes and Rods for Surfacing, AWS 5.21, Miami:
American Welding Society (AWS).
9. International Organization for Standardization (ISO), Covered
Electrodes for Manual Metal Arc Welding of Stainless and HeatResisting Steels, ISO 3581; Wire Electrodes, Strip Electrodes, Wires
and Rods for Fusion Welding of Stainless and Heat Resisting Steels,
ISO 14343; and, Tubular Cored Electrodes and Rods for Gas
Shielded and Non-Gas Shielded Metal Arc Welding of Stainless and
Heat-Resisting Steels, ISO 17633; Geneva, Switzerland: International
Organization for Standardization (ISO).
Table 2.25
Typical Electrodes for Arc Welding Austenitic Manganese Steels
AWS A5.13
Covered
Electrode
AWS A5.21
Flux Cored
Electrode
EFeMn-A
EFeMn-B
EFeMn-C
ERCFeMn-C
EFeMn-D
EFeMn-E
EFeMn-F
EFeMnCr
Typical Composition, %
C
Mn
Si
Cr
Ni
Mo
V
0.7
14
0.5
—
4
—
—
0.7
14
0.5
—
—
1
—
0.7
14
0.5
4
4
—
—
0.7
17
0.5
6
—
—
0.8
0.7
17
0.5
5
—
—
—
ERCFeMn-F
1.0
19
0.5
4
—
—
—
—
—
1
0.3
ERCFeMn-G
0.7
14
0.5
4
—
ERFeMn-H
0.5
14
0.5
6
1
ERCFeMnCr
0.5
15
0.5
15
1
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
127
Table 2.26
Chemical Composition of Austenitic Manganese Steel All-Weld-Metal Deposits for FCAW Wires
Deposit Composition, %
FCAW Wire
C
Mn
Si
Cr
Ni
Mo
V
N
M14A
M14B
M14C
M20A
M20B
MC15A
MC15B
MC15C
0.97
0.58
1.03
1.01
1.07
0.40
0.41
0.28
14.25
13.25
15.00
20.0
25.5
16.5
15.0
15.5
0.42
0.45
0.38
0.24
0.17
0.25
0.43
0.23
3.51
5.19
3.51
5.15
4.59
13.5
17.8
18.4
2.73
0.57
0.37
0.04
0.00
0.07
0.03
0.89
0.01
0.01
0.01
0.01
0.00
0.01
0.01
0.01
0.008
0.042
0.012
0.010
0.000
0.026
0.012
0.022
0.065
0.103
0.072
0.050
0.091
0.213
0.096
0.295
Source: Adapted from Kotecki, D. J., and V. B. Rajan, 1998, Work Hardening of Austenitic Manganese Hardfacing Deposits, Welding Journal 77(7): 293-s to 298-s.
Table 2.27
Mechanical Properties of Austenitic Manganese Steel Weld Metal Produced by Self-Shielded FCAW
Deposit Type
Test Specimen
Tensile, MPa (ksi)
Yield, MPa (ksi)
% Elongation
3000 kg Brinell
Ordinary Austenitic Manganese
A 36
N.M.
N.M.
N.M.
166
Rich Austenitic Manganese
Austenitic Manganese-Chromium
M14A
M14B
M14C
M20A
M20B
MC15A
MC15B
MC15C
698 (101.2) 816 (118.3) 812 (117.8) 871 (126.3) 889 (129.0) 888 (128.8) 951 (137.9) 833 (120.8)
597 (86.6) 545 (79.0) 617 (89.5) 634 (92.0) 696 (101.0) 606 (87.9) 645 (93.5) 703 (101.9)
11
19
16
23
24
33
31
10
250
246
255
268
261
274
263
266
Source: Adapted from Kotecki, D. J., and V. B. Rajan, 1998, Work Hardening of Austenitic Manganese Hardfacing Deposits, Welding Journal 77(7): 293-s to 298-s.
electrodes.10 It should be noted that the “rich austenitic
manganese” (20% to 25% Mn) and the Mn-Cr electrodes in general produced weld metal with significantly higher yield strength than the 13% to 15% Mn
electrodes with low Cr content. The excellent notch
toughness of Mn-Ni weld metal is shown in Table 2.28.
Covered electrodes and flux cored electrodes should
be stored and used according to the manufacturers’ recommendations. Weld joints with excellent mechanical
properties and cracking resistance can be produced using
covered and flux cored electrodes when the phosphorus
content is low (less than 0.03%), and manufacturers of
these electrodes strive for even lower P content.
Composite electrodes with a phosphorous content
below 0.030% are recommended for fabrication and
repair welding. In many applications, austenitic manganese steel can be directly joined to carbon steel or lowalloy steel using low-phosphorus austenitic manganesechromium steel electrodes. The welding procedures
selected should minimize dilution with the carbon steel
or low-alloy steel.
10. Kotecki, D. J., and V. B. Rajan, 1998, Work Hardening of Austenitic
Manganese Hardfacing Deposits, Welding Journal, 77(7): 293-s to 298-s.
Table 2.28
Charpy V-Notch Impact Strength of
Austenitic Manganese-Nickel Steel
Weld Metal at Room and Low Temperatures
Test Temperature
Impact Strength
°C
°F
J
ft·lb
24
–18
–59
–1010
75
0
–75
–1500
160
130
108
75
118
96
80
55
In addition to austenitic manganese steel electrodes,
several other electrode compositions are available
for welding austenitic manganese steel. The corrosionresistant manganese-chromium and chromium-nickelmanganese compositions are among the most commonly used. They provide significant advantages for
certain applications: higher ability to work-harden
rapidly under impact, and higher tolerance for dilution
when joining austenitic manganese steel to carbon steel
128
CHAPTER 2—HIGH-ALLOY STEELS
or low-alloy steel. However, a disadvantage of using the
higher chromium, corrosion-resistant weld metal
deposits is that they are difficult to cut with oxyfuel cutting methods. Austenitic chromium-nickel corrosionresistant steel electrodes also may be used to weld austenitic manganese steels to carbon steels or to deposit a
buttering layer on the carbon steel before depositing
austenitic manganese steel.
Welding Conditions
Work-hardened metal is more susceptible to cracking
than as-quenched metal. Cracks or other defective areas
should be removed by grinding or by air-carbon arc
gouging prior to welding any work-hardened metal.
During metal removal, as with welding, the steel should
not be overheated.
Preheat should not be used. The interpass temperature of the metal adjacent to the weld should not exceed
about 315°C (600°F) after a one-minute period to
avoid excessive heating and embrittlement of the heataffected zone.
The welding heat input should be the minimum
required to obtain complete fusion and joint penetration. A short arc length and direct current (electrode
positive) should be used to deposit stringer beads. Intermittent welding may be used to limit heat buildup. If
peening the weld bead to upset it and relieve welding
stresses is desired, peening should be done while the
weld bead is very hot.
When depositing weld buildup on an approximately
vertical surface, the recommended technique is to stack
a series of horizontal stringer beads one on top of
another, deposited at relatively high travel speed. Rock
crusher mantles and crusher cones routinely are rebuilt
with this method. As mentioned, it is important to limit
temperature buildup in the workpiece and in the weld
buildup.
Multiple-pass welds are preferred over single-pass
welds to minimize temperature buildup. Heat input
must be controlled and interpass temperature and
adherence to restrictions must be followed in weldments
involving austenitic manganese steel.
Semiautomatic or automatic arc welding may be performed with tubular electrodes. These methods are
advantageous for shop operations. Heat input into the
base metal is less than with shielded metal arc welding
because smaller electrodes and higher travel speeds can
be used.
Commonly produced SMAW electrodes and selfshielded FCAW electrodes for depositing austenitic
manganese steel weld metal are available in a variety of
sizes. Table 2.29 shows operating ranges for common
sizes, according to the manufacturer’s technical literature.
AWS WELDING HANDBOOK 9.4
Table 2.29
Typical Operating Ranges for
Austenitic Manganese SMAW
and Self-Shielded FCAW Electrodes
Diameter, mm (in.)
Current Range, Amps
SMAW Electrodes
3.2 (1/8)0
4.0 (5/32)
4.8 (3/16)
Diameter, mm (in.)
95–105
130–140
175–225
Current Range,
Amps
Voltage Range,
Volts
FCAW Electrodes
5/64 (2.0)
7/64 (2.8)
240–360
400–550
24–29
26–30
Repair Welding
The buildup of worn areas of equipment is the most
common repair application of austenitic manganese
steel. The service life of hard-surfaced areas subject to
extreme wear may be appreciably extended.
In rebuilding worn areas, it is important to determine
whether the surfaces have become work hardened in
service. These surfaces should be removed before resurfacing to prevent possible cracking in the heat-affected
zone and subsequent spalling of the weld metal. The
hardness of the exposed surface should be checked to
ensure that all work-hardened metal has been removed.
Cracked or broken castings can be repaired by welding. To prepare the workpiece for welding, the crack
should be removed by grinding or air carbon-arc gouging, leaving a generous radius at the bottom and at each
end of the groove. Welding should progress from the
end to the start of the groove to minimize welding
stresses. Intermittent (skip) welding can minimize heat
buildup, and each bead can be peened while hot. Austenitic manganese steel or austenitic stainless steel electrodes (such as Types 307, 308, 309, 310, 312 or 18-8
Mn) may be used for the repair of cracks. The stainless
steel filler metals 307, 312 and 18-8 Mn generally have
better crack resistance than austenitic manganese steel
filler metals or the other stainless steels. Type 312 filler
metal generally does not provide as much toughness as
the other stainless filler metals.
Foundry repairs of casting defects by welding are
made after solution-heat treatment and quenching. This
is because castings in the as-cast condition are too brittle and are prone to cracking during welding. The faces
of a cavity to be filled should have a bevel of at least
15 degrees to provide ready access for welding.
AWS WELDING HANDBOOK 9.4
Dissimilar Steels
CHAPTER 2—HIGH-ALLOY STEELS
129
while fewer chromium carbides are apparent in Figure
2.21. In contrast, Figure 2.22 shows an interface
between austenitic manganese base metal and austenitic
manganese-molybdenum weld metal deposited by shielded
metal arc welding. In this case, dilution has no significance, as there are no carbides along the interface.
Austenitic manganese steel can be welded to carbon
steel or low-alloy steel with austenitic manganese steel
electrodes. Proper welding procedures must be used.
Best results are obtained when the filler metal contains
more than 14% manganese, more than 10% chromium
and less than 0.03% phosphorus, and when dilution
with the carbon steel or low-alloy steel is 25% or less.
Otherwise, cracking may occur. Carbon steel or lowalloy steel filler metal should not be used because the
deposit will become martensitic, resulting in poor
toughness. In many cases, the use of 307 or 18-8 Mn
filler metal provides the best combination of crack resistance and toughness for joints in dissimilar steels.
Austenitic manganese-chromium electrodes are preferred when the weld will be subject to wear and when
high yield strength is needed. Type 307, 308, 309, 310,
312, or 18-8 Mn stainless steel filler metal can be used
when the welded joint will be exposed to little or no
wear and to only moderate stresses. The weld interface
may be hard and brittle if the dilution is excessive, because of the high carbon in the austenitic manganese steel.
Figure 2.20 shows a weld interface between cast
austenitic manganese steel and AWS Class E308 chromium-nickel stainless steel weld metal deposited by
shielded metal arc welding. The weld metal in Figure
2.21 was deposited using an austenitic manganesechromium electrode containing 16.5% manganese and
16.6% chromium. The dilution at the interface is Figure 2.21—Weld Interface between Cast Austenitic
apparent in both microstructures. In Figure 2.20, fine Manganese Steel (left) and Austenitic Manganesechromium carbides are apparent along the interface,
Chromium Steel Weld Metal (right) (x250)
Figure 2.20—Weld Interface between Cast
Austenitic Manganese Steel (left) and Type
308 Stainless Steel Weld Metal (right) (x250)
Figure 2.22—Weld Interface between Cast Austenitic
Manganese Steel (left) and Austenitic ManganeseMolybdenum Steel Weld Metal (right) (x250)
130
CHAPTER 2—HIGH-ALLOY STEELS
APPLICATIONS
A few of the many applications of high-alloy steel are
represented by classic examples of weldments used in
the fabrication of a solid-fuel motor chamber from
maraging steel, the welding of a K92580 tubular steel
bicycle, and weldments used in manganese steel castings
of railroad accessories.
SOLID-FUEL ROCKET MOTOR CHAMBER
During the 1970s, the United States Air Force and
the National Aeronautics and Space Administration
experimented with maraging steels to fabricate largediameter solid-fuel rocket motor chambers such as
the one shown in Figure 2.23. Maraging steels were
selected for these applications because they were readily
formed and welded; they required aging heat treatment
only after fabrication; they had excellent dimensional
stability during heat treatment; and they had superior
fracture toughness at yield strength levels above
1380 MPa (200 ksi). Although this example is somewhat dated, it still is suitable for showing the utility of
maraging steel in the construction of a complex, largescale structure.
Gas tungsten arc welding (GTAW) proved to be the
most reliable welding process for fabricating the rocket
motor chamber. This process provided sufficient gas
shielding to protect the face and root of the weld from
excessive oxidation, and so maintained the required
toughness. Standard precautions included the removal
of surface scale from the face of each weld prior to
AWS WELDING HANDBOOK 9.4
depositing subsequent weld beads, to minimize porosity. Welding wire surfaces were cleaned also, to minimize porosity and hydrogen cracking.
The rocket motor chamber shown in Figure 2.23 was
fabricated by the use of mechanized welding operations
and conventional joint designs (e.g., single-U, double-U,
and V joints). All welds were deposited in the flat position to ensure maximum reliability during the welding
operation, and grooved backing bars were used to
direct the inert gas to both sides of the root bead.
Figure 2.24 shows a single-U joint in 12.5 mm
(0.5 in.) maraging steel plate, typical of the joint designs
used in this application. A 1.5 mm (0.06 in.) root land
and a zero root opening were used. No preheat was
applied, and the interpass temperature was maintained
below 93°C (200°F) to minimize austenite reversion. A
weld-pass sequence of 10 small stringer beads was specified, with low-to-intermediate heat input, to further
minimize austenite reversion. Parameters for the weld
pass sequence are presented in Table 2.30.
Each cylindrical section of the rocket motor chamber
was fabricated from two plates that were roll-formed
into a semicircular profile, and then joined with two
longitudinal welds. The cylindrical sections were subsequently placed on power-driven rolls and joined by circumferential welds deposited in the flat position.
The hemispherical head for the rocket motor chamber was formed out of multiple gores, as diagrammed in
Figure 2.25. Elaborate fixturing was required in order
30
12.5 mm (0.5 in.)
1.52 mm
(0.06 in.)
R = 2.38 mm
(0.094 in.)
8
Figure 2.23—Solid-Fuel Rocket Motor Chamber
9
7
6 5
4
3
2
1
10
Figure 2.24—Joint Design and Weld Pass
Sequence for Typical Gas Tungsten Arc
Weld in Rocket Motor Chamber
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
131
Table 2.30
Parameters for GTAW of 12.5 mm (0.5 in.) Maraging
Steel Plate in Fabrication of Solid Rocket Motor Chamber
a.
b.
c.
d.
Weld Passa
Ampsb
Volts
Travel Speed
mm/s (in./min)
Wire Feed Speedc
mm/s (in./min)
Orifice Gas Flowd
L/min (ft3/h)
Backup Gas Flow
L/min (ft3/h)
1
150
10
2.5 (6)
7.6 (18)
11.8 (25)
4.7 (10)
2
150
.8.5
2.5 (6)
7.6 (18)
11.8 (25)
4.7 (10)
3
160
10
2.5 (6)
24 (10.2)
11.8 (25)
4.7 (10)
4
160
10
2.5 (6)
24 (10.2)
11.8 (25)
4.7 (10)
5
180
10
2.5 (6)
24 (10.2)
11.8 (25)
4.7 (10)
6
180
10
2.5 (6)
24 (10.2)
11.8 (25)
4.7 (10)
7
180
10
3.0 (7)
24 (10.2)
11.8 (25)
4.7 (10)
8
180
10
3.0 (7)
24 (10.2)
11.8 (25)
4.7 (10)
9
180
10
3.0 (7)
24 (10.2)
11.8 (25)
4.7 (10)
10
180
10
4.2 (10)
24 (10.2)
11.8 (25)
4.7 (10)
3.2 mm (1/8 in.) thoriated tungsten electrode.
Direct current, electrode negative.
1.6 mm (1/16 in.) filler wire.
Using argon shielding gas.
Figure 2.25—Diagram of Gores in Head
Assembly of Rocket Motor Chamber
to deposit flat-position welds for the chamber head
assembly. An internal fixture conforming to the inside
dimension of the head was mounted on a welding positioner capable of tilting. The gore sections were then
placed on the internal fixture, and held in place by more
external fixturing.
Once the gores were in position, the head assembly
was tack-welded to maintain alignment. Then the tack
welds were ground so that they would not interfere
with the actual welding operation. During welding, the
tilting speed of the positioner maintained the desired travel
speed as each joint traversed beneath the welding head.
Age hardening was performed on the completed
rocket motor chamber, which was fabricated entirely
out of solution-treated material. To perform this operation, a large furnace was constructed around the chamber. Air was heated and circulated through the furnace
with a gas-fired heat exchanger, and the chamber was
aged at about 482°C (900°F) for eight hours.
Despite the extensive precautions taken in the welding procedures of the rocket motor chamber, porosity in
the maraging steel weldments was still a major concern.
Porosity is particularly troublesome in large multiplepass welds such as those used in this application.
Hydrogen is the major cause of porosity in weld metal,
and weld cracking may be encountered whenever
hydrogen is introduced in amounts exceeding 5 ppm.
Radiographic, ultrasonic, and liquid-penetrant examination techniques were available to inspect the maraging steel weldments in the chamber.
WELDING K92580 TUBING
One application for K92580 tubing has been in racing bicycle frames such as the one shown in Figure 2.26.
Frames are fabricated from tubing with 0.51 mm
(0.020 in.) wall thickness. Welding this material requires special setup and techniques because of the high
hardness, tensile strength, and ductility of this alloy.
132
CHAPTER 2—HIGH-ALLOY STEELS
AWS WELDING HANDBOOK 9.4
REPAIR WELDING RAILROAD FROGS AND
CROSSING DIAMONDS
from austenitic manganese steel, an extremely tough,
nonmagnetic alloy with unique properties that differ
from those of common structural and wear-resistant
steels. One of these properties is its capacity for work
hardening at the surface under impact while the underlying body retains its original toughness. Metal-tometal wear resistance of austenitic manganese steel is
excellent, which is essential in rail applications.
For rail track-work castings, the American Railway
Engineering Association (AREA) requires conformance
with ASTM A 128, Standard Specification for Steel
Castings, Austenitic Manganese, except for slightly
modified chemical requirements that include 1% to
1.3% carbon and a minimum of 12% manganese.11
The high manganese content stabilizes the austenite
by retarding its transformation to other structures. Silicon acts mainly as a deoxidizer, while phosphorus is
limited because it tends to promote hot cracking during
casting as well as in subsequent welding operations.
Manganese steel castings may be relatively brittle
before heat treatment, as normal cooling rates in the
mold are too slow to retain a fully austenitic structure.
However, this is rectified by heating and holding at the
appropriate austenitizing temperature (generally between
1010°C to 1066°C [1850°F and 1950°F]), then quenching in cold, agitated water. Proper procedures are
important, because either inadequate austenitizing or
cooling too slowly can result in excessive carbides that
will lower the mechanical properties. Reheating manganese steels also can cause carbide precipitation resulting
in embrittlement, with the degree of embrittlement
depending on exposure time and temperature. Thus, it
is necessary to use welding procedures that will minimize or avoid prolonged overheating.
Figure 2.27 shows a manganese “frog” casting. Historically, a manganese-based formulation has been used
in electrodes and wire intended for the repair welding
of manganese castings. However, research has shown
that greater resistance to hot cracking may be achieved
by depositing a light layer of austenitic stainless steel
weld metal (e.g., 307, 308L, 309L, 310, 312, or 18-8
Mn) to seal cracks prior to building up the surface with
an austenitic manganese steel electrode. Evidence indicates that cracks in the base casting will grow along the
austenite boundary until they reach the stainless steel
deposit. The deposit retards the growth of the cracks
and protects the weld deposit.12
Lower heat input while welding also can help reduce
hot cracking. Wire-fed welding processes that favor
lower heat input are highly recommended in preference
to shielded metal arc welding.
The stresses incurred by railroad frogs and crossing
diamonds require that they be made of a material with
high strength and durability that will resist failure
under impact and heavy loading. To achieve these properties, railroad frogs and crossings typically are cast
11. ASTM International, 2007, Standard Specification for Steel Castings, Austenitic Manganese, A 128/A 128M-93 (2007), West Conshohocken, Pennsylvania: ASTM International.
12. Meade, B, 1997, Railroad Welding Demands Specialized Processes, Welding Journal 76(9): 47–52.
Figure 2.26—Racing Mountain Bicycle
Frame Made from K92580 Tubing
The tubing manufacturer receives annealed strip
from the mill, then forms, prepares, and welds tubing
without the use of filler rod. After welding and planishing, the tubing undergoes a precise series of drawing
and heat treatment cycles to achieve its full metallurgical and mechanical properties. The tubes are then
placed in inventory for shipping.
Tubing sections are joined using the gas tungsten arc
welding (GTAW) process. Current is set at 20 A to 30 A
DCEN, at 8 V to 9 V. Argon shielding gas is used, with
post-purge of 12 seconds to 15 seconds. Mitres are
made with a bench grinder, maintaining a clearance of
0.025 mm (0.001 in.). After fitup, the tubes are set in a
fixture, tacked, and then welded with the GTAW process, using 0.9 mm (0.035 in.) or 0.51 mm (0.020 in.)
welding wire.
Weld penetration to 75% of the tube wall thickness
is desirable to minimize residual stresses in the
unwelded portion of the joint. However, complete joint
penetration must be avoided, because the inside diameter of the tubing is not purged, and penetrating the
inner wall could introduce oxygen into the molten weld
metal, which would result in pinholes. The practice of
maintaining an argon purge for 12 seconds to 15 seconds
is intended to prevent oxidation of the weld.
AWS WELDING HANDBOOK 9.4
CHAPTER 2—HIGH-ALLOY STEELS
133
dard is published by the American Welding Society and
can be downloaded from the Internet at www.aws.org.
ANSI Z49.1 discusses the ventilation required during
welding. Further information concerning ventilation
can be found in AWS F3.2, Ventilation Guide for Weld
Fume.15
The five major factors governing the quantity of
fumes in the atmosphere to which welders and welding
operators are exposed during welding are the following:
Figure 2.27—Close-Up View of Crack in
the Damaged Area of a Manganese Steel
Frog Casting Used on Railroad Tracks
SAFE PRACTICES
Safe practices for welding, brazing, soldering, and
cutting are presented comprehensively in Chapter 17 of
the Welding Handbook, 9th edition, Volume 1; thus,
safe practices for welding, brazing or joining are not
fully addressed in this section.13 Safety and health concerns regarding the metals and materials discussed in
this chapter are covered briefly in this section.
Welding fumes from the more commonly welded
materials, e.g., carbon- and low alloy steels and stainless steels, are fairly well characterized, and there is a
good basis for developing exposure limits for personnel.
The unusual compositions of the high alloy steels, however, may produce fume or other exposures that depart
from these more common norms. Users should be
aware of this, and apply exposure and ventilation standards with due care.
The American National Standards Institute (ANSI)
standard, Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1, should be consulted.14 This stan-
13. Welding Handbook Committee, Jenney, C. L. and A. O’Brien,
ed., 2001, Welding Handbook, Vol. 1, Welding Science and Technology,
Chapter 17, Miami: American Welding Society.
14. American National Standards Institute (ANSI) Accredited Standards Committee Z49, 2005, Safety in Welding, Cutting, and Allied
Processes, ANSI Z49.1:2005, Miami: American Welding Society.
Available on the Internet at www.aws.org.
1. Dimensions of the space in which welding is
done (with special attention to the height of the
ceiling);
2. Number of welders working in that space;
3. Rate of evolution of fumes, gases, or dust,
according to the materials and processes used;
4. The proximity of the welders to the fumes, as
these fumes issue from the welding zone, and to
the gases and dusts in the space in which they are
working; and
5. The ventilation provided to the space in which
the welding is performed.
For purposes of assessing the exposure of welders
and others in the workspace, measurement of fume concentrations in the worker’s breathing zone may be
appropriate. If so, reference to AWS F1.3, A Sampling
Strategy Guide for Evaluating Contaminants in the
Welding Environment,16 is suggested.
A comprehensive list of safety and health codes and
standards for the welding and related industries is
included in Appendix A of this volume. The Safety and
Health Fact Sheets published by the American Welding
Society (listed in Appendix A) may be downloaded and
printed directly from the AWS website at www.aws.org.
The Safety and Health Fact Sheets are revised periodically and updated sheets are added.
CONCLUSION
The high-alloy steels discussed in this chapter contain more than about 10% total alloying elements, and
in many cases, more than 25% total alloy content.
Thus, by composition and alloy expense alone, these
15. American Welding Society (AWS) Committee on Safety and Health,
2001, Ventilation Guide for Weld Fume, AWS F3.2M/F3.2:2001,
Miami American Welding Society.
16. American Welding Society (AWS) Committee on Safety and
Health, 2006, A Sampling Strategy Guide for Evaluating Contaminants in the Welding Environment, AWS F1.3M:2006. Miami: American
Welding Society.
134
CHAPTER 2—HIGH-ALLOY STEELS
materials are costly. In addition to this cost, ultra-highstrength steels generally require vacuum processing,
special control of impurities, and multiple-step heat
treatment to develop the full potential for strength and
toughness. These metals typically are only used in applications requiring a special combination of strength and
toughness. As a result, the typical quality levels generally used for most welding fabrications may not be
adequate to maintain the superior properties required
for the applications for which these type steels would be
selected. That is, the quality requirements carry through
the full range of welding fabrication, from weld preparation and cleanliness, to gas purity and final inspections.
Consequently, these materials generally are specified
only for specialized applications when the property
needs of the application warrant the additional costs
associated with the purchase and fabrication.
The weldability of these steels generally is excellent,
with little or no preheat required. The steels that rely on
the precipitation-hardening mechanism, such as some
of the Ni-Co steels and the maraging steels, require special consideration, especially with respect to heat input.
The limitation of low heat input that is often necessary
for these materials limits productivity, especially if compared to low-alloy, high-strength steels, and stainless
steels. However, when required for critical applications,
properly fabricated weldments of these high-alloy steels
provide functional and successful service.
In contrast to the ultra-high-strength steels, the austenitic manganese steels described in this chapter
require care only to avoid overheating the steel and to
avoid hot cracking during welding. Otherwise, they are
relatively simple to weld, and have many welding characteristics in common with austenitic stainless steels.
BIBLIOGRAPHY
American National Standards Institute (ANSI) Accredited Standards Committee Z49. 2005. Safety in
welding, cutting, and allied processes. ANSI
Z49.1:2005. Miami: American Welding Society.
Available on the Internet at www.aws.org.
American Welding Society (AWS) Committee on Definitions and Symbols. 2010. Standard welding terms
and definitions. AWS A3.0M/A3.0:2010. Miami:
American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. W. R. Oates, ed. 1996. Materials and
Applications—Part 1. Welding handbook. Vol. 3.
8th ed. Miami: American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. Jenney, C. L. and A. O’Brien, eds. 2001.
AWS WELDING HANDBOOK 9.4
Welding science and technology. Vol. 1. 9th ed.
Welding handbook. Miami: American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. O’Brien, A., ed. 2007. Welding processes—Part 2. Welding handbook. Vol. 3. 9th ed.
Miami: American Welding Society.
American Welding Society (AWS). 2000. Specification
for surfacing electrodes for shielded metal arc welding. AWS 5.13:2000. Miami: American Welding
Society.
American Welding Society (AWS). 2001. Specification
for bare electrodes and rods for surfacing. AWS
5.21:2001. Miami: American Welding Society.
ASTM International. 2007. Standard specification for
steel castings, austenitic manganese. A 128/A 128M93 (2007). West Conshohocken, Pennsylvania: ASTM
International.
International Organization for Standardization (ISO).
Covered electrodes for manual metal arc welding
of stainless and heat-resisting steels. ISO 3581.
Geneva, Switzerland: International Organization for
Standardization.
International Organization for Standardization (ISO).
Wire electrodes, strip electrodes, wires and rods for
fusion welding of stainless and heat resisting steels.
ISO 14343. Geneva, Switzerland: International
Organization for Standardization.
International Organization for Standardization (ISO).
Tubular cored electrodes and rods for gas shielded
and non-gas shielded metal arc welding of stainless
and heat-resisting steels. ISO 17633. Geneva, Switzerland: International Organization for Standardization.
Kotecki, D. J. and V. B. Rajan. 1998. Work hardening
of austenitic manganese hardfacing deposits. Welding journal 77(7): 293-s–298-s.
Meade, B. 1997. Railroad welding demands specialized
processes. Welding journal 76(9): 47–52.
Robino, C. V., P. M. Novotny, J. R. Michael, and D. A.
Englehart. 1999. Fusion welding of AerMet® 100
Alloy. Report SAND99-1833. Albuquerque, New
Mexico: Sandia National Laboratories.
Society of Automotive Engineers (SAE) Aerospace
Materials Division. Aerospace Materials Specification (AMS). Steel, maraging, welding wire, 18Ni 8.0Co - 4.9Mo - 0.40Ti - 0.10Al, vacuum induction
melted, environment controlled packaging. AMS
6501. Warrendale, Pennsylvania: Society of Automotive Engineers.
Society of Automotive Engineers (SAE) Aerospace
Materials Division. Aerospace Materials Specification (AMS). Wire, steel welding, 18.5Ni - 8.5Co 5.2Mo - 0.72Ti - 0.10Al, vacuum melted, environment controlled packaging. AMS 6463. Warrendale,
Pennsylvania: Society of Automotive Engineers.
AWS WELDING HANDBOOK 9.4
SUPPLEMENTARY
READING LIST
Ayer, R. and P. M. Machmeier. 1996. Microstructural
basis for the effect of chromium on the strength and
toughness of AF1410-based high performance steels.
Metallurgical and materials transactions A 27A(9):
2510–2517.
Chinella, J. F. 1993. Mechanical properties and microstructure of thermomechanically processed, high
manganese steel. ARL-TR-146, DTIC file no. ADA269 321. Watertown, MA: U.S. Army Research
Laboratory.
Bailey, N. 1971. Weldability and toughness of maraging
steel. Metal construction 3(1): 1–5.
Bailey, N. and C. Roberts, 1978. Maraging steel for
structural welding. Welding journal 57(1): 15–28.
Blauel, J. G., H. R. Smith, and G. Schulze. 1974. Fracture toughness study of Grade 300 maraging steel
weld joint. Welding journal 53(5): 211s–8s.
Brown, W. F. Jr., Ed. 2000. Aerospace structural metals
handbook. West Lafayette, Indiana: CINDAS/Purdue
University.
Connor, L. P. and A. M. Rathbone. 1964. Welding
characteristics of 12Ni-5Cr-3M0 maraging steel.
United States steel report (40.018-002) (12). DTIC
file no. AD-600 736.
Garrison, W. M., Jr. 1992. An investigation of the role
of second phase particles in the design of ultra-highstrength steels of improved toughness. U.S. Army
research office. DTIC file no. AD-A266 774.
Garrison, W. M. Jr. 1990. Ultra-high-strength steels for
aerospace applications. Journal of metals 42(5): 20–
24.
Khare, A. K. 1993. Production and evaluation of an
AF1410 liner for high pressure application. Proceedings of the 1993 Pressure Vessels and Piping Conference. PVP v263: 155–163.
CHAPTER 2—HIGH-ALLOY STEELS
135
Lang, F. H. and N. Kenyon. 1971. Welding of maraging
steels. Bulletin 159. New York: Welding Research
Council.
Little, C. D. and P. M. Machmeier. 1975. Development
of a weldable high strength steel. Technical report
AFML-TR-75-148. Wright Patterson air force base.
Ohio: Air Force Materials Laboratory.
National Aeronautics and Space Administration
(NASA). 1968. The metallurgy, behavior, and application of the 18-percent nickel maraging steels – a
survey. NASA SP-5051. Washington DC: National
Aeronautics and Space Administration.
Novotny, P., R. D. Nye, and C. V. Robino. 1995. Fabricating characteristics of an ultra-high-strength steel.
Welding journal 74(2): 51–54.
Pelletier, J. M., F. Oucherif, P. Sallamand, and A. B.
Vannes. 1995. Hadfield steel coatings on low carbon
steel by laser cladding. Materials science & engineering A A202(1-2): 142–147.
Pepe, J. J. and W. F. Savage. 1970. The heat-affected
zone of the 18Ni maraging steels. Welding journal
49(1): 545s–53s.
Roa, K. P. and P. V. Venkitakrishnan. 1993. Electron
beam welding of M-250 maraging steel. Practical
metallography 30(3): 135–136.
Rorhbach, K. and M. Schmidt. 1991. Maraging Steels.
Metals handbook: properties and selection: irons,
steels, and high-performance alloys. Vol. 1. 10th ed.
793–800. Materials Park, Ohio: ASM International.
Sinha, P. P., S. Arumugham, and K. V. Nagarajan. 1993.
Influence of repair welding of aged 18Ni 250 maraging steel weldments on tensile and fracture properties. Welding journal 72(8): 391s–6s.
Tsay, L. W., W. B. Huang, and C. Chen. 1997. Gaseous
hydrogen embrittlement of T-250 laser welds. Journal of materials engineering and performance 6(2):
182–186.
Xiaofeng, C., J. Li, Z. Li, and F. Liu. 1994. Study on
local heat transfer of 18Ni maraging steel after electron beam welding. Steel research 65(12): 557–560.
Yushchenko, K. A. 1995. Materials for aerospace welded
structures. Welding research abroad 41(12): 33–34.
137
AWS WELDING HANDBOOK 9.4
CHAPTER
C H A P T E3 R 9
Prepared by the
Welding Handbook
Chapter Committee
on Coated Steels:
G. W. Dallin, Chair
GalvInfo Center
COATED STEELS
C. Jiang
AET Integration, Inc.
A. F. Gibson
Palmate Technologies
T. J. Langill
American Galvanizing
Association
D. F. Toner
Consultant
Welding Handbook
Volume 4 Committee
Member:
D. D. Kautz
Los Alamos National
Laboratory
Contents
Photograph courtesy of American Galvanizers Association—Galvanized Steel Structure, Delta Port Expansion
Introduction
138
Terneplate
138
Tin-Plated Steel
(Tinplate)
142
Joining Processes
for Tinplate
143
Galvanized Steels
145
Aluminized Steels
186
Chromized Steels
193
Other Coated Steels
196
Painted Steels
207
Applications
209
Safe Practices
216
Bibliography
217
Supplementary
Reading List
218
138
AWS WELDING HANDBOOK 9.4
CHAPTER 3
COATED STEELS
INTRODUCTION
One of the most active segments of the steel industry
is the fabrication of metal-coated and prepainted steel
products made of sheet steel. Coated sheet steel is supplied by manufacturers in coils produced on continuous
coating lines. Products made of coated steels provide
the following advantages over sheet steels that are
metallic-coated or painted after fabrication: lower production costs; more consistent product quality; less
energy usage; easier compliance with environmental,
health, and safety concerns; and quick response to market
changes.
Metallic or paint coatings usually are applied to provide a protective surface to improve resistance to oxidation
and corrosion or to provide a decorative finish to a product. Welding coated steels is the major topic of this chapter.
Metallic coatings are applied by hot dipping, thermal
spraying, or electro-deposition. The five common types
of metal-coated steels discussed in this chapter are the
following:
1. Terneplate, coated with lead alloyed with a small
amount of tin;
2. Tinplate, coated with tin;
3. Galvanized steels, coated with zinc or zinc alloys;
4. Aluminized steels, coated with aluminum or aluminum alloys; and
5. Chromized steels, coated with chromium or chromium alloys.
Coating designations for continuous hot-dipped sheet
metals generally are based on the total mass (weight) of
the coating on both sides per unit area of sheet; however, electrogalvanized sheet is designated by mass per
unit area of each surface.
Paints used for coatings on steel may be either
organic or inorganic and may have a zinc fill (zinc powder added to the paint). Organic paints include epoxies,
lacquers, acrylics, polyurethanes, polyesters, and polyvinyl chloride. Inorganic paints may be sodium silicate,
ethyl silicate, or another inorganic material, and usually
have a zinc fill.
Products or components made from coated steel are
joined by fusion welding processes (e.g., resistance, arc,
arc stud, friction, and laser beam), brazing, braze welding, soldering, adhesive bonding, and mechanical joining or interlocking. These processes can be used alone,
or in combination with another process, such as weld
bonding. The welding processes are discussed individually under the heading of each the five types of coated
steel described in this chapter. (Mechanical joining and
adhesive bonding processes are not included.)
When coated steels are fusion welded, the effectiveness of the coating adjacent to the weld often is significantly degraded by the heat of welding. The metallic
coating melts and then may alloy with the steel, or it
may oxidize or volatilize. An organic (resinous) coating
usually is scorched, burned or charred. The result is a
coating of reduced usefulness adjacent to the weld. A
reconditioning operation often is required to restore
corrosion resistance or the desired visual appearance to
the affected areas. These topics and others are discussed
in this chapter.1, 2
TERNEPLATE
Terneplate, or terne, is sheet steel coated with a leadtin alloy. The minimum tin content normally is 8%,
with higher percentages used if required by the type of
1. Standard welding terms and definitions are used throughout this
chapter as published in American Welding Society (AWS) Committee
on Definitions and Symbols, 2010, Standard Welding Terms and Definitions, AWS A3.0M/A3.0:2010. Miami: American Welding Society.
2. At the time of the preparation of this chapter, the referenced codes
and other standards were valid. If a code or other standard is cited
without a date of publication, it is understood that the latest edition
of the document referred to applies. If a code or other standard is
cited with the date of publication, the citation refers to that edition
only, and it is understood that any future revisions or amendments to
the code or standard are not included; however, as codes and standards undergo frequent revision, the reader should consult the most
recent edition.
AWS WELDING HANDBOOK 9.4
coating equipment in use. Terne formerly was used in
large quantities for roofing, but has been replaced in the
United States market to a large extent by either galvanized sheet steel or zinc-based alloy-coated sheet steel,
notably Galvalume.™ The welding of these two types of
coated steels is discussed in this section. 3
Much of terneplate production is consumed in the
manufacture of gasoline tanks for vehicles. The tanks
are made either from two drawn halves, which are subsequently joined by resistance seam welding, or may be
made from rolled cylinders that are lock-seamed and
soldered. Many other vehicle components, such as tubing, are terne coated; however, these generally are
coated after welding. Another area of use for terne in
which joining is important is the manufacture of burial
caskets, with the exposed side polished to a high luster.
Seam welding or soldering of lock-seam joints are common joining processes for this application.
Standard coatings for terneplate, as specified by
ASTM A 308/A 305M, are listed in Table 3.1.4
WELDING AND JOINING PROCESSES
Two variations of resistance welding, seam welding
and spot welding, and an arc welding process, gas tungsten arc welding, are the major processes used to join
terneplate. Soldering also can be used. These processes
are discussed in detail in Volumes 2 and 3 of the Welding
Handbook, 9th edition.5
Resistance Seam Welding
Resistance seam welding (RSEW) is a resistance
welding process producing a weld at the faying surfaces
of overlapped parts progressively along a length of a
joint. The weld may be made with overlapping weld
nuggets, a continuous weld nugget, or by forging the
joint as it is heated to the welding temperature by resistance to the flow of the welding current.
Resistance seam welding is commonly used to join
formed sheets of terne to make leak-tight containers for
fluids or gases. The typical thickness of steels used for
leak-tight applications is 0.6 millimeters (mm) to 1.6 mm
(0.025 inches [in.] to 0.062 in.); the coating weight (on
one or both sides) usually is 50 grams per square meter
3. Galvalume is a registered trademark of BEIC International, Inc.
4. ASTM International, Subcommittee A05.11, 2006, Standard Specification for Steel Sheet, Terne (Lead-Tin Alloy) Coated by the Hot-Dip
Process, ASTM A 308/A 308M-06, West Conshohocken, Pennsylvania:
ASTM International.
5. American Welding Society (AWS) Welding Handbook Committee,
2007, Welding Processes—Part 2, Volume 3 of the Welding Handbook, 9th edition, Chapter 1, Resistance Spot and Seam Welding; and
WHC, 2004, Welding Processes—Part 1, Volume 2 of the Welding Handbook, 9th edition, Chapter 13, Soldering, Miami: American Welding
Society.
CHAPTER 3—COATED STEELS
139
Table 3.1
Standard Terneplate Coatings
(ASTM A 308/A 308M) a, b
Minimum Requirements
Triple-Spot Test
Single-Spot Test
SI Units
g/m2
g/m2
No minimumc
No minimumc
LTZ75
75
60
LTZ110
110
75
LTZ120
120
90
LTZ170
170
120
Coating Designation
LTZ01
LTZ260
260
215
LTZ335
335
275
Coating Designation
oz/ft2
oz/ft2
LT01
No minimumc
No minimumc
LT25
0.25
0.20
LT35
0.35
0.25
LT40
0.40
0.30
LT55
0.55
0.40
LT85
0.85
0.70
LT110
1.10
0.90
Inch-Pound Units
Note: Coating Thickness/Weight (Mass) Equivalence—The coating thickness
may be estimated from the coating weight (mass) by using the following
relationship: 75 g/m2 (0.25 oz/ft2) total both sides (LTZ75 [LT25]) is equal to
0.00508 mm (0.00027 in. or 0.27 mils) total both sides. This formula is not
to be used for calculation of tensile strength of the base metal, which must
be based on actual base metal thickness measurement.
a. The coating designation number is the term by which this material is
specified. The weight (mass) of coating in grams per square meter
(ounces per square foot) of sheet refers to the total coating on both
surfaces. Because of the many variables and changing conditions that
are characteristic of continuous terne coating, the terne coating is not
always evenly divided between the two surfaces of the terne-coated
sheet, nor is the terne coating always evenly distributed from edge to
edge. However, it can normally be expected that not less than 40% of the
single-spot check limit will be found on either surface.
b. As the performance for the long terne-coated sheet is related to the coating
thickness, material carrying the statement “meets ASTM A 308M (A 308)
requirements” should also specify the particular coating designation.
c. “No minimum” means that there are no established minimum requirements for triple- and single-spot tests.
(g/m2) to 127 g/m2 (0.16 ounces per square foot [oz/ft2]
to 0.42 oz/ft2). Steels thicker than 3.2 mm (0.125 in.) are
difficult to weld with this process.
Coated steel surfaces to be joined should be cleaned
to remove residues of dirt or oil. The joint is prepared
by pressing together the surfaces to be joined and forming a lap or flange joint to be welded with a seam
140
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
welding machine. Seam welding machines use two circular electrodes in the form of copper wheels that are
spaced with a gap that allows the prepared joint to
enter between the electrode wheels; then the machine
applies a predetermined force ranging from 2.2 kilonewtons (kN) to 4.4 kN (500 pounds [lb] to 1000 lb),
depending on the thickness of the steel. Some machines
use a single electrode wheel and a stationary mandrel.
Sufficient alternating current (ac), typically 17 000 amperes (A) to 22 000 A, depending on steel thickness, is
applied to fuse the two sheets making up the joint.
In a typical welding schedule, current is applied for
three cycles at 60 Hz (an interval of 50 milliseconds).
Then the current is shut off for two cycles at 60 Hz (an
interval of 33 milliseconds), and applied again for three
cycles. The copper electrode wheels can build up significant heat, thus the introduction of cooling water to the
electrodes is required, usually by flood cooling. Metal
oxides that transfer from the joint and accumulate on
the circular electrode (wheel) surfaces are removed
from the circumference by continuous cleaning.
The width of a typical electrode face is 5 mm to 8 mm
(0.20 in. to 0.31 in.); these electrodes produce seam
welds of approximately the same width. Typical welding
speeds are 25 millimeters per second (mm/s) to 42 mm/s
(60 inches per minute [in./min] to 100 in./min). Typical
conditions for seam welding terneplate are shown in
Table 3.2.
Table 3.2
Typical Resistance Seam Welding Conditions for Terneplate
Electrode Shapeb, c
Material Thickness (T)a
W
Electrode Net
Force
E
Approx. Weld Time,
Current Cycles (60 Hz)
Welding Speed
Min.
Contacting
Overlap, Lb
mm
in.
mm
in.
mm
in.
kN
lb
A
Heat
Cool
mm/s
in./min
mm
in.
0.6 to 0.6
0.025 to 0.025
9.5
0.38
6.4
0.25
2.9
650
20 000
1
3
27.9
66
11.1
0.44
0.8 to 0.8
0.031 to 0.031
10.0
0.41
5.5
0.22
2.8
620
18 500
3
2
41.7
98
11.1
0.44
0.8 to 0.8
0.031 to 0.031
12.7
12.7
0.50
0.50
7.1
7.1
0.28
0.28
4.0
4.0
900
900
17 000
18 000
3
5
2
2
25.4
42.3
60
100
11.1
11.1
0.44
0.44
0.9 to 0.9
0.036 to 0.036
12.7
12.7
0.50
0.50
7.1
7.1
0.28
0.28
4.4
4.4
1000
1000
17 500
18 500
2
5
1
1
25.4
42.3
60
100
12.7
12.7
0.50
0.50
0.95 to 0.95
0.037 to 0.037
12.7
12.7
12.7
0.50
0.50
0.50
7.1
7.1
7.1
0.28
0.28
0.28
2.2
3.3
2.5
500
750
560
17 100
21 000
19 000
3
3
3
3
3
3
17.8
30.5
38.6
42
72
91
12.7
12.7
12.7
0.50
0.50
0.50
0.95 to 1.60
0.037 to 0.062
12.7
0.50
7.1
0.28
3.0
680
19 000
3
3
32.0
76
12.7
0.50
1.0 to 1.0
0.039 to 0.039
10.0
0.41
5.5
0.22
3.1
700
20 000
3
2
41.7
98
12.7
0.50
1.2 to 1.2
0.047 to 0.047
10.0
0.41
5.5
0.22
3.1
700
21 500
3
2
41.7
98
14.3
0.56
1.2 to 1.2
0.049 to 0.049
12.7
12.7
0.50
0.50
7.1
7.1
0.28
0.28
4.9
4.9
1100
1100
18 000
19 000
2
4
1
1
25.4
42.3
60
100
14.3
14.3
0.56
0.56
W
L
30°
E
(A) Electrode Width and Shape
(B) Minimum Contacting Overlap
a. Individual thickness for both joint members are given (i.e., T1 welded to T2).
b. Dimensional variables are as shown in sketches A and B.
c. Electrode Material RWMA Group A, Class 2. Nominal electrode diameter ranges between 203 mm to 254 mm (8 in. to 10 in.).
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
Resistance Spot Welding
The resistance spot welding (RSW) process can be
used to join terneplate with standard equipment used
for cold rolled or galvanized steel. Steel and coating
characteristics are similar to those described for resistance seam welding. Good results are achieved using
RWMA Class 2 electrodes or standard Cu-Cr-Zr truncated electrodes with a face diameter of 6.4 mm (0.25 in.).6
Welding current, time, and electrode-force conditions
for welding terneplate are 15% to 30% higher than for
welding bare steel. Thus, depending on the thickness of
the sheet, an electrode force of 4.0 kN to 6.7 kN (900 lb
to 1500 lb) would be used with welding currents of
12 000 A to 22 000 A. Current is applied for six to sixteen cycles, again depending on the steel thickness. Typical conditions for spot welding terneplate are shown in
Table 3.3. Some experimentation always is required to
obtain the desired weld nugget size. Welding rates of
one weld per second can be obtained. The service life of
an electrode face may exceed 2000 welds.
6. For RWMA electrode classification, refer to Resistance Welding
Manufacturing Alliance (RWMA), 2003, Resistance Welding Manual,
revised 4th edition, Miami: American Welding Society.
141
To establish the suitability of a particular terneplate
product (e.g., sheet) for resistance spot welding, the
product should be evaluated according to the test methods and recommended practices published in Recommended Practices for Test Methods for Evaluating the
Resistance Spot Welding Behavior of Automotive Sheet
Steel Materials, AWS/SAE D8.9M.7
Arc Welding
Lap joints in terneplate can be welded successfully
without filler metal with the gas tungsten arc welding
(GTAW) process. As short an arc length as possible
should be maintained. The lead-tin coating in the joint
will not disturb the flow of the base weld metal, allowing a defect-free joint to be produced. However, for
highest joint strength, the lead-tin coating should be
removed from the faying surfaces by grinding during
preparation of the joint, so that no lead-tin alloy
becomes incorporated in the weld interface.
7. American Welding Society (AWS), 2002, Recommended Practices
for Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials, AWS/SAE D8.9M, Miami:
American Welding Society.
Table 3.3
Resistance Spot Welding Conditions for Carbon Steel Terneplate
Electrode Diameter and Shapea, c
Minimum
Tension-Shear
Strength,
kN (lb)
α,
deg.
Net
Electrode
Force,
lb (kN)
Approx.
Current,
A
Weld
Time,
Cycles
(60 Hz)
Weld
Nugget
Size,a
mm (in.)
0.18 (4.4)
120
450 (2.0)
11 000
12
0.19 (4.8)
900 (4.0)
0.63 (15.9)
0.50 (12.7)
0.25 (6.4)
120
500 (2.2)
12 000
13
0.22 (5.6)
1000 (4.4)
0.75 (19.0)
0.56 (14.3)
0.63 (15.9)
0.25 (6.4)
120
650 (2.9)
15 000
15
0.24 (6.1)
1500 (6.7)
0.88 (22.2)
0.69 (17.5)
0.75 (19.0)
0.25 (6.4)
120
700 (3.1)
17 500
18
0.27 (6.9)
1900 (8.5)
1.25 (31.8)
0.75 (19.0)
Material
Thickness,b
mm (in.)
D,
mm (in.)
d,
mm (in.)
0.029 (0.7)
0.63 (15.9)
0.036 (0.9)
0.63 (15.9)
0.052 (1.3)
0.063 (1.6)
D
Minimum
Weld
Spacing,
mm (in.)
Minimum
Contacting
Overlap,a
mm (in.)
L
α
d
Dw
(A) Electrode Diameter and Shape
(B) Weld Nugget Diameter
(C) Minimum Contacting Overlap
a. Dimensional variables are as shown in sketches A, B, and C.
b. Two equal metal thicknesses of each gauge. Commercial coating weights up to 137 g/m2 (0.45 oz/ft2). Material must be free from dirt, grease, paint, etc.,
prior to welding, but may have light oil.
c. Electrode Material Group A, Class 2. Water cooling with 7.5 L/min (2 gal/min).
142
CHAPTER 3—COATED STEELS
Soldering
Solder produces a bond by capillary action as a
result of heating an assembly to the soldering temperature using a soldering filler metal distributed and
retained between the closely fitted faying surfaces of the
joint.
The terneplate coating assists the soldering process
by facilitating the wetting of the filler metal. No preparation of the surface is needed other than removal of
dirt, oil, and grease. If the surface has been discolored
by weathering, light brushing will be necessary to improve wetting.
Gas or electric soldering irons or other common
heating methods may be used to heat the joint area,
which typically consists of a lapped or interlocking
joint. However, joint clearances of 0.02 mm to 0.15 mm
(0.001 in. to 0.005 in.) are suitable. Rosin fluxes are
satisfactory in most instances. Corrosive fluxes may be
used if complete removal of flux residues is possible.
Oxyfuel Gas Welding
Terneplate can be welded without filler metal. However, the thin workpieces involved require careful control of heat input. For this reason, oxyfuel gas and other
gas welding processes are not recommended.
AWS WELDING HANDBOOK 9.4
electrolyte used for plating; the choices normally are an
acid sulfate solution, a halogen solution, a fluoroborate
solution, or a methane sulfonate solution. In all cases,
the strip is cleaned and pickled in-line, then plated with
tin, and the coating normally is reflowed to produce a
mirror-bright finish. Still on the line, the tinplate is
chemically treated with a chromate passivation film and
then given a light oil film on the surface. Some lines
have alternative plating cells to produce the ECCS chromium coating on the tin-free product. This coating is
essentially the same as the passivation coating applied
to tinplate, except that it is thicker.
Tinplate is a complicated product that has evolved to
meet the demanding needs of the food preservation
industry, and each of the layers of coating in tinplate
serves a particular purpose. Most, but not necessarily
all, may be present in a given product. When tinplate
material is to be joined, it may be important to carefully
specify the following tinplate conditions:
1. The chemical composition, thickness, temper,
and surface finish of the steel base material;
2. The thickness (i.e., coating mass) per side of the
tin coating, and whether it is reflowed;
3. The passivation treatment, if used, and the
method of application; and
4. The oil treatment (particularly, the type of oil
used by the tinplate manufacturer).
Further information on the specifics of tinplate is
available in the following ASTM Specifications:8
TIN-PLATED STEEL (TINPLATE)
About 80% to 90% of tinplate production goes into
food container applications. Tinplate is cold-rolled lowcarbon steel that has been electroplated with commercialpurity grade (+99.8%) tin on both sides. A light-gauge
steel strip, about 0.15 mm to 0.38 mm (0.006 in. to
0.015 in.) thick is typically used in the plating process.
The thickness of the tin plating usually is 0.15 microns
(μm) to 0.80 μm (6 micro inches (μin) to 30 μin.). Often
the plating is not the same thickness on both sides. The
strip is called blackplate before it is plated. The same
strip can be used to produce electrolytic chromiumcoated steel (ECCS), a chromium-plated tin-free steel
(TFS) product that is also used for container applications.
The steel base for tinplate usually is processed for
low metalloid content to enhance corrosion resistance.
It is continuously cast, hot rolled, cold reduced, and
annealed. Subsequently, another cold reduction step
may be employed to produce the double-reduced tinplate
product.
Tin is plated on the steel base using plating lines with
the strip moving at about 610 m/min (2000 ft/min) or
faster. The process details differ somewhat with the
1. A 599/A 599M, Standard Specification for Tin
Mill Products, Electrolytic Tin-Coated, ColdRolled Sheet;
2. A 623/A 623M, Standard Specification for Tin
Mill Products, General Requirements;
3. A 624/A 624M, Standard Specification for Tin
Mill Products, Electrolytic Tin Plate, Single
Reduced;
4. A 625/A 625M, Standard Specification for Tin
Mill Products, Black Plate, Single Reduced;
5. A 626/A 626M, Standard Specification for Tin
Mill Products, Electrolytic Tin Plate, Double
Reduced;
6. A 630/A 630M, Standard Test Methods for
Determination of Tin Coating Weights for Electrolytic Tin Plate; and
7. A 650/A 650M, Standard Specification for Tin
Mill Products, Black Plate, Double Reduced.
The Producers of the American Iron and Steel Institute
and the International Tin Research Institute (England)
8. ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania, http://www.astm.org.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
are additional sources of information for consumers of
tinplate9, 10
JOINING PROCESSES FOR
TIN PLATE
Tin as an impurity embrittles steel. The level of tin
that can be tolerated in steel in modern steelmaking has
risen over the years to approximately 0.15%. This level
is high enough to allow the easy recycling of tinplate
scrap into new steel. A problem in welding tinplate,
however, is ensuring that tin is not incorporated into
the seam material.
Resistance Seam Welding
A major use of tinplate is the production of food
cans. In previous years, tinplate was formed into food
cans in three pieces—a rolled body that was soldered
9. American Iron and Steel Institute (AISI) Committee of Tin Mill
Products, 1140 Connecticut Ave., NW, Suite 705, Washington, D.C.,
20036, http://www.steel.org.
10. International Tin Research Institute (ITRI), Unit 3, Curo Park, Frogmore St. Albans, Hertfordshire, AL2 2DD, UK, http://www.itri.co.uk/.
together, and two ends that were then seamed onto the
body. When concerns over lead contamination of foods
caused can producers to eliminate soldering, one of the
alternatives was welding. Producers retained the threepiece construction, trying at first to use conventional
resistance seam welding. However, when using resistance seam welding for either tinplate or the ECCS
product it was necessary to remove the tin coating from
the seam edges before welding to produce reliably
strong seams that would withstand the pressures of
food sterilization.
The difficulty and expense of removing the tin plating from the surface were overcome with the development of electrode wire seam welding, such as the
Soudronic Process™11 This process uses a moving,
intermediate electrode wire of consumable copper, supported by a roller electrode. Tin melts at a low temperature (232°C [450°F]) and molten tin readily alloys with
copper. The copper wire carries away the tin so that it
does not interfere with the functioning of the copper
electrode. Figure 3.1 illustrates the principle of this process for both overlap seam welding and mash seam
welding.
Single-purpose welding machines can be built specifically to accommodate the high-speed production of
cans. Figure 3.2 shows a high-speed can body welding
11. Trade name of a can-welding process developed by Soudronic AG.
(A)
(A)
(B)
(B)
(C)
(C)
(C)
(B)
(B)
143
(A)
(A)
OVERLAP SEAM WELD
MASH SEAM WELD
Source: Soudronic Automotive AG.
Figure 3.1—Roll Seam Welding Process with (A) Wire Electrodes,
(B) Circular Electrode Wheel Support, and (C) Sheet Metal Workpiece
144
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Photograph courtesy of Soudronic AG
Figure 3.2—High-Speed Can Body Welding Machine
machine capable of welding 800 cans per minute. Production rates of up to 1100 units per minute are possible, welding at 125 m/min (4920 in./min).12
Other Welding Processes
Other welding processes can be used with tinplate,
depending on the requirements of the application. For
example, resistance spot welding is used in some cases
to intermittently weld tinplate sections together temporarily until the joint is later soldered and sealed. The
laser beam welding of can stock has been developed to
compete with electrode wire seam welding, although
with laser beam welding the tin coating may evaporate
in the weld zone, so that the coating ceases to function
as intended (e.g., for corrosion resistance or for solderability). As a result, a repair may require organically
coating the weld zone.
SOLDERING TINPLATE
As previously indicated, the former method used to
join the sections of a tinplate food container was solder12. For additional information, refer to Chapter 1, Electrode Wire
Seam Welding in Welding Processes—Part 2, Volume 3 of the Welding
Handbook, 9th edition.
ing with a solder composition of roughly 30% tin and
70% lead. However, tin is several times more expensive
than lead, so to reduce costs, solder evolved into a composition of 2% tin and 98% lead. Soldering of tinplate
food containers was discontinued in the late 1980s.
Although other joining methods or processes have
replaced soldering in the production of food cans, some
tinplate containers are still joined by soldering for nonfood applications.
Soldering is easily accomplished with clean tinplate.
The surface is fluxed, typically with an organic or inorganic acid flux. Heat is applied to the surface, and the
solder is quickly brought into contact with the joint
area while heat is maintained.
The many variations to the soldering process relate
to the method of heating. The heat source could be a
hand-held electric soldering iron, a gas torch, or a copper bit heated in an external gas flame. Other heat
sources could be a hotplate, a resistance heating element, an infrared heating source, or even a radiofrequency induction heating coil. For higher production
rates, several automated versions of these soldering
methods are used.
The soldered joint of tinplate containers consists of a
lock-seam design for mechanical strength; the solder
mainly serves as a sealant to keep the contents from
being exposed to the outside environment. The capil-
AWS WELDING HANDBOOK 9.4
lary action of the joint design provides enough strength
to withstand the temperature and pressure of the food
sterilization process.
Comprehensive information on the soldering process
is published in the Soldering Handbook, 3rd Edition, 13
and Volume 2 of the Welding Handbook, 9th Edition,
Chapter 13.14
VARIATIONS OF TINPLATE
Tin can be applied to ferrous alloys in several forms
other than strip, for the purpose of solderability. Electrical and electronic chassis components and shields are
examples of these applications. The steel chassis base
and the tin coating are often thicker than standard
tinplate. Typically, the minimum mean tin coating
thickness is 0.004 mm (0.00015 in.); the maximum is
0.020 mm (0.0008 in.).
Historical Background
Concern over the growth of tin “whiskers,” common
to welds made in pure tin in past years made the use of
tin-lead coatings more prevalent. Whiskers are metallic,
crystalline filaments that can grow to 9.5 mm (3/8 in.)
or more in length during idle storage. Normal paints or
enamels were ineffective in preventing the occurrence of
this phenomenon. However, the presence of more than
1% lead significantly reduced the chance of whisker
growth, so it was common for tinplate coatings to contain additions of 8% to 10% lead. However, when
health concerns about the presence of lead were recognized, lead-free solders and solderable finishes were
developed. The joining behavior of tin coatings was not
greatly affected by the addition of lead in moderate
amounts. If tinplate is to be welded, it may be more
convenient to weld before the tin or tin-alloy coating is
applied, thereby avoiding some of the complications
due to the absence of lead.
GALVANIZED STEELS
Galvanized steels are coated with zinc or zinc alloys
for protection against rust. Most zinc coatings are
applied for atmospheric corrosion resistance. When
used for underground or underwater applications, the
thickest possible zinc coatings are applied. Coating
13. American Welding Society (AWS), P. T. Vianco, 2000, Soldering
Handbook, 3rd edition., Miami: American Welding Society.
14. American Welding Society (AWS), Welding Handbook Committee,
A. O’Brien, Ed., 2004, Welding Processes—Part 1, Volume 2 of the
Welding Handbook, 9th edition, Miami: American Welding Society.
CHAPTER 3—COATED STEELS
145
methods include electro-galvanizing (EG) and hot-dip
galvanizing. Steel may be hot-dip galvanized either by
the hot-dip batch method (known as general galvanizing) or the continuous hot-dip process.
The primary difference between general galvanized
steel products and continuous hot-dip galvanized products is the sequence of galvanizing and fabrication.
General galvanized products usually are fabricated
before galvanizing, and the coating usually is the finishing operation. The products are used for a wide variety
of products, including building frames, girders and
beams for bridges, electric power pylons, street lighting
poles and television transmitting towers; also, automobile and truck chasses, railway rolling stock and trackside structures, piers, and deck equipment for ships.
Continuous hot-dip galvanized finished products are
fabricated from pre-galvanized metal, and the coating
may be the substrate for an additional coating, typically
paint. Continuous hot-dip galvanized sheet is used to
fabricate items such as automobile parts, appliance
parts, and construction products such as the cladding of
buildings and light steel framing.
GENERAL GALVANIZED PRODUCTS
General galvanizing takes place when cleaned steel is
immersed in a bath of molten zinc, where a coating
forms through interdiffusion of the iron and zinc. Figure 3.3 shows a load of coated beams as they are withdrawn from the galvanizing kettle with a hot-dip
galvanized coating.
In general galvanizing, a metallurgical reaction
begins between the molten zinc of the bath and the iron
of the cleaned and preheated workpiece (of any configuration) as it enters the zinc bath. While the workpiece
is submerged in the bath, a series of four layered binary
zinc-iron alloys are formed. The four layers, starting at
the substrate-to-coating interface, are the gamma (γ)
phase (Fe3Zn10); delta (δ) phase (FeZn7); zeta (ζ ) phase
(FeZn13); and eta (η) phase (solid solution of 0.005%
Fe max in Zn). The γ, δ, and ζ layers result from the diffusion of iron into the zinc coating. The layer forms
from the molten zinc, which clings to the intermetallic
layers as the workpiece is removed from the bath.
(Refer to ASTM A 123/A 123M for detailed information about galvanized products.)15 The malleability of
the coating is limited because of the brittle nature of the
intermetallic layers. This is not a serious problem for
general galvanized products, but it is a major problem
for continuous-galvanized sheet, as explained in the
Continuous Galvanized Steel section of this chapter.
15. ASTM International, Subcommittee A05.13, Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products, ASTM A 123/A 123M, West Conshohocken, Pennsylvania: ASTM
International.
146
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Photograph courtesy of American Galvanizers Association
Figure 3.3—A Batch of Hot-Dip Galvanized Beams Emerging from Molten Zinc Bath
When feasible, most general galvanized components
are welded before galvanizing because welding of
uncoated steel is simpler: the joint requires less preparation, and galvanizing the welded area can be accomplished in the same procedure as the rest of the
workpiece. Welding before galvanizing is sometimes
limited by the dimensions of the available galvanizing
baths, which typically are 12 m to 18 m (39 ft to 60 ft)
long, or the requirement to perform further welding in
the field, or during final assembly or erection.
Filler metals used to fabricate structures for galvanizing must have steel chemistry similar to that of the base
metal. The silicon content of filler metals for rimmed
steels should be less than 0.04% to produce a uniform
galvanized coating. Higher silicon content can increase
the reaction of the weld metal with zinc, producing a
much thicker, rougher coating. The ASTM publication
A 385, Practice for Providing High-Quality Zinc Coatings, (Hot-Dip), provides guidance for the design and
fabrication of weldments that undergo general galvanizing after fabrication.16
Resistance Welding
Resistance welding commonly is used to join steel
sections thinner than 5 mm (0.20 in.) if the coating is
lighter than 300g/m2 (1 oz/ft2). Coatings up to 450 g/m2
(1.5 oz/ft2) have been successfully welded, although the
service life of the electrode is much shorter than that of
the electrode used with lighter coatings. On heavy coatings, it is necessary to redress or replace worn electrodes frequently.
Galvanized parts can be resistance welded without
removing the zinc coating if the coating is thin. The
16. ASTM International, Subcommittee A05.13, Practice for Providing
High-Quality Zinc Coatings (Hot-Dip), A 385, West Conshohocken,
Pennsylvania: ASTM International.
AWS WELDING HANDBOOK 9.4
coating usually is only slightly disturbed, so that a subsequent touch-up of the coating in the weld area is not
needed. For thin coatings, the recommendations in the
section on resistance welding of continuous-galvanized
steel can be used. If the galvanized coatings are thick,
resistance welding is impractical.
To establish the suitability of a particular general galvanized product, such as plate sheet for resistance spot
welding, the product should be evaluated according to
the test methods and recommended practices published
in AWS/SAE D8.9.17
Embrittlement of Steel by Liquid Zinc
Embrittlement of general galvanized steel can occur
during arc welding, arc brazing or oxyfuel gas welding
when using carbon steel electrodes. Unless properly
designed, arc welded or brazed joints in general galvanized steel (after coating deposition) can be prone to
cracking as a result of embrittlement by liquid zinc.
This type of cracking can be caused by intergranular
penetration of the zinc into the weld metal, a phenomenon sometimes called zinc-penetration cracking. This
type of cracking occurs most often along the throat of a
fillet weld, but sometimes is observed also in the heataffected zone (HAZ) starting from the toe of the weld.
An example is illustrated in Figure 3.4, which shows
cracks along the throat of a gas metal arc fillet weld
17. See Reference 7.
Figure 3.4—Through-Cracking in the Throat
of Fillet Welds in General Galvanized Steel
Plate 6.4 mm (0.25 in.) Made with Gas
Metal Arc Welding with CO2 Shielding
CHAPTER 3—COATED STEELS
147
joining two 6.4 mm (0.24 in.) general galvanized steel
plates. The shielding gas used in this example was carbon dioxide (CO2).
Zinc-penetration cracking is attributed to the development of a brittle, zinc-rich phase. This mechanism
explains the cracks that occur over extended periods of
time in steel pots that contain fused zinc. However, the
chances are remote for forming this phase during the
short intervals that characterize arc welding.
Based on general observations, if excessive amounts
of silicon or magnesium are introduced to carbon steel
weld metal, these elements may concentrate within the
dendrites in the microstructure during the solidification
process and produce critical compositions into which
molten zinc can easily intrude. Therefore, given favorable metallurgical conditions in the hot weld metal (for
example, fused zinc at the weld root and high shrinkage
stresses) the zinc could penetrate into the alloy-rich dendrites, weaken the matrix, and crack. The cracks shown
in Figure 3.4 developed in heavily deoxidized weld
metal designed for shielding with CO2. The weld metal
could contain more than 1% silicon, well above the
maximum of 0.4% allowed to avoid zinc-induced cracks.
Cracking is most often observed when zinc is present
at the weld root, particularly with fillet welds. Properly
designed joints welded according to the procedures discussed below can minimize the occurrence of embrittlement and the residual tensile stresses that exacerbate
the problem.
The tendency for cracking in fillet welds depends on
several key factors: the thickness of the galvanized coating, the method of galvanizing, the thickness of the galvanized steel, the width of the root opening of the joint,
the method of joint restraint, the welding process, the
parameters of the welding process, the chemistry of the
filler metal chemistry, and the electrode classification.
The tendency for cracking is proportional to the
amount of zinc present in the weld joint. For that reason, cracking occurs most often when thick coatings are
applied by general galvanizing. Cracking may not
develop at all with thin, electro-deposited coatings. It
tends to be less prevalent with low-penetrating shielded
metal arc welding (SMAW) and more prevalent with
gas metal arc welding (GMAW), especially when CO2 is
used as the shielding gas. Intergranular penetration of
zinc is more likely to occur in fillet welds made with the
GMAW process in plate thicker than 6.4 mm (0.25 in.),
and it is less likely in plate thicknesses of less than
12.7 mm (0.5 in.) welded with the SMAW process. The
higher heat input and slower welding speed with
SMAW cause more zinc to volatilize ahead of the weld
pool. Under the same circumstances, the tendency for
cracking may be higher when welding advanced highstrength steels.
148
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
The methods for minimizing fillet weld cracking on
galvanized steel due to zinc penetration are categorized
as follows:
1. Using the proper root opening between the
plates,
2. Choosing the correct electrode,
3. Selecting the appropriate galvanized base metal,
4. Preparing the base plate to reduce the available
zinc, and
5. Removing the zinc coating in the weld area
before welding.
Root Opening for T-Joints. For T-joints, providing
a suitable root opening between the vertical (standing)
plate and the horizontal plate is a simple but effective
means of reducing fillet weld cracking. A root opening
of 1.6 mm (1/16 in.), as shown in Figure 3.5, generally
is sufficient.
Electrode Selection. The choice of electrodes also is
important; this depends on the welding process being
used. Low silicon content in the weld metal is relatively
important. For example, with the GMAW process,
welds made with ER70S-3 alloyed with about 0.5% silicon are less likely to crack than welds made with
ER70S-6 containing about 1.0% silicon. In some situations, an ER70S-3 filler metal might be selected for
making the more critical root pass, followed with
deposits of ER70S-6 filler to obtain the desired weld
soundness or other qualities that characterize the more
heavily alloyed steels.
ROOT
OPENING
Figure 3.5—Typical 1.6 mm
(1/16 in.) Root Opening
Similarly, to avoid cracking, the titania (rutile) electrodes E6012 or E6013 for SMAW are more suitable
than low-hydrogen (basic) electrodes, such as E7015 or
E7016, because these electrodes make a larger angle
and create much more slag when used with zinc-coated
parts.18 Different electrodes could be selected for the
root passes and fill passes.
Selection of Base Metal. The following variables
must be considered when selecting a suitable galvanized
steel base metal:
1. The amount of zinc needed for the application,
2. The welding procedure that will meet fabrication
requirements, and
3. The range of heat that can be applied to the base
metal.
Because of the varying amount of zinc needed for
specific applications and the varying welding procedures required to satisfy fabrication requirements, simple procedural tests in the proposed base metal may be
necessary to develop the most suitable method for making crack-free welds in galvanized steels. A reasonable
amount of reliable experience may substitute for some
of the tests. While developing these procedures it should
also to be noted that different heats of steel plate sometimes demonstrate significant differences in cracking
behavior.
Preparation of Base Plate. Three methods of prep-
aration for a T-joint are described in this section. First is
the use of a single-beveled or double-beveled edge shape
that has been oxygen-cut or machined into the vertical
plate of a T-joint, as shown in Figure 3.6. This method
of preparation will prevent the formation of a pool of
molten zinc between the faying surfaces at the root of
the joint, even if the prepared edge is galvanized after
cutting or machining. A 15° bevel angle is sufficient.
The second method of base plate preparation is the
removal of zinc from the faying surfaces by burning it
off with an oxyfuel gas torch or by shot blasting the
areas shown in Figure 3.7. As illustrated, zinc is
removed from both sides of the joint to minimize the
chance of cracking. Adjacent to the area where the zinc
has been removed, a region can be observed where the
zinc has lost its luster and has a gray, matted look. The
18. The rutile, or titania electrode group usually includes E6012,
E6013, and E6014. The basic, or low-hydrogen electrode group usually includes E7015, E7016, and E7018. Refer to American Welding
Society Specification for Carbon Steel Electrodes for Shielded Metal
Arc Welding, AWS A5.1. See also American Welding Society (AWS)
Committee on Filler Metals and Allied Materials, 2004, Specification
for Carbon Steel Electrodes for Shielded Metal Arc Welding, AWS
A5.1/A5.1M:2004, Miami: American Welding Society, Annex A7, pp
34–36.
AWS WELDING HANDBOOK 9.4
SINGLE-BEVEL
CHAPTER 3—COATED STEELS
DOUBLE-BEVEL
(A) Beveled before Galvanizing
149
corrosion resistance of this region has not changed,
even though the appearance has been altered.
A third method of preparing galvanized base plate is
by heat treating. Heat treating will cause the formation
of a zinc-iron alloy which can reduce the incidence of
cracking in fillet welds. It is important to note that cooling the heat-treated base metal or welded structure
should be done slowly, at rates typically not exceeding
28°C/h (50°F/h). Heat treating the base plate generally
is costly and inconvenient because it is a prolonged procedure, typically requiring holding at 400°C (752°F) for
up to ten hours. However, heat treating may be worthwhile for small, easily handled components.
The first two procedures, beveled edge preparation
and the removal of zinc by burning or abrasion, will
eliminate cracking completely and should not raise further welding problems. Depending on the circumstances, the third method, heat treating the base metal,
may not eliminate cracking but only reduce it, because
the zinc is not removed from the weld zone.
Welding Procedure Qualification
SINGLE-BEVEL
DOUBLE-BEVEL
(B) Beveled after Galvanizing
Figure 3.6—Beveled Edge Shapes
for a T-Joint in Galvanized Plate
Qualification requirements for making fillet welds in
galvanized steel 6.4 mm (1/4 in.) or greater in thickness
should include a simple procedure test to determine the
tendency for intergranular penetration of zinc into the
weld joint.
Specifications and recommended practices are published
in the following American Welding Society documents:19
1. B2.1/B2.1M-BMG:2009, Base Metal Grouping for
Welding Procedure and Performance Qualification;
2. D8.1M:2007, Specification for Automotive Weld
Quality—Resistance Spot Welding of Steel;
3. D8.6:2005, Specification for Automotive Resistance Spot Welding Electrodes;
4. D8.7M:2005, Recommended Practices for Automotive Weld Quality—Resistance Spot Welding;
5. D8.8M:2007, Specification for Automotive Weld
Quality—Arc Welding of Steel; and
6. D8.9M:2002, Recommended Practices for Test
Methods for Evaluating the Resistance Spot
Welding Behavior of Automotive Sheet Steel
Materials.
A suitable test specimen is shown in Figure 3.8. A
single-pass weld of similar size to those to be used in
production or, if this information is not known, a fillet
weld with a leg length of 6.4 mm (1/4 in.) will be suitable.
If multiple-pass fillet welds are to be used in production,
Figure 3.7—T-Joint Prepared by
Local Removal of Zinc by Grit
Blasting or Oxyfuel Heating
19. American Welding Society (AWS) B2 Committee on Procedures
and Performance Qualifications, and AWS D8 Committee on Automotive Welding, Miami: American Welding Society.
150
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
76 mm (3 in.)
MINIMUM
BEND TO
FRACTURE
WELD
1.6 mm
(1/16 in.)
NOTCH
152 mm (6 in.)
MINIMUM
152 mm (6 in.)
MINIMUM
Figure 3.8—Specimen for Testing Fillet Welds on Galvanized Steel
Oxyfuel Gas Welding
the procedure test should be made with a single-pass fillet weld of similar size deposited on the first pass of the
multiple-pass production weld.
A separate specimen should be welded in each of the
welding positions to be used in production. As an
exception, if welding in both the flat and the horizontal
positions is to be carried out in production, it will be
sufficient to perform a procedure test in only one of
these welding positions. After welding, a notch 1.6 mm
(1/16 in.) deep made with a hacksaw or with an abrasive wheel should be cut longitudinally in the face of the
weld to facilitate fracture through the weld throat. The
weld should be fractured by means of hammer blows or
in a press in the direction of the “bend-to-fracture”
arrow shown in Figure 3.8. This test is similar to the
nick-break test described in API 1104.20
The fracture surfaces of the weld should be examined for zinc penetration, as indicated by a light silvery
color. To aid inspection, it is helpful to heat the vertical
plate to 330°C ± 14°C (625°F ± 25°F) for 30 minutes,
which will oxidize the zinc-free areas of the fracture
surface and reveal a tan or brown color. The areas of
cracking caused by intergranular penetration of zinc
retain their silvery appearance. If fracture does not
occur through the weld but occurs through the fusion
boundary or through the base plate, the weld should be
retested. Tests should be carried out on plates of each
composition to be used in production. The thickest zinc
coating to be used should be applied to each test plate.
When various thicknesses of plate are to be used, additional tests should be carried out, but the number of
tests can be minimized by testing different thicknesses
only if they vary by 12.7 mm (1/2 in.) or more.
Oxyfuel gas welding (OFW) includes a group of
welding processes producing coalescence of workpieces
by heating them with an oxyfuel gas flame. The processes are used with or without the application of pressure and with or without filler metal.
Galvanized steel can be welded with the oxyfuel gas
process with copper-coated mild steel filler metal rods
such as R45, R60, and R65.21 Preparation for welding
is similar to that used for welding uncoated steel.
Grease, dirt or other contaminants must be removed
from the weld area. Fixtures and clamps are used to
position the weld and to prevent distortion caused by
heat buildup. A neutral flame should be used, and the
size of the welding tip should be the same as that used
for welding uncoated steel of similar thickness.
Because of the low travel speed used with oxyfuel gas
welding, the zinc coating is volatilized and completely
removed for at least 6.4 mm (1/4 in.) on each side of the
weld. Partial volatilization extends for an additional 6.4
mm (1/4 in.) or more on each side of the weld. These
changes result in reduced corrosion resistance. The
appearance of the zinc coating may be degraded in an
area up to 19 mm (3/4 in.) beyond this depleted region;
however, no deterioration in corrosion resistance has
been observed in this matted region.
Side-to-side movement of the torch should be
avoided in order to minimize the area from which the
galvanizing is removed and to reduce the amount of
repair required after welding. The forehand welding
technique should be used, in which the torch flame
points in the direction of welding and the welding rod
precedes the flame. The forehand technique will vola-
20. American Petroleum Institute (API), Welding of Pipelines and
Related Facilities, API 1104, Washington, DC: American Petroleum
Institute.
21. Refer to American Welding Society (AWS), 2007, Specification
for Carbon and Low Alloy Steel Rods for Oxyfuel Gas Welding, AWS
A5.2/A5.2M:2007, Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
tize more zinc in advance of the weld and will cause less
interference with welding compared to the less effective
backhand welding technique, in which the torch flame
points back at the completed weld and the welding rod
is interposed between the flame and the completed weld.
The practice of remelting the weld with the flame to
improve the appearance should be avoided, because this
will result in additional loss of the galvanized coating.
Damage to the coating can be minimized by applying
copper-silver paste to each side of the weld before
applying heat.
Gas Tungsten Arc Welding
Gas tungsten arc welding (GTAW) is an arc welding
process using an arc between a tungsten electrode (nonconsumable) and the weld pool. The process is used
with shielding gas and without the application of pressure. The gas tungsten arc welding process is discussed
in detail in Chapter 3 of the Welding Handbook, Volume 3, Welding Processes.22 (Refer to Appendix B.)
The GTAW process is not recommended for general
galvanized steel unless the zinc coating is removed from
the weld zone. The zinc vapor formed when galvanized
steel is heated may contaminate the electrode, which
will cause erratic arc operation and poor weld quality.
If the zinc coating is removed, the bare steel can be
22. See Reference 14.
151
welded using procedures suitable for uncoated steel.
Gas tungsten arc braze welding, with its attendant
lower temperatures, can be carried out with less joint
preparation, as noted in the subsection Gas Metal Arc
Braze Welding.
Shielded Metal Arc Welding
Shielded metal arc welding (SMAW) is an arc welding process that uses an arc between a covered electrode
and the weld pool. The process is used with shielding
from the decomposition of the electrode covering, without the application of pressure, and with filler metal
from the electrode. Detailed information on shielded
metal arc welding is published in Volume 2 of the Welding Handbook, Welding Processes, Chapter 2.23
Typical conditions for the shielded metal arc welding
of butt joints and T-joints in general galvanized plate
are presented in this section. Shielded metal arc downhill
welding and radiographic appearance also are discussed.
Welding Conditions. Tables 3.4 and 3.5 provide
welding conditions for SMAW suitable for making the
root pass of groove welds in butt joints in 6.35 mm and
12.7 mm (1/4 in. and 1/2 in.) general galvanized steel
plate. Table 3.4 lists conditions for rutile covered electrodes; Table 3.5 provides conditions for basic covered
23. See Reference 22, Chapter 2.
Table 3.4
Typical Shielded Metal Arc Welding Conditions for
Groove Weld Root Pass on Butt Joints in 6.35 mm and 12.7 mm
(1/4 in. and 1/2 in.) General Galvanized Steel Plate with Rutile Electrodes*
Plate Thickness
mm
in.
Electrode Diameter
mm
in.
Root Opening
Welding
Position
mm
in.
Typical Welding
Current (ac),
A
6.4
1/4
2.5
3/32
Flat
2.5
3/32
73–89
6.4
1/4
2.5
3/32
Uphill
1.6
1/16
73–83
6.4
1/4
2.5
3/32
Horizontal
2.5
3/32
70–83
6.4
1/4
3.25
1/8
Horizontal
1.6
1/16
109
6.4
1/4
2.5
3/32
Overhead
2.5
3/32
89
12.7
1/2
3.25
1/8
Flat
2.5
3/32
95–109
12.7
1/2
3.25
1/8
Uphill
2.5
3/32
83–95
12.7
1/2
4
5/32
Uphill
2.5
3/32
101–117
12.7
1/2
3.25
1/8
Horizontal
1.6
1/16
117
12.7
1/2
2.5
3/32
Overhead
2.5
3/32
89
*AWS E7013.
152
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.5
Typical Shielded Metal Arc Welding Conditions for
Groove Weld Root Pass on Butt Joints in 6.35 mm and 12.7 mm
(1/4 in. and 1/2 in.) General Galvanized Steel Plate with Basic Electrodes*
Plate Thickness
Electrode Diameter
mm
in.
Root Opening
Welding
Position
mm
in.
6.4
1/4
2.5
3/32
Flat
6.4
1/4
2.5
3/32
Uphill
in.
Typical Welding
Current (ac),
A
1.6
1/16
85–90
2.5
3/32
85
83
mm
6.4
1/4
2.5
3/32
Horizontal
1.6
1/16
6.4
1/4
2.5
3/32
Horizontal
2.5
3/32
78
6.4
1/4
3.25
1/8
Horizontal
2.5
3/32
109
6.4
1/4
2.5
3/32
Overhead
2.5
3/32
80
12.7
1/2
3.25
1/8
Flat
2.5
3/32
100
12.7
1/2
3.25
1/8
Uphill
2.5
3/32
100
12.7
1/2
3.25
1/8
Horizontal
2.5
3/32
95
12.7
1/2
2.5
3/32
Overhead
2.5
3/32
90
*AWS E7016.
electrodes. The welding conditions are similar to those
used on uncoated steel, except that the root opening is
increased in certain cases to ensure complete joint penetration and allow for drainage of liquefied zinc.
Figure 3.9 shows a cross section of a well-designed
butt joint and root pass that can be used in coated or
uncoated steel. The joint was prepared for a 70°, singleV-groove weld, with a 1.6 mm (1/16 in.) root opening
and a 1.6 mm (1/16 in.) root face.
Figure 3.9(A) shows a weld in uncoated steel plate
deposited with an electrode travel angle of 70°. The
welding current was 83 amperes. Figure 3.9(B) shows a
weld in a counterpart galvanized plate using an electrode travel angle of 30°. The change in electrode angle
was necessary because the greater angle resulted in
incomplete joint penetration. Joint penetration was
improved further by moving the electrode backward
and forward in a whipping motion in line with the
joint, as shown in Figure 3.9(C). This method of manipulation, however, results in a 40% decrease in travel
speed, compared to the travel speed on uncoated steel,
and produces a more fluid slag and more spatter.
Alternatively, the root pass can be deposited, subsequently removed by gouging from the reverse side, and
rewelded, a normal procedure on critical fabrications.
Similarly, for butt joints in galvanized steel welded in
the vertical and overhead positions, a root opening of
2.4 mm (3/32 in.) is necessary to obtain complete penetration. Although a root opening of 1.6 mm (1/16 in.) is
sufficient to provide complete penetration in the horizontal position, the solidified root pass tends to have a
peak, or bulbous shape, resulting in slag entrapment at
the edges of the weld. The slag can be removed only by
grinding. However, slag entrapment can be prevented
by increasing the root opening from 1.6 mm (1/16 in.)
to 2.4 mm (3/32 in.), as shown in Figure 3.10, a weld in
12.7 mm (1/2 in.) general galvanized plate.
Reduced travel speed is necessary when making the
root pass in the flat or vertical position for butt joints in
galvanized steel; however welds made in the horizontal
or overhead positions can be deposited at speeds similar
to welds on uncoated steel. After the root pass has been
made, subsequent weld passes can be deposited with
techniques similar to those used for uncoated steel
because the weld beads are deposited on essentially
uncoated weld metal. The slight galvanizing remaining
on the beveled edges generally is insufficient to affect
welding. If excessively thick zinc coatings are present,
however, and if they interfere with the stability of the
arc, it is better to use the oscillating motion of the electrode despite the slight reduction in travel speed.
Joint Designs. When making shielded metal arc
welds in butt joints in 25 mm to 50 mm (1 in. to 2 in.)
thick plate with covered electrodes, either rutile
(EXX12, EXX13) or basic (EXX15, EXX16, EXX18)
joints in the horizontal or uphill position can be deposited at the same welding speed as joints in uncoated
steel and with similar welding current. When making
the root pass in the flat position, however, the travel
speed should be reduced approximately 25% compared
to the welding speed required for uncoated steel, as
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
(A) Uncoated Steel and 70° Electrode Travel Angle
ENTRAPPED
SLAG
(B) General Galvanized Steel and
30° Electrode Travel Angle
(A) 1.6 mm (1/16 in.)
Root Opening
(C) General Galvanized Steel and 30° Electrode
Travel Angle with Electrode Manipulated in
a Backward/Forward Whipping Motion
Figure 3.9—Comparison of Electrode Travel
Angles in (A) Uncoated Steel, (B) General
Galvanized Steel, and (C) Steel Plate,
6.4 mm (1/4 in.) with Electrode
Manipulation; Current 83 A
shown in Table 3.6. The root opening should be
increased to allow for the drainage of molten zinc.
(B) 2.4 mm (3/32 in.)
Root Opening
T-Joints. The same basic welding technique used for
butt joints should be employed for T-joints made with
shielded metal arc welding: a slower travel speed than
normal and a slight whipping action of the electrode.
Undercut is the most prevalent discontinuity occurring
in fillet welds deposited in the horizontal and uphill
positions with either rutile or basic covered electrodes.
Figure 3.10—(A) Slag Entrapment
on the Root Pass of a
Horizontal Weld in
12.7 mm (1/2 in.) General
Galvanized Plate and
(B) Slag Entrapment Reduced
by Wider Root Opening
153
154
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.6
Typical Shielded Metal Arc Welding Conditions for
Groove Weld Root Pass on Butt Joints in 44.5 mm (1.75 in.)
General Galvanized or Spray-Coated Steel with Rutile or Basic Electrodes*
Electrode Diameter
Electrode Type
AWS E7013
AWS E7016
Welding Position
Flat
mm
in.
Current,
A
4
5/32
135
Reduction in Speed
Compared with Welding
Uncoated Steel, %
25
Uphill
3.2
1/8
100
0
Horizontal
4
5/32
140
0
Flat
4
5/32
135
25
Uphill
3.2
1/8
115
0
Horizontal
4
5/32
135
0
*Edge preparation: 60° double-V, 1.6 mm (1/16 in.) root face, 3.2 mm (1/8 in.) root opening.
An illustration of undercut is shown in Figure 3.11,
in which the vertical plate has an irregular groove at the
vertical toe of the weld. This type of discontinuity can
occur at either side in uphill welds, but in the horizontal
position an irregular groove generally is restricted to the
vertical plate of the T-joint. Undercut is more likely to
occur with rutile electrodes when slag is allowed to
solidify slowly and when the weld has a concave profile, as shown in Figure 3.11(A); whereas with faster
solidification and a more convex profile, as shown in
Figure 3.11(B), the tendency to produce this discontinuity is lessened.
The occurrence of undercut is apparent to a skilled
welder while welding is in progress. However, it is not
easy to interrupt the forward progress in order to fill an
undercut when using an electrode that produces a very
fluid slag and a concave weld profile because the fluid
(A)
slag flows in front of the electrode and becomes
entrapped in the weld. Rutile electrodes can be manipulated more readily and create a less fluid slag, producing a weld profile similar to that shown in Figure
3.10(B). Typical welding conditions for fillet welded Tjoints in 3.2 mm (1/8 in.) thick continuous or general
galvanized steel are shown in Table 3.7.
The zinc coating on general galvanized steel is
thicker than the zinc deposited on continuous-coated
sheet. The faying surfaces also are zinc coated, unless
the plate has been cut after galvanizing. This extra zinc
may cause trouble in the vertical position, because the
molten metal tends to run down into the weld pool,
which makes the slag difficult to control. This can be
minimized (and often prevented) by maintaining as
short an arc length as possible. Tables 3.8 and 3.9 show
typical welding conditions for T-joints in 6.4 mm and
(B)
Figure 3.11—Macrosections of (A) Undercut with Slow Slag Solidification and Concave
Weld Profile and (B) Less Undercut with Faster Slag Solidification and Convex Profile
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
Table 3.7
Typical Shielded Metal Arc Welding Conditions for Fillet Welds
in T-Joints in 3.2 mm (1/8 in.) Continuous or General Galvanized Steel
Electrode Diameter
Electrode Type
Specification
mm
in.
Welding Position
Current (ac),
A
Rutile
AWS E7013
3.2
1/8
Horizontal
117–126
Basic
AWS E7016
3.2
1/8
Horizontal
109–117
Rutile
AWS E7013
2.5
3/32
Uphill
89
Table 3.8
Typical Shielded Metal Arc Welding Conditions for Fillet Welds in T-Joints in 6.35 mm
and 12.7 mm (1/4 in. and 1/2 in.) General Galvanized Steel Plate Using Rutile Electrodes*
Plate Thickness
mm
in.
Electrode Diameter
mm
in.
Welding Position
Current (ac), A
6.4
1/4
3.2
1/8
Flat
6.4
1/4
2.5
3/32
Vertical
120
90
6.4
1/4
3.2
1/8
Vertical
105
6.4
1/4
3.2
1/8
Horizontal
110
6.4
1/4
4
5/32
Horizontal
170
6.4
1/4
3.2
1/8
Overhead
110
12.7
1/2
4
5/32
Flat
170
12.7
1/2
4
5/32
Vertical
145
12.7
1/2
4
5/32
Horizontal
170
12.7
1/2
4
5/32
Overhead
170
*AWS E7013; B.S. 1719, Class E317.
Table 3.9
Typical Shielded Metal Arc Welding Conditions for Fillet Welded T-Joints in 6.35 mm
and 12.7 mm (1/4 in. and 1/2 in.) General Galvanized Steel Plate Using Basic Electrodes*
Plate Thickness
mm
in.
Electrode Diameter
mm
in.
Welding Position
Current (ac), A
6.4
1/4
3.2
1/8
Flat
120
6.4
1/4
3.2
1/8
Vertical
89–109
6.4
1/4
3.2
1/8
Horizontal
109–135
6.4
1/4
3.2
1/8
Overhead
109–117
12.7
1/2
4
5/32
Flat
12.7
1/2
4
5/32
Vertical
147
12.7
1/2
4
5/32
Horizontal
170
12.7
1/2
4
5/32
Overhead
158–170
*AWS E7016; B.S. 1719, Class E616H.
107
155
156
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
12.7 mm (1/4 in. and 1/2 in.) galvanized steel plate
welded in all positions with and basic covered electrodes. The travel speeds are 20% to 30% lower in the
vertical and overhead positions compared to welding
speeds on uncoated steel.
The fill passes for multiple-pass T-joints can be
deposited on galvanized steel in the vertical position
using uphill progression without any reduction in welding speed compared to welding speeds on uncoated
steel. As stated previously, undercut may occur at either
or both sides of welds deposited in the vertical position.
Grinding may be necessary after the initial pass to
remove slag so that it does not become trapped by subsequent passes.
Two different techniques can be used to avoid undercut. For the root pass, the first technique involves holding the electrode at a travel angle of 90° to the joint
line, and moving it up and down in a whipping motion
over a distance of approximately 8 mm (5/16 in.). The
second technique involves using the same whipping
motion, but with the electrode held at a travel angle of
70° to the joint line. For the intermediate passes, commonly called filler passes, the first technique involves
using a triangular weave, whereas the second technique
involves using a side-to-side weave.
Electrodes for Downhill SMAW. The basic covered
electrode, AWS E7048, is highly suitable for the
shielded metal arc welding of galvanized steel in buttjoints and T-joints in the horizontal position or the vertical position with downhill progression.24 The E7048
provides easier welding than the conventional basic cov-
ered electrodes; bead shape is improved and slag removal
is easier.
An edge shaped with a 50° groove angle, instead of
the 60° groove angle that is normal for uncoated steels,
will make downhill-welded butt joints easier to deposit.
The 50° angle makes it easier to maintain a short arc
and to ensure sidewall fusion of the root pass. A thin,
flowing slag is advantageous for welding in positions
other than vertical with downhill progression. In horizontal butt joints, for example, slag removal is facilitated so that the danger of slag entrapment is negligible.
Radiographic Appearance of SMAW Welds.
Groove welds in butt joints in all thickness of continuous and general galvanized steel made with rutile or
basic covered electrodes should be free from porosity.
Porosity can occur in fillet welds on 3.2 mm (1/8 in.)
galvanized steel made with basic covered electrodes.
(Refer to Table 3.10.) Fillet welds in thicker galvanized
steel made with either rutile or basic covered electrodes
usually are free from porosity or may contain small isolated pores.
For groove welds in butt joints made in the horizontal position on 6.4 mm (1/4 in.) and thicker general galvanized steel, it is necessary to maintain a root opening
of at least 2.4 mm (3/32 in.) to avoid trapped slag at the
edges of the root pass. This does not apply to the basic
covered electrode developed principally for downhill
welding (E7048), which leaves a thin slag cover that is
easily removed when the electrode is used in the horizontal position.
Gas Metal Arc Welding
24. Refer to American Welding Society (AWS), 2004, Specification
for Carbon Steel Electrodes for Shielded Metal Arc Welding, AWS
A5.1/A5.1M:2004, Miami: American Welding Society.
Gas metal arc welding (GMAW) is an arc welding
process using an arc between a continuous filler metal
Table 3.10
Radiographic Appearance of Shielded Metal Arc Welding Fillet Welds
in T-Joints in 3.2 mm (1/8 in.) Continuous and General Galvanized Sheet
Radiographic Appearance
Zinc Coating Thickness
Rutile Electrode
Basic Electrode
Welding
Position
First Side
Second Side
First Side
Second Side
381
1.25
(includingiboth sides)
Horizontal
Clear
Clear
4 pores per
152 mm (6 in.)
6 pores per
152 mm (6 in.)
Vertical*
Clear
Clear
Clear
Clear
610
Horizontal
Clear
Clear
17 pores per
152 mm (6 in.)
34 pores per
152 mm (6 in.)
Vertical*
Clear
Clear
Clear
Clear
g/m2
oz/ft2
2.00
(each side)
*Uphill progression.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
electrode and the weld pool. The process is used with
shielding from an externally supplied gas and without
the application of pressure. Detailed information on
the gas metal arc welding process is available in Chapter 4 of the Welding Handbook, Volume 2, Welding
Processes.25
Welding Conditions for General Galvanized
Plate. Welding conditions for butt joints made with
25. See Reference 14.
157
the short-circuit gas metal arc welding (GMAW-S) process in 6.4 mm (1/4 in.) galvanized plate are provided in
Table 3.11. Conditions for T-joints in 12.7 mm (1/2 in.)
galvanized plate are provided in Table 3.12. The shielding gas for both applications is CO2.
The short-circuit gas metal arc (GMAW) spray transfer mode produces less distortion and damage to the
zinc coating than the gas metal arc pulsed welding
mode (GMAW-P). The purpose of the 1.6 mm (1/16 in.)
root opening between the 12.7 mm (1/2 in.) plates in
the T-joint is to reduce intergranular cracking, which is
possible in fillet welds made by GMAW using carbon
Table 3.11
Typical Welding Conditions for V-Groove Welds in Butt Joints in
6.35 mm (1/4 in.) General Galvanized or Metallized Steel Using GMAW-S with CO2a
Welding Conditions
Wire Feed Speed
Welding
Position
Travel Speed on
Uncoated Steel
Travel Speed
Number of
Passes
Pass
Number
Current,
A
Voltage,
V
mm/s
in./min
mm/s
2
1
135
19.5
61
145
2.96
7
4.23
10
2
165
21
89
210
3.39
8
4.66
11
1
115
18
57
135
2.54
6
2.54
6
2
115
18
57
135
2.12
5
2.96
7
4.5
Flat
Overhead
2
in./min
mm/s
in./min
Verticalb
1
1
135
19.5
61
145
1.27
3
1.91
Horizontal
3
1
135
19.5
61
145
2.12
5
3.81
9
2
135
19.5
61
145
7.2
17
7.20
17
3
135
19.5
61
145
4.23
10
6.77
16
a. Electrode stickout 6.4 mm to 9.5 mm (1/4 in. to 3/8 in.). 1 mm (0.035 in.) diameter ER70S-3 deoxidized wire. Gas flow rate 14 L/min (30 ft3/h). Edge
preparation 60° V. 1.6 mm (1/16 in.) root face, 1.6 mm (1/16 in.) root opening.
b. Uphill progression.
Table 3.12
Typical Welding Conditions for Fillet Welds in T-Joints in
12.7 mm (1/2 in.) General Galvanized or Metallized Steel Using GMAW-S with CO2a
Welding Conditions
Wire Feed Speed
Travel Speed
Travel Speed
on Uncoated Steel
Current,
A
Voltage,
V
mm/s
in./min
mm/s
in./min
mm/s
in./min
Horizontal
135
20
61
145
2.1
5
8.4
8
Verticalb
135
20
61
145
4.2
10
4.2
10
Verticalc
135
20
61
145
2.1
5
2.1
5
Overhead
135
20
61
145
2.3
5.5
3.4
8
Welding Position
a. Electrode stickout 6.4 mm to 9.5 mm (1/4 in. to 3/8 in.). 1 mm (0.035 in.) diameter ER70S-3 deoxidized wire. Gas flow rate 14 L/min (30 ft3/h). 1.6 mm
(1/16 in.) root opening.
b. Downhill progression.
c. Uphill progression.
158
CHAPTER 3—COATED STEELS
dioxide as a shielding gas on galvanized plates thicker
than 6.4 mm (1/4 in.). Intergranular cracking caused
by zinc penetration can be prevented even without a
root opening by using ER70S-2 filler metal in place of
ER70S-3.
Spatter Formation. When using GMAW in the
short-circuiting transfer mode with CO2 as the shielding
gas, each short circuit during the transfer of metal
causes a rapid momentary rise in current followed by
extinguishing of the arc. Re-ignition is accompanied by
the ejection of small particles of molten metal in the
form of spatter. When a shielding gas of either carbon
dioxide or a mixture of 80% argon-20% carbon dioxide
is used, spatter is increased when welding galvanized
steel compared to uncoated steel.
When welding uncoated steel, the rate of the increase
in short-circuit current and the amount of spatter
formed can be reduced by increasing the inductance of
the circuit. When welding galvanized steel, considerable
spatter is still emitted when the variable inductance is at
the optimum setting.
Solid-state or electronically controlled power sources
change the effective inductance with electrical adjustments and often the spatter level can be reduced. Some
older power sources may require that inductance be
adjusted by changing the setting of a mechanically
adjustable choke built into the power source.
If the spatter particles adhering to the workpiece are
unsightly, the problem can be minimized by spraying an
anti-spatter compound onto the workpiece before welding. Available anti-spatter products are based on silicone, petroleum, or graphite compounds. Applying one
of these products will allow the spatter particles to be
brushed off easily. Another problem may be the buildup
of spatter in the gas nozzle of the welding gun, which
can interrupt the flow of shielding gas and in extreme
cases, can cause erratic wire feeding. Again, the application of anti-spatter compound reduces the adherence of
spatter particles so that they can be removed easily after
a short distance of welding by simply tapping the gas
nozzle of the welding gun lightly against the bench or
the workpiece. If an anti-spatter compound is used
before welding galvanized steel with GMAW-S and a
shielding gas of either carbon dioxide or a mixture of
80% argon-20% carbon dioxide, it is possible to make
welds at least 3 m (10 ft) long before welding has to be
interrupted to clean the gas nozzle.
Spatter formation increases with the thickness of the
zinc coating and therefore is greater on batch-galvanized steel than on continuous-coated sheet. As noted
previously, when T-joints in general galvanized steel are
welded in the flat position, spatter particles tend to roll
into the corner of the joint causing difficulty in welding.
Spatter formation is also troublesome when welding in
the overhead position, as spatter particles are apt to fall
AWS WELDING HANDBOOK 9.4
into the gas nozzle of the welding gun. Spatter formation can be reduced by replacing the 1.14 mm (0.045
in.) diameter wire with 0.8 mm (0.030 in.). However,
the use of a smaller-diameter filler wire, for example,
0.6 mm (0.02 in.) does not produce any further
improvement.
Radiographic Examination. Butt joints welded by
the GMAW process on galvanized sheet thinner than
3.2 mm (1/8 in.) should be free from discontinuities and
yield clear radiographs. Fillet-welded T-joints may contain variable amounts of porosity, usually restricted to
the root of the weld and not visible at the weld surface.
This internal porosity generally is more extensive in the
second weld of a double-fillet joint, probably because
the first weld cuts off one avenue of escape for volatilized zinc. With continuous-coated sheet, an increase in
zinc coating thickness (for example, from 381 g/m2 to
762 g/m2 [1.25 oz/ft2 to 2.50 oz/ft2]) may lead to
increased porosity in both the first and the second
welds.
Porosity is produced by the nucleation and growth of
gas or vapor bubbles while the weld metal is in the process of solidifying. One of the variables is the amount of
the gas or vapor source that is present in the system.
Also critical is the rate of solidification. At very low
solidification rates, the bubbles have a chance to escape;
whereas at high rates they either do not have an opportunity to nucleate, or they nucleate and are trapped
before their growth is sufficient to be noticed. Trouble
develops at intermediate cooling rates. Therefore,
changes in welding conditions that affect solidification
rates of the weld metal (such as the welding current,
voltage, or travel speed) will affect the amount of
porosity observed. Another rate-controlling factor is the
amount of zinc that dissolves in the fused weld metal.
Porosity might be difficult to control, particularly in fillet welds, because the coating thickness on the plate
edges may vary. Fortunately, if porosity occurs when
welding galvanized steel, the mechanical properties of
the welds generally are not significantly impaired.
Welded butt joints in galvanized plate 6.4 mm (1/4 in.)
and thicker should be free from porosity. Fillet welds
made by the GMAW process with carbon dioxide as the
shielding gas generally are sound, although occasionally
pores may be present if the plate edges have excessively
thick coatings of zinc.
Flux Cored Arc Welding
Flux cored arc welding (FCAW) is an arc welding
process that uses an arc between a continuous filler
metal electrode and the weld pool. The process is used
with shielding from a flux contained within the tubular
electrode, with or without additional shielding from an
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
externally supplied gas, and without the application of
pressure.
General galvanized steels can be joined with the flux
cored arc welding process with flux cored electrodes.
Manufacturers of these electrodes have developed slag
systems for use with carbon-dioxide shielding and for
gas-free applications. The self-shielded electrodes are
favored for fabricating sheet metal because of the low
penetration and high travel speeds that are possible.
The FCAW electrodes contain magnesium, which seems
to exacerbate weld metal cracking, so special magnesium-free formulations have been developed for welding galvanized sheet. The recommendations of the
electrode manufacturer should be followed, and the
welding procedure should be qualified by appropriate
tests. Detailed information on flux cored arc welding
is presented in Chapter 5 of the Welding Handbook,
Volume 2.26
Submerged Arc Welding
Submerged arc welding is a welding process using an
arc or arcs between a bare metal electrode or electrodes
and the weld pool. The arc and molten metal are
shielded by a blanket of granular flux on the workpieces. The process is used without pressure and with
filler metal from the electrode and sometimes from
a supplemental source (welding rod, flux, or metal
granules).
Submerged Arc Welding is discussed in detail in Volume 2 of the Welding Handbook, Chapter 6. (Refer to
26. See Reference 14.
159
Appendix B). The welding of butt-joints and T-joints in
general galvanized plate using the submerged arc welding (SAW) process is described in this section.
Butt Joints. The SAW process can be used to make
butt joints in galvanized plate thicker than 6.35 mm
(1/4 in.) using the same edge shapes as those used for
uncoated steel. However, to avoid porosity, it helps in
some cases to reduce the travel speed and welding current. If the edges are shaped for welding after galvanizing, (i.e., they are uncoated), the welding conditions
used for uncoated steel will produce sound welds in
both 12.7 mm and 25.4 mm (1/2 in. and 1 in.) galvanized plate. This also applies for closed joints (i.e., with
no root opening) square-groove butt joints and for plate
surfaces with a heavy coating of zinc, as described in
Tables 3.13, 3.14, and 3.15.
When the plate edges are galvanized, a 70° V-groove
angle with a 6.4 mm (1/4 in.) root face facilitates the
escape of volatilized zinc and produces minimal porosity, as shown in Table 3.16. This edge shape would also
be suitable for butt joints in plates thicker than 12.7 mm
(1/2 in.). Square-groove butt joints with galvanized
edges can be welded satisfactorily, but weld soundness
depends on the travel speed and the zinc coating thickness, which can be variable, especially on edges. (Refer
to Table 3.13 for the effect of travel speed.) Table 3.17
indicates that high currents can be used to weld plate
with a heavy zinc coating.
Depending on travel speed and the thickness of the
zinc coating, porosity can be reduced or eliminated by
supporting the workpieces to keep them free from the
Table 3.13
Typical Welding Conditions for Square-Groove Submerged
Arc Welds in Butt Joints in 12.7 mm (1/2 in.) General Galvanized Platea
Welding Conditions
Root Opening
Condition of
Plate Edges
First Side
Second Side
Radiographic
Appearanceb
Travel Speed
Current, Voltage, Current, Voltage,
A
V
A
V
mm/s
in./min
Max. Pore Size
No. of
Pores
mm
in.
Visual
Appearance
mm
in.
Galvanized
0
0
540
32
540
32
6
14
0
—
—
Satisfactory
Galvanized
0
0
600
39
610
37
10
24
60
4.8
3/16
Peaky
Galvanized
1.6
1/16
600
39
610
37
10
24
10
2.4
3/32
Satisfactory
Galvanized
3.2
1/8
600
39
610
37
10
24
0
—
—
Satisfactory
Uncoated (oxygen-cut)
0
0
600
39
610
37
10
24
0
—
—
Good
Zinc coating weight 762 g/m2 (2.5 oz/ft2). 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive.
a.
b. Length of radiograph = 375 mm (15 in.).
160
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.14
Typical Welding Conditions for Square-Groove Submerged
Arc Welds in Butt Joints in 25.4 mm (1 in.) General Galvanized Platea
Radiographic Appearanceb
Welding Conditions
First Side
Condition of
Plate Edges
Root
Opening
Galvanized
Uncoated
(oxygen-cut)
Second Side
Travel Speed
Max. Pore Size
Current, Voltage, Current, Voltage,
A
V
A
V
mm/s
in./min.
Number
of Pores
mm
in.
Visual Appearance
0
1000
37
1000
37
4.66
11
4
1.6
1/16
First side good,
second side uneven
0
1000
37
1000
37
4.66
11
0
—
—
Good
a. 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive. Plates supported free from bench.
b. Length of radiograph = 375 mm (15 in.).
Table 3.15
Typical Welding Conditions for Bevel-Groove Submerged
Arc Welds in Butt Joints in 12.7 mm (1/2 in.) General Galvanized Platea
Radiographic Appearanceb
Welding Conditions (Both Sides)
Travel Speed
Zinc Coating Weight
oz/ft2
Current,
A
Voltage,
V
mm/s
762
2.5
750
42
Galvanized
1525
5
750
Uncoated
(oxygen-cut)
1525
5
750
Condition of
Plate Edges
g/m2
Galvanized
Max. Pore Size
in./min
Number
of Pores
mm
in.
Visual Appearance
10
24
0
—
—
Good
42
10
24
27
4.8
3/16
First side uneven,
second side good
42
10
24
0
—
—
Good
a. Edge shape 35° bevel, root opening nil; 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive.
Plates supported free from bench.
b. Length of radiograph = 375 mm (15 in.).
Table 3.16
Typical Welding Conditions for V-Groove Submerged
Arc Welds in Butt Joints in 12.7 mm (1/2 in.) General Galvanized Platea
Welding Conditions
Backing Pass
Prepared Side
Radiographic Appearance
Max. Pore Sizeb
Travel Speed
Condition of
Plate Edges
Current,
A
Voltage,
V
Current,
A
Voltage,
V
mm/s
in./min.
Number
of Pores
mm
in.
Visual
Appearance
Galvanized
500
45
760
45
8
20
1
1.6
1/16
Good
a. Edge shape, 70° included angle. 6.4 mm (1/4 in.) root face. Root opening nil. 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate
flux. Direct current electrode positive. Zinc coating weight 762 g/m2 (2.5 oz/ft2).
b. Length of radiograph = 375 mm (15 in.).
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
161
Table 3.17
Typical Welding Conditions for Square-Groove Submerged Arc Welds
in Butt Joints in 12.7 mm (1/2 in.) General Galvanized Plate with Heavy Zinc Coatinga
Welding Conditions
First Side
Second Side
Travel Speed
Condition of
Plate Edges
Root
Opening
Current,
A
Voltage,
V
Current,
A
Voltage,
V
in./min
mm/s
Radiographic
Appearanceb
Visual
Appearance
Galvanized
0
720
40
820
42
19
8
Clear
Uneven
1525 g/m2 (5 oz/ft2). 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive. Root opening nil.
a.
b. Length of radiograph = 375 mm (15 in.).
welding bench, which allows the zinc vapor to escape
from beneath the joint and above it.
Submerged arc welds on galvanized steel sometimes
have a slightly uneven surface, which makes slag
removal more difficult compared to welds on uncoated
steel.
The submerged arc welding process produces sound
welds with good appearance and easy slag removal in
butt joints in general galvanized steel. Bevel-groove
welds, square-groove welds, and V-groove welds also
are used. To weld uncoated edges when using these
three weld designs, the edges should be oxygen-cut, or
if possible, machined because the joints as easily welded
as those in uncoated steels.
Bevel-Groove Welds. It is necessary to burn off the
zinc from the galvanized edges when preparing for
bevel-groove submerged arc welds in galvanized steel
plate. Welding conditions should include increased root
openings and slower travel speeds. This is especially
true for heavily coated plate. Table 3.15 shows typical
welding conditions for bevel-groove welds in butt joints
in 12.7 mm (1/2 in.) general galvanized plate.
V-Groove Welds. For submerged arc V-groove welds
in general galvanized plate, the groove edges should be
shaped at a 70° angle. Table 3.16 shows typical welding
conditions for V-groove welds in butt joints in 12.7 mm
(1/2 in.) general galvanized plate.
Square-Groove Welds. For galvanized edges in
square-groove welds made with the submerged arc process, travel speed should be reduced; a root opening up
to 3.2 mm (1/8 in.) should be used, and the workpieces
should be supported so that they are free from the
bench or other support. Increased current is needed to
burn the zinc off of the edges of heavily coated steels to
obtain complete joint penetration.
T-Joints. Tandem submerged arc fillet welds, in which
both sides of a T-joint can be welded simultaneously,
can be deposited on galvanized steel. The welding head
on one side travels approximately 23 cm (9 in.) behind
the welding head on the other side. However, for sound,
porosity-free welds, the maximum travel speed must be
considerably less than travel speeds that are possible on
uncoated steel. The maximum travel speed depends on
the thickness of the zinc coating, and travel speed can
be increased if the standing plate has an uncoated oxygencut edge. A root opening of 1.6 mm (1/16 in.) between
the plates allows the volatilized zinc to escape, allowing
higher travel speed. Table 3.18 shows typical welding
conditions for tandem fillet welds in T-joints in 12.7 mm
(1/2 in.) galvanized plate.
Arc Stud Welding
Arc stud welding (SW) is an arc welding process
using an arc between a metal stud, or similar part, and
the other workpiece. The process is used without filler
metal, with or without shielding gas or flux, with or
without partial shielding from a ceramic or graphite ferrule surrounding the stud, and with the application of
pressure after the faying surfaces are sufficiently heated.
Arc stud welding provides a method for rapidly
attaching studs or other suitably shaped parts to metal
surfaces. The stud (one workpiece) is held in a manually
operated welding gun which is placed against the surface to which the stud will be attached (the other workpiece). An arc is initiated between the end of the stud
and the plate surface. After a predetermined time,
between 0.1 seconds (s) and 0.8s and depending on the
area of the stud or attachment, the current is automatically switched off, and under spring pressure, the stud is
forced into the weld pool. This action welds the full
cross-sectional area of the stud to another surface. The
tensile strength of the resulting weld should be equivalent to that of the stud material. Plain and threaded
162
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.18
Typical Welding Conditions for Submerged Arc Tandem
Fillet Welds in T-Joints in 12.7 mm (1/2 in.) General Galvanized Platea
Radiographic Appearanceb
Welding Conditions
Leading Weld
Trailing Weld
Leading Weld
Travel Speed
Root Opening
Condition of
Plate Edges
in.
mm
Galvanized
0.0
0
480
Current, Voltage, Current, Voltage,
A
V
A
V
32
440
mm/s
30
Max. Pore Size
No. of
in./min Pores
6
15
Trailing Weld
0
Max. Pore Size
mm
in.
No. of
Pores
—
—
0
—
mm
in.
—
Galvanized
0.0
0
500
33
450
32
8
20
8
1.6
1/16
21
2.4
3/32
Uncoated
0.0
0
500
33
450
32
8
20
4
1.6
1/16
5
1.6
1/16
Galvanized
1.6
1/16
500
33
450
32
8
20
2
1.6
1/16
1
1.6
1/16
3.2 mm (1/8 in.) diameter, 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive. Zinc coating weight 762 g/m2 (2.5 oz/ft2).
a.
b. Length of radiograph = 375 mm (15 in.).
studs are available from 3.2 mm to 31.7 mm (1/8 in. to
1-1/4 in.) in diameter.
Arc stud welding conditions and tensile test results
for 12.7 mm (1/2 in.) uncoated steel (0 coating weight)
and general galvanized mild steel are provided in Table
3.19.
Macrosections of studs welded to 12.7 mm (1/2 in.)
plate are shown in Figure 3.12. Figure 3.12(A) shows
the initial position of the stud, in this instance, a 16 mm
(5/8 in.) stud with an uncoated end. Typical of an arc
stud weld on galvanized steel, weld metal tends to pile
up on one side, as shown in Figure 3.12(C). This pileup
is not observed on the uncoated plate shown in Figure
3.12(B). For galvanized studs, it is essential to remove
the zinc from the faying surface of the stud before welding. If the surface is zinc coated, weld metal may be vio-
lently expelled from the joint as the zinc volatizes and
exits the faying surfaces.
Friction Welding
Friction welding (FRW) is a solid-state welding process that produces a weld under the compressive force
contact of workpieces rotating or moving relative to
one another to produce heat and plastically displace
material from the faying surfaces.
Friction welding can be used in applications similar
to arc stud welding; for example, attaching shear connectors to steel beams for the anchoring of concrete in
composite steel-concrete structures.
Flat-ended studs, whether uncoated or galvanized,
cannot be welded to galvanized plate because the alloy
Table 3.19
Arc Stud Welding Conditions and Breaking Loads, 12.7 mm (1/2 in.) Plate
Stud Diameter
Zinc Coating
Weight on Plate
Spring Tension Setting
mm
in.
g/m2
oz/ft2
Coarse
Fine
Current,
A
kN
lb
Position of Fracture
6.4
1/4
0
0.0
2
5
300
18.2
4090
Stud, remote from weld
Weld junction
Breaking Load
(Average of Three Tests)
6.4
1/4
762
2.5
2
5
350
16.5
3700
19.9
5/8
0
0.0
3
10
750
10.4
23 370
Stud, remote from weld
19.9
5/8
762
2.5
2
10
750
10.5
23 630
Stud, remote from weld
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
(A) Initial Position
(B) Uncoated Plate
163
(C) Coated Plate
Figure 3.12—Comparison of Upset Displacement Caused by Base Metal Coating
in Arc Stud Welds in 12.7 mm (1/2 in.) General Galvanized Plate
layers in the zinc coatings act as low-friction bearing
surfaces, and insufficient heat is developed for welding.
However, studs can be welded to galvanized surfaces
with the friction welding process if pointed studs are
used. Best results are obtained with a point shaped with
a 120° included angle. Welding conditions for friction
welding with pointed studs are provided in Table 3.20,
showing that the presence of a zinc coating on the steel
plate increases the time required for welding. Figure
3.13(A) shows a cross section of a pointed stud and (B)
the profile of a weld attaching it to uncoated plate and
(C) general galvanized plate.
Induction Brazing
Induction brazing (IB) is a brazing process using heat
from the resistance of the assembly to the induced electric current.
High-frequency induction brazing can be performed
on general galvanized sheet with very good results using
filler alloys of silicon bronze or 60% copper-40% zinc.
Careful control of heating rates will result in sound
joints with very little damage to the zinc coating.
Braze Welding
Braze welding (BW) is a joining process in which the
brazing filler metal is deposited in the joint without
capillary action or melting of the base material.
General galvanized steel can be braze welded using
heat provided by the oxyfuel gas process or an electric
arc. The gas metal arc, shielded metal arc, and gas tungsten arc welding processes can be used.
Oxyfuel Braze Welding. Braze welds are made at a
lower temperature than fusion welds. The base metal is
not melted and there is less loss of the zinc coating from
the steel. The brazing alloy generally used is 60% copper-40% zinc. It melts at temperatures between 900°C
and 930°C (1650°F and 1700°F) and flows over the root
Table 3.20
Direct-Drive Friction Welding Conditions for 16 mm (5/8 in.) Diameter
Pointed Steel Studs Welded to 12.7 mm (1/2 in.) General Galvanized Steel Plate
Frictional Force
Upset Force
Burn Off
Condition
of Point
Weld
Time, s
Rotational
Speed, rpm
MN/m2
ksi
MN/m2
ksi
mm
in.
Braking
Forces
Uncoated
3–4
1900
76.5
11.2
76.5
11.2
8.0
0.30
0
Galvanized
18
1900
76.5
11.2
76.5
11.2
8.0
0.30
0
164
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
(A) Pointed Stud
(B) Uncoated Plate
(C) Galvanized Plate
Figure 3.13—Friction Weld Between (A) 16 mm (5/8 in.) Diameter
Galvanized Pointed Stud, (B) Welded to and 12.7 mm (1/2 in.)
Uncoated Plate, and (C) Welded to General Galvanized Plate
and groove faces of the joint and alloys or “tins” with
the steel to produce a strong corrosion-resistant joint.
Alternatively, silicon bronze (Cu-1.5-3.0% Si) can be used
if higher strength is needed, although higher temperatures
are required. Following are typical parameters and techniques for braze welding galvanized steel:
1. Grease or dirt must be removed from the regions
of the joint by means of degreasing agents, wire
brushing, or steel wool;
2. Sheet edges for butt joints should be shaped as
shown in Table 3.21;
3. Sheet edges for lap joints or T-joints should be
shaped as illustrated in Table 3.22;
4. Fixtures or clamps should be used to hold the
workpieces and to prevent distortion during welding, or tack welds on can be used on workpieces
that are known not to be subject to distortion;
5. Braze welding flux should be mixed with water
to a stiff paste and applied generously to the
upper and reverse sides of the joint and also to
the filler rod;
6. A torch tip that is two sizes smaller than tips
specified for fusion welding of sheet of the same
thickness should be used;
7. The filler rod should be a 60% copper 40% zinc
alloy, AWS A5.8, RBCuZn-A with a diameter
one and one-half times the thickness of the sheet
for material up to 4.8 mm (3/16 in.) and 6.4 mm
(1/4 in.) diameter rod for material over 4.8 mm
(3/16 in.) thick; 27
27. American Welding Society (AWS), 2004, Specification for Filler
Metals for Brazing and Braze Welding, AWS A5.8/A5.8M:2004,
Miami: American Welding Society.
Table 3.21
Edge Shapes for Braze Welds in Butt Joints in General Galvanized Sheet Steel
Sheet Thickness, t
Joint Design
mm
in.
Edge Preparation
Root Opening
Root Face
3.2 max.
1/8 max.
Square
t/2
—
Over 3.2
and up to 6.4
Over 1/8
and up to 1/4
70–90°
groove angle
t/4
See Note*
*Root face is not generally specified but sharp corners should be rounded off which will result in a root face of 1.6 mm (1/16 in.).
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
general galvanized sheet metal with either the shortcircuiting or pulsed-arc variations of the process. Argon
or an argon-helium mixture is used to shield the arc and
the weld pool. Silicon-bronze electrodes are preferred.
Typical gas metal arc braze welding conditions for
short-circuiting transfer are shown in Table 3.23.
The welding currents should be maintained within
five amperes of the values in Table 3.23. High currents
can cause the inclusion of too much iron from the base
metal into the weld metal, which can lead to transverse
cracks in the weld. Low currents, however, can cause
incomplete fusion and uneven deposits. The latter problem can be partially solved by using the pulsed arc
variation.
Because of the low heat input involved, root openings are required when welding butt joints to obtain
complete joint penetration. To control penetration, the
use of a grooved copper backing bar is recommended.
The high travel speeds indicated in Table 3.23 are necessary to decrease heat input and prevent cracking.
Mechanized travel systems must be used to maintain
control at high speeds. The use of hand-held torches is
limited to making tack welds only.
In addition to silicon-bronze electrodes, aluminumbronze electrodes also can be used for braze welding
galvanized steels. Typical conditions for braze welding
with aluminum-bronze electrodes are provided in Table
3.24.
Table 3.22
Lap-Joint and T-Joint Designs for Braze
Welds in General Galvanized Sheet Steel*
Joint Design
Type of Joint
Type of Weld
Lap
Single fillet
Lap
Double fillet
T
Single fillet
T
Double fillet
165
*There is no thickness limit, and dissimilar thicknesses can be joined.
8. The flame should be adjusted to a slightly oxidizing condition;
9. When the joint temperature reaches a dull red
heat, the filler metal should be deposited, with
the flame directed more onto the rod than the
workpiece; and
10. The backhand or forehand technique should be
used, avoiding any lateral or weaving motion of
the torch to reduce the buildup of heat.
Shielded Metal Arc Braze Welding. Aluminumbronze, phosphor-bronze, or tin-bronze covered electrodes can be used for the shielded metal arc braze
welding of general galvanized steel. The low melting
point of these electrodes (1000°C to 1050°C [1832°F to
1922°F]) minimizes the amount of zinc burn-off and
results in welds with good corrosion resistance and
Gas Metal Arc Braze Welding. The gas metal arc
welding process can be used for the braze welding of
Table 3.23
Gas Metal Arc Braze Welding Conditions for Butt Joints and Lap Joints in General Galvanized Steel*
Sheet Thickness
mm
in.
Root Opening
Joint
Type
mm
in.
Welding
Position
Electrode
Angle,
degrees
Travel Speed
mm/s
in./min
Wire Feed Speed
Current,
A
Voltage,
V
mm/s
in./min
1.2
0.048
Lap
—
—
Horizontal
60
17
40
135
14.5
169
400
1.2
0.048
Butt
0.8
0.031
Flat
90
15
35
110
14
157
370
1.5
0.058
Lap
—
—
Horizontal
60
11
25
110
14
127
300
1.5
0.058
Butt
0.8
0.031
Flat
90
11
25
110
13.5
144
340
1.9
0.075
Lap
—
—
Horizontal
60
11
25
130
15
157
370
1.9
0.075
Butt
0.8
0.035
Flat
90
11
25
110
14
133
315
2.7
0.108
Lap
—
—
Horizontal
60
11
25
140
15
169
400
*Argon shielding gas. Gas flow rate 14 L/min (30 ft3/h). Electrode composition: Si 2.8%–4.0%, Cu balance; 1 mm (0.035 in.) diameter. Copper backing bar
grooved for butt joints, 3.2 mm × 0.03 mm (1/8 in. × 0.010 in.) groove.
166
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.24
Typical Conditions for Braze Welding Galvanized Sheet Steel with Aluminum-Bronze Electrodesa
Joint Type
Sheet Thickness
Welding Wire
Diameter
Wire Feed Speed
mm
in.
mm
in.
mm/s
1.6
0.062
0.80
0.031
1.6
2.0
0.062
0.080
0.80
1.19
1.6
2.0
0.062
0.080
1.6
0.062
in./min
Welding
Current,b
A
Welding
Voltage,
V
mm/s
in./min
108
256
100
18
8
18
0.031
0.047
118
69
280
162
130
150
19
16
8
7
18
16
0.80
1.19
0.031
0.047
108
161
256
380
100
140
18
16
6
8
14
18
0.80
0.031
110
260
110
18
8
18
Travel Speed
a. Aluminum bronze (Cu 90%, Al 10%) welding wire. Argon shielding gas. Gas flow rate 19 L/min (40 ft3/h).
b. Direct current electrode positive.
CONTINUOUS-GALVANIZED STEEL
Figure 3.14—Cross Section of Shielded
Metal Arc Braze Weld with Aluminum
Bronze Filler Metal on 15.2 mm (0.6 in.)
Thick General Galvanized Steel
strength. A cross section of a shielded-metal-arc brazewelded butt joint is shown in Figure 3.14.
Gas Tungsten Arc Braze Welding. The gas tungsten
arc braze welding process is best suited for general galvanized products with thin sections, as described in the
subsection Braze Welding of Continuous-Galvanized Steel.
Soldering
Soldering is best suited for joining materials of thinner gauge than those normally produced for general
galvanized steel, as described in the in the next section.
The continuous hot-dip process of galvanizing of
sheet steel provides coating masses (weights) of 75 g/m2
to 1100 g/m2 (0.25 oz/ft2 to 3.6 oz/ft2) total of both sides,
corresponding to thicknesses of 6 microns (μm) to 83 μm
(0.0002 in. to 0.0032 in.) of zinc on each surface. The
ASTM specification for continuous-galvanized sheet steel
is Standard Specification for Steel Sheet, Zinc-Coated
(Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed)
by the Hot-Dip Process, ASTM A 653/A 653M.28 This
specification contains 14 types of zinc coatings (G01
through G235) and four zinc-alloy coatings (A01 through
A60). The zinc-alloy coatings are produced by galvannealing. General galvanizing of shaped and prefabricated
components usually results in thicker coatings (masses),
from 300 g/m2 to 1200 g/m2 (1 oz/ft2 to 4 oz/ft2), corresponding to thicknesses of 40 μm to 170 μm (0.0016 in.
to 0.0067 in.).
Coating masses (weights) on automotive body panels
usually are less than 70 g/m2 (0.23 oz/ft2) per side,
whereas coatings for general construction use are typically designated as Z275 (G90), corresponding to a
nominal 137 g/m2 (0.45 oz/ft2 per side. Zinc coatings
for sheet steels are produced in a wide variety of com28. American Society for Testing and Materials (ASTM International) Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip
Process, ASTM A 653/A 653M, West Conshohocken, Pennsylvania:
ASTM International.
AWS WELDING HANDBOOK 9.4
positions, from nearly 100% zinc to alloys of up to
55% aluminum, or up to 20% other additions including iron, magnesium, and nickel. General hot-dip galvanized shapes almost always use a relatively pure zinc
coating metal containing less than 1.4% lead. The zinciron reaction and the alloys produced during hot-dip
galvanizing are discussed in the section ContinuousGalvanized Steel.
Zinc coatings often are alloyed with aluminum to
improve performance. The two most widely used zincaluminum hot-dip galvanizing coatings are Galfan,® a
zinc-5% aluminum-0.1% misch-metal coating, and
Galvalume,® a 55% aluminum/43.5% zinc/1.5% silicon
coating.29 A hot-dip coating called MagiZinc® introduced in the 2000s also is available, and consists of zinc,
5% to 13% aluminum, and 2% to 4% magnesium.30
The key requirement of a continuous-galvanized
coating is that it must withstand the forces of fabrication (e.g., bending, drawing, and stretching) without
flaking or cracking, while retaining a surface suitable
for finishing. To achieve these properties, the composition of the zinc bath and methods of sheet processing
are modified and are different from those described for
general galvanized coatings.
In general galvanizing, the malleability of the coating
is limited because of the brittle nature of the intermetallic layers. This is not a detriment for generalgalvanized products, but is a major problem for continuous-galvanized sheet. To suppress the formation of the
intermetallic reaction, aluminum is added to continuous
galvanizing zinc baths. The aluminum alloys with the
iron and zinc and forms an extremely thin ternarycompound layer at the interface of the coating and substrate. This layer inhibits the diffusion of iron into the
zinc, which is the reason the coating is extremely malleable. Also, to improve surface appearance and affinity
for painting, the size of zinc surface crystals (spangles)
is minimized by using a lead-free zinc bath (lead content
0.005% maximum). Before the use of lead-free zinc,
crystal growth on zinc surfaces was suppressed by rapidly cooling the surface of the sheet as it emerged from
the zinc bath.
Continuous-galvanized products typically are lighter
gauge steel and have a thinner coating than general galvanized products. Like the ASTM designations used for
aluminized sheet, designations for galvanized sheet
coatings refer to total coating mass (weight) on both
sides of the sheet. However, as of 2008, galvanized
sheet can be ordered to designations specifying coating
mass on each side. Of the many designations for coated
sheet, the most commonly used is G90 (Z275). The
ASTM document, Standard Specification for Steel
Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy29. Galfan is a registered trademark of the Galfan Technology Center,
Inc. Galvalume is a registered trademark of BEIC International, Inc.
30. MagiZinc is a registered trademark of Corus Group, the Netherlands.
CHAPTER 3—COATED STEELS
167
Coated (Galvannealed) by the Hot-Dip Process, ASTM
A 653/A 653M, provides a complete list of available
designations.31
Resistance Spot Welding
Resistance spot welding (RSW) is a resistance welding process that produces coalescence of the faying surfaces with the heat obtained from the resistance of the
workpieces to the flow of the welding current in a circuit (the workpieces form part of the circuit) and by the
application of pressure.
Figure 3.15 shows face designs and taper designs of
the electrodes for the standard letter designations (A
through F) assigned by the Resistance Welding Manufacturing Alliance (RWMA) for various applications of
resistance spot welding.
Resistance spot welding production rates on continuous-galvanized sheet may be comparable to those
achieved with uncoated steel, provided proper attention
is given to welding equipment variables and details such
as coating characteristics. The welding conditions for
uncoated low-carbon steel are changed by the zinc coating on the base steel in two major ways: it results in the
buildup of zinc on the electrode face and it changes the
electrical and thermal characteristics of the weld zone.
31. See Table 1 of ASTM A 653/A 653M, ASTM International, Subcommittee A05.11, 2007, Standard Specification for Steel Sheet,
Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed)
by the Hot-Dip Process, West Conshohocken, Pennsylvania: ASTM
International.
Type A
Pointed
Type B
Dome
Type C
Flat
Type D
Eccentric
Type E
Truncated
Type F
Radius
Figure 3.15—Standard RWMA Letter
Designations for Resistance Spot Welding
Electrode Face and Taper Designs
168
CHAPTER 3—COATED STEELS
Comprehensive information on resistance spot welding is provided by the Resistance Welding Manufacturing Alliance in Resistance Welding Manual, 4th revised
edition.32
Zinc Pickup on the Electrode Face. Zinc melts at
419°C (787°F), a temperature well below that produced
momentarily at the electrode-to-workpiece interface.
Molten zinc easily alloys with the surface of the copperbased electrode, often resulting in the buildup (called
pickup) of zinc on the face of the electrode. In a relatively short time, the buildup creates a broader contact
surface at the electrode face that reduces the current
density in the weld zone. This buildup can be delayed
by using an electrode with a truncated face (Type E as
shown in Figure 3.15), with an included angle of 90° to
140° and a flat-face diameter of four to five times the
thickness of the workpiece. Even larger-diameter electrodes are recommended when welding the zinc-aluminum alloy coatings, as described in this chapter in
Other Coated Steels.
Domed electrodes generally give unsatisfactory
results and should be used only when fit-up is a problem. Domed electrodes are more prone to buildup at the
outer junction of the curved face of the electrode and
the workpiece; this effect is accelerated with increasing
electrode radius. Generally, electrodes with low
included angles, as low as 90°, ensure that alloy buildup
occurs on the shoulder of the electrode, allowing it to
be easily sheared off. The degrading stability of current
density caused by electrode wear is also improved at the
lower angle. Electrodes should be adequately cooled;
for example, a coolant (usually water) at a flow rate of
at least 7.5 liters per minute (L/min) (2 gallons per
minute [gal/min]) should be applied to all electrodes.
The coolant tube should direct the water onto the back
side of the working face of the electrode.33
In addition to alloy buildup, erosion of the electrode
surface also reduces electrode performance. It is of
utmost importance that suitable electrode refacing techniques be used. Electrodes should never be hand filed,
as it is detrimental to electrode service life and weld
quality. Electrode face dressing can be an on-line process, or it can be off-line. In the automotive industry,
electrodes are exchanged and dressed off-line; this
reduces system down time while maintaining proper
geometry of the electrode face. When mushroomed
electrodes (electrodes with enlarged face diameters due
to the heat and pressure of welding) are dressed back to
their original contact-face diameter, only material from
32. Resistance Welding Manufacturing Alliance (RWMA), 2003,
Resistance Welding Manual, revised 4th edition, Miami: Resistance
Welding Manufacturing Alliance.
33. For examples of electrode water cooling, refer to Figure 4.22,
Page 132, Chapter 4, Resistance Welding Equipment, of Volume 3 of
the Welding Handbook, 9th Edition.
AWS WELDING HANDBOOK 9.4
the edge or side of the electrode should be removed,
leaving the conditioned face intact, unless it is badly pitted. If the electrode faces are not dressed frequently, the
contact faces become so large that they no longer concentrate enough welding current or heat to make a
weld. This may not be immediately obvious because the
coatings form a braze bond, sometimes called a zinc
halo, that holds the sheet together. The braze, while
having some strength in tensile shear, usually will not
stand even moderate shock, bend, or peel loads. However, on occasion this no-weld-nugget bond will seem to
be a good weld and even pull a button in a slow peel
test. For structural applications, the loading must be
through a steel-to-steel weld—that is, a true weld nugget.
Changes in Weld Zone Characteristics. The
presence of the soft, highly conductive zinc coating
changes the electrical and thermal characteristics of the
weld zone. Galvanized steel does not exhibit the high
contact resistance generally found at the faying surface
of uncoated low-carbon steel. Thus, under equivalent
conditions, less heat is generated at the faying surface
of galvanized steel. In addition, the zinc coating in contact with the electrodes provides an excellent path for
heat to flow from the weld zone into the water-cooled
electrodes.
Compensation for the galvanized coating can be
made by increasing both the welding current and welding time on galvanized steel by 25% to 50% over that
recommended for uncoated steel. For example, to
obtain quality welds in sheet with a coating weight of
90 g/m2 (0.3 oz/ft2), these variables should be increased
by 25% to 30%. A marked improvement in weldability
is possible by modifying the coating composition to
increase the hardness, melting point, and surface contact resistance, and to achieve greater ease of oxidation.
Aluminum cannot be used as an alloying addition to
improve weldability because it increases the current
required to make a weld and also increases electrode
wear and sticking.
The acceptable ranges for weld current and time are
narrower for galvanized steel than for uncoated steel,
indicating less tolerance for process variations. Tests
with sheet thicknesses between 1 mm to 2 mm (0.04 in.
to 0.08 in.) have shown that it takes over two times
longer for weld formation to begin on coated steel than
on uncoated steel. However, most resistance spot welding applications involve sheet thicknesses between 0.5 mm
to 1 mm (0.025 in. to 0.040 in.).
Hold time should be long enough to prevent the electrodes from separating while the zinc on the surface is
still molten. If this occurs, the zinc can be removed but
leaves an unprotected surface. However, hold times
should not be so long as to cause sticking of the electrode-face, which can lead to increased pitting and
AWS WELDING HANDBOOK 9.4
alloying of the electrode. The hold time must bear some
relationship to the thickness of the workpiece, and long
hold times generally are recommended for materials
thicker than 1.8 mm (0.069 in.). In general, hold time
should not be any longer than necessary for the weld
nugget to solidify.
The type of steel being welded also can affect welding conditions. For instance, welding lobes, defined as
the combinations of weld current and time that produce
acceptable welds in galvanized high-strength low-alloy
steels, do not necessarily overlap those for galvanized
mild steels. The dynamic resistance curve of galvanized
high-strength low-alloy steels has a greater variability
than the uncoated steel.
Several types of electrode materials can be used,
including alloys of copper-1% cadmium; copper-chromium; and copper-chromium-zirconium. The selection
of an electrode depends on the welding schedule and
the workpieces, which can only be determined by practical trials. Zirconium may have two positive effects: it
inhibits pickup on the surface of the electrode, and
because the zirconium tends to segregate to the grain
boundaries, it reduces the rate of alloy penetration
along these boundaries. The diameter of the electrode
shank should be as large as feasible. With correct welding conditions and optimum electrode configurations,
it is possible to make 3000 welds or more on
hot-dipped galvanized steel sheet and 5000 or more
welds on galvanneal steel sheet before redressing is
necessary. Further improvement with another class of
electrodes, dispersion-strengthened copper alloys, has
been reported.
Dual-pulse weld cycles have been successful in
improving the consistency of spot welds in production,
but can shorten electrode service life. It is possible to
increase the range of acceptable welding currents by
using upslope current for preheating and downslope
current for post heating. This approach has proven beneficial for the zinc-5% aluminum coating (described in
the section Other Coated Steels in this chapter), and
also can improve electrode service life when spot welding galvanneal. Typical schedules for spot welding galvanized low-carbon steels` are listed in Table 3.25.
These schedules should be considered as a guide for
good welding practice, but it should be recognized that
some modifications may have to be made for specific
applications.
To establish the suitability of a particular continuous-galvanized product (for example, sheet for resistance spot welding), the products should be evaluated
according to the test methods in Recommended Practices for Test Methods for Evaluating the Resistance
Spot Welding Behavior of Automotive Sheet Steel Materials, AWS/SAE D8.9M.34
34. See Reference 7.
CHAPTER 3—COATED STEELS
169
Series Welding
Series welding is a resistance welding secondary circuit variation in which the welding current is conducted
through electrodes and workpieces in a series electrical
path to form multiple resistance, spot, seam, or projection welds simultaneously.
In series welding, all the current flowing through one
weld area must flow through the other. Frequently, difficulty is encountered when a single secondary-current
circuit is used to make more than one weld at a time. If
the conditions at the two weld locations are approximately equivalent, and the current is proper, two satisfactory welds will be made, as shown in the preferred
arrangement in Figure 3.16(A). However, if the contact
tip faces are not the same size, the location with the
smaller contact area will be much hotter than the other.
With bare steel, the wide latitude of the material compensates for all but the grossest imbalance; but this is
not the case with coated steels.
The series welding configuration poses another problem: maintaining heat balance. With this method, often
an additional current path (a shunting path) allows
flow from one electrode to the other and circumvents
the weld locations. Additional current must be supplied
to compensate for this diversion of current, which
causes the electrode faces to run even hotter and the
welding current range to become even narrower. If the
current path through the top workpiece (sheet) is low
enough in resistance (that is, the path is shorter), as
shown in Figure 3.16(B), then series welding may not
be possible. While series welding can be practical under
certain conditions in coated steels, the design of the
weldment, joint design, welding procedure, and the
welding schedule should be well planned and tested.
The contact face is not the only factor that influences
the welding heat balance between series welds. The
electrode force, the thickness of the workpieces, the
effectiveness of the water cooling, and other factors can
upset the necessary balance, making one weld too hot
and the other too cold. If an imbalance between welds
can be traced to a malfunction, such as a sticking air
cylinder or loss of electrode cooling, the solution is
obvious. If the imbalance results because sheet thicknesses are not the same at each location, a slightly
larger contact tip face should be used at the hotter location (that is, the one from which expulsion occurs first)
and the welding current should be incrementally increased.
In some applications, more than one secondary circuit is operated from a single set of contactors. The
variables that upset the heat balance between series
welds also can upset the balance between welds made in
different secondary circuits controlled by the same contactor. In addition, differences in the secondary circuits
will have the same effect. The length and size of the secondary conductors, the cleanliness and quality of the
electrical joints, and the relative amounts of steel in
Table 3.25
Typical Spot Welding Schedules for Galvanized Low-Carbon Steel
Electrode Diameter and Shape (Sketch A) a, c
Material
Thicknessb
mm
D
in.
mm
d
in.
mm
in.
α,
Degrees
Net Electrode
Force
lb
kN
Approx.
Welding
Current,
A
Weld
Time,
Cycles
(60 Hz)
Weld Nugget
Diameter, Dw
(Sketch B) a
Minimum
Tension Shear
Strength
Minimum
Weld Spacing
Min. Contacting
Overlap, L
(Sketch C) a
mm
kN
mm
mm
in.
lb
in.
in.
0.56
0.022
15.9
0.63
4.8
0.18
120
300
1.3
13 000
8
3.8
0.15
2.4
550
15.9
0.63
15.9
0.63
0.76
0.030
15.9
0.63
4.8
0.18
120
400
1.8
13 000
10
4.1
0.16
4.4
1000
15.9
0.63
15.9
0.63
0.91
0.036
15.9
0.63
6.4
0.25
120
500
2.2
13 500
12
4.8
0.19
5.2
1180
19.1
0.75
15.9
0.63
0.99
0.039
15.9
0.63
6.4
0.25
120
650
2.9
14 000
13
5.3
0.21
6.2
1400
19.1
0.75
15.9
0.63
1.32
0.052
15.9
0.63
6.4
0.25
120
725
3.2
14 500
16
5.6
0.22
7.6
1700
22.2
0.88
17.5
0.69
1.60
0.063
19.1
0.75
6.4
0.25
120
850
3.8
15 500
22
6.1
0.24
11.1
2500
28.6
1.12
19.1
0.75
1.93
0.076
19.1
0.75
7.9
0.31
120
1200
5.3
19 000
24
7.1
0.28
14.2
3200
31.8
1.25
22.2
0.88
2.36
0.093
19.1
0.75
9.5
0.38
120
1400
6.8
21 000
30
8.6
0.34
18.7
4200
38.1
1.50
25.4
1.00
2.69
0.106
22.2
0.88
9.5
0.38
120
1750
7.8
20 000
37
10.2
0.40
26.2
5900
44.5
1.75
28.6
1.12
3.12
0.123
22.2
0.88
9.5
0.38
120
2000
8.9
20 000
42
12.2
0.48
32.0
7200
50.8
2.00
3.2
1.12
D
170 CHAPTER 3—COATED STEELS
`
L
α
Dw
(A) Electrode Diameter and Shape
(B) Weld Nugget Diameter
(C) Minimum Contacting Overlap
a. Dimensional variables are as shown in sketches A, B, and C.
b. Two equal metal thicknesses of each gauge. Commercial coating weight: 381 g/m2 (1.25 oz/ft2). Material must be free from dirt, grease, paint, etc., prior to welding, but may have light oil.
c. Electrode Material Group A, Class 2. Water cooling with 7.5 L/min (2 gal/min).
AWS WELDING HANDBOOK 9.4
d
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
171
SECONDARY
METALCOATED
STEEL
ELECTRODES
ELECTRODE
CONTACT
AREA
COPPER ALLOY
BACKUP BAR
WELDING CURRENT PATH
(A) Preferred Series Welding Setup: All the Welding Current
Flowing through One Workpiece Flows through the Others
SECONDARY
METAL-COATED
STEEL
ELECTRODES
SHUNTING
PATH
COPPER ALLOY
BACKUP BAR
WELDING CURRENT PATH
(B) Less Effective Series Welding Setup: a Shunting Path Allows
Significant Current to Flow Between the Electrodes Without
Passing Through the Desired Weld Location
Figure 3.16—Variations of Series Welding Arrangements and
Current Paths (A) Preferred Setup and (B) Less Effective Setup
each secondary circuit will influence the amount of heat
developed at each weld location. When a large number
of welds are controlled from one set of contactors, considerable maintenance may be required to keep the
welding conditions within satisfactory limits at all weld
locations. If they are severe enough, outside factors
such as variations in line voltage associated with the
operation of other equipment also can upset an otherwise satisfactory operation.
Resistance Seam Welding, Galvanized
Steel
Although seam welding schedules for pressure-type
welds are provided in Table 3.26, resistance seam welding
of galvanized steels is not recommended. Unlike terneplate (refer to Table 3.3), the seam welding of galvanized
steels results in zinc contamination of the wheel electrodes, requiring replacement and excessive maintenance.
172
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.26
Typical Seam Welding Schedules for Continuous Galvanized Low-Carbon Steel
Electrode Width and
Shape (Sketch A) a, b
Material
Thicknessc
W
mm
Net Electrode
Force
E
in.
mm
in.
kN
lb
Approx.
Welding
Current,
A
Weld Time,
Cycles (60 Hz) Welding Speed
Welds per
Unit Length
Minimum
Contacting
Overlap, L
(Sketch B) a
Heat
w/m
mm
mm
in.
Cool
mm/s in./min
w/in.
in.
0.38
0.015
9.5
0.38
6.3
0.25
4.00
900
15 000
2
2
51
120
295
7.5
9.5
0.38
0.91
0.036
12.7
0.50
6.3
0.25
4.90
1100
18 000
4
2
25
60
390
10.0
12.7
0.50
0.99
0.039
12.7
0.50
6.3
0.25
5.34
1200
19 000
4
3
25
60
355
9.0
12.7
0.50
1.32
0.052
12.7
0.50
6.3
0.25
6.00
1350
20 000
5
1
38
90
275
7.0
14.2
0.56
1.60
0.063
12.7
0.50
7.9
0.31
6.67
1500
19 800
8
2
23
54
275
7.0
15.8
0.63
1.98
0.078
15.8
0.63
7.9
0.31
8.23
1850
23 000
10
7
13
30
275
7.0
17.4
0.69
L
W
30°
E
(A) Electrode Width and Shape
(B) Minimum Contacting Overlap
a. Dimensional variables are as shown in sketches A and B.
b. Electrode Material RWMA Group A, Class 2. Typical electrode diameter ranges between 203 mm to 254 mm (8 in. to 10 in.).
c. Two equal metal thicknesses of each gauge. Commercial coating weight: 381 g/m2 (1.25 oz /ft2). Pressure-tight joints require stripping the zinc coating
prior to welding. Material must be free from dirt, grease, paint, etc., prior to welding, but may have light oil.
Another result may be welds of inconsistent quality
because small transverse cracks can occur at the outer
surfaces of the weld.
While seam welding schedules are not recommended,
intermittent-current welding can be used. Intermittentcurrent seam welding, in which current is supplied in
timed pulses, is recommended to avoid surface melting
and the resulting weld cracking. The off-time of the
intermittent schedule usually is considerably longer
than the on-time.
Resistance welding techniques have been developed
to overcome electrode contamination in seam welding.
One method uses narrow electrode wheels and profiled
drive rollers to clean and shape the wheels as welding
progresses. Marked improvement in electrode service
life is possible with this arrangement. The profiled drive
rollers are knurled only on the angled sides that engage
and drive the wheel electrodes. The root face of each
roller is smooth and contoured to match the face of the
mating wheel electrode. Each roller is hydraulically
loaded with sufficient force to reshape the wheel face; it
also maintains a relatively clean surface condition on
the electrodes. The applied force of the roller drive
breaks up the coating layer and removes it from the
electrode face. This type of drive also ensures a uniform
welding speed independent of the electrode wheel diameter. A spring-loaded scraping device is placed ahead of
the profiling roller to remove heavy buildup of coating
on the electrode.
For welding sheet up to 1.2 mm. (0.047 in.) thick,
the electrode wheel is 7.8 mm to 9.7 mm (0.31 in. to
0.38 in.) thick with a face radius of 5.1 mm to 6.1 mm
(0.20 in. to 0.24 in.). The seam width under these conditions is the following, in metric units (3.1(A) and U.S.
customary (3.1(B).
W mm = 2.5 T mm
where
Wmm = Seam width, mm
T mm = Sheet thickness, mm
(3.1A)
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
W in. = 0.5 T in.
(3.1B)
where
Win. = Seam width, in.
Tin. = Sheet thickness, in.
These dimensions are suitable for sheet thicknesses
up to 1.2 mm (0.047 in.). The electrode contact width
is 1.5 mm to 2.5 mm (0.06 in. to 0.10 in.), depending
on the wheel profile. The welds produced are narrow
(1.5 mm to 3.6 mm [0.06 in. to 0.14 in.]) compared to
those of conventional resistance seam welding, (3 mm
to 6.1 mm [90.12 in. to 0.24 in.]), but are stronger in
shear than the galvanized steel sheet base metal. The
narrowness of the weld makes it possible to reduce the
power requirements of the welding machine. With the
lower heat input, damage to the coating adjacent to the
weld zone can be minimized. However, caution must be
exercised when using a narrow wheel. Narrow wheels
may cause indentation which can cause cracking in the
weld, especially when using knurled drive wheels. Typical seam welding schedules for this technique are provided in Table 3.27.
Another method uses an intermediate foil or wire
electrode sandwiched between the workpiece sheets and
the main welding electrode, as illustrated in Figure 3.17.
The spray jets in Figure 3.17 provide water cooling for
the workpieces and the electrodes. The intermediate
electrode can be an integral part of the final joint, similar to a seam weld in a butt joint. The intermediate electrode also can be continuously replaced during welding.
This method is colloquially known as foil butt welding.
Projection Welding
Projection welding (PW) is a resistance welding process in which the weld size, shape, and placement is
determined by the presence of a projection, embossment, or intersection in one overlapping member which
serves to localize the applied heat and force.
Continuous-galvanized sheet steel can be welded
with the projection welding process; however, the limitations of this process must be recognized and adaptive
precautions must be followed. Due to the high heat
conductivity of zinc coatings, heat losses to the electrodes during the passage of welding current are higher
than the heat losses encountered when welding
uncoated steel. However, the contact resistance at the
faying surfaces is only slightly lower for galvanized steel
because of the deformation and subsequent melting of
the soft zinc coating. Therefore, somewhat lower electrode forces are recommended for the projection welding of galvanized steel.
On sheet thinner than 2.4 mm (0.094 in.), projection
welding produces a forged bond at the interface surface
rather than a fusion bond as in uncoated steel. An
increase in welding current beyond the recommended
current will result in the burning off and expulsion of
the projection from the weld zone. Even though a full
fusion bond does not develop in lighter gauges, satisfactory weld shear strengths are readily attainable if a line
of fusion is produced. Liquid-phase welds are easily
obtained with an iron-zinc alloy coated steel; the weld
size generally is greater than the projection size and is
dependent on weld time.
Projection welding schedules are listed in Table 3.28.
Larger projections than those used for uncoated steel
are recommended for galvanized steel in thicknesses less
than 2.4 mm (0.094 in.) to obtain shear strengths comparable to uncoated steel.
During projection welding of galvanized steel, the
cold upset distance, (sometimes called set-down) of any
one projection should not exceed 10% of its height.
Appropriate tests must be made to establish a suitable
Table 3.27
Typical Seam Welding Schedules for Continuous
Galvanized Steel Sheet with Radius-Faced Wheel Electrodes
mm
Welding Current, kA, with
Heat and Cool Time of
Electrode Forcea
Sheet Thickness
in.
173
kN
lb
20 msc
40 msb
0.41–0.61
0.016–0.024
2.2–3.0
500–675
13.0–14.1
10.2–11.1
0.61–0.79
0.024–0.031
3.0–3.4
675–775
13.7–14.8
11.1–12.0
0.79–0.99
0.031–0.039
3.2–4.0
725–900
14.2–15.4
11.8–12.8
0.99–1.19
0.039–0.047
4.0–4.4
900–1000
15.0–16.2
12.5–13.6
a. Copper alloy wheel electrodes with 5 mm (0.2 in.) face radius.
b. Welding speed—33.8 mm/s (80 in./min) [1 weld every 2.7 mm (9.4 welds/in.)].
c. Welding speed—67.7mm/s (160 in./min) [1 weld every 2.7 mm (9.4 welds/in.)].
174
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
FOILS
SPRAY
JETS
WORKPIECES
Figure 3.17—Principles of Seam Welding a Butt Joint
in Galvanized Sheet Steel Using a Foil Electrode
electrode force so that this limit is not exceeded. Excessive upset distance causes the interface area of the projection to be too large, and the projection may be blown
out or may not weld. Excessive upset distance also may
cause a large variation in the current through the several projections. All projections must contact at the same
time, without using more than 10% of the electrode
force.
The resistance welding machine should be equipped
with a low-inertia head for fast follow-up as the projections collapse during heating. The pressure system
should be capable of moving the head at about 330 mm/s
(13 in./s).
Oxyfuel Gas Welding
This process generally is not used for joining the thin
gauges normally encountered in continuous-galvanized
products. However, if oxyfuel welding is necessary, it
should be performed using the guidelines provided for
general galvanized steel.
Oxyfuel gas equipment is more widely employed in
braze welding, which is described in the subsection
Oxyfuel Braze Welding under Braze Welding.
Gas Tungsten Arc Welding
Gas tungsten arc welding (GTAW) of continuousgalvanized steel, unlike the welding of general galvanized steel, is recommended when precautions for preventing electrode contamination and arc stability are
instituted. Argon should be used as the shielding gas
with the GTAW process because it allows the arc to
operate quietly and with less depth of fusion. The lower
arc voltage obtained with argon facilitates the welding
of thin sheet, wire, or tubing because the risk of meltthrough is lessened; also, the lower energy input reduces
the amount of zinc volatilized. Melt-through also can
be minimized with an argon-purged copper backing
bar.
Contamination of the tungsten electrode by zinc can
be a serious problem, particularly when it blunts the tip
and causes erratic arc operation. The torch tip also can
AWS WELDING HANDBOOK 9.4
Table 3.28
Typical Seam Welding Schedules for Projection Welding of Continuous Galvanized Low-Carbon Steel (AWS C1.3)
Electrode Diameter and Shape
(Sketch A) a, c
Weld Nugget
Diameter, Dw
(Sketch B) a
mm
in.
mm
in.
mm
in.
kN
lb
Approx.
Welding
Current,
A
0.99
0.039
15.9
0.63
9.5
0.38
1.11
250
10 000
15
3.8
0.15
Material
Thickness b
D
Net Electrode
Force
d
Minimum
Tension-Shear
Strength (for Single
Projections Only)
Projection Size (Sketch C) a
Weld
Time,
Cycles
(60 Hz)
mm
in.
kN
lb
mm
in.
mm
in.
4.11
925
4.75
0.187
1.04
0.041
0.048
Diameter, Dp
Height, Hp
1.60
0.063
15.9
0.63
11.1
0.44
1.78
400
11 500
20
6.4
0.25
9.12
2050
5.54
0.218
1.22
1.98
0.078
19.1
0.75
12.7
0.50
2.45
550
16 000
25
6.4
0.25
12.01
2700
6.35
0.250
1.37
0.054
2.36
0.093
19.1
0.75
12.7
0.50
3.34
750
16 000
30
7.6
0.30
19.13
4300
6.35
0.250
1.37
0.054
2.74
0.108
22.2
0.88
12.7
0.50
4.23
950
22 000
33
7.9
0.31
21.80
4900
6.35
0.250
1.37
0.054
D
d
Dw
(B) Weld Nugget Diameter
a. Dimensional variables are as shown in sketches A, B, and C.
b. Two equal metal thicknesses of each gauge. Material must be free from dirt, grease, paint, etc., prior to welding, but may have light oil.
c. Electrode Material RWMA Group A, Class 2.
(C) Projection Size
Hp
CHAPTER 3—COATED STEELS
(A) Electrode Diameter and Shape
Dp
175
176
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
be blocked by spatter particles, which inhibit the flow
of shielding gas. When redressing the tungsten tip, it
should be ground with the grinding marks parallel to
the axis of the electrode. This prevents tungsten fragments from entering the weld pool.
Electrode contamination can be minimized by holding the torch at a travel angle of 70° to the plate surface
instead of the conventional 80° to 90°, and by increasing the gas flow rate from the conventional 7 L/min
(15 ft3/h) to 12 L/min (25 ft3/h). However, a nozzle
must be carefully selected so that it is capable of feeding
the gas at the higher rate to prevent the stream from
becoming turbulent and aspirating air into the gas. This
is a potential cause of more significant problems. Properly done, the higher volume of flow can provide the
effect of flushing the zinc vapor from the arc area. It is
also helpful to use no more current than necessary to
obtain joint penetration. This restricts the amount of
volatilized zinc and results in clean welds in butt joints.
Corner-joint welds in which the sheet has been
sheared have edges that are free from zinc, and therefore can be relatively easy to make. T-joints can be more
troublesome, however, because of the zinc at the faying
surface of the horizontal or flat member. Suitable conditions for making square-groove welds in butt joints in
1.6 mm (1/16 in.) sheet are shown in Table 3.29.
If the base metal is rimmed steel, the same precautions that apply to uncoated rimmed steel must be
taken (e.g., a deoxidized welding wire must be used to
prevent the formation of porosity). The techniques used
for uncoated rimmed steel must be changed to the following for coated steel:
1. The lowest current consistent with adequate
joint penetration must be used;
2. Gas flow should be increased;
3. Torch travel angle should be decreased to 70°;
4. A long arc, 4.8 mm (3/16 in.) should be used;
5. Filler metals should be deoxidized using manganese, and very little silicon should be used;
6. Uncoated (sheared) edges should be provided;
and
7. The workpiece should be sheet with a lowweight zinc coating.
Shielded Metal Arc Welding
The procedures and currents for the shielded metal
arc welding of continuous-galvanized steel with covered
electrodes generally are similar to those for welding
uncoated steels, as shown in Tables 3.30 and 3.31.
The covered electrodes generally recommended for
welding galvanized steel sheet are E6012 and E6013.
These electrodes produce rutile slags and deposit silicon
levels of around 0.2%; they can be expected to produce
crack-free fillet welds.
The E6010 and E6011 electrodes also contain low
levels of silicon, which is highly desirable. However,
because they have deeper joint penetration, they are not
as suitable for welding sheet steels. Conversely, they are
recommended when fabricating heavier galvanized
steels such as structural components, when deeper joint
penetration is an advantage.
Electrodes with basic coverings such as E7016 or
E7018 contain more than 0.4% silicon, and for that reason, may produce cracking in welds because of the greater
susceptibility of the weld metal to zinc contamination.
Butt Joints—Square-Groove Welds. To obtain
complete joint penetration, the root opening for a single-pass square-groove weld in galvanized steel should
be wider than that for a similar weld in bare steel. For
example, a root opening of 2.3 mm (0.09 in.) is recommended for galvanized sheet 3.2 mm (0.125 in.) thick.
As welding progresses, the arc should be repeatedly
advanced onto the zinc coating ahead of the weld pool
to melt and vaporize the coating from the steel.
Removal of the coating will reduce weld metal porosity
caused by entrapment of zinc vapor. This whipping
motion or transverse oscillating motion of the electrode
will reduce welding speed by 80% or 90% compared to
welding speeds obtained on uncoated steel.
Table 3.29
Typical Welding Conditions for Gas Tungsten Arc Groove Welds
in Butt Joints in 1.6 mm (1/16 in.) Continuously Galvanized Sheet*
Root Opening
Argon Flow Rate
Edge Shape
Condition of Edges
mm
in.
Current,
A
Square
Uncoated (sheared)
1
1/32
60
Torch Angle,
degree
L/min
ft3/h
70
12
25
*Zinc coating weight 381 g/m2 (1-1/4 oz/ft2) including both sides. 3.2 mm (1/8 in.) thoriated tungsten electrode; direct current electrode negative.
1.2 mm (3/64 in.) diameter ER70S-3 deoxidized filler rod. Copper backing bar, 4.8 mm × 0.64 mm (3/16 in. × 0.025 in.) groove.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
Table 3.30
Typical Shielded Metal Arc Welding Conditions for Continuous Galvanized Sheeta
Sheet Thickness
Electrode Diameter
mm
in.
Welding
Current Type
Welding
Current, A
Rutile
Basic
1.6
1.6
1/16
1/16
ac or DCENb
DCEP
40
45
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60
60
0.04
Rutile
Basic
1.6
1.6
1/16
1/16
ac or DCENb
DCEP
40–45c
40–45c
1.3
0.05
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60–70c
60–70c
1.7
0.07
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60–70c
60–75c
2.5
0.10
Rutile
Basic
2.4
2.4
3/32
3/32
ac or DCENb
DCEP
80–100c
80–100c
1.0
0.04
Rutile
Basic
1.6
1.6
1/16
1/16
ac or DCENb
DCEP
40
45
1.3
0.05
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60
60
mm
in.
1.0
0.04
1.3
0.05
1.0
Type of Weld
Square-edge butt joint,
welded from one side
Square-edge butt joint,
welded from both sides
Flanged butt joint
Electrode
Type
1.0
0.04
Rutile
Basic
1.6
1.6
1/16
1/16
ac or DCENb
DCEP
40
45
1.3
0.05
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
50
50
1.7
0.07
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60
60
2.5
0.10
Rutile
Basic
2.4
2.4
3/32
3/32
ac or DCENb
DCEP
80
80
1.3
0.05
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
60–70c
60–70b
1.7
0.07
Rutile
Basic
2.0
2.0
5/64
5/64
ac or DCENb
DCEP
70
70
2.5
0.10
Rutile
Basic
Rutile
2.4
2.4
3.2
3/32
3/32
1/8
ac or DCENb
DCEP
ac or DCENb
90–100c
90–100c
120
Corner joint
T-joint
a. Based on data published by Lundin, S.: “Arc welding of hot-dip galvanized steel plate,” Svetsaren, 5(1–2), 1969.
b. Some rutile electrodes may operate better when connected to the positive pole. In this case, DCEP would be a third option.
c. The lower current is used for the first pass and the higher for subsequent passes.
Table 3.31
Typical Shielded Metal Arc Welding Conditions for Square-Groove Welds in
Butt Joints in 3.2 mm (1/8 in.) Continuous Galvanized or General Galvanized Steel*
Electrode Diameter
Electrode Type
Specification
mm
in.
Welding Position
Welding Current,
A
Rutile
AWS E6012
(B.S. 1719, Class E233)
3.2
1/8
Flat
126
Basic
AWS E7016
(B.S. 1719, Class E616H)
3.2
1/8
Flat
109
Rutile
AWS E7013
(B.S. 1719, Class E317)
2.5
3/32
Uphill
89
*Square edge shape; 2.5 mm (3/32 in.) root opening.
177
178
CHAPTER 3—COATED STEELS
Fillet Welds. The heat of the arc is used to volatilize
the zinc coating ahead of the weld pool, the same as
with groove welds. This action should be incorporated
in the electrode manipulation needed to produce an
acceptable fillet weld geometry. The arc should be
moved ahead approximately 8 mm (0.3 in.) to burn off
the coating and then return as welding progresses along
the joint.
A frequent problem when welding in the horizontal
and vertical positions is undercut. It may occur on the
vertical member in the horizontal position, and on both
members in the vertical position. This can be minimized
by keeping the welding current at the low end of the
recommended range and by keeping the arc as short as
possible. In any case, proper electrode manipulation is
required for the first pass to vaporize the coating ahead
of the weld pool.
Gas Metal Arc Welding
Welding conditions for continuous-galvanized steel
welded with the short-circuiting gas metal arc welding
arc process are shown in Tables 3.32 through 3.35.
Shielding Gases. The most common shielding gas
(and least expensive) for the gas metal arc welding of
steel is carbon dioxide. When welding uncoated mild
steel, there are certain advantages to using a shielding
gas consisting of 80% argon-20% carbon dioxide
instead of 100% carbon dioxide. The 80/20 gas mixture reduces spatter and provides superior weld bead
shape and appearance. These advantages do not appear
to apply to galvanized steel, but a welding shop that
normally uses the argon-carbon-dioxide gas mixture
also can use it for zinc-coated steels. Suitable conditions
for welding with 80% argon-20% carbon dioxide
shielding gas are shown in Tables 3.36 and 3.37.
Welding Procedures for Galvanized Sheet. The
welding procedures recommended for welding galvanized sheet differ somewhat from those used for
uncoated steel. Joint penetration is reduced slightly
when welding galvanized steel compared with that
obtained on uncoated steel. This means that wider root
openings are required in square-groove welds in sheet
up to 3.2 mm (1/8 in.) thick. For flat-position welds in
3.2 mm (1/8 in.) galvanized sheet, the slightly wider
root opening makes the control of joint penetration difficult, so it is necessary to move the welding gun with a
slight side-to-side weaving motion to prevent meltthrough or excessive penetration. Table 3.32 shows that
welds in butt joints in 1.6 mm (1/16 in.) galvanized steel
with 378 g/m2 or 750 g/m2 (1.25 oz/ft2 or 2.5 oz/ft2)
coatings generally can be made with the same welding
conditions. However, the following exceptions apply to
these conditions: welds made in the overhead position,
AWS WELDING HANDBOOK 9.4
and welds in butt joints on sheet with a 750 g/m2 (2.5 oz/
ft2) coating, where it generally is necessary to increase
the current by 10 A and the voltage by 1 V to achieve
complete joint penetration.
For fillet welds, however, sheet with the thicker coating may be welded more readily if the current is
increased by 10 A because the increased heat input
helps to burn away the extra zinc at the front of the
weld pool.
When welding galvanized steel sheet, lower welding
travel speeds are necessary to allow the zinc to burn off
at the front of the weld pool. The reduced travel speed
is related to the thickness of the zinc coating, the joint
type, and the welding position. For example, travel
speeds are lower on batch-galvanized sheet than on
continuous-coated sheet and lower on T-joints than on
butt joints. T-joints have extra zinc at the faying surface, and lower travel speed is required to allow at least
some of the extra zinc to burn away. Welds made in the
downhill position require a reduction in travel speed of
25% to 50%, depending on the coating thickness and
joint type. This reduction is necessary because zinc
vapors tend to rise into the arc zone and interfere with
arc stability.
Square-groove welds made in the overhead and horizontal positions require very little reduction in speed
because zinc vapors tend to rise away from the arc
zone.
For fillet welds made in the horizontal and flat positions, welding is easier if a 1.6 mm (1/16 in.) root opening is maintained between the workpieces.
A weld deposited on the second side of a T-joint may
be difficult to make because the zinc vapor must escape
through the weld as it is being deposited or it may
become trapped. This increases the risk of weld cracks
and porosity. With care, however, these problems can
be avoided and satisfactory welds can be made.
Fillet welds are difficult to make in the flat position
unless a root opening is left between the workpieces to
allow the zinc vapor to escape. Without the root opening, increased spatter is formed, causing arc instability
when particles of spatter fall into the root of the joint.
The spatter accumulation problem on the workpiece
can be minimized by spraying the area with a silicone,
petroleum, graphite, or lime-based anti-spatter compound before welding. Silicon-based anti-spatter compounds must be used with care because silicone
compounds left on the workpiece can adversely affect
the adherence of paint.
The buildup of spatter in the gas nozzle of the welding gun may interrupt the flow of shielding gas and, in
extreme cases, can cause erratic feeding of the welding
wire. The application of anti-spatter compound to the
gas nozzle reduces the adherence of spatter particles so
that they can be easily removed with nozzle-cleaning
tools.
AWS WELDING HANDBOOK 9.4
179
CHAPTER 3—COATED STEELS
Table 3.32
Typical Gas Metal Arc Welding Conditions for Butt Joints
and T-Joints in 1.6 mm (1/16 in.) Continuous Galvanized Sheet*
Welding Conditions
Zinc Coating Weight
Welding
Position
Wire Feed Speed
Travel Speed
Travel Speed on
Uncoated Steel
mm/s
in./min
mm/s
in./min
mm/s
in./min
Current,
A
Voltage,
V
Butt joint,
unbacked
70
90
20
17
59
81
140
192
5
7
12
17
—
8
—
19
Flat
Butt joint, copper
backing bar
85
95
20
21
72
85
170
200
5
6
12
14
—
—
—
—
1.25 or
2.5
Downhill
Butt joint,
unbacked
90
17
82
194
6
14
8
19
381 or
763
1.25 or
2.5
Flat
Butt joint,
unbacked
80
18
38
90
—
—
—
—
381 or
763
1.25 or
2.5
Downhill
Butt joint,
unbacked
100
18
49
117
—
—
—
—
381 or
763
1.25 or
2.5
Horizontal
Butt joint,
unbacked
100
18
49
117
8
20
8
19
381
763
1.25
2.5
Overhead
Butt joint,
unbacked
100
110
18
19
49
56
117
132
—
—
—
—
—
—
—
—
381
763
1.25
2.5
Flat
T-joint, fillet welds
100
110
18
18
50
56
117
132
—
—
—
—
—
—
—
—
381
763
1.25
2.5
Downhill
T-joint, fillet welds
110
120
19
19
56
66
132
156
—
—
—
—
—
—
—
—
381
763
1.25
2.5
Overhead
T-joint, fillet welds
110
110
19
20
56
56
132
132
6
—
14
—
7
—
16
—
381
763
1.25
2.5
Horizontal
T-joint, fillet welds
100
18
50
117
—
—
—
—
763
2.5
Horizontal
T-joint, fillet welds
110
120
20
20
56
59
132
140
—
5
—
12
—
7
—
17
g/m2
oz/ft2
381 or
763
1.25 or
2.5
Flat
381 or
763
1.25 or
2.5
381 or
763
Type of Weld
*Zinc coating weight (including both sides) 381 g/m2 or 762 g/m2 (1.25 oz/ft2 or 2.5 oz/ft2). Electrode stickout 6.4 mm to 9.5 mm (0.25 in. to 0.38 in.).
ER70S-3 deoxidized wire 1 mm (0.035 in.) diameter. Gas flow rate 19 L/min (40 ft3/h). Root opening nil.
Table 3.33
Typical Gas Metal Arc Welding Conditions for Lap Joints in
1.6 mm (1/16 in.) Continuous Galvanized Sheet Using CO2 Shielding Gas*
Welding Conditions
Zinc Coating Weight
Wire Feed Speed
Travel Speed
Travel Speed on
Uncoated Steel
g/m2
oz/ft2
Welding Position
Current,
A
Voltage,
V
mm/s
in./min
mm/s
in./min
mm/s
in./min
381 or
762
1.25 or
2.5
Horizontal (sheets horizontal)
100
18
50
117
7
16
7.6
18
381 or
762
1.25 or
2.5
Horizontal (sheets vertical)
100
18
50
117
5
12
8
19
381
1.25
Downhill
100
18
50
117
7
16
9.3
22
762
2.5
Downhill
100
18
50
117
6
13
9.3
22
381
762
1.25
2.5
Overhead (sheets vertical)
100
100
18
18
50
50
117
117
5
4
12
10
6.3
6.3
15
15
381 or
762
1.25 or
2.5
Overhead (sheets horizontal)
100
18
50
117
4
10
6.3
15
*Electrode stickout 6.4 mm to 9.5 mm (0.25 in. to 0.38 in.). ER70S-3 deoxidized wire 1.1 mm (0.045 in.) diameter. Gas flow rate 19 L/min (40 ft3/h).
180
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.34
Typical Gas Metal Arc Welding Conditions for 3.2 mm
(1/8 in.) Continuous Galvanized Sheet Using CO2 Shielding Gas a
Welding Conditions
Root Opening
Type
of Weld
Wire Diameter
Wire Feed Speed
Travel Speed
Travel Speed
on Uncoated Steel
mm/s
in./min
mm/s
in./min
mm/s
in./min
mm
in.
Welding
Position
mm
in.
Current, Voltage,
A
V
Butt joint,
unbacked
1.6
1/16
Flat
1.1
0.045
130
20
55
130
5
12
6.3
15
Butt joint,
copper
backing barb
1.6
1/16
Flat
1.1
0.045
130
20
55
130
5
12
6.3
15
Butt joint,
unbacked
1.6
1/16
Downhill
1.1
0.045
130
20
55
130
5.9
14
7.6
18
Butt joint,
unbacked
0.8–
1.6
1/32–
1/16
Flat
1
0.035
135
20
71
168
5.5
13
7.6
18
Butt joint,
unbacked
0.8–
2.5
1/32–
3/32
Downhill
1
0.035
135
20
71
168
7.6
18
8.4
20
Butt joint,
unbacked
0.8–
1.6
1/32–
1/16
Horizontal
1
0.035
135
20
71
168
7
16
7
16
Butt joint,
unbacked
0.8
1/32
Overhead
1
0.035
135
20
71
168
5.5
13
6.3
15
T-joint,
fillet welds
—
—
Flat
1
0.035
135
20
71
168
4.7
11
5
12
T-joint,
fillet welds
—
—
Horizontal
1
0.035
135
20
71
168
5
12
5.9
14
T-joint,
fillet welds
—
—
Overhead
1
0.035
135
20
71
168
4
10
5
12
T-joint,
fillet welds
—
—
Downhill
1
0.035
135
20
71
168
5.9
14
5.9
14
a. Zinc coating weight (including both sides) 381 g/m2 (1.25 oz/ft2). Electrode stickout 6.4 mm to 9.5 mm (0.25 in. to 0.38 in.). ER70S-3 deoxidized wire.
Gas flow rate 19 L/min (40 ft3/h).
b. 4.8 mm × 1.3 mm (3/16 in. × 0.050 in.) groove in backing bar.
Table 3.35
Typical Gas Metal Arc Welding Conditions for Lap Joints in
3.2 mm (1/8 in.) Continuous Galvanized Sheet Using CO2 Shielding Gas*
Welding Conditions
Wire Feed Speed
Travel Speed
Travel Speed on
Uncoated Steel
Welding Position
Current,
A
Voltage,
V
mm/s
in./min
mm/s
in./min
mm/s
in./min
Horizontal (sheets horizontal)
130
19
68
160
4.2
10
5.9
14
Horizontal (sheets vertical)
130
19
68
160
3.8
9
6.3
15
Downhill
130
19
68
160
5.1
12
6.3
15
Overhead (sheets vertical)
120
19
59
140
3.8
9
5.9
14
Overhead (sheets horizontal)
120
19
59
140
3.4
8
5.9
14
*Zinc coating weight (including both sides) 381 g/m2 (1.25 oz/ft2). Electrode stickout 6.4 mm to 9.5 mm (0.25 in. to 0.38 in.). ER70S-3 deoxidized wire 1 mm
(0.035 in.) diameter. Gas flow rate 19 L/min (40 ft3/h).
AWS WELDING HANDBOOK 9.4
181
CHAPTER 3—COATED STEELS
Table 3.36
Gas Metal Arc Welding Conditions for Continuous
Galvanized Sheet Using 80% Argon–20% CO2 Shielding Gasa
Sheet Thickness
Wire Diameter
Wire Feed Speed
Welding
Position
mm
in.
mm/s
Travel Speed
in./min
Current,
A
Voltage,
V
mm/s
in./min
mm
in.
Type of Weld
1.6
1/16
Butt joint, no root opening,
Cu backing barb
Flat
0.030
0.8
93.1
220
18
120
18
7.6
1.6
1/16
Butt joint, no root opening,
unbacked
Flat
0.030
0.8
93.1
220
18
120
15
6.3
3.2
1/8
Butt joint, root opening
= 1.6 mm (1/16 in.),
Cu backing barb
Flat
0.8
0.030
122.7
290
130
20
5.1
12
3.2
1/8
Butt joint, unbacked root
opening = 1.6 mm (1/16 in.)
Flat
0.8
0.030
122.7
290
130
20
5.1
12
1.6
1/16
Butt joint, unbacked root
opening = 0.8 mm (1/32 in.)
Downhill
0.8
0.030
74.1
175
90
18.5
7.6
18
3.2
1/8
Butt joint, unbacked root
opening = 3 mm (1/8 in.)
Downhill
1.1
0.045
42.3
100
140
19.5
6.8
16
1.6
1/16
Fillet
Horizontal
0.8
0.030
118.5
280
120
19
5.9
14
12
3.2
1/8
Fillet
Horizontal
1.1
0.045
76.1
180
150
20
5.1
1.6
1/16
Fillet
Horizontal
0.8
0.030
76.1
180
100
18
6.8
16
3.2
1/8
Fillet
Horizontal
1.1
0.045
52.9
125
135
18.5
5.9
14
1.6
1/16
Double-lap joint
Horizontal
0.8
0.030
93.1
220
120
19
4.7
11
3.2
1/8
Double-lap joint
Horizontal
1.1
0.045
78.3
185
155
19.5
5.5
13
a. Electrode stickout 6.4 mm to 9.5 mm (1/4 in. to 3/8 in.). ER70S-3 deoxidized steel welding wire. Gas flow rate 19 L/min (40 ft3/h).
b. 4.8 mm × 1.3 mm (3/16 in. × 0.050 in.) groove in backing bar.
Flux Cored Arc Welding
Continuous-galvanized steels may be arc welded
with flux cored electrodes. As with other types of electrodes, products containing low levels of silicon should
be selected when possible to avoid weld cracking. Selfshielded flux cored welding wires specifically designed
for welding galvanized steels are recommended (e.g.,
wires containing very low levels of magnesium). The
recommendations of the electrode manufacturer should
be followed, and the welding procedure should be qualified by appropriate tests.
Laser Beam Welding
Laser beam welding (LBW) is a welding process that
produces coalescence with the heat from a laser beam
impinging on the joint.
Laser beam welding machines using CO2 as the lasing gas are used to make lap welds on continuous-galvanized sheet. A major application is in the automotive
industry for the production of tailored press blanks,
formed by combining pieces of varying sheet thickness,
shape, type, and level of coating. Blanks are engineered
to optimize production, performance, and cost. A 1500watt laser is capable of welding 0.8 mm (0.031 in.)
thick galvanized steel sheet at a rate of 14.8 mm/s (35 in./
min). Production rates range from 40 to 500 blanks per
hour. Argon is often used as the lasing gas. Because
helium can be fed from a nozzle at much higher-volume
flow rates than argon without producing turbulence,
helium is used at 9.4 L/min (20 ft3/h). Helium at this
flow rate produces a smoother weld than argon at 2.36 L/
min (5 ft3/h). Welds as strong as the base steel can be
produced.
Pulsed laser beam welding uses a laser that provides
a controlled output that produces a pulse with a duration of 25 milliseconds or less. Laser beam pulsing
improves weld quality by reducing porosity. For example, using a laser with an average power of 1020 watts,
pulses of 1660 W for 2.06 milliseconds at a frequency
of 300 Hz (3.33 milliseconds) allows travel speed to be
reduced to 8.5 mm/s (20 in./min) and results in less surface porosity than continuous-power laser beam welding. The typical standoff distance for a laser beam
182
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.37
Typical Short-Circuiting Gas Metal Arc Welding Conditions
for Continuous Galvanized Sheet with 80% Ar–20% CO2 Shielding Gas*
Sheet Thickness
mm
in.
0.7
0.03
Electrode Diameter
Type of Weld
mm
in.
Current,
A
Voltage,
V
0.6
0.020
45
16
1.0
0.04
0.6
0.020
60
16
1.3
0.05
0.8
0.030
80
18
1.7
0.07
0.8
0.030
100
20
Square-edge butt joint
welded from one side
2.5
0.10
1.0
0.040
140
22
1.3
0.05
0.8
0.030
80
18
1.7
0.07
2.5
0.10
0.7
0.03
Square-edge butt joint
welded from both sides
0.8
0.030
100
20
1.0
0.040
140
22
0.6
0.020
45
16
1.0
0.04
0.6
0.020
60
16
1.3
0.05
0.8
0.030
80
18
0.7
0.03
0.6
0.020
45
16
Flanged butt joint
1.0
0.04
0.6
0.020
60
16
1.3
0.05
0.8
0.030
80
18
1.7
0.07
0.8
0.030
100
20
2.5
0.10
1.0
0.040
140
22
Corner joint
1.3
0.05
0.8
0.030
80
20
1.7
0.07
0.8
0.030
110
22
2.5
0.10
1.0
0.040
140
24
T-joint
*Silicon-manganese deoxidized steel welding wire.
focusing head is 1.8 mm to 1.9 mm (0.07 in. to 0.075 in.)
from the workpiece.
Braze Welding
Several welding processes can be adapted for the
braze welding of continuous-galvanized sheet, including
oxyfuel gas, gas tungsten arc, gas metal arc and
shielded metal arc welding.
Oxyfuel Gas Braze Welding. Bare 60% copper40% zinc (brass) welding rods are commonly used
for oxyfuel gas braze welding, although copper-silicon
(silicon-bronze), copper-tin (phosphor-bronze), and copper-aluminum (aluminum-bronze) filler metals also may
be used. The welding rod diameter should be 1.5 times
the sheet thickness, but should not exceed 6.4 mm
(0.25 in.).
A borax-boric acid braze welding flux is needed for
good wetting. A generous application of flux to the faying surfaces and the welding rod as welding progresses,
or the use of flux-coated rods usually will reduce the
loss of the galvanized coating.
To limit flame spread, a small oxyfuel gas torch tip
consistent with the thickness of the galvanized steel
workpieces should be used. A neutral or slightly oxidizing flame with the lowest practical heat input should be
used. After the workpiece has reached a dull red heat,
the flame is directed onto the welding rod as welding
progresses along the joint. The flame should not be
oscillated. The joint strength of a properly made oxyfuel gas braze weld in galvanized steel using a siliconbronze filler rod will equal or exceed the strength of the
steel. The corrosion resistance of the joint is excellent
because the filler metal covers the area that has lost the
zinc coating. A cross section of a braze-welded butt
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
joint on 15.2 mm (0.06 in.) continuous-galvanized steel
using 60% copper-40% zinc filler metal is illustrated in
Figure 3.18.
Arc Processes for Braze Welding. The arc welding processes that adapt well for braze welding galvanized steel include gas tungsten arc welding, gas metal
arc welding, and shielded metal arc welding. These processes are discussed in the previous section, General
Galvanized Products. Additional information on gas tungsten arc brazing is provided in the following paragraphs.
The gas tungsten arc process can be adapted to produce braze welded joints in galvanized steel with minimal melting of the base metal. Filler metal is added
either by inserting a welding rod into the joint or by
laying a welding wire flat in the joint and maintaining
the arc between the tungsten electrode and the filler rod
or welding wire. Gas tungsten arc brazing can be carried out with either alternating current or direct current
electrode negative (DCEN) in combination with suitable welding rods such as silicon-bronze.
Table 3.38 provides typical conditions for the gas
tungsten arc braze welding of butt joints and lap joints
in 1.2 mm (3/64 in.) galvanized sheet with siliconbronze or tin-bronze filler rod.
A typical cross section of a braze weld made with silicon-bronze filler metal on 15.2 mm (0.6 in.) continuous-galvanized steel is shown in Figure 3.19. X-ray
evaluation shows that gas tungsten arc braze welds usually are very sound. Joint strengths equal to those of the
base metal are readily obtainable. The use of a flux is
not necessary.
SOLDERING
Continuous-galvanized steel can be soldered using
either an acid or an organic flux. Zinc-chloride base
and ammonium-chloride base fluxes usually are adequate when using tin-lead solders containing 20% to
50% tin. The most commonly used solder composition
is 40% tin-60% lead. The recommended heat source is
a soldering iron. Applying a wash composed of dilute
ammonium or sodium hydroxide solution, or trisodium phosphate (TSP) prior to soldering helps to
improve wettability. For coating alloys containing aluminum, abrading the surfaces to remove the aluminum
oxide prior to tinning is recommended.
Some chemical surface treatments (chromate and
nonchromate) used to prevent staining during humid
Figure 3.18—Cross Section of a Braze Weld
Made with the Oxyfuel Gas Process
Table 3.38
Typical Gas Tungsten Arc Braze Welding
Conditions for Continuous 1.2 mm (3/64 in.) Galvanized Sheet*
Diameter of
Tungsten Electrode
Type of Joint
Diameter of
Filler Rod
Argon Flow Rate
Type of Current
mm
in.
mm
in.
L/min
ft3/h
Current,
A
Butt
ac
2
5/64
1.6
1/16
8
17
45
0.8 mm (1/32 in.)
root opening
dc
1.6
1/16
1.6
1/16
8
17
35
Lap
ac
dc
2
1.6
5/64
1/16
1.6
1.6
1/16
1/16
8
8
17
17
45
35
*Filler rod: Copper, 2.5% tin.
183
184
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Figure 3.19—Cross Section of a Braze Weld
Made with the Gas Tungsten Arc Process
storage may interfere with solder flow, while others
improve solderability. If chemical surface treatments are
to be removed, the stronger amino-borate fluxes can be
used.
Phosphated galvanized surfaces are difficult to solder. The phosphate films must be removed prior to soldering unless strong mineral acid fluxes or corrosive
acid fluxes containing sodium bifluoride are used.
Aged galvanized sheet is soldered more readily than
freshly produced sheet. Soldering of workpieces with
zinc-aluminum alloy coatings is not recommended
because of the tenacious aluminum-oxide films and the
possibility of intergranular corrosion that lead-tin solders can create. Recommendations for these coatings
are provided in the subsection Other Coated Steels.
Electronic assemblies made of galvanized sheet must
be precoated with solder and then cleaned before joining. They are then soldered in the usual manner with a
noncorrosive flux. Rosin-core solders rapidly remove
the light oxide film and promote solder flow. The residues of these solders are noncorrosive and nonconductive. After soldering, all corrosive flux residues must be
carefully removed.
GALVANNEALED STEEL
Typical galvanneal steel is continuously hot-dip galvanized steel sheet that is heat treated in-line while the
zinc coating is molten to modify the coating composition by alloying it with the iron in the steel. Electrodeposited galvanneal is made by co-depositing zinc and
iron.
The commonly used definition for galvanneal is sheet
steel that is coated with a zinc-iron alloy (containing no
free zinc). It has a smooth and usually dull gray surface
that is readily paintable. The weldability of galvanneal
sheet using the resistance spot welding process is significantly better than galvanized sheet. The coating is produced on hot-dip production lines by heating the sheet
from 540°C to 600°C (1000°F to 1110°F) before the
liquid zinc solidifies using gas-fired or induction heat-
treating equipment that is an integral part of the galvanizing line. The zinc alloys with the steel substrate in
about 10 seconds. When painted, the coating has significantly better corrosion resistance compared to pure
zinc coatings of the same thickness because of the superior adherence of paint coatings to the micro zinc-iron
crystals on the galvanneal surface.
The existence of the iron-zinc intermetallics (γ, δ, and
ζ) results in limited malleability of the coating. This
condition is known as powdering, in which small particles break off from the surface of the sheet during drawing or bending. Powdering can be limited by careful
control of the aluminum content of the zinc bath and
restricting the iron content of the alloy coating to
10.5% or less. These precautions keep the formation of
the brittle phase under control.
When welded with the resistance spot welding
(RSW) process, galvannealed steel sheet has the advantage of improved electrode life (approximately double
the life) when compared to pure zinc galvanized coatings, but has the disadvantage of a narrower current
range.
Data from the RSW schedules for galvanized and
galvannealed sheet stock (0.6 mm to 3 mm [0.025 in. to
0.12 in.]) of an automobile manufacturer showed that
electrode force was reduced by approximately 20% for
the thinnest sheet, and by approximately 15% for
thickest sheet. Similarly, current was reduced by about
24% for the thinnest sheet and by about 22% for the
thickest sheet. These tests were made on welds with the
same minimum nugget size, and using the same weld
time (increasing from 4 cycles to 7 cycles for thinnest
sheet, to 23 cycles to 26 cycles at 60 Hz for thickest
sheet) for each nugget size. The differences are based on
comparison of the mean values for the ranges given for
force and current.
To establish the suitability of a particular galvannealed product for RSW, an evaluation should be
performed using the test methods and recommended
practices of AWS/SAE D8.9.35
35. See Reference 7.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
Galvannealed surfaces are extremely difficult to solder, but some success has been achieved with fluxes
similar to those used in soldering stainless steel. However, vigorous gas evolution occurs when these fluxes
are used, and this creates enough back pressure to prevent the flow of solder into narrow joint clearances.
ELECTRO-GALVANIZED STEEL
The electro-galvanizing (EG) of sheet and wire generally is performed on continuous production lines. Continuous EG coating application lines for sheeting
generally produce lighter coating designations than the
continuous hot-dip process because of the high cost of
the capital equipment and electrical energy that would
be needed to apply heavier coating masses.
All galvanized steels may be treated after galvanizing
with one of a variety of inorganic or organic treatments
such as chromates, phosphates, and paint systems.
However, these treatments make the resistance spot
welding process more difficult and, if needed, should be
applied after welding when possible.
Electrogalvanized coatings can be pure zinc or alloys
of zinc with iron, nickel, cobalt, or other metals. Techniques for welding steels with these various coatings,
185
coatings of zinc-rich paint, and thermally sprayed zinc
are discussed in separate sections of this chapter.
Electro-galvanized steels tend to be more weldable
than hot-dip galvanized steels because the coatings are
thinner and more uniform. Many electro-galvanized
coatings are alloyed, which increases the hardness,
melting point, and electrical resistance and also contributes to greater ease of oxidation. Thin electro-galvanized
sheet (less than 20 g/m2 [0.07 oz/ft2] per side) tends to
be as weldable as uncoated steel. Zinc-iron electrogalvanized coatings require only slightly higher welding
currents than uncoated steel, while pure zinc coatings
normally require a current increase of 20% to 30%.
Additional current may be necessary to weld coatings of
designation 60 and heavier. Beyond these special considerations, the recommendations made for continuous
hot-dip galvanized steel sheet should be applied.
The ASTM specification for electrolytic zinc coated
sheet steel is A 879/A 879M, Standard Specification for
Steel Sheet, Zinc Coated by the Electrolytic Process for
Applications Requiring Designation of the Coating Mass
on Each Surface.36 Coating designations are shown in
Table 3.39.
36. See Reference 2.
Table 3.39
Coating Weight and Mass per Surfacea for Steel Sheet, Zinc Coated by the Electrolytic Processb
SI Units, g/m2
Inch-Pound Units, oz/ft2
Coating Designationc
Minimum
Maximum
Coating Designationc
Minimum
Maximum
00G
no coating
no coating
00Z
no coating
no coating
03Gd
3
15
01Zd
0.01
0.05
06Ge
6
25
02Z3
0.02
0.08
0.04
0.10
12Gf
12
30
04Zf
20G
20
40
07Z
0.07
0.13
24Gg
24
45
08Zg
0.08
0.16
40G
40
70
13Z
0.13
0.23
60G
60
90
20Z
0.20
0.30
70G
70
110
23Z
0.23
0.36
90G
90
130
30Z
0.30
0.43
98G
98
140
32Z
0.32
0.46
Conversion for coating weight and mass are: 1 gm2 = 0.00328 oz/ft2 and 1 oz/ft2 = 305.15 g/m2.
a.
b. The product shall be coated on at least one surface; therefore, the combination 00G/00G or 00Z/00Z shall not be specified.
c. See ASTM A 917-08, Standard Specification for Steel Sheet, Coated by the Electrolytic Process for Applications Requiring Designation of the Coating
Mass on Each Surface.
d. Formally Flash Coating.
e. Formally Intermediate Coating.
f. Formally Full Coating.
g. Formally Double Coating.
186
CHAPTER 3—COATED STEELS
ALUMINIZED STEELS
The aluminizing of metals is accomplished primarily
by hot-dipping using a continuous or batch method.
Electroplating, thermal spraying, and diffusion coating
are used in limited applications. Two of these methods
are discussed in this section, the continuous hot-dip and
the diffusion coating processes.
When welding aluminized steels, it is important that
the amount of aluminum incorporated in the weld be
held below 1%. At 1% and above, a significant reduction in ductility occurs in the weld metal and it behaves
in a brittle manner, especially when impact loaded. The
problem of aluminum content in the weld increases in
proportion to decreases in sheet gauge, or in proportion
to increases in the coating thickness, or both.
CONTINUOUS HOT-DIP ALUMINIZING
The aluminum coatings applied to sheet steel by the
continuous hot-dip process are composed of either aluminum 5% to 11%; silicon alloy (Type 1); or a commercially pure aluminum (Type 2), as described in
ASTM Specification A 463/A 463M.37 The pure aluminum (Type 2) coating provides improved resistance to
atmospheric corrosion when in service at near room
temperature. The alloy coating (Type 1) provides oxidation resistance up to about 649°C (1200°F), but malleability is not as good as the pure aluminum coating. Type
Z aluminum coatings, used in the past for roofing, have
largely been replaced by aluminum zinc alloy-coated
sheet.
Coating designations are shown in Table 3.40. The
coating is specified as total mass (weight) on both
surfaces.
AWS WELDING HANDBOOK 9.4
Table 3.40
Requirements for Weight (Mass) of Coatings
(ASTM A 463/A 463M)
Minimum Requirement
Triple-Spot Test,
Total Both Sides
Single-Spot Test,
Total Both Sides
SI Units
Coating Designationa
g/m2
g/m2
T1M 40
40
30
T1M 75
75
60
T1M 120
120
90
T1M 300
300
270
T2M LC
no minimum b
no minimum b
T2M 200
200
180
T2M 300
300
270
Coating Designationa
oz/ft2
oz/ft2
Inch-Pound Units
T1–13
0.13
0.10
T1–25
0.25
0.20
0.30
T1–40
0.40
T1–100
1.00
0.90
T2–LC
no minimum b
no minimum b
T2–65
0.65
0.60
T2–100
1.00
0.90
a. The coating designation number is the term by which this product is
specified. Because of the many variables and changing conditions that
are characteristic of continuous hot-dip coating lines, the weight (mass)
of coating is not always evenly divided between the two surfaces of a
sheet, nor is the coating evenly distributed from edge to edge. However,
normally not less than 40% of the single-spot test limit will be found on
either surface.
b. No minimum means that there are no established minimum requirements
for triple- and single-spot tests, but aluminum coating shall be present.
Diffusion Aluminizing
Diffusion aluminizing is a commonly used method
for increasing the high-temperature corrosion resistance
of fabricated parts made from steels and other alloys.38
Various methods of diffusion aluminizing are commercially available. Single-step methods usually are
based on chemical vapor deposition (CVD) techniques.
Pack cementation, a modified CVD technique, is the
most commonly used large-scale aluminizing process.
Conventional gas-phase CVD aluminizing processes
37. ASTM International, Subcommittee A05.11, Standard Specification for Steel Sheet, Aluminum-Coated, by the Hot-Dip Process,
ASTM A 463/A 463M, West Conshohocken, Pennsylvania: ASTM
International.
38. The first United States patent for pack cementation of aluminizing processes was issued to Van Aller in 1911.
also are employed, but usually are limited to smaller
components.
Several two-step methods consist of the initial deposition of a layer of pure aluminum followed by a diffusion heat treatment. The aluminum deposition methods
include thermal spraying, hot dipping, and slurry coating. Without the diffusion heat-treatment step, these
deposition methods do not produce a true aluminum
diffusion coating, but these products are often used
when only a pure aluminum surface is required for corrosion resistance. The two-step methods also are applicable to large-scale diffusion aluminizing, but are more
expensive than pack cementation.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
187
Aluminum Diffusion Zone
Diffusion aluminizing creates a compositionally gradient alloy on the surface of the substrate alloy. The
surface alloy formed when carbon and other ferritic
steels are diffused consists primarily of a single-phase
aluminum-rich solid solution, with a diffusion zone
containing approximately 50 atomic percent aluminum
at the surface.
Figure 3.20 is a photomicrograph of a typical aluminum diffusion zone found in carbon steels and lowchromium-molybdenum steels. In the case of an austenitic stainless steel or nickel-containing superalloy, two
distinct diffusion bands are encountered. This can be
observed in Figure 3.21, a photomicrograph of a typical
aluminum diffusion zone found in austenitic stainless
steels. The outer (light) band is an aluminum-rich single-phase solid solution with approximately 50 atomic
percent aluminum at the surface. The inner (dark)
band, or so-called interdiffusion zone, is a two-phase
region; the light areas are iron-aluminum rich and the
dark areas are nickel-aluminum rich.
Micrograph courtesy of Alon Surface Technologies
Figure 3.21—The Aluminum Diffusion Zone of a
Typical Aluminized Austenitic Stainless Steel
(x100, Vilella Reagent Etch)
Applications
The excellent corrosion resistance of diffusion aluminized alloys in high-temperature service is obtained by
the formation of a thermodynamically and mechanically stable aluminum oxide scale on the alloy surface,
which inhibits further corrosion of the substrate alloy.
In addition to enhancing the oxidation resistance of an
alloy, diffusion aluminizing also greatly improves hightemperature resistance to sulfidation, carburization,
metal dusting, catalytic coke formation, molten salt
attack, and permeation with hydrogen and nitrogen.
Table 3.41 provides a partial list of commercial applications of diffusion-aluminized alloys and the industries,
process technologies, and products to which diffusion
aluminizing has been applied.
WELDING CONDITIONS FOR DIFFUSIONALUMINIZED METALS
Micrograph courtesy of Alon Surface Technologies
The welding conditions for metals that have been
modified with aluminum via the diffusion processes are
not appreciably different from those of bare, uncoated
metals. Any previously qualified process and welding
procedure specification (WPS) can be used to weld these
modified materials. The presence of aluminum in the
surface presents a challenge only if the alloy being
welded is subject to cracking from a concentration of
the lower-melting constituent that is too high, such as
aluminum. The higher the nickel content, the greater is
the potential of hot short cracking. For more detailed
information about the weldability of aluminum, refer to
Chapter 1, Aluminum and Aluminum Alloys, in the
Welding Handbook, Volume 3, 8th Edition.39
Figure 3.20—The Aluminum Diffusion Zone of a
Typical Diffusion-Aluminized Carbon Steel or Low
Chromium-Molybdenum Steel (x100, Nital Etch)
39. American Welding Society (AWS) Welding Handbook Committee,
1996, Welding Handbook, 8th edition, Volume 3, Materials and
Applications—Part 1, Volume 3 of Miami: American Welding Society.
188
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.41
Partial List of Applications of Diffusion-Aluminized Alloys
Industry
Component
Typical Materials Aluminized
Hydrocarbon processing
Refinery heater tubes
Ethylene pyrolysis furnace tubes
Hydrodesulfurizer furnace tubes
Delayed coker furnace tubes
Catalyst reactor screens
Catalyst reactor grating
2-1/4% Cr–1% Mo steel
Ni Alloy 802
2-1/4% Cr–1% Mo steel
9% Cr–1% Mo steel
347 stainless steel
Carbon steel
Sulfuric acid
Gas-to-gas heat exchanger tubes
Carbon steel
Industrial furnace components
Aluminum plant furnace parts
Heat treating pots
Structural members
Thermowells
Carbon steel
Carbon steel
High-nickel alloy steel
Carbon and stainless steels
Steam power and cogeneration
Waterwall tubes
Fluidized bed combustor tubes
Waste heat boiler tubes
Economizer and air preheater tubes
Superheater tubes
2-1/4% Cr–1% Mo steel
2-1/4% C–1% Mo steel
Carbon steel
2-1/4% Cr–1% Mo steel
2-1/4% Cr–1% Mo steel
Aerospace
Turbine blades
Turbine vanes
Nickel-base superalloy
Nickel-base superalloy
Flue gas scrubbers
NOx /SOx removal units
304 stainless steel
Chemical processing
Reactor vessels and tubing
304/316 stainless steel
Cement
Cooler grates
Stainless steel, HP, HK
*Provided by Alon Surface Technologies.
After the critical amount of allowable aluminum
content is calculated and addressed in the weld preparation, the filler metal can be chosen. Filler metal is
selected on the basis of the corrosive or erosive service
environment anticipated for the application. One of
two options can be selected: matching the chemistry of
the base metal or utilizing a filler material that is more
resistant to the environment than the base metal. With
either choice, the same key welding conditions for
uncoated materials are used when welding aluminum
diffused materials. Figure 3.22 illustrates the tie-in
between a concave ER316 weld bead and the aluminized carbon steel layer.
Weld Bevel Preparation
Weld bevel preparation is the same as the preparation required for general welding procedures. Cleanliness is paramount with aluminum-diffused materials. In
addition to strict cleanliness, the only special preparation needed for aluminum-diffused materials is the
removal of enough of the aluminum-rich diffusion zone
Micrograph courtesy of Alon Surface Technologies
Figure 3.22—Tie-in between
Concave 316 Weld Bead and the
Aluminized Carbon Steel Layer
(x100, Nital Etch)
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
ALUMINUM-RICH
BISQUE
DIFFUSED
ALUMINUM
SURFACES
189
GRIND 0.08 mm–0.13 mm (0.003 in.–0.005 in.)
FROM THE OUTSIDE SURFACE DIMENSION
BASE METAL
ALUMINUM-RICH
BISQUE
GRIND BACK FROM THE BEVEL
A DISTANCE OF 3.2 mm–6.4 mm (0.125 in.–0.250 in.)
Figure 3.23—Typical Weld Bevel Preparation of Diffusion Aluminized Materials
at the surface as required for the welding process and
the filler material selected for the application. Figure
3.23 illustrates a typical weld bevel shaped for aluminized materials.
ALUMINIZED CARBON STEELS
The welding processes used for joining aluminized
carbon steels discussed in this section are resistance
welding, arc welding processes, oxyfuel gas welding,
and soldering.
Resistance Welding
The resistance welding processes used for joining
aluminized carbon steels are resistance spot welding
(RSW), projection welding (PW), resistance seam welding (RSEW), high-frequency seam welding (RSEW-HF)
and upset welding (UW).
Resistance Spot Welding. The welding conditions
for the resistance spot welding of aluminized steel sheet
are similar to those of zinc-coated steel sheet of the
same thickness, but welding is somewhat more difficult.
As is true for making satisfactory welds in zinc-coated
steel, aluminized steel requires the welding current and
electrode force to be higher (20% to 50%), the weld
time longer (40% to 60%), and the current range narrower than for uncoated steel. Frequent electrode cleaning and redressing are necessary. The frequency of
dressing is somewhat greater than that for galvanized
steel welding. Truncated cone electrodes of RWMA
Type A, Class 2 copper alloy are recommended for the
best service life between dressings.
Typical spot welding schedules for equal thicknesses
of both types of aluminized steel sheet are provided in
Table 3.42. Electrode indentation and the reduction of
current density are encountered to a greater extent
when welding Type 2 aluminized sheet because the Type
2 coating usually is thicker and has relatively lower
electrical resistivity than the Type 1 coating. The schedules are intended only as guides in setting up production schedules. Some variations may be necessary
because of the configuration of the workpiece or the
welding machine.
Steels with Type 1 coatings can be spot welded with
a flat, large-area backup electrode on one side of the
workpiece, provided localized pressure is exerted from
the opposite side by a suitable electrode tip. This minimizes marking of the surface placed against the flat,
backup electrode. A slight increase in the tabulated values of welding force and current may be required to
produce equivalent diameter weld nuggets when a large
backup electrode is used.
To establish the suitability of a particular aluminized
stainless steel product (e.g., sheet steel) for RSW, the
proposed steel should be evaluated according to the test
methods and recommended practices of AWS/SAE
D8.9.40
40. See Reference 7.
190
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.42
Typical Spot Welding Schedules for Aluminized Steel Sheet
Sheet Thicknessb
Electrode Face a, c
Diameter (d)
Electrode Force
mm
mm
kN
in.
in.
lb
Approx.
Welding
Current,
kA
Weld
Time,
Cycles
(60 Hz)
Approx. Nugget
Diameter (Dw) a
Minimum
Shear Strength
mm
N
in.
lb
0.46
0.018
4.06
0.16
1.3
300
8.6
8
3.81
0.15
2.2
500
0.53
0.021
4.06
0.16
1.6
350
8.8
9
4.06
0.16
2.5
570
0.69
0.027
4.83
0.19
1.8
400
9.0
10
4.32
0.17
3.7
840
0.84
0.033
4.83
0.19
2.2
500
9.2
11
4.57
0.18
4.8
1080
0.99
0.039
6.35
0.25
2.7
600
11.4
14
5.33
0.21
6.7
1500
1.32
0.052
6.35
0.25
3.6
800
11.8
18
5.84
0.23
8.9
2000
1.60
0.063
6.35
0.25
4.9
1100
12.0
24
6.10
0.24
9.8
2200
1.98
0.078
7.87
0.31
6.8
1400
16.0
30
8.38
0.33
19.1
4300
2.36
0.093
9.65
0.38
8.0
1800
19.0
36
10.16
0.40
20.0
4500
d
Dw
(A) Electrode Face Diameter
(B) Weld Nugget Diameter
a. Dimensional variables are as shown in sketches A and B.
b. Two equal metal thicknesses of each gauge. Commercial coating, Type 1 or Type 2, ASTM A 463/A 463M-06, Standard Specification for Steel Sheet, AluminumCoated, by the Hot-Dip Process. Material must be free from dirt, grease, paint, etc., prior to welding, but may have light oil.
c. Truncated cone electrodes of RWMA Group A, Class 2. Water cooling with 7.5 L/min (2 gal/min).
Projection Welding. Projection welding reduces the
need for frequent electrode dressing and ensures more
consistent weld size. Large, flat electrodes are used
against the sheet on the face side or “show side” and
the sheet containing the embossed projection. Electrodes may be made of Class 1, 2, or 3 alloys, depending on the desired service life. Class 2 electrodes are the
most commonly used.
Resistance Seam Welding. Aluminized steel sheet
can be seam welded using schedules similar to those
used for bare low-carbon steel sheet (refer to Table 1.6),
except that, as in spot welding, the welding current and
pressure required to make satisfactory seam welds are
20% to 50% greater than for welding bare steel. The
general recommendations for resistance spot welding
also apply to resistance seam welding. Class 2 alloy circular electrodes (sometimes called welding wheels, a
nonstandard term) are widely used for seam welding
sheet steel with the Type 1 coating.
To maintain a constant electrode face on the circular
electrode and thus the proper welding current density,
the pickup of aluminum on the wheel must be countered. Welding under water or directing copious streams
of water at both the upper and lower wheels, particularly at the point of contact with the workpieces, will
reduce aluminum pickup. In addition to water cooling,
knurled circular electrodes and drive wheels help
remove coating particles that adhere to the working
face of the electrode. Even more effective are powered
wire brushes that continuously brush the working face
of the electrode.
When making a pressure-tight resistance seamwelded joint, intermittent timing of the weld current
that produces overlapping weld nuggets is preferable to
continuous-current welding.
AWS WELDING HANDBOOK 9.4
Mash seam welding (RSEW-MS) is another resistance welding process that can be used to weld coated
steels, but this process operates at much slower speeds
and requires greater electrode maintenance. Mash seam
welding primarily is a type of forge welding and is
sometimes hampered by the refractory oxide present on
the aluminum-coated steel.
High-Frequency Upset Welding. Aluminized steel
tubing is produced in tube mills using a resistance welding process, high-frequency upset welding (UW-HF),
which is a variation of upset welding (UW). Both 60-Hz
and high-frequency currents are used for welding.
Proper edge shaping and preparation is essential for
sound welds. To join aluminized steel tubing, the edge
of the steel should be sheared square and be free of aluminum. This will prevent any aluminum oxide from
being at the faying surfaces during upsetting, thus
reducing a major cause of center-line discontinuities.
(Refer to Fabricating Aluminized 409 Stainless Steel
Tubing in the Applications section of this chapter).
CHAPTER 3—COATED STEELS
191
with the carbon steel base metal. Type 309 stainless
steel electrodes (22Cr-12Ni) are commonly used to
ensure enough alloy content; however, for conditions of
high base-metal dilution, the Type 312 (28Cr-12Ni)
electrode may be needed.
Stainless steel weld metal may cause differential
expansion problems resulting in thermal fatigue in
applications involving thermal cycling during service.
Flux Cored Arc Welding. Many flux cored arc welding filler metals, especially those that are self-shielding,
contain considerable amounts of aluminum and other
deoxidizers. The required weld pool deoxidation is
obtained from the aluminum in the electrode coating.
When the aluminum is added to the elements contributed by the coating, the aluminum content of the weld
metal may exceed the limits necessary for adequate ductility in the weld metal. Flux cored arc welding filler
metals intended for use with a shielding gas usually
have much lower aluminum content. In some cases,
they can be used without the normally required shielding
gas.
Arc Welding
Several arc welding processes can be used for the
welding of aluminized steels, although some difficulties
may be encountered. Among the conditions that may
arise are porosity and cracking due to the effect of outgassing of the coating material; the effect on weld metal
toughness and ductility caused by the incorporation of
aluminum into the weld metal; and the depletion and
deterioration of the protective coating along the weld
zone.
Shielded Metal Arc Welding. Welding aluminized
steel with the shielded metal arc process requires an
electrode that provides fluxing of the welding slag that
will accommodate the aluminum oxide developed by
oxidation of the surface coating. The formation of aluminum oxide has an adverse effect on the characteristics of the weld pool, and it may prevent proper wetting
and shaping of the weld bead. A basic type of flux, such
as that contained in the all-mineral coverings on the
low-hydrogen electrodes E7015, E7016, and E7018 are
somewhat better than the ordinary cellulose-type coverings of the E6010 or E6011 electrodes. E7016 electrodes and ac power may have some advantage, but
erratic arc operation may be encountered.
Stainless steel electrodes (EXXX-15 or EXXX-16)
provide advantages that often outweigh the higher cost.
The flux coverings of these electrodes have substantial
fluoride content and thus good fluxing of the slag that
forms by oxidation of the aluminum. Strong, tough
weld metal with an austenitic microstructure can be
achieved by selecting a stainless steel-type electrode
with an adequate alloy content that tolerates dilution
Gas Tungsten Arc Welding. Sound, clean welded
joints can be made with the gas tungsten arc process. A
shielding gas, either argon or helium, protects the coating and prevents the formation of aluminum oxide.
When aluminized steel is welded without filler metal
(an autogenous weld), almost all of the aluminum coating alloys with the steel weld metal and provides adequate deoxidation, even with rimmed or capped steel.
However, excessive alloying of the weld metal with the
aluminum coating must be minimized. This can be done
by using butt joints rather than edge joints or lap joints,
by adding filler metal, or by removing the aluminum
coating from the surfaces to be fused.
The gauge of the material largely controls the likelihood of embrittlement from aluminum pickup. The
thinner the sheet, the higher is the aluminum content of
the weld metal. For sheet greater than 1 mm (0.040)
thick, a square-groove butt joint, preferably with filler
metal added, usually produces satisfactory results.
Below this thickness, the question of adding filler metal
or removing the aluminum from the surfaces adjacent
to the weld joint becomes more important. Also, a thick
aluminum coating adds more aluminum to the weld
metal, and welds containing 1% aluminum or more will
have reduced ductility.
Gas Metal Arc Welding. Welding with a consumable electrode wire and a gas shield with gas metal arc
welding is a very satisfactory process for aluminized
steel. Loss of ductility due to aluminum pickup in the
weld metal usually is not a problem with this process. A
highly deoxidized electrode is not required because the
192
CHAPTER 3—COATED STEELS
aluminum from the coating will deoxidize the weld
metal.
Like gas tungsten arc welding, gas metal arc welding
requires adequate shielding gas coverage to avoid oxidation of the aluminum coating of the base metal. With
improper shielding, aluminum oxide can form a film on
the surface of the weld pool and cause weld contour or
soundness problems, or both.
Shielding gas may be argon, carbon dioxide, or a
mixture of these two gases. Argon shielding provides
weld beads with better appearance. When shielding the
weld pool with argon, a minimum addition of oxygen
or CO2 to stabilize the arc is recommended. Weld beads
shielded with CO2 have a rougher surface appearance,
but composition and soundness are normal. Mixtures
of the two gases are used for the short-circuiting transfer arc, which is often employed on very light gauges of
aluminized steel sheet.
Oxyfuel Gas Welding
Oxyfuel gas welding processes are not ordinarily recommended for aluminized steel because they tend to
damage the aluminum coating more than other welding
processes. However, oxyfuel gas welding can produce
sound joints. Using a flux of the type often used on
stainless steel (i.e., proprietary fluoride-type welding
fluxes) is helpful in overcoming the heavy viscous slag
that tends to form on the weld pool. For good fluxing
action, flux should be applied to both sides of the workpieces and to the welding filler rod. Filler metal can be
made up of shearings of bare low-carbon steel or oxyfuel gas welding filler rod with a composition of 1%
Mn and 0.25% Si, AWS A5.2 Class R60.41
The problem with using oxyfuel gas welding on aluminum-coated sheet steel is that the coating adjacent to
the weld is damaged by the large amount of heat introduced into the weld area. To minimize this effect, the
smallest torch tip possible should be used, and when
practical, a backing plate can be used. Following welding, the flux must be thoroughly removed to prevent
corrosion by the flux, flux residue, or both.
Soldering
Chemical or mechanical cleaning methods should be
used to remove the oxide film on aluminum-coated steel
before soldering. Dipping the workpiece in a solution of
5% trisodium phosphate followed by water rinsing and
drying will assist in preparing the aluminum coating for
soldering.
Heating aluminum-coated steel to soldering temperature must be rapid. Electric or ultrasonic soldering irons
with sufficient heating capacity should be used.
41. See Reference 22.
AWS WELDING HANDBOOK 9.4
Some aluminum-coated steels may be abrasion soldered without fluxes by heating the metal surface sufficiently and melting a small amount of solder on the hot
surface. The aluminum under the solder pool is then
abraded using a stick of solder, the tip of the soldering
iron, or a specially designed brush that assists in displacing the oxide film.
Fluxes formulated especially for soldering aluminum-coated steel sheets are commercially available.
These fluxes should be applied sparingly with a fine
brush. Soldering should be performed quickly to avoid
excessive oxidation of the aluminum surface and undesirable alloying of the aluminum coating with the steel.
The flux residue must be completely removed after soldering, or the corrosion resistance and the surface integrity of the sheet will be lost.
Soldering filler metals suitable for joining aluminum
can be used to join aluminum-coated steel. The solders
are available in the form of sticks, flux cored wire, and
paste.
Restoring Corrosion Resistance to
Welded Area
Many welding processes produce a weld zone that is
unprotected from corrosion. To match the corrosion
resistance of the weld zone to the rest of the aluminized
sheet, the weld zone should be cleaned, preferably by
grit blasting, and coated with aluminum. The use of
stainless steel electrodes or filler rods in any of the arc
welding processes is an excellent way to ensure corrosion resistance without subsequent treatment of the
weld area. If welding is performed with care, the aluminum coating will be undamaged virtually to the edge of
the stainless steel weld metal. When proper arc welding
techniques are used, the protective aluminum coating
stays intact up to the weld bead and alloying with the
filler metal takes place. By using stainless steel filler
metal, overall corrosion resistance along the weld is
ensured. Stainless steel filler metals can create undesirable galvanic cells in wet corrosion situations. In situations with wet corrosion, it is desirable to surface the
weld with sprayed aluminum.
It must be noted with caution that in applications in
which thermal cycling occurs, austenitic weld metal
may cause thermal fatigue because of differential
expansion.
WELDING ALUMINIZED STAINLESS STEEL
Aluminized 409 stainless steel was introduced as a
material for use in automotive exhaust systems. This
material consists of a 409 stainless steel substrate with a
continuously applied thin coating of 8 μm (0.0003 in.)
aluminum on each surface. (Aluminized 439 also is
AWS WELDING HANDBOOK 9.4
being used in applications in which the temperature
limitations of 409 is are a factor.) The benefits of 409
stainless steel are extended life due to better corrosionresisting characteristics and improved appearance. This
material has been successfully welded with the gas tungsten arc, gas metal arc, resistance spot, resistance seam,
and high-frequency resistance seam welding processes.
No general welding procedures have yet been developed. Most of the problems that occur due to the aluminum coating on coated carbon steel also occur with
coated stainless steel. The same shielding and cleanliness requirements applicable to welding stainless steel
are also required for welding aluminized stainless.
Resistance Spot and Seam Welding
The resistance spot welding and resistance seam
welding processes can be used on aluminized stainless
steel with procedures that are very similar to those for
welding aluminized carbon steel, with the exception
that more current is required to make a weld in aluminized stainless steel.
High-Frequency Seam Welding
High-frequency seam welding (RSEW-HF) can be
used to weld aluminized 409 stainless steel, which has
weldability factors similar to bare 409. More upset
force is necessary to remove aluminum from the interface or to remove aluminum from the edges prior to
welding. Argon shielding during welding is recommended. (Refer to Fabricating Aluminized 409 Stainless
Steel Tubing in the Applications section of this chapter.)
Gas Metal Arc Welding
The most commonly used filler metals for the gas
metal arc welding of aluminized stainless steels are
409Nb, 308L, and 309L. The choice depends on the
particular materials being joined. It is necessary to
match welding filler metals to the base metals and to
meet required properties such as strength and resistance
to corrosion. Like welding aluminized carbon steel, the
welding of aluminized 409 stainless steel may require
slower travel speeds due to a sluggish weld pool.
Gas Tungsten Arc Welding
Best results for the of aluminized stainless steels with
the gas tungsten arc welding process are obtained by
using filler metal similar to those used with gas metal
arc welding. Excess aluminum in an autogenous weld
reduces weld ductility; but similar to welding aluminized carbon steel, adding filler material can compensate for the excess aluminum.
CHAPTER 3—COATED STEELS
193
CHROMIZED STEELS
Chromium diffusion coating, or chromizing, is a process that has been used for decades to diffuse chromium
into the surface of various steels and superalloys. Chromium as an alloying element in steels has long been recognized for its ability to increase resistance to hightemperature oxidation and corrosion. Similar to aluminum
diffusion coatings, chromium diffusion coatings can be
applied by thermochemical techniques such as pack
cementation and chemical vapor deposition processes.
METALLURGY OF THE CHROMIUM
DIFFUSION ZONE
When chromium alone is diffused into a medium-tohigh carbon steel substrate, the formation of surface
chromium carbide may result in substrate decarburization. The formation of surface chromium carbide can
block and inhibit chromium diffusion into the substrate. Because of the thermochemical affinity of carbon
for chromium, substrate decarburization can occur near
the interface of the diffusion coating and the substrate,
leading to a degradation of the mechanical properties
and alteration of weldability characteristics of the substrate. Columnar grain boundaries that form during the
diffusion coating process also are prone to extending
the entire distance from the diffusion zone-substrate
interface to the diffusion zone surface, providing potential short-circuit diffusion paths for corroding species to
reach the substrate. This is evident in Figure 3.24, a
photomicrograph that illustrates the chromium diffusion zone and decarburized substrate zone for a diffusioncoated chromium-molybdenum steel (1.25% chromium0.5% molybdenum). The thickness of the decarburized
substrate zone exceeds the thickness of the chromium
diffusion zone.
DIFFUSION COATING ELEMENTS
The addition of diffusion coating elements such as
silicon to the chromizing process greatly reduces the
formation of the surface chromium carbide layer, thus
providing a thicker and more uniform chromium (and
silicon) diffusion zone. In this situation, the silicon acts
as a ferrite stabilizer. When compared to conventional
chromizing, substrate decarburization is decreased due
to the ability of the silicon to reduce the thermochemical affinity of the chromium for carbon. Also, silicon
additions reduce the presence of columnar grain boundaries extending throughout the entire thickness of the
diffusion zone. Figure 3.25 shows a photomicrograph
of chromium-silicon diffusion-coated AISI 1018 carbon
steel.
194
CHAPTER 3—COATED STEELS
Micrograph courtesy of Alon Surface Technologies
Figure 3.24—Chromium Diffusion-Coated Steel,
1/25% Cr-5%Mo (x25, Nital Etch)
AWS WELDING HANDBOOK 9.4
sure to organic acids, high-temperature oxidation,
sulfidation and halide corrosive attack. This type of
coating system has numerous applications for boilers in
power generation plants, waste incineration and wasteto-energy facilities, petroleum refining, and chemical
and petrochemical processing.
Aluminum also can be added as another diffusion
coating element to the chromium or chromium-silicon
system. The additional aluminum will provide the benefits of reducing coking, fouling, and carburization in
petrochemical applications such as ethylene furnaces
and steam reformers. Petrochemical applications
employ cast alloys such as HK and HP, and wrought
alloys such as Alloy 800 and 802. When using these
alloys, the aluminum in the diffusion zone provides stabilization against decarburization via a dense adherent
oxide film, which is renewable during the steam-air
decoking cycle. The chromium (+ silicon) in the zone
establishes a barrier for nickel exposure at the surface,
and also stabilizes and supports the aluminum oxide
film that has been formed.
WELDING CHROMIUM-DIFFUSED
MATERIALS
Micrograph courtesy of Alon Surface Technologies
Figure 3.25—Chromium-Silicon Diffusion-Coated
AISI 1018 Carbon Steel (x100, Nital Etch)
Along with enhancing the affinity of chromization to
steels, silicon additions in the diffusion zone can
improve resistance to corrosion over conventional
chromized steels, due to the synergistic effects of combining these two corrosion-resisting elements. The addition of silicon provides an alloyed steel substrate of
chromium (and silicon) with excellent corrosion resistance in aqueous corrosive environments, such as expo-
Carbon steels, chromium-molybdenum steels, and
austenitic stainless steels are the most commonly used
chromium-diffused substrate materials. The chromium
content in the diffusion zone ranges from 30+ weight
percent on the surface to about 5 weight percent at the
interface of the diffusion zone and substrate. When silicon is added to chromium in the diffusion coating process, less than 3 weight percent silicon remains on the
surface, and it tapers off to less than 1 weight percent at
the interface of the diffusion zone and substrate.
Figure 3.26 provides a typical energy-dispersive
x-ray (EDX) chemical analysis of the chromium-silicon
distribution in a chromium-silicon diffusion-coated carbon steel, AISI 1018. The thickness of the diffusion
zone in these substrate materials typically ranges from
0.20 mm to 0.51 mm (0.008 in. to 0.020 in.), which
allows for good dilution and mixing of the substrate
material, diffusion zone, and filler metal. Weld preparation and operating variables for the most commonly
used welding processes (GTAW, SMAW, SAW and
GMAW) usually are the same as those used to join the
substrate material.
Carbon steel and the chromium-molybdenum steels
(up to 5 weight percent chromium) can be welded when
matched with the chemistry of the substrate material, or
a corrosion-resistant filler metal can be substituted. In
the utility boiler industry, the most common filler material is Type 312 stainless steel. Figure 3.27 is a photomicrograph of a tie-in between a convex 312 stainless
weld bead and a chromium-silicon diffusion-coated
carbon steel, Type A 106, Grade B. Depending on the
AWS WELDING HANDBOOK 9.4
LIVE GRAPH CHAPTER 3—COATED STEELS
195
Click here to view
35
30
25
WEIGHT %
20
CHROMIUM
15
10
5
SILICON
0
0
2
4
6
8
10
12
14
DEPTH (MILS)
Source: Alon Surface Technologies.
Figure 3.26—EDX Analysis, Chromium and Silicon Distribution,
Chromium-Silicon Diffusion-Coated AISI 1018 Carbon Steel
Micrograph courtesy of Alon Surface Technologies
Figure 3.27—Tie-in between a Convex Weld Bead
and Cr-Si Diffusion-Coated A 106 Grade B Carbon
Steel Layer (x50, Vilella’s Reagent, Nital Etch)
application, austenitic filler materials such as 308,
309, and 316 have been used, and also the nickel-base
materials NiCr, NiCrFe and NiCoCrFeSi. Welds in
chromium-silicon diffused austenitic stainless steels are
best when the chemistry of the substrate material is
matched.
When used in applications subject to high-temperature
erosion, coking, and carburization, the more complex
chromium-silicon-aluminum diffusion coatings are welded
with filler materials that have the same chemistry as the
substrate material. The joint is made with matching
chemistry to maintain the high-temperature strength
and creep properties required of the service conditions.
Weld preparation is critical in that the diffusion zone
surface must be clean and free of any excess aluminum
buildup that may occur as a result of the slower diffusion rates produced when using alloys with high nickel
content. Cast and wrought alloys alike require small
lands and as narrow a root opening as possible. The
GTAW welding process is the preferred method of joining; however, SMAW has been used with equal success.
196
CHAPTER 3—COATED STEELS
OTHER COATED STEELS
Other coated steel products include aluminum-zinc
and zinc-aluminum alloy coated steels, sprayed zinc
steels, and zinc-rich painted steels.
ALUMINUM-ZINC AND ZINC-ALUMINUM
ALLOY COATED STEELS
Sheet steels also can be coated with aluminum-zinc
or zinc-aluminum alloys, which are applied by the continuous hot-dip process similar to that used for zinc
coatings. Alloy coatings of aluminum and zinc combine
the best properties of both metals. Aluminum provides
durability in marine and industrial atmospheres and
resistance to high-temperature oxidation; zinc provides
malleability and galvanic protection at cut edges. The
normal range of coating weights is 153 g/m2 (0.5 oz/ft2)
of surface area of the sheet (both sides), equivalent to a
thickness of about 0.02 mm (0.008 in.) on each side.
Galvalume® and Galfan® are two commonly used
coated steel sheet products.42 Galvalume consists of
55% aluminum, 43.5% zinc, and 1.5% silicon. The
ASTM specification for Galvalume is A 792/A 792M,
with the following coating designations:43
AZM150 (AZ50) —150 g/m2 (0.50 min oz/ft2),
1.
2. AZM165 (AZ55) —160 g/m2 (0.55 min oz/ft2),
and
3. AZM180 (AZ60) —180 g/m2 (0.60 min oz/ft2).
Galfan consists of 95% zinc and 5% aluminum. Galfan has 12 coating designations ranging from ZGF001
(no minimum) to ZGF700 (GF235). The ASTM specification for Galfan is A 875/ A 875M, with the following
two coating types:44
Type I—Zn-5Al-MM (Zn + 5%Al + misch metal), and
Type II—Zn-5Al-Mg (Zn + 5%Al + 0.1% Mg).
Typical applications for Galvalume and Galfan
include roofing and siding for residential and commercial buildings, automotive underbody parts and exhaust
systems, agricultural equipment, and appliance components such as air conditioner housings.
42. See Reference 27.
43. ASTM International, latest edition, Subcommittee A05.11, Standard Specification for Steel Sheet, 55% Aluminum-Zinc Alloy-Coated
by the Hot-Dip Process, A 792/A 792M, West Conshohocken, Pennsylvania: ASTM International.
44. ASTM International, latest edition, Subcommittee A05.11, Standard Specification for Steel Sheet, Zinc-5% Aluminum Alloy-Coated
by the Hot-Dip Process, A 875/A 875M, West Conshohocken, Pennsylvania: ASTM International.
AWS WELDING HANDBOOK 9.4
Resistance Spot Welding
Both Galvalume and Galfan can be welded with conventional resistance spot welding processes using conditions similar to those for conventional continuousgalvanized sheet.
For Galvalume, a truncated-cone electrode geometry
with an included angle of 90° to 120° is preferred. For
Galfan, a 90° included angle is preferred. These geometries give more uniform current flow at the electrodecoating interface compared to electrode geometries used
with conventional galvanized coatings. For sheet up
to 1.6 mm (0.062 in.) thick, the electrode diameters
should be greater than those recommended for conventional galvanized steel (4 times to 5 times base metal
thickness), as shown in the typical welding schedules in
Tables 3.43 and 3.44.
The electrode diameter that will obtain the largest
weld nugget size generally is selected because it will
provide more cooling, and will reduce mushrooming of
the electrode face. Electrode diameters for thicker sheet
can be calculated by Equation (3.2A) in metric units and
Equation (3.2B) in U.S. customary units.
dmm = B Tmm
(3.2A)
where
dmm = Electrode diameter, mm
Tmm = Sheet thickness, mm
B
= 4 to 5 (acceptable range)
din. = A T in.
(3.2B)
where
din. = Electrode diameter, in.
Tin. = Sheet thickness, in.
A
= 0.8 to 1 (acceptable range)
Aluminum oxide dispersion-strengthened copper
electrodes are recommended in preference to typical
RWMA Class 2 electrodes. Adequate cooling with a
coolant flow rate of 7.6 L/min (2 gal/min) will give best
results. A typical weldability lobe curve for Galfan is
shown in Figure 3.28.
To establish the suitability of a particular zinc-aluminum alloy coated product (e.g., sheet) for resistance
seam welding, the product should be evaluated according to the test methods and recommended practices of
AWS/SAE D8.9.45
Resistance Seam Welding
Resistance seam welding of Galvalume and Galfan
requires slightly higher currents and lower electrode
45. See Reference 7.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
Table 3.43
Typical Spot Weld Schedules for 55% Aluminum-Zinc Coated Sheet
Sheet Thickness
mm
in.
Weld Current,
A
0.43
0.56
0.86
1.0
1.3
1.6
2.0
2.7
0.017
0.022
0.034
0.040
0.050
0.063
0.080
0.105
10 800
11 000
12 000
12 800
13 000
13 400
18 500
23 000
Electrode Force
kN
lb
Weld Time,
Cycles (60 Hz)
1.6
1.6
2.2
2.2
2.4
2.9
4.4
6.7
350
350
500
500
550
650
1000
1500
10
10
14
14
14
18
24
33
Electrode Face Diameter
mm
in.
4.8
4.8
6.4
6.4
6.4
6.4
7.9
9.5
0.188
0.188
0.250
0.250
0.250
0.250
0.312
0.375
Table 3.44
Typical Spot Weld Schedules for Zinc-5% Aluminum Coated Sheet
Sheet Thickness
mm
in.
Weld Current,
A
0.8
0.9
0.032
0.036
10 500
10 500
Electrode Force
kN
lb
Weld Time,
Cycles (60 Hz)
2.4
2.9
530
650
12
12
Electrode Face Diameter
mm
in.
6.4
6.4
0.25
0.25
LIVE GRAPH
Click here to view
14
0.9 mm (0.036 in.) GALFAN
WELDING TIME, CYCLES (60 Hz)
12
10
8
6
4
10 000
12 000
14 000
CURRENT, AMP
Figure 3.28—Resistance Spot Welding Lobe Curve for Zinc-5% Aluminum Coated Sheet Steel
197
198
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
forces than those required for conventional hot-dip galvanized sheet. Seam welding schedules for Galvalume
are shown in Table 3.45. Flood cooling of the workpiece and the circular electrodes is recommended. For
weld speeds higher than those shown in Table 3.46,
approximately the same number of welds per unit
length should be maintained. This may be done by
increasing the proportion of heat time to cool time in a
way that will also increase the sum of heat time and
cool time, which can be calculated with Equation 3.3.
Increasing seam-welding speed for Galvalume and
Galfan has the same effect on weld quality as it has on
conventional galvanized sheet, except that the degree of
joint penetration decreases more rapidly because of the
higher aluminum content. A knurled drive wheel with a
12.7 mm (1/2 in.) radius face is recommended. Current
ranges and limitations on welding speed for Galvalume
are shown in Table 3.46.
Welds
3600 ---------------- = ---------------------------L
S(TH + TC)
Galvalume sheet may be projection welded according to the schedule shown in Table 3.47. Like galvanized steel, Galvalume can be welded without upslope,
but the current range is reduced, as is the service life of
the electrode tip. Also, the likelihood of metal expulsion
from the weld zone is greater, especially for larger electrodes without upslope. When upslope is employed,
larger electrodes can be readily used.
Projection Welding
(3.3)
where
L = Unit length, in. or mm
S = Welding speed, unit length per min (L/min)
TH = Heat time, cycles
TC = Cool time, cycles
Table 3.45
Typical Seam Welding Schedules for 55% Aluminum-Zinc Coated Sheet Steel a
Welds per
Unit Length
Minimum
Contacting
Overlap
lb
Weld Time,
Weld Cycles (60 Hz) Weld Speed
Current,
A
Heat Cool mm/s in./min
w/m
w/in.
mm
in.
3/8
Material
Thickness
Electrode
Face Typeb
Electrode
Thickness
Electrode
Force
mm
mm
in.
mm
in.
kN
in.
0.43
0.017 12.7 rad
1/2 rad
9.5
3/8
3.11
700
14 500
2
2
25.4
60
590
15
9.5
0.56
0.022 12.7 rad
1/2 rad
9.5
3/8
3.78
850
16 000
3
2
25.4
60
470
12
9.5
3/8
0.86
0.034
6.35 flt
1/4 flt
12.7
1/2
4.45
1000
21 500
4
2
25.4
60
395
10
12.7
1/2
1.25
0.049
6.35 flt
1/4 flt
12.7
1/2
4.89
1100
22 000
4
2
25.4
60
395
10
14.3
9/16
1.25
0.049
6.35 flt
1/4 flt
12.7
1/2
4.89
1100
23 000
4
1
38.1
90
315
8
14.3
9/16
2.11
0.083
6.35 flt
5/16 flt
15.8
5/8
7.12
1600
27 000
10
6
25.4
60
295
7-1/2
17.5
11/16
a. Electrode material RWMA Group A, Class 2 electrodes. 12.7 mm (1/2 in.) radius-faced electrodes can be used for all sheet thicknesses if desired.
b. rad = radius, flt = flat.
Table 3.46
Current Ranges for Seam Welds in 55% Aluminum-Zinc Coated Sheet Steel
Sheet Thickness
Weld Speed
mm
in.
Circular Electrode
mm/s
in./min
Current Range, Aa
Limiting Factor for
Upper Current
0.43
0.017
12.7 mm (1/2 in.) radius face
25.4
60
13 000–16 000
Electrode sticking
0.56b
0.022b
4.8 mm (3/16 in.) flat face
25.4
60
15 500–16 500b
Surface burning
0.86
0.034
6.4 mm (1/4 in.) flat face
25.4
60
20 500–24 000
Surface burning
1.25
0.049
6.4 mm (1/4 in.) flat face
25.4
60
18 500–25 000
Surface burning
1.25
0.049
6.4 mm (1/4 in.) flat face
38.1
90
19 000–26 500
Surface burning
2.11
0.083
7.9 mm (5/16 in.) flat face
12.7
30
23 000–34 500
Metal expulsion
2.11
0.083
7.9 mm (5/16 in.) flat face
25.4
60
24 000–32 000
Metal expulsion
a. Weld schedules used were those recommended in Table 3.46; the lower current listed is the smallest current which produces a continuous weld.
b. For 0.56 mm (0.022 in.) sheet, 12.7 mm (1/2 in.) radius wheels should broaden the current range.
AWS WELDING HANDBOOK 9.4
199
CHAPTER 3—COATED STEELS
Table 3.47
Typical Welding Schedules for Projection Welding of 55% Aluminum-Zinc Coated Sheet Steel
Electrode Diameter
and Shape (Sketch A)a, c
Material
Thicknessb
Diameter, Dp
Height, Hp
mm
in.
mm
in.
mm
in.
Projection Size (Sketch C) a
mm
in.
kN
lb
0.625
9.5
0.375
1.11
250
10 000
5
3.8
0.15
4.75
0.187
1.04
0.041
0.625
11.1
0.438
1.78
400
12 000
5
5.1
0.20
5.54
0.218
1.22
0.048
D
d
mm
in.
mm
in.
1.0
0.040
15.9
1.7
0.065
15.9
Upslope
Time,
Cycles
(60 Hz)b
Weld Nugget
Diameter,
Dw (Sketch B)a
Approx.
Weld
Current,
Ad, e
Net Electrode
Forcee
D
d
Dw
(A) Electrode Diameter and Shape
a.
b.
c.
d.
e.
Dp
(B) Weld Nugget Diameter
Hp
(C) Projection Size
Dimensional variables are as shown in sketches A, B, and C.
Weld time should be 10 cycles for both thicknesses. Two equal metal thicknesses of each gauge.
Electrode material is RWMA Class 2.
Initial upslope current is 20% of welding current.
For multiple projections, multiply force and current by number of projections.
When welding dissimilar thicknesses, the recommended projection for the lighter gauge should be
placed in the heavier sheet, and welding conditions for
the thinner gauge should be used. The projection welding of material thinner than 1 mm (0.040 in.) is difficult
and therefore not recommended. The edges to be
welded must be free from dirt, grease, and paint prior
to welding, although it may have a light oil coating.
Gas Tungsten Arc Welding
Gas tungsten arc welding of Galvalume and Galfan
is not recommended because of the electrode contamination that occurs, which leads to arc instability.
Shielded Metal Arc Welding
Shielded metal arc welding procedures for Galvalume and Galfan sheet steels are similar to those used
for conventional galvanized steel. Electrodes E6012 and
E6013 are recommended for welding these coated
steels, although the more deeply penetrating E6010 and
E6011 electrodes can be used with care. The same
whipping technique when manipulating the arc is used
to burn off the coating in front of the weld pool.
Gas Metal Arc Welding
Galvalume and Galfan sheet can be welded with the
gas metal arc welding process using shielding gas mixtures of argon-1% oxygen or argon-20% CO2. Mild
steel welding wire can be used with the gas nozzle at a
workpiece distance of 10 mm (0.4 in.). The welding
current should be 80 A with a voltage of 19 V to 20 V.
This produces a wire feed rate of 51 mm/s (120 in./min)
when using 0.8 mm (0.032 in.) diameter rods. A minimum shielding gas flow rate of 14.2 L/min (30 ft3/h) is
recommended.
Soldering
Soldering is not recommended for joining Galvalume
and Galvan coated steels. Mechanical fastening should
be used when possible. If it is necessary to join these
200
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
coated steels by soldering, the general recommendations
for conventional soldering of continuous-galvanized
sheet can be used. Zinc-aluminum solder can be used
for either the Galvalume or Galvan coating, while a
zinc-tin is acceptable only for Galvalume. Mechanical
abrading prior to fluxing will help remove the aluminum oxide surface layer and aid the solder in wetting.
Fluxes should be the same as those used for soldering
aluminum or aluminum-coated steel. The flux residue
must be completely removed after soldering, or the corrosion resistance and surface integrity of the sheet will be lost.
SPRAYED ZINC-COATED STEELS
Surfacing of pure zinc or an alloy of zinc-15% aluminum typically is sprayed onto steel to provide protection from corrosion. The zinc coating thickness
generally is at least 0.1 mm (0.004 in.). Sprayed zincaluminum surfaces provide corrosion protection for a
large variety of components without limitations on size.
Surfacing can be applied in situ to large workpieces,
towers, bridges, and other structures that are too large
for conventional galvanizing baths. Unlike the coated
steels discussed previously, steels with sprayed coatings
cannot be resistance welded, brazed, or soldered. The
fabrication of spray-coated steel products by welding is
limited to the arc welding processes.
Gas Metal Arc Welding
Typical welding conditions for the gas metal arc
welding of fillet welds in T-joints and butt joints in
12.7 mm (1/2 in.) thick zinc-sprayed steel are shown in
Tables 3.48 and 3.49. Carbon dioxide is used as the
shielding gas. A root opening of 1.6 mm (1/16 in.)
between the plates in the T-joint, as shown in Table
3.48, reduces the chance of intergranular zinc penetration. The amount of spatter formed when welding
spray-coated steel is equal to that formed with galvanized steel. The use of an anti-spatter agent is essential
both on the workpiece and on the nozzle of the welding
gun, which should be cleaned frequently to remove the
spatter.
Table 3.48
Typical Gas metal Arc Welding Conditions for Fillet Welds in
12.7 mm (1/2 in.) Spray-Coated Steel Plate with CO2 as the Shielding Gas*
Welding Conditions
Wire Feed Speed
Travel Speed
on Uncoated Steel
Travel Speed
Welding Position
Current,
A
Voltage,
V
mm/s
in./min
mm/s
in./min
mm/s
in./min
Horizontal
135
20
61.4
145
2.1
5
3.4
8
Downhill
135
20
61.4
145
4.2
10
4.2
10
Uphill
135
20
61.4
145
2.1
5
2.1
5
Overhead
135
20
61.4
145
2.3
.5.5
3.4
8
*Electrode stickout 6.4 mm to 9.5 mm (1/4 in. to 3/8 in.). 1 mm (0.035 in.) diameter Si-Mn deoxidized wire. Gas flow rate 14 L/min (30 ft3/h). 1.6 mm (1/16 in.)
root opening.
Table 3.49
Typical Gas Metal Arc Welding Conditions for Butt Joints in
12.7 mm (1/2 in.) Spray-Coated Steel Plate with CO2 as the Shielding Gas*
Number of Passes
Current,
A
Voltage,
V
Decrease in Speed Compared
with Welding Uncoated Steel, %
Flat
6 Plus Sealing Pass
160
31
10
Welding Position
Uphill
3
115
19
0
Overhead
3
115
19
13
Horizontal
9
115
19
15
flow rate 14 L/min (30 ft3/h). Electrode stickout 6.4 mm to 9.5 mm (1/4 in. to 3/8 in.). Edge preparation:
*1 mm (0.035 in.) diameter Si-Mn deoxidized wire; CO2
Root face 1.6 mm (1/16 in.); Root opening 2.4 mm (3/32 in.); 60° included angle.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
V-groove butt joints in spray-coated steel can be free
from porosity even when the plate edges are sprayed
after beveling. Fillet welds may contain extensive porosity at the root. This can be reduced by using a 1.6 mm
(1/16 in.) root opening between the standing plate of
the T-joint or by removing the zinc coating from the
edge of the plate. (Plates will be free from zinc if they
are cut after spray coating). A zinc-sprayed coating can
cause more extensive porosity than any other form of
zinc coating. Porosity can be remedied by using organic
sealers on the faying surfaces of the joint.
201
Table 3.51
Radiographic Appearance of Shielded
Metal Arc Double-Fillet Welds in T-Joints
in 12.7 mm (1/2 in.) Spray-Coated Steel Plate
No. of Pores in 305 mm (12 in.) of Weld
Type of Electrode
First Side
Second Side
Rutile
3
0
Basic
28
1
Shielded Metal Arc Welding
Shielded metal arc welding procedures suitable for
uncoated steel can be used satisfactorily on spraycoated steel. As with galvanized steel, it is advisable to
use a back-and-forth whipping motion of the electrode
along the weld joint to burn off some of the zinc in
front of the weld pool. This results in reduced travel
speed compared to fillet welds made in the horizontal
position on uncoated steel, but there is no reduction in
speed in the vertical position. Typical welding conditions are shown in Table 3.50.
The formation of undercut when welding spraycoated steel is not as prevalent as when welding galvanized steel. However, if undercut occurs, for example,
because of excessive coating thickness, the same techniques used for avoiding undercut when welding galvanized steel are effective.
Groove-welded butt joints in spray-coated steel
should be sound and free from porosity. Fillet welds
may contain porosity when the edge (i.e., the joint face
of the standing plate) is coated; the extent of porosity
depends on the type of electrode used, as shown in
Table 3.51.
Submerged Arc Welding
Spray-coated steel with a zinc coating thickness of
0.10 mm (0.004 in.) gives rise to slightly more porosity
in groove-welded butt joints than galvanized steel with
a similar coating thickness: 762 g/m2 (2-1/2 oz/ft2). The
reason for the increased porosity in welds on spraycoated sheet is not completely understood, but it may
be caused by entrained air or moisture in the coating.
Typical conditions for welding butt joints in spraycoated steel are shown in Table 3.52. To obtain sound
welds, the general principles for welding galvanized
steel apply.
Fillet welds in T-joints made with the submerged arc
process on spray-coated steel may contain considerably
more porosity than welds on galvanized steel. However,
by using an oxygen-cut edge on the standing plate that
is free of zinc and a root opening of 1.6 mm (1/16 in.)
between the plates, sound welds can be obtained at
travel speeds up to 8.5 mm/s (20 in./min). Typical
welding conditions are listed in Table 3.53. Attention
should be given to the significant reduction in porosity
to be gained by incorporating a root opening of 1.6 mm
(1/16 in.) instead of butting the sections together. For
example, the change in the trailing weld from 4.2 pores/
mm to 0.20 pores/mm (106 pores/in. to 5 pores/in.)
can be observed for coated edges and 2 pores/mm to
0 pores/mm (52 pores/in. to 0 pores/in.) for the uncoated
edges.
Table 3.50
Typical Shielded Metal Arc Welding Conditions for
Fillet Welds in 12.7 mm (1/2 in.) Spray-Coated Steel Plate
Electrode Size
Electrode Type
Specification
mm
in.
Welding Position
Current (ac),
A
Reduction in Speed
Compared with Welding
Uncoated Steel, %
Rutile
AWS E6013
4
5/32
Horizontal
170
10
Rutile
AWS E6013
4
5/32
Vertical
147
0
Basic
AWS E7016
4
5/32
Horizontal
160
10
Basic
AWS E7016
4
5/32
Vertical
113
0
202
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.52
Typical Submerged Arc Welding Conditions for Butt Joints in Spray-Coated Steela
Radiographic
Appearanceb
Welding Conditions
Root
Opening
Edge Shape
First Side
Second Side
mm
in.
Condition
of Edges
mm
in.
13
1/2
Coated
0
0
540
32
540
32
6
14
13
1/2
Coated
1.6
1/16
540
32
540
32
6
1/2
Coated
0
0
540
32
540
32
1
Coated
0
0
1000
36
1000
1/2
Coated
0
0
740
40
740
13
Max.
Pore Size
Travel Speed
Current, Voltage, Current, Voltage,
No. of
A
V
A
V
mm/s in./min Pores
mm
in.
5
0.8
1/32
14
0
—
—
6
14
0
—
—
36
5
11
4
1.6
1/16
40
10
24
0
—
—
0
—
—
Supported above bench
25
Supported above bench
13
Supported above bench
1st side
8
20
10
13
1/2
Coated
0
0
500
45
800
45
2nd side
9
22
6.4 mm (1/4 in.)
a. 3.2 mm (1/8 in.) diameter, 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive.
b. Length of radiograph = 375 mm (15 in.).
Table 3.53
Typical Welding Conditions for Series Submerged Arc
Welding of T-Joints in 12.5 mm (1/2 in.) Spray-Coated Steela
Welding Conditions
Lead Weld
Radiographic Appearance b
Trailing Weld
Root Opening
Leading Weld
Travel Speed
Condition
of Edges
mm
in.
Coated
0
0
500
33
450
Coated
1.6
1/16
500
33
Current, Voltage, Current, Voltage,
A
V
A
V
Trailing Weld
Max. Pore Size
Max. Pore Size
mm/s
in./min
No.of
Pores
32
9
20
80
3.2
1/8
106
3.2
1/8
450
32
9
20
4
1.6
1/16
5
2.4
3/32
mm
in.
No. of
Pores
mm
in.
Uncoated
0
0
500
33
450
32
9
20
28
1.6
1/16
52
1.6
1/16
Uncoated
1.6
1/16
500
33
450
32
9
20
0
—
—
0
—
—
a. 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive.
b. Length of radiograph = 375 mm (15 in.).
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
203
ZINC-RICH PAINTED STEEL
Shielded Metal Arc Welding
Zinc-rich or zinc-dust paints have been developed
that provide protection similar to galvanizing or spraycoating if sufficient zinc is present in the paint film.
Zinc-rich paints are widely used as zinc primers or
welding primers applied after shot blasting for the temporary (up to 12 months) protection of steel during the
period of fabrication by welding. For welding primers,
92 weight percent to 95 weight percent of zinc is used
in a variety of binding agents such as sodium silicate,
sodium ethylsilicate, epoxy resin, or chlorinated rubber.
Film thicknesses vary from 12 μm to 75 μm (0.0005 in.
to 0.003 in.), depending on the type of paint and
method of application.
The most widespread use of zinc-rich paint is for
ship hulls, zinc plating, and for all forms of structural
steel work. Most shipyards have incorporated an automatic shot blasting and painting plant, and steelmakers
routinely supply primed plate products directly from
the steel works.
Groove welds and fillet welds on zinc-rich painted
steel can be made with the same currents and welding
procedures used for the shielded metal arc welding of
uncoated steel, without the usual reduction in travel
speed, even when the zinc-rich primer has been applied
to the beveled plate edges of a butt joint or to the edges
of the standing plate in a T-joint. Spatter can be reduced
by removing the paint in the immediate area of the
weld.
Welds in T-joints made in plate coated with film of
normal thickness can be welded without complications.
Single-fillet or double-fillet welds made with rutile-covered electrodes (E6012, E6013, E6014) on plate coated
with normal film thicknesses of zinc-rich primers generally are free from porosity, whether the edge of the
standing plate is coated or uncoated. Welds made with
basic covered electrodes (E7015, E-7016, E7018) on
plate coated with normal film thicknesses of zinc-rich
primers and with the edge of the standing plate
uncoated are either free from porosity or contain only
occasional pores.
If plates with excessive coating thicknesses are used,
or if the edge of the standing plate of a T-joint is coated,
a slight arc disturbance might be noted.
Porosity can develop in the fillet welds, as shown in
Table 3.54, particularly if they are made with basic electrodes. With groove welds in butt joints, however, the
welds should be free of porosity.
Excessive coating thicknesses can slightly affect the
functional characteristic of the electrode and can make
the weld pool either more turbulent or more sluggish.
This may lead to an increase in spatter loss, a slight
undercut, or deterioration in the appearance of the
weld. In general, rutile electrodes do not seem to be
affected to the same extent as basic covered electrodes,
which sometimes produce slightly bulbous-shaped fillet
welds in the presence of heavy primer coatings. Another
characteristic of thick coatings is that they can cause
occasional arc-starting difficulties. While these difficulties may be minor, the following recommendations will
ensure the optimum results:
Gas Metal Arc Welding
Gas metal arc welding is used to weld butt joints and
T-joints in 12.7 mm (0.5 in.) plate coated with the normal film thicknesses of zinc-rich primers. Carbon dioxide is used as the shielding gas, and welding can be in all
positions with the welding conditions used for uncoated
steels. There is no reduction in travel speed. Coatings of
zinc-rich primers produce less spatter than galvanized
or spray-coated steel, but more than uncoated steel. The
use of anti-spatter agents on the workpiece is not necessary because the spatter particles do not adhere to the
primed surface and can be easily brushed off. The inside
of the GMAW gun nozzle, however, should be sprayed
with an anti-spatter agent to facilitate periodic removal
of accumulated spatter. Spatter can be reduced by
removing the paint in the immediate area of the weld.
Variable amounts of porosity occur in welds on zincprimed plate in all welding positions, the amount
depending on the coating thickness and, to a certain
extent, on the welding conditions. The welding conditions shown in Tables 3.48 and 3.49 for spray-coated
steel can be used for welding zinc-rich painted steel, but
the welds will contain porosity. Porosity in welds made
in the flat or horizontal positions can be minimized by
increasing the heat input. Welding conditions of 170 A
and 22 V produce double-fillet welds in which the first
weld deposited usually is free from porosity, while the
second-side weld may contain a few pores. In the vertical and overhead positions, porosity may be slightly
more extensive, but usually can be eliminated from
double-fillet welds by using a 1.6 mm (1/16 in.) root
opening between the plates.
1. The primer should be applied in coating thicknesses recommended by the manufacturer; and
2. For T-joints, it is preferable that coatings be
removed from the edges of the standing plate,
even if the plates are oxygen-cut before assembly.
Submerged Arc Welding
When welding steel with the submerged arc welding
process, the use of primed plate, whether coated with
zinc-rich paint or zinc-free paint, can cause adverse
effects. The primer can be removed from the weld area
204
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Table 3.54
Radiographic Appearance of Shielded Metal Arc Welding
Double-Fillet Welded T-Joints in 12.7 mm (1/2 in.) Zinc-Epoxy Coated Plates*
Overhead Weld (Deposited First)
Horizontal Weld (Deposited Second)
Diameter
Diameter
No. of Pores in
381 mm (15 in.)
mm
in.
Rutile
0
—
—
0
—
—
Basic
10
—
—
15
1.6
1/16
Type of Electrode
No. of Pores in
381 mm (15 in.)
mm
in.
*4 mm (0.160 in.) diameter rutile and basic electrodes. Welding current 140 A. Travel speed 2.1 mm/s (5 in./min).
before welding, but this is an additional and expensive
operation. There are obvious economic advantages in
welding steel plate before it is primed.
The main problem associated with welding primed
plate is porosity. It is principally produced by hydrogen,
one of the thermal decomposition products of the
organic binders of the paint film. The hydrogen escapes
from the solidifying weld metal by the process of nucleation and growth. If the weld cools very rapidly, pores
might not nucleate or might only grow into small bubbles that are not detectable. With very slow rates of
solidification, large bubbles have a chance to develop
and escape. Porosity is a problem at the intermediate
cooling rate, although this also is strongly affected by
the amount of hydrogen present.
Square-groove welds in butt joints in oxygen-cut
plate (e.g., with the edges free from primer) will probably be free from porosity. If the edges are coated, the
variable film thickness on the edges with possible local
buildup primer can cause slight porosity. If squaregroove butt joints are to be made on plates that have
primer on the edges, sound joints can be obtained by
leaving a root opening of 1.6 mm (1/16 in.) between the
plates, as shown in Table 3.55.
Groove-welded butt joints in plates with beveled
edges do not normally contain porosity even when the
prepared edges are coated with thick films of primer.
The reason for the relative freedom from porosity in
this instance is that there is time for any gases that are
formed to escape before the weld solidifies.
In a T-joint in which a vertical plate is attached to a
horizontal plate by means of a double-fillet weld, gases
may become trapped at the faying surface when the
second weld is deposited and thus may cause porosity.
Because of the higher travel speed, welds made by
automatic welding processes (particularly double-fillet
Table 3.55
Typical Submerged Arc Welding Conditions for
Square-Groove Welds in Butt Joints in 12.7 mm (1/2 in.) Primed Platea
Welding Conditions (Both Sides)
Coating Thickness
Root Opening
Travel Speed
Condition
of Edges
μm
in.
mm
in.
Zinc Epoxy
Coated
Coated
Uncoated
38
38
38
0.0015
0.0015
0.0015
0
1.6
0
0
1/16
0
540
540
540
Zinc Silicate
Coated
Uncoated
51
51
0.0020
0.0020
0
0
0
0
Zinc Ethyl Silicate
Coated
Uncoated
25
25
0.0010
0.0010
0
0
0
0
Coating
Radiographic Appearanceb
Current, Voltage,
A
V
Max. Pore Size
mm/s
in./min
No. of
Pores
32
32
32
5.9
5.9
5.9
14
14
14
3
0
0
1.6
—
—
1/16
—
—
540
540
32
32
5.9
5.9
14
14
5
0
1.6
—
1/16
—
540
540
32
32
5.9
5.9
14
14
2
0
1.2
—
3/64
—
a. 3.2 mm (1/8 in.) diameter 2% Mn steel welding wire. Manganese silicate flux. Direct current electrode positive.
b. Length of radiograph = 375 mm (15 in.).
mm
in.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
welds in which both sides of a standing plate are welded
simultaneously) are more prone to porosity than those
produced by manual welding processes. In making double fillets with submerged arc welding, the leading electrode, which welds one side of the joint, usually is
positioned about 150 mm to 230 mm (6 in. to 9 in.) in
front of the following electrode on the other side of the
joint. Thus, the first weld effectively seals off one avenue of escape for gases evolved at the faying surface,
and consequently the second (trailing) weld on the other
side of the standing plate is more likely to contain
porosity.
Table 3.56 shows the results of radiographic examination of submerged arc double-fillet welds on zincprimed plate. The importance of the binder on porosity
is very apparent in this table. It can be noted that the
number of pores in the trailing weld is an order of magnitude higher with the epoxy binder than with the silicate binders. However, the number of pores in the
leading welds appears to be somewhat independent of
the binder and relatively high, although at 5 pores/mm
to 13 pores/mm (2 pores/in. to 5 pores/in.), this number
could be acceptable for many applications.
Porosity can be avoided by a combination of reduced
travel speed and the use of a thin coating of primer. A
root opening of 1.6 mm (1/16 in.) between the plates
also is effective when welding 12.7 mm (1/2 in.) plate.
This method is not recommended for a double-fillet
weld in thicker plate. When welding 25.4 mm (1 in.)
plate, a root opening of 1.6 mm (1/16 in.) can cause
large slag inclusions associated with porosity at the root
of the weld.
Another method of preventing porosity in welds on
12.7 mm (1/2 in.) primed plate is to increase the current
to a level at which complete penetration welds are
obtained.
In summary, the following steps are recommended to
obtain sound fillet welds by submerged arc welding:
205
1. A primer applied by an automatic spraying
method should not exceed the film thickness recommended by the manufacturer;
2. The edge of the standing plate of a T-joint should
be free from primer, (e.g., oxygen cut); and
3. In plate up to 12.7 mm (1/2 in.) thick, root openings of 1.6 mm (1/16 in.) between plates should
be used, as shown in Figure 3.29(A), or high
welding current should be used to obtain complete penetration, as shown in Figure 3.29(B).
RECONDITIONING WELDED JOINTS
When galvanized or spray-coated steels are welded,
some of the zinc-iron coating is volatilized on each side
of the weld, and although a thin layer of zinc alloy
remains, there is a considerable loss of corrosion resistance. In zinc-rich painted steel, welding causes decomposition of the paint film that is burned off for some
distance on each side of the weld. The width of the
damage to the zone will depend on the heat input,
which is greater with a slow welding process such as
oxyfuel gas welding than with a high-speed arc welding
process.
The weld metal itself, if it is ferritic, will soon start
to rust in most atmospheres except those that are very
dry, so it is essential to apply some form of protective
coating.
Suitable materials for coating welds in zinc-depleted
areas are zinc-rich paints, repair sticks consisting of
alloys of zinc-cadmium or zinc-tin-lead, or zinc sprayed
coatings. A reconditioning material should have the following characteristics:
1.
2.
3.
4.
Ease of application,
Thick adherent coating in a single application,
Preferably anodic to the steel, and
Good wear resistance when welded components
have to be transported.
Table 3.56
Results of Radiographic Examination of Submerged Arc Double-Fillet Welds on Zinc-Primed Platea, b
Leading Weld
Trailing Weld
Maximum Pore Size
Coating/Binder
Condition
of Edges
Number
of Pores
mm
Zinc/Epoxy
Coated
40
Zinc/Silicate
Coated
75
Zinc/Ethyl Silicate
Coated
30
Maximum Pore Size
in.
Number
of Pores
mm
in.
1.2
3/64
100
1.6
1/16
1.6
1/16
10
2.4
3/32
1.2
3/64
9
3.2
1/8
a. Welding conditions: leading weld 500 A, 33 V; trailing weld 450 A, 32 V; 8.5 mm/s (20 in./min); 3.2 mm (1/8 in.) diameter 2% Mn steel filler wire. Manganese
silicate flux Root opening nil.
b. Length of radiograph = 375 mm (15 in.).
206
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
mance of painted coatings over welds whether applied
with a brush or by a spray technique. A good color
match will be obtained on zinc-rich primed steel, but to
improve the color match on spray-coated steel or on
bright coated galvanized steel, a top coating of aluminum paint can be used.
Repair Rods and Zinc Wire
(A)
(B)
Figure 3.29—(A) Incomplete Joint Penetration of
Fillet Weld with 1.6 mm (1/16 in.) Root Opening,
and (B) Complete Joint Penetration
Welds in primed plate generally are recoated with
zinc-rich paints, but for galvanized or spray-coated
steel, any of the methods discussed in this section may
be used.
Zinc-Rich Paints
The application of zinc-rich paint is the most rapid
and convenient method of repair. It is recommended
that the percentage of zinc dust in these paints be over
90% to provide good corrosion resistance and also to
allow a thick film, approximately 50 μm (0.002 in.), to
be obtained in each coat.
Surface preparation consists of removing the welding
slag with a chipping hammer, followed by vigorous
brushing with a powered wire brush. The paint is
applied with a paint brush, preferably in two coats. It
has been shown that there is no difference in the perfor-
The most common types of repair rods are zinc-cadmium alloys (melting range, 270°C to 275°C [518°F to
527°F]), zinc-tin-lead alloys (melting range, 230°C to
260°C [446°F to 500°F]), and zinc-based solders (melting range, 484°C to 572°C [250°F to 300°F]). The zinctin-lead alloys contain fluxing ingredients. Repair rods
are more expensive than zinc-rich paints. They are
slightly more difficult to apply, but the corrosion resistance of the coating is equivalent to that of galvanizing.
Therefore, there are applications in which the use of
these repair rods is essential.
The ASTM specification that covers repair rods is
ASTM A 780, Standard Practice for Repair of
Damaged and Uncoated Areas of Hot-Dip Galvanized
Coatings.46 The procedure for using repair rods is as
follows:
1. Welding slag should be removed with a chipping
hammer and the weld or damaged area should
be cleaned by vigorous wire brushing, grinding,
or sanding, and this preparation should include
the surrounding undamaged coating;
2. The region to be repaired should be reheated to
315°C (600°F) by means of an oxyfuel gas torch
or another adequate method, as the alloys do not
spread well at lower temperatures;
3. The surface should be wire-brushed again;
4. The area should be fluxed with chloride-base
flux (if the repair rod is not self-fluxing) and
heated until the flux produces smoke;
5. The coating should be applied by rubbing an
alloy bar over the heated surface while it is hot
enough to melt the alloy;
6. The area should be fully tinned and wetted and
then built up to the desired thickness of coating;
7. The molten alloy should be spread by brisk wirebrushing or by rubbing with a flat-edge strip of
steel or a palette knife; and
8. Flux residues should be removed by wiping with
a damp cloth or rinsing with water.
It is possible to make use of the residual heat in the
weld to melt the repair rod. The procedure for welds
46. ASTM International, Subcommittee A05.11, 2006, Standard
Practice for Repair of Damaged and Uncoated Areas of Hot-Dip
Galvanized Coatings, ASTM A 780-01 (2006), West Conshohocken,
Pennsylvania: ASTM International.
AWS WELDING HANDBOOK 9.4
that still are hot (315°C [600°F] or over) is to remove
the slag and brush the weld vigorously with a wire
brush, then apply the alloy coating as above. In all
cases, the repair rod should not be applied to a surface
much above 315°C (600°F) because too much dross
will be formed. Some of the repair compounds also are
available in powder form, which is applied in a similar
manner as the rods. Zinc welding wire can be used
instead of an alloy repair rod, but the procedure is more
complicated and involves the application of acid to
clean the surface, followed by fluxing. For this reason,
the method is not recommended.
Zinc Spraying
The zinc spraying method of reconditioning, which is
applicable to welds on galvanized or spray-coated steel,
provides a coating with corrosion resistance equivalent
to that of the surrounding areas. The method is to blast
the area to be coated with grit or sand, then apply a thick
coating (60 μm to 122 μm [0.0024 in. to 0.0048 in.]) of
zinc.
While zinc spraying of damaged areas results in
excellent corrosion resistance, it has the following disadvantages:
1. It requires grit blasting or sand blasting of the
surface;
2. It is difficult to restrict grit blasting to the weld
or damaged area, although the use of good
masking techniques should minimize damage to
adjacent surfaces;
3. Overblasting can result in counterproductive
thinning of the coating of the steel;
4. Elaborate equipment is required; and
5. Metal spraying must be carried out by a skilled
operator.
CHAPTER 3—COATED STEELS
207
organic-painted before forming (i.e., for tailored press
blanks) are another type of painted steel.
Joining painted metal is readily accomplished when
the joining procedure, which includes joint design, joining process, and tooling, is well planned. When organic
coatings are used, a key to planning is to recognize several factors: the coatings are heat sensitive, usually will
scorch or burn if overheated, usually are good electrical
insulators, and are intended to be used without any
post-fabrication finishing.
When welding a sheet material with a film coating, it
is important not to cause the film to separate from the
sheet. This could result in bubbling of the film. The
joining techniques covered in the following sections
include the fusion welding processes.
WELD JOINT DESIGN
When welding of painted sheet steel is the joining
technique of choice or is required, it generally is best to
use single-sided material with the face side (“show
side”) coated and the other side bare. An alternate
method is to provide local areas of bare metal where
welding can be done. If no bare areas are allowable,
then the welding process must be tolerant of the coating
material on the metal.
Placing the weld joint in a hidden area has several
benefits, including removing from sight any deterioration of the coating at the weld. Also, there is no need to
cover any bare areas after welding. Figure 3.30 shows a
design for a refrigerator where the prepainted wrapper
has a bare strip left on the edge so that the back panel
can be welded to it. The bare strip is designed to be
hidden by the foam insulation. Hidden joints can be
used if it is ensured that the item will not be used in an
area where the joint may be exposed to a corrosive
atmosphere.
PAINTED STEELS
Painted steels include coiled sheet products that are
either coated with organic paint or laminated with a
film (e.g., polyvinyl chloride or Teflon®).47, 48 Painted
steels also include pretreated (e.g., phosphated) steels
and metal-coated (e.g., galvanized) steels. Bare or
metal-coated sheet steel that are powder-coated or
47. Teflon is a registered trademark and brand name of the DuPont
Company.
48. CAUTION: Hazardous gases usually are formed when organic
paints or films, or both, are decomposed by the heat of welding. This
is especially true for PVC and PTFE. Therefore, when welding parts
coated with these materials, it is essential that there be adequate ventilation. See the Material Safety Data Sheet (MSDS) for the particular
coating being used.
WELD
PAINT STOPS
AT THIS POINT
PREPAINTED STEEL
CABINET WRAPPER
UNPAINTED STEEL
BACK PANEL
Figure 3.30—A Strip of Bare Area Retained for
Welding a Prepainted Steel Cabinet Wrapper
208
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
WELDING PROCESSES
The welding processes used on painted steels are
resistance welding, capacitor discharge stud welding,
arc spot welding, and laser beam welding.
ELECTRODES
PROJECTIONS
(ANNULAR RING)
Resistance Welding
Spot welding and projection welding are often used
on painted sheet steel.49 The preferred technique is
series welding on the bare side or at a bare area of the
sheet, as shown in Figure 3.31.
To establish the suitability of a particular painted
product (e.g., sheet) for resistance spot welding, the
product should be evaluated according to the test methods and recommended practices of AWS/SAE D8.9.50
Projection welding is used in preference to spot welding when bare areas are not available at the faying surfaces, because properly designed projections can pierce
49. For more information on resistance spot welding and projection
welding, see Chapter 1, Resistance Spot and Seam Welding, and
Chapter 2, Projection Welding, in Volume 3 of the Welding Handbook,
9th Edition.
50. See Reference 7.
PAINT
PAINTED SURFACES
Figure 3.32—Arrangement for
Projection Welds on a Prepainted Surface
through the paint. For two-sided or fully painted surfaces, the projections can be on either workpiece or on
both, as shown in Figure 3.32.
Projection welding also can be used to attach weld
nuts, standoffs, and threaded studs for use in mechanical fastening of components to the sheet.
Capacitor Discharge Stud Welding
All three methods of capacitor discharge stud welding (initial contact, initial gap, and drawn arc) are suitable for use with prepainted sheet. (Refer to Welding
Handbook, Volume 2, Chapter 9.)51 The process requires
the welding to be done at bare areas and requires good
grounding. Since the welds are of short duration and
are made with low energy, the ground must dissipate
the energy at the weld and not at the ground point.
Because of the short duration of the weld and the low
heat required, the process has the advantage of leaving
little or no indication of a weld on the face side of the
sheet.
(A) Resistance Spot Weld
Arc Spot Welding
PAINT
(B) Projection Weld
Figure 3.31—Series Resistance Welding
Arrangement for (A) Spot Weld and
(B) Projection Weld on Painted Surface
Arc spot welding can be used with edge joints, which
typically are hidden, as shown in Figure 3.33. Arc spot
welds can be made with the gas tungsten arc, plasma
arc, or gas metal arc welding process.52 The welding
procedure should be developed to minimize porosity
caused by outgassing of the coating. Conventional arc
welding processes such as SMAW, GTAW, and GMAW,
are generally not considered as they cause excessive
damage to painted steels.
51. For more information on capacitor discharge stud welding, see
Chapter 9, Arc Stud Welding, in Volume 2 of the Welding Handbook,
9th edition.
52. For more details on arc spot welding with these processes, see
Chapters 3, 4, and 7 in Volume 2 of the Welding Handbook, 9th edition.
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
WELDS
PAINT
209
The noncontact nature of laser beam welding makes
the process suitable for the welding of prepainted sheet
(i.e., the electrical properties of the prepainted sheet
coating are not a detrimental factor). However, the
coating is a problem in that it adds significantly to the
plasma or smoke plume generated during welding.
Therefore it is necessary that a jet of gas be used to suppress a plasma or smoke plume when welding these
materials.
In addition to seam welds in lap joints, laser beam
spot welding can be used to make a series of spiral welds
in lap joints.
Figure 3.33—Arc Spot Welds on an Edge Joint
COATING-TO-COATING WELDS
Laser Beam Welding
Laser beam welding is used for longitudinal seam
welds, for example, in the prepainted small-diameter
tubing shown in Figure 3.34. Two advantages of the
process are the small heat-affected zone and the narrow
weld bead, which minimize damage to the coating.
Laser beam welding is discussed in detail in Chapter 14
of the Welding Handbook, Volume 2, 9th edition.53
53. American Welding Society (AWS) Welding Handbook Committee,
A. O’Brien and C. Guzman, eds., 2007, Welding Processes—Part 2,
Volume 3 of the Welding Handbook, Chapter 14, Miami: American
Welding Society.
0.8 mm (0.03 in.)
LASER SEAM
Precoating sheet steel with paints and laminates that
produce a thick film of polyvinyl chloride (PVC) allows
the coating of one sheet to be welded to the coating of
another sheet, thus joining the sheets. This is done by
heating the paint films or laminates until they melt and
coalesce, forming a weld between the overlapped paint
films or laminates. A number of heating methods are
suitable. Dielectric heating, shown in Figure 3.35, and
induction heating are good choices. Examples of this
type of application are the successful fabrication of an
automotive glove box and the inner liner of an automobile door.
APPLICATIONS
Coated steels, principally coiled sheet steels, are specified for corrosion control or the elimination of postfabrication finishing, or both. In the manufacture of major
appliances, the elimination of a finishing procedure is
A
HEATING
ELEMENT
PAINT
COATED
BASE METAL
HEATING
ELEMENT
Figure 3.34—Laser Beam
Weld in a Prepainted Tube
Figure 3.35—Coating-to-Coating Weld
210
CHAPTER 3—COATED STEELS
the primary reason, with corrosion control a second
consideration. In the automotive industry, corrosion
control is the main reason for using coated sheet steel.
COATED AUTOMOTIVE STEEL
Some areas of North America have the most aggressive automobile corrosion environments in the world.
As shown in Figure 3.36, this region covers the coastal
regions from the Gulf of Mexico, along the Atlantic
Coast, up the St. Lawrence River, through the Great
Lakes, and ending in the upper Midwest.
During the winter months, millions of tons of salt are
used to clear ice and snow from streets, roads and highways in North America. Motorists expect and insist on
dry, bare pavement all year round. While alternatives
are being sought, the use of road salt is likely to continue. The corrosive action of salt takes place not only
during the cold, icy months of the year, but also in the
warm months, when deposits of road salt residue on
vehicles can be dissolved by rain. Road splash also may
contain salt residue. Before the use of coated steels, it
AWS WELDING HANDBOOK 9.4
was common to see advanced cosmetic deterioration
caused by corrosion, sometimes in less than five years,
on automobile bodies subjected to road salt.
Types of Corrosion
Vehicle corrosion is classified as either perforation
corrosion or cosmetic corrosion. Perforation corrosion
proceeds from the inside to the outside, whereas cosmetic corrosion develops from the outside to the inside.
Five types of corrosion mechanisms may be involved:
uniform, galvanic, crevice, pitting, and filiform.
Uniform corrosion is the most common mechanism
and is the result of uniform chemical attack over the
entire metal surface exposed to the environment.
Galvanic corrosion occurs when dissimilar metals
are in electrical contact in an electrolyte, causing the
less noble metal (anode) to be attacked.
Crevice corrosion occurs at joints between the metal
surfaces or between metallic and nonmetallic surfaces and
can proceed rapidly.
Pitting corrosion is extremely localized corrosion that
generally produces sharply defined holes.
Negligible
Mild
Moderate
Severe
Extremely Severe
Figure 3.36—Vehicle Corrosion Environments in Canada and the Continental United States
AWS WELDING HANDBOOK 9.4
Filiform corrosion is a special type of crevice corrosion that occurs under protective films.
COATING METHODS AND MATERIALS
The following processes and materials are used by
the automobile industry and others to stave off corrosive attack.
Continuous Hot-Dip
1.
2.
3.
4.
Pure zinc,
Galvanneal,
Type I aluminum for exhaust systems,
Zinc 5% aluminum (Galfan) for brake line tubing,
and
5. Long terne (lead and tin [8%]) for fuel tanks.
Electroplate
1. Pure zinc;
2. Zinc-alloy (zinc and iron [10%–20%], or zinc
and nickel [10%–14%]); and
3. Duplex (secondary flash coat over thick primary
coat [e.g., iron 80%–90%], zinc over zinc-iron, or
chrome-chrome oxide over pure zinc).
Experience has shown that the aggressive chloridebearing regions of North America are too severe for all
of the organic coatings and most of the thin electrolytic
coatings to provide the required performance against
auto body corrosion. Pure zinc coatings with at least
60 g/m2 (0.20 oz/ft2) per side are needed to provide the
necessary protection. Galvanneal coatings having a
minimum of about 45 g/m2 (0.15 oz/ft2) perform very
well. The excellent bond that forms between the galvanneal zinc-iron alloy and automotive paint systems
strongly resists under-film corrosion of the paint. All
automotive bodies constructed for use in North America are made from zinc-iron alloy or zinc coated steel
sheet entirely (except for roofs in some cases). Some
manufacturers prefer using only zinc-iron coatings,
some pure zinc, while others use a mixture of both.
Most automotive sheet is produced on continuous
hot-dip coating lines. Electrogalvanized sheet is used for
some exposed parts but it is in decline due to the cost of
producing the required coating masses (weights). Nevertheless, the conversion of auto body construction to
coated steels, has not only dramatically increased the
demand for these products, but also resulted in much
longer lasting automobiles.
CHAPTER 3—COATED STEELS
211
Welding Processes and Products
Resistance spot welding (RSW) is the principal
method used by the automobile industry for assembly
of body-in-white. Other commonly used processes and
applications are listed below.
1. Resistance seam welding (RSEW) for assembly
and subassemblies (e.g., tailored blanks);
2. Laser beam welding (LBW) for subassemblies
(e.g., tailored blanks) and limited assembly
usage;
3. Gas metal arc welding (GMAW) for subassemblies and assembly;
4. Stud arc welding (SW) for subassemblies and
assembly;
5. Braze welding (BW) for subassemblies and
assembly;
6. Soldering (S) for subassemblies and assembly;
and
7. Other joining processes, including clinching and
adhesive bonding.
Automotive Fuel Tanks. The use of terneplate (usually long terne) for automotive fuel tanks is standard
practice, since it is corrosion-resistant and can be
readily soldered or welded using the resistance seam
welding process (RSEW) to produce an economical,
leak-proof unit. A resistance seam-welding machine is
shown in Figure 3.37, adapted for welding fuel tanks.
A recently developed material variant is the top coating of long terne sheet with organic coatings. A zincrich organic coating is used for additional protection on
the outside of the fuel tank and an aluminum-rich
organic coating is used for additional protection on the
inside. The aluminum augments the resistance of long
terne to the newer automobile fuels (e.g., those containing low concentrations (about 10%) of methanol, ethanol, or both).
Refinement in welding terne-plated steel for use in
automotive fuel tanks has resulted in welding speeds
of 127 mm/s (300 in./min) for 20 gauge to 22 gauge
(0.93 mm to 0.78 mm) material. Welding normally is
accomplished with seam welding machines either facing
each other or operated in tandem. Welding is performed
in a straight line across one side or end of the fuel tank,
with automatic equipment handling the tanks.
Welding at the indicated travel speed requires heavyduty equipment, using a one-cycle-on/one-cycle-off timing schedule (or similar) for ac machines, or a continuous schedule for dc machines to obtain consistently
sound welds. Tack welding is required, and care must
be exercised when crossing prior welds at the corners in
order to prevent leaks or blowholes.
To give consistent production quality, careful attention must be paid to the knurl drive wheel design. The
knurl drive wheel can control the buildup of tin and
212
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
Photograph courtesy of Soudronic Automotive AG
Figure 3.37—Automobile Fuel Tank Welded by Resistance Seam Welding
lead on the wheel electrodes by breaking up the
buildup. Also, the knurl drive wheels may function to
control the shape of the contact face of the wheel electrodes. This can be accomplished by using knurlers
designed with a radius in the wheel contact area, or by
using a flat knurler design equipped with side cutters
that constantly trim the wheel contact face to a specific
width. Both electrodes should be knurl-driven, ideally,
to deliver a more positive drive, lessen the possibility of
skidding, and provide constant maintenance of both
contact faces of the electrode.
FABRICATING ALUMINIZED 409
STAINLESS STEEL TUBING
Ferritic stainless steel (Type 409) exhaust systems
were developed in the late 1980s to increase quality and
extend the service life of automobiles. The systems were
put into general production in the early 1990s, but soon
after, a perception problem with the appearance of the
material was encountered. The 409 material develops a
red patina perceived by the general public that the
material is rusting and will fail. This is not the case; the
409 exhaust system will last for 4 to 5 times longer than
a conventional carbon-steel exhaust; however, the perception of inferior or diminished quality was established in the car-buying population, and aluminized 409
was developed to overcome this false impression.
Operating conditions necessary to make quality tubing utilizing aluminized 409 stainless steel are more
stringent than those necessary for other currently used
materials. Although more stringent, the conditions are
attainable in conventional tube mills using the highfrequency induction welding process. The following
paragraphs provide important variables and recommen-
AWS WELDING HANDBOOK 9.4
CHAPTER 3—COATED STEELS
dations to be considered in the production of quality
tubing when welding aluminized 409 stainless steel and
other similar materials. Examples of welding problems
which have been encountered during the development
of aluminized 409 tube are included.
Tube Mill Practices
As a method of avoiding potential problems that
may occur during the welding of tube, a step-by-step
evaluation of tube mill practices that might affect weldability are described in the following paragraphs.
Steel Strip. Incoming strip should be shear cut to the
proper width for the tube diameter to be produced.
Because of differences in equipment (tooling) and material (stainless steel or carbon steels), the following formula was developed for estimating strip widths:
Ws = Gf – 2.1 Ts
(3.4)
where
Ws = Width of strip
Gf = Girth in last finish pass
Ts = Thickness of strip
The width calculations of the strip are used as a
starting point. The width is added or subtracted to
determine the optimum strip width for a specific diameter of tube for a particular material (stainless steel or
carbon steel). Because of tube mill tooling variations,
strip width calculations should be optimized for each
particular tube mill.
No burrs, gouges, folds or dents should be observed
on the incoming strip. Proper coil storage and loading
should be used to avoid damaging the edges. Typical
damage includes sidewall marks from pushing or pulling a coil along the floor or against another coil with a
forklift truck, or indentation marks from chains when
loading coils onto the uncoiler. This sort of damage to
the material edges cannot be corrected during further
processing.
Edge Shaping. A vertical edge beveling station for
strip edges should be located at the entry end of the
tube mill, immediately after the side guides. This station
removes any shear lips, leaving a fresh and clean surface
to be welded. On aluminized materials, a layer of aluminum typically is wiped across the edges during the
shearing process. An edge-preparation station removes
this excess aluminum, which is detrimental to weld
quality, prior to welding.
Bare stainless steels also tend to form a strong oxide
layer that is detrimental to weld quality. Therefore, it is
213
recommended that the edges of bare stainless steels be
beveled immediately prior to welding.
Tube Mill Roll Maintenance. Tube mill roll maintenance is necessary to guarantee that a properly formed
tube is presented to the weld box. The requirement for
the tooling is to consistently form the strip into a tube.
Problems in this area include:
1. Grooves worn into the tooling, resulting in strip
edge damage and causing material to roll transverse to the forming direction (i.e., twist) within
the mill;
2. Dirty rolls that can grind dirt, oils, and aluminum into the edges;
3. Eccentric or worn rolls that form the tubing
improperly; and
4. Worn bearings and bent shafts that also contribute to improperly formed tubing.
Mill Setup. Tube mill alignment and setup are important in producing quality tubing. Gradual forming of
the strip into tubing is desired. If some forming stands
are performing most of the forming operation and others are performing none, then the material may workharden faster than intended, and a wrinkle or permanent set is likely to appear. Wrinkles affect the weld
quality in that an inconsistent edge is presented to the
weld box (i.e., the weld V will move, causing inconsistent heating).
A twist in the tube is another problem related to
setup and the over-forming or under-forming that
occurs at various forming stands. This condition can
put undesirable stresses in the weld during welding and
can vary the welding forces and how they are applied. A
misaligned tube mill will tend to roll the tube to one
side or the other within the weld squeeze rolls. This
problem also causes undesirable stresses and varies the
forces at the weld.
Squeeze Roll Pressure. The weld is made by the
weld head (squeeze rolls) in an area called the weld box,
as shown in Figure 3.38A). Typically a three-roll weld
box is used in high frequency tube welding for control
of the tube and upset pressures. When welding any
material, the upset pressure must be high enough to
expel any contaminants (i.e., coolant, aluminum, oils,
and oxides) and any heat-affected regions from the
weld interface. Also, the squeeze roll pressure must be
constant. Any fluctuations in upset pressure could
result in poor weld quality (in areas where contaminants were not removed). Figure 3.38(B) is a drawing of
the components of the welding box.
Roll Coolant. Most squeeze rolls are cooled externally
by coolant flowing onto the roll. This is a good practice
214
CHAPTER 3—COATED STEELS
AWS WELDING HANDBOOK 9.4
(A) Actual Unit
POINT OF WELDED
WELDING
SEAM
PRESSURE ROLL
CURRENT
INDUCTION
COIL
WELD
V
V ANGLE
4° to 7°
TUBE TRAVEL
IMPEDER
(B) Illustration of Weld Box Components
Figure 3.38—(A) Welding Head of a High-Frequency Induction Welding
Machine and (B) Illustration of Welding Head Components
as long as the coolant is not flooding the weld V. Flooding the weld V adds contaminants to the weld zone. The
coolant to the squeeze rolls should be directed to the
back of the rolls and wiped off at the front of the rolls.
Strip Edge Alignment. The biggest problem which
occurs at the weld head is misalignment of the strip
edges. This problem typically is caused by improperly
presenting the strip to the weld squeeze rolls. Alignment
at the squeeze rolls can be checked by using a piece of
solder wire. The solder is placed in the weld V then the
strip is jogged forward and back. The solder is removed
and examined to see if the impression of the grooves
formed by the strip edges are parallel. Another way to
check for misalignment is to turn the machine off and
wait until it has cooled; then rub a finger along the weld
joint immediately after the squeeze rolls to feel if the
material is flush across the joint. (This must be done on
a section which has not been welded (i.e., a section that
has no weld flash.)
Impeder. The impeder is a device used to improve the
electrical efficiency of the welding circuit. A coil induces
a current in the tube while the impeder forces the cur-
AWS WELDING HANDBOOK 9.4
rent to concentrate at the outer edges of the material.
Proper maintenance of the impeder is important for
consistent and efficient welding. Maintenance includes
setting the proper cooling and shielding, which ensures
that the impeder will not deteriorate and lose efficiency.
Efficiency loss can be recognized by the constant need
to increase the welding current (coil current) in order to
achieve a good weld. Proper placement of the impeder
in the welding circuit is necessary for optimum efficiency. The impeder should be placed as close as possible to the point of welding without subjecting it to
damage by weld drop-off particles from the inside the
tube. Coolant to the impeder should be adequate to
cover and cool the impeder but not bubble out the weld
V. Coolant in the weld V adds contaminants to the weld
interface and is detrimental to weld quality.
Induction Coil. The induction coil typically is made
of tubular water-cooled copper, formed into two or
three turns. The coil should be approximately 6.4 mm
to 12.7 mm (0.25 in. to 0.50 in.) greater in diameter
than the tube diameter. The coil should be placed as
close to the squeeze rolls as possible without overheating the squeeze rolls. Two common problems with coils
are that the location may be too far from the squeeze
rolls, and that there may be arcing across the coil turns.
The first problem reduces the efficiency and preheats
the edges. Efficiency loss results in more power being
needed to make a weld; preheating reduces control of
the strip edges in the weld V and tends to cause mismatch. The second problem, arcing, can cause power
fluctuations in the welding circuit resulting in erratic
welding. Arcing is associated with dirt and metal slivers
in the coolant and on the mill, and it can be controlled
with proper mill maintenance.
Weld V. The weld V is the area formed by the strip
edges coming together at the point of welding. The V
width and apex position should not vary during welding, as variation at the V causes variation in the weld.
The weld V must be kept free of contaminants. Coolant
in the weld V adds contaminants to the weld interface
and is detrimental to weld quality. It is recommended
that an argon shielding gas be used to shield this area
from oxygen.
Weld Scarfing. The outside dimension (OD) and
inside dimension (ID) of the scarf units must be rigid so
that no tool chatter occurs. The cutting tools must be
kept sharp. Placement of these two units is dependent
on line speed and post weld cooling capabilities. They
must be located in an area where the flash is not so cold
that the tools chip, but also not so hot that the tool
accumulates buildup. It is essential that both OD and
ID flash be removed from the tube. On some steels (e.g.,
stainless and aluminized), ID flash can become hard
CHAPTER 3—COATED STEELS
215
enough to push through the wall thickness on expansion of the tubing.
Miscellaneous Techniques. Other areas of concern
are the sizing stands, the cut-off and the unloader. The
sizing stands should share the amount of forming or sizing, so that no twist in the tubing is developed.
The cut-off should be in good repair, so that exact
cut-off sizes can be maintained. Oversized lengths
increase yield loss. Also, the cut-off should be a smooth
motion timed with the line speed (i.e., a flying cut-off).
A jerky motion that interrupts the front of the mill will
result in poor-quality tubing. The cut-off tool should be
sharp to minimize dimpling of the tube, as dimpling
overworks the affected area and can cause the tube to
break.
Finally, the unloader (manual or mechanical) dictates
the line speed and the number of starts and stops. Good
unloading, with minimum stops, increases production
yield.
Oxide Entrapment
The biggest problem that occurs when welding aluminized 409 stainless steel is the entrapment of oxides
in the weld. The aluminum oxide appears as a linear
formation along the weld centerline. In bare stainless
steel, it is chromium oxide that becomes entrapped.
Sources of the aluminum include the shearing operation (shear wash-over), unclean tooling, and coolant.
The oxygen comes from the surrounding air or from
coolant in the weld.
Following is a list of ways to reduce or eliminate aluminum and oxygen as problems when joining steel tubing using high-frequency induction welding (HFIW).
These measures will reduce the problem of oxides in
aluminized carbon steels and stainless steels.
1. Using a vertical scarfing station to remove aluminum wash-over from the strip prior to tube
forming, for clean edge preparation;
2. Keeping rolls clean by attaching wipers and
directing coolant onto them, thus reducing the
amount of pickup;
3. Filtering the coolant and changing the coolant as
necessary to keep it clean;
4. Applying argon shielding gas to the weld V area,
thus reducing the availability of oxygen at the
welding zone;
5. Directing coolant away from the weld V by
applying wipers to the squeeze box rolls; and
6. Controlling the impeder coolant so that is does
not bubble out of the weld V.
216
CHAPTER 3—COATED STEELS
Weld Grain Structure
Another problem with ferritic stainless steels is grain
growth and grain size of the as-welded material. A difference in grain size can be obtained: ideally, a grain
size similar to the base material is desired. The consistent grain size and structure allows for uniform deformation of the entire tube diameter during forming.
Welds having a large or coarse grain will tend to focus
the forming stresses into the area with the different
structure (i.e., the courser grains). This typically results
in a weld failure. Following are ways to minimize or
reduce the grain size.
1. Increasing upset pressure to squeeze out all heat
affected material;
2. Increasing the line speed so the weld is exposed
to less time at high temperature, and can cool
faster; and
3. Changing coolant locations to be positioned immediately after the weld box for faster cooling.
SAFE PRACTICES
Chapter 17 of the Welding Handbook, 9th edition,
Volume 1 is a comprehensive presentation of safety in
welding, brazing, soldering, and cutting intended for
reference collectively for the five volumes of the 9th edition; thus details of these topics are not fully addressed
in this chapter.54 Safety and health concerns regarding
the metals and materials discussed in this chapter are
covered briefly in this section.
The American National Standards Institute (ANSI)
standard, Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1, should be consulted.55 This standard is published by the American Welding Society and
can be downloaded from the Internet at http://
www.aws.org. Appendix A provides a list of safety and
health standards, publishers, and facts of publication.
Sections on safe practices in chapters of this volume
dealing with materials that are coated or used as coatings also should be consulted. This includes Chapter 1,
Carbon and Low-Alloy Steels; Chapter 5, Stainless and
Heat-Resisting Steels; Chapter 7, Surfacing Materials;
and Volume 3, 8th Edition, Chapter 1, Aluminum and
Aluminum Alloys; and Chapter 5, Lead and Zinc.56
54. Welding Handbook Committee, Jenney, C. L. and A. O’Brien,
Eds., 2001, Welding Handbook, Vol. 1, Welding Science and Technology, Chapter 17, Miami: American Welding Society.
55. American National Standards Institute (ANSI) Accredited Standards Committee Z49, 2005, Safety in Welding, Cutting, and Allied
Processes, ANSI Z49.1:2005, Miami: American Welding Society.
Available for downloading from the Internet at www.aws.org.
56. See Reference 37.
AWS WELDING HANDBOOK 9.4
Proper ventilation must be observed for the welding
or bonding environment being considered, whether
indoors, outdoors, or in a confined space. Coatings
found on steels can become airborne or may release
fumes, smoke, or dust, during joining and cutting. Of
particular importance is that the ventilation system,
or worker respiratory protection, must maintain the
environment at or below the current OSHA regulations
and Permissible Exposure Limits (PELs) or ACGIH
Threshold Limit Values (TLVs) for the metals and
fluxes used. 57, 58
For the paint or coating system being used, information is available from the supplier in the Material Safety
Data Sheet (MSDS) for each paint or coating being
used. Close attention must be paid to the compounds
and the decomposition products that may be released
during curing or from the heat of the joining process.
Protective coatings on steels can contain chromium,
lead, tin, zinc or other materials. It is recommended
that the welder understands the coating types of the
materials. If not, the welder should get this information
from his supervisor or employer.
Paints are made from compounds that may release
hazardous materials into the air when heated, paints
usually are used on a “phosphated” and passivated
(often with chromium) metal surface. The heat from the
arc can cause paints to release unsafe amounts of gases,
such as carbon monoxide and carbon dioxide.
Steels coated with plastic materials should not be cut
or welded unless proper precautions are taken. It is best
to remove coating to a distance away from the weld or
cut where the temperature will not go above the point
where the material starts to break down.
PROCEDURES FOR AVOIDING HAZARDS
FROM OVEREXPOSURE
Welders and their supervisors or employers should
make sure they know what the workpiece coating might
release when heated or burned and should take the following steps to avoid overexposure:
1. Obtain the Material Safety Data Sheets (MSDSs)
for all materials used;
2. Read and understand the specification for coating type and coating weights;
3. Research what hazardous materials are present
or might be released by the coating when it is
exposed to an arc or high temperatures;
57. Occupational Safety and Health Administration (OSHA), Code
of Federal Regulations, Title 29, Labor, Parts 1910.1 to 1910.1450,
United States Government Printing Office, Superintendent of Documents, Washington, DC: Department of Labor. www.osha.gov.
58. American Conference of Industrial Hygienists (ACGIH), 1330
Kemper Meadow Drive, Cincinnati, Ohio 45240, www.acgih.org.
AWS WELDING HANDBOOK 9.4
4. Use adequate ventilation whenever an airborne
fume gas or dust must be controlled. Use enough
ventilation exhaust at the arc or flame to keep
the air the welder breathes below recommended
safe levels such as the PEL and TLV®;
5. Monitoring the air as necessary to test for exposure levels in the breathing zone of the welder
and other persons working nearby;
6. Use a respirator when required; and
7. Orient the work so the welder’s head is kept out
of the fume plume.
Related safety information is provided by the American
Society of Testing and Materials (ASTM).59
BIBLIOGRAPHY
American National Standards Institute (ANSI) Accredited
Standards Committee Z49. 2005. Safety in welding,
cutting, and allied processes. ANSI Z49.1:2005.
Miami: American Welding Society. Available on line:
www.aws.org.
American Welding Society (AWS). 2000. Soldering
handbook. 5th edition. Miami: American Welding
Society.
American Welding Society (AWS) Committee on Definitions and Symbols. 2010. Standard welding terms
and definitions. AWS A3.0M/A3.0:2010. Miami:
American Welding Society.
American Welding Society (AWS). 2004. Specification
for carbon steel electrodes for shielded metal arc
welding. AWS A5.1/A5.1M:2004. Miami: American
Welding Society.
American Welding Society (AWS). 2007. Specification
for carbon and low alloy steel rods for oxyfuel gas
welding. AWS A5.2/A5.2M:2007. Miami: American
Welding Society.
American Welding Society (AWS). 2004. Specification
for filler metals for brazing and braze welding. AWS
A5.8/A5.8M:2004. Miami: American Welding Society.
American Welding Society (AWS). 2002. Recommended
practices for test methods for evaluating the resistance spot welding behavior of automotive sheet
steel materials. AWS/SAE D8.9M:2002. Miami:
American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. 1996. William R. Oates, Ed. Materials
and applications—Part 1. Volume 3 of Welding
handbook. 8th edition. Miami: American Welding
Society.
59. American Society for Testing and Materials ASTM International
(ASTM), Documents: A 308, A 463, A 653, A 780, A 792, and A 879.
West Conshohocken, Pennsylvania: ASTM International. www.astm.org.
CHAPTER 3—COATED STEELS
217
American Welding Society (AWS) Welding Handbook
Committee. 2001. Jenney, C. L. and A. O’Brien,
Eds., Welding science and technology. Volume 1 of
Welding handbook. 9th edition. Miami: American
Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. 2004. A. O’Brien, Ed. Welding processes—Part 1. Volume 2 of Welding handbook. 9th
edition. Miami: American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. 2007. Annette O’Brien, Ed. Welding
processes—Part 2. Volume 3 of Welding handbook.
9th edition. Miami: American Welding Society.
American Petroleum Institute (API). 2005. Welding of
pipelines and related facilities. API 1104. 20th edition. Washington, DC: American Petroleum Institute.
ASTM International. Subcommittee: A05.13. 2002.
Standard specification for zinc (hot-dip galvanized)
coatings on iron and steel products. ASTM A 123/A
123M-02. West Conshohocken, Pennsylvania:
ASTM International.
ASTM International. Subcommittee A05.11. 2006.
Standard specification for steel sheet, terne (lead-tin
alloy) coated by the hot-dip process. ASTM A 308/A
308M-06. West Conshohocken, Pennsylvania: ASTM
International.
ASTM International. Subcommittee A05.13. 2005.
Practice for providing high-quality zinc coatings
(hot-dip). A 385-05. West Conshohocken, Pennsylvania: ASTM International.
ASTM International. Subcommittee A05.11. 2006.
Standard specification for steel sheet, aluminumcoated, by the hot-dip process. ASTM A 463/
A 463M-06. West Conshohocken, Pennsylvania:
ASTM International.
ASTM International. Subcommittee A05.11. 2007.
Standard specification for steel sheet, zinc-coated
(galvanized) or zinc-iron alloy-coated (galvannealed) by the hot-dip process. ASTM A 653/
A 653M-07. West Conshohocken, Pennsylvania: ASTM
International.
ASTM International. Subcommittee A05.11. 2006.
Standard practice for repair of damaged and
uncoated areas of hot-dip galvanized coatings.
ASTM A780-01 (2006). West Conshohocken, Pennsylvania: ASTM International.
ASTM International. Subcommittee A05.11. 2006.
Standard specification for steel sheet, 55% aluminum-zinc alloy-coated by the hot-dip process. A 792/
A 792M-06a. West Conshohocken, Pennsylvania:
ASTM International.
ASTM International. Subcommittee A05.11. 2006.
Standard specification for steel sheet, zinc-5% aluminum alloy-coated by the hot-dip process. A 875/
A 875M-06. West Conshohocken, Pennsylvania:
ASTM International.
218
CHAPTER 3—COATED STEELS
ASTM International. Subcommittee A05.11. 2006.
Standard specification for steel sheet, aluminumcoated, by the hot-dip process. ASTM A 879/
A 879M-06. West Conshohocken, Pennsylvania:
ASTM International.
Resistance Welding Manufacturing Alliance (RWMA).
2003. Resistance welding manual. Revised 4th edition.
Miami: Resistance Welding Manufacturing Alliance.
SUPPLEMENTARY
READING LIST
American Welding Society (AWS). 2007. Brazing manual. 5th edition. Miami: American Welding Society.
American Welding Society (AWS). 2000. Recommended
practices for resistance welding. AWS C1.1M/C1.1:
2000 (R2006). Miami: American Welding Society.
ASM International (ASM). 1990. Properties and selection: iron, steels, and high-performance alloys. Metals handbook. Vol. 1. 10th edition. Materials Park,
Ohio: ASM International.
ASM International (ASM). 1993. Welding, brazing, and
soldering. Metals handbook. Vol. 6. 10th edition.
Materials Park, Ohio: ASM International.
Association of Iron and Steel Engineers, and U.S. Steel.
1985. The making, shaping and treating of steel.
Chapters 35–38. Pittsburgh: Association of Iron and
Steel Engineers, and U.S. Steel.
ASTM International (ASTM). 2007. Standard practice
for safeguarding against embrittlement of hot-dip
galvanized structural steel products and procedure
for detecting embrittlement. ASTM A 143/A 143M-07.
West Conshohocken, Pennsylvania: ASTM International.
ASTM International (ASTM). 2007. Standard practice
for safeguarding against warpage and distortion during hot-dip galvanizing of steel assemblies. ASTM
A 384/A 384M-07. West Conshohocken, Pennsylvania:
ASTM International.
ASTM International (ASTM). 2009. Standard practice
for repair of damaged and uncoated areas of hot-dip
galvanized coatings. ASTM A 780/A 780M-09. West
Conshohocken, Pennsylvania: ASTM International.
ASTM International (ASTM). 2004. Standard practice
for conducting case studies on galvanized structures.
ASTM A 896-89 (2004). West Conshohocken, Pennsylvania: ASTM International.
Bouaifi, B. 2003. Low-heat process enhances joining of
coated sheet metals. Welding journal 82(1): 26–30.
Bouaifi, B. 2001. Low-heat joining of surface-coated
sheet metal materials by plasma brazing. DVS Jahrbuch Schweißtechnik. 115–122.
AWS WELDING HANDBOOK 9.4
Chatterjee, K. L. and W. Waddell. 1996. Electrode wear
during spot welding of coated steels. Welding and
metal fabrication 64(3): 110–114.
Fletcher, George A. 1992. Fastening and joining prepainted metal. SME technical paper FCR92-05.
Dearborn: Society of Manufacturing Engineers.
Geiger, M., H. Hanebuth, and P. Hoffmann. 1994.
Laser-beam brazing in the automotive industry.
Blech, rohre, profile 41(12): 825–828.
Geiger, M., H. Hanebuth, and P. Hoffmann. 1996.
Laser-beam brazing of shaped sheet metal components with the Nd:YAG laser. Precision processing
with solid-state lasers. VDI-Verlag. 63–70.
Gould, J. E. and M. Kimchi. 1986. Effects of coating
weight on the resistance spot weldability of galvanized steel. SAE technical paper series No. 860435.
Warrendale, Pa.: Society of Automotive Engineers.
Hackl, H. 1998. MIG brazing of zinc-coated steel sheets
and sections. Schweißen & Schneiden 50(6): 351–354.
Haferkamp, H., F. W. Bach, and K. Kreutzburg, 1995.
New results concerning laser-beam brazing of highalloy steels. Metall 49(10): 642–644.
Hanebuth, H. 1996. Brazing of shaped sheet metal components with the Nd:YAG laser. Final report BMBF
FE (13 N 6052-3). University of Erlangen-Nürnberg.
Hughes, R. V., G. Dryburgh, and S. Garbett. 1995.
Plasma braze welding in autobody production at Jaguar cars. Welding & metal fabrication 3: 110–111.
Klein, R. and L. Abram. 1996. Low-flux laser brazing
of vehicle-body materials. Precision processing with
solid-state lasers. VDI-Verlag. 85–90.
Krauss, G. and D. K. Matlock, eds. 1990. Zinc-based
steel coating systems. Metallurgy and performance.
Warrendale, Pa.: The minerals, metals, and metallurgy of society.
Lindsay, J. H. 1990. The impact of the zinc layer on the
manufacture of automotive sheet steel. Zinc-based
steel coating systems: metallurgy and performance.
281–294. Warrendale, Pa.: The Minerals, Metal and
Materials Society.
Lugscheider, E. 1996. New results in brazing technology. Aachen, Germany: Verlag Mainz.
Minichelli, J. L. 1988. Bonding with structural adhesives: Meeting the challenge of assembling precoated
metal substrates. Philadelphia, Pa.: National Coil
Coaters Association.
Munger, Charles G. 1984. Corrosion prevention by
protective coatings. Houston: National Association of
Corrosion Engineers.
Natale, T. V. 1986. A comparison of the resistance spot
weldability of hot dip and electrogalvanized steel.
SAE technical paper series No. 860435. Warrendale,
Pa.: Society of Automotive Engineers.
National Coil Coaters Association. 1986. Selecting the
proper structural adhesives to match your client’s needs.
Philadelphia. Pa.: National Coil Coaters Association.
AWS WELDING HANDBOOK 9.4
National Coil Coaters Association. 1989. Joining prepainted metals with adhesives. Philadelphia, Pa.:
National Coil Coaters Association.
Porter, F. C. 1983. Galvanizing and welding structural
steel (Parts 1 and 2). Metal construction 5(10-11):
606–609. 676–679.
Radscheit, C. 1998. Breakthrough with MIG brazing.
Automobilproduktion 12(3): 117–121.
Radscheit, C. and J. Müller-Rogait. 2000. Plasma brazingbasic principles and applications. New brazing technologies for sheet metal applications. München: SLV.
CHAPTER 3—COATED STEELS
219
Steffens, H. D., J. Wilden, C. Buchmann, and M.
Berthold. 1996. Basic investigations on the properties of joints brazed with a solid-state laser in comparison with joints brazed by conventional methods.
Final report BMBF-FE (13 N 6044). University of
Dortmund.
Waddell, W., D. E., Thomas, and N. T. Williams. 1986.
Highspeed seam welding of low-tin substrates. Metal
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Walduck, B. 1999. Using plasma braze in car body fabrication. Welding & metal fabrication (8): 11–14.
221
AWS WELDING HANDBOOK 9.4
CHAPTER
C H A P T E4 R 9
Prepared by the
Welding Handbook
Chapter Committee on
Tool and Die Steels:
TOOL AND
DIE STEELS
G. A. Knight, Chair
Chrysler Corporation, Ret.
C. M. Beadnell
Weld Mold
R. S. Frasso
COR-MET
J. R. Kerchkof
Eureka Welding Alloys
T. W. Webb
Eureka Welding Alloys
Welding Handbook
Volume 4 Committee
Member:
D. D. Kautz
Los Alamos National
Laboratory
Contents
Photograph courtesy of Cor-Met Inc.—Forging Dies Repaired by Flood Welding
Introduction
222
Metallurgical
Properties
222
Tool Steel
Classifications
223
Weldability
229
Heat Treatment
229
Arc Welding of
Tool and Die Steels
233
Flash Welding and
Friction Welding
244
Tool Steel Welding
Applications
246
Safe Practices
253
Conclusion
253
Bibliography
253
Supplementary
Reading List
254
222
AWS WELDING HANDBOOK 9.4
CHAPTER 4
TOOL AND DIE STEELS
INTRODUCTION
Tool steels are high-quality ferrous metals used to
make industrial tools, dies, cutting and forming tools,
and other tools used in highly demanding service conditions. These steels are specially designed to accommodate the specific mechanical properties required for
particular applications. The processes used by manufacturers to produce tool steels enable them to deliver
clean, homogeneous material made according to precise
requirements for chemical composition and microstructure. The cost of precise production requirements and
rigid quality control is justified by the high cost of constructing intricate tools, dies, and molds and the potential downtime associated with premature tool failure.
Preserving the unique as-manufactured properties of
these steels is a factor that always must be taken into
consideration before welding.
Because of the carbon and alloy content in tool steels
and the heat treatment necessary to obtain the required
mechanical properties, welding must be performed by
highly skilled technicians using accepted methods and
process controls. The welding process greatly affects the
workpiece in the heat-affected zone (HAZ). Therefore,
welders must have a good working knowledge of heattreating processes as well as the manipulative skills
required for the welding operations.1, 2
This chapter discusses the classifications, metallurgy,
and weldability of tool steels and the processes involved
with welding them. Information on repair welding procedures for tool steels is coordinated with the order
in which the tasks should be performed, and is supple1. Welding terms and definitions used throughout this chapter are
from American Welding Society, (AWS) Committee on Definitions
and Symbols, 2010, Standard Welding Terms and Definitions, AWS
A3.0M/A3.0:2010, Miami: American Welding Society.
2. At the time of the preparation of this chapter, the referenced codes
and other standards were valid. If a code or other standard is cited
without a date of publication, it is understood that the latest edition
of the document referred to applies. If a code or other standard is
cited with the date of publication, the citation refers to that edition
only, and it is understood that any future revisions or amendments to
the code or standard are not included; however, as codes and standards
undergo frequent revision, the reader is encouraged to consult the most
recent edition.
mented by several detailed descriptions in the section on
applications.
METALLURGICAL
PROPERTIES
The properties of tool steels are characterized by
high hardness and wear resistance. When welding tool
steels, procedures must be designed to maintain these
and other properties in the weld metal and heat-affected
zone (HAZ). Figure 4.1 shows the weld metal and
coarse-grained HAZ of a weld in steel. The properties
of various tool steels discussed in subsequent sections of
this chapter are evaluated as excellent, good, fair, or
poor.
In addition to other alloying elements, tool steels
generally contain carbon in proportions ranging from
0.30% to over 1.0%. The high carbon content provides
a martensitic hardness capability of up to 60 Rockwell
hardness, C scale (HRC), as illustrated in Figure 4.2.
Carbides increase the wear resistance of the steel. Some
grades of tool steels designed with less carbon provide
better toughness and a property called hot hardness
(resistance to softening at elevated temperatures). The
hardenability of tool steels follows the same general
rule that governs other alloy steels: the higher the alloy
content, the greater is the hardenability factor. Volume
1 of the Welding Handbook, Welding Science and
Technology contains detailed information on welding
metallurgy.3
Tool steels contain significant amounts of other elements such as chromium, cobalt, manganese, molyb3. American Welding Society (AWS) Welding Handbook Committee,
2001, C. Jenney and A. O’Brien, eds., Welding Science and Technology,
Vol. 1 of Welding Handbook, 9th ed., Chapter 4, Miami: American
Welding Society. Refer to Appendix A, Guide to Welding Handbook
Contents.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
223
optimum combination of properties required for a particular application. These properties are primarily a
function of the chemical composition of the alloy
and the type of heat treatments applied to the alloy,
including quenching media. Table 4.1 shows the effects
of various alloying elements on the properties of tool
steels.
TOOL STEEL
CLASSIFICATIONS
HAZ
W
Figure 4.1—A Single-Pass Weld in Steel, Showing
Weld Metal (W) and Coarse-Grained
Heat-Affected Zone (HAZ)
LIVE GRAPH
MAJOR STEEL GROUPS
MAXIMUM HARDNESS, HRC
Click here to view
70
60
50
40
30
20
10
0
Tool steels are classified into eight major groups by
the American Iron and Steel Institute (AISI),4 the Society
of Automotive Engineers (SAE),5 and North American
Automotive Standards (NAAMS).6 The classifications
generally are based on common applications, chemical
compositions, or quenching media (water, oil, or air).
The tool steel groups and the alloy types that comprise
them are shown in Table 4.2.
0.20
0.40
0.60
0.80
1.0
CARBON, wt %
Figure 4.2—Influence of Carbon Content on the
Maximum Hardness of As-Quenched
Carbon Steels and Alloy Steels
denum, nickel, silicon, tungsten, and vanadium. These
elements are involved in forming various alloy carbides
that increase the hardness, wear resistance, hot hardness, or some combination of these properties. No single
alloy will provide all of these properties, so the selection
of a tool steel is based on trade-offs that achieve the
In addition to classifications published by AISI, SAE,
and NAAMS, tool steels also are produced according to
several specifications published by the American Society
for Testing and Materials (ASTM International), including ASTM A 600, A 681, and A 686. Standards such as
those from the American Iron and Steel Institute (AISI),
the Society of Automotive Engineers (SAE), and ASTM
may be used as the basis for procurement or for detailed
specifications that may be required for a particular
application or for improved weldability.7, 8, 9 Table 4.3
lists the commonly used tool steels, the composition of
the steels, and the Unified Numbering System (UNS)
designations.
4. American Iron and Steel Institute (AISI), 1101 7th Street N.W.,
Washington, DC 20036-4700. www.aisi.org.
5. Society of Automotive Engineers (SAE International), 400 Commonwealth Drive, Warrendale, Pennsylvania, 15096-0001. www.sae.org.
6. North American Automotive Standards (NAAMS), Administrator,
Auto/Steel Partnership, 200 Town Center, Suite 320, Southfield, MI
48075. www.naamsstandards.org.
7. American Society for Testing and Materials (ASTM International),
100 Barr Harbor Drive, West Conshohocken, Pennsylvania, 194282959. www.astm.org.
8. Society of Automotive Engineers (SAE International), 1993, Metals
and Alloys in the Unified Numbering System, 6th ed., Warrendale,
Pennsylvania: Society of Automotive Engineers. www.sae.org.
9. American Iron and Steel Institute, 1140 Connecticut Ave., N.W., Suite
705, Washington, D.C. 20036.
224
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Table 4.1
Effects of Various Alloying Elements on the Properties of Tool Steel
Alloying Element
Contents, %
Effects on Properties
Carbon
0.30–2.34
Increases hardness and wear resistance.
Silicon
0.15–2
Increases the likelihood of decarburization with manganese, molybdenum, or chromium;
greatly increases strength and toughness.
Manganese
0.15–3
Increases depth of hardness.
In small quantities, increases deoxidation of steels in final melt stages.
Decreases temperature required for hardening.
Chromium
0.2–14
Increases depth of hardness (although to a lesser degree than manganese).
Increases wear resistance and toughness.
Increases temperature required for hardening.
Molybdenum
0.15–10
Increases depth of hardness (more effectively than tungsten).
Increases red hardness.
Increases wear resistance.
Causes decarburization in forging and heat treating with silicon.
Increases toughness.
Tungsten
0.5–20
With carbon: increases wear resistance.
Vanadium
0.15–5
With molybdenum, chromium, and tungsten: increases toughness, red hardness, wear
resistance (with medium-to-high vanadium content).
Increases maximum allowable hardening temperature. Decreases growth of grains in
heat-treated steel.
Niobium
<0.1
Increases wear resistance, maximum allowable hardening temperature. Decreases
tendency toward decarburization.
Nickel
0.29–0.3
Increases toughness, wear resistance, and slightly increases depth of hardness.
Increases annealing difficulties in high-alloy steels. Decreases temperature (by a small
amount) required for hardening.
Cobalt
5–12
Increases red hardness.
Increases tendency toward decarburization.
Decreases toughness.
Aluminum, Titanium, Zirconium
<0.1
Increases deoxidation of steels in final melt stages. Decreases size of grain growth.
Water-Hardening Tool Steels
Tool steels in the water-hardening group (AISI W
series) essentially are carbon steels, defined as steels
containing only residual quantities of other elements.
The terms carbon steel and plain carbon steel are used
interchangeably. Some of the high-carbon types of tool
steel have small additions of chromium and vanadium
to improve toughness and wear resistance. The carbon
content varies between 0.60% and 1.40%. In general,
carbon tool steels are less expensive than alloy tool
steels. With proper heat treatment, carbon tool steels
will have a hard martensitic surface with a tough core.
They must be water-quenched for high hardness and
therefore are subject to considerable distortion. Steels in
the water-hardening group have the best machinability
ratings of all tool steels, and they are the best with
respect to lessening the loss of carbon during heat treatment. However, resistance to wear and the effects of
elevated temperatures of water-hardened steels is poor
compared to higher-alloyed tool steels. Carbon steels
also are hardened at lower temperatures.
Shock-Resistant Tool Steels
Tool steels in the shock-resistant group (AISI S series)
are used in applications for which toughness and the
ability to withstand repeated shock are paramount.
They are comparatively low in carbon content, varying
between 0.40% and 0.65%. The principal alloying
elements in shock-resistant tool steels are silicon, chromium, tungsten, and sometimes molybdenum. Silicon
strengthens the ferrite; chromium increases hardenability and contributes slightly to wear resistance. Tungsten
imparts some resistance to softening at elevated temperature, and molybdenum aids in increasing hardenability. Most shock-resistant steels are air-hardening or
oil-hardening.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
225
Table 4.2
Major Tool Steel Groups
Group
Letter
Designation*
Type
Properties
Uses
Water-hardening
W
Plain carbon
Tough core and hard wearresistance surface
Cutlery, trim dies, cold header dies, wood chisels, hand punches
Oil hardening
O
Oil hardening
Wear resistant to moderate
temperatures
Dies and punches where high temperatures are
not generated
Shock resisting
S
Medium carbon,
low alloy
Excellent toughness and high
strength
Blank and trim dies, chisels, rivet sets, forming
rolls, slitting cutters, and structural applications.
Cold work
A
Medium alloy,
air hardening
Medium distortion and cracking
on quenching
Dies, punches, and forming rolls
D
High carbon,
high chromium
High hardness and excellent wear
resistance
Shear, blades, long-run stamping dies and brick
applications
Hot work
H
Chromium (H1–H19)
Tungsten (H20–H39)
Molybdenum (H40–H59)
Good toughness and resistance to
softness at elevated temperatures
Highly stressed components and high-temperature extrusion dies (may be water cooled in service without cracking)
High speed
T
Tungsten
High hardenability and hardness
Cutting tools and high-temperature structural
components, drills, reamers, broaches, milling
cutters, punches, and dies
AISI A11
A
High vanadium
Powdered metal air hardening
Excellent candidate to handle abrasive plastics.
Can replace carbide and other highly wear resistant materials
Mold
P
Low carbon
Low hardness and low resistance
to work hardening
Dies and molds for low-temperature die-casting
and for molds for plastics
Special purpose
L
Low alloy
High toughness and good
strength
Arbors, cams, chucks, spindles, drift pins, coldforming rolls, and slitting cutters.
*Letter designations of the specifications of the American Iron and Steel Institute and the Society of Automotive Engineers. These specifications for three
water-hardening tool steels, for example, are AISI W-1, W-2, and W-5. Tool steels also are specified by the American Society for Testing and Materials. (Also
see ASTM A600, Standard Specification for High-Speed Tool Steels; ASTM A681, Standard Specification for Alloy Tool Steels; and ASTM A686, Standard
Specification for Carbon Tool Steels.)
The high silicon content in shock-resistant tool steels
tends to accelerate decarburization, and suitable precautions should be taken during heat treatment to minimize this. The wear resistance and machinability of these
steels are considered to be only fair. Hardness usually is
kept below 60 HRC.
Shock-resistant tool steels are used in the manufacture of forming tools, punches, chisels, pneumatic tools,
shear blades and other applications requiring high resistance to impact loading and moderate wear resistance.
Oil-Hardening Tool Steels
The oil-hardening, low-alloy steels (AISI O Series)
contain manganese and small amounts of chromium and
tungsten. These steels have very good resistance to deformation and they are less likely to distort or crack during
heat treatment than the water-hardening steels. Oilhardening steels are relatively inexpensive, and their high
carbon content produces adequate wear resistance for
short-run applications at or near room temperature. They
also have good machinability, toughness, and resistance to
decarburization. Typical applications are the manufacturing
of threaded taps, solid threading dies, and forming tools.
Air-Hardening Tool Steels
The air-hardening, medium-alloy tool steels (AISI A
series) contain about 1% carbon, up to 2% manganese,
up to 5% chromium, and 1% molybdenum. The
increased alloy content, particularly with manganese
and molybdenum, provides greater hardenability and
gives this alloy series its characteristic air-hardening
properties. These medium-alloy types also have excellent resistance to deformation and good wear resistance. They possess fair hot hardness properties, and
fair resistance to decarburization. These steels are used
for blanking, forming, trimming, and thread-rolling dies.
226
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Table 4.3
Composition of Typical Tool Steels
Type
UNS
Number
Composition, % a
C
Mn
W1
W2
W5
T72301
T72302
T72305
0.70–1.50
0.85–1.50
1.05–1.15
0.10–0.40
0.10–0.40
0.10–0.40
S1
S2
S5
S6
S7
T41901
T41902
T41905
T41906
T41907
0.40–0.55
0.40–0.55
0.50–0.65
0.40–0.50
0.45–0.55
0.10–0.40
0.30–0.50
0.60.1.00
1.20–1.50
0.20.0.80
O1
O2
O6b
O7
T31501
T31502
T31506
T31507
0.85–1.00
0.85–0.95
1.25–1.55
1.10–1.30
1.00–1.40
1.40–1.80
0.30–1.10
1.00 max.
A2
A3
A4
A6
A7
A8
A9
A10b
T30102
T30103
T30104
T30106
T30107
T30108
T30109
T30110
0.95–1.05
1.20–1.30
0.95–1.05
0.65–0.75
2.00–2.85
0.50–0.60
0.45–0.55
1.25–1.50
1.00 max.
0.40–0.60
1.80–2.20
1.80–2.50
0.80 max.
0.50 max.
0.50 max.
1.60–2.10
D2
D3
D4
D5
D7
T30402
T30403
T30404
T30405
T30407
1.40–1.60
2.00–2.35
2.05–2.40
1.40–1.60
2.15–2.50
0.60 max.
0.60 max.
0.60 max.
0.60 max.
0.60 max.
H10
H11
H12
H13
H14
H19
T20810
T20811
T20812
T20813
T20814
T20819
0.35–0.45
0.33–0.43
0.30–0.40
0.32–0.45
0.35–0.45
0.32–0.45
0.25–0.70
0.20–0.50
0.20–0.50
0.20–0.50
0.20–0.50
0.20–0.50
H21
H22
H23
H24
H25
H26
T20821
T20822
T20823
T20824
T20825
T20826
0.26–0.36
0.30–0.40
0.25–0.35
0.42–0.53
0.22–0.32
0.45–0.55
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
Si
Cr
Ni
V
Water-Hardening
0.10–0.40
0.15 max.
0.20 max.
0.10 max.
0.10–0.40
0.15 max.
0.20 max.
0.15–0.35
0.10–0.40
0.40–0.60
0.20 max.
0.10 max.
Shock-Resisting
0.15–1.20
1.00–1.80
0.30 max.
0.15–0.30
0.90–1.20
—
0.30 max.
0.50 max.
1.75–2.25
0.35 max.
—
0.35 max.
2.00–2.50
1.20–1.50
—
0.20–0.40
0.20–1.00
3.00–3.50
—
0.20–0.30c
Cold-Work: Oil-Hardening
0.50 max.
0.40–0.60
0.30 max.
0.30 max.
0.50 max.
0.35 max.
0.30 max.
0.30 max.
0.55–1.50
0.30 max.
0.30 max.
—
0.60 max.
0.35–0.85
0.30 max.
0.40 max.
Cold-Work: Medium-Alloy, Air-Hardening
0.50 max.
4.75–5.50
0.30 max.
0.15–0.50
0.50 max.
4.75–5.50
0.30 max.
0.80–1.40
0.50 max.
0.90–2.20
0.30 max.
—
0.50 max.
0.90–1.20
0.30 max.
—
0.50 max.
5.00–5.75
0.30 max.
3.90–5.15
0.75–1.10
4.75–5.50
0.30 max.
—
0.95–1.15
4.75–5.50
1.25–1.75
0.80–1.40
1.00–1.50
—
1.55–2.05
—
Cold-Work: High-Carbon, High-Chromium
0.60 max. 11.00–13.00 0.30 max.
1.10 max.
0.60 max. 11.00–13.50 0.30 max.
1.00 max.
0.60 max. 11.00–13.00 0.30 max.
1.00 max.
0.60 max. 11.00–13.00 0.30 max.
1.00 max.
0.60 max. 11.50–13.50 0.30 max.
3.80–4.40
Hot-Work: Chromium
0.80–1.20
3.00–3.75
0.30 max.
0.25–0.75
0.80–1.20
4.75–5.50
0.30 max.
0.30–0.60
0.80–1.20
4.75–5.50
0.30 max.
0.50 max.
0.80–1.20
4.75–5.50
0.30 max.
0.80–1.20
0.80–1.20
4.75–5.50
0.30 max.
—
0.20–0.50
4.00–4.75
0.30 max.
1.75–2.20
Hot-Work: Tungsten
0.15–0.50
3.00–3.75
0.30 max.
0.30–0.60
0.15–0.40
1.75–3.75
0.30 max.
0.25–0.50
0.15–0.60 11.00–12.75 0.30 max.
0.75–1.25
0.15–0.40
2.50–3.50
0.30 max.
0.40–0.60
0.15–0.40
3.75–4.50
0.30 max.
0.40–0.60
0.15–0.40
3.75–4.50
0.30 max.
0.75–1.25
W
Mo
Co
0.15 max.
0.15 max.
0.15 max.
0.10 max.
0.10 max.
0.10 max.
—
—
—
1.50–3.00
—
—
—
—
0.50 max.
0.30–0.60
0.20–1.35
0.30–0.50
1.30–1.80
—
—
—
—
—
0.40–0.60
—
—
1.00–2.00
—
0.30 max.
0.20–0.30
0.30 max.
—
—
—
—
—
—
—
—
0.50–1.50
1.00–1.50
—
—
0.90–1.40
0.90–1.40
0.90–1.40
0.90–1.40
0.90–1.40
1.15–1.65
1.30–1.80
1.25–1.75
—
—
—
—
—
—
—
—
—
1.00 max.
—
—
—
0.70–1.20
—
0.70–1.20
0.70–1.20
0.70–1.20
1.00 max.
—
—
2.50–3.50
—
—
—
1.00–1.70
—
4.00–5.25
3.75–4.50
2.00–3.00
1.10–1.60
1.25–1.75
1.10–1.75
—
0.30–0.55
—
—
—
—
—
4.00–4.50
8.50–10.00
10.00–11.75
11.00–12.75
14.00–16.00
14.00–16.00
17.25–19.00
—
—
—
—
—
—
—
—
—
—
—
—
a. All steels except Type W have content maximums of 0.25 Cu, 0.03 P, and 0.03 S. Sulfur, where specified, may be increased to 0.06% to 0.15% to improve
the machinability of Type H, T, and M steels.
b. Contains free graphite in the microstructure to improve machinability.
c. Optional.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
227
Table 4.3 (Continued)
Composition of Typical Tool Steels
Type
UNS
Number
Composition, % a
C
Mn
Si
Cr
Ni
V
W
Mo
Co
1.75–2.20
0.90–1.30
1.80–2.40
0.80–1.20
1.80–2.40
1.50–2.10
1.80–2.40
4.50–5.25
5.50–6.75
17.25–18.75
17.50–19.00
17.50–19.00
17.50–19.00
18.50–21.00
13.25–14.75
11.75–13.00
4.50–5.50
—
1.00 max.
0.40–1.00
0.50–1.25
0.40–1.00
0.40–1.00
1.00 max.
—
—
—
4.75–5.75
7.00–9.50
11.00–13.00
4.25–5.75
4.75–5.25
1.00–1.35
1.75–2.20
1.40–2.10
5.50–6.75
8.20–9.20
4.50–5.50
—
—
H42
T1
T2
T3
T4
T5
T6
T7
T20842
T12001
T12002
T12004
T12005
T12006
T12008
T12015
0.55–0.70
0.65–0.80
0.80–0.90
0.70–0.80
0.75–0.85
0.75–0.85
0.75–0.85
1.50–1.60
0.15–0.70
0.10–0.40
0.20–0.40
0.10–0.40
0.20–0.40
0.20–0.40
0.20–0.40
0.15–0.40
M1
M2
T11301
T11302
0.15–0.40
0.15–0.40
M3,
class 1
M3,
class 2
M4
M6
M7
M10
T11313
0.78–0.88
0.78–0.88:
0.95–1.05
1.00–1.10
Hot-Work: Molybdenum
––
3.75–4.50
0.30 max.
0.20–0.40
3.75–4.00
0.30 max.
0.20–0.40
3.75–4.50
0.30 max.
0.20–0.40
3.75–4.50
0.30 max.
0.20–0.40
3.75–5.00
0.30 max.
0.20–0.40
4.00–4.75
0.30 max.
0.20–0.40
3.75–4.50
0.30 max.
0.15–0.40
3.75–5.00
0.30 max.
High-Speed: Molybdenum
0.20–0.50
3.50–4.00
0.30 max.
0.20–0.45
3.75–4.50
0.30 max.
0.15–0.40
0.20–0.45
3.75–4.50
0.30 max.
2.25–2.75
5.00–6.75
4.75–6.50
—
T11323
1.15–1.25
0.15–0.40
0.20–0.45
3.75–4.50
0.30 max.
2.75–3.75
5.00–6.75
4.75–6.50
—
T11304
T11306
T11307
T11310
0.15–0.40
0.15–0.40
0.15–0.40
0.10–0.40
0.20–0.45
0.20–0.45
0.20–0.55
0.20–0.45
3.75–4.75
3.75–4.50
3.50–4.00
3.75–4.50
0.30 max.
0.30 max.
0.30 max.
0.30 max.
3.75–4.50
1.30–1.70
1.75–2.25
1.80–2.20
5.25–6.50
3.75–4.75
1.40–2.10
—
4.25–5.50
4.50–5.50
8.20–9.20
7.75–8.50
—
11.00–13.00
—
—
M30
M33
M34
M36
M41
M42
M43
M44
M46
M47
A11
T11330
T11333
T11334
T11336
T11341
T11342
T11343
T11344
T11346
T11347
T30111
1.25–1.40
0.75–0.85
0.97–1.05
0.84–0.94:
0.95–1.05
0.75–0.85
0.85–0.92
0.85–0.92
0.80–0.90
1.05–1.15
1.05–1.15
1.15–1.25
1.10–1.20
1.22–1.30
1.05–1.15
2.40–2.50
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
0.20–0.60
0.15–0.40
0.20–0.40
0.20–0.40
0.20–0.40
0.15–0.40
0.35–0.60
0.20–0.45
0.15–0.50
0.20–0.45
0.20–0.45
0.15–0.50
0.15–0.65
0.15–0.65
0.30–0.55
0.40–0.65
0.20–0.45
0.75–1.10
1.00–1.40
1.00–1.35
1.90–2.30
1.75–2.25
1.75–2.25
0.95–1.35
1.50–1.75
1.85–2.20
3.00–3.30
1.15–1.35
9.25–10.25
1.30–2.30
1.30–2.10
1.40–2.10
5.50–6.50
6.25–7.00
1.15–1.85
2.25–3.00
5.00–5.75
1.90–2.20
1.30–1.80
7.75–9.00
4.50–5.50
9.00–10.00 7.75–8.75
7.75–9.20
7.75–8.75
4.50–5.50
7.75–8.75
3.25–4.25
4.75–5.75
9.00–10.00 7.75–8.75
7.50–8.50
7.75–8.75
6.00–7.00 11.00–12.00
8.00–8.50
7.80–8.80
9.25–10.00 4.75–5.25
1.10–1.50
P2
P3
P4
P5
P6
P20
P21
T51602
T51603
T51604
T51605
T51606
T51620
T51621
0.10 max.
0.10 max.
0.12 max.
0.10 max.
0.05–0.15
0.28–0.40
0.18–0.22
0.10–0.40
0.20–0.60
0.20–0.60
0.20–0.60
0.35–0.70
0.20–0.60
0.20–0.60
0.10–0.40
0.40 max.
0.10–0.40
0.40 max.
0.10–0.40
0.20–0.80
0.20–0.40
—
—
—
—
—
—
0.15–0.25
—
—
—
—
—
—
—
0.15–0.40
—
0.40–1.00
—
—
0.30–0.55
– Note d
—
—
—
—
—
—
—
L2
L6
T61202
T61206
0.45–1.00
0.65–0.75
0.10–0.90
0.25–0.80
0.50 max.
0.50 max.
3.50–4.25
0.30 max.
3.50–4.00
0.30 max.
3.50–4.00
0.30 max.
3.75–4.50
0.30 max.
3.75–4.50
0.30 max.
3.50–4.25
0.30 max.
3.50–4.25
0.30 max.
4.00–4.75
0.30 max.
3.70–4.20
0.30 max.
3.50–4.00
0.30 max.
4.75–5.75
Mold
0.75–1.25
0.10–0.50
0.40–0.75
1.00–1.50
4.00–5.25
—
2.00–2.50
0.35 max.
1.25–1.75
3.25–3.75
1.40–2.00
—
0.20–0.30
3.90–4.25
Special Purpose
0.70–1.20
—
0.60–1.20
1.25–2.00
0.10–0.30
0.20–0.30
—
—
0.25 max.
0.50 max.
—
—
a. All steels except Type W have content maximums of 0.25 Cu, 0.03 P, and 0.03 S. Sulfur, where specified, may be increased to 0.06% to 0.15% to improve
the machinability of Type H, T, and M steels.
b. Contains free graphite in the microstructure to improve machinability.
c. Optional.
d. Also contains 1.05% to 1.25% Al.
228
CHAPTER 4—TOOL AND DIE STEELS
High-Carbon, High-Chromium Steels
The high-carbon, high-chromium tool steels (AISI D
series) contain up to 2.25% carbon and 12.0% chromium. They also may contain molybdenum, vanadium,
and cobalt. The combination of high carbon and high
chromium content gives these steels excellent resistance
to wear and deformation. They also have good resistance to abrasion. The small dimensional change during
hardening makes the D Series steels useful for manufacturing blanking and piercing dies, drawing dies for wire,
bars, and tubes, thread-rolling dies, and master gauges.
Cold-Work Tool Steels
Cold-work tool steels (AISI O, A, and D Series) are
used for a variety of shearing and forming applications
in which the operation is performed cold (requiring no
preheat). An example of this is the shearing of automotive sheet metal. This series of tool steels is especially
important because the majority of tool applications can
be served by one or more of these steels.
Hot-Work Tool Steels
Tool steels in the hot-work group (the AISI H series)
have good resistance to hot hardness. In many applications, a tool is exposed to high temperatures in service
because it is being used to hot-work some other material, as in the case of hot forging and extruding, die
casting, or plastic molding. The AISI H series of tool
steels was developed for these applications.
The alloying elements that promote hot hardness are
chromium, tungsten, and molybdenum. This group of
tool steels is divided into three types, depending on the
primary alloying element. The amounts of chromium,
tungsten, and molybdenum must total at least 5% in
order for hot hardness to be adequate.
AWS WELDING HANDBOOK 9.4
Tungsten Steels. The tungsten steels in the AISI H21
to AISI H26 groups contain 9% to 18% tungsten and
2% to 12% chromium. The higher alloy content of
tungsten relative to chromium increases resistance to
softening at high temperatures. However, it also makes
tungsten steels more susceptible to brittleness at hardness values from 45 HRC to 55 HRC. Tungsten steels
can be air hardened to reduce distortion, or quenched
in oil or hot brine to minimize scaling. These steels have
many of the characteristics of the high-speed tool steels
used to make cutting tools, but have better toughness.
They can be used for high-temperature applications
such as mandrels and extrusion dies for work with brass,
nickel alloys, and steel.
Molybdenum Steel. Molybdenum steel (AISI H42) is
a hot-work steel with characteristics and applications
similar to the tungsten hot-work steels. The composition of the various types of molybdenum steel resembles
high-speed tool steels, but molybdenum steel has lower
carbon content and provides greater toughness. The
principal advantages of molybdenum steels over tungsten hot-work steels are greater resistance to heat cracking or checking and lower initial cost. Like all highmolybdenum steels, AISI H42 steel requires care during
heat treatment to avoid decarburization.
Vanadium Tool Steel. Vanadium tool steel is a
versatile air-hardening powder metal that provides
extremely high wear resistance and relatively high
impact toughness. The high wear resistance is the result
of the addition of a very large volume of hard vanadium
carbides. Good impact toughness is the result of fine
grain size, small carbides, and superior cleanliness of
the microstructure of the powdered metal.
Chromium Steels. The chromium steels in Series
High-Speed Tool Steels
AISI H10 to AISI H19 contain at least 3.25% chromium and smaller amounts of vanadium, tungsten, and
molybdenum. They have good hot hardness properties
because of the moderate chromium content combined
with the three other strong carbide-forming elements.
The low carbon content and relatively low total alloy
content promote toughness at hardness levels registering 40 HRC to 50 HRC. Increased content of tungsten
and molybdenum will increase hot hardness, but will
slightly reduce toughness.
These steels are extremely deep hardening, with the
capacity to be air-hardened to full hardness in sections
up to 305 millimeters (mm) (12 inches [in.]) thick. The
air-hardening qualities and balanced alloy content are
responsible for low distortion during hardening. In service applications, these steels are especially adapted to
hot die work of all kinds, particularly extrusion dies,
die-casting dies, forging dies, mandrels, and hot shears.
High-speed tool steels are defined by application;
they are used to manufacture tools capable of many
forms of high-speed cutting, such as tools used for drilling, trimming, milling, turning scribing, reaming, and
gouging. High-speed tool steels are divided into two
groups: those with molybdenum (AISI M Series) and
tungsten type (AISI T Series). The significant mechanical properties are about the same. These steels are
highly alloyed and normally contain large amounts of
molybdenum or tungsten in addition to chromium,
vanadium, and sometimes cobalt for increased hothardness properties. The carbon content ranges between
0.75% and 1.5%.
The major application for high-speed steel is the
manufacturing of cutting tools, but they also are used
to manufacture extrusion dies, burnishing tools, and
blanking and piercing punches and dies.
AWS WELDING HANDBOOK 9.4
Molybdenum Steels. Molybdenum high-speed tool
steels classified in the AISI M Series contain from 3.0%
to 9.5% molybdenum. All contain some chromium, and
many have up to 12.0% cobalt. These steels are rated as
deep hardening, have good wear resistance, fair machinability, and fair-to-poor resistance to decarburization.
Tungsten Steels. Tungsten tool steels classified in
the AISI T Series contain from 0.75% to 1.5% carbon
and from 12.0% to 18.0% tungsten. These steels have
all of the characteristics of molybdenum steels, but are
not recommended for welding due to the high tungsten
and carbon content.
Mold Steels
Mold-making steels (AISI P Series) are relatively low
in carbon, but the alloy content of this type can be as
high as 5%. Mold steels are used throughout the plastic
molding industry to make injection molds, extrusion
molds, and compression molds. A large percentage of
the mold steel production is used in the as-tempered
condition, with hardness in the range of 28 HRC to
32 HRC. These steels can be carburized and nitrided,
using the standard heat-treating practices applied to lowcarbon steels.
Special-Purpose Steels
Special-purpose steels (AISI L Series) are not categorized in the usual classifications because they are
formulated to handle the requirements of specific
applications.
Special-purpose steels contain chromium as the principal alloying element, combined with molybdenum,
nickel, and vanadium. The high chromium content not
only increases hardenability but also promotes wear resistance by the formation of hard complex iron-chromium
carbides. Molybdenum also increases hardenability; nickel
increases toughness; and vanadium refines the grain size.
These steels are oil-hardening, therefore, they are evaluated as only fair in resistance to dimensional change.
Typical applications include various machine tools,
such as bearings, rollers, clutch plates, cams, collets,
and wrenches, that require both high wear resistance
and good toughness, The high-carbon types are used for
arbors, dies, drills, taps, knurls, and gauges.
WELDABILITY
The increased alloy content of tool steels generally
achieves increased wear resistance, depth of hardening,
and dimensional stability. For example, tools or dies
CHAPTER 4—TOOL AND DIE STEELS
229
made of the air-hardening steels, which contain more
alloy additions than the water-hardening steels, possess
better mechanical properties and usually provide superior performance in service. However, the high alloy
content of air-hardening steels also diminishes weldability, thus they require great attention to specific welding
conditions during welding to avoid cracking. In the
AISI classification of tool steels, there generally is an
inverse relationship between the alloy content of the
steels and weldability. The principal element influencing
weldability is carbon: as the carbon content increases,
welding becomes more difficult. Therefore, the carbon
equivalent of a steel alloy is a good indicator of the ease
of welding. The following carbon-equivalent equation
(4.1) from the International Institute of Welding is frequently applied to this type of steel:10
(4.1)
+ %Mn- + %
( Cr + Mo + V )- + %
( Ni + Cu -)
CE = %C
------------------------------------------------------------------------------------------------------6
5
15
HEAT TREATMENT
Tool steels usually are received from the supplier in
the annealed condition. If practical, tool and die products should be welded in this condition because the steel
has the best ductility. If feasible, previously hardened
tools should be annealed prior to welding. The welded
tool should then be heat treated to provide the desired
properties. Heat treatments for the annealing and hardening of several tool steels are suggested in Table 4.4;
however, the appropriate heat treatment for a specific
tool steel should be obtained from the manufacturer.
When a hardening heat treatment is required after
welding, the weld metal also must respond favorably to
the treatment. This must be considered when selecting
an appropriate filler metal for the specific job.
Almost all repair welding of tools falls into the category of hardened tools. When hardened tools must be
welded, appropriate procedures must be followed to
minimize cracking. Suitable preheat and postweld heat
treatments may include stress relieving or tempering.11
In general, the temperature of the workpiece should not
exceed the original tempering temperature. Techniques
10. Secretariat of the International Institute of Welding, 90 Rue del
Vanesses, 93420 Villepinte, France (ZI Paris Nord 2 BP:50362-F95942
ROISSY CDG Cedex, France).
11. Information on heat treating tool steels is provided in ASM International (ASM), Metals Handbook, Vol. 4, 9th ed., pp 711–725. Also refer
to ASM International (ASM), 1990, Introduction to Heat Treating of Tool
Steels, Revised by B. A. Becherner and T. J. Witheford, ASM Handbook, Vol. 4, Heat Treating, Materials Park, OH: ASM International.
230
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Table 4.4
Typical Heat Treating Temperatures for Welding Tool Steels
Type
Group
Annealing Temperature
°C (°F)
Austenitizing Temperature
°C (°F)
Quenching
Media*
Tempering Temperature Hardness
°C (°F)
HRC
W1, W2
Water hardening
738–788 (1360–1450)
760–843 (1400–1550)
B, W
177–343 (350–650)
54–64
01
Oil hardening
760–788 (1400–1450)
788–816 (1450–1500)
O
177–260 (350–500)
57–62
06
Oil hardening
760–788 (1400–1450)
788–816 (1450–1500)
O
177–316 (350–600)
58–63
S1
Shock resisting
788–816 (1450–1500)
899–954 (1650–1750)
O
204–649 (400–1200)
40–58
S5
Shock resisting
773–801 (1425–1475)
871–927 (1600–1700)
O
177–426 (350–800)
50–60
S7
Shock resisting
816–843 (1500–1550)
927–954 (1700–1750)
A, O
204–621 (400–1100)
47–58
A2
Air hardening
843–871 (1550–1600)
927–982 (1700–1800)
A
177–538 (350–1000)
57–62
A4
Air hardening
738–760 (1360–1400)
816–871 (1500–1600)
A
177–426 (350–800)
54–62
D2
Air hardening
871–899 (1600–1650)
982–1023 (1800–1875)
A
204–538 (400–1000)
54–61
H12, H13, H19
Hot work
843–871 (1550–1600)
996–1037 (1825–1900)
A
538–649 (1000–1200)
38–56
M1
High speed
816–871 (1500–1600)
1177–1218 (2150–2225)
A, O, S
538–593 (1000–1100)
60–65
M2
High speed
871–899 (1600–1650)
1190–1232 (2175–2250)
A, O, S
538–593 (1000–1100)
60–66
M10
High speed
816–871 (1500–1600)
1177–1218 (2150–2225)
A, O, S
538–593 (1000–1100)
60–67
A11
CPM**
870–899 (1600–1650)
1063–1175 (1950–2150)
B, O, V
540–593 (1000–1100)
48–64
T1, T2, T4
High speed
871–899 (1600–1650)
1260–1301 (2300–2375)
A, O, S
538–593 (1000–1100)
60–66
P20
Mold steel
760–788 (1400–1450)
816–871 (1500–1600)
O
482–593 (900–1100)
28–42
*A—Air cool, B—Brine quench, O—Oil quench, S—Salt bath quench, W—Water quench, V— Vacuum or atmosphere.
**Compacted powder metal.
such as intermittent welding (sometimes called skip
welding) and backstep-sequence welding using short
stringer beads will help control interpass temperature
and in turn, eliminate underbead cracking.
ANNEALING
The purpose of annealing tool steel is to soften the
steel prior to welding. Annealing typically involves the
following steps:
1. Slow, gradual heating of the workpiece to a temperature that is slightly above the transformation
range of the steel;
2. Holding at temperature long enough to allow the
entire workpiece to reach temperature, and completely transform to austenite; and
3. Cooling at a slow rate to prevent martensitic transformation, which yields a soft microstructure.
Austenite is the interstitial solid solution of carbon in
gamma iron. Martensite is a change in the microstructure as a result of rapidly cooling from the austenite
phase below the M5 temperature; its microstructure is
characterized by a needle-like pattern.12
Figure 4.3 illustrates the use of a transformation diagram to plan a cooling cycle that avoids transformation
from austenite to martensite. A maximum cooling rate
for a typical tool steel is approximately 14°C to 28°C
(25°F to 50°F) per hour, depending on the specific alloy
involved, down to about 538°C (1000°F). Further cooling usually can be performed at ambient temperatures
to drive faster rates. The cooling rate must be adjusted
to suit the workpiece size so that thermal stresses are
minimized. Small tools can be cooled at faster rates
than large ones. If an isothermal transformation diagram rather than a continuous cooling transformation
diagram is used to plan the cooling cycle, compensation
should be made for the fact that the continuous cooling
diagram is shifted to longer times and lower temperatures.
The annealing equipment must provide the means to
prevent carburization or decarburization. Controlledatmosphere furnaces or salt baths may be used for heating. Pack annealing also may be recommended in some
12. Linnert, G. E., 1994, Welding Metallurgy, Carbon and Alloy
Steels, Vol. 1: Fundamentals, 4th ed., Miami: American Welding
Society.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
welding would soften only the heat-affected zone
(HAZ). The heating and cooling rates for stress relieving should be similar to those used for annealing.
800
TEMPERATURE, °C
1200
600
COOLING CURVE
500
1000
400
800
300
600
MS
200
400
100
200
MF
1 2 5 10 20 60 2 5 10 20 60 2 5 10 20 60
MINUTES
SECONDS
HOURS
TEMPERATURE, °F
1400
700
231
TIME
Figure 4.3—Cooling Curve Designed to
Avoid Martensitic Transformation Plotted
Over an Isothermal Transformation Diagram
cases, particularly for high-speed steels. Pack annealing
is a technique in which the steel is packed in clean charcoal or other carburizing material mixed with dry ashes,
lime, or sand in a controlled-temperature atmospheric
furnace. Graphitic tool steels should always be pack
annealed.13
STRESS RELIEVING
Internal stresses in the workpiece caused by welding,
heavy machining, or other cold working processes can
be reduced by stress relieving. Stress relieving is accomplished by heating the workpiece to a temperature below
the transformation range of the steel (the temperatures
at which a change in phase occurs).
For materials that have not been hardened, a stressrelieving temperature of approximately 510°C to 590°C
(950°F to 1100°F) normally is used. When working
with a tool in the hardened condition, stress relieving
may be accomplished by tempering. The temperature
used for stress relief of a tool that was welded in the
hardened condition should not be above the tempering
temperature of the steel. This treatment would alter the
hardness and toughness of the entire tool, whereas
13. Jefferson, T. B. and G. Woods, 1990, Metals and How to Weld
Them, 2nd ed., Cleveland: The James F. Lincoln Arc Welding
Foundation.
NORMALIZING
Normalizing, a process used to change the microstructure of the steel, is accomplished by heating the
steel to a temperature above the transformation range,
followed by cooling to a temperature substantially
below the transformation range. The cooling rate should
be sufficient to form a microstructure suitable for subsequent hardening. Normalizing is sometimes combined
with stress relieving. Most tool steels that have been
annealed do not require normalizing.
AUSTENITIZING
Austenitizing is accomplished by slowly heating the
steel to a temperature above the transformation range
and holding at that temperature long enough for resolution of the carbides. Small tools may be heated more
quickly than large ones. High-alloy steels normally are
heated very slowly to a temperature just below the
transformation range of the steel. They are then heated
quickly into the austenitizing temperature range, which
may be several hundred degrees higher.
Austenitizing should be the most carefully controlled
of the heat treatments applied to tool steels, especially
the high-speed tool steels. Temperatures that are too
high and holding times that are too long may cause
abnormal grain growth and distortion, with loss of ductility and strength. Austenitizing temperatures that are
too low may cause the tool to lose hardness and resistance to wear. Quenching also must be controlled, especially with water-hardened tools, because if the
temperature is lower at the center of the tool than the
exterior, the result might be spalling or cracking.14
Several precautions are necessary when austenitizing
tool steels. First, tools and dies should be heated in a
suitable protective atmosphere or vacuum to avoid scaling and decarburization. Steels will scale heavily in an
oxidizing atmosphere, depending on the temperature
and time at temperature. Decarburization also will
occur, especially in the austenitizing temperature range.
As a precaution against grain growth, excessive time at
temperature should be avoided. The tool should be
properly supported during austenitizing to prevent sagging and distortion.
14. Refer to ASM International (ASM) Metals Handbook, Vol. 4,
Materials Park, Ohio: ASM International.
232
CHAPTER 4—TOOL AND DIE STEELS
LIVE GRAPH AWS WELDING HANDBOOK 9.4
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QUENCHING
TEMPERING
Tempering is a reheating process used to increase
toughness and decrease hardness in hardened steel.
Tempering should be performed immediately after
quenching to relieve stresses, prevent cracking, and
toughen the alloy. In most cases, the workpiece (usually
a tool) should not be cooled below 66°C (150°F) between
quenching and tempering. Instead, the tool should be
removed from the quenching medium while at 66°C to
93°C (150°F to 200°F) and tempered immediately.
Typical temperatures for various tool steels are shown
in Table 4.4. (Refer also to Table 4.7.) Tempering
curves, such as the one shown in Figure 4.4, are available from materials suppliers or industry handbooks.15
Within the recommended tempering range for the
specific steel, a higher temperature provides greater
toughness, but at some sacrifice to hardness. Tempering
at the low end of the range gives maximum hardness
and resistance to wear, but lowers toughness. Two or
more tempering cycles, with cooling to room tempera15. ASM International (ASM), 1996, H. Chandler, ed., Heat
Treater’s Guide: Practices and Procedures for Nonferrous Alloys, 2nd
ed., Materials Park, Ohio: ASM International.
65
TEMPERING TEMPERATURE, °C
200 300 400 500 600 700
60
HARDNESS, HRC
Quenching (cooling hot metal by plunging it into
cool water or other medium) is performed to provide
the cooling required for transformation from austenite
to martensite. Tool steels are quenched in water, brine,
oil, polymers or air, depending on the composition of
the alloy and the thickness of the workpiece. The
quenching medium must cool the workpiece at a sufficient rate to obtain full hardness. However, an excessively fast cooling rate should be avoided because of the
danger of cracking the workpiece.
Air-hardening tool steels may be quenched at a
temperature between 538°C and 649°C (1000°F and
1200°F). The workpiece should be removed from the
quenching medium as soon as the temperature has stabilized. If the holding time is too long, austenite will
start to transform. After hot quenching, the tool can be
air cooled or oil quenched to about 66°C (150°F)
before tempering.
Water-hardening steels tend to distort and change
size during quenching. Internal stresses developed during water quenching may easily crack workpiece components with sharp corners or abrupt section changes
that constitute stress raisers. For this reason, shallow
hardening using a fine water spray is often performed.
Where submersion is required, a brine solution is used
to break up air bubbles. Brine provides uniform cooling
with less distortion than that associated with a plain
water bath.
55
50
45
40
35
200
400 600 800 1000 1200 1400
TEMPERING TEMPERATURE, °F
Figure 4.4—Typical Tempering
Curve for AISI D-2 Tool Steel
ture between cycles, are recommended to produce an
optimum metallurgical structure. Welding is not recommended on hardened but untempered tool steel because
it probably will crack the workpiece.
Flame Hardening
Flame hardening is the process of heat treating localized areas of a workpiece, for example, a tool or die,
using an oxyfuel gas torch, usually hand held, and cooling with an air or liquid quench. Hardening is accomplished by progressively heating the workpiece to the
proper austenitizing temperature and then quenching at
a rate sufficient to form hard martensite.
Flame hardening is used to harden working areas of
tools and dies when the entire component is too large to
put into a furnace or when a furnace is not available.
It may also be employed when a hard edge and a soft
core are required to meet the needs of a particular
application.
Induction Hardening and Laser Beam
Hardening
Other methods of local hardening include induction
hardening and laser beam hardening, which use the
induction process or a laser beam as the heat source.
Induction hardening can be done manually or with a
AWS WELDING HANDBOOK 9.4
robotic system. Laser beam hardening involves closer
control, and therefore a mechanized motion system is
required.
ARC WELDING OF TOOL
AND DIE STEELS
The most commonly used processes for the welding
of tool steels are gas tungsten arc welding (GTAW),
shielded metal arc welding (SMAW), gas metal arc
welding (GMAW), flux cored arc welding (FCAW), and
submerged arc welding (SAW). Other processes, such as
powder flame spraying (FLSP) and plasma arc welding
(PAW) can be used successfully in appropriate applications to deposit surfacing material.16
The arc welding of tool steels often involves the addition of filler metal into the weld pool, (the molten metal
in a weld prior to solidification as weld metal) melted
by the arc. The arc is shielded with an inert gas, flux, or
an electrode coating that decomposes during welding.
Tool steels are welded to accomplish one or more of the
following purposes:
1. Assemble components to form a tool or die,
2. Fabricate a composite tool or die using hardsurfacing techniques,
3. Alter a tool or die for engineering changes,
4. Correct machining or grinding errors,
5. Repair worn areas by weld buildup, or
6. Repair cracks or other damaged areas.
Assembling components by welding for use in the
fabrication of composite tools is a technique that permits the strategic placement of tool steel on the work
area of a tool and the use of less expensive material for
noncritical areas. This technique can be used on a tool
or die with components that do not require the hardness or wear resistance of tool steel for satisfactory performance. Tougher metals may be used to support tool
steel components or to support the weld deposits. Another
significant application of welding tool steels is in modifying the shapes of tools and dies and in salvaging components by restoring them to original dimensions.
The next section discusses arc welding repair and
fabrication procedures for tools and dies composed of
two or more materials.
16. Refer to Welding Handbook Committee, 2004, A, O’Brien, ed.,
Welding Processes, Part 1, Vol. 2 of Welding Handbook, 9th ed.,
Chapters 2–7 for detailed information on arc welding processes,
Miami: American Welding Society.
CHAPTER 4—TOOL AND DIE STEELS
233
REPAIR AND FABRICATION PROCEDURES
The importance of controlling the entire repair process from material identification through postweld heat
treatment cannot be overemphasized.17 Specific welding
repair procedures such as those listed below provide the
means to maintain the necessary control in a variety of
circumstances. The welder should perform the following procedures:
1. Determine the type of material to be welded and
its condition relative to heat treatment;
2. Perform any heat treatment needed to prepare
the tool or die (the workpiece) for welding;
3. Prepare the surface to be welded;
4. Select the appropriate welding process and filler
metal to satisfy the requirements of the application;
5. Select the smallest-diameter welding electrode,
wire, or bare rod that will do the job efficiently
and leave a deposit with the required properties;
6. Preheat the steel to the proper temperature, making sure the workpiece is heated to the center;
7. Deposit the filler metal using the proper welding
procedure for the alloy being welded;
8. During welding, maintain the interpass temperature without exceeding the upper limit of the
tempering curve of the base metal;
9. Postheat immediately after welding to minimize
the temperature difference between the weld
deposit and the base metal; and
10. Cool slowly to slightly above room temperature,
then stress relieve or temper to achieve the
desired properties.
An example of a typical welding procedure specification
(WPS) for repair welding is shown in Figure 4.5.
Figure 4.6 is a welding procedure specification for
the welding of forming dies made with unalloyed and
alloyed gray cast iron, SAE-J431 G2500 or SAE-J431
G3500. Two welders are required for this repair, as
noted in Figure 4.6. Using a torch, one welder preheats
the workpiece approximately 152 mm (6 in.) ahead of
the weld and maintains an even preheat. The other
welder deposits the weld bead and stops the welding
progression to peen the weld metal every 76 mm (3 in.).
Welding Repair Procedures for Annealed
Tool Steel
The sequence of operations for the repair welding
of a tool or die depends on prior heat treatment of the
17. For a systematic approach to repair welding, refer to Chapter 9,
“Maintenance and Repair Welding,” in this volume.
234
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Figure 4.5—Sample of Repair Weld Procedure Specification (WPS)
AWS WELDING HANDBOOK 9.4
(A) Area to be Repaired
CHAPTER 4—TOOL AND DIE STEELS
Identification:
Cast Iron Forming Surface
Revision:
(Month-day-year)
(B) Sequence of Welding
235
(C) Complete Repair
Note: When local preheating is used, a second welder or helper is required to assist with preheat and peening, and to provide relief to
the welder so that the repair can be continued to completion without interruption.
Welding Technique
a. Maximum bead length is 100 mm (3 in.).
b. For repairs less than 5 mm (0.20 in.) thick and greater than 100 mm (3 in.) long, a cascade welding technique should be used to
apply the finish to the repair as welding progresses.
(D) Cascade Sequence
c. For repairs greater than 5 mm (0.20 in.) thick, a cascade technique should be used for each layer.
d. Stops and starts should be staggered.
e. Each bead should be lightly peened with a pneumatic peening hammer as quickly as possible.
f. Allow approximately 2 mm (0.08 in.) excess weld buildup after the arc goes out.
Figure 4.6—Welding Procedure Specification for Unalloyed and Alloyed Gray Cast Iron
tool steel, the amount of metal to be deposited, and the
location of the repair. When a tool or die in the annealed condition is to be welded, the following sequence
is suggested:
1. Preheating the workpiece,
2. Welding with the appropriate filler metal,
3. Annealing to the correct specification,
4. Performing preliminary machining,
5. Hardening and tempering, and
6. Finishing by machining or grinding.
Procedures for Hardened Tool Steel
When the tool or die is to be welded in the hardened
condition, the following repair sequence is recommended:
236
CHAPTER 4—TOOL AND DIE STEELS
1.
2.
3.
4.
Preheating the workpiece,
Selecting the appropriate filler metal,
Welding the workpiece,
Applying postheat and allow the workpiece to
cool,
5. Tempering, and
6. Finishing by machining or grinding.
In the past, it was common to anneal previously
hardened tools and dies before and after welding to
facilitate machining prior to rehardening. However, the
requirement for annealing has been reduced through
the use of milling cutters made of modern materials
such as carbide, ceramic, diamond, and cubic boron
nitride (CBN), thus simplifying the entire process.
When circumstances permit, tools such as dies or
molds should be welded in the hardened condition. This
will avoid the need to anneal and reharden, which will
reduce the distortion, dimensional changes, and rework
associated with heat treatments. A base metal that has
been previously hardened but not yet tempered cannot
be welded unless it is annealed or tempered prior to
welding.
In some cases, if the repair is in an area that is not
critical, a nonhardening filler metal can be used. If the
weld area will be subjected to wear, it may be partially
filled with a softer alloy and then completed with an
appropriate tool steel overlay. The underlying layer
should have sufficient strength to support the surface
layer under service conditions. The tool steel layer
should have the properties required in service for the
die or mold. The required properties usually are similar
to those of the hardened base material after tempering.
Also, the tool steel layer should be thick enough to
accommodate some dilution with the nonhardening
underlay. Common practice is to use a minimum thickness of 3.2 mm (1/8 in.) for the tool steel layer.
Identification of Base Metal
The heat-treatment history from the original specifications for the tool is the best source for identifying the
type of tool steel to be welded. If the specifications are
not available, a chemical analysis must be performed to
determine the carbon and alloy content of the steel.
When other methods are not available, experienced
welders can perform a spark test that will sometimes
yield a rough approximation of the type of steel used in
the workpiece.
The heat-treated condition can be determined by
conducting a hardness test using bench-mounted or
portable instruments, depending on the size and configuration of the workpiece. This sometimes can be done
by filing with hardness-test files. If filing reveals that the
steel is hard, then obviously it has been heat treated. If
it is soft, it is in the annealed condition.
AWS WELDING HANDBOOK 9.4
Process Selection
Several arc welding processes, SMAW, GMAW,
GTAW, FCAW, and SAW, are acceptable for repairing,
upgrading, and the composite fabrication of tools, dies,
and molds. The selection depends on the amount of
weld metal to be deposited, the size and complexity of
the tool, and the alloy involved. If surfacing is involved
in the application, powder flame spraying or plasma arc
welding are the processes frequently used. Tools, dies,
and molds with small repair areas are most commonly
welded using the GTAW process because it provides
precise control with minimum heat input. Larger tools
and dies with more extensive repair areas are more efficiently repaired using FCAW, SMAW, or GMAW,
which have much higher deposition rates. The SAW
process is often used when the application requires tool
steel weld deposits with uniform bead width and thickness, for example, when repairing mill rolls and large
die sections.
The SMAW process is used extensively to repair
forging tools when the removal of the discontinuity or
defect requires gouging out large areas of the tool and
filling them with tough, dense weld metal. Electrodes
up to 19 mm (3/4 in.) in diameter are used. More than
27 kilograms (kg) (60 pounds [lb]) of metal per hour
can be deposited with the SMAW process for the repair
of items such as impression blocks, rams, sow blocks,
and hammer bases.
Filler Metal Selection
Filler metals are available for welding most classifications of tool steels. The size of the electrode to be
used depends on the width and depth of the repair
required for the damaged area. Most covered electrodes
for tool steels are available in diameters of 1.6 mm to
6.4 mm (0.062 in. to 0.25 in.). Large covered electrodes
in diameters up to 19 mm (0.75 in.) are available for
the repair of large areas in molds and dies. Solid and
flux-cored wires are available in diameters from 0.9 mm
to 4.0 mm (0.035 in. to 0.16 in.). The welder should
select the smallest size that will do the job efficiently,
especially on sharp cutting edges, in order to keep the
heat input to a minimum. Direct-current electrode positive (DCEP) is recommended for most tool steel electrodes. Recommended ranges for welding current usually
are provided by the supplier of the electrodes. When
making repairs on annealed sections, the welder should
deposit metal that will respond satisfactorily to the heat
treatment normally applied to the base metal. For repairs
on hardened tool steels, the deposited metal should have
characteristics best suited for the service requirements of
the tool.
Factors such as the thickness of metal to be cut or
formed and resistance to heat, abrasion, and shock should
AWS WELDING HANDBOOK 9.4
be considered when selecting an appropriate filler metal
for tool and die welding. Other pertinent factors are the
following:
1. Chemical composition of the base metal;
2. Heat-treated condition of the workpiece, such as
annealed, hardened, or tempered;
3. Machinability and grinding requirements of the
workpiece;
4. Service conditions to which the welded area will
be subjected;
5. The effect on production requirements for hardness, toughness, and wear resistance;
6. Welding efficiency, such as deposition rate, heat
input, and material costs;
7. Ease of welding and skill requirements of the
operator; and
8. Postweld heat treatment requirements.
When welding tool steel that has been annealed, it is
preferable to select a filler metal with a chemical composition that matches that of the base metal. The
response of the weld deposit to hardening heat treatment will then be uniform. However, when the workpiece has been hardened and will not be heat treated
again, the filler metal can be selected strictly on the
basis of service requirements.
The hardness of the weld metal deposited on tool
steels will vary among the different alloys according to
the following conditions:
1. Preheat temperature;
2. Welding procedure and sequence, including heat
input;
3. Filler metal dilution by the base metal;
4. Cooling rate; and
5. Postweld heat treatment.
Filler Metal Categories
CHAPTER 4—TOOL AND DIE STEELS
Low-Alloy Steel. Low-alloy steel filler metals are
classified as low-alloy steels. These filler metals produce
deposits that have moderate hardness and toughness at
room temperature, and most will respond somewhat to
heat treatment, especially when diluted with the base
material. Commonly used low-alloy steels include AISI/
SAE 8620, 6150, 4130, 4140, and 1060.
Special-Purpose
and Underlayment Steels.
Filler metals categorized as special-purpose joining and
underlay materials include high-strength and stainless
steels used for joining dissimilar materials and for the
repair of cracks. This category also includes various
nickel-copper-iron alloys used for cast-iron repairs and
underlayment for thick buildups. These weld deposits
subsequently can be surfaced or overlayed with a hard,
wear-resistant tool steel material. Some of the specialpurpose steels also are used when resistance to heat or
corrosion, or both, is required.
Filler Metal Forms
Filler metals for welding tool steels are available in
several forms for use with the various arc welding processes, as listed in Table 4.5. Commercial filler metals,
available from suppliers of specialty welding alloys,
include coated electrodes for SMAW, bare rods for
GTAW, solid spooled wire for GMAW, and flux cored
wire for FCAW. When an identical alloy match is not
Table 4.5
Forms of Tool Steel Filler Metal Available for
Various Welding Processes
Filler Metal
Type (AISI)*
SMAW
GTAW
GMAW
W1, W2
✔
✔
✔
01, 06
✔
✔
✔
FCAW
Filler metals normally used for welding tool and die
steels are classified into the following main categories:
AISI standard tool steels, low-alloy steels, and specialpurpose joining and underlay materials.
S7
✔
✔
✔
A2
✔
✔
✔
D2
✔
✔
✔
H12
✔
✔
✔
✔
AISI Standard Tool Steel. American Iron and Steel
H13
✔
✔
✔
✔
✔
Institute (AISI) standard tool steel filler metals produce
weld deposits that correspond to the basic industry
standard tool grades: water, oil, and air hardening; hot
worked, and high-speed steel. (Refer to Table 4.4 for a
list of commonly used AISI tool steels and corresponding heat treating temperatures.) Generally, these deposits are hard in the as-welded condition, regardless of the
composition of the base metal.
237
H19
✔
✔
✔
M1
✔
✔
✔
M2
✔
✔
✔
✔
AISI A11
T1
P20
✔
✔
✔
✔
✔
*AWS does not specify filler metals for tool steels.
✔
238
CHAPTER 4—TOOL AND DIE STEELS
obtainable, the manufacturer normally can recommend
a substitute that will react the same way as the base
metal during heat treatment, or will provide comparable properties in the as-welded state.
Covered SMAW electrodes for tool steels are
designed in the same manner as standard carbon steel
and low-alloy steel electrodes. The coverings contain
specific elements to stabilize the arc, provide flux for
the molten metal, and form a protective slag over the
weld bead. Alloying elements also may be added to the
weld metal by incorporating them in the electrode covering or in the electrode itself.
Spooled flux cored wires for FCAW contain similar
ingredients in the core material within a mild steel
tubular wire. Bare rods for GTAW and solid wires
for GMAW must incorporate the alloying elements in
AWS WELDING HANDBOOK 9.4
the rod or wire because there is no coating or core
material.
Preparation for Welding
When making repairs of cutting edges or other working surfaces, the damaged areas should be undercut to a
uniform depth to remove any discontinuities and to
provide a deposit with the required thickness, hardness,
and wear characteristics. Dilution of the base metal also
must be considered.
Undercutting and Surface Preparation. Whether
the edge repair involves only a part of the edge, as
shown in Figure 4.7 or the entire edge as shown in Figure 4.8, the type and depth of undercut or groove to be
Figure 4.7—Preparation for a Partial Repair
Figure 4.8—Preparation for a Full Repair
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
used depends on the amount of metal to be deposited.
For small deposits, a 6 mm (1/4 in.) chamfer of 45°
is common. Larger deposits require a U-groove or Jgroove to support the deposited bead.
When preparing to weld cast-iron dies, for example,
for the automotive industry, great care must be exercised with undercutting to ensure good adherence to the
base material. It is imperative that the welded area be
undercut enough to accommodate at least two layers of
a filler metal designed to adhere to the casting, such as a
nickel alloy, in addition to enough depth for two layers
of the selected tool steel used for the working surface.
Table 4.6 shows standard cast-iron grades for the automotive industry that require this procedure.
These dies usually are overlaid with an S-7, H-12,
H-13, or H-19 filler material. Because these alloys have
good impact properties, they also are used for blanking
and trimming applications. Weldments planned for use
in severe service atmospheres require a more wear-resistant
material, such as A-2 or M-2.
The welding of a tool steel should not be attempted
unless the surfaces are clean, dry, and smooth. When
preparing the surfaces, care must be taken to remove
any tool marks that may later act as stress raisers and
weaken the steel. Notch sensitivity is especially acute in
tool steels with high hardenability. Therefore, all cracks
should be removed completely from the area to be
welded, and the surface should be smooth.
Cleanliness is very important for successful welding.
Whenever possible, workpieces should be cleaned with
an alkaline cleaning solution and steam cleaned or rinsed
in hot water. This treatment is necessary to remove all
traces of lubricants and other hydrocarbons because they
will promote cracking if left on or near the region to be
welded.
Common methods of metal removal prior to welding
include conventional machining, electrical discharge
machining (EDM), grinding, air-carbon arc gouging,
and thermal cutting with the oxyfuel gas or plasma arc
processes. Carbon-arc gouging and oxygen cutting require
preheating and should not be used for high-alloy tool
steels.
Table 4.6
Automotive Cast Irons Requiring Deep
Undercutting for Weld Adherence
Designation
SAE Designation and NAAMS
Unalloyed gray iron
J431/G2500
Alloyed gray iron
J431/G3500
Unalloyed ferritic (nodular) iron
J434/D4512
Alloyed pearlitic (nodular) iron
J434/D5506
239
Preheating. Tool steel should be preheated for welding regardless of its composition or the particular service
conditions. Determining the best preheating temperature,
however, depends on the alloy content, workpiece configuration, and the heat-treated condition of the metal.
Generally, the high-alloy air-hardening steels require
higher and more closely controlled preheat temperatures. Typical preheat temperature ranges for several
types of tool steel are listed in Table 4.7. It should be
noted that these temperatures are not the same as those
used when preheating during the hardening process
prior to austenitizing. When preheating a hardened tool
steel for welding, the preheat temperature should not
exceed the temperature previously used for tempering.
Exceeding that temperature will over-temper and soften
the tool steel. If the tempering temperature is unknown
or the workpiece is a thick section, the preheat temperature should be selected at the lower end of the range
recommended for that steel. With annealed pieces or
thin sections, the workpiece should be preheated at the
upper end of the range for that specific alloy. In all
cases, the same preheat temperatures should be maintained as closely as possible between heating processes
to avoid cracking. Preheating a hardened tool steel also
involves controlling the heat input during the entire
welding process. The importance of preheating cannot
be overemphasized, especially for highly alloyed tool
steels.
Some of the commonly used methods of preheating
include electric or gas-fired furnaces, open gas flame
heating tables, and infrared hot beds. For localized
heating, hand-held torches or gas blowers can be used.
Welding Techniques
Techniques discussed in this section address workpiece
positioning, bead formation, maintaining interpass temperatures, peening, and the use of underlayments in thick
buildups.
Workpiece Positioning. When repairing the edges
of cutting tool blades with the shielded metal arc welding process, the blade should be positioned so that the
weld metal will flow or roll over the edges. Startup
marks can be avoided by striking the arc on an adjacent
plate.
Welding should be done in the flat position with the
axis slightly inclined. The direction of welding should
be uphill, if possible. Gravity will cause the molten weld
metal to flow downhill and form an even buildup. Slag,
if present, also will flow back and keep the crater clean.
Stringer beads rather than weave beads should be used.
Bead Formation. Welding travel speed should be
adjusted to produce an even deposit and to ensure uniform
fusion of the weld metal with the base metal. The weld
240
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Table 4.7
Typical Preheating, Postheating, and Tempering Temperatures for Welding Tool Steels
Annealed Base Metal
Hardened Base Metal
Deposit
Hardness,
HRCb
Preheat and
Postheat, °C (°F)a
Tempering
Temperature, °C (°F)
Deposit
Hardness,
HRCc
Type
Group
Preheat and
Postheat, °C (°F)a
W1, W2
Water-hardening
121–232 (250–450)
50–64
121–232 (250–450)
177–343 (350–650)
56–62
S1
Shock-resisting
149–260 (300–500)
40–58
149–260 (300–500)
204–649 (400–1200)
52–56
S5
Shock-resisting
149–260 (300–500)
50–60
149–260 (300–500)
177–426 (350–800)
52–56
S7
Shock-resisting
149–260 (300–500)
47–58
149–260 (300–500)
204–621d (400–1100)
52–56
O1
Oil-hardening
149–204 (300–400)
57–62
149–204 (300–400)
177–260 (350–500)
56–61
O6
Oil-hardening
149–204 (300–400)
58–63
149–204 (300–400)
177–316 (350–600)
56–61
A2
Air-hardening
149–204 (300–400)
57–62
149–204 (300–400)
177–538d (350–1000)
56–61
60–62
A4
Air-hardening
149–204 (300–400)
54–62
149–204 (300–400)
177–426d (350–800)
D2
Air-hardening
371–482 (700–900)
54–61
371–482 (700–900)
204–538d (400–1000)
58–60
H12, H13, H19
Hot-work
371–538 (700–1000)
38–56
371–538 (700–1000)
538–649d (1000–1200)
46–54
M1
High-speed
510–566 (950–1050)
60–65
510–566 (950–1050)
538–593d (1000–1100)
60–63
M2
High-speed
510–566 (950–1050)
60–65
510–566 (950–1050)
538–593d (1000–1100)
60–63
M10
High-speed
510–566 (950–1050)
60–65
510–566 (950–1050)
538–593d (1000–1100)
60–63
T1, T2, T4
High-speed
510–566 (950–1050)
60–66
510–566 (950–1050)
538–593d (1000–1100)
61–64
P20
Mold steel
426–538 (800–1000)
28–42
426–538 (800–1000)
480–595 (900–1100)
28–37
a.
b.
c.
d.
Preheat and postheat temperatures for welding.
Hardness varies with heat input and cooling rate.
Hardness after postheat and temper; hardness varies with heat input and cooling rate.
Double temper.
should be cleaned by frequent chipping or brushing, or
both.
A number of small passes should be used to fill the
groove. The bead size of final passes should be adjusted
so that the repair will be as close as possible to final
size, thereby minimizing subsequent grinding. When
extinguishing the arc, the arc length should be
decreased gradually. The electrode should be moved
back rapidly over the hot weld metal as the arc length
decreases. This will avoid deep craters and the melting
of adjacent sharp edges.
When repairing sections of cutting edges, a welding
technique should be used that will avoid craters and the
melting of the edges at the extreme ends of the repair.
Welding should progress in one direction, from one end
of the prepared groove to within a short distance of the
other end, as shown in Figure 4.9(A). Welding then
should progress in the opposite direction and overlap
the first bead, as illustrated in Figure 4.9(B). When
repairing deeply damaged cutting edges or drawing and
forming surfaces, welding should start at the bottom of
the groove and gradually fill the groove. Slightly higher
amperage should be used for the first and second passes
than for succeeding passes.
Interpass Temperature. The temperature of the
base metal should be kept as uniform as possible during
welding to ensure uniform hardness of the weld metal.
The base-metal temperature should not exceed its tempering temperature. Techniques such as intermittent
welding (sometimes called skip welding) and backstep
sequence welding using short stringer beads will help
control interpass temperature and, in turn, eliminate
underbead cracking.
Peening. Peening is a mechanical means of working
the weld metal and relieving stresses caused by shrinkage. Each weld bead should be peened before the metal
cools to below about 371°C (700°). This might require
occasional interruption of welding when the repair is
extensive. Ball peen hammers generally are used, but
pneumatic hammers are more efficient for large repairs.
The benefits of peening weld metal are well recognized,
and the method is commonly practiced. However, peen-
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
241
OVERLAP
Figure 4.9—Technique for Avoiding Craters or Edge Damage During Repair Welding
ing must be performed correctly to stretch the hot weld
metal deposit, or more harm than benefit may result.
Too little peening will not adequately relieve shrinkage
stresses; severe peening may cause cracking or have
other harmful effects on the weld.
Large Buildups and Underlayments. A thick
buildup of weld metal is often required to restore a
severely worn tool or die to original dimensions. The
deposition of a thick layer of hard weld metal may
cause the workpiece to crack. To minimize this possibility, the initial buildup should be accomplished with a
ductile, high-strength, nonhardenable filler metal, such
as low-alloy steel. Then this layer can be covered with a
harder weld metal that will provide the desired wear
resistance and toughness in the as-welded condition.
This procedure should not be used, however, if the
welded tool or die subsequently will be hardened and
tempered, because the deposited metal would be prone
to cracking during heat treatment.
When adhesion with the base metal is critical but difficult to achieve, such as when depositing buildups on
cast iron, the use of studs with screws or threaded
inserts can improve adhesion by providing a mechanical
bond. This will add strength and avoid possible underbead cracking in the heat-affected zone (HAZ).
Warping or distortion that occurs during welding
can be counteracted by preheating and peening. The use
of shims and clamps also is helpful. For example, before
welding the entire edge of a long shear blade, the blade
can be clamped into a reverse curvature to counteract
the shrinkage stress developed in the weld metal. If the
proper curvature is used, the welded blade will be
straight when released.
Postweld Heat Treatment
After welding, the repaired tool should be returned
to the furnace and the temperature of the tool should be
allowed to stabilize. Postheating permits the temperature to equalize throughout the tool prior to any subsequent treatment, thereby reducing internal stresses.
(Refer to Table 4.7 for typical postheat temperatures.)
The postweld heat treatments described below are
important, especially for high-alloy tool steels. For
example, these treatments can help with the major
problem of underbead cracking in air-hardening steels.
As a general rule, tools that have been welded in the
annealed condition should be annealed again to reduce
stresses and to facilitate subsequent reworking. Ideally,
this should be done immediately after welding and
postheat stabilization.
Slow Cooling. Tools or dies welded in the hardened
state that will be placed in service in that condition
should be slow-cooled to approximately 65°C (150°F)
242
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
following postheating. The cooling rate is critical because
it is during this cycle that the weld deposit achieves aswelded hardness. An accelerated cooling rate will produce a higher hardness, however, it may cause cracking
in the HAZ.
Tempering. The workpiece should be tempered immediately after postheating and slow cooling. This relieves
any stresses set up during welding, helps prevent cracking, and adds toughness to the weld deposit. The tool
should be brought up to temperature and held at that
temperature for 2.4 min/mm (1 hr/in.) of thickness.
After tempering, tools should be slow-cooled to room
temperature. Refer to Tables 4.4 and 4.7 for specific
temperatures for various types of tool steels.
AISI 4340
AISI H-12
(A)
COMPOSITE WELDING
For some applications, a tool can be fabricated with
a composite of dissimilar metals by depositing a base of
carbon steel or low-alloy steel, and then building up the
cutting edge or the working area, using a tool steel electrode that will provide the specific characteristics
required. An example of a composite tool is the design
of a hot punch shown in Figure 4.10(A). The composites are AISI 4340 for the steel base and AISI H-12 for the
cutting edge, as shown as the finished product in
4.10(B).
Many tools and dies are susceptible to breakage
because of the inherent hardness. Composite fabrication with a resilient core can reduce the likelihood of
this occurrence. Composite fabrication can provide a
working surface with the specified characteristics with a
tough, shock-resistant core. Another advantage is the
elimination of a hardening heat treatment, which means
that machining or drilling can be a final operation.
Sometimes it is impractical or impossible to construct a die from one type of tool steel that can satisfactorily perform multiple functions such as trim, form,
and restrike. However, this can be accomplished by
building up the cutting or working areas of a composite
die with dissimilar weld metals that have the required
characteristics.
To improve the service life of an existing tool steel
unit, the cutting edges or working surfaces can be resurfaced with tool steel that is more appropriate for the
application. However, the procedures must be designed
to consider prior heat treatment of the unit.
Base Metal
The base steel for a composite tool or die must have
the mechanical properties required for service at the
specific operating temperature. These properties may
include strength, toughness, or hardness, or any combination of these. Toughness is important for impact
(B)
Photograph courtesy of Cor-Met Inc.
Figure 4.10—(A) Design of a Hot
Punch and (B) the Finished Product
with AISI H-12 Tool Steel Cutting Edge
Welded to AISI 4340 Steel Base
loading. Hardness may be important for proper support
of the tool steel weld metal under high-compression
loading.
Carbon steels and low-alloy steels may be suitable
for most applications. When the service environment of
the tool is an elevated temperature, however, an alloy
steel with acceptable properties at service temperature
must be used for the base metal. Any heat treatment
AWS WELDING HANDBOOK 9.4
needed to provide the desired strength and hardness of
a low-alloy base should be performed prior to welding.
Filler Metals for Composite Welding
The filler metal for composite welding should be
selected to provide a weld deposit with the characteristics best suited for the service conditions and the type of
work that the tool will perform. Factors to be considered include resistance to heat, abrasion, and shock,
and also the thickness of metal to be cut or formed. In
fabrications with highly dissimilar components, the
matching of thermal expansion must be considered, especially in weldments that must handle high temperature or
cyclic temperature extremes.
CHAPTER 4—TOOL AND DIE STEELS
243
The size of the electrode depends on the extent of
welding and the type of preparation selected. Dilution
of the base metal also must be considered in the selection. Welding electrodes used for composite welding
include tool steel, cobalt, and nickel-base alloys. Applications include stamping, forging, and die-casting dies,
using AISI types S-7, H-12, and M-2.
Groove Design
Various designs may be used to prepare areas of cutting or forming tools for composite construction. Figure
4.11 illustrates several common types of preparation:
angle or chamfer, J-groove, U-groove, and flat buildup.
With the exception of the buildup type, the design should
RADIUS
(A) Angle or Chamfer
(B) J-Groove
(C) U-Groove Buildup
(D) Flat Buildup
Figure 4.11—Types of Preparation Designs for Work Areas of Cutting or Forming Tools
244
CHAPTER 4—TOOL AND DIE STEELS
provide a thickness that will minimize the effects of
dilution and provide the required strength after the edge
has been machined to size. A minimum thickness of
3.2 mm (1/8 in.) is common practice. Two or more
weld passes may be needed to fill the groove and minimize the dilution of the filler metal with the base metal.
The base metal surface of units that have large areas
to be filled should be prepared so that the finished weld
deposit will have adequate thickness (3.2 mm [1/8 in.]).
When converting existing tool steel units into composite units, an angle shown in Figure 4.11(A), or a Jgroove preparation 4.11(B) should be used. The edge
should be machined or ground back far enough to
allow for the deposition of a sufficient thickness of finished weld metal. U-groove buildup, shown in Figure
4.11(C) is common for a draw bead on automotive
stamping dies. Flat buildup, as shown in Figure 4.11(D)
commonly is used for engineering changes during die
construction.
Composite fabrications should be oversized to allow
for distortion during welding and metal loss during
finish machining. On ring or circular units, at least
3.2 mm (1/8 in.) generally should be provided for
grinding or machining to finished dimensions.
For the composite construction of cast-iron drawing
and forming dies, edges or areas to be faced generally
are prepared uniformly so that finished deposits are at
least 3.2 mm (1/8 in.) thick. Nickel alloy, copper-nickel,
or nickel-copper filler metal can be used as a transitional material for the tool- steel weld metal. Provisions
should be made during preparation to allow for transitional passes. This can be accomplished by removing
additional material during surface preparation to allow
for increased depth.
Preheat for Composite Fabrication
Typically, composite dies are constructed from mediumcarbon or low-alloy steels and are generally preheated in
the range of 427°C to 538°C (800°F to 1000°F). Small
units can be heated to the lower temperatures of the
preheat range and large units heated to the higher temperatures of the range.
Welding Procedures
In general, the welding procedures for composite
fabrication should be similar to those used in making
repairs to existing units, as described in the section
“Repair Procedures.” Because the base metal in composite fabrications is softer and usually has a low alloy
content, welding procedures (including heat input) are
less critical for composites than for the highly alloyed
tool steels. This is not the case for welding hard edges
or surfaces on cast irons. For these materials, greater
AWS WELDING HANDBOOK 9.4
care must be exercised to ensure a good weld without
underbead cracking.
Bonding to cast iron can be enhanced with threaded
studs that provide a mechanical attachment to the base
metal. Threaded studs are especially helpful for large
buildups.
Postweld Heat Treatment
As postweld heat treatment, a composite unit with
tool-steel weld deposits should be heated, cooled, and
tempered after the welding process is completed. Composite tools should be tempered in accordance with the
overall hardness requirement of the finished tool. When
nonhardenable low-alloy steel electrodes are used to provide the desired wear characteristics at certain locations on
the tool, a stress-relief heat treatment is recommended.
FLASH WELDING AND
FRICTION WELDING
The flash welding and friction welding processes can
be used to manufacture drills, reamers and similar cutting tools. High-speed tool steel bodies can be flash
welded or friction welded to carbon or alloy steel
shanks. This composite technique will provide a tough,
ductile shank at lower material cost than a one-piece unit.
Tool steels can be welded by the flash or friction
welding processes before and after heat treatment. Changes
in hardness are restricted to a relatively narrow heataffected zone (HAZ). Rapid cooling will reharden the
metal at the weld interface, including the expelled flash.
Preheating prior to welding will reduce the cooling rate
in the HAZ, producing a more ductile joint and minimizing the likelihood of cracking.18
BRAZING
For brazing applications, it is expedient to place tool
steels into two broad classifications: carbon steels and
high-speed steels. The carbon tool steels depend primarily on the high carbon content (0.60% to 1.40%) for
hardness. Alloying elements may be added to these
steels to impart special properties, such as reduced dis18. For detailed information on flash welding and friction welding,
refer to Chapters 3 and 5 of American Welding Society (AWS) Welding Handbook Committee, 2007, A. O’Brien and C. Guzman, eds.,
Welding Processes, Part 2, Vol. 3 of Welding Handbook, 9th ed.,
Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
245
tortion during heat treatment, greater wear resistance,
increased toughness, and better properties when placed
in high-temperature service. Because these alloy steels
retain substantial carbon content, however, they are
classified with the carbon tool steels for brazing considerations. Except for thin-section brazements, carbon
tool steels must be quenched rapidly during heat treatment to achieve optimum properties after tempering.
High-speed tool steels are classified separately because
the properties of these types depend on relatively high
percentages of alloying elements, such as tungsten, molybdenum, chromium, and vanadium. High-speed tool steels
and also some of the alloy tool steels previously mentioned require high austenitizing temperatures. This characteristic must be considered when developing a brazing
procedure.
brazing ranges are published by the American Welding
Society in Specification for Filler Metals for Brazing and
Braze Welding AWS A5.8/A5.8M.19
Filler Metals
Brazing Equipment
The choice of brazing filler metal depends on the
properties of the workpiece and the heat treatment
required to develop optimum properties. Most of the
brazing filler metals in the silver, copper, and copperzinc classifications may be used. The best filler metal
should be determined for each specific application. Various brazing alloy classifications, compositions, and
Oxyfuel gas torches, controlled-atmosphere furnaces, and induction heating equipment provide the
Joint Design
Generally, either butt joints or lap joints are used for
brazing tool steels. When a silver-bearing filler metal is
to be used, the joint clearance should be minimal, but
not less than 0.038 mm (0.0015 in.). Conversely, if the
joint clearance is wider than necessary, the strength of
the joint will be reduced almost to that of the filler
metal. Also, capillary action is reduced, so the filler
metal may fail to fill the joint completely, again lowering joint strength. The effect of joint thickness on tensile strength is shown in Figure 4.12.
19. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2004, Specification for Filler Metals for Brazing
and Braze Welding, AWS A5.8/A5.8M:2004, Miami: American Welding
Society.
LIVE GRAPH
Click here to view
0.05
0.15
THICKNESS OF JOINT, mm
0.25
0.35
0.45
0.55
0.65
140
120
800
100
650
80
500
60
350
0
0.003
0.006
0.009
0.012
0.015
0.018
0.021
0.024
40
0.027
THICKNESS OF JOINT, in.
Figure 4.12—Effect of Joint Thickness on Tensile Strength
TENSILE STRENGTH, ksi
TENSILE STRENGTH, MPa
950
246
CHAPTER 4—TOOL AND DIE STEELS
heating sources most commonly used for brazing tool
steels. The availability of equipment is frequently the
main factor when deciding the heating method to be
used.
Surface Preparation
The base metal surfaces must be clean and free from
oil, oxide, and other foreign material to ensure the
proper wetting and flow of the filler metal. A machined
or roughened surface is always preferable to a smoothly
ground or polished surface, since flux paste and brazing
filler metals do not wet and flow well on extremely
smooth surfaces.
Fluxes and Atmospheres
In general, brazing flux types 4A and 4B (classified
by the American Welding Society) are used for brazing
tool steels. However, some applications may require
modification of the flux, depending on the type of tool
steel and the brazing temperature. Brazing fluxes and
atmospheres are discussed in the Brazing Handbook,
published by the American Welding Society.20
Brazing in a controlled-atmosphere furnace (i.e.,
inert, vacuum, or reducing) may prevent oxidation during heating and may avoid the necessity of a postbraze
cleaning operation. If a controlled atmosphere is used,
steps must be taken to prevent carburization or decarburization of the tool steel.
Brazing Techniques
The brazing of carbon tool steel is best accomplished
prior to or during the hardening operation. The hardening temperature for carbon steel normally is in the
range of 760°C to 816°C (1400°F to 1500°F). If brazing is completed prior to hardening, the filler metal
must solidify at a temperature well above this range so
that the assembly can be handled without joint failure
when the unit is reheated to its hardening temperature.
A copper filler metal is frequently used for this purpose.
However, the high brazing temperature required when
using copper filler metal may adversely affect the microstructure and properties of some steels. Silver and copper-zinc filler metals are available that can be brazed at
temperatures in the range of 927°C to 982°C (1700°F
to 1800°F).
When brazing and hardening operations are combined, a filler metal that solidifies just above the austenitizing temperature generally is used. In this case, particular
attention must be given to the joint design with respect
20. American Welding Society (AWS) Committee on Brazing and Soldering, C. L. Jenney, ed., 2007, Brazing Handbook, 5th ed., Miami:
American Welding Society. Also see Reference 16.
AWS WELDING HANDBOOK 9.4
to handling the assembly, because the joint strength will
be very low at the austenitizing temperature of the steel.
The quenching procedure should be planned so that any
stress developed during quenching places the brazed
joint in compression rather than in tension.
Techniques for brazing alloy tool steels depend on
properties of the particular steel involved. The alloy
tool steels include a wide range of compositions and,
therefore, wide differences in behavior when heated.
The tool steel to be brazed should be studied carefully
to determine the proper heat-treating cycle, quenching
medium, brazing filler metal, and the technique for
combining the heat-treating and the brazing operations
to achieve maximum service qualities.
Quenching may produce steep temperature gradients
in a brazement, and the differential expansions and
contractions in the brazed joint may cause it to rupture.
Initially, the austenitic steel contracts as the temperature
lowers. Then, when the transformation to martensite
takes place, the steel expands. Finally, the martensitic
steel contracts as the temperature continues to decrease.
These changes do not take place uniformly because
cooling begins from the surface. If the assembly can be
properly supported during quenching, a filler metal that
solidifies well below the austenitizing temperature can
be used.
High-speed tool steels require hardening treatments
at temperatures above the usual silver brazing temperatures. Therefore, it is common practice to harden the
steels prior to brazing, then braze them during or after
the second tempering treatment. Tempering usually is
performed in the range of 538°C to 649°C (1000°F to
1200°F). Brazing filler metals such as BAg-1 or BAg-1a
can be used at temperatures above 566°C (1150°F) if
short brazing cycles are used. Hardened high-speed tool
steel may be brazed in this manner without over-tempering.
Broken tools made of high-speed tool steel may be
quickly repaired by brazing, a process often used to
avoid delays in production while awaiting a replacement tool. Broaches, circular saws, and milling cutters
are examples of tools that can be salvaged by brazing.
TOOL STEEL WELDING
APPLICATIONS
The die-casting industry relies on welding technology
to extend the life of a die and to reduce down time in
manufacturing processes. This increases profitability by
reducing the per-casting cost of manufacturing.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
247
REPAIR OF DIE-CASTING DIES
The die-casting or pressure-casting process provides
several advantages over other manufacturing processes.
Die castings are capable of producing complex shapes
to almost finished dimensions. Castings can be produced with thin walls, reducing metal costs. Multiplecavity dies are possible, resulting in increased production rates and improved surface qualities. However,
tooling must be carefully maintained in order to fully
realize these advantages, and welding is an integral part
of any die maintenance program.
Die castings frequently are exposed to extreme thermal fatigue and liquid-metal erosion. Dies made of various hot-working tool steels are designed to overcome
these adverse environments. The most common tool
steel used in the die-casting industry is AISI H-13,
quenched and tempered to 46-48 HRC.
Restoration Procedure
Photograph courtesy of Weld Mold Company
Figure 4.14—Cover Die Used
in Casting Pneumatic Motor Housing
As an example of a restoration procedure, the application described in this section is the reconditioning of
a set of dies for the housing of a pneumatic motor used
in the aluminum die-casting process. The dies originally
were constructed of AISI H-13 tool steel, quenched and
tempered to 46-48 HRC. The tooling consisted of an
ejector die and slides and a companion cover die. The
restoration procedure is illustrated in Figures 4.13, 4.14,
and 4.15.
Several steps were involved in the restoration of the
dies. The slides were secured first; then the cover-die
half was joined with the ejector-die half and locked in
Photograph courtesy of Weld Mold Company
Figure 4.15—Pneumatic Motor-Housing
Casting Being Ejected from Die
Photograph courtesy of Weld Mold Company
Figure 4.13—Ejector Die and Slides Used
in Casting a Pneumatic Motor Housing
place. A shot of molten metal 643°C to 666°C (1190°F
to 1230°F) was forced under great pressure at a high
velocity into the die set. The shot traveled through the
opening of the sprue (the vertical channel in the mold
used to pour molten metal) and was deflected by the
sprue spreader so that it flowed into the runners and
248
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
The weld deposits can be further age-hardened at
510°C (950°F), achieving hardness up to 49 HRC.
Deposits of maraging 18Ni (250) have exceptionally
high strength and a high level of toughness. As in all
tool and die welding, proper welding procedures must
be followed to achieve optimum results.
The tool steel was prepared for welding by grinding
to remove all impurities and defects in the metal. To
ensure an undiluted maraging deposit at the working
surface of the die, the base metal was undercut 3.2 mm
to 4.0 mm (1/8 in. to 5/32 in.), which is enough to facilitate at least three layers of weld metal. The die was
then preheated to 482°C (900°F) according to requirements of the base metal, AISI H-13. The maraging steel
18Ni (250) was deposited using GTAW. Direct current,
electrode negative (DCEN) was used with argon shielding gas dispensed at a flow rate of 7 L/min to 9 L/min
(15 ft3/h to 20 ft3/h). Short stringer beads of 76 mm to
101 mm (3 in. to 4 in.) were applied. The deposits were
peened thoroughly after each pass to offset shrinkage
stress. During welding, the interpass temperature was
maintained within ±56°C (±100°F) of the preheat temperature. After welding, the die was allowed to cool
slowly to room temperature, then it was machined in
the conventional way. Following machining, the die was
age-hardened at 496°C (925°F) for approximately two
hours, achieving a hardness value of 46 HRC to 49
HRC.
When die failures occur in the die-casting industry,
the die caster is faced with a decision: build new tooling
then into the die cavity. A system of runners and gates
directed the flow of metal into the die cavity, ensuring a
complete fill. Cooling water flowed through channels in
the die block to prevent overheating. After the casting
solidified, the slides were withdrawn, the cover die
opened, and the casting ejected. The die halves were
further cooled with a cold-water spray on the die surfaces following ejection of the casting.
In this example, the rapid cycle of heating and cooling caused thermal fatigue, or heat checking. A shortterm consequence of heat checking may be poor ejection, or hang-up, and also may result in cosmetic discontinuities in the castings. If not corrected, heat
checking could cause severe cracking or die breakage
that would have rendered the die unrepairable. The diecasting process also subjected the complex configuration of the die and the gating systems to severe liquidmetal erosion, or die wash. Die wash causes the die system to lose tolerance, which creates unusable castings.
Heat-checked and die-washed sections of the dies
were repaired successfully with maraging steel 18Ni
(250), employing the gas tungsten arc welding process.
This maraging steel was selected for the application
because it resists thermal fatigue and liquid-metal erosion. Table 4.8 shows the composition of the maraging
steel 18Ni (250) weld deposits, and Table 4.9 shows the
mechanical properties of these deposits.
Maraging 18Ni (250) weld deposits, in the as-welded
condition, are solution heat-treatable and are conventionally machinable in the 30 HRC to 32 HRC range.
Table 4.8
Composition of Maraging Steel 18Ni (250) Deposits
Ni
Co
Mo
Ti
Si
Mn
Fe
C
S
P
Zr
B
Al
18.50
7.50
4.80
0.40
0.10*
0.10*
Bal.
0.03*
0.01*
0.01*
0.01
0.003
0.10
*Maximum.
Table 4.9
Mechanical Properties of Maraging Steel 18Ni (250) Deposits
Tensile Strength
MPa
ksi
Yield Strength
MPa
Charpy V-Notch Impact Strength
ksi
Elongation,
%
Reduction in
Area, %
J
ft·lb
58
27
20
56
33.9
25
Tested at Room Temperature, Aged at 510°C (950°F)
1793
260
1758
255
11
Tested at 316°C (600°F), Aged at 510°C (950°F)
1609
233.4
Source: Eureka Welding Alloys.
1548
224.5
11.5
AWS WELDING HANDBOOK 9.4
or repair the damaged die by welding. In this example,
a new die set would be extremely costly and would take
several weeks to complete. An average weld repair
using maraging steel 18Ni (250) could be accomplished
in two days. This repair, including machining, was done
at a small fraction of the cost of a new die set.
Other advantages of weld repairs using maraging
steels are the following:
1. Quick turnaround time reduces the need for
back-up die sets;
2. Minor repairs can be made without removing
the die set from service; and
3. Weld deposits can be age hardened with localized heat treating with a torch, or age hardened
while in service.
REPAIR OF FORGING DIES
A wide range of low-alloy steels and tool steels are
used to construct forging dies, but the most commonly
used are low-alloy steels similar to AISI Type 4350 or
AISI Type H-13. The forging industry primarily uses
two types of hot-forging processes: open die and closed
die. The open-die process forms metals without completely restricting metal flow. The closed-die process
totally encompasses the hot steel being forged, and results
in high dimensional definition.
Two major types of equipment are used to make
forgings: press and hammer. The press squeezes hot
steel into shape, and the hammer pounds hot steel into
shape. In many cases, forging is accomplished using
three separate sets of dies called busters, blockers, and
finishers. First, a heated billet of steel (the metal to be
forged) is heated to 1149°C to 1260°C (2100°F to
2300°F). Then it is transferred through the three progressive sets of die impressions, forming it into its final
shape.
During the forming process, the die steel is subjected
to environments that include abrasion, impact, high
mechanical load, and extreme thermal fatigue. With
these adverse environmental conditions, die failure is a
frequent occurrence in the forging industry. Failure may
occur in the form of heat checking, wear, cracking, and
deformation. Cost factors in die manufacturing make
repair welding a value-driven means of reclaiming forging dies that have lost dimensional tolerances or cosmetic qualities. As a result, many forgers rely heavily on
weld deposits to function as the working surfaces of
their forging impressions.
A method of repairing forging dies called flood welding produces high-quality weld deposits at outstanding
deposition rates. Flood welding is not a specific welding
process; it is a special application of one of the highdeposition arc welding processes, such as shielded metal
arc welding or flux cored arc welding, in which large-
CHAPTER 4—TOOL AND DIE STEELS
249
diameter electrodes can be used. Flood welding is performed by removing the worn impression and flooding
it with molten weld metal at a deposition rate of up to
14 kg/h (30 lb/h). Shielded metal arc welding electrodes
are available in diameters up to 19 mm (0.75 in.). Flux
cored arc welding electrodes are available in wire form
in diameters up to 4 mm (0.156 in.).
Figure 4.16 shows the repair of a forging die in
progress. The flood-welding manipulating fixture contains a wire-feed system and water-cooled gas defusing
gun. The fixture is designed to keep the welder removed
from the excessive heat produced while preheating large
dies and during welding.
Procedure for Forging Die Reclamation
As an example of a flood welding application, the
procedure used to reclaim forging dies is described in
this section. The dies being reclaimed (the workpieces)
were a set of hot-press closed-die finisher impressions
used to forge automotive connecting rods. The dies
were originally constructed of a medium-carbon, lowalloy steel similar to AISI Type 4350. The press dies
consisted of a two-piece platter, (upper and lower),
making it possible to forge two connecting rods at once.
The dies had been used extensively until they began
to yield products with dimensional and visual quality
that was out of specification. The connecting rod
impressions showed cracking in the lower radii and
were exhibiting heat checking and wear on the raised
areas of the impressions. Reclamation began by preheating the dies to 538°C (1000°F) in a convection furnace. Then the die surface impressions were removed
using the air carbon arc gouging process with 16 mm
(5/8 in.) carbon electrodes at 1000 amperes (A). Figure
4.17 shows a welder peening weld deposits.
The workpiece surface removal was approximately
10 mm to 13 mm (3/8 in. to 1/2 in.) below the depth of
the deepest impression. The undercut was made to prevent dilution and to place the heat-affected zones in a
noncritical area. Next, the impressions were flood
welded with two chemically different filler metals.
Table 4.10 shows the composition of the materials
involved, heat-treatment, and hardness data. Table 4.11
shows the mechanical properties obtained from tests on
the filler metals.
Tough modified martensitic stainless-steel filler metal
was applied to the lower area of the impression, where
cracking was observed. In the upper impression areas,
where heat checking and wear were observed, a hotworking tool steel alloy similar to AISI Type H-12 was
applied. Welding was performed using 3.2 mm (1/8 in.)
flux cored wire and shielding gas of 75% argon, 25%
carbon dioxide, at 24 L/min (50 ft3/h). Welding current
was 700 A at 32 volts (V). During welding, the die
blocks were covered with a ceramic blanket to maintain
250
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Photograph courtesy of Cor-Met Inc.
Figure 4.16—Flood Welding Fixture for Repairing Dies
a minimum interpass temperature of 427°C (800°F).
The deposits were then peened with a 13 mm (1/2 in.)
pneumatic hammer fitted with a blunt chisel to reduce
shrinkage stresses. After welding, the dies were postheated at 538°C (1000°F) to equalize thermal gradients,
then slowly cooled in still air at room temperature to
allow the deposits to fully air-harden. A total of 73 kg
(160 lb) of the two filler metals was used to weld both
dies. The welded dies were then double tempered at
552°C (1025°F). The repair took four days to complete,
including double tempering. The actual welding took
one day.
The dies were machined with electrical-discharge
equipment and polished, then put back into service to
continue the forging of connecting rods. The reclamation procedure increased the life of a die by about 50%.
Final results will vary in other cases because of the
many variations that exist with the products of individual forging companies. The major variations are the
following:
1.
2.
3.
4.
Type of die design,
Mechanical loads applied,
Type and quality of forging equipment used,
Preheating temperature of dies before running,
and
5. Lubrication and coolants used on the dies during
service.
AWS WELDING HANDBOOK 9.4
CHAPTER 4—TOOL AND DIE STEELS
251
with an appropriate filler metal that has high tensile
strength.
Preheat
It is mandatory that sections be preheated to the
required temperature in a controlled and careful manner. Table 4.12 shows preheat temperatures and other
parameter values for the weld repair of AISI-P20 and
AISI-D2 tool steels. In some cases, preheating requires
large and sophisticated equipment. In all instances,
however, the preheat procedure requires far more than
simply heating the section with a torch. Sections must be
allowed to stabilize thoroughly at the preheat temperature.
Welding Process Selection
Micrograph courtesy of Cor-Met Inc.
Figure 4.17—Peening Weld Deposits
with a Blunt-Chisel Pneumatic Hammer
Gas tungsten arc welding and gas metal arc welding
provide superior control for repairing AISI-P20 and
AISI-D2 steels when finished sections and delicate
repairs are involved. Shielded metal arc welding is frequently acceptable with these steels and is often used,
although interpass temperature control can be a problem when using SMAW.
Peening
REPAIR OF AISI P20 AND D2 TOOLING
The discussion in this section applies to the repair of
tools, dies, and molds made of AISI P20 or AISI D2 tool
steels. An example is the repair of a die casting for an
auto body.
In general, sound welding procedures must be closely
followed to avoid a wide variety of potential problems.
Prior to welding, careful visual examination of the
failed section is necessary. In certain cases, a liquid penetrant inspection or a more sophisticated method, such
as ultrasonic inspection or magneflux, may be required.
The first obvious failure often is signaled by other problems within the entire section. A hardness test sometimes aids in revealing problem areas.
Ideally, peening should occur immediately prior to
and during transformation to martensite. This relieves
transformational stresses, which often can exceed the
yield strength of the material. These stresses also are
quite subtle, and during subsequent production they
tend to manifest themselves as peripheral cracks that
either were not visible or did not exist at the conclusion
of an otherwise successful repair-welding operation.
Stringer beads with a maximum length of 75 mm (3 in.)
are recommended. The bead should not be peened
while it still shows color from the heat.
Postheat
Postheat is a necessity when welding tool steels. The
workpiece temperature must be equalized as soon as
possible after welding in order to reduce the level of
residual stress. Postheat and preheat temperatures generally are the same as those shown in Table 4.7.
Preparation
To prepare the workpiece for repair welding, cracks
must be entirely removed down to sound metal. A clean
surface is required, ground to remove the surface material a minimum of 5 mm (3/16 in.) below the general
work surface. In cases involving catastrophic failures,
pieces must be clamped together and firmly tack-welded
Cooling
Weld repairs in tool steel must be cooled in a
controlled manner. Sections should be covered with
insulating blankets to ensure uniform cooling. The temperature should not fall below the range of 66°C to
93°C (150°F to 200°F) prior to tempering.
252
CHAPTER 4—TOOL AND DIE STEELS
AWS WELDING HANDBOOK 9.4
Table 4.10
Materials Used in Forging-Die Reclamation
Composition, %
C
Mn
Si
Cr
Mo
Ni
W
V
Heat
Treatment
Hardness,
HRC
Austenitized at 871°C (1600°F).
Oil quenched, tempered at 605°C
(1120°F).
37–40a
Austenitized at 871°C (1600°F).
Oil quenched, tempered at 605°C
(1120°F).
37–40a
Double tempered for 1 h at 552°C
(1025°F).
44–48b
41–45a
Fe
Original Die Block
0.55
0.40
0.25
1.0
0.40
1.0
—
—
Bal.
Filler Metal in Upper Impression Areas
0.55
0.40
0.25
1.0
0.40
1.0
—
—
Bal.
Filler Metal in Lower Impression Areas
0.20
0.40
0.40
10.5
2.0
2.0
—
—
Bal.
a. Tempered hardness.
b. As-welded hardness.
Source: Eureka Welding Alloys.
Table 4.11
Mechanical Properties of Filler Materials in Forging-Die Reclamation
Tensile Strengtha
MPa
Charpy V-Notch Impact Strengthb
Yield Strength
ksi
MPa
ksi
Elongation,
%
Reduction in
Area, %
J
ft·lb
5.0
—
—
30.5
28.1
20.7
Filler Metal in Upper Impression Areas
1262
183
1103
160
2.0
Filler Metal in Lower Impression Areas
1144
166
889
129
9.6
a. Samples tested at 370°C (700°F).
b. Samples tested at 230°C (450°F).
Source: Eureka Welding Alloys.
Table 4.12
Some Parameter Values for Weld Repair of Tool and Die Steels
Preheat and Postheat Temperatures
Tempering Temperature
Steel
°C
°F
Filler Metal
°C
°F
AISI-P20
510
950
P20
510–538
950–1000
AISI-D2
482
900
M2/H19
482–510
900–950
AWS WELDING HANDBOOK 9.4
Fluxes and Atmospheres
Tempering after welding generally is required for
tool and die steels. Tempering further reduces the martensitic transformational stresses in the weld deposit
and heat-affected zone (HAZ). The tempering temperature should not exceed the original tempering temperature of the type of steel involved.
SAFE PRACTICES
Chapter 17 of the Welding Handbook, 9th edition,
Volume 1 is a comprehensive presentation of safety in
welding, brazing, soldering, and cutting intended for
reference collectively for the five volumes of the 9th edition; thus details of these topics are not fully addressed
in this chapter.21 Safety and health concerns regarding
the metals and materials discussed in this chapter are
covered briefly in this section.
The American National Standards Institute (ANSI)
standard, Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1, should be consulted.22 This standard is published by the American Welding Society and
can be downloaded from the Internet at http://www.
aws.org. Appendix A of this volume provides a list of
safety and health standards, publishers, and facts of
publication.
Safe practices must be followed during the welding
and heat treatment of tool steel to prevent injury to personnel and damage to the plant and equipment. The
equipment must be installed properly and must include
appropriate safety devices for the particular operation.
All equipment should be installed and operated according to the safety recommendations of the equipment
manufacturer.
Personnel must be equipped with appropriate eye,
ear, face, and body protection to avoid burns from the
arc, spatter, hot metal, or quenching media. Adequate
ventilation must be provided to remove harmful fumes
and gases from the breathing zone of persons working
in the area. Since tool steels (and the consumables
used to weld or braze them) contain significant
amounts of elements such as chromium, manganese,
molybdenum, nickel, and vanadium, compounds
including these elements can be expected in the fumes
generated. Material Safety Data Sheets should be
reviewed and the recommended safety precautions
21. Welding Handbook Committee, Jenney, C. L. and A. O’Brien,
eds., 2001, Welding Science and Technology, Vol. 1 of Welding Handbook, 9th ed., Chapter 17, Miami: American Welding Society.
22. American National Standards Institute (ANSI) Accredited Standards Committee Z49, 2005, Safety in Welding, Cutting, and Allied
Processes, ANSI Z49.1:2005, Miami: American Welding Society.
Available on the Internet at www.aws.org.
CHAPTER 4—TOOL AND DIE STEELS
253
should be followed. Appropriate PPE (personal protective equipment) should be used as required, based on an
evaluation of both the fume composition and the potential exposure levels.
Applicable federal, state, and local codes should be
followed when welding and heat treating tool steels.
The United States Department of Labor, Occupational
Safety and Health Administration, publishes safety
requirements in Occupational Safety and Health Standards for General Industry, in Code of Federal Regulations (CFR) Title 29, CFR 1910, Subpart Q.23
CONCLUSION
Descriptions of tool steels, their classifications and
properties, welding processes and techniques, and
examples of several welding applications in this chapter
provide basic information on the fabrication or repair
of tools and dies by welding. This information may provide significant advantages to manufacturers and users
in terms of cost savings and high performance. For
example, a worn or damaged tool or die can be
restored, saving the cost of design, material, machining,
heat treatment, tryout, and transportation related to
producing a custom one-of-a-kind tool or die. A tool or
die can be designed for fabrication so that the work
areas of a tool perform the intended service while less
expensive base metal provides the properties required
by less critical areas.
Repairs and restorations can be done quickly and the
component placed back in service with minimum down
time. Successful repairs or upgrading wear resistance
properties on critical work surfaces can be accomplished by carefully following the sound welding and
heat treatment procedures provided in this chapter.
BIBLIOGRAPHY
American National Standards Institute (ANSI) Accredited
Standards Committee Z49. 2005. Safety in welding,
cutting, and allied processes. ANSI Z49.1:2005.
Miami: American Welding Society. Available on line:
www.aws.org.
American Welding Society (AWS) Committee on Definitions and Symbols. 2010. Standard Welding Terms and
Definitions. AWS A3.0M/A3.0:2010. Miami: American
Welding Society.
23. Occupational Health and Safety Administration (OSHA) Title 29—
Labor. Occupational Safety and Health Standards for General Industry. In Code of Federal Regulations (CFR) 1910, Subpart Q. Washington, D.C.: United States Government Printing Office.
254
CHAPTER 4—TOOL AND DIE STEELS
American Welding Society (AWS) Committee on Filler
Metals and Allied Materials. 2004. Specification for
filler metals for brazing and braze welding. AWS A5.8/
A5.8M:2004 Miami: American Welding Society.
American Welding Society (AWS) Welding Handbook
Committee. C. Jenney and A. O’Brien, eds. 2001.
Welding science and technology. Vol. 1 of Welding
handbook. 9th ed. Miami: American Welding Society.
www.aws.org.
American Welding Society (AWS) Welding Handbook
Committee. A. O’Brien, ed. 2004. Welding processes, Part 1. Vol. 2. of Welding handbook. 9th ed.
Miami: American Welding Society. www.aws.org.
American Welding Society (AWS) Welding Handbook
Committee. A. O’Brien and C. Guzman, eds. 2007.
Welding Processes, Part 2. Vol. 3 of Welding Handbook. 9th ed. Miami: American Welding Society.
www.aws.org.
ASM International (ASM). 1993. ASM handbook.
Welding, brazing, and soldering. Vol. 6. 9th ed.
Materials Park, Ohio: ASM International. www.
asminternational.org.
ASM International (ASM). 1996. H. Chandler, ed. Heat
treater’s guide: Practices and procedures for nonferrous alloys. 2nd ed. Materials Park, Ohio: ASM
International.
ASM International (ASM). 1991. Heat treating. Vol. 4
of ASM handbook. Materials Park, Ohio: ASM
International.
Becherner, B. A. and T. J. Witheford. Rev. 1990. Introduction to heat treating of tool steels. Materials
Park, Ohio: ASM International.
Jefferson, T. B. and G. Woods. 1990. Metals and How
to Weld Them. 2nd ed. Cleveland: The James F.
Lincoln Arc Welding Foundation.
Linnert, G. E. 1994. Welding Metallurgy: Carbon and
alloy steels, Vol. 1. Fundamentals. 4th ed. Miami:
American Welding Society.
North American Automotive Standards (NAAMS).
Auto/Steel Partnership, 2000 Town Center, Southfield, Michigan 48075. www.naamsstandards.org.
Occupational Health and Safety Administration
(OSHA) Title 29—Labor. Occupational safety and
health standards for general industry in Code of federal regulations (CFR) 1910, Subpart Q. Washington, D.C.: United States Government Printing Office.
www.osha.gov.
Secretariat, International Institute of Welding, 90 Rue
del Vanesses, 93420 Villepinte, France (ZI Paris
Nord 2 BP:50362-F95942 ROISSY CDG, Cedex,
France).
Society of Automotive Engineers (SAE International).
1993. Metals and alloys in the unified numbering
system. 6th ed. Warrendale, Pennsylvania: Society of
Automotive Engineers. www.sae.org.
AWS WELDING HANDBOOK 9.4
SUPPLEMENTARY
READING LIST
American Society for Metals (ASM International).
1980. Metals handbook: properties and selection:
stainless steels, tool materials and special-purpose
metals. Vol. 3. 9th ed. Materials Park, Ohio: American
Society for Metals.
Bailey, N. 1971. Weldability and toughness of maraging
steel. Metal construction 3(1): 1–5.
Bailey, N. and C. Roberts. 1978. Maraging steel for
structural welding. Welding journal 57(1): 15–28.
Blauel, J. G., H. R. Smith, and G. Schulze. 1974. Fracture toughness study of a Grade 300 maraging steel
weld joint. Welding journal 53(5): 211-s–218-s.
Cary, H. B. 1994. Modern welding technology. 3rd ed.
Troy, Ohio: Hobart Brothers Company.
Eureka Welding Alloys. Tool and die welding manual:
tool and die welding procedures. Madison Heights,
Michigan: Eureka Welding Alloys.
Hall, A. M. 1971. Introduction to today’s ultra-highstrength structural steels. STP 498. Philadelphia:
American Society for Testing and Materials.
Irving, R. 1992. Plasma arc welding takes on the advanced
solid rocket motor. Welding journal 71(12): 49–50.
Krauss, G. and H. Nordberg. 1987. Tool materials for
molds and dies—application and performance. Proceedings of a conference at the Colorado School of
Mines, Golden, Colorado.
Lang, F. H. and N. Kenyon. 1971. Welding of maraging
steels. Bulletin 159. New York: Welding Research
Council.
Philip, T. V. and T. J. McCaffery. 1991. Ultrahighstrength steels. Metals handbook: properties and
selection—irons, steels, and high-performance alloys.
Vol. 1. 10th ed. 43048. Materials Park, Ohio: ASM
International.
Roberts, G. A. and R. A. Cary. 1980. Tool steels. 4th ed.
Materials Park, Ohio: American Society for Metals.
Rorhbach, K. and M. Schmidt. 1991. Maraging steels.
Metals handbook: properties and selection: irons,
steels, and high-performance alloys. Vol. 1. 10th ed.
793–800. Materials Park, Ohio: ASM International.
Sinha, P. P., S. Arumugham, and K. V. Nagarajan. 1993.
Influence of repair welding of aged 18Ni 250 maraging steel weldments on tensile and fracture properties. Welding journal 72(8): 391-s–396-s.
Stout, R. D. 1987. Weldability of steels. 4th ed. New
York: Welding Research Council.
Weld Mold Company. Technical welding handbook:
tool and die welding procedures. Vol. 1. 3rd ed.
Brighton, Mich.: Weld Mold Company.
Wilson, R. 1975. Metallurgy and heat treatment of tool
steels. New York: McGraw-Hill.
AWS WELDING HANDBOOK 9.4
255
CHAPTER
C H A P T E5 R 9
STAINLESS AND
HEAT-RESISTANT
STEELS
Prepared by the
Welding Handbook
Chapter Committee
on Stainless and HeatResistant Steels:
T. J. Lienert, Chair
Los Alamos National
Laboratory
M. C. Balmforth
Exponent, Inc.
S. D. Brandi
University of Sao Paulo
J. F. Grubb
ATI Allegheny Ludlum
P. W. Hochanadel
Los Alamos National
Laboratory
D. J. Kotecki
Damian Kotecki Welding
Consultants
L. Li
Utah State University
M. J. Perricone
RJ Lee Group
P. F. Stratton
The Linde Group
Welding Handbook
Volume 4 Committee
Member:
W. Lin
Pratt & Whitney
Contents
Introduction
256
Martensitic
Stainless Steels
272
Ferritic Stainless Steels 282
Austenitic
Stainless Steels
289
Precipitation-Hardening
Stainless Steels
334
Superferritic
Stainless Steels
340
Superaustenitic
Stainless Steels
343
Duplex Stainless Steels 351
Brazing and Soldering
of Stainless Steels
369
Thermal Cutting
378
Applications
380
Safe Practices
385
Bibliography
386
Supplementary
Reading List
390
Photograph courtesy of Duna Photography—Brushed Stainless Steel-Clad BP Bridge in Millennium Park, Chicago
256
AWS WELDING HANDBOOK 9.4
CHAPTER 5
STAINLESS AND HEATRESISTANT STEELS
INTRODUCTION
Stainless steels are alloy steels with a nominal chromium (Cr) content of at least 11 weight percent (wt %),
with or without other alloy additions.1, 2 The oxidation
and corrosion resistance of these alloy steels are attributed to the presence of a passive chromium-rich oxide
film on the surface. The chromium-rich oxide can be
damaged, but will quickly reform if oxygen is available.
When exposed to conditions that damage the passive oxide
film, stainless steels are subject to corrosive attack. The
rate at which a stainless steel develops a passive film in
the atmosphere depends on its chromium content. Polished stainless steels remain bright and tarnish-free
under most atmospheric conditions. Exposure to elevated
temperatures increases the thickness of the oxide film.
An example of the use of stainless steel combining
art with utility is shown on the title page of this chapter:
the stainless steel-clad BP Bridge and the Jay Pritzker
Pavillion in the Millennium Park, Chicago. The bridge,
a first-prize winner in national competition, is an architectural work of art, provides conveyance to the 120 ft
high pavilion, and is a sound barrier to street noises.
GENERAL CATEGORIES OF STAINLESS
STEELS
Stainless steels normally are classified according to
their crystal structures at room temperature. Several
general categories of stainless steels exist, including the
following:
1. The following chromium-molybdenum steels, with less than 11%
chromium, are not covered in this chapter: 2-1/4Cr-1Mo, 2-1/4Cr1Mo-Nb, 5Cr-1Mo, 7Cr-1Mo, 9Cr-1Mo, and 9Cr-1Mo-V. These steels
are discussed in Chapter 1 of this Volume.
2. Definitions of welding processes and standard welding terms used
in this chapter are from American Welding Society (AWS) Committee
on Definitions and Symbols, 2010, Standard Welding Terms and Definitions, AWS A3.0M/A3.0:2010, Miami: American Welding Society.
1. Austenitic type based on the face-centered cubic
(FCC) crystal structure;
2. Ferritic type with a body-centered cubic (BCC)
structure;
3. Martensitic type with a body-centered tetragonal
(BCT) crystal structure;
4. Duplex alloys containing two of these crystal
structures; for example, a common type contains
FCC and BCC structures; and
5. Precipitation-hardening (PH) alloys.
Austenitic, ferritic, martensitic and duplex stainless
steels (1, 2, 3, and 4 in the list) are categorized according to their crystal structure, and if they are additionally
strengthened via precipitation hardening they are referred
to as the PH types (5 in the list). For example, one type
of PH stainless steel alloy has a martensitic matrix that
is strengthened by precipitation of submicron-sized intermetallic phases during heat treatment.
This chapter is divided into sections that discuss
common grades and specialty grades of stainless steels.
The four common grades are austenitic, ferritic,
martensitic, and duplex. The specialty grades include
precipitation-hardening, superaustenitic, superferritic,
supermartensitic and superduplex types. Some of the
information presented in this chapter is expressed in
generic terms for the common grades; however, specialty
grades—many of which are known by proprietary
names—are discussed in more specific metallurgical terms.
The metallurgical characteristics of stainless steels
are related to the effects of alloying additions on phase
transformations. The alloying additions essentially expand
or constrict the various phase fields of the steel. The
major alloying elements that affect these characteristics
are chromium (Cr), nickel (Ni), and carbon (C). Other
alloying elements also contribute to the metallurgical
characteristics and corrosion resistance of the stainless
steels.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
The martensitic stainless steels are hardenable by heat
treatment because of the austenite-to-martensite transformation during cooling. In martensitic precipitationhardening steels, transformation strengthening may be
augmented by precipitation of a second phase in a lowcarbon martensitic matrix. In semiaustenitic, precipitationhardening stainless steels, precipitation occurs in the
austenite prior to martensite formation. The austenite is
then destabilized and transforms to martensite during
cooling. A few specialty alloys may be hardened by the
precipitation of a second phase in austenite. Other stainless steels are nonhardenable, either because they cannot
be transformed to austenite on heating (ferritic types) or
because the austenite is stable at room temperature and
below (austenitic types).
A continuum exists between the austenitic stainless
steels and the nickel alloys containing chromium and
iron. A steel (or ferrous alloy) is an alloy in which iron
is the major constituent; a nickel alloy has nickel as the
main constituent. In either case, the amount of the major
constituent may be less than 50%.
CLASSIFICATION
The common-grade wrought stainless steels are classified and assigned designations by the American Iron and
Steel Institute (AISI) according to chemical composition.3, 4
Table 5.1 shows the AISI classification series for three
common-grade wrought stainless steels. In the 2XX Series,
manganese and nitrogen are substituted for part of the
nickel.
3. American Iron and Steel Institute, 1140 Connecticut Ave., N.W.,
Suite 705, Washington D.C., 20036, www.steel.org.
4. At the time of the preparation of this chapter, the referenced codes
and other standards were valid. If a code or other standard is cited
without a date of publication, it is understood that the latest edition
of the document referred to applies. If a code or other standard is
cited with the date of publication, the citation refers to that edition
only, and it is understood that any future revisions or amendments to
the code or standard are not included; however, as codes and standards undergo frequent revision, the reader should consult the most
recent edition.
Table 5.1
Classifications of
Common-Grade Wrought Stainless Steels
AISI Classification Series
Major Alloy Elements
2XX
Cr-Ni-Mn
3XX
Cr-Ni
4XX
Cr
257
Wrought stainless steels developed after AISI ceased
issuing designations, and a number of earlier alloys are
not classified in the AISI system. The common designation for some of these use the same numbering system
as the AISI types; others are known by trade names.
Many of the stainless steels also have minor variations
in composition designed to achieve special carbon control for corrosion resistance or to use in high-temperature
applications. Other variations provide chemical stabilization with aluminum (Al), niobium (Nb), or titanium
(Ti), and higher sulfur (S) or selenium (Se) for better
machinability.
ASTM International (formerly the American Society
for Testing and Materials) developed another designation
system for stainless steels, the “XM” system, which was
used for a number of stainless steels.5 Following the
introduction of the UNS system (noted below), the XM
system was discontinued. However, a few specifications
still use the XM designations and a few alloys (e.g.,
XM-12 [15-5PH]) still are frequently described by these
designations.
Corrosion-resistant stainless steel castings are standardized by the Alloy Casting Institute, a division of the
Steel Founders Society of America.6 These cast types typically are designated by a letter-number system (HX-XX
or CX-XXX) such as HC, HK-30, or CF-8M. Many
cast types (e.g., ASTM A 351) are similar to their counterparts in the AISI wrought stainless steel classification
system.
Most stainless steels also have been assigned numbers in the SAE-ASTM publication, Metals and Alloys
in the Unified Numbering System (UNS). Wrought and
cast stainless steels are identified by the letters S and J,
respectively, followed by five digits (e.g., UNS S30403
is the designation for Type 304L).
PHYSICAL METALLURGY OF STAINLESS
STEELS
As previously mentioned, stainless steels are defined
as steels with a minimum of 11 wt % chromium content. Consequently, salient features of the physical metallurgy of stainless steels can be understood with the
aid of the iron-chromium (Fe-Cr) phase diagram, shown
in Figure 5.1. All alloys in this binary system solidify as
delta (δ) ferrite. The austenite gamma (γ) phase exists
in a region referred to as the γ loop. The addition of
chromium to pure iron promotes constriction of the
temperature range over which the austenite phase exists
until it disappears at ~13% chromium. Hence, alloys with
5. ASTM International, 100 Barr Harbor Drive, West Conshohocken,
Pennsylvania 19428-2959, www.astm.org.
6. Steel Founders Association of America (SFAA), 780 McArdle Dr.,
Unit G, Crystal Lake, IL 60014, www.sfaa.org.
258
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
Click here to view
Source: Adapted from ASM International (ASM), 1996, Cr-Fe Phase Diagram, Binary Alloy Phase Diagrams, 2nd edition, Materials Park, Ohio: ASM International.
Figure 5.1—The Fe-Cr Binary Phase Diagram
chromium content less than ~13% undergo transformations from ferrite to austenite during heating into the γ
loop and then back to ferrite on cooling. The minimum
point in the loop occurs at ~850°C (~1562°F) and ~6.5%
chromium. Rapid cooling of an alloy from the austenite
phase field promotes the formation of the nonequilibrium
martensite phase.
At chromium levels around 45% to 50%, the brittle
sigma (σ) phase precipitates from the ferrite phase
during cooling at temperatures below about 830°C
(1526°F). Sigma is an intermetallic phase with a composition near FeCr (1:1 stoichiometric ratio). The formation of sigma normally results in loss of toughness
and can lower corrosion resistance because it removes
chromium from the surrounding matrix as it forms. At
temperatures below approximately 475°C (885°F), the
ferrite phase separates into a low-chromium ferromagnetic alpha (α) phase and a high-chromium paramag-
netic α' phase via a spinodal decomposition reaction.
This separation leads to the so-called 475°C (885°F)
embrittlement phenomenon that strongly influences
mechanical properties. Further discussions of the sigma
phase and the 475°C (885°F) embrittlement phenomenon are presented in subsequent sections of this chapter.
Alloy additions to the Fe-Cr system will modify
phase stabilities and produce changes to the Fe-Cr diagram. Figure 5.2 illustrates the influence of nickel additions on the shape and extent of the γ loop. Additions of
nickel act to extend the single-phase γ region to higher
chromium levels and to lower temperatures. With 6%
nickel, the γ loop extends to ~22% chromium and the γto-α transformation drops to about 700°C (1292°F).
Like nickel, manganese acts to stabilize the γ phase but
to a lesser extent on a wt % basis.
Similar effects of the extension of the γ loop occur
with additions of carbon and are shown in Figure 5.3.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
259
LIVE GRAPH
Click here to view
Source: Adapted from Kunze, E., 1976, Special Alloy Region of the Quaternary System Fe-C-Cr-Ni, TEW Technische Berichte 2(1): 70–74.
Figure 5.2—The Effects of Nickel Additions on the Extent of the Gamma (γ) Loop in the Fe-Cr System
The combined effects of nickel and carbon (or nitrogen)
additions allow for suppression of the low temperature
γ-to-α transformation and subsequent retention of the
metastable γ phase to room temperature. These effects
provide the foundation for production of the austenitic
stainless steel classification.
In addition to the expansion of the γ loop region to
higher chromium levels and to lower temperatures, carbon additions have another effect (refer to Figure 5.3).
Precipitation of mixed Fe-Cr carbides, (shown by the
symbol “C” in the diagram), usually (Fe,Cr)23C6, occurs
when the solubility limit for carbon is exceeded in the
matrix for the Fe-Cr-C system. The formation of these
carbides can have an effect on the local corrosion resistance of the alloy if considerable amounts of chromium
are depleted from the matrix. (Two types of ferrite are identified in Figure 5.3.) The δ ferrite is the high-temperature
ferrite phase that forms from the liquid during solidifi-
cation, whereas the α ferrite is the low-temperature ferrite that forms from decomposition of the austenite (γ).
The primary (initial) solidification phase of alloys
within the Fe-Cr-Ni ternary system may be ferrite or
austenite, depending on the composition. Figure 5.4
shows the liquidus projection of the Fe-Cr-Ni ternary
system. The boundary curve or line of two-fold saturation extending from the peritectic reaction (at ~5%
nickel, lower left) in the Fe-Ni binary system to the
eutectic reaction (at ~50% nickel, upper right) in the
Ni-Cr binary system separates the composition regions
with different primary solidification modes. Solidification isotherms are plotted in each region. Alloys with
composition to the right and below the boundary curve
(i.e., nickel-rich alloys) solidify as austenite with the FCC
structure. Conversely, alloys with compositions lying to
the left and above the boundary curve (chromium-rich
alloys) solidify as ferrite with the BCC structure.
260
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
Click here to view
Source: Adapted from Bungardt, K., E. Kunze, and E. Horn, 1958, Investigations into the Structure of the System Iron-ChromiumCarbon (in German), Arch. Eisenhuttenwes 29(3): 193–203.
Figure 5.3—Pseudo-Binary Section of the Fe-Cr-C System with 0.05 wt % Carbon
PROPERTIES
WELDABILITY
The physical and mechanical properties of stainless
steels are controlled by the composition, the volume
fraction, the morphology of the metallurgical phases
present, and the prior work history of the steels.7 Typical physical properties of the various common and specialty grades of stainless steels are shown in Table 5.2,
with the physical properties of carbon steel placed in
the final column for comparison.
Thermal expansion, thermal conductivity, and electrical resistivity have significant effects on the weldability of stainless steels. The relatively high coefficient of
thermal expansion and the low thermal conductivity of
austenitic stainless steels require more complex techniques to minimize distortion during welding than are
needed for the other stainless steels, low-alloy steels, and
carbon steels. Because of lower thermal conductivity,
stainless steel base metals and filler metals require lower
heat input than carbon steel. Also, stainless steels can be
welded with the resistance spot and resistance seam processes with lower welding current because the electrical
resistivity of stainless steels is higher than that of carbon
steel.
7. The mechanical and physical properties, heat treatment, corrosion
resistance, and fabrication of specific stainless steels are discussed in
the ASM Handbook, Vol. 1, 10th ed., 1990, Materials Park, Ohio:
ASM International.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
261
Source: Adapted from Jenkins, C. M., E. H. Bucknall, C. R. Austin, and G. A. Mellor, 1937, Some Alloys for Use at High Temperatures, Part IV: The
Constitution of Some Alloys of Nickel, Chromium and Iron, Journal of the Iron and Steel Institute 136: 187–222.
Figure 5.4—Partial Liquidus Projection for the
Fe-Cr-Ni System (Temperatures in °C)
Fully austenitic stainless steels are essentially nonmagnetic, or more correctly, they are paramagnetic.
Typical relative magnetic permeabilities for various austenitic stainless steels are less than 1.01. Relative magnetic permeability relates to the ability of a material to
support a magnetic field compared to the ability of vacuum to support a magnetic field. However, the relative
magnetic permeability of austenitic stainless steels can
be increased by cold working, because of the formation
of stress-induced martensite, and by alloying with elements that produce some ferrite. Ferritic and martensitic
stainless steels are ferromagnetic materials with relative
magnetic permeabilities in the range of 600 to 1200.
GENERAL WELDING CHARACTERISTICS
The metallurgical features of the common-grade
stainless steels generally determine the weldability characteristics of the steel alloys in that group. The weldability of martensitic stainless steels is affected greatly
by their propensity for hydrogen-induced cold cracking.
Welded joints in ferritic stainless steel can have low
ductility as a result of grain coarsening that is related to
the absence of an allotropic phase transformation on
cooling. The weldability of austenitic stainless steels is
governed by their susceptibility to solidification and liquation cracking.
Stainless steels can be joined by most welding processes, with some restrictions. In general, stainless steels
that contain aluminum or titanium, or both, can be arcwelded only with the gas-shielded processes using similar filler metals. These steels also can be resistance
welded. The weld joint efficiency depends on the ability
of the welding process and procedures to produce
nearly uniform mechanical properties in the weld metal,
heat-affected zone (HAZ), and base metal in the aswelded or postweld heat-treated condition. These properties can vary considerably with ferritic, martensitic,
and the specialty grade stainless steels.
The weldability of the steel, the choice of welding
consumables, and various suitability-for-service conditions (including temperature, pressure, creep, toughness,
and corrosion resistance in various environments) require
careful evaluation because of the complex metallurgical
aspects of stainless steels. When specific information is
not available, the steel manufacturer should be consulted for technical data on the suitability for service of
the weldment.
Stainless Steels
Precipitation Hardening
Units
Martensitic
Ferritic
Austenitic
Martensitic and
Semiaustenitic
Austenitic
(A 286)
Superaustenitic
Superferritic
Duplex
Carbon
Steel
Density
Mg/m3
[lb/in.3]
7.8
[0.28]
7.8
[0.28]
7.8–8.0
[0.28–0.29]
7.8
[0.28]
7.9
[0.29]
8.0–8.3
[0.29–0.30]
7.8
[0.28]
7.8–8.0
[0.28–0.29]
7.8
[0.28]
Elastic modulus
GPa
[Msi]
200
[29]
200
[29]
193–200
[28–29]
200
[29]
200
[29]
186–197
[27–28.5]
200–214
[29–31]
193–200
[28–29]
200
[29]
Mean coeff. of thermal
expansion, 0°C–538°C
[32°F–1000°F]
μm/(m · °C)
[μin./(in. · °F)]
11.6–12.1
[6.4–6.7]
11.2–12.1
[6.2–6.7]
17.0–19.2
[9.4–10.7]
11.9
[6.6]
16.5
[9.2]
16.0–17.0
[8.9–9.4]
10.3–11.2
[5.7–6.2]
13.3–13.7
[7.4–7.6]
11.7
[6.5]
Thermal conductivity
100°C [212°F]
W/(m · K)
[Btu/(h · ft · °F)]
28.7
[16.6]
24.4–26.3
[15.0–15.8]
18.7–22.8
[10.8–12.8]
21.8–23.0
[12.6–13.1]
14.2
[8.2]
11.8–16.8
[6.8–9.7]
15.2–17.3
[8.8–10.0]
16.2–19.0
[9.4–11.0]
60
[34.7]
Electrical resistivity
nΩ · m
550–720
590–670
690–1020
770–1020
910
800–1080
520–720
770–1000
120
Melting range
°C
[°F]
1480–1530
[2700–2790]
1480–1530
[2700–2790]
1400–1450
[2550–2650]
1400–1440
[2560–2625]
1370–1430
[2500–2600]
1320–1400
[2410–2550]
1430–1510
[2600–2750]
1430–1450
[2600–2650]
1538
[2800]
Property
262 CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
Table 5.2
Typical Physical Properties of Wrought Stainless Steels
AWS WELDING HANDBOOK 9.4
AWS WELDING HANDBOOK 9.4
WELDING PROCESS SELECTION
The common grades of stainless steel are readily
joined by arc, electron beam, laser beam, resistance,
and friction welding processes. Gas metal arc (GMAW),
gas tungsten arc (GTAW), flux cored arc (FCAW), and
shielded metal arc (SMAW) welding are commonly used.
Plasma arc welding (PAW) and submerged arc welding
(SAW) also are suitable joining methods. The welding
processes available for the specialty grades are more
limited because of the effects on weldability due to individual metallurgical characteristics.
Sound welds can be produced by use of SAW techniques, but certain restrictions may need to be placed
on the process. Generally, the composition of the weld
metal deposited by this process is more difficult to control than that produced with other arc welding processes because of the effect of arc voltage variations on
elemental pickup from fluxes and potentially high levels
of dilution. For example, the silicon content might be
high and result in solidification cracking of the weld
metal if ferrite content is low or absent. Silicon pickup
may occur, but is easily avoided by selecting a chemically basic flux (low in silicon dioxide [SiO2] content).
Heat input is higher and solidification rate of the weld
metal is slower with SAW than with other arc welding
processes. In ferritic stainless steels, these conditions
can lead to large grain sizes in the weld metal that may
result in lower toughness than that produced by many
other processes. Submerged arc welding is often not
recommended when an austenitic stainless steel weld
deposit must be fully austenitic or low in ferrite content. However, it is suitable when a ferrite content of
over 4 FN (ferrite number) is permissible in the weld
metal. (Refer to the section, Ferrite in Austenitic Stainless Steel Weld Metal, in this chapter.) Proprietary
fluxes are available for welding of stainless steels with
the SAW process. Alloying elements, including chromium, nickel, molybdenum (Mo), and niobium (Nb),
can be added to the weld metal by use of suitable
fluxes.
Resistance welding processes, such as spot welding
(RSW), seam welding (RSEW), projection welding (PW),
flash welding (FW), high-frequency seam welding (RSEWHF), and stud welding are suited for joining stainless
steels. The higher electrical resistance and higher strength
of stainless steels require lower welding current and
higher electrode force or upsetting force than are needed
for carbon steels.
Oxyacetylene welding (OAW) is not recommended
except for emergency repairs when suitable arc welding
equipment is not available. A neutral or slightly reducing acetylene flame is recommended but may produce
carbon pickup. A welding flux with good solvent power
for chromium oxide is essential. Careful flame control
with proper heat input is required.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
263
Brazing and soldering are commonly employed on all
stainless steels. In brazing, the brazing temperature is
controlled by the grade of stainless steel. Of necessity,
the fluxes employed are more corrosive than those used
for mild steel, and special care must be taken to remove
the residual flux.
PROTECTION AGAINST OXIDATION
The welding process selected for stainless steels must
protect the molten weld metal from atmospheric contamination during metal transfer across the arc and
during solidification. Some welding processes require
fluxing to remove chromium and other oxides from the
surfaces of the workpieces and from the molten weld
metal. The chromium-rich oxide is a refractory compound that melts well above the liquidus temperature of
the stainless steels. Fluorides are the most effective agents
for removing chromium oxide during welding. Calcium
fluoride and sodium fluoride are the most common fluorides used in covered electrode coatings, fluxes for flux
cored electrodes, and SAW fluxes.
The fluoride residuals in slags on a weldment can be
quite corrosive and can attack the metal during service at
elevated temperatures. Welding slag should be completely
removed by chipping or brushing before postweld heat
treatment (PWHT) or placing the weldment in elevatedtemperature service.
Gas-shielded welding processes do not require flux to
protect against oxidation, but a flux can be employed
for other reasons, such as improving out-of-position
welding and bead shape and as a vehicle for alloy additions. Inert gas protection is frequently provided in
flash welding to prevent the formation of chromium
oxide that can be trapped at the weld interface during
upsetting.
PREWELD AND POSTWELD CLEANING
Surface contaminants affect stainless steel welds to a
greater degree than carbon and low-alloy steel welds.
To obtain sound welds, the surfaces to be joined require
thorough cleaning prior to welding. The area to be
cleaned should include the weld groove faces and the
adjacent surfaces for at least 13 mm (0.5 in.) on each
side of the groove. Cleaning of a wider band is recommended on thick plate. The surfaces of workpieces to
be joined by resistance spot or seam welding should be
cleaned.
The degree of cleaning necessary depends on the
weld quality requirements of the application and the
welding process employed. Special care is required with
gas shielded welding processes because fluxing is not
used.
264
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
Carbon contamination can adversely affect both
metallurgical characteristics and corrosion resistance.
Care should be taken to prevent embedded particles,
pickup of carbon from surface contaminants (such as
oil or other hydrocarbons), and improper air carbon arc
gouging.
The surfaces of areas to be welded must be completely cleansed with suitable solvents to remove all
hydrocarbon and other contaminants such as cutting
fluids, grease, oil, waxes, and primers. Light oxide films
can be removed by pickling, but they normally are
removed by mechanical methods. Acceptable preweld
cleaning techniques include the following:
1. Brushing with stainless steel wire brushes that
have been used only for stainless steel,
2. Blasting with clean sand or grit,
3. Machining and grinding with a suitable tool and
chloride-free cutting fluid, and
4. Pickling with a solution of 10% to 20% nitric
acid with 2% to 3% hydrofluoric acid (HF) added.
Thorough postweld cleaning is required to remove
welding slag when it is present. Objectionable surface
discoloration from welding is best removed by wire
brushing or grinding, but often pickling is preferred.
Postweld wire brushing to remove surface oxidation
must be done thoroughly with stainless steel brushes
used only for stainless steel.
Light brushing can produce a bright surface, but
brightness may not be indicative of complete removal of
all oxides and the surface may rust later. Pickling by
immersion in acid solutions, such as 10% nitric acid
and 2% hydrofluoric acid (HNO3-HF) or by the use of
pickling paste, will remove oxides, chromium-depleted
layers, and foreign materials. However, pickling may
introduce other corrosion-related problems. Careful attention to the pickling process and thorough cleaning
afterward will prevent most pickling-induced corrosion
problems. Heavy grinding, if properly performed, will
produce a clean, bright, corrosion-resistant surface. The
cleaning methods employed must be tailored to the service requirements.8 It is important to note that spent
pickling and rinse fluids present an environmental
safety concern, and must be disposed of in accordance
with federal, state and local regulations.
FILLER METALS
Covered electrodes and flux-cored electrodes for arc
welding are commercially available for most of the
8. Dillon, C. P., 1994, Cleaning, Pickling, and Passivation of Stainless
Steels, Materials Performance 33(5): 62–64; and Tuthill, A. H., 1986,
Fabrication and Post-Fabrication Cleanup of Stainless Steels, Chemical
Engineering 93(18): 141–146.
AWS WELDING HANDBOOK 9.4
common-grade stainless steels. Bare welding rods, bare
wire, and metal-cored wire are produced for use with
the gas metal arc, gas tungsten arc, plasma arc, submerged arc, and electron beam welding (EBW) processes.
A number of filler metals are available for brazing stainless steel for room-temperature and elevated-temperature
service.
Specifications for Welding and Brazing
Filler Metals
Specifications for welding and brazing filler metals
commonly used for stainless steels are issued by the
American Welding Society (AWS). The Society of Automotive Engineers (SAE) also issues standards for filler
metals, for example, Aerospace Materials Specifications.9 In the past, military standards had covered filler
metals suitable for military products, although these
standards now have been phased out in favor of AWS
or other standards. Other filler metals designed for joining stainless steels are proprietary and fall outside of
standard specification requirements. However, these filler
metals also are suitable for many special applications.
Stainless steel filler metals for the common grades of
stainless steels are covered by AWS specifications. Table
5.3 shows chemical composition requirements for undiluted weld metal for corrosion-resisting chromium,
chromium-nickel and chromium-nickel-manganese steel
covered welding electrodes.10 Table 5.4 shows the chemical composition requirements for bare stainless steel
welding electrodes and rods.11 Table 5.5 shows the chemical composition requirements for flux-cored corrosionresisting chromium and chromium-nickel steel electrodes.12
Nickel-base filler metals also can be used to join stainless steel to stainless steel or to other alloys.13, 14, 15
In most cases, the chemical composition of the electrode, welding rod, or all-weld-metal deposit from a
particular electrode varies slightly from the correspond9. SAE World Headquarters, 400 Commonwealth Drive, Warrendale,
PA 15096-0001, USA.
10. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2006, Specification for Stainless Steel Electrodes
for Shielded Metal Arc Welding, AWS A5.4/A5.4M:2006, Miami:
American Welding Society.
11. See Reference 10.
12. See Reference 10.
13. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2010, Specification for Nickel and Nickel Alloy
Welding Electrodes for Shielded Metal Arc Welding, AWS A5.11/
A5.11M:2010, Miami: American Welding Society.
14. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2009, Specification for Nickel and Nickel Alloy
Bare Welding Electrodes and Rods, AWS A5.14/A5.14M:2009, Miami:
American Welding Society.
15. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2007, Specification for Nickel-Alloy Electrodes
for Flux Cored Arc Welding, AWS A5.34/A5.34M:2007, Miami:
American Welding Society.
AWS WELDING HANDBOOK 9.4
ing base metal with the same three-digit designation.
Such adjustments in the filler metal chemical composition are necessary to produce weld metal having the
desired microstructure that is free of cracks or other
unacceptable discontinuities.
Usability Classifications of Shielded
Metal Arc Welding Electrodes
The American Welding Society has established
usability classifications for four SMAW electrode designations in AWS A5.4/A5.4M:2006 that are based on
the coating composition, welding position, and the type
of current with which the electrodes are usable.16 The
type of covering applied to a core wire during manufacture of a shielded metal arc welding electrode determines the usability characteristics of the electrode.
Usability Designation EXXX(X)-15. The EXXX-15
electrodes are usable only with direct current, electrode
positive (DCEP) power. While these electrodes sometimes are used with alternating current (ac), they are not
intended to qualify for use with ac power. Electrode sizes
of 4.0 mm (5/32 in.) and smaller may be used in all
positions of welding.
Usability Designation EXXX(X)-16. The covering
for EXXX-16 electrodes generally contains readily ionizable elements, such as potassium, to stabilize the arc
for welding with ac power, although the electrodes
work equally well or better with DCEP power. Electrode sizes of 4.0 mm (5/32 in.) and smaller may be
used in all positions of welding.
Usability Designation EXXX(X)-17. The covering
for EXXX(X)-17 electrodes is a modification of the -16
covering in which some of the titania is replaced with silica. Because both the -16 and the -17 electrode coverings
permit ac operation, prior to 1992 both covering types
were classified as -16. The 1992 revision of ANSI/AWS
A5.4 provided for the alternative -17 classification, with
significant operational differences between the two types.
On horizontal fillet welds, electrodes with a -17 covering tend to produce more of a spray arc and a finer rippled weld bead surface than those produced by the -16
covering. The slower-freezing slag of the -17 covering
also permits improved handling characteristics when
employing a drag technique. The bead shape on horizontal fillet welds typically is flat to concave with -17
covered electrodes, compared to flat to slightly convex
with -16 covered electrodes. For uphill vertical fillet
welds, the larger coatings and the slower-freezing solidifying slag of the -17 covered electrodes require a wider
16. See Reference 10.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
265
weave technique to produce the proper bead shape. For
this reason, the minimum fillet-weld leg size that can be
properly made with a -17 covered electrode is larger
than that with a -16 covered electrode. While these electrodes are designed for all-position operation, electrode
sizes 4.8 mm (3/16 in.) and larger are not recommended
for vertical or overhead welding.
Usability Designation EXXX(X)-26. The slag sys-
tem for this type of coating is very similar in composition and operating characteristics to the true -17
designation and some electrodes with -16 designation,
so the usability guidelines for -16 and -17 also apply to
the -26 designation. The -26 electrode differs from the 16 and -17 types in that the core wire may be of a substantially different composition, such as mild steel, that
may require or permit a much higher welding current.
The additional alloys necessary to obtain the required
analysis are contained in the covering, which results in
a much larger covering diameter for a given size than
the corresponding -16 type.
An electrode with a core wire dissimilar to the weld
metal is not uncommon. The practice of using the core
wire from a stainless steel electrode for GTAW rods is
therefore not advisable unless the manufacturer has been
consulted. Even some of the -15 and -16 electrodes may
have mild steel as core wire, especially for alloys in the
400 Series. Stainless steel SMAW electrode coverings may
absorb moisture that may cause porosity in the weld
metal and also hydrogen-induced cracking when welding
martensitic stainless steels. When removed from hermetically sealed containers or from baking ovens, stainless
steel covered electrodes should be stored in holding ovens
at about 90°C to 120°C (200°F to 250°F) until withdrawn for welding. Electrodes that have been exposed to
humid conditions should be rebaked at high temperatures prior to use, as recommended by the electrode manufacturer. However, rebaking at high temperatures may
loosen the flux attachment to the core wire and may
cause the coating to spall off during welding. The electrode manufacturer should be consulted for the recommended number of rebaking cycles permissible without
the potential degradation of the electrode covering.
Bare and Flux Cored Filler Metals
The description and intended use of the filler metals
listed in Tables 5.4 and 5.5 are covered in the appendices
of AWS A5.9/A5.9M and A5.22/A5.22M, respectively.17
17. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, Specification for Bare Stainless Steel Welding
Electrodes and Rods, AWS A5.9/A5.9M:2006; and Specification for
Stainless Steel Electrodes for Flux Cored Arc Welding and Stainless
Steel Flux Cored Rods for Gas Tungsten Arc Welding, AWS A5.22/
A5.22M:2010, Miami: American Welding Society.
Weight Percent a, b
AWS
Classification
UNS
Number d
C
Cr
Ni
Mo
Nb (Cb)
Plus Ta
Mn
Si
P
S
N
Cu
Other
V = 0.10–0.30
E209-XX
W32210
0.06
20.5–24.0
9.5–12.0
1.5–3.0
—
4.0–7.0
1.00
0.04
0.03
0.10–0.30
0.75
E219-XX
W32310
0.06
19.0–21.5
5.5–7.0
0.75
—
8.0–10.0
1.00
0.04
0.03
0.10–0.30
0.75
E240-XX
W32410
0.06
17.0–19.0
4.0–6.0
0.75
—
10.5–13.5
1.00
0.04
0.03
0.10–0.30
0.75
E307-XX
W30710
0.04–0.14
18.0–21.5
9.0–10.7
0.5–1.5
—
3.30–4.75
1.00
0.04
0.03
—
0.75
E308-XX
W30810
0.08
18.0–21.0
9.0–11.0
0.75
—
0.5– 2.5
1.00
0.04
0.03
—
0.75
E308H-XX
W30810
0.04 –0.08
18.0–21.0
9.0–11.0
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E308L-XX
W30813
0.04
18.0–21.0
9.0–11.0
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E308Mo-XX
W30820
0.08
18.0–21.0
9.0–12.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E308LMo-XXe
W30823
0.04
18.0–21.0
9.0–12.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E309-XX
W30910
0.15
22.0–25.0
12.0–14.0
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E309H-XX
W30910
0.04–0.15
22.0–25.0
12.0–14.0
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E309L-XX
W30913
0.04
22.0–25.0
12.0–14.0
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E309Nb-XXf
W30917
0.12
22.0–25.0
12.0–14.0
0.75
0.70–1.00
0.5–2.5
1.00
0.04
0.03
—
0.75
W30920
0.12
22.0–25.0
12.0–14.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E309LMo-XXe
W30923
0.04
22.0–25.0
12.0–14.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E310-XX
W31010
0.08–0.20
25.0–28.0
20.0–22.5
0.75
—
1.0–2.5
0.75
0.03
0.03
—
0.75
E310H-XX
W31015
0.35–0.45
25.0–28.0
20.0–22.5
0.75
—
1.0–2.5
0.75
0.03
0.03
—
0.75
E310Nb-XXf
W31017
0.12
25.0–28.0
20.0–22.0
0.75
0.70–1.00
1.0–2.5
0.75
0.03
0.03
—
0.75
E310Mo-XX
W31020
0.12
25.0–28.0
20.0–22.0
2.0–3.0
—
1.0–2.5
0.75
0.03
0.03
—
0.75
E312-XX
W31310
0.15
28.0–32.0
8.0–10.5
0.75
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E316-XX
W31610
0.08
17.0–20.0
11.0–14.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E316H-XX
W31610
0.04–0.08
17.0–20.0
11.0–14.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E316L-XX
W31613
0.04
17.0–20.0
11.0–14.0
2.0–3.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E316LMn-XX
W31622
0.04
18.0–21.0
15.0–18.0
2.5–3.5
—
5.0–8.0
0.90
0.04
0.03
0.10–0.25
0.75
E317-XX
W31710
0.08
18.0–21.0
12.0–14.0
3.0–4.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E317L-XX
W31713
0.04
18.0–21.0
12.0–14.0
3.0–4.0
—
0.5–2.5
1.00
0.04
0.03
—
0.75
E318-XX
W31910
0.08
17.0–20.0
11.0–14.0
2.0–3.0
6 × C, min.
to 1.00 max.
0.5–2.5
1.00
0.04
0.03
—
0.75
E320-XX
W88021
0.07
19.0–21.0
32.0–36.0
2.0–3.0
8 × C, min.
to 1.00 max.
0.5–2.5
0.60
0.04
0.03
—
3.0–4.0
AWS WELDING HANDBOOK 9.4
E309Mo-XX
266 CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
Table 5.3
Chemical Composition Requirements for Undiluted Weld Metala
Weight Percent a, b
Nb (Cb)
Plus Ta
AWS
Classification
UNS
Number d
C
Cr
Ni
Mo
Mn
Si
P
S
N
Cu
E320LR-XX
W88022
0.03
19.0–21.0
32.0–36.0
2.0–3.0
8 × C, min.
to 0.40 max.
1.50–2.50
0.30
0.020
0.015
—
3.0–4.0
E330-XX
W88331
0.18–0.25
14.0–17.0
33.0–37.0
0.75
—
1.0–2.5
1.00
0.04
0.03
—
0.75
E330H-XX
W88335
0.35–0.45
14.0–17.0
33.0–37.0
0.75
—
1.0–2.5
1.00
0.04
0.03
—
0.75
E347-XX
W34710
0.08
18.0–21.0
9.0–11.0
0.75
8 × C, min.
to 1.00 max.
0.5–2.5
1.00
0.04
0.03
—
0.75
E349-XX
W34910
0.13
18.0–21.0
8.0–10.0
0.35–0.65
0.75–1.20
0.5–25
1.00
0.04
0.03
—
0.75
E383-XX
W88028
0.03
26.5–29.0
30.0–33.0
3.2–4.2
—
0.5–2.5
0.90
0.02
0.02
—
0.6–1.5
E385-XX
W88904
0.03
19.5–21.5
24.0–26.0
4.2–5.2
—
1.0–2.5
0.90
0.03
0.02
—
1.2–2.0
E409Nb-XX
W40910
0.12
11.0–14.0
0.6
0.75
0.50–1.50
1.0
1.00
0.04
0.03
—
0.75
E410-XX
W41010
0.12
11.0–13.5
0.7
0.75
—
1.0
0.90
0.04
0.03
—
0.75
E410NiMo-XX
W41016
0.06
11.0–12.5
4.0–5.0
0.40–0.70
—
1.0
0.90
0.04
0.03
—
0.75
W43010
0.10
15.0–18.0
0.6
0.75
—
1.0
0.90
0.04
0.03
—
0.75
E430Nb-XX
W43011
0.10
15.0–18.0
0.6
0.75
0.50–1.50
1.0
1.00
0.04
0.03
—
0.75
E630-XX
W37410
0.05
16.00–16.75
4.5–5.0
0.75
0.15–0.30
0.25–0.75
0.75
0.04
0.03
—
3.25–
4.00
E16-8-2-XX
W36810
0.10
14.5–16.5
7.5–9.5
1.0–2.0
—
0.5–2.5
0.60
0.03
0.03
—
0.75
E2209-XX
W39209
0.04
21.5–23.5
8.5–10.5
2.5–3.5
—
0.5–2.0
1.00
0.04
0.03
0.08–0.20
0.75
E2553-XX
W39553
0.06
24.0–27.0
6.5–8.5
2.9–3.9
—
0.5–1.5
1.00
0.04
0.03
0.10–0.25
1.5–2.5
E2593-XX
W39593
0.04
24.0–27.0
8.5–10.5
2.9–3.9
—
0.5–1.5
1.00
0.04
0.03
0.08–0.25
1.5–3.0
V = 0.10–0.30
Ti = 0.15 max.
W = 1.25–1.75
E2594-XX
W39594
0.04
24.0–27.0
8.0–10.5
3.5–4.5
—
0.5–2.0
1.00
0.04
0.03
0.20–0.30
0.75
E2595-XX
W39595
0.04
24.0–27.0
8.0–10.5
2.5–4.5
—
2.5
1.20
0.03
0.025
0.20–0.30
0.4–1.5
W = 0.4–1.0
E3155-XX
W73155
0.10
20.0–22.5
19.0–21.0
2.5–3.5
0.75–1.25
1.0–2.5
1.00
0.04
0.03
—
0.75
Co = 18.5–21.0
W = 2.0–3.0
E33-31-XX
W33310
0.03
31.0–35.0
30.0–32.0
1.0–2.0
—
2.5–4.0
0.9
0.02
0.01
0.3–0.5
0.4–0.8
267
a. Analysis shall be made for the elements for which specific values are shown in the table. If, however, the presence of other elements is indicated in the course of analysis, further analysis shall be
made to determine that the total of these other elements, except iron, is not present in excess of 0.50 percent.
b. Single values are maximum percentages.
c. Classification suffix -XX may be -15, -16, -17, or -26. See Clause A8 of Annex A for an explanation.
d. ASTM DS-56H/SAE HS-1086, Metal & Alloys in the Unified Numbering System.
e. E308LMo-XX and E309LMo-XX were formerly named E308MoL-XX and E309MoL-XX, respectively.
f. E309Nb-XX and E310Nb-XX were formerly named E309Cb-XX and E310Cb-XX. The change was made to conform to the worldwide uniform designation of the element niobium.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
E430-XX
Other
AWS WELDING HANDBOOK 9.4
Table 5.3 (Continued)
Chemical Composition Requirements for Undiluted Weld Metala
Composition, wt %b
AWS
UNS
Classificationc, d Numbere
C
Cr
Ni
Mo
Mn
Si
P
S
N
Cu
Other
Element
S20980
S21880
S21980
S24080
S30780
S30880
S30880
S30883
S30882
S30886
S30881
S30888
S30980
S30983
S30982
S30986
S30981
S30988
S31080
S31380
S31680
S31680
S31683
S31681
S31688
S31780
S31783
S31980
0.05
0.10
0.05
0.05
0.04–0.14
0.08
0.04–0.08
0.03
0.08
0.04
0.08
0.03
0.12
0.03
0.12
0.03
0.12
0.03
0.08–0.15
0.15
0.08
0.04–0.08
0.03
0.08
0.03
0.08
0.03
0.08
20.5–24.0
16.0–18.0
19.0–21.5
17.0–19.0
19.5–22.0
19.5–22.0
19.5–22.0
19.5–22.0
18.0–21.0
18.0–21.0
19.5–22.0
19.5–22.0
23.0–25.0
23.0–25.0
23.0–25.0
23.0–25.0
23.0–25.0
23.0–25.0
25.0–28.0
28.0–32.0
18.0–20.0
18.0–20.0
18.0–20.0
18.0–20.0
18.0–20.0
18.5–20.5
18.5–20.5
18.0–20.0
9.5–12.0
8.0–9.0
5.5–7.0
4.0–6.0
8.0–10.7
9.0–11.0
9.0–11.0
9.0–11.0
9.0–12.0
9.0–12.0
9.0–11.0
9.0–11.0
12.0–14.0
12.0–14.0
12.0–14.0
12.0–14.0
12.0–14.0
12.0–14.0
20.0–22.5
8.0–10.5
11.0–14.0
11.0–14.0
11.0–14.0
11.0–14.0
11.0–14.0
13.0–15.0
13.0–15.0
11.0–14.0
1.5–3.0
0.75
0.75
0.75
0.5–1.5
0.75
0.50
0.75
2.0–3.0
2.0–3.0
0.75
0.75
0.75
0.75
2.0–3.0
2.0–3.0
0.75
0.75
0.75
0.75
2.0–3.0
2.0–3.0
2.0–3.0
2.0–3.0
2.0–3.0
3.0–4.0
3.0–4.0
2.0–3.0
4.0–7.0
7.0–9.0
8.0–10.0
10.5–13.5
3.3–4.75
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
1.0–2.5
0.90
3.5–4.5
1.00
1.00
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.65–1.00
0.65–1.00
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.65–1.00
0.65–1.00
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.30–0.65
0.65–1.00
0.65–1.00
0.30–0.65
0.30–0.65
0.30–0.65
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.10–0.30
0.08–0.18
0.10–0.30
0.10–0.30
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
V
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
Nbg
ER320
NO8021
0.07
19.0–21.0
32.0–36.0
2.0–3.0
2.5
0.60
0.03
0.03
—
3.0–4.0
Nbg
ER320LR
NO8022
0.025
19.0–21.0
32.0–36.0
2.0–3.0
1.5–2.0
0.15
0.015
0.02
—
3.0–4.0
Nbg
ER321
S32180
0.08
18.5–20.5
9.0–10.5
0.75
1.0–2.5
0.30–0.65
0.03
0.03
—
0.75
Ti
ER330
ER347
NO8331
S34780
0.18–0.25
0.08
15.0–17.0
19.0–21.5
34.0–37.0
9.0–11.0
0.75
0.75
1.0–2.5
1.0–2.5
0.30–0.65
0.30–0.65
0.03
0.03
0.03
0.03
—
—
0.75
0.75
—
Nbg
0.10–0.30
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
8 × %C min.,
1.0 max.
8 × %C min.,
1.0 max.
8 × %C min.,
0.40 max.
9 × %C min.,
1.0 max.
—
10 × %C min.,
1.0 max.
AWS WELDING HANDBOOK 9.4
ER209
ER218
ER219
ER240
ER307
ER308
ER308H
ER308L
ER308Mo
ER308LMo
ER308Si
ER308LSi
ER309
ER309L
ER309Mo
ER309LMo
ER309Si
ER309LSi
ER310
ER312
ER316
ER316H
ER316L
ER316Si
ER316LSi
ER317
ER317L
ER318
Amount
of Other
Element
268 CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
Table 5.4
Chemical Composition Requirements for Bare Stainless Steel Welding Electrodes and Rodsa
Composition, wt %b
AWS
UNS
Classificationc, d Numbere
C
Cr
Ni
Mo
Mn
Si
P
S
N
Cu
Other
Element
S34788
0.08
19.0–21.5
9.0–11.0
0.75
1.0–2.5
0.65–1.00
0.03
0.03
—
0.75
Nbg
ER383
ER385
ER409
NO8028
NO8904
S40900
0.025
0.025
0.08
26.5–28.5
19.5–21.5
10.5–13.5
30.0–33.0
24.0–26.0
0.6
3.2–4.2
4.2–5.2
0.50
1.0–2.5
1.0–2.5
0.8
0.50
0.50
0.8
0.02
0.02
0.03
0.03
0.03
0.03
—
—
—
0.70–1.5
1.2–2.0
0.75
—
—
Ti
ER409Cb
S40940
0.08
10.5–13.5
0.6
0.50
0.8
1.0
0.04
0.03
—
0.75
Nbg
ER410
ER410NiMo
ER420
ER430
ER446LMo
ER502
ER505
ER630
ER19–10H
S41080
S41086
S42080
S43080
S44687
S50280
S50480
S17480
S30480
0.12
0.06
0.25–0.40
0.10
0.015
0.10
0.10
0.05
0.04–0.08
11.5–13.5
11.0–12.5
12.0–14.0
15.5–17.0
25.0–27.5
4.6–6.0
8.0–10.5
16.0–16.75
18.5–20.0
0.6
4.0–5.0
0.6
0.6
Note f
0.6
0.5
4.5–5.0
9.0–11.0
0.75
0.4–0.7
0.75
0.75
0.75–1.50
0.45–0.65
0.8–1.2
0.75
0.25
0.6
0.6
0.6
0.6
0.4
0.6
0.6
0.25–0.75
1.0–2.0
0.5
0.5
0.5
0.5
0.4
0.5
0.5
0.75
0.30–0.65
0.03
0.03
0.03
0.03
0.02
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.02
0.03
0.03
0.03
0.03
—
—
—
—
0.015
—
—
—
—
0.75
0.75
0.75
0.75
Note f
0.75
0.75
3.25–4.00
0.75
ER16–8–2
ER2209
ER2553
ER3556
S16880
S39209
S39553
R30556
0.10
0.03
0.04
0.05–0.15
14.5–16.5
21.5–23.5
24.0–27.0
21.0–23.0
7.5–9.5
7.5–9.5
4.5–6.5
19.0–22.5
1.0–2.0
2.5–3.5
2.9–3.9
2.5–4.0
1.0–2.0
0.50–2.0
1.5
0.50–2.00
0.30–0.65
0.90
1.0
0.20–0.80
0.03
0.03
0.04
0.04
0.03
0.03
0.03
0.015
—
0.08–0.20
0.10–0.25
0.10–0.30
0.75
0.75
1.5–2.5
—
—
—
—
—
—
—
—
Nbg
Nbg
Ti
—
—
—
Co
W
Nb
Ta
Al
Zr
La
B
10 × %C min.,
1.0 max.
—
—
10 × %C min.,
1.5 max.
10 × %C min.,
0.75 max.
—
—
—
—
—
—
—
0.15–0.30
0.05
0.05
—
—
—
16.0–21.0
2.0–3.5
0.30
0.30–1.25
0.10–0.50
0.001–0.100
0.005–0.10
0.02
269
a. Analysis shall be made for the elements for which specific values are shown in this table. If the presence of other elements is indicated in the course of this work, the amount of those elements
shall be determined to ensure that their total, excluding iron, does not exceed 0.50%.
b. Single values shown are maximum percentages.
c. In the designator for composite, stranded, and strip electrodes, the “R” shall be deleted. A designator “C” shall be used for composite and stranded electrodes, and a designator “Q” shall be used
for strip electrodes. For example, ERXXX designates a solid wire and EQXXX designates opa strip electrode of the same general analysis and the same UNS number. However, ECXXX designates a
composite metal cored or stranded electrode and may not have the same UNS number. Consult ASTM/SAE Uniform Numbering System for the proper UNS number. Metal cored stainless electrodes
and rods are described in Specification for Stainless Steel Electrodes for Flux Cored Arc Welding and Stainless Steel Flux Cored Rods for Gas Tungsten Arc Welding, AWS A5.22/A5.22M:2010, and will
be removed from the next edition of Specification for Bare Stainless Steel Welding Electrodes and Rods, AWS A5.9/A5.9M:2006.
d. For special applications, electrodes and rods may be purchased with less than the specified silicon content.
e. ASTM/SAE Unified Numbering System for Metals and Alloys.
f. 0.5% (Ni + Cu) max.
g. Nb may be reported as Nb + Ta.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
ER347Si
Amount
of Other
Element
AWS WELDING HANDBOOK 9.4
Table 5.4 (Continued)
Chemical Composition Requirements for Bare Stainless Steel Welding Electrodes and Rodsa
Composition, wt %b
AWS
Classificationc
UNS
Numberd
C
Cr
Ni
E307TX-X
E308TX-X
E308LTX-X
E308HTX-X
E308MoTX-X
E308LMoTX-X
E309TX-X
E309LCbTX-X
E309LTX-X
E309MoTX-X
E309LMoTX-X
E309LNiMoTX-X
E310TX-X
E312TX-X
E316TX-X
E316LTX-X
E317LTX-X
E347TX-X
E409TX-Xe
E410TX-X
E410NiMoTX-X
E410NiTiTX-Xe
E430TX-X
E502TX-X
E505TX-X
W30731
W30831
W30835
W30831
W30832
W30838
W30931
W30932
W30935
W30939
W30938
W30936
W31031
W31331
W31631
W31635
W31735
W34731
W40931
W41031
W41036
W41038
W43031
W50231
W50431
0.13
0.08
0.04
0.04–0.08
0.08
0.04
0.10
0.04
0.04
0.12
0.04
0.04
0.20
0.15
0.08
0.04
0.04
0.08
0.10
0.12
0.06
0.04
0.10
0.10
0.10
18.0–20.5
18.0–21.0
18.0–21.0
18.0–21.0
18.0–21.0
18.0–21.0
22.0–25.0
22.0–25.0
22.0–25.0
21.0–25.0
21.0–25.0
20.5–23.5
25.0–28.0
28.0–32.0
17.0–20.0
17.0–20.0
18.0–21.0
18.0–21.0
10.5–13.5
11.0–13.5
11.0–12.5
11.0–12.0
15.0–18.0
4.0–6.0
8.0–10.5
9.0–10.5
9.0–11.0
9.0–11.0
9.0–11.0
9.0–11.0
9.0–12.0
12.0–14.0
12.0–14.0
12.0–14.0
12.0–16.0
12.0–16.0
15.0–17.0
20.0–22.5
8.0–10.5
11.0–14.0
11.0–14.0
12.0–14.0
9.0–11.0
0.60
0.60
4.0–5.0
3.6–4.5
0.60
0.40
0.40
Mo
Nb + Ta
Si
P
S
N
Cu
3.30–4.75
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
1.0–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.80
1.2
1.0
0.70
1.2
1.2
1.2
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.50
1.0
1.0
1.0
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.03
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.03
0.04
0.04
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
3.30–4.75
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
1.25–2.25
1.0
1.0
1.0
1.0
1.0
1.0
0.25–0.80
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
—
—
—
—
—
—
—
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Gas Shielded Flux Cored Arc Welding
0.5–1.5
0.5
0.5
0.5
2.0–3.0
2.0–3.0
0.5
0.5
0.5
2.0–3.0
2.0–3.0
2.5–3.5
0.5
0.5
2.0–3.0
2.0–3.0
3.0–4.0
0.5
0.5
0.5
0.40–0.70
0.5
0.5
0.45–0.65
0.85–1.20
—
—
—
—
—
—
—
0.70–1.00
—
—
—
—
—
—
—
—
—
Note h
—
—
—
—
—
—
—
Self-Shielded Flux Cored Arc Welding
E307T0-3
E308T0-3
E308LT0-3
E308HT0-3
E308MoT0-3
E308LMoT0-3
E308HMoT0-3
W30733
W30833
W30837
W30833
W30839
W30838
W30830
0.13
0.08
0.03
0.04–0.08
0.08
0.03
0.07–0.12
19.5–22.0
19.5–22.0
19.5–22.0
19.5–22.0
18.0–21.0
18.0–21.0
19.0–21.5
9.0–10.5
9.0–11.0
9.0–11.0
9.0–11.0
9.0–11.0
9.0–12.0
9.0–10.7
0.5–1.5
0.5
0.5
0.5
2.0–3.0
2.0–3.0
1.8–2.4
—
—
—
—
—
—
—
AWS WELDING HANDBOOK 9.4
Mn
270 CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
Table 5.5
Chemical Composition Requirements for Flux Cored Arc Welding and Flux Cored Gas Tungsten Arc Welding Filler Metala
Composition, wt %b
UNS
Numberd
C
Cr
E309T0-3
E309LT0-3
E309LCbT0-3
E309MoT0-3
E309LMoT0-3
E310T0-3
E312T0-3
E316T0-3
E316LT0-3
E316LKT0-3f
E317LT0-3
E347T0-3
E409T0-3e
E410T0-3
E410NiMoT0-3
E410NiTiT0-3e
E430T0-3
E2209T0-X
E2553T0-X
W30933
W30937
W30934
W30939
W30938
W31031
W31231
W31633
W31637
W31630
W31737
W34733
W40931
W41031
W41036
W41038
W43031
W39239
W39533
0.10
0.03
0.03
0.12
0.04
0.20
0.15
0.08
0.03
0.04
0.03
0.08
0.10
0.12
0.06
0.04
0.10
0.04
0.04
23.0–25.5
23.0–25.5
23.0–25.5
21.0–25.0
21.0–25.0
25.0–28.0
28.0–32.0
18.0–20.5
18.0–20.5
17.0–20.0
18.5–21.0
19.0–21.5
10.5–13.5
11.0–13.5
11.0–12.5
11.0–12.0
15.0–18.0
21.0–24.0
24.0–27.0
Ni
Mo
Nb + Ta
Mn
Si
P
S
N
Cu
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
1.0–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
0.80
1.0
1.0
0.70
1.0
0.5–2.0
0.5–1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.50
1.0
1.0
0.75
0.04
0.04
0.04
0.04
0.04
0.03
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.03
0.04
0.04
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.08–0.20
0.10–0.20
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
1.5–2.5
—
—
—
—
—
—
0.5–2.5
0.5–2.5
0.5–2.5
0.5–2.5
1.2
1.2
1.2
1.2
0.04
0.04
0.04
0.04
0.03
0.03
0.03
0.03
—
—
—
—
0.5
0.5
0.5
0.5
Self-Shielded Flux Cored Arc Welding (Continued)
12.0–14.0
12.0–14.0
12.0–14.0
12.0–16.0
12.0–16.0
20.0–22.5
8.0–10.5
11.0–14.0
11.0–14.0
11.0–14.0
13.0–15.0
9.0–11.0
0.60
0.60
4.0–5.0
3.6–4.5
0.60
7.5–10.0
8.5–10.5
0.5
0.5
0.5
2.0–3.0
2.0–3.0
0.5
0.5
2.0–3.0
2.0–3.0
2.0–3.0
3.0–4.0
0.5
0.5
0.5
0.40–0.70
0.5
0.5
2.5–4.0
2.9–3.9
—
—
0.70–1.00
—
—
—
—
—
—
—
—
Note h
—
—
—
—
—
—
—
Special Category Flux Cored Arc Welding
EXXXTX-Gg
Unspecified
—
—
—
—
—
Flux Cored Gas Tungsten Arc Welding
R308LT1-5
R309LT1-5
R316LT1-5
R347T1-5
W30835
W30935
W31635
W34731
0.03
0.03
0.03
0.08
18.0–21.0
22.0–25.0
17.0–20.0
18.0–11.0
9.0–11.0
12.0–14.0
11.0–14.0
9.0–11.0
0.5
0.5
2.0–3.0
0.5
—
—
—
Note h
271
a. The weld metal shall be analyzed for the specific elements in this table. If the presence of other elements is indicated in the course of this work, the amount of those elements shall be determined
to ensure that their total (excluding iron) does not exceed 0.50%.
b. Single values shown are maximum percentages.
c. In this table, the “X” following the “T” refers to the position of welding (1 for all-position operation or 0 for flat or horizontal operation) and the “X” following the hyphen refers to the shielding
medium (-1 for carbon dioxide, -3 for none (self-shielded), -4 for 75–80% argon/25–20% carbon dioxide, or -5 for 100% argon). Also see footnote g.
d. ASTM/SAE Unified Number System for Metals and Alloys.
e. 10 × %C Ti min., 1.5% Ti max.
f. This alloy is designed for cryogenic applications.
g. For information concerning the “G” following the hyphen, see AWS A5.22/A5.22M:2010, Annex items A2.3.7 and A2.3.8.
h. 8 × %C (Nb + Ta) min., 1.0% (Nb + Ta) max.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS
Classificationc
AWS WELDING HANDBOOK 9.4
Table 5.5 (Continued)
Chemical Composition Requirements for Flux Cored Arc Welding and Flux Cored Gas Tungsten Arc Welding Filler Metala
272
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
Table 5.6
External Shielding Medium, Polarity, and Welding Process
AWS Designationa
External Shieldingb
Welding Polarity
Welding Process
EXXXTX-1
100% carbon dioxide (CO2)
DCEP
FCAW
EXXXTX-3
None (self-shielded)
DCEP
FCAW
EXXXTX-4
75–80% Ar, remainder CO2
DCEP
FCAW
RXXXT1-5
100% argon (Ar)
DCEN
GTAW
EXXXTX-Gc
Not specified
Not specified
FCAW
RXXXT1-Gc
Not specified
Not specified
GTAW
a. The letters “XXX” stand for the designation of the chemical composition. The “X” after the “T” designates the position of operation. A “0” indicates flat or
horizontal operation; a “1” indicates all-position operation.
b. A restrictive requirement only for classification tests; suitability may be determined for other applications.
c. Refer to Specification for Stainless Steel Electrodes for Flux Cored Arc Welding and Stainless Steel Flux Cored Rods for Gas Tungsten Arc Welding, AWS
A5.22/A5.22M:2010.
Flux-cored stainless steel electrodes are formulated
to weld either with or without external gas shielding.
The two gases most commonly used are 100% carbon
dioxide and 75% to 80% argon (Ar) with the remainder carbon dioxide. The type of shielding is indicated
by a suffix digit as listed in Table 5.6. Other suitable
external shielding gases recommended by the filler metal
manufacturer can be used.
selection of a brazing filler metal for a stainless steel
assembly depends on its end use because of the wide
variation in melting points of the metals, base metal
interface reactions, resulting service properties, and costs.
Commercial brazing filler metals are available that have
copper (Cu), silver (Ag), nickel (Ni), cobalt (Co), platinum (Pt), palladium (Pd), manganese (Mn), and gold
(Au) as the base or as added elements.18
Welding Position
Self-shielded flux-cored arc welding (FCAW) electrodes usually are selected for flat and horizontal welds
and for surfacing. The self-shielded FCAW process produces voluminous fumes and requires good ventilation.
The positional capability of a gas-shielded stainless steel
FCAW electrode usually depends on the flux. and to a
lesser extent, on the shielding gas. The all-position types
(EXXXT1-4) tend to provide a faster solidifying slag,
and the use of argon-carbon dioxide (Ar-CO2) gas
mixes tends to reinforce this with lower oxygen potentials. The EXXXT1-1 type may be preferred for welding in the vertical position. Many flux-cored flat and
horizontal electrodes (EXXXTO-X) designed for welding with carbon dioxide (CO2) can be used with Ar
mixtures if minimal spatter is desired. If the selfshielded FCAW filler metals are shielded with CO2 or
Ar-O mixture, the nitrogen, carbon, and chromium levels will be changed, which may affect susceptibility to
weld cracking. (Refer to the subsequent section, Influence of Ferrite on Weld Cracking in this chapter.)
Brazing Filler Metals
A wide variety of filler metals is commercially available for the brazing of stainless steel components. The
MARTENSITIC
STAINLESS STEELS
From a historical perspective, martensitic stainless
steels were the first stainless steels to be produced. They
essentially are iron-chromium-carbon alloys with nominally 11.5% to 18% chromium and are hardenable by
appropriate heat treatments. They can also be hardened
by cold working. Martensitic stainless steels normally
exhibit a microstructure comprised of a distribution of
fine carbides (rich in Fe and Cr) dispersed in a matrix of
tempered martensite with a body centered tetragonal
(BCT) crystal structure in the hardened condition. These
steels are known for moderate corrosion resistance, oxidation resistance, strength at service temperatures up to
about 590°C (1100°F), ability to develop a wide range
of mechanical properties, and relatively low cost.
18. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2004, Specification for Filler Metals for Brazing
and Braze Welding, A5.8/A5.8M:2004, Miami: American Welding
Society.
AWS WELDING HANDBOOK 9.4
Martensitic stainless steels undergo an austenite-tomartensite transformation under almost all cooling conditions. Subsequent tempering softens the martensite and
can produce materials ranging from very hard martensite to soft materials that are essentially ferritic, depending on the tempering time and temperature. These steels
also can be fully annealed to provide a ferritic structure
by austenitizing and slow cooling, but they normally
are used with a tempered martensitic structure.
The martensitic stainless steels can be grouped into
the 12% chromium, low-carbon, engineering grades
and the higher chromium, high-carbon cutlery grades.
Low carbon and medium carbon martensitic stainless
steels typically are used in steam turbines, gas turbines
and jet engines. Certain martensitic stainless steels also
can be used in applications related to elevated temperature pressure containment. Higher carbon versions of
these steels are employed for gears, valves, shafts, cams
and ball bearings.
Developed during the 1980s, the supermartensitic stainless steels contain chromium in the range of 11.5 wt %
to 13 wt %, 1.5 wt % to 7 wt % nickel, up to 2.5 wt %
molybdenum, and have low carbon content of about
0.01 wt %. Typically, these steels also have low nitrogen
content and contain nickel, molybdenum and copper.
Supermartensitic stainless steels may be classified into
three grades according to the degree of corrosion resistance
and toughness:
1. Lean grades with nickel content less than about
4 wt % and little or no molybdenum additions;
2. Medium grades with nickel content in the range
of 4.5 wt % to 5 wt % and molybdenum content
of approximately 1.5 wt %; and
3. High grades, with greater than 4 wt % nickel
and 2 wt % to 2.5 wt % molybdenum.
The microstructure of supermartensitic stainless
steels is predominantly tempered martensite with some
austenite, but delta (δ) ferrite and untempered martensite may form in the heat-affected zone (HAZ) of the
weld. The supermartensitic grades combine high-strength
and low-temperature toughness with acceptable corrosion resistance in many applications. The weldability of
these alloys is enhanced by their low carbon content.
These steels are increasingly used for applications in the
oil and gas industry, especially for the handling of
mildly sour gas. Supermartensitic stainless steels offer a
combination of cost and properties that falls between
those of carbon steels and duplex stainless steels, providing the impetus for the increasing use.
COMPOSITION
The chemical compositions of typical martensitic
stainless steels are shown in Table 5.7. Some of those
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
273
listed have one or more elements that provide special
properties. Molybdenum, vanadium, niobium, and
tungsten are added to some of the alloys to improve elevated-temperature properties. The martensitic stainless
steels approved for ASME pressure vessel and piping
applications are listed under the P-6 Grouping in Boiler
and Pressure Vessel Code, Section IX for procedure
qualification purposes.19 Table 5.8 shows the chemical
composition of selected supermartensitic stainless steels.
METALLURGICAL CHARACTERISTICS
Martensitic alloys are classed as stainless steels
because they contain sufficient chromium to develop
the characteristic passive oxide film that renders them
resistant to oxidizing corrosion conditions. The effects
of carbon content on an iron-12% chromium alloy are
illustrated in a pseudobinary section of the Fe-Cr-C
phase diagram shown in Figure 5.5. Carbon additions
to the baseline Fe-12% Cr alloy constrict the size of the
delta (δ) and alpha (α) ferrite phase fields, and initially
expand the austenite (γ) phase field. Comparison of this
pseudobinary section of the Fe-Cr-C phase diagram
with the Fe-Fe3C phase diagram also indicates that the
addition of 12% Cr to Fe-C alloys decreases the maximum carbon solubility in γ to 0.7%, decreases the
eutectoid composition to 0.35% C, and raises the eutectoid temperature.20 From a metallurgical standpoint,
the response of martensitic stainless steels to hardening
and tempering is similar to that of hardenable carbon
steel and low-alloy steel.
Martensitic stainless steels contain sufficient chromium, carbon and other alloy content to render them
air-hardening from temperatures above 815°C (1500°F)
for all but very thick sections. Maximum hardness is
achieved by quenching in oil from above 950°C (1750°F)
followed by tempering in the temperature range from
250°C to 400°C (480°F to 750°F). Figure 5.6 shows a
continuous cooling transformation (CCT) diagram for
Type 410 stainless steel illustrating that martensite can
form at cooling rates as low as approximately 10°C/
min. These diagrams typically are presented on a plot of
log time (x-axis) against temperature (y-axis). However,
the original scale of x-axis in this plot corresponds to
bar diameters during air cooling, not time. Consequently,
the cooling rate scale shown in the inset should be used
when working with this plot.
19. American Society of Mechanical Engineers (ASME), 2010, Boiler
and Pressure Vessel Code, Section IX—Welding and Brazing Qualifications, New York: American Society of Mechanical Engineers.
20. Refer to American Welding Society (AWS) Welding Handbook
Committee, 2001, Welding Science and Technology, Volume 1 of Welding Handbook, 9th edition, Figure 4.10, page 123, for Fe-Fe3C phase
diagram. Miami: American Welding Society.
274
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
Table 5.7
Chemical Composition of Typical Martensitic Stainless Steels
Composition, wt %*
Type
UNS
Number
C
Mn
Si
Cr
Ni
P
S
Other
Wrought Alloys
403
S40300
0.15
1.00
0.50
11.5–13.0
—
0.04
0.03
—
410
S41000
0.15
1.00
1.00
11.5–13.5
—
0.04
0.03
—
414
S41400
0.15
1.00
1.00
11.5–13.5
1.25–2.50
0.04
0.03
—
416
S41600
0.15
1.25
1.00
12.0–14.0
—
0.04
0.15 min.
—
420
S42000
0.15 min.
1.00
1.00
12.0–14.0
—
0.04
0.03
—
422
S42200
0.20–0.25
1.00
0.75
11.0–13.0
0.5–1.0
0.025
0.025
0.75–1.25 Mo;
0.75–1.25 W;
0.15–0.3 V
431
S43100
0.20
1.00
1.00
15.0–17.0
1.25–2.50
0.04
0.03
—
440A
S44002
0.60–0.75
1.00
1.00
16.0–18.0
—
0.04
0.03
0.75 Mo
440B
S44003
0.75–0.95
1.00
1.00
16.0–18.0
—
0.04
0.03
0.75 Mo
440C
S44004
0.95–1.20
1.00
1.00
16.0–18.0
—
0.04
0.03
0.75 Mo
Casting Alloys
CA-6NM
J91540
0.06
1.00
1.00
11.5–14.0
3.5–4.5
0.04
0.03
0.40–1.0 Mo
CA-15
J91150
0.15
1.00
1.50
11.5–14.0
1.0
0.04
0.03
0.5 Mo
CA-40
J91153
0.20–0.40
1.00
1.50
11.5–14.0
1.0
0.04
0.03
0.5 Mo
*Single values are maximum percentages.
Table 5.8
Chemical Composition of Selected Supermartensitic Stainless Steels
Typical Composition (wt %)
Grades
C
Mn
Si
Cr
Ni
Mo
Cu
N
Other
Lean Alloy Grades
X80 11Cr-2Ni
<0.015
<2
0.15
11.0
2.0
<0.5
0.4
<0.012
HP13Cr
<0.03
0.4
<0.3
13.0
4.0
1.0
—
0.05
Medium Alloy Grades
D 13.5.2N
0.02
0.7
0.3
13.3
4.8
1.6
0.1
0.08
X80 12Cr-4.5Ni-1.5Mo
<0.015
<2
0.15
12.0
4.5
1.5
0.4
<0.012
CRS (>95 ksi)
0.02
0.5
0.3
12.5
4.5
1.5
1.5
0.05
Super13Cr (12-5-2)
0.02
0.5
0.2
12.2
5.5
2.0
0.2
0.02
High Alloy Grades
Super13Cr (13-5-2)
0.02
0.4
0.2
12.5
5.0
2.0
—
<0.08
Super13Cr (13-6-2.5-Ti)
<0.01
0.4
0.3
12.0
6.2
2.5
—
<0.01
CRS (>110 ksi)
0.02
0.5
0.3
12.8
5.9
2.0
1.5
X80 12Cr-6.5Ni-2.5Mo
<0.015
<2
0.15
12.0
6.5
2.5
0.4
Source: Adapted from Stainless Steel World Website: http://www.stainless-steel-world.net.
V 0.2
Ti 0.07
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
TEMPERATURE, °C
1600
δ + LIQ.
δ
LIQUID
γ + LIQ.
δ+γ
1200
γ + (CrFe)4 C
α+γ
800
α
α + (CrFe)4 C
0
2600
2400
2000
1200
400
0.5
1.0
CARBON, %
275
TEMPERATURE, °F
AWS WELDING HANDBOOK 9.4
800
1.5
LIVE GRAPH
Click here to view
Figure 5.5—Pseudobinary Phase Diagram of Iron—
12% Chromium Alloys with Various Carbon Contents
The hardness of martensitic stainless steel is increased with increasing carbon content to about 0.60%.
Higher carbon content does not appreciably increase
the hardness, and excess carbon is observed as primary
carbides that enhance abrasion resistance. Types 440A,
440B, and 440C steels are examples. The normal engineering welding grades have carbon contents below
0.15%. Other alloying elements are sometimes added in
proprietary alloys to stabilize the microstructure, retard
the effect of tempering, and improve tensile strength,
ductility, toughness, and elevated-temperature strength.
Within the limits of chromium and carbon contents,
martensitic stainless steels transform completely to austenite above about 1010°C (1850°F). Rapid cooling
from this temperature results in a microstructure that is
essentially all martensite. When martensitic stainless steels
are heated to temperatures between 815°C and 955°C
(1500°F and 1750°F), transformation to austenite can
be incomplete, and cooling from this temperature range
results in a microstructure of ferrite and martensite.
Martensitic stainless steels lack toughness in the asquenched condition and generally require tempering to
provide adequate toughness. The tempering treatment can
be adjusted to provide a variety of strength and ductility
levels. The precipitation of chromium-rich carbides that
occurs during tempering can reduce the corrosion resistance of these alloys. As-quenched microstructures typically have the greatest corrosion resistance, followed by
those tempered at low or high temperatures. Alloys tem-
pered at intermediate temperatures (400°C to 600°C
[750°F to 1110°F]) typically have the poorest corrosion
resistance. The effect of tempering for one hour on
the mechanical and corrosion properties of Type 420
(0.22% carbon) martensitic stainless steel is shown in
Figure 5.7.
The chromium content also influences the metallurgical behavior of martensitic stainless steels during
welding. Significant changes take place as the chromium content increases from about 11% to 17%.
These changes can be understood with the aid of Figure
5.8. For a steel containing ≤12% chromium with a carbon content of about 0.1%, (for example, Type 410)
the heat-affected zone (HAZ) of a weld will pass into
the austenite (γ) phase field on heating and cooling, and
will have a fully martensitic structure upon further
cooling back to room temperature. If the chromium
content of the steel is increased to about 15%, the ferrite-stabilizing effect of chromium would be expected to
inhibit complete transformation to austenite on heating.
Specifically, the HAZ of a weld would pass into the
two-phase austenite + ferrite (γ + δ) phase field on heating and some untransformed ferrite would remain in the
room temperature microstructure. Consequently, with
increasing chromium content (above ~12%), smaller
volume fractions of the rapidly cooled HAZ would be
martensite; the remainder will be ferrite. The presence
of soft ferrite in a martensitic structure decreases the
hardness of the steel and reduces the likelihood of
276
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
Source: Adapted from Atkins, M., 1980, Atlas of Continuous Cooling Transformation Diagrams for Engineering Steels, Materials Park, Ohio: American Society for Metals; Sheffield,
Eng.: British Steel Corp, pp 129 and 231.
Figure 5.6—Continuous Cooling Transformation Diagram for Type 410 Stainless Steel
cracking. Martensitic stainless steels with chromium contents above about 17% and carbon contents less than
0.25% cannot be hardened, because increasing the chromium continually decreases the size of the austenitic field
until it disappears. This effect is shown in Figure 5.9.
The steep thermal gradients that are accentuated by
the low thermal conductivity combined with volumetric
changes during phase transformation can cause high
internal stresses. The stresses can be sufficiently high to
cause hydrogen-induced cracking unless suitable precautions are taken during welding to minimize them.
WELDABILITY
Martensitic stainless steels can be welded in the
annealed, hardened, stress-relieved, or tempered condition. The initial heat-treatment condition has a minimal
effect on the hardenability of the heat-affected zone (HAZ)
of the weld; however, weldability is somewhat improved
in the annealed condition because the overall ductility
of the steel is higher than in the hardened condition.
The hardness of the HAZ depends primarily on the
carbon content of the steel and can be controlled only
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
277
LIVE GRAPH
Click here to view
Source: Adapted from Barker, R., 1967, Metallurgia, August, p 49, Manchester: Kennedy Press.
Figure 5.7—Effect of Tempering (1 Hour) on the Properties of Type 420 Martensitic Stainless Steel
to a degree by the welding procedure. As the hardness of
the HAZ increases, its susceptibility to hydrogen-induced
cold cracking becomes greater and toughness decreases.
Weldability is improved when an austenitic-type
(stainless or nickel-alloy) filler metal is used. This filler
metal provides lower yield strength and good ductility
in the weld metal. The austenitic weld metal can deform
during cooling and minimize the strain imposed on the
hardened HAZ. When welding processes are used that
involve electrode coatings or fluxes, such as shielded
metal arc welding (SMAW) and submerged arc welding
(SAW), hydrogen can be introduced, and austenitic
weld metal provides an additional advantage in that it
does not reject hydrogen into the HAZ on cooling. Care
should be taken when using austenitic weld metal to
ensure that the resulting weldment is not subject to
stress corrosion cracking because of the austenitic structure. Care also should be taken because the presence of
high nickel increases the likelihood of attack by sulfurrich gases.
Because martensitic stainless steels often produce
hardened HAZs, the ability to use these steels in the aswelded condition with their hard HAZs is a function of
the balance of the mechanical properties in those zones,
including hardness and ductility. In general, welded
joints in martensitic stainless steels should be given
postweld heat treatment (PWHT) to develop optimum
weld properties.
Martensitic stainless steels are subject to hydrogeninduced cracking in the same manner as low-alloy
steels. Appropriate precautions must be taken in welding process selection, storage and handling of the filler
278
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
LIVE GRAPH
Click here to view
Source: Adapted from Bungardt, K., E. Kunze, and E. Horn, 1958, Investigations Into the Structure of the
System Iron-Chromium-Carbon (in German), Arch. Eisenhuttenwes 29(3): 193–203.
Figure 5.8—Pseudobinary Section of the Fe-Cr-C
Ternary Phase Diagram at a Constant C Content of 0.1%
metal, cleanliness, and welding procedures to avoid hydrogen pickup and associated cracking problems during
welding. In particular, covered electrodes must be lowhydrogen types, and they must be stored and handled in
the same manner as low-hydrogen, covered electrodes
of low-alloy steel. (Refer to Chapter 1 for information
on hydrogen-induced cracking in low-alloy steels and
appropriate precautions that should be taken.)
ARC WELDING
Arc welding is the usual technique for joining or
repairing martensitic stainless steels. The hardenability
of the martensitic stainless steels requires preheat precautions that are appropriate for other alloy steels, while still
giving significant consideration to corrosion resistance.
Filler Metals
Only types 410, 410 NiMo, and 420 martensitic stainless steel filler metals are available as standard grades (see
Tables 5.3, 5.4, and 5.5). Other proprietary filler metals
are commercially available. Type 410 filler metal is used
to weld Types 403, 410, 414, and 420 martensitic stainless steels. Type 410 NiMo filler metal is designed to weld
Type CA-6NM castings or similar alloys or to produce
deposits with no ferrite in the as-welded condition.
When the use of filler metal with carbon content that
matches the base metal is desired, Type 420 stainless
steel is welded with ER420 filler metal. This filler metal
is sometimes used for surfacing of carbon steels to provide corrosion and wear resistance.
Martensitic stainless steel weld metals, except for
ER410NiMo, lack good toughness in the as-welded
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
279
2800
1500
2600
1400
TEMPERATURE, °C
1200
2200
19%
Cr
1100
2000
12% Cr
1000
1800
15% Cr
TEMPERATURE, °F
2400
1300
5% Cr
900
1600
800
CARBON STEEL
0% Cr
1400
700
1200
0
0.2
0.4
0.6
0.8
1.0
CARBON, %
1.2
1.4
1.6
1.8
LIVE GRAPH
Click here to view
Figure 5.9—Effect of Chromium and Carbon Content
on the Austenite Phase Field at Elevated Temperature
condition. When toughness is required, the weldment
should be given a suitable PWHT before it is placed in
service.
Austenitic stainless steel filler metals, such as a Type
308 or 309, are often used to weld martensitic stainless
steels to martensitic stainless steels or to other types of
stainless steels to provide weld metal with good aswelded toughness. Nickel-alloy filler metals of the nonhardenable nickel-chromium and NiCrFe types can also
be used. The effect of using filler metals with dissimilar
coefficients of expansion should be reviewed prior to
using dissimilar filler metals.
Before a dissimilar filler metal is used in production,
a careful evaluation should be made of the following
variables:
1. Differences in the mechanical properties of the
weld metal, the HAZ, and the base metal;
2. Possible adverse effects from a PWHT;
3. Environmental effects. e.g., corrosion; and
4. Potential for solidification cracking.
Weldments made with austenitic stainless steel or
nickel alloy filler metals normally are placed in service
in the as-welded condition; however, it must be noted
that the untempered HAZ will be hard and brittle
regardless of the filler metal employed. The use of a ductile, relatively low-yield-strength filler metal increases the
weldability.
Preheating
Application of preheat and correct interpass temperature control are the best means of avoiding hydrogeninduced cracking in welds in martensitic stainless steels.
The preheating temperature usually is in the range of
205°C to 315°C (400°F to 600°F).
The martensitic transformation temperature ranges
and air-hardening characteristics of these steels are sufficiently high that preheating to 315°C (600°F) or below
has minimal effect on the hardness of the HAZ or weld
metal (refer to Figure 5.6, which shows the Type 410 martensite start [MS] temperatures). A recommended technique
280
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
Preheating generally is beneficial regardless of carbon content. Whether interruption of preheat is acceptable also depends on carbon content. When the carbon
content is over 0.20%, it is recommended to maintain
the preheat temperature during welding and heat-treat
the weldment before it is allowed to cool below 95°C
(200°F) but after the martensite transformation is finished.
is to maintain high preheat and interpass temperatures
and ensure a very slow cooling rate into the martensite
transformation temperature range to about 90°C to 120°C
(200°F to 250°F), directly followed by tempering. In
other words, the weldment should not be cooled to room
temperature, and the tempering treatment should be
started before the martensite finish (Mf) temperature is
reached.
The carbon content of the steel is the most important
factor in determining preheating requirements. Joint
thickness, filler metal, welding process, and degree of
restraint are other considerations. Typical preheat temperature and postweld requirements based on carbon
content are given in Table 5.9.
Postweld Heat Treatment
The functions of postweld heat treatments are to
temper the weld metal and heat-affected zone (HAZ) to
decrease hardness and improve toughness, and to anneal
these regions to decrease residual stresses associated with
welding. Postweld heat treatments normally used for
martensitic stainless steels involve either subcritical tempering or supercritical full annealing.
The necessity of a postweld heat treatment depends
on the composition of the steel, the filler metal, and the
service requirements. Full annealing transforms a multiplephase weld zone to a largely ferritic structure with scattered carbides. This annealing procedure requires
proper control of the complete thermal cycle. It should
not be used unless minimum hardness is required because
of the formation of coarse carbides in the microstructure that take longer to dissolve at the austenitizing
temperature. Typical PWHT temperatures are listed in
Table 5.10.21
Table 5.9
Typical Preheat and Postweld Heat Treatment
Requirements for Martensitic Stainless Steels
Preheat (minimum)a
Carbon, %
°C
°F
Postweld Heat
Treatment
Requirementsb
<0.05
121
250
Optional
0.05–0.15
204
400
Recommended
>0.15
316
600
Necessary
a. The ASME Boiler and Pressure Vessel Code recommends a minimum
preheat of 204°C (400°F) for those materials listed as P-6 in Section IX.
b. The required heating and cooling rates are specified in the applicable
Construction Code section of the ASME Boiler and Pressure Vessel Code.
21. ASM International (ASM), 1981, Metals Handbook, 10th ed., Vol.
4, Materials Park, Ohio: ASM International, 623–646.
Table 5.10
Postweld Heat Treatments for Martensitic Stainless Steels
Subcritical Postweld
Heat Treatment Temperature Rangea, b
Type
a.
b.
c.
d.
°C
Full Annealing Temperature Rangec
°F
°C
°F
403, 410, 416
649–760
1200–1400
829–885
1525–1625
414
649–732
1200–1350
Note d
Note d
420
677–760
1250–1400
829–885
1525–1625
431
621–704
1150–1300
Note d
Note d
440A, 440B, 440C
677–760
1250–1400
843–899
1550–1650
CA-6NM
593–621
1100–1150
788–816
1450–1500
CA-15, CA-40
621–649
1150–1200
843–899
1550–1650
Air cool from temperature; lowest hardness is obtained by heating near the top of the range.
Specific postweld heat treatment rules for ASME boiler and pressure vessel applications are indicated in the applicable code sections.
Furnace cool to 593°C (1100°F); weldment can then be air cooled.
Not recommended.
AWS WELDING HANDBOOK 9.4
If the carbon content of the steel is higher than
0.20%, the weldment may be given a subcritical heat
treatment immediately on completion of welding. It
may be held at 700°C to 750°C (1290°F to 1380°F) for
1 h/25 mm (1 h/in.) of weld thickness, with a minimum
of 1 h. The weldment can then be air cooled below the
martensite finish temperature (MF) to produce an
annealed weldment.
When the filler metal composition closely matches
that of the base metal, including carbon content, the
weldment can be quenched and tempered to produce
uniform mechanical properties throughout the weldment.
Welding Precautions
Types 416 and 416Se steels are free-machining grades
that may be welded, provided the welding process or
filler metal does not supply hydrogen to the extent that
it can react with the sulfur or selenium in the base metal
to produce porosity. The amount of sulfur and selenium
that enters the weld metal by dilution must be held to a
minimum, and filler metal should be selected to provide
weld metal that can tolerate these elements without solidification cracking. E312-15 austenitic stainless steel filler
metal is one choice. In these free-machining materials,
nickel-alloy filler metals cannot be used because of the
formation of low-melting nickel eutectics, which cause
solidification cracking.
If the actual carbon content of a heat of Type 431
steel approaches the permissible maximum of 0.20%, care
is required when welding to avoid hydrogen-induced
cracking. A hardened HAZ can be kept from cracking
by using a thorough preheat, maintaining the preheat
temperature during welding, and slow cooling the weld.
High-carbon Types 420 and 440 martensitic stainless
steel weldments usually are heat-treated to a high hardness
immediately following welding. These steels require appropriate welding procedures to avoid hydrogen-induced
cracking because of relatively high carbon contents.
When welding the casting alloy CA-6NM, 410NiMo
filler metal is normally used. Preheat is not normally
required, but a subcritical PWHT is recommended to
improve mechanical properties. Prior to subcritical PWHT,
the weldment should be cooled to room temperature to
ensure complete transformation from austenite to martensite. Some fabricators even cool to –18°C (0°F),
since the Mf temperature is believed to be in this temperature range. This procedure will minimize the amount
of untempered martensite present after heat treatment,
and hence produce lower hardness.
The cast stainless steel CA-6NM welded with 410NiMo filler metal is often used for service in corrosive
environments that can charge the weldment with
hydrogen. Some specifications of NACE International
require that the weldment not exceed a hardness of 22
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
281
Rockwell C to avoid cracking when in service.22 To
meet this requirement, a double tempering heat treatment is employed, starting with an intercritical (677°C
[1250°F]) heat treatment followed by cooling to ambient and a subcritical (616°C [1140°F]) heat treatment.
RESISTANCE WELDING
If appropriate care is used, martensitic stainless steels
can be welded with resistance welding processes, such
as resistance spot welding and flash welding.
Spot Welding
Martensitic stainless steels can be spot welded in the
annealed, hardened, or quenched-and-tempered condition. Regardless of the initial base metal hardness and
the welding schedule, the HAZ adjacent to the weld
nugget quenches to martensite. The hardness of the weld
nugget and HAZ mainly depends on the carbon content
of the steel, although it can be controlled somewhat
with preheat, postheat, and tempering during the spot
welding cycle. The likelihood of hydrogen-induced
cracking in the HAZ increases with the carbon content
of the steel.
Satisfactory spot welds often can be obtained in the
martensitic stainless steels containing 0.15% carbon or
less (Types 403, 410, 414, and 416) without PWHT.
Spot-welded assemblies of steels with higher carbon
content (Types 420, 422, and 431) should be given a
postweld heat treatment.
Flash Welding
The martensitic stainless steels can be joined by flash
welding. Like spot welding, a hard HAZ is formed that
can be softened somewhat by a tempering cycle in the
welding machine, if it has this feature. Alternatively, the
weldment can be given a PWHT.
The high chromium content of martensitic stainless
steels requires precise control of flashing and upsetting
during welding to avoid entrapment of oxides at the
weld interface. Oxide inclusions in the weld are unacceptable. The use of a protective atmosphere, such as
dry nitrogen or inert gas, will prevent oxidation during
welding.
OTHER WELDING PROCESSES
Martensitic stainless steels can be joined by other
welding processes, including electron beam welding, laser
22. NACE International, 1440 South Creek Drive, Houston, Texas
77084, USA, www.nace.org.
282
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
beam welding, plasma arc welding, friction welding,
and high-frequency welding. The precautions required for
arc welding and resistance welding also apply to these
processes.
FERRITIC STAINLESS STEELS
Ferritic stainless steels are iron-chromium-carbon
alloys containing 11% to 30% chromium, along with
other ferrite stabilizers, such as molybdenum, aluminum,
niobium, or titanium. They possess a body-centered
cubic (BCC) crystal structure and are not hardenable by
heat treatment. These steels normally are not strengthened by cold working. Ferritic stainless steels exhibit
good ductility, and have good resistance to stress corrosion cracking, pitting, and crevice corrosion. Toughness
levels of these steels decrease at lower temperatures, and
their strength at high temperatures is inferior to austenitic
stainless steels.
Low chromium ferritic stainless steels (~11%), such
as Type 409, are used extensively in automotive exhaust
systems. Ferritic stainless steel alloys with intermediate
chromium contents (16% to 18%) are often utilized in
food handling and automotive trim applications. Alloys
with high chromium levels and additions of molybdenum, often referred to as superferritic stainless steels,
commonly are employed in applications that require
high levels of corrosion and oxidation resistance such as
heat exchangers and piping systems for seawater.
COMPOSITION
Table 5.11 shows the composition of typical ferritic
stainless steel alloys. Complete chemical compositions are
published in the applicable AISI or ASTM specifications.
Table 5.11
Chemical Compositions of Typical Ferritic Stainless Steels, wt %
Composition
Type
UNS
Number
C
Mn
Si
Cr
Ni
P
S
Others
Wrought Alloys
405
S40500
0.08
1.00
1.00
11.5–14.5
—
0.04
0.03
0.10–0.30 Al
409-10
S40910
0.030
1.00
1.00
10.5–11.7
0.50
0.040
0.020
Ti, 6 × (%C + %N) min.,
0.50 max.; Cb 0.17
409-20
S40920
0.030
1.00
1.00
10.5–11.7
0.50
0.040
0.020
Ti, 8 × (%C + %N) min.,
0.15–0.50 max.; Cb 0.10
409-30
S40930
0.030
1.00
1.00
10.5–11.7
0.50
0.040
0.020
(Ti + Cb), [0.08 + 8 × (%C + %N)] min.,
0.75 max.; Ti 0.05 min.
429
S42900
0.12
1.00
1.00
14.0–16.0
—
0.04
0.03
—
430
S43000
0.12
1.00
1.00
16.0–18.0
—
0.04
0.03
—
430Ti
S43036
0.10
1.00
1.00
16.0–19.5
0.75
0.04
0.03
Ti, 5 × %C min., 0.75 max.
434
S43400
0.12
1.00
1.00
16.0–18.0
—
0.04
0.03
0.75–1.25 Mo
436
S43600
0.12
1.00
1.00
16.0–18.0
—
0.04
0.03
—
439
S43035
0.07
1.00
1.00
17.0–19.0
0.50
0.04
0.03
0.1 Al max.; 0.04 N max.;
Ti, 0.20 + 4(%C + %N) min., 1.10 max.
442
S44200
0.20
1.00
1.00
18.0–23.0
—
0.04
0.03
Ti, 0.20 + 4(%C + %N)
444
S44400
0.025
1.00
1.00
17.5–19.5
1.00
0.04
0.03
0.75–1.25 Mo; (Nb + Ti),5 × %C min.
446
S44600
0.20
1.50
1.00
23.0–27.0
—
0.04
0.03
0.25 N
Casting Alloys
CB-30
J91803
0.30
1.50
1.00
18.0–21.0
2.0
0.04
0.04
—
CC-50
J92616
0.50
1.50
1W
26.0–30.0
4.0
0.04
0.04
—
a. Single values are maximum.
b. S40900 (Type 409) has been replaced by S40910, S40920, and S40930. Unless otherwise specified, an order for S40900 or Type 409 may be satisfied by any
one of S40910, S40920, or S40930 at the option of the seller. Material meeting the requirements of S40910, S40920, or S40930 may be certified as S40900.
AWS WELDING HANDBOOK 9.4
The first-generation ferritic stainless steels (Types 430,
442, and 446) contain mainly chromium as a ferrite stabilizer, along with relatively high carbon content. They
are subject to intergranular corrosion after welding
unless a PWHT is applied. They also exhibit low toughness. These steels will form some austenite when heated
to elevated temperatures. The austenite that forms at
elevated temperatures transforms to martensite and
remains in the structure on cooling.
The second-generation ferritic stainless steels (Types
405 and 409) have lower chromium and carbon content, but contain ferrite formers. Aluminum is added to
Type 405 and titanium to Type 409. These steels are
sometimes referred to as pseudoferritic because they
require other ferrite formers in addition to chromium.
Titanium and niobium react with carbon to form carbides, decreasing the amount of carbon in solid solution.
These steels are largely ferritic, although welding or
heat treating can result in a small amount of martensite
in the structure. They are lower in cost, have useful corrosion resistance, and possess better fabrication characteristics than the first-generation ferritic stainless steels,
but they often have low toughness.
Superferritic stainless steels, also referred to as thirdgeneration ferritic stainless steels, have higher chromium,
very low carbon and nitrogen content, and low impurity
levels. These high-chromium ferritic alloys have improved
toughness and ductility and superior corrosion resistance.
These alloys are discussed as the superferritic specialty
grades in the section, Superferritic Stainless Steels of this
chapter.
The coefficients of thermal expansion of ferritic
stainless steel and mild steel are similar (refer to Table
5.2), but the thermal conductivity of ferritic stainless
steels is approximately one-half that of carbon steels.
The ferritic stainless steels approved by ASME for pressure vessel and piping applications are listed under the
P-7 group in Boiler and Pressure Vessel Code, Section
IX for procedure qualification purposes.23
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
283
similar to that of carbon. Because these elements promote the formation of austenite on heating, their presence must be offset by the addition of chromium or
other ferrite stabilizers such as aluminum, niobium,
titanium, and molybdenum in order to reduce the formation of austenite, which transforms to martensite on
cooling. Titanium and niobium also can form stable
carbonitrides at elevated temperatures, which remove
carbon and nitrogen from solution and reduce the tendency of the steel to transform to austenite. The lowand medium-chromium, high interstitial ferritic stainless
steels may contain some fraction of martensite at room
temperature. Both beneficial and detrimental effects
have been shown to exist as a result of the presence of
martensite in ferritic stainless steels. Several investigators
have reported improved toughness for iron-chromiummanganese and iron-chromium-nickel alloys exhibiting
a duplex ferritic-martensitic microstructure over a fully
ferritic or martensitic microstructure.24, 25 In contrast, a
number of investigators argue that martensite is a
source of brittleness because of its fracture and deformation characteristics relative to the ferrite matrix, and
that it lowers ductility and toughness.26, 27, 28 It also has
been reported that an appreciable volume fraction of martensite promotes hydrogen-induced cracking similar to
that found in structural steels. The presence of martensite in low-chromium ferritic stainless steels also is related
to a decrease in corrosion resistance. Although the ferritic grades that contain high levels of chromium do not
normally transform to austenite on heating, chromiumrich carbides can form at the ferrite grain boundaries of
those containing appreciable carbon, even when cooled
rapidly from high temperatures. Depletion of chromium
from the matrix associated with the formation of these
carbides makes the steel susceptible to intergranular
corrosion and increases the potential for loss of ductility.
Susceptibility of ferritic stainless steels to intergranular corrosion can be evaluated using the procedures described
in ASTM A 763, Standard Practices for Detecting Susceptibility to Intergranular Attack in Ferritic Stainless
Steels.29
METALLURGICAL CHARACTERISTICS
The important metallurgical feature of ferritic stainless steels is that their compositions produce a microstructure with ferrite as the predominant phase. The
phase balance is achieved with additions of sufficient
chromium and other ferrite stabilizing elements.
Because minimal austenite forms and the ferrite essentially is stable at all temperatures up to melting, these
steels generally cannot be hardened by heat treatment.
The minimum chromium addition necessary to prevent
austenite formation in steel is a function of the carbon
content, as shown in Figure 5.9. Nitrogen has an effect
23. See Reference 19.
24. Hayden, H. W. and S. Floreen, 1970, The Influence of Martensite
and Ferrite on the Properties of Two-Phase Stainless Steels Having
Microduplex Structures, Metallurgical Transactions 1(7): 1955–1959.
25. Wright, R. N. and J. R. Wood, 1977, Fe-Cr-Mn Microduplex
Ferritic-Martensitic Stainless Steels, Metallurgical Transactions A
8A(12): 2007–2011.
26. Castro, R. J. and J. J. de Cadenet, 1968, Welding Metallurgy of
Stainless and Heat-Resisting Steels, London, U.K.: Cambridge University Press.
27. Kaltenhauser, R. H, 1971, Improving the Engineering Properties
of Ferritic Stainless Steels, Metals Engineering Quarterly 11(2): 41–47.
28. Nishio, Y., T. Ohmae, Y. Yoshida, and A. Miura, 1971, Weld
Cracking and Mechanical Properties of 17% Chromium Steel Weldments, Welding Journal 50(1): 9-s.
29. ASTM International (ASTM), 2009, Standard Practices for Detecting
Susceptibility to Intergranular Attack in Ferritic Stainless Steels, ASTM
A 763-93 (2009), West Conshohocken, Pennsylvania: ASTM International.
284
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
All ferritic stainless steels are susceptible to severe grain
growth when heated above about 927°C (1700°F), and
as a result, toughness decreases. Toughness can be regained only by refining the grain size through cold
working and annealing. Fine-grained ferritic stainless
steels that contain appreciable amounts of carbon also
have low toughness. Typical Charpy V-notch impact
transition temperatures can be above room temperature. In contrast, the low-interstitial types can have
transition temperatures well below room temperature.
The ferritic stainless steels containing more than
about 13% Cr are susceptible to the 475°C (885°F)
embrittlement phenomenon and embrittlement due to
the formation of sigma (σ) and chi (χ) phases when
exposed to intermediate temperatures for long periods.
Because of this, many ferritic stainless steels have temperature exposure limitations of around 400°C (750°F)
in service. Type 409 routinely is used in automobile
exhaust systems above 400°C (750°F).
WELDABILITY
Precautions taken during welding to prevent martensite formation generally are not necessary with the ferritic stainless steels because they cannot be hardened by
quenching. Some martensite formation does not occur
in many ferritic grades. Types 430, 434, 442, and 446
stainless steels, however, are exceptions because they
have both high chromium and high carbon content.
They can have ductile-to-brittle fracture transition temperatures above room temperature. Welds in these alloys
are susceptible to hydrogen-induced cracking on cooling
when they are made under conditions of high restraint,
such as heavy weldments or surfacing welds on carbon
steel. A preheat of 150°C (300°F) or higher can be
used to minimize residual stresses that contribute to weld
cracking.
Ferritic stainless steels that contain unwanted martensite as a consequence of welding should be annealed
at approximately 760°C (1400°F) to restore ductility and
optimize corrosion resistance. This annealing treatment
will transform the martensite to ferrite and spheroidized
carbides.
Microstructure Prediction
The amount of martensite in ferritic stainless steel
weld metal can be predicted from the chemical composition of the weld deposit. A number of equivalency
relationships and diagrams have been developed for this
purpose. Although much more work has been focused
on the development of constitution diagrams for predicting weld metal microstructure in austenitic alloys,
considerable effort has been extended in predicting the
AWS WELDING HANDBOOK 9.4
ferrite/martensite balance in ferritic stainless steel welds.
The Schaeffler diagram, shown in Figure 5.10, has
been employed extensively for many years and provides a good basis for determining weld metal microstructures, but it has been shown to be inaccurate for
predicting weld metal constitution in the ferrite-plusmartensite region.
The Balmforth diagram, shown in Figure 5.11, is a
recently developed ferritic-martensitic stainless steel
constitution diagram. It is currently the most accurate
diagram for predicting ferritic stainless steel weld metal
microstructures. This diagram is considered very accurate up to Nieq = 6 and Creq = 24.
It has slightly extended axes to accommodate a
wider range of alloys. The composition ranges within
which the diagram was developed and considered valid
are as follows: Cr, 11% to 30%; Ni, 0.1% to 3.0%; Si,
0.3% to 1.0%; C, 0.07% to 0.2%; Mn, 0.3% to 1.8%;
Mo, 0% to 2.0%; Al, 0% to 0.3%; Ti, 0% to 0.5% and
N, 0% to 0.25%. It should be noted that microstructures of welds made with processes other than arc welding, and with compositions containing very low carbon
(less than 0.03 wt %) or Al + Ti exceeding 1.0 wt %,
may not be accurately predicted by the diagram.
Corrosion Resistance
Aluminum stabilizes ferrite against austenite formation but does not significantly affect chromium-carbide
precipitation. If properly stabilized, the corrosion resistance of low-chromium ferritic stainless steels stabilized
with aluminum (Type 405) or titanium (Type 409) generally is not affected by the heat of welding.30
Consequently, these steels often are used in the aswelded condition. However, because steels that are
higher in chromium and carbon (Types 430, 434, 442,
and 446) tend to form chromium carbides at grain
boundaries in the HAZ, the weld area is susceptible to
intergranular corrosion in certain corrosive environments.
These steels generally require annealing after welding to
spheroidize carbides and restore corrosion resistance and
toughness.
Hydrogen Embrittlement
Although less susceptible than the martensitic stainless steels, ferritic stainless steels also can be affected by
hydrogen embrittlement, particularly when martensite
is present along ferrite grain boundaries in the weld
metal or HAZ.
30. Fritz, J. D., and I. A. Franson, 1997, Sensitization and Stabilization of Type 409 Ferritic Stainless Steel, Materials Performance (8):
57–61.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
285
LIVE GRAPH
Click here to view
Source: Adapted from Schaeffler, A. L., 1949, Constitution Diagram for Stainless Steel Weld Metal, Metal Progress 56: 560–560B.
Figure 5.10—Schaeffler Diagram for Estimating the Microstructure of Stainless Steel Weld Metal
LIVE GRAPH
Click here to view
Source: Adapted from Balmforth, M. C. and J. C. Lippold, 2000, A New Ferritic-Martensitic Stainless Steel Constitution Diagram, Welding Journal
79(12): 339-s–345-s.
Figure 5.11—Balmforth Diagram
286
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
High-Temperature Embrittlement
The weld metal and HAZs of welds in ferritic stainless steels are subject to grain growth as a result of the
heat of welding. The extent of grain growth depends on
the highest sustained temperature of exposure and the
time at temperature. Along with grain growth, higher
chromium alloys and those with high levels of interstitial
elements (particularly carbon and nitrogen) are susceptible to high-temperature embrittlement (HTE). This condition can result in a dramatic loss of toughness and
ductility in the weld metal and the HAZ relative to the
base metal.
Solidification Cracking
Weld solidification cracking in ferritic stainless steels
is relatively rare, because the primary solidification phase
is ferrite. Alloys containing additional alloying elements,
such as titanium and niobium, or with high impurity
level, have increased susceptibility to solidification cracking, because liquid films with low melting points can form
along solidification grain boundaries. Welds resulting in
high restraint also are more susceptible to cracking during solidification.
ARC WELDING
Arc welding is the usual technique for joining or
repairing ferritic stainless steels. The selection of the
process, the filler metal (if any), and welding variables
are the keys to obtaining satisfactory weldments.
Ferritic Stainless Filler Metals
Filler metals used for welding ferritic stainless steels
to matching steels and to other steels generally are one
of three types:
1. Those with compositions approximately matching
those of the base metals,
2. Austenitic stainless filler metals, or
3. Nickel-alloy filler metals.
The use of ferritic stainless steels for weld filler metal
is limited because the resulting welds lack toughness in
both the weld metal and the HAZ. The availability of
matching filler metal compositions may also be limited.
The difficulty of transferring aluminum and titanium
across the arc further limits the availability of matching
covered electrodes and flux cored electrodes.
Filler metals matching Types 409 and 430 stainless
steels are readily available. (Refer to Tables 5.3, 5.4,
and 5.5.) Types 409 and 430 flux cored filler metals
are specified in AWS A5.22/A5.22M, and also are
AWS WELDING HANDBOOK 9.4
specified in AWS A5.9/A5.9M, along with 409Cb and
446LMo-type filler metals.31 Although shown as ERXXX,
the metal-cored filler metals in A5.9/A5.9M are designated as ECXXX. While the 409 compositions are predominantly metal cored, 409Cb is available also as a
solid filler metal. The ER446LMo is formulated for
welding the 26Cr-1Mo, low-interstitial, superferritic
stainless steels. This filler metal requires special gas
shielding techniques. Gas-shielded and self-shielded
variations of Type 430 filler metal for flux cored arc
welding are listed in A5.22/A5.22M.
Unclassified proprietary filler metals that match
other ferritic stainless steels are sometimes available,
including Types 439, 442, and 446 covered electrodes.
Bare solid wires of Types 434 and 442 steels are seldom available because of the poor wire-drawing characteristics of the wire and limited demand. When
matching base and weld metals are required, proprietary shielded metal arc welding and metal cored electrodes may be available. These compositions are often
used for surfacing on mild or low-alloy steel.
A modified Type 409 bare electrode known as
AM363 alloy, which contains 4% nickel and a small
amount of titanium, has been used in the past to join
Type 409 stainless steel by gas metal arc welding with
argon-oxygen shielding gas. This electrode produces
low-carbon martensitic weld metal with excellent resistance to cracking, although it is largely obsolete today.
Austenitic stainless steel or nickel-alloy filler metals
often are selected for joining ferritic stainless steels to
matching stainless steels or to dissimilar metals. Austenitic stainless filler metals that are relatively high in delta
ferrite, such as Types 309 and 312, are preferred for
joining ferritic stainless steel to other types of stainless
steel and to mild or low-alloy steel. Nickel-alloy filler
metal, such as ERNiCr-3, ENiCrFe-2, or ENiCrFe-3,
can provide sound joints when welding ferritic stainless
steels to other ferritic stainless steels or to mild or lowalloy steels, nickel alloys, and copper-nickel alloys. Type
444 stainless steel can be successfully joined to matching steel with Type 316L weld metal. There is a risk in
using austenitic stainless steel filler metal with ferritic
stainless steel base metals, such as third-generation
alloys, that will be used in environments where resistance to chloride stress corrosion cracking (SCC) is
essential. Austenitic stainless steels generally are less
resistant to chloride SCC than ferritic stainless steel
alloys. In general, the producer of the steel should be
consulted for recommendations on joining these steels
with dissimilar filler metals.
Low-chromium ferritic stainless steels, such as 405
and 409, can be welded to mild steel with carbon steel
filler metals, provided care is taken to avoid excessive
dilution. With normal dilution rates, the weld deposit
31. Refer to Reference 17, AWS A5.22.
AWS WELDING HANDBOOK 9.4
will contain about 2% chromium and have mechanical
properties similar to low-alloy steel with corrosion
resistance superior to the mild steel.
Service conditions must be evaluated prior to selecting a filler metal for joining ferritic stainless steels. In
some cases, the weld joint configuration and thermal
cycling conditions require the use of a filler metal with
matching thermal expansion, even though the mechanical properties of the ferritic stainless weld deposits are
inferior to the austenitic-type weld metal. Austenitic
stainless steel filler metals should not be used in environments where resistance to chloride SCC may be essential.
Preheating
The HAZ of welded joints in ferritic stainless steels
undergoes grain growth and an attendant loss of ductility when slowly cooled.
Certain ferritic stainless steels have a tendency to
form martensite at the grain boundaries. The main
reason for preheating these steels is to help eliminate
hydrogen-induced cracking in the HAZ of the weld and
to limit welding stresses. The need for preheating is
determined to a large extent by composition, desired
mechanical properties, workpiece thickness, and conditions of restraint. Preheating is normally required only
for the ferritic stainless steels with lower chromium or
high-carbon content, and is normally within the range
of 150°C to 230°C (300°F to 450°F). The peak interpass temperature should be limited to the lowest practical level above the preheat temperature, and heat input
should be minimized to avoid grain growth.
Shielded Metal Arc Welding
The only ferritic stainless steel electrode for shielded
metal arc welding (SMAW) listed in AWS A5.4/A5.4M
is E430.32 When a ferritic stainless steel is welded with
austenitic stainless steel electrodes, the electrodes should
have a higher content of chromium than the base metal
and should have sufficient nickel to maintain austenite
stability while allowing for dilution. The most common
austenitic stainless SMAW electrodes used for welding
the ferritic stainless steels are E309 and E309L, except
for Type 430 steel, which is most often welded with E308
and E308L. Electrodes E312 and E310 also are used.
For the free-machining grades of ferritic stainless
steels, E309L-15 lime-type electrodes often are preferred because they will produce about 10 FN (ferrite
number) in the diluted weld metal and because they
produce a convex bead that is more resistant to solidifi32. American Welding Society (AWS) Committee on Filler Metals
and Allied Materials, 2006, Specification for Stainless Steel Electrodes
for Shielded Metal Arc Welding, AWS A5.4/A5.4M:2006, Miami:
American Welding Society.
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
287
cation cracking. For the titanium-bearing or aluminumbearing ferritic stainless steels, electrode selection should
be based on the service requirements of the weldment.
Ferritic stainless steel electrodes require a short welding arc to prevent excessive chromium oxidation and
nitrogen contamination. The short arc length also reduces
the likelihood of porosity in the weld metal. Conversely,
a long arc results in a loss of chromium, increases nitrogen contamination, and might cause porosity in the weld
metal. The weave bead technique is not recommended
because it promotes grain growth.
Gas Tungsten Arc Welding
Direct current electrode negative (DCEN) polarity
should be used for gas tungsten arc welding (GTAW) of
ferritic stainless steels. Argon usually is employed for
shielding, but helium or mixtures of the two can be
used on thick sections. For complete joint penetration
or thin-section welds, a backing gas is used to prevent
oxidation of the backside. Nitrogen never should be used
as a backing gas for welds in ferritic steel (as sometimes
used for austenitic welds) because it causes embrittlement
and loss of corrosion resistance.
The weave bead technique should be avoided. Excessive weaving will lead to contamination of the weld
pool and subsequent embrittlement and loss of corrosion resistance. Overheating and embrittlement of the
weld metal and HAZ in multipass welds can be avoided
by minimizing heat input and by limiting the interpass
temperature to below 95°C (200°F).
Electrode classes ER430, EC409, ER409Cb, and the
superferritic ER446LMo are included in the AWS A5.9/
A5.9M specification, which covers filler metals for
GTAW, GMAW, and SAW.33 The metal cored electrodes
are now also included in AWS A5.22/A5.22M:2010, and
will be deleted from the next revision of AWS A5.9/A5.9M.
Gas Metal Arc Welding
Gas metal arc welding (GMAW) normally is performed with direct current electrode positive (DCEP)
polarity. A shielding gas of argon with 1% oxygen is
recommended with regular spray transfer or pulsedspray transfer. A mixture of helium-argon with 2.5%
carbon dioxide is recommended for short-circuiting transfer. The best shielding gas for an application depends on
the particular steel to be welded and the type of metal
transfer desired.
Short-circuiting transfer requires a small-diameter electrode with low arc voltage and welding current, which
is well suited for welding thin sections. An advantage of
short-circuiting transfer is the relatively low heat input
that tends to limit grain growth in the HAZ, which is
33. See Reference 17.
288
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
advantageous when welding the ferritic stainless steels.
Unfortunately, low heat input can result in incomplete
fusion. As a result, the use of short-circuiting transfer is
often restricted to noncritical applications. This type of
transfer has an advantage when an austenitic stainless
steel filler metal is used to weld a ferritic stainless steel.
Dilution rates as low as 10% can be obtained with a
relatively low heat input.
With spray-type transfer and its high dilution rates,
suitable austenitic stainless filler metals might not be
available to weld all ferritic stainless steel combinations.
In semiautomatic GMAW, spray transfer normally is done
using 0.9 mm and 1.1 mm (0.035 in. and 0.045 in.)
diameter electrodes with higher arc voltages and welding currents than those used for short-circuiting transfer. It gives better assurance against incomplete fusion
and incomplete penetration than short-circuiting transfer. However, welding normally is restricted to the flat
or horizontal positions.
With an electrode of proper size, pulsed spray welding can be used in all welding positions because it permits better control of the weld pool. While the
deposition rate is lower for pulsed spray than for continuous-spray transfer, the pulsed-spray variation develops less total heat input, and minimizes undesirable
grain growth and incomplete fusion.
Flux-Cored Arc Welding
Flux-cored arc welding (FCAW) is similar to GMAW,
except that the electrode is a sheath surrounding alloying elements and flux. Weld deposits produced by
FCAW are never as clean as those produced by the
solid-wire, inert-gas processes (i.e., GMAW and GTAW).
The welding of ferritic stainless steels with FCAW may
be acceptable in less critical applications or when austenitic filler metals can normally be used. FCAW is not recommended for superferritic stainless steels for purity
reasons. Grain growth is a potential problem because
FCAW operates in spray-transfer mode, which results in
higher heat input. Classes E409T-X and E430T-X are
included in the AWS A5.22/A5.22M specification.
Submerged Arc Welding
Some of the ferritic stainless steels can be welded
with the submerged arc welding (SAW) process using
single-pass or multiple-pass procedures. Consideration
must be given to the recovery of chromium when selecting an appropriate flux for these steels because the
efficiency of transfer for this element across the arc varies with the type of flux. Acidic fluxes require highly
alloyed electrodes to compensate for losses across the
arc. Bonded or agglomerated fluxes can be used to add
alloying elements to the weld metal, which permits the
AWS WELDING HANDBOOK 9.4
use of lower alloy electrodes. The flux must not contribute excessive quantities of carbon, manganese, or
silicon to the weld metal. Sulfur and phosphorus must
also remain low because these elements promote solidification cracking.
Heat input may vary widely with submerged arc welding, and this fact should be considered when selecting
this process for joining ferritic stainless steels. High heat
input leads to grain growth in the weld metal and the
HAZ. Austenitic stainless steel electrodes might be desirable for certain applications to avoid the problem of coarsegrained ferritic weld metal. However, grain growth in
the HAZ still occurs, and it will be coarse-grained in
any case. However, a softer filler metal may be beneficial in limiting loss of joint ductility. In such cases, the
effects of dilution must be considered when selecting
the electrode-flux combination. Dilution in submerged
arc welds can range from 30% to more than 50%.
Therefore, an electrode-flux combination that accounts
for dilution should be selected to provide a desirable
weld metal composition for improved weldability.
RESISTANCE WELDING
Ferritic stainless steels frequently are joined via resistance welding processes. Considerations for the various
processes are presented below.
Resistance Spot Welding
General considerations regarding grain growth and
lack of toughness in the ferritic stainless steels that
apply to arc welding also apply to resistance spot welding. When practical, argon should be applied to both
the front and back of the weld joint to protect it from
oxidation and nitrogen pickup. Spot welding of ferritic
steels is not recommended when weld ductility is critical. In the absence of specific recommendations for spot
welding the ferritic stainless steels, welding schedules
recommended for the austenitic stainless steels can be used
as guides. Increased current may be required if large
amounts of ferromagnetic material are in the welding
circuit.
Resistance Seam Welding
The same limitations for resistance spot welding
apply to resistance seam welding of ferritic stainless
steels. Welding schedules recommended for the austenitic stainless steels can be used as guides or starting
points when developing suitable schedules for ferritic
stainless steels.
AWS WELDING HANDBOOK 9.4
Flash Welding
Flash welding may be used to join the ferritic stainless steels, provided the low ductility associated with
welds in these steels can be tolerated. Standard flash
welding techniques are used.
Steels containing as much as 16% chromium can be
flash welded to matching steels without difficulty and
to other chromium-molybdenum steels and plain carbon steels. Higher chromium steels also can be welded
with this process, but will lose ductility resulting from
exposure to high temperatures during welding. The use
of an inert gas atmosphere to protect the steel from oxidation during the flashing period improves the mechanical properties of flash welds. The use of an inert
atmosphere limits the amount of chromium oxide that
forms, thus providing a sounder weld joint. A relatively
long flashing time and a large upset distance should be
used to ensure that all oxides are expelled from the
weld interface.
OTHER WELDING PROCESSES
Ferritic stainless steels can be joined by other welding
processes, such as friction, plasma arc, electron beam,
laser beam, and high-frequency resistance welding. A
vacuum or inert gas shield should be used to protect the
weld zone.
POSTWELD HEAT TREATMENT
The older ferritic stainless steels (Types 430, 442, and
446) often are given postweld heat treatment (PWHT)
to promote one or more of the following effects:
1. Temper any martensite that formed during welding
(usually to ferrite containing some spheroidized
carbide),
2. Reduce stresses caused by welding,
3. Remove the effects of high-temperature embrittlement, and
4. Improve corrosion resistance.
However, PWHT will not remove the effects of ferrite grain growth. When PWHT of first-generation ferritic stainless steels is required, it should be conducted
at temperatures designed to prevent further grain coarsening. Temperatures should range from 700°C to 840°C
(1300°F to 1550°F). These low PWHT temperatures are
essentially spheroidizing anneals for precipitating excess
carbon as coarse chromium carbides in a matrix having
minimum chromium depletion. They also are safely below
the two-phase ferrite-plus-austenite range.
Care must be taken during heat treatment to minimize oxidation, and to avoid embrittlement and loss of
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
289
toughness during cooling through the 540°C to 370°C
(1000°F to 700°F) temperature range. Rapid cooling
through this range is a metallurgical necessity for some
grades. This practice requires appropriate consideration
relative to the effects on distortion and residual stresses.
As long as the standard grades are not furnace-cooled,
problems caused by 475°C (885°F) embrittlement are
unlikely to occur.
Stabilized grades of ferritic stainless steels (Types 405
and 409) can be postweld heat treated at higher temperatures—up to at least 1040°C (1900°F)—without problem.
AUSTENITIC
STAINLESS STEELS
Austenitic stainless steels are the most widely used
stainless steels of all the types. They exhibit a facecentered cubic (FCC) crystal structure and essentially
are nonmagnetic in the annealed condition. They cannot be strengthened by heat treatment, but can be hardened by cold working. They possess good corrosion
resistance, excellent ductility, high toughness, and good
strength. These steels offer excellent cryogenic properties, and good strength and oxidation resistance at high
temperatures.
COMPOSITION
The austenitic stainless steels contain a total chromium, nickel, manganese, and silicon content in excess
of 25% by weight, with chromium content generally
above 16%. The chromium-rich surface oxide provides
oxidation and corrosion resistance in service temperatures approaching 650°C (1200°F) in a variety of environments. Nickel, and to a lesser extent, manganese,
are added to stabilize the austenite phase over a wide
temperature range and prevent its transformation to
martensite when the steel is cooled to room temperature.
These steels generally are fully austenitic, although some
high-temperature ferrite (delta ferrite) may be retained
in the structure.
WROUGHT ALLOYS
The composition, type, and UNS numbers for many
commercially available wrought austenitic stainless
steels are provided in Table 5.12. Alloys based on the
Fe-Cr-Mn-N system have a three-digit alloy designation
starting with 2, such as 201. Alloys based on the Fe-CrNi-C system have a three-digit alloy designation starting
290
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
Table 5.12
Composition of Typical Wrought Austenitic Stainless Steels
Composition
a.
b.
c.
d.
Type
UNS
Number
C
Mn
Si
Cr
Ni
P
S
Other
201
S20100
0.15
5.5–7.5
1.00
16.0–18.0
3.5–5.5
0.06
0.03
0.25 N
202
S20200
0.15
7.5–10.0
1.00
17.0–19.0
4.0–6.0
0.06
0.03
0.25 N
301
S30100
0.15
2.00
1.00
16.0–18.0
6.0–8.0
0.045
0.03
—
302
S30200
0.15
2.00
1.00
11.0–19.0
8.0–10.0
0.045
0.03
—
302B
S30215
0.15
2.00
2.0–3.0
17.0–19.0
8.0–10.0
0.045
0.03
—
303
S30300
0.15
2.00
1.00
17.0–19.0
8.0–10.0
0.20
0.15 min.
0–0.6 Mo
303Se
S30323
0.15
2.00
1.00
17.0–19.0
8.0–10.0
0.20
0.06
0.15 Se min.
304
S30400
0.08
2.00
1.00
18.0–20.0
8.0–10.5
0.045
0.03
—
304H
S30409
0.04–0.10
2.00
1.00
18.0–20.0
8.0–11.0
0.045
0.03
—
304L
S30403
0.03
200
1.00
18.0–20.0
8.0–12.0
0.045
0.03
—
304LN
S30453
0.03
2.00
1.00
18.0–20.0
8.0–12.0
0.045
0.03
0.10–0.16 N
304N
S30451
0.08
2.00
1.00
18.0–20.0
8.0–10.5
0.045
0.03
0.10–0.16 N
305
S30500
0.12
2.00
1.00
17.0–18.0
10.0–13.0
0.045
0.03
—
—
S30601
0.015
0.50–0.80
5.0–5.6
17.0–18.0
17.0–18.0
0.030
0.013
0.20 Mo, 0.35 Cu,
0.05 N
308
S30800
0.08
2.00
1.00
19.0–21.0
10.0–12.0
0.045
0.03
—
309
S30900
0.20
2.00
1.00
22.0–24.0
12.0–15.0
0.045
0.03
—
309S
S30908
0.08
2.00
1.00
22.0–24.0
12.0–15.0
0.045
0.03
—
310
S31000
0.25
2.00
1.50
24.0–26.0
19.0–22.0
0.045
0.03
—
310S
S31008
0.08
2.00
1.50
24.0–26.0
19.0–22.0
0.045
0.03
—
316
S31600
0.08
2.00
1.00
16.0–18.0
10.0–14.0
0.045
0.03
2.0–3.0 Mo
316H
S31609
0.04–0.10
2.00
1.00
16.0–18.0
10.0–14.0
0.040
0.03
2.0–3.0 Mo
316L
S31603
0.03
2.00
1.00
16.0–18.0
10.0–14.0
0.045
0.03
2.0–3.0 Mo
317
S31700
0.08
2.00
1.00
18.0–20.0
11.0–15.0
0.045
0.03
3.0–4.0 Mo
317L
S31703
0.03
2.00
1.00
18.0–20.0
11.0–15.0
0.045
0.03
3.0–4.0 Mo
321
S32100
0.08
2.00
1.00
17.0–19.0
9.0–12.0
0.045
0.03
5 × %C Ti min.
330
N08330
0.08
2.00
0.75–1.5
17.0–20.0
34.0–37.0
0.04
0.03
—
334
S33400
0.08
1.00
1.00
18.0–20.0
19.0–21.0
0.030
0.015
0.15–0.60 Al,
0.15–0.60 Ti
347
S34700
0.08
2.00
1.00
17.0–19.0
9.0–13.0
0.045
0.03
Note c
348
S34800
0.08
2.00
1.00
17.0–19.0
9.0–13.0
0.045
0.03
0.20 Coc, d
384
S38400
0.08
2.00
1.00
15.0–17.0
17.0–19.0
0.045
0.03
—
Single values are maximum percentages unless indicated otherwise.
Higher percentages are required for certain tube manufacturing processes.
10 × %C (Nb + Ta) min.
0.10% Ta max.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
with 3, such as 304. Some of the alloys have several
variations. The addition of nitrogen, denoted by the
suffix “N,” increases the yield strength of the steel and
the stability of the austenite. The high carbon content
of some types, denoted by the suffix H, is controlled
between specific levels for high-temperature strength.
Low-carbon variations are denoted by the suffix L.
Improved machinability is achieved by increasing the
sulfur content or by adding selenium (at the expense of
weldability), such as with Types 303 and 303Se. Increasing the silicon content improves scaling resistance at
elevated temperatures, for example, Type 302B. The
austenitic stainless steels acceptable for ASME boiler and
291
pressure vessel code applications are listed under the P-8
grouping in Boiler and Pressure Vessel Code, Section
IX.34
CAST ALLOYS
The alloy designation, compositions, and UNS designations of some of the cast austenitic stainless steels are
listed in Table 5.13. As noted, some of these are similar to
the corresponding wrought types. The H-grade steels are
34. See Reference 19.
Table 5.13
Composition of Typical Cast Austenitic Stainless Steels
Alloy
Designation
UNS
Number
Composition, %a
Similar
Wrought
Typeb
C
Si
Cr
Ni
Mo
Other
CE-30
J93423
312
0.30
2.0
26–30
8–11
—
—
CF-3
J92700
304L
0.03
2.0
17–21
8–12
—
—
—
CF-3M
J92800
316L
0.03
1.5
17–21
9–13
2.0–3.0
CF-8
J92600
304
0.08
2.0
18–21
8–11
—
—
CF-8C
J92710
347
0.08
2.0
18–21
9–12
—
Note c
CF-8M
J92900
316
0.08
1.5
18–21
9–12
2.0–3.0
—
CF-12M
—
316
0.12
1.5
18–21
9–12
2.0–3.0
—
CF-16F
J92701
303
0.16
2.0
18–21
9–12
1.5
0.20–0.35 Se
CF-20
J92602
302
0.20
2.0
18–21
8–11
—
—
CG-8M
—
317
0.08
1.5
18–21
9–13
3.0–4.0
—
CH-20
J93402
309
0.20
2.0
22–26
12–15
—
—
CK-20
J94202
310
0.20
2.0
23–27
19–22
—
—
CN-7M
J95150
—
0.07
1.5
18–22
27.5–30.5
2.0–3.0
3–4 Cu
HE
J93403
—
0.2–0.5
2.0
26–30
8–11
0.5
—
HF
J92603
304
0.2–0.4
2.0
19–23
9–12
0.5
—
HH
J93503
309
0.2
—
—
—
0.5
—
HI
J94003
—
0.2–0.5
2.0
26–30
14–18
0.5
—
HK
J94224
310
0.2–0.6
2.0
24–28
18–22
0.5
—
HL
J94604
—
0.2–0.6
2.0
28–32
18–22
0.5
—
HN
J94213
—
0.2–0.5
2.0
19–23
23–27
0.5
—
HP
—
—
0.35–0.75
2.0
24–28
33–37
0.5
—
HT
J94605
330
0.35–0.75
2.5
15–19
33–37
0.5
—
HU
—
—
0.35–0.75
2.5
17–21
37–41
0.5
—
a. Single values are maximum percentages. 1.50% Mn max. for CX-XX types. 2.0% Mn max. for HX types. 0.04% P max. (exception: CF-16F has 0.17%
P max.). 0.04% S max.
b. Compositions are similar but not exactly the same as the cast types.
c. 8 × %C Nb, 1.0% Nb max., or 9 × %C (Nb + Ta), 1.1% (Nb + Ta) max.
292
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
used under oxidizing or reducing conditions at elevated
temperatures. The carbon contents of the H-grade steels
generally are higher than those of the CX-XXX alloys
to give the H-grades better strength at elevated temperatures. This increased strength results from finely dispersed carbides in the austenitic matrix.
AUSTENITIC STAINLESS STEEL FILLER
METALS
In addition to standard filler metals for welding most
of the grades of austenitic stainless steels (refer to
Tables 5.3, 5.4, and 5.5), other filler metals are available for welding proprietary austenitic stainless steels.
Consumable inserts for many types of austenitic stainless steels are available.35 They are used most often for
pipe welding.
PROPERTIES
Austenitic stainless steels (refer to Table 5.2) exhibit
greater thermal expansion than the ferritic or martensitic
stainless steels, which means that distortion during
welding can be greater. Type 301 stainless steels often are
magnetic when cold worked because of partial martensitic
transformation. The remaining alloys are used most often
in the solution-annealed condition and have low magnetic
permeability.
Austenitic stainless steels have better ductility and
toughness than carbon steels and alloy steels because of
their face-centered-cubic crystal structure. Notch toughness at cryogenic temperatures is excellent. They are
stronger than carbon steels and low-alloy steels at temperatures above 540°C (1000°F) while maintaining good
resistance to oxidation. Type 316H stainless steels have
the best stress-rupture behavior of the Series 300 alloys.
METALLURGICAL CHARACTERISTICS
Steels of the austenitic group exhibit good resistance
to corrosion and oxidation at temperatures up to 650°C
(1200°F) or higher. These steels also exhibit excellent
ductility and toughness in this temperature range.
Base Metals
Corrosion and oxidation resistance is imparted primarily by a high chromium content, generally greater
than 16 wt %. The addition of the austenite-stabilizing
35. American Welding Society (AWS) Committee on Filler Metals and
Allied Materials, 2007, Specification for Consumable Inserts, AWS
A5.30/A5.30M:2007, Miami: American Welding Society.
AWS WELDING HANDBOOK 9.4
elements carbon, nickel, and nitrogen in various combinations and content, promotes an austenitic structure in
the service temperature range. In some alloys, austenite is
stable from room temperature to the melting-temperature
range. The austenitic (gamma [γ]) phase has a facecentered-cubic crystal structure, is nonmagnetic, and
consists of a solid solution of carbon, chromium, nickel,
and other alloying elements in iron. The predominance
of an austenitic crystal structure in these steels is
responsible for their excellent ductility and toughness.
The austenitic stainless steels contain other intentionally added alloying elements, including manganese
and silicon, and may contain molybdenum, niobium,
titanium, and nitrogen. Manganese is effective in combining with sulfur to form relatively stable manganese
sulfides. Manganese increases solubility of nitrogen, which
in turn, helps stabilize austenite.
Silicon generally is added for deoxidizing purposes in
concentrations up to 1 wt %. At higher levels, silicon is
effective in improving high-temperature oxidation and
scaling resistance. Silicon also enhances the fluidity of
the molten metal, which has important implications for
both welding and casting behavior. However, silicon in
weld metal that has very low or no ferrite promotes
solidification cracking. Molybdenum, a ferrite-forming
element, is added to improve resistance to pitting corrosion and also to provide solid-solution strengthening.
Niobium and titanium are both potent carbide-forming
elements; they are also ferrite formers and are added to
improve resistance to intergranular corrosion.
Nitrogen is a potent austenite-forming element that
increases both the strength and pitting corrosion resistance of the steel when added in concentrations in the
range from 0.1 wt % to 0.25 wt %. Table 5.14 summarizes the effects of the various alloying elements in austenitic stainless steels.
Many surface-active elements, such as sulfur, oxygen
and selenium will significantly affect weld penetration,
depending on their concentration. For example, consider the case of a weld pool produced by the gas tungsten arc welding (GTAW) process on a stainless steel
alloy that is considered low in sulfur (less than 0.005 wt %
or 50 ppm of sulfur). In this case, the surface tension
gradient with respect to temperature is always negative,
as shown in Figure 5.12. Because the liquid metal flows
from regions of low surface tension to regions of high
surface tension, the flow of the liquid metal in this case
is from the center of the weld pool to the fusion boundary (or center-to-edge flow), as shown in Figure 5.13.
This condition results in a wide but shallow weld (low
depth-to-width ratio or D/W).
When sufficient amounts of surface-active elements are
present in the weld pool (such as greater than 0.010 wt %
or 100 ppm sulfur) the surface tension gradient with
respect to temperature is positive, as shown in Figure
5.12. Again, the liquid metal flows from low to high
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
293
Table 5.14
Effects of Alloying Elements in Austenitic Stainless Steels
Element
Types or
Grades of Steel
Effects
Carbon
All types
Strongly promotes the formation of austenite. Can form a carbide with chromium that can lead to
intergranular corrosion.
Chromium
All types
Promotes formation of ferrite. Increases resistance to oxidation and corrosion.
Nickel
All types
Promotes formation of austenite. Increases high-temperature strength, corrosion resistance, and ductility.
Nitrogen
XXXN
Is a very strong austenite former. Like carbon, nitrogen is many times as effective as nickel in forming
austenite. Increases strength, especially at cryogenic temperatures. Increases resistance to pitting
corrosion.
Niobium
347
Added primarily to combine with carbon to reduce susceptibility to intergranular corrosion. Acts as a
grain refiner. Promotes the formation of ferrite. Improves creep strength, but decreases creep ductility.
Manganese
2XX
Promotes the stability of austenite at or near room temperature but forms ferrite at high temperatures.
Inhibits solidification cracking by forming manganese sulfide.
Molybdenum
316, 317
Improves strength at high temperatures. Improves corrosion resistance to reducing media. Promotes
the formation of ferrite.
Selenium
or Sulfur
303, 303Se
Increases machinability but promotes solidification cracking during welding. Lowers corrosion resistance
slightly. Increases weld penetration in gas tungsten arc welding.
Silicon
302B
Increases resistance to scaling. Promotes formation of ferrite, and of sigma when greater than 1%.
Small amounts are added to all grades for deoxidizing purposes. Increases fluidity including wetting of
weld metal to base metal.
Titanium
321
Added primarily to combine with carbon to reduce susceptibility to intergranular corrosion. Acts as a
grain refiner. Promotes the formation of ferrite. Improves creep strength.
Copper
CN-7M
Generally added to stainless steels to increase corrosion resistance to reducing environments. Decreases
susceptibility to stress-corrosion cracking and provides age-hardening effects.
surface tension, meaning that the liquid metal in the
weld pool flows from fusion boundary to weld center
(or edge-to-center flow) that results in a deeper, narrower weld (high depth-to-width ratio or D/W), as seen
in Figure 5.13. Oxygen produces similar effects but is
less potent than sulfur on a wt % basis. Elements that
bind these surface-active elements, such as calcium and
aluminum, will oppose their effect and tend to promote
wide, shallow welds. Penetration in fluxed welding processes depends on the flux ingredients. For more details
and additional theoretical analysis of this subject, refer
to the section Convective Heat Transfer in the Weld Pool
in Volume 1 of the Welding Handbook, 9th edition,
Chapter 3.36 Many of these surface active elements,
such as sulfur, phosphorus and selenium, when present
in sufficient amounts, will increase the susceptibility of
the weld to solidification cracking.
In practice, many austenitic stainless steel base metals contain a small amount of ferrite. Under normal
production conditions, some of this ferrite may persist
36. American Welding Society (AWS) Welding Handbook Committee,
2001, Welding Science and Technology, Volume 1 of Welding Handbook,
9th edition, Miami: American Welding Society.
and remain in the wrought microstructure. If present in
wrought base metals, the ferrite level generally is less
than 2 volume%. The solidification and solid-state
transformation of some austenitic stainless steels often
result in the retention of high-temperature ferrite (designated delta ferrite) in the microstructure to room temperature, a phenomenon described in the next two
subsections of this chapter. Cast alloys may contain
much higher levels of ferrite, depending on the ratio
of elements that stabilize ferrite to those that stabilize
austenite.
Weld Metal
Austenitic stainless steel weld metals can vary significantly from the base metals with respect to both microstructure and mechanical properties. Alloys that are
fully austenitic in the wrought form often exhibit a twophase austenitic/ferritic microstructure in the weld
metal after cooling to room temperature. With some
filler metals, such as Type 16-8-2, small amounts of
martensite also can form in the weld metal, although
this behavior is not typical of the majority of austenitic
294
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
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Note: The data labeled “HIGH D/W HEAT” is from metal that had approximately 160 ppm more
sulfur compared to the metal labeled “LOW D/W HEAT.” Dashed lines indicate expected changes
in surface tension as the temperature is raised.
Source: Adapted from Keene, B. J., K. C. Mills, and R. F. Brooks, 1985, Material Science and Technology 1(7): 569–571.
Figure 5.12—Surface Tension Relative to Temperature
for Two Liquid Steels with Variable Sulfur Content
stainless steels. Carbides, nitrides, and carbonitrides
also have been observed in austenitic stainless steel weld
metal, particularly when titanium or niobium is present
in the base metal or filler metal.
In general, the nominally austenitic microstructure of
as-deposited stainless steel weld metal at room temperature consists primarily of austenite, with a ferrite content ranging from 0 FN to 30 FN. (The concept of
ferrite measurement using the ferrite number (FN) is
discussed more fully in a subsequent section of this
chapter.) For arc welding processes, this phase balance
depends primarily on the weld metal composition, and
to a lesser extent, on process conditions as they influence base metal dilution, weld solidification, and cooling rates.
Austenitic stainless steel weld metals can solidify
with either austenite or ferrite as the primary phase.
When austenite is the primary solidification phase, the
as-deposited weld metal will either be fully austenitic or
may contain ferrite in a small fraction by volume (generally less than 2 FN to 3 FN). This type of ferrite, called
eutectic ferrite, is found at solidification subgrain (cellular
or dendritic) boundaries.
When ferrite is the primary solidification phase, the
final ferrite content of the as-deposited weld metal is
determined by the nature of the ferrite-to-austenite
transformation that occurs in the solid state on cooling.
Under these conditions, the ferrite content generally
ranges from 3 FN to 20 FN, although some highly
alloyed filler materials (such as Type 312) may generate
higher ferrite levels, depending on the degree of basemetal dilution. As described in the following section,
the ferrite may take several morphological forms. The
phase fractions in austenitic stainless steel welds can be
estimated from the chemical composition of the deposited weld metal with the aid of a number of constitution
diagrams and empirical relationships. Foremost among
these diagrams are those developed by Schaeffler, DeLong,
and the Welding Research Council. The utility of some
of these diagrams and the implications of the predictive
capability are detailed in the section, Prediction and Measurement of Ferrite.
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
295
Source: Adapted from Heiple, C. R. and J. R. Roper, Welding Journal 61(4): 97-s–102-s.
Figure 5.13—Fluid Flow on the Surface and Below the Surface of a Weld Pool
Ferrite in Austenitic Stainless Steel Weld
Metal
The presence of delta ferrite in austenitic stainless steel
weld metal is closely correlated with reductions in weld
solidification cracking and weld metal liquation cracking (microfissuring). Since the 1940s, numerous investigations have shown that austenitic stainless steel weld
metals containing 3 FN to 20 FN in the room-temperature
microstructure are resistant to cracking in a wide variety of applications. Although fully austenitic weld metal
also may exhibit acceptable resistance to cracking, the
inherent resistance of ferrite-containing weld metals has
been repeatedly shown to be superior. As a result, many
of the commonly used austenitic stainless steel filler
materials are formulated so that the as-deposited weld
metal contains ferrite in the range of 3 FN to 20 FN,
as previously noted. The use of these filler materials
should be avoided in applications in which the presence
of ferrite can pose problems with respect to service per-
formance, such as at cryogenic temperatures where ductile-to-brittle transitions occur, at elevated temperatures
where sigma-phase formation causes embrittlement, or
where the presence of ferromagnetic materials cannot
be tolerated.
Origin and Nature of Delta Ferrite. The volume
fraction and morphology of delta ferrite observed in the
as-deposited microstructure of austenitic stainless steels
is a product of the solidification and solid-state transformation sequence that occurs during cooling.37 This
sequence can be considered in a qualitative manner
with the aid of a schematic of the 70% iron pseudobinary section of the Fe-Cr-Ni ternary phase diagram
shown in Figure 5.14. It is important to note that tielines on pseudo binary sections do not necessarily lie in the
plane of the sections, and that accurate determinations
37. Brooks, J. A., and A. W. Thompson, 1991, Microstructural
Development and Solidification Cracking Susceptibility of Austenitic
Stainless Steel Welds, International Materials Review 36(1): 16–44.
296
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
SOLIDIFICATION MODE
A
1600
AF
FA
F
LIQUID, L
2600
2200
+
γ
1800
US
γ
δ
S
δ
γ SOLV
1000
VU
OL
γ+δ+L
1200
δ+L
γ
800
+
σ
γ
δ
+
1400
+
δ
σ
+
σ
600
TEMPERATURE, °F
γ+L
δS
TEMPERATURE, °C
1400
1000
70% Fe
400
wt % Cr 5
wt % Ni 25
10
20
15
15
Key:
A = Austenite solidification
AF = Primary austenite solidification
FA = Primary ferrite solidification
F = Ferrite solidification
20
10
25
5
30
0
LIVE GRAPH
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Figure 5.14—Fe-Cr-Ni Pseudobinary Phase
Diagram, 70% Constant Iron Section
of the phase fractions and compositions cannot be
made with these diagrams. Moreover, it should be
understood that the presence of additional alloying elements will change the positions of the phase boundaries
relative to the Fe-Cr-Ni ternary system, and thus, these
diagrams are not well suited for quantitative analysis of
commercial austenitic stainless steels.
The primary phase of solidification may be either
austenite or delta ferrite, depending on the composition
of the specific heat. When solidification occurs as primary austenite (modes A and AF), the as-deposited
microstructure at room temperature may be either fully
austenitic (Mode A) or may contain a small amount of
ferrite (Mode AF). During AF-mode solidification conditions, the ferrite is distributed along solidification
grain and subgrain boundaries (cells and dendrites) and
results from the partitioning of ferrite-forming elements
to these boundaries during weld solidification. This
type of ferrite is often termed eutectic ferrite because it
is believed to form via a eutectic reaction during the
final stages of solidification. A representative microstructure containing eutectic ferrite is shown in Figure
5.15(A).
When solidification occurs as primary ferrite (F or
FA mode), the as-deposited weld metal can exhibit levels of ferrite ranging from 3 FN to 45 FN at room temperature. Weld metals with even higher levels of ferrite
may be classified as duplex stainless steels. (Refer to the
subsequent section Duplex Stainless Steels.) Complete
solidification to ferrite is not thought to occur with the
primary FA mode of solidification in austenitic stainless
steel weld metal. Instead, an invariant reaction (either a
peritectic or eutectic reaction) is believed to intervene
during the final stages of solidification, resulting in the
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
297
F
25 μm
25 μm
(A) Eutectic Ferrite (AF)
(B) Skeletal, or Vermicular, Ferrite (FA)
Figure 5.15—Representative Microstructures of Austenitic Stainless Steel Weld Metal
formation of austenite along solidification grain and
subgrain boundaries. Thus, when solidification concludes, the microstructure is predominantly ferrite with
austenite along solidification subgrain boundaries. On
further cooling, much of the ferrite transforms to austenite, which grows from the boundary austenite preexistent
in the structure. This transformation occurs at elevated
temperatures in the solid state within the two-phase ferrite-plus-austenite region (δ + γ), shown in Figure 5.14.
The extent of this solid-state transformation depends
on the composition and the cooling rate of the weld
metal. These two factors also influence the volume fraction and morphology of the ferrite. A representative
microstructure resulting from primary ferrite solidification
and subsequent transformation to austenite is shown in
Figure 5.15(B).
The range of ferrite morphologies that is observed in
austenitic stainless steel weld metal is shown schematically in Figure 5.16. These ferrite morphologies are
associated with the solidification modes A, AF, FA, and
F. The morphological forms are a strong function of
composition and can be schematically related to the FeCr-Ni pseudobinary diagram, as shown in Figure 5.14.
The following descriptions of the origins of the various ferrite morphologies refer to microstructures that
are generated during arc welding. Under rapid thermal
cycling with commensurate rapid heating and cooling
rates (such as those resulting from laser beam and electron beam welding), microstructural evolution and resultant ferrite morphology may be radically altered. This
behavior is described in the section The Effect of Rapid
Thermal Cycles.
Eutectic Ferrite. Eutectic ferrite forms in the later
stages of primary austenite solidification (Type AF) and
is located along solidification subgrain boundaries (cell
or cellular dendrite interstices). It forms over a narrow
compositional range and is the result of a eutectic reaction during the final stages of solidification. Refer to
Figure 5.15(A).
Vermicular Ferrite. The vermicular, or skeletal, mor-
phology of ferrite is most commonly observed in the
weld metal of austenitic stainless steel. It results from a
diffusion-controlled, solid-state transformation of ferrite
to austenite, following solidification as primary ferrite
(FA mode). Ferrite of this type is located along the original dendrite cores of the primary ferrite solidification
structure. Refer to Figure 5.15(B).
Acicular Ferrite. Acicular or lathy ferrite also results
from primary ferrite solidification (FA mode) but is characteristically in the form of laths or needles that span
the solidification subgrain. This ferrite morphology is typical in high-ferrite weld metal or lower ferrite welds that
have been rapidly cooled. A mixed lathy and vermicular
microstructure often is observed.
Matrix Ferrite with Widmanstätten Austenite.
As the ferrite content increases in the weld metal, the
ferrite phase becomes more stable at elevated temperatures and the transformation to austenite occurs at
lower temperatures. Solidification is believed to occur
completely as delta ferrite (F mode), and that austenite
forms only in the solid state. As a result, the austenite
298
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
AWS WELDING HANDBOOK 9.4
FULLY AUSTENITE
EUTECTIC
VERMICULAR
LATHY
WIDMANSTÄTTEN
LIQUID
LIQUID
LIQUID
LIQUID
LIQUID
TYPE A
TYPE AF
AUSTENITE
TYPE FA
TYPE F
DELTA FERRITE
Figure 5.16—Various Ferrite Morphologies
precipitates preferentially along ferrite-ferrite grain boundaries and nucleates Widmanstätten-like sideplates that
propagate into the grain interiors. This ferrite morphology
is relatively uncommon in austenitic stainless steel weld
metal and is more typical of the duplex stainless steels.
Prediction and Measurement of Ferrite
Aspects of the room temperature microstructure,
including ferrite content, of austenitic stainless steel weld
metal can be estimated from the chemical composition
of the weld deposit. Over the past 40 years, a number of
empirical relationships and diagrams have been developed
for this purpose.
Empirical Relationships and Diagrams. Empirical relationships and diagrams typically use the concepts of chromium and nickel equivalents. Elements
such as Mo, Si and Nb that act like chromium in stabilizing the ferrite phase typically are combined into a
chromium-equivalent equation; whereas elements such
as carbon, nitrogen, copper and manganese that act like
nickel in stabilizing the austenite phase are grouped into
a nickel-equivalent equation. Both equations take the
form of summations of the weight percent of each pertinent element in the alloy with pre-multiplying factors to
indicate the potency of each element relative to chromium
or nickel. A list of various equivalency relationships and
origins is provided in Table 5.15. Examination of the
relationships indicates that elements such as carbon and
nitrogen are much more potent austenite promoters
than nickel, and that small variations in these elements
can significantly influence the ferrite content. Other
alloying elements have less significant effects.
On the basis of these empirical relationships, a number of constitution diagrams have been developed to
AWS WELDING HANDBOOK 9.4
CHAPTER 5—STAINLESS AND HEAT-RESISTANT STEELS
299
Table 5.15
Chromium- and Nickel-Equivalency Relationships for Austenitic Stainless Steels (wt %)
Author
Year
Schaeffler
1949
Creq
Nieq
%Cr + %Mo + (1.5 × %Si) + (0.5 × %Nb)
%Ni + (0.5 × %Mn) + (30 × %C)
DeLong et al.
1956
%Cr + %Mo + (1.5 × %Si) + (0.5 × %Nb)
%Ni + (0.5 × %Mn) + (30 × %C) + (30 × %N)
Hull
1973
%Cr + (1.21 × %Mo) + (0.48 × %Si) +
(0.14 × %Nb) + (2.27 × %V) + (0.72 × %W) +
(2.2 × %Ti) + (0.21 × %Ta) + (2.48 × %Al)
%Ni + [(0.11 × %Mn) – (0.0086 × %Mn2)] +
(24.5 × %C) + (14.2 × %N) + (0.41 × %Co) +
(0.44 × %Cu)
Hammer and
Svenson
1979
%Cr + (1.37 × %Mo) + (1.5 × %Si) +
(2 × %Nb) + (3 × %Ti)
%Ni + (0.31 × %Mn) + (22 × %C) + (14.2 × %N) + %Cu
Espy
1982
%Cr + %Mo + (1.5 × %Si) + (0.5 × %Nb) +
(5 × %V) + (3 × %Al)
%Ni + (30 × %C) + (0.87 × %Mn) + (0.33 × %Cu) +
[A × (%N – 0.045)], where A = 30 for N 0.00 to 0.20%,
A = 22 for N 0.21 to 0.25%, A = 20 for N 0.26 to 0.35%
McCowan, Siewert,
and Olson
(WRC-1988)
1988
%Cr + %Mo + (0.7 × %Nb)
%Ni + (35 × %C) + (20 × %N)
Kotecki and Siewert
(WRC-1992)
1992
%Cr + %Mo + (0.7 × %Nb)
%Ni + (35 × %C) + (20 × %N) + (0.25 × %Cu)
facilitate prediction of weld metal microstructures. One
of the first was the Schaeffler diagram, as shown in Figure 5.10. In the development of the Schaeffler diagram,
the volume percent of ferrite was determined using metallographic measurement methods. The subsequent
DeLong, WRC-1988, and WRC-1992 diagrams cover
subsets of the Schaeffler range for a specific set of stainless steel welds.38, 39, 40, 41 The DeLong diagram (shown
in Figure 5.17) and the WRC-1992 diagram (shown in
Figure 5.18) present ferrite predictions in terms of ferrite number (FN), a magnetically determined standard,
rather than in percentage of ferrite. Each of these diagrams represents an improvement or refinement over a
previous version, and as a result, discrepancies may
result when comparing estimated ferrite content data
from one diagram to another.
38. DeLong, W., G. Ostrom, and E. Szumachowski, 1956, Measurement and Calculation of Ferrite in Stainless Steel Weld Metal, Welding Journal 35(11): 521-s–528-s. DeLong also reported modifying his
diagram to predict Ferrite Number in the following: DeLong, W. T.,
1974, Ferrite in Austenitic Stainless Steel Weld Metal, Welding Journal 53(7): 273-s–286-s.
39. Siewert, T. A., C. N. McCowan, and D. L. Olson, 1988, Ferrite
Number Prediction to 100 FN in Stainless Steel Weld Metal, Welding
Journal 67(12): 289-s–298-s.
40. Kotecki, D. J. and T. A. Siewert, 1992, The WRC-1992 Constitution Diagram for Stainless Steel Weld Metals: A Modification of the
WRC-1988 Diagram, Welding Journal 71(5): 171-s–178-s.
41. Kotecki, D. J., 1997, Ferrite Determination in Stainless Steel
Welds—Advances Since 1974, Welding Journal 76(1): 24-s–37-s. (This
is a comprehensive review of advances in the determination of ferrite
content of stainless steel welds since DeLong.)
The Schaeffler diagram incorporates a much wider
range of compositions than either the DeLong, or
WRC-1992 diagrams and thus has great utility when
evalu