Guide to Weldability
Carbon and Low Alloy Steels
GUIDE TO WELDABILITY:
CARBON and
LOW ALLOY STEELS
How to get the needed results
and stay out of trouble
Written by
Fritz Saenger, Jr., P.E., IWE
This publication is designed to provide information in regard to the subject matter covered. It is made available
with the understanding that the publisher is not engaged in the rendering of professional advice. Reliance upon
the information contained in this document should not be undertaken without an independent verification of
its application for a particular use. The publisher is not responsible for loss or damage resulting from use of this
publication. This document is not a consensus standard. Users should refer to the applicable standards for their
particular application.
550 N.W. LeJeune Road, Miami, Florida
INTRODUCTION
You are responsible for the operation of an independent fabrication
shop, a similar facility within a manufacturing organization, or a
maintenance facility in a factory of any type. “Things” are brought
to you to fabricate or repair. This guide is intended to help you
ask the right questions, and from the answers, select the method,
materials, and procedures that will produce the result desired from
your “customer,” or direct you to more comprehensive guidance that
may be needed to produce the desired results.
ACKNOWLEDGMENTS
Most of the information in this reference guide is condensed from information in the current edition of The
Welding Handbook and Welding Metallurgy, Linnert Volume 1, both published by The American Welding
Society. Additional sources include AWS D1.1/D1.1M:2004, Structural Welding Code—Steel, Jefferson’s Welding Encyclopedia, 18th Edition, The Lincoln Electric Company Procedure Handbook of Arc Welding, and the
ASM Handbook, Volume VI.
Photocopy Rights
Authorization to photocopy items for internal, personal, or educational classroom use only, or the internal,
personal, or educational classroom use only of specific clients, is granted by the American Welding Society
(AWS) provided that the appropriate fee is paid to the Copyright Clearance Center, 222 Rosewood Drive,
Danvers, MA 01923, Tel: 978-750-8400; online: http://www.copyright.com.
ISBN: 0-87171-000-5
© 2005 by the American Welding Society. All rights reserved.
Printed in the United States of America.
Cover photomicrographs courtesy of the AWS Welding Journal, and welding a structure with the SMAW
process photograph courtesy of the AWS Welding Handbook, Vol. 2, 8th Edition, “Welding Processes.”
ii
TABLE OF CONTENTS
Page No.
CHAPTER 1—The Questions (you need to ask) ................................................................................................1
What is the product and how will it be used?..................................................................................................1
What is the material?............................................................................................................................................1
What specifications or codes apply to the welding rods or electrodes (wires), and to the
finished product, if any? ......................................................................................................................................1
Are there welding procedure requirements? Make sure you understand what is required! ...................1
What are the postweld requirements?...............................................................................................................1
CHAPTER 2—Key Background Information......................................................................................................3
What is Steel?.........................................................................................................................................................3
Why is Steel a Unique Structural Material? ......................................................................................................3
Common Steels You May Encounter .................................................................................................................6
What if no information or identification is available?.....................................................................................6
Properties of Steel—What the “Numbers” Mean ............................................................................................6
Some Additional Important Terms ....................................................................................................................6
Alloying Elements in Steels...............................................................................................................................11
Weldability—What is it?....................................................................................................................................14
CHAPTER 3—What Happens When You Weld ...............................................................................................19
Where Does the Welding Heat Go? .................................................................................................................19
The Weld Zones ..................................................................................................................................................19
Shrinkage, Residual Stresses, and Distortion .................................................................................................20
Restraint, Preheat and Interpass Temperatures, and Hydrogen Control...................................................21
Other Effects of Welding ...................................................................................................................................22
CHAPTER 4—Selection of Proper Welding Filler Metal (Rods, Electrodes, etc.) .....................................29
CHAPTER 5—Metallurgically-Related Weld Discontinuities (Defects) and Typical Causes................31
Cracking ...............................................................................................................................................................31
Porosity.................................................................................................................................................................31
Inclusions .............................................................................................................................................................34
CHAPTER 6—Weld Examination and Testing.................................................................................................35
The Weld Cross Section .....................................................................................................................................35
Mechanical Tests—What They Can Tell You .................................................................................................35
CHAPTER 7—Postweld Treatments...................................................................................................................39
CHAPTER 8—Good Practice Reminders...........................................................................................................41
A Basic Welding Procedure Worksheet ..........................................................................................................41
A Qualified Procedure Should be Used by a Qualified Welder ..................................................................41
CHAPTER 9—Additional Information and Guidance ...................................................................................43
APPENDIX 1—Alternative Methods for Determining Preheat (and Preventing Cracking) ...................45
APPENDIX 2—Additional Filler Metal Recommendations ..........................................................................51
iii
LIST OF TABLES
Table
Page No.
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
3.1
3.2
4.1
Composition and Strength Requirements of Typical ASTM Carbon Steels.......................................7
Typical SAE–AISI Compositions ..............................................................................................................8
ASTM Specifications for High-Strength Low-Alloy Structural Steels ................................................9
ASTM Specifications for High-Strength Low-Alloy Steels for Pressure-Vessel Plate ....................10
Composition of Selected Heat-Treatable Low-Alloy (HTLA) Steel......................................................11
Properties for Steel and/or Welds..........................................................................................................12
Effects of Common Alloying Elements at Levels Used in Carbon and Low-Alloy Steels .............12
Carbon Equivalent of Some Steels from Tables 2.1–2.5 .......................................................................17
Prequalified Minimum Preheat and Interpass Temperature .............................................................23
Minimum Preheat and Interpass Temperature for Three Levels of Restraint .................................26
Recommended Base Metal-Filler Metal Combinations for Matching Electrode
Tensile Strengths Nominally of 70 ksi (483 MPa) Minimum..............................................................30
5.1
Common Causes and Potential Solutions to Cracking........................................................................33
5.2
Common Causes of and Remedies for Porosity ...................................................................................33
A2.1 Recommended Base Metal–Filler Metal Combinations for Matching Electrode
Tensile Strengths Nominally of 80–90 ksi (552–620 MPa) Minimum................................................51
A2.2 Recommended Base Metal–Filler Metal Combinations for Steels with Tensile
Strengths Nominally of 100 ksi (689 MPa) Minimum .........................................................................52
A2.3 Suggested Welding Filler Metals for Exposed Applications of ASTM A 242 and A 588 Steels ........53
iv
LIST OF FIGURES
Figure
2.1
2.2
2.3
2.4
2.5
2.7
2.8
2.9
2.10
3.1
3.2
3.3
Page No.
Structural changes in low carbon steel weld metal on cooling from liquid .......................................4
Pattern of dendritic growth from a crystal during solidification.........................................................4
Grain size and shape in solidified metal are determined by the manner in which
the branches of dendrites meet .................................................................................................................5
Weld cross section showing grains...........................................................................................................5
Schematic illustration of (A) Substitutional and (B) Interstitial solid solutions ................................5
Typical tensile specimens: (A) Rectangular and (B) Round................................................................13
Typical tensile test specimen before and after testing to failure, showing maximum
elongation...................................................................................................................................................13
Stress/strain diagram for complete history of a metal tension test specimen from the
start of loading and carried to the breaking point ...............................................................................14
Charpy V-notch impact specimen ..........................................................................................................15
3.5
Schematic showing the different discrete regions present in a single-pass weld............................19
Effect of weld geometry and relative plate thickness on heat flow characteristics.........................20
Multi-pass weld in C-Mn steel plate 1-1/2 in. (40 mm) thick showing
positions of individual weld beads and their heat-affected zones lying both in
weld metal and in base metal ..................................................................................................................20
Longitudinal shrinkage in a butt joint (distribution of longitudinal residual stress, sx,
is also shown).............................................................................................................................................21
Types of distortion ....................................................................................................................................22
5.1
Crack types of weld related cracking .....................................................................................................32
6.1
6.2
6.3
Specimen and test orientation of the guided bend test .......................................................................36
Schematic illustration of typical guided bend test fixtures.................................................................36
Typical tension test specimens for the evaluation of welded joints ..................................................37
8.1
Basic Welding Procedure Worksheet .....................................................................................................42
3.4
v
BASIC SAFETY PRECAUTIONS
Burn Protection. Molten metal, sparks, slag, and hot work surfaces are produced by welding, cutting, and
allied processes. These can cause burns if precautionary measures are not used. Workers should wear protective clothing made of fire-resistant material. Pant cuffs, open pockets, or other places on clothing that can
catch and retain molten metal or sparks should not be worn. High-top shoes or leather leggings and fireresistant gloves should be worn. Pant legs should be worn over the outside of high-top shoes. Helmets or
hand shields that provide protection for the face, neck, and ears, and a head covering to protect the head
should be used. In addition, appropriate eye protection should be used.
Electrical Hazards. Electric shock can kill. However, it can be avoided. Live electrical parts should not be
touched. The manufacturer’s instructions and recommended safe practices should be read and understood.
Faulty installation, improper grounding, and incorrect operation and maintenance of electrical equipment
are all sources of danger.
All electrical equipment and the workpiece should be grounded. The workpiece lead is not a ground lead. It
is used only to complete the welding circuit. A separate connection is required to ground the workpiece. The
workpiece should not be mistaken for a ground connection.
Fumes and Gases. Many welding, cutting, and allied processes produce fumes and gases which may be
harmful to health. Avoid breathing the air in the fume plume directly above the arc. Do not weld in a confined area without a ventilation system. Use point-of-welding fume removal when welding galvanized steel,
zinc, lead, cadmium, chromium, manganese, brass, or bronze. Do not weld on piping or containers that have
held hazardous materials unless the containers have been inerted properly.
Compressed Gas Cylinders. Keep caps on cylinders when not in use. Make sure that gas cylinders are
chained to a wall or other structural support. Do not weld on cylinders.
Radiation. Arc welding may produce ultraviolet, infrared, or light radiation. Always wear protective clothing and eye protection to protect the skin and eyes from radiation. Shield others from light radiation from
your welding operation.
The use of filtering masks or airline respirators will be required if it is determined that personnel are being
exposed to excessive pollutants.
Additional information on welding safety may be obtained from the American Welding Society, 550 N.W.
LeJeune Road, Miami, FL 33126. ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes, and the
AWS Safety and Health Fact Sheets are available online and free of charge on the AWS website:
http://www.aws.org/technical/facts/.
vi
Carbon and Low Alloy Steels
CHAPTER 1
The Questions (you need to ask)
What is the product and how will it be
used?
In other words, what does the product do? Is the
weld a simple connection that bears a light static
(non-fluctuating) load, or are the welds subject to
highly fluctuating loads so that a small defect could
grow into a crack and cause a catastrophic failure?
Will it be subjected to low temperatures, e.g., winters in the north where temperatures well below
0°F can be encountered? (Some steels become brittle
at such temperatures.)
Steel, the American Society of Mechanical Engineers
(ASME) Pressure Vessel Code, various U.S. Military
Standards, and others. If you see reference to such
codes and standards on drawings, notes, or specifications, you and your customer need to reach an
agreement on how these requirements will be handled. Certification, qualification, or conformance to
such “third party” requirements is covered in detail
by each code, and is outside the scope of this guide.
Are there welding procedure
requirements? Make sure you
understand what is required!
Your customer may require the use of:
• a specific welding process,
What is the material?
Find out what specification is used to purchase the
steel. Some of the more common types of steel are
discussed in Chapter 2. If there is no specification, ask
if the material is “plain carbon steel” or “mild steel,”
or (at the other extreme) “tool steel.” In most cases,
the former materials are relatively easy to weld and
somewhat “forgiving.” The latter materials require
extreme care if they are to be welded satisfactorily.
There are some simple tests to help determine the
general class of material that you have, but there is
no substitute for the actual composition or the purchasing specification.
What specifications or codes apply to
the welding rods or electrodes (wires),
and to the finished product, if any?
Most general fabrication is covered by agreement
between the customer and the fabricator, with applicable specifications on drawings and related
notes. However, you need to know if the work is
covered by a code or specification that has legal
standing and/or requires approval of a third party,
which may require qualification of procedures, operators, materials, or other factors. Examples are the
AWS D1.1/D1.1M:2004, Structural Welding Code—
• a specific welding material (type and perhaps
even the brand or manufacturer),
• a specific range of welding conditions,
• “qualified” welding operators (qualified by whom
and to what standard?),
• a written welding procedure subject to the customer’s approval.
NOTE: Even if your customer does not require a formal
procedure, you should consider preparing one. Then, test
your operators to ensure that they can produce satisfactory welds using the procedure. A sample form for preparing an internal record or “control document” is
included in Part 8 of this guide. Such a record has many
benefits, especially if the job is to be repeated. The control
document can be particularly useful if there are problems
with the finished product on inspection or in service.
What are the postweld requirements?
Postweld requirements are as follows:
• Specific inspection and/or testing of the finished
product,
• A specific post-weld heat treatment, e.g., stress
relief,
• Painting, plating, or other surface treatment.
AWS Guide to Weldability 1
Carbon and Low Alloy Steels
NOTES
2 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 2
Key Background Information
What is Steel?
Steel is by far the world’s most widely used structural material, largely because it is relatively inexpensive to produce. Steel also can be modified to
perform in a wide variety of applications by the
addition of small amounts of other materials, called
alloying, and by a wide range of heat treatments and
mechanical treatments, e.g., hot and cold rolling.
The steels covered by this guide contain more than
90% iron (Fe), iron that is usually produced by
smelting iron ore in blast furnaces or the melting of
steel scrap. The iron produced has a high level of
carbon (C), typically as much as 3%, and if poured
into a mold it will solidify into cast iron. Cast iron is
still widely used for machine bases, engine blocks,
and other applications where its ability both to absorb vibration and to provide dimensional stability
are valuable characteristics. However, because of its
structure, cast iron cannot be rolled into thin sections, is difficult to weld, and is unable to handle
bending stresses—all of which limit its use. Converting this iron into steel by processes that reduce
the carbon content well below 1% and allow the
introduction of small amounts of other elements,
results in a wide range of materials that are the
basis for most of the steel products we use today.
Why is Steel a Unique Structural
Material?
Steel is uniquely valuable because of phase transformation—a fundamental characteristic of iron that is
found in only a few other metals (most of which are
not suitable for general use). All metals in solid
state have a distinct crystal structure, i.e., the arrangement of the atoms of the metal and any other
elements that may be present. Iron is different because its crystal structure changes as it is heated
and cooled. These changes in crystal structure,
along with the resulting changes in mechanical
properties (e.g., strength, ductility, and toughness),
can be greatly affected by small changes in chemical composition and rates of heating and cooling.
For example, even the simplest carbon steel, with
carbon content below 0.2% and less than 1% (total)
of manganese and silicon (the most common alloying elements) will become hard and brittle if
quenched rapidly when still “red” hot. If cooled
more slowly, the structure at room temperature
will likely be relatively soft and ductile.
Terms You May Hear
Austenite—the high temperature solid phase (in
carbon and low-alloy steels).
FCC (face-centered cubic).
Ferrite, BCC (body-centered cubic), in several
forms:
• Acicular—desirable structure in low alloy
weld metal.
• Grain Boundary—undesirable structure.
• Polygonal—undesirable structure, formed on
slow cooling.
Martensite—a hard, brittle phase, body-centered
tetragonal (BCT) formed on rapid cooling (or at
slow cooling rates in certain high alloy materials).
Pearlite—a layered structure of ferrite and
cementite, an iron-carbon compound, found in
medium to high carbon steels.
Bainite (lower)—generally desirable structure
found in alloy steel weld metal.
As illustrated in Figure 2.1, simple carbon steel
solidifies into BCC “delta” ferrite then transforms
to FCC austenite, then to BCC “alpha” ferrite, when
cooled slowly. If cooled very rapidly, or quenched,
the structure called martensite may be formed.
When a phase transformation takes place there is a
change in density, which causes high internal
stresses and sometimes results in cracking. Also,
particularly with the rapid cooling rate of welds
and range of composition due to the incomplete
mixing of the filler metal with the base metal, the
room temperature weld may be a mixture of
ferrite(s), pearlite, bainite, martensite, and other
structures.
Solidification typically starts at many points in a
liquid, called nucleation sites. From these points the
individual atoms arrange themselves in a geometric
structure, growing as a single grain until they encounter other grains growing toward them from
other directions. Figure 2.2 is a simplistic representation of grain growth from a single nucleation site.
Where grains meet they form a grain boundary. Here
AWS Guide to Weldability 3
Carbon and Low Alloy Steels
Figure 2.1—Structural changes in low carbon steel weld metal on cooling from liquid.
Note: Depending on
the direction of heat
flow, growth in all
directions may not
be symmetrical.
Figure 2.2—Pattern of dendritic growth from a
crystal during solidification.
4 AWS Guide to Weldability
the orientation of atoms will not be orderly and
there may be concentrations of some elements that
didn’t fit into the expanding grains. Figure 2.3 illustrates boundaries between grains with different orientations, and Figure 2.4 is a cross section of a weld
where these boundaries are clearly visible. Because
of the rapid cooling associated with most welding,
the solidification grain size may persist to room
temperature. However, in a multi-pass weld, the
heating associated with successive passes will often
cause the grains to “recrystallize,” as they pass
through phase changes, resulting in a finer grain
structure that is usually associated with improved
mechanical properties, particularly ductility and
toughness. (This phenomenon may not occur with
alloys that do not exhibit phase changes on heating/cooling, such as the austenitic stainless steels.
In this case, repeated heating may cause undesirable grain growth.)
Carbon and Low Alloy Steels
(A)
Figure 2.3—Grain size and shape in solidified
metal are determined by the manner in which
the branches of dendrites meet.
(B)
Figure 2.5—Schematic illustration of
(A) Substitutional and (B) Interstitial
solid solutions.
0.4 in.
(10 mm)
Photograph courtesy of Edison Welding Institute (EWI)
Figure 2.4—Weld cross section showing
grain structure from initial solidification and
“recrystallization” caused by heat of successive
weld passes.
Alloying elements such as manganese (Mn), Silicon
(Si), Molybdenum (Mo), Chromium (Cr), Nickel
(Ni), Vanadium (V), Copper (Cu) and sometimes
others are added to control these transformations
and achieve the desired combination of mechanical
properties. These elements can replace iron in the
basic matrix (substitutional alloying), while a few are
small enough to fit in between the iron atoms (interstitial alloying). These structures are illustrated in
Figure 2.5. Both types of alloying place stresses on
the matrix and strengthen it, but interstitial elements have a very powerful effect and can initiate
cracking. From the point of view of welding, hydrogen is perhaps the most dangerous element in this
respect, but others, such as arsenic, must also be
kept very low by the steel maker, or the base metal
will be sensitive to cracking.
Both substitutional and interstitial alloying have
limits, and above these limits the alloy elements
may form chemical compounds with iron or other
elements. For example, sulfur forms a low-melting
compound with iron that will remain liquid long
after the alloy has solidified, and shrinkage stresses
may result in cracks. Sulfur compounds in base
metal can also wind up being rolled to films that
can result in lamellar tearing. (Lamellar tearing is
described in Table 5.1.)
Note: A reminder to the reader is that a weld “sees” a
much different pattern of heating and cooling than may
have been experienced by the base material. That is the
AWS Guide to Weldability 5
Carbon and Low Alloy Steels
fundamental reason that welding filler metals may have
substantially different compositions than the base materials. More on that in Chapter 4.
Figure 2.9 is a typical “stress/strain” curve from a
tensile test, illustrating the basis for the measurements described above.
Common Steels You May Encounter
Some Additional Important Terms
Tables 2.1–2.5 list many of the steels in common
use, but there are others. See Chapter 9 for a list of
the groups that publish steel specifications.
Elastic Behavior—most structures are designed to
function in a range where the materials are not
loaded to the point at which permanent deformation takes place. Perhaps the best example of this is
a spring. If you pull (or push) on a spring up to a
certain point, it will return to its original shape
when released. If you pull further, it will take a
“set” and will not return to its original shape. Some
points in the spring have been loaded beyond their
“elastic limit” and plastic deformation has occurred.
What if no information or identification
is available?
If no one can tell you what you have, there are some
simple tests that can help avoid serious difficulty.
These are shown on Figure 2.6. This guide covers
only the carbon steel group; if any of the tests
shown in Figure 2.6 indicate you have another type
of material, e.g., stainless steel, manganese steel,
high sulfur steel, etc., the recommendations of this
guide may not apply.
Note: if you are given material identified as “wrought
iron,” but it is going to be used for decorative or security
purposes, it is probably just low or medium carbon steel,
as true wrought iron is only produced in limited quantities for special applications.
Properties of Steel—What the
“Numbers” Mean
Table 2.6 lists some of the properties that may
accompany specifications for steel and/or welds.
It is important that you understand these characteristics. In many cases, it is just as important to
know how the test was conducted in order to interpret these numbers properly.
Figure 2.7 illustrates typical tensile test specimens.
Note that the “rectangular” specimen shows the
weld in the center, an example of a “transverse tensile test”; the round specimen could have the same
orientation, but it is often oriented longitudinally
(in the direction of welding) and used to measure
weld metal properties separately from the base material. The published properties of filler metals are measured in this manner.
6 AWS Guide to Weldability
Plastic Behavior—materials loaded beyond their
elastic limit either permanently deform, or they
break. Some materials, such as glass, exhibit essentially no plastic behavior, while soft metals such as
copper can be extensively deformed before they
fail. Most steels can be formed by stamping, forging, swaging, or rolling to achieve their final shape,
a common example of plastic behavior.
Transition Temperature—the temperature or range
of declining temperatures over which the impact
energy absorbed in a Charpy V-Notch (CVN) test
drops sharply, and the fracture appearance changes
from rough and torn (shear fracture) to crystalline or
faceted (brittle fracture). In general, though individual codes have specific requirements and limitations, it is considered risky to place structures in
service at temperatures below the transition temperature exhibited in the CVN test, or in other fracture toughness tests.
Work Hardening—virtually all metals become
harder and stronger when they are permanently
deformed (by rolling, drawing, swaging, forging,
etc.) They also lose ductility and will eventually fail
if cold working is continued beyond a certain point.
Ductility of a work-hardened steel can often be
largely restored by annealing, but the more complex alloys may require special heat-treating to obtain original properties.
Residual Stress—stress present in parts of a structure due to mechanical working, or due to shrinkage resulting from the uneven heating and cooling
effects of welding. (See Chapter 3.)
Carbon and Low Alloy Steels
Table 2.1—Composition and Strength Requirements of Typical ASTM Carbon Steels
Application
ASTM
Standard
Type
or
Grade
Tensile Strength
Minimum
Yield Strength
Si
ksi
MPa
ksi
MPa
Typical Composition Limits, %a
C
Mn
Structural Steels
Welded buildings, bridges,
and general structural
purposes
A 360
—
0.29
0.80–1.20
0.15–0.40
58–80
440–552
36
248
Welded buildings and
general purposes
A 529
—
0.27
1.20
—
60–85
414–586
42
290
General purpose sheet
and strip
A 570
30, 33,
36, 40,
45, 50,
0.25
0.25
0.90
1.35
—
—
49–55
60–65
338–379
414–448
30
45
207
310
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
58–71
65–77
70–90
440–489
448–531
483–621
32
35
42
221
241
290
Plate, low and intermediate
tensile strength
A 285
A
B
C
0.17
0.22
0.28
0.90
0.90
0.90
—
—
—
45–65
50–70
55–75
310–448
345–483
379–517
24
27
30
165
186
207
Plate, manganese-silicon
A 299
—
0.30
0.90–1.40
0.15–0.40
75–95
517–655
40
276
Plate, low-temperature
applications
A 442
55
60
0.24
0.27
0.60–0.90
0.60–0.90
0.15–0.40
0.15–0.40
55–75
60–80
379–517
414–552
30
32
207
221
Plate, intermediate and
high-temperature service
A 515
55
60
65
70
0.28
0.31
0.33
0.35
0.90
0.90
0.90
1.20
0.15–0.40
0.15–0.40
0.15–0.40
0.15–0.40
55–75
60–80
65–85
70–90
379–517
414–552
448–586
483–621
30
32
35
38
207
221
241
262
Plate, moderate and
low-temperature 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
55–75
60–80
65–85
70–90
379–517
414–552
448–586
483–621
30
32
35
38
207
221
241
262
Plate, carbon-manganesesilicon heat-treated
A 537
1b
2c
0.24
0.24
0.70–1.60
0.70–1.60
0.15–0.50
0.15–0.50
65–90
75–100
448–621
517–689
45
55
310
379
Pressure Vessel Steels
Piping and Tubing
Welded and seamless
pipe, black and galvanized
A 530
A
B
0.25
0.30
0.95–1.20
0.95–1.20
—
—
48 min.
60 min.
331
414
30
35
207
241
Seamless pipe for
high-temperature 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.
48 min.
60 min.
70 min.
331
414
483
30
35
40
207
241
276
Structural tubing
A 501
—
0.26
—
—
58 min.
400
36
248
Cast Steels
General use
A 270
60–30
0.30
0.60
0.80
60 min.
414
30
207
Valves and fittings for
high-temperature service
A 216
WCA
WCB
WCC
0.25
0.30
0.25
0.70
1.00
1.20
0.60
0.60
0.60
60–85
70–95
70–95
207–586
483–655
483–655
30
36
40
207
248
276
Valves and fittings for
low-temperature service
A 352
LCAc,d
LCBc,d
LCCc,d
0.25
0.30
0.25
0.70
1.00
1.20
0.60
0.60
0.60
60–85
65–90
70–95
414–586
448–621
483–655
30
35
40
207
241
276
a. Single values are maximum unless otherwise noted.
b. Normalized condition.
c. Quenched and tempered condition.
d. Normalized and tempered condition.
AWS Guide to Weldability 7
Carbon and Low Alloy Steels
Table 2.2 Typical AISI–SAE Compositions
Composition wt.% (single values are maximums)
AISI-SAE No.
C
Mn
Si*
P
S
Carbon Steels
1006
0.08
0.45
0.25
0.04
0.05
1010
0.08–0.13
0.30–0.60
0.35
0.04
0.05
1020
0.17–0.23
0.60–0.90
0.35
0.04
0.05
1030
0.27–0.34
0.60–0.90
0.35
0.04
0.05
1040
0.36–0.44
0.60–0.90
0.35
0.04
0.05
1050
0.47–0.55
0.60–0.90
0.35
0.04
0.05
1060
0.55–0.66
0.60–0.90
0.35
0.04
0.05
1070
0.65–0.73
0.60–0.90
0.35
0.04
0.05
1080
0.74–0.88
0.60–0.90
0.35
0.04
0.05
1095
0.90–1.04
0.30–0.50
0.35
0.04
0.05
Manganese-Carbon
1513
0.10-0.16
1.10-1.40
0.35
0.04
0.05
1527
0.20-0.29
1.20-1.50
0.35
0.04
0.05
1541
0.36-0.44
1.35-1.65
0.35
0.04
0.05
1566
0.60-0.71
0.60-0.71
0.35
0.04
0.05
*Silicon levels may vary widely by manufacturer, and can be significantly lower than the maximum shown here.
Stress Relieving—uniform heating of a structure to
a temperature sufficient to relieve all or most of the
residual stresses resulting from welding, followed
by uniform cooling. This works because all steels
“lose” strength as temperatures increase, so local
yielding, sometimes called relaxation takes place.
Stress relieving typically reduces welding-induced
distortion, and makes the structure more stable.
Annealing—heating to eliminate the effect of cold
working, or of rapid or uneven cooling that has created an undesirable (micro)structure. Full annealing takes the material above the full transformation
to austenite, followed by slow cooling to create a
uniform “soft” structure. “Process” annealing
raises the temperature to a point below any transformation to austenite, lowering the hardness and
removing most residual stresses.
8 AWS Guide to Weldability
Normalizing—as with annealing, the material is
heated uniformly to a temperature above the full
transformation to austenite, but it is usually following by rapid cooling, i.e., quenching in water or oil,
and subsequent tempering to achieve the desired
combination of strength and toughness.
Tempering—heating to temperatures below the
transformation point to restore ductility to a
quenched structure.
Note: If terms such as Dynamic Tear, Drop Weight, Explosion Bulge, and Fracture Toughness are used in relation to the structure, do not make welds without the close
guidance of a technical professional, e.g welding engineer, metallurgist, designer; one who is familiar with the
service that the structure will see, and the relevant specification that will almost certainly apply.
Carbon and Low Alloy Steels
Table 2.3—ASTM Specifications for High-Strength Low-Alloy Structural Steels
Composition, %a
ASTM
Specification
Type
or
Grade
C
Mn
A 242
1
0.150
1.000
A 441
—
0.220
A 572
42b
50b
60b
65b
A 588
A 633
A 710
Minimum
Tensile
Strength
P
S
Cr
Ni
Mo
V
Other
ksi
MPa
ksi
MPa
0.150 0.050
—
—
—
—
0.20 min Cu
63–
700
434–
4820
42–
500
289–
3440
0.85–
1.250
0.040 0.050 0.300
—
—
—
—
0.20 min Cu,
0.02 min V
60–
700
413–
4820
40–
500
275–
3440
0.210
0.230
0.260
0.260
1.350
1.350
1.350
1.650
0.040
0.040
0.040
0.040
0.300
0.300
0.300
0.300
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0.20 min Cu
0.20 min Cu
0.20 min Cu
0.20 min Cu
600
650
750
800
4130
4480
5170
5510
420
500
600
650
2890
3440
4130
4480
A
0.10–
0.190
0.90–
1.250
0.040 0.050 0.15– 0.40–
0.300 0.650
—
—
0.02–
0.100
0.25–0.40 Cu
63–
700
434–
4820
42–
500
289–
3440
B
0.200
0.75–
1.250
0.040 0.050 0.15– 0.40– 0.25–
0.300 0.700 0.500
—
0.01–
0.100
0.20–0.40 Cu
—
—
—
—
C
0.150
0.80–
1.350
0.040 0.050 0.15– 0.30– 0.25–
0.300 0.500 0.500
—
0.01–
0.100
0.20–0.50 Cu
—
—
—
—
D
0.10–
0.200
0.75–
1.250
0.040 0.050 0.50– 0.50–
0.900 0.900
—
—
0.30 Cu,
0.05–0.15 Zr;
0.04Nb
—
—
—
—
E
0.150
1.200
0.040 0.050 0.15–
0.300
0.75– 0.10– 0.050
1.250 0.250
0.50–0.80 Cu
—
—
—
—
F
0.10–
0.200
0.50–
1.000
0.040 0.050
0.300 0.40– 0.10– 0.01–
1.100 0.200 0.100
0.30–1.00 Cu
—
—
—
—
G
0.200
1.200
0.040 0.050 0.25– 0.50– 0.800 0.100
0.700 1.000
0.30–0.50 Cu;
0.07 Ti
—
—
—
—
H
0.200
1.250
0.035 0.040 0.25– 0.10– 0.30– 0.150 0.02–
0.750 0.250 0.600
0.100
0.20–0.35 Cu;
0.005–0.030 Ti
—
—
—
—
J
0.200
0.60–
1.000
0.040 0.050 0.30–
0.500
—
0.50–
0.700
—
—
0.30 min Cu;
0.03–0.05 Ti
—
—
—
—
A
0.180
1.00–
1.350
0.040 0.050 0.15–
0.500
—
—
—
—
0.05 Nb
63–
83
434–
5720
420
289
C
0.200
1.15–
1.500
0.040 0.050 0.15–
0.500
—
—
—
—
0.01–0.05 Nb
65–
90
448–
6200
46–
500
317–
3440
D
0.200
0.70–
1.600
0.040 0.050 0.15– 0.250 0.250 0.080
0.500
0.35 Cu
65–
90
448–
6200
46–
500
317–
3440
E
0.220
1.15–
1.500
0.040 0.050 0.15–
0.500
0.04–
0.110
0.01–0.03 N
75–
1000
517–
6890
55–
600
379–
4130
A
0.070
0.40–
0.700
0.025 0.025 0.350 0.60– 0.70– 0.15–
0.900 1.000 0.250
—
1.00–1.30 Cu;
0.02 min Nb
65–
90
448–
6200
55–
850
379–
5860
B
0.060
0.40–
0.650
0.025 0.025 0.20–
0.350
—
1.00–1.30 Cu;
0.02 min Nb
88–
90
606–
6200
75–
850
517–
5860
0.050
0.050
0.050
0.050
Si
Minimum
Yield Strength
0.30
—
—
—
—
—
1.20–
1.500
—
—
—
a. Single values are maximum unless otherwise noted.
b. These grades may contain niobium, vanadium, or nitrogen.
AWS Guide to Weldability 9
Carbon and Low Alloy Steels
Table 2.4—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
1.400
B
0.25
A
Mo
V
Other
ksi
MPa
ksi
MPa
0.040 0.60– 0.35–
0.900 0.600
—
—
—
—
75–
950
517–
6550
450
3100
1.05– 0.035
1.400
0.040 0.60– 0.35–
0.900 0.600
—
—
—
—
85–
1100
586–
7580
470
3240
0.23
0.800 0.035
0.040 0.15–
0.300
—
2.10–
2.500
—
—
—
65–
850
448–
5860
370
2550
B
0.25
0.800 0.035
0.040 0.15–
0.300
—
2.10–
2.500
—
—
—
70–
900
482–
6200
400
2750
D
0.20
0.800 0.035
0.040 0.15–
0.300
—
3.25–
3.750
—
—
—
65–
850
448–
5860
370
2550
E
0.23
0.800 0.035
0.040 0.15–
0.300
—
3.25–
3.750
—
—
—
70–
900
482–
6200
400
2750
A
0.25
0.900 0.035
0.040 0.15–
0.300
—
—
0.45–
0.600
—
—
65–
850
448–
5860
370
2550
B
0.27
0.900 0.035
0.040 0.15–
0.300
—
—
0.45–
0.600
—
—
70–
900
482–
6200
400
2750
C
0.28
0.900 0.035
0.040 0.15–
0.300
—
—
0.45–
0.600
—
—
75–
950
517–
6550
430
2960
C
0.25
1.600 0.035
0.040 0.15–
0.400
—
0.40–
0.700
—
0.13–
0.180
—
105–
1350
723–
9300
700
4820
D
0.20
1.700 0.035
0.040 0.10–
0.500
—
0.40–
0.700
—
0.10–
0.180
—
75–
1050
517–
7230
55–
600
379–
4130
A
0.25
0.95– 0.035
1.300
0.040 0.15–
0.300
—
—
0.45–
0.600
—
—
75–
950
517–
6550
450
3100
B
0.25
1.15– 0.035
1.500
0.040 0.15–
0.300
—
—
0.45–
0.600
—
—
80–
1000
551–
6890
500
3440
C
0.25
1.15– 0.035
1.500
0.040 0.15–
0.300
—
0.40– 0.45–
0.700 0.600
—
—
80–
1000
551–
6890
500
3440
D
0.25
1.15– 0.035
1.500
0.040 0.15–
0.300
—
0.70– 0.45–
1.000 0.600
—
—
80–
1000
551–
6890
500
3440
A 353
—
0.13
0.900 0.035
0.040 0.15–
0.300
—
8.50–
9.500
—
—
—
100–
1200
689–
8270
750
5170
A 735
—
0.06
1.20– 0.040
2.200
0.025 0.400
—
—
0.23–
0.470
—
0.20–0.35
Cu;0.03–0.09
Nb
80–
1150
551–
7920
65–
800
448–
5510
A 736
—
0.07
0.40– 0.025
0.700
0.025 0.350 0.60– 0.70– 0.15–
0.900 1.000 0.250
—
1.00–1.30
Cu;0.02 min Nb
72–
1050
496–
7230
55–
750
379–
5170
A 737
B
0.20
1.15– 0.035
1.500
0.030 0.15–
0.500
—
—
—
—
0.05 Nb
70–
900
482–
6200
500
3440
C
0.22
1.15– 0.035
1.500
0.030 0.15–
0.500
—
—
—
0.04–
0.110
0.03 Nb
80–
1000
551–
6890
600
4130
A 204
A 225
A 302
S
Si
*Single values are maximum unless otherwise noted.
10 AWS Guide to Weldability
Cr
Minimum
Yield
Strength
Ni
A 203
P
Minimum
Tensile
Strength
Carbon and Low Alloy Steels
Table 2.5—Composition of Selected Heat-Treatable Low-Alloy (HTLA) Steel
Composition, wt.%
AISI-SAE or
Other
Designation
C
Mn
Si
Cr
Ni
Mo
V
1330
0.28–0.33
1.60–1.90
0.15–0.30
—
—
—
—
1340
0.38–0.43
1.60–1.90
0.15–0.30
—
—
—
—
4023
0.20–0.25
0.70–0.90
0.15–0.30
—
—
0.20–0.30
—
4028
0.25–0.30
0.70–0.90
0.15–0.30
—
—
0.20–0.30
—
4047
0.45–0.50
0.70–0.90
0.15–0.30
—
—
0.20–0.30
—
4118
0.18–0.23
0.70–0.90
0.15–0.30
0.40–0.60
—
0.08–0.15
—
4130
0.28–0.33
0.40–0.60
0.15–0.30
0.80–1.10
—
0.15–0.25
—
4140
0.38–0.43
0.75–1.00
0.15–0.30
0.80–1.10
—
0.15–0.25
—
4150
0.48–053
0.75–1.00
0.15–0.30
0.80–1.10
—
0.15–0.25
—
4320
0.17–0.22
0.45–0.65
0.15–0.30
0.40–0.60
1.65–2.00
0.20–0.30
—
4340
0.38–0.43
0.60–0.80
0.15–0.30
0.70–0.90
1.65–2.00
0.20–0.30
—
4620
0.17–0.22
0.45–0.65
0.15–0.30
—
1.65–2.00
0.20–0.30
—
5120
0.17–0.22
0.70–0.90
0.15–0.30
0.70–0.90
—
—
—
5145
0.43–0.48
0.70–0.90
0.15–0.30
0.70–0.90
—
—
—
6150
0.48–0.53
0.70–0.90
0.20–0.35
0.80–1.10
—
—
0.15–0.25
8620
0.18–0.33
0.70–0.90
0.15–0.30
0.40–0.60
0.40–0.70
0.15–0.25
—
8630
0.28–0.33
0.70–0.90
0.15–0.30
0.40–0.60
0.40–0.70
0.15–0.25
—
8640
0.38–0.43
0.70–0.90
0.15–0.30
0.40–0.60
0.40–0.70
0.15–0.25
—
Alloying Elements in Steels
The family of steels is created by several factors:
• The steelmaking process
• Addition of alloying elements
— for “conditioning,” e.g., deoxidizing, grain
size control
— for mechanical properties, e.g., strength, ductility, toughness
• The rolling and forming processes
• Heat treatment
• Combinations of the above
Modern steelmaking technology permits very close
control of undesirable elements such as sulfur and
phosphorous, and precision additions of desired elements in order to assure the desired properties.
Alloying elements are added to increase strength,
to achieve higher strength in thick sections, (gener-
ally described as hardenability,) to increase ductility
and toughness, to provide resistance to softening at
elevated temperatures, to resist corrosion, and for
other purposes. Table 2.7 is a brief summary of the
effects of common alloying elements at the levels
used in carbon and low-alloy steels. These effects
can be quite different at other levels, e.g., in the
steels covered here, chromium is used for strengthening and elevated temperature performance. At
much higher levels, it promotes corrosion resistance in stainless steels.
Most structural alloys have been developed with
comprehensive weldability considerations, but in
general, as the strength and thickness of a material
increase, the level of care and control required to
assure a satisfactory weld increases rapidly. Some
materials have intentional additions of sulfur or
lead to enhance their performance in machining operations. So-called free-machining steels are often
quite difficult to weld, and special techniques may
be required to make satisfactory welds.
AWS Guide to Weldability
11
Carbon and Low Alloy Steels
Table 2.6—Properties for Steel and/or Welds
Tensile Properties (Refer to Figures 2.7, 2.8, and 2.9)
U.S.
SI (Metric)
Strength—this term is always quoted or specified in units that reflect a
(tension) load over a specific area. Following are common terms for strength in
the U.S. Customary Units and International (metric) Units.
psi (pounds/
square inch)
MPa (newtons/
square meter)
Yield Strength—the load at which the material takes a permanent “set,” i.e.,
plastic deformation has begun. In a tensile test, this is customarily defined as
the point at which 0.2% (plastic) deformation has occurred.
psi
MPa
Tensile Strength (or Ultimate Tensile Strength)—the point in loading where
the maximum unit load is recorded. Because the specimen will normally “neck
down” and reduce its cross-sectional area before failing, the load at failure may
actually be lower. Also, since some reduction in area will likely have occurred
prior to reaching the maximum load, the number isn't accurate, but it is the one
normally used.
psi
MPa
Elongation—a measure of the “stretch” of a tensile specimen from initial
loading to failure. It is the percentage change in the “Gage Length” in Figures
2.7 and 2.8.
%
%
Reduction of Area—this indicator of ductility is the reduction of cross section
from the original to the area of the tensile test specimen when it breaks. Figure
2.8 illustrates how a tensile specimen typically “necks down” before failure.
Reduction in Area is calculated as 1 – (Area at Df /Area at Ds) × 100.
%
%
Toughness—a term intended to measure the resistance of the material to
catastrophic failure when under load. A variety of tests and indicators have
been developed to provide assurance that a structure will not fail in a
catastrophic, i.e., brittle or glasslike manner, but the most common is the
Charpy V-Notch Test. See Figure 2.10. This test is often conducted over a
range of temperatures to determine the tendency of a structure to become
“brittle” at low temperatures. (See “Transition Temperature” definition on page 6.)
ft-lb
Joules
Table 2.7—Effects of Common Alloying Elements at Levels Used in Carbon and Low-Alloy Steels
Common
Alloying
Elements
Range in Carbon and
Low-Alloy Steels (%)
Carbon (C)
0.01–0.80
Most powerful hardener
Manganese (Mn)
0.02–2.50
Deoxidizes, ties up sulfur, increases hardenability
Silicon (Si)
0.3–2.0
Strong deoxidizer, increases hardenability
Chromium (Cr)
0.1–3.0
Strongly increases hardenability, improves high temperature strength
Nickel (Ni)
0.25–5.00
Promotes thick section hardenability
Molybdenum (Mo)
0.05–1.50
Strong hardener, improves creep resistance
Niobium (Nb)
0.01–0.15
Strong hardener, “micro alloying” agent
Vanadium (V)
0.05–0.10
Very strong hardener, “micro alloying” agent
Copper (Cu)
0.1–1.2
Moderate hardener, high levels promote corrosion resistance, can cause weld
cracking sensitivity
Sulfur (S)
0.005–0.040
Undesirable, can result in solidification cracking
Phosphorus (P)
0.005–0.040
Undesirable, can promote embrittlement
12 AWS Guide to Weldability
Effect
Carbon and Low Alloy Steels
Test
Material
Low
Carbon
Steel
Appearance
Test
Dark Grey
Magnetic
Test
Strongly
Magnetic
Chisel Test
Continuous Chip
Smooth Edges
Chips Easily
Fracture
Test
Flame
Test
Bright Grey
Melts Fast
Becomes
Bright Red
Before
Melting
Spark Test*
Long Yellow Carrier Lines
(Approx. 20% Carbon or Below)
Medium
Carbon
Steel
Dark Grey
Strongly
Magnetic
Continuous Chip
Smooth Edges
Chips Easily
Very Light
Grey
Melts Fast
Becomes
Bright Red
Before
Melting
Yellow Lines Sprigs Very Plain Now
(Approx. 20% to 45% Carbon)
High
Carbon
Steel
Dark Grey
Strongly
Magnetic
Hard to Chip
Can Be
Continuous
Very Light
Grey
Melts Fast
Becomes
Bright Red
Before
Melting
Yellow Lines Bright Burst
Very Clean Numerous Star Burst
(Approx. 45% Carbon and Above)
High
Sulphur
Steel
Dark Grey
Strongly
Magnetic
Continuous Chip
Smooth Edges
Chips Easily
Bright Grey
Fine Grain
Melts Fast
Becomes
Bright Red
Before
Melting
Manganese
Steel
Dull Cast
Surface
Non
Magnetic
Extremely Hard
to Chisel
Coarse
Grained
Melts Fast
Becomes
Bright Red
Before
Melting
Stainless
Steel
Bright,
Silvery
Smooth
Depends
on Exact
Analysis
Continuous Chip
Smooth Bright
Color
Depends
on Type
Bright
Melts Fast
Becomes
Bright Red
Before
Melting
Swelling Carrier Lines, Cigar Shape
Bright White, Fan-Shaped Burst
Cast Iron
Wrought
Iron
Dull Grey
Evidence of
Sand Mold
Light Grey
Smooth
Strongly
Magnetic
Strongly
Magnetic
Small Chips
About 1/8 in., Not
Easy to Chip,
Brittle
Continuous Chip
Smooth Edges,
Soft and Easily
Cut and Chipped
Brittle
Bright Grey
Fibrous
Appearance
Melts
Slowly
Becomes
Dull Red
Before
Melting
Melts Fast
Becomes
Bright Red
Before
Melting
1. Nickel-Black Shape Close to Wheel
2. Moly-Short Arrow Shape Tongue (only)
3. Vanadium-Long Spearpoint Tongue (only)
Red Carrier Lines
(Very Little Carbon Exists)
Long, Straw Color Lines
(Practically Free of Bursts or Springs)
*For best results, use at least 5000 surface feet per minute on grinding equipment.
(Cir. × R.P.M.)/12 = S.F. per Min.
Figure 2.6—Visual identification techniques.
AWS Guide to Weldability
13
Carbon and Low Alloy Steels
Key:
T =
W =
D =
L =
R =
P =
G =
Thickness of the reduced section (rectangular), in. (mm)
Width of the reduced section (round), in. (mm)
Diameter of the reduced section (round), in. (mm)
Specimen length, in. (mm)
Radius, in. (mm)
Parallel (“reduced”) section
Gauge length, in. (mm)
Figure 2.7—Typical tensile specimens:
(A) Rectangular and (B) Round.
Weldability—What is it?
The official definition of weldability is the capacity
of a material to be welded under the imposed fabrication conditions into a specific, suitably designed
structure, and to perform satisfactorily in the intended service. In practical terms, this means that
the material can be subjected to the welding process, e.g., preparation for welding, heating, mixing
with filler material, cooling, and possible postweld
heat treatment—all without cracking and while
maintaining required mechanical properties.
One key indicator of the potential difficulty in
welding any carbon or low-alloy steel is its Carbon
Equivalent (CE). Several formulas have been developed to provide this indicator, and although each
of these formulas produces slightly different results, they all show that as the CE increases, there
are increased risks of cracking from a variety of
causes, and degradation of the base metal from the
14 AWS Guide to Weldability
Figure 2.8—Typical tensile test specimen before
and after testing to failure, showing maximum
elongation.
effects of welding heat. These risks must be mitigated by control of weld preheat and post heat, selection of filler metals, control of the welding
process, including heat input, etc.
The Carbon Equivalent becomes much more important as section thickness increases, because most alloying elements are added to enhance the “deep
hardening” characteristics of a material. A good
rule of thumb is to consider this factor when the
thickness of any section to be welded is more than
1/2 in. (13 mm) thick, as it is above this thickness
that heat flow from the weld increases rapidly. (See
Table 2.8.)
CE Formulas
Simplest: CE = %C +
% Mn + %Si
4
(suitable for carbon steels only)
(Eq. 1)
Carbon and Low Alloy Steels
Figure 2.9—Stress/strain diagram for complete history of a metal tension test specimen from the start
of loading and carried to the breaking point.
For low-alloy steels:
% Mn %Cr + % Mo + % V
+
6
5
%Si + % Ni + %Cu
+
15
CE = %C +
(Eq. 2)
The Carbon Equivalent provides an indication of
the hardness/strength that will result from rapid
cooling of a particular composition. It does not in-
dicate depth of hardening, a key factor in the selection of materials for specific applications. In other
words, an AISI 1040 steel will develop high
strength in sections up to about 3/8 in. (10 mm)
thick when quenched, while an A 514 Grade 70
will develop full strength in a 2 in. (50 mm) thickness. This reinforces the importance of preheat, interpass temperature control and stress relief
and/or tempering in such sections, as well as the
importance of controlling hydrogen and the risk of
cracking.
AWS Guide to Weldability
15
Carbon and Low Alloy Steels
Figure 2.10—Charpy V-notch impact test.
16 AWS Guide to Weldability
Carbon and Low Alloy Steels
Table 2.8—Carbon Equivalent of Some Steels from Tables 2.1–2.5
Carbon and Composition Parameter* Equivalents for Some Common Steels
Code
AISI*
ASTM
Carbon
Equiv.
P
(comp)*
Code
Type
Grade
Carbon
Equiv.
P
(comp)*
1010
0.25
0.17
ASTM
A572
45
0.47
0.30
1020
0.35
0.27
50
0.49
0.32
1030
0.51
0.40
60
0.52
0.35
1040
0.61
0.50
65
0.57
0.36
1060
0.83
0.72
A
0.42
0.30
1080
1.05
0.94
B
0.49
0.36
C
0.54
0.41
A588
Typ
0.75
0.39
A514–517
A
0.72
0.44
Type
Grade
A36
A106
0.52
0.36
58
0.40
0.29
65
0.49
0.33
70
0.58
0.42
G
0.72
0.36
55
0.46
0.34
Q
0.99
0.43
60
0.49
0.37
4130
0.72
0.44
65
0.51
0.39
4140
0.89
0.56
70
0.58
0.42
4340
0.83
0.55
A537
0.53
0.33
A441
0.22
0.22
11
0.66
0.30
22
1.02
0.40
A573
A515
AISI*
ASTM
A387
*P (comp), the Composition Parameter, along with a factor relating to the hydrogen content of the weld metal, is used to calculate the
cracking potential related to hydrogen, the Susceptibility Index, which is described in more detail in Chapter 3.
AWS Guide to Weldability
17
Carbon and Low Alloy Steels
NOTES
18 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 3
What Happens When You Weld
It has been said that fusion welding is essentially a
mini steelmaking process! It is certainly a new alloy
making process, taking place under very dynamic
conditions. In a matter of seconds, the base metal at
the joint is taken from, at, or near room temperature
to above its melting point, new molten metal of a
different composition is added, and the mixed material solidifies and begins cooling back toward
room temperature. In addition, the base metal just
next to the weld zone, or heat-affected zone (HAZ),
will experience a range of conditions from partially
melted to barely disturbed. Figure 3.1 shows typical
effects, some of which may be beneficial, while others can result in damage or defects that can affect
the performance of the structure.
Where Does the Welding Heat Go?
In arc welding, most of the heat produced by the
arc goes into the weld, though the amount can vary
greatly by process, speed of welding, and other factors. So-called arc efficiency can vary from 65–90%,
though this factor is not included in standard calculations of “heat input.”
The commonly used heat input calculation is (Arc)
Amps × (Arc) Volts × 60/Travel Speed (ipm) with
the result in joules per inch.
An example:
Arc Current
Arc Voltage
Travel Speed
250 amps
22 volts
10 ipm/sec (4.2 mm/sec)
Heat input will be calculated as 250 × 22 × 60/10 =
33,000 joules/in. (13 × 105 kj/m).
Most of the heat that enters the workpiece from arc
and molten filler metal flows into the base material
before radiating into the surrounding air. The rate
at which the heat is removed from the weld area is
primarily affected by the base metal thickness. With
commonly used welding conditions on plate material, at thicknesses below 1/2 in., heat flow is generally “two dimensional, i.e., it flows primarily to the
sides (or the legs of a fillet weld), and ahead of the
arc in the direction of welding. At thicknesses
above 3/4 in., heat flow becomes “three dimensional,” as heat flow in the thickness direction becomes significant, resulting in much more rapid
cooling rates. (Thicknesses between 1/2 in. and
3/4 in. are a transition area.) Figure 3.2 illustrates
these effects in a single pass weld; the effects are
equivalent in multipass welds, as the thicker section is a much greater “heat sink.” One can see that
three-dimensional heat flow would occur in a much
thinner section if very low welding current were
used. This is the reason that arc strikes on thick
plate are to be avoided, because the very rapid cooling that takes place following the strike can cause
formation of martensite and initiate cracking.
Some of the practical effects of these differences are:
• Low-alloy steels that rely on fairly rapid cooling
to obtain strength and toughness may require
rigid controls on heat input to develop expected
properties in thin sections.
• As section thickness increases, preheat and interpass temperature levels must increase, particularly in the low-alloy steels.
• In the high-carbon steels, postheating may be
required to prevent cracking.
The Weld Zones
Figure 3.1—Schematic showing the different
discrete regions present in a single-pass weld.
Figure 3.1 is a drawing of the cross section of a single pass weld in steel. The central part has been fully
melted and is a mixture of base and filler metal. At
the “fusion line,” we move to an area that has been
partially melted, then to one that has fully transformed to austenite with some grain growth, to an
area of grain refinement, to an area of tempering
AWS Guide to Weldability
19
Carbon and Low Alloy Steels
welding speed consistent with adequate penetration of the
base metal and good (multi-pass) bead tie-in.
(A) Three-Dimensional Heat Flow
(B) Two-Dimensional Heat Flow
Shrinkage, Residual Stresses, and
Distortion
Another effect of the heating and cooling process is
the changes in shape that may occur in a structure
when welding is done. This is caused by the expansion due to heating and shrinkage due to cooling. If
we heat a structure uniformly, it will tend to expand and contract, returning to the same shape as
before. However, when welding, we move a “spot
source” of heat across the structure.
As material is heated, it wants to expand, but well
before melting, it effectively loses its strength and
“yields” to fit into the available space.
(C) Intermediate Condition—Neither Thick Nor Thin
Figure 3.2—Effect of weld geometry and relative
plate thickness on heat flow characteristics.
When material cools, it regains its strength, and as
it shrinks, it places very high (local) loads on the
undisturbed material around it. When the loads
reach the yield point of the material it will stretch,
but when it reaches room temperature, stresses
(heating below the transformation temperature),
and then to the undisturbed base metal. In a carbon
steel, the major effect may be a softening of the base
metal. In low-alloy steels, and particularly those
using “micro-alloying” for strength and toughness,
this heating cycle may degrade both strength and
toughness. Further, hydrogen from the weld metal
may migrate into the HAZ, and result in underbead
cracking. The “family” of possible weld defects is
described and discussed in Chapter 5 of this guide.
In thicker sections, where a weld may involve
many passes, weld beads deposited first will be reheated by succeeding passes, in most cases resulting in grain refinement and improvement of
mechanical properties. However, in thick sections,
the heat flows away from the weld much more rapidly, and preheat and/or postheating may be required to prevent a martensite transformation and
its associated brittleness and/or cracking. Figure
3.2 illustrates this situation.
Simple cross sections like this are valuable tools
in establishing a welding procedure, and preparation
of a basic weld cross-section is described in Chapter 6.
Note: In general, it is usually best to establish a welding
procedure that minimizes the size of the heat-affected zone,
i.e., the heating and cooling cycle is as rapid as possible.
This is usually accomplished by using the highest practical
20 AWS Guide to Weldability
Photograph courtesy of The Welding Institute, England
NOTE: Weld beads at top and bottom faces on right-hand side of
weld zone in this transverse full-section specimen are in the asdeposited condition. As subsequent weld beads were deposited,
those regions of their HAZ that exceeded the AC1–AC3 critical
range have a light color on the etched surface. Those regions
that were heated to a lower temperature, that is, below the AC1
temperature, underwent tempering, and these tend to have
darker coloration upon being etched. The horizontal streaks in
the plate on the right-hand side indicate a small amount of segregation of carbon and/or other residual elements.
AC1 = Temperature on heating at which transformation to austenite
begins
AC3 = Temperature on heating at which transformation to austenite
is complete
Figure 3.3—Multi-pass weld in C-Mn steel
plate 1-1/2 in. (40 mm) thick showing
positions of individual weld beads and
their heat-affected zones lying both in
weld metal and in base metal.
Carbon and Low Alloy Steels
equal to the yield point will remain. Depending on
the location in or adjacent to the weld, this residual
stress pattern is likely to vary from yield point tensile at the center of the weld to somewhat lower
compressive at the edge of the heat-affected zone,
then tapering off to zero some distance from the
weld. Thus, if it can, the material around the
shrinking metal will bend to reduce the load on it.
Figure 3.4 illustrates a typical residual stress pattern in a single pass butt weld, while Figure 3.5 illustrates typical distortion patterns that can occur
in butt and fillet welds.
Distortion can be reduced by restraining the assembly so it cannot bend (use of clamps, fixtures, temporary braces, etc.). However, this will tend to
increase the residual stress in the structure—and in
some cases it will result in cracking. It may also
make the structure unstable, i.e., small loads placed
on it may cause permanent deformation because
the loaded section was already at its yield point due
to residual stresses.
You can sometimes compensate for distortion by
assembling the parts to be welded so that distortion
will move them into the proper position, e.g., a
fillet-welded joint can be tacked at an angle
somewhat greater than the intended angle, and
distortion will move it toward the desired position.
Many times, however, this is not possible.
The best way to reduce distortion is to use the least
amount of heat possible. For example:
(1) Obtain the best fitup possible. Gapped or mismatched joints require more filler metal, meaning
more heat and more shrinkage stresses.
(2) Don’t “overweld,” i.e., don’t make a weld larger
than absolutely necessary to meet service
requirements.
(3) Wherever possible, deposit a deeply penetrating fillet weld. (If the root of the weld is below the
surface of the plate it is less likely to cause angular
distortion.)
(4) Weld as quickly as possible, so a minimum
amount of weld and base metal is subjected to
welding heat. Remember, increased heat means increased expansion, more shrinkage and shrinkage
forces (residual stress).
(5) Stress-relieve the weldment. By heating to temperatures below transition point, local stresses are
greatly reduced, reducing distortion and increasing
the stability of the structure
Restraint, Preheat and Interpass
Temperatures, and Hydrogen Control
Benefits and Risks of Restraint
As mentioned previously, restraint can reduce the
distortion caused by weld shrinkage. If restraint is
used or present due to material thickness and joint
design, however, higher preheat and interpass temperatures may be required to prevent cracking due
to residual stresses and hydrogen.
Restraint can be classified in three categories:
RESIDUAL STRESS
TENSION
COMPRESSION
Y
Low—joint members have reasonable freedom to
move with shrinkage stresses
Medium—joint members have limited freedom of
movement due to connections to other structures,
use of heavy clamping, strongbacks, etc.
High—joint members have virtually no freedom
of movement due to thickness, or repair in thick
sections.
Y
Reprinted with permission of the
Welding Research Council (adapted)
Figure 3.4—Longitudinal shrinkage in a
butt joint (distribution of longitudinal
residual stress, σx, is also shown).
Preheat requirements are part of many codes. Requirements of AWS D1.1/D1.1M:2004, Structural
Welding Code—Steel, are shown in Table 3.1. These
requirements are based on medium restraint as described above.
There is a more detailed method available to deal
with a wide range of special situations. This
AWS Guide to Weldability
21
Carbon and Low Alloy Steels
Figure 3.5—Types of distortion.
involves the use of the Composition Parameter as
shown in Table 2.8 and a factor for the level of
hydrogen in the weld metal. (This is especially
important if you are welding steel greater than
1/2 in. (13 mm) thick, and if the carbon equivalent
is greater than 0.5%.)
Appendix 1 is reprinted from AWS D1.1. It provides detailed directions for determining preheat,
interpass and post heating levels for any alloy, but
it is particularly important with low-alloy steels in
thick sections. In summary, to determine if preheat
is required and at what level:
(1) Using the composition of the base material, find
the composition parameter from Table 2.8 or calculate it using the formula provided.
(2) Using guidance on hydrogen levels and restraint, calculate the Susceptibility Index using the
method described.
22 AWS Guide to Weldability
(3) Determine the Susceptibility Index Grouping
(4) Find the recommended preheat and interpass
temperature level from tables provided.
This method is somewhat more time-consuming
that using the information in Table 3.1, but it reduces risk, and in many cases, it may result in
lower preheat temperatures with reduced costs.
Other Effects of Welding
These can vary greatly, depending on the type of
steel you are welding, making it even more important that you know what you have.
On carbon steels, the effects are usually moderate,
e.g., some grain growth just outside the fusion
zone. This doesn’t often affect the performance of
the joint.
Table 3.1—Prequalified Minimum Preheat and Interpass Temperature
Thickness of Thickest Part
at Point of Welding
C
a
t
e
g
o
r
y
Steel Specification
Welding Process
Minimum Preheat and
Interpass Temperature
in.
mm
°F
°C
1/8 to 3/4 incl.
3 to 20 incl.
1321
1 01
Over 3/4
thru 1-1/2 incl.
Over 20
thru 38 incl.
150
65
Over 1-1/2
thru 2-1/2 incl.
Over 38
thru 65 incl.
225
110
Over 2-1/2
Over 65
300
150
ASTM A 36
ASTM A 53
Grade B
ASTM A 106
Grade B
ASTM A 131
Grades A, B, CS, D, DS, E
ASTM A 139
Grade B
ASTM A 381
Grade Y35
ASTM A 500
Grade A
Grade B
Grade C
ASTM A 501
ASTM A 516
A
ASTM A 524
Grades I & II
ASTM A 573
Grade 65
ASTM A 709
Grade 36
ASTM A 1008 SS
Grade 30
Grade 33 Type 1
SMAW with
other than
low-hydrogen
electrodes
Grade 40 Type 1
ASTM A 1011 SS
Grade 30
Grade 33
Grade 40
Grade 45
Grade 50
Grade 55
API 5L
Grade B
Grade X42
ABS
Grades A, B, D, CS, DS
Grade E
(continued)
Carbon and Low Alloy Steels
AWS Guide to Weldability 23
Grade 36 Type 1
Thickness of Thickest Part
at Point of Welding
C
a
t
e
g
o
r
y
Steel Specification
ASTM A 36
ASTM A 53
ASTM A 106
ASTM A 131
ASTM A 139
ASTM A 381
ASTM A 441
ASTM A 500
ASTM A 501
ASTM A 516
B
ASTM A 524
ASTM A 529
ASTM A 537
ASTM A 572
ASTM A 573
ASTM A 588
ASTM A 595
ASTM A 606
ASTM A 618
ASTM A 633
ASTM A 709
ASTM A 710
ASTM A 808
ASTM A 9132
ASTM A 992
ASTM A 1008 HSLAS
Grade B
Grade B
Grades A, B,
CS, D, DS, E
AH 32 & 36
DH 32 & 36
EH 32 & 36
Grade B
Grade Y35
ASTM A 1008 HSLAS-F
ASTM A 1011 HSLAS
Grade A
Grade B
Grades 55 & 60
65 & 70
Grades I & II
Grades 50 & 55
Classes 1 & 2
Grades 42, 50, 55
Grade 65
ASTM A 1011 HSLAS-F
ASTM A 1018 HSLAS
ASTM A 1018 HSLAS-F
ASTM A 1018 SS
Grades A, B, C
Grades Ib, II, III
Grades A, B
Grades C, D
Grades 36, 50, 50W
Grade A, Class 2
(>2 in. [50 mm])
Grade 50
API 5L
API Spec. 2H
API 2MT1
API 2W
API 2Y
ABS
ABS
Welding Process
Grade 45 Class 1
Grade 45 Class 2
Grade 50 Class 1
Grade 50 Class 2
Grade 55 Class 1
Grade 55 Class 2
Grade 50
Grade 45 Class 1
Grade 45 Class 2
Grade 50 Class 1
Grade 50 Class 2
Grade 55 Class 1
Grade 55 Class 2
Grade 50
Grade 45 Class 1
Grade 45 Class 2
Grade 50 Class 1
Grade 50 Class 2
Grade 55 Class 1
Grade 55 Class 2
Grade 50
Grade 30
Grade 33
Grade 36
Grade 40
Grade B
Grade X42
Grades 42, 50
Grades 42, 50, 50T
Grades 42, 50, 50T
Grades AH 32 & 36
Grades DH 32 & 36
Grades EH 32 & 36
Grades A, B, D,
Grades CS, DS
Grades Grade E
(continued)
SMAW with
low-hydrogen
electrodes, SAW,
GMAW, FCAW
in.
mm
1/8 to 3/4 incl.
3 to 20 incl.
Over 3/4
thru 1-1/2 incl.
Minimum Preheat and
Interpass Temperature
°F
°C
321
1 01
Over 20 thru
38 incl.
50
10
Over 1-1/2
thru 2-1/2 incl.
Over 38 thru
65 incl.
150
65
Over 2-1/2
Over 65
225
110
1
Carbon and Low Alloy Steels
24 AWS Guide to Weldability
Table 3.1 (Continued)—Prequalified Minimum Preheat and Interpass Temperature
Table 3.1 (Continued)—Prequalified Minimum Preheat and Interpass Temperature
Thickness of Thickest Part
at Point of Welding
C
a
t
e
g
o
r
y
Steel Specification
ASTM A 572
Grades 60, 65
ASTM A 633
Grade E
API 5L
Grade X52
ASTM A 9132
Grades 60, 65
ASTM A 710
Grade A, Class 2 (≤2 in. [50 mm])
ASTM A 710
Grade A, Class 3 (>2 in. [50 mm])
ASTM A 7093
Grade HPS70W
C
Welding Process
SMAW with low-hydrogen electrodes, SAW, GMAW,
FCAW
ASTM A 8523
D
API 2W
Grade 60
API 2Y
Grade 60
ASTM A 710
ASTM A 9132
Grade A (All classes)
Grades 50, 60, 65
SMAW, SAW, GMAW, and FCAW with electrodes or
electrode-flux combinations capable of depositing
weld metal with a maximum diffusible hydrogen
content of 8 ml/100 g (H8), when tested according to
AWS A4.3.
in.
Minimum Preheat and
Interpass Temperature
mm
°F
°C
1/8 to 3/4 incl.
3 to 20 incl.
50
10
Over 3/4
thru 1-1/2 incl.
Over 20 thru
38 incl.
150
65
Over 1-1/2
thru 2-1/2 incl.
Over 38 thru
65 incl.
225
110
Over 2-1/2
Over 65
300
150
321
1 01
All thicknesses ≥ 1/8 in. [3 mm]
1
Notes:
1. When the base metal temperature is below 32°F [0°C], the base metal shall be preheated to a minimum of 70°F [20°C] and the minimum interpass temperature shall be maintained during welding.
2. The heat input limitations of 5.7 shall not apply to ASTM A 913.
3. For ASTM A 709 Grade HPS70W and ASTM A 852 Grade 70, the maximum preheat and interpass temperatures shall not exceed 400°F [200°C] for thicknesses up to 1-1/2 in.
[40 mm], inclusive, and 450°F [230°C] for greater thicknesses.
Carbon and Low Alloy Steels
AWS Guide to Weldability 25
General Notes:
• For modification of preheat requirements for SAW with parallel or multiple electrodes, see 3.5.3.
• See 5.12.2 and 5.6 for ambient and base-metal temperature requirements.
• ASTM A 570 and ASTM A 607 have been deleted.
Carbon and Low Alloy Steels
Table 3.2—Minimum Preheat and Interpass Temperature for Three Levels of Restraint
Minimum Preheat and Interpass Temperature
Susceptibility Index Grouping a
Thickness b
A
B
C
D
E
F
G
Restraint
Level
in.
mm
°F
°C
°F
°C
°F
°C
°F
°C
°F
°C
°F
°C
°F
°C
Lowc
<0.38
<9.5
<65
<18
<65
<18
<65
<18
<65
<18
140
60
280
138
300
149
0.38–0.75
9.5–19.1
<65
<18
<65
<18
65
18
140
60
210
99
280
138
300
149
0.75–1.50
19.1–38.1
<65
<18
<65
<18
65
18
175
80
230
110
280
138
300
149
1.50–3.0
38.1–76
65
18
65
18
100
38
200
93
250
121
280
138
300
149
>3.0
>76
65
18
65
18
100
38
200
93
250
121
280
138
300
149
<0.38
<9.5
<65
<18
<65
<18
<65
<18
<65
<18
160
71
280
138
320
160
0.38–0.75
9.5–19.1
<65
<18
<65
<18
65
18
175
80
240
116
290
143
320
160
0.75–1.50
19.1–38.1
<65
<18
65
18
165
74
230
110
280
138
300
149
320
160
1.50–3.0
38.1–76
65
18
175
80
230
110
265
130
300
149
300
149
320
160
>3.0
>76
200
93
250
121
280
138
300
149
320
160
320
160
320
160
<0.38
<9.5
<65
<18
<65
<18
<65
<18
100
38
230
110
300
149
320
160
0.38–0.75
9.5–19.1
<65
<18
65
18
150
66
220
104
280
138
320
160
320
160
0.75–1.50
19.1–38.1
65
18
185
85
240
116
280
138
300
149
320
160
320
160
1.50–3.0
38.1–76
240
116
265
130
300
149
300
149
320
160
320
160
320
160
>3.0
>76
240
116
265
130
300
149
300
149
320
160
320
160
320
160
Mediumd
Highe
a. Susceptibility index values for groupings: A, 3.0; B, 3.1–3.5; C, 3.6–4.0; D, 4.1–4.5; E, 4.6–5.0; F, 5.1–5.5; G, 5.6–7.0.
b. Thickness is that of the thicker part welded.
c. Low restraint describes welded joints in members with reasonable freedom of movement.
d. Medium restraint describes welded joints with reduced freedom of movement (for example, those attached to other structures).
e. High restraint describes welded joints where there is almost no freedom of movement (for example, with thick material or repair
welds).
With increasing carbon content, or carbon equivalent, the risk of hydrogen migration from the weld
metal into the HAZ increases, and underbead cracking may occur. (Types of cracking and their causes
are discussed in Chapter 5.) This risk is increased
when a thin section is welded to thick section.
(rapid cooling, possible formation of martensite)
Thus, even if welding a carbon steel, if you are
welding a 3/16 in. (5 mm) flange to a 1 in. (25 mm)
plate, the welding procedure should be based on the
requirements for the thicker section, e.g., use a lowhydrogen electrode, and consider use of preheat.
As alloy content increases, the likelihood of these
potential problems also increases.
26 AWS Guide to Weldability
On heat-treated steels, heat applied during welding
will effectively eliminate the heat treatment effect
in the HAZ. However, in many cases, by restricting
heat input, the “damaged” area can be kept small
enough that the effect on the structure is not significant. This often means the use of many small weld
beads. Each successive pass tends to refine the previous passes, usually improving its properties.
If the structure is to be fully heat-treated after welding, e.g., heated above the transition point,
quenched and tempered, every attempt should be
made to find a filler metal that most closely
matches the base metal, or one that exhibits heattreatment response similar to the base material.
Electrode manufacturers and steel producers are
Carbon and Low Alloy Steels
usually the best source of guidance for this situation.
On micro-alloyed steels, e.g., ASTM type A 572—
these steels acquire their properties largely by having very small amounts of certain alloying elements
“in solution” when the steel is cooled. Then by careful low temperature “aging,” these elements, such
as vanadium, move into positions in the crystal
structure where they resist movement, hence increasing the strength of the alloy. However, if this
“aging” process is carried on too long or at too high
a temperature, the effect is lost, and in some cases,
embrittlement may occur.
Thus it is obvious that welding can degrade or destroy the aging effect. But again, with low (welding)
heat input, and possible low temperature treatment
after welding, at least part of the micro-alloying benefits can often be retained. If specific postweld aging
treatment is not available from your customer, the
steel supplier can often provide recommendations.
AWS Guide to Weldability
27
Carbon and Low Alloy Steels
NOTES
28 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 4
Selection of Proper Welding Filler
Metal (Rods, Electrodes, etc.)
As mentioned above, weld metal “sees” a significantly different thermal cycle than the base metal,
and as a result, filler metals for carbon and lowalloy steels will usually have a different composition than the base material—one that produces required strength and toughness under welding
conditions.
Thus, as a first step, assuming the weld must match
or exceed the strength of the base metal (this is usually a requirement, though not always): select an
electrode that produces weld metal with UTS equal
or higher than the base metal. For carbon steels, it
will usually be higher. (The lowest tensile strength
of steel filler metals is 60 ksi, much higher than
many common structural steels.)
Note: The “published” strength and toughness properties of filler metals are measured under conditions that
allow consistent measurement, but that rarely exist during fabrication. Most codes covering construction of
bridges, pressure vessels, rail cars or other structures
specify development of procedures with testing designed
to demonstrate performance in the intended application.
The total effort that is required to meet those requirements is described in the applicable codes. Commonly
used codes are listed in Chapter 9.
If a specified toughness value is based on the “standard AWS test, “a filler metal with the required
CVN toughness can be selected from AWS Filler
Metal Specifications (A5.XX) or from manufacturer’s data sheets.
Table 4.1 provides basic filler metal selection guidelines for many carbon steels. Additional recommendations are found in the Appendix 2.
If the base material has a tensile strength above
50 ksi, or a carbon equivalent higher than 0.50, a
low-hydrogen SMAW electrode, or “low hydrogen” process, such as GMAW, FCAW, or SAW
must be used. Preheating, interpass temperature
control, and post heating may also be required to
suppress a martensite transformation, and to allow
the hydrogen that is present to diffuse out of the
structure. Guidelines for preheat, interpass temperatures, and post heating are described in Chapter 3.
As strength levels increase it is also critical that hydrogen control is followed. SMAW electrodes must
be handled in accordance with the manufacturers’
recommendations, e.g., used within the maximum
time allowed from opening of the package, kept at
minimum temperatures, and rebaked (if allowed)
when necessary. Some FCAW electrodes have similar requirements.
As a second step, determine if there are “toughness” requirements for the weld, usually expressed
as Charpy V-Notch test results in ft-lb or joules at
one or more specified temperatures.
GMAW and FCAW equipment must be properly
maintained, especially shielding gas hoses, torches,
and connections, as leaks will admit air with moisture. Use only hoses specified for shielding gas use
(rubber hoses should not be used), and check for
leaks on a regular schedule.
Note: It is again important to determine if toughness
measurements are to be made according to the “standard
AWS test,” or as part of a procedure qualification as
mentioned above.
Note: With gas-shielded processes, use gas flow rates recommended by the torch manufacturer. Gas flow rates
that are too high often generate turbulence that will
admit air and defeat the purpose of the shielding gas.
AWS Guide to Weldability
29
Carbon and Low Alloy Steels
Table 4.1—Recommended Base Metal-Filler Metal Combinations for Matching Electrode
Tensile Strengths Nominally of 70 ksi (483 MPa) Minimum
Steels
Steel Specificationa,b
ASTM A 203
ASTM A 204
Matching Filler Metals
Minimum
Yield Point/
Strength
Tensile
Strength Range
ksi
MPa
ksi
MPa
Grade A
370
2550
65–85
448–586
Grade B
400
2760
70–90
483–620
Grade D
370
2550
65–85
448–586
Grade E
400
2760
70–90
483–620
Grade A
370
2550
65–85
448–586
Grade B
400
2760
70–90
483–620
ASTM A 242
—
42–
500
290–
3450
63–70
435–483
ASTM A 441
—
40–
500
275–
3450
60–70
415–483
ASTM A 572
Grade 42
420
2900
60 min.
415 min.
Grade 50
500
3450
65 min.
450 min.
ASTM A 588
4 in. (102 mm)
and under
500
3450
70 min.
483 min.
ASTM A 633
Grade A
420
2900
63–83
430–570
Grades C and D
2.5 in. (64 mm)
and under
500
3450
70–90
483–620
ASTM A 710
Grade A, Class
2, under 2 in.
(51 mm)
550
3800
65 min.
450 min.
API 2H
Grade 42
420
2900
62–80
430–550
Grade 50
500
3450
70 min.
483 min.
API 5L
Grade X-52
520
3600
66–72
455–495
Grade X-56
560
3860
71–75
489–517
Grade X-60
600
4140
75–78
517–537
Electrode
Specificationc
Minimum Yield
Point/Strength
Tensile
Strength Range
ksi
ksi
MPa
MPa
Shielded Metal Arc Welding
(See AWS A5.1 or A5.5)e
E7015, E7016,
E7018, E7028
60
414
72 min. 496 min.
E7015-X, E7016X, E7018-X
57
390
70 min. 483 min.
E7010-Xd
60
414
70 min. 483 min.
Submerged Arc Welding
(See AWS A5.17 or A5.23)e
F7XX-EXXX or
F7XX-EXX-XX
58
400
70–95
483–
6600
Gas Metal Arc Welding
(See AWS A5.18)
ER70S-X
60
414
72 min. 496 min.
Flux Cored Arc Welding
(See AWS A5.20)
E7XT-X (except
-2, -3, -10, -GS)
60
414
72 min. 496 min.
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be
used. The low-hydrogen 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 20 ft•lb (27.1 J) at 0°F (–18°C) when Charpy V-notch specimens are
required.
30 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 5
Metallurgically-Related Weld
Discontinuities (Defects) and
Typical Causes
Weld discontinuities can result from a variety (and
combination) of causes. This guide is focused on the
metallurgical aspects of base and filler materials,
and their response to the arc welding processes.
These are cracking, porosity, and inclusions. Discussion and guidelines regarding incomplete fusion, incomplete joint penetration, and overlap can
be found in guides and/or handbooks covering the
specific welding processes.
Cracking
There are many types of cracks that can result from
welding and related operations. Figure 5.1 illustrates 13 types that can be encountered. Cracks can
be divided into two categories:
Hot Cracking—associated with solidification. The
fundamental mechanism of hot cracking is the inability of the material to cope with the shrinkage
stresses associated with cooling in the last area(s) to
solidify.
Cold Cracking—almost always associated with
hydrogen. Cold cracking occurs some time after
solidification (sometimes hours or days, even
weeks), and results from the intense forces of
hydrogen atoms in the crystal lattice that literally
force the metal apart as they recombine into gaseous hydrogen.
Cracking of any type must be avoided in any repetitive operation, for one simple reason: Cracks of almost any type may “grow” in service and cause
failure of the structure. If there is the need to make
repairs on a regular basis, there is something wrong
with at least one of the following factors:
(5) Control of the welding procedure.
(6) Operator training and skill.
Note: Most importantly, if cracks are found regularly,
some will likely go undetected, increasing the risk of
failure!
Referring to Figure 5.1, Table 5.1 shows some of the
common causes and potential solutions to the
cracking described there.
Porosity
Molten steel can dissolve fairly large amounts of
gases such as hydrogen, nitrogen, and oxygen, but
as the steel cools and begins to solidify, these gases
either are forced out of solution and form bubbles
that escape or are entrapped, or may react with
elements in the steel itself to form other gases or
inclusions.
In some cases, the shielding gas, e.g., argon, can be
“stirred” into the puddle and form porosity, but
this is less common. Most porosity is sub-surface
and can only be detected by radiography, but if
voids do appear on the surface of the weld, this
usually indicates a serious problem that needs to be
addressed.
Small amounts of internal porosity are usually acceptable, and all codes and standards have specific
levels of acceptability. Since the voids are spherical,
they are less likely to grow in service and initiate
failures.
Table 5.2 lists many common causes of porosity and
suggests remedies. Some additional comments are
appropriate:
(1) Cleanliness of the base metal, the filler metal
and the integrity of the gas shielding system (if
used) are essential to process consistency.
(3) Selection and quality consistency of the filler
material.
(2) A common source of porosity is formation of
carbon monoxide (CO) from the reaction of carbon
in the steel with oxygen in the welding atmosphere.
Deoxidizers, e.g., silicon are used in the filler metal
to suppress this reaction. However, if the deoxidizer level is too high for the specific situation, the
weld puddle may appear “sluggish” and porosity
can be entrapped by the viscous metal.
(4) The welding procedure itself, including preparation, preheating, interpass temperature control,
post heating, stress relieving, etc.
(3) Contamination of the weld puddle with air
can occur if shielding gas flows are too high as
well as too low! Flow rates in excess of torch
(1) The design of the welded joint, e.g., excessive
restraint.
(2) Base metal characteristics.
AWS Guide to Weldability
31
Carbon and Low Alloy Steels
Figure 5.1—Crack types of weld-related cracking.
32 AWS Guide to Weldability
Carbon and Low Alloy Steels
Table 5.1—Common Causes and Potential Solutions to Cracking
Type of Cracking
Cause(s)
Possible Solution
Crater Crack
Weld heat terminated too rapidly, concave puddle
cannot accommodate shrinkage
Slow or stop travel before terminating arc, allow
reinforcement to build up.
Face Crack (Longitudinal)
(1) Welding procedure causes concave weld bead;
potential increased with rapid cooling.
(2) Solidification mode “rejects” low-melting compounds to centerline. (More common in highly
alloyed materials.) Both conditions aggravated
by restraint.
Adjust welding conditions to produce (slightly)
reinforced weld bead.
Heat-Affected-Zone Crack
(aka Underbead Crack)
Migration of hydrogen from weld metal; formation of
martensite in HAZ; high residual stress.
Assure low-hydrogen process. Increase preheat and maintain interpass temperature longer
after welding.
Lamellar Tears
Separation of “layers” in base metal (typically thin
non-metallic films formed by the rolling processes)
caused by weld shrinkage stresses.
Redesign joint to reduce through-thickness
stresses; adjust procedure to increase penetration into the base material; change base metal.
Root Crack
Incomplete penetration; inadequate surface preparation; excess travel speed.
Modify procedure and/or preparation to assure
fusion of root bead with base metal.
Root Surface Crack
Shrinkage with inadequate filler metal to accommodate need. Aggravated by excess joint spacing;
poor fitup.
Modify procedure to assure convexity on one or
both faces of the root pass.
Throat Crack
Longitudinal crack typically associated with fillet
welds.
See longitudinal crack above.
Transverse Crack
Hydrogen Embrittlement aggravated by shrinkage
stresses and high restraint.
Same as HAZ cracks.
Underbead Crack
Diffusion of hydrogen from weld into base material;
increasing base metal hardenability (carbon
equivalent).
Same as with HAZ cracking.
Weld Interface Crack
Inadequate melting of the base material, or inclusion at fusion line.
Modify procedure to assure consistent base
metal penetration.
Weld Metal Crack
Subsurface longitudinal crack often associated with
heat flow away from the weld that prevents liquid
from “filling in” to accommodate shrinkage following
solidification.
Modify procedure so weld bead depth/width
ratio is reduced, allowing solidification to proceed toward the centerline and the surface.
Table 5.2—Common Causes of and Remedies for Porosity
Cause
Remedies
Excessive hydrogen, nitrogen, or oxygen in welding atmosphere
Use low-hydrogen welding process; filler metals high in
deoxiders; increase shielding gas flow
High solidification rate
Use preheat or increase heat input
Dirty base metal
Clean joint faces and adjacent surfaces
Dirty filler wire
Use specially cleaned and packaged filler wire, and store in
clean area
Improper arc length, welding current, or electrode manipulation
Change welding conditions and techniques
Volatization of zinc from brass
Use copper-silicon filler metal; reduce heat input‘
Galvanized steel
Use E6010 electrodes and manipulate the arc heat to volatilize
the zinc ahead of the molten weld pool
Excessive moisture in electrode covering or on joint surfaces
Use recommended procedures for baking and storing electrodes
Preheat the base metal
High sulfur base metal
Use electrodes with basic slagging reactions
AWS Guide to Weldability
33
Carbon and Low Alloy Steels
manufacturers’ recommendations can result in turbulence that will “stir in” air.
(4) “Wormhole” type surface porosity can be encountered with flux-cored arc welding when the
slag solidifies before the weld metal itself. A typical
cause for this problem is the use of electrodes designed for out-of-position welding for horizontal or
flat joints.
34 AWS Guide to Weldability
Inclusions
Inclusions such as entrapped slag or other foreign
material usually mean that inadequate pre-weld
cleaning and/or interpass slag removal has taken
place, the welding procedure or the selection of
filler metal are inadequate for the application, or
that the operator is not following the procedure
properly or consistently.
Carbon and Low Alloy Steels
CHAPTER 6
Weld Examination and Testing
The Weld Cross Section
In addition to visual inspection, almost any “new”
weld should be examined by making a transverse
cut, sanding or grinding it smooth, and etching it
with a simple acid solution.
Steps for making the cross section (for “macro”
examination) are:
• Cut with saw or milling cutter. Do not use a thermal process such as plasma or oxyfuel. Heat
from the cutting process will change the grain
structure of the weld and make the specimen
useless.
• Belt sand—80–100 grit. Do not allow specimen to
become too hot to hold with bare hand.
• Hand sand to minimum of 220 grit; finer okay.
Again, do not overheat specimen.
• Apply Nitol etching solution (5% nitric acid in
ethyl alcohol).
• Rinse with distilled water.
• Dry in warm air (hand held hair dryer is good
for this).
Do not dispose of acids or etching solutions in ordinary drains.
Caution: Wear appropriate hand and face protection and work only in a well-ventilated space on in
a fume hood. Avoid breathing fumes. In addition,
fumes are very corrosive and continued exposure
will damage nearby metal structures. Mix only
small quantities of etching solution at a time.
Refer to the weld cross section in Figure 2.4. With
the naked eye, or as little as 10X magnification,
much can be learned: bead shape is easily evaluated
and penetration can be measured.
The following defects can be easily found:
• Lack of fusion at sidewalls or between passes.
• Large inclusions.
• Gross porosity.
• Excess undercut.
• Cracking parallel to the weld centerline (longitudinal) (centerline, shrinkage, lamellar tears,
underbead)
Note: However, if such defects are not continuous, a
single cross section may not uncover them!
Mechanical Tests—What They Can Tell
You
Bend Tests
Bend tests are excellent tools to evaluate the ductility and the soundness of the weld. Details for preparation and testing are shown in Figures 6.1 and 6.2.
(1) The “side bend” can assure that adequate “tiein” between weld passes and the base plate have
been achieved; it will also expose longitudinal
cracks, and inclusions.
(2) The face and root bends are usually used only
with single pass welds; they will expose fusion-line
defects and centerline cracking
(3) Bend tests can be misleading if there is a major
difference in strength between weld and base
metal. If most of the bending is “forced” into the
base metal or the weld metal, cracking or breaking
may occur, but it may not mean that the weld is unsatisfactory.
Tensile Tests
Tensile tests can be used to evaluate strength and
ductility of the weld metal with an all-weld metal
(longitudinal) test, or of the joint with a transverse
or longitudinal test. The transverse test can also
evaluate fusion line tie in, and, will quickly expose
longitudinal cracking if present in the test specimen. A description of the orientation of various
types of tensile tests is shown in Figure 6.3.
If your customer requires any of the above tests, it
is critical that he provide references to the standards by which the tests are to be run and how the
results are to be interpreted. Other types of tests
may be specified by the customer, based on the specific type of service.
AWS Guide to Weldability
35
Carbon and Low Alloy Steels
Figure 6.1—Specimen and test orientation of the guided bend test.
Key:
A = Bend radius, in. (mm)
T = Specimen thickness, in. (mm)
Figure 6.2—Schematic illustration of typical guided bend test fixtures.
36 AWS Guide to Weldability
Carbon and Low Alloy Steels
Key:
T = Weldment thickness, in. (mm)
W = Specimen width at the reduced section, in. (mm)
Figure 6.3—Typical tension test specimens for the evaluation of welded joints.
AWS Guide to Weldability
37
Carbon and Low Alloy Steels
NOTES
38 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 7
Postweld Treatments
These treatments may desirable or required to prevent unwanted structural transformation, e.g., martensite, to reduce distortion, improve ductility and
toughness, and to restore base metal properties.
Postweld Heating (postheating)—usually used on
high carbon (or high CE) steels to prevent cracking
by keeping the weld cooling rate slow enough to
prevent the martensite transformation, and/or to
allow entrapped hydrogen to diffuse out of the
weld. The postweld temperature is typically the
same as the preheat temperature, but can be higher.
Stress Relieving—uniform heating of the structure
to temperatures below the transformation temperatures to remove or reduce stresses resulting from
welding. This is typically done in special furnaces,
but it sometimes can be done locally where furnace
heating is impractical.
Aging—postweld treatment of certain steels that
obtain strength by precipitation of chemical compounds at fairly low temperatures. Normal welding
procedures result in cooling too rapid to allow
aging to occur, so it may be done after the structure
is completed. Steel suppliers and/or electrode manufacturers can supply aging temperature and time
recommendations.
Full Heat Treatment—the structure is subjected to
the full heat treatment cycle that is used to produce
base material properties. If this treatment is to be
used, the welding material composition should
closely duplicate the base metal, or the filler metal
supplier should be able to show that the material
will respond to heat treatment in a manner comparable with the base metal.
AWS Guide to Weldability
39
Carbon and Low Alloy Steels
NOTES
40 AWS Guide to Weldability
Carbon and Low Alloy Steels
CHAPTER 8
Good Practice Reminders
This chapter is a quick summary of what is covered
in this guide
• Know what steel you are welding.
• Prepare plates properly and establish good fitup.
— Large gaps require extra weld metal resulting
in more cost and more distortion
• Record your welding machine settings
• Control all welding parameters
— With continuous electrode processes GMAW,
FCAW, SAW, control wire feed speed, arc
voltage, tip-to-work distance, and travel
speed. (By itself, welding current is not a
good indicator of consistency.)
— With SMA, control current, voltage (arc
length) and travel speed.
— When gas shielding is used, be sure that
torches are kept clear of spatter and flow
rates are in the recommended range. High
gas flow rates can cause turbulence that disrupts the shielding effect!
• Never weld on cold (below ambient temperature) or wet steel.
• Moisture trapped in crevices or under scale can
be a devastating source of hydrogen that can
cause cracking in alloy steels, and/or in highly
restrained joints.
• If heat input must be controlled, make sure you
calculate the level being used.
• Prepare a welding procedure, and evaluate it
with a weld cross section and other tests required by your customer.
A Basic Welding Procedure Worksheet
Figure 8.1 is taken from the AWS D1.1/D1.1M:2004,
Structural Welding Code—Steel. It is strongly recom-
mended that this type of worksheet be used for all
repetitive welds and those where the weld is part of
a complex or critical structure. It becomes a de-facto
record of what you did, and can be especially important if you need to do the same work again, or if
there are problems at any time.
There are three types of procedure qualifications
under the AWS Structural Welding Code, as well as
some others.
(1) A prequalified procedure—one developed by
someone else and deemed generally acceptable by
competent authority. (However, you are still responsible for the results!)
(2) A procedure qualified by (your own) testing—
you do the testing yourself.
(3) A procedure qualified by (your own) past work.
You have qualified it before, so you don’t need to
do it again.
Note: Use of this worksheet does not qualify your procedure or your welder to any code or specification. It is
shown here only as an example. If you are required to
produce welds meeting a specific standard, you must assure yourself and your customer that you are meeting all
of the requirements that standard, only part of which
may be met by use of the procedure worksheet.
A Qualified Procedure Should be Used
by a Qualified Welder
It must also be emphasized that in order to meet requirements of virtually all codes, a welding operator must demonstrate his/her ability to produce
acceptable welds using the qualified procedure. If
the welder who developed the procedure is the one
who will do the “production” welding, he/she has
demonstrated the required skill. If, however, others
are to produce welds, each of them should prepare
test welds representative of your procedure, and
these should be examined in the same manner as
those for the procedure itself. Each code has its particular requirements, so be sure you know what
they are.
AWS Guide to Weldability
41
Carbon and Low Alloy Steels
WELDING PROCEDURE SPECIFICATION (WPS) Yes X
PREQUALIFIED __________ QUALIFIED BY TESTING __________
X
or PROCEDURE QUALIFICATION RECORDS (PQR) Yes
PQR 231
Identification # _________________________________
1
12-1-87 By ____________
W. Lye
Revision _______
Date __________
J. Jones
1-18-88
Authorized by __________________
Date __________
Type—Manual
Semi-Automatic X
Machine
Automatic
RED Inc.
Company Name _______________________________
FCAW
Welding Process(es) ____________________________
PQR 231
Supporting PQR No.(s) __________________________
JOINT DESIGN USED
Butt
Type: ________________________________________
Single X
Double Weld
Backing: Yes X No
ASTM A 131A
Backing: Backing Material: ______________________
—
1/4" Root Face Dimension ________
Root Opening ______
—
52-1/2° Radius (J–U) _________
Groove Angle: ___________
—
Back Gouging: Yes
No X
Method _______
POSITION
—
O.H.
Position of Groove: ______________
Fillet: __________
Vertical Progression: Up
Down
ELECTRICAL CHARACTERISTICS
______________________
Transfer Mode (GMAW)
Short-Circuiting
Globular X Spray
Current: AC
DCEP X DCEN
Pulsed
Other ________________________________________
Tungsten Electrode (GTAW)
Size: ______________
Type: ______________
BASE METALS
ASTM A 131
Material Spec. _________________________________
A
Type or Grade _________________________________
3/4—1 1/2" Fillet ________
—
Thickness: Groove ______________
—
Diameter (Pipe) ________________________________
FILLER METALS
A5.20
AWS Specification______________________________
E71T-1
AWS Classification _____________________________
TECHNIQUE
Stringer
Stringer or Weave Bead: _________________________
Multipass
Multi-pass or Single Pass (per side)_________________
1
Number of Electrodes ___________________________
—
Electrode Spacing
Longitudinal ____________
—
Lateral_________________
—
Angle _________________
SHIELDING
—
CO2
Flux ___________________
Gas _________________
Composition __________
100% CO2
45-55CFH
Electro-Flux (Class)_______ Flow Rate ____________
#4
______________________ Gas Cup Size _________
1/2-1"
Contact Tube to Work Distance ____________________
None
Peening ______________________________________
Wire Brush
Interpass Cleaning: _____________________________
PREHEAT
60°
Preheat Temp., Min _____________________________
350°F
60°
Interpass Temp., Min____________
Max__________
POSTWELD HEAT TREATMENT
N.A.
Temp. ________________________________________
N.A.
Time _________________________________________
WELDING PROCEDURE
Filler Metals
Current
Pass or
Weld
Layer(s)
Process
Class
Diam.
Type &
Polarity
Amps or Wire
Feed Speed
Volts
All
FCAW
E71T-1
.045"
DC+
180-220A
25-26V
Form E-1 (Front)
Figure 8.1—Basic Welding Procedure Worksheet
42 AWS Guide to Weldability
Travel
Speed
8-12
ipm
Joint Details
Carbon and Low Alloy Steels
CHAPTER 9
Additional Information and
Guidance
The following is a list of some of the groups that
publish steel specifications.
• ASTM—American Society for Testing and Materials—by far the most comprehensive.
• SAE–AISI—Society of Automotive Engineers,
formerly known only as AISI Steels (American
Iron and Steel Institute).
• API—American Petroleum Institute.
• Ship Classification Societies, e.g., American
Bureau of Shipping, Det Norske Veritas.
• The U.S. Military (“MIL” Specifications).
Additional sources of information are as follows:
• AWS Jefferson’s Welding Encyclopedia, 18th Edition.
• AWS Welding Handbook.
• AWS Welding Metallurgy, Linnert Volume 1.
• ASM Handbook, Volume 6.
• The Lincoln Electric Company Procedure Handbook
of Arc Welding.
• Filler metal manufacturers’ literature.
• Numerous internet websites such as globalspec.
com and metalinfo.com.
AWS Guide to Weldability
43
Carbon and Low Alloy Steels
NOTES
44 AWS Guide to Weldability
Carbon and Low Alloy Steels
APPENDIX 1
Alternative Methods for Determining Preheat (and Preventing Cracking)
Reprint of Annex XI, pages 299–303 from AWS D1.1/D1.1M: 2004.
Annex XI
Guideline on Alternative Methods for Determining Preheat
(This Annex is a part of AWS D1.1/D1.1M:2004, Structural Welding Code—Steel,
and includes mandatory requirements for use with this standard.)
XI1. Introduction
The purpose of this guide is to provide some optional
alternative methods for determining welding conditions
(principally preheat) to avoid cold cracking. The methods are based primarily on research on small scale tests
carried out over many years in several laboratories
world-wide. No method is available for predicting optimum conditions in all cases, but the guide does consider
several important factors such as hydrogen level and
steel composition not explicitly included in the requirements of Table 3.2. The guide may therefore be of value
in indicating whether the requirements of Table 3.2 are
overly conservative or in some cases not sufficiently
demanding.
The user is referred to the Commentary for more detailed presentation of the background scientific and research information leading to the two methods proposed.
In using this guide as an alternative to Table 3.2, careful consideration shall be given to the assumptions made,
the values selected, and past experience.
XI2. Methods
Two methods are used as the basis for estimating
welding conditions to avoid cold cracking:
(1) HAZ hardness control
(2) Hydrogen control
XI3. HAZ Hardness Control
XI3.1 The provisions included in this guide for use of
this method are restricted to fillet welds.
XI3.2 This method is based on the assumption that
cracking will not occur if the hardness of the HAZ is kept
below some critical value. This is achieved by controlling the cooling rate below a critical value dependent on
the hardenability of the steel. Hardenability of steel in
welding relates to its propensity towards formation of a
hard HAZ and can be characterized by the cooling rate
necessary to produce a given level of hardness. Steels
with high hardenability can, therefore, produce hard
HAZ at slower cooling rates than a steel with lower
hardenability.
Equations and graphs are available in the technical literature that relate the weld cooling rate to the thickness
of the steel members, type of joint, welding conditions
and variables.
XI3.3 The selection of the critical hardness will depend
on a number of factors such as steel type, hydrogen level,
restraint, and service conditions. Laboratory tests with
fillet welds show that HAZ cracking does not occur if the
HAZ Vickers Hardness No. (Vh) is less than 350 Vh,
even with high-hydrogen electrodes. With low-hydrogen
electrodes, hardnesses of 400 Vh could be tolerated without cracking. Such hardness, however, may not be tolerable in service where there is an increased risk of stress
corrosion cracking, brittle fracture initiation, or other
risks for the safety or serviceability of the structure.
The critical cooling rate for a given hardness can be
approximately related to the carbon equivalent (CE) of the
steel (see Figure XI-2). Since the relationship is only approximate, the curve shown in Figure XI-2 may be conservative for plain carbon and plain carbon-manganese
steels and thus allow the use of the high hardness curve
with less risk.
AWS Guide to Weldability
45
Carbon and Low Alloy Steels
Some low-alloy steels, particularly those containing
columbium (niobium), may be more hardenable than
Figure XI-2 indicates, and the use of the lower hardness
curve is recommended.
XI3.4 Although the method can be used to determine a
preheat level, its main value is in determining the minimum heat input (and hence minimum weld size) that prevents excessive hardening. It is particularly useful for
determining the minimum size of single-pass fillet welds
that can be deposited without preheat.
XI3.5 The hardness approach does not consider the possibility of weld metal cracking. However, from experience it is found that the heat input determined by this
method is usually adequate to prevent weld metal cracking, in most cases, in fillet welds if the electrode is not a
high-strength filler metal and is generally of a lowhydrogen type (e.g., low-hydrogen (SMAW) electrode,
GMAW, FCAW, SAW).
XI3.6 Because the method depends solely on controlling the HAZ hardness, the hydrogen level and restraint
are not explicitly considered.
XI3.7 This method is not applicable to quenched and
tempered steels [see XI5.2(3) for limitations].
XI4. Hydrogen Control
XI4.1 The hydrogen control method is based on the assumption that cracking will not occur if the average
quantity of hydrogen remaining in the joint after it has
cooled down to about 120°F [50°C] does not exceed a
critical value dependent on the composition of the steel
and the restraint. The preheat necessary to allow enough
hydrogen to diffuse out of the joint can be estimated
using this method.
XI4.2 This method is based mainly on results of restrained PJP groove weld tests; the weld metal used in
the tests matched the parent metal. There has not been
extensive testing of this method on fillet welds; however,
by allowing for restraint, the method has been suitably
adapted for those welds.
XI4.3 A determination of the restraint level and the
original hydrogen level in the weld pool is required for
the hydrogen method.
In this guide, restraint is classified as high, medium,
and low, and the category must be established from
experience.
XI4.4 The hydrogen control method is based on a single
low-heat input weld bead representing a root pass and assumes that the HAZ hardens. The method is, therefore,
particularly useful for high strength, low-alloy steels
46 AWS Guide to Weldability
having quite high hardenability where hardness control is
not always feasible. Consequently, because it assumes
that the HAZ fully hardens, the predicted preheat may be
too conservative for carbon steels.
XI5. Selection of Method
XI5.1 The following procedure is recommended as a guide
for selection of either the hardness control or hydrogen
control method.
Determine carbon and carbon equivalent:
(Mn + Si)
+ Mo + V)- + (Ni
+ Cu)CE = C + ----------------------- + (Cr
------------------------------------------------------6
5
15
to locate the zone position of the steel in Figure XI-1 (see
XI6.1.1 for the different ways to obtain chemical analysis).
XI5.2 The performance characteristics of each zone and
the recommended action are as follows:
(1) Zone I. Cracking is unlikely, but may occur with
high hydrogen or high restraint. Use hydrogen control
method to determine preheat for steels in this zone.
(2) Zone II. The hardness control method and selected hardness shall be used to determine minimum energy input for single-pass fillet welds without preheat.
If the energy input is not practical, use hydrogen
method to determine preheat.
For groove welds, the hydrogen control method shall
be used to determine preheat.
For steels with high carbon, a minimum energy to control hardness and preheat to control hydrogen may be required for both types of welds, i.e., fillet and groove welds.
(3) Zone III. The hydrogen control method shall be
used. Where heat input is restricted to preserve the HAZ
properties (e.g., some quenched and tempered steels), the
hydrogen control method should be used to determine
preheat.
XI6. Detailed Guide
XI6.1 Hardness Method
XI6.1.1 The carbon equivalent shall be calculated as
follows:
(Mn + Si)
+ Mo + V)- + (Ni
+ Cu)------------------------------------------------------CE = C + ----------------------- + (Cr
6
5
15
The chemical analysis may be obtained from:
(1) Mill test certificates
(2) Typical production chemistry (from the mill)
(3) Specification chemistry (using maximum values)
(4) User tests (chemical analysis)
Carbon and Low Alloy Steels
XI6.1.2 The critical cooling rate shall be determined
for a selected maximum HAZ hardness of either 400 Vh
or 350 Vh from Figure XI-2.
XI6.1.3 Using applicable thicknesses for “flange”
and “web” plates, the appropriate diagram shall be selected from Figure XI-3 and the minimum energy input
for single-pass fillet welds shall be determined. This energy input applies to SAW welds.
XI6.1.4 For other processes, minimum energy input
for single-pass fillet welds can be estimated by applying
the following multiplication factors to the energy estimated for the SAW process in XI6.1.3:
Welding Process
Multiplication Factor
SAW
SMAW
GMAW, FCAW
1
1.50
1.25
XI6.1.5 Figure XI-4 may be used to determine fillet
sizes as a function of energy input.
XI6.2 Hydrogen Control Method
XI6.2.1 The value of the composition parameter,
Pcm , shall be calculated as follows:
Si- + Mn
V- + 5B
P cm = C + ------------ + Cu
------- + Ni
------ + Cr
------ + Mo
-------- + ----30 20 20 60 20 15 10
The chemical analysis shall be determined as in XI6.1.1.
XI6.2.2 The hydrogen level shall be determined and
shall be defined as follows:
(1) H1 Extra-Low Hydrogen. These consumables
give a diffusible hydrogen content of less than 5 ml/100g
deposited metal when measured using ISO 3690-1976
or, a moisture content of electrode covering of 0.2%
maximum in conformance with AWS A5.1 or A5.5. This
may be established by testing each type, brand, or
wire/flux combination used after removal from the package or container and exposure for the intended duration,
with due consideration of actual storage conditions prior
to immediate use. The following may be assumed to
meet this requirement:
(a) Low-hydrogen electrodes taken from hermetically sealed containers, dried at 700°F–800°F [370°–
430°C] for one hour and used within two hours after
removal.
(b) GMAW with clean solid wires
(2) H2 Low Hydrogen. These consumables give a
diffusible hydrogen content of less than 10 ml/100g deposited metal when measured using ISO 3690-1976, or a
moisture content of electrode covering of 0.4% maximum in conformance with AWS A5.1. This may be established by a test on each type, brand of consumable, or
wire/flux combination used. The following may be assumed to meet this requirement:
(a) Low-hydrogen electrodes taken from hermetically sealed containers conditioned in conformance with
5.3.2.1 of the code and used within four hours after
removal
(b) SAW with dry flux
(3) H3 Hydrogen Not Controlled. All other consumables not meeting the requirements of H1 or H2.
XI6.2.3 The susceptibility index grouping from
Table XI-1 shall be determined.
XI6.2.4 Minimum Preheat Levels and Interpass.
Table XI-2 gives the minimum preheat and interpass
temperatures that shall be used. Table XI-2 gives three
levels of restraint. The restraint level to be used shall be
determined in conformance with XI6.2.5.
XI6.2.5 Restraint. The classification of types of
welds at various restraint levels should be determined on
the basis of experience, engineering judgment, research,
or calculation.
Three levels of restraint have been provided:
(1) Low Restraint. This level describes common fillet and groove welded joints in which a reasonable freedom of movement of members exists.
(2) Medium Restraint. This level describes fillet and
groove welded joints in which, because of members
being already attached to structural work, a reduced freedom of movement exists.
(3) High Restraint. This level describes welds in
which there is almost no freedom of movement for members joined (such as repair welds, especially in thick
material).
AWS Guide to Weldability
47
Carbon and Low Alloy Steels
Table XI-1
Susceptibility Index Grouping as Function of Hydrogen Level “H”
and Composition Parameter Pcm (see XI6.2.3)
Susceptibility Index2 Grouping3
1
Carbon Equivalent = P cm
Hydrogen
Level, H
< 0.18
< 0.23
< 0.28
< 0.33
< 0.38
H1
A
H2
B
B
C
D
E
C
D
E
F
H3
C
D
E
F
G
Notes:
Si Mn Cu Ni Cr Mo V
1. P cm = C + ------ + -------- + ------- + ------ + ------ + -------- + ------ + 5B
30 20 20 60 20 15 10
2. Susceptibility index—12 Pcm + log10 H.
3. Susceptibility Index Groupings, A through G, encompass the combined effect of the composition parameter,
Pcm , and hydrogen level, H, in conformance with the formula shown in Note 2.
The exact numerical quantities are obtained from the Note 2 formula using the stated values of Pcm and the
following values of H, given in ml/100g of weld metal (see XI6.2.2, a, b, c):
H1—5; H2—10; H3—30.
For greater convenience, Susceptibility Index Groupings have been expressed in the table by means of letters, A
through G, to cover the following narrow ranges:
A = 3.0; B = 3.1–3.5; C = 3.6–4.0; D = 4.1–4.5; E = 4.6–5.0; F = 5.1–5.5; G = 5.6–7.0
These groupings are used in Table XI-2 in conjunction with restraint and thickness to determine the minimum
preheat and interpass temperature.
Table XI-2
Minimum Preheat and Interpass Temperatures for Three Levels of Restraint (see XI6.2.4)
Minimum Preheat and Interpass Temperature ( °F)
Restraint
Level
Low
Medium
High
Susceptibility Index Grouping
0Thickness1
in.
A
B
C
D
E
F
G
< 3/8
< 65
< 65
< 65
< 65
140
280
300
3/8–3/4
< 65
< 65
65
140
210
280
300
3/4–1-1/2
< 65
< 65
65
175
230
280
300
1-1/2–3
65
65
100
200
250
280
300
>3
65
65
100
200
250
280
300
< 3/8
< 65
< 65
< 65
< 65
160
280
320
3/8–3/4
< 65
< 65
65
175
240
290
320
3/4–1-1/2
< 65
65
165
230
280
300
320
1-1/2–3
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
< 65
65
150
220
280
320
320
3/4–1-1/2
65
185
240
280
300
320
320
1-1/2–3
240
265
300
300
320
320
320
>3
240
265
300
300
320
320
320
Note:
1. Thickness is that of the thicker part welded.
48 AWS Guide to Weldability
(continued)
Carbon and Low Alloy Steels
Table XI-2 (Continued)
Minimum Preheat and Interpass Temperature ( °C)
Restraint
Level
Low
Medium
High
Susceptibility Index Grouping
0Thickness1
mm
A
B
C
D
E
F
G
< 10 <
< 20
< 20
< 20
< 20
60
140
150
10–20
< 20
< 20
20
60
100
140
150
20–38
< 20
< 20
20
80
110
140
150
38–75
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
< 20
< 20
20
80
115
145
160
20–38
20
20
75
110
140
150
160
38–75
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
< 20
20
65
105
140
160
160
20–38
20
85
115
140
150
160
160
38–75
115
130
150
150
160
160
160
> 75<
115
130
150
150
160
160
160
Note:
1. Thickness is that of the thicker part welded.
AWS Guide to Weldability
49
Carbon and Low Alloy Steels
NOTES
50 AWS Guide to Weldability
Carbon and Low Alloy Steels
APPENDIX 2
Additional Filler Metal Recommendations
Tables A2.1–A2.3 list filler metal recommendations for additional steels that may be encountered.
Table A2.1—Recommended Base Metal–Filler Metal Combinations for Matching Electrode
Tensile Strengths Nominally of 80–90 ksi (552–620 MPa) Minimum
Steels
Matching Filler Metals
Minimum
Yield Point/
Strength
Tensile
Strength Range
ksi
MPa
ksi
MPa
Grade A
45
3100
75–95
517–655
Grade B
47
3240
85–110
586–758
ASTM A 204
Grade C
43
2960
75–95
517–655
E8015-X, E8016-X,
E8018-X
67
460
80 min. 552 min.
ASTM A 302
Grade A
45
3100
75–95
517–655
E8010-Gd
67
460
80 min. 552 min.
Grade B
50
3450
80–100
552–689
E9010-Gd
70
483
90 min. 620 min.
Grade C
50
3450
80–100
552–689
Grade D
50
3450
80–100
552–689
Grade 60
60
4140
75 min.
515 min.
Grade 65
65
4500
80 min.
552 min.
ASTM A 633
Grade E
55–60
380–
4140
75–100
517–689
ASTM A 710
Grade A, Class
2, 2 in. (51 mm)
and under
60–65
414–
4500
72 min.
495 min.
Grade A, Class
3, above 2 in.
(51 mm)
60–65
414–
4500
70 min.
483 min.
ASTM A 736
—
55–75
379–
5170
72–105
496–724
ASTM A 737
Grade B
50
3450
70–90
483–620
Grade C
60
4140
80–100
552–689
X-65
65
4500
77–80
min.
530–552
X-70
70
4830
82 min.
565
Steel Specificationa,b
ASTM A 202
ASTM A 572
API 5L
Electrode
Specificationc
Minimum Yield
Point/Strength
Tensile
Strength Range
ksi
ksi
MPa
MPa
Shielded Metal Arc Welding
(See AWS A5.5)e
Submerged Arc Welding
(See AWS A5.23)e
F8XX-EXX-XX
68
470
80–100 552–690
Gas Metal Arc Welding
(See AWS A5.28)e
ER80S-X
68
470
80 min. 552 min.
Flux Cored Arc Welding
(See AWS A5.29)e
E8XTX-X
68
470
80–100 552–690
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be
used. The low-hydrogen 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 20 ft•lb (27.1 J) at 0°F (–18°C) when Charpy V-notch specimens are
required.
AWS Guide to Weldability
51
Carbon and Low Alloy Steels
Table A2.2—Recommended Base Metal–Filler Metal Combinations for Steels with
Tensile Strengths Nominally of 100 ksi (689 MPa) Minimum
Steels
Minimum
Yield Point/
Strength
Tensile Strength
Range
ksi
MPa
ksi
MPa
Grade C
70
4830
105–
135
724–931
Grade D
55–60
379–
4140
75–
105
517–724
Grade A, Class
1, 0.75 in.
(19 mm) and
under
80
5520
90 min.
620 min.
Grade A, Class
3, 2 in. (51 mm)
and under
75
5170
85 min.
586 min.
Steel Specificationa,b
ASTM A 225
ASTM A 710
Filler Metals
Minimum Yield
Point/Strength
Electrode
Specificationc
ksi
Tensile Strength
Range
MPa
ksi
MPa
Shielded Metal Arc Welding
(See AWS A5.5) d
E10015-X, E10016-X,
E10018-X
87
6000
100
min.
690
min.
100–
1200
690–
8300
100
min.
690
min.
100–
1200
690–
8300
Submerged Arc Welding
(See AWS A5.23) d
ASTM A 735
—
65–80
448–
552
80–
115
552–723
API 5Le
X-80
80
552
90 min.
620 min.
F10XX-EXX-XX
88
6100
Gas Metal Arc Welding
(See AWS A5.28) d
ER100S-X
88–102
610–
7000
Flux Cored Arc Welding
(See AWS A5.29) d
E10XTX-X
ASTM A 353f —
75
517
100–
120
689–827
88
6050
Shielded Metal Arc Welding
(See AWS A5.11) g
E310
60
4140
80
550
ENiCrFe-2
45
3100
80
550
ENiCrMo-3
60
4140
110
760
Gas Metal Arc Welding
(See AWS A5.14) g
ERNiCr-3
40
2760
80
550
ERNiCrFe-6
40
2760
80
550
a. In joints involving base metals of different groups, low-hydrogen filler metal requirements applicable to lower strength group may be
used. The low-hydrogen 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 20 ft•lb (27.1 J) at 0°F (–18°C) when Charpy V-notch specimens are
required.
e. Undermatching cellulose electìrodes 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.
g. Yield strength may not match base metal properties.
52 AWS Guide to Weldability
Carbon and Low Alloy Steels
Table A2.3—Suggested Welding Filler Metals for Exposed Applications of ASTM A 242 and A 588 Steelsa
Shielded Metal Arc Welding
(AWS A5.5)
E8016 or 18-Gb,c
Submerged Arc Welding
(AWS A5.23)
Gas Metal Arc Welding
(AWS A5.28)
Flux Cored Arc Welding
(AWS A5.29)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
—
—
—
Notes:
a. See Table 3.3, Page 48, ANSI/AWS D1.1-96, Structural Welding Code—Steel.
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 20 ft•lb (27.1 J) at 0°F (–18°C) 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.
AWS Guide to Weldability
53
Carbon and Low Alloy Steels
NOTES
54 AWS Guide to Weldability
--`,``,,`,`,,``,`,`,``,,`,````,-`-`,,`,,`,`,,`---