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Welding Metallurgy
Module 3
Module 3 – Welding Metallurgy
Module 3 – Welding Metallurgy
ƒ 3A – Basics of Metallurgy Principles
ƒ 3B – Basics of Welding Metallurgy
ƒ 3C – Carbon and Low Alloy Steels
ƒ 3D – Stainless Steels
ƒ 3E – Nickel-base Alloys
ƒ 3F – Other
Oth N
Nonferrous
f
All
Alloys
ƒ 3G – Polymers
3-2
Module 3 – Welding Metallurgy
Module 3 Learning Objectives
ƒ Describe basic metallurgical principles including
strengthening mechanisms
ƒ Describe the basic concepts of welding metallurgy,
microstructure influences on properties and weldability
ƒ Understanding different types of carbon and low alloy steels,
stainless steels,, nickel alloys
y including
g microstructure
development and weldability issues of each alloy system
ƒ Understanding the effect of preheat, PWHT and temper bead
welding on carbon and low alloy steels
ƒ General understanding aluminum, titanium, and copper alloys
characteristics including welding metallurgy and weldability
issues
ƒ General understanding and properties of polymers and
methods of joining
3-3
Basics of Metallurgy Principles
Module 3A
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Types of Atomic Bonds
ƒ Primary Bonds (strong bonds)
z
z
z
Ionic (table salt: NaCl)
Covalent (ceramics and glasses)
Metallic (metals and alloys)
Š Easy movement of electrons leads to high conductivity
Š Lack of bonding directionality leads to high atomic packing
ƒ Secondary
S
d
B
Bonds
d ((weak
kb
bonds)
d )
z
z
Van der Waals (dipole interactions)
Hydrogen bonding
3-5
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Metallic Bonding
ƒ Metal stiffness is proportional to the bonding strength
ƒ Metallic bonds behave as though they were attached with a
spring
ƒ Bringing the atoms close
increases the repulsion and
attraction
+
Attractive force
(Coulomb attraction)
Metallic Bonding
Metal ions
“Sea” of
electrons
+ - + - + - +
- + - + - + + - + - + - +
Force
Total
force
Bond
Distance
Length
Repulsive force
3-6
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Elastic Modulus
ƒ Elastic behavior of metals
ΔF
Δr
Stress
Strong
Bond
Force
means that bonds are stretching
+
(but not breaking)
ƒ Metal stiffness is proportional to
the bonding strength
ƒ The linear behavior of bonds
near the equilibrium bond length
results in the linear elastic
region of a stress strain curve
ƒ Such behavior is observed
during tensile testing
E ∝
Distance
Weak
Bond
σ
E =
ε
Strain
Tensile
Test
3-7
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Crystal Structure
ƒ Atoms arrange themselves into different structures
ƒ Body-centered cubic (BCC) structure
z
z
Iron
Ferritic steels
BCC
ƒ Face-centered cubic (FCC) structure
z
z
Nickel ((and its alloys)
y )
Aluminum (and its alloys)
ƒ Hexagonal close-packed (HCP) structure
z
z
z
FCC
Titanium (room temperature)
Magnesium
Zirconium
HCP
3-8
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Defects in Metal Crystals
ƒ Defects within a crystal structure can change the chemical
and physical properties
ƒ Some of the important defects are as follows:
ƒ Point defects (0-Dimensions)
z
z
Vacancies
Solid Solutions
ƒ Line defects (1-Dimensional)
z
Dislocations
ƒ Planar defects (2-Dimensional)
z
z
Grain boundaries
Surfaces
3-9
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Point Defects
Self-interstitial defects
ƒ Metals will always contain these two
Vacancy defects
types of defects
ƒ The number of vacancies is temperature
dependent (important for diffusion)
Equilibrium number of
vacancies
⎛ QV ⎞
NV = N exp⎜ −
⎟
⎝ kT ⎠
3-10
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Solid Solutions
ƒ Metal alloys contain at least two or more elements
ƒ Even “pure” metals typically contain some impurities
ƒ Two types of metal solutions:
z
Substitutional solutions contain a solvent and solute where the solute
occupies lattice sites of the solvent
Ni is the solvent
Cu is the solute
z
Cu and Ni both have
the FCC crystal structure.
Interstitial solutions contain a solute that occupies non-lattice sites
Fe has the BCC structure
Fe is the solvent and C occupies interstitial sites.
This is a common arrangement
C is the solute
in steels.
3-11
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Line Defects
ƒ Line defects are known as dislocations
ƒ Movement of dislocations through a material results in plastic
deformation
ƒ Edge and screw dislocations are both found in metals
Edge dislocation
Screw dislocation
3-12
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Planar Defects
ƒ Each unique crystal of atoms
has a surface
ƒ Metals typically contain
multiple crystals which have
their own orientation
ƒ Each crystal
y
is referred to as a
grain
ƒ The region between two
different grains is called a
grain boundary
z
z
Low angle boundaries
High angle boundaries
Grain Boundaries
Low
angle
High
angle
3-13
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Phase Diagrams
ƒ A phase is a homogenous system with uniform physical and
chemical properties (i.e., crystal structures)
ƒ Metals and alloys may have different phases
ƒ Composition and temperature are used to predict the phases
(crystal structure) present in an alloy
ƒ Reactions occur at equilibrium (infinite time)
ƒ Common phase diagram types include:
z
z
z
z
Complete solid solution (isomorphous)
Eutectic
Peritectic
Eutectoid
ƒ The Lever Rule is used to determine the phase balance and
composition of constituents
ƒ Microstructure evolution during slow (equilibrium) cooling
3-14
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
What is a Phase Diagram?
ƒ Describes structure of materials based on temperature and
composition
ƒ Assumes constant pressure
ƒ Features
z
z
Liquidus
Solidus
Solvus
ƒ Phase transformations
z
z
z
z
z
z
Composition 1
L→L+α→α→α+β
Composition 2
L→L+α→α+β
Composition 3
L→α+β
2
3
L
Temperatu
ure
z
1
α
L+α
L+β
β
α+β
A
Composition
B
3-15
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Phase Diagrams
Isomorphous
Eutectic
Liquid
Liquid
Temperature
Temperature
Liquid + Solid
Solid
A
Composition
α
L+α
L+β
β
α+β
B
A
Composition
B
3-16
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Phase Diagrams
Peritectic
Eutectoid
L+αÆβ
γÆα+β
γ
α
Temperature
Temperature
Liquid
L+α
α+β
L+β
α
Composition
γ+β
α+β
β
A
α+γ
B
A
Composition
B
3-17
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Microstructure Evolution During Slow Cooling
Microstructure for Three
Different Compositions
Eutectic System
1
2
3
Temperature
Liquid
α
L+α
L+β
L
L+α
L+α
α
L
L+α
L+α
α+β
L
L+α+β
α+β
1
β
2
α+β
A
Composition
B
α+β
3
3-18
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Determining Phase Balance
ƒ The Lever Rule
Temp
perature
Liquidus
z
2
L
Solidus
L+α
L+β
α
z
β
T1
Solvus
A
X
α+β
Y
Composition
B
Determines the
percentage of phases
present at a given
temperature
At temperature T1,
Composition
p
2 is a
mixture of α + β
ƒ Percent α =
Y
X+Y
ƒ Percent β = X
X+Y
3-19
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Some Examples of Phase Diagrams
3-20
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Diffusion
ƒ Diffusion Mechanisms
z
z
Vacancy Diffusion
Vacancy diffusion
Interstitial diffusion
Interstitial Diffusion
Reference: Defects in Crystals. Prof. Helmut Föll,
University of Kiel, Germany.
3-21
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Interdiffusion of Two Metals
Before Heat
After Heat
Treatment
Treatment
At High
At High
Temperature
Temperature
3-22
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Fick’s First Law of Diffusion
ƒ Flux is the mass diffusing through a fixed
area per unit of time
ƒ Diffusion flux (J) does not change with
time during stead-state diffusion
Fick’s First Law:
dC
J = −D
dx
J, diffusion flux (g/m2s)
D diff
D,
diffusion
i coefficient
ffi i t (m
( 2/s)
/)
C, concentration (g/m3)
x, position (m)
Reference: Callister, W.D. (2000)
3-23
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Fick’s Second Law of Diffusion
ƒ Diffusion flux and the composition gradient typically vary with
time
ƒ This results in concentration profiles such as the one shown
ƒ Fick’s second law describes transient diffusion
Fick’s Second Law:
∂C
∂ 2C
=D 2
∂t
∂x
t, time (s)
D, diffusion coefficient (m2/s)
C, concentration (g/m3)
x, position (m)
Reference: Callister, W.D. (2000)
3-24
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Diffusion Coefficients
ƒ Temperature has a
strong influence on
diffusion coefficients
ƒ This temperature
dependence takes on
the following form
⎛ Qd ⎞
D = D0 exp⎜ −
⎟
⎝ RT ⎠
Reference: Callister, W.D. (2000)
3-25
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Strengthening Mechanisms of Metals
ƒ Grain Size Reduction
ƒ Solid Solution Strengthening
z
z
Interstitial
Substitutional
ƒ Strain Hardening (cold work)
ƒ Precipitation
3-26
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Importance of Grain Size
ƒ Reducing grain size acts as a barrier to dislocation motion
increasing strength and toughness
z
The dislocation must change directions when reaching a grain
boundary since adjacent crystals have different crystal orientations
Slip of atomic planes is not continuous across the boundary
Increasing Grain size →
Yield strength varies with
grain size according to the
Hall-Petch equation
σ Y = σ 0 + kd −1/ 2
σY, yield strength
σo, k, material constants
d, average grain diameter
Yield strength
z
σ0
0
Grain size (d -1/2)
3-27
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Solid-Solution Strengthening
ƒ Intentional alloying with impurity atoms exerts strains on the
lattice surrounding the impurity
Ductility
Interstitial
Alloying
Yield strength
Substitutional
Alloying
Increasing the alloying
content results in an increase
i yield
in
i ld strength
t
th
Alloy content (wt-%)
3-28
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Strain Hardening
ƒ “Cold work” or “work hardening” is done by plastically
deforming a ductile metal at or near room temperature
Ductility
Yield strength
Increasing the cold work
results in an increase in yield
strength
Cold work expressed in terms
of area reduction:
⎛ Ainitial − A final
%CW = ⎜⎜
Ainitial
⎝
⎞
⎟⎟ *100
⎠
Percent cold work
3-29
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Precipitation Hardening
ƒ A metal alloy can be hardened and strengthened by
precipitating small secondary phase particles from a
supersaturated solid solution
Reference: Callister, W.D. (2000)
3-30
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Annealing
ƒ Cold Work
ƒ Recovery
ƒ Recrystallization
ƒ Grain Growth
Reference: Callister, W.D. (2000)
3-31
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
What is a Phase Transformation?
ƒ A change in the number and/or character of phases contained
within an alloy
ƒ Three types of transformations
z
z
z
Diffusional transformations – No change in the number or composition
of the phases present
Diffusional transformations – Phase composition and number of
phases
h
may change
h
Diffusionless transformations – Metastable phase is produced
3-32
Module 3 – Welding Metallurgy
Basics of Metallurgy Principles
Phase Transformations
ƒ Isothermal transformation
diagrams (TTT) describe the
nucleation and growth
behavior at a hold
temperature
γ Æ α + Fe3C
γ
Temperature
γ
α
α+γ
γ + Fe3C
α + Fe3C
γ
Fe
γ
Composition
γ
C
Reference: Callister, W.D. (2000)
3-33
Basics of Welding Metallurgy
Module 3B
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
Welding Metallurgy
ƒ Welding metallurgy describes a microcosm of metallurgical
processes occurring in and around a weld that influence the
microstructure, properties, and weldability of the material
ƒ Due to the rapid heating and cooling rates associated with
most welding processes, metallurgical reactions often occur
under transient, non-equilibrium conditions
3-35
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
Microstructure and Properties
ƒ The cooling rate and
Chemical
Composition
Thermal
Cycle
Microstructure
chemical composition
affect the microstructure of
the welded joint
ƒ The mechanical properties
of a welded joint depend
on the microstructure
produced by welding
Mechanical
Properties
3-36
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
Metallurgical Processes
ƒ Melting and solidification
ƒ Nucleation and growth
ƒ Phase transformations
ƒ Segregation and diffusion
ƒ Precipitation
ƒ Recrystallization
R
t lli ti and
d grain
i growth
th
ƒ Liquation mechanisms
ƒ Embrittlement
ƒ Thermal expansion, contraction, and residual stress
3-37
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
Regions of a Fusion Weld
ƒ The microstructure can
Fusion zone
Base metal
vary from region to
region in a weld
ƒ Microstructure has a
profound effect on weld
properties
Heat-affected zone
3-38
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
History
ƒ Pre-1976
z
z
Fusion zone
Heat-affected zone
ƒ Post-1976
z
Fusion zone
Š Composite region
Š Unmixed zone
ƒ Heat-affected zone
z
z
Partially melted zone
“True” heat-affected zone
3-39
Module 3 – Welding Metallurgy
Basics of Welding Metallurgy
Current
Fusion Zone
Heat-Affected
HeatZone
Partially Melted
Zone
Unmixed Zone
ƒ Fusion zone
z
z
Composite zone
Unmixed zone (UMZ)
ƒ Heat-Affected Zone (HAZ)
z
z
Partially-melted zone (PMZ)
True heat-affected zone (T-HAZ)
3-40
Module 3 – Welding Metallurgy
Fusion Zone
The Fusion Zone
ƒ Region of the weld that is completely melted and resolidified
ƒ Microstructure dependent on composition and solidification
conditions
ƒ Local variations in composition
ƒ Distinct from other regions of the weld
ƒ May exhibit three regions
z
z
z
Composite zone
Transition zone
Unmixed zone
3-41
Module 3 – Welding Metallurgy
Fusion Zone
Types of Fusion Zones
ƒ Autogenous
z
z
No filler metal addition
GTAW on thin sheet, EBW of square butt joint
ƒ Homogeneous
z
z
Addition of filler metal of matching composition
4130 filler used to join 4130 Cr-Mo steel
ƒ Heterogeneous
z
z
z
Addition of filler metal with dissimilar composition to the base material
4043 filler used to join 6061 aluminum
Ni-based alloys for joining stainless steels
3-42
Module 3 – Welding Metallurgy
Dilution
Dilution
ƒ Amount of melted base
metal mixing with filler
ƒ Expressed as percent base
metal dilution of the filler
metal
z
z
100% is an autogenous weld
10-40% common in arc welds
ƒ Significant effect on
Dilution (%) =
a + c x 100
a+b+c
microstructure and
properties
ƒ Controlled by joint design,
process, and parameters
3-43
Module 3 – Welding Metallurgy
Dilution
Dilution of 308L SS Filler Metal by
304 SS Base Metal
High Dilution
304
Low Dilution
304
A
a
C
c
B
b
304
Figure 1
304
Figure 2
3-44
Module 3 – Welding Metallurgy
Dilution
Dilution of 4043 Filler Metal by 6061 Aluminum
Base Metal
Low Dilution
High Dilution
V-Groove with Root Opening
V-Groove without Root Opening
6061
C
A
B
6061
6061
a
c
b
6061
3-45
Module 3 – Welding Metallurgy
Dilution
Dilution of 4043 Filler Metal by 6061 Aluminum
Base Metal
Material Cu
6061
0.25
4043
0.30
Fe
0.50
0.80
Mg
1.10
0.05
Mn
0.12
0.05
High Dilution
Si
0.55
5.20
Low Dilution
45%
Cu
Fe
Mg
Mn
Si
10%
Cu
Fe
Mg
Mn
Si
Weld Metal
0 278
0.278
0 665
0.665
0 523
0.523
0 082
0.082
3 108
3.108
Weld Metal
0 295
0.295
0 770
0.770
0 155
0.155
0 057
0.057
4 735
4.735
Silicon levels above 4 wt% help prevent weld solidification cracking
3-46
Module 3 – Welding Metallurgy
Fusion Zone
Weld Pool Shape
ƒ Material properties
z
z
z
Melting point
Thermal conductivity
Surface tension
Š Marangoni effect
ƒ Process parameters
z
z
Heat input
Travel speed
ƒ Heat flow conditions
z
z
2-D (full penetration)
3-D (partial penetration)
3-47
Module 3 – Welding Metallurgy
Fusion Zone
Surface Tension Induced Fluid Flow
ƒ Surface tension of liquid a
function of composition and
temperature
z
Marongoni effect
ƒ Influence of gradient on weld
pool fluid flow
z
z
Negative gradient promotes
outward flow and shallow
penetration
Positive gradient promotes
inward (downward) flow and good
penetration
ƒ Strong influence of sulfur and
oxygen
Figure modified from Heiple and Roper
3-48
Module 3 – Welding Metallurgy
Solidification
Nucleation of Solid during Solidification
ƒ Homogeneous
z
z
Critical radius size, where r* = 2γslTm
ΔHM ΔT
Liquid undercooling
ƒ Heterogeneous
z
z
Nucleation from existing substrate or particle
Little or no undercooling required
3-49
Module 3 – Welding Metallurgy
Solidification
Types of Heterogeneous Nucleation
ƒ Dendrite fragmentation
ƒ Grain detachment
ƒ Nucleant particle formation
ƒ Surface nucleation
ƒ Epitaxial nucleation
Courtesy Kou and Le
3-50
Module 3 – Welding Metallurgy
Solidification
Epitaxial Nucleation at the Fusion Boundary
ƒ Nucleation from an existing
solid substrate
ƒ Crystallographic orientation
of base metal “seed crystal”
is maintained
ƒ Growth p
parallel to cube edge
g
in cubic materials
z
z
z
⟨100⟩ in FCC and BCC
⟨1010⟩ in HCP
Called “easy growth” directions
3-51
Module 3 – Welding Metallurgy
Solidification
Solidification Modes
ƒ Multiple solidification modes (morphologies) are possible
z
z
z
z
z
Planar
Cellular
Cellular dendritic
Columnar dendritic
Equiaxed dendritic
ƒ Controlled by
z
z
z
Temperature gradient in the liquid, GL
Solidification growth rate, R
Composition
3-52
Module 3 – Welding Metallurgy
Solidification
Solidification Growth Modes
High GL and Low R
3-53
Module 3 – Welding Metallurgy
Solidification
Solidification Growth Modes
3-54
Module 3 – Welding Metallurgy
Solidification
Effect of Travel Speed
ƒ Travel speed has significant
effect on weld pool shape
ƒ Low travel speeds
z
z
z
Elliptical pool shape
Curved columnar grains
Gradual change in GL and R
ƒ High travel speeds
z
z
z
Teardrop pool shape
Distinct centerline
R is constant along most of
S-L interface
3-55
Module 3 – Welding Metallurgy
Solidification
Temperature Gradient, GL
Effect of GL and R
Planar
Cellular
Finer
structure
Cellular
Dendritic
High G·R
Columnar
Dendritic
Low G·R
Equiaxed Dendritic
Solidification Rate, R
3-56
Module 3 – Welding Metallurgy
Solidification
Effect of GL, R, and Composition
Columnar
Dendritic
Composition
Equiaxed
Dendritic
Cellular
Dendritic
Cellular
Typical Range of
Solidification
Planar
Solidification Parameter, GL/R½
3-57
Module 3 – Welding Metallurgy
Solidification
Dendrite Arm Spacing
Effect of Cooling Rate
Higher Cooling Rate
Finer
Structure
Castings
Welds
Splat Cooling
Log Cooling Rate, G ·R, degrees/sec
3-58
Module 3 – Welding Metallurgy
Solidification
Weld Metal Epitaxial Nucleation
ƒ Nucleation from and
existing solid substrate at
the fusion boundary
ƒ Crystallographic orientation
of HAZ grain is maintained
ƒ “Easyy growth”
g
directions
parallel to cube edge in
cubic materials
z
z
⟨100⟩ in FCC and BCC
⟨1010⟩ in HCP
3-59
Module 3 – Welding Metallurgy
Solidification
Competitive Growth
ƒ Random orientation of base
metal grains in
polycrystalline materials
ƒ Growth most favorable
when easy growth direction
is parallel to heat flow
direction
ƒ Grains “compete”
depending on orientation
ƒ Intersection of grains forms
SGBs
From Nelson and Lippold
3-60
Module 3 – Welding Metallurgy
Solidification
Fusion Zone Boundaries
ƒ Differentiated by
z
z
Composition
Structure
ƒ Solidification subgrain
boundaries (SSGBs)
z
z
Composition (Case 2)
Low angle misorientation
ƒ Solidification grain boundaries
(SGBs)
z
z
Composition (Case 3)
High or low angle misorientation
ƒ Migrated grain boundaries
(MGBs)
z
z
Local variation in composition
High angle misorientation
3-61
Module 3 – Welding Metallurgy
Solidification
Solidification Subgrain Boundary
ƒ Boundaries between cells
and dendrites
(solidification subgrains)
ƒ Composition dictated by
Case 2 solute
redistribution
ƒ Low misorientation
between adjacent
subgrains - low angle
boundary
50 μm
3-62
Module 3 – Welding Metallurgy
Solidification
Solidification Grain Boundary
ƒ Boundary between
SGB
25 μm
packets of subgrains
ƒ Results from competitive
growth
ƒ Composition dictated by
Case 3 solute
redistribution
ƒ Large misorientation
across boundary at end of
solidification - high angle
boundary
ƒ Most likely site for
solidification cracking
3-63
Module 3 – Welding Metallurgy
Solidification
Migrated Grain Boundary
ƒ Crystallographic
MGB
25 μm
component of SGB
ƒ Migrates away from SGB
in the solid state following
solidification or during
reheating
ƒ Large misorientation
across boundary - high
angle boundary
ƒ Composition varies locally
ƒ Possible boundary
“sweeping” and
segregation
ƒ Liquation and ductility dip
cracking
3-64
Module 3 – Welding Metallurgy
Fusion Zone
Fusion Zone Microstructure - Stainless Steels
50 µm
Austenitic Stainless Steel
50 µm
Duplex Stainless Steel
3-65
Module 3 – Welding Metallurgy
Fusion Zone
Microstructure - Ni-Base Alloy
20 μm
3-66
Module 3 – Welding Metallurgy
Fusion Zone
Filler Metal 82 – Nickel-Base Alloy
50 μm
Arrows indicate migrated grain boundaries
3-67
Module 3 – Welding Metallurgy
Fusion Zone
Microstructure - Aluminum Alloy
3-68
Module 3 – Welding Metallurgy
Fusion Zone
Transition Region
Ferrite +
Austenite
Ferrite
Martensite Band
50μm
Carbon steel base metal with austenitic stainless steel filler metal
3-69
Module 3 – Welding Metallurgy
Unmixed Zone
Unmixed Zone (UMZ)
Fusion Zone
Heat-Affected
Zone
Unmixed Zone
Partially Melted
Zone
ƒ Narrow region adjacent to the fusion boundary
ƒ Completely melted and resolidified base metal
ƒ No mixing with the bulk fusion zone (composite region)
3-70
Module 3 – Welding Metallurgy
Unmixed Zone
Factors Influencing UMZ Formation
ƒ Base metal/filler metal composition
ƒ Physical properties
z
z
z
Melting point
Fluid viscosity
Miscibility
ƒ Welding
gp
process
z
z
Most prevalent in arc welding processes (GTAW, GMAW)
Not observed in EBW and LBW
ƒ Process conditions
z
z
Heat input
Fluid flow
3-71
Module 3 – Welding Metallurgy
Unmixed Zone
Alloy Systems
Low Alloy Steels
HY-80
Austenitic Stainless Steels
310/304L, 312/304L
Superaustenitic Stainless Steels
AL6XN, 254SMO
Aluminum Alloys
4043/6061, 2319/2195
Nickel-based Alloys
Alloys 600 and 625
Dissimilar combinations
308L/625
3-72
Module 3 – Welding Metallurgy
Unmixed Zone
Austenitic Stainless Steels
Weld
Metal
Former UMZ
UMZ
100 μm
From Baeslack and Lippold
SEM
3-73
Module 3 – Welding Metallurgy
Partially Melted Zone
Partially Melted Zone (PMZ)
Fusion Zone
Heat-Affected
Zone
Unmixed Zone
Partially Melted
Zone
ƒ Region separating the fusion zone from the “true” heat-
affected zone
ƒ Transition from 100% liquid at the fusion boundary to 100%
solid in the HAZ
ƒ Localized melting normally observed at grain boundaries
ƒ Constitutional liquation of certain particles
3-74
Module 3 – Welding Metallurgy
Partially Melted Zone
Grain Boundary Liquation in the PMZ
ƒ Segregation of solute/
impurities to grain
boundaries depresses the
local melting point
ƒ Temperature gradient has a
strong effect on the extent of
melting
Steep Gradient
Shallow Gradient
3-75
Module 3 – Welding Metallurgy
Heat-Affected Zone
The “True” Heat-Affected Zone (HAZ)
Fusion Zone
Heat-Affected
Zone
Unmixed Zone
Partially Melted
Zone
ƒ Adjacent to the PMZ
ƒ All metallurgical reactions occur in the solid state
ƒ Strongly dependent on weld thermal cycle and heat flow
conditions
3-76
Module 3 – Welding Metallurgy
Heat-Affected Zone
Metallurgical Reactions
ƒ Solid-state metallurgical reactions
z
z
z
z
z
z
Recrystallization
Grain growth
Allotropic / phase transformations
Dissolution / overaging of precipitates
Formation of precipitates
Formation of residual stresses
ƒ Degradation of weldment properties is often associated with
the HAZ
3-77
Module 3 – Welding Metallurgy
Heat-Affected Zone
Effect of Heat Input and Heat Flow
HAZ
Fusion Zone
PMZ
• Low HI
• Effective heat flow
• High HI
• Restricted heat flow
ƒ HAZ width dictated by weld thermal conditions
ƒ HAZ temperature gradient
z
z
Heat input
Heat flow
3-78
Module 3 – Welding Metallurgy
Heat-Affected Zone
Effect of Recrystallization on Strength and
Ductility
ƒ Recrystallization promotes
z
z
loss in strength
Increase in ductility
ƒ Grain growth promotes
some additional softening
From W.D. Callister
3-79
Module 3 – Welding Metallurgy
Heat-Affected Zone
Hardness or Strength
Annealed vs. Cold Worked HAZs
Annealed
Base Metal
HAZ
Fusion Zone
HAZ
Cold Worked
Base Metal
3-80
Module 3 – Welding Metallurgy
Heat-Affected Zone
HAZ Softening
Aluminum Alloy 5356-H3
from AWS Handbook
Nickel-base Alloy 718
3-81
Module 3 – Welding Metallurgy
Heat-Affected Zone
HAZ Transformations in Steels
ƒ Function of composition and cooling rate
ƒ Regions that form austenite during heating transform during
cooling
z
z
z
z
z
Ferrite
Pearlite
Bainite
Martensite
Combinations of phases
ƒ CCT diagrams
3-82
Module 3 – Welding Metallurgy
Heat-Affected Zone
Continuous Cooling Transformation Diagrams
Ferrite Start
Bainite Start
Martensite Start
3-83
Module 3 – Welding Metallurgy
Heat-Affected Zone
Phase Transformations
ƒ Most engineering alloy systems undergo phase
transformations in the HAZ
z
z
Copper alloys, β (BCC) → α (FCC)
Stainless steels, δ (BCC) → γ (FCC)
ƒ Nature of transformations
z
z
Diffusion-controlled
Diffusionless, or shear-type
Š Martensitic
Š Massive
3-84
Module 3 – Welding Metallurgy
Regions of a Solid-State Weld
HAZ of Non-Fusion Joining Processes
ƒ Solid-state joining processes have no fusion zone but can
have a HAZ
z
z
z
z
Friction welding
Flash butt welding
Diffusion welding
Explosion welding
ƒ Friction and flash butt welding
z
z
z
Base metal is heated until it is easily deformable
Two ends of the joint are forged together
Hot base metal is extruded from the joint to form a flash
3-85
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX – Base Material Variables
ƒ ASME Section IX groups similar materials into P-No.
categories
z
Similar composition, weldability and mechanical properties
ƒ In addition to P-No., materials can be further described by
Group No., grade, specification, grade, etc.
z
Materials can be specified as P-No.1 Group 1 or P-No.1 Group 2
ƒ P-No. and Group No. are listed in QW/QB 422 of ASME
Section IX
ƒ Typically the base material requirements defined by ASME
Section IX are independent of the welding process
3-86
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX – Base Material Variables
3-87
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX – Base Material Variables
P-No.
Description
1
C, C-Mn, and C-Mn-Si steels
3
Low-alloy steels [Mo, Mn-Mo, Si-Mo and Cr-Mo (Cr ≤ ¾% and total
alloy content < 2%)]
4
Cr-Mo low-alloy steels with Cr between ¾% and 2% and total alloy
content < 2 ¾%
5A Cr-Mo low-alloy steels with Cr ≤ 3% and < 85 ksi minimum tensile
strength
5B Cr-Mo low-alloy steels with Cr > 3% and ≤ 85 ksi minimum tensile
strength
5C Cr-Mo low-alloy steels with Cr between 2 ¼ % and 3% and ≥ 85 ksi
minimum tensile strength
6
Martensitic stainless steels
7
Ferritic stainless steels - nonhardneable
8
Austenitic stainless steels
3-88
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX – Base Material Variables
P-No.
Description
9A, 9B, 9C Nickel alloy steels with 4.5% Ni
10A – 10K Mn-V and Cr-V steels, 26% Cr-3% Ni-3% Mo, and 29% Cr-4%
Mo-2% Ni steels and duplex stainless steels
11A, 11B
Low-alloy quench and tempered steels with > 95 ksi minimum
tensile strength
21 – 25
Aluminum and aluminum-base alloys
31 – 35
Copper and copper-base alloys
41 – 47
Nickel and nickel-base alloys
51 – 53
Titanium and titanium-base alloys
61, 62
Zirconium and zirconium-base alloys
3-89
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX – Base Material Variables
Paragraph
QW-402
Joint
QW-403
Base Material
Brief of Variables
Essential
Supplementary
Essential
.3
Φ Backing Composition
.1
φ P-No. Qualified
.4
φ Group Number
X
.5
φ Group Number
X
.11
φ P-No. Qualified
X
.12
φ P-No./Melt-in
X
.15
φ P-No. Qualified
X
.17
φ Base Metal or Stud
Metal P-No.
X
.19
φ Base Metal
X
.24
φ Specification, Type, or
Grade
X
Nonessential
X
X
3-90
Carbon and Low Alloy Steels
Module 3C
Module 3 – Welding Metallurgy
Classification of Steels
Classification by Composition
ƒ Plain carbon
z
z
z
z
Low carbon, < 0.2 wt%
Medium carbon, 0.2-0.6 wt%
High carbon, 0.6-1.0 wt%
Ultrahigh carbon, 1.25-2.0 wt%
ƒ Low alloy, up to 8% alloying
addition
z
z
z
Low carbon, quench and
tempered
Medium carbon, ultrahigh
strength
Cr-Mo heat resistant
ƒ High strength, low alloy (HSLA)
z
z
z
z
z
z
Micro-alloyed
Dual-phase
Control-rolled
Weathering
Pearlite-reduced
Acicular ferrite
ƒ High alloy, > 8% alloy addition
z
z
High Cr, heat-resistant
Stainless
3-92
Module 3 – Welding Metallurgy
Classification of Steels
Steel Classification Systems
ƒ AISI/SAE
ƒ ASTM
1020
z
z
z
1 = carbon steel
0 = plain carbon steel
20 = 20/100 % carbon
4340
z
z
z
4 = molybdenum steel
3 = Ni-Cr-Mo (1.8% Ni)
40 = 40 / 100 % carbon
A516
z
z
C-steel pressure vessel plates
Graded by tensile strength
ƒ ASME Boiler and Pressure
Vessel Code
P1
z
z
P groups of similar steel
Simplified qualification
3-93
Module 3 – Welding Metallurgy
Classification of Steels
Carbon Steels Used in the Nuclear Industry
Designation
Composition
(wt%)
Mechanical
Properties
Uses
SA-36
0.2C, 0.15-0.4Si,
0.8-1.2Mn
UTS: 58-80 ksi
YS: 36 ksi min.
Elong: 20% min.
General structural
SA508,,
Class 3
0.2C,, 0.15-0.40Si,,
UTS: 90-115 ksi
1.2-1.5Mn, 0.4-1.0Ni, YS: 65 ksi min
0.45-0.6Mo
Elong: 16% min.
Quench and tempered
p
forgings for pressure
vessels
SA-533,
Type C
0.25C, 0.15-0.40Si,
1.15-1.5Mn, 0.40.7Ni, 0.45-0.6Mo
Quench and tempered
steel plates for pressure
vessels
UTS: 100-125 ksi
YS: 83 ksi min.
Elong: 16% min.
3-94
Module 3 – Welding Metallurgy
Microstructure of Steels
Different Phases in Steel
ƒ Iron can exhibits 3 separate solid phases between room
temperature and its melting temperature
z
z
z
Low temperature ferrite (bcc) – alpha ferrite
Austenite (fcc)
High temperature ferrite (bcc) – delta ferrite
ƒ When carbon is added to iron to form steel, another phase
known as cementite (Fe3C) can form
ƒ Steels are known as “allotropic” materials because the same
composition can have different phases depending on
temperature
3-95
Module 3 – Welding Metallurgy
Fe-Fe3C Phase Diagram
Iron-Iron Carbide Phase Diagram
0.09%
δ + Liquid
1538
(2800)
Temperature, °C
C [°F]
equilibrium phase
diagram
ƒ Equilibrium phases
Liquid
0.53%
1495 (2723)
δ
1394
(2541)
ƒ Iron-rich end of Fe-C
0.17%
δ+γ
Liquid
+ Fe3C
γ + Liquid
1148 (2098)
γ
α+γ
α
0.02%
0
z
γ+
Fe3C
0.77%
Ferrite (alpha and delta)
Austenite
Cementite (Fe3C)
ƒ Invariant reactions
z
Fe3C
770
(1418)
z
z
4.3%
2.11%
912
(1674)
z
727 (1341)
z
α + Fe3C
Carbon, wt%
6.67
Peritectic (1495°C,
0.17%C)
Eutectic (1148°C,
4.3%C)
Eutectoid (727°C,
0.77%C)
3-96
Module 3 – Welding Metallurgy
Fe-Fe3C Phase Diagram
Iron-Iron Carbide Phase Diagram
ƒ Steels
z
z
z
C content generally less
than 1.0 wt%
Hypoeutectoid – less than
0.77% carbon
Hypereutectoid – between
0.77 and 2.1% C
ƒ Cast irons
z
z
Greater than 2.1% carbon
High volume fraction
cementite
3-97
Module 3 – Welding Metallurgy
Effect of Cooling Rate
Continuous Cooling Transformation Diagram
3-98
Module 3 – Welding Metallurgy
Effect of Cooling Rate
Continuous Cooling Transformation Diagrams
Ferrite Start
Bainite Start
Martensite Start
3-99
Module 3 – Welding Metallurgy
Effect of Cooling Rate
Slow Cooling → Ferrite + Pearlite
ƒ Ferrite is a soft and ductile
phase found in steel
microstructures
z
Ferrite can contain
£ 0.025% carbon
ƒ Pearlite is a banded mixture of
f it and
ferrite
d cementite
tit (Fe
(F 3C)
z
Cementite contains the excess
carbon that the ferrite can’t hold
3-100
Module 3 – Welding Metallurgy
Effect of Cooling Rate
Bainite
ƒ Medium/high cooling rates
ƒ Suppressed proeutectoid
and eutectoid
transformations
ƒ Undercooled austenite
ƒ Short range diffusion of
carbon
ƒ Precipitation of Fe3C and
carbides
ƒ Formation of bainitic ferrite
ƒ Low toughness of upper
bainite
3-101
Module 3 – Welding Metallurgy
Effect of Cooling Rate
Fast Cooling → Martensite
ƒ Martensite is very strong,
hard, and brittle
ƒ Body centered tetragonal
crystal structure (bct)
ƒ High dislocation density
ƒ Metastable structure
3-102
Module 3 – Welding Metallurgy
Martensite
Martensite: Good or Bad?
ƒ GOOD Aspects of Martensite
z
z
High strength and hardness compared to ferrite + pearlite
Many steels are designed to be quenched to form martensite then
tempered to improve their ductility and toughness
Š 4130
Š 4340
ƒ BAD Aspects of Martensite
z
z
Martensite results in low ductility and toughness
Increases the possibility of hydrogen induced cracking (HIC)
particularly in highly restrained joints
3-103
Module 3 – Welding Metallurgy
Hardness of Steels
Hardness - Effect of Carbon
ƒ Carbon is the most
important alloying element
in steel
ƒ Interstitial element
ƒ Forms carbides with Fe and
other alloying
y g elements ((Cr,,
Mo, V)
ƒ Greatly facilitates
transformation hardening
ƒ Controls the maximum
hardness achievable in the
alloy
3-104
Module 3 – Welding Metallurgy
Carbon and Low Alloy Steels
Hardness versus Hardenability
ƒ Hardenability is the ease with which hardening occurs upon
cooling from the austenite phase field
ƒ Associated with the formation of martensite
ƒ Factors which influence hardenability
z
z
z
z
z
Carbon content
Alloying
y g additions
Prior austenite grain size
Homogeneity of the austenite
Section thickness
3-105
Module 3 – Welding Metallurgy
Hydrogen Cracking
Hydrogen Induced Cracking and Martensite
ƒ Four factors are required for hydrogen cracking
z
z
Susceptible microstructure
Source of hydrogen
Š Moisture in flux
Š Grease/oil on plates
z
Stress
Š Residual
Š Applied
z
Temperature between -100 and
200°C (-150 and 390°F)
Hydrogen crack at root of multipass weld
ƒ Eliminate only one factor and HIC goes away!!
3-106
Module 3 – Welding Metallurgy
Hydrogen Cracking
Using Preheat to Avoid Hydrogen Cracking
ƒ If the base material is preheated, heat flows more slowly out
of the weld region
z
Slower cooling rates avoid martensite formation
ƒ Preheat allows hydrogen to diffuse from the metal
T base
Cooling rate ∝ (T - Tbase)3
Cooling rate ∝ (T - Tbase)2
T base
3-107
Module 3 – Welding Metallurgy
Hydrogen Cracking
Interaction of Preheat and Composition
CE = %C + %Mn/6 + %(Cr+Mo+V)/5 + %(Si+Ni+Cu)/15
ƒ Carbon equivalent (CE) measures potential to form
martensite, which is generally necessary for hydrogen
cracking
z
z
z
CE < 0.35
0.35 < CE < 0.55
0.55 < CE
no preheat or PWHT
preheat
preheat and PWHT
ƒ Preheat temperature ↑ as CE ↑ and plate thickness ↑
3-108
Module 3 – Welding Metallurgy
Hydrogen Cracking
Postweld Heat Treatment and Hydrogen Cracking
ƒ Postweld heat treatment (1100-1250°F) tempers any
martensite that may have formed
z
z
Increase in ductility and toughness
Reduction in strength and hardness
ƒ Residual stress is decreased by postweld heat treatment
ƒ Rule of thumb: hold at temperature
p
for 1 hour p
per inch of p
plate
thickness; minimum hold of 30 minutes
ƒ Postweld heat treatment temperatures vary for different steels
ƒ In general, PWHT for tempering must be done below the
lower critical (A1) temperature
3-109
Module 3 – Welding Metallurgy
Preheat and Post Weld Heat Treatment
Preheat and PWHT
Temperatu
ure
Preheat
Weld Thermal Cycle
PWHT
No/Low Preheat
Medium Preheat
High Preheat
Time
3-110
Module 3 – Welding Metallurgy
Consumables
Welding Consumables for Carbon Steels
ƒ Processes used in the Nuclear Industry for Primary
Fabrication and Repair
z
z
z
z
Shielded Metal Arc Welding (SMAW)
Gas Metal Arc Welding (GMAW)
Gas Tungsten Arc Welding (GTAW)
Flux Cored Arc Welding (FCAW)
3-111
Module 3 – Welding Metallurgy
Coated Electrodes
AWS Standards Specific to SMAW
ƒ AWS A5.1 - Specification for Carbon Steel Electrodes for
Shielded Metal Arc Welding
ƒ AWS A5.5 - Specification for Low-Alloy Electrodes for
Shielded Metal Arc Welding
ƒ AWS A5.4 - Specification for Corrosion-Resisting Chromiumand Chromium-Nickel Steels for Shielded Metal Arc Welding
g
3-112
Module 3 – Welding Metallurgy
Coated Electrodes
SMAW Electrode Designation
Welding Position
Digit
Position
1
Flat, Horizontal, Vertical, Overhead
2
Flat and Horizontal only
3
Flat only
4
Flat, Horizontal, Vertical Down, Overhead
3-113
Module 3 – Welding Metallurgy
Coated Electrodes
SMAW Electrode Designation
Alloying Content of Weld Metal Deposit
Type of Coating and Current
Digit
Type of Coating
Current
Suffix
%Mn
%Ni
%Cr
%Mo
0
Cellulose sodium
DC+
A1
1
Cellulose potassium
AC, DC±
B1
0.50
0.50
2
Titania sodium
AC, DC-
B2
1.25
0.50
3
Titania potassium
AC, DC+
B3
2.25
1.00
4
Iron powder titania
AC, DC±
C1
2.50
5
Low hydrogen sodium
DC+
C2
3.25
6
Low hydrogen potassinm
AC, DC+
C3
1.00
0.15
0.35
7
Iron powder iron oxide
AC, DC±
D1/D2
8
Iron powder low hydrogen
AC, DC±
G(1)
%V
0.50
1.25-2.00
0.25-0.45
0.50
0.30 min.
0.20 min.
0.10 min.
Examples
E6010
Cellulosic, all position, DCEP, 60 ksi min UTS
E7018
Low hydrogen, all position, AC or DCEP, 70 ksi min UTS
E7010-A Cellulosic, all position, DCEP, 70 ksi min, carbon/moly
3-114
Module 3 – Welding Metallurgy
Coated Electrodes
Common SMAW Electrode Coating Descriptions
ƒ XX10- High cellulose sodium, DCEP
ƒ XX11- High cellulose potassium, AC or DCEP
ƒ XX12- Rutile sodium AC, DCEP, DCEN
ƒ XX13- Rutile potassium AC, DCEP, DCEN
ƒ XX14XX14 Rutile
R til + F
Fe – powder
d additions
dditi
AC
AC, DCEP
DCEP, DCEN
ƒ XX15- Low hydrogen, sodium, DCEP
ƒ XX16- Low hydrogen potassium AC, DCEP
ƒ XX18- Low hydrogen, Fe powder additions AC, DCEP
3-115
Module 3 – Welding Metallurgy
Wire Electrodes
Types of Continuous Wire Electrodes
3-116
Module 3 – Welding Metallurgy
Wire Electrodes
AWS Standards Specific to GTAW
and GMAW Electrodes
ƒ AWS A5.18 - Specification for Carbon Steel Electrodes for
Gas Shielded Arc Welding
ƒ AWS A5.28 - Specification for Low-Alloy Steel Electrodes
and Rods for Gas Shielded Arc Welding
ƒ AWS A5.9 - Specification for Stainless Steel Electrodes and
Rods for Gas Shielded Arc Welding
g
3-117
Module 3 – Welding Metallurgy
Wire Electrodes
AWS Classification for Solid Steel Wires
AWS A5.18
ER70S-3 H4
Use as an electrode or rod
Tensile strength in ksi
Solid wire
Chemical composition of electrode (2, 3, 4, 6, 7, G)
Optional diffusible hydrogen designator
(4, 8 or 16 ml/100 g)
Examples
ER70S-6
ER80S-B2
ER100S-2
C-Mn, high Si, 70 ksi min UTS
Cr-Mo grade, 80 ksi min UTS
HSLA grade (Cr, Ni, Mo, Cu), 100 ksi min UTS
3-118
Module 3 – Welding Metallurgy
Wire Electrodes
AWS Classification for Composite Steel Wires
Examples
E70C-3C
0.12%C-1.75%Mn-0.9%Si-0.5%Ni-0.2%Cr-0.3%Mo0.5%Cu, high Si, 70 ksi min UTS, 100% CO2
3-119
Module 3 – Welding Metallurgy
Wire Electrodes
FCAW Electrode Classification
AWS A5.29
E80T5-K2M JH4
Electrode
Tensile strength in ksi x10
Welding position (0 F and H; 1 all)
Fl cored
Flux
d electrode
l t d
Electrode polarity and usability
Chemical composition of deposited weld
Shielding gas (M 75-80% Ar, bal. CO2;
without M 100% CO2 or selfshielded)
Toughness requirement (J improved; without J normal)
Optional diffusible hydrogen designator (4, 8 or 16 ml/100 g)
Example
E91T1-D1
90-110 min ksi, all position, CO2 shielded, DCEP,
1.25/2.00 Mn and 0.25/0.55 Mo
3-120
ASME Requirements
Preheat, PWHT and Temper Bead
Welding
Module 3 – Welding Metallurgy
Preheat Requirements
ASME Section III Division 1 – NB –
Preheat Requirements
ƒ NB-4610, Welding Preheat Requirements
z
NB-4611, When is Preheat Necessary
Š States preheat temperature is dependent on a number of factors
z
z
z
z
z
Chemical analysis
Degree of restraint
Elevated temperature
Physical properties
Material thickness
Š Provides suggested preheat temperatures depending on the P-Number of
the material
Š Refers to non-mandatory Appendix D
z
z
z
Preheat temperature is based on chemistry, thickness and/or strength of the
material
NB-4612, Preheating Methods
NB-4613, Interpass Temperature
Š Applicable to quench and tempered materials
3-122
Module 3 – Welding Metallurgy
Preheat Requirements
ASME B31.1 – Power Piping –
Preheat Requirements
ƒ 131, Welding Preheat
z
131.1, Minimum Preheat Requirements
Š Provides minimum preheat temperatures depending on the material P-No.
Š The preheat temperature should be achieved 3 in. or 1.5 times the
material thickness which ever is greater from the weld joint
z
131.2, Different P-Number Materials
Š The minimum preheat temperature shall be the highest of the two
recommended temperatures
z
z
z
131.3, Preheat Temperature Verification
Š Specifies how to monitor the preheat temperature
131.4, Preheat Temperature
Š Should be 50ºF unless otherwise specified depending on material P-No.
Š Identifies the governing thickness as the thicker of the two nominal base
materials being welded
131.6, Interruption of Welding
Š Provides requirements for when welding is interrupted and varies
depending on material being welded
3-123
Module 3 – Welding Metallurgy
Preheat Requirements
Comparison of ASME Preheat Requirements
Material
Preheat Recommendations
ASME Section III - NB
P-No. 1
(Carbon Steel)
200ºF for ≤ 0.30%C and >1.5”
thick
ASME B31.1
175ºF for > 0.30%C and >1”
thick
250ºF for > 0.30%C and >1”
thick
P-No. 5
(2.25Cr 1 Mo)
50ºF for all other materials
50ºF for all other materials
400ºF for 60 ksi SMTS or
specified minimum Cr >6.0%
and 01.5” thick
400ºF for 60 ksi SMTS or
specified minimum Cr >6.0%
and 0.5” thick
300ºF for all other materials
300ºF for all other materials
3-124
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Requirements
ƒ NB-4620, Postweld Heat Treatment
z
NB-4621, Heating and Cooling Methods
Š PWHT may be performed by suitable means provided heating and cooling
rates, metal temperature , uniformity and temperature control are
maintained
z
NB-4622, PWHT Time and Temperature Requirements
Š
Š
Š
Š
NB-4622.1, General PWHT requirements
q
NB-4622.2, Time-Temperature Recordings
NB-4622.3, Definition of Nominal Thickness Governing PWHT
NB-4622.4, Hold Time at Temperature
z
Does allow for lower temperatures for longer times with addition testing
requirements
Š NB-4622.5, Requirements for different P-No.
Š NB-4622.7, Exemptions to Mandatory Requirements
3-125
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Requirements
3-126
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Requirements
ƒ NB-4620, Postweld Heat Treatment
z
NB-4622, PWHT Time and Temperature Requirements
Š NB-4622.4, Hold Time at Temperature
z
Does allow for lower temperatures for longer times with addition testing
requirements
3-127
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Exemptions
ƒ NB-4620, Postweld Heat Treatment
z
NB-4622, PWHT Time and Temperature Requirements
Š NB-4622.7, Exemptions to Mandatory Requirements
z
z
z
z
z
z
z
Nonferrous material
Exempted welds (Table NB-4622.7 (b)-1)
Welds subjected to temperatures above the PWHT temperature
Welds connecting nozzles to components or branch to pipe in accordance to
NB 4622 8 repairs
NB-4622.8
i tto vessels
l (i
(i.e., ttemper b
bead
d weld
ld repair)
i)
Weld repairs to vessels in accordance to NB-4622.9 (i.e., temper bead weld
repair)
Weld repairs to cladding after final PWHT in accordance to NB-4622.10
Weld repairs to dissimilar metal welds after final PWHT in accordance to NB4622.11 (i.e., temper bead weld repair)
3-128
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Exemptions
3-129
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Exemptions
3-130
Module 3 – Welding Metallurgy
PWHT Requirements
ASME Section III Division 1 – NB –
PWHT Requirements
ƒ NB-4620, Postweld Heat Treatment
z
NB-4623, PWHT Heating and Cooling Rates
Š Above 800ºF, the heating and cooling rate shall not exceed 400ºF divided
by the maximum material thickness per hour
Š Heating and cooling rates shall be between 400 and 100ºF/hr
Š There shall not be a temperature gradient greater than 250ºF per 15 feet
of weld length
z
NB-4624, Methods of PWHT
ƒ NB-4630, PWHT of Welds Other Than Final PWHT
ƒ NB-4650, PWHT after Bending or Forming
ƒ NB-4660, PWHT of Electroslag Welds
z
Electroslag welds in ferritic material over 1.5-in. thick shall be given a
grain refining heat treatment
3-131
Module 3 – Welding Metallurgy
PWHT Requirements
ASME B31.1 – Power Piping –
PWHT Requirements
ƒ 132, Postweld Heat Treatment
z
132.1, Minimum PWHT Requirements
Š Refers to Table 132
Š Allows for lower temperature and
longer time
z
132.2, Mandatory PWHT
Requirements
q
Š PWHT may be performed by
suitable means provided heating
and cooling rates, metal
temperature , uniformity and
temperature control are
maintained
Š Refers to Table 132 for time and
temperature
3-132
Module 3 – Welding Metallurgy
PWHT Requirements
ASME B31.1 – Power Piping –
PWHT Requirements
3-133
Module 3 – Welding Metallurgy
PWHT Requirements
ASME B31.1 – Power Piping –
PWHT Requirements
3-134
Module 3 – Welding Metallurgy
PWHT Requirements
ASME B31.1 – Power Piping –
PWHT Requirements
ƒ 132, Postweld Heat Treatment
z
132.3 Exemptions to Mandatory PWHT Requirements
Š Welds in nonferrous materials
Š Welds exempted in Table 132
Š Welds subject to temperatures above the lower critical temperature
provided proper qualification
Š Exemptions
p
are based on the actual chemistry
y of the material
z
132.4 Definition of Thickness Governing PWHT
Š Table 132 uses weld thickness (i.e., “nominal thickness”) to determine time
and temperature but use material thickness (i.e., “nominal material
thickness”) for exemptions
z
132.5 PWHT Heating and Cooling Rates
Š Above 600ºF, the heating and cooling rate shall not exceed 600ºF per hour
divided by the ½ the maximum material thickness
Š Heating and cooling rates shall not exceed 600ºF/hr
z
z
More specifics depending on material
132.6 and 132.7 describe furnace heating and local heating
requirements
3-135
Module 3 – Welding Metallurgy
PWHT Requirements
Comparison of ASME PWHT Requirements
ASME
Code
PNo.
Sec. III – 1
NB
B31.1
Hold
Temperature
1100 ºF –
1250 ºF
5A
1250 ºF –
1400 ºF
1
1100 ºF –
1200 ºF
1300 ºF –
1400 ºF
5A
Material Thickness
Up to 0.5 in. – > 2 in. – 5 in.
Over 5 in.
0.5 in.
2 in.
30 min. 1 hr/in.
2 hr plus 15
5 hr. plus 15
min. each
min. each
additional in.
additional in.
30 min. 1 hr/in.
1 hr/in.
5 hr. plus 15
min each
min.
additional in.
1 hr/in. (15 min.
2 hr. plus 15 min. each
minimum)
additional in.
1 hr/in. (15 min.
2 hr. plus 15 min. each
minimum)
additional in.
3-136
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX –
Preheat and PWHT Procedure Variables
Paragraph
Brief of Variables
.1
QW-406
Preheat
.2
φ Preheat Maintenance
.3
Increase > 100ºF (IP)
X
X
.7
X
.1
φ PWHT
X
.2
φ PWHT (T & T Range)
.8
T Limits
φ PWHT, PWHT Cycles, or
Separate PWHT Time or
Temperature
Nonessential
X
φ > 10% Amperage,
Number of Cycles, etc
.4
QW-407
PWHT
Decrease > 100ºF
Essential
Supplementary
Essential
X
X
X
3-137
Module 3 – Welding Metallurgy
Preheat and Post Weld Heat Treatment
Typical ASME Section IX Requirements
ƒ For SMAW process
z
Preheat variables
Š Decrease by more than 100ºF requires requalification
z
Interpass variables
Š Increase by more than 100ºF requires requalification if toughness is a
requirement
z
PWHT variables
Š Change in PWHT temperature schedules requires requalification
z
PWHT above upper transformation temperature, PWHT below lower
transformation temperature, etc.
Š Change in PWHT time and temperature ranges requires requalification if
toughness is a requirement
Š For specific ferrous materials (e.g., P-No. 7, 8 and 49), a change in
material thickness greater than 1.1X the thickness of the material qualified
requires requalification
3-138
Module 3 – Welding Metallurgy
Temper Bead Welding
Temper Bead Welding – Background
ƒ Temper bead welding uses the heat from welding of
subsequent beads to temper HAZ of previous deposited
passes
z
Tempering reduces HAZ
hardness
ƒ Temper bead welding is
mostt commonly
l used
d ffor
repair applications as an
alternative to repairs
using PWHT
z
Temper bead welding is
essentially a local PWHT
3-139
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
ƒ NB-4622.9, Temper Bead Weld Repair
z
z
z
Limited to P-No. 1 (C. Steel) and P-No.3 (0.5 Mo Steel) materials
using A-No. 1, 2, 10 and 11 filler metals
Repair shall be no more than 100 in.2 in area and no greater than 1/3
material thickness
Qualified in accordance with ASME IX with additional requirements
Š Use SMAW welding with low-hydrogen
low hydrogen electrodes and low-hydrogen
low hydrogen
welding practice
Š Preheat temperature shall be a minimum of 350ºF
Š Interpass temperature shall be a maximum of 450ºF
Š The weld are shall be maintained at a temperature of 450 – 550ºF after
welding for 2 hours for P-No. 1 materials and 4 hours for P-No. 3
materials
Š Specific weld bead locations specified and electrode diameter specified
per layer
z
Inspection requirements prior to welding, during welding and after the
welding is complete
3-140
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
3-141
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
3-142
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
3-143
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
ƒ NB-4622.9(f), Welding Procedure Qualification Test Plate
z
z
z
z
Qualification plate shall be the same P-No as the material in the field
including same PWHT conditions
Depth of cavity shall be at least half the depth of the actual repair but
not less than 1 in.
Test plate assembly shall be at least twice the depth of the cavity
The test assembly around the groove shall be at least the thickness of
the test assembly but not less than 6 in.
3-144
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section III Division 1 – NB –
Temper Bead Welding
3-145
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX –
Temper Bead Welding Requirements
ƒ Temper bead weld procedure qualification is more restrictive
than typical welding procedures
z
Additional variables need to be addressed in addition to the weld
process variables
ƒ QW-290, Temper Bead Welding
z
z
QW-290.1, Basic Qualification and Upgrading Existing WPS
QW-290.2, Welding Process Restrictions
Š SMAW, GTAW, SAW, GMAW (including FCAW) and PAW is permitted
z
z
QW-290.3, Variables for Temper Bead Welding Qualification
QW-290.5, Test Coupon Preparation and Testing
Š Includes hardness testing requirements
Š Refers to the code of construction for additional testing
3-146
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX –
Preheat and PWHT Procedure Variables
Paragraph
QW-402
Joints
QW-403
Base
Materials
QW-404
Filler Metals
QW-406
Preheat
Brief of Variables
Hardness
Essential
Impact Test
Essential
.23
+ Fluid Backing
.24
+ Fluid Backing
X
.25
φ P-No. or Group No.
X
.26
> Carbon Equivalent
X
.27
27
>T
X
Nonessential
X
.51
Storage
X
.52
Diffusible Hydrogen
X
.8
> Interpass Temperature
.9
< Preheat Maintenance
.10
Preheat Soak Time
X
.11
Postweld Bake Out
X
X
X
3-147
Module 3 – Welding Metallurgy
ASME Section IX Requirements
ASME Section IX –
Preheat and PWHT Procedure Variables
Paragraph
Brief of Variables
Hardness
Essential
Impact Test
Essential
QW-408
Gas
.24
Gas Moisture
QW-409
Gas
.29
φ Heat Input Ratio
X
X
.10
10
φ Single to Multiply
Electrodes
X
X
.58
- Surface Temper Bead
X
X
.59
Φ Type of Welding
X
X
.60
+ Thermal Preparation
X
X
X
X
QW-410
Technique
.61
Surface Bead Placement
.62
Surface Bead Removal
Method
.63
Bead Overlap
.65
± Grinding
Nonessential
X
X
X
X
X
X
3-148
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section IX – Temper Bead Welding
3-149
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section IX – Temper Bead Welding
3-150
Module 3 – Welding Metallurgy
Temper Bead Welding
ASME Section IX – Temper Bead Welding
3-151
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