Department of Mechanical Engineering
Hauz Khas, New Delhi-110016, India
Welding and Allied Processes
Course Number: MCL135
Welding and Allied Processes
Course Coordinator:
Dr. Abhishek Das
Assistant Professor
Department of Mechanical Engineering
Indian Institute of Technology Delhi
Hauz Khas –110 016
Welding and Allied Processes
Course Number: MCL135
Course Title
Welding and Allied Processes
Course Number
MCL 135
Lecture Credit
Three
Net Credit Model
Three
Course Faculty
Dr. Abhishek Das
Semester
Semester I (2023-24)
Date of Commencement
25/07/2023 (Tuesday)
Slot
F- slot (T-Th-F 11:00-12:00)
Room
Course TAs:
LH 510 (Lecture Hall Complex)
• Shitanshu Arya (Shitanshu.Arya@mech.iitd.ac.in)
• Indranil Manna (mez228336@mech.iitd.ac.in)
• Rukaiya Azma (mez228446@mech.iitd.ac.in)
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Evaluation Pattern
Attributes
Weightage
Quiz/Assignment
15 %
Seminar/Viva/Project
15 %
Minor Test
30 %
Major Test
40 %
Audit marks
40
Reference Books
•
Fundamentals of Modern Manufacturing (Materials, Processes, and Systems); 4th Edition; Mikell P Groover; John Wiley & Sons, Inc.
•
Manufacturing Engineering and Technology; 7th Edition; Serope Kalpakjian and Steven R. Schmid; Pearson Education
•
Manufacturing Science; 2nd Edition; Amitabha Ghosh and Asok Kumar Mallik; East-West Press Pvt. Ltd.
•
Callister’s Materials Science and Engineering; 2nd Edition; Adapted by R Balasubramaniam; Wiley India Pvt. Ltd.
•
Degarmo’s Materials and Processes in Manufacturing; 11th Edition; J T Black and R A Kosher; Wiley Publishers
•
Mechanical Metallurgy, 3rd Edition; George E. Dieter; Tata McGraw-Hill Edition
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Course Content - Welding and Allied Processes
• Overview of joining processes
• Importance of joining
• Types of joining
✓ Welding
✓ Soldering and brazing
✓ Adhesive bonding
✓ Mechanical fastening
• Welding processes
• Fusion welding processes
•
•
•
•
Various arc welding processes
Resistance welding
Gas welding
Various high-energy beam welding processes
• Solid-state welding processes
• Allied processes
• Metal joining/depositing processes
•
•
•
•
•
Soldering
Brazing
Adhesive bonding
Surfacing
Metal spraying
• Diffusion and cold welding
• Friction welding
• Ultrasonic welding
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Introduction to Manufacturing Process
• Production System: Produces useful product and services
• Production: a process of transformation of the input elements to output with the increased utility of goods
or services
• Manufacturing: the application of physical and chemical processes to alter the geometry, properties,
and/or appearance of a given starting material to make parts or products; manufacturing also includes
assembling multiple parts to make products.
Two ways to define
manufacturing:
1. Technical process
2. Economic process
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Introduction to Manufacturing Processes
Manufacturing as an input-output systems
Objective
Inputs
Technological
Transformation
Outputs
Feedback
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Introduction to Manufacturing Processes
Manufacturing
Processes (principal types)
Process-type
Fabrication-type
Assembly-type
A continuous flow of
materials through a
series of process steps
Manufacturing of
parts/components by a
series of operations
Multiple parts
/components are put
together
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Introduction to Manufacturing Processes
Manufacturing Processes
(Broad classification)
Constant Mass
Processes
Metal Removing
Processes
Casting
Machining
Forming
Finishing
Powder
metallurgy
Nontraditional
machining
Material Addition
Processes
Welding and
allied processes
Mechanical
fastening
Heat
treatment
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Introduction to Manufacturing Processes
Selection of the manufacturing process
• Cost
• Volume
• Cycle time
• Base material properties
• Geometric limitations
• Functional requirements
• Surface finish
• Tolerance
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Welding and Allied Processes
Course Number: MCL135
Evaluation Pattern
Attributes
Weightage
Quiz/Assignment
15 %
Seminar/Viva/Project
15 %
Minor Test
30 %
Major Test
40 %
Audit marks
40
Minimum 75 % attendance; otherwise, the final grade will be lowered by one. In case of ‘D and E’ grades, it
will be lowered down to ‘F’. Students with less than 50% attendance will be directly awarded ‘F’ grade.
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Overview of Joining Processes
• An assembly process where two or more components are joined to
obtain desired part/configuration
• For example, a typical automotive body assembly consists of 200 - 250 sheet
metal parts assembled at 60 -100 assembly stations
• On the Eiffel Tower, 2.5 million rivets hold together 12,000 metallic pieces
• Joining is inclusive of processes such as welding, brazing, soldering,
adhesive bonding, and mechanical fastening
✓Welding+ brazing + soldering → two or more parts are fused together by
means of heat, pressure or both forming a join as the parts cool
✓Adhesive bonding → by employing synthetic glue such as epoxy resins
✓Mechanical fastening → nut and bolt, screws and rivets
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Why Joining is Critical ?
1988 – BOEING 737 - Lap joint failure
✓ A Boeing 747 is made up of six million parts
✓ From rivets and bolts, to seats and engines, an
A380 is made up of about four million
individual parts
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Why Joining is Critical ?
Resistance spot
welding (Al-Al)
Four materials—
aluminium, steel,
magnesium and
carbon fiberreinforced polymer
(CFRP)
MIG welding
(Al-Al)
Flow drill
screw
Self-piercing riveting
MIG welding
(steel-steel)
Laser beam
welding (Steel-steel)
Grip punch riveting
https://www.greencarcongress.com/2017/04/20170
406-asf.html
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Classification of Joining Processes
Type of bonding mechanism
i.
Mechanical bonding (strength is less than the combined strength of parent material)
✓ Semi-permanent – Rivets, Stitches, Staples, Shrink-fits (in case of rivets, the joint can be separated by destroying
the rivet without harming the parent materials)
✓ Temporary - nut & bolt assembly and screws (can be easily disassembled as necessary)
ii.
Atomic bonding (Type of assembly – Permanent)
✓ Solid state - may be carried out at room temperature or elevated temperature without melting the joining surfaces
✓ Liquid state - also called Fusion welding - the joining surfaces of the parent material melted and fused upon
cooling. Filler material can also be used.
✓ Solid / liquid state - The parent material is not melted, but a molten filler material is used to form the joint.
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Classification of Joining Processes
• Solid-State
i.
ii.
iii.
iv.
Cold welding - ultrasonic welding, pressure welding
Friction welding
Diffusion welding
Hot forge welding
• Liquid-State (Fusion)
i.
ii.
Electric – arc welding, resistance welding, laser beam welding, electron beam welding
etc.
Chemical – gas welding, thermit welding
• Solid/Liquid-State
i. Brazing
ii. Soldering
iii. Adhesive bonding
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Selection of Joining Processes
• Three types of joining methods (i) Welding+ brazing + soldering, (ii) adhesive joining, and (iii)
mechanical fastening are commonly used for manufacturing a variety of engineering product/component
• The following aspects are considered while selecting the type of joints for an application:
✓ type of joint required for an application is temporary or permanent
✓ Material stack-up combination – similar or dissimilar
✓ Physical, chemical metallurgical properties of materials
✓ Joint service life is subjected to temperature, corrosion, environment, and reliability
✓ type and nature of loading conditions (static and dynamic loading under tension, shear, compression,
bending etc.)
✓ cost effectiveness influencing the selection of joint
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Overview of Welding
• Welding is a joining process in which two or more parts are coalesced at their contacting surfaces by a
suitable application of heat and/or pressure (joining of materials as AWS)
• In some welding processes, a filler material is added to facilitate coalescence
• The assemblage of parts that are produced by welding is called a weldment
• As per AWS, joining of materials where metallurgical continuity and coalescence of materials are observed
Advantages of welding
Limitations of welding
• provides a permanent joint
• manual and expensive in terms of labour cost
• welded joint strength can be more than parent
metal
• involve high energy sources and dangerous
/hazardous
• economical in terms of material usage and
fabrication cost
• welding joint defects substantially reduce strength
• can be accomplished in the field as well
• it does not allow convenient disassembly
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Applications of welding
• Industrial applications:
✓ Construction industry - steel building structures, large structures
✓ Oil & Gas – pipes, tankers, offshore structures, dockyards, loading and unloading cranes
✓ Nuclear Industry - nuclear reactor, joining of pipes
✓ Electronic industry – welding limited but brazing and soldering are widely use
✓ Electrical Industry - electrical transmission towers, distribution system equipment, turbine blades and
cooling fins
✓ Surface transport –
• Railway - fabrication of coaches and wagons, repair of a wheel, laying of new railway tracks,
repair of cracked/damaged tracks
• Automotive – body-in-white, closure panels (doors, bonnets/hoods, skin panels) fuels tanks
✓ Ship Industry – ship and submarines various structures
✓ Aerospace Industry - aircraft structure, joining of skin panel to body
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Classification of Welding Processes
Source of energy
Arc and non-arc
with or without filler
material
Fusion and pressure
welding
• Chemical energy:
Gas welding,
explosive welding,
thermite welding
• Mechanical energy:
Friction welding,
ultrasonic welding
• Electrical energy:
Arc welding,
resistance welding
• Radiation energy:
Laser beam welding,
electron beam
welding
• Arc-based
processes:
SMAW, GTAW,
PAW, GMAW,
FCAW, SAW
• Non-arc-based
processes:
Resistance welding,
Gas welding, Thermit
welding, Ultrasonic
welding, Diffusion
welding, Explosive
welding
• Without filler
material: Laser beam
welding, Electron
beam welding,
Resistance welding,
Friction stir welding
• A filler may or may
not be used: Plasma
arc welding, Gas
tungsten arc welding,
Gas welding
• With filler: GMAW,
SAW, FCAW
• Pressure Welding:
Resistance welding
processes, Ultrasonic
welding, Diffusion
welding, Explosive
welding
• Fusion welding: Gas
welding, Arc
welding, Laser beam
welding, electron
beam welding
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Overview of Welding
Types of welding processes
Fusion welding
In this process heat is used to melt the base
materials. In some of the fusion welding
process, filler is added to the molten pool to
facilitate the process and provide bulk and
strength to the welded joint.
Solid-state welding
It refers to joining processes in which coalescence
results from application of pressure alone or a
combination of heat and pressure. If heat is used,
the temperature is below the melting point of the
metals being welded.
Based on the composition of the weld
a. Autogenous
b. Homogeneous
c. Heterogeneous
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Major Welding Processes
Fusion welding
(widely used)
Arc Welding (AW)
A group of welding
processes in which
heating is
accomplished by an
electric arc, also
most utilised filler
metal
Resistance
Welding (RW)
coalescence using
heat from electrical
resistance when
electric current
passes between the
faying surface of two
base materials held
together under
pressure
Oxyfuel gas
welding (OFW)
oxygen + acetylene
or other gas mixture
produces a hot
flame to melt base
material with filler
metal, if used
Laser Beam Welding
(LBW)
Electron Beam Welding
(EBW)
High energy focused
beam is used to melt
the materials and
fuse them
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Major Arc Welding Processes
https://www.youtube.c
om/watch?v=aq-rIpiYy0
YouTube Channel: TWI Ltd.
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Major Welding Processes
Solid-state welding
(widely used)
High heat input
Low heat input
Friction Welding
(FRW)
Ultrasonic Welding
(USW)
Diffusion Welding
(DFW)
Cold pressure
Welding
Forge welding
Explosion Welding
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Types of Joints
There are five basic types of joints
Butt joint
Corner
joint
Lap joint
T-joint
Edge joint
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Types of Welds/ Beads
Fillet weld
A fillet weld is used to fill in the edges of plates created by
corner, lap, and tee joints. Fillet welds can be single or double
(i.e., welded on one side or both) and can be continuous or
intermittent (i.e., welded along the entire length of the joint or
with unwelded spaces along the length).
Groove weld
Groove welds usually require that the edges of the
parts be shaped into a groove to facilitate weld
penetration. The grooved shapes include square,
bevel, V, U, and J, in single or double sides. Filler
metal is used to fill in the joint, usually by arc or
oxyfuel welding.
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Types of Welds/ Beads
Plug weld
Spot weld
Slot weld
Plug welds and slot welds are used for attaching flat
plates, using one or more holes or slots in the top part
and then filling with filler metal to fuse together the
two parts.
A spot weld is a small fused section between the surfaces of two sheets or plates.
Multiple spot welds are typically required to join the parts. It is most closely
associated with resistance welding.
A seam weld is similar to a spot weld except that it consists of a more or less
continuously fused section between the two sheets or plates.
Seam weld
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Types of Welds/ Beads
Flange
weld
A flange weld is made on the edges of two (or more) parts, usually sheet
metal or thin plate, at least one of the parts being flanged.
A surfacing weld is not used to join parts, but rather to deposit filler metal
onto the surface of a base part in one or more weld beads. The weld beads can
be made in a series of overlapping parallel passes, thereby covering large
areas of the base part. The purpose is to increase the thickness of the plate or
to provide a protective coating on the surface.
Surfacing
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Power Density in Fusion Welding
• Fusion welding processes can be looked into on the basis of range of energy density which they can apply
for melting the faying surfaces of base metal for joining.
• To accomplish the fusion, a source of high-density heat energy is supplied to the faying surfaces and the
resulting temperatures are sufficient to cause localised melting of the base metals
𝑃𝑜𝑤𝑒𝑟 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 =
𝑇ℎ𝑒 𝑟𝑎𝑡𝑒 𝑜𝑓 ℎ𝑒𝑎𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 𝑡𝑜 𝑡ℎ𝑒 𝑤𝑜𝑟𝑘𝑝𝑖𝑒𝑐𝑒
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎
, W/mm2
• The issue is more complicated than this equation, due to (i) moving power source, (ii) preheating, (iii) post
heating. Also, power density is not uniform, it is distributing as a function of area.
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Power Density in Fusion Welding
Heat required for fusion of faying surfaces of components being welded comes from different sources in
different fusion welding processes (gas, arc and high energy beam)
Approx. Power Density
10000
10000
9000
8000
W/mm2
Remarks:
6000
4000
2000
1000
10
50
0
Oxyfuel
Welding
Arc Welding
Resistance
Welding
Laser Beam
Welding
Electron Beam
Welding
• The time to melt the metal is inversely
proportional to the power density
• If the power density is too low, the heat is
conducted into the work as rapidly as it is added
to the surface, and melting/fusion does not happen.
• Minimum power density to melt most metals is
about 10 W/mm2
Major Fusion welding processes
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Power Density in Fusion Welding
• Effect of the power density of heat source on heat input required for welding
Remarks:
• Lower the power density of the heat source greater
will be the heat input needed for the fusion of
faying surface welding
• Neither too low nor too high heat input is
considered good for developing a sound weld joint
• Low heat input can lead to a lack of penetration
and poor fusion of faying surfaces during welding
• Excessive heat input may cause damage to the
base metal in terms of distortion, softening of HAZ
and reduced mechanical properties
*S Kou, 2003
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Power Density in Welding
• A heat source transfers 3000 W to the surface of a metal part. The heat impinges the surface in a circular area, with
intensities varying inside the circle. The distribution is as follows: 70% of the power is transferred within a circle of
diameter =5 mm, and 90% is transferred within a concentric circle of diameter =12 mm. What are the power densities
in (a) the 5 mm diameter inner circle, and (b) the 12 mm diameter ring that lies around the inner circle?
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Heat Source in Fusion Welding
• One of the most important factors governing a fusion welding process are the
characteristics of heat source
• A heat source, suitable for welding, should release the required amount of heat in a
sharply defined, isolated zone
• Most common sources are of heat include:
i.
ii.
iii.
iv.
The electric arc
The chemical flame
An electric resistance heating
An exothermic chemical reaction
heat loss
Work surface
heat used
for melting
heat transferred to work
heat dissipated
into work
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Heat Balance in Fusion Welding
• The quantity of heat required to melt a given volume of metal depends on
1.
2.
3.
The heat required to raise the temperature of the solid metal to its melting point, which depends on
metal’s volumetric specific heat
The melting point of the metal
Heat of fusion: The heat required to transform the metal from solid phase to liquid phase at the
melting point
Um= unit energy for melting (the quantity of heat required to melt a unit volume of metal starting from room
temperature, J/mm3)
Tm = melting point of the metal, K
K = constant 3.33 x 10-6 when Kelvin scale is used
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Heat Balance in Fusion Welding
Work surface
heat used
for melting
• Not all energy generated at the heat source
used for melting
heat loss
• Two heat transfer mechanism, both of which
heat transferred to work reduce the generated heat used for welding
process
𝐻𝑊
✓Heat transfer factor, f1
heat dissipated
into work
𝐴𝑐𝑡𝑢𝑎𝑙 ℎ𝑒𝑎𝑡 𝑟𝑒𝑐𝑒𝑖𝑣𝑒𝑑 𝑏𝑦 𝑡ℎ𝑒 𝑤𝑜𝑟𝑘
𝑓1 =
𝑇𝑜𝑡𝑎𝑙 ℎ𝑒𝑎𝑡 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑒𝑑 𝑎𝑡 𝑠𝑜𝑢𝑟𝑐𝑒
✓Melting factor, f2
Hw = net heat available for welding
H= total heat generated by the heat source, J
f2 = proportion of heat received at the
surface that can be used for melting
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Heat Balance in Fusion Welding
• The heat transfer factor, f1 is determined largely by the welding process and the capacity to
convert the power source (e.g., electrical energy) into usable heat at the work surface
• The melting factor f2 depends on the welding process, but it is also influenced by the thermal
properties of the metal, joint configuration, and work thickness
• In general, a high power density combined with a low conductivity work material results in a
high melting factor
• A balance equation between the energy input and energy needed for welding can be written as
Hw = net heat available for welding, J
Um= unit energy for melting, J/mm3
V = the volume of metal melted , mm3
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Heat Balance in Fusion Welding
• Most welding operations are rate processes, the weld bead is made at a certain travel velocity
• The rate balance can be written as
RHw = rate of heat energy delivered to the operation for welding, J/s
Um= unit energy for melting, J/mm3
RWV = volume rate of metal welded, mm3/s
• In the welding of a continuous bead, the volume rate of metal welded is the product of weld
cross-sectional area (𝐴𝑊 ) and travel velocity (𝑣)
RH = rate of input energy generated by the welding power source, W
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Heat Balance in Fusion Welding
The power source in a particular welding process generates 4000 W that can be transferred to the
work surface with a heat transfer factor = 0.7 . The metal to be welded is low-carbon steel, whose
melting temperature = 1760°K. The melting factor in the operation is 0.5. A continuous fillet weld is
to be made with a cross-sectional area = 20 mm2 . Determine the travel speed at which the welding
operation can be accomplished.
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Formation of a Fusion Welded Joint
Considering a typical butt joint configuration
(with filler wire added), the following crosssectional zones can be observed:
1)
Fusion Zone: consists of a mixture of filler metal,
if any, and base metal that was completely melted
and then solidified
2)
Weld interface: a narrow boundary between
fusion zone and heat affected zone
3)
Heat-affected zone (HAZ): this zone is affected
by the heat below the melting point, yet high
enough to cause microstructural changes in the
solid metal
4)
Unaffected base metal zone: no change in
comparison to the base material
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Typical Microstructure of a Fusion Welded Joint
Typical weld microstructure characteristics
Fusion Zone:
• It consists of a mixture of filler metal, if any, and
base metal that was completely melted and then
solidified
• A high degree of homogeneity is present among the
component metals that have been melted during
welding
• Solidification is similar to casting; mould is formed
by the unmelted edges/surface of the component
being welded
Columnar grains
in the fusion zone
Coarse grains in HAZ
near weld interface
Finer grains in HAZ
away from weld interface
Original cold-worked grains
• Epitaxial grain growth is observed
• The grains are roughly perpendicular to the weld
interface
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Typical Microstructure of a Fusion Welded Joint
Typical weld microstructure characteristics
Weld interface:
• A narrow boundary between fusion zone and
heat affected zone
• This zone consists of a thin band of base metal
that was partially melted during the welding
process but immediately solidified without
mixing with the metal in the fusion zone
• Chemical composition is generally same as that
of the base metal
Columnar grains
in the fusion zone
Coarse grains in HAZ
near weld interface
Finer grains in HAZ
away from weld interface
Original cold-worked grains
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Typical Microstructure of a Fusion Welded Joint
Typical weld microstructure characteristics
Heat-affected zone (HAZ):
• This zone is between weld interface and base
material
• This experience temperatures below melting
point, but sufficient to change the microstructure
and hence the mechanical properties
• The amount of metallurgical damage in the HAZ
depends on (i) heat input and peak temperature,
(ii) distance from FZ, (iii) cooling rate, (iv)
thermal properties of the metal, and (v) exposed
time to elevated temperature
Columnar grains
in the fusion zone
Coarse grains in HAZ
near weld interface
Finer grains in HAZ
away from weld interface
Original cold-worked grains
• The mechanical properties are such that most of
the failures occur in this region
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Typical Microstructure of a Fusion Welded Joint
Typical weld microstructure characteristics
Unaffected base metal zone:
• As the distance from the fusion zone increases,
the unaffected base metal zone is reached
• No metallurgical change in comparison to the
base material
• However, the base metal around the HAZ is
likely to be in a state of high residual stress as a
result of shrinkage in the fusion zone
Columnar grains
in the fusion zone
Coarse grains in HAZ
near weld interface
Finer grains in HAZ
away from weld interface
Original cold-worked grains
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