Brief introduction to various welding processes and co-relating them with welding metallurgy and comparing the heat affected zones in various welding processes

1. Seminar-31
Welding Metallurgy and Different Welding Processes
Guide
Dr. Jagannatha Nayak
Dept. of MME
Presented by
Harshan
14MT18
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2. Introduction
• Welding is a fabrication process that joins materials
• It is distinct from lower temperature metal-joining techniques such as brazing
and soldering.
• In addition to melting the base metal, a filler material is typically added
History
• Early examples of welding have been found in locations ranging from Ireland to
India, with some dating back to the Bronze Age.
• Naturally, these civilizations lacked the vast array of tools and machinery that
welders have access to now.
• The process they used is known as forge welding
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3. • Heating → Place together → Pounding
• Only relatively soft metals can be forge welded, and the process is very labour
intensive
• Forge welding was the only game in town until the 19th century.
• With the onset of the industrial revolution, however numerous discoveries
pushed welding forward fast.
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4. Heat affected zone (HAZ)
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5. Case 1: Structure of HAZ in 0.2% carbon steel
• These steels are easily welded and they do not form hard, brittle martensitic
phase in their HAZ while welding.
• HAZ can be further divided into 3 regions:
 Overheated region
 Refined or normalised region
 Transition region
Below this region structure of the base metal is not altered and is referred to as
Unaffected zone.
In the overheated region:
 Grains of austenite become very coarse
 The hardness and strength of the crystals of ferrite and pearlite that would
form on cooling are rather low
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6. In the refined or normalised region:
 The structure is transformed to austenite
 The resulting structure consists of fine-grained ferrite and pearlite with close
layers or lamellae of ferrite and cementite
 Fairly high hardness and strength
In the transition region:
 Initial structure will be ferrite and austenite at high temperature.
 On cooling the austenite → pearlite.
 The resulting structure shows fine grains of ferrite and pearlite
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7. Case 2: Structure of HAZ in 0.3% carbon steel
• In these steels the possibility of formation of martensite takes place.
Formation of martensite:
Martensite is a phase that forms from austenite on continuous cooling of steel
from Ms to Mf temperature
Properties of martensite:
 Hard and brittle
The hardness of martensite is related to carbon content
• Because of martensite underbead cracking takes place
• This cracking occurs only if the 3 following factors are obtained:
a) Martensite
b) Diffusion of Hydrogen
c) Restraint-induced stresses 7

8. Structure of HAZ
In the overhead region
 Coarse austenite grains are formed if cooling rate is high enough then they
can readily transform to martensite.
 High hardness
In the normalised or refined region
 Structure will be fine grained
 Moderate hardness
In the transition region
 Mixture of ferrite and austenite
 Small amount of martensite may form
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9. Gas welding
• Gas welding is a welding process that melts and joins metals by heating them
with a flame
• The most commonly used method is Oxyacetylene welding, due to its high
flame temperature.
• The flux may be used to deoxidize and cleanse the weld metal.
• The flux melts, solidifies and forms a slag skin on the resultant weld metal
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10. Two types of combustion takes place:
1) Primary 2) Secondary
Different types of flames:
 Carburising flame- Advantageous for welding high carbon steel or
carburising the surface of low carbon or mild steel.
oIt has a temperature of about 3149°C at the inner cone tips.
 Neutral flame- Used for welding steels, aluminium, copper and cast iron.
o The temperature at the inner cone tip is approximately 3232°C.
 Oxidising flame- Oxidising flame gives the highest temperature possible.
o Slightly oxidising flame is used for welding copper-based alloys, zinc based
alloys and cast irons.
oThe temperature of this flame is approximately 3482ºC
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11. Advantages:
It is easy to operate and dose not required high skill operator.
Equipment cost is low compare to other welding processes like MIG, TIG etc.
Equipment’s are more portable than other type of welding.
Disadvantages:
It provides low surface finish. This process needs a finishing operation after welding.
Gas welding have large heat affected zone which can cause change in mechanical
properties of parent material.
Higher safety issue due to naked flame of high temperature. Slow metal joining
process. 11

12. Metal inert gas welding( MIG )
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13. Advantages:
• Doesn’t require the degree of operator skill
• Continuous welding is possible
• Welding speed is high
• Deeper penetration
Limitations:
• The welding equipment is more costly and less portable
• It is difficult to weld in small corners
Summary:
• Electric arc process
• Consumable wire electrode
• Filler is added automatically
• Shielding gas ( Ar+CO2) from high pressure cylinders
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14. Tungsten inert gas welding (TIG )
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15. • The electrode materials are pure tungsten, tungsten with 1 to 2% thorium and
tungsten with 0.5% zirconium.
• In DC welding the connection can be DCSP or DCRP.
• The shape of the weld bead depends on connection.
• DCSP produces a narrow deep weld
Applications:
• Welding Al, stainless steel, Ti and other metals
• It is suitable for thicknesses <4mm; for large thicknesses W. speed is very slow
Summary:
• Electric arc process and non consumable electrode
• Ar and He as shielding gases
• Filler added separately as filler rod
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16. Laser welding(LW)
• Beam of light, coherent and strictly monochromatic.
• The intense power of the beam with a small cross sectional area enables
welding to be performed over small areas
Two types of lasers:
1) Ruby laser 2) CO2 laser
Applications:
• Microelectronic circuits
• Can weld metals such as gold, nickel and tantalum
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17. Plasma arc welding(PAW)
• The term ‘Plasma arc’ is used to describe processes which use constricted
electric arc
• PAW results in deep penetration
• Less sensitive to torch-to-workpiece distance
• Maximum temperatures vary in the range 10000-14000K.Near the electrode
tip, the temperature is 24000K
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18. Welding technique
Keyhole method - Gives uniform penetration
Melt-in technique - A grooved Cu bar is used to support the molten weld
pool and removes heat
• Depth/width is large(5 to 10).
• The weld bead has a shape of wine glass and this is called wine glass effect
Advantages:
• No contamination
• Greater depth/width ratio
• Key-hole effect ensures complete penetration
Limitations:
• Limited to metal thickness 25mm or less
• Welding torch and equipment can be expensive 18

19. • Restricted to flat and horizontal positions only
• Operator must be well protected from exposure of skin to these rays
Applications:
• For joining Stainless steels, nickel alloys, refractory metals and for special
applications particularly in aerospace industry
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20. Electron beam welding ( EBW)
• Electron beam employs a beam of high velocity electrons.
• KE→ TE
• Narrow HAZ
• The filament can be tungsten or tungsten + thoria or tantalum
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21. Applications:
• Welding titanium, zirconium, nickel, stainless steel and high alloy steels in the
aerospace, nuclear and automotive industries
• Because of high penetration a single pass welding is possible upto 100mm
thickness
• Small welds can be produced particularly for electronic components
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22. Similarities and differences
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23. Comparison of HAZ
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24. References
Welding technology by N.K Srinivasan
https://commons.wikimedia.org/w/index.php?title=File%3ARemote_Fibre_Las
er_Welding_WMG_Warwick.ogv
http://nptel.ac.in/courses/112101005/downloads/Module_4_Lecture_3_final.
pdf
http://ispatguru.com/heat-affected-zone-and-weld-metal-properties-in-
welding-of-steels/
http://weldguru.com/laser-welding/
http://www.pro-fusiononline.com/welding/plasma.htm
https://www.millerwelds.com/resources/article-library/tig-it-how-a-tig-welder-
works-and-when-to-tig-weld
https://www.youtube.com/watch?v=B-2nzWfJE-k
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25. Thank you
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