welding metallurgy 1
TRANSCRIPT
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Welding Technology
for Welding Engineers
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Fe-C Phase diagram
Steel is an alloy
of Iron and carbon
Iron C < 0.02%
Steel 0.02C 0.21%
Cast iron : 0.21% < C
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Phase transformation in cooling - I
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Phase transformation in cooling - II
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Diffusion of carbon plays an important role in
phase transformation
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Heattreatment of steels
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Weldability of steels
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Welding heat input
Energy Input (AWS D1.1), Arc Energy(EN standard)
EI(J/mm) = 60 (EI/v)
E(V), I(A), v(mm/min)
6025170/150 1700 (J/mm), 1.7(kJ/mm)
Heat Input
HI(J/mm) = hEIh: Arc thermal efficiency 1.0 for SAW
0.8 for SMAW, GMAW
0.6 for autogenus TIG
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Welding cooling rate, cooling time
CR(oC/s) at 540oC
t8/5(s):
Cooling time between800oC and 500oC
1.7kJ/mm on 20mm thick
7s in t8/5
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Cooling rate, Cooling time
Heat input
Plate thickness
Joint shape (Butt-joint, fillet-joint)
Preheat temperature
Prediction of cooling time, t8/5
JWES IT-Center
(http://www-it.jwes.or.jp/index_e.jsp)
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Microstructure of HAZ
Normalizing heat treatment
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Cooling curve (log-scale)
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HAZ maximum hardness
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Prediction of HAZ hardness
HAZ hardness
Welding conditions
Heat input
Plate thickness
Preheat temperature
t8/5
Chemical composition of steel
C
Carbon Equivalent
JWES IT-Center
(http://www-it.jwes.or.jp/index_e.jsp)
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Carbon equivalent
CEIIW= C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5
CEWES= C + Si/24 + Mn/6 + Ni/40 + Cr/5 + Mo/4 + V/14
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Weld cracking
Hot cracking (>1200oC)
Solidification crackingLiquation cracking
Cold cracking (
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Hot cracking
Solidification crack Liquation crack
Stainless steel, Al
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Weld metal cracking
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Segregation of impurities during solidification
Phase diagram Residual liquid phase
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Direction of solidification growthH/W
Welding velocity
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Cold cracks
Root crack (HAZ) Toe crack (HAZ) Transverse crack(Weld metal)
Under-bead crack(HAZ)
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Generation and diffusion of hydrogen
Generation of hydrogen Hydrogen diffusion in weld
Mineral water in flux, Moisture in flux
Moisture in atmosphere,
Rust, oil, grease in groove
Arc
H (hydrogen)
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Effect of preheat on HAZ hydrogen
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Cause of hydrogen-assisted cold cracking
Cold cracking
Diffusible hydrogen
Weld metal hydrogen
Preheat temperature
Hardness (HAZ, Weld metal)
Steel chemical composition
t8/5 HI, thickness
Tensile residual stressYield strength of weld metal
Notch concentration factor
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Determination of necessary preheat temperature
AWS D1.1 Annex IHardness control method (CEIIW) C>0.11%
Hydrogen control method (Pcm) C
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Flux type of covered electrode
Basic type CaCO3 CaO + CO2
lime
Decrease of partial pressure of H
High basicity Low oxygen in weld metal
Low hydrogen