Welding Metallurgy 1

Welding Tech Welding echnolo nology gy for Welding Engineers

Fe-C Phase diagram

Steel is an alloy of Iron and carbon

Iron

C < 0.02%

Steel 0.02 C  0.21% Cast iron : 0.21% < C

Phase transformation in cooling - I

Phase transformation in cooling - II

Diffusion of carbon plays an important role in phase transformation

Heat treatment

of steels

Weldability of steels

Welding heat input Energy Input (AWS D1.1), Arc Energy(EN standard) EI(J/mm) = 60 · (E·I/v) E(V), I(A), v(mm/min) 60·25·170/150  1700 (J/mm), 1.7(kJ/mm) Heat Input HI(J/mm) = h EI h : Arc thermal efficiency 1.0 for SAW 0.8 for SMAW, GMAW 0.6 for autogenus TIG

Welding cooling rate, cooling time CR(oC/s) at 540oC t8/5(s): 

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Cooling time between 800oC and 500oC 1.7kJ/mm on 20mm thick 7s in t8/5

Cooling rate, Cooling time 

Heat input

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Plate thickness

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Joint shape (Butt-joint, fillet-joint) Preheat temperature Prediction of cooling time, t 8/5 JWES IT-Center (http://www-it.jwes.or.jp/index_e.jsp)

Microstructure of HAZ

Normalizing heat treatment

Cooling curve (log-scale)

CCT (Low-hardenability)

HAZ maximum hardness

Prediction of HAZ hardness  Welding conditions

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t8/5

Heat input Plate thickness Preheat temperature

HAZ hardness

 Chemical composition of steel C Carbon Equivalent

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JWES IT-Center (http://www-it.jwes.or.jp/index_e.jsp)

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

Weld cracking

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Hot cracking (>1200oC) Solidification cracking Liquation cracking

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Cold cracking (0.11% Hydrogen control method (Pcm) C