Toughness Improvement of the HAZ for Machine Structural Carbon and Low Alloy Steels (Report 2) : Effect of Cooling Time and Isothermal Heating Treatment on Medium and High Carbon Low Alloy Steels(Materials, Metallurgy & Weldability)

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Succeeding to Report 1, medium and high carbon low alloy steels have been treated in this paper. The toughness of the simulated HAZ using Gleeble 1500 was investigated for commercial steels which contain 0.21 to 0.48% C with 1.6N_i-0.5C_r-0.17M_o (SNCM) and 0.36 to 0.96% C with 1C_r-0.15M_o (SCM) or 1-1.5C_r (SC_r and SUJ2). Main conclusions obtained are as follows: (1) For Continuous Cooling Method an increase in Δt_C up to 300sec improved a little the ductility only in SNCM420 steel (C:0.21%) but did not improve obviously for the other higher carbon steels. (2) For Isothermal Heating Treatment at 473, 673 and 923K during weld heat cycle, ductilities were improved fairly for SNCM420 and SNCM439 and merely for SNCM447 at 673K, and merely for SCM435 and SC_r440 at 473 to 673K. However isothermal heating treatment at 923K is decreased the ductility for all steels, which is estimated due to tempered embrittlement.
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