Microstructural and mechanical aspects of tempered ICCGHAZ of SQV-2A low alloy steel weld

Abstract

Effect of simulated welding cycles consisting of austenitizing at 1623K/6s and cooling for Δt_8/5=6s (the 1^st cycle), reheating at 873-1123K/6s and cooling for Δt_8/5eff=6 or 40s (the 2^nd one), and annealing at 473-893K/6s and cooling for Δt_8/5eff=6s (the 3^rd one) on the evolution of microstructure and changes in absorbed energy (Charpy test at 293K) of SQV-2A low alloy steel was investigated. Light microscopy, TEM, electron diffraction, SEM, EDX, and measurement of hardness HV10 were used to characterize the microstructure of the steel including type of observed phases and morphology of fracture surfaces. The formation of M-A constituent and its internal evolution during 2^nd and 3^rd welding cycles (i.e. precipitation and growth of carbide particles) as well as the morphology of intragranular interlath M-A islands were found to be responsible for changes in absorbed energy. The role of M₃C and M₂C carbides in influencing the absorbed energy seems to be more significant than suggested earlier.