Microstructure and hydrogen embrittlement of Q690 bainitic steel welded using electron beam

Abstract

In this study, Q690 bainitic steel was welded through vacuum electron beam welding under currents of 350 and 500 mA, resulting in samples with different microstructures and fusion and heat-affected zones.Furthermore, H 2 S immersion tests were performed to determine the susceptibility of the welded microstructure to hydrogen embrittlement. The results indicated fracture occurrence in the coarse-grain heat-affected zone (CGHAZ) and the fusion zone of the samples welded under currents of 350 and 500 mA, respectively. Under the 350-mA welding current, fracture occurred in the CGHAZ because of the high dislocation density in the bainitic ferrite plates and the low amount of retained austenite in the CGHAZ. Under the 500-mA current, hydrogen embrittlement and fracture occurred because of the high weldinginduced heat input that led to coarse precipitation and micro-void coalescence in the upper bainite of the fusion zone.