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

This investigation focused on the welding of Q690 bainitic steel using vacuum electron beam welding with currents of 350 and 500 mA, yielding samples with diverse microstructures and distinct fusion and heat-affected zones. Additionally, H₂S immersion tests were conducted to evaluate the susceptibility of the welded microstructure to hydrogen embrittlement. The results indicated different fracture sites in the samples welded under currents of 350 and 500 mA. Under the 350-mA welding current, fracture occurred in the coarse-grain heat-affected zone (CGHAZ) because of the high dislocation density in the bainitic ferrite plates and the low concentration of retained austenite in the CGHAZ. Under the 500-mA current, hydrogen embrittlement and fracture occurred in the upper bainite of the fusion zone because of the high welding-induced heat input that led to coarse precipitation and micro-void coalescence.