In-depth understanding in the effect of hydrogen on microstructural evolution, mechanical properties and fracture micro-mechanisms of advanced high-strength steels welded joints

The hydrogen embrittlement (HE) mechanism of QP980 steels laser welded joints with complex microstructures is unclear. The joint with hydrogen pre-charging fractured at the inter-critical heat affected zone (ICHAZ) in slow strain rate tensile test, and the relative loss of elongation amounted to 84.8 %. Hydrogen-induced microcracks mainly initiated inside martensite (∼ 60 %). Hydrogen-induced crack propagation paths of the joint were transgranular propagation of martensite and intergranular propagation of ferrite/martensite interface. The HE mechanism of the joint was the combination of the effects in hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE).