Effect of δ–ferrite and strain-induced martensite on hydrogen embrittlement of STS 308 L and STS 316 L all-weld metals

Abstract

The susceptibility of multipass flux-cored arc welds of STSs 308 L and 316 L to hydrogen embrittlement (HE) was investigated at various temperatures. Cracks predominantly initiated and propagated along the δ-ferrite in the interdendritic region at 25 °C. δ-ferrite served as preferred hydrogen trap sites, and the δ/γ boundary became the stress concentration site. At −100 °C, STSs 308 L and 316 L exhibited high susceptibility to HE owing to strain-induced martensite formation, providing additional hydrogen trap sites and dislocation accumulation. Despite strain-induced martensite actively transformed at −196 °C, the HE disappeared owing to the sluggish diffusion of hydrogen to stress-concentrated areas.