Motomichi Koyama, Zhipeng Yang, Wenwu Xu, Eiji Akiyama
In situ electron channeling contrast imaging was applied to investigate local deformation and microstructure evolution in an electrochemically hydrogen-pre-charged type 304 austenitic stainless steel. The imaging results revealed an acceleration of γ-ε-α' martensitic transformation on the surface by hydrogen; however, no cracking was observed immediately after the transformation. A plastic deformation over 10% induced stress concentration and localized plasticity near a grain boundary, which led to hydrogen-related intergranular cracking. A side of the grain boundary acting as the cracking site was composed of α' martensite; however, the other side neighboring an intergranular crack remained austenite. Interestingly, many intergranular cracks were terminated at the α'-martensite region, which indicated that the retained austenite played a significant role in hydrogen-related intergranular cracking. The retained austenite was suggested to result in a state of high hydrogen concentration at the prior austenite grain boundary. • In situ ECCI was applied to hydrogen embrittlement study. • Martensite cracking did not occur immediately after the transformation. • Plastic deformation over 10% induced localized plasticity near a grain boundary. • The locally deformed portion showed martensite and hydrogen-related intergranular cracking. • A side of the grain boundary acting as the cracking site was composed of α' martensite.