Hydrogen embrittlement properties of several stainless steels

The hydrogen embrittlement (HE) characteristics of various stainless steels were investigated. In this study, as-received, heated (1100 °C, 15 h), and cold-rolled (30% strain) γ-austenite (AS), α-ferrite (FS), α′-martensite (MS), and γ–α duplex (DS) stainless steels were employed. For as-received stainless steels, severe HE occurred for DS and MS with static tensile loading, while no clear and weak HE was observed for AS and FS, respectively. This could be attributed to the different extent of hydrogen diffusivity in the stainless steel. A large amount of hydrogen penetrated to (i) lattice vacancy with low atomic density for body-centered cubic FS, DS, and MS, compared to that for face-centered cubic (AS); (ii) the phase boundary between γ-austenite and α-ferrite for DS; and (iii) the boundary between the Cr base precipitate and the martensite matrix for MS. HE also occurred strongly for heated-DS owing to the grain growth, i.e., a high hydrogen concentration in grain and phase boundaries. Although no clear HE was detected in as-received AS with static loading, HE occurred in cold-rolled AS, where hydrogen penetrated lattice vacancies and α′-martensite formed through strain-induced martensite. Owing to strain-induced martensite created during cyclic loading, HE was detected even for as-received AS, which is dissimilar to the result of the tensile test. Details of HE characteristics of the strainless steels were examined using the four stainless steels with different microstructures, diferent strain level and oxide layer. Moreover, those were investigated under different loading conditions, such as constant, static, and cyclic loading.