Effect of external/internal hydrogen on SSRT properties of austenitic stainless steels and the role of martensitic transformation-induced plasticity

In order to investigate the effect of hydrogen on Slow Strain Rate Tensile (SSRT) test of austenitic stainless steels, SUS304, SUS316 and SUS316L, two types of SSRT tests were conducted. One is the external hydrogen SSRT test that was conducted in hydrogen gas at temperatures of T = −40 ~ 200℃ and pressures of p = 87 ~ 115 MPa using non-charged specimen. Another is the internal hydrogen SSRT test that was conducted in ambient air or 0.1 MPa nitrogen gas at T = −120 ~ 200°C using hydrogen-charged specimen exposed to hydrogen gas at p = 68 or 100 MPa. SSRT properties (i.e., relative reduction in area, RRA, and relative tensile strength, RTS) obtained in the external and internal hydrogen tests corresponded to each other. The results inferred that the internal hydrogen test can be a substitute for the external hydrogen test. Furthermore, the temperature dependence of RRA and RTS was evaluated based on the austenite stability of materials, which was represented by Md30 temperature, in association with martensitic transformation-induced plasticity. It was found that RRA and RTS of SUS304, SUS316 and SUS316L having different austenitic stabilities were successfully unified by using the novel parameter, T−Md30.