析出硬化型高Mnオーステナイト鋼の水素脆化挙動に及ぼすNi含有量および時効熱処理の影響

The effects of Ni concentration and dispersed conditions of vanadium carbide (VC) nano-particles on the hydrogen embrittlement (HE) behavior of precipitation-hardened high-Mn austenitic steels were investigated under the presence of thermally pre-charged hydrogen. Slow strain-rate tensile tests revealed that HE susceptibility decreased with an addition of Ni. VC precipitates functioned as the trapping sites for dissolved hydrogen, though its effect on resisting the HE was trivial. Hydrogen enhanced intergranular (IG) fracture wherein its area fraction was increased with the hardening by VC as well as with the escalation of internal hydrogen concentration. The IG fracture was the primary rationale for the hydrogen-induced loss of ductility. Possible mechanisms of the IG-related HE as well as future strategy for mitigating the mechanical degradation is discussed based on the fractographic observation and post-mortem microstructural analyses.