Microstructure, deformation mechanisms and influence of hydrogen on tensile properties of the Co based super alloy DIN 2.4711/UNS N30003

The Co-based alloy 2.4711 investigated in this study consists of an austenitic martix with ε-martensite from both strain hardening and aging. Upon deformation, the microstructure shows strain-induced γ→ε transformation. Mechanical twinning could not be verified in this study using EBSD. Tensile testing in hydrogen gas and with H-precharged specimens revealed negligible embrittlement for the specimens tested in H2 gas, whereas severe embrittlement was found for the H-precharged specimen. This was interpreted and explained by hydrogen transport during the two test configurations. It appears that the ε-martensite in alloy 2.4711, unlike strain-induced martensite in type 304 austenitic stainless steels, does not enhance hydrogen ingress over long distances during tensile testing in gaseous hydrogen. Limiting hydrogen transport during testing in gaseous hydrogen precludes observation of intrinsic hydrogen effects, while saturation of hydrogen by H-precharging illuminates intrinsic hydrogen sensitivity.