Effect of strain-induced martensite on hydrogen environment embrittlement of sensitized austenitic stainless steels at low temperatures

Abstract Hydrogen environment embrittlement (HEE) of the austenitic stainless steels of types 304, 316 and 310S with the solution-annealed, sensitized and desensitized heat treatments was investigated in hydrogen and helium of 1 MPa in the temperature range from 295 to 80 K. The effect of the strain-induced martensite, distinguished from that of the carbides, both existing along the grain boundaries in the sensitized materials, on HEE was examined. Metastable austenitic stainless steels of types 304 and 316 showed considerable HEE, but stable austenitic stainless steel of type 310S was not affected by the hydrogen environment. HEE of types 304 and 316 stainless steels depended on the testing temperature, and the maximum HEE occurred at around 220 K independent of the type of heat treatment. The susceptibility of the materials to HEE was enhanced by the sensitization, that caused intergranular fracture, and was recovered upon a transition from the intergranular fracture to the transgranular fracture due to desensitization. The strain-induced martensite was observed together with the carbides, both along the grain boundaries of the sensitized materials. As a result of desensitization, the formation of martensite along the grain boundaries was inhibited. It was evident that HEE of the sensitized materials was not due to the carbides, but to the strain-induced α ′ martensite along the grain boundaries.