Tensile behaviour of type 304 austenitic stainless steels in hydrogen atmosphere at low temperatures

The tensile behaviour of solution annealed type 304L, solution annealed typ e 304, and solution annealed and sensitised type 304 stainless steels was i nvestigated in hydrogen and helium under a pressure of 1.1 MPa over the tem perature range 300-80 K at strain rates ranging from 4.2 x 10(-5) to 4.2 x 10(-2) s(-1). For 304L steel, hydrogen environment embrittlement (HEE) incr eased with decreasing strain rate. For 304L and 304 steels, HEE increased w ith decreasing temperature, reached a maximum, and then decreased with furt her decrease in temperature: the decrease was particularly rapid near the m inimum temperature for HEE, Sensitisation enhanced the HEE of 304 steel. Ab ove the maximum HEE temperature, the HEE behaviour was similar to the hydro gen embrittlement behaviour of materials in previous studies, but near the minimum temperature for HEE it was different. Three types of hydrogen induc ed brittle fracture were observed as a result of HEE: transgranular fractur e along strain induced martensite laths and twin boundary fracture on the f racture surfaces of solution annealed 304L and 304 steels, and grain bounda ry fracture on the sensitised 304 steel. It was found that from room temper ature to the maximum HEE temperature, the HEE of the materials depended on the transformation of strain induced martensite and below the maximum HEE t emperature it depended on the diffusion of hydrogen.