Abstract
The tensile behaviour of solution annealed type 304L, solution annealed type 304, and solution annealed and sensitised type 304 stainless steels was investigated in hydrogen and helium under a pressure of 1·1 MPa over the temperature range 300–80 K at strain rates ranging from 4·2×10-5 to 4·2×10-2 s-1. For 304L steel, hydrogen environment embrittlement (HEE) increased with decreasing strain rate. For 304L and 304 steels, HEE increased with decreasing temperature, reached a maximum, and then decreased with further decrease in temperature: the decrease was particularly rapid near the minimum temperature for HEE. Sensitisation enhanced the HEE of 304 steel. Above the maximum HEE temperature, the HEE behaviour was similar to the hydrogen embrittlement behaviour of materials in previous studies, but near the minimum temperature for HEE it was different. Three types of hydrogen induced brittle fracture were observed as a result of HEE: transgranular fracture along strain induced martensite laths and twin boundary fracture on the fracture surfaces of solution annealed 304L and 304 steels, and grain boundary fracture on the sensitised 304 steel. It was found that from room temperature to the maximum HEE temperature, the HEE of the materials depended on the transformation of strain induced martensite and below the maximum HEE temperature it depended on the diffusion of hydrogen.
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