Micro-mechanical characterisation of hydrogen embrittlement in nano-twinned metastable austenitic stainless steel

Abstract

Micro-tensile tests were performed on single variants of nano-twinned 304 stainless steel with hard and soft orientations to determine the effect of nano-twins on hydrogen embrittlement in the metastable austenitic steel. Nano-twins were introduced into the 304 steel by deformation above the martensite-start temperature. The introduction of nano-twins increased the yield stress to 647 MPa for the hard-oriented crystals and 540 MPa for the soft-oriented crystals. For the soft-oriented crystals, the hydrogen charge induced quasi-cleavage although it did not change the uniform strain. For the hard-oriented crystals, the introduction of nano-twins retarded hydrogen-induced twin boundary separation. The relationship between the reduction of area and ultimate tensile strength revealed that the degree of strengthening and mitigation of hydrogen-induced ductility loss depended on the orientation of the nano-twins. These suggest that controlling the orientation and distribution of nano-twins allows for simultaneous strengthening and mitigation of hydrogen-induced ductility loss in metastable austenitic steel.