Hydrogen diffusivity and tensile-ductility loss of solution-treated austenitic stainless steels with external and internal hydrogen

The effects of external and internal hydrogen on the slow-strain-rate tensile (SSRT) properties at room temperature were studied for ten types of solution-treated austenitic stainless steels containing a small amount of additive elements. The hydrogen diffusivity and solubility of the steels were measured with high-pressure hydrogen gas. The remarkable tensile-ductility loss observed in the SSRT tests was attributed to hydrogen-induced successive crack growth (HISCG) and was successfully quantified according to the nickel-equivalent content (Nieq), which represents the stability of the austenitic phase. The relative reduction in area (RRA) of the steels with a larger Nieq was influenced by the hydrogen distribution, whereas that of the steels with a smaller Nieq was not. This unique trend was interpreted with regard to the hydrogen distribution and fracture morphology (HISCG or microvoid coalescence).