Determination of hydrogen compatibility for solution-treated austenitic stainless steels based on a newly proposed nickel-equivalent equation

• A new nickel-equivalent equation was proposed for materials selection.
• Eight types of solution-treated austenitic stainless steels were tested.
• The reduction in area was lower with higher strain-induced martensite contents.
• The strain-induced martensite content correlated well with the proposed equation.
• The reduction in area was successfully quantified by the proposed equation.

The nickel-equivalent equation for the materials selection of solution-treated austenitic stainless steels in present Japanese regulations does not consider nitrogen, which can improve resistance to hydrogen embrittlement. For the authorization of various austenitic stainless steels for use in high-pressure hydrogen gas and based on investigations of eight types of solution-treated austenitic stainless steels, this paper presented a newly proposed nickel-equivalent equation considering nitrogen. After tensile testing to the true strain ε of 0.3 in air at both room temperature (RT) and 228 K, the strain-induced martensite content VM was measured by a saturation magnetization technique; the VM correlated well with the proposed nickel-equivalent equation. For slow strain rate tensile (SSRT) testing in hydrogen gas at RT, the relative reduction in area (RRA) was consistently lower with increased VM for ε = 0.3 at 228 K. This suggests that the austenitic phase stability is crucial in determining the RRA of the present austenitic stainless steels and the RRA was successfully quantified by the proposed equation.