Analysis of martensitic transformation in 304 type stainless steels tensile tested in high pressure hydrogen atmosphere by means of XRD and magnetic induction

Tensile specimen of several 304 type stainless steels tested under pressurized hydrogen and helium atmospheres were investigated with the focus on the γ → α′ transformation as a function of Ni content. Martensite contents on the fracture surfaces increased with decreasing Ni content and were independent of the test atmosphere (He or H2) despite different macroscopic plastic deformations. This was attributed to similar plastic deformations at the crack tip which governs the γ → α′ transformation at the fracture surface. The severity of hydrogen environment embrittlement was quantified by RA measurements which is a measure of the maximum macroscopic plastic deformation. RA values in H2 decrease with decreasing Ni content and RA is almost exactly inverse proportional to the martensite content measured by Feritscope in the uniform elongation area. This implies that the influence of hydrogen of the steels investigated here is dominated by surface effects.