Hydrogen-induced γ → ɛ transformation and the role of ɛ-martensite in hydrogen embrittlement of austenitic steels

The fraction of hydrogen-induced ɛH martensite and mechanical properties of hydrogen-charged austenitic steels were studied as a function of their chemical composition. It is shown that alloying elements affect the intensity of γ → ɛH transformation due to their influence on stacking fault energy. A decisive role of dislocation splitting in the ɛH formation is also confirmed by results obtained on differently oriented single crystals. Due to hydrogen-caused γ → ɛ transformation, the hydrogen charging changes the relation between the “soft” and “hard” crystallographic orientations of single crystals. It is obtained that, at variance with the generally accepted “pseudo-hydride” concept of hydrogen embrittlement, the hydrogen-induced ɛH martensite increases resistance of austenitic steels to hydrogen-caused brittleness.