Hydride Phases in Austenitic Stainless Steels

Abstract

Electrolytic charging of austenitic stainless steels with hydrogen induces formation of two distinct alloy hydride phases, both being unstable under normal atmospheric conditions. One of the new phases denoted Hγ, has the same Bravais lattice as austenite (fcc), whereas another, denoted Hϵ, exhibits an hcp structure. Compared with hydrogen-free austenite and ϵ-martensite, respectively, the lattice constants of hydride phases are larger by about 5%. During charging of austenitic stainless steels with hydrogen evolved electrolyticaily from promoter containing acid solutions, these hydrides form a hard and brittle surface layer, several μm thick with numerous microcracks, and it is probable that these hydride phases play an important role during stress corrosion cracking (SCC) of austenitic stainless steels.