Abstract
The features and mechanisms of hydrogen embrittlement of metals that undergo hydride formation and martensitic transformation during service are reviewed. Metastable austenitic stainless steels, Nb and V as well as Ti and its alloys are the metals examined. The embrittlement of austenitic stainless steels is susceptible to the stability of austenite, and hydrogen promotes the martensitic transformation forming hydride as a precursor. However, martensite per se is not always the origin of the embrittlement, but.lattice defects associated with dislocation dynamics in the crack front is noted as a factor. In Nb and V, stress-induced hydride formation successively taking place at the crack front supplies a crack path with a reduced resistance for growth. In Ti, the primary role of hydrides is not always the case. In superelastic and shape memory Ni-Ti alloys, the embrittlement appears prominent in the martensitic transformation, and some dynamic process invoking lattice defects is suggested to play a role. In an appendix, the assessment of the susceptibility in terms of the critical hydrogen concentration is critically discussed, and some mechanical response to hydrogen is proposed as new criteria for the susceptibility of materials to hydrogen embrittlement.
