Martensitic transformation fcc(γ)→hcp(ε)

Criteria of the thermoelastic martensitic transformation are suggested, on the basis of which the martensitic transformation fcc(γ)→hcp(ε) in Fe−Mn−Si based alloys is classified as a semi-thermoelastic transformation. In contrast with the martensitic transformation fcc(γ)→bct(bcc)α′ in iron-based alloys, the thermoelastic transformation in Cu-based alloys and the t→m transformation in ceramics containing ZrO2, in γ→ε of Fe−Mn−Si, the strengthening and grain size of the parent phase will not markedly affect theMs and the internal friction peak indicating the martensitic transformation does not correspond to a significant lowering of the elastic modulus, implying that the nucleation of ε-martensite may occur directly through the stacking fault and may not strongly depend on soft mode. A comparison between the thermal and stress induced ε martensites is made and a brief discussion is given.