Kyung-Keun Um

Effect of deformation induced transformation of ɛ-martensite on ductility enhancement in a Fe-12 Mn steel at cryogenic temperatures

Metastable ɛ-martensite (ɛ-Ms) formed during a prior heat treatment of Fe-12Mn steel has been reported to transform into α-Ms during subsequent inelastic deformation. This deformation induced phase transformation (DIPT) from ɛ-Ms to α-Ms has been investigated in the present study within the framework of kinetics relation proposed based upon an internal variable theory of inelastic deformation. The ɛ-Ms phase was found to become more stable at lower temperatures to provide more prolonged DIPT from ɛ-Ms to α-Ms during an inelastic deformation at cryogenic temperatures, contrary to the case of austenite phase in various transformation induced plasticity steels being more stable at higher temperatures. This reversed stability-temperature relationship in Fe-12Mn steel appeared to provide a significant ductility enhancement at lower temperatures as well as significant strengthening effect.