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

Abstract

Metastable E >-martensite (E >-Ms) formed during a prior heat treatment of Fe-12Mn steel has been reported to transform into alpha-Ms during subsequent inelastic deformation. This deformation induced phase transformation (DIPT) from E >-Ms to alpha-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 E >-Ms phase was found to become more stable at lower temperatures to provide more prolonged DIPT from E >-Ms to alpha-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.