Effect of cold rolling on stability of HCP and FCC phases in Fe-Mn alloys

The phase transformation behavior during heating process after various cold-rolling reductions was investigated for Fe - 20% Mn alloy and the phase stabilities of γ and ϵ phases were discussed. The initial hot-rolled material was composed of ϵ martensite matrix and a small amount of γ austenite phase at room temperature. The deformation of the martensite alloy in cold rolling was not homogeneous and the microstructure in some regions was clearly inherited from that in the hot rolled sample. Moreover, the residual γ phase was still detected even after 35% cold rolling reduction. In the heating stage, the reverse transformation to the γ phase remarkably started at 200°C or higher and the reverse transformation finishing temperature obviously rose with rolling reduction ratio. However, it was confirmed by in-situ XRD and EBSD observation that the reverse transformation had already started from the residual γ phase particles even at temperatures below 200 °C. In addition, from the EBSD-IQ map, distribution of dislocations was considered to remain even in the γ phase after the reverse transformation.