Effect of Cold Rolling on Stability of HCP and FCC Phases in Fe–Mn Alloys

抄録

The phase transformation behavior of an Fe–20%Mn alloy during a heating process after various cold-rolling reductions was investigated, and the phase stabilities of the γ and ε phases were discussed. The initial hot-rolled material was composed of an ε martensite matrix and a small amount of the γ austenite phase at room temperature. The deformation of the martensite alloy in the cold rolling was not homogeneous, and the microstructure of some regions was clearly adopted from that in the hot-rolled sample. Moreover, a residual γ phase was still detected even after 35% cold-rolling reduction. In the heating stage, a remarkable reverse transformation to the γ phase started at 200°C or higher, and its finishing temperature clearly increased with the rolling reduction ratio. However, the in situ X-ray diffraction and electron back scatter diffraction (EBSD) observations revealed that the reverse transformation had already started from the residual γ phase particles even at temperatures below 200°C. In addition, from the EBSD–image-quality map, the distribution of the dislocations was considered to remain in the γ phase even after the reverse transformation.