3. Results and Discussion
An optical micrograph (OM) is shown in Fig. 1(a), of the Fe–C–Mn alloy after solution heat treatment. Similar grains with annealing twins indicate that the steel is single phase at 1373 K. There are irregular thin plates distributed in the matrix grains. Fig. 1(b) shows the XRD analysis of alloy steel which received the same heat treatment as in Fig. 1(a). Some peaks, with Miller indices underlined, came from the FCC phase and the others from the HCP phase. We also performed a TEM study, not shown here, to investigate the constituent phases of the as-quenched steel. We found that the matrix is FCC and the irregular thin plates which formed during cooling are either HCP ε-martensite or FCC micro-twin [18]. ε-martensite is common in high Mn alloy steels [23] and [24].