The formation of austenite annealing twins from the ferrite phase during aging in an Fe–Mn–Al alloy

The alloy with a composition of Fe–23.0wt.%Mn–7.4wt.%Al–0.03wt.%C has a small amount of austenite distributed discontinuously along the grain boundaries of the ferrite phase after the alloy being water-quenched from 1050 °C. During aging the as-quenched alloy at higher temperatures, the austenite phase precipitated within the ferrite matrix. The precipitation of the austenite phase within the ferrite matrix prefers the form of Widmanstätten side-plates. The orientation relationships between the austenite Widmanstätten side-plate and the ferrite matrix are (1 1̄ 1)FCC//(1 0 1)BCC and [1 0 1̄]FCC//[1 1 1̄]BCC which correspond to the Kurdjumov-Sachs (K-S) orientation relationships. The formation of austenite annealing twins from the ferrite phase at the initial stage of the nucleation during aging was observed for the first time in the Fe–Mn–Al alloys. It is interesting to note that both twin grains grow within the ferrite matrix, and keep both the K-S orientation relationships with the parent ferrite phase and the twinning orientation relationships between them, simultaneously.