Evolution of Microstructure During the In Situ Heating of 42 Pct Cold-Rolled High Mn Steel

An Fe-17Mn-3Al-2Si-1Ni-0.06C wt pct high Mn steel was cold rolled to 42 pct thickness reduction, leading to a mixed microstructure of ε- and α′-martensite along with a trace amount of austenite (γ). The reverse transformation of ε- and α′-martensite to γ was tracked by in situ heating from room temperature up to 800 °C followed by 600 seconds holding in a transmission electron microscope. The transformation of ε- and α′-martensite to γ followed the Shoji–Nishiyama (S–N) and Kurdjumov–Sachs (K–S) orientation relationships, respectively. No changes in the grain shape or motion of any interfaces between ε-martensite/γ and α′-martensite/γ were observed during the reverse transformation process. The γ reverted from ε-martensite contained fine twins upon recovery, and a mechanism is proposed for the formation of these twins.