Ultra-Fine Heterogeneous Microstructure Enables High Strength-Ductility in a Cold-Rolled Medium Mn Steel

The objective of the present study is to develop heterogeneous microstructure in cold-rolled medium Mn steels (MMSs) annealing strategy. The cold-rolled Fe-4.7Mn-0.15C (wt%) steel is annealed twice at different temperatures to produce an ultra-fine heterogeneous microstructure with lath-shaped and granular-shaped retained austenite. Excellent mechanical behavior of significant strength enhancement with negligible ductility loss can be achieved. The high strength-ductility properties are attributed to the active transformation induced plasticity effect over a broad strain range owing to dispersive mechanical stabilities of the heterogeneous austenite. Furthermore, the typical yield point elongation phenomenon which is commonly observed in cold-rolled MMSs can be effectively reduced by this microstructural strategy.