Enhanced the Strength–Toughness Synergy in a Microalloyed Medium Manganese Steel by Tailoring Austenite Stability

Medium manganese steels often suffer from a strength–ductility–toughness trade‐off, particularly regarding transverse impact performance, making it challenging to unify these properties in a low‐cost system without expensive alloying. In this study, we report a low‐cost 1.3 GPa grade V–Nb microalloyed steel achieving 29.7% elongation and 36.3 J/cm 2 transverse toughness at −50°C, realized through V–Nb synergistic microalloying and precise intercritical annealing. The optimized IA620 sample possesses a refined duplex microstructure containing 37.0 vol.% highly stable retained austenite (RA). Unlike unstable RA, this mechanically stable RA enables a sustained transformation‐induced plasticity effect, ensuring continuous work hardening. Furthermore, the stable RA triggers crack tip blunting, which, combined with crack deflection by high‐density high‐angle grain boundaries, simultaneously improves crack initiation and propagation energies. Consequently, the optimized steel achieves an outstanding synergy of properties compared to microstructures with unstable austenite.