Transformation and Twinning-Induced Plasticity Effect in a Novel Heterogeneous Microstructural Medium-Mn Steel Processed by ART Annealing

A novel medium-Mn steel with 9.7 wt.% Mn content was developed through warm-rolling, cold-rolling and austenite-reverted transformation (ART) annealing processes, which presented an excellent combination of mechanical properties (the product of strength and ductility being >= 60 GPa.%). The tensile behavior and microstructure evolution of the novel medium-Mn steel with different ART processes were studied in detail. The steel inherited the banded microstructure produced by warm rolling when annealed at 600 degrees C. Heterogeneous microstructures composed of fine recrystallized equiaxed dual-phase grains and coarse non-recrystallization austenite grains were obtained after ART annealing at 700 degrees C and 750 degrees C. Moreover, the heterogeneous microstructure resulted in a higher strain-hardening rate than the banded microstructure. In addition, the different morphology distributions of austenite grains gave rise to austenite mechanical stability, thus triggering the multistage transformation and twinning-induced plasticity (TRIP and TWIP) effects during tensile deformation. Multiple strengthening and ductility-enhancing mechanisms including the TRIP effect, TWIP effect and dislocation strengthening contribute to the combination of ultrahigh strength and uncompromised ductility.

Automated summary

A novel medium-Mn steel with excellent mechanical properties and microstructure evolution was successfully developed through specific processes.