Deformation mechanisms of a novel Mn-based 1 GPa TRIP/TWIP assisted lightweight steel with 63% ductility

The deformation mechanisms of a novel Mn-based transformation/twinning induced plasticity (TRIP/TWIP) lightweight steel (10.12Mn-0.31C-3.81Al-0.56Si, wt.%) was investigated through the as-termed Mn preservation-cold rolling-intercritical annealing (PR-IA) route. A recrystallized equiaxed microstructure with fine and ultrafine-bimodal grain size distribution was obtained after IA at 800 degrees C, which exhibited an excellent balance of high ultimate tensile strength (UTS = 1048 MPa) and total elongation (TE = 63%). The bimodal-size distribution of austenite grains gave rise to the differences in the austenite stability, thus triggering the multi-stage TRIP effects (positive TRIP, slow TRIP effect) and the TWIP-coordinated TRIP effect in the entire tensile deformation. Activation of multi-stage strengthening mechanisms improved the strain hardening ability of the present medium Mn lightweight steel while maintaining its high tensile ductility.

Automated summary

By utilizing the Mn preservation-cold rolling-intercritical annealing route, a novel Mn-based lightweight steel with bimodal grain size distribution was obtained, showing a good balance of high strength and high ductility. The bimodal distribution of austenite grains triggered multi-stage TRIP effects and TWIP-coordinated TRIP effects, improving strain hardening ability while maintaining high tensile ductility.