Warm Deformation at the (α plus γ) Dual-Phase Region to Fabricate 2 GPa Ultrafine-Grained TRIP Steels

Transformation-Induced Plasticity (TRIP) steels have a range of applications in the vehicle engineering field. Developing TRIP steels with improved mechanical properties would not only allow for lightweight designs, but would also improve the safety of the materials in service. In this study, we report novel 0.4C-(3, 5, 7)Mn-1.2Mo-0.8V TRIP steels; these steels were melted and then warm-deformed at the (alpha + gamma) dual-phase region to fabricate ultrafine-grained microstructures with average grain sizes of 200-500 nm. Results show that the tensile strengths of the steels range between 1.9 and 2.1 GPa, and their elongations range between 7% and 8.5%. The microstructural thermostability of the steels gradually decreases with an increase in the manganese content. Compared with conventional TRIP steels fabricated using the cold-rolling and annealing method, the warm-deformed TRIP steels presented here can prevent cracks forming during the fabrication process. More importantly, these steels have significantly lower dislocation densities, thus improving their ductility. The present research results provide new ideas for the design of future ultrahigh-strength TRIP steels.