Effect of Rolling Temperature on Microstructure and Mechanical Properties of a Nb-Mo Microalloyed Medium Mn Steel

Warm rolling of medium Mn steel is a promising technology to meet the needs of vehicle weight reduction and energy conservation while ensuring the safety for passengers. In this study, a novel Nb-Mo microalloyed 6.6Mn steel was subjected to a series of warm rolling tests at temperatures ranging from 630 to 690 ºC, based on the thermodynamic-based prediction of inter-critical annealing using a Thermo-Calc software. As a comparison, a conventional multi-stage thermo- mechanical process involving hot rolling, cold rolling and inter-critical annealing was carried out as well. The optimal rolling temperature parameters for warm rolling was explored through tensile tests and the detailed microstructural characterization. The experimental results show that the microstructure and mechanical characteristics strongly depended on the warm rolling temperature. A better combination of UTS and TE products (~32.0 GPa·%) was achieved in the 660ºC-warm-rolled specimen, which is much higher than 12.3 GPa·% for the hot formed 22MnB5 steel and is also comparable to 38.3 GPa·% for the annealed cold-rolled specimens.