Quenching and partitioning (Q&P) processed medium Mn steel starting from heterogeneous microstructure

We examine the microstructure and tensile properties of the quenching and partitioning (Q&P) processed medium Mn steels having different starting microstructure. Heterogeneous Mn distribution led by intercritical annealing prior to the Q&P process is more effective in retaining higher fraction of austenite; a major fraction of austenite exists as Mn-rich islands surrounded by martensite. Starting with uneven Mn distribution prior to the Q&P process enhanced the austenite stability by high Mn concentration and shielding effect by neighboring martensite. It contributed to the impressive tensile properties by operating multiple plasticity mechanisms: transformation-induced plasticity (TRIP) with twinning-induced plasticity (TWIP).