A quench and partition (Q&P) process was combined with tempering in a medium Mn steel. The partitioning treatment enriched the austenite in carbon, and stabilised the austenite against transformation during cooling. The ductility of Q&P steel is significantly improved by tempering, with negligible loss in strength. The ductility was found to be determined by the martensite in the structure, rather than the austenite in the present case. The reason for the significant improvement in the ductility with tempering was suggested to be the reduction in the dislocation density after extended tempering treatment. The energy absorption of this alloy was increased to 28.5 GPa·% together with an ultrahigh tensile strength ∼1400 MPa, which is one of the largest observations in this system.
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