Microstructural and Mechanical Properties of One-Step Quenched and Partitioned 65Mn Steel

The novel quenching and partitioning processes concerned with the stabilization of carbon enriched austenite and provision of higher strength with higher toughness. The microstructural and mechanical properties of one-step quenched and partitioned 65Mn steel were investigated under various partitioning times, ranging from 30 to 600 s. The optical microscopy revealed that microstructure transformed from ferrite and pearlite to supersaturated lath martensite and retained austenite phases after one-step quenching and 30 s of partitioning. The unstable epsilon carbides were nucleated with the increase in partitioning time to 60 s and 180 s, whereas a further increase in partitioning time to 300 s transformed these unstable epsilon carbides into a stable cementite phase. Prolonged partitioning for 600 s produced carbon depleted martensite phase and nucleated ferrite phase. A maximum improvement of 88% in hardness and tensile strength and maximum reduction of 64% in elongation and 44% in impact toughness were achieved after 30 s of partitioning, compared to the as-received steel sample. On the other hand, partitioning for 600 s offered almost identical mechanical properties to the as-received steel. Partitioning for 180 s offered an optimum combination of mechanical properties of one-step quenched and partitioned 65Mn steel.