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Herein, an attempt has been made to investigate effect of C and Mn partitioning during quenching and partitioning heat-treatment process on microstructure, mechanical, and electrochemical properties of experimental 3 wt% Mn steel. The quenching and partitioning heat-treatment process was applied to the experimental steel with varying partitioning time periods ranging from 15 to 120 s at a constant partitioning temperature of 425 °C. The partitioning time period of 15 s resulted in a high volume fraction of supersaturated lath martensite with a small volume fraction of retained austenite. With increasing partitioning time period to 45–60 s, diffusion of C and Mn from martensite to retained austenite occurred resulting in the formation of decreased volume fraction of martensite phase with a reduced carbon and increased volume fraction of retained austenite phase with increased carbon. Partitioning for 90 s produced a moderate volume fraction of both lath martensite and retained austenite phases with nucleation of secondary phase, epsilon carbides. This phase transformation provided an optimum combination of 21% improved Vickers hardness and threefold improved impact toughness compared to as-received steel. Electrochemical properties of quenched and partitioned 3 wt% Mn steel were also evaluated in a 3 wt% NaCl solution. The highest corrosion resistance was achieved after prolonged partitioning of 120 s, whereas slightly low corrosion resistance was achieved after partitioning of 90 s. [ABSTRACT FROM AUTHOR]