Effects of temperature on the microstructural evolution and mechanical properties of copper − bearing medium manganese steel during tempering

• The content of reversed austenite may be nearly identical, yet its contribution to the toughness and plasticity can exhibit differences. • The majority of the reversed austenite transforms into fresh martensite during cooling at excessively high temperatures. • The reversed austenite retained at room temperature tends to form twins readily, and its internal dislocation density is significantly enhanced. • In the over-aged condition, each 1% precipitation of copper still yields approximately 193-234 MPa of precipitation strengthening. This work introduced the effects of higher tempering temperatures on the microstructural evolution of Cu − bearing medium Mn steel. After quenching steel at 860 °C for 1 h, it was tempered at 600, 640, and 670 °C for 2 h. The results indicated that the low − temperature impact toughness initially increased and then decreased, while the yield strength consistently decreased with increasing temperature. At a tempering temperature of 640 °C, the steel exhibited a relatively high content of reversed austenite and demonstrated the best low − temperature toughness and plasticity. The low − temperature toughness and plasticity of the steel significantly diminished, when the temperature exceeded 640 °C. This is because the degree of alloying element enrichment in the reversed austenite is reduced, accompanied by an increase in dislocation density and the formation of twins. These reversed austenites exhibit a diminished ability to hinder crack nucleation and propagation. The yield strength decreased with increasing temperature, primarily due to the coarsening of the Cu particles, which reduces their precipitation strengthening effect. This study advances the development of high − strength tough medium − manganese steels.