Effects of Tempering Temperature on the Microstructure, Strength, and Toughness of Medium-Carbon Ti–Mo-Bearing Martensitic Steel

Titanium (Ti) and molybdenum (Mo) were added simultaneously to improve the strength and toughness of medium-carbon martensitic steel. The influences of tempering temperatures on the microstructure, strength, and toughness of the as-developed martensitic steel were investigated. The microstructure of Ti–Mo-bearing martensitic steel consisted of martensite without apparent recovery and fine precipitates at the optimal tempering temperature of 200 °C, and the tensile strength of 1700 MPa and − 40 °C impact energy of 43 J were simultaneously realized. With increasing tempering temperature, carbides were transformed from ε-carbides to (Ti, Mo)C and Fe₃C particles. Moreover, both the content and size of precipitates increased with increasing tempering temperature. The decreased impact energy of the quenching-tempering steel tempered at 650 °C could be ascribed to the increased coarsening of (Ti, Mo)C and Fe₃C particles. In addition, (Ti, Mo)C particles mainly precipitated on Fe₃C particles and at dislocations.