Effect of tempering temperature on microstructure and mechanical properties of a low carbon bainitic steel treated by quenching-partitioning-tempering (QPT) process

The quenching-partitioning-tempering (QPT) treatment was carried out on a low carbon bainitic steel, and the effect of tempering temperature on the microstructure and mechanical properties of the QPT processed steel was investigated. The findings demonstrate that as the tempering temperature increases, the yield strength decreases gradually, while the tensile strength decreases first and then increases. However, the elongation exhibits a trend of increasing first and then decreasing with increasing the tempering temperature. When the tempering temperature is 340 °C, the best mechanical properties can be obtained with the yield strength of 1495 MPa, tensile strength of 1806 MPa, elongation of 17.7%, and product of strength and elongation up to 32.92 GPa%. Such excellent mechanical properties are related to the synergistic combination of tempered martensite, low carbon bainite, retained austenite and carbides.