Evolution of microstructures and mechanical properties with tempering temperature of a pearlitic quenched and tempered steel

Instead of conventional quenching and tempering, fast austenitization from an initial microstructure of lamellar pearlite followed by quenching and tempering was carried out, leading to the formation of inhomogeneous microstructure. It comprised different morphologies of lath martensite and retained austenite (RA). The effect of tempering temperature on microstructure evolution and tensile properties was systematically investigated. With increasing tempering temperature from 150 to 250 °C, transition carbides gradually coarsened and their amount increased, the dislocation density in martensitic laths gradually decreased, and RA fraction decreased from 10.9% to 2.2%. The precipitation and dislocation strengthening can ensure a high strength, while RA can ensure a good ductility, leading to a simultaneous increase in the strength and ductility when decreasing tempering temperature. Specifically, the best combination of tensile properties (ultimate tensile strength of 2133 ± 41 MPa and total elongation of 11.1% ± 1.3%) was achieved after tempering at 150 °C.