Effect of Cycling Heat Treatment on the Microstructure and Properties of H13 Steel Prepared for Hot-Extrusion Die

In this study, the effects of conventional quenching + tempering (QT), cyclic quenching + tempering (CQT), and long-period heating on the microstructure and mechanical properties of H13 steel were investigated. The results show that CQT treatment could improve the mechanical properties of H13 steel at room temperature and 500 °C. The enhancement of properties is attributed to the refined martensite substructure and the precipitation of fine carbides during CQT treatment. After heating at 500 °C up to 100 h, the impact toughness of H13 steel under QT and CQT decreases by about 58% and 52%, respectively. The growth and coalescence of carbides along prior austenite grain boundaries and block boundaries and in the matrix are the reasons for the reduction of the impact toughness. CQT treatment could suppress the growth of carbides, thereby maintaining a higher toughness of CQT-treated steel than that of QT-treated steel.