Effect of direct quenching on microstructure and mechanical properties of a wear-resistant steel

A wear-resistant steel was hot rolled at the same finish temperature, and subsequently treated with conventional reheat quenching and tempering process (RQ&T) and direct quenching and tempering process (DQ&T), respectively. The effect of direct quenching on the microstructure and mechanical properties was investigated in detail by using optical microscope, transmission electron microscope and scanning electron microscope equipped with electron backscattered diffraction. The results showed that the microstructures of both the RQ and DQ specimens were complex constituents of lath martensite and lower bainite. Compared with the RQ specimen, the lower bainite content in DQ specimen was much higher. Furthermore, the bainite in the DQ specimen extended into and segmented the prior austenite grains, which can decrease martensite packet size. The proportion of high-angle boundary in the DQ specimen was higher than that in the RQ specimen, which may improve the impact toughness. The carbides in DQ&T specimen were much finer and distributed even dispersively because direct quenching can retain substantive defects which may provide more nucleation sites for carbide precipitation in the tempering process. Besides, the mechanical properties of DQ and DQ&T specimens were superior than those subjected to RQ and RQ&T processes, respectively.