The novel process of spheroidizing-critical annealing used to optimize the properties of carburized steel and its effect on hardening mechanism of quenching and tempering

A new annealing process, spheroidation-critical annealing, was designed to optimize the properties of carburized steel 15CrNiMo instead of the traditional process. In this study, four factors and three levels of orthogonal experiment were used to design annealing experiments with different parameters, and the optimal combination of performance was obtained, giving consideration to both surface hardness and core toughness. After complete heat treatment, the vickers hardness of the surface of experimental steel could reach 752HV, and the impact energy of the core could reach 175 J/cm(2). On this basis, the effects of new annealing process and traditional high temperature tempering process on the machinability of the experimental (the surface hardness of the experimental is taken as the performance index after the treatment of the two processes) are studied. At the same time, the effects of two processes on the surface hardening mechanism and core toughness of subsequent quenching and tempering processes of experimental steel are discussed. The results show that the new annealing process can hardly reduce the cutting property of the surface of experimental steel (after two kinds of process, the surface of the experimental steel vickers hardness is 302 HV and 325 HV), through the way of stable carbides, promote the quenching process of experimental steel surface high carbon martensite hardened, promoted 70 HV hardness compared with the traditional process. However, the toughness of the experimental core is insensitive to the two processes, so the new process can improve the surface hardness without reducing the toughness of the experimental.