Effect of carburizing temperature on the microstructure and hardness of carburized layer of 18CrNiMo7-6 gear steel

The reasonable selection of carburizing temperature is one of the key factors to improve carburizing efficiency and obtain favorable microstructure and properties of the carburized layer. In this paper, taking 18CrNiMo7-6 gear steel as the research object, the finite element method was used to simulate the influence of carburizing temperature in the range of 920~960 ℃ on the carbon diffusion behavior in the carburized layer, and electron backscatter diffraction (EBSD) technology was employed to quantitatively analyze the types and contents of carbides in the carburized layer. The results show that with the increase of carburizing temperature, the carbon concentration on the sample surface remains almost unchanged, but the carbon concentration inside the sample increases significantly, and the increase of carburizing temperature can effectively improve the depth of the carburized layer. The carbides of 18CrNiMo7-6 gear steel are mainly composed of M23C6, M7C3 and cementite. As the carburizing temperature increases, both the content and size of carbides in the carburized layer increase significantly. Compared with carburizing at 940 ℃, carburizing at 960 ℃ increases the depth of the carburized layer by 0.9 mm and the hardness of the surface carburized layer by 43.1 HV1.