Take 300 points at the axis of the gear shaft for analysis. The path taken is shown in figure (a). Comparing the distortion of direct carburization and carburization after preheating at 400 ℃ for 3 hours (Figure (a)), it can be seen that the distortion trend of the gear shaft after two heat treatment processes is roughly the same, but the distortion after preheating is generally less than that of direct carburization. It can be seen from the figure that the radial distortion is 0.7 mm when the gear is preheated from about 143 mm, and the maximum distortion is 0.7 mm when there is a radial distortion at the top of the gear. During direct carburizing, the distortion range at the axis is 0.016 ~ 0.143 mm, and the distortion range is 0.127 mm; The distortion range with preheating is 0.018 ~ 0.126 mm, and the distortion range is 0.108 mm.
In order to explore the distortion at the gear teeth, take 100 points at the gear teeth of the gear shaft for analysis, as shown in figure (b). It can be seen that the radial distortion in the middle of the gear tooth is the largest, the distortion of the gear tooth directly carburized here is 0.072 mm, and the distortion of the gear tooth carburized after preheating is 0.061 mm; The distortion range of directly carburized gear teeth is -0.218 ~ 0.072 mm, and the distortion range is 0.29 mm. After preheating, the distortion range of carburized gear teeth is -0.189 ~ 0.061 mm, and the distortion range is reduced to 0.25 mm. It can be seen that the preheating process can effectively reduce the heat treatment distortion of gear shaft.