Heat treatment nitriding process is one of the traditional heat treatment processes. However, whether it can be successfully applied to automobile gears has always been doubted and debated, mainly due to the bearing capacity of heat treatment nitriding gears. Therefore, the application of heat treatment nitriding gears has been limited for a long time. For example, the American Petroleum Institute stipulates that the heat treated nitrided gear can only bear 75% of the contact fatigue limit of carburized gear, and the bending fatigue limit of gear should be reduced by 30%.
However, due to the advantages of low temperature, small distortion and less processing procedures, the heat treatment nitriding process has been widely used in gears in recent years. For example, 43% of the high parameter gears produced by the famous Philadelphia gear company adopt heat treatment nitriding.
At present, the most widely used heat treatment nitriding process is ion nitriding. The application scope of conventional ion nitriding is limited due to the problems of thin heat treatment nitriding layer (generally below 0.6mm), shallow effective hardening layer depth and unsuitable for working under heavy load conditions. However, compared with ordinary gas nitriding, ion nitriding has the advantages of significantly shortening the nitriding operation time of heat treatment, reducing workpiece distortion and easy to obtain uniform nitriding layer. For example, the depth of ordinary gas nitriding is more than 100h, while that of ion nitriding is only about 60H. It is widely used in gear treatment at home and abroad. Germany is represented by Klockner ion engineering company, Ion nitriding is widely used in some automobile gears.
In recent years, composite strengthening methods combining optimized heat treatment nitriding process with various new rapid heat treatment nitriding technologies continue to appear, such as controlling nitrogen potential, periodic cyclic nitriding, etc. combined application of optimized heat treatment nitriding process with new technologies such as rare earth catalysis, surface pre oxidation and surface nano pretreatment, heat treatment nitriding gears will show a broader application prospect. The research of Lin et al. Shows that surface ultrasonic shot peening nano treatment can make the nitriding process of heat treatment controlled by the diffusion process at the initial stage. Jisen Wang et al. Carried out heat treatment Nitriding on 45 steel at 300 ℃ through surface nano treatment, and obtained 200 thick steel μ M nitrided layer.