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The effective hardened layer depth and hardness of the tooth surface are normal, but the hardness of the gear core is at the lower limit of the standard (HRC30-45), and the gear hardness gradient changes rapidly, reducing the bending strength of the tooth. The metallographic analysis of the core of the tooth is mainly granular bainite, and the structure is coarse, indicating that the heating temperature is too high during heat treatment. After the carburizing and quenching heat treatment, there is a non-martensitic structure in the layered structure, which is related to the fact that the core structure is not in an optimal state, which reduces the bending fatigue strength of the gear material, so that it is easy under complicated working conditions. Early fatigue failure occurred. The shallow spalling phenomenon of the surface of the planetary differential tooth surface indicates that there is a large non-metallic inclusion in the material.
In the assembly inspection, it was found that part of the tooth meshing point was close to the small end of the bevel gear. The meshing point of the Huanghai auto parts was close to the pivot point, which did not meet the requirements of the meshing point from the big end 60 or so. Therefore, when the same torque is transmitted, the stress load near the small end is high, and the small end tooth end is easily damaged. The main reason for failure According to the above analysis and research, the main reasons for gear failure can be summarized as follows: (1) gear fracture failure is typical overload fatigue fatigue failure; (2) improper adjustment of gear assembly, resulting in near-small end of meshing point, not reaching The standard requirements are to make the tip of the tooth partially overloaded; (3) The gear material is selected from Japan SCM420H, compared to the national standard 20crM. , mechanical properties, must, hardness and other relative deficiencies; (4) segregation in the original material, after carburizing and quenching, martensite and non-martensitic mixed structure appeared in the layered structure, the heart tissue is granular The bainite is mainly composed and the structure is coarse. The structure affects the toughness of the material and causes poor bending fatigue resistance. The root of the tooth is soft and the hardness gradient of the carburized layer changes rapidly. The depth of the localized hardened layer is insufficient, which makes the carburized layer easy to peel off. Redesigning the assembly and protection measures to troubleshoot the gears, redesigning and assembling the gears, and adding safety protection measures. The gear parameters were redesigned due to insufficient gear strength and overload fatigue fatigue failure. Therefore, the modulus and tooth width of the gear were redesigned.