Causes of scar defects on root surface of large modulus gear

In the process of producing a large modulus gear with 50CrMoA steel, obvious scars were found on the tooth root surface after induction heat treatment. Macroscopic observation, chemical composition analysis and metallographic examination were used to analyze the causes of surface scars of the gear tooth root. The results show that the induction heat treatment of the gear was quenched by single tooth buried oil, due to the improper adjustment of the inductor or the deviation of the tooth shape, so the tooth side clearance was too small, resulting in the burning of the gear surface and local melting. At the same time, the quenching oil adhered on the gear surface was also burned, a large amount of carbon generated by the burning of quenching oil dissolved into the surface melting part, after cooling, a local hypereutectic structure with high carbon was formed at the root of the gear tooth, which was macroscopically characterized by scar-shaped defects.