用50CrMoA钢生产某大模数齿轮的过程中，经感应热处理后，在齿根表面发现明显斑疤。采用宏观观察、化学成分分析和金相检验等方法对该齿轮齿根表面斑疤产生的原因进行了分析。结果表明：该齿轮感应热处理采用齿廓单齿埋油淬火，因感应器调整不当或齿形有偏差，故其齿侧间隙过小，导致齿轮表面烧熔并产生局部熔融；同时，齿轮表面黏有的淬火油也被烧化，淬火油烧化后产生的大量碳元素溶入了表层熔融部位，冷却后在齿轮齿根区域形成局部高碳的过共晶组织，宏观表现为斑疤状的缺陷。

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.