关键词: 高合金钢齿轮, 疲劳失效, 碳化物, 粗针状马氏体

Abstract: Causes of the bidirectional bending fatigue failure of high alloy steel gears were studied by means of stereomicroscope, scanning electron microscope, metallographic microscope, and microhardness testing. The results show that fatigue cracks mainly initiate and propagate at the junction between the tooth root and the end face. The fatigue source area is a point and no metallurgical defects, machining damage, or other damage characteristic are found in the source area. The carburized layer structure is composed of coarse acicular martensite, granular carbides, and retained austenite. Among them, the martensite on the end face of the gear presents coarse acicular morphology, and its grade exceeds grade 6, which is the main cause of premature fatigue failure. The excessively high content of retained austenite in the surface layer of the gear end face after carburizing leads to the microstructure inheritance during the quenching process, resulting in a coarse martensite structure, which is the main factor contributing to the low fatigue performance of the gear. It is recommended to reduce the content of retained austenite in the gear structure, refine the grain size of austenite during the quenching holding process, decrease the proportion of coarse acicular martensite, and then avoid premature failure.

Key words: high alloy steel gear, fatigue failure, carbides, coarse acicular martensite