An investigation of surface failure of surface-hardened gears by scanning electron microscopy observations

The tooth surface of surface-hardened gears often becomes grey stained under a heavy load before pitting or spalling occur. The grey-stained area increases with running time and this failure causes degradation of the tooth profile.The nature of grey staining and the influence of surface conditions on the phenomena are investigated by scanning electron microscopy observations of the surfaces of gear teeth and rollers. It is established that the grey staining consists of many microcracks and micropits. Their formation and wearing off occur successively. It is reconfirmed that surface roughness has a significant influence on grey staining.