The corrugation, arris and cold deformation of gears are less, and the damage seems less. They show a surface state of material change and surface deformation.

As shown in the figure, the surface of the gear has corrugation, which is a typical state of corrugation on the hardened off-axis bevel gear. Corrugations usually occur on gears with high load.

As shown in the figure, the edge of hardened gear may be caused by overload.

As shown in the figure is the case of cold deformation propulsion stage of medium hardness gear. This kind of gear is easier to produce cold deformation than the case hardened gear. The material has been turned over to the top edge of the gear, resulting in the damage of the gear profile. Heavy loads are mostly responsible for the movement of this metal. The arring of hardened gear shown may be caused by overload.

As shown in the figure, the surface deformation of medium hardness gear caused by rolling and knocking. This gear is likely to be overloaded and used for a long time after initial damage, resulting in surface damage.