Carburizing and quenching is a heat treatment method in which carbon is infiltrated into the surface of low carbon steel to make it into a state of high carbon content. This method is a heat treatment method that only hardens the steel surface.

The hardness of the surface and core (C = 0.15%) that penetrate the carbon continuously changes from soft to hard. The core hardness is lower than the surface hardness.

Similar to high-frequency hardening, the gears that have undergone carburizing and hardening are prone to deformation (such as increased size) and distortion, which will lead to a decrease in gear accuracy. In order to improve the gear accuracy, it is necessary to increase the subsequent process to do the grinding of the gear.