Carburizing and quenching: For gears with large impact loads, carburizing and quenching should be used. Commonly used materials include low carbon steel or low carbon alloy steel, such as 15, 20, 15Cr, 20Cr, 20CrMnTi, etc. After carburizing and quenching of low carbon steel, due to the low strength of the core and difficulty in combining well with the carburized layer, there is a possibility of peeling off when the load is large, and the bending strength of the gear is also low. Low carbon alloys should be used in important occasions. Steel, its tooth surface hardness can reach 58HRC~63HRC. After the gear is carburized and quenched, the gear deforms greatly and should be ground.

Carbonitriding: The process of carbonitriding is short and has the advantages of nitriding. It can replace carburizing and quenching. Its materials are the same as carburizing and quenching.

Nitriding: Nitriding gears have high hardness and small deformation, and are suitable for internal gears and gears that are difficult to grind. Commonly used materials include 42CrMo, 38CrMoA1, etc. Since the hardened layer is very thin, it is easily broken under impact load. If the wear is serious, the hardened layer will be worn away and scrapped. Therefore, it is suitable for transmission with stable load and good lubrication.