Overall quenching: After overall quenching, it is tempered at low temperature. Commonly used materials are medium carbon steel or medium carbon alloy steel, such as 45, 40Cr, etc. The surface hardness can reach 45HRC~55HRC. This heat treatment process is relatively simple, but the gear deformation is large and the core toughness is low. The quality is not easy to guarantee and it is not suitable to bear impact load. After heat treatment, finishing processing such as gear grinding and grinding must be carried out.

Surface quenching: Surface quenching and then low temperature tempering. Commonly used materials are medium carbon steel or medium carbon alloy steel, with surface hardness up to 48HRC~54HRC. Due to the high toughness of the core, it can be used to withstand moderate impact loads. Small and medium-sized gears can be heated by medium-frequency or high-frequency induction, and large-sized gears can be heated by flame. Flame heating is relatively simple, but it is difficult to obtain uniform hardness on the tooth surface and the quality is not easy to guarantee. Heating should only be done on the surface of the thin layer. The gear deformation is not large and the final gear grinding is not required. However, if the hardened layer is deep, the deformation will be large and final finishing machining should be performed.

Normalizing and quenching and tempering: Normalizing or quenching and tempering are often used when the batch size is small, single-piece production is performed, and there are no strict restrictions on the transmission size. The material is medium carbon steel or medium carbon alloy steel. The surface hardness can reach 40HRC~55HRC. After the heat treatment of the gear finishing, in order to reduce the risk of gluing and make the life of the large and small gears similar, the tooth surface hardness of the small gear should be dozens of HB units higher than that of the large gear.