Choosing good material of planetary gear reducer is helpful to improve its bearing capacity and service life.
In view of the structural characteristics of Starred-River reducer and the load characteristics of gears, hard-tooth surface gears should be widely used. There are many heat treatment methods to obtain hard face gear. For example, surface quenching, whole quenching, carburizing quenching and nitriding should be selected according to the characteristics of gear reducer.

1.Surface hardening
The common surface quenching methods are high frequency quenching (for small size gears) and flame quenching (for large size gears). When the hardened layer of surface hardening includes the bottom of the tooth root, the effect is good. The hardness of the tooth surface can reach 45-55HRC.

2. Nitriding
Nitriding can ensure high hardness and wear resistance of gears under the condition of small deformation, and no good finishing after heat treatment can be carried out to improve the bearing capacity.

3. Carburizing and Quenching
Carburizing and quenching gears have relatively large bearing capacity, but finishing process (grinding) must be used to eliminate heat treatment deformation to ensure accuracy.
The hardness of the alloy steel with 0.2%-0.3% carbon before carburizing is usually in the range of 58-62 HRC. When the hardness is lower than 57 HRC, the strength of the hard surface decreases significantly, while the brittleness increases when the hardness is higher than 62 HRC. The hardness of carburized and quenched gears decreases gradually from the surface to the depth, while the effective depth of carburization is defined as the depth from the surface to the hardness of 5.25 HRC.
The effect of carburizing and quenching on the bending fatigue strength of gears not only improves the hardness of the center part, but also lies in the residual compressive stress on the surface. It can reduce the stress in the area of large compressive stress, so it can not grind the root part of the tooth when grinding.