What are the common materials and heat treatment methods for gears?

There are two common materials for gears:

One is carburized steel, which is mainly used to manufacture gears with low load but high requirements for wear resistance and impact resistance. The heat treatment method of this steel is as follows

Carburizing+quenching+low temperature tempering;

The other is quenched and tempered steel, which is mainly used to manufacture gears with heavy load. The heat treatment method of this steel is as follows

Quenching+high temperature tempering+surface quenching.