The common heat treatment methods of gears are surface quenching, carburizing quenching, nitriding, tempering and normalizing,
- Surface quenching: surface quenching is a heat treatment method to quench the surface of steel parts while the core remains the original structure. It is commonly used in medium carbon steel or medium carbon alloy steel, such as 45, 40Cr steel, etc. After quenching, the surface hardness can reach HRC45-50, the core is soft, has high toughness, the tooth surface contact strength is high, and the wear resistance is good. It is generally used for important gear transmission under medium impact load.
- Carburizing and quenching: carburizing and quenching is to infiltrate carbon atoms into the surface of steel parts and then adopt the process of quenching and low temperature tempering. The surface of steel parts has high hardness and wear resistance, while the core still maintains a certain strength and high toughness. The commonly used materials are low carbon steel or low alloy steel, such as 20, 20Cr, 20CrMnTi, etc. After carburizing and quenching, the surface hardness can reach hrc56-62, the core still has high toughness, the tooth surface contact strength is high, and the wear resistance is good. It is generally used for important gear transmission under impact load.
- Nitriding: nitriding is the process of penetrating nitrogen atoms into the surface of steel. Its purpose is to improve the surface hardness and wear resistance of steel as well as the fatigue strength and corrosion resistance. After nitriding, the surface hardness can reach HRC > 65, and the deformation is small. Common materials such as 38CrMoAl, etc.
- Quenching and tempering: commonly used in medium carbon steel, such as 45, 40Cr steel, etc. The hardness of tooth surface after tempering treatment is generally hb200-280. Because the hardness is not high, it can be finished after heat treatment. Generally, it is used for gear transmission with small batch and no strict limit on transmission size.
- Normalizing: normalizing treatment can eliminate internal stress, improve strength and toughness, and improve cutting performance. The gear transmission with low mechanical strength can be normalized with medium carbon steel or cast steel. After normalizing, the hardness of tooth surface is generally hb160-220.