1. Forged steel is the main material for making a gear, because it has relatively high strength and toughness. The general method can be divided into soft tooth surface and hard tooth surface.
Generally, the optional soft tooth surface shall be used for gear cutting after heat treatment. In order to facilitate gear cutting, the gear cutting tool will not wear and become blunt rapidly. This gear is cut after normalizing and tempering treatment. For important applications, the hardened tooth surface can be selected, and the surface hardening treatment shall be carried out after cutting the tooth. The heat treatment methods include surface hardening, carburizing and nitriding. The treated tooth surface has high hardness, good toughness, high bearing capacity and good wear resistance.
2. Cast steel has high strength and good wear resistance, but it must be normalized or annealed due to high internal stress during casting. Cast steel is often used for gears that are too large to be forged.
3. Cast iron is brittle, with poor impact resistance and wear resistance, but it is easy to process by casting and cutting technology. Therefore, cast iron is commonly used in open gear transmission with low speed, medium load, no impact and no vibration. The mechanical properties and impact resistance of nodular cast iron are much higher than that of gray cast iron, so it is used more and more.
