Gear heat treatment

Carburizing is widely used in critical parts of equipment such as aircraft, automobiles, and machine tools, including gears, shafts, and camshafts. Carburizing is the most widely used and comprehensively developed chemical heat treatment process. Microprocessors can automate the entire carburizing process, allowing control over the surface carbon content and the distribution of carbon within the carburized layer.
Nitriding is a chemical heat treatment process that diffuses nitrogen atoms into the surface of a metal workpiece. After nitriding, steel forms a surface layer mainly composed of nitrides. When the steel contains nitrides such as chromium, aluminum, and molybdenum, it can achieve higher hardness, wear resistance, corrosion resistance, and fatigue resistance than a carburized layer. Nitriding is mainly used for workpieces requiring high precision, distortion, fatigue strength, and wear resistance, such as boring machine spindles and boring bars, grinding machine spindles, and cylinder liners.
Carbonitriding and nitrocarburizing are chemical heat treatment processes in which carbon and nitrogen are simultaneously diffused into the surface of a metal workpiece. The former is mainly carburizing. Compared with carburizing, carbonitrided parts have less distortion after quenching, higher wear and corrosion resistance, and better fatigue resistance. Since the 1970s, carbonitriding has developed rapidly and can be used not only for some automotive and tractor parts, but also for surface strengthening of various gears and shafts. The latter is mainly nitriding. Its main characteristics are faster diffusion rate, shorter production cycle, less surface brittleness, and less stringent requirements on workpiece material. The disadvantage is that the diffusion layer is thinner and it is not suitable for working under high loads.