Heat treatment technology is a traditional method to improve the surface strength of materials. The heat treatment of gear material is an indispensable key technology to give full play to the material characteristics and improve its surface performance. Correct and appropriate heat treatment can improve the surface characteristics of gear, such as wear resistance, fatigue resistance, corrosion resistance, adhesion resistance and aesthetics. It can not only prolong the service life of products, but also improve the utilization rate of gears.
Automobile gears can meet the required performance requirements only after corresponding heat treatment. The main treatment methods include carburizing (C-N co carburizing) quenching, nitriding, induction (flame) heating quenching and other heat treatment processes.
At present, the carburizing of automobile gears is mainly gas carburizing, and the carburizing temperature determines the microstructure and properties of carburized layer. The carburized and quenched automobile gear can obtain high surface hardness and good core toughness, improve the wear resistance and fatigue resistance of the tooth surface, improve the residual compressive stress of the tooth surface, and have good comprehensive mechanical properties. It is the leading heat treatment process in the automobile gear industry at present.
After nitriding process, the biggest advantage of automobile gear is small deformation. At the same time, it also has the same high surface hardness as carburized gear. The process is less than carburization and the cost is low. 43% of the high parameter gears produced by the famous Philadelphia gear company adopt nitriding, and even the demanding aviation gears adopt nitriding technology. In Germany, represented by clockner ion company, ion nitriding is widely used in some automobile gears, turbine and machine tool gears, as well as herringbone gear shafts of rolling mills. In Japan, nitriding is used on automobile gearbox gears and motorcycle driving and passive gears; Some gears in the dolphin engine produced by TM company of France are nitrided. Through the improvement of the equipment, the depth and hardness of the nitrided layer can be accurately controlled; BBC of Switzerland has successfully nitrided the d = 3300mm steam turbine gear and marine large gear.
Induction hardening plays an important role in the manufacturing process of gears from soft tooth surface to hard tooth surface. Induction quenching has higher efficiency and less deformation than carburizing quenching; It is finer than the depth of nitrided hardened layer and can reach millimeter level. According to the American AGMA gear strength standard, the contact fatigue strength of induction hardened gear can reach 1200-1300mpa, which is close to carburized gear; Under the condition that the tooth root is well hardened, the bending fatigue strength can also reach 310-380mpa, which can be compared with the nitrided gear. Induction hardened gears also account for a certain proportion in automobiles, locomotives and mining machines, especially in machine tool gears, accounting for more than 70% of the total; Especially in automobile transmission, some thin-walled small gear sleeves and splines adopt high-frequency induction quenching. Due to high efficiency, small distortion and low pollution, they have been successfully incorporated into the production line and have good technical economy.