Study on chemical heat treatment process of gears

1) Chongqing Changjiang diesel engine factory has carried out rapid gas nitrocarburizing process test and mass production assessment on 45 steel driven gear of motorcycle clutch. The results show that:

① The rapid gas nitrocarburizing process of 580 ℃ x Z H used in the test can make the compound layer of 45 steel driven gear ≥ 10 μ m. Surface hardness ≥ 450hv0.2.

② The long-term production test shows that by using the rapid gas nitrocarburizing process, the gear can actually obtain 15-25 foot thick compound layer, which is very dense and has little brittleness. The effective hardened layer depth can reach more than 0.4mm, and the full diffusion layer depth can reach more than 0.8mm. The surface hardness is generally in the range of 500-600 HV 0.2. It is at the leading level in China and has reached the level of foreign advanced products.

③ The distortion of 45 steel driven gear after CO infiltration by this process is small and uniform, and the qualified rate of loading is close to the level of foreign advanced products.

④ The key process of localization of the gear is nitrocarburizing process. Due to the success of rapid gas nitrocarburizing test and the standard of mass and long-time production test, it has brought obvious economic benefits.

2) nitriding is one of the traditional heat treatment processes, but whether it can be successfully applied to gears has always been doubted and debated. The main reason for suspecting the bearing capacity of nitrided gears is that the thin and brittle nitrided layer is attached to the soft substrate, which is difficult to bear the load. Therefore, the application of nitrided gears has been limited for a long time. Some authoritative institutions such as the American Petroleum Association stipulated in its api613 document that the nitrided gears can only bear 75% of the contact fatigue limit of carburized gears, The bending fatigue limit of gears should be reduced by 30%.

However, the advantages of low nitriding temperature, small distortion and less processing procedures to reduce the cost greatly attract gear manufacturers. According to the data, the accuracy of nitrided gears generally decreases by only 1-2 levels, while the accuracy of carburized quenched and medium hard quenched and tempered gears decreases by 2-3 levels.

Although there are still doubts and disputes about the bearing capacity of nitrided gears, industrial applications are booming. Since the 1960s, Britain began to boldly respond to the month on destroyers, and then widely used in all kinds of industrial gear devices. With the development of floe two-way nitriding process in the United States, the application of nitriding gears has expanded. For example, 43% of the high parameter gears produced by the famous Philadelphia gear company adopt nitriding, and even the aviation gears with strict requirements adopt nitriding treatment. In Germany, represented by clockner ion company, ion nitriding is widely used in some automobile gears, worms and machine tool gears, and the herringbone gear shaft of rolling mill with a weight of 1.5T and a length of 2m has been successfully treated. Most of Halton flying shear and winch gears in 1700 rolling mill imported by WISCO adopt nitriding treatment. In Japan, nitriding is used on automobile gearbox gears and motorcycle driving and passive gears; Osaka lock making machine (strain) adopts 0.8mm deep nitriding for the large gear of high-power medium speed diesel engine with a diameter of 3 m, which is in good use. In France, some gears of dolphin engine produced by im company adopt nitriding treatment. Through the improvement of equipment, the depth and hardness of nitriding layer can be accurately controlled. Bema ion company in Switzerland has long used ion nitriding to treat gears. Company B and C Φ 3300 ~ steam turbine gears and some marine large gears have been successfully nitrided. The ion nitriding equipment of brukens harderkstader company in Sweden can be automatically controlled and used to process all kinds of gears. In the former Soviet Union, nitriding technology is widely used for machine tool gears and traction machine gears.

China is one of the earliest countries in the application of ion nitriding process, especially in the application of gears. Zhengzhou Institute of machinery has carried out systematic experimental research. In recent ten years, a large number of various types of industrial gears have been treated, and there have been no problems caused by nitriding process.

3) Sulfur nitrocarburizing process has the characteristics of low treatment temperature, no pollution and small workpiece deformation. It can significantly improve the friction reduction, anti bite, self-lubricating and adhesive wear resistance of workpiece surface. At present, the carburizing process is the most widely used in China. In the shallow carburizing with the carburizing layer depth less than 1mm, except that the thin-walled stamping parts still retain the carburizing of low carbon steel, other machining processes are formed.

For a large number of workpieces, medium carbon steel or medium carbon alloy steel will be used for sulfur nitrocarburizing or nitrocarburizing. Motorcycle disc-shaped starting gear combination is formed by stamping 20 steel disc-shaped starting gear and hydrogen arc welding with spline seat. The technical requirements are that the surface hardness is 550 ~ 750hv 0.2, and the infiltration layer thickness is 0.3-0.5 mm. Generally, the gear combination of low-temperature chemical heat treatment has good deformation, but the surface hardness and carburizing layer do not meet the technical requirements. According to the characteristics that the cyclic chemical heat treatment of steel can improve the chemical heat infiltration on the surface of parts, accelerate the diffusion process, and obtain the microstructure and properties that can not be obtained by ordinary chemical heat treatment, the twice cyclic low-temperature salt bath chemical heat treatment process is adopted, the results meet the production technical requirements, and the technical problems of heat treatment of the assembly are solved.

Aiming at the disadvantages of poor carburizing structure, low contact accuracy, high noise, large deformation and low service life of special gear carburizing and quenching process in production, some production enterprises have carried out production experimental research on the conventional carburizing and quenching process of gear, adjusted and improved the carburizing and quenching heat treatment process, and achieved good results.

4) Focusing on improving the heat treatment process and improving the product quality, Chongqing Zujiang gear factory analyzes the quality indexes of Automobile Carburized Gears, summarizes the heat treatment experience to effectively and economically ensure the product quality, and puts forward the process measures to improve the heat treatment quality of Automobile Carburized Gears. It includes optimizing the process method and improving the surface residual compressive stress; Surface carbon content and carbon concentration gradient control; Microstructure control of carburized gear; Hot oil quenching

Fire reduces distortion; Adopt preheating heat treatment to improve carburizing quality, etc. The practice shows that the above technical measures are not only an important means to optimize the quality index of gears, but also the key to improve the internal quality of Automobile Carburized Gears.

Scroll to Top