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Gear vacuum carburizing process

Agricultural vehicles and tractor transmission gears are generally made of 20CrMnTi low carbon alloy steel. Because agricultural vehicles and tractors mostly drive on country roads, fields and poor road conditions, high strength, high wear resistance, high hardness, high impact toughness, and high fatigue strength are required for transmission gears. The commonly used vacuum heat treatment process is carburizing and quenching process. But in the process of vacuum heat treatment, deformation easily occurs, and the rejection rate is high. Later, the carbonitriding process was adopted. Due to the presence of nitrogen, the carbonitriding process generally has a lower temperature and a shallower carburized layer, which has a greater impact on the surface hardness. In order to overcome the above difficulties, the BH carburizing process was adopted. These three processes are now compared and analyzed, in order to seek the best process to ensure product quality, improve production efficiency and save energy.

The carburizing temperature of conventional vacuum carburizing process is high, generally 900 ~ 950 ℃. The higher the temperature, the faster the diffusion rate and the deeper the infiltration layer, but it will cause the growth of austenite grains and reduce the mechanical properties of the parts; increase the shape deformation of the workpiece and reduce the service life of the equipment. Using kerosene as the penetrant, the decomposition of kerosene is insufficient when the temperature is lower than 800℃, and the macromolecular chain scission is the main factor, followed by the dehydrogenation reaction. Above 800℃, the hydrogen content of the dehydrogenation reaction increases significantly. Therefore, carburizing with kerosene below 850 ℃ is often poor in cracking, and the low molecular weight olefin is more, which is easy to produce carbon black and coke. Only carburizing at a higher temperature of 900 ~ 950 ℃ can obtain better results.

During carbonitriding, the carbonitriding temperature is lower than that of conventional vacuum carburizing, and the carbides are fine and uniform. However, due to the infiltration of nitrogen, carbonitriding will be formed, hindering the diffusion of carbon, and the interaction of carbon and nitrogen will make the infiltration layer shallower.

The BH infiltration technology is a technology that increases the infiltration rate by 20% or lowers the process temperature by more than 40 °C by adding a small amount of infiltration agent to the carburizing medium kerosene, and keeps the infiltration rate in the original process. The temperature is reduced on the basis of the conventional vacuum carburizing process, and the temperature is determined to be 870 ℃ through experiments, which can ensure the depth of the carburized layer and shorten the time of the vacuum carburizing and quenching process.

It can be seen from the data that the performance parameters of the gear after carbonitriding are better than the conventional vacuum carburizing process, and the BH catalyzing process is better than the carbonitriding process. The main technical indicators such as surface hardness, core hardness and carburizing layer of gears treated by conventional vacuum carburizing process all meet the requirements, but there are high temperature, short life of electric furnace heat-resistant materials and carburizing tank, frequent maintenance, long process cycle, and production efficiency. Low, gear deformation, high scrap rate, obvious defects. After the improvement of the carbonitriding process, the process temperature is reduced, the problem of frequent maintenance of the electric furnace is solved, and the cost is saved, but new problems have also arisen. The infiltration layer is shallow and unstable, and the surface hardness is sometimes low. , more rework. Due to the lower carburizing temperature, more carbon black is produced. Due to the addition of ammonia gas, ammonia gas leaks from time to time, and the production environment is poor. Compared with the conventional carburizing process, the use of BH catalysis technology reduces the carburizing temperature, reduces the process cycle, improves labor productivity, saves production costs, and improves product quality. Compared with the carbonitriding process, ammonia gas is eliminated, the working environment is improved, the production of carbon black is reduced, the thickness of the carburized layer fluctuates less, and the carbides are fine and evenly distributed, usually ≤ grade 2; residual austenite The grades of martensite and martensite are less than or equal to grade 3; the carbon concentration gradient is gentle, which reduces the quenching deformation, improves the product quality, shortens the process cycle, and improves the labor productivity.

Conclusion

BH infiltration technology is a better carburizing technology found after many tests and comparative analysis with the previous process. The process is stable and reproducible, the thickness fluctuation of the carburized layer is small, the carbides are small and evenly distributed, usually ≤ grade 2; the grade of retained austenite and martensite is ≤ grade 3; the carbon concentration gradient is gentle, reducing heat treatment distortion of the workpiece, The precision of the gear after carburizing and quenching is improved, the product quality is guaranteed, the labor environment is improved, the process cycle is shortened, the labor productivity is improved, the process temperature is reduced, the service life of heat-resistant materials and fixtures is improved, and the Frequent equipment maintenance problems, saving maintenance costs.

Selection of carburizing equipment: RVC series vacuum carburizing furnaces and GH-GCF series gas carburizing furnaces produced by SIMUWU are high-quality products for the vacuum carburizing process of tools and molds. Good temperature control accuracy and temperature control uniformity ensure the vacuum carburizing process. of effective conduct.