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Influence of Vacuum Carburizing and Quenching on New Gears

Due to the current production and service conditions, the main forms of gear tooth failure are the fatigue fracture of the gear tooth and the fatigue damage of the tooth surface, and the main factors affecting the two major fatigue life include: tooth surface and core hardness; effective The carburized layer is deep; the tissue of the surface and the heart, etc. Generally, the higher the surface hardness of the gear, the longer the fatigue life of the gear tooth; the effective carburized layer depth and core hardness are important factors affecting the fatigue fracture of the gear tooth, and the effective carburized layer depth must ensure that there is a gap between the carburized layer and the core. Sufficient strength to prevent the peeling of the carburized layer, but the effective carburized layer depth should not be too large, especially if the depth of the root part is too large, and the hardness of the center is too high, which will cause the decrease of the residual compressive stress on the surface and the decrease of the toughness of the center, which will affect the Fatigue performance, it can be seen that it is particularly important to correctly control the heat treatment process of vacuum carburizing and quenching.

1 Chemical composition of new gear steel

Select a batch of forged and vacuum heat-treated gear steel bars, and process them into spiral bevel gears by machining. Two vacuum carburizing and quenching processes are adopted for a batch of processed spiral bevel gears, normal carburizing and extended carburizing. For two kinds of carburized and quenched gears, and treated by the same shot peening process and grinding process, three of each are selected for fatigue bench test.

2 Grain size determination of gear fatigue fracture

The grain size of fatigue fractures of two kinds of gears and six samples were observed with a metallographic microscope, and the area with the largest grain size was selected to take pictures. The typical results are shown in Figure 1.

It can be clearly seen from the grain size structure in Figure 1 that the grains at the local area of the fatigue fracture of the gears treated by the two vacuum carburizing processes have an abnormal growth trend. For gears treated by normal vacuum carburizing and quenching, the trend of abnormal grain size growth is much milder, and sometimes it is almost impossible to see the abnormal growth of grain size; while the gear treated by the 915°C strong infiltration stage for 1 hour , the abnormal growth of the grain size is generally much more serious than that of gears treated by normal carburizing process.

(1) The reproducibility of the experimental data of the fatigue life of each gear bench is high, indicating that the experimental results are credible;

(2) The average fatigue life of extended carburized and quenched gears is more than 30% lower than that of normal carburized and quenched gears. , resulting in the reduction of hardness and strength and easy cracking; on the other hand, the abnormal growth of the grain size of the extended carburized gear is much more serious, and these factors will reduce the fatigue life of the gear.

3 Conclusion

3.1 The normal carburizing and quenching process adopted by the spiral bevel gear, the obtained structure and properties meet the technical requirements.

3.2 Prolonging the vacuum carburizing and quenching for 1 hour in the strong infiltration stage has almost no effect on the depth of the carburized layer, but it will cause non-martensitic structure on the local surface of the tooth root; in addition, the grain size of the gear will grow abnormally Phenomenon.

3.3 The average fatigue life of gears processed by vacuum carburizing and quenching for 1 hour is more than 30% lower than that of gears treated by normal carburizing and quenching process.

Vacuum carburizing equipment selection: RVC series vacuum carburizing furnace produced by SIMUWU company is a high-quality product for vacuum carburizing process. Good temperature control accuracy and temperature control uniformity ensure the effective vacuum heat treatment process. The equipment is easy to manage and maintain, greatly reducing maintenance costs. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc, which are widely sold in developed and developing countries.