Among the introduced steel grades of the driving and driven gears of the rear axle, there are mainly Ni Cr Mo, Cr Mo and ZF series safa320h, 21nicrmo5h, ZF7, SCM 822h and other steels. After heat treatment, Ni Cr Mo series gear steel has high strength, good toughness, strong compressive capacity and easy quality assurance. As long as the heat treatment process is reasonable and does not lead to too high core hardness, the service performance is better. In recent years, the rear axle gear of medium-sized truck has gradually introduced SAE8620H steel and sae8822h steel from the United States.
In terms of gearbox gear, due to the poor strength toughness matching of Mn CR series steel, the grain is easy to grow and prone to quality problems, Cr steel and Cr Mo steel series commonly used in Japanese automobile industry are gradually adopted. For parts with small bearing, high precision and good wear resistance, scr420h and scm415h with low carbon content and small deformation can be introduced. SCM420H can be introduced for parts with high load and used to transmit engine torque, mainly considering fatigue performance. ZF steel in Germany has good properties, simple alloy elements and low price, and has the prospect of popularization. However, due to the imperfect strengthening mechanism of this kind of steel on boron, further theoretical and application research is needed.
The domestic heavy truck gear steel basically follows the brand of the former Soviet Union. In the past, 20CrMnTi steel was used for a long time. It not only has a single variety, but also has a wide fluctuation range of steel composition, wide hardenability bandwidth and many inclusions, resulting in large gear heat treatment deformation and low service life. With the introduction of foreign advanced models and the localization of various gear steels, the level of gear steel in China has reached a new level. At present, Cr Mn series steel in Germany, Cr Mo series steel in Japan and sae86 series steel in the United States have been gradually localized, which basically meets the domestic demand for small and medium modulus automobile gear steel. According to the application status of domestic heavy-duty vehicles, 20CrNi2Mo steel in the United States and 17CrNiMo6 steel in Germany are widely accepted as gear materials for high modulus heavy-duty vehicles, and Cr Ni or Cr Ni Mo series steels are popularized.