China’s truck gear steel basically follows the brand of the former Soviet Union. For a long time in the past, 20CrMnTi dominated the world. China’s truck gear not only has a single brand, but also has large fluctuations in steel composition, wide hardenability bandwidth and many inclusions, resulting in large heat treatment deformation and low service life of truck gear. With the introduction of foreign advanced models and the localization of various truck gear steel, 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 localized, which basically meets the domestic demand for medium and small modulus automobile and truck gear steel.
Stahl Steyr series truck gear steel adopts German standard, which is divided into large, medium and small according to truck gear module, and 18crnis, 20mncrs and 16mncr are used respectively. Among them, the localization of medium and small module gear steel zomncrs and 16mncrs has been solved, and the materials supplied by the steel factory basically meet the German standards. However, for 18crnis, due to the high content of Cr and Ni and high hardenability, the heat treatment process is difficult to control and the price is high. Direct localization is not the best scheme. The large module heavy-duty truck gear used in domestic construction machinery generally adopts the 18crzni4w of the former Soviet Union. Although the use effect is good, it is expensive and not suitable for truck gear material. From the domestic gear steel brand, 20crni3 is similar to 18crnis, but the hardenability is far lower than 18crni18, and the price is also high. Therefore, using 20crni3 as large module truck gear can only be an expedient measure.
According to the analysis of the current situation of heavy vehicles in China, the two problems of overload and poor road conditions are more serious and can not be overcome in the short term, which makes the truck gears often bear more overload impact load. Overload impact load is between fatigue strength and fracture stress. It has a great impact on the service life of truck gears and often leads to early failure of truck gears. This view is also confirmed by the analysis results of truck gears with early failure of star Steyr. Therefore, the overload resistance of the material must be considered when selecting the truck gear material. The overload resistance of carburized steel mainly depends on the core strength and its related toughness indexes. A large number of tests show that the critical overload load and impact fracture stress are related to the fracture toughness of carburized steel. Therefore, alloy elements that can improve the toughness of materials, such as Ni and Mo, can improve the overload resistance of materials. Although the conventional properties of 20CrMnTi steel are better, the impact toughness of notchless impact specimen when the infiltration layer reaches 1mm is nearly 10 times lower than that of Cr Ni steel. From this point, Cr Ni or Cr Ni Mo series steel should be selected for the gear of large modulus heavy-duty truck.