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Micro-alloyed vacuum carburized gear steel

The common feature of the new gear steel is that it is micro-alloyed and used after vacuum carburizing, so that resources and energy can be saved in the production process of gears, and it has high performance during use.

1 High temperature carburizing gear steel

Experiments show that in order to obtain an effective hardened layer depth of 0.9 ~ 1.0 mm, when carburizing at a temperature of 1050 °C, the entire treatment time is shortened by 44% compared with the conventional carburizing at a temperature of 930 °C, and the effective hardening layer depth is It can be controlled within the range of ±0.1 mm, and the carburizing time can be greatly shortened when the carburizing temperature is increased from the commonly used 930 °C to 1 000 °C. The steel is prone to oxidation at high temperature, so vacuum carburizing should be used. Because vacuum carburizing does not produce grain boundary oxidation, it does not reduce strength and toughness, and vacuum carburizing is carried out at a high temperature where the diffusion rate of carbon is quite large, so that the carburizing time is greatly shortened. Promising carburizing treatments.

High temperature carburized steel (970 ~ 1 050 ℃ vacuum carburizing) is easy to coarsen the austenite grains due to the high temperature. In Japan, AI is often used to solidify N to form AIN to suppress abnormal grain growth. However, only adding Al and N at a temperature of 970 to 1050 °C cannot prevent the coarsening of austenite grains, so elements such as Nb, V, and Ti should be added. The carbonitride of these elements is used to prevent grain coarsening.

2 High strength and toughness gear steel

With the demands of high output, high performance and light weight of automobiles, it is necessary to increase the load of gears and increase the strength of steel in order to restrain the enlargement of gears.

For heavy-duty gears subjected to impact, on the premise that the matrix has high strength and toughness, it is important to prevent the formation of carburizing cracks, and the key to improving the crack resistance of the carburizing layer is to reduce or eliminate the grain boundaries that may occur during carburization. Incomplete quenching structure formed by oxidation and improve the toughness of the infiltrated layer. Usually by increasing the fatigue strength to improve the strength of gear steel, it is necessary to limit the content of Si, Mn and Gr to reduce the oxidation and black structure in the surface; increase the content of Mo to increase the hardenability of the carburized layer and improve the surface hardness of the carburized layer; in order to improve the For the toughness of the carburized layer and the core, Al, N and Nb can be appropriately added. In addition, the most effective measure is to use ultra-low oxygen steel with oxygen content ≤10×10^-6.

3 Conclusion

In order to adapt to the development of the automobile industry in the future, a vacuum carburizing gear steel that saves resources, energy and low cost and high performance is developed. By adding microalloying elements Al, Nb, Ti, N and B, the grains of cold forged steel are refined and the cutting performance is enhanced. The addition of Nb, Ti and other elements also saves carburizing time during high temperature vacuum carburizing, thereby reducing production costs; adding trace elements also enhances the fatigue properties of high-strength and toughness gear steels.