Research progress of gear materials and heat treatment technology in China

As one of the most basic transmission parts in the mechanical industry, gear can continuously transmit power by using tooth contact. Gear transmission is the most widely used transmission form in mechanical transmission. It has the advantages of high efficiency, compact structure, reliable operation, long service life and constant transmission ratio. Many automation equipments, such as instruments, automobiles, machine tools, heavy machinery and so on, are inseparable from gears.

In the process of gear operation, the tooth part and the tooth surface will be subjected to large friction, bending stress and contact stress, and even to large overload impact force when the mesh is uneven, which will cause different forms of damage and failure of the gear, thus affecting the service life of the gear. In order to prolong the service life of the gear, it is required that the gear can bear many kinds of damages in the working process. The basic requirement is that the surface has high hardness and wear resistance, while the center can resist large impact and large bending deformation as a whole. Not only that, with the improvement of industrial production and national living standards, the technical parameters of mechanical equipment are developing towards high speed, high load, low noise and lightweight, which puts forward higher requirements for the use performance of basic components such as gears. In the era of environmental protection and efficient use of energy, the utilization ratio of materials and energy in gear production has also become an important indicator in gear production.

Although, there are still many deficiencies in the current gear production and manufacturing technology in China, such as high oxygen content of gear steel, too wide harden band, low machining accuracy of gear, and insufficient utilization of materials. But researchers have done a lot of research work for each link of gear production process, and also made some valuable breakthroughs and progress. This paper mainly expounds the development and breakthrough of gear production technology in recent years from the four angles of gear material, gear heat treatment process, gear machining process and new gear forming process, so as to provide reference for further innovation of gear production technology in the future.

At present, there are some problems in domestic steel, such as too high oxygen content, large hardenability bandwidth dispersion and immature metallurgical process, resulting in too high level of sulfide inclusions. The improvement of gear materials in our country is mainly from the optimization of existing gear materials and the creation of new gear materials.

The low Cr Ni steel researched and developed by the scholars of Xi’an University of science and technology is based on the existing composition of carburizing steel. Through fine-tuning the alloy element content and relevant research and development work, the demand for Cr and Ni alloy elements in this new steel is relatively low, and these two elements are rare alloy elements in China. Compared with Cr MNTI series steel, the hardenability of the steel is better. With proper heat treatment, the plasticity, impact toughness and strength index can be improved. From the existing practice results, the characteristics of good performance, long life and low cost are the significant advantages of the steel for gear production.

ZHY gear proves that Ti Nb microalloyed 20crmntinb steel is more suitable for gear production. By means of thermal simulation carburizing method, two kinds of Ti Nb microalloyed gear steels 20CrMnTi and 20crmntinb were tested. From the test results, the growth rule of austenite grain was obtained when they were kept at 930 ℃ ~ 1200 ℃. The results show that after adding 0.048% niobium and 0.038% titanium, the particle spacing of 20CrMnTi Nb steel is significantly lower than that of 20CrMnTi steel containing 0.054% titanium, and the austenite grains of the steel do not grow and mix obviously after austenizing at 1000 ℃ for ten hours, which shows that it is suitable for high temperature carburizing process.

The new bainite steel developed by Xi’an University of technology has strong hardenability. After rolling, forging or die forging and air cooling, new bainite structure can be obtained. The new bainite steel obtained by non tempering and low temperature tempering has better mechanical properties. This process is relatively simple. In the actual production process, the heat forming and heat treatment process can be combined. Large deformation stress and quenching crack will not appear in the heat treatment process of this new bainite steel. It has the characteristics of high strength, toughness, low cost and easy to weld and alloy.

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