There are many steel grades for gears of medium and heavy duty trucks in China, mainly to meet the requirements of the introduction of foreign advanced automobile technology at that time. In the 50s, China introduced the production technology of medium-sized cargo vehicles (that is, the original model of the "Liberation" brand) from the former Soviet Union Rikhachev Automobile Plant, and also introduced the 20CrMnTi steel grade of automobile gears produced in the former Soviet Union.
After the reform and opening up, with the rapid development of China's economic construction, in order to meet the needs of the rapid development of China's transportation, since the 80s, China has planned to introduce all kinds of advanced models from industrially developed countries, and all kinds of foreign advanced medium and heavy cargo vehicles have also been continuously introduced. At the same time, China's large automobile factories cooperate with famous foreign automobile companies to introduce foreign advanced automobile production technology, including the production technology of automobile gears. At the same time, the level of steel smelting technology in China is also constantly improving, the use of ladle secondary smelting and composition fine-tuning and continuous casting and rolling and other advanced smelting technologies, so that steel mills can produce high purity, hardened performance band narrowed gear steel, so as to achieve the introduction of automotive gear steel localization, so that China's gear steel production level to a new level. Nickel-containing high hardenability steel for domestic heavy-duty vehicle gears suitable for China's national conditions has also been applied and achieved good results. The heat treatment technology of automotive gears has also developed from the original 50-60s using well-type gas carburizing protection to the current widespread use of computer-controlled continuous gas carburizing automatic line and box-type multi-purpose furnace and automatic production line (including low-pressure (vacuum) carburizing technology), gear carburizing pre-oxidation treatment technology, gear quenching control cooling technology (due to the use of special quenching oil and quenching cooling technology), gear forging billet isothermal normalizing technology, etc. The adoption of these technologies not only makes the carburizing quenching distortion of gear effectively controlled, the gear processing accuracy is improved, and the service life is extended, but also meets the needs of mass production of modern heat treatment of gears.
Relevant literature points out that the life of automobile gears is mainly assessed by two major indicators, one is the contact fatigue strength of the gear, and the other is the bending fatigue strength of the gear. The former is mainly determined by the quality of carburizing and quenching, and the latter is mainly determined by the gear material. To this end, it is necessary to have a more comprehensive understanding of the requirements, properties and heat treatment characteristics of carburized steel for automotive gears.
