Since the mid-1980s, China’s gear industry has developed rapidly. Due to the high requirements of technical parameters, the gear required by automobile puts forward higher requirements for the quality of gear heat treatment. In order to further improve the quality level of gear heat treatment in China, meet the needs of automobile gear industry and catch up with the international advanced level faster, a large number of new gear heat treatment processes have been introduced while independently developing new processes in China, and great development has been made. The following introduces several new heat treatment processes of automobile gears with broad application prospects.
1. Laser quenching
Laser quenching has the characteristics of small workpiece deformation, fine and uniform grains in the quenching area, clean working environment and no need to grind teeth after treatment. It has a unique effect on improving the mechanical properties of gears. In order to improve the absorption rate of laser, the gear surface is often blackened before treatment. Many beam conversion systems have been developed at home and abroad to obtain uniform quenching belt. In recent 10 years, the research and development of laser quenching have developed rapidly. After laser quenching, the effective hardened layer depth of gears with certain geometric parameters is about 0.8mm, and the hardness of hardened layer reaches hrc48 ~ HRC55. The practical application effect is ideal. At present, laser quenching has been widely used in many industrial fields, such as automobile, metallurgy, heavy machinery and so on.
2. Low pressure vacuum carburizing
Low pressure vacuum carburizing not only makes the workpiece surface not oxidized and has no pollution to the environment, but also improves the deformation when combined with gas quenching. Increasing the carburizing temperature can reduce the treatment time and reduce the gas consumption and energy consumption. Through the improvement of furnace technology and the optimization of process parameters, the problems of carbon black damage to insulation and insufficient uniformity after vacuum carburizing can be eliminated. The process has been gradually applied in the automotive industry in developed countries. For example, Opel automotive company of Austria has introduced low-pressure vacuum carburizing heat treatment production line, which has been applied to the development and production of F17 and m20-32 transmissions.
3. BH catalytic infiltration process
By changing the cracking process of carburizing agent and destroying the formation of gas film layer, BH catalyzing process makes carburizing agent produce a certain number of positive tetravalent carbon ions and a small amount of active nitrogen atoms in the cracking process, and promotes the full cracking of carburizing agent at low temperature, so as to activate the surface of parts and increase the absorption of carbon by parts. In a factory, BH technology is used for carburizing the half shaft gear, the production efficiency is increased by 20%, and the power saving per heat is 90kw · H. At present, the problems that need to be further solved in this process are pipe blockage and carbide morphology control of carburized layer.
4. Rare earth co infiltration technology
Rare earth co infiltration technology makes rare earth penetrate into the surface layer of steel to play the role of microalloying, refine the structure and improve the performance. It has a good effect of promoting infiltration, saving energy and improving production efficiency. When the carbon potential CP > 1, the catalytic infiltration effect is more obvious. The production practice of a factory shows that the rare earth co infiltration technology can greatly improve the uniformity of tissue composition and prolong the service life of the die. The gears produced by this technology meet the gear metallographic inspection standards, the qualified rate is significantly improved, and the return rate of users is only 1% ～ 2%.
5. Liquid oxynitride surface strengthening treatment technology
Liquid oxynitride surface treatment technology is the latest metal salt bath surface strengthening and modification technology in the world. It can greatly improve the surface hardness, wear resistance and corrosion resistance of gears, and make gears have excellent performance of anti fatigue and no deformation. In recent years, this technology has been widely used in industry, involving many industries such as automobile, locomotive gear and so on.