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Using rare earth co infiltration technology to solve the problems of carburization of automobile gears

at present, China's automobile gears still have the problems of high carburization temperature, long process cycle, large gear deformation, short service life, poor quality and high energy consumption. How to solve the above-mentioned long-standing and difficult problems is a serious task for our scientific and engineering workers. After long-term research and production practice, we propose that the rare earth co infiltration technology can solve the above problems in many aspects. The technology of gear Carburization in China has reached a new level, and the product quality has reached or exceeded international standards

since China entered the WTO, the automotive market has gradually opened to the outside world. Some well-known foreign manufacturers of economically improved technology have set up factories in China and introduced a large number of advanced manufacturing equipment and advanced technology. It is expected that the production of all kinds of automobiles will exceed 4million this year, which will bring great impact and development opportunities to China's automotive industry. J with the development of the globalization trend of the automotive market, China is bound to become a major market for global auto parts manufacturers and suppliers. To seize this business opportunity, we must produce according to international standards. Automobile gears and their assemblies are extremely important parts of automobiles. If we can overcome the above problems (see Abstract), make them famous brand products, and make their gearboxes and rear axles become the direct suppliers of world-famous brand automobiles, participate in the world market competition and win market share, it will make great contributions to China's automobile manufacturing industry

rare earth co infiltration technology is a major scientific and technological invention of Harbin Institute of technology in the mid-1980s. Scholars first found that rare earth atoms whose atomic radius is 40% larger than that of iron can penetrate into the surface of steel. At the same time, they found that rare earth has a very obvious catalytic effect on chemical heat treatment processes such as carburizing, carbonitriding, nitriding, etc., which can increase the infiltration rate by 20% - 30%. Theoretical research points out that a small amount of rare earth (dozens of PPM) can also play the role of microalloying after penetrating into the surface of steel. It can effectively become the core of precipitation of the second phase such as carbide, carbon nitride or nitride, and then precipitate fine dispersed granular carbide and carbon nitride. These highly dispersed particles will become an obstacle to the growth of austenite to martensite shear, forcing martensite to transform into ultra-fine. This ultra-fine martensite has high strength and toughness. As a matrix, it is distributed with fine dispersed granular carbides, which is the best microstructure obtained after rare earth co infiltration. This best microstructure has higher contact fatigue and bending fatigue strength, as well as sufficiently high hardness, wear resistance and adhesive wear resistance. It can be seen from the above that the correct introduction of rare earth carburizing technology into gear carburizing can not only increase the carburizing rate by 20% - 30%, but also obtain the most metallographic structure that is difficult to obtain by other methods, resulting in a sharp increase in service performance

since the addition of rare earth into the carburizing agent can not only improve the carburizing speed, reduce energy consumption, reduce deformation, but also significantly improve the structure and performance, the introduction of rare earth into gear carburizing will raise China's chemical heat treatment process to a new level, and the product quality to a new level, so as to achieve the goal of international integration as soon as possible and participate in international competition

I. current problems and gaps in carburization of automotive gears

1. common problems

(1) carburization speed is slow, production efficiency is low, and energy consumption remains high

(2) high carburizing temperature and high carbon potential CP lead to poor metallographic structure, high grades of carbide, martensite, residual austenite, etc., large grade fluctuation and poor stability

(3) after heat treatment, the size distortion of the gear is large, the accuracy level is greatly reduced, the assembly interchangeability is poor, the transmission is unstable and the noise is high

(4) poor performance ① there are black structure and non martensitic structure on the surface. ② There is residual austenite on the outer surface. 6. Press the button switch too much on the lower body. ③ The hardness of the outer surface layer is low, and the phenomenon of low head of the surface layer of the hardness distribution curve is generally expected to reach 1.338 billion yuan this year, resulting in a sharp decline in wear resistance. ④ the contact fatigue and wear resistance of gears are not high, resulting in pitting and spalling on the tooth surface, resulting in early fatigue failure damage, which is particularly prominent in load vehicles and heavy engineering vehicles

2. There is a gap with the supporting exports in line with international standards

as mentioned earlier, China's automobile production has leapt to the third place in the world. Automobile production is basically monopolized by foreign investors. The way out for China's automobile industry is to provide a large number of high-quality spare parts. The automobile transmission system based on gears is extremely important for automobiles. If the automobile engine gearbox assembly and front and rear axle assembly based on gears can be matched with the world automobile manufacturers, it will be a major opportunity for China's automobile industry. Therefore, the gear industry, especially the gear heat treatment industry, should recognize the situation and make due efforts to reach the export level

in general, to achieve export supporting facilities, we must strengthen the process control of the following links in the processing process, otherwise there will be a gap

(1) the machining quality before heat treatment includes: surface roughness and dimensional tolerance, that is, the appearance quality and assembly accuracy before and after heat treatment. Everyone in our factory admires him for his technology

(2) materials and processing technology related to properties and dimensional deformation, including: steel composition control and purity, hardenability band control, band structure control, pre heat treatment of forging stock, isothermal normalizing and structure uniformity, cold processing stress relief, etc

(3) distortion control and accuracy grade control of gears in the process of carburization, quenching and tempering, assembly interchangeability, transmission stability and noise

(4) in terms of tooling and equipment, oxidation decarburization, workpiece surface cleaning, quenching oil cooling characteristics and cooling uniformity (including workpiece basket placement), etc

(5) metallographic structure difference: surface hardness and hardness gradient distribution, carbide, martensite and residual austenite grade control

(6) performance sampling inspection: ① gear bending fatigue and contact fatigue test. ② Bench life test of gearbox and rear axle assembly, etc

foreign businessmen usually carry out the following inspections on gear products:

(1) gear appearance inspection: ① commodity color. ② Tolerance dimension inspection. ③ Surface roughness

(2) assembly interchangeability inspection: inspection of assembly transmission vibration and stability, inspection of assembly transmission noise

(3) heat treatment quality inspection: ① surface hardness 62 ~ 64hrc. ② The layer depth inspection is evaluated according to 550hv. ③ Metallographic structure: General carbide, martensite and retained austenite

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