Vacuum carburizing process for gearbox shafts and gears

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Features of vacuum heat treatment

Compared with the traditional controllable atmosphere carburizing heat treatment, the vacuum heat treatment technology has the technical characteristics of “green, environmental protection, energy saving and high efficiency”. The technology of automobile products is gradually improving, and the shaft tooth vacuum carburizing heat treatment technology will gradually replace the conventional controllable atmosphere carburizing heat treatment technology as the main heat treatment production technology.

Transmission Shaft and Gear Specifications

When the car is running, the gearbox shaft and gear not only bear the torque and impact during high-speed rotation, but also bear strong vibration and friction, and must meet the requirements of running in a high temperature environment; as the key components in the gearbox, the shaft and gear products It needs to have good mechanical properties, comprehensive mechanical properties and high temperature resistance; after carburizing and quenching, the carbon content on the surface of the gearbox gear increases to form acicular martensite and retained austenite, which enhances the surface strength and wear resistance , the core still maintains a low carbon content, which can ensure high strength and impact toughness.

Principle of vacuum carburizing process

The carburizing medium in vacuum carburizing heat treatment often uses acetylene (C2H2) or propane (C3H8). Research data show that the use of acetylene can significantly improve the uniformity of carburizing layer depth at different positions of parts, especially for blind holes. Gears Parts, using acetylene medium, the depth uniformity of the root and pitch circle parts of the gear is the best; using propane is very easy to produce tar during production, and it is easy to cause the hardened layer in the contact area between the workpiece and the tooling to be unqualified, so we infiltrate in a vacuum furnace Acetylene is used as the carburizing medium for carbon heat treatment. In addition to larger shaft parts and large gear parts that require faster cooling rates that require oil quenching, general gear parts and gear shafts can be gas quenched. The picture below shows the actual vacuum furnace.

The difference between vacuum carburizing heat treatment and traditional controllable atmosphere carburizing heat treatment process

The basic process of the general traditional controllable atmosphere carburizing heat treatment process is described as degreasing, heating, strong infiltration (carburizing or carbonitriding), diffusion, heat preservation after cooling, vacuum quenching, post-cleaning, and vacuum tempering. In the strong infiltration (carbonitriding) and diffusion stage, a certain concentration of carbon and nitrogen atoms continuously infiltrate the surface of the part that has been completely austenitized. Through the strong infiltration and diffusion process, the surface of the part can be reasonably distributed in a gradient distribution. Then through the vacuum quenching process and vacuum tempering process, the hardened layer depth, surface hardness and core hardness that meet the technical requirements are finally achieved.

The process of vacuum heat treatment technology is basically similar to the traditional controllable atmosphere carburizing heat treatment process, the differences are as follows.

a.The strong infiltration and diffusion stage is in a vacuum state, using the principle of pulse carburizing, that is, through multiple strong infiltration (carburizing medium) + diffusion (nitrogen) and a concentrated diffusion process to achieve the final carburizing layer required process;

b.In a vacuum state, it can effectively avoid surface oxidation of parts, and no non-horse structure will be produced after heat treatment. At the same time, it can avoid the oxidation reaction of alloy elements on the surface of parts. The carburizing speed and efficiency are significantly improved, and the production cycle is significantly shortened. The surface hardness of parts, The residual compressive stress is effectively guaranteed to prolong the service life of parts. The figure below shows the surface metallographic structure after traditional carburizing heat treatment and vacuum carburizing heat treatment. It can be seen that the surface structure after traditional heat treatment is oxidized to form a non-martensitic structure layer.

Surface non-martensitic structure after traditional carburizing heat treatment (500×)

There is no non-martensitic structure on the surface after vacuum carburizing heat treatment (500×)

c.No CO, SO2 and other harmful gases or surface substances will be produced during the vacuum carburizing heat treatment process, and the environmental pollution is small, and it has the characteristics of green environmental protection;

d.The quenching process of vacuum heat treatment is quenched by gas continuous convection cooling, which has the characteristics of small heat treatment deformation;

e.Vacuum heat treatment quenching generally adopts the gas quenching method, and the quenching gas can be recovered to avoid the pollution of the quenching oil to the workpiece. The above picture shows the gear and gear shaft after vacuum carburizing heat treatment. Oil quenching is also used in the vacuum quenching chamber, which avoids a large amount of gas and liquid pollution. Vacuum technology has a strong purification effect on the surface of parts, and parts can save the cleaning and shot blasting process after heating;

Vacuum carburizing equipment selection: The vacuum carburizing furnace produced by SIMUWU company overcomes the blind hole carburizing problem that cannot be solved by traditional atmosphere thermal carburizing, and can avoid internal oxidation. The temperature of the vacuum carburizing process can reach 1700 degrees Celsius. The vacuum carburizing technology combined with high-pressure air-cooled quenching reduces deformation and shortens the process time. Vacuum carburizing combined with gas quenching can improve product quality by controlling the cooling rate in the quenching process, with low emissions, low energy consumption, and reliable quality. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.

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