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Influencing Factors of 20CrMnTi Gear Vacuum Carburizing and Quenching Deformation

Vacuum carburizing is the most widely used surface heat treatment process in the machinery manufacturing industry. It is a chemical heat treatment process in which steel workpieces are placed in carbon-containing media and heated to a high temperature to increase the carbon content of the surface layer of the workpiece. The vacuum carburizing process includes three basic processes of decomposition, absorption and diffusion.
The vacuum carburizing temperature has the following influences on the vacuum carburizing process and results:
① Influence the speed of vacuum carburizing, increasing the temperature can significantly accelerate the diffusion process, accelerate the speed of vacuum carburizing, and shorten the time of vacuum carburizing; ② affect the carbon concentration of the vacuum carburizing layer. It is ideal between 0.8% and 1.1%; ③If the temperature is too high, it is easy to cause the grain growth of the steel, reduce the toughness, and increase the possibility of warping and deformation of the parts; ④If the direct quenching process after vacuum carburizing is used, the vacuum carburizing The increase of carbon temperature will easily lead to the increase of residual austenite in the carburized layer and the corresponding prolongation of the time from vacuum carburizing temperature to quenching temperature; 920～930℃ are used most.
1 Vacuum carburizing holding time
The vacuum carburizing time is mainly determined according to the depth of the carburizing layer, but the influence of the vacuum carburizing temperature and the activity of the vacuum carburizing medium, the geometry of the parts, equipment and process characteristics must be considered at the same time. The actual carburized layer depth should be based on the required depth plus the grinding allowance after vacuum carburizing.
When the temperature is constant, there is a certain relationship between the depth of the seepage layer and the holding time. When the thickness of the required carburizing layer is deeper, the vacuum carburizing holding time is longer, which is usually determined by sampling inspection during the vacuum carburizing process.
2 vacuum carburizing depth
The appropriate depth of vacuum carburized layer depends on the working conditions of the part and the strength of the core material. The strength of the high carbonized layer is higher than that of the low carbon core. When the part is subjected to an external force, the surface stress is the largest, and gradually weakens towards the center. The depth of the vacuum carburized layer of the part should be able to ensure that the stress transmitted to the core is less than the strength of the core. Therefore, when the parts are subjected to the same load, the permeation layer can be correspondingly shallower for parts with higher core strength.
3. Technical measures for gear vacuum carburizing and quenching deformation.

Aiming at the factors of vacuum carburizing and quenching deformation of 20CrMnTi gears, the solutions are summarized as follows:
3.1 The effect of isothermal cooling after vacuum carburizing is obvious, and it is difficult to control in actual production, but it can be cooled by blowing after vacuum carburizing, and the air cooling time can be controlled, and it will stop when the gear surface temperature is close to 450°C (austenite stable zone). Blowing, the effect of suppressing deformation is ideal;
3.2 High-temperature tempering treatment after vacuum carburizing, the purpose is to transform the coarse structure obtained after vacuum carburizing into uniform fine-grained or point-like sorbite, which is convenient for machining and prepares for subsequent vacuum quenching; quenching When cooling, in order to reduce deformation, it is advisable to delay the stirring of quenching oil;
3.3 When selecting materials, select materials that are just hardenable or slightly alloyed, and strictly control the carbon concentration on the surface of the workpiece during vacuum carburizing;
3.4 Carry out the following technological process: hair damage normalizing → machining → vacuum carburizing → high temperature vacuum tempering → machining (pull keyway) → vacuum quenching, vacuum tempering → machining. The furnace is placed flat, the thin-walled gears are separated layer by layer with iron mesh, and the thin large disc-shaped gears are stacked one by one with washers.
Vacuum carburizing equipment selection: The RVC vacuum carburizing furnace provided by SIMUWU is an excellent product for this kind of process, with the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and is committed to giving customers the most convenient and efficient experience.