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Vacuum heat treatment of main and driven gears of automobile main reducer

The driven large gear and the driving pinion used in the automobile reducer are generally made of 20CrMnTi material, and the quality requirements are very strict. In actual production, we have formulated and implemented the following vacuum heat treatment process. The driven large gear adopts three heat treatment processes, and selects the best process parameters for quenching with a quenching machine tool. After the inspection of metallographic structure and mechanical properties, it fully meets the requirements of the drawings. Now take the driven large gear and the driving pinion as an example to introduce as follows. The materials of the workpieces are all 2OCrMnTi steel, and the geometry is shown in the figure. The process is forging→heat treatment→roughing→vacuum heat treatment→machining→vacuum heat treatment→finishing.

Also according to this process, there will be no problem of inner hole expansion.

The above treatment, heating is carried out in the box furnace, and the quenching machine tool is cooled by a water spray device, which has nothing to do with the frequency of the high-frequency machine. Before operation, the height of the mandrel of the quenching machine and the relative position of the water spray ring should be properly adjusted. When the heated workpiece is loaded into the mandrel, the upper opening of the workpiece should be tightly covered with a cover plate to prevent cooling water from being sprayed into the inner hole and affecting the shrinkage effect. This method is also suitable for inner hole shrinkage treatment of medium wall thickness tubular workpieces.

The vacuum heat treatment process is as follows:

1 Normalizing

This is the first heat treatment process. The workpieces are heated in a bell-type furnace, 20 pieces are installed in each furnace, and processed according to the process curve shown in the figure below, and three samples of the same material are placed in the same furnace, with a size of φ20×200mm.

The purpose of normalizing is to eliminate the stress and structural defects of forging, obtain the most favorable organization and hardness for cutting, and prepare the organization for the final heat treatment of the workpiece.

2 Tempering

This is the second heat treatment process. The purpose of quenching and tempering treatment for important parts such as large gears and driving shafts that work under alternating loads is to obtain certain strength, hardness and good comprehensive mechanical properties to ensure the technical requirements of the core.

3 Gas carburizing, vacuum quenching, vacuum tempering

3.1 Carburizing
It is carried out in a gas carburizing furnace, and the process is shown in Fig. After carburizing treatment, the carburized layer of the large gear is 1.8mm, and the depth of the carburized layer of the driving shaft is 1.9mm.

3.2 Vacuum quenching, vacuum tempering

After carburizing, the workpiece is slowly cooled to room temperature, and then quenched and tempered at low temperature. Quenching and heating use a gas carburizing resistance furnace (appropriately drip some medium oil during the heating process to prevent the workpiece from being oxidized and decarburized), and the tempering is carried out in a vacuum tempering furnace. The large gear is vacuum quenched and vacuum tempered according to the process curve shown in the figure below.

In order to prevent and reduce the deformation of the large gear, the press quenching process is adopted, and the large gear that has been heated and quenched for a period of time is quickly hung on the special mold of the quenching machine tool, so that it is automatically pressed according to the pre-input process parameters. Quenching to complete the entire quenching process.

The large gear after vacuum tempering, the inner hole deformation is less than 0.02mm, the bottom surface warpage deformation is less than 0.10mm; the surface hardness is HRC60, the core hardness is HRC38; the metallographic structure surface is martensite and retained austenite grade 2, Carbide grade 1, core ferrite grade 1, meet the technical requirements.

Deformation after vacuum tempering: deformation at φdmm ≤ 0.15mm; tooth hardness HRC61, core hardness HRC39; metallographic structure surface martensite and retained austenite grade 3, carbide grade 1, core ferrite Level 1 also meets the technical requirements.

4 Summary

20CrMnTi carburized steel is superior in strength and toughness to 20CrMnMo steel. It has the advantages of fine grain, high strength and high toughness, but carburizing is easy to be saturated to form network carbides. Therefore, the carburizing temperature should be reduced in production, and weak penetrant. It is suitable to use this steel to make gears with large modules.

We use this material to manufacture and produce large gears and pinions, and formulate and implement heat treatment processes according to the current production conditions to make the products meet the technical requirements. Therefore, the selection of 20CrMnTi steel is completely suitable.

Using a quenching press is a better way to reduce gear deformation at present. In order to minimize the deformation, it is first necessary to design a suitable quenched tire to ensure accuracy. In addition, it is necessary to select the best process parameters, such as formulating the inner ring and outer ring. , The matching pressure of the center pressure head, the temperature of the quenching oil and the amount of fuel injection, etc., the only way to ensure the high quality of the gear and the technical requirements of micro-deformation.

Selection of heat treatment equipment: GH-GCF series gas carburizing furnaces produced by SIMUWU are high-quality products for carburizing carbon steel parts. SIMUWU specializes in 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.