Is the medium frequency induction hardening machine the best equipment for heat treatment of half shafts?

The half shaft is an important structural part of the automobile's rear axle that is subject to torque and a certain impact force, and is the main component for transmitting power. Therefore, the half shaft is required to have good fatigue resistance and impact toughness. In order to improve its service life and performance requirements, a medium frequency induction quenching machine is generally used to heat treat it to meet its performance requirements. From the technical requirements of the half shaft, it needs to be tempered and surface quenched to obtain ideal mechanical properties. Therefore, the formulation of the heat treatment process must be based on the requirements of the half shaft and carried out by scientific, reasonable and economical means.

(1) Quenching and tempering process of half shaft. The purpose of the quenching and tempering treatment of automobile half shafts is to obtain a uniform tempered sorbite structure, so that the center part of the half shaft has good comprehensive mechanical properties, ensure the strength and good toughness of the matrix, and prepare for the final surface quenching Organizational preparation. The quenching and tempering process specifications for several types of steel are as follows:

Process specifications for quenching and tempering treatment of some automobile half shafts:

(2) Surface quenching treatment of half shaft. The preparatory heat treatment before surface quenching is normalizing, annealing or quenching and tempering, which obtains reasonable matrix hardness and strength, and prepares the structure for surface quenching.

1. Heat treatment technical requirements. The depth of the hardened layer of the flange-type axle shaft (diameter below 50mm) of light trucks and cars is determined according to the requirements. Taking 40Cr as an example, the surface quenching technical requirements of the axle are briefly described. The hardness of the quenched and tempered substrate before quenching is: 321 to 375HBS, the hardness after quenching reaches 45~58HRC, the hardness after tempering is required to be 45~50HRC, and the hardened layer is between 2.5~5mm.

The depth requirements of the hardened layer are as follows: the fillet at the root of the flange must be hardened. The minimum diameter of the fillet hardened area is 25% larger than the diameter of the half-shaft rod, 10% of the diameter, and 15% of the diameter of the rod. A small amount of ferrite is allowed in the hardened zone, and the amount of ferrite at semi-martensite should be ≤ 20%. According to the working conditions of the half shaft and the main link that causes quality problems, the hardened layer must start from the root of the flange to the end of the spline 4 to 7 mm. If the root of the packing is not hardened or the hardness is not enough, the overall quality of the half shaft will be greatly reduced strength.

Generally, automobile half shafts use ring inductors for continuous quenching and heating, and some use half-turn inductors for continuous quenching and heating. The half-turn half-shaft inductor continuous quenching technology has the following advantages compared with ring inductors:

a. Solve the problem of low hardness of spline tooth top

b. Eliminates the problem of soft band in spline transition, prevents "magnetic field jump" in the spline transition area, and avoids the occurrence of soft band phenomenon.

c. It can make the hardened layer at the small diameter shaft root of the stepped shaft straight and continuous.

2. Process parameters of surface quenching. The heating power is 150~300kW, the frequency is 2500~3000Hz, the half shaft uses medium frequency induction heating for surface quenching, the cooling water flow rate is not less than 10m/s, the surface compressive stress of the workpiece after quenching can reach 700~800MPa, after tempering at 250℃ , dropped to 400~500 MPa. Therefore, ensuring that there is a certain residual compressive stress on the surface of the half shaft will help the half shaft have a higher fatigue strength. Self-tempering can be used or tempered in a furnace. The temperature is controlled at 180~250°C and the time is 90～120min. In order to ensure uniform heating of the flange fillet, a magnet can be added to the inductor. Tempering after surface quenching is generally performed by induction heating and tempering immediately after quenching, and then further tempering in a pit furnace or box furnace; it can also be tempered in the furnace immediately after induction quenching.

Most of the heat treatment of half shafts is carried out by medium frequency induction hardening machine. This equipment can not only be used for quenching heat treatment of half shafts, but also can be used for heat treatment of gears, sprockets, spline shafts, etc. As a leader in the induction heating equipment industry, Zhengzhou Gou's has rich theoretical knowledge and practical experience. Welcome to call us for consultation.