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Heat Treatment Process of Automobile Half Shaft

The semi-axle is an important structural part for the rear axle of the automobile to receive torque and a certain impact force. It is one of the main components for transmitting power. During the working process, the torque from the main reducer and differential is finally transmitted to the driving wheels. To transmit the torque of the engine and drive the conical teeth of the rear axle to move the wheels forward, the spline has both sliding and impact. The service life of the semi-shaft depends on the compression resistance of the spline teeth and requires high static torsion. Strength and torsion fatigue life, good fatigue resistance and impact toughness, etc., deep hardened layer, etc., to meet the normal needs of solid semi-shafts.

1. Material Selection And Technical Requirements

Automobile half-shafts are usually made of medium carbon steel or medium carbon alloy steel, etc., and are quenched and tempered or normalized. In order to prevent quenching cracking, oil-immersion or water-immersion cooling methods are used. Intermediate frequency quenching uses water, polyvinyl alcohol or polyether solution as the cooling medium, which can effectively inhibit the occurrence of quenching cracks. Generally, trucks use full-floating semi-axles, and the vulnerable parts are at the connection between the rod and flange, or the spline torsion and the connection between the spline and the rod due to impact, resulting in fatigue fracture, and its service life mainly depends on the spline tooth The compressive and abrasion resistance performance. The passenger car is a semi-floating axle.

For small cars, 40Cr and 40MnB are mostly used. For half-shafts with a diameter of less than 40mm, medium-carbon quenched and tempered steels such as 40 and 45 steel are used. For heavy-duty vehicles, the half-shafts are made of alloy structural steels with higher hardenability, such as 40Cr and 40CrMn, 40MnB, 40CrMo, 40CrNiMo, 47MnTi, 40CrMnMo, 40CrMnTi, 40CrNi, etc.

2. Preparatory Heat Treatment Process of Half Shaft

The semi-shafts are usually made of medium carbon steel or medium carbon alloy steel, etc., and individual low carbon steel is carburized and then quenched. The purpose of the quenching and tempering treatment of the automobile half shaft is to obtain a uniform tempered sorbite structure, so that the half shaft center has good comprehensive mechanical properties, to ensure the strength and good toughness of the matrix, and to make the final surface quenching. Organizational preparation.

3. Surface Hardening Treatment of Half Shaft

For light-duty trucks and cars, the depth of the hardened layer of flanged semi-shafts (with a diameter of less than 50mm) is determined as required, as shown in Figure 3-39. Here, 40Cr is taken as an example to briefly describe the technical requirements for surface hardening of the semi-shafts: quenching The hardness of the pre-tempered matrix is 321～375 (HBS), the hardness after quenching reaches 45～58 (HRC), the hardness after tempering is required to be 45～50 (HRC), and the depth of the hardened layer is between 2.5～5mm.

Generally, the semi-shafts of automobiles use ring inductors for continuous quenching and heating. In order to enhance the efficiency of heating, silicon steel sheet magnets are often installed on the effective ring. The medium-frequency current on the circle is driven from the rounded corner to the place corresponding to the rounded corner, where rapid heating can be obtained within 10s, and a very reasonable surface hardening layer can be obtained.

The process parameters and technical requirements of the surface heating and quenching are as follows: the heating power is 150-300kW, the frequency is 2500-3000Hz, the half-shaft adopts intermediate frequency induction heating for surface quenching, the cooling water flow rate is not less than 10m/s, and the surface compressive stress of the workpiece after quenching It can reach 700-800MPa, and after tempering at 250℃, it will drop to 400-500MPa. Therefore, to ensure that there is a certain residual compressive stress on the surface of the half shaft, it will help to make the half shaft have a higher fatigue strength. It can be self-tempered or tempered in the furnace. The temperature is controlled at 180 ~ 250 ℃, and the time is 90～120 min. In order to ensure uniform heating of the rounded corners of the flange, a permeable 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 tempered in a pit furnace or box furnace; it can also be tempered in a furnace immediately after induction quenching. Facts have proved that the former tempering method is beneficial to prevent cracks before tempering.

The surface quenching hardness of the half shaft can be tested by a hardness tester and a file. The Rockwell hardness tester is usually used to determine whether the hardness after quenching meets the technical requirements. In the practice of heat treatment, it is necessary to ensure that the surface hardness of the part is qualified.

The straightening of the half shaft is as cold as possible, because after heating with oxyacetylene hot spot, once the temperature is higher than the phase transition temperature, coarse martensite will be formed after quenching, and the stress will be great, so the half shaft is subjected to repeated loads. , The gradual expansion will cause fatigue fracture.

Multi-turn cylindrical induction coil is used for induction heating to ensure the uniform heating temperature of the half shaft. The recommended size is Φ60mm×(15～25)mm, and the quenching movement speed of the spline and the rod are 0.36m/min and 0.30m, respectively /min.