Process analysis and implementation key points of heat treatment of connecting rod bolts using medium frequency induction forging heating furnace

The connecting rod bolt is a key component in the engine's working process. It cooperates with the crankshaft to complete the movement of the piston, allowing the engine to obtain power. During the working process, the bolts are subjected to uniform tensile stress. Therefore, production usually requires the bolts to have high hardness and long service life. In order to meet the needs of work, many heat treatment manufacturers use medium frequency induction forging heating furnaces for heat treatment, with good results.

1. Quenching temperature and heating time

After spheroidizing annealing, 40Cr has obtained a spherical pearlite structure. Considering that the transformation speed of spherical pearlite into austenite is slower than that of flaky pearlite, the heating temperature is increased to 860-870°C, which can give full play to the carbon and Chromium improves the hardenability and ensures that the core matrix of the connecting rod bolt is a medium-sized martensite structure. When it exceeds 870°C, coarse martensite will appear, so the heating temperature should be strictly controlled. The heating equipment should be a medium frequency induction forging heating furnace. The occurrence of oxidation and decarburization during the heating process should be avoided. The heating time should be determined through process tests based on the heating medium, power, and specific heating characteristics of the equipment. The basic principle is to ensure that the heat penetration, and the cementite particles are fully dissolved in the austenite to make the composition uniform.

2. Cooling medium, tempering temperature and time

The hardenability of 40Cr steel is very good. The required structure and performance can be obtained by using oil cooling instead of water cooling. At the same time, it can effectively prevent the drilled hexagonal head from quenching cracks. The hardness of the surface and core is above 50HRC.

40Cr steel is tempered in a medium frequency induction forging heating furnace at a temperature of 520-550°C.

3. Add normalizing process

If possible, adding a normalizing process before quenching and tempering can help improve the overheated structure that may occur during hot stamping, eliminate processing stress, and effectively prevent cracking during the quenching process. It should be noted that the heating temperature and time must be strictly controlled during the hot stamping heating process, otherwise it will cause early failure of the bolt.

4. In order to prevent early failure of bolts (such as fracture, plastic deformation due to stretching, etc.), during the quenching heating process using a medium frequency induction forging heating furnace, it is necessary to ensure that the heating speed meets the requirements to avoid oxidation of the thread surface during the heating process. Decarbonize. In addition, the micro-cracks present in the surface deformation layer during thread processing will reduce the strength and hardness of the thread, leading to early fracture failure.

It is very important to understand and master the heat treatment process and implementation points of the workpiece. It is the basis for ensuring the quality of the heat treatment of the workpiece. If you don’t understand anything about the above content, you can read more books on heat treatment. I believe you will gain a lot.