Process analysis and implementation key points of heat treatment using medium frequency induction heating machine for connecting rod forging dies

The size of the automobile engine connecting rod forging die is 340mm*180mm*70mm. The forging die works on a 25t mechanical forging press. During the working process, the die cavity of the forging die has to withstand impact loads and high temperatures, plus water-based graphite Liquid is used as the cooling and lubricating medium, and the surface of the cavity is subject to alternating hot and cold effects. Therefore, the mold should have high hardness, good thermal conductivity, good impact toughness and high temperature strength. In order to meet the working requirements of connecting rod forging dies, many heat treatment manufacturers use medium frequency induction heating machines for heat treatment, and the results are very good.

1. For hot forging dies, parts with large thickness differences and sharp corners should be protected to prevent local overheating. Methods such as wrapping asbestos ropes and wrapping iron sheets can be used to prevent the parts from cooling too quickly during the quenching of the forging dies. As for cracking, and in order to prevent the stress generated after high-temperature tempering, a medium-frequency induction heating machine was finally used for supplementary stress relief tempering, and the specification is 200°C.

2. In order to reduce quenching deformation and prevent cracking of large molds, it is important to note that the key to cooling is to control the pre-cooling time in air and the cooling time in oil. Pre-cooling can effectively reduce quenching internal stress to reduce deformation. . 5CrNiMo steel should be pre-cooled to about 780℃ (above the phase transformation point) and quenched with oil. Generally, the cooling time in the air is controlled within the range of 3 to 8 minutes, and the oil is discharged at about 200℃ (circulating oil is used, and the oil temperature is 70℃ (below), it can be air-cooled if it smokes but does not catch fire. The hardness after quenching is above 45HRC, otherwise it may cause cracking due to the huge internal stress inside the mold.

3. After the mold is oiled, it is not allowed to cool to room temperature before tempering to prevent cracking. It is advisable to temper the forging die multiple times to eliminate the stress of structural transformation, transform the retained austenite into tempered martensite, and stabilize the structure and size of the forging die.

4. The heat treatment process of automobile connecting rod forging dies made of 5CrNiMo and 4Cr5MoSiV steel is relatively mature. According to data, the service life of the former is 4,000 to 5,000 pieces, and the life of the latter reaches 10,000 pieces.

5. Some data recommend that the quenching temperature of 5CrNiMo steel be increased from 840 to 860°C to 900°C for heating and quenching, and then tempered at 500°C to obtain a single lath martensite, which can effectively prevent mold damage. early brittleness while also achieving the highest hardness.

The heat treatment process is a key factor affecting the quality of the heat treatment of the workpiece. Therefore, it is very important to master the heat treatment process of the workpiece. This article briefly introduces the heat treatment process of connecting rod forging dies and its implementation points, hoping to help you produce high-quality connecting rod forging dies.