To prolong the service life of the mold, the optimization of the heat treatment process is very important. The main factors affecting the quality of the heat treatment are heating speed, quenching temperature, cooling rate and tempering temperature. After analysis and practice, the following heat treatment process is suitable for general enterprises, which can meet the mechanical performance requirements of 4Cr5MoSiV steel at high temperature.
The temperature is 600 ~ 630 ° C, the holding time is 1.5 ~ 2h depending on the size of the mold, and then the temperature is raised to 830 ~ 850 ° C, and the temperature is maintained for 1.5 ~ 2 h. This process is pretreatment before quenching, which can reasonably adjust the microscopic defects inside the workpiece. Prepare the necessary conditions for quenching.
On the basis of pretreatment, the heating temperature is raised to 1040 ~ 1080 ° C, the temperature is 2 ~ 2.5h, and the oil quenching is performed. When the temperature of the workpiece drops to about 130 °C, the air cooling is taken out from the oil.
After quenching, there is a large internal stress inside the workpiece, and the workpiece must be tempered in time to eliminate the stress generated during quenching. In order to avoid cracking of the workpiece, it should be heated evenly before tempering. The specific method is to heat the workpiece to 380~400°C for 1h, then slowly heat up to 580~600°C for a tempering. The holding time is 2h, then the air is cooled to normal temperature. The second tempering was carried out, the tempering temperature was 560-580 ° C, the holding time was 2 h, and then the air was cooled.