Die steel contains more alloy elements, and elements with higher vapor pressure (such as Al, Mn, Cr, Si, Pb, Zn, Cu, etc.) are prone to evaporation when heated in vacuum. Therefore, the vacuum degree during quenching and heating should be properly controlled to prevent the evaporation of alloy elements. Especially the steel with high Cr content.
In order to reduce the thermal effect and structural stress caused by the temperature difference between the inside and outside of the heated die steel or parts, the complex or large section die parts should be preheated many times, and the heating speed should not be too fast, which is one of the keys to reduce or prevent deformation.
Large section gas quenched steel die parts should be treated in high pressure gas quench furnace as much as possible. If the air cooling speed is not enough, the oil quenching process must be adopted to prevent the white layer structure on the surface of the workpiece after oil quenching.
The heating temperature of vacuum quenching can be basically the same as or slightly lower than that of salt bath heating and air heating. However, it should be noted that the heating speed of the workpiece is much slower than the furnace temperature, so the average temperature and the holding time should be appropriately extended depending on the furnace loading.
Whether the charging is reasonable or not has a great influence on the quality after heat treatment. Considering that the vacuum heating is mainly based on radiation, the mold parts should be placed properly in the furnace, and the small parts need to be separated by metal mesh to make the heating and cooling uniform.
On 2018-08-08 11:45:46
