Analysis on heat treatment methods of die materials by die manufacturers

The properties of materials themselves need to be achieved by proper heat treatment. Only good heat treatment can achieve our expected performance expectations. According to the performance requirements of plastic mold materials, the heat treatment methods of plastic mold are mainly high temperature quenching, cryogenic treatment, high temperature tempering, and repeated for many times to achieve good mold performance through these different treatments.

1. High temperature quenching

In order to improve the rigidity and wear resistance of materials, general materials need to be heated to above 1030 ℃. At high temperature, various alloy elements are fully dissolved in the austenite, so as to obtain high matrix hardness during quenching. At the same time, vacuum treatment is adopted to ensure that parts will not be decarburized and oxidized. At present, the high-speed gas quenching furnace used in the semiconductor industry can heat the workpiece under high vacuum conditions through nitrogen protection, which not only ensures the decarburization and oxidation of the workpiece, but also prevents the evaporation of alloy elements. At the same time, the adjustable gas pressure within the range of 200-500Kpa is used to quench and cool the workpiece, which ensures full quenching of the workpiece while reducing deformation.

2. Cryogenic treatment and high temperature tempering

After quenching, the martensite transformation point (Ms point) of high alloy steel is higher than the room temperature. In order to improve the hardness and ensure dimensional stability, cryogenic treatment and high temperature tempering are usually required to ensure that the residual austenite is fully transformed into stable tempered martensite. We will calibrate the workpieces after vacuum quenching at room temperature to 100 ℃, and then put them into a cryogenic treatment box at - 140 ℃ for cryogenic treatment. The workpiece can be cooled and heated between - 140 ℃ and 230 ℃ without leaving the furnace to ensure that the workpiece will not be deformed or cracked due to entering or leaving the furnace. At the same time, due to the nitrogen protection, the oxidation cracking of the workpiece during tempering is also avoided. At present, for D2 materials, we usually directly complete three cycles from - 140 ℃ cryogenic to 230 ℃ tempering in cryogenic equipment. For steel grades tempered above 230 ℃, such as SAM97, ELmax, ASP23, we use vacuum tempering furnace. After vacuuming, 99.999% high-purity nitrogen is added as the medium to form convection by changing the blowing direction, which ensures the temperature uniformity of the workpiece and saves the tempering time.

3. Other auxiliary means

At the same time of improving the quality of quenching, tempering and cryogenic treatment, mold manufacturers have paid full attention to other aspects of the workpiece. The view that the cleanliness of heat treated workpieces has nothing to do with the treatment has been abandoned, and clean pretreatment has been added. The parts that will not be put into the furnace shall be vacuum degreased, degreased and dried through the vacuum cleaner. It removes all kinds of processing oil stains and debris from the workpiece, ensures that the workpiece into the furnace will not bring other impurities, avoids the decomposition of impurities during high temperature heating, pollutes the furnace environment and the workpiece itself, ensures the organizational cleanliness of the workpiece and the perfection of the processing quality from a microscopic perspective, and improves the service life of the workpiece.