The heat treatment of the mold includes annealing after forging, high temperature tempering or low temperature tempering after roughing, quenching and tempering after finishing, and low stress tempering after electric spark and wire cutting. Only the hot and cold processing works well together to ensure a good mold life.

When the mold cavity is large and the wall is thin, the upper limit of the normal quenching temperature is required to increase the amount of retained austenite so that the mold does not swell. The rapid heating method has a short heating time, a reduced tendency to oxidative decarburization, and a small grain size, and the quenching deformation of the large tool of the carbon tool steel is small. For high-speed steel, low quenching and high-returning process are better, quenching temperature is low, and tempering temperature is high, which can greatly improve toughness. Although the hardness is reduced, it is extremely effective for improving the life of the mold due to fracture or fatigue failure. Usually Cr12MoV steel is quenched and heated at 1000 ° C, oil cooled, and then tempered at 220 ° C. If the heat treatment can be performed once before the heat treatment, that is, heating to 1100 ° C for heat preservation, oil cooling, and 700 ° C high temperature tempering, the mold life can be greatly improved. In the early 1970s, we also achieved good results in the high-quenching and high-return heat treatment of wire-clamp hot forging die for 3Cr2W8V steel, and the life expectancy was more than doubled. Using a low-temperature nitrocarburizing process, the surface hardness can reach 1200HV, which can greatly improve the life of the mold.

Low-temperature electrolytic sulphurization can reduce the friction during metal deformation and improve the anti-seizure performance. The cold extrusion punch is made by using 6W6Mo5Cr4V steel. After low temperature nitrocarburizing, the service life is increased by more than 1 time on average, and then the low temperature electrolytic sulfurizing treatment can further improve the service life by 50%. There is a large residual stress after the mold is quenched, which often causes the mold to deform or even crack. In order to reduce the residual stress, the mold should be tempered after being quenched, the tempering should be sufficient, and the tempering is insufficient to produce pre-grinding cracks. For carbon tool steel, after tempering at 200 °C for 1 h, the residual stress can be eliminated by about 50%, and the residual stress after tempering for 2 hours can be eliminated by about 75% to 80%, and if it is tempered at 500 to 600 °C for 1 hour, the residual stress can be eliminated. 90%.

A punch of CrWMn steel in a factory was tempered for 1 h after quenching, and it was broken shortly after use. When tempered for 2.5 h, no cracking was found during use. This indicates that the tempering is uneven. Although the surface hardness meets the requirements, the internal organization of the work is not uniform, the residual stress is not sufficiently eliminated, and the mold is prone to early failure.

After tempering, it is generally air-cooled. During the tempering and cooling process, new tensile stress may appear inside the material. It should be cooled to 100~120 °C and then discharged, or after high temperature tempering, add a low temperature temper. PVD and CVD in surface coating hardening technology have made great progress in recent years. Vacuum evaporation, vacuum sputtering and ion plating are commonly used in PVD, in which the ion plating layer has strong adhesion, good plating property and deposition speed. Fast, pollution-free and so on. The ion plating process can be coated with TiC and TiN on the surface of the mold, and its service life can be extended several times to several tens of times. Ion plating is a deposition technique that combines vacuum evaporation film with gas discharge. Hollow cathode discharge method (HCD method) is to first vacuum the vacuum pump, then pass the reaction gas to the vacuum pump, and maintain the vacuum within the range of 10-5-10-2 Pa, using a low-pressure high-current HCD electron gun to evaporate the metal or The compound is ionized to form a protective film on the working surface. To increase plating efficiency, a negative voltage is typically applied to the workpiece.

There are not many domestic applications of surface treatment technology for forging dies, and there is a great need for development in this field. The surface hardening support of carburizing, nitriding, boronizing, carbonitriding and partial cavity spraying, brush plating and surfacing of the cavity is very promising. Breaking through this field will enable China to mold The technology has been greatly improved. After the mold failure, the welding repair technology, the factory in the early 1990s has been researched and applied, such as Qinghai Forge, the life of the forging die after welding can be doubled.

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