Differences in the composition of cold work die steels and hot work die steels
Cold work die steel
Cold work die steels include dies (blanking punching dies, trimming dies, punches, and scissors), cold heading dies and cold extrusion dies, bending dies, and wire drawing dies.
1. Working conditions and performance requirements of cold work die steel
When cold work die steel is working. Due to the relatively large deformation resistance of the material to be processed, the working part of the mold is subjected to great pressure, bending force, impact force and friction force. Therefore, the normal scrap cause of cold work molds is generally wear. There are also early failures due to fractures, crushing forces, and out-of-tolerance deformations.
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Hot work die steel
1. Working conditions of hot work molds
Hot work die making includes hammer forging die, hot extrusion die and die casting die. As mentioned earlier. The working state of the hot mold is mainly manifested in contact with the hot metal, which is the main difference from the working state of the cold mold. As a result, it raises the following two problems:
(L) Heating the surface metal of the mold cavity. Usually when the hammer forging die is working. The surface temperature of the mold cavity can reach more than 300~400°C, and the hot extrusion die can reach more than 500~800°C. The temperature of the die-casting cavity is related to the type of die-casting material and the pouring temperature. For example, in the case of ferrous metal die-casting, the cavity temperature can reach more than 1000°C. Such a high operating temperature will significantly reduce the hardness and strength of the cavity surface, and it is easy to cause accumulation during use. For this.
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The basic performance requirements of hot work die steel are high thermoplastic deformation resistance, including high temperature hardness and strength, and high thermoplastic deformation resistance, which actually reflects the high tempering stability of the steel. Therefore, the first way to alloy hot work die steel can be found, that is, to add CR, W, Si. Alloying elements can improve the tempering stability of steel.
(2) Thermal fatigue (cracking) occurs in the surface metal of the cavity. The working characteristics of the mold are intermittent. Every time a hot metal is formed, the cavity surface is cooled with water, oil, air, and other media. Therefore.
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The working state of the mold is repeated heating and cooling, so that the metal on the surface of the mold cavity repeatedly expands and contracts, that is, repeatedly bears tensile stress and compressive stress. As a result, cracks appear on the surface of the mold cavity, known as thermal fatigue. Therefore, the second basic performance requirement of hot work die steel is proposed. That is, it has high resistance to thermal fatigue.