Plastic mold steel and its heat treatment
The main features of plastic mold steel:
1. Wide range: from ordinary steel to special steel. The special steel has become a self-contained system, and SM is added before the steel number
2. Strict performance requirements, difficult heat treatment, polishability and mirror quality are required
3. Avoid deformation
4. Corrosion resistance
5. Easy machinability
Heat treatment of various steel types
▇Heat treatment of pre-hardened plastic mold steel
▇Heat treatment of free-cutting pre-hardened plastic mold steel
▇Heat treatment of unalloyed medium carbon plastic die steel
▇Heat treatment of C-type plastic mold steel
▇Heat treatment of corrosion-resistant plastic mold steel
▇Heat treatment of age-hardening plastic mold steel
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●Pre-hardened steel generally refers to the steel that has undergone final heat treatment (quenching and tempering) in the steel mill.
●Typical pre-hardened plastic mold steel is: SM3CR2MO. Its heat treatment process is: 840-880 °C quenching, oil cooling, 600-650 °C tempering, air cooling, supply hardness 32HRC.
●The corresponding American steel is P20, German steel 40CRMNMO7, and Japanese HPM2. The heat treatment process of P20 steel after C penetration is: 820-870 °C quenching, 150-260 °C tempering, air cooling, and the hardness of the C layer is 58-64HRC. German steel 40CRMNMO7 has better hardenability than SM3CR2MO, and better machinability and polishability.
●On the premise of ensuring the original performance, one or several free-cutting alloying elements are added to the free-cutting pre-hardened steel.
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●Typical materials are: 8CRMNWMOVS (8CRS), including S free-cutting steel, when the heat treatment hardness reaches 40-42HRC, its machinability is equivalent to that of annealed T10A steel (200HBS), and the polishability and lithography are good. Typical heat treatment: 800±10 °C annealing, holding for 2-4 h, cooling to 700-720 °C, holding for 4-6 h, furnace cooling, hardness <=229HBS, 880-920 °C quenching, air cooling, hardness 63HRC, tempering at 160-200 °C, air cooling, hardness >=58HRC.
●高 :5CRNIMNMOVSCA
●The unalloyed medium carbon plastic mold steel is a medium carbon structural steel with higher metallurgical quality (purity), with a C content of 0.4%-0.6%.
●Typical materials are: SM45, SM50, the same kind of Japanese steel grade is S45C-S58C. The heat treatment process is no different from the conventional process, and this steel grade is preferred for small, low-precision plastic mold parts.
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●C-permeable plastic mold steel: For plastic mold parts with large impact, the surface is required to be hard and tough, and C-permeable steel is used. 20CR is used for general parts. Parts with high surface quality requirements use a special steel grade: 12CRNI3A.
●Corrosion-resistant plastic mold steel is used to manufacture plastic product mold parts that have a corrosive effect on metal.
●Typical steel grades are: CR13, 9CR18 and other martensitic stainless steels that can be strengthened. Its heat treatment is the same as that of general stainless steel products.
●Age-hardening plastic mold steel: For plastic mold parts with complex shape, high precision and long life, in order to reduce heat treatment deformation and improve the accuracy retention of mold parts, age-hardening steel is used. The mold parts are soft (28-34HRC) after solution treatment, which is convenient for processing and molding, and then hardened with aging to obtain the required comprehensive mechanical properties.