Selection of punching die materials and heat treatment requirements
Steel for traditional molds
For a long time, the steel used in domestic sheet stamping die is T10A, Crwmn, 9MN2V, CR12 and CR12MOV, etc.
Among them, T10A is a carbon tool steel with certain strength and toughness. However, the wear resistance is not high, the quenching is easy to deform and crack, and the hardenability is poor, so it is only suitable for the blanking die with simple workpiece shape, small size and small quantity.
The heat treatment process of T10A carbon tool steel is: 760~810 °C water or oil quenching, 160~180 °C tempering, hardness 59~62HRC.
Crwmn and 9MN2V are high-carbon and low-alloy steels, which are easy to quench and operate, and the hardenability is better than that of carbon tool steels, and the deformation is easy to control. However, the wear resistance and toughness are still low, and it is used in medium-volume punching dies with complex workpiece shapes. The heat treatment process of Crwmn steel is: quenching temperature 820~840 °C oil cooling, tempering temperature 200 °C, hardness 60~62HRC. The heat treatment process of 9MN2V steel is: quenching temperature 780~820 °C oil cooling, tempering temperature 150~200 °C, air cooling, hardness 60~62HRC. Note: The tempering temperature in the range of 200~300 °C has tempering brittleness and significant volume expansion, which should be avoided.
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CR12 and CR12MOV are high-carbon and high-chromium steels with high wear resistance, low deformation during quenching, and good hardenability, which can be used for high-volume production of molds, such as silicon steel sheet blanking dies. However, this type of steel has carbide inhomogeneity, which is easy to produce carbide segregation, and is prone to chipping or fracture during blanking. Among them, CR12 has a higher carbon content, and the uneven distribution of carbides is more serious than that of CR12MOV, and the brittleness is greater.
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The selection of heat treatment process of CR12 steel depends on the use requirements of the mold, when the mold requires relatively small deformation and a certain toughness, low temperature quenching and tempering can be used (CR12 is 950~980 °C quenching, 150~200 °C tempering; CR12MOV is 1020~1050 °C quenching, 180~200 °C tempering). In order to increase the service temperature of the mold and improve its hardenability and red hardness, high temperature quenching and tempering can be used (CR12 is 1000~1100 °C quenching, 480~500 °C tempering; CR12MOV is 1110~1140 °C quenching, 500~520 °C tempering).
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High chromium steels have tempering brittleness in the 275~375 °C region and should be avoided.
SKD12 Material Properties
- SKD12 die steel has a high carbon content (about 1.5%) and chromium content (about 12%), which makes it have good wear resistance and corrosion resistance.
—— The moderate molybdenum content (about 1%) improves its thermal stability, so that it can maintain good hardness and toughness under high temperature conditions.
In addition, the right amount of cobalt or nickel is added to improve the thermal expansion properties and processability of the steel.