For some high-alloy die steels, such as Cr12MoV steel die, after quenching and low-temperature tempering, the length, width and height of the die shrink, which is caused by the excessive amount of retained austenite after the die is quenched.
1. Reasons for deformation
Because alloy steel (such as Cr12MoV steel) contains a large amount of retained austenite after quenching, various structures in the steel have different specific volumes, and the specific volume of austenite is the smallest. This is the volume reduction of high-alloy steel molds after quenching and tempering at low temperature. The main reason. The specific volume of various structures of steel decreases in the following order: martensite-tempered sorbite-pearlite-austenite
2. Preventive measures
(1) Appropriately reduce the quenching temperature. As mentioned earlier, the higher the quenching heating temperature, the greater the amount of retained austenite. Therefore, choosing an appropriate quenching heating temperature is an important measure to reduce mold shrinkage. Generally, in the case of ensuring the technical requirements of the mold, the comprehensive performance of the mold should be considered, and the quenching heating temperature of the mold should be appropriately reduced.
(2) Some data show that after quenching the Cr12MoV steel mold, the amount of retained austenite after 500ºC tempering is less than that of 200ºC tempering, so the tempering temperature should be appropriately increased under the premise of ensuring the technical requirements of the mold. The production practice shows that the deformation of the Cr12MoV steel mold tempered at 500ºC is the smallest, and the hardness is not reduced much (2″3HRC).
(3) Cold treatment after mold quenching is the best process to reduce the amount of retained austenite, and it is also the best measure to reduce mold deformation and stable use of dimensional changes. Therefore, precision and complex molds should generally be cryogenically treated.