The die steel is widely used. The conventional heat treatment process is quenched at 1050 °C ~ 1100 °C, tempered at 550 °C ~ 620 °C, and the hardness is generally 45 HRC ~ 50 HRC. The early fracture phenomenon often occurs in use, and the die life is often low.
For example, the new high temperature quenching and high temperature tempering process, that is, 1150 °C high temperature quenching, 640 °C~ 680 °C high temperature tempering, hardness of about 40HRC, to obtain tempered sorbite structure. Thus, although the hardness is lowered, the thermal fatigue resistance and the fracture toughness are greatly improved, the occurrence of the fracture phenomenon is avoided during use, and the service life is remarkably prolonged. If the tempering temperature is controlled at 620 °C to 640 °C, the hardness is maintained at about 43 HRC, which can delay the occurrence of collapse time for some convex mold shapes.