What is the cause of insufficient mold hardness and uneven hardness?
Mold heat treatment hardness is a very important mechanical property index, and unqualified hardness is a very serious defect. Insufficient or uneven hardness of the mold after heat treatment will reduce the wear resistance and fatigue strength of the mold. The plastic mold manufacturer said that this will cause the mold to fail early and seriously reduce the service life of the mold.
1) The cross-section of the mold is large, and the hardenability of steel is poor. For example, a steel with low hardenability is selected for large-scale molds.
2) The carbide segregation in the original structure of the die steel is serious or the structure is coarse, and there is segregation and aggregation of graphite carbon and carbide in the steel.
3) The die forging process is incorrect, and the spheroidizing annealing is not carried out well after forging, resulting in poor spheroidizing structure of the die steel.
4) The processed surface of the plastic mold has not been cleaned of the decarburized layer produced during annealing or quenching heating.
5) The mold quenching temperature is too high, and the amount of retained austenite after quenching is too much; or the quenching temperature is too low, and the heating and holding time is insufficient, which makes the phase transformation of the mold steel incomplete.
6) After the mold is quenched and heated, the cooling rate is too slow, the grading and isothermal temperature is too high or the time is too long, and the quenching cooling medium is not properly selected.
7) Too little water in the alkaline bath, or too much impurities in the quenching cooling medium, or aging of the quenching cooling medium.
8) After the mold is quenched and cooled, the temperature of the quenching cooling medium is too high and the cooling is insufficient.
9) Insufficient tempering and excessive tempering temperature.