The hardness of die heat treatment is a very important mechanical property index, and the unqualified hardness is a very serious defect. After heat treatment, insufficient or uneven hardness will reduce the wear resistance and fatigue strength of the mold. Plastic mold processing manufacturers say that this will lead to early failure of the mold and seriously reduce the service life of the mold.

Causes:

1) The mold section is large, and the hardenability of steel is poor. For example, the steel grade with low hardenability is selected for large molds.

2) Carbide segregation in the original structure of die steel is serious or coarse, and graphite carbon and carbide segregation and aggregation exist in the steel.

3) The mold forging process is not correct, and the spheroidizing annealing is not carried out well after forging, so that the spheroidizing organization of the die steel is poor.

4) The decarburization layer produced by annealing or quenching heating is not removed from the processed surface of the plastic mold.

5) The quenching temperature of the die is too high, and too much austenite remains after quenching; Or the quenching temperature is too low, heating and holding time is insufficient, so that the phase transformation of the die steel is not complete.

6) The cooling speed of the die after quenching heating is too slow, the grading and isothermal temperature is too high or the time is too long, and the quenching cooling medium is improperly selected.

7) Too little water in alkali bath, or too many impurities in the quenching cooling medium, or aging of the quenching cooling medium.

8) After quenching and cooling, the temperature of quenching and cooling medium is too high and the cooling is insufficient.

9) Insufficient tempering and too high tempering temperature.