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What are the reasons for the insufficient hardness of the mold after heat treatment?

Update:30-04-2021
Summary:

Hardness is a very important mechanical property index […]

Hardness is a very important mechanical property index in mold heat treatment, and unqualified hardness is a very serious defect. Zhongshan Fahrenheit mold steel technicians pointed out that after the mold is heat treated, its hardness is insufficient or uneven, which will reduce the wear resistance and fatigue strength of the mold, leading to early failure of the mold and shortening the life of the mold. So, what are the reasons for the insufficient hardness of the mold after heat treatment?hot working die steel

Reasons for insufficient hardness of the mold after heat treatment:

1) The cross-section of the die is large, and the steel with low hardenability is selected.

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 performed well after forging, resulting in poor spheroidizing structure of the die steel.

4) The surface of the 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, so that the phase transformation of the mold steel is 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 improperly selected.

7) The water in the alkaline bath is too little, or the quenching cooling medium contains too much impurities, or the quenching cooling medium is aging.

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 too high tempering temperature.

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