1. The mold cross-section is large and the steel has poor hardenability. For example, a large mold uses steel with low hardenability.
2. The carbide segregation in the original structure of the mold steel is serious or the structure is coarse, and graphite carbon and carbide segregation and aggregation exist in the steel.
3. The mold forging process is incorrect, and good spheroidizing annealing is not performed after forging, resulting in a poor spheroidized structure of the mold steel.
4. The decarburization layer produced during annealing or quenching heating is not removed from the mold surface.
5. The mold quenching temperature is too high, the amount of residual austenite after quenching is too much, the quenching temperature is too low, and the heating and holding time is insufficient, resulting in incomplete phase change of the mold steel.
6. The cooling speed of the mold 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. There is too little water in the alkali bath, or there are too many impurities in the quenching cooling medium, or the quenching cooling medium is aged.
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, etc.

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