Causes of uneven hardness of die steel

　　1. Steel with low hardenability is selected for large molds.

　　2. the original structure of the mold steel carbide segregation is serious.

　　3. the mold forging process is not correct, the forging is not a good nodularization, so that the mold steel nodularization is poor.

　　4. the mold surface residual annealing decarburization layer or quenching heating when the decarburization layer.

　　5. the quenching temperature of the mold is too high, and the residual austenite volume is too much after quenching; Or the quenching temperature is too low, so that the mold steel phase change is not complete.

　　6. die quenching heating cooling speed is slow, grading, isothermal is too high or too long, improper selection of cooling medium.

　　7. the quenching medium contains too much impurities or aging.

　　8. die quenching cooling quenching medium after the temperature is too high, insufficient cooling.

　　9. Insufficient tempering and high tempering temperature.