The spheroidized structure of the graphite mold is coarse and uneven. The final nodular structure of graphite mould is reticulated, banded and chain carbide. This will make the graphite die easy to crack and scrap after quenching.

(1)   Cause

　　1)There is serious carbide segregation in the original microstructure of graphite die steel.

2)The forging process is not good, for example, too high forging heating temperature, small deformation, high stop forging temperature,slow cooling rate of the post-forging, and so on. All of these conditions will cause thick and reticulated forging structure, banded and chain carbides, and make them difficult to be eliminated during spheroidizing annealing.　　

3)The spheroidizing annealing process is not good. If the annealing temperature is too high or too low, or the annealing time is short, then non-uniform spheroidizing annealing or poor spheroidization will occur.

(2)Preventive Measures

1)Generally, the steel of graphite die with good quality should be selected according to the working conditions of graphite die, the production batch and the strengthening and toughness of the material itself.

2)Improving the forging process or adopting the normalizing preparation heat treatment to eliminate the non-uniformity of the mesh and the chain carbide and the carbide in the raw material.

3)Carrying out solution refinement heat treatment on the high-carbon graphite die steel which cannot be forged and the carbide is segregated.

4)The correct spheroidizing annealing process specification is established for the forged die blank. The tempering heat treatment and the rapid and uniform fine spheroidizing annealing process can be adopted.

　　5)Reasonable charging. Ensure the uniformity of mold blank temperature in the furnace.

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