Method for reducing cracks in graphite mold

The reason for the problem:

1. The reticular cementite of graphite material shrinks severely;

2. There is mechanical processing or cold plastic deformation stress in the graphite mold;

3. Improper mold heat treatment operation;

4. The shape of the mold is complex and difficult, the thickness is uneven, the oil point and the threaded hole make the thermal stress and tissue stress too large;

5. If the temperature is too high, the mold will be overheated or burned too much;

6. After quenching, the graphite mold is not tempered in time, or the tempering holding time is not enough;

7. After heat treatment, the EDM mold has high tensile stress and microcracks in the hardened layer.

How about reducing these problems:

1. Strictly control the intrinsic quality of graphite raw materials;
2. Remove the mesh, band, and chain cementite, and improve the calcination and spheroidizing annealing process;
3. The mold after machining should be stress annealed (>600°C) before heating and quenching;
4. For molds with too complicated shapes, asbestos plugging bags should be used in risky parts, threaded holes and thin walls, and graded quenching or austempering should be carried out;
5. Annealing or high-temperature tempering must be carried out when the mold is repaired or refurbished;

6. Strictly control the quenching heating temperature and time to reduce overheating and overheating;