There are soft spots on the surface of the graphite mold after heat treatment, which will affect the wear resistance of the graphite mold and reduce the service life of the graphite mold.

cause

1. The graphite mold has oxide scales, rust spots and local decarburization on the surface before heat treatment.

2. After the graphite mold is quenched and heated, the cooling and quenching medium is improperly selected, and there are too many impurities or aging in the quenching medium.

Precaution

1. The oxide scale and rust spots should be removed before the heat treatment of the graphite mold. The surface of the graphite mold should be properly protected during quenching and heating. Vacuum electric furnace, salt bath furnace and protective atmosphere furnace should be used as far as possible to heat.

2. When the graphite mold is cooled after quenching and heating, a suitable cooling medium should be selected, and the cooling medium used for a long time should be filtered frequently or replaced regularly.

Poor organization of graphite mold before heat treatment

The final spheroidization structure of the graphite mold is coarse and uneven, and the spheroidization is imperfect. The structure has mesh, ribbon and chain carbides, which will make the graphite mold prone to cracks after quenching and cause the graphite mold to be scrapped.

cause

1. There is severe carbide segregation in the original structure of the graphite die steel material.

2. Poor forging process, such as high forging heating temperature, small deformation, high stop forging temperature, slow cooling rate after forging, etc., so that the forging structure is coarse and there are network, band and chain carbides, which make the ball

It is difficult to eliminate during chemical annealing.

3. Poor spheroidizing annealing process, such as too high or too low annealing temperature, short isothermal annealing time, etc., can cause uneven spheroidizing annealing structure or poor spheroidization.

Precaution

1. Generally, according to the working conditions of the graphite mold, the production batch and the strength and toughness of the material itself, the graphite mold steel material of good quality should be selected as far as possible.

2. Improve the forging process or use normalizing preparation heat treatment to eliminate the unevenness of the network and chain carbides and carbides in the raw materials.

3. High-carbon graphite die steel with severe segregation of carbides that cannot be forged can be subjected to solid solution refining heat treatment.

4. Formulate the correct spheroidizing annealing process specification for the forging die blank, and adopt quenching and tempering heat treatment and rapid uniform spheroidizing annealing process.

5. Reasonably install the furnace to ensure the uniformity of the mold blank temperature in the furnace.