Methods for treating surface soft spots and poor microstructure of graphite molds

Methods for treating surface soft spots and poor microstructure of graphite molds

After heat treatment, there are soft spots on the surface of graphite molds, which will affect their wear resistance and reduce their service life.

1. The surface of graphite molds has oxide scale, rust spots, and localized decarburization before heat treatment.

2. After quenching and heating of graphite molds, improper selection of cooling and quenching medium may result in excessive impurities or aging in the quenching medium.

1. Before heat treatment of graphite molds, the oxide scale and rust spots should be removed. During quenching and heating, the surface of the graphite mold should be appropriately protected. Vacuum electric furnaces, salt bath furnaces, and protective atmosphere furnaces should be used for heating as much as possible.

2. When cooling graphite molds after quenching and heating, appropriate cooling media should be selected. Cooling media that have been used for a long time should be filtered regularly or replaced regularly.

The final spheroidization structure of graphite molds is coarse and uneven, with incomplete spheroidization and the presence of network, strip, and chain like carbides. This will make the graphite molds prone to cracking after quenching, resulting in the scrapping of the graphite molds.

1. The original structure of graphite mold steel material exhibits severe carbide segregation.

2. Poor forging process, such as high forging heating temperature, small deformation, high stopping forging temperature, slow cooling rate after forging, etc., results in coarse forging structure and the presence of network, strip and chain carbides, which are difficult to eliminate during spheroidization annealing.

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

1. Generally, high-quality graphite mold steel materials should be selected based on the working conditions, production batch size, and the toughness of the material itself.

2. Improve forging processes or adopt normalizing pre heat treatment to eliminate the unevenness of network and chain carbides and carbides in raw materials.

3. High carbon graphite mold steel with severe carbide segregation that cannot be forged can be subjected to solid solution refinement heat treatment.

4. The correct spheroidization annealing process specification can be formulated for the forged die blank, which can be achieved through quenching and tempering heat treatment and rapid uniform spheroidization annealing.

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