Defects and prevention in the heat treatment of Expandable Graphite mould
In recent years, the Expandable Graphite mould has become a favorite in the mould industry with its excellent characteristics. In this paper, we can discuss the defects and prevention methods of the expanded graphite mould heat treatment.
There are soft spots on the surface of the Expandable Graphite mould
A soft spot on the surface of the expanded graphite mould will affect the wearability of the Expandable Graphite mould and the service life of the Expandable Graphite mould.
1) the Expandable Graphite mould has oxidized skin, rust spot and local decarburization before heat treatment.
2) after the expansion of graphite mould quenching and heating, the quenching medium is not suitable, and the impurities in the quenching medium are excessive or aging.
(2) preventive measures
1) Expandable Graphite mould should be removed before heat treatment scale, rusty spot, appropriate protection when quenching heating surface of Expandable Graphite mould, should try to adopt the vacuum furnace, salt bath furnace with protective atmosphere heating furnace.
The suitable cooling medium should be selected in the cooling medium of the Expandable Graphite mould quenching, and the cooling medium must be constantly filtered or replaced regularly.
2. Pre-heat treatment of Expandable Graphite mould is not well organized
Expandable Graphite mould spheroidizing eventually organization bulky inequalities, imperfect spheroidizing, organizations have mesh, belt and chain carbide, this will make the Expandable Graphite mould after quenching cracks easily, cause Expandable Graphite mould scrap.
1) there is a serious carbide segregation in the original structure of the expanded graphite mould steel materials.
2) poor forging process, such as forging heating temperature is too high, small deformation, slow stop forging temperature is high, the cooling speed after forging, etc., make forging organization bulky and mesh, belt and chain carbide exists, the spheroidizing annealing is difficult to eliminate.
3) the ball annealing technology is not good, such as the annealing temperature is too high or too low, the isothermal annealing time is short, which can cause the spheroidization annealing organization or the spheroidization.
(2) prevention measures
1) in general, the quality of the Expandable Graphite mould steel materials should be selected according to the working conditions of the Expandable Graphite mould, the production volume and the strength and toughness of the material itself.
2) improve the forging process or use positive heat for heat treatment to eliminate the inhomogeneity of mesh and chain carbide and carbide in raw materials.
3) the high carbon dilatable graphite mold can be treated with solid solubility and heat treatment by means of carbide that can not be forged.
4) the correct ball annealing process specification is developed for the forged mould, which can be used for heat treatment and rapid uniform ball annealing.
5) reasonable furnace, ensure the uniformity of temperature of mold billet.
Expandable Graphite mould
3. The expansion graphite mould can produce quenching crack
Expandable Graphite mould after quenching crack is the biggest shortcoming of Expandable Graphite mould heat treatment process, will make the expansible graphite mould scrap processed, make production and economy caused great loss.
1) there is a serious network carbide segregation in the Expandable Graphite mould materials.
2) there is mechanical processing or cold plastic deformation stress in the expanded graphite mould.
3) improper operation of the expansion graphite mould (heating or cooling too fast, the cooling medium is not suitable, the cooling temperature is too low, the cooling time is too long, etc.).
4) the expanded graphite mould has a complex shape, uneven thickness, sharp Angle and threaded hole, etc., which makes the thermal stress and tissue stress excessive.
5) can expand graphite mould quenching heating temperature too high to generate overheating or overheat.
6) the expansion of graphite molds is less than the time of quenching and tempering less time.
7) when the Expandable Graphite die retakes the quenching heating, the quenching is heated without the middle annealing.
8) the expansion graphite mould is treated with heat treatment, and the grinding process is not appropriate.
9) there are high tensile stresses and microcracks in the hardened layer when the expansion graphite mould is processed by electric spark.