After heat treatment, the surface of the mold has a soft spot, which will affect the wear resistance of the mold and reduce the service life of the mold.
(1) cause
1) dies before heat treatment the surface oxide skin, rust and partial decarburization.
2) after the quenching of the mould, the selection of the cooling medium is improper, the impurities in the quenching medium is too much or aging.
(2) preventive measures
Removal of oxide scale, rust, in quenching when appropriate to protect the mold surface, should try to use the vacuum furnace, salt bath furnace and furnace with protective atmosphere heating 1) die before heat treatment.
2) after the quenching of the mold cooling, should choose the appropriate cooling medium, the long-term use of the cooling medium to often filter, or regular replacement.
Two. Before the mold heat treatment organization is not good
Mold the final ball of coarse microstructure, spheroidization is not perfect, the organization has mesh belt and chain carbides, which will make the mold after the quenching cracks easily, cause mold to scrap.
(1) preventive measures
1) shall be, in general, according to the work condition of mould and mass production and material toughness, try to choose good quality mold steel materials.
2) improved forging process or by normalizing the preparatory heat treatment, to eliminate the nonuniformity of raw materials in the network and chain like carbides and carbide.
3) can not be forged carbide segregation of high carbon die steel can be a solid solution refinement heat treatment.
4) develop right spheroidization annealing technology of forging blank, a quenching and tempering heat treatment and rapid even and fine ball annealing device.
5) reasonable charging furnace to ensure the uniformity of furnace temperature uniformity.
(2) cause
1) the original structure of the wire drawing die has the serious carbide segregation.
2) forging process is poor, such as forging heating temperature is too high, deformation, stop forging temperature is high, the cooling after forging speed slow, make forging microstructure was coarse and mesh, ribbon and the chain of carbide and the spheroidizing annealing is difficult to eliminate.
3) the annealing process is not good, such as the annealing temperature is too high or too low, the isothermal annealing time is short, which can cause the uneven or poor.
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