Mold heat treatment deformation is one of the main defects in the mold processing process. For some precision and complex molds, they are often scrapped due to heat treatment deformation. Therefore, controlling the deformation of precision and complex molds has always been a key issue in heat treatment production.
As we all know, during the heat treatment of the mold, especially in the quenching process, the temperature difference caused by the inconsistency of the heating and cooling rates of the various parts of the mold section, coupled with the unequal time of the structure transformation, causes the volume of each part of the mold section to expand and contract. Inhomogeneity, the uneven transformation of the structure, resulting in “organization stress” and thermal stress caused by the temperature difference between the inside and outside of the mold. When the internal stress exceeds the yield limit of the mold, it will cause the deformation of the mold.
Therefore, reducing and controlling the deformation of precision and complex molds is an important research topic for the majority of heat treatment workers.
This article attempts to study the deformation conditions and causes of precision and complex molds to discuss measures to reduce and control the deformation of precision and complex molds to improve the quality and service life of mold products.
1. The influence of mold material
1. Mold selection
Considering the simplicity of material selection and heat treatment, a machinery factory chooses T10A steel to make more complex molds with large differences in cross-sectional dimensions and small deformation after quenching. The hardness requires 56-60HRC. After the heat treatment, the hardness of the mold meets the technical requirements, but the mold is deformed and cannot be used, resulting in the mold being scrapped. Later, the factory used micro-deformed steel Cr12 steel, and the hardness and deformation of the mold after heat treatment met the requirements.
Therefore, to manufacture sophisticated and complex molds that require less deformation, micro-deformed steel, such as air-quenched steel, should be used as much as possible.
2. The influence of mold material
A certain factory sent a batch of Cr12MoV steel relatively complicated molds. The molds all had round holes of ￠60mm. After the heat treatment of the mold, some of the mold holes appeared elliptical, which caused the mold to be scrapped.
Generally speaking, Cr12MoV steel is slightly deformed steel and should not be deformed significantly. We conducted a metallographic analysis of the severely deformed mold and found that the mold steel contains a large amount of eutectic carbides, which are distributed in bands and blocks.
(1) The reason for the ellipse (deformation) of the mold is the existence of uneven carbides distributed in a certain direction in the mold steel. The expansion coefficient of the carbide is about 30% smaller than the matrix structure of the steel. It prevents the mold from being heated when heated. The hole expands and prevents the inner hole of the mold from shrinking during cooling, causing uneven deformation of the inner hole of the mold and making the round hole of the mold ellipse.
(2) Preventive measures
① When manufacturing precision and complex molds, try to choose mold steels with less carbide segregation. Don’t try to be cheap, and use steels with poor materials produced by small steel plants.
②The die steel with severe segregation of carbides should be forged reasonably to break up the carbide crystal blocks, reduce the grade of uneven carbide distribution, and eliminate the anisotropy of performance.
③The forging die steel should be quenched and tempered to obtain a uniform, fine and dispersed sorbite structure of carbide distribution, thereby reducing the deformation of the precision and complex die after heat treatment.
④For molds that are larger in size or cannot be forged, solid solution double refinement treatment can be used to make carbides refined and uniformly distributed, and rounded edges and corners, which can achieve the purpose of reducing heat treatment deformation of the mold.