The effect of deep cooling process on the performance of heat treatment products
I. What is deep cooling treatment
Deep-cooling treatment is to treat the metal at -150 ℃, so that almost all the soft residual austenite into high-strength martensite, and can reduce the surface looseness, reduce the surface roughness of a post-heat treatment process, when this process is completed, not only the surface, almost the entire metal can make the strength increased, increased wear resistance, increased toughness, other performance indicators to improve, thus making the mold and tool After several refurbishments, they still have high wear resistance and high strength, and their life expectancy increases exponentially. The life span of the knife and shear products without deep cooling treatment will be significantly reduced after refurbishment. Deep cooling treatment is not only applied to knife and shear products, but also can be applied to the production of knife and shear products on the mold, the same can make the mold life significantly improved.
Second, the mechanism of deep cooling treatment
1, eliminate residual austenite: general quenching and tempering residual austenite in 8 ~ 20 %, residual austenite will be further martensitized over time, in the martensitic transformation process, will cause volume expansion, which affects the dimensional accuracy, and the lattice internal stress increases, seriously affecting the metal properties, deep cooling treatment can generally make residual austenite reduced to 2 % below, eliminate residual Austenite influence. If there are more residual austenite, the strength is reduced, under the action of cyclic stress, easy fatigue off, resulting in the nearby carbide particles suspended, soon with the matrix off, resulting in spalling pits, the formation of a large roughness of the surface.
2, fill the internal voids, so that the metal surface area that the wear surface increases: deep cooling treatment makes martensite fill the internal voids, so that the metal surface more dense, so that the wear area increases, the lattice is smaller, the alloy into a uniform analysis, quenching layer depth increases, and not only the surface, so that the number of renovations increase, life increase.
3、 Precipitation of carbide particles: Deep cooling treatment not only reduces residual martensite, but also precipitates carbide particles, and can refine the martensite twin crystals, because the shrinkage of martensite during deep cooling forces the lattice to reduce, driving the precipitation of carbon atoms, and because of the difficulty of diffusion of carbon atoms at low temperatures, so the formation of carbides up to nanometer size, and attached to the martensite twin crystal belt, increasing hardness and toughness. The wear pattern of the deep-cooled metal is significantly different from that of the non-deep-cooled metal, indicating that their wear mechanisms are different. This change cannot be explained by the traditional metallurgical and phase transformation theory, nor is it carried out in the form of atomic diffusion, generally at -150 °C to -180 °C, the atoms have lost their diffusion ability, and can only be explained from the physical energy point of view. The transformation mechanism has not yet been clearly studied. Therefore, we need to further explore.
4、Reduce residual stress
5、Make the metal matrix more stable
6 、 Increase the strength and toughness of the metal material
7, to increase the hardness of the metal about HRC1 ~ 2
8, red hardness increased significantly