Mechanism of cryogenic treatment

1. Elimination of retained austenite: generally, the retained austenite after quenching and tempering is about 8-20%, and the retained austenite will be further martensitized with the passage of time. In the process of martensite transformation, the volume expansion will be caused, which will affect the dimensional accuracy, and increase the stress inside the lattice, which will seriously affect the metal properties. Cryogenic treatment can generally reduce the residual austenite The effect of retained austenite is eliminated when the content is less than 2%. If there is more retained austenite, the strength will be reduced. Under the action of periodic stress, it is easy to fall off from fatigue, resulting in carbide particles hanging in the vicinity, falling off quickly with the matrix, resulting in spalling pits and forming a surface with larger roughness.

2. Fill the internal gap, so that the metal surface area, namely wear-resistant surface, increases: cryogenic treatment makes martensite fill the internal gap, makes the metal surface more dense, increases the wear-resistant area, smaller lattice, alloy composition analysis is uniform, the depth of quenching layer increases, and not only the surface, so that the number of renovations and life is increased.

3. Precipitation of carbide particles: cryogenic treatment can not only reduce the residual martensite, but also precipitate carbide particles, and refine the martensite twins. Because of the shrinkage of martensite during cryogenic cooling, the lattice decreases and the carbon atoms precipitate. Moreover, due to the difficulty of carbon atom diffusion at low temperature, the size of carbides formed reaches nanometer level and adheres to the Martensite Twin band and increases Hardness and toughness. The wear patterns of cryogenic treated metals are significantly different from those of uncooled metals, which indicates that their wear mechanisms are different. Cryogenic treatment can make the majority of retained austenite martensite, and precipitate carbide particles with high dispersion in the martensite. With the refinement of matrix structure, this change can not be explained by the traditional metallurgic and phase transformation theory, nor is it carried out in the form of atomic diffusion. Generally, at – 160C to – 180C, atoms have lost their expansion ability and can only use physical energy The transformation mechanism has not been studied clearly. Therefore, it needs to be further explored.

4. Reduce residual stress.

5. It makes the metal matrix more stable.

6. Increase the strength and toughness of metal materials

7. The hardness of the metal increased about hrc1-28, and the red hardness increased significantly.

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