Shenzhen Su's heat treatment has been deeply mechanism of cryogenic treatment on steel, and basic consensus, main points:
(1) from the martensite in ultrafine carbides, and dispersion strengthening. Some scholars explain the causes for precipitation: martensite after cryogenic -196 ℃, the volume shrinkage, the lattice constant Fe a narrowing trend, thus strengthening the driving force of carbon precipitation, but due to diffusion at low temperature is more difficult, the diffusion distance is shorter, so in the martensite matrix precipitates on the super fine carbide large dispersion.
(2) the change of residual austenite. The decomposition of residual austenite in low temperature, transforms into martensite, improve the hardness and strength of the workpiece. Some people think that cryogenic treatment can completely eliminate residual austenite, also some people thought that the cryogenic can only reduce the number of retained austenite, but can not be completely eliminated, there are people that cryogenic changed shape, distribution of retained austenite and the sub structure, favorable to improve the strength and toughness of steel.
(3) the microstructure refinement. Microstructure refinement cause the workpiece to the strengthening and toughening. This mainly refers to the fragmentation of the original coarse lath martensite. Some people think that changed martensite lattice constant, some scholars think that the decomposition of Martensite Precipitation of fine carbides caused refinement.
(4) surface compressive residual stress, the stress can reduce the damage to the local strength of the material defects. For the final performance of the abrasive wear resistance improvement.
(5) part of the transfer of kinetic energy of atoms of cryogenic treatment of metal atoms both exist between the atoms close to the binding force together, and the existence of kinetic energy to separate. Cryogenic processing part of the transfer of energy between atoms, so that the atoms combined more closely, improves the performance of metal.
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