2) Mechanism of cryogenic treatment
The quenching process of steel is the process of obtaining martensite, but quenching can not make all austenite in steel transform into quenching structure. After heat treatment of various steels, some austenite remains. The residual amount varies with the steel type and heating temperature, and there is a certain amount of residual stress. Cryogenic treatment can make austenite in steel further transform into martensite, improve and eliminate the distribution of residual stress in steel, precipitate more and more fine carbides, so as to play the role of dispersion strengthening. For non phase change materials, grain boundaries can be distorted and matrix properties can be enhanced.
3) Advantages of cryogenic treatment
The biggest advantage of SSZ treatment is that the hardness of the workpiece increases due to the martensitization of γ R, thus improving the corrosion resistance and grinding performance of the workpiece. At the same time, to prevent aging deformation, cryogenic treatment of the workpiece has the following advantages:
① In essence, γ R has almost completely transformed into M;
② Compared with the workpiece without SSZ treatment or with common cold treatment, the wear resistance is improved;
③ The microstructure was refined and fine carbides were precipitated;
④ The hardness is almost the same as that of CSZ.
(4) Precautions for cryogenic treatment
① It is not allowed to put the workpiece that is not cooled to room temperature during quenching directly into the industrial refrigerator to avoid cracking
② The workpiece cooled to room temperature should be put into industrial refrigerator as soon as possible, so as not to stabilize austenite and affect the treatment effect.
③ Generally, steel should not be tempered before cryogenic treatment. High speed steel can be cryogenic treated after tempering once