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Cryogenic treatment - heat treatment cryogenic process
- Sep 05, 2018 -

The cold treatment technology of metal materials is a new process that has been developed in recent years to improve the performance of metal workpieces. The so-called cryogenic treatment is to use liquid nitrogen (-196 ° C) as a cooling medium to continue the cooling process of the quenched metal material, reaching a temperature far below room temperature, and promoting the retained austenite existing after the conventional heat treatment. Further conversion to improve the properties of the metal material. After cryogenic treatment, the wear resistance, toughness and dimensional stability of the metal workpiece can be significantly improved, and the service life of the workpiece can be doubled.

The improvement of chilled metal for ferrous metals is mainly in the following aspects:

Improve the hardness and strength of the workpiece

Improve the wear resistance of the workpiece

The mechanism of action of metal material cold treatment technology is as follows:

1. Improve the hardness and strength of the workpiece

Cryogenic treatment is a continuation of quenching in a sense, so that the lower material of Mf continues to complete the transformation from A to M. After conventional quenching, some materials retain austenite up to 25% or even higher, and by continuing to change, usually Can ** RC 1-3 degrees, and even up to HRC 5-6 degrees. The martensite matrix precipitates nano-scale ultra-fine carbides, which slightly increases the hardness of the workpiece. Qian Shiqiang of Shanghai Jiaotong University used the 16Mn experiment to basically break the influence of the Paralympic transformation. After several times of deep-cooling the workpiece, the HRC was increased by about 1.5 degrees compared with the uncooled hardness, indicating the distribution of ultrafine carbide to the microstructure. Played a role of dispersion strengthening. According to the material manual, when the hardness of the material is above HRC50, we can see that the hardness of the HRC is 0.5 degree, and the tensile strength of chrome steel, chrome vanadium steel and chrome molybdenum steel is usually increased by about 30MPA.

2, improve the wear resistance of the workpiece

Increased hardness, martensite is more wear-resistant than austenite. For materials such as W18CR4VCR12, when the hardness is increased from HV600 to HV800, the relative wear resistance is increased by about 15% to 20%, respectively. A large amount of ultrafine carbides are precipitated and dispersed on the Markov's staggered and twinned belts, which play a role in pinning and supporting the martensite matrix. Even if cryogenic sometimes does not significantly increase the hardness of the workpiece, we It can be clearly seen that the wear resistance is improved. For high carbon and high alloy workpieces, a 50% increase in wear resistance is still relatively common.