Technological steps of ultra-cryogenic treatment equipment
Ultra-cryogenic treatment technology, the treatment process is the key to determine the treatment effect. The key influencing factors of the cryogenic treatment process mainly include: cryogenic treatment method, temperature ramp speed, pre-tempering treatment or post-tempering treatment, holding time, cryogenic times, etc.
1. Ultra-cryogenic treatment can
be divided into two types: liquid method and gas method. The liquid method is to put the workpiece directly into liquid nitrogen at a processing temperature of -150°C. The disadvantage of this method is that the thermal shock is large, and sometimes even causes the workpiece to crack. The gas method is cooled by the latent heat of vaporization of liquid nitrogen and the heat absorption of low-temperature nitrogen, and the treatment temperature reaches -196 °C, and the treatment effect is better.
2. Heating rate At
present, there are two main views on the cryogenic rise and cooling speed. One view is that the temperature ramp and fall rate of cryogenic should not be too fast, that is, it is not approved to immerse the workpiece directly in liquid nitrogen, because the cold will lead to an increase in the stress inside the workpiece, which is easy to cause deformation or cracking of the workpiece. For example, Japan's "deep cold and rapid heating method", the workpiece is not immediately cold treated after quenching, but first put into a water bath, and then put into the treatment tank for cold treatment at -80 °C or -180 °C, and immediately put it in a 60C hot water bath after keeping warm for a period of time, so that the sample can be quickly warmed back to reduce the internal stress, and then tempered at different temperatures for 1h.
Another view is that it should be cooled or heated quickly, which will make austenite more likely to convert to martensite, and the direct immersion cooling rate is slower than that of oil quenching, which is less likely to cause deformation or cracking of the material. For example, the "impact method" of the former Soviet Union, the workpiece to be treated is directly and quickly put into liquid nitrogen, deep cold to the required temperature and kept warm for 5 ~ 30min, and then taken out and placed at room temperature, and after it is restored to room temperature, it is tempered in oil at 200 ~ 500 °C for 1h. This method significantly improves the service life of high-speed steel tools.
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