The general low temperature treatment means that in. The treatment below 0 ℃ is also called cryogenic treatment. According to the temperature below zero, such cold treatment can be divided into two types:
(1) general low temperature treatment: the treatment with the lowest temperature of – 100 “C.
(2) ultra low temperature treatment; treatment below 130 ℃. Dry ice is usually used for low temperature treatment, while industrial refrigerator is usually used for ultra-low temperature treatment. There is no difference in academic judgment, but in practice, -130 ℃ is taken as the boundary, which is divided into general low temperature treatment and ultra-low temperature treatment. Ultra low temperature treatment can also be called refrigeration treatment.
Ultra low temperature treatment is suitable for quenching other parts, but it is not necessary to carry out this treatment immediately after quenching. In order to avoid the stabilization of retained austenite, it must be carried out within six minutes after quenching when dry ice is used for general low temperature treatment. However, ultra-low temperature treatment can be used even after a long time. And it doesn’t matter how long it stays at low temperatures. Low temperature cooling is very important. When returning from low temperature to room temperature, the workpiece is usually placed in air. If it is put into water or hot water, it is more effective to eliminate residual stress. This method is called up hill queuing. Tempering after ultra-low temperature treatment is of course not necessary
After ultra-low temperature treatment, the service life of products can be prolonged. Generally, the improvement of wear resistance and dimensional stability is taken as the goal. The main purpose of using low temperature such as dry ice (-85 ℃) is to transform retained austenite into martensite. Because retained austenite is soft and unstable, hardness and wear resistance can be improved if it is transformed into martensite. The size can also be stable. However, the general low temperature treatment at about – 100 ℃ can not eliminate all retained austenite and improve the microstructure. If ultra-low temperature treatment is carried out, all retained austenite can be transformed into martensite and the microstructure can be refined. But the hardness changes little. The results show that:
- (1) the retained austenite can be transformed into martensite in essence.
- (2) compared with general heat treatment and low temperature treatment, the wear resistance can be improved.
- (3) the microstructure was refined and dispersed carbides were precipitated.
- (4) compared with other parts treated at low temperature, the hardness has no change.
Ultra low temperature treatment is effective not only for steel products, but also for copper products. After ultra-low temperature treatment, the wear loss and plastic deformation of copper electrode for resistance welding are reduced, and the service life is increased by 3-5 times. After ultra-low temperature treatment, the microstructure of copper is fine and the plastic deformation resistance is increased, so the service life of copper can be significantly prolonged.
Which products are suitable for ultra-low temperature treatment？
Ultra low temperature treatment is suitable for carburizing, nitriding, hard chromium plating and other surface treated tools and parts. Because the structure of carbide, Zn, Pb, Cu and so on is improved and the wear resistance is improved, it is suitable for cutting tools used in metal processing, such as broach, cutting tool, die, die holder and cutting tool for paper industry. The cutting tools of shearing machine and trimming machine used in plastic and rubber industry can improve the wear resistance and prevent bite after ultra-low temperature treatment. In electric welding, such as ultra-low temperature treatment of electrode rod for resistance welding can prevent wear and plastic deformation and prolong service life