Ultra low temperature treatment is a new type of low temperature treatment technology below 160 ℃. Since 1933, ultra-low temperature technology has been applied in metal treatment in the world. The experience of many countries shows that the tools, dies and metal materials treated by ultra-low temperature treatment have excellent performance, thus improving the service life of tools and dies.
In the manufacture of bearings and measuring tools, in order to stabilize the size and improve the wear resistance, the cold treatment process of about 80 ℃ is adopted, and the ultra-low temperature treatment pushes the cold treatment temperature down. The typical process is to cool the quenched and tempered workpiece to a temperature below 160 ℃ at a certain cooling rate for a period of time, then reheat to room temperature, and then apply stress relief treatment.
After ultra-low temperature treatment, the internal microstructure of the steel changes, that is, the soft retained austenite structure changes into hard martensite structure, the microstructure is refined and a large number of fine hard carbides are precipitated, which leads to the obvious improvement of the wear resistance of the steel, the more stable size, and the slightly increased hardness of the steel. This is the method of transforming retained austenite into martensite and stable size at low temperature.