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Cryogenic treatment refers to the use of liquid nitrogen as a refrigerant to treat the workpiece at temperatures below - 130 ° C. Low temperature treatment can significantly improve the toughness of the workpiece without reducing the strength and hardness of the workpiece. Let's analyze the factors that affect the effect of liquid nitrogen processor.For liquid nitrogen cryogenic processor, the treatment process is the key to determine the treatment effect. The key factors in the process of low temperature treatment mainly include: low temperature treatment method, temperature rising and falling speed, treatment before or after tempering, holding time, low temperature time, etc.It can be divided into liquid method and gas method. Liquid method is to put the workpiece into liquid nitrogen directly, and the processing temperature is - 150 ℃. The disadvantage of this method is that the thermal shock is very large, and sometimes even leads to the fracture of the workpiece. The gas method is cooled by the latent heat of vaporization of liquid nitrogen and the endothermic heat of low temperature nitrogen. The processing temperature reaches - 196 ℃, and the processing effect is better.Heating and cooling rate, at present, there are two main views on the rate of low temperature cooling. One view is that the rising and falling speed of low temperature should not be too fast, that is to say, it is not in favor of directly immersing the workpiece in liquid nitrogen, because cooling will increase the internal stress of the workpiece, which is easy to cause deformation or deformation. The workpiece is cracked. For example, in Japan's "low temperature and rapid heating method", the workpiece will not be cold treated immediately after quenching. Instead, it is first placed in a water bath and then cold treated in a treatment tank at - 80 ℃ or - 180 ℃. The samples were heated rapidly in a hot water bath at 60 ℃ to reduce the internal stress, and then tempered at different temperatures for 1 hour.