There is no significant improvement on the workpiece. It is found that there is no need to extend the holding time of tool steel. Even when the extended sample is treated in liquid nitrogen, the retained austenite still exists stably in the martensite lamella. Therefore, extending heat preservation time can not improve the arrangement and function of tool steel. It is found that when the holding time is less than 4 hours at liquid nitrogen temperature, with the addition of holding time, the wear loss decreases, and the impact energy absorption and hardness increase. However, the wear and hardness change little after holding for more than 4 hours.

也有人提出，在深冷温度下保持的时刻，应根据具体情况而定。若改变为非等温改变时，不需求在深冷温度下进行保温，比如残留奥氏体向马氏体改变;若改变为等温改变时，则需求保温时刻，比如在安排中分出碳化物在研讨高速钢时，设置了深冷温度共同，但保温时刻分别为50min和90min的两组实验。

It has also been suggested that the time of holding at cryogenic temperature should be determined according to the specific situation. If the change is non isothermal, it does not need to be kept at cryogenic temperature, such as the change of retained austenite to martensite; If it is changed to isothermal change, the holding time is required, such as carbide separation in the arrangement. In the study of high speed steel, two groups of experiments with the same cryogenic temperature but holding time of 50 min and 90 min are set.

成果发现，适当延伸在液氮温度下逗留时刻，资料的红硬性、冲击功能和抗弯强度都有不同程度的添加。延伸保温时刻，不仅能提升高速钢的功能，还能够改进其安排。在研讨M42高速钢时发现，延伸保温时刻，能够改进晶粒度大小和促 进细小碳化物的分出，而且保温时刻越长，这种效果越显着。一起也指出，保温时刻对残留奥氏体向马氏体的改变没有影响。

It is found that the red hardness, impact function and bending strength of the data are increased in varying degrees when the residence time at liquid nitrogen temperature is properly extended. Extending the holding time can not only improve the function of high speed steel, but also improve its arrangement. In the study of M42 high speed steel, it is found that extending holding time can improve the grain size and promote the separation of fine carbides, and the longer the holding time is, the more significant the effect is. It is also pointed out that holding time has no effect on the transformation from retained austenite to martensite.

在深冷过程中，保温时刻的长短不影响残留奥氏体向马氏体的改变，可是对于资料安排和功能是否受保温时刻长短的影响，现在还没有共同的意见。

In the cryogenic process, the length of holding time does not affect the change of retained austenite to martensite, but there is no common opinion on whether the data arrangement and function are affected by the length of holding time.