However, different scholars still put forward different views on the length of heat preservation time. Fan Dongli [[5] proposed that the amount of retained austenite transformed into martensite only depends on the temperature reached by cooling and has nothing to do with the holding time at low temperature. Because the transformation of retained austenite into martensite is instantaneous, it is not necessary to extend the holding time as long as the workpiece is thoroughly cooled from outside to inside.

在研究模具钢时，分别选取冰冷处理和深冷处理进行对比。发现在低温下的保持时间对材料的性能没有明显的影响，甚还略有下降，能够对性能产生影响的主要是低温处理所达到的温度。低温处理的温度越低，则影响越明显。换句话说，低温时间相同的情况下，深冷处理比冰冷处理更能改善材料性能。

In the study of die steel, cold treatment and cryogenic treatment are selected for comparison. It is found that the holding time at low temperature has no obvious effect on the properties of the material, or even decreases slightly. The temperature reached by low temperature treatment can mainly affect the properties. The lower the temperature of low temperature treatment, the more obvious the effect. In other words, when the low temperature time is the same, Cryogenic treatment can improve the properties of materials better than cold treatment.

既然冰冷处理对保温时间不敏感，那不妨着重了解深冷处理时保温时间对材料的影响。

Since the cold treatment is not sensitive to the holding time, we might as well focus on understanding the influence of holding time on materials during cryogenic treatment.

W6Mo5Cr4V2高速钢研究后发现，在进行深冷处理时的保温时间对组织和力学性能影响不大。在低温一次停留3h的奥氏体含量为25.8%抗弯强度、硬度、冲击性能分别为2034MPa,62.1HRC,0.116MJ/mz，停留12h后的奥氏体含量为24.7%，抗弯强度、硬度、冲击性能分别为2048MPa,62.2HRC,0.185MJ/耐。由数据可知，随着深冷时间的增加，材料组织和力学性能变化不大。

After the study of W6Mo5Cr4V2 high speed steel, it is found that the holding time during cryogenic treatment has little effect on the microstructure and mechanical properties. The austenite content after staying at low temperature for 3h is 25.8%, and the bending strength, hardness and impact properties are 2034mpa, 62.1hrc and 0.116mj/mz respectively. The austenite content after staying at low temperature for 12h is 24.7%, and the bending strength, hardness and impact properties are 2048mpa, 62.2hrc and 0.185mj respectively/ It can be seen from the data that the microstructure and mechanical properties of the material change little with the increase of cryogenic time.

由此可见，延长保温时间对材料的组织和力学性能并不起主要作用。在研究粉末冶金高速钢时同样发现，深冷处理低温保温时间取决于工件冷透的时间，即使延长冷处理时间，对硬度和残留奥氏体含量变化也不大。故在实际生产中，应根据试样的尺寸、温度等综合条件来决定试样冷处理时间，冷处理时间以工件冷透为准。故延长保温时间对高速钢作用不大。

It can be seen that prolonging the holding time does not play a major role in the microstructure and mechanical properties of the material. In the study of powder metallurgy high-speed steel, it is also found that the low-temperature holding time of cryogenic treatment depends on the cold penetration time of the workpiece. Even if prolonging the cold treatment time, there is little change in the hardness and residual austenite content. Therefore, in actual production, it should be combined according to the size and temperature of the sample The condition determines the cold treatment time of the sample, and the cold treatment time is subject to the cold penetration of the workpiece. Therefore, prolonging the holding time has little effect on the high-speed steel.