In the steel rolling industry, the production ratio of sheet and strip has exceeded 50%, and the demand for alloy thin strip is also increasing. In various rolling equipment, four-high mills are not suitable for rolling cold-rolled sheets and strips of high-strength steel and precision alloys due to the elastic deformation of the rolls and the large rolling force during the rolling process. In terms of technical feasibility and economy, the use of multi-roll mills to cold-roll sheets and strips has unparalleled advantages. The accuracy and life of the bearing of the backup rolls of the multi-roll mill have a very important influence on the production and quality of the rolled sheet. Compared with other types of cold rolling mills, multi-roll rolling mills have the following characteristics: (1) In order to reduce the elastic flattening value of the rolls, small-diameter work rolls are used to ensure the size of the rolled sheet. . (2) Using a multi-roller roll system, the component force of the rolling force is transmitted to the stand by the support rolls with multiple fulcrums, so that the rigidity is greatly improved. (3) The manufacturing precision of each component of the working stand and the roll is high, and the precision of the entire rolling mill is also quite high. Since the multi-roll mill places special emphasis on rigidity and precision, it can roll out extremely thin steel plates and ensure that the steel plates have extremely high precision and surface quality, such as stainless steel plates; the thickness is 0.1 D: 'ln3. Even 0.002 mill high-precision electrical silicon steel plate Harbin HRB bearings and so on. Since the first multi-roll rolling mill appeared in 1932, multi-roll rolling mills have developed rapidly and have different structural shapes and geometric dimensions. The models include Sendzimir type and Sandvik type. Two-high and twenty-high rolling mills, etc., but the most are twenty-high rolling mills, of which the Sendzimir type is dominant. For ease of introduction, the multi-roll mills mentioned below all refer to Sendzimir-type mills. The stand arch of the Sendzimir mill is an integral structure with a complete set of rolls inside, with high rigidity, which can fully ensure the stability of the work rolls in the rolling direction and compensate for the deflection of the small diameter work rolls. The working machine base is a complex block, and the working machine base includes arches, backup rolls, pressing devices, wear compensation mechanisms, roll shape control and balance mechanisms, transmission devices, guides, lubrication and cooling parameter control systems, etc. [ ]. It can be seen from Table 1 that the grade of the network carbide in the annealed state of the same sample is 0.51 grade higher than that in the quenched and tempered state, which is consistent with the theoretical interpretation. Judging from the daily metallographic inspection, the grades of network carbides under normal conditions are generally around 1-3, and the annealing picric acid corrosion method can be used. For the samples whose reticulated carbide grade is equal to or higher than 2.5 in the annealed state, quenching inspection can be carried out to ensure the rationality and accuracy of the inspection. Conclusion: (1) There is a certain correspondence between the reticulated carbides in the annealed state and the reticulated carbides in the quenched and tempered state. Generally, the reticulated carbide in the annealed state is 0.51 grade higher than that in the quenched and tempered state. (2) The network carbide is corroded with picric acid in the annealed state, which is clearly visible. If the reticulated carbide grade is below 2.5, the reticulated carbide is qualified, and the quenching method is no longer used for inspection; when it is greater than 2.5, the quenching method is used to evaluate the grade, which saves inspection time.