Evaluation of the Influence of Temperature State and Dynamics of Softening of Rolled Metal on Rolling Force Parameters in PSM 380/4 Mill Conditions

The history of three-high stands application for more than 50 years has proven their high technological effectiveness due to more uniform deformation in the rod cross-section, which contributes to the formation of a uniform structure and, as a result, to the achievement of required properties. At the same time, the high compactness of modern reducing and calibrating blocks of the PSM 380/4 type has determined the need for a more in-depth study of not only the nature of metal behavior during deformation and in inter-deformation pauses, but also an assessment of possible changes in the force loads on the stand elements. This article presents the results of a comprehensive study of the effect of temperature state and the dynamics of rolled metal softening on the force parameters of rolling under the PSM 380/4 mill conditions. The use of the true deformation resistance value as a basic parameter has proven its correctness, since as deformation occurs in the block’s stands, only partial softening occurs and its cumulative growth is observed. In further calculations, the metal’s initial deformation resistance value changes, taking into account the accumulation that has occurred. Only in the first pass is it assumed that the metal is in a state of complete softening. It has been established that the effect of reducing the temperature is most pronounced on carbon steels, as well as on austenitic stainless steels. In particular, the residual hardening value of stainless steels at a temperature of 970°C fluctuates at 85.0%, and at a temperature of 820°C it already reaches almost 96.0%. At the same time, a significantly lower degree of residual hardening is characteristic of carbon steels: at a temperature of 970°C it fluctuates at 53.5–63.9%, and at a temperature of 820°C it reaches 81.1–85.1%. The revealed nature of change in the degree of metal’s residual hardening has a dominant effect on the growth of both the force and power load on the stand.