Research On Microstructure Inhomogeneity In Large Steel Bar During Continuous Rolling

With the continuous development of manufacturing industry in recent years, thedemand of large bar, which is an important raw material for heavy equipment andmetallurgical machinery, has been increased, as well as the higher quality requirements.Uniformity and stability problems of how to solve the internal organization of theperformance of the large-scale bars, has been the focus of attention of domestic andforeign scholars and industry. This paper probes into the each field quantity’s distributionand varying pattern of the rolled piece’s internal temperature, stress-strain and grain sizeby using nonlinear finite element method to complete the numerical simulation of coupledthermal-mechanical-microstructure and density change during rolling process. Supportedby National Natural Science Foundation of China(51005179), this paper focuses on thebar rolling process metal deformation inhomogeneity, temperature nonuniformity andresulting organizational performance inhomogeneity problems, and verifies thecorrectness of the numerical simulation by physical experiment.Based on recrystallization theoretical model of the high-temperature austeniticdeformation, this paper analyzed the42CrMo steel austenite grain dynamicrecrystallization during hot rolling, static recrystallization and grain growth behavior andits mathematical model, and with the production process of the domestic factory of Ф150large bars, rigid-plastic finite element method, the large bar rolling process of heat-force-microstructure coupled finite element model was founded. By simulation of FEM, theevolution of the field variables of the rod internal stress and strain, rolling temperature,grain size were analyzed. In order to characterize the uniformity of the cross-sectionalmicrostructure, the introduction of non-uniform factor M as quantitative indicators byDEFORM secondary development will be uneven factor formula written to the finiteelement software subroutine. We researched the law of the rolling temperature, rollingspeed, pass extension coefficient of process parameters on high temperature Austrian ’sbody recrystallized grain size and organization of the uniformity. The simulation resultsshow that the low-temperature rolling can effectively refine the grain, but with pooruniformity. However, appropriately increasing the extension coefficient can compensate for this deficiency, and the low temperature with large reduction rolling can get a goodrolling cross-section the grain size and uniformity, And from the rolling force parameterswe analyzed the feasibility of the process in the implementation of the existing units.With the horizontal two-roll mill in Yanshan University rolling laboratory, this papercarried out experimental study of42CrMo materials steel billet by box pass systemdesigned by myself, and measured the rolling force, the grain size and other parameters.At the same time, the FEM model was founded with the same of experimental conditions.Compared with the results of the finite element, it was found that the two basic agreement,Then the experimental study verified the correctness of the finite element analysis results.