Numerical Analysis And Simulations Of H-Beam Hot Rolling Process

The demands of the diversity and consistence of mechanical performances for long products have been going high in recent years, and the mechanical performance depends on the chemical elements of the steel, grain size, and the critical rolling and cooling parameters. The researches were mainly focusing on creating metallurgy models for recrystallization and phase transformation, and were utilized to the rolling processes of strip and small cross-section shape-metal, but leaving the complex cross-section shape-metal under-researched.This dissertation focuses on the integrated numerical analysis of the medial size H-beam rolling process. The rolling force, temperature and the microstructure were analyzed during the rolling process, so get the knowledge of the effects on the H-beam performances from a microstructure point of view. The results play a vital role in constructing the dimension precision and mechanical performances predications system, optimizing rolling parameters et al.The dissertation is consisted of the following parts:First, a unitary flow stress model of Q235 steel was developed. Gleeble-1500 tester system was used to study the plastic deformation behaviors of the material under high temperature. A unitary flow stress model, capable of taking the stress softening caused by recrystallization into account, was created based on the experiments results. The model can be used to calculate the size and volume fraction of the austemte grains, including the flow stress inside the stock during the hot deformation process. So, the interactions between the deformation parameters and microstructure can also be studied at the same time of performing temperature-displacement finite element method (FEM) analyses.Second, an austenite grain growth model of Q235 steel during the heat up process was developed. Relationship between the austenite grain size and the heat preservation time was studied at different temperature using the WZK-1 heater and the MM-6 graphic analyzer. The model coefficients were figured out by regression analysis of the test results, and it's capable of calculating the origin austenite grain size of the hot stock. So the effects on the grain size of the heater temperature and preservation time could be studied during the following deformation process.Third, an austenite grain evolution model of Q235 steel during the hot deformation was developed. Hardly after compressed by the punchers of the Gleeble-1500 tester, the cylindrical samples were quenched. Samples were made by splitting along the direction of compressing and polished for austenite grain observation. Eroded in the corrosive mixed by supersaturation picric acid and scour for 5 to 10 minutes at the temperature of 50-70℃, the austenite grain boundaries at different zones of the cross-section , when the compression was barely completed, can be observed by the MM-6 graphic analyzer. The austenite grain recrystallization model of the Q235 material was developed on the results, with a prediction error of 13.6%. Compared with the prediction error of 15.4% of the general C-Mn model, its prediction precision is 11.7% higher.Fourth, an analysis approaches for numerical analysis of multi-pass shape metal hot rolling process was developed based on element re-mesh. The data transfer between different passes analyses, mainly including the node temperature, the accumulated plastic strain and user defined filed variables, were completed by PYTHON and FORTRAN program. The numerical analysis of the H-Beam hot rolling, a big plastic deformation process, could be completed successfully utilizing the approaches. The efficiency and precision were assured by the re-mesh, data transfer provided by the user-defined programs and the steady state detection provide by the ABAQUS.Fifth, the experiential formulas were developed for computing the rolling force, temperature, and the austenite grain size at the middle part of H-shape cross section. Although the stress, strain, temperature, and austenite grain size could be presented in detail from the FEM analysis results, it also has the following shortcomings, such as long calculating time, complicated steps etc. And this makes it difficulty to meet with real-time production requirements. The parameters affecting the rolling force and austenite grain size were investigated through four parameters and three levels numerical experiments after the FEM model has been validated by the measuring results.Sixth, user subroutines were programmed to implement the user-defined models. All kinds of user-defined models could be embedded into the numerical calculating process of the ABAQUS. The following subroutines, including user-defined material (VUMAT), user-defined friction (VFRIC), user-defined field (VSDFLD), and user-defined film (FILM) were presented in the dissertation. The solution precision could be enhanced the embedded subroutines, and the most important part is the analysis of user-defined parameters.The effects of the hot rolling parameters adjustment on the microstructure were analyzed by the temperature-displacement-microstructure analysis. So the hot rolling schedule optimization could be implemented for improving the quality by the view of microsturuture.