Simulation Of Macroscopic Behavior And Mesostructure Evolution For Hot Rolled Flat

With the development of science and technology, the quality of steel products is made increasing demands and the computer numerical simulation technology in the rolling process is widely used to provide a new way to analyze the rolling process and enhance the quality of steel. Numerical simulation not only realizes the forecast of size and shape of workpiece, but also could be used to simulate the evolution of mesostructure. The use of computer makes the solving of rolling process to be more convenient, fast and accurate, at the same time, the traditional methods are no longer sufficient to meet human demands for new materials. The reappearance of material forming process on the computer model and auxiliary experiments could contribute greatly to the cost-saving experiment, and speed up the development cycle of new products. It has played an important role in guiding the products development process and optimizing the design. Therefore, this article takes the process of hot rolled flat as the research background, and the comprehensive simulation of macroscopic behavior and mesostructure evolution for hot rolled flat is carried out by finite element method and cellular automaton. The research would make the understanding deeply for the law on the mesostructure evolution of the flat in process of rolling. The main work of the paper is as follows:(1) The ideas and methods of the comprehensive simulation of macroscopic behavior and mesostructure evolution for hot rolled flat were put forward. The finite element method and the basic theory, by which macroscopic behavior (temperature field, strain field, and so on) of hot rolled flat was simulated, were introduced. The cellular automaton theory and methods, by which mesostructure evolution (recrystallization, transformation, etc.) of hot rolled flat was simulated, were also introduced.(2) The macroscopic behavior of hot rolled flat, such as the temperature field and strain field of hot rolled flat were established by finite element model to simulate rolling temperature changes over time and the temperature distribution of workpiece, as well as the distribution of strain in the rolling deformation zone. It provided a basis for further analysis of the evolution of the mesostructure and mechanical changes of hot rolled flat.(3) The mesostructure evolution of recrystallization of deformed austenite of hot rolled flat was mainly simulated by cellular automaton. The two-dimensional cellular automaton model of the dynamic and static recrystallization of deformed austenite was established. A series of the process, including dynamic recrystallization of the austenite, and dynamic recovery in the deformation region and the static recrystallization, back to the static, sub-dynamic recrystallization and grain growth after deformation was considered. The evolution of the mesostructue of austenite recrystallization was simulated dynamically, such as the parameters:the grain size, volume, static softening rate curve, dislocation density, the flow stress and grain shape, were quantitatively, accurately and visually described.(4) According to the simulation results of cellular automaton, the effects of the deformation temperature, strain rate, and other technical parameters on the austenite dynamic and static recrystallization mesostructure were analyzed. Through thermal simulation experiments, the flow stress in dynamic recrystallization was measured, and the mesostructure was observed, with the comparison to the results of the simulation.(5) According to the austenitic transformation theory, the the two-dimensional cellular automaton model of the austenite transformation of the hot rolled flat during cooling was established.The ferrite, pearlite and bainite transformation during the continuous cooling were simulated. On the condition of different cooling rates, the transformation types, the beginning temperature of transformation, kinetics curve of transformation, distribution of carbon concentration and grain size and so on, were obtained. The effects of the temperature and cooling rate on the mesostructure of austenitic transformation were analyzed.(6) In combination simulation by finite element method and cellular automaton, the finite element simulation results in the deformation region and between the rolling pass were used as initial conditions of cellular automaton calculation. Micro-area in the worpiece along the lines of metal deformation flow was selected. The evolution process of dynamic and static recrystallization of micro-area was simulated by cellular automaton, and the effects of the different macroscopic behavior on the final grain size, volume, and the flow stress and so on were analyzed. The mesostructure of the hot rolled flat during the accelerated cooling was simulated. The effects of the temperature range and the cooling rates on the type of transformation, the beginning temperature of transformation and the mesostructure of transformation were analyzed.(7) Through the results of combination simulation, the display maps of the recrystallization and transformation process were obtained, which realized the visual and figurative description of the mesostructure evolution.The above-mentioned research has established a link between the macro-deformation analysis and meso-simulation in the process of metal forming. The simulation of multi-scale coupling has been explored, and a new method has been provided in order to make the understanding deeply for the physical nature of the metal forming process.