Microscopic-Macroscopic Multi-Parameter Coupling Model Building For Low-Alloy Steel Strip Hot Rolling Process

Iron and steel industry has long been an important industry in industrialized countries, especially the metal plate and strip is playing very important role in the national economy and the modernization of national defense. Strip rolling process control mainly includes two aspects: one is the final shape and size of products to meet the requirements of external quality control, the other is the performanceof products to meet the requirements of internal quality control. Effective control for microstructure and structure is necessary in production, especially hot rolling. Therefore, based on the relationship among the thermal processing, microstructure and performance, how to develop the multi-parameter (thermal, mechanical and microstructure evolution) coupling simulation system of hot rolling strip steel has become a leading topic of current research, which is the powerful tool to instruct production and improve product quality.First, constitutive of metal materials (deformation resistance) is one of the most basic parameters for theoretical calculation, process optimization, force and energy parameters in the hot rolling process. Therefore, according to the relationship of deformation conditions and deformation resistance, the deformation resistance of Q345B low-alloy steel during single-pass hot compression deformation is investigated at different deformation conditions on Gleeble-3500 thermo-simulation machine. By analyzing the effects of deformation conditions to deformation resistance, dynamic recrystallization and dynamic recovery deformation resistance models are set up. The error analysis of these models proved that the model had good accuracy, which can provide reliable data for the rolling process.Second, metal material can occur dynamic softening (mainly dynamic recrystallization), static softening (mainly static recrystallization and metadynamic recrystallization) and grain growth. This microstructure (austenite) evolution has a great influence of the final performance of the strip. The austenite recrystallization behavior of low-alloy steel Q345B during single-pass and double-pass hot compression deformation tests is investigated at different deformation conditions on Gleeble-3500 thermo-simulation machine. Static softening mechanism during the interpass time is researched deeply. Austenite evolution kinetics model, grain size model and grain growth model are set up. According to analyzing and calculating hot rolling process, the intensive study of austenite evolution is proven to more accurately reveal complex relationship between deformation conditions and the phenomenon of the physical metallurgy, which deepen the understanding of the microstructure evolution to control the rolling process more accurately, thereby enhancing the product's mechanical properties.Third, based on the stream surface strip element method and finite difference method to build three dimensional deformation model and the temperature field model, which provide the necessary computing prerequisite to forecast microstructure evolution during hot rolling and establish a theoretical foundation to development hot strip multi-parameter coupled simulation system.Finally, coupled the metal deformation model, the temperature field model, the deformation resistance model and the microstructure evolution model, the multi-parameter coupling visual simulation system software is developed by the visualization integrated software Visual C++6.0 and stand computer graphics technology language OpenGL. The simulation for the 1750 mm 6 stand hot continuous rolling calculates the distribution of the fields, such as the strain, the strain rate and temperature and so on and predicts the changes of austenite grain size and recrystallization volume fraction in hot rolling process. The results show that the simulation system can greatly reduce the experimental time, reduce experimental costs and the risk of industrial experiments, which provide a good basis to develop the scientific of rolling process and more accurate control rolling process.