Computer Simulation, Microstructure Prediction And Technology Optimization Of Plate And Strip Hot Rolling

The rolling process should effectively control the external and internal quality of products.The external quality includes the thickness precision and flatness of plate and strip.The grain size is an important index of the internal quality of rolled products,and the comprehensive properties of materials can be strikingly improved by refining the austenite grain. Based on this understanding, a number of models concerning microstructure and properties have been established by experimental results. The computer simulation of a plate rolling process of B-micro-alloyed steel has been carried out by using deformation finite element method(FEM), heat conduct finite element method and grain size computing program. The optimum combination of technological parameters has been determined on the basis of the results of grain size of rolled products. The research work includes:1 The establishment of constitutive relationships and experimental research of materials under high temperature deformation.A systematic research has been carried out of function relationships between flow stress and thermo-mechanical parameters and constitutive models describing work hardening and dynamic softening stress-strain curves have been developed based on the experimental results of isothermal constant strain rate single hit compress test on gleeble-1500 system.The experimental results show that the models are ideal for its high accuracy and convenient to numerical modelling. The establishment of constitutive models provides reliable criteria for simulating metal forming process.2 The analysis and experimental research of main factors affecting internal quality of rolled products. The activation energy for hot deformation, the function relationships between peak strain as well as critical strain and Zener-Hollomon parameter Z have been determined. The critical conditions and kinetics of dynamic recrystallization as well as the kinetics of static and metadynamic recrystallization reflecting softening behavior of materials between interpass have been established. Also, the function relationship between grain size, austenite grain growth and hot working parameters have been developed to predict the grain size of the rolled products. The establishment of all of these models lays a theoretical foundation for forecasting the grain size of products.3 The establishment of simulating system determining heat conduct and plastic deformation of rolled materials. Two modelling systems have been established. These systems include one that can simulate three dimensional rolling process using rigid viscoplastic FEM on the basis of mathematical models of thermo-mechanical coupled rigid viscoplastic FEM,one that can predict the grain size of hot rolled products. All of these computer programs provides a real computing mean of simulating rolling process,forecasting grain size of rolled products,optimizing technological parameters.4 The establishment of rolled product quality controlling system and experiment verification. The experimental results show that the models of materials and the modelling system is correct and reliable in view of the prediction of grain size of rolled products. The effect of strain distribution, strain rate, temperature and interpass time on internal quality of rolled products has been analysed thoroughly in example of plate rolling. The technological parameters have been optimized on the basis of calculating results.All of this research work is important for warranting the internal properties of the products, increasing the rolling productivity, shortening trial-manufacturing time, reducing trial-produce fee and so on. This technology of simulation and optimization may become an important mean of designing metal forming technology.