Simulation Of Q235 Steel Recrystallized Microstructure During Hot Forming Process

The grain size is an important index of the internal quality of products during hot forming, and the comprehensive properties of materials can be strikingly improved by refining the austenite crystal. A number of models concerning microstructure and properties have been established by experimental results. The computer simulation of a hot forming process of Q235 steel has been carried out by using deformation finite element method, 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.The research work includes four parts as follows: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 modeling. 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 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 reflecting softening behavior of materials between interposes have been established. The establishment of the model lays a theoretical foundation for forecasting the grain size of products.3. The establishment of simulating system determining heat conduct and plastic deformation. The system can predict the grain size of products using rigid/viscoplastic FEM on the basis of mathematical models of thermo-mechanical coupled rigid/viscoplastic FEM. All of these computer programs provide a real computing mean of simulating hot forming process, forecasting grain size of products, optimizing technological parameters.4. The establishment of product quality controlling system and experiment verification. The experimental results show that the models of materials and the modeling system are correct and reliable in view of the prediction of grain size of products. The effect of strain distribution, strain rate, temperature and interpass time on internal quality of products has been analyzed. 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 hot forming 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.