Bar Hot Rolling Of Austenitic Recrystallization Process And The Flow Stress Simulation Study

Hence recrystallization and flow stress during the hot rolling process influences highly on the final mechanical properties of products and the rolling force or rolling energy of a rolling mill, it is of significant importance to make a comprehensive simulation of the two aspects. Numerical simulation will be very effective for the prediction of microstructure evolution and properties, and furthermore, the optimization of rolling process will be much more efficient with it. In this thesis, the recrystallization and mean flow stress during the multi-pass hot bar rolling has been simulated integratedly according to a real factory' s bar mill layout, where the roughing, the first, and the second intermediate stands are included in the calculations.The deformation analysis was a basic of the following the austenite recrystallization and the mean flow stress calculation , the validity of which was heavily affected by the results of deformation analysis. A rectangle approximation of workpiece has been applied because a detailed demonstration of caliber and workpiece interaction often requires an exclusive skill, and the deformation results have been carried out via Rigid Plastic Finite Element Method codes. With this approach, deformation of simple crossectional bar or shape rolling can be efficiently calculated. Combining the production parameters, equivalent strain and strain rate of each pass has been obtained. Results showed that strain rates during the hot bar rolling might be as high as over 100 per second, and the strains were relatively lower, which were seldom over 0. 5.The model utilized in the recrystallization and mean flow stress simulation of φ14 mm GCr15 bar in roughing mill and intermediate mills were all from literatures. The C-Mn grade hypereutectoid steels based models are used here for their validity and high frequency of application. The average grain sizes, recrystallization fractions, the critical states ofrecrystallization, the critical mean flow stresses, and the steady state mean flow stresses, etc, have been calculated. A rough estimation of roll force has also been made. The results showed that according to the prescribed rolling schedule, GCrl5 had very good recrystallization fraction and the products could have an ideal refinement such as from 100 u m to 20 u m. At the same time, the mean roll force were tolerable for modern rolling equipment.In order to validate the rationality of the simulation results, comparison between the calculation results and the measuring ones have been made. Although there are some differences found, the simulation results are acceptable, while the causes of errors have been discussed in the thesis. On the other hand, the practical factors may influence the hot deformation, austenite recrystallization and mean flow stress have been mentioned in the thesis, and the future of rolling simulation has also been prospected.