The Simulation Of The Temperature Evolution And Phase Transformation During The Hot Bar Rolling

In multi pass hot bar rolling, there are many complicated influences which may affect the final dimensional precision and mechanical properties. It is of significant importance to set up a computer simulation based method to make a comprehensive analysis of the temperature evolution and phase transformation which is very effective for the prediction and solution of production problems and for the optimization of rolling process.In this thesis, PC based temperature evolution model and phase transformation models have been established according to the real hot bar production procedure in our country of the typical steel GCrl5.By using two powerful analysis tools often applied in numerical analysis, Compaq Visual Fortran and Origin 7.0,simulation codes are programmed and the final results are visualized.The temperature evolution model is based on the Fourier heat transformation equations and the boundary conditions by the shape regarded as the circle applying the method of the cross-section of equality and the full degree of the pass are derived from some simplification of factors such as deformation heat, phase transformation latent heat, contact problems and work piece shape changed. The final results of temperature distribution are simulated by solving the equations with Finite Difference Method in terms of various aspects during the production, including thermo mechanical process, air cooling process and water cooling process. In order to certify the simulation accuracy, comparison between simulation results and measuring results has been made. Also the simulation methods are generally introduced in the thesis. The initial austenite grain size for the phase transformation calculation was provided by cooperator. Equations in literatures have been used in the austenite transformation kinetics calculations. Continuous cooling was subdivided into a series of isothermal procedures and the final results were carried out by an incremental method. In a single step, volume fraction of each phase transformation outcome was calculated by the Avrami Kinetics Formula, and the maximum fraction value was determined applying the Equilibrium Fe-Fe₃C phase diagram. Because thephase transformation of austenite to pearlite generates heat, also the latent heat was included. An experimental certification was made in order to check the accuracy of phase transformation simulation, based on which, the influences were discussed.The results of the temperature simulation and phase transformation simulation are directive for the optimization and direction of TCMP during the hot bar rolling in some extent.