Study On Modeling And Simulation Of Recrystallization Annealing Process For Material With Second Phase Particle By Cellular Automata Method

With the development of material science and computer technology, the science of material preparation is changing from traditional design manner to its reverse one. By the aid of computer simulation, material properties can be predicted based on its components microstructure, vice versa, and the optimum manufacturing techniques can be selected to derive some functional materials which can meet the actual needs.The sceond phase particle in material is mainly the product caused by adding alloy elements to improve the performance of material. Alloying and controlled rolling and cooling technology have been widely used in the process of low-canbon steel manifacture to control the grain growth. The aim of alloying is to generate sufficient amount and fine second phase particles in the material, which affect the behaviors of dynamic recrystallization and static recrystallization and corresponding microstructure changes in the process of thermal deformation and cold one. Especially, the effects of the second phase particle on recrystallization and grain growth during the annealing directly determine the ultimate microstructure and performance of the cold deformed material.Cellular Automata (shortly called CA) model which developed in recent more than ten years has been widely used in the simulation of grain growth and recrystallization, but it has not been applied in the simulation of the deformed material with second phase particle yet. This status is inappropriate to compare with the character of the model which suits to simulate the local interaction between the second phase particle and body organization. Actually, constructing CA model for the deformed material with second phase particle to simulate the grain growth and recrystallization process not only studies the effects of the second phase particle's size, volume fraction and distribution on annealing microstructure, and achieves the microstructure organizational design and process control of and performance prediction to establish the foundation for the annealing technology optimization and development of better performance material, but also further explores the potential of extending its application. So it has an important significance of theory and practice to study the modeling and simulation of the annealing microstructure evolving for the deformed material with second phase particle by CA method in time .In present thesis, based on the CA method, metallography and recrystallization theory and so on, two CA models for the recrystallization and grain growth for single phase material were proposed with better physical basis, respectively. Based on the models, two CA models for the recovery - recrystallization and grain growth for the material with second phase particle under the change of annealing temperature were constructed, respectively, which formed a CA model for annealing microstructure evolution of the material with second phase particle. According to the new models and the corresponding key technologies for simulation, a computer program was compiled to simulate the annealing microstructure evolving of the material with second phase particle under the change of annealing temperature, and some experiments were finished to verify the rationality of the models.Firstly, the limitations of previous CA models for grain growth were well analyzed, and a new criterion with the judgement of two times was proposed for the attempted transition of cell state and a new CA model was constructed with a better physical basis, based on the mechanisms of grain boundary curvature driving and the thermodynamic one. In the new CA model, the main driving force of grain growth is grain boundary energy and the influence of grain boundary curvature on the direction of grain boundary movement is also considered so that the problem that the direction of grain boundary moving to its curvature center differs to the direction of its energy decrease is solved and the distribution of grain size is more ideal.Secondly, based on the grain growth CA model for single phase material, a new model with a modified transition rule of cell state was constructed to simulate the effects of the second phase particle on grain growth. The results gained by the model correctly reflect the effects of the second phase particle's volume fraction, size and its distribution on grain growth, which is consistent with the experimental results.Thirdly, the limitations of stored energy distribution, nucleation, temperature change and recovery effect of previous recrystallization CA models were well analyzed, and based on corresponding experimental research and MC models, a recovery-recrystallization CA model for single phase material which has strong physical basis was constructed. The new model has the following advantages: 1) A new stored energy distribution model is constructed by using inhomogeneous distribution of stored energy. 2) A recovery model is built on the basis of subgrain abnormal growth nucleation model and considered the effect of recovery on nucleation. 3) The influences of annealing temperature change on recrystallization process are considered in the new model. In comparison with the results of previous models, the results simulated by the new model more really reflect the influence laws of annealing temperature and deformation degree on recrystallization, which is in good agreement with the experiment results.Then, based on the experimental research on the effects of the small and large second phase particles on recrystallization and the recovery- recrystallization model for single phase material, a new recovery- recrystallization model for the material with second phase particle was proposed by CA method. In the new model, the dislocation movement and its distribution related to the second particle's size are generally considered, and the modified storage energy model and nucleation one are applied. The results simulated by the new model coincide with the experimental laws which show the effects of the second phase particle on recrystallization.Finally, based on the recovery-recrystallization and grain growth CA models, a new annealing microstructure CA model for the material with second phase particle was obtained. To verify the rationality and application effect of the model constructed in present thesis, the annealing processes of cold-rolled steel plates which contain the second phase particle with different content are investigated in detail. The comparison of experimental results and simulated ones indicate that: 1) The initial microstructure, the nucleation sites, recrystallized microstructure and the subsequent grain growth microstructure can be better simulated by the model constructed in present thesis. 2) The simulation results are consistent with the experimental results and related recrystallization theories. 3) The second phase particle delays the process of nucleation and nucleus growth, and then hinders the whole recrystallization process. There exists definite error between simulated annealing speed and experiment one because of model hypothesis and experimental error, so that it is helpful to perfect this model further for improving its simulation accuracy and practical application.