A new cellular automaton (CA) model of abnormal grain growth (AGG) that considers anisotropic grain boundary energies was developed in this paper. The anisotropic grain boundary energy was expressed based on two types of grains, which correspond to two components of different crystallographic orientation in textured materials. The CA model was established by assigning different grain boundary energies and grain-growth-driven mechanisms to four types of grain boundaries formed by two types of grains. The grain boundaries formed by different kinds of grains adopted the lowest energy principle, while the grain boundaries formed by the same kind of grains adopted the curvature-driven mechanism. The morphology calculated by the CA model shows the characteristics of AGG. Then, the Johnson–Mehl–Avrami (JMA) model was fitted to predict the growth kinetics. By analyzing the fitting results, the JMA model is capable of predicting the growth kinetics of AGG. The Avrami exponent p decreases from about 1.5 to 1 with the initial number of Type II grains increasing. The investigation of the Hillert model and grain size distribution further indicates that the microstructure evolution is consistent with AGG. Therefore, the analysis of morphology and kinetics indicates that AGG can be fairly well-simulated by the present CA model.
The modeling of austenite grain growth of 25Cr2Ni4MoV steel for super-large nuclear-power rotors was investigated during the common heating process including the continuous heating and isothermal heating process. Based on the isothermal grain growth model considering the steady-state grain size and the rule of additivity, a new grain growth model during the continuous heating process was established. The comparison between experimental and predicted results indicates the model has good predictability. To describe the anisotropic and isotropic grain growth during the different isothermal heating stages of the super-large nuclear-power rotor, a cellular automaton model considering anisotropic grain boundary energy for grain growth of 25Cr2Ni4MoV steel was developed. It is found that the anisotropic grain boundary energy mainly exists in the early isothermal heating stage at lower temperatures, and the normal grain growth occurs under anisotropic grain boundary energy conditions. When the temperature is not less than 1273 K and the cellular automaton step is not less than 15, the normal grain growth containing only isotropic grain boundary energy occurs. The analysis of the morphology, energy variance, topology and growth kinetics further indicates that normal grain growth of 25Cr2Ni4MoV steel can be simulated fairly well by the present CA model.
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