Research On Numerical Simulation Method Of Recrystallization Texture Evolution Of Nuclear Power Large Forgings

In the process of thermal deformation of nuclear power large forging materials,textured large grains are easily formed due to the local large deformation and following with the long holding time at high temperature.However,at present,the correlation mechanism between the preferred orientation of grain nucleation and growth,and the formation and evolution mechanism of textured large grains of nuclear power steel during complex thermal deformation is not clear.In this article,316 LN stainless steel was taken as the research object and the multilevel cellular automaton model that can describe the mechanisms of the effective nucleation of recrystallization and the topological deformation of grains was developed.By combining the multilevel cellular automaton model with the crystal plasticity model to construct and verify the crystal plasticity-multilevel cellular automaton model which can consider the initial crystallographic information and the gradient of dislocation density distribution in grains.Based on this,according to the cellular state transformation rules of recrystallization texture evolution with the tendency to form the recrystallization texture on the basis of the "Oriented Growth" theory,the simulation of recrystallization texture evolution was carried out.It will serve for the further study of the recrystallization texture and the evolution mechanism of the textured large grains related to it.The main conclusions of this article are as follows:(1)By introducing the idea of multilevel cellular space into the traditional cellular automaton simulation framework and formulating cellular state transformation rules in recrystallization and data transfer rules between different levels of cellular space,the multilevel cellular automaton model for simulating the dynamic recrystallization was constructed for the first time.The established multilevel cellular automaton model includes a multilevel recrystallized nucleation module and a full-field multilevel grain topological deformation module.The results show that the developed multilevel cellular automaton model was not only more in line with the physical mechanism of recrystallization nucleation,but also closer to the actual deformation process.Furthermore,it can ensure the high accuracy of grain topological mapping,and solve the problem of "loss" of grain boundary area in the existing cellular automaton model.(2)The thermal compression experiments and microscopic observation experiments were performed on 316 LN stainless steel,and the developed multilevel cellular automaton model was applied to the numerical simulation of the dynamic recrystallization process for 316 LN steel.By comparing the simulation results with the experimental results,it is proved that the developed multilevel cellular automaton model can accurately describe the dynamic recrystallization behavior of 316 LN material,and the accuracy of the simulation results is higher than the existing cellular automaton model.In addition,the effects of the grain boundary mapping strain increment in the multilevel cellular automaton model and the number of levels in the full-field multilevel grain topological deformation module on the simulation results were also discussed.The results show that the discrete cellular space area(i.e.,the accuracy of the grain topological mapping)in the multilevel cellular automaton model increases with the number of levels,but decreases with the increase of the discrete strain increment.Besides,in the simulation,the simulation parameters(grain boundary mapping strain increment and the number of levels)can be selected according to actual requirements and the required accuracy of the grain topological mapping.(3)Based on the crystallographic information of the initial materials measured by microscopic observation experiments,the crystal plasticity model based on physical mechanisms was constructed.The developed and verified multilevel cellular automaton model was combined with the constructed crystal plasticity model,and the selection rules of new nuclei orientation in consideration of the genetic relationship between the orientation of new nuclei and the orientation of neighboring deformed grains were formulated.The crystal plasticity-multilevel cellular automaton model that can consider the initial crystallographic information and the gradient of dislocation density distribution within grains was established,and the validity of the model was verified by microscopic observation experiments.Furthermore,the simulation of recrystallization texture evolution was carried out by the crystal plasticity-multilevel cellular automaton model according to the cellular state transformation rules of the recrystallized texture evolution that tends to form the recrystallized texture based on the "Oriented Growth" theory.This work can not only serve the in-depth study of the recrystallization texture and the evolution mechanism of the large grains related to it but also provide a reliable numerical simulation method for determining the range of forming limit parameters of the textured large grains.