CA Modelling The Texture Evolution During Recrystallization Of Ferritic Stainless Steel

Recrystallization of metal materials during plastic processing and heat treatment is one of the important physical and metallurgical mechanisms for regulating microstructure and improving mechanical properties.In the process of recrystallization,under the dual action of deformation microstructure and nucleation mechanism,crystal orientation will shift to some preferred orientation,forming recrystallization texture.The formation of recrystallization texture is the main reason for the anisotropy of material properties,and changing texture composition is also the main means to optimize the forming properties of ferrite stainless steel.Ferritic stainless steel,as a typical nickel stainless steel,has the advantages of atmospheric corrosion resistance and stress corrosion resistance,but its application in some fields is limited by the lack of excellent formability.The forming performance of ferritic stainless steel is closely related to its orientation texture and grain size,so it is important to control the development of recrystallization microstructure and texture.Recrystallization is a continuous process,it is difficult for traditional experimental methods to directly show the internal micro-mechanism of the material.In the aspect of computer simulation,good results have been obtained in the topological evolution and recrystallization kinetics of microstructure in the process of recrystallization.However,the evolution of crystal orientation in the process of recrystallization is affected by many factors,such as the orientation of deformed matrix,the location and orientation of recrystallization nucleation,the preferred growth of oriented grains and the interaction of regional grains,which makes the computer simulation of recrystallization texture very difficult.In this study,based on the(EBSD)experimental analysis of electron backscattering,the computer simulation method of cellular automata(CA)with crystal orientation state variables and transition rules is explored,and the characteristics of nucleation,grain boundary migration and texture evolution during recrystallization are simulated and analyzed.The main research contents and conclusions are as follows:1.The experimental data of crystal orientation distribution in microzone of ferritic stainless steel after cold rolling and annealing were obtained by EBSD technique.The crystal orientation information(Euler angle)was introduced into the computer model by programming,and the data reconstruction of crystal orientation distribution was realized.Based on the corresponding relationship between EBSD Kikuchi contrast and relative dislocation density distribution proposed by D.Raabe et al.,based on the Kikuchi band contrast in EBSD experimental data,the relative dislocation density distribution is constructed in the computer model.Based on the crystallographic theory,a program for calculating the angle between the orientations of cubic crystals is compiled,and the functions of determining the grain boundary based on Euler angle information and calculating the orientation angle between cells are realized.2.Based on the physical metallurgy principle of recrystallization process,the dislocation density model,nucleation rate model and grain boundary migration model of two-dimensional cellular automata are established,the recrystallization CA calculation flow with crystal orientation state variables is constructed,and the recrystallization CA computer program is compiled.Compared with the experimental results of EBSD,the parameters of recrystallization dislocation density nucleation model of ferritic stainless steel were optimized.3.The recrystallization process of ferritic stainless steel was simulated,and the simulation results were verified by quasi-in-situ experiments.Through the analysis of the simulated and experimental results,it is clear that the nucleation priority occurs on the original grain boundary and micro-deformation zone with higher storage energy,and the grain boundary nucleation takes precedence over the deformation band.At the same time,it is proved that in the process of grain growth,only when the misorientation angle is between 15 °and 45 °,the grain boundary can have a large mobility and the new crystal nucleus can grow.4.The energy distribution,angular grain boundary distribution,microstructure and texture distribution of ferritic stainless steel in deformed and annealed state were simulated and analyzed by EBSD technique and cellular automaton.The results show that the deformed grains of ferritic stainless steel show strong α-fiber texture and relatively weak γ-fiber texture,and the microstructure is elongated into bands after deformation,and a large number of small-angle grain boundaries are formed inside the grains and at the grain boundaries.In the process of recrystallization,because of the high deformation energy storage,the nucleation of γ-fiber texture takes precedence over other oriented deformed grains,while the nucleation of α-fiber texture is slow.With the occurrence of recrystallization,the grain orientation changes as follows: the strength of α-fiber texture decreases,the strength of γ-fiber texture increases gradually,the microstructure changes to equiaxed crystal,and the small-angle grain boundary disappears at recrystallization.5.The microstructure and texture of ferritic stainless steel under different deformation and annealing temperature were observed by EBSD and simulated by CA.The results show that at the same annealing temperature,with the increase of deformation,the small angle grain boundary density increases,the deformation energy storage increases,the nucleation density increases,the recrystallized grain size decreases and the grain distribution is uniform,and the strength of γ-fiber texture increases.With the same amount of cold rolling deformation,with the increase of annealing temperature,the grain size increases and the strength of γ-fiber texture further increases.