Texture Evolution,Control And Simulation In Initial Columnar-grained Electrical Steels

Columnar grains are generally found in the cast ingots and slabs of electrical steels, and the texture is characterized as{001}-fiber. This study investigates the deformation and recrystallization behaviors of different{001} oriented columnar grains along the processing routes including cold rolling and annealing, hot rolling as well as following cold rolling and annealing processes, and the microstructure and texture evolution is discussed. Based on the investigation, non-oriented electrical steel with high permeability is pursued by texture control. At the meanwhile, this study calculates the texture and orientation evolution during cold rolling deformation in use of Reaction Stress model and other crystal plasticity models, with the focus on the reliability and application of Reaction Stress model. The results are shown as follows:During cold rolling to 90% reduction and annealing, the deformation and recrystallization behaviors of columnar grains show strong dependence on specific {001} orientations. Initial cube oriented grains lead to fine recrystallized microstructure with strong nucleation priority of{001}<120> grains; Initial {001}<120> oriented grains contribute to coarse recrystallized microstructure showing advantage of{001}<120> and{113}<361> grains; Initial rotated cube grains lead to uniform deformed microstructure, in which nucleation is hard to occur. Regarding the formation of strong a*-fiber recrystallization texture, it is determined by both nucleation superiority of a*-fiber grains and growth advantage of {113}<361> grains, corresponding to the higher intensity of{113}<361> texture component. Besides the orientation dependence, the cold rolling behavior shows the effect of neighboring grains. The activation of slip systems is affected by the initial orientations of adjacent grains and then determine the orientation change and microstructure evolution in cube oriented columnar grains.For conventional hot rolling (and annealing)-cold rolling-annealing process in electrical steel production,{001} texture of initial columnar grains can be retained after hot rolling and annealing, and it is enhanced by the implementation of inter-pass annealing during hot rolling. After being submitted to cold rolling and annealing,{001} grains in the annealed hot bands exhibit similar behaviors as columnar grains, that is, cube and{001}<120> nuclei are obtained in{001}-{113} oriented deformed matrix at medium rolling strain, and these{001} grains greatly contribute to a*-fiber recrystallization texture at high rolling strain. Comparing the cold rolling to high strain and hot rolling behaviors, the relationship between initial columnar-grained structure and{001} as well as a*-fiber recrystallizaiton texture can be deduced. When{110}<229>-{110}<112> grains, which are shear-texture components in BCC steel, are cold rolled and annealed, the deformation orientation change show the combined effect of initial orientation, shear near the surface and the deformed matrix. After annealing,{hk0}<001> nucleation in y-fiber deformed regions is obtained and leads to{hk0}<001> recrystallization texture, meanwhile initial{110}<112>grains lead to{112}<110> deformed matrix, which makes the recrystallized microstructure coarser and results in the weakened texture.Based on the previous analysis on texture as well as microstructure evolution, columnar grains are applied to non-oriented electrical steel production. The magnetic induction is improved by texture optimization, including the retaining of {001} texture, the increase of{hk0}<001> texture and the decrease of ?-fiber texture, among which{001} texture is essential for the decrease of magnetic anisotropy. For the non-oriented electrical steel with medium thickness prepared by one-stage cold rolling method, warm rolling greatly increase{hk0}<001> nucleation and leads to the stronger{hk0}<001> texture. Meanwhile, warm rolling show beneficial effect on microstructure homogenization, showing the effect of the formation of deformation heterogeneities, which could be explained by different activation of slip systems under warm rolling. Thin-gauge non-oriented electrical steels with high permeability could be prepared with Fe-Si columnar-grained initial materials containing C and MnS particles. The texture control shows the effect of moderate inhibiting effect of coarse MnS particles and cold rolling methods, and the increase of{hk0}<001> recrystallization texture could be actualized by the normal growth of{hk0}<001> grains and abnormal growth of Goss grains to different extent.Cube texture could be strengthened in two ways:First, on the basis of initial cube texture in columnar grains, strong cube texture could be obtained in the sample experiencing medium rolling of ?68% reduction with three inter-pass recovery annealing. In the situation that the stored energy of deformed matrix is decreased by recovery annealing, the cube nucleation superiority is determined by the energy difference with surrounding matrix and high orientation gradient induced by the existence of various kinds of deformation heterogeneity; Second, for the cube nucleation occurring inside shear bands in y-fiber deformed grain, higher percentage of{ 110}<229>-{110}<112> grains and fewer a-fiber grains in annealed hot bands, warm rolling process is beneficial. However, this type of cube nuclei show inferiority in comparison with{210}<001> and Goss nuclei inside shear bands, corresponding to weak effect in the formation of cube texture.The simulation results in use of Reaction Stress model cover the results using both Sachs model and Taylor model. By modifying the critical reaction stress values in different directions, the calculated results can be consistent with the the experimental results in references and in this study, namely a-fiber and y-fiber texture. Compared to 012 that could accumulate to 0.2?y, the values of ?12 and ?13 only reach a much lower level as 0.05?y. The relaxation of ?23 or ?13 strengthens {111}<110> or{111}<112> texture respectively, meanwhile the intensity of {111}<110> texture could be increased when{110}<111> slip systems are easier to activate. Based on this model, the strain continuity (in particular, ?12) is fulfilled in pure consideration of stress condition. Taking the calculated texture or orientation change, slip system activation and strain distribution into consideration, the deformation microstrcuture and orientation evolution in BCC steel could be explained.