Study On Correlation Between Deformation And Recrystallization Textures And Rolling Parameters In Non-oriented Silicon Steel

Non-oriented silicon steel is an important soft magnetic material widely used in electric power, electronic and military industries. Its magnetic properties are codetermined by recrystallization grain size and texture. At present, both theoretical and technical researches are mainly focused on controlling processing variables to optimize grain size, whereas texture control has received little attention and there is tremendous room for improvement. Since recrystallization texture is strongly dependent on deformation texture and microstructure and deformation texture is largely affected by shear strain distribution, magnetic properties can be improved by adjusting rolling parameters to modify shear strain distribution and deformed microstructure. Therefore, it is of great significance to study on correlation among shear strain distribution, deformation texture, deformed microstructure and recrystallization texture for texture optimization and magnetic properties improvement in non-oriented silicon steel.Based on the above research background, shear strain distribution in symmetric and asymmetric rolling was calculated using finite element methods. And the effects of rolling temperature and warm rolling reduction on deformation texture, shear band characteristics and Goss recrystallization texture were investigated by ODF, EBSD analysis and optical, SEM microstructure observation. Besides, deformation and recrystallization textures in heavily rolled silicon steel were studied. The main results are as follows:Effects of rolling parameters on shear strain distribution: In symmetric rolling, shear strain distribution exhibits a complex dependence on roll gap geometry and friction coefficient. Shear strain magnitude decreases with increasing roll gap geometry and friction coefficient when roll gap geometry plays a dominant role, whereas it increases with increasing roll gap geometry and friction coefficient when friction is the dominated factor. A shear strain distribution diagram (SSDD) was established based on the calculated results, which can conveniently characterize the relationship between shear strain distribution and rolling parameters. In asymmetric rolling, the dependence of through-thickness shear strain distribution on asymmetric ratio can be reasonably attributed to the evolution of neutral points and roll pressure, which jointly determines the direction and magnitude of shear strain. Compared with differential-friction rolling, differential-speed and differential-radius rolling modes can efficiently modify shear strain distribution by means of the broad shift of neutral point adjacent to slower/smaller roll.Effects of rolling temperature on deformation texture, shear band and recrystallization texture:The conventional silicon steel hot band, which is characterized by texture gradients with Goss({110}<001>) and a-fiber(RD//<110>) as dominated texture respectively at surface and center layer, was rolled by 75% to form deformation texture with through-thickness gradients and develop in-grain shear bands in the microstructure. And deformation texture and shear band characteristics change with rolling temperature. When rolled at 20? and 400?, deformation texture consists of a and y-fiber(ND//<111>), whereas s(TD//<110>) and weak a-fiber are formed between surface layer and quarter thickness together with strong a and y-fiber textures at center layer when rolled at 600?. As rolling temperature increased, a-fiber between surface layer and quarter thickness decreases. As for shear band in the microstructure, its characteristics change slightly as rolling temperature varied from 20? to 400?, while shear band decreases remarkably in 600? rolled sheet due to the effects of recovery on microband formation, resulting in suppression of shear band formation. After annealing, the recrystallization texture is dominated by Goss or near Goss orientation at all rolling temperatures, and rolling temperature has no significant effect on distribution of grain size and grain boundary character of primary recrystallization Goss grains. The results show that rolling temperature range used in present experiments does not make substantive change on shear band characteristic which affects recrystallization nucleation.Effects of warm rolling reduction on deformation texture, shear band and recrystallization texture:The deformation texture exhibits through-thickness gradients and shear bands with inclination angles 35° and 17° to the rolling direction develop in deformed structure of the sheet rolled at 400? within reduction range from 50% to 85%. And, deformation texture and shear bands characteristics vary with rolling reduction. As rolling reduction increased, ?-fiber and{111}<110> component increase consistently, while the {111}<112> component increases firstly and then decreases, with maximum intensity at reduction of 65% and 75% respectively at surface layer and quarter thickness. As for shear bands in the microstructure, its number and density increase consistently with rolling reduction ranging from 50% to 75%, and then decrease at 85% reduction, with 17° shear band as the main type in deformed grains. After annealing, the recrystallization texture is dominated by Goss and near Goss orientation except at center layer in 85% rolled sheet. But, the intensity of Goss and the direction of intensity peak deviated from exact Goss orientation change with rolling reduction. As rolling reduction increased, Goss texture increases firstly and then decreases, with maximum intensity at all layers in 65% rolled sheet. The evolution of the direction of intensity peak deviated from exact Goss orientation at surface layer and quarter thickness behaves as firstly deviated along TD//<110> at 50% and then to exact Goss orientation at 65% and 75% and then deviated along ND//<110> at 85%, while the Goss at center layer is deviated along ND//<110> at all reductions. The variation of Goss texture intensity and accurancy is closely related to the number, density and intensity of shear bands and the orientation of deformed grain where shear bands form.Evolution of deformation and recystallization textures under heavy rolling:The deformation texture is composed of ? and ? -fiber, but the texture intensity is affected by rolling temperature. As rolling temperature increased, ?-fiber and{111}<110> component are weakened, while{111}<112> component is strengthened. After annealing, recrystallization texture varies significantly with rolling temperature. A strong ?-fiber and weak{114}<481> are developed in the steel sheet rolled at 20? and 400?, whereas a relatively weak ?-fiber and{114}<481> are produced at center layer and a dominated ?-fiber is formed between surface layer and quarter thickness due to the profuse shear band in deformed structure of the steel sheet rolled at 600?. With annealing temperature increasing, the ?-fiber decreases significantly, while{114}<481> increases consistently, which can be attributed to the significant size advantage and some higher frequency of high energy grain boundary with misorienation angle located at 20°?45°. These results can provide an effective way to produce near{100} recrystallization texture.Under the research conditions described in present paper, variation of recrystallization texture is mainly derived from modification of deformed microstructure, and deformation texture plays its role by affecting deformed structure. Therefore, further study should be conducted on adjusting initial texture and microstructure of hot band and the process in warm and cold rolling in order to make deformed microstructure fully develop its role in optimization of recrystallization texture in non-oriented silicon steel.