Study On Recrystallization Texture In Two-Stage Cold Rolled High Silicon Steel Thin Sheets

High silicon steel with silicon content of 6.5wt.%exhibits high resistivity,low magnetocrystalline anisotropy and near zero magnetostriction,resulting in the excellent performance of low iron loss and low noise.It is considered to be the ideal core material for motors and transformers,and one of the critical materials for energy saving and emission reduction in electric power field.Rolling and texture control are two key factors for manufacturing high-quality high silicon steel sheets,however,it is difficult to fabricate high silicon steel sheets through rolling process owing to high ambient brittleness.Therefore,the research on high silicon steel has long been focused on the preparation methods.In recent years,the progress on conventional rolling of high silicon steel has been made by domestic researchers and texture control based on rolling becomes research hotspots gradually.Owing to the high flow stress,it is basically inevitable to apply two-stage cold rolling process to fabricate high silicon steel thin sheets.For silicon steel,enhancing favorable η(<001>//RD,rolling direction)fiber and weakening detrimental γ(<111>//ND,normal direction)fiber is one of key problems.It is,however,difficult to improve η fiber because γgrains usually gain both number and size advantages during primary recrystallization.Initial grain size and cold rolling reduction are the important factors affecting the development of ηfiber.Nevertheless,how the initial grain size and cold rolling reduction influence the strengthening of η fiber during grain growth stage is still lack of systematic investigation in high silicon steel thin sheets.Moreover,the magnetic properties of high silicon steel can be remarkably improved by the development of Goss({110}<001>)and Cube({100}<001>)secondary recrystallization textures,which are very sensitive to alloy composition,grain size distribution,grain boundary character distribution,and so on.However,the formation mechanism of secondary recrystallization texture in high silicon steel thin sheets is still unclear so far.In present work,high silicon steel thin sheets of 0.10～0.30mm were fabricated through two-stage cold rolling process.The strengthening mechanism of η fiber during high temperature annealing,as well as the formation mechanism of Goss and Cube secondary recrystallization textures were investigated by means of X-ray and electron backscattered diffraction(EBSD)techniques.Intermediate grain size(the grain size after intermediate annealing,acting as the initial grain size prior to the second-stage cold rolling)has an important effect on η primary recrystallization texture.As the intermediate grain size increases from 40pμm to 120μm,η fiber is enhanced and y fiber is significantly weakened after final annealing.Intermediate grain size can effectively regulate the ratio of high stored-energy regions including shear bands and grain boundaries,thus encourage η grains to gain both number and size advantages during primary recrystallization.Finally sharp η fiber is developed after considerable grain growth.Second-stage cold rolling reduction also has obvious effects on η primary recrystallization texture.As rolling reduction increases form 60%to 80%,sharp η fiber is achieved irrespective of rolling reductions,however,excessive rolling reduction can enhance y fiber.Second-stage cold rolling reduction affects η fiber by changing the width of deformed grains,the number and intensity of shear bands.The appropriately increased intermediate grain size may ameliorate recrystallization texture under high second-stage cold rolling reduction.In high silicon steel thin sheets containing NbC inhibitor,Goss secondary recrystallization texture is developed.According to analysis,Goss grains occupy a small amount of area fraction in primary matrix.However,some of Goss grains with size advantage can grow abnormally by virtue of high-frequency HE(high energy)boundaries as matrix grains are strongly pinned by inhibitor particles.Secondary recrystallization of Goss grains can be explained through HE theory in present study.In high silicon steel thin sheets,strong deformation textures including λ(<001>//ND),γand a(<110>//RD)fibers are responsible for the formation of η fiber with the peak at{210}<001>,X fiber with the peak at Cube and y fiber after primary annealing.The formation of Cube primary recrystallization texture is attributed to the combined effect of oriented nucleation and oriented growth.The shear band orientation within {111}<112>-<110>and{112}<110>deformed matrices,as well as the orientation rotation of initial λ-oriented grains during rolling process are analysed through crystal plasticity finite element method(CPFEM).The relationship between η and λ recrystallization textures and the orientation distribution of deformed matrices is proposed.In some regions of primary recrystallization matrix,numerous grains with similar orientation gather and form colonies,where Cube grains are surrounded by higher frequency of HE boundaries,inducing the abnormal growth of Cube grains finally.In present study,the manufacturing process of high silicon steel thin sheets is similar to that of conventional silicon steel sheets.Therefore,the strengthening mechanism of primary recrystallization texture and the mechanism of secondary recrystallization proposed in this study can provide a theoretical and technological foundation for industrialization of high silicon steel thin sheets.