Study On Microstructure,Texture And Ordered Phase Of Strip-cast Grain-oriented High Silicon Steel

Grain-oriented 6.5wt%Si silicon steel shows low core losses and high permeability,which is an ideal soft magnetic material.In this study,a grain-oriented 6.5wt%Si steel was produced by the strip casting process with features of short process and rapid solidification.The Goss texture development,secondary recrystallization behavior and the effect of rolling and annealing process on microstructure,texture and ordered phase were studied.The main research are as follows:(1)The micro structure of the as-cast strip varies along the width and thickness and an appropriate normalizing temperature can effectively improve the uniformity of microstructure and promote the precipitation of AlN particles.A large rolling reduction rate is unfavorable for texture evolution.The moderate reduction rate of 60?70%increases the intensity of recrystallized Goss texture.(2)The microstructure of cold rolling is composed of the grains with low stored energy and shear bands with severe deformation.The corresponding texture consists of a-fiber and yfiber components.With the increase of the secondary rolling reduction,shear bands and the intensity of y-fiber are significant increased.The microstructures of the primary annealing sheets are composed of uniform equiaxed grains,and the textures mainly consist of moderate Goss component and strong ?-fiber component.With increasing rolling reduction,the average grain size decreases and the intensity of Goss texture increases.Correspondingly,the magnetic induction B8 is increased while the core loss P10/50 is weakened.The secondary annealed sheet with the second rolling reduction of 80%shows the superior magnetic properties,i.e.the B8 is 1.48 T and the P10/50 is 1.93 W/kg.(3)The Goss grains randomly distribute across the thickness of the as-cast strip and the normalized sheet.After two-stage rolling,Goss grains nucleate within the shear bands of the deformed y-fiber grains,and the number of Goss grains nucleated within the shear bands of{111}<112>grains is significantly higher than the case of {111}<110>grains.The volume fraction of Goss grains in the intermediate annealed sheet is approximately 12%,which is higher than the initial as-cast strip.(4)During the primary annealing process,Goss grains nucleate by consuming the{111?<112>deformed matrix,and the growth rate is not changed significantly.The formation of recrystallized Goss texture is attributed to the oriented nucleation mechanism.The CSL(Coincidence Site Lattice)boundaries of ?5??9 around Goss grains are similar with the matrix,while the HE(High Energy)boundaries of 20-45° show apparent advantage.Thus,the HE model can explain the mechanism of abnormal growth of Goss grains during secondary recrystallization.(5)The formation of ordered phases can be inhibited by rapid cooling after the intermediate annealing.As the cooling rate increases,the order parameter decreases and the size of ordered phase B2 decreases.However,the rapid cooling leads to limited improvement of the plasticity in grain-oriented 6.5wt%Si steel.The different cooling modes all lead to cleavage fracture in the room-temperature stretching and bending experiments.In addition,cooling rate affects the texture evolution during the subsequent rolling and annealing process.Shear bands are reduced by water-cooling and oil-cooling,and the ?-fiber texture in the annealed sheet is weakened.The annealing texture in the furnace-cooled sample only has an ?fiber texture.Air cooling results in the superior magnetic properties with a magnetic induction B8 of 1.48 T and an iron loss P10/50 of 1.92 W/kg.