| Ultra-thin grain-oriented silicon steel is widely used in power and military industries for its excellent magnetic properties at medium frequency,and its magnetic properties show a strong microstructure and texture dependence.The production of an ultra-thin grain-oriented silicon steel starts with grain-oriented silicon steel sheets with different thicknesses,and the steel sheets are subjected to one-stage cold rolling and annealing processes in this study.The effects of raw material characteristics as well as cold rolling and annealing process parameters on microstructure and texture evolutions along the processing route of ultra-thin grain-oriented silicon steel are investigated,and the deformation and recrystallization behaviors of Goss oriented grains during cold rolling and annealing processes are discussed with emphasis.Based on the investigations,industrial preparation routes for ultra-thin grain-oriented silicon steel are pursued.The results are shown as follows:1)Considering the different microstructure and texture evolution laws for different oriented grains in raw material during cold rolling and annealing processes,this study analyzes the cold rolling and recrystallization behaviors of three types of grains with different deviation from exact Goss orientation.ForⅠ-type grains,sharp{111}<112>texture and abundant shear bands and deformation bands are formed during cold rolling,and a small amount of Goss oriented areas are observed in shear bands and deformation bands.During annealing,Goss oriented grains in shear bands and deformation bands nucleate preferentially,with the majority existing in shear bands,thenη-fiber texture peaked at Goss component and uniform structure with relative lower average grain size are obtained.ForⅡ-type（{0kl}<001>）oriented grains,{111}<112>and{113}<361>textures are formed during cold rolling.There exist a small amount ofηfiber areas exists in shear bands and deformation bands,while no shear bands are obtained in{113}<361>oriented region.During annealing,η-fiber nucleation in shear bands and deformation bands occurs preferentially,and a large number of non-ηfiber oriented nuclei present an uneven distribution,then show obvious growth advantage in following stage and thus obtain an uneven annealing structure with a lower proportion ofη-fiber grains.The deformation and recrystallization behaviors ofⅢ-type（{011}<uvw>）grains are similar to that ofⅠ-type grains,while a lower intensity of{111}<112>texture is obtained during cold rolling,and the recrystallization texture shows a diffuse distribution characteristic alongη-fiber.During annealing,η-fiber orientated grains also nucleate preferentially mainly in shear bands and deformation bands.The nucleated non-η-fiber grains present a uniform distribution,and not marked uneven annealed microstructure with a higher proportion ofη-fiber grains and relative larger average grain size is achieved.By overall considering microstructure and texture,the raw material with lower proportion ofⅡ-type grains and moderate proportion ofⅢ-type grains can be used to prepare ultra-thin oriented-grain silicon steel.2)The effects of grain size and thickness of raw material on the evolution of microstructure and texture are analyzed.The grain size of raw material has no obvious impact on the deformed and recrystallization structure of ultra-thin oriented silicon steel because every raw material is coarse-grained material.The deformation reductions during cold rolling process of ultra-thin oriented silicon steel are different for the raw materials with different thicknesses,and the density of shear bands in cold rolling structure is related to the deformation reduction.The thicker raw materials obtain more shear bands after cold rolling,and more nuclei inside shear bands,a smaller average grain size as well as strongerη-fiber recrystallization texture are achieved.Considering both microstructure and texture,the thickness of raw material that guarantees cumulative reduction of cold rolling higher than 70%is beneficial for preparing ultra-thin grain-oriented silicon steel.3)The effects of deformation parameters of cold rolling on the evolution of microstructure and texture are analyzed.The less cold rolling passes,the greater rolling force and surface shear strain when being rolled to the same final thickness.The surface shear at early stage of deformation could be increased by appropriately increasing the first pass reduction under the same rolling passes,and the higher surface shear at early stage of deformation exerts higher effect on the cold rolling deformation process.ForⅡ-type grains,the surface shear could weaken the orientation transition degree alongη-fiber during cold rolling,and reduceα*-fiber as well as other non-η-fiber oriented areas during cold rolling.ForⅢ-type grains,the surface shear could weaken the diffuse degree of{111}<112>texture during cold rolling,and decrease non-ηfiber oriented areas.When considering both microstructure and texture,cold rolling process with four passes and the first pass with a reduction from 35%to 50%are better when using 0.35mm raw material.4)Twinning behavior during cold rolling is discussed.Twinning can occur at different stages of rolling deformation in Goss oriented grain.The twin area fraction increases with the increase of rolling reduction,and the twin orientations are mainly located atα-fiber and are mostly around{100}<011>component.The actual activated{112}<111>twinning systems are shown to have the maximum Schmid factor and shear mechanical work.The greater Schmid factor and shear mechanical work a twinning system has achieved,the easier it is to be activated.In preparation of ultra-thin grain-oriented silicon steel,when an initial material has more grains with exact Goss orientation,more twins are observed in the deformed grains and the twin orientation is closer to exact{100}<011>.The nucleation of{100}<011>orientation grains never happened during annealing process,and the deformation twins are consumed by the surrounding grains during annealing.5)The effects of annealing temperature and time on the evolution of microstructure and texture are analyzed.The effects are linked to the time that non-η-fiber grains show growth advantage to high extent.The lower the annealing temperature,the higher the nucleation proportion in the shear bands and moreη-fiber oriented nuclei,and vice versa.With the prolongation of holding time,{111}<112>deformed regions are consumed by surrounding new grains,and nucleation stage completes quickly.The growth advantage of non-η-fiber oriented grains begin apparently when the growth ofη-fiber grains is blocked by orientation pinning effect.In consequence,the uniformity of the microstructure is gradually deteriorated,and the proportion ofη-fiber oriented grains decreases and the average grain size increases.when the annealing temperature is higher,the growth ofη-fiber grains is blocked earlier,and the growth advantage of non-η-fiber oriented grains appears earlier,then more heterogeneous microstructure and weakerη-fiber recrystallization texture is obtained.When considering both microstructure and texture,annealing temperature and time should not exceed 850℃and 20 mins respectively.6)Industrial trial production:Ultra-thin oriented-grain silicon steel with optimum comprehensive magnetic properties is prepared using a 0.35mm commercial glassless grain-oriented silicon steel plate by N2 company.Four passes with the first pass having a reduction from 35%to 50%are used for cold rolling process.The annealing temperature is 820℃,and the annealing time is 8 min.The optimum B800is higher than 1.8T,and P1.5/400 is lower than 12 W/kg. |
