Study On Microstructure And Texture Of Primary And Secondary Recrystallization In High Si Grain-Oriented Silicon Steel Thin Sheets

Grain-oriented silicon steel is mainly used to manufacture transformer cores.The control of microstructure and texture is very difficult and its manufacturing process is very strict.It is known as handicraft" in iron and steel industry.Iron loss is the core index to evaluate the magnetic properties of grain-oriented silicon steel.Increasing resistivity and reducing the thickness of grain-oriented silicon steel sheets can effectively reduce their iron loss.At present,the main products produced internationally are grain-oriented silicon steel with 3.0-3.5%silicon content.Therefore,the development of thin-gauge products with high resistivity is the main development direction of grain-oriented silicon steel in the future.In this paper,hot rolling,cold rolling,decarburization annealing,nitriding annealing and high temperature annealing process are used to produce high silicon(4.5%)grain-oriented silicon steel sheets with high resistivity and high Al(3.2%Si+0.8%Al)grain-oriented silicon steel sheets with thickness of 0.12?0.30 mm.On this basis,4.5%Si grain-oriented silicon steel sheets with thickness of 0.05?0.10 mm are further prepared.And XRD,EBSD and B-H Magnetic Analyzer are used to analysis microstructure and texture evolution of grain-oriented silicon steel sheets and ultra-thin sheets during primary and secondary recrystallization.The following conclusions were drawn:(1)The grain size before the second cold rolling is an important factor in affecting the magnetic properties of 0.12 mm 4.5%Si grain-oriented silicon steel sheets.The suitable size range is 35-45 ?m.When the grain size is less than 20?m,the primary recrystallization grain sizes are too small,and the onset temperature of secondary recrystallization is low,which is not conducive to the excellent growth of accurate Goss grains.(2)It is found that the primary recrystallized ? grains can also occur secondary recrystallization under the condition of high aluminum,thus obtaining the strong ?secondary recrystallization texture,which leads to the maximum magnetic induction B8 reaching at 1.71 T.Compared to high silicon grain-oriented silicon steel,the secondary recrystallization grain size of silicon steel with high aluminum content is obviously smaller,and the average grain size is about 500 ?m.The obvious fine secondary recrystallization microstructure provides a good condition for the use of high aluminum grain-oriented silicon steel sheets at high frequency.(3)The reduction rate is an important factor in affecting the deformation mechanism of ultra-thin grain-oriented silicon steel sheets during rolling,When the reduction rate is less than 47%,the deformation mechanism is dominated by deformation twinning and it is difficult to form and develop the favorable texture after annealing.While at 67%reduction rate,the effect of deformation twins is weakened,and shear bands obviously appear.Goss texture develops preferentially after annealing.