| 6.5wt.%Si steel is a type of Fe-Si soft magnetic material,which exhibits exceptional magnetic properties.Its outstanding features include high permeability,high resistivity,low coercivity,low iron loss,and an extremely low magnetostrictive coefficient.Due to these properties,it has a wide range of potential applications.It can significantly reduce noise and iron loss in equipment,promote energy conservation,emission reduction,and the development of small-scale lightweight devices.The addition of 6.5wt.%Si content in steel matrix results in the formation of numerous ordered phases and Fe-Si covalent bonds.This leads to a notable increase in brittleness and hardness,a decrease in room temperature plasticity,and the occurrence of edge cracks during rolling.It is difficult to achieve the industrial production of 6.5wt.%Si steel strip by using traditional rolling technology,which severely restricts the large-scale application of 6.5wt.%Si steel.In response to the above issues,the main work of this dissertation is as follows:(1)In response to the problems of high hardness,high brittleness,and poor processing performance of 6.5wt%Si steel,this dissertation analyzes the influence of different process parameters on the top side-pouring twin-roll strip casting process through numerical simulation,revealing the formation mechanism of equiaxed grain structure under the momentum stirring effect in the melt-pool.The process parameters are suitable for preparing 6.5wt.%Si steel as-cast strips were obtained,and the 6.5wt.%Si steel as-cast strip with low order,fine and uniform solidification structure,and good mechanical properties was prepared.(2)The rolling process of 6.5wt%Si steel is complex,with severe edge cracks during medium-temperature rolling and reordering phenomena occurring during cooling.In response to the above issues,the mechanical properties of 6.5wt.%Si steel as-cast strip at medium-temperature were systematically studied through a medium-temperature tensile test.The medium-temperature plastic deformation mechanism of the 6.5wt.%Si steel strip was revealed,and the effect of the cooling method on the mechanical properties of the 6.5wt.%Si steel warm rolled sheet was analyzed.The results show that temperature is the main factor that determines the deformation ability of 6.5wt.%Si steel strip at medium-temperature.After the strip is rolled at 700℃ at 76.5%,the surface quality of the strip is good and there is no obvious crack.Warm rolled sheets treated with oil cooling can effectively reduce residual tensile stress and inhibit the matrix reordering phenomenon.After 50%room temperature cold rolling,the surface quality of the sheets is good and there are no obvious edge cracks.After recrystallization annealing,the magnetic induction B8 is 1.28 T,and the iron loss P10/50,P10/400 and P2/1000 are 0.61 W/kg,7.85 W/kg and 1.73 W/kg,respectively.(3)In response to the possibility of edge cracking during the cold rolling process of 6.5wt.%Si steel sheets,this dissertation investigates the effect of stressrelieving annealing temperature on the processing performance of the sheets.The results show that the ordered recovery phenomenon occurs during the annealing process of 6.5wt%Si steel warm rolled sheets.When the annealing temperature is higher than 350℃,the growth rate of the B2 ordered phase begins to accelerate;When the annealing temperature is higher than 450℃,the D03 ordered phase begins to nucleate and gradually grows.350℃×1 h stress relieving annealing treatment can eliminate the residual tensile stress in the 6.5wt.%Si steel sheet.At this time,the dislocation density,residual tensile stress,and order degree in the sample are lower,showing excellent plasticity at room temperature and cold rolling performance.After stress relieving annealing at 350℃×1h,the warm rolled sheet with a width of 50 mm was cold rolled to 0.15 mm at room temperature without obvious edge cracks and the surface was smooth and bright,and the warm rolled sheet with a width of 100 mm was rolled to 0.15 mm at 300℃ without obvious edge cracks.The recrystallized grain size and y texture of the cold rolled sheet after annealing are smaller than that of the 300℃ warm rolled sheet,and the comprehensive magnetic properties are better.(4)To solve the problem of poor magnetic properties of 6.5wt.%Si steel sheet after annealing,the evolution of microstructure,texture,and magnetic properties of 0.15 mm thick warm rolled sheets under recrystallization annealing temperature were studied.0.08 mm thick 6.5wt.%Si steel ultra-thin sheets were prepared through process optimization and the influence of thickness on the magnetic properties of 6.5wt.%Si steel was analyzed.The results show that with the increase of recrystallization annealing temperature,the coercivity of 6.5wt.%Si steel decreases gradually,the λ-oriented grains and α-oriented grains decrease,and theγ-oriented grains increase.The magnetic induction B8 and B50 of 0.15 mm thick 6.5wt.%Si steel are 1.28 T and 1.58 T,respectively,under the annealing process at 1200℃×1 h.The iron losses of P10/50,P10/400 and P2/1000 are 0.49 W/kg,6.90 W/kg and 1.23 W/kg,respectively.After annealing at 1200℃ for 1 h,the magnetic inductance B8 and B50 of 0.08 mm thick 6.5wt.%Si steel ultra-thin plate reaches 1.36 T and 1.66 T,respectively.The iron losses of P10/50,P10/400,P2/1000 and P10/1000 are 0.41 W/kg,4.84 W/kg,0.78 W/kg and 16.90 W/kg,respectively. |
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