Thermal deformation structure and behavior of silicon steel

In order to refine the microstructure of silicon steel ingot and improve its machinability, the effect of low voltage pulse magnetic field on the solidification microstructure of silicon steel was studied, and the thermal deformation behavior and microstructure of different solidification microstructure were compared. The results show that the traditional columnar crystal structure is transformed into equiaxed crystal structure when pulsed magnetic field is applied in the solidification process of silicon steel. With the increase of magnetic field frequency, the equiaxed crystal ratio (equiaxed crystal area/whole area) first increases and then decreases, and the equiaxed grain size first decreases and then increases. With the increase of excitation voltage, the ratio of equiaxed crystal increases, and the grain size of equiaxed crystal increases continuously. The optimal process parameters of pulsed magnetic field are obtained. The magnetic field frequency is 5 Hz and the excitation voltage is 200 V. Under the process parameter of pulsed magnetic field, the equiaxed crystal size in the solidification structure of silicon steel is refined to 1/2 of that without magnetic field, and the equiaxed crystal ratio is increased to 100%. Hot compression tests (950 ℃, strain rates 0.01 s-1 and 0.1 s-1) and hot rolling tests (1 100 ℃) were carried out on the cylindrical crystal structure without pulsed magnetic field and equiaxed crystal structure with pulsed magnetic field frequency of 5 Hz and excitation voltage of 200 V. The microstructure results show that a small amount of dynamic recrystallization occurs in the solidification structure without pulsed magnetic field during the hot compression process, and there are deformed grains in the structure which are difficult to eliminate, which affects the subsequent machining performance. The fine and uniform recrystallization microstructure was obtained under the same thermal compression condition under pulsed magnetic field, and the average grain size was 670 μm. Compared with the microstructure and texture results of hot-rolled sheet, it is also found that the equiaxed crystal solidification structure is more prone to dynamic recrystallization during hot deformation, and the rolling texture strength and anisotropy of sheet are weaker.

As an important magnetic material, silicon steel is widely used as the iron core of various motors, generators and transformers. Silicon steel is mostly produced by continuous casting and rolling, but when the silicon mass fraction is greater than 2%, the surface of the silicon steel sheet often produces uneven "corrugated" defects, which affects the lamination coefficient, leading to the decline of electromagnetic properties and the reduction of insulation film resistance. The main factor affecting corrugating defects is the uniformity of microstructure of hot rolled plate. Improving the microstructure uniformity of hot rolled sheet is beneficial to uniform deformation during rolling process, and has the effect of reducing corrugating defects. The microstructure uniformity of hot rolled plate can be improved by adjusting chemical composition, refining casting grain, adjusting hot rolling process and regularization after hot rolling. Among them, the most effective measures are to control the solidification process, refine the solidification structure, improve the equiaxed crystal rate, and increase the microstructure uniformity of hot and cold rolled silicon steel, so as to obtain the sheet with excellent electromagnetic properties and lamination coefficient.

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