Formation Mechanisms And Control Methods Of Recrystallization Microstructure And Texture Of Fe-6.5Si Electrical Steel Sheets

High silicon electrical steel (Fe-6.5 wt% Si alloy) has high magnetic permeability, low coercivity, low core loss and near-zero magnetostriction. It serves as the key material of high-performance electromotor and transformers, low noise and low energy consumption electrical devices as well as the equipments & components using in the high frequency fields, such as high frequency reactor. Texture is one of the main influences on magnetic properties of electrical steel. Favorable texture is helpful for the improvement of magnetic induction and the reduction of core loss. For grain-oriented electrical steel, the desired texture is strong <001> texture paralleled to rolling direction. For non-oriented electrical steel, the ideal texture is {100} texture. So far, grain-oriented high silicon electrical steel with strong <001> texture is not able to produce by commercial chemical vapor deposition (CVD) method. The non-oriented high silicon electrical steel products by CVD method do not have strong {100} texture, which leads to a comparatively low magnetic induction and large core loss. In order to develop advance technology for fabricating grain-oriented and non-oriented electrical steel with high performance, it is essential to achieve pratical control of recrystallization microstructure & texture in high silicon electrical steel sheet. Therefore, the evolution of microstructure & texture of high silicon electrical steel during solidification, rolling, annealing and the effect of microstructure & texture on magnetic properties should be clarified.Several issues of high silicon electrical steel were invetigated systematically in the present studies, including the inheritance of {100} texture during rolling & annealing, the formation mechnisms of {100} & <001> texture, the effect of grain boundaries on recrystallization texture, the comprehensive effect of grain size & texture on magnetic properties. The present studies may serve as theoretical basis for the fabrication of grain-oriented & non-oriented electrical steel with high magnetic induction and low core loss.When high silicon electrical steel with initial columnar grains were rolled as the axial of the columnar grains paralleled to the rolling direction (RD method), the volume fraction of {100} initial texture was 40～49% and the rolling texture was evolved along γ and λ fibers instead of a fiber. After annealing, the volume fraction of {100} recrystallization texture reached 47.3%. This process exhibited a pronounced{100} texture inheritance, because when rolling as the KIJ method, the microstructure of the columnar-grained slab had few boundaries paralleled to the transverse direction, the rolling sample had low dislocation density & deformation stored energy, which was favorable to form{100} recrystallization texture during annealing.The effect of grain size on core loss of high silicon electrical steel was larger than recrystallization texture, while the effect of recrystallization texture on magnetic induction was larger than grain size. The magnetic induction improved with the enhancement of{100}&<001> recrystallization texture and decreased with the increase of grain size. For non-oriented electrical steel with{100} texture, the average grain size to seek minimum core loss was 536～615 μm in the high silicon electrical steel sheets with thicknesses of 0.2～0.4 mm, which was larger than 100～200 μm for the electrical steel with common silicon content.High silicon electrical steel with initial columnar grains were rolled as the RD method with a reduction of 97% and annealing at 1000℃ for 1 h, then, the annealed sheets were further secondary cold rolling with reduction of 5% to 40% and annealing at 1000℃ for 1 h. The prepared samples had strong<001> recrystallization texture. In addition, the<001> texture component of the annealed samples initially enhanced and then weakened with the increase of secondary cold rolling reduction. The volume fraction of <001> texture component reached the maximum in the samples after secondary cold rolling with a reduction of 30%. For the same secondary cold rolling reduction of 30%, the<001> texture component of the annealed samples enhanced from 20% to 34% with increasing the annealing temperature from 1000℃ to 1300℃. When annealing at 1300℃, the <001> texture component enhanced from 34% to 44% with increasing holding time from 1 h to 5 h. The volume fractions of cube and Goss texture in the samples after annealing at 1300℃ for 5 h were 23% and 21%, respectively.According to the above results, an advance process for preparing non-oriented high silicon electrical steel sheets with high magnetic induction or low core loss were proposed by using the{100} texture inheritance of columnar-grained rolled as RD method. Sheets with thickness of 0.2～0.4 mm were obtained by controlling the parameters of solidification, rolling and annealing. After annealing, the highest magnetic iniduction B8 of the samples with thickness of 0.2 mm was 1.38 T, the lowest core loss P10/so was 0.5 W/kg and P10/400 was 6.3 W/kg. In addition, the highest magnetic iniduction B8 of the samples with thickness of 0.3 mm was 1.43 T, the lowest core loss Pio/so was 0.6 W/kg and P10/400 was 7.7 W/kg.Another advance process for preparing grain-oriented high silicon electrical steel sheets with strong<001> texture was proposed by using the advantages of nucleation and surface energy of cube & Goss grains during annealing. Sheets with thickness of 0.14 mm were obtained by controlling the parameters of secondary cold rolling and annealing. After annealing, the highest magnetic iniduction Bz of the sheets was 1.40 T, the lowest core loss P10/50 was 0.4 W/kg and P10/400 was 5.9 W/kg.