In this work, we report on the effects of high static magnetic field on the formation of desirable crystallographic orientation of grains ("rotating" cube) during the primary recrystallization of non-oriented steels. Vacuum degassed non-oriented steel with the silicon content about 1 wt% was taken from industrial line after final cold rolling with 80% of deformation and then it was subjected to the laboratory annealing at temperature of primary recrystallization. Whole annealing process was carried with and without the applied external magnetic field of 14 T. The analysis of crystallographic orientation of experimental material was studied by electron backscattered diffraction technique. The microstructural and textural observations have shown a small difference in average grain size between samples annealed with and without magnetic field as well as increase of the "rotating" Cube component and decrease of the intensity of deformation texture by application of magnetic field. The magnetic measurements show that the coercivity value of the sample annealed in the magnetic field of 14 T can be reduced by approximately 3% in comparison with sample annealed under the zero field conditions.
The present work investigates the influence of laser scribing of grain-oriented silicon steel on the improvement of its soft magnetic properties via magnetic domains modification. The experimental material was represented by conventional Fe-3%Si grain-oriented electrical steel that was taken directly from industrial line after the final box annealing. The laser scribing treatments were applied onto the material surface in order to induce thermal stresses having crucial influence on the magnetic domains refinement. The laser scribing conditions have been optimized by introducing thermal stresses onto the experimental material surface leading to optimal refinement of final domains structures and desired magnetic softness minimization. A semiquantitative relationship has been found between the domain patterns and the used fiber laser treating method. The obtained modified domain structure led to a significant decrease in coercivity measured in DC magnetic field from 20 A/m to 12 A/m.
The effects of heat transport phenomena and deformation gradient through the sheet cross-section on the microstructure, texture and magnetic properties of non-oriented Fe-Si steel were investigated. In order to achieve desired conditions for the steel microstructural and textural parameters improvement, a temper rolling process at elevated temperature was examined in combination with subsequent short term annealing, employing fast heating rate in laboratory conditions. The experimental material was represented by conventional medium silicon, vacuum degassed non-oriented steel that was taken directly from industrial line after final annealing. Performed electron back scattered diffraction measurements revealed that the experimental steel, treated by our proposed thermomechanical treatment, was characterized by coarse-grained microstructure with enhanced intensity of rotating cube texture. The magnetic losses of experimental samples were measured in ac magnetic field with 50 Hz frequency on the toroid with external and internal diameters of 25 mm and 15 mm, respectively. These measurements with magnetic field intensity of 2500 A/m showed that the application of our suggested treatment led to clear power losses reduction of the investigated material from initial 9.9 W/kg to 6.4 W/kg, i.e. by more than 35%.
Fiber laser scribing of Fe-3.2Si grain-oriented electrical steel was carried out using three different laser pulse regimes, namely a single pulse laser regime, multipulse laser regime and multipulse laser regime with modulation of laser pulses. The samples were tested for coercivity and nanohardness before and after laser processing. Clear improvements in soft magnetic characteristics were observed for all the regimes using the lowest single pulse energy of 0.6 mJ. The best improvement i.e. the most significant decrease in coercivity was obtained after the regime with 5 pulses. Further increasing in both pulse energy and pulse number resulted only in detrimental effects on both magnetic and mechanical characteristics. Introduction of 50 kHz pulse modulation within 100-pulse laser regimes resulted in lower coercivity values in comparison with the same regimes without modulation. The major effects responsible for the observed improvement are related to optimal refinement and rearrangement of magnetic domains determined by the balance of laser-induced residual stresses and plastic deformation at the surface of the treated material. Thus the fiber laser pulse processing has been recognised as a useful and energy efficient tool in obtaining electrical steels for power transformers with lower core losses.
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