1R. & D. Laboratories-III, Nippon Steel Corporation, Kitakyushu
In general, decrease in sheet thickness decreases the core loss due to the decreased classical eddy current loss. However, at small thickness, surface pinning effects on the domain wall movement become dominant. The proportion of anomalous eddy-current loss arising from the domain wall movement is as much as about 45% of the total loss at the commercial frequencies, 50 and 60 Hz, but the relationship between the anomalous loss and the sheet thickness has not been clarified yet. The tensile stress imparted by the inorganic coating decreases the core loss, but there is no evaluation of the effect of thickness with tensile stress on the core loss.
The systematic investigation has been made on specimens with various sheet thickness, for which the chemical polishing technique has been used.
The decrease in core loss with tensile stress was greater for smaller thickness. Especially, for B8=1.77 T, the applied tensile stress increased the core loss for larger thickness and decreased the core loss for smaller thickness. The greater tensile stress decreases the domain wall spacing. The decrease in domain wall spacing with tensile stress was greater for larger thickness than for smaller thickness.
The magnetostriction measurements indicated that the 90°ree domain volume at a demagnetized state was smaller for smaller thickness, and the volume of new 90°ree domains created at intermediate inductions due to the need of reducing magnetostatic energy was smaller for smaller thickness. The applied stress decreased the 90°ree domain volume at a demagnetized state and suppressed the formation of 90°ree domains at intermediate inductions. The magnetostatic energy due to free poles appearing on the surface was less effective in reducing the domain wall spacing and creating 90°ree domains for smaller thickness.
The decrease in core loss with stress was due mainly to the decreasing supplementaly domains, especially 90°ree domain volume. The behavior of magnetization for a smaller thickness sheet was similar to that for a larger thickness sheet with larger B8.
iron-silicon alloy, grain oriented electrical steel, domain structure, domain wall spacing, magnetostriction, core loss, eddy current loss, applied stress
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