Effect of Surface State on Domain Structure and Core Loss of Grain-Oriented Electrical Steel with High Permeability

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  • 高透磁率方向性けい素鋼板の磁区および鉄損に及ぼす表面性状の影響
  • コウ トウジリツ ホウコウセイ ケイソ コウハン ノ ジク オヨビ テッソン

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Abstract

Improved orientation results in the greater permeability which in turn lowers the core loss. The additional benefit of the greater permeability material is a further decrease in the core loss resulting from a tensile stress imparted by the glass film (forsterite coating) and inorganic insulation coating (S2). In the case of a (110) [001] single crystal, domain observations using scanning electron microscopy indicate a decreasing domain wall spacing with the applied stress. Comparison between two adjacent portions, one with coating and the other without, in a single grain shows the effect of the coating on the domain structure, that is reduction of 180° wall spacings and supression of the supplementary domain structure. A great part of the decrease in core loss with the applied tensile stress or the tensile stress imparted by the coating is believed to be due to the decreased domain wall spacing.<BR>However, the domain structure of large specimens (60 mm×300 mm) observed using the magnetic powder technique, shows that the tensile stress of about 7 MPa is far less effective in reducing the 180° wall spacing, but the domain wall spacing is decreased remarkably by the coating. The glass film imparts about 3 MPa, and the stress coating (S2) imparts about 4 MPa. The stress coating (S2) without the glass film results in the most significant decrease in the 180° wall spacing, and a coating (S) without the glass film is also effective in reducing the domain wall spacing. The tensile stress is not imparted by the coating (S). The domain wall spacing is decreased by an oxidizing annealing in wet hydrogen atmosphere. The tensile stress is not imparted by the oxidized surface film. The stress coating (S2) on the oxidized film is not effective in reducing the 180° wall spacing, when the coating dose not penetrate the oxidized film. With partial removal of the glass film, the core loss is found to increase significantly, but the domain wall spacing increases slightly. Surface roughness is not effective in reducing the domain wall spacing. From these results, the tensile stress applied in the rolling direction or imparted by the coating is effective in lowering the core loss, but not effective in reducing the domain wall spacing. Localized stress imparted by some boundary layer or inclusions lying just below the sheet surface is thought to be effective in reducing the domain wall spacing.

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