Nobuyuki Morito

Nonoriented electrical steel sheet with low iron loss for high-efficiency motor cores

A new material was studied for high-efficiency motor cores that need higher magnetic flux density, lower iron loss, and lower mechanical hardness. Excessively high Si content tends to decrease magnetic flux density of nonoriented electrical steel sheets. The composite addition of rare-earth metals (REM) and Al into molten steel was found to make inclusions coarse and remarkably improve grain growth during stress relief annealing, which resulted in decreased iron loss. A new nonoriented electrical steel sheet (50RMA350) with Si, Al, and REM has been successfully developed to give a higher efficiency to inverter drive model motors than a conventional material.

Influence of surface roughness on magnetic properties of Fe-Si-B amorphous alloys

Influence of surface roughness on magnetic properties of Fe/sub 78/Si/sub 9/B/sub 13/ and Fe/sub 78/Si/sub 14/B/sub 8/ amorphous alloy ribbons was investigated. Magnetic induction in an external field of 800 A/m, B/sub 8/ of Fe/sub 78/Si/sub 9/B/sub 13/ ribbon increased slightly with decreasing surface roughness, while iron loss W/sub 13/50/, at 1.3 T 50 Hz excitation, remained almost at the same level. In Fe/sub 78/Si/sub 14/B/sub 8/ amorphous alloy, however, quite different behaviors were observed. Both B/sub 8/ and W/sub 13/50/ were improved remarkably with decreasing surface roughness of the ribbon. Fe/sub 78/Si/sub 14/B/sub 8/ amorphous ribbon showed as good a magnetic performance as Fe/sub 78/Si/sub 9/B/sub 13/ only if it had a smooth surface. The drastic improvement of iron loss with decreasing surface roughness was mainly due to the decrease in hysteresis loss. According to the analysis of the iron loss and surface roughness of the ribbons, it was considered that gentle and large undulations of the ribbon surface did not prevent the domain wall from moving, but steep and small irregularities such as air pockets pinned the domain wall. This behavior seems to be caused by the different mechanism of domain wall pinning in these two amorphous alloys.

Magnetic properties and surface crystallization induced by selective oxidation in Fe-B-Si amorphous alloy

The relationship between the annealing atmosphere and the magnetic properties of Fe78.5B13Si8.5 amorphous alloy has been studied, showing that annealing in nitrogen, argon, hydrogen and air significantly improved the iron loss of the amorphous ribbon, giving much better results than annealing in an H2 + H2O atmosphere. A boron-depletion zone with the alloy composition O to 3 mol % B and 9 to 11 mol% Si was detected by Auger electron spectroscopy under the oxide film formed during annealing in H2 + H2O. The iron crystalline phase is formed only on the ribbon surface after annealing in H2 + H2O. A mechanism is proposed explaining the deleterious effect of annealing in the H2 + H2O, whereby the H2O in this atmosphere selectively oxides boron in the amorphous alloy to form a B2O3 film and the boron-depletion zone, and the alloy in this zone is then crystallized into α-Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous alloy ribbon (which was observed by transmission Mössbauer spectroscopy) and thus deterioration of the iron loss.

Surface crystallization of amorphous Fe-B-Si alloy annealed in a gas atmosphere containing organic vapour

The relationship between the annealing atmosphere and the magnetic properties of Fe78.5B13Si8.5 amorphous alloy has been studied, showing that annealing in an inert gas atmosphere containing a borosiloxane resin significantly improves the core loss of the amorphous ribbon, and that annealing in an inert gas without any organic resins, gives much better results than annealing in an inert gas atmosphere containing cellulose and vinyl acetate resins. A boron-depletion zone was detected by Auger electron spectroscopy under the oxide film formed during annealing in the inert gas atmosphere containing cellulose and vinyl acetate resins. Annealing of the amorphous ribbon in the cellulose and vinyl acetate resins selectively oxidizes boron in the alloy to form a B2O3 film and a boron depletion zone; the alloy in this zone is then crystallized into α-Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous ribbon and thus deterioration of the core loss. On the other hand, annealing in the borosiloxane resin results in neither selective oxidation of boron nor surface crystallization of the amorphous ribbon