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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 AI 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. Index Terms - Aluminum, iron loss, magnetic flux density, motor, nonoriented electrical steel sheet, rare-earth metals, silicon.

The influence of stresses on the magnetic properties of nonoriented electrical steels was studied. The dependence of iron loss on compressive stress was affected by grain size. The magnetic polarization J in strong magnetic fields such as 5000 and 10,000 A/m increased due to compressive stresses and decreased due to tensile stresses in samples with low Si content. Using Kerr-effect domain observation, it was found that the reduction in J caused by tensile stresses was attributable to residual striped domains. Magnetostriction measurements in strong magnetic fields indicated that the increase in J under compressive stresses originated from the Villari effect (inverse magnetostrictive effect) due to negative magnetostriction in low-Si materials. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 10-18, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22320 [ABSTRACT FROM AUTHOR]