Development of non-oriented silicon steel sheet with very low core loss

In the development of the highest grade non-oriented silicon steel sheet, W15/50 = 2.35 w/kg and B50 = 1.68 Tesla (at a sheet thickness of 0.5 mm), two factors responsible for the deterioration of core loss were made clear. One factor was zirconium nitrides as fine precipitates or as the nuclei of AlN, TiN, precipitation restricting the overall grain growth of silicon steel sheets. The other factor was the oxidation of a subsurface layer under the annealing atmosphere resulting in the formation of fine alumina which inhibited grain growth in the subsurface zone. This discovery has finally led to the development of a process for commercially producing the new product.