Improved low loss high permeability grades, processing and properties

Abstract
Non-oriented electrical steels are sub-divided into "fully processed" and "semi-processed" types. The history of loss reduction has generally been associated with silicon additions for both types of steel which unfortunately is detrimental to high field permeability. More recently the availability of ultra low carbon and ultra low sulphur steels has permitted a shift in the loss/permeability compromise associated with silicon addition by adopting a "lean and clean" approach in which losses are lowered by improved purity and, perhaps, thickness selection whilst good high field permeability is maintained by a restriction on silicon additions. This paper deals with recently developed steels of this type, particularly "Polycor" aimed at the high efficiency induction motor market. The changing rôle of insulative coatings on new materials is also considered. Potential further development of low loss high permeability grades is discussed.