Evidence for the effectiveness of stress coatings in improving the magnetic properties of high permeability 3% Si-Fe

Application of a stress coating to high permeability 3% Si-Fe imparts a biaxial tensile stress to the material with the greatest component of strain in the rolling direction. Depending upon material quality, the tensile stress can lead to lower core loss values and to improved magnetostriction characteristics. The response of a material to either uniaxial or biaxial tensile stresses is strongly related to permeability (μ at 10 Oe.) and not quite as strongly to grain size. Compressive stresses can be inadvertantly introduced into 3% Si-Fe at a number of stages during its production and subsequent fabrication into transformer cores. The application of a stress coating to oriented 3% Si-Fe reduces the deterioration of magnetostriction and core loss which occurs due to compressive stresses. This reduction in deterioration has been studied for both high permeability and conventional permeability 3% Si-Fe.