Effect of several stress inducing coatings on magnetostriction property of a high induction 3% silicon steel

The stress inducing behavior of various coatings by applying coating solutions mainly composed of colloidal silica and one of (Mg,Ca,Sr,Ba,Fe,Zn and Al) phosphates onto high permeability 3% silicon steel sheet (RG-H) were examined. The results of magnetostriction measurements showed that the coating formed by colloidal silica and Mg phosphate mixed solution gave the largest tensile stress to the steel sheets and that the coating by colloidal silica and Al phosphate was second to it. Though the thermal expansion coefficients (α) which were measured on sintered bodies prepared from dried reagents of coating solutions were about 4×10^-6for both coatings containing Al and Mg phosphate, X-ray diffraction peaks of exfoliated powder from coating containing Al phosphate showed the presence of α-cristobalite even after one minute baking at 800°C and showed a remarkable increase of it after the stress relief annealing of 800°C-5h in N2atm. The presence of α-cristobalite seemed to be harmful because of its large α value of 53×10^-6below 300°C. It was concluded that the good magnetostriction property of the coating formed by colloidal silica and Mg phosphate was due to the amorphous structure with low α value even after the stress relief annealing.