Influence of Sulfur on Initial Permeability of Commercial 49% Ni–Fe Alloys

Abstract

Attainment of high initial permeability in commercial 49% Ni–Fe alloys is shown to be a function of the sulfur content and grain size. Low sulfur material was obtained by desulfurization during melting or by strip annealing. μ₄₀ of the low sulfur material was significantly higher than that of normal commercial material at annealing temperatures below 1200°C. When annealed at 1200°C, μ₄₀ for the initially low sulfur material was slightly lower because of a smaller grain size or a higher final sulfur level. Analysis of sulfur content of annealed material by the methylene‐blue technique allowed a direct correlation between μ₄₀ and sulfur content in secondary recrystallized structures. In general, μ₄₀ values in excess of 10 000 cannot be obtained unless final sulfur content is less than 12 ppm. Highest initial permeabilities result from a coarse‐grained secondary recrystallized structure and low impurity contents.