A Comparison of the Magnetic Properties of Hot Repressed and 7.4 g/cm ³ Iron and 0.45% Phosphorus Iron Cores

Atomized iron powder was screened to narrow fractions and annealed. Intermetallic Fe₃P powder was blended with the fractions to provide an alloy containing 0.45% phosphorus after sintering. Cores were pressed to a density of 7.4 g/cm³ and sintered at temperatures ranging from 1600°F (870°C) to 2600°F (1430°C) in hydrogen. Magnetic properties were determined from the sintered cores and compared with previous properties measured for iron and hot repressed 0.45% phosphorus iron.

It was found that the induction at any density level was approximately 500 gausses (0.05 teslas) lower than for iron. Remanent magnetization was influenced by the size of the pores. If pores were large, remanent magnetization was 8 K gausses (0.8 teslas) and increased to 12 K gausses (1.2 teslas) as the pores become finer. Both maximum permeability and the coercive force were improved when 0.45% phosphorus was added. The emperical equations developed for iron could be used to predict the properties of the 0.45% phosphorus iron cores. In the case of maximum permeability, the data points for the 0.45% phosphorus iron fall on the upper two sigma line of the equation. The data points for induction and coercive force fall upon the equation for iron. Structure sensitive properties are generally improved because liquid phase sintering occurs in the 0.45% phosphorus alloys causing grain growth and purification to occur at lower sintering temperatures than for iron.

Resistivity is almost double that of iron at equivalent densities, owing to the addition of 0.45% phosphorus. The effect of the porosity on the phosphorus iron is similar to that upon iron.