Effect of Magnetic Transition on the Solubility of Alloying Elements in Alpha Iron

Abstract

The solubility of ferrite forming elements, Be, Ti, Mo, P and Sb, in αFe at temperatures between 600 and 1200°C was determined by X-ray diffraction and microprobe analysis. It was confirmed that the solubility decreased abnormally in the ferro-magnetic region, especially in the case where the alloying element had a pronounced tendency to lower the Curie temperature. Thermodynamic analysis was made on these data, separating the free energy of αFe-X solid solution into their magnetic and non-magnetic components, and approximating the former by a modification of the magnetic free energy of pure αFe, as proposed by Zener and Hillert et al. It was cansidered that the more abruptly the solute atoms lower the Curie temperature the more pronounce the tendency to destroy the magnetic spin ordering and receive an additional repulsive force from the neighboring Fe atoms. This seems to account for the extraordinarily low solubility.