Removal of P and Cr, which are impurities in a Fe-36%Ni alloy, was investigated by conducting experiments 30 kg scale on oxidation refining of a 36% Ni melt containing 0.1 mass% P and 0.4-1.5 mass% Cr with a CaO-SiO₂-CaF₂-Fe_tO slag. FeCr₂O₄ was identified of X-ray diffraction analysis of water-cooled slag sample just after the experiments. Therefore, the oxygen potential of the dephosphorization reaction was taken to be controlled by the formation reaction of FeCr₂O₄. The removal reaction of P and Cr occurred along the P-Cr equilibrium (Eq. (A)), and consequently high temperature treatment was effective in lowering the P content in the range of the present Cr contents.

2[P]+5/4FeCr₂O₄(s)=(P₂O₅)(l)+5/4Fe(l)+5/2[Cr] ......................(A)

The phosphorus distribution ratio (L_P) decreased with increasing Cr content in the metal. This was considered because the oxygen partial pressure was lowered by increasing the content of Cr. In addition, L_P increased with increasing in Ni content in the metal. It was concluded that this was because the oxygen partial pressure was increased with increasing Ni content mainly.