Dephosphorization of Molten Iron by Addition of Calcium under Low Argon Gas Pressure

Abstract

This work was carried out to give scientific support to the dephosphorization of molten iron by metallic calcium. Metallic calcium was added onto molten iron under argon atmosphere the pressure of which is kept higher than that of calcium vapour at experimental temperature of 1 600°C to retain liquid calcium on the meniscus. Calcium-oxide was selected as the crucible material. The experimental results showed that the yield of the added calcium was markedly increased as the argon gas pressure was increased since the rate of vapourization of the liquid calcium into gaseous phase depends on the applied pressure of argon gas. With the sequential addition of calcium at one minute intervals for ten minutes under a argon gas pressure of 8 atmosphere, molten iron was continuously dephosphorized, resulting in 0.0010 wt%P for a low initial phosphorus concentration of 0.0018 wt%. X-ray micro analysis revealed that calcium metal layer existed on top of solidified specimens. This layer can be considered to be the liquid calcium which existed at a higher temperature than the boiling point of calcium under atmospheric pressure. Hydrogen-phosphide(PH₃) was detected in the gaseous mixture obtained by treating the calcium layer with water, so that the dephosphorization products are concluded to be calcium-phosphide (Ca₃P₂).