Dephosphorization of Molten 18%/Cr-4%C-Fe Alloy by Alkali Metal Carbonate-Halide Mixtures

Abstract

Molten 18%Cr-4%C-Fe alloy whose composition is close to the ternary eutectic one (m.p.=1150°C) was subjected to the treatment by alkali metal carbonate-halide fluxes at a temperature of 1300°C. Thermodynamically phosphates of potassium and sodium are very stable and their halides are expected to increase activity coefficient of chromium in the fluxes. From those considerations, various mixtures of carbonates and halides of sodium, potassium and calcium were examined for dephosphorization of molten high chromium alloy containing 0.1% phosphorus of 300 g in weight. Higher dephosphorization was obtained with potassium carbonate than with sodium carbonate, and the best dephosphorization degree was 60% without appreciable chromium oxidation when 15 g of potassium carbonatepotassium chloride or-potassium fluoride mixture was used.