Thermodynamic and kinetic aspects of the refining of Fe-Cr alloys using calcium under very low oxygen partial pressure

The removal of phosphorus and other elements, e.g. Sn, Pb, As from liquid i ron alloys containing chromium through oxidation is not possible from the t hermodynamic point of view. Under very strong reducing conditions, when oxy gen partial pressure po(2) less than or equal to1.10(-17) atm and when alka line earth metals, mainly calcium, axe used as a reacting substance, the re action proceeds according to the following scheme: n\[Ca](Fe), Ca-(l), {Ca}((g))\+m[X](Fe) double left right arrow CanXm, wher e: X = P, N, sn, As,... etc. The investigations concerning this type of reaction axe the main subject of the present study. It was found, that the characteristic minimum [%X](min) occurs on the curve s [%X] = f(tau), where tau - refining time. The thermodynamic-kinetic model and computer program have been developed to find out how the main physicoc hemical factors determine the location of the [%X](min). The program allows to determine simultaneously the changes of content of six elements, i.e. O , S, P, N, C and Ca vs. refining time for arbitrarily selected values of te mperature, pressure, metal composition, calcium addition etc. As the refini ng substance, the solution of calcium in calcium fluoride, metallic calcium and hydride calcium have been tested. The investigations were carried out under argon pressure within the furnace elevated up to 1.0 MPa at 1743 and 1823 K, respectively, using the CaF2-Ca equimolar solution. The good agreem ent between the experimental results and calculated curves [%X](Fe) = f(tau ) has been achieved.