OXYGEN SOLUBILITY IN CARBON-CONTAINING Fe –Co MELTS

Abstract

Thermodynamic analysis of oxygen solutions in carbon-containing Fe – Co melts has been carried out. The equilibrium constants of interaction of carbon and oxygen, the activity coefficients at infinite dilution, and the interaction parameters for melts of different composition at 1873 K were determined. The dependences of the oxygen solubility on the contents of cobalt and carbon in the studied melts were calculated. Carbon has a high affinity for oxygen in iron-cobalt melts. Deoxidation ability of carbon increases significantly with the increasing of cobalt content in the melt. Deoxidation ability of carbon in pure cobalt more than an order of magnitude higher than that in pure iron. Reaction products of carbon deoxidation are gaseous oxides – monoxide (CO) and carbon dioxide (CO 2 ). The interaction reaction of carbon and oxygen dissolved in the melt, and hence deoxidation ability of carbon depends on the total pressure of the gaseous phase above the melt. Deoxidation ability of carbon increases significantly with the gaseous phase pressure lowering. The minimum oxygen concentration achieved for alloys of the same composition decreased practically an order of magnitude at decrease 10 times the total pressure of the gaseous phase. The gaseous phase composition above Fe – Co melts and equilibrium carbon and oxygen concentrations in the melt at a total pressure of the gaseous phase P, of 1.0; 0.1 and 0.01 atm were calculated. Optimum oxygen concentration (1 – 10 ppm) in Fe – Co melts, depending on the total pressure of the gaseous phase (0.01 – 1 atm) is achieved at carbon contents from 0.01 to 1 %. The curves of the oxygen solubility in carbon-containing iron-cobalt melts pass through a minimum, which shifts toward lower carbon contents with increasing cobalt content in the melt. Further carbon additions leads to an increase in the oxygen concentration of the melt so that the higher cobalt content of the melt, the steeper the increase in the oxygen content after the minimum as carbon is added to the melt.