MATCHED THERMOCHEMICAL DIAGRAM FOR VACUUM DECARBURIZATION OF FERROALLOYS

The carbon content of high carbon ferroalloy melts can be reduced by a vacuum treatment. Carbon and oxygen dissolved in the melt react to fo rm CO. Although this process has been suggested in the literature, no comprehensive analysis of the equilibrium partial pressure of CO over an alloy melt with a given carbon and oxygen content has been reported . In this paper, a new type of matched thermochemical diagram is intro duced, from which the feasibility of decarburization at reduced CO pre ssure and the minimum achievable carbon level can be graphically evalu ated for any alloy composition and temperature. Carbon and oxygen pote ntials of different alloys are plotted as functions of temperature on two terminal diagrams. By projecting information from these plots onto a central diagram, containing data on the Gibbs' energy of mixing for the C-O system, equilibrium partial pressures of CO and CO2 are obtai ned. Nomograms on the central diagram give a direct indication of the equilibrium partial pressures at any given temperature. The carbon and oxygen activities in ferrochromium alloys have been assessed and the results are presented to illustrate the construction and use of the ma tched thermochemical diagrams.