Thermodyanmics of CaO in Slag Reduced by Carbon during VD Process of Hollow Steel 95CrMo and its Effect on Inclusions

Abstract

With the help of thermodynamics calculation and kinetic model, the generation mechanism of calcium aluminate inclusions in hollow steel 95CrMo was analyzed. The steel was produced in a certain steelmaking factory whose smelting process is EAF-LF-VD-CC and the micreostructure of the hollow steel 95CrMo samples have been investigated by SEM and EDS. Based on Lumsden’s regular solution model to molten slags, the possibility of CaO in slags reduced by carbon during hollow steel refining in VD furnace was calculated. The influence of furnace vacuum, slag basicity and liquid steel temperature on the reduction of CaO in slag by carbon was discussed. It was showed that the carbon dissolving in liquid steel might reduce CaO in slags to dissolved calcium which could also react with Al2O3 and turn into dot calcium-aluminate inclusions in the steel. The calcium-aluminate existing in the hollow steel easily turned into dot inclusions, which would decrease the fatigue life of the hollow steel. According to the thermodynamic conditions of dot calcium-aluminate inclusions, the influence of slag basicity, temperature of liquid steel, vacuum degree and the Ca treatment process on the quantity of dot inclusions in hollow steel 95CrMo was analyzed.