Thermodynamic Research on Medium Carbon Aluminum Killed Steel by Calcium Treatment

The modification mechanism of alumina,MgO·Al₂O₃ spinel and the condition of precipitation of calcium sulfide was thermodynamically analyzed in this paper.Thermodynamic calculations showed that in order to modify the alumina inclusions into liquid 12CaO·7Al₂O₃,20×10^-6 content of calcium in steel was needed when the aluminum in steel was 0.016% at 1 873 K,meanwhile,sulfur content should be no more than 0.008% to avoid the precipitation of calcium sulfide.When the content of aluminum was 0.02%,and magnesium required for MgO·Al₂O₃ spinel formation was 0.3×10^-6~10×10^-6 at 1 873 K,and 1×10^-6 calcium was sufficient to transfer spinel inclusion into liquid complex inclusions.Incompletely modified spheric inclusions where solid MgO·Al₂O₃ covered by liquid spinel would form depending on the reaction time and size of spinel inclusions.