EFFECTS OF MGO AND AL_2O_3-MGO·AL_2O_ REFRACTORIES ON OXYGEN CONTENT OF INTERSTITIAL FREE STEEL IN A VACUUM CONDITION

摘要

The samples of interstitial free (IF) steel were heated at 1700-1770 ℃ in induction furnace under vacuum condition in MgO-based and Al_2O_3-MgO · Al_2O_3 based crucibles, respectively. The steel samples were taken out from furnace for every 0.5hr by a fused silica pipe and the Total Oxygen Content (TOC) of steel sample were determined. It was found that TOC of steel samples heated in MgO crucibles was more than that in Al_2O_3-MgO·Al_2O_3 crucibles, and addition of MgO powder into Al_2O_3-MgO·Al_2O_3 crucibles increased TOC of steel samples. Addition of calcium alumina (CA) cement in Al_2O_3-MgO·Al_2O_3 crucibles increases TOC of IF steel heated in these crucibles. Two mechanisms of reoxidation of IF steel by refractories, volatilization-dissolution and reaction-diffusion through a liquid layer between molten steel were proposed. The volatilization rate of MgO is much more than Al_2O_3-MgO·Al_2O_3, resulting in that TOC of steel samples heated in crucibles containing MgO more than that in Al_2O_3-MgO·Al_2O_3 crucibles. CA addition improves formation of liquid layer that is rich in CaO and dissolution of oxygen. The high purity and low volatilization oxides are beneficial to avoid oxidation of steel in vacuum condition.