A Thermodynamic Study on the Inclusion Formation in Ferritic Stainless Steel Melt

Abstract

A type 430 stainless steel melt containing different Al levels was equilibrated with an AOD type slag saturated with Al₂O₃ or MgO to clarify the formation mechanism of slag-type inclusions containing MgO · Al₂O₃ spinel. The Al-O deoxidation equilibrium in the stainless steel melt was examined as a function of melt temperature to check the validity of available thermodynamic data, and to estimate the secondary deoxidation by Al picked up from the ladle slag. During the temperature drop from AOD to tundish, a small amount of entrapped AOD slag particles in molten steel can easily change their composition to a level where the MgO · Al₂O₃ spinel can crystallize. The refractory material, MgO or Al₂O₃ for a ladle, is one of critical factors to affect the Al level in the melt, and hence the formation of MgO · Al₂O₃ spinel inclusions in the final products.