Non-metallic Inclusion Evolution during Argon Oxygen Decarburization and Ladle Processing

In this work we use thermodynamic and kinetic models to predict evolution of spinel and MgO non-metallic inclusions after argon oxygen decarburization (AOD) processing of an aluminum-deoxidized stainless steel. Inclusions form during liquid steel processing and are generally detrimental to downstream processing and steel properties. Models predicting inclusion evolution pathways have typically been applied to lower alloy content carbon steels. In this work we investigated a steel composition with alloying elements such as Cr, Co, Mo, and Nb, processed in the AOD, which utilized higher stirring rates and temperatures compared to ladle refining. Calculations were made with FactSage, with effective equilibrium reaction zone (EERZ) kinetic calculations made using the macro processing feature. Results were compared to plant sample compositions and automated inclusion analysis. The high temperatures and stirring rates present in AOD processing were observed to facilitate Mg transfer to the steel and inclusions. Modeling without the Mg*O associate in FactSage more closely fit the observed data. Additional alloying elements did not significantly change slag/metal reactions or inclusion compositions in modeling, but the strong stirring led to inclusion generation processes (reoxidation or slag entrainment) that were not accounted for in the present work. The reduction stage of AOD processing was found to be vital to inclusions in this process route.