Compositional Evolution of Oxide Inclusions in Austenitic Stainless Steel during Continuous Casting

Composition evolution and number density of oxide inclusions in austenitic stainless steel were investigated by analyzing inclusions in a commercial austenitic stainless steel slab. The composition of inclusions was observed to be strongly dependent on size of the inclusion and location in the slab, both, where the inclusions were found. The number density of inclusions increased as the inclusions were found at deeper location from the slab surface. The basicity (%CaO/%SiO2) of the inclusions decreased with decreasing the inclusion size, while the manganese oxide content (%MnO) increased with decreasing the inclusion size. As the inclusions were located deeper from the slab surface, the basicity (%CaO/%SiO2) was found decreased but (%MnO) increased. Such composition changes along with the position in the slab was attributed to the combination of pre‐existing inclusions which were entrapped from the argon oxygen decaburization slag and inclusions precipitated during solidification due to decrease in solubility limit of concerned elements. A theoretical model was developed in order to represent the inclusion composition in the austenitic stainless steel during continuous casting, as a function of the size and location of the inclusion. The model predictions for the composition of inclusion, such as (%CaO/%SiO2), (%MnO), and Al2O3 content, were in good agreement with the measured data. Composition evolution and number density of oxide inclusions in austenitic stainless steel during continuous casting are demonstrated by plant data as well as mathematical modeling. Origin of the inclusions is argon oxygen decaburization (AOD) slag, and the inclusions grow by subsequent oxide formation due to decrease of solubility limit of O, Al, Mn, Si, etc, during casting. A simple mathematical model is presented to account for the composition evolution.