Composition and Morphological Analysis of MnO–SiO2–Al2O3 Inclusions during Solidification of Steel

Abstract

To understand the extent of the temperature dependence on the deoxidation reactions during cooling of molten steel and the influence of solute microsegregation during solidification on the formation of oxide inclusions, changes in the morphology and composition of Mn–Si–Al deoxidation products of two actual steel samples are experimentally investigated herein. It is found that from 1823 K to just above the liquidus temperature of steel, oxide inclusion composition does not change significantly, suggesting that the temperature dependence of the deoxidation reactions on oxide inclusion formation can be ignored. Meanwhile, during solidification from the liquidus to the solidus temperature of steel, it is found that positive segregation of Mn and Si in the residual molten steel phase largely influences oxide inclusion composition such that the equilibrium oxide phase shifts from high- to low-Al2O3 region. It is confirmed that the higher Al2O3 oxide inclusions are present in the solid, while the lower Al2O3 oxide inclusions are present in the liquid steel phase. These results suggest that the microsegregation behavior of solute elements in molten steel plays an important role in the formation of inclusions, which is of great importance in the production of high-quality steels.