Effect of Ce-La on inclusion evolution in Al-killed high strength steel

Abstract

The mechanism of inclusion evolution after rare earth addition based on oxide metallurgy was investigated experimentally and using thermodynamic calculations, where Ce-La was added to Al-killed high strength steel during Ruhrstahl-Heraeus refining to modify the oxide inclusions within the steel. The typical inclusions observed before Ce-La addition were spherical magnesium aluminate spinel inclusions. And fewer individual Al2O3 inclusions and Al2O3–TiOx inclusions were also observed. The addition of Ce-La led to transformation of MgO · Al2O3 spinel inclusions to (Ce,La)2O3, (Ce,La)2O2S and (Ce,La)2O2S + MgO · Al2O3 inclusions. Thermodynamic calculations indicated that Ce-La combined with dissolved oxygen and sulfur in molten steel to form rare earth inclusions, while the remainder of the Ce and La modified MgO · Al2O3 to (Ce,La)2O3 and (Ce,La)2O2S.