Effect of Al Deoxidation on the Formation Behavior of Inclusions in Ce-Added Stainless Steel Melts

The effect of Al deoxidation on the oxygen content and the inclusion properties (composition, size and morphology) of Ce-added stainless steel melts at 1873 K was investigated. The total oxygen content was about 310(+/- 40) ppm before Al addition and slightly decreases with holding time when Al content was lower than 0.01%, whereas the oxygen content drastically decreased when Al content was greater than about 0.05%. Al content initially decreased, followed by an increase by addition of Ce, which originates from the reduction of Al2O3 in the refractory and/or inclusions by added Ce. The initial inclusions before Al addition were mainly Mn(Cr)-silicates. When Ce was added without Al deoxidation, small amounts of Ce oxide were detected after Ce addition. However, the content of Ce oxide decreased with holding time, and the inclusion composition reverted to the MnO-SiO2-Cr2O3 system. The initial Mn(Cr)-silicate inclusions transformed to Al2O3-rich inclusions by Al addition, and then Ce2O3 was enriched by Ce addition due to local enrichment of Ce around Al2O3 particles, resulting in the founation of AlCeO3-type inclusions. However, the Ce2O3 in the inclusions was continuously reduced by Al due to higher chemical potential of Al than Ce, finally forming the Al2O3-CeAl11O18 complex inclusions.