Effect of tellurium on the morphology of alumina inclusions in molten iron

Surface active elements in liquid steel may accumulate at the interface of non-metallic inclusions and liquid steel, and thus affect the morphology of the inclusions. In the present work, the effect of Te on the morphology of alumina inclusions was studied at different conditions. After acid extraction, mainly five types of alumina inclusions were identified with SEM, i.e., dendritic, spherical, faceted, plate-like and clustered inclusions. Te was found to considerably modify the morphology of alumina inclusions. At low supersaturation degree, defined by [Al] and [O], and no stirring conditions, 1000 ppm Te addition decreases the percentage of spherical inclusions in number from 68.0 % to 33.9 % whereas it increases the percentages of faceted and plate-like inclusions from 21.6 % to 32.1 % and 8.8 % to 30.5 %, respectively. Stirring the melt for 30 s after Al addition strengthens the effect of Te on the morphological modification, resulting in more plate-like alumina inclusions. In contrast, increasing the supersaturation degree makes the morphological modification by Te less obvious. Moreover, the morphology of faceted inclusions changes considerably due to the addition of Te. Faceted inclusions become more angular and large flat faces develop, forming octahedral shape and plate-like shape (small in size). Based on the attachment energy model, the growth morphology of alumina inclusions was calculated from first principles with VASP software. Starting from the growth morphology, the formation mechanisms of octahedral and plate-like alumina inclusions are discussed.

Publication year:2015

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