Transient Inclusion Evolution During Modification of Alumina Inclusions by Calcium in Liquid Steel: Part II. Results and Discussion

This study investigates the formation of intermediate reaction products following the addition of calcium to aluminum-killed steel. Steel samples were collected from both laboratory and industrial heats, and inclusions were characterized using automated and manual scanning electron microscopy alongside X-ray microanalysis of the polished cross sections and inclusions extracted by steel dissolution. Results indicate that in industrial and laboratory melts with over 40 parts per million (by mass) of dissolved sulfur, calcium sulfide emerged as the primary reaction product post-calcium treatment, while calcium aluminates materialized subsequently. The study proposes that calcium aluminates are formed through reaction between calcium sulfide and alumina. In contrast, for a laboratory heat with only 7 parts per million of sulfur, calcium oxide was identified as the main initial calcium reaction product. A straightforward mechanism is proposed for the modification of alumina inclusions by calcium, which accounts for the transient formation of CaO and CaS, elucidating the alteration of inclusion compositions during the treatment process.