Abstract: When aluminum is used for deoxidation in tinplate production, a large amount of hard, brittle Al₂O₃ inclusions are formed. As the cold-rolled thin sheet of this steel demands high surface quality, it is necessary to control the quantity and morphology of hard, brittle alumina-type inclusions. The calcium treatment process can modify the morphology and particle size of alumina inclusions. The influence of calcium and sulfur content in the steel on the modification of alumina inclusions was investigated through industrial trials and thermodynamic calculations, and the effect of temperature on inclusion types was also studied. The industrial trial results demonstrated that after 3 minutes of calcium treatment, the average size of inclusions decreased from 2.01-2.61 μm to 1.44-1.60  μm, while the number density of inclusions increased from 29.85-46.51 counts/mm² to 69.85-94.91 counts/mm². Upon exiting the ladle furnace, the average inclusion size increased to 1.82-2.43 μm, and the number density decreased to 39.95-53.05 counts/mm². From refining to casting, the decrease in molten steel temperature leads to the precipitation of CaS inclusions, resulting in a narrowing of the liquid window. Therefore, the molten steel composition significantly affects the efficacy of Ca treatment for inclusion modification. Rational control of the molten steel composition enables the Ca to modify Al₂O₃ inclusions into liquid calcium aluminates, thereby reducing the risk of nozzle clogging.

Key words: tinplate, Al₂O₃ inclusions, calcium treatment, liquid window, industrial trials