Abstract: The effect ofw(CaO)/w(Al₂O₃) on the physical and chemical properties of the refining slag was investigated through the Factsage thermodynamic software, and the slag composition was determined which had low FeO activity, high CaO activity and low Al₂O₃ activity. The semi-killed tapping technology was developed, after industrial application, the temperature drop of converter tapping was abled to lower about 7.7 ℃, and the deoxidation products were large scaled-clustered Al₂O₃ inclusions which were easily removed from molten steel. Though the synergistic effect of the converter semi-killed tapping process and two slag upgrading processes after steelmaking and RH vacuum break, the TFe mass fraction of slag can be controlled to 4%–6%, and the quantity density of the large scaled inclusions (more than 20 μm) in tinplate has significantly decreased, from 2.2 per 100 mm² before to less than 1 per 100 mm².

Key words: tinplate, inclusion, slag system, number density