Abstract: Based on analyzing the reasons of flocculation during casting, combined with industrial test results, some key measures to deal with flocculation during casting were established, such as optimizing operation system of converter, tapping with skimming, skimming in ladle, modifing the top slag in ladle, stiring by blowing Ar from the bottom of ladle, nozzle design, deoxidization process, modifing inclusion in molten steel by feeding cored wire etc. The results showed that, controlling the tapping carbon mass fraction at the range of 0.04 %—0.06 % for ultra-low carbon steel, slag quantity at the range of 3—5 kg/t, adding 3—5 kg/t active lime for modifying the top slag in ladle, acid aluminium content at lower limit, optimizing design of submerged nozzle structure, increasing the nozzle diameter and side flow hole diameter, the temperature of firing tundish above 1200 ℃ etc, the flocculation could be alleviated. Comparison with aluminum deoxidization, Si+Al deoxidization process had failed to ease flocculation, but the shape of inclusion was changed, the requirement of thin sheet steel for inclusion also could be satisfied.

Key words: flocculation, tapping with skimming, bottom blowing argon, nozzle, deoxidization