Abstract: Aiming at the problem of large inclusions in the surface of IF steel slab, the influence of electromagnetic braking and casting speed on the amount and distribution of these inclusions was studied by slims method. Besides, the type and source of large inclusions were also discussed by scanning electron microscopy and numerical simulation. The results showed that large inclusions could accumulate in the edge of slab when the electromagnetic braking was kept off. And the accumulation of large inclusions would be weakened with the increase of casting speed. The degree of this accumulation was decreased by 17 % and amount of inclusions was also reduced by 5.3 % with the casting speed increased from 1.2 m/min to 1.5 m/min. The amount of inclusions decreased by 52% with a homogeneous distribution when the electromagnetic braking was kept on in the condition of 1.2 m/min. Due to low surface tension, the SiO2based complex inclusions was the main inclusion type of IF steel, and MgObased, Al2O3based, TiO2based were also found in IF steel. Meanwhile, refractory corrosion, reoxidation oxide and nozzle clogs were the main source for the large inclusions.

Key words: IF steel, large inclusions, composition, source, distribution