Research on Behaviour of Large Inclusions in IF Steel

In this paper,comprehensive analysis had been carried on the macro inclusion with regard to the type,source,composition and quantity and the main factors influencing the cleanliness of casting slab had been identified. Composition analysis shows that the [O] and [N] contents of the first slab are 82.5 ×10^-6and 61.5 × 10^-6,respectively,both are significant higher than these of other slabs; and the inclusions are mainly divided into three categories: block and cluster of Al₂O₃,compound Al₂O₃·TiOx and CaO（SiO₂） ·Al₂O₃·Ti inclusions,which come from re-oxidation products,slag entrapment in mould or tundish,and stuffing sand. First slab has the highest content of macro inclusions with average value of 3.287 mg / kg,followed by the last slab （2.739 mg / kg） and the mixed casting slab （1.557 mg / kg）,while the content of macro inclusions of the normal slab is 1.227 mg / kg. the distribution of macro inclusions is non-homogeneous along thickness direction of slab,where contents of inner arc slab are obviously higher than those of outer arc slab. Macro inclusions comprise of small particle with size of 140~300 μm and large particle bigger than 300μm in first slab,which account for 38.3% and 61.7% of total inclusions,respectively.