Study on Cleanliness of IF Steel First Slab

The cleanliness of IF steel first slab produced by BOF-RH-CC and the difference with the cleanliness of normal slab were studied by means of total oxygen and nitrogen content analysis,SLIME,SEM,EDS,etc.It is found that the T[O] and [N] of first slab are obviously decreasing along casting direction.The large-sized inclusions contents of first slab are obviously higher than those of normal slab,and generally decrease along casting direction,and are close to those of normal slab after the position of 4.4 m along first slab.The distribution of large-sized inclusions is non-homogeneous along thickness direction of slab,which contents of inner arc slab are obviously higher than those of outer arc slab.The size of large-sized inclusions are mainly from 140 to 300 μm and the size over 300 μm,which accounts individually for 22.6% and 56.8% of total large-sized inclusions and are from slag entrapment in mould or tundish,reoxidation products and stuffing sand.