Effect of ladle change process on the surface cleanliness of IF steel continuous casting slabs

The effect of ladle change process (the 4th heat to the 5th heat) on the surface cleanliness of IF steel continuous casting slabs was investigated by total oxygen measurement and automatic feature analysis equipped on ASPEX. A comparison of surface cleanliness was performed between transition slabs (cast during ladle change process) and normal slabs (cast under normal condition). It is found that inclusions larger than 20μm are classified into three types:(1) cluster alumina (including bubble + cluster alumina inclusions);(2) cluster TiO_x-Al₂O₃ inclusions; and (3) mold powder inclusions. In terms of surface inclusions in normal slabs, most of the inclusions detected in the scanning area are cluster alumina, and no mold powder inclusions are found. While for transition slabs, the total oxygen content increases from 14×10^-6 to 17×10^-6, and the number density of Type 2 inclusions goes up since the cast start of the 5th heat, indicating re-oxidation of the steel melt during ladle change process. Furthermore, level fluctuation in the mold is also severe since the cast start of the 5th heat, leading to mold powder entrapments. The affected length of cast slabs during ladle change process is about 11 m under the present casting condition.