Influencing factors on center segregation in continuously cast Nb-V-Ti-contained micro-alloying slabs

The factors which influence center segregation of continuously cast slabs were obtained through analyzing the database of sulphur print. It was indicated that center segregation became severer with the increasing contents of carbon, phosphorus and sulfur. Center segregation was reduced obviously if the content of manganese was higher than 1.5% and the ratio of manganese to sulfur was higher than 300. High degree of superheat, high pulling rate and increasing slab width increased the degree of center segregation. Since center segregation below Class B had little effect on the properties of steel, in order to low the ratio of center segregation of Class B-1.0 down to 10%, several control strategies were presented as follows. The contents of carbon, phosphorus and sulfur should be focalized in the lower range of steel grade demanded, but manganese upper operating range control. The referenced contents of the elements in molten steel are required as the following:C<0.07%,P<0.01%,S<0.005%,Mn>1.5%, and Mn/S>300. The degree of superheat is lower than 24℃ and the pulling rate is defined to 1.0-1.1 m·min^-1. At the same time, a proper secondary cooling system of water distribution should be developed and the precision of continuous casters should be also improved.