Influencing factors on center segregation in continuously cast pipeline steel slabs

The factors influencing center segregation in continuously cast slabs are identified through an analysis of the sulfur print database. It indicates that center segregation becomes severer with the increasing content of carbon, phosphorus, and sulfur. Center segregation is significantly reduced when the manganese content exceeds 1.5% and the manganese-to-sulfur ratio is greater than 300. High degree of superheat, high pulling rate and increasing width of slabs will increase the degree of center segregation. Since center segregation below class B has little effect on steel properties, several control strategies are proposed to reduce the proportion of class B-1.0 center segregation to 10%: the contents of carbon, phosphorus, and sulfur must be kept within the lower range of the specified steel grade, while manganese should be controlled at the upper operating range. The recommended elemental contents in molten steel are as follows: [C] < 0.07%, [P] < 0.01%, [S] < 0.005%, [Mn] > 1.5%, and [Mn]/[S] > 300. The degree of superheat should be lower than 24 °C and the pulling rate should be defined to 1.0 – 1.1 m·min −1 . Additionally, an appropriate water distribution system for secondary cooling should be developed, and the precision of the continuous caster should be enhanced.