Solidification structure and semi-macro segregation of pipeline steel continuous casting slabs

Center segregation with different solidification structures was investigated in pipeline steel. Macrostructure photographs show that center segregation in continuous casting slabs is composed of many semi-macro segregates, which are relatively independent and separated spot-like segregates with different sizes. The features of semi-macro segregation are different for different solidification structures. Chemical analysis shows that negative segregation is formed across the equiaxed zone in the center of the slab, while positive segregation is observed in the center of the slab surrounded by columnar crystals. It is revealed that the semi-macro segregation area in the center of the slab increases with the increase of the maximum segregation ratios of C and Mn. However, compared with the method of segregation area measurement, only local segregation could be obtained by chemical analysis, and it is obvious that the method of segregation area measurement is more helpful to industrial practice. Furthermore, the segregation area with different solidification structures under different superheats was calculated. The results indicate that as the soft reduction technology is applied reasonably, columnar crystals in the center of the slab are more advantageous to the reduction of segregation area, and finally would be better for the improvement of center segregation.