Centerline inhomogeneity of flat products

Defect free casting requires an excellent accordance between steel properties being cast and the technological parameters, especially from the aspect of inner quality and homogeneity of cast products. Typical serious defects of cast slabs is the centerline segregation (CLS). The centerline segregation in slabs develops in a very complicated way, the main factors influencing the CLS pattern are the macrosegregation and the shrinkage of solidifying melt in the mushy area. The centerline section of the slab can be characterized by different chemical composition compared to the average composition and it can contain shrinkage holes, discontinuities and inclusions. In the hot rolling process the complex shape of interdendritic holes will be modified depending on the strain applied. In chemical composition the difference remains and it can be identified even after the soaking period (over 1050 degC). As an example, the center part of an St52 grade hot rolled heavy plates and strips containing CLS can be characterized by a carbon content of 0,3-0,5 wt% and manganese content of 1,7-1,9 wt%. The segregation level - including the carbon content - can hardly be decreased by post heat treatment or annealing.