On the Formation of Centerline Segregation in Continuous-Cast Slab

Abstract

The formation mechanism of the centerline segregation of the slabs casted by the curved mold type continuous casting machine, are investigated by means of sulfur-print, X-ray photograph, specific gravity measurement, chemical analysis and EPMA. The results are summarized as follows:
(1) The degree of the centerline segregation can be closely related to the macro-structures of slabs, which are represented by the width of columnar zone and bulging.
(2) The centerline segregation is caused by the accumulation of the microsegregated liquid steel in the interdendrite owing to bulging or bridging at the end of solidification.
(3) The degree of the centerline segregation can be estimated by the volume fraction of the accumulated portion, because the chemical compositions of the enriched portion are constant independently to the different types of solidification.
(4) Elements such as S, P, N, Mn and Si have the same tendency of macro-segregation, which can be explained by the micro-segregation.
(5) The macro-structure shows the tendency of the accumulation of the enriched liquid.
(6) The formation model of the centerline segregation is proposed.