Solidification morphology and segregation in continuously cast steel slab

Abstract

Solidification morphology and centreline macrosegregation in continuously cast, thick steel slab samples were investigated in order to evaluate the liquid steel solidification characteristics and determine the severity of macrosegregation in cast slabs. Experimental studies were undertaken to establish the true solidification behaviour of industrial slab caster without electromagnetic stirring. Several slab samples collected from the continuous casting shop were utilized to characterize the solidification macrostructure, morphology of cast structure, and macrosegregation patterns. Macrostructural examination revealed predominantly coarse, columnar structure associated with high level of segregation which is detrimental to internal soundness of cast slabs. Liquid steels cast at high superheat (≥32°C) were generally having finer cast structures as compared to those cast at lower superheats (≤21°C). Degree of centreline segregation of Carbon (C), Phosphorus (P) and Manganese (Mn) were significantly high. Several unwanted phases (cementite, sulphide and phosphide) were also observed in the central segregated region of slab samples. An attempt was made to correlate the experimental observations with the operating parameters of the caster, and appropriate measures for improving the product quality were suggested.