INFLUENCE OF SOFT REDUCTION WITH ONE-PIECE ROLLS ON CENTER SEGREGATION IN CONTINUOUSLY CAST SLABS

A test on soft reduction employing conventional one-piece rolls was conducted to analyze the influence of soft reduction and reduction timing on center segregation. As a result, the following findings were obtained. Center segregation was improved when soft reduction was applied only in the final stage of solidification in which the fraction of solid at the slab center is larger than 0.25. When soft reduction was applied employing one-piece rolls over the wide range of solidification stage including the solidification stage with the fraction of solid at the slab center below 0.25, center segregation deteriorated with increasing amount of reduction and the amplitude of variations in center segregation in the casting direction was also increased. It is estimated that the deteriorating tendency of center segregation by soft reduction on the upper stream side is attributable to the new flow of molten steel caused by uneven reduction due to mechanical factors such as roll bending. For the improvement of center segregation, therefore, the optimization of reduction timing is indispensable especially when mechanical factors of uneven reduction are present.