The Effect of Soft Reduction on Center Segregation in C.C. Slab

Abstract

Soft reduction technology is known to be the best way to minimize center segregation through the compensation of negative pressure by reduction of the shrinkage cavity. The crater end positions were investigated by pin shoting, surface temperature measurements and numerical analysis of heat transfer. Based on the results, soft reduction was applied to the No. 2 CC plant for wide slab at Pohang Works of POSCO by reducing roll gaps in a specific zone and reduction ratio ranged from 0.5 to 0.76 mm/m. The delayed solidification region was 300 mm away from the slab edge, where surface temperature was about 30°C higher than that measured at the center of slab width. In a series of tests for soft reduction, the area fraction of phosphorus segregation was reduced from 0.72 to 0.3% and an optimum soft reduction zone was found of which solid fraction ranged from 0.4 to 0.8.