Improving Cast Structure and Centerline Segregation of Continuously Cast Slabs by Adding Steel Strip into Mold

A method has been developed which increases the fraction of equiaxed crystals and results in decreasing centerline segregation in continuously cast slab by adding steel strip into mold. The effect of shape, liquidus temperature, feeding speed of the strip and superheat of melt in mold on the melting behavior of the strip in crater has been evaluated by a mathematical model. Then, the effect of the amount of the strip addition on the ratio of the equiaxed zone and the centerline segregation has experimentally been investigated by use of strip with low liquidus temperature. The equiaxed zone of 50 to 75% has been obtained and the centerline segregation has disappeared by adding 6 to 8 kg/t of the strip at 15 to 30°C of superheat. A countermeasure to prevent the contamination of molten steel caused by adding the strip is established. The mechanism for the increase in the fraction of equiaxed crystals has also been discussed.