Reduction of macrosegregation by applying a DC magnetic field at the final stage of solidification

Abstract

A new technique using a static magnetic field (DC field) for the modification of macroscopic segregations and porosities in continuously cast billets or blooms has been investigated. If the DC field is applied to the crater end area in a strand, numbers of the V-segregations and porosities could be expected to result in a decrease, since the molten steel flow in the semi-solid region seems to be modified by the DC field. This phenomenon was observed when the magnetic flux density of the DC field of 0.2 to 0.42 Tesla was applied during the solidification of the center of the cast ingots, where the solid fraction had values of 0 to 1.0, which is in the final stage of solidification. In addition, the application of the DC field to the center part of the ingot with a solid fraction range, 0 to 0.3, showed similar effects. Hence, the application of a higher magnetic flux density, when the ingot contains a low solid fraction at the center part, was found to result in a decrease of the V-segregation and porosity. It is suggested that the DC field homogenized the fluid flow velocity in the semi-solid region at the center part of the ingot.