Application of static magnetic field to casting of steel

Abstract

A magnetic field was applied in the continuous caster in steelmaking. A static magnetic field has advantages in the steelmaking processes, in that the apparatus for generating a static magnetic field is simpler than alternating magnetic coils, and stabilization of the flow is enhanced by a static magnetic field because a larger force acts on a faster steel flow. Therefore, application to industrial processes has been investigated. In this presentation, two applications are discussed, as follows: 1) Steel flow control in mold The steel flow is controlled in the mold to produce high quality steel products with high productivity. An unbalanced steel flow causes surface defects. A static magnetic field is effective for stabilizing the steel flow in the mold. Instability becomes more severe with larger throughput or a thinner mold. A static magnetic field is effective for reducing this instability. Furthermore, because an insufficient steel velocity causes entrapment of bubbles and inclusions on the solidified shell, optimization of the steel flow velocity by controlling the strength of the two domain magnetic fields is important. 2) Microstructure control of cast metal A static magnetic field suppresses the liquid flow, and the microstructure can be controlled by this flow control. In a Sn-Zn alloy casting test, the columnar grain ratio increased when a magnetic field stronger than 0.1 T was applied. These phenomena occurred because thermal convection was reduced by the magnetic brake, followed by less supercooling at the dendrite end. The equiaxed crystal size increases with a magnetic field. Since the magnetic field in the early stage has a larger effect, nuclear generation of equiaxed crystals is considered to be restrained by reducing the steel flow and the temperature gradient.