Effect of liquid steel flow pattern on slab quality and the need for dynamic electromagnetic control in the mould

Abstract

This paper addresses surface/subsurface quality (slivers, pipe, pinholes, blowholes, inclusion content) and diversion rate (slab casting abnormality codes) of products cast on high or low throughput thick slab machines. Examples from LTV, NKK and TKS pertaining to curved mould and vertical/bending casters are reviewed, which make apparent the important effect of steel flow stability and steel flow pattern in the mold on defect occurrence. The first conclusion, which pertains mostly to slow speed or wide slab machines, is that creating or maintaining a stable double roll flow is key to eliminating slab defects. The second conclusion, relating mostly to high speed casters, is that the intensity of the double roll flow pattern must not be excessive. With this in mind, the efficiency of an existing versatile electromagnetic based technology that allows accelerating, slowing down, and stirring the liquid steel was examined. The analysis shows good response of the liquid steel to various imposed magnetic fields, presents corresponding slab/coil quality improvements, and demonstrates the relevance of the proposed hydrodynamic and metallurgical concepts.