UNDERSTANDING THE ROLE OF MOULD SLAG AND SLAG FILM IN SURFACE QUALITY OF CONTINUOUSLY CAST SEMIS

Abstract

It is accepted that the majority of surface defects in the continuous casting process originate at, or within 25
mm of, the meniscus in the mould. Whether the defects propagate into cracks is dependent on the heat transfer
down the remainder of the mould and events and conditions at and below mould exit. One major influence
at the meniscus and down the mould is the performance of the mould flux in terms of its melting, lubrication,
solidification and transformations. The formation of slag film between the solidifying shell and the copper
mould plate is critical in terms of lubrication and heat transfer, both of which are influenced by its thickness
and degree of crystallisation. The films are usually only two to four millimetres thick, but the temperature
difference between one face and the other can be 950 °C. Varying the glass/crystalline ratio of the solid part
of this film, has a significant and important effect on lubrication, heat transfer and thereby surface quality.
This paper describes current and recent work to understand the role of mould slag and slag film in the surface
quality of continuously cast semis within Corus UK.