Mould flux film between mould and steel shell

Samples of the mould flux film have been taken during tailout. The locations of the samples varied from the meniscus to 40 cm below the meniscus. Samples have been analysed using various techniques including SEM/EDS microscopy. Surprisingly, the flux film structure concerning different slag phases changes from the meniscus region downwards. Casting time also has an influence on the structure: it becomes more, complex during hours of casting. Near the meniscus, there are no significant changes in film layer composition from mould side to shell side. Farther away from the meniscus, however, large differences in composition developed. For example, the concentrations of sodium and fluorine can be 50% in the film layer against mould. Also, the concentrations of other elements can be multiples of their levels in the powder. Zirconium and barium oxides have been used as tracers. Some results of these investigations are presented. All samples were taken from the Outokumpu Polarit caster at the Tornio works, where the annual production of stainless steel slabs is about 640 kt.