Attack of Submerged Entry Nozzles by Mould Flux and Dissolution of Refractory Oxides in the Flux*

Research on mould flux attack of oxide-graphite submerged entry nozzle refractories is reviewed and discussed in light of recent work by the authors. There is general agreement that the mechanism must involve attack of both the oxide and the carbon phase, but there is some uncertainty about the process of attack of the carbon. Some workers have suggested dissolution in the steel but some recent work shows that oxidation has an important role to play. There is some debate over the importance of surface tension driven stirring in a system where forced convection rates are fairly high. Additives such as metallic silicon accelerate the breakup of zirconia grains but also appear to protect the carbon bond. Dissolution of the oxide phase is the predominant rate determining step and the relationship between diffusion of refractory oxides in mould flux as a function of viscosity is consistent with the relationship between attack and flux viscosity.