Development of fluoride-free fluxes for billet casting

More than 90% of the world's steel is produced using the continuous casting process, a method that has seen enormous advances over the last forty years. Mould fluxes play an important part in this process. These fluxes contain fluorides, which can volatilize at operational temperatures polluting both the plant air and cooling water. Airborne fluoride could potentially be a health and safety issue. Waterborne fluoride forms hydrofluoric acid (HF), which can cause plant corrosion, and may lead to contamination of watercourses necessitating water treatment schemes. This adds to production costs and may present potential environmental hazards. These concerns could be reduced or eliminated by removing fluoride from mould fluxes. The present study examines the effect of different fluxing agents upon key mould flux properties. When substituting fluorides for alternative fluxing agents the key design properties of the fluoride-containing flux must be replicated; namely, (i) flux viscosity at 1 300 degrees C, (ii) break temperature and (iii) percentage of crystallinity in the solid slag layer. This is to ensure 'optimal casting' where operational problems, such as sticker breakouts and defects such as longitudinal cracking, are minimized. In addition, the quality of the steel should not be affected by the substitution. Therefore, any substitute/additive or combination of additives would have to possess the capacity to replicate the effects that fluorine has on mould flux behaviour. This study focuses on B2O3 and CaF2 as alternative substitutes for CaF2, in billet fluxes. The new flux has been successfully tested in a plant trial on a continuous casting plant.