Abstract: The pre⁃fused RH flux has never been industrial application on big scale until Calderys put such product to silicon steel product lines. This paper introduced the whole process of developing RH desulphur fluxes from design by FactSage to industrial trials. In practical terms, Calderys’ pre⁃fused RH fluxes helped overcome the pulverization problem of CaO⁃CaF2 flux. By FactSage simulation, four new recipes were designed for production and industrial trials. The several trial results showed that the new recipe 3 containing a small amount of F element is the best one which increased desulphurization rate with max increase of 10 %. Additionally, pre⁃fused RH fluxes could control the non⁃uniform refractory corrosion of down snorkel well compared to CaO⁃CaF2 flux which is easy to cause non⁃uniform corrosion due to the content of free lime.

Key words: RH, desulphur flux, desulphurization rate, recipe, corrosion