Exothermic slag mixtures for removing sulphur and oxygen - from ferrous metals, where mixt. contains aluminium and sodium nitrate

Slag-forming mixt. for the refining of metals, contg. CaO, an oxidant, an oxidisable component, and fluorospar, the novelty being that the mixt. contains, by wt. 15-30% NaNO3 as oxidant; 8-25% of an Al-contg. material as the oxidisable component, and the ratio of the remaining components is: 30-70% CaO, balance fluorspar. The Al-contg. material is pref. Al powder, esp. sieve residues of Al chips contg. min. 50% Al and with size 0.5-1.5 mm; alternatively, aluminium casting dross of the same compsn. and size may be used. When 8-15% Al is used, the mixt. pref. also contains 6-8% of a material which includes min. 65% silicon. Refining of molten ferrous metals outside the furnace, when the metal is required for special applications demanding high purity w.r.t. sulphur and O2 contents and a low amt. of non-metallic inclusions. The above slag mixt. contains exothermic materials, thereby raising the slag temp. and increasing the degree of refining attainable.