Abstract: The invention relates to a casting flux for steels or alloys on an iron, nickel or cobalt basis which make heavy demands on the degree of oxidic purity for continuous or ingot casting and contain as the main components calcium oxide (CaO), aluminium oxide (Al.sub.2 O.sub.3) and strontium oxide (SrO), the characterizing feature of the invention being that the chemical composition lies within the following limits (in % by weight):20 to 40% CaO,15 to 30% SrO,0 to 6% Mgo,0 to 8% MgF.sub.2,0 to 8% CaF.sub.2,0 to 8% NaF0 to 6% LiFresidue Al.sub.2 O.sub.3,the flux having a total content not exceeding 15% of oxygen-yielding compounds, such as SiO.sub.2, FeO, MnO, K.sub.2 O, Na.sub.2 O, P.sub.2 O.sub.5, Cr.sub.2 O.sub.3 and B.sub.2 O.sub.3.