Abstract: Boric acid-free fluxes based on inorganic boron compounds for brazing metallic materials in combination with silver, copper or nickel base solders are known. Starting from this, in order to provide a further flux for brazing that is free of boric acid and contributes to a good wetting of the workpieces to be joined and that is distinguished by residues of low corrosivity, it is suggested according to the invention that the boron compounds should comprise potassium pentaborate and potassium metaborate, the ratio of the weight parts of potassium pentaborate and potassium metaborate being in the range between 4 and 10.