An improvement in the refining of molten metals in a converter by means of oxygen introduced into the metal through tuyeres which include two concentric pipes, oxygen being passed into the melt through the central pipe and a protective fluid being passed into the melt as a sheath or screen around the oxygen, through the clearance space between the two pipes. In the present invention two tuyeres, disposed horizontally and each passing through the convertor sidewall permit refining to be accomplished without any slopping or splashing of the melt and with only minor wear of the convertor lining.