Pig-iron is refined into steel by blowing oxygen and a protective screen of an encasing gas through injecting means located at or near the bottom of a converter containing a melt of molten metal. The encasing gas while protecting the injecting means, allows it to be consumed at substantially the same rate as the bottom of the converter so that the injecting means is not left projecting from the bottom of the converter. The encasing gas can be one which is inert to the melt or the metal of the injecting means or both, or it can be a gas which reacts sluggishly with the melt or the material of the oxygen feed pipe or both. Desirably, the oxygen jet is circular in cross-section and the encasing gas is in the form of a concentric jet.A converter for carrying out the method is made up of a pear-shaped sheet-steel casing having a refractory lining and an inserted bottom provided with nozzles in the form of metal tubes for the oxygen and encasing gas. Preferably, a substantial portion (for example about half) of the converter bottom is free of nozzles. The nozzles can be arranged in groups and there can be rows running parallel with the tilting axis of the converter. The nozzles may also be arranged to cause circulation of the molten metal in the converter. The nozzles can be constructed to provide for swirling movement of the encasing gas. Examples of encasing gas which may be used are hydrogen, nitrogen, noble-gases, carbon monoxide, carbon dioxide, ammonia, hydrogen-fluoride, furnace-mouth gas, coke-oven gas, natural gas and other gases containing hydrocarbons.