Abstract: A hign-carbon ferro-alloy, specifically ferrochrome or ferromanganese, is carburized in a converter in which oxygen or air is blown from below into the melt together with a surrounding protective gas. With the bath preheated to a temperature somewhat higher than the melting point of the ferro-alloy, the oxygen is introduced at such a rate that its reaction with the chromium or the manganese locally superheats the bath, in a region well below the surface and spaced from the converter walls, to a temperature high enough to let the resulting oxides react endothermically with the carbon. This reaction takes place in combustion zones believed to be localized in gas bubbles formed above the injection nozzles, the oxidation of the ferrous and nonferrous constitutents occurring at the interface between the gas and the melt with formation of a very thin and highly reactive oxide skin around each bubble.