Abstract: Industrially pure oxygen is blown into molten pig iron surmounted by a layer of slag in a converter by means of at least one tuyere located below the upper surface of the molten metal. Input and output parameters are monitored and input parameters are controlled in order to obtain steel of a desired quality (e.g. composition and/or temperature). The intensity of sound emitted by the converter (e.g. in the range of from 20 to 50 Hz) is measured while the oxygen is blown in. The instant at which the intensity undergoes a sudden and considerable decrease is detected. From that instant, only that amount of oxygen is blown in which is necessary and sufficient to provide the steel with the desired quality at the end of the refining operation.