ES356521A1 - Method of treatment of liquid steel under vacuum - Google Patents

Abstract

Steel is vacuum treated in a ladle 9, when covered by a layer of reducing slag 16, by immersing the lower extremities of 2 vertical refractory pipes 5 and 6. The upper parts of which open into the bottom of an evacuable, vacuum-tight, refractory, heat-insulated chamber 1 of cylindrical vertical cross section. Circulation of the steel is effected up the pipe 6 and down pipe 5 by means of a centripetal electromagnetic force acting towards the centre of the vacuum chamber 1 set up by passing an A. C. current through inductor windings 7 surrounding said chamber and within the metal casing 11. These windings 7 also heat the steel in the vacuum chamber by induction, and are themselves water-cooled, and are supplied with frequencies of 1-20 Hz for providing the circulation only or higher frequencies to act as a heat source. After treatment, the vacuum is removed by introduction of a neutral or reducing gas into the chamber after each vacuum treatment. To aid the setting up of the centripetal force the upward pipe 6 opens out into the bottom of a peripheral channel 10 around the base of chamber 1, the radial width of which is less than the thickness of the induced skin effect currents in the steel. The chamber is heated internally before each treatment by means of a coaxial, graphite ring 13 located inside the chamber and heated by induction by means of winding 14 outside the refractory chamber but within the metal casing 11 supplied with frequencies in the range 150-1500 Hz. Packs of magnetic iron sheets 12 are provided between the metal casing 11 and the windings 7 and 14, to channel the electromagnetic field on the interior of the metal casing but exterior of the refractory chamber and inductor windings. The process is started by sticking diaphragms of thin steel sheet over the lower openings of pipes 5 and 6, evacuating the chamber, and heating it to the required temperature. The vacuum is destroyed by introducing nitrogen or a reducing gas to the chamber and then immersing pipes 5 and 6 into the metal bath in a ladle and evacuating, and supplying current to windings 7. Additives can be introduced via a lock chamber 18, 19, 20. After treatment the vacuum is destroyed with nitrogen or reducing gas