Patent ID: 7094271

Claim:
A process for producing stainless steel, especially steel containing chromium and chromium-nickel, using melting equipment including a metallurgical vessel for supplying a steel casting plant, the process including operating an electric-arc furnace process and an air-refining process in the vessel, and, in a first treatment steps in which the electric-arc process is carried out, melting down a charge that is essentially composed of solid and/or molten pig iron and raw materials, especially scrap and in part alloy carriers that contain carbon and silicon, and subsequently decarbonizing the melt, the process comprising a reversive treatment of unreduced slag after the air-refining process in the electric-arc furnace operation comprising the steps of: (a) heating high-chromium slag in the first treatment step together with melting down the charge; (b) reducing the high-chromium slag during the melting process with silicon and carbon under favorable thermodynamic conditions of the arc after the melt has reached a minimum temperature of 1,490° C., and subsequently removing the slag; (c) treating the melt in the same vessel with an air-refining process in which oxygen or oxygen mixtures are blown through top lances, side lances, side below-bath tuyeres, side tuyeres, bottom tuyeres, or porous plugs, individually or in combination, so as to decarbonize the melt to a carbon value of <0.9% and heating the melt to a tapping temperature of 1,620–1,720° C.; (d) thoroughly mixing the melt with an inert gas introduced through top lances, side lances, side below-bath tuyeres, side tuyeres, bottom tuyeres, or porous plugs, individually or in combination; (e) injecting or top-blowing of alloying agents, fluxus, reducing agents, metal oxides/metal-containing dusts, or mixtures thereof through top lances, side lances, side below-bath tuyeres, side tuyeres, bottom tuyeres, or porous plugs, individually or in combination; and (f) subsequently tapping the melt such that unreduced high-chromium slag of the air-refining process remains in the treatment vessel and is reduced in a next cycle of the electric-arc melting process in accordance with step (a); terminating the air-refining process at a carbon content of less than 0.9% and a temperature of more than 1,680 W, emptying the molten metal into a ladle, while the slide remains in the vessel, and carrying out a secondary metallurgical treatment in which the molten metal is brought to a desired final carbon content of less than 0.1%.