Briquette for producing a foamed slag effect in eaf technology in stainless steel production

Abstract

It is known that a foamed slag can be produced on stainless steel melts in an electric arc furnace by introducing a mixture of metal oxides, limestone, carbon and a binder in the form of briquettes into the furnace so that the briquettes become arranged there in such a way that the metal oxides are reduced by the carbon and the limestone is thermally dissociated at the metal-slag interface beneath the slag and the resulting gases bring about foaming of the slag by bubble formation. This foaming on steels having a high chromium content, due to the significant uptake of chromium oxide by the slag, leads to problems which result from the physicochemical properties of slags having a high chromium oxide content. To provide, according to the invention, briquettes suitable for producing foamed slag having a high chromium oxide content, which is carried out, in particular by the process of WO 2010/003401 A1, all briquette properties to be taken into account and all materials suitable for briquette production are tabulated in the form of a matrix.

1 . Briquette for producing a foamed slag on stainless steel melts in an electric arc furnace, containing a mixture of metal oxides, limestone, carbon and a binder, which is introduced into the furnace and arranged there such that below the slag at the metal-slag interface, the metal oxides are reduced by the carbon and the limestone is thermally dissociated and the gases produced in this process cause foaming of the slag by forming bubbles, characterized in that the briquette for use in different melts such as stainless steel, low alloy steel or high alloy steel is made up of defined arbitrary mixtures of individual or multiple substances of the following basic components:
 O 2  carrier
 Dust, sludge or slag with ≧10% FeO/Fe 2 O 3 , 
 Dust, sludge or slag with ≧1% Cr 2 O 3 , 
 Dust, sludge or slag with ≧1% MnO, 
 Dust, sludge or slag with ≧1% NiO, 
 Scale with ≧10% FeO/Fe 2 O 3    
   Gas carrier Dust with ≧40% CaCO 3 ,   Density adjuster
 Dust with FeCr, 
 Dust with Fe/low alloy fine scrap, 
 Dust with Cr/ferritic fine scrap, 
 Dust with Ni/austenitic fine scrap, grinding dust, 
 Dust with Mn/ferritic or low alloy fine scrap, 
   Reducing agent Carbon-containing substances ≧90% C,
 Dust or fine granulate of coke, coal or graphite, 
   Binder Molasses, cement, Ca(OH) 2  (slaked lime), in each case ≦5%.   
     
     
         2 . (canceled) 
     
     
         3 . Briquette according to  claim 1 , characterized in that the briquette for use in foamed slag production for stainless steel is made up as desired from all substances of the six basic components mentioned. 
     
     
         4 . Briquette according to  claim 1 , characterized in that the briquette for use in foamed slag production for low alloy steel or high alloy steel as an O 2  carrier contains only mixtures of dust, sludge, slag or scale with in each case ≧10% FeO/Fe 2 O 3  and as a density adjuster only mixtures of dust with Fe/low alloy fine scrap and dust with Mn/ferritic or low alloy fine scrap. 
     
     
         5 . Briquette according to  claim 1 , characterized in that as a briquette additionally usable in all melts, as a pure gas carrier it contains no substances of the basic component O 2  carrier. 
     
     
         6 . Briquette according to  claim 1 , characterized in that the CO/CO 2  gas evolution in the standard state (20° C., 1 bar) is ≧0.15 Nm 3 /kg briquette. 
     
     
         7 . Briquette according to  claim 6 , characterized in that the briquette density is between 2.5 and 7.0 g/cm 3 . 
     
     
         8 . Briquette according to  claim 6 , characterized in that after drying for 24 hr and at ≦4% humidity the compressive strength of the briquette ≧0.5 N/mm 2  and the disintegration strength from 2 m on a 120 mm thick plate is ≧97%. 
     
     
         9 . Briquette according to  claim 6 , characterized in that the briquette, the diagonal size of which is between 20 and 100 mm and the height of which is between 15 and 40 mm with a briquette volume of ≦800 cm 3 , is designed variably as an ellipsoid, as a hexagonal cuboid, as a cuboid, or as a cylinder.