Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/0087—Treatment of slags covering the steel bath, e.g. for separating slag from the molten metal

Definitions

• the invention relates to a mixture comprising magnesium, carbon and aluminium to be introduced into the slag located on a metal melt in iron and steel metallurgy, the use of such a mixture, and a method for conditioning a slag located on a metal melt in a metallurgical vessel, for example in a converter, in an electric arc furnace, or in a ladle, in iron and steel metallurgy.
• oxygen is blown for this purpose by means of a lance onto the pig iron melt located in a converter lined with an alkaline refractory material.
• the process of this blowing of oxygen onto the pig iron melt is also referred to as refining.
• iron contaminants in particular iron contaminants in the form of carbon, manganese, silicon and phosphorous, are oxidised by the oxygen blown in and together with added burnt lime form a slag layer floating on the metal melt.
• the crude steel melt is produced by melting scrap metal, pig iron, liquid iron and/or direct reduced iron and further raw materials.
• the slag must be selectively influenced or conditioned with regard to chemical and physical properties.
• the basicity i.e. the mass or molar ratio of the alkaline components to the other components of the slag (which for example can be calculated in accordance with the following formula: [xCaO+MgO]/[xSiO 2 +Al 2 O 3 +further components]), of the initially acidic or non-alkaline slag must therefore be increased in order to reduce the corrosive attack of the slag on the alkaline lining of the metallurgical vessel in which the metal melt is located and thus attenuate the erosion of the lining and increase the service life thereof.
• slag conditioners have a component increasing the basicity of the slag, this component in particular being lime, dolomite lime, or dolomite.
• the viscosity of the slag may also be desirable to adjust the viscosity of the slag by the slag conditioner. It is often desirable for the viscosity of the slag during the refinement to be as low as possible such that the iron constituents oxidised by the applied oxygen can be incorporated well into the slag. Furthermore, it may be desirable when tapping or following tapping for the slag to have a high viscosity such that the slag remaining in the converter following the tapping can be better applied to the refractory lining of the converter. Due to this applied slag layer, a corrosive attack of a metal melt on the lining of the converter can be reduced. The process of applying the slag to the converter is also referred to as “maintaining” the converter.
• the known methods for maintaining the converter on the one hand include what is known as “slag washing”, in which the slag is distributed over the tapping and charging side by pivoting the converter.
• a further maintaining method is what is known as “slag splashing”, in which the slag is mechanically sprayed with the aid of a nitrogen gas flow of a lance.
• slag foaming slag is chemically foamed by adding a carbon carrier. The slag foamed in the case of slag foaming is also referred to as “foamed slag”.
• the foamed slag has insulating properties, such that the heat losses from the melt can be attenuated and energy can be saved. Furthermore, components of the metallurgical vessel in which the iron melt is located may be protected by the foamed slag against heat radiation.
• one object of the invention is to provide a slag conditioner by means of which the basicity and the MgO content of the slag can be quickly increased in order to be able to reduce the attack of the slag on the refractory lining of the metallurgical vessel in which the metal melt is located with the slag located thereon.
• a further object of the invention lies in providing a slag conditioner by means of which the viscosity of the slag can be selectively adjusted.
• a further object of the invention lies in providing a slag conditioner by means of which a foaming of the slag can be achieved.
• a further object of the invention lies in providing a slag conditioner by means of which an increase of the iron output of the primary metallurgical process can be achieved.
• a mixture or a slag conditioner to be introduced into the slag located on a metal melt in iron and steel metallurgy is provided in accordance with the invention, wherein the mixture comprises magnesium, carbon and aluminium in the following mass proportions:
• the mixture according to the invention or the slag conditioner according to the invention is suitable to be introduced into slags on metal melts in any metallurgical vessel, but in particular for slags in converters, electric arc furnaces and ladles.
• the proportions of magnesium and aluminium in the mixture according to the invention are specified as proportions of the oxides thereof Mgo and Al 2 O 3 in the mixture, as is usual in refractory technology.
• magnesium and in particular aluminium may also be present in the mixture according to the invention in a form other than the oxide form, for example in metallic form or, with regard to aluminium, in the form of carbide.
• the MgO saturation of the slag is achieved more quickly by the proportion of MgO in the mixture according to the invention, such that the corrosive attack of the slag on the refractory lining of the metallurgical vessel holding the metal melt is reduced. Furthermore, the viscosity of the slag increases with rising MgO content.
• Magnesium is present in the mixture according to the invention preferably as oxide, i.e. in the form of MgO.
• the proportions of magnesium in the mixture according to the invention are preferably present exclusively in the form of MgO, particularly preferably in the form of sintered or fused magnesia.
• MgO may be present in the mixture according to the invention in proportions of at least 45 mass %, i.e. for example also in proportions of at least 48, 50, 52, 54, 56, 57, 58, 59, 60 or 61 mass %. Furthermore, MgO may be present in the mixture in proportions of at most 90 mass %, i.e. for example also in proportions of at most 88, 86, 84, 82, 80, 78, 76, 74, 72, 70, 69, 68, 67, 66, 65, 64 or 63 mass %.
• the proportion of carbon in the mixture according to the invention when the mixture is added to the slag, reacts with oxygen located in the slag to form carbon oxides, in particular to form carbon monoxide CO and carbon dioxide CO 2 .
• the carbon in the mixture oxidises immediately and fiercely with oxygen proportions of the slag, such that the slag foams up spontaneously when the mixture is introduced.
• the slag thus rises in height, as with slag foaming, and covers the refractory lining of the metallurgical vessel.
• the radiation of the electric arcs is shielded partially or completely with respect to the furnace wall as a result of the increased volume of the foamed slag. Due to the increased content of MgO, the slag at the same time obtains the necessary viscosity in order to also remain adhered to the wall during and after the foaming.
• the carbon in the mixture may react directly with oxygen of the metal melt and may remove oxygen from the metal melt. This oxygen removed from the metal melt must not later be removed to a greater extent from the metal melt in additional steps by deoxidising agents, for example aluminium.
• At least some of the oxygen with which the carbon from the mixture according to the invention introduced into the slag reacts originates from iron oxides in the slag that are reduced by the carbon to form metallic iron.
• iron oxides are fluxing agents, which reduce the viscosity of the slag. Since the proportion of iron oxides in the slag is reduced by the edition of the mixture, the viscosity of the slag can thus be increased. The output of recovered iron in the overall process is also increased.
• a foaming of the slag can thus be achieved on the one hand.
• the viscosity of the slag can be increased.
• the extent of the foaming of the slag and also the viscosity thereof can thus be set selectively by the proportion of carbon in the mixture.
• the carbon may be present in the mixture substantially in pure form, for example in the form of graphite or coke, but for example also combined with further constituents, for example with aluminium proportions or magnesium proportions of the mixture.
• the proportions according to the invention of carbon in the mixture are present partially, largely, or also completely in the form of aluminium carbide (Al 4 C 3 ).
• Carbon is present in the mixture according to the invention in proportions of at least 5 mass %, i.e. for example also in proportions of at least 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 or 23 mass %. Furthermore, carbon is present in the mixture according to the invention in proportions of at most 40 mass %, i.e. for example also in proportions of at most 38, 36, 34, 32, 31, 30, 29, 28, 27, 26 or 25 mass %.
• Aluminium calculated as Al 2 O 3
• aluminium may be present in the mixture in a proportion of at least 1 mass %, i.e. for example also in a proportion of at least 2, 3, 4 or 5 mass %.
• aluminium, calculated as Al 2 O 3 may be present in the mixture in proportions of at most 20 mass %, i.e. for example also in proportions of at most 18, 16, 14, 13, 12, 11, 10, 9, 8 or 7 mass %.
• the proportion of aluminium in the mixture according to the invention is calculated herein as Al 2 O 3 , wherein, however, the proportions according to the invention of aluminium in the mixture preferably are not present in oxide form as Al 2 O 3 , but are preferably present partially, largely, or also completely in metallic form and/or in the form of carbide, i.e. as Al 4 C 3 .
• this aluminium carbide at the same time forms a carrier both of the proportion of aluminium and of carbon in the mixture.
• the aluminium carbide component is particularly advantageous inasmuch as both the aluminium and the carbon of the aluminium carbide can react with oxygen proportions in the slag, and oxidic constituents of the slag, in particular iron oxides, can be reduced as a result. With corresponding reactions the aluminium proportion of the aluminium carbide oxidises into Al 2 O 3 and the carbon proportion of the aluminium carbide oxidises into CO 2 .
• slag conditioners comprise magnesium proportions, these are regularly present in the form of magnesium carbonate (MgCO 3 ), dolomite, or sometimes also in the form of magnesium hydroxide (Mg(OH) 2 ).
• MgCO 3 magnesium carbonate
• dolomite magnesium hydroxide
• Mg(OH) 2 magnesium hydroxide
• magnesium present in the form of magnesium carbonate, dolomite or magnesium hydroxide leads only to a delayed increase of the basicity and of the MgO content of the slag. Furthermore, it has been found in accordance with the invention that the basicity and the MgO content of the slag can be increased much more quickly and effectively by introducing magnesium in the form of magnesium oxide into the slag.
• the mixture according to the invention is produced, in contrast with the prior art, in such a way that the component comprising magnesium is provided in particular in the form of MgO and merely to increase the basicity and MgO content in the mixture, whereas the foaming of the slag is caused by other components in the mixture, in particular by the components comprising carbon and aluminium.
• the slag conditioner according to the invention no further carbonates have to be introduced either into the primary metallurgical process, the resource efficiency is higher, i.e. the specific consumption and the total weight of slag conditioner to be introduced into the slag and to be transported is lower than in the prior art.
• the emissions of carbon dioxide can be reduced by the slag conditioner according to the invention if carbonate-containing slag formers are replaced by the slag former according to the invention.
• the mixture may contain a proportion of magnesium carbonate less than 10 mass %, i.e. for example also a proportion less than 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 mass %.
• the mixture may contain a proportion of Mg(OH) 2 less than 10 mass %, i.e. for example also a proportion less than 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 mass %.
• the mixture may contain a proportion of dolomite, in particular of raw dolomite, less than 10 mass %, i.e. for example also a proportion less than 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 mass %.
• the mixture may contain a proportion of calcium carbonate or of limestone less than 10 mass %, i.e. for example also a proportion less than 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 mass %.
• the mixture is preferably present in a relatively low grain size, for example % in a grain size less than 0.5 mm to an extent of at least 70 mass %, 80 mass %, or at least 90 mass %, or also 100 mass.
• the grain size of the components of the mixture according to the invention below the grain sizes specified hereinafter may be present in the respective specified mass proportions, wherein the mixture according to the invention for example also may fulfil only one of the following conditions in respect of its grain size:
• the mixture according to the invention has this very small mean grain size, a particularly good and uniform distribution and particularly also a quick dissolution of the mixture in a slag can be achieved.
• the mixture may be provided in compacted or pressed form, for example in the form of pellets.
• a mixture according to the invention which in particular may have the previously described grain size distribution, can be pressed into pellets without addition of additives.
• these pellets may have an almond-shaped, rod-shaped or spherical form, for example with a maximum length of for example 50 mm, 40 mm, or 30 mm.
• the pellets may also have a minimum diameter for example of 5, 10, 15, 20, or 25 mm. Pellets with a corresponding size can be easily handled, but at the same time are still small enough that they quickly disintegrate in a slag following addition thereto, and the advantages of the small grain size distribution according to the invention can materialise there quickly.
• the mixture according to the invention contains a proportion of calcium oxide (CaO), since the basicity of the slag can be further increased thereby and the attack of the slag on the refractory lining of the metallurgical vessel can be lowered.
• the CaO of the mixture in particular then has an advantageous basicity-reducing effect when the ratio of CaO to SiO 2 in the mixture does not exceed a certain measure.
• the basicity of the slag can be increased in particular by the CaO when the ratio of mass proportions of CaO to SiO 2 in the mixture is not below 0.7.
• the ratio of the mass proportions of CaO to SiO 2 in the mixture according to the invention may not lie below 0.7.
• SiO 2 may enter the mixture according to the invention fundamentally via impurities of the raw materials of said mixture.
• the mixture may comprise calcium oxide and silicon dioxide in the following mass proportions:
• SiO 2 0 to 7 mass %.
• CaO may also be present in the mixture for example in proportions of at least 0.1 or 0.2 or 0.5 or 1 or 1.5 or 2 mass %, and for example in proportions of at most 10, 9, 8, 7, 6, 5, 4, 3 or 2.5 mass %.
• SiO 2 may be present in the mixture for example in proportions of at least 0.1 or 0.2 or 0.5 or 1 or 1.5 or 2 mass %, and for example in proportions of at most 7, 6, 5, 4, 3 or 2.5 mass %.
• the mixture may be provided in the form of pellets, wherein the mixture is pressed into pellets without the addition of additives. If, however, additives are used in order to press the mixture into pellets, CaO may be used as such a press additive.
• the mixture in contrast to the previously disclosed inventive concept, in accordance with which the mixture contains proportions of CaO of at most 10 mass %, the mixture may contain proportions of CaO of up to 40 mass %.
• the mixture preferably does not contain any additive for pressing, such that the proportion of CaO in the mixture, as described above, does not lie above 10 mass %.
• the mixture may comprise iron oxides in the following mass proportions:
• iron oxide stands for the sum of all iron oxides in the mixture, i.e. in particular FeO and Fe 2 O 3 , but for example also Fe 3 O 4 and Fe 2 O.
• Iron oxides may be present in the mixture for example also in proportions of at least 0.1 mass %, 0.2 mass %, 0.4 mass %, 0.6 mass %, or 0.8 mass %, and for example at most in proportions of 7 mass %, 6 mass %, 5 mass %, 4 mass %, 3 mass %, 2.8 mass %, 2.6 mass %, 2.4 mass %, 2.2 mass %, or 2 mass %.
• the mixture may also comprise only small proportions of further components, for example in proportions less than 5 mass %, 4 mass %, 3 mass %, 2.5 mass %, 2 mass %, 1.5 mass %, or also less than 1 mass %.
• the mixture may comprise proportions of the following components below the mass proportions specified hereinafter:
• magnesia-carbon products that have been used in the steel industry, in particular as inner linings of basic oxygen furnace converters, in electric arc furnaces or in ladles, are suitable in part as raw material for the mixture according to the invention.
• correspondingly recycled magnesia-carbon products can be used partially, largely or exclusively as raw material for the mixture according to the invention.
• the invention also relates to the use of recycled magnesia-carbon products as raw material for the mixture according to the invention and the use of such recycled magnesia-carbon products as slag conditioner according to the invention.
• magnesia in particular sintered magnesia
• carbon in particular graphite
• corundum in particular aluminium carbide
• the invention also relates to a method for conditioning a slag located on a metal melt in a metallurgical vessel in iron and steel metallurgy, said method comprising the following steps:
• the mixture can be provided in compacted or pressed form, for example in the form of pellets.
• the mixture provided is introduced onto the slag and sinks thereinto, such that it can develop its effect there.
• the mixture according to the invention is suitable in principle as a slag conditioner for slags on a metal melt in any metallurgical vessel, for example for metal melts in converters, electric arc furnaces, or ladles.
• the mixture according to the invention is particularly preferably used as a slag conditioner for slags on metal melts located in a metallurgical vessel with an alkaline lining, i.e. in particular with a lining based on at least one of the following materials: magnesia, magnesia-carbon, doloma or doloma-carbon.
• the invention also relates to the use of a mixture according to the invention described herein for conditioning a slag located on a metal melt in a metallurgical vessel in iron and steel metallurgy.
• the carbon was present in the mixture in the form of graphite and aluminium carbide.
• Aluminium was present in the mixture in the form of metallic aluminium and in the form of aluminium carbide.
• Recycled magnesia-carbon products were used exclusively as raw materials.
• the mixture was provided in the form of pressed, almond-shaped pellets without additional additives, with a thickness of approximately 15 mm and a length of approximately 30 mm.
• the grain size distribution of the mixture in the pellets is specified in Table 2.
• the mixture was used as a slag conditioner for a slag on a metal melt located in an oxygen converter.
• the mixture was placed on the slag located on the melt. Due to the placement of the mixture on the slag, the basicity of the slag could be increased. Furthermore, due to the proportions of carbon, aluminium and aluminium carbide in the mixture, it was possible to achieve a foaming of the slag. Lastly, the viscosity of the slag could be adjusted to the desired measure.

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• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Carbon Steel Or Casting Steel Manufacturing (AREA)
• Treatment Of Steel In Its Molten State (AREA)

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• 2013
  • 2013-12-02 PL PL13195334T patent/PL2878685T3/pl unknown
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  • 2013-12-02 ES ES13195334.1T patent/ES2559024T3/es active Active
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• 2014
  • 2014-10-01 WO PCT/EP2014/071022 patent/WO2015082093A1/de active Application Filing
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• 2015
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