RU2113496C1 - Method for melting naturally alloyed steels and alloys in hearth furnaces - Google Patents

Abstract

FIELD: ferrous metallurgy; may be used in melting of naturally alloyed iron-carbon steels and alloys in hearth furnaces, more specifically, in open-hearth and electric furnaces. SUBSTANCE: charged concurrently on layer of iron-containing burden on hearth of hearth furnace to zone of slowest melting are carburizer and materials containing deoxidizing and alloying elements with subsequent charging of a layer of light-weight iron charge over them with uniform distribution over them of lime or limestone. Prolonged residence of easily oxidizable alloying components in contact with carburizer in reduction zone makes it possible to preserve freshly reduced elements in metal melt and to remove slag of the first period to cold period without losses of these elements. EFFECT: reduced cost of steel making, provision of operation on fresh burden and use of ores and production wastes containing oxidized and reduced alloying elements. 7 cl, 1 tbl

Description

 The invention relates to ferrous metallurgy, to the smelting of naturally alloyed iron-carbon steels and alloys in hearth furnaces, namely in open-hearth and electric furnaces.

Known is the oxidative method of electric melting on a mixture of alloyed waste to produce alloyed alloys, which includes calculating the mixture according to the lower limit of the alloying content, so that the carbon concentration in the mixture is 0.15 - 0.25% higher than the lower limit for smelting steel. To reduce the fumes of alloying, 0.4-0.6% Cr is introduced into the mixture in the form of siliceous waste. On the bottom give limestone, feldspar or fireclay. On these heats, a reduced amount of limestone is used for filling (2.0 - 2.5%). The temperature of the metal at the beginning of the purge should be in the range of 1480 - 1520 ^o C.

When smelting mild steel, the carbon content in the metal should not be lower than 0.08 - 0.09%. By melting the bath, the slag is removed after it is heated to 1600 - 1640 ^o C.

 The disadvantage of this method is the difficulty in removing phosphorus (low basicity of the slag and the content of iron oxides in it), getting into the specified composition on carbon, significant fumes of alloying elements, thick slag when using chromium waste, a certain composition of alloyed waste is required for smelting different grades of steel .

 Also known is the chromium-reducing method of the open-hearth redistribution of chromium-containing charges, including a special selection of the charge for the content of phosphorus and carbon. In addition, 2.5 to 3.4% is introduced into the charge; 13% ferrosilicon by weight of the charge and 0.75-0.95% resin coke as a substitute for cast iron (partial carburetion). To reduce the loss of chromium, the minimum amount of slag was maintained due to the low consumption of limestone in the filling (2%), and the iron content in the slag was also limited (not more than 8%).

 The disadvantage of this method is the low basicity and oxidation of the slag at the beginning of a clean boil, which complicates the removal of phosphorus, the additional consumption of ferrosilicon to reduce the transition of chromium to slag, the negative chemical effect of the first period slag on the slopes of the bath, and strict requirements on the composition of the charge.

 The closest in technical essence and the achieved result is a method of steel smelting in hearth furnaces with a carburetor scrap-process, which involves closing the bottom with a “pillow” of charge materials, loading slag-forming (lime or limestone), loading materials containing deoxidizing and alloying elements in a mixture or on top carburetor, loading the rest of the charge, melting, lapping and restoring alloying and deoxidizing agents. This method is adopted as a prototype.

 The disadvantage is the use of a mixture with a minimum, strictly regulated content of sulfur and phosphorus, significant losses of alloying and deoxidizing agents with slag and the formation of foamy slag in the first period of melting.

 The objective of the invention is to obtain iron-carbon and alloyed alloys using alloyed waste or fresh charge.

 In solving this problem, a technical result is achieved associated with the recovery of deoxidizing and alloying elements from oxidized production wastes or from ore materials, ensuring minimum losses of alloying with slag, which leads to savings of deoxidizing and alloying materials and the disposal of oxidized wastes containing oxides of these elements, and allows you to provide a one-step process.

 The problem is solved in that in the method of smelting naturally-alloyed steels and alloys in hearth furnaces, including closing the hearth with a layer of iron-containing charge material, loading a carburetor, feeding lime or limestone, filling part of a light metal charge, loading materials containing deoxidizing and alloying elements, filling steel scrap, the formation of at least one zone of the slowest melting of the charge, periods of melting and lapping, restoration of alloying and deoxidizing elements, m Tally the invention carburizer and materials containing deoxidizing and alloying elements are charged together to the layer of iron-containing feed material in the melting zone of the slowest charge, then they were charged layer of a lightweight metal stock, as limestone and / or lime evenly distributed over them.

 As a layer of iron-containing charge material, you can use the remainder of the liquid metal of the previous melting or small scrap metal, in the latter case, the amount of which is 5 - 7% by weight of the metal charge.

 Materials containing deoxidizing agents and alloying elements, and the carburizer can be separated from lime and / or limestone by small scrap metal, the amount of which should preferably be 5-7% by weight of the metal charge.

 Deoxidizers and alloying elements are loaded into the furnace in the form of compounds (oxides, carbides, carbonates) or alloys (FeSI, FeMn, FeCr, SiMn, etc.), as well as mixtures thereof.

 Polymetallic ores from the group of manganese, chromium, chromium and molybdenum concentrates, uranovanadite, vanadite, decluazite, ilmenite, rutile, titanomagnetite can also be used.

From the theory of reduction of oxides and the practice of production of ferroalloys, it is known that carbothermal reduction reactions are possible in hearth units with respect to steelmaking furnaces when the reaction zone is heated to 700 - 1650 ^o C. At these temperatures, the necessary conditions are created for the reduction of Fe, Ni, Mn, Cr, Mo , V, Si, Ti. The presence of a metal melt contributes to this process by the removal of reaction products due to their dissolution and melt and volatilization of CO ₂ from the reaction zone (R. Durrer, G. Volkert. Metallurgy of ferroalloys. M: Metallurgy, 1976, p. 22 - 23; N.L. Goldstein. A short course in the theory of metallurgical processes. Sverdlovsk, 4, pp. 170 - 195).

 Studies have shown that in steelmaking units, when a carburetor is loaded in a separate layer between a metal charge (in this layer) a zone with a reducing atmosphere is created, and loading of a carburetor with alloying components in the zones of later penetration provides a longer contact of these materials with the carburetor in a reducing atmosphere. To enhance this effect, limestone or lime, which have a thermal conductivity coefficient 40 times lower than that of scrap metal, is uniformly dispersed over the mixture of the carburizer with alloying materials, which allows phosphorus and slag to be removed during the colder melting period without loss of alloying components.

 The amount of carburizer and oxidized material should be taken in an amount determined by the stoichiometric ratio according to the composition of the substance. Materials can be introduced into the mixture, in layers or by other means. The loading of oxidized materials onto the carburetor allows you to adjust the process of reducing alloying oxides and carburizing the bath, which facilitates the conduct of smelting.

 A "cushion" covering the bottom can be obtained by composing the metal of the previous heat, which allows the method to be implemented in electric furnaces. In the case of using small scrap metal for the “pillow”, its amount should preferably be in the range of 5-7% of the weight of the metal charge.

 In the event that less than 5% of scrap by weight of the metal charge is spent on the “cushion”, the conditions for protecting the furnace hearth from the mechanical effects of the heavy charge loaded later worsen and the likelihood of welding coke ash to the bottom increases. When loading more than 7% of small scrap onto the hearth, an increased amount of foamy primary slag is observed, slag formation worsens, which lengthens the smelting.

 Materials containing alloying and deoxidizing elements, and the carburizer can be loaded with fractions of 0.1 - 0.5 cm. The fractional composition of materials and carburizer is established from the conditions of melting (technology and thermal power of the furnace).

 In order not to impede the process of reduction of the oxides of deoxidizing and alloying elements from the material, limestone and / or lime should be separated from them.

 For this, various techniques can be used, in particular, filling with materials whose mass exceeds the buoyancy of the carburizer and alloying materials, for example, pig-iron shavings. Fine scrap can also be used.

 Fine scrap, separating the carburetor with alloying components from limestone or lime, can be loaded with a mass of 5 - 7% by weight of the metal charge.

 When loading small scrap between the carburizer and alloying lime and / or limestone in an amount of less than 5%, limestone and / or lime may come into contact with materials, which impedes the recovery process. When loading small scrap of more than 7%, the melting period lengthens due to the deterioration of heat transfer to the scrap layer.

 As oxidized alloying materials, in addition to production waste, natural minerals (ores) and concentrates are loaded: manganese, chromium, chromium and molybdenum concentrates, uranovanadite, vanadite, decluazite, ilmenite, rutile, titanomagnetite, etc.

 The proposed method was implemented on 5- and 350-400-ton, respectively, arc electric and open-hearth furnaces with the main lining. Cast iron and steel were smelted.

 Example 1. In a 5-ton electric arc furnace with an uncontrolled atmosphere, 0.5 tons of small steel scrap was loaded and 0.2 tons of coke breeze fraction 0.2 - 2.0 mm in it on the slope zone and a mixture of carburetor titanium-ore ore in quantity 1.5 tons of ore and 0.4 tons of coke breeze, which was covered with 2.0 tons of steel scrap and 1.0 tons of lime was scattered on top of it. Oxygen was not used. At the end of the melting period, one slag slag of the first period was lowered. The remaining operations were carried out using conventional technology, except deoxidation and alloying (the latter were excluded). As a result of melting, cast iron corresponding to the composition was obtained,%: C 3.75; Mn 0.05; Si 0.01; S 0.170; P 0.047; Ni 0.17; Cr 0.20; Co 0.07; V 0.116; Ti 0.015.

 Example 2. In a 350-ton open-hearth furnace, 30 small scrap of low-carbon scrap, which was heated for 5 minutes, was loaded onto a hearth, then 12 tons of coke breeze were loaded onto this “pillow” on top of which 3 tons of manganese ore were scattered on top of the carburetor, which loaded 25 tons of small steel scrap. After that, limestone was covered over the entire surface without passes, then the remaining 315 tons of low-carbon steel scrap were dumped. At the end of the melting period, 1 cup of primary slag was added and a sample was taken for carbon and manganese, the contents of which were, respectively, 0.93 and 0.26%. The addition was carried out by conventional technology.

Example 3. In a 400-ton open-hearth furnace, 40 tons of small steel scrap were loaded onto the hearth, which was heated for 5 minutes, then 10 tons of coke breeze was loaded into the middle filling window and 6 tons of manganese ore were placed on top of it, then 30 tons of fine steel scrap and 25 limestones were loaded without passes on top of the coke-manganese ore mixture over the entire area, then 130 tons of the remaining steel scrap were dumped. After heating the mixture for 1 h 10 min, 200 tons of molten iron were poured. From the beginning of pouring to the deoxidation period, the bath was purged with oxygen at a flow rate of 1000 m ³ / h.

 During the melting process, 1.5 cups of slag are removed. A carbon and manganese sample was taken by melting the bath, the content of which was 1.48 and 0.26%, respectively. The refinement was carried out according to the usual technology, at the end of which the manganese content in the metal additionally increased by 0.076%. As a result of melting, P-65 steel was obtained.

Example 4. In a 400-ton open-hearth furnace, 80 tons of small steel scrap were loaded onto the hearth, which was heated for 5 minutes, then 4.8 tons of coke breeze was loaded onto this “pillow” in the middle filling window, and manganese was scattered over the entire coke area ore in the amount of 2.5 tons. 26 tons of limestone were scattered over the last without passes, then 120 tons of the remaining steel scrap were heaped up and after heating for 270 hours, 270 tons of molten iron were poured. From the beginning of pouring and until the deoxidation period, the bath was purged with oxygen at a flow rate of 1600 m ³ / h. A molten sample was taken for carbon and manganese, the contents of which were 1.21 and 0.11%, respectively.

 As a result of melting, P-65 steel was obtained.

 Example 5. From the previous melting on the bottom left 4 tons of molten metal, onto which 3 tons of coke breeze was scattered. 3 t of manganese ore were evenly dispersed over the latter. Then a layer of small steel scrap was loaded and 2 tons of lime were completely covered, 2 lime steel scrap dumps were made into the lime during melting. Further melting, fine-tuning and production were carried out using conventional technology. By melting the bath, 0.63% carbon and 0.24% manganese were obtained. Upon release, they received finished steel 35 GS.

 To compare the technical and economic data, melting was carried out according to the technology of the prototype.

 The results of all swimming trunks are given in the table.

 The table shows that the use of the proposed technology allows to reduce the specific consumption of pig iron by 25% in the same furnaces, to increase the absorption of alloying and deoxidizing agents from all sources by 15%, not to regulate the content of sulfur and phosphorus in the charge, to use waste and to reduce the cost products.

Claims (7)

 1. A method of smelting naturally alloyed steels and alloys in hearth furnaces, including closing the hearth with a layer of iron-containing charge material, loading a carburetor, feeding lime or limestone, filling part of a lightweight metal charge, loading materials containing deoxidizing and alloying elements, filling steel scrap, at least the formation of steel scrap one zone of the slowest melting of the charge, the periods of melting and lapping, the restoration of alloying and deoxidizing elements, the release of metal, characterized in that the carburetate together with materials containing deoxidizing and alloying elements, they are loaded onto a layer of iron-containing charge material into the slowest melting zones, then a layer of lightweight metal charge is loaded onto them, after which lime or limestone are evenly distributed over them.  2. The method according to claim 1, characterized in that the remainder of the molten metal from the previous heat is used as a layer of iron-containing charge material covering the hearth.  3. The method according to claim 1, characterized in that the bottom is covered with a layer of small scrap metal in an amount of 5-7% by weight of the metal charge, which is heated before loading the carburizer and materials containing deoxidizing and alloying elements.  4. The method according to any one of claims 1 to 3, characterized in that on the carburetor and materials containing deoxidizing and alloying elements, load a layer of small scrap metal in an amount of 5-7% by weight of the metal charge.  5. The method according to claim 1, characterized in that cast iron is additionally loaded onto steel scrap.  6. The method according to any one of claims 1 to 5, characterized in that as materials containing deoxidizing and alloying elements using production waste containing these elements in the form of their oxides, carbides, carbonates, alloys and / or their alloys with iron.  7. The method according to any one of claims 1 to 5, characterized in that as materials containing deoxidizing and alloying elements, polymetallic ores from the group of manganese, chromium, chromium or molybdenum concentrates, balanced vanadium, vanadite, decluazite, ilmenite, rutile or titanomagnetite.

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