RU2335564C2 - High titanium ferro alloy produced by two stages reduction out of ilmenite - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to high titanium ferroalloy, produced by two stages melting in electric furnace; alloy is used as alloying component at production of steel with high level of physic-mechanical properties. For producing of ferroalloy the charge prepared out of ilmenite, iron and/or steel scrap, crushed electrodes and/or coke, lime and/or lime stone is used; then slag containing titanium oxide and part of iron melt on the first stage are withdrawn; a consumable electrode in a steel coat is melted under the layer of flux; the said electrode contains crushed slag of the first stage and aluminium as filler. Ferro alloy contains components at a following ratio, wt %: titanium 68.02-78.7; iron 19.32-30.0; impurities to 1.98.

EFFECT: invention facilitates production of finished product in form of compact commodity ingot of ferrotitanium with specified contents of basic component.

2 ex, 2 tbl

Description

The present invention relates to the field of ferrous metallurgy, in particular to a high titanium ferroalloy obtained by two-stage reduction in an electric furnace from ilmenite and which can be used as an alloying component in the production of alloy steels with a high level of physical and mechanical properties.

The need for structural materials with a high level of physico-mechanical and special properties for use in space engineering, oil, chemical, food industry and medicine is constantly increasing. Design tasks for the selection of materials with a high range of required properties and, at the same time, relatively low cost, require the improvement of existing and the development of new structural materials. Steel is still the most acceptable structural material for most of the tasks posed by science, since the introduction of relatively small amounts of various chemical elements into the composition of an iron-carbon alloy substantially changes the structure of the resulting material — steel, and, accordingly, increases the level of required properties or gives this alloy new previously unknown properties.

Among the alloying steel chemical elements that increase its tensile strength, corrosion resistance, impact strength, blocking the propagation of cracks in the matrix structure, the best results are provided by titanium, which forms mono- and polycarbides with carbon steel, as well as intermetallic compounds with other alloying elements of steel. However, the technology for its production with the subsequent processing of titanium sponge into a form convenient for alloying is complex, energy intensive, and expensive. Therefore, the resolution of the problem between the use of titanium-based alloys as an alloying component of steel and the search for ways to reduce the cost of commercial titanium alloy without losing the complex of its physical and mechanical properties is still very acute.

Titanium-based casting alloys containing aluminum, molybdenum, zirconium, niobium (Ukrainian patent No. 51032, A, publ. November 15, 2002, Bull. 11) or containing aluminum, zirconium, molybdenum, vanadium, yttrium (Ukrainian patent) are known from the prior art. No. 58671, A, publ. 08/15/2003, Bull. 8), or containing up to 5 wt.% Aluminum, up to 4 wt.% Iron, up to 2.5 wt.% Manganese, up to 1.0 wt.% Zirconium ( patent of Ukraine No. 38805, A, publ. 05/15/2001, Bull. 4). These alloys are obtained according to traditional foundry technology — by composing a mixture of crushed sponge titanium and these alloys, melting in furnaces and crystallizing the melt poured into molds, followed by ingots of these alloys.

The disadvantages of these alloys include:

- complex alloying of the resulting final product, which is supposed to be used as an alloying composition in the same complex composition of steel, which, accordingly, complicates the calculation of the number of alloying steel introduced into the composition;

- the high cost of the specified alloying composition due to the lack of industrial production of its components (Al, Mo, Zr, Nb, V, Y) in Ukraine, as well as the high cost of obtaining the initial main component of the alloy - sponge titanium;

- the lack of constant need for the introduction into the composition of the steel as alloying specified alloy components, which in this case are mandatory components.

Known powder of a titanium alloy with magnesium (Ukrainian patent No. 51917, A, publ. February 16, 2002, Bull 12), obtained by melting in an electric furnace of a consumable electrode, which consists of a partially vacuum separated 80-90% recovered crushed to a large size by the magnesium thermal method 5-70 mm sponge titanium mixed with magnesium granules with a particle size of 1-5 mm in an amount of 0.3-5 wt.% And residual magnesium chloride (up to 5 wt.%). When the consumable electrode is melted, magnesium and magnesium chloride vapors, due to the high vapor pressure many times higher than the vapor pressure of titanium, manifest themselves as atomizing agents and provide atomization of the electrode material in the form of powder particles that solidify into spherical particles of an alloy of titanium with magnesium. The fineness of the final product according to the specified patent - titanium alloy powder in the best case is 43.5% of the fraction - 1.0 + 0.5 mm, 20.2% of the fraction - 0.5 + 0.315 mm, 12.2% of the fraction -0.315+ 0.2 mm, 17.9% of the fraction - 0.2 + 0.09 mm, 5.4% less than 0.09 mm.

The disadvantages of the final product obtained according to this invention should include its prevailing maximum fineness (1.0-0.5 mm), since the introduction of such a titanium-containing alloy as alloying in, for example, a converter in a charge at its melting temperature of 1500-1700 ° C or in the process of out-of-furnace treatment of the melt in the ladle at a temperature of 1450-1600 ° C, it will cause increased titanium fumes and will lead to a significant reduction in its amount required for steel processing. In addition, alloyed steel production volumes amount to tens of thousands of tons per year, for which (in terms of the amount of alloying component) titanium alloy powder will require hundreds of tons, due to its low density, which, in turn, will require the construction of new powerful and energy-intensive enterprises for the production of titanium powder.

The prior art high-titanium ferroalloy containing 65-75 wt.% Titanium, 34.5-24.5 wt.% Iron, up to 0.5 wt.% Nitrogen (RF patent No. 2131479, C1, publ. 10.06.1999) . The high-titanium ferroalloy according to this patent is obtained from waste from the production of titanium alloys, for example TL-3, in the form of lump waste and shavings and steel waste, for example, steel 20 in a ratio of 3: 1 to 4: 1 by melting in an induction furnace without flux. Ferrite-titanium is charged onto the induced liquid bath of iron as the mixture contains iron and titanium-containing elements, and titanium-containing shavings are introduced onto the liquid surface of the alloy in the form of a layer with a thickness that prevents reddening of its surface. The resulting ferroalloy is partially drained and the process is repeated.

The disadvantages of this invention include the presence in the composition of the final product to 0.5 wt.% Nitrogen. Nitrogen is an extremely undesirable component of the steel composition because it causes red cracking and, thus, reduces the level of strength properties of steel at elevated temperatures of its operation. In addition, since the components of a titanium and iron-containing mixture are melted in an induction furnace without flux, the smelted ferroalloy contains a certain amount of oxygen, which it assimilates from air and is easily bound by titanium due to its high affinity for oxygen. Even a significant layer of chips on the surface of a liquid ferroalloy cannot prevent the penetration of gaseous oxygen to it. The maximum oxygen content in high-quality alloy steels according to the quality standard should not exceed 0.004-0.007 wt.%.

The closest analogue from the prior art is the patent of Ukraine No. 599720, A, publ. September 15, 2003, on a method for producing a high-titanium ferroalloy from ilmenite by means of two step reductive electric arc melting of a batch of ilmenite concentrate, crushed carbon reducing agent, such as electrode fight and lime, charged in batches of iron melt at the first stage of the process. Moreover, before the first stage, they form a bath of iron melt by loading iron scrap into the furnace with further melting it and removing the resulting slag. The slag containing titanium oxide formed after the first stage is poured, cooled and crushed. In the second stage, the main charge is prepared from a mixture of crushed slag, lump aluminum and lime, which is loaded onto an iron melt mirror, melted and reduced titanium and iron oxides to ferrotitanium. Obtained by the specified method, the ferroalloy contains up to 55-60 wt.% Titanium, the rest is reduced iron and up to 1.5 wt.% Impurities.

The disadvantages of this invention are the need for preliminary preparation of the starting material for producing a ferroalloy - ilmenite by enrichment according to the content of the main component of the process into a concentrate, which increases the cost of the resulting product - ferrotitanium. The final ferrotitanium obtained according to this invention contains from 55 to 60 wt.% Titanium, which is insufficient for the production of the introduced component in the composition of alloy steels, since the constantly increasing volumes of production of alloy steels with this ratio of the main component in ferrotitanium will require the introduction of significant volumes of ferroalloy produced per ton of alloy steel produced. The disadvantages also include the lack of protection of the process at its second stage from oxidation by atmospheric oxygen, which significantly impairs the quality of the final product and reduces the yield of the product after the process. The main disadvantage of this invention is the inability to obtain the final product in the form of a commodity ingot of ferrotitanium. Ferrotitanium after two stages of reduction and melting is obtained in the form of kings, enclosed in a mass of slag, which requires additional operations of extracting the kings, cleaning them from slag and fusion, and thereby increases the cost of a unit of the resulting product.

The basis of the claimed invention is the task of producing a high-titanium ferroalloy with a titanium content of not less than 68 wt.% In the final product, reducing the cost per unit weight of the product, eliminating the possibility of air pollution of the ferroalloy during titanium reduction, ensuring the conditions for obtaining the finished product in the form of a compact commodity ferrotitanium ingot with the specified content of the main component by changing the technological operations of titanium recovery from the titanium oxide contained in the slag to Torah known process step,

The problem is solved in that a high-titanium ferroalloy containing titanium and iron, obtained by two-stage melting in an electric furnace of a mixture of ilmenite, cast iron and / or steel scrap, electrode battle and / or coke, lime and / or limestone, removing slag containing titanium oxide and part of the molten iron in the first stage, by melting the main mixture of crushed slag of the first stage and aluminum and the formation of a ferroalloy. At the same time, at the second stage, the sacrificial electrode is melted under the flux layer, containing the main charge in the form of a filler enclosed in a steel shell, with the formation of a ferroalloy containing 68.02-78.7 wt.% Titanium, 19.32-30.0 wt. .% iron and up to 1.98 wt.% impurities.

The essence of the claimed invention lies in the fact that high-titanium ferroalloy from ilmenite is obtained in two stages. At the first stage, titanium slag is obtained with a high content of titanium oxide and a minimum content of iron oxides. The melting of slag containing titanium oxide is carried out in an electric arc furnace of alternating or direct current at the second stage of the process.

Cast iron or steel scrap is melted in an electric furnace. After the scrap is melted from the furnace, the slag formed as a result of melting is removed, and a mixture consisting of ilmenite ore and a reducing agent (electrode fight or coke) is loaded in separate portions onto the surface of the liquid metal bath. To slag the gangue contained in ilmenite ore, limestone or lime is added to the mixture. In the process of melting the mixture, the iron oxides contained in the ore are reduced. The reduced iron goes into a metal melt, which leads to an increase in the concentration of titanium oxide in the resulting slag.

The amount of slag formed depends on the technical characteristics of the equipment used: the capacity of the electric furnace, its power, the duration of the process of reducing iron from oxides contained in ilmenite ore. Therefore, depending on the selected melting equipment, in accordance with the theoretical reactions for the reduction of iron from its oxides that are contained in the starting material, the weight of the charge components and its total amount are selected by calculation. Ilmenite ore contains, in wt.%: 60,00 TiO ₂ ; 31.70 Fe ₂ O ₃ ; 1.10 Al ₂ O ₃ ; 2.84 SiO ₂ ; 2.34 S; 0.28 P; 0.43 V ₂ O ₅ ; 0.56 MnO. The degree of reduction of iron from its oxide is 80-85%. When the degree of reduction is less than 80%, the amount of titanium oxide in the slag is significantly reduced, which ultimately leads to a decrease in the titanium content in ferrotitanium. Enriched with titanium oxide slag, with a content of at least 78 wt.% TiO ₂ , after the completion of the recovery period of the melting mixture is poured into the molds.

At the second stage of the process for producing high-titanium ferroalloy, a mixture is prepared consisting of a metered amount of ground slag obtained in the first stage and aluminum powder with a particle size of not more than 800 microns. The charge mixture is loaded into a metal shell with its subsequent use as a consumable electrode in an electroslag melting unit. A consumable electrode, which is a metal shell filled with filler from the above mixture, is connected to the positive pole of the current source and lowered into the flux hitch located on the bottom of the melting crucible until it contacts the hearth to which the negative pole of the current source is fed. As a flux, a mixture of aluminum and calcium oxides is used. After the contact of the electrode with the bottom of the crucible is applied, voltage is applied and the sacrificial electrode is raised until an electric arc is formed with optimal electrical parameters, which ensure stable burning of the electric arc.

As a result of heat generation from the electrical resistance of the flux and exothermic reactions of the recovery of the filler components, the consumable electrode is melted. Reduced titanium and iron, passing through a layer of liquid slag formed, accumulate on the bottom of the crucible. After the molten electrode is completely melted, the furnace power is turned off and the melting products are allowed to cool. The resulting ferrotitanium ingot is freed of slag and, together with other ingots, after previous melts, is melted in an induction furnace into a salable ingot with an average chemical composition, wt.%: 68.00-78.70 titanium, 19.30-30.00 iron, up to 1.98 impurities containing aluminum, silicon, manganese, vanadium and sulfur.

EXAMPLES OF PRODUCING HIGH-TITANIUM FERROALLOY

As a melting furnace for producing high-titanium slag, we used a DC electric arc furnace ДСП - 3.0 with a main lining with the following technical characteristics:

1. Nominal capacity, t - 3.0;

2. Power of the transformer, kVA - 2000;

3. The maximum current, A - 4800;

4. Secondary voltage, V - 243-124.

An electrode battle with a carbon content of 86 wt.% Was used as a reducing agent. For fluxing of silica contained in ilmenite ore, freshly calcined lime was used with a piece size of not more than 100 mm. Ilmenite ore contained the following components, in wt.%: 60.00 TiO ₂ ; 31.70 Fe ₂ O ₃ ; 1.10 Al ₂ O ₃ ; 2.84 SiO ₂ ; 2.34 S; 0.28 P; 0.43 V ₂ O ₅ ; 0.56 MnO.

The preparation of the mixture included weight dosing of its components and thorough mixing with averaging over the composition. The melting technology consisted in loading the pig iron scrap included in the charge into an electric furnace, its melting and heating to a temperature of 1350-1400 ° С. After that, the slag formed during the melting of the metal part of the charge was removed from the furnace, and the prepared charge was periodically, in separate portions, loaded onto the surface of the metal bath of the melt and melted. Additive charge materials was carried out during the melting process as the previously loaded batches of the mixture were melted. After the last portion of the charge loaded into the furnace was melted, the electric furnace was turned off and the slag and some metal were drained into the molds. The cooled slag was crushed, crushed, and a sample was taken to determine its chemical composition. The optimal chemical composition of the slag obtained after the first stage of the process is 79.5 wt.% TiO ₂ , 7.8 wt.% Fe ₂ O ₃ , the rest are impurities of aluminum oxides, silicon vanadium manganese, as well as sulfur and phosphorus.

The production of high-titanium ferroalloy was carried out in a direct current laboratory electric furnace with a main lining with the following technical characteristics:

1. The capacity of the laboratory direct current arc furnace, kg - 20;

2. The nominal value of the current, A - 800-850;

3. The rated voltage, V - 35-40.

Ferrotitanium was melted with the reduction of the titanium, iron, and silicon oxides contained in the main charge with aluminum during melting of the consumable electrode under a protective flux layer. The main charge used as a filler of a consumable electrode included crushed slag containing titanium oxide of the above composition, aluminum powder and liquid glass as a binder. The fluxing of silicon oxide was carried out by limestone introduced into the charge. After dosing of slag, aluminum powder and liquid glass, the mixture of the main charge was mixed in order to average the composition. The prepared mixture was loaded into the steel shell of the consumable electrode and compacted using press equipment.

The prepared consumable electrode was connected to the positive pole of the DC power source, and under the melting crucible, to the negative pole. Using the movement mechanism, the electrode was lowered until it became in contact with the hearth of the melting crucible, while passing a layer of protective flux on the bottom of the crucible. After turning on the power source, exciting an electric arc between the consumable electrode and the hearth of the crucible, the consumable electrode was melted. The speed of movement of the consumable electrode ensured the melting of its end in the slag phase so that the end of the consumable electrode was constantly below the surface of the flux and the resulting slag. A mixture of 50 wt.% Al ₂ O ₃ and 50 wt.% CaO was used as a protective flux for melting the consumable electrode. As the electrode melted, limestone was fed in separate portions to the surface of the formed melt to flux alumina, which was formed as a result of reduction processes, and to obtain low-melting and liquid-moving slag.

After the consumable electrode was melted, the electric furnace was turned off, and the resulting compact ferrotitanium ingot and slag were left in the electric furnace until completely cooled.

To confirm the industrial applicability of the claimed invention, a series of experimental swimming trunks was carried out, 3 for each mode in order to average the results. Data technical characteristics of obtaining high-titanium ferroalloy and comparative chemical composition of the product and according to the claimed invention and the closest analogue of the prior art are presented in tables 1 and 2.

The data of tables 1 and 2 for sample 3 indicate a high (72.00 wt.%) Content in the ingot of titanium ferroalloy. The quality of the ingot obtained is high, and the content of impurities, which include aluminum, silicon, manganese, vanadium and sulfur, does not exceed 2.4 wt.%.

The presented description does not limit the claimed invention in all its possible modifications, improvements and equivalents that do not go beyond the scope of the claimed formula, but serves only as an illustration, addition and clarification of specific embodiments of the invention.

Claims (1)

High-titanium ferroalloy obtained by two-stage melting in an electric furnace of a mixture of ilmenite, pig-iron and / or steel scrap, electrode breakdown and / or coke, lime and / or limestone, removing slag containing titanium oxide and part of the molten iron in the first stage, melting under a flux layer of the spent an electrode in a steel shell containing crushed slag of the first stage and aluminum containing titanium, iron and impurities as a filler in the following ratio, wt.%: titanium 68.02-78.7 iron 19.32-30.0 impurities up to 1.98