HIGH CONTENT OF TITANIUM

Technical Field

[001] The present invention relates to the field of ferrous metallurgy, in particular for the production of a ferrotitanium alloy having high titanium content - ferrotitanium - obtained by the melting process of a molten composite electrode and used as an alloying component in the production of steel alloys having high physical and mechanical properties.

Background Art

[002] The need for construction materials with high physical and mechanical properties for use in the space engineering, petroleum, chemical, food and medical industries is constantly increasing. Design tasks in the selection of materials with a high set of required properties and at the same time relatively low costs require the improvement of existing construction materials and creation of new materials, as well as the reduction of the cost of existing high-performance materials. So far, steel has been the most suitable construction material for most technical tasks. If a relatively small amount of different chemical elements is added to a carbon-iron alloy, the structure of the resulting material changes significantly - the level of different properties increases for steel and the corresponding alloys, or even gives this alloy new, hitherto unknown properties.

[003] Among the chemical elements of alloy steel, which increase its tensile strength, corrosion resistance, impact resistance and crack propagation in the matrix structure, titanium, which produces mono- and polycarbides with steel carbon, as well as intermetallic compounds with other compounds, titanium show the best results. However, the existing titanium production technology with the Kroll process with further processing of porous titanium by repeated remelting until an alloy suitable for alloying is obtained is complex, energy-intensive and expensive. The steel can be alloyed with a titanium alloy, in which a certain level of iron impurity is permissible. It is therefore possible to reduce the cost of a titanium-iron alloy product without losing its complex of mechanical properties, which is still a very difficult task. [004] From a technical point of view titanium-based casting alloys containing aluminium, molybdenum, zirconium, niobium (UA 51032) or those containing aluminium, zirconium, molybdenum, vanadium, yttrium (UA 58671) are known. These alloys are obtained in the form of traditional casting techniques by melting a combination of porous titanium and the specified alloying components mainly in arc furnaces and casting the material into crystallization moulds obtaining bars of said alloys. The disadvantages of such alloys are: complicated alloying of the final product to be used, which is intended to be used as an alloying composition in steel of the same complexity, which makes it difficult to calculate the alloying elements to be introduced into the steel composition; the high price of the indicated alloying composition, because it is not possible to obtain its components (Al, Mo, Zr, Nb, V, Y) in an industrial way, as well as the cost of obtaining the main raw material, the alloy component - porous titanium; there is no need to dissolve the additional alloying compounds in the steel, as it is already in the form of a solution.

[005] A titanium alloy powder with magnesium is known (UA 51917), which is obtained by melting in an electric arc furnace a consumable electrode consisting of porous titanium, which is melted in vacuum arc furnaces in an amount of 80-90% and reduced by a magnesium thermal method by grinding to a fraction of 5 to 70 mm, mixed with 1 to 5 mm of magnesium granules containing 0,3 to 5% by weight and with the remaining magnesium chloride (up to 5% by weight). During the melting of a consumable electrode, magnesium and magnesium chloride vapours due to their high partial pressure (several times higher than the titanium vapour pressure) ensure sublimation of the electrode material in the titanium-magnesium alloy in the form of spherical particles. According to the known solution, the volume of the final product (titanium alloy powder) in the best case is 43.5% (with a fraction size of 1.0 + 0.5 mm), 20.2% (with a fraction size of 0.5 + 0.315 mm), 12.2% (with a fraction size of 0.315 + 0.2 mm), 17.8% (with a fraction size of 0.2 + 0.09 mm) and 5.4% with a fraction size of less than 0.09 mm. The disadvantages of the final product of the known material are its predominant maximum casting fraction volume (1.0-0.5 mm), as the addition of a titanium-containing alloy such as an alloy, for example in a converter at a melting point of 1500-1700 °C or in an alloy processing process outside the furnace in the ladle 1450- 1600 °C, will increase titanium losses. In addition, alloy steel production is in the tens of thousands of tonnes per year and (taking into account the volumes of the alloying component) requires hundreds of tonnes of titanium alloy powder due to its low density, which in turn means the need to build new, high capacity, energy-intensive titanium powder plants.

[006] There is known an iron alloy with a high titanium content of 65-75% by weight of titanium, 34.5-24.5% by weight of iron, up to 0.5% by weight of nitrogen (RU 2131479 C1). The high titanium content ferrotitanium alloy described in this patent, is obtained from the production of titanium alloys, such as TL-Z, by melting in the form of titanium waste, chip and steel waste, such as 20 grades of steel, in a ratio of 3: 1 to 4: 1 in an induction furnace. In the liquid ferrotitanium bath is formed, iron and titanium- containing elements are added during the melting process, and the titanium-containing chips are added to the liquid top layer of the alloy in the form of salt in such a thickness as to prevent redness (overheating) at the top of the alloy. The resulting iron alloy is partially decanted and the process is repeated. The disadvantage of the known solution is the nitrogen present in the final product - up to 0.5% by weight. Nitrogen is a highly undesirable component in steel, as it causes cracks during heat treatment, thus reducing the strength of the steel during its use in high temperature conditions. In addition, since the titanium and iron-containing mixture is melted in an induction furnace without an electric arc, the resulting iron alloy contains a certain amount of oxygen, which it obtains from the air by easily combining with titanium. The access of gaseous oxygen to the ferrous alloy is not stopped by a significant layer of chips. According to quality standards, high-quality alloy steels must not contain more than 0.004-0.007% by weight of oxygen.

[007] There is known solution (UA 59720), which describes how to obtain an iron alloy with a high titanium content from ilmenite using a two-stage regeneration electric arc, where a mixture of ilmenite concentrate, crushed carbon regenerator, such as electrode pieces and lime, is added to the iron alloy in portions in the first process step. Before the first stage, an iron-melted bath is formed by placing ferrous scrap in a furnace, further melting it and removing slag (flux). Slags from the first stage containing titanium oxide are poured off, cooled and grinded. In the second stage, the basic composite is prepared from crushed slag, pieces of aluminium and lime, which is added to an iron alloy mirror, is melted and the titanium and iron oxides are restored to ferrotitanium. The iron alloy thus obtained contains 55-60% by weight of titanium, the rest is iron and up to 1.5% by weight - impurities. The final ferrotitanium obtained under the known solution contains from 55 to 60% by weight of titanium, which is not sufficient for the particular application of the ligature, as it would mean that it would have to be added in excessive amounts during its production process. Another disadvantage is that in the second stage of the process there is no protection against oxidation with oxygen in the air, which significantly reduces the quality of the final product obtained and reduces the amount of useful product at the end of the process. The main disadvantage of this solution is that it is not possible to obtain the final product in the form of a ferrotitanium bar. Ferrotitanium, after two stages of regeneration and melting, comes out in the form of crumbs that are incorporated into the slag mass. Thus, additional steps are needed to remove these crumbs from the slag and alloys, which increase the unit price of the resulting product.

[008] The use of an electromagnetic field in the process of remelting electroslag for the production of other alloys is proposed in US 6349107. However, the electromagnetic interaction proposed for the production of the alloy in question is not strong enough compared to the one proposed here. The disclosure only deals with the use of a slow pulsating field and not with the use of several different combinations of fields that complement each other, where the constant component of time is obtained by a special permanent magnet system, thus, the basic time component is obtained in a more efficient way, without additional power losses.

Summary of the Invention

[009] The object of the proposed invention is to obtain an iron alloy with a high titanium content in the final product - not less than 70% by weight, to reduce the unit cost of the product, to prevent the possibility of contamination of the iron alloy with air oxygen during titanium regeneration, to provide the conditions for obtaining a finished product in the form of a compact ferrotitanium bar with a certain content of the main component.

Brief Description of Drawings

[010] Fig. 1 - schematic representation of the electroslag remelting equipment provided by an electromagnetic system in the crystallization zone;

Fig. 2 - a consumable electrode obtained by placing a mixture of raw materials in a metal (iron, steel or cast iron) shell;

Fig. 3 - a permanent magnet system which is located around the crystallization reservoir to create a strong permanent magnetic field in the region of fluxes and crystallization;

Fig. 4 - a capacitor block adapted for generating a pulsed current for generating a pulsed magnetic field in the crystallization region;

Fig. 5 - a diagram showing the dependence of the current of the coil on the time obtained with the pulse battery;

Fig. 6 - the trajectories of the droplets in the region of the liquid melt and their radial distribution in the crystallizer, as well as the flow in the region of the liquid melt: Fig. 6.A - without magnetic field, Fig. 6.B with transverse magnetic field;

Fig. 7 - one embodiment of the arrangement of permanent magnets according to the proposed invention.

Detailed Description of Invention

[011] The proposed method for obtaining a high titanium content ferrotitanium compound from a rutile-based mixture of chemical elements by an electromagnetically supplemented electroslag remelting method comprising the following sequential steps: (i) providing an electrode adapted for its melting, by placing a mixture of powdered chemical elements based on rutile in a metal shell; (ii) melting electrode in the molten flux layer (5), subjecting the molten metal layer (6) and the crystallizing alloy to a combined action of a permanent magnetic and pulsed electromagnetic field source (the permanent magnetic field creates a cross field with respect to the molten flux layer (5), the molten metal layer (6) and/or the cooled crystallizer (4), while the pulsed electromagnetic field has an axial direction), wherein, the permanent magnetic field is selected in the range of 200-400 mT and the pulsed magnetic field in the range of 400- 800 mT with a pulse frequency of 1-10 Hz; (iii) after melting the electrode - cooling the molten product and removing the slag.

[012] According to the invention, the composition of the consumable electrode is selected from the group consisting of rutile, iron (can be also cast iron or steel, which is the source of iron), carbon, coke, quicklime and aluminium powder having fraction in the range of 600-900 μm . The material of the metal shell may be cast iron, iron, steel or other iron-based alloys.

[013] According to the invention, prior to melting of the electrode on step (ii), the electroslag can be melted in an electric arc furnace, by first melting the cast iron or steel electroslag, removing the smelting slag from the furnace and adding a mixture of rutile and reducer - carbon or coke - to the top of the liquid metal bath, optionally also adding limestone or lime to the mixture.

[014] According to another embodiment of the invention, after step (hi), the slag-free melt product is subjected to melting in an induction furnace to form a high titanium content ferrotitanium rod.

[015] The apparatus (Fig. 1) for carrying out the method comprises: an electrode holder (1); a closed atmosphere reservoir (2); a consumable electrode (3); a coolable crystallizer (4); a coolable base (9) and an electromagnetic system (8) located outside the reservoir (2) at the level of the molten flux layer (5), the molten metal layer (6) and/or at the level of the cooled crystallizer (4), the electromagnetic system (8) comprising permanent magnets and an inductor connected to a capacitor unit for pulsed current generation; the electromagnetic system (8) is adapted to generate a permanent magnetic field, which is a cross field with respect to the molten flux layer (5), the molten metal layer (6) and a coolable crystallizer (4), as well as a pulsed electromagnetic field, which is an axial field in relation to the molten flux layer (5), the molten metal layer (6) and the coolable crystallizer (4), wherein the permanent magnets being adapted to generate a permanent magnetic field in the range of 200 to 400 mT and the inductor to generate a pulsed electromagnetic field in the range of 400 to 800 mT with pulse frequency in the range of 1-10 Hz. According to a preferred embodiment of the invention, the inductor is a single-winding inductor.

[016] The set goal is reached by obtaining an iron alloy with a high titanium content from the mixture (rutile, cast iron and/or steel scrap, crushed electrodes or coke, lime and/or limestone and aluminium) placed in a metal shell (Fig. 2) and melted as a consumable electrode in an electric slag remelting furnace under the melt layer. Additional sources of electromagnetic fields are connected to the standard electric melting furnace - placed around the crystallization region: permanent magnet system - Fig. 3, which creates a cross field of 200-400 mT in relation to the crystallization reservoir.

[017] A single-winding inductor powered by a capacitor bank (Fig. 4) which, with a pulsed current (Fig. 5), generates a pulsed axial magnetic field reaching 400-800 mT with a pulse frequency of 1-10 Hz. Using this combination of the two fields and the mentioned smelting process, it is possible to obtain an iron alloy with the following composition: 69.0-78.1% by weight of titanium, 14.32-30.0% by weight of iron and up to 2.6% by weight of impurities.

[018] According to the present invention, the combination of pulsed and permanent magnetic field created interacts with the discharge current and, firstly, causes movement in liquid fluxes and molten droplets, which promotes melting of molten material and, consequently, increases chemical reaction rates, and secondly, crystallization of the ingot, significantly reducing the formation of possible dentrides and other irregularities (including pores, gas inclusions). Intense stirring of the reaction medium allows it to proceed with less residue, reducing the amount of residual impurities and allowing a higher titanium content to be achieved. Strong flow in the flux region and the effect of electromagnetic force on the molten droplets also ensures a significantly more uniform ingot formation, because the droplets do not settle only in the middle part of the ingot, but evenly over the entire plane of the crystallizer - Fig. 6. Induction of strong pressure fluctuations in the droplets and the liquid metal area before crystallization also ensures the transport of gases and light fraction (slag residue) from the liquid metal, ensuring a good and even crystallization structure of the ingot - a homogeneous ingot is formed instead of a flaky or granular product.

[019] The permanent magnetic field is created by a permanent magnetic system comprising pieces of permanent magnets arranged in a toroidal shape as shown in Fig. 7, where the top of the toroidally arranged magnets has a magnetization directed radially in the axial direction, but at the bottom - in the opposite direction. In addition to amplifying the magnetic field, a so-called ferromagnetic yoke can be used on the outer side surface of the toroid of the magnetic system. The size of the magnetic system (toroid dimensions, magnet magnetization, magnetic yoke dimensions) must be selected according to the reactor dimensions so that a constant magnetic field of 200- 400 mT is reached on the axis. The toroidal arrangement relative to the reactor is designed so that its centre coincides with the lower surface of the flux (5) - the initial crystallization front - and at the same time with the central plane of one winding inductor.

[020] In addition to improving of the efficiency, especially if rutile with an impurity content of> 5% is used, the steel and rutile can be pre-fused in an electric arc furnace. First, cast iron or steel scrap is melted. After melting, the slags from the melting are removed from the furnace and a mixture of rutile and a reducing agent (carbon or coke) is added in separate portions to the top of the liquid metal bath. Limestone or lime (depending on the purity of the rutile used) is added to the rutile composition used to burn any remaining impurities and other rocks, which requires a source of TiO ₂ of at least 95% by mass. During the melting of the mixture, the iron oxide normally present in the composition is reduced. Recovered iron is converted into a metallic melt, which causes an increase in the concentration of titanium oxide in the generated slag.

[021] To obtain a ferrous alloy with a high titanium content, the mixture of rutile, iron and aluminium powder having a fraction in the range of 600-900 μm is first prepared. The mixture is placed in a metal shell, which is then used as a consumable electrode in an electrical slag remelting plant. A consumable electrode formed by a metal shell filled with the above mixture is connected to the positive pole of the power supply source and lowered into the molten flux layer at the bottom of the melting reservoir until it contacts the bottom where the negative pole of the power supply source is fed. A mixture of aluminium and calcium oxides is provided in the fluxes. After the contact is established between the electrode and the bottom of the reservoir, voltage is applied and the consumable electrode is raised until an electric arc with optimal electrical parameters is formed, which ensures a stable combustion mode of the electric arc.

[022] As a result of the release of heat from the electrical resistance of the flux current and from the reduction of the filling components by exothermic reactions, the electrode melts. This occurs in the region, starting with the end of the electrode to be melted, and continuing as it passes through the molten layer of melt until it crystallizes at the bottom of the reservoir in the form of an ingot. The melt is continuously affected by a pulsed magnetic field from melting to crystallization, which there causes pulsed pressure fluctuations, which in turn improves the reaction rate and, secondly, creates micromotion in each drop, which in turn improves reagent transport and, accordingly, reaction rate. Although the fluxes have a relatively low electrical conductivity, due to the flowing current, the external magnetic field creates a macroscopic flow in these fluxes as well, which in turn means that it ensures more efficient removal of other impurities from the melt droplets.

[023] Reduced titanium and iron as it passes through the layer of liquid slag accumulates at the bottom of the reservoir. After the consumable electrode is completely melted, the power supply to the furnace is turned off and the melt products are allowed to cool. The generated ferrotitanium casting is freed from slag and together with other smelters (from previous smelting processes) is melted in an induction furnace, forming a product-looking rod with a medium chemical composition, mass%: titanium - 70-80%, iron - 12-17%, aluminium - 3 -6%, other impurities up to 2.6%, including silicon, manganese, vanadium and sulfur.

Examples of Implementation of the Invention

[024] For obtaining high titanium content slag an experimental direct current smelting furnace ESAB-LF-40M with the following main technical parameters was used as a melting furnace: nominal volume - 20 kg; transformer power - 40 kVA; maximum current - 1200 A; secondary voltage - 12-40 V.

[025] Electrode chips with a carbon content of 86% by weight and aluminium powder PA-2 (800 μm ) were used as reducing agents. Freshly calcined lime with a particle size of no more than 100 mkm was used to reduce the silica. Rutile concentrate (TiO ₂ > 95%) and steel (0.5-3mm) were used to form the consumable electrode.

[026] Ferrotitanium smelting was performed by reducing the oxides of titanium, iron and silicon present in the main mixture of rutile and steel chips (at least 82% by weight TiO ₂ , max 9% by weight Fe ₂ O ₃ , the rest: admixture of oxides of aluminium, silicon, vanadium and manganese, and possibly sulphur and phosphorus) with aluminium by melting the consumable electrode under protective melt. The composition of the raw materials (from which the consumable electrode is formed) is: rutile - 48-55%; aluminium powder - 22-25%, iron - 12-16%, lime or limestone - 10-15% and other impurities 0-7%. The main mixture used as a consumable electrode filler contained crushed slag (titanium oxide, aluminium powder and liquid glass as a binder of the above composition). The flow of silica was ensured by the limestone added to the mixture. After dosing the slag, aluminium powder and liquid glass, the composition of the main mixture was stirred to make its composition more even. The prepared mixture was placed in a consumable electrode steel shell and sealed with pressing equipment. [027] The prepared consumable electrode was connected to the positive pole of the DC supply and the bottom of the melting reservoir - to the negative pole. By use of an electric mechanism, the electrode was lowered until it made contact with the bottom of the melting reservoir, passing through the protective melt layer at the bottom of the reservoir. When the power was turned on, an electric circuit between the consumable electrode and the bottom of the reservoir was activated, causing the consumable electrode to melt. At the same time, power was supplied to the source of pulse power supply, which discharged through a winding located against the flux region. The speed of movement of the consumable electrode was ensured by the melting of its end in the slag phase so that the tip of the electrode was below the surface of the melt at all times. As melting protection fluxes for the consumable electrode, a mixture was used, by weight: 50 - AI ₂ O ₃ and 50 - CaO. Calcium aluminates of different stoichiometries can be formed in the liquid phase, with varying melting points. Limestone was added in separate portions to the top of the melt generated during electrode smelting to improve the flowability of the alumina formed during the regeneration process to obtain easily meltable and liquid slag.

[028] After melting the consumable electrode, the electric furnace was turned off, but the formed compact ferrotitanium rod and slag were left in the electric arc furnace for complete cooling.

[029] To confirm the industrial applicability of the present invention, a series of experimental melting processes were performed: three in each mode. The technical characteristics for obtaining a high titanium content ferrotitanium alloy and the comparative chemical composition of the product are given in Tables 1 and 2. [030] Table 1. Comparative characteristics of obtaining high titanium content ferrotitanium alloys

[031] Table 2. Comparable chemical composition and quality of the obtained ferrotitanium compound according to the described invention and the closest prior art solution

[032] Sample 2 of Tables 1 and 2 shows a high (79% by weight) titanium content in the ferrotitanium alloy, but the aluminium content is increased as well. The quality of the casting obtained is high, while the amount of other impurities, including silicon, manganese, vanadium and sulphur, does not exceed 2.6% by weight.