A method for preparing low-cost titanium alloy by carbon-hydrogen assisted electrothermal reduction-vacuum refining

Abstract

The present invention provides a method for preparing low-cost titanium alloy by carbon-hydrogen assisted electrothermic reduction-vacuum refining, which belongs to the field of non-ferrous metal smelting. The steps are as follows: (1) mechanically activating titanium raw materials and carbon pre-reducing them in a reducing atmosphere to obtain low-valent titanium oxides; (2) electrothermic reduction, in which the low-valent titanium oxides are subjected to aluminothermic reduction under the cooperation of external field heat, and alloyed with scrap stainless steel or other Fe-Cr-based furnace materials. After the reduction is completed, the primary reduction melt is discharged from the bottom water outlet of the electric furnace, and the upper slag is separated; (3) secondary reduction and refining of the primary reduction melt in vacuum; (4) online detection of composition and fine-tuning; (5) vacuum casting. The technical solution has a wide range of titanium raw materials and furnace charges; carbon-hydrogen pre-reduction of titanium raw materials significantly reduces the metal reducing agent, reduces the slag production from the source, and is conducive to gold slag separation; secondary reduction and refining under vacuum and deep deoxidation by casting; the process flow is short, energy consumption is low, cost is low, and quality is high.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal smelting, and specifically relates to a method for preparing low-cost titanium alloy by carbon-hydrogen assisted electrothermic reduction-vacuum refining. Background Art

[0002] Titanium metal boasts numerous advantages, including high specific strength, low density, corrosion resistance, heat resistance, and biocompatibility. It is widely used in a wide range of fields, including aerospace, petrochemicals, defense, and biomedicine, earning it the nickname "strategic metal" and "metal of the future." However, the extraction, smelting, and processing costs of titanium metal are extremely high, resulting in the high price of titanium alloys. This "aristocratic" nature of titanium alloys is one of the fundamental factors limiting their widespread application. TC4 titanium alloy is the most commercially successful titanium alloy, accounting for approximately 90% of all titanium alloys. However, due to its high content of expensive vanadium (V), it has limited acceptance in the civilian sector. TIMET, a US company, pioneered the use of inexpensive elements to replace precious elements such as V and Nb, successfully developing the low-cost Timetal 62S / LCB titanium alloy. In recent years, cheap elements such as Fe, Cr, Mn, Cu, C, O, and N have been used to replace expensive elements, and more brands of low-cost titanium alloys (TIX800N, DAT 57M, KS Ti-531C, TFC / TFCA, Ti12LC, XRF001, etc.) have been developed.

[0003] Currently, the Kroll method for extracting titanium metal is still the dominant method for producing titanium sponge. This method's technology, processes, and equipment are already quite mature, leaving limited room for cost reduction and efficiency gains. Boeing has calculated that titanium sponge accounts for 80% of the cost of a titanium ingot and 40% of the total cost of titanium alloy products. Therefore, to significantly reduce production costs, it is necessary to bypass the lengthy and energy-intensive Kroll method and rely on emerging technologies to directly extract titanium metal from titanium dioxide. Emerging methods for extracting titanium metal in recent years include molten salt electrolysis (EDO), self-propagating high-temperature synthesis (SHS), and electrothermal methods. These new methods offer shorter processes, lower energy consumption, and 30%-40% lower production costs than the Kroll method. However, high oxygen content and incomplete gold-slag separation are two major obstacles to their industrialization. Currently, key technologies for extracting titanium metal focus on reducing oxygen content and enhancing gold-slag separation.

[0004] A search of existing patents revealed that patent application number 201710443771.1 discloses a method for preparing Ti-6Al-4V titanium alloy using titanium-rich materials (high-titanium slag, rutile, or titanium dioxide) through a process called self-propagating aluminum heat refining and slag washing. The driving force for the first stage of the self-propagating aluminum heat refining reaction is the heat of reduction between the exothermic agent KClO3 and titanium vanadium oxide. Heat is supplemented by adding 20% ​​to 25% of the weight of the exothermic agent to maintain self-propagating combustion. The second stage of reduction and refining utilizes electromagnetic induction and mechanical stirring, relying on electromagnetic induction heat to maintain the necessary conditions for gold-slag separation, ultimately producing a low-oxygen, pure titanium alloy ingot.

[0005] In the prior art, S. Hassan-Pour et al. published "Aluminothermic production of titanium alloys (Part 2): Impact of activated rutile on process sustainability" in Metallurgical and Materials Engineering, Vol. 21, No. 2, pp. 101-114, 2015. This article notes that the inherent heat of reaction between TiO2 and aluminum is insufficient to sustain spontaneous reaction, necessitating the addition of a large amount of an exothermic agent to achieve the required energy density. Exothermic agents are expensive, so to reduce their use, mechanical activation of rutile using eccentric vibration ball milling increases the reaction enthalpy by introducing lattice defects and enhancing interphase diffusion rates, saving up to 42% of KClO4. The oxygen content of the alloy melt produced by self-propagating aluminothermic heat through charge activation treatment was reduced to 0.9% to 0.3% by weight, and then further reduced by electroslag remelting.

[0006] A search also revealed that the US patent publication number US20130164167 A1 discloses the preparation of Ti-6Al-4V titanium alloy using electromagnetic induction heating, aluminothermic reduction and molten salt electrolytic refining. Completely different from traditional self-propagating high-temperature synthesis, since the charge reactants are heated to a molten state of 1750°C by an off-site heat source and kept warm, the gold slag can be effectively separated, and then the alloy purity is further improved by NaCl-KCl molten salt electrolytic refining. Since no exothermic agent (CaSO4, S and NaClO2, etc.) and ignition agent (magnesium powder, KMnO4 and glycerol) are used in the thermal reduction process, the alloy contains few impurity elements introduced by the exothermic agent and ignition agent, and the chemical composition of the slag is relatively simple, and it can be directly recycled or easily processed.

[0007] The main problems with the above methods are:

[0008] (1) In the existing technology, the self-propagating aluminum heat extraction of titanium has a low reaction enthalpy (3TiO2+4Al=3Ti+2Al2O, ΔH=-1437kJ / kg), and without an external heat source and insulation, it is insufficient to maintain the spontaneous progress of the entire reaction. The rapid cooling after the reaction results in the unseparated gold slag and excessively high oxygen content. The heat of reaction of the heat-generating agent is much higher than that of the titanium raw material, but the reaction of the heat-generating agent with aluminum will increase aluminum consumption and slag production (KClO3+2Al=Al2O3+KCl↑, ΔH=-10119kJ / kg; 3KClO4+8Al=4Al2O3+3KCl↑, ΔH=-9470 kJ / kg). Therefore, more aluminum has to be added for deoxidation. However, the deoxidation is not thorough and the slag volume increases, resulting in high inclusions and oxygen content in the alloy. The energy density window for self-propagating thermite is very narrow. Even a slight difference of 50 kJ / kg can cause the alloy melt to transition from premature solidification due to insufficient heat to intense turbulent splashing due to localized overheating. Furthermore, the complex composition of chlorine-based exothermic agents and igniters can introduce impurities and release toxic Cl2 and KCl gases. Potassium chlorate is a key hazardous chemical, difficult to purchase, and poses safety risks, making it unsuitable for industrial-scale production. Therefore, the electrothermic method, replacing self-propagating high-temperature synthesis, is an inevitable trend in the transition from experimental stage to industrialization.

[0009] (2) In the existing technology, aluminothermic reduction is mainly used to prepare Ti-Al-V alloy. Because it contains expensive vanadium (V), the raw material cost is very high and it is not widely recognized in the civilian field. Therefore, there is an urgent need to develop low-cost titanium alloys that use cheap elements such as Fe, Cr, and O to replace V.

[0010] (3) In the existing technology, the methods for achieving gold-slag separation are basically to increase the melt temperature far above the slag melting point, or to use a large amount of slag conditioning agents to reduce the melting point and viscosity of the slag, or to use supergravity or electromagnetic levitation. There is no method of increasing the melt density by adding high-density elements such as Fe, Cr, and Mn to make the slag float and thus achieve effective separation and alloying of gold-slag at the same time. Summary of the Invention

[0011] The present invention addresses the shortcomings of the existing Kroll method, such as high titanium raw material requirements, long process, high energy consumption, and severe pollution. It also addresses the technical difficulties of high oxygen content and incomplete gold-slag separation in existing self-propagating aluminum heat or electrothermal reduction methods. The invention provides a novel technical route for preparing Ti-Al-Fe-Cr titanium alloys using carbon-hydrogen-assisted electrothermal reduction and vacuum refining. The three main steps of the method, carbon-hydrogen pre-reduction, electrothermal reduction, and secondary reduction refining, fully utilize off-site electric heat and internal reaction heat, replacing high-cost chemical heat with low-cost electric heat, and the off-site heating temperature is easy to control. The carbon-hydrogen-assisted composite thermal reduction significantly reduces aluminum consumption, slag-forming agents, and slag production, effectively reducing slag at the source, facilitating gold-slag separation and reducing oxygen content. Secondary refining and pouring in a vacuum environment facilitate deep deoxidation and avoid secondary oxidation. Furthermore, multiple technical innovations, such as increasing the melt density by adding high-density elements, achieve gold-slag separation, reduce oxygen content, and simultaneously achieve alloying.

[0012] The present invention provides a method for extracting and smelting titanium from titanium raw materials. However, the present invention is not limited thereto. Other technical solutions and embodiments of the present invention can also be used to extract and smelt other metal products. For example, but not limited to, transition metals such as chromium, manganese, iron, cobalt, nickel, copper, and tin; refractory metals such as vanadium, niobium, molybdenum, tantalum, and tungsten; rare earth metals such as scandium and yttrium; alkaline earth metals such as calcium, barium, and strontium; and alloys composed of the above elements.

[0013] The present invention is achieved through the following technical solutions:

[0014] A method for preparing low-cost titanium alloy by carbon-hydrogen assisted electrothermic reduction-vacuum refining comprises the following steps:

[0015] (1) Mechanical activation treatment of titanium raw materials, and pre-treatment of the activated titanium raw materials with carbon powder in a reducing atmosphere to reduce the high-valent TiO2 in the titanium raw materials to low-valent titanium oxide Ti n O 2n-1 , wherein n = 4, 3, 2 or 1, to obtain a hydrocarbon pre-reduction product;

[0016] (2) crushing the hydrocarbon pre-reduction product obtained in step (1) and then performing electrothermal reduction, adding an aluminum reducing agent, an alloying charge, and a composite slagging agent; after the electrothermal reduction is completed, a primary aluminothermic reduction melt is discharged from the water outlet at the bottom of the electric furnace, and the slag is retained in the furnace and separated to obtain a primary aluminothermic reduction melt;

[0017] (3) subjecting the primary aluminothermic reduction melt obtained in step (2) to secondary reduction refining, adding titanium residue to the reactants; adding a secondary reduction reaction reducing agent to perform a secondary reduction reaction deep deoxidation, and heat-refining to obtain a secondary reduction melt close to the target composition; the secondary reduction reaction reducing agent is selected from a strong reducing agent containing calcium and magnesium, such as magnesium-calcium, aluminum-magnesium, and aluminum-calcium alloy;

[0018] (4) Detect the composition online and add alloying charge to fine-tune the composition to meet the target composition range;

[0019] (5) Vacuum casting to obtain a final product, wherein the final product is a casting, a billet or a remelted consumable electrode.

[0020] The titanium raw material is titanium slag, preferably low-grade electric furnace slag with high calcium and magnesium impurities, to minimize titanium raw material costs. The titanium slag has a TiO2 content of 74% to 85%, a CaO+MgO content of 6.5% to 10%, preferably 6.5% to 7.8%, and a TFe (total iron) content of 9% to 11%, preferably 4% to 9%.

[0021] Step (1) The reducing atmosphere uses flowing water gas as the reducing gas, which contains H2 and CO in a volume ratio of 1:2 to 2:1, with a gas supply pressure range of 0.2MPa to 5MPa and a flow rate of 0.5 to 5m 3 / m 2 ·min; the carbon powder is selected from any one or at least two of coke, activated carbon, and graphite; the carbon reduction pretreatment temperature is 1050℃~1150℃; and the reduction time is 0.5h~3h.

[0022] Preferably, the reactants in step (2) include the hydrocarbon pre-reduction product, aluminum reducing agent, alloying charge and composite slag-forming agent in step (1); the reactants are in a mass ratio of hydrocarbon pre-reduction product: aluminum reducing agent: alloying charge: composite slag-forming agent = 1: 0.35~0.75: 0.1~0.15: 0.15~0.35, preferably 1: 0.5~0.7: 0.12~0.15: 0.2~0.3; the composite slag-forming agent is CaO-CaF2 binary slag, with a mass ratio of CaO: CaF2 = 70%~90%: 30%~10%.

[0023] In the embodiment provided by the present invention, the titanium raw material is subjected to ball milling activation treatment, and the particle size is 50μm~200μm, D50=110μm; the aluminum reducing agent is any one of aluminum chips, titanium aluminum alloy, and aluminum particles, or a combination of at least two of them, and the maximum particle size range is 0.5mm~5mm; the alloying charge is one or a combination of at least two of scrap stainless steel containing Fe and Cr as main elements and / or micro-carbon Fe-Cr intermediate alloy, and the maximum particle size range is 0.5mm~5mm; the particle size range of the composite slag-making agent is 0.2mm~2mm, and D50=1.0mm.

[0024] Preferably, in step (2), the central electrode on the top of the electric furnace is a hollow graphite electrode, the top of the hollow graphite electrode is a feeding port, the hollow graphite electrode serves as both a plasma arc initiating device and a feeding device, a slag outlet and a melt outlet are provided on the side wall, and the slag outlet is higher than the melt outlet.

[0025] Furthermore, the electrothermal reduction temperature in step (2) is 1500° C. to 1800° C., and the time is 0.1 to 0.5 h.

[0026] Preferably, the reactants of the secondary reduction reaction in step (3) are in the following mass ratio: primary reduction melt: titanium residue: secondary reduction reaction reducing agent: composite slagging agent = 1:0-0.2:0.2-0.3:0.1-0.15; the secondary reduction reaction reducing agent is a calcium-magnesium alloy with a mass ratio of Mg:Ca = 60%-80%:20%-40%, and a particle size range of 30mm-120mm;

[0027] Step (3) is carried out in a vacuum induction melting furnace. The vacuum induction melting furnace is pre-evacuated and then flushed with inert gas, and the operation is repeated 1 to 2 times; a water gas (H2 and CO) mixed gas is filled, and the gas pressure is less than the standard atmospheric pressure to prevent the volatilization of aluminum and titanium elements with high saturated vapor pressure; the secondary reduction temperature is 1500°C to 1750°C, and the secondary reduction holding time is 0.1h to 0.5h.

[0028] As one of the means to further reduce costs, a layer of titanium residue not exceeding 20% ​​by weight of the primary reduction melt is uniformly distributed on the bottom of the vacuum induction melting furnace crucible in advance, and the melt is introduced into the vacuum induction melting furnace crucible by tilted upward pouring through the tundish.

[0029] Preferably, in step (5), the secondary reduction refined product of step (4) is poured under vacuum; the pouring temperature is 1580°C to 1620°C, and after cooling to 400°C to 600°C, the vacuum is broken and the mold is demoulded to obtain the final product casting, ingot and / or remelted consumable electrode as needed.

[0030] In the embodiment provided by the present invention, the final product Ti-Al-Fe-Cr low-cost titanium alloy prepared by the method of the present invention has the following main components by mass fraction: Al 2.5% to 3.5%, Fe 3% to 5%, Cr 5% to 9%, O 0.2% to 0.35%, and Ti as the balance.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] (1) Compared with the traditional Kroll method, the method of the present invention has the following advantages:

[0033] 1. The titanium raw material of the present invention has a wide source, has low requirements on the grade of titanium slag and calcium and magnesium impurities, and has low raw material cost.

[0034] 2. The process of the present invention is short, and metallic titanium is directly extracted from titanium oxide, omitting the complicated process steps of chlorination-reduction-vacuum distillation-electrolysis of the Kroll method;

[0035] 3. The present invention has low energy consumption. Since aluminothermic reduction releases a large amount of heat, only a small amount of electric heat is needed to maintain the reaction. The energy consumption is much lower than the 4.34t to 5.22t of standard coal required to produce 1 ton of sponge titanium by the Kroll process.

[0036] 4. After the second stage of refining, the single furnace production cycle is shortened from 14 to 21 days of Kroll titanium sponge to a few hours, which significantly shortens the production cycle.

[0037] 5. After the second stage of refining, the total production cost of the ingot is reduced by 30% to 40% compared with the Kroll method;

[0038] 6. The present invention does not emit "three wastes", while the Kroll method produces a large amount of waste acid and solid waste, and the by-product slag in the process can be converted into high-alumina cement, realizing resource utilization, which is in line with the concept of green and low-carbon.

[0039] (2) Compared with the existing self-propagating aluminum heat reduction method and the electric aluminum heat reduction method, the method of the present invention has the following advantages:

[0040] 1. The present invention uses carbon-hydrogen pre-reduction on the titanium raw material, and the oxygen in the titanium oxide is ultimately discharged directly in the form of gas. This is completely different from existing methods that produce a large amount of calcium aluminate (CaO-Al2O3) slag, which has a high melting point, high viscosity, and is extremely difficult to separate. The present invention uses carbon-hydrogen to assist in aluminothermic reduction. The composite thermal reduction reduces the burden of aluminothermic reduction, reduces the amount of metal reducing agent used at the source, and naturally reduces the amount of slag produced accordingly. Therefore, the present invention is conducive to the complete separation of gold slag and the reduction of oxygen content. In addition, titanium oxide easily forms Al2O3-CaO-TiO composite slag with slag, that is, a portion of titanium oxide does not participate in the reduction in the slag, resulting in a low titanium yield. The present invention improves the degree of reduction through technical means such as low-cost conversion of titanium oxide and reduction of slag volume, thereby significantly improving the titanium yield.

[0041] 2. The present invention is based on off-site electric heating and a vacuum environment. The reaction thermodynamic conditions are sufficient, and the reaction temperature and energy density in the furnace are easy to control. This is conducive to maintaining the temperature of the alloy melt, promoting the effective separation of gold and slag, and thus reducing the oxygen content in the alloy.

[0042] 3. The present invention is based on off-site electric heating and has low requirements for the type and form of reactants. Unlike traditional self-propagating high-temperature synthesis methods, the powder charge must meet a certain particle size distribution and strict ratio, and also requires special furnace charging and distribution methods such as pre-pelleting or multi-batch layered charging. The reactant raw materials of the present invention can be selected from titanium slag, titanium waste, titanium aluminum alloy recycling, scrap stainless steel, or low-carbon Fe-Cr master alloy, etc. Such raw materials are widely available and low in cost. In addition, the reactant size, form, and furnace charging and distribution methods are relatively flexible.

[0043] 4. The alloying elements of the present invention are Fe, Cr and other elements with relatively high density, which enhance the separation of gold and slag by increasing the specific gravity of the alloy melt, and the extraction and smelting of metallic titanium and the preparation of Ti-Al-Fe-Cr low-cost titanium alloy are combined in the same process.

[0044] 5. The present invention does not use any chlorine-based, phosphate, peroxide or other heating agents and ignition agents, and will not introduce impurity elements due to heating agents and ignition agents, and further reduces the cost of raw materials, making it suitable for industrial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a process flow chart of the present invention;

[0046] Figure 2 It is a schematic structural diagram of the electric aluminum thermal reduction furnace of the present invention;

[0047] Among them, 101. furnace body, 102. gold outlet, 103. slag outlet, 104. hollow graphite electrode, 105. charging port, 106. bottom electrode;

[0048] Figure 3 It is a schematic structural diagram of the vacuum induction melting furnace of the present invention;

[0049] Among them: 201. Vacuum induction melting chamber, 202. Melting crucible, 203. Induction coil, 204. Vacuum charging hopper, 205. Vacuum valve for charging hopper, 206. Melting observation hole, 207. U-shaped bell jar, 208. Vacuum pouring chamber, 209. Mold, 210. Chassis, 211. Slag screen, 212. Launder, 213. Vacuum valve connecting the two chambers, 214. Bottom pouring pipe;

[0050] Figure 4 It is the oxygen potential diagram of several substances;

[0051] Figure 5 ΔG-T curve of the reduction reaction of carbon and titanium oxide. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the technical solution of the present invention, this embodiment is based on the technical solution of the present invention and further illustrates the present invention in combination with comparative examples. The specific implementation methods and operating steps cited are only used to illustrate the present invention, but the scope of protection of the present invention is not limited to the following examples.

[0053] The flow chart of the present invention is as follows Figure 1 As shown, the following steps are included:

[0054] Step (1): Hydrocarbon pre-reduction

[0055] The titanium raw material is mechanically activated and pre-reduced with carbon powder under a reducing atmosphere, wherein the titanium raw material is low-grade, high-impurity titanium slag, which has a wide source and is relatively cheap.

[0056] The carbon powder reducing agent is not particularly limited, for example, any one or at least two of coke, activated carbon, and graphite, wherein typical but non-limiting combinations are: coke and activated carbon, coke and graphite, activated carbon and graphite, and a mixture of coke, activated carbon, and graphite.

[0057] The carbon-hydrogen pre-reduction is carried out in a mixed atmosphere of H2 and CO, using carbon powder to convert the high-valent TiO2 in the titanium raw material into low-valent titanium oxide Ti n O 2n-1 (n=4, 3, 2, 1).

[0058] according to Figure 4 In the ΔG-T oxygen potential diagram provided, the hydrogen line is located near the top, and the Gibbs free energy is small and negative, which means that titanium oxide cannot be reduced. When the temperature exceeds the intersection of the carbon line and the titanium line, carbon can reduce titanium oxide. The chemical reaction is relatively complex, including solid-solid reaction and gas-solid reaction. The solid-solid reaction is TiO2(s)+C(s)→Ti n O 2n-1 (s)+CO(g)↑, the gas-solid reaction is TiO2(s)+CO(g)→Ti n O 2n-1 (s)+CO2(g)↑, where Ti n O 2n-1It is a low-valent oxide (n=4, 3, 2, 1). Metal oxides such as Fe and Mn in the titanium raw material can also be reduced to elemental metals: Fe2O3+3CO=2FeO+3CO2↑, FeO+CO=Fe+CO2↑, MnO2+2CO=Mn+2CO2↑. No slag is produced during the pre-reduction process, and the oxygen in the titanium raw material is continuously extracted in the form of CO and CO2 gases. After pre-reduction, the proportion of titanium oxide increases, which is beneficial to the next step of metal thermal reduction. More importantly, low-valent titanium oxides with dissolved hydrogen are structurally and thermodynamically more unstable than TiO2. The more H content that enters the solid solution, the higher the instability, which is more conducive to reducing the burden of aluminum deoxidation, that is, reducing the consumption of metal reducing agents from the source, and the slag production is correspondingly reduced, providing favorable conditions for the subsequent steps of electrothermal reduction and secondary reduction of gold slag separation and deep deoxidation.

[0059] The titanium raw material is titanium slag, preferably low-grade electric furnace slag with high calcium and magnesium impurities, to minimize titanium raw material costs. The titanium slag contains 74% to 85% TiO2, with a maximum TiO2 content of no more than 85%, 6.5% to 7.8% CaO + MgO, and 4% to 9% TFe (total iron).

[0060] Before the implementation of step (1), the titanium raw material is first mechanically activated to introduce lattice defects, increase the diffusion rate of solid-solid and gas-solid reaction interfaces, which is conducive to lowering the reduction reaction temperature and maximizing the reduction of TiO2 to low-valent titanium oxide Ti. n O 2n-1 (In order of reaction priority, they are Ti4O7, Ti3O5, Ti2O3, TiO, etc.) conversion rate.

[0061] The form of mechanical activation is not particularly limited, and any method known to those skilled in the art may be used, such as eccentric vibration milling, planetary ball milling, drum milling, vertical / horizontal ball milling, etc.

[0062] The mechanical activation time is 0.5 h to 3 h, for example, 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, preferably 1.0 h to 2.5 h, and more preferably 1.5 h to 2.0 h.

[0063] The particle size of the titanium slag after mechanical activation is 80 μm to 150 μm, for example, 80 μm, 90 μm, 100 μm, 110 μm, 130 μm, 140 μm, 150 μm, preferably 90 μm to 140 μm, and more preferably 110 μm to 130 μm.

[0064] The hydrocarbon pre-reduction equipment is not particularly limited and can be any method known to those skilled in the art, such as an atmosphere sintering furnace, a HDH hydrogenation furnace, a microwave pyrolysis furnace, or a resistance furnace with a simple structure.

[0065] The reducing gas used is water gas, that is, a mixture of H2 and CO, with a volume fraction of H2 and CO not less than 95%, a volume ratio of H2 to CO of 1:2 to 2:1, a gas supply pressure range of 0.2MPa to 5MPa, and a flow rate of 0.5 to 5m 3 / m 2 The reducing gas may be supplied in a non-sealed continuous manner or in a sealed intermittent manner.

[0066] The hydrocarbon pre-reduction temperature is 1050°C to 1150°C, for example, 1050°C, 1070°C, 1090°C, 1110°C, 1130°C, or 1150°C. Figure 5 As shown in the ΔG-T curve of the reduction reaction of carbon and titanium oxide, in order to avoid excessively high temperature production of TiC hard particles, the reduction temperature is not higher than 1150°C, preferably 1050°C to 1130°C, and more preferably 1050°C to 1100°C.

[0067] The hydrocarbon pre-reduction time is 0.5 h to 3 h, for example, 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, preferably 1.0 h to 2.5 h, more preferably 1.5 h to 2.0 h.

[0068] The conversion rate of the low-valent titanium oxide is 50% to 95%, for example, 50%, 60%, 70%, 80% or 95%. The conversion rate should take into account the balance between the degree of conversion, energy consumption and cost, and is preferably 70% to 95%, and more preferably 80% to 90%.

[0069] Step (2): Electrothermal reduction

[0070] The carbon-hydrogen pre-reduction product is subjected to electro-aluminothermic reduction (or primary aluminothermic reduction) in a heating furnace, wherein the electro-aluminothermic reduction reactants include the pre-reduced titanium raw material in step (1), an aluminum reducing agent, an Fe-Cr alloy charge and a composite slag-forming agent.

[0071] The reactant is a mixture containing multiple furnace charges, and the weight ratio of the mixture is pre-reduced titanium raw material: aluminum reducing agent: Fe-Cr alloy furnace charge: composite slag-forming agent = 1: 0.35-0.75: 0.1-0.15: 0.15-0.35.

[0072] The pre-reduced titanium raw material is ball-milled to a particle size of 50 μm to 200 μm, with D50=110 μm, for example, 80 μm, 100 μm, 125 μm, 150 μm, 180 μm, or 200 μm, preferably 80 μm to 180 μm, and more preferably 100 μm to 125 μm.

[0073] There is no special limitation on the ball milling form of the pre-reduced titanium raw material, and reference may be made to the ball milling form described in step (1).

[0074] The aluminum reducing agent is any one or at least two of aluminum chips, titanium aluminum alloy, and aluminum particles, among which typical but non-limiting combinations are: aluminum chips and titanium aluminum alloy, aluminum chips and aluminum particles, titanium aluminum alloy and aluminum particles, and a mixture of aluminum chips, titanium aluminum alloy and aluminum particles.

[0075] The aluminum chips have no specific shape, and the maximum size range is 0.5 mm to 5 mm, for example, it can be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, preferably 2 mm to 4 mm.

[0076] The Fe-Cr alloy charge is one or at least two of waste stainless steel containing Fe and Cr as main elements and / or a low-carbon Fe-Cr master alloy.

[0077] The scrap stainless steel is common ferritic or martensitic stainless steel (400 series) with Fe and Cr as primary elements, such as SUS436L and SUS410L. The alloy charge contains a carbon content of ≤0.03% by weight, along with unavoidable trace elements such as Mn, Si, Ni, Mo, and C. However, these contents are very low, and the amount added is relatively small. Therefore, their impact on the chemical composition and properties of the titanium alloy is negligible.

[0078] The scrap stainless steel blanks are cut into blocks without specific shapes, and the maximum size range is 0.5mm to 5mm, for example, it can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, preferably 2mm to 4mm.

[0079] The low carbon Fe-Cr master alloy is not particularly limited and may be any one known to those skilled in the art, for example, including but not limited to any one or a combination of at least two of the low carbon ferrochrome FeCr69C0.25-0.5, low carbon ferrochrome FeCr69C0.03-0.15, and AlCr2-10 specified in industry standards.

[0080] The micro-carbon Fe-Cr master alloy has no specific shape, and the maximum size range is 0.5 mm to 5 mm, for example, it can be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, preferably 2 mm to 4 mm.

[0081] The composite slag-forming agent is based on CaO and forms a binary slag with CaF2. CaO-CaF2 binary slag is a commonly used slag-forming agent in the industry. CaO acts as a solvent and forms a low-melting-point, low-viscosity slag with Al2O3. The addition of CaF2 can promote gold slag separation.

[0082] The mass fraction ratio of the CaO and CaF2 composite slagging agent is CaO:CaF2=70%~90%:30%~10%, preferably 75%~85%:25%~15%.

[0083] The particle size range of the composite slag-making agent is 0.2mm~2mm, D50=1.0mm, for example, it can be 0.2mm, 0.5mm, 1.0mm, 1.2mm, 1.5mm, 1.8mm, 2mm, preferably 0.5mm~1.5mm, more preferably 0.8mm~1.2mm.

[0084] The electrothermal reduction temperature is 1500°C to 1800°C, such as 1600°C, 1650°C, 1700°C, 1750°C or 1800°C, preferably 1650°C to 1750°C. Too high a temperature is not conducive to reducing the oxygen content, and more preferably 1650°C to 1700°C.

[0085] The electrothermal reduction time is 0.1h to 0.5h, such as 0.1h, 0.2h, 0.3h, 0.4h, 0.5h, preferably 0.2h to 0.5h. The refining time should not be too long, and is more preferably 0.2h to 0.3h.

[0086] The form of the electrothermic reduction device is not particularly limited. Any electric heating furnace known to those skilled in the art may be used, and should be understood as an industrial furnace with both electric heating and heat preservation functions. Examples include DC arc furnaces, AC arc furnaces, and electromagnetic induction furnaces. Alternatively, it may be a sintering furnace (vacuum or hot pressing), an electron beam or plasma heating furnace, or a simple resistance furnace. A DC arc furnace is preferred.

[0087] The DC arc furnace used in this embodiment has the following structure: Figure 2As shown, the furnace comprises a furnace body 101, a tapping port 102, a slag tapping port 103, a hollow graphite electrode 104, a charging port 105, and a bottom electrode 106. The tapping port 102 and slag tapping port 103 are located on the sidewalls of the furnace body 101. The tapping port 102 serves as the melt outlet and is vertically lower than the slag tapping port 103. The hollow graphite electrode 104 is hollow, with the charging port 105 at its top. The hollow graphite electrode serves as both a plasma arc initiator, providing heat to the molten pool, and a charging device. Furthermore, the DC hollow electrode exhibits no "yield effect," a long arc, strong molten pool agitation, and minimal heat loss, enabling rapid adjustment of input current and reduction temperature. When the molten pool level is above the tapping port, the melt is discharged through the tapping port, and the topmost slag is removed through the tapping port. After removing most of the slag, a primary aluminothermic reduction melt is obtained, achieving gold-slag separation. The structure can continuously add materials, reduce and remove slag, thereby realizing continuous or semi-continuous production.

[0088] Step (3): Secondary reduction refining

[0089] The primary aluminothermic reduction melt obtained in step (2) is introduced into the melting crucible 202 in the vacuum induction melting furnace, deeply deoxidized with a calcium or magnesium alloy having stronger reducing properties, and a composite slag-forming agent is added. The melt is then heat-refined to obtain a secondary reduction melt having a composition close to the target composition.

[0090] Vacuum induction refining and casting equipment such as Figure 3 As shown, the vacuum induction melting chamber 201 includes a vacuum induction melting chamber 201 and a melting crucible 202 disposed in the vacuum induction melting chamber 201. An induction coil 203 is disposed outside the melting crucible 202 to heat the melting crucible 202. The top of the vacuum induction melting chamber 201 is connected to a vacuum charging bin 204. A charging bin vacuum valve 205 is disposed between the vacuum charging bin 204 and the vacuum induction melting chamber 201. A melting observation hole 206 is also disposed on the top of the vacuum induction melting chamber 201. and a U-shaped bell jar 207; a flow channel 212 is provided on the side wall of the vacuum induction melting chamber 201, and a slag retaining net 211 and a bottom pouring pipe 214 are provided on the flow channel 212; the vacuum induction melting chamber 201 is connected to the vacuum pouring chamber 208 through a vacuum valve 213 connecting the two chambers; a casting mold 209 and a chassis 210 are provided in the vacuum pouring chamber 208, and one end of the bottom pouring pipe 214 is connected to the bottom hole of the flow channel 212, and the other end is connected to the chassis 210, and is finally injected into the casting mold 209 through the runner.

[0091] The secondary reduction reactants contain a certain proportion of titanium residue, and the weight ratio is primary reduction melt: titanium residue: calcium-magnesium alloy: composite slag forming agent = 1:0-0.2:0.2-0.3:0.1-0.2.

[0092] The secondary refining temperature is 1500°C to 1750°C, such as 1550°C, 1600°C, 1650°C, 1700°C or 1750°C, preferably 1600°C to 1700°C. Too high a refining temperature is not conducive to reducing the oxygen content, and more preferably 1600°C to 1650°C.

[0093] The secondary refining holding time is 0.1h to 0.5h, such as 0.5h, 0.1h, 0.2h, 0.3h, 0.4h, preferably 0.2h to 0.4h. The refining time should not be too long, and more preferably 0.2h to 0.3h.

[0094] The secondary refining atmosphere is to pre-evacuate the vacuum induction melting chamber, then flush the furnace with inert gas, repeating this operation 1-2 times. Water gas (a mixture of H2 and CO) is then injected to prevent the volatilization of aluminum and titanium elements with high saturated vapor pressure.

[0095] The calcium- or magnesium-containing alloy is not particularly limited and may be any of the alloys known to those skilled in the art, such as calcium-magnesium alloys, aluminum-calcium alloys, and / or aluminum-magnesium alloys, preferably calcium-magnesium alloys (Mg 80% to 60%, Ca 20% to 40%). According to the ΔG-T oxygen potential diagram, the magnesium and calcium lines are located lower. Oxides with greater negative ΔG values ​​or lower oxygen potentials are more stable, i.e., they have greater oxygen binding capacity. Calcium-magnesium alloys have higher reducibility than pure aluminum, stronger deoxidation capabilities, and will not form alloys with titanium, thus reducing both slag viscosity and melting point.

[0096] The calcium- or magnesium-containing alloy is added in the form of irregular blocky fragments with a particle size range of 30mm to 120mm. Unlike existing methods that use pure calcium and pure magnesium blown in as steam, this calcium- and magnesium-containing alloy is pressed into the furnace bottom using a high-temperature resistant tool such as an inverted U-shaped "bell jar" made of aluminum oxide or molybdenum to prevent boiling and splashing, burning, and volatilization caused by excessive reduction temperatures. Small amounts are added in multiple batches. The calcium-magnesium alloy melts within the melt, and bubbles generated by the reaction float up, entraining a portion of the slag.

[0097] The secondary reduction refining method is not particularly limited and may be any electric heating furnace known to those skilled in the art, which should be understood as an industrial furnace with electric heating and heat preservation functions in a vacuum environment. Examples include a vacuum induction melting furnace, a vacuum electroslag furnace, a vacuum consumable remelting furnace, a vacuum shell furnace, a vacuum electromagnetic suspension furnace, or a simple vacuum resistance furnace. A vacuum induction melting furnace is preferred.

[0098] Step (3) also includes titanium residue, which is titanium processing chips and scraps, with few impurity elements and relatively low price; the titanium residue is TA1-TA4 industrial pure titanium, with an oxygen content of ≤0.5wt%, and should be cleaned, dried and magnetically separated before use. The amount of titanium residue added is not more than 20% of the weight of the primary reduction melt, and the size range is 0.5mm to 5mm, for example, it can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, preferably 2mm to 4mm. The addition method is: pre-spread a layer of titanium residue not exceeding 20% ​​of the weight of the primary reduction melt on the bottom of the vacuum induction melting furnace melting crucible, and the melt is introduced into the melting crucible through the inclined upward pouring method of the tundish.

[0099] Step (4): Online component detection and fine-tuning

[0100] The alloy charge is used to adjust the alloy composition to bring the titanium alloy into the target range. It includes pure metals and common master alloys, with one or more of these added based on the composition test results. The alloy charge can include titanium sponge, pure aluminum, Fe-Cr master alloy, pure iron, or pure chromium. The average particle size of the alloy charge is no greater than 5 mm.

[0101] The titanium-containing alloy charge is industrial-grade sponge titanium, with a titanium content greater than 99.5%, an oxygen content less than 0.1 wt%, and a particle size range of 0.83 mm to 5 mm.

[0102] The aluminum-containing alloy charge comprises one or two of high-aluminum master alloys such as pure aluminum, aluminum-calcium master alloy AlCa10, aluminum-magnesium master alloy AlMg10, and aluminum-chromium master alloy AlCr2, and is preferably 99.9-99.99% pure aluminum.

[0103] The Fe-Cr alloy charge for adjusting the composition is mainly composed of a low-carbon Fe-Cr master alloy, supplemented by pure iron and pure chromium. The purity of the pure iron is preferably 99.9-99.99%, and the purity of the pure chromium is preferably 99.9-99.99%.

[0104] The alloy charge is pre-stored in a vacuum charging bin 204, and is added into the vacuum induction melting chamber 201 in small batches by opening the vacuum valve 205 of the charging bin. It is then pressed into the bottom of the melting crucible through an inverted U-shaped bell jar 207 made of alumina to accelerate the uniform mixing of the alloy elements and the melt and reduce the refining time.

[0105] Step (5): Vacuum casting

[0106] like Figure 3As shown, the vacuum pouring chamber 208 is connected to the vacuum induction melting chamber 201 through a vacuum valve 213 connecting the two chambers in the middle. As an embodiment, the melt secondary reduced and refined by tilting the furnace body is poured from the upper furnace mouth through the slag retaining net 211, the flow channel 212, the bottom pouring pipe 214 and the bottom plate 210 into the mold 209.

[0107] As another embodiment, the vertical height of the vacuum induction melting chamber is higher than that of the vacuum pouring chamber, and a sliding nozzle or a stopper is provided at the bottom of the melting crucible, and pouring is completed through the bottom nozzle.

[0108] As another embodiment, the casting method can also be plane flow casting, in which the melt is poured onto a water-cooled copper roller to obtain a quick-setting sheet, which is convenient for crushing and powdering.

[0109] The vacuum casting is carried out in a vacuum, so secondary oxidation does not occur due to high reduction temperature, which is conducive to deep deoxidation and low oxygen content in the alloy.

[0110] The pouring temperature is 1580° C. to 1620° C., and after cooling to 400° C. to 600° C., the vacuum is broken and the mold is demoulded to obtain castings, ingots, remelted electrodes and / or thin sheets as needed.

[0111] The scheme is described in detail below with reference to specific embodiments:

[0112] The material parameters processed in the embodiment of the present invention are listed as follows:

[0113] Table 1 Chemical composition of titanium raw materials (mass percentage)

[0114]

[0115] Table 2 Composition range of Fe-Cr alloy charge (mass percentage)

[0116]

[0117] Example 1

[0118] The Ti-Al-Fe-Cr titanium alloy is prepared by carbon-hydrogen assisted electrothermal reduction-vacuum refining, which specifically includes the following steps:

[0119] Step (1) Mechanical activation-pre-reduction

[0120] The 85 titanium slag is mechanically activated in a ball mill for 2.0 hours. The particle size of the activated titanium slag is 110 μm to 130 μm. The activated titanium slag is reduced in hydrogen at a pre-reduction temperature of 1100°C to 1140°C for 2.0 hours. After reduction, the high-valent TiO2 is finally converted into low-valent titanium oxide TiO.

[0121] Step (2) Electrothermal reduction

[0122] The electrothermic reduction reaction mixture consists of a mixture of various charge materials, with the weight ratio of pre-reduced titanium feedstock: aluminum reducing agent: Fe-Cr alloy charge: composite slag-forming agent being 1:0.5:0.12:0.2. The average particle size of the pre-reduced titanium feedstock is <120μm, the aluminum chips are <5mm in size, and the Fe-Cr charge is recycled SUS410L scrap with a particle size no larger than 5mm. The slag-forming agent has a mass ratio of CaO:CaF2 of 75%:25% and a particle size <1mm. The electrothermic reduction is carried out in a DC electric arc furnace at a temperature of 1680°C to 1700°C for 0.25h. The DC electric arc furnace allows for continuous top loading, slag removal from the upper sidewall, and primary reduced melt discharge from the lower sidewall, enabling semi-continuous production.

[0123] Step (3) Secondary reduction refining

[0124] The primary reduction melt is introduced into the crucible of a vacuum induction melting furnace for secondary reduction refining. The weight ratio of primary reduction melt: titanium residue: calcium-magnesium alloy: composite slag-forming agent is 1:0.15:0.25:0.15. The amount of titanium residue added to the reactants should not exceed 20% of the weight of the primary reduction melt. The secondary reduction temperature is 1650°C, and the reduction time is 0.2h. The slag-forming agent has a mass ratio of CaO:CaF2 = 75%:25%. The reducing agent is MgCa30 alloy block crushed material with an average particle size of no more than 30mm.

[0125] Step (4) Online component detection and fine-tuning

[0126] After the secondary reduction refining is completed, the chemical composition of the melt is tested. Based on the test results, alloying charges are added to the melt to fine-tune the composition to the target range. The alloying charges include titanium sponge, pure aluminum, Fe-Cr master alloy, pure iron, and pure chromium. The average particle size of the alloying charges is no larger than 5mm.

[0127] Step (5) Vacuum casting

[0128] After the secondary reduction and refining melt composition is qualified, it is poured in a vacuum environment with a pouring temperature of 1650°C. The temperature is cooled to below 600°C and the vacuum is broken to obtain a casting, ingot or remelted electrode.

[0129] Table 3-1 Main components of titanium alloy ingots (weight %):

[0130]

[0131] Table 3-2 Mechanical properties of solution annealed titanium alloy

[0132]

[0133] Example 2

[0134] The Ti-Al-Fe-Cr titanium alloy is prepared by carbon-hydrogen assisted electrothermal reduction-vacuum refining, which specifically includes the following steps:

[0135] Step (1) Mechanical activation-pre-reduction

[0136] The 85 titanium slag is mechanically activated in a ball mill for 1.5 hours, and the particle size of the activated titanium slag is 110μm to 130μm. The activated titanium slag is reduced in hydrogen at a pre-reduction temperature of 1100-1140°C for 2.0 hours. After reduction, the high-valent TiO2 is finally converted into low-valent titanium oxide TiO.

[0137] Step (2) Electrothermal reduction

[0138] The electrothermic reduction reaction mixture consists of a mixture of various charge materials, with the weight ratio of pre-reduced titanium feedstock: aluminum reducing agent: Fe-Cr alloy charge: composite slag-forming agent being 1:0.7:0.15:0.2. The average particle size of the pre-reduced titanium feedstock is less than 120μm, the aluminum chips have a particle size range of less than 5mm, and the Fe-Cr charge is SUS436L with an average particle size no larger than 5mm. The slag-forming agent has a mass ratio of CaO:CaF2 of 70%:30% and a particle size less than 1mm. The electrothermic reduction is carried out in a DC electric arc furnace at a temperature of 1680°C to 1700°C for 0.25 hours. The DC electric arc furnace allows for continuous top loading, slag removal from the upper sidewall, and primary reduced melt discharge from the lower sidewall, enabling semi-continuous production.

[0139] Step (3) Secondary reduction refining

[0140] The primary reduction melt is introduced into a vacuum induction melting furnace for secondary reduction refining. The weight ratio of primary reduction melt: titanium residue: calcium-magnesium alloy: composite slag-forming agent is 1:0.15:0.25:0.15. The secondary reduction temperature is 1650°C, and the reduction time is 0.2h. The slag-forming agent consists of a mass ratio of CaO:CaF2 of 70%:30%. The reducing agent is commercial grade MgCa30 alloy block scrap with an average particle size of no more than 30mm.

[0141] Step (4) Online component detection and fine-tuning

[0142] After the secondary reduction refining is completed, the chemical composition of the melt is tested. Based on the test results, alloying charge is added to the melt to fine-tune the composition to the target range. The alloying charge consists of titanium sponge, pure aluminum, Fe-Cr master alloy, pure iron, and pure chromium. The average particle size of the alloying charge is no larger than 5mm.

[0143] Step (5) Vacuum casting

[0144] After the secondary reduction and refining melt composition is qualified, the pouring temperature is 1650℃ under vacuum environment, and the temperature is cooled to below 600℃ and the vacuum is broken to obtain castings, ingots or remelted electrodes.

[0145] Table 4-1 Main components of titanium alloy ingots (weight %):

[0146]

[0147] Table 4-2 Mechanical properties of solution annealed titanium alloy

[0148]

[0149] Example 3

[0150] Step (1) Mechanical activation-pre-reduction

[0151] The 74 titanium slag is mechanically activated in a ball mill for 2 hours, and the particle size of the activated titanium slag is 110 to 130 μm. The activated titanium slag is reduced in hydrogen at a pre-reduction temperature of 1100 to 1140°C for 2 hours, and the high-valent TiO2 is finally converted into low-valent titanium oxide TiO after reduction.

[0152] Step (2) Electrothermal reduction

[0153] The electrothermic reduction reaction mixture consists of a mixture of various charge materials, with the weight ratio of pre-reduced titanium feedstock: aluminum reducing agent: Fe-Cr alloy charge: composite slag-forming agent being 1:0.5:0.12:0.2. The average particle size of the pre-reduced titanium feedstock is <120μm, and the aluminum chips have a particle size range of <5mm. The Fe-Cr charge is low-carbon FeCr69C0.03 with an average particle size of <5mm. The slag-forming agent has a mass ratio of CaO:CaF2 of 70%:30% and a particle size of <1mm. The electrothermic reduction is carried out in a DC electric arc furnace at a temperature of 1680-1700°C and a reduction time of 0.25h. The DC electric arc furnace allows for continuous top loading, slag removal through the upper sidewall outlet, and primary reduced melt discharge through the lower sidewall outlet, enabling semi-continuous production.

[0154] Step (3) Secondary reduction refining

[0155] The primary reduction melt is introduced into a vacuum induction melting furnace for secondary reduction refining. The weight ratio of primary reduction melt: titanium residue: calcium-magnesium alloy: composite slag-forming agent is 1:0.15:0.25:0.15. The amount of titanium residue added to the reactants should not exceed 20% of the weight of the primary reduction melt. The secondary reduction temperature is 1650°C, and the reduction time is 0.2h. The slag-forming agent composition is a composite slag-forming agent with a mass ratio of CaO:CaF2 of 70%:30%. The average particle size of the titanium residue is no larger than 5mm. The reducing agent is a commercial grade MgCa30 alloy with an average particle size range of less than 100mm.

[0156] Step (4) Online component detection and fine-tuning

[0157] After the secondary reduction refining is completed, the chemical composition of the melt is tested. Based on the test results, alloying charge is added to the melt to fine-tune the composition to the target range. The alloying charge consists of titanium sponge, pure aluminum, Fe-Cr master alloy, pure iron, and pure chromium. The average particle size of the alloying charge is less than 5mm.

[0158] Step (5) Vacuum casting

[0159] After the secondary reduction and refining melt composition is qualified, the pouring temperature is 1650℃ under vacuum environment, and the temperature is cooled to below 600℃ and the vacuum is broken to obtain castings, ingots or remelted electrodes.

[0160] Table 5-1 Main components of titanium alloy ingots (weight %):

[0161]

[0162] Table 5-2 Mechanical properties of solution annealed titanium alloy

[0163]

[0164] Due to the use of 74 titanium slag, the SiO2 content is relatively high, and the alloy contains Si. The oxygen content of Fe-Cr master alloys is higher than that of stainless steel. These factors lead to a high concentration of oxygen and other impurities in the alloy, resulting in relatively low alloy properties. Furthermore, the low proportion of CaF2 in the slag-forming agent results in high slag viscosity, resulting in a low titanium yield. While these factors may contribute to the deterioration of alloy properties, they still maintain a high level.

[0165] The following are comparative examples, in which certain test conditions are changed based on the examples and are presented only in table form.

[0166] Comparative Example 1

[0167] Table 6-1 Alloy composition of Comparative Example 1

[0168]

[0169] Table 6-2 Mechanical properties of alloys in comparative example 1

[0170]

[0171] Since the pre-reduction temperature is raised to 1350℃, according to Figure 5 The ΔG-T curve of the reduction reaction of carbon and titanium oxide shows that TiC hard particles are produced during the pre-reduction process. TiC has a melting point higher than 3140°C and is difficult to be reduced to elemental Ti. TiC seriously affects the mechanical properties of the alloy and causes brittle fracture of the tensile specimen.

[0172] Comparative Example 2

[0173] Table 7-1 Alloy composition of Comparative Example 2

[0174]

[0175] Table 7-2 Mechanical properties of alloys in comparative example 2

[0176]

[0177] Increasing the refining temperature and reducing refining may cause secondary oxidation, resulting in a higher oxygen content in the alloy and a decrease in the elongation of the alloy.

[0178] Comparative Example 3

[0179] Table 8-1 Alloy composition of Comparative Example 3

[0180]

[0181] Table 8-2 Mechanical properties of alloys in comparative example 3

[0182]

[0183] The reducing agent in the secondary reduction is pure aluminum powder instead of MgCa30 alloy. The deoxidation ability of pure aluminum is not as good as that of calcium-magnesium alloy, and more Al2O3-CaO-TiO slag is produced in the process. It is difficult to separate the gold slag, resulting in a low titanium yield and a high oxygen content.

[0184] Comparative Example 4

[0185] Table 9-1 Alloy composition of Comparative Example 4

[0186]

[0187] Table 9-2 Mechanical properties of alloys in comparative example 4

[0188]

[0189] In the process of electrothermal reduction and secondary reduction refining, a single slag-forming agent CaO without CaF2 is used instead of a composite slag-forming agent. Since CaF2 has the effect of reducing the viscosity and melting point of the slag, the slag using only CaO has high viscosity and high melting point, making it difficult to separate the gold from the slag, and the titanium yield is low. The alloy contains a large amount of inclusions Al2O3 and oxygen elements, which ultimately leads to an increase in the strength of the alloy, but a significant decrease in the elongation, which is not conducive to processing and forming.

[0190] The basic principles, preparation processes, and advantages of the present invention have been described above through specific embodiments and accompanying drawings, but the present invention is not limited to the details of the above embodiments. It should be understood by those skilled in the art that any transformation, modification, and combination of the present invention, as well as equivalent replacements and additions of the main and auxiliary materials and equipment components of the present invention, without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for preparing low-cost titanium alloy by carbon-hydrogen assisted electrothermic reduction-vacuum refining, characterized in that: The method comprises the following steps: (1) Mechanical activation treatment of titanium raw materials, pre-treatment of the activated titanium raw materials with carbon powder reduction in a reducing atmosphere, and reduction of the high-valent TiO2 in the titanium raw materials to low-valent titanium oxide Ti n O 2n-1 , wherein n = 4, 3, 2 or 1, to obtain a hydrocarbon pre-reduction product; (2) crushing the hydrocarbon pre-reduction product obtained in step (1) and then performing electrothermal reduction, adding an aluminum reducing agent, an alloying charge, an aluminum reducing agent, and a composite slag-forming agent; after the electrothermal reduction is completed, the primary aluminothermic reduction melt is released from the bottom of the electric furnace, and the slag remains in the furnace for separation; (3) subjecting the primary aluminothermic reduction melt obtained in step (2) to secondary reduction refining, adding titanium residue to the reactants; adding a secondary reduction reaction reducing agent to perform a secondary reduction reaction deep deoxidation, and heat-refining to obtain a secondary reduction melt close to the target composition; the secondary reduction reaction reducing agent is selected from magnesium-calcium, aluminum-magnesium and aluminum-calcium alloy; (4) Detect the composition online and add alloying charge to fine-tune the composition to meet the target composition range; (5) Vacuum casting to obtain a final product, wherein the final product is a casting, a billet or a remelted consumable electrode; In step (1), the titanium raw material is low-grade titanium slag with high calcium and magnesium impurities, wherein the TiO2 content of the titanium slag is 74% to 85%, the CaO+MgO content is 6.5% to 10%, and the TFe content is 9% to 11%; In step (2), the central electrode on the top of the electric furnace is a hollow graphite electrode, the top of the hollow graphite electrode is a feeding port, the hollow graphite electrode serves as both a plasma arc initiation device and a feeding device, a slag outlet and a melt outlet are provided on the side wall, and the slag outlet is higher than the melt outlet; The electrothermal reduction temperature in step (2) is 1500°C to 1800°C, and the time is 0.1h to 0.5h; In step (3), the vacuum induction refining and pouring equipment includes a vacuum induction melting chamber, and a melting crucible arranged in the vacuum induction melting chamber, an induction coil is arranged outside the melting crucible to heat the melting crucible, the top of the vacuum induction melting chamber is connected to a vacuum feeding bin, a feeding bin vacuum valve is arranged between the vacuum feeding bin and the vacuum induction melting chamber, and a melting observation hole and a U-shaped bell cover are also arranged on the top of the vacuum induction melting chamber; a flow trough is arranged on the side wall of the vacuum induction melting chamber, a slag retaining net and a bottom pouring pipe are arranged on the flow trough; the vacuum induction melting chamber and the vacuum pouring chamber are connected through a vacuum valve connecting the two chambers; a casting mold and a chassis are arranged in the vacuum pouring chamber, one end of the bottom pouring pipe is connected to the bottom hole of the flow trough, and the other end is connected to the chassis, and is finally injected into the casting mold through the runner; The final product is Ti-Al-Fe-Cr titanium alloy, with the mass fractions of the components being: Al 2.5% to 3.5%, Fe 3% to 5%, Cr 5% to 9%, O 0.2% to 0.35%, and Ti as the balance.

2. The method according to claim 1, characterized in that Step (1) The reducing atmosphere uses flowing water gas as the reducing gas, which contains H2 and CO in a volume ratio of 1:2 to 2:1, with a gas supply pressure range of 0.2MPa to 5MPa and a flow rate of 0.5 to 5m 3 / m 2 ·min; the carbon powder is selected from any one or at least two of coke, activated carbon, and graphite; the hydrocarbon reduction pretreatment temperature is 1050℃~1150℃; and the reduction time is 0.5h~3h.

3. The method according to claim 1, characterized in that The reactants in step (2) include the hydrocarbon pre-reduction product in step (1), an aluminum reducing agent, an alloying charge, and a composite slag-forming agent; the reactants are in a mass ratio of hydrocarbon pre-reduction product: aluminum reducing agent: alloying charge: composite slag-forming agent = 1: 0.35-0.75: 0.1-0.15: 0.15-0.35, and the composite slag-forming agent is CaO-CaF2 binary slag, with a mass ratio of CaO:CaF2 = 70%-90%: 30%-10%.

4. The method according to claim 3, characterized in that The titanium raw material is ball-milled and activated, and has a particle size of 50 μm to 200 μm, with D50 of 110 μm; the aluminum reducing agent is any one of aluminum chips, titanium-aluminum alloy, and aluminum particles, or a combination of at least two of them, with a maximum particle size range of 0.5 mm to 5 mm; the alloying charge is any one of scrap stainless steel containing Fe and Cr as main elements and / or a low-carbon Fe-Cr intermediate alloy, or a combination of at least two of them, with a maximum particle size range of 0.5 mm to 5 mm; the composite slag-forming agent has a particle size range of 0.2 mm to 2 mm, with D50 of 1.0 mm.

5. The method according to claim 1, wherein The reactants of the secondary reduction in step (3) are primary reduction melt: titanium residue: secondary reduction reaction reducing agent: composite slagging agent in a mass ratio of 1:0-0.2:0.2-0.3:0.1-0.15, wherein the secondary reduction reaction reducing agent is a calcium-magnesium alloy with a mass ratio of Mg:Ca = 60%-80%:20%-40%, and a maximum particle size range of 30 mm to 120 mm; Step (3) is carried out in a vacuum induction melting furnace. The vacuum induction melting furnace is pre-evacuated and then flushed with inert gas, and the operation is repeated 1 to 2 times; a mixed gas of H2 and CO is filled, and the gas pressure is less than the standard atmospheric pressure to prevent the volatilization of aluminum and titanium elements with high saturated vapor pressure; the secondary reduction temperature is 1500°C to 1750°C, and the secondary reduction holding time is 0.1h to 0.5h.

6. The method according to claim 1, characterized in that Step (5) pouring the secondary reduction refined product of step (4) under vacuum; the pouring temperature is 1580°C to 1620°C, and after cooling to 400°C to 600°C, the vacuum is broken and demoulded to obtain the final product as needed.

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