Method for titanium or titanium alloy production

Abstract

A method for titanium or titanium alloy production is provided in which titanium or a titanium alloy is melted and reacted together with a rare-earth metal and a rare-earth metal halide salt to produce titanium or a titanium alloy having an oxygen concentration of 0.1 mass% (1,000 mass ppm) or less.

Description

Titanium or titanium alloy manufacturing method

[0001] This application claims priority from Japanese Patent Application No. 2023-117129, filed on July 18, 2023, the contents of which are incorporated herein by reference.

[0002] Titanium (Ti) and titanium-based alloys (titanium alloys) have the highest specific strength and outstanding corrosion resistance of any metallic material. Despite being an inexhaustible resource, titanium and titanium alloys have not been widely used due to the high affinity between titanium and oxygen, which makes smelting, melting, and casting difficult, resulting in high manufacturing costs for titanium products.

[0003] Currently, the mainstream method is to extract titanium ore (TiO ２ , FeTiO ｘ ) in a reducing atmosphere in the presence of carbon to obtain an oxygen-free chloride (TiCl ４ This is then reduced with metallic magnesium (Mg) to produce metallic titanium with a low oxygen concentration of 0.05 mass % (500 mass ppm) or less. The current titanium production process, the chloride smelting method, is expensive, has a large environmental impact, and produces a large amount of CO ２ Gas is generated. In order to realize mass production of titanium, it is necessary to develop a revolutionary new smelting method.

[0004] However, at present, no efficient method has been established for removing oxygen from titanium ore and metallic titanium to low concentrations (up to 500 mass ppm) without going through chlorides, and mass production of titanium has not been realized.

[0005] For example, titanium oxide (TiO ２ To directly convert titanium oxide into metallic titanium, reduction of titanium oxide with aluminum (Al) or magnesium is considered. However, crude titanium alloy (ATR-Ti) obtained by reducing titanium oxide with aluminum, and crude titanium (MTR-Ti) obtained by reducing titanium oxide with magnesium contain large amounts of oxygen as an impurity, and therefore cannot be used industrially as a structural material as is.

[0006] The present inventors have developed a technology that can directly remove oxygen from titanium by reacting a rare earth metal such as yttrium (Y) and a rare earth metal chloride with oxygen present in solid titanium at about 1000°C for 24 to 48 hours, thereby producing titanium with an extremely low oxygen concentration of 0.01 mass % (100 mass ppm) or less (see Non-Patent Document 1).

[0007] According to the method described in Non-Patent Document 1, oxygen can be removed efficiently from relatively thin scrap with a thickness of a few millimeters, making it possible to recycle titanium scrap with a high oxygen concentration. However, because the diffusion of oxygen in solid titanium is the rate-limiting step in the process, the reaction time required to remove oxygen from inside the solid is too long, and the method cannot be used for relatively large titanium ingots, etc.

[0008] Furthermore, when the method described in Non-Patent Document 1 is used on titanium alloy ingots containing a large amount of oxygen, such as ATR-Ti or MTR-Ti, it takes a long time to remove the oxygen present inside the ingot. Therefore, it is impossible to mass-produce low-oxygen concentration titanium for structural material applications from ATR-Ti or MTR-Ti using the method described in Non-Patent Document 1. In order to directly remove oxygen from a relatively large titanium or titanium alloy ingot in a short period of time, it is preferable to treat the molten titanium or titanium alloy.

[0009] Heating methods using high-frequency induction heating equipment, plasma arc melting equipment, electron beam melting equipment, etc. are effective for melting titanium. When using high-frequency induction heating equipment, the molten metal is thoroughly mixed, making it possible to produce homogeneous titanium or titanium alloys. However, because molten titanium is highly reactive with oxygen, it is not easy to directly remove impurity oxygen from molten titanium or molten titanium alloys during the melting process.

[0010] For example, a method for removing oxygen from titanium by adding rare earth metals and calcium fluoride when melting titanium using a cold crucible levitation melting apparatus, which is a type of high-frequency induction heating apparatus, is known (see Patent Document 1). According to the method described in Patent Document 1, oxygen can be removed from molten titanium down to 0.5 mass% (5000 mass ppm) by adding the rare earth metal cerium (Ce) or a misch metal, a mixture of rare earth metals, to the molten titanium. However, the method described in Patent Document 1 was unable to remove oxygen down to the oxygen concentration level of 0.1 to 0.2 mass% (1000 to 2000 mass ppm) required for structural material applications. Furthermore, even when the method described in Patent Document 1 is used on molten titanium alloys such as ATR-Ti and MTR-Ti, oxygen cannot be removed down to 0.1 to 0.2 mass% (1000 to 2000 mass ppm). Therefore, it is impossible to produce low-oxygen-concentration titanium for structural material applications from ATR-Ti or MTR-Ti using the method described in Patent Document 1.

[0011] Furthermore, a method for removing oxygen from a Ti-46Al-8Nb alloy is known, in which rare earth metals yttrium (Y) and calcium fluoride are added when the alloy is melted using a cold crucible melting apparatus, which is a type of high-frequency induction heating apparatus (see Non-Patent Document 2). According to the method described in Non-Patent Document 2, oxygen can be removed from the molten Ti-46Al-8Nb alloy down to 0.08 mass% (800 mass ppm). However, titanium alloys containing a large amount of aluminum are thermodynamically easy to remove oxygen from, and the method described in Non-Patent Document 2 was unable to remove oxygen from melts of pure titanium or titanium alloys with a low aluminum concentration down to the oxygen concentration level of 0.1 to 0.2 mass% (1000 to 2000 mass ppm), which is the oxygen concentration level required for structural material applications.

[0012] Furthermore, a method for removing oxygen from a titanium-aluminum alloy containing 40% or more by mass of aluminum is known, using an arc melting method, a plasma arc melting method, or an induction melting method in a water-cooled copper container. According to the method described in Patent Document 2, oxygen can be removed from the molten titanium-aluminum alloy down to 0.022% by mass (220 ppm by mass). However, the method described in Patent Document 2 is only effective for titanium-aluminum alloys containing 40% or more by mass of aluminum, and was unable to remove oxygen down to a concentration of 0.6% by mass (6000 ppm by mass) or less from titanium-aluminum alloys containing 60% or more by mass of titanium and an aluminum concentration of 40% or less by mass.

[0013] Japanese Patent No. 2949222 Japanese Patent Application Laid-Open No. 2016-135907

[0014] 'Ultimate Deoxidation Method of Titanium Utilizing Y / YOCl / YCl3 Equilibrium', Akihiro Iizuka, Takanari Ouchi, and Toru H. Okabe: Metall. Mater. Trans. B, vol. 51 (2020) pp. 433-442. DOI:10.1007 / s11663-019-01742-6)'Direct oxygen removal from titanium aluminide scraps by yttrium reduction', Li-na JIAO, Qi-sheng FENG, Shi-yu HE, Bao-hua DUAN, Zhi-he DOU, Chong-he LI, and Xiong-gang LU: Trans. Nonferrous Met. Soc. China, vol. 32 (2022) pp. 2428-2437. DOI: 10.1016 / S1003-6326(22)65958-2)

[0015] The present invention has been made in light of the above-mentioned problems, and has as its object to provide a method for producing titanium or titanium alloys with low oxygen concentrations by directly removing impurity oxygen from molten titanium or titanium alloys to a concentration as low as 0.1 mass % (1000 mass ppm) or less.

[0016] (1) According to one aspect of the present invention, there is provided a method for producing titanium or a titanium alloy, which comprises dissolving and reacting titanium (Ti) or a titanium alloy with a rare earth metal and a rare earth metal halide salt to produce titanium or a titanium alloy having an oxygen concentration of 0.1 mass % (1000 mass ppm) or less.

[0017] (2) According to one aspect of the present invention, there is provided a method for producing titanium or a titanium alloy, which utilizes the deoxidizing ability of rare earth metals and the reaction of producing rare earth metal oxyhalides to directly remove impurity oxygen from molten titanium or a molten titanium alloy, thereby producing titanium or a titanium alloy with a low oxygen concentration.

[0018] (3) In the method of (1) or (2), the titanium alloy may be an alloy having a titanium concentration of 65 mass % or more.

[0019] (4) In any one of (1) to (3), one or more rare earth metals selected from yttrium (Y), cerium (Ce), and lanthanum (La) and yttrium fluoride (YF ３ ), cerium fluoride (CeF ３ ), lanthanum fluoride (LaF ３ ) may be used.

[0020] (5) In any one of (1) to (4), the production method may be such that a flux of a metal halide salt is used in addition to the rare earth metal and the rare earth metal halide salt.

[0021] (6) In any one of (1) to (5), the production method may use titanium or a titanium alloy containing a large amount of impurity oxygen as the titanium raw material, which is produced by reducing titanium oxide with aluminum (Al) or magnesium (Mg).

[0022] (7) In any one of (1) to (5), the production method may be such that titanium or a titanium alloy containing a large amount of impurity oxygen, which is produced by reducing titanium oxide with a rare earth metal or a rare earth metal alloy, is used as the titanium raw material.

[0023] (8) In any one of (1) to (5), the manufacturing method may be such that scrap of titanium or titanium alloy is used as the titanium raw material.

[0024] (9) In any one of (1), (4), and (5), the method may be such that titanium and titanium alloys are melted using a metal halide salt that lowers the melting point of the halide salt melt in addition to the rare earth metal and the rare earth metal halide salt.

[0025] (10) In any one of (1) to (9), the manufacturing method may be such that the amount of the rare earth metal added is adjusted to control the oxygen concentration in the titanium.

[0026] (11) In any one of (1) to (8), the method may be a production method in which titanium and titanium alloys are melted together with rare earth metals and rare earth metal halide salts in an inert atmosphere using a melting device selected from a high-frequency induction heating device, a plasma arc melting device, and an electron beam melting device.

[0027] (12) In (11), the manufacturing method may be such that a cold crucible induction melting furnace is used as the high-frequency induction heating device, and a heat-resistant adhesive is applied to the slit of the crucible of the cold crucible induction melting furnace to prevent the rare earth metal halide salt or the flux from adhering to the crucible.

[0028] According to one aspect of the present invention, there is provided a method for directly removing impurity oxygen from molten titanium or titanium alloy to produce titanium or titanium alloy with a low oxygen concentration.

[0029] Fig. 1 is a process diagram showing a method for producing titanium or titanium alloy from titanium oxide according to an embodiment. Fig. 2 is an example of a process diagram for a method for producing titanium or titanium alloy with a low oxygen concentration directly from titanium or titanium alloy scrap according to an embodiment. Fig. 3 is a process diagram showing a method for producing titanium or titanium alloy with a low oxygen concentration directly from titanium or titanium alloy scrap according to an embodiment. ２ O３ -YF ３ This is a pseudo-binary phase diagram. Figure 4 is an isothermal chemical potential diagram for yttrium-oxygen-fluorine at 1727°C. Figure 5 shows the thermodynamic relationship between the equilibrium oxygen partial pressure and the equilibrium oxygen concentration in titanium in various deoxidation reaction systems. Figure 6 shows the equilibrium oxygen concentration in titanium for each deoxidation reaction system in the titanium-oxygen binary phase diagram. Figure 7 is an overall view of a titanium or titanium alloy melting apparatus according to an embodiment. Figure 8 is a cross-sectional schematic diagram of a metal sample in a cold crucible induction melting furnace obtained after melting and cooling. Figure 9 is a photograph of a titanium sample in a water-cooled copper crucible obtained by directly removing oxygen from molten titanium using a cold crucible induction melting furnace and then cooling and solidifying it in Example 1 of Table 1. Figure 10 is a photograph (side view) of a titanium sample removed from a water-cooled copper crucible after directly removing oxygen from molten titanium using a cold crucible induction melting furnace and then cooling and solidifying it in Example 1 of Table 1. Fig. 11 is a photograph of the top surface of the titanium sample shown in Fig. 10 in Example 1 of Table 1. Fig. 12 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 1 of Table 1. Fig. 13 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 2 of Table 1. Fig. 14 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 8 of Table 1. Fig. 15 is a photograph of the titanium sample piece for analysis cut out from the titanium sample obtained in Example 8 of Table 1. ３ 16 shows the results of X-ray diffraction measurements of the yttrium fluoride (YF) flux used to deoxidize the titanium sample. ３ 17 shows the results of X-ray diffraction measurements of the yttrium fluoride (YF) flux used to deoxidize the titanium sample. ３ 18 is a conceptual diagram of a novel titanium smelting method for producing titanium or a titanium alloy directly from titanium oxide using the manufacturing method of the above embodiment.

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0031] The manufacturing method of this embodiment basically involves reacting oxygen-containing titanium or titanium alloy dissolved using a high-frequency induction device as the melting device with a rare earth metal and a rare earth metal halide salt, and using the resulting rare earth metal oxyhalide to directly remove oxygen from the molten titanium or titanium alloy to a low concentration, thereby producing titanium or titanium alloy with a low oxygen concentration.

[0032] 1 is a process diagram showing a method for producing titanium or a titanium alloy from titanium oxide according to an embodiment. As shown in FIG. 1, the method for producing titanium or a titanium alloy developed according to the present invention mainly comprises three steps (first step S11 to third step S13).

[0033] First step S11: First, titanium oxide is reduced with aluminum, magnesium, or the like to produce titanium or a titanium alloy. Titanium ore or titanium oxide produced from titanium ore can be used as the titanium oxide. In the first step, calcium fluoride (CaF ２ By adding a catalyst such as calcium fluoride, the products of the reduction reaction, aluminum oxide and magnesium oxide, can be absorbed into the reaction aid. Metal halide salts other than calcium fluoride can also be used as fluxes. Second Step S12: Because the titanium or titanium alloy obtained in Step 1 contains a large amount of impurity oxygen, the impurity-containing titanium or titanium alloy is then melted, and rare earth metals and a reaction aid are added to remove oxygen. In Step 2, a rare earth metal halide salt is added as a reaction aid to convert the rare earth metal oxides, the products of the reaction, into rare earth metal oxyhalides. A metal halide salt may also be used to lower the melting point of the halide salt melt. Third Step S13: Finally, the low-oxygen molten titanium or titanium alloy obtained in Step 2 is cast and rolled. Fourth Step S14: The rare earth metal oxyhalides, the reaction products of Step 2 S12, can be reused as the rare earth metals used in Step 2 S12 through a rare earth metal separation and recovery process.

[0034] FIG. 2 is a process diagram showing another embodiment of the manufacturing method. FIG. 2 is an example of a process diagram for producing low-oxygen titanium or titanium alloy directly from titanium or titanium alloy scrap. The manufacturing method shown in FIG. 2 includes steps S21 to S23. In step S21, a rare earth metal and a reaction aid containing a rare earth metal halide salt are added to the titanium or titanium alloy scrap to remove oxygen. In step S22, the low-oxygen molten titanium or titanium alloy obtained in step S21 is cast and rolled. In step S23, the rare earth metal is recovered from the rare earth metal oxyhalide produced in step S21 and recycled as the rare earth metal used in step S21. As shown in FIG. 2, by using the titanium or titanium alloy manufacturing method of this embodiment, low-oxygen titanium or titanium alloy can be produced directly from scrap containing a large amount of impurity oxygen.

[0035] The principle of producing low-oxygen-concentration titanium or titanium alloy directly from molten titanium or titanium alloy using the oxygen removal method of the embodiment that utilizes the rare earth metal oxyhalide generation reaction will be described below. The oxygen removal method from molten titanium or titanium alloy of the embodiment involves melting oxygen-containing titanium or titanium alloy, rare earth metal, and rare earth metal halide salt in an inert atmosphere in a high-frequency induction device such as a cold crucible induction melting furnace, and holding the mixture for approximately 10 to 20 minutes to remove oxygen (O) and rare earth metal (RE (Y, La, Ce, etc.)), rare earth metal halide salt (REX)) from the molten titanium or titanium alloy. ３ (REF ３ The method is characterized by utilizing a reaction step with a methyl group (e.g., methyl group) [see formula (1)].

[0036] O (in Ti) + 2 / 3 RE (l) + 1 / 3 REX ３ (l) → REOX(s) ... (1) RE: rare earth metal element such as Y, La, Ce, etc. X: halogen element such as Cl, F, etc.

[0037] In the oxygen removal process from molten titanium or titanium alloy according to the embodiment, rare earth metal halide salt is added to generate rare earth metal oxyhalide (REOX) through the reaction of formula (1). The titanium deoxidation reaction, which is the basis of the manufacturing method of this embodiment, utilizes the deoxidizing ability of rare earth metals and the reaction of generating rare earth metal oxyhalide. If it is possible to generate rare earth metal oxyhalide, rare earth metal halide salt REX is added. ３ For example, the method is not limited to the method using a rare earth metal and CaF ２ It is also possible to form rare earth metal oxyhalides in situ and proceed with deoxidation of titanium by maintaining a metal halide salt that is stable at high temperatures, such as the above, under conditions that generate rare earth metal oxyhalides.

[0038] As representative examples of rare earth metals and halide salts according to the embodiment, a thermodynamic study was conducted to determine the deoxidation limit in the deoxidation reaction of molten titanium using yttrium (Y) and fluoride, respectively. ３ ) is used, yttrium oxyfluoride (YOF) is produced, and the yttrium / yttrium oxyfluoride / yttrium fluoride equilibrium (Y / YOF / YF ３ Equilibrium) is established.

[0039] FIG. ２ O ３ -YF ３ This is a pseudo-binary phase diagram (Source: 'Phase diagram study and thermodynamic assessment of the Y2O3-YF3 system', Seungjoo Baek and In-Ho Jung: J. Eur. Ceram. Soc., vol. 42 (2022) pp. 5079-5092. DOI: 10.1016 / j.jeurceramsoc.2022.05.005). The dotted lines in the diagram indicate the temperature conditions of this embodiment. At high temperatures exceeding the melting point of titanium, yttrium oxyfluoride (Y ｘ O ｙ F ｚ ) phase is YF ３While it can thermodynamically coexist with yttrium oxide (Y ２ O ３ ) phase is YF ３ Therefore, YF ３ In the system where excess yttrium is present, the deoxidation product in the deoxidation of titanium with yttrium is yttrium oxyfluoride (Y ｘ O ｙ F ｚ ) and the deoxidation reaction of formula (1) proceeds.

[0040] 4 is an isothermal chemical potential diagram of yttrium-oxygen-fluorine at 1727° C. The circles in the diagram represent the conditions of this embodiment, and Y / YOF / YF ３ Under equilibrium conditions, impurity oxygen in titanium or titanium alloys is removed. Figure 5 shows the thermodynamic relationship between the equilibrium oxygen partial pressure and the equilibrium oxygen concentration in titanium in various deoxidation reaction systems. The Y / YOF / YF deoxidation reaction is represented by the elliptical region in the figure. ３ Equilibrium and temperature are the main conditions for this embodiment. ３ It can be seen that, in principle, oxygen in titanium can be reduced to a level of 0.01 mass % (100 mass ppm) by utilizing equilibrium. Figure 6 shows the equilibrium oxygen concentration in titanium for each deoxidation reaction system in the titanium-oxygen binary phase diagram. From the diagram, it can be seen that the equilibrium oxygen concentration in titanium for Y / YOF / YF ３ By utilizing equilibrium, it is thermodynamically predicted that titanium with a low oxygen concentration of less than 0.1 mass % (1000 mass ppm) can be obtained.

[0041] In this embodiment, it was discovered that, in principle, impurity oxygen can be removed directly from molten titanium by utilizing the generation reaction of rare earth metal oxyhalides (REOX). However, the thermodynamic stability of rare earth metal oxyhalides (REOX) at high temperatures is largely unknown, and the above calculation predictions have a large degree of uncertainty. Since the actual deoxidation limit of titanium must be measured experimentally, the effectiveness of this method was demonstrated as shown in the examples described below.

[0042] In the method described in Patent Document 1, rare earth metal halide salts are not added. In this case, rare earth metal oxides (RE) are produced by the reaction of oxygen in titanium and titanium alloys with rare earth metals. ２ O ３ On the other hand, rare earth metal halide salts (REX ３ In this embodiment, the rare earth metal oxide produced reacts with the rare earth metal halide salt, making the rare earth metal oxide thermodynamically unstable and producing rare earth metal oxyhalide (REOX). In this embodiment, the chemical activity (activity) of the rare earth metal oxide is reduced, making it possible to produce titanium or titanium alloys with a thermodynamically high oxygen removal capability and a lower oxygen concentration.

[0043] In the manufacturing method according to the present embodiment, the titanium or titanium alloy containing impurity oxygen used as the titanium raw material in the deoxidation step can be not only ATR-Ti or MTR-Ti, but also scrap generated during the cutting process of titanium ingots or titanium scrap contained in used products. Alternatively, titanium or titanium alloys containing a large amount of impurity oxygen produced by reducing titanium oxide with a rare earth metal or rare earth metal alloy can be used as the titanium raw material. Titanium alloys contain alloying elements such as aluminum and vanadium. In the manufacturing method according to the present embodiment, alloys with a titanium mass concentration of 65% or more can be used as the raw titanium alloy. Removal of impurity oxygen from titanium alloys with a high titanium mass concentration is difficult, and conventional refining methods have not been able to produce titanium alloys with low oxygen concentrations. In contrast, the manufacturing method according to the present embodiment can directly remove impurity oxygen from molten titanium alloys, even when using titanium alloys containing 65% or more titanium as the raw material, thereby producing titanium alloys with low oxygen concentrations.

[0044] The rare earth metal used in the deoxidation reaction in the manufacturing method of the embodiment is preferably one or more selected from, for example, yttrium (Y), lanthanum (La), and cerium (Ce). It is also possible to add a misch metal, which is a mixture of these metals. Rare earth metals other than these rare earth metals can also be used. However, with the recent increase in production of magnet raw materials such as neodymium (Nd), dysprosium (Dy), and terbium (Tb), there has been an excess supply of Y, La, and Ce, which are simultaneously produced as by-products. Therefore, from the standpoint of economic rationality and resource utilization, it is preferable to use by-product rare earth metals such as Y, La, and Ce.

[0045] For the rare earth metal halide salt used in the deoxidation reaction of the manufacturing method of the embodiment, fluorides of Y, La, Ce, etc. can be used. These rare earth metal fluorides are preferably used because they remain stable as liquid even at high temperatures of 1700°C or higher, at which titanium or titanium alloys dissolve. The rare earth metal constituting the rare earth metal halide salt and the rare earth metal added to the titanium raw material may be different types of rare earth metal. For example, cerium fluoride (CeF ３ ) and yttrium (Y) may be used in combination.

[0046] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0047] FIG. 7 is an overall view of an embodiment of a melting apparatus for titanium or titanium alloys. The melting apparatus shown in FIG. 7 is a cold crucible induction melting furnace, a type of high-frequency induction heating device. The cold crucible induction melting furnace 10 of this embodiment includes a crucible 1, an induction coil 3 disposed around the crucible 1, and a water-cooling mechanism 4 for cooling the crucible 1. The crucible 1 is a cylindrical, heat-resistant container with an open top and a bottom wall at the bottom. The sidewall of the crucible 1 has multiple vertically extending slits (not shown). The induction coil 3 is disposed around the outer periphery of the lower part of the crucible 1. A high-frequency power source (not shown) is connected to the induction coil 3. A heat-resistant adhesive 2 is applied to the slits on the inner surface of the crucible 1. Applying the heat-resistant adhesive 2 prevents adhesion between the metal sample and flux in the crucible 1 and the inner wall of the crucible 1. This facilitates removal of the metal sample after deoxidation. In this embodiment, the heat-resistant adhesive 2 is applied along the slit from the lower end to the upper end. The upper end of the applied heat-resistant adhesive 2 is located above the installation range of the induction coil 3. Figure 8 is a cross-sectional schematic diagram of a metal sample in a cold crucible induction melting furnace obtained after melting and cooling. The metal sample 5 is located at the center of the bottom of the crucible 1, and the flux 6 is located between the metal sample 5 and the inner wall surface of the crucible 1.

[0048] After cooling, the metallic titanium block was removed and sliced ​​into small pieces, and the concentrations of oxygen, nitrogen, and rare earth metals were determined. The oxygen and nitrogen concentrations of the metallic titanium samples obtained by melting and cooling are shown in Table 1, along with the melting experiment conditions.

[0049]

[0050] In this example, a yttria-based heat-resistant adhesive was applied to the slit of a water-cooled copper crucible (inner diameter 62 mm, depth 130 mm) in a cold crucible induction melting furnace. After the application of the heat-resistant adhesive, 350 g of titanium (Ti), 2 to 65 g of yttrium (Y), and yttrium fluoride (YF ３ ) was placed in a water-cooled copper crucible.

[0051] In some experiments, the initial concentration of oxygen in titanium was set to 1 mass % (10,000 mass ppm), so titanium oxide (TiO ２ 9 g of molten iron was also charged. The temperature was raised under an argon atmosphere, and after visually confirming that the sample had completely dissolved, the temperature was maintained for 10 to 20 minutes. The furnace power was then reduced, the sample was air-cooled, and the metal sample was removed.

[0052] Fig. 9 is a photograph of a titanium sample in a water-cooled copper crucible obtained by directly removing oxygen from molten titanium using a cold crucible induction furnace and then cooling and solidifying the molten titanium in Example 1 of Table 1. Figs. 10 and 11 are photographs (appearance) of a titanium sample obtained by directly removing oxygen from molten titanium using a cold crucible induction furnace and then cooling and solidifying the molten titanium in Example 1 of Table 1, and then removing it from the water-cooled copper crucible. Fig. 12 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 1 of Table 1. Fig. 13 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 2 of Table 1. Fig. 14 is a photograph of a titanium sample piece for analysis cut out from the titanium sample obtained in Example 8 of Table 1.

[0053] When titanium was melted under the conditions of Example 1 in Table 1, a metal sample with an extremely low oxygen concentration of 0.011 to 0.023 mass% (110 to 230 mass ppm) was obtained. As can be seen from the analysis points of the sample shown in Figure 12, the oxygen concentration decreased to 0.02 mass% (200 mass ppm) throughout the entire sample, a result that closely matches thermodynamic predictions. It also shows that deoxidation proceeded uniformly throughout the entire sample. The nitrogen concentration in the metal sample at this time was 0.012 to 0.015 mass% (120 to 150 mass ppm), and the yttrium concentration was approximately 2 mass%. This experimental result is particularly noteworthy because it is generally difficult to obtain titanium with a low oxygen concentration of 0.02 mass% (200 mass ppm) or less, even when using the Kroll process, which produces high-purity titanium via chlorides.

[0054] When titanium was melted under the conditions of Example 2 in Table 1, a metal sample with a low oxygen concentration of approximately 0.06 mass% (600 mass ppm) was obtained. As can be seen from the analysis points of the sample shown in Figure 13, the oxygen concentration was reduced to 0.06 mass% (600 mass ppm) throughout the entire sample. The yttrium concentration in the metal sample at this time was 1 mass% or less. It was revealed that oxygen could be removed to a concentration of approximately 0.1 mass% (1000 mass ppm) while suppressing the incorporation of yttrium into titanium.

[0055] When titanium was melted under the conditions of Examples 3, 4, and 5 in Table 1, metal samples with oxygen concentrations of 0.1 mass % (1000 mass ppm) or less were obtained.

[0056] As in the dissolution experiments of Examples 6, 7, 8, 10, and 11 in Table 1, titanium oxide (TiO ２ In an experiment in which an oxide was added to the titanium to set the initial oxygen concentration in the titanium to 1 mass % (10,000 mass ppm), oxygen was removed from the molten titanium to 0.1 mass % (1,000 mass ppm). As can be seen from the analysis points of the sample shown in Figure 14, in Example 8 of Table 1, the oxygen concentration was reduced to approximately 0.1 mass % (1,000 mass ppm) throughout the entire sample area. It is noteworthy that even if a large amount of oxide is intentionally added to the titanium sample, the impurity oxygen can be reduced to 0.1 mass % (1,000 mass ppm) by using the method of the above embodiment.

[0057] As in the melting experiments of Examples 9 to 11 in Table 1, it was confirmed that even when the rare earth metal was changed to lanthanum (La) or cerium (Ce), titanium with a low oxygen concentration equivalent to that obtained when yttrium (Y) was used was obtained.

[0058] On the other hand, when deoxidation treatment was performed without using a rare earth metal halide salt, as in the dissolution experiment of the comparative example in Table 1, it was not possible to obtain a metal sample with a low oxygen concentration of 0.1 mass % (1000 mass ppm) or less.

[0059] 15 and 16 show the results of the deoxidation of titanium samples using yttrium fluoride (YF ３The results of X-ray diffraction measurement of the flux after the experiment show that the flux contains yttrium oxyfluoride (Y ｘ O ｙ F ｚ ) was confirmed to be produced, while yttrium oxide (Y ２ O ３ ) was not detected. Figure 17 is a scanning electron microscope photograph of the yttrium fluoride flux used to deoxidize the titanium sample. Table 2 shows the results of energy dispersive X-ray spectroscopy analysis at the points indicated on the scanning electron microscope photograph in Figure 17. In the flux after the experiment, a metallic yttrium (Y) phase, an yttrium oxyfluoride phase, and an yttrium fluoride phase were detected, while an yttrium oxide phase was not detected. The above results suggest that under the conditions of the embodiment, the removal of oxygen from titanium proceeded through the reaction shown in formula (1).

[0060]

[0061] These results demonstrate that low-oxygen titanium can be produced by removing oxygen from high-oxygen ATR-Ti or MTR-Ti. Furthermore, removing oxygen from high-oxygen titanium scrap enables the reuse of the scrap. After both experiments, the nitrogen concentration in the metal samples was approximately 0.02 mass% (200 mass ppm), and the amount of nitrogen contamination due to the addition of rare earth metals or flux was negligible. It was also revealed that the oxygen concentration in titanium can be controlled to a low value by adjusting the yttrium concentration, i.e., the amount of rare earth metal added.

[0062] As is clear from the above examples, by using the method for producing titanium or a titanium alloy according to the above embodiment, it is possible to directly produce titanium or a titanium alloy having a low oxygen concentration of 0.1 mass % (1000 mass ppm) or less, without going through chlorides, which was not possible with conventional melting techniques.

[0063] FIG. 18 shows a graph showing the structure of a titanium oxide (TiO ２18 is a conceptual diagram of a novel titanium smelting method for producing titanium or titanium alloys directly from titanium dioxide. As shown in FIG. 18, in this novel smelting method, a first device 101 for reducing titanium oxide, a second device 102 for deoxidizing titanium, and a third device 103 for casting low-oxygen titanium are connected in sequence. The first device 101 has a reaction vessel 101a, a titanium discharge section 101b, and a slag discharge section 101c. The second device 102 has a reaction vessel 102a, a titanium discharge section 102b, and a slag discharge section 102c. The third device 103 has a mold 103a.

[0064] Titanium ore or titanium oxide, a metal reducing agent such as aluminum (Al) or magnesium (Mg), and a flux such as calcium oxide (CaO) are charged into a reaction vessel 101a of the first device 101. The titanium ore or titanium oxide in the reaction vessel 101a is reduced by the metal reducing agent to produce high-oxygen-concentration titanium. The titanium discharge section 101b of the first device 101 is a pipe extending from the side of the reaction vessel 101a to the reaction vessel 102a of the second device 102. The tip of the titanium discharge section 101b opens onto the opening of the reaction vessel 102a. The high-oxygen-concentration molten titanium produced in the first device 101 is supplied to the reaction vessel 102a of the second device 102 through the titanium discharge section 101b. The slag discharge section 101c of the first device 101 is a pipe extending outward from the upper side of the reaction vessel 101a. The slag produced in the first device 101 is discharged to the outside of the reaction vessel 101a through the slag discharge section 101c and collected.

[0065] In the reaction vessel 102a of the second device 102, molten titanium with a high oxygen concentration supplied from the first device 101, rare earth metals such as yttrium (Y), lanthanum (La), and cerium (Ce), and yttrium fluoride (YF ３A rare earth metal halide salt such as ammonium hydroxide is charged into the reaction vessel 102a. In the reaction vessel 102a, impurity oxygen is removed from the molten titanium by utilizing the rare earth metal oxyhalide production reaction, producing titanium with a low oxygen concentration. The titanium discharge section 102b of the second device 102 is a pipe extending from the side of the reaction vessel 102a to the mold 103a of the third device 103. The tip of the titanium discharge section 102b opens above the opening of the mold 103a. The molten titanium with a low oxygen concentration produced in the second device 102 is supplied to the mold 103a of the third device 103 through the titanium discharge section 102b. The slag discharge section 102c of the second device 102 is a pipe extending from the upper side of the reaction vessel 102a to the outside. The slag produced in the second device 102 is discharged to the outside of the reaction vessel 102a through the slag discharge section 102c and collected.

[0066] A low-oxygen concentration titanium ingot can be obtained from the low-oxygen concentration molten titanium by casting in the third device 103. By using the new smelting method shown in Figure 18, it is possible to produce low-oxygen concentration titanium or titanium alloy directly from titanium oxide without going through chlorides.

[0067] 1...water-cooled copper crucible, 2...slit and heat-resistant adhesive, 3...induction coil, 4...water-cooling mechanism, 5...metal sample, 6...flux, S11, S21...first step, S12, S22...second step, S13, S23...third step, S14...fourth step

Claims

1. A method for producing titanium or a titanium alloy, comprising dissolving and reacting titanium (Ti) or a titanium alloy with a rare earth metal and a rare earth metal halide salt to produce titanium or a titanium alloy having an oxygen concentration of 0.1 mass % (1000 mass ppm) or less.

2. A method for producing titanium or titanium alloys, which utilizes the deoxidizing ability of rare earth metals and the generation reaction of rare earth metal oxyhalides to directly remove impurity oxygen from molten titanium or molten titanium alloys, thereby producing titanium or titanium alloys with low oxygen concentrations.

3. A method for producing titanium or a titanium alloy according to any one of claims 1 to 2, wherein the titanium alloy is an alloy having a titanium mass concentration of 65% or more.

4. One or more rare earth metals selected from yttrium (Y), cerium (Ce), and lanthanum (La), and yttrium fluoride (YF ３ ), cerium fluoride (CeF ３ ), lanthanum fluoride (LaF ３ 3. The method for producing titanium or a titanium alloy according to claim 1, wherein one or more rare earth metal halide salts selected from the group consisting of:

5. A method for producing titanium or a titanium alloy according to any one of claims 1 and 2, wherein a flux of a metal halide salt is used in addition to the rare earth metal and the rare earth metal halide salt.

6. A method for producing titanium or a titanium alloy according to any one of claims 1 to 2, in which titanium or a titanium alloy containing a large amount of impurity oxygen produced by reducing titanium oxide with aluminum (Al) or magnesium (Mg) is used as the titanium raw material.

7. A method for producing titanium or a titanium alloy according to any one of claims 1 and 2, in which titanium or a titanium alloy containing a large amount of impurity oxygen produced by reducing titanium oxide with a rare earth metal or a rare earth metal alloy is used as the titanium raw material.

8. A method for producing titanium or a titanium alloy according to any one of claims 1 and 2, wherein titanium or titanium alloy scrap is used as the titanium raw material.

9. The method for producing titanium or titanium alloys as set forth in claim 1, wherein the titanium or titanium alloy is melted using, in addition to the rare earth metal and the rare earth metal halide salt, a metal halide salt which lowers the melting point of the halide salt melt.

10. A method for producing titanium or a titanium alloy as set forth in any one of claims 1 and 2, wherein the amount of the rare earth metal added is adjusted to control the oxygen concentration in the titanium.

11. A method for producing titanium or a titanium alloy according to any one of claims 1 and 2, in which titanium or a titanium alloy is melted together with a rare earth metal and a rare earth metal halide salt in an inert atmosphere using a melting apparatus selected from the group consisting of a high-frequency induction heating apparatus, a plasma arc melting apparatus, and an electron beam melting apparatus.

12. The method for producing titanium or a titanium alloy according to claim 11, wherein a cold crucible induction melting furnace is used as the high frequency induction heating device, and a heat resistant adhesive is applied to a slit in the crucible of the cold crucible induction melting furnace to prevent adhesion between the rare earth metal halide salt and the crucible.

Images