Method for manufacturing titanium ingots

Abstract

The present invention provides a method for producing titanium ingots that can obtain titanium ingots with component values ​​close to predetermined target values. [Solution] The method for manufacturing a titanium ingot of this invention includes a raw material blending step of blending a molten raw material containing sponge titanium, and a melting and casting step of melting the molten raw material and solidifying the molten metal obtained thereby. In the raw material blending step, sponge titanium is extracted from each of the four or more sponge titanium assemblies and mixed based on the component analysis values ​​of four or more types of sponge titanium assemblies and the component target values ​​of the titanium ingot, and the mixture of sponge titanium is included in the molten raw material.

Description

Technical Field

[0001] This invention relates to a method for melting a melting raw material containing sponge titanium and producing a titanium-based ingot by casting.

Background Art

[0002] Titanium-based ingots such as cylindrical or prismatic ingots or slabs with a polygonal cross-section, or other titanium or titanium alloy products, may be produced by melting and casting using an electron beam melting furnace (so-called EB furnace) or an arc melting furnace.

[0003] For example, in melting and casting using an electron beam melting furnace, generally, in a state where the inside of the electron beam melting furnace is sealed to form a reduced-pressure atmosphere such as a vacuum, a melting raw material in the form of a briquette, rod, powder, or granule containing titanium (Ti) is melted in a hearth by irradiation with an electron beam. The molten metal obtained by melting the melting raw material is cooled and solidified in a mold to become a titanium-based ingot. In many cases, in an electron beam melting furnace, a titanium-based ingot is continuously cast while being pulled out downward from the mold.

[0004] Sponge titanium can be used as at least a part of the above-mentioned melting raw material. Such sponge titanium may be required to have a low oxygen content.

[0005] In relation to this, Patent Document 1 proposes "a method for producing a titanium material in which a sponge titanium cake produced by the Kroll process is cut and sorted, and the sorted sponge titanium is pulverized using a tool, and the pulverization is carried out in an atmosphere with an absolute humidity of 10 g-H2O / m <00​​​​​[Patent Documents]

[0006] [Patent Document 1] Patent No. 2921790 [Overview of the project] [Problems that the invention aims to solve]

[0007] Sponge titanium may be used by extracting a predetermined amount from a sponge titanium aggregate stored in a container, for example, and blending it into the raw material for melting. Here, the amount of sponge titanium extracted from the sponge titanium aggregate blended into the raw material for melting is determined based on the pre-analyzed component analysis values ​​of the sponge titanium aggregate and predetermined component target values ​​of the titanium ingot.

[0008] In this case, even though sponge titanium was incorporated into the molten raw material, based on the component analysis values ​​of the sponge titanium aggregate and the target component values ​​of the titanium ingot, the titanium ingot cast using such molten raw material sometimes had component values ​​that deviated from the above target values.

[0009] The object of this invention is to provide a method for manufacturing titanium ingots that can obtain titanium ingots with component values ​​close to predetermined target values. [Means for solving the problem]

[0010] After diligent investigation, the inventor noticed that the component analysis values ​​of the sponge titanium aggregate were specific to a particular sample, and that the magnitude of the deviation varied depending on the sponge titanium aggregate. The inventor then considered that in order to compensate for this difference in magnitude, it would be effective to extract sponge titanium from each of four or more types of sponge titanium aggregates and include them in the dissolution raw material.

[0011] The present invention provides a method for manufacturing a titanium ingot, comprising a raw material blending step of blending a molten raw material containing sponge titanium, and a melting and casting step of melting the molten raw material and solidifying the resulting molten metal. In the raw material blending step, sponge titanium is extracted from each of the four or more sponge titanium assemblies and mixed based on the component analysis values ​​of four or more types of sponge titanium assemblies and the component target values ​​of the titanium ingot, and the mixture of sponge titanium is incorporated into the molten raw material.

[0012] In the above manufacturing method, when producing one titanium ingot in the melting and casting step, if the melting raw material is melted multiple times with time intervals between them, it is preferable that the melting raw material melted in each step contains the sponge titanium mixture.

[0013] In the above manufacturing method, it is preferable that the components in the component analysis value and the component target value include oxygen.

[0014] In the above manufacturing method, it is preferable that the mixture of sponge titanium consists of sponge titanium extracted from each of the 4 to 11 types of sponge titanium aggregates.

[0015] In the above manufacturing method, the raw material to be dissolved may include a recycled material containing Ti, and / or a modifying material containing O and / or Fe.

[0016] In the above manufacturing method, the raw material to be dissolved may contain the recycled material in an amount of 40% by mass or less. [Effects of the Invention]

[0017] According to the method for manufacturing titanium ingots of this invention, it is possible to obtain titanium ingots with component values ​​close to predetermined target values. [Brief explanation of the drawing]

[0018] [Figure 1]It is a plan view schematically showing an example of an electron beam melting furnace that can be used in a method for producing a titanium-based ingot according to an embodiment of the present invention. [Figure 2] It is a plan view schematically showing another example of an electron beam melting furnace. [Figure 3] It is a plan view schematically showing yet another example of an electron beam melting furnace. [Figure 4] It is a graph showing the oxygen content of each part of the titanium-based ingot obtained in each of the comparative examples. [Figure 5] It is a graph showing the oxygen content of each part of the titanium-based ingot obtained in each of the examples.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. A method for producing a titanium-based ingot according to an embodiment of the present invention includes a raw material blending step of blending a melting raw material containing sponge titanium, and a melting and casting step of melting the melting raw material and solidifying the molten metal obtained thereby. In the melting and casting step, an electron beam melting furnace as shown in FIG. 1, FIG. 2 or FIG. 3 may be used. However, although not described in detail here, an arc melting furnace or other melting furnaces may also be used.

[0020] (Electron Beam Melting Furnace) The electron beam melting furnaces 1, 10 and 100 include a melting hearth 2 for melting the melting raw material, a purification hearth 3 for purifying the molten metal by precipitating or evaporating impurities in the molten metal obtained by melting the melting raw material on the melting hearth 2, a pouring hearth 4 for distributing the purified molten metal to one or more of the following-described molds as necessary and then pouring the molten metal, one or more molds 5 such as water-cooled copper molds for cooling and solidifying the molten metal poured from the pouring hearth 4, and a plurality of electron guns 6 appropriately arranged on the side of the feeding path (runner) of the melting raw material and the molten metal from the melting hearth 2 to the mold 5 for irradiating the melting raw material and the molten metal with an electron beam.

[0021] In the electron beam melting furnace 1 in Figure 1 and the electron beam melting furnace 10 in Figure 2, the only difference is the number of molds 5, and in Figure 2, the pouring hearth 4 distributes molten metal to the two molds 5. The electron beam melting furnace 100 in Figure 3 has substantially the same structure as shown in Figure 1, except that the pouring hearth 4 in Figure 1 is formed integrally with the refining hearth 3, the path for supplying molten metal from the melting hearth 2 to the refining hearth 3 is configured to bend at almost a right angle, and the position and number of electron guns 6 are different.

[0022] The melting hearth 2, the refining hearth 3, and / or the pouring hearth 4 can be cold hearths such as water-cooled copper hearths. In electron beam melting furnaces 1, 10, and 100 equipped with such cold hearths, the raw material can be melted while a skull, often with the same composition as the raw material, is formed on the inner surface of the cold hearth. This reduces the amount of low-density inclusions and suppresses variations in the composition of the cast titanium ingots.

[0023] In melting and casting using electron beam type melting furnaces 1, 10, and 100, high-purity titanium ingots can be obtained by forming the aforementioned skull on the cold hearth, operating under high vacuum conditions, and separating impurities in the molten metal in the refining hearth 3.

[0024] (Raw material blending process) The molten raw material contains at least sponge titanium as a raw material. To formulate this molten raw material, the required amount of sponge titanium may be extracted from the sponge titanium aggregate stored in a container. The amount of sponge titanium included in the molten raw material can be determined based on the component analysis values ​​of the sponge titanium aggregate and the target component values ​​of the titanium ingot to be manufactured.

[0025] Here, the component analysis values ​​for the sponge titanium aggregate may be obtained by taking one or more samples from the sponge titanium aggregate in advance and analyzing those samples using ICP emission spectrometry or similar methods. However, these component analysis values ​​are those of a sample and may be close to or significantly deviate from the standard values, such as the average values ​​of the components in the actual sponge titanium aggregate. Therefore, depending on the sponge titanium aggregate, the component analysis values ​​may deviate significantly from the standard values. If such component analysis values ​​are used to extract a predetermined amount of sponge titanium from the sponge titanium aggregate and blend it into the raw material for melting, the component values ​​of the titanium ingot obtained after melting and casting may deviate significantly from the component target values.

[0026] To address this, in this embodiment, when formulating the molten raw material, sponge titanium is extracted from each of four or more types of sponge titanium assemblies and mixed, and this mixture is included in the molten raw material. At this time, the amount of sponge titanium extracted from each sponge titanium assembly in the mixture is determined by referring to the component analysis values ​​of each of the four or more types of sponge titanium assemblies, so that a titanium ingot with predetermined component target values ​​can be obtained. Even if the component analysis values ​​of the sponge titanium assemblies deviate from the standard values, here, since sponge titanium is extracted from each of the four or more types of sponge titanium assemblies with varying degrees of deviation to form a mixture, the magnitude of the deviations cancels out. As a result, when a titanium ingot is cast using a molten raw material containing such a mixture, a titanium ingot with component values ​​close to the component target values ​​can be obtained.

[0027] Sponge titanium can be produced by dropping titanium tetrachloride onto molten metallic magnesium and then reducing the titanium tetrachloride with metallic magnesium. The sponge titanium obtained in this way may be stored in a container, with information such as the date of manufacture and the values ​​of each component linked to it. A collection of sponge titanium in a single container can be considered as a single type of sponge titanium aggregate. Typically, sponge titanium of similar grades is stored in a single container. When using sponge titanium from a sponge titanium aggregate for blending raw materials, all of the sponge titanium in the sponge titanium aggregate may be extracted, but it is common to extract only a portion of the sponge titanium from the sponge titanium aggregate.

[0028] When obtaining a mixture to be included in the molten raw material, it is acceptable to use four or more types of sponge titanium aggregates from which sponge titanium is extracted. However, using too many types is undesirable because it complicates the blending process. Therefore, it is preferable that the sponge titanium mixture consists of sponge titanium extracted from each of four to eleven types of sponge titanium aggregates. If there are too few types of sponge titanium aggregates (three or fewer), the content of components such as oxygen and iron in the titanium ingot will deviate from the target values ​​in some areas, resulting in greater variation in the titanium ingot as a whole, which is undesirable.

[0029] The components targeted in the component analysis values ​​of sponge titanium assemblies and the component target values ​​of titanium ingots can be selected from a variety of options, but at least one of them may be oxygen (O). In this case, a predetermined amount of sponge titanium can be extracted from each of the four types of sponge titanium assemblies based on the component analysis values ​​of the oxygen content of each of the four types of sponge titanium assemblies, so that the oxygen content of the titanium ingot reaches the target value. Other components that may be targeted besides oxygen include iron (Fe). Although it varies depending on the titanium ingot to be manufactured, the component target value for oxygen content may be 0.01 mass% to 0.15 mass%, and especially 0.01 mass% to 0.07 mass%. Similarly, the component target value for iron content may be 0 mass% to 0.07 mass%, and especially 0.025 mass% to 0.07 mass%.

[0030] The dissolution raw material may contain only sponge titanium, but it may also contain one or more of the following: recycled materials containing Ti, and adjusting materials containing O and / or Fe. The dissolution raw material may also contain other raw materials. When the dissolution raw material contains other raw materials such as recycled materials and / or adjusting materials other than sponge titanium, it is desirable to consider the component analysis values ​​of the other raw materials, extract sponge titanium from each of the four or more types of sponge titanium aggregates, and further blend the dissolution raw material.

[0031] The recycled materials mentioned above include cutting powder (so-called metal shavings), and scrap in the form of plates, blocks, or rods. When the raw material for melting contains recycled materials, the recycled material content in the raw material for melting is preferably 40% by mass or less, and more preferably 15% by mass or more and 25% by mass or less. If the recycled material content is high, the variation in component values ​​in the longitudinal direction of the titanium ingot is reduced, but the component values ​​may not approach the target values ​​as closely. On the other hand, if the recycled material content is too low, the relative content of sponge titanium in the raw material for melting will be high. As a result, there is a concern that the content of components such as oxygen and iron in the titanium ingot will deviate from the target values ​​in some areas, leading to greater variation in the titanium ingot as a whole. Adjusting materials such as titanium oxide powder and iron powder may be used.

[0032] The mixing of the molten raw materials is sometimes carried out by putting each raw material into a hopper, and then mixing the raw materials in the drum feeder while sending a certain proportion of each raw material from the hopper to a drum feeder. The resulting molten raw material is then sent to the melting and casting process described below.

[0033] (Melting and casting process) In the melting and casting process, for example, the inside of the electron beam melting furnace 1 shown in Figure 1 is kept in a predetermined atmosphere, such as a reduced pressure or vacuum atmosphere. If necessary, hydrogen gas may be flowed into the electron beam melting furnace 1 to an extent that does not affect the irradiation of the electron beam. By performing the melting and casting process in such an atmosphere, gases such as oxygen that may be contained in the raw materials to be melted are removed during the melting and casting process. Oxygen, in particular, is more easily removed by flowing hydrogen gas.

[0034] The raw material to be melted is introduced into the melting hearth 2, where it is irradiated with an electron beam and melted. This yields molten metal in the melting hearth 2. The molten metal passes through the refining hearth 3 and is poured into the mold 5 from the pouring hearth 4. Inside the mold 5, the molten metal cools and solidifies, forming a titanium ingot shaped according to the internal shape of the mold 5. In continuous casting, the molten metal is poured into the mold 5, and the solidified portion of the molten metal is pulled out from the bottom of the mold 5. In this way, long titanium ingots can be manufactured.

[0035] In some cases, to produce a single titanium ingot, the molten raw material is introduced into the melting hearth 2 multiple times at time intervals and melted in each batch. In this case, the molten raw material melted in each batch constitutes different parts of the titanium ingot along its longitudinal direction. To ensure that the component values ​​in each part of the titanium ingot are close to the target values, it is preferable that the molten raw material melted in each batch contains a mixture of sponge titanium, obtained by extracting and mixing sponge titanium from each of the four or more types of sponge titanium aggregates, as described above. This makes it possible to produce a titanium ingot with the desired component values ​​throughout.

[0036] Titanium ingots come in cylindrical or prismatic forms with polygonal cross-sections, such as ingots or slabs. Titanium ingots are sometimes used as materials for hot rolling, and may be made of titanium with a purity of 6N or higher (pure titanium).

[0037] Alternatively, titanium ingots made from titanium alloys can also be manufactured. Examples of titanium alloys include alloys of Ti with metallic elements (alloying elements) such as Fe, Sn, Cr, Al, V, Mn, Zr, and Mo. Specific examples include Ti-6-4 (Ti-6Al-4V), Ti-5Al-2.5Sn, Ti-8-1-1 (Ti-8Al-1Mo-1V), Ti-6-2-4-2 (Ti-6Al-2Sn-4Zr-2Mo-0.1Si), Ti-6-6-2 (Ti-6Al-6V-2Sn-0.7Fe-0.7Cu), Ti-6-2-4-6 (Ti-6Al-2Sn-4Zr-6Mo), and SP7. 00(Ti-4.5Al-3V-2Fe-2Mo), Ti-17(Ti-5Al-2Sn-2Zr-4Mo-4Cr), β-CEZ(Ti-5Al-2Sn-4Zr-4Mo-2Cr-1Fe), TIMETAL555(Ti-5Al-5Mo-5V-3Cr -0.6Fe) ("TIMETAL" is a registered trademark), Ti-5553 (Ti-5Al-5Mo-5V-3Cr-0.5Fe), TIMETAL21S (Ti-15Mo-2.7Nb-3Al-0.2Si) ("TIMETAL" is a registered trademark), TIMETAL Examples include LCB (Ti-4.5Fe-6.8Mo-1.5Al) ("TIMETAL" is a registered trademark), 10-2-3 (Ti-10V-2Fe-3Al), Beta C (Ti-3Al-8V-6Cr-4Mo-4Cr), Ti-8823 (Ti-8Mo-8V-2Fe-3Al), 15-3 (Ti-15V-3Cr-3Al-3Sn), BetaIII (Ti-11.5Mo-6Zr-4.5Sn), and Ti-13V-11Cr-3Al. In the above, the numbers preceding each alloying element indicate the content (mass%) of that alloying element. For example, "Ti-6Al-4V" means a titanium alloy containing 6 mass% Al and 4 mass% V as alloying elements. [Examples]

[0038] Next, we will describe the experimental testing of the titanium ingot manufacturing method of this invention to confirm its effectiveness. However, this description is for illustrative purposes only and is not intended to be limiting.

[0039] The raw materials containing sponge titanium were melted in a hearth in an electron beam melting furnace. The resulting molten metal was then poured into a mold and allowed to solidify, thereby casting a titanium ingot. In this process, the raw materials were melted in the hearth multiple times at intervals to obtain a single titanium ingot.

[0040] In the comparative example, when blending each dissolving raw material that was added to the hearth multiple times, the process involved sequentially blending each dissolving raw material by removing sponge titanium from the container storing the sponge titanium aggregates until the sponge titanium was depleted. Once the sponge titanium in a container was depleted, sponge titanium was removed from the next container and sequentially blended with each dissolving raw material. As a result, each dissolving raw material dissolved in each step contained a mixture of sponge titanium extracted from one or two types of sponge titanium aggregates.

[0041] On the other hand, in the examples, each of the dissolving raw materials introduced into the hearth multiple times contained a mixture obtained by extracting sponge titanium from each of the nine or ten types of sponge titanium assemblies in each of the nine or ten containers.

[0042] For the four titanium ingots obtained in both the comparative example and the example, the oxygen content was measured at the Btm, BM, Mid, TM, and Top sections, which were equally spaced along the longitudinal direction. The results are shown in Figures 4 and 5.

[0043] Figures 4 and 5 show that the titanium ingots of the examples had less variation in oxygen content than those of the comparative examples, and their component values ​​were closer to the target values.

[0044] These results suggest that the method for manufacturing titanium ingots according to this invention may make it possible to produce titanium ingots with component values ​​close to the target values. [Explanation of Symbols]

[0045] 1, 10, 100 electron beam melting furnace 2 Dissolve Hearth 3. Refining Hearth 4. Pouring Hearth 5. Mold 6. Electron gun

Claims

1. A method for manufacturing titanium ingots, The process includes a raw material blending step of blending a molten raw material containing sponge titanium, and a melting and casting step of melting the molten raw material and solidifying the resulting molten metal. A method for producing a titanium ingot, comprising the following steps in the raw material blending process: in the raw material blending process, a predetermined amount of sponge titanium is extracted from each of the four or more types of sponge titanium assemblies and mixed based on the component analysis values ​​of each of the four or more types of sponge titanium assemblies and the component target values ​​of the titanium ingot, and the mixture of sponge titanium is included in the molten raw material.

2. In the melting and casting process described above, in order to produce one titanium ingot, the raw material is melted multiple times at time intervals, A method for producing a titanium ingot according to claim 1, wherein the raw material to be dissolved in each step includes the mixture of sponge titanium.

3. A method for manufacturing a titanium ingot according to claim 1 or 2, wherein the components of the component analysis value and the component target value include oxygen.

4. The method for manufacturing a titanium ingot according to claim 1 or 2, wherein the mixture of sponge titanium consists of sponge titanium extracted from each of four to eleven types of sponge titanium aggregates.

5. A method for producing a titanium ingot according to claim 1 or 2, wherein the melting raw material includes a recycled material containing Ti and / or a modifying material containing O and / or Fe.

6. The method for producing a titanium ingot according to claim 5, wherein the melting raw material contains the recycled material in an amount of 40% by mass or less.

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