Manufacturing method of alloy ingot

Abstract

To provide an alloy ingot production method capable of reducing a constriction generation ratio upon alloy ingot production to improve a production yield, and an alloy ingot production bottom tap nozzle.SOLUTION: An alloy ingot production method has a process of tapping an alloy molten metal 7 from a crucible 2 to a bottomed mold 3 to produce an alloy ingot. A rate of tapping the alloy molten metal 7 from a bottom tap nozzle 2a provided at a bottom part of the crucible 2 is controlled to be 0.06 kg / s or more to 0.30 kg / s or less, and the inside diameter of the bottom tap nozzle 2a is controlled to be 3.5 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an alloy ingot and a bottom tapping nozzle for manufacturing an alloy ingot, and in particular to a method for manufacturing an alloy ingot and a bottom tapping nozzle for manufacturing an alloy ingot that can suppress the occurrence of defects such as narrow necking of the ingot, thereby improving the yield of ingot production. [Background technology]

[0002] Turbochargers are used in engines of transportation aircraft, industrial machinery, etc. to obtain high combustion energy. Recently, TiAl alloys, which have excellent high-temperature resistance and are lightweight, have been put to practical use as turbocharger components in order to improve engine fuel efficiency and response speed.

[0003] With the expansion of such use of TiAl alloys, various studies have been conducted on techniques for producing TiAl alloy ingots. For example, the method using an induction melting furnace (CCIM: cold crucible induction melting apparatus) with a water-cooled copper crucible is suitable for melting high-melting-point TiAl-based alloys, as it prevents impurities from being mixed into the molten metal from the melting atmosphere and crucible. Furthermore, an induction melting furnace can melt raw materials smaller than the crucible size without any shape restrictions, so scrap and other materials can be effectively used as raw materials.

[0004] Furthermore, the electromagnetic induction that generates heat in an induction melting furnace also generates electromagnetic repulsion that stirs the molten metal, making it possible to maintain the homogeneity of the components in the molten metal by stirring using electromagnetic repulsion. Therefore, casting of TiAl-based alloys using an induction melting furnace is considered an effective method for obtaining high-quality ingots with a high yield, as TiAl-based alloy ingots require a high yield due to the high cost of raw materials.

[0005] Generally, metals have a higher density in the solid state than in the liquid state, and so the volume of the casting decreases during solidification. In other words, shrinkage occurs during solidification, and defects during casting, such as cavities called shrinkage cavities, are likely to occur in areas where the cooling rate is relatively slow and solidification is delayed. In addition to shrinkage cavities, defects during casting also include defects formed on the casting surface of the ingot.

[0006] Of these defects, a method for suppressing porosity during casting has been proposed, for example, in Patent Document 1. The casting method described in Patent Document 1 involves pouring molten metal melted in a cold crucible induction melting furnace (CCIM) from a nozzle at the bottom of a crucible and casting it into a mold, and involves controlling the relationship between the casting speed V and the ingot height H (V / H) based on predetermined conditions such as the diameter of the ingot, the ratio of the ingot height to the ingot diameter, and the weight of the molten metal being poured. Patent Document 1 also describes that by setting V / H within a predetermined range, directional solidification from the bottom of the ingot can be achieved, resulting in a maximum yield of 86%.

[0007] Furthermore, Patent Document 2 proposes a casting method for Ti-Al alloys that can reduce defects such as shrinkage cavities and also reduce defects such as Al concentration outside the standard range. The casting method described in Patent Document 2 specifies the degree of vacuum in an induction melting furnace and the Al concentration of the cast ingot when melting and casting a Ti-Al-based alloy, and can significantly improve overall quality.

[0008] Furthermore, as a method for improving the condition of the casting surface among defects that occur during casting, Patent Document 3 discloses a method of providing a tapered shape at a predetermined angle in the flow path through which the molten metal passes inside a bottom-tapping graphite nozzle. Patent Document 3 describes that by adjusting the shape of the nozzle as described above, it is possible to control the flow path of the molten metal and suppress turbulence and variation in the tapping flow, and that by optimizing the nozzle material, it is possible to suppress the incorporation of impurities (carbon) into the ingot in the mold. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2018-094628 [Patent Document 2] Patent Publication No. 2021-023967 [Patent Document 3] Patent Publication No. 2021-154304 Summary of the Invention [Problem to be solved by the invention]

[0010] However, in addition to the above-mentioned cavities and irregularities, a defect called "necking" in which the diameter of the ingot is partially narrowed may occur during the casting of the alloy, and the above-mentioned conventional patent documents do not sufficiently consider necking. Therefore, further study is required on a casting method that reduces necking.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing an alloy ingot, and a bottom tapping nozzle for manufacturing an alloy ingot, which can reduce the rate at which necking occurs during the manufacturing of the alloy ingot, thereby improving the manufacturing yield. [Means for solving the problem]

[0012] The above object of the present invention is achieved by the following configuration [1] relating to a method for producing an alloy ingot.

[0013] [1] A method for producing an alloy ingot by pouring a molten alloy from a crucible into a mold with a bottom, The speed at which the molten alloy is poured from the bottom pouring nozzle provided at the bottom of the crucible is set to 0.06 kg / s or more and 0.30 kg / s or less; A method for producing an alloy ingot, characterized in that the inner diameter of the bottom tapping nozzle is 3.5 mm or more.

[0014] Furthermore, preferred embodiments of the present invention relating to a method for producing an alloy ingot relate to the following [2] to [4].

[0015] [2] The method for producing an alloy ingot according to [1], characterized in that the crucible is made of water-cooled copper and the materials for the molten alloy are melted by induction melting.

[0016] [3] The method for producing an alloy ingot according to [1] or [2], wherein the alloy ingot is an ingot made of an alloy containing Ti and Al.

[0017] [4] The method for producing an alloy ingot according to any one of [1] to [3], characterized in that, when the maximum inner diameter of the mold in the horizontal direction is D (mm) and the height of the alloy ingot in the vertical direction is H (mm), H / D is 1.5 or more.

[0018] The above object of the present invention can also be achieved by the following configuration [5] relating to a bottom tapping nozzle for producing an alloy ingot.

[0019] [5] A bottom tapping nozzle for producing an alloy ingot, used in the method for producing an alloy ingot according to any one of [1] to [4], A bottom tapping nozzle for producing alloy ingots, having an inner diameter of 3.5 mm or more and made of graphite. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a method for manufacturing an alloy ingot, and a bottom tapping nozzle for manufacturing an alloy ingot, which can reduce the rate at which necking occurs during the production of the alloy ingot, thereby improving the production yield. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram showing an example of an apparatus for manufacturing an alloy ingot. [Figure 2] Figure 2 is a photograph showing the condition of the casting surface. [Figure 3] FIG. 3 is a graph showing the state of the casting surface versus the casting speed, with the vertical axis representing the ratio indicating the state of the casting surface and the horizontal axis representing the casting speed. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present inventors have focused on the state of the casting surface and have conducted extensive research into a casting method for alloys that can reduce the occurrence of necking in particular. First, the inventors considered the following two phenomena as causes of the occurrence of necking. Cause (1): When the molten metal is poured from the nozzle, it scatters, and when this scattered metal comes into contact with the mold, it solidifies. Cause (2): The molten metal solidifies before it fills the mold due to the low temperature of the molten metal.

[0023] Therefore, the present inventors considered increasing the temperature of the molten metal in order to eliminate the causes (1) and (2) above, but it was difficult to increase the temperature of the molten metal due to the limitations of the casting equipment. Next, in order to eliminate the cause of (1) above, the inventors investigated the use of a tapered nozzle to reduce the splashing of molten metal and thereby suppress the occurrence of necking. Also, in order to eliminate the cause of (2) above, they adjusted the speed at which the molten metal was discharged from the nozzle and investigated the effect on the occurrence of necking.

[0024] As a result, it was found that eliminating problem (2), i.e., inhibiting the solidification of the molten metal before it is filled into the mold, is more effective in suppressing necking. Therefore, it was concluded that it is important to adjust the balance between the rate at which the molten metal solidifies in the mold and the rate at which the molten metal is tapped into the mold. Specifically, by setting the inner diameter of the nozzle to a predetermined value or greater and controlling the amount of molten alloy tapped per unit time when the molten alloy is tapped from the nozzle, the rate at which necking occurs can be reduced, and as a result, yield can be improved.

[0025] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be carried out with any modifications within the scope of the gist of the present invention.

[0026] [1. Manufacturing method of alloy ingot] 1 is a schematic diagram showing an example of an apparatus for manufacturing an alloy ingot. Referring to FIG. 1, a method for manufacturing an alloy ingot according to this embodiment will be described. As shown in FIG. 1 , a manufacturing apparatus 1 used to manufacture an alloy ingot according to this embodiment includes a water-cooled copper crucible 2 disposed inside a chamber 4 and a bottomed mold 3 disposed below the crucible 2. High-frequency coils (not shown) for induction heating a metal 6 disposed inside the crucible 2 are disposed on the circumferential outer side and the outer bottom of the crucible 2, and the crucible 2 and the high-frequency coils constitute an induction melting furnace 5. The crucible 2 is formed into a bottomed cylindrical shape that is open at the top. A bottom-dispensing nozzle 2a (hereinafter also referred to as "nozzle 2a") is formed at the bottom of the crucible 2 for injecting the metal 6 (molten alloy 7) heated and melted by the high-frequency coil into the mold 3. A titanium bottom plug (not shown) is attached to the nozzle 2a before the molten metal is discharged.

[0027] A method for producing an alloy ingot using the alloy ingot production apparatus 1 configured as above will be described below. First, the gas atmosphere and pressure inside the chamber 4 are controlled to a predetermined range, and then a magnetic field is generated by a high-frequency coil to heat and melt the metal 6 inside the water-cooled crucible 2. This method using an induction melting furnace 5 with a water-cooled crucible is generally called the cold crucible induction melting method (CCIM).

[0028] Next, a coil installed at the bottom is energized to induction melt a titanium bottom plug installed at the bottom, which is then melted and removed to open the mold, thereby pouring the molten alloy 7 from the nozzle 2a into the bottomed mold 3. In this embodiment, the speed at which the molten alloy 7 is poured from the nozzle 2a (casting speed) is 0.06 kg / s or more and 0.30 kg / s or less, and the inner diameter of the nozzle 2a is 3.5 mm or more. The poured molten alloy 7 then solidifies in the mold 3, producing an alloy ingot.

[0029] In this embodiment, the speed at which the molten alloy 7 is poured from the nozzle 2a and the inner diameter of the nozzle 2a are appropriately controlled, so that a good balance can be maintained between the speed at which the molten alloy 7 solidifies in the mold 3 and the speed at which the molten alloy 7 is poured into the mold 3. As a result, the condition of the casting surface can be improved, and in particular, the rate at which necking occurs can be reduced. In addition, in this embodiment, the metal 6, which is the material for the molten alloy 7, is melted by induction melting using a water-cooled copper crucible 2, so refractory materials that are generally used as materials for crucibles are not used, which prevents impurities from being mixed into the alloy ingot from the refractory material.

[0030] However, the present invention is not limited to the production of alloy ingots by CCIM, but can also be applied to casting using a general crucible. As a method for adjusting the inner diameter of the nozzle 2a, a method of adjusting the opening diameter electromagnetically or mechanically, or a method of preparing multiple valve members with different opening diameters in advance and replacing the valve members can be adopted.

[0031] Various conditions for the method for producing an alloy ingot according to this embodiment will be described in more detail below.

[0032] <Casting speed: 0.06 kg / s or more and 0.30 kg / s or less> If the casting speed is less than 0.06 kg / s, the molten alloy 7 begins to solidify in the mold 3 before the high-temperature molten alloy 7 is poured into the mold 3 to a predetermined height, increasing the likelihood of necking. On the other hand, from the perspective of safety, it is difficult to increase the nozzle inner diameter to achieve a casting speed exceeding 0.30 kg / s, and therefore the molten alloy 7 cannot be stably poured at a speed exceeding 0.30 kg / s. Therefore, the casting speed is set to 0.06 kg / s or more and 0.30 kg / s or less, and preferably 0.12 kg / s or more.

[0033] The casting speed varies depending on the inner diameter of the nozzle 2a as well as the height of the molten alloy surface in the crucible 2, but it is difficult to control the height of the molten alloy surface during the production of an alloy ingot. Therefore, in this embodiment, the rate at which necking occurs is reduced by adjusting the inner diameter of the nozzle 2a and controlling the casting speed to be within the above range as much as possible. In this embodiment, the casting speed can be calculated by measuring the time it takes for the molten alloy to be poured into one mold to a predetermined height, and dividing the weight (kg) of the molten alloy poured into the mold by the pouring time (seconds).

[0034] <Nozzle inner diameter: 3.5 mm or more> The inner diameter of the nozzle has a significant effect on the casting speed. If the inner diameter of the nozzle is less than 3.5 mm, the probability of the casting speed being 0.06 kg / s or higher decreases, resulting in an increased incidence of necking. Therefore, the inner diameter of the nozzle is set to 3.5 mm or more, preferably 4 mm or more, and more preferably 5 mm or more. Although there is no particular upper limit to the inner diameter of the nozzle, since the molten alloy is dispensed while scraping the inner wall surface of the nozzle, if the inner diameter of the nozzle is too large, safety will be reduced. Therefore, the inner diameter of the nozzle is preferably 10 mm or less.

[0035] <Alloy> In the present invention, the composition of the alloy ingot to be produced is not particularly limited, and the production method of the present invention can be applied to alloy ingots of any composition. However, it is preferable to apply the method to the production of alloy ingots containing Ti and Al, for example, to meet the recent demands for high temperature resistance and light weight as aircraft components.

[0036] Examples of alloys containing Ti and Al (hereinafter also referred to as "Ti-Al-based alloys") include Ti-3Al-2.5V alloy, Ti-6Al-6V-2Sn-0.5Fe-0.5Cu alloy, Ti-3Al-10V-2Fe alloy, Ti-5Al-5V-5Mo-3Cr-0.5Fe alloy, Ti-3Al-8V-6Cr-4Mo-4Zr alloy, Ti-3Al-15V-3Cr-3Sn alloy, Ti-6Al-4V alloy, Ti-3Al-15Mo-2 .7Nb-0.2Si alloy, Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy, Ti-6Al-2Sn-4Zr-6Mo alloy, Ti-6Al-2Sn-4Zr-2Mo alloy, Ti-6Al-5Zr-0.5Mo-0 Examples include .25Si alloy, Ti-5.5Al-3.5Sn-3Zr-1Nb-0.25Mo-0.3Si alloy, Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C alloy, etc.

[0037] <Mold size> In the method for producing an alloy ingot according to the present invention, the size of the mold 3 used is not particularly limited. However, to further suppress the occurrence of shrinkage cavities, it is preferable to appropriately design the ratio between the height of the alloy ingot and the inner diameter of the mold 3. For example, the molten metal poured into the mold 3 is cooled and solidified from the bottom and sides. However, if the influence of solidification from the sides is significant, casting defects such as shrinkage cavities are likely to occur in the center of the alloy ingot. If the maximum inner diameter of the mold in the horizontal direction is D (mm) and the height of the alloy ingot in the vertical direction is H (mm), if H / D is 1.5 or more, the mold warms as the molten metal is poured, and cooling from the mold sides becomes relatively weak. This results in directional solidification from the bottom to the top of the mold, thereby suppressing the occurrence of casting defects. Therefore, H / D is preferably 1.5 or more, more preferably 5 or more, even more preferably 10 or more, and particularly preferably 20 or more.

[0038] The maximum horizontal inner diameter of the mold 3 is preferably 250 mm or less, more preferably 100 mm or less, and the vertical height of the resulting alloy ingot is preferably 100 mm or more, more preferably 400 mm or more, and even more preferably 800 mm or more.

[0039] [2. Bottom tapping nozzle for alloy ingot production] The bottom tapping nozzle for producing alloy ingots according to this embodiment is used in the above-mentioned [1. Method for producing alloy ingots], has an inner diameter of 3.5 mm or more, and is made of graphite. The reason for making the nozzle inner diameter 3.5 mm or more is as described above. Furthermore, by using graphite as the material, induction heating occurs in the nozzle, which melts the bottom plug and enables the molten metal to be tapped. Therefore, by using the bottom tapping nozzle according to this embodiment, the molten metal can be easily tapped and the rate at which necking occurs on the surface of the resulting alloy ingot can be reduced. [Example]

[0040] Hereinafter, an example of the method for producing an alloy ingot according to the present invention and a comparative example will be described.

[0041] [Manufacturing of alloy ingots] First, a Ti-Al-based alloy material, which is the raw material for the molten alloy, was placed in a crucible 2 of an induction melting furnace 5 shown in Figure 1, and heated and melted by cold crucible induction melting (CCIM). Next, the molten alloy 7 was tapped from a bottom tapping nozzle 2a with various inner diameters provided at the bottom of the crucible 2, and poured into a graphite mold 3 to produce an alloy ingot.

[0042] In this example, Ti-Al-based alloy materials of various compositions were used, but as an example, an alloy material with a composition of Ti-48Al-2Nb-2Cr (at%) was used. It was confirmed that the alloy composition did not affect the condition of the casting surface. In addition, a crucible capable of charging 50 kg of Ti-Al-based alloy material at one time was used, and the molten alloy melted in the crucible was sequentially poured into a total of four molds. An Ar atmosphere was created in chamber 4, and the degree of vacuum was controlled in the range of 80 torr to 680 torr. The shape of the alloy ingot that can be produced can be changed to match the shape of the mold, so in this example, cylindrical ingots of the following sizes were produced.

[0043] Cylindrical: diameter 60 mm or diameter 72 mm (inner diameter in the horizontal direction of mold 3) The vertical height of the alloy ingots obtained using the bottomed cylindrical mold was 110 mm to 1490 mm. Ingots with a rectangular cross section, each of which had one side and the other side measuring 55 mm, were produced, and the condition of the casting surface was examined. It was also confirmed that, similar to the composition of the alloy material, the horizontal cross section of the produced alloy ingot did not affect the condition of the casting surface.

[0044] [Evaluation of the casting surface of the ingot] The casting surface of each of the obtained cylindrical alloy ingots was visually observed and classified into three types: good, irregular, and constricted. Figure 2 is a photograph showing the condition of the casting surface. "Good" indicates that the casting surface was in good condition and no scratches or other defects were observed. "Irregular" indicates that some scratches had occurred on the casting surface, but that it was still usable after cutting. "Constricted" indicates that part of the ingot was narrowly constricted, making it difficult to use even after cutting.

[0045] FIG. 3 is a graph showing the state of the casting surface versus the casting speed, with the vertical axis representing the percentage of the state of the casting surface and the horizontal axis representing the casting speed. In FIG. 3, the casting surfaces of multiple ingots were observed at each casting speed, and the percentages of necking, irregularities, and the casting surface state judged to be good are shown. In the casting speed shown in FIG. 3, for example, 0.02 to 0.03 indicates a range of 0.02 (kg / s) or more and less than 0.03 (kg / s). In other words, this means that the number before "to" is included as the lower limit, but the number after "to" is not included.

[0046] Table 1 also shows the relationship between the casting speed and the number of ingots that experienced necking and the necking incidence rate when the nozzle inner diameter was changed to 3.2 mm, 3.5 mm, 4 mm, and 5 mm. Table 1 only measured the occurrence of necking, and shows the number of ingots that experienced necking and the necking incidence rate. In Table 1 below, no ingots were produced at a casting speed of 0.20 kg / s or more but less than 0.28 kg / s, and therefore these are all listed together in the table. In Table 1, the range enclosed by the bold line is the range specified in the present invention.

[0047] [Table 1]

[0048] As shown in Figure 3, a correlation was found between the occurrence of necking and the casting speed. In other words, increasing the casting speed reduced the rate of necking. Note that, when the casting speed was between 0.09 kg / s and 0.10 kg / s, there was no turbulence or necking, but this is likely due to experimental variability. Furthermore, when the casting speed was 0.12 kg / s or higher, no necking occurred, and only good and turbulent results were observed.

[0049] Furthermore, as shown in Table 1 above, by setting the nozzle inner diameter to 3.5 mm or more and the casting speed to 0.06 kg / s or more and less than 0.30 kg / s, the occurrence rate of necking could be kept to 20% or less. This improved the yield when producing ingots. Furthermore, because the casting speed is significantly affected by the nozzle inner diameter, it was shown that the occurrence of necking could be further prevented by setting the nozzle inner diameter to 3.5 mm or more and the casting speed to 0.12 kg / s or more. [Explanation of symbols]

[0050] 1 Manufacturing equipment 2 Crucible 2a Bottom outlet nozzle 3. Mold 4 chambers 5 Induction melting furnace 6 metal 7 Molten alloy

Claims

1. A method for producing an alloy ingot comprising pouring a molten alloy from a crucible into a bottomed mold to produce an alloy ingot made of an alloy containing Ti and Al, comprising: a speed at which the molten alloy is poured from a bottom pouring nozzle provided at the bottom of the crucible is set to 0.12 kg / s or more and 0.30 kg / s or less; 1. A method for producing an alloy ingot, wherein the bottom tapping nozzle has an inner diameter of 3.5 mm or more and 10 mm or less.

2. 2. The method for producing an alloy ingot according to claim 1, wherein the crucible is made of water-cooled copper and the materials for the molten alloy are melted by induction melting.

3. 3. The method for producing an alloy ingot according to claim 1, wherein H / D is 1.5 or more, where D (mm) is the maximum inner diameter of the mold in the horizontal direction and H (mm) is the height of the alloy ingot in the vertical direction.

Images