JP2010269334A - Method for manufacturing ingot and cold crucible induction melting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an ingot capable of suppressing generation of cast defects and of manufacturing a large sound ingot, and also to provide a cold crucible induction melting device. <P>SOLUTION: In the method for manufacturing the ingot 6 by pulling out a crucible bottom 1 downward while supplying a melting raw material 3 with a CCIM method, the ingot 6 is manufactured by allowing height dimension of a high-frequency coil 4 to be 0.5-0.8 times of an inner diameter dimension of a water-cooled copper crucible 2. In the cold crucible induction melting device A for manufacturing the ingot 6, the height dimension of the high-frequency coil 4 is made to be 0.5-0.8 times of the inner diameter dimension of the water-cooled copper crucible 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is a cold crucible induction melting (CCIM) method for producing a large ingot made of Ti, Ti alloy, TiAl base alloy, Zr, Zr alloy, Fe base alloy, Ni base alloy, Co base alloy or the like. The present invention relates to a lump manufacturing method and a cold crucible induction melting apparatus used for manufacturing the ingot.

  Ingots made of Ti alloys, alloys containing active metals such as Zircaloy, and Fe-based alloys, Ni-based alloys, and Co-based alloys that require ultra-high cleanliness are currently industrially vacuum arc melting. It is manufactured by the method, plasma arc melting method, electron beam melting method and the like. These melting methods are all melting methods using a water-cooled copper material as a crucible melting container. These melting methods are characterized in that the entire amount of alloy raw material is not melted all at once, but is supplied and dissolved little by little, and the formed molten metal bath is solidified sequentially from the lower side to produce an ingot. It is said. Currently, ingots of about 1 to 10 tons are manufactured using these melting methods. However, these melting methods also have the problem that the stirring power of the molten metal is small and the alloy components are likely to be uneven.

  On the other hand, the cold crucible induction melting (CCIM) method is a method in which an alloy raw material is melted in a batch to form an alloy and then solidified to produce an ingot. This melting method is considered to be able to produce a homogeneous ingot without generating non-uniform alloy components, but the technology itself for producing large ingots by the CCIM method is still under development. It is a middle stage.

As a method for manufacturing a relatively large and long ingot by the CCIM method, a manufacturing method described in Non-Patent Document 1 is known. In this manufacturing method, a water-cooled copper crucible is used, a high-frequency current is passed through a high-frequency coil installed on the outer periphery thereof, the alloy raw material supplied into the water-cooled copper crucible is induced and melted, and the bottom of the water-cooled copper crucible is directed downward. It is a method of drawing and producing a large and long ingot. In this manufacturing method, fluoride-based slag such as calcium fluoride (CaF ₂ ) is added between the water-cooled copper crucible and the molten metal pool for the purpose of refining effect, electrical insulation effect, or lubrication effect during drawing. It is characterized by. By this method, it is shown that a long ingot having a diameter of 5 inches can be produced using sponge Ti as a melting raw material, but since molten calcium fluoride (CaF ₂ ) comes into contact with the molten Ti, As a result, about several tens of ppm of fluorine (F) is mixed in the ingot, and there is a problem in producing a highly clean ingot.

In addition, as a method for producing a large and long ingot by the CCIM method, a molten metal bath is held by electromagnetic force from a coil without adding a refining material such as calcium fluoride (CaF ₂ ), and water cooling A method of producing a long ingot by pulling out the bottom of the copper crucible can also be considered. However, even if a long ingot is manufactured by this manufacturing method, if inappropriate operating conditions are used, undissolved raw materials may remain inside the ingot or a large surface defect may occur on the ingot surface. Thus, problems such as a significant deterioration in yield occur, and it is difficult to produce a sound ingot.

  The inventors of the present invention do not leave unmelted alloy raw materials or the like by optimizing the operating conditions of the melt casting by pulling the crucible bottom of the water-cooled copper crucible downward while supplying the bulk alloy raw materials by the CCIM method. A patent application has been filed for a method for producing a healthy large ingot (Patent Documents 1 and 2). However, even in these manufacturing methods, there is a problem that extremely large irregularities are formed on the surface of the ingot when a slightly inappropriate operating condition is used. On the other hand, as a result of developing a method to improve the ingot surface defects by optimizing the molten metal pool amount, input power, etc. during the ingot drawing operation, it was possible to achieve considerable improvements. The current situation is that no ingot surface defects can be eliminated.

JP 2006-122920 A JP 2006-281291 A

P.G.Clites, “Inductslag Melting Process”, US, Bureau of Mines Bulletin 673, 1982

  The present invention has been made in view of the above-described conventional situation, and can more reliably suppress the occurrence of casting defects such as surface defects in the ingot, and can stably produce a healthy large ingot. An object of the present invention is to provide a method for producing an ingot that can be produced, and a cold crucible induction melting apparatus.

  The method for producing an ingot of the present invention is a water-cooled copper crucible formed by combining a plurality of copper segments in a cylindrical shape and having a crucible bottom movable in the vertical direction at the bottom. The molten raw material is supplied inside, and the molten raw material is melted by induction heating by a high frequency coil surrounding the periphery of the water-cooled copper crucible to form a molten metal pool, and by moving the crucible bottom downward, the crucible bottom An ingot manufacturing method for manufacturing an ingot by drawing the molten metal pool out of an induction heating area by the high frequency coil and solidifying the molten metal pool, wherein the height dimension of the high frequency coil is equal to the inner diameter of the water-cooled copper crucible. An ingot is produced by producing an ingot at 0.5 to 0.8 times.

  The cold crucible induction melting device of the present invention is configured by combining a plurality of copper segments in a cylindrical shape through a slit, and a bottom portion is provided with a crucible bottom that is movable in the vertical direction. A cold-crucible induction melting apparatus comprising a water-cooled copper crucible and a high-frequency coil surrounding the water-cooled copper crucible, wherein the height dimension of the high-frequency coil is 0.5-0. It is a cold crucible induction melting apparatus characterized by being 8 times.

  According to the ingot manufacturing method and the cold crucible induction melting apparatus of the present invention, it is possible to more reliably suppress the occurrence of casting defects such as surface defects in the ingot, and to stabilize a healthy large ingot. Can be manufactured.

It is a longitudinal cross-sectional view which shows the outline | summary of the method of manufacturing an ingot by the cold crucible induction melting method. It is a longitudinal cross-sectional perspective view which shows a cold crucible induction dissolution apparatus. It is a longitudinal section showing a cold crucible induction dissolving device of one embodiment of the present invention. It is a longitudinal cross-sectional view of the cold crucible induction dissolution apparatus for demonstrating the mechanism in which a solidification shell is formed. It is a longitudinal cross-sectional view which shows the state by which the constriction defect and the double skin defect were produced | generated. It is a longitudinal cross-sectional view which shows the state which changes the magnification with respect to the internal-diameter size of the said water-cooled copper crucible of the height dimension of a high frequency coil, respectively, Comprising: (A) is operated by setting the magnification over 0.8 times. Comparative examples (B), (C), and (D) were operated in such a manner that the magnification was within the range of 0.5 to 0.8, and (E) was multiplied by 0.5. Comparative examples operated as less than each are shown. It is an EPDA (electron beam microanalyzer) photograph showing the mechanism of occurrence of constricted defects and double skin defects.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  The ingot 6 manufactured by the method for manufacturing an ingot of the present invention includes a water-cooled copper crucible 2 in which a crucible bottom 1 is formed to be movable up and down as shown in FIGS. 1 and 2, and the water-cooled copper crucible. 2 can be produced using a cold crucible induction melting (CCIM) apparatus A consisting of a high-frequency coil 4 arranged so as to surround the periphery of 2.

The water-cooled copper crucible 2 constituting the cold crucible induction melting apparatus A is configured by combining a plurality of copper segments 7 in a cylindrical shape, and a circular copper crucible bottom 1 is disposed at the bottom. ... Are provided between the plurality of copper segments 7, 7,..., And yttria (Y ₂ O) for electrical insulation. ₃ ) An insulating material such as cement or alumina (Al ₂ O ₃ ) cement is embedded. The high-frequency coil 4 is provided slightly apart from the surface of the water-cooled copper crucible 2 so that it surrounds the water-cooled copper crucible 2 around the water-cooled copper crucible 2 while leaving its upper and lower ends somewhat, and is connected to a high-power high-frequency power source 13. ing.

  As shown in FIG. 3, the greatest characteristic point of this cold crucible induction melting apparatus A in the present invention is that the height dimension H of the high-frequency coil 4 is 0.5 to 0.8 of the inner diameter dimension D of the water-cooled copper crucible 2. That is doubled. This point will be described in detail later.

  The reason why the slit 8 is provided is that the electromagnetic force from the high-frequency coil 4 can easily penetrate through the slit 8 into the molten metal pool 5 or the melting raw material 3 formed in the water-cooled copper crucible 2. This is because the heat generation efficiency when the raw material 3 is melted is aimed to be maximized.

  The copper segment 7, the crucible bottom 1, and the high frequency coil 4 are hollow, and cooling water is injected into the hollow. The crucible bottom 1 is connected to a pull-out mechanism 9 such as a lower cylinder, and is configured to be movable in the vertical direction. The crucible bottom 1 is moved so as to be pulled down from a cylindrical main body formed of the copper segment 7 of the water-cooled copper crucible 2. be able to.

  An ingot 6 made of Ti, Ti alloy, TiAl base alloy, Zr, Zr alloy, Fe base alloy, Ni base alloy, Co base alloy or the like is manufactured using this cold crucible induction melting apparatus A. The cold crucible induction melting apparatus A is provided in the vacuum chamber B. Further, a bottom plate 10 serving as a starting material at the start of melting is attached to the upper surface of the crucible bottom 1. The bottom plate 10 is formed of a metal material that takes into account the material of the ingot 6 to be manufactured, such as pure titanium material, titanium alloy material, carbon steel, and stainless steel.

  Incidentally, the size of the large ingot 6 targeted by the present invention is not particularly limited. For example, the size is 200 mm or more in diameter, and the height dimension with respect to the diameter is 1.5 times or more, that is, 300 mm. The above is preferable. If it is the small ingot 6 which does not reach the above-mentioned size, it can be manufactured relatively easily without using the cold crucible induction melting apparatus A, and the ingot 6 made of a metal material having a heavy specific gravity. Even if it is, it is 50 kg or less and is not particularly practical. The diameter of the ingot 6 is preferably 1000 mm or less, and the magnification of the height dimension with respect to the diameter is preferably 5 times or less.

  Next, a method for manufacturing a large ingot 6 by moving the crucible bottom 1 downward using the cold crucible induction melting apparatus A of the present invention will be described.

  Before starting the operation of manufacturing the ingot 6 using the cold crucible induction melting apparatus A or the like, the melting raw material 3 is prepared. The melted raw material 3 includes a bulk melted raw material 3 (not shown) that is initially supplied into the water-cooled copper crucible 2 and a plurality of rod-shaped melts that are supplied into the water-cooled copper crucible 2 after the initial melting is completed. There is raw material 3. The melting raw material 3 does not necessarily need to be divided into the bulk melting raw material 3 to be supplied initially and the plurality of rod-shaped melting raw materials 3 to be additionally supplied, and only the rod-shaped melting raw material 3 may be used.

  First, the initial melting raw material 3 is supplied to the inside of the water-cooled copper crucible 2 in a state where the crucible bottom 1 to which the bottom plate 10 serving as a starting material at the start of melting is attached is disposed at a predetermined height position. In this state, by applying a high-frequency current to the high-frequency coil 4, the upper part of the bottom plate 10 in the induction heat generation region by the high-frequency coil 4 and the initial melting raw material 3 are simultaneously melted. The melted upper part of the bottom plate 10 and the initial molten raw material 3 form an initial molten metal pool 5.

  Next, if the crucible bottom 1 is gradually lowered downward, the molten metal pool 5 on the crucible bottom 1 is gradually extracted downward from the induction heat generation region by the high-frequency coil 4, and solidification starts from below. . Since the molten pool 5 is cooled from the outer surface in contact with the inner wall surface of the water-cooled copper crucible 2, a solidified layer of the ingot 6 is formed in a ring shape on the outer peripheral portion of the molten pool 5. Even if 5 is extracted downward, it does not flow out.

  As the molten pool 5 is gradually pulled downward, the amount of the molten pool 5 in the water-cooled copper crucible 2 decreases, so that an amount of the rod-shaped melting raw material 3 corresponding to the amount of withdrawal is gradually supplied from above and melted. As a result, the amount of the molten metal pool 5 can be kept constant at all times. The portion solidified by this drawing becomes the target ingot 6. In addition, the rod-shaped melt | dissolution raw material 3 supplied from upper direction is the amount of reduction | decrease of the molten metal pool 5 from the lower end part in the state suspended in the suspension mechanism 11 provided in the upper part of the vacuum chamber B in a bundle. It is gradually supplied in an appropriate amount.

  The ingot 6 produced by this pultrusion casting method does not have a shrinkage cavity defect in the central portion unlike the ingot 6 produced by a generally performed gravity casting method. Can be manufactured. In particular, as a method for manufacturing an ingot 6 of an alloy material that is easily cracked, such as a TiAl-based alloy, cracking due to shrinkage defects does not occur, and therefore this drawing casting method can be said to be suitable.

  When the large ingot 6 is simply manufactured by the above manufacturing method, according to the manufacturing conditions, a constricted defect a having a depth of 20 mm or more as shown in FIG. There is a possibility that a surface defect such as a double skin defect b in which the molten metal flows into the deep constriction defect and becomes a double solidified structure is generated. If surface defects such as such deep constriction defects a and double skin defects b are generated on the surface of the ingot 6, the surface of the ingot 6 needs to be cut (skinned). The yield is significantly reduced, and depending on the conditions, it cannot be used.

  In addition, even in Fe-based alloy materials that are relatively difficult to generate surface defects, under improper operating conditions, cracks in the horizontal direction (width 1 to 5 mm, length 20 to 100 mm, depth May occur in a large number.

  Conventionally, a cold crucible induction melting apparatus A generally used for manufacturing the ingot 6 has a height dimension H of the high-frequency coil 4 of 0.9 to 1.1 which is an inner diameter dimension D of the water-cooled copper crucible 2. It is set to be doubled. The reason is that in order to efficiently dissolve the melting raw material 3 in the water-cooled copper crucible 2, the high-frequency coil 4 having a certain length or more is required, and for that purpose, the height dimension H of the high-frequency coil 4 is increased. This is because we thought it was necessary.

  However, when the ingot 6 is manufactured by a method in which the rod-shaped melting raw material 3 is melted while being supplied from above and the molten metal pool 5 formed by the melting is drawn downward to form the ingot 6, the surface quality is high. In order to manufacture a good ingot 6, if the height dimension H of the high-frequency coil 4 is 0.9 to 1.1 times the inner diameter dimension D of the water-cooled copper crucible 2, the length of the high-frequency coil 4 is Conversely, it will be long. As described above, if the length of the high-frequency coil 4 is too long, the melting raw material 3 is excessively dissolved and scattered as fine droplets (splash), and the splash is aggregated in the slit 8 of the water-cooled copper crucible 2. As a result, the solidified shell 12 that has entered the slit 8 is formed. As a result, a constricted defect a or double skin defect b having a depth of 20 mm or more is formed in the ingot 6 manufactured by drawing. Such surface defects occur, and the surface quality deteriorates.

  On the other hand, when the ingot 6 is manufactured by setting the height dimension H of the high-frequency coil 4 to an appropriate dimension according to the present invention, even if the constriction defect a is generated, it is relatively small (within a depth of 15 mm). Thus, only the constriction defect a having no problem in use is generated, and the ingot 6 to be manufactured can be used as the ingot 6. Moreover, according to the conditions, it cannot be said that there is no possibility of the occurrence of a constricted defect a having a depth of 20 mm or more, but the probability of occurrence is suppressed to 1/10 or less as compared with the conventional case. Can do.

  The inventors manufactured the ingot 6 with the actual cold-crucible induction melting apparatus A for the observation to confirm the occurrence of surface defects such as the deep constriction defect a, double skin defect b, or crack defect. Carried out at the operation site. Although the molten metal starts to solidify at the solidification interface between the molten metal pool 5 and the ingot 6, when the solidified shell 12 is formed in a state where the molten metal has entered the slit 8 of the water-cooled copper crucible 2, the solidified shell 12 becomes the slit 8. It will be in the state firmly fixed to. When the ingot 6 is pulled out in this state, cracks occur on the surface of the solidified shell 12 and the solidified layer of the ingot 6, and the crack expands by further drawing of the ingot 6. It was confirmed that the defect was a shape defect a.

  In addition, the double skin defect b is formed so that the crack tip of the formed constriction defect a reaches the solid-liquid phase coexistence region (region where solid and liquid coexist) of the molten metal pool 5, so that the liquid ( It was confirmed that the molten metal was formed by filling the constricted defects a.

  As a precaution, this generation mechanism is observed and confirmed in a small cold-crucible induction dissolving apparatus A by an EPDA (electron beam microanalyzer) photograph in FIG. Here, Fe is introduced into the molten pool 5 as a marker, and the cracked tip of the constricted defect a reaches the solid-liquid phase coexistence region of the molten pool 5, thereby causing the constricted defect from the molten pool 5 containing Fe. It can be confirmed that a double skin defect b having a high Fe concentration is formed by flowing and filling the molten metal into a. 7, the upper photo shows the right half of the molten metal pool 5 and the ingot 6, and the lower photo shows the right half of the molten metal pool 5 and the ingot 6.

  From the above observation results, it was confirmed that the constriction defect a occurred first, and the double skin defect b was formed by the molten metal flowing into and filling the constriction defect a from the molten metal pool 5. . That is, in order to suppress the occurrence of these surface defects, it has been confirmed that it is most important to suppress the generation of the constricted defect a.

  Therefore, the inventors decided to investigate the cause of the formation of the solidified shell 12 formed in the state of entering the slit 8 of the water-cooled copper crucible 2 that causes the constriction defect a. As a result, the hot water flow on the surface of the molten metal pool 5 becomes unbalanced, the amount of hot water flow locally increases, and the solidified shell 12 is formed in a situation where it hits the inner surface of the water-cooled copper crucible 2, The molten metal 5 flowing from the melted raw material 3 is struck violently and scattered as fine droplets (splashes), and the splash is agglomerated and solidified in the slits 8 of the water-cooled copper crucible 2. It has been found that when the shell 12 is formed, the solidified shell 12 is formed in a state where it enters the slit 8 of the water-cooled copper crucible 2.

  Therefore, in order to suppress the generation of the solidified shell 12 formed in the state of entering the slit 8 of the water-cooled copper crucible 2, the state of the hot water flow in the molten pool 5 is stabilized and further the occurrence of splash is suppressed. Is considered important.

  The inventors conducted the above observations and examinations earnestly and repeatedly, and as a result of searching for operating conditions capable of suppressing the generation of the solidified shell 12 formed in the state of entering the slit 8 of the water-cooled copper crucible 2. The present inventors have succeeded in finding out the proper operation conditions for melting and casting, and have completed the present invention.

  Hereinafter, the process until the present invention is completed will be described in detail.

  When melting the melting raw material 3 that is a raw material for manufacturing the large ingot 6 by the cold crucible induction melting method, first, a high-frequency current is passed through the high-frequency coil 4 and the induced current generated in the melting raw material 3 is reduced. The molten raw material 3 is heated by resistance heat generation, the heating temperature is raised to the melting point (liquidus) of the molten raw material 3 or higher, and the molten raw material 3 is melted to form the molten metal pool 5. At that time, as shown in FIG. 4, in the molten metal pool 5, a magnetic force (indicated by a horizontal arrow) due to an induced magnetic field acts to balance the molten metal static pressure (indicated by a downward arrow). It is assumed that In principle, the molten metal in the molten pool 5 comes into contact with the inner wall surface of the water-cooled copper crucible 2 at the position where the magnetic force and the static pressure of the molten metal are balanced, and the solidified shell 12 starts to be formed. It swells in the center due to electromagnetic force, and it flows violently as molten metal flows down the surface.

  At that time, a part of the molten metal in the molten fluid pool 5 that violently strikes the molten raw material 3 charged from above and scatters as fine droplets (splash). The solidified shell 12 in which the splash enters the slit 8 of the water-cooled copper crucible 2 and is aggregated and solidified is formed in a state of entering the slit 8 of the water-cooled copper crucible 2, and the solidified shell 12 is formed in the molten metal pool. 5 and the ingot 6 are welded to a solidified layer formed on the surface of the ingot 6 at the solidification interface.

  In addition, when the hot water flow in the surface layer of the molten metal pool 5 becomes uneven and a region where a large amount of molten metal flows locally occurs, a large amount of molten metal hits the inner surface of the water-cooled copper crucible 2 in that region. The solidified shell 12 is formed into a solidified shell 12 that is longer in the vertical direction than other positions, and further, the solidified shell 12 is formed in a state where it enters the slit 8 of the water-cooled copper crucible 2; and The solidified shell 12 is welded to the ingot 6 at the solidification interface between the molten metal pool 5 and the ingot 6.

  In this state, when the crucible bottom 1 of the water-cooled copper crucible 2 is moved downward, the molten pool 5 is drawn downward together with the solidified shell 12 formed on the surface layer. As shown in FIG. 5, a part of the water-cooled copper crucible 2 forms a state where it bites into a slit 8 formed between the copper segments 7, 7 and is firmly fixed (FIG. 4, FIG. 5). In other words, the fixed part is not easily pulled down. As a result, a tensile stress acts on the lower part of the solidified shell 12, and particularly when the solidified shell 12 is firmly fixed, for example, by deeply biting into the slit 8, a crack occurs in the lower part of the solidified shell 12, and the crack is generated. It grows and becomes a large and deep constriction defect a. In addition, the longer the solidified shell 12 is, the higher the possibility that a strong fixing portion such as a fixing portion that bites into the slit 8 is formed, and the possibility that a deep constriction defect a is generated increases. Therefore, it was considered that the operation not to form the solidified shell 12 formed in the state of entering the slit 8 of the water-cooled copper crucible 2 would reduce the possibility of generating the deep constriction defect a. .

  In addition, when a large and deep constriction defect a is generated directly under the molten pool 5, a relatively thin portion of the solidified shell 12 between the molten pool 5 and the constriction defect a is broken as shown in FIG. Sometimes. In that case, the molten metal in the molten metal pool 5 flows into the constricted defect a, and the molten metal filled in the constricted defect a is solidified to form a double skin defect b. Note that the molten metal forming the double skin defect b does not completely adhere to the inner surface of the original constricted defect a, so that it is detected as a defective portion when the penetration inspection test is performed.

  Therefore, in order to prevent the occurrence of surface defects such as the above-mentioned large and deep constriction defects a and double skin defects b, it is important not to generate the constriction defects a, The occurrence conditions were explored.

  As described above, the constriction defect “a” is formed when the solidified shell 12 formed on the surface layer of the molten metal pool 5 enters the slit 8 of the water-cooled copper crucible 2, and as a result, tensile stress is generated below the solidified shell 12. The crack is generated by receiving the crack, and the crack is formed by growing.

  Therefore, in order to prevent the occurrence of the constricted defect a, it is considered effective to suppress the formation of the solidified shell 12 formed in the slit 8 of the water-cooled copper crucible 2. The solidified shell 12 is also formed above the position where the magnetic force and the molten metal static pressure are balanced, and as the region becomes longer upward, the frequency of occurrence of cracks increases.

  In order to suppress the formation of the constricted defect a, it is effective to stabilize the flow state of the molten metal pool 5. As a countermeasure, the height dimension H of the high-frequency coil 4 is determined from the height dimension H of the high-frequency coil 4 of the cold crucible induction melting apparatus A that has been conventionally used in the manufacture of the ingot 6. This is to reduce the length of the high-frequency coil 4.

  By shortening the length of the high-frequency coil 4, when the melting raw material 3 is melted, excessive melting such as formation of a large cavity 3 a can be suppressed, and stable melting of the melting raw material 3 can be prevented. As a result, it is possible to suppress splash splashing, which is a cause of formation of the solidified shell 12 formed in the state of entering the slit 8 of the water-cooled copper crucible 2.

  The specific height dimension H of the high-frequency coil 4 is 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible 2. When the magnification exceeds 0.8 times, the splash amount increases, and the melting raw material 3 may be excessively dissolved to form a large cavity 3a in the melting raw material 3 (lower end). . As a result, due to these causes, the solidified shell 12 is formed in a state of entering the slit 8 of the water-cooled copper crucible 2. On the other hand, when the magnification is less than 0.5, it is difficult to dissolve the melting raw material 3. Therefore, the range of the magnification is set to 0.5 to 0.8 times.

  Next, the reason why the height dimension H of the high-frequency coil 4 is 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible 2 will be described in more detail with reference to FIG.

  FIG. 6A shows an example in which the height dimension H of the high-frequency coil 4 is operated to be more than 0.8 times the inner diameter dimension D of the water-cooled copper crucible 2. When the ingot 6 is manufactured by such a method, the induction heat generation of the molten fuel 3 charged from above becomes too large, and the melting of the melting raw material 3 is excessively promoted. In some cases, the melting of the inside of the raw material 3 proceeds too much, and a large cavity 3a is formed in the inside (lower end).

  If it becomes such a situation, the quantity of the molten metal pool 5 at the time of operation will fluctuate | variate greatly, and the hot water flow of the molten metal pool 5 will be disturbed violently. Furthermore, when a part of the molten metal flowing so as to rise in the central portion by electromagnetic force hits a thin portion of the molten raw material 3 in the cavity 3a, a gap is formed between the molten metal pool 5 and the molten raw material 3. It becomes minute droplets (splash) and scatters around. Since the solidified shell 12 is formed in a state where the splash enters the slit 8 of the water-cooled copper crucible 2, a large and deep constricted defect a is likely to occur.

  In contrast, FIGS. 6B to 6D are examples in which the height dimension H of the high-frequency coil 4 is operated within the range of 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible 2. is there. When the ingot 6 is manufactured by such a method, a large and deep constricted defect a hardly occurs. Therefore, if the ingot 6 is manufactured by this method, it can be said that a healthy large ingot 6 can be stably manufactured.

  However, even when the height dimension H of the high frequency coil 4 is operated within the range of 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible 2, splash may be scattered. The splash amount tends to decrease as the height dimension H of the high-frequency coil 4 decreases, that is, in the order of (B) → (C) → (D) in FIG. 6. When the splash amount is reduced, the generation amount of the solidified shell 12 is reduced, and the constricted defect a is hardly generated. In addition, in the order of (B) → (C) → (D) in FIG. 6, the cavity 3a formed in the melting raw material 3 becomes smaller, and in FIG. 6 (D), the formation of the cavity 3a is hardly recognized. .

  FIG. 6E shows an example in which the height dimension H of the high-frequency coil 4 is set to less than 0.5 times the inner diameter dimension D of the water-cooled copper crucible 2. When the ingot 6 is manufactured by such a method, the induction heating to the melting raw material 3 becomes insufficient, so that the melting raw material 3 becomes difficult to be dissolved, and it becomes difficult to obtain a stable dissolution rate. In some cases, the ingot 6 cannot be pulled out.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and the present invention is implemented with appropriate modifications within a range that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

  The test which manufactures an ingot by the method of pulling out an ingot downward using the cold crucible induction melting apparatus was implemented. The material of the ingot to be manufactured is a TiAl alloy (Ti-30Al-3Cr-3V-4Mn alloy (mass%)). In the test, under the condition that the coil voltage of the high-frequency coil is held at a constant value, the descending speed (feeding speed) of the rod-shaped melted raw material is changed according to the fluctuation of the input power, or the ingot is drawn first. The ingot was manufactured by adjusting the temperature by stopping it.

  The cold crucible induction melting apparatus has a high frequency power source having a frequency of 3000 Hz and an output of 500 kW (Max), and is connected to a high frequency coil by a water-cooled cable via a matching panel. The high frequency coil surrounds the outer periphery of the water-cooled copper crucible, and its height H and number of turns are 230 mm and 6 turns in Comparative Example 1, 190 mm and 5 turns in Example 1, 170 mm and 5 turns in Example 2, In Example 3, 140 mm and 5 turns, and in Comparative Example 2, 110 mm and 4 turns.

The water-cooled copper crucible has an inner diameter D of φ250 mm, and is composed of 24 copper segments assembled in a cylindrical shape and a crucible bottom attached to a drawing mechanism. The lower end position of the slit formed between the copper segments is the same height position as the lower end position of the high frequency coil. Moreover, cooling water is flowing inside the copper segment, the crucible bottom, and the like, and the cooling water flow rate is 400 L / min. The internal volume of the vacuum chamber in which this cold crucible induction melting apparatus is accommodated is 10 m ³ .

  Incidentally, the magnification H / D with respect to the inner diameter dimension D of the water-cooled copper crucible having the height dimension H of the high-frequency coil is 230/250 = 0.92 in Comparative Example 1, 190/250 = 0.76 in Example 1, and Example In Example 2, 170/250 = 0.68, in Example 3, 140/250 = 0.56, and in Comparative Example 2, 110/250 = 0.44.

  The test body (ingot) is manufactured by attaching a bottom plate as a starting material at the start of melting to the upper surface of the crucible bottom and placing it at a predetermined start position inside a water-cooled copper crucible and Ti-30Al-3Cr. The initial melting raw material consisting of -3V-4Mn alloy (mass%) was charged and started.

  The melting material for additional supply is also made of the same Ti-30Al-3Cr-3V-4Mn alloy (mass%) as the initial melting material, but the melting material for additional supply is made of a plurality of rod-shaped melting materials in a cylindrical shape. It is bundled in. The total diameter is 180 mm and the length is 1000 mm. This additional raw material for supply is sequentially supplied from the lower end to the inside of the water-cooled copper crucible while being suspended by a suspension mechanism provided at the top of the vacuum chamber.

First, the bottom plate was placed at a predetermined height position at the start of melting, and a lump of molten raw material was supplied into the water-cooled copper crucible. Thereafter, the air inside the vacuum chamber was evacuated with a diffusion pump to 6.7 × 10 ⁻² Pa, and then filled with high-purity Ar to a maximum of 78 KPa to form an inert gas atmosphere. Next, turn on the output of the high-frequency power supply and hold at 100 kW (10 minutes) → 200 kW (10 minutes) → 260 kW (10 minutes) to melt the bulk molten raw material and the upper part of the bottom plate, Formed.

  After that, the rod-shaped melting raw material is pushed down and the lower end of the molten material is melted by immersing it in the molten metal pool. The ingot was produced so that the amount was substantially constant. In addition, the position at which the solidification interface between the molten metal pool and the ingot is in contact with (or closest to) the inner surface of the water-cooled copper crucible is controlled so that it is several tens of millimeters above the lower end of the slit. Carried out.

  In addition, the input power when pulling the ingot downwards is 210 kW, which is slightly higher than the lower limit value that can maintain the amount of the molten pool, so that the molten pool is kept as small as possible (approximately 15 kg as a guide). The test was conducted.

  Under the above conditions, a test was conducted to produce an ingot using a cold crucible induction melting apparatus, and an evaluation was conducted by measuring the maximum depth of a constricted defect formed on the surface of the produced ingot. . An ingot with a maximum depth of constriction defects of 15 mm or less is evaluated as acceptable (O) because there is no problem in use, and an ingot with a maximum depth of constriction defects of more than 15 mm is evaluated as reject (×). did.

  In addition, the number of occurrences of splash causing the occurrence of constricted defects and the volume of cavities formed in the rod-shaped melted raw material (lower end) were also measured.

  In Comparative Example 1 in which the height dimension H of the high-frequency coil is 0.92 times the inner diameter dimension D of the water-cooled copper crucible, the maximum depth of the constricted defect formed on the surface of the ingot is not problematic in use. It was over 15mm.

  In addition, since the height dimension H of the high-frequency coil is large, severe molten metal splash (splash) occurs during melting, and it is observed that a large solidified shell is formed in a state where this splash enters the slit of the water-cooled copper crucible. It was done. It is considered that this solidified shell was welded to the ingot, a tensile stress was applied when the ingot was pulled out, and a large constriction defect was generated. Moreover, when the melt | dissolution raw material after completion | finish of a test was observed, the huge cavity was formed in the lower end inside.

  In Example 1 in which the height dimension H of the high-frequency coil is 0.76 times that is close to the upper limit of the range of 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible, the high-frequency coil is formed on the surface of the ingot. The maximum depth of the constriction defect is 12 mm, which is within 15 mm, which is not problematic in use.

  In addition, it was observed that the amount of splash was significantly reduced compared to Comparative Example 1, the number of occurrences was reduced, and the solidified shell formed in the state of entering the slit of the water-cooled copper crucible was also reduced. It was. In addition, the size of the cavity formed in the lower end of the melting raw material was also reduced.

  Furthermore, the height dimension H of the high-frequency coil was reduced, and the height dimension H of the high-frequency coil was 0.68 times the inner diameter dimension D of the water-cooled copper crucible. In Example 3 in which the inner diameter of the copper crucible was 0.56 times, the maximum depth of the constricted defect formed on the surface of the ingot was 5 mm, and no constricted defect that would cause a problem in use was generated. .

  In addition, no splash was generated, and the solidified shell formed while entering the slit of the water-cooled copper crucible was greatly reduced. Furthermore, no cavities were formed inside the lower end of the melting raw material.

On the other hand, in the case of Comparative Example 2 in which the height dimension H of the high-frequency coil is 0.44 times the inner diameter dimension D of the water-cooled copper crucible, since the molten metal pool is raised, the lower end of the rod-shaped melting raw material is the high-frequency coil. Since the melting raw material is almost removed from the induction heat generation region by the high frequency coil, the melting raw material generates less heat and the melting rate is remarkably slowed. Not observed. In Table 1, the volume of the cavity is shown as −60 cm ³ , but this indicates that the melting raw material is not formed with a cavity, but the lower end of the melting raw material protrudes in a U-shaped cross section. .

  As a result, the ingot is manufactured by setting the height dimension H of the high-frequency coil to 0.5 to 0.8 times the inner diameter dimension D of the water-cooled copper crucible, thereby manufacturing the ingot with almost no surface defects. It was confirmed that it was possible.

DESCRIPTION OF SYMBOLS 1 ... Crucible bottom 2 ... Water-cooled copper crucible 3 ... Melting raw material 3a ... Cavity 4 ... High frequency coil 5 ... Molten pool 6 ... Ingot 7 ... Copper segment 8 ... Slit 9 ... Drawing mechanism 10 ... Bottom board 11 ... Suspension mechanism 12 ... Solidification Shell 13 high frequency power supply a ... Constriction defect b ... Double skin defect A ... Cold crucible induction melting device B ... Vacuum chamber

Claims (2)

A plurality of copper segments are formed in a cylindrical shape, and a melting raw material is supplied to the inside of a water-cooled copper crucible configured with a crucible bottom that is movable in the vertical direction at the bottom. The melting raw material is melted by induction heating with a high-frequency coil surrounding the periphery of a water-cooled copper crucible to form a molten pool, and the molten metal pool on the bottom of the crucible is moved downward by induction heating with the high-frequency coil. An ingot manufacturing method for manufacturing an ingot by drawing out of the region and solidifying the ingot,
A method for producing an ingot, comprising producing the ingot with a height dimension of the high-frequency coil being 0.5 to 0.8 times an inner diameter dimension of the water-cooled copper crucible. A water-cooled copper crucible composed of a plurality of copper segments combined in a cylindrical shape through a slit, with a crucible bottom movable in the vertical direction at the bottom, and the periphery of the water-cooled copper crucible A cold crucible induction melting device comprising a high-frequency coil surrounding
A cold crucible induction melting apparatus, wherein a height dimension of the high-frequency coil is 0.5 to 0.8 times an inner diameter dimension of the water-cooled copper crucible.

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