JP5636316B2 - Ingot manufacturing method - Google Patents

Description

  The present invention is an alloy containing an active metal such as Ti or Zr, or an Fe-based alloy, Ni-based alloy, Co-based alloy or the like that requires ultra-high cleanliness, by a cold crucible induction melting (CCIM) method. The present invention relates to an ingot manufacturing method for manufacturing a large and long 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. The plasma arc melting method, the electron beam melting method, the electroslag melting method, etc. are used. 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. 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. With this melting method, alloying is easy and a homogeneous ingot can be produced without causing non-uniformity of alloy components. However, the technology itself for producing a large ingot by this CCIM method is Currently, it is still in the development stage.

Conventionally, a manufacturing method described in Non-Patent Document 1 is known as a method for manufacturing a relatively large and long ingot by the CCIM method. In this manufacturing method, using a water-cooled copper crucible, a high-frequency current is passed through a high-frequency coil installed on the outer periphery thereof to inductively dissolve the alloy raw material supplied into the water-cooled copper crucible, and then the bottom of the water-cooled copper crucible is removed. This is a method for producing a large and long ingot by pulling downward. 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.

  Furthermore, in order to solve this problem, the inventors have controlled the supply rate of the melting raw material supplied from above and / or withdraw it downward while keeping the coil voltage of the high frequency coil at a constant value. By controlling the drawing speed of the ingot, the ingot is manufactured with the fluctuation range of the power value input when melting the molten raw material being used as the molten metal pool within a range of ± 5% of the predetermined power value. A method is proposed as Patent Document 3. When this manufacturing method was used to experimentally manufacture a large and long ingot, the occurrence of casting defects in the ingot was almost completely suppressed. It was confirmed that it was difficult to suppress the constricted defects formed on the surface of the ingot.

JP 2006-122920 A JP 2006-281291 A JP 2009-113064 A

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

  The present invention has been made as a solution to the above-mentioned conventional problems, and can suppress the occurrence of constricted defects formed on the surface of the ingot during initial operation, 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.

According to the first aspect of the present invention, the raw material supplied to the inside of the water-cooled copper crucible having the crucible bottom movable in the vertical direction is melted by induction heating with a high-frequency coil surrounding the water-cooled copper crucible. After making the molten metal pool and moving the crucible bottom downward, the molten metal pool on the bottom of the crucible is pulled out of the induction heating area by the high frequency coil and solidified from below to make the molten metal pool a predetermined capacity. The crucible is supplied to the inside of the water-cooled copper crucible from above with the additional charging material consisting of the rod-shaped melting raw material being melted from the lower end by induction heating by the high-frequency coil. The bottom is moved downward, and the molten pool is pulled out of the induction heating region, so that the molten pool is kept in a state where a predetermined capacity is maintained. By more coagulation, a process for the preparation of the ingot for manufacturing an ingot of long, the dissolution power immediately before immersing the lower end of the additional charging material consisting of the rod-shaped raw material for melting in the melt pool, the bar dissolution The ingot is manufactured with a power value in the range of 85% or more and less than 95% when the melting power in the steady state after the lower end of the additional charging raw material made of the raw material is immersed in the molten metal pool is 100%. It is a manufacturing method of the ingot which makes it.

  According to the method for producing an ingot of the present invention, it is possible to suppress the occurrence of constricted defects formed on the surface of the ingot during initial operation, and it is possible to stably produce a healthy large ingot.

It is a longitudinal cross-sectional view which shows the outline | summary of the method of manufacturing an ingot with the manufacturing method of this invention, and shows the state which supplied the initial stage raw material and formed the initial molten metal pool. It is a longitudinal cross-sectional view which shows the outline | summary of the method of manufacturing an ingot with the manufacturing method of this invention, and shows the state which supplies the additional charging raw material. It is a longitudinal cross-sectional view which shows the state by which the constriction defect and the double skin defect were produced | generated.

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

  The ingot 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 so as to be movable in the vertical direction 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 comprising a high-frequency coil 4 arranged so as to surround the periphery thereof.

The water-cooled copper crucible 2 constituting the cold crucible induction melting apparatus A is formed by combining a plurality of hollow shaft copper segments 7 in a cylindrical shape, and a circular copper crucible bottom 1 is disposed at the bottom. ing. Between the plurality of copper segments 7, 7,..., 0.05 to 2 mm slits 13 are provided, and these slits 13 are provided with yttria (Y ₂ O ₃ ) cement for electrical insulation. Alternatively, an insulating material such as 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 the upper and lower ends to some extent, and is connected to a high-power high-frequency power source 8. ing. The copper segment 7, the crucible bottom 1, and the high frequency coil 4 are each hollow, and cooling water is injected into the hollow interior. The crucible bottom 1 is connected to a drawing 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 drawn downward from the 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 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 first prepared. The melted raw material 3 includes, in the water-cooled copper crucible 2, a bulky initial raw material 3 a that is supplied at the initial stage of operation, and a plurality of pieces that are supplied into the water-cooled copper crucible 2 after the initial raw material 3 a is completely dissolved. There is an additional charging raw material 3b made of a rod-shaped melting raw material.

  First, the raw material 3a is supplied to the inside of the water-cooled copper crucible 2 in a state where the crucible bottom 1 with the bottom 10 serving as a starting material at the start of melting 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 and the initial raw material 3 a in the induction heating region by the high-frequency coil 4 are dissolved simultaneously. As shown in FIG. 2, the melted upper part of the bottom base 10 and the initial raw material 3 a form an initial molten metal pool 5.

  After the completion of melting, the crucible bottom 1 is moved downward, whereby the molten metal pool 5 on the crucible bottom 1 is drawn out of the induction heating region by the high frequency coil 4 and cooled and solidified from below to form the initial ingot 6. . In addition, the capacity | capacitance of the molten metal pool 5 left above the ingot 6 is a predetermined capacity | capacitance suitable for drawing out the molten metal pool 5 continuously out of an induction heating area | region when supplying the additional charging raw material 3b at the next process. And

  Next, if the crucible bottom 1 is gradually lowered downward, the molten metal pool 5 on the crucible bottom 1 is gradually drawn downward from the induction heating region by the high frequency coil 4 and is cooled from below to solidify. Start. In addition, since the solidification layer 12 is started in advance by water cooling from the outer surface in contact with the inner wall surface of the water-cooled copper crucible 2 in the molten metal pool 5, the molten metal pool 5 flows out even if it is pulled downward. There is no.

  If the molten pool 5 is simply pulled out of the induction heating area below, the capacity of the molten pool 5 in the water-cooled copper crucible 2 gradually decreases, so that the additional charged raw material 3b having a capacity commensurate with the extracted amount. Are gradually added from above and dissolved in order from the lower end. By the additional supply of the additional charging raw material 3b, the capacity of the molten metal pool 5 can be always kept constant. The portion solidified by this drawing becomes a long ingot 6. The additional charging raw material 3b supplied from above is, for example, a molten metal from the lower end side in a state where a plurality of rod-shaped melting raw materials are bundled and hung on a hanging mechanism 11 provided at the upper part of the vacuum chamber B. An amount corresponding to the amount of decrease in the pool 5 is gradually supplied.

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

  However, when a large and long ingot 6 is manufactured simply by the above manufacturing method, according to the manufacturing conditions, a constriction with a depth of 20 mm or more is formed on the surface of the ingot 6 as shown in FIG. There is a possibility that a surface defect such as a double defect f or a double skin defect b in which the molten metal flows into the deep constriction defect a and a deep solidified defect a. 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.

  On the other hand, when the ingot 6 is manufactured by an appropriate manufacturing method according to the present invention, serious defects such as irregularities and cracks are hardly generated on the surface, and even a TiAl-based alloy that is representative of an alloy material that easily breaks, Only a constricted defect a which is relatively minor (within a depth of 5 mm) and has no problem in use is generated, and the manufactured ingot 6 can be used as the ingot 6.

  In order to prevent the occurrence of solidification defects such as the deep constriction defect a, double skin defect b, and crack defect, it is indispensable to select an appropriate operation condition for melting and casting. If there is a problem in the operating conditions, the solidification state at the solidification interface may change abruptly, and the possibility of occurrence of solidification defects increases. In particular, if there is a change in input power or a change in the capacity of the molten pool 5 during the initial operation from the start of melting the initial charged raw material 3a to the supply of the additional charged raw material 3b, the shape of the molten pool 5 is directly affected. May cause solidification defects.

  In particular, when the ingot 6 is manufactured by the method of pulling out the ingot 6 using the cold crucible induction melting apparatus A, it is important to define the melting power at the initial operation so that no solidification defects occur. It can be said.

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

  When melting the melting raw material 3 (initial raw material 3a), which is a raw material for manufacturing a large ingot 6, by the cold crucible induction melting method, first, a high frequency current is applied to the high frequency coil 4 and the initial melting is performed. The molten raw material 3 is heated by the resistance heat generation of the induced current generated in the raw material 3, and the molten raw material 3 is melted by raising the heating temperature to the melting point (liquidus) of the molten raw material 3 or higher. Form. At that time, as shown in FIG. 2, in the molten metal pool 5, a magnetic force (indicated by a horizontal arrow) due to the 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 a position where the magnetic force and the static pressure of the molten metal are balanced, and the solidified layer 12 starts to be formed. It swells in the center due to electromagnetic force, and it has a violent flow such that the molten metal flows down the surface. As a result, a part of the molten metal comes into contact with the inner wall surface of the water-cooled copper crucible 2 above the above-described balance position, and the formed solidified layer 12 is elongated vertically, and the inner side surrounded by the solidified layer 12 In this state, the molten metal pool 5 is formed.

  In such a state, when the crucible bottom 1 of the water-cooled copper crucible 2 is moved downward, the molten metal pool 5 is drawn downward together with the solidified layer 12 formed on the surface layer. However, when a long solidified layer 12 is formed vertically, as shown in FIG. 3, a part of the solidified layer 12 on the surface layer is a slit provided between the copper segments 7 and 7 constituting the water-cooled copper crucible 2 13 (shown in FIG. 2), and when it is firmly fixed to the inner wall surface of the water-cooled copper crucible 2 (shown by a circle in FIG. 3), the fixed part is pulled down. There will be no. As a result, a tensile stress acts on the lower portion of the solidified layer 12, a crack is generated at the lower portion of the solidified layer 12, and the crack grows to form a large and deep constricted defect a. In particular, when the volume (capacity) of the molten metal pool 5 is large and deep, this effect is promoted, and it is considered that the probability of occurrence of the constricted defect a is further increased.

  In addition, as shown in FIG. 3, when the lower end of the additional charging raw material 3b is immersed in the molten metal pool 5, the melting power rises rapidly, and the solidified layer 12 formed in contact with the inner wall surface of the water-cooled copper crucible 2 is formed. It is considered that a constricted defect a occurs as a result of adverse effects. Moreover, since the possibility of the occurrence of the constriction defect a increases as the volume (capacity) of the molten metal pool 5 increases, even when the molten metal pool 5 formed initially by melting the initial raw material 3a is melted, it is dissolved. It is considered desirable to operate with low power.

  As described above, the constriction defect “a” is caused by the fact that the solidified layer 12 formed on the surface layer of the molten metal pool 5 is firmly fixed to the inner wall surface of the water-cooled copper crucible 2. Thus, a crack is generated, and the crack grows to form.

  Therefore, in order to prevent the occurrence of the constricted defect a, it is considered effective to reduce the region of the solidified layer 12 firmly fixed to the inner wall surface of the water-cooled copper crucible 2. The solidified layer 12 is also formed above the position where the magnetic force and the static pressure of the molten metal are balanced, and the frequency of cracks increases as the region becomes longer upward. In order to prevent the formation of the constricted defect a, the capacity of the molten metal pool 5 is reduced to prevent the solidified layer 12 from growing upward, and the solidification adhered to the inner wall surface of the water-cooled copper crucible 2. It is considered effective to reduce the area of the layer 12.

  In the case of the cold crucible induction melting method-gravity casting method when manufacturing a general large ingot 6, it is highly efficient to form a molten metal pool 5 as much as possible. The molten raw material 3 is charged so that the molten metal pool 5 exists in the entire height range of the high frequency coil 4.

  As described above, the shape of the molten metal pool 5 is a dome shape in which the center portion rises, but the volume (capacity) of the molten metal pool 5 is assumed to be a cylindrical shape inside the water-cooled copper crucible 2. It can be expressed using the height (h) of the pool.

  The volume (capacity) of the molten pool 5 used in the cold crucible induction melting method-gravity casting method when producing a general large ingot 6 is the height (h: unit mm) of the virtual molten pool and the high frequency. In the relationship with the total length (L: unit mm) of the coil 4, the range satisfies the formula 0.6 <h / L <0.9.

  However, in the cold crucible induction melting method-drawn casting method as in the present invention, if the capacity of the molten metal pool 5 is the same as that of the cold crucible induction melting method-gravity casting method, the inner wall surface of the water-cooled copper crucible 2 is used. The region of the solidified layer 12 to be attached becomes longer in the vertical direction, and the possibility that surface defects such as a constricted defect a and a double skin defect b are generated on the surface of the ingot 6 increases.

  Therefore, in the case of the cold crucible induction melting method-drawing casting method as in the present invention, reducing the region of the solidified layer 12 adhering to the inner wall surface of the water-cooled copper crucible 2 can cause surface defects on the surface of the ingot 6. Considering that it is effective as a countermeasure for preventing the generation, the test operation was actually performed by changing the volume (capacity) of the molten metal pool 5. As a result, in order to make it difficult to generate surface defects, when it is assumed that the molten metal pool 5 has a cylindrical shape inside the water-cooled copper crucible 2, the height (h: unit mm) of the virtual molten metal pool and the high frequency coil It was found that it is effective that the relationship of the total length (L) of 4 is in a range satisfying the mathematical formula of 0.15 <h / L <0.5.

  However, even if the operation is performed so that the volume of the molten metal pool 5 falls within a range that satisfies the formula of 0.15 <h / L <0.5, the actual volume of the molten metal pool 5 under various conditions ( (Capacity) may fluctuate. As a result of further investigations, it was found that the load amount of the melting power corresponding to the volume (capacity) of the molten metal pool 5 is greatly related to the surface quality of the ingot 6. In particular, if the melting power when melting the initial raw material 3a is too large, the shape of the initial molten pool 5 is greatly changed, and the region of the solidified layer 12 becomes longer in the vertical direction, thereby causing casting defects such as surface defects. It is more likely that it will be generated.

  In particular, the melting power required to immerse the lower end of the additional charging raw material 3b in the molten metal pool 5 only needs to be able to dissolve the initial charging raw material 3a having a smaller capacity compared to the additional charging raw material 3b. There is no problem even if the power value is somewhat lower than the melting power in a steady state after the lower end of the steel is immersed in the molten metal pool 5. Specifically, the melting power immediately before immersing the lower end of the additional charging raw material 3b in the molten metal pool 5 is 100% of the melting power at the steady state after the lower end of the additional charging raw material 3b is immersed in the molten metal pool 5. If it is controlled within the range of 85% or more and less than 95%, it is possible to suppress the occurrence of constriction defects formed during the initial operation.

  After the initial raw material 3a and the like are melted to form the initial molten pool 5, the bottom 1 of the crucible is moved downward, and when the molten pool 5 reaches a predetermined capacity, the additional charged raw material 3b is sequentially melted from the lower end. Charge the pool 5. The charging speed is controlled so as to melt by an amount commensurate with the amount with which the molten metal pool 5 is pulled out of the induction heating area, and the additional charging raw material 3b is continuously charged, but the melting power is added. When the lower end of the charging raw material 3b is immersed, it rises almost simultaneously. Therefore, in order to alleviate the overshoot, the melting power until the lower end of the additional charging raw material 3b is immersed in the molten metal pool 5 is as low as possible. It is necessary to keep it down.

  In this way, until the lower end of the additional charging raw material 3b is immersed in the molten metal pool 5, the melting power is kept as low as possible (controlled to a range of 85% or more and less than 95% when the melting power in the steady state is 100%), After the lower end of the additional charging raw material 3b is immersed in the molten metal pool 5, the ingot 6 is manufactured while adjusting the supply speed of the additional charging raw material 3b and the drawing speed of the ingot 6 as appropriate by using the melting power at the steady state. As a result, it was found that the occurrence of a neck defect formed during the initial operation can be suppressed, and the present invention has been completed.

Note that, as described in Patent Document 3, the ingot 6 is drawn out in a steady state while the supply power of the additional charging raw material 3b and the drawing speed of the ingot 6 are appropriately adjusted, and the melting power is controlled within a control range. If it is within the range of ± 5%, it is possible to suppress the occurrence of coagulation defects such as constriction defect a and double skin defect b associated with drawing.

  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. In the test, under the condition that the coil voltage is held at a constant value, the descending speed (charging speed) of the melting raw material is changed according to the fluctuation of the input power, or the ingot drawing is temporarily stopped. An ingot was produced. The basic specifications of the cold crucible induction melting apparatus used are as shown below.

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 over 7 turns, and its height is 256 mm. The water-cooled copper crucible is composed of 24 water-cooled copper segments assembled in a cylindrical shape and the crucible bottom attached to the drawing mechanism. Cooling water is flowing inside the water-cooled copper segment, the crucible bottom, etc., and the flow rate of the cooling water is 400 L / min. The internal volume of the vacuum chamber in which the cold crucible induction melting apparatus is accommodated is 10 m ³ .

  The material of the ingot to be manufactured was a TiAl-based alloy (Ti-30Al-3Cr-3V-4Mn alloy (mass%)), and the ingot was manufactured using a water-cooled copper crucible having an inner diameter of 250 mm.

  For the production of the ingot, a bottom plate made of an industrial pure titanium material that is a starting material at the start of melting is attached to the top surface of the crucible, and the top surface of the bottom plate is arranged at a position 5 to 20 mm above the lower end of the high-frequency coil. In this state, 20 to 25 kg of the initial material made of the same metal material as the ingot to be manufactured is charged into the inside of the water-cooled copper crucible.

  The additional charging raw material is made of the same metal material (Ti-30Al-3Cr-3V-4Mn alloy (mass%)) as the ingot as in the case of the initial loading raw material. A lump was used. Its diameter is 200 mm, its length is 1000 mm, and its mass is about 110 kg. In addition, this additional charging raw material is continuously supplied from the lower end to the inside of the water-cooled copper crucible while being suspended by a suspension mechanism provided at the upper part of the vacuum chamber.

First, the upper surface of the bottom plate was placed at the predetermined position described above, and the initial raw material was supplied into the water-cooled copper crucible. Next, the air inside the vacuum chamber was evacuated to 6.7 × 10 ⁻² Pa with a diffusion pump, 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 50 kW (10 minutes) → 200 kW (10 minutes) → 250 kW (10 minutes) → 350 kW (10 minutes) to dissolve the initial material and the upper part of the bottom plate, Formed a molten metal pool.

  Thereafter, the output is lowered and held for a certain time. At this time, as shown in Table 1, the melting power immediately before immersing the lower end of the additional charging raw material in the molten pool is set at the lower end of the additional charging raw material. When the melting power at steady state after being immersed in 100% is set to six power values in the range of 80% or more and 104%, the molten metal pool has a predetermined capacity by moving the crucible bottom downward Pulled out until. In addition, since the capacity | capacitance of the molten metal pool decreased and melting power changed with the start of drawing | extracting, it adjusted so that melting power might maintain a fixed electric power value.

  After confirming that the capacity of the molten pool reached a predetermined amount, the additional charged raw material suspended by the suspension mechanism was lowered downward and continuously charged into the molten pool from its lower end. In addition, pulling out downward of the molten metal pool was started at the same time so that the capacity of the molten metal pool was maintained at a predetermined amount. When the lower end of the additional charging raw material was immersed in the molten metal pool, as shown in Table 1, the melting power suddenly increased and the maximum power value was shown. This melting power may gradually decrease as the charging speed of the additional charging raw material is slow, and gradually decreases with the progress of drawing, but conversely, if the power value is high, the capacity of the molten metal pool decreases. When the value was low, the operation was carried out by adjusting the charging speed of the additional charging raw material and the drawing speed so as to increase the capacity of the molten metal pool. The test results are shown in Table 1.

  According to Table 1, the melting power immediately before immersing the lower end of the additional charging raw material in the molten metal pool is 96% compared with the melting electric power at normal time after the lower end of the additional charging raw material is immersed in the molten metal pool. In Comparative Examples 1 to 3 in which the power value is in the range of ˜105%, the fluctuation of the melting power (the highest power value is high) becomes large, and as a result, the occurrence of constricted defects in the ingot after drawing is recognized. It was. On the other hand, the electric power value of 80% is compared with the electric power for melting just before the lower end of the additional charged raw material is immersed in the molten metal pool and the electric power for melting after the lower end of the additional charged raw material is immersed in the molten metal pool. In Comparative Example 4, the solidification was observed on the surface of the molten metal pool, and the subsequent operation itself was not possible.

  On the other hand, the melting power immediately before immersing the lower end of the additional charging raw material in the molten metal pool is 85% or more in comparison with the melting electric power at normal time after the lower end of the additional charging raw material is immersed in the molten metal pool. In Invention Examples 1 and 2 having power values in the range of less than 95%, no constricted defects were observed in the ingot after drawing, and a good casting surface was exhibited.

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

Claims (1)

The raw material supplied to the inside of the water-cooled copper crucible formed so that the bottom of the crucible can move up and down is melted by induction heating with a high-frequency coil surrounding the water-cooled copper crucible to form a molten metal pool. The molten metal pool on the bottom of the crucible by moving downward is pulled out of the induction heating area by the high frequency coil and solidified from below, to make the molten metal pool a predetermined capacity,
The crucible bottom is supplied to the inside of the water-cooled copper crucible from above with the additional charging raw material consisting of a rod-shaped melting raw material being melted from the lower end by induction heating by the high frequency coil. Is moved downward, and the molten pool is pulled out of the induction heating region, so that the molten pool is solidified from below while maintaining a predetermined capacity to produce a long ingot. A method for producing an ingot, comprising:
The dissolution power immediately before the lower end of the additional charging material consisting of rod-dissolved material is immersed in the molten metal pool, the bar dissolution of additional charging material consisting of raw material lower end of the steady state after being immersed in the melt pool A method for producing an ingot, wherein the ingot is produced with an electric power value in a range of 85% or more and less than 95% when the melting power is 100%.