JP2011017482A - Method and device for removing inclusion in molten metal, and metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an easily executable method of removing inclusions capable of efficiently removing fine inclusions in molten metal which cannot be removed by floatation and filtration.SOLUTION: The method of removing the inclusions in the molten metal includes steps for applying a high-frequency electric current of a frequency fto an induction coil applying magnetic field to an induction heating melting furnace, melting and stirring the metal charged into a furnace body of the induction heating melting furnace, and then applying a high-frequency electric current of a frequency fdifferent from the frequency fto separate the inclusions in the molten metal.

Description

  The present invention relates to an inclusion removal method and an inclusion removal apparatus for removing inclusions in molten metal, and a metal material.

Due to the demand for high quality and high reliability of metal materials, it is indispensable to separate and remove inclusions in the melting and casting process of metal materials. Conventionally, techniques such as flotation separation and filtration have been put to practical use as a method for separating and removing inclusions in the melt casting process.
As a method for separating and removing inclusions by flotation separation, a method is generally used in which the inclusion is levitated and separated due to the density difference between the molten metal and the inclusion. However, in the current situation, inclusions of a minute size such as several tens of microns or less have a low flying speed and do not float. Further, in the method for separating and removing inclusions by filtration, the size of inclusions that can be captured is determined by the size of the pores of the filtration medium. Further, there is a lower limit to the actual pore size from the viewpoint of the amount of molten metal treatment and blockage, and the target fine inclusions cannot always be removed.

Therefore, various methods for capturing and removing inclusions in molten metal by moving them in a predetermined direction using electromagnetic force have been proposed as new technologies. For example, the following method has been proposed as a method of capturing inclusions using electromagnetic force.
Patent Document 1 discloses a method in which a ladle floats and separates by trapping or agglomerating the inclusions into the bottom by using an induction coil arranged at the bottom, or by flowing, in a ladle.
Patent Document 2 discloses a method of promoting floating separation of inclusions by applying a horizontal magnetic field to a molten metal and a current flow in a direction perpendicular thereto.
Patent Document 3 discloses a method in which, in continuous casting, a high-frequency magnetic field is applied to a nozzle or a hot top portion to trap inclusions on the inner wall of the nozzle or the hot top portion.
Non-Patent Document 1 describes the basic theory of a method for removing non-metallic inclusions in molten metal using an alternating magnetic field and a bundle of thin tubes.

  However, when the inclusion removal method using electromagnetic force is applied to the casting process on an industrial production scale, the removal effect is insufficient, there is a problem in the processing method of the trapped inclusions, and the device configuration is Due to the complexity and the like, various problems have occurred in the introduction into the actual casting process.

For example, in the method described in Patent Document 1, there is a problem that flow and separation are contradictory functions, and that efficient separation and removal is difficult.
Further, the method described in Patent Document 2 has a problem that the molten metal is agitated due to the problem of electrode consumption and the non-uniform electromagnetic force distribution, and the fine inclusions follow the flow and do not float.

  Further, in the method of Patent Document 3, since the nozzle generally has a very large flow velocity, the force of the molten metal to push the inclusions is stronger than the force of the electromagnetic force to move the inclusions to the wall surface. There was a problem that the inclusion removal efficiency was significantly reduced. Further, the flow velocity in the nozzle varies by adjusting the flow rate by a sliding gate or the like. At this time, the inclusions once trapped on the wall surface fall off and get caught in the molten metal again, and there is no means to capture the fallen inclusions again and flow into the mold as it is, and it is mixed into the ingot. There was also. Further, in the hot top portion, the skin thickness region of the high-frequency magnetic field is very small compared to the cross-sectional area in the mold, so that the inclusion removal efficiency is low even if the movement of inclusions due to the molten metal flow is taken into consideration. End up. In addition, there has been a problem that the trapped inclusions fall off due to fluctuations in the flow of molten metal in the mold and fluctuations in solidification conditions, or they are trapped in the solidified shell and caught in the ingot.

  Further, the method of Non-Patent Document 1 proposes a solution to the problem that when an alternating magnetic field is applied to the molten metal, the region where the electromagnetic force acts is limited to the surface portion of the molten metal due to the skin effect, and the removal efficiency decreases. ing. By using a non-conductive bundle of thin tubes, an alternating magnetic field acts on the molten metal in each flow path almost evenly, so that the proportion of the electromagnetic force acting area as a whole can be increased, and inclusions are removed. Efficiency is improved. However, when the inclusions accumulate in the thin tube bundle, it is necessary to replace the thin tube bundle, but this point is not considered at all. When such an apparatus is simply arranged in series with the molten metal flow path, there is a problem that it is very difficult to cope with a case where the flow path in the apparatus is blocked during continuous casting. Moreover, even if it is replaced at the time of casting stoppage, very large construction is required and the feasibility is poor. In order to introduce into an actual process, an installation method, an exchange method, and the like are important matters, and no proposal is made for them in this document.

JP 2001-011525 A JP-A-2-122011 Japanese Patent No. 3127736

Fumitaka Yamao, Kensuke Sasa, Kazuhiko Iwai, Shigeo Asai, “Iron and Steel”, 83 (1997) 1, p. 30

As described above, a method for removing inclusions in molten metal using an electromagnetic force that can be introduced into an actual process has not yet been established in the conventional melting and casting process of metal materials.
The present invention has been made to solve the above problems, and efficiently removes micro-inclusions that cannot be removed by flotation separation or filtration, and can be easily implemented and installed easily. It is an object of the present invention to provide an inclusion removal method, an inclusion removal apparatus, and a metal material with few inclusions.

That is, the present invention
(1) _A high frequency current having a frequency f _{A is} applied to an induction coil that applies a magnetic field to the induction heating melting furnace to melt and stir the metal charged in the furnace body of the induction heating melting furnace, and then the frequency f _A A method of removing inclusions in the molten metal, wherein a high frequency current having a frequency f _B different from the above is applied to separate the inclusions in the molten metal,
(2) _A high frequency current having a frequency f _{A is} applied to an induction coil that applies a magnetic field to the induction heating melting furnace to melt and stir the metal charged into the furnace body of the induction heating melting furnace, and then the frequency f _A A high frequency current having a frequency f _B different from that of the molten metal is added, and then a high frequency current having a frequency f _{A and} a high frequency current having a frequency f _B are alternately applied to separate inclusions in the molten metal. A method for removing inclusions in metal,
(3) When a high-frequency current having the frequency f _A (Hz) is applied, the power P _A (kW) applied to the metal in the furnace body of the induction heating melting furnace satisfies the following formula 1. (1) or the method for removing inclusions in molten metal according to (2),

(In the formula, D represents the crucible inner diameter (m) of the furnace body of the induction heating melting furnace),
(4) When a high-frequency current having the frequency f _B (Hz) is applied, the power P _B (kW) applied to the metal in the furnace body of the induction heating melting furnace satisfies the following formula 2. (1) or the method for removing inclusions in molten metal according to (2),

(In the formula, D represents the crucible inner diameter (m) of the furnace body of the induction heating melting furnace),
(5) The removal of inclusions in molten metal according to any one of (1) to (4), wherein the frequency f _B is 2 to 10 times the frequency f _A Method,
(6) A furnace body of a crucible type induction heating melting furnace, an induction coil surrounding the furnace body, and a high frequency that generates a high frequency current having a frequency f _A for generating a magnetic field for melting and stirring the metal in the furnace body. A generator (A), and a high-frequency generator (B) for generating a high-frequency current having a frequency f _B different from the frequency f _A for generating a magnetic field for separating inclusions in the melted metal, Inclusion removal in molten metal, wherein the high-frequency generator (A) and the high-frequency generator (B) are connected to the induction coil via a switching circuit that can be switched to either one apparatus.
(7) The switching circuit operates so as to connect the high-frequency generator (A) and the high-frequency generator (B) to the induction coil alternately. Inclusion removal device in molten metal,
(8) The inclusion removal apparatus for molten metal according to (6) or (7), wherein the frequency f _B is 2 to 10 times the frequency f _A.
(9) A metal ingot obtained from a molten metal from which inclusions have been removed by the method for removing inclusions in molten metal according to any one of (1) to (5) is formed by plastic working. Metal material.

In the present invention, the inclusion is an undissolved component element constituting the alloy, oxides, carbides, sulfides, other compounds, unavoidable impurities, etc. of the component elements, which are mixed in the ingot in subsequent processing steps. Those that cause a hindrance to sound processing and those that cause deterioration of various performances in the final product.
In the present invention, the high frequency means a frequency higher than 50 Hz, but is preferably higher than the commercial frequency (50 Hz or 60 Hz) of the commercial power source used.

According to the present invention, in an existing crucible type induction heating and melting furnace, by adding a high-frequency generator having an appropriate frequency higher than the existing frequency, it is possible to perform molten metal cleaning that also removes minute inclusions. As a result, a clean ingot with few inclusions can be obtained. The metal material obtained from the ingot is a high quality material with very few inclusions.
Further, in the method of the present invention, inclusions are floated and separated, so that they are easy to remove, and no inclusion capturing member or the like is required, so that consumption and replacement are not necessary.

It is explanatory drawing of one preferable embodiment of the inclusion removal method in the molten metal of this invention. 5 is a graph in which test results in Reference Example 1 are arranged.

  When an alternating magnetic field is applied to the molten metal, an electromagnetic force in the direction toward the center of the molten metal acts due to the interaction between the induced current and the magnetic field within the skin thickness of the surface of the molten metal. Molten metal inclusions are, for example, non-metallic inclusions such as oxides, sulfides, and carbides, and generally have a lower electrical conductivity than the molten metal. Therefore, the direction of the electromagnetic force acting on the molten metal as a reaction is reversed. Will move in the direction. Hereinafter, the force acting on the inclusion in this way is referred to as electromagnetic separation force. By using electromagnetic separation force, inclusions can be moved and captured in a predetermined direction.

  However, as described above, the range in which the electromagnetic separation force acts is limited to a certain region of the molten metal surface layer, so that the inclusion removal efficiency can be improved when the furnace inner diameter is much larger than the skin thickness as in a crucible melting furnace. Is remarkably low. Furthermore, generally in a crucible induction heating melting furnace, the molten metal is agitated by electromagnetic force, so the force to move inclusions by the molten metal flow (hereinafter referred to as separation inhibiting force by flow) is superior to the electromagnetic separation force and inclusions. Are not separated. In the present invention, with respect to the molten metal, a high frequency frequency for the purpose of separating inclusions and a high frequency frequency for the purpose of stirring are used, and preferably by repeating alternately, any location in the molten metal. It is also possible to realize removal by inclusion, movement, aggregation, and flotation separation. As a result, the molten metal can be purified, a good quality ingot with few inclusions can be obtained, and inclusion defects in the product can be reduced.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory view of a preferred embodiment of the method for removing inclusions in molten metal of the present invention. In FIG. 1, 1 is a furnace body (crucible) of an induction heating melting furnace, 2 is an induction coil, 3 is a high frequency generator (A), 4 is a high frequency generator (B), and 5 is a switch (switching device).
Further, the furnace body 1 as a holding container and the annular induction coil 2 surrounding the furnace body constitute a crucible type induction heating type melting furnace similar to the conventional one. In FIG.

The high frequency f _A generated by the high frequency generator (A) 3 is preferably selected from the range of 100 Hz to 5000 Hz, more preferably from the range of 300 Hz to 3000 Hz. The high frequency of the frequency _{f B} generated by the high-frequency generator (B) 4 is different from the frequency of the frequency _{f A} generated by the high-frequency generator (A) 3, 2 to 10 times the frequency _{f A} It is preferably 3 to 7 times.
As the high-frequency generator used in the present invention, a normal high-frequency generator that is connected to an AC power source and can apply an AC current whose frequency, voltage, and current are controlled can be used.

The switch 5 switches the high frequency generator connected to the induction coil 2 via a circuit, and is connected to the high frequency generator (A) 3 and is generated in the initial state as shown by the solid line in FIG. After the metal raw material charged into the furnace body 1 of the induction heating melting furnace is melted and stirred by the high frequency magnetic field to become the molten metal 6, the metal raw material is switched as shown by the broken line to the high frequency generator (B) 4 side. Connected.
The switch 5 is preferably controlled so that the high-frequency generator connected to the induction coil 2 is alternately switched between the high-frequency generator (A) 3 and the high-frequency generator (B) 4.

  The frequency of the high frequency current generated by the high frequency generator (A) 3 is a frequency whose primary purpose is efficient melting in the induction heating melting furnace. For example, the frequency of said preferable range is mentioned, In a general high frequency induction heating melting furnace, it is often several hundred Hz-several kHz according to the melting scale. At this frequency, the main purpose is to carry out efficient heating of the material to be heated and appropriate stirring of the molten metal, and it is not intended to actively separate and remove inclusions in the molten metal. .

  The frequency of the high frequency current generated by the high frequency generator (B) 4 is a frequency whose primary purpose is electromagnetic separation of inclusions in the molten metal. In the electromagnetic separation, the force acting on the inclusions due to the molten metal flow in the stirring becomes an inhibition force of the electromagnetic separation, so that the inclusions cannot be separated in the state where the molten metal is strongly stirred. The higher the frequency, the lower the stirring force, but the smaller the skin thickness, the less the amount of inclusions that can be separated. From the viewpoint of securing a large skin thickness while suppressing the stirring force to some extent, a frequency in the above preferable range, for example, optimal for electromagnetic separation is selected.

  According to the method of the present invention, the high-frequency generator (A) 3 is used to efficiently dissolve the metal and the molten metal is stirred, and the high-frequency generator (B) 4 is used to improve the efficiency of inclusions in the molten metal. It is possible to realize the cleaning of the molten metal by performing a general separation.

  According to the method of the present invention, when the high frequency generator (B) 4 is used, the molten metal flow due to the electromagnetic force is small, so that the separation inhibiting force due to the flow is small. Therefore, inclusions present in the skin thickness region are separated and aggregated in the furnace wall. Further, although there is a certain amount of flow even though the molten metal flow is small, some of the inclusions existing outside the skin thickness region enter the skin thickness region, separate, and agglomerate following the molten metal flow. If the inclusions separated and aggregated on the furnace wall adhere firmly to the furnace wall, they remain attached to the furnace wall even after the molten metal in the furnace has been tapped. Can be removed. When discharged to the outside of the furnace together with the molten metal discharged without adhering to the furnace wall, it can be removed by means such as filtration with a filter in the tundish.

  Next, when the high-frequency generator (A) 3 is used again, since the molten metal flow is large, the separation inhibition force due to the flow is superior to the electromagnetic separation force, and the inclusions are not easily separated into the furnace wall. Inclusions already separated into the furnace wall when using the high-frequency generator B remain on the furnace wall when the adhesion to the furnace wall is strong. However, in many cases, the adhesive force is weak and leaves the furnace wall. However, since the inclusions once separated on the furnace wall are agglomerated and coarsened, they are easily levitated and separated even if they are separated from the furnace wall and re-wound into the molten metal.

  By alternately using the high-frequency generator (A) 3 and the high-frequency generator (B) 4 for the molten metal, inclusions present at any location in the molten metal can be added to the furnace wall. After being separated, it is separated and floated and separated, and for example, it can be removed by means such as scraping out slag on the surface of the molten metal.

  As described above, the frequency of the high frequency generator (B) 4 is a frequency whose primary purpose is electromagnetic separation of inclusions in the molten metal. It is preferable that the frequency is in a range suitable for electromagnetic separation, in which a large skin thickness is ensured while suppressing the stirring force with respect to the frequency of the high-frequency generator A for melting the metal and stirring the molten metal.

In the present invention, from the viewpoint of efficient metal melting and molten metal stirring, when a high-frequency current of frequency f _A (Hz) is applied, D is the inner diameter of the crucible of the furnace body of the induction heating melting furnace ( m), the power P _A (kW) applied to the metal in the furnace body preferably satisfies the following formula 1.

In addition, when a high frequency current having a frequency f _B is applied, it is preferable that the electric power P _B applied to the molten metal satisfies the following formula 2 in order to efficiently perform electromagnetic separation of inclusions in the molten metal.

The metal ingot obtained from the molten metal from which inclusions have been removed by the inclusion removal method of the present invention is plastically processed by any method to form various high-quality metal materials with few inclusions. Can do.
Moreover, the raw material metal which can use the inclusion removal method of this invention is not specifically limited, However, It can use suitably for a copper alloy, an aluminum alloy, etc.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to this.

（Ｄはるつぼ径（ｍ）、Ｆは周波数（Ｈｚ）を示す）であり、分離を○、非分離は×で示した。本例において、好ましい分離条件を示す境界線としてｙ＝５ｘおよびｙ＝ｘが導き出された。すなわち、本例では、ｘ＜ｙ＜５ｘに示される出力範囲ｙにおいては分離が良好に進行することが分かった。また、本例ではｙ＝５ｘで示される出力範囲より大きい条件では溶融金属の攪拌力が大きいために分離が進行しにくいことがわかった。 Reference example 1
Using a melting furnace X with a crucible diameter = 80 mm, frequency = 1, 10, and 30 kHz and a melting furnace Y with a crucible diameter = 280 mm, frequency = 1 kHz, each was tested for the case where the electric power P applied to the molten metal was changed. . Oxygen-free copper is dissolved in the crucible, and about 20 micron chromium carbide particles are dispersed in the molten copper by 1.0 mass%, and then a high frequency current is applied to the induction coil to solidify the sample in the crucible. A horizontal section at the center was observed. When the horizontal cross-section is observed, particles are accumulated on the crucible wall surface, and the state where the central area and the peripheral area in contact with the crucible wall surface are in different colors is `` separated '', and the case where particle accumulation is not observed is "Non-separated". The graph which arranged a series of test results is shown in FIG. In FIG. 2, the vertical axis y is power P (kW), and the horizontal axis x is

(D indicates the diameter of the crucible (m), F indicates the frequency (Hz)), separation is indicated by ○, and non-separation is indicated by ×. In this example, y = 5x and y = x were derived as boundary lines indicating preferable separation conditions. In other words, in this example, it was found that separation proceeds well in the output range y indicated by x <y <5x. Further, in this example, it was found that the separation is difficult to proceed because the stirring power of the molten metal is large under conditions larger than the output range indicated by y = 5x.

Reference example 2
Using an induction heating melting furnace having a crucible inner diameter = 80 mm, the relationship between the applied frequency and the presence or absence of separation of inclusions in the molten copper into the furnace wall was tested. Using chromium carbide particles having a diameter of about 20 μm as inclusions, 1 mass% of chromium carbide particles were dispersed in 4 kg of molten copper, and the state in which chromium carbide particles were separated to the furnace wall at various frequencies was observed. In the test method, a high-frequency magnetic field having the same predetermined frequency as that used for dissolution was applied to molten copper in which chromium carbide particles were dispersed for 60 seconds, and then solidified by natural cooling. With respect to the obtained cylindrical solidified product, an arbitrary longitudinal section including the central axis was examined, and in particular, a portion in contact with the furnace wall was investigated in detail. The induction frequency of the induction heating melting furnace is 3 kHz.
When a high frequency magnetic field of 5 kHz was applied to the molten copper in which chromium carbide particles were dispersed, chromium carbide particles were separated from the furnace wall, but the particles were accumulated on a very small part of the furnace wall. No accumulation of particles was observed in the part. This is because the separation inhibiting force due to the molten metal flow is large. At 10 kHz, particle accumulation on most of the furnace wall due to separation was observed. Separation (accumulation) was also observed at 15 kHz and 20 kHz. Although separation was observed even at 30 kHz, the thickness of the particle accumulation portion due to separation was very thin. This is because as the frequency increases, the skin thickness decreases and the separation efficiency decreases significantly. From the above, it was found that the frequency suitable for electromagnetic separation is preferably 2 to 10 times the frequency for dissolution, and more preferably 3 to 7 times.

Comparative Example 1
In a crucible type induction heating melting furnace with a crucible diameter = 80 mmφ, two induction generators of 3 kHz and 10 kHz were installed in the induction coil in a circuit that can be switched to either one. A Cu-0.25 mass% Cr alloy was used as a material to be heated, and normal dissolution was performed at 3 kHz to quantitatively evaluate oxide inclusions in the molten metal. In the Cu-0.25 mass% Cr alloy, Cr is an easily oxidizable element, so chromium oxide is generated in the molten metal and becomes a harmful inclusion. The amount of chromium oxide can be quantitatively evaluated by oxygen analysis of the molten metal sample.
That is, in a crucible type induction heating melting furnace with a crucible diameter = 80 mmφ, a high frequency magnetic field of 3 kHz is applied, 4 kg of Cu-0.25 mass% Cr alloy in the furnace is melted, and oxygen analysis of a sample taken from a homogeneous portion of the molten metal is performed. went.
The sample of the molten metal was collected using a known pin sampler, and immediately after sampling, the sample was immediately cooled with water to obtain a rod-shaped solidified sample. Five molten metal samples were collected, an analysis sample was cut out from each sample and analyzed, and an average value of the five data was calculated.
The results are shown in Table 1.

Example 1
A melt of Cu-0.25 mass% Cr alloy was prepared in the same manner as in Comparative Example 1 except that 10 kHz-25 kW was applied for 60 seconds after the metal was melted at 3 kHz, and the amount of oxide inclusions in the melt was determined. Evaluation was performed. The results are shown in Table 1.

Example 2
A Cu-0.25 mass% Cr alloy was prepared in the same manner as in Comparative Example 1 except that the metal was melted at 3 kHz and then repeatedly applied 10 times at 10 kHz-25 kW for 10 seconds and 3 kHz-25 kW for 10 seconds continuously. A molten metal was prepared and quantitative evaluation of oxide inclusions in the molten metal was performed. The results are shown in Table 1.

Comparative Example 2
In a crucible type induction heating and melting furnace with a crucible diameter of 900 mmφ, two induction generators of 500 Hz and 3 kHz are installed in the induction coil with a circuit that can be switched to either one, and 6 tons of Cu-0.25 mass% Cr alloy is installed. The oxygen analysis of the sample which melt | dissolved at 500 Hz-1000 kW and extract | collected from the molten metal homogeneous part was performed.
The above oxygen analysis results are shown in FIG. The sample of the molten metal was collected using a known pin sampler, and immediately after sampling, the sample was immediately cooled with water to obtain a rod-shaped solidified sample. Five molten metal samples were collected under each condition, and samples for analysis were cut out from each sample and analyzed, and an average value of five data was calculated. The results are shown in Table 1.

Example 3
The Cu-0.25 mass% Cr alloy was the same as Comparative Example 2 except that the Cu-0.25 mass% Cr alloy was dissolved and then 3 kHz-150 kW for 30 seconds and 500 Hz-150 kW for 30 seconds were repeated continuously 5 times. A molten metal was prepared, and quantitative evaluation of oxide inclusions in the molten metal was performed. The results are shown in Table 1.

  As is clear from the data shown in Table 1, compared to the comparative example in which only normal melting was performed, in the example in which the inclusion separation frequency different from the melting frequency was used for the molten copper, The amount of chromium oxide inclusions represented by the average oxygen concentration of the molten copper was reduced. In particular, in Examples 2 and 3 in which the frequency for dissolution and the frequency for separating inclusions were repeated, the amount of chromium oxide inclusions in the molten copper was very small, Copper cleaning was realized.

DESCRIPTION OF SYMBOLS 1 Furnace body of induction heating melting furnace 2 Induction coil of induction heating melting furnace 3 High frequency generator (A)
4 High frequency generator (B)
5 Switch (switching device)
6 Molten metal

Claims (9)

_A high frequency current of frequency f _{A is} applied to an induction coil that applies a magnetic field to the induction heating melting furnace to melt and stir the metal charged in the furnace body of the induction heating melting furnace, and then different from the frequency f _A A method for removing inclusions in molten metal, comprising applying a high-frequency current having a frequency f _B to separate inclusions in the molten metal. _A high frequency current of frequency f _{A is} applied to an induction coil that applies a magnetic field to the induction heating melting furnace to melt and stir the metal charged in the furnace body of the induction heating melting furnace, and then different from the frequency f _A In the molten metal, a high-frequency current having a frequency f _B is applied, and then a high-frequency current having a frequency f _{A and} a high-frequency current having a frequency f _B are alternately applied to separate inclusions in the molten metal. Inclusion removal method. The electric power P _A (kW) applied to the metal in the furnace body of the induction heating melting furnace when the high frequency current of the frequency f _A (Hz) is applied satisfies the following formula 1. Or the inclusion removal method in the molten metal of Claim 2.

(In the formula, D represents the crucible inner diameter (m) of the furnace body of the induction heating melting furnace) The electric power P _B (kW) applied to the metal in the furnace main body of the induction heating melting furnace when the high frequency current of the frequency f _B (Hz) is applied satisfies the following formula 2. Or the inclusion removal method in the molten metal of Claim 2.

(In the formula, D represents the crucible inner diameter (m) of the furnace body of the induction heating melting furnace) The frequency f _B is characterized by 2 to 10 times the frequency of the frequency f _A, inclusions method for removing molten metal according to any one of claims 1 to 4. A furnace body of a crucible type induction heating melting furnace, an induction coil surrounding the furnace body, and a high frequency generator for generating a high frequency current having a frequency f _A for generating a magnetic field for melting and stirring the metal in the furnace body ( A) and a high-frequency generator (B) for generating a high-frequency current having a frequency f _B different from the frequency f _A for generating a magnetic field for separating inclusions in the melted metal, the high-frequency generation The inclusion removal apparatus for molten metal, wherein the apparatus (A) and the high-frequency generator (B) are connected to the induction coil via a switching circuit that can be switched to either one.   The said switching circuit operates to connect the said high frequency generator (A) and the said high frequency generator (B) to the said induction coil alternately, The molten metal in molten metal of Claim 6 characterized by the above-mentioned. Inclusion removal device. The frequency f _B is characterized in that said 2-10 times the frequency of the frequency f _A, inclusions apparatus for removing molten metal according to claim 6 or claim 7.   A metal formed by plastic working a metal ingot obtained from a molten metal from which inclusions have been removed by the method for removing inclusions in molten metal according to any one of claims 1 to 5. material.

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