JP2017031463A - Production method of water atomization metal powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of water atomization metal powder capable of securing cooling speed which is required for amorphization by avoiding reduction of cooling speed due to formation of a steam film generated on each droplet of molten metal being divided by a water atomization method, and producing at low cost, atomization metal powder having a high amorphization ratio.SOLUTION: A production method of water atomization metal powders 11 is configured to: jet high pressure water 8 to a molten metal stream 6 which flows down; then divide the molten metal stream 6 for making water atomization metal powders 11. In the production method, each droplet 9 of the molten metal 6 which is divided and in a midway of falling is made to collide with a rotary disk 10 which rotates at peripheral speed equal to or higher than falling speed of each droplet during collision, at a position where a temperature is in a range of a coagulation start temperature of each droplet 9 to coagulation start temperature+50°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a metal powder (hereinafter also referred to as a water atomized metal powder) by a water atomization method, and more particularly to an improvement in the amorphization rate of the water atomized metal powder.

  In recent years, from the viewpoint of energy saving, for example, a reduction in iron loss and a reduction in size of a motor core used in an electric vehicle or the like has been demanded. Conventionally, a motor core has been manufactured by laminating electromagnetic steel plates, but recently, a motor core produced by compression molding metal powder (electromagnetic iron powder) having a high degree of freedom in shape design has attracted attention. In order to reduce the iron loss of such a motor core, it is necessary to reduce the iron loss of the metal powder used. In order to obtain a metal powder with low iron loss, it is one effective means to make the metal powder amorphous. In addition, it is necessary to improve the magnetic flux density of the metal powder in order to reduce the size and weight.

  On the other hand, as a method for producing metal powder, an atomizing method is known in which a molten metal flow is divided by some means to obtain metal powder. In this atomizing method, mainly, a water atomizing method for obtaining metal powder by injecting high-pressure water into a molten metal flow and dividing the molten metal flow, and injecting an inert gas instead of high-pressure water. There are two types of gas atomization methods.

  Compared to the gas atomization method, the water atomization method has advantages that are suitable for mass production of metal powders in terms of productivity and manufacturing cost, and the obtained powder shape has an atypical shape, so that the gas atomization close to a true spherical shape is achieved. Compared to powder, powders are more likely to be entangled during heat molding, and the strength after molding and compactability are stable.

  However, compared with the gas atomization method in which the molten metal is divided by injecting an inert gas or the like, the water atomization method has a water film or a water vapor film on the surface of the metal powder (droplet) containing the molten state after being divided with high-pressure water. Is formed. For this reason, the interface between the metal powder (droplet) partially containing the molten state and the cooling water becomes a film boiling state that prevents direct contact, making it difficult to increase the cooling rate of the metal powder (droplet) including the molten state. Among the amorphous materials, the heteroatomized material with a high proportion of Fe composition developed in recent years and the amorphous forming ability is low, nanocrystalline material, or powder containing a lot of amorphous material as a raw material of these materials is a water atomization method There was a problem that it was difficult to manufacture with.

  For this reason, the gas atomization method is conventionally used as a method for producing an amorphous metal powder that has a low amorphous forming ability and needs to be solidified from a molten state at a high cooling rate, such as an iron-based amorphous powder. Technology based on it has been developed. For example, in Patent Document 1, a refrigerant is supplied to the surface of a rotating disk to form a liquid film of the refrigerant, and intermediate particles obtained by primary pulverization of molten metal by a gas atomization method are applied to the liquid film on the rotating disk. A method for producing an amorphous soft magnetic alloy powder that is rapidly cooled while being pulverized is disclosed. Patent Document 2 discloses a primary pulverization step in which molten metal flowing down from a nozzle is first pulverized by high-pressure inert gas to obtain primary pulverized particles, and rotated at a peripheral speed of 400 m / s to 800 m / s. A step of causing the primary pulverized particles to collide with the disk on which the refrigerant film of the first refrigerant liquid is formed on the surface to perform secondary pulverization and quenching to obtain secondary pulverized particles; And further cooling the secondary pulverized particles released around the disk together with the refrigerant liquid with a refrigerant film of a second refrigerant liquid formed around the disk. A method is disclosed.

  Patent Document 3 discloses a metal powder manufacturing apparatus that can efficiently manufacture an amorphous metal powder having a larger particle size. The metal powder manufacturing apparatus described in Patent Document 3 includes a supply unit that supplies molten metal, and a liquid ejecting unit that includes a flow path through which the molten metal can pass and an orifice that ejects liquid into the flow path. , A traveling direction changing means for forcibly changing the traveling direction of the dispersion liquid is provided below the liquid ejecting unit, and the molten metal is brought into contact with the liquid ejected from the orifice, so that the molten metal is converted into a large number of fine droplets. The liquid droplets are divided and transferred as a dispersion in which the droplets are dispersed in a liquid, and the droplets in the dispersion are cooled and solidified to produce an amorphous metal powder. The traveling direction changing means has a nozzle that ejects the second liquid and ejects the second liquid from the nozzle toward the dispersion liquid to collide, or the middle in the longitudinal direction is curved on an arc. And a means for forcibly changing the traveling direction of the dispersion along the inner wall surface of the curved portion, thereby ensuring a vapor layer formed around the powder. It can be separated and can cool a large number of powders evenly.

In addition, as an example of an alloy composition serving as a starting material for obtaining an Fe-based nanocrystalline alloy having a high saturation magnetic flux density and excellent soft magnetic properties, for example, Patent Document 4 discloses an amorphous phase as a main phase. in formula has a _{Fe a B b Si c P x} C y Cu z, a: 79~86at%, b: 5~13at%, c: 0~8at%, x: 1~8at%, y The alloy composition is described as follows: 0-4 at%, z: 0.4-1.4 at%. This alloy composition has an amorphous phase as a main phase, and exhibits a nanoheterostructure composed of an amorphous phase and initial microcrystals present in the amorphous phase. Moreover, when heat-treating these alloy compositions, nanocrystals composed of bccFe phases can be precipitated, and Fe-based nanocrystal alloy powders having a high saturation magnetic flux density can be obtained.

Patent Document 5 discloses an alloy composition of the composition formula Fe _{(100-X—Y—Z)} B _X P _Y Cu _Z whose main phase is an amorphous phase, and X, Y, and Z are 100-X—. An alloy composition satisfying YZ: 79 to 86 at%, X: 4 to 13 at%, Y: 1 to 10 at%, and Z: 0.5 to 1.5 at% is described. In this alloy composition, a part of Fe may be substituted with one or more elements of Co and Ni. Fe element is an element responsible for magnetism, and it is preferable to increase the proportion of Fe element to improve the saturation magnetic flux density. This alloy composition has an amorphous phase as a main phase, and can also be made into an alloy powder exhibiting a nanoheterostructure consisting of an amorphous phase and initial microcrystals present in the amorphous phase. And when heat-treating these alloy compositions, it is said that nanocrystals consisting of bccFe phase can be precipitated, and Fe-based nanocrystal alloy powder with high saturation magnetic flux density can be obtained.

Although not in the powder, as an amorphous alloy composition, for example, Patent Document 6, an amorphous alloy composition _{Fe a B b Si c P x} Cu y, a: 73~85at%, b: 9.65~ An alloy composition in which 22 at%, b + c: 9.65 to 24.75 at%, x: 0.25 to 5 at%, y: 0 to 0.35 at%, y / x: 0 over 0.5 is described.

Although not in the powder, as an amorphous alloy composition, Patent Document 7, an amorphous alloy composition _{Fe a B b Si c P x} Cu y, a: 73~85at%, b: 9.65~22at %, B + c: 9.65 to 24.75 at%, x: 0.25 to 5 at%, y: 0 to 0.35 at%, and y / x: 0 to 0.5 at%.

JP 2010-209409 A JP2013-55182A JP 2007-291454 A Japanese Patent No. 4584350 Japanese Patent No. 4815014 Japanese Patent No. 4288687 Japanese Patent No. 4310480

  However, in the technique described in Patent Document 1 or 2, since metal powder is manufactured using the gas atomization method, a large amount of inert gas is required for atomization, resulting in an increase in manufacturing cost. was there.

  Further, in the technique described in Patent Document 3, the dispersion liquid whose traveling direction is forcibly changed by the traveling direction changing means is removed from the vapor film, but when the dispersion liquid temperature is high, it exists in the surroundings. There is a possibility that a vapor film is formed again due to the moisture to be formed. On the other hand, when the temperature of the dispersion liquid is low, there is a problem that crystallization proceeds by solidification by the second liquid from the traveling direction changing means.

  The present invention has been made in view of the above-described problems, and is made amorphous by avoiding a decrease in cooling rate due to formation of a vapor film generated in molten metal droplets divided by a water atomization method. It is an object of the present invention to provide a method for producing a water atomized metal powder that can secure a necessary cooling rate and can produce an atomized metal powder having a high amorphization rate at a low cost.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on a method for producing atomized metal powder in which droplets separated by a water atomization method collide with a rotating disk.

  In the method combining the gas atomizing method and the rotating disk described in Patent Document 1 or 2, since the molten metal flow is divided by the high-pressure gas, the divided droplets are not covered with the vapor film, and the rotating disk is not covered. A sufficient cooling rate to obtain an amorphous metal powder upon collision is obtained. On the other hand, in the water atomization method, the divided droplets are covered with a vapor film of high-pressure water, and a sufficient cooling rate cannot be obtained when the droplets collide with the rotating disk. Therefore, as a result of investigating a method for improving the cooling rate of the liquid droplet colliding with the rotating disk, the temperature of the liquid droplet when the rotating disk collides is controlled within the range of the solidification start temperature of the liquid droplet to the solidification start temperature + 50 ° C. As a result, it was found that the water vapor film covered with the droplets can be removed and the cooling rate when colliding with the rotating disk is improved.

The present invention has been completed by further studies based on such findings, and the gist of the present invention is as follows.
(1) In the method for producing water atomized metal powder, high pressure water is sprayed onto a falling molten metal stream, and the molten metal stream is divided to form a water atomized metal powder. A method for producing a water atomized metal powder, wherein the droplet is caused to collide with a rotating disk at a position within a range of solidification start temperature to solidification start temperature + 50 ° C.
(2) The method for producing water atomized metal powder according to (1), wherein the rotating disk is rotated at a peripheral speed equal to or higher than a dropping speed of the droplet when colliding with the rotating disk.
(3) The method for producing a water atomized metal powder according to (1) or (2), wherein a refrigerant film is formed by a refrigerant liquid on a surface of the rotating disk.
(4) The method for producing a water atomized metal powder according to any one of (1) to (3), wherein a ratio between the flow rate of the high-pressure water and the flow rate of the molten metal flow is 5 or more.
(5) The molten metal is an Fe-based soft magnetic alloy composition or an Fe-based soft magnetic alloy composition in which a part of Fe is replaced with Ni and / or Co, and is the total amount of Fe, Fe, Ni, and Co The method for producing a water atomized metal powder according to any one of (1) to (4), wherein the alloy composition has an Fe-based element ratio of more than 82.5 at% and less than 86 at%.
(6) The method for producing a water atomized metal powder according to (5), wherein the water atomized metal powder is further subjected to a heat treatment for heating to a temperature within a range of 400 to 500 ° C.
(7) A water atomized Fe-based soft material produced by the method for producing a water atomized metal powder according to (5), having an average particle size of 5 μm or more and an amorphous ratio of 85% or more. Magnetic alloy powder.
(8) A water atomized Fe-based soft magnetic alloy powder, which is a water atomized metal powder produced by the method for producing a water atomized metal powder according to (6) and has a nanocrystalline structure.

  According to the present invention, an amorphous powder having a composition in which the proportion of Fe (including Ni and Co in which part of Fe is substituted) -based element ratio, which has been difficult by the conventional water atomization method, exceeds 82.5 at%, It becomes possible to manufacture by the atomizing method, and it becomes possible to mass-produce metal powder having a composition exhibiting excellent performance as a soft magnetic material at low cost. Therefore, it greatly contributes to the recent trend of resource saving and energy saving such as miniaturization of transformers and reduction of motor loss.

It is explanatory drawing which shows the manufacturing method of this invention typically.

  An example of an embodiment of the present invention is schematically shown in FIG.

  A molten metal 2 having a predetermined component produced in the melting furnace 1 is poured into a molten metal holding container 4 installed at the top of the spray tank 3 and dropped as a molten metal stream 6 from a molten metal nozzle 5 at the bottom. A high-pressure water injection nozzle 7 is installed around the dropping path of the molten metal flow 6, and the molten metal flow 6 is divided into droplets 9 by the high-pressure water 8 injected from the high-pressure water injection nozzle 7. The droplet 9 collides with the surface of the rotating disk 10 disposed below the dropping path, and is blown off by the centrifugal force in the radial direction of the rotating disk 10 to become the water atomized metal powder 11, and is slurryed on the spray tank bottom 12. It accumulates and is recovered from the recovery valve 13.

  The rotating disk 10 only needs to have a strength that is not broken by the centrifugal force due to the rotational peripheral speed within the range of the present invention. For example, the rotating disk 10 is made of a metal material (such as stainless steel) or ceramic that has been used in the conventional disk atomizing method. A rotating disk made of (such as boron nitride) is preferably used. For the purpose of rapidly cooling the droplets 9, it is more effective to use a rotating disk made of a metal material having a high thermal conductivity such as copper.

  The droplets 9 separated by jetting high-pressure water into the molten metal stream are covered with a vapor film formed by evaporation of the high-pressure water, so that a high cooling rate cannot be obtained as it is. However, when the droplet 9 collides with the rotating disk 10, a strong shearing stress acts on the vapor film to tear the vapor film, and the metal surface of the droplet 9 directly contacts the surface of the rotating disk 10. A high cooling rate is obtained.

  In the present invention, the temperature of the droplet 9 when colliding with the rotating disk 10 is adjusted to be within the range of the solidification start temperature of the droplet 9 to the solidification start temperature + 50 ° C. The temperature of the droplet 9 when colliding with the rotating disk 10 changes the temperature of the molten metal 2 injected into the molten metal holding container 4 or the distance between the molten metal nozzle 5 or atomizing point 14 and the rotating disk 10. Can be controlled by. When the temperature of the droplet 9 when colliding with the rotating disk 10 is lower than the solidification start temperature of the droplet 9, crystallization starts with the droplet 9 covered with the water vapor film at a low cooling rate. Therefore, a water atomized metal powder having a high degree of amorphousness cannot be obtained. When the temperature of the droplet 9 when colliding with the rotating disk 10 is higher than the solidification start temperature of the droplet 9 + 50 ° C., the droplet 9 is blown from the rotating disk 10 before being cooled to a sufficiently low temperature. A water atomized metal powder having a sufficiently high crystallinity cannot be obtained.

  In the present invention, it is preferable that the peripheral speed of the rotating disk 10 at the point where the droplet 9 collides is equal to or higher than the dropping speed of the droplet 9. By setting the peripheral speed of the rotating disk 10 within this range, the effect of tearing off the water vapor film covered with the droplets 9 is more remarkably exhibited. The drop speed of the droplet 9 at the collision point is directly measured by observing the droplet 9 with a high-speed camera or the like, but the velocity of the high-pressure water near the collision point flying with the droplet 9 It is also possible to approximate with a value measured by a similar method.

  Furthermore, in the present invention, it is preferable to form a refrigerant layer made of a refrigerant liquid such as water on the surface of the rotating disk 10. Thereby, the cooling rate of the droplet 9 when colliding with the rotating disk 10 is further improved. In forming the refrigerant layer, for example, as disclosed in Patent Document 3, the refrigerant liquid is sent out from the liquid feeding port 15 provided on the rotating shaft, and is uniformly applied to the disk surface using the centrifugal force of the disk. It is possible to apply a conventionally known method such as a method of diffusing in a layer. The temperature of the refrigerant liquid is preferably as low as possible. For example, when water is used, the cooling rate can be improved by setting the temperature to 10 ° C. or lower.

  Further, in the present invention, the higher the ratio of the flow rate of the high-pressure water 8 and the flow rate of the molten metal stream 6 (hereinafter referred to as the “water-solution ratio”), the more the above-mentioned cooling rate improvement effect is manifested. Is preferably 5 or more. More preferably, it is 10 or more.

  INDUSTRIAL APPLICABILITY The present invention is effective for the production of metal powders that require a particularly large cooling rate for amorphization, and the molten metal is composed of Fe-based soft magnetic alloy composition or a part of Fe with Ni and / or Co. The substituted Fe-based soft magnetic alloy composition preferably has an alloy composition in which the Fe-based element ratio, which is the total amount of Fe or Fe, Ni, and Co, is more than 82.5 at% and less than 86 at%. Conventionally, amorphization of an Fe-based soft magnetic alloy, which has been difficult to be amorphized by the water atomization method, can be achieved by the water atomization method. Note that the alloy with the Fe-based element ratio exceeding 86 at% could not be completely amorphized even by this method, so the upper limit of the composition limitation range was set.

  When the amorphous powder of the Fe-based soft magnetic alloy manufactured by the above-described manufacturing method is a nanocrystalline powder, the amorphous powder is further heated to a temperature in the range of 400 to 500 ° C. It is preferable to apply. When the heat treatment temperature is less than 400 ° C, nanocrystallization does not proceed sufficiently, and when it exceeds 500 ° C, the crystal grains become coarse.

  According to the method of the present invention described above, water atomization has an alloy composition with an Fe-based element ratio of more than 82.5 at% and less than 86 at%, an average particle diameter of 5 μm or more, and an amorphization ratio of 90% or more. Fe-based soft magnetic alloy powder can be produced. Furthermore, a water atomized Fe-based soft magnetic alloy powder having a nanocrystal structure and a high saturation magnetic flux density can be produced.

  The “average particle size” mentioned here is a particle size at which the volume-based cumulative particle size distribution measured by the laser diffraction / scattering method is 50%, and the “amorphization ratio” is determined by the X-ray diffraction method. Then, the halo peak from the amorphous (amorphous) and the diffraction peak from the crystal were measured, and the amorphization rate was calculated by the WPPD method. The “WPPD method” here is an abbreviation for Whole-powder-pattern decomposition method. The WPPD method is detailed in Hideho Toraya: Journal of the Crystallographic Society of Japan, vol.30 (1988), No. 4, P253-258.

  Using the apparatus shown in FIG. 1, water atomized metal powder was produced with the components and conditions shown in Table 1. The amount of raw material dissolved was 20 kg per charge, and the solidification start temperature of each raw material was determined by a thermodynamic calculation method. The average particle size and crystallization rate of the produced water atomized metal powder were measured. In Table 1, the powder No. 1-1, no. 2, and no. About the metal powder of 3, it heated to the temperature of 300, 400, 500, 600 degreeC by nitrogen atmosphere, and performed the heat processing hold | maintained for 20 minutes. The crystal grain size D of α-Fe was evaluated together with the crystallization rate of the metal powder after the heat treatment.

  The crystallization rate is calculated by the above WPPD method, and the crystal grain size D (nm) is calculated from Scherrer's formula D = 0.9λ / from the half-value width β of the X-ray diffraction peak by the α-Fe (110) plane. It calculated using (beta) cos (theta). Here, λ is the X-ray wavelength (nm), θ is the diffraction angle of the α-Fe (110) plane, and 2θ = 52.505 °.

  Tables 1 and 2 show the measurement results.

  The comparative example (powder No. 1-4) in which the temperature of the droplet at the time of collision with the rotating disk was (solidification start temperature −5 ° C.) outside the production conditions of the present invention, and the temperature of the droplet at the time of collision with the rotating disk Of the comparative example (powder No. 1-5) having a (solidification start temperature + 55 ° C.) was 82 to 75%, whereas the examples of the present invention had both the amorphization rate It was a value exceeding 85%, and it was confirmed that a water atomized metal powder having a high amorphization rate can be produced by the method of the present invention.

  Moreover, as shown in Table 2, when the heat treatment temperature is 400 ° C. or 500 ° C., all the metal powders have a crystallization rate after heat treatment of 41 to 46% and an α-Fe crystal grain size D of 19 to 24 nm. In contrast, when the heat treatment temperature was 300 ° C., the crystallization rate was 8% or less, and when the heat treatment temperature was 600 ° C., the α-Fe crystal grain size D was as coarse as 48 nm or more.

DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Molten metal 3 Spraying tank 4 Molten metal holding container 5 Molten metal nozzle 6 Molten metal flow 7 High pressure water injection nozzle 8 High pressure water 9 Droplet 10 Rotating disk 11 Water atomized metal powder 12 Spray tank bottom 13 Recovery valve 14 Atomizing point 15 Liquid feeding port

Claims (8)

  In the method for producing water atomized metal powder, high pressure water is sprayed onto a falling molten metal stream, and the molten metal stream is divided to form water atomized metal powder. A method for producing a water atomized metal powder characterized by causing the rotating disk to collide with a rotating disk at a position within a range of the solidification start temperature to the solidification start temperature + 50 ° C.   The method for producing water atomized metal powder according to claim 1, wherein the rotating disk is rotated at a peripheral speed equal to or higher than a dropping speed of the droplet when colliding with the rotating disk.   The method for producing water atomized metal powder according to claim 1, wherein a refrigerant film is formed by a refrigerant liquid on a surface of the rotating disk.   The ratio of the flow volume of the said high pressure water and the flow volume of the said molten metal flow is 5 or more, The manufacturing method of the water atomized metal powder in any one of Claims 1-3 characterized by the above-mentioned.   The molten metal is an Fe-based soft magnetic alloy composition or an Fe-based soft magnetic alloy composition in which a part of Fe is replaced with Ni and / or Co, and is an Fe-based element that is the total amount of Fe or Fe, Ni, and Co The method for producing a water atomized metal powder according to any one of claims 1 to 4, wherein the composition has an alloy composition in which the ratio is greater than 82.5 at% and less than 86 at%.   The method for producing a water atomized metal powder according to claim 5, wherein the water atomized metal powder is further subjected to a heat treatment for heating to a temperature within a range of 400 to 500 ° C.   6. A water atomized Fe-based soft magnetic alloy powder produced by the method for producing a water atomized metal powder according to claim 5, having an average particle size of 5 μm or more and an amorphous ratio of 85% or more. .   A water atomized Fe-based soft magnetic alloy powder, which is a water atomized metal powder produced by the method for producing a water atomized metal powder according to claim 6 and having a nanocrystal structure.

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