JP2020105593A - Method for producing atomized metal powder - Google Patents

Abstract

To provide a method for producing a water-atomized metal powder capable of enhancing non-crystallization ratio and apparent density even if of a metal powder having a high Fe concentration.SOLUTION: A method for producing an atomized metal powder includes primarily fragmenting a fused metal by water atomization or gas atomization, and carrying out secondary cooling with a nano-fluid containing a nanoparticle by 0.05-2.0 wt.% after elapsing a time of 0.0004 seconds or more after performing the primary fragmentation.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for producing atomized metal powder. The present invention particularly relates to the production of atomized metal powder in which the total content of iron-based components (Fe, Ni, Co) is 76% or more in atomic fraction.

The production volume of hybrid vehicles (HV), electric vehicles (EV) and fuel cell vehicles (FCV) is increasing, and it is expected that reactors and motor cores used in these vehicles will have lower iron loss, higher efficiency, and smaller size. Is requested.

These reactors and motor cores have been manufactured by thinning and stacking electromagnetic steel sheets. Recently, attention has been focused on a motor core produced by compression molding a metal powder having a high degree of freedom in shape design.

In order to reduce the iron loss of the reactor and the motor core, it is considered effective to amorphize the metal powder used.

Further, in order to reduce the size and increase the output, it is necessary to increase the magnetic flux density of the metal powder, and for that purpose, it is important to increase the concentration of the Fe-based element containing Ni and Co. Therefore, there is an increasing demand for an amorphized soft magnetic metal powder in which the concentration of the Fe-based element (Fe, Ni, Co) is about 76 to 90% in atomic content.

When iron powder, which is one of the metal powders, is made amorphous, the molten state after atomization is rapidly cooled to make it amorphous. In order to increase the magnetic flux density, it is necessary to cool rapidly as the concentration of the Fe-based element increases, and especially when the Fe-based element reaches an atomic content of about 82%, a cooling rate of 106 K/s or more is required. .. Therefore, it is very difficult to reduce the iron loss of the metal powder and increase the magnetic flux density at the same time.

In particular, when water comes into contact with molten metal, water vaporizes instantly to form a vapor film around the molten metal, which causes a decrease in the cooling rate of metal powder in a high-temperature molten state. It can be mentioned that a film boiling state that prevents

Further, when the atomized metal powder is compression-molded and used as a reactor or a motor core, it is required that the core loss be low in order to reduce iron loss and increase efficiency. In order to reduce the core loss, it is important that the atomized metal powder is amorphous and that the atomized metal powder has a more spherical shape. This is because the core loss tends to decrease as the atomized metal powder has a spherical shape. There is a close relationship between spheroidization and apparent density. The higher the apparent density, the more spherical the shape of the powder. In recent years, an apparent density of 3.0 g/cm ³ or more is required as the performance required for atomized metal powder.

In particular, the powder having a high apparent density (for example, 3.0 g/cm ³ or more) has a spherical shape, and therefore has a higher cooling capacity than the powder having a low apparent density (for example, about 1.0 g/cm ³ ). It is important to. Since the powder having a low apparent density is flattened as shown in FIG. 1, the distance from the surface to the center of the powder is short, so that the heat transfer coefficient on the surface of the powder on which cooling acts is 10,000 W/m ² K to 20000 W. Cooling is possible even at about /m ² K. On the other hand, in the powder having a high apparent density, since it has a spherical shape as shown in FIG. 2, the distance from the surface to the center of the powder is long and always constant, so that the heat transfer coefficient on the powder surface is 50,000 W/m ² K to 200,000 W/ Up to about m ² K is required.

From the above, 1) and 2) are required as the performance used for the atomized metal powder used as the reactor and the motor core.
1) Fe-based elements can be highly concentrated in order to reduce the size and increase the output of the motor.
2) Due to low loss and high efficiency, the metal powder is amorphous and has a high apparent density.
Furthermore, 3) is required as the manufacturing method.
3) In order to amorphize a spherical powder having an apparent density of 3.0 g/cm ³ or more and a high concentration of Fe-based elements of 76% or more in atomic content, the powder was fragmented in a molten state. The molten metal surface can be cooled sufficiently.

In producing amorphous iron powder, in order to obtain a high cooling capacity, in particular, in order to solve the problem of cooling suppression due to a vapor film/film boiling, studies described in Patent Documents 1 to 11 have been made.

For example, Patent Document 1 describes a method for producing a metal powder in which a cooling rate until solidification is 105 K/s or more when a metal powder is obtained by cooling and solidifying while scattering molten metal.
In the technique described in Patent Document 1, the scattered metal is brought into contact with the cooling liquid flow generated by swirling the cooling liquid along the inner wall surface of the tubular body, whereby the above cooling rate is obtained. It is supposed to be. The flow velocity of the cooling liquid flow generated by swirling the cooling liquid is preferably 5 to 100 m/s.

Patent Document 2 describes a method for producing a rapidly solidified metal powder. In the technique described in Patent Document 2, the cooling liquid is supplied from the outer peripheral side of the upper end of the cylindrical portion of the cooling container whose inner peripheral surface is a cylindrical surface, and the cooling liquid is dropped while swirling along the inner peripheral surface of the cylindrical portion, By the centrifugal force generated by the swirling, a layered swirling cooling liquid layer having a cavity at the center is formed, and the molten metal is supplied to the inner peripheral surface of the swirling cooling liquid layer to rapidly solidify. As a result, it is said that a high-quality rapidly solidified powder can be obtained with good cooling efficiency.

Patent Document 3 includes a gas jet nozzle for injecting a gas jet into a flowing molten metal to divide it into droplets, and a cooling cylinder having a cooling liquid layer flowing down while rotating on an inner peripheral surface. , An apparatus for producing metal powder by a gas atomizing method is described. In the technique described in Patent Document 3, the molten metal is divided into two stages by the gas jet nozzle and the swirling cooling liquid layer, and finely cooled rapidly solidified metal powder is obtained.

In Patent Document 4, molten metal is supplied into a liquid coolant, a vapor film covering the molten metal is formed in the coolant, and the vapor film thus formed is collapsed to bring the molten metal and the coolant into direct contact with each other to form a natural nucleus. A method for producing amorphous metal fine particles is described, in which boiling caused by generation is caused and the pressure wave is used to tear off the molten metal to rapidly cool it to become amorphous, thereby forming amorphous metal fine particles. Disintegration of the vapor film covering the molten metal is such that when the temperature of the molten metal supplied to the refrigerant is directly in contact with the refrigerant, the interface temperature is below the film boiling lower limit temperature and above the spontaneous nucleation temperature, or ultrasonic irradiation is performed. It is said that it is possible by

In Patent Document 5, when the molten material is supplied into the liquid refrigerant as a droplet or a jet stream, the temperature of the molten material is set to be in a molten state at a temperature higher than the spontaneous nucleation temperature of the liquid refrigerant. Further, the relative velocity difference between the velocity of the molten material when entering the flow of the liquid coolant and the velocity of the flow of the liquid coolant is set to 10 m/s or more so that it is formed around the molten material. There is described a method for producing fine particles in which a vapor film is forcibly collapsed to cause boiling due to spontaneous nucleation, atomized and cooled and solidified. As a result, it is said that even a material that was difficult in the past can be made into fine particles and made amorphous.

In Patent Document 6, by melting a raw material obtained by adding a functional additive to a base material and supplying the raw material into a liquid refrigerant, the cooling rate is controlled during atomization and solidification by cooling due to vapor explosion. To obtain homogeneous functional fine particles that are polycrystal or amorphous without segregation, and a step of solidifying the functional fine particles and the fine particles of the base material to obtain a functional member. A method of manufacturing the functional member included therein is described.

Patent Documents 7 and 8 describe that a suction pipe is installed below the water atomizer, and the vapor film around the powder can be destroyed by sucking the powder after the melt pulverization.

Patent Document 9 describes that a cooling block is installed below a water atomizer, a liquid of 80 kgf/cm ² or more is sprayed, and the powder after melt pulverization is applied to the cooling block to destroy the vapor film around the powder. Has been done.

In Patent Document 10, a device for injecting the second liquid is installed below the atomizing device, and the injection pressure of the liquid is 5 MPa to 20 MPa, by forcibly changing the traveling direction of the dispersion liquid containing the molten metal. , Removing the vapor film that is covered is described.

Patent Document 11 is a patented-iron-boron-based ferromagnetic material (permanent magnet) containing a rare earth, pulverized by water atomization, the water pressure and 750kgf ^/ cm ² ~1200kgf ^/ cm 2 Upon made amorphous It is said that it is desirable to set the water temperature to 20° C. or lower and to set the water amount (kg) per 1 kg of iron to 25 to 45 [−].

JP, 2010-150587, A Japanese Patent Publication No. 7-107167 Japanese Patent No. 3923573 Japanese Patent No. 3461344 Japanese Patent No. 4793872 Japanese Patent No. 4784990 JP-A-60-24302 JP 61-204305 A JP-A-60-24303 JP, 2007-291454, A JP, 2004-349364, A

The techniques described in Patent Documents 1 to 3 supply the molten metal to the separated metal particles in a cooling liquid layer formed by swirling the cooling liquid to form a vapor film formed around the metal particles. It is a technique to peel off. However, when the temperature of the separated metal particles is high, a film boiling state is likely to occur in the cooling liquid layer, and further, the metal particles supplied into the cooling liquid layer move together with the cooling liquid layer, so that the cooling liquid layer There is a problem that the relative speed difference is small and it is difficult to avoid the film boiling state.

The techniques disclosed in Patent Documents 4 to 6 utilize steam explosion to divide the molten metal by pressure propagation, and further destroy the steam film to perform rapid cooling. Since the molten metal is rapidly cooled immediately after the molten metal is divided, the molten metal is rapidly cooled and solidified in a state where the molten metal is torn off, so that there is a problem that the powder has an indefinite shape other than a spherical shape. The irregularly shaped powder has a low apparent density.

The techniques described in Patent Documents 7 to 10 relate to a water atomizing method. The techniques described in Patent Documents 7 and 8 are said to be able to remove the vapor film by suctioning the powder, but if there is water around the high temperature object, the water from inside the object continuously vaporizes the water. Since water and molten metal are sucked together, it is difficult to remove the vapor film.

In Patent Document 9, it is possible to destroy the vapor film by installing a cooling block below the atomizer and applying the molten metal covered with the vapor film to the cooling block, but a liquid was used for the division. In this case, since the temperature of the liquid rises, the formation of a vapor film becomes easier with it, and the injection pressure (pressure energy) of the liquid is used for division, so the amount of energy to destroy the vapor film when hitting the cooling block. Run out. Even if the vapor film is destroyed, as long as the molten metal (powder) is at a high temperature, the vapor film is immediately restored. Therefore, it is necessary to keep taking the vapor film.

In Patent Document 10 as well, it is said that the vapor film can be removed by changing the traveling direction of the dispersion liquid containing the molten metal that has become droplets after atomization by a liquid jet spray. However, when changing the traveling direction, the vapor film is removed. If the temperature of the molten metal is too high, it may cover the vapor film again due to the surrounding cooling water, and conversely, if the temperature when it hits the cooling block is too low, the molten metal solidifies. Then, crystallization may proceed. In particular, when the content of the iron-based element (Fe+Co+Ni) is large, the melting point becomes high, so that the cooling start temperature is high and film boiling tends to occur from the beginning of cooling, and it cannot be said that the liquid injection pressure of about 5 MPa to 20 MPa is sufficient.

There is a Patent Document 11, powder for permanent magnets, but finely divided powder, be 750kgf ^/ cm ² ~1200kgf ^/ cm 2 to amorphization, that the water temperature and 20 ° C. or less, per iron 1kg It is described that the amount of water is 25 L to 45 L (liter), and it is not shown that a film boiling or a vapor film is taken by these, but it is a high-pressure pump and a high-pressure pipe to make the injection pressure a high pressure of 60 MPa or more. Costly, which means higher product prices. Further, the amount of water per kg of iron is set to 25 L to 45 L, but this is not sufficient for a soft magnetic material having a high iron-based element.

The water atomizing method is advantageous from the viewpoint of productivity and adhesiveness between particles. In the case of water atomization, since the steam is covered with the cooling water that has been atomized around the molten metal that has been divided after atomization, another means (such as the atomizing direction or the atomizing direction of the atomizing) is used as in Patent Technologies 7 to 11. It is necessary to add atomized water injection conditions such as water volume and injection pressure.
On the other hand, when performing rapid cooling for amorphization, it is advantageous to perform rapid cooling with water after gas atomizing, as in Patent Documents 1 to 6. However, in particular, in order to amorphize a soft magnetic material having a high concentration of iron-based elements of 76% or more in atomic content, the cooling capacities of Patent Documents 1 to 6 are insufficient, and higher cooling capacities are required. ..

The present invention has been made in order to solve the above-mentioned problems, and in producing a metal powder in which an iron-based element has an atomic content of 76.0% to 86.0% by atomization, the powder has a spherical shape and a high apparent appearance. It is an object of the present invention to provide a method for producing an atomized metal powder having a high cooling capacity, which is capable of densifying and making the powder amorphous.

The present inventors have conducted extensive studies to solve the above problems.
In order to increase the density or increase the apparent density, the molten metal is divided by gas atomization or water atomization, and then the divided molten metal is allowed to fall for 0.0004 seconds or more while allowing the molten metal to fall by itself. It is made spherical by the surface tension that it has. The time required for the divided molten metal to spheroidize due to surface tension is called spheronization time. If the spheroidizing time is less than 0.0004 seconds, the spheroidizing is insufficient. There is no problem if the spheroidizing time is longer than 0.0004 seconds, but since the crystallization starts when the temperature of the molten metal falls below the solidification temperature, it is desirable that the spheronizing time is 0.01 seconds at maximum. ..
Regarding gas atomization, atomization of molten metal is difficult unless it is injected at an injection pressure of 0.5 MP or more. For gas atomization, an inert gas such as nitrogen (N2) or argon (Ar) is used to prevent oxidation and ignition of molten steel.
For water atomization, it is preferable to divide the molten metal with a jet pressure of 5 MPa or more. If it is less than 5 MPa, it is difficult to finely divide the molten metal.
After the spheroidizing time has elapsed, secondary cooling is performed immediately before the molten metal solidifies, and rapid solidification is performed. In the present invention, a nanofluid is used for this secondary cooling to perform rapid solidification. The nanofluid referred to here is a liquid containing nanoparticles. The nanoparticles referred to here are particles having an average particle size of 5 to 100 nm.
Although the factors that improve the cooling characteristics by using nanoparticles have not been accurately grasped, the following verifications were performed. An ultrafine thermocouple is heated to 1300°C or higher with a gas burner, and from about 1200°C, the thermocouple is placed in a beaker containing each cooling medium (nanofluid) containing 1% by weight of silica, alumina, and titania nanoparticles. Pickled and cooled. In the cooling experiment, as shown in FIG. 3, the cooling rate of the nanofluid was higher than that of pure water. In the nanofluid, cooling is promoted particularly in the high temperature portion, and it is expected that the nanofluid makes it difficult for the film boiling to occur in the high temperature portion. The following reasons are considered as factors that suppress the occurrence of film boiling due to the nanofluid.
1) The wettability between the cooling surface and the cooling medium changes (becomes easier)
2) The cooling area expands due to the fine irregularities formed on the cooling surface. 3) The coating layer of nanoparticles forms on the surface of the cooling surface and the temperature gradient increases. When the nanoparticles are mixed with cooling water, the concentration is 1 weight. % Is desirable, but 0.05% by weight of silica or alumina is effective. Further, although 2.0% by weight or more is effective, the viscosity and kinematic viscosity of water increase, so that a load is applied to the high pressure pump for injecting the cooling water. From the viewpoint of cost, it is desirable that the maximum content of nanoparticles is 2.0% by weight or less.

The average particle size of the nanoparticles is preferably 5 nm to 100 nm. If it is less than 5 nm, this effect is difficult to appear. Also, if it is 100 nm or more, it easily precipitates in the cooling water, making it difficult to operate, and the piston of the (plunger type) high-pressure pump is likely to be greatly worn, resulting in high maintenance costs and maintenance of the factory. The operating time is shortened. The average particle diameter can be obtained by measuring the specific surface area by a gas adsorption method, for example. Cooling water can be jetted at a high pressure by using a spray nozzle of molten metal that has been divided from the periphery of the molten metal that has been divided, or by dividing the molten metal so that high-pressure water flows along the plate. The molten metal may be sprayed.

Therefore, the gist of the present invention is as follows.
[1] Cooling water is sprayed from around the molten metal falling in the vertical direction to divide the molten metal, and after the division, the molten metal is dropped for 0.0004 seconds or more,
After being dropped, cooling water containing 0.05% by weight to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, is jetted from around the molten metal to cool the molten metal,
A method for producing an atomized metal powder, which comprises producing a metal powder having a total content of Fe, Ni, and Co of 76.0% to 86.0% in atomic fraction.
[2] A high-pressure inert gas having an injection pressure of 0.5 MPa or more is injected from the periphery of the molten metal falling in the vertical direction to divide the molten metal, and after the division, the molten metal is dropped for 0.0004 seconds or more,
After being dropped, cooling water containing 0.05% by weight to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, is jetted from around the molten metal to cool the molten metal,
A method for producing an atomized metal powder, which comprises producing a metal powder having a total content of Fe, Ni, and Co of 76.0% to 86.0% in atomic fraction.
[3] The nanoparticles are
The method for producing atomized metal powder according to [1] or [2], containing at least one of pure metal particles, metal oxide particles, metal nitride particles, and metal carbide particles.
[4] The method for producing atomized metal powder according to [3], wherein the metal oxide-based particles are any one of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), and titania (TiO ₂ ).
[5] The method for producing atomized metal powder according to any one of [1] to [4], wherein the atomized metal powder produced contains at least two kinds selected from Si, P and B and Cu.

According to the present invention, the atomized metal powder having a total content of iron-based components (Fe, Ni, Co) of 76.0% to 86.0% in atomic fraction has an apparent density of 3.0 g/cm ³ or more, It is possible to make the atomization rate of the atomized metal powder 90% or more. Further, by subjecting the atomized metal powder obtained in the present invention to an appropriate heat treatment after molding, nano-sized crystals can be precipitated. As a result, the Fe-based element can be highly concentrated, and the motor can be downsized and the output can be increased.

It is a figure which shows the flattened powder with low apparent density. It is a figure which shows the spheroidized powder with high apparent density. It is a figure which shows the cooling rate in each surface temperature at the time of cooling using a nanofluid. It is a figure which shows typically the manufacturing apparatus of the atomized metal powder by water atomization used for the manufacturing method of embodiment of this invention. It is a figure which shows typically the atomizing part of the manufacturing apparatus shown in FIG. It is a figure which shows typically the cone cooling of the primary cooling of the atomization metal powder manufacture by the water atomizing used for the manufacturing method of embodiment of this invention, and a division part. It is a figure which shows typically the manufacturing apparatus of the atomized metal powder by gas atomization used for the manufacturing method of embodiment of this invention. It is a figure which shows typically the atomized part of atomized metal powder manufacture by gas atomizing used for the manufacturing method of embodiment of this invention in detail. FIG. 8 is a diagram schematically showing an atomized portion and a secondary cooling method for producing atomized metal powder by gas atomizing of Example 5. It is a figure which shows the area division in the numerical simulation in the case of water atomization. It is a figure which shows a LS starting point. It is a figure which shows a LS end point.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention. The atomizing method will be described separately for water atomizing and gas atomizing.
Water atomizing method of the present invention, the molten metal is sprayed from the periphery of the molten metal falling in the vertical direction to divide the molten metal, and after the split, the molten metal is dropped for 0.0004 seconds or more, and after being dropped, Cooling water containing 0.05% to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, is jetted from around the molten metal to cool the molten metal. This produces a metal powder having a total content of Fe, Ni, and Co of 76.0% to 86.0% in atomic fraction. For water atomization, it is preferable to divide the molten metal with a jet pressure of 5 MPa or more. This is because if it is less than 5 MPa, it is not easy to divide the molten metal into fine pieces.

The gas atomizing method of the present invention divides the molten metal by injecting a high-pressure inert gas with an injection pressure of 0.5 MPa or more from the periphery of the molten metal falling in the vertical direction to divide the molten metal for 0.0004 seconds or more. After being dropped, the molten metal is cooled by injecting cooling water containing 0.05% by weight to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, around the molten metal. However, the total content of Fe, Ni and Co is 76.0 to 86.0% in terms of atomic fraction. Regarding gas atomization, the molten metal can be finely divided by injecting at an injection pressure of 0.5 MP or more. For gas atomization, it is preferable to use an inert gas such as nitrogen (N ₂ ) or argon (Ar) for preventing oxidation and ignition of molten steel.

In the water atomizing method and the gas atomizing method, the spheroidizing time for dropping the divided molten metal to make it spherical is not less than 0.0004 seconds because it is necessary for spheroidizing. This is because if the spheroidizing time is less than 0.0004 seconds, the spheroidizing is insufficient. There is no problem if the spheroidizing time is longer than 0.0004 seconds, but since the crystallization starts when the temperature of the molten metal falls below the solidification temperature, it is desirable that the spheronizing time is 0.01 seconds at maximum. ..

It is desirable to use nanoparticles containing at least one of pure metal particles, metal oxide particles, metal nitride particles, and metal carbide particles. As the metal oxide particles, any of silica (SiO ₂ ), alumina (Al ₂ O ₃ ) and titania (TiO ₂ ) can be used.

It is preferable that the atomized metal powder to be produced is one containing at least two kinds selected from Si, P and B and Cu.

FIG. 4 is a diagram schematically showing an apparatus for producing water atomized metal powder used in the production method according to the embodiment of the present invention. FIG. 5 is a diagram schematically showing an atomized portion of the manufacturing apparatus shown in FIG. FIG. 6 is a schematic diagram showing a cone guide portion described separately.

As shown in FIGS. 4 and 5, the apparatus for producing water atomized metal powder divides the molten metal 2 from the portion where the molten metal 2 in which the raw material is melted is received by the tundish 1 and the molten metal 2 is poured by the molten metal nozzle 3. It is divided into a primary water splitting injection device 40 and a secondary cooling injection nozzle 37. The water jetting device 40 for primary cutting has a primary cooling water nozzle header 4 and a primary cooling water jetting nozzle 5.

The capacity of the tundish 1 is selected in accordance with the amount of metal powder produced once. If the production amount per batch is 100 kg, the yield is taken into consideration and a tundish capacity larger than that is selected.
The molten metal nozzle 3 may have a thin tip. When adjusting the falling amount of the molten metal 2, the tip diameter of the molten metal nozzle 3 becomes important. If it is about 7 kg per minute, φ2 mm, if it is about 15 kg per minute, φ3 mm, if it is about 30 kg per minute, φ4 mm or the like is selected. Alternatively, the amount of molten metal dropped may be adjusted by sealing (not shown) the tundish 1 and applying back pressure (pressurization) with an inert gas. The tundish 1 and the molten metal nozzle 3 perform preheating with a gas burner, an electric heater or the like (not shown) before pouring the molten metal 2 in order to prevent cracking and heat shock due to a temperature difference when the molten metal 2 is poured. ..

In the case of water atomization, the primary division is performed by injecting cooling water from around the molten metal 2 from the primary cooling water injection nozzle 5. The cooling water is temporarily stored in the cooling water tank 15, and the cooling water temperature is adjusted by the temperature controller 16 if necessary. The primary cutting has only to fulfill the function of cutting the molten metal 2, and it is not necessary to lower the water temperature, so the temperature is adjusted to 20 to 50°C. The cooling water becomes high-pressure water by the primary cooling high-pressure pump 17 and is sent to the primary cooling water nozzle header 4 to which the primary cooling water injection nozzle 5 is attached through the primary cooling pipe 18. A hole 4a is formed in the center of the primary cooling water nozzle header 4. The molten metal nozzle 3 is inserted into the hole 4 a, and the molten metal 2 passes through the molten metal nozzle 3.
A plurality of primary cooling water injection nozzles 5 are mounted on the circumference of the cylindrical primary cooling water nozzle header 4. The number of primary cooling water injection nozzles 5 is preferably about 4 to 24. The primary cooling water injection nozzles 5 extend diagonally downward facing each other so that the molten metal 2 drops vertically downward.
As shown in FIGS. 5 and 6, the cooling water sprayed from the primary cooling water spray nozzle 5 collides with the cone guide 8 to change the focusing angle, and the cooling waters collide with each other. The focusing angle α by the cone guide 8 is preferably about 25 to 15°. If the focusing angle α is large, the cooling action works to lower the temperature of the molten metal 2, and conversely, if the angle is small, the distance from the molten metal nozzle 3 to the contact with the cooling water increases, which also causes the molten metal 2 to come into contact with the cooling water. The temperature drops. It is desirable that the average temperature of the molten metal 2 in the primary cutting be 100° C. or more higher than the solidification temperature of the molten metal 2. This is because when the average temperature of the molten metal 2 is low, solidification starts and the amorphization rate decreases by the time when secondary cooling starts after being divided.
In the present embodiment, while the molten metal 2 that has been divided into the primary parts is naturally dropped, the molten metal 2 is dropped for 0.0004 seconds or more, and the molten metal 2 is spherical due to the surface tension of the molten metal 2 itself. In order to realize this, a spheroidizing distance LS is provided from the position where the molten metal is divided (hereinafter, also referred to as atomizing point or AP point) to the start of secondary cooling.
FIG. 11 is a diagram showing the LS start point. FIG. 11A is a diagram showing the LS starting point when the cone guide 8 is provided in the atomizing device. In this case, the intersection of the extension line of the side surface of the cone guide 8 and the central axis of the molten metal nozzle 3 in the sectional view is the LS start point. FIG. 11B is a diagram showing the LS starting point in the case where the cone guide 8 is not provided in the atomizing device. In this case, the intersection of the extension line of the central axis of the primary cooling water injection nozzle 5 (injection direction) and the central axis of the molten metal nozzle 3 becomes the LS start point.

FIG. 12 is a diagram showing the LS end point. FIG. 12A is a diagram showing the LS end point when the secondary cooling injection nozzle 37 is a solid spray type (type in which cooling water goes straight). In this case, the intersection of the extension line of the central axis (injection direction) of the secondary cooling injection nozzle 37 and the central axis (injection direction) of the molten metal nozzle 3 becomes the LS end point. FIG. 12B is a diagram showing the LS end point in the case where the secondary cooling injection nozzle 37 is a flat spray type (type in which the cooling water has a wide spray angle). In this case, the intersection of the upper surface of the cooling water spraying region and the central axis (spraying direction) of the molten metal nozzle 3 becomes the LS end point.
LS [m] is determined by the required sphering time (Ts [s: seconds]) and the falling velocity (Vd [m/s]) of the molten metal that has been divided.
LS>Vd×Ts ··· Formula (1)
It is necessary to

For the secondary cooling, cooling water containing nanoparticles (hereinafter referred to as nanofluid) is used. As shown in FIGS. 4 and 5, the nanofluid is a mixture of the cooling water stored in the secondary cooling tank 32 with a predetermined amount of nanoparticles from the nanoparticle feeder 34 and mixed by the stirrer 33. In the nanofluid, the content of nanoparticles is adjusted to 0.05 wt% to 2.0 wt %. If necessary, the cooling water temperature is adjusted by a temperature controller. The water temperature on the secondary cooling side is preferably low and is adjusted to about 4 to 15°C. The nanofluid mixed with nanoparticles is pressurized to a predetermined pressure by the high-pressure secondary cooling pump 36, and is supplied to the secondary cooling jet nozzle 37 by the secondary cooling water pipe 35. A plurality of secondary cooling jet nozzles 37 are installed on the circumference of the chamber 19. The number of the secondary cooling injection nozzles 37 is preferably about 4 or more and 32 or less. It is desirable that the total cooling water amount (Q2 kg/min) of the secondary cooling be about 45 times (=Q2/M) with respect to the falling molten metal amount (Mkg/min). The average temperature of the molten metal at which the secondary cooling is started is 100°C or less, more preferably 50°C or less than the solidification temperature. The nanofluid cooling water may be collected and sent to the secondary cooling tank 32 again for reuse. In the case of water atomization, the cooling water not mixed with the nanoparticles is used in the primary division, so that the concentration of the nanoparticles decreases, so it is necessary to adjust the concentration by the nanoparticle feeder 34.
FIG. 7: is a figure which shows typically the manufacturing apparatus of the gas atomized metal powder used for the manufacturing method of this embodiment (a comparative method is included). FIG. 8 is a schematic diagram showing the gas atomized portion in detail.

The gas atomized metal powder manufacturing apparatus of FIGS. 7 and 8 is a primary cutting gas for cutting the molten metal 2 from the portion where the molten metal 2 in which the raw material is melted is received by the tundish 1 and the molten metal 2 is poured by the molten metal nozzle 3. It is divided into an injection device 26 and a secondary cooling injection nozzle 37.

The capacity of the tundish 1 is selected according to the amount of metal powder produced at one time. The amount of gas atomized produced once is smaller than that of water atomized. If the production amount per batch is 50 kg, a large tundish capacity is selected with a view to yield. The molten metal nozzle 3 may have a thin tip. When adjusting the falling amount of the molten metal 2, the tip diameter of the molten metal nozzle 3 becomes important. If it is about 7 kg per minute, φ2 mm, if it is about 15 kg per minute, φ3 mm, if it is about 30 kg per minute, φ4 mm or the like is selected. Alternatively, the falling amount of the molten metal 2 may be adjusted by sealing (not shown) the tundish 1 and applying back pressure (pressurization) with an inert gas. The tundish 1 and the molten metal nozzle 3 perform preheating with a gas burner, an electric heater or the like (not shown) before pouring the molten metal 2 in order to prevent cracking and heat shock due to a temperature difference when the molten metal 2 is poured. ..
In the case of gas atomization for the primary division, the inert gas 27 is injected from the primary injection gas injection device 26 to perform the division. The inert gas is nitrogen (N ₂ ), argon (Ar), helium (He) or the like, and the inert gas is pressurized by the compressor 24 and stored in the gas holder 25. Alternatively, the inert gas may be supplied by a high pressure gas cylinder (not shown). The pressurized inert gas is supplied through the high pressure gas pipe 23. A plurality of nozzle injection holes are formed on the circumference of the cylindrical primary dividing gas injection device 26. An inert gas is injected obliquely downward toward the molten metal 2 from the injection hole of the primary cutting gas injection device 26, whereby the molten metal 2 is cut. In addition, a hole is opened in the central portion of the primary dividing gas injection device 26, and the molten metal nozzle 3 enters and the molten metal 2 passes through.
Since the gas has a larger attenuation of the injection pressure and the injection speed than the cooling water injection nozzle for injecting water, the distance between the nozzle injection hole of the primary dividing gas injection device 26 and the molten metal 2 is as short as about 5 to 30 mm. In many cases. It is desirable that the nozzle injection holes of the primary cutting gas injection device 26 be about φ0.05 to φ0.3 mm, and the number of injection holes be about 8 to 72. It is necessary to adjust the injection pressure and the injection amount so that the injection pressure and injection amount become predetermined. The point at which the molten metal 2 is divided by the inert gas is called AP (atomize point). The average temperature of the molten metal 2 in the primary cutting is preferably 100° C. or higher than the solidification temperature of the molten metal 2. This is because when the average temperature of the molten metal 2 is low, solidification starts and the amorphization rate decreases by the time when secondary cooling starts after being divided. Since the gas atomization has a smaller temperature drop than the water atomization, the average temperature of the molten metal 2 in the primary cutting may be low.

A spheroidizing distance LS is provided from the AP point to the start of secondary cooling. LS[m] is determined by the required sphering time (Ts[s:seconds) and the falling velocity (Vd[m/s]) of the molten metal that has been divided, as shown in equation (1).

In the secondary cooling, the cooling water is accumulated in the secondary cooling tank 32, a predetermined amount of nanoparticles is charged from the nanoparticle charging device 34, and the nanoparticles are mixed by the stirrer 33. This is adjusted to 0.05% to 2.0% by weight. If necessary, the cooling water temperature is adjusted by the secondary cooling water temperature controller 31. The water temperature on the secondary cooling side is preferably low and is adjusted to about 4 to 15°C. The nanofluid mixed with nanoparticles is pressurized to a predetermined pressure by the secondary cooling high-pressure pump 36, and is supplied to the secondary cooling jet nozzle 37 by the secondary cooling water pipe 35. A plurality of secondary cooling jet nozzles 37 are installed on the circumference of the chamber 19. It is desirable that the number is 4 or more and 32 or less. It is desirable that the total amount of cooling water (Q2 kg/min) for the secondary cooling be about 45 times (=Q2/M) with respect to the amount of falling molten metal (Mkg/min). The average temperature of the molten metal 2 at which the secondary cooling is started is 100° C. or less, more preferably 50° C. or less than the solidification temperature. The nanofluid cooling water may be collected and sent again to the secondary cooling tank 32 for reuse. In the case of gas atomization, the concentration of nanoparticles when reused is less likely to decrease as compared with water atomization, but since it adheres to molten metal and is consumed, it is necessary to adjust the concentration by the nanoparticle feeder 34.

FIG. 9 is a diagram showing another gas atomizing method of the present invention. In this example, as shown in FIG. 9, the secondary cooling is performed using the oblique collision plate 39. A high-pressure nanofluid mixed with nanoparticles is caused to flow along the oblique collision plate 39 from the secondary cooling injection nozzle 38, and the molten metal 2 that has been primary-divided is dropped on the oblique collision plate 39 to perform secondary cooling.
A spheroidizing distance LS is provided between the AP point and the start of secondary cooling. LS is defined in equation (1) above.

It is desirable that the total cooling water amount (Q2 kg/min) of the secondary cooling be about 45 times (=Q2/M) with respect to the amount of molten metal that falls (Mkg/min). The average temperature of the molten metal 2 at which the secondary cooling is started is within the solidification temperature +100°C, more preferably within the solidification temperature +50°C. The nanofluid may be collected and sent again to the secondary cooling tank 32 for reuse. In the case of gas atomization, the concentration of nanoparticles upon reuse is less likely to decrease than in water atomization, but since nanoparticles adhere to molten metal 2 etc. and the nanoparticles decrease, the concentration of nanoparticles is adjusted by the nanoparticle feeder 34. There is a need.

The secondary cooling method using the oblique collision plate 39 as shown in FIG. 9 may be applied to the water atomizing shown in FIG.

In the method for producing atomized metal powder using the water atomizing method and the gas atomizing method of the present invention, the atomized metal powder is produced while confirming the temperatures of the molten metal 2, the molten metal 6 and the metal powder 9. Hereinafter, a specific method of checking the temperature will be described.

In the production of the water atomized metal powder of the present embodiment, the average temperature when the molten metal 6 is divided by the primary cooling water 7 and the average temperature when the metal powder 9 is cooled by the secondary cooling water 10 are estimated by numerical simulation. ,decide. FIG. 10 shows the area classification used in the numerical simulation in the case of water atomization, and Table 1 shows the calculation conditions and boundary conditions. Energy exchange at the boundary between the molten metal and other substances (air, water, etc.) was performed by the following equation (2). The first term on the right side of the equation (2) is heat transfer and the second term is radiation.
Q/A=h(θ ₀ −θ _∞ )+εσ(θ ₀ ⁴ −θ _∞ ⁴ )... (2)
Q: Calorie (W)
A: Cross-sectional area (m ² )
h: Contact heat transfer coefficient (W/m ² ·K)
θ0: Initial temperature (K)
θ∞: Atmospheric temperature or water temperature, etc. (K) (when the molten metal is in contact with the atmosphere, the atmospheric temperature is used, and when the molten metal is in contact with water, the water temperature is used)
ε: Emissivity (-)
σ: Stefan-Boltzmann coefficient (W/m ² ·K ⁴ ).
The region (i) in FIG. 10 is set in the molten metal nozzle 3 and calculation is performed in a cylindrical coordinate system. In the molten metal nozzle 3, the time interval is changed according to the length of the molten metal nozzle 3 and the moving speed of the molten metal 2 so that the calculated value does not diverge. The heat transfer to the molten metal nozzle 3 is calculated by the contact heat transfer coefficient. The contact heat transfer coefficient is about 2000 to 10000 W/m ² ·K, the emissivity is 0, and the radiation is not calculated. The molten metal temperature was measured by measuring the temperature at the time of melting the raw materials with a radiation thermometer or a thermocouple.

In the region (ii) of FIG. 10, the calculation is performed in the cylindrical coordinate system from the outlet of the molten metal nozzle 3 to the point before the primary cutting start point (corresponding to the AP point in FIGS. 5, 8 and 9) by the primary cooling water. I do. The heat of the molten metal escapes into the space by allowing it to cool, and the radiation is calculated by giving a heat transfer coefficient of about 18 to 50 W/m ² ·K and an emissivity (about 0.8 to 0.95). The average temperature of the molten metal at the time when this calculation was finished was taken as the primary cutting start temperature.

The region (iii) in FIG. 10 is from the first division start point to the first division end point, and is within the first division (in the region where the molten metal is divided into metal powder), and from here the spherical coordinate system Calculated by. The diameter of the spherical coordinates was calculated using the average particle size (production target average particle size). The heat of the molten metal is transferred to the cooling water by forced convection, but film boiling conditions were included. The heat transfer coefficient is about 200 to 1000 W/m ² ·K. Radiation was also calculated. In the case of gas atomization, it was set to about 100 to 400 W/m ² ·K.

The area (iv) in FIG. 10 is an area for performing spheroidization from the primary cutting end point to the secondary cooling start point, and the distance from the primary cutting end point to the secondary cooling start point is the spheroidizing distance (LS). ). Since there is water around the molten metal, a larger heat transfer coefficient than that in the region (ii) was given (about 100 to 200 W/m ² ·K). In the case of gas atomization, it was set to about 30 to 100 W/m ² ·K. Radiation was also calculated, and the average temperature of the metal powder at this time was taken as the secondary cooling start temperature.

The region (v) in FIG. 10 is the region of secondary cooling, and the temperature of the metal powder was calculated by the forward difference calculation from the conditions shown in Table 1 and the equation (1).

When the content of iron-based elements (Fe+Co+Ni) is high, the melting point becomes high, so the cooling start temperature is high, and film boiling tends to occur from the beginning of cooling, and the amorphization ratio should be increased to 90% or more by the conventional method. It is difficult. Specifically, the total content of iron-based components (Fe, Ni, Co) is 76% or more in atomic fraction, and the content of Cu is 0.1% or more and 2.0% or less in atomic fraction. If so, it is difficult to increase the amorphization rate. However, according to the present invention, even if the composition of the metal powder is such a composition, the amorphization rate can be increased, so that the magnetic flux density can be increased. As a result, the manufacturing method of the present invention contributes to downsizing and high output of the motor.

Further, the total content of the iron-based components (Fe, Ni, Co) is more than 82.9% and less than 86.0% in atomic fraction, and contains at least three kinds selected from Si, P, B and Cu. In the composition described above, if the average particle size of the metal powder to be produced is set to 5 μm or more, it has been extremely difficult to increase the amorphization rate to 90% or more. However, according to the present invention, the total content of iron-based components (Fe, Ni, Co) is more than 82.9% and less than 86.0% in atomic fraction, and at least 2 selected from Si, P and B is used. When the seed and Cu are contained, the amorphization rate can be 90% or more even if the average particle diameter is 5 μm or more. Here, in the present invention, the upper limit of the average particle diameter that can make the amorphization rate 90% or more is 75 μm. The particle diameter is measured by classifying by a sieving method, and the average particle diameter (D50) is calculated by an integrating method. Laser diffraction/scattering particle size distribution measurement may also be used.

If the atomized metal powder contains a large amount of iron-based elements, it is possible to achieve both low loss and high magnetic flux density by subjecting the present metal powder to an appropriate heat treatment.

In addition, in recent years, Materia Vol. 41 No. 6 P. 392, Journal of Applied Physics 105, 013922 (2009), Japanese Patent No. 4288687, Japanese Patent No. 4310480, Japanese Patent No. 4815014, WO2010/084900, Japanese Patent Publication No. 2008-231534, Japanese Patent Publication No. 2008-231533. Hetero-amorphous materials having high magnetic flux density and nano-crystalline materials have been developed as disclosed in Japanese Patent Publication No. 2710938 and Japanese Patent Publication No. 2710938. The present invention is very advantageously applicable to the production of the metal powder containing a large amount of these iron-based elements by the water atomizing method. In particular, when the Fe-based component concentration in the atomic content (%) is in the range of 80%, it was difficult to increase the amorphization rate by the conventional technique. However, when the production method of the present invention is applied, the amorphization rate after water atomization can be set to 90% or more, and the apparent density can be set to 3.5 g/cm ³ or more.

Furthermore, in the prior art, it was extremely difficult to set the amorphization rate to 90% or more and the average particle diameter of iron powder particles to 5 μm or more. When the particle size is large, the inside of the particles, which is cooled later than the surface, is gradually cooled, so that a large amorphization rate tends not to be stably obtained. However, if the manufacturing method of the present invention is applied, the amorphization rate can be 90% or more even if the average particle size is increased. Since the amorphization ratio can be set to 90% or more and the average particle size of 5 μm or more, the saturation magnetic flux density value becomes high if an appropriate heat treatment is performed after molding.

Examples and comparative examples of the method for producing atomized metal powder according to the present embodiment will be described. The effects of the present invention were verified by using the manufacturing equipment schematically shown in FIGS. 4, 5 and 6 for water atomization and the manufacturing equipment schematically shown in FIGS. 7, 8 and 9 for gas atomization. 4 to 9, some components (eg, pressure gauge, thermometer, flow meter, etc.) are not shown.
In carrying out the manufacturing methods of Examples and Comparative Examples, soft magnetic materials having the following compositions were prepared. "%" means "at (atomic content)%". (I) to (v) are compositions of the Fe-based soft magnetic raw material. (Vi) is the composition of the Fe+Co based soft magnetic material. (Vii) is the composition of the Fe+Co+Ni soft magnetic material.
(I) Fe76%-Si9%-B10%-P5%
(Ii) Fe 78%-Si 9%-B 9%-P 4%
(Iii) Fe 80%-Si 8%-B 8%-P 4%
(Iv) Fe82.8%-B11%-P5%-Cu1.2%
(V) Fe84.8%-Si4%-B10%-Cu1.2%
(Vi) Fe69.8%-Co15%-B10%-P4%-Cu1.2%
(Vii) Fe69.8%-Ni1.2%-Co15%-B9.4%-P3.4%-Cu1.2%
Although the composition components were adjusted so as to have the above composition, the actual composition may contain an error of about ±0.3% in atomic content or other impurities at the time of melting and atomizing. is there. In addition, during composition, during atomization, and after atomization, some compositional changes may occur due to oxidation, mixing of nanoparticles, and the like.

In this example, the average particle size of the nanoparticles was determined by measuring the specific surface area by the gas adsorption method.

<Example 1>
Example 1 is based on the equipment of FIGS. 4 and 5, and the primary division is water atomization. The amount of molten metal dropped was adjusted to 8 to 10 kg/min. The conditions for the primary cutting were that the focusing angle α of the cone guide 8 was 23°, and the average temperature of the molten metal at the primary cutting was 100° C. or higher than the solidification temperature of each raw material. Twelve solid nozzles were used as the cooling water injection nozzles for the primary division, and they were arranged at intervals of 30° on the circumference. The injection pressure of cooling water was 10 MPa, and the amount of cooling water was 180 L/min. The falling speed of the molten metal was 110 m/s, and the spheroidization time was 0.002 seconds by setting LS to 0.22 m.

In the secondary cooling, the average temperature of the molten metal at the start of cooling was set within 50° C. from the solidification temperature. The nozzle is a flat spray, the spray angle is 30°, and the mounting angle is 15° downward, and the spray is performed in a diagonal direction. The number of nozzles is 12, and they are arranged at intervals of 30° in the circumferential direction. Nanoparticles are mixed with 1.0% by weight of nano silica having an average particle size of 25 nm in cooling water. C.), the cooling water injection amount was 480 L/min, and the injection pressure was 10 MPa.
<Example 2>
Example 2 was carried out by mixing 1% by weight of cooling water with alumina particles having an average particle diameter of 31 nm for secondary cooling. The other points are the same as in Example 1.
<Example 3>
Example 3 was carried out by mixing 1% by weight of cooling water with titania particles having an average particle size of 36 nm in the secondary cooling. The other points are the same as in Example 1.
<Example 4>
Example 4 uses the equipment of FIGS. 7 and 8, and the primary division is by gas atomization. The amount of molten metal dropped was adjusted to be 4 to 5 kg/min. The condition of the primary cutting was that the focusing angle α of the nozzle was 40°, and the average temperature of the molten metal at the time of the primary cutting was 100° C. or higher than the solidification temperature of each raw material. The gas injection pressure for the primary division was 1.0 MPa, the hole diameter of the injection nozzle was 0.15 mm, and 36 holes were arranged at equal intervals in the circumferential direction at intervals of 10°. The dropping speed of the molten metal was about 45 m/s, and the spheroidizing time was 0.002 seconds by setting LS to 0.09 m. In the secondary cooling, the average temperature of the molten metal at the start of cooling was set within 50° C. from the solidification temperature. The nozzle is a flat spray, the spray angle is 30°, and the mounting angle is 15° downward, and the spray is performed in a diagonal direction. The number of nozzles is 12, and they are arranged at intervals of 30° in the circumferential direction. Nanoparticles are mixed with 1.0% by weight of nano silica having an average particle size of 25 nm in cooling water. ), the cooling water injection amount was 240 L/min, and the injection pressure was 10 MPa.
<Example 5>
In Example 5, the primary division according to FIG. 9 is due to gas atomization. The amount of molten metal dropped was adjusted to be 4 to 5 kg/min. The conditions for the primary cutting were that the focusing angle α of the nozzle was 40°, and the average temperature of the molten metal at the time of the primary cutting was 100° C. or higher than the solidification temperature of each raw material. The gas injection pressure for the primary division was 1.0 MPa, the hole diameter of the injection nozzle was 0.15 mm, and 36 holes were arranged at equal intervals in the circumferential direction at intervals of 10°. The dropping speed of the molten metal was about 45 m/s, and the spheroidizing time was 0.002 seconds by setting LS to 0.09 m.
In the secondary cooling, the average temperature of the molten metal at the start of cooling was set within 50° C. from the solidification temperature. A diagonal plate having a width of 250 mm and a length of 300 mm is installed at an angle of 45° so that the LS of the jet center is 0.09 m, and four solid type water jet nozzles are arranged from the upper part of the diagonal plate. Nanofluidic cooling water was jetted along. For nanoparticles, silica with an average particle size of 25 nm was mixed in cooling water at 1.0% by weight, the cooling water was adjusted to 10° C. (±2° C.) by a temperature controller, the cooling water injection amount was 240 L/min, and the injection pressure was 10 MPa. did.
<Comparative Example 1>
In Comparative Example 1, the secondary cooling water was cooled without mixing the nanoparticles. The other conditions are the same as in Example 1.
<Comparative example 2>
In Comparative Example 2, the secondary cooling water was cooled without mixing the nanoparticles. The other conditions are the same as in Example 4.
<Comparative example 3>
In Comparative Example 3, the secondary cooling water was cooled without mixing the nanoparticles. The other conditions are the same as those in Example 5.
<Comparative example 4>
In Comparative Example 4, the LS distance was set to 0 mm, and secondary cooling water was carried out immediately after the primary division. The other conditions are the same as in Example 1.
<Comparative Example 5>
In Comparative Example 5, the LS distance was set to 0 mm, and secondary cooling water was carried out immediately after the primary division. The other conditions are the same as in Example 4.
<Comparative example 6>
In Comparative Example 6, the LS distance was set to 135 mm, and the secondary cooling water was implemented 0.0003 seconds after the primary disconnection. The other conditions are the same as in Example 4.
<Comparative Example 7>
In Comparative Example 7, 0.01% by weight of silica, which is nanoparticles, was mixed in the secondary cooling water and cooled. The other conditions are the same as in Example 4.

In each of the examples and comparative examples, the average temperature of the molten metal during the primary cutting and the average temperature of the divided molten metal during the secondary cooling were estimated by the method shown in FIG.

Tables 2 and 3 show the results of measuring the average particle size, the amorphization ratio, and the apparent density after the conditions of this example and comparative example and after the execution.

The average particle size was determined by a wet measurement using a laser diffraction scattering method. The apparent density was measured according to JIS Z 2504:2012. The degree of amorphization is obtained by removing dust other than the metal powder from the obtained metal powder, and then measuring a halo peak from the amorphous (amorphous) and a diffraction peak from the crystal by an X-ray diffraction method. It was calculated by the WPPD method. The “WPPD method” here is an abbreviation for Whole-powder-pattern decomposition method. For the WPPD method, refer to Hideho Toraya: Journal of the Crystallographic Society of Japan, vol. 30 (1988), No. 4, P253-258 for detailed explanation.
In Tables 2 and 3, those having an apparent density of 3.0 g/cm ³ or more and an amorphization rate of 90% or more were rated as “◯”. A sample having an apparent density of 3.0 g/cm ³ or more and an amorphization rate of 98% or more was marked with “⊚”. The case where the apparent density was 3.0 g/cm ³ or more and the amorphization rate was 90% or more and at least one of them was not satisfied was defined as “x”.

In each of Examples 1 to 5, the apparent density was 3.0 g/cm ³ or more and the amorphization rate was 90% or more within the scope of the present invention. Further, when the metal powder of the example was subjected to an appropriate heat treatment after molding, nano-sized crystals were precipitated. The size (crystal size) of the deposited nano-precipitates was measured by XRD (X-ray diffractometer) and then determined by using Scherrer's formula. In this Scherrer's formula, K is a form factor (generally 0.9 is used), β is a peak full width at half maximum (but radian value), θ is 2θ=52.505° (Fe110 plane), and τ is a crystal size. ..
τ=Kλ/βcooθ (Scherrer's formula)
In Comparative Examples 1 to 3, the nanoparticles were not mixed, so the apparent density was 3.0 g/cm ³ , but the cooling rate was insufficient and the amorphization rate was not improved.

In Comparative Examples 4 and 5, since the LS distance was not provided, the spheronization time was insufficient and the degree of amorphization was achieved, but the apparent density was less than 1.2 g/cm ³ . In Comparative Example 6, the LS distance was short, the spheronization time was insufficient, and the apparent density was less than 3.0 g/cm ³ .

In Comparative Example 7, nanoparticles were mixed, but the concentration was too low, so the amorphization ratio was partially improved, but it was not 90% or more.
As a result, it was found that the apparent density was 3.0 g/cm ³ or more when the spheroidizing time of 0.0004 seconds or more was secured.

1 Tundish 2 Molten metal 3 Molten metal nozzle 4 Primary cooling water nozzle header 5 Primary cooling water injection nozzle 6 Molten metal 7 Primary cooling water 8 Cone guide 9 Separated metal powder 10 Secondary cooling water 14 Water atomizing device 15 Cooling Water Tank 16 Temperature Controller 17 High Pressure Pump for Primary Cooling 18 Primary Cooling Pipe 19 Chamber 23 High Pressure Gas Pipe 24 Compressor 25 Gas Holder 26 Primary Gas Injection Device 27 Inert Gas 28 Gas Atomizing Device 31 Secondary Cooling water temperature controller 32 Secondary cooling tank 33 Stirrer 34 Nanoparticle charging machine 35 Secondary cooling water piping 36 Secondary cooling high pressure pump 37 Secondary cooling injection nozzle 38 Secondary cooling injection nozzle 39 Oblique collision plate AP Atomization point of primary cooling (division) LS Sphericalization distance

Claims (5)

Cooling water is sprayed from the periphery of the molten metal falling in the vertical direction to divide the molten metal, and after the division, the molten metal is dropped for 0.0004 seconds or more,
After being dropped, cooling water containing 0.05% by weight to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, is jetted from around the molten metal to cool the molten metal,
A method for producing an atomized metal powder, which comprises producing a metal powder having a total content of Fe, Ni, and Co of 76.0% to 86.0% in atomic fraction. A high-pressure inert gas with an injection pressure of 0.5 MPa or more is jetted from the periphery of the molten metal falling in the vertical direction to divide the molten metal, and after the division, the molten metal is dropped for 0.0004 seconds or more,
After being dropped, cooling water containing 0.05% by weight to 2.0% by weight of nanoparticles, which are particles having an average particle size of 5 nm to 100 nm, is jetted from around the molten metal to cool the molten metal,
A method for producing an atomized metal powder, which comprises producing a metal powder having a total content of Fe, Ni, and Co of 76.0% to 86.0% in atomic fraction. Nanoparticles are
The method for producing atomized metal powder according to claim 1, comprising at least one of pure metal particles, metal oxide particles, metal nitride particles, and metal carbide particles. The method for producing atomized metal powder according to claim 3, wherein the metal oxide-based particles are any of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), and titania (TiO ₂ ). The method for producing an atomized metal powder according to any one of claims 1 to 4, wherein the atomized metal powder produced contains at least two kinds selected from Si, P and B and Cu.