CN111971761A - Iron-based soft magnetic powder and method for producing same, and article comprising iron-based soft magnetic alloy powder and method for producing same - Google Patents
Iron-based soft magnetic powder and method for producing same, and article comprising iron-based soft magnetic alloy powder and method for producing same Download PDFInfo
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Abstract
An iron-based soft magnetic powder is an iron-based soft magnetic powder in which a part of an amorphous phase is crystallized by heat treatment to precipitate microcrystals, and is characterized by containing Si, B, Cu, Nb and unavoidable impurities and having a higher crystallinity than that at which the coercive force is minimum.
Description
Technical Field
The present invention relates to an iron-based soft magnetic powder exhibiting good magnetic properties even in a state of being subjected to stress, a method for producing the same, an article containing the iron-based soft magnetic alloy powder, and a method for producing the same.
Background
A dust core for choke coils, reactor coils, and the like is manufactured by adding an insulating binder such as an epoxy resin to soft magnetic powder and molding the mixture into a predetermined shape by injection molding, press molding, or the like. At this time, the powder magnetic core is manufactured in a state where the soft magnetic powder is loaded with stress.
As soft magnetic powder used for producing a dust core, for example, iron-based nanocrystalline alloy powder as described in patent document 1 has been conventionally used. Such an iron-based nanocrystalline alloy powder is produced by producing an alloy having an amorphous phase as a whole, and then performing heat treatment to crystallize it into a nanocrystalline state.
Then, as disclosed in patent document 2, for example, an iron-based soft magnetic alloy powder is subjected to a heat treatment for precipitating a bcc phase, and the magnetic powder system is adjusted and used so as to minimize the coercive force.
Patent document 1: japanese patent laid-open No. Hei 1-79342
Patent document 2: japanese patent laid-open publication No. 2010-280956
Disclosure of Invention
However, even in the case where the magnetostatic characteristics (coercive force) of the obtained magnetic powder have been optimized, there still remains the following problem: when the magnetic powder is subjected to stress in a powder magnetic core manufacturing process accompanied by pressurization such as injection molding or press molding to form a powder magnetic core, optimum magnetic properties (permeability and core loss) of the magnetic core are not necessarily exhibited.
Accordingly, an object of the present invention is to provide an iron-based soft magnetic powder that exhibits optimum core magnetic characteristics as a dust core even in a state where stress is applied by injection molding, compression molding, or the like, a method for producing the same, and an article containing the iron-based soft magnetic alloy powder and a method for producing the same.
The present inventors have found that iron-based soft magnetic powder having excellent magnetostatic properties and further optimized magnetostatic properties does not necessarily exhibit optimum magnetic core properties when it is used as a powder magnetic core under stress caused by injection molding or compression molding with pressurization. The present inventors have made extensive studies and as a result, have found that by adjusting the crystallinity, optimum magnetic properties of a core such as a dust core can be exhibited even in a state where the iron-based soft magnetic powder is subjected to stress by injection molding or press molding accompanied by pressurization, and have completed the present invention.
That is, the present invention is an iron-based soft magnetic powder in which a part of an amorphous phase is crystallized by heat treatment to precipitate microcrystals, the iron-based soft magnetic powder containing Si, B, Cu, Nb and inevitable impurities and having a higher crystallinity than that when the coercive force is minimum.
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, wherein the iron-based soft magnetic powder has a composition of:
Fe100-(x+y+z+r)SixByCuzNbr
[ wherein x, y, z and r are in at% ]
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
A relation of (c) ].
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, wherein the crystallinity is 80 to 95%.
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, wherein the powder hardness is 1000 to 1250HV measured according to ISO 14577-1.
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, which is substantially spherical.
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, wherein the average particle diameter is 0.5 to 50 μm.
According to an aspect of the present invention, there is provided the iron-based soft magnetic powder, wherein 0.5 to 2.0 at% of Fe is replaced with Cr.
According to an aspect of the present invention, there is provided an article including the iron-based soft magnetic powder subjected to stress by press molding.
According to an aspect of the present invention, there is provided the above-mentioned article, which is a dust core.
According to one aspect of the present invention, there is provided a method for producing an iron-based soft magnetic powder, including the steps of:
1 st step
Weighing raw materials so that Fe, Si, B, Cu, and Nb constituting the iron-based soft magnetic powder have a predetermined composition, and melting the raw materials to obtain an alloy melt;
2 nd step
Obtaining substantially spherical amorphous particles from the alloy melt obtained in the step 1 by an atomization method;
step 3
And (3) a step of heat-treating the amorphous particles obtained in the step (2) to crystallize a part of the amorphous phase and precipitate microcrystals, wherein the degree of crystallinity is higher than that when the coercivity is at a minimum.
According to one aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein in step 1, raw materials are weighed so as to have the following composition, the raw materials are melted to obtain an alloy melt,
Fe100-(x+y+z+r)SixByCuzNbr
[ wherein x, y, z and r are in at% ]
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
The relationship (2) of (c). ]
According to an aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein the heat treatment temperature in the 3 rd step is higher than the heat treatment temperature at which the coercivity is minimized and lower than the crystallization temperature of the amorphous phase.
According to an aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein the crystallinity in the 3 rd step is set to 80 to 95%.
According to an aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein the powder hardness is made smaller than the hardness at which the coercivity is the minimum.
According to one aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein the powder hardness is set to 1000 to 1250HV on the basis of the powder hardness measured according to ISO 14577-1.
According to an aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein the average particle diameter is set to 0.5 to 50 μm.
According to an aspect of the present invention, there is provided the method for producing an iron-based soft magnetic powder, wherein 0.5 to 2.0 at% of Fe is replaced with Cr.
According to an aspect of the present invention, there is provided a method for producing an article, including a press molding step after the method for producing the iron-based soft magnetic powder.
According to an aspect of the present invention, there is provided the method of manufacturing the above-described article, wherein the article is a dust core.
Effects of the invention
According to the iron-based soft magnetic powder and the method for producing the same of the present invention, in the iron-based soft magnetic powder containing Si, B, Cu, and Nb and having a microcrystalline precipitated by crystallizing a part of an amorphous phase by heat treatment, the iron-based soft magnetic powder can exhibit good magnetic properties as a dust core or the like even in a state where the iron-based soft magnetic powder is subjected to stress by injection molding, compression molding, or the like by making the crystallinity higher than that when the coercive force is the minimum.
Drawings
FIG. 1 is a graph showing the relationship between the crystallinity and the magnetic permeability in examples.
FIG. 2 is a graph showing the relationship between the crystallinity and the core loss in the examples.
Detailed Description
Hereinafter, an embodiment of the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be implemented by applying appropriate modifications within a range not impairing the effects of the present invention. In the following description, "a to B" mean "a is not less than a but not more than B".
The iron-based soft magnetic powder of the present embodiment contains Si, B, Cu, and Nb, and is formed by crystallizing a part of an amorphous phase by heat treatment to precipitate fine crystals. In such an iron-based soft magnetic powder, an alloy in which crystallites having a body-centered cubic structure (bcc phase) containing Fe as a main component and crystallites having a face-centered cubic structure (fcc phase) containing Cu as a main component are dispersed in an amorphous phase can be formed by heat treatment, and excellent magnetostatic characteristics can be obtained.
Then, since the precipitation form of the nanocrystallites can be changed by the heat treatment temperature, the magnetostatic characteristics of the iron-based soft magnetic powder can be adjusted to a desired state.
In particular, when the iron-based soft magnetic powder has the following composition, it can be an iron-based soft magnetic powder exhibiting more excellent magnetic characteristics when used in a state in which a powder magnetic core or the like is subjected to stress by pressure molding such as injection molding or press molding.
Fe100-(x+y+z+r)SixByCuzNbr
[ wherein x, y, z and r are in at% ]
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
The relationship (2) of (c). ]
Si improves amorphous phase forming ability. In order to have sufficient amorphous phase forming ability and obtain good magnetic properties, the amount x of Si is preferably such that the amount ratio of Si/Fe to Fe is substantially constant and is 3.0 to 16.0 at%.
B and Nb improve the amorphous phase forming ability. In particular, when an iron-based soft magnetic powder is produced by the atomization method, Nb is an essential component. Here, it is preferable that the amount of B is 6.0 at% or more because the amorphous phase forming ability is increased and 13.0 at% or less because good magnetic properties are exhibited.
The sum y + r of the amount y of B and the amount r of Nb is preferably 11.5. ltoreq. y + r. ltoreq.14.5 (at%). When the amount is 11.5 at% or more, the ability to form an amorphous phase becomes large, and when the amount is 14.5 at% or less, good magnetic characteristics are exhibited.
Cu and Nb are elements having an effect of controlling the particle size of the precipitated nanocrystals. Here, the effect of controlling the grain size of the nanocrystallites is greatly influenced by the amount of Cu, and when the amount of Cu z is 0.5 at% or more, a structure in which nanocrystallites having a grain size number of 10nm are dispersed in an amorphous phase can be easily obtained. This makes it possible to produce an iron-based soft magnetic powder exhibiting good magnetic properties after heat treatment. Further, when the content is 2.0 at% or less, it is preferable because it shows good magnetic properties.
Further, the sum z + r of the Cu amount z and the Nb amount r is preferably 1.5. ltoreq. z + r. ltoreq.4.5 (at%). When the content is 1.5 at% or more, the effect on the control of the particle size of the nanocrystal is effectively exerted, and when the content is 4.5 at% or less, the excellent magnetic properties are exhibited.
The crystallinity of the iron-based soft magnetic powder formed by the following heat treatment is higher than that when the coercive force is the minimum in the powder state.
The crystallinity of the iron-based soft magnetic powder is preferably 80 to 95%. Thus, an iron-based soft magnetic powder exhibiting good magnetic characteristics even when used for a magnetic component manufactured under a state of being loaded with a compressive stress can be produced.
The "crystallinity" in the present invention is the proportion of crystal phases precipitated in the powder, and for example, "crystallinity 80%" means that the proportion of crystal phases is 80%, and the remainder of 20% is an amorphous phase. The "crystallinity" in the present invention was calculated by the following peak separation using an X-ray diffraction method. (Kabushiki Kaishi science (2010 issue.) X-ray analysis Manual (6 th edition) Kabushiki Kaishi science)
(1) Separation of background
A straight line is drawn from the low angle side to the high angle side by linear approximation, and the area below the straight line is set as the background.
(2) Separation of halos
The halo pattern due to the amorphous component is estimated, and the halo portion is separated from the scattering curve obtained by subtracting the substrate.
(3) Separation of crystalline diffraction lines
The crystalline diffraction line was separated by the same method as in (2) above.
(4) Calculation of degree of crystallinity
The crystallinity was calculated by the following equation using the area under the curve (integrated intensity) of the diffraction curve of the amorphous component and the crystalline component separated from the total scattering curve.
(math formula 1)
Xc＝Ic/(Ic+Ia)
Xc: crystallinity, Ic: crystalline scattering intensity, Ia: amorphous scattering intensity
A dust core for choke coils, reactor coils, and the like is manufactured by adding an insulating binder such as an epoxy resin to soft magnetic powder and molding the mixture into a predetermined shape by injection molding, press molding, or the like. At this time, the powder magnetic core is manufactured in a state where the soft magnetic powder is loaded with stress.
The hardness of the iron-based soft magnetic powder is preferably 1000 to 1250 HV. Thus, since the fluidity is good when injection molding or press molding is performed, an iron-based soft magnetic powder exhibiting good magnetic properties can be obtained when the powder is formed into a dust core or the like.
The iron-based soft magnetic powder is formed into a substantially spherical shape. This makes it possible to increase the filling ratio of the iron-based soft magnetic powder in the dust core during injection molding or compression molding, and thus to improve the magnetic properties. Here, not all the powder shapes need to be substantially spherical, and for example, when the major diameter of the particles is a and the minor diameter is b, the proportion of particles satisfying the relationship of 1. ltoreq. a/b. ltoreq.1.2 may be 70% or more.
When the average particle size of the iron-based soft magnetic powder is 0.5 to 50 μm, the iron-based soft magnetic powder can be made into a dust core or the like, and the filling ratio of the iron-based soft magnetic powder can be increased while ensuring insulation of the dust core or the like, thereby improving the magnetic properties. If the particle diameter is small, the eddy current loss becomes small when the dust core is used in a high frequency band, and therefore, the loss can be low, but if the particle diameter is too small, a sufficient magnetic permeability μ cannot be obtained, and therefore, it is preferably 0.5 μm or more. Further, if the average particle size of the iron-based soft magnetic powder is 10 μm or less, it is more preferable to use a dust core in a high frequency band of 1MHz or more because eddy current loss can be reduced and a necessary and sufficient magnetic permeability μ can be obtained.
The article of the present embodiment contains the iron-based soft magnetic powder that is subjected to stress by press molding. The article of the present embodiment is a member having soft magnetism used for various applications such as electronic devices and parts for automobiles, and particularly a dust core. An article, particularly a dust core, containing the iron-based soft magnetic powder subjected to stress by pressure molding such as injection molding or press molding exhibits good magnetic properties (permeability and core loss) of the iron-based soft magnetic powder.
(production method)
A method for producing the iron-based soft magnetic powder will be described.
In step 1, raw materials are weighed so that Fe, Si, B, Cu, and Nb have a predetermined composition (for example, a preferable composition described below), and melted to obtain an alloy melt.
Fe100-(x+y+z+r)SixByCuzNbr
[ wherein x, y, z and r are in at% ]
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
The relationship (2) of (c). ]
In the subsequent 2 nd step, substantially spherical amorphous particles are obtained from the alloy melt obtained in the 1 st step by an atomization method.
In the present embodiment, a known water atomization method is used. The alloy melt obtained in step 1 is dropped from the melt orifice, and the molten raw material is rapidly solidified by a water film sprayed from an atomizing nozzle. The powder is recovered, dried and classified to obtain amorphous particles having a predetermined particle diameter and a substantially spherical particle shape.
In the subsequent 3 rd step, the amorphous particles obtained in the 2 nd step are subjected to a heat treatment to crystallize a part of the amorphous phase. At this time, the crystallinity of the powder is made higher than that when the coercive force is minimum.
The heat treatment in the present invention is used for: the magnetic properties are adjusted by maintaining the amorphous phase at a predetermined temperature in a nitrogen atmosphere, crystallizing a part of the amorphous phase, and precipitating nano-crystallites of several tens of nanometers. Here, the heat treatment may be performed in the atmosphere without considering prevention of oxidation of the powder and the like.
When a thermal analysis (DSC) curve of the iron-based soft magnetic powder was performed, 2 exothermic peaks were seen. The temperature Tx of the exothermic peak on the low temperature side is the bcc phase precipitation temperature for precipitating the body-centered cubic structure crystal phase, and the temperature T1 of the exothermic peak on the high temperature side is the crystallization temperature of the amorphous phase.
In the iron-based soft magnetic powder of the present invention, an alloy in which crystallites having a body-centered cubic structure (bcc phase) containing Fe as a main component and crystallites having a face-centered cubic structure (fcc phase) containing Cu as a main component are dispersed in an amorphous phase can be formed by heat treatment, and excellent magnetostatic characteristics can be obtained.
Then, since the precipitation form of the nanocrystallites can be changed by the heat treatment temperature, the magnetostatic characteristics of the iron-based soft magnetic powder can be adjusted to a desired state.
As magnetic characteristics reflecting the characteristics of the dust core, the magnetic permeability μ and the core loss Pcv are important. Here, the permeability μ is preferably high, and the core loss Pcv is preferably low.
In the state of the powder body, when the coercive force Hc is low, the magnetic permeability μ becomes high, and the core loss can be reduced, so heat treatment has been conventionally performed so that the coercive force Hc is minimum.
However, even in the case where the magnetostatic characteristics (coercive force) of the obtained magnetic powder have been optimized, there still remains the following problem: when the magnetic powder is subjected to stress in the process of producing a powder magnetic core such as injection molding or press molding to form a powder magnetic core, optimum magnetic properties (permeability and core loss) of the core are not necessarily exhibited.
When the heat treatment temperature exceeds the heat treatment temperature T2 at which the coercive force Hc is minimum, the coercive force Hc increases, which is not a preferable condition in view of the static magnetic properties of the powder. In this case, the crystallinity increases and the hardness decreases.
On the other hand, at a heat treatment temperature of not less than the heat treatment temperature T2 at which the coercive force Hc is the minimum, there is a heat treatment temperature T3 at which the magnetic permeability μ, which indicates the magnetic properties of the core of the dust core, exhibits the maximum value and the core loss exhibits the minimum value.
The present inventors have found an iron-based soft magnetic powder that exhibits optimum magnetic properties (permeability, core loss) of a magnetic core by setting a heat treatment temperature to T3 higher than a heat treatment temperature T2 at which coercivity Hc is minimum and lower than a crystallization temperature T1 of an amorphous phase, and adjusting crystallinity, hardness, and the like.
The heat treatment temperature T3 is preferably set so that the crystallinity of the iron-based soft magnetic powder is 80 to 95%.
The heat treatment temperature T3 is preferably set to 1000 to 1250 HV.
Thus, when a powder magnetic core is formed by applying stress by injection molding or press molding in the process of manufacturing the powder magnetic core, it is possible to produce an iron-based soft magnetic powder having an optimum magnetic characteristic of the core.
The method for producing an article according to the present embodiment includes a press molding step after the method for producing an iron-based soft magnetic powder. An article (particularly, a dust core) obtained by the method for producing a dust core according to the present embodiment exhibits good magnetic properties (permeability, core loss) of the core due to the properties of the iron-based soft magnetic powder.
(modification example)
When a dust core is used for electronic parts and the like, a material having high corrosion resistance against moisture and the like is required. In the iron-based soft magnetic powder, 0.5 to 2.0 at% of Cr in Fe may be substituted. This improves corrosion resistance while maintaining good magnetic properties.
As the atomization method, a gas atomization method, an oil atomization method, or the like may be employed.
According to the iron-based soft magnetic powder and the method for producing the same of the present invention, by making the crystallinity higher than that when the coercive force is minimum, it is possible to produce an iron-based soft magnetic powder in which the dust core exhibits good magnetic properties of the core even in a state where the iron-based soft magnetic powder is loaded with stress by injection molding or press molding.
Examples
The following shows an embodiment of the present invention. The contents of the present invention are not to be interpreted as being limited to these examples.
The mixed materials prepared to have the compositions shown in table 1 were melted in a high-frequency induction furnace, and soft magnetic powder was obtained by a water atomization method. The results of measurement of the bcc phase precipitation temperature Tx and saturation magnetization (Bs) are also shown in the table. The evaluation conditions for powder production are as follows.
< Water atomization Condition >
Water pressure: 100MPa
Amount of water: 100L/min
Water temperature: 20 deg.C
The orifice diameter:
molten raw material temperature: 1800 deg.C
[ Table 1]
The obtained soft magnetic powder was collected and dried by a vibration vacuum dryer (VU-60: manufactured by CENTRAL CHEMICAL Co., Ltd.). Since the drying is performed under a reduced pressure atmosphere, the drying can be performed under a low oxygen atmosphere as compared with a drying method performed under an atmospheric pressure atmosphere, and further, the drying can be performed at a low temperature for a short time. Further, by applying vibration to the soft magnetic powder during drying, drying can be performed in a shorter time, and aggregation or oxidation of the powder can be prevented. In this example, the drying temperature: pressure in drying chamber at 100 ℃: -0.1MPa (gauge pressure), drying time: for 60 minutes.
Then, the obtained soft magnetic powder was classified by a gas flow Classifier (Turbo Classifier, Nisshin works Co., Ltd.) to obtain powder materials (6 μm, 2 μm) having the desired average particle diameters. The particle size distribution of the powder material was measured by a laser diffraction particle size distribution measuring apparatus (MT3300 EXII: manufactured by Microtrac Bel corporation).
Then, the obtained soft magnetic powder was evaluated for the crystallite diameter, crystallinity, hardness, and coercive force Hc.
The apparatus and conditions for measuring the diameter and crystallinity of the microcrystal are as follows.
The measurement device: powder X-ray diffraction device (MinFlex 600: manufactured by Kyowa Kagaku Co., Ltd.)
Measurement conditions: voltage 40kV, current 15mA, step size of 0.01 degree, speed of 1 degree/min
The crystallite diameter was calculated for the bcc FeSi peak by using the Scherrer equation shown below. Here, a peak near 78 ° was used as the FeSi peak.
[ mathematical formula 2]
Crystallite size
Kappa: scherrer constant
λ: wavelength of X-ray tube
Beta: broadening of diffraction lines due to crystallite size
θ: diffraction angle 2 theta/theta
The hardness measuring apparatus and the measuring method are as follows.
The measurement device: nano-indentor (ENT-2000: manufactured by ELIONIX corporation)
The measurement method: the powder hardness was calculated by applying a load of 5 μ N to 100mN to the particle cross section according to ISO14577-1 and then measuring the size of the indentation.
The coercivity Hc was measured by the following apparatus and method.
The measurement device: vibrating sample magnetometer (VSM-C7 manufactured by Dongyin industries Co., Ltd.)
The measurement method: the VSM measuring capsules were filled with 200mg of the obtained powder material having each particle size distribution, fixed with paraffin, and subjected to a maximum magnetic field of 10000Oe to perform saturation magnetization measurement (Bs) and coercive force measurement (Hc).
Then, the obtained powder material having each particle size distribution was mixed with an epoxy resin (binder) and toluene (organic solvent) to obtain a mixture. The amount of the epoxy resin added was 3 wt% based on the soft magnetic powder material.
The thus-prepared mixture was heated at a temperature of 80 ℃ for 30 minutes and dried to obtain a dried body in the form of a block. Then, the dried product was passed through a sieve having a mesh size of 200 μm to prepare a powder material (granules).
The powder material was filled in a molding die, and a molded body (dust core) was obtained under the following conditions.
< Molding conditions >
The molding method: press forming
Shape of the molded article: in the form of a ring
Dimension of the molded body: the external shape is 13mm, the internal diameter is 8mm, and the thickness is 2mm
Molding pressure: 5t/cm2(490MPa)
Hardening conditions of the molded article: 150 ℃ for 30 minutes
< conditions for coil production >
A lead wire was wound around the molded body under the following conditions to produce a choke coil.
Wire material: cu
Wire diameter of the wire: 0.2mm
Winding number: 45 turns for 1 time and 45 turns for 2 times
< measurement conditions and evaluation >
The magnetic properties (μ, Pcv) of the cores of the choke coils produced under the above conditions were evaluated under the following conditions.
The measurement device: AC magnetic characteristic measuring instrument (rock ventilation instrument B-H analyzer SY8258)
Measurement frequency: 1MHz
Magnetic permeability μmeasurement conditions: applying a magnetic field of 10mT
Magnetic core loss measurement conditions: applying a magnetic field of 25mT
The evaluation results are shown below. For compositions 7 and 8, the heat treatment conditions were set to the following 6 levels, and the coercive force Hc and the hardness HV in the powder state, and the magnetic properties (permeability μ, core loss) of the dust core were evaluated for those with different degrees of crystallinity. The evaluation results are shown in table 2 and fig. 1 and 2. Here, in table 2, test 1 corresponds to the results of composition 7, and test 2 corresponds to the results of composition 8.
[ Table 2]
In both of the tests 1 and 2, the crystallinity increased with the increase in the heat treatment temperature, and the amorphous phase was entirely crystallized at 600 ℃. Here, the crystallization temperature of the amorphous phase can be considered to be about 600 ℃. The reason why crystallization starts at 500 ℃ or lower than the bcc phase precipitation temperature Tx is presumed to be that there is a portion having a local temperature higher than the set temperature due to an exothermic reaction of the powder.
Further, as the magnetostatic properties of the powder, those having a low coercive force Hc and exhibiting the best magnetic properties were subjected to heat treatment at 530 ℃ (tests 1-3 and 2-3). At this time, the crystallinity was 76 in runs 1 to 3 and 74 in runs 2 to 3. Further, the hardness HV was 1250HV in tests 1 to 3 and 1270HV in tests 2 to 3, respectively, showing the highest values.
Conventionally, this state was set as a target state, and the heat treatment temperature was set to 530 ℃.
When the heat treatment temperature exceeds 530 ℃ which is the heat treatment temperature at which the coercive force Hc is minimum, the coercive force Hc increases, which is not a preferable condition from the viewpoint of the magnetostatic properties of the powder.
Here, when the heat treatment temperature is exceeded 530 ℃, the crystallinity increases. Further, the grain size of the precipitated fine crystals becomes large, and the hardness HV decreases.
On the other hand, among the magnetic properties of the core of the dust core, at a heat treatment temperature of 570 ℃, the permeability μ shows the maximum value and the core loss shows the minimum value.
As shown in fig. 1, the crystallinity of the magnetic permeability which is the same as the magnetic permeability of the crystallinity when the coercive force Hc is the minimum (heat treatment temperature 530 ℃) is 94% in test 1 and 93% in test 2.
As shown in fig. 2, the crystallinity of the core loss equivalent to the core loss of the crystallinity with the lowest coercivity Hc was shown, and was 91% in both test 1 and test 2.
That is, it was confirmed that the conditions for optimizing the magnetic properties of the core of the powder magnetic core were that the heat treatment temperature was higher than the heat treatment temperature at which the coercivity was minimum and lower than the crystallization temperature of the amorphous phase, and the crystallinity was higher than the crystallinity at which the coercivity Hc was minimum. In addition, it was also confirmed that when the heat treatment is performed at an excessive temperature, the crystallinity becomes excessively high, and the magnetic properties of the core deteriorate. Accordingly, it was also confirmed that the crystallinity is preferably 80 to 95%.
In addition, the same tendency was confirmed in compositions 1 to 6.
As described above, it was confirmed that the iron-based soft magnetic powder is a material having the optimum magnetic properties of the core when it is used as a dust core with the composition, crystallinity and hardness specified in the present invention.
Claims (19)
1. An iron-based soft magnetic powder comprising an amorphous phase partially crystallized by heat treatment and fine crystals precipitated, characterized in that,
contains Si, B, Cu, Nb and unavoidable impurities,
the crystallinity is higher than that at which the coercive force is minimum.
2. An iron-based soft magnetic powder according to claim 1, having the following composition:
Fe100-(x+y+z+r)SixByCuzNbr
wherein x, y, z and r are in at%
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
The relationship (2) of (c).
3. An iron-based soft magnetic powder according to claim 1 or claim 2, wherein the crystallinity is 80 to 95%.
4. An iron-based soft magnetic powder according to any one of claims 1 to 3, wherein the powder hardness is 1000 to 1250HV measured according to ISO 14577-1.
5. An iron-based soft magnetic powder according to any one of claims 1 to 4, which is substantially spherical.
6. An iron-based soft magnetic powder according to any one of claims 1 to 5, wherein the average particle diameter is 0.5 to 50 μm.
7. An iron-based soft magnetic powder according to any one of claims 1 to 6, wherein 0.5 to 2.0 at% of Fe is replaced by Cr.
8. An article comprising the iron-based soft magnetic powder according to any one of claim 1 to claim 7, which is subjected to stress by press molding.
9. The article of claim 8 which is a dust core.
10. A method for producing an iron-based soft magnetic powder, comprising the steps of:
1 st step
Weighing raw materials so that Fe, Si, B, Cu, and Nb constituting the iron-based soft magnetic powder have a predetermined composition, and melting the raw materials to obtain an alloy melt;
2 nd step
Obtaining substantially spherical amorphous particles from the alloy melt obtained in the step 1 by an atomization method;
step 3
And (3) a step of heat-treating the amorphous particles obtained in the step (2) to crystallize a part of the amorphous phase and precipitate microcrystals, wherein the degree of crystallinity is higher than that when the coercivity is at a minimum.
11. A method for producing an iron-based soft magnetic powder according to claim 10, wherein in the step 1, raw materials are weighed so as to have the following composition, and melted to obtain an alloy melt:
Fe100-(x+y+z+r)SixByCuzNbr
wherein x, y, z and r are in at%
3.0≤x≤16.0
6.0≤y≤13.0
0.5≤z≤2.0
0.5≤r≤4.0
1.5≤z+r≤4.5
11.5≤y+r≤14.5
The relationship (2) of (c).
12. A method for producing an iron-based soft magnetic powder according to claim 10 or claim 11, wherein the heat treatment temperature in the 3 rd step is set to be higher than the heat treatment temperature at which the coercivity is minimum and lower than the crystallization temperature of the amorphous phase.
13. A method for producing an iron-based soft magnetic powder according to any one of claims 10 to 12, wherein the degree of crystallinity in the 3 rd step is set to 80 to 95%.
14. A method for manufacturing an iron-based soft magnetic powder according to any one of claims 10 to 13, wherein the powder hardness is made smaller than the hardness at which the coercive force is the minimum.
15. A method for producing an iron-based soft magnetic powder according to claim 14, wherein the powder hardness is set to 1000 to 1250HV in terms of powder hardness measured according to ISO 14577-1.
16. A method for producing an iron-based soft magnetic powder according to any one of claims 10 to 15, wherein the average particle diameter is set to 0.5 to 50 μm.
17. A method for producing an iron-based soft magnetic powder according to any one of claims 9 to 16, wherein 0.5 to 2.0 at% of Fe is replaced with Cr.
18. A method for producing an article, comprising a press molding step after the method for producing an iron-based soft magnetic powder according to any one of claims 10 to 17.
19. The method of manufacturing an article according to claim 18, the article being a dust core.
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