CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2019/017920 filed on Apr. 26, 2019, claiming priority based on Japanese Patent Application No. 2018-086307 filed on Apr. 27, 2018, Japanese Patent Application No. 2018-089826 filed on May 8, 2018, Japanese Patent Application No. 2018-096304 filed on May 18, 2018, and Japanese Patent Application No. 2018-229113 filed on Dec. 6, 2018.

FIELD OF THE INVENTION

The present invention relates to an alloy powder, an Fe-based, nanocrystalline alloy powder, and a magnetic core.

BACKGROUND OF THE INVENTION

Fe-based nanocrystalline alloys, typically FeCuNbSiB alloys, are used for magnetic devices used in high frequency ranges, because they have excellent magnetic properties such as low loss and high permeability.

The above nanocrystalline Fe-based alloy having excellent magnetic properties can be obtained by rapidly solidifying an alloy melt by quenching by a single-roll method, etc. to obtain an amorphous alloy ribbon, winding the amorphous alloy ribbon to a magnetic core shape, etc., and heat-treating it in a magnetic field to precipitate nano-crystal grains (see, for example, JP 4-4393 A).

Because the alloy obtained by the above single-roll method is in a ribbon shape, the degree of freedom of a magnetic core shape is limited. Namely, because the magnetic core is formed by slitting an alloy ribbon to a width corresponding to the desired height of a magnetic core, and winding the alloy ribbon to the desired inner and outer diameters, its shape is limited to a toroidal or racetrack shape, etc.

With various magnetic core shapes requested, if alloy powders were produced, magnetic cores of various shapes would be easily formed by them, by forming methods such as pressing, extrusion, etc.

Because magnetic cores having various shapes can be obtained by using magnetic material powders, investigation has been conducted to obtain amorphous alloy powders by rapidly solidifying Fe-based alloy melts for Fe-based nanocrystalline alloys including the above FeCuNbSiB alloys by quenching.

For example, as a method for obtaining powder by rapidly solidifying an alloy melt for the above nanocrystalline Fe-based alloy, an atomizing method by water stream rotating at a high speed (see JP 2017-95773 A), and a water-atomizing method are known. Also, J P 2014-136807 A discloses a method of spraying a flame jet onto a molten metal, which may be called “jet-atomizing method.”

However, the production of amorphous alloy powders by quenching a melt by an atomizing method with a high-speed-rotating water stream, etc., encounters problems described below, as compared with the production of alloy ribbons by a single-roll method.

(a) While a single-roll method produces alloy ribbons by rapidly cooling and solidifying an alloy melt by direct contact with a cooled copper alloy, a water-atomizing method, etc. suffer the problem that a steam film generated from water coming into contact with alloy melt particles hinders heat conduction from the alloy to water, resulting in a limited cooling speed.

As a method of overcoming the above problem of hindering heat conduction, there is an atomizing method with a high-speed-rotating water stream for suppressing the formation of a steam film by supplying a high-speed water stream. However, the generation of a steam film cannot completely be prevented theoretically, even by using a steam film-suppressing method such as the atomizing method with a high-speed-rotating water stream, etc., resulting in a more limited cooling speed than in the single-roll method.

(b) While the cooling speed can be easily kept constant with good reproducibility by controlling the thickness of an alloy ribbon to about 20 μm in the single-roll method, the control of alloy melt particle sizes is difficult in the atomizing method with a high-speed-rotating water stream, etc. Because of the unevenness of particle sizes, smaller particles have higher cooling speeds, and larger particles (particularly their inner portions) have lower cooling speeds. Namely, an amorphous phase or a mixed phase of an amorphous phase and fine crystal phases [(Fe—Si) bcc phases] is easily obtained by quenching small particles, while Fe2B crystals deteriorating magnetic properties tend to be precipitated by quenching large particles. In the quenched alloy powder containing a large amount of Fe2B crystals deteriorating magnetic properties, Fe2B crystals remain after heat treatment, making it difficult to obtain low loss, one of excellent magnetic properties.

With respect to the magnetic alloy powder, there are further the following problems.

(c) The phenomenon (skin effect) that a high-frequency magnetic flux flows only near a surface of the magnetic alloy powder takes place more remarkably in higher-frequency applications, and when surface portions of the magnetic alloy powders are magnetically saturated, the surface portions loose a function as a magnetic material, likely resulting in the deterioration of the magnetic properties of the magnetic alloy powders.

(d) Because magnetic cores formed by the Fe-based, nanocrystalline alloy powder have low initial permeability μi, their permeability becomes lower than the initial permeability μi at higher magnetic field intensity H, failing to exhibit good DC superimposition characteristics.

As described above, there are the following requirements in the Fe-based, nanocrystalline alloy powder.

(1) The quenched alloy powder before nanocrystallization should be in an amorphous phase or a mixed phase of an amorphous phase and fine crystal phases [(Fe—Si) bcc phases]. Also, the formation of Fe2B crystals should be suppressed. The fine crystal phases are those not becoming coarser (growing) by heat treatment.

(2) The alloy should have a composition exhibiting as high a saturation magnetic flux density Bs as suppressing magnetic saturation in high-frequency applications.

(3) Magnetic cores formed by the heat-treated, Fe-based, nanocrystalline alloy powder should have high initial permeability μi and excellent DC superimposition characteristics.

OBJECTS OF THE INVENTION

Accordingly, an object of the present invention is to provide an alloy powder stably composed of an amorphous phase or a mixed phase of an amorphous phase and fine crystal phases [(Fe—Si) bcc phases], with the formation of Fe2B crystals suppressed, after quenching.

Another object of the present invention is to provide an Fe-based, nanocrystalline alloy powder obtained by heat-treating the above alloy powder for having excellent magnetic properties, and a magnetic core formed by the Fe-based, nanocrystalline alloy powder for exhibiting excellent magnetic properties.

SUMMARY OF THE INVENTION

As a result of intensive research in view of the above objects, the inventors have found that the above problems can be solved by the alloy powder, the Fe-based, nanocrystalline alloy powder and the magnetic core described below. The present invention has been completed based on such findings.

Thus, the alloy powder of the present invention has an alloy composition represented by Fe100-a-b-c-d-e-fCuaSibBcCrdSneCf, wherein a, b, c, d, e and f are atomic % meeting 0.80≤a≤1.80, 2.00≤b≤10.00, 11.00≤c≤17.00, 0.10≤d≤2.00, 0.01≤e≤1.50, and 0.10≤f≤0.40.

The Fe-based, nanocrystalline alloy powder of the present invention has an alloy composition represented by Fe100-a-b-c-d-e-fCuaSibBcCrdSneCf, wherein a, b, c, d, e and f are atomic % meeting 0.80≤a≤1.80, 2.00≤b≤10.00, 11.00≤c≤17.00, 0.10≤d≤2.00, 0.01≤e≤1.50, and 0.10≤f≤0.40, and an alloy structure containing 20% or more by volume of nanocrystalline structures having an average crystal grain size of 10-50 nm.

The Fe-based, nanocrystalline alloy powder preferably has a saturation magnetic flux density Bs of 1.50 T or more.

The Fe-based, nanocrystalline alloy powder preferably contains in the alloy structure substantially rectangular structures having longitudinal lengths of 20 nm or more and transverse widths of 10-30 nm.

The substantially rectangular structures are preferably observed in Fe-based, nanocrystalline alloy powders having particle sizes of more than 20 μm.

It is preferable that in the Fe-based, nanocrystalline alloy powder, powder having particle sizes of more than 40 μm is 10% or less by mass of the entire powder, powder having particle sizes of more than 20 μm and 40 μm or less is 30% or more and 90% or less by mass of the entire powder, and powder having particle sizes of 20 μm or less is 5% or more and 60% or less by mass of the entire powder.

The magnetic core of the present invention is formed by the above Fe-based, nanocrystalline alloy powder.

The magnetic core preferably has μ10 k/μi of 0.90 or more, wherein μ10 k is permeability at a magnetic field intensity H=10 kA/m, and μi is initial permeability. The initial permeability μi is preferably 15.0 or more.

Effects of the Invention

Because the alloy powder of the present invention is composed of an amorphous phase or a mixed phase of an amorphous phase and fine crystal phases, with the formation of Fe2B crystals suppressed, before nanocrystallization after quenched, an Fe-based, nanocrystalline alloy powder having excellent magnetic properties can be obtained by heat-treating this alloy powder for nanocrystallization. Using this Fe-based, nanocrystalline alloy powder of the present invention, magnetic cores having excellent magnetic properties can be obtained.

