U.S. patent application number 16/971477 was filed with the patent office on 2020-12-03 for soft magnetic alloy and magnetic component.
This patent application is currently assigned to TDK CORPORATION. The applicant listed for this patent is TDK CORPORATION. Invention is credited to Hajime AMANO, Kensuke ARA, Akihiro HARADA, Akito HASEGAWA, Kenji HORINO, Hiroyuki MATSUMOTO, Seigo TOKORO, Kazuhiro YOSHIDOME.
Application Number | 20200377982 16/971477 |
Document ID | / |
Family ID | 1000005087439 |
Filed Date | 2020-12-03 |
United States Patent
Application |
20200377982 |
Kind Code |
A1 |
AMANO; Hajime ; et
al. |
December 3, 2020 |
SOFT MAGNETIC ALLOY AND MAGNETIC COMPONENT
Abstract
Provided is a soft magnetic alloy which has high saturation flux
density, low coercivity, and a high specific resistance, and is
represented by the compositional formula
(Fe.sub.(1-(.alpha.+.beta.))X1.sub..alpha.X2.sub..beta.).sub.(1-(a+b+c+d+-
e))M.sub.aSi.sub.bCu.sub.cX3.sub.dB.sub.e, wherein X1 is at least
one element selected from the group consisting of Co and Ni, X2 is
at least one element selected from the group consisting of Ti, V,
Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth elements, X3 is at
least one element selected from the group consisting of C and Ge,
and M is at least one element selected from the group consisting of
Zr, Nb, Hf, Ta, Mo, and W, and wherein 0.030.ltoreq.a.ltoreq.0.120,
0.020.ltoreq.b.ltoreq.0.175, 0.ltoreq.c.ltoreq.0.020,
0.ltoreq.d.ltoreq.0.100, 0.ltoreq.e.ltoreq.0.030, .alpha..gtoreq.0,
.beta..gtoreq.0, and 0.ltoreq..alpha.+.beta..ltoreq.0.55).
Inventors: |
AMANO; Hajime; (Tokyo,
JP) ; HARADA; Akihiro; (Tokyo, JP) ;
YOSHIDOME; Kazuhiro; (Tokyo, JP) ; HORINO; Kenji;
(Tokyo, JP) ; MATSUMOTO; Hiroyuki; (Tokyo, JP)
; ARA; Kensuke; (Tokyo, JP) ; HASEGAWA; Akito;
(Tokyo, JP) ; TOKORO; Seigo; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TDK CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
1000005087439 |
Appl. No.: |
16/971477 |
Filed: |
February 15, 2019 |
PCT Filed: |
February 15, 2019 |
PCT NO: |
PCT/JP2019/005514 |
371 Date: |
August 20, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 2301/35 20130101;
B22F 2304/054 20130101; B22F 2009/0828 20130101; C22C 45/02
20130101; C21D 9/52 20130101; B22F 1/0018 20130101; C22C 2202/02
20130101; B22F 9/082 20130101 |
International
Class: |
C22C 45/02 20060101
C22C045/02; C21D 9/52 20060101 C21D009/52; B22F 9/08 20060101
B22F009/08; B22F 1/00 20060101 B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2018 |
JP |
2018-028915 |
Claims
1. A soft magnetic alloy represented by a compositional formula
(Fe.sub.(1-(.alpha.+.beta.))X1.sub..alpha.X2.sub..beta.).sub.(1-(a+b+c+d+-
e))M.sub.aSi.sub.bCu.sub.cX3.sub.dB.sub.e, in which X1 represents
one or more selected from a group consisting of Co and X2
represents one or more selected from a group consisting of Ti, V,
Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth elements, X3
represents one or more selected from a group consisting of C and
Ge, M represents one or more selected from a group consisting of
Zr, Nb, Hf, Ta, Mo, and W, 0.030.ltoreq.a.ltoreq.0.120,
0.020.ltoreq.b.ltoreq.0.175, 0.ltoreq.c.ltoreq.0.020,
0.ltoreq.d.ltoreq.0.100, 0.ltoreq.e.ltoreq.0.030, .alpha..gtoreq.0,
.beta..gtoreq.0, and 0.ltoreq..alpha.+.beta..ltoreq.0.55 are
satisfied.
2. The soft magnetic alloy according to claim 1, wherein
0.ltoreq.e.ltoreq.0.010 is satisfied.
3. The soft magnetic alloy according to claim 1, wherein
0.ltoreq.e>0.001 is satisfied.
4. The soft magnetic alloy according to claim 1, wherein
0.730.ltoreq.1-(a+b+c+d+e).ltoreq.0.930 is satisfied.
5. The soft magnetic alloy according to claim 1, wherein
0.ltoreq..alpha.{1-(a+b+c+d+e)}.ltoreq.0.40 is satisfied.
6. The soft magnetic alloy according to claim 1, wherein .alpha.=0
is satisfied.
7. The soft magnetic alloy according to claim 1, wherein
0.ltoreq..beta.{1-(a+b+c+d+e)}.ltoreq.0.030 is satisfied.
8. The soft magnetic alloy according to claim 1, wherein .beta.=0
is satisfied.
9. The soft magnetic alloy according to claim 1, wherein
.alpha.=.beta.=0 is satisfied.
10. The soft magnetic alloy according to claim 1 having a
nano-hetero structure in which initial fine crystals are in an
amorphous.
11. The soft magnetic alloy according to claim 10, wherein an
average grain size of the initial fine crystals is 0.3 to 10
nm.
12. The soft magnetic alloy according to claim 1 having a structure
including Fe-based nanocrystals.
13. The soft magnetic alloy according to claim 12, wherein an
average grain size of the Fe-based nanocrystals is 5 to 30 nm.
14. The soft magnetic alloy according to claim 1 having a thin
ribbon form.
15. The soft magnetic alloy according to claim 1 having a powder
form.
16. A magnetic component comprising the soft magnetic alloy
according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a soft magnetic alloy and a
magnetic component.
BACKGROUND
[0002] Recently, a nano-crystal material has become a main stream
as a soft magnetic material for magnetic component, particularly as
a soft magnetic material for power inductor. For example, Patent
Document 1 discloses an Fe-based soft magnetic alloy having fine
grain size. The nano-crystal material attains a higher saturation
magnetic flux density and the like compared to a conventional
crystal material such as FeSi and an amorphous based material such
as FeSiB and the like.
[0003] However, currently, the magnetic component, particularly the
power inductor, has adapted to a higher frequency and also has
become more compact; thus, a soft magnetic alloy capable of
obtaining a magnetic core with a higher DC superimposition property
and a lower core loss (magnetic loss) is in demand.
[0004] [Patent Document 1] JP Patent Application Laid Open No.
2002-322546
SUMMARY
[0005] Note that, as a method for reducing a core loss of the
above-mentioned magnetic core, it has been considered to decrease a
coercive force and a resistivity particularly of the magnetic body
constituting the magnetic core. Also, as a method of obtaining a
high DC superimposition property, it has been considered to
increase a saturation magnetic flux density particularly of the
magnetic body constituting the magnetic core.
[0006] The object of the present invention is to provide a soft
magnetic alloy and the like having a high saturation magnetic flux
density, a low coercive force, and a high resistivity.
[0007] In order to attain the above object, the soft magnetic alloy
according to the present invention is a soft magnetic alloy
represented by a compositional formula
(Fe.sub.(1-(.alpha.+.beta.))X1.sub..alpha.X2.sub..beta.).sub.(1-(a+b+c+d+-
e))M.sub.aSi.sub.bCu.sub.cX3.sub.dB.sub.e, in which
[0008] X1 represents one or more selected from a group consisting
of Co and
[0009] X2 represents one or more selected from a group consisting
of Ti, V, Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth
elements,
[0010] X3 represents one or more selected from a group consisting
of C and Ge,
[0011] M represents one or more selected from a group consisting of
Zr, Nb, Hf, Ta, Mo, and W,
[0012] 0.030.ltoreq.a.ltoreq.0.120,
[0013] 0.020.ltoreq.b.ltoreq.0.175,
[0014] 0.ltoreq.c.ltoreq.0.020,
[0015] 0.ltoreq.d.ltoreq.0.100,
[0016] 0.ltoreq.e.ltoreq.0.030,
[0017] .alpha..gtoreq.0,
[0018] .beta..gtoreq.0, and
[0019] 0.ltoreq..alpha.+.beta..ltoreq.0.55 are satisfied.
[0020] By satisfying the above-mentioned characteristics, the soft
magnetic alloy according to the present invention tends to easily
attain a structure which easily becomes a Fe-based nanocrystal
alloy by performing a heat treatment. Further, the Fe-based
nanocrystal alloy satisfying the above-mentioned characteristics
becomes a soft magnetic alloy having preferable soft magnetic
properties which are a high saturation magnetic flux density and a
low coercive force, and also having further higher resistivity.
[0021] The soft magnetic alloy according to the present invention
may satisfy 0.ltoreq.e.ltoreq.0.010.
[0022] The soft magnetic alloy according to the present invention
may satisfy 0.ltoreq.e>0.001.
[0023] The soft magnetic alloy according to the present invention
may satisfy 0.730.ltoreq.1-(a+b+c+d+e).ltoreq.0.930.
[0024] The soft magnetic alloy according to the present invention
may satisfy 0.ltoreq..alpha.{1-(a+b+c+d+e)}.ltoreq.0.40.
[0025] The soft magnetic alloy according to the present invention
may satisfy .alpha.=0.
[0026] The soft magnetic alloy according to the present invention
may satisfy 0.ltoreq..beta.{1-(a+b+c+d+e)}.ltoreq.0.030.
[0027] The soft magnetic alloy according to the present invention
may satisfy .beta.=0.
[0028] The soft magnetic alloy according to the present invention
may satisfy .alpha.=.beta.=0.
[0029] The soft magnetic alloy according to the present invention
may have a nano-hetero structure in which initial fine crystals
exist in an amorphous.
[0030] In the soft magnetic alloy according to the present
invention, an average grain size of the initial fine crystals may
be 0.3 to 10 nm.
[0031] The soft magnetic alloy according to the present invention
may have a structure including Fe-based nanocrystals.
[0032] In the soft magnetic alloy according to the present
invention, an average grain size of the Fe-based nanocrystals may
be 5 to 30 nm.
[0033] The soft magnetic alloy according to the present invention
may be a thin ribbon form.
[0034] The soft magnetic alloy according to the present invention
may be a powder form.
[0035] Also, a magnetic component according to the present
invention is made of the above-mentioned soft magnetic alloy.
DETAILED DESCRIPTION
[0036] Hereinafter, an embodiment of the present invention is
described.
[0037] The soft magnetic alloy according to the present embodiment
is represented by a compositional formula
(Fe.sub.(1-(.alpha.+.beta.))X1.sub..alpha.X2.sub..beta.).sub.(1-(a+b+c+d+-
e))M.sub.aSi.sub.bCu.sub.cX3.sub.dB.sub.e, in which
[0038] X1 represents one or more selected from a group consisting
of Co and
[0039] X2 represents one or more selected from a group consisting
of Ti, V, Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth
elements,
[0040] X3 represents one or more selected from a group consisting
of C and Ge,
[0041] M represents one or more selected from a group consisting of
Zr, Nb, Hf, Ta, Mo, and W,
[0042] 0.030.ltoreq.a.ltoreq.0.120,
[0043] 0.020.ltoreq.b.ltoreq.0.175,
[0044] 0.ltoreq.c.ltoreq.0.020,
[0045] 0.ltoreq.d.ltoreq.0.100,
[0046] 0.ltoreq.e.ltoreq.0.030,
[0047] .alpha..gtoreq.0,
[0048] .beta..gtoreq.0, and
[0049] 0.ltoreq..alpha.+.beta..ltoreq.0.55 are satisfied.
[0050] The soft magnetic alloy having the above composition tends
to easily become a soft magnetic alloy made of an amorphous and not
including crystal phases made of crystals having a grain size
larger than 15 nm. Further, in case the soft magnetic alloy is heat
treated, Fe-based nanocrystals tend to easily precipitate. Also,
the soft magnetic alloy including the Fe-based nanocrystals tends
to easily attain a high saturation magnetic flux density, a low
coercive force, and a high resistivity. Further, an oxidation
resistance tends to easily increase.
[0051] In other words, the soft magnetic alloy having the
above-mentioned composition tends to be a starting material of the
soft magnetic alloy in which the Fe-based nanocrystals are
precipitated.
[0052] The Fe-based nanocrystal refers to a crystal of which the
grain size is nano order and a crystal structure of Fe is bcc (body
center cubic structure). In the present embodiment, it is
preferable to precipitate the Fe-based nanocrystals having an
average grain size of 5 to 30 nm. The soft magnetic alloy in which
such Fe-based nanocrystals are precipitated tends to attain a high
saturation magnetic flux density and a low coercive force. Also, a
resistivity tends to be higher.
[0053] Note that, the soft magnetic alloy before the heat treatment
may be solely consisted by an amorphous, however, the soft magnetic
alloy before the heat treatment preferably includes an amorphous
and an initial fine crystal having a grain size of 15 nm or less;
and also preferably the soft magnetic alloy has a nano-hetero
structure in which the initial fine crystals are in the amorphous.
By having the nano-hetero structure in which the initial fine
crystals are in the amorphous, the Fe-based nanocrystals tend to
easily precipitate during the heat treatment. Note that, in the
present embodiment, the initial fine crystals preferably have an
average grain size of 0.3 to 10 nm.
[0054] Hereinafter, each component of the soft magnetic alloy
according to the present embodiment is described.
[0055] M is one or more selected from the group consisting of Zr,
Nb, Hf, Ta, Mo, and W. Also, M is preferably one or more selected
from the group consisting of Nb, Hf, and Zr. As M is one or more
selected from the group consisting of Nb, Hf, and Zr; the
saturation magnetic flux density tends to easily increase and the
coercive force tends to easily decrease.
[0056] M content (a) satisfies 0.030.ltoreq.a.ltoreq.0.120. M
content (a) is preferably 0.050.ltoreq.a.ltoreq.0.100. When a is
small, the crystal phases made of crystals having an average grain
size larger than 15 nm tend to be formed easily in the soft
magnetic alloy before the heat treatment; and the Fe-based
nanocrystals cannot be precipitated by the heat treatment, thus the
coercive force tends to easily increase. When a is large, the
saturation magnetic flux density tends to easily decrease.
[0057] Si content (b) satisfies 0.020.ltoreq.b.ltoreq.0.175. Si
content (b) preferably satisfies 0.030.ltoreq.b.ltoreq.0.100. When
b is small, the coercive force tends to easily increase. Also, in
case b is too large, the saturation magnetic flux density tends to
easily decrease.
[0058] Note that, when M content (a) is small, by increasing Si
content (b), good properties tend to be obtained. On the other
hand, when M content (a) is large, by decreasing Si content (b),
good properties tend to be obtained.
[0059] Cu content (c) satisfies 0.ltoreq.c.ltoreq.0.020. That is,
Cu may not be included. As Cu content decreases, the saturation
magnetic flux density increases; and as Cu content increases, the
coercive force tends to decrease. When c is too large, the
saturation magnetic flux density tends to become low.
[0060] X3 is one or more selected from the group consisting of C
and Ge. X3 content (d) satisfies 0.ltoreq.d.ltoreq.0.100. That is,
X3 may not be included. X3 content (d) is preferably
0.ltoreq.d.ltoreq.0.050. When X3 content is too large, the
saturation magnetic flux density tends to easily decrease, and the
coercive force tends to easily increase.
[0061] B content (e) satisfies 0.ltoreq.e.ltoreq.0.030. That is, B
may not be included. Further, B content (e) preferably satisfies
0.ltoreq.e.ltoreq.0.010, and preferably B is substantially not
included. Note that, "B is substantially not included" means that B
content (e) is 0.ltoreq.e.ltoreq.0.001. When B content is too
large, the saturation magnetic flux density tends to easily
decrease and the coercive force tends to easily increase.
[0062] Fe content (1-(a+b+c+d+e)) is not particularly limited, and
preferably 0.730.ltoreq.1-(a+b+c+d+e).ltoreq.0.930 is satisfied.
Also, 0.780.ltoreq.1-(a+b+c+d+e).ltoreq.0.930 may be satisfied.
When the above-mentioned range is satisfied, the saturation
magnetic flux density tends to easily improve and the coercive
force tends to easily decrease.
[0063] Also, in the soft magnetic alloy according to the present
embodiment, part of Fe may be substituted by X1 and/or X2.
[0064] X1 is one or more selected from the group consisting of Co
and Ni. X1 content (a) may be .alpha.=0. That is, X1 may not be
included. Also, a number of X1 atoms is preferably 40 at % or less
when a number of atoms of entire composition is 100 at %. That is,
0.ltoreq..alpha.{1-(a+b+c+d+e)}.ltoreq.0.40 may be preferably
satisfied.
[0065] X2 is one or more selected from the group consisting of Ti,
V, Mn, Ag, Zn, Al, Sn, As, Sb, Bi, and rare earth elements. X2
content (.beta.) may be .beta.=0. That is X2 may not be included.
Also, a number of X2 atoms is preferably 3.0 at % or less when a
number of atoms of entire composition is 100 at %. That is,
0.ltoreq..beta.{1-(a+b+c+d+e)}.ltoreq.0.030 may be preferably
satisfied.
[0066] The amount of X1 and/or X2 substituting Fe may be within a
range of 0.ltoreq..alpha.+.beta..ltoreq.0.55. When .alpha. and
.beta. are .alpha.+.beta.>0.55, it becomes difficult to obtain
the Fe-based nanocrystal alloy by the heat treatment, and even if
the Fe-based nanocrystal alloy is obtained, the coercive force
tends to easily increase.
[0067] Note that, the soft magnetic alloy according to the present
embodiment may include elements other than mentioned in above as
inevitable impurities. Also, the elements other than mentioned in
above may be included by less than 1 wt % in total with respect to
100 wt % of the soft magnetic alloy.
[0068] Hereinbelow, a method for producing the soft magnetic alloy
according to the present embodiment is described.
[0069] The method for producing the soft magnetic alloy according
to the present embodiment is not particularly limited. For example,
a method of producing a thin ribbon of the soft magnetic alloy
according to the present embodiment by a single roll method may be
mentioned. Also, the thin ribbon may be a continuous thin
ribbon.
[0070] In a single roll method, first, a pure metal of each metal
element included in the soft magnetic alloy obtained at the end is
prepared. Then, it is weighed so that a same composition as the
soft magnetic alloy obtained at the end is obtained. Then, the pure
metal of each element is melted and mixed to produce a mother
alloy. Note that, a method of melting the pure metal is not
particularly limited. For example, a method of melting by high
frequency heat after vacuuming the chamber may be mentioned. Note
that, the mother alloy and the soft magnetic alloy including the
Fe-based nanocrystals obtained at the end has the same
composition.
[0071] Next, the produced mother alloy is heated and melted to
produce a molten metal. A temperature of the molten metal is not
particularly limited, and it can be 1200 to 1500.degree. C.
[0072] In a single roll method, a thickness of the thin ribbon can
be regulated mainly by adjusting a rotational speed of a roll of
the thin ribbon. For example, a thickness of the thin ribbon can
also be regulated by adjusting a space between a nozzle and a roll;
and also by adjusting a temperature of the molten metal. The
thickness of the thin ribbon is not particularly limited, and for
example it can be 5 to 30 .mu.m.
[0073] Prior to the heat treatment, the thin ribbon is an amorphous
which does not include the crystal having a grain size larger than
15 nm. By performing the heat treatment to the thin ribbon which is
an amorphous, the Fe-based nanocrystal alloy can be obtained.
[0074] Note that, a method of verifying whether the thin ribbon of
the soft magnetic alloy before the heat treatment includes the
crystal having a grain size larger than 15 nm is not particularly
limited. For example, the presence of the crystal having a grain
size larger than 15 nm can be verified by a usual X ray diffraction
analysis.
[0075] Also, the thin ribbon before the heat treatment may be
completely free of the initial fine crystal having a grain size of
less than 15 nm, however the initial fine crystal is preferably
included. That is, the thin ribbon before the heat treatment
preferably has a nano-hetero structure made of the amorphous and
the initial fine crystals which are in the amorphous. Note that,
the grain size of the initial fine crystal is not particularly
limited, and an average grain size of the initial fine crystals may
preferably be 0.3 to 10 nm.
[0076] Also, a method for observing the presence of the
above-mentioned initial fine crystals and the average grain size of
the initial fine crystals is not particularly limited. For example,
the presence of the above-mentioned initial fine crystals and the
average grain size of the initial fine crystals can be verified by
obtaining a selected area diffraction pattern, a nano beam
diffraction pattern, a bright field image, or a high resolution
image using a transmission electron microscope to a sample which is
thinned by an ion milling. In case of using the selected area
diffraction pattern and the nano beam diffraction pattern,
regarding the diffraction pattern, the amorphous forms a ring shape
pattern, and non-amorphous forms diffraction dots which are derived
from the crystal structure. Also, in case of using the bright field
image or the high-resolution image, the presence of the initial
fine crystals and the average grain size of the initial fine
crystals can be observed by visual observation under a
magnification of 1.00.times.10.sup.5 to 3.00.times.10.sup.5.
[0077] A temperature of roll, a rotational speed, and an atmosphere
inside the chamber are not particularly limited. The temperature of
the roll is preferably 4 to 30.degree. C. to form an amorphous. As
the rotational speed of the roll increases, the average grain size
of the initial fine crystals tends to decrease, and it is
preferably 30 to 40 m/sec in order to obtain the initial fine
crystals having an average grain size of 0.3 to 10 nm. The
atmosphere inside the chamber is preferably in air considering the
cost.
[0078] Also, a heat treatment condition for producing the Fe-based
nanocrystal alloy is not particularly limited. A preferable heat
treatment condition differs depending on the composition of the
soft magnetic alloy. Usually, the preferable heat treatment
temperature is about 400 to 600.degree. C., and a preferable heat
treatment time is about 10 minutes to 10 hours. However, the
preferable heat treatment temperature and time may be outside the
above-mentioned range depending on the composition. Also, the
atmosphere during the heat treatment is not particularly limited.
It may be carried out under active atmosphere such as in air, or it
may be carried out under inert atmosphere such as in Ar gas or
so.
[0079] Also, a method of calculating the average grain size of the
obtained Fe-based nanocrystal alloy is not particularly limited.
For example, the average grain size can be calculated using a
transmission electron microscope. Also, a method of verifying bcc
(body center cubic structure) of the crystal structure is not
particularly limited. For example, the crystal structure can be
confirmed using X ray diffraction analysis.
[0080] As a method of obtaining the soft magnetic alloy according
to the present embodiment, other than the above-mentioned single
roll method, for example, a method of obtaining a powder of the
soft magnetic alloy according to the present embodiment by a water
atomization method or a gas atomization method may be mentioned.
Hereinafter, a gas atomization method is described.
[0081] In a gas atomization method, a molten metal of temperature
range of 1200 to 1500.degree. C. is obtained as same as the
above-mentioned single roll method. Then, the molten metal is
injected in a chamber, thereby a powder is produced.
[0082] Here, by setting a gas injecting temperature to 4 to
30.degree. C. and setting a vapor pressure inside the chamber to 1
hPa or less, the above-mentioned preferable nano-hetero structure
tends to be obtained easily.
[0083] After producing the powder by a gas atomization method, a
heat treatment at 400 to 600.degree. C. for 0.5 to 10 minutes is
carried out. Thereby, element diffusion is facilitated while the
powder is restricted from sintering with each other and becoming
too large, and the powder can reach to a thermodynamic equilibrium
in short period of time. Thereby, strain and stress can be removed,
and the Fe-based soft magnetic alloy having the average grain size
of 10 to 50 nm tends to be easily formed.
[0084] Hereinabove, an embodiment of the present invention is
described, however the present invention is not limited
thereto.
[0085] The shape of the soft magnetic alloy according to the
present embodiment is not particularly limited. As described in
above, a thin ribbon form and a powder form are mentioned as
examples, however, other than these, a block form and the like may
be mentioned.
[0086] The use of the soft magnetic alloy (Fe-based nanocrystal
alloy) according to the present embodiment is not particularly
limited. For example, magnetic components may be mentioned, and
among these, a magnetic core may be particularly mentioned. It can
be suitably used as a magnetic core for inductor, particularly for
a power inductor. The soft magnetic alloy according to the present
embodiment can be suitably used for a thin film inductor, a
magnetic head, and the like other than the magnetic core.
[0087] Hereinafter, a method of obtaining a magnetic component,
particularly a magnetic core and an inductor from the soft magnetic
alloy according to the present embodiment is described. However,
the method of obtaining the magnetic core and the inductor from the
soft magnetic alloy according to the present embodiment is not
particularly limited thereto. Also, as the use of the magnetic
core, other than the inductor, a transformer, a motor, and the like
may be mentioned.
[0088] As a method of obtaining the magnetic core from the soft
magnetic alloy of a thin ribbon form, for example, a method of
winding the soft magnetic alloy of thin ribbon form and a method of
stacking the soft magnetic alloy of thin ribbon form may be
mentioned. In case of stacking an insulator between the soft
magnetic alloys of thin ribbon form, the magnetic core with even
more enhanced properties can be obtained.
[0089] As a method of obtaining the magnetic core from a powder
form soft magnetic alloy, for example, a method of molding using a
metal mold after mixing the powder form soft magnetic alloy with a
binder may be mentioned. Also, before mixing with the binder, by
performing an oxidizing treatment, an insulation coating, and the
like to the powder surface, a resistivity improves and the magnetic
core suited for even higher frequency range can be obtained.
[0090] A method of molding is not particularly limited, and for
example, a method of molding using a metal mold, a mold pressing,
and the like may be mentioned. A type of the binder is not
particularly limited, and a silicone resin may be mentioned. A
mixing ratio between the soft magnetic alloy powder and the binder
is not particularly limited. For example, 1 to 10 mass % of the
binder may be mixed with respect to 100 mass % of the soft magnetic
alloy powder.
[0091] For example, 1 to 5 mass % of the binder is mixed with
respect to 100 mass % of the soft magnetic alloy powder, then press
molding is performed using a metal mold. Thereby, the magnetic core
having 70% or more of a space factor (powder filling rate), 0.45T
or more of a magnetic flux density when 1.6.times.10.sup.4 A/m of
magnetic field is applied, and 1 .OMEGA.cm or more of a resistivity
can be obtained. The above-mentioned properties are equal or better
than a generally known ferrite magnetic core.
[0092] Also, for example, 1 to 3 mass % of the binder is mixed with
respect to 100 mass % of the soft magnetic alloy. Then, press
molding is performed at a temperature higher than the softening
point of the binder using a metal mold. Thereby, a dust core having
80% or more of a space factor, 0.9T or more of a magnetic flux
density when 1.6.times.10.sup.4 A/m of magnetic field is applied,
and 0.1 .OMEGA.cm or more of a resistivity can be obtained. The
above-mentioned properties are better than a generally known dust
core.
[0093] Further, by performing a heat treatment as a strain relief
heat treatment after molding into a molded article which forms the
above-mentioned magnetic core, a core loss is further decreased and
a functionality is enhanced. Note that, the core loss of the
magnetic core decreases as the coercive force of the magnetic body
constituting the magnetic core decreases.
[0094] Also, an inductor component can be obtained by winding a
wire around the magnetic core. A method of winding the wire around
the core is not particularly limited, and also a method of
producing the inductor component is not particularly limited. For
example, a method of winding the wire for at least one turn around
the magnetic core produced by the above-mentioned method may be
mentioned.
[0095] Further, in case of using the soft magnetic alloy particle,
there is a method of producing an inductor component by press
molding the magnetic body while the wound coil is incorporated in
the magnetic body. In such case, an inductor component which
corresponds to high frequency range and large electric current tend
to be easily obtained.
[0096] Further, in case of using the soft magnetic alloy particle,
the inductor component can be obtained by print stacking a soft
magnetic alloy paste and a conductor paste in an alternating manner
and then firing may be carried out. The soft magnetic alloy paste
is obtained by forming a paste by adding the binder and the solvent
to the soft magnetic alloy particle. The conductor paste is
obtained by forming a paste by adding the binder and the solvent to
a conductor metal for coil. Alternatively, a soft magnetic alloy
sheet is produced using the soft magnetic alloy paste, and a
conductor paste is printed to the surface of the soft magnetic
alloy sheet, then these are stacked and fired. Thereby, the
inductor component in which a coil is incorporated in the magnetic
body can be obtained.
[0097] Here, in case of producing the inductor component using the
soft magnetic alloy particle, from the point of obtaining an
excellent Q property, it is preferable to use a soft magnetic alloy
powder having a maximum grain size by a sieve gauge of 45 .mu.m or
less, and a median grain size (D50) of 30 .mu.m or less. In order
to have the maximum grain size by a sieve gauge of 45 .mu.m or
less, a sieve having a gauge of 45 .mu.m is used, and the soft
magnetic alloy powder which passed through the sieve may be only
used.
[0098] As the soft magnetic alloy powder having large maximum grain
size is used more, the Q value under high frequency range tends to
decrease. In case the soft magnetic alloy powder having a maximum
grain size larger than 45 .mu.m by a sieve gauge is used, the Q
value under high frequency range may decrease significantly. Note
that, in case the Q value under a high frequency range is not an
important factor, then the soft magnetic alloy powder having
various sizes can be used. Since, the soft magnetic alloy powder
having various sizes can be produced at relatively low cost, in
case of using the soft magnetic alloy powder having various sizes,
a cost can be reduced.
EXAMPLES
[0099] Hereinafter, the present invention is described based on
examples.
[0100] Raw material metals were weighed to obtain an alloy
composition of Examples and Comparative examples shown in below
Tables, then the raw material metals were melted by high frequency
heating, thereby a mother alloy was produced.
[0101] Then, the produced mother alloy was heated and melted to
form a molten metal of 1300.degree. C., then the molten metal was
injected on a roll of 20.degree. C. in air rotating at a rotational
speed of 40 m/sec by a single roll method. Thereby, a thin ribbon
was formed. A thickness of the thin ribbon was 20 to 25 .mu.m, a
width of the thin ribbon was about 15 mm, and a length of the thin
ribbon was about 10 m.
[0102] The obtained thin ribbon was subjected to X ray diffraction
analysis, and a crystal having a grain size larger than 15 nm was
verified. In case the crystal having the grain size larger than 15
nm was not found, it was considered that the thin ribbon was made
of amorphous phases; and in case the crystal having grain size
larger than 15 nm was found, then it was considered that the thin
ribbon was made of crystal phases.
[0103] Then, to the thin ribbon of Examples and Comparative
examples, a heat treatment was performed at 550.degree. C. for 60
minutes. Each thin ribbon after the heat treatment was measured
with a saturation magnetic flux density and a coercive force. The
saturation magnetic flux density (Bs) was measured using a
Vibrating Sample Magnetometer (VSM) at a magnetic field of 1000
kA/m. The coercive force (Hc) was measured using a DC BH tracer at
a magnetic field of 5 kA/m. The resistivity (.rho.) was measured
using a resistivity measurement by a four-point probe method. In
the present examples, the saturation magnetic flux density of 1.30
T or more was considered good and 1.45 or more considered even
better. The coercive force of 10.0 A/m or less was considered good
and 7.0 A/m or less was considered even better. The resistivity
(.rho.) was evaluated with respect to the resistivity (.rho.) of a
thin ribbon formed by the same production method as Example 3
except for using Fe.sub.90Zr.sub.7B.sub.3 (hereinafter, this may be
referred as Fe.sub.90Zr.sub.7B.sub.3 thin ribbon). When the
resistivity (.rho.) increased by 20% or more and less than 40% with
respect to the resistivity of Fe.sub.90Zr.sub.7B.sub.3 thin ribbon,
it was considered good; and when it increased by 40% or more then
it was considered even better. In below Tables, when the
resistivity (.rho.) increased by 40% or more from the resistivity
of Fe.sub.90Zr.sub.7B.sub.3 thin ribbon it is indicated
"Excellent"; when the resistivity (.rho.) increased by 20% or more
and less than 40% from the resistivity of Fe.sub.90Zr.sub.7B.sub.3
thin ribbon, it is indicated "Good"; when the resistivity (.rho.)
was same or increased by less than 20% from the resistivity of
Fe.sub.90Zr.sub.7B.sub.3 thin ribbon, it is indicated "Fair"; and
when the resistivity (.rho.) lower than the resistivity of
Fe.sub.90Zr.sub.7B.sub.3 thin ribbon, it is indicated "Poor". Note
that, the result of the resistivity (.rho.) does not necessarily
have to show excellent result in order to attain the object of the
present invention.
[0104] Also, Table 7 shows changes in the saturation magnetic flux
density and the coercive force over time. Specifically, a thin
ribbon which was measured with the saturation magnetic flux density
Bs.sub.0 and the coercive force Hc.sub.0 was subjected to an
oxidation treatment for 3000 minutes, then the saturation magnetic
flux density Bs.sub.3000 and the coercive force Hc.sub.3000 after
the oxidation treatment were measured. The oxidation treatment was
carried out at 150.degree. C. for 50 hours.
[0105] In Table 7, it was considered good when
Bs.sub.0.gtoreq.1.30T, Bs.sub.3000/Bs.sub.0.ltoreq.0.85,
Hc.sub.0.ltoreq.10.0 A/m, and Hc.sub.3000/Hc.sub.0.ltoreq.1.30 were
satisfied.
[0106] Note that, in below shown Examples, unless mentioned
otherwise, all Examples were confirmed to have Fe-based
nanocrystals having an average grain size of 5 to 30 nm, and a
crystal structure of bcc was confirmed by observation using an X
ray diffraction analysis and a transmission electron microscope.
Also, all of Examples and Comparative examples shown in below
Tables did not include X1 and X2 except for Table 8.
TABLE-US-00001 TABLE 1 Fe.sub.(1-(a+b))M.sub.aSi.sub.b(c = d = e =
0, .alpha. = .beta. = 0) M(Zr) Si Bs Hc Sample No. Fe a b XRD (T)
(A/m) .rho. Comparative 0.935 0.025 0.040 Crystal 1.84 318 Poor
example 1 phase Example 1 0.930 0.030 0.040 Amorppous 1.80 9.6 Fair
phase Example 2 0.910 0.050 0.040 Amorppous 1.74 4.7 Good phase
Example 3 0.890 0.070 0.040 Amorppous 1.61 3.9 Excellent phase
Example 4 0.880 0.080 0.040 Amorppous 1.56 3.6 Excellent phase
Example 5 0.860 0.100 0.040 Amorppous 1.45 4.1 Excellent phase
Example 6 0.840 0.120 0.040 Amorppous 1.33 5.7 Excellent phase
Comparative 0.830 0.130 0.040 Amorppous 1.27 7.1 Excellent example
2 phase
TABLE-US-00002 TABLE 2 Fe.sub.(1-(a+b))M.sub.aSi.sub.b(c = d = e =
0, .alpha. = .beta. = 0) M(Nb) Si Bs Hc Sample No. Fe a b XRD (T)
(A/m) .rho. Cmparative 0.895 0.025 0.080 Crystal 1.77 492 Fair
example 3 phase Example 7 0.890 0.030 0.080 Amorphous 1.71 9.9 Good
phase Example 8 0.870 0.050 0.080 Amorphous 1.65 4.8 Execellent
phase Example 9 0.850 0.070 0.080 Amorphous 1.53 3.7 Execellent
phase Example 10 0.840 0.080 0.080 Amorphous 1.47 3.3 Execellent
phase Example 11 0.820 0.100 0.080 Amorphous 1.38 3.9 Execellent
phase Example 12 0.800 0.120 0.080 Amorphous 1.30 5.8 Execellent
phase Comparative 0.790 0.130 0.080 Amorphous 1.22 9.2 Execellent
example 4 phase
TABLE-US-00003 TABLE 3 Fe.sub.(1-(a+b+c))M.sub.aSi.sub.bCu.sub.c (d
= e = 0, .alpha. = .beta. = 0) M(Zr) Si Cu Bs Hc Sample No. Fe a b
c XRD (T) (A/m) .rho. Example 3 0.890 0.070 0.040 0.000 Amorphous
1.61 3.9 Excellent phase Example 13 0.889 0.070 0.040 0.001
Amorphous 1.60 3.9 Good phase Example 14 0.885 0.070 0.040 0.005
Amorphous 1.55 2.7 Good phase Example 15 0.880 0.070 0.040 0.010
Amorphous 1.50 2.2 Good phase Example 16 0.870 0.070 0.040 0.020
Amorphous 1.38 2.3 Good phase Comparative 0.860 0.070 0.040 0.030
Crystal 1.19 125 Good example 5 phase
TABLE-US-00004 TABLE 4 Fe.sub.(1-(a+b+d))M.sub.aSi.sub.bX3.sub.d (c
= e = 0, .alpha. = .beta. = 0) M(Zr) Si C Ge Bs Hc Sample No. Fe a
b d XRD (T) (A/m) .rho. Example 3 0.890 0.070 0.040 0.000 0.000
Amorphous 1.61 3.9 Excellent phase Example 17 0.880 0.070 0.040
0.010 0.000 Amorphous 1.62 3.8 Excellent phase Example 18 0.840
0.070 0.040 0.050 0.000 Amorphous 1.55 4.0 Excellent phase Example
19 0.790 0.070 0.040 0.100 0.000 Amorphous 1.43 4.6 Excellent phase
Example 20 0.880 0.070 0.040 0.000 0.010 Amorphous 1.60 3.9
Excellent phase Example 21 0.840 0.070 0.040 0.000 0.050 Amorphous
1.52 4.2 Excellent phase Example 22 0.790 0.070 0.040 0.000 0.100
Amorphous 1.38 5.8 Excellent phase Comparative 0.770 0.070 0.040
0.000 0.120 Amorphous 1.28 11.2 Excellent example 7 phase Example
23 0.840 0.070 0.040 0.025 0.025 Amorphous 1.54 3.8 Excellent
phase
TABLE-US-00005 TABLE 5 Fe.sub.(1-(a+b+e))M.sub.aSi.sub.bB.sub.e (c
= d = 0, .alpha. = .beta. = 0) M(Zr) Si B Bs Hc Sample No. Fe a b e
XRD (T) (A/m) .rho. Example 3 0.890 0.070 0.040 0.000 Amorphous
1.61 3.9 Excellent phase Example 24 0.885 0.070 0.040 0.005
Amorphous 1.56 3.9 Excellent phase Example 25 0.880 0.070 0.040
0.010 Amorphous 1.52 4.1 Excellent phase Example 26 0.870 0.070
0.040 0.020 Amorphous 1.44 5.9 Excellent phase Example 27 0.860
0.070 0.040 0.030 Amorphous 1.35 8.0 Excellent phase Comparative
0.850 0.070 0.040 0.040 Amorphous 1.24 13.3 Excellent example 8
phase
TABLE-US-00006 TABLE 6 Fe.sub.(1-a+b))MaSib (c = d = e = 0, .alpha.
= .beta. = 0) Zr Hf Nb Ta W Mo Si Bs Hc Sample No. Fe a b XRD (T)
(A/m) .rho. Example 3 0.890 0.070 0.000 0.000 0.000 0.000 0.000
0.040 Amorphous 1.64 5.3 Excellent phase Example 28 0.890 0.060
0.010 0.000 0.000 0.000 0.000 0.040 Amorphous 1.63 5.3 Excellent
phase Example 29 0.890 0.060 0.000 0.010 0.000 0.000 0.000 0.040
Amorphous 1.61 5.7 Excellent phase Example 30 0.890 0.060 0.000
0.000 0.010 0.000 0.000 0.040 Amorphous 1.59 5.9 Good phase Example
31 0.890 0.060 0.000 0.000 0.000 0.010 0.000 0.040 Amorphous 1.57
6.3 Good phase Example 32 0.890 0.060 0.000 0.000 0.000 0.000 0.010
0.040 Amorphous 1.58 6.2 Good phase
TABLE-US-00007 TABLE 7 Fe.sub.(1-(a+b))M.sub.aSi.sub.b (c = d = e =
0, .alpha. = .beta. = 0) M(Zr) Si Bs.sub.0 Bs.sub.3000/Bs.sub.0
Hc.sub.0 Hc.sub.3000/Hc.sub.0 Sample No. Fe a b XRD (T) -- (A/m) --
.rho. Comparative 0.925 0.070 0.010 Amorphous 1.63 0.77 47.0 1.57
Poor example 8a phase Example 32a 0.920 0.070 0.020 Amorphous 1.62
0.86 7.1 1.29 Fair phase Example 32b 0.920 0.070 0.030 Amorphous
1.62 0.86 4.4 1.29 Good phase Example 3 0.890 0.070 0.040 Amorphous
1.61 0.92 3.9 1.17 Excellent phase Example 32c 0.850 0.070 0.080
Amorphous 1.59 0.94 3.8 1.15 Excellent phase Example 32d 0.780
0.070 0.155 Amorphous 1.47 0.96 9.7 1.13 Excellent phase Example 52
0.880 0.040 0.080 Amorphous 1.68 0.92 6.1 1.19 Excellent phase
Example 53 0.860 0.040 0.100 Amorphous 1.64 0.93 6.7 1.17 Excellent
phase Example 54 0.840 0.040 0.120 Amorphous 1.60 0.94 7.8 1.16
Excellent phase Example 55 0.805 0.040 0.155 Amorphous 1.53 0.95
9.2 1.15 Excellent phase Example 56 0.785 0.040 0.175 Amorphous
1.49 0.95 9.8 1.13 Excellent phase Comparative 0.765 0.040 0.195
Amorphous 1.44 0.96 10.8 1.12 Excellent example 11 phase
TABLE-US-00008
Fe.sub.(1-(.alpha.+.beta.))X1.sub..alpha.X3.sub..beta.(a and b are
same as Example 3, c = d = e = 0) X1 X2 Bs Hc Sample No. Type
.alpha.{1 - (a + b)} Type .beta.{1 - (a + b)} XRD (T) (A/m) Example
3 -- 0.000 -- 0.000 Amorphous 1.61 3.9 phase Example 33 Co 0.010 --
0.000 Amorphous 1.62 4.2 phase Example 34 Co 0.100 -- 0.000
Amorphous 1.68 4.9 phase Example 34a Co 0.400 -- 0.000 Amorphous
1.73 6.9 phase Example 35 Co 0.500 -- 0.000 Amorphous 1.75 9.8
phase Comparative Co 0.600 -- 0.000 Amorphous 1.80 27.0 example 9
phase Example 36 Ni 0.010 -- 0.000 Amorphous 1.57 3.9 phase Example
37 Ni 0.100 -- 0.000 Amorphous 1.45 4.7 phase Example 39 -- 0.000 V
0.030 Amorphous 1.59 4.0 phase Example 40 -- 0.000 Mn 0.030
Amorphous 1.57 4.2 phase Example 41 -- 0.000 Zn 0.030 Amorphous
1.60 4.1 phase Example 42 -- 0.000 Al 0.030 Amorphous 1.58 3.7
phase Example 43 -- 0.000 Sn 0.030 Amorphous 1.59 4.2 phase Example
44 -- 0.000 La 0.030 Amorphous 1.52 4.0 phase Example 45 Co 0.100
Zn 0.030 Amorphous 1.62 5.3 phase
TABLE-US-00009 TABLE 9 Composition is same as Example 3 Average
grain Average grain Rotational Heat treatment Heat treatment size
of initial size of Fe based speed of roll Temp time fine crystal
nano crysgtal alloy Bs Hc Sample No. (m/sec.) (.degree. C.) (min)
(nm) (nm) XRD (T) (A/m) Example 46 55 550 60 No initial 10
Amorphous 1.62 4.2 fine crystal phase Example 47 40 550 10 0.3 10
Amorphous 1.51 5.1 phase Example 3 40 550 60 0.3 10 Amorphous 1.61
3.9 phase Example 48 40 550 120 0.3 20 Amorphous 1.64 5.5 phase
Example 49 40 550 180 0.3 20 Amorphous 1.66 6.9 phase Example 50 40
600 180 0.3 30 Amorphous 1.67 8.0 phase Example 51 30 550 60 10.0
20 Amorphous 1.58 4.9 phase Comparative 20 550 60 20.0 50 Crystal
1.62 130 example 10 phase
[0107] Table 1 shows Examples and Comparative examples wherein M
was Zr only; and Cu, X3, and B were not included while Zr content
(a) was varied.
[0108] Examples 1 to 6 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs and coercive force Hc.
[0109] On the contrary to this, regarding Comparative example 1 in
which Zr content was too small, the thin ribbon before the heat
treatment was made of crystal phases; and the coercive force Hc
after the heat treatment increased significantly and the
resistivity p decreased. Also, Comparative example 2 in which Zr
content was too large had a decreased saturation magnetic flux
density.
[0110] Table 2 shows Examples and Comparative examples wherein M
was Nb only; and Cu, X3, and B were not included while Nb content
(a) was varied.
[0111] Examples 7 to 12 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs and coercive force Hc.
[0112] On the contrary to this, regarding Comparative example 3 in
which Nb content was too small, the thin ribbon before the heat
treatment was made of crystal phases; and the coercive force Hc
after the heat treatment increased significantly. Also, Comparative
example 4 in which Nb content was too large had a decreased
saturation magnetic flux density.
[0113] Table 3 shows Examples and Comparative examples wherein M
was Zr only; and X3 and B were not included while Cu content (c)
was varied.
[0114] Examples 13 to 16 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs and coercive force Hc.
[0115] On the contrary to this, regarding Comparative example 5 in
which Cu content was too large, the thin ribbon before the heat
treatment was made of crystal phases; and the coercive force Hc
after the heat treatment increased significantly. Further, the
saturation magnetic flux density Bs decreased.
[0116] Table 4 shows Examples and Comparative examples in which M
was Zr only; and Cu and B were not included while a type and
content (d) of X3 were varied.
[0117] Examples 17 to 23 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs, coercive force Hc, and resistivity .rho..
[0118] On the contrary to this, regarding Comparative example 7 in
which X3 content was too large, the saturation magnetic flux
density Bs decreased and the coercive force Hc increased.
[0119] Table 5 shows Examples and Comparative examples in which M
was Zr only; and Cu and X3 were not included while B content (e)
was varied.
[0120] Examples 24 to 27 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs, coercive force Hc, and resistivity .rho..
[0121] On the other hand, Comparative example 8 in which B content
was too large had a decreased saturation magnetic flux density Bs
and an increased coercive force Hc.
[0122] Table 6 shows Examples in which a type of M was changed from
Example 3.
[0123] Examples 28 to 32 in which a content of each component was
within the predetermined range had good saturation magnetic flux
density Bs, coercive force Hc, and resistivity p even when the type
of M was changed.
[0124] Table 7 shows Examples and Comparative examples in which M
was Zr only; and Cu, X3, and B were not included while Zr content
(a) and Si content (b) were changed. Also, as mentioned in above,
Examples and Comparative examples shown in Table 7 were measured
with changes of saturation magnetic flux density and coercive force
over time.
[0125] Examples 32a to 32d and 52 to 56 had good saturation
magnetic flux density, coercive force, and resistivity; and also
the changes in saturation magnetic flux density and coercive force
over time were small. On the other hand, Comparative example 8a in
which Si content was too small had an increased coercive force and
also the changes in saturation magnetic flux density and coercive
force over time were large. Comparative example 11 in which Si
content was too large had an increased coercive force. When
Examples 52 to 56 are compared with Comparative example 11 having
the same amount of Zr content, Comparative example 11 had a
decreased saturation magnetic flux density.
[0126] Table 8 shows Examples in which part of Fe of Example 3 was
substituted by X1 and/or X2.
[0127] Good properties were obtained even when part of Fe was
substituted by X1 and/or X2. However, Comparative example 9 in
which a .alpha.+.beta. was larger than 0.55 had an increased
coercive force.
[0128] Table 9 shows Examples and Comparative examples in which an
average grain size of the initial fine crystals and the average
grain size of Fe-based nanocrystal alloy were varied by changing a
rotational speed of a roll, a heat treatment temperature, and/or
heat treatment time of Example 3.
[0129] Good properties were obtained even when the average particle
size of the initial fine crystals and the average grain size of the
Fe-based nanocrystal alloy were changed if a crystal having a
particle size larger than 15 nm was not included in the thin ribbon
before the heat treatment. On the contrary to this, if the crystal
having a particle size larger than 15 nm was included in the thin
ribbon before the heat treatment, that is in case the thin ribbon
was formed of crystal phases, then the average grain size of the
Fe-nano crystal after the heat treatment increased significantly
and the coercive force increased significantly.
* * * * *