[0001]The present invention relates to a grain-oriented electrical steel sheet having
excellent magnetic characteristics suitable as an iron core material of a transformer.
Priority is claimed on Japanese Patent Application No. 2019-005084 filed in Japan on
January 16, 2019, the content of which is incorporated herein by reference.
10 [Background Art]
[0002]
Grain-oriented electrical steel sheets are mainly used for transformers. Since a
transformer is continuously excited for a long period of time from installation to disposal
and continuous energy loss is caused, the energy loss when it is magnetized by an
15 alternating current, that is, the iron loss, is a major indicator that determines the
performance of a transformer. Generally, a grain-oriented electrical steel sheet includes
a base steel sheet containing 7% by mass or less of Si and having a texture controlled so
that a crystal orientation of each grain is aligned with a {110} <001> orientation called
the Goth orientation, and an insulation coating for imparting insulation properties to the
20 base steel sheet.
[0003]
In order to reduce the iron loss of grain-oriented electrical steel sheets, many
methods have been proposed so far. For example, a method of increasing alignment in
the Goth orientation in a texture of a base steel sheet, a method of increasing an amount
25 of a solid solution element such as Si that increases the electrical resistance in a base
steel sheet, a method of reducing a sheet thickness of a base steel sheet, and the like are
known.
[0004]
Also, it is known that applying tension to a base steel sheet is an effective
30 method for reducing iron loss. In order to apply tension to a base steel sheet, it is
effective to form a film formed of a material having a thermal expansion coefficient
smaller than that of the base steel sheet on a surface of the base steel sheet at a high
temperature.
[0005]
35 A forsterite film that is formed when oxides present on a surface of a base steel
sheet react with an annealing separator in a final annealing process can apply tension to a
base steel sheet. Since unevenness is present at an interface between the forsterite film
and the base steel sheet, the forsterite film also functions as an intermediate film that
enhances adhesion between the insulation coating and the base steel sheet by an anchor
40 effect due to the unevenness.
[0006]
A method of forming an insulation coating by baking a coating liquid mainly
composed of colloidal silica and phosphate, which is disclosed in Patent Document 1, has
a large effect on applying tension to a base steel sheet and is effective in reducing iron
45 loss. Therefore, applying an insulation coating mainly composed of phosphate after
leaving a forsterite film formed in a final annealing process is a general method of
manufacturing a grain-oriented electrical steel sheet. Further, in the specification of the
present application, an insulation coating capable of applying tension as well as
insulation properties to the base steel sheet is referred to as a tension-insulation coating.
2
[0007]
On the other hand, in recent years, it has become apparent that a forsterite film
hinders domain wall motion and adversely affects iron loss. In a grain-oriented
electrical steel sheet, magnetic domains change with domain wall motion under an
alternating magnetic 5 field. Smooth domain wall motion is effective in improving iron
loss, but domain wall motion is hindered due to unevenness present at an interface
between the forsterite film and the base steel sheet, as a result, it has been found that an
effect of improving iron loss by applying tension is canceled out and a sufficient effect of
improving iron loss cannot be obtained.
10 [0008]
Therefore, a technology for inhibiting formation of a forsterite film and
smoothing a surface of a base steel sheet has been developed. For example, in Patent
Documents 2 to 5, a technology for smoothing a surface of a base steel sheet without
forming a forsterite film after final annealing by controlling a dew point in an atmosphere
15 of decarburization annealing and using alumina as an annealing separator has been
disclosed.
[Citation List]
[Patent Document]
[0009]
20 [Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. S48-039338
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. H07-278670
[Patent Document 3]
25 Japanese Unexamined Patent Application, First Publication No. H11-106827
[Patent Document 4]
Japanese Unexamined Patent Application, First Publication No. H07-118750
[Patent Document 5]
Japanese Unexamined Patent Application, First Publication No. 2003-268450
30 [Summary of the Invention]
[Problems to be Solved by the Invention]
[0010]
As in the conventional technologies described above, it is thought that, when a
forsterite film is not formed on a surface of the base steel sheet, since unevenness that
35 hinders domain wall motion is not present on the surface of the base steel sheet, iron loss
of the grain-oriented electrical steel sheet can be improved. However, even with these
technologies, an effect of improving iron loss could not be sufficiently obtained.
[0011]
The present invention has been made in view of the above circumstances, and an
40 object thereof is to reduce the iron loss of a grain-oriented electrical steel sheet in which
a forsterite film is not present between a base steel sheet and a tension-insulation coating
compared with in conventional cases.
[Means for Solving the Problem]
[0012]
45 In order to solve the above-described problems, the present inventors have
conducted intensive research on the cause of not being able to obtain a sufficient effect of
improving iron loss when a grain-oriented electrical steel sheet in which a forsterite film
is not present between a base steel sheet and a tension-insulation coating is
manufactured. As a result, it has been found that a large number of needle-like
3
inclusions are present in a surface layer region of the base steel sheet in a grain-oriented
electrical steel sheet in which a sufficient effect of improving iron loss cannot obtained.
The present inventors have speculated that these needle-like inclusions are a
cause that hinders domain wall motion, that is, a cause that adversely affects iron loss,
and as a result of conducting 5 further research, it has been found that, when the following
conditions are satisfied, iron loss of the grain-oriented electrical steel sheet in which a
forsterite film is not present between the base steel sheet and the tension-insulation
coating can be reduced compared with in conventional cases.

10 In a case in which a cross section perpendicular to a rolling direction of a base
steel sheet is viewed when a region having a length of 10 μm from a surface of the base
steel sheet toward the inside of the base steel sheet in a sheet thickness direction of the
base steel sheet and a length of 20 mm in a direction perpendicular to the sheet thickness
direction is an observation region, needle-like inclusions having a length of 1 μm or more
15 are not present in the observation region.
[0013]
The present invention has been made on the basis of the above-described
findings, and the gist thereof is as follows.
[0014]
20 (1) A grain-oriented electrical steel sheet according to one aspect of the present
invention is a grain-oriented electrical steel sheet in which a forsterite film is not present
between a base steel sheet and a tension-insulation coating. In the grain-oriented
electrical steel sheet, the base steel sheet contains 0.085% by mass or less of C, 0.80 to
7.00% by mass of Si, 0.05 to 1.00% by mass of Mn, 0.065% by mass or less of acid25
soluble Al, 0.003% by mass or less of S, 0.0040% by mass or less of N, 0.0005 to
0.0080% by mass of B, 0 to 0.50% by mass of P, 0 to 1.00% by mass of Ni, 0 to 0.30%
by mass of Sn, 0 to 0.30% by mass of Sb, 0 to 0.40% by mass of Cu, 0 to 0.30% by mass
of Cr, and 0 to 0.01% by mass of Bi, and a remainder of Fe and impurities as a chemical
composition thereof, and in a case in which a cross section perpendicular to a rolling
30 direction of the base steel sheet is viewed, when a region having a length of 10 μm from
a surface of the base steel sheet toward the inside of the base steel sheet in a sheet
thickness direction of the base steel sheet and a length of 20 mm in a direction
perpendicular to the sheet thickness direction is an observation region, needle-like
inclusions having a length of 1 μm or more are not present in the observation region.
35 [0015]
(2) In the grain-oriented electrical steel sheet according to above-described (1),
the needle-like inclusion may contain mullite represented by 3Al2O3·2SiO2.
[Effects of the Invention]
[0016]
40 According to the above-described aspect of the present invention, iron loss of
the grain-oriented electrical steel sheet in which a forsterite film is not present between
the base steel sheet and the tension-insulation coating can be reduced as compared with
conventional cases.
[Brief Description of Drawings]
45 [0017]
Fig. 1 is a ternary phase diagram of Al2O3-MgO-SiO2.
Fig. 2 is a diagram showing a relationship between an amount of MgO by
mass% in an annealing separator and the number of mullite.
Fig. 3 is a diagram showing a relationship between an amount of MgO by
4
mass% in the annealing separator and an iron loss (W17/50).
Fig. 4 is a diagram showing a relationship between an application amount of the
annealing separator per side and the number of mullite.
[Embodiments for implementing the Invention]
5 [0018]
A grain-oriented electrical steel sheet according to one embodiment of the
present invention is a grain-oriented electrical steel sheet in which a forsterite film is not
present between a base steel sheet and a tension-insulation coating. Hereinafter, the
grain-oriented electrical steel sheet according to the present embodiment is abbreviated
10 as “the present electrical steel sheet”, and a surface of the base steel sheet is abbreviated
as a “steel sheet surface”.
The present electrical steel sheet is characterized in that, in a case in which a
cross section (C cross section) perpendicular to a rolling direction of the base steel sheet
is viewed, when a region having a length of 10 μm from the steel sheet surface toward
15 the inside of the base steel sheet in a sheet thickness direction of the base steel sheet and
a length of 20 mm in a direction perpendicular to the sheet thickness direction (sheet
width direction) is an observation region, needle-like inclusions having a length of 1 μm
or more are not present in the observation region.
In the following, a length of the observation region in the sheet thickness
20 direction of the base steel sheet is referred to as a “sheet thickness direction length,” and
a length of the observation region in the sheet width direction of the base steel sheet is
referred to as a “sheet width direction length”.
[0019]
Hereinafter, the present electrical steel sheet will be described.
25 [0020]
The present inventors postulated that one of the reasons why the iron loss could
not be sufficiently reduced in a grain-oriented electrical steel sheet in which a forsterite
film is not present between a base steel sheet and a tension-insulation coating might be
that inclusions adversely affecting magnetism were formed during final annealing, and
30 took a sample from an (inferior) grain-oriented electrical steel sheet having a large iron
loss so that a cross section (C cross section) perpendicular to a rolling direction of the
base steel sheet was exposed to observe the sample cross section with a microscope.
[0021]
As a result, in a case of the grain-oriented electrical steel sheet having large iron
35 loss, it was found that a large number of needle-like inclusions were present in a surface
layer region of the base steel sheet appeared in the C cross section, more specifically, a
region having a length of 10 μm from the steel sheet surface toward the inside of the base
steel sheet in the sheet thickness direction of the base steel sheet. Further, it was found
that these needle-like inclusions contained mullite (3Al2O3·2SiO2). These observation
40 results are findings that serve as a basis of the present invention.
[0022]
In manufacturing a grain-oriented electrical steel sheet, decarburization
annealing is performed for the purpose of removing C (carbon) before final annealing.
In the decarburization annealing, C is removed, and at the same time, a SiO2 film is
45 formed on the steel sheet surface. After the decarburization annealing, final annealing
is performed with an annealing separator containing alumina as a main component
applied on the SiO2 film on the steel sheet surface for the purpose of preventing the base
steel sheet coiled in a coil shape from seizing during the final annealing.
[0023]
5
Since mullite is a complex oxide of alumina (Al2O3) and SiO2, it is conceivable
that mullite will be formed and remain due to insufficient removal of the SiO2 that has
been formed by the decarburization annealing during the final annealing.
[0024]
Initially, the SiO2 formed 5 in the decarburization annealing is adsorbed on the
alumina having a high BET specific surface area contained in the annealing separator
during the final annealing and is removed from the steel sheet surface when the annealing
separator is washed with water after the final annealing. Therefore, as a cause of
insufficient removal of the SiO2 formed in the decarburization annealing, an insufficient
10 application amount of the annealing separator is conceivable.
[0025]
That is, it is conceivable that there was a limit to an amount of the SiO2 that
could be adsorbed per unit weight of alumina, an application amount of the annealing
separator was insufficient, all the SiO2 was not adsorbed and removed, and the SiO2
15 remained on the steel sheet surface. As a result, it is conceivable that Al (Al generated
by decomposition of AlN that functions as an inhibitor), which has moved from the
inside of the base steel sheet toward the steel sheet surface during the final annealing,
reacts with the SiO2 remaining on the steel sheet surface, and thereby mullite is formed
and remains inside the base steel sheet (particularly in a surface layer region near the
20 steel sheet surface).
[0026]
Based on a technical idea of inhibiting formation of mullite by adjusting a
component composition and an application amount of the annealing separator, the present
inventors have intensively studied a component composition and an application amount
25 of the annealing separator that can inhibit formation of mullite. As a result, it was
found that the formation of mullite can be inhibited by adding MgO to an annealing
separator containing alumina as a main component in a specific proportion and
controlling an application amount of the annealing separator such that it is within a
specific range.
30 [0027]
Fig. 1 shows a ternary phase diagram of alumina Al2O3-MgO-SiO2. As shown
in Fig. 1, theoretically, when MgO is present in a proportion of 50 mol% (28% by mass)
or more with respect to alumina, mullite is not formed. Therefore, the present inventors
investigated a relationship between an amount of MgO added to the annealing separator
35 containing alumina as a main component and the number of mullite formed in the surface
layer region of the base steel sheet.
[0028]
A decarburization-annealed sheet having a sheet thickness of 0.23 mm was used
as a test material, and an annealing separator containing alumina was applied to the
40 decarburization-annealed sheet at an application amount of 8.0 g/m2 per side while
varying an addition amount of MgO in a range of 0 to 80% by mass. After the
annealing separator was dried, the decarburization-annealed sheet was subjected to final
annealing, and a grain-oriented electrical steel sheet in which a forsterite film was not
present on a surface of a base steel sheet was obtained. Further, the final annealing was
45 executed by stacking the decarburization-annealed sheets coated with the annealing
separator.
[0029]
The steel sheets after the final annealing obtained in this way were washed with
water to remove a surplus annealing separator, and then a test piece of 20 mm square was
6
taken from each of the steel sheets after the final annealing from which the surplus
annealing separator had been removed. A cross section (C cross section) perpendicular
to a rolling direction of the test piece was polished with a diamond buff and then
observed with a microscope at a magnification of 1000 times, and the number of needlelike
inclusions having a length of 5 1 μm or more that were present in a region (observation
region) having a length of 10 μm from a steel sheet surface toward the inside of the base
steel sheet in a sheet thickness direction of the base steel sheet and a length of 20 mm in a
sheet width direction of the base steel sheet was measured. The needle-like inclusion
was defined as an inclusion in which a maximum major axis/maximum minor axis was
10 10 or more.
[0030]
Next, an iron loss (W17/50) was measured in the test pieces having different
amounts of MgO added to the annealing separator, and an average at 10 points was taken
as an iron loss (W17/50) of a test piece.
15 [0031]
Measurement results of these are shown in Figs. 2 and 3. Fig. 2 is a diagram
showing a relationship between an amount of MgO in the annealing separator and the
number of mullite. Fig. 3 is a diagram showing a relationship between an amount of
MgO in the annealing separator and iron loss (W17/50).
20 [0032]
As shown in Fig. 2, when the amount of MgO in the annealing separator was
28% by mass or more, mullite was not formed. On the other hand, as shown in Fig. 3, it
can be seen that when the amount of MgO in the annealing separator was within a range
of 28% by mass or more and 50% by mass or less, the iron loss was less than 1.00 W/kg,
25 and an effect of the iron loss being improved was exhibited, but when the amount of
MgO in the annealing separator exceeded 50% by mass, the iron loss was 1.00 W/kg or
more, and an inferior iron loss was exhibited.
[0033]
In order to clarify the cause, a surface of the obtained steel sheet was analyzed
30 by an X-ray diffraction (XRD) method. As a result, it was ascertained that forsterite
was detected when the amount of MgO was 54% by mass or more, and that an XRD peak
height of the forsterite increased as the amount of MgO increased. From this, it is
conceivable that, when the amount of MgO in the annealing separator exceeds 50% by
mass, mullite is not formed (see Fig. 2), but on the other hand, forsterite is formed to
35 cause inferior iron loss.
[0034]
Next, an annealing separator containing alumina as a main component and MgO
in an amount of 45% by mass was applied to a decarburization-annealed sheet having a
sheet thickness of 0.23 mm. An application amount of the annealing separator was
40 varied in a range of 5.0 to 15.0 g/m2 per side. A plurality of decarburization-annealed
sheets coated with the annealing separator and dried were stacked and subjected to final
annealing to fabricate grain-oriented electrical steel sheets.
[0035]
The grain-oriented electrical steel sheets obtained in this way were washed with
45 water to remove a surplus annealing separator, and then a test piece of 20 mm square was
taken from each of the grain-oriented electrical steel sheets from which the surplus
annealing separator had been removed. A cross section (C cross section) perpendicular
to a rolling direction of the test piece was polished with a diamond buff and then
observed with a microscope at a magnification of 1000 times, and the number of needle7
like inclusions having a length of 1 μm or more that were present in a region (observation
region) having a length of 10 μm from a steel sheet surface toward the inside of a base
steel sheet in a sheet thickness direction of the base steel sheet and a length of 20 mm in a
sheet width direction of the base steel sheet was measured.
5 [0036]
The results are shown in Fig. 4. Fig. 4 is a diagram showing a relationship
between an application amount of the annealing separator per side and the number of
mullite. From Fig. 4, it can be seen that “needle-like inclusions (mullite) having a
length of 1 μm or more” were formed when the application amount of the annealing
10 separator per side was less than 6.0 g/m2.
[0037]
Since mullite is not formed when MgO is present in a proportion of 50 mol%
(28% by mass) or more with respect to alumina according to the ternary phase diagram of
Al2O3-MgO-SiO2 shown in Fig. 1, mullite should not be formed when the application
15 amount of MgO is 45% by mass. However, as shown in Fig. 4, “needle-like inclusions
(mullite) having a length of 1 μm or more” were formed when the application amount of
the annealing separator containing 45% by mass of MgO per side was less than 6.0 g/m2.
The reason for this can be considered as follows.
[0038]
20 (x) When an application amount of the annealing separator is small, adsorption
and removal of SiO2 by Al2O3 of the annealing separator becomes insufficient during
final annealing.
(y) During final annealing, Al generated by decomposition of AlN (inhibitor) is
added to an Al component of the annealing separator, a proportion of MgO in the
25 annealing separator is relatively reduced, and a component composition of the annealing
separator shifts to a mullite forming region (see Fig. 1).
[0039]
Therefore, it is important to adsorb and remove SiO2 with the Al2O3 of the
annealing separator sufficiently during the final annealing in order to inhibit the
30 formation of mullite, and for that purpose, not only is it necessary to perform control
such that the amount of MgO added to the annealing separator is 28% by mass or more,
but in addition, it is necessary to perform control such that the application amount of the
annealing separator is 6.0 g/m2 or more.
[0040]
35 As described above, the present inventors found that, when an MgO addition
amount and an application amount of the annealing separator containing alumina as a
main component were controlled within a specific range, formation of the needle-like
inclusions (mullite) could be inhibited in the surface layer region of the base steel sheet
of the grain-oriented electrical steel sheet, and thereby reduction in iron loss of the grain40
oriented electrical steel sheet could be realized. That is because the present electrical
steel sheet is characterized in that, in a case in which the C cross section of the base steel
sheet is viewed, when a region having a sheet thickness direction length of 10 μm from
the steel sheet surface toward the inside of the base steel sheet and a sheet width direction
length of 20 mm is an observation region, the needle-like inclusions having a length of 1
45 μm or more are not present in the observation region on the basis of the above-described
research results by the present inventors.
Further, an upper limit of a length of the needle-like inclusion in the observation
region of the grain-oriented electrical steel sheet having a large iron loss is not
particularly limited, and may be, for example, 5 μm.
8
[0041]
Hereinafter, characteristics of the present electrical steel sheet will be described.
[0042]

When the needle-like inclusions a 5 re present in the surface layer region of the
base steel sheet appeared in the C cross section, that is, the region having a length of 10
μm from the steel sheet surface toward the inside of the base steel sheet, since domain
wall motion is hindered and thus reduction in iron loss becomes difficult, and a thickness
of SiO2 formed on a surface of the decarburization-annealed sheet is about several
10 micrometers, a sheet thickness direction length of the observation region for measuring
the number of needle-like inclusions is set to 10 μm.
[0043]

15 As described above, the needle-like inclusion having a length of 1 μm or more is
an inclusion in which a maximum major axis/maximum minor axis is 10 or more. Since
the needle-like inclusions hinder domain wall motion significantly, the present inventors
focused on the number of needle-like inclusions present inside the grains in the
observation region.
20 [0044]
In the C cross-section polishing of the base steel sheet with a diamond buff, a
sample length in which a uniform and smooth polished surface can be obtained is about
20 mm. Therefore, in order to accurately measure the number of “needle-like inclusions
having a length of 1 μm or more” that hinder domain wall motion significantly, a sheet
25 width direction length of the observation region was set to 20 mm, and the number of
needle-like inclusions having a length of 1 μm or more present in the observation region
was measured.
[0045]
As a result, it was found that the iron loss W17/50 could be reduced to less than
30 1.00 W/kg when the needle-like inclusions having a length of 1 μm or more were not
present in the observation region (when the number of needle-like inclusions in the
observation region was zero), but on the other hand, the iron loss W17/50 increased to
more than 1.00 W/kg when the needle-like inclusions having a length of 1 μm or more
were present in the observation region (see Table 2). Therefore, from the perspective of
35 reducing iron loss, it is an essential condition that the needle-like inclusions (mullite)
having a length of 1 μm or more are not present in the observation region.
[0046]
Identification of substances constituting needle-like inclusions can be performed
by qualitative analysis using a wide-angle X-ray diffraction (WAXD) method for the
40 needle-like inclusions. For example, a test piece cut out from the base steel sheet is
immersed in a nital solution (5 vol% of nitric acid/ethanol) for 90 seconds, and a surface
thereof is removed by about several microns to make needle-like inclusions appear.
Ascertaining of the needle-like inclusions that have appeared can be performed using an
optical microscope. The surface of the test piece on which the needle-like inclusions
45 have appeared is analyzed by the wide-angle X-ray diffraction method. Specifically, an
obtained X-ray diffraction spectrum is collated with a power diffraction file (PDF). For
identification of mullite, for example, JCPDS No.: 15-776 may be used. Since mullite
is not formed in a portion of the base steel sheet other than the needle-like inclusions,
whether or not the mullite is included in the needle-like inclusions can be determined by
9
the method described above.
[0047]

Next, a chemical composition (component composition) of the base steel sheet
of the present electrical steel shee 5 t will be described. The chemical composition of the
base steel sheet is not limited to a specific composition as long as magnetic
characteristics and mechanical characteristics required for the grain-oriented electrical
steel sheet can be obtained, but an example of the chemical composition of the base steel
sheet is as follows.
10 [0048]
That is, the base steel sheet of the present electrical steel sheet contains 0.085%
by mass or less of C, 0.80 to 7.00% by mass of Si, 0.05 to 1.00% by mass of Mn, 0.065%
by mass or less of acid-soluble Al, 0.003% by mass or less of S, 0.0040% by mass or less
of N, and 0.0005 to 0.0080% by mass of B, and a remainder of Fe and impurities as a
15 chemical composition thereof.
Hereinafter, each of the elements will be described. In the following
description, all “%” relating to the chemical composition denotes “% by mass”.
[0049]
C: 0.085% or less
20 C is an element effective for controlling a primary recrystallization structure, but
since it adversely affects magnetic characteristics, it is an element removed by
decarburization annealing before final annealing. When an amount of C exceeds
0.085% in a final product, aging precipitation occurs and hysteresis loss deteriorates, and
therefore the amount of C is set to 0.085% or less. The amount of C is preferably
25 0.070% or less, and more preferably 0.050% or less.
[0050]
A lower limit thereof includes 0%, but when the amount of C is reduced to less
than 0.0001%, a manufacturing cost increases significantly, and therefore 0.0001% is a
practical lower limit on a practical steel sheet. In the grain-oriented electrical steel
30 sheet, the amount of C is normally reduced to about 0.002% or less by decarburization
annealing.
[0051]
Si: 0.80 to 7.00%
Si is an element that increases electric resistance of a steel sheet and improves
35 iron loss characteristics. When an amount of Si is less than 0.80%, γ transformation
occurs during final annealing, a crystal orientation of the steel sheet is impaired, and
therefore the amount of Si is set to 0.80% or more. The amount of Si is preferably
1.50% or more, and more preferably 2.50% or more.
[0052]
40 On the other hand, when the amount of Si exceeds 7.00%, processability
decreases and cracks occur during rolling, and therefore the amount of Si is set to 7.00%
or less. The amount of Si is preferably 5.50% or less, and more preferably 4.50% or
less.
[0053]
45 Mn: 0.05 to 1.00%
Mn is an austenite-forming element and is an element that prevents cracking
during hot rolling and combines with S and/or Se to form MnS and/or MnSe that
function as an inhibitor.
[0054]
10
Mn is an element that prevents cracking during hot rolling and combines with S
to form MnS that functions as an inhibitor. When an amount of Mn is less than 0.05%,
an addition effect is not sufficiently exhibited, and therefore the amount of Mn is set to
0.05% or more. The amount of Mn is preferably 0.07% or more, and more preferably
5 0.09% or more.
[0055]
On the other hand, when the amount of Mn exceeds 1.00%, precipitation and
dispersion of MnS become non-uniform, a required secondary recrystallization structure
cannot be obtained, a magnetic flux density decreases, and therefore the amount of Mn is
10 set to 1.00% or less. The amount of Mn is preferably 0.80% or less, and more
preferably 0.60% or less.
[0056]
Acid-soluble Al: 0.065% or less
Acid-soluble Al is an element that combines with N to generate (Al, Si) N that
15 function as an inhibitor. When the amount of acid-soluble Al exceeds 0.065%,
precipitation and dispersion of (Al, Si) N become non-uniform, a required secondary
recrystallization structure cannot be obtained, a magnetic flux density decreases, and
therefore the amount of acid-soluble Al is set to 0.065% or less. The amount of acidsoluble
Al is preferably 0.050% or less, and more preferably 0.040% or less. A lower
20 limit thereof includes 0%, but when the amount of acid-soluble Al is reduced to less than
0.0001%, a manufacturing cost increases significantly, and therefore 0.0001% is a
practical lower limit on the practical steel sheet. The amount of acid-soluble Al is
normally reduced to 0.002% or less by final annealing.
[0057]
25 S: 0.003% or less
S combines with Mn to function as an inhibitor, but when an amount of S
exceeds 0.003% in a final product, it is precipitated as MnS in the steel sheet and
hysteresis loss increases, and therefore the amount of S is set to 0.003% or less. A
lower limit thereof includes 0%, but when the amount of S is reduced to less than
30 0.0001%, a manufacturing cost increases significantly, and therefore 0.0001% is a
practical lower limit on the practical steel sheet.
[0058]
The S content of the base steel sheet changes depending on the amount of MgO
added to the annealing separator. When the amount of MgO added to the annealing
35 separator is controlled to 28% by mass or more so that the needle-like inclusions
(mullite) with a length of 1 μm or more are not present in the observation region
appeared in the C cross section of the base steel sheet, the S content of the base steel
sheet of the grain-oriented electrical steel sheet obtained as the final product is
suppressed to 0.003% or less, and as a result, formation of fine sulfides is suppressed as
40 described above, which contributes to reduction in iron loss.
Accordingly, the larger the amount of MgO added to the annealing separator is,
the more preferable it is also from the perspective of reducing the S content of the base
steel sheet, but forsterite is formed when the amount of MgO added to the annealing
separator exceeds 50% by mass as described above, and therefore an upper limit of the
45 amount of MgO added to the annealing separator needs to be controlled to 50% by mass.
[0059]
N: 0.0040% or less
N is an element that combines with Al to form AlN that functions as an inhibitor,
but when an amount thereof is more than 0.0040% in a final product, it is precipitated as
11
AlN in the steel sheet and hysteresis loss increases, and therefore the amount of N is set
to 0.0040% or less. A lower limit thereof includes 0%, but when the amount of N is
reduced to less than 0.0001%, a manufacturing cost increases significantly, and therefore
0.0001% is a practical lower limit on the practical steel sheet. Further, in the grainoriented
electrical steel shee 5 t, the amount of N is normally reduced to about 0.003% by
final annealing.
[0060]
B: 0.0005 to 0.0080%
B is an element that combines with N and complex precipitates with MnS to
10 form BN that functions as an inhibitor.
[0061]
When an amount of B is less than 0.0005%, an addition effect is not sufficiently
exhibited, and therefore the amount of B is set to 0.0005% or more. The amount of B is
preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand,
15 when the amount of B exceeds 0.0080%, precipitation and dispersion of BN become nonuniform,
a required secondary recrystallization structure cannot be obtained, and a
magnetic flux density decreases, and therefore the amount of B is set to 0.0080% or less.
The amount of B is preferably 0.0060% or less, and more preferably 0.0040% or less.
[0062]
20 In components of the base steel sheet, the remainder excluding the abovedescribed
elements is Fe and impurities. Impurities are elements that are inevitably
mixed from a steel raw material and/or in the process of steelmaking and are elements
that are allowed within a range not impairing characteristics of the present electrical steel
sheet.
25 [0063]
Also, the base steel sheet may contain at least one selected from the group
consisting of 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less
of Ni, 0.30% or less of Sn, 0.30% or less of Sb, and 0.01% or less of Bi instead of a part
of Fe within a range not impairing magnetic characteristics and enhancing other
30 characteristics. Since these elements are not essential elements, a lower limit of each
content of them is 0%.
[0064]
The above-described steel components may be measured by a general method
for analyzing a steel. For example, the steel components may be measured using
35 inductively coupled plasma-atomic emission spectrometry (ICP-AES). Further, acidsoluble
Al may be measured by ICP-AES using a filtrate obtained after the sample is
decomposed by heating with an acid. Also, C and S may be measured using a
combustion-infrared absorption method, N may be measured using an inert gas fusionthermal
conductivity method, and O may be measured using an inert gas fusion40
nondispersive infrared absorption method.
[0065]

In order to determine each layer in a cross-sectional structure of the present
electrical steel sheet, a line analysis is performed in the sheet thickness direction and a
45 quantitative analysis of chemical components of each layer is performed using EDS
attached to SEM of TEM. Elements to be quantitatively analyzed are 6 elements of Fe,
P, Si, O, Mg, and Al.
[0066]
A region which is a layer-shaped region present at a deepest position in the sheet
12
thickness direction and having an Fe content of 80 atomic% or more and an O content of
less than 30 atomic% excluding measurement noise is determined to be a base steel sheet.
[0067]
Regarding a region excluding the base steel sheet determined above, a region
having a Fe content of 5 less than 80 atomic%, a P content of 5 atomic% or more, and an O
content of 30 atomic% or more excluding measurement noise is determined to be an
insulation coating.
[0068]
The present electrical steel sheet does not have a forsterite film on the base steel
10 sheet. Presence or absence of the forsterite film on the base steel sheet can be
ascertained by analyzing a surface of the steel sheet from which the insulation coating
has been removed using an X-ray diffraction method. Specifically, an obtained X-ray
diffraction spectrum is collated with a PDF. For example, JCPDS number: 34-189 may
be used to determine presence or absence of the forsterite.
15 In the present electrical steel sheet, even if the surface of the steel sheet from
which the insulation coating has been removed is analyzed by the X-ray diffraction
method, a peak of the forsterite is not detected. Further, the insulation coating from the
present electrical steel sheet can be removed, for example, by immersing the present
electrical steel sheet in a 20% NaOH aqueous solution at 80ºC for 20 minutes.
20 [0069]

Next, a manufacturing method of the present electrical steel sheet will be
described.
[0070]
25
As components of a silicon steel slab of the present electrical steel sheet, 0.085%
by mass or less of C, 0.80 to 7.00% by mass of Si, 0.05 to 1.00% by mass of Mn, 0.010
to 0.065% by mass of acid-soluble Al, 0.0040 to 0.0120% by mass of N, 0.010% by mass
or less of S, and 0.0005 to 0.0080% by mass of B are contained.
30 [0071]
C: 0.085% or less
C is an element effective for controlling a primary recrystallization structure, but
since it adversely affects magnetic characteristics, it is an element removed by
decarburization annealing before final annealing. When an amount of C exceeds
35 0.085%, a decarburization annealing time becomes long and productivity decreases, and
therefore the amount of C is set to 0.085% or less. The amount of C is preferably
0.070% or less, and more preferably 0.050% or less.
[0072]
A lower limit thereof includes 0%, but when the amount of C is reduced to less
40 than 0.0001%, a manufacturing cost increases significantly, and therefore 0.0001% is a
practical lower limit on the practical steel sheet. Further, in the grain-oriented electrical
steel sheet, the amount of C is normally reduced to about 0.001% or less by
decarburization annealing.
[0073]
45 Si: 0.80 to 7.00%
Si is an element that increases electrical resistance of a steel sheet and improves
iron loss characteristics. When an amount of Si is less than 0.80%, γ transformation
occurs during final annealing, a crystal orientation of the steel sheet is impaired, and
therefore the amount of Si is set to 0.80% or more. The amount of Si is preferably
13
1.50% or more, and more preferably 2.50% or more.
[0074]
On the other hand, when the amount of Si exceeds 7.00%, processability
decreases and cracks occur during rolling, and therefore the amount of Si is set to 7.00%
or less. The amount of Si is pre 5 ferably 5.50% or less, and more preferably 4.50% or
less.
[0075]
Mn: 0.05 to 1.00%
Mn is an element that prevents cracking during hot rolling and combines with S
10 and/or Se to form MnS that functions as an inhibitor. When an amount of Mn is less
than 0.05%, an addition effect is not sufficiently exhibited, and therefore the amount of
Mn is set to 0.05% or more. The amount of Mn is preferably 0.07% or more, and more
preferably 0.09% or more.
[0076]
15 On the other hand, when the amount of Mn exceeds 1.00%, precipitation and
dispersion of MnS become non-uniform, a required secondary recrystallization structure
cannot be obtained, a magnetic flux density decreases, and therefore the amount of Mn is
set to 1.00% or less. The amount of Mn is preferably 0.80% or less, and more
preferably 0.60% or less.
20 [0077]
Acid-soluble Al: 0.010 to 0.065%
Acid-soluble Al is an element that combines with N to form (Al, Si) N that
functions as an inhibitor. When an amount of acid-soluble Al is less than 0.010%, an
addition effect is not sufficiently exhibited and secondary recrystallization does not
25 proceed sufficiently, and therefore the amount of acid-soluble Al is set to 0.010% or
more. The amount of acid-soluble Al is preferably 0.015% or more, and more
preferably 0.020% or more.
[0078]
On the other hand, when the amount of acid-soluble Al exceeds 0.065%,
30 precipitation and dispersion of (Al, Si) N become non-uniform, a required secondary
recrystallization structure cannot be obtained, a magnetic flux density decreases, and
therefore the amount of acid-soluble Al is set to 0.065% or less. The amount of acidsoluble
Al is preferably 0.050% or less, and more preferably 0.040% or less.
[0079]
35 N: 0.0040 to 0.0120%
N is an element that combines with Al to form AlN that functions as an inhibitor,
but on the other hand, it is also an element that forms blisters (voids) in the steel sheet
during cold rolling. When an amount of N is less than 0.0040%, formation of the AlN
is insufficient, and therefore the amount of N is set to 0.0040% or more. The amount of
40 N is preferably 0.0060% or more, and more preferably 0.0070% or more.
[0080]
On the other hand, when the amount of N exceeds 0.0120%, there is a concern
that blisters (voids) may be formed in the steel sheet during cold rolling, and therefore
the amount of N is set to 0.0120% or less. The amount of N is preferably 0.0100% or
45 less, and more preferably 0.0090% or less.
[0081]
S: 0.010% or less
S is an element that combines with Mn to form MnS that functions as an
inhibitor.
14
[0082]
When an amount of S exceeds 0.010%, precipitation and dispersion of MnS
become non-uniform, a desired secondary recrystallization structure cannot be obtained,
a magnetic flux density decreases, hysteresis loss increases after purification, or MnS
remains, and hysteresis loss increases 5 after purification. A lower limit of the amount of
S is not particularly set but is preferably 0.003% or more. The amount of S is more
preferably 0.007% or more.
[0083]
B: 0.0005 to 0.0080%
10 B is an element that combines with N and complex precipitates with MnS to
form BN that functions as an inhibitor.
[0084]
When an amount of B is less than 0.0005%, an addition effect is not sufficiently
exhibited, and therefore the amount of B is set to 0.0005% or more. The amount of B is
15 preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand,
when the amount of B exceeds 0.0080%, precipitation and dispersion of BN become nonuniform,
a required secondary recrystallization structure cannot be obtained, and a
magnetic flux density decreases, and therefore the amount of B is set to 0.0080% or less.
The amount of B is preferably 0.0060% or less, and more preferably 0.0040% or less.
20 [0085]
In the silicon steel slab, the remainder excluding the above-described elements is
Fe and impurities. Impurities are elements that are inevitably mixed from a steel raw
material and/or in the process of steelmaking and are elements that are allowed within a
range not impairing characteristics of the present electrical steel sheet.
25 [0086]
Also, the silicon steel slab may contain at least one selected from the group
consisting of 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less
of Ni, 0.30% or less of Sn, 0.30% or less of Sb, and 0.01% or less of Bi instead of a part
of Fe within a range not impairing magnetic characteristics of the electrical steel sheet
30 and enhancing other characteristics.
[0087]

A molten steel having the above-described component composition is cast into a
silicon steel slab by a normal method, and then subjected to normal hot rolling to form a
35 hot band, which is wound in a coil shape. Next, the hot band is subjected to hot-band
annealing and then subjected to one cold rolling or a plurality of times of cold rolling
with intermediate annealing sandwiched therebetween to obtain a steel sheet of a final
sheet thickness.
[0088]
40 Next, decarburization annealing is performed on the steel sheet of the final
thickness. The decarburization annealing is a heat treatment in wet hydrogen, reduces
an amount of C in the steel sheet to an amount that does not cause magnetic aging in the
product sheet, and causes primary recrystallization to occur in the steel sheet to be
prepared for the next secondary recrystallization. Further, nitriding annealing, which is
45 annealing performed in an ammonia atmosphere, is performed to form an AlN inhibitor.
[0089]
Next, the steel sheet after the decarburization annealing is subjected to final
annealing at a temperature of 1100ºC or higher. This final annealing is a heat treatment
performed in a form of a coil in which the steel sheet is coiled, but for the purpose of
15
preventing seizure of the steel sheet and forming a primary film, the final annealing is
performed with an annealing separator containing alumina (Al2O3) as a main component
and 28% by mass to 50% by mass of MgO applied to the steel sheet surface. An
application amount of the annealing separator is 6.0 g/m2 or more per side.
As described above, wh 5 en the amount of MgO added to the annealing separator
containing alumina as a main component is controlled in the range of 28% by mass to
50% by mass and the application amount of the annealing separator is controlled to 6.0
g/m2 or more per side, it is possible to obtain a grain-oriented electrical steel sheet in
which the needle-like inclusions (mullite) having a length of 1 μm or more are not
10 present in the base steel sheet. An upper limit of the application amount of the
annealing separator is not particularly limited, but from the perspective of cost, it is
preferably 12.0 g/m2 or less per side.
[0090]
In order to effectively inhibit formation of the needle-like inclusions (mullite), it
15 is preferable to control a BET specific surface area of alumina to 3 to 10 m2/g in the
annealing separator containing Al2O3 as a main component. When the BET specific
surface area of the alumina is controlled to 3 to 10 m2/g, an amount of SiO2 adsorbed by
the alumina can be increased, and formation of the needle-like inclusions can be
inhibited.
20 [0091]
When the BET specific surface area of the alumina is less than 3 m2/g, it is
difficult to adsorb and remove SiO2 sufficiently, and therefore the BET specific surface
area of the alumina is preferably 3 m2/g or more. On the other hand, when the BET
specific surface area of the alumina exceeds 10 m2/g, a viscosity of the annealing
25 separator slurry becomes too high, coating spots occur, and portions at which SiO2
cannot be sufficiently adsorbed and removed are formed, and therefore the BET specific
surface area of the alumina is preferably 10 m2/g or less.
[0092]
Even when the annealing separator in the above-described range of the BET
30 specific surface area is used, if the application amount of the annealing separator is
insufficient, SiO2 cannot be adsorbed and removed sufficiently, and the needle-like
inclusions (mullite) are formed.
After the final annealing, a coating liquid containing colloidal silica is applied to
the steel sheet from which a surplus annealing separator has been removed by washing
35 with water, and the colloidal silica is baked to form a tension-insulation coating. As
described above, a grain-oriented electrical steel sheet having a low iron loss in which the
forsterite film is not present between the base steel sheet and the tension-insulation
coating can be obtained.
[Example]
40 [0093]
Next, examples of the present invention will be described, but each of conditions
in the examples is one condition example employed for ascertaining feasibility and
effects of the present invention, and the present invention is not limited to each of the
condition examples. Also, the present invention can employ various conditions as long
45 as the object of the present invention is achieved without departing from the gist of the
present invention.
[0094]
(Example 1)
Slabs having component compositions shown in Table 1 were each heated to
16
1100ºC to be subjected to hot rolling to obtain a hot band having a sheet thickness of 2.6
mm, and the hot band was subjected to hot-band annealing at 1100ºC, and then subjected
to one cold rolling or a plurality of times of cold rolling with intermediate annealing
sandwiched therebetween to obtain a steel sheet with a final thickness of 0.23 mm.
5 [0095]
[Table 1]
Steel
No.
Steel slab chemical composition (mass%) (remainder is Fe and impurities)
C Si Mn Al N S B
A1 0.085 3.45 0.10 0.028 0.0040 0.008 0.0015
A2 0.031 1.21 0.10 0.029 0.0100 0.009 0.0020
A3 0.033 6.52 0.10 0.029 0.0100 0.007 0.0018
A4 0.041 3.45 0.08 0.028 0.0070 0.005 0.0019
A5 0.044 3.33 0.80 0.029 0.0060 0.004 0.0021
A6 0.052 4.52 0.12 0.020 0.0050 0.003 0.0016
A7 0.055 3.12 0.09 0.055 0.0017 0.001 0.0017
A8 0.061 2.81 0.09 0.030 0.0120 0.009 0.0018
A9 0.062 3.12 0.11 0.030 0.0040 0.001 0.0019
A10 0.071 2.92 0.13 0.030 0.0050 0.001 0.0021
[0096]
The above-described steel sheets were each rewound to be subjected to
decarburization annealing at 820ºC in a humid atmosphere of 75% hydrogen, 25%
10 nitrogen, and a dew point of 40ºC, and then were each subjected to nitriding annealing in
which annealing was performed in an ammonia atmosphere for the purpose of forming an
inhibitor AlN in each of the steel sheets. Thereafter, an aqueous slurry of an annealing
separator containing alumina with a BET specific surface area of 3 to 10 m2/g and 0 to
80% by mass of MgO was applied to a steel sheet surface while varying an application
15 amount of a solid content of the annealing separator per side in a range of 5 to 15 g/m2,
and then the steel sheet was wound in a coil shape.
[0097]
The coil-shaped steel sheet that had been coated with the above-described
annealing separator and dried was subjected to final annealing at 1200ºC for 20 hours.
20 After the final annealing, a surplus annealing separator was removed from the steel sheet
by washing with water to obtain a grain-oriented electrical steel sheet in which secondary
recrystallization was completed.
[0098]
Components of a base steel sheet in the manufactured grain-oriented electrical
25 steel sheet were measured using ICP-AES. Acid-soluble Al was measured by the ICPAES
using a filtrate obtained after the sample was decomposed by heating with an acid.
Also, C and S were measured using a combustion-infrared absorption method, N was
measured using an inert gas fusion-thermal conductivity method, and O was measured
using an inert gas fusion-nondispersive infrared absorption method.
30 [0099]
A test piece of 20 mm square was taken from a central portion in a width
direction of an outermost circumference of the coil-shaped grain-oriented electrical steel
sheet obtained in this way, a cross section (C cross section) perpendicular to a rolling
direction was polished with a diamond buff, the cross section of one side (20 mm) of the
35 test piece was observed with a microscope (1000 times), and the number of needle-like
inclusions having a length of 1 μm or more present in the observation region having a
sheet thickness direction length of 10 μm and a sheet width direction length of 20 mm
17
was measured. Identification of substances constituting the needle-like inclusions was
performed by the following methods. The test piece cut out from the base steel sheet
was immersed in a nital solution (5 vol% of nitric acid/ethanol) for 90 seconds, and a
surface thereof was removed by about several microns to make needle-like inclusions
appear. The surface of the 5 test piece on which the needle-like inclusions had appeared
was analyzed by a wide-angle X-ray diffraction method. Further, ascertaining of the
needle-like inclusions that had appeared was performed using an optical microscope.
Specifically, an obtained X-ray diffraction spectrum was collated with a data of JCPDS
No.: 15-776. Also, the iron loss W17/50 of the test piece was measured according to JIS
10 C 2550:2011. Chemical compositions of the obtained grain-oriented electrical steel
sheets are shown in Table 2, and evaluation results are shown in Table 3.
[0100]
[Table 2]
No. No.
Steel
No.
Product steel chemical composition (mass%) (remainder is Fe and impurities)
C Si Mn Al N S B
Invention
example
B1 A1 ≤ 0.002 3.45 0.10 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0015
B2 A2 ≤ 0.002 1.21 0.10 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0020
B3 A3 ≤ 0.002 6.52 0.10 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0018
B4 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
B5 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
B6 A6 ≤ 0.002 4.52 0.12 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0016
B7 A7 ≤ 0.002 3.12 0.09 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0017
B8 A8 ≤ 0.002 2.81 0.09 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0018
B9 A9 ≤ 0.002 3.12 0.11 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
B10 A10 ≤ 0.002 2.92 0.13 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
Comparative
example
b1 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b2 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b3 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b4 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b5 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b6 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b7 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b8 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b9 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b10 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b11 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b12 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b13 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b14 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
b15 A4 ≤ 0.002 3.45 0.08 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0019
15 [0101]
[Table 3]
No. No.
Steel
No.
Annealing separator Needle-like
inclusions
having length
of 1 μm or
more (pcs/20
mm)
Iron loss
W17/50
(W/kg)
Presence or
absence of
forsterite
formation
Amount of
MgO (mass%)
Application
amount (g/m2)
Invention
example
B1 A1 28 6.0 0 0.98 Absent
B2 A2 32 6.4 0 0.89 Absent
B3 A3 34 7.1 0 0.87 Absent
B4 A4 35 7.8 0 0.85 Absent
B5 A5 36 8.2 0 0.84 Absent
B6 A6 38 9.0 0 0.83 Absent
B7 A7 40 9.5 0 0.81 Absent
B8 A8 45 10.8 0 0.82 Absent
B9 A9 48 11.1 0 0.84 Absent
B10 A10 50 12.0 0 0.82 Absent
18
Comparative
example
b1 A4 0 10.0 54 1.43 Absent
b2 A4 12 10.0 38 1.20 Absent
b3 A4 22 10.0 2 1.24 Absent
b4 A4 60 10.0 0 1,21 Present
b5 A4 80 10.0 0 1.48 Present
b6 A4 28 5 49 1.24 Absent
b7 A4 32 4.2 42 1.19 Absent
b8 A4 34 4.5 38 1.17 Absent
b9 A4 35 4.8 14 1.14 Absent
b10 A4 36 4.9 10 1.01 Absent
b11 A4 38 5.1 20 1.11 Absent
b12 A4 40 5 12 1.08 Absent
b13 A4 45 5.1 39 1.21 Absent
b14 A4 48 4.9 58 1.32 Absent
b15 A4 50 5.2 41 1.24 Absent
[0102]
As shown in Table 2, base steel sheets of B1 to B10 and b1 to b15 contained
0.002% by mass or less of C, 1.21 to 6.52% by mass of Si, 0.08 to 0.80% by mass of Mn,
0.002% by mass or less of acid-5 soluble Al, 0.002% by mass or less of S, 0.003% by mass
or less of N, 0.0015 to 0.0021% by mass of B, and included a remainder of Fe and
impurities as chemical compositions thereof.
[0103]
As shown in Table 3, in invention examples B1 to B10, as a result of controlling
10 the amount of MgO in the annealing separator within the range of 28% by mass to 50%
by mass and controlling the application amount of the annealing separator within a range
of 6.0 to 12.0 g/m2 per side, the needle-like inclusions (mullite) with a length of 1 μm or
more were not present in the observation region of each of the base steel sheets, and the
iron loss W17/50 was suppressed to less than 1.00 W/kg. Also, the grain-oriented
15 electrical steel sheets of invention examples B1 to B10 did not have the forsterite film
and had mirror gloss.
[0104]
As shown in Table 3, in comparative examples b1 to b3, since the amount of
MgO in the annealing separator was less than 28% by mass while the application amount
20 of the annealing separator was controlled in the range of 6.0 to 12.0 g/m2 per side, a
plurality of needle-like inclusions (mullite) with a length of 1 μm or more were present in
the observation region of the base steel sheet, and the iron loss W17/50 increased to more
than 1.00 W/kg.
In comparative examples b4 and b5, the amount of MgO in the annealing
25 separator was more than 50% by mass while the application amount of the annealing
separator was controlled in the range of 6.0 to 12.0 g/m2 per side. In this case, the
needle-like inclusions (mullite) with a length of 1 μm or more were not present in the
observation region of the base steel sheet, but the forsterite was formed, and as a result,
the iron loss W17/50 increased to more than 1.00 W/kg.
30 In comparative example b6, since the application amount of the annealing
separator was less than 6.0 g/m2 per side while the amount of MgO in the annealing
separator was 28% by mass or more, a plurality of needle-like inclusions (mullite) with a
length of 1 μm or more were present in the observation region of the base steel sheet, and
the iron loss W17/50 increased to more than 1.00 W/kg.
35 In comparative examples b7 to b15, since the application amount of the
annealing separator was less than 6.0 g/m2 per side while the amount of MgO in the
annealing separator was controlled in the range of 28% by mass to 50% by mass, a
19
plurality of needle-like inclusions (mullite) with a length of 1 μm or more were present in
the observation region of the base steel sheet, and the iron loss W17/50 increased to more
than 1.00 W/kg.
[0105]
5 (Example 2)
A slab having a component composition of steel No. A5 shown in Table 1 was
heated to 1100ºC to be subjected to hot rolling to obtain a hot-rolled steel sheet of 2.60
mm, and the hot-rolled steel sheet was subjected to hot-band annealing at 1100ºC, and
then subjected to a plurality of times of cold rolling with intermediate annealing
10 sandwiched therebetween to obtain a steel sheet with a final thickness of 0.23 mm.
[0106]
The above-described steel sheet was rewound to be subjected to decarburization
annealing at 820ºC in a humid atmosphere of 75% hydrogen, 25% nitrogen, and a dew
point of 40ºC, and then was subjected to nitriding annealing in which annealing was
15 performed in an ammonia atmosphere for the purpose of forming an inhibitor AlN in the
steel sheet.
[0107]
Thereafter, an aqueous slurry of an annealing separator containing alumina with
a BET specific surface area varied in a range of 3.0 to 10.0 m2/g and 35.0 to 48.0% by
20 mass of MgO was applied to the steel sheet surface while varying an application amount
of a solid content of the annealing separator per side in a range of 8.2 to 11.2 g/m2, and
then the steel sheet was wound in a coil shape.
[0108]
The coil-shaped steel sheet that had been coated with the above-described
25 annealing separator and dried was subjected to final annealing at 1200ºC for 20 hours.
After the final annealing, a surplus annealing separator was removed from the steel sheet
by washing with water to obtain a grain-oriented electrical steel sheet which had no
forsterite film and had mirror gloss and in which secondary recrystallization had been
completed.
30 [0109]
A test piece of 20 mm square was taken from a central portion in a width
direction of an outermost circumference of the coil-shaped grain-oriented electrical steel
sheet obtained in this way, a cross section (C cross section) perpendicular to a rolling
direction was polished with a diamond buff, the cross section of one side (20 mm) of the
35 test piece was observed with a microscope (1000 times), and the number of needle-like
inclusions having a length of 1 μm or more present in the observation region having a
sheet thickness direction length of 10 μm and a sheet width direction length of 20 mm
was measured. Also, the iron loss W17/50 of the test piece was measured according to
JIS C 2550:2011. Chemical compositions of the obtained grain-oriented electrical steel
40 sheets are shown in Table 4, and evaluation results are shown in Table 5.
[0110]
[Table 4]
No.
Steel
No.
Product steel chemical composition (mass%) (remainder is Fe and impurities)
C Si Mn Al N S B
C1 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
C2 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
C3 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
C4 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
C5 A5 ≤ 0.002 3.33 0.80 ≤ 0.002 ≤ 0.003 ≤ 0.002 0.0021
[0111]
20
[Table 5]
No. No.
Steel
No.
Annealing separator
Alumina
BET
specific
surface
area (m2/g)
Needle-like
inclusions
having
length of 1
μm or more
(pcs/20
mm)
Iron loss
W17/50
(W/kg)
Presence or
absence of
forsterite
formation
Amount of
MgO
(mass%)
Application
amount
(g/m2)
Invention
example
C1 A5 35 8.2 3.0 0 0.88 Absent
C2 A5 38 9.8 4.8 0 0.84 Absent
C3 A5 42 10.1 6.2 0 0.80 Absent
C4 A5 45 10.8 7.5 0 0.77 Absent
C5 A5 48 11.2 10.0 0 0.72 Absent
[0112]
As shown in Table 4, the base steel sheets of C1 to C5 contained 0.002% by
5 mass or less of C, 3.33% by mass of Si, 0.80% by mass of Mn, 0.002% by mass or less of
acid-soluble Al, 0.002% by mass or less of S, 0.003% by mass or less of N, 0.0021% by
mass of B, and included a remainder of Fe and impurities as chemical compositions
thereof.
[0113]
10 As shown in Table 5, it can be seen that the iron loss W17/50 could be
significantly reduced by controlling the amount of MgO in the annealing separator within
the range of 28% by mass to 50% by mass, controlling the application amount of the
annealing separator within the range of 6.0 to 12.0 g/m2 per side, and furthermore,
controlling the BET specific surface area of the alumina, which was a main component of
15 the annealing separator, within a range of 3.0 to 10.0 m2/g. It is conceivable that this is
because the needle-like inclusions are not formed, and moreover, the amount of SiO2
adsorbed by the alumina is increased.
[Industrial Applicability]
[0114]
20 According to the present invention, in a grain-oriented electrical steel sheet in
which a forsterite film is not present between a base steel sheet and a tension-insulation
coating, it is possible to provide a grain-oriented electrical steel sheet in which iron loss
can be significantly reduced and to which a tension-insulation coating having lower iron
loss than that of conventional cases is provided. Therefore, the present invention has
25 high applicability in an electrical steel sheet manufacturing industry and an industry of
utilizing the electrical steel sheet.

WE CLAIMS

1. A grain-oriented electrical steel sheet in which a forsterite film is not present
between a base steel sheet and a tension-insulation coating, wherein
5 the base steel sheet contains:
0.085% by mass or less of C;
0.80 to 7.00% by mass of Si;
0.05 to 1.00% by mass of Mn:
0.065% by mass or less of acid-soluble Al;
10 0.003% by mass or less of S;
0.0040% by mass or less of N;
0.0005 to 0.0080% by mass of B;
0 to 0.50% by mass of P;
0 to 1.00% by mass of Ni;
15 0 to 0.30% by mass of Sn;
0 to 0.30% by mass of Sb;
0 to 0.40% by mass of Cu;
0 to 0.30% by mass of Cr;
0 to 0.01% by mass of Bi; and
20 a remainder of Fe and impurities as a chemical composition thereof, and
in a case in which a cross section perpendicular to a rolling direction of the base
steel sheet is viewed, when a region having a length of 10 μm from a surface of the base
steel sheet toward the inside of the base steel sheet in a sheet thickness direction of the
base steel sheet and a length of 20 mm in a direction perpendicular to the sheet thickness
25 direction is an observation region, needle-like inclusions having a length of 1 μm or more
are not present in the observation region.
2. The grain-oriented electrical steel sheet according to claim 1, wherein the needle-like
inclusion contains mullite represented by 3Al2O3·2SiO2.