[Technical Field of the Invention]
[0001]
The present invention relates to a grain-oriented electrical steel sheet mainly
used as a core of an electric device such as a transformer and a method for
manufacturing a grain-oriented electrical steel sheet.
[Related Art]
[0002]
A grain-oriented electrical steel sheet is used in many electric devices as a
magnetic core.
The grain-oriented electrical steel sheet is a steel sheet in which 0.8% to 4.8%
of Si is contained and the crystal orientation of the product is highly concentrated in a
{ 110 }<001> orientation. As the magnetic characteristics, the grain-oriented electrical
steel sheet is required to have a high magnetic flux density (represented by Bs value)
and a low iron loss (represented by W17 /50). In particular, recently, there is an
increasing demand for a r eduction in power loss from the viewpoint of energy saving.
[0003]
In response to this demand, a technique for refining magnetic domains has
been developed to reduce an iron loss in a grain-oriented electrical steel sheet. A
method for refining magnetic domains and reducing an iron loss by irradiating a steel
sheet after final annealing with a laser beam is disclosed in, for example, Patent
Document 1. However, since the reduction in iron loss according to this method is by
- 1 -
strain introduced by the laser irradiation, the method cannot be used for a wound core
transformer that requires stress relief annealing after forming the transformer.
[0004]
As an improved technique for this, for example, Patent Document 2 discloses
a method of removing a part of the surface glass layer of a grain-oriented electrical
steel sheet by laser irradiation or the like after final annealing, dissolving the base steel
sheet metal using an acid such as hydrochloric acid or nitric acid to form grooves, and
thereafter forming a tension coating, thereby refining magnetic domains.
In the steel sheet subjected to such a magnetic domain refinement treatment,
when the grooves are formed, the coating is locally fractured, which causes problems
of insulation properties and corrosion resistance. Therefore, a coating is further
formed after the grooves are formed.
[Prior Art Documents]
[Patent Documents]
[0005]
[Patent Document 1] Japanese Examined Patent Application, Second
Publication No. S58-26405
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. S61-117284
[Patent Document 3] Japanese Examined Patent Application, Second
Publication No. S62-45285
[Patent Document 4] Japanese Examined Patent Application, Second
Publication No. S40-15644
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
- 2 -
[0006]
An object of the present invention is to provide a grain-oriented electrical
steel sheet having grooves formed on the surface of the base steel sheet, in which the
iron loss is lower than that of an existing product by appropriately controlling the
morphology of a tension coating formed on the grooves while maintaining insulation
properties and corrosion resistance.
[Means for Solving the Problem]
[0007]
Aspects of the present invention are as follows.
( 1) According to a first aspect of the present invention, there is provided a
grain-oriented electrical steel sheet including: a base steel sheet having a flat surface
and a groove forming surface on which a groove is formed; and a tension coating
formed on the base steel sheet and containing a compound of phosphoric acid,
phosphate, chromic anhydride, chromate, alumina, or silica, in which the tension
coating has a flat surface coating portion formed on the flat surface and a groove
forming surface coating portion formed on the groove forming surface, when an
average coating thickness of the flat surface coating portion is referred to as tl (J.lm), a
minimum coating thickness of the groove forming surface coating portion is referred to
as t2Min (J.lm), and a maximum coating thickness of the groove forming surface coating
portion is referred to as t2Max (J.lm), Expressions (1) and (2) are satisfied, and when a
value of 0.95 times a distanceD of the tension coating along a sheet thickness direction
from a bottom surface position of the groove forming surface coating portion to a
bottom surface position of the flat surface coating portion is referred to as an effective
depth d (J.lm), Expression (3) is satisfied.
t2Mmltl 2: 0.4 (1)
- 3 -
t2Max/tl ~ 3.0 (2)
t2Max ~ d/2 (3)
(2) The grain-oriented electrical steel sheet according to (1) may further
include: a glass coating formed between the base steel sheet and the tension coating
and containing MgzSi04.
(3) In the grain-oriented electrical steel sheet according to (1) or (2), when a
width of the groove forming surface is referred to as w (J.lm), Expression ( 4) may be
satisfied.
d/w ~ 113 (4)
(4) In the grain-oriented electrical steel sheet according to any one of (1) to
(3), when a width of the groove forming surface is referred to as w (J.lm), Expression
(5) may further be satisfied.
(d/w) X t2Max ~ tl (5)
[0008]
(5) According to a second aspect of the present invention, there is provided a
method for manufacturing a grain-oriented electrical steel sheet including: cold rolling
step of manufacturing a cold-rolled steel sheet; a final annealing step of performing
final annealing with secondary recrystallization on the cold-rolled steel sheet; a groove
forming step of forming a linear groove on the cold-rolled steel sheet before or after
the final annealing step in a direction intersecting a rolling direction of the cold-rolled
steel sheet; and a tension coating applying step of forming a tension coating containing
a compound of phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or
silica on the groove.
(6) The method for manufacturing a grain-oriented electrical steel sheet
according to (5) may further include: after the tension coating applying step, a tension
- 4 -
coating shaping step of shaping the tension coating by processing the tension coating
to leave a part of the tension coating in a thickness direction and reduce a thickness of
a portion of the tension coating formed on the groove in a range narrower than a width
of the groove.
(7) The method for manufacturing a grain-oriented electrical steel sheet
according to (5) or (6) may further include: an annealing separating agent applying
step of applying an annealing separating agent to the cold-rolled steel sheet after the
cold rolling step and before the final annealing step, in which the annealing separating
agent contains magnesia.
[Effects of the Invention]
[0009]
According to the above aspects of the present invention, there is provided a
grain-oriented electrical steel sheet having a lower iron loss than that in an existing
product while maintaining insulation properties and corrosion resistance, and a method
for manufacturing the same.
[Brief Description of the Drawings]
[0010]
FIG. 1 is a plan view of a grain-oriented electrical steel sheet according to a
first embodiment.
FIG. 2 is a schematic end face view for describing a configuration in the
vicinity of a groove of the grain-oriented electrical steel sheet according to the first
embodiment.
FIG. 3 is a schematic end face view for describing a configuration in the
vicinity of a groove of a grain-oriented electrical steel sheet according to a second
embodiment.
- 5 -
FIG. 4 is a schematic end face view for describing a configuration in the
vicinity of a groove of a grain-oriented electrical steel sheet according to a
modification example of the second embodiment.
FIG. 5 is a flowchart for describing a method for manufacturing a grainoriented
electrical steel sheet.
[Embodiments of the Invention]
[0011]
In general, in a grain-oriented electrical steel sheet, a coating is formed on the
surface of the base steel sheet to apply tension in a magnetization direction (rolling
direction) of the steel sheet, thereby achieving a reduction in iron loss. However, the
present inventor recognized that in a grain-oriented electrical steel sheet in which
grooves are formed on the surface of the base steel sheet by a chemical treatment, a
physical treatment, or a thermal treatment for magnetic domain control, the formation
of a coating after the formation of the grooves may cause an increase in iron los s.
While examining the reason for this, it was thought that the formation of the
coating on a groove wall surface had an adverse effect on the magnetization of the steel
sheet in the rolling direction.
[0012]
The groove wall surface is a surface (a surface having a component in a sheet
thickness direction) deviating from the surface of the base steel sheet. Therefore, in a
case where a coating is formed on the groove wall surface, tension due to the coating
acts in a direction deviating from the magnetization direction of the base steel sheet (a
direction parallel to the surface of the base steel sheet, the rolling direction), and
becomes a factor to an increase in the iron los s. In particular, a coating solution for
forming a coating tends to accumulate in the groove, and it is considered that the
- 6 -
formation of a thick coating also has a large adverse effect on the increase in iron loss.
Furthermore, in a grain-oriented steel sheet in which grooves are formed, a
magnetic flux that reaches one groove wall through the inside of the steel sheet passes
through the groove space along the magnetization direction by leaking from the
domain wall (that is, due to the leakage of the magnetic flux), reaches the other groove
wall, and is directed again in the magnetization direction inside the steel sheet.
Here, a coating formed on the groove wall surface having a component in a
direction nearly perpendicular to the rolling direction X suppress the leakage of the
magnetic flux as tension is applied in a direction deviating from the magnetization
direction of the steel sheet as described above. Therefore, the effect of reducing the
iron loss is hindered.
Accordingly, in order to allow the groove wall surface to leak a large amount
of magnetic flux, it can be said that it is effective to make the coating formed on the
groove wall surface as thin as possible. However, from the viewpoint of insulation
properties and corrosion resistance, excessively thinning the coating formed on the
groove is not a practical solution.
[0013]
Based on the above examination, the present inventor found that in a grainoriented
electrical steel sheet in which a part of a coating formed in a groove is
processed to appropriately control the thickness of the coating, excellent magnetic
characteristics can be exhibited while insulation properties and corrosion resistance are
maintained.
[0014]
The present invention made based on the above findings will be described in
detail with reference to the drawings.
- 7 -
In the following description, there are cases where in a grain-oriented
electrical steel sheet, a rolling direction is indicated by X, a sheet width direction is
indicated by Y, and a sheet thickness direction is indicated by Z. The sheet width
direction Y is a direction perpendicular to the rolling direction X and the sheet
thickness direction Z.
[0015]
(First Embodiment)
FIG. 1 is a plan view of a grain-oriented electrical steel sheet 100 according to
a first embodiment of the present invention. As shown in FIG. 1, in the grain-oriented
electrical steel sheet 100 according to the present embodiment, grooves G extending
linearly in the sheet width direction Y (that is, a direction intersecting the rolling
direction X) are formed.
[0016]
FIG. 2 is a schematic end face view corresponding to the line A-A in FIG. 1
and shows a configuration in the vicinity of the groove G.
As shown in FIG. 2, the grain-oriented electrical steel sheet 100 according to
the present embodiment is configured to include a base steel sheet 110, and a tension
coating 130 which is formed on the base steel sheet llO and contains a compound of
phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or silica.
[0017]
As shown in FIG. 2, the base steel sheet 110 has a flat surface 11 OF, which is a
surface on which the groove G is not formed, and a groove forming surface 11 OG,
which is a surface on which the groove G is formed.
The tension coating 130 is formed on the base steel sheet llO.
In the following description, in the tension coating 130, a portion formed on
- 8 -
the flat surface 11 OF of the base steel sheet 110 is referred to as a flat surface coating
portion 130F, and a portion formed on the groove forming surface ll OG of the base
steel sheet 110 is referred to as a groove forming surface coating portion 130G.
[0018]
Hereinafter, dimensions for specifying the morphology of the tension coating
130 in the vicinity of the groove G will be described.
Each dimension can be determined by extracting n (n ~ 10) grooves G as
measurement targets, machining the cross section in a surface perpendicular to the
extension direction of each groove G to a mirror finish, and observing the cross section
with a scanning electron microscope.
[0019]
The average value of the thicknesses of the flat surface coating portion 130F
in the sheet thickness direction Z is defined as an average coating thickness t1 of the
flat surface coating portion 130F.
The average coating thickness t1 can be determined as follows. First, for
each of the n grooves G, the thickness of the flat surface coating portion 130F in the
sheet thickness direction Z is measured at at least 10 points in the flat surface coating
portion 130F in the vicinity of the grooves G, and an average value is obtained. Then,
the average coating thickness t1 is determined by calculating the average value of the n
average values.
[0020]
The minimum value of the thickness of the groove forming surface coating
portion 130G in the direction perpendicular to the surface is defined as a minimum
coating thickness t2Min of the groove forming surface coating portion 130G.
The minimum coating thickness t2Min can be determined as follows. First,
- 9 -
for each of the n grooves G, the minimum value of the thickness of the groove forming
surface coating portion 130G in the direction perpendicular to the surface thereof is
measured. Then, the minimum coating thickness t2Mm is determined by calculating
the average value of the n measurement values.
[0021]
The maximum value of the thickness of the groove forming surface coating
portion 130G in the direction perpendicular to the surface is defined as a maximum
coating thickness t2Max of the groove forming surface coating portion 130G.
The maximum coating thickness t2Max can be determined as follows. First,
for each of the n grooves G, the maximum value of the thickness of the groove forming
surface coating portion 130G in the direction perpendicular to the surface thereof is
measured. Then, the maximum coating thickness t2Max is determined by calculating
the average value of the n measurement values.
[0022]
A value of 0.95 times a distanceD in the sheet thickness direction Z from a
bottom surface position 130Ga of the groove forming surface coating portion 130G to
a bottom surface position 130Fa of the flat surface coating portion 130F (that is, the
boundary between the flat surface coating portion 130F and the base steel sheet 110) is
defined as an effective depth d.
The distance D is a dimension corresponding to the depth of the groove G
formed in the base steel sheet ll 0. The thickness of the tension coating 130 formed
on a groove wall surface in the vicinity of a shoulder portion of the groove G (a portion
connected to the flat surface 11 OF) has a small effect on iron loss. Therefore, the
value of 0.95 x D, which corresponds to a depth of95% on the bottom side of the
groove G, is used here as the effective depth d that contributes to an iron loss reduction
- 10 -
effect.
The effective depth d can be determined as follows. First, for each of the n
grooves G, the distance in the sheet thickness direction Z from the bottom surface
position 130Ga to the bottom surface position 130Fa is measured. Then, the distance
Dis obtained by calculating the average value of then measurement values, and the
effective depth dis determined based on the distance D.
[0023]
The separation distance between the two flat surfaces llOF and llOF adjacent
to the groove forming surface 11 OG in the direction perpendicular to the extension
direction of the groove G and the sheet thickness direction Z is defined as a width w of
the groove forming surface 11 OG.
The width w can be determined as follows. First, the above-mentioned
separation distance is measured for each of the n grooves G. Then, the width w is
determined by calculating the average value of the n measurement values.
[0024]
In the grain-oriented electrical steel sheet 100 according to the present
embodiment, the tension coating 130 is formed so that the average coating thickness tl
()lm) of the flat surface coating portion 130F, the minimum coating thickness t2Mm
()lm) of the groove forming surface coating portion 130G, and the maximum coating
thickness t2Max ()lm) of the groove forming surface coating portion 130G satisfy
Expressions (1) and (2) as follows.
t2Mm/tl ~ 0.4 (1)
t2Max/tl ~ 3.0 (2)
[0025]
In Expressions (1) and (2), the ranges of the minimum value and the
- 11 -
maximum value of the thickness (thickness in the direction perpendicular to the
surface) of the groove forming surface coating portion 130G are each specified based
on the coating thickness of the flat surface coating portion 130F.
In a case where Expression (1) is satisfied, there is no point where the coating
of the groove forming surface coating portion 130G is excessively thin with respect to
the average coating thickness tl, so that excellent insulation properties and corrosion
resistance can be exhibited.
In a case where Expression (2) is satisfied, it can be said that there is no point
where the coating of the groove forming surface coating portion 130G is excessively
thick with respect to the average coating thickness tl. Therefore, the tension
generated in the direction intersecting the surface direction of the steel sheet due to the
coating formed on the groove wall surface is not excessively generated. Therefore,
the iron loss reduction effect can be sufficiently obtained.
[0026]
Furthermore, in the grain-oriented electrical steel sheet 100 according to the
present embodiment, the maximum coating thickness t2Max (llm) of the tension coating
130 and the effective depth d (llm) of the tension coating 130 satisfy Expression (3) as
follows.
t2Max :::; d/2 (3)
[0027]
In Expression (3 ), the range of the maximum value of the thickness of the
groove forming surface coating portion 130G (thickness in the direction perpendicular
to the surface thereof) is specified based on the effective depth d, which is an index
depending on the depth of the groove G.
In a case where Expression (3) is satisfied, it can be said that there is no point
- 12 -
where the coating of the groove forming surface coating portion 130G is excessively
thick with respect to the effective depth d. Therefore, the tension generated in the
direction intersecting the surface direction of the steel sheet due to the coating formed
on the groove wall surface is not excessively generated. Therefore, the iron loss
reduction effect can be sufficiently obtained.
[0028]
In the grain-oriented electrical steel sheet 100 according to the present
embodiment, it is preferable that the effective depth d ()lm) of the tension coating 130
and the width w ()lm) ofthe groove forming surface 110G satisfy Expression (4).
d/w2: 113 (4)
[0029]
d/w is an index indicating the inclination of the groove wall surface of the
groove forming surface 110G. In a case where the inclination of the groove wall
surface of the groove forming surface 11 OG is large, it can be said that the groove
shape i s suitable from the viewpoint of magnetic domain refinement. However,
according to the findings of the present inventor, in a case where the d/w is large, the
angle difference between the magnetization direction (X direction) of the grainoriented
electrical steel sheet 100 and the tension direction along the groove wall
surface due to the tension coating 130 (groove forming surface coating portion 130G)
formed on the groove wall surface of the groove forming surface 11 OG is large.
Therefore, in a case where the thickness of the tension coating 130 is not properly
controlled, the problem of an increase in iron loss becomes significant.
On the other hand, in the grain-oriented electrical steel sheet 100 according to
the present embodiment, since the tension coating 130 is formed in which the thickness
is controlled so as to satisfy Expressions (1) to (3) as described above, the problem of
- 13 -
an increase in iron loss caused by the groove wall surface with a large d/w has been
solved.
Therefore, in a case where not only Expressions (1) to (3) but also Expression
(4) are satisfied, a reduction in iron loss can be realized while providing a suitable
groove shape from the viewpoint of magnetic domain refinement and maintaining
insulation properties and the corrosion resistance, which is preferable.
[0030]
Furthermore, in the grain-oriented electrical steel sheet 100 according to the
present embodiment, it is preferable that the maximum coating thickness t2Max (J.lm),
the width w (J.lm), the average coating thickness tl (J.lm), and the effective depth d
(J.lm) satisfy Expression (5).
(d/w) X t2Max :S t1 (5)
[0031]
As described above, the problem of an increase in iron loss that occurs in a
case where the thickness of the groove forming surface coating portion 130G of the
tension coating 130 is not properly controlled becomes more significant as the angle
difference between the magnetization direction of the grain-oriented electrical steel
sheet 100 and the tension direction of the groove forming surface coating portion 130G
becomes larger. That is, the larger the d/w, which is the inclination of the groove wall
surface, the thinner should be the maximum coating thickness t2Max of the groove
forming surface coating portion 130G from the viewpoint of a reduction in iron loss.
Furthermore, in the present application, considering that the maximum coating
thickness t2Max is specified based on the average coating thickness tl , this effect is
specified by Expression (5).
Therefore, in a case where not only Expressions (1) to (3) but also Expression
- 14 -
(5) are satisfied, the maximum coating thickness t2Max is more strictly limited in
consideration of d/w, the inclination of the groove wall surface. Therefore, the
problem of an increase in iron loss can be avoided more reliably.
[0032]
The morphology of the groove G is preferably in the following range in
relation to the effect of the present invention.
[0033]
The average coating thickness t1 is preferably 1 )lm or more, and more
preferably 2 )lm or more. This is because when the average coating thickness tl is 1
)lm or more, the insulation properties and the corrosion resistance can be exhibited
more reliably.
The average coating thickness t1 is preferably 10 )lm or less, and more
preferably 5 )lm or less. This is because when the average coating thickness t1 is 10
)lm or less, it is possible to prevent the space factor of the base steel sheet 110 from
being significantly lowered.
[0034]
The width w is preferably 20 )lm or more, and more preferably 30 )lm or more.
This is because when the width w is 20 )lm or more, it is technically easy to control the
thickness of the groove forming surface coating portion 130G.
The width w is preferably 150 )lm or less, and more preferably 90 )lm or less.
The case where the width w is 150 )lm or less is suitable from the viewpoint of
magnetic domain refinement. As the width w becomes smaller, the problem of an
increase in iron loss caused by the angle difference between the magnetization
direction of the grain-oriented electrical steel sheet 100 and the tension direction along
the groove wall surface due to the groove forming surface coating portion 130G
- 15 -
becomes significant, although the problem also depends on the depth of the groove G.
Therefore, it can be said that the effect of the present invention is large by
appropriately controlling the thickness of the tension coating 130, so that the width w
is preferably 150 11m or less.
[0035]
The distanceD is preferably 5 11m or more, and more preferably 15 11m or
more. In a case where the distance D is 5 11m or more, the problem of an increase in
iron loss caused by the angle difference between the magnetization direction of the
grain-oriented electrical steel sheet 100 and the tension direction along the groove wall
surface due to the groove forming surface coating portion 130G becomes significant,
although the problem also depends on the width w. Therefore, it can be said that the
effect of the present invention is large by appropriately controlling the thickness of the
tension coating 130, so that the distanceD is preferably 5 11m or more.
The distanceD is preferably 50 11m or less, and more preferably 30 11m or less.
This is because when the distance D is 50 11m or less, it is technically easy to
control the thickness of the groove forming surface coating portion 130G. In addition,
when the distanceD exceeds 50 11m, there are cases where the sheet thickness is
partially greatly reduced and the iron loss reduction effect cannot be obtained.
[0036]
From the viewpoint of a reduction in iron loss, the extension direction of the
groove G is preferably in a range of goo to 60° with respect to the rolling direction X,
and more preferably in a range of goo to 80°.
When the extension direction of the groove G is 60° or more with respect to
the rolling direction X, the angle between the groove wall surface of the groove
forming surface 11 OG and the rolling direction X also becomes large, so that the need
- 16 -
for the effect of the present invention to act increases.
[0037]
The pitch between the grooves Gin the rolling direction X (rolling direction
pitch) is preferably set in a range of 1 to 20 mm according to the need for magnetic
domain refinement. It is more preferable to set the rolling direction pitch between the
grooves G to a range of 2 to 10 mm. It is more preferable that the upper limit of the
rolling direction pitch between the grooves G is 8 mm. It is more preferable that the
upper limit of the rolling direction pitch between the grooves G is 5 mm.
[0038]
The base steel sheet 110 may contain, as a chemical composition, Si: 0.8% to
4.8% by mass%, and the remainder consisting of Fe and impurities. The chemical
composition is a preferable chemical composition for controlling the crystal
orientations to be integrated in a { 110}<001> orientation.
[0039]
Furthermore, the base steel sheet 110 may contain known optional elements
instead of a portion of Fe for the purpose of improving the magnetic characteristics.
Examples of the optional elements contained instead of a portion of Fe include the
following elements. Each numerical value means an upper limit in a case where
those elements are contained as the optional elements.
By mass%, C: 0.005% or less, Mn: 0.3% or less, S: 0.015% or less, Se:
0.015% or less, Al: 0.050% or less, N: 0.005% or less, Cu: 0.40% or les s, Bi: 0.010%
or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb:
0.10% or less, Cr: 0.30% or less, Ni: 1.00% or less, and one or two or more of Nb, V,
Mo, Ta, and W: 0.030% or less in total.
Since these optional elements may be contained according to a known
- 17 -
purpose, it is not necessary to set a lower limit for the amount of the optional elements,
and the lower limit may be 0%.
[0040]
The impurities are not limited to the examples of the optional elements, but
mean elements that do not impair the effect of the present invention even if the
elements are contained. The impurities are not limited to a case of intentionally
adding such elements, and also include elements that are unavoidably incorporated in
from ore as a raw material, scrap, or a manufacturing environment when the base steel
sheet is industrially manufactured. A target for the upper limit of the total amount of
the impurities may be about 5% by mass%.
[0041]
A grain-oriented electrical steel sheet is generally subjected to decarburization
annealing and purification annealing at the time of secondary recr ystallization, and is
subjected to a relatively large change in chemical composition (a reduction in amount)
in a manufacturing process. Depending on the element, the amount thereof is reduced
to 50 ppm or less, and may reach a level that cannot be detected by a general analysis
(1 ppm or less) when purification annealing is sufficiently performed. The chemical
composition of the base steel sheet 110 is a chemical composition in the final product,
and is different from the composition of a slab described later, which is also a starting
materiaL
[0042]
For example, the chemical composition of the base steel sheet 110 may be
measured using inductively coupled plasma-atomic emission spectrometry (ICP-AES).
Specifically, the chemical composition is identified by measuring a 35 mm square test
piece collected from the base steel sheet 110 with ICPS-8100 manufactured by
- 18 -
Shimadzu Corporation (measuring device) or the like under conditions based on a
calibration curve prepared in advance. In addition, C and S can be measured using a
combustion-infrared absorption method, and N can be measured using an inert gas
fusion-thermal conductivity method.
[0043]
(Second Embodiment)
Hereinafter, a grain-oriented electrical steel sheet 200 according to a second
embodiment of the present invention will be described.
The grain-oriented electrical steel sheet 200 according to the second
embodiment is different from the grain-oriented electrical steel sheet 100 according to
the first embodiment in that a glass coating is formed between a base steel sheet and a
tension coating. Descriptions that overlap the descriptions in the first embodiment
will be omitted.
[0044]
FIG. 3 is a schematic end face view for describing a configuration in the
vicinity of a groove G of the grain-oriented electrical steel sheet 200 according to the
present embodiment.
As shown in FIG. 3, the grain-oriented electrical steel sheet 200 according to
the present embodiment is configured to include a base steel sheet 210, and a tension
coating 230 which is formed on the base steel sheet 210 and contains a compound of
phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or silica, and a
glass coating 250 formed between the base steel sheet 210 and the tension coating 230
and containing Mg2Si04.
In the grain-oriented electrical steel sheet 200 according to the present
embodiment, since the glass coating 250 is formed, high adhesion be obtained between
- 19 -
the tension coating 230 and the base steel sheet 210, and stronger tension can be
applied.
[0045]
As shown in FIG. 3, the base steel sheet 210 has a flat surface 210F, which is a
surface on which the groove G is not formed, and a groove forming surface 21 OG,
which is a surface on which the groove G is formed.
The tension coating 230 is formed on the base steel sheet 210.
In the grain-oriented electrical steel sheet 200 according to the present
embodiment, the glass coating 250 is formed between the flat surface 210F of the base
steel sheet 210 and the tension coating 230, the glass coating 250 is not formed
between the groove forming surface 210G of the base steel sheet 210 and the tension
coating 230.
In the following description, in the tension coating 230, a portion formed on
the flat surface 210F of the base steel sheet 210 is referred to as a flat surface coating
portion 230F, and a portion formed on the groove forming surface 21 OG of the base
steel sheet 210 is referred to as a groove forming surface coating portion 230G.
[0046]
Since an average coating thickness tl of the flat surface coating portion 230F,
a minimum coating thickness t2Min of the groove forming surface coating portion 230G,
and a maximum coating thickness t2Max of the groove forming surface coating portion
230G overlap the average coating thickness tl, the minimum coating thickness t2Min,
and the maximum coating thickness t2Max described in the first embodiment,
description thereof will be omitted.
In addition, since a width w of the groove forming surface 210G overlaps the
width w described in the first embodiment, description thereof will also be omitted.
- 20 -
[0047]
In the grain-oriented electrical steel sheet 200 according to the present
embodiment, the glass coating 250 is formed between the flat surface 210F of the base
steel sheet 210 and the tension coating 230. Therefore, a bottom surface position
230Fa of the flat surface coating portion 230F is the boundary between the flat surface
coating portion 230F and the glass coating 250.
Here, since an effective depth d is an index for determining a range that
effectively contributes to the reduction in iron loss by controlling the thickness of the
groove forming surface coating portion 230G, the effective depth d is determined
depending on the shape of the tension coating 230 even in a case where the glass
coating 250 exists as in the present embodiment. That is, as in the definition
described in the first embodiment, in the present embodiment, a value of 0.95 times a
distance D in the sheet thickness direction Z from a bottom surface position 230Ga of
the groove forming surface coating portion 230G to the bottom surface position 230Fa
of the flat surface coating portion 230F is the effective depth d.
[0048]
Therefore, even in the grain-oriented electrical steel sheet 200 according to
the present embodiment, the tension coating 230 is formed to satisfy Expressions (1) to
(3) as follows. Therefore, an iron loss lower than that of an existing product can be
realized while maintaining insulation properties and corrosion resistance.
t2Mmltl 2: 0.4 (1)
t2Max/t1 :S 3.0 (2)
t2Max :S d/2 (3)
[0049]
A preferable aspect des cribed in the first embodiment is similarly adopted in
- 21 -
the grain-oriented electrical steel sheet 200 according to the present embodiment.
[0050]
In the grain-oriented electrical steel sheet 200 according to the present
embodiment, the glass coating 250 is formed only between the flat surface 21 OF of the
base steel sheet 210 and the tension coating 230, and is not formed between the groove
forming surface 210G of the base steel sheet 210 and the tension coating 230.
However, as in a grain-oriented electrical steel sheet 200A according to a
modification example shown in FIG. 4, the glass coating 250 may also be formed
between the groove forming surface 210G of the base steel sheet 210 and the tension
coating 230. Even in this case, the definitions of the average coating thickness tl, the
minimum coating thickness t2Min, the maximum coating thickness t2Max, and the
effective depth d do not change.
[0051]
(Third Embodiment)
Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet
according to a third embodiment of the present invention will be described.
[0052]
The method for manufacturing a grain-oriented electrical steel sheet to the
present embodiment includes at least a cold rolling step of manufacturing a cold-rolled
steel sheet, a final annealing step of performing final annealing on the cold-rolled steel
sheet, a groove forming step of forming grooves G on the cold-rolled steel sheet before
or after the final annealing step, and a tension coating applying step of applying a
tension coating onto the grooves G. In addition, a tension coating shaping step of
shaping the tension coating by processing the tension coating can also be added.
Furthermore, as an example of a specific manufacturing method, in addition
- 22 -
to the above steps, a casting step, a hot rolling step, a hot-rolled steel sheet annealing
step, a decarburization annealing step, a nitriding treatment step, and an annealing
separating agent applying step are included. These steps are examples adopted to
show the feasibility of the present invention, and the present invention is not limited to
these steps and conditions.
[0053]
FIG. 5 is a flowchart for describing a specific example of the method for
manufacturing a grain-oriented electrical steel sheet according to the present
embodiment. Hereinafter, each step will be described.
[0054]
(Casting Step S1)
In a casting step S 1, a slab is prepared. An example of a method for
manufacturing the slab is as follows. Molten steel is manufactured (melting). A
slab is manufactured using the molten steel. The slab may also be manufactured by a
continuous casting method. An ingot may be manufactured using the molten steel,
and the ingot may be subjected to blooming to manufacture a slab. The thickness of
the slab is not particularly limited. The thickness of the slab i s, for example, 150 mm
to 350 mm. The thickness of the slab is preferably 220 mm to 280 mm. As the slab,
a so-called thin slab having a thickness of 10 mm to 70 mm may be used. In a case
where the thin slab is used, rough rolling before finish rolling can be omitted in a hot
rolling step S2.
[0055]
The composition of the slab may be any composition that causes secondary
recrystallization. Specifically, the base elements and optional elements of the slab are
as follows. The notation of% used for the component means mass%.
- 23 -
Si is an important element for increasing electric resistance and reducing iron
loss. When the Si content exceeds 4.8%, the material tends to crack during cold
rolling, and rolling cannot be performed. On the other hand, when the amount of Si is
lowered, a to y transformation occurs during final annealing and the directionality of
crystals is impaired. Therefore, 0.8%, which does not affect the directionality of
crystals during final annealing, may be set as the lower limit.
[0056]
Although Cis an element effective in controlling the primary recrystallization
structure in the manufacturing process, an excessive amount of C in the final product
has an adverse influence on the magnetic characteristics. Therefore, the C content
may be set to 0.085% or less. A preferable upper limit of the C content is 0.075%.
C is purified in a decarburization annealing step S5 and a final annealing step S8
described later, and reaches an amount of 0.005% or less after the final annealing step
S8. In a case where Cis contained, the lower limit of the C content may exceed 0%
or may be 0.001% in consideration of productivity in industrial production.
[0057]
Acid-soluble Al is an element that is bonded toN and functions as an inhibitor
as AlN or (Al,Si)N. The range for limiting the amount may be 0.012% to 0.050%, at
which the magnetic flux density is increased. When N is added in an amount of
0.01% or more during steelmaking, vacancies called blister are generated in the steel
sheet. Therefore, the upper limit may be set to 0.01 %. Since N can be contained by
nitriding in the middle of the manufacturing process, the lower limit is not specified.
[0058]
Mn and S precipitate as MnS and serve as inhibitors. When the amount of
Mn is less than 0.02% and the amount of Sis less than 0.005%, a predetermined
- 24 -
amount of effective MnS inhibitor cannot be secured. When the amount of Mn is
more than 0.3% and the amount of S is more than 0.04%, solutionizing at the time of
heating the slab becomes insufficient, and secondary recrystallization is not stably
performed. Therefore, Mn: 0.02% to 0.3% and S: 0.005% to 0.04% may be set.
[0059]
As other inhibitor constituent elements, B, Bi, Se, Pb, Sn, Ti, and the like can
also be added. The addition amounts thereof may be appropriately adjusted, and may
be set to, by mass%, B: 0.080% or less, Bi: 0.010% or less, Se: 0.035% or less, Pb:
0.10% or less, Sn: 0.10% or less, and Ti: 0.015% or less. Since these optional
elements may be contained according to a known purpose, it is not necessary to set a
lower limit for the amount of the optional elements, and the lower limit may be 0%.
[0060]
The remainder of the chemical composition of the slab consists of Fe and
impurities. It should be noted that the "impurities" mentioned here mean elements
that are unavoidably incorporated in from components contained in a raw material or
components incorporated in a manufacturing process when the slab is industrially
manufactured and do not have a substantial influence on the effect of the present
invention.
[0061]
The chemical composition of the slab may contain known optional elements
instead of a portion of Fe in consideration of, in addition to solving the manufacturing
problems, enhancing the function of inhibitors by the formation of a compound, or an
influence on the magnetic characteristics. Examples of the optional elements
contained instead of a portion of Fe include the following elements. Each numerical
value means an upper limit in a case where those elements are contained as the
- 25 -
optional elements.
By mass%, Cu: 0.40% or less, P: 0.50% or less, Sb: 0.10% or less, Cr: 0.30%
or less, and Ni: 1.00% or less.
Since these optional elements may be contained according to a known
purpose, it is not necessary to set a lower limit for the amount of the optional elements,
and the lower limit may be 0%.
[0062]
(Hot Rolling Step S2)
The hot rolling step S2 is a step of performing hot rolling on the slab heated to
a predetermined temperature (for example, llOOoc to 1400°C) to obtain a hot-rolled
steel sheet. As an example, the slab having the above-mentioned composition may be
subjected to hot rolling after being heated to a temperature of 11 oooc or higher from
the viewpoint of securing a temperature for hot rolling and 1280°C or lower at which
solutionizing of AlN is incompletely achieved, based on a manufacturing method using
(Al,Si)N as an inhibitor as described in Patent Document 3. Alternatively, based on a
manufacturing method using AlN and MnS as main inhibitors as described in Patent
Document 4 , hot rolling may be performed after heating at a temperature of 1300°C or
higher at which solutionizing is completely achieved.
[0063]
(Hot-Rolled Steel Sheet Annealing Step S3)
A hot-rolled steel sheet annealing step S3 is a step of annealing the hot-rolled
steel sheet obtained in the hot rolling step S2 immediately or in a short period of time
to obtain an annealed steel sheet. The annealing is performed in a temperature range
of 750°C to 1200°C for 30 seconds to 30 minutes. This annealing is effective for
enhancing the magnetic characteristics of the product.
- 26 -
[0064]
(Cold Rolling Step S4)
A cold rolling step S4 is a step of performing cold rolling (for example, with a
total cold-rolling reduction of 80% to 95%) once or a plurality of (two or more) times
with annealing (process annealing) on the annealed steel sheet obtained in the hotrolled
steel sheet annealing step S3 to obtain a cold-rolled steel sheet.
The thickness of the cold-rolled steel sheet may be 0.10 mm to 0.50 mm.
[0065]
(Decarburization Annealing Step S5)
The decarburization annealing step S5 is a step of performing decarburization
annealing on the cold-rolled steel sheet obtained in the cold rolling step S4 to obtain a
decarburization-annealed steel sheet in which primary recrystallization has occurred.
The decarburization annealing may be performed, for example, at 700°C to 900°C for
1 to 3 minutes.
By performing the decarburization annealing, C contained in the cold-rolled
steel sheet is removed. The decarburization annealing is preferably performed in a
moist atmosphere in order to remove "C" contained in the cold-rolled steel sheet.
[0066]
(Nitriding Treatment Step S6)
A nitriding treatment step S6 is a step performed as necessary in order to
adjust the strength of the inhibitor in the secondary recrystallization. The nitriding
treatment increases the amount of nitrogen in the steel sheet by about 40 ppm to 200
ppm from the start of the decarburization treatment to the start of the secondary
recrystallization in the final annealing. Examples of the nitriding treatment include a
treatment of performing annealing in an atmosphere containing a gas having a nitriding ability, such as ammonia, and a treatment of applying an annealing separating agent
containing a powder having a nitriding ability, such as MnN, in an annealing
separating agent applying step S7 described later.

CLAIMS
1. A grain-oriented electrical steel sheet comprising:
a base steel sheet having a flat surface and a groove forming surface on which
a groove is formed; and
a tension coating formed on the base steel sheet and containing a compound
of phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or silica,
wherein the tension coating has a flat surface coating portion formed on the
flat surface and a groove forming surface coating portion formed on the groove
forming surface,
when an average coating thickness of the flat surface coating portion is
referred to as t1 (llm), a minimum coating thickness of the groove forming surface
coating portion is referred to as t2Min (llm), and a maximum coating thickness of the
groove forming surface coating portion is referred to as t2Max (llm), Expressions (1)
and (2) are satisfied, and
when a value of 0. 95 times a distance D of the tension coating along a sheet
thickness direction from a bottom surface position of the groove forming surface
coating portion to a bottom surface position of the flat surface coating portion is
referred to as an effective depth d (llm), Expression (3) is satisfied,
t2Mm/t1 ~ 0.4 (1)
t2Max/tl :S 3.0 (2)
t2Max :S d/2 (3 ).
2. The grain-oriented electrical steel sheet according to claim 1, further
compnsmg:
a glass coating formed between the base steel sheet and the tension coating
and containing Mg2Si04.
- 46 -
3. The grain-oriented electrical steel sheet according to claim 1 or 2,
wherein, when a width of the groove forming surface is referred to as w (J.lm),
Expression ( 4) is satisfied,
dlw 2: 1/3 (4).
4. The grain-oriented electrical steel sheet according to any one of claims 1
to 3,
wherein, when a width of the groove forming surface is referred to as w (J.lm),
Expression (5) is further satisfied,
(d/w) X t2Max :S t1 (5).
5. A method for manufacturing a grain-oriented electrical steel sheet,
comprising:
a cold rolling step of manufacturing a cold-rolled steel sheet;
a final annealing step of performing final annealing with secondary
recrystallization on the cold-rolled steel sheet;
a groove forming step of forming a linear groove on the cold-rolled steel sheet
before or after the final annealing step in a direction intersecting a rolling direction of
the cold-rolled steel sheet; and
a tension coating applying step of forming a tension coating containing a
compound of phosphoric acid, phosphate, chromic anhydride, chromate, alumina, or
silica on the groove.
6. The method for manufacturing a grain-oriented electrical steel sheet
according to claim 5, further comprising:
after the tension coating applying step, a tension coating shaping step of
shaping the tension coating by processing the tension coating to leave a part of the
tension coating in a thickness direction and reduce a thickness of a portion of the
tension coating formed on the groove in a range narrower than a width of the groove.
7. The method for manufacturing a grain-oriented electrical steel sheet
according to claim 5 or 6, further comprising:
an annealing separating agent applying step of applying an annealing
separating agent to the cold-rolled steel sheet after the cold rolling step and before the
final annealing step,
wherein the annealing separating agent contains magnesia.