FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the Invention
GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND MANUFACTURING METHOD
THEREFOR
2. Applicant(s)
Name Nationality Address
POSCO South Korean (Goedong-dong) 6261
Donghaean-ro, Nam-gu, Pohang-si
Gyeongsangbuk-do 37859, Republic of
Korea
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be
performed.
2
【DESCRIPTION】
【Technical Field】
The present invention relates to an oriented electrical steel sheet
and a manufacturing method thereof.
5 【Background Art】
An oriented electrical steel sheet includes grains having an
orientation of {110}<001> as the so-called Goss orientation, and it is a soft
magnetic material with excellent magnetic characteristics in a rolling
direction.
10 The oriented electrical steel sheet is rolled to a final thickness of
about 0.15 to 0.35 mm through slab heating, hot rolling, hot rolled sheet
annealing, and cold rolling, and then high temperature annealing is
performed for first recrystallization and second recrystallization.
In this case, it is known that, in the high temperature annealing, as
15 an increase rate of temperature is low, a degree of integration of the Goss
orientation of the second recrystallization is high, thus the oriented
electrical steel sheet has excellent magnetic properties. In the high
temperature annealing of a typical oriented electrical steel sheet, since the
temperature increase rate is about 15 °C or less per hour, it takes about 2
20 to 3 days to raise the temperature, and more than about 40 hours is
necessary for purification annealing, thus the high temperature annealing
3
may become a process which consumes an enormous amount energy.
In addition, in a current final high temperature annealing process, since a
batch of a coil state is annealed, the following difficulties may occur. First,
since a temperature difference between an outer winding portion and an
inner winding portion of the coil occurs due to 5 heat treatment in the coil
state, the same heat treatment pattern may not be applied to each winding
portion, resulting in magnetic deviation between the outer winding portion
and the inner winding portion. Second, after decarburization annealing,
MgO is coated on a surface of the coil, and then while base coating is
10 performed in the high temperature annealing, various surface defects are
generated, thus an actual production yield may be reduced. Third, since
the decarburized annealed sheet is wound in a form of a coil, annealed at
high temperature, and then processed by planarization annealing and
insulation-coated, that is, since a production process is divided into three
15 stages, an actual production yield may be reduced.
【DISCLOSURE】
【Technical Problem】
The present invention has been made in an effort to provide an
oriented electrical steel sheet and a manufacturing method thereof.
20 【Technical Solution】
An exemplary embodiment of the present invention provides a
4
method of manufacturing an oriented electrical steel sheet, including:
providing a slab including Si at 1.0 to 4.0 wt%, C at 0.1 to 0.4 wt%, and the
remaining portion including Fe and other inevitably incorporated impurities;
reheating the slab; producing a hot rolled steel sheet by hot rolling the
slab; performing annealing of the hot rolled 5 steel sheet; cold rolling the
annealed hot rolled steel sheet; decarburizing and annealing the cold
rolled steel sheet; cold rolling the decarburized and annealed steel sheet;
and final annealing the cold rolled steel sheet.
The final annealing may be continuously performed after the cold
10 rolling.
The decarburizing and annealing of the cold rolled steel sheet and
the cold rolling of the decarburized and annealed steel sheet may be
repeated two or more times.
A size of a grain of a surface of the decarburized and annealed
15 steel sheet may be in a range of about 150 μm to about 250 μm.
The decarburizing and annealing may be performed in a region
where a single phase of austenite or a composite phase of ferrite and
austenite exists.
The decarburizing and annealing may be performed at an
20 annealing temperature of about 850 °C to about 1000 °C and at a dew
point temperature of about 50 °C to about 70 °C.
When the decarburizing and annealing is performed, a
5
decarburized amount may be in a range of about 0.0300 wt% to about
0.0600 wt%.
When the cold rolling is performed, a reduction ratio may be in a
range of about 50 % to about 70 %.
The final annealing may include a first step that 5 is performed at an
annealing temperature of about 850 °C to about 1000 °C and a dew point
temperature of about 70 °C or less, and a second step that is performed at
an annealing temperature of about 1000 °C to about 1200 °C and in an
atmosphere of about 50 volume% of H2.
10 A carbon amount of the electrical steel sheet after the final
annealing step may be about 0.002 wt% or less.
The first step may be performed for 300 seconds or less, and the
second step may be performed for about 60 to 300 seconds.
A reheating temperature of the slab may be in a range of about
15 1100 °C to about 1350 °C.
The slab may include Mn at more than about 0 % and about 0.1%
or less, and S at more than about 0 wt% and about 0.005 wt% or less.
Another embodiment of the present invention provides an oriented
electrical steel sheet, including Goss grains in which a ratio (D2/D1) of a
20 diameter (D1) of a circumscribed circle thereof to a diameter (D2) of an
inscribed circle thereof is greater than about 0.5 is about 95 % or more of
total Goss grains.
6
Grains of the oriented electrical steel sheet having a grain size of
about 30 μm to about 1000 μm is about 80 % or more of total grains.
The oriented electrical steel sheet may include Mn at more than
about 0 % and about 0.1% or less, S at more than about 0 wt% and about
0.005 wt% or less, and the remaining 5 portion including Fe and other
inevitably impurities.
The oriented electrical steel sheet may include Si at about 1.0 wt%
to about 4.0 wt% and C at about 0.002 wt% or less (excluding 0 wt%).
A content of Mg at a depth of about 2 μm to about 5 μm from a
10 surface of the electrical steel sheet may be about 0.0050 wt% or less.
【Advantageous Effects】
According to the method of manufacturing the oriented electrical
steel sheet of the embodiment of the present invention, it is possible to
perform continuous annealing without performing batch-type annealing in
15 a coil state during final annealing.
In addition, it is possible to produce an oriented electrical steel
sheet through a short time of annealing.
Further, unlike a conventional method of manufacturing an
oriented electrical steel sheet, a step of winding a cold rolled steel sheet is
20 unnecessary.
According to the method of manufacturing the oriented electrical
steel sheet of the embodiment of the present invention, it is also possible
7
to provide an oriented electrical steel sheet which does not use a grain
growth inhibitor.
In addition, a nitriding annealing process may be omitted.
【Description of the Drawings】
FIG. 1A is a photograph showing 5 Goss grain distribution of an
oriented electrical steel sheet according to an embodiment of the present
invention through EBSD analysis. Portions indicated by gray or black
other than portions indicated by white indicate Goss grains.
FIG. 1B is a photograph indicating a circumscribed circle and an
10 inscribed circle on each grain of the oriented electrical steel sheet shown
in FIG. 1A.
FIG. 2A is an optical microscope photograph showing grain
distribution of a conventional oriented electric steel sheet.
FIG. 2B is a photograph indicating a circumscribed circle and an
15 inscribed circle on each grain of the oriented electrical steel sheet shown
in FIG. 2A.
FIG. 3 is a photograph showing change in a microstructure
observed during a decarburization annealing process in a method of
manufacturing an oriented electrical steel sheet according to an
20 embodiment of the present invention.
FIG. 4A to FIG. 4I are photographs showing change of a Goss
fraction in a texture of an oriented electrical steel sheet during a final
8
annealing process in a method of manufacturing an oriented electrical
steel sheet according to an embodiment of the present invention through
EBSD analysis.
【Mode for Invention】
The advantages and features of the present 5 invention and the
methods for accomplishing the same will be apparent from the exemplary
embodiments described hereinafter with reference to the accompanying
drawings. However, the present invention is not limited to the exemplary
embodiments described hereinafter, but may be embodied in many
10 different forms. The following exemplary embodiments are provided to
make the disclosure of the present invention complete and to allow those
skilled in the art to clearly understand the scope of the present invention,
and the present invention is defined only by the scope of the appended
claims. Throughout the specification, the same reference numerals
15 denote the same constituent elements.
In some exemplary embodiments, detailed description of wellknown
technologies will be omitted to prevent the disclosure of the present
invention from being ambiguously interpreted. Unless otherwise defined,
all terms (including technical and scientific terms) used herein have the
20 same meaning as commonly understood by one of ordinary skill in the art.
In addition, throughout the specification, unless explicitly described to the
contrary, the word "comprise" and variations such as "comprises" or
9
"comprising" will be understood to imply the inclusion of stated elements
but not the exclusion of any other elements. Further, as used herein, the
singular forms "a", "an", and "the" are intended to include the plural forms
as well, unless the context clearly indicates otherwise.
A method of manufacturing an oriented 5 electrical steel sheet
according to an exemplary embodiment of the present invention first
provides a slab including Si at 1.0 to 4.0 wt%, C at 0.1 to 0.4 wt%, and the
remaining portion including Fe and other inevitably incorporated impurities.
In addition, the slab may further include more than 0 wt% and 0.1 wt% or
10 less of Mn, and more than 0 wt% and 0.005 wt% or less of S.
The reason for limiting the composition is as follows.
Si reduces iron loss by lowering magnetic anisotropy of the
electrical steel sheet and increasing specific resistance thereof. When a
content of Si is less than 1.0 %, the iron loss reduces, and when the
15 content of Si is more than 4.0 %, brittleness increases. Accordingly, a
content of Si in the slab and a content of Si in the grain oriented electrical
steel sheet after a final annealing process may be about 1.0 % to about
4.0 %.
Since a process in which C of a central portion escapes from a
20 surface is required so that Goss grains in the surface may be diffused to
the center portion during an intermediate decarburization annealing
process and a final decarburization annealing process, the content of C in
10
the slab may be about 0.1 to 0.4 %. In addition, after the final annealing
process in which decarburization is completed, an amount of carbon in the
oriented electrical steel sheet may be about 0.0020 wt% or less.
Since Mn and S form MnS precipitates, they interfere with growth
of Goss grains diffusing to the center portion 5 during the decarburization
process. Accordingly, it is preferable that Mn and S are not added.
However, considering an amount inevitably added during a steelmaking
process, it is preferable to adjust Mn and S in the slab and the oriented
electrical steel sheet after the final annealing process to more than 0 %
10 and 0.1 % or less of Mn, and more than 0 % and 0.005 % or less of S,
respectively.
The steel slab having the above composition is reheated. The
slab reheating temperature may be about 1100 °C to about 1350 °C higher
than a typical reheating temperature.
15 When the slab reheating temperature is high, there is a problem
that a hot rolled structure is coarsened and magnetism thereof is
adversely affected. However, in the method of manufacturing the
oriented electrical steel sheet according to the exemplary embodiment of
the present invention, since the content of carbon is more than that of the
20 prior art, even though the slab reheating temperature is high, the hot rolled
structure is not coarsened, and it is advantageous in hot rolling by
reheating at a higher temperature than usual.
11
A hot rolled steel sheet is manufactured by hot-rolling the slab after
reheating.
The hot rolled steel sheet is then annealed. In this case, an
annealing temperature for the hot rolled sheet may be about 850 °C to
about 1000 °C. In addition, a dew point temperature 5 may be 50 °C to
about 70 °C.
After the decarburization annealing of the hot rolled sheet, an acid
pickling process is performed, and then a cold rolling process is performed
to produce a cold rolled steel sheet. The cold rolled steel sheet is
10 decarburized and annealed. In addition, the steel sheet on which the
decarburization annealing has been completed is cold rolled.
The decarburization annealing of the cold rolled steel sheet and
the cold-rolling of the steel sheet after the decarburization annealing may
be repeated two or more times.
15 In the method of manufacturing the oriented electrical steel sheet
according to the exemplary embodiment of the present invention, a
description of the decarburization annealing process will now be provided.
The decarburization annealing process may be performed at a dew
point temperature of about 50 °C to about 70 °C in a region where a single
20 phase of austenite or a composite phase of ferrite and austenite exists.
In this case, the annealing temperature may be in a range of about 850 °C
to about 1000 °C. In addition, an atmosphere for the annealing process
12
may be a mixed gas atmosphere of hydrogen and nitrogen. Moreover,
while the decarburization annealing process is performed, a
decarburization amount may be about 0.0300 wt% to about 0.0600 wt%.
In the decarburization annealing process, as shown in FIG. 3,
grains of a surface of the electric steel 5 sheet may coarsely grow, but
grains inside the electric steel sheet remain in a microstructure state.
After the decarburization annealing process, sizes of the surficial ferrite
grains may be about 150 μm to about 250 μm.
In the method of manufacturing the oriented electrical steel sheet
10 according to the exemplary embodiment of the present invention, a cold
rolling process will now be described.
It is known that it is effective to perform cold rolling one time at a
high reduction ratio close to about 90 % in a manufacturing process of a
conventional high magnetic flux density oriented electric steel sheet. This
15 is because only Goss crystal grains of primary recrystallized grains create
an environment favorable for grain growth.
However, since the method of manufacturing the oriented electrical
steel sheet according to the exemplary embodiment of the present
invention internally diffuses the Goss grains in the surface caused by
20 decarburization annealing and cold rolling without using abnormal grain
growth of the Goss oriented grains, it is advantageous to form a plurality of
Goss oriented grains in the surface.
13
Therefore, when the cold rolling is performed at a reduction ratio of
about 50 % to about 70 % during the cold rolling, a plurality of Goss
textures may be formed in the surficial portion. Alternatively, when the
cold rolling is performed at a reduction ratio of about 55 % to about 65 %
during the cold rolling, a plurality of Goss textures 5 may be formed in the
surficial portion.
In addition, when the decarburization annealing and the cold rolling
are performed two or more times, a plurality of Goss textures may be
formed in the surficial portion.
10 After the decarburization annealing and the cold rolling are
completed, the electrical steel sheet is finally annealed.
Unlike a conventional batch method, the method of manufacturing
the oriented electrical steel sheet according to the exemplary embodiment
of the present invention may continuously perform the final annealing after
15 the cold rolling.
In the method of manufacturing the oriented electrical steel sheet
according to the exemplary embodiment of the present invention, the final
annealing process may be divided into a first step of performing annealing
at an annealing temperature of about 850 °C to about 1050 °C and a dew
20 point temperature of about 50 °C to about 70 °C, and a second step of
annealing at an annealing temperature of about 1000 °C to about 1200 °C
and an atmosphere of about 50 volume% of H2. In addition, the
14
atmosphere of the second step may be 90 volume% or more of H2.
FIG. 4 is a photograph showing change of texture through EBSD
analysis of the oriented electric steel sheet during the final annealing
process in the method of manufacturing the oriented electrical steel sheet
according to the exemplary embodiment. In 5 FIG. 4, portions indicated by
gray or black other than portions indicated by white indicate Goss oriented
texture, and the change of the texture is progressed in order from FIG. 4A
to FIG. 4I.
Before the final annealing, since the decarburization annealing
10 proceeds, an amount of carbon of about 40 wt% to about 60 wt%
compared to a minimum amount of carbon of the slab may remain in the
cold rolled sheet. Accordingly, in the first step of the final annealing,
while the carbon escapes from the surface, the grains formed in the
surface are diffused to the inside. In the first step, the steel sheet may be
15 decarburized such that the carbon amount thereof may be about 0.01 wt%
or less.
Then, in the second step, the Goss oriented texture diffused in the
first step grows. Unlike a case in which grains are grown by a
conventional abnormal grain growth, a size of the grains of the texture
20 may be about 1 mm or less in the method of manufacturing the oriented
electrical steel sheet according to the exemplary embodiment of the
present invention. Accordingly, it is possible to form a texture in which a
15
plurality of Goss grains having a smaller size than that of a conventional
oriented electrical steel sheet exist.
The oriented electrical steel sheet on which the final annealing is
completed may be dried after applying an insulating coating liquid thereon,
5 as necessary.
In the prior art, a MgO coating layer exists because an annealing
separator including MgO as a main component is coated in a batch form
during the final annealing, but since the final annealing is performed in a
continuous form, not in a batch form, no MgO coating layer may exist in
10 the oriented electrical steel sheet according to the embodiment of the
present invention.
Accordingly, in the oriented electrical steel sheet according to the
exemplary embodiment of the present invention, a Mg content at a depth
of about 2 μm to about 5 μm from the surface of the steel sheet may be
15 about 0.0050 wt% or less. This is because only Mg of the insulating
coating layer diffuses and penetrates into the texture of the oriented
electrical steel sheet.
According to the method of manufacturing the oriented electrical
steel sheet according to the exemplary embodiment of the present
20 invention, the following oriented electrical steel sheet may be provided.
FIG. 1A is a photograph showing grain distribution of an oriented
electrical steel sheet according to an embodiment of the present invention
16
through EBSD analysis. In addition, FIG. 1B is a photograph indicating a
circumscribed circle and an inscribed circle on each grain of the oriented
electrical steel sheet shown in FIG. 1A.
Referring to FIG. 1, in the oriented electrical steel sheet according
to the exemplary embodiment of the present 5 invention, grains of which a
ratio (D2/D1) of a diameter (D1) of a circumscribed circle of each grain to
a diameter (D2) of an inscribed circle of each grain is greater than 0.5 may
be 95 % or more of total grains.
Herein, the circumscribed circle means a smallest circle among
10 virtual circles surrounding the outsides of the grains, and the inscribed
circle means a largest circle of virtual circles inside the grains.
Table 1 shows the ratio (D2/D1) of the relative sizes of the
inscribed circles and the circumscribed circles of the grains of the oriented
electrical steel sheet according to the embodiment of the present invention
15 shown in FIG. 1B.
[Table 1]
Circumscribed circle
D1
Inscribed circle D2 Ratio (D2/D1)
2.4 1.6 0.67
2.6 1.5 0.58
2.8 2 0.71
17
1.7 1.1 0.65
1.9 1.3 0.68
2.5 1.3 0.52
2.2 1.2 0.55
2.9 1.7 0.59
2.2 1.4 0.64
1.9 1.1 0.58
1.3 0.9 0.69
1.8 1.2 0.67
1.2 0.7 0.58
1.7 1.1 0.65
1.8 1 0.56
1.7 0.9 0.53
1.2 0.8 0.67
1.3 1 0.77
2 1 0.5
1.5 0.9 0.6
1.2 0.7 0.58
Referring to Table 1, in the oriented electrical steel sheet according
to the exemplary embodiment of the present invention, it can be seen that
18
the grains of which the ratio (D2/D1) of a diameter (D1) of a circumscribed
circle of each grain to a diameter (D2) of an inscribed circle of each grain
is greater than 0.5 is 95 % or more of total grains.
This is because, in the texture of the oriented electrical steel sheet
according to the embodiment of the 5 present invention, since the Goss
grains of the surface grow into the steel sheet, grains with a round shape
are generated.
FIG. 2A show a texture of a conventional oriented electric steel
sheet. FIG. 2B is a photograph indicating a circumscribed circle and an
10 inscribed circle on each grain of the oriented electrical steel sheet shown
in FIG. 2A.
It can be seen that an oriented grain electrical steel sheet
produced by a prior art includes grains with an oval shape that are longer
than that of the oriented grain steel sheet produced by the embodiment of
15 the present invention.
Table 2 shows the ratio (D2/D1) of the relative sizes of the
inscribed circles and the circumscribed circles of the grains of the oriented
electrical steel sheet shown in FIG 2B.
[Table 2]
Circumscribed circle
D1
Inscribed circle D2 Ratio (D2/D1)
19
1.6 0.8 0.5
2.2 1.2 0.55
2.6 0.9 0.35
3.3 1.6 0.48
4.7 1.7 0.36
1.1 0.5 0.45
2.5 0.9 0.36
1 0.5 0.5
2.3 1.4 0.61
1.2 0.9 0.75
5.1 2.3 0.45
1.9 0.7 0.37
3.6 2.1 0.58
2.7 1.7 0.63
1.4 0.6 0.43
0.8 0.4 0.5
1.3 0.5 0.38
0.7 0.3 0.43
1.8 1.1 0.61
1.1 0.5 0.45
0.9 0.35 0.39
20
The oriented electrical steel sheet produced by the prior art
includes grains with a long oval shape, so that values of D2/D1 are smaller
than those of the oriented electrical steel sheet according to the
embodiment 5 of the present invention.
In addition, grains of the oriented electrical steel sheet according to
the exemplary embodiment of the present invention having a grain size of
about 30 μm to about 1000 μm may be about 80 % or more of the total
grains.
10 Hereinafter, the present invention will be described in detail with
reference to exemplary embodiments. However, the following exemplary
embodiments are only examples of the present invention, and the present
invention is not limited to the exemplary embodiments.
[Exemplary Embodiment 1]
15 A slab including Si at 2.0 wt%, C at 0.20 wt%, and the remaining
portion including Fe and other inevitably impurities was heated at a
temperature of 1150 °C, then hot rolled, and then the hot rolled sheet was
annealed at an annealing temperature of 900 °C and a dew point of 60 °C.
Then, the steel sheet was cooled, pickled, and then cold rolled at a
20 reduction ratio of 65 % to prepare a cold rolled sheet having a thickness of
0.8 mm.
The cold rolled sheet was again decarburized and annealed at a
21
temperature of 900 °C in a wet mixed gas atmosphere of hydrogen and
nitrogen (a dew point temperature of 60 °C) as shown in Table 3, and was
again cold rolled at a reduction ratio of 65 % to prepare a cold rolled sheet
having a thickness of 0.28 mm.
Then, in the final annealing, the decarburization 5 annealing was
performed at a temperature of 950 °C for 2 minutes in a wet mixed gas
atmosphere of hydrogen and nitrogen (a dew point temperature of 60 °C),
and then heat treatment was performed for 3 minutes in a hydrogen
atmosphere at 1100 °C.
10 [Table 3]
Decarburization
time (s)
Grain
Size (μm)
Goss
fraction (%)
B10 (T) W17/50 (W/Kg) Classification
10 35 14 1.55 3.21 Comparative material
25 65 20 1.59 2.92 Comparative material
50 102 41 1.68 2.11 Comparative material
80 150 72 1.81 1.59 Inventive material
90 165 75 1.84 1.47 Inventive material
90 150 78 1.85 1.45 Inventive material
100 195 81 1.87 1.33 Inventive material
200 390 32 1.62 2.58 Comparative material
100 201 80 1.86 1.38 Inventive material
22
As shown in Table 3, when the sizes of the grains of the surface of
the sheet after the decarburization annealing process are in a range of
150 μm to 250 μm by securing the appropriate decarburization annealing
time during the decarburization annealing process, it can be seen that a
Goss fraction increases and magnetic flux 5 density and iron loss are
excellent.
[Exemplary Embodiment 2]
A slab including Si at 2.0 wt%, C at 0.20 wt%, and the remaining
portion including Fe and other inevitably impurities was heated at a
10 temperature of 1150 °C, then hot rolled, and then the hot rolled sheet was
annealed at an annealing temperature of 900 °C and a dew point of 60 °C
for 150 seconds, cooled, and then pickled, and cold rolled at a reduction
ratio of 45 % to 75 % as shown in Table 4. The cold rolled sheet was
again decarburized and annealed at a temperature of 900 °C in a wet
15 mixed gas atmosphere of hydrogen and nitrogen (a dew point temperature
of 60 °C) for 150 seconds, and was again cold rolled at a reduction ratio of
45 % to 75 % as shown in Table 4 to prepare a cold rolled sheet having a
thickness of 0.18 mm to 0.36 mm. Then, in the final annealing, the
decarburization annealing was performed at a temperature of 950 °C for 2
20 minutes in a wet mixed gas atmosphere of hydrogen and nitrogen (a dew
point temperature of 60 °C), and then heat treatment was performed for 3
minutes in a hydrogen atmosphere of 1100 °C. The related contents are
23
shown in Table 4.
[Table 4]
Primary
cold rolling
Secondary
cold rolling
Final material Classification
Reduction ratio (%) reduction ratio Goss fraction B10 W17/50
45 75 67 1.72 1.75 Comparative material
50 70 74 1.8 1.49 Inventive material
60 65 82 1.87 1.33 Inventive material
60 60 81 1.88 1.3 Inventive material
70 70 72 1.84 1.39 Inventive material
75 65 58 1.71 1.77 Comparative material
75 60 61 1.7 1.81 Comparative material
75 55 60 1.7 1.8 Comparative material
As shown in Table 4, it can be seen that the reduction ratio during
the primary and secondary cold rolling influences 5 a Goss fraction and
magnetization of a product sheet after the final annealing process.
From this result, it can be seen that a better magnetic flux density
may be obtained when the reduction ratio during the cold rolling process is
in a range of 50 % to 70 %.
10 [Exemplary Embodiment 3]
A slab including Si at 2.0 wt%, C at 0.20 wt%, and the remaining
24
portion including Fe and other inevitably impurities was heated at a
temperature of 1150 °C, then hot rolled to a thickness of 3 mm, and then
the hot rolled sheet was annealed at an annealing temperature of 900 °C
and a dew point of 60 °C for 150 seconds, cooled, and then pickled, and
cold rolled 5 at a reduction ratio of 60 %.
The cold rolled sheet was again decarburized and annealed at a
temperature of 900 °C in a wet mixed gas atmosphere of hydrogen and
nitrogen (a dew point temperature of 60 °C) for 150 seconds.
The cold rolling process was repeated two to four times.
10 The repeating of the cold rolling process twice means that the hot
rolled sheet is first cold rolled, decarburized and annealed, and then
second cold rolled. The repeating of the cold rolling process three times
means that the hot rolled sheet is first cold rolled, decarburized, and
annealed, and again second cold rolled, decarburized, and annealed, and
15 then third cold rolled. The repeating of the cold rolling process four times
means that the hot rolled sheet is first cold rolled, decarburized, and
annealed, and again second cold rolled, decarburized, and annealed, and
third cold rolled, decarburized, and annealed, and then fourth cold rolled.
Then, in the final annealing, the decarburization annealing was
20 performed at a temperature of 950 °C in a wet mixed gas atmosphere of
hydrogen and nitrogen (a dew point temperature of 60 °C), and then heat
treatment was performed for 2 minutes in a hydrogen atmosphere at
25
1100 °C. The related contents are shown in Table 5.
[Table 5]
Number of cold rolling Goss fraction B10 W17/50
2 80 1.87 1.33
3 88 1.92 1.28
4 92 1.95 1.17
As shown in Table 5, it can be seen that while maintaining the
reduction ratio at 60 %, as the number of 5 the cold rolling increases, the
Goss fraction increases and the magnetism improves.
While the exemplary embodiments of the present invention have
been described hereinbefore with reference to the accompanying
drawings, it will be understood by those skilled in the art that various
10 changes in form and details may be made thereto without departing from
the technical spirit and essential features of the present invention.
Therefore, the embodiments described above are only examples
and should not be construed as being limitative in any respects. The
scope of the present invention is determined not by the above description,
15 but by the following claims, and all changes or modifications from the spirit,
scope, and equivalents of claims should be construed as being included in
the scope of the present invention.
26
WE CLAIM:
【Claim 1】
A method of manufacturing an oriented electrical steel sheet,
comprising:
providing a slab including Si at 1.0 to 4.0 wt%, 5 C at 0.1 to 0.4 wt%,
and the remaining portion including Fe and other inevitably incorporated
impurities;
reheating the slab;
producing a hot rolled steel sheet by hot rolling the slab;
10 performing annealing of the hot rolled steel sheet;
cold rolling the annealed hot rolled steel sheet;
decarburizing and annealing the cold rolled steel sheet;
cold rolling the decarburized and annealed steel sheet; and
final annealing the cold rolled steel sheet.
15
【Claim 2】
The method of manufacturing the oriented electrical steel sheet of
claim 1, wherein
the final annealing is continuously performed after the cold rolling.
20
【Claim 3】
27
The method of manufacturing the oriented electrical steel sheet of
claim 2, wherein
the decarburizing and annealing of the cold rolled steel sheet and
the cold rolling of the decarburized and annealed steel sheet are repeated
5 two or more times.
【Claim 4】
The method of manufacturing the oriented electrical steel sheet of
claim 3, wherein
10 a size of a grain of a surface of the decarburized and annealed
steel sheet is in a range of about 150 μm to about 250 μm.
【Claim 5】
The method of manufacturing the oriented electrical steel sheet of
15 claim 4, wherein
the decarburizing and annealing is performed in a region where a
single phase of austenite or a composite phase of ferrite and austenite
exists.
20 【Claim 6】
The method of manufacturing the oriented electrical steel sheet of
28
claim 4, wherein
the decarburizing and annealing is performed at an annealing
temperature of about 850 °C to about 1000 °C and at a dew point
temperature of about 50 °C to about 70 °C.
5
【Claim 7】
The method of manufacturing the oriented electrical steel sheet of
claim 5, wherein
when the decarburizing and annealing is performed, a
10 decarburized amount is in a range of about 0.0300 wt% to about 0.0600
wt%.
【Claim 8】
The method of manufacturing the oriented electrical steel sheet of
15 claim 2, wherein
when the cold rolling is performed, a reduction ratio is in a range of
about 50 % to about 70 %.
【Claim 9】
20 The method of manufacturing the oriented electrical steel sheet of
claim 2, wherein
29
the final annealing includes a first step that is performed at an
annealing temperature of about 850 °C to about 1000 °C and a dew point
temperature of about 70 °C or less, and a second step that is performed at
an annealing temperature of about 1000 °C to about 1200 °C and in an
atmosphere of 5 about 50 volume% of H2.
【Claim 10】
The method of manufacturing the oriented electrical steel sheet of
claim 9, wherein
10 a carbon amount of the electrical steel sheet after the final
annealing step is about 0.002 wt% or less.
【Claim 11】
The method of manufacturing the oriented electrical steel sheet of
15 claim 10, wherein
the first step is performed for 300 seconds or less, and the second
step is performed for about 60 to 300 seconds.
【Claim 12】
20 The method of manufacturing the oriented electrical steel sheet of
claim 11, wherein
30
a reheating temperature of the slab is in a range of about 1100 °C
to about 1350 °C.
【Claim 13】
The method of manufacturing the oriented 5 electrical steel sheet of
claim 12, wherein
the slab includes Mn at more than about 0 % and about 0.1% or
less, and S at more than about 0 wt% and about 0.005 wt% or less.
10 【Claim 14】
An oriented electrical steel sheet, comprising
Goss grains in which a ratio (D2/D1) of a diameter (D1) of a
circumscribed circle thereof to a diameter (D2) of an inscribed circle
thereof is greater than about 0.5 is about 95 % or more of total Goss
15 grains.
【Claim 15】
The oriented electrical steel sheet of claim 14, wherein
grains of the oriented electrical steel sheet having a grain size of
20 about 30 μm to about 1000 μm is about 80 % or more of total grains.
31
【Claim 16】
The oriented electrical steel sheet of claim 15, wherein
the oriented electrical steel sheet includes Mn at more than about
0 % and about 0.1 % or less, S at more than about 0 wt% and about 0.005
wt% or less, and the remaining portion including 5 Fe and other inevitably
impurities.
【Claim 17】
The oriented electrical steel sheet of claim 16, wherein
10 the oriented electrical steel sheet includes Si at about 1.0 wt% to
about 4.0 wt% and C at about 0.002 wt% or less (excluding 0 wt%).
【Claim 18】
The oriented electrical steel sheet of claim 17, wherein
15 a content of Mg at a depth of about 2 μm to about 5 μm from a
surface of the electrical steel sheet is about 0.0050 wt% or less.
Dated this 25th day of May, 2017
MOHAN DEWAN
20 of R.K. DEWAN & COMPANY
APPLICANT’S PATENT ATTORNEY