U.S. patent application number 16/957943 was filed with the patent office on 2021-03-04 for oriented electrical steel sheet and method for preparing same.
The applicant listed for this patent is POSCO. Invention is credited to Kyu-Seok HAN, Jae Kyoum KIM, Chang Soo PARK, Yujun PARK, Jin-Wook SEO.
Application Number | 20210062309 16/957943 |
Document ID | / |
Family ID | 1000005224479 |
Filed Date | 2021-03-04 |
United States Patent
Application |
20210062309 |
Kind Code |
A1 |
KIM; Jae Kyoum ; et
al. |
March 4, 2021 |
ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR PREPARING SAME
Abstract
An oriented electrical steel sheet according to an embodiment of
the present invention includes, in a unit of wt %, Si at 1.0 wt %
to 5.0 wt %, C at 0.005 wt % or less (excluding 0 wt %), Mn at
0.001 wt % to 0.1 wt %, Cu at 0.001 wt % to 0.1 wt %, S at 0.001 wt
% to 0.020 wt %, Se at 0.001 wt % to 0.050 wt %, Al at 0.0005 wt %
to 0.010 wt %, N at 0.0005 wt % to 0.005 wt %, and the remainder of
Fe and inevitable impurities. The oriented electrical steel sheet
according to the embodiment of the present invention satisfies
Equation 1.
16.ltoreq.(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation 1] (In Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
Inventors: |
KIM; Jae Kyoum; (Pohang-si,
Gyeongsangbuk-do, KR) ; HAN; Kyu-Seok; (Pohang-si,
Gyeongsangbuk-do, KR) ; PARK; Chang Soo; (Pohang-si,
Gyeongsangbuk-do, KR) ; SEO; Jin-Wook; (Pohang-si,
Gyeongsangbuk-do, KR) ; PARK; Yujun; (Pohang-si,
Gyeongsangbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO |
Pohang-si, Gyeongsangbuk-do |
|
KR |
|
|
Family ID: |
1000005224479 |
Appl. No.: |
16/957943 |
Filed: |
May 17, 2018 |
PCT Filed: |
May 17, 2018 |
PCT NO: |
PCT/KR2018/005676 |
371 Date: |
June 25, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 8/0236 20130101;
C21D 9/0081 20130101; C22C 38/001 20130101; C22C 38/06 20130101;
C21D 8/0226 20130101; C22C 38/04 20130101; C22C 38/002 20130101;
C22C 38/16 20130101; C22C 38/02 20130101; C21D 8/0205 20130101 |
International
Class: |
C22C 38/16 20060101
C22C038/16; C22C 38/04 20060101 C22C038/04; C22C 38/02 20060101
C22C038/02; C22C 38/06 20060101 C22C038/06; C22C 38/00 20060101
C22C038/00; C21D 8/02 20060101 C21D008/02; C21D 9/00 20060101
C21D009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2017 |
KR |
10-2017-0179927 |
Claims
1. An oriented electrical steel sheet, comprising, in a unit of wt
%, Si at 1.0 wt % to 5.0 wt %, C at 0.005 wt % or less (excluding 0
wt %), Mn at 0.001 wt % to 0.1 wt %, Cu at 0.001 wt % to 0.1 wt %,
S at 0.001 wt % to 0.020 wt %, Se at 0.001 wt % to 0.050 wt %, Al
at 0.0005 wt % to 0.010 wt %, N at 0.0005 wt % to 0.005 wt %, and
the remainder of Fe and inevitable impurities, wherein the oriented
electrical steel sheet satisfies Equation 1:
16.ltoreq.(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation 1] (in Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
2. The oriented electrical steel sheet of claim 1, wherein the
oriented electrical steel sheet satisfies Equation 2:
0.016.ltoreq.[S]+[Se].ltoreq.0.05 [Equation 2] (in Equation 2, [S]
and [Se] represent contents (wt %) of S and Se, respectively.)
3. The oriented electrical steel sheet of claim 1, wherein the
oriented electrical steel sheet satisfies Equation 3:
0.5.ltoreq.[Al]/[N].ltoreq.3.0 [Equation 3] (in Equation 3, [Al]
and [N] represent contents (wt %) of Al and N, respectively.)
4. A preparing method of an oriented electrical steel sheet,
comprising: preparing a slab including, in a unit of wt %, Si at
1.0 wt % to 5.0 wt %, C at 0.001 wt % to 0.10 wt %, Mn at 0.001 wt
% to 0.1 wt %, Cu at 0.001 wt % to 0.1 wt %, S at 0.001 wt % to
0.020 wt %, Se at 0.001 wt % to 0.050 wt %, Al at 0.0005 wt % to
0.010 wt %, N at 0.0005 wt % to 0.005 wt %, and the remainder of Fe
and inevitable impurities, and satisfying Equation 1; heating the
slab; hot rolling the slab to prepare a hot rolled sheet; cold
rolling the hot rolled sheet to prepare a cold rolled sheet;
primary recrystallization annealing the cold rolled sheet; and
secondary recrystallization annealing the cold rolled sheet in
which the primary recrystallization annealing is completed:
16(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation1] (in Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
5. The preparing method of the oriented electrical steel sheet of
claim 4, wherein the heating of the slab includes heating the slab
at 1000 to 1250.degree. C.
6. The preparing method of the oriented electrical steel sheet of
claim 4, wherein the cold rolled sheet in which the primary
recrystallization annealing is completed includes one or more
precipitates of (Fe,Mn,Cu)S and (Fe,Mn,Cu)Se.
7. The preparing method of the oriented electrical steel sheet of
claim 4, wherein the primary recrystallization annealing is
performed in a hydrogen and nitrogen mixed atmosphere at a dew
point temperature of 50.degree. C. to 70.degree. C.
Description
TECHNICAL FIELD
BACKGROUND ART
(a) Field of the Invention
[0001] The present invention relates to an oriented electrical
steel sheet and a method for preparing the oriented electrical
steel sheet. Specifically, the present invention relates to an
oriented electrical steel sheet and a method for preparing the
oriented electrical steel sheet that may be excellent in magnetism
by stably growing grains with a very high degree of integration
into a Goss orientation during secondary recrystallization high
temperature annealing using S- and Se-based precipitates. More
specifically, the present invention relates to an oriented
electrical steel sheet and a method for preparing the oriented
electrical steel sheet that may have excellent magnetic properties
by controlling a correlation between Mn, Cu, S, Se, Al, and N in an
alloy component.
(b) Description of the Related Art
[0002] An oriented electrical steel sheet is a soft magnetic
material used as an iron core for electronic equipment that has
excellent magnetic properties in a rolling direction and requires
excellent magnetic properties in one direction, such as a
transformer, and it is made by forming a Goss texture
({110}<001> aggregate) on an entire steel sheet by using an
abnormal grain growth phenomenon called secondary
recrystallization. Generally, the magnetic properties may be
described by a magnetic flux density and iron loss, and a high
magnetic flux density may be obtained by precisely arranging an
orientation of grains in a {110}<001> orientation. The
electrical steel sheet having a high magnetic flux density not only
makes it possible to reduce a size of an iron core material of an
electric device, but also reduces hysteresis loss, thereby
achieving miniaturization and high efficiency of the electric
device at the same time. Iron loss is power loss consumed as heat
energy when an arbitrary alternating magnetic field is applied to a
steel sheet, and it largely changes depending on a magnetic flux
density and a thickness of the steel sheet, an amount of impurities
in the steel sheet, specific resistance, and a size of a secondary
recrystallization grain, wherein the higher the magnetic flux
density and the specific resistance and the lower the thickness and
the amount of impurities in the steel sheet, the lower the iron
loss and the higher the efficiency of the electric device. Unlike
typical grain growth, the secondary recrystallization of the
oriented electrical steel sheet occurs when movement of a grain
boundary in which grains normally grow is suppressed by
precipitates, inclusions, or elements that are dissolved or
segregated in the grain boundaries
[0003] In addition, in order to grow grains with a high degree of
integration with respect to the Goss orientation, complex processes
such as component control in steel making, slab reheating and hot
rolling process factor control in hot rolling, hot rolled sheet
annealing heat treatment, primary recrystallization annealing, and
secondary recrystallization annealing, are required, and these
processes should also be managed very accurately and rigorously. As
described above, the precipitates and inclusions that inhibit the
grain growth are specifically referred to as grain growth
inhibitors, and studies on a preparation technology of the oriented
electrical steel sheets by the secondary recrystallization of Goss
orientation have been focused on securing superior magnetic
properties by using a strong grain growth inhibitor to form
secondary recrystallization with high integration to Goss
orientation. MnS was used as a grain growth inhibitor in the
oriented electrical steel sheet which was initially developed, and
it was prepared by a method of cold rolling two times. Accordingly,
the secondary recrystallization was stably formed, but the magnetic
flux density was not so high and the iron loss was high.
Thereafter, a method of preparing an oriented electrical steel
sheet by using a combination of AIN and MnS precipitates and then
one-time cold rolling has been proposed. Recently, an oriented
electrical steel sheet preparing method in which secondary
recrystallization is caused by an Al-based nitride exhibiting a
strong grain growth inhibiting effect by supplying nitrogen into
the steel sheet through a separate nitriding process using ammonia
gas after decarburizing after one-time cold rolling without using
MnS has been proposed. So far, a preparing method in which
precipitates such as AlN and MnS [Se] are used as the grain growth
inhibitor to cause secondary recrystallization have been mainly
used. Such a preparing method has an advantage of stably forming
secondary recrystallization, but in order to having a strong grain
growth inhibiting effect, the precipitates should be distributed
very finely and uniformly on the steel sheet. In order to uniformly
distribute the fine precipitates in this manner, a slab should be
heated at a high temperature for a long period of time before hot
rolling to dissolve coarse precipitates present in the steel, and
then hot rolled in a very short time to complete the hot rolling
without precipitation. This requires a large-sized slab heating
equipment, and in order to minimize precipitation as much as
possible, there are restrictions that a hot rolling and a winding
process must be strictly controlled in order to suppress the
precipitation as much as possible, and that the precipitates
solidified in a hot rolled sheet annealing step after hot-rolling
should be controlled so as to be finely precipitated. In addition,
when the slab is heated at a high temperature, a slab washing
phenomenon occurs due to formation of Fe.sub.2SiO.sub.4 having a
low melting point, thereby decreasing actual yields. Recently, a
preparing method of an oriented electrical steel sheet by a slab
low temperature heating method in which secondary recrystallization
is formed by AlN-based nitride precipitates through nitriding after
decarburization annealing after cold rolling, has been developed
and proposed. However, in order to use this method, it is
substantially necessary to additionally prepare a nitride-based
inhibitor in the annealing process after the slab heating. To this
end, nitriding is performed using ammonia gas in the primary
recrystallization annealing process. The ammonia gas has a property
of decomposing into hydrogen and nitrogen at a temperature of about
500.degree. C. or higher, and by using this, nitriding is performed
and then penetrated nitrogen reacts with a nitride forming element
in the steel sheet to form nitrides such as AlN and (Al,Si)N to act
as an inhibitor. The low temperature heating method also has many
limitations in the preparing process so as to control precipitates,
and thus does not solve problems caused by complexity in the
preparing process. Therefore, in order to improve the magnetism and
productivity of the oriented electrical steel sheet, there is a
need for an oriented electrical steel sheet preparing technology
using a precipitate that is easy to control because the
precipitation decomposition temperature is not excessively
high.
DISCLOSURE
[0004] The present invention has been made in an effort to provide
an oriented electrical steel sheet and a method for preparing the
oriented electrical steel sheet. Specifically, the present
invention has been made in an effort to provide an oriented
electrical steel sheet and a method for preparing the oriented
electrical steel sheet that may be excellent in magnetism by stably
growing grains with a very high degree of integration into a Goss
orientation during secondary recrystallization high temperature
annealing using S- and Se-based precipitates. More specifically,
the present invention has been made in an effort to provide an
oriented electrical steel sheet and a method for preparing the
oriented electrical steel sheet that may have excellent magnetic
properties by controlling a correlation between Mn, Cu, S, Se, Al,
and N in an alloy component.
[0005] An embodiment of the present invention provides an oriented
electrical steel sheet, including, in a unit of wt %, Si at 1.0 wt
% to 5.0 wt %, C at 0.005 wt % or less (excluding 0 wt %), Mn at
0.001 wt % to 0.1 wt %, Cu at 0.001 wt % to 0.1 wt %, S at 0.001 wt
% to 0.020 wt %, Se at 0.001 wt % to 0.050 wt %, Al at 0.0005 wt %
to 0.010 wt %, N at 0.0005 wt % to 0.005 wt %, and the remainder of
Fe and inevitable impurities.
[0006] The oriented electrical steel sheet according to the
embodiment of the present invention satisfies Equation 1.
16(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation 1]
[0007] (In Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
[0008] The oriented electrical steel sheet may satisfy Equation
2.
0.016.ltoreq.[S]+[Se].ltoreq.0.05
[0009] (In Equation 2, [S] and [Se] represent contents (wt %) of S
and Se, respectively.)
[0010] The oriented electrical steel sheet may satisfy Equation
3.
0.5.ltoreq.[Al]/[N].ltoreq.3.0
[0011] (In Equation 3, [Al] and [N] represent contents (wt %) of Al
and N, respectively.)
[0012] Another embodiment of the present invention provides a
preparing method of an oriented electrical steel sheet, including:
preparing a slab including, in a unit of wt %, Si at 1.0 wt % to
5.0 wt %, C at 0.001 wt % to 0.10 wt %, Mn at 0.001 wt % to 0.1 wt
%, Cu at 0.001 wt % to 0.1 wt %, S at 0.001 wt % to 0.020 wt %, Se
at 0.001 wt % to 0.050 wt %, Al at 0.0005 wt % to 0.010 wt %, N at
0.0005 wt % to 0.005 wt %, and the remainder of Fe and inevitable
impurities, and satisfying Equation 1; heating the slab; hot
rolling the slab to prepare a hot rolled sheet; cold rolling the
hot rolled sheet to prepare a cold rolled sheet; and secondary
recrystallization annealing the cold rolled sheet in which the
primary recrystallization annealing is completed.
16.ltoreq.(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation 1]
[0013] (In Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
[0014] The heating of the slab may include heating the slab at 1000
to 1250.degree. C. The cold rolled sheet in which the primary
recrystallization annealing is completed may include one or more
precipitates of (Fe,Mn,Cu)S and (Fe, Mn,Cu)Se.
[0015] The primary recrystallization annealing may be performed in
a hydrogen and nitrogen mixed atmosphere at a dew point temperature
of 50.degree. C. to 70.degree. C.
[0016] Magnetism of the oriented electrical steel sheet according
to the embodiment of the present invention is excellent by control
a correlation between Mn, Cu, S, Se, Al, and N in an alloy
component and by stably growing grains with a very high degree of
integration into a Goss orientation during secondary
recrystallization high temperature annealing using S- and Se-based
precipitates, in which it is easy to control the precipitates.
MODE FOR INVENTION
[0017] It will be understood that, although the terms first,
second, third, etc. may be used herein to describe various
elements, components, regions, layers, and/or sections, they are
not limited thereto. These terms are only used to distinguish one
element, component, region, layer, or section from another element,
component, region, layer, or section. Therefore, a first part,
component, area, layer, or section to be described below may be
referred to as second part, component, area, layer, or section
within the range of the present invention.
[0018] The technical terms used herein are to simply mention a
particular embodiment and are not meant to limit the present
invention. An expression used in the singular encompasses an
expression of the plural, unless it has a clearly different meaning
in the context. In the specification, it is to be understood that
the terms such as "including", "having", etc., are intended to
indicate the existence of specific features, regions, numbers,
stages, operations, elements, components, and/or combinations
thereof disclosed in the specification, and are not intended to
preclude the possibility that one or more other features, regions,
numbers, stages, operations, elements, components, and/or
combinations thereof may exist or may be added.
[0019] When referring to a part as being "on" or "above" another
part, it may be positioned directly on or above another part, or
another part may be interposed therebetween. In contrast, when
referring to a part being "directly above" another part, no other
part is interposed therebetween.
[0020] Unless otherwise defined, all terms used herein, including
technical or scientific terms, have the same meanings as those
generally understood by those with ordinary knowledge in the field
of art to which the present invention belongs. Terms defined in
commonly used dictionaries are further interpreted as having
meanings consistent with the relevant technical literature and the
present disclosure, and are not to be construed as having idealized
or very formal meanings unless defined otherwise.
[0021] Unless otherwise stated, % means % by weight, and 1 ppm is
0.0001% by weight.
[0022] Further, in exemplary embodiments of the present invention,
inclusion of an additional element means replacing remaining iron
(Fe) by an additional amount of the additional elements.
[0023] The present invention will be described more fully
hereinafter, in which exemplary embodiments of the invention are
shown. As those skilled in the art would realize, the described
embodiments may be modified in various different ways, all without
departing from the spirit or scope of the present invention.
[0024] An oriented electrical steel sheet according to an
embodiment of the present invention includes, in a unit of wt %, Si
at 1.0 wt % to 5.0 wt %, C at 0.005 wt % or less (excluding 0 wt
%), Mn at 0.001 wt % to 0.1 wt %, Cu at 0.001 wt % to 0.1 wt %, S
at 0.001 wt % to 0.020 wt %, Se at 0.001 wt % to 0.050 wt %, Al at
0.0005 wt % to 0.010 wt %, N at 0.0005 wt % to 0.005 wt %, and the
remainder of Fe and inevitable impurities.
[0025] Hereinafter, the reason for limiting the components of the
oriented electrical steel sheet will be described.
[0026] Si at 1.0 to 5.0 wt %
[0027] Silicon (Si) increases specific resistance of the oriented
electrical steel sheet, and thus serves to decrease core loss, that
is, iron loss. When a Si content is excessively small, the specific
resistance decreases, eddy current loss increases, and thus the
iron loss may deteriorate. In addition, during primary
recrystallization annealing, phase transformation between ferrite
and austenite occurs, so a primary recrystallized texture may be
severely damaged. In addition, phase transformation between ferrite
and austenite occurs during secondary recrystallization annealing,
thus the second recrystallization may become unstable, and a Goss
texture may be severely damaged. When the Si content is excessively
large, oxide layers of SiO.sub.2 and Fe.sub.2SiO are excessively
and densely formed during decarburization in primary
recrystallization annealing, thus decarburization behavior may be
delayed. In addition, brittleness of the steel increases, and
toughness thereof decreases, so an occurrence rate of plate rupture
during a rolling process may be intensified. In addition,
weldability between plates may be degraded, making it difficult to
secure easy workability. Therefore, Si may be included at 1.0 to
5.0 wt %. Specifically, it may be included at 2.0 to 4.0 wt %.
[0028] C at 0.005 wt % or less
[0029] Carbon (C) is an element that contributes to refining grains
and to improve elongation by causing phase transformation between
ferrite and austenite. C is an essential element for improving
rollability of an electric steel sheet having poor rolling
properties due to high brittleness. However, when it remains in a
final product, it must be controlled to an appropriate content
because it is an element that deteriorates magnetic properties by
precipitating carbides formed due to a magnetic aging effect in a
product sheet. In the embodiment of the present invention, during
the primary recrystallization annealing in the preparing process, a
decarburization process is performed, and the C content in the
final electrical steel sheet prepared after the decarburization
annealing may be 0.005 wt % or less. More specifically, it may be
0.003 wt % or less.
[0030] C of 0.001 to 0.10 wt % may be included in the slab. When
the slab contains too little C, phase transformation between
austenite does not sufficiently occur, causing unevenness of the
slab and the hot-rolled microstructure. As a result, cold rolling
properties are also deteriorated. When it contains too much C,
sufficient decarburization may not be obtained in a decarburization
process. Therefore, due to the phase transformation phenomenon
caused by this, the secondary recrystallized texture is severely
damaged. Further, when the final product is applied to a power
apparatus, it may cause deterioration of magnetic properties due to
self-aging. More specifically, C at 0.01 to 0.1 wt % may be
included in the slab.
[0031] Mn at 0.001 to 0.1 wt %
[0032] Manganese (Mn) has the effect of reducing the iron loss by
increasing the specific resistance, like Si. In addition, it is an
important element for forming secondary precipitates as a grain
growth inhibitor by forming S- and Se-based precipitates. When a
content of Mn is excessively small, a sufficient effect as an
inhibitor may not be expected because the amount and volume formed
are small. When the content of Mn is excessively large, a large
amount of (Fe, Mn) and Mn oxide in addition to Fe.sub.2SiO.sub.4 is
formed on a surface of the steel sheet, which inhibits formation of
a base coating formed during the secondary recrystallization
annealing, thereby lowering surface quality, and in the primary
recrystallization annealing process, non-uniformity of phase
transformation between ferrite and austenite causes a size of the
primary recrystallized grains to be non-uniform, resulting in
unstable secondary recrystallization. Therefore, the content of Mn
may be limited to 0.001 to 0.10 wt %. Specifically, Mn may be
included in an amount of 0.01 to 0.05 wt %.
[0033] Cu at 0.001 to 0.10 wt %
[0034] Copper (Cu) is an important element for forming secondary
recrystallization as a grain growth inhibitor by forming S- and
Se-based precipitates like Mn. When a Cu content is excessively
small, a sufficient effect as an inhibitor may not be expected. In
contrast, when the content thereof is excessively large, a
decomposition temperature of the precipitate is excessively high,
which makes it difficult to control the precipitate. Therefore, the
content of Cu may be limited to 0.001 to 0.10 wt %. Specifically,
Cu may be included in an amount of 0.01 to 0.07 wt %.
[0035] S at 0.001 to 0.020 wt %
[0036] Sulfur (S) is an important element for forming secondary
precipitates as a grain growth inhibitor by forming S- and Se-based
precipitates. When a S content is excessively small, an effect of
inhibiting grain growth may be deteriorated. When the S content is
excessively large, occurrence of edge cracks in continuous casting
and hot rolling processes may increase, so that an actual yield may
decrease. Therefore, the content of S may be limited to 0.001 to
0.020 wt %. Specifically, S may be included in an amount of 0.007
to 0.015 wt %.
[0037] Se at 0.001 to 0.050 wt %
[0038] Selenium (Se) is an important element for forming secondary
precipitates as a grain growth inhibitor by forming S- and Se-based
precipitates like S. In the embodiment of the present invention, Se
is added in combination with S in order to inhibit edge cracking
during slab continuous casting and hot rolling processes due to an
excessive S content. When a Se content is excessively small, an
effect of inhibiting grain growth may be deteriorated. When the Se
content is excessively large, occurrence of edge cracks in
continuous casting and hot rolling processes may increase, so that
an actual yield may decrease. Therefore, the Se content may be
limited to 0.001 to 0.050 wt %. Specifically, Se may be included in
an amount of 0.007 to 0.03 wt %.
[0039] Al at 0.0005 to 0.010 wt %
[0040] Aluminum (Al) is combined with nitrogen in the steel to form
AIN precipitates. In the present invention, S- and Se-based
precipitates are used as a grain growth inhibitor, and insufficient
grain growth inhibition is solved by using the AlN precipitates.
When an Al content is excessively large, a decomposition
temperature of the AlN precipitate becomes excessively high, and
the grain growth inhibition ability by the AlN increases, which
affects the secondary recrystallization by the S- and Se-based
precipitates. When the Al content is excessively small, the grain
growth inhibition ability by the AlN precipitate may not be
expected. Therefore, the Al content may be limited to 0.0005 to
0.010 wt %. Specifically, Al may be included in an amount of 0.0015
to 0.01 wt %.
[0041] N at 0.0005 to 0.005 wt %
[0042] Nitrogen (N) reacts with Al to form AlN precipitates. For
the same reason as Al, a content of N may be limited to 0.0005 to
0.005 wt % in order to not affect secondary recrystallization by S-
and Se-based precipitates. Specifically, N may be included in an
amount of 0.003 to 0.005 wt %. In the embodiment of the present
invention, during the preparing process, a nitriding process is not
included, and the slab and the content of N in the final prepared
oriented electrical steel sheet may be the same.
[0043] In the embodiment of the present invention, the oriented
electrical steel sheet may satisfy Equation 1.
16.ltoreq.(10.times.[Mn]+[Cu])/([S]+[Se])+(0.02-[Al])/[N].ltoreq.20
[Equation 1]
[0044] (In Equation 1, [Mn], [Cu], [S], [Se], [Al], and [N]
represent the contents (wt %) of Mn, Cu, S, Se, Al, and N,
respectively.)
[0045] When a value of Equation 1 is excessively small, rolling
rupture may occur, or a large amount of S- and Se-based
precipitates may be precipitated, thereby deteriorating the
magnetic properties. When the value of Equation 1 is excessively
large, the S- and Se-based precipitates are not properly formed,
and the secondary recrystallized texture is damaged, and the
magnetism may deteriorate. Specifically, the value of Equation 1
may be 16.2 to 19.9.
[0046] In the embodiment of the present invention, the oriented
electrical steel sheet may satisfy Equation 2.
0.016.ltoreq.[S]+[Se].ltoreq.0.05
[0047] (In Equation 2, [S] and [Se] represent the contents (wt %)
of S and Se, respectively.)
[0048] When a value of Equation 2 is excessively small, the S- and
Se-based precipitates are not properly formed, the secondary
recrystallized texture is damaged, and the magnetism may
deteriorate. When the value of Equation 2 is excessively large, a
large amount of S- and Se-based precipitates may be precipitated,
thereby deteriorating the magnetic properties. Specifically, the
value of Equation 2 may be 0.02 to 0.03.
[0049] In the embodiment of the present invention, the oriented
electrical steel sheet may satisfy Equation 3.
0.5.ltoreq.[Al]/[N].ltoreq.3.0
[0050] (In Equation 3, [Al] and [N] represent the contents (wt %)
of Al and N, respectively.)
[0051] When the value of Equation 3 is excessively small, the grain
growth inhibition ability by the AlN may not be expected. When the
value of Equation 3 is excessively large, the grain growth
inhibition ability by the AlN increases, which affects the
secondary recrystallization by the S- and Se-based precipitates.
Specifically, the value of Equation 3 may be 0.5 to 2.8. Impurity
element
[0052] In addition to the above elements, impurities such as Ni,
Zr, and V, which are inevitably added, may be included. In the case
of Ni, it reacts with impurity elements to form fine sulfides,
carbides, and nitrides, which have a undesirable effect on
magnetism, and thus these contents are limited to 0.05 wt % or
less, respectively. Since Zr, V, etc. are also elements strongly
forming carbonitrides, it is preferable that they are added as
little as possible, and they are contained in an amount of 0.01 wt
% or less, respectively.
[0053] In the embodiment of the present invention, by controlling
the correlation between Mn, Cu, S, Se, Al, and N in the alloy
component, magnetic properties may be further improved.
Specifically, in a thickness standard of 0.30 mm, the iron loss in
a condition of 1.7 Tesla and 50 Hz of the oriented electrical steel
sheet may be 1.5 W/kg or less. More specifically, in the thickness
standard of 0.30 mm, the iron loss in the condition of 1.7 Tesla
and 50 Hz of the oriented electrical steel sheet may be 0.9 to 1.1
W/kg. A magnetic flux density B8 induced under the magnetic field
of 800 A/m of the oriented electrical steel sheet may be 1.88 T or
more. Specifically, it may be 1.88 to 1.95 T. When the magnetic
flux density B8 is 1.88 T or more, there is an advantage of high
transformer efficiency and low noise.
[0054] A preparing method of an oriented electrical steel sheet
according to an embodiment of the present invention includes:
preparing a slab; heating the slab; hot rolling the slab to prepare
a hot rolled sheet; cold rolling the hot rolled sheet to prepare a
cold rolled sheet; primary recrystallization annealing the cold
rolled sheet; and secondary recrystallization annealing the cold
rolled sheet in which the primary recrystallization annealing is
completed.
[0055] Hereinafter, each step will be described in detail.
[0056] First, a slab is prepared.
[0057] In a steel making process, Si, C, Mn, Cu, S, Se, Al, and N
may be controlled to an appropriate amount, and alloy elements,
which are advantageous for forming a Goss texture, may be added as
necessary. Molten steel whose components have been adjusted in the
steel making process is prepared into a slab through continuous
casting.
[0058] Each composition of the slab has been described in detail in
the above-described oriented electrical steel sheet, so a duplicate
description thereof is omitted. Equations 1 to 3 described above
may be identically satisfied even in an alloy component of the
slab.
[0059] Next, the slab is heated.
[0060] The heating of the slab is preferably performed at a low
temperature of 1250.degree. C. or less, more preferably
1150.degree. C. or less, so that the precipitates are partially
solvated. This is because, when the slab heating temperature is
increased, a surface of the slab is melted, and thus it is required
that a heating furnace is repaired and life of the heating furnace
may be shortened. In addition, when the slab is heated at a
temperature of 1250.degree. C. or lower, and more preferably
1150.degree. C. or lower, it is prevented that a columnar structure
of the slab is coarsely grown, thereby preventing cracks from
occurring in a width direction of the sheet in a subsequent
hot-rolling process to improve an actual yield. When the
temperature is less than 1000.degree. C., the hot rolling
temperature is low, so that deformation resistance of the steel
sheet increases, which increases a rolling load. Therefore, the
slab heating temperature may be 1000.degree. C. to 1250.degree.
C.
[0061] Next, a hot rolled sheet is prepared by hot rolling the
slab. A hot rolled sheet having a thickness of 1.5 to 4.0 mm may be
prepared by the hot rolling.
[0062] The hot-rolled hot rolled sheet may be subjected to hot
rolled sheet annealing or may be subjected to cold rolling without
performing hot rolled sheet annealing, as necessary. In the case of
performing the hot rolled sheet annealing, in order to make a
hot-rolled structure uniform, it may be heated to a temperature of
900.degree. C. or higher, and then cooled.
[0063] Next, a cold rolled sheet is prepared by cold rolling the
hot rolled sheet. The cold rolling is performed by using a reverse
mill or a tandem mill by cold rolling once or two times or more
including intermediate annealing to prepare a cold rolled sheet
having a final product thickness. It is advantageous to improve the
magnetic property to perform warm rolling that maintains a
temperature of the steel sheet at 100.degree. C. or higher during
the cold rolling.
[0064] Next, the cold-rolled cold rolled sheet is subjected to
primary recrystallization annealing. In the primary
recrystallization annealing process, primary recrystallization
occurs in which nuclei of Goss grains are generated. In the primary
recrystallization annealing process, decarburization of the steel
sheet may be performed. For the decarburization, it may be
performed in a dew point temperature of 50.degree. C. to 70.degree.
C. and a mixed atmosphere of hydrogen and nitrogen. The primary
recrystallization annealing temperature may be 800 to 950.degree.
C. When the annealing temperature is low, decarburization may take
a long time. When the annealing temperature is high, the primary
recrystallized grains grow coarse, and grain growth driving force
is lowered, so that stable secondary recrystallization is not
formed. In addition, an annealing time is not a big problem for the
effect of the present invention, but may be set within 5 minutes in
consideration of productivity. In the embodiment of the present
invention, only decarburization is performed, and nitriding may not
be performed. That is, the primary recrystallization annealing may
be performed only at a dew point temperature of 50.degree. C. to
70.degree. C. and a mixed atmosphere of hydrogen and nitrogen.
[0065] The cold rolled sheet subjected to the primary
recrystallization annealing includes S- and Se-based precipitates,
and is used as a grain growth inhibitor during secondary
recrystallization annealing. Specifically, the S- and Se-based
precipitates may include one or more precipitates of (Fe,Mn,Cu)S
and (Fe,Mn,Cu)Se. (Fe,Mn,Cu)S means a precipitate in which one or
more of S, Fe, Mn, and Cu are combined.
[0066] Next, the cold rolled sheet in which the primary
recrystallization annealing is completed is subjected to the
secondary recrystallization annealing. In this process, a Goss
{110}<001> texture is formed in which a {110} plane is
parallel to the rolling plane and a <001> direction is
parallel to the rolling direction. In this case, after an annealing
separator is applied to the cold rolled sheet in which the primary
recrystallization annealing is completed, the secondary
recrystallization annealing may be performed. In this case, the
annealing separator is not particularly limited, and an annealing
separator containing MgO as a main component may be used.
[0067] In the secondary recrystallization annealing, a temperature
is raised at an appropriate heating rate to form the second
recrystallization of a {110}<001> Goss orientation, and then,
after purification annealing, which is an impurity removal process,
it is cooled. In the process, an annealing atmosphere gas is
heat-treated using a mixed gas of hydrogen and nitrogen during the
temperature rising process as in the general case, and 100%
hydrogen gas is used in the purification annealing for a long time
to remove impurities.
[0068] Hereinafter, preferred examples of the present invention and
comparative examples will be described. However, the following
examples are only preferred examples of the present invention, and
the present invention is not limited to the following examples.
EXAMPLES
[0069] A slab including Si at 3.2 wt %, C at 0.055 wt %, and the
contents of Mn, Cu, S, Se, Al, and N that were changed as shown in
Table 1, and a remainder Fe and inevitable impurities was prepared.
Subsequently, the slab was heated to 1250.degree. C. and then hot
rolled to prepare a 2.3 mm thick hot rolled sheet. The hot rolled
sheet was heated at a temperature of 1085.degree. C., then
maintained at 910.degree. C. for 160 seconds and quenched in water.
Next, after pickling the hot-rolled annealing sheet, it was
cold-rolled to a thickness of 0.30 mm, and the primary
recrystallization annealing was performed for the cold-rolled steel
sheet by maintaining it at a temperature of 850.degree. C. for 180
seconds in a mixed gas atmosphere of hydrogen and nitrogen at a dew
point of 60.degree. C. After applying MgO, which is an annealing
separator, to this steel sheet, the secondary recrystallization
annealing was performed therefor, wherein the secondary
recrystallization annealing was performed in a mixed gas atmosphere
of "25 v % nitrogen +75 v % hydrogen" up to 1200.degree. C. and in
a gas atmosphere of 100 v % hydrogen after reaching 1200.degree. C.
for 10 hours or more, and then was furnace-cooled. Table 1 shows
the magnetic properties of the oriented electrical steel sheet
according to each component.
[0070] The iron loss was measured under the condition of 1.7 Tesla
and 50 Hz using a single sheet measurement method, and the magnetic
flux density (Tesla) induced under the magnetic field of 800 Nm was
measured. Each iron loss value was an average of each
condition.
TABLE-US-00001 TABLE 1 Mn Cu S Se Al N Classification (wt %) (wt %)
(wt %) (wt %) (wt %) (wt %) Comparative 0.025 0.01 0.024 0.005
0.002 0.0038 Example 1 Comparative 0.025 0.01 0.003 0.059 0.0018
0.0039 Example 2 Comparative 0.024 0.011 0.003 0.006 0.0017 0.0035
Example 3 Comparative 0.025 0.01 0.007 0.008 0.0018 0.0038 Example
4 Inventive 0.025 0.012 0.01 0.011 0.0018 0.0035 Example 1
Inventive 0.025 0.031 0.01 0.01 0.002 0.0033 Example 2 Inventive
0.024 0.05 0.011 0.009 0.0017 0.0034 Example 3 Comparative 0.025
0.072 0.01 0.011 0.0015 0.0036 Example 5 Comparative 0.026 0.089
0.01 0.01 0.0016 0.0035 Example 6 Inventive 0.025 0.01 0.01 0.012
0.0051 0.0034 Example 4 Inventive 0.026 0.012 0.01 0.01 0.0098
0.0036 Example 5 Comparative 0.025 0.011 0.01 0.011 0.013 0.0037
Example 7 Inventive 0.036 0.011 0.01 0.015 0.01 0.0045 Example 6
Inventive 0.036 0.032 0.008 0.016 0.008 0.0043 Example 7 Inventive
0.036 0.052 0.009 0.016 0.007 0.0044 Example 8 Comparative 0.036
0.072 0.009 0.014 0.007 0.0045 Example 8 Comparative 0.036 0.104
0.009 0.015 0.008 0.0043 Example 9 Inventive 0.035 0.012 0.01 0.016
0.0019 0.0034 Example 9 Inventive 0.034 0.01 0.012 0.012 0.0066
0.0035 Example 10 Comparative 0.049 0.01 0.01 0.018 0.002 0.0038
Example 10 Comparative 0.05 0.011 0.018 0.041 0.0017 0.0035 Example
11
TABLE-US-00002 TABLE 2 Magnetic Iron loss Equation Equation
Equation flux density (W 17/50, Classification 1 value 2 value 3
value (B8, Tesla) W/kg) Comparative 13.7 0.029 0.526 Rolling crack
Example 1 Comparative 8.86 0.062 0.462 Rolling crack Example 2
Comparative 33.12 0.009 0.486 1.48 2.39 Example 3 Comparative 22.12
0.015 0.474 1.83 1.23 Example 4 Inventive 17.68 0.021 0.514 1.94
0.91 Example 1 Inventive 19.5 0.02 0.606 1.92 0.95 Example 2
Inventive 19.88 0.02 0.5 1.91 0.96 Example 3 Comparative 20.47
0.021 0.417 1.85 1.17 Example 5 Comparative 22.71 0.02 0.457 1.82
1.27 Example 6 Inventive 16.2 0.022 1.5 1.92 0.96 Example 4
Inventive 16.43 0.02 2.722 1.9 0.98 Example 5 Comparative 14.32
0.021 3.514 1.86 1.15 Example 7 Inventive 17.06 0.025 2.222 1.88
1.03 Example 6 Inventive 19.12 0.024 1.86 1.9 0.99 Example 7
Inventive 19.43 0.025 1.591 1.92 0.96 Example 8 Comparative 21.67
0.023 1.556 1.68 1.80 Example 8 Comparative 22.12 0.024 1.86 1.71
1.71 Example 9 Inventive 19.25 0.026 0.559 1.88 1.03 Example 9
Inventive 18.41 0.024 1.886 1.91 0.97 Example 10 Comparative 22.59
0.028 0.526 1.47 2.48 Example 10 Comparative 13.89 0.059 0.486 1.48
2.45 Example 11
[0071] As can be seen in Table 1 and Table 2, it can be confirmed
that the magnetic flux density and the iron loss was excellent in
the inventive examples satisfying Equation 1 by controlling the Mn,
Cu, S, Se, Al, and N contents.
[0072] In contrast, in the comparative example that did not satisfy
Equation 1, it can be confirmed that the edge crack occurred or the
magnetic flux density and iron loss were deteriorated.
[0073] The present invention may be embodied in many different
forms, and should not be construed as being limited to the
disclosed embodiments. In addition, it will be understood by those
skilled in the art that various changes in form and details may be
made thereto without departing from the technical spirit and
essential features of the present invention. Therefore, it is to be
understood that the above-described exemplary embodiments are for
illustrative purposes only, and the scope of the present invention
is not limited thereto.
* * * * *