CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of Korean Patent Application
No.
10-2015-0182839 filed in the Korean Intellectual Property Office on December 21, 2015, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
[0002] The present invention relates to an oriented electrical steel sheet and a manufacturing
method thereof.
(b) Description of the Related Art
[0003] An oriented electrical steel sheet is a soft ferrite material that has an excellent
magnetism characteristic in a rolling direction and includes grains having a crystal
orientation of a steel sheet of {110}<001>, a so-called Goss orientation. The oriented
electrical steel sheet is manufactured by rolling the same to a final thickness of
0.15 to 0.35 mm through hot-rolling, hot-rolled steel sheet annealing, and cold-rolling
after heating a slab, and then allowing the same to undergo high-temperature annealing
for primary recrystallization annealing and secondary recrystallization formation.
In this instance, it is known that a degree of integration of the Goss orientation
that is secondarily recrystallized as a temperature raising rate is slower at the
time of a high-temperature annealing, and the magnetism is excellent. The temperature
raising rate during conventional high-temperature annealing of an oriented electrical
steel sheet is equal to or less than 15 °C per hour, the temperature raising requires
two to three days, and a purification annealing process of more than forty hours is
needed, so it is a process that consumes a large amount of energy. Further, the present
final high-temperature annealing process performs a batch-type annealing in a coiled
state, so subsequent difficulties during the process are generated as follows. First,
a temperature deviation of an external winding portion and an internal winding portion
of the coil caused by a heat treatment in a coiled state occurs, as the same heat
treatment pattern may not be applied to respective portions, so a magnetism deviation
of the external winding portion and the internal winding portion is generated. Second,
MgO is coated on the surface after decarburization-annealing, and various surface
defects are generated during a process for forming a base coating during high-temperature
annealing, thereby lowering an actual yield. Third, as the decarburization-annealed
decarburization plate is wound in a coil form, it undergoes flattening annealing and
insulating coating after high-temperature annealing, so a production process is divided
into three steps and the actual yield is reduced. Patent Document
US 2003/116236 A1 relates to a method of manufacturing a grain-oriented electrical steel sheet.
[0004] The above information disclosed in this Background section is only for enhancement
of understanding of the background of the invention and therefore it may contain information
that does not form the prior art that is already known in this country to a person
of ordinary skill in the art.
SUMMARY OF THE INVENTION
[0005] The present invention has been made in an effort to provide a method for manufacturing
an oriented electrical steel sheet and an oriented electrical steel sheet manufactured
by the same.
[0006] An exemplary embodiment of the present invention provides a method for manufacturing
an oriented electrical steel sheet that includes: providing a slab including, as wt%,
Si at equal to or less than 4.0 % excluding 0 %, C at 0.001 % to 0.4 %, and Mn at
0.001 to 2.0 %, and including a balance including Fe and inevitably mixed and input
impurities, and optionally including Al at equal to or less than 0.01 wt% excluding
0 wt%; reheating the slab; manufacturing a hot steel sheet by hot-rolling the slab;
performing hot-rolled steel sheet annealing to the hot steel sheet; primarily cold-rolling
the hot-rolled steel sheet annealed hot steel sheet; decarburization-annealing the
cold-rolled steel sheet; secondarily cold-rolling the decarburization-annealed steel
sheet; and finally annealing the cold-rolled steel sheet, wherein in the step of finally
annealing the cold-rolled steel sheet includes a first step for performing the same
in an atmosphere with a dew point temperature of 10 °C to 70 °C at a temperature of
850 °C to 1150 °C, and a second step for performing the same in a mixed gas atmosphere
including hydrogen and nitrogen with a dew point temperature that is equal to or less
than 10 °C at a temperature of 900 °C to 1200 °C, wherein the first step is performed
for equal to or less than 300 seconds, and the second step is performed for 60 seconds
to 300 seconds. The slab may include Si at equal to or less than 1 wt% excluding 0
wt%.
[0007] Reduction rates in the primarily cold-rolling and the secondarily cold-rolling may
respectively be 50 % to 70 %.
[0008] The decarburization-annealing of the cold-rolled steel sheet and the secondarily
cold-rolling of the decarburization-annealed steel sheet may be repeated at least
twice.
[0009] The decarburization-annealing may be performed in an atmosphere including hydrogen
with a dew point temperature of equal or greater than 0 °C at a temperature of 800
°C to 1150 °C.
[0010] The finally annealing may be continuously performed after the cold-rolling.
[0011] Another embodiment of the present invention provides an oriented electrical steel
sheet including, as wt%, Si at equal to or less than 4.0 % (excluding 0 %), C at equal
to or less than 0.003 % (excluding 0 %), and Mn at 0.001 to 2.0 %, and a balance including
Fe and an impurity that is inevitably mixed and input, and optionally comprising Al
at equal to or less than 0.01 wt% excluding 0 wt%, wherein a size 2L of a magnetic
domain existing in a grain is less than a thickness (D) of a steel sheet, wherein
a volumetric fraction of a grain with a particle diameter of 20 µm to 1000 µm may
be equal to or greater than 50 %.
[0012] Si may be included to be equal to or less than 1.0 wt% (excluding 0 wt%).
[0013] A size 2L of a magnetic domain existing in a grain may be 10 to 500 µm.
[0014] A volumetric fraction of a grain with an orientation that is within 15 degrees from
an orientation {110}<001> may be equal to or greater than 50 %.
[0015] According to an exemplary embodiment of the present invention, the method for manufacturing
an oriented electrical steel sheet by performing continuous annealing without performing
batch-type annealing in a coiled state in the case of the final annealing is provided.
[0016] Further, according to an exemplary embodiment of the present invention, an oriented
electrical steel sheet may be manufactured by short-time annealing.
[0017] Also, according to an exemplary embodiment of the present invention, an oriented
electrical steel sheet manufactured by not using a grain growth control agent may
be provided.
[0018] In addition, according to an exemplary embodiment of the present invention, the nitriding-annealing
may be omitted.
BRIEF DESCRIPTION OF THE DRAWING
[0019] FIG. 1 shows a photograph for indicating a microstructure and a magnetic domain of
an oriented electrical steel sheet manufactured in Example 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0020] 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. Thus, a first element, component, region, layer, or section discussed
below could be termed a second element, component, region, layer, or section without
departing from the teachings of the present invention.
[0021] The technical terms used herein are to simply mention a particular exemplary 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 terms such as "including",
"having", etc., are intended to indicate the existence of specific features, regions,
numbers, stages, operations, elements, components, or combinations thereof disclosed
in the specification, and are not intended to preclude the possibility that one or
more other specific features, regions, numbers, operations, elements, components,
or combinations thereof may exist or may be added.
[0022] When a part is referred to as being "on" another part, it can be directly on the
other part or intervening parts may also be present. In contrast, when an element
is referred to as being "directly on" another element, there are no intervening elements
therebetween.
[0023] 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. Such terms as
those defined in a generally used dictionary are to be interpreted to have the same
meanings as contextual meanings in the relevant field of art, and are not to be interpreted
to have idealized or excessively formal meanings unless clearly defined in the present
application.
[0024] Further, as used herein, % means wt%, unless the context clearly indicates otherwise,
and 1 ppm is 0.0001 wt%.
[0025] The present invention will be described more fully hereinafter with reference to
the accompanying drawings, in which exemplary embodiments of the invention are shown.
[0026] In general, required characteristics of an oriented electrical steel sheet used to
transform electric power as a core material of a transformer are a high magnetic flux
density characteristic and a low iron loss characteristic. The high magnetic flux
density characteristic may increase electric power transforming efficiency and may
increase design magnetic flux density, so it has a merit of reducing a size of the
transformer by using a small core material. Further, in the case of iron loss that
is generated by the oriented electrical steel sheet in a process of changing electric
power, it has a merit of reducing a no-load loss of the transformer.
[0027] Studies and technical developments on the oriented electrical steel sheet have mostly
progressed so as to reduce the iron loss. The iron loss of the oriented electrical
steel sheet is generally divided into a hysteresis loss, a classical eddy current
loss, and an anomalous eddy current loss.
[0028] The hysteresis loss is a loss of the electrical steel sheet generated by a magnetization
degree of the oriented electrical steel sheet, and the loss is reduced when the oriented
electrical steel sheet has no impurity or defects and the degree of integration of
the Goss orientation is high.
[0029] The classical eddy current loss is a loss generated by an eddy current generated
to the steel sheet for a magnetization process of the oriented electrical steel sheet,
and efforts for reducing the loss by minimizing the eddy current of the steel sheet
have been made by increasing the amount of Si and reducing a thickness of the steel
sheet. Another abnormal eddy current loss is a loss relating to a movement and shift
of a magnetic domain of the oriented electrical steel sheet in an AC in which the
transformer is operated, and it has a characteristic in that the loss is reduced as
the magnetic domain size (2L) becomes minute. Studies for improving the abnormal eddy
current loss have been relatively recently progressed compared to studies on the hysteresis
loss and the classical eddy current loss, and a method for applying a partial stress
to a surface of the steel sheet and temporarily miniaturizing the magnetic domain
by irradiating laser beams to the surface of the steel sheet and a method for permanently
miniaturizing the magnetic domain through a structural change of the magnetic domain
by providing a curve with a predetermined pattern to the surface of the steel sheet
have been developed. Regarding another method for miniaturizing a magnetic domain,
a method for providing a tension caused by a difference of expansion coefficients
to the surface of the steel sheet and miniaturizing the magnetic domain by applying
a coating material with a different expansion coefficient to the surface of the steel
sheet has been developed.
[0030] The present inventors found that, after having repeatedly studied the reduction of
the abnormal eddy current loss of the oriented electrical steel sheet, the size of
the magnetic domain may be reduced when the size of grains of the oriented electrical
steel sheet is reduced, and it is accordingly possible to substantially reduce the
entire iron loss of the oriented electrical steel sheet.
[0031] A conventional size of the magnetic domain has a relationship with the size of the
grain as expressed in Equation 1.
[0032] That is, as the grains become smaller, the magnetic domain becomes small, and the
abnormal eddy current loss is resultantly reduced.
[0033] The abnormal eddy current loss has a relationship of Equation 2 with the classical
eddy current loss.
[0034] Here, Wea is an abnormal eddy current loss, Wec is a classical eddy current loss,
2L is a size of the magnetic domain, and d is a thickness of the steel sheet.
[0035] As expressed in Equation 2, when the size of the magnetic domain is reduced in the
assumption that the thickness of the steel sheet is constant, the abnormal eddy current
loss is also reduced.
[0036] When the size of the Goss orientation grains is reduced, it is possible to substantially
reduce the size of the magnetic domain based on Equation 1 for expressing the relationship
between the size of the grains and the size of the magnetic domain, and accordingly,
the iron loss of the oriented electrical steel sheet may be substantially reduced.
[0037] To sum up, in order to reduce the iron loss of the oriented electrical steel sheet,
it is needed to reduce the hysteresis loss according to the excellent magnetization
characteristic through formation of recrystallized grains of the Goss orientation,
reduce the classical eddy current loss according to an increase of an amount of Si
and a reduction of the thickness of the steel sheet, and reduce the abnormal eddy
current loss by miniaturizing the size of the Goss orientation grain and miniaturizing
the size of the magnetic domain. It is desirable to reduce the hysteresis loss, the
classical eddy current loss, and the abnormal eddy current loss so as to reduce the
entire loss of the oriented electrical steel sheet, but depending on the cases, the
oriented electrical steel sheet that is easy to produce and has an excellent magnetism
characteristic may be manufactured by minimizing the size of the Goss orientation
grain and thereby substantially improving the abnormal eddy current loss without a
big improvement of the hysteresis loss or the classical eddy current loss.
[0038] A method for manufacturing an oriented electrical steel sheet according to an exemplary
embodiment of the present invention includes: providing a slab including, as wt ,
Si at equal to or less than 4.0 % (excluding 0 %), C at 0.001 % to 0.4 %, and Mn at
0.001 % to 2.0 %, and including a balance including Fe and an impurity that is inevitably
mixed and input; reheating the slab; manufacturing a hot steel sheet by hot-rolling
the slab; performing hot-rolled steel sheet annealing on the hot steel sheet; primarily
cold-rolling the hot-rolled steel sheet annealed hot steel sheet; decarburization-annealing
the cold-rolled steel sheet; secondarily cold-rolling the decarburization-annealed
steel sheet; and finally annealing the cold-rolled steel sheet. In addition, if needed,
the method for manufacturing an oriented electrical steel sheet may include other
steps.
[0039] The respective steps will now be described in detail.
[0040] A slab including, as wt%, Si at equal to or less than 4.0 % (excluding 0 %), C at
0.001 % to 0.4 %, and Mn at 0.001 % to 2.0 %, and a balance including Fe and an impurity
that is inevitably mixed and input, is provided.
[0041] Reasons for limiting the compositions are as follows.
[0042] Silicon (Si) improves the iron loss by reducing magnetic anisotropy of the oriented
electrical steel sheet and increasing specific resistance. An exemplary embodiment
of the present invention has a characteristic of substantially reducing the abnormal
eddy current loss by reducing the size of the grain of the final product, but the
iron loss may be further improved when more Si is added, so it may be effective to
add more than a predetermined amount. Therefore, the content of Si is added up to
the range of 4 wt% indicating a cold-rolling allowable content. When there is a high
content of Si, a brittleness property increases in the case of the cold rolling, and
the cold rolling may become impossible. In detail, Si may be included at equal to
or less than 1 wt% (excluding 0 wt%).
[0043] Carbon (C) is an element for catalyzing austenite phase transformation, and is an
important element for making a hot-rolled structure of the oriented electrical steel
sheet uniform, catalyzing a formation of grains of the Goss orientation in the case
of cold rolling, and thereby manufacturing an oriented electrical steel sheet with
excellent magnetism. However, when the carbon C exists in the final product, a magnetic
aging phenomenon is generated to deteriorate the magnetism characteristic, so the
carbon C must exist at equal to or less than 0.003 wt% in the finally manufactured
electrical steel sheet. To catalyze the phase transformation by addition of carbon
C and recrystallization of the Goss orientation grains, an effect will be generated
when the carbon C is added at equal to or greater than 0.001 wt% in the slab, and
when the content is less than the above-noted case, secondary recrystallization is
unstably formed because of a non-uniform hot-rolled structure. However, when carbon
C is added to the slab at greater than 0.4 wt%, the primary recrystallized grain becomes
minute by formation of a minute hot-rolled structure caused by an austenite phase
transformation at the time of hot rolling, a coarse carbide may be formed during a
cooling process after a spiral-winding process or hot-rolled steel sheet annealing
after the hot rolling is finished, and non-uniformity may be generated to tissues
by forming Fe
3C (cementite) at room temperature. In addition, there is a drawback that the annealing
time increases during decarburization to equal to or less than 0.003 wt% in the decarburization
process and the final annealing process. Therefore, the content of carbon C in the
slab is limited to 0.001 to 0.4 wt%.
[0044] Manganese (Mn), in a like manner of Si, increases specific resistance to reduce the
iron loss, and in a like manner of C, it is an important element for catalyzing the
austenite phase transformation to miniaturize a particle diameter of the grain during
the hot rolling and annealing process. When such Mn is added to be less than 0.001
wt%, the phase transformation is not sufficiently performed like with the effect of
carbon C, so the slab and the hot-rolled structure become coarse, the particle diameter
of the grain of the final product does not become minute, and the effect of the improvement
of the iron loss caused by an increase of specific resistance becomes small. In addition,
when Mn is added to be greater than 2.0 wt%, a manganese oxide (Mn Oxide) as well
as Fe
2SiO
4 is formed on the surface of the steel sheet, and decarburization is not fluently
performed in the final annealing process. Therefore, a preferable added amount of
Mn is 0.001 to 2.0 wt%. In detail, the added amount of Mn may be 0.01 to 1.0 wt%.
[0045] According to an exemplary embodiment of the present invention, aluminum (Al) is treated
as an inevitable impurity. That is, the content of Al may be minimized in the slab
and the steel sheet. In detail, when Al is further added, its range may be provided
to be equal to or less than 0.01 wt%.
[0046] The above-noted components form a basic configuration of the present invention, and
when other alloy elements for improving the magnetism characteristic are added or
inevitably included, the effect of improving the iron loss caused by miniaturization
of the Goss orientation grain that is the characteristic of the present invention
may not be weakened.
[0047] A method for manufacturing a slab from the molten steel of the above-described composition
includes a blooming method, a continuous casting method, a thin slab casting method,
or a strip casting method.
[0048] The slab is reheated. The slab reheating temperature may be 1050 °C to 1350 °C. When
the slab is reheated and the temperature is low, a rolling load increases, and when
the temperature is high, a slab washing phenomenon may be generated by formation of
a high-temperature oxide with a low melting point to deteriorate the actual yield,
and the hot-rolled structure may also become coarse to provide a bad effect to the
magnetism. Therefore, the slab reheating temperature may be controlled within the
above-described range.
[0049] The reheated slab is hot-rolled to manufacture a hot steel sheet. At the time of
hot-rolling, a hot-rolled steel sheet may be manufactured by applying hot-rolling
within the temperature range where the austenite phase exists. At a low temperature
where no austenite phase exists, the rolling load increases, and the effect of miniaturizing
grains caused by a phase transformation may be acquired.
[0050] The hot steel sheet undergoes hot-rolled steel sheet annealing. The hot-rolled steel
sheet may undergo the hot-rolled steel sheet annealing at a temperature that is higher
than the temperature at which the recrystallization and the phase transformation are
allowable. In detail, to prevent the production of an oxidation layer with a low melting
point caused by a high-temperature heating, the hot-rolled steel sheet annealing may
be performed at a temperature of 850 to 1150 °C. An atmosphere at the time of the
hot-rolled steel sheet annealing may be an atmosphere having a dew point temperature
which is equal to or greater than 0 °C, for generating a decarburization reaction
of the hot-rolled steel sheet, and hydrogen gas.
[0051] The hot-rolled steel sheet annealed hot steel sheet is primarily cold-rolled. After
performing the hot-rolled steel sheet annealing, the steel sheet may be pickled and
cold-rolled. At the time of a cold-rolling, a reduction rate may be 50 % to 70 %.
[0052] The cold-rolled steel sheet is then decarburization-annealed. The cold-rolled steel
sheet undergoes annealing for recrystallization, and in this instance, in order to
generate a decarburization reaction, annealing is performed in the atmosphere having
a dew point temperature that is equal to or greater than 0 °C and including hydrogen
gas at a temperature of 800 °C to 1150 °C. When the temperature is very low, it is
difficult to perform decarburization, and when the temperature is very high, a thick
oxidation layer may be formed and the decarburization reaction may be deteriorated.
When the dew point temperature is very low, the decarburization reaction may be deteriorated.
In detail, the dew point temperature may be 10 to 70 °C.
[0053] The decarburization-annealed steel sheet is secondarily cold-rolled. At the time
of cold-rolling, the reduction rate may be 50 % to 70 %. The step for decarburization-annealing
the cold-rolled steel sheet and the step for secondarily cold-rolling the decarburization-annealed
steel sheet may be repeated a plurality of times. For example, when the steps are
repeated twice, they may be performed in order of performing primary cold-rolling,
performing decarburization-annealing, performing secondary cold-rolling, performing
decarburization-annealing, performing third cold-rolling, and performing final annealing.
In this instance, the cold-rolling is performed up to the thickness of the final product
in the step of performing final cold-rolling, each decarburization process performs
annealing in the atmosphere having the dew point temperature that is equal to or greater
than 0 °C and including hydrogen gas at the temperature of 800 °C to 1150 °C so as
to generate a decarburization reaction.
[0054] The cold-rolled steel sheet then undergoes final annealing.
[0055] The method for manufacturing an oriented electrical steel sheet according to an exemplary
embodiment of the present invention may consecutively perform final annealing in succession
to the secondary cold-rolling, differing from the existing batch method.
[0056] The final annealing step includes a first step to be performed in the atmosphere
with the dew point temperature of 10 °C to 70 °C at the temperature of 850 °C to 1150
°C and a second step to be performed in the atmosphere of a mixed gas including hydrogen
and nitrogen with the dew point temperature that is equal to or less than 10 °C at
a temperature of 900 °C to 1200 °C. The first step is performed for under 300 seconds,
and the second step is performed for 60 to 300 seconds.
[0057] The cold-rolled steel sheet, before it is finally annealed, undergoes decarburization-annealing
so that an amount of silicon steel carbon of 40 wt% to 60 wt% remains with respect
to the carbon amount of the minimum slab. Therefore, in the final annealing, in the
first step, carbon escapes, and the grains formed on the surface portion are diffused
to the inside. The first step may perform decarburization so that the amount of carbon
in the steel sheet may be equal to or less than 0.01 wt%.
[0058] In the second step, a texture with the Goss orientation diffused in the first step
grows. Regarding the method for manufacturing an oriented electrical steel sheet according
to an exemplary embodiment of the present invention, a particle diameter of the grain
of the Goss texture may be within 1 mm, differing from the conventional case in which
the grains grow by the growth of abnormal particles. Therefore, compared to the conventional
oriented electrical steel sheet, a microstructure made of Goss orientation grains
with a very small particle diameter of the grain may be provided.
[0059] The amount of carbon in the finally annealed electrical steel sheet may be equal
to or less than 0.003 wt%.
[0060] The finally annealed oriented electrical steel sheet may be dried, if necessary,
when an insulating coating liquid is applied thereto.
[0061] Further, an annealing separating agent with MgO as a major component is coated during
the final annealing in the conventional batch type, so a MgO coating layer exists,
but the oriented electrical steel sheet according to an exemplary embodiment of the
present invention may undergo final annealing not in a batch type but in a continuous
manner, and accordingly may not have a MgO coating layer.
[0062] The grains of the Goss orientation (an orientation within 15 degrees from the orientation
of {110}<001>) produced through an exemplary embodiment of the present invention tend
to further increase as the cold rolling and the decarburization-annealing are repeated,
and when the cold-rolling and the decarburization-annealing are performed at least
twice, a volumetric fraction of the grain having the Goss orientation in the steel
sheet increases by at least 50 %.
[0063] The grains produced through an exemplary embodiment of the present invention have
a particle diameter of less than 5 mm, and the volumetric fraction of the grain to
be 20 µm to 1000 µm becomes equal to or greater than 50 %. As a result, the size of
the magnetic domain existing in the grain becomes very small. The size of the magnetic
domain shown in the conventional oriented electrical steel sheet is greater than the
thickness of the conventional steel sheet, but regarding the steel sheet produced
through an exemplary embodiment of the present invention, the magnetic domain size
(2L) existing in the grain is formed to be less than the thickness (D) of the steel
sheet.
[0064] The oriented electrical steel sheet according to an exemplary embodiment of the present
invention includes, as wt%, Si at equal to or less than 4.0 % (excluding 0 %), C at
equal to or less than 0.003 % (excluding 0 %), and Mn at 0.001 to 2.0 %, the balance
includes Fe and impurities that are inevitably mixed, and the size (2L) of the magnetic
domain existing in the grain is less than the thickness (D) of the steel sheet.
[0065] A composition on the oriented electrical steel sheet corresponds to the composition
of the above-noted slab, and a composition range in the process for manufacturing
an oriented electrical steel sheet does not substantially change, so no repeated description
will be provided. As described above, carbon is decarburized in the decarburization-annealing
and the final annealing, so the content of carbon becomes equal to or less than 0.003
wt%.
[0066] Regarding the oriented electrical steel sheet according to an exemplary embodiment
of the present invention, the volumetric fraction of the grain with the Goss orientation
in the steel sheet increases by at least 50 % to provide excellent iron loss and magnetic
flux density, the particle diameter of 20 to 1000 um of the grain in the oriented
electrical steel sheet is equal to or greater than 50 %, the size is not greater than
5 mm at a maximum, and the size of the magnetic domain existing in the grain becomes
less than the thickness of the steel sheet. Because of the minute magnetic domain
structure, the abnormal eddy current loss of the steel sheet produced according to
the present invention is substantially reduced compared to the abnormal eddy current
loss of the oriented electrical steel sheet produced by the prior art, thereby substantially
improving the iron loss.
[0067] In detail, the size (2L) of the magnetic domain existing in the grain may be 10 to
500 µm.
[0068] The present invention will now be described in detail through examples. The examples
exemplify the present invention, and the present invention is not limited thereto.
Example 1
[0069] A slab including, as wt%, Si at 2.0 %, C at 0.15 %, and Mn at 0.05 %, and including
a balance including Fe and inevitable impurities, is heated at a temperature of 1100
°C, it is hot rolled with a thickness of 3 mm, hot-rolled steel sheet annealing is
performed at an annealing temperature of 1000 °C, it is cooled, it is pickled, and
a cold rolling is performed up to the thickness of 0.27 mm. When the cold rolling
is performed up to the final thickness, a method for performing cold rolling up to
the final thickness without including decarburization-annealing between cold rolling
and cold rolling, and a method for including decarburization-annealing between cold
rolling and cold rolling at least once and performing cold rolling with a plurality
of steps, are provided. The decarburization-annealing is performed in the atmosphere
(with the dew point temperature of 60 °C) of a wet mixed gas of hydrogen and nitrogen
at the temperature of 1000 °C.
[0070] At the time of final annealing, annealing is performed for two minutes in the atmosphere
(with the dew point temperature 60 °C) of a wet mixed gas of hydrogen and nitrogen
at the temperature of 1000 °C, and annealing is performed for three minutes in the
dry atmosphere of a mixed gas of hydrogen and nitrogen at the temperature (with a
dew point temperature 0 °C) of 1100 °C.
[0071] A relationship between a fraction of the Goss orientation grain from the finally
annealed steel sheet and a magnetism characteristic is compared and is expressed in
Table 1.
[0072] Here, a method for estimating a fraction of the Goss orientation grain includes measuring
a volume fraction of grains of an orientation indicating an error of within 15 degrees
from the ideal orientation of {110}<001> by using a conventional method for measuring
a crystal orientation.
[0073] In addition, the method includes measuring an average size of the magnetic domain
through observation of a magnetic domain while the electrical steel sheet is demagnetized,
by using Kerr microscopy.
(Table 1)
Number of times of cold rolling to final thickness |
Goss orientation grain fraction (%) |
Magnetic domain size (µm) |
Magnetic flux density (B10) |
Iron loss (W17/50) |
Etc. |
1 |
32 |
31 |
1.65 |
1.88 |
Comparative material |
2 |
53 |
55 |
1.89 |
0.99 |
Exemplary embodiment |
3 |
85 |
40 |
1.92 |
0.95 |
Exemplary embodiment |
4 |
87 |
86 |
1.95 |
0.91 |
Exemplary embodiment |
[0074] When the process for performing cold rolling up to the final thickness after hot-rolled
steel sheet annealing is performed as expressed in Table 1 includes intermediate annealing
generating decarburization at least once, the fraction of the Goss orientation grains
may be acquired for the final product of equal to or greater than 50 %, and a minute
magnetic domain size may be obtained. The characteristics of an excellent magnetic
flux density and a low iron loss may be acquired from the final product by the high
Goss orientation fraction and the minute magnetic domain size.
Example 2
[0075] A slab including, as wt%, C at 0.2 % and Mn at 0.05 %, and including a balance of
Fe and inevitable impurities, is manufactured by varying the content of Si, as expressed
in Table 2. The slab is heated at a temperature of 1150 °C, it is hot rolled to a
thickness of 3 mm, hot-rolled steel sheet annealing is performed at a annealing temperature
of 950 °C, it is cooled, it is pickled, and cold rolling is performed with a reduction
rate of 60 %. The cold-rolled sheet is recrystallized and decarburization-annealed
in the mixed gas atmosphere of hydrogen and nitrogen with a dew point temperature
60 °C at a temperature of 900 °C. The same cold-rolling and decarburization-annealing
are repeated twice. Cold rolling is performed up to the thickness of the steel sheet
of 0.23 mm, decarburization-annealing is performed for 180 seconds in the mixed gas
atmosphere of hydrogen and nitrogen with the dew point temperature of 60 °C at the
temperature of 950 °C (first step), and heat treatment is performed for 100 seconds
in the dry (the dew point of 0 °C) hydrogen atmosphere at the temperature of 1000
°C (second step). Magnetism characteristics of the final annealing steel sheet according
to changes of the content of Si are expressed in Table 2.
(Table 2)
Si content (%) |
Particle diameter of grain (um) |
Magnetic domain size (um) |
Magnetic flux density (B10) |
Iron loss (W17/50) |
Etc. |
0.0005 |
210 |
84 |
1.90 |
0.97 |
Exemplary embodiment |
0.1 |
156 |
56 |
1.89 |
0.99 |
Exemplary embodiment |
0.5 |
365 |
137 |
1.91 |
0.97 |
Exemplary embodiment |
1.0 |
423 |
181 |
1.89 |
0.99 |
Exemplary embodiment |
1.5 |
510 |
229 |
1.92 |
0.91 |
Exemplary embodiment |
2.0 |
198 |
91 |
1.93 |
0.93 |
Exemplary embodiment |
3.0 |
257 |
173 |
1.91 |
0.91 |
Exemplary embodiment |
3.5 |
454 |
125 |
1.90 |
0.92 |
Exemplary embodiment |
4.0 |
781 |
89 |
1.89 |
0.90 |
Exemplary embodiment |
4.3 |
15 |
23 |
1.68 |
1.22 |
Comparative material |
[0076] As expressed in Table 2, when the content of Si is equal to or less than 4 wt%, a
microstructure with the final particle diameter of the grain that is equal to or less
than 1000 µm is acquired through a plurality of cold rolling and decarburization-annealing
steps, and in this instance, the size of the magnetic domain that is less than the
thickness of the steel sheet is acquired, thereby acquiring excellent iron loss. When
the content of Si is greater than 4 wt%, a brittleness property increases, so it is
difficult to perform cold rolling up to the final thickness because of a strip breakage
when performing cold rolling, and decarburization is not performed during a decarburization-annealing
time, thereby showing a very small particle diameter of the grain and a deteriorated
magnetism characteristic.
Example 3
[0077] A slab including, as wt%, Si at 3.0 %, C at 0.25 %, and Mn at 0.5 %, and a balance
including Fe and inevitable impurities, is heated at the temperature of 1200 °C, it
is hot rolled with the thickness of 2.5 mm, hot-rolled steel sheet annealing is performed
in the mixed gas atmosphere of hydrogen and nitrogen with the dew point temperature
of 40 °C at the annealing temperature 1100 °C, it is cooled, it is pickled, and it
is primarily cold rolled with the reduction rate of 65 %. The cold-rolled sheet is
decarburization-annealed in the wet mixed gas atmosphere of hydrogen and nitrogen
with the dew point temperature of 60 °C at the temperature of 1050 °C. The primarily
decarburization-annealed sheet is secondarily cold rolled up to the thickness of 0.30
mm, and it is finally annealed. The final annealing changes the temperature of annealing
and performs decarburization-annealing as expressed in Table 3 in the wet mixed gas
atmosphere of hydrogen and nitrogen with the dew point temperature of 65 °C so that
the content of carbon may be equal to or less than 0.003 wt% (1step). The temperature
is increased following the decarburization-annealing to perform a finishing heat treatment
in the dry hydrogen atmosphere with the dew point of 0 °C at the temperature of 1150
°C (2step). The particle diameter of the grain of the finally annealed steel sheet
and the magnetic domain size were measured using Kerr microscopy, and are shown in
Table 3 in comparison with the magnetism characteristic.
(Table 3)
first-step final annealing temperature (°C) |
Particle diameter of grain (um) |
Grain ratio of 20 to 1000 µm (%) |
Magnetic domain size (um) |
Magnetic flux density (B10) |
Iron loss (W17/50) |
Etc. |
830 |
18 |
43 |
8 |
1.68 |
1.95 |
Comparative material |
850 |
25 |
51 |
21 |
1.89 |
1.05 |
Exemplary embodiment |
870 |
50 |
58 |
45 |
1.91 |
0.97 |
Exemplary embodiment |
890 |
128 |
67 |
108 |
1.90 |
1.00 |
Exemplary embodiment |
910 |
253 |
85 |
117 |
1.89 |
0.99 |
Exemplary embodiment |
930 |
391 |
92 |
196 |
1.90 |
0.97 |
Exemplary embodiment |
950 |
510 |
97 |
207 |
1.92 |
0.99 |
Exemplary embodiment |
1000 |
732 |
99 |
266 |
1.91 |
0.98 |
Exemplary embodiment |
1080 |
805 |
98 |
295 |
1.92 |
0.91 |
Exemplary embodiment |
1170 |
1038 |
48 |
505 |
1.82 |
1.52 |
Comparative material |
[0078] As expressed in Table 3, when the final annealing temperature (1step) is 850 to 1150
°C, the particle diameter of the grain of the final product is shown to be 20 to 1000
µm, and the ratio is shown to be equal to or greater than 50 %, and accordingly, the
magnetic domain size is shown to be less than the thickness of the steel sheet, thereby
indicating an excellent iron loss characteristic. When the decarburization-annealing
temperature is less than 850 °C, the magnetic domain size is shown to be very small,
and the reason that the magnetism characteristic is deteriorated is that the fraction
of the Goss orientation among the grains is equal to or less than 50 %. On the contrary,
when the same is greater than 1150 °C, the particle diameter of the grain becomes
coarse, and the size of the magnetic domain is greater than the thickness of the steel
sheet, so the iron loss is not improved.
[0079] While this invention has been described in connection with what is presently considered
to be practical exemplary embodiments, it is to be understood that the invention is
not limited to the disclosed embodiments, but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within the spirit and scope
of the appended claims. Therefore, the embodiments described above are only examples
and should not be construed as being limitative in any respects.
1. A method for manufacturing an oriented electrical steel sheet, comprising:
providing a slab including, as wt%, Si at equal to or less than 4.0 % excluding 0
%, C at 0.001 % to 0.4 %, and Mn at 0.001 to 2.0 %, and including a balance including
Fe and inevitably mixed and input impurities and optionally including Al at equal
to or less than 0.01 wt% excluding 0 wt%;
reheating the slab;
manufacturing a hot steel sheet by hot-rolling the slab;
performing hot-rolled steel sheet annealing to the hot steel sheet;
primarily cold-rolling the hot-rolled steel sheet annealed hot steel sheet;
decarburization-annealing the cold-rolled steel sheet;
secondarily cold-rolling the decarburization-annealed steel sheet; and
finally annealing the cold-rolled steel sheet,
wherein in the step of finally annealing the cold-rolled steel sheet includes a first
step for performing the same in an atmosphere with the dew point temperature of 10
°C to 70 °C at the temperature of 850 °C to 1150 °C, and a second step for performing
the same in a mixed gas atmosphere including hydrogen and nitrogen with a dew point
temperature that is equal to or less than 10 °C at a temperature of 900 °C to 1200
°C,
wherein the first step is performed for equal to or less than 300 seconds, and the
second step is performed for 60 seconds to 300 seconds.
2. The method of claim 1, wherein
the slab includes Si at equal to or less than 1 wt% excluding 0 wt%.
3. The method of claim 1, wherein
reduction rates in the primarily cold-rolling and the secondarily cold-rolling are
respectively 50 % to 70 %.
4. The method of claim 1, wherein
the decarburization-annealing of the cold-rolled steel sheet and the secondarily cold-rolling
of the decarburization-annealed steel sheet are repeated at least twice.
5. The method of claim 1, wherein
the decarburization-annealing is performed in an atmosphere including hydrogen with
a dew point temperature of equal to or greater than 0 °C at a temperature of 800 °C
to 1150 °C.
6. The method of claim 1, wherein
the finally annealing is continuously performed after the cold-rolling.
7. An oriented electrical steel sheet comprising,
as wt%, Si at equal to or less than 4.0 % excluding 0 %, C at equal to or less than
0.003 % excluding 0 %, and Mn at 0.001 to 2.0 %, and a balance including Fe and an
impurity that is inevitably mixed and input and optionally comprising Al at equal
to or less than 0.01 wt% excluding 0 wt%,
wherein a size 2L of a magnetic domain existing in a grain is less than a thickness
(D) of a steel sheet, and
wherein a volumetric fraction of a grain with a particle diameter of 20 µm to 1000
µm is equal to or greater than 50 %.
8. The oriented electrical steel sheet of claim 7, wherein
Si is included to be equal to or less than 1.0 wt% excluding 0 wt%.
9. The oriented electrical steel sheet of claim 7, wherein
a size 2L of a magnetic domain existing in a grain is 10 to 500 µm.
10. The oriented electrical steel sheet of claim 7, wherein
a volumetric fraction of a grain with an orientation that is within 15 degrees from
an orientation {110}<001> is equal to or greater than 50 %.
1. Verfahren zum Herstellen eines orientierten Elektrostahlblechs, umfassend:
Bereitstellen einer Bramme, die, in Gew.-%, Si zu kleiner gleich 4,0%, ausschließlich
0 %, C zu 0,001 % bis 0,4 % und Mn zu 0,001 bis 2,0 % enthält und einen Rest enthält,
der Fe und unvermeidbar eingemischte und eingetragene Verunreinigungen enthält, und
gegebenenfalls Al zu kleiner gleich 0,01 Gew.-%, ausschließlich 0 Gew.-% enthält;
Nachwärmen der Bramme;
Herstellen eines warmen Stahlblechs durch Warmwalzen der Bramme;
Durchführen eines Warmwalzstahlblech-Glühens an dem warmen Stahlblech;
primäres Kaltwalzen des Warmwalzstahlblech-Glühen unterzogenen warmen Stahlblechs;
Entkohlungsglühen des kaltgewalzten Stahlblechs;
sekundäres Kaltwalzen des Entkohlungsglühen unterzogenen Stahlblechs; und
Endglühen des kaltgewalzten Stahlblechs,
wobei der Schritt zum Endglühen des kaltgewalzten Stahlblechs einen ersten Schritt
zum Durchführen desselben in einer Atmosphäre mit der Taupunkttemperatur von 10 °C
bis 70 °C bei der Temperatur von 850 °C bis 1150 °C und einen zweiten Schritt zum
Durchführen desselben in einer gemischten Wasserstoff und Stickstoff enthaltenden
Gasatmosphäre mit einer Taupunkttemperatur, die kleiner gleich 10 °C ist, bei einer
Temperatur von 900 °C bis 1200 °C beinhaltet,
wobei der erste Schritt für kleiner gleich 300 Sekunden durchgeführt wird und der
zweite Schritt für 60 Sekunden bis 300 Sekunden durchgeführt wird.
2. Verfahren nach Anspruch 1, wobei
die Bramme Si zu kleiner gleich 1°Gew.-%, ausschließlich 0 Gew.-%, enthält.
3. Verfahren nach Anspruch 1, wobei
Reduktionsraten beim primären Kaltwalzen und beim sekundären Kaltwalzen jeweils 50
% bis 70 % betragen.
4. Verfahren nach Anspruch 1, wobei
das Entkohlungsglühen des kaltgewalzten Stahlblechs und das sekundäre Kaltwalzen des
Entkohlungsglühen unterzogenen Stahlblechs mindestens zweimal wiederholt werden.
5. Verfahren nach Anspruch 1, wobei
das Entkohlungsglühen in einer Wasserstoff enthaltenden Atmosphäre mit einer Taupunkttemperatur
von kleiner gleich 0 °C bei einer Temperatur von 800 °C bis 1150 °C durchgeführt wird.
6. Verfahren nach Anspruch 1, wobei
das Endglühen kontinuierlich nach dem Kaltwalzen durchgeführt wird.
7. Orientiertes Elektrostahlblech, umfassend:
in Gew.-%, Si zu kleiner gleich 4,0%, ausschließlich 0 %, C zu kleiner gleich 0,003
%, ausschließlich 0 %, und Mn zu 0,001 bis 2,0 % und einen Rest, der Fe und eine Verunreinigung
enthält, die unvermeidbar eingemischt und eingetragen wird, und gegebenenfalls umfassend
Al zu kleiner gleich 0,01 Gew.-%, ausschließlich 0 Gew.-%,
wobei eine Größe 2L eines Weiss-Bezirks, der in einem Korn vorhanden ist, kleiner
als eine Dicke (D) eines Stahlblechs ist, und
wobei ein Volumenanteil eines Korns mit einem Partikeldurchmesser von 20 µm bis 1000
µm größer gleich 50 % ist.
8. Orientiertes Elektrostahlblech nach Anspruch 7, wobei
Si zu kleiner gleich 1,0 Gew.-%, ausschließlich 0 Gew.-%, enthalten ist.
9. Orientiertes Elektrostahlblech nach Anspruch 7, wobei
eine Größe 2L eines Weiss-Bezirks, der in einem Korn vorhanden ist, 10 bis 500 µm
beträgt.
10. Orientiertes Elektrostahlblech nach Anspruch 7, wobei
ein Volumenanteil eines Korns mit einer Orientierung, die innerhalb von 15 Grad von
einer Orientierung {110}<001> liegt, größer gleich 50 % ist.
1. Procédé de fabrication d'une tôle d'acier magnétique orientée, comprenant :
la fourniture d'une brame incluant, en % en poids, du Si inférieur ou égal à 4,0 %
à l'exclusion de 0 %, du C à 0,001 % à 0,4 %, et du Mn à 0,001 à 2,0 %, et incluant
un reste incluant du Fe et des impuretés d'entrée et mixtes inévitables et incluant
facultativement de l'Al inférieur ou égal à 0,01 % en poids à l'exclusion de 0 % en
poids ;
le réchauffage de la brame ;
la fabrication d'une tôle d'acier à chaud par laminage à chaud de la brame ;
la réalisation d'un recuit de tôle d'acier laminée à chaud sur la tôle d'acier à chaud
;
le laminage à froid principal de la tôle d'acier à chaud recuit en tôle d'acier laminée
à chaud ;
le recuit de décarburation de la tôle d'acier laminée à froid ;
le laminage à froid secondaire de la tôle d'acier ayant subi un recuit de décarburation
; et
le recuit final de la tôle d'acier laminée à froid,
dans lequel l'étape de recuit final de la tôle d'acier laminée à froid inclut une
première étape de réalisation de celui-ci dans une atmosphère avec la température
de point de rosée de 10 °C à 70 °C à la température de 850 °C à 1150 °C, et une seconde
étape de réalisation de celui-ci dans une atmosphère de gaz mixte incluant de l'hydrogène
et de l'azote avec une température de point de rosée qui est inférieure ou égale à
10 °C à une température de 900 °C à 1200 °C,
dans lequel la première étape est réalisée pendant une durée inférieure ou égale à
300 secondes, et la seconde étape est réalisée pendant 60 secondes à 300 secondes.
2. Procédé selon la revendication 1, dans lequel
la brame inclut du Si inférieur ou égal à 1 % en poids à l'exclusion de 0 % en poids.
3. Procédé selon la revendication 1, dans lequel
des taux de réduction dans le laminage à froid principal et le laminage à froid secondaire
sont respectivement de 50 % à 70 %.
4. Procédé selon la revendication 1, dans lequel
le recuit de décarburation de la tôle d'acier laminée à froid et le laminage à froid
secondaire de la tôle d'acier ayant subi un recuit de décarburation sont répétés au
moins deux fois.
5. Procédé selon la revendication 1, dans lequel
le recuit de décarburation est réalisé dans une atmosphère incluant de l'hydrogène
avec une température de point de rosée supérieure ou égale à 0 °C à une température
de 800 °C à 1150 °C.
6. Procédé selon la revendication 1, dans lequel
le recuit final est réalisé en continu après le laminage à froid.
7. Tôle d'acier magnétique orientée comprenant,
en % en poids, du Si inférieur ou égal à 4,0 % à l'exclusion de 0 %, du C inférieur
ou égal à 0,003 % à l'exclusion de 0 %, et du Mn à 0,001 à 2,0 %, et un reste incluant
du Fe et une impureté d'entrée et mixte inévitable et incluant facultativement de
l'Al inférieur ou égal à 0,01 % en poids à l'exclusion de 0 % en poids,
dans laquelle une taille 2L d'un domaine magnétique existant dans un grain est inférieure
à une épaisseur (D) d'une tôle d'acier, et
dans laquelle une fraction volumétrique d'un grain avec un diamètre de particule de
20 µm à 1000 µm est supérieure ou égale à 50 %.
8. Tôle d'acier magnétique orientée selon la revendication 7, dans laquelle
du Si est inclus pour être inférieur ou égal à 1,0 % en poids à l'exclusion de 0 %
en poids.
9. Tôle d'acier magnétique orientée selon la revendication 7, dans laquelle
une taille 2L d'un domaine magnétique existant dans un grain est de 10 à 500 µm.
10. Tôle d'acier magnétique orientée selon la revendication 7, dans laquelle
une fraction volumétrique d'un grain avec une orientation qui est à moins de 15 degrés
d'une orientation {110}<001> est supérieure ou égale à 50 %.