[0001]The present invention relates to a method for manufacturing a grain-oriented
electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2019-005202, filed
10 January 16, 2019, the content of which is incorporated herein by reference.
[Background Art]
[0002]
Grain-oriented electrical steel sheets are soft magnetic material and are used for
iron cores of transformers and other electric devices. Grain-oriented electrical steel
15 sheets are steel sheets which contain about 7 mass% or less of Si and include grains
highly aligned in the {110} <001> orientation in the Miller index.
[0003]
As the magnetic characteristics of the grain-oriented electrical steel sheets used
for the above applications, it is required that magnetic flux density (represented by a
20 magnetic flux density B8 value when a magnetic field of 800 A/m is applied) is high and
iron loss (represented by energy loss W17/50 when magnetization has been performed at a
maximum magnetic flux density 1.7 T with an alternating current (AC) at a frequency of
50Hz) is low. Particularly, in recent years, there is an increasing demand for reducing
electric power loss from the viewpoint of energy saving.
25 [0004]
2
The iron loss of electrical steel sheets is determined using a sum of the eddy
current loss which depends on the specific resistance, the sheet thickness, the size of the
magnetic domain, and the like and the hysteresis loss which depends on the crystal
orientation, the smoothness of the surface, and the like. Therefore, in order to reduce
the iron loss, it is necessary to reduce one or both of 5 the eddy current loss and the
hysteresis loss.
[0005]
As a method for reducing eddy current loss, a method for increasing the content
of Si having a high electric resistance, a method for reducing a sheet thickness of a steel
10 sheet, a method for subdividing a magnetic domain, and the like are known.
Furthermore, as a method for reducing hysteresis loss, a method for increasing a
magnetic flux density B8 by increasing a degree of alignment of an easy magnetization
orientation of a crystal orientation and a method for removing a glass coating made of an
oxide on the surface of the steel sheet to smooth the surface and eliminating a pinning
15 effect in which the movement of a magnetic domain is hindered are known.
[0006]
In these method for reducing iron loss, as a method for smoothing a surface of a
steel sheet, for example, Patent Documents 1 to 5 describe a method in which
decarburization annealing is performed in an atmosphere gas with an oxidation degree in
20 which Fe-based oxides (Fe2SiO4, FeO, and the like) are not generated and a glass coating
(a forsterite coating) is not formed using an annealing separator which contains alumina
as a main component as an annealing separator arranged between steel sheets.
[0007]
Although a method for reducing a sheet thickness through rolling is known as a
25 method for reducing a sheet thickness of a steel sheet, if a thin sheet thickness is
3
provided, there is a problem in which secondary recrystallization in final annealing is
unstable and it is difficult to stably manufacture a product having excellent magnetic
characteristics.
[0008]
In order to solve this problem, for example, 5 Patent Document 6 proposes a
method for manufacturing a grain-oriented electrical steel sheet in which a cold-rolled
steel sheet having a sheet thickness d mm of 0.10 to 0.25 mm is subjected to
decarburization annealing and nitriding and AlN is utilized as an inhibitor and a thin
grain-oriented electrical steel sheet is stably manufactured by setting acid-soluble Al to
10 0.015 to 0.050%, making the nitrogen content [N] of a steel sheet satisfy
13d−25≥[N]≥46d−1030 using nitric acid, and strengthening an inhibitor.
[0009]
However, the method of Patent Document 6 has a problem in which the coating
properties are poor because a large amount of nitrogen is released after a glass coating is
15 formed.
[Prior Art Document]
[Patent Document]
[0010]
[Patent Document 1]
20 Japanese Unexamined Patent Application, First Publication No. H07-118750
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. H07-278668
[Patent Document 3]
Japanese Unexamined Patent Application, First Publication No. H07-278669
25 [Patent Document 4]
4
Japanese Unexamined Patent Application, First Publication No. 2003-003213
[Patent Document 5]
Published Japanese Translation No. 2011-518253 of the PCT International
Publication
5 [Patent Document 6]
Japanese Unexamined Patent Application, First Publication No. H05-302122
[Summary of the Invention]
[Problems to be Solved by the Invention]
[0011]
10 Although it is assumed that the problems of the method of Patent Document 6
can be solved by incorporating a method for smoothing a surface of a steel sheet without
forming a glass coating (a forsterite coating) as shown in Patent Documents 1 to 5, in the
method for smoothing a surface of a steel sheet, it is difficult to secure a good
decarburization property and an inferior decarburization property is provided when the Al
15 content increases. Therefore, if the Al content increases to stably obtain a secondary
recrystallization structure in a thin electrical steel sheet, it is difficult to achieve both
decarburization property and excellent magnetic characteristics.
[0012]
Thus, in order to stably obtain a good secondary recrystallization structure, in a
20 grain-oriented electrical steel sheet containing a required amount of Al, the problems of
the present invention is to reduce iron loss by reducing a sheet thickness, to secure a good
decarburization property, to improve magnetic characteristics (to reduce iron loss and to
secure a high magnetic flux density) and an object of the present invention is to provide a
method for manufacturing a grain-oriented electrical steel sheet in which the problems
25 are solved.
5
[Means for Solving the Problem]
[0013]
In order to solve the above problems, the inventors of the present invention have
investigated a relationship between the Al content and a sheet thickness to stably obtain
secondary recrystallization and secure a good decarburization p 5 roperty in a thin grainoriented
electrical steel sheet manufactured using a method for smoothing a surface of
the steel sheet.
[0014]
As a result, it was found that, if a mass ratio: Sol. Al/N between acid-soluble Al
10 (Sol. Al) and N in a steel slab which is used as a material is controlled within an
appropriate range in accordance with a product sheet thickness, that is, a final sheet
thickness d after cold rolling, it is possible to secure a good decarburization property in
decarburization annealing, and if the N content in the steel sheet which has been
subjected to nitriding is controlled within an appropriate range, it is possible to obtain
15 good secondary recrystallization in final annealing. This point will be described later.
[0015]
The present invention was made on the basis of the above findings, and the gist
of the present invention is as follows.
[0016]
20 (1) A method for manufacturing a grain-oriented electrical steel sheet according
to an aspect of the present invention is a method for manufacturing a grain-oriented
electrical steel sheet, including: heating a steel slab which contains, in terms of mass%,
C: 0.100% or less; Si: 0.80 to 7.00%; Mn: 0.05 to 1.00%; Sol. Al: 0.0100 to 0.0700%; N:
0.0040 to 0.0120%; Seq=S+0.406×Se: 0.0030 to 0.0150%; Cr: 0 to 0.30%; Cu: 0 to
25 0.40%; Sn: 0 to 0.30%; Sb: 0 to 0.30%; P: 0 to 0.50%; B: 0 to 0.0080%; Bi: 0 to
6
0.0100%; Ni: 0 to 1.00%, and the remainder: Fe and impurities to lower than 1250 °C
and subjecting the steel slab to hot rolling to obtain a hot-rolled steel sheet; performing
hot-band annealing on the hot-rolled steel sheet; pickling the hot-rolled steel sheet which
has been subjected to the hot-band annealing; subjecting the hot-rolled steel sheet which
has been subjected to the pickling 5 to cold rolling to obtain a cold-rolled steel sheet having
a final sheet thickness d of 0.15 to 0.23 mm; performing a decarburization nitriding
treatment including decarburization annealing and nitriding on the cold-rolled steel sheet;
performing final annealing on the cold-rolled steel sheet which has been subjected to the
decarburization nitriding treatment; and a coating liquid for insulation coating formation
10 to the cold-rolled steel sheet which has been subjected to the final annealing and baking
the coating liquid, wherein Sol. Al/N which is a mass ratio between Sol. Al and N in the
steel slab and the final sheet thickness d satisfy the following expression (i), the N
content of the cold-rolled steel sheet which has been subjected to the decarburization
nitriding treatment is 40 to 1000 ppm, and a decarburization annealing temperature in the
15 decarburization annealing is lower than 1000 °C: −4.17×d+3.63≤Sol.
Al/N≤−3.10×d+4.84 (i).
(2) In the method for manufacturing a grain-oriented electrical steel sheet
according to (1) above, the steel slab may contain, in terms of mass%, one or more of Cr:
0.02 to 0.30%; Cu: 0.10 to 0.40%; Sn: 0.02 to 0.30%; Sb: 0.02 to 0.30%; P: 0.02 to
20 0.50%; B: 0.0010 to 0.0080%; Bi: 0.0005 to 0.0100%; and Ni: 0.02 to 1.00%.
[Effects of the Invention]
[0017]
According to the present invention, it is possible to provide a method for stably
manufacturing a grain-oriented electrical steel sheet having a sheet thickness of 0.15 to
25 0.23 mm and having excellent magnetic characteristics (low iron loss and a high
7
magnetic flux density).
[Brief Description of Drawings]
[0018]
Fig. 1 is an example of a structure of a grain-oriented electrical steel sheet
obtained through a manufacturing 5 method in which a slab heating temperature is 1250 °C
and a decarburization annealing temperature is 800 °C.
Fig. 2 is an example of a structure of a grain-oriented electrical steel sheet
obtained through a manufacturing method in which a slab heating temperature is 1150 °C
and a decarburization annealing temperature is 800 °C.
10 [Embodiments for implementing the Invention]
[0019]
A method for manufacturing a grain-oriented electrical steel sheet according to
an embodiment of the present invention (hereinafter may be referred to as a
“manufacturing method according to this embodiment”)
15 includes: heating a steel slab which contains, in terms of mass%, C: 0.100% or
less; Si: 0.80 to 7.00%; Mn: 0.05 to 1.00%; acid-soluble Al (Sol. Al): 0.0100 to 0.0700%;
N: 0.0040 to 0.0120%; and Seq=S+0.406×Se: 0.0030 to 0.0150%, further optionally, Cr:
0.30% or less; Cu: 0.40% or less; Sn: 0.30% or less; Sb: 0.30% or less; P: 0.50% or less;
B: 0.0080% or less; Bi: 0.0100% or less; Ni: 1.00% or less, and the remainder: Fe and
20 impurities to lower than 1250 °C and subjecting the steel slab to hot rolling to obtain a
hot-rolled steel sheet; performing hot-band annealing on the hot-rolled steel sheet;
pickling and performing cold rolling on the hot-rolled steel sheet to obtain a cold-rolled
steel sheet having a final sheet thickness of 0.15 to 0.23 mm; performing a
decarburization nitriding treatment including decarburization annealing and nitriding on
25 the cold-rolled steel sheet; performing final annealing on the cold-rolled steel sheet; and
8
then applying and baking a coating liquid for insulation coating formation to the coldrolled
steel sheet which has been subjected to the final annealing, in which
(i) a mass ratio: Sol. Al/N between acid-soluble Al (Sol. Al) and N in the steel
slab and the final sheet thickness d (mm) satisfy the following expression (1);
(ii) the N content of the cold-5 rolled steel sheet which has been subjected to the
decarburization nitriding treatment is 40 to 1000 ppm; and
(iii) a decarburization annealing temperature in the decarburization annealing is
lower than 1000 °C:
−4.17×d+3.63≤Sol. Al/N≤−3.10×d+4.84 (1)
10 [0020]
The manufacturing method according to this embodiment will be described
below. Although it is desirable that the manufacturing method according to this
embodiment be applied to a method for manufacturing a grain-oriented electrical steel
sheet which does not have a forsterite coating, even if the manufacturing method
15 according to this embodiment is applied to a method for manufacturing a grain-oriented
electrical steel sheet which has a forsterite coating, a significant effect can be obtained.
[0021]
First, the reason for limiting a component composition of a steel slab which is
used as a material in the manufacturing method according to this embodiment will be
20 described. Hereinafter, % means mass%.
[0022]

C: 0.100% or less
C is an element which is effective for controlling a primary recrystallization
25 structure, but adversely affects the magnetic characteristics, and thus is removed through
9
decarburization annealing before final annealing. If the C content in the steel slab
exceeds 0.100%, a decarburization annealing time increases and the productivity
deteriorates. For this reason, the C content is 0.100% or less. The C content is
preferably 0.070% or less, and more preferably 0.060% or less.
5 [0023]
Although a lower limit of the C content includes 0%, if the C content is reduced
to less than 0.0001%, the manufacturing costs significantly increases. Thus, in view of
a practical steel sheet, 0.0001% is a practical lower limit of the C content. A lower limit
of the C content may be 0.0010%, 0.0020%, 0.0022%, or 0.0030%.
10 [0024]
Si: 0.80 to 7.00%
Si is an element which improves the iron loss characteristics of the grainoriented
electrical steel sheet by increasing electric resistance of the steel sheet. If the
Si content is less than 0.80%, γ transformation occurs during final annealing and the
15 alignment of a preferable crystal orientation of the steel sheet is impaired. Thus, the Si
content is 0.80% or more. The Si content is preferably 1.80% or more, 1.90% or more,
2.00% or more, and more preferably 2.50% or more.
[0025]
On the other hand, if the Si content exceeds 7.00%, the workability deteriorates
20 and cracks occur during rolling. For this reason, the Si content is 7.00% or less. The
Si content is preferably 4.50% or less, and more preferably 4.00% or less.
[0026]
Mn: 0.05 to 1.00%
Mn is an element which prevents cracks during hot rolling and form MnS and/or
25 MnSe functioning as an inhibitor by binding with S and/or Se. If Mn content is less
10
than 0.05%, a sufficient effect is not exhibited. Thus, the Mn content is 0.05% or more.
The Mn content is preferably 0.07% or more, and more preferably 0.09% or more.
[0027]
On the other hand, if the Mn content exceeds 1.00%, a non-uniform precipitation
and dispersion of MnS and/or MnSe 5 is provided, the required secondary recrystallization
structure cannot be obtained, and the magnetic flux density deteriorates. For this
reason, the Mn content is 1.00% or less. The Mn content is preferably 0.80% or less,
and more preferably 0.60% or less or 0.55% or less.
[0028]
10 Acid-soluble Al (Sol. Al): 0.0100 to 0.0700%
Acid-soluble Al (Sol. Al) is an element which binds with N to generate (Al, Si)
N functioning as an inhibitor. If the Sol. Al content is less than 0.0100%, a sufficient
effect is not exhibited and a sufficient secondary recrystallization does not proceed.
Thus, the Sol. Al content is 0.0100% or more. The Sol. Al content is preferably
15 0.0150% or more, and more preferably 0.0200% or more or 0.0220% or more.
[0029]
On the other hand, if the Sol. Al content exceeds 0.0700%, a non-uniform
precipitation and dispersion of (Al, Si) N is provided, the required secondary
recrystallization structure cannot be obtained, and a magnetic flux density decreases.
20 For this reason, the acid-soluble Al (Sol. Al) content is 0.0700% or less. The Sol. Al
content is preferably 0.0550% or less, and more preferably 0.0500% or less or 0.0400%
or less.
[0030]
N: 0.0040 to 0.0120%
25 N is an element which binds with Al to form AlN functioning as an inhibitor, but
11
forms blisters (voids) in the steel sheet during cold rolling. If the N content is less than
0.0040%, an insufficient formation of AlN is provided. Thus, the N content is 0.0040%
or more. The N content is preferably 0.0050% or more or 0.0060% or more, and more
preferably 0.0070% or more.
5 [0031]
On the other hand, if the N content exceeds 0.0120%, there is a concern
concerning the generation of blisters (voids) in the steel sheet during cold rolling. Thus,
the N content is 0.0120% or less. The N content is preferably 0.0100% or less, and
more preferably 0.0090% or less.
10 [0032]
Seq=S+0.406×Se: 0.0030 to 0.0150%
S and Se are elements which bind with Mn to form MnS and/or MnSe
functioning as an inhibitor. A total content of S and Se is defined using
Seq=S+0.406×Se in consideration of an atomic weight ratio of S and Se.
15 [0033]
If Seq is less than 0.0030%, a sufficient effect is not exhibited. Thus, Seq is
0.0030% or more. Seq is preferably 0.0050% or more, and more preferably 0.0070% or
more. On the other hand, if Seq exceeds 0.0150%, a non-uniform precipitation and
dispersion of MnS and/or MnSe is provided, the required secondary recrystallization
20 structure cannot be obtained, and a magnetic flux density decreases. For this reason,
Seq is 0.0150% or less. Seq is preferably 0.0130% or less, and more preferably
0.0110% or less.
[0034]
In a chemical composition of a steel slab which is used as a material in the
25 manufacturing method according to this embodiment, the remainder other than the above
12
elements is Fe and impurities, but may contain one or more of Cr: 0.30% or less; Cu:
0.40% or less; Sn: 0.30% or less; Sb: 0.30% or less; P: 0.50% or less; B: 0.0080% or
less; Bi: 0.0100% or less, and Ni: 1.00% or less as long as the characteristics of the
electrical steel sheet are not impaired. Here, even if the steel slab does not contain these
components, a good effect ca 5 n be obtained through the manufacturing method according
to this embodiment. Therefore, the lower limit of the contents of these components are
each 0%.
[0035]
Cr: 0 to 0.30%
10 Cr is an element which contributes to the improvement of an oxide layer
generated during decarburization annealing of the steel sheet, increases the intrinsic
resistance of the steel sheet, and contributes to the reduction of iron loss. If the Cr
content exceeds 0.30%, the effect is saturated. Thus, the Cr content is 0.30% or less.
The Cr content is preferably 0.25% or less. Although a lower limit of the Cr content
15 includes 0%, Cr content is preferably 0.02% or more from the viewpoint of surely
obtaining the effect of the inclusion.
[0036]
Cu: 0 to 0.40%
Cu is an element which binds with S and/or Se to form a precipitate functioning
20 as an inhibitor, increases the intrinsic resistance of the steel sheet, and contributes to the
improvement of the magnetic characteristics. When this effect is obtained, the Cu
content is preferably 0.10% or more.
On the other hand, if the Cu content exceeds 0.40%, a non-uniform dispersion of
the precipitate is provided and the effect of reducing iron loss is saturated. Thus, the Cu
25 content is 0.40% or less. The Cu content is preferably 0.25% or less.
13
[0037]
Sn: 0 to 0.30%
Sb: 0 to 0.30%
Sn and Sb are elements which increase intrinsic resistance, contributes to the
reduction of iron loss, and segregates a 5 t the grain boundaries to prevent Al from being
oxidized due to moisture released due to an annealing separator during final annealing
(inhibitor intensities differ in accordance with coil positions due to this oxidation, a
difference occurs between Goss orientation alignments of the texture, and the magnetic
characteristics fluctuate in accordance with coil position).
10 [0038]
If the contents of each of Sn and Sb exceed 0.30%, the effect of containing these
is saturated. Thus, each of the Sn content and the Sb content are 0.30% or less. The
contents of both of these elements are preferably 0.25% or less. Although lower limits
of the Sn content and the Sb content include 0%, the contents of each of these elements
15 are preferably 0.02% or more from the viewpoint of surely obtaining the effect.
[0039]
P: 0 to 0.50%
P is an element which increases a degree of Goss orientation alignment of a
texture and intrinsic resistance of the steel sheet and contributes to the reduction of iron
20 loss. If the P content exceeds 0.50%, the effect is saturated and the rollability
deteriorates. Thus, the P content is 0.50% or less. The P content is preferably 0.35%
or less. Although a lower limit of the P content includes 0%, the P content is preferably
0.02% or more from the viewpoint of surely obtaining the effect.
[0040]
25 B: 0 to 0.0080%
14
B is an element which binds with N and precipitates as complex-precipitation
with MnS or MnSe to form BN functioning as an inhibitor and which contributes to the
reduction of iron loss by increasing a degree of Goss orientation alignment of a texture.
When this effect is obtained, the B content is preferably 0.0010% or more.
On the other hand, if th 5 e B content exceeds 0.0080%, a non-uniform
precipitation and dispersion of BN is provided, the required secondary recrystallization
structure cannot be obtained, and a magnetic flux density decreases. For this reason, the
B content is 0.0080% or less. The B content is preferably 0.0060% or less, and more
preferably 0.0040% or less.
10 [0041]
Bi: 0 to 0.0100%
Bi is an element which stabilizes precipitates such as sulfides, strengthens a
function of an inhibitor, increases a degree of Goss orientation alignment of a texture,
and contributes to the reduction of iron loss. If the Bi content exceeds 0.0100%, the
15 effect is saturated. Thus, the Bi content is 0.0100% or less. The Bi content is
preferably 0.0070% or less. Although a lower limit of the Bi content includes 0%, the
Bi content is preferably 0.0005% or more from the viewpoint of surely obtaining the
effect of the inclusion.
[0042]
20 Ni: 0 to 1.00%
Ni is an element which increases intrinsic resistance of the steel sheet,
contributes to the reduction of iron loss, controls a metal structure of the hot-rolled steel
sheet, and contributes to the improvement of the magnetic characteristics. If the Ni
content exceeds 1.00%, a secondary recrystallization proceeds unstably. Thus, the Ni
25 content is 1.00% or less. The Ni content is preferably 0.25% or less. Although a
15
lower limit of the Ni content includes 0%, the Ni content is preferably 0.02% or more
from the viewpoint of surely obtaining the effect of the inclusion.
[0043]
In the steel slab which is used as a material in the manufacturing method
according to this embodi 5 ment, the remainder other than the above elements is Fe and
impurities. The impurities are elements which are mixed in from a steel raw material
and/or in a steelmaking process and are acceptable elements as long as the characteristics
of the electrical steel sheet are not impaired. For example, Mg, Ca, and the like are
allowed as long as the characteristics of the electrical steel sheet are not impaired.
10 [0044]
A relationship between the mass ratio (a ratio of content in mass%): Sol. Al/N
between acid-soluble Al (Sol. Al) and, N and the final sheet thickness d of the steel sheet
will be described below.
[0045]
15 Sol. Al/N: the following expression (1) is satisfied:
−4.17×d+3.63≤Sol. Al/N≤−3.10×d+4.84 (1).
In the manufacturing method according to this embodiment, in the steel slab
which is used as a material, it is important that Sol. Al/N is controlled so that the
foregoing expression (1) is satisfied in accordance with the final sheet thickness of the
20 grain-oriented electrical steel sheet to be manufactured.
[0046]
The inventors of the present invention evaluated the magnetic flux density B8 by
changing Sol. Al/N of the steel slab which is used as a material in the manufacturing
method according to this embodiment and preparing electrical steel sheets having
25 different final sheet thicknesses with each Sol. Al/N.
16
[0047]
As a result, it is found that a magnetic flux density B8 of 1.930 T or more is
obtained in a region in which Sol. Al/N satisfies the forgoing expression (1).
[0048]
On the other hand, if Sol. Al/N exceeds 5 “−3.10×d+4.84,” it is not possible to
stably obtain a magnetic flux density B8 of 1.930 T or more. For this reason, Sol. Al/N
is “−3.10×d+4.84” or less.
[0049]
The reason for this is because, if Sol. Al/N exceeds “−3.10×d+4.84,” a coarse
10 primary recrystallization inhibitor is provided, a non-uniform dispersion thereof is
provided, a non-uniform primary recrystallization structure after decarburization
annealing is provided, and good secondary recrystallization cannot be obtained on the
entire surface of the steel sheet, and in decarburization annealing, in order to reduce the C
content in the steel sheet to 25 ppm or less, it is necessary to increase an annealing
15 temperature, and as a result, a grain size of primary recrystallization increases and it is
not possible to secure a good driving force for secondary recrystallization.
[0050]
On the other hand, it is found that, if Sol. Al/N is less than “−4.17×d+3.63,” a
magnetic flux density B8 of 1.930 T or more cannot be obtained. For this reason, Sol.
20 Al/N is “−4.17×d+3.63” or more.
[0051]
The reason for this is because, if Sol. Al/N is less than “−4.17×d+3.63,” crystals
in orientation other than the Goss orientation develop in secondary recrystallization (a
degree of Goss orientation alignment decreases), a magnetic flux density is reduced, and
25 iron loss increases.
17
[0052]
The process conditions of the manufacturing method according to this
embodiment will be described below.
[0053]
5
Steel slab
A steel slab which is used as a material in the manufacturing method according
to this embodiment is obtained by subjecting molten steel melted using a converter
furnace, an electric furnace, or the like to vacuum degassing as necessary and then
10 subjecting the steel to continuous casting or blooming rolling after ingot casting. The
steel slab is usually cast to have a thickness of 150 to 350 mm, preferably 220 to 280
mm, but may be a thin slab with a thickness of 30 to 70 mm. In the case of a thin slab,
there is an advantage that it is not necessary to perform a rough process to have an
intermediate thickness when a hot-rolled steel sheet is manufactured.
15 [0054]
Hot rolling
Heating temperature: lower than 1250ºC
If a heating temperature of the steel slab to be subjected to hot rolling is 1250 °C
or higher, an amount of melt scale may increase and it may be necessary to further
20 provide a heating furnace dedicated to the implementation of the manufacturing method
according to this embodiment to a manufacturing line in some cases.
[0055]
Also, when the heating temperature is 1250 °C or higher, the grain growth
properties in the primary recrystallization annealing significantly deteriorate and good
25 secondary recrystallization cannot be achieved. This is because of the use of acid18
soluble Al as an inhibitor in this embodiment. After primary recrystallization in
decarburization annealing which will be described later, it is essential to keep an average
crystal grain size of the steel sheet within the range of 20 to 23 μm to secure the magnetic
characteristics of the grain-oriented electrical steel sheet. The slab heating temperature
before hot rolling has a great influence on the average 5 crystal grain size after the primary
recrystallization. When the slab heating temperature is 1250 °C or higher, a large
number of fine AlN precipitates on the hot-rolled steel sheet which has been subjected to
hot rolling, which hinders the growth of crystal grains. On the other hand, when the
slab heating temperature is lower than 1250 °C, it is possible to coarsen the AlN to be
10 precipitated, reduce the number thereof, and suppress the grain refinement due to AlN.
[0056]
Furthermore, when the heating temperature is 1250 °C or higher, MnS and/or
MnSe is fully dissolved and finely precipitated in the subsequent processes. This also
hinders grain growth like AlN.
15 [0057]
Fig. 1 is an example of a structure of a grain-oriented electrical steel sheet
obtained through a manufacturing method in which a slab heating temperature is 1250 °C
and a decarburization annealing temperature is 800 °C. Fig. 2 is an example of a
structure of a grain-oriented electrical steel sheet obtained through a manufacturing
20 method in which a slab heating temperature is 1150 °C and a decarburization annealing
temperature is 800 °C. Other manufacturing conditions of the grain-oriented electrical
steel sheets of Figs. 1 and 2 are the same.
When Figs. 1 and 2 are compared, a metal structure of the steel sheet of Fig. 1
having the slab the heating temperature of 1250 °C is clearly smaller than that of the steel
25 sheet of Fig. 2 having the slab the heating temperature of 1150 °C. It is presumed that a
19
difference between these steel sheets is caused by the inhibition of crystal grain growth
due to fine precipitates.
[0058]
Even if the heating temperature of the steel slab is higher than 1250 °C, it is
possible to obtain the above-described desired grain si 5 ze of the primary recrystallization
by increasing the decarburization annealing temperature (for example, making it higher
than 1000 °C). However, if the decarburization annealing temperature increases, a nonuniform
primary recrystallization structure is provided and good secondary
recrystallization cannot be obtained.
10 [0059]
For the above reasons, the heating temperature of the steel slab is set to lower
than 1250 °C. The heating temperature is preferably 1200 °C or lower, 1180 °C or
lower, or 1150 °C or lower. It is not necessary to particularly limit a lower limit of the
heating temperature of the steel slab and the conditions for carrying out normal hot
15 rolling may be appropriately adopted. For example, the steel slab may be heated to
1000 °C or higher, 1050 °C or higher, or 1100 °C or higher. The heated steel slab is
subjected to hot rolling. Hot rolling may be performed under known conditions and the
rolling conditions are not particularly limited.
[0060]
20 Hot-band annealing
The hot-rolled steel sheet is subjected to hot-band annealing so that a nonuniform
structure generated during hot rolling is made uniform as much as possible.
The annealing conditions may be any conditions as long as the non-uniform structure
generated during hot rolling can be made uniform as much as possible and are not
25 particularly limited to specific conditions.
20
[0061]
For example, if the hot-rolled steel sheet is heated to 1000 to 1150 °C (a first
stage temperature) to recrystallize and then annealed at 850 to 1100 °C (a second stage
temperature) lower than the first stage temperature, it is possible to eliminate the non-
5 uniform structure generated during hot rolling.
[0062]
In the case of this two-stage annealing, the first stage temperature has a great
influence on the behavior of an inhibitor. If the first stage temperature is too high, the
fine inhibitor is precipitated in a subsequent process and the decarburization annealing
10 temperature for obtaining the desired grain size of the primary recrystallization increases.
Thus, the first stage temperature is preferably 1150 °C or lower.
[0063]
If the first stage temperature is too low, insufficient recrystallization is provided
and the non-uniform structure generated during hot rolling cannot be made uniform.
15 Thus, the first stage temperature is preferably 1000 °C or higher, and more preferably
1120 °C or higher.
[0064]
As with the first stage temperature, if the second stage temperature is too high,
the fine inhibitor is precipitated in a subsequent process and the decarburization
20 annealing temperature for obtaining the desired grain size of the primary recrystallization
increases. For this reason, the second stage temperature is preferably 1100 °C or lower.
If the second stage temperature is too low, a γ phase is not generated and a hot-rolled
structure cannot be made uniform. Thus, the second stage temperature is preferably 850
°C or higher, and more preferably 900 °C or higher.
25 [0065]
21
Pickling and cold rolling
Final sheet thickness: 0.15 to 0.23 mm
A cold-rolled the steel sheet having a final sheet thickness of 0.15 to 0.23 mm is
obtained by performing pickling and then cold rolling on a hot-rolled steel sheet which
has been subjected to hot-band 5 annealing so that a non-uniform structure during hot
rolling has been eliminated. It is desirable that the cold rolling be a single cold rolling
process or two or more cold rolling processes having intermediate annealing performed
between the cold rolling processes.
[0066]
10 The cold rolling may be performed at room temperature or may be performed by
increasing the temperature of the steel sheet to a temperature higher than room
temperature, for example, about 200 °C (so-called warm rolling). The pickling may be
performed under normal conditions.
[0067]
15 If the final sheet thickness of the cold-rolled steel sheet is less than 0.15 mm,
rolling is not easy and secondary recrystallization tends to be unstable. For this reason,
the final sheet thickness of the cold-rolled steel sheet is 0.15 mm or more, and preferably
0.17 mm or more.
[0068]
20 On the other hand, if the final sheet thickness of the cold-rolled steel sheet
exceeds 0.23 mm, the secondary recrystallization is too stable and an angle difference
between the recrystallized grain orientation and the Goss orientation increases. For this
reason, the final sheet thickness of the cold-rolled steel sheet is 0.23 mm or less, and
preferably 0.21 mm or less.
25 [0069]
22
Decarburization annealing
In order to remove C contained in the cold-rolled steel sheet which has reached
the final sheet thickness, the cold-rolled steel sheet is subjected to decarburization
annealing in a wet hydrogen atmosphere. The wet hydrogen atmosphere, for example,
is a humidifying gas with a 5 dew point of 70 °C and is an atmosphere including a small
amount of hydrogen as a gas type. To be more specific, for example, annealing is
performed in a humidifying gas atmosphere with a dew point of 70 °C containing 10%
hydrogen.
As described above, when the temperature of the decarburization annealing is
10 too high, a non-uniform primary recrystallization structure is provided and good
secondary recrystallization cannot be obtained. For this reason, the decarburization
annealing temperature is set to lower than 1000 °C. A lower limit of the decarburization
annealing temperature may be appropriately selected within the range in which the
above-described effects can be obtained. For example, the decarburization annealing
15 temperature may be 750 °C or higher, 800 °C or higher, or 850 °C or higher. Although
the lower limit does not necessarily need to be set, if the decarburization annealing
temperature is lower than 700 °C, there is a concern that grain growth and
decarburization may not proceed sufficiently. Thus, the decarburization annealing
temperature is preferably 700 °C or higher.
20 Also, it is desirable that the decarburization annealing be performed by
controlling an annealing atmosphere in an oxidation degree at which an iron-based oxide
is not generated. For example, the oxidation degree of the annealing atmosphere is
preferably 0.01 or more and less than 0.15. The oxidation degree is an oxidation
potential represented by PH2O/PH2.
25 [0070]
23
If the oxidation degree is less than 0.01, a decarburization rate decreases and the
productivity deteriorates. On the other hand, if the oxidation degree is 0.15 or more,
inclusions are formed below the surface of the product steel sheet and iron loss increases.
A rate of temperature rise in a heating process is not particularly limited and may be, for
example, 50 °5 C/second or faster from the viewpoint of productivity.
[0071]
Nitriding
The cold-rolled steel sheet which has been subjected to the decarburization
annealing (hereinafter referred to as a “steel sheet”) is subjected to nitriding so that the N
10 content of the steel sheet is 40 to 1000 ppm. The nitriding is not limited to specific
nitriding. For example, the nitriding is performed in an atmosphere gas having a
nitriding ability such as ammonia.
[0072]
If the N content in the steel sheet which has been subjected to nitriding is less
15 than 40 ppm, a sufficient amount of AlN is not precipitated and AlN does not sufficiently
function as an inhibitor. In this case, since sufficient secondary recrystallization does
not proceed in the final annealing, the N content in the steel sheet which has been
subjected to nitriding is 40 ppm or more, and preferably 100 ppm or more.
[0073]
20 On the other hand, if the N content in the steel sheet which has been subjected to
nitriding exceeds 1000 ppm, AlN is present even after the secondary recrystallization is
completed in the final annealing, which causes an increase in iron loss. For this reason,
N in the steel sheet which has been subjected to nitriding is set to 1000 ppm or less, and
preferably 850 ppm or less. A means for adjusting the N content in the steel sheet
25 which has been subjected to nitriding to 40 to 1000 ppm is not particularly limited.
24
Usually, the N content after the completion of the nitriding can be controlled by
controlling a partial pressure of a nitrogen source (for example, ammonia) in a nitriding
atmosphere, a nitriding time, and the like.
[0074]
5 Final annealing
Annealing separator
An annealing separator is applied to the steel sheet which has been subjected to
nitriding and is subjected to final annealing. It is desirable that an annealing separator
containing alumina as a main component which does not easily react with silica
10 (containing 50 mass% or more of alumina) be used as the annealing separator and be
applied to the surface of the steel sheet through water slurry application, electrostatic
application, or the like. When the above annealing separator is utilized, the surface of
the steel sheet which has been subjected to final annealing can be finished to be smooth
and iron loss can be significantly reduced.
15 [0075]
The steel sheet coated with the annealing separator is subjected to final
annealing to allow secondary recrystallization to proceed and the crystal orientations to
be aligned in the {110} <001> orientation.
[0076]
20 For example, in the final annealing, a temperature is raised to 1100 to 1200 °C at
a rate of temperature rise of 5 to 15 °C/hour in an annealing atmosphere in which
nitrogen is included, the annealing atmosphere is changed to an atmosphere of 50 to
100% hydrogen at this temperature, and annealing which also serves as purification is
performed for about 20 hours. However, the final annealing conditions are not limited
25 thereto and can be appropriately selected from known conditions.
25
[0077]
Formation of insulation coating
When a coating liquid for insulation coating formation is applied to the surface
of the steel sheet which has been subjected to final annealing (after the completion of
secondary recrystallization) and baked, an insulation coa 5 ting is formed to make a grainoriented
electrical steel sheet which is a final product. A type of the insulation coating
is not limited to a specific type and may be a known insulation coating.
[0078]
For example, there are insulation coatings formed by applying an aqueous
10 coating liquid containing phosphate and colloidal silica. In the case of this insulation
coating, the phosphate is preferably a phosphate such as metal phosphate of Ca, Al, Sr,
and the like and more preferably an aluminum phosphate salt among these.
[0079]
Colloidal silica is not limited to colloidal silica having specific properties. A
15 particle size is also not limited to a specific particle size, but is preferably 200 nm
(number average particle size) or less. If the particle size exceeds 200 nm, the
settlement may occur in the coating liquid. On the other hand, although there is no
problem concerning dispersion even when a particle size of colloidal silica is less than
100 nm, the manufacturing costs increase, which is not practically used.
20 [0080]
The coating liquid for insulation coating formation is applied to the surface of
the steel sheet through, for example, a wet coating method such as a roll coater and baked
in air at a temperature of 800 to 900 °C for 10 to 60 seconds to form a tension insulation
coating.
25 [0081]
26
The grain-oriented electrical steel sheet may be subjected to a magnetic domain
subdivision treatment. The magnetic domain subdivision treatment is preferable
because grooves are formed in the surface of the steel sheet and a width of the magnetic
domains is reduced, resulting in a reduction in iron loss. Although a specific method of
the magnetic domain subdivision treatment 5 is not particularly limited, for example, laser
irradiation, electron beam irradiation, etching, groove formation through gears or the like
can be exemplified.
[Examples]
[0082]
10 Although examples of the present invention will be described below, the
conditions in the examples are one condition example adopted for confirming the
feasibility and the effect of the present invention and the present invention is not limited
to this one condition example. The present invention may adopt various conditions as
long as the gist of the present invention is not deviated and the object of the present
15 invention is achieved.
[0083]
(Example 1)
A cold-rolled steel sheet having a final sheet thickness of 0.27 mm, 0.23 mm,
0.20 mm, 0.18 mm, 0.15 mm, or 0.13 mm was obtained by heating the steel slab having
20 the component composition shown in Table 1 (the remainder: Fe and impurities) to 1150
°C and subjecting the steel slab to hot rolling to obtain a hot-rolled steel sheet having a
sheet thickness of 2.6 mm, subjecting the hot-rolled steel sheet to hot-band annealing at
the first stage temperature of 1100 °C and the second stage temperature of 900 °C, and
pickling the hot-rolled steel sheet and performing a single cold rolling process or multiple
25 cold rolling processes having intermediate annealing performed between the cold rolling
27
processes.
[0084]
[Table 1]
Steel
No.
Chemical composition (mass%)
C Si Mn Al N Seq Sol-Al/N Others
A1 0.082 3.45 0.12 0.0285 0.0070 0.0065 4.07
A2 0.060 3.35 0.10 0.0290 0.0070 0.0055 4.14
A3 0.072 2.50 0.45 0.0241 0.0090 0.0070 2.68 B 0.0015
A4 0.088 3.60 0.10 0.0241 0.0090 0.0066 2.68 Cr 0.02
A5 0.045 3.95 0.08 0.0240 0.0080 0.0063 3.00 Cu 0.18
A6 0.032 4.20 0.30 0.0350 0.0080 0.0080 4.38 P 0.25
A7 0.045 1.92 0.05 0.0390 0.0090 0.0082 4.33
A8 0.048 3.45 0.10 0.0240 0.0055 0.0066 4.36 Ni 0.05
A9 0.055 4.21 0.13 0.0321 0.0120 0.0063 2.68
A10 0.091 3.35 0.25 0.0262 0.0060 0.0054 4.37 Bi
0.0015
A11 0.099 3.45 0.14 0.0350 0.0083 0.0040 4.22
A12 0.025 3.35 0.12 0.0350 0.0080 0.0100 4.38
A13 0.031 3.92 0.10 0.0330 0.0079 0.0060 4.18 Sb 0.2
A14 0.045 3.15 0.32 0.0330 0.0080 0.0055 4.13 Sn 0.01
A15 0.077 4.32 0.12 0.0300 0.0100 0.0065 3.00
A16 0.089 3.35 0.52 0.0350 0.0081 0.0065 4.32
A17 0.046 0.93 0.12 0.0285 0.0070 0.0065 4.07
A18 0.046 6.68 0.12 0.0285 0.0070 0.0065 4.07
A19 0.060 3.35 0.05 0.0290 0.0070 0.0055 4.14
A20 0.060 3.35 0.98 0.0290 0.0070 0.0055 4.14
A21 0.045 1.92 0.05 0.0150 0.0040 0.0082 3.75
A22 0.048 3.45 0.10 0.0500 0.0120 0.0066 4.17
[0085]
The cold-rolled steel sheet 5 having a final sheet thickness of 0.27 mm, 0.23 mm,
0.20 mm, 0.18 mm, 0.15 mm, or 0.13 mm was subjected to the decarburization annealing
and nitriding (annealing in which the nitrogen content in the steel sheet is increased).
To be specific, the decarburization annealing was performed at a rate of temperature rise
of 100 °C/second with an oxidation degree of an atmosphere set to 0.12. A soaking
10 temperature of decarburization annealing is shown in Table 2. After that, the coldrolled
steel sheet was subjected to nitriding so that the nitrogen content shown in Table 2
was obtained.
An annealing separator containing alumina as a main component was applied to
the surface of the steel sheet which has been subjected to decarburization annealing and
28
nitriding, heated at a rate of temperature rise of 15 °C/hour, and subjected to final
annealing at 1200 °C. Furthermore, an aqueous coating liquid containing phosphate and
colloidal silica was applied and baked in air at a temperature of 800 °C for 60 seconds to
form an insulation coating (a tension insulation coating).
5 [0086]
It was confirmed whether the foregoing expression (1) was satisfied in the steel
sheet which has not been subjected to nitriding and the nitrogen content and the carbon
content of the steel sheet which has been subjected to a decarburization nitriding
treatment were measured.
10 A magnetic flux density B8 (T) and iron loss W17/50 of the steel sheet which has
been subjected to the final annealing and the insulation coating formation and the
magnetic domain control were measured. Since the iron loss W17/50 varies significantly
depending on a sheet thickness, examples in which sheet thicknesses were 0.27 mm, 0.23
mm, 0.20 mm, 0.18 mm, 0.15 mm, and 0.13 mm and iron losses were 0.75 W/kg or less,
15 0.65 W/kg or less, 0.62 W/kg or less, 0.55 W/kg or less, 0.50 W/kg or less, and 0.45
W/kg or less, respectively, were regarded as examples in which good magnetic
characteristics were obtained. If the magnetic flux density B8 (T) was 1.930 T or more,
it was regarded as an example in which good magnetic characteristics were obtained.
29
[0087]
[Table 2]
No. Steel No.
Slab heating temperature
(ºC)
Sheet thickness of coldrolled
steel sheet (mm)
Expression (1)
Lower limit Sol-Al/N Upper limit
Example of
present
invention
B1 A1 1150 0.20 2.80 4.07 4.22
B2 A2 1150 0.20 2.80 4.14 4.22
B3 A3 1150 0.23 2.67 2.68 4.13
B4 A4 1150 0.23 2.67 2.68 4.13
B5 A5 1150 0.20 2.80 3.00 4.22
B6 A6 1150 0.15 3.00 4.38 4.38
B7 A7 1150 0.15 3.00 4.33 4.38
B8 A8 1150 0.15 3.00 4.36 4.38
B9 A9 1150 0.23 2.67 2.68 4.13
B10 A10 1150 0.15 3.00 4.37 4.38
B11 A11 1150 0.20 2.80 4.22 4.22
B12 A12 1150 0.15 3.00 4.38 4.38
B13 A13 1150 0.20 2.80 4.18 4.22
B14 A14 1150 0.23 2.67 4.13 4.13
B15 A15 1150 0.18 2.88 3.00 4.28
B16 A16 1150 0.15 3.00 4.32 4.38
B17 A17 1150 0.23 2.67 4.07 4.13
B18 A18 1150 0.23 2.67 4.07 4.13
B19 A19 1150 0.18 2.88 4.14 4.28
B20 A20 1150 0.18 2.88 4.14 4.28
B21 A21 1150 0.15 3.00 3.75 4.38
B22 A22 1150 0.15 3.00 4.17 4.38
Comparative
example
C1 A1 1150 0.27 2.50 4.07 4.00
C2 A2 1150 0.27 2.50 4.14 4.00
C3 A3 1150 0.20 2.80 2.68 4.22
C4 A4 1150 0.18 2.88 2.68 4.28
30
C5 A5 1150 0.13 3.09 3.00 4.44
C6 A6 1150 0.18 2.88 4.38 4.28
C7 A7 1150 0.23 2.67 4.33 4.13
C8 A8 1150 0.18 2.88 4.36 4.28
C9 A9 1150 0.18 2.88 2.68 4.28
C10 A10 1150 0.23 2.67 4.37 4.13
C11 A11 1150 0.23 2.67 4.22 4.13
C12 A12 1150 0.18 2.88 4.38 4.28
C13 A13 1150 0.23 2.67 4.18 4.13
C14 A14 1150 0.27 2.50 4.13 4.00
C15 A15 1150 0.13 3.09 3.00 4.44
C16 A16 1150 0.27 2.50 4.32 4.00
(Continuation of table2)
No.
Decarburization
annealing temperature
(ºC)
Nitrogen content
after
decarburization
and nitriding
(ppm)
Carbon content
after
decarburization
and nitriding
(ppm)
Magnetic domain control method
Magnetic characteristics
Magnetic flux density
B8 (T)
Iron loss W17/50 (W/kg)
B1 820 200 12 Laser irradiation 1.945 0.59
B2 830 210 15 Laser irradiation 1.944 0.61
B3 870 198 17 Laser irradiation 1.943 0.63
B4 880 185 23 Laser irradiation 1.942 0.62
B5 870 190 22 Laser irradiation 1.944 0.60
B6 780 230 19 Laser irradiation 1.945 0.40
B7 820 211 21 Laser irradiation 1.950 0.45
B8 790 198 22 Laser irradiation 1.938 0.48
B9 850 211 24 Laser irradiation 1.938 0.65
B10 800 213 21 Laser irradiation 1.939 0.48
B11 810 225 19 Laser irradiation 1.941 0.61
B12 800 241 18 Laser irradiation 1.942 0.49
B13 810 251 22 Laser irradiation 1.942 0.62
B14 790 255 22 Gear 1.939 0.62
31
B15 880 194 21 Etching 1.941 0.54
B16 810 201 22 Electron beam 1.942 0.50
B17 820 220 18 Laser irradiation 1.941 0.63
B18 830 222 21 Electron beam 1.939 0.61
B19 820 232 22 Gear 1.939 0.52
B20 820 210 24 Laser irradiation 1.941 0.54
B21 825 214 22 Electron beam 1.940 0.48
B22 830 221 19 Laser irradiation 1.940 0.49
C1 810 201 35 Laser irradiation 1.940 0.80
C2 810 206 52 Laser irradiation 1.943 0.81
C3 840 211 21 Laser irradiation 1.750 1.00
C4 830 188 22 Laser irradiation 1.763 1.05
C5 820 189 25 Laser irradiation 1.823 0.90
C6 780 255 43 Laser irradiation 1.935 0.70
C7 780 186 35 Laser irradiation 1.941 0.75
C8 780 190 33 Laser irradiation 1.943 0.72
C9 840 189 22 Laser irradiation 1.560 1.04
C10 790 189 45 Laser irradiation 1.939 0.72
C11 800 190 42 Laser irradiation 1.934 0.75
C12 800 191 41 Laser irradiation 1.941 0.65
C13 810 199 44 Laser irradiation 1.938 0.82
C14 810 188 51 Gear 1.937 0.81
C15 900 210 21 Etching 1.821 0.88
C16 810 222 36 Electron beam 1.933 0.83
32
[0088]
In the example of the present invention in which the conditions of the present
invention are satisfied, the carbon content (the C content) after the decarburization
nitriding treatment is as small as 25 ppm or less and the magnetic characteristics shown
by the magnetic flux density B8 and the 5 iron loss W17/50 are good. On the other hand, in
comparative examples in which the conditions of the present invention are not satisfied,
the carbon content is large. Thus, an inferior iron loss W17/50 is provided or a poor
secondary recrystallization is provided, and a low magnetic flux density is provided and
an inferior iron loss W17/50 is provided.
10 [0089]
(Example 2)
A cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
was obtained by subjecting the steel slab having the component composition shown in
Table 1 to hot rolling at various slab heating temperatures listed in Table 3 to obtain a
15 hot-rolled steel sheet having a sheet thickness of 2.6 mm, subjecting the hot-rolled steel
sheet to hot-band annealing at the first stage temperature of 1100 °C and the second stage
temperature of 900 °C, and pickling the hot-rolled steel sheet and performing a single
cold rolling process or multiple cold rolling processes having intermediate annealing
performed between the cold rolling processes.
20 The cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
was subjected to the decarburization annealing and nitriding (annealing in which the
nitrogen content in the steel sheet is increased). The decarburization annealing was
performed at a rate of temperature rise of 80 °C/second with an oxidation degree of an
atmosphere set to 0.12. A soaking temperature of decarburization annealing was as
25 shown in Table 3. After that, the cold-rolled steel sheet was subjected to nitriding so
33
that the nitrogen content (the N content) listed in Table 3 was obtained. An annealing
separator containing alumina as a main component was applied to the surface of the steel
sheet which has been subjected to decarburization annealing and nitriding, heated at a
rate of temperature rise of 15 °C/hour, and subjected to final annealing at 1200 °C.
Furthermore, an aqueous coating 5 liquid containing phosphate and colloidal silica was
applied and baked in air at a temperature of 800 °C for 60 seconds to form a tension
insulation coating.
[0090]
It was confirmed whether the foregoing expression (1) was satisfied in the steel
10 sheet which has not been subjected to nitriding and the nitrogen content and the carbon
content of the steel sheet which has been subjected to a decarburization nitriding
treatment were measured. Furthermore, a magnetic flux density B8 (T) and iron loss
W17/50 of the steel sheet which has been subjected to the final annealing and the
insulation coating formation and the magnetic domain control through laser irradiation
15 were measured. The evaluation criteria were the same as in Example 1. The results
are shown in Table 3.
34
[0091]
[Table 3]
No. Steel No.
Slab heating temperature
(ºC)
Sheet thickness of cold-rolled
steel sheet (mm)
(1) Expression
Lower limit Sol-Al/N Upper limit
Example of
present
invention
D1 A1 1150 0.20 2.80 4.07 4.22
D2 A2 1200 0.20 2.80 4.14 4.22
D3 A3 1240 0.23 2.67 2.68 4.13
D4 A5 1230 0.20 2.80 3.00 4.22
D5 A9 1200 0.23 2.67 2.68 4.13
D6 A11 1180 0.20 2.80 4.22 4.22
D7 A13 1200 0.20 2.80 4.18 4.22
D8 A14 1230 0.23 2.67 4.13 4.13
Comparative
example
E1 A1 1260 0.20 2.80 4.07 4.22
E2 A2 1280 0.20 2.80 4.14 4.22
E4 A3 1350 0.23 2.67 2.68 4.13
E5 A5 1270 0.20 2.80 3.00 4.22
E6 A9 1280 0.23 2.67 2.68 4.13
E7 A11 1300 0.20 2.80 4.22 4.22
E8 A13 1280 0.20 2.80 4.18 4.22
E9 A14 1270 0.23 2.67 4.13 4.13
(Continuation of table 3)
No.
Decarburization
annealing
temperature (ºC)
Nitrogen content after
decarburization and
nitriding (ppm)
Carbon content after
decarburization and
nitriding (ppm)
Magnetic domain control method
Magnetic characteristics
Magnetic flux
density B8 (T)
Iron loss W17/50
(W/kg)
D1 820 200 12 Laser irradiation 1.945 0.59
D2 830 210 15 Laser irradiation 1.944 0.61
D3 870 198 17 Laser irradiation 1.943 0.63
35
D4 870 190 22 Laser irradiation 1.944 0.60
D5 850 211 24 Laser irradiation 1.938 0.65
D6 810 225 19 Laser irradiation 1.941 0.61
D7 810 251 22 Laser irradiation 1.942 0.62
D8 790 255 22 Laser irradiation 1.939 0.62
E1 880 211 21 Laser irradiation 1.880 0.70
E2 890 188 22 Laser irradiation 1.870 0.72
E4 920 186 22 Laser irradiation 1.560 1.25
E5 880 190 23 Laser irradiation 1.870 0.73
E6 830 189 22 Laser irradiation 1.850 0.77
E7 880 189 18 Laser irradiation 1.560 1.20
E8 880 190 22 Laser irradiation 1.780 1.21
E9 920 191 24 Laser irradiation 1.820 0.87
36
[0092]
In the example of the present invention in which the slab the heating temperature
is lower than 1250 °C, good magnetic characteristics shown by the magnetic flux density
B8 and the iron loss W17/50 are provided, whereas in the comparative examples in which
the slab heating conditions of the present i 5 nvention are not satisfied, poor secondary
recrystallization is provided, a low magnetic flux density is provided, and an inferior iron
loss W17/50 is provided.
[0093]
(Example 3)
10 A cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
was obtained by subjecting the steel slab having the component composition shown in
Table 1 to hot rolling at 1150 °C to obtain a hot-rolled steel sheet having a sheet
thickness of 2.6 mm, subjecting the hot-rolled steel sheet to hot-band annealing at the
first stage temperature of 1100 °C and the second stage temperature of 900 °C, subjecting
15 the hot-rolled steel sheet to annealing at 900 °C, and then pickling the hot-rolled steel
sheet and performing a single cold rolling process or multiple cold rolling processes
having intermediate annealing performed between the cold rolling processes.
[0094]
The cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
20 was subjected to the decarburization annealing and nitriding (annealing in which the
nitrogen content in the steel sheet is increased). The decarburization annealing was
performed at a rate of temperature rise of 100 °C/second with an oxidation degree of an
atmosphere set to 0.12. A soaking temperature of decarburization annealing is shown in
Table 4. After that, the cold-rolled steel sheet was subjected to nitriding so that the
25 nitrogen content shown in Table 4 was obtained. An annealing separator containing
37
alumina as a main component was applied to the surface of the steel sheet which has
been subjected to decarburization annealing and nitriding, heated at a rate of temperature
rise of 15 °C/hour, and subjected to final annealing at 1200 °C. Furthermore, an
aqueous coating liquid containing phosphate and colloidal silica was applied and baked
in air at a temperature of 800 5 °C for 60 seconds to form a tension insulation coating.
[0095]
It was confirmed whether the foregoing expression (1) was satisfied in the steel
sheet which has not been subjected to nitriding and the nitrogen content and the carbon
content of the steel sheet which has been subjected to a decarburization nitriding
10 treatment were measured. Furthermore, a magnetic flux density B8 (T) and iron loss
W17/50 of the steel sheet which has been subjected to the final annealing and the
insulation coating formation and the magnetic domain control through laser irradiation
were measured. The evaluation criteria were the same as in Example 1. The results
are shown in Table 4.
38
[0096]
[Table 4]
No. Steel No.
Slab heating
temperature (ºC)
Sheet thickness of
cold-rolled steel sheet
(mm)
(1) Expression Decarburization
annealing temperature
(ºC)
Lower limit Sol-Al/N Upper limit
Example of
present
invention
F1 A1 1150 0.20 2.80 4.07 4.22 820
F2 A2 1150 0.20 2.80 4.14 4.22 830
F3 A3 1150 0.23 2.67 2.68 4.13 870
F4 A5 1150 0.20 2.80 3.00 4.22 870
F5 A9 1150 0.23 2.67 2.68 4.13 850
F6 A11 1150 0.20 2.80 4.22 4.22 810
Comparative
example
G1 A1 1150 0.20 2.80 4.07 4.22 840
G2 A2 1150 0.20 2.80 4.14 4.22 780
G3 A3 1150 0.23 2.67 2.68 4.13 790
G4 A5 1150 0.20 2.80 3.00 4.22 800
G5 A9 1150 0.23 2.67 2.68 4.13 810
G6 A11 1150 0.20 2.80 4.22 4.22 810
(Continuation of table 4)
No.
Nitrogen content after
decarburization and
nitriding (ppm)
Carbon content after
decarburization and
nitriding (ppm)
Magnetic domain control method
Magnetic characteristics
Magnetic flux density
B8 (T)
Iron loss W17/50
(W/kg)
F1 820 12 Laser irradiation 1.945 0.59
F2 936 15 Laser irradiation 1.944 0.61
F3 71 17 Laser irradiation 1.943 0.63
F4 82 22 Laser irradiation 1.944 0.60
F5 60 24 Laser irradiation 1.938 0.65
F6 882 19 Laser irradiation 1.941 0.61
G1 1012 21 Laser irradiation 1.902 0.72
G2 1121 24 Laser irradiation 1.905 0.75
G3 38 23 Laser irradiation 1.901 0.78
39
G4 35 22 Laser irradiation 1.898 0.72
G5 39 19 Laser irradiation 1.887 0.79
G6 1105 18 Laser irradiation 1.901 0.75
40
[0097]
In the example of the present invention in which the nitrogen content after
decarburization and nitriding is within the range of 40 to 1000 ppm, a good magnetic flux
density and iron loss W17/50 are provided. In contrast, in the comparative examples in
which the nitrogen content of the present i 5 nvention is not satisfied, a poor secondary
recrystallization is provided, residual nitrides precipitates even after final annealing, and
inferior magnetic flux density B8(T) and iron loss W17/50 are provided.
[0098]
(Example 4)
10 A cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
was obtained by subjecting the steel slab having the component composition shown in
Table 1 to hot rolling at 1150 °C to obtain a hot-rolled steel sheet having a sheet
thickness of 2.6 mm, subjecting the hot-rolled steel sheet to hot-band annealing at the
first stage temperature of 1100 °C and the second stage temperature of 900 °C, subjecting
15 the hot-rolled steel sheet to annealing at 900 °C, and then pickling the hot-rolled steel
sheet and performing a single cold rolling process or multiple cold rolling processes
having intermediate annealing performed between the cold rolling processes.
[0099]
The cold-rolled steel sheet having a final sheet thickness of 0.23 mm or 0.20 mm
20 was subjected to the decarburization annealing and nitriding (annealing in which the
nitrogen content in the steel sheet is increased). The decarburization annealing was
performed at a rate of temperature rise of 100 °C/second with an oxidation degree of an
atmosphere set to 0.12. A soaking temperature of decarburization annealing is shown in
Table 5. After that, the cold-rolled steel sheet was subjected to nitriding so that the
25 nitrogen content shown in Table 5 is obtained. An annealing separator containing
41
alumina as a main component was applied to the surface of the steel sheet which has
been subjected to decarburization and nitriding, heated at a rate of temperature rise of 15
°C/hour, and subjected to final annealing at 1200 °C. Furthermore, an aqueous coating
liquid containing phosphate and colloidal silica was applied and baked in air at a
temperature of 800 °5 C for 60 seconds to form a tension insulation coating.
[0100]
It was confirmed whether the foregoing expression (1) was satisfied in the steel
sheet which has not been subjected to nitriding and the nitrogen content and the carbon
content of the steel sheet which has been subjected to a decarburization nitriding
10 treatment were measured. Furthermore, a magnetic flux density B8 (T) and iron loss
W17/50 of the steel sheet which has been subjected to the final annealing and the
insulation coating formation and the magnetic domain control through laser irradiation
were measured. The evaluation criteria were the same as in Example 1. The results
are shown in Table 5.
42
[0101]
[Table 5]
No. Steel No.
Slab heating
temperature (ºC)
Sheet thickness of
cold-rolled steel
sheet (mm)
(1) Expression
Decarburization annealing
Lower limit Sol-Al/N Upper limit temperature (ºC)
Example
of present
invention
H1 A1 1230 0.20 2.80 4.07 4.22 980
H2 A2 1230 0.20 2.80 4.14 4.22 890
H3 A3 1230 0.23 2.67 2.68 4.13 880
H4 A5 1230 0.20 2.80 3.00 4.22 920
H5 A9 1230 0.23 2.67 2.68 4.13 890
H6 A11 1230 0.20 2.80 4.22 4.22 880
Comparat
ive
example
I1 A1 1230 0.20 2.80 4.07 4.22 1020
I2 A2 1230 0.20 2.80 4.14 4.22 1010
I3 A3 1230 0.23 2.67 2.68 4.13 1005
I4 A5 1230 0.20 2.80 3.00 4.22 1010
I5 A9 1230 0.23 2.67 2.68 4.13 1020
I6 A11 1230 0.20 2.80 4.22 4.22 1020
(Continuation of table 5)
No.
Nitrogen content after
decarburization and
nitriding (ppm)
Carbon content after
decarburization and
nitriding (ppm)
Magnetic domain control method
Magnetic characteristics
Magnetic flux density
B8 (T)
Iron loss W17/50
(W/kg)
H1 230 12 Laser irradiation 1.945 0.59
H2 280 15 Laser irradiation 1.944 0.61
H3 270 17 Laser irradiation 1.943 0.63
H4 192 22 Laser irradiation 1.944 0.60
H5 199 24 Laser irradiation 1.938 0.65
H6 210 19 Laser irradiation 1.941 0.61
I1 220 21 Laser irradiation 1.932 0.67
I2 221 24 Laser irradiation 1.922 0.70
I3 298 23 Laser irradiation 1.930 0.76
43
I4 276 22 Laser irradiation 1.931 0.69
I5 256 19 Laser irradiation 1.929 0.79
I6 212 18 Laser irradiation 1.921 0.71
44
[0102]
In the example of the present invention in which the decarburization annealing
temperature is within the range of lower than 1000 °C, magnetic characteristics shown by
magnetic flux density B8 and iron loss W17/50 are good, and when the decarburization
annealing temperature is 1000 5 °C or higher and outside of the range of the present
invention, a magnetic flux density B8 and iron loss W17/50 are inferior to that of the
examples of the present invention.
[Industrial Applicability]
[0103]
10 As described above, according to the present invention, it is possible to stably
provide a grain-oriented electrical steel sheet having a sheet thickness of 0.15 to 0.23 mm
and having excellent magnetic characteristics. Therefore, the present invention is
highly applicable when an electrical steel sheet is manufactured and in utilization
industries.

WE CLAIMS

1. A method for manufacturing a grain-oriented electrical steel sheet, comprising:
heating a steel slab which contains, in terms of mass%, C: 0.100% or less; Si:
0.80 to 7.00%; Mn: 0.05 to 1.00%; Sol. Al: 0.0100 to 0.0700%; N: 0.0040 to 0.0120%;
Seq=S+5 0.406×Se: 0.0030 to 0.0150%; Cr: 0 to 0.30%; Cu: 0 to 0.40%; Sn: 0 to 0.30%;
Sb: 0 to 0.30%; P: 0 to 0.50%; B: 0 to 0.0080%; Bi: 0 to 0.0100%; Ni: 0 to 1.00%, and
the remainder: Fe and impurities to lower than 1250 °C and subjecting the steel slab to
hot rolling to obtain a hot-rolled steel sheet;
performing hot-band annealing on the hot-rolled steel sheet;
10 pickling the hot-rolled steel sheet which has been subjected to the hot-band
annealing;
subjecting the hot-rolled steel sheet which has been subjected to the pickling to
cold rolling to obtain a cold-rolled steel sheet having a final sheet thickness d of 0.15 to
0.23 mm;
15 performing a decarburization nitriding treatment including decarburization
annealing and nitriding on the cold-rolled steel sheet;
performing final annealing on the cold-rolled steel sheet which has been
subjected to the decarburization nitriding treatment; and
applying a coating liquid for insulation coating formation to the cold-rolled steel
20 sheet which has been subjected to the final annealing and baking the coating liquid,
wherein Sol. Al/N which is a mass ratio between Sol. Al and N in the steel slab
and the final sheet thickness d satisfy the following expression (1),
the N content of the cold-rolled steel sheet which has been subjected to the
decarburization nitriding treatment is 40 to 1000 ppm, and
25 a decarburization annealing temperature in the decarburization annealing is
46
lower than 1000 °C:
−4.17×d+3.63≤Sol. Al/N≤−3.10×d+4.84 (1).
2. The method for manufacturing a grain-oriented electrical steel sheet according to
claim 1, wherein 5 the steel slab contains, in terms of mass%,
one or more of Cr: 0.02 to 0.30%;
Cu: 0.10 to 0.40%;
Sn: 0.02 to 0.30%;
Sb: 0.02 to 0.30%;
10 P: 0.02 to 0.50%;
B: 0.0010 to 0.0080%;
Bi: 0.0005 to 0.0100%; and
Ni: 0.02 to 1.00%.