DESCRIPTION
TITLE OF INVENTION: NON-ORIENTED ELECTRICAL STEEL
SHEET AND MANUFACTURING METHOD THEREOF
TECHNICAL FIELD
[0001] The present invention relates to a nonoriented
electrical steel sheet suitable for an iron
core material of a motor and a manufacturing method
thereof.
BACKGROUND ART
[0002] Making an electrical apparatus more efficient
has been desired strongly, and a further achievement
of lower core loss has been required for a nonoriented
electrical steel sheet used for an iron core
material of a motor contained in an electrical
apparatus. Then, there have been studied a technique
of containing Si, Al, and so on in a non-oriented
electrical steel sheet to increase resistivity and
increase a grain diameter, a technique of adjusting
hot-rolled sheet annealing and a cold rolling ratio
to thereby improve texture, and so on.
[0003] Further, a non-oriented electrical steel
sheet is an electrical steel sheet having random
crystal orientations in the direction parallel to its
surface, but depending on the use of a non-oriented
electrical steel sheet, there is also sometimes a
case that one having a magnetic property in one
direction parallel to its surface, for example, a
- 1 -
rolling direction more excellent than that in the
other direction is preferable. For example, in the
case when a divided core is used as a stator of a
motor, the electrical steel sheet as described above
is preferably used for the divided core. As an
electrical steel sheet having an excellent magnetic
property in the rolling direction, a grain-oriented
electrical steel sheet is also considered, but a
glass coating film exists on surfaces of the grainoriented
electrical steel sheet, so that punching is
difficult to be performed. Further, as compared to
the non-oriented electrical steel sheet, more
controls are required for manufacturing the grainoriented
electrical steel sheet, and the grainoriented
electrical steel sheet is expensive.
Incidentally, in the case of the divided core being
used as a stator of a motor, the direction of easy
magnetized of the electrical steel sheet is allowed
to agree with the direction in which the magnetic
flux flows, and thus the efficiency of the motor can
be improved. Further, it is possible to improve the
yield of the electrical steel sheet being a material
and to increase a winding filling factor.
[0004] Various proposals regarding the non-oriented
electrical steel sheet for a divided core have been
made. However, in conventional techniques, it is
difficult to obtain the sufficient magnetic property
in the rolling direction.
- 2 -
CITATION LIST
PATENT LITERATURE
[0005] Patent Literature 1: Japanese Laid-open
Patent Publication No. 2004-332042
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2006-265720
Patent Literature 3: Japanese Laid-open Patent
Publication No. 2008-260996
Patent Literature 4: Japanese Laid-open Patent
Publication No. 56-55574
Patent Literature 5: Japanese Laid-open Patent
Publication No. 2001-140018
Patent Literature 6: Japanese Laid-open Patent
Publication No. 2001-279400
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006] The present invention has an object to
provide a non-oriented electrical steel sheet capable
of obtaining a better magnetic property in a rolling
direction, and a manufacturing method thereof.
SOLUTION TO PROBLEM
[0007] The present inventors focused on the
technique disclosed in Patent Literature 4 and
thought that by using a tension applying type
insulating film as an insulating film formed on
surfaces of a base iron of a non-oriented electrical
steel sheet, it may be possible to improve the
magnetic property in the rolling direction, and
- 3 -
conducted various experiments. However, it turned
out that in the case when the tension applying type
insulating film is simply used, the insulating film
cannot sufficiently resist various workings
(punching, interlocking, and so on) for forming a
divided core. That is, peeling off of the insulating
film or the like sometimes occurs. Further, the
magnetic property in the rolling direction was
improved, but the improvement was not sufficient.
The present inventors conducted an earnest study in
order to examine these causes, and then found that
adhesiveness between the tension applying type
insulating film and the base iron is low, and due to
that, sufficient tension does not act on the base
iron. Then, the present inventors further conducted
an earnest study based on the knowledge, and then
found that in the case of a specific oxide layer
existing on the surfaces of the base iron, the oxide
layer contributes to the improvement of the
adhesiveness between the base iron and the tension
applying type insulating film, and the magnetic
property in the rolling direction is significantly
improved. Further, it was also found that with the
improvement of the adhesiveness, peeling off of the
insulating film or the like is suppressed.
[0008] The gist of the present invention is as
follows.
[0009] (1) A non-oriented electrical steel sheet
including:
- 4 -
a base iron, an oxide layer containing at least
one type of oxide selected from the group consisting
of Si, Al, and Cr and having a thickness of not less
than 0.01 pm nor more than 0.5 pm being formed on a
surface of the base iron; and
a tension applying type insulating film of not
less than 1 g/m2 nor more than 6 g/m2 on the surface
of the base iron, wherein
the base iron contains:
Si, Al, and Cr: not less than 2 mass% nor more
than 6 mass% in total content; and
Mn: not less than 0.1 mass% nor more than 1.5
mass%,
a content of C of the base iron is equal to or
less than 0.005 mass%, and
a balance of the base iron is composed of Fe and
inevitable impurities.
[0010] (2) The non-oriented electrical steel sheet
according to (1), wherein the total content of Al and
Cr of the base iron is equal to or more than 0.8
mass%.
[0011] _(3) The non-oriented electrical steel sheet
according to (1) or (2), wherein the insulating film
is formed by baking of a coating solution containing
phosphate and colloidal silica.
[0012] (4) The non-oriented electrical steel sheet
according to (1) or (2), wherein the insulating film
is formed by baking of a coating solution containing
boric acid and an alumina sol.
- 5 -
[0013] (5) A manufacturing method of a non-oriented
electrical steel sheet including:
performing finish annealing of a cold-rolled
steel strip; and
forming a tension applying type insulating film
.of not less than 1 g/m2 nor more than 6 g/m2 on a
surface of the cold-rolled steel strip, wherein
the cold-rolled steel strip contains:
Si, Al, and Cr: not less than 2 mass% nor more
than 6 mass% in total content; and
Mn: not less than 0.1 mass% nor more than 1.5
mass%,
a content of C of the cold-rolled steel strip is
equal to or less than 0.005 mass%,
a balance of the cold-rolled steel strip is
composed of Fe and inevitable impurities, and
the performing the finish annealing includes
forming an oxide layer containing at least one type
of oxide selected from the group consisting of Si and
Al and having a thickness of not less than 0.01 pm
nor more than 0.5 pm on the surface of the coldrolled
steel strip with setting a temperature of the
cold-rolled steel strip to not lower than 800°C nor
higher than 1100°C in an atmosphere where when the
total content of Si and Al of the cold-rolled steel
strip is represented as X (mass%), a partial pressure
ratio of water vapor to hydrogen is equal to or less
than 0.005 x X2.
[0014] (6) The manufacturing method of a non-
- 6 -
oriented electrical steel sheet according to (5),
wherein the forming the insulating film includes,
after the performing the finish annealing:
applying a coating solution to the surface of the
cold-rolled steel strip; and
performing baking of the coating solution with
setting the temperature of the cold-rolled steel
strip to not lower than 800°C nor higher than 1100°C.
[0015] (7) The manufacturing method of a nonoriented
electrical steel sheet according to (5),
wherein the forming the insulating film includes:
applying a coating solution to the surface of the
cold-rolled steel strip before the performing the
finish annealing; and
performing baking of the coating solution during
the finish annealing.
[0016] (8) The manufacturing method of a nonoriented
electrical steel sheet according to (6) or
(7), wherein the coating solution contains phosphate
and colloidal silica.
[0017] (9) The manufacturing method of a nonoriented
electrical steel sheet according to (6) or
(7), wherein the coating solution contains boric acid
and an alumina sol.
[0018] (10) The manufacturing method of a nonoriented
electrical steel sheet according to any one
of (5) to (9), wherein the total content of Al and Cr
of the cold-rolled steel strip is equal to or more
than 0.8 mass%.
- 7 -
ADVANTAGEOUS EFFECTS OF INVENTION
[0019] According to the present invention, it is
possible to obtain high adhesiveness between a base
iron and a tension applying type insulating film, and
to significantly improve a magnetic property in a
rolling direction.
BRIEF DESCRIPTION OF DRAWINGS
[0020] [Fig. lA] Fig. IA is a view showing a
scanning electron microscope cross-sectional
photograph of an oxide on a surface of a steel strip
having had finish annealing performed thereon in an
atmosphere of a partial pressure ratio (PH20/PH2) being
0.1;
[Fig. 1B] Fig. 1B is a view illustrating a
scanning electron microscope cross-sectional
photograph of an oxide on a surface of a steel strip
having had finish annealing performed thereon in an
atmosphere of the partial pressure ratio (PH20/PH2)
being 0.01;
[Fi'g. 2] Fig. 2 is a view illustrating an
infrared reflection-absorption spectrum of an
external oxide film 102;
[Fig. 3] Fig. 3 is a view illustrating the
relationship between a composition of a cold-rolled
steel strip and an atmosphere of finish annealing,
and a state of a surface of a base iron;
[Fig. 4] Fig. 4 is a cross-sectional view
- 8 -
illustrating a structure of a non-oriented electrical
steel sheet according to an embodiment of the present
invention;
[Fig. 5] Fig. 5 is a flowchart illustrating an
example of a manufacturing method of a non-oriented
electrical steel sheet; and
[Fig. 6] Fig. 6 is a flowchart illustrating
another example of the manufacturing method of the
non-oriented electrical steel sheet.
DESCRIPTION OF EMBODIMENTS
[0021] First, an experiment regarding the
application of a tension applying type insulating
film to a non-oriented electrical steel sheet,
conducted by the present inventors will be explained.
[0022] In the experiment, two cold-rolled steel
strips for a non-oriented electrical steel sheet each
containing Si: 3 mass%, Mn: 0.15 mass%, and Al: 1.2
mass%, and a balance being composed of Fe and
inevitable impurities and each having a thickness of
0.35 mm were manufactured. Then, finish annealing at
1000°C was performed in an annealing atmosphere
different in every cold-rolled steel strip. In one
annealing atmosphere, a partial pressure ratio of
water vapor to hydrogen (Px20/PH2) was set to 0.01, and
in the other annealing atmosphere, the partial
pressure ratio (Px20/PH2) was set to 0.1. Then, a core
loss value (W10/50) under an excitation condition of
the frequency being 50 Hz and the maximum magnetic
- 9 -
flux density being 1.0 T was measured in a rolling
direction ( an L direction ) and a direction
perpendicular to the rolling direction in a surface
of the cold - rolled steel strip ( a C direction).
Thereafter , 3 g/m2 per one surface of a coating
solution composed of aluminum phosphate, colloidal
silica , and chromic acid was applied to both the
surfaces of each of the steel strips to be baked at
800°C. That is, tension applying type insulating
films were formed. Then , the core loss value
( W10/50 ) was measured again in the L direction and
the C direction . These results are listed in Table
1.
[0023] [Table 1]
Table 1
PARTIAL PRESSURE
RATIO ( Px2o/Pu2)
0.1 I 0.01
EXITATION DIRECTION L DIRECTION C DIRECTION L DIRECTION C DIRECTI
CORE LOSS
BEFORE FORMING
0.894 0.961 0.883 0.974
INSULATING FILM
( W10/50 ( W/kg))
CORE LOSS
AFTER FORMING
0.821 0.971 0.736 0.977
INSULATING FILM
(W10/50 (W/kg))
CORE LOSS
IMPROVEMENT RATE
BETWEEN BEFORE AND 8.20% -1.00% 16.70% -0.30%
AFTER FORMING
INSULATING FILM
[0024] As listed in Table 1, in the case of
annealing in the atmosphere of the partial pressure
ratio (PH2o/PH2) being 0.1, an improvement of 8% or so
- 10 -
was confirmed with respect to the core loss in the L
direction. However, when a divided core was desired
to be formed from the non-oriented electrical steel
sheet provided with the insulating films formed in
this manner, the insulating films were not able to
resist.workings such as punching and interlocking.
[0025] On the other hand, in the case of annealing
in the atmosphere of the partial pressure ratio
(Px2o/Px2) being 0,01, an improvement as high as 17%
was confirmed with respect to the core loss in the L
direction, and further the insulating films were able
to sufficiently resist workings such as punching and
interlocking.
[0026] The present inventors observed the cross
section of an oxide on the surface of the steel strip
after the finish annealing in order to examine the
cause of the working resistance difference of the
insulating films due to the finish annealing
atmosphere described above. Fig. lA illustrates a
scanning electron microscope cross-sectional
photograph of an oxide on the surface of the steel
strip having had the finish annealing performed
thereon in the atmosphere of the partial pressure
ratio (PH20/Px2) being 0.1, and Fig. 1B illustrates a
scanning electron microscope cross-sectional
photograph of an oxide on the surface of the steel
strip having had the finish annealing performed
thereon in the atmosphere of the partial pressure
ratio (Px2o/Px2) being 0.01.
1 -
[0027] As illustrated in Fig. 1A, on the surface of
a base iron 101 of the steel strip having had the
finish annealing performed thereon in the atmosphere
of the partial pressure ratio (PH20/PH2) being 0.1, a
thick internal oxide layer 103 existed. On the other
hand, as illustrated in Fig. 1B, an the surface of a
base iron 101 of the steel strip having had the
finish annealing performed thereon in the atmosphere
of the partial pressure ratio (PH2o/PH2) being 0.01, a
thin external oxide film 102 having a thickness of 50
nm or so existed. Incidentally, a An deposited layer
104 existing on the external oxide film 102 and the
internal oxide layer 103 was formed for protecting
the external oxide film 102 and the internal oxide
layer 103 when making samples for the cross section
observation.
[0028] Further, Fig. 2 illustrates an infrared
reflection-absorption spectrum of the external oxide
film 102. From the spectrum illustrated in Fiq.. 2,
it was possible to confirm that the external oxide
film 102 is mainly made of A12O3.
[0029] From the above, it was found that in
manufacturing the non-oriented electrical steel
sheet, the external oxide film is formed at the time
of finish annealing of the cold-rolled steel strip
and thereafter the tension applying type insulating
film is formed, and thereby adhesiveness between the
insulating film and the base iron is improved
significantly and further the magnetic property in
- 12 -
the L direction is improved significantly.
Incidentally, as will be described later, even though
the application of the raw material (coating
solution) of the tension applying type insulating
film is performed and then the finish annealing is
performed, and thereby the formation of the external
oxide film and the formation of the insulating film
by baking of the coating solution are performed in
parallel, the improvement of the adhesiveness and the
significant improvement of the magnetic property in
the L direction are achieved.
[0030] Here, the annealing condition is important
for forming the external oxide film during finish
annealing. Then, the present inventors examined the
relationship between the composition of the coldrolled
steel strip,to be finish annealed and the
atmosphere of finish annealing, and the state of the
surface of the base iron. In the examination,
various cold-rolled steel strips different in the
total content (X (mass%)) of Si, Al, and Cr were
manufactured to be subjected to finish annealing
under atmospheres of the various partial pressure
ratios (P520/PH2). Then, the state of a surface of
each of base irons after the finish annealing was
observed. Incidentally, the temperature of the
finish annealing was set to 900°C. The result is
illustrated in Fig. 3. In Fig. 3, the open mark
signifies that the internal oxide layer was formed,
and the closed mark signifies that the external oxide
- 13 -
film was formed.
[0031] From Fig„ 3, it is found that as long as the
total content (X (mass%)) of Si, Al, and Cr is under
the condition that the partial pressure ratio
(Px20/PH2) is less than 0.005 x X2, the external oxide
film can be formed.
[0032] Hereinafter, an embodiment of the present
invention will be explained with reference to the
attached drawings. Fig. 4 is a cross-sectional view
illustrating the structure of a non-oriented
electrical steel sheet according to the embodiment of
the present invention.
[0033] As illustrated in Fig. 4, in the non-oriented
electrical steel sheet according to the embodiment, a
tension applying type insulating film 2 having not
less than 1 g/m2 nor more than 6 g/m2 is formed on
surfaces of a base iron 1. Further, on the surfaces
of the base iron 1, an external oxide film 3
containing at least one type of oxide selected from
the group consisting of Si, Al, and Cr and having a
thickness of not less than 0.01 pm nor more than 0.5
pm is formed. In the base iron 1, a base 4 and the
external oxide films 3 are contained. The external
oxide film 3 is one example of an oxide layer.
[0034] The base iron 1 contains Si, Al, and Cr: not
less than 2 mass % nor more than 6 mass % in total
content and Mn: not less than 0.1 mass% nor more than
1.5 mass%. The content of C in the base iron 1 is
equal to or less than 0.005 mass%, and the balance of
- 14 -
the base iron 1 may be composed of Fe and inevitable
impurities.
[0035] Next, a manufacturing method of the nonoriented
electrical steel sheet as above will be
explained. Fig. 5 is a flowchart illustrating an
example of the manufacturing method of the nonoriented
electrical steel sheet.
[0036] In the embodiment, first, hot rolling of a
slab (steel material) having a predetermined
composition heated to a predetermined temperature is
performed to manufacture ,a hot-rolled steel strip
(Step Sl). Next, scales are removed by acid
pickling, and cold rolling of the hot-rolled steel
strip is performed to manufacture a cold-rolled steel
strip (Step S2). As the cold rolling, the cold
rolling may be performed only one time, or the cold
rolling may also be performed two times or more with
intermediate annealing being interposed therebetween.
Incidentally, annealing may also be performed as
necessary before the cold rolling.
[0037] Here, the components contained in the slab
(steel material) will be explained.
[0038] C increases the core loss and causes magnetic
aging. Thus, the content of C is set to 0.005 mass%
or less.
[0039] Si, Al, and Cr exhibit an effect of
increasing the resistivity of the non-oriented
electrical steel sheet to decrease eddy current loss.
Further, Si, Al, and Cr are used for forming the
- 15 -
external oxide film 3, of which the detail will be
described later. If the total content of Si, Al, and
Cr is less than 2 mass%, the effects cannot be
obtained sufficiently. Thus, the total content of
Si, Al, and Cr is set to 2 mass% or more. If the
total content. of Si, Al, and Cr is in excess of 6
mass%, cold working such as cold rolling- is difficult
to be performed. Thus, the total content of Si, Al,
and Cr is set to 6 mass% or less.
[0040] Mn exhibits an effect of decreasing solid
solution S at the time of slab heating. If the
content of Mn is less than 0.1 mass%, the effect
cannot be obtained sufficiently. Thus, the content
of Mn is set to 0.1 mass% or more. On the other
hand, if the content of Mn is in excess of 1.5 mass%,
the magnetic property deteriorates. Thus, the
content of Mn is set to 1.5 mass% or less.
[0041] Incidentally, the content of inevitable
impurities such as S, N, and 0, and Ti, V, Zr, and Nb
having the potential to bond to S, N and 0 to thereby
form non-magnetic inclusions may be decreased as much
as possible. Further, rare-earth elements, Ca, and
so on may also be contained in order to scavenge S,
N, and 0. The preferable content of rare-earth
elements, Ca, and so on is not less than 0.002 mass%
nor more than 0.01 mass%.
[0042] Sn and Sb have an effect of improving the
property in the L direction by the improvement of
texture. By adding Sn and Sb, the synergistic effect
- 16 -
with the effect by the present invention can be
expected.
[0043] After the cold rolling (Step S2), finish
annealing of the cold-rolled steel strip is performed
in a predetermined atmosphere to manufacture the base
iron 1 with the external oxide film 3 on,the surfaces
(Step S3). In the finish annealing, the temperature
of the cold-rolled steel strip is set to not lower
than 800°C nor higher than 1100°C. If the temperature
is lower than 800°C, it is difficult to sufficiently
form the external oxide films 3. On the other hand,
if the temperature is in excess of 1100°C, the cost is
increased significantly, and the stable operation is
difficult to be performed. Further, as the
atmosphere of the finish annealing, in consideration
of the above-described knowledge, the partial
pressure ratio (PH2o/PH2) of water vapor to hydrogen is
set to less than 0.005 x X2 with respect to the total
content (X (mass%)) of Si, Al, and Cr. As long as
the condition is satisfied, a desired external oxide
film can be formed as an oxide layer 3 as described
above. The external oxide film 3 contributes to the
significant improvement of the adhesiveness between
the tension applying type insulating film 2 and the
base iron 1. Then, with the improvement of the
adhesiveness, tension acts effectively and the
magnetic property in the L direction is further
improved.
[0044] Incidentally, if the thickness of the
- 17 -
external oxide film 3 is less than 0.01 pm, it is
difficult to obtain the sufficient adhesiveness.
Thus, the thickness of the external oxide film 3 is
desirably equal to or more than 0.01 pm. Further,
also in the case of the thickness of the external
oxide film 3 being in excess of 0.5 pm, it is
difficult to obtain the sufficient adhesiveness.
This is supposed because if the external oxide films
3 are formed thickly, unnecessary stress thereby
occurs on the surfaces of the base 4 of the base iron
1. Thus, the thickness of the external oxide film 3
is desirably equal to or less than 0.5 pm. The
thickness of the external oxide film 3 may be
controlled by adjusting, for example, the temperature
of the finish annealing and a soaking time. That is,
as the soaking temperature is higher and the soaking
time is longer, the external oxide films 3 are formed
thickly.
[0045] The substances composing the external oxide
film 3 are determined according to each of the
contents of Si, Al, and Cr, and the main component of
the external oxide film 3 may be, for example, Si02,
A1203, Cr203 , and so on. In the case when Al and Cr in
the cold-rolled steel strip are small, for example,
the main component of the external oxide film 3 is
Si02, and if the total content of Al and Cr is equal
to or more than 0.8 mass%, the main component of the
external oxide film 3 is A1203 and Cr203, or (Al,
Cr)203. The main component of the external oxide film
- 18 -
3 is not limited in particular. In the case when the
main component is A1203 and Cr203, or (Al, Cr)203, the
high adhesiveness can be obtained in particular.
Thus, the total content of Al and Cr is desirably
equal to or more than 0.8 mass%. Incidentally, the
external oxide film 3 is not composed of only these
main components, and even in the case of Al and Cr
being small, A1203, Cr203, and so on are sometimes
contained, and even in the case of the total content
of Al and Cr being in excess of 0.8 mass%, Si02 may be
contained.
[0046] After the finish annealing and the formation
of the oxide layer (Step S3), the tension applying
type insulating film 2 is formed on the surfaces of
the base iron 1 (Step S4). In the formation of the
insulating films 2, application and baking of a
predetermined coating solution are performed. As the
coating solution, a coating solution used for a
grain-oriented electrical steel sheet may be used.
For example, a coating solution containing phosphate
and colloidal silica as its main component may be
used. The ratio of phosphate and colloidal silica
are not limited in particular. The ratio of
colloidal silica is preferably 4 mass% to 24 mass%,
and the ratio of phosphate is preferably 5 mass% to
30 mass%. A coating solution like that is described
in, for example, Japanese Laid-open Patent
Publication No. 48-39338, Japanese Laid-open Patent
Publication No. 50-79442, and so on. Further, a
- 19 -
coating solution containing boric acid and an alumina
sol as its main component may also be used. The
component ratio of aluminum and boron is not limited
in particular. In oxide equivalent of aluminum and
boron, an aluminum oxide is preferably 50 mass% to 95
mass%. A coating solution like that is described in,
for example, Japanese Laid-open Patent Publication
No. 06-65754 and Japanese Laid-open Patent
Publication No. 06-65755.
[0047] Further, the formation amount of the tension
applying type insulating film 2 is set to not less
than 1 g/m2 nor more than 6 g/m2 per one surface. If
the formation amount of the insulating film 2 is less
than 1 g/m2, tension is not applied sufficiently, thus
being difficult to sufficiently improve the magnetic
property in the rolling direction (L direction). On
the other hand, if the formation amount of the
insulating film 2 is in excess of 6 g/m2, the space
factor decreases.
[0048] Further, the baking temperature is preferably
set to not lower than 800°C nor higher than 1100°C.
If the baking temperature is lower than 800°C, tension
is not applied sufficiently, thus being difficult to
sufficiently improve the magnetic property in the
rolling direction (L direction). On the other hand,
if the baking temperature is in excess of 1100°C, the
cost is increased significantly, and the stable
operation is difficult to be performed.
[0049] Through a series of processes as above, the
- 20 -
non-oriented electrical steel sheet according to the
embodiment may be manufactured. Then, in the nonoriented
electrical steel sheet, the external oxide
film 3 makes the base iron 1 and the tension applying
type insulating film 2 strongly adhere to each other.
Therefore, higher tension is applied to further
improve the magnetic property in the rolling
direction (L direction), and even in the case when
various workings (punching, interlocking, and so on)
for forming a divided core are performed, peeling off
of the insulating film 2 or the like can be
suppressed.
[0050] Incidentally, in the manufacturing method,
the application and baking of the coating solution
for the formation of the insulating films 2 (Step S4)
are performed after the finish annealing (Step S3).
The baking may also be performed in parallel to the
finish annealing. That is, as illustrated in Fig. 6,
it is also possible that after the cold rolling (Step
S2), the coating solution is applied to the coldrolled
steel strip (Step S11) and the finish
annealing combined with the baking of the coating
solution (Step S12) may be performed.
[0051] Further, after the formation of the tension
applying type insulating films 2, a coating film made
of only resin and/or a coating film composed of an
inorganic substance and resin may also be formed on
the tension applying type insulating films 2 in order
to improve the punching performance when forming a
- 21 -
core such as a divided core. That is, the
application and baking of a coating solution normally
used for forming an insulating film for a nonoriented
electrical steel sheet may be performed, and
thereby the punching performance can be made better.
As the coating solution as above, a coating solution
containing chromate and an acrylic resin may be used.
For example, a coating solution in which in/to a
chromic acid aqueous solution, a metal oxide, a metal
hydroxide, and a metal carbonate are dissolved, and
further an emulsion type resin is added may be used.
A coating solution like that is described in Japanese
Examined Patent Application Publication No. 50-15013,
for example. Further, a coating solution containing
phosphate and an acrylic resin may also be used. For
example, acoating solution to which 1 part by mass
to 300 parts by mass of an organic resin emulsion is
added with respect to 100 parts by mass of phosphate
may be used. A coating solution like that is
described in Japanese Laid-open Patent Publication
No. 06-330338, for example.
EXAMPLE'
[0052] Next, experiments conducted by the present
inventors will be explained. The conditions and so
on in these experiments are examples employed for
confirming the practicability and the effects of the
present invention, and the present invention is not
limited to these examples.
[0053] (First Experiment)
- 22 -
First, steel slabs (steel No. 1 to No. 7) each
containing various components listed in Table 2 and a
balance being composed of Fe and inevitable
impurities were hot rolled to manufacture hot-rolled
steel strips each having a thickness of 2.5 mm.
Next, annealing of the hot-rolled steel strips (hotrolled
sheet annealing) was performed at 900°C for 1
minute. Thereafter, acid pickling was performed and
cold rolling was performed to manufacture cold-rolled
steel strips each having a thickness of 0.35 mm.
[0054] [Table 2]
TABLE 2
STEEL COMPONENT (MASSa)
No. Si Al Cr Mn
1 3 0.3 <0.01^ 0.5
2 2 1.5 1<0.01 0,5
6 1
7 3
2 <0.01
2 2
2 1
1 1<0.01
1.2 1<0.01
0.5
0.5
0.5
0.5
0.5
[0055] Subsequently, finish annealing was performed
under the condition listed in Table 3, and the main
component and thickness of each of formed external
oxide films (oxide layers) were examined. The
identification of the main component of the external
oxide film was performed with an infrared reflectionabsorption
spectrum, and the thickness of the
external oxide film was examined by transmission
- 23 -
electron microscopic observation.
[0056] Next, under the condition listed in Table 3,
application and baking of a coating solution were
performed to form tension applying type insulating
films. In Table 3, in the column of "COATING
SOLUTION," "S" signifies that a coating solution
containing colloidal silica, aluminum phosphate, and
chromic acid was used, and "A" signifies that a
coating solution containing boric acid and an alumina
sol was used.
[0057] Then, the adhesiveness of each of the
insulating films was evaluated. The result is also
listed in Table 3. In Table 3, "X" in the column of
"ADHESIVENESS" signifies that in the case of a nonoriented
electrical steel sheet being wound around a
round bar having a diameter of 30 mm, the insulating
film was peeled off. Further, "O" signifies that in
the case of the non-oriented electrical steel sheet
being wound around a round bar having a diameter of
30 mm, the insulating film was not peeled off, but in
the case of the non-oriented electrical steel sheet
being wound around a round bar having a diameter of
20 mm, the insulating film was peeled off. "©"
signifies that even in the case of the non-oriented
electrical steel sheet being wound around a round bar
having a diameter of 20 mm, the insulating film was
not peeled off.
[0058] Further, the evaluation of a core loss
improvement rate in the L direction was also
- 24 -
performed. In the evaluation, a core loss value W1
(W10/50) of each of the non-oriented electrical steel
sheets manufactured by the above-described method was
measured to be compared to a core loss value Wo
(W10/50) of a reference sample. As the reference
sample, one. on which in place of the tension applying
type insulating films, insulating films were formed
by application and baking of a coating solution
containing phosphate and an acrylic resin described
in Japanese Laid-open Patent Publication No. 06-330338
was used. The reason why such evaluation was
performed is because the absolute value of core loss
depends on the component and process condition. The
result is also listed in Table 3. The numerical
value in the column of "CORE LOSS IMPROVEMENT RATE IN
L DIRECTION" is the value expressed by (Wo - W1) / Wo..,
[0059] [Table 3]
TABLE 3
CONDITION OF EXTERNAL OXIDE FILM TENTION APPLYING TYPE
STEEL
FINISH ANNEALING (OXIDE LAYER) INSULATING FILM CORE LOSS
No PARTIAL SOARING BAKING ADHESIVENESS
IMPROVEMENT
RATE IN
NOTE
.
PRESSURE TEMPERATURE
MAIN THICKNESS COATING AMOUNT
TEMPERATURE
(Pxzo/Pez) ( C)
COMPONENT 4-) SOLUTION (g/m z) (°C) L DIRECTION
0 1
(INTERNAL COMPARATIVE . 950
OXIDE LAYER)
S 5 850 X 0.07
EXAMPLE
0.03 800 Si02 0.01 S 5 850 0 0.16 EXAMPLE
1 0.03 950 SiO2 0.02 A 6 900 0 0.18 EXAMPLE
L 0.03 750 Sic, 0.002 5 3 850 x 0.07
COMPARATIVE
EXAMPLE
0.03 950 Si03 0.02 A 0.5 900 0 0.1
COMPARATIVE
EXAMPLE
0.1 950
(INTERNAL
S 3 I 850 x 0.06
COMPARATIVE
OXIDE LAYER) EXAMPLE
0.05 800 A1,03 0.02 S 800 Qo 0.18 EXAMPLE
2 0.05 950 A1203. 0.1 A 3 900 O 0.19 EXAMPLE
0.05 750 A12O3 0.005 5 3 850 x 0.07
COMPARATIVE
EXAMPLE
0.05 950 A1203 0.02 A on 900 Q 0.08
COMPARATIVE
EXAMPLE
0.06 1100 A12O3 0.5 A 5 1100 Qo 0.2 EXAMPLE
0.06 1100 A1203 0.5 A 5 750 Qo 0 1
COMPARATIVE
.
EXAMPLE
0.06 1150 A1203 0.7 A 3 900 X 0.06
COMPARATIVE
EXAMPLE
(INTERNAL COMPARATIVE
0.2 950 S 5 850 X 0.07 OXIDE LAYER) EXAMPLE
0.15 800 (A1,Cr)203 0.02 S 1 800 Qo 0.19 EXAMPLE
0.01 950 (A1,Cr)201 0.1 A 3 900 0 0.19 EXAMPLE
4 0.1 750 (A1,Cr)20, 0.005 S 3 850 X 0.09
COMPARATIVE
0.1 950 (A1,Cr)3O3 0.02 A 0.5 900 O 0 1 COMPARATIVE
EXAMPLE
0.1 1100 (A1,Cr)203 0.9 A 3 900 X 0.07 COMPARATIVE
EXAMPLE
5 0.05 1000 1223 0.2 A 6 1000 Q 0.21 EXAMPLE
6 0.01 950 Si02 0.02 5 5 850 0 0.18 EXAMPLE
0.01 1000 A1203 0.03 A 3 900 Q 0.19 EXAMPLE
7
0.1 1000
(INTERNAL
S 3 850 x 0.05
COMPARATIVE
OXIDE LAYER) EXAMPLE
condition of the present invention being satisfied,
the adhesiveness of the insulating film and the
magnetic property in the L direction were extremely
good. Further, in the case when the external oxide
film was not formed and an internal oxide layer was
f.ormed, the adhesiveness was extremely low.
[0061] (Second Experiment)
The steel slabs of steel No. 1, No. 3, and No. 4
listed in Table 2 were hot rolled to manufacture hotrolled
steel strips each having a thickness of 2.5
mm. Next, annealing of the hot-rolled steel strips
(hot-rolled sheet annealing) was performed at 900°C
for 1 minute. Thereafter, acid pickling was
performed and cold rolling was performed to
manufacture cold-rolled steel strips each having a
thickness of 0.35 mm.
[0062] Subsequently, application of a coating
solution was performed under the condition listed in
Table 4. Next, finish annealing combined with baking
of the coating solution was performed under the
condition listed in Table 4. That is the processes
according to the flowchart illustrated in Fig. 6 were
performed in the second experiment, while the
processes according to the flowchart illustrated in
Fig. 5 were performed in the first experiment. Then,
similarly to the first experiment, the adhesiveness
of each of insulating films and the core loss
improvement rate in the L direction were evaluated.
The result is also listed in Table 4.
- 27 -
TABLE 4
1
4
TETENTION APPLYING TYPE
;INSULATING FILM,
FINISH ANNEALING (BAKING)
ADHESIVENESS
CORE LOSS
IMPROVEMENT
NOTE
COATING
SOLUTION
AMOUNT
( 9/m')
PARTIAL
PRESSURE
( Pa2o /PH2 )
SOAKING
TEMPERATURE
(c)
RATE IN
L DIRECTION
S 5 0.03 800 0 0.16 EXAMPLE
6 0.03 950 0.18 PLE
S 5 0.06 1100 © 0.2 EXAMPLE
A 5 0.06 1100 0.2 EXAMPLE1
S 1 0.15 800 © 0.19 EXAMPLE
A 3 0.01 950 © 0.19 EXAMPLE
[0064] As listed in Table 4, also in the case when
the finish annealing combined with the baking of the
coating solution was performed according to the
flowchart illustrated in Fig. 6, the extremely good
adhesiveness of the insulating film and the extremely
good magnetic property in the L direction were able
to be obtained.
INDUSTRIAL APPLICABILITY
[0065] The present invention may be utilized in, for
example, an industry of manufacturing electrical
steel sheets and an industry in which electrical
steel sheets are used.

CLAIMS
[Claim 1] A non-oriented electrical steel sheet
comprising:
a base iron, an oxide layer containing at least
one type of oxide selected from the group consisting
of Si, Al, and Cr and having a thickness of not less
than 0.01 pm nor more than 0.5 pm being formed on a
surface of the base iron; and
a tension applying type insulating film of not
less than 1 g/m2 nor more than 6 g/m2 on the surface
of the base iron, wherein
the base iron contains:
Si, Al, and Cr: not less than 2 mass% nor more
than 6 mass% in total content; and
Mn: not less than 0.1 mass% nor more than 1.5
mass%,
a content of C of the base iron is equal to or
less than 0.005 mass%, and
a balance of the base iron is composed of Fe and
inevitable impurities.
[Claim 2] The non-oriented electrical steel sheet
according to claim 1, wherein the total content of Al
and Cr of the base iron is equal to or more than 0.8
mass%.
[Claim 3] The non-oriented electrical steel sheet
according to claim 1, wherein the insulating film is
formed by baking of a coating solution containing
phosphate and colloidal silica.
[Claim 4] The non-oriented electrical steel sheet
- 30 -
according to claim 1, wherein the insulating film is
formed by baking of a coating solution containing
boric acid and an alumina sol.
[Claim 5] The non-oriented electrical steel sheet
according to claim 2, wherein the insulating film is
formed by baking of a coating solution containing
phosphate and colloidal silica.
[Claim 6] The non-oriented electrical steel sheet
according to claim 2, wherein the insulating film is
formed by baking of a coating solution containing
boric acid and an alumina sol.
[Claim 7] A manufacturing method of a non-oriented
electrical steel sheet comprising:
performing finish annealing of a cold-rolled
steel strip; and
forming a tension applying type, insulating film
of not less than 1 g/m2 nor more than 6 g/m2 on a
surface of the cold-rolled steel strip, wherein
the cold-rolled steel strip contains:
Si, Al, and Cr: not less than 2 mass % nor more
than 6 mass% in total content; and
Mn: not less than 0.1 mass% nor more than 1.5
mass%,
a content of C of the cold-rolled steel strip is
equal to or less than 0.005 mass%,
a balance of the cold-rolled steel strip is
composed of Fe and inevitable impurities, and
the performing the finish annealing includes
forming an oxide layer containing at least one type
- 31 -
of oxide selected from the group consisting of Si and
Al and having a thickness of not less than 0.01 pm
nor more than 0.5 pm on the surface of the coldrolled
steel strip with setting a temperature of the
cold-rolled steel strip to not lower than 800°C nor
higher than 1100°C in an atmosphere where when the
total content of Si and Al of the cold-rolled steel
strip is represented as X (mass%), a partial pressure
ratio of water vapor to hydrogen is equal to or less
than 0.005 x X2.
[Claim 8] The manufacturing method of a non-oriented
electrical steel sheet according to claim 7, wherein
the forming the insulating film comprises, after the
performing the finish annealing:
applying a coating solution to the surface of the
cold-rolled steel strip; and
performing baking of the coating solution with
setting the temperature of the cold-rolled steel
strip to not lower than 800°C nor higher than 1.100°C.
[Claim 9] The manufacturing method of a non-oriented
electrical steel sheet according to claim 8, wherein
the coating solution contains phosphate and colloidal
silica.
[Claim 10] The manufacturing method of a nonoriented
electrical steel sheet according to claim 8,
wherein the coating solution contains boric acid and
an alumina sol.
[Claim 11] The manufacturing method of a nonoriented
electrical steel sheet according to claim 7,
- 32 -
wherein the forming the insulating film comprises:
applying a coating solution to the surface of the
cold-rolled steel strip before the performing the
finish annealing; and
performing baking of the coating solution during
the finish annealing.
[Claim 12] The manufacturing method of a nonoriented
electrical steel sheet according to claim
11, wherein the coating solution contains phosphate
and colloidal silica.
[Claim 13] The manufacturing method of a nonoriented
electrical steel sheet according to claim
11, wherein the coating solution contains boric acid
and an alumina sot.
[Claim 14] The manufacturing method of a nonoriented
electrical steel sheet according to claim 7,
wherein the total content of Al and Cr of the coldrolled
steel strip is equal to or more than 0.8
mass%.
[Claim 15] The manufacturing method of a nonoriented
electrical steel sheet according to claim 8,
wherein-the total content of Al and Cr of the coldrolled
steel strip is equal to or more than 0.8
mass%.
[Claim 16] The manufacturing method of a nonoriented
electrical steel sheet according to claim 9,
wherein the total content of Al and Cr of the coldrolled
steel strip is equal to or more than 0.8
mass%.
- 33 -
[Claim 17] The manufacturing method of a nonoriented
electrical steel sheet according to claim
10, wherein the total content of Al and Cr of the
cold-rolled steel strip is equal to or more than 0:8
mass%.
[Claim 18] The manufacturing method of a nonoriented
electrical steel sheet according to clam
11, wherein the total content of Al and Cr of the
cold-rolled steel strip is equal to or more than 0.8
mass%.
[Claim.19] The manufacturing method of a non-
-oriented electrical steel sheet according to claim
12, wherein the total content of Al and Cr of the
cold-rolled steel strip is equal to or more than 0.8
mass%.
[Claim 20] The manufacturing method of a nonoriented
electrical steel sheet according to.claim
13, wherein the total content of Al and Cr of the
cold-rolled steel strip is equal to or more than 0.8
mass%.
Table 1
PARTIAL PRESSURE
RATIO (PH2O/PH2)
0.1 0.01
EXITATION DIRECTION L DIRECTION C DIRECTION L DIRECTION C DIRECTION
CORE LOSS
BEFORE FORMING
0.894 0.961 0.883 0.974 INSULATING FILM
(W10/50 (W/kg))
CORE LOSS
AFTER FORMING
0.821 0.971 0.736 0.977 INSULATING FILM
(W10/50 (W/kg))
CORE LOSS
IMPROVEMENT RATE
BETWEEN BEFORE AND 8.20% -1.00% 16.70% -0.30%
AFTER FORMING
INSULATING FILM
------------ - - - - - - - -
TABLE 2
STEEL COMPONENT (MASS%)
No. SiAl Cr Mn
1 3 1 0.3 1 <0.01 1 0.5
2 2 1.5 <0.01 0.5
3 2 2 <0.01 0.5
4 0.5
2 0.5
6 1 1 <0.01 0.5
7 1 3 1 1.2 1 <0.011 0.5
TABLE 3
CONDITION OF EXTERNAL OXIDE FILM TENTION APPLYING TYPE
FINISH ANNEALING (OXIDE LAYER) INSULATING FILM CORE LOSS
STEEL IMPROVEMENT
No PARTIAL SOAKING BAKING ADHESIVENESS
RATE IN
NOTE
.
PRESSURE TEMPERATURE
°
MAINENT
COMPON
THICKNESS
(pm)
COATING
SOLUTION (q/m
AMOUNT
2 )
TEMPERATURE
°
L DIRECTION
(PH20/2E2 ) ( C) ( C)
0 1 950
(INTERNAL COMPARATIVE .
OXIDE LAYER)
S 5 850 X 0.07
EXAMPLE
0.03 800 SiC2 0.01 S 5 850 0 0.16 EXAMPLE
0.03 950 SiO2 0.02 A 6 900 0 0.18 EXAMPLE
1
0.03 750 SiO2 0.002 S 3 850 X 0.07
COMPARATIVE
EXAMPLE
0.03 950 SiO2 0.02 A 0.5 900 0 0.1
COMPARATIVE
EXAMPLE
0 1 950
(INTERNAL,
S 3
COMPARATIVE
.
OXIDE LAYER)
850 X 0.06
EXAMPLE
0.05 800 A12O3 0.02 S 1 800 00 0.18 EXAMPLE
0.05 950 A12O3 0.1 A 3 900 Do 0.19 EXAMPLE
2
0.05 750 A1,03 0.005 S 3 850 X 0.07
COMPARATIVE
EXAMPLE
0.05 950 A12O3 0.02 A 0.5 900 0 0.08
COMPARATIVE
EXAMPLE
0.06 1100 A12O3 0.5 A. 5 1100 Do 0.2 EXAMPLE
0.06 1100 A1203 0.5 A 5 750 © 0.1
COMPARATIVE
3 EXAMPLE
0.06 1150 A.12O3 0.7 A 3 900 0.06
COMPARATIVE
EXAMPLE
0.2 950
(INTERNAL
S 5 850 X 0 07
COMPARATIVE
OXIDE LAYER) .
EXAMPLE
0.15 800 (Al,Cr)20, 0.02 S 1 800 Do 0.19 EXAMPLE
0.01 950 (Al,Cr)203 0.1 A 3 900 Oo 0.19 EXAMPLE
0.1 750 (Al,Cr)203 0.005 S 3 850 X 0.09
COMPARATIVE
EXAMPLE
0.1 950 (Al,Cr)2O3 0.02 A 0.5 900 0 0.1
COMPARATIVE
EXAMPLE
0.1 1100 (Al,Cr),0, 0.9 A 3 900 X 0.07
COMPARATIVE
EXAMPLE
5 0.05 1000 A1203 0.2 A 6 1000 © 0.21 EXAMPLE
6 0.01 950 510, 0.02 S 5 850 0 0.18 EXAMPLE
0.01 1000 A120, 0.03 A 3 900 C 0.19 EXAMPLE
7 (INTERNAL COMPARATIVE
0.1 1000 S 3 850 X 0.05
OXIDE LAYER) EXAMPLE
TABLE 4
TEEL
TETENTION APPLYING TYPE
INSULATING FILM,
FINISH ANNEALING (BAKING)
A
CORE LOSS
IMPROVEMENT
No . DHESIVENESS NOTE
COATING
SOLUTION
AMOUNT
(g/m2)
PARTIAL
PRESSURE
(Px2o /PH2)
SOAKING
TEMPERATURE
(°C)
RATE IN
L DIRECTION
S 5 0.03 800 O 0.16 EXAMPLE
A 6 0.03 950 O 0.18 EXAMPLE
S 5 0.06 1100 0.2 EXAMPLE
3
A 5 0.06 1100 0.2 EXAMPLE
S 1 0.15 800 0.19 EXAMPLE
4 -
A 3 0.01 1 950 0.19 EXAMPLE