DESCRIPTION
TITLE OF INVENTION: NON-ORIENTED ELECTRICAL STEEL
SHEET, MANUFACTURING METHOD THEREOF, LAMINATE FOR
MOTOR IRON CORE, AND MANUFACTURING METHOD THEREOF
TECHNICAL FIELD
[0001] The present invention relates to a non-
) oriented electrical steel sheet suitable for an iron
core material of an electric apparatus, a
manufacturing method thereof, and so on,
BACKGROUND ART
[0002] In recent years, as a driving motor of an
electric vehicle, a hybrid vehicle, and the like, a
motor rotating at a high speed and having a
relatively large capacity is increasingly used. For
this reason, an iron core material to be used for a
driving motor is required to have achievement of low
core loss in a range of several hundred Hz to several
kHz, which is higher than a commercial frequency.
Further, an iron core to be used for a rotor is also
required to have required mechanical strength in
order to withstand a centrifugal force and stress
variation. An iron core material to be used for
other than a driving motor of a vehicle sometimes
needs to have such a requirement.
[0003] Conventionally, techniques have been proposed
in order to achieve core loss reduction and/or
strength improvement (Patent Literatures 1 to 12).
[0004] However, with these techniques, it is
difficult to attain achievement of the core loss
- 1 -
reduction and the strength improvement. Further, in
actuality, some of the techniques have difficulty in
manufacturing a non-oriented electrical steel sheet.
CITATION LIST
PATENT LITERATURE
[0005] Patent Literature 1: Japanese Laid-open Patent
Publication No. 02-008346
Patent Literature 2: Japanese Laid-open Patent
Publication No. 06-330255
Patent Literature 3: Japanese Laid-open Patent
Publication No, 2006-009048
Patent Literature 4: Japanese Laid-open Patent
Publication No. 2006-070269
Patent Literature 5: Japanese Laid-open Patent
Publication No. 10-018005
Patent Literature 6: Japanese Laid-open Patent
Publication No. 2004-084053
Patent Literature 7: Japanese Laid-open Patent
Publication No. 2004-183066
Patent Literature 8: Japanese Laid-open Patent
Publication No. 2007-039754
Patent Literature 9: International Publication
Pamphlet No. W02009/128428
Patent Literature 10: Japanese Laid-open Patent
Publication No. 10-88298
Patent Literature 11: Japanese Laid-open Patent
Publication No. 2005-256019
Patent Literature 12: Japanese Laid-open Patent
Publication No. 11-229094
- 2 -
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006] The present invention has an object to
provide a non-oriented electrical steel sheet capable
of attaining achievement of core loss reduction and
strength improvement, a manufacturing method thereof,
and so on.
SOLUTION TO PROBLEM
[0007] The present invention has been made in order
to solve the above-described problems, and the gist
thereof is as follows.
[0008] (1) A non-oriented electrical steel sheet
containing: in mass%,
C: not less than 0.002% nor more than 0.01%;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.5%;
Al: not less than 0.01% nor more than 3.0%; and
at least one selected from the group consisting
of Ti, V, Zr, and Nb,
a balance being composed of Fe and inevitable
impurities,
wherein
a value of a parameter Q represented by "Q =
([Ti]/48 + [V]/51 + [Zr]/91 + [Nb]/93)/{[C]/12)" is
not less than 0.9 nor more than 1.1, when contents of
Ti, V, Zr, Nb, and C (mass%) are represented as [Ti],
[V], [Zr], [Nb], and [C] respectively,
a matrix of a metal structure is a ferrite phase,
the metal structure does not include a non-
- 3 -
i
41
recrystallized structure,
an average grain size of ferrite grains
constituting the ferrite phase is not less than 30 pm
nor more than 200 pm,
a precipitate containing at least one selected
from the group consisting of Ti, V, Zr, and Nb exists
with a density of 1 particle/iam^ or more in the
ferrite grain, and
an average grain size of the precipitate is not
less than 0.002 yim nor more than 0.2 ym.
[0009] (2) The non-oriented electrical steel sheet
according to (1), further containing at least one
selected from the group consisting of: in mass%,
N: not less than 0.001% nor more than 0.004%;
Cu: not less than 0.5% nor more than 1.5%; and
Sn: not less than 0.05% nor more than 0.5%.
[0010] (3) The non-oriented electrical steel sheet
according to (1) or (2), wherein the precipitate is
at least one selected from the group consisting of
carbide, nitride, and carbonitride.
[0011] (4) A manufacturing method of a non-oriented
electrical steel sheet including:
performing hot rolling of a slab to obtain a hotrolled
steel sheet;
performing cold rolling of the hot-rolled steel
sheet to obtain a cold-rolled steel sheet; and
performing finish annealing of the cold-rolled
steel sheet under a condition in which a soaking
temperature is not lower than 950°C nor higher than
- 4 -
1100°C, a soaking time period is 20 seconds or longer,
and an average cooling rate from the soaking
temperature to 700°C is not less than 2°C/sec nor more
than 60°C/sec,
wherein
the slab contains: in mass%,
C: not less than 0.002% nor more than 0.01%;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.5%;
Al: not less than 0.01% nor more than 3.0%; and
at least one selected from the group consisting
of Ti, V, Zr, and Nb,
a balance being composed of Fe and inevitable
impurities, and
a value of a parameter Q represented by "Q =
([Ti]/48 + [V]/51 + [Zr]/91 + [Nb]/93)/([C]/12)" is
not less than 0.9 nor more than 1.1, when contents of
Ti, V, Zr, Nb, and C (mass%) are represented as [Ti],
[V], [Zr], [Nb], and [C] respectively.
[0012] (5) The manufacturing method of the nonoriented
electrical steel sheet according to (4),
wherein the slab further contains at least one
selected from the group consisting of: in mass%,
N: not less than 0.001% nor more than 0.004%;
Cu: not less than 0.5% nor more than 1.5%; and
Sn: not less than 0.05% nor more than 0.5%.
[0013] (6) The manufacturing method of the nonoriented
electrical steel sheet according to (4) or
(5), further including, before the performing cold
- 5 -
rolling, performing hot-rolled sheet annealing of the
hot-rolled steel sheet.
[0014] (7) A manufacturing method of a non-oriented
electrical steel sheet including:
performing hot rolling of a slab to obtain a hotrolled
steel sheet;
performing cold rolling of the hot-rolled steel
sheet to obtain a cold-rolled steel sheet;
performing cold-rolled sheet annealing of the
cold-rolled steel sheet under a condition in which a
first soaking temperature is not lower than 950°C nor
higher than 1100°C, a soaking time period is 20
seconds or longer, and an average cooling rate from
the first soaking temperature to 700°C is 20°C/sec or
more; and
after the cold-rolled sheet annealing, performing
finish annealing of the cold-rolled steel sheet under
a condition in which a second soaking temperature is
not lower than 400°C nor higher than 800°C, a soaking
time period is not shorter than 10 minutes nor longer
than 10 hours, and an average cooling rate from the
second soaking temperature to 300°C is not less than
0.0001°C/sec nor more than 0.1°C/sec,
wherein
the slab contains: in mass%,
C: not less than 0.002% nor more than 0.01%;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.5%;
Al: not less than 0.01% nor more than 3.0%; and
- 6 -
at least one selected from the group consisting
of Ti, V, Zr, and Nb,
a balance being composed of Fe and inevitable
impurities, and
a value of a parameter Q represented by "Q =
([Ti]/48 + [V]/51 + [Zr]/91 + [Nb]/93) / ( [C]/12)" is
not less than 0.9 nor more than 1.1, when contents of
Ti, V, Zr, Nb, and C (mass%) are represented as [Ti],
[V], [Zr], [Nb], and [C] respectively.
[0015] (8) The manufacturing method of the nonoriented
electrical steel sheet according to (7),
wherein the slab further contains at least one
selected from the group consisting of: in mass%,
N: not less than 0.001% nor more than 0.004%;
Cu: not less than 0.5% nor more than 1.5%; and
Sn: not less than 0.05% nor more than 0.5%.
[0016] (9) The manufacturing method of the nonoriented
electrical steel sheet according to (7) or
(8), further including, before the performing cold
rolling, performing hot-rolled sheet annealing of the
hot-rolled steel sheet.
[0017] (10) A laminate for a motor iron core
including:
non-oriented electrical steel sheets laminated to
one another,
wherein
the non-oriented electrical steel sheets contain:
in mass%,
C: not less than 0.002% nor more than 0.01%;
- 7 -
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.5%;
Al: not less than 0.01% nor more than 3.0%; and
at least one selected from the group consisting
of Ti, V, Zr, and Nb,
a balance being composed of Fe and inevitable
impurities,
a value of a parameter Q represented by "Q =
([Ti]/48 + [V]/51 + [Zr]/91 + [Nb]/93)/( [ C]/12)" is
not less than 0.9 nor more than 1.1, when contents of
Ti, V, Zr, Nb, and C (mass%) are represented as [Ti],
[V], [Zr], [Nb], and [C] respectively,
a matrix of a metal structure is a ferrite phase,
the metal structure does not include a nonrecrystallized
structure,
an average grain size of ferrite grains
constituting the ferrite phase is not less than 30 ym
nor more than 200 \im,
a precipitate containing at least one selected
from the group consisting of Ti, V, Zr, and Nb exists
with a density of 1 particle/pm^ or more in the
ferrite grain, and
an average grain size of the precipitate is not
less than 0.002 \iTa nor more than 0.2 \im.
[0018] (11) The laminate for the motor iron core
according to (10), wherein the non-oriented
electrical steel sheets further containing at least
one selected from the group consisting of: in mass%,
N: not less than 0.001% nor more than 0.004%;
- 8 -
Cu: not less than 0.5% nor more than 1.5%; and
Sn: not less than 0.05% nor more than 0,5%.
[0019] (12) The laminate for the motor iron core
according to (10) or (11), wherein the precipitate is
at least one selected from the group consisting of
carbide, nitride, and carbonitride.
[0020] (13) A manufacturing method of a laminate for
a motor iron core including:
laminating non-oriented electrical steel sheets
to one another to obtain a laminate; and
performing annealing on the laminate under a
condition in which a soaking temperature is not lower
than 400°C nor higher than 800°C, a soaking time
period is not shorter than 2 minutes nor longer than
10 hours, and a cooling rate from the soaking
temperature to 300°C is not less than 0.0001°C/sec nor
more than 0.1°C/sec,
wherein
the non-oriented electrical steel sheets contain:
in mass%,
C: not less than 0,002% nor more than 0.01%;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.5%;
Al: not less than 0.01% nor more than 3.0%; and
at least one selected from the group consisting
of Ti, V, Zr, and Nb,
a balance being composed of Fe and ine"vitable
impurities,
a value of a parameter Q represented by "Q =
- 9 -
([Ti]/48 + [V]/51 + [Zr]/91 + [Nb]/93)/([C]/12)" is
not less than 0.9 nor more than 1.1, when contents of
Ti, V, Zr, Nb, and C (inass%) are represented as [Ti],
[V], [Zr], [Nb], and [C] respectively,
a matrix of a metal structure is a ferrite phase,
the metal structure does not include a nonrecrystallized
structure,
an average grain size of ferrite grains
constituting the ferrite phase is not less than 30 ]im
nor more than 200 \im,
a precipitate containing at least one selected
from the group consisting of Ti, V, Zr, and Nb exists
with a density of 1 particle/ym^ or more in the
ferrite grain, and
an average grain size of the precipitate is not
less than 0.002 jam nor more than 0.2 \im.
[0021] (14) The manufacturing method of the laminate
for the motor iron core according to (13), wherein
the non-oriented electrical steel sheets further
contain at least one selected from the group
consisting of: in mass%,
N: not less than 0.001% nor more than 0.004%;
Cu: not less than 0.5% nor more than 1.5%; and
Sn: not less than 0.05% nor more than 0.5%.
[0022] (15) The manufacturing method of the laminate
for the motor iron core according to (13) or (14),
wherein the precipitate is at least one selected from
the group consisting of carbide, nitride, and
carbonitride.
- 10 -
4
ADVANTAGEOUS EFFECTS OF INVENTION
[0023] According to the present invention, the
composition and structure of a non-oriented
electrical steel sheet are defined appropriately, so
that it is possible to attain achievement of core
loss reduction and strength improvement.
BRIEF DESCRIPTION OF DRAWINGS
[0024] [Fig. 1] Fig. 1 is a schematic view depicting
a structure of a laminate for a motor iron core
according to an embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0025] First, a non-oriented electrical steel sheet
according to an embodiment of the present invention
and a manufacturing method thereof will be explained.
[0026] The non-oriented electrical steel sheet
according to the present embodiment has a
predetermined composition, a matrix of a metal
structure is a ferrite phase, and the metal structure
does not contain a non-recrystallized structure.
Further, an average grain size of ferrite grains
constituting the ferrite phase is not less than 30 pm
nor more than 200 ]ixa, a precipitate containing at
least one selected from the group consisting of Ti,
V, Zr, and Nb exists in the ferrite grain with a
density of 1 particle/pm^ or more, and an average
grain size of the precipitate is not less than 0.002
pm nor more than 0.2 \im. Such a constitution makes
it possible to attain achievement of core loss
reduction and strength improvement. As a result, it
- 11 -
is possible to greatly contribute to achievement of
high efficiency of a motor, and the like.
[0027] Further, in a first manufacturing method of
the non-oriented electrical steel sheet according to
the present embodiment, hot rolling of a slab having
a predetermined composition is performed to obtain a
hot-rolled steel sheet. Next, cold rolling of the
hot-rolled steel sheet is performed to obtain a coldrolled
steel sheet. Next, finish annealing of the
cold-rolled steel sheet is performed under a
condition in which a soaking temperature is not lower
than 950°C nor higher than 1100°C, a soaking time
period is 20 seconds or longer, and an average
cooling rate from the above-described soaking
temperature to 700°C is not less than 2°C/sec nor more
than 60°C/sec.
[0028] Further, in a second manufacturing method of
the non-oriented electrical steel sheet according to
i
the present embodiment, hot rolling of a slab having
a predetermined composition is performed to obtain a
hot-rolled steel sheet. Next, cold rolling of the
hot-rolled steel sheet is performed to obtain a coldrolled
steel sheet. Next, cold-rolled sheet
annealing of the cold-rolled steel sheet is performed
under a condition in which a first soaking
temperature is not lower than 950°C nor higher than
1100°C, a soaking time period is 20 seconds or longer,
and an average cooling rate from the first soaking
temperature to 700°C is 20°C/sec or more. Next, after
- 12 -
the cold-rolled sheet annealing, finish annealing of
the cold-rolled steel sheet is performed under a
condition in which a second soaking temperature is
not lower than 400°C nor higher than 800°C, a soaking
time period is not shorter than 10 minutes nor longer
than 10 hours, and an average cooling rate from the
second soaking temperature to 300°C is not less than
0.0001°C/sec nor more than 0.1°C/sec.
[0029] Here, the composition of the non-oriented
electrical steel sheet will be explained.
Hereinafter, "%" being the unit of a content means
"mass%." Further, the composition of the slab is
handed over to the non-oriented electrical steel
sheet as it is, and thus the composition of the nonoriented
electrical steel sheet to be explained here
is also a composition of a slab to be used for the
manufacture. The non-oriented electrical steel sheet
according to the present embodiment contains: for
example, C: not less than 0.002% nor more than 0.01%,
Si: not less than 2.0% nor more than 4.0%, Mn: not
less than 0.05% nor more than 0.5%, and Al: not less
than 0.01% nor more than 3.0%, and further contains
at least one selected from the group consisting of
Ti, V, Zr, and Nb. Further, the balance of the nonoriented
electrical steel sheet is composed of Fe and
inevitable impurities, and a value of a parameter Q
represented by "Q = ([Ti]/48 + [V]/51 + [Zr]/91 +
[Nb]/93)/( [C]/12)" is not less than 0.9 nor more than
1.1, when contents of Ti, V, Zr, Nb, and C (mass%)
- 13 -
are represented as [Ti], [V], [Zr], [Nb], and [C]
respectively.
[0030]
C forms fine precipitates with Ti, V, Zr, and Nb.
The fine precipitate contributes to improvement of
strength of steel. When the C content is less than
0.002%, it is not possible to obtain precipitates in
an amount sufficient for the improvement of the
strength. When the C content is greater than 0.01%,
precipitates are likely to precipitate coarsely. The
coarse precipitates are not likely to contribute to
the improvement of the strength. Further, when
precipitates precipitate coarsely, core loss is
likely to deteriorate. Thus, the C content is not
less than 0.002% nor more than 0.01%. Further, the C
content is preferably 0.006% or more, and is also
preferably 0.008% or less.
[0031]
Si increases resistivity of steel to reduce core
loss. When the Si content is less than 2.0%, it is
not possible to obtain the effect sufficiently. When
the Si content is greater than 4.0%, steel is brittle
to thereby make it difficult to perform rolling.
Thus, the Si content is not less than 2.0% nor more
than 4.0%. Further, the Si content is preferably
3.5% or less.
[0032]
Mn, similarly to Si, increases resistivity of
steel to reduce core loss. Further, Mn coarsens
- 14 -
sulfide to make it harmless. When the Mn content is
less than 0.05%, it is not possible to obtain the
effects sufficiently. When the Mn content is greater
than 0.5%, a magnetic flux density is likely to
decrease and cracking is likely to occur during cold
rolling. Further, an increase in cost also is
significant. Thus, the Mn content is not less than
0.05% nor more than 0.5%. Further, the Mn content is
preferably 0.1% or more, and is also preferably 0.3%
or less .
[0033]
Al, similarly to Si, increases resistivity of
steel to reduce core loss. Further, Al functions as
a deoxidizing material. When the Al content is less
than 0.01%, it is not possible to obtain the effects
sufficiently. When the Al content is greater than
3.0%, steel is brittle to thereby make it difficult
to perform rolling. Thus, the Al content is not less
than 0.01% nor more than 3.0%. Further, the Al
content is preferably 0.3% or more, and is also
preferably 2.0% or less.
[0034]
Ti, V, Zr, and Nb form fine precipitates with C
and/or N. The precipitates contribute to improvement
of strength of steel. When the value of the
parameter Q is less than 0.9, C is excessive with
respect to Ti, V, Zr, and Nb, and thus C strongly
tends to exist in the steel sheet in a solid solution
state after the finish annealing. When C exists in a
- 15 -
solid solution state, magnetic aging is likely to
occur. When the value of the parameter Q is greater
than 1.1, C is insufficient with respect to Ti, V,
Zr, and Nb, and thus it is difficult to obtain fine
precipitates to thereby make it impossible to obtain
the desired strength. Thus, the value of the
parameter Q is not less than 0.9 nor more than 1.1.
Further, the value of the parameter Q is preferably
0.95 or more, and is also preferably 1.05 or less.
[0035] The non-oriented electrical steel sheet
according to the present embodiment may further also
contain at least one selected from the group
consisting of N: not less than 0.001% nor more than
0.004%, Cu: not less than 0.5% nor more than 1.5%,
and Sn: not less than 0.05% nor more than 0.5%.
[0036]
N, similarly to C, forms fine precipitates with
Ti, V, Zr, and Nb. The fine precipitates contribute
to improvement of strength of steel. When the N
content is less than 0.001%, it is not possible to
obtain precipitates in an amount sufficient for
further improvement of strength. Thus, the N content
is preferably 0.001% or more. When the N content is
greater than 0.004%, precipitates are likely to
precipitate coarsely. Thus, the N content is 0.004%
or less.
[0037]
The present inventors found out that when Cu is
- 16 -
contained in steel, precipitates containing at least
one selected from the group consisting of Ti, V, Zr,
and Nb are likely to precipitate finely. The fine
precipitates contribute to improvement of strength of
steel. When the Cu content is less than 0.5%, it is
not possible to obtain the effect sufficiently.
Thus, the Cu content is preferably 0.5% or more.
Further, the Cu content is more preferably 0.8% or
more. When the Cu content is greater than 1.5%,
steel is likely to be brittle. Thus, the Cu content
is 1.5% or less. Further, the Cu content is also
preferably 1.2% or less.
[0038] The reason why in the case of Cu being
contained in steel, the above-described precipitate
precipitates finely is unclear, but the present
inventors suppose that this is because a local
concentration distribution of Cu is generated in a
matrix to be a precipitation site of carbide. Thus,
it is also acceptable that Cu has not precipitated
when the above-described precipitate is made to
precipitate. On the other hand, a precipitate of Cu
contributes to improvement of strength of a nonoriented
electrical steel sheet. Thus, it is also
acceptable that Cu has precipitated.
[0039]
The present inventors also found out that when Sn
is contained in steel, precipitates containing at
least one selected from the group consisting of Ti,
V, Zr, and Nb are likely to precipitate finely. The
- 17 -
m
fine precipitates contribute to improvement of
strength of steel. When the Sn content is less than
0.05%, it is not possible to obtain the effect
sufficiently. Thus, the Sn content is preferably
0.05% or more. Further, the Sn content is more
preferably 0.08% or more. When the Sn content is
greater than 0.5%, steel is likely to be brittle.
Thus, the Sn content is 0.5% or less. Further, the
Sn content is also preferably 0.2% or less.
[0040]
Ni of not less than 0.5% nor more than 5% and P
of not less than 0.005 nor more than 0.1% may also be
contained. Ni and P contribute to solution hardening
of the steel sheet, and the like.
[0041] Next, the metal structure of the non-oriented
electrical steel sheet will be explained.
[0042] As described above, the matrix (matrix) of
the metal structure of the non-oriented electrical
steel sheet according to the present embodiment is a
ferrite phase, and the non-recrystallized structure
is not contained in the metal structure. This is
because the non-recrysta H i zed structure improves the
strength but deteriorates core loss significantly.
Further, when the average grain size of the ferrite
grains constituting the ferrite phase is less than 30
pm, hysteresis loss increases. When the average
grain size of the ferrite grains is greater than 200
jam, an effect of fine grain hardening decreases
significantly. Thus, the average grain size of the
- 18 -
ferrite grains is not less than 30 pm nor more than
200 pm. Further, the average grain size of the
ferrite grains is preferably 50 ym or more, and is
more preferably 80 ym or more. The average grain
size of the ferrite grains is also preferably 100 pm
or less.
[0043] In the present embodiment, a precipitate
containing at least one selected from the group
consisting of Ti, V, Zr, and Nb exists in the ferrite
grain. As the precipitate is smaller and a number
density of the precipitate is higher, high strength
can be obtained. Further, the size of the^
precipitate is important also in terms of magnetic
properties. For example, in the case when the
diameter of the precipitate is smaller than a
thickness of a magnetic domain wall, it is possible
to prevent deterioration (increase) of hysteresis
loss caused by pinning of domain wall displacement.
When the average grain size of the precipitate is
greater than 0.2 ym, it is not possible to obtain the
effects sufficiently. Thus, the average grain size
of the precipitate is 0.2 \im or less. The average
grain size is preferably 0.1 ym or less, is more
preferably 0.05 ym or less, and is still more
preferably 0.01 ym or less.
[0044] Incidentally, when a theoretical thickness of
a magnetic domain wall of pure iron is estimated in
terms of exchange energy and anisotropy energy, it is
0.1 ym or so, but an actual thickness of the magnetic ^ .
- 19 - ' -t:.
domain wall changes according to the orientation in
which the magnetic domain wall is formed. Further,
as is an non-oriented electrical steel sheet, in the
case when elements other than Fe are contained, the
thickness of the magnetic domain wall is also
affected by their types, amounts and the like. From
the viewpoint as well, it is conceivable that the
average grain size of the precipitate, which is 0.2
Jim or less, is appropriate.
[0045] When the average grain size of the
precipitate is less than 0.002 \im (2 nm) , an effect
of increasing the mechanical strength is saturated.
Further, it is difficult to control the average grain
size of the precipitate in a range of less than 0.002
pm. Thus, the average grain size of the precipitate
is 0.002 pm or more.
[0046] Further, as the number density of the
precipitate is higher, the high strength can be
obtained, and when the number density of the
precipitate in the ferrite grain is less than 1
particle/pm'^, it is difficult to obtain the desired
strength. Therefore, the number density of the
precipitate is 1 particle/pm'^ or more. The number
density is preferably 100 particles/pm'^ or more, is
more preferably 1000 particles/ym^ or more, is further
preferably 10000 particles/pm^ or more, and is still
more preferably 100000 particles/pm^ or more.
[0047] Next, the manufacturing method of the nonoriented
electrical steel sheet will be explained.
- 20 -
In the first manufacturing method of the non-oriented
electrical steel sheet according to the present
embodiment, as described above, the hot rolling of
the slab having the predetermined composition is
performed to obtain the hot-rolled steel sheet.
Next, the cold rolling of the hot-rolled steel sheet
is performed to obtain the cold-rolled steel sheet.
Next, the finish annealing of the cold-rolled steel
sheet is performed under the condition in which the
soaking temperature is not lower than 950°C nor higher
than 1100°C, the soaking time period is 20 seconds or
longer, and the average cooling rate from the abovedescribed
soaking temperature to 700°C is not less
than 2°C/sec nor more than 60°C/sec. Further, in the
second manufacturing method, the hot rolling of the
slab having the predetermined composition is
performed to obtain the hot-rolled steel sheet.
Next, the cold rolling of the hot-rolled steel sheet
is performed to obtain the cold-rolled steel sheet.
Next, the cold-rolled sheet annealing of the coldrolled
steel sheet is performed under the condition
in which the first soaking temperature is not lower
than 950°C nor higher than 1100°C, the soaking time
period is 20 seconds or longer, and the average
cooling rate from the first soaking temperature to
700°C is 20°C/sec or more. Next, after the coldrolled
sheet annealing, the finish annealing of the
cold-rolled steel sheet is performed under the
condition in which the second soaking temperature is
- 21 -
not lower than 400°C nor higher than 800°C, the
soaking time period is not shorter than 10 minutes
nor longer than 10 hours, and the average cooling
rate from the second soaking temperature to 300°C is
not less than 0.0001°C/sec nor more than 0.1°C/sec.
[0048] First, the first manufacturing method will be
explained.
[0049] When a slab heating temperature of the hot
rolling is lower than 1050°C, the hot rolling is
likely to be difficult to be performed. When the
slab heating temperature is higher than 1200°C,
sulfide and the like are once dissolved and the
sulfide and the like precipitate finely in a cooling
process of the hot rolling, and thus the growth of
the ferrite grains in the finish annealing (the
annealing after the cold rolling) is likely to be
prevented. Thus, the slab heating temperature is
preferably not lower than 1050°C nor higher than
1200°C.
[0050] In the hot rolling, for example, rough
rolling and finish rolling are performed. A finish
temperature of the finish rolling (finishing
temperature) is preferably not lower than 750°C nor
higher than 950°C. This is to obtain high
productivity.
[0051] The thickness of the hot-rolled steel sheet
is not limited in particular. However, it is not
easy to set the thickness of the hot-rolled steel
sheet to less than 1.6 mm, which also leads to a
- 22 -
decrease in productivity. On the other.hand, when
the thickness of the hot-rolled steel sheet is 2.7
mm, it is sometimes necessary to excessively increase
a reduction ratio in the following cold rolling. In
the case when the reduction ratio in the cold rolling
is high excessively, a texture of a non-oriented
electrical steel sheet may deteriorate and magnetic
properties (magnetic flux density and core loss) may
deteriorate. Thus, the thickness of the hot-rolled
steel sheet is preferably not less than 1.6 mm nor
more than 2.7 mm.
[0052] The cold rolling may be performed only one
time, or may also be performed two or more times with
intermediate annealing being interposed therebetween.
The final reduction ratio in the cold rolling is
preferably not less than 60% nor more than 90%. This
is to make the metal structure (texture) of the nonoriented
electrical steel sheet obtained after the
finish annealing better to obtain the high magnetic
flux density and the low core loss. Further, in the
case of the intermediate annealing being performed,
its temperature is preferably not lower than 900°C nor
higher than 1100°C. This is to make the metal
structure better. The final reduction ratio is more
preferably 65% or more, and is also more preferably
82% or less.
[0053] In the finish annealing, in a soaking
process, the precipitates containing Ti, V, Zr,
and/or Nb that are contained in the cold-rolled steel
- 23 -
sheet are made to be once solid-dissolved, and in the
following cooling process, the precipitates
containing Ti, V, Zr, and/or Nb are made to
precipitate finely. When the soaking temperature is
lower than 950°C, it is difficult to sufficiently grow
the ferrite grains and sufficiently solid-dissolve
the precipitates containing Ti, V, Zr, and/or Nb.
When the soaking temperature is higher than 1100°C,
energy consumption is increased, and incidental
facilities such as a hearth roll are likely to be
damaged. Thus, the soaking temperature is not lower
than 950°C nor higher than 1100°C. Further, when the
soaking time period is shorter than 20 seconds, it is
difficult to sufficiently grow the ferrite grains and
sufficiently solid-dissolve the precipitates
containing Ti, V, Zr, and/or Nb. Thus, the soaking
temperature is 20 seconds or longer. When the
soaking time period is longer than 2 minutes, a
decrease in productivity is significant. Thus, the
soaking temperature is preferably shorter than 2
minutes .
[0054] Incidentally, a dissolution temperature of
the precipitates containing Ti, V, Zr, and/or Nb is
affected by the contents of Ti, V, Zr, Nb, C, and N.
For this reason, the temperature of the finish
annealing is preferably adjusted according to the
contents of Ti, V, Zr, Nb, C, and N. That is, the
temperature of the finish annealing is appropriately
adjusted, thereby making it possible to obtain the
- 24 -
higher mechanical strength (tensile strength).
[0055] In the cooling process of the finish
annealing, as described above, the precipitates
containing Ti, V, Zr, and/or Nb are made to
precipitate finely. When the average cooling rate
from the soaking temperature to 700°C is less than
2°C/sec, the precipitates are likely to precipitate
coarsely, thereby making it impossible to obtain the
sufficient strength. When the average cooling rate
is greater than 60°C/sec, it is not possible to make
the precipitates containing Ti, V, Zr, and/or Nb
precipitate sufficiently and obtain the sufficient
strength thereby. Thus, the average cooling rate
from the soaking temperature to 700°C is not less than
2°C/sec nor more than 60°C/sec.
[0056] Incidentally, before performing the cold
rolling, annealing of the hot-rolled steel sheet,
namely hot-rolled sheet annealing may also be
performed. The appropriate hot-rolled sheet
annealing is performed, thereby making the texture of
the non-oriented electrical steel sheet more
desirable and making it possible to obtain the more
excellent magnetic flux density. In the case when a
soaking temperature of the hot-rolled sheet annealing
is lower than 850°C, and in the case when a soaking
time period is shorter than 30 seconds, it is
difficult to make the texture more desirable. In the
case when the soaking temperature is higher than
1100°C, and in the case when the soaking time period
- 25 -
is longer than 5 minutes, the energy consumption is
increased, and the incidental facilities such as a
hearth roll are likely to be damaged, and an increase
in cost is significant. Thus, in the hot-rolled
sheet annealing, the soaking temperature is
preferably not lower than 850°C nor higher than 1100°C
and the soaking time period is preferably not shorter
than 30 seconds nor longer than 5 minutes.
[0057] In this manner, the non-oriented electrical
steel sheet according to the present embodiment can
be manufactured. Then, the non-oriented electrical
steel sheet manufactured in this manner is provided
with the metal structure as described above to be
able to obtain the high strength and the low core
loss. That is, in the soaking process of the finish
annealing, recrystallization is caused and the abovedescribed
ferrite phase is generated, and in the
following cooling process, the above-described
precipitates are generated. Incidentally, after the
finish annealing, an insulating film may also be
formed according to need.
[0058] Next, the second manufacturing method will be
explained.
[0059] In the second manufacturing method, under the
condition similar to that of the first manufacturing
method, the hot rolling and the cold rolling are
performed. Incidentally, although the reason why in
the first manufacturing method the slab heating
temperature is 1200°C or lower is because when the
- 26 -
slab heating temperature is higher than 1200°C as
described above, the growth of the ferrite grains in
the finish annealing is likely to be prevented, the
reason why in the first manufacturing method the slab
heating temperature is 1200°C or lower is because when
the slab heating temperature is higher than 1200°C,
the growth of the ferrite grains in the cold-rolled
sheet annealing (the annealing after the cold
rolling) is likely to be prevented. Further, hotrolled
sheet annealing may also be performed under
the condition similar to that of the first
manufacturing method.
[0060] In the cold-rolled sheet annealing, the
precipitates containing Ti, V, Zr, and/or Nb that are
contained in the cold-rolled steel sheet are made to
be solid-dissolved. When the soaking temperature is
lower than 950°C, it is difficult to sufficiently grow
the ferrite grains and sufficiently solid-dissolve
the precipitates containing Ti, V, Zr, and/or Nb.
When the soaking temperature is higher than 1100°C,
the energy consumption is increased, and the
incidental facilities such as a hearth roll are
likely to be damaged. Thus, the soaking temperature
is not lower than 950°C nor higher than 1100°C.
Further, when the soaking time period is shorter than
20 seconds, it is difficult to sufficiently grow the
ferrite grains and sufficiently solid-dissolve the
precipitates containing Ti, V, Zr, and/or Nb. When
the heating time period is longer than 2 minutes, a
- 27 -
decrease in productivity is significant. Thus, the
soaking temperature is preferably shorter than 2
minutes.
[0061] In the cooling process of the cold-rolled
sheet annealing, solid-dissolved Ti, V, Zr, and/or Nb
are/is prevented from being precipitated as much as
possible and their/its solid-solution states/solidsolution
state as they are/as it is are/is
maintained. When the average cooling rate from the
soaking temperature to 700°C is less than 20°C/sec,
Ti, V, Zr, and/or Nb are/is likely to precipitate in
large amounts. Thus, the average cooling rate from
the soaking temperature to 700°C is 20°C/sec or more.
The average cooling rate is preferably 60°C/sec or
more, and is more preferably 100°C/sec or more.
[0062] In the finish annealing, with Ti, V, Zr,
and/or Nb that are/is solid-dissolved in the coldrolled
steel sheet obtained after the cold-rolled
sheet annealing, precipitates containing Ti, V, Zr,
and/or Nb are made to precipitate finely. In the
case when the soaking temperature is lower than 400°C,
and in the case when the soaking time period is
shorter than 10 minutes, it is difficult to make the
precipitates containing Ti, V, Zr, and/or Nb
precipitate sufficiently. In the case when the
soaking temperature is higher than 800°C, and in the
case when the soaking time period is longer than 10
hours, the energy consumption is increased, or the
incidental facilities such as a hearth roll are
- 28 -
likely to be damaged, and an increase in cost is
significant. Further, the precipitates precipitate
coarsely, thereby making it impossible to obtain the
sufficient strength. Thus, the soaking temperature
is not lower than 400°C nor higher than 800°C, and the
soaking time period is not longer than 10 minutes nor
shorter than 10 hours. Further, the soaking
temperature is preferably 500°C or higher. When the
average cooling rate from the soaking temperature to
300°C is less than 0.0001°C/sec, the precipitates are
likely to precipitate coarsely, thereby making it
impossible to obtain the sufficient strength. When
thise average cooling rate is greater than 0.1°C/sec,
it is not possible to make the precipitates
containing Ti, V, Zr, and/or Nb precipitate
sufficiently and obtain the sufficient strength
thereby. Thus, the average cooling rate from the
soaking temperature to 300°C is not less than
0.0001°C/sec nor more than 0.1°C/sec.
[0063] In this manner, the non-oriented electrical
steel sheet according to this embodiment can be
manufactured. Then, the non-oriented electrical
steel sheet manufactured in this manner is provided
with the metal structure as described above to be
able to obtain the high strength and the low core
loss. That is, in the cold-rolled sheet annealing,
recrystallization is caused and the above-described
ferrite phase is generated, and in the following
finish annealing, the above-described precipitates
- 29 -
are generated. Incidentally, after the finish
annealing, an insulating film may also be formed
according to need.
[0064] Incidentally, subsequent to the cooling in
the cold-rolled sheet annealing, the finish annealing
may also be performed continuously. That is, after
the cooling down to 700°C in the cold-rolled sheet
annealing, the finish annealing may also be started
in a range of not lower than 400°C nor higher than
800°C without cooling down to lower than 400°C.
[0065] As above, in each of the first manufacturing
method and the second manufacturing method, in the
annealing after the cold rolling, the ferrite grains
are grown sufficiently, and then the precipitates are
made to precipitate. Therefore, it is possible to
avoid the growth of crystal grains from being
inhibited by the precipitates in advance. Further,
it is also possible to make the precipitates
precipitate smaller than the thickness of the
magnetic domain wall. Thus, it is also possible to
suppress the deterioration of the core loss caused by
pinning of domain wall displacement.
[0066] Next, a laminate for a motor iron core
constituted by using the non-oriented electrical
steel sheets according to the present embodiment will
be explained. Fig. 1 is a schematic view depicting a
laminate for a motor iron core constituted by using
the non-oriented electrical steel sheets according to
the present embodiment.
- 30 -
[0067] In a laminate 2 for a motor iron core
depicted in Fig. 1, non-oriented electrical steel
sheets 1 according to the embodiment are included.
The laminate 2 for a motor iron core can be obtained
in a manner that the non-oriented electrical steel
sheets 1 are formed into a desired shape by a method
such as punching and are laminated to be fixed by a
method such as caulking, for example. The nonoriented
electrical steel sheets 1 are included, so
that of the laminate 2 for a motor iron core, a core
loss is low and mechanical strength is high.
[0068] It is also possible to complete the laminate
2 for a motor iron core at the time when the fixation
as described above is finished. Further, it is also
possible that after the above-described fixation,
annealing is performed under a condition in which a
soaking temperature is not lower than 400°C nor higher
than 800°C, a soaking time period is not shorter than
2 minutes nor longer than 10 hours, and an average
cooling rate from the above-described soaking
temperature to 300°C is not less than 0.0001°C nor
more than 0.1°C, and after such annealing is finished,
the laminate 2 for a motor iron core is completed.
By performing such annealing, precipitates are
precipitated, thereby making it possible to further
improve the strength.
[0069] In the case when the soaking temperature of
the annealing is lower than 400°C, and in the case
when the soaking time period is shorter than 2
- 31 -
minutes, it is difficult to make the precipitates
precipitate sufficiently. In the case when the
soaking temperature is higher than 800°C, and in the
case when the soaking time period is longer than 10
hours, the energy consumption is increased, or the
incidental facilities are likely to be damaged, and
an increase in cost is significant. Further, the
precipitates may precipitate coarsely to thereby make
it difficult to increase the strength sufficiently.
Thus, the soaking temperature is preferably not lower
than 400°C nor higher than 800°C, and the soaking time
period is preferably not shorter than 2 minutes nor
longer than 10 hours. Further, the soaking time
period is more preferably 500°C or higher, and the
soaking time period is more preferably 10 minutes or
longer. When the average cooling rate from the
soaking temperature to 300°C is less than
0. 0001°C/sec, carbide is likely to precipitate
coarsely. When the average cooling rate is greater
than 0.1°C/sec, it is difficult to make the
precipitates precipitate sufficiently. Thus, the
average cooling rate from the soaking temperature to
300°C is preferably not less than 0.0001°C/sec nor
more than 0.1°C/sec.
[Example]
[0070] Next, experiments conducted by the present
inventors will be explained. Conditions and so on in
these experiments are examples employed for
confirming the applicability and effects of the
- 32 -
present invention, and the present invention is not
limited to these examples.
[0071] (Experimental example 1)
First, steels having various compositions listed
in Table 1 were melted by vacuum melting. Then, hot
rolling of each of obtained slabs was performed to
obtain hot-rolled steel sheets. The thickness of
each of the hot-rolled steel sheets (hot-rolled
sheets) was set to 2.0 mm. Subsequently, pickling of
each of the hot-rolled steel sheets was performed,
and cold rolling of each of the hot-rolled steel
sheets was performed to obtain cold rolling. The
thickness of each of the cold-rolled steel sheets
(cold-rolled sheets) was set to 0.35 mm. Thereafter,
finish annealing of each of the cold-rolled steel
sheets was performed. In the finish annealing, a
soaking temperature was set to 1000°C, a soaking time
period was set to 30 seconds, and an average cooling
rate from the soaking temperature (1000°C) to 700°C
was set to 20°C/sec. In this manner, various nonoriented
electrical steel sheets were manufactured.
Thereafter, a metal structure of each of the nonoriented
electrical steel sheets was observed. In
the observation of the metal structure, for example,
measurement of a grain size (JIS G 0552) and
observation of precipitates were performed. Further,
from each of the non-oriented electrical steel
sheets, a JIS No. 5 test piece was cut out, and its
mechanical property was measured. Further, from each
- 33 -
of the non-oriented electrical steel sheets, a test
piece of 55 mm x 55 mm was cut out, and its magnetic
property was measured by a single sheet magnetic
property measurement method (JIS C 2556). As the
magnetic property, a core loss (WlO/400) under a
condition of a frequency being 400 Hz and a maximum
magnetic flux density being 1.0 T was measured.
Further, in order to observe an effect of magnetic
aging, the core loss (WlO/400) was measured also
after an aging treatment at 200°C for 1 day. That is,
with respect to each of the non-oriented electrical
steel sheets, the core loss (WlO/400) was measured
before and after the aging treatment. These results
are listed in Table 2.
[0072] [Table 1]
TABLE 1
STEEL I , , , . COMPOSITION (MASSX) . , , I PARAMETER I
No. ~ C I Si I Mn I Al I Ti I V I Zr I Nb I N I Cu I 5 n ~ Q
A1 0.0025 2.9 022 0.6 0.0010 0.0009 0.0009 0.0150 - - - 1.01
A2 0.0098 2.9 022 07 00010 0.0009 0.0010 0.0700 - - - 0.98
A3 0.0100 2.1 0.2 0.7 0.0010 0.0011 0.0010 0.0730 - - - 1.01
A4 0.006B 3 7 0.2 07 0.0010 0.0010 00010 0.0490 - - - 1.02
A5 0.0071 2.9 0.08 0.6 0.0010 0.0010 0.0010 0.0500 - - - 1
A6 0.0066 2.9 0.5 06 0.0010 0.0010 00010 0.0510 - - - 1.09
A7 0.0072 3 0.2 0.012 0.0010 0.0010 0.0010 0.0500 - - - 0.98
A8 00062 3 023 2.87 0.0010 0.0008 0.0011 0.0480 - - - 1.09
A9 0.0063 2.9 0.23 0.6 0.0010 0.0010 0.0010 0.0430 - - - 0.98
A10 0.0070 2.9 0.2 0.6 0.0009 0.0011 0.0009 0.0550 - - - 1.1
A11 0.0068 3 05 0.2 0.6 0.0010 0.0010 0.0010 0.0500 - - - 1.04
A12 0.0064 3.05 0.2 06 0.0010 0.0010 0.0480 0.0010 - - - 1.08
A13 00068 3.05 0 21 07 0.0010 0.0280 0.0010 0.0010 - - - 1.04
A14 0.0068 3.05 0.21 0.7 0.0260 0.0010 00010 O.OOtO - - - 1.03
A15 0.0065 2.9 0.2 0.7 0.0010 0.0010 0.0010 0.0600 0.0030 1.09
A16 0.0068 3 0.2 0.6 00010 0.0010 00010 00490 - 0.7000 1.02
A17 0.0067 3 022 0.6 0.0010 0.0009 0.0011 0.0510 - 1.0000 1.07
A18 0.0071 3 022 0.7 0.0011 0.0010 0.0010 0.0500 - 1.4000 1
A19 00070 2.7 02 09 00010 00010 0.0010 0.0500 - - 00800 1.01
B1 0.0009 2.9 02 0.6 0.0010 0.0009 0.0010 0.0620 - - - 6.11
B2 0.0310 2.9 02 0.6 0.0011 0.0010 0.0010 0.0100 0.06
B3 0.0070 1.5 02 0.7 0.0010 0.0010 0.0010 0.0530 - - - 1.07
B4 0.0070 4.4 02 0.7 0.0010 0.0010 0.0010 0.0510 - - - 1.03
B5 00070 2.9 0003 07 00010 0.0010 0.0010 0.0520 - - - 1 05
B6 0.0070 2.9 1 06 0.0010 0.0010 0.0010 0.0600 - - - 1.01
B7 0.0070 3 02 Q.C02 0.0011 0.0009 0.0010 0.0510 - - - 1.03
B8 10.00701 3 I 02 I 32 10.0011 10.001010001010.05101 - I - I - I 1.03 I
- 34 -
[0073] [Table 2]
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- 35 -
[0074] As listed in Table 2, in conditions No. CI to
No. C19 each falling within the range of the present
invention, it was possible to obtain the tensile
strength of 550 MPa or more and the core loss
(WlO/400) of 30 W/kg or less. On the other hand, in
conditions No. Dl to No. D8 each falling outside the
range of the present invention, it was difficult to
achieve the tensile strength and the core loss.
[0075] (Experimental example 2)
First, hot rolling of slabs each made of a steel
No. All listed in Table 1 was performed to obtain
hot-rolled steel sheets. The thickness of each of
the hot-rolled steel sheets was set to 2.0 mm.
Thereafter, annealing (hot-rolled sheet annealing) of
a part of the hot-rolled steel sheet (a condition No.
E7) was performed under the condition listed in Table
3. Subsequently, pickling of each of the hot-rolled
steel sheets was performed, and cold rolling of each
of the hot-rolled steel sheets was performed to
obtain cold rolling. The thickness of each of the
cold-rolled steel sheets was set to 0.35 mm. Then,
finish annealing of each of the cold-rolled steel
sheets was performed under the condition listed in
Table 3. In this manner, various non-oriented
electrical steel sheets were manufactured.
Thereafter, with respect to each of the non-oriented
electrical steel sheets, the evaluations similar to
those of Experimental example 1 were performed.
These results are also listed in Table 3.
- 36 -
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[0080] As listed in Table 4, in conditions No. Gl to
No. G12 each falling within the range of the present
invention, it was possible to obtain the tensile
strength of 550 MPa or more and the core loss
(WlO/400) of 30 W/kg or less. On the other hand, in
conditions No. HI to No. HIO each falling outside the
range of the present invention, it was difficult to
achieve the tensile strength and the core loss.
[0081] (Experimental example 4)
First, hot rolling of slabs made of the steels
No. All and No. A17 listed in Table 1 was performed
to obtain hot-rolled steel sheets. The thickness of
each of the hot-rolled steel sheets was set to 2.0
mm. Thereafter, pickling of each of the hot-rolled
steel sheets was performed, and cold rolling of each
of the hot-rolled steel sheets was performed to
obtain cold rolling. The thickness of each of the
cold-rolled steel sheets was set to 0.35 mm.
Subsequently, cold-rolled sheet annealing (only
conditions No. 17 and No. 14) and finish annealing of
the cold-rolled steel sheets were performed under the
conditions listed in Table 5. Then, an insulating
film was formed on the surface of each of the coldrolled
steel sheets obtained after the finish
annealing. In this manner, various non-oriented
electrical steel sheets were manufactured.
[0082] Thereafter, from each of the non-oriented
electrical steel sheets, 30 steel sheets each having
a size in a rolling direction of 300 mm and a size in
- 40 -
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a direction perpendicular to the rolling direction of
60 mm were punched out. The steel sheet having such
a shape and size is sometimes used for an actual
motor core. Then, the 30 steel sheets were laminated
to one another to obtain a laminate. Subsequently,
annealing of annealing of each of the laminates was
performed under the condition listed in Table 5.
Then, a steel sheet for a test was extracted from
each of the laminates, and with respect to this steel
sheet, the evaluations similar to those of
Experimental example 1 were performed. That is, the
evaluation intended for a laminate used for a motor
core was performed. These results are also listed in
Table 5. Here, ones with the annealing condition
deviating from the above-described favorable
condition were each set as a comparative example.
[0083] [Table 5]
- 41 -
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