DESCRIPTION
TITLE OF INVENTION: HIGH-STRENGTH NON-ORIENTED
ELECTRICAL STEEL SHEET
TECHNICAL FIELD
[0001] The present invention relates to a high strength
non-oriented electrical steel sheet suitable
for an iron core material of an electrical apparatus,
BACKGROUND ART
[0002] In recent years, higher performance ' ;
properties have been required for a non-oriented
electrical steel sheet to be used as an iron core
material of a rotary machine due to a worldwide
increase in achievement of energy saving of an
electrical apparatus. Recently in particular, as a
motor to be used for an electric vehicle or the like,
-
a demand for a small-sized high-power motor has been
high. Such an electric vehicle motor has been
designed to make high-speed rotation possible to
thereby obtain high torque.
[0003] A high-speed rotation motor has also been
used for a machine tool and an electrical apparatus • /
such as a vacuum cleaner. The outer shape of a high-speed
rotation motor for an electric vehicle is
larger than that of a high-speed rotation motor for
an electrical apparatus. Further, as a high-speed
rotation motor for an electric vehicle, a DC
brushless motor has been mainly used. In a DC
brushless motor, magnets, are embedded in the vicinity
of an outer periphery of a rotor. In the above
- 1 -
structure, the width of a bridge portion in an outer
periphery portion of the rotor (the width between
magnets from the most outer periphery of the rotor to
a steel sheet) is extremely narrow, which is 1 to 2
mm, depending on a place. Therefore, a high-strength
steel sheet has been required for a high-speed
rotation motor for an electric vehicle rather than a
conventional non-oriented electrical steel sheet.
[0004] A non-oriented electrical steel sheet is
disclosed in which Mn and Ni are added to Si to
achieve solid solution strengthening in Patent
Literature 1,. However, it is not possible to obtain
• sufficient strength even by the non-oriented
electrical steel sheet. Further, due to the addition
of Mn and Ni, its toughness is likely to be reduced/
and sufficient productivity and a sufficient yield
cannot be obtained. Further, the prices of alloys to
be added are high. In recent years in particular,
the price of Ni has suddenly risen due to a worldwide
demand balanced
[0005] Non-oriented electrical steel sheets are
disclosed in which carbonitride is dispersed in a
steel to achieve strengthening in Patent Literatures
2 and 3. However, it is not possible to obtain
sufficient strength even by the non-oriented
electrical steel sheets.
: [Q006] A non-oriented electrical steel sheet is
•disclosed in which Cu precipitates are used to
achieve str4ngtheining in Patent Literature 4
- 2 -
However, it is difficult to obtain sufficient
strength. For obtaining sufficient strength,
annealing at high temperature is required to be
performed in order to ®nce solid-dissolve Cu.
However, when the annealing at high temperature is
performed, crystal grains coarsen. That is, even
though precipitation strengthening by Cu precipitates j ,
is obtained, by the coarsening of crystal grains,
strength decreases and thus sufficient strength
cannot be obtained. Further, due to the synergistic
effect of precipitation strengthening and coarsening
of crystal grains, fracture elongation significantly
decreases.
[0007] Anon-oriented electrical steel sheet is
disclosed in which suppression of the coarsening of
crystal grains in Patent Literature 4 is intended in
Patent Literature 5,. In the technique, C, Nb, Zr,
Ti, V, and so are contained. However, at 150°C to
200°C, being a heat generation temperature range of a
motor, carbide precipitates finely and magnetic aging
is likely to occur.
[0008] A non-oriented electrical steel sheet is •':
disclosed in which by precipitates of Al and N,
achievement of making crystal grains fine and
precipitation strengthening by Cu is intended in
Patent Literature 6,. However, Al is contained in
large amounts and thus it is difficult to
sufficiently suppress the growth of crystal grains.
Further, when an N content is increased, a cast
- 3 -
defect is likely to occur.
[0009] A non-oriented electrical steel sheet
containing Cu is disclosed in Patent Literature 7,. *<
However, in the technique, a heat treatment for a
long period of time, and so on are performed, to
thereby make it difficult to obtain good fracture
elongation and soon.
CITATION LIST '
PATENT LITERATURE
[0010] Patent Literature 1: Japanese Laid-open
Patent Publication No. 62-256917
Patent literature 2: Japanese Laid-open Patent
Publication No. 06-330255
Patent literature 3: Japanese Laid-open Patent
Publication No. 10-18005' !
Patent literature 4: Japanese Laid-open Patent
Publication No. 2004-84053
Patent literature 5: International Publication
Pamphlet No. W02009/128428
Patent literature 6: Japanese Laid-open Patent
Publication No. 2010-24509
Patent literature 7; International Publication
Pampihlet No. WO2005/33349
SUMMARY OF INVENTION
i , ' ' '
TECHNICAL PROBLEM
[0011] The present invention has an object to >
provide a high-strength non-oriented electrical steel'
sheet allowing excellent strength and fracture
elongation to be obtained while a good magnetic
- 4 -
property being obtained.
SOLUTION TO PROBLEM
[0012] The present invention has been made in order
to solve the above-described problems, and the gist
thereof is as follows. ;
[0013] (1) A high-strength non-oriente,d electrical
steel sheet contains:
in mass%,
C : 0 . 0 1 0 % o r l e s s ;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.50%;
Al: not less than 0.2% nor more than 3.0%;
N: 0.005% orless;
S: not less than 0.005% nor more than 0.030%; and
Cu: not less than 0.5% nor more than 3.0%,
a balance being composed of Fe and inevitable
impurities,
an expression (1) being established where a Mn
content is represented as [Mn] and a S content is
represented as [S],
not less than 1.0x10'' pieces nor more than 1.0x10^
pieces of sulfide having a circle-equivalent diameter
of not less than 0.1 pm nor more than 1.0 jam being
contained per 1 mm^, and
hot rolling having been performed at a finishing
temperature of 1000°C or higher and a coiling
temperature of 650°C or lower,
10 ^ [Mn]/ [S] < 50 ... (1) .
[0014] (2) The high-strength non-oriented electrical
- 5 -
'^^steel sheet according to (1) further contains, in '
mass%, Ni: not less than 0.5% nor more than 3.0%.
[0015] (3) The high-strength non-oriented electrical
steel sheet according to (1) or (2) further contains,
in mass%, 0.5% or less of one or more of Ti, Nb, V,
Zr, B, Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, Co, Cr, and REM
in total.
ADVANTAGEOUS EFFECTS OF INVENTION
[0016] According to the present invention, the
interaction of Cu precipitates and sulfide makes it
possible to obtain excelient strength and fracture
elongation while obtaining a good magnetic property.
DESCRIPTION OF EMBODIMENTS
[0017] The present inventors earnestly examined the
technique of finely keeping crystal grains even if
annealing is performed at a high temperature from a
viewpoint different from that of Patent Literatures 5
and 6. As a result, it was found that the
relationship between a S content and a Mn content is
made appropriate and a content of sulfide having a
predetermined size is made appropriate, thereby
jmaking it possible to finely keep crystal grains even
if annealing is performed at a high temperature. In
this case, an element which causes magnetic a'ging is
not needed.
[0018] Here, there will be explained an experiment ' ;
leading to the present invention. Hereinafter, "%" :
bein'g the unit of a content means "ma6s%."
[0019] In the experiment, first, steels each
- 6 -
1
containing C: 0.002%,^ Si: 3.2%, Mn: 0,20%, Al: 0.7%,
N: 0.002%, and Cu: 1.5%, and further S having a
content listed in Table 1, in which a balance is
composed of Fe and inevitable impurities, were melted
in a vacuum melting furnace in a laboratory, and a
steel billet (slab) was made from each of the steels.
In Table 1, [Mn] represents a Mn content ('0.20%) and
[S] represents a iS content. Then, each of the steel
billets was heated at 11'00°C for 60 minutes and was
subjected to hot rolling immediately, whereby hotrolled
sheets each having a thickness of 2.0 mm wer6
obtained. Thereafter, each of the hot-rolled sheets
was subjected to hot-rolled sheet annealing at 1050°C
for one minute, pickling, and one time of cold
rolling, whereby cold-rolled sheets each having a
thickness of 0.35 mm were obtained. Subsequently,
each of the cold-rolled sheets was subjected to
finish annealing at 800°C to 1000°C for 30 seconds.
' The temperature of the finish annealing is listedin
Table 1.
[0020] Then, a number density of sulfide in each of
obtained rton-o^iented electrical steel sheets was
measured. At this time, an object to be measured was
one having a circle-equivalent diameter of not less
than 0.1 ]ixa nor more than 1.0 ^m. Further, a yield
stress, a fracture elongation, and a core loss were
also measured. As the core loss, a core loss WlO/400
was measured. Here, the core loss WlO/400 is a core
loss under the condition of frequency of 400 Hz and a
. . - 7 -
maximum magnetic flux density of 1.0 T. These
results are also listed in Table 1,
[0021] [Table 1]
[0022] As listed in Table 1, in Material symbols B,
- 9 -
C, and D each having the value of [Mn]/[S] being not
less than 10 nor more than 50, a good property was
obtained. However, even in Material symbol B, in the
case where the finish annealing was performed at
1000°C.> the number density of sulfide was low and the
fracture elongation was low. On the whole, there is '
a tendency that, if the temperature of the finish
annealing is increased, the number density of sulfide ,
decreases even in the same material. This is '
conceivably because sulfide coarsens during the
finish annealing. Then, when sulfide coarsens, the
deterrent against the: growth of crystal grains is
weakened. This conception also applies to the result
of the case when the finish annealing was performed
at 1000°C in Material symbol B. That.is, it is
conceivable that in the example, the temperature of
the finish annealing was 1000°C, which was high, and
thus sulfide coarsened, the number density of sulfide
decreased, and the growth of crystal grains was not
suppressed sufficiently.-
[0023] On the other hand, in Material symbol A
having the value of [Mn]/[S] being greater than 50,
the fracture elongation was low and the yield stress
was low. This is conceivably because [Mn]/[S] was
high, and thus the number density of sulfide was low
, and the growth of crystal grains advanced.
[0024] Further, in Material symbol E having the
value of [Mnl/[S] being less than 10, the core loss
was high significantly. This is conceivably because
- 10 -
[Mn]'/[S] was low, and thus the number density of
sulfide was high and the growth of crystal grains was
suppressed significantly. Further, in the case where
the temperature of the finish annealing was 900°C, the
core loss was high and further the fracture -
elongation was low. This is conceivably because the
number density of sulfide was extremely high, and
thus not only the growth of crystal grains but also
recrystallizationwas inhibited.
[0025] From the above experimental result, it is
said that the S content, [Mn]/[S], and the number
density of sulfide are each made to fall within a
predetermined range, and thereby it is possible to
obtain a high-strength non-oriented electrical steel
sheet,excellent in allthe core loss, strength, and
ductility. Such a property excellent in balance is a
property that has not been obtained in a conventional
steel sheet utilizing carbonitride, or steel sheet
having only Cu added thereto simply.
[0026] Next, reasons for limiting the numerical
values in the present invention will be explained. ••'
[0027] C is effective for making crystal grains
fine, but when a temperature of a non-oriented
electrical steel sheet becomes 200°C or so, C forms
carbide to deteriorate a core loss. For example,
when used' for a high-speed rotation motor for an
electric vehicle, a non-oriented electrical steel
sheet is likely to reach this level of temperature.
Then, when a C content is greater than 0.010%, such ^^ ,
- 11 - i
- i
magnetic aging is significant. Thus, the C content
is 0,010% or less, and is more preferably 0.005% or
less.
[0028] Si is effective for a reduction in eddy
current loss. Si is effective also for solid
solution strengthening. However, when a Si content
is less than 2.0%, these effects are insufficient.
On the other hand, when the Si content is greater
than 4.0%, cold rolling during manufacturing a non- -
oriented electrical steel sheet is likely to be
difficult to be performed. Thus, the Si content is
I not less than 2.0% nor more than 4.0%.
[0029] Mn reacts with S to form sulfide. In the
present invention, crystal grains are controlled by
sulfide, so that Mn is an important element. When a
i Mn content is less thanO.05%, fixation of S is
insufficient to cause hot shortness. On the other
hand, when the Mn content is greater than 0.50%, it
is difficult to sufficiently suppress growth of
crystal grains. Thus, the Mn content is not less
than 0.05% nor more than 0.50%.
[0030] Al is effective for a reduction in eddy
current loss and solid solution strengthening,
similarly to Si. Further, Al also exhibits an effect
of causing nitride to coarsely precipitate to make
nitride harmless'. However, when an Al content^is
less than 0.2%>< these effects are insufficient. On
, the other hand, "when the Al content is greater than
3.0%, cold rolling during manufacturing a non-
- 12 -
oriented electrical steel sheet is likely to be
difficult to be performed. Thus, the Al content is
not less than 0.2% nor more than 3.0%.
[0031] N forms nitride such as TIN to deteriorate a
core loss. Particularly, in the case where a N
content is greater than 0.005%, deterioration of a
j core loss is significant. Thus, the nitrogen content
is0.005%orless.
[0032] Cu improves strength through precipitation
strengthening. However, when a Cu content is less
than 0.5%, almost all the content of Cu is soliddissolved
and thus the effect of precipitation
strengthening cannot be obtained. On the other hand,
even when the Cu content is greater than 3.0%, the
effect is saturated and an effect measuring up to the
; content cannot be obtained. Thus, the Cu content is
not less than 0.5% nor more than 3.0%.
[0033] S reacts with Mn to form sulfide. In the
present invention, crystal grains are controlled by
sulfide, so that S is an important element. When a S
•
content is less than 0.005%, the effect cannot be
obtained sufficiently. On the other hand, even when
the S content is greater than 0.030%, the effect is
saturated and an effect measuring up to the content
cannot be obtained. Further, as the S contehjt is
increased, hot shortness is more likely to occur.
Thus, the S content is not less than 0.005% nor more
than 0.030%.
[0034] In the present invention, [Mn]/[S] is an
'1 3
important parameter for obtaining a good yield
stress, a good fracture elongation, and a good core
loss. When [Mn]/[S] is greater than 50, the effect
of suppressing growth of crystal grains is
insufficient and a yield stress and a fracture
elongation decrease. On the other hand, when
[Mn]/[S] is less than 10, a fracture elongation
decreases significantly and a core loss deteriorates
significantly. Thus, [Mn]/[S] is not less than 10
nor more than 50. That is, an expression (1) is
established where a Mn content is represented as [Mn]
and a S content is represented as [S].
10 < [Mn] / [S] < 5 0 ... (1)
[0035] Ni is an effective element capable of
achieving a high strength of a steel sheet without
embrittling it so much. But, Ni is expensive and
/thus is preferably contained according to need. In
the case of Ni being contained, for obtaining the
; sufficient effect, the content is preferably 0.5% or
more and Is preferably 3.0% or less in consideration
of its cost. Further, Ni also haS an effect of
, suppressing scabs caused by Cu being containedT For
obtaining this effect, the Ni content is preferably
1/2 or more of a Cu content.
[0036] Further, Sn has an effect of improving a
texture and suppressing nitridation and oxidation
during annealing. Particularly, there is a
significant effect of compensating a magnetic flux
density, which is decreased due to Cu being
- 14 -
contained, by improving the texture. For obtaining
this effect, Sn may be contained to fall within a
range of not less than 0.01% nor more than 0.10%.
[0037] Further, as for other trace elements, adding
them because of various purposes in addition to their
amount inevitably contained does not impair the
effect of the present invention at all. Inevitable
contents of these trace elements each are normally
about 0.005% or less, but about 0.01% or more may be
I added for various purposes. Also in this case, it is
possible to contain 0.5% or less of one or more of
Ti, Nb, V, Zr, B, Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, Co,
Cr, and REM in total in view of the cost and magnetic
property.
[0038] Next, the number density of sulfide will be
explained. As is clear from the above-described
\ experimental result, as for the number density of
sulfide having a circle-equivalent diameter of not
less than 0.1 ]xm. nor more than 1.0 )im, an appropriate
range exists in terms of a fracture elongation'and a
core loss. When the above number density is less
than 1.0x10^' pieces/mm^, sulfide is insufficient to
thereby make it impossible to sufficiently suppress
growth of crystal grains, and although a good core
loss can be obtained, a fracture elongation decreases'
extremely. On the other hand, when the above number
density is greater than 1.0x10^ pieces/mm^, growth of
•crystal grains is suppressed excessively and a core
loss deteriorates extremely. Further, " •
1 5 - .
recrystallization is sometimes suppressed, and in
this case, not only the core loss but a^'so a fracture
elongation deteriorates. Thus, the number density of
sulfide having a circle-equivalent diameter of not
less than 0.1 \xm. nor more than 1.0 pm is not less
than l.OxlO'' pieces/mm^ nor more than l.OxlQ^
pieces/mm^.
[0039] In the case when these conditions are
satisfied, for example, a yield stress is likely to
be 700 MPa or more, and a fracture elongation is
likely to be 10% or more. Further, in the case when
the preferable conditions are satisfied, the fracture .
elongation is likely to be 12% or more. Further, for
example, a recrystallization area ratio is likely to
be 50% or more, and when the thickness of a steel
sheet is represented as.t (mm), a core loss WlO/400
is likely to be lOOxt or less.
[0040] Next, there will be explained a manufacturing
method of a high-strength non-oriented electrical
steel sheet according to an embodiment of the present
invention.
[0041], In the present embodiment, a slab having the
above-described composition is first heated at 1150°C
to 1250°C or so and is subjected to hot rolling, and
thereby a hot-rolled sheet is made to then be coiled.
Then, the hot-rolled sheet is subjected to cold
rolling while being uncoiled, and thereby a' coldrolled
sheet is made to then be coiled. Thereafter, :
finish annealing is performed. Then, an insulating
- 16 -
-film is formed on the front surface of a steel sheet
obtained in this manner. That is, the manufacturing
method according to the present embodiment is based
on a substantially well-known manufacturing method of
a non-oriented electrical steel sheet.
[0042] The condition of each treatmept is not
limited in particular, but preferable ranges exist as
described below. For example, a finishing
temperature of the hot rolling is preferably 1000°C or
higher and a coiling temperature is preferably 650°C
or lower, and both of the temperatures are preferably
• determined appropriately according to the contents of
Mn, S, and Cu.; This is to obtain the above-described
number density of sulfide. If a finishing
) temperature is too low or a coiling temperature is
too high, fine MnS sometimes precipitates
excessively. In this case, there is sometimes a case
that growth of crystal grains during the finish
annealing is suppressed excessively to thereby make
it impossible to obtain a good core loss.
[0043] A temperature of the finish annealing is
preferably approximately 800°C to 1100°C, and its
period of time is preferably shorter than 600
I seconds. Further, in the finish annealing,
continuous annealing is preferably performed. [
[0044] In terms of improving a magnetic flux
density, hot-rolled sheet annealing is preferably ;
performed before the c6ld rolling. Its oonditioh is ;
hot limited in particular, but the hot-rolled sheet
• - 17 - * annealing is preferably performed in a range of 1000°C
tollOO°C for 30 seconds or longer. The hot-rolled
sheet annealing performed in the temperature range
makes it possible to moderately grow MnS in the hotrolled
sheet and to decrease variation in the degree
of MnS precipitation in the longitudinal direction.
As a result, a property stable in the longitudinal
direction can be obtained even after,the finish
annealing. When the temperature of the hot-rolled
she'et annealing is lower than 1000°C, or its period of
j times is shorter than 30 seconds, these effects are
small. On the other hand, when the temperature of
the hot-rolled sheet annealing is greater than 1100°C,
^art of sulfide is solid-dissolved and a crystal
i grain diameter after the finish annealing is too
; fine-, and thus a good core loss sometimes cannot be
; obtained.
i
EXAMPLE [0045] Next, experiments conducted by the present
inventors will be explained. The conditions and so
on in these experiments are examples employed for
confirming the applicability and effects of the
present invention, and the present invention is not
limited to these examples.
• •
[00461 First, steels each containing Si: 3.3%, Mn:
0.10%, Al: 0.8'%, N: 0.002%, and Cu: 1.2%, and further I
Ni having acontent listed in Table 2, and S having a
content listed in Table 2, in which a balance, is
composed of Fe and inevitable impurities, were melted I
- 18 - 4.
-^m a vacuum melting furnace in a laboratory, and a
steel billet (slab) was made from each of the steels.
Then, each of the steel billets was heated at 1100°C
for 60 minutes and was subjected to hot rolling
immediately, whereby hot-rolled sheets each having a
thickness of 2.0 mm were obtained. Thereafter, each
of the hot-rolled sheets was subjected to hot-rolled
sheet annealing at 1020°C for 60 seconds, pickling,
and one time of cold rolling, whereby cold-rolled
sheets each having a thickness of 0.30 mm were
obtained. Subsequently, each of the cold-rolled
sheets was subjected to finish annealing at 9O0°C for
45 seconds.
' [0047] Then, a number density of sulfide in each of
obtained non-oriented electrical steel sheets was
measured. At this time, an object to be measured was
. one having a circle-equivalent diameter of not less
j than 0.1 pm nor more than 1.0 ym. Further, a yield
i sttess, a fracturfe elongation, and a core loss were
also measured. As the core loss, a core loss WlO/400
was measured. These results are also listed in Table
[0049] As listed in Table 2, in Material symbols b,
c, and d each having the value of [Mn]/[S] being not r
- 20 -
less than 10 nor more than 50 and the number density
of sulfide being not less than l.OxlO'* pieces nor more
than 1.0x10^ pieces, a good yield strength, a good
fracture elongation, and "'a good core loss were
obtained. Further, in Material symbols g, h, and i
each having the Ni content of 1.0%, as compared with
i Material symbols b, c, and d each having the Ni
content of 0.02% (containing substantially no Ni
I ' added thereto) , an approximately equal fracture
I elongation and an approximately equal core loss were
obtained, and further a high yield strength by about
50 MPa was obtained. In Material symbols 1, m, and n
[ each having the Ni content of 2.5%, as compared with
I Material symbols b, c, and d each having the Ni
content of 0.02% of % (containing substantially no Ni
added thereto), an approximately equal fracture
j elongation and an approximately core loss were
< obtained, and further a high yield strength by about
i 100 MPa was obtained.
[0050] It should be noted that the above-described
embodiment merely illustrates a concrete example of
implementing the present invention, and the technical
scope of the present invention is not to be construed
•
in a restrictive manner by the embodiment. That is,
•
the present invention may be implemented in various
forms without departing from the technical spirit or
main featuresthereof.
•
: INDUSTRIAL APPLICABILITY
[0051] The present invention may be utilized in ah
- 21 -
industry of manufacturing electrical steel sheets and
in an industry of utilizing electrical s'teel sheets
such as motors.

CLAIMS
[Claim 1] (Amended) A high-strength non-oriented
electrical steel sheet, containing:
in mass%,
C: 0.010% or less;
Si: not less than 2.0% nor more than 4.0%;
Mn: not less than 0.05% nor more than 0.50%;
Al: not less than 0.2% nor more than 3.0%;
N: 0.005% or less;
S: not less than 0.005% nor more than 0.030%; and
Cu: not less than 0.5% nor more than 3.0%,
a balance being composed of Fe and inevitable
impurities,
! an expression (1) .being established where a Mn
content is represented as [Mn] and a S content is
[ represented as [S],
not less than 1.0x10^ pieces nor more than 1.0x10^
pieces of sulfide having a circle-equivalent diameter
of not less than 0.1 ym nor more than 1.0 \xm being
contained per 1 mm^, and
hot rolling having been performed at a finishing
temperature of 1000°C or higher and a coiling
temperature of 650°C or lower, • • , ;
10 < [Mn] / [S] < 50 ... (1) .
I [Claim 2] The high-strength non-oriented electrical
I steel sheet according to claim 1, further containing,
m mass%, Ni: not less than 0.5% nor more than'3.0%. '
[Claim 3] The high-strength non-oriented electrical :
steel sheet according to claim 1 or 2, further ;
- 23 -
j
-containing, in mass%, 0.5% or less of one or more of
Ti, Nb, V, Zr, B, Bi, Mo, W, Sn, Sb, Mg, Ca, Ce, Co,
,Cr, and REM in total.