TOLE D'ACIER ELECTROMAGNETIQUE NON ORIENTE ET SON PROCEDE DE FABRICATION

NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME

Abrégé français

La présente invention porte sur une tôle d'acier électromagnétique non orienté ayant des propriétés magnétiques supérieures et des propriétés mécaniques supérieures et également une qualité de tôle d'acier supérieure pouvant être obtenue à un faible coût par la formation d'une composition de composants qui contient, en pourcentage en masse, 5,0 % ou moins de Si, 2,0 % ou moins de Mn, 2,0 % ou moins d'Al et 0,05 % ou moins de P dans une plage qui satisfait à la formule (1) et qui contient en outre 0,008-0,040 % de C, 0,003 % ou moins de N et 0,04 % ou moins de Ti dans une plage qui satisfait à la formule (2), le reste étant constitué de Fe et d'impuretés inévitables. 300 = 85[Si %] + 16[Mn %] + 40[Al %] + 490[P %] = 430 (1) 0,008 = Ti* < 1,2[C %] (2) Ici, Ti* = Ti - 3,4[N %]

Abrégé anglais

The present invention provides a non-oriented electrical steel sheet at
low cost that has excellent magnetic properties and mechanical properties as
well as excellent quality of steel sheet. The non-oriented electrical steel
sheet has a chemical composition containing, by mass%, Si: 5.0 % or less,
Mn: 2.0 % or less, Al: 2.0 % or less, and P: 0.05 % or less, in a range
satisfying formula (I), and furthermore, C: 0.008 % or more and 0.040 % or
less; N: 0.003 % or less, and Ti: 0.04 % or less, in a range satisfying
formula
(2), with the balance composed of Fe and incidental impurities:
300 .ltoreq. 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] .ltoreq.430 .....(1)
0.008 .ltoreq.Ti* < 1.2 [C%] .... (2)
, where Ti* = Ti ¨ 3.4[N%].

Revendications

- 26 -
CLAIMS:
1. A non-oriented electrical steel sheet having a chemical composition
consisting
of, by mass%:
Si: 5.0 % or less;
Mn: 2.0 % or less;
Al: 2.0 % or less; and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less;
N: 0.003 % or less; and
Ti: 0.04 % or less,
in a range satisfying formula (2), and the balance being Fe and incidental
impurities:
300 .ltoreq. 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] .ltoreq. 430 .multidot.
(1)
0.008 .ltoreq. Ti* < 1.2[C%] .multidot. (2),
where Ti* = [Ti%] - 3.4[N%].
2. The non-oriented electrical steel sheet according to claim 1, wherein
the Si,
Mn, Al and P contents are, by mass%,
Si: more than 3.5 % but not more than 5.0 %,
Mn: 0.3 % or less,
Al: 0.1 % or less, and

- 27 -
P: 0.05 % or less.
3. A
non-oriented electrical steel sheet having a chemical composition consisting
of, by mass%:
Si: 5.0 % or less;
Mn: 2.0 % or less;
Al: 2.0 % or less; and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less;
N: 0.003 % or less; and
Ti: 0.04 % or less,
in a range satisfying formula (2), and
at least one of:
Sb: 0.0005 % or more and 0.1 % or less;
Sn: 0.0005 % or more and 0.1 % or less;
B: 0.0005 % or more and 0.01 % or less;
Ca: 0.001 % or more and 0.01 % or less;
REM: 0.001 % or more and 0.01 % or less;
Co: 0.05 % or more and 5 % or less;
Ni: 0.05 % or more and 5 % or less; and

- 28 -
Cu: 0.2 % or more and 4 % or less, and the balance being Fe and incidental
impurities:
300.ltoreq. 85[Si%] + 16[Mn%]+ 40[Al%] + 490[P%] .ltoreq. 430 ..... (1)
0.008.ltoreq. Ti* < 1.2[C%] ..... .. (2),
where Ti* = [Ti%] - 3.4[N%].
4. The non-oriented electrical steel sheet according to claim 3, wherein
the Si,
Mn, Al and P contents are, by mass%,
Si: more than 3.5 % but not more than 5.0 %,
Mn: 0.3 % or less,
Al: 0.1 % or less, and
P: 0.05 % or less.
5. A method for manufacturing a non-oriented electrical steel sheet,
comprising:
subjecting a steel slab to soaking, where the steel slab is retained at a
soaking
temperature of 1000°C to 1200°C, the steel slab having a
chemical composition consisting of,
by mass%,
Si: 5.0 % or less,
Mn: 2.0 % or less,
Al: 2.0 % or less, and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less,

- 29 -
N: 0.003 % or less, and
Ti: 0.04 % or less,
in a range satisfying formula (2) and the balance being Fe and incidental
impurities;
subjecting the steel slab to subsequent hot rolling to obtain a hot-rolled
steel
material;
then subjecting the steel material to cold rolling or warm rolling once, or
twice
or more with intermediate annealing performed therebetween, to be finished to
a final sheet
thickness; and
subjecting the steel material to final annealing, wherein prior to the final
annealing, the steel material is subjected to heat treatment at least once
where the steel
material is retained at a temperature of 800°C or higher and
950°C or lower for 30 seconds or
more, and subsequently to the final annealing at 700°C or higher and
850°C or lower:
300 .ltoreq. 85[Si%]+ 16[Mn%] + 40[Al%] + 490[P%] .ltoreq. 430 .multidot.
(1)
0.008 .ltoreq.Ti* < 1.2[C%] .multidot. (2),
where Ti* = [Ti%] - 3.4[N%].
6. The method for manufacturing a non-oriented electrical steel sheet
according
to claim 5, wherein the Si, Mn, Al and P contents are, by mass%,
Si: more than 3.5 % but not more than 5.0 %,
Mn: 0.3 % or less,
Al: 0.1 % or less, and
P: 0.05 % or less.
7. A method for manufacturing a non-oriented electrical steel sheet
comprising:

- 30 -
subjecting a steel slab to soaking, where the steel slab is retained at a
soaking
temperature of 1000°C to 1200°C, the steel slab having a
chemical composition consisting of,
by mass %,
Si: 5.0 % or less,
Mn: 2.0 % or less,
Al: 2.0 % or less, and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less,
N: 0.003 % or less, and
Ti: 0.04 % or less,
in a range satisfying formula (2), and
at least one of:
Sb: 0.0005 % or more and 0.1 % or less,
Sn: 0.0005 % or more and 0.1 % or less,
B: 0.0005 % or more and 0.01 % or less,
Ca: 0.001 % or more and 0.01 % or less,
REM: 0.001 % or more and 0.01 % or less,
Co: 0.05 % or more and 5 % or less,
Ni: 0.05 % or more and 5 % or less, and

- 31 -
Cu: 0.2 % or more and 4 % or less, and the balance being Fe and incidental
impurities;
subjecting the steel slab to subsequent hot rolling to obtain a hot-rolled
steel
material;
then subjecting the steel material to cold rolling or warm rolling once, or
twice
or more with intermediate annealing performed therebetween, to be finished to
a final sheet
thickness; and
subjecting the steel material to final annealing, wherein prior to the final
annealing, the steel material is subjected to heat treatment at least once
where the steel
material is retained at a temperature of 800°C or higher and
950°C or lower for 30 seconds or
more, and subsequently to the final annealing at 700°C or higher and
850°C or lower:
300 .ltoreq. 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] .ltoreq. 430 .multidot.
(1)
0.008 .ltoreq. Ti* < 1.2[C%] .multidot. (2),
where Ti* = [Ti%] - 3.4[N%].
8. The method for manufacturing a non-oriented electrical steel sheet
according
to claim 7, wherein the Si, Mn, Al and P contents are, by mass %,
Si: more than 3.5% but not more than 5.0%,
Mn: 0.3% or less,
Al: 0.1% or less, and
P: 0.05% or less.

Description

CA 02822206 2013-06-18
- I -
DESCRIPTION
NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR
MANUFACTURING THE SAME
TECHNICAL FIELD
[0001] The present invention relates to a non-oriented electrical steel
sheet, and in particular, to a non-oriented electrical steel sheet having high
strength and excellent fatigue properties, and furthermore, excellent magnetic
properties that is suitably used for components that are subject to high
stress,
typically, drive motors for turbine generators, electric vehicles and hybrid
vehicles, or rotors for high-speed rotating machinery, such as servo motors
for
robots, machine tools or the like, and a method for manufacturing the same.
Additionally, the present invention provides the above-described non-oriented
electrical steel sheet at low cost as compared to the conventional art.
BACKGROUND ART
[0002] As recent advances in motor drive systems have enabled frequency
control of drive power sources, more and more motors are offering
variable-speed operation and enabling high-speed rotation at frequencies
higher than the commercial frequency. In such motors enabling high-speed
rotation, the centrifugal force acting on a rotating body is proportional to
the
radius of rotation and increases in proportion to the square of the rotational
speed. Accordingly, in particular, rotor materials for middle- and
large-sized high speed motors require high strength.
[0003] In addition, in IPM (interior permanent magnet)-type DC inverter
control motors, which ha1e been increasingly employed for motors in hybrid
vehicles, such as drive motors or compressor motors, stress is concentrated on
portions between grooves for embedding magnets in a rotor and the outer
circumference of the rotor, or at narrow bridge portions of several
millimeters
width between the grooves for embedding magnets. Since motors can be
reduced in size with increasing rotational speed, there is a growing demand
for increasing the rotational speed of motors, such as in drive motors for
hybrid vehicles with space and weight constraints. As such, high strength
P0110494-PCT-ZZ (1/29)

CA 02822206 2013-06-18
- 2 -
materials are advantageously used as core materials for use in rotors of high
speed motors.
[0004] On the other hand, since rotating equipment such as motors or
generators makes use of electromagnetic phenomenon, the core materials of
iron cores of rotating equipment are also required to have excellent magnetic
properties. In particular, it is necessary for rotors of high speed motors to
assume low iron loss at high frequency; iron loss at high frequency would
otherwise lead to a rise in core temperature due to the eddy current induced
by
a high-frequency magnetic flux, causing thermal demagnetization of
embedded permanent magnets, reducing motor efficiency, and so on.
Therefore, there is a demand for such an electrical steel sheet as a material
for
rotors that possesses high strength and excellent magnetic properties.
[0005] Steel-strengthening mechanisms include solid solution
strengthening, precipitation strengthening, crystal grain refinement, work
hardening, and so on. To date, a number of high-strength non-oriented
electrical steel sheets have been considered and proposed to meet the needs,
such as those of rotors of high speed motors.
As an example utilizing solid solution strengthening, for instance, JP
60-238421 A (PTL 1) proposes a method for increasing the strength of steel
by adding elements such as Ti, W, Mo, Mn, Ni, Co or Al to the steel for the
purposes of primarily increasing Si content from 3.5 % to 7.0%, and
furthermore, achieving solid solution strengthening. Moreover, in addition
to the above-described strengthening methods, JP 62-112723 A (PTL 2)
proposes a method for improving magnetic properties by controlling the
crystal grain size in the range of 0.01 mm to 5.0 mm through manipulation of
the final annealing conditions.
[0006] However, when these methods are applied to factory production,
the factory production may be more prone to a trouble such as sheet fracture
in a rolling line after hot rolling, which would cause a reduction in yield
and
production line stop by necessity. Sheet fracture may be reduced if cold
rolling is performed in warm conditions at sheet temperatures of hundreds of
degrees centigrade, in which case, however, process control issues will be of
considerable concern, such as adaptation of the facility to warm rolling,
tighter production constraints, and so on.
P0110494-PCT-ZZ (2/29)

CA 02822206 2013-06-18
- 3 -
[0007] In addition, as a technique utilizing precipitation of
carbonitrides,
JP 06-330255 A (PTL 3) proposes a technique that makes use of strengthening
by precipitation and grain refining effects provided by carbonitrides in
steel,
the steel containing Si in the range of 2.0 % or more and less than 4.0 %, C
in
the range of 0.05 % or less, and one or two of Nb, Zr, Ti and V in the range
of
0.1 < (Nb + Zr)! 8(C + N) < 1.0, and 0.4 < (Ti + V)! 4(C + N) <4Ø
Similarly, JP 02-008346 A (PTL 4) proposes a technique, in addition to the
features described in PTL 3, to add Ni and Mn in a total amount of 0.3 % or
more and 10 % or less to steel for solid solution strengthening, and further
add
Nb, Zr, Ti and V in the same ratios as those described in PTL 3 to the steel,
thereby balancing high strength with magnetic properties.
[0008] However, if these methods are applied to obtain high strength,
problems arise that not only unavoidably cause a deterioration of magnetic
properties, but also make the resulting products susceptible to surface
defects
such as scabs caused by precipitates, internal defects, and so on, resulting
in
lower product quality, and furthermore, prone to a reduction in yield due to
removal of defects and a fracture trouble during production of steel sheets,
resulting in an increased cost. In addition, the technique described in PTL 4
will lead to an even greater increase in cost because it involves adding an
expensive solid-solution-strengthening element, such as Ni.
[0009] Further, as a technique utilizing work hardening, JP 2005-113185
A (PTL 5) proposes a technique for enhancing the strength of steel containing
Si in the range of 0.2 % to 3.5 % by allowing worked microstructures to
remain in the steel material. Specifically, PTL 5 discloses means that does
not perform heat treatment after cold rolling, or, if it does, retains the
steel
material at 750 C for 30 seconds at most, preferably at 700 C or lower, more
preferably at 650 C or lower, 600 C or lower, 550 C or lower, and 500 C
or lower. PTL 5 reports the actual results indicating that the worked
microstructure ratio is 5 % with annealing at 750 C for 30 seconds, 20 % with
annealing at 700 C for 30 seconds, and 50 % with annealing at 600 C for 30
seconds. In this case, there is a problem that such low annealing
temperatures lead to insufficient shape correction of rolling strips.
Improperly-shaped steel sheets have a problem that would lead to a lower
stacking factor after worked into a motor core in a stacked fashion, a
P0110494-PCT-ZZ (3/29)

CA 02822206 2013-06-18
- 4 -
non-uniform stress distribution when rotating at high speed as a rotor, and so
on. There is another problem that the ratio of worked grains to
recrystallized
grains varies greatly with the steel compositions and annealing temperatures,
which makes it difficult to obtain stable properties. Further, a non-oriented
electrical steel sheet is generally subjected to final annealing using a
continuous annealing furnace, which is usually maintained in an atmosphere
containing at least several percent of hydrogen gas in order to reduce
oxidation of surfaces of the steel sheet. To carry out low-temperature
annealing at temperatures below 700 C in such a continuous annealing
facility, there will be tremendous operational constraints, such as
requirements of time-consuming switching of furnace temperature settings,
replacement of the atmosphere in the furnace for avoiding hydrogen explosion,
and so on.
[0010] In view of the aforementioned technical background, the inventors
of the present invention proposed in JP 2007-186790 A (PTL 6) a high
strength electrical steel sheet balancing the ability of shape correction of
the
steel sheet with the ability of strengthening by non-recrystallized
microstructures during final annealing, which steel sheet is obtained by
adding Ti sufficiently and excessively in relation to C and N to a silicon
steel
with reduced C and N contents and thereby raising the recrystallization
temperature of the silicon steel. This method still has a difficulty in that
it
may increase alloy cost due to a relatively high Ti content, cause variations
in
mechanical properties due to the remaining recrystallized microstructures, and
so on.
CITATION LIST
Patent Literature
[0011] PTL 1: JP 60-238421 A
PTL 2: JP 62-112723 A
PTL 3: JP 6-330255 A
PTL 4: JP 2-008346 A
PTL 5: JP 2005-113185 A
PTL 6: JP 2007-186790 A
P0110494-PCT-ZZ (4/29)

CA 02822206 2013-06-18
- 5 -
SUMMARY OF INVENTION
(Technical Problem)
[0012] As described above, some proposals have been made on
high-strength non-oriented electrical steel sheets. In the proposals made to
date, however, it has not been possible until now to manufacture, with the use
of an ordinary facility for manufacturing electrical steel sheets, such a
high-strength non-oriented electrical steel sheet in an industrially stable
manner with good yield and at low cost that has good magnetic properties in
addition to high tensile strength and high fatigue strength, and furthermore,
satisfy the quality requirements of steel sheet, such as those relating to
surface defects, internal defects, sheet shape or the like. Particularly, the
high-strength electrical steel sheets that have so far been provided for
rotors
of high speed motors are in a situation where the resulting rotors will be
subject to unavoidable heat generation due to their magnetic property, i.e.,
high iron loss at high frequency, which necessarily poses limitations on the
design specification of the motors.
[0013] Therefore, an object of the present invention is to provide a
high-strength non-oriented electrical steel sheet at low cost, having
excellent
magnetic properties and quality of steel sheet, and a method for
manufacturing the same. Specifically, an object of the present invention is
to provide means for manufacturing such a non-oriented electrical steel sheet
in an industrially stable manner and yet at low cost that has both a tensile
strength of 650 MPa or more, desirably 700 MPa or more, and good low iron
loss properties at high frequency such that, for example, a steel material
having a sheet thickness of 0.35 mm has a value of W10/400 of 40 W/kg or
lower, desirably 35 W/kg or lower.
(Solution to Problem)
[0014] The inventors of the present invention made intensive studies on
high-strength electrical steel sheets that can achieve the above-described
objects at a high level and methods for manufacturing the same. As a result,
the inventors have revealed that the amount and ratio of Ti and C to be added
to steel are deeply concerned with the balance between the strength properties
and the magnetic properties of an electrical steel sheet, and that a
high-strength electrical steel sheet having excellent properties may be
P0110494-PCT-ZZ (5/29)

CA 02822206 2013-06-18
- 6 -
manufactured in an stable manner and at low cost by optimizing the amount of
precipitation of Ti carbides.
That is, the present invention relies upon the following findings:
(A) The growth of crystal grains of an electrical steel sheet during final
annealing may be inhibited by the presence of a relatively small
amount of Ti carbides, whereby strengthening by refinement of
crystal grains may be achieved.
(B) The presence of excessive Ti carbides does not contribute to effective
inhibition of the growth of crystal grains, but rather has adverse
effects such as causing more surface defects and internal defects,
degrading quality of steel sheet, contributing to origins of fracture,
and so on. To this extent, surface defects such as scabs and internal
defects are significantly reduced by controlling the amount of Ti to
be added to the steel within an appropriate range.
On the other hand, Ti nitrides are formed at higher temperatures than
Ti carbides. Thus, they are less effective for inhibiting the growth
of crystal grains and not useful for crystal grain refinement control
intended by the present invention. Therefore, in an approach for
inhibiting the growth of crystal grains by controlling the amount of
Ti carbides, it is desirable to reduce the N content in a stable manner.
This is entirely different from the conventional approaches utilizing
strengthening by precipitation, where the effects of C and N are dealt
with in the same manner.
(C) In a steel sheet with refined crystal grains, solute C has an effect of
not only enhancing tensile strength, but also improving fatigue
properties essentially required for a rotor material rotating at high
speed.
(D) Major alloy components that are normally added for the purpose of
reducing iron loss by increasing the electrical resistance of an
electrical steel sheet are Si, Al and Mn. These three substitutional
alloy elements also have an effect of implementing solid solution
strengthening of steel. Accordingly, the balance between high
strength and low iron loss is effectively ensured on the basis of the
solid solution strengthening by these elements. However, there is a
P0110494-PCT-ZZ (6/29)

CA 02822206 2013-06-18
- 7 -
limit in adding these elements since excessive addition leads to
embrittlement of steel and poses difficulty in manufacturing steel.
Si-based addition is desirable for satisfying the requirements of solid
solution strengthening, lower iron loss and productivity in most
efficient way.
[0015] Based on these findings, the inventors of the present invention
found that a properly balanced utilization of solid solution strengthening
with
the use of the substitutional alloy elements mainly composed of Si, crystal
grain refinement with Ti carbides, and solid solution strengthening with an
interstitial element of C may provide a non-oriented electrical steel sheet
that
has high strength, excellent fatigue properties under the conditions of use,
and
furthermore, excellent magnetic properties and quality of steel sheet, without
substantially adding extra constraints on manufacture of steel sheets or
additional steps to the normal production of non-oriented electrical steel
sheets, and also found a method necessary for manufacturing the same. As a
result, the inventors accomplished the present invention.
[0016] That is, the primary features of the present invention are as
follows.
(i) A non-oriented electrical steel sheet comprising, by mass%:
Si: 5.0 % or less;
Mn: 2.0 % or less;
Al: 2.0 % or less; and
P: 0.05 % or less,
in a range satisfying formula (1), and the steel sheet further comprising, by
mass%:
C: 0.008 % or more and 0.040 % or less;
N: 0.003 % or less; and
Ti: 0.04 % or less,
in a range satisfying formula (2), the balance being composed of Fe and
incidental impurities:
300 85[SiN + 16[Mn%] + 40[Al%] + 490[P%] 430 ==== (1)
0.008 Ti* < 1.2[C%] ==== (2)
where Ti* = Ti ¨ 3.4[N%], and
P0110494-PCT-ZZ (7/29)

CA 02822206 2013-06-18
- 8 -
the [Si%], [Mn%], [Al%], [P%], [C%] and [N%] represent
the contents (mass%) of the indicated elements, respectively.
[0017] (ii) The non-oriented electrical steel sheet according to (i)
above,
wherein the Si, Mn, Al and P contents are, by mass%,
Si: more than 3.5 % but not more than 5.0 %,
Mn: 0.3 % or less,
Al: 0.1 % or less, and
P: 0.05 % or less.
[0018] (iii) The non-oriented electrical steel sheet according to (i) or
(ii)
above, further comprising, by mass%, at least one of:
Sb: 0.0005 % or more and 0.1 % or less;
Sn: 0.0005 % or more and 0.1 % or less;
B: 0.0005 % or more and 0.01 % or less;
Ca: 0.001 % or more and 0.01 % or less;
REM: 0.001 % or more and 0.01 % or less;
Co: 0.05 % or more and 5 % or less;
Ni: 0.05 % or more and 5 % or less; and
Cu: 0.2 % or more and 4 % or less.
[0019] (iv) A method for manufacturing a non-oriented electrical steel
sheet, comprising:
subjecting a steel slab to soaking, where the steel slab is retained at a
soaking temperature of 1000 C to 1200 C, the steel slab containing, by
mass%,
Si: 5.0 % or less,
Mn: 2.0 % or less,
Al: 2.0 % or less, and
P: 0.05 % or less,
in a range satisfying formula (1), and the steel slab further containing, by
mass%,
C: 0.008 % or more and 0.040 % or less,
N: 0.003 % or less, and
Ti: 0.04 % or less,
in a range satisfying formula (2);
P0110494-PCT-ZZ (8/29)

CA 02822206 2015-08-13
64881-518
- 9 -
subjecting the steel slab to subsequent hot rolling to obtain a hot-rolled
steel material;
then subjecting the steel material to cold rolling or warm rolling once, or
twice or more with intermediate annealing performed therebetween, to be
finished to a final sheet thickness; and
subjecting the steel material to final annealing, wherein prior to the final
annealing, the steel material is subjected to heat treatment at least once
where
the steel material is retained at temperatures of 800 C or higher and 950 C
or lower for 30 seconds or more, and subsequently to the final annealing at
to 700 C or higher and 850 C or lower:
300 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] 430 .. (1)
0.008 Ti* < 1.2[C%] .............. (2)
, where Ti* = Ti ¨ 3.4[N%].
[0020] (v) The method for manufacturing a non-oriented electrical
steel
sheet according to (iv) above, wherein the Si, Mn, Al and P contents are, by
mass%,
Si: more than 3.5 % but not more than 5.0 %,
Mn: 0.3 % or less,
Al: 0.1 % or less, and
P: 0.05 % or less.
[0021] (vi) The method for manufacturing a non-oriented electrical
steel
sheet according to (iv) or (v) above, wherein the steel slab further contains,
by
mass%, at least one of:
Sb: 0.0005 % or more and 0.1 % or less;
Sn: 0.0005 % or more and 0.1 % or less;
B: 0.0005 % or more and 0.01 % or less;
Ca: 0.001 % or more and 0.01 % or less;
REM: 0.001 % or more and 0.01 % or less;
Co: 0.05 % or more and 5 % or less;
Ni: 0.05 % or more and 5 % or less; and
Cu: 0.2 % or more and 4 % or less.

CA 02822206 2015-08-13
64881-518
- 9a -
[0021a] (vii) A non-oriented electrical steel sheet having a chemical
composition
consisting of, by mass%:
Si: 5.0 % or less;
Mn: 2.0 % or less;
Al: 2.0 % or less; and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less;
N: 0.003 % or less; and
Ti: 0.04 % or less,
in a range satisfying formula (2), and the balance being Fe and incidental
impurities:
300 5_ 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] < 430 ............. (1)
0.008 < Ti* < 1.2[C%[ ............... (2),
where Ti* = [Ti%] - 3.4[N%].
[0021b] (viii) A method for manufacturing a non-oriented electrical steel
sheet,
comprising:
subjecting a steel slab to soaking, where the steel slab is retained at a
soaking
temperature of 1000 C to 1200 C, the steel slab having a chemical composition
consisting of,
by mass%,
Si: 5.0 % or less,
Mn: 2.0 % or less,
Al: 2.0 % or less, and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less,
N: 0.003 % or less, and
Ti: 0.04 % or less,
in a range satisfying formula (2) and the balance being Fe and incidental
impurities;
subjecting the steel slab to subsequent hot rolling to obtain a hot-rolled
steel

CA 02822206 2016-02-12
64881-518
- 9b -
material;
then subjecting the steel material to cold rolling or warm rolling once, or
twice
or more with intermediate annealing performed therebetween, to be finished to
a final sheet
thickness; and
subjecting the steel material to final annealing, wherein prior to the final
annealing, the steel material is subjected to heat treatment at least once
where the steel
material is retained at a temperature of 800 C or higher and 950 C or lower
for 30 seconds or
more, and subsequently to the final annealing at 700 C or higher and 850 C or
lower:
300 < 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] <430 ............... (1)
0.008 < Ti* < 1.2[C%] .. (2),
where Ti* = [Ti%] - 3.4[N%].
[0021c] (ix) A non-oriented electrical steel sheet having a chemical
composition
consisting of, by mass%:
Si: 5.0 % or less;
Mn: 2.0 % or less;
Al: 2.0 % or less; and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less;
N: 0.003 % or less; and
Ti: 0.04 % or less,
in a range satisfying formula (2), and
=
at least one of:
Sb: 0.0005 % or more and 0.1 % or less;
Sn: 0.0005 % or more and 0.1 % or less;
B: 0.0005 % or more and 0.01 % or less;
Ca: 0.001 % or more and 0.01 % or less;
REM: 0.001 % or more and 0.01 % or less;
Co: 0.05 % or more and 5 % or less;

CA 02822206 2016-02-12
64881-518
- 9c -
Ni: 0.05 % or more and 5 % or less; and
Cu: 0.2 % or more and 4 % or less, and the balance being Fe and incidental
impurities:
300 85[SiVo] + 16[Mn%]+ 40[A1N + 490[P%] < 430 .. (1)
0.008 Ti* < 1.2[C%] .. (2),
where Ti* = [Ti%] - 3.4[N%].
[0021d] (x) A method for manufacturing a non-oriented electrical steel
sheet
comprising:
subjecting a steel slab to soaking, where the steel slab is retained at a
soaking
temperature of 1000 C to 1200 C, the steel slab having a chemical composition
consisting of,
by mass %,
Si: 5.0 % or less,
Mn: 2.0 % or less,
Al: 2.0 % or less, and
P: 0.05 % or less,
in a range satisfying formula (1), and
C: 0.008 % or more and 0.040 % or less,
N: 0.003 % or less, and
Ti: 0.04 % or less,
in a range satisfying formula (2), and
at least one of:
Sb: 0.0005 % or more and 0.1 % or less,
Sn: 0.0005 % or more and 0.1 % or less,
B: 0.0005 % or more and 0.01 % or less,
Ca: 0.001 % or more and 0.01 % or less,
REM: 0.001 % or more and 0.01 % or less,
Co: 0.05 % or more and 5 % or less,
Ni: 0.05 % or more and 5 % or less, and
Cu: 0.2 % or more and 4 % or less, and the balance being Fe and incidental

CA 02822206 2016-02-12
64881-518
- 9d -
impurities;
subjecting the steel slab to subsequent hot rolling to obtain a hot-rolled
steel
material;
then subjecting the steel material to cold rolling or warm rolling once, or
twice
or more with intermediate annealing performed therebetween, to be finished to
a final sheet
thickness; and
subjecting the steel material to final annealing, wherein prior to the final
annealing, the steel material is subjected to heat treatment at least once
where the steel
material is retained at a temperature of 800 C or higher and 950 C or lower
for 30 seconds or
more, and subsequently to the final annealing at 700 C or higher and 850 C or
lower:
300 < 85[Si%] + 16[Mn%] + 40[Al%] + 490[P%] < 430 ............. (1)
0.008 < Ti* < 1.2[C%] ............... (2),
where Ti* = [Ti%] - 3.4[N%].
(Advantageous Effect of Invention)
100221 According to the present invention, a non-oriented electrical steel
sheet
may be provided that is excellent in both mechanical properties and

= CA 02822206 2013-06-18
- 10 -
magnetic properties required for a rotor material of motors rotating at high
speed, and that has excellent quality of steel sheet in terms of scab, sheet
shape, and so on. The present invention also allows stable production of
such non-oriented electrical steel sheets with high yield, without incurring a
significant increase in cost or imposing severe constraints on manufacture or
requiring extra steps, as compared to the normal production of non-oriented
electrical steel sheets. Therefore, the present invention is applicable in the
field of motors, such as drive motors of electric vehicles and hybrid vehicles
or servo motors of robots and machine tools, where demand for higher
rotational speed is expected to grow in the future. Thus, the present
invention has a high industrial value and makes a significant contribution to
the industry.
BRIEF DESCRIPTION OF THE DRAWING
[0023] The present invention will be further described below with
reference to the accompanying drawings, wherein:
FIG. 1 is a graph illustrating the relationship between Ti content and
tensile strength;
FIG. 2 is a graph illustrating the relationship between Ti content and
iron loss; and
FIG. 3 is a graph illustrating the relationship between Ti content and
surface scab defect rate.
DESCRIPTION OF EMBODIMENTS
[0024] The experimental results underlying the present invention will be
described in detail below.
That is, the inventors of the present invention investigated in detail how Ti,
which is a major carbonitride forming element, affects the quality of steel
sheet in terms of strengthening by precipitation, recrystallization, grain
growth behavior, scabs, and so on. As a result, it was found that Ti has
significantly different effects, in particular, when added so that the
resulting
Ti content is equal to or less than a total content of C and N in atomic
fraction,
and has an optimum range of addition for satisfying the requirements at a high
level regarding high strength as well as magnetic properties and quality of
P0110494-PCT-ZZ (10/29)

turvn =4.
CA 02822206 2013-06-18
- 11 -
=
steel sheet. The major experimental results will be described below. The
percentage "%" of each steel component represents "mass%," unless otherwise
specified.
100251 <Experiment 1>
Steel samples, which have steel compositions mainly composed of silicon
(Si): 4.0 % to 4.1 %, manganese (Mn): 0.03 % to 0.05 %, aluminum (Al):
0.001 % or less, phosphorus (P): 0.007 % to 0.009 %, and sulfur (S): 0.001 %
to 0.002 %, containing substantially constant amounts of carbon (C): 0.024 %
to 0.026 % and nitrogen (N): 0.001 % to 0.002 %, and different amounts of
titanium (Ti) in the range of 0.001 % to 0.36%, were obtained by steelmaking
in a vacuum melting furnace. These steel samples were heated to 1100 C
and then subjected to hot rolling to be finished to a thickness of 2.1 mm,
respectively. Then, the steel samples were subjected to hot band annealing
at 900 C for 90 seconds and further to cold rolling to be finished to a
thickness of 0.35 mm, after which the occurrence of scab defects on the
surfaces of the steel sheets (scab size per unit area) was determined.
Subsequently, the steel samples were subjected to final annealing at 800 C
for 30 seconds and evaluated for their mechanical properties (by using JIS No.
5 tensile test specimens cut parallel to the rolling direction) and magnetic
properties (by using Epstein test specimens cut in the rolling direction and
transverse direction, measuring iron loss W10/400 with a magnetizing flux
density of 1.0 T and frequency of 400 Hz). The research results of tensile
strength, magnetic property and occurrence of surface scab defect are depicted
in FIGS. 1, 2 and 3 as a function of Ti content, respectively.
100261 Firstly, as illustrated in FIG. 1, tensile strength increases with
addition of Ti. However, it was found that this effect is less pronounced
within a Ti content range indicated by "A" (Range A) in FIG. 1 where Ti
content is smaller, while stable improvements in strength are observed within
a Ti content range indicated by "B" (Range B) in the figure. Additionally,
even further improvements in strength are achieved within a range indicated
by "C" (Range C) in the figure where Ti content is higher. Upon observation
of steel structure in these regions, it was found that in Range B, the steel
structure contains homogeneous microstructures with a crystal grain size of 10
pm or less, whereas in Range A, it involves crystal grains grown more than in
P0110494-PCT-ZZ (11/29)

CA 02822206 2013-06-18
- 12 -
Range B, particularly, mixed-grain-size microstructures with partial grain
growth. On the other hand, in Range C, the steel structure assumes a
multi-phase of non-recrystallized grains and recrystallized grains.
[0027] FIG. 2 illustrates the relationship between Ti content and iron
loss
W10/400= While good iron loss properties are obtained in Range A with the
lowest iron loss, as illustrated in FIG. 1, Range A shows lower strength
levels.
On the other hand, while high strength materials are obtained in Range C and
D in FIG. 2, iron loss is also high in these ranges. In contrast, Range B
offers materials that have iron loss properties almost as good as in Range A,
while yielding strength results comparable to those obtained in Range C.
[0028] On the other hand, as illustrated in FIG. 3, the scab defect rate
starts to increase when Ti content exceeds 0.04 %, and continues to rise up to
around a point at which the equivalent ratio of elements of Ti to C and N is
equal to 1, where a substantially constant rate of scab generation is reached.
Assuming constant C and N contents, the amount of Ti carbonitride
precipitates continues to increase up to around a point at which this
equivalent
ratio of elements is equal to 1, and then remains constant. Thus, it is
considered that the amount of Ti carbonitride precipitates is related to the
amount of scab generation.
These results revealed that by controlling Ti content within range B, it
becomes possible to balance high strength and low iron loss, while reducing
scab defects that would otherwise cause a reduction in yield and a sheet
fracture trouble and be directly linked to an increase in manufacturing cost.
That is, it is advantageous to contain Ti in an amount of 0.04 % or less in
terms of reducing scab defects, provided that it is sufficient for forming a
certain amount of Ti carbonitrides.
[0029] In addition, as a result of further studies conducted with the
same
components except for the above-described steel and N content and with
varying N contents, it was also found that the lower limit of Ti content to
which high strength can be obtained increases with increasing N contents.
Still further studies revealed that it is necessary to satisfy a relation of
0.008
Ti* (where Ti* = Ti ¨ 3.4[N%]). From this, it is believed that since Ti
carbides make a large contribution to enhancement of strength while Ti
nitrides contribute less, control of Ti carbides is more important.
P0110494-PCT-ZZ (12/29)

= =-=.--v
CA 02822206 2013-06-18
- 13 -
100301 These results revealed that by controlling Ti content at a level
of
Range B, it becomes possible to balance high strength and low iron loss, while
reducing scab defects that would otherwise cause a reduction in yield and a
sheet fracture trouble and be directly linked to an increase in manufacturing
cost.
[0031] <Experiment 2>
Then, to investigate details of the influence of Ti carbonitrides, steel
samples
having compositions shown in Table 1 were prepared by steelmaking in a
vacuum melting furnace to obtain steel sheets, each having a sheet thickness
of 0.35 mm, following the same procedure as in Experiment 1. C and N
contents of steel samples were varied using steel sample "a," which has small
C and N contents, as a reference. Steel samples "c" and "d" contain C and N
so that the total content thereof is within a predetermined range. The surface
scab defect rate, iron loss and tensile strength of the resulting samples are
shown in Table 2. While steel samples "b," "c" and "d" show an increase in
strength in relation to steel sample "a," comparing steel samples "c" and "d"
having substantially the same total amount of C and N to evaluate the effect
of
addition of C and N, it can be seen that steel sample "c" having a lower N
content has higher strength. Upon observation of microstructures, it was
found that the steel samples are listed as a>d>b>c in descending order of
crystal grain size, as is the case with in descending order of tensile
strength.
[0032] [Table 1]
Table 1
(mass%)
Steel Si Mn Al P C N Ti
a 4.33 0.07 0.0005 0.010 0.0019 0.0021 0.0302
4.32 0.05 0.0010 0.010 0.0240 0.0009 0.0295
4.29 0.03 0.0007 0.010 0.0293 0.0009 0.0298
4.25 0.08 0.0018 0.020 0.0249 0.0052 0.0301
P0110494-PCT-ZZ (13/29)

rrIer.rrre,Ar.en
CA 02822206 2013-06-18
- 14 -
[0033] [Table 2]
Table 2
Steel W10/400 Tensile Strength Fatigue Limit Strength Strength Ratio Surface
Scab Defect Rate
(W/kg) TS (MPa) FS (MPa) FS/TS om,m2)
a 26.9 641 535 0.83 0.000
b 33.0 722 630 0.87 0.003
c 32.5 730 665 0.91 0.003
d 31.0 676 540 0.80 0.004
[0034] These samples were further investigated for their fatigue
properties.
Tests were conducted in a tension-to-tension mode with a stress ratio of 0.1
at
a frequency of 20 Hz, where the fatigue limit strength is defined as a stress
which allows a sample to survive 10 million stress amplitude cycles. The
results thereof are also shown in Table 2. While a tendency is observed that
materials having a higher tensile strength TS possess a higher fatigue limit
strength FS, the strength ratio FS/TS differs for different materials. In this
case, steel sample "c" gave the best result. On the other hand, steel sample
"d" does not improve so much in fatigue limit strength for its high tensile
strength. Given these circumstances, and as a result of our detailed
investigations of the microstructures of steel sample "d," many precipitates,
presumably TiN precipitates having a grain size of greater than 5 inn were
scattered over the microstructures, and these precipitates were estimated as
contributing to origins of fatigue fracture. It should be noted here that
nitrogen reacts with titanium at relatively high temperatures of 1100 C or
higher and tends to precipitate as TiN coarsely. It was thus believed that
TiN tends to provide origins of fatigue fracture and is less effective as
compared to Ti carbides for inhibiting the growth of crystal grains, which is
one of the goals of the present invention.
[0035] On the other hand, when comparing steel samples "b" and "c," it
was also found that steel sample "c" gives better results in terms of tensile
strength and fatigue limit strength, and is particularly characterized by its
relatively high fatigue limit strength and high strength ratio FS/TS. Since
steel samples "b" and "c" have substantially the same Ti and N contents, they
exhibit similar precipitation behavior of Ti nitrides and Ti carbides. It is
P0110494-PCT-ZZ (14/29)

= at Al. eF=ka..=
=
CA 02822206 2013-06-18
- 15 -
thus believed that the difference between them is attributed to the difference
in the amount of solute carbon. Accordingly, it is estimated that the
presence of solute carbon reduced the occurrence and propagation of cracks
and increased fatigue limit strength by locking dislocations introduced during
repeated stress cycles such as found in fatigue test. Therefore, it is also
important to ensure formation of solute carbon.
[0036] Based on the above-described experimental results, the
inventors of
the present invention made further studies on how these factors including Ti
carbides, Ti nitrides and solute carbon, with the addition of a relatively
small
to amount of Ti, affect the steel structure, quality of steel sheet
surface, as well
as mechanical properties and magnetic properties of steel sheets. As a result,
the inventors discovered the rules comprehensively applicable to these factors
and accomplished the present invention.
[0037] The present invention will now be described in detail below for
each requirement.
Firstly, the grounds for the limitations with regard to the major steel
components are described.
Steel of the present invention contains Si: 5.0 % or less, Mn: 2.0 % or less,
Al:
2.0 % or less, and P: 0.05 % or less in a range satisfying formula (1):
300 5_ 85[SiN + 16[Mn%] + 40[Al%] + 490[P%] 430 .......... (1)
[0038] An object of the present invention is to provide an electrical
steel
sheet having high strength and excellent magnetic properties at low cost. To
this end, it is necessary to achieve solid solution strengthening above a
certain
level by means of the above-described four major alloy components. Thus, it
is important to specify the contents of the four major alloy components as
described later, and to add these components to the steel so that the total
amount of these alloy components is within a range satisfying the above
formula (1), considering individual contributions to solid solution
strengthening. That is, if formula (1) gives a result less than 300, the
strength of the resulting material is insufficient, whereas if formula (1)
gives
a result more than 430, there are more troubles with sheet cracking at the
time
=
P0110494-PCT-ZZ (15/29)

CA 02822206 2013-06-18
- 16 -
of manufacture of steel sheets, leading to a deterioration in productivity and
a
significant increase in manufacturing cost.
[0039] Next, the grounds for the limitations on the individual contents
of
the four major alloy components are described.
Si 5 5.0 %
Silicon (Si) is generally used as a deoxidizer and one of the major elements
that are contained in a non-oriented electrical steel sheet and have an effect
of
increasing the electrical resistance of steel to reduce its iron loss.
Further, Si
has high solid solution strengthening ability. That is, Si is an element that
is
positively added to the non-oriented electrical steel sheet because it is
capable
of achieving higher tensile strength, higher fatigue strength and lower iron
loss at the same time in a most balanced manner as compared to other
solid-solution-strengthening elements, such as Mn, Al or Ni, that are added to
the non-oriented electrical steel sheet. To this end, it is advantageous to
contain Si in steel in an amount of 3.0 % or more, more preferably exceeding
3.5 %. However, above 5.0 %, toughness degradation will be pronounced,
which should necessitate highly-sophisticated control during sheet passage
and rolling processes, resulting in lower productivity. Therefore, the upper
limit of the Si content is to be 5.0 % or less.
[0040] Mn 5 2.0 %
Manganese (Mn) is effective in improving hot shortness properties, and also
has effects of increasing the electrical resistance of steel to reduce its
iron
loss and enhancing the strength of steel by solid solution strengthening.
Thus, Mn is preferably contained in steel in an amount of 0.01 % or more.
However, addition of Mn is less effective in improving the strength of steel
as
compared to Si and excessive addition thereof leads to embrittlement of the
resulting steel. Therefore, the Mn content is to be 2.0 % or less.
[0041] Al 5 2.0 %
Aluminum (Al) is an element that is generally used in steel refining as a
strong deoxidizer. Further, as is the case with Si and Mn, Al also has effects
of increasing the electrical resistance of steel to reduce its iron loss and
enhancing the strength of steel by solid solution strengthening. Therefore,
Al is preferably contained in steel in an amount of 0.0001 % or more.
However, addition of Al is less effective in improving the strength of steel
as
P0110494-PCT-ZZ (16/29)

,
CA 02822206 2013-06-18
- 17 -
compared to Si and excessive addition thereof leads to embrittlement of the
resulting steel. Therefore, the Al content is to be 2.0 % or less.
[0042] P 0.05 %
Phosphorus (P) is extremely effective in enhancing the strength of steel
because it offers a significantly high solid solution strengthening ability
even
when added in relatively small amounts. Thus, P is preferably contained in
steel in an amount of 0.005 % or more. However, excessive addition of P
leads to embrittlement of steel due to segregation, causing intergranular
cracking or a reduction in rollability. Therefore, the P content is limited to
to 0.05 % or less.
[0043] Additionally, among these major alloy elements Si, Mn, Al and P,
a
Si-based alloy design is advantageous for balancing solid solution
strengthening/low iron loss and productivity in a most efficient way. That is,
it is advantageous to contain Si in steel in an amount of more than 3.5 % for
optimizing the balance of properties of the non-oriented electrical steel
sheet,
where the contents of the remaining three elements are preferably controlled
as follows: Mn: 0.3 % or less, Al: 0.1 % or less, and P: 0.05 % or less. The
grounds for the limitations on the upper limit are as described above.
[0044] In addition, C, N and Ti are also important elements in the
present
invention. This is because it is important to inhibit the growth of crystal
grains during steel sheet annealing with the use of a proper amount of fine Ti
carbides and to develop an ability of reinforcing crystal grain refinement.
For this purpose, it is necessary to contain C: 0.008 % or more and 0.040 % or
less, N: 0.003 % or less, and Ti: 0.04 % or less in steel, in a range
satisfying
formula (2):
0.008 Ti* < 1.2[C%] ........... (2)
where Ti* = Ti ¨ 3.4[N%].
[0045] 0.008 % C 0.040 %
Carbon (C) needs to be contained in steel in an amount of 0.008 % or more.
That is, a carbon content of less than 0.008 % makes it difficult to provide
stable precipitation of fine Ti carbides and results in an insufficient amount
of
solute C, in which case a further improvement in fatigue strength is no longer
P0110494-PCT-ZZ (17/29)

CA 02822206 2013-06-18
- 18 -
possible. On the other hand, excessive addition of C leads to a deterioration
in magnetic properties, while becoming a factor responsible for an increase in
cost, such as making work hardening more pronounced during cold rolling and
causing sheet fracture, forcing more rolling cycles due to an increased
rolling
load, and so on. Therefore, the upper limit of C is limited to 0.04 %.
[0046] N 5 0.003 %
Nitrogen (N) forms nitrides with Ti, which are, however, formed at higher
temperatures than Ti carbides. Thus, N is less effective in inhibiting the
growth of crystal grains and not effective so much in refining crystal grains.
Rather, N sometimes causes adverse effects such as providing origins of
fatigue fracture. Therefore, N content is limited to 0.003 % or less.
Additionally, without limitation, the lower limit is preferably about 0.0005 %
in terms of steelmaking degassing ability and for avoiding a deterioration in
productivity due to a long refining duration.
[0047] Ti 5 0.04 %
Control of titanium (Ti) carbides is important in the present invention. Ti
tends to form nitrides rather than carbides at high temperatures. Thus, it is
necessary to control the amount of Ti forming carbides. If the amount of Ti
that is capable of forming carbides is denoted as Ti*, Ti* is represented as
the
Ti content minus the atom equivalent with N, namely:
Ti* = Ti ¨ 3.4[N%]
To allow the added Ti to precipitate as Ti carbides for enhancing the strength
of steel, while inhibiting the growth of crystal grains for preventing an
increase in iron loss of the steel, it is necessary to use a proper amount of
C
and satisfy Ti* 0.008. On the other hand, if Ti content is increased in
relation to C content, there is a reduction in the amount of solute C, in
which
case a further improvement in fatigue strength is no longer possible.
Therefore, it is also necessary to satisfy Ti* < 1.2[C%] at the same time.
[0048] In addition, if Ti content exceeds 0.04 %, as previously
described
with reference to FIG. 3, more scab defects will occur and the quality of
steel
sheet and yield will be reduced, resulting in an increase in cost. Therefore,
the upper limit of Ti content is to be 0.04 %.
P0110494-PCT-ZZ (18/29)

CA 02822206 2013-06-18
-19-
100491 The present invention may also contain elements other than the
aforementioned elements without impairing the effects of the invention. For
example, the present invention may contain: antimony (Sb) and tin (Sn), each
of which has an effect of improving magnetic properties of steel, in the range
of 0.0005 % to 0.1 %; boron (B), which has an effect of enhancing grain
boundary strength of steel, in the range of 0.0005 % to 0.01 %; Ca and REM,
each of which has an effect of controlling the form of oxide and sulfide and
improving magnetic properties of steel, in the range of 0.001 % to 0.01 %; Co
and Ni, each of which has an effect of improving magnetic flux density of
steel, in the range of 0:05 % to 5 %; and Cu, which is expected to provide
strengthening by precipitation by means of aging precipitation, in the range
of
0.2 % to 4 %, respectively.
[0050] The grounds for the limitations with regard to a manufacturing
method according to the present invention will now be described below.
In the present invention, the manufacturing process from steelmaking to cold
rolling may be performed in accordance with methods commonly used for
manufacturing general non-oriented electrical steel sheets. For example,
steel, which was prepared by steelmaking and refined with predetermined
components in a converter or electric furnace, may be subjected to continuous
casting or blooming after ingot casting to obtain steel slabs, which in turn
may
be subjected to process steps, including hot rolling, optional hot band
annealing, cold rolling, final annealing, insulating coating application and
baking, and so on to manufacture steel sheets. In these steps, the conditions
for properly controlling the precipitation state will be described below. It
should be noted that hot band annealing may optionally be carried out after
the hot rolling, and that the cold rolling may be performed once, or twice or
more with intermediate annealing performed therebetween.
[0051] The steel slabs composed of the aforementioned chemical
compositions are to be subjected to hot rolling at a slab heating temperature
of
1000 C or higher to 1200 C or lower. That is, if the slab heating
temperature is below 1000 C, it is not possible to achieve an effect of
inhibiting the growth of crystal grains during final annealing in a sufficient
manner due to the precipitation and growth of Ti carbides during slab heating.
Alternatively, if the slab heating temperature is above 1200 C, this is not
P0110494-PCT-ZZ (19/29)

CA 02822206 2013-06-18
- 20 -
only disadvantageous in terms of cost, but also causes slab deformation due to
a reduction in strength at high temperature, which interferes with, e.g.,
extraction of the steel slabs from the heating furnace, resulting in lower
operability. Therefore, the slab heating temperature is to be within the range
of 1000 C to 1200 C. Additionally, the hot rolling itself is not limited to
a
particular type and may be performed under the conditions of, for example,
hot rolling finishing temperature in the range of 700 C to 950 C and coiling
temperature of 750 C or lower.
[0052] Then, the resulting hot rolled steel materials are subjected to
optional hot band annealing and cold rolling or warm rolling once, or twice or
more with intermediate annealing performed therebetween to be finished to a
final sheet thickness before final annealing. Prior to the final annealing, it
is
important to subject the steel materials to heat treatment at least once where
the steel materials are retained at temperatures of 800 C or higher and 950
C
or lower for 30 seconds or more. This heat treatment may allow
precipitation of Ti carbides in microstructures prior to the final annealing
and
thereby inhibit the growth of crystal grains during final annealing.
[0053] That is, if the above-described heat treatment is performed at
temperatures below 800 C, the resulting precipitation may be insufficient,
while above 950 C, the effect of inhibiting the growth of crystal grains
during final annealing would be insufficient due to the growth of
precipitates.
[0054] Additionally, the aforementioned heat treatment is preferably
performed in combination with either hot band annealing or intermediate
annealing prior to the final annealing.
[0055] The subsequent final annealing may be performed at 700 C or
higher and 850 C or lower to thereby control the microstructure of
recrystallized grains into a homogeneous and fine state, providing an
electrical steel sheet having high strength and excellent magnetic properties.
If the final annealing is performed at temperatures below 700 C, the
resulting
recrystallization is insufficient, while above 850 C, crystal grains are
prone
to grow even when applying the present invention, resulting in a reduction in
strength of the products. Following this final annealing, the steel materials
are subjected to processes for applying and baking insulating coating thereon
to obtain final products.
P0110494-PCT-ZZ (20/29)

,
CA 02822206 2013-06-18
- 21 -
[Example 1]
[0056] Steel samples having compositions shown in Table 3 were obtained
by steelmaking in a vacuum melting furnace, heated to 1100 C, and then
subjected to hot rolling to be a thickness of 2.1 mm. Then, the samples were
subjected to hot band annealing at 900 C for 90 seconds and further to cold
rolling to be finished to a thickness of 0.35 mm. At this moment, an
evaluation was made of the occurrence of scab defects on the surfaces of the
steel sheets, using the scab size per unit area as a reference. Subsequently,
the samples were subjected to final annealing for 30 seconds under two
different conditions at 750 C and 800 C, respectively. Then, test
specimens were cut parallel to the rolling direction from the steel sheet
samples thus obtained for tensile test and fatigue test. In addition, the
magnetic properties were evaluated based on the iron loss with a magnetizing
flux density of 1.0 T and frequency of 400 Hz of the Epstein test specimens
that were cut from the samples in the rolling direction and transverse
direction,
respectively. The evaluation results are shown in Table 4.
[0057] [Table 3]
Table 3
(mass %)
Steel Si Mn Al P C N Ti Formula (1) Ti*
Remarks
1 4.08 0.08 0.0010 0.012 0.0250 0.0015
0.0010 354 -0.0041 Comparative Example
2 4.10 0.05 0.0010 0.010 0.0247 0.0013
0.0189 354 0.0145 Inventiw Example
3 4.05 0.04 0.0004 0.018 0.0251 0.0016
0.0349 354 0.0295 Inventiw Example
4 4.08 0.05 0.0015 0.011 0.0245 0.0012 0.0641 353 0.0600
Comparative Example
5 4.02 0.04 0.0020 0.017 0.0258 0.0017
0.1164 351 0.1106 Comparative Example
6 4.07 0.08 0.0019 0.014 0.0260 0.0019 0.1630 354
0.1565 Comparative Example
=
P0110494-PCT-ZZ (21/29)

Table 4
7:3
CZ
800 C Annealing 750 C Annealing C.11
Surface Scab
00
Steel Defect Rate W101400 Tensile Strength
Fatigue Limit Strength Strength Ratio W10/400 Tensile Strength Fatigue
Limit Strength Strength Ratio Remarks ,
,
(m/m2) (W/kg) TS (MPa) FS (MPa) FS/TS (W/kg) TS
(MPa) FS (MPa) FS/TS
1 0.000 27.4 634 540 0.85 33.4 707
570 0.81 Comparative Example ,
2 0.000 31.5 710 635 0.89 33.9 727
650 0.89 Inventive Example
3 0.005 33.7 715 650 0.91 34.6 731
665 0.91 Inventive Example
4 0.159 42.7 722 600 0.83 44.4 737
620 0.84 Comparative Example -1=. ,
0.189 46.5 . ' 726 560 0.77 48..3 744
575 0.77 Comparative Example ,
,
6 0.211 48.0 734 565 0.77 51.0 750
580 0.77 Comparative Example n
.,
0
1..) .
op .
1..)
1..) .
1..) ..
0
0,
n.)
1..)
tv
0
H
u
LO
O
61
I .
H
OD
:
,
,
,
,
*IV
.
0
,
,
8
,
,
-4.
'
't
C")
.
,
,
'73
.
,
N
.
'
N
,
"R.3
.'
,
IQ
..
,
l=-)
:
1:)
.
,
,
,
,

CA 02822206 2013-06-18
- 23 -
[0059] It can be seen from Table 4 that Steel Sample No. 1, which has a
Ti* value out of the scope of the present invention, exhibits significantly
different properties depending on the final annealing temperatures, which is
considered problematic in terms of quality control. On the other hand, steel
samples containing a proper amount of Ti show smaller difference in their
properties depending on the final annealing temperatures, yielding high
tensile strength in a stable manner. However, as compared to Steel Sample
No. 2 and 3 having steel compositions within the range specified by the
present invention, Steel Sample No. 4, 5 and 6, each having a Ti content out
of
the scope of the present invention, exhibit not so high fatigue limit strength
for their high tensile strength and have inferior scab rate and magnetic
properties.
[Example 2]
[0060] Steel samples having compositions shown in Table 5 were obtained
by steelmaking in a vacuum melting furnace, heated to 1050 C, and then
subjected to hot rolling to be a thickness of 2.1 mm. Then, the samples were
subjected to hot band annealing at 850 C for 120 seconds and further to cold
rolling to be finished to a thickness of 0.35 mm. At this moment, an
evaluation was made of the occurrence of scab defects on the surfaces of the
steel sheets, using the scab size per unit area as a reference. Subsequently,
the steel samples were subjected to final annealing at 800 C for 30 seconds.
Then, test specimens were cut parallel to the rolling direction from the steel
sheet samples thus obtained for tensile test and fatigue test. In addition,
the
magnetic properties were evaluated based on the iron loss with a magnetizing
flux density of 1.0 T and frequency of 400 Hz of the Epstein test specimens
that were cut from the samples in the rolling direction and transverse
direction,
respectively. The results thereof are also shown in Table 6.
Additionally, Steel Sample No. 18, which does not satisfy the relation of
formula (1) specified by the present invention, experienced sheet fracture
during cold rolling, and so was not subjected to the subsequent evaluation
process.
P0110494-PCT-ZZ (23/29)

_
Table 5
7i)
cz
a\
(mass%)
..
Steel Si Mn Al P C N Ti Others Formula (1)
Ti* Remarks
7 3.05 0.15 0.3500 0.018 0.0165 0.0014
0.0174 - 284 0.0126 Comparative Example
8 3.75 0.08 0.0010 0.019 0.0043 0.0015 0.0172
- 329 0.0121 Comparative Example )-3
AD
9 , 3.78 0.05 0.0008 0.014 0.0159
0.0017 0.0166 - 329 0.0108 Inventive Example cr.
4.01 0.04 0.0001 0.015 0.0135 0.0013 0.0154 - 349
0.0109 Inventive Example LA
._,
11 4.01 0.04 0.0004 0.015 0.0320 0.0016
0.0148 - 349 0.0093 Inventive Example
12 4.05 0.05 0.0004 0.013 0.0572 0.0016
0.0166 - 351 0.0111 Comparative Example
n
13 4.03 0.01 0.0004 0.001 0.0175 0.0041
0.0168 - 343 0.0027 Comparative Example
0
1.)
14 4.82 0.04 1.0300 0.018 0.0158 0.0016 0.0188
- 419 0.0133 Inventive Example co
1.)
1.)
3.02 0.88 0.7000 0.010 0.0289 0.0016 0.0333 -
317 0.0278 Inventive Example N)
0
0,
16 3.55 0.59 1.2100 0.010 0.0294 0.0021 0.0328
- 344 0.0256 Inventive Example I
n.)
1\)
17 4.30 0.11 0.1800 0.012 0.0285 0.0025 0.0322
- 380 0.0236 Inventive Example
H
1
CA
1
18 4.60 0.59 1.2100 0.010 0.0296 0.0011 0.0311
- 454 0.0293 Comparative Example 0
19 4.03 0.15 0.0005 0.010 0.0144 0.0009
0.0244 Sb: 0.015 350 0.0213 Inventive Example 0,
1
H
4.11 0.08 0.0009 0.011 0.0167 0.0021 0.0217 Sn: 0.043
356 0.0145 Inventive Example co
21 4.30 0.18 0.2530 0.007 0.0145 0.0009
0.0191 B: 0.003 382 0.0160 Inventive Example
22 4.25 0.09 , 0.2310 0.018 0.0181 0.0011
0.0155 Ca: 0.003 381 0.0117 Inventive Example
23 4.22 0.15 0.0830 0.015 0.0226
0.0016 0.0185 REM: 0.004 372 0.0130 Inventive Example
-t
0 24 3.98 0.25 0.2250 0.013 0.0284 0.0018
0.0355 Co: 0.25 358 0.0293 Inventive Example
_
8 25 4.05 0.20 0.2840 0.016 0.0133 0.0015 0.0211
Ni: 0.15 367 0.0160 Inventive Example
4.
-1' 26 3.87 0.18 0.2760 0.011 0.0336 0.0013 0.0347
Cu: 0.22 348 0.0302 Inventive Example
.o
n
7 3
N
N
41,
ts.)
V7:,

Ul
e-t- ,I= ..
CD 0 P Table 6
73
Surface Scab
(17,, CD C...4 w10/400 Tensile Strength Fatigue
Limit Strength Strength Ratio t...)
*cs Steel
Defect Rate Remarks
v.).-,
,-, (W/kg) IS (MPa) FS (MPa)
FS/TS
cp
-I ,_,m2)
co km'
CD
C)'-' 7 0.001 28.6 625 510 0.82
Comparative Example
p== 5 = E 8 0.000 32.7 673 535
0.79 Comparative Example H
il)
9 0.001 34.5 685 624 0.91 Inventive
Example
Fr
(1)
CD 3' CD10 0.005 32.2 708
631 0.89 Inventive Example
_ = = CD
=CD
= 11 0.005 31.2 705 650 0.92 Inventive
Example
P
n
12 0.230 38.7 694 575 0.93 Comparative
Example
= 0
13 0.110 36.8 701 540 0.77 Comparative
Example 0
1.)
,- go 14 0.005 28.8 779 715
0.92 Inventive Example 1.)
1.)
15 0.035 34.5 668 607 0.91 Inventive
Example
cr7; c4 (1'
c7,
,
cn 0.1 16 0.026 33.3 703 645 0.92
Inventive Example
CD (=-;
0
,--, PO 5t
CA H
= = Cr p 17 0.039 33.5 735 680
0.93 Inventive Example
di3 e+
I
18 - - - - - Comparative
Example 0
Clg ty
Ol
Cl) 0 0
1
.7t 0 19 0.003 31.9 701 620
0.88 Inventive Example H '
OD
'
CD Cl.,
= 0 20 0.004 31.2 707 635
0.90 Inventive Example
Cr,re gt. ,--f"
21 0.006 33.4 733 640 0.87 Inventive
Example
co
O- v) 22 0.003 31.6 729 640 0.88
Inventive Example
c.) -I-
C4 (1)
.-tv co 23 0.003 32.0 721 633
0.88 Inventive Example
0
24 0.007 33.3 723 645 0.89 Inventive
Example
-8 o m-,
*1i n
4.
CD cp 25 0.005 34.1 718 625 0.87
Inventive Example
1' .-1 t".
r-p. õ,
'1:1 CI = co 26 0.008 33.5 706
608 0.86 Inventive Example
n En 0
73 A) 0
N 0
N
Ca..
= '-' =
t./1 .
---.
N.) Ciq CM
='
....,

Dessin représentatif