U.S. patent application number 12/922772 was filed with the patent office on 2011-03-10 for high-strength non-oriented electrical steel sheet and method of manufacturing the same.
Invention is credited to Yoshihiro Arita, Takeshi Kubota, Hidekuni Murakami, Yoshiyuki Ushigami.
Application Number | 20110056592 12/922772 |
Document ID | / |
Family ID | 41199119 |
Filed Date | 2011-03-10 |
United States Patent
Application |
20110056592 |
Kind Code |
A1 |
Arita; Yoshihiro ; et
al. |
March 10, 2011 |
HIGH-STRENGTH NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF
MANUFACTURING THE SAME
Abstract
A high-strength non-oriented electrical steel sheet contains: by
mass %, C: not less than 0.002% nor more than 0.05%; Si: not less
than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more than
1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not less
than 0.5% nor more than 3.0%. An Al content is 3.0% or less, and
when a Nb content (%) is set to [Nb], a Zr content (%) is set to
[Zr], a Ti content (%) is set to [Ti], a V content (%) is set to
[V], a C content (%) is set to [C], and an N content (%) is set to
[N], Formula (1) and Formula (2) are satisfied. A balance is
composed of Fe and inevitable impurities, a recrystallization area
ratio is 50% or more, yield stress at a tensile test is 700 MPa or
more, fracture elongation is 10% or more, and an eddy current loss
We.sub.10/400 (W/kg) satisfies Formula (3) in relation to a sheet
thickness t (mm) of the steel sheet.
2.0.times.10.sup.-4.ltoreq.[Nb]/93+[Zr]/91+[Ti]/48+[V]/51 (1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51-
).ltoreq.3.0.times.10.sup.-3 (2)
We.sub.10/400.ltoreq.70.times.t.sup.2 (3)
Inventors: |
Arita; Yoshihiro; (Tokyo,
JP) ; Murakami; Hidekuni; (Tokyo, JP) ;
Ushigami; Yoshiyuki; (Tokyo, JP) ; Kubota;
Takeshi; (Tokyo, JP) |
Family ID: |
41199119 |
Appl. No.: |
12/922772 |
Filed: |
April 13, 2009 |
PCT Filed: |
April 13, 2009 |
PCT NO: |
PCT/JP2009/057453 |
371 Date: |
September 15, 2010 |
Current U.S.
Class: |
148/504 ;
148/330; 148/332 |
Current CPC
Class: |
C22C 38/08 20130101;
C22C 38/16 20130101; H01F 1/16 20130101; C21D 2211/004 20130101;
C22C 38/001 20130101; C21D 8/1272 20130101; C22C 38/002 20130101;
H01F 1/147 20130101; C22C 38/04 20130101; C22C 38/14 20130101; C21D
2201/05 20130101; C22C 38/008 20130101; C22C 38/06 20130101; C22C
38/12 20130101; C21D 8/1222 20130101; C22C 38/02 20130101; C22C
38/004 20130101 |
Class at
Publication: |
148/504 ;
148/332; 148/330 |
International
Class: |
C22C 38/16 20060101
C22C038/16; C21D 11/00 20060101 C21D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 14, 2008 |
JP |
2008-104940 |
Claims
1. A high-strength non-oriented electrical steel sheet containing:
by mass %, C: not less than 0.002% nor more than 0.05%; Si: not
less than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more
than 1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not
less than 0.5% nor more than 3.0%, and wherein an Al content is
3.0% or less, when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied, a
balance is composed of Fe and inevitable impurities, a
recrystallization area ratio is 50% or more, yield stress at a
tensile test is 700 MPa or more, fracture elongation is 10% or
more, and an eddy current loss We.sub.10/400 (W/kg) satisfies
Formula (3) in relation to a sheet thickness t (mm) of the steel
sheet. 2.0.times.10.sup.-4.ltoreq.[Nb]/93+[Zr]/91+[Ti]/48+[V]/51
(1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)-
.ltoreq.3.0.times.10.sup.-3 (2)
We.sub.10/400.ltoreq.70.times.t.sup.2 (3)
2. The high-strength non-oriented electrical steel sheet according
to claim 1, further containing, by mass %, Ni: not less than 0.5%
nor more than 3.0%.
3. The high-strength non-oriented electrical steel sheet according
to claim 1, further containing, by mass %, Sn: not less than 0.01%
nor more than 0.10%.
4. The high-strength non-oriented electrical steel sheet according
to claim 2, further containing, by mass %, Sn: not less than 0.01%
nor more than 0.10%.
5. The high-strength non-oriented electrical steel sheet according
to claim 1, further containing, by mass %, B: not less than 0.0010%
nor more than 0.0050%.
6. The high-strength non-oriented electrical steel sheet according
to claim 2, further containing, by mass %, B: not less than 0.0010%
nor more than 0.0050%.
7. The high-strength non-oriented electrical steel sheet according
to claim 3, further containing, by mass %, B: not less than 0.0010%
nor more than 0.0050%.
8. The high-strength non-oriented electrical steel sheet according
to claim 4, further containing, by mass %, B: not less than 0.0010%
nor more than 0.0050%.
9. A method of manufacturing a high-strength non-oriented
electrical steel sheet comprising: manufacturing a slab containing:
by mass %, C: not less than 0.002% nor more than 0.05%; Si: not
less than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more
than 1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not
less than 0.5% nor more than 3.0% and in which an Al content is
3.0% or less, when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied, and a
balance is composed of Fe and inevitable impurities; obtaining a
hot-rolled sheet by hot rolling the slab; pickling the hot-rolled
sheet; next, obtaining a cold-rolled sheet by cold rolling the
hot-rolled sheet; and finish-annealing the cold-rolled sheet,
wherein a soaking temperature T (.degree. C.) of said
finish-annealing and a Cu content "a" (mass %) of the cold-rolled
sheet satisfy Formula (4).
2.0.times.10.sup.-4[Nb]/93+[Zr]/91+[Ti]/48+[V]/51 (1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)-
.ltoreq.3.0.times.10.sup.-3 (2) T.ltoreq.200.times.a+500 (4)
10. The method of manufacturing a high-strength non-oriented
electrical steel sheet according to claim 9, further comprising
annealing the hot-rolled sheet between said obtaining the
hot-rolled sheet and said pickling the hot-rolled sheet.
11. A method of manufacturing a high-strength non-oriented
electrical steel sheet comprising: manufacturing a slab containing:
by mass %, C: not less than 0.002% nor more than 0.05%; Si: not
less than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more
than 1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not
less than 0.5% nor more than 3.0% and in which an Al content is
3.0% or less, when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied, and a
balance is composed of Fe and inevitable impurities; obtaining a
hot-rolled sheet by hot rolling the slab; next, pickling the
hot-rolled sheet; next, obtaining a cold-rolled sheet by cold
rolling the hot-rolled sheet; and finish-annealing the cold-rolled
sheet, wherein a coiling temperature of said hot rolling is
550.degree. C. or less, and a ductile/brittle fracture transition
temperature at a Charpy impact test of the hot-rolled sheet is
70.degree. C. or less.
2.0.times.10.sup.-4[Nb]/93+[Zr]/91+[Ti]/48+[V]/51 (1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)-
.ltoreq.3.0.times.10.sup.-3 (2)
12. A method of manufacturing a high-strength non-oriented
electrical steel sheet comprising: manufacturing a slab containing:
by mass %, C: not less than 0.002% nor more than 0.05%; Si: not
less than 2.0% nor more than 4.0%; Mn: not less than 0.05% nor more
than 1.0%; N: not less than 0.002% nor more than 0.05%; and Cu: not
less than 0.5% nor more than 3.0% and in which an Al content is
3.0% or less, when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied, and a
balance is composed of Fe and inevitable impurities; obtaining a
hot-rolled sheet by hot rolling the slab; next, annealing the
hot-rolled sheet; next, pickling the hot-rolled sheet; next,
obtaining a cold-rolled sheet by cold rolling the hot-rolled sheet;
and finish-annealing the cold-rolled sheet, wherein a cooling rate
from 900.degree. C. to 500.degree. C. of said annealing is
50.degree. C./sec or more, and a ductile/brittle fracture
transition temperature at a Charpy impact test of the hot-rolled
sheet is 70.degree. C. or less.
2.0.times.10.sup.-4[Nb]/93+[Zr]/91+[Ti]/48+[V]/51 (1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51)-
.ltoreq.3.0.times.10.sup.-3 (2)
Description
TECHNICAL FIELD
[0001] The present invention relates to a high-strength
non-oriented electrical steel sheet suitable for an iron core
material of an electric vehicle motor and an electrical apparatus
motor, and a method of manufacturing the same.
BACKGROUND ART
[0002] In recent years, higher performance properties are 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 is high. Such an
electric vehicle motor is designed to make high-speed rotation
possible to thereby obtain high torque.
[0003] A high-speed rotation motor is also used for a machine tool
and an electrical apparatus such as a vacuum cleaner. An outer size
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 the high-speed rotation motor for an
electric vehicle, a DC brushless motor is mainly used. In the DC
brushless motor, magnets are embedded in the vicinity of an outer
periphery of a rotor. In the above structure, a width of a bridge
portion in an outer periphery portion of the rotor (a 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
position. Thus, a high-strength steel sheet has been required for
the high-speed rotation motor for an electric vehicle rather than a
conventional non-oriented electrical steel sheet.
[0004] In Patent Document 1, there is disclosed a non-oriented
electrical steel sheet in which Mn and Ni are added to Si to
achieve solid solution strengthening. However, it is not possible
to obtain sufficient strength even by the above 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, 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
balance.
[0005] In Patent Documents 2 and 3, there are disclosed
non-oriented electrical steel sheets in which carbonitrides are
dispersed in steel to achieve strengthening. However, it is not
possible to obtain sufficient strength even by these non-oriented
electrical steel sheets.
[0006] In Patent Document 4, there is disclosed a non-oriented
electrical steel sheet in which a Cu precipitate is used to achieve
strengthening. However, when manufacturing the above non-oriented
electrical steel sheet, a thermal treatment condition is
restricted. Thus, strength and magnetic properties to be required
cannot be obtained.
[0007] Patent Document 1: Japanese Patent Application Laid-open No.
sho 62-256917
[0008] Patent Document 2: Japanese Patent Application Laid-open No.
Hei 06-330255
[0009] Patent Document 3: Japanese Patent Application Laid-open No.
Hei 10-018005
[0010] Patent Document 4: Japanese Patent Application Laid-open No.
2004-084053
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a
high-strength non-oriented electrical steel sheet capable of easily
obtaining high strength and magnetic properties and a method of
manufacturing the same.
[0012] In the present invention, the following is set as the gist
in order to solve the above-described problems.
[0013] (I) A high-strength non-oriented electrical steel sheet
contains: [0014] by mass %, [0015] C: not less than 0.002% nor more
than 0.05%; [0016] Si: not less than 2.0% nor more than 4.0%;
[0017] Mn: not less than 0.05% nor more than 1.0%; [0018] N: not
less than 0.002% nor more than 0.05%; and [0019] Cu: not less than
0.5% nor more than 3.0% and in which [0020] an Al content is 3.0%
or less, [0021] when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied,
[0022] a balance is composed of Fe and inevitable impurities,
[0023] a recrystallization area ratio is 50% or more, yield stress
at a tensile test is 700 MPa or more, [0024] fracture elongation is
10% or more, and [0025] an eddy current loss We.sub.10/400 (W/kg)
satisfies Formula (3) in relation to a sheet thickness t (mm) of
the steel sheet.
[0025] 2.0.times.10.sup.-4.ltoreq.[Nb]/93+[Zr]/91+[Ti]/48+[V]/51
(1)
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51-
).ltoreq.3.0.times.10.sup.-3 (2)
We.sub.10/400.ltoreq.70.times.t.sup.2 (3)
[0026] (II) The high-strength non-oriented electrical steel sheet
described in (I), further contains by mass %, Ni: not less than
0.5% nor more than 3.0%.
[0027] (III) The high-strength non-oriented electrical steel sheet
described in (I) or (II), further contains by mass %, Sn: not less
than 0.01% nor more than 0.10%.
[0028] (IV) The high-strength non-oriented electrical steel sheet
described in any one of (I) to (III), further contains by mass %,
B: not less than 0.0010% nor more than 0.0050%.
[0029] (V) A method of manufacturing a high-strength non-oriented
electrical steel sheet includes:
[0030] manufacturing a slab containing:
[0031] by mass %, [0032] C: not less than 0.002% nor more than
0.05%; [0033] Si: not less than 2.0% nor more than 4.0%; [0034] Mn:
not less than 0.05% nor more than 1.0%; [0035] N: not less than
0.002% nor more than 0.05%; and [0036] Cu: not less than 0.5% nor
more than 3.0% and in which [0037] an Al content is 3.0% or less,
[0038] when a Nb content (%) is set to [Nb], a Zr content (%) is
set to [Zr], a Ti content (%) is set to [Ti], a V content (%) is
set to [V], a C content (%) is set to [C], and an N content (%) is
set to [N], Formula (1) and Formula (2) are satisfied, and [0039] a
balance is composed of Fe and inevitable [0040] impurities;
obtaining a hot-rolled sheet by hot rolling the slab;
[0041] pickling the hot-rolled sheet; [0042] next, obtaining a
cold-rolled sheet by cold rolling the hot-rolled sheet; and [0043]
finish-annealing the cold-rolled sheet, wherein [0044] a soaking
temperature T (.degree. C.) of the finish-annealing and a Cu
content "a" (mass %) of the cold-rolled sheet satisfy Formula
(4).
[0044] T.ltoreq.200.times.a+500 (4)
[0045] (VI) The method of manufacturing a high-strength
non-oriented electrical steel sheet described in (V), further
includes: annealing the hot-rolled sheet between the obtaining the
hot-rolled sheet and the pickling the hot-rolled sheet.
[0046] (VII) A method of manufacturing a high-strength non-oriented
electrical steel sheet includes: [0047] manufacturing a slab
containing: [0048] by mass %, [0049] C: not less than 0.002% nor
more than 0.05%; [0050] Si: not less than 2.0% nor more than 4.0%;
[0051] Mn: not less than 0.05% nor more than 1.0%; [0052] N: not
less than 0.002% nor more than 0.05%; and [0053] Cu: not less than
0.5% nor more than 3.0% and in which [0054] an Al content is 3.0%
or less, [0055] when a Nb content (%) is set to [Nb], a Zr content
(%) is set to [Zr], a Ti content (%) is set to [Ti], a V content
(%) is set to [V], a C content (%) is set to [C], and an N content
(%) is set to [N], Formula (1) and Formula (2) are satisfied, and
[0056] a balance is composed of Fe and inevitable impurities;
[0057] obtaining a hot-rolled sheet by hot rolling the slab; [0058]
next, pickling the hot-rolled sheet; [0059] next, obtaining a
cold-rolled sheet by cold rolling the hot-rolled sheet; and [0060]
finish-annealing the cold-rolled sheet, wherein [0061] a coiling
temperature of the hot rolling is 550.degree. C. or less, and a
ductile/brittle fracture transition temperature at a Charpy impact
test of the hot-rolled sheet is 70.degree. C. or less.
[0062] (VIII) A method of manufacturing a high-strength
non-oriented electrical steel sheet includes: [0063] manufacturing
a slab containing: [0064] by mass %, [0065] C: not less than 0.002%
nor more than 0.05%; [0066] Si: not less than 2.0% nor more than
4.0%; [0067] Mn: not less than 0.05% nor more than 1.0%; [0068] N:
not less than 0.002% nor more than 0.05%; and [0069] Cu: not less
than 0.5% nor more than 3.0% and in which [0070] an Al content is
3.0% or less, [0071] when a Nb content (%) is set to [Nb], a Zr
content (%) is set to [Zr], a Ti content (%) is set to [Ti], a V
content (%) is set to [V], a C content (%) is set to [C], and an N
content (%) is set to [N], Formula (1) and Formula (2) are
satisfied, and [0072] a balance is composed of Fe and inevitable
impurities;
[0073] obtaining a hot-rolled sheet by hot rolling the slab; [0074]
next, annealing the hot-rolled sheet; [0075] next, pickling the
hot-rolled sheet; [0076] next, obtaining a cold-rolled sheet by
cold rolling the hot-rolled sheet; and [0077] finish-annealing the
cold-rolled sheet, and in which [0078] a cooling rate from
900.degree. C. to 500.degree. C. of the annealing is 50.degree.
C./sec or more, and a ductile/brittle fracture transition
temperature at a Charpy impact test of the hot-rolled sheet is
70.degree. C. or less.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0079] The present inventors have investigated the reason why
strength and magnetic properties are greatly affected by thermal
treatment conditions in a conventional steel strengthening method
in which a Cu precipitate is used. As a result, it has been found
that a high annealing temperature making Cu once solid-dissolving
is needed at finish-annealing after cold rolling in order to
strengthen a steel sheet by precipitation of Cu.
[0080] However, it has also been learned that simply increasing the
finish-annealing temperature coarsens crystal grains, and
strengthening margin by the Cu precipitation is reduced.
[0081] Further, it has also been learned that when crystal grain
coarsening and strengthening by the Cu precipitation are
overlapped, fracture elongation at a tensile test is remarkably
reduced. The above remarkable reduction in fracture elongation, in
the case when a motor core is punched out from the steel sheet in
particular, causes a crack in a punched-out end surface to thereby
develop to a remarkable reduction in a yield and productivity of
the motor core. Thus, it is desirable to avoid the remarkable
reduction in fracture elongation.
[0082] Thus, the present inventors have further advanced earnest
researches on a method of solving these various problems while
enjoying strengthening by the Cu precipitation. As a result, it has
been learned that some determined amounts of C, N, Nb, Zr, Ti, and
V are contained, thereby enabling both strengthening by the Cu
precipitation and making crystal grains fine to be achieved and
enabling the previously described various problems to be
solved.
[0083] Further, it has been learned that a magnetic property
required for a rotor being the main use of a high-strength
electrical steel sheet is an eddy current loss (We) at a high
frequency of 400 Hz or more, and as for a reduction in the eddy
current loss (We) as well, making crystal grains fine by containing
C, N, Nb, Zr, Ti, and V is effective.
[0084] Here, experimental results that have led to the present
invention will be explained.
[0085] (Experiment 1)
[0086] In a vacuum melting furnace in a laboratory, steels
containing, by mass %, Si: 3.1%, Mn: 0.2%, Al: 0.5%, and Cu: 2.0%
with C, N, Nb, Zr, Ti, and V by mass % shown in Table 1 were
manufactured and heated at 1100.degree. C. for 60 minutes, and then
the steels were hot rolled immediately, and hot-rolled sheets
having sheet thicknesses of 2.0 mm were obtained. Thereafter, these
hot-rolled sheets were pickled, and by cold rolling once,
cold-rolled sheets having sheet thicknesses of 0.35 mm were
obtained. Finish-annealing at 800.degree. C. to 1000.degree. C. for
30 seconds was applied to these cold-rolled sheets. In Table 2,
measured results of various properties after finish-annealing are
shown.
[0087] [Table 1]
TABLE-US-00001 TABLE 1 (mass %) Material symbol C (%) N (%) Nb (%)
Zr (%) Ti (%) V (%) A 0.001 0.003 0.001 0.002 0.003 0.004 B 0.008
0.003 0.012 0.002 0.003 0.004 C 0.028 0.003 0.030 0.002 0.003 0.004
D 0.045 0.003 0.040 0.040 0.040 0.040 E 0.055 0.003 0.035 0.002
0.003 0.004
TABLE-US-00002 TABLE 2 Finish annealing Recrystallization Yield
Fracture Eddy current Material temperature area ratio stress
elongation loss We10/400 symbol (.degree. C.) (%) (MPa) (%) (W/Kg)
Evaluation Note A 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 100 632 11 9.1 X Low yield strength and
high We 1000 100 633 2 10.5 X Low yield stress and elongation, and
high We B 800 0 -- -- -- X Out of evaluation due to low
recrystallization area ratio 900 20 -- -- -- X Out of evaluation
due to non-recrystallization 1000 100 635 8 10.8 X Low yield stress
and elongation, and high We C 800 0 -- -- -- X Out of evaluation
due to non-recrystallization 900 100 732 22 7.5 .largecircle. Good
properties in all 1000 100 768 18 8.2 .largecircle. Good properties
in all D 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 100 789 26 7.7 .largecircle. Good
properties in all 1000 100 823 23 7.8 .largecircle. Good properties
in all E 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 0 -- -- -- X Out of evaluation due to
non-recrystallization 1000 100 879 8 7.7 X Low elongation
(Evaluation: .largecircle. Good, X Bad)
[0088] As shown in Table 2, in Materials C and D, in which Nb, Zr,
Ti, and V satisfied Formula (1), yield strength and fracture
elongation were high, and an eddy current loss was low, resulting
that good properties were obtained. In Material A hardly containing
C, N, Nb, Zr, Ti, and V, both the yield strength and the fracture
elongation were low, and the eddy current loss was high. This is
because crystal grains were coarsened at finish-annealing at
900.degree. C. and 1000.degree. C.
[0089] As for Material B, a recrystallization area ratio at
finish-annealing at 900.degree. C. was low. This is inferred that
Nb, which was a little contained, precipitated immediately before
recrystallization during finish-annealing to delay
recrystallization. Further, it is inferred that by finish-annealing
at 1000.degree. C., Nb solid-dissolved to coarsen crystal grains,
and thus a result similar to that of Material A was exhibited.
[0090] It is inferred that as for Material C in which good
properties were obtained, a Nb precipitate was appropriately
dispersed to precipitate, and as for Material D, a Ti precipitate
was appropriately dispersed to precipitate to suppress crystal
grain growth at 900.degree. C. and 1000.degree. C. On the other
hand, Cu once solid-dissolved at finish-annealing temperatures of
900.degree. C. and 1000.degree. C., and further at the time of
cooling during finish-annealing, Cu precipitated finely, so that
strengthening by the Cu precipitation could be optimized. As a
result, it is inferred that the high yield strength and fracture
elongation and the low eddy current loss could be obtained.
[0091] As for Material E, the yield strength was high, but the
fracture elongation was low. This can be considered that excess C
adversely affected Material E. Incidentally, under any one of the
conditions as well, recrystallization did not occur at
finish-annealing at 800.degree. C. This can be considered that Cu,
which had solid-dissolved before annealing, precipitated during
annealing to delay recrystallization.
[0092] (Experiment 2)
[0093] In a vacuum melting furnace in a laboratory, steels
containing, by mass %, Si: 2.8%, Mn: 0.1%, Al: 1.0%, and Cu: 1.8%
with C, N, Nb, Zr, Ti, and V by mass % shown in Table 3 were
manufactured and heated at 1150.degree. C. for 60 minutes, and then
the steels were hot rolled immediately, and hot-rolled sheets
having sheet thicknesses of 2.2 mm were obtained. Thereafter, these
hot-rolled sheets were pickled, and by cold rolling once,
cold-rolled sheets having sheet thicknesses of 0.35 mm were
obtained. Finish-annealing at 800.degree. C. to 1000.degree. C. for
30 seconds was applied to these cold-rolled sheets. In Table 4,
measured results of various properties after finish-annealing are
shown.
TABLE-US-00003 TABLE 3 (mass %) Material symbol C (%) N (%) Nb (%)
Zr (%) Ti (%) V (%) F 0.003 0.001 0.001 0.002 0.003 0.004 G 0.003
0.009 0.011 0.002 0.003 0.004 H 0.003 0.033 0.031 0.002 0.003 0.004
I 0.003 0.049 0.041 0.039 0.039 0.039 J 0.003 0.064 0.036 0.002
0.003 0.004
TABLE-US-00004 TABLE 4 Finish Eddy current annealing
Recrystallization Yield Fracture loss Material temperature area
ratio stress elongation We10/400 symbol (.degree. C.) (%) (MPa) (%)
(W/Kg) Evaluation Note F 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 100 630 12 9.3 X Low yield strength and
high We 1000 100 632 3 10.4 X Low yield stress and elongation, and
high We G 800 0 -- -- -- X Out of evaluation due to low
recrystallization area ratio 900 20 -- -- -- X Out of evaluation
due to non-recrystallization 1000 100 632 7 10.7 X Low yield stress
and elongation, and high We H 800 0 -- -- -- X Out of evaluation
due to non-recrystallization 900 100 735 20 7.6 .largecircle. Good
properties in all 1000 100 769 19 8.1 .largecircle. Good properties
in all I 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 100 787 24 7.8 .largecircle. Good
properties in all 1000 100 826 21 7.9 .largecircle. Good properties
in all J 800 0 -- -- -- X Out of evaluation due to
non-recrystallization 900 0 -- -- -- X Out of evaluation due to
non-recrystallization 1000 100 884 7 7.8 X Low elongation
(Evaluation: .largecircle. Good, X Bad)
[0094] As shown in Table 4, in Materials H and I, in which Nb, Zr,
Ti, and V satisfied Formula (1), the yield strength and the
fracture elongation were high, and the eddy current loss was low,
resulting that good properties were obtained. As for Material F
hardly containing C, N, Nb, Zr, Ti, and V, both the yield strength
and the fracture elongation were low, and the eddy current loss was
high. This is because crystal grains were coarsened at
finish-annealing at 900.degree. C. and 1000.degree. C.
[0095] As for Material G, the recrystallization area ratio at
finish-annealing at 900.degree. C. was low. This is inferred that
Nb, which was a little contained, precipitated immediately before
recrystallization during finish-annealing to delay
recrystallization. Further, it is inferred that at finish-annealing
at 1000.degree. C., Nb solid-dissolved to coarsen crystal grains,
and thus a result similar to that of Material F was exhibited.
[0096] It is inferred that as for Material H in which good
properties were obtained, a Nb precipitate was appropriately
dispersed to precipitate, and as for Material I, a Ti precipitate
was appropriately dispersed to precipitate to suppress crystal
grain growth at 900.degree. C. and 1000.degree. C. On the other
hand, Cu once solid-dissolved at finish-annealing temperatures of
900.degree. C. and 1000.degree. C., and further at the time of
cooling during finish-annealing, Cu precipitated finely, so that
strengthening by the Cu precipitation could be optimized. As a
result, it is inferred that the high yield strength and fracture
elongation and the low eddy current loss could be obtained.
[0097] As for Material J, the yield strength was high, but the
fracture elongation was low. This can be considered that excess N
adversely affected Material J. Incidentally, under any one of the
conditions as well, recrystallization did not occur at
finish-annealing at 800.degree. C. This can be considered that Cu,
which had solid-dissolved before annealing precipitated during
annealing to delay recrystallization.
[0098] Finish-annealing at 800.degree. C. has been so far performed
as a process of making crystal grains fine. That is,
finish-annealing at 800.degree. C. has been performed under a
purpose in which by finish-annealing as above, Cu once
solid-dissolves to achieve high-strengthening, and a steel sheet is
recrystallized, and then crystal grains are not allowed to be
coarsened. However, from Experiments 1 and 2, it has been found
that even if the annealing temperature is adjusted while adding Cu,
only with the above, it is difficult to obtain sufficient strength.
That is, in a conventional technique, it is difficult to achieve
both mechanical properties and magnetic properties. On the other
hand, the present invention as will be described below makes it
possible to achieve both mechanical properties and magnetic
properties.
[0099] Next, a reason for limiting a numerical value in a
high-strength non-oriented electrical steel sheet according to the
present invention will be described. Hereinafter, % means mass
%.
[0100] C is an element necessary for making crystal grains fine.
Fine carbide increases nucleation sites at the time of
recrystallization and further has an effect of suppressing crystal
grain growth. In order to enjoy the effect, a C content is 0.002%
or more. When N is less than 0.005% in particular, the preferable C
content is 0.01% or more, and more preferably 0.02% or more. On the
other hand, when C is added over 0.05%, the fracture elongation is
remarkably reduced. Thus, an upper limit of the C content is set to
0.05%.
[0101] Si is effective for reducing the eddy current loss, and is
an element effective for solid solution strengthening as well.
However, when Si is added excessively, cold rolling performance is
remarkably reduced. Thus, an upper limit of a Si content is set to
4.0%. On the other hand, from the viewpoint of solid solution
strengthening and the eddy current loss, a lower limit is set to
2.0%.
[0102] Mn, similarly to Si, reduces the eddy current loss, and is
an element effective for increasing strength. However, even when a
Mn content exceeds 1.0%, an effect does not improve to be
saturated, and thus an upper limit of the Mn content is set to
1.0%. On the other hand, from the viewpoint of sulfide generation,
a lower limit is set to 0.05%.
[0103] Al, similarly to Si, is an element effective for increasing
resistivity. However, when an Al content exceeds 3.0%, castability
is reduced, and thus considering productivity, an upper limit of
the Al content is set to 3.0%. A lower limit is not set in
particular. However, from the viewpoint of stabilizing deoxidation
(nozzle clogging prevention during casting), it is preferable that
the Al content in the case of Al deoxidation is 0.02% or more, and
the Al content in the case of Si deoxidation is 0.01% or more.
[0104] N is an element necessary for making crystal grains fine.
Fine nitride increases nucleation sites at the time of
recrystallization, and further has an effect of suppressing crystal
grain growth. In order to enjoy the effect, an N content is set to
0.002% or more. When N of 0.005% or more is contained greatly over
a normal level, the effect of suppressing crystal grain growth
becomes further remarkable. The higher the N content is, the larger
the above effect is, so that the N content is preferably further
increased to 0.01% or more, and more preferably to 0.02% or more.
In the case when the C content is less than 0.005% in particular,
the effect to be obtained by the N addition as above appears more
strongly. On the other hand, when N is added over 0.05%, the
fracture elongation is remarkably reduced. Thus, an upper limit of
the N content is set to 0.05%.
[0105] Cu is an important element of bringing precipitation
strengthening. When a Cu content is less than 0.5%, Cu completely
solid-dissolves in the steel and an effect of the precipitation
strengthening cannot be obtained, so that a lower limit of the Cu
content is set to 0.5%. An upper limit is set to 3.0% in
consideration of the fact that strength is to be saturated.
[0106] Ni is an effective element that hardly embrittles the steel
sheet to enable the steel sheet to be high-strengthened. Ni may be
added depending on strength to be required because it is expensive.
In the case when Ni is added, 0.5% or more is preferably contained
in order to sufficiently obtain an effect of Ni. Further, an upper
limit is set to 3.0% in consideration of its cost. Further, from
the viewpoint of suppressing a scab to occur by the Cu addition, Ni
of 1/2 or more of a Cu addition amount is preferably added.
[0107] Sn improves texture and further has an effect of suppressing
nitriding and oxidation at the time of annealing. Particularly, an
effect of improving a magnetic flux density to be reduced by the Cu
addition is large. When an Sn content is less than 0.01%, the
desired effects cannot be obtained, and on the other hand, when Sn
is added over 0.10%, there is sometimes a case that an increase in
a scab is caused. Thus, an Sn addition amount is preferably not
less than 0.01% nor more than 0.10%.
[0108] B segregates in grain boundaries and has an effect of
increasing toughnesses of a hot-rolled sheet and a
hot-rolled-annealed sheet. When a B content is less than 0.0010%,
the desired effect cannot be obtained, and on the other hand, when
B is added over 0.0050%, there is sometimes a case that a slab
crack at the time of casting occurs. Thus, a B addition amount is
preferably not less than 0.0010% nor more than 0.0050%.
[0109] Four elements of Nb, Zr, Ti, and V generate carbide or
nitride and have an effect of suppressing coarsening of a crystal
grain diameter. Then, in the case when Formula (1) constituted by
using values obtained after mass % of each of the elements is
divided by an atomic weight is satisfied, the remarkable effect is
exhibited. [Nb] represents a Nb content (mass %), [Zr] represents a
Zr content (mass %), [Ti] represents a Ti content (mass %), and [V]
represents a V content (mass %).
2.0.times.10.sup.-4.ltoreq.[Nb]/93+[Zr]/91+[Ti]/48+[V]/51 (1)
[0110] In Formula (1), in the case when a value on the right side
is less than 2.0.times.10.sup.-4, a precipitation amount becomes
insufficient, and the sufficient effect of suppressing crystal
grains cannot be obtained. Thus, a lower limit of the value on the
right side is set to 2.0.times.10.sup.-4. On the other hand, excess
contents of these elements solid-dissolve in the steel and do not
affect properties of the steel, so that an upper limit of the value
on the right side is not defined in particular. However, in
consideration of properties and costs, the value on the right side
is preferably 1.0.times.10.sup.-2 or less.
[0111] Formula (2), where a relationship of the six elements of C,
N, Nb, Zr, Ti, and V is defined, is an important parameter for
making crystal grains fine in alliance with Formula (1). [C]
represents the C content (mass %) and [N] represents the N content
(mass %).
1.0.times.10.sup.-3.ltoreq.[C]/12+[N]/14-([Nb]/93+[Zr]/91+[Ti]/48+[V]/51-
).ltoreq.3.0.times.10.sup.-3 (2)
[0112] Formula (1) is merely such that a maximum amount capable of
forming carbide or nitride is defined, and it is not possible to
sufficiently suppress crystal grain growth during final annealing
only by the above condition.
[0113] The second term in Formula (2) is such that the right side
in Formula (1) is subtracted from the sum of a value obtained after
mass % of C is divided by an atomic weight and a value obtained
after mass % of N is divided by an atomic weight, and is a
parameter representing the excess C amount and/or N amount that
do/does not form carbonitride.
[0114] Excess C and/or N as above are/is extremely important for
making crystal grains fine. This is because in the case when C
and/or N are/is contained excessively, carbonitride is
appropriately dispersed to precipitate before finish-annealing to
thereby enable crystal grain growth at the time of annealing to be
suppressed securely.
[0115] In the present invention, carbide, nitride, and carbonitride
have extremely important roles, and among them, nitride and
carbonitride are effective, and particularly, nitride has a
remarkable effect. That is, when carbide and nitride are compared,
nitride is more effective for the effect of the present invention,
and nitride rather exhibits the effect contributing to the effect
of the present invention by a reduced amount. Further, when carbide
and nitride in the same amount are compared, nitride rather can
obtain a large favorable effect, and can suppress an unfavorable
side effect. The "favorable effect" to be described here means
making crystal grains fine, high-strengthening, and stability at a
high temperature, and the "unfavorable side effect" means an
increase in a core loss and a crack originating from a precipitate
(embittlement in particular).
[0116] A mechanism in which properties of a non-oriented electrical
steel sheet change depending on types of the precipitates as above
is unclear, but it is possible to consider that this is because the
properties of a non-oriented electrical steel sheet are affected by
precipitate sizes, forms (anisotropy), consistency with a parent
phase, precipitation places, and so on. Further, it is possible to
consider that the precipitate sizes and so on are affected by
difference in solubility of the constituent elements, difference in
crystal structures of the precipitates, difference in sizes of
constituent atoms, and so on.
[0117] As described above, balances with not only the Nb, Zr, Ti,
and V contents but also the C content and a thermal history in a
manufacturing process are considered to set the N content
appropriately, so that in the present invention, nitride is
preferentially formed as compared with a conventional electrical
steel sheet. As a result, crystal grain growth at a high
temperature is suppressed, thereby enabling an increase in a core
loss and embrittlement to be suppressed.
[0118] Further, as for carbonitride, a composition thereof varies
depending on forming processes, so that properties and effects of
carbonitride do not become the same, but it is said that
carbonitride exhibits a more favorable effect than the precipitate
composed of at least only carbide. Thus, a ratio of the N content
to the C content is preferably high, and [N]/[C] is preferably
three or more, and more preferably five or more. Incidentally, a
composition of carbonitride is considered to change by effects such
that, for example, carbide is set as initial formation, nitride is
set as initial formation, structure similar to that of carbide is
held in a growth process, structure similar to that of nitride is
held in a growth process and the like.
[0119] In the case when the value (parameter value) of the second
term in Formula (2) is less than 1.0.times.10.sup.-3, thermal
stability of carbonitride weakens. For example, when carbonitride
precipitates immediately before recrystallization during
finish-annealing to delay recrystallization, and further an
annealing temperature is increased, the precipitate solid-dissolves
again and crystal grains are coarsened, resulting that it becomes
difficult to form fine grains stably. On the other hand, when C
and/or N become/becomes excessive to a level where the parameter
value exceeds 3.0.times.10.sup.-3, hardening occurs during cooling,
and elongation and toughness of the steel sheet deteriorate.
[0120] From the reasons as above, a lower limit of the parameter
value in Formula (2) is set to 1.0.times.10.sup.-3, and an upper
limit is set to 3.0.times.10.sup.-3.
[0121] In the case when a recrystallization area ratio of the
high-strength non-oriented electrical steel sheet itself is less
than 50%, product properties, particularly, the fracture elongation
is remarkably reduced. Thus, the above recrystallization area ratio
is set to 50% or more.
[0122] The yield stress at a tensile test is set to 700 MPa or more
in consideration of strength to be required for a rotor to rotate
at a high speed. Note that the yield stress to be defined here is a
lower yield point.
[0123] The fracture elongation is set to 10% or more from the
viewpoint of suppressing a crack in a punched-out end surface of a
motor core.
[0124] The eddy current loss is a loss to occur after current flows
through a steel sheet at excitation, and in the case when the above
loss is large, the motor core easily generates heat to cause
demagnetization of magnets. An eddy current loss We.sub.100/400 has
large dependence on a sheet thickness of the steel sheet, and thus
a sheet thickness t (mm) is set as a parameter to set the eddy
current loss We.sub.100/400 to 70.times.t.sup.2 or less as shown in
Formula (3) as a tolerance range of the rotor heat generation.
We.sub.10/400.ltoreq.70.times.t.sup.2 (3)
[0125] As a method of calculating the above eddy current loss, a
dual frequency method is used. When, for example, at a maximum
magnetic flux density Bmax of 1.0 T, a core loss at a frequency
f.sub.l is set to W.sub.1 and a core loss at a frequency f.sub.2 is
set to W.sub.2, the eddy current loss We.sub.10/400 of W.sub.10/400
can be calculated by
"(W.sub.2/f.sub.2-W.sub.1)/(f.sub.2-f.sub.1).times.400.times.400".
[0126] As long as a plurality of core loss values at different
frequencies exist at the maximum magnetic flux density Bmax of 1.0
T, the calculation is possible to be performed, and thus a
measurement frequency is not defined in particular. However, if
possible, the calculation is preferably performed at a frequency
close to 400 Hz, or in a frequency range of, for example, 100 to
800 Hz or so. Note that the maximum magnetic flux density Bmax is a
maximum magnetic flux density to be excited when measuring a core
loss.
[0127] Next, a reason for limiting a numerical value in a method of
manufacturing the high-strength non-oriented electrical steel sheet
according to the present invention will be described.
[0128] At finish-annealing, Cu once solid-dissolves and
precipitates during cooling, and thereby high strength can be
obtained. Thus, a soaking temperature T (.degree. C.) of
finish-annealing has to be a solid solution temperature of Cu or
more. The solid solution temperature depends on the Cu content.
When the Cu content is set to "a" (mass %), when a temperature
(.degree. C.) is 200.times.a+500 or more, Cu completely
solid-dissolves, so that the soaking temperature T (.degree. C.) of
finish-annealing is set to 200.times.a+500 or more as shown in
Formula (4).
T.gtoreq.200.times.a+500 (4)
[0129] When a coiling temperature at the time of hot rolling
exceeds 550.degree. C., carbonitride and a Cu precipitate,
depending on a hot-rolled sheet, remarkably reduce its toughness.
Thus, the coiling temperature at the time of hot rolling is set to
550.degree. C. or less. With regard to the toughness of a
hot-rolled sheet, a ductile/brittle fracture transition temperature
at a Charpy impact test is set to 70.degree. C. or less from the
viewpoint of fracture suppression at the time of cold rolling.
[0130] With regard to annealing of the hot-rolled sheet, when a
cooling rate from 900.degree. C. to 500.degree. C. is lower than
50.degree. C./sec, toughness of a hot-rolled-annealed sheet is
remarkably reduced by carbonitride and the Cu precipitate. Thus,
the cooling rate in the above temperature range is set to
50.degree. C./sec or more. With regard to the toughness of the
steel sheet after annealing, the ductile/brittle fracture
transition temperature at the Charpy impact test is set to
70.degree. C. or less from the viewpoint of fracture suppression at
the time of cold rolling.
[0131] Incidentally, an annealing temperature of the hot-rolled
sheet is not defined in particular, but the purpose of annealing of
the hot-rolled sheet is recrystallization and grain growth
promotion of the hot-rolled sheet, and thus the annealing
temperature is preferably 900.degree. C. or more, and on the other
hand, from the viewpoint of brittleness, it is preferably
1100.degree. C. or less.
[0132] The transition temperature defined here is a temperature
such that as defined in Japan Industrial Standard (JIS), in a
transition curve showing a relationship between a test temperature
and a ductile fracture rate, the ductile fracture rate is 50%. A
temperature corresponding an average value of absorbed energy at
the ductile fracture rate of 0% and absorbed energy at the ductile
fracture rate of 100% may also be employed.
[0133] A length and height of a test piece to be used for the
Charpy impact test are set to sizes defined in JIS. On the other
hand, a width of the test piece is set to a thickness of the
hot-rolled sheet. Thus, the size, in a rolling direction, is 55 mm
in length and 10 mm in height, and the width is 1.5 mm to 3.0 mm or
so depending on the thickness of the hot-rolled sheet. Further,
when performing the test, it is rather preferable that the plural
test pieces are stacked to approximate a thickness of 10 mm that is
a regular test condition.
EMBODIMENT 1
[0134] In a vacuum melting furnace, steels containing, by mass %,
Si: 2.9%, Mn: 0.2%, Al: 0.7%, and Cu: 1.5%, in which C, N, Nb, Zr,
Ti, and V differ in mass %, were manufactured and heated at
1150.degree. C. for 60 minutes, and then the steels were hot rolled
immediately, and hot-rolled sheets having sheet thicknesses of 2.3
mm were obtained. Thereafter, these hot-rolled sheets were pickled,
and by cold rolling once, cold-rolled sheets having sheet
thicknesses of 0.5 mm were obtained. Finish-annealing at
900.degree. C. for 60 seconds was applied to these cold-rolled
sheets. In Table 5, measured results of components and various
properties are shown.
TABLE-US-00005 TABLE 5 Recrystallization Yield Fracture Material
Formula (1) Formula (2) area ratio stress elongation Formula (3)
symbol C N Nb Zr Ti V (.times.10.sup.-4) (.times.10.sup.-3) (%)
(MPa) (%) We10/400*.sup.1 Note a1 0.012 0.003 0.005 0.002 0.003
0.002 1.77 1.04 100 540 15 20.2 Comparative example a2 0.022 0.003
0.012 0.002 0.003 0.004 2.92 1.76 100 750 19 16.3 Invention example
a3 0.031 0.003 0.030 0.002 0.003 0.004 4.85 2.31 100 770 19 16.5
Invention example a4 0.025 0.003 0.045 0.002 0.003 0.004 6.47 1.65
100 780 19 16.5 Invention example a5 0.024 0.003 0.003 0.007 0.003
0.002 2.11 2.00 100 790 15 17.0 Invention example a6 0.036 0.003
0.003 0.015 0.003 0.002 2.99 2.92 90 795 19 16.4 Invention example
a7 0.033 0.003 0.003 0.037 0.003 0.002 5.41 2.42 80 801 18 16.3
Invention example a8 0.026 0.003 0.003 0.002 0.006 0.002 2.18 2.16
60 783 12 16.3 Invention example a9 0.037 0.003 0.003 0.002 0.011
0.002 3.23 2.98 90 790 19 16.6 Invention example a10 0.041 0.003
0.003 0.002 0.032 0.002 7.60 2.87 60 810 11 16.8 Invention example
a11 0.014 0.003 0.003 0.002 0.003 0.005 2.15 1.17 100 740 19 16.4
Invention example a12 0.034 0.003 0.003 0.002 0.003 0.013 3.72 2.68
90 760 18 16.3 Invention example a13 0.024 0.003 0.003 0.002 0.003
0.028 6.66 1.55 70 780 15 16.5 Invention example a14 0.003 0.002
0.033 0.002 0.003 0.002 4.79 -0.09 30 800 5 16.2 Comparative
example a15 0.003 0.003 0.003 0.034 0.003 0.002 5.08 -0.04 40 760 8
16.1 Comparative example a16 0.003 0.003 0.003 0.002 0.032 0.002
7.60 -0.30 10 850 2 16.5 Comparative example a17 0.003 0.003 0.003
0.002 0.003 0.029 6.85 -0.22 20 820 6 16.4 Comparative example a18
0.045 0.002 0.033 0.002 0.003 0.002 4.79 3.41 90 680 5 16.5
Comparative example a19 0.032 0.008 0.033 0.002 0.003 0.002 4.79
2.76 90 680 19 16.3 Invention example a20 0.054 0.003 0.003 0.002
0.032 0.002 7.60 3.95 100 820 4 16.4 Comparative example
*.sup.1From Formula (3), We10/400 .ltoreq. 17.5 W/kg at a sheet
thickness of 0.5 mm
[0135] In Symbol a1 not satisfying Formula (1), the yield stress
and the eddy current loss We.sub.10/400 were out of the range
defined in the present invention. Further, in Symbols a14 to a17
not satisfying Formula (2), the recrystallization area ratio and
the fracture elongation were out of the range defined in the
present invention. In Symbol a20, whose C content exceeds the upper
limit of the range defined in the present invention and which does
not satisfy Formula (2), the fracture elongation was out of the
range defined in the present invention. In other samples (Symbols
a2, a3, a18, and a19), whose requirements each fell within the
range defined in the present invention, good properties were
obtained.
EMBODIMENT 2
[0136] In a vacuum melting furnace, steels containing, by mass %,
Si: 3.7%, Mn: 0.1%, Al: 0.2%, and Cu: 1.4%, in which C, N, Nb, Zr,
Ti, and V differ in mass %, were manufactured and heated at
1150.degree. C. for 60 minutes, and then the steels were hot rolled
immediately, and hot-rolled sheets having sheet thicknesses of 2.3
mm were obtained. Thereafter, these hot-rolled sheets were pickled,
and by cold rolling once, cold-rolled sheets having sheet
thicknesses of 0.5 mm were obtained. Finish-annealing at
900.degree. C. for 60 seconds was applied to these cold-rolled
sheets. In Table 6, measured results of components and various
properties are shown.
TABLE-US-00006 TABLE 6 Recrystallization Yield Fracture Material
Formula (1) Formula (2) area ratio stress elongation Formula (3)
symbol C N Nb Zr Ti V (.times.10.sup.4) (.times.10.sup.-3) (%)
(MPa) (%) We10/400*.sup.1 Note b1 0.003 0.014 0.005 0.002 0.003
0.002 1.77 1.07 100 542 14 20.1 Comparative example b2 0.003 0.022
0.012 0.002 0.003 0.004 2.92 1.53 100 755 20 16.2 Invention example
b3 0.003 0.018 0.030 0.002 0.003 0.004 4.85 1.05 100 776 22 16.7
Invention example b4 0.003 0.020 0.045 0.002 0.003 0.004 6.47 1.03
100 782 22 16.3 Invention example b5 0.003 0.017 0.003 0.007 0.003
0.002 2.11 1.25 100 793 20 16.8 Invention example b6 0.003 0.018
0.003 0.015 0.003 0.002 2.99 1.24 90 792 22 16.2 Invention example
b7 0.003 0.019 0.003 0.037 0.003 0.002 5.41 1.07 80 803 21 16.1
Invention example b8 0.008 0.009 0.003 0.002 0.006 0.002 2.18 1.09
60 784 13 16.4 Invention example b9 0.003 0.016 0.003 0.002 0.011
0.002 3.23 1.07 90 793 22 16.7 Invention example b10 0.005 0.019
0.003 0.002 0.032 0.002 7.60 1.01 60 804 12 16.2 Invention example
b11 0.005 0.012 0.003 0.002 0.003 0.005 2.15 1.06 100 750 18 16.1
Invention example b12 0.003 0.016 0.003 0.002 0.003 0.013 3.72 1.02
90 766 23 16.0 Invention example b13 0.008 0.016 0.003 0.002 0.003
0.028 6.66 1.14 70 782 14 16.8 Invention example b14 0.003 0.009
0.033 0.002 0.003 0.002 4.79 0.41 30 803 4 16.3 Comparative example
b15 0.003 0.011 0.003 0.034 0.003 0.002 5.08 0.53 40 763 6 16.2
Comparative example b16 0.003 0.009 0.003 0.002 0.032 0.002 7.60
0.13 10 849 1 16.6 Comparative example b17 0.003 0.008 0.003 0.002
0.003 0.029 6.85 0.14 20 823 6 16.8 Comparative example b18 0.003
0.007 0.033 0.002 0.003 0.002 4.79 0.27 90 688 4 16.4 Comparative
example b19 0.006 0.015 0.033 0.002 0.003 0.002 4.79 1.09 90 679 20
16.2 Invention example b20 0.032 0.043 0.003 0.002 0.032 0.002 7.60
4.98 100 821 3 16.7 Comparative example *.sup.1From Formula (3),
We10/400 .ltoreq. 17.5 W/kg at a sheet thickness of 0.5 mm
[0137] In Symbol b1 not satisfying Formula (1), the yield stress
and the eddy current loss We.sub.10/400 were out of the range
defined in the present invention. Further, in Symbols b14 to b17
not satisfying Formula (2), the recrystallization ratio and the
fracture elongation were out of the range defined in the present
invention. Similarly, in Symbol b20 not satisfying Formula (2), the
fracture elongation was out of the range defined in the present
invention. In other samples (Symbols b2, b3, b18, and b19), whose
requirements each fell within the range defined in the present
invention, good properties were obtained.
EMBODIMENT 3
[0138] In a vacuum melting furnace, steels containing, by mass %,
C: 0.022%, Mn: 0.5%, Al: 2.0%, N: 0.003%, Ni: 1.0%, Nb: 0.031%, Zr:
0.004%, Ti: 0.003%, and V: 0.004%, in which the Si amount and the
Cu amount were changed, were manufactured and heated at
1120.degree. C. for 120 minutes, and then the steels were hot
rolled immediately, and hot-rolled sheets having sheet thicknesses
of 2.0 mm were obtained. Thereafter, these hot-rolled sheets were
pickled, and by cold rolling once, cold-rolled sheets having sheet
thicknesses of 0.25 mm were obtained. Finish-annealing at
1000.degree. C. for 45 seconds was applied to these cold-rolled
sheets. In Table 7, measured results of the Si amount, the Cu
amount, and various properties are shown.
TABLE-US-00007 TABLE 7 Eddy current Yield Fracture loss Material Si
Cu stress elongation We10/400*.sup.2 symbol (%) (%) Ni/Cu (MPa) (%)
(W/kg) Scab Note c1 1.8 0.4 2.5 540 15 5.4 Non- Comparative
existence example c2 0.6 1.7 570 19 5.5 Non- Comparative existence
example c3 1.1 0.9 620 21 5.7 Non- Comparative existence example c4
1.7 0.6 670 21 5.9 Non- Comparative existence example c5 2.4 0.4
690 15 6.2 Existence Comparative example c6 2.1 0.3 3.3 610 21 4.3
Non- Comparative existence example c7 0.7 1.4 700 18 4.3 Non-
Invention existence example c8 1.3 0.8 720 12 4.2 Non- Invention
existence example c9 1.7 0.6 740 21 4.2 Non- Invention existence
example c10 2.5 0.4 760 11 4.1 Existence Invention example c11 3.5
0.4 2.5 650 17 3.4 Non- Comparative existence example c12 0.6 1.7
710 14 3.3 Non- Invention existence example c13 1.1 0.9 730 13 3.2
Non- Invention existence example c14 2.1 0.5 790 13 3.3 Non-
Invention existence example c15 2.5 0.4 810 12 3.2 Existence
Invention example c16 3.9 0.4 2.5 690 15 2.9 Non- Comparative
existence example c17 0.6 1.7 720 11 2.8 Non- Invention existence
example c18 1.1 0.9 770 11 2.9 Non- Invention existence example c19
1.9 0.5 880 11 3.0 Non- Invention existence example c20 2.6 0.4 900
10 2.8 Existence Invention example c21 4.1 0.4 2.5 820 1 2.6 Non-
Comparative existence example c22 0.6 1.7 850 1 2.5 Non-
Comparative existence example c23 1.1 0.9 880 1 2.4 Non-
Comparative existence example c24 1.9 0.5 910 1 2.5 Non-
Comparative existence example c25 2.6 0.4 950 1 2.6 Existence
Comparative example *.sup.2From Formula (3), We10/400 .ltoreq. 4.4
W/kg at a sheet thickness of 0.25 mm
[0139] In samples (Symbols c1 to c5), in which the Si content is
1.8%, which is lower than the range defined in the present
invention, the yield stress and the eddy current loss We.sub.10/400
were out of the range defined in the present invention. Further, in
samples (Symbols c21 to c25), in which the Si content is 4.1%,
which exceeds the range defined in the present invention, the
fracture elongation is remarkably reduced.
[0140] Further, in samples (Symbols c6, c11, and c16), in which the
Si content was within the range defined in the present invention,
but the Cu content was less than 0.5%, the yield stress was reduced
to be out of the range defined in the present invention. Further,
in samples (Symbols c1 to c4, c6, to c9, c11 to c14, c16 to c19,
and c21 to c24), in which Ni/Cu was 0.5 or more, scabs did not
exist.
EMBODIMENT 4
[0141] In a vacuum melting furnace, steels containing, by mass %,
C: 0.003%, Si: 3.3%, Mn: 0.2%, Al: 0.7%, N: 0.022%, Ni: 1.5%, Nb:
0.032%, Zr: 0.004%, Ti: 0.003%, and V: 0.003%, in which the B
amount and the Sn amount were changed, were manufactured and heated
at 1110.degree. C. for 80 minutes, and then the steels were hot
rolled immediately, and hot-rolled sheets having sheet thicknesses
of 2.7 mm were obtained. The coiling temperature in hot rolling as
above is set to 530.degree. C. Thereafter, these hot-rolled sheets
were annealed (intermediate annealed) at 1050.degree. C. for 60
seconds and further are pickled, and by cold rolling once,
cold-rolled sheets having sheet thicknesses of 0.35 mm were
obtained. Finish-annealing at 950.degree. C. for 60 seconds was
applied to these cold-rolled sheets. In Table 8, the B amount, the
Sn amount, the transition temperature after intermediate annealing,
and the magnetic flux density after finish-annealing are shown.
TABLE-US-00008 TABLE 8 Magnetic flux Yield Transition density
Material B Sn stress temperature B50 symbol (%) (%) (MPa) (.degree.
C.) (T) Scab Note d1 0.0008 0.008 751 60 1.60 Non- Low magnetic
existence flux density d2 0.012 763 60 1.63 Non- .largecircle.
existence d3 0.056 761 70 1.65 Non- .largecircle. existence d4
0.096 759 60 1.66 Non- .largecircle. existence d5 0.012 762 70 1.66
Existence Scab exists d6 0.0012 0.009 766 30 1.59 Non- Low magnetic
existence flux density d7 0.013 767 40 1.63 Non- .circleincircle.
existence d8 0.058 768 30 1.64 Non- .circleincircle. existence d9
0.094 760 40 1.65 Non- .circleincircle. existence d10 0.014 758 30
1.66 Existence Scab exists d11 0.0031 0.007 759 40 1.60 Non- Low
magnetic existence flux density d12 0.011 760 40 1.65 Non-
.circleincircle. existence d13 0.053 763 30 1.66 Non-
.circleincircle. existence d14 0.091 765 20 1.66 Non-
.circleincircle. existence c15 0.011 767 20 1.66 Existence Scab
exists d16 0.0048 0.008 760 30 1.59 Non- Low magnetic existence
flux density d17 0.015 762 30 1.64 Non- .circleincircle. existence
d18 0.049 768 20 1.64 Non- .circleincircle. existence d19 0.089 764
20 1.65 Non- .circleincircle. existence d20 0.012 758 30 1.66
Existence Scab exists d21 0.0056 0.007 753 40 1.60 Non- Low
magnetic existence flux density d22 0.012 755 30 1.65 Non- Slab
crack existence exists d23 0.047 757 30 1.65 Non- Slab crack
existence exists d24 0.085 760 20 1.65 Non- Slab crack existence
exists d25 0.012 763 30 1.65 Existence Scab exists .largecircle.
the magnetic flux density is good. .circleincircle. the magnetic
flux density is good and the transition temperature is also
good.
[0142] In Symbols d6 to d25, in which the B amount was 0.0010% or
more, the transition temperature of hot-rolled-annealed sheets was
low. In Symbols d2 to d5, d7 to d10, d12 to d15, d17 to d20, and
d22 to d25, in which the Sn amount was 0.010% or more, the high
magnetic flux density was obtained.
Incidentally, in Symbols d21 to d25, in which the B amount exceeded
0.0050%, slab cracks occur, and in Symbols d5, d10, d15, d20, and
d25, in which the Sn amount exceeded 0.010%, scabs occurred.
EMBODIMENT 5
[0143] In a vacuum melting furnace, steels containing, by mass %,
C: 0.028%, Si: 2.9%, Mn: 0.8%, Al: 1.4%, N: 0.012%, Ni: 1.4%, Nb:
0.003%, Zr: 0.04%, Ti: 0.003%, and V: 0.003%, in which the Cu
amount was changed, were manufactured and heated at 1120.degree. C.
for 90 minutes, and then the steels were hot rolled immediately,
and hot-rolled sheets having sheet thicknesses of 2.0 mm were
obtained. Thereafter, these hot-rolled sheets were hot-rolled sheet
annealed at 950.degree. C. for 60 seconds and further were pickled,
and by cold rolling once, cold-rolled sheets having sheet
thicknesses of 0.35 mm were obtained. Finish-annealing was applied
to these cold-rolled sheets while changing the soaking temperature.
In Table 9, results of the Cu amount, the temperature of
finish-annealing, and various properties are shown.
TABLE-US-00009 TABLE 9 Eddy current Soaking Recrystallization Yield
Fracture loss Material Cu temperature Formula (4) area ratio stress
elongation We10/400*.sup.3 symbol (%) (.degree. C.) (200 .times. a
+ 500) (%) (MPa) (%) (W/kg) Note e1 0.6 700 620 60 701 11 7.5
Invention example e2 750 80 652 14 7.3 Invention example e3 800 100
654 21 7.0 Invention example e4 900 100 652 16 7.9 Invention
example e5 1000 100 656 14 8.3 Invention example e6 1.0 700 700 60
689 11 7.6 Invention example e7 750 80 676 18 7.4 Invention example
e8 800 100 679 12 7.1 Invention example e9 900 100 679 21 7.8
Invention example e10 1000 100 680 11 8.2 Invention example e11 1.5
700 800 0 850 2 7.5 Comparative example e12 750 20 790 6 6.9
Comparative example e13 800 100 770 19 7.3 Invention example e14
900 100 730 15 7.7 Invention example e15 1000 100 710 13 7.9
Invention example e16 2.1 800 920 0 860 1 7.4 Comparative example
e17 900 40 840 3 7.7 Comparative example e18 950 100 780 16 7.6
Invention example e19 1000 100 790 15 7.9 Invention example e20
1050 100 750 11 8.1 Invention example e21 2.6 800 1020 0 870 1 7.5
Comparative example e22 900 0 860 1 7.6 Comparative example e23 950
20 840 4 7.4 Invention example e24 1000 40 800 8 7.7 Comparative
example e25 1050 100 890 12 7.9 Comparative example *.sup.3From
Formula (3), We10/400 .ltoreq. 8.6 W/kg at a sheet thickness of
0.35 mm
[0144] In samples (Symbols e1 to e10, e13 to e15, e18 to e20, and
e23), in which the soaking temperature satisfied Formula (4), the
yield stress, the fracture elongation, the eddy current loss
We.sub.10/400 were within the range defined in the present
invention, resulting that good properties were obtained.
[0145] In samples (Symbols e11, e12, e16, e17, e21, and e22), in
which the soaking temperature did not satisfy Formula (4), the
recrystallization area ratio was less than 50% and/or the fracture
elongation was less than 10%, resulting that the recrystallization
area ratio and/or the fracture elongation were/was out of the range
defined in the present invention.
EMBODIMENT 6
[0146] In a vacuum melting furnace, a plurality of steel pieces
containing, by mass %, C: 0.027%, Si: 3.6%, Mn: 0.1%, Al: 1.8%, N:
0.005%, Ni: 2.0%, Nb: 0.003%, Zr: 0.004%, Ti: 0.03%, and V: 0.01%
were manufactured. These steel pieces were heated at 1170.degree.
C. for 90 minutes, and then they are hot rolled immediately, and
hot-rolled sheets having sheet thicknesses of 2.5 mm were obtained.
When manufacturing the above hot-rolled sheets, the coiling
temperature was changed. Further, the manufactured hot-rolled
sheets were annealed at 1000.degree. C. for 60 seconds and annealed
sheets were obtained. When annealing as above, the cooling rate
from 900.degree. C. to 500.degree. C. was changed. From these
hot-rolled sheets and annealed sheets, Charpy test pieces were
manufactured, and the transition temperature was measured by the
impact test. Results thereof are shown in Table 10.
TABLE-US-00010 TABLE 10 Hot rolling Cooling rate of coiling
hot-rolled Transition Material temperature sheet annealing
temperature symbol (.degree. C.) (.degree. C./sec) (.degree. C.)
Note f1 500 No hot-rolled 30 Invention sheet annealing example f2
520 40 Invention example f3 540 60 Invention example f4 560 80
Comparative example f5 620 100 Comparative example f6 540 20 100
Comparative example f7 40 80 Comparative example f8 60 60 Invention
example f9 80 40 Invention example f10 100 20 Invention example f11
560 20 100 Comparative example f12 40 80 Comparative example f13 60
60 Invention example f14 80 40 Invention example f15 100 20
Invention example f16 620 20 100 Comparative example f17 40 80
Comparative example f18 60 60 Invention example f19 80 40 Invention
example f20 100 20 Invention example
[0147] In samples (Symbols f1 to f3), in which the coiling
temperature was 550.degree. C. or less, the good toughness at the
transition temperature of 70.degree. C. or less was obtained.
Further, as for the annealed sheets, regardless of the coiling
temperature, in samples (Symbols f8 to f10, f13 to f15, and f18 to
f20), in which the cooling rate from 900.degree. C. to 500.degree.
C. was 50.degree. C./sec or more, the good toughness at the
transition temperature of 70.degree. C. or less was obtained.
INDUSTRIAL APPLICABILITY
[0148] According to the present invention, without sacrificing
yields and productivity at the time of manufacturing a motor core
and a steel sheet, a non-oriented electrical steel sheet excellent
in strength can be provided at a low cost.
* * * * *