U.S. patent application number 10/056153 was filed with the patent office on 2002-10-03 for steel sheet for heat shrink band.
This patent application is currently assigned to NKK CORPORATION. Invention is credited to Hiratani, Tatsuhiko, Matsuoka, Hideki, Ono, Yoshihiko, Tanaka, Yasushi.
Application Number | 20020139450 10/056153 |
Document ID | / |
Family ID | 18696787 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139450 |
Kind Code |
A1 |
Ono, Yoshihiko ; et
al. |
October 3, 2002 |
Steel sheet for heat shrink band
Abstract
The present invention provides a steel sheet for a heat shrink
band, containing, by mass %, 0.005% or less of C, 0.5 to 4% of Si,
2% or less of Mn, 0.2% or less of P, 0.04% or less of S, 0.2% or
less of sol.Al, 0.01% or less of N, 0.0003 to 0.004% of B, 0.005%
or less of O, and 0.002 to 0.1% of Sb, the balance being
substantially formed of Fe, or a steel sheet for a heat shrink band
further having a ratio of content of B to content of N (B/N) in the
range from 0.2 to 1. This steel sheet realizes a heat shrink band
having high strength and sufficient magnetic shielding
properties.
Inventors: |
Ono, Yoshihiko; (Fukuyama,
JP) ; Matsuoka, Hideki; (Fukuyama, JP) ;
Hiratani, Tatsuhiko; (Fukuyama, JP) ; Tanaka,
Yasushi; (Fukuyama, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
NKK CORPORATION
TOKYO
JP
|
Family ID: |
18696787 |
Appl. No.: |
10/056153 |
Filed: |
January 24, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10056153 |
Jan 24, 2002 |
|
|
|
PCT/JP01/05002 |
Jun 13, 2001 |
|
|
|
Current U.S.
Class: |
148/330 ;
148/320 |
Current CPC
Class: |
H01J 29/867 20130101;
C22C 38/02 20130101; H01J 29/87 20130101; C22C 38/04 20130101; C22C
38/60 20130101; C22C 38/004 20130101; C21D 8/0236 20130101; C22C
38/002 20130101; C21D 8/0226 20130101 |
Class at
Publication: |
148/330 ;
148/320 |
International
Class: |
C22C 038/00; C22C
038/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2000 |
JP |
2000-198653 |
Claims
1. A steel sheet for a heat shrink band, containing, by mass %,
0.005% or less of C, 0.5 to 4% of Si, 2% or less of Mn, 0.2% or
less of P, 0.04% or less of S, 0.2% or less of sol.Al, 0.01% or
less of N, 0.0003 to 0.004% of B, 0.005% or less of O, and 0.002 to
0.1% of Sb, the balance being substantially formed of Fe.
2. The steel sheet for a heat shrink band according to claim 1,
wherein content of Sb is 0.004 to 0.05%.
3. The steel sheet for a heat shrink band according to claim 1,
wherein the ratio of content of B to content of N (B/N) is further
in the range from 0.2 to 1.
4. The steel sheet for a heat shrink band according to claim 2,
wherein the ratio of content of B to content of N (B/N) is further
in the range from 0.2 to 1.
5. The steel sheet for a heat shrink band according to claim 3,
wherein the (B/N) is in the range from 0.5 to 0.8.
6. The steel sheet for a heat shrink band according to claim 4,
wherein the (B/N) is in the range from 0.5 to 0.8.
7. A heat shrink band formed of the steel sheet according to any
one of claims 1 to 6.
Description
TECHNICAL FIELD
[0001] The present invention relates to a steel sheet for a heat
shrink band (hereinafter referred to as an HS band) for fastening a
panel periphery of a color cathode ray tube (hereinafter referred
to as a CRT).
BACKGROUND ART
[0002] A CRT must be subjected to treatment for preventing
deformation in a panel ace and internal explosion of a tube body
because the tube interior is in a high vacuum state of about 1
.times.10.sup.-7Torr. As one type of such treatment, what we call
heat shrinking treatment has been done. In this treatment, a steel
sheet f or an HS band formed into a band shape is heated to
temperatures in the range from 400 to 600.degree. C. for several
seconds to several tens seconds to be expanded, and then is fitted
on a glass panel of a CRT. Subsequently, the steel sheet is cooled
to be shrunk, thereby fastening a panel periphery.
[0003] As a steel sheet for an HS band subjected to heat shrinking
treatment, a plated cold rolled steel sheet with a thickness of 0.8
to 2 mm has so far been used because the steel sheet for an HS band
must be light in weight and have high strength and ductility. In
recent years, in order to decrease the weight of a CRT, a demand
for decreasing the thickness of the steel sheet for an HS band has
been increasing, so that the steel sheet for an HS band has further
been required to have higher strength. Also, since it was found
that if the magnetic shielding properties of the steel sheet for an
HS band against an external magnetic field such as geomagnetism are
improved, color deviation caused by landing error of electron beam
on the screen can be reduced significantly, a demand for excellent
magnetic shielding properties (that is, high magnetic permeability)
has become strong increasingly as a TV screen has been made large
and flat and as images of computer monitor have been made fine.
[0004] As a method for achieving high strength and high magnetic
permeability of a steel sheet for an HS band, for example,
JP-A-11-86755 has disclosed a method in which 1 to 2 mass % of Si
is contained to achieve high strength and high magnetic
permeability in a magnetic field of geomagnetism level owing to the
solid solution strengthening ability of Si. Also, JP-A-11-158549
has proposed a method in which the crystal grain size of a
Si-containing steel sheet is optimized to achieve high strength and
the composition of inclusions is optimized to achieve high magnetic
permeability.
[0005] A problem with the method described in JP-A-11-86755 is that
either of the obtained strength and magnetic permeability is not
sufficiently high. Also, a problem with the method described in
JP-A-11-158549 is that although high strength can be achieved by a
finer crystal grain, the finer crystal grain leads to a decrease in
magnetic permeability, so that not both of high strength and high
magnetic permeability can be achieved.
DISCLOSURE OF THE INVENTION
[0006] An object of the present invention provides a steel sheet
for an HS band, which has high strength and high magnetic
permeability at the same time.
[0007] The above object is achieved by a steel sheet for an HS
band, containing, by mass %, 0.005% or less of C, 0.5 to 4% of Si,
2% or less of Mn, 0.2% or less of P, 0.04% or less of S, 0.2% or
less of sol.Al, 0.01% or less of N, 0.0003 to 0.004% of B, 0.005%
or less of O, and 0.002 to 0.1% of Sb, the balance being
substantially formed of Fe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a graph showing the-relationship between relative
permeability and content of O;
[0009] FIG. 2 is a graph showing the relationship between relative
permeability and content of Sb; and
[0010] FIG. 3 is a graph showing the relationship between relative
permeability and content of B and B/N.
EMBODIMENT FOR CARRYING OUT THE INVENTION
[0011] The inventors paid attention to B that easily forms coarse
precipitates advantageous in achieving high magnetic permeability,
and conducted studies on the achievement of high magnetic
permeability of a B-contained steel sheet. As a result, the
following findings were obtained.
[0012] 1) Since B, which is effective in achieving high magnetic
permeability, has a high affinity for O, fine B.sub.2O.sub.5
capable of being observed under an electron microscope is easily
yielded at the time of slab casting, which tends to decrease
magnetic permeability.
[0013] 2) At the time of slab heating before hot rolling, the
oxidation of B proceeds in the surface layer of slab and thus a
B-exhausted layer is formed, which leads to a decrease in magnetic
permeability.
[0014] 3) Since B has an affinity for N, coarse nitrides are easily
formed. However, at the time of slab heating or at the time of
annealing after cold rolling, nitriding reaction with N in an
atmosphere of heating proceeds in the surface layer of slab or
steel sheet, so that it is impossible to-sufficiently make the most
of the effect of B addition.
[0015] 4) In order to prevent the yielding of B.sub.2O.sub.5 at the
time of slab casting and the formation of B-exhausted layer or
nitrides in the surface layer of slab or steel sheet, a decrease in
content of O and addition of Sb at the time of slab casting are
effective.
[0016] The present invention has been made based on the
above-described findings. The detail will be described below.
[0017] 1. Relationship between relative permeability and content of
O
[0018] B-added steels containing 0.002% C, 1.2% Si, 1% Mn, 0.07% P,
0.004% S, trace or 0.01sol.Al, 0.002% N, 0.0016% B, and varied
amounts of O in the range from 0.001 to 0.01% were produced by
melting, then hot rolled and cold rolled into steel sheets having a
thickness of 1.2 mm. Subsequently, the steel sheets were annealed
at a temperature of 680 to 730.degree. C. to change the crystal
grain size, by which a yield point (YP) of 330 to 340 MPa was
prepared. In this case, the content of O was changed by adjusting
the degassing time after the addition of Si or Al. Also, if B is
added in a state in which the quantity of dissolved oxygen is
large, B might be consumed as oxides. Therefore, B was added after
degassing and just before casting.
[0019] From the obtained steel sheet samples, 25 cm Epstein test
pieces were taken to measure relative permeability
(.mu./.mu..sub.0: .mu..sub.0 denotes permeability of vacuum) in the
case where the test piece was magnetized to 23.9A/m (0.30e). For
content of O, because a difference was scarcely found between the
analytical values after hot rolling and after annealing, the value
after annealing was adopted.
[0020] FIG. 1 shows the relationship between relative permeability
and content of O. In FIG. 1, .largecircle. denotes samples
containing trace of sol.Al, and .circle-solid. denotes samples
containing 0.01% of sol.Al.
[0021] FIG. 1 reveals that the magnetic permeability of B-added
steel closely relates to content of O, and for both of the samples
containing trace of sol.Al and 0.01% of sol.Al, high relative
permeability can be obtained when the content of O is 0.005% or
less. The precipitates and inclusions of the sample containing
0.005% or less of O were observed, and it was found that B existed
as coarse nitrides almost completely. Also, for the samples
containing trace of sol.Al, almost all of oxides were SiO.sub.2,
and for the samples containing 0.01% of sol.Al, almost all of
oxides were Al.sub.2O.sub.3.
[0022] 2. Relationship between relative permeability and content of
Sb
[0023] Steels containing 0.002% C, 1.2% Si, 1% Mn, 0.07% P, 0.004%
S, 0.02% sol.Al, 0.002% N, trace or o.0015%B, 0.002%0, and varied
amounts of Sb in the range from trace to 0.2% were produced by
melting, then hot rolled, cold rolled, and annealed under the
aforementioned conditions to prepare samples. The relative
permeability was measured by the aforementioned method.
[0024] FIG. 2 shows the relationship between -relative permeability
and content of Sb. In FIG. 2, .largecircle. denotes samples
containing 0.0015% of B, and .circle-solid. denotes samples
containing trace of B.
[0025] FIG. 2 reveals that the samples to which 0.0015% of B is
added exhibit higher relative permeability than the samples
containing trace of B, and if Sb in the range from 0.002 to 0.1%,
preferably in the range from 0.004 to 0.05%, is added, far higher
relative permeability can be obtained.
[0026] Chemical analyses of B and N were made in the sheet
thickness direction from the surface layer for the samples
containing trace and 0.02% of Sb to which B was added, and it was
found that for the sample containing trace of Sb, B content
decreased to a point nearly 50 .mu.m from the surface layer. The
reason for this is thought to be that B was oxidized
preferentially. Also, N content in a region to nearly 30 .mu.m from
the surface layer was slightly higher than that in the central
portion of the sheet thickness, and nitriding of B was observed. On
the other hand, for the sample containing 0.02% of Sb, neither
oxidation nor nitriding of B was observed.
[0027] 3. Relationship between relative permeability and content of
B and B/N
[0028] Steels containing 0.002% C, 1.2% Si, 1% Mn, 0.07% P, 0.004%
S, 0.01% sol.Al, 0.003% N, 0.002% 0, 0.01% Sb, and varied amounts
of B in the range from trace to 0.006% were produced by melting,
then hot rolled, cold rolled, and annealed under the aforementioned
conditions to prepare samples. The relative permeability was
measured by the aforementioned method. Also, for samples containing
0.002% C, 1.2% Si, 1% Mn, 0.07% P, 0.004% S, 0.01% sol.Al, 0.003%
N, 0.002 or 0.006% O, and varied amounts of B in the range from
trace to 0.006% without the addition of Sb, the same test was
conducted.
[0029] FIG. 3 shows the relationship between relative permeability
and content of B and B/N. In FIG. 3, .largecircle. denotes samples
containing 0.002% O and 0.01% Sb, .circle-solid. denotes samples
containing 0.002% O, and .tangle-solidup. denotes samples
containing 0.006% O.
[0030] FIG. 3 reveals that for the sample containing 0.01% of Sb,
higher magnetic permeability than that of the sample without the
addition of Sb can be obtained in the range from 0.0003 to 0.004%
of B, and if B/N is in the range from 0.2 to 1.0, preferably in the
range from 0.5 to 0.8, far higher relative permeability can be
obtained. In particular, remarkably high relative permeability can
be obtained when B/N is 0.7. On the other hand, in the case where
Sb is not added, the sample containing 0.002% O and the sample
containing 0.006% O exhibit the respective highest relative
permeability when B/N is about 0.9 and about 1.2, respectively, but
the relative permeability of these samples are not sufficiently
high as compared with the sample containing 0.01% Sb.
[0031] The following is a description of the reasons for limiting
composition elements other than O, Sb and B.
[0032] C: If the content of C exceeds 0.005%, carbide precipitates,
which decreases the magnetic permeability. Therefore, the content
of C should be 0.005% or less.
[0033] Si: Si improves the magnetic permeability and increases the
strength. For this reason, the content of Si must be 0.5% or more.
However, the content of Si exceeding 4% has little effect on the
increase in magnetic permeability, and causes deterioration in
weldability and brittleness. Therefore, the content of Si should be
0.5 to 4%.
[0034] Mn: Mn is an element that has little effect on the magnetic
permeability and increases the strength due to solid solution
strengthening. For this reason, Mn must be contained to maintain
the strength, but the content of Mn exceeding 2% deteriorates the
magnetic permeability. Therefore, the content of Mn should be 2% or
less.
[0035] P: P has little effect on the magnetic permeability, and
also has solid solution strengthening ability even with a minute
amount. For this reason, P should preferably be contained, but the
content of P exceeding 0.2% significantly deteriorates the
weldability. Therefore, the content of P should be 0.2% or
less.
[0036] sol.Al: sol.Al should preferably be contained to decrease O
as oxides, but the content of sol.Al exceeding 0.2% increases the
cost. Therefore, the content of sol.Al should be 0.2% or less.
Also, in order to stably form SiO.sub.2 as an oxide, the content of
sol.Al should preferably be 0.001% or less, and in order to stably
form Al.sub.2O.sub.3, the content of sol.Al should preferably be
0.005% or more.
[0037] N: N easily yields precipitates and deteriorates the
magnetic permeability. Therefore, the content of N should be 0.01%
or less.
[0038] Besides, at least one kind of Sn of 0.003 to 0.15% and Cu of
0.05 to 0.2% can be contained to prevent the formation of oxides of
B and the nitriding of surface layer, although these elements have
less effect than Sb.
[0039] The manufacturing method for the steel sheet for an HS band
in accordance with the present invention is not subject to any
special restriction. For example, after being produced by melting
using a converter, a steel whose composition has been controlled by
degassing is cast, then hot rolled, cold rolled, and annealed in
the ordinary manner. As necessary, the hot rolled steel can be
annealed after hot rolling, or a double cold rolling and annealing
method in which a process of cold rolling and annealing is repeated
two times can be applied.
[0040] Also, from the viewpoint of corrosion resistance, the steel
sheet for an HS band can be provided with a plating layer of Zn,
Ni, Al, Sn, Cr, Zn--Ni alloy, Zn--Al alloy, etc. Also, the steel
sheet can be plated with the above-described metals in multiple
layers, or the plating metal and base iron can be alloyed partially
or wholly. Furthermore, as necessary, chemical surface treatment
can be carried out on the steel sheet or the plating layer.
EXAMPLE
[0041] After being melted using a converter, slabs with various
composition which had been controlled by degassing were cast, then
heated at 1150.degree. C. for one hour, hot rolled to a thickness
of 3. 2 mm and coiled at a coiling temperature of 680.degree. C.
After being pickled, the obtained hot rolled steel sheets were cold
rolled to a thickness of 1.2 mm, and annealed at a temperature of
680 to 820.degree. C. for 60 seconds in an atmosphere of
10%H.sub.2-90%N.sub.2, by which steel sheet samples 1 to 12 were
prepared. Subsequently, steel sheet samples 2 and 9 were subjected
to skin pass rolling of an elongation ratio of 0.3 to 1.5%. For
steel sheet samples 1 to 12, the chemical analysis of composition
and the measurement of yield point using a JIS No. 5 tensile test
piece and relative permeability in the case where a 25 cm Epstein
test piece was magnetized to 23.9A/m were made.
[0042] The results of chemical analysis are given in Table 1, and
the results of measurement of yield point and relative permeability
are given in Table 2.
[0043] It can be seen from Table 2 that the steel sheets for an HS
band according to the present invention have both of high yield
point and high relative permeability at the same time.
[0044] For the comparative examples, when the yield point is high,
the relative permeability is low, or when the relative permeability
is high, the yield point is low, that is, both of the
characteristics cannot be achieved at the same time.
1TABLE 1 Steel sheet Chemical composition (mass %) No. C Si Mn P S
sol.Al N B Sb O B/N Remarks 1 0.0015 0.5 0.7 0.11 0.002 0.02 0.0012
0.0011 0.003 0.002 0.92 Example 2 0.0018 1.2 1.1 0.07 0.004 0.03
0.0021 0.0015 0.005 0.003 0.71 Example 3 0.0029 2.4 1.6 0.05 0.002
0.02 0.0018 0.0015 0.008 0.003 0.83 Example 4 0.0024 1.2 1.0 0.08
0.001 0.01 0.0016 0.0002 0.012 0.002 0.13 Example 5 0.0010 1.3 1.1
0.07 0.003 0.02 0.0018 0.0024 0.030 0.004 1.33 Example 6 0.0018 1.2
1.0 0.07 0.003 tr. 0.0022 0.0012 0.080 0.002 0.55 Example 7 0.0022
1.3 1.0 0.08 0.002 0.11 0.0015 0.0011 0.050 0.001 0.73 Example 8
0.0016 1.3 1.0 0.07 0.002 0.02 0.0025 0.0010 tr. 0.002 0.40
Comparative example 9 0.0023 1.3 1.1 0.07 0.005 0.01 0.0021 0.0019
0.005 0.008 0.90 Comparative example 10 0.0021 1.2 1.1 0.07 0.004
0.03 0.0018 tr. 0.007 0.003 0 Comparative example 11 0.0019 1.2 1.0
0.07 0.002 0.02 0.0022 0.0045 0.003 0.003 2.05 Comparative example
12 0.0018 1.2 1.0 0.07 0.004 0.27 0.0021 0.0018 0.004 0.003 0.86
Comparative example
[0045]
2TABLE 2 Steel sheet Skin pass elongation No. ratio (%) YP
(N/mm.sup.2) .mu./.mu.O Remarks 1 -- 310 660 Example 2 -- 350 750
Example 2 0.3 320 700 Example 2 0.8 330 620 Example 2 1.5 370 540
Example 3 -- 390 830 Example 4 -- 340 680 Example 5 -- 350 680
Example 6 -- 350 690 Example 7 -- 350 740 Example 8 -- 350 650
Comparative example 9 -- 340 640 Comparative example 9 0.3 310 590
Comparative example 9 0.8 320 510 Comparative example 9 1.5 350 440
Comparative example 10 -- 340 650 Comparative example 11 -- 350 580
Comparative example 12 -- 350 610 Comparative example
* * * * *