U.S. patent application number 10/149494 was filed with the patent office on 2003-03-06 for cr containing steel for welded structure.
Invention is credited to Hasuno, Sadao, Hirasawa, Junichiro, Kitazawa, Makoto, Kobayashi, Makoto, Miyazaki, Atsushi, Satoh, Susumu, Toyooka, takaaki.
Application Number | 20030044305 10/149494 |
Document ID | / |
Family ID | 18791171 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030044305 |
Kind Code |
A1 |
Miyazaki, Atsushi ; et
al. |
March 6, 2003 |
Cr containing steel for welded structure
Abstract
The present invention provides Cr-containing steel that has
satisfactory levels in all of toughness, strength (hardness) and
corrosion resistance of HAZ, and that is suitably used as parts for
welded structures. Specifically, the present invention provides
Cr-containing steel used for a welded structure, the steel being
featured or characterized by containing, by mass %, C: not more
than 0.020%, Si: not more than 1.00%, Mn: 1.0 to 5.0%, P: not more
than 0.050%, S: not more than 0.020%, Cr: 6.0 to 15.0%, Ni: not
more than 1.0%, Al: not more than 0.100%, N: not more than 0.020%,
and V: 0.03 to 0.30%, the balance consisting of Fe and unavoidable
impurities, or further containing Cu: 0.10 to 2.00% or less and Mo:
0.40 to 3.00% or less, wherein an F or F' value calculated by
putting values of contents (mass %) of the respective components in
the following formula (1) or (2) is not larger than 13.50: 1 F
value = Cr + 0.4 .times. Si + 0.2 .times. Al + 5 .times. P - 0.4
.times. Mn - 0.7 .times. Ni - 35 .times. C - 10 .times. N + 10
.times. V ( 1 ) F ' value = Cr + 0.6 .times. Mo + 0.4 .times. Si +
0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7 .times. Ni -
0.6 .times. Cu - 35 .times. C - 10 .times. N + 10 .times. V ( 2
)
Inventors: |
Miyazaki, Atsushi; (Chiba,
JP) ; Hirasawa, Junichiro; (Chiba, JP) ;
Satoh, Susumu; (Chiba, JP) ; Hasuno, Sadao;
(Tokyo, JP) ; Kobayashi, Makoto; (Chiba, JP)
; Toyooka, takaaki; (Aichi, JP) ; Kitazawa,
Makoto; (Aichi, JP) |
Correspondence
Address: |
SCHNADER HARRISON SEGAL & LEWIS, LLP
1600 MARKET STREET
SUITE 3600
PHILADELPHIA
PA
19103
|
Family ID: |
18791171 |
Appl. No.: |
10/149494 |
Filed: |
June 12, 2002 |
PCT Filed: |
October 11, 2001 |
PCT NO: |
PCT/JP01/08933 |
Current U.S.
Class: |
420/61 |
Current CPC
Class: |
C22C 38/58 20130101;
C22C 38/004 20130101; C22C 38/42 20130101; C22C 38/46 20130101;
B23K 2103/05 20180801; B23K 2103/04 20180801; C22C 38/54 20130101;
C22C 38/44 20130101 |
Class at
Publication: |
420/61 |
International
Class: |
C22C 038/44 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2000 |
JP |
2000-311398 |
Claims
1. Cr-containing steel used for a welded structure, the steel
containing, by mass %, C: not more than 0.020%, Si: not more than
1.00%, Mn: 1.0 to 5.0%, P: not more than 0.050%, S: not more than
0.020%, Cr: 6.0 to 15.0%, Ni: 0.10 to 1.00% or less, Al: not more
than 0.100%, N: not more than 0.020%, and V: 0.03 to 0.30%, the
balance consisting of Fe and unavoidable impurities, wherein an F
value calculated by putting values of contents of the respective
components in the following formula (1) is not larger than 13.50: 6
F value = Cr + 0.4 .times. Si + 0.2 .times. Al + 5 .times. P - 0.4
.times. Mn - 0.7 .times. Ni - 35 .times. C - 10 .times. N + 10
.times. V . ( 1 )
2. Cr-containing steel used for a welded structure according to
claim 1, wherein the steel further contains Cu: 0.10 to 2.00% and
Mo: 0.40 to 3.00%, the balance consisting of Fe and unavoidable
impurities, and an F' value calculated by putting values of
contents of the respective components in the following formula (2)
is not larger than 13.50: 7 F ' value = Cr + 0.6 .times. Mo + 0.4
.times. Si + 0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7
.times. Ni - 0.6 .times. Cu - 35 .times. C - 10 .times. N + 10
.times. V . ( 2 )
3. Cr-containing steel used for a welded structure according to
claim 1 or 2, wherein the steel further contains B: 0.0003 to
0.0050% by mass %.
4. Cr-containing steel used for a welded structure according to any
one of claims 1 to 4, wherein the Cr-containing steel is a
hot-rolled plate.
5. Cr-containing steel used for a welded structure according to any
one of claims 1 to 4, wherein the Cr-containing steel is a
cold-rolled plate subjected to cold rolling after hot rolling.
Description
TECHNICAL FIELD
[0001] The present invention relates to Cr-containing steel used
for a welded structure, in particular, suitably used as members
arranged around the tire attachment area in an automobile.
BACKGROUND ART
[0002] Hitherto, coated steel obtained by welding, machining and
then coating plain steel has been primarily employed as members
arranged around the tire attachment area in an automobile.
[0003] The members arranged around the tire attachment area in an
automobile are required to have high strength for ensuring
sufficient rigidity. Also, because those members are used as welded
structure parts that are welded to a vehicle body, etc., they are
required to have sufficient toughness and high strength in welding
area, such as a bead and a welding-heat affected zone (abbreviated
to "HAZ" hereinafter). Further, the members arranged around the
tire attachment area in an automobile are located in positions
where they are directly exposed to, e.g., splash water from the
road surface, and hence are required to have superior corrosion
resistance as well.
[0004] A welded bead has no problems because satisfactory levels of
strength, toughness and corrosion resistance can be ensured by
selecting a proper welding wire. However, characteristics of HAZ,
such as strength, toughness and corrosion resistance, are easily
affected by characteristics of a basic material itself. It is hence
important to improve the characteristics of HAZ.
[0005] Conventionally, plain steel is employed as a basic material
for a member arranged around the tire attachment area in an
automobile, and the plain steel must be subjected to a coating step
after welding and machining steps. The necessity of the coating
step has noticeably deteriorated manufacturability and
productivity.
[0006] In view of the above situation, attention has been focused
on Cr-containing steel as a basic material for a member arranged
around the tire attachment area in an automobile, and a variety of
studies have been conducted.
[0007] In a member arranged around the tire attachment area in an
automobile, stresses are apt to concentrate on a weld toe of a bead
formed by MIG (Metal Inert Gas) or MAG (Metal Active Gas) welding,
and the weld toe tends to become a start point of fatigue failure.
For that reason, it is important to ensure mechanical
characteristics, particularly strength and toughness, of an area
around the weld toe, i.e., of HAZ. One example of Cr-containing
steel having improved strength and toughness of a welding area is a
structure-oriented martensitic stainless steel having superior
weldability and workability, which is disclosed in Japanese
Unexamined Patent Publication No. 55-21566. Such stainless steel
has been initially studied as being employed as members arranged
around the tire attachment area in an automobile.
[0008] The above-mentioned martensitic stainless steel is able to
noticeably improve the toughness of HAZ by preparing a component
system containing low C-low N martensite and low Ni, but cannot
provide sufficient corrosion resistance of HAZ. Therefore, in spite
of a parent material having superior corrosion resistance, HAZ must
be coated as conventional. Eventually, a merit resulting from
employing stainless steel is lessened.
[0009] As means for improving corrosion resistance of HAZ in
stainless steel, it has hitherto been known with regard to ferritic
stainless steel that adding Ti is effective. However, addition of
Ti causes a problem in reducing the martensite phase in HAZ or
lowering the strength of the martensite phase itself, thus
resulting in a reduction of strength and toughness of HAZ. Note
that since the strength of HAZ cannot be directly measured, it is
usually determined by measuring the Vickers hardness of HAZ in
accordance with the method stipulated by SAE J417, and then
converting a measured result into strength.
[0010] In the state of the art, as described above, there exists no
Cr-containing steel that has satisfactory levels in all of (1)
toughness of HAZ, (2) strength (hardness) of HAZ, and (3) corrosion
resistance of HAZ, and that is suitably used as members arranged
around the tire attachment area in an automobile.
[0011] Accordingly, it is an object of the present invention to
provide Cr-containing steel that has satisfactory levels in all of
toughness, strength (hardness) and corrosion resistance of HAZ, and
that is suitably used as parts arranged around the tire attachment
area in an automobile.
DISCLOSURE OF THE INVENTION
[0012] To achieve the above object, the inventors conducted close
studies on effects of various elements added in steel. As a result,
the inventors found that corrosion resistance of HAZ could be
noticeably improved by adding V in proper amount.
[0013] Various kinds of Cr-containing steel having different V
contents on the basis of Fe-12 mass% Cr-2 mass % Mn-0.5 mass % Ni,
for example, were produced by way of experiment. Each sample of the
produced steel was subjected to MIG welding, and then HAZ strength
(actually hardness) of each sample was measured. Also, corrosion
resistance of each sample after the welding was evaluated. Obtained
results are plotted in FIG. 1. The welding conditions of each
sample, the method for measuring HAZ hardness, and the method for
evaluating HAZ corrosion resistance were set similarly to those in
Examples described later.
[0014] As seen from the results of FIG. 1, by adding V in steel in
predetermined amount or more, the corrosion resistance of HAZ is
noticeably improved, but the hardness is noticeably reduced when
the V content exceeds 0.30 mass %.
[0015] From the above-mentioned finding, it was confirmed that, by
adding V in steel in proper amount, both the hardness, i.e., the
strength, and the corrosion resistance of HAZ could be obtained at
high levels.
[0016] Further, it was confirmed that satisfactory toughness and
strength of HAZ could be obtained by setting an F or F' value to be
not larger than a predetermined value, the F or F' value being
calculated by putting values of contents of respective components
contained in steel in a formula (1) or (2) described later.
[0017] The present invention has been made on the basis of the
above-mentioned findings, and the gist of the invention is as
follows.
[0018] The present invention provides Cr-containing steel used for
a welded structure, the steel containing, by mass %, C: not more
than 0.020%, Si: not more than 1.00%, Mn: 1.0 to 5.0%, P: not more
than 0.050%, S: not more than 0.020%, Cr: 6.0 to 15.0%, Ni: not
more than 1.00%, Al: not more than 0.100%, N: not more than 0.020%,
and V: 0.03 to 0.30%, the balance consisting of Fe and unavoidable
impurities, wherein an F value calculated by putting values of
contents (mass %) of the respective components in the following
formula (1) is not larger than 13.50: 2 F value = Cr + 0.4 .times.
Si + 0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7 .times. Ni
- 35 .times. C - 10 .times. N + 10 .times. V ( 1 )
[0019] In addition, the present invention provides Cr-containing
steel used for a welded structure, wherein the steel further
contains Cu: not more than 2.0% and Mo: not more than 3.0%, and an
F' value calculated by putting values of contents (mass %) of the
respective components in the following formula (2) is not larger
than 13.50: 3 F ' value = Cr + 0.6 .times. Mo + 0.4 .times. Si +
0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7 .times. Ni -
0.6 .times. Cu - 35 .times. C - 10 .times. N + 10 .times. V ( 2
)
[0020] Moreover, the present invention provides Cr-containing steel
used for a welded structure, wherein the steel further contains B:
0.0003 to 0.0050% by mass %.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graph plotting hardness and corrosion resistance
of HAZ versus V content (mass %) in Cr-containing steel that
contains Fe-12 mass % Cr-2 mass % Mn-0.5 mass % Ni as basic
components.
[0022] FIG. 2 is an illustration showing positions at which HAZ
hardness was measured.
[0023] FIG. 3 is an illustration showing a position at which a
Charpy impact test piece was sampled.
[0024] FIG. 4 is an illustration showing a test piece sampled for a
salt-spray test.
BEST MODE OF CARRYING OUT THE INVENTION
[0025] The reasons why the contents of components of Cr-containing
steel according to the present invention (referred to simply as
"inventive steel" hereinafter) are limited to the above-mentioned
ranges will be described below in detail.
[0026] C: not more than 0.020 mass % and N: not more than 0.020
mass %
[0027] In the inventive steel, C and N are components adversely
affecting corrosion resistance of HAZ. If any of the contents of C
and N in the steel exceeds 0.020 mass %, the corrosion resistance
is noticeably deteriorated. Therefore, the contents of C and N are
both set to be not more than 0.020 mass %.
[0028] Additionally, for increasing strength (hardness) of HAZ, C
and N are both preferably not less than 0.005 mass %.
[0029] Si: 0.05 mass % to 1.00 mass %
[0030] Si has a deoxidizing action and is a component essential
from the viewpoint of steel-making. Therefore, Si of not less than
0.05 mass % is usually contained in molten steel after the
steel-making process. If the Si content exceeds 1.00 mass % in the
component system of the present invention, the martensite phase
produced in HAZ would be noticeably reduced. Accordingly, the Si
content is limited to be not more than 1.00 mass %.
[0031] Mn: 1.0 to 5.0 mass %
[0032] Mn is a component essential for stabilizing the .gamma.
(austenite) phase at high temperature and achieving satisfactory
hardenability. Therefore, a lower limit of the Mn content is set to
1.0 mass %. On the other hand, if the Mn content exceeds 5.0 mass
%, toughness of HAZ would be deteriorated. Accordingly, an upper
limit of the Mn content is set to 5.0 mass %.
[0033] P: not more than 0.050 mass %
[0034] The P content is preferably as low as possible from the
viewpoint of workability. However, from the viewpoint of economic
restriction imposed on the dephosphorizing process in steel-making,
an upper limit of the P content is set to 0.050 mass %.
[0035] S: not more than 0.020 mass %
[0036] The S content is preferably as low as possible from the
viewpoint of corrosion resistance. However, from the viewpoint of
economic restriction imposed on the desulfurizing process in
steel-making, an upper limit of the S content is set to 0.020 mass
%.
[0037] Cr: 6.0 to 15.0 mass %
[0038] Cr is a component effective in improving corrosion
resistance. When the Cr content is set to be not less than 6.0 mass
%, the corrosion resistance is noticeably improved, and hence a
lower limit of the Cr content is set to 6.0 mass %. On the other
hand, if the Cr content exceeds 15.0 mass %, a larger amount of Ni
would be required to produce the martensite phase in HAZ and the
cost would be increased. Therefore, an upper limit of the Cr
content is set to 15.0 mass %. Preferably, the Cr content is set to
the range of 10.0 to 15.0 mass %.
[0039] Ni: 0.10 to 1.00 mass %
[0040] Ni is a component for stabilizing the .gamma. phase at high
temperature. To develop the stabilizing effect, Ni requires to be
added in amount not less than 0.10 mass %. However, Ni is expensive
and positive addition of Ni increases the cost. Accordingly, an
upper limit of the Ni content is set to 1.00 mass %.
[0041] Al: not more than 0.100 mass %
[0042] Al is an essential component serving as a deoxidizer from
the viewpoint of steel-making. Therefore, Al of not less than 0.02
mass % is usually contained in molten steel after the steel-making
process. However, when Al is not used as a deoxidizer, it is usual
that Al of not less than 0.002 mass % is unavoidably contained. If
Al is overly added in excess of 0.100 mass %, inclusions are more
apt to generate and toughness tends to deteriorate. Accordingly, an
upper limit of the Al content is set to 0.100 mass %.
[0043] V: 0.03 to 0.30 mass %
[0044] V is a component effective in improving corrosion resistance
of HAZ when added in steel in proper amount. The effect is
developed at the V content of not less than 0.03 mass %, but if V
is overly added in excess of 0.30 mass %, strength and toughness of
HAZ would be deteriorated. Therefore, the V content is set to the
range of 0.03 to 0.30 mass %. For satisfying both the corrosion
resistance and strength (hardness) of HAZ at high levels, the V
content is preferably set to the range of 0.06 to 0.15 mass %.
[0045] In the present invention, for ensuring satisfactory
toughness and strength (hardness) of HAZ, it is an essential
feature in addition to the above-described limitations of steel
composition that an F value calculated by putting values of
contents (mass %) of the respective components in the following
formula (1) is not larger than 13.50: 4 F value = Cr + 0.4 .times.
Si + 0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7 .times. Ni
- 35 .times. C - 10 .times. N + 10 .times. V ( 1 )
[0046] In the above formula (1), Cr, Si, Al, P and V are the
so-called ferrite generating elements and impede generation of the
.gamma. phase at high temperature. On the other hand, Mn, Ni, C and
N are the so-called austenite generating elements and promote
generation of the .gamma. phase at high temperature. It was found
that an increase of the F value made it harder to generate the
.gamma. phase at high temperature and to obtain toughness and
strength of HAZ at sufficient levels. As a result of conducting
closer studies, it was also found that, by setting the F value to
be not larger than 13.50, fine and soft martensite phase was
precipitated in HAZ and sufficient levels of toughness and strength
were ensured in a welding area.
[0047] For those reasons, the F value is limited to be not larger
than 13.50 in the component system of the present invention.
[0048] Thus, by employing the features set forth above, the present
invention has succeeded in developing Cr-containing steel that has
satisfactory levels in all of toughness, strength (hardness) and
corrosion resistance of HAZ, and that is suitably used as, in
particular, parts arranged around the tire attachment area in an
automobile.
[0049] Also, in the present invention, Cu and Mo may be added in
the steel as other suitable components if necessary.
[0050] Cu: 0.10 to 2.00 mass %
[0051] Cu is a component effective in not only improving corrosion
resistance, but also stabilizing the .gamma. phase at high
temperature. To develop those effects, Cu is required to be added
in amount not less than 0.10 mass %. However, if Cu is overly added
in excess of 2.00 mass %, hot workability of the steel would be
deteriorated. Therefore, an upper limit of the Cu content is set to
2.00 mass %. Preferably, the Cu content is set to be not more than
1.00 mass %.
[0052] Mo: 0.40 to 3.00 mass %
[0053] Mo is a component effective in improving corrosion
resistance. To develop that effect, Mo is required to be added in
amount not less than 0.40 mass %. However, if Mo is overly added in
excess of 3.00 mass %, the basic material would be embrittled
because Mo is the ferrite generating element. Therefore, an upper
limit of the Mo content is set to 3.00 mass %.
[0054] In the component system containing Cu and Mo in the steel,
it is an essential feature that, instead of the F value, an F'
value calculated by putting values of contents (mass %) of the
respective components in the following formula (2), in which the
contents of both Cu and Mo components are taken into account, is
not larger than 13.50: 5 F ' value = Cr + 0.6 .times. Mo + 0.4
.times. Si + 0.2 .times. Al + 5 .times. P - 0.4 .times. Mn - 0.7
.times. Ni - 0.6 .times. Cu - 35 .times. C - 10 .times. N + 10
.times. V ( 2 )
[0055] In the Cr-containing steel described above, B may be added
in the steel if necessary.
[0056] B: 0.0003 to 0.0050 mass %
[0057] B is a component effective in improving hardenability,
increasing hardness of HAZ, as well as suppressing cracks due to
embrittlement. Those effects are developed at the B content of not
less than 0.0003 mass %, but if the B content exceeds 0.0050 mass
%, toughness would be deteriorated. Therefore, the B content is set
to the range of 0.0003 to 0.0050 mass %. Preferably, the B content
is set to the range of 0.0005 to 0.0015%.
[0058] A method for manufacturing the Cr-containing steel according
to the present invention is not limited to a particular one. For
example, the method that is generally employed in manufacturing
Cr-containing steel, such as stainless steel, may be applied
substantially as it is. One example of the manufacturing method
will be described below.
[0059] A basic steel material obtained through continuous casting
is first heated up to a predetermined temperature as required. The
basic steel material is then subjected to hot rolling, whereby a
hot-rolled plate having a desired plate thickness is obtained.
Subsequently, the hot-rolled plate is subjected to box annealing at
600 to 900.degree. C. depending on a required strength level, and
it is brought into practical use as it is or after pickling.
Otherwise, the annealed plate is subjected to cold rolling, whereby
a cold-rolled plate having a predetermined thickness is obtained.
Then, the cold-rolled plate is subjected to continuous annealing at
preferably 700 to 900.degree. C. and pickling. As a result,
Cr-containing steel is manufactured in the form of a cold-rolled
and annealed plate.
[0060] Note that the above-described manufacturing process merely
represents one example of embodiments of the present invention,
various processes can be added depending on applications.
EXAMPLES
[0061] The present invention will be described below in more detail
in connection with Examples of the invention and Comparative
Examples.
[0062] A hot-rolled plate having a thickness of 4 mm was produced
by smelting 50 kg of a steel ingot having the chemical composition,
shown in Table 1, in a vacuum smelting furnace, and hot-rolling the
ingot under ordinary hot-rolling conditions. Then, the hot-rolled
plate was annealed at 700.degree. C..times.8 hours and subjected to
MIG welding under conditions given below. Subsequently, the welded
plate was evaluated for not only Vickers hardness as evaluation of
HAZ hardness, but also toughness and corrosion resistance of
HAZ.
Welding Conditions
[0063] Butt Welding
[0064] Welding Wire: wire diameter 1.2 mm.phi., material: SUS309S
(JIS G4309)
[0065] Shield Gas: 95 vol. % Ar-5% vol. % Oxygen
[0066] Welding Current: 170 A, Welding Voltage: 24 V,
[0067] Welding Rate: 400 mm/min
[0068] (1) Method for Measuring HAZ Hardness
[0069] Hardness of HAZ was measured in accordance with the Vickers
hardness testing method stipulated by JIS (Japanese Industrial
Standard) Z 2244-1992. A test load was set to 9.8 N (1 kgf), and
the HAZ hardness was measured at three positions (spaced from each
other at a pitch of 0.8 mm) shown in FIG. 2. The HAZ hardness was
evaluated based on an average of the measured hardness values. The
measured results are listed in Table 1.
[0070] (2) Method for Evaluating HAZ Toughness
[0071] Toughness of HAZ was evaluated as follows. Three No. 4 test
pieces stipulated by JIS Z 2202-1980 were each sampled from a
position shown in FIG. 3 (each of the test pieces being a sub-size
test piece finished to have a thickness of 2 mm by cutting and
grinding the front and rear sides of the test piece, and having a
2-mm V-notch formed in a HAZ position to extend parallel to the
welding direction). Each test piece was set on a Charpy impact
tester and then tested in accordance with the Charpy impact testing
method stipulated by JIS Z 2242-1993. Energy absorbed in the test
for breaking the test piece was calculated, and the HAZ toughness
was evaluated based on an average of absorbed energy values
obtained from three test pieces. Incidentally, the test temperature
was set to 0.degree. C. The absorbed energy value calculated for
each type of test piece was listed in Table 1.
[0072] (3) Method for Evaluating HAZ Corrosion Resistance
[0073] Corrosion resistance of HAZ was evaluated as follows. After
welding, two samples having a size of 60 mm.times.80 mm were each
cut out from a position shown in FIG. 4. After polishing an area of
a 20-mm width on the rear side of each test piece, including a
weld, with a #400 sandpaper, a salt-spray test (SST) was performed
on the test piece for 4 hours in accordance with JIS Z 2371. The
corrosion resistance of HAZ was evaluated by regarding an area of a
10-mm width including a welded bead at the center as HAZ (10
mm.times.80 mm), and then measuring the size of a rusty area in
HAZ. The evaluated results are listed in Table 1. In table 1, a
mark ".largecircle." represents the case in which the rusty area
given as an average obtained from the two samples is 5% (rusty area
of 40 mm.sup.2/HAZ area of 800 mm.sup.2) or less. A mark ".DELTA."
represents the case in which the rusty area given as an average
obtained from the two samples is in the range of 5% to 50% (rusty
area of 40 mm.sup.2 to 400 mm.sup.2). A mark "X" represents the
case in which the rusty area given as an average obtained from the
two samples was over 50% (rusty area of 400 mm.sup.2 or over).
[0074] As seen from the results of Table 1, in inventive steels 1
to 3 and 10 in which a proper amount of V is added, the corrosion
resistance of HAZ is noticeably superior to that of comparative
steels A and B in which the V content in the steel deviates from
the proper range in the present invention. Also, it is seen that,
in inventive steels 4 and 5, since B is further added in the steel
within a preferred range of content, hardenability is improved and
hence the hardness of HAZ is increased correspondingly. In
inventive steels 6 to 9 and 11, since at least one of Mo and Cu is
further added in the steel within a preferred range of content, the
effects of reducing a pit depth and improving the corrosion
resistance in comparison with the case of adding neither Mo nor Cu
are obtained. Hence, satisfactory levels are achieved in all of
toughness, hardness and corrosion resistance of HAZ.
[0075] On the other hand, in a comparative steel C, since V is
added in the steel over the proper range in the present invention,
both the hardness and toughness of HAZ are deteriorated. In a
comparative steel D, since Mn is added in the steel over the proper
range in the present invention, the toughness of HAZ is
deteriorated. In a comparative steel E, since the F value exceeds
the proper range in the present invention, the toughness of HAZ is
deteriorated.
Industrial Applicability
[0076] Since the Cr-containing steel according to the present
invention is superior in all of toughness, strength (hardness) and
corrosion resistance of HAZ, it can be used for a welded structure,
particularly it is suitably used as members arranged around the
tire attachment area in an automobile.
[0077] Note that the Cr-containing steel according to the present
invention can be used in any desired form such as a pipe and plate.
While Examples of the present invention were described in
connection with the case of employing a hot-rolled plate, similar
advantages are also obtained in the case of employing a cold-rolled
plate. Further, the Cr-containing steel according to the present
invention may be used after coating, as required, for the purpose
of further improving the corrosion resistance of HAZ, and such a
case also falls within the scope of the present invention.
1TABLE 1 F OR STEEL CHEMICAL COMPOSITION (mass %) F' No. C Si Mn P
S Cr Ni Al N V B Mo Cu VALUE T U W REMARKS 1 0.008 0.15 1.5 0.012
0.003 12.0 0.54 0.005 0.007 0.08 -- -- -- 11.59 253 295
.smallcircle. INVENTIVE 2 0.011 0.15 1.5 0.020 0.003 11.5 0.64 0.01
0.008 0.12 -- -- -- 11.35 260 280 .smallcircle. STEEL 3 0.008 0.18
1.6 0.023 0.002 11.2 0.26 0.02 0.009 0.30 -- -- -- 13.20 289 265
.smallcircle. 4 0.010 0.16 1.5 0.011 0.003 11.8 0.55 0.02 0.015
0.12 0.0008 -- -- 11.64 250 305 .smallcircle. 5 0.009 0.18 1.5
0.022 0.004 11.9 0.45 0.05 0.008 0.12 0.0015 -- -- 11.98 265 315
.smallcircle. 6 0.009 0.15 2.8 0.019 0.005 14.8 0.81 0.08 0.009
0.08 -- -- 0.45 13.41 200 260 .smallcircle. 7 0.004 0.27 1.5 0.033
0.003 10.8 0.35 0.005 0.009 0.06 0.0015 0.48 0.35 10.68 253 305
.smallcircle. 8 0.015 0.08 2.0 0.011 0.018 12.3 0.95 0.005 0.015
0.12 0.0009 1.25 0.31 12.01 223 325 .smallcircle. 9 0.011 0.08 2.0
0.012 0.005 14.8 0.88 0.02 0.015 0.05 0.0014 0.48 0.56 13.40 170
335 .smallcircle. 10 0.002 0.15 2.5 0.024 0.005 12.3 0.67 0.04
0.002 0.12 -- -- -- 12.13 200 250 .smallcircle. 11 0.008 0.45 1.4
0.012 0.003 9.5 0.54 0.005 0.007 0.13 -- 1.5 0.5 10.35 305 300
.smallcircle. A 0.011 0.18 1.5 0.031 0.006 10.9 0.31 0.02 0.018 0
-- -- -- 9.75 230 320 x COMPARA- B 0.018 0.16 1.4 0.036 0.004 11.0
0.41 0.04 0.018 0.02 -- -- -- 9.80 240 320 .DELTA. TIVE C 0.004
0.15 2.2 0.028 0.003 11.1 0.99 0.03 0.009 0.38 -- -- -- 13.30 58
180 .smallcircle. STEEL D 0.004 0.35 5.6 0.018 0.010 11.5 0.15 0.02
0.008 0.15 -- -- -- 10.67 100 280 .smallcircle. E 0.007 0.16 1.5
0.032 0.008 14.5 0.12 0.03 0.005 0.15 -- -- -- 15.25 68 200
.smallcircle. T: HAZ TOUGHNESS (J/cm.sup.2) (ABSORBED ENERGY AT
0.degree. C.) U: HAZ HARDNESS (Hv) W: DEGREE OF RUSTING (HAZ
CORROSION RESISTANCE)
* * * * *