U.S. patent application number 13/876093 was filed with the patent office on 2013-07-18 for ferritic stainless steel excellent in heat resistance property and formability.
This patent application is currently assigned to JFE STEEL CORPORATION. The applicant listed for this patent is Yasushi Kato, Tetsuyuki Nakamura, Hiroyuki Ogata, Hiroki Ota. Invention is credited to Yasushi Kato, Tetsuyuki Nakamura, Hiroyuki Ogata, Hiroki Ota.
Application Number | 20130183190 13/876093 |
Document ID | / |
Family ID | 45938442 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130183190 |
Kind Code |
A1 |
Nakamura; Tetsuyuki ; et
al. |
July 18, 2013 |
FERRITIC STAINLESS STEEL EXCELLENT IN HEAT RESISTANCE PROPERTY AND
FORMABILITY
Abstract
An object is to provide ferritic stainless steel excellent in
heat resistance (oxidation resistance, a thermal fatigue property
and a high-temperature fatigue property) and formability, while
preventing a decrease in oxidation resistance due to Cu, without
adding expensive chemical elements such as Mo and W. Specifically,
ferritic stainless steel having a chemical composition containing,
by mass %, C: 0.015% or less, Si: 0.4% or more and 1.0% or less,
Mn: 1.0% or less, P: 0.040% or less, S: 0.010% or less, Cr: 12% or
more and less than 16%, N: 0.015% or less, Nb: 0.3% or more and
0.65% or less, Ti: 0.15% or less, Mo: 0.1% or less, W: 0.1% or
less, Cu: 1.0% or more and 2.5% or less and Al: 0.2% or more and
1.0% or less, while the relationship Si.gtoreq.Al is satisfied, and
the balance being Fe and inevitable impurities.
Inventors: |
Nakamura; Tetsuyuki;
(Chiba-shi, JP) ; Ota; Hiroki; (Chiba-shi, JP)
; Kato; Yasushi; (Tokyo, JP) ; Ogata;
Hiroyuki; (Chiba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nakamura; Tetsuyuki
Ota; Hiroki
Kato; Yasushi
Ogata; Hiroyuki |
Chiba-shi
Chiba-shi
Tokyo
Chiba-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
|
Family ID: |
45938442 |
Appl. No.: |
13/876093 |
Filed: |
October 12, 2011 |
PCT Filed: |
October 12, 2011 |
PCT NO: |
PCT/JP2011/073980 |
371 Date: |
March 26, 2013 |
Current U.S.
Class: |
420/39 ;
420/61 |
Current CPC
Class: |
C22C 38/40 20130101;
C22C 38/001 20130101; F01N 13/16 20130101; C22C 38/30 20130101;
C21D 2211/005 20130101; C21D 8/0273 20130101; C22C 38/02 20130101;
C22C 38/26 20130101; C22C 38/06 20130101; C22C 38/004 20130101;
C21D 8/0236 20130101; C22C 38/04 20130101; C21D 9/46 20130101; C21D
6/002 20130101; C22C 38/24 20130101; C21D 8/0226 20130101; C22C
38/20 20130101; C22C 38/22 20130101; C22C 38/28 20130101 |
Class at
Publication: |
420/39 ;
420/61 |
International
Class: |
F01N 13/16 20060101
F01N013/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 14, 2010 |
JP |
2010-231562 |
Oct 6, 2011 |
JP |
2011-221763 |
Claims
1. Ferritic stainless steel having a chemical composition
containing, by mass %, C: 0.015% or less, Si: 0.4% or more and 1.0%
or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.010% or less,
Cr: 12% or more and less than 16%, N: 0.015% or less, Nb: 0.3% or
more and 0.65% or less, Ti: 0.15% or less, Mo: 0.1% or less, W:
0.1% or less, Cu: 1.0% or more and 2.5% or less and Al: 0.2% or
more and 1.0% or less, while the relationship Si.gtoreq.Al is
satisfied, and the balance being Fe and inevitable impurities.
2. Ferritic stainless steel having a chemical composition further
containing one, two or more chemical elements selected from among,
by mass %, B: 0.003% or less, REM: 0.08% or less, Zr: 0.5% or less,
V: 0.5% or less, Co: 0.5% or less and Ni: 0.5% or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to ferritic stainless steel
having high heat resistance (a thermal fatigue property, oxidation
resistance and a high-temperature fatigue property) and formability
which can be ideally used for the parts of an exhaust system which
are used in a high temperature environment such as an exhaust pipe
and a catalyst outer cylinder (also called a converter case) of an
automobile and a motorcycle and an exhaust air duct of a thermal
electric power plant.
BACKGROUND ART
[0002] The parts of an exhaust system such as an exhaust manifold,
an exhaust pipe, a converter case and a muffler which are used in
the environment of the exhaust system of an automobile are required
to be excellent in a thermal fatigue property, a high-temperature
fatigue property and oxidation resistance (hereinafter, these
properties are collectively called heat resistance). Since the
parts such as an exhaust manifold are subjected to heating and
cooling due to the repetition of start and stop of engine operation
in a state in which they are restrained by the surrounding parts,
the thermal expansion and contraction of the material of the parts
are restricted, which results in the occurrence of thermal strain.
The fatigue phenomenon due to this thermal strain is thermal
fatigue. On the other hand, the parts are continuously subjected to
vibration while they are heated in the initiation of engine
operation. The fatigue phenomenon due to the accumulation of strain
caused by this vibration is high-temperature fatigue. The former is
low-cycle fatigue and the latter is high-cycle fatigue and both are
completely different fatigue phenomena.
[0003] For applications in which heat resistance are required as
described above, nowadays, Cr containing steel to which Nb and Si
are added such as Type429 (containing 14Cr-0.9Si-0.4Nb) is often
used. However, since an exhaust gas temperature has become higher
than 900.degree. C. with the improvement of engine performance, the
thermal fatigue property of Type429 has become unsatisfactory.
[0004] In order to solve this problem, Cr containing steel having a
high-temperature yield strength increased by adding Nb and Mo,
SUS444 (containing 19Cr-0.5Nb-2Mo) conforming to JIS G 4305 and
ferritic stainless steel containing less Cr to which Nb, Mo and W
are added and the like have been developed (refer to, for example,
Patent Literature 1). However, since the prices of rare metals such
as Mo and W have been markedly rising recently, the development of
a material having heat resistance equivalent to those of these
kinds of steel by using inexpensive raw materials has become to be
required.
[0005] Examples of materials having excellent heat resistance
without using expensive chemical elements such as Mo and W are
disclosed by Patent Literatures 2 through 4. Patent Literature 2
discloses ferritic stainless steel to be used for the parts of an
exhaust gas flow channel of an automobile. In Patent Literatures 2,
Nb: 0.50 mass % or less, Cu: 0.8 mass % or more and 2.0 mass % or
less and V: 0.03 mass % or more and 0.20 mass % or less are added
to steel having a Cr content of 10 mass % or more and 20 mass % or
less. Patent Literature 3 discloses ferritic stainless steel
excellent in a thermal fatigue property. In Patent Literatures 3,
Ti: 0.05 mass % or more and 0.30 mass % or less, Nb: 0.10 mass % or
more and 0.60 mass % or less, Cu: 0.8 mass % or more and 2.0 mass %
or less and B: 0.0005 mass % or more and 0.02 mass % or less are
added to steel having a Cr content of 10 mass % or more and 20 mass
% or less. Patent Literature 4 discloses ferritic stainless steel
to be used for the parts of an exhaust gas flow channel of an
automobile. In Patent Literatures 4, Cu: 1 mass % or more and 3
mass % or less is added to steel having a Cr content of 15 mass %
or more and 25 mass % or less. These kinds of disclosed steel are
all characterized by having a thermal fatigue property improved by
adding Cu.
CITATION LIST
Patent Literature
[0006] [PTL 1] Japanese Unexamined Patent Application Publication
No. 2004-018921 [0007] [PTL 2] International Publication No.
WO2003/004714 [0008] [PTL 3] Japanese Unexamined Patent Application
Publication No. 2006-117985 [0009] [PTL 4] Japanese Unexamined
Patent Application Publication No. 2000-297355
SUMMARY OF INVENTION
Technical Problem
[0010] However, according to investigations carried out by the
present inventors, in the case where Cu is added as in the methods
disclosed by Patent Literatures 2 through 4, it has been found
that, while a thermal fatigue property is improved, contrarily
oxidation resistance is decreased, which results in the
deterioration of the overall heat resistance.
[0011] In addition, since a space which an exhaust manifold can
occupy in an engine space has become smaller with the weight
reduction of an automobile, it has come to be required that an
exhaust manifold can be formed into a complex shape.
[0012] The present invention has been completed in view of the
situation described above, and an object of the present invention
is to provide ferritic stainless steel excellent in heat resistance
(oxidation resistance, a thermal fatigue property and a
high-temperature fatigue property) and formability, while
preventing a decrease in oxidation resistance due to Cu, without
adding expensive chemical elements such as Mo and W.
[0013] Incidentally, the meaning of "excellent in heat resistance"
according to the present invention is that oxidation resistance, a
thermal fatigue property and a high-temperature fatigue property
are equivalent to or better than those of SUS444. Specifically, it
means that oxidation resistance at a temperature of 950.degree. C.
is equivalent to or better than that of SUS444, that a thermal
fatigue property when temperature fluctuations repeatedly occur
between the temperatures of 100.degree. C. and 850.degree. C. is
equivalent to or better than that of SUS444 and that a
high-temperature fatigue property at a temperature of 850.degree.
C. is equivalent to or better than that of SUS444. In addition, the
meaning of "excellent in formability" according to the present
invention is that a mean elongation in the three directions at room
temperature is 36% or more.
Solution to Problem
[0014] The present inventors diligently conducted investigations in
order to develop ferritic stainless steel excellent in oxidation
resistance and a thermal fatigue property by preventing a decrease
in oxidation resistance due to Cu which occurs in the conventional
methods without adding expensive chemical elements such as Mo or W.
As a result, the present inventors found that a high strength in
high-temperature can be achieved by adding the combination of Nb:
0.3 mass % or more and 0.65 mass % or less and Cu: 1.0 mass % or
more and 2.5 mass % or less. By getting the high strength, a
thermal fatigue property can be improved in a wide temperature
range. The present inventors found that a decrease in oxidation
resistance due to the addition of Cu can be prevented by adding an
appropriate amount of Al (0.2 mass % or more and 1.0 mass % or
less). The present inventors found that, therefore, heat resistance
(a thermal fatigue property and oxidation resistance) equivalent to
or better than that of SUS444 can be achieved only by controlling
the contents of Nb, Cu and Al to the appropriate range as described
above without adding Mo or W. In addition, the present inventors
diligently conducted investigations regarding a method for
improving oxidation resistance in an environment containing water
vapor which is assumed in the case where the ferritic stainless
steel is practically used for an exhaust manifold and the like, and
found that oxidation resistance in an atmosphere containing water
vapor (hereinafter, called water vapor oxidation resistance) also
becomes equivalent to or better than that of SUS444 by adjusting a
Si content (0.4 mass % or more and 1.0 mass % or less).
[0015] In addition, a fatigue resistance property against vibration
in practical service conditions of the parts of the exhaust system
of an automobile such as an exhaust manifold is also important.
Therefore, the present inventors diligently conducted
investigations regarding a method for improving a high-temperature
fatigue property, and found that a high-temperature fatigue
property also becomes equivalent to or better than that of SUS444
by adjusting the balance of a Si content and an Al content
(Si.gtoreq.Al).
[0016] Moreover, the present inventors diligently conducted
investigations regarding the influence of Cr on formability and
oxidation resistance, and found that formability can be improved by
reducing a Cr content without there being a significant influence
on oxidation resistance.
[0017] Although it has been well known in the past that formability
can be improved by reducing a Cr content. But there is a decrease
in oxidation resistance by reducing a Cr content. The decrease in
oxidation resistance has been compensated for by adding Mo and W,
instead of Cr, in the past as disclosed by Patent Literature 1. In
contrast to this, according to the present invention, it has been
found that both excellent oxidation resistance and formability can
be achieved by adding an appropriate amount of Al without adding
expensive chemical elements such as Mo and W, even if a Cr content
is reduced.
[0018] The present invention has been completed on the basis of the
knowledge of the present inventors described above.
[0019] That is to say, the present invention provides ferritic
stainless steel excellent in heat resistance and formability having
a chemical composition containing, by mass %, C, 0.015% or less,
Si: 0.4% or more and 1.0% or less, Mn: 1.0% or less, P: 0.040% or
less, S: 0.010% or less, Cr: 12% or more and less than 16%, N:
0.015% or less, Nb: 0.3% or more and 0.65% or less, Ti: 0.15% or
less, Mo: 0.1% or less, W: 0.1% or less, Cu: 1.0% or more and 2.5%
or less and Al: 0.2% or more and 1.0% or less, while the
relationship Si.gtoreq.Al is satisfied, and the balance being Fe
and inevitable impurities.
[0020] In addition, the present invention provides ferritic
stainless steel excellent in heat resistance and formability having
a chemical composition further containing one, two or more chemical
elements selected from among, by mass %, B: 0.003% or less, REM:
0.08% or less, Zr: 0.5% or less, V: 0.5% or less, Co: 0.5% or less
and Ni: 0.5% or less.
Advantageous Effects of Invention
[0021] According to the present invention, ferritic stainless steel
having heat resistance (a thermal fatigue property, oxidation
resistance and a high-temperature fatigue property) equivalent to
or better than that of SUS444 (JIS G 4305) and excellent
formability can be obtained without adding expensive Mo or W.
Therefore, the steel according to the present invention can be
ideally used for the parts of the exhaust system of an
automobile.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a diagram illustrating a thermal fatigue test
specimen.
[0023] FIG. 2 is a diagram illustrating conditions of temperature
and constraint in a thermal fatigue test.
[0024] FIG. 3 is a diagram illustrating a high-temperature fatigue
test specimen.
[0025] FIG. 4 is a graph illustrating the influence of a Cu content
on a thermal fatigue property.
[0026] FIG. 5 is a graph illustrating the influence of an Al
content on oxidation resistance (an increase in weight due to
oxidation).
[0027] FIG. 6 is a graph illustrating the influence of a Si content
on water vapor oxidation resistance (an increase in weight due to
oxidation).
[0028] FIG. 7 is a graph illustrating the influence of a Si
content--an Al content (Si--Al) on a high-temperature fatigue
property.
[0029] FIG. 8 is a graph illustrating the influence of a Cr content
on water vapor oxidation resistance (an increase in weight due to
oxidation).
[0030] FIG. 9 is a graph illustrating the influence of a Cr content
on a mean elongation in the three directions at room
temperature.
DESCRIPTION OF EMBODIMENTS
[0031] Firstly, the fundamental experiments which led to the
completion of the present invention will be described. Hereinafter,
% used when describing chemical composition always denotes mass
%.
[0032] Steel having a basic chemical composition containing C,
0.005% or more and 0.007% or less, N: 0.004% or more and 0.006% or
less, P: 0.02% or more and 0.03% or less, S: 0.002% or more and
0.004% or less, Si: 0.85%, Mn: 0.4%, Cr: 14%, Nb: 0.45%, Al: 0.35%,
Ti: 0.007%, Mo: 0.01% or more and 0.03% or less and W: 0.01% or
more and 0.03% or less and a Cu content which was adjusted
variously in the range of 0% or more and 3% or less was smelted by
using an experimental method and made into a steel ingot of 50 kg,
then the steel ingot was subjected to forging and a heat treatment
into a steel material having a cross section of 35 mm.times.35 mm,
then a thermal fatigue test specimen having the dimensions
illustrated in FIG. 1 was made of the steel material. Then, the
thermal fatigue life of the specimen was observed by performing a
thermal cycle heat treatment in which a restraint ratio was 0.30
and in which heating and cooling were repeated so that temperature
fluctuations repeatedly occurred between 100.degree. C. and
850.degree. C. as illustrated in FIG. 2. The thermal fatigue life
represents as the number of cycles at which the stress first
started to continuously decrease from that in the previous cycle.
The stress was derived by calculated as the quotient of the load
detected at 100.degree. C. divided by the cross section area of the
soaked parallel portion of a test specimen indicated in FIG. 1.
This number of cycles corresponded to that at which a crack
occurred in the test specimen. Incidentally, a similar test was
performed with SUS444 (19% Cr-2% Mo-0.5% Nb steel) for
comparison.
[0033] FIG. 4 illustrates the influence of Cu content on thermal
fatigue life in the thermal fatigue test described above. This
figure indicates that thermal fatigue life equivalent to or longer
than that of SUS444 (about 1350 cycles) can be achieved by setting
the Cu content to be 1.0% or more. Therefore, it is necessary that
the Cu content be 1.0% or more in order to improve a thermal
fatigue property.
[0034] Steel having a basic chemical composition containing C,
0.006%, N: 0.007%, P: 0.02% or more and 0.03% or less, S: 0.002% or
more and 0.004% or less, Mn: 0.2%, Si: 0.85%, Cr: 14%, Nb: 0.49%,
Cu: 1.5%, Ti: 0.007%, Mo: 0.01% or more and 0.03% or less and W:
0.01% or more and 0.03% or less and an Al content which was
adjusted variously in the range of 0% or more and 2% or less was
smelted by using an experimental method and made into a steel ingot
of 50 kg, then the steel ingot was subjected to hot rolling, hot
rolled annealing, cold rolling and finishing annealing and made
into a cold rolled and annealed steel sheet having a thickness of 2
mm. A test specimen of 30 mm.times.20 mm was cut out of the cold
rolled steel sheet obtained as described above, then a hole of 4
mm.phi. was punched in the upper part of the test specimen, then
the surface and the edge face of the specimen was polished with a
#320 emery paper, then degreased and then used in a continuous
oxidation test in air described below.
[0035] <Continuous Oxidation Test in Air>
[0036] The test specimen described above was held in a furnace in
air at a temperature of 950.degree. C. for a duration of 200 hours,
and then an increase in weight per unit area due to oxidation
(g/m.sup.2) was derived from the observed difference in the mass of
the test specimen before and after the heating test.
[0037] FIG. 5 illustrates the influence of Al content on the
increase in weight due to oxidation in the continuous oxidation
test in air described above. This figure indicates that an
oxidation resistance equivalent to or better than that of SUS444
(increase in weight due to oxidation: 19 g/m.sup.2 or less) can be
achieved by setting the Al content to be 0.2% or more.
[0038] Steel having a basic chemical composition containing C,
0.006%, N: 0.007%, P: 0.02% or more and 0.03% or less, S: 0.002% or
more and 0.004% or less, Mn: 0.2%, Al: 0.45%, Cr: 14%, Nb: 0.49%,
Cu: 1.5%, Ti: 0.007%, Mo: 0.01% or more and 0.03% or less and W:
0.01% or more and 0.03% or less and a Si content which was adjusted
variously was smelted by using an experimental method and made into
a steel ingot of 50 kg. Then the steel ingot was subjected to hot
rolling, hot rolled annealing, cold rolling and finishing annealing
and made into a cold rolled and annealed steel sheet having a
thickness of 2 mm. A test specimen of 30 mm.times.20 mm was cut out
of the cold rolled steel sheet obtained as described above. Then a
hole of 4 mm.phi. was punched in the upper part of the test
specimen, then the surface and the edge face of the specimen was
polished with a #320 emery paper. Then degreased and then used in a
continuous oxidation test in water vapor atmosphere described
below.
[0039] <Continuous Oxidation Test in Water Vapor
Atmosphere>
[0040] The test specimen described above was held in a furnace in a
water vapor atmosphere in which a gas of 10 vol % CO.sub.2-20 vol %
H.sub.2O-5 vol % O.sub.2-bal. N.sub.2 was blown at a rate of 0.5
L/min, and then an increase in weight per unit area due to
oxidation (g/m.sup.2) was derived from the observed difference in
the mass of the specimen before and after the heating test.
[0041] FIG. 6 illustrates the influence of the Si content on the
increase in weight due to oxidation in the oxidation test in water
vapor atmosphere described above. This figure indicates that water
vapor oxidation resistance equivalent to that of SUS444 (increase
in weight due to oxidation: 37 g/m.sup.2 or less) cannot be
achieved, unless the Si content is set to be 0.4% or more.
[0042] Steel having a basic chemical composition containing C,
0.006%, N: 0.007%, P: 0.02% or more and 0.03% or less, S: 0.002% or
more and 0.004% or less, Mn: 0.2%, Cr: 14%, Nb: 0.49%, Cu: 1.5%,
Ti: 0.007%, Mo: 0.01% or more and 0.03% or less and W: 0.01% or
more and 0.03% or less and the contents of Si and Al which were
adjusted variously was smelted by using an experimental method and
made into a steel ingot of 50 kg. Then the steel ingot was
subjected to hot rolling, hot rolled annealing, cold rolling and
finishing annealing and made into a cold rolled and annealed steel
sheet having a thickness of 2 mm. A high-temperature fatigue test
specimen having a shape illustrated in FIG. 3 was made of the cold
rolled steel sheet obtained as described above and then used in a
high-temperature fatigue test described below.
[0043] <High-Temperature Fatigue Test>
[0044] The high-temperature fatigue property of the test specimen
described above was evaluated by using a Schenck type fatigue
testing machine and by performing reversed vibration of 22 Hz (1300
rpm) at a temperature of 850.degree. C. Here, a bending stress of
70 MPa was exerted on the surface of the steel sheet during the
test, and the fatigue property was evaluated in terms of a number
of cycles until fracture occurred.
[0045] FIG. 7 illustrates the influence of Si--Al on the number of
cycles in the high-temperature fatigue test described above. This
figure indicates that it is necessary to satisfy the relationship
Si.gtoreq.Al in order to achieve a high-temperature fatigue
property equivalent to that of SUS444 (24.times.10.sup.5
cycles).
[0046] Steel having a basic chemical composition containing C,
0.006%, N: 0.007%, P: 0.02% or more and 0.03% or less, S: 0.002% or
more and 0.004% or less, Mn: 0.2% Si: 0.85%, Al: 0.45%, Nb: 0.49%,
Cu: 1.5%, Ti: 0.007%, Mo: 0.01% or more and 0.03% or less and W:
0.01% or more and 0.03% or less and a Cr content which was adjusted
variously was smelted by using an experimental method and made into
a steel ingot of 50 kg. Then the steel ingot was subjected to hot
rolling, hot rolled annealing, cold rolling and finishing annealing
and made into a cold rolled and annealed steel sheet having a
thickness of 2 mm. A test specimen of 30 mm.times.20 mm was cut out
from the cold rolled steel sheet obtained as described above, then
a hole of 4 mm.phi. was punched in the upper part of the test
specimen. Then the surface and the edge face of the specimen was
polished with a #320 emery paper, then degreased and then used in
the oxidation test in water vapor atmosphere described above.
[0047] FIG. 8 illustrates the influence of the Cr content on the
increase in weight due to oxidation in the oxidation test in water
vapor atmosphere described above. This figure indicates that water
vapor oxidation resistance equivalent to that of SUS444 (increase
in weight due to oxidation: 37 g/m.sup.2 or less) can be achieved
in the case where the Cr content is 12% or more.
[0048] In addition, tensile tests were conducted at room
temperature with tensile test pieces conforming to JIS NO. 13B
which were made of these cold rolled and annealed steel sheets.
Tensile test pieces had the directions of tension respectively in
the rolling direction (L direction), in the direction at right
angles to the rolling direction (C direction) and in the direction
at a 45.degree. angles to the rolling direction (D direction). A
mean elongation was derived from the breaking elongations which
were obtained by performing tensile tests in the three directions
at room temperature and calculated by the equation below.
Mean elongation El(%)=(E.sub.L+2E.sub.D+E.sub.C)/4,
[0049] where E.sub.L: El (%) in L direction, E.sub.D: El (%) in D
direction and E.sub.C: El (%) in C direction.
[0050] FIG. 9 illustrates the influence of the Cr content on the
mean value of elongations in the three directions (L, C and D
directions) in the tensile test. This figure indicates that
excellent formability in terms of the mean elongation in the three
directions (L, C and D directions) of 36% or more can be achieved
in the case where the Cr content is less than 16%.
[0051] The present invention has been completed by conducting
further investigations on the basis of the results of the
fundamental experiments described above.
[0052] The ferritic stainless steel according to the present
invention will be described in detail hereafter.
[0053] Firstly, the chemical composition according to the present
invention will be described.
[0054] C: 0.015% or Less
[0055] Although C is a chemical element which is effective for
increasing the strength of steel, there is a significant decrease
in toughness and formability in the case where C content is more
than 0.015%. Therefore, according to the present invention, the C
content is set to be 0.015% or less. Incidentally, it is preferable
that the C content be as small as possible from the viewpoint of
achieving formability and that the carbon content be 0.008% or
less. On the other hand, it is preferable that the C content be
0.001% or more in order to achieve strength which is required of
the parts of an exhaust system, more preferably 0.002% or more and
0.008% or less.
[0056] Si: 0.4% or More and 1.0% or Less
[0057] Si is a chemical element which is important for improving
oxidation resistance in a water vapor atmosphere. As FIG. 6
indicates, it is necessary to set Si content to be 0.4% or more in
order to achieve water vapor oxidation resistance equivalent to
that of SUS444. On the other hand, there is a significant decrease
in formability in the case where the Si content is more than 1.0%.
Therefore, the Si content is set to be 0.4% or more and 1.0% or
less, preferably 0.5% or more and 0.9% or less. Although the
mechanism through which water vapor oxidation resistance is
increased in the case where the Si content is 0.4% or more is not
clear, it is considered that a dense continuous oxide layer is
formed on the surface of a steel sheet in the case where the Si
content is 0.4% or more and the penetration of gas elements from
outside is prevented, which results in an increase in water vapor
oxidation resistance. It is preferable that the Si content be 0.5%
or more in the case where there is a necessity of oxidation
resistance in a severer environment.
[0058] Mn: 1.0% or Less
[0059] Although Mn is a chemical element which causes an increase
in the strength of steel and which is effective as a deoxidation
agent, a .gamma. phase tends to be formed at a high temperature in
the case where Mn content is excessively large, the excessive Mn
content results in a decrease in heat resistance. Therefore, the Mn
content is set to be 1.0% or less, preferably 0.7% or less. It is
preferable that the Mn content be 0.05% or more in order to realize
the effect of increasing strength and deoxidation.
[0060] P: 0.040% or Less
[0061] Since P is a harmful chemical element which causes a
decrease in ductility, it is preferable that P content be as small
as possible. Therefore, the P content is set to be 0.040% or less,
preferably 0.030% or less.
[0062] S: 0.010% or Less
[0063] Since S is a harmful chemical element which causes a
decrease in elongation and an r value. S has a negative influence
on formability and S causes a decrease in corrosion resistance
which is the basic property of stainless steel. It is preferable
that S content be as small as possible. Therefore, the S content is
set to be 0.010% or less, preferably 0.005% or less.
[0064] Cr: 12% or More and Less than 16%
[0065] Cr is a chemical element which is effective for increasing
corrosion resistance and oxidation resistance, which are the
characteristics of stainless steel. Sufficient oxidation resistance
cannot be achieved in the case where Cr content is less than 12%.
On the other hand, Cr is a chemical element which causes an
increase in hardness and a decrease in ductility of steel at room
temperature by solid solution strengthening, in particular, these
negative influences become significant in the case where the Cr
content is 16% or more. Therefore, the Cr content is set to be 12%
or more and less than 16%, preferably 12% or more and 15% or
less.
[0066] N: 0.015% or Less
[0067] N is a chemical element which causes a decrease in the
ductility and the formability of steel, and these negative
influences are significant in the case where N content is more than
0.015%. Therefore, the N content is set to be 0.015% or less.
Incidentally, it is preferable that the N content be as small as
possible from the viewpoint of achieving ductility and formability
and that the N content be less than 0.010%.
[0068] Nb: 0.3% or More and 0.65% or Less
[0069] Nb is a chemical element which is effective for increasing
corrosion resistance, formability and intergranular corrosion
resistance at welds by forming carbide, nitride and carbonitride in
combination with C and N. Nb is effective for increasing a thermal
fatigue property by increasing high-temperature strength. These
effects can be realized by setting Nb content to be 0.3% or more.
On the other hand, a Laves phase (Fe.sub.2Nb) tends to be
precipitated in the case where the Nb content is more than 0.65%,
which results in the acceleration of embrittlement. Therefore, the
Nb content is set to be 0.3% or more and 0.65% or less, preferably
0.4% or more and 0.55% or less.
[0070] Mo: 0.1% or Less
[0071] Since Mo is an expensive chemical element, additionally in
view of the purpose of the present invention, Mo is not added
positively. However, Mo may be mixed in from the material of steel
such as scrap in the range of 0.1% or less. Therefore, Mo content
is set to be 0.1% or less.
[0072] W: 0.1% or Less
[0073] Since W is an expensive chemical element like Mo,
additionally in view of the purpose of the present invention, W is
not added positively. However, W may be mixed in from the material
of steel such as scrap in the range of 0.1% or less. Therefore, W
content is set to be 0.1% or less.
[0074] Cu: 1.0% or More and 2.5% or Less
[0075] Cu is a chemical element which is very effective for
improving a thermal fatigue property. As FIG. 3 indicates, it is
necessary that Cu content be 1.0% or more in order to achieve a
thermal fatigue property equivalent to or better than that of
SUS444. However, in the case where the Cu content is more than
2.5%, .epsilon.-Cu is precipitated when cooling is performed after
a heat treatment, which results in an increase in the hardness of
steel and results in embrittlement tending to occur when hot work
is performed. More importantly, while a thermal fatigue property is
improved by adding Cu, contrarily the oxidation resistance of steel
is decreased, which results in the deterioration of the overall
heat resistance. The reason for this has not been fully identified.
However, Cu seems to concentrate in a Cr depletion layer where
scale has formed thereon and prevent Cr, an element that should
improve intrinsic oxidation resistance of stainless steel, from
diffusing again. Therefore, the Cu content is set to be 1.0% or
more and 2.5% or less, preferably 1.1% or more and 1.8% or
less.
[0076] Ti: 0.15% or Less
[0077] Ti is effective for improving corrosion resistance,
formability and intergranular corrosion resistance of a welded part
by fixing C and N like Nb does. However, this effect saturates and
there is an increase in the hardness of steel in the case where Ti
content is more than 0.15% in the present invention in which Nb is
contained. Therefore, the Ti content is set to be 0.15% or less.
Since Ti has higher affinity for N than Nb does, Ti tends to form
TiN of a large size. Since TIN of a large size tends to become the
origin of a crack and causes a decrease in toughness, it is
preferable that the Ti content be 0.01% or less in the case where
the toughness of a hot rolled steel sheet is necessary.
Incidentally, since it is not necessary to positively add Ti in the
present invention, the lower limit of the Ti content includes
0%.
[0078] Al: 0.2% or More and 1.0% or Less
[0079] Al is a chemical element which is essential for increasing
the oxidation resistance of Cu containing steel as FIG. 5
indicates. In addition, since Al is effective as a solid solution
strengthening element and, in particular, is effective for
increasing high-temperature strength at a temperature of higher
than 800.degree. C., Al is a chemical element which is important
for improving a high-temperature fatigue property in the present
invention. It is necessary that Al content be 0.2% or more in order
to achieve oxidation resistance equivalent to or better than that
of SUS444. On the other hand, there is a decrease in formability
due to an increase in the hardness of steel in the case where the
Al content is more than 1.0%. Therefore, the Al content is set to
be 0.2% or more and 1.0% or less, preferably 0.3% or more and 1.0%
or less, more preferably 0.3% or more and 0.5% or less.
[0080] Si.gtoreq.Al
[0081] Since Al is effective as a solid solution strengthening
element and, in particular, effective for increasing
high-temperature strength at a high temperature of higher than
800.degree. C., Al is a chemical element which is important for
improving a high-temperature fatigue property in the present
invention as described above, and Si is a chemical element which is
important for effectively utilizing this effect of solid solution
strengthening of Al. In the case where the amount of Si is less
than that of Al, there is a decrease in the amounts of solid
solution Al, because Al preferentially forms oxides and nitrides at
high temperature, which decreases the contribution of Al to
strengthening. On the other hand, in the case where the amount of
Si is larger than that of Al, Si is preferentially oxidized and
forms a dense continuous oxide layer on the surface of a steel
sheet. Since this oxide becomes a barrier to the diffusion of
oxygen and nitrogen, Al is kept in the state of a solid solution
without being oxidized or nitrided, which makes it possible to
improve a high-temperature fatigue property by strengthening steel
through solid solution strengthening. Therefore, it is necessary
that the relationship Si.gtoreq.Al be satisfied in order to achieve
a high-temperature fatigue property equivalent to or better than
that of SUS444.
[0082] One, two or more chemical elements selected from among B,
REM, Zr, V, Co and Ni may be further contained in the ferritic
stainless steel according to the present invention in addition to
the chemical composition described above.
[0083] B: 0.003% or Less
[0084] B is a chemical element which is effective for improving
formability, in particular, secondary formability. However, in the
case where B content is more than 0.003%, B causes a decrease in
formability by forming BN. Therefore, in the case where B is
contained, the B content is set to be 0.003% or less. Since the
effect described above is realized in the case where the B content
is 0.0004% or more, it is more preferable that the B content be
0.0004% or more and 0.003% or less.
[0085] REM: 0.08% or Less and Zr: 0.5% or Less
[0086] REM (rare earth elements) and Zr are chemical elements which
are effective for improving oxidation resistance and may be added
as needed in the present invention. However, in the case where the
content of REM is more than 0.080%, the steel become easier to
occur the embrittle crack and, in the case where Zr content is more
than 0.50%, the steel also become easier to occur the embrittle
crack due to the precipitation of a Zr intermetallic compound.
Therefore, in the case where REM is contained, the content of REM
is set to be 0.080% or less, and, in the case where Zr in
contained, the Zr content is set to be 0.50% or less. Since the
effect described above is realized in the case where the content of
REM is 0.01% or more and in the case where the Zr content is
0.0050% or more, it is preferable that the content of REM be 0.001%
or more and 0.080% or less and that the Zr content be 0.0050% or
more and 0.50% or less.
[0087] V: 0.5% or Less
[0088] V is a chemical element which is effective for improving
formability and oxidation resistance. However, in the case where V
content is more than 0.50%, V(C,N) of a large size is precipitated,
which results in the deterioration of surface quality. Therefore,
in the case where V is contained, the V content is set to be 0.50%
or less. It is preferable that the V content be 0.15% or more and
0.50% or less in order to realize the effect of improving
formability and oxidation resistance, more preferably 0.15% or more
and 0.4% or less.
[0089] Co: 0.5% or Less
[0090] Co is a chemical element which is effective for improving
toughness. However, Co is an expensive chemical element and the
effect of Co saturates in the case where Co content is more than
0.5%. Therefore, in the case where Co is contained, the Co content
is set to be 0.5% or less. Since the effect described above is
effectively realized in the case where the Co content is 0.02% or
more, it is preferable that the Co content be 0.02% or more and
0.5% or less, more preferably 0.02% or more and 0.2% or less.
[0091] Ni: 0.5% or Less
[0092] Ni is a chemical element which improves toughness. However,
since Ni is expensive and a chemical element which strongly forms a
.gamma. phase, Ni causes a decrease in oxidation resistance by
forming a .gamma. phase at a high temperature in the case where Ni
content is more than 0.5%. Therefore, in the case where Ni is
contained, the Ni content is set to be 0.5% or less. Since the
effect described above is effectively realized in the case where
the Ni content is 0.05% or more, it is preferable that the Ni
content be 0.05% or more and 0.5% or less, more preferably 0.05% or
more and 0.4% or less.
[0093] The remainder of the chemical composition consists of Fe and
inevitable impurities. Among the inevitable impurities, it is
preferable that an O content be 0.010% or less, a Sn content be
0.005% or less, a Mg content be 0.005% or less and a Ca content be
0.005% or less, more preferably the 0 content be 0.005 or less, the
Sn content be 0.003% or less, the Mg content be 0.003% or less and
the Ca content be 0.003% or less.
[0094] The method for manufacturing the ferritic stainless steel
will be described hereafter.
[0095] The stainless steel according to the present invention may
be manufactured in a common method for manufacturing ferritic
stainless steel and there is no particular limitation on
manufacturing conditions. Examples of ideal manufacturing methods
include smelting steel by using a well-known, melting furnace such
as a steel converter or an electric furnace, further, optionally,
making the steel have the chemical composition according to the
present invention described above by performing secondary refining
such as ladle refining or vacuum refining, then making a slab of
the steel by using a continuous casting method or an ingot
casting-blooming rolling method, and then making the slab a cold
rolled and annealed steel sheet through the processes such as hot
rolling, hot rolled annealing, pickling, cold rolling, finishing
annealing, pickling and so forth. Incidentally, the cold rolling
described above may be performed one time or repeated two times or
more with process annealing in between, and the processes of cold
rolling, finishing annealing and pickling may be performed
repeatedly. Moreover, optionally, hot rolled annealing may be
omitted, and skin pass rolling may be performed after cold rolling
or finishing annealing in the case where brightness of a steel
sheet is required.
[0096] Examples of more preferable manufacturing conditions are as
follows.
[0097] It is preferable that some of the conditions of a hot
rolling process and a cold rolling process be specified. In
addition, in a steel making process, it is preferable to smelt
molten steel having the essential chemical composition described
above and the optional chemical elements to be added as needed and
to perform secondary refining by using a VOD method (Vacuum Oxygen
Decurbarization method). Although the smelted molten steel may be
made into a steel material by using a well-known method, it is
preferable to use a continuous casting method from the viewpoint of
productivity and material quality. The steel material obtained
through a continuous casting process is heated up to a temperature
of, for example, from 1000.degree. C. or higher and 1250.degree. C.
or lower, and then made into a hot rolled steel sheet having a
specified thickness. It is needless to say that the steel material
may be made into a material of a shape other than a sheet. This hot
rolled steel sheet is subjected to, as needed, batch annealing at a
temperature of 600.degree. C. or higher and 800.degree. C. or lower
or continuous annealing at a temperature of 900.degree. C. or
higher and 1100.degree. C. or lower, and then made into a hot
rolled sheet product after being descaled by performing pickling or
the like. In addition, as needed, descaling may be performed by
using a shot blasting method before pickling being performed.
[0098] Moreover, in order to obtain a cold rolled steel sheet, the
hot rolled and annealed steel sheet obtained as described above is
made into a cold rolled steel sheet through a cold rolling process.
In this cold rolling process, in accordance with manufacturing
circumstances, cold rolling may be performed two times or more with
process annealing in between as needed. The total rolling ratio of
the cold rolling process, in which cold rolling is performed for
one, two or more times, is set to be 60% or more, preferably 70% or
more. The cold rolled steel sheet is subjected to continuous
annealing (finishing annealing) at a temperature of 900.degree. C.
or higher and 1150.degree. C. or lower, preferably 950.degree. C.
or higher and 1120.degree. C. or lower, and pickling, and then made
into a cold rolled and annealed steel sheet. In addition, in
accordance with use application, the shape of and the material
quality of the steel sheet may be adjusted by performing rolling
with a light reduction ratio such as skin pass rolling after cold
rolled annealing being performed.
[0099] The hot rolled sheet product or cold rolled and annealed
sheet product obtained as described above are formed into the
exhaust pipe of an automobile or a motor bicycle, a material to be
used for a catalyst outer cylinder, the exhaust air duct of a
thermal electric power plant, or a part related to a fuel cell
(such as a separator, an inter connector or a reformer) by
performing bending work or other kinds of work in accordance with
use application. There is no limitation on welding methods for
assembling these parts, and common arc welding methods such as MIG
(Metal Inert Gas), MAG (Metal Active Gas) and TIG (Tungsten Inert
Gas), resistance welding methods such as spot welding and seam
welding, high-frequency resistance welding methods such as electric
resistance welding and high-frequency induction welding methods may
be applied.
EXAMPLES
Example 1
[0100] Each of the steel No. 1 through 23 having chemical
compositions given in Table 1 was smelted by using a vacuum melting
furnace and made into steel ingot of 50 kg, then the steel ingot
was subjected to forging, and then the forged ingot was divided
into two pieces. Thereafter, one of the divided ingots was heated
up to a temperature of 1170.degree. C., then subjected to hot
rolling and made into a hot rolled steel sheet having a thickness 5
mm, then subjected to hot rolled annealing, pickling, cold rolling
with a rolling ratio of 60%, finishing annealing at a temperature
of 1040.degree. C., cooling at a cooling rate of 5.degree. C./sec,
pickling and then made into a cold rolled and annealed steel sheet
having a thickness of 2 mm. Each of the steel No. 1 through 11 is
an example in the range according to the present invention, and
each of the steel No. 12 through 23 is a comparative example out of
the range according to the present invention. Incidentally, among
the comparative examples, steel No. 19 has a chemical composition
corresponding to Type429, No. 20 has a chemical composition
corresponding to SUS444, and No. 21, No. 22 and No. 23 respectively
have chemical compositions corresponding to example 3 of Patent
Literature 2, example 3 of Patent Literature 3 and example 5 of
Patent Literature 4.
[0101] The cold rolled steel sheets No. 1 through 23 were used in
the two kinds of continuous oxidation tests, a high-temperature
fatigue test and a tensile test at room temperature as described
below.
[0102] <Continuous Oxidation Test in Air>
[0103] A sample of 30 mm.times.20 mm was cut out of each of the
cold rolled and annealed steel sheet obtained as described above,
then a hole of 4 mm.phi. was punched in the upper part of the
sample, then the surface and the edge face of the sample was
polished with a #320 emery paper, then degreased and then the
sample was suspended in a furnace heated up to a temperature of
950.degree. C. in air for a holding time of 200 hours. After the
test, the mass of the sample was observed, and then an increase in
weight due to oxidation (g/m.sup.2) was calculated by deriving the
difference between the mass observed before and after the test.
Incidentally, the test was repeated two times, and oxidation
resistance in air was evaluated by using the mean value of the
difference in mass.
[0104] <Continuous Oxidation Test in Water Vapor
Atmosphere>
[0105] A sample of 30 mm.times.20 mm was cut out from each of the
cold rolled and annealed steel sheet obtained as described above.
Then a hole of 4 mm.phi. was punched in the upper part of the
sample, then the surface and the edge face of the sample was
polished with a #320 emery paper and then degreased. Thereafter,
the sample was held in a furnace heated up to a temperature of
950.degree. C. in a water vapor atmosphere in which a gas of 10 vol
% CO.sub.2-20 vol % H.sub.2O-5 vol % O.sub.2-bal. N.sub.2 was blown
at a rate of 0.5 L/min for a holding time of 200 hours, then, after
the test, the mass of the sample was observed, and then an increase
in weight due to oxidation (g/m.sup.2) was calculated by deriving
the difference between the mass observed before and after the
test.
[0106] <High-Temperature Fatigue Test>
[0107] A test specimen illustrated in FIG. 3 was cut out from the
cold rolled and annealed steel sheet obtained as described above
was subjected to reversed vibration of 1300 rpm (22 Hz) at a
temperature of 850.degree. C. by using a Schenck type fatigue
testing machine. Incidentally, a bending stress of 70 MPa was
exerted on the surface of the steel sheet during the test, and
evaluation was done in terms of a number of cycles (cycle) until
fracture occurred.
[0108] <Tensile Test at Room Temperature>
[0109] A tensile test piece conforming to JIS No. 13B which had the
directions of tension respectively in the rolling direction (L
direction), in the direction at right angle to the rolling
direction (C direction) and in the direction at 45.degree. angles
to the rolling direction (D direction) was cut out from the cold
rolled and annealed steel sheet described above. Then tensile tests
in these directions were conducted at room temperature, then
breaking elongations were observed and then a mean elongation was
derived by using the equation below.
Mean elongation El(%)=(E.sub.L+2E.sub.D+E.sub.C)/4,
[0110] where E.sub.L: El (%) in L direction, E.sub.D: El (%) in D
direction and E.sub.C: El (%) in C direction.
Example 2
[0111] The rest of the pieces which were obtained by dividing the
ingot of 50 kg into two pieces in Example 1 was heated up to a
temperature of 1170.degree. C., and then hot rolled into a sheet
bar having a thickness of 30 mm and a width of 150 mm. Thereafter,
this sheet bar was subjected to forging and made into a bar of 35
mm.times.35 mm, annealing at a temperature of 1040.degree. C., then
machined into a thermal fatigue test specimen having the dimensions
illustrated in FIG. 1, and then used in a thermal fatigue test as
described below.
[0112] <Thermal Fatigue Test>
[0113] In a thermal fatigue test, a thermal fatigue life was
observed by repeatedly heating and cooling the test specimen
between the temperatures of 100.degree. C. and 850.degree. C. at a
restraint ratio of 0.30. Here, a heating rate and a cooling rate
were both 10.degree. C./sec, a holding time at a temperature of
100.degree. C. was 2 minutes and a holding time at a temperature of
850.degree. C. was 5 minutes. The thermal fatigue life represents
as the number of cycles at which the stress first started to
continuously decrease from that in the previous cycle. The stress
was derived by calculated as the quotient of the load detected at
100.degree. C. divided by the cross section area of the soaked
parallel portion of a test specimen indicated in FIG. 1.
[0114] The results of the continuous oxidation test in air, the
continuous oxidation test in water vapor atmosphere, the
high-temperature fatigue test and the tensile test at room
temperature in Example 1 and those of the thermal fatigue test in
Example 2 are summarized in Table 2. As Table 2 indicates, it is
clear that any of the steel of the example of the present invention
which is within the range of the present invention has heat
resistance (oxidation resistance, a thermal fatigue property and a
high-temperature fatigue property) equivalent to or better than
that of SUS444 and excellent formability in terms of a mean
elongation in the three directions (L, C and D direction) at room
temperature of 36% or more, which means it has been confirmed that
the steel satisfies the object of the present invention. In
contrast, the steel of the comparative example which is out of the
range according to the present invention is poor in either of
oxidation resistance, thermal fatigue resistance, a
high-temperature fatigue property or formability, which means it
has been confirmed that the steel does not satisfy the object of
the present invention.
INDUSTRIAL APPLICABILITY
[0115] The steel according to the present invention can be ideally
used not only for the parts of an exhaust system of an automobile
but also the parts of an exhaust system of a thermal electric power
system and the parts of a solid-oxide fuel cell for which similar
properties as that of the parts of an exhaust system of an
automobile are required.
TABLE-US-00001 TABLE 1 Sample No. C Si Mn Al P S Cr Cu Nb 1 0.008
0.84 0.25 0.51 0.031 0.002 12.8 1.32 0.48 2 0.007 0.76 0.28 0.40
0.029 0.003 14.5 1.45 0.46 3 0.008 0.91 0.31 0.67 0.030 0.003 15.1
1.48 0.49 4 0.009 0.69 0.29 0.38 0.028 0.003 13.4 1.23 0.47 5 0.006
0.54 0.54 0.31 0.027 0.004 15.2 1.37 0.44 6 0.007 0.89 0.48 0.43
0.028 0.003 14.3 1.54 0.49 7 0.009 0.76 0.24 0.37 0.029 0.003 14.9
1.19 0.46 8 0.007 0.80 0.73 0.45 0.025 0.003 13.7 1.67 0.45 9 0.007
0.73 0.81 0.4 0.026 0.004 15.5 1.59 0.45 10 0.008 0.68 0.89 0.32
0.026 0.002 12.9 1.24 0.43 11 0.007 0.94 0.39 0.52 0.028 0.002 13.5
1.55 0.45 12 0.006 1.34 0.5 0.37 0.024 0.003 14.0 1.15 0.48 13
0.007 0.69 0.44 1.49 0.025 0.002 12.7 1.46 0.47 14 0.008 0.92 0.78
0.13 0.027 0.003 15.6 1.29 0.48 15 0.009 0.47 0.63 0.68 0.029 0.002
14.4 1.51 0.46 16 0.008 0.81 0.35 0.54 0.026 0.003 13.9 0.53 0.44
17 0.008 0.52 0.21 0.39 0.030 0.004 17.1 1.46 0.48 18 0.007 0.76
0.84 0.43 0.027 0.003 9.7 1.64 0.43 19 0.007 0.87 0.33 0.03 0.029
0.002 14.8 0.02 0.44 20 0.008 0.31 0.42 0.02 0.031 0.003 18.7 0.02
0.52 21 0.008 0.32 0.05 0.01 0.028 0.002 17.0 1.93 0.33 22 0.009
0.46 0.54 0.00 0.029 0.003 18.9 1.36 0.35 23 0.006 0.22 0.05 0.05
0.005 0.005 18.8 1.65 0.42 Sample mass % No. Ti Mo W N Others Si-Al
Note 1 0.008 0.02 0.02 0.008 0.33 Example 2 0.007 0.03 0.01 0.009
0.36 Example 3 0.009 0.02 0.02 0.007 0.24 Example 4 0.007 0.02 0.03
0.008 0.31 Example 5 0.006 0.01 0.02 0.008 0.23 Example 6 0.008
0.01 0.03 0.007 0.46 Example 7 0.009 0.03 0.02 0.006 0.39 Example 8
0.007 0.02 0.01 0.007 V: 0.21 0.35 Example 9 0.008 0.02 0.01 0.007
B: 0.0015 0.33 Example 10 0.008 0.01 0.02 0.008 Co: 0.09 0.36
Example 11 0.007 0.01 0.02 0.007 Ni: 0.34 0.42 Example 12 0.006
0.01 0.03 0.006 0.97 Comparative Example 13 0.009 0.02 0.02 0.007
-0.8 Comparative Example 14 0.007 0.02 0.02 0.008 0.79 Comparative
Example 15 0.008 0.03 0.02 0.006 -0.21 Comparative Example 16 0.007
0.02 0.01 0.008 0.27 Comparative Example 17 0.003 0.02 0.02 0.008
V: 0.06 0.13 Comparative Example 18 0.008 0.01 0.03 0.007 0.33
Comparative Example 19 0.030 0.01 0.01 0.008 0.84 Comparative
Example*1 20 0.003 1.87 0.02 0.008 0.291 Comparative Example*2 21
0.002 0.01 0.02 0.01 Ni: 0.10, 0.31 Comparative V: 0.10 Example*3
22 0.080 0.01 0.02 0.007 Ni: 0.10, 0.458 Comparative V: 0.03,
Example*4 B: 0.0030 23 0.090 0.02 0.02 0.006 Ni: 0.15 0.168
Comparative Example*5 Underline indicates the value out of the
range according to the present invention. *1: Type429 *2: SUS444
*3: Example 3 of Patent literature 2 *4: Example 3 of Patent
literature 3 *5: Example 5 of Patent literature 4
TABLE-US-00002 TABLE 2 High- Temper- Weight ature gain by Mean
Fatigue Weight Thermal water Elongation Life at gain by Fatigue
vapor in Three 850.degree. C. Sample oxidation Life oxidation
Directions (.times.l 0.sup.-5 No. (g/m.sup.2) (cycle) (g/m.sup.2)
(%) cycles) Note 1 18 1330 34 36 30 Example 2 17 1340 34 36 33
Example 3 16 1350 33 36 26 Example 4 17 1370 34 37 29 Example 5 16
1340 35 37 27 Example 6 16 1310 33 36 32 Example 7 16 1370 34 37 31
Example 8 17 1360 34 36 36 Example 9 16 1340 34 36 27 Example 10 18
1300 34 37 29 Example 11 17 1410 33 36 33 Example 12 17 1280 39 32
30 Comparative Example 13 18 1380 71 31 9 Comparative Example 14 55
1400 40 37 15 Comparative Example 15 17 1290 77 36 11 Comparative
Example 16 15 910 32 38 26 Comparative Example 17 13 1440 29 34 31
Comparative Example 18 52 1300 >100 38 14 Comparative Example 19
45 630 >100 34 8 Comparative Example*1 20 19 1250 37 31 24
Comparative Example*2 21 >100 1650 >100 31 15 Comparative
Example*3 22 >100 1380 >100 35 10 Comparative Example*4 23
>100 1540 >100 34 12 Comparative Example*5 Underline
indicates the value out of the range according to the present
invention. *1: Type429 *2: SUS444 *3: Example 3 of Patent
literature 2 *4: Example 3 of Patent literature 3 *5: Example 5 of
Patent literature 4
* * * * *