U.S. patent application number 12/735156 was filed with the patent office on 2010-10-28 for ferritic stainless steel with excellent brazeability.
Invention is credited to Nobuhiko Hiraide.
Application Number | 20100272594 12/735156 |
Document ID | / |
Family ID | 40824240 |
Filed Date | 2010-10-28 |
United States Patent
Application |
20100272594 |
Kind Code |
A1 |
Hiraide; Nobuhiko |
October 28, 2010 |
FERRITIC STAINLESS STEEL WITH EXCELLENT BRAZEABILITY
Abstract
This ferritic stainless steel with excellent brazeability
includes, in terms of mass percent, 0.03% or less of C, 0.05% or
less of N, 0.015% or more of C+N, 0.02 to 1.5% of Si, 0.02 to 2% of
Mn, 10 to 22% of Cr, 0.03 to 1% of Nb, and 0.5% or less of Al, and
further includes Ti in a content that satisfies the following
formulae (1) and (2), with the remainder composed of Fe and
unavoidable impurities. Ti--3N.ltoreq.0.03 (1)
10(Ti--3N)+Al.ltoreq.0.5 (2) (Here, the atomic symbols in formulae
(1) and (2) indicate the content (mass %) of the respective
element, and the numerical values that precede the atomic symbols
are constants.)
Inventors: |
Hiraide; Nobuhiko;
(Hiraki-shi, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
40824240 |
Appl. No.: |
12/735156 |
Filed: |
December 24, 2008 |
PCT Filed: |
December 24, 2008 |
PCT NO: |
PCT/JP2008/073394 |
371 Date: |
June 18, 2010 |
Current U.S.
Class: |
420/41 ; 420/60;
420/61; 420/64; 420/70 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/26 20130101; C22C 38/04 20130101 |
Class at
Publication: |
420/41 ; 420/60;
420/61; 420/64; 420/70 |
International
Class: |
C22C 38/32 20060101
C22C038/32; C22C 38/18 20060101 C22C038/18; C22C 38/20 20060101
C22C038/20; C22C 38/22 20060101 C22C038/22; C22C 38/00 20060101
C22C038/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2007 |
JP |
2007 339732 |
Dec 2, 2008 |
JP |
2008 307534 |
Claims
1. A ferritic stainless steel with excellent brazeability
comprising, in terms of mass percent, 0.03% or less of C, 0.05% or
less of N, 0.015% or more of C+N, 0.1 to 1.5% of Si, 0.02 to 2% of
Mn, 13.15 to 22% of Cr, 0.03 to 1% of Nb, and 0.5% or less of Al,
and further comprising Ti in a content that satisfies the following
formulae (1) and (2), with the remainder composed of Fe and
unavoidable impurities. Ti--3N.ltoreq.0.03 (1)
10(Ti--3N)+Al.ltoreq.0.5 (2) (Here, the atomic symbols in formulae
(1) and (2) indicate the content (mass %) of the respective
element, and the numerical values that precede the atomic symbols
are constants.)
2. The ferritic stainless steel with excellent brazeability
according to claim 1, which further comprises one or more selected
from the group consisting of, in terms of mass %, 3% or less of Mo;
3% or less of Ni; 3% or less of Cu; 3% or less of V; and 5% or less
of W.
3. The ferritic stainless steel with excellent brazeability
according to claim 1 or 2, which further comprises one or more
selected from the group consisting of, in terms of mass %, 0.002%
or less of Ca; 0.002% or less of Mg; and 0.005% or less of B.
Description
TECHNICAL FIELD
[0001] The present invention relates to ferritic stainless steel
which is used as members that are assembled by braze joining.
Examples of such members include EGR (Exhaust Gas Recirculation)
coolers, oil coolers, heat exchange equipments used in automobiles
and various types of plants, aqueous urea solution tanks used in
automotive urea SCR (Selective Catalytic Reduction) systems,
automotive fuel delivery system components, and the like. These
members are generally complex in shape, and many of them are
precision parts. As the brazing method, the case of interest is
where braze joining is conducted at high temperatures under low
oxygen partial pressures, such as Ni braze and Cu braze.
[0002] The present application claims priority on Japanese Patent
Application No. 2007-339732, filed on Dec. 28, 2007, and Japanese
Patent Application No. 2008-307534, filed on Dec. 2, 2008, the
contents of which are incorporated herein by reference.
BACKGROUND ART
[0003] In recent years, due to growing awareness of environmental
issues, exhaust gas regulations have been further tightened, and
initiatives with a view to suppressing carbon dioxide emissions
have advanced. In the automotive field, in addition to initiatives
from the fuel standpoint such as bioethanol and biodiesel fuels,
initiatives have been taken which seek improvements in fuel
efficiency by weight-saving measures and by attachment of heat
exchangers that conduct heat recovery of exhaust heat, and which
install exhaust gas treatment devices such as EGR coolers, DPFs
(Diesel Particulate Filters), and urea SCR systems.
[0004] Among these, the objective of EGR coolers is to lower
combustion temperature and reduce NO.sub.x which is a harmful gas
by cooling engine exhaust gas and subsequently returning it to the
intake side for recombustion. For this purpose, thermal efficiency
is required in the heat exchanger portion of the EGR cooler, and
satisfactory thermal conductivity is desirable. Conventionally, in
these members, austenitic stainless steel such as SUS 304 and SUS
316 is used, and assembly is generally conducted by braze
joining.
[0005] Recently, in order to further lower combustion temperature,
there has been a need to seek lower temperatures on the outlet side
of the EGR cooler, and circumstances have arisen that also require
thermal fatigue properties to be taken into account. In this
regard, attention has come to be focused on ferritic stainless
steel which has better thermal conductivity, which has a lower
thermal expansion coefficient, and which is less expensive, rather
than austenitic stainless steel.
[0006] Conventionally, as stainless steel for brazing, there are,
for example, the following types of steel sheet.
[0007] Patent Document 1 discloses a precoated braze-covered metal
sheet fabricated by conducting suspension of Ni brazing material
with organic binders, and conducting spray application onto the
surface of a stainless steel sheet, after which heating is
conducted. In addition, Patent Document 2 discloses a method for
manufacturing a nickel braze-covered stainless steel sheet with
excellent self-brazing properties, wherein a stainless steel sheet
having regulated surface roughness is coated with Ni brazing
material by plasma spraying. In both Patent Documents, stainless
steel which is covered in Examples is austenitic stainless steel,
and ferritic stainless steel is not particularly disclosed.
[0008] Patent Document 3 discloses a ferritic stainless steel for
an ammonia-water absorption cycle heat exchanger which has
excellent brazeability and which includes 0.08% or less of C, 0.01
to 2.0% of Si, 0.05 to 1.5% of Mn, 0.05% or less of P, 0.01% or
less of S, 13 to 32% of Cr, 3.0% or less of Mo, 0.005 to 0.1% of
Al, 1.0% or less of Ni, 1.0% or less of Cu, and 0.05% or less of
Ti. Here, Ti is limited to 0.05% or less, because carbides or
nitrides of Ti form a film that inhibits brazing. Furthermore,
Table 1 records 18 types of ferritic stainless steel, and the C
contents are in a range of 0.031 to 0.032% which are higher values
than the C content range of the high-purity ferritic stainless
steel that is now generally manufactured.
[0009] Patent Document 1: Japanese Unexamined Patent Application,
First Publication No. H1-249294
[0010] Patent Document 2: Japanese Unexamined Patent Application,
First Publication No. 2001-26855
[0011] Patent Document 3: Japanese Unexamined Patent Application,
First Publication No. H11-236654
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0012] The present invention aims to provide a ferritic stainless
steel having excellent brazeability in the case where brazing is
conducted at high temperatures under low oxygen partial pressures,
as with Ni braze and Cu braze.
Means to Solve the Problems
[0013] As a result of diligent study of the effects of alloy
elements on brazeability in the case where brazing is conducted at
high temperatures under low oxygen partial pressures as with Ni
braze and Cu braze in order to resolve the aforementioned problems,
the present inventors found that in a ferritic stainless steel,
there are upper limits enabling assurance of satisfactory
brazeability with respect to the content of Ti which is often added
for the purpose of enhancing workability and intergranular
corrosion properties, and the content of Al which is added for the
purpose of deoxidation.
[0014] Ni brazing and Cu brazing are usually conducted at 1000 to
1100.degree. C. in a hydrogen atmosphere or a vacuum on the order
of 10.sup.-3 to 10.sup.-4 torr. Moreover, in the case of Ag
brazing, although conditions depend on the type of braze, there are
cases where brazing is conducted at 800 to 900.degree. C. in a
vacuum atmosphere on the order of 10.sup.-4 to 10-5 torr. However,
these conditions are often for cases of ideal conditions such as
small-scale experiments, while in the case of using large-scale,
mass-production facilities, it is thought that the atmosphere would
be inferior in a degree of vacuum or that the atmosphere would have
a high dew point due to limitations imposed by the structure of the
facilities and requirements of the manufacturing process.
[0015] In order to obtain satisfactory brazeability, it is
necessary for the molten braze to broadly wet the surface of the
stainless steel, and wettability is affected by the surface film
that is formed on the stainless steel. In the aforementioned types
of atmosphere, even if it is possible to maintain conditions in
which oxides of Fe and Cr are reduced, Ti and Al which tend to
oxidize more easily than Fe and Cr form oxides. These oxides
inhibit the wetting of the braze, and degrades brazeability. What
contributes to this type of film formation that inhibits
brazeability is solid-soluble Ti and Al, but in the case where they
exist as relatively stable nitrides even at brazing temperature,
they do not contribute to film formation, and do not inhibit the
wetting of braze.
[0016] From this standpoint, a study was made of the relation of
the Ti content and the Al content to the wettability of braze.
[0017] FIG. 1 shows the results of evaluation of the wettability of
braze under the same test steels and test conditions as the
below-mentioned examples. As shown in FIG. 1, it was found that the
wettability of braze is satisfactory within a region where, in
terms of the mass % of elements, Ti--3N.ltoreq.0.03 and
Al.ltoreq.0.5 are satisfied, and 10(Ti--3N)+Al.ltoreq.0.5 is
further satisfied (here, the atomic symbols in the above formulae
indicate the content (mass %) of the respective element, and the
numerical values that precede the atomic symbols are
constants).
[0018] With respect to materials wherein the Ti content and the Al
content do not satisfy the aforementioned conditions, analysis of
the surface film was conducted after brazing heat treatment. As a
result, it was found that an oxide film in which Ti and Al were
concentrated was uniformly formed at a thickness of several tens of
nm to several hundreds of nm, and it would seem that such film
formation inhibits the wetting of braze.
[0019] As elements that are similar to Ti and Al in their tendency
to oxidize, there are the elements Si, Nb, Ca, and Mg. With respect
to these elements, although the phenomenon of concentration in
oxide film is observable, they do not achieve a thick and uniform
oxide film formation, and do not inhibit the wettability of
braze.
[0020] Moreover, austenitic stainless steels such as SUS 304 and
SUS 316 are used in EGR coolers, but diffusion of elements is
quicker in ferrite than in austenite, and oxide film formation is
also concomitantly quicker. Therefore, a satisfactory compositional
range is limited to a narrower range in ferritic stainless
steel.
[0021] Among the members for which the stainless steel of the
present invention is intended, many members require strength, and
it is necessary to inhibit strength reduction after brazing. In
particular, in the case where brazing is conducted at high
temperatures of 1000 to 1100.degree. C. as with Ni brazing and Cu
brazing, it is considered important to inhibit the strength
reduction associated with crystal grain coarsening. Pinning by
precipitates is useful in inhibiting crystal grain coarsening, and
it has been found that by fully utilizing carbonitrides of Nb as
the precipitate, and by setting the Nb content within a range of
0.03% or more and C+N within a range of 0.015% or more, the
precipitation amount and stability of Nb carbonitrides useful in
inhibiting crystal grain coarsening are assured.
[0022] The present invention is a ferritic stainless steel with
excellent brazeability that was made based on the aforementioned
findings, and a summary thereof is as follows.
[0023] The ferritic stainless steel with excellent brazeability of
the present invention contains, in terms of mass percent, 0.03% or
less of C, 0.05% or less of N, 0.015% or more of C+N, 0.02 to 1.5%
of Si, 0.02 to 2% of Mn, 10 to 22% of Cr, 0.03 to 1% of Nb, and
0.5% or less of Al, and further contains Ti in a content that
satisfies the following formulae (1) and (2), with the remainder
composed of Fe and unavoidable impurities.
Ti--3N.ltoreq.0.03 (1)
10(Ti--3N)+Al.ltoreq.0.5 (2)
[0024] Here, Ti, N, and Al indicate the contents of the respective
elements expressed in mass %.
[0025] With respect to the ferritic stainless steel with excellent
brazeability of the present invention, one or more selected from
the group consisting of, in terms of mass %, 3% or less of Mo; 3%
or less of Ni; 3% or less of Cu; 3% or less of V; and 5% or less of
W may further be included.
[0026] One or more selected from the group consisting of, in terms
of mass %, 0.002% or less of Ca; 0.002% or less of Mg; and 0.005%
or less of B may further be included.
EFFECT OF THE INVENTION
[0027] According to the present invention, it is possible to
provide a ferritic stainless steel with excellent brazeability,
which is suitable for members that are fabricated by braze joining
such as parts of complex shape and precision parts of small size in
EGR coolers, oil coolers, heat exchange equipment used in
automobiles and various types of plants, aqueous urea tanks used in
automotive urea SCR systems, automotive fuel delivery system
components, and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a drawing which shows the relation of the
wettability of braze to the Ti content and the Al content.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] The present invention was made based on the aforementioned
findings concerning Ti and Al, in particular, as well as Nb and
C+N. The chemical composition of steel prescribed by the present
invention is explained below in further detail. It should be noted
that % signifies mass %.
[0030] C: As it lowers intergranular corrosion resistance and
workability, it is necessary to suppress its content to a low
level. Consequently, it is set to be within a range of 0.03% or
less. However, in the case where the C content is excessively
lowered, crystal grain coarsening is promoted during brazing, and
the cost of refinement is increased. Therefore, it is preferable to
set the C content to be within a range of 0.002% or higher, and the
C content is more preferably within a range of 0.005 to 0.02%.
[0031] N: This is a useful element for pitting corrosion
resistance, but it is necessary to lower its content to a low
level, because it degrades intergranular corrosion resistance and
workability. Consequently, it is set to be within a range of 0.05%
or less. However, in the case where the N content is excessively
lowered, crystal grain coarsening is promoted during brazing, and
the cost of refinement is increased. Therefore, it is preferable to
set the N content to be within a range of 0.002% or higher, and the
N content is more preferably within a range of 0.005 to 0.03%.
[0032] C+N: Given that carbonitrides of Nb inhibits crystal grain
coarsening during heating in brazing and strength reduction of the
member is inhibited, 0.015% or higher of C+N is required, and 0.02%
or higher is preferable. In the case where C and N are excessively
added, intergranular corrosion resistance and workability are
degraded. Therefore, it is preferable to set the upper limit to be
within a range of 0.04% or less.
[0033] Si: This is useful as a deoxidizing element, and is also an
element that is effective in corrosion resistance, but as it lowers
workability, its content is set to be within a range of 0.02 to
1.5%, and the Si content is more preferably within a range of 0.1
to 1%.
[0034] Mn: This is useful as a deoxidizing element, but in the case
where Mn is excessively included, corrosion resistance is degraded,
it is set to be within a range of 0.02 to 2%, and the Mn content is
preferably within a range of 0.1 to 1%.
[0035] Cr: Examples of assumed corrosive environments include open
air environments, cooling water environments, exhaust
gas-condensate environments, and the like, and from the standpoint
of ensuring corrosion resistance in such environments, at least 10%
or more of Cr is required. Corrosion resistance improves as its
content increases, but workability and manufacturability decline.
Therefore, the upper limit is set to be within a range of 22% or
less, and the Cr content is preferably within a range of 15 to
21%.
[0036] Ti: Ti is often added with the objective of fixing C and N,
and enhancing intergranular corrosion resistance of welded parts,
workability, and the like. However, as mentioned above, Ti is an
element which inhibits brazeability, and it is necessary to
strictly limit its content including its content as an impurity.
Consequently, the Ti content is set to be within a range where the
value of Ti--3N satisfies 0.03% or less, and it is preferable that
the value of Ti--3N be within a range of 0.02% or less. Conversely,
as workability is degraded when the Ti content is too low, it is
preferable to set the Ti content to be within a range where the
value of Ti--3N satisifies -0.08% or more. In cases where there are
no particular requirements for workability and the like, it is also
acceptable to omit Ti.
[0037] Nb: It is an important element from the standpoint that
carbonitrides of Nb inhibits crystal grain coarsening during
heating in brazing, and strength reduction of the member is
inhibited. Moreover, it is useful in enhancing high-temperature
strength and enhancing intergranular corrosion properties of welded
parts, and it is necessary to include Nb at a content of 0.03% or
more. However, in the case where Nb is excessively added,
workability and manufacturability are degraded. Therefore, its
upper limit is set to be within a range of 1% or less. The Nb
content is preferably within a range of 0.2 to 0.8%, and more
preferably within a range of 0.3 to 0.6%. Here, from the standpoint
of assuring intergranular corrosion properties, it is preferable
that the value of Nb/(C+N) be set to be within a range of 8 or more
(the atomic symbols in the aforementioned formula indicate the
content (mass %) of the respective element).
[0038] Al: This is a useful element in terms of refinement for its
deoxidizing effects and the like, and it is also effective in
enhancing formability. No particular lower limit is set, but in
order to stably obtain these effects, the Al content is preferably
within a range of 0.002% or more. However, in the case where the Al
content is more than 0.5%, it inhibits brazeability which is the
most important property of the present invention. Therefore, the Al
content is set to be within a range of 0.5% or less. The Al content
is preferably within a range of 0.003 to 0.1%. In the case where
deoxidation is accomplished by an element other than Al such as Si,
it is acceptable to omit Al.
[0039] 10(Ti--3N)+Al.ltoreq.0.5: In terms of brazeability which is
the most important property of the present invention, in order to
obtain satisfactory wettability of the braze, as described using
FIG. 1, it is necessary to simultaneously satisfy the formula
10(Ti--3N)+Al.ltoreq.0.5 and the formula Ti--3N.ltoreq.0.03.
[0040] The foregoing is the chemical composition that is the basis
of the ferritic stainless steel of the present invention. In
addition, the following elements may be included as necessary.
[0041] Mo: For purposes of enhancing corrosion resistance, it may
be included at a content within a range of 3% or less. Stable
effects are obtainable when the content is within a range of 0.3%
or higher. In the case where Mo is excessively added, workability
is degraded, and cost is increased due to its expensiveness.
Accordingly, it is preferable that its content be within a range of
0.3 to 3%.
[0042] Ni: For purposes of enhancing corrosion resistance, it may
be included at a content within a range of 3% or less. Stable
effects are obtainable when the content is within a range of 0.2%
or higher. In the case where Ni is excessively added, workability
is degraded, and cost is increased due to its expensiveness.
Accordingly, it is preferable that its content be within a range of
0.2 to 3%.
[0043] Cu: For purposes of enhancing corrosion resistance, it may
be included at a content within a range of 3% or less. Stable
effects are obtainable when the content is within a range of 0.2%
or higher. In the case where Cu is excessively added, workability
is degraded, and cost is increased due to its expensiveness.
Accordingly, it is preferable that its content be within a range of
0.2 to 3%.
[0044] V: For purposes of enhancing corrosion resistance, it may be
included at a content within a range of 3% or less. Stable effects
are obtainable when the content is within a range of 0.2% or
higher. In the case where V is excessively added, workability is
degraded, and cost is increased due to its expensiveness.
Accordingly, it is preferable that its content be within a range of
0.2 to 3%.
[0045] W: For purposes of enhancing corrosion resistance, it may be
included at a content within a range of 5% or less. Stable effects
are obtainable when the content is within a range of 0.5% or
higher. In the case where W is excessively added, workability is
degraded, and cost is increased due to its expensiveness.
Accordingly, it is preferable that its content be within a range of
0.5 to 5%.
[0046] From the standpoint of cost and the like, it is preferable
that the total content of two or more selected from the group
consisting of Mo, Ni, Cu, V, and W be within a range of 6% or
less.
[0047] Ca: This is a useful element in terms of refinement for its
deoxidation effects and the like, and Ca may be included at a
content within a range of 0.002% or less. In the case where it is
included, it is preferable that the content be within a range of
0.0002% or higher because stable effects are obtainable.
[0048] Mg: This is a useful element in terms of refinement for its
deoxidation effects and the like, and is also useful in structural
refinement, and enhancing workability and toughness. Mg may be
included at a content within a range of 0.002% or less. In the case
where it is included, it is preferable that the content be within a
range of 0.0002% or higher because stable effects are
obtainable.
[0049] B: This is a useful element in enhancing secondary
workability, and B may be included at a content within a range of
0.005% or less. In the case where it is included, it is preferable
that the content be within a range of 0.0002% or higher because
stable effects are obtainable.
[0050] From the standpoint of weldability, it is preferable to set
the content of P which is an unavoidable impurity to be within a
range of 0.04% or less. From the standpoint of corrosion
resistance, it is preferable to set the S content to be within a
range of 0.01% or less.
[0051] With respect to the manufacturing method of the stainless
steel of the present invention, the general process for
manufacturing ferritic stainless steel is acceptable. In general, a
molten steel is produced in a converter furnace or electric
furnace, the molten steel is refined in an AOD furnace or VOD
furnace or the like, and the refined molten steel is made into a
slab by the continuous casting method or the ingot-making method.
Thereafter, stainless steel is manufactured via the processes of
hot rolling, annealing of hot-rolled steel sheet, acid pickling,
cold rolling, finish annealing, and acid pickling. As necessary, it
is also acceptable to omit annealing of hot-rolled steel sheet, and
it is also acceptable to repeatedly conduct cold rolling, finish
annealing, and acid pickling.
Examples
[0052] The implementation possibilities and effects of the present
invention are described below in further detail using examples.
[0053] Steels with the chemical compositions shown in Table 1 were
subjected to casting, and then the steels were subjected to
processes of hot rolling, cold rolling, and annealing so as to
manufacture cold-rolled steel sheets having a thickness of 0.4
mm.
[0054] After cutting out test specimens having a width of 50 mm and
a length of 70 mm from these cold-rolled steel sheets, the surfaces
of the specimen were subjected to wet polishing using emery paper
until #400. Subsequently, Ni braze of 0.1 g was placed on top of
the polished surface, and then heating was conducted for 10 minutes
at 1100.degree. C. under a vacuum atmosphere of 5.times.10.sup.-3
torr. Then cooling to room temperature was conducted, and the
brazing area on the test specimens after heating was measured.
[0055] With respect to brazeability, an evaluation of "good" was
given when the brazing area after heating was double or more the
brazing area before heating, and an evaluation of "bad" was given
when it was less than double.
[0056] Subsequently, the sectional microstructure of the test
specimens after heating was observed. The number of crystal grains
existing in the thickness direction was measured across a range of
20 mm length in parallel with the rolling direction. An evaluation
of "good" was given when there existed two or more crystal grains
in the thickness direction, and an evaluation of "bad" was given
when there existed only one.
[0057] The test results are shown in Table 2.
[0058] In Table 2, Formula (1) is Ti--3N, and Formula (2) is
10(Ti--3N)+Al. Moreover, the underlined parts in Table 1 and Table
2 indicate values outside the range of the present invention.
TABLE-US-00001 TABLE 1 Chemical Composition (mass %) No. C Si Mn P
S Cr Ti Nb Al N Other Inventive example 1 0.012 0.42 0.15 0.028
0.0015 19.42 0.004 0.39 0.025 0.018 0.42Cu, 0.32Ni, 0.0010Ca
Inventive example 2 0.013 0.55 0.45 0.029 0.0008 16.58 0.002 0.55
0.004 0.015 0.32Ni, 0.35Cu Inventive example 3 0.006 0.12 0.19
0.022 0.0010 18.84 0.004 0.42 0.036 0.010 1.86Mo, 0.0003B Inventive
example 4 0.007 0.95 0.35 0.020 0.0005 13.15 0.003 0.45 0.042 0.009
Inventive example 5 0.016 0.25 0.18 0.029 0.0011 18.23 0.021 0.36
0.036 0.014 0.52Cu, 1.02Mo Inventive example 6 0.007 0.16 0.15
0.022 0.0008 20.25 0.012 0.22 0.015 0.009 1.03Ni, 1.08Mo Inventive
example 7 0.014 0.33 0.45 0.030 0.0014 18.15 0.015 0.36 0.055 0.015
2.15W, 0.35V Inventive example 8 0.015 0.40 0.32 0.025 0.0019 20.88
0.042 0.40 0.046 0.010 0.34Ni Inventive example 9 0.016 0.41 0.29
0.024 0.0016 19.19 0.066 0.42 0.086 0.015 1.88W, 0.0005Mg Inventive
example 10 0.018 0.39 0.33 0.023 0.0015 19.34 0.032 0.39 0.35 0.009
0.56Ni, 0.38V, 0.0004Ca Comparative example 11 0.008 0.18 0.15
0.026 0.0011 17.25 0.25 0.002 0.042 0.010 1.12Mo, 0.0005B
Comparative example 12 0.007 0.11 0.12 0.025 0.0012 18.85 0.12 0.22
0.056 0.012 1.80Mo, 0.0004B Comparative example 13 0.012 0.33 0.25
0.025 0.0012 18.22 0.004 0.35 0.58 0.014 0.29Ni Comparative Example
14 0.010 0.42 0.36 0.026 0.0007 16.89 0.062 0.003 0.36 0.012
Comparative example 15 0.011 0.15 0.22 0.028 0.0009 19.12 0.073
0.25 0.041 0.008 1.90Mo
TABLE-US-00002 TABLE 2 Value of Value of Wettability No. formula
(1) formula (2) of braze Microstructure Inventive example 1 -0.050
-0.48 good Good Inventive example 2 -0.043 -0.43 good Good
Inventive example 3 -0.026 -0.22 good Good Inventive example 4
-0.024 -0.20 good Good Inventive example 5 -0.021 -0.17 good good
Inventive example 6 -0.015 -0.14 good good Inventive example 7
-0.030 -0.25 good good Inventive example 8 0.012 0.17 good good
Inventive example 9 0.021 0.30 good good Inventive example 10 0.005
0.40 good good Comparative example 11 0.220 2.24 bad bad
Comparative example 12 0.084 0.90 bad good Comparative example 13
-0.038 0.20 bad good Comparative example 14 0.026 0.62 bad bad
Comparative example 15 0.049 0.53 bad good
[0059] With respect to the steels of No. 1 to 10 which were within
the ranges of the present invention, the wettability of the braze
was satisfactory, and coarsening of crystal grains was inhibited.
With respect to the steels of No. 11, No. 12, and No. 15 which
satisfied neither Formula (1) nor Formula (2), the steel of No. 13
of which the Al content was outside the range of the present
invention, and the steel of No. 14 which did not satisfy Formula
(2), the wettability of the braze was in all cases inferior. With
respect to the steels of No. 11 and No. 14 of which the Nb content
was outside the range of the present invention, conspicuous
coarsening of crystal grains was observed.
INDUSTRIAL APPLICABILITY
[0060] The ferritic stainless steel with excellent brazing of the
present invention is suitable for members that are fabricated by
braze joining as with parts of complex shape and precision parts of
compact size such as EGR coolers, oil coolers, heat exchange
equipment used in automobiles and various types of plants, aqueous
urea tanks in automotive urea SCR systems, automotive fuel delivery
system components, and the like.
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