U.S. patent application number 12/539065 was filed with the patent office on 2010-02-11 for carburization resistant metal material.
Invention is credited to Satoshi Matsumoto, Yoshitaka Nishiyama, Takahiro Osuki.
Application Number | 20100034690 12/539065 |
Document ID | / |
Family ID | 41015979 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100034690 |
Kind Code |
A1 |
Nishiyama; Yoshitaka ; et
al. |
February 11, 2010 |
CARBURIZATION RESISTANT METAL MATERIAL
Abstract
There is provided a metal material having excellent workability
and metal dusting resistance, which is suitable as a raw material
for cracking furnaces, reforming furnaces, heating furnaces, heat
exchangers, etc. in petroleum refining, petrochemical plants, and
the like. The metal material is characterized by consisting of, by
mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn: 0.05 to 2.5%, P:
0.04% or less, S: 0.015% or less, Cr: 18 to 30%, Ni: 20% or higher
and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to 1%, Ti: 0.01 to
1%, N: 0.15% or less, and O (oxygen): 0.02% or less, the balance
being Fe and impurities, and satisfying Expression (1).
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1) in
which the symbol of element in Expression (1) represents the
content of that element in mass %.
Inventors: |
Nishiyama; Yoshitaka;
(Nishinomiya-shi, JP) ; Osuki; Takahiro;
(Nishinomiya-shi, JP) ; Matsumoto; Satoshi;
(Houston, TX) |
Correspondence
Address: |
CLARK & BRODY
1090 VERMONT AVENUE, NW, SUITE 250
WASHINGTON
DC
20005
US
|
Family ID: |
41015979 |
Appl. No.: |
12/539065 |
Filed: |
August 11, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2009/053212 |
Feb 23, 2009 |
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12539065 |
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Current U.S.
Class: |
420/49 ;
420/582 |
Current CPC
Class: |
C22C 38/04 20130101;
C22C 38/50 20130101; C22C 38/42 20130101; C22C 38/06 20130101; C22C
38/02 20130101 |
Class at
Publication: |
420/49 ;
420/582 |
International
Class: |
C22C 38/42 20060101
C22C038/42; C22C 30/02 20060101 C22C030/02; C22C 38/50 20060101
C22C038/50; C22C 38/58 20060101 C22C038/58; C22C 38/44 20060101
C22C038/44; C22C 38/46 20060101 C22C038/46; C22C 38/52 20060101
C22C038/52; C22C 38/54 20060101 C22C038/54 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2008 |
JP |
2008-046228 |
Claims
1. A carburization resistant metal material characterized by
consisting of, by mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn:
0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 22 to 30%,
Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to
1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or less
the balance being Fe and impurities, and satisfying Expression (1).
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1) in
which the symbol of element in Expression (1) represents the
content of that element in mass %.
2. A carburization resistant metal material characterized by
consisting of, by mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn:
0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 18 to 30%,
Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to
1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or
less, the balance being Fe and impurities, and satisfying
Expression (1).
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1) in
which the symbol of element in Expression (1) represents the
content of that element in mass %.
3. The carburization resistant metal material according to claim 1,
characterized by further containing, by mass %, at least one kind
of a component selected from at least one group of the first group
to the fifth group described below: first group: Co: 10% or less,
second group: Mo: 2.5% or less and W: 5% or less, third group: B:
0.1% or less, V: 0.5% or less, Zr: 0.1% or less, Nb: 2% or less,
and Hf: 0.5% or less, fourth group: Mg: 0.1% or less and Ca: 0.1%
or less, fifth group: Y: 0.15% or less, La: 0.15% or less, Ce:
0.15% or less, and Nd: 0.15% or less.
4. The carburization resistant metal material according to claim 2,
characterized by further containing, by mass %, at least one kind
of a component selected from at least one group of the first group
to the fifth group described below: first group: Co: 10% or less,
second group: Mo: 2.5% or less and W: 5% or less, third group: B:
0.1% or less, V: 0.5% or less, Zr: 0.1% or less, Nb: 2% or less,
and Hf: 0.5% or less, fourth group: Mg: 0.1% or less and Ca: 0.1%
or less, fifth group: Y: 0.15% or less, La: 0.15% or less, Ce:
0.15% or less, and Nd: 0.15% or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a metal material that has
excellent high-temperature strength and superior corrosion
resistance, and in particular is used in a carburizing gas
atmosphere containing hydrocarbon gas and CO gas. More
particularly, it relates to a metal material having excellent
weldability and metal dusting resistance, which is suitable as a
raw material for cracking furnaces, reforming furnaces, heating
furnaces, heat exchangers, etc. in petroleum refining,
petrochemical plants, and the like.
BACKGROUND ART
[0002] Demand for clean energy fuels such as hydrogen, methanol,
liquid fuels (GTL: Gas to Liquids), and dimethyl ether (DME) is
expected to significantly increase in the future. Therefore, a
reforming apparatus for producing such a synthetic gas tends to be
large in size, and an apparatus that achieves higher thermal
efficiency and is suitable for mass production is demanded. Also,
heat exchange for recovering exhaust is often used to enhance
energy efficiency in reforming apparatuses in the conventional
petroleum refining, petrochemical plants, and the like, and ammonia
manufacturing apparatuses, hydrogen manufacturing apparatuses; and
the like, in which raw materials such as petroleum are used.
[0003] To effectively use the heat of such a high-temperature gas,
heat exchange in a temperature range of 400 to 800.degree. C.,
which is relatively low, has become important, and corrosion caused
by carburization of a high Cr-- high Ni--Fe alloy based metal
material used for reaction tubes, heat exchangers, and the like in
this temperature range poses a problem.
[0004] Usually, a synthetic gas reformed in the above-described
reactors, that is, a gas containing H.sub.2, CO, CO.sub.2,
H.sub.2O, and hydrocarbon such as methane comes into contact with
the metal material of a reaction tube and the like at a temperature
of about 1000.degree. C. or higher. In this temperature range, on
the surface of the metal material, elements such as Cr and Si,
which have higher oxidation tendency than Fe or Ni or the like, are
oxidized selectively, and a dense film of chromium oxide or silicon
oxide or the like is formed, by which corrosion is restrained. In a
portion such as a heat exchange part in which the temperature is
relatively low, however, the diffusion of element from the inside
to the surface of metal material is insufficient. Therefore, the
formation of oxide film, which achieves a corrosion restraining
effect, delays, and additionally, such a gas having a composition
containing hydrocarbon comes to have carburizing properties, so
that carbon intrudes into the metal material through the surface
thereof, and carburization occurs.
[0005] In an ethylene cracking furnace tube and the like, if
carburization proceeds and a carburized layer comprising carbide of
Cr or Fe or the like is formed, the volume of that portion
increases. As a result, fine cracks are liable to develop, and in
the worst case, the tube in use is broken. Also, if the metal
surface is exposed, carbon precipitation (coking) in which metal
serves as a catalyst occurs on the surface, so that the flow path
area of the tube decreases and the heat-transfer characteristics
degrade.
[0006] In a heating furnace tube and the like for a catalytic
cracking furnace for increasing the octane value of naphtha
obtained by distillation of crude oil as well, a heavily
carburizing environment consisting of hydrocarbon and hydrogen is
created, so that carburization and metal dusting occur.
[0007] On the other hand, in an environment in which the
carburizing properties of gas in the reforming furnace tube, heat
exchanger, and the like are severer, the carbide is supersaturated,
and thereafter graphite precipitates directly. Therefore, a base
material metal is exfoliated away and the thickness of base
material decreases, that is, corrosion loss called metal dusting
proceeds. Further, coking occurs with the exfoliated metal powder
serving as a catalyst.
[0008] If the cracks, loss, and in-tube closure increase, an
apparatus failure or the like occurs. As a result, operation may be
suspended. Therefore, careful consideration must be given to the
selection of material used for an apparatus member.
[0009] To prevent the aforementioned carburization and the
corrosion caused by metal dusting, various countermeasures have
conventionally been studied.
[0010] For example, Patent Document 1 proposes an Fe-based alloy or
a Ni-based alloy containing 11 to 60% (mass %, the same shall apply
hereinafter) of Cr concerning the metal dusting resistance in an
atmospheric gas of 400 to 700.degree. C. containing H.sub.2, CO,
CO.sub.2 and H.sub.2O. Specifically, it is shown that the invention
of an Fe-based alloy containing 24% or more of Cr and 35% or more
of Ni, a Ni-based alloy containing 20% or more of Cr and 60% or
more of Ni, and an alloy material in which Nb is further added to
these alloys is excellent. However, even if a Cr or Ni content in
the Fe-based alloy or the Ni-based alloy is merely increased, a
sufficient carburization restraining effect cannot be achieved, so
that a metal material having higher metal dusting resistance has
been demanded.
[0011] Also, in a method disclosed in Patent Document 2, to prevent
corrosion caused by metal dusting of a high-temperature alloy
containing iron, nickel, and chromium, one or more kinds of metals
of the VIII group, the IB group, the IV group, and the V group of
the element periodic table and a mixture thereof are adhered to the
surface by the ordinary physical or chemical means, and the alloy
is annealed in an inert atmosphere to form a thin layer having a
thickness of 0.01 to 10 .mu.m, by which the alloy surface is
protected. In this case, Sn, Pb, Bi, and the like are especially
effective. Although effective at the early stage, this method may
lose effectiveness in that the thin layer is exfoliated in
long-term use.
[0012] Patent Document 3 relates to the metal dusting resistance of
a metal material in an atmospheric gas of 400 to 700.degree. C.
containing H.sub.2, CO, CO.sub.2 and H.sub.2O. As the result of an
investigation of the interaction with carbon made from the
viewpoint of solute element in iron, Patent Document 3 discloses
that the addition of an element producing stable carbide in the
metal material, such as Ti, Nb, V and Mo, or the alloying element
in which the interaction co-factor .OMEGA. represents a positive
value, such as Si, Al, Ni, Cu and Co is effective in restraining
metal dusting in addition to enhancing the protecting properties of
oxide film. However, the increase of Si, Al and the like sometimes
leads to the decrease in hot workability and weldability.
Therefore, considering the manufacturing stability and plant
working, this metal material leaves room for improvement.
[0013] Next, to break off the contact of carburizing gas with the
metal surface, there have been disclosed a method for oxidizing a
metal material in advance and a method for performing surface
treatment.
[0014] For example, Patent Document 4 and Patent Document 5
disclose a method for pre-oxidizing a low Si-based 25Cr-20Ni (HK40)
heat resistant steel or a low Si-based 25Cr-35Ni heat-resisting
steel at a temperature near 1000.degree. C. for 100 hours or longer
in the air. Also, Patent Document 6 discloses a method for
pre-oxidizing an austenitic heat-resisting steel containing 20 to
35% of Cr in the air. Further, Patent Document 7 proposes a method
for improving the carburization resistance by heating a high Ni--Cr
alloy in a vacuum and by forming a scale film.
[0015] Patent Document 8 proposes an austenitic alloy whose
contents of Si, Cr and Ni satisfy the formula of
Si<(Cr+0.15Ni-18)/10; thereby a Cr-based oxide film having high
adhesiveness even in an environment, in which the alloy is
subjected to a heating/cooling cycle, is formed to provide the
alloy with excellent carburization resistance even in an
environment in which the alloy is exposed to a corrosive gas at
high temperatures. Patent Document 9 proposes an austenitic
stainless steel having excellent scale exfoliation resistance even
in an environment in which the steel is subjected to a
heating/cooling cycle, which is produced by containing Cu and a
rare earth element (Y and Ln group) therein and thereby forming a
uniform oxide film having high Cr concentration in the film. Also,
Patent Document 10 proposes a method for improving the
carburization resistance by forming a concentrated layer of Si or
Cr by performing surface treatment. Unfortunately, all of these
prior arts require special heat treatment or surface treatment, and
therefore they are inferior in economy. Also, since scale
restoration (scale recycling) after the pre-oxidized scale or the
surface treatment layer has exfoliated away is not considered, if
the material surface is damaged once, the subsequent effect cannot
be anticipated.
[0016] Patent Document 11 proposes a stainless steel pipe having
excellent carburization resistance and containing 20 to 55% of Cr,
which is produced by forming a Cr-deficient layer, which has a Cr
concentration of 10% or higher and lower than the Cr concentration
of the base material, on the surface of steel pipe. In this patent
document, however, the improvement of weldability, which is an
issue of the Cu-containing steel, has not been studied.
[0017] Besides, a method for adding H.sub.2S into the atmospheric
gas has been thought of. However, the application of this method is
restricted because H.sub.2S may remarkably decrease the activity of
a catalyst used for reforming.
[0018] Patent Document 12 and Patent Document 13 propose a metal
material in which the gas dissociative adsorption (gas/metal
surface reaction) is restrained by containing a proper amount of
one kind or two or more kinds of P, S, Sb and Bi. Since these
elements segregate on the metal surface, even if the elements are
not added excessively, the elements can restrain carburization and
metal dusting corrosion significantly. However, since these
elements segregate not only on the metal surface but also at the
grain boundary of metal grainy, a problem associated with hot
workability and weldability remains to be solved.
[0019] Techniques for enhancing corrosion resistance and crevice
corrosion resistance by adding Cu have also been proposed. Patent
Document 14 describes a technique for enhancing corrosion
resistance by containing Cu, and on the other hand, for increasing
the hot workability improving effect due to B by reducing S and O
as far as possible. Patent Document 15 describes a technique for
improving corrosion resistance and crevice corrosion resistance
excellent in sulfuric acid and sulfate environments by setting the
G.I. value (General Corrosion Index) represented by
"-Cr+3.6Ni+4.7Mo+11.5Cu" at 60 to 90 and by setting the C.I. value
(Crevice Corrosion Index) represented by "Cr+0.4Ni+2.7Mo+Cu+18.7N"
at 35 to 50. Patent Document 16 describes a technique for improving
hot workability by adding B exceeding 0.0015% while increasing a Cu
content and by keeping an oxygen content low. In all of these
techniques, the upper limit of a C content is restricted to a low
level to avoid the decrease in corrosion resistance. Therefore, the
solid-solution strengthening of C cannot be anticipated, and a
sufficient high-temperature strength cannot be obtained. For this
reason, these techniques are unsuitable for a metal material used
at high temperatures.
[Patent Document 1] JP9-78204A
[Patent Document 2] JP 11-172473A
[Patent Document 3] JP2003-73763A
[Patent Document 4] JP53-66832A
[Patent Document 5] JP53-66835A
[Patent Document 6] JP57-43989A
[Patent Document 7] JP 11-29776A
[Patent Document 8] JP2002-256398A
[Patent Document 9] JP2006-291290A
[Patent Document 10] JP2000-509105A
[Patent Document 11] JP2005-48284A
[Patent Document 12] JP2007-186727A
[Patent Document 13] JP2007-186728A
[Patent Document 14] JP1-21038A
[Patent Document 15] JP2-170946A
[Patent Document 16] JP4-346638A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0020] As described above, various techniques for enhancing the
metal dusting resistance, the carburization resistance, and the
coking resistance of metal material have been proposed
conventionally. However, all of these techniques require special
heat treatment and surface treatment, so that cost and labor are
needed. Also, these techniques have no function of scale
restoration (scale recycling) after the pre-oxidized scale or the
surface treatment layer has exfoliated away. Therefore, if the
material surface is damaged once, the subsequent metal dusting
cannot be restrained. Also, these techniques have a problem
associated with weldability of metal material.
[0021] Also, there is a method for restraining metal dusting by
adding H.sub.2S into the atmospheric gas in the tube of a reforming
apparatus and manufacturing apparatus for synthetic gas as
described above, not by improving the metal material itself.
However, since H.sub.2S may remarkably decrease the activity of a
catalyst used for reforming hydrocarbon, the technique for
restraining metal dusting by adjusting the components of
atmospheric gas is merely applied limitedly.
[0022] The present invention has been made in view of the present
situation, and accordingly an object thereof is to provide a metal
material that has metal dusting resistance, carburization
resistance, and coking resistance, and further has improved
weldability due to the restraint of reaction between carburizing
gas and the metal surface in an ethylene plant cracking furnace
tube, a heating furnace tube of catalytic reforming furnace, a
synthetic gas reforming furnace tube, and the like.
Means for Solving the Problems
[0023] The inventors analyzed a phenomenon that carbon intrudes
into a metal in a molecular state, and revealed that this
phenomenon progresses in an elementary process consisting of the
following items (a) to (c).
[0024] (a) Gas molecules consisting of C compounds such as
hydrocarbon and CO approach the metal surface.
[0025] (b) The approaching gas molecules are dissociatively
adsorbed onto the metal surface.
[0026] (c) The dissociated atomic carbon intrudes into the metal
and diffuses.
[0027] As the result of various studies on methods for restraining
the aforementioned phenomenon, it was found that the following
methods (d) and (e) are effective.
[0028] (d) Oxide scale is formed positively on the metal surface
during the use of metal material, by which the contact with the
metal of the gas molecules consisting of C compounds is broken
off.
[0029] (e) The dissociative adsorption of the gas molecules
consisting of C compounds is restrained on the metal surface.
[0030] As the result that the study on oxide scale having a
breaking-off effect as in the item (d) was conducted, it was
revealed that oxide scale consisting of Cr and Si acts effectively.
In particular, in a carburizing gas environment such as an ethylene
plant cracking furnace tube, a heating furnace tube of catalytic
reforming furnace, and a synthetic gas reforming furnace tube, the
partial pressure of oxygen in gas is low. Therefore, it was
revealed that oxide scale consisting mainly of Cr can be formed on
the gas side and oxide scale consisting mainly of Si can be formed
on the metal side by containing proper amounts of Cr and Si.
[0031] On the other hand, as the result that the study was
conducted from the viewpoint of dissociative adsorption as in the
item (e), it was revealed that if proper amounts of noble metal
elements such as Cu, Ag and Pt and elements of the VA group and the
VIA group in the periodic table are added, an effect of restraining
the dissociative adsorption of gas molecules consisting of C
compounds is achieved. In particular, Cu is low in cost among the
noble metal elements, and additionally less problems occur in
melting and solidification when Cu is contained in an Fe--Ni--Cr
based metal material. Therefore, the use of Cu is preferable.
[0032] It was revealed that according to the methods (d) and (e),
the intrusion of carbon into the metal in the above-described
elementary process of items (a) to (c) can be restrained
effectively, and by applying the methods (d) and (e)
simultaneously, the metal dusting resistance, the carburization
resistance, and the coking resistance can be improved
dramatically.
[0033] However, if an element such as Si and Cu is added, the
corrosion resistance can be improved; on the other hand, the
weldability is deteriorated. In particular, in a region subjected
to an influence of heat cycle of rapid heating/rapid cooling caused
by welding, that is in a welding heat affected zone (hereinafter,
referred to as "HAZ"), cracks caused by grain boundary melting are
liable to develop. Specifically, if Si, Cu or the like element
segregates at the crystal grain boundary of the base material, the
melting point of grain boundary lowers. At this time, when the
grain boundary is subjected to welding heat cycle and is heated to
a temperature just below the melting point, the grain boundary
melts and is torn off by the thermal stress at the time of welding,
which develops a crack. This is a HAZ crack. Therefore, in the case
where the metal material is used for a welded structure, weld
cracks of this kind must be restrained.
[0034] The inventors studied various methods capable of restraining
HAZ cracks at the time of welding while improving the corrosion
resistance by adding a considerable amount of Si or Cu. As a
result, the inventors came to obtain a knowledge that the HAZ
cracks can be restrained by the following methods (f) and (g).
[0035] (f) Cr-based carbides are precipitated at the crystal grain
boundary of the base material by increasing the C content, by which
the melting point of grain boundary is raised.
[0036] (g) The grain coarsening in the HAZ at the time when the
welding heat cycle occurs is restrained by the precipitation of Cr
carbides of high melting point, by which the surface area of grain
boundary is increased, and thereby the segregation of Si, Cu or the
like at the grain boundary is decreased.
[0037] Based on this knowledge, in a metal material containing 18
to 30% of Cr or 22 to 30% of Cr, the contents, i.e. C, Si and Cu,
were changed variously, by which the HAZ crack susceptibility was
studied. As a result, it was revealed that the lower limit of C
content capable of preventing HAZ cracks changes according to the
Si, Cu and Cr contents. Specifically, it was revealed that as the
Si and Cu contents lowering the melting point of grain boundary
increase, the allowable lower limit of C content is raised, and as
the Cr content constituting the carbides raising the melting point
of grain boundary increases, the allowable lower limit of C content
is lowered.
[0038] From the results of systematical experiments in which
components were changed variously, a relational expression between
the C content capable of preventing HAZ cracks and the Si, Cu and
Cr contents was estimated experimentally. As a result, the
inventors obtained a knowledge that by satisfying Expression (1),
both of excellent metal dusting resistance and excellent HAZ crack
susceptibility resistance can be obtained.
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1)
in which the symbol of element in Expression (1) represents the
content of that element in mass %.
[0039] The present invention has been completed based on the
above-described knowledge, and the gists of the present invention
are as described in the following items (1) to (3). Hereunder, the
gists are called invention (1) to invention (3), and are sometimes
generally named the present invention.
[0040] (1) A carburization resistant metal material characterized
by consisting of, by mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn:
0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 22 to 30%,
Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to
1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or
less, the balance being Fe and impurities, and satisfying
Expression (1).
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1)
in which the symbol of element in Expression (1) represents the
content of that element in mass %.
[0041] (2) A carburization resistant metal material characterized
by consisting of, by mass %, C: 0.08 to 0.4%, Si: 0.6 to 2.0%, Mn:
0.05 to 2.5%, P: 0.04% or less, S: 0.015% or less, Cr: 18 to 30%,
Ni: 20% or higher and less than 30%, Cu: 0.5 to 10.0%, Al: 0.01 to
1%, Ti: 0.01 to 1%, N: 0.15% or less, and O (oxygen): 0.02% or
less, the balance being Fe and impurities, and satisfying
Expression (1).
C.gtoreq.0.062.times.Si+0.033.times.Cu-0.004.times.Cr+0.043 (1)
in which the symbol of element in Expression (1) represents the
content of that element in mass %.
[0042] (3) The carburization resistant metal material described in
item (1) or (2) above, characterized by further containing, by mass
%, at least one kind of a component selected from at least one
group of the first group to the fifth group described below:
first group: Co: 10% or less, second group: Mo: 2.5% or less and W:
5% or less, third group: B: 0.1% or less, V: 0.5% or less, Zr: 0.1%
or less, Nb: 2% or less, and Hf: 0.5% or less, fourth group: Mg:
0.1% or less and Ca: 0.1% or less, fifth group: Y: 0.15% or less,
La: 0.15% or less, Ce: 0.15% or less, and Nd: 0.15% or less.
ADVANTAGES OF THE INVENTION
[0043] The metal material in accordance with the present invention
has an effect of restraining reaction between carburizing gas and
the metal surface, and has excellent metal dusting resistance,
carburization resistance, and coking resistance. Further, since the
weldability is improved, the metal material can be used for welded
structure members of cracking furnaces, reforming furnaces, heating
furnaces, heat exchangers, etc. in petroleum refining,
petrochemical plants, and the like, and can significantly improve
the durability and operation efficiency of apparatus.
[0044] In particular, the metal material in accordance with the
present invention is suitable as a metal material used for reaction
tubes and heat exchangers used for heat exchange in a temperature
range (400 to 800.degree. C.) lower than the conventional
temperature range, so that metal dusting, which poses a problem in
this temperature range, can be restrained effectively.
BEST MODE FOR CARRYING OUT THE INVENTION
[0045] The reason why the composition range of metal material is
restricted according to the invention is as described below. In the
explanation below, the "%" representation of the content of each
element means "mass %".
[0046] C: 0.08 to 0.4%
[0047] C (carbon) is one of important elements in the present
invention. Carbon not only enhances the strength at high
temperatures but also achieves an effect of improving the
weldability in combination with chromium to form carbides. In
particular, the effect is remarkable in the metal material in
accordance with the present invention that has high Si and Cu
contents. To sufficiently achieve this effect, 0.08% or more of C
must be contained. However, if C content exceeds 0.4%, the
toughness of alloy lowers extremely, so that the upper limit of C
content is set at 0.4%. The C content is preferably in the range of
higher than 0.1% and 0.35% or less, further preferably in the range
of higher than 0.15% and 0.25% or less.
[0048] Si: 0.6 to 2.0%
[0049] Si (silicon) is one of important elements in the present
invention. Since silicon has a strong affinity with oxygen, it
forms Si-based oxide scale in the lower layer of a protective oxide
scale layer such as Cr.sub.2O.sub.3, and isolates carburizing gas.
This action is brought about when the Si content is 0.6% or higher.
However, if the Si content exceeds 2.0%, the weldability decreases
remarkably, so that the upper limit of Si content is set at 2.0%.
The Si content is preferably in the range of 0.7 to 2.0%, further
preferably in the range of 0.8 to 1.5%.
[0050] Mn: 0.05 to 2.5%
[0051] Mn (manganese) has deoxidizing ability and also improves the
workability and weldability, so that 0.05% or more of Mn is added.
Also, since manganese is an austenite-generating element, some of
Ni can be replaced with Mn. However, excessive addition of Mn harms
the carburizing gas isolating properties of protective oxide scale
layer, so that the upper limit of Mn content is set at 2.5%. The Mn
content is preferably in the range of 0.1 to 2.0%, further
preferably in the range of 0.7 to 1.6%.
[0052] P: 0.04% or less
[0053] P (phosphorus) decreases the hot workability and
weldability, so that the upper limit of P content is set at 0.04%.
In particular, when the Si and Cu contents are high, this effect is
important. The upper limit of P content is preferably 0.03%,
further preferably 0.025%. However, since phosphorus acts to
restrain the dissociative adsorption reaction on the metal surface
of carburizing gas, it may be contained when the decrease in
weldability can be permitted.
[0054] S: 0.015% or less
[0055] S (sulfur) decreases the hot workability and weldability
like phosphorus, so that the upper limit of S content is set at
0.015%. In particular, when the Si and Cu contents are high, this
effect is important. The upper limit of S content is preferably
0.01%, further preferably 0.003%. However, like phosphorus, since
sulfur acts to restrain the dissociative adsorption reaction on the
metal surface of carburizing gas, it may be contained when the
decrease in weldability can be permitted.
[0056] Cr: 18 to 30% or 22 to 30%
[0057] Cr (chromium) forms oxide scale such as Cr.sub.2O.sub.3
stably, and has an effect of isolating carburizing gas. Therefore,
even in a severe carburizing gas environment, chromium provides
sufficient carburization resistance, metal dusting resistance, and
coking resistance. Also, chromium improves the weldability because
it combines with carbon to form carbides. In particular, when the
Si and Cu contents are high, this effect is important. To
sufficiently achieve this effect, 18% or more of Cr must be
contained. However, since excessive addition decreases not only the
workability but also the structural stability, the upper limit of
Cr is set at 30%. The lower limit of Cr content is preferably 19%,
further preferably 22%, and still further preferably 23%. Also, the
upper limit of Cr content is preferably 28%, further preferably
27%.
[0058] Ni: 20% or higher and less than 30%
[0059] Ni (nickel) is an element necessary for obtaining a stable
austenitic micro-structure according to the Cr content, and
therefore 20% or more of Ni must be contained. Also, when carbon
intrudes into the metal material, nickel has a function of reducing
the intrusion rate. Further, nickel acts to secure the
high-temperature strength of the metal micro-structure. However,
the nickel content higher than necessary may lead to cost increase
and manufacturing difficulties, and may also accelerate coking and
metal dusting especially in a gas environment that contains
hydrocarbon. Therefore, the upper limit of Ni content is restricted
to less than 30%. Preferably, the content of Ni is 22.5% or higher
and less than 30%. Further preferably, the content of Ni is higher
than 25% and 29.5% or less.
[0060] Cu: 0.5 to 10.0%
[0061] Cu (copper) is one of important elements in the present
invention. Copper restrains reaction between carburizing gas and
the metal surface, and greatly improves the metal dusting
resistance and the like. Also, since copper is an
austenite-generating element, some of Ni can be replaced with Cu.
To achieve the metal dusting resistance improving effect, 0.5% or
more of Cu must be contained. However, if Cu exceeding 10.0% is
contained, the weldability decreases, so that the upper limit of Cu
content is set at 10.0%. The Cu content is preferably 1.0 to 6.0%,
further preferably 2.1 to 4.0%.
[0062] Al: 0.01 to 1%
[0063] Al (aluminum) is an element effective in improving the
high-temperature strength. Also, aluminum has an effect as a
deoxidizer because it has a high affinity with oxygen. In addition,
aluminum serves as one of the constituent elements of oxide scale,
and enhances the gas isolating properties. This effect can be
anticipated especially in an environment in which the carburizing
properties are strong. To achieve this effect, it is effective to
contain 0.01% or more of Al. On the other hand, if the Al content
exceeds 1%, the weldability is impaired. Therefore, the Al content
is set in the range of 0.01 to 1%. The Al content is preferably in
the range of 0.12 to 0.8%, further preferably in the range of 0.2
to 0.6%.
[0064] Ti: 0.01 to 1%
[0065] Ti (titanium) is an element effective in improving the
high-temperature strength. Also, since titanium has an affinity
with oxygen, it serves as one of the constituent elements of oxide
scale, and enhances the gas isolating properties. This effect can
be anticipated especially in an environment in which the
carburizing properties are strong. Therefore, titanium is contained
positively. To achieve this effect, it is effective to contain
0.01% or more of Ti. However, if titanium is contained excessively,
the workability and weldability decrease, so that the upper limit
of Ti content is set at 1%. The Ti content is preferably in the
range of 0.12 to 0.8%, further preferably in the range of 0.2 to
0.6%.
[0066] N: 0.15% or less
[0067] N (nitrogen) need not necessarily be contained. If nitrogen
is contained, it acts to enhance the high-temperature strength of
metal material. However, if the N content exceeds 0.15%, the
workability is impaired. Therefore, the upper limit of N content is
set at 0.15%. The preferred upper limit thereof is 0.05%. To
achieve the effect of enhancing the high-temperature strength of
metal material, preferably 0.0005% or more, further preferably
0.001% or more, of N is contained.
[0068] O: 0.02% or less
[0069] O (oxygen) is an impurity element mingled from a raw
material or the like when the metal material is melted. If the O
content exceeds 0.02%, large amounts of oxide inclusions exist in
the metal material, so that the workability decreases, and also a
flaw may occur on the surface of metal material. Therefore, the
upper limit of O content is set at 0.02%.
[0070] Next, in addition to the method of invention (1) or
invention (2), invention (3) relating to a metal material whose
strength, ductility, and toughness are improved is explained.
[0071] Invention (3) relates to a carburization resistant metal
material characterized by further containing, by mass %, at least
one kind of a component selected from at least one group of the
first group to the fifth group described below in a metal material
specified in
invention (1) or (2): first group: Co: 10% or less, second group:
Mo: 2.5% or less and W: 5% or less, third group: B: 0.1% or less,
V: 0.5% or less, Zr: 0.1% or less, Nb: 2% or less, and Hf: 0.5% or
less, fourth group: Mg: 0.1% or less and Ca: 0.1% or less, fifth
group: Y: 0.15% or less, La: 0.15% or less, Ce: 0.15% or less, and
Nd: 0.15% or less.
[0072] Next, these optionally added elements are explained.
[0073] First group (Co: 10% or less, by mass %)
[0074] Co (cobalt) acts to stabilize the austenite phase, so that
it can replace some of Ni component. Therefore, cobalt may be
contained as necessary. However, if the Co content exceeds 10%,
cobalt deteriorates the hot workability. Therefore, when cobalt is
contained, the content is 10% or less. From the viewpoint of hot
workability, the Co content is preferably in the range of 0.01 to
5%, further preferably in the range of 0.01 to 3%.
[0075] Second group (Mo: 2.5% or less and W: 5% or less, by mass
%)
[0076] Mo (molybdenum) and W (tungsten) are solid-solution
strengthening elements, so that either one or both of them may be
contained as necessary. However, when molybdenum is contained,
molybdenum deteriorates the workability and impairs the structural
stability if the content exceeds 2.5%. Therefore, when molybdenum
is contained, the content is 2.5% or less. The Mo content is
preferably 0.01 to 2.3%. Also, when tungsten is contained, tungsten
deteriorates the workability and impairs the structural stability
if the content exceeds 5%. Therefore, when tungsten is contained,
the content is 5% or less. The W content is preferably 0.01 to
2.3%.
[0077] Third group (B: 0.1% or less, V: 0.5% or less, Zr: 0.1% or
less, Nb: 2% or less, and Hf: 0.5% or less, by mass %)
[0078] B (boron), V (vanadium), Zr (zirconium), Nb (niobium) and Hf
(hafnium) are elements effective in improving the high-temperature
strength characteristics, so that one kind or two or more kinds of
these elements may be contained. However, when boron is contained,
boron deteriorates the weldability if the content exceeds 0.1%.
Therefore, when boron is contained, the content is 0.1% or less.
The B content is preferably 0.001 to 0.05%. When vanadium is
contained, vanadium deteriorates the weldability if the content
exceeds 0.5%. Therefore, when vanadium is contained, the content is
0.5% or less. The V content is preferably 0.001 to 0.1%. When
zirconium is contained, zirconium deteriorates the weldability if
the content exceeds 0.1%. Therefore, when zirconium is contained,
the content is 0.1% or less. The Zr content is preferably 0.001 to
0.05%. When niobium is contained, niobium deteriorates the
weldability if the content exceeds 2%. Therefore, when niobium is
contained, the content is 2% or less. The Nb content is preferably
0.001 to 0.1%. Also, when hafnium is contained, hafnium
deteriorates the weldability if the content exceeds 0.5%.
Therefore, when hafnium is contained, the content is 0.5% or less.
The Hf content is preferably 0.001 to 0.1%.
[0079] Fourth group (Mg: 0.1% or less and Ca: 0.1% or less, by mass
%)
[0080] Mg (magnesium) and Ca (calcium) have an effect of improving
the hot workability, so that one kind or two or more kinds of these
elements may be contained as necessary. However, when magnesium is
contained, magnesium deteriorates the weldability if the content
exceeds 0.1%. Therefore, when magnesium is contained, the content
is 0.1% or less. The Mg content is preferably 0.0005 to 0.1%. Also,
when calcium is contained, calcium deteriorates the weldability if
the content exceeds 0.1%. Therefore, when calcium is contained, the
content is 0.1% or less. The Ca content is preferably 0.0005 to
0.1%.
[0081] Fifth group (Y: 0.15% or less, La: 0.15% or less, Ce: 0.15%
or less, and Nd: 0.15% or less, by mass %)
[0082] Y (yttrium), La (lanthanum), Ce (cerium) and Nd (neodymium)
have an effect of improving the oxidation resistance, so that one
kind or two or more kinds of these elements may be contained as
necessary. However, when these elements are contained, these
elements deteriorate the workability if the content of any one
element thereof exceeds 0.15%. Therefore, when these elements are
contained, the content of any one element thereof is 0.15% or less.
The content is preferably 0.0005 to 0.15%.
[0083] The metal material in accordance with the present invention
having a function of restraining the reaction between carburizing
gas and the metal surface has only to satisfy the requirements
specified in the above-described items (f) and (g) because the
metal material has problems of metal dusting, carburization, and
coking.
[0084] The metal material in accordance with the present invention
may be formed into a required shape such as a thick plate, sheet,
seamless tube, welded tube, forged product, and wire rod by means
of melting, casting, hot working, cold rolling, welding, and the
like. Also, the metal material may be formed into a required shape
by means of powder metallurgy, centrifugal casting, and the like.
The surface of the metal material having been subjected to final
heat treatment may be subjected to surface treatment such as
pickling, shotblasting, shotpeening, mechanical cutting, grinding,
and electropolishing. Also, on the surface of the metal material in
accordance with the present invention, one or two or more irregular
shapes such as protruding shapes may be formed. Also, the metal
material in accordance with the present invention may be combined
with various kinds of carbon steels, stainless steels, Ni-based
alloys, Co-based alloys, Cu-based alloys, and the like to be formed
into a required shape. In this case, the joining method of the
metal material in accordance with the present invention to the
various kinds of steels and alloys is not subject to any
restriction. For example, mechanical joining such as pressure
welding and "staking" and thermal joining such as welding and
diffusion treatment can be performed.
[0085] Next, the present invention is explained in more detail with
reference to examples. The present invention is not limited to
these examples.
Example 1
[0086] A metal material having a chemical composition given in
Table 1 was melted by using a high-frequency heating vacuum
furnace, and a metal plate having a plate thickness of 6 mm was
manufactured by hot forging and hot rolling. The metal plate was
subjected to solid-solution heat treatment at 1160 to 1230.degree.
C. for 5 minutes, a part of which was cut to produce a test
piece.
[0087] From the metal material described in Table 1, a test piece
measuring 15 mm wide and 20 mm long was cut. This test piece was
isothermally maintained at 650.degree. C. in a 45% CO-42.5%
H.sub.2-6.5% CO.sub.2-6% H.sub.2O (percent by volume) gas
atmosphere. The test piece was taken out after 200 hours had
elapsed, and the presence of a pit formed on the surface of test
piece was examined by visual observation and by optical microscope
observation. The results are summarized in Table 2.
TABLE-US-00001 TABLE 1 Chemical composition (mass %, balance being
Fe and impurities) Right-hand side of No. C Si Mn P S Cr Ni Cu Al
Ti N O Others Expression (1) 1 0.18 1.16 1.23 0.021 0.0010 25.4
25.2 2.91 0.49 0.57 0.01 <0.01 0.005Ca, 0.002B 0.109 2 0.18 1.16
1.21 0.021 0.0010 25.2 29.9 2.92 0.48 0.54 0.01 <0.01 0.004Ca
0.110 3 0.11 0.98 1.18 0.024 0.0012 23.8 25.3 2.75 0.36 0.47 0.01
<0.01 -- 0.099 4 0.16 1.07 0.15 0.019 0.0016 24.8 25.6 3.05 0.35
0.40 0.01 <0.01 -- 0.111 5 0.14 0.95 1.81 0.014 0.0011 23.2 28.7
2.18 0.47 0.46 0.02 <0.01 1.9Mo 0.081 6 0.23 0.62 1.14 0.012
0.0002 27.5 24.4 4.61 0.03 0.12 0.01 <0.01 1.1W 0.117 7 0.09
0.65 0.75 0.022 0.0004 23.7 21.6 1.46 0.02 0.03 0.12 <0.01
0.11V, 1.4Co 0.030 8 0.18 1.15 0.98 0.022 0.0015 24.9 25.6 2.51
0.16 0.25 0.01 0.02 -- 0.098 9 0.18 1.04 0.97 0.017 0.0013 23.8
26.7 1.97 0.40 0.37 0.01 <0.01 0.003Mg, 1.1Mo 0.077 10 0.16 1.13
1.04 0.005 0.0010 25.3 25.7 2.88 0.41 0.46 0.01 <0.01 0.032Nd,
0.003Ca 0.107 11 0.21 1.16 1.34 0.013 0.0010 24.9 29.3 1.44 0.32
0.33 0.02 <0.01 0.4Nb, 0.027Ce 0.063 12 0.15 0.89 1.28 0.026
0.0012 26.5 26.0 1.25 0.35 0.39 0.01 <0.01 0.2Hf, 0.003B, 0.02Zr
0.033 13 0.10 0.87 1.29 0.035 0.0083 22.4 24.8 1.21 0.39 0.75 0.02
<0.01 -- 0.047 14 0.12 0.94 1.22 0.021 0.0005 23.2 29.3 0.62
0.88 0.52 0.01 <0.01 0.005Ca 0.029 15 0.16 1.44 1.17 0.009
0.0011 25.0 24.5 3.24 0.42 0.55 0.01 <0.01 0.011La, 0.023Ce
0.139 16 0.18 1.01 0.64 0.019 0.0010 28.6 22.4 2.67 0.46 0.56 0.01
<0.01 5.3Co 0.079 17 0.21 0.89 1.48 0.024 0.0032 26.3 27.5 3.32
0.41 0.51 0.01 <0.01 0.8W, 0.8Nb 0.103 18 0.27 1.16 0.82 0.024
0.0016 26.1 25.6 3.05 0.35 0.50 0.01 <0.01 -- 0.111 19 0.24 1.74
1.29 0.019 0.0014 28.6 25.2 2.77 0.39 0.42 0.01 <0.01 -- 0.128
20 0.12 0.61 1.16 0.022 0.0012 24.9 27.1 2.58 0.48 0.40 0.01
<0.01 -- 0.066 21 0.11 0.97 1.12 0.018 0.0007 25.5 25.8 2.97
0.46 0.48 0.01 <0.01 0.035Y 0.099 22 0.15 0.96 0.52 0.022 0.0009
20.4 27.2 3.05 0.47 0.49 0.01 <0.01 -- 0.122 23 0.15 0.92 0.47
0.019 0.0007 18.5 25.7 3.11 0.48 0.52 0.01 <0.01 0.3Nb 0.129 24
0.06* 0.30* 1.20 0.021 0.0014 25.2 25.8 2.97 0.50 0.54 0.01
<0.01 0.002Ca 0.059 25 0.12 1.62 0.87 0.020 0.0002 23.6 27.9
3.11 0.31 0.44 0.01 <0.01 -- 0.152* 26 0.11 0.40* 0.63 0.017
0.0015 23.5 25.6 2.96 0.52 0.52 0.01 <0.01 0.001B, 0.02Nd 0.071
27 0.09 0.40* 0.63 0.051* 0.0004 24.3 26.7 3.00 0.82 0.43 0.01
<0.01 -- 0.070 28 0.17 0.87 1.14 0.021 0.0010 25.2 24.3 0.32*
0.32 0.37 0.01 <0.01 -- 0.007 29 0.21 0.68 1.21 0.018 0.0011
25.8 20.5 12.30* 0.44 0.06 0.02 0.04* 2.6W, 0.08Zr 0.382* 30 0.21
2.51* 1.27 0.019 0.0015 26.2 26.6 2.87 0.22 0.49 0.01 <0.01
0.003B, 0.003Ca 0.189 31 0.16 1.15 1.10 0.023 0.0230* 25.7 26.8
3.02 0.35 0.47 0.01 <0.01 1.3Mo 0.111 32 0.17 1.23 1.08 0.025
0.0022 25.5 25.9 2.74 <0.01* 0.56 0.01 <0.01 -- 0.108 33 0.15
1.04 0.63 0.024 0.0015 26.1 25.5 2.21 0.52 <0.01* 0.01 <0.01
0.004Mg, 0.5Hf 0.076 Note: *Mark indicates out of the scope of the
present invention.
TABLE-US-00002 TABLE 2 650.degree. C., 200 h, Restraint weld in 45%
CO--42.5% 650.degree. C., 10 h, in crack test H.sub.2--6.5% 30%
C.sub.3H.sub.6--70% (Number of CO.sub.2--6% H.sub.2O H.sub.2 gas
HAZ cracks)/ Presence of Presence of (Number of cross No. Pit or
not Pit or not sections observed) 1 Absent Absent 0/10 2 Absent
Absent 0/10 3 Absent Absent 0/10 4 Absent Absent 0/10 5 Absent
Absent 0/10 6 Absent Absent 0/10 7 Absent Absent 0/10 8 Absent
Absent 0/10 9 Absent Absent 0/10 10 Absent Absent 0/10 11 Absent
Absent 0/10 12 Absent Absent 0/10 13 Absent Absent 0/10 14 Absent
Absent 0/10 15 Absent Absent 0/10 16 Absent Absent 0/10 17 Absent
Absent 0/10 18 Absent Absent 0/10 19 Absent Absent 0/10 20 Absent
Absent 0/10 21 Absent Absent 0/10 22 Absent Absent 0/10 23 Absent
Absent 0/10 24 Present Present 6/10 25 Absent Absent 10/10 26
Present Present 0/10 27 Absent Present 0/10 28 Present Present 2/10
29 Absent Absent 5/10 30 Absent Absent 10/10 31 Absent Present 3/10
32 Present Present 0/10 33 Present Present 0/10
[0088] Table 2 indicates that, among Nos. 24 to 33 metal materials
in which the chemical composition deviates from the condition
specified in the present invention, Nos. 24, 26, 28, 32 and 33
metal materials had a pit formed after 200 hours had elapsed.
Therefore, the metal dusting resistance is poor in a synthetic gas
environment containing CO. On the other hand, in all of the metal
materials specified in the present invention, no pit is formed, and
therefore, these metal materials have excellent metal dusting
resistance.
Example 2
[0089] A metal material having a chemical composition given in
Table 1 was melted by using a high-frequency heating vacuum
furnace, and a metal plate having a plate thickness of 6 mm was
manufactured by hot forging and hot rolling. The metal plate was
subjected to solid-solution heat treatment at 1160 to 1230.degree.
C. for 5 minutes, a part of which was cut to produce a test piece.
From the metal material described in Table 1, a test piece
measuring 15 mm wide and 20 mm long was cut. This test piece was
isothermally maintained at 650.degree. C. in a 30%
C.sub.3H.sub.8-70% H.sub.2 (percent by volume) gas atmosphere. The
test piece was taken out after 10 hours had elapsed, and the
presence of a pit formed on the surface of test piece was examined
by visual observation and by optical microscope observation. The
results are summarized in Table 2.
[0090] Table 2 indicates that, among Nos. 24 to 33 metal materials
in which the chemical composition deviates from the condition
specified in the present invention, Nos. 24, 26 to 28, and 31 to 33
metal materials had a pit formed in the 10-hour test. Therefore,
the metal dusting resistance is poor in a hydrocarbon gas
environment. On the other hand, in all of the metal materials
specified in the present invention, no pit is formed, and
therefore, these metal materials have excellent metal dusting
resistance.
Example 3
[0091] A metal material having a chemical composition given in
Table 1 was melted by using a high-frequency heating vacuum
furnace, and two metal plates each having a plate thickness of 12
mm, a width of 50 mm, and a length of 100 mm was manufactured from
each metal material by hot forging and hot rolling. The metal
plates were subjected to solid-solution heat treatment at
1200.degree. C. for 5 minutes, a part of which was cut to produce a
test piece.
[0092] Then, on one side in the lengthwise direction of the test
piece, a V-type edge having an angle of 30 degrees and a root
thickness of 1.0 mm was prepared. Thereafter, the periphery of the
test pieces was restraint-welded onto a commercially available
metal plate of SM400C specified in JIS G3106 (2004) measuring 25 mm
thick, 150 mm wide, and 150 mm long by using a covered electrode of
DNiCrMo-3 specified in JIS Z3224 (1999). Subsequently, multi-layer
welds were made by TIG welding under a condition of heat input of 6
kJ/cm by using a TIG welding wire of YNiCrMo-3 specified in JIS
Z3334 (1999). After the aforementioned welding, ten test pieces for
observing the sectional microstructure of joint were cut from each
test piece, and the cross sections thereof were mirror polished and
corroded. Thereby, the presence of cracks in the HAZ was observed
by an optical microscope at .times.500 magnification. The results
are summarized in Table 2.
[0093] Table 2 indicates that in No. 24 metal material in which the
C content deviates from the condition specified in the present
invention and No. 25 metal material that does not satisfy
Expression (1), HAZ cracks are recognized. Also, it is indicated
that for Nos. 28 to 31 metal materials in which the Cu, Si and S
contents deviate from the condition specified in the present
invention though the C content meets the specified condition, the
HAZ crack restraining effect is small. On the other hand, in all of
the metal materials specified in the present invention, HAZ cracks
are not generated. Therefore, the weldability thereof is
excellent.
INDUSTRIAL APPLICABILITY
[0094] There is provided a metal material that has an effect of
restraining reaction between carburizing gas and the metal surface,
has excellent metal dusting resistance, carburization resistance,
and coking resistance, and further has improved weldability. This
metal material can be used for welded structure members of cracking
furnaces, reforming furnaces, heating furnaces, heat exchangers,
etc. in petroleum refining, petrochemical plants, and the like, and
can significantly improve the durability and operation efficiency
of apparatus.
* * * * *