Note: Descriptions are shown in the official language in which they were submitted.
CA 02711415 2010-07-02
DESCRIPTION
CARBURIZATION RESISTANT METAL MATERIAL
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 C, which is relatively low, has become
important, and
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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 H2, CO, CO2, H2O, 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 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
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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 C containing H2,
CO, CO2
and H2O. 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.
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[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 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 C containing H2, CO, CO2 and H2O. 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 Q 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]
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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 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
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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 H2S into the atmospheric gas has been thought of.
However, the application of this method is restricted because H2S 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 0 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
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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.
[0020]
[Patent Document I] 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 i 1-29776A
[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] JP 1-2103 8A
[Patent Document 15] JP2-170946A
[Patent Document 16] JP4-346638A
Disclosure of the Invention
Problems to be Solved by the Invention
[0021]
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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.
[0022]
Also, there is a method for restraining metal dusting by adding H2S 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 H2S 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.
[0023]
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
[0024]
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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).
[0025]
(a) Gas molecules consisting of C compounds such as hydrocarbon and CO
approach the metal surface.
[0026]
(b) The approaching gas molecules are dissociatively adsorbed onto the metal
surface.
[0027]
(c) The dissociated atomic carbon intrudes into the metal and diffuses.
[0028]
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.
[0029]
(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.
[0030]
(e) The dissociative adsorption of the gas molecules consisting of C compounds
is
restrained on the metal surface.
[0031]
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.
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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.
[0032]
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.
[0033]
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.
[0034]
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
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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.
[0035]
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).
[0036]
(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.
[0037]
(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.
[0038]
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.
[0039]
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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.
[0040]
C ? 0.062xSi + 0.033xCu - 0.004xCr+ 0.043 ... (1)
in which the symbol of element in Expression (1) represents the content of
that element
in mass%.
[0041]
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.
[0042]
(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 0 (oxygen): 0.02% or less , the
balance
being Fe and impurities, and satisfying Expression (1).
[0043]
C ? 0.062xSi + 0.033xCu - 0.004xCr + 0.043 ... (1)
in which the symbol of element in Expression (1) represents the content of
that element
in mass%.
[0044]
(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%
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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 0 (oxygen): 0.02% or less , the
balance
being Fe and impurities, and satisfying Expression (1).
[0045]
C >_ 0.062xSi + 0.033xCu - 0.004xCr + 0.043 ... (1)
in which the symbol of element in Expression (1) represents the content of
that element
in mass%.
[0046]
(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
[0047]
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
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petroleum refining, petrochemical plants, and the like, and can significantly
improve the
durability and operation efficiency of apparatus.
[0048]
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 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
[0049]
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%".
[0050]
C: 0.08 to 0.4%
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.
[0051]
Si: 0.6 to 2.0%
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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 Cr203, 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%.
[0052]
Mn: 0.05 to 2.5%
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%.
[0053]
P: 0.04% or less
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
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
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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.
[0055]
Cr: 18 to 30% or 22 to 30%
Cr (chromium) forms oxide scale such as Cr2O3 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%.
[0056]
Ni: 20% or higher and less than 30%
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
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22.5% or higher and less than 30%. Further preferably, the content of Ni is
higher
than 25% and 29.5% or less.
[0057]
Cu: 0.5 to 10.0%
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%.
[0058]
Al: 0.01 to 1%
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%.
[0059]
Ti: 0.01 to 1%
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
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CA 02711415 2010-07-02
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%.
[0060]
N: 0.15% or less
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.
[0061]
0: 0.02% or less
O (oxygen) is an impurity element mingled from a raw material or the like when
the metal material is melted . If the 0 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 0
content is
set at 0.02%.
[0062]
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.
[0063]
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CA 02711415 2010-07-02
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 H
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, Cc: 0.15% or less, and Nd:
0.15% or
less.
[0064]
Next, these optionally added elements are explained.
[0065]
First group (Co: 10% or less, by mass%)
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%.
[0066]
Second group (Mo: 2.5% or less and W: 5% or less, by mass%)
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
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CA 02711415 2010-07-02
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%.
[0067]
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%)
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%.
[0068]
Fourth group (Mg: 0.1% or less and Ca: 0.1% or less, by mass%)
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
-20-
CA 02711415 2010-07-02
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 %.
[0069]
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%)
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%.
[0070]
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.
[0071]
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.
-21-
CA 02711415 2010-07-02
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.
[0072]
Next, the present invention is explained in more detail with reference to
examples.
The present invention is not limited to these examples.
[Example 1]
[0073]
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 C for 5
minutes, a part of
which was cut to produce a test piece .
[0074]
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 C
in a
45%CO-42.5%H2-6.5%CO2-6%H20 (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.
-22-
CA 02711415 2010-07-02
[0075]
[Table 1]
48
y p ON O T .-+ .--~ h O 00 t - h M M t-, m ON ON M .-+ oo ~o m N as Ol O N. a
'-. oo \D
C' 00 .-+ M rn t` O b m 7 N M t` O --~ N rn N NW) N l~ l~ O N 00 .-~ O N
O O O -I 0 0 0 0 -I O -! '-. O O -+ O D O O M . . .--= O
,.q 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 d 0 0 0 Co
0 0 0 0
N
N
CO O
M M "C U
U G N cn NO N w MO
~OO.o , o0 0 00
UU Z U.`~7 'IT 00 MN ~+ U. ~ e N
M O 3 m.4 0
O O O M O .-+ O O O
O O o .-: .-+ Co O 7 N O O M 00 O M O O \D O M O
O O O 0 0 0 0 C. C. h Co . . . O 0 0 . O . N O =--~ . O
O O O cOi 0 0 0 0 0 cO O O O O O 0 0 0 0 0 0 0 0 0 d' O O O
O v v O v v v v v v V v v v v VQ v v v v v v c v v v v
0 0 0 0 0 0 .--~ O O O O O O O O O O O O O O O O . 0 0 O O o 0
O 0 O O O O O O O C. 0 O O O C. O O O O 0 O O O O O O O O O O O O O
b l~ d' O b N M %n tN \O m ON to N In %D O N O co ON N N M N \D v, t` ~o ,--.
Cy' Eõy Vl Vl V d: ~t =--~ O N M ti: m M h vl v) 7 Vl h cr d: 7 Vl vl u> d:
c/1 O rt V vl O
0 0 0 0 0 0 0 0 co c:,, C> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
au *
01 00 b vt t, m N ~O O N vt O', 00 N 'D in O', 00 'D N 00 O -+ N N N N ,n ^' N
y d <} m Cpl O O d rn m m 00 !~ (~ M ci d d V f M V 00 m N en o vl
.O Q O O O O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Co Co 0 0 0 0 0 0 0 0 0 0 V 0
N Vl I 00 iD - N 00 vn N I- N vl t- 00 N v) .-+ t, .-+ ~D O * O N N V
CO U 01 Qi [` O .--~ b <J: v) O~ 00 7 N N b ~D M O [~ V1 01 O 01 .--~ O~ O 11
M w O r-
' N N N M N 't - N . ~ N .-= O Cn N m m N N N M M N m N m O N N M N N
N O, Cl ~O d: ~D "D t~ t` O 00 C9 wi "t h N -I 00 N t` 00 0\ ` m Ut oo Q\ q
vt .n
z vn rn 'n vi 0o V ri h vl b Oi A N t-- vt vt l-- vi t- vt vn t- W) C.
"~. N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N CN1 N N
O
U V1 V1 D? m N -----
: O a N N N N N N N N N '+ N N N N N N N N N N
_O O N ~D +-. N 7 _h m C. O N M vl -+ O N 7D N N O= N .fir N on d' _O ,:: n *
N vl "
cn O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O m O O 6.
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
C. O O O O O O O O O O O O O o O O 0 O O O O O 0 0 0 O O O O O O O
o O
Ol N N l- h M ~D v1 =--~ 01 d' 01 N 00 N O~ =-~ O l, 00 rn m vl V 2.
N N N N N '- O .--+ N m N O N N- N N N N N N N N o
~ w o o 0 0 0 0 0 0 0 0 0 0 0 0 o o o o O o o O o o O o
Id 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 o O o 0 0 0 0 0 0 0 0
H Y
m co Ut d' N 00 tN d' ct 00 0' N N I:t 00 N O\ \O N N N O N m M 7 t~ O 00 M p
N O, ON O M N 00 N - .--= vl V: N 00 'o 'o
N
~O \O 00 N V'1 N v) on ~' M %D O1 l~ d <t O~ ~D d t- 'D N N * * t- oo ',~ In
M Ct N
.--~ .-. O\ 0 (71 10 =O .-. O -. --. a0 00 O\ . . 0 . O~ Oti Oi 'D 00 'O N 2
O
=-~ .--~ =-~ O O -00 ) . -~ ~ 0 0 0 0 '~ '-' .--~
00 00 .~ lD M V) O N ~D 00 N N V"7 h * N O\ N .~ ~D l~ ./'1
N N .-. .- ~ .--i .. .. C =-+ N N --. ,-. .--~
O O O O O O C. O O 0 O O 0 O O O O O O 0 O O O O O o O CD O O o O O*
kn 10 0 N m h [~ oo O~ O N M V t` oo N N N N N N N N N 00 N m M m
0
z
-23-
CA 02711415 2010-07-02
[0076]
[Table 2]
Table 2
650 C, 200h, 650 C, 10h, Restraint weld crack test
No. in 45%CO-42.5%H2-6,5%C02-6%H20 in 30%C3H6-70%H2 gas
o.
Presence of Pit or not Presence of Pit or not (Number of HAZ cracks)
(Number of cross sections observed)
1 Absent Absent 0/10
2 Absent Absent 0/10
3 Absent Absent 0/10
4 Absent Absent 0/10
Absent Absent 0/10
6 Absent Absent 0/10
7 Absent Absent 0/10
8 Absent Absent 0/10
9 Absent Absent 0/10
Absent Absent 0/10
11 Absent Absent 0/10
12 Absent Absent 0/10
13 Absent Absent 0/10
14 Absent Absent 0/10
Absent Absent 0/10
16 Absent Absent 0/10
17 Absent Absent 0/10
18 Absent Absent 0/10
19 Absent Absent 0/10
Absent Absent 0/10
21 Absent Absent 0/10
22 Absent Absent 0/10
23 Absent Absent 0/10
24 Present Present 6/10
Absent Absent 10/10
26 Present Present 0/10
27 Absent Present 0/10
28 Present Present 2/10
29 Absent Absent 5/10
Absent Absent 10/10
31 Absent Present 3/10
32 Present Present 0/10
33 Present Present 0/10
[0077]
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
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CA 02711415 2010-07-02
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]
[0078]
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 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 C in a 30%C3H8-70%H2 (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.
[0079]
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]
[0080]
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
-25-
CA 02711415 2010-07-02
solid-solution heat treatment at 1200 C for 5 minutes, a part of which was cut
to produce
a test piece.
[0081]
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 x500 magnification. The results are
summarized in Table 2.
[0082]
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
[0083]
-26-
CA 02711415 2010-07-02
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.
-27-
