DESCRIPTION
WELDING MATERIAL FOR NI-BASED HEAT RESISTANT ALLOY, AND WELD
METAL AND WELDED JOINT FORMED USING THE SAME
TECHNICAL FIELD
[OOOl]
The present invention relates to a welding material for Ni-based heat resistant
alioy, and a weld metal and a welded joint formed using the welding material, in more
detail relates to a welding material that is suitable for welding a Ni-based heat resistant
alloy utihized for equipment operated at high temperatures such as a power generation
boiler, and a weld metal and a welded joint obtained by utilizing the welding material.
BACKGROUND ART
[0002]
In recent years, from the viewpoint of reducing environmental loads, higher
temperature/pressure conditions for operating power generation boilers and the like have
been promoted on a worldwide scale, and a material used therefor is required to have
more excellent high-temperature strengths.
[0003]
For example, materials meeting such a demand include a Ni-based heat resistant
alloy defined as UNS06617. In addition, Patent Documents 1 to 5 disclose various Nibased
alloys. These all define many different alloying element ranges, in order to satisfy
performances necessary for a base metal.
[0004]
Meanwhile, when these Ni-based heat resistant alloys are used for structures, the
structures are typically assembled by welding, and as a welding material for Ni-based
heat resistant alloy used therefor, "AWS A5.14-2009 ER NiCrCoMo-1" has already been
available.
[0005]
Furthermore, Patent Document 6 proposes a welding material for Ni-based alloy
that achieves high strengthening by taking advantage of solid-solution strengthening by
Mo and W and a precipitation strengthening effect by A1 and Ti. In addition, Patent
Document 7 proposes a welding material that secures creep strength by similarly taking
advantage of a precipitation strengthening effect by A1 and Ti and has high-speed
weldability by homogeneously dispersing M6C carbide and MC carbide in the welding
material.
[0006]
Now, welded structures formed using these Ni-based heat resistant alloys and
welding materials for Ni-based heat resistant alloy are used at high temperatures, but there
is a problem in that a cracking (a stress relaxation cracking) occurs in a welded zone in
long-term and high-temperature use.
[0007]
On that account, Patent Document 8 proposes a welding material that secures
stress relaxation cracking resistance by adjusting the contents of Al and Mo within
appropriate ranges and achieves the prevention of solidification cracking by defining the
contents of C and Cr.
LIST OF PRIOR ART DOCUMENTS
PATENT DOCUMENT
[OOOS]
Patent Document 1: US4877461A
Patent Document 2: US4765956A
Patent Document 3: US5372662A
Patent Document 4: JP9-157779A
Patent Document 5: JP2001-073053A
Patent Document 6: WO 2010/013565
Patent Document 7: WO 20071119847
Patent Document 8: JP2012-000616A
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0009]
A welding material for Ni-based heat resistant alloy, or "AWS A5.14-2009 ER
NiCrCoMo-1", and the welding materials for Ni-based alloy disclosed in Patent
Documents 6 to 8, which are described above, indeed satisfy given performances that are
the respective objectives. However, in multi-layer welding, in particular when the
multi-layer welding is performed with a low heat input to prevent hot cracking in welding
such as solidification cracking, it has been found that these welding materials exhibit poor
weldability in fabrication and are prone to cause a so-called "lack of fusion", one of the
welding defects, raising usability problems.
[OOl 01
An objective of the present invention is to provide a welding material for Nibased
heat resistant alloy having an excellent weldability in fabrication and a weld metal,
formed using the welding material, that has an excellent creep strength at high
temperatures and an excellent stress relaxation cracking resistance while in use.
Furthermore, another objective of the present invention is to provide a welded joint that
is formed of a weldmetal formed using this welding material and a base metal having an
excellent creep strength at high temperatures.
MEANS FOR SOLVING THE PROBLEMS
[OOll]
The present inventors conducted detailed researches to solve the problems.
Specifically, the present inventors conducted detailed researches on lack of fusion that
occurred in a welded joint, and consequently the matters described as the following (a)
and (b) were clarified.
[OO 121
(a) The lack of fusion occurred on the boundary between a preceding bead and
a succeeding bead in multi-layer welding.
(b) In the portion where the lack of fusion occurred, welding slag remained that
contained Al and Si.
[0014]
In addition, the present inventors conducted detailed observation of welding
phenomena, and consequently the matter described as the following (c) was clarified.
[00 151
(c) Welding slag is formed by reaction in a molten pool and also formed by the
agglomeration of oxides that remains on a welding material surface and migrates on the
surface of the molten pool with the melting of welding material.
[0016]
From the matters (a) to (c) described above, the present inventors estimated that
a lack of fusion occurs for the following reason described as (d).
[0017]
(d) Oxides agglomerate in welding to remain on a weld bead in the form of
welding slag, the oxides including those formed by the reaction in a molten pool between
Al, Si, and the like, and oxygen (O), and those of A1 and Si remaining on a weldmg
material surface in producing the welding material. When welding is performed on the
bead in a succeeding pass, the welding slag cannot be melted sufficiently, particularly in
low heat input welding, because the welding slag has high melting points, resulting in a
lack of fusion.
[00 181
On the basis of the estimation described above, the present inventors conducted
studies on preventing lack of fusion. Consequently, the matter described as the
following (e) was clarified.
[0019]
(e) It is effective in preventing lack of fusion to reduce oxides formed by
deoxidation reaction in a molten pool and to reduce an oxide layer present on a welding
material surface, specifically, to reduce the contents of Al, Si, and oxygen (0) in a welding
material, as well as to control the thickness of the oxide layer remaining on the welding
material surface.
[0020]
Note that, for the Ni-based heat resistant welding material that is the subject of
the present invention, it is effective in securing stress relaxation cracking resistance to
reduce the content of A1 because A1 considerably increases stress relaxation cracking
susceptibility in long-term use at high temperatures. However, A1 precipitates in the
form of an intermetallic compound in a weld metal in long-term use, and is an essential
element for securing creep strength in the Ni-based heat resistant welding material
described above.
[0021]
Hence, the present inventors further proceeded with the detailed studies, and
consequently the following matters (f) and (g) were clarified.
[0022]
(f) Adjusting the contents of Al, Si, and 0 and controlling the contents of Ni, Co,
Cr, Mo, and Mn within appropriate ranges are effective in preventing lack of fusion
described in (e) above, and also effective in delaying the start time of precipitation of the
intermetallic compound without reducing the amount of the intermetallic compound.
[0023]
(g) By controlling the contents of Al, Si, 0 , Ni, Co, Cr, Mo, and Mn described
above, as well- as the contents of C, P, S, Ti, and N within predetermined ranges, and by
sett:ng the thickness of an oxide layer on a welding material surface at 30 pm or less, it
is possible to prevent lack of fusion through securing excellent weldability in fabrication
during welding, and further to provide both of a good stress relaxation cracking resistance
and an excellent creep strength in long-term use at high temperatures. Specifically, it is
necessary to determine the chemical composition of the welding material as, by mass%,
C: 0.08 to 0.12%; Si: 0.10% or less; Mn: 0.02 to 1.50%; P: 0.008% or less; S: 0.002% or
less; Ni: more than 56.0% and 60.0% or less; Co: 8.0 to 12.0%; Cr: 18.0 to 22.0%; Mo:
6.0 to 10.0%; Ti: 0.01 to 0.50%;Al: 0.50 to 1.00%; 0 : 0.010% or less; andN: 0.010% or
less, with the balance: Fe and impurities. Through the adjustment of the chemical
composition described above and the thickness adjustment of the oxide layer on the
surface, it is possible to obtain a Ni-based heat resistant welding material that secures
weldability in fabrication, as well as the creep strength and the stress relaxation cracking
resistance properties of the weld metal.
[0024]
Then, with the welding material for Ni-based heat resistant alloy satisfying (g)
described above, it is possible to obtain a weld metal and a welded joint that is formed of
a base metal of a Ni-based heat resistant alloy, the weld metal having stress relaxation
cracking resistance and an excellent creep strength in high-temperature use, the base
metal being excellent in high temperature strength.
[0025]
The present invention has been made based on the findings described above, and
the gist of the present invention is a welding material for Ni-based heat resistant alloy, a
weld metal, and a welded joint, described as follows.
[0026]
(1) A welding material for Ni-based heat resistant alloy having a chemical
composition consisting, by mass%, of:
C: 0.08 to 0.12%,
Si: 0.10% or less,
Mn: 0.02 to 1.50%,
P: 0.008% or less,
S: 0.002% or less,
Ni: more than 56.0% to 60.0% or less,
Co: 8.0 to 12.0%,
Cr: 18.0 to 22.0%,
Mo: 6.0 to 10.0%,
Ti: 0.01 to 0.50%,
Al: 0.50 to 1.00%,
N: 0.010% or less,
0: 0.010% or less,
Nb: 0 to 0.50%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
REM: 0 to 0.20%, and
the balance: Fe and impurities, wherein
a thickness of an oxide layer formed on the surface of the welding material is 30
pm or less.
[0027]
(2) The welding material for Ni-based heat resistant alloy according to (I),
wherein
the chemical composition contains one or more elements selected from, by
mass%:
Co: 9.0 to 11.0%,
Cr: 19.0 to 21.0%, and
Mo: 7.0 to 9.0%.
[0028]
(3) The weldingmaterial for Ni-based heat resistant alloy according to (1) or (2),
wherein
the chemical composition contains one or more elements selected from, by
mass%:
Nb: 0.01 to 0.50%,
B: 0.0002 to 0.0050%,
Ca: 0.0005 to 0.050%,
Mg: 0.0005 to 0.050%, and
REM: 0.01 to 0.20%.
[0029]
(4) The welding material for Ni-based heat resistant alloy according to any one
of (1) to (3), wherein
the chemical composition satisfies a following formula (i):
wherein each symbol of an element in the formula denotes the content of each
element (mass%) in welding material.
[0030]
(5) A weld metal comprising the welding material for Ni-based heat resistant
alloy according to any one of (1) to (4).
[003 11
(6) A welded joint comprising the weld metal according to (5) and a base metal
of a Ni-based heat resistant alloy.
[0032]
(7) The welded joint according to (6), wherein
the base metal has a chemical composition comprising, by mass%:
Ni: 41.0 to 60.0%,
Cr: 18.0 to 25.0%, and
one or more elements of Mo and W: 6.0 to 10.0% in total.
[0033]
(8) The welded joint according to (7), wherein
the base metal has a chemical composition consisting, by mass%, of:
C: 0.04 to 0.12%,
Si: 1.00% or less,
Mn: 1.50% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 41.0 to 60.0%,
Co: 15.0% or less,
Cr: 18.0 to 25.0%,
one or more elements of Mo and W: 6.0 to 10.0% in total,
Ti: 0.01 to 0.50%,
Nb: 0.50% or less,
N: 0.010% or less,
B: 0.0050% or less,
Al: 1.50% or less, and
the balance: Fe and impurities.
ADVANTAGEOUS EFFECTS OF THE INVENTION
[0034]
According to the present invention, it is possible to provide a welding material
for Ni-based heat resistant alloy having an excellent weldability in fabrication and to
provide a weld metal, formed using the welding material, that has an excellent creep
strength at high temperatures and an excellent stress relaxation cracking resistance while
in use. Furthermore, it is also possible to provide a welded joint that is formed of the
weld metal including this welding material and a base metal having an excellent creep
strength at high temperatures.
MODE FOR CARRYING OUT THE INVENTION
[0035]
In the present invention, the reasons for limiting the requirements for the
composition of a welding material for Ni-based heat resistant alloy are as follows. Note
that "%" for the content of each element in the following description represents "mass%".
[0036]
(A) Chemical Composition of Welding Material for Ni-Based Heat Resistant
Alloy
C: 0.08 to 0.12%
C (carbon) is an element effective in increasing creep strength because C
increases the structural stability of weld metal in high-temperature use and precipitates in
the form of carbides in long-term use. Therefore, the content of C has to be 0.08% or
more. However, excessively contained C causes carbides to precipitate coarsely,
resulting in a decrease in creep strength instead. For this reason, the content of C is 0.08
to 0.12%. The content of C is desirably 0.09% or more, and desirably 0.11% or less.
[0037]
Si: 0.1 0% or less
6
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: 3
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; '
Si (silicon) is contained as a deoxidizer and reacts with oxygen in a molten pool
in welding to form oxides. The oxides remain on the surface of a bead in the form of
welding slag together with oxides that have been present as oxides on a welding material
surface and migrate to the molten pool with the melting of weldmg material. This
welding slag does not melt by welding in the succeeding pass, becoming a cause of lack
of fusion. For this reason, it is necessary to set the content of Si at 0.10% or less. The
content of Si is desirably 0.08% or less. The lower limit of the content of Si is not
specially provided because the smaller the content of Si is, the better. However, if the
content of Si is excessively reduced, the deoxidation effect becomes insufficient, and the
index of cleanliness of an alloy increases, which means the cleanliness of the alloy
decreases, leading to a rise in producing costs of the welding material. For this reason,
the content of Si is desirably 0.005% or more, and more desirably 0.01% or more.
[0038]
Mn: 0.02 to 1.50%
As in the case of Si, Mn (manganese) is contained as a deoxidizer. Mn also
contributes to securing creep strength, and thus the content of Mn has to be 0.02% or
more. However, it is necessary to set the content of Mn at 1.50% or less because
excessively contained Mn leads to embrittlement. The content of Mn is desirably 0.05%
or more and is desirably 1.20% or less.
[0039]
Note that, in order to prevent lack of fusion, it is preferable to adjust the content
of Mn in the welding material appropriately in accordance with the content of Al, which
will be described later. This reason seems to be as follows. Mn has a high vapor
pressure as compared with the other alloying elements, therefore evaporates fiom the
surface of the molten pool in weldmg, and ionizes to form an energizing channel of an
arc, increasing the current density, which provides the effect of increasing the temperature
immediately below an arc. Then, Mn consequently exerts the effect of efficiently
dissolving the welding slag that remains in a preceding pass. In particular, the more the
content of A1 is, the more the welding slag remains in the preceding pass, and thus it is
preferable to take advantage of this effect of Mn. For this reason, it is desirable to
contain Mn such that the content of Mn satisfies the following formula (i) in accordance
with the amount ofAl contained in the welding material.
Mn> 0.2 x A1 - 0.1 (i)
Note that each symbol of an element in the formula denotes the content of each
element (mass%) in welding material.
[0040]
P: 0.008% or less
P (phosphorus) is contained as an impurity and is an element that considerably
increases solidification susceptibility during welding and even increases the stress
relaxation cracking susceptibility of weld metal in high-temperature use. For this reason,
it is necessary to set the content of P at 0.008% or less. The content of P is desirably
0.007% or less. The lower limit of the content of P is not specially provided because the
less the content of P is, the more preferable it is, but an excessive reduction of the content
of P leads to a rise in producing costs. For this reason, the content of P is desirably
0.0005% or more, and more desirably 0.001% or more.
[0041]
S: 0.002% or less
As in the case of P, S (sulfur) is contained as an impurity and is an element that
considerably increases solidification cracking and stress relaxation cracking
susceptibilities. For this reason, it is necessary to set the content of S at 0.002% or less.
The content of S is desirably 0.0015% or less. The lower limit of the content of S is not
specially provided because the less the content of S is, the preferable it is, but an excessive
reduction of the content of S leads to a rise in producing costs. For this reason, the
content of S is desirably 0.0002% or more, and more desirably 0.0005% or more.
[0042]
Ni: more than 56.0% to 60.0% or less
Ni (nickel) is an element that secures the structural stability of the weld metal in
long-term use, contributing to securing creep strength. In addition, Ni is also an element
that has an influence on driving force for precipitation of intermetaklic compounds
containing A1 and has an indirect influence on the creep strength and stress relaxation
cracking susceptibility of the weld metal. In order to secure a required creep strength
and stress relaxation cracking resistance within the ranges of the other alloying elements
in the present invention, it is necessary to set the content of Ni at more than 56.0% and
60.0% or less. The content of Ni is desirably 57.0% or more and is desirably 59.0% or
less.
[0043]
Co: 8.0 to 12.0%
As in the case of Ni, Co (cobalt) is an element that secures the structural stability .-
in long-term use, contributing to securing creep strength. In addition, Co is also an
." . . element that has an influence on driving force for precipitation of intermetallic .. ..
compounds containing A1 and has an indirect influence on the creep strength and stress ,.:
relaxation cracking susceptibility of the weldmetal. In order to secure an essential creep
strength and stress relaxation cracking resistance within the ranges of the other alloying .:
elements in the present invention, it is necessary to set the content of Co at 8.0 to 12.0%. . ,
The content of Co is desirably 9.0% or more and is desirably 11.0% or less.
[0044]
Cr: 18.0 to 22.0%
Cr (chromium) is an element that is essential for securing the oxidation
resistance and corrosion resistance of the weld metal at high temperatures. In addition,
Cr is also an element that has an influence on driving force for precipitation of
intermetallic compounds containing A1 and has an indirect influence on the creep strength
and stress relaxation cracking susceptibility of the weld metal. However, excessively
contained Cr causes structural stability at high temperatures to decrease, leading to a
decrease in creep strength. In order to secure required performances within the ranges
of the other alloying elements in the present invention, it is necessary to set the content
of Cr at 18.0 to 22.0%. The content of Cr is desirably 19.0% or more and is desirably
2 1.0% or less.
[0045]
Mo: 6.0 to 10.0%
Mo (molybdenum) is an element that considerably contributes to enhancing the
creep strength of the weld metal by being dissolved in a matrix. In order to secure the
effect sufficiently, it is necessary to contain 6.0% or more of Mo. However, Mo has an
influence on driving force for precipitation of intermetallic compounds containing Al,
and within the ranges of the other alloying elements in the present invention, excessively
contained Mo rather causes the creep strength to decrease and causes the stress relaxation
cracking resistance to decrease. For this reason, the content of Mo is 10.0% or less.
The content of Mo is desirably 7.0% or more and is desirably 9.0% or less.
[0046]
Ti: 0.01 to 0.50%
Ti (titanium) combines with Ni to precipitate finely in grains in the form of an
intermetallic compound, contributing to enhancing the creep strength of the weld metal.
To obtain the effect, it is necessary to set the content of Ti at 0.01% or more. However,
excessively contained Ti leads to an excessive precipitation of intermetallic compound
phases, increasing the stress relaxation cracking susceptibility of the weld metal. For
this reason, the content of Ti is 0.50% or less. The content of Ti is desirably 0.05% or .
more and is desirably 0.40% or less.
[0047]
Al: 0.50 to 1.00%
A1 (aluminum) is contained as a deo-xidizer. Al combines with Ni to precipitate
finely in grains in the form of an intermetallic compound, and is an element also effective
for securing the creep strength of the weld metal. On the other hand, excessively
contained A1 leads to an excessive precipitation of intermetallic compound phases,
increasing stress relaxation cracking susceptibility. Additionally, A1 reacts with oxygen
in the molten pool in welding to form its oxide. The oxides remain on the surface of a
bead in the form of welding slag together with oxides that have been present as oxides on
a welding material surface and migrate to the molten pool with the melting of welding
material, causing a lack of fusion. In order to, within the ranges of the other alloying
elements in the present invention, secure a required creep strength and stress relaxation
cracking resistance as well as to achieve the prevention of a lack of fusion owing to an
excellent weldability in fabrication, it is necessary to set the content of Al at 0.50 to 1.00%.
The content of Al is desirably 0.60% or more and is desirably 0.90% or less.
100481
N: 0.010% or less
N (nitrogen) is an element that contributes to enhancing the structural stability
of the weld metal, but excessively contained N causes nitrides to precipitate in large
quantity in high-temperature use, leading to a decrease in the ductility and toughness of
the weld metal. For this reason, it is necessary to set the content of N at 0.010% or less.
The content of N is desirably 0.008% or less. Although there is no special need to
provide the lower limit of the content of N, an extreme decrease in the content of N leads
to a rise in the producing costs of the welding material, and thus the content of N is
desirably 0.0005% or more.
[0049]
0: 0.010% or less
0 (oxygen) is contained as an impurity and reacts with elements having strong
affinities, such as Al and Si, in the molten pool in welding to form oxides. These oxides
remain on the surface of a bead in the form of welding slag together with oxides that have
been present as oxides on a welding material surface and migrate to the molten pool with
the melting of welding material, causing a lack of fusion. For this reason, it is necessary
to set the content of 0 at 0.010% or less. The content of 0 is desirably 0.008% or less.
The lower limit of the content of 0 is not specially provided because the less the content
of 0 is, the better it is, but an excessive reduction of the content of S leads to a rise in
producing costs. For this reason, the content of 0 is desirably 0.0005% or more, and
more desirably 0.001% or more.
[0050]
Nb: 0 to 0.50%
Nb (niobium) combines with Ni to precipitate in the form of an intermetallic
compound or combines withcarbon and nitrogen to precipitate in the form of a fine carbonitride,
contributing to the enhancement of the creep strength of the weld metal. For this
reason, Nb may be contained to obtain the effects described above. However,
excessively contained Nb leads to an excessive precipitation of the intermetallic
compound and the carbo-nitride, increasing the stress relaxation cracking susceptibility
of the weld metal. For this reason, the amount of Nb is 0.50% or less if contained. The
content of Nb is desirably 0.40% or less.
[0051]
In order to obtain the effects of Nb stably, the content of Nb is desirably 0.01%
or more, and more desirably 0.05% or more.
[0052]
B: 0 to 0.0050%
In the weld metal, B (boron) segregates on grain boundaries in high-temperature
use so as to strengthen the grain boundaries and subjects grain boundary carbides to fme
dispersion, and is an element effective in enhancing creep strength. For this reason, B
may be contained to obtain the effects described above. However, containing a large
quantity of B considerably increases solidification susceptibility. For this reason, the
amount of B is 0.0050% or less if contained. The content of B is desirably 0.0040% or
less.
[0053]
In order to obtain the effects of B stably, the content of B is desirably 0.0002%
or more, more desirably 0.0005% or more.
[0054]
Ca: 0 to 0.050%
Ca (calcium) improves the hot workability of the alloy, enhancing the
productivity of the welding material. For this reason, Ca may be contained to obtain this
effect. However, when Ca is excessively contained, Ca combines with oxygen in
welding to generate welding slag, causing a lack of fusion. For this reason, the amount
of Ca is 0.050% or less if contained. The content of Ca is desirably 0.020% or less.
[0055]
In order to obtain the effects of Ca stably, the content of Ca is desirably 0.0005%
or more, more desirably 0.001% or more.
[0056]
Mg: 0 to 0.050%
As in the case of Ca, Mg (magnesium) improves the hot workability of the alloy,
increasing the productivity of the welding material. For this reason, Mg may be
contained to obtain this effect. However, when Mg is excessively contained, Mg
combines with oxygen in welding to generate welding slag, causing a lack of fusion. For
this reason, the amount of Mg is 0.050% or less if contained. The content of Mg is
desirably 0.020% or less.
[0057]
In order to obtain the effects of Mg stably, the content of Mg is desirably
0.0005% or more, more desirably 0.001% or more.
[0058]
REM: 0 to 0.20%
As in the cases of Ca and Mg, REM improves the hot workability of the alloy,
increasing the productivity of the welding material. For this reason, REM may be
contained to obtain this effect. However, when REM is excessively contained, REM
combines with oxygen in welding to generate welding slag, causing a lack of fusion. For
this reason, the amount of REM is 0.20% or less if contained. The content of REM is
desirably 0.10% or less.
[0059]
In order to obtain the effects of REM stably, the content of REM is desirably
0.01% or more, and more desirably 0.02% or more.
[0060]
Note that the term "REM" is a generic term for Sc, Y, and lanthanoids, 17
elements in total, and "the content of REM" refers to the total content of one, or two or
more elements selected from REM. In addition, REM is typically contained in the form
of misch metal. For this reason, the REM may be contained, for example, in the form
of misch metal such that the amount of REM falls within the range described above.
[0061]
As to the welding material for Ni-based heat resistant alloy according to the
present invention, the chemical composition includes the elements mentioned above, and
the balance of Fe and impurities. The term "impurities" herein means components that
are mixed in steel in producing the steel industrially due to various factors including raw
materials such as ores and scraps, and a producing process, and are allowed to be mixed
in the steel within ranges in which the impurities have no adverse effect on the present
invention.
[0062]
(B) Oxide Layer Thickness Existing on Surface of Welding Material for Ni-
Based Heat Resistant Alloy
Oxides present on a welding material surface migrate to a molten pool with the
melting of the welding material and, particularly when the thickness of the oxides present
on the welding material surface exceeds 30 pm, remain on the surface of a head in the
form of welding slag together with oxides formed by reaction in welding. These oxides
have high melting points and do not melt in welding of a succeeding pass, thus causing a
lack of fusion. For this reason, it is necessary to set the thickness of the oxides on the
welding material surface at 30 pm or less. Note that the smaller the thickness of an
oxide layer existing on the welding material surface is, the more preferable.
[0063]
For example, in producing the welding material, performing heat treatment in
reducing gas such as hydrogen prevents the oxidation of the surface, enabling the oxide
layer thickness on the welding material surface to be adjusted to 30 pm or less. In
addition, in producing the welding material, in the case where an oxide layer (oxide
scales) is formed on the surface by heat treatment performed in the atmosphere or
combustion gas, mechanical removal through treatment such as pickling, grinding, and
abrading enables the oxide layer thickness on the welding material surface to be adjusted
to 30 pm or less.
[0064]
The welding material for Ni-based heat resistant alloy according to the present
invention has been described above in detail, and the use of the welding material for Nibased
heat resistant alloy described above can provide an excellent weldability in
fabrication. Then, using this welding material, it is possible to obtain a weld metal that
is excellent in stress relaxation cracking resistance and creep strength in high-temperature
use. Furthermore, using this welding material, it is possible to obtain a welded joint that
is formed of a weld metal having the properties described above and a base metal of a Nibased
heat resistant alloy excellent in high temperature strength.
[0065]
(C) Chemical Composition of Base Metal of Ni-Based Heat Resistant Alloy
In obtaining a welded joint using the welding material for Ni-based heat resistant
alloy described above, the use of a Ni-based heat resistant alloy, as the base metal,
containing Ni: 41.0 to 60.0%, Cr: 18.0 to 25.0%, and one or more elements of Mo and W:
6.0 to 10.0% in total and being excellent in high temperature strength allows the base
metal to have an excellent ductility and creep strength in a high-temperature range, which
is preferable.
[0066]
When a Ni-based heat resistant alloy excellent in high temperature strength is
used as a base metal, the base metal preferably has the chemical composition described
above. The reason for this will be described below.
[0067]
Ni: 41.0 to 60.0%
Ni stabilizes a metal micro-structure at high temperatures, and is an element
effective in securing creep strength. For the base metal, there is no need to consider a
lack of fusion, which raises an issue in the weld metal, and thus it is desirable for the base
metal to contain 41.0% or more of Ni, to obtain the effect. However, since Ni is an
expensive element, the use of it in large quantity leads to a rise in costs. For this reason,
the upper limit of the content of Ni is desirably 60.0%. The content of Ni is more
desirably 42.0% or more, and more desirably 59.0% or less
[0068]
Cr: 18.0 to 25.0%
As in the case of the weld metal, Cr is an element that is effective in securing the
oxidation resistance and corrosion resistance of the base metal at high temperatures. To
obtain the effects sufficiently, it is desirable for the base metal to contain 18.0% or more
of Cr. For the base metal, there is no need to consider a lack of fusion, which raises an
issue in the weld metal, but an excessive content of Cr degrades the stability of the metal
micro-structure at high temperatures, leadlng to a decrease in creep strength. For this
reason, the content of Cr is desirably 25.0% or less. The content of Cr is more desirably
19.0% or more, and more desirably 24.0% or less.
[0069]
One or more elements of Mo and W: 6.0 to 10.0% in total
Mo and W (tungsten) are both dissolved in the matrix, and are elements that
considerably contribute to the enhancement of creep strength at high temperatures. For
the base metal, there is no need to consider a lack of fusion, which raises an issue in the
weld metal, and thus both elements of Mo and W can be utilized for the base metal to
obtain the effect described above. Therefore, 6.0% or more of one or more elements of
Mo and W may be contained in total. However, since Mo and W are both expensive
elements, the use of them in large quantity leads to a rise in costs. For this reason, the
total content of one or more elements of Mo and W is desirably 10.0% or less. The total
content of one or more elements of Mo and W in the base metal is more desirably 6.5%
or more, and more desirably 9.5% or less.
[0070]
Note that there is no need to contain Mo and Win combination. In the case of
containing Mo alone, the content of Mo may be 6.0 to 10.0%, and in the case of containing
W alone, the content of W may be 6.0 to 10.0%.
[0071]
It is preferable for the base metal of a Ni-based heat resistant alloy excellent in
high temperature strength to contain Ni, Cr, and one or more elements of Mo and W
within the ranges described above, as well as elements of the amounts to be described
below, with the balance of Fe and impurities.
[0072]
C: 0.04 to 0.12%
C is an element that increases the structural stability of the base metal and
precipitates in the form of carbides, contributing to the enhancement of creep strength.
Unlike the weld metal, which is used as it is solidified, the base metal is subjected to heat
treatment to achieve its homogenization, which makes it easier to obtain the effects. For
this reason, it is preferable for the base metal to contain C, the amount of which may be
0.04% or more. However, excessively contained C causes coarse carbides to be
generated in high-temperature use, leading to a decrease in creep strength instead. For
this reason, when the base metal contains C, the amount of C is desirably 0.12% or less.
The content of C is more desirably 0.06% or more, and more desirably 0.10% or less.
[0073]
Si: 1.00% or less
Si has a deoxidation function, but an excessive content of Si causes toughness to
decrease. However, for the base metal, there is no need to consider a lack of fusion,
which raises an issue in the weld metal, and thus when the base metal contains Si, the
amount of Si is desirably 1.00% or less, more desirably 0.80% or less. Note that the
lower limit of the content of Si is not specially provided, but if the content of Si is
excessively reduced, the deoxidation effect becomes insufficient, and the index of
cleanliness of the alloy increases, which means the cleanliness of the alloy decreases,
leading to a rise in producing costs. For this reason, the content of Si is desirably 0.01%
or more, and more desirably 0.02% or more.
[0074]
Mn: 1.50% or less
As in the case of Si, Mn has a deoxidation function and moreover increases
structural stability, contributing not a little to securing creep strength. For this reason, it
is preferable for the base metal to contain Mn. However, an excessive content of Mn
leads to embrittlement. Therefore, when the base metal contains Mn, the amount of Mn
is desirably 1.50% or less, more desirably 1.20% or less. The lower limit of the content
of Mn is not specially provided, but the content of Mn is desirably 0.01% or more, and
more desirably 0.02% or more.
[0075]
P: 0.03% or less
P is contained as an impurity, and excessively contained P leads to a decrease in
creep ductility and increases the liquation cracking susceptibility and stress relaxation
cracking susceptibility of a weld heat affected zone (HAZ). For this reason, the content
of P in the base metal is desirably 0.03% or less, more desirably 0.015% or less. The
lower limit of the content of P is not specially provided, but an extreme reduction of the
content of P leads to a significant rise in alloy producing costs, and thus the content of P
is desirably 0.001% or more, and more desirably 0.002% or more.
[0076f
S: 0.01% or less
As in the case of P, S is contained as an impurity, and excessively contained S
leads to a decrease in creep ductility and increases the liquation cracking susceptibility
and stress relaxation cracking susceptibility of a weld heat affected zone. For this reason,
the content of S in the base metal is desirably 0.01% or less, more desirably 0.005% or
less. The lower limit of the content of S is not specially provided, but an extreme
reduction of the content of S leads to a significant rise in alloy producing costs, and thus
the content of S is desirably 0.0002% or more, and more desirably 0.0005% or more.
[0077]
Co: 15.0% or less
Also in the base metal, Co increases structural stability at high temperatures,
contributing to securing creep strength. For this reason, it is preferable for the base
metal to contain Co. However, since Co is a very expensive element, when the base
metal contains Co, the amount of Co is desirably 15.0% or less, more desirably 13.0% or
less. The content of Co is desirably 0.01% or more, and more desirably 0.03% or more.
[0078]
Ti: 0.01 to 0.50%
Also in the base metal, Ti precipitates in grains in the form of a fine intermetallic
compound and a carbo-nitrides, and is an element contributing to creep strength at high
temperatures. For this reason, it is preferable for the base metal to contain Ti, and the
amount of Ti may be 0.01% or more. However, excessively contained Ti causes the
intermetallic compound and the carbo-nitride to be generated in large quantity, leading to
a decrease in toughness. For this reason, when the base metal contains Ti, the amount
of Ti is desirably 0.50% or less. The content of Ti is more desirably 0.05% or more, and
more desirably 0.40% or less.
[0079]
Nb: 0.50% or less
Also in the base metal, Nb combines with Ni to precipitate in the form of an
intermetallic compound, or combines with carbon and nitrogen to precipitate in the form
of a fine carbo-nitride, contributing to the enhancement of creep strength at high
temperatures. For this reason, it is preferable for the base metal to contain Nb.
However, excessively contained Nb leads to an excessive precipitation of the intermetallic
compound and the carbo-nitride, leading to a decrease in toughness. For this reason,
when the base metal contains Nb, the amount of Nb is desirably 0.50% or less, more
desirably 0.40% or less. The content of Nb is desirably 0.01% or more, and more
desirably 0.05% or more.
[OOSO]
N: 0.010% or less
N is an element that is effective in stabilizing the metal micro-structure. For
this reason, it is preferable for the base metal to contain N. However, excessively
contained N causes carbo-nitrides to precipitate in large quantity while in use, leading to
a decrease in ductility and toughness. For this reason, when the base metal contains N,
the amount of N is desirably 0.010% or less, more desirably 0.008% or less. There is
no special need to provide the lower limit of the content of N, but an extreme reduction
of the content of N leads to a rise in producing costs, and thus the content of N is desirably
0.0005% or more.
[OOSl]
B: 0.0050% or less
Also in the base metal, B segregates at grain boundaries in high-temperature use
so as to strengthen the grain boundaries and subjects grain boundary carbides to fine
dispersion, and is an element effective in enhancing creep strength. For this reason, it is
preferable for the base metal to contain B. However, containing a large quantity of B
increases the liquation cracking susceptibility of a weld heat affected zone. For this
reason, when the base metal contains B, the amount of B is desirably 0.0050% or less,
more desirably 0.0040% or less. Note that the content of B is desirably 0.0002% or
more, and more desirably 0.0005% or more.
[0082]
Al: 1.50% or less
A1 is contained as a deoxidizer, combines with Ni to finely precipitate in grains
in the form of an intermetallic compound, and is an element effective in increasing creep
strength. For the base metal, there is no need to consider a lack of fusion, which raises
an issue in a weld metal, and unlike the weld metal, which is used as it is solidified, the
base metal is subjected to heat treatment to achieve its homogenization, which makes it
easier to obtain the creep strength. For this reason, it is preferable for the base metal to
contain Al. However, containing a large quantity of A1 gives rise to a loss of workability,
leading to a decrease in productivity. For this reason, when the base metal contains Al,
the amount ofA1 is desirably 1.50% or less, more desirably 1.30% or less. The content
of A1 is desirably 0.001% or more, and more desirably 0.005% or more.
[0083]
Hereafter, the present invention will be described more specifically by way of
examples, but the present invention is not limited to these examples.
EXAMPLE
[0084]
Alloys X and Y having chemical compositions shown in Table 1 were subjected
to laboratorymelting and cast into ingots, and hot forging, hot rolling, heat treatment, and
machining were performed on the ingots to fabricate alloy plates each having a thickness
of 12 mm, a width of 50 mm, and a length of 100 mm, as welding base metals.
[OOSS]
Furthermore, alloys Ato K having chemical compositions shown in Table 2 were
subjected to laboratory melting and cast into ingots, and hot forging, hot rolling, and heat
treatment were performed on the ingots to fabricate welding materials (welding wires)
each having an outer diameter of 1.2 mm. Note that, in fabricating each welding
material, the thickness of an oxide layer (oxide scales) on a welding material surface was
changed by adjusting the atmosphere of the heat treatment in fabricating the welding
material. Then, the thickness of each oxide layer was measured on a cross section
obtained by cutting the welding material along a direction perpendicular to the lengthwise
direction of the welding material (hereafter, referred to as a crosscut), and the airerage of
the thicknesses was determined.
[0086]
[Table 11
Chemical composition (by mass%, balance: Fe and impunities)
AUoy
C I Si ) M n I P I S ) N i I C o I Cr I M o I W I Ti l N b l A11 B ( N
[0087]
[Table 21

[OOSS]
The alloy plate for welding base metal described above was beveled to include
a V-type groove, having an angle of 30" and a root thickness of 1 mm, in the longitudinal
direction of the alloy plate and thereafter placed on a commercial steel plate of SM400B
defined in JIS G 3106 (2008) having a thickness of 25 mm, a width of 200 mm, and a
length of 200 mm, with the circumference of the alloy plate subjected to restraint-weld
using E Ni 6182 defined in JIS Z 3224 (2010) as a covered electrode.
[0089]
Thereafter, multi-layer welding was performed in the bevel using the welding
materials A to K mentioned above, by TIG welding with a heat input of 6 to 12 kJ/cm to
fabricate two welded joints for each welding material.
[0090]
For each welding material, one of the welded joints was used as being welded,
and the other was used after being subjected to an aging heat treatment at 700°C and for
500 hours, for the following test.
[0091]
First, five crosscuts were taken from each of the welded joints as being welded
and after being subjected to the aging heat treatment, subjected to mirror polishing and
etching, and thereafter subjected to microscopic examination under an optical microscope
to be examined for the presencelabsence of a defect in weld metal. The welded joint
was determined to be "good" when no lack of fusion nor crack was recognized at all in
all the five taken crosscuts, or determined to be "acceptable" when at least one of a lack
of fusion and a crack measuring 0.2 mm or less was recognized in only one crosscut out
of five, and such a welded joint was judged to be "passed". On the other hand, the
welded joint was judged to be "failed" when a lack of fusion or a crack was recognized
in two or more crosscuts out of five, when a lack of fusion or a crack was recognized in
only one crosscut, but the size of lack of fusion or the crack exceeds 0.2 mm, or when
there were two or more lacks of fusion or cracks.
[0092]
Next, from a welded joint judged to be "passed" as a result of the microscopic
examination, as being welded, a round bar specimen for creep rupture test was taken such
that the weld metal is positioned at the center of the parallel portion of the specimen, a
creep rupture test was conducted under the condition of 700°C and 196 MPa, in which
the target rupture time of an alloy plate for base metal was 1000 hours, and when the
rupture time of the round bar creep rupture test specimen satisfies the target rupture time
(1000 hours) of the base metal alloy plate described above, the welded joint was judged
to be "passed".
[0093]
Table 3 shows collectively the oxide layer thicknesses on the surfaces of welding
materials and the results of the test described above. Note that the marks "oo" and "ow
in the column "OBSERVATIONS ON CROSS SECTION" in Table 3 indicate a passed
welded joint that was judged to be "good" and "acceptable", respectively. In contrast,
the mark "x" indicates that the welded joint was judged to be "failed". In addition, the
mark "ow in the column "CREEP RUPTURE TEST RESULT" indicates that the creep
rupture test result on the welded joint was "passed" satisfying the target rupture time
(1000 hours) of a base metal alloy plate, and the mark "-" indicates that the creep rupture
test was not conducted because a lack of fusion was observed in a cross section
observation of the welded joint as being welded.
Ieyaleur Zuyp1am e u! q,q 30 ~ u n o mat p a.xayM ase3 atp u! 'ley1 u ~ o q sy l y 'leln3!3.led
UI ',,passed,, sy uoalayl qnsal lsaq amdm daa.13 a q asnesaq y@uaqs daam q8q
e sey lu!of papIaM atp ley1 pue 'Kl~ua!~r~p~eanqs 8uypa3ard e qaur 01 ssed Butpaa33ns e
SMOIIe cpg~pe aq plaMe uo Zu!u!emarZep 8n!p[a~a mpal ue3 luyofpapla~am asne3aq
8uy8e lave Zuppe.13 uo!lexe[al ssaqs ou pue uojsq 30 y3ey on t p y ~luy oc papla& punos
e s! lu!of paplam aql 'uo!luanu! quasa~da yl u! pauyap sa3m aql8u&js!les a3ejms st! uo
ssampw ~aiCe[a pyxo e pue uog!sodmo3 1e3!maq3 e Zuyney iCol[e lue)s!sal leay paseq-!N
satisfies the formula (i) described above in the relation with the amount of Al, and in the
case where the contents of Ni, Cr, Mo, and Co satisfy more desirable ranges, there are no
minute lacks of fusion nor stress relaxation cracks after aging at all, and thus the welding
material has an excellent weldability.
[0096]
In contrast to this, as to the welded joint Nos. 4,8, and 11, although the chemical
compositions of the alloy for welding material A and B satisfied the ranges defined in the
present invention, the thickness of the oxide layer on the welding material surface
exceeded 30 pm, causing oxides on the welding material surface to migrate to the surface
of a molten pool with the melting of the welding material and to remain on a weld bead
in the form of welding slag in large quantity, which prevented a succeeding pass from
melting a preceding bead sufficiently, resulting in the occurrence of a lack of fusion.
[00971.
As to the welded joint No. 14, since an alloy for welding material E had a content
of A1 of 1.44%, which exceeded the upper limit defined in the present invention, A1
reacted with oxygen (0) in a molten pool in welding to form an oxide, remaining on a
weld bead in the form of welding slag in large quantity, which prevented a succeeding
pass from melting a preceding bead sufficiently, resulting in the occurrence of a lack of
fusion. Furthermore, a stress relaxation cracking occurred as well because intermetallic
compounds were generated in large quantity in aging heat treatment.
[0098]
As to the welded joint No. 15, since an alloy for welding material F had contents
ofSi and 0 that exceeded the ranges defined in the present invention, oxides were formed
in a molten pool in welding, remaining on a weld bead in the form of welding slag in
large quantity, which prevented a succeeding pass from melting a preceding bead
sufficiently, resulting in the occurrence of a lack of fusion.
[0099]
As to the welded joint No. 16, an alloy for welding material G had the contents
of Ni, Co, and Mo that fell out of the ranges defined in the present invention, thus leading
to eariy precipitation of intermetallic compounds with A1 in large quantity. For this
reason, a stress relaxation cracking occurred in aging heat treatment whereas the creep
rupture test result was "passed".
INDUSTRIAL APPLICABILITY
[OlOO]
According to the present invention, it is possible to provide a welding material
for Ni-based heat resistant alloy having an excellent weldability in fabrication and to
provide a weld metal, formed using the welding material, that has an excellent creep
strength at high temperatures and an excellent stress relaxation cracking resistance while
in use. Furthermore, it is also possible to provide a welded joint that is formed of the
weld metal formed using this welding material and a base metal having an excellent creep

We claim:
1. A welding material for Ni-based heat resistant alloy having a chemical
composition consisting, by mass%, oE
C: 0.08 to (L12%,
Si: 0.10% or less, .
Mn: 0.02 to 1.50%,
P: 0.008% or less,
S: 0.002% or less,
Ni: more than 56.0% to 60.0% or less,
Co: 8.0 to 12.0%,
Cr: 18.0 to 22.0%,
Mo: 6.0 to 10.0%,
Ti: 0.01 to 0.50%,
Al: 0.50 to 1.00%,
N: 0.010% or less,
0: 0.010% or less,
Nb: 0 to 0.50%,
B: 0 to 0.0050%,
Ca: 0 to 0.050%,
Mg: 0 to 0.050%,
REM: 0 to 0.20%, and
the balance: Fe and impurities, wherein
a thickness of an oxide layer formed on the surface of the welding material is 30
pm or Iess.
2. The welding material for Ni-based heat resistant alloy according to claim 1,
wherein
the chemical composition contains one or more elements selected from, by
mass%:
Co: 9.0 to 11.0%,
Cr: 19.0 to 21.0%, and
Mo: 7.0 to 9.0%.
3. The welding material for Ni-based heat resistant alloy according to claim 1 or
claim 2, wherein
the chemical composition contains one or more elements selected from, by
mass%:
Nb: 0.01 to 0.50%,
B: 0.0002 to 0.0050%,
Ca: 0.0005 to 0.050%,
Mg: 0.0005 to 0.050%, and
REM: 0.01 to 0.20%.
4. The welding material for Ni-based heat resistant alloy according to any one of
claim 1 to claim 3, wherein
the chemical composition satisfies a following formula (i):
Mn20.2xAl-6.1 6)
wherein each symbol of an element in the formula denotes the content of each
element (mass%) in welding material.
5. A weld metal comprising thewelding material for Ni-based heat resistant alloy
according to any one of claim 1 to claim 4.
6. A welded joint comprising the weld metal according to claim 5 and a base metal
of a Ni-based heat resistant alloy.
7. The welded joint according to claim 6, wherein
the base metal has a chemical composition comprising, by mass%:
Ni: 41.0 to 60.0%,
Cr: 18.0 to 25.0%, and
one or more elements of Mo and W: 6.0 to 10.0% in total.
8. The welded joint according to claim 7, wherein
the base metal has a chemical composition consisting, by mass%, of:
C: 0.04 to 0.12%,
Si: 1.00% or less,
Mn: 1.50% or less,
P: 0.03% or less,
S: 0.01% or less,
Ni: 41.0 to 60.0%,
Co: 15.0% or less,
Cr: 18.0 to 25.0%,
one or more elements of Mo and W: 6.0 to 10.0% in total,
Ti: 0.01 to 0.50%,
Nb: 0.50% or less,
N: 0.010% or less,
B: 0.0050% or less,
Al: 1.50% or less, and
the balance: Fe and impurities.