JP2020116584A - Austenitic heat-resistant steel welding material, weld metal, welded structure and method for manufacturing welded structure - Google Patents

Abstract

To provide an austenitic heat-resistant steel welding material that is used for welding an austenitic heat-resistant steel used at high temperature and can acquire a weld metal that is excellent in crack resistance at the beginning of use start at high temperature and has high-creep strength.SOLUTION: An austenitic heat-resistant steel welding material includes, by mass, 0.03 to 0.10% C, 0.15 to 0.40% Si, 0.8 to 2.3% Mn, 0 to 0.02% P, 0 to 0.003% S, 2.0 to 4.0% Cu, 17.0 to 23.0% Ni, 25.0 to 29.0% Cr, 0.5 to 1.5% Mo, 0.25 to 0.75% Nb, 0.001 to 0.1% Ta, 0.15 to 0.40% N, 0 to 0.03% Al, 0 to 0.02% O and the balance Fe with inevitable impurities.SELECTED DRAWING: None

Description

The present invention relates to a welding material for austenitic heat resistant steel, a weld metal, a welded structure, and a method for manufacturing a welded structure.

In recent years, from the viewpoint of environmental load reduction, operating temperature and pressure of boilers for power generation have been promoted on a global scale, and the materials used for the superheater tubes and reheater tubes are more excellent. It is required to have high temperature strength and corrosion resistance.

As a material satisfying such requirements, a large amount of nitrogen was added to increase the high temperature strength, and the Cr content was increased to more than 20% to increase the corrosion resistance and steam oxidation resistance at high temperature. Various austenitic heat resistant steels have been disclosed.

For example, Patent Document 1 proposes an austenitic heat-resisting steel containing 0.1% to 0.35% of N and Cr of more than 22% and less than 30% and defining a metallographic structure and having excellent high temperature strength and corrosion resistance. ing. Further, Patent Document 2 also proposes an austenitic heat-resisting steel which contains 0.1% to 0.35% of N and more than 22% and less than 30% of Cr and which defines an impurity element and is excellent in high temperature strength and corrosion resistance. ing.

When these austenitic heat-resistant steels having a high N content and a high Cr content are used as a structure, they are generally assembled by welding. At the time of welding, existing welding materials for high Ni-containing alloys such as AWS A5.14-2005 ERNiCr-3 and ERNiCrMo-3 may be used for welding.

However, although the above-mentioned welding materials have excellent creep strength, they are expensive and therefore not preferable from the economical viewpoint. Furthermore, when the composition differs greatly from the material to be welded, sufficient weld hot crack resistance, specifically solidification crack resistance, may not be obtained.

Therefore, in Patent Document 3, 23% to 28% of Cr, 0.25% to 0.7% of Nb, and 0.15% to 0.35% of N are contained, and regulation of P and S and Mg are performed. 0.003 to 0.02% is added, a welding material for high-nitrogen austenitic heat-resistant steel that achieves both high temperature strength and solidification crack resistance has been proposed.

In Patent Document 4, 23% to 28% of Cr and 0.01% to 0.7% of Nb are contained, 0.20% to 0.40% of N is contained, and 0.01% to B is contained. A welding material for high-nitrogen-containing austenitic heat-resisting steel, in which S, Al and O are contained and which has both high temperature strength and welding workability, has been proposed.

Patent Document 5 also contains 23% to 28% of Cr, 0.01% to 0.7% of Nb, and contains 0.20% to 0.40% of N, and 1% to if necessary. A welding material for high-nitrogen-containing austenitic heat-resisting steel, which contains 4% Cu and regulates the total amount of P and S to 0.02% or less and has both high temperature strength and weldability, has been proposed.

In Patent Document 6, 15% to 25% of Cr, 0.15% to 1.5% of Nb, 0.5% to 3% of W, and 0.1% to 0.35% of N are contained. , A welding material for high-nitrogen-containing austenitic heat-resisting steel having excellent high temperature strength is disclosed.

As described above, in order to weld the base metal containing more than 20% of Cr, various welding materials having a high Cr content and a high N content and further containing Nb have been proposed.

Patent Document 7 discloses a duplex stainless steel material composed of a ferrite phase and an austenite phase, in which Cr is 20.0% to 28.0%, Nb is 0.0005% to 0.0500%, and N is 0.10% to 0.50%, Ta 0.01% to 0.50%, Ni 3.0% to 7.0%, and stress corrosion cracking resistance in a welded portion when formed into a stainless steel pipe. A duplex stainless steel material having improved properties is disclosed.

Furthermore, in patent document 8, Ta is 0.25%-0.8%, Ni is 15%-25%, Cr is 20%-30%, Nb is 0.1%-0.8%, N. Austenitic stainless steel containing 0.10% to 0.35% of Al and having excellent toughness after long-term exposure to high temperature is disclosed.

Patent Document 9 discloses that C and N are 0.25% to 0.36% in total, Ni and Co are 18% to 22% in total, Cr is 22% to 28%, and Nb is 0.15% to 0%. Austenitic stainless steel containing 0.4% of Ta and 0.2% to 0.5% of Ta and having improved hot workability during manufacturing is disclosed.

Further, in Patent Document 10, Ni is 15.0% to 25.0%, Cr is 20.0% to 30.0%, Nb is 0.10% to 0.60%, and Ta is 0.20%. Austenitic stainless steel containing 0.1 to 1.00%, N of 0.10% to 0.30%, and having a Ta/Nb ratio of 0.8 to 4.0 and improved long-term creep strength. It is disclosed.

Japanese Patent No. 4424471 Japanese Patent No. 4946758 Japanese Patent No. 2722893 Japanese Patent No. 2800661 JP-A-7-60481 Japanese Patent No. 3329261 JP, 2017-95794, A JP, 2014-8859, A JP, 2015-98630, A Japanese Patent No. 5547825

By the way, when a large welding structure used at high temperature, such as a boiler, is assembled using the welding materials disclosed in Patent Documents 3 to 6, it is sure that the weld metal has sufficient creep strength and corrosion resistance. Is obtained. However, in such a weld metal, cracks may occur at the beginning of use at high temperature, and particularly under certain conditions, for example, when the welded joint shape is complicated and strongly constrained, at the beginning of use at high temperature. Cracking of the weld metal may occur significantly.
Further, Patent Document 7 discloses a stainless steel material and does not pay attention to the point of using it as a welding material. If this stainless steel material is diverted to a welding material, the stability of the austenite structure at high temperatures may be reduced due to the inclusion of Ta, and cracking of the weld metal may occur remarkably at the beginning of use at high temperatures. Conceivable.
Further, Patent Documents 8 to 10 disclose a stainless steel material like Patent Document 7, and do not pay attention to the point of using it as a welding material. If this stainless steel material is diverted to a welding material, since Ta is contained in a large amount, Ta precipitates may be deposited at an early stage and cracks in the weld metal may occur at the beginning of use at high temperatures. Conceivable.

The present invention has been made in view of the above-mentioned current situation, and is used for welding austenitic heat-resistant steel used at high temperature, excellent in crack resistance at the beginning of use at high temperature, and a weld metal having high creep strength is provided. It is intended to provide the obtained welding material for austenitic heat-resistant steel. Another object of the present invention is to provide a weld metal having excellent crack resistance at the beginning of use at high temperature and having high creep strength, a welded structure having the weld metal, and a method for producing the weld metal.

As a result of repeated studies based on the above situation, it has been found that the above problems can be solved by the following means.
<1>
In mass %,
C: 0.03% to 0.10%,
Si: 0.15% to 0.40%,
Mn: 0.8% to 2.3%,
P: 0% to 0.02%,
S: 0% to 0.003%,
Cu: 2.0% to 4.0%,
Ni: 17.0% to 23.0%,
Cr: 25.0% to 29.0%,
Mo: 0.5% to 1.5%,
Nb: 0.25% to 0.75%,
Ta: 0.001% to 0.1%,
N: 0.15% to 0.40%,
A welding material for austenitic heat-resisting steel containing Al:0% to 0.03% and O:0% to 0.02%, with the balance being Fe and impurities.
<2>
The welding material for austenitic heat-resistant steel according to <1>, containing at least one element selected from the following group in place of part of the Fe as an alloy component.
Group V: 0.5% or less,
Ti: 0.5% or less,
Co: 2% or less,
B: 0.02% or less,
Ca: 0.02% or less,
Mg: 0.02% or less,
REM: 0.06% or less <3>
A weld metal in which austenitic heat-resistant steel is welded using the welding material for austenitic heat-resistant steel according to <1> or <2>.
<4>
A welded structure having the weld metal according to <3>.
<5>
A method for producing a welded structure, which comprises producing a welded structure by welding austenitic heat resistant steel using the welding material for austenitic heat resistant steel according to <1> or <2>.

According to the present invention, used for welding austenitic heat-resistant steel used at high temperature, excellent in crack resistance at the beginning of use at high temperature, and a weld metal for austenitic heat-resistant steel, which can provide a weld metal having high creep strength Material can be provided. Further, according to the present invention, it is possible to provide a weld metal having excellent crack resistance at the beginning of use at high temperature and having high creep strength, a welded structure having the weld metal, and a method for producing the weld metal.

Hereinafter, the welding material for austenitic heat-resistant steel (hereinafter, also simply referred to as “welding material”) according to the embodiment of the present invention will be described in detail.
In the description of the present specification, the “%” display of the content of each element means “mass %”.
In addition, in the present specification, a numerical range represented by “to” means a range including numerical values before and after “to” as a lower limit value and an upper limit value, unless otherwise specified.

[Welding material for austenitic heat resistant steel]
The welding material according to the present embodiment is mass%,
C: 0.03% to 0.10%,
Si: 0.15% to 0.40%,
Mn: 0.8% to 2.3%,
P: 0% to 0.02%,
S: 0% to 0.003%,
Cu: 2.0% to 4.0%,
Ni: 17.0% to 23.0%,
Cr: 25.0% to 29.0%,
Mo: 0.5% to 1.5%,
Nb: 0.25% to 0.75%,
Ta: 0.001% to 0.1%,
N: 0.15% to 0.40%,
Al: 0% to 0.03% and O: 0% to 0.02%, with the balance being Fe and impurities.

In addition, the welding material according to the present embodiment may contain at least one element selected from the following group, instead of part of the Fe as an alloy component.
Group V: 0.5% or less,
Ti: 0.5% or less,
Co: 2% or less,
B: 0.02% or less,
Ca: 0.02% or less,
Mg: 0.02% or less,
REM: 0.06% or less

The present inventors have made various studies in order to overcome the cracks that occur in the weld metal at the early stage of use at high temperatures. As a result, the following findings were clarified.
(A) Cracks generated in the weld metal occurred at the columnar crystal boundaries of the weld metal, the fracture surface had poor ductility, and S enrichment was detected.
(B) Nitride or carbonitride having Cr or Nb as a constituent element was finely and abundantly precipitated in the columnar crystal.
From this, it is considered that the cracks generated in the weld metal are so-called stress relaxation cracks. In other words, due to the fine precipitation of Nb-containing nitrides or carbonitrides during use at high temperatures, the deformation resistance in the grains increases, and the residual stress generated by welding is released in the process of releasing at high temperatures. It is considered that the resulting creep deformation was concentrated at the columnar crystal boundaries and opened and cracked. Then, S is segregated to the columnar crystal boundaries during welding or during use at high temperature and reduces the bonding force thereof, so that it was thought that when the S content increases, cracking is likely to occur.

Therefore, the present inventors have examined the preventive measures. As a result, in a welding material containing more than 25% of Cr, the stability of the austenite structure at high temperature is lowered, so 0.001% or more of Ta, which has not been positively contained in the past, is contained. , It has been clarified that by reducing the S content to 0.003% or less, it is possible to suppress the occurrence of cracks occurring in the weld metal at the initial stage of use at high temperature.
This is because Ta is contained in the nitride or carbonitride having Cr or Nb as a constituent element, whereby the precipitation of the nitride or carbonitride is delayed, and it remains in the weld metal in the initial stage of use. It is presumed that this is because the increase in deformation resistance during the stress relaxation process is reduced and the concentration of creep deformation at the columnar crystal boundaries is relaxed. It is also presumed that the segregation of S to the columnar crystal boundaries is suppressed, whereby the decrease in the binding force is reduced.
The decrease in the stability of the austenite structure at high temperature due to the inclusion of Ta is caused by containing Ni in an amount of 17.0% or more and Cu in an amount of 2.0% or more in the Cr content range of the present embodiment. It was also clarified that it can be reduced by.
The present embodiment has been conceived based on the above knowledge.

That is, in the present embodiment, Cr is contained in an amount of 25.0% to 29.0%, Ni is contained in an amount of 17.0% to 23.0%, the S content is restricted to 0.003% or less, and Ta is set to 0. By using the austenitic heat-resistant steel welding material containing 0.001% to 0.1% of the above composition, a weld metal having excellent crack resistance at the beginning of use at high temperature and having high creep strength can be obtained. It is a solution to the problem of being obtained.
It should be noted that even under a specific condition in which the occurrence of cracking of the weld metal at the beginning of use at high temperature becomes remarkable, for example, even when the weld metal has a complicated and strongly restrained weld joint shape, the present embodiment According to the method, cracking at the beginning of use at high temperature is suppressed.

Here, the “use at high temperature” in the present embodiment includes, for example, an aspect of being used in an environment of 350° C. or higher and 750° C. or lower (further 400° C. or higher and 700° C. or lower).

Examples of welded structures used at high temperatures include boiler pipes such as coal-fired power plants, oil-fired power plants, refuse incineration power plants and biomass power plants; decomposition pipes in petrochemical plants; and the like.

In the present embodiment, the reason for limiting the chemical composition of the welding material for austenitic heat resistant steel is as follows.

C: 0.03% to 0.10%
C is an austenite-forming element, which enhances the stability of the austenite structure of the weld metal at high temperatures and also produces fine carbides, which contributes to ensuring creep strength. In order to obtain the effect sufficiently, it is necessary to contain 0.03% or more. However, if the content exceeds 0.10%, coarse and large amounts of carbides are precipitated, which rather deteriorates the creep strength and the corrosion resistance at high temperatures. The preferable lower limit of the C content is 0.04% or more, and the preferable upper limit thereof is 0.09% or less. A more preferable lower limit of the C content is 0.05% or more, and a preferable upper limit thereof is 0.08% or less.

Si: 0.15% to 0.40%
Si is contained as a deoxidizer, but when it is contained in excess, it increases the solidification cracking susceptibility during welding. Therefore, the Si content needs to be 0.40% or less. However, if the Si content is excessively reduced, the deoxidizing effect cannot be sufficiently obtained, the cleanability is deteriorated, and the manufacturing cost of the welding material is increased. Therefore, 0.15% or more. The preferable lower limit of the Si content is 0.18% or more, and the preferable upper limit thereof is 0.38% or less. A more preferable lower limit of the Si content is 0.20% or more, and a preferable upper limit thereof is 0.35% or less.

Mn: 0.8% to 2.3%
Mn, like Si, is contained as a deoxidizing agent, but it suppresses the scattering of nitrogen from the surface of the molten pool by reducing the nitrogen activity of the molten metal during welding, and indirectly increases tensile strength and creep. Contributes to securing strength. In order to obtain the effect, Mn needs to be contained at 0.8% or more. However, excessive Mn content causes embrittlement, so the Mn content needs to be 2.3% or less. The preferable lower limit of the Mn content is 1.0% or more, and the preferable upper limit thereof is 2.0% or less. The more preferable lower limit of the Mn content is 1.2% or more, and the preferable upper limit thereof is 1.8% or less.

P: 0% to 0.02%
P is contained as an impurity and segregates in the final solidified portion during solidification of the weld metal, lowers its melting point and increases solidification cracking susceptibility. Therefore, the P content needs to be 0.02% or less. The content of P is preferably 0.015% or less, more preferably 0.010% or less. The lower limit of the P content is not particularly required to be set, that is, the content may be 0%, but an excessive reduction leads to an increase in the manufacturing cost of the welding material, so the preferable lower limit is 0.0005% or more, A preferred lower limit is 0.001% or more.

S: 0% to 0.003%
S, which is contained as an impurity like P, lowers the melting point of the final solidified portion during solidification of the weld metal and significantly increases solidification cracking susceptibility. In addition to this, it segregates at the columnar crystal boundaries during use at high temperature, lowers the bonding force, and causes stress relaxation cracking. Therefore, the S content needs to be 0.003% or less. The S content is preferably 0.0025% or less, and more preferably 0.002% or less. The lower limit of the P content does not have to be particularly set, that is, the content may be 0%, but an excessive reduction causes an increase in the manufacturing cost of the welding material, so the preferable lower limit is 0.0002% or more, A preferred lower limit is 0.0005% or more.

Cu: 2.0% to 4.0%
Cu is an element effective for enhancing the stability of the austenite structure of the weld metal at high temperatures and improving the creep strength. In order to obtain the effect, it is necessary to contain 2.0% or more. However, even if the content exceeds 4.0%, the effect is saturated. The preferable lower limit of the Cu content is 2.3% or more, and the preferable upper limit thereof is 3.8% or less. The more preferable lower limit of the Cu content is 2.5% or more, and the preferable upper limit thereof is 3.5% or less.

Ni: 17.0% to 23.0%
Ni is an element effective in ensuring the stability of the austenite structure of the weld metal at high temperatures and improving the creep strength. In order to obtain the effect, the content of 17.0% or more is required. However, Ni is an expensive element, and if its content is excessive, it lowers the nitrogen solubility of the molten metal during welding, and conversely impairs the creep strength. Therefore, the upper limit is set to 23.0% or less. The preferable lower limit of the Ni content is 18.0% or more, and the preferable upper limit is 22.0% or less. A more preferable lower limit of the Ni content is 19.0% or more, and a preferable upper limit thereof is 21.0% or less.

Cr: 25.0% to 29.0%
Cr is contained in order to secure the oxidation resistance and the corrosion resistance of the weld metal at high temperatures. In addition, it precipitates as a carbide or carbonitride and contributes to creep strength. In order to obtain this effect, the content of 25.0% or more is required. However, if the Cr content becomes excessive and exceeds 29.0%, the stability of the austenite structure of the weld metal at high temperatures is impaired, and rather the creep strength is reduced. The preferable lower limit of the Cr content is 25.5% or more, and the preferable upper limit thereof is 28.5% or less. A more preferable lower limit of the Cr content is 26.0% or more, and a further preferable upper limit thereof is 28.0% or less.

Mo: 0.5% to 1.5%
Mo is an element that forms a solid solution in the matrix and contributes to the improvement of the creep strength of the weld metal. In order to obtain this effect, the content of 0.5% or more is required. However, if the content exceeds 1.5%, the effect is saturated, and the stability of the austenite structure of the weld metal at high temperature is reduced, which rather leads to a reduction in creep strength. The preferable lower limit of the Mo content is 0.6% or more, and the preferable upper limit thereof is 1.4% or less. A more preferable lower limit of the Mo content is 0.8% or more, and a further preferable upper limit thereof is 1.2% or less.

Nb: 0.25% to 0.75%
Nb precipitates in the grains as fine carbides, nitrides or carbonitrides during use at high temperatures, and contributes to the improvement of the creep strength of the weld metal. In order to obtain the effect, the content of 0.25% or more is required. However, when the content is excessive, the effect is saturated, and a large amount is precipitated in the early stage of use at high temperature, which promotes stress relaxation cracking. Therefore, the upper limit of the Nb content is 0.75%. The preferable lower limit of the Nb content is 0.30% or more, and the preferable upper limit is 0.60% or less. A more preferable lower limit of the Nb content is 0.40% or more, and a preferable upper limit thereof is 0.50% or less.

Ta: 0.001% to 0.1%
Ta, like Nb, precipitates in the grains as fine nitrides or carbonitrides during use at high temperatures, and contributes to the improvement of the creep strength of the weld metal. In addition, the solid solution in nitride or carbonitride has the effect of delaying the initiation of precipitation and reducing stress relaxation cracking. In order to obtain the above effect, the content of 0.001% or more is required. However, if the content is excessive, a large amount of carbide mainly composed of Ta precipitates at an early stage, rather increasing the stress relaxation cracking susceptibility. Therefore, the upper limit is set to 0.1% or less. A preferable lower limit of the Ta content is 0.002% or more, and a preferable upper limit thereof is 0.06% or less. A more preferable lower limit of the Ta content is 0.005% or more, and a preferable upper limit thereof is 0.04% or less.

N: 0.15% to 0.40%
N enhances the stability of the austenite structure of the weld metal at a high temperature, and forms a solid solution in the matrix or finely precipitates in the grains as a nitride, which greatly contributes to the improvement of creep strength. In order to obtain this effect, it is necessary to contain 0.15% or more. However, when the content exceeds 0.40%, a large amount of nitride is precipitated in the early stage of use at high temperature, which causes an increase in stress relaxation cracking susceptibility and also a decrease in creep ductility. The preferable lower limit of the N content is 0.18% or more, and the preferable upper limit thereof is 0.38% or less. A more preferable lower limit of the N content is 0.20% or more, and a preferable upper limit thereof is 0.35% or less.

Al: 0% to 0.03%
Al is contained as a deoxidizer, but if contained in a large amount, the cleanliness is significantly impaired, and the workability of the welding material and the ductility of the weld metal are reduced. Therefore, the upper limit of the Al content needs to be 0.03% or less. The Al content is preferably 0.025% or less, more preferably 0.02% or less. The lower limit of the Al content does not have to be particularly set, that is, the content may be 0%, but an extreme reduction causes an increase in the manufacturing cost of the welding material, and therefore is preferably 0.0005% or more, more preferably Is 0.001% or more.

O: 0% to 0.02%
O is contained as an impurity, but when contained in a large amount, it deteriorates the workability of the welding material and the ductility of the weld metal. Therefore, the O content is 0.02% or less. The O content is preferably 0.015% or less, and more preferably 0.01% or less. The lower limit of the O content does not have to be set in particular, that is, the content may be 0%, but an excessive reduction causes an increase in the manufacturing cost of the welding material, and is therefore preferably 0.0005% or more, more preferably Is 0.001% or more.

In addition to the above, the welding material for austenitic heat-resistant steel of the present embodiment belongs to at least one of the following groups (first to third groups) instead of part of Fe as an alloy component. You may contain at least 1 sort(s) of element. The reasons for the limitation are described below.

First group V: 0.5% or less, Ti: 0.5% or less V: 0.5% or less V forms a fine carbide, nitride or carbonitride by combining with carbon or nitrogen, and creeps. It may be contained if necessary in order to contribute to the strength. However, if it is contained excessively, a large amount is precipitated and the susceptibility to stress relaxation cracking is increased. It is preferably 0.45% or less, more preferably 0.4% or less. The preferable lower limit of the content is 0.01% or more, and the further preferable lower limit is 0.02% or more.

Ti: 0.5% or less Ti is precipitated as fine carbides, nitrides, or carbonitrides in the grains similarly to V, and contributes to the creep strength at high temperature, so Ti may be contained if necessary. However, if it is contained excessively, a large amount is precipitated and the susceptibility to stress relaxation cracking is increased. It is preferably 0.45% or less, more preferably 0.4% or less. The preferable lower limit of the content is 0.01% or more, and the further preferable lower limit is 0.02% or more.

Second group Co: 2% or less, B: 0.02% or less Co: 2% or less Like Ni and Cu, it is contained because it enhances the stability of the austenite structure of the weld metal at high temperature and contributes to the improvement of creep strength. You may. However, since it is an extremely expensive element, excessive inclusion causes a significant cost increase. Therefore, the upper limit is 2% or less. A preferred upper limit is 1.5% or less, and a more preferred upper limit is 1% or less. The preferable lower limit of the content is 0.01% or more, and the further preferable lower limit is 0.02% or more.

B: 0.02% or less It is an element effective in improving creep strength by segregating at columnar crystal boundaries of the weld metal during high temperature use to strengthen grain boundaries and finely disperse grain boundary carbides. Therefore, it may be contained. However, if contained excessively, the solidification cracking susceptibility during welding is increased, so the upper limit is made 0.02% or less. It is preferably 0.018% or less, more preferably 0.015% or less. The preferable lower limit of the content is 0.001% or more, and the further preferable lower limit thereof is 0.002% or more.

Third group Ca: 0.02% or less, Mg: 0.02% or less, REM: 0.06% or less Ca: 0.02% or less Since it has an effect of improving hot workability at the time of manufacturing a welding material, You may contain as needed. However, an excessive content is combined with oxygen to significantly reduce the cleanability and rather deteriorate the hot workability, so the content is made 0.02% or less. It is preferably 0.015% or less, more preferably 0.01% or less. The preferred lower limit of the content is 0.0005% or more, and the more preferred lower limit thereof is 0.001% or more.

Mg: 0.02% or less Like Ca, it has an effect of improving hot workability during the production of a welding material, and thus may be contained if necessary. However, an excessive content is combined with oxygen to significantly reduce the cleanability and rather deteriorate the hot workability, so the content is made 0.02% or less. It is preferably 0.015% or less, more preferably 0.01% or less. The preferred lower limit of the content is 0.0005% or more, and the more preferred lower limit thereof is 0.001% or more.

REM: 0.06% or less Similar to Ca and Mg, it has an effect of improving hot workability at the time of manufacturing a welding material, and thus may be contained if necessary. However, an excessive content binds to oxygen, significantly lowers cleanability, and rather deteriorates hot workability, so the content is made 0.06% or less. It is preferably 0.05% or less, more preferably 0.04% or less. The preferable lower limit of the content is 0.001% or more, and the further preferable lower limit thereof is 0.002% or more.

In addition, "REM" is a general term for a total of 17 elements of Sc, Y, and a lanthanoid, and the content of REM refers to the total content of one or more elements of REM. Further, REM is generally contained in misch metal. For this reason, for example, it may be added in the form of misch metal and contained so that the amount of REM falls within the above range.

The welding material for austenitic heat-resistant steel of the present embodiment has a chemical composition containing the above-mentioned elements and the balance being Fe and impurities. The "impurities" refer to those that are mixed in from the ore as raw material, scrap, or the manufacturing environment when the welding material is industrially manufactured.

[Welding metal]
The weld metal of the present embodiment is produced by welding the base material of the austenitic heat-resistant steel, and, when welding the base material, the austenitic heat-resistant steel welding material (the filler metal) of the present embodiment described above. It is made by welding using.
The base material of the austenitic heat-resistant steel is not particularly limited, but the base material having the following composition is exemplified as a preferable base material. That is, in mass%, C: 0.03% to 0.12%, Si: 0% to 0.5%, Mn: 0% to 1.5%, P: 0% to 0.03%, S: 0% to 0.01%, Ni: 18% to 22%, Cr: 23% to 27%, Mo: 0% to 0.8%, Cu: 0% to 4%, Nb: 0.3% to 0. Mother containing 0.8%, N: 0.1% to 0.35%, B: 0.0005% to 0.01%, and Al: 0% to 0.03% with the balance being Fe and impurities. It is preferably a material. However, the base material is not necessarily limited to the above composition.

The weld metal of this embodiment is not limited by the welding method for obtaining it. The welding method for obtaining the weld metal of the present embodiment is not particularly limited, but examples thereof include TIG welding, MIG welding, covered arc welding, submerged arc welding, and laser welding.

[Welded structure and manufacturing method thereof]
The welded structure of the present embodiment is a structure including the above-described weld metal of the present embodiment. For example, a welded structure is composed of a weld metal and another base material made of metal. The other base material is preferably a steel material. Stainless steel is more preferable, and austenitic heat-resistant steel is further preferable. The specific shape of the welded structure and the specific mode (welding posture) of welding for obtaining the welded structure are not particularly limited. The welded structure of the present embodiment is manufactured by welding austenitic heat resistant steel using the above-described welding material for austenitic heat resistant steel of the present embodiment.

Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

From an ingot obtained by melting and casting a material having the chemical composition shown in Table 1 in a laboratory, a plate thickness of 12 mm, a width of 50 mm, and a length are obtained by hot forging, hot rolling, cold rolling, heat treatment and machining. A 100 mm base material was prepared.

Further, from the ingot obtained by melting and casting the material of the symbols A to M having the chemical composition shown in Table 2 in the laboratory, hot forging, hot rolling, heat treatment and machining were performed to obtain a 2 mm square and 500 mm length. A cut filler (filler material) was prepared.

<Cross section observation test>
A V groove having an angle of 30° and a root thickness of 1 mm was processed in the longitudinal direction of the base material. The grooves of the two base materials are butted against each other, "YNiCrFe-3" specified in JIS Z3334 (1999) is used as a filler wire, and 20 mm from each end is laminated and welded by TIG welding, and the groove is formed at a center length of 60 mm. A test body with a surface remaining was prepared. After that, on "SM400B" specified in JIS G 3160 (2008) having a thickness of 25 mm, a width of 200 mm, and a length of 200 mm, "DNiCrFe-3" specified in JIS Z3224 (1999) was used as a covered arc welding rod. Four laps were restrained and welded. Then, by using the above-mentioned cut fillers A to M, the heat input was set to 9 to 15 kJ/cm by TIG welding, and laminated welding was performed in the remaining groove. Two weld joints were formed for each substitute. It was made.

For each substitute, one of the obtained joints was subjected to heat treatment at 650° C. for 500 hours. After that, from the portion welded using the cut filler of the as-welded welded joint and the heat-treated welded joint, three cross-sections of the welded portion were exposed by mirror polishing and corrosion, and examined by an optical microscope to examine the weld metal. The presence or absence of cracks was investigated.
A weld joint in which no crack was found in the weld metal as a result of the speculum was determined to be “pass”. Next, a creep rupture test was performed on both the as-welded welded joint and the heat-treated welded joint that passed.

<Creep test>
A V-groove having an angle of 30° and a root thickness of 1 mm was processed in the longitudinal direction of the base material. The grooves of the two base materials were abutted against each other, and a welded joint was produced by TIG welding at a heat input of 9 to 15 kJ/cm using a substitute cut filler that did not crack in the cross-section observation test. A round bar creep rupture test piece was sampled from the obtained welded joint so that the weld metal was located at the center of the parallel portion. A creep test (creep rupture test) was performed on this test piece under the conditions of 650° C. and 245 MPa at which the target rupture time of the base material was about 1000 hours, and the base material also passed when it exceeded 90% of the target rupture time. And

Table 3 also shows the results of the above tests.
“Pass” in the “Cross-section observation” column of Table 3 indicates that all three samples are welded joints that are acceptable and have no cracks in the weld metal. On the other hand, "fail" indicates that cracks were found in the weld metal of at least one of the three samples.

Further, "pass" in the "creep test" column indicates that the creep rupture test exceeded 90% of the target rupture time of the base metal. On the other hand, "fail" indicates that the target breaking time of the base metal was 90% or less. In addition, “not performed” indicates that the creep rupture test was not performed because cracks were observed in the weld metal as a result of cross-sectional observation.

From Table 3, it is clear that the welded joints having the chemical compositions within the scope of the present invention, denoted by reference signs A to F, do not cause cracks in the weld metal as they are welded and after heat treatment, and have high creep strength.
On the other hand, in the welded joints with the substitutions G and I, since Ta was not contained in the welding material, under the severe restraint conditions as in the embodiment of the present invention, the weld metal did not crack as-welded, After the heat treatment, cracks judged to be stress relaxation cracks were observed in the weld metal.
Further, as for the substitutes H and J, since Ta was contained in the welding material in an amount exceeding the range of the present invention, cracks did not occur in the weld metal under the as-welded condition under severe restraint conditions as in the examples of the present invention. However, cracks that were judged to be stress relaxation cracks were observed in the weld metal after the heat treatment.
Further, in the substitution mark K, since S of the welding material was contained in an amount exceeding the range of the present invention, cracks did not occur in the weld metal under the as-welded condition under the severe restraint conditions as in the example of the present invention. After the heat treatment, cracks judged to be stress relaxation cracks were observed in the weld metal.
As for the substitutes L and M, the Cu and Ni contents of the welding material were lower than the ranges of the present invention, respectively, so that the effect of suppressing the reduction of the stability of the austenite structure at high temperature by containing Ta is not sufficient, and the creep rupture occurs. Time was below target.

As described above, only when the requirements of the present invention are satisfied, it is found that a weld metal having crack resistance at the beginning of use at high temperature and excellent creep strength can be obtained.

Claims (5)

In mass %,
C: 0.03% to 0.10%,
Si: 0.15% to 0.40%,
Mn: 0.8% to 2.3%,
P: 0% to 0.02%,
S: 0% to 0.003%,
Cu: 2.0% to 4.0%,
Ni: 17.0% to 23.0%,
Cr: 25.0% to 29.0%,
Mo: 0.5% to 1.5%,
Nb: 0.25% to 0.75%,
Ta: 0.001% to 0.1%,
N: 0.15% to 0.40%,
A welding material for austenitic heat-resisting steel containing Al:0% to 0.03% and O:0% to 0.02%, with the balance being Fe and impurities. The welding material for austenitic heat-resistant steel according to claim 1, containing at least one element selected from the following group in place of part of the Fe as an alloy component.
Group V: 0.5% or less,
Ti: 0.5% or less,
Co: 2% or less,
B: 0.02% or less,
Ca: 0.02% or less,
Mg: 0.02% or less,
REM: 0.06% or less A weld metal in which austenitic heat-resistant steel is welded using the welding material for austenitic heat-resistant steel according to claim 1 or 2. A welded structure comprising the weld metal according to claim 3. A method for producing a welded structure, which comprises producing a welded structure by welding austenitic heat resistant steel using the welding material for austenitic heat resistant steel according to claim 1 or 2.