JP2019173122A - Weld joint - Google Patents

Abstract

To provide a weld joint of an austenitic heat resistant alloy excellent in both of creep breaking strength and stress relaxation cracking resistance.SOLUTION: There is provided a weld joint having a chemical composition containing a base material of, by mass%, C≤0.009%, Si≤2.0%, Mn≤3.0%, P≤0.040%, S≤0.0100%, O≤0.01%, Cr:25.0-38.0%, Ni:40.0-60.0%, W:3.0-10.0%, Ti:0.01-1.20%, N≤0.020%, Al≤0.30%, B:0.0001-0.01%, Zr:0.0001-0.50%, Ca:0-0.010%, Mg:0-0.050%, REM:0-0.100%, Co:0-1.0%, Cu:0-1.0%, Mo:0-1.0%, V:0-0.5%, Nb:0-0.5% and the balance:Fe with impurities, and a weld metal of C≤0.15%, Si≤2.0%, Mn≤3.0%, P≤0.040%, S≤0.0100%, O≤0.01%, Cr:18.0-38.0%, Ti:0.01-2.50%, N≤0.020%, Al≤2.0%, Fe≤15.0%, B:0.0001-0.01%, Zr:0.0001-0.50%, W:0.01-10.0%, Co:0.5-25.0%, Ca:0-0.010%, Mg:0-0.050%, REM:0-0.100%, Cu:0-1.0%, Mo:0-12.0%, V:0-0.5%, Nb:0-2.5%, and the balance:Ni with impurities.SELECTED DRAWING: None

Description

  The present invention relates to a welded joint, and more particularly to a welded joint of an austenitic heat-resistant alloy.

  In recent years, high-temperature and high-pressure operating conditions have been promoted on a global scale in power generation boilers and the like from the viewpoint of reducing environmental impact, and austenitic heat-resistant alloys used as materials for superheater tubes and reheater tubes Therefore, it is required to have a better creep rupture strength.

  Based on such a technical background, technologies relating to various austenitic heat-resistant alloys have been proposed. For example, Patent Document 1 discloses that after surface processing is performed to form a plastic working hardened layer having a surface temperature of 330 HV or higher on the surface, sufficient recrystallization is generated on the hardened surface portion and the inside of the recrystallized grains. Also disclosed is an austenitic alloy structure that has been subjected to localized heat treatment for dispersing and precipitating Cr carbide at the grain boundaries to enhance the intergranular corrosion resistance and stress corrosion cracking resistance, and a method for producing the same. ing.

  Patent Document 2 discloses a high Ni, high Cr stainless steel that has improved hot workability by minimizing crystal grains and suppressing S precipitated in the crystal grain boundaries. Yes. Patent Document 3 proposes a Ni-based alloy product. This Ni-based alloy product uses W to increase the high-temperature strength and manage the amount of effective B, thereby improving hot workability and preventing weld cracking. It is an alloy product.

  Further, Patent Document 4 proposes an austenitic heat-resistant alloy that uses the α-Cr phase as a strengthening phase by utilizing Cr, Ti, and Zr to increase the creep strength, a heat-resistant pressure-resistant member made of the alloy, and a method for manufacturing the same. ing. Patent Document 5 proposes a Ni-base heat-resistant alloy that contains a large amount of W and uses Al and Ti to increase the strength by solid solution strengthening and precipitation strengthening of the γ 'phase.

  Patent Documents 6 and 7 propose austenitic heat-resistant alloy members that are excellent in cracking during hot working and can be suitably used as thick, large-sized high-temperature members. Patent Document 8 discloses that austenite that can prevent both HAZ liquefaction cracking and HAZ embrittlement cracking, can also prevent defects caused by welding workability that occurs during welding work, and has excellent creep strength at high temperatures. Based heat resistant alloys have been proposed.

  Moreover, when using these austenitic heat-resistant alloys as a structure, it is common to assemble by welding. AWS A5.14-2005ER NiCrCoMo-1 is known as a welding material for austenitic heat-resistant alloys used when assembling by welding.

  Furthermore, Patent Documents 9 to 12 propose various welding materials for austenitic heat-resistant alloys.

  Patent Document 9 describes a welding material used for welding an oxide dispersion strengthened alloy having high strength and a heat-resistant alloy, and by actively containing a solid solution strengthening element such as Mo and Nb, There has been proposed a welding material for oxide dispersion-strengthened alloys that has improved strength.

  Patent Document 10 proposes a welding material for an austenitic heat-resistant alloy that uses solid solution strengthening with Mo and W and precipitation strengthening hardening with Al and Ti to increase the strength. Patent Document 11 proposes a welding material for an austenitic heat-resistant alloy that contains Nb and W to achieve both solidification cracking during welding and creep strength.

  In Patent Document 12, a Ni-base heat-resistant alloy welding material having excellent hot crack resistance during welding, hot crack resistance during welding using the same, and stress relaxation crack resistance during long-term use at high temperatures. And a weld joint comprising a weld metal having a good creep strength and a base material of a Ni-base heat-resistant alloy having an excellent temperature drop strength.

JP 2000-265249 A JP 2002-80942 A JP 2011-63838 A International Publication No. 2009/154161 International Publication No. 2010/038826 JP 2014-34725 A JP 2014-145109 A JP 2010-150593 A Japanese Patent Laid-Open No. 10-193174 International Publication No. 2010/013565 JP 2008-207242 A JP 2013-94827 A

  Austenitic heat-resistant alloys used as materials for superheater tubes and reheater tubes have superior creep rupture strength and excellent resistance to stress relaxation cracking during heat treatment after use or during use. It is also required to have stress relaxation cracking properties. In general, it is difficult to obtain both superior creep rupture strength and stress relaxation crack resistance. In any of Patent Documents 1 to 12, the above-mentioned problems have not been solved, and there remains room for improvement. ing.

  An object of the present invention is to solve the above problems and to provide a welded joint of an austenitic heat-resistant alloy that is excellent in both creep rupture strength and stress relaxation crack resistance.

  This invention is made | formed in order to solve said subject, and makes a summary the following welded joint.

(1) The chemical composition is mass%,
C: 0.009% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.040% or less,
S: 0.0100% or less,
O: 0.01% or less,
Cr: 25.0-38.0%,
Ni: 40.0-60.0%,
W: 3.0 to 10.0%
Ti: 0.01-1.20%,
N: 0.020% or less,
Al: 0.30% or less,
B: 0.0001 to 0.01%
Zr: 0.0001 to 0.50%,
Ca: 0 to 0.010%,
Mg: 0 to 0.050%,
REM: 0 to 0.100%,
Co: 0 to 1.0%,
Cu: 0 to 1.0%
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
The balance: a base material that is Fe and impurities,
Chemical composition is mass%,
C: 0.15% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.040% or less,
S: 0.0100% or less,
O: 0.01% or less,
Cr: 18.0 to 38.0%,
Ti: 0.01-2.50%,
N: 0.020% or less,
Al: 2.0% or less,
Fe: 15.0% or less,
B: 0.0001 to 0.01%
Zr: 0.0001 to 0.50%,
W: 0.01 to 10.0%,
Co: 0.5-25.0%
Ca: 0 to 0.010%,
Mg: 0 to 0.050%,
REM: 0 to 0.100%,
Cu: 0 to 1.0%
Mo: 0 to 12.0%,
V: 0 to 0.5%
Nb: 0 to 2.5%,
Balance: including weld metal that is Ni and impurities,
Welded joints.

(2) The chemical composition of the base material is mass%,
Ca: 0.0001 to 0.010%,
Mg: 0.0001 to 0.050%, and REM: 0.0001 to 0.10%,
Containing one or more selected from
The welded joint according to (1) above.

(3) The chemical composition of the base material is mass%,
Co: 0.01 to 1.0%
Cu: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.01 to 0.5%, and Nb: 0.01 to 0.5%,
Containing one or more selected from
The welded joint according to (1) or (2) above.

(4) The chemical composition of the base material is mass%,
C: 0.0001 to 0.009%,
Containing
The weld joint according to any one of (1) to (3) above.

  The welded joint of the austenitic heat-resistant alloy of the present invention is excellent in both stress relaxation crack resistance and long-term creep rupture strength.

  In order to solve the above-described problems, the present inventors have investigated in detail the stress relaxation crack resistance and creep rupture characteristics of an austenitic heat resistant alloy, and as a result, have obtained the following knowledge.

  In general, in order to obtain excellent creep rupture strength, it is considered that precipitation strengthening of grain boundaries needs to be performed by containing a predetermined amount or more of C. However, when a large amount of C is contained, grain boundary weakening occurs with intragranular precipitation strengthening due to carbide, which causes stress relaxation cracking. That is, a so-called trade-off relationship exists between the stress relaxation cracking resistance and the creep rupture property.

Therefore, as a result of studies conducted by the present inventors to solve the above-mentioned problems, excellent creep rupture strength is obtained even when the C content is reduced by utilizing precipitates such as α-Cr phase and Ni ₃ Ti. It was found that it would be possible to secure. And by reducing C content, the grain boundary weakening which generate | occur | produces relatively by the intragranular precipitation strengthening of a carbide | carbonized_material is suppressed, and it becomes possible to improve stress relaxation cracking resistance.

  The present invention has been made based on the above findings. The welded joint according to the present invention includes a base material having a chemical composition described below and a weld metal. Hereinafter, each requirement of the present invention will be described in detail.

1. Chemical composition of base material The reasons for limitation of each element are as follows. In the following description, “%” for the content means “% by mass”.

C: 0.009% or less C is generally known to be an element that stabilizes austenite, forms fine carbides at grain boundaries, and improves creep rupture strength at high temperatures. However, in the present invention, when the C content is excessive, the stress relaxation cracking resistance is lowered. For this reason, C content shall be 0.009% or less. The C content is preferably 0.008% or less, and more preferably 0.005% or less.

  In addition, although it is not necessary to set a minimum in particular about C content, an extreme reduction causes the raise of manufacturing cost. Therefore, the C content is preferably 0.0001% or more, more preferably 0.0005% or more, and further preferably 0.0008% or more.

Si: 2.0% or less Si is an element that has a deoxidizing action and is effective in improving corrosion resistance and oxidation resistance at high temperatures. However, when Si is contained excessively, the stability of austenite is lowered, and the toughness and the creep rupture strength are lowered. Therefore, the Si content is 2.0% or less. The Si content is preferably 1.5% or less, more preferably 1.0% or less, and even more preferably 0.5% or less.

  In addition, it is not necessary to provide a lower limit for the Si content. However, when the Si content is extremely reduced, a sufficient deoxidation effect cannot be obtained, and the cleanliness of the alloy increases and the cleanliness deteriorates. In addition, it becomes difficult to obtain the effect of improving the corrosion resistance and oxidation resistance at high temperatures, and the manufacturing cost is greatly increased. Therefore, the Si content is preferably 0.02% or more, and more preferably 0.05% or more.

Mn: 3.0% or less Mn is an element that not only has a deoxidizing action, but also contributes to stabilization of austenite, like Si. However, when the Mn content is excessive, embrittlement is caused, and further, toughness and creep ductility are reduced. Therefore, the Mn content is 3.0% or less. The Mn content is preferably 2.8% or less, and more preferably 2.5% or less.

  In addition, it is not necessary to provide a lower limit for the Mn content. However, if the Mn content is extremely reduced, the deoxidation effect cannot be obtained sufficiently and the cleanliness of the alloy is deteriorated. Moreover, not only the hot workability is deteriorated but also the austenite stabilizing effect is difficult to obtain, and the manufacturing cost is greatly increased. Therefore, the Mn content is preferably 0.005% or more, and more preferably 0.010% or more.

P: 0.040% or less P is contained in the alloy as an impurity. When P is contained in a large amount, P significantly reduces hot workability and weldability, and further reduces creep ductility after long-term use. . Therefore, the P content is 0.040% or less. The P content is preferably 0.030% or less, and more preferably 0.020% or less.

  Although the P content is preferably reduced as much as possible, the extreme reduction leads to an increase in manufacturing cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.0008% or more.

S: 0.0100% or less S is contained in the alloy as an impurity in the same manner as P. When S is contained in a large amount, the hot workability and weldability are remarkably deteriorated, and the creep ductility for a long time is also reduced. Reduce. Therefore, the S content is 0.0100% or less. The S content is preferably 0.0080% or less, and more preferably 0.0050% or less. In addition, it is preferable to reduce S content as much as possible.

O: 0.01% or less O (oxygen) is contained as an impurity in the alloy, and when its content is excessive, hot workability is lowered, and further, toughness and ductility are deteriorated. For this reason, the O content is set to 0.01% or less. The O content is preferably 0.008% or less, and more preferably 0.005% or less.

  In addition, although it is not necessary to set a minimum in particular about O content, an extreme reduction causes the raise of manufacturing cost. Therefore, the O content is preferably 0.0005% or more, and more preferably 0.0008% or more.

Cr: 25.0-38.0%
Cr is an essential element for securing oxidation resistance and corrosion resistance at high temperatures. Moreover, it precipitates as an α-Cr phase and contributes to improvement of creep rupture strength. In order to acquire said effect, it is necessary to make Cr content 25.0% or more. However, if the Cr content exceeds 38.0%, the stability of austenite at a high temperature deteriorates and the creep rupture strength decreases. Therefore, the Cr content is 25.0 to 38.0%. The Cr content is preferably 25.5% or more, and more preferably 26.0% or more. Moreover, it is preferable that Cr content is 37.5% or less, and it is more preferable that it is 37.0% or less.

Ni: 40.0-60.0%
Ni is an effective element for obtaining austenite, and is an essential element for ensuring the structural stability when used for a long time. Moreover, it precipitates as Ni ₃ Ti and contributes to the improvement of creep rupture strength. In order to obtain the above-described effect of Ni sufficiently within the above Cr content range, the Ni content needs to be 40.0% or more. However, Ni is an expensive element, and if it is contained in a large amount, the cost increases. Therefore, the Ni content is 40.0 to 60.0%. The Ni content is preferably 41.0% or more, and more preferably 42.0% or more. Moreover, it is preferable that Ni content is 58.0% or less, and it is more preferable that it is 56.0% or less.

W: 3.0 to 10.0%
W is an element that contributes greatly to the improvement in creep rupture strength at high temperatures by dissolving in the matrix. In order to exhibit the effect sufficiently, the W content needs to be 3.0% or more. However, even if W is contained excessively, the effect is saturated and the creep rupture strength is lowered. Furthermore, since W is an expensive element, if it is excessively contained, the cost increases. Therefore, the W content is 3.0 to 10.0%. The W content is preferably 3.5% or more, and more preferably 4.0% or more. Moreover, it is preferable that W content is 9.5% or less, and it is more preferable that it is 9.0% or less.

Ti: 0.01 to 1.20%
Ti precipitates in the grains as Ni ₃ Ti and contributes to the creep rupture strength at high temperatures. In order to obtain the effect, the Ti content needs to be 0.01% or more. However, when the Ti content is excessive, a large amount of Ni ₃ Ti precipitates, resulting in a decrease in creep ductility and toughness. Therefore, the Ti content is set to 0.01 to 1.20%. The Ti content is preferably 0.03% or more, and more preferably 0.05% or more. Further, the Ti content is preferably 1.00% or less, and more preferably 0.80% or less.

N: 0.020% or less N is an element effective for stabilizing austenite. However, if it is excessively contained, a large amount of fine nitride precipitates in the grains during use at high temperatures and creeps. It causes a reduction in ductility and toughness. Therefore, the N content is 0.020% or less. The N content is preferably 0.018% or less, and more preferably 0.015% or less.

  In addition, it is not necessary to provide a lower limit for the N content. However, when the N content is extremely reduced, not only is the effect of stabilizing austenite difficult to obtain, but the manufacturing cost is also greatly increased. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

Al: 0.30% or less Al is an element having a deoxidizing action. However, when the Al content is excessive, the cleanliness of the alloy is remarkably deteriorated and hot workability and ductility are lowered. Therefore, the Al content is set to 0.30% or less. The Al content is preferably 0.20% or less, and more preferably 0.10% or less.

  In addition, it is not necessary to provide a lower limit for the Al content. However, if the Al content is extremely reduced, the deoxidation effect cannot be sufficiently obtained, and the cleanliness of the alloy is deteriorated, and the manufacturing cost is increased. Therefore, the Al content is preferably 0.0005% or more. In order to obtain the deoxidation effect of Al stably and to ensure good cleanliness, the Al content is more preferably 0.001% or more.

B: 0.0001 to 0.01%
B is an element necessary for improving the creep rupture strength by segregating at the grain boundary during use at a high temperature to strengthen the grain boundary and finely dispersing the grain boundary carbide. In addition, it contributes to improvement of stress relaxation crack resistance. In order to obtain these effects, the B content needs to be 0.0001% or more. However, when the B content is excessive, in addition to deterioration of weldability, hot workability is deteriorated. Therefore, the B content is set to 0.0001 to 0.01%. The B content is preferably 0.0005% or more, and more preferably 0.001% or more. Further, the B content is preferably 0.008% or less, and more preferably 0.006% or less.

Zr: 0.0001 to 0.50%
Zr has the effect of improving the creep rupture strength. That is, Zr is a grain boundary strengthening element and contributes to the improvement of creep rupture strength at high temperatures, and further contributes to the improvement of creep ductility. In order to obtain this effect, the Zr content needs to be 0.0001% or more. However, when the Zr content exceeds 0.50%, the hot workability decreases. Therefore, the Zr content is set to 0.0001 to 0.50%. The Zr content is preferably 0.01% or more, and preferably 0.40% or less.

Ca: 0 to 0.010%
Ca has the effect of forming a compound with S to reduce the amount of S in the matrix and improving hot workability, so Ca may be contained as necessary. However, when the Ca content is excessive, it combines with O to significantly reduce the cleanliness and, on the contrary, deteriorate the hot workability. Therefore, the Ca content is 0.010% or less. The Ca content is preferably 0.0080% or less. In order to obtain the above effect, the Ca content is preferably 0.0001% or more, more preferably 0.0002% or more, and further preferably 0.0003% or more.

Mg: 0 to 0.050%
Since Mg has the effect of forming a compound with S in the same manner as Ca to reduce the amount of S in the matrix and improving hot workability, it may be included as necessary. However, when the Mg content is excessive, it combines with O to significantly reduce cleanliness and, on the contrary, deteriorate hot workability. Therefore, the Mg content is 0.050% or less. The Mg content is preferably 0.045% or less. In order to obtain the above effect, the Mg content is preferably 0.0001% or more, more preferably 0.0002% or more, and further preferably 0.0003% or more.

REM: 0 to 0.100%
Since REM has the effect of forming a compound with S in the same manner as Ca to reduce the amount of S in the matrix and improving hot workability, it may be included as necessary. However, when the REM content is excessive, it combines with O to significantly reduce the cleanliness and, on the contrary, deteriorate the hot workability. Therefore, the REM content is 0.100% or less. The REM content is preferably 0.080% or less. When it is desired to obtain the above effect, the REM content is preferably 0.0001% or more, more preferably 0.0002% or more, and further preferably 0.0003% or more.

  Note that REM is a generic name for a total of 17 elements of Sc, Y, and lanthanoid, and the REM content 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 adjusted so that the amount of REM falls within the above range.

Co: 0 to 1.0%
Co has the effect of improving the creep rupture strength. That is, Co is an austenite-forming element like Ni, and contributes to the improvement of creep rupture strength by increasing phase stability. Therefore, Co may be included. However, since Co is an extremely expensive element, excessive addition of Co causes a significant cost increase. Therefore, the Co content is 1.0% or less. The Co content is preferably 0.8% or less. On the other hand, when the above effect is desired, the Co content is preferably 0.01% or more.

Cu: 0 to 1.0%
Cu has the effect of improving the creep rupture strength. That is, Cu is an austenite-forming element like Ni and Co, and contributes to improvement of creep rupture strength by increasing phase stability. Therefore, you may contain Cu. However, when Cu is contained excessively, the hot workability is lowered. Therefore, the Cu content is 1.0% or less. The Cu content is preferably 0.8% or less. On the other hand, when it is desired to obtain the above effect, the Cu content is preferably 0.01% or more.

Mo: 0 to 1.0%
Mo has the effect of improving the creep rupture strength. That is, Mo has a function of improving the creep rupture strength at a high temperature by dissolving in a matrix. Therefore, you may contain Mo. However, when Mo is contained excessively, the stability of austenite is lowered, and instead the creep rupture strength is lowered. Therefore, the Mo content is 1.0% or less. The Mo content is preferably 0.8% or less. On the other hand, when it is desired to obtain the above effect, the Mo content is preferably 0.01% or more.

V: 0 to 0.5%
V has the effect of improving the creep rupture strength. That is, V combines with C or N to form fine carbides or carbonitrides and has the effect of improving the creep rupture strength. Therefore, V may be contained. However, when V is contained excessively, it precipitates in a large amount as a carbide or carbonitride, resulting in a decrease in creep ductility. Therefore, the V content is 0.5% or less. The V content is preferably 0.4% or less. On the other hand, when it is desired to obtain the above effect, the V content is preferably 0.01% or more.

Nb: 0 to 0.5%
Nb combines with C or N in the same manner as V and precipitates as fine carbides or carbonitrides in the grains, contributing to the improvement of creep rupture strength at high temperatures. Therefore, you may contain Nb. However, when the Nb content is excessive, it precipitates in a large amount as a carbide or carbonitride, resulting in a decrease in creep ductility and toughness. Therefore, the Nb content is 0.5% or less. The Nb content is preferably 0.4% or less. On the other hand, when it is desired to obtain the above effect, the Nb content is preferably 0.01% or more.

  Said Co, Cu, Mo, V, and Nb can be contained only in any 1 type or 2 or more types in combination. The total amount when these elements are contained in combination may be 4.0%.

  In the chemical composition of the base material of the present invention, the balance is Fe and impurities. Since Fe is an inexpensive raw material, it is preferably contained in an amount of 0.1% to 20%. In addition, “impurities” as used herein are components that are mixed due to various factors of raw materials such as ores and scraps and manufacturing processes when the alloy is industrially manufactured, and do not adversely affect the present invention. It means what is allowed.

2. Chemical composition of weld metal In the weld joint of the present invention, the weld metal is:
% By mass
C: 0.15% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.040% or less,
S: 0.0100% or less,
O: 0.01% or less,
Cr: 18.0 to 38.0%,
Ti: 0.01-2.50%,
N: 0.020% or less,
Al: 2.0% or less,
Fe: 15.0% or less,
B: 0.0001 to 0.01%
Zr: 0.0001 to 0.50%,
W: 0.01 to 10.0%,
Co: 0.5-25.0%
Ca: 0 to 0.010%,
Mg: 0 to 0.050%,
REM: 0 to 0.100%,
Cu: 0 to 1.0%
Mo: 0 to 12.0%,
V: 0 to 0.5%
Nb: 0 to 2.5%,
The balance: Ni and chemical composition that is an impurity.

  In addition, in this invention, the chemical composition of a weld metal shall refer to the chemical composition of the first layer part in a welded joint.

  Among the above, the C content is preferably 0.01% or more, and preferably 0.14% or less. The Si content is preferably 0.01% or more, and preferably 1.8% or less. The Mn content is preferably 0.01% or more, and preferably 2.8% or less. The P content is preferably 0.030% or less, the S content is 0.008% or less, and the O content is preferably 0.008% or less.

  Moreover, it is preferable that Cr content is 18.5% or more, and it is preferable that it is 37.5% or less. The Ti content is preferably 0.15% or more, and preferably 2.40% or less.

  Further, the N content is preferably 0.0005% or more, and preferably 0.018% or less. The Al content is preferably 0.25% or more, and preferably 1.8% or less. The Fe content is preferably 0.01% or more, and preferably 10.0% or less.

  The B content is preferably 0.0002% or more, and preferably 0.009% or less. The Zr content is preferably 0.001% or more, and preferably 0.40% or less. The W content is preferably 0.10% or more, and preferably 9.0% or less. The Co content is preferably 1.0% or more, and preferably 24.0% or less.

  The Ca content is preferably 0.0001% or more, and preferably 0.0080% or less. The Mg content is preferably 0.0001% or more, and preferably 0.045% or less. The REM content is preferably 0.0001% or more, and preferably 0.080% or less.

  The Cu content is preferably 0.01% or more, and preferably 0.8% or less. The Mo content is preferably 0.01% or more, and preferably 9.5% or less. The V content is preferably 0.01% or more, and preferably 0.4% or less. The Nb content is preferably 0.01% or more, and preferably 2.3% or less.

  The chemical composition of the weld metal is determined by the inflow ratio between the base material and the welding material during welding. Below, the suitable chemical composition of the welding material used for manufacturing the welded joint which concerns on this invention is demonstrated.

3. Chemical composition of welding material The reasons for limitation of each element are as follows. In the following description, “%” for the content means “% by mass”.

C: 0.06-0.15%
C is an element that has the effect of improving the phase stability in the weld metal after welding, and also has the effect of forming fine carbides and improving the creep strength during use at high temperatures. Furthermore, by forming eutectic carbide with Cr during welding solidification, it contributes to reduction of solidification cracking sensitivity. However, if the C content is excessive, a large amount of carbide precipitates, which may reduce the creep strength and ductility. Therefore, the C content is preferably 0.06 to 0.15%. The C content is more preferably 0.07% or more, and further preferably 0.08% or more. Further, the C content is more preferably 0.14% or less, and further preferably 0.12% or less.

Si: 1.0% or less Si is an element that is effective for deoxidation at the time of manufacturing a welding material and is effective for improving the corrosion resistance and oxidation resistance of the weld metal after welding at a high temperature. However, when Si is excessively contained, the phase stability is lowered, and there is a possibility that the toughness and the creep strength are lowered. Therefore, the Si content is preferably 1.0% or less. The Si content is more preferably 0.8% or less, and further preferably 0.6% or less.

  Although there is no need to set a lower limit in particular for the Si content, if it is extremely reduced, the deoxidation effect cannot be sufficiently obtained, the cleanliness of the alloy deteriorates, and the effect of improving the corrosion resistance and oxidation resistance at high temperatures. Is difficult to obtain, and the manufacturing cost is also greatly increased. Therefore, the Si content is preferably 0.01% or more, and more preferably 0.03% or more.

Mn: 2.0% or less Mn, like Si, is an element effective for deoxidation during the production of a welding material. Mn also contributes to the improvement of phase stability in the weld metal after welding. However, when the content of Mn is excessive, embrittlement is caused and there is a possibility that the toughness and creep ductility are lowered. Therefore, the Mn content is preferably 2.0% or less. The Mn content is more preferably 1.8% or less, and further preferably 1.5% or less.

  Note that there is no need to set a lower limit for the Mn content. However, if it is extremely reduced, the deoxidation effect cannot be sufficiently obtained, the cleanliness of the alloy is deteriorated, and the effect of improving the phase stability is difficult to obtain. In addition, the manufacturing cost also increases greatly. Therefore, the Mn content is preferably 0.02% or more, and more preferably 0.05% or more.

P: 0.030% or less P is an element that is contained in the welding material as an impurity and increases the sensitivity to solidification cracking during welding. Furthermore, the creep ductility of the weld metal after long time use at high temperature is reduced. Therefore, the P content is preferably 0.030% or less. The content of P is more preferably 0.025% or less, and further preferably 0.020% or less.

  Although the P content is preferably reduced as much as possible, the extreme reduction leads to an increase in manufacturing cost. Therefore, the P content is preferably 0.0005% or more, and more preferably 0.0008% or more.

S: 0.0100% or less S is an element that is contained in the welding material as an impurity as in the case of P, and increases solidification cracking susceptibility during welding. Furthermore, S segregates at columnar grain boundaries during use for a long time in weld metal, leading to embrittlement and increasing stress relaxation crack sensitivity. Therefore, the S content is preferably 0.0100% or less. The S content is more preferably 0.0080% or less, and further preferably 0.0050% or less.

  Although the S content is preferably reduced as much as possible, the extreme reduction leads to an increase in manufacturing cost. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0002% or more.

O: 0.01% or less O (oxygen) is contained as an impurity in the welding material, and when its content is excessive, hot workability is lowered, which may lead to deterioration of manufacturability. Therefore, the O content is preferably 0.01% or less. The O content is more preferably 0.008% or less, and further preferably 0.005% or less.

  Although there is no particular need to set a lower limit for the O content, an extreme reduction leads to an increase in manufacturing cost. Therefore, the content of O is preferably 0.0005% or more, and more preferably 0.0008% or more.

Co: 8.0 to 25.0%
Co, like Ni, contributes to the improvement of creep strength by increasing the stability of the structure. However, since Co is an extremely expensive element, excessive inclusion in the welding material causes a significant increase in cost. Therefore, the Co content is 8.0 to 25.0%. The Co content is preferably 8.5% or more, and more preferably 9.0% or more. Further, the Co content is preferably 23.5% or less, and more preferably 22.0% or less.

Cr: 18.0 to 27.0%
Cr is an effective element for ensuring oxidation resistance and corrosion resistance at high temperatures of the weld metal after welding. Further, Cr contributes to ensuring creep strength by forming fine carbides. Furthermore, forming eutectic carbide with C during welding also contributes to a reduction in solidification cracking susceptibility. However, if the Cr content exceeds 27.0%, the phase stability at high temperatures may deteriorate, leading to a decrease in creep strength. Therefore, the Cr content is preferably 18.0 to 27.0%. The Cr content is more preferably 18.5% or more, and further preferably 19.0% or more. Further, the Cr content is more preferably 26.5% or less, and further preferably 26.0% or less.

Ti: 0.1 to 2.5%
Ti is an element that precipitates as a fine intermetallic compound phase and contributes to improvement in creep strength and tensile strength at high temperatures. However, when the Ti content is excessive, a large amount of an intermetallic compound phase is precipitated, which may cause a decrease in creep ductility and toughness. Therefore, the Ti content is preferably 0.1 to 2.5%. The Ti content is more preferably 0.15% or more, and further preferably 0.2% or more. Further, the Ti content is more preferably 2.4% or less, and further preferably 2.3% or less.

N: 0.02% or less N is an element that stabilizes the structure in the weld metal, improves the creep strength, and contributes to securing the tensile strength by solid solution. However, if it is contained excessively, a large amount of fine nitride precipitates in the grains during use at high temperatures, which may lead to a decrease in creep ductility and toughness. Therefore, the N content is preferably 0.02% or less. The N content is more preferably 0.018% or less, and further preferably 0.015% or less.

  Although there is no particular need to set a lower limit for the N content, it is difficult to obtain the effect of improving the phase stability if the amount is extremely reduced, and the production cost is greatly increased. Therefore, the N content is preferably 0.0005% or more, and more preferably 0.0008% or more.

Al: 0.2-2.0%
Al, like Ti, is an element that precipitates as a fine intermetallic compound phase and contributes to the improvement of creep strength and tensile strength at high temperatures. However, when the Al content is excessive, a large amount of intermetallic compound phases are precipitated, which may cause a decrease in creep ductility and toughness. Therefore, the Al content is preferably 0.2 to 2.0%. The Al content is more preferably 0.25% or more, and further preferably 0.3% or more. Further, the Al content is more preferably 1.8% or less, and further preferably 1.6% or less.

B: 0 to 0.005%
Since B is an element effective for improving the creep strength of the weld metal, it may be contained. However, if the B content is excessive, the susceptibility to solidification cracking during welding is significantly increased. Therefore, the B content is preferably 0.005% or less. The B content is more preferably 0.004% or less, and further preferably 0.003% or less. In order to obtain the above effect, the B content is preferably 0.0001% or more, and more preferably 0.0005% or more.

Mo: 0 to 12.0%
Mo is an element having a function of improving the creep strength and tensile strength at a high temperature by being dissolved in a matrix of the weld metal, and thus may be contained. However, even if Mo is excessively contained, the effect is saturated, and the creep strength may be lowered. Furthermore, since it is an expensive element, excessive inclusion causes an increase in cost. Therefore, the Mo content is preferably 12.0% or less. The Mo content is more preferably 11.0% or less, and even more preferably 10.0% or less. In addition, when obtaining said effect, it is preferable to make Mo content into 0.01% or more, and it is more preferable to set it as 0.03% or more.

W: 0 to 10.0%
W, like Mo, is an element having a function of improving the creep strength and tensile strength at a high temperature by dissolving in a matrix, and therefore may be contained. However, even if W is contained excessively, the effect is saturated, and the creep strength may be lowered instead. Moreover, since it is an expensive element, when it contains excessively, an increase in cost will be caused. Therefore, the W content is preferably 10.0% or less. The W content is more preferably 9.0% or less, and even more preferably 8.0% or less. In addition, when obtaining said effect, it is preferable to make W content into 0.01% or more, and it is more preferable to set it as 0.03% or more.

Nb: 0 to 0.5%
Nb, like Ti, binds to C or N and precipitates in the grains as fine carbides or carbonitrides, and contributes to the improvement of creep strength at high temperatures, so may be contained. However, when the Nb content is excessive, a large amount of carbide or carbonitride precipitates, which may cause a decrease in creep ductility and toughness. Therefore, the Nb content is preferably 0.5% or less. The Nb content is more preferably 0.48% or less, and further preferably 0.45% or less. In addition, when obtaining said effect, it is preferable that Nb content shall be 0.01% or more, and it is more preferable to set it as 0.03% or more.

Fe: 0 to 15.0%
Fe is an element that has the effect of improving the hot workability when contained in a trace amount in the Ni-base alloy, so it may also be contained in the welding material and utilized. However, when the Fe content is excessive, the thermal expansion coefficient of the weld metal increases and the steam oxidation resistance also deteriorates. Therefore, the Fe content is preferably 15.0% or less. The Fe content is preferably 10.0% or less, and more preferably 8.0% or less. In addition, when obtaining said effect, it is preferable to make Fe content 0.01% or more, and it is more preferable to set it as 0.02% or more.

  In the chemical composition of the welding material, the balance is Ni and impurities. Here, “impurities” are components mixed in due to various factors of raw materials such as ores and scraps and manufacturing processes when the alloy is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.

4). Manufacturing method Although there is no restriction | limiting in particular about the manufacturing method of the base material of the welded joint of this invention, For example, it can manufacture by giving hot work to the steel ingot or slab which has the above-mentioned chemical composition. Moreover, you may further give hot processing of different methods, such as hot extrusion, as needed after the said hot processing.

  Furthermore, after the above steps, in order to suppress the variation in the metal structure and mechanical properties of each part and maintain a high creep rupture strength, a final heat treatment is performed by heating to a temperature range of 1100 to 1250 ° C. Also good. After the heating and holding, it is desirable to cool the base material with water.

  Moreover, there is no restriction | limiting in particular also about the manufacturing method of a welded joint. It is manufactured by welding the above base material. The welding method is not particularly limited, and for example, gas tungsten arc welding, gas metal arc welding, covered arc welding, or the like can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.

  Austenitic heat-resistant alloys (base materials 1 to 18 and A to D) having chemical compositions shown in Table 1 were melted in the laboratory to prepare ingots. And after forming by hot forging and rolling with respect to the said ingot, the final heat processing was performed and the two test materials were obtained from each alloy, respectively. One of them has a thickness of 15 mm, a width of 50 mm, and a length of 100 mm, and one has a thickness of 32 mm, a width of 150 mm, and a length of 200 m.

  Further, from an ingot in which an alloy having the chemical composition shown in Table 2 (welding materials W, X, Y, and Z) was melted and cast in a laboratory, hot forging, rolling, and machining were performed to obtain an outer diameter of 1. A 2 mm welding wire was produced.

  For the test material having a thickness of 15 mm, after processing a V groove having an angle of 30 ° in the longitudinal direction and a root thickness of 1 mm, multilayer welding is performed in the groove by TIG welding using the above-described welding material, A welded joint was produced.

  And in said weld joint, the chemical composition of the first layer part of a weld metal was measured. Table 3 shows the chemical composition of the weld metal of each weld joint.

  Thereafter, a round bar creep rupture test piece having a diameter of 6 mm and a gauge distance of 30 mm described in JIS Z 2241 (2011) was collected from the welded joint so that the weld metal was in the center of the parallel part, and 700 ° C, 160 MPa. A creep rupture test was conducted under the conditions. The test was conducted according to JIS Z 2271 (2010). In addition, the thing whose creep rupture time becomes 2000 h or more was set as the pass ((circle)), and the thing below 2000 h was set as the disqualification (x).

  On the other hand, in order to reproduce a severe stress state in a complicated welded portion shape, a specimen conforming to the y-type weld crack specimen described in JIS Z 3158 (1993) is applied to the alloy plate for a weld base material having a thickness of 32 mm. Fabricated by machining, single layer welding was performed on the groove by TIG welding, and a welded joint was fabricated.

  The obtained welded joint was subjected to an aging heat treatment at 700 ° C. for 500 hours and subjected to the next test. The cross section of the sample taken from each of the five welded joints was mirror-polished and corroded, and then examined with an optical microscope to investigate the presence or absence of cracks in the weld heat affected zone. A weld joint having no cracks in all five samples was evaluated as “◯”, and a crack was observed in at least one sample among the five samples.

  The results are summarized in Table 4.

  As shown in Table 4, test Nos. Using base materials 1 to 18 whose C content is within the specified range of the present invention. The welded joints 1 to 18 showed good results in both creep rupture strength and stress relaxation crack resistance. On the other hand, Test No. using the base materials A to D whose C content is outside the specified range. The weld joints 19 to 22 did not have sufficient stress relaxation crack resistance.

The welded joint of the austenitic heat-resistant alloy of the present invention is excellent in both stress relaxation crack resistance and long-term creep rupture strength. For this reason, the welded joint of the present invention is used not only as a material for a superheater tube and a reheater tube of a power generation boiler, but also as a large-diameter, thick-walled high-temperature member such as a main steam tube and a reheat steam tube. It is suitable to be done.

Claims (4)

Chemical composition is mass%,
C: 0.009% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.040% or less,
S: 0.0100% or less,
O: 0.01% or less,
Cr: 25.0-38.0%,
Ni: 40.0-60.0%,
W: 3.0 to 10.0%
Ti: 0.01-1.20%,
N: 0.020% or less,
Al: 0.30% or less,
B: 0.0001 to 0.01%
Zr: 0.0001 to 0.50%,
Ca: 0 to 0.010%,
Mg: 0 to 0.050%,
REM: 0 to 0.100%,
Co: 0 to 1.0%,
Cu: 0 to 1.0%
Mo: 0 to 1.0%,
V: 0 to 0.5%
Nb: 0 to 0.5%,
The balance: a base material that is Fe and impurities,
Chemical composition is mass%,
C: 0.15% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.040% or less,
S: 0.0100% or less,
O: 0.01% or less,
Cr: 18.0 to 38.0%,
Ti: 0.01-2.50%,
N: 0.020% or less,
Al: 2.0% or less,
Fe: 15.0% or less,
B: 0.0001 to 0.01%
Zr: 0.0001 to 0.50%,
W: 0.01 to 10.0%,
Co: 0.5-25.0%
Ca: 0 to 0.010%,
Mg: 0 to 0.050%,
REM: 0 to 0.100%,
Cu: 0 to 1.0%
Mo: 0 to 12.0%,
V: 0 to 0.5%
Nb: 0 to 2.5%,
Balance: including weld metal that is Ni and impurities,
Welded joints. The chemical composition of the base material is mass%,
Ca: 0.0001 to 0.010%,
Mg: 0.0001 to 0.050%, and REM: 0.0001 to 0.100%,
Containing one or more selected from
The welded joint according to claim 1. The chemical composition of the base material is mass%,
Co: 0.01 to 1.0%
Cu: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
V: 0.01 to 0.5%, and Nb: 0.01 to 0.5%,
Containing one or more selected from
The welded joint according to claim 1 or 2. The chemical composition of the base material is mass%,
C: 0.0001 to 0.009%,
Containing
The welded joint according to any one of claims 1 to 3.