Weld joint

Abstract

Provided is a weld joint comprising a weld metal and a parent material, wherein: the chemical composition of the weld metal is, by mass%, 0.050% or less C, 0.05-0.50% Si, 0.05-1.00% Mn, 0.035% or less P, 0.0020% or less S, 33.0-45.0% Ni, 20.0-30.0% Cr, 0.20-1.00% Nb, 0.10-0.30% N, 0.10% or less Al, 0.0035% or less B, 0.020% or less O, 0.50% or less V, and 1.00% or less Ta, with the remainder being Fe and impurities; and 0.05≤V+Ta, 0.50≤[Nb]ER, and [Nb]ER+[V]ER+[TA]ER≤0.350 are satisfied.

Description

Welded joints

[0001] This invention relates to welded joints.

[0002] In recent years, clean energy from solar power generation has been attracting attention. In particular, because solar power generation does not emit carbon dioxide, its importance in preventing global warming is increasing year by year. Incidentally, when manufacturing solar power generation equipment, polycrystalline silicon is often used as the power generation element. Polycrystalline silicon is manufactured by repeatedly distilling and refining liquid trichlorosilane as a raw material.

[0003] In this context, the inside of the reaction tower used to produce polycrystalline silicon is an extremely harsh environment, with reaction gas pressures exceeding 100 MPa and temperatures exceeding 600°C. Therefore, there is a need for materials with excellent high-temperature strength that can be used in such environments. Patent documents 1 and 2 disclose alloy materials containing Nb to enhance high-temperature strength.

[0004] Japanese Patent Publication No. 2017-57461 Japanese Patent Publication No. 2024-25945

[0005] To improve high-temperature strength, it is effective to include Nb and precipitate fine carbides, nitrides, and carbonitrides containing Nb. However, when welding alloy materials with increased Nb content to manufacture the aforementioned equipment, solidification cracking may occur in the weld metal. Furthermore, if the carbon content in the weld metal is increased to precipitate carbides, stress relaxation cracking may occur in the weld metal during use in high-temperature environments. Therefore, there is a need for welded joints that contain a predetermined amount of Nb while exhibiting excellent resistance to solidification cracking and stress relaxation cracking. Patent documents 1 and 2 do not address solidification cracking and stress relaxation cracking.

[0006] The present invention aims to solve the above problems and provide a welded joint with excellent resistance to solidification cracking and stress relaxation cracking.

[0007] This invention was made to solve the above problems, and its essence is the following welded joint.

[0008] (1) A welded joint comprising a weld metal and a base metal, wherein the chemical composition of the weld metal is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.10 to 0.30%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, the remainder being Fe and impurities, and satisfying the following formulas (i) to (iii). 0.05≦V+Ta...(i) 0.050≦[Nb] ＥＲ ...(ii) [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ ≤0.350 ... (iii) However, the element symbols in formula (i) above mean the content (mass%) of each element in the weld metal, and [Nb] in formulas (ii) and (iii) above ＥＲ [V] ＥＲ , and [Ta] ＥＲ These terms represent the mass percentages (%) of Nb, V, and Ta in the residue obtained by the extraction residue analysis.

[0009] (2) A welded joint comprising a weld metal and a base material, wherein the chemical composition of the weld metal is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.10 to 0.30%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, and further contains one or more selected from the groups A, B and C below, with the remainder being Fe and impurities. A welded joint that satisfies equations (i) to (iii) below: 0.05 ≤ V + Ta ... (i) 0.050 ≤ [Nb] ＥＲ・・・ (ii) [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ ≤ 0.350 ・・・ (iii) However, the element symbols in the above formula (i) represent the content (mass %) of each element contained in the weld metal, and [Nb] in the above formulas (ii) and (iii) ＥＲ , [V] ＥＲ , and [Ta] ＥＲ each represent the content (mass %) of Nb, V, and Ta in the residue obtained by extraction residue analysis. [Group A] One or more selected from the group consisting of Mo: 2.00% or less, W: 2.00% or less, Cu: 1.00% or less, Co: 1.00% or less, Ti: 0.10% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group B] One or more selected from the group consisting of Sn: 0.010% or less, Zn: 0.010% or less, Pb: 0.010% or less, and Sb: 0.010% or less [Group C] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.10% or less

[0010] (3) The welded joint according to (2) above, wherein the chemical composition of the weld metal contains one or more elements selected from the above Group A.

[0011] (4) The welded joint according to (2) above, wherein the chemical composition of the weld metal contains one or more elements selected from the above Group B.

[0012] (5) The welded joint according to (2) above, wherein the chemical composition of the weld metal contains one or more elements selected from the above Group C.

[0013] (6) A welded joint according to any of (1) to (5) above, wherein the chemical composition of the base material is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.12 to 0.35%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, the remainder: Fe and impurities, and satisfies the following formula (iv). 0.05 ≤ V + Ta ... (iv) where the element symbols in equation (iv) above represent the mass percentage of each element contained in the base material.

[0014] (7) The chemical composition of the base material is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.12 to 0.35%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, and further contains one or more selected from the groups consisting of groups D, E and F below, with the remainder being Fe and impurities, and satisfying the following formula (iv): A welded joint as described in any of (1) to (5) above. 0.05 ≤ V + Ta ... (iv) However, the element symbols in formula (iv) above mean the content (mass%) of each element contained in the base material. [Group D] One or more selected from the group consisting of Mo: 2.00% or less, W: 2.00% or less, Cu: 1.00% or less, Co: 1.00% or less, Ti: 0.10% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group E] One or more selected from the group consisting of Sn: 0.010% or less, Zn: 0.010% or less, Pb: 0.010% or less, and Sb: 0.010% or less [Group F] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.10% or less

[0015] (8) The welded joint according to (7) above, wherein the chemical composition of the base material contains one or more elements selected from the D group.

[0016] (9) The welded joint according to (7) above, wherein the chemical composition of the base material contains one or more elements selected from the E group.

[0017] (10) The welded joint according to (7) above, wherein the chemical composition of the base material contains one or more elements selected from the F group.

[0018] (11) The chemical composition of the weld metal is, in mass%, V: 0.03 to 0.50%, and Ta: 0.01 to 1.00%, and satisfies the following formulas (v) and (vi). The welded joint according to any one of (1) to (5) above. 0.003 ≦ [V] ＥＲ ・・・(v) 0.001 ≦ [Ta] ＥＲ ・・・(vi) However, [V] in the above formulas (v) and (vi) ＥＲ and [Ta] ＥＲ each mean the contents (mass%) of V and Ta in the residue obtained by extraction residue analysis.

[0019] According to the present invention, a welded joint excellent in solidification cracking resistance and stress relaxation cracking resistance can be obtained.

[0020] FIG. 1 is a diagram for explaining a welding method. FIG. 2 is a diagram for explaining an observation position of the presence or absence of cracks. FIG. 3 is a diagram for explaining the shape of a test piece for stress relaxation cracking resistance evaluation.

[0021] In order to solve the above-described problems, the present inventors have conducted a detailed investigation on solidification cracking resistance and stress relaxation cracking resistance, and as a result, have obtained the following findings.

[0022] As mentioned above, to improve high-temperature strength, it is effective to include a high amount of Nb and allow Nb-containing carbides, nitrides, and carbonitrides to precipitate during use in high-temperature environments. However, if the carbon content in the weld metal is increased to precipitate carbides, stress relaxation cracking may occur in the weld metal during use in high-temperature environments. This is thought to be due to the following mechanism.

[0023] If the C content is high, M ２３ C ６ (M represents Cr, Fe, etc.) precipitates at the grain boundaries. And M ２３ C ６ The surrounding Cr content decreases, and a Cr-deficient layer is formed. In this Cr-deficient layer, the Z phase (CrNbN) cannot precipitate, and a Precipitation Free Zone (PFZ) is formed. In the PFZ, the precipitation strengthening effect is not obtained, resulting in low strength. Therefore, strain caused by stress relaxation in high-temperature environments concentrates, and stress relaxation cracks occur. For this reason, in this invention, the C content of the weld metal is limited to 0.050% or less.

[0024] Furthermore, increasing the Nb content in the weld metal can sometimes lead to solidification cracking. Solidification cracking in weld metal when Nb content is increased is thought to occur through the following mechanism: During the solidification process of the weld metal, as the cellular dendritic structure grows, microsegregation occurs, and solute elements become concentrated in the spaces between the cellular dendritic trees. Among the solute elements, Nb is prone to microsegregation and significantly lowers the solidus temperature, so a liquid phase tends to remain in the spaces between the trees as a film. When tensile stress caused by solidification and thermal shrinkage acts on this liquid film, the area opens up, and solidification cracking occurs.

[0025] One possible method to prevent solidification cracking in Nb-containing alloy materials is to include C along with Nb, causing Nb to crystallize as carbides. However, in this invention, as mentioned above, the C content is reduced, making it difficult to crystallize Nb carbides. Therefore, by incorporating Nb and N within appropriate ranges into the weld metal and strictly controlling the welding conditions, Nb nitrides (e.g., Z phase) are actively crystallized to ensure resistance to solidification cracking.

[0026] However, simply crystallizing Nb nitrides was sometimes insufficient to obtain adequate resistance to solidification cracking. Therefore, the inventors conducted further investigations. As a result, they found that by including V and / or Ta in the weld metal within a predetermined range, in addition to Nb, solidification cracking resistance can be improved. V and Ta are less prone to microsegregation than Nb, and do not lower the solidus temperature as much. Furthermore, they increase the amount of nitride crystallized, which is thought to improve solidification cracking resistance.

[0027] On the other hand, if Nb, V, and Ta crystallize in excess, the crystal grains harden significantly during use in high-temperature environments, reducing stress relaxation crack resistance. Therefore, the total content of Nb, V, and Ta in the residue obtained by extraction residue analysis was set to 0.350% or less.

[0028] In this way, by controlling the chemical composition of the weld metal and the chemical composition of nitrides within the weld metal, excellent resistance to solidification cracking and stress relaxation cracking can be obtained.

[0029] This invention is based on the above findings. The requirements of this invention will be described in detail below.

[0030] (A) The reasons for limiting the elements in the chemical composition of the weld metal are as follows. In the following explanation, "%" for content means "mass%". Furthermore, the chemical composition of the weld metal refers to the chemical composition at a height of half the total thickness of the weld metal and at the center of the total width of the weld metal.

[0031] C: 0.050% or less. Carbon (C) is an element necessary to ensure high-temperature strength. However, excessive C content deteriorates stress relaxation crack resistance. Therefore, the C content should be 0.050% or less. Preferably, the C content is 0.045% or less, and more preferably 0.040% or less. There is no lower limit to the C content, and the C content may be 0%. On the other hand, if the effect of improving high-temperature strength due to C is to be obtained, it is preferable that the C content is greater than 0%, and more preferably 0.010% or more.

[0032] Si: 0.05-0.50% Si is an element that has a deoxidizing effect. However, if Si is included in excess, the resistance to solidification cracking in the weld metal will decrease. Therefore, the Si content should be 0.05-0.50%. Preferably, the Si content should be 0.10% or more, and more preferably 0.20% or more. Furthermore, preferably, the Si content should be 0.45% or less, and more preferably 0.40% or less.

[0033] Mn: 0.05-1.00% Mn is an element that has a deoxidizing effect. However, if Mn is included in excess, the stability of the austenite phase decreases and the high-temperature strength decreases. For this reason, the Mn content should be 0.05-1.00%. Preferably, the Mn content should be 0.10% or more, and more preferably 0.20% or more. Furthermore, preferably, the Mn content should be 0.95% or less, and more preferably 0.90% or less.

[0034] P: 0.035% or less. P is an element contained as an impurity and reduces the solidification crack resistance of the weld metal. Therefore, the P content should be 0.035% or less. Preferably, the P content is 0.030% or less, and more preferably 0.025% or less. Since it is preferable to reduce the P content as much as possible, the lower limit of the P content is 0%. However, extreme reduction of the P content increases steelmaking costs. Therefore, it is preferable that the P content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.005% or more.

[0035] S: 0.0020% or less. S is an element contained in weld metal because it has the effect of improving weldability by increasing penetration during welding. However, if S is included in excess, the solidification crack resistance of the weld metal decreases. For this reason, the S content should be 0.0020% or less. Preferably, the S content should be 0.0015% or less. There is no need to set a lower limit for the S content, and the S content may be 0%. On the other hand, if the effect of improving weldability by S is to be obtained, it is preferable that the S content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0003% or more.

[0036] Ni: 33.00–45.00% Ni is an important element for stabilizing the austenite phase and maintaining high-temperature strength. However, excessive Ni content leads to a significant increase in manufacturing costs. Therefore, the Ni content is set to 33.00–45.00%. The Ni content is preferably 35.00% or more, and more preferably 36.50% or more. Furthermore, the Ni content is preferably 43.00% or less, and more preferably 41.00% or less.

[0037] Cr: 20.00-30.00% Cr forms a dense oxide film at high temperatures, which helps maintain oxidation resistance and / or corrosion resistance at high temperatures. However, excessive Cr content reduces the stability of the austenite phase and degrades the high-temperature strength. Therefore, the Cr content should be 20.00-30.00%. Preferably, the Cr content is 22.00% or more, and more preferably 23.00% or more. Furthermore, preferably, the Cr content is 29.00% or less, and more preferably 28.00% or less.

[0038] Nb: 0.20-1.00% Nb is an element that forms nitrides and is effective in improving high-temperature strength. However, if Nb is included in excess, the resistance to solidification cracking deteriorates significantly. Therefore, the Nb content should be 0.20-1.00%. A Nb content of 0.40% or more is preferable. Furthermore, a Nb content of 0.80% or less is preferable.

[0039] N: 0.10-0.30% N improves solidification crack resistance by forming nitrides with Nb, V, and Ta. N is also an effective element for improving high-temperature strength by solid dissolving in the austenite phase. However, if N is included in excess, welding defects such as blowholes will occur in the weld metal. Therefore, the N content should be 0.10-0.30%. The N content is preferably more than 0.10%, 0.11% or more, or 0.12% or more, and more preferably 0.14% or more. Furthermore, the N content is preferably 0.28% or less, and more preferably 0.26% or less.

[0040] Al: 0.10% or less. Al is an element that has a deoxidizing effect. However, if Al is included in excess, Al will form Al nitrides, so sufficient Nb, V, and Ta nitrides cannot crystallize, and the resistance to solidification cracking deteriorates. For this reason, the Al content should be 0.10% or less. Preferably, the Al content is 0.08% or less. There is no need to set a lower limit for the Al content, and the Al content may be 0%. On the other hand, if you want to obtain the effect of improving high-temperature properties with Al, it is preferable that the Al content be greater than 0%, more preferably 0.03% or more, and even more preferably 0.05% or more.

[0041] B: 0.0035% or less. B has the effect of increasing high-temperature strength. However, if B is included in excess, the solidification crack resistance of the weld metal will decrease. For this reason, the B content should be 0.0035% or less. Preferably, the B content is 0.0030% or less, and more preferably 0.0025% or less. There is no lower limit to the B content, and the B content may be 0%. On the other hand, if the effect of increasing high-temperature strength due to B is to be obtained, preferably, the B content is greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0042] O: 0.020% or less. O is an element contained as an impurity. Therefore, the O content should be 0.020% or less. Preferably, the O content should be 0.018% or less, and more preferably 0.016% or less. Since it is preferable to reduce the O content as much as possible, the lower limit of the O content is 0%. However, extreme reduction of the O content increases steelmaking costs. Therefore, preferably, the O content should be greater than 0%, more preferably 0.001% or more, and even more preferably 0.002% or more.

[0043] V: 0.50% or less V has the effect of forming fine nitrides, thereby improving solidification crack resistance and high-temperature strength. However, if V is included in excess, a large amount of nitrides containing V will be generated during the solidification process, and the inside of the crystal grains will harden significantly during use in a high-temperature environment, thus reducing stress relaxation crack resistance. Therefore, the V content should be 0.50% or less. Preferably, the V content should be 0.45% or less, and more preferably 0.40% or less. In addition, as long as formula (i) described later is satisfied, the V content may be 0%, but if the above effect is to be obtained more reliably, it is preferable to have a V content greater than 0%, more preferably 0.03% or more, and even more preferably 0.05% or more.

[0044] Ta: 1.00% or less. Ta has the effect of improving solidification crack resistance and high-temperature strength by forming fine nitrides. However, if Ta is included in excess, a large amount of nitrides containing Ta will be generated during the solidification process, causing the inside of the crystal grains to harden significantly during use in high-temperature environments and reducing stress relaxation crack resistance. Also, since Ta is an expensive element, including too much Ta will lead to increased costs. Therefore, the Ta content should be 1.00% or less. Preferably, the Ta content should be 0.90% or less, and more preferably 0.80% or less. In addition, as long as the formula (i) described later is satisfied, the Ta content may be 0%, but if the above effects are to be obtained more reliably, it is preferable that the Ta content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0045] Furthermore, our inventors' research has shown that by incorporating V and Ta in combination, we can further improve stress relaxation crack resistance during use in high-temperature environments. Although the detailed mechanism is unknown, V has the effect of increasing the strength within the crystal grains by promoting the precipitation of the Z phase and solid solution strengthening, while Ta has the effect of increasing the strength near the crystal grain boundaries by precipitating Ta nitride in the Cr-deficient layer. Therefore, by incorporating V and Ta in combination, it is believed that the concentration of deformation both within the crystal grains and at the crystal grain boundaries is suppressed, and the occurrence of cracks can be suppressed even during use in high-temperature environments.

[0046] To obtain further improvements in stress relaxation crack resistance, it is preferable to have a V content of 0.03 to 0.50% and a Ta content of 0.01 to 1.00%.

[0047] In the chemical composition of the weld metal of the present invention, the remainder is Fe and impurities. Here, impurities refer to components that are mixed in during the industrial production of the weld metal due to raw materials such as ore and scrap, or other factors, and are acceptable within a range that does not adversely affect the properties of the welded joint according to the present invention.

[0048] 0.05 ≤ V + Ta As described above, by including V and / or Ta in the weld metal in addition to Nb and allowing nitrides of V and / or Ta to crystallize, the resistance to solidification cracking can be improved. To achieve this, the total content of V and Ta, as defined by the right-hand side value of equation (i) below, should be 0.05 or more. The right-hand side value of equation (i) below is preferably 0.06 or more, and more preferably 0.08 or more. 0.05 ≤ V + Ta ... (i) However, the element symbols in the above formula represent the content (mass %) of each element contained in the weld metal.

[0049] Furthermore, V and Ta may be included individually or together. If V is included individually, the V content shall be 0.05% or more. If Ta is included individually, the Ta content shall be 0.05% or more. If both V and Ta are included together, the total content of V and Ta shall be 0.05% or more.

[0050] The upper limit of the right-hand side value in equation (i) above is not particularly limited, as long as it satisfies equation (iii) described later. However, in the chemical composition specified in the present invention, the upper limit of the right-hand side value in equation (i) is 1.50.

[0051] To improve resistance to solidification cracking, it is preferable to adjust the content of V, Ta, N, Nb, and B to satisfy the following equation (a). By setting the right-hand side value of equation (a) below to 1.50 or higher, resistance to solidification cracking can be further improved. The right-hand side value of equation (a) below is preferably 2.00 or higher, and more preferably 3.00 or higher. 1.50 ≤ 3V + 2Ta + 20N - Nb - 800B ... (a) However, the element symbols in the above equation represent the content (mass %) of each element contained in the weld metal.

[0052] To improve resistance to stress relaxation cracking, it is preferable to adjust the content of C, V, Ta, and B to satisfy the following equation (b). By setting the left-hand side value of equation (b) below to 1.00 or less, the resistance to stress relaxation cracking can be further improved. The left-hand side value of equation (b) below is preferably 0.90 or less, and more preferably 0.70 or less. 10C + V + 0.5Ta - 30B ≤ 1.00 ... (b) However, the element symbols in the above equation represent the content (mass %) of each element contained in the weld metal.

[0053] In the chemical composition of the weld metal of the present invention, in order to improve high-temperature strength, one or more elements selected from Mo, W, Cu, Co, Ti, Zr, and Hf may be included within the ranges shown below. Since these elements are not necessarily essential in the weld metal, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0054] Mo: 2.00% or less Mo dissolves in the austenite phase and greatly contributes to improving high-temperature strength. For this reason, Mo may be included as needed. However, if Mo is included in excess, the σ phase will be formed and the toughness will decrease. Therefore, the Mo content should be 2.00% or less. Preferably, the Mo content should be 1.50% or less, and more preferably 1.00% or less. If the above effects are to be obtained more reliably, it is preferable that the Mo content be greater than 0%, more preferably 0.10% or more, and even more preferably 0.50% or more.

[0055] W: 2.00% or less. W dissolves in the austenite phase and greatly contributes to improving high-temperature strength. For this reason, W may be included as needed. However, the effect saturates if W is included in excess. Also, since W is an expensive element, including it in excess will lead to increased costs. Therefore, the W content should be 2.00% or less. Preferably, the W content should be 1.50% or less, and more preferably 1.00% or less. Furthermore, if the above effect is to be obtained more reliably, it is preferable that the W content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.10% or more.

[0056] Cu: 1.00% or less. Cu is an austenite-forming element and contributes to improved phase stability and high-temperature strength. For this reason, Cu may be included as needed. However, excessive Cu content reduces the solidification crack resistance of the weld metal. Therefore, the Cu content should be 1.00% or less. Preferably, the Cu content should be 0.80% or less, and more preferably 0.60% or less. If the above effects are to be obtained more reliably, it is preferable that the Cu content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0057] Co: 1.00% or less. Co is an austenite-forming element that enhances phase stability and contributes to improved high-temperature strength. For this reason, Co may be included as needed. However, since Co is an extremely expensive element, excessive Co content will lead to a significant increase in costs. Therefore, the Co content should be 1.00% or less. Preferably, the Co content should be 0.80% or less, and more preferably 0.60% or less. If the above effects are to be obtained more reliably, it is preferable that the Co content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0058] Ti: 0.10% or less. Ti precipitates within the grains as fine carbonitrides, contributing to improved high-temperature strength. For this reason, Ti may be included as needed. However, excessive Ti content leads to the precipitation of large amounts of coarse Ti nitrides, resulting in a decrease in toughness. Therefore, the Ti content should be 0.10% or less. Preferably, the Ti content is 0.08% or less, and more preferably 0.06% or less. If the above effects are to be obtained more reliably, it is preferable that the Ti content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0059] Zr: 0.10% or less. Zr has the effect of improving high-temperature strength as a grain boundary strengthening element. For this reason, Zr may be included as needed. However, if Zr is included in excess, a large amount of coarse Zr nitride will precipitate, leading to a decrease in toughness. Therefore, the Zr content should be 0.10% or less. Preferably, the Zr content should be 0.08% or less, and more preferably 0.06% or less. If the above effect is to be obtained more reliably, it is preferable that the Zr content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0060] Hf: 0.10% or less. Hf contributes to precipitation strengthening as a carbonitride and improves high-temperature strength. For this reason, Hf may be included as needed. However, excessive Hf content will impair weld crack resistance. Therefore, the Hf content should be 0.10% or less. Preferably, the Hf content should be 0.08% or less, and more preferably 0.06% or less. If the above effects are to be obtained more reliably, it is preferable that the Hf content be greater than 0%, more preferably 0.01% or more, and even more preferably 0.03% or more.

[0061] In the chemical composition of the weld metal of the present invention, in order to improve weldability, one or more elements selected from Sn, Zn, Pb, and Sb may be included within the ranges shown below. Since these elements are not necessarily essential in the weld metal, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0062] Sn: 0.010% or less. Sn has the effect of improving weldability by increasing penetration during welding. For this reason, Sn may be included as needed. However, if Sn is included in excess, the solidification crack resistance of the weld metal will decrease. Therefore, the Sn content should be 0.010% or less. Preferably, the Sn content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Sn content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0063] Zn: 0.010% or less. Zn has the effect of improving weldability by increasing penetration during welding. For this reason, Zn may be included as needed. However, if Zn is included in excess, the solidification crack resistance of the weld metal will decrease. Therefore, the Zn content should be 0.010% or less. Preferably, the Zn content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Zn content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0064] Pb: 0.010% or less. Pb has the effect of improving weldability by increasing penetration during welding. For this reason, Pb may be included as needed. However, if Pb is included in excess, the solidification crack resistance of the weld metal will decrease. Therefore, the Pb content should be 0.010% or less. Preferably, the Pb content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Pb content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0065] Sb: 0.010% or less. Sb has the effect of improving weldability by increasing penetration during welding. For this reason, Sb may be included as needed. However, if Sb is included in excess, the solidification crack resistance of the weld metal will decrease. Therefore, the Sb content should be 0.010% or less. Preferably, the Sb content should be 0.008% or less, and more preferably 0.006% or less. If the above effects are to be obtained more reliably, it is preferable that the Sb content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.003% or more.

[0066] In the chemical composition of the weld metal of the present invention, in order to improve hot workability, one or more elements selected from Ca, Mg, and REM may be further included within the ranges shown below. Since these elements are not necessarily essential in the weld metal, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0067] Ca: 0.0050% or less. Ca is an element that has a deoxidizing effect, and may be included as needed. However, if Ca is included in excess, slag spots (oxides) will occur on the surface of the weld bead, impairing the aesthetics. Therefore, the Ca content should be 0.0050% or less. Preferably, the Ca content should be 0.0045% or less, and more preferably 0.0040% or less. If the above effects are to be obtained more reliably, it is preferable that the Ca content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0068] Mg: 0.0050% or less. Mg is an element that has a deoxidizing effect, and it may be included as needed. However, if Mg is included in excess, slag spots (oxides) will be generated on the surface of the weld bead, impairing the aesthetics. Therefore, the Mg content should be 0.0050% or less. Preferably, the Mg content should be 0.0045% or less, and more preferably 0.0040% or less. If the above effects are to be obtained more reliably, it is preferable that the Mg content be greater than 0%, more preferably 0.0001% or more, and even more preferably 0.0005% or more.

[0069] REM: 0.10% or less. REM is an element that has a deoxidizing effect, and may be included as needed. However, if REM is included in excess, slag spots (oxides) will form on the surface of the weld bead, impairing the aesthetics. Therefore, the REM content should be 0.10% or less. Preferably, the REM content should be 0.09% or less, and more preferably 0.08% or less. If the above effects are to be obtained more reliably, it is preferable that the REM content be greater than 0%, more preferably 0.001% or more, and even more preferably 0.005% or more.

[0070] Here, REM is a collective term for 17 elements including Sc, Y, and lanthanides, and the REM content refers to the total amount of these elements. Note that lanthanides are industrially added in the form of mischmetal.

[0071] (B) Electrolytic extraction residue (B-1) 0.050≦[Nb] ＥＲ As described above, resistance to solidification cracking can be ensured by actively crystallizing Nb nitrides in the weld metal. If the Nb content in the residue obtained by extraction residue analysis is less than 0.050, resistance to solidification cracking cannot be ensured. Therefore, as shown in equation (ii) below, [Nb] ＥＲ The value shall be 0.050 or higher. [Nb] ＥＲ It is preferably 0.080 or higher, and more preferably 0.100 or higher. 0.050 ≤ [Nb] ＥＲ ... (ii) However, [Nb] in equation (ii) above ＥＲ This refers to the Nb content (mass %) in the residue obtained by extraction residue analysis.

[0072] [Nb] ＥＲ The upper limit is not particularly limited as long as it satisfies formula (iii) described later. In the chemical composition specified in this application and the manufacturing conditions described later, [Nb] ＥＲ The upper limit is, for example, 0.250 or 0.240.

[0073] (B-2) [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ≤0.350 As described above, if the left-hand side value of equation (iii) below is greater than 0.350, excessive crystallization of Nb, V, and Ta will cause significant hardening within the crystal grains during use in high-temperature environments, reducing stress relaxation crack resistance. Therefore, the left-hand side value of equation (iii) below should be 0.350 or less. Preferably, the left-hand side value of equation (iii) below is 0.330 or less, and more preferably 0.310 or less. [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ ≤0.350 ... (iii) where [Nb] in equation (i) above ＥＲ [V] ＥＲ , and [Ta] ＥＲ These terms represent the mass percentages (%) of Nb, V, and Ta in the residue obtained by the extraction residue analysis.

[0074] The lower limit of the left-hand side of equation (iii) above is not particularly limited. In the chemical composition specified in this application and the manufacturing conditions described later, the lower limit of the left-hand side of equation (iii) above is 0.050, 0.070, or 0.090.

[0075] As described above, when Ta is included in the weld metal along with V, the stress relaxation cracking resistance can be further improved. To achieve this, it is preferable that the content of V and Ta in the residue obtained by extraction residue analysis satisfies the following equations (v) and (vi). [V] ＥＲ It is more preferable that it be 0.005 or higher. [Ta] ＥＲ It is more preferable that it be 0.010 or greater. 0.003 ≤ [V] ＥＲ ...(v) 0.001≦[Ta] ＥＲ ... (vi) However, [V] in equation (v) and equation (vi) above ＥＲ and [Ta] ＥＲ These terms represent the content (mass %) of V and Ta in the residue obtained by the extraction residue analysis, respectively.

[0076] [V] ＥＲ and [Ta] ＥＲ The upper limit of is not particularly limited as long as it satisfies equation (iii) above. In the chemical composition specified in this application and the manufacturing conditions described later, [V]ＥＲ The upper limit is, for example, 0.025 or 0.020. [Ta] ＥＲ The upper limit is, for example, 0.200 or 0.180.

[0077] The content (mass %) of each element in the residue analyzed as the electrolytic extraction residue in the above formula can be measured by the following procedure. Specifically, first, a test piece of a predetermined size is taken from the welded joint at a height of half the total thickness of the weld metal and from the center of the total width of the weld metal. Then, using an electrolyte of 10 vol% acetylacetone - 1 mass% tetramethylammonium chloride - methanol, an aqueous solution of 20 mA / cm² is applied. ２ The test specimen is electrolyzed at the specified current density. After electrolysis, the solution is filtered through a 0.2 μm filter, and the residue is acid-decomposed. Then, the content (mass%) of Nb, V, and Ta is measured using an ICP (inductively coupled plasma) emission spectrometer, and the content of each element and the left-hand side value of equation (iii) above are calculated.

[0078] (C) Chemical composition of the base material In the welded joint of the present invention, as long as the weld metal has the chemical composition described above, the chemical composition of the alloy material which is the base material is not particularly limited, but for example, it is preferable to have the following chemical composition.

[0079] The reasons for limiting each element are as follows. In the following explanation, "%" for content refers to "mass%". Furthermore, the chemical composition of the base material refers to the chemical composition of the welded joint excluding the weld metal and heat-affected zone.

[0080] C: 0.050% or less. Carbon (C) is an element necessary to ensure the high-temperature strength of the alloy. Furthermore, by limiting the C content to 0.050% or less, the formation of large amounts of carbides during the solidification process of the alloy can be suppressed, thereby preventing deterioration of manufacturability due to a decrease in hot workability. For this reason, it is preferable that the C content be 0.050% or less. It is more preferable that the C content be 0.045% or less. There is no need to set a lower limit for the C content, and the C content may be 0%. On the other hand, if the effect of improving high-temperature strength due to C is to be obtained, it is more preferable that the C content be greater than 0%, and even more preferable that it be 0.010% or more.

[0081] Si: 0.05-0.50% Si is an element that has a deoxidizing effect. Furthermore, by keeping the Si content at 0.50% or less, resistance to liquefaction cracking in the heat-affected zone can be ensured. For this reason, it is preferable that the Si content be 0.05-0.50%. It is more preferable that the Si content be 0.10% or more, and even more preferable that it be 0.45% or less.

[0082] Mn: 0.05 to 1.00% Mn is an element that has a deoxidizing effect. Furthermore, by keeping the Mn content at 1.00% or less, the stability of the austenite phase can be ensured and the decrease in high-temperature strength can be suppressed. For this reason, it is preferable that the Mn content be 0.05 to 1.00%. It is more preferable that the Mn content be 0.10% or more, and even more preferable that be 0.95% or less.

[0083] P: 0.035% or less. P is an element contained as an impurity. Therefore, it is preferable that the P content be 0.035% or less. It is more preferable that the P content be 0.020% or less. It is preferable to reduce the P content as much as possible, and it may be 0%, but an extreme reduction in the P content will lead to an increase in manufacturing costs. Therefore, it is more preferable that the P content be greater than 0%, and even more preferable that it be 0.001% or more.

[0084] S: 0.0020% or less. S is an element that improves weldability by increasing penetration during welding. Furthermore, by keeping the S content at 0.0020% or less, the decrease in hot workability can be suppressed, thereby reducing the deterioration of manufacturability. For this reason, it is preferable that the S content be 0.0020% or less. It is more preferable that the S content be 0.0015% or less. There is no need to set a lower limit for the S content, and the S content may be 0%. On the other hand, if the effect of improving weldability due to S is to be obtained, it is more preferable that the S content be greater than 0%, and even more preferable that it be 0.0001% or more.

[0085] Ni: 33.00–45.00% Ni is an important element for stabilizing the austenite phase and maintaining high-temperature strength. Furthermore, by keeping the Ni content below 45.00%, the increase in manufacturing costs can be suppressed. For this reason, the Ni content is preferably between 33.00 and 45.00%. A Ni content of 35.00% or more is more preferable, and 40.00% or less is even more preferable.

[0086] Cr: 20.00-30.00% Cr forms a dense oxide film at high temperatures, which helps maintain oxidation resistance and / or corrosion resistance at high temperatures. Furthermore, by keeping the Cr content below 30.00%, the stability of the austenite phase can be ensured, and the deterioration of high-temperature strength can be suppressed. For this reason, the Cr content is preferably 20.00-30.00%. The Cr content is more preferably 22.00% or more, and even more preferably 29.00% or less.

[0087] Nb: 0.20-1.00% Nb is an element that forms nitrides and is effective in improving high-temperature strength. Furthermore, by keeping the Nb content at 1.00% or less, the decrease in liquefaction cracking resistance can be suppressed. For this reason, the Nb content is preferably 0.20-1.00%. The Nb content is more preferably 0.40% or more, and even more preferably 0.80% or less.

[0088] N: 0.12-0.35% N is an effective element for forming nitrides and for improving high-temperature strength by solid dissolving in the austenite phase. Furthermore, by keeping the N content at 0.35% or less, the decrease in hot workability can be suppressed, thereby reducing the deterioration of manufacturability. For this reason, the N content is preferably 0.12-0.35%. The N content is more preferably 0.15% or more, and even more preferably 0.30% or less.

[0089] Al: 0.10% or less. Al is an element that has a deoxidizing effect and contributes to improving high-temperature properties by reducing oxide inclusions. Furthermore, by keeping the Al content at 0.10% or less, the excessive formation of Al nitrides can be suppressed, and the deterioration of high-temperature strength can be suppressed. For this reason, it is preferable that the Al content be 0.10% or less. It is more preferable that the Al content be 0.08% or less. There is no need to set a lower limit for the Al content, and the Al content may be 0%. On the other hand, if the above effects of Al are to be obtained, it is more preferable that the Al content be greater than 0%, and even more preferable that it be 0.03% or more.

[0090] B: 0.0035% or less. B has the effect of increasing high-temperature strength and / or hot workability. In addition, by keeping the B content at 0.0035% or less, the decrease in liquefaction crack resistance can be suppressed. For this reason, it is preferable that the B content be 0.0035% or less. It is more preferable that the B content be 0.0030% or less. There is no need to set a lower limit for the B content, and the B content may be 0%. On the other hand, if you want to obtain the effect of increasing high-temperature strength and / or hot workability by B, it is more preferable that the B content be greater than 0%, and even more preferable that it be 0.0001% or more.

[0091] O: 0.020% or less. O is present in the alloy as an impurity. Therefore, it is preferable that the O content be 0.020% or less. It is more preferable that the O content be 0.018% or less. It is preferable to reduce the O content as much as possible, and it may even be 0%, but extreme reduction of the O content leads to increased manufacturing costs. Therefore, it is more preferable that the O content be greater than 0%, and even more preferable that it be 0.001% or more.

[0092] V: 0.50% or less V has the effect of improving high-temperature strength by forming fine nitrides. In addition, by keeping the V content at 0.50% or less, the generation of large amounts of carbonitrides containing V during the solidification process of the alloy can be suppressed, thereby suppressing a decrease in hot ductility and deterioration of manufacturability. For this reason, it is preferable to keep the V content at 0.50% or less. It is more preferable to keep the V content at 0.45% or less. There is no need to set a lower limit for the V content, and the V content may be 0%. On the other hand, if the above effects of V are to be obtained, it is more preferable to have a V content greater than 0%, and even more preferable to have a V content of 0.01% or more.

[0093] Ta: 1.00% or less. Ta forms fine nitrides and acts as a solid solution strengthening element, improving high-temperature strength. By limiting the Ta content to 1.00% or less, the formation of large amounts of carbonitrides containing Ta during the alloy solidification process is suppressed, thereby reducing the decrease in hot ductility and the deterioration of manufacturability. Furthermore, since Ta is an expensive element, limiting the Ta content to 1.00% or less also helps to suppress cost increases. For this reason, it is preferable to limit the Ta content to 1.00% or less. It is more preferable to limit the Ta content to 0.90% or less. There is no lower limit to the Ta content, and the Ta content may be 0%. On the other hand, if the above effects of Ta are to be obtained, it is preferable to limit the Ta content to more than 0%, and more preferably to 0.01% or more.

[0094] In the chemical composition of the base material of the present invention, the remainder is Fe and impurities. Here, impurities refer to components that are mixed in during the industrial production of the base material due to raw materials such as ore and scrap, or other factors, and are acceptable within a range that does not adversely affect the characteristics of the welded joint according to the present invention.

[0095] 0.05 ≤ V + Ta As described above, by including V and / or Ta in the weld metal in addition to Nb and allowing nitrides of V and / or Ta to crystallize, the resistance to solidification cracking can be improved. Furthermore, the chemical composition of the weld metal is determined by the inflow ratio of the base metal and the welding material. For this reason, it is preferable that the total content of V and Ta, as defined by the right-hand side value of equation (iv) below, be 0.05 or more in the base metal. It is more preferable that the right-hand side value of equation (iv) below be 0.06 or more, and even more preferable that be 0.08 or more. 0.05 ≤ V + Ta ... (iv) However, the element symbols in the above formula represent the content (mass %) of each element contained in the base metal.

[0096] Furthermore, V and Ta may be included individually or both simultaneously. When V is included individually, it is preferable that the V content be 0.05% or more. When Ta is included individually, it is preferable that the Ta content be 0.05% or more. Also, when both V and Ta are included simultaneously, it is preferable that the total content of V and Ta be 0.05% or more.

[0097] The upper limit of the right-hand side value of equation (iv) above is not particularly limited. However, in the chemical composition specified in the present invention, the upper limit of the right-hand side value of equation (iv) is 1.50.

[0098] In the chemical composition of the base material of the present invention, in order to improve high-temperature strength, one or more elements selected from Mo, W, Cu, Co, Ti, Zr, and Hf may be included within the ranges shown below. Since these elements are not necessarily essential in the base material, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0099] Mo: 2.00% or less Mo dissolves in the austenite phase and greatly contributes to improving high-temperature strength. For this reason, Mo may be included as needed. Furthermore, by limiting the Mo content to 2.00% or less, the formation of the σ phase can be suppressed, thereby preventing a decrease in hot workability and toughness. Therefore, it is preferable to limit the Mo content to 2.00% or less. It is more preferable to limit the Mo content to 1.50% or less. If the above effects are to be obtained more reliably, it is more preferable to limit the Mo content to over 0%, and even more preferable to limit it to 0.10% or more.

[0100] W: 2.00% or less. W dissolves in the austenite phase and greatly contributes to improving high-temperature strength. For this reason, W may be included as needed. Also, since W is an expensive element, the increase in cost can be suppressed by keeping the W content at 2.00% or less. Therefore, it is preferable that the W content be 2.00% or less. It is more preferable that the W content be 1.50% or less. Furthermore, if the above effects are to be obtained more reliably, it is more preferable that the W content be greater than 0%, and even more preferable that it be 0.01% or more.

[0101] Cu: 1.00% or less. Cu is an austenite-forming element and contributes to improved high-temperature strength by enhancing phase stability. For this reason, Cu may be included as needed. Furthermore, by limiting the Cu content to 1.00% or less, the decrease in hot workability can be suppressed. Therefore, it is preferable that the Cu content be 1.00% or less. It is more preferable that the Cu content be 0.80% or less. If the above effects are to be obtained more reliably, it is more preferable that the Cu content be greater than 0%, and even more preferable that it be 0.01% or more.

[0102] Co: 1.00% or less. Co is an austenite-forming element that enhances phase stability and contributes to improved high-temperature strength. For this reason, Co may be included as needed. Furthermore, since Co is an extremely expensive element, a significant increase in cost can be suppressed by limiting the Co content to 1.00% or less. Therefore, it is preferable to have a Co content of 1.00% or less. It is even more preferable to have a Co content of 0.80% or less. If the above effects are to be obtained more reliably, it is even more preferable to have a Co content of more than 0%, and even more preferable to have a Co content of 0.01% or more.

[0103] Ti: 0.10% or less. Ti precipitates within the grains as fine carbonitrides, contributing to improved high-temperature strength. For this reason, Ti may be included as needed. Furthermore, by limiting the Ti content to 0.10% or less, the precipitation of large amounts of coarse Ti nitrides can be suppressed, thereby preventing a decrease in toughness. Therefore, it is preferable that the Ti content be 0.10% or less. It is more preferable that the Ti content be 0.08% or less. If the above effects are to be obtained more reliably, it is more preferable that the Ti content be greater than 0%, and even more preferable that it be 0.01% or more.

[0104] Zr: 0.10% or less. Zr has the effect of improving high-temperature strength as a grain boundary strengthening element. For this reason, Zr may be included as needed. Furthermore, by keeping the Zr content at 0.10% or less, the precipitation of a large amount of coarse Zr nitride can be suppressed, and the decrease in toughness can be suppressed. For this reason, it is preferable that the Zr content be 0.10% or less. It is more preferable that the Zr content be 0.08% or less. If the above effects are to be obtained more reliably, it is more preferable that the Zr content be greater than 0%, and even more preferable that it be 0.01% or more.

[0105] Hf: 0.10% or less. Hf contributes to precipitation strengthening as a carbonitride and improves high-temperature strength. For this reason, Hf may be included as needed. Furthermore, by keeping the Hf content at 0.10% or less, a decrease in workability and weld crack resistance can be suppressed. Therefore, it is preferable that the Hf content be 0.10% or less. It is more preferable that the Hf content be 0.08% or less. If the above effects are to be obtained more reliably, it is more preferable that the Hf content be greater than 0%, and even more preferable that it be 0.01% or more.

[0106] In the chemical composition of the base material of the present invention, in order to improve weldability, one or more elements selected from Sn, Zn, Pb, and Sb may be included within the ranges shown below. Since these elements are not necessarily essential in the base material, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0107] Sn: 0.010% or less. Sn has the effect of improving weldability by increasing penetration during welding. For this reason, Sn may be included as needed. Furthermore, by keeping the Sn content at 0.010% or less, the decrease in hot workability can be suppressed. Therefore, it is preferable that the Sn content be 0.010% or less. It is more preferable that the Sn content be 0.008% or less. If the above effects are to be obtained more reliably, it is more preferable that the Sn content be greater than 0%, and even more preferable that it be 0.001% or more.

[0108] Zn: 0.010% or less. Zn has the effect of improving weldability by increasing penetration during welding. For this reason, Zn may be included as needed. Furthermore, by keeping the Zn content at 0.010% or less, the decrease in hot workability can be suppressed. Therefore, it is preferable that the Zn content be 0.010% or less. It is more preferable that the Zn content be 0.008% or less. If the above effects are to be obtained more reliably, it is more preferable that the Zn content be greater than 0%, and even more preferable that it be 0.001% or more.

[0109] Pb: 0.010% or less. Pb has the effect of improving weldability by increasing penetration during welding. For this reason, Pb may be included as needed. Furthermore, by keeping the Pb content at 0.010% or less, the decrease in hot workability can be suppressed. Therefore, it is preferable that the Pb content be 0.010% or less. It is more preferable that the Pb content be 0.008% or less. If the above effects are to be obtained more reliably, it is more preferable that the Pb content be greater than 0%, and even more preferable that it be 0.001% or more.

[0110] Sb: 0.010% or less. Sb has the effect of improving weldability by increasing penetration during welding. For this reason, Sb may be included as needed. In addition, by keeping the Sb content at 0.010% or less, the decrease in hot workability can be suppressed. Therefore, it is preferable that the Sb content be 0.010% or less. It is more preferable that the Sb content be 0.008% or less. Furthermore, if the above effects are to be obtained more reliably, it is more preferable that the Sb content be greater than 0%, and even more preferable that it be 0.001% or more.

[0111] In the chemical composition of the base material of the present invention, in order to improve hot workability, one or more elements selected from Ca, Mg, and REM may be further included within the ranges shown below. Since these elements are not necessarily essential in the base material, the lower limit of their content is 0%. The reasons for limiting each element are explained below.

[0112] Ca: 0.0050% or less. Ca forms compounds with S, reducing the amount of S in the austenite phase and improving hot workability. For this reason, Ca may be included as needed. Furthermore, by limiting the Ca content to 0.0050% or less, deterioration of hot workability can be suppressed. Therefore, it is preferable to limit the Ca content to 0.0050% or less. It is more preferable to limit the Ca content to 0.0045% or less. If the above effects are to be obtained more reliably, it is more preferable to limit the Ca content to over 0%, and even more preferable to limit it to 0.0001% or more.

[0113] Mg: 0.0050% or less. Like Ca, Mg forms compounds with S, reducing the amount of S in the austenite phase and improving hot workability. For this reason, Mg may be included as needed. Furthermore, by keeping the Mg content at 0.0050% or less, deterioration of hot workability can be suppressed. Therefore, it is preferable to keep the Mg content at 0.0050% or less. It is more preferable to keep the Mg content at 0.0045% or less. If the above effects are to be obtained more reliably, it is more preferable to keep the Mg content above 0%, and even more preferable to keep it at 0.0001% or more.

[0114] REM: 0.10% or less. REM, like Ca, forms compounds with S to reduce the amount of S in the austenite phase and improve hot workability, so it may be included as needed. Furthermore, by keeping the REM content at 0.10% or less, significant deterioration of manufacturability can be suppressed. Therefore, it is preferable to keep the REM content at 0.10% or less. It is more preferable to keep the REM content at 0.09% or less. If the above effects are to be obtained more reliably, it is more preferable to keep the REM content above 0%, and even more preferable to keep it at 0.001% or more.

[0115] Here, REM is a collective term for 17 elements including Sc, Y, and lanthanides, and the REM content refers to the total amount of these elements. Note that lanthanides are industrially added in the form of mischmetal.

[0116] (E) Manufacturing Method (E-1) Method for Manufacturing the Base Material A preferred method for manufacturing the welded joint according to the present invention will be described. First, there are no particular restrictions on the method for manufacturing the base material used in the production of the welded joint according to the present invention, but for example, it can be manufactured by applying hot forging, hot rolling, and heat treatment in order to steel with an adjusted chemical composition using a conventional method. The type of alloy material used for the base material is not particularly limited, and may be, for example, an alloy plate or an alloy pipe. The dimensions of the alloy material are not particularly limited, but if the alloy material is an alloy pipe, the outer diameter of the alloy pipe may be 12 to 600 mm and the wall thickness may be 1.5 to 50 mm. If the alloy material is an alloy plate, for example, the plate thickness may be 5 to 100 mm.

[0117] (E-2) Method for Manufacturing Welded Joints The weld metal according to the present invention is produced by beveling the base material manufactured as described above and welding it. During welding, the heat input per pass is set to 7 to 15 kJ / cm. If the heat input is less than 7 kJ / cm, the base material and welding material cannot be sufficiently melted, resulting in welding defects such as blowholes and poor fusion. On the other hand, if the heat input is greater than 15 kJ / cm, the molten pool area (reaction area) in contact with the shielding gas increases, and the melting time (reaction time) also increases, causing N to evaporate from the molten pool and reducing the N content of the weld metal. As a result, it becomes impossible to properly crystallize nitrides of Nb, V, and Ta. For this reason, the heat input is set to 7 to 15 kJ / cm per pass.

[0118] The welding speed should be 5 cm / min or higher. If the welding speed is less than 5 cm / min, the melting time (reaction time) increases, causing nitrogen to evaporate from the molten pool and reducing the nitrogen content of the weld metal. There is no particular upper limit to the welding speed, but if it is too fast, the base metal and welding material may not be sufficiently melted, which may result in welding defects such as blowholes and poor fusion. Therefore, it is preferable to keep the welding speed at 15 cm / min or lower.

[0119] Furthermore, when performing multi-layer welding, it is preferable to keep the interpass temperature below 150°C. If the interpass temperature exceeds 150°C, for the same reasons as when the heat input exceeds 15 kJ / cm, it may become impossible to properly crystallize the nitrides of Nb, V, and Ta. For this reason, the interpass temperature should be kept below 150°C. The interpass temperature can be evaluated by measuring the surface temperature of the weld bead immediately before the start of welding using a contact-type temperature sensor.

[0120] Welding may be performed in a single layer, but when welding alloy materials of the dimensions described above, multi-layer welding is preferable. A welding material may also be used when welding the base metal. There are no particular restrictions on the type of welding material, but it is necessary to select a welding material such that the chemical composition of the weld metal satisfies the above requirements. When using a welding material with a different chemical composition from the base metal when welding the base metal, the chemical composition of the weld metal should be measured and confirmed to fall within the range of chemical compositions specified in this invention. Furthermore, while the groove shape is not particularly limited, groove shapes such as V-grooves and U-grooves are preferable.

[0121] The welding method for obtaining the weld metal according to the present invention is not particularly limited, but arc welding is preferred. Examples of arc welding methods include TIG welding, plasma welding, MIG welding, shielded metal arc welding, and submerged arc welding. Alternatively, laser welding may be performed.

[0122] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0123] A 50 kg ingot having the chemical composition shown in Table 1 was melted in the laboratory. The ingot was then hot-rolled to produce 18 mm thick alloy sheets (test numbers 1-26). Furthermore, to produce the cut filler described later, the same ingot was hot-rolled to produce 5 mm thick alloy sheets. Hot rolling was performed at a temperature of 1000°C or higher on an ingot heated to 1250°C.

[0124] Figure 1 is a diagram illustrating the welding method. Figure 1(a) shows the shape of test piece 1, (b) is a magnified view of the V-groove, and (c) is a diagram illustrating the area to be welded. First, as shown in Figure 1(a), test pieces 1 with a width of 50 mm, a length of 100 mm, and a thickness of 12 mm were machined from each of the alloy plates mentioned above. Then, as shown in Figures 1(a) and (b), a V-groove was made on one side of the long edge of test piece 1, such that the root surface 2 was 1 mm and the bevel angle was 30°. Two test pieces 1 made of the same material were prepared and placed on an SS400 steel plate 3 with a width of 150 mm, a length of 150 mm, and a thickness of 30 mm, so that the root surfaces 2a and 2b of test pieces 1a and 1b were in contact (see Figure 1(c)).

[0125] Using shielded metal arc welding, the region 4 shown by the dashed line in Figure 1(c) was welded in a constrained position. Then, the V-groove 5 was melt-trans welded as the first layer using TIG welding at a current of 150 A, a voltage of 13 V, and a welding speed of 10 cm / min. Next, a 1.2 mm square cut filler was prepared from a 5 mm thick alloy plate. The chemical composition of the cut filler was the same as that of each alloy plate described above. Using this cut filler, lamination welding was performed on the V-groove 5, which had been melt-trans welded as the first layer, using TIG welding under the conditions shown in Table 2.

[0126] Ar gas was used as the shielding gas, with a gas flow rate of 10 L / min. The chemical composition of the weld metal is basically the same as that of the base metal. However, regarding the nitrogen content, nitrogen evaporates during melting, so the nitrogen content in the weld metal is lower than that in the base metal. The chemical composition of the weld metal was analyzed from test specimens after the evaluation of solidification crack resistance described later, at a height of half the initial layer of the weld metal and in the center of the entire width of the initial layer. The chemical composition of the weld metal is shown in Table 3.

[0127]

[0128]

[0129]

[0130] <Electrolytic Extraction Residue> The content (mass%) of each element in the residue analyzed as electrolytic extraction residue was measured using the following procedure. Specifically, first, from the test piece after the evaluation of solidification crack resistance described later, a test piece measuring 5 mm in width, 20 mm in length, and 2 mm in thickness was machined from the center of the total width of the weld metal, at a height of 1 / 2 of the total thickness of the weld metal. Then, 10 vol% acetylacetone - 1 mass% tetramethylammonium chloride - methanol was used to measure at 20 mA / cm². ２ The test specimens were electrolyzed at the specified current density. The solution of the electrolyzed sample was then filtered through a 0.2 μm filter, and the residue was acid-decomposed. The content of each element, Nb, V, and Ta, and the left-hand side value of equation (iii) above were calculated using an ICP emission spectrometer.

[0131] <Resistance to Solidification Cracking> The resistance to solidification cracking was evaluated using the following procedure. Figure 2 is a diagram illustrating the observation locations for the presence or absence of cracks. As shown by the dashed line in Figure 2, a total of five cross-sections were taken from the specimen 1 so that they could be observed at the center line A in the longitudinal direction of the specimen, and at positions 20 mm apart from the center line A. After mirror polishing and etching, the presence or absence of cracks in the weld metal of the V-groove 5 was checked using an optical microscope. If no cracks were observed in the weld metal, it was judged as good (Excellent), and if cracks occurred in even one cross-section, it was judged as poor (Bad).

[0132] <Stress Relaxation Cracking Resistance> The stress relaxation cracking resistance was evaluated using the following procedure. First, after the evaluation of solidification cracking resistance described above, a C-ring type constrained weld crack test specimen was taken from the center of the weld metal in the V-groove of the test specimen. Figure 3 is a diagram illustrating the shape of the test specimen for evaluating stress relaxation cracking resistance. (a) is a perspective view of the test specimen, (b) is an enlarged view of the area enclosed by the dashed line in (a), and (c) is a diagram illustrating the method of welding the test specimen. As shown in Figure 3(a), this test specimen 10 is a C-shaped test specimen with an outer diameter of 8 mm, an inner diameter of 5.5 mm, and a length of 10 mm. As shown in Figures 3(a) and (b), a notch 11 with a width of 0.4 mm, a depth of 0.75 mm, and a tip radius of 0.2 R was machined on the outer surface of the test specimen 10, and a slit 12 with a width of 2 mm was provided on the opposite side.

[0133] Subsequently, as shown in Figure 3(c), loads were applied from both sides of the specimen 10 to bring the slits together, and a welded section 13 was formed by non-filler welding using TIG welding, thereby generating a constraining stress at the tip 11a of the notch 11. After aging this specimen at 600°C for 2500 hours, the presence or absence of cracks at the notch tip 11a was evaluated by cross-sectional observation. If no cracks were observed at the notch tip 11a, it was judged as good (Excellent); if cracks occurred, it was judged as bad (Bad). In addition, if no cracks occurred but voids were observed at the grain boundaries, it was judged as good (Good).

[0134] Table 4 contains [Nb] ＥＲ [V] ＥＲ [Ta] ＥＲ The left-hand side value of equation (iii), and the evaluation results for solidification crack resistance and stress relaxation crack resistance are summarized below. Note that in the evaluation results for stress relaxation crack resistance in Table 4, "-" means that cracks occurred in the weld metal during the solidification crack resistance test, and therefore a test specimen for stress relaxation crack resistance could not be obtained.

[0135]

[0136] As shown in Table 4, tests No. 1 to 16, which fully satisfied the provisions of the present invention, showed excellent resistance to solidification cracking and stress relaxation cracking. In contrast, comparative examples No. 17 to 26 showed deterioration in solidification cracking resistance or stress relaxation cracking resistance.

[0137] According to the present invention, a welded joint with excellent resistance to solidification cracking and stress relaxation cracking can be obtained.

[0138] 1. Test specimen 2. Root surface 3. Steel plate 4. Area 5. V-groove 10. Test specimen 11. Notch 12. Slit 13. Weld

Claims

1. A welded joint comprising a weld metal and a base metal, wherein the chemical composition of the weld metal is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.10 to 0.30%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, the remainder being Fe and impurities, and satisfying the following formulas (i) to (iii). 0.05≦V+Ta...(i) 0.050≦[Nb] ＥＲ ...(ii) [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ ≤0.350 ... (iii) However, the elemental symbols in formula (i) above mean the content (mass%) of each element in the weld metal, and [Nb] in formulas (ii) and (iii) above ＥＲ [V] ＥＲ , and [Ta] ＥＲ These terms represent the mass percentages of Nb, V, and Ta in the residue obtained by the extraction residue analysis, respectively.

2. A welded joint comprising a weld metal and a base metal, wherein the chemical composition of the weld metal is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.10 to 0.30%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, and further contains one or more selected from the group consisting of the following Group A, Group B, and Group C, the balance: Fe and impurities, a welded joint that satisfies the following (i) to (iii) formulas. 0.05 ≦ V + Ta... (i) 0.050 ≦ [Nb] ＥＲ ... (ii) [Nb] ＥＲ + [V] ＥＲ + [Ta] ＥＲ ≦ 0.350... (iii) However, the element symbols in the above formula (i) mean the content (mass%) of each element contained in the weld metal, and [Nb] in the above formulas (ii) and (iii) ＥＲ , [V] ＥＲ , and [Ta] ＥＲ each mean the content (mass%) of Nb, V, and Ta in the residue obtained by extraction residue analysis. [Group A] One or more selected from the group consisting of Mo: 2.00% or less, W: 2.00% or less, Cu: 1.00% or less, Co: 1.00% or less, Ti: 0.10% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group B] One or more selected from the group consisting of Sn: 0.010% or less, Zn: 0.010% or less, Pb: 0.010% or less, and Sb: 0.010% or less [Group C] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.10% or less 3. The welded joint according to claim 2, wherein the chemical composition of the weld metal contains one or more elements selected from group A.

4. The welded joint according to claim 2, wherein the chemical composition of the weld metal contains one or more elements selected from group B.

5. The welded joint according to claim 2, wherein the chemical composition of the weld metal contains one or more elements selected from group C.

6. The welded joint according to any one of claims 1 to 5, wherein the chemical composition of the base material is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.12 to 0.35%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, the remainder: Fe and impurities, and satisfies the following formula (iv). 0.05 ≤ V + Ta ... (iv) where the element symbols in equation (iv) above represent the mass percentage of each element contained in the base material.

7. The chemical composition of the base material is, in mass%, C: 0.050% or less, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.035% or less, S: 0.0020% or less, Ni: 33.00 to 45.00%, Cr: 20.00 to 30.00%, Nb: 0.20 to 1.00%, N: 0.12 to 0.35%, Al: 0.10% or less, B: 0.0035% or less, O: 0.020% or less, V: 0.50% or less, Ta: 1.00% or less, and further contains one or more selected from the groups consisting of groups D, E and F below, with the remainder being Fe and impurities, and satisfying the following formula (iv). A welded joint according to any one of claims 1 to 5. 0.05 ≤ V + Ta ... (iv) where the elemental symbols in formula (iv) above mean the content (mass%) of each element contained in the base material. [Group D] One or more selected from the group consisting of Mo: 2.00% or less, W: 2.00% or less, Cu: 1.00% or less, Co: 1.00% or less, Ti: 0.10% or less, Zr: 0.10% or less, and Hf: 0.10% or less [Group E] One or more selected from the group consisting of Sn: 0.010% or less, Zn: 0.010% or less, Pb: 0.010% or less, and Sb: 0.010% or less [Group F] One or more selected from the group consisting of Ca: 0.0050% or less, Mg: 0.0050% or less, and REM: 0.10% or less 8. The welded joint according to claim 7, wherein the chemical composition of the base material contains one or more elements selected from group D.

9. The welded joint according to claim 7, wherein the chemical composition of the base material contains one or more elements selected from group E.

10. The welded joint according to claim 7, wherein the chemical composition of the base material contains one or more elements selected from group F.

11. The welded joint according to any one of claims 1 to 5, wherein the chemical composition of the weld metal is, in mass%, V: 0.03 to 0.50% and Ta: 0.01 to 1.00%, and satisfies the following equations (v) and (vi): 0.003 ≤ [V] ＥＲ ...(v) 0.001≦[Ta] ＥＲ ... (vi) However, [V] in equation (v) and equation (vi) above ＥＲ and [Ta] ＥＲ These terms represent the content (mass %) of V and Ta in the residue obtained by the extraction residue analysis, respectively.

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