Austenitic stainless steel alloy weld joint and austenitic stainless steel alloy welding material

Abstract

The present invention provides an austenitic stainless alloy welded joint which comprises a welding metal that has excellent high-temperature welding cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance and aging toughness. According to the present invention, a welding metal (20) contains, in mass%, 0.020% or less of C, 0.01-1.00% of Si, 0.20-2.00% of Mn, 0.030% or less of P, 0.010% or less of S, 16.0-25.0% of Cr, 15.0-40.0% of Ni, 2.5-5.0% of Mo, 0.10-2.00% of Nb, 0.05-0.30% of N, 0.001-0.100% of sol. Al and 0.0010-0.0050% of B, with F1 defined by formula (1) being 2.30 or less and F2 defined by formula (2) being 2.5 or less.　(1): F1 = 130B + 8C + 0.025Cr + 0.25Mn + 0.08Mo + 0.6Nb + 12P + 7.6S + 0.78Si + 0.12W (2): F2 = [Mo]H / [Mo]L

Description

[Technical Field]

[0001] The present disclosure relates to weld joints and welding materials, and more particularly to austenitic stainless alloy weld joints and austenitic stainless alloy welding materials. [Background technology]

[0002] Austenitic stainless steel alloy welded joints are produced by welding austenitic stainless steel alloy materials. Austenitic stainless steel alloy welded joints include a base metal made of an austenitic stainless steel alloy and a weld metal. Austenitic stainless steel alloy welded joints are used in welded structures of chemical plant facilities such as thermal boilers, oil refineries, and petrochemical plants. Examples of welded structures in chemical plant facilities include peripheral equipment for distillation columns, heating furnace tubes, reaction tubes, heat exchangers, and piping. Some of the components used in these welded structures in chemical plant facilities are used in high-temperature environments of 600 to 700°C, which contain corrosive fluids containing sulfides and / or chlorides. In this specification, high-temperature environments of 600 to 700°C, which contain corrosive fluids containing sulfides and / or chlorides, are referred to as "high-temperature corrosive environments."

[0003] Welded structures used in high-temperature corrosive environments are shut down during periodic inspections of chemical plants. During shutdowns, the temperature of the welded structure drops to room temperature. At this time, air, moisture, and sulfide scale react to form polythionic acid on the surface of the welded structure. This polythionic acid induces stress corrosion cracking at grain boundaries (hereinafter referred to as polythionic acid SCC). Therefore, welded joints used in the above-mentioned high-temperature corrosive environments, especially the weld metal, are required to have excellent polythionic acid SCC resistance.

[0004] Furthermore, when inferior crude oil is used in chemical plant facilities, not only polythionic acid SCC corrosion but also naphthenic acid corrosion may occur. Naphthenic acid is a cyclic saturated hydrocarbon having one or more carboxyl groups. Unlike polythionic acid, naphthenic acid does not cause SCC, but rather causes general corrosion. Therefore, it is preferable that the weld metal of welded joints used in the above-mentioned plant facilities has excellent resistance to naphthenic acid corrosion as well as polythionic acid SCC.

[0005] Furthermore, the toughness of welded joints used for a long time in a high-temperature environment may decrease, so the weld metal of welded joints used for a long time in a high-temperature environment is required to have excellent aging toughness.

[0006] Furthermore, in the weld metal of a welded joint that requires polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness, it is also required that hot weld cracking during welding be suppressed.

[0007] Therefore, the weld metal of austenitic stainless steel alloy weld joints used in the above-mentioned high-temperature corrosive environments is required to have resistance to weld hot cracking, resistance to polythionic acid SCC, resistance to naphthenic acid corrosion, and excellent aging toughness.

[0008] Alloy materials for use in such high-temperature corrosive environments have been proposed in Japanese Patent Laid-Open Publication No. 2003-166039 (Patent Document 1) and International Publication No. 2009 / 044802 (Patent Document 2).

[0009] The austenitic heat-resistant steel disclosed in Patent Document 1 contains, by mass%, C: 0.005 to less than 0.03%, Si: 0.05 to 0.4%, Mn: 0.5 to 2%, P: 0.01 to 0.04%, S: 0.0005 to 0.005%, Cr: 18 to 20%, Ni: 7 to 11%, Nb: 0.2 to 0.5%, V: 0.2 to 0.5%, Cu: 2 to 4%, N: 0.10 to 0.30%, B: 0.0005 to 0.0080%, and the balance consisting of Fe and unavoidable impurities. The total content of Nb and V is 0.6% or more, and the amount of Nb in solid solution in the steel is 0.15% or more. Furthermore, it satisfies N / 14≧Nb / 93+V / 51 and Cr-16C-0.5Nb-V≧17.5. In Patent Document 1, the polythionic acid SCC resistance is improved by reducing the C content and specifying the relationships between Cr and C, Nb, and V.

[0010] The austenitic stainless steel disclosed in Patent Document 2 contains, by mass%, less than 0.04% C, 1.5% or less Si, 2% or less Mn, 15-25% Cr, 6-30% Ni, 0.02-0.35% N, and 0.03% or less Sol-Al, and further contains one or more of 0.5% or less Nb, 0.4% or less Ti, 0.4% or less V, 0.2% or less Ta, 0.2% or less Hf, and 0.2% or less Zr, with the balance being Fe and impurities, such as 0.04% or less P, 0.03% or less S, 0.1% or less Sn, 0.01% or less As, 0.01% or less Zn, 0.01% or less Pb, and 0.01% or less Sb. Furthermore, the following conditions are satisfied: F1 = S + {(P + Sn) / 2} + {(As + Zn + Pb + Sb) / 5} ≦ 0.075, and 0.05 ≦ Nb + Ta + Zr + Hf + 2Ti + (V / 10) ≦ 1.7 - 9 × F1. In Patent Document 2, polythionic acid SCC resistance is improved by reducing the C content to less than 0.05%. Furthermore, embrittlement cracking resistance in the weld heat-affected zone (HAZ) is improved by reducing the C-immobilizing elements such as Nb and Ti and reducing the grain boundary embrittlement elements such as P, S, and Sn in the steel. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-166039 [Patent Document 2] International Publication No. 2009 / 044802 Summary of the Invention [Problem to be solved by the invention]

[0012] However, Patent Documents 1 and 2 do not consider the weld metal of the welded joint.

[0013] An object of the present disclosure is to provide an austenitic stainless steel alloy weld joint including a weld metal that has excellent weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness, and an austenitic stainless steel alloy welding material used therefor. [Means for solving the problem]

[0014] The austenitic stainless steel alloy weld joint according to the present disclosure has the following configuration.

[0015] A base material and a weld metal are provided, The chemical composition of the base material is, in mass%, C: 0.030% or less, Si: 0.10 to 1.00%, Mn: 0.20 to 2.00%, P: 0.040% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 10.0 to 30.0% Mo: 0.1 to 5.0% Nb: 0.20 to 1.00%, N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0~0.0080%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities, The chemical composition of the weld metal is, in mass%, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P:0.030% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 15.0~40.0%, Mo: 2.5-5.0% Nb: 0.10 to 2.00% N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0.0010~0.0050%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities, and F1 defined by formula (1) being 2.30 or less; In a cross section of the weld metal perpendicular to the extending direction of the weld metal, a 1 mm × 1 mm square region at the width center on the surface of the weld metal and at the thickness center of the weld metal was divided into minute square areas of 100 μm × 100 μm, the Mo content in mass% in each minute square area was determined, and the arithmetic average value of all the obtained Mo contents was defined as [Mo] AVEOf all the Mo contents obtained, the [Mo] AVE The arithmetic mean value of the Mo content higher than [Mo] H Of all the Mo contents obtained, the [Mo] AVE The arithmetic mean value of the Mo content lower than [Mo] L When we define F2 defined by formula (2) is 2.5 or less; Austenitic stainless steel alloy welded joints. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) F2=[Mo] H / [Mo] L (2) Here, each element symbol in formula (1) is substituted with the content of the corresponding element in the weld metal in mass %.

[0016] The austenitic stainless alloy welding material according to the present disclosure has the following configuration.

[0017] The chemical composition is, in mass%, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P:0.030% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 15.0~40.0%, Mo: 2.5-5.0% Nb: 0.10 to 2.00% N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0.0010~0.0050%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities; Austenitic stainless steel alloy welding material. [Effects of the Invention]

[0018] The weld metal of the austenitic stainless alloy weld joint according to the present disclosure has excellent resistance to weld hot cracking, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness. The austenitic stainless alloy welding material according to the present disclosure can be used as a raw material for the weld metal that exhibits the above-mentioned effects. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a plan view showing an example of an austenitic stainless alloy welded joint of this embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the austenitic stainless alloy welded joint of FIG. 1 cut in the weld metal width direction. [Figure 3] FIG. 3 is a cross-sectional view of the austenitic stainless alloy welded joint of FIG. 1 cut in the direction in which the weld metal extends. [Figure 4] FIG. 4 is a cross-sectional view of an austenitic stainless alloy welded joint cut in the direction in which the weld metal extends, which is different from FIG. [Figure 5] FIG. 5 is a cross-sectional view perpendicular to the direction in which the weld metal extends in an austenitic stainless alloy weld joint of this embodiment. [Figure 6] FIG. 6 is a schematic diagram for explaining the groove shape of the base material in the example. [Figure 7] FIG. 7 is a schematic diagram of a welded joint using the base material of FIG. [Figure 8] FIG. 8 is a schematic diagram showing the positions where the plate-shaped test pieces used in the examples were collected. [Figure 9]FIG. 9 is a schematic diagram showing the positions where the V-notch test pieces used in the examples were taken. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present inventors have investigated means for improving the weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness of the weld metal of austenitic stainless alloy weld joints, and have obtained the following findings.

[0021] The present inventors first studied the chemical composition of the base metal constituting an austenitic stainless alloy weld joint, and as a result, they concluded that it would be appropriate for the base metal of an austenitic stainless alloy weld joint to satisfy the following characteristic 1 from the viewpoints of weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness of the weld metal. (Feature 1) The chemical composition of the base metal is, in mass%, C: 0.030% or less, Si: 0.10-1.00%, Mn: 0.20-2.00%, P: 0.040% or less, S: 0.010% or less, Cr: 16.0-25.0%, Ni: 10.0-30.0%, Mo: 0.1-5.0%, Nb: 0.20-1.00%, N: 0.05-0.30%, sol.A I: 0.001-0.100%, B: 0-0.0080%, Cu: 0-5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0-0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0-0.010%, rare earth elements: 0-0.100%, and the balance being Fe and impurities.

[0022] The present inventors further studied the chemical composition of the weld metal of austenitic stainless alloy weld joints, and concluded that the weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness would be improved if the chemical composition of the weld metal satisfied the following characteristic 2. (Feature 2) The chemical composition of the weld metal is, in mass%, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ni: 15.0 to 40.0%, Mo: 2.5 to 5.0%, Nb: 0.10 to 2.00%, N: 0.05 to 0.30%, sol.Al: 0.001 to 0.100%, B: 0.0010 to 0.0050%, Cu: 0 to 5.00%, W: 0 to 5.00%, Co: 0 to 1.00%, V: 0 to 1.00%, Ta: 0 to 0.20%, Hf: 0 to 0.20%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, rare earth elements: 0 to 0.100%, and the balance being Fe and impurities.

[0023] However, even in welded joints including a base metal having the above-mentioned chemical composition and a weld metal having the above-mentioned chemical composition, there are still cases in which the weld metal does not sufficiently exhibit any of the following: weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness. Weld metal is formed by welding. In this respect, it differs from the base metal, which is produced by hot working. Therefore, it is effective to improve the weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness of the weld metal by a means different from that of the base metal.

[0024] Therefore, the present inventors further investigated means for improving the weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness of the weld metal. As a result, it was found that the weld hot cracking resistance, polythionic acid SCC resistance, naphthenic acid corrosion resistance, and aging toughness of the weld metal of a welded joint can be sufficiently improved by the weld metal of a welded joint further satisfying the following characteristics 3 and 4. (Feature 3) In the weld metal, F1 defined by formula (1) is 2.30 or less. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) Here, the content of the corresponding element in the weld metal in mass % is substituted for each element symbol in formula (1). (Feature 4) In the cross section of the weld metal perpendicular to the extending direction of the weld metal, a 1 mm x 1 mm square area at the center of the width on the surface of the weld metal and at the center of the thickness of the weld metal was divided into minute square areas of 100 μm x 100 μm, the Mo content in mass% in each minute square area was determined, and the arithmetic mean value of all the obtained Mo contents was defined as [Mo] AVE Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content higher than [Mo] H Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content lower than [Mo] L When this is defined, F2 defined by formula (2) is 2.5 or less. F2=[Mo] H / [Mo] L (2)

[0025] The austenitic stainless alloy weld joint and austenitic stainless alloy welding material according to this embodiment, which have been completed based on the above findings, have the following configurations.

[0026] [1] A base material and a weld metal are provided, The chemical composition of the base material is, in mass%, C: 0.030% or less, Si: 0.10 to 1.00%, Mn: 0.20 to 2.00%, P: 0.040% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 10.0 to 30.0% Mo: 0.1 to 5.0% Nb: 0.20 to 1.00%, N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0~0.0080%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities, The chemical composition of the weld metal is, in mass%, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P:0.030% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 15.0~40.0%, Mo: 2.5-5.0% Nb: 0.10 to 2.00% N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0.0010~0.0050%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities, and F1 defined by formula (1) being 2.30 or less; In a cross section of the weld metal perpendicular to the extending direction of the weld metal, a 1 mm × 1 mm square region at the width center on the surface of the weld metal and at the thickness center of the weld metal was divided into minute square areas of 100 μm × 100 μm, the Mo content in mass% in each minute square area was determined, and the arithmetic average value of all the obtained Mo contents was defined as [Mo] AVEOf all the Mo contents obtained, the [Mo] AVE The arithmetic mean value of the Mo content higher than [Mo] H Of all the Mo contents obtained, the [Mo] AVE The arithmetic mean value of the Mo content lower than [Mo] L When we define F2 defined by formula (2) is 2.5 or less; Austenitic stainless steel alloy welded joints. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) F2=[Mo] H / [Mo] L (2) Here, each element symbol in formula (1) is substituted with the content of the corresponding element in the weld metal in mass %.

[0027] [2] [1] An austenitic stainless steel alloy weld joint according to the present invention, The chemical composition of the base material is B: 0.0001~0.0080%, Cu: 0.01 to 5.00%, W: 0.01 to 5.00%, Co: 0.01 to 1.00%, V: 0.01 to 1.00%, Ta: 0.01 to 0.20%, Hf: 0.01 to 0.20%, Ca: 0.001 to 0.010%, Mg: 0.001 to 0.010%, and Rare earth elements: 0.001~0.100%, Contains one or more elements selected from the group consisting of Austenitic stainless steel alloy welded joints.

[0028] [3] [1] or [2], an austenitic stainless steel alloy weld joint, The chemical composition of the weld metal is Cu: 0.01 to 5.00%, W: 0.01 to 5.00%, Co: 0.01 to 1.00%, V: 0.01 to 1.00%, Ta: 0.01 to 0.20%, Hf: 0.01 to 0.20%, Ca: 0.001 to 0.010%, Mg: 0.001 to 0.010%, and Rare earth elements: 0~0.100%, Contains one or more elements selected from the group consisting of Austenitic stainless steel alloy welded joints.

[0029] [4] The chemical composition is, in mass%, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P:0.030% or less, S: 0.010% or less, Cr: 16.0~25.0%, Ni: 15.0~40.0%, Mo: 2.5-5.0% Nb: 0.10 to 2.00% N: 0.05 to 0.30%, sol.Al: 0.001~0.100%, B: 0.0010~0.0050%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010% Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities; Austenitic stainless steel alloy welding material.

[0030] The austenitic stainless alloy weld joint and austenitic stainless alloy welding material of this embodiment will be described in detail below. In this specification, "%" relating to elements means mass % unless otherwise specified.

[0031] [Composition of austenitic stainless steel alloy welded joints] Fig. 1 is a plan view showing an example of an austenitic stainless alloy welded joint 1 of this embodiment. Referring to Fig. 1, the austenitic stainless alloy welded joint 1 of this embodiment includes a base material 10 and a weld metal 20. The weld metal 20 is formed by butting together ends of a pair of base materials 10, the ends of which have been grooved, and then welding them. Examples of welding methods include gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW), flux-cored wire arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW).

[0032] In Fig. 1, the direction in which the weld metal 20 extends is defined as the weld metal extending direction L. The direction perpendicular to the weld metal extending direction L in a plan view is defined as the weld metal width direction W. The direction perpendicular to the weld metal extending direction L and the weld metal width direction W is defined as the weld metal thickness direction T. Fig. 2 is a cross-sectional view of the austenitic stainless alloy welded joint 1 of Fig. 1 cut in the weld metal width direction W. As shown in Figs. 1 and 2, the weld metal 20 is disposed between a pair of base materials 10.

[0033] Fig. 3 is a cross-sectional view of the austenitic stainless alloy welded joint 1 of Fig. 1 cut in the weld metal extending direction L. Fig. 4 is a cross-sectional view of the austenitic stainless alloy welded joint 1 cut in the weld metal extending direction L, different from Fig. 3. As shown in Fig. 3, the base material 10 may have a plate shape. Also, as shown in Fig. 4, the base material 10 may have an alloy pipe shape. Although not shown, the base material 10 may have a bar shape or a steel section.

[0034] [Features of the austenitic stainless steel alloy weld joint 1 of this embodiment] The austenitic stainless alloy welded joint 1 of this embodiment satisfies the following features 1 to 4. (Feature 1) The chemical composition of the base material 10 is, in mass %, C: 0.030% or less, Si: 0.10 to 1.00%, Mn: 0.20 to 2.00%, P: 0.040% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ni: 10.0 to 30.0%, Mo: 0.1 to 5.0%, Nb: 0.20 to 1.00%, N: 0.05 to 0.30%, sol. Al: 0.001-0.100%, B: 0-0.0080%, Cu: 0-5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0-0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0-0.010%, rare earth elements: 0-0.100%, and the balance being Fe and impurities. (Feature 2) The chemical composition of the weld metal 20 is, in mass %, C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ni: 15.0 to 40.0%, Mo: 2.5 to 5.0%, Nb: 0.10 to 2.00%, N: 0.05 to 0.30%, sol.Al : 0.001 to 0.100%, B: 0.0010 to 0.0050%, Cu: 0 to 5.00%, W: 0 to 5.00%, Co: 0 to 1.00%, V: 0 to 1.00%, Ta: 0 to 0.20%, Hf: 0 to 0.20%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, rare earth elements: 0 to 0.100%, and the balance being Fe and impurities. (Feature 3) In the weld metal 20, F1 defined by the formula (1) is 2.30 or less. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) Here, the content of the corresponding element in the weld metal 20 is substituted for each element symbol in the formula (1) in mass %. (Feature 4) In a cross section of the weld metal perpendicular to the extending direction of the weld metal 20, a 1 mm × 1 mm square region at the center of the width on the surface of the weld metal and at the center of the thickness of the weld metal was divided into minute square areas of 100 μm × 100 μm, the Mo content in mass% in each minute square area was determined, and the arithmetic average value of all the obtained Mo contents was defined as [Mo] AVE Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content higher than [Mo] H Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content lower than [Mo] L When this is defined, F2 defined by formula (2) is 2.5 or less. F2=[Mo] H / [Mo] L (2) Features 1 to 4 will be explained below.

[0035] [(Feature 1) Chemical composition of base material 10] The chemical composition of the base material 10 of the austenitic stainless alloy welded joint 1 of this embodiment contains the following elements.

[0036] C: 0.030% or less Carbon (C) is inevitably contained. In other words, the C content is more than 0%. C forms Cr carbides (M) at the grain boundaries of the base material 10 during use in a high-temperature corrosive environment of 600 to 700°C. 23 The formation of Cr carbides reduces the amount of dissolved Cr, which reduces the polythionic acid SCC resistance of the base material 10. Therefore, the C content is 0.030% or less. The C content is preferably as low as possible. However, excessive reduction in the C content increases production costs. Therefore, from the viewpoint of industrial production, the lower limit of the C content is preferably 0.001%, and more preferably 0.002%. The upper limit of the C content is preferably 0.025%, more preferably 0.020%, even more preferably 0.018%, even more preferably 0.016%, and even more preferably 0.015%.

[0037] Si: 0.10 to 1.00% Silicon (Si) deoxidizes the alloy. If the Si content is less than 0.10%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 1.00%, sigma phases (σ phases) precipitate in the base material 10, reducing the aging toughness of the alloy. Therefore, the Si content is 0.10 to 1.00%. The lower limit of the Si content is preferably 0.15%, more preferably 0.17%, even more preferably 0.18%, even more preferably 0.20%, and even more preferably 0.25%. The upper limit of the Si content is preferably 0.95%, more preferably 0.90%, even more preferably 0.85%, even more preferably 0.80%, even more preferably 0.75%, even more preferably 0.70%, even more preferably 0.50%, and even more preferably 0.45%.

[0038] Mn: 0.20 to 2.00% Manganese (Mn) deoxidizes the alloy. Mn also stabilizes austenite and prevents a decrease in the aging toughness of the base material 10. If the Mn content is less than 0.20%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mn content exceeds 2.00%, the high-temperature strength of the base material 10 decreases. Therefore, the Mn content is 0.20 to 2.00%. The lower limit of the Mn content is preferably 0.30%, more preferably 0.35%, even more preferably 0.40%, even more preferably 0.50%, even more preferably 0.60%, even more preferably 0.70%, and even more preferably 0.80%. The upper limit of the Mn content is preferably 1.90%, more preferably 1.85%, even more preferably 1.80%, even more preferably 1.75%, even more preferably 1.70%, even more preferably 1.60%, and even more preferably 1.50%.

[0039] P:0.040% or less Phosphorus (P) is an unavoidable impurity. In other words, the P content is greater than 0%. If the P content exceeds 0.040%, the weld hot cracking resistance of the base material 10 will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the P content is 0.040% or less. The lower the P content, the better. However, excessive reduction in the P content increases production costs. Therefore, from the viewpoint of industrial production, the lower limit of the P content is preferably 0.001%, and more preferably 0.002%. The upper limit of the P content is preferably 0.035%, more preferably 0.032%, even more preferably 0.028%, and still more preferably 0.026%.

[0040] S: 0.010% or less Sulfur (S) is an unavoidably contained impurity. In other words, the S content is greater than 0%. If the S content exceeds 0.010%, the weld hot cracking resistance of the base material 10 will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the S content is 0.010% or less. The S content is preferably as low as possible. However, excessive reduction in the S content increases production costs. Therefore, in terms of industrial production, the preferred lower limit of the S content is 0.001%. The upper limit of the S content is preferably 0.007%, more preferably 0.006%, even more preferably 0.005%, even more preferably 0.004%, and even more preferably 0.003%.

[0041] Cr: 16.0~25.0% Chromium (Cr) improves the polythionic acid SCC resistance of the base material 10. If the Cr content is less than 16.0%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Cr content exceeds 25.0%, the aging toughness of the base material 10 decreases. Therefore, the Cr content is 16.0 to 25.0%. The lower limit of the Cr content is preferably 16.5%, more preferably 17.0%, even more preferably 17.2%, and still more preferably 17.4%. The upper limit of the Cr content is preferably 24.0%, more preferably 23.0%, and even more preferably 22.0%.

[0042] Ni: 10.0 to 30.0% Nickel (Ni) stabilizes austenite and improves the aging toughness of the base material 10. If the Ni content is less than 10.0%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Ni content exceeds 30.0%, the above effects saturate and the manufacturing cost increases. Therefore, the Ni content is 10.0 to 30.0%. The lower limit of the Ni content is preferably 11.0%, more preferably 12.0%, even more preferably 13.0%, and still more preferably 13.5%. The upper limit of the Ni content is preferably 27.0%, more preferably 26.0%, even more preferably 25.0%, even more preferably 22.0%, even more preferably 20.0%, even more preferably 18.0%, and even more preferably 17.0%.

[0043] Mo: 0.1 to 5.0% When used in a high-temperature corrosive environment of 600 to 700°C, the solute Mo in the base material 10 combines with S in the environment to form a sulfide film on the surface of the base material 10. The formation of this sulfide film enhances naphthenic acid corrosion resistance. If the Mo content is less than 0.1%, the above effects cannot be sufficiently achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mo content exceeds 5.0%, hot welding cracking may occur in the HAZ during welding, or aging toughness may decrease. Therefore, the Mo content is 0.1 to 5.0%. The lower limit of the Mo content is preferably 0.2%, more preferably 0.3%, even more preferably 0.5%, even more preferably 1.0%, even more preferably 1.5%, and even more preferably 2.0%. The upper limit of the Mo content is preferably 4.5%, and more preferably 4.0%.

[0044] Nb: 0.20 to 1.00% Niobium (Nb) combines with C to form MX-type carbonitrides and reduce the amount of dissolved C in the base material 10 during use in a high-temperature corrosive environment of 600 to 700°C. This improves the polythionic acid SCC resistance of the base material 10. If the Nb content is less than 0.20%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Nb content exceeds 1.00%, δ-ferrite is formed, and the aging toughness of the base material 10 decreases. Therefore, the Nb content is 0.20 to 1.00%. The lower limit of the Nb content is preferably 0.25%, more preferably 0.28%, even more preferably 0.30%, and still more preferably 0.32%. The upper limit of the Nb content is preferably 0.90%, more preferably 0.85%, even more preferably 0.80%, even more preferably 0.70%, and even more preferably 0.65%.

[0045] N: 0.05 to 0.30% Nitrogen (N) dissolves in the matrix (parent phase) to stabilize austenite and increase the high-temperature strength of the base material 10. N also forms fine carbonitrides within the grains, increasing the high-temperature strength of the base material 10. If the N content is less than 0.05%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the N content exceeds 0.30%, Cr nitrides are formed at the grain boundaries. In this case, the polythionic acid SCC resistance and naphthenic acid corrosion resistance of the weld heat-affected zone (HAZ) of the base material 10 decrease. Therefore, the N content is 0.05 to 0.30%. The lower limit of the N content is preferably 0.06%, more preferably 0.07%, even more preferably 0.08%, and still more preferably 0.10%. The upper limit of the N content is preferably 0.25%, more preferably 0.20%, and even more preferably 0.19%.

[0046] sol.Al: 0.001~0.100% Aluminum (Al) deoxidizes the alloy. If the Al content is less than 0.001%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Al content exceeds 0.100%, the cleanliness of the alloy decreases, and the workability and ductility of the alloy decrease. Therefore, the Al content is 0.001 to 0.100%. The lower limit of the Al content is preferably 0.002%, and more preferably 0.003%. The upper limit of the Al content is preferably 0.050%, more preferably 0.030%, even more preferably 0.026%, and still more preferably 0.025%. In this embodiment, the Al content means the content of acid-soluble Al (sol. Al).

[0047] The remainder of the chemical composition of the base metal 10 of the austenitic stainless alloy welded joint 1 according to this embodiment is composed of Fe and impurities. Here, the impurities refer to those that are mixed in from raw materials such as ore or scrap or the manufacturing environment when the base metal 10 is industrially manufactured, but are not intentionally contained, and are allowed within a range that does not adversely affect the base metal 10 of the austenitic stainless alloy welded joint 1 of this embodiment.

[0048] [Optional Elements] The chemical composition of the base material 10 of the austenitic stainless alloy weld joint 1 of this embodiment further contains, in place of a part of Fe, B: 0~0.0080%, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010%, and Rare earth elements: 0~0.100%, It may contain one or more elements selected from the group consisting of: These optional elements will be explained below.

[0049] [Group 1: B, Cu, W and Co] The chemical composition of the base material 10 according to this embodiment may further contain one or more elements selected from the group consisting of B, Cu, W, and Co, in place of a portion of Fe. These elements are optional and may not be included. When included, B, Cu, W, and Co all increase the high-temperature strength of the base material 10.

[0050] B: 0 to 0.0080% Boron (B) is an optional element and does not necessarily need to be contained. That is, B may be 0%. When B is contained, that is, when the B content exceeds 0%, B segregates at grain boundaries during use in a high-temperature corrosive environment at 600 to 700°C, and increases grain boundary strength. As a result, the high-temperature strength of the base metal 10 increases in a high-temperature corrosive environment at 600 to 700°C. Even if even a small amount of B is contained, the above effect can be obtained to some extent. On the other hand, if the B content exceeds 0.0080%, the B content of the weld metal increases during welding, and the weld hot cracking resistance of the weld metal 20 decreases. Therefore, the B content is 0 to 0.0080%. The lower limit of the B content is preferably 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, even more preferably 0.0015%, even more preferably 0.0018%, even more preferably 0.0020%, and even more preferably 0.0022%. The upper limit of the B content is preferably less than 0.0060%, more preferably 0.0050%, and even more preferably 0.0040%.

[0051] Cu: 0 to 5.00% Copper (Cu) is an optional element and may not be contained. In other words, Cu may be 0%. When Cu is contained, that is, when the Cu content exceeds 0%, Cu precipitates as a Cu phase within grains during use in a high-temperature corrosive environment of 600 to 700°C, thereby increasing the high-temperature strength of the base material 10 through precipitation strengthening. Even if even a small amount of Cu is contained, the above effects can be obtained to some extent. However, if the Cu content exceeds 5.00%, the hot workability and weldability of the alloy deteriorate. Therefore, the Cu content is 0 to 5.00%. The lower limit of the Cu content is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, even more preferably 0.50%, even more preferably 1.00%, even more preferably 2.00%, and even more preferably 2.50%. The upper limit of the Cu content is preferably 4.50%, more preferably 4.00%, even more preferably 3.80%, even more preferably 3.70%, even more preferably 3.60%, even more preferably 3.50%, and even more preferably 3.00%.

[0052] W:0~5.00% Tungsten (W) is an optional element and does not necessarily need to be contained. In other words, W may be 0%. When W is contained, that is, when the W content exceeds 0%, W dissolves in the matrix (parent phase) and increases the high-temperature strength of the base material 10 of the austenitic stainless alloy welded joint 1. Even if even a small amount of W is contained, the above effect can be obtained to some extent. However, when the W content exceeds 5.00%, the stability of austenite decreases, and the aging toughness of the base material 10 decreases. Therefore, the W content is 0 to 5.00%. The lower limit of the W content is preferably 0.01%, more preferably 0.02%, even more preferably 0.05%, and still more preferably 0.10%. The upper limit of the W content is preferably 4.50%, more preferably 4.00%, and even more preferably 3.50%.

[0053] Co: 0 to 1.00% Cobalt (Co) is an optional element and does not necessarily need to be contained. In other words, the Co content may be 0%. When Co is contained, that is, when the Co content exceeds 0%, Co stabilizes austenite and increases the high-temperature strength of the base metal 10 of the austenitic stainless alloy welded joint 1. Even if even a small amount of Co is contained, the above effects can be obtained to some extent. However, when the Co content exceeds 1.00%, the raw material cost increases. Therefore, the Co content is 0 to 1.00%. The lower limit of the Co content is preferably 0.01%, more preferably 0.02%, even more preferably 0.03%, and still more preferably 0.10%. The upper limit of the Co content is preferably 0.90%, more preferably 0.80%, and even more preferably 0.60%.

[0054] [Group 2: V, Ta, and Hf] The chemical composition of the base material 10 according to this embodiment may further contain one or more elements selected from the group consisting of V, Ta, and Hf in place of a portion of Fe. These elements are optional and may not be included. When included, V, Ta, and Hf all enhance the polythionic acid SCC resistance of the base material 10.

[0055] V: 0 to 1.00% Vanadium (V) is an optional element and may not be contained. In other words, the V content may be 0%. When V is contained, that is, when the V content exceeds 0%, V bonds with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of dissolved C in the base material 10 and improves the polythionic acid SCC resistance of the base material 10. Even if even a small amount of V is contained, the above effects can be obtained to some extent. However, when the V content exceeds 1.00%, δ-ferrite is formed and the aging toughness of the base material 10 decreases. Therefore, the V content is 0 to 1.00%. The lower limit of the V content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%. The upper limit of the V content is preferably 0.90%, more preferably 0.80%, even more preferably 0.60%, even more preferably 0.40%, and even more preferably 0.20%.

[0056] Ta: 0 to 0.20% Tantalum (Ta) is an optional element and may not be contained. In other words, the Ta content may be 0%. When Ta is contained, that is, when the Ta content exceeds 0%, Ta combines with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of solute C in the base material 10 and improves the polythionic acid SCC resistance of the base material 10. Even if even a small amount of Ta is contained, the above effects can be obtained to some extent. However, when the Ta content exceeds 0.20%, δ-ferrite is formed and the aging toughness of the base material 10 decreases. Therefore, the Ta content is 0 to 0.20%. The lower limit of the Ta content is preferably 0.01%, and more preferably 0.02%. The upper limit of the Ta content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0057] Hf: 0 to 0.20% Hafnium (Hf) is an optional element and may not be contained. That is, the Hf content may be 0%. When Hf is contained, that is, when the Hf content exceeds 0%, Hf bonds with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of dissolved C in the base material 10 and improves the polythionic acid SCC resistance of the base material 10. Even if even a small amount of Hf is contained, the above effects can be obtained to some extent. However, when the Hf content exceeds 0.20%, δ-ferrite is formed, and the creep strength, toughness, and weldability of the base material 10 decrease. Therefore, the Hf content is 0 to 0.20%. The lower limit of the Hf content is preferably 0.01%, and more preferably 0.02%. The upper limit of the Hf content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0058] [Group 3: Ca, Mg and rare earth elements] The chemical composition of the base material 10 according to this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Ca, Mg, and rare earth elements (REM). All of these elements are optional and may not be included. When included, Ca, Mg, and rare earth elements all improve the hot workability of the base material.

[0059] Ca: 0 to 0.010% Calcium (Ca) is an optional element and may not be contained. In other words, the Ca content may be 0%. When Ca is contained, that is, when the Ca content exceeds 0%, Ca fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the base material 10. Even if even a small amount of Ca is contained, the above effects can be obtained to some extent. However, when the Ca content exceeds 0.010%, the hot workability and creep ductility of the base material 10 decrease. Therefore, the Ca content is 0 to 0.010%. The lower limit of the Ca content is preferably 0.001%, and more preferably 0.002%. The upper limit of the Ca content is preferably 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0060] Mg: 0 to 0.010% Magnesium (Mg) is an optional element and may not be contained. In other words, the Mg content may be 0%. When Mg is contained, that is, when the Mg content exceeds 0%, Mg fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the base material 10. Even if even a small amount of Mg is contained, the above effects can be obtained to some extent. However, when the Mg content exceeds 0.010%, the hot workability and creep ductility of the base material 10 decrease. Therefore, the Mg content is 0 to 0.010%. The lower limit of the Mg content is preferably 0.001%, and more preferably 0.002%. The upper limit of the Mg content is preferably 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0061] Rare earth elements: 0~0.100% Rare earth elements (REM) are optional elements and may not be contained. In other words, the REM content may be 0%. When REM is contained, that is, when the REM content exceeds 0%, the REM fixes O (oxygen) and S (sulfur) as inclusions, improving the hot workability of the base material. Even if even a small amount of REM is contained, the above effects can be obtained to some extent. However, when the REM content exceeds 0.100%, the hot workability and creep ductility of the base material decrease. Therefore, the REM content is 0 to 0.100%. The lower limit of the REM content is preferably 0.001%, and more preferably 0.002%. The upper limit of the REM content is preferably 0.080%, and more preferably 0.060%.

[0062] In this specification, REM includes at least one of Sc, Y, and lanthanoids (La with atomic number 57 to Lu with atomic number 71), and the REM content means the total content of these elements.

[0063] [(Feature 2) Chemical composition of weld metal 20] FIG. 5 is a cross-sectional view perpendicular to the weld metal extending direction L of an austenitic stainless alloy welded joint 1 of this embodiment. Referring to FIG. 5, in the cross-section of the weld metal 20 perpendicular to the weld metal extending direction L, the width at the surface of the weld metal 20 is defined as w (mm). The thickness of the weld metal 20 at the center of the width w is defined as t (mm). In this case, the center of the width of the weld metal 20 and the center of the thickness of the weld metal 20 (i.e., the portion at a depth of t / 2 from the surface of the weld metal 20) is defined as region P. The chemical composition of region P is defined as the chemical composition of the weld metal 20. The chemical composition of the weld metal 20 contains the following elements.

[0064] C: 0.020% or less Carbon (C) is inevitably contained. In other words, the C content is more than 0%. C forms Cr carbides (M) at the grain boundaries of the weld metal 20 during use in a high-temperature corrosive environment of 600 to 700°C. 23C forms C6 type carbides. The formation of Cr carbides reduces the amount of dissolved Cr, which reduces the polythionic acid SCC resistance of the weld metal 20. Therefore, the C content is 0.020% or less. The C content is preferably as low as possible. However, excessive reduction in the C content increases production costs. Therefore, from the viewpoint of industrial production, the lower limit of the C content is preferably 0.001%, and more preferably 0.005%. The upper limit of the C content is preferably 0.019%, more preferably 0.018%, even more preferably 0.017%, and still more preferably 0.015%.

[0065] Si: 0.01 to 1.00% Silicon (Si) deoxidizes the weld metal 20 during welding. If the Si content is less than 0.01%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 1.00%, the aging toughness of the weld metal 20 decreases. Therefore, the Si content is 0.01 to 1.00%. The lower limit of the Si content is preferably 0.02%, more preferably 0.03%, even more preferably 0.05%, and still more preferably 0.10%. The upper limit of the Si content is preferably 0.95%, more preferably 0.90%, even more preferably 0.80%, even more preferably 0.76%, even more preferably 0.65%, even more preferably 0.40%, and even more preferably 0.35%.

[0066] Mn: 0.20 to 2.00% Manganese (Mn) deoxidizes the weld metal 20 during welding. If the Mn content is less than 0.20%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mn content exceeds 2.00%, the high-temperature strength of the weld metal 20 decreases. Therefore, the Mn content is 0.20 to 2.00%. The lower limit of the Mn content is preferably 0.25%, more preferably 0.28%, even more preferably 0.30%, even more preferably 0.35%, and even more preferably 0.40%. The upper limit of the Mn content is preferably 1.90%, more preferably 1.85%, even more preferably 1.80%, even more preferably 1.75%, even more preferably 1.70%, even more preferably 1.50%, and even more preferably 1.30%.

[0067] P:0.030% or less Phosphorus (P) is an unavoidable impurity. In other words, the P content is greater than 0%. If the P content exceeds 0.030%, the weld hot cracking resistance of the weld metal 20 will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the P content is 0.030% or less. The lower the P content, the better. However, excessive reduction in the P content increases production costs. Therefore, from the viewpoint of industrial production, the lower limit of the P content is preferably 0.001%, more preferably 0.002%, and even more preferably 0.003%. The upper limit of the P content is preferably 0.025%, and more preferably 0.020%.

[0068] S: 0.010% or less Sulfur (S) is an unavoidably contained impurity. In other words, the S content is greater than 0%. If the S content exceeds 0.010%, the weld hot cracking resistance of the weld metal 20 will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the S content is 0.010% or less. The S content is preferably as low as possible. However, excessive reduction of the S content increases production costs. Therefore, from the viewpoint of industrial production, the lower limit of the S content is preferably 0.001%, and more preferably 0.002%. The upper limit of the S content is preferably 0.009%, and more preferably 0.007%.

[0069] Cr: 16.0~25.0% Chromium (Cr) improves the polythionic acid SCC resistance of the weld metal 20. If the Cr content is less than 16.0%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Cr content exceeds 25.0%, the aging toughness of the weld metal 20 decreases. Therefore, the Cr content is 16.0 to 25.0%. The lower limit of the Cr content is preferably 16.5%, and more preferably 17.0%. The upper limit of the Cr content is preferably 24.5%, more preferably 24.0%, even more preferably 23.5%, and still more preferably 23.0%.

[0070] Ni: 15.0 to 40.0% Nickel (Ni) stabilizes austenite and improves the aging toughness of the weld metal 20. If the Ni content is less than 15.0%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Ni content exceeds 40.0%, the above effects saturate and the manufacturing cost increases. Therefore, the Ni content is 15.0 to 40.0%. The lower limit of the Ni content is preferably 15.5%, more preferably 16.0%, even more preferably 17.0%, even more preferably 18.0%, and even more preferably 19.0%. The upper limit of the Ni content is preferably 39.0%, more preferably 38.0%, even more preferably 36.5%, even more preferably 35.0%, and even more preferably 33.0%.

[0071] Mo: 2.5 to 5.0% Molybdenum (Mo) forms Cr carbides (M) at the grain boundaries in the weld metal 20 during use in a high-temperature corrosive environment of 600 to 700°C. 23Mo suppresses the formation of C6-type carbides, thereby enhancing the polythionic acid SCC resistance of the weld metal 20. Furthermore, when a welded joint is used in a high-temperature corrosive environment, solute Mo in the weld metal 20 combines with S in the use environment to form a sulfide film on the surface of the weld metal 20. The formation of this sulfide film enhances the naphthenic acid corrosion resistance of the weld metal 20. If the Mo content is less than 2.5%, the above effects cannot be sufficiently obtained even if the contents of the other elements are within the ranges of this embodiment. On the other hand, if the Mo content exceeds 5.0%, sufficient aging toughness cannot be obtained. Therefore, the Mo content is 2.5 to 5.0%. The lower limit of the Mo content is preferably 2.6%, more preferably 2.7%, and even more preferably 2.8%. The upper limit of the Mo content is preferably 4.5%, and more preferably 4.0%.

[0072] Nb: 0.10 to 2.00% Niobium (Nb) combines with carbon to form MX-type carbonitrides and reduce the amount of dissolved carbon in the weld metal 20 during use in a high-temperature corrosive environment of 600 to 700°C. This improves the polythionic acid SCC resistance of the weld metal 20. The formed MX-type carbonitrides of Nb also improve creep strength. If the Nb content is less than 0.10%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Nb content exceeds 2.00%, δ-ferrite is formed, and the long-term creep strength, toughness, and weldability of the weld metal 20 decrease. Therefore, the Nb content is 0.10 to 2.00%. The lower limit of the Nb content is preferably 0.11%, more preferably 0.12%, even more preferably 0.15%, and still more preferably 0.20%. The upper limit of the Nb content is preferably 1.90%, more preferably 1.80%, even more preferably 1.40%, even more preferably 1.00%, even more preferably 0.75%, even more preferably 0.70%, and even more preferably 0.65%.

[0073] N: 0.05 to 0.30% Nitrogen (N) dissolves in the matrix (parent phase) to stabilize austenite and increase the high-temperature strength of the weld metal 20. N also forms fine carbonitrides within the grains, increasing the high-temperature strength of the weld metal 20. If the N content is less than 0.05%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the N content exceeds 0.30%, Cr nitrides are formed at the grain boundaries, and the polythionic acid SCC resistance and naphthenic acid corrosion resistance of the weld metal 20 decrease. Therefore, the N content is 0.05 to 0.30%. The lower limit of the N content is preferably 0.06%, more preferably 0.07%, even more preferably 0.08%, and still more preferably 0.10%. The upper limit of the N content is preferably 0.28%, and more preferably 0.25%.

[0074] sol.Al: 0.001~0.100% Aluminum (Al) deoxidizes the weld metal 20 during welding. If the Al content is less than 0.001%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Al content exceeds 0.100%, the ductility of the weld metal 20 decreases. Therefore, the Al content is 0.001 to 0.100%. The lower limit of the Al content is preferably 0.002%, and more preferably 0.010%. The upper limit of the Al content is preferably 0.085%, more preferably 0.080%, even more preferably 0.060%, even more preferably 0.040%, even more preferably 0.030%, even more preferably 0.025%, and even more preferably 0.020%. In this embodiment, the Al content means the content of acid-soluble Al (sol. Al).

[0075] B: 0.0010~0.0050% Boron (B) segregates at grain boundaries during use in a high-temperature corrosive environment of 600 to 700°C, increasing grain boundary strength. As a result, the high-temperature strength of the weld metal 20 is increased in a high-temperature corrosive environment of 600 to 700°C. If the B content is less than 0.0010%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the B content exceeds 0.0050%, the weld hot cracking resistance of the weld metal 20 decreases. Therefore, the B content is 0.0010 to 0.0050%. The lower limit of the B content is preferably 0.0011%, more preferably 0.0012%, even more preferably 0.0015%, even more preferably 0.0020%, and even more preferably 0.0030%. When the B content in the weld metal 20 is 0.0030% or more, excellent creep strength can be obtained in the welded joint 1. The upper limit of the B content is preferably 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

[0076] The balance of the chemical composition of the weld metal 20 of the austenitic stainless alloy welded joint 1 according to this embodiment is composed of Fe and impurities. Here, the impurities are those that are mixed in from the welding material as a raw material or the environment during welding when the weld metal 20 is formed, and are not intentionally contained, but are allowed within a range that does not adversely affect the weld metal 20.

[0077] [Optional Elements] The chemical composition of the weld metal 20 of the austenitic stainless alloy weld joint 1 of this embodiment further contains, in place of a portion of Fe, Cu: 0-5.00% W: 0~5.00%, Co: 0-1.00%, V: 0~1.00%, Ta: 0 to 0.20%, Hf: 0~0.20%, Ca: 0 to 0.010% Mg: 0 to 0.010%, and Rare earth elements: 0~0.100%, It may contain one or more elements selected from the group consisting of: These optional elements will be explained below.

[0078] [Group 1: Cu, W and Co] The chemical composition of the weld metal 20 according to this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Cu, W, and Co. All of these elements increase the creep strength of the weld metal 20.

[0079] Cu: 0 to 5.00% Copper (Cu) is an optional element and may not be contained. In other words, Cu may be 0%. When Cu is contained, that is, when the Cu content exceeds 0%, Cu precipitates as a Cu phase within grains during use in a high-temperature corrosive environment of 600 to 700°C, thereby increasing the high-temperature strength of the weld metal 20 through precipitation strengthening. Even if even a small amount of Cu is contained, the above effects can be obtained to some extent. However, if the Cu content exceeds 5.00%, the weldability of the alloy decreases. Therefore, the Cu content is 0 to 5.00%. The lower limit of the Cu content is preferably 0.01%, more preferably 0.05%, even more preferably 0.10%, even more preferably 0.50%, even more preferably 1.00%, even more preferably 2.00%, and even more preferably 2.50%. The upper limit of the Cu content is preferably 4.50%, more preferably 4.00%, even more preferably 3.80%, even more preferably 3.70%, even more preferably 3.60%, even more preferably 3.50%, and even more preferably 1.90%.

[0080] W:0~5.00% Tungsten (W) is an optional element and does not necessarily need to be contained. That is, W may be 0%. When W is contained, that is, when the W content exceeds 0%, W dissolves in the matrix (parent phase) and increases the high-temperature strength of the weld metal 20. Even if even a small amount of W is contained, the above effect can be obtained to some extent. However, when the W content exceeds 5.00%, the stability of austenite decreases, and the aging toughness of the weld metal 20 decreases. Therefore, the W content is 0 to 5.00%. The lower limit of the W content is preferably 0.01%, more preferably 0.02%, even more preferably 0.05%, and still more preferably 0.10%. The upper limit of the W content is preferably 4.50%, more preferably 4.00%, even more preferably 3.80%, and still more preferably 3.50%.

[0081] Co: 0 to 1.00% Cobalt (Co) is an optional element and does not necessarily need to be contained. In other words, the Co content may be 0%. When Co is contained, that is, when the Co content exceeds 0%, Co stabilizes austenite and increases the high-temperature strength of the weld metal 20. Even if even a small amount of Co is contained, the above effects can be obtained to some extent. However, if the Co content exceeds 1.00%, the raw material cost increases. Therefore, the Co content is 0 to 1.00%. The lower limit of the Co content is preferably 0.01%, more preferably 0.02%, even more preferably 0.03%, and still more preferably 0.10%. The upper limit of the Co content is preferably 0.90%, more preferably 0.80%, even more preferably 0.60%, even more preferably 0.50%, and still more preferably 0.45%.

[0082] [Group 2: V, Ta, and Hf] The chemical composition of the weld metal 20 according to this embodiment may further contain one or more elements selected from the group consisting of V, Ta, and Hf in place of a portion of Fe. These elements are optional and may not be contained. When contained, V, Ta, and Hf all enhance the polythionic acid SCC resistance of the weld metal 20.

[0083] V: 0 to 1.00% Vanadium (V) is an optional element and does not necessarily need to be contained. That is, the V content may be 0%. When V is contained, that is, when the V content exceeds 0%, V combines with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of dissolved C in the weld metal 20 and improves the polythionic acid SCC resistance of the weld metal 20. Even if even a small amount of V is contained, the above effects can be obtained to some extent. However, when the V content exceeds 1.00%, δ-ferrite is formed and the aging toughness of the weld metal 20 decreases. Therefore, the V content is 0 to 1.00%. The lower limit of the V content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%. The upper limit of the V content is preferably 0.90%, more preferably 0.80%, even more preferably 0.60%, even more preferably 0.40%, even more preferably 0.20%, even more preferably 0.15%, and even more preferably 0.10%.

[0084] Ta: 0 to 0.20% Tantalum (Ta) is an optional element and may not be contained. That is, the Ta content may be 0%. When Ta is contained, that is, when the Ta content exceeds 0%, Ta combines with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of dissolved C in the weld metal 20 and improves the polythionic acid SCC resistance of the weld metal 20. Even if even a small amount of Ta is contained, the above effects can be obtained to some extent. However, when the Ta content exceeds 0.20%, δ-ferrite is formed, and the aging toughness of the weld metal 20 decreases. Therefore, the Ta content is 0 to 0.20%. The lower limit of the Ta content for more effectively improving the polythionic acid SCC resistance is preferably 0.01%, and more preferably 0.02%. The upper limit of the Ta content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0085] Hf: 0 to 0.20% Hafnium (Hf) is an optional element and may not be contained. That is, the Hf content may be 0%. When Hf is contained, that is, when the Hf content exceeds 0%, Hf bonds with C to form carbonitrides during use in a high-temperature corrosive environment of 600 to 700°C. This reduces the amount of dissolved C in the weld metal 20 and improves the polythionic acid SCC resistance of the weld metal 20. Even if even a small amount of Hf is contained, the above effects can be obtained to some extent. However, when the Hf content exceeds 0.20%, δ-ferrite is formed, and the creep strength, toughness, and weldability of the weld metal 20 decrease. Therefore, the Hf content is 0 to 0.20%. The lower limit of the Hf content is preferably 0.01%, and more preferably 0.02%. The upper limit of the Hf content is preferably 0.18%, more preferably 0.16%, and even more preferably 0.14%.

[0086] [Group 3: Ca, Mg and rare earth elements] The chemical composition of the weld metal 20 according to this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Ca, Mg, and rare earth elements. All of these elements are optional elements and may not be contained. When contained, Ca, Mg, and rare earth elements all increase the ductility of the weld metal 20.

[0087] Ca: 0 to 0.010% Calcium (Ca) is an optional element and may not be contained. In other words, the Ca content may be 0%. When Ca is contained, that is, when the Ca content exceeds 0%, Ca fixes O (oxygen) and S (sulfur) as inclusions, thereby increasing the ductility of the weld metal 20. Even if even a small amount of Ca is contained, the above effect can be obtained to some extent. However, when the Ca content exceeds 0.010%, the ductility of the weld metal 20 decreases. Therefore, the Ca content is 0 to 0.010%. The lower limit of the Ca content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%. The upper limit of the Ca content is preferably 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0088] Mg: 0 to 0.010% Magnesium (Mg) is an optional element and may not be contained. In other words, the Mg content may be 0%. When Mg is contained, that is, when the Mg content exceeds 0%, Mg fixes O (oxygen) and S (sulfur) as inclusions, thereby increasing the ductility of the weld metal 20. Even if even a small amount of Mg is contained, the above effect can be obtained to some extent. However, when the Mg content exceeds 0.010%, the ductility of the weld metal 20 decreases. Therefore, the Mg content is 0 to 0.010%. The lower limit of the Mg content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%. The upper limit of the Mg content is preferably 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0089] Rare earth elements: 0~0.100% Rare earth elements (REM) are optional elements and may not be contained. That is, the REM content may be 0%. When REM is contained, that is, when the REM content exceeds 0%, the REM fixes O (oxygen) and S (sulfur) as inclusions, thereby increasing the ductility of the weld metal 20. Even if even a small amount of REM is contained, the above effect can be obtained to some extent. However, when the REM content exceeds 0.100%, the ductility of the weld metal 20 decreases. Therefore, the REM content is 0 to 0.100%. The lower limit of the REM content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%. The upper limit of the REM content is preferably 0.080%, and more preferably 0.060%.

[0090] [(Feature 3) F1 with Weld Metal 20] Furthermore, in the weld metal 20, F1 defined by the formula (1) is 2.30 or less. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) Each element symbol in formula (1) is substituted with the content (mass %) of the corresponding element.

[0091] F1 is an index relating to the resistance to weld hot cracking of the weld metal 20. B, C, Cr, Mn, Mo, Nb, P, S, Si, and W are all elements that promote weld hot cracking during welding. If F1, which is composed of the contents of these elements, exceeds 2.30, the resistance to weld hot cracking of the weld metal 20 decreases during welding even if the other features 1, 2, and 4 are satisfied. If F1 is 2.30 or less, sufficient resistance to weld hot cracking can be obtained in the weld metal 20, provided that the other features 1, 2, and 4 are satisfied. Therefore, F1 is 2.30 or less. The upper limit of F1 is preferably 2.28, more preferably 2.25, even more preferably 2.22, even more preferably 2.20, even more preferably 2.18, even more preferably 2.15, even more preferably 2.10, and even more preferably 2.05. F1 is a value obtained by rounding the obtained value to two decimal places (the value to one decimal place).

[0092] [(Feature 4) F2 in Weld Metal 20] In a cross section of the weld metal perpendicular to the extending direction of the weld metal 20, a 1 mm × 1 mm square region at the center of the width on the surface of the weld metal and at the center of the thickness of the weld metal was divided into minute square areas of 100 μm × 100 μm, the Mo content in mass% in each minute square area was determined, and the arithmetic average value of all the obtained Mo contents was defined as [Mo] AVE Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content higher than [Mo] H Of all the Mo contents obtained, [Mo] AVE The arithmetic mean value of the Mo content lower than [Mo] L When this is defined, F2 defined by formula (2) is 2.5 or less. F2=[Mo] H / [Mo] L (2)

[0093] F2 is an index relating to the degree of Mo segregation in the square region of the weld metal 20. In the austenitic stainless alloy welded joint 1 of this embodiment, the Mo content is high in order to improve naphthenic acid corrosion resistance. Although Mo improves naphthenic acid corrosion resistance, it is prone to segregation at grain boundaries.

[0094] [Mo] H is the average value of Mo content in the square area [Mo] AVE This means the Mo content in the higher region. H is an index of the segregated Mo content. L is the average value of Mo content in the square area [Mo] AVEThis means the Mo content in the lower region. L is an index of the Mo content in regions other than the region where Mo is segregated.

[0095] If F2 is high, the degree of Mo segregation in the square region is high. In other words, it is considered that the degree of Mo segregation at the grain boundary is high. In this case, the Mo concentration at the grain boundary is high and the Mo concentration within the grain is low. Therefore, the strength of the grain boundary is excessively higher than the strength within the grain. In other words, the difference between the grain boundary strength and the intragranular strength in the weld metal 20 becomes large. As a result, sufficient naphthenic acid corrosion resistance and aging toughness cannot be obtained.

[0096] If F2 is 2.5 or less, the degree of Mo segregation in the square region is sufficiently suppressed, thereby reducing the difference between the grain boundary strength and the intragranular strength in the weld metal 20. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness are obtained.

[0097] The upper limit of F2 is preferably 2.4, more preferably 2.3, even more preferably 2.2, even more preferably 2.1, even more preferably 2.0, even more preferably 1.8, even more preferably 1.6, even more preferably 1.4.

[0098] [F2 measurement method] F2 can be measured by the following method. Referring to FIG. 5, a region P is identified in a cross section of the weld metal 20 perpendicular to the weld metal extending direction L, at the width center of the surface of the weld metal 20 and at the thickness center of the weld metal 20. Furthermore, a test piece having a surface (observation surface) including a 1 mm × 1 mm square area is taken from the region P. The observation surface of the test piece is mirror-polished. An arbitrary square area is selected from the mirror-polished observation surface. A surface analysis is performed on the selected square area using a field emission electron probe microanalyzer (FE-EPMA). Specifically, the square area is divided into minute square areas of 100 μm × 100 μm. Then, elemental analysis is performed on each minute square area. The acceleration voltage is 15 kV, the probe current is 400 nA, the beam diameter is 2 μm, and the integration time is 0.1 seconds. The element to be measured is Mo, and the Mo content in mass % in each minute square area is determined. The arithmetic mean value of all the obtained Mo contents (mass %) is calculated as [Mo]. AVE It is defined as:

[0099] Of all the measured Mo contents, [Mo] AVE and small square areas with a higher Mo content than [Mo] AVE It separates the small square areas with lower Mo content than [Mo] AVE The small square area with the same Mo content is excluded.

[0100] [Mo] AVE The arithmetic mean value of the Mo content in the small square area with a higher Mo content than [Mo] H Define it as [Mo]. AVE The arithmetic mean value of the Mo content in the small square area with a lower Mo content than [Mo] L The obtained [Mo] H and [Mo] H Based on this, F2 is calculated using equation (2).

[0101] [Regarding the austenitic stainless steel alloy welding material of this embodiment] The welding material for the weld metal 20 of the austenitic stainless alloy weld joint 1 of this embodiment has a chemical composition, in mass %, of C: 0.020% or less, Si: 0.01 to 1.00%, Mn: 0.20 to 2.00%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0 to 25.0%, Ni: 15.0 to 40.0%, Mo: 2.5 to 5.0%, Nb: 0.10 to 2.00%, N: 0.05 to 0.30%, An austenitic stainless steel alloy welding material is used, which contains sol.Al: 0.001-0.100%, B: 0.0010-0.0050%, Cu: 0-5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0-0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0-0.010%, rare earth elements: 0-0.100%, and the balance being Fe and impurities. The function, preferred lower limit, and preferred upper limit of each element in the chemical composition of the austenitic stainless steel alloy welding material are the same as the function, preferred lower limit, and preferred upper limit of each element in the chemical composition of the weld metal 20.

[0102] An austenitic stainless alloy welding material having the above-mentioned chemical composition is welded to a base material 10 by a welding method described below to form a weld metal 20. If the chemical composition of the austenitic stainless alloy welding material is outside the above-mentioned range, the weld metal 20 cannot be formed.

[0103] [Effects of austenitic stainless steel alloy welded joint 1] The austenitic stainless alloy welded joint 1 of this embodiment satisfies Features 1 to 4. Therefore, in the weld metal 20, sufficient resistance to weld hot cracking is obtained, sufficient resistance to polythionic acid SCC is obtained, sufficient resistance to naphthenic acid corrosion is obtained, and sufficient aging toughness is obtained.

[0104] [Manufacturing method] An example of a manufacturing method for the austenitic stainless alloy weld joint 1 of this embodiment will be described. The manufacturing method for the austenitic stainless alloy weld joint 1 described below is one example for manufacturing the austenitic stainless alloy weld joint 1 of this embodiment. Therefore, the austenitic stainless alloy weld joint 1 having the above-mentioned configuration may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferred example of a manufacturing method for the austenitic stainless alloy weld joint 1 of this embodiment.

[0105] An example of the manufacturing method includes the following steps. (Process 1) Base material preparation process (Process 2) Welding process Steps 1 and 2 will be explained below.

[0106] [(Process 1) Base material preparation process] In the preform preparation step, a preform 10 that satisfies Feature 1 is prepared. The shape of the preform 10 is not particularly limited. As described above, the preform 10 may be an alloy plate or an alloy pipe. The preform 10 may also be a bar or a shaped steel.

[0107] When manufacturing the base material 10, the base material preparation process includes the following steps. (Step 11) Preparation step (Process 12) Hot processing process (Process 13) Cold working process (Step 14) Solution treatment step Steps 11 to 14 will be explained below.

[0108] [(Step 11) Preparation step] A molten alloy satisfying Feature 1 is manufactured. For example, the molten alloy is manufactured using an electric furnace, an AOD (Argon Oxygen Decarburization) furnace, or a VOD (Vacuum Oxygen Decarburization) furnace. The manufactured molten alloy is subjected to a well-known degassing treatment as necessary. A material is manufactured from the molten alloy that has been degassed. A continuous casting method, for example, is used to manufacture the material. A continuous cast material (material) is manufactured by the continuous casting method. Examples of continuous cast material include slabs, blooms, and billets. The molten alloy may be made into an ingot by an ingot casting method.

[0109] [(Process 12) Hot processing process] A prepared material (continuously cast material or ingot) is hot worked to produce a base material. For example, the material is hot rolled to produce an alloy plate, which is the base material 10. Alternatively, the material is hot extrusion, hot piercing, or the like to produce an alloy pipe, which is the base material 10. The specific method of hot working is not particularly limited, and hot working may be performed according to the shape of the final product. The processing end temperature of the hot working is, for example, 1000°C or higher, and more preferably 1050°C or higher. The processing end temperature here refers to the temperature of the base material 10 immediately after the final hot working is completed.

[0110] [(Process 13) Cold working process] The base material after the hot working step may be subjected to cold working as necessary. When the base material 10 is an alloy pipe, the cold working may be, for example, cold drawing or cold rolling. When the base material 10 is an alloy plate, the cold working may be, for example, cold rolling.

[0111] [(Step 14) Solution treatment step] After the hot working step or the cold working step, the base material 10 may be subjected to a solution treatment, if necessary. In the solution treatment step, the structure is homogenized and carbonitrides are dissolved. The solution treatment temperature is preferably 1000 to 1250°C. The holding time at the solution treatment temperature is not particularly limited, but is, for example, 2 to 60 minutes.

[0112] [(Process 2) Welding process] Welding is performed on the prepared base material 10 to produce an austenitic stainless alloy weld joint 1. A groove is formed at the end of the base material 10. Two base materials 10 with grooves formed therein are prepared. The grooves of the prepared base materials 10 are butted together. Then, welding is performed on the pair of butted grooves using an austenitic stainless alloy welding material having the above-mentioned chemical composition to form a weld metal 20 having the above-mentioned chemical composition.

[0113] The austenitic stainless steel alloy welding material is manufactured by the following method. A molten alloy having the above-mentioned chemical composition is manufactured. For example, the molten alloy is manufactured using an electric furnace, an AOD furnace, or a VOD furnace. The manufactured molten alloy is subjected to a well-known degassing treatment as necessary. A material (continuously cast material or ingot) is manufactured from the degassed molten alloy. The material is subjected to well-known hot working to manufacture a wire-shaped austenitic stainless steel alloy welding material.

[0114] The welding method of the base material 10 using the austenitic stainless steel alloy welding material is, for example, TIG welding (GTAW), shielded metal arc welding (SMAW), flux-cored wire arc welding (FCAW), gas metal arc welding (GMAW), or submerged arc welding (SAW).

[0115] In the welding process, when the base material 10 is an alloy plate, for example, a groove is formed on the end face or side face of the alloy plate. When the base material 10 is an alloy pipe, a groove is formed on the end of the alloy pipe in the axial direction. When the base material 10 is an alloy pipe, for example, austenitic stainless steel alloy welded joint 1 is formed by performing circumferential welding.

[0116] In the welding process, welding is performed so as to satisfy the following conditions. (Condition 1) Heat input: 3.0kJ / mm or less (Condition 2) Interlayer temperature: 150℃ or less (Condition 3) When the cooling rate at 1300°C during welding is CR (°C / sec) and the welding speed is V (mm / sec), FA, defined by the following formula, is made greater than 0.60. FA=V-0.0056×(CR / V) Here, the interlayer temperature means the surface temperature (°C) of the layer of the weld immediately before starting welding of the next layer in multi-layer welding. An interlayer temperature of 150°C or less means that the interlayer temperature after each layer is formed is 150°C or less. In other words, the interlayer temperature of condition 2 means that the highest temperature of one or more interlayer temperatures is 150°C or less.

[0117] FA is an index for suppressing Mo segregation. The higher the welding speed V or the smaller the temperature gradient (= CR / V) in the extending direction of the weld metal 20, the more Mo segregation is suppressed during solidification of the weld metal 20. If FA is made larger than 0.60, Mo segregation in the weld metal 20 can be sufficiently suppressed.

[0118] Here, the cooling rate CR at 1300°C can be measured as follows: During welding in the welding process, a thermocouple is inserted into the molten pool to obtain a cooling curve. From the obtained cooling curve, the cooling rate CR (°C / sec) at 1300°C is calculated. In addition, the welding speed V (mm / sec) is determined by the setting of the movement speed of the welding torch of the welding equipment in the case of automatic welding, and by the setting of the movement speed of the welding equipment or positioner (rotating device) in the case of circumferential welding of alloy pipes. If the above conditions 1 to 3 are satisfied, the weld metal 20 that satisfies the features 2 to 4 can be formed.

[0119] The above manufacturing process allows for the manufacture of an austenitic stainless alloy welded joint that satisfies Features 1 to 4. The manufacturing method for the austenitic stainless alloy welded joint 1 according to this embodiment is not limited to the manufacturing method described above. As long as an austenitic stainless alloy welded joint 1 that satisfies Features 1 to 4 can be manufactured, other methods may be used.

[0120] The effects of the austenitic stainless steel alloy weld joint of this embodiment will be explained more specifically below using examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the austenitic stainless steel alloy weld joint of this embodiment. Therefore, the austenitic stainless steel alloy weld joint of this embodiment is not limited to this one example of conditions. [Example]

[0121] [Manufacturing of austenitic stainless steel alloy welded joints] [Base material manufacturing] Molten alloys for base metals having the chemical compositions shown in Tables 1-1 and 1-2 were produced.

[0122] [Table 1-1]

[0123] [Table 1-2]

[0124] Specifically, a 30 kg ingot with an outer diameter of 120 mm was produced using the molten alloy. The ingot was hot forged to form an alloy plate with a thickness of 30 mm. The ingot was then hot rolled to form an alloy plate with a thickness of 15 mm. The processing end temperature during hot rolling was 1050°C or higher in all cases. The alloy plate after hot rolling was subjected to a solution treatment. In all alloy plates, the solution treatment temperature was 1150°C, and the solution treatment time was 10 minutes. The base material after the solution treatment was water-cooled. Through the above manufacturing process, an alloy plate (base material) with a thickness of 15 mm, width of 50 mm, and length of 100 mm was produced.

[0125] [Welding material manufacturing] Welding materials having the chemical compositions shown in Tables 2-1 and 2-2 were prepared. The remainder of the chemical composition of each welding material number, other than the elements shown in Tables 2-1 and 2-2, was Fe and impurities.

[0126] [Table 2-1]

[0127] [Table 2-2]

[0128] The molten alloy was used to produce an ingot weighing 30 kg and having an outer diameter of 120 mm, which was then hot forged, hot rolled, cold rolled, and heat treated by known methods to produce a welding wire (austenitic stainless alloy welding material) having an outer diameter of 1.2 mm.

[0129] [Manufacturing of austenitic stainless steel alloy welded joints] Using the base metals in Tables 1-1 and 1-2 and the welding materials in Tables 2-1 and 2-2, austenitic stainless alloy welded joints were produced by the following production method.

[0130] Two alloy plates shown in Figure 6 were machined to serve as the base materials for Tables 1-1 and 1-2. In Figure 6, the numbers with "mm" indicate the dimensions (unit: mm) of the alloy plate, which was the base material. The alloy plate had a groove on the side extending in the longitudinal direction. The groove was a V-groove with a groove angle of 30° and a root thickness of 1 mm.

[0131] A restraint plate 30 was prepared as shown in Fig. 7. The restraint plate 30 had a thickness of 25 mm, a width of 200 mm, and a length of 200 mm, and had a chemical composition equivalent to "SM400C" described in JIS G 3106 (2008).

[0132] Two base materials (plate materials) 10 were placed on a restraint plate 30. At this time, the groove faces of the two base materials 10 were butted against each other. After the two base materials 10 were placed, four peripheries of the base materials 10 were restrained and welded using a covered arc welding rod. The covered arc welding rod used had a chemical composition equivalent to "ENiCrMo-3" specified in JIS Z 3224 (2010).

[0133] After the four circumferences of the base material 10 were restrained and welded, multi-layer welding was performed by gas-tungsten inert gas (GTAW) using the welding materials shown in Tables 2-1 and 2-2 to form weld metal. For each test number, the heat input during welding (kJ / mm), the maximum interlayer temperature (°C) at each layer during multi-layer welding, the welding speed V (°C / sec), the cooling rate CR at 1300°C (mm / sec), and the FA were as shown in the "Heat input (kJ / mm)," "Interlayer temperature (°C)," "Welding speed V (mm / sec)," "Cooling rate CR (°C / sec)," and "FA" columns in the "Welding conditions" column of Table 4. Austenitic stainless steel alloy weld joints with each weld metal number were produced by the above manufacturing process.

[0134] [Chemical composition analysis of weld metal] The chemical composition of the weld metal at the center of width and thickness of the austenitic stainless steel alloy weld joints for each weld metal number was measured using a known elemental analysis method in accordance with JIS G0321:2017. Specifically, chips were collected using a drill from region P at the center of the width and thickness of the weld metal. The collected chips were dissolved in acid to obtain a solution. The solution was subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis of the chemical composition. The carbon and sulfur contents were determined using a known high-frequency combustion method (combustion-infrared absorption method). The nitrogen and oxygen contents were determined using a known inert gas fusion-thermal conductivity method.

[0135] The chemical compositions of the obtained weld metals are shown in Tables 3-1 and 3-2.

[0136] [Table 3-1]

[0137] [Table 3-2]

[0138] [Evaluation test] The following tests were carried out on the manufactured austenitic stainless alloy welded joints. (Test 1) F2 measurement test (Test 2) Weld hot crack resistance evaluation test (Test 3) Polythionic Acid SCC Resistance Evaluation Test (Test 4) Naphthenic acid corrosion resistance evaluation test (Test 5) Aging toughness evaluation test Tests 1 to 5 will be explained below.

[0139] [(Test 1) F2 measurement test] The F2 values ​​of the weld metal for each test number were determined based on the method described in the above [F2 measurement method]. The obtained F2 values ​​are shown in Table 4.

[0140] [Table 4]

[0141] [(Test 2) Welding hot cracking resistance evaluation test] The weld hot cracking resistance of austenitic stainless alloy weld joints with each weld metal number was evaluated using the following method. Ten test specimens for microstructural observation of the cross section perpendicular to the weld line were taken from the weld metal portion of the austenitic stainless alloy weld joint with each weld metal number. The size of the test specimens was 15 mm × 30 mm × 10 mm. The surface of the sampled test specimen corresponding to the cross section perpendicular to the weld line was designated the "observation surface." The observation surface was 15 × 30 mm. The observation surface was mirror-polished and etched with mixed acid. The etched surface of the test specimen was observed using an optical microscope at 200x magnification. The occurrence of weld hot cracking in the weld metal on the observation surface was then visually determined. The evaluation results are shown in Table 4. If no cracks were observed in the weld metal of any of the ten sampled test specimens, it was determined that sufficient weld hot cracking resistance was obtained ("E (Excellent)" in Table 4). On the other hand, if cracking was confirmed in even one of the 10 test pieces, it was determined that sufficient resistance to weld hot cracking had not been obtained ("NA (Not Accepted)" in Table 4). Note that for test numbers that were judged as "NA" in the welded steel pipe cracking resistance evaluation test, tests from test 3 onwards were not conducted.

[0142] [(Test 3) Polythionic Acid SCC Resistance Evaluation Test] The polythionic acid SCC resistance of the weld metal of the austenitic stainless alloy weld joints of each weld metal number was evaluated by the following method. First, the austenitic stainless alloy welded joints of each weld metal number were subjected to aging treatment at 650°C for 3,000 hours, assuming use in a high-temperature environment. Plate-shaped test specimens 40 were prepared from the aging-treated austenitic stainless alloy welded joints, including region P, as shown in Figure 8. The 2-mm thickness of the plate-shaped test specimen 40 corresponded to the length in the weld metal thickness direction T, the 75-mm length of the plate-shaped test specimen 40 corresponded to the length in the weld metal width direction W, and the 10-mm width of the plate-shaped test specimen 40 corresponded to the length in the weld metal extension direction L. The plate-shaped test specimens 40 were prepared so that region P of the weld metal 20 was located at the center of the 75-mm length of the plate-shaped test specimen 40.

[0143] Polythionic acid SCC resistance evaluation tests were conducted in accordance with JIS G 0576:2001, "Test Method for Stress Corrosion Cracking of Stainless Steels." Specifically, plate specimens were bent around a punch with an inner radius of 5 mm to form a U-bend (the curved portion corresponds to the weld metal). The U-bend plate specimens were immersed in Wackenroder's solution (a solution prepared by injecting SO2 gas into distilled water to form a saturated H2SO3 solution, to which a large amount of H2S gas was injected) at room temperature for 100 hours. After immersion, the plate specimens were microscopically observed at 500x magnification to check for cracks in the weld metal portion of the plate specimens. The evaluation results are shown in Table 4. If no cracks were observed in the weld metal portion of the specimen, the weld metal was deemed to have sufficient polythionic acid SCC resistance ("E" in Table 4). On the other hand, when cracks were found in the weld metal portion of the test piece, it was determined that sufficient polythionic acid SCC resistance was not obtained ("NA" in Table 4).

[0144] [(Test 4) Naphthenic acid corrosion resistance evaluation test] The naphthenic acid corrosion resistance of the weld metal of the austenitic stainless alloy weld joints of each weld metal number was evaluated by the following method. First, a weld metal test piece including region P was taken from the austenitic stainless alloy weld joint of each weld metal number. Specifically, a test piece including region P and having a thickness of 3 mm, a width of 10 mm, and a length of 30 mm was prepared, similar to the plate-shaped test piece 40 shown in FIG. 8. The thickness of the test piece, 3 mm, corresponded to the length in the weld metal thickness direction T, the length of the test piece, 30 mm, corresponded to the length in the weld metal width direction W, and the width of the test piece, 10 mm, corresponded to the length in the weld metal extending direction L. The test piece was prepared so that region P was at the center of the test piece in both the length direction and the thickness direction.

[0145] The prepared test piece was immersed for 720 hours in a 100% cyclohexanecarboxylic acid solution (test solution) at 200° C. under normal pressure. After 720 hours had passed, the test piece was taken out.

[0146] After 720 hours had passed, the test piece was taken out and subjected to ultrasonic cleaning using acetone for 3 minutes.

[0147] The difference between the mass of the test piece before the test and the mass of the test piece after ultrasonic cleaning was calculated as the corrosion weight loss. Furthermore, the corrosion rate (mm / y) was calculated from the surface area, specific gravity, and test time of the test piece. The evaluation results are shown in Table 4. When the corrosion rate was 0.010 mm / y or less, it was determined that the weld metal had sufficient naphthenic acid corrosion resistance. On the other hand, when the corrosion rate exceeded 0.010 mm / y, it was determined that sufficient naphthenic acid corrosion resistance was not obtained.

[0148] [(Test 5) Aging toughness evaluation test] The aging toughness of the weld metal of the austenitic stainless alloy weld joints with each weld metal number was evaluated using the following method. First, a V-notch test specimen 50 including region P was prepared from the position shown in Figure 9 for each austenitic stainless alloy weld joint with each weld metal number. The width of the test specimen 50 was 10 mm, the thickness was 10 mm, and the length was 55 mm. The 10 mm thickness of the test specimen corresponded to the length in the weld metal thickness direction T, the 10 mm width of the test specimen corresponded to the length in the weld metal width direction W, and the 55 mm length of the test specimen corresponded to the length in the weld metal extension direction L. The test specimen 50 was prepared so that region P of the weld metal 20 was located at the center of the width of the test specimen 50. A V-notch was formed at the center of the length of the test specimen 50. The V-notch angle was 45°, the notch depth was 2 mm, and the notch root radius was 0.25 mm. Three V-notch test specimens 50 were prepared.

[0149] Test piece 50 was subjected to aging treatment by holding it at 650°C for 1000 hours. After holding it for 1000 hours, the test piece was allowed to cool to room temperature. After the aging treatment, a Charpy impact test was performed in the air at room temperature in accordance with JIS Z 2242:2005. The three impact values ​​(J / cm) obtained from the test were 2 ) is calculated as the impact value (J / cm 2 The evaluation results are shown in Table 4. The obtained impact value was 20 J / cm 2 If the impact value was 20 J / cm or more, sufficient aging toughness was obtained in the weld metal. 2If the difference was less than 1 / 2, it was determined that sufficient aging toughness was not obtained in the weld metal.

[0150] [Test Results] With reference to Tables 1-1, 1-2, 2-1, 2-2, 3-1, 3-2, and 4, the chemical compositions of the base material, welding material, and weld metal were appropriate, and the manufacturing conditions were also appropriate, for test numbers 1 to 25. Therefore, the austenitic stainless alloy welded joints of these test numbers satisfied Features 1 to 4. Therefore, these test numbers obtained sufficient weld hot cracking resistance, sufficient polythionic acid SCC resistance, sufficient naphthenic acid corrosion resistance, and sufficient aging toughness.

[0151] On the other hand, in test numbers 26 and 31, the Mo content of the welding material was too low, and therefore the Mo content of the weld metal was too low, so sufficient naphthenic acid corrosion resistance was not obtained.

[0152] In test numbers 27 and 28, the C content of the welding material was too high, and therefore the C content of the weld metal was too high, which meant that sufficient polythionic acid SCC resistance was not obtained.

[0153] In test numbers 29 and 32, the Mo content of the welding material was too high. As a result, the Mo content of the weld metal was too high. As a result, test number 29 did not achieve sufficient aging toughness. In test number 32, F1 also exceeded 2.30. As a result, sufficient resistance to weld hot cracking was not achieved.

[0154] In test numbers 30 and 33, the Ni content of the welding material was too low, and therefore the Ni content of the weld metal was too low, so sufficient aging toughness was not obtained.

[0155] In test number 34, the B content of the welding material was too high. As a result, the B content of the weld metal was too high. As a result, sufficient resistance to weld hot cracking was not obtained.

[0156] In test number 35, although the chemical compositions of the base metal and welding materials were appropriate, the heat input in the welding conditions was too high. As a result, F2 exceeded 2.5. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness were not obtained.

[0157] In Test No. 36, the C content of the base metal was too high. As a result, the C content of the weld metal was too high. Furthermore, the interlaminar temperature exceeded 150°C. As a result, F2 exceeded 2.5. As a result, sufficient polythionic acid SCC resistance, sufficient naphthenic acid corrosion resistance, and sufficient aging toughness were not obtained.

[0158] In test number 37, the B content of the base metal was too high. As a result, the B content of the weld metal was too high. As a result, sufficient resistance to weld hot cracking was not obtained.

[0159] In test number 38, the Mo content of the base metal was too low, and therefore the Mo content of the weld metal was too low, so sufficient naphthenic acid corrosion resistance was not obtained.

[0160] In test numbers 39 and 40, although the chemical compositions of the base metal and weld metal were appropriate, F1 exceeded 2.30, and therefore sufficient resistance to weld hot cracking was not obtained.

[0161] In test number 41, although the chemical compositions of the base metal and welding material were appropriate, both the heat input and interlaminar temperature were high. As a result, F2 exceeded 2.5. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness were not obtained.

[0162] In test number 42, although the chemical compositions of the base metal and welding material were appropriate, the heat input was too high. As a result, F2 exceeded 2.5. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness were not obtained.

[0163] In test number 43, although the chemical compositions of the base metal and welding material were appropriate, the interlaminar temperature was too high. As a result, F2 exceeded 2.5. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness were not obtained.

[0164] In test number 44, although the chemical compositions of the base metal and welding material were appropriate, FA was 0.60 or less. Therefore, F2 exceeded 2.5. As a result, sufficient naphthenic acid corrosion resistance and sufficient aging toughness were not obtained.

[0165] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure. [Explanation of symbols]

[0166] 1. Austenitic stainless steel alloy welded joints 10 Base material 20 Weld metal

Claims

1. A base material and a weld metal are provided, The chemical composition of the base material is, in mass%, C: 0.030% or less, Si: 0.10-1.00%, Mn: 0.20-2.00%, P: 0.040% or less, S: 0.010% or less, Cr: 16.0-25.0%, Ni: 10.0 to 30.0%, Mo: 0.1 to 5.0%, Nb: 0.20-1.00%, N: 0.05-0.30%, sol. Al: 0.001 to 0.100%, B: 0 to 0.0080%, Cu: 0 to 5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0 to 0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0 to 0.010%, Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities; The chemical composition of the weld metal is, in mass %, C: 0.020% or less, Si: 0.01-1.00%, Mn: 0.20-2.00%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0-25.0%, Ni: 15.0 to 40.0%, Mo: 2.5-5.0%, Nb: 0.10-2.00%, N: 0.05-0.30%, sol. Al: 0.001 to 0.100%, B: 0.0010 to 0.0050%, Cu: 0 to 5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0 to 0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0 to 0.010%, Rare earth elements: 0 to 0.100%, and the balance being Fe and impurities, and F1 defined by formula (1) being 2.30 or less; In a cross section of the weld metal perpendicular to the extending direction of the weld metal, a 1 mm × 1 mm square region at the width center on the surface of the weld metal and at the thickness center of the weld metal was divided into 100 μm × 100 μm minute square areas, and the Mo content in mass% in each minute square area was determined, and the arithmetic average value of all the obtained Mo contents was defined as [Mo] ＡＶＥ Of all the Mo contents obtained, the [Mo] ＡＶＥ The arithmetic mean value of the Mo content higher than [Mo] Ｈ Of all the Mo contents obtained, the [Mo] ＡＶＥ The arithmetic mean value of the Mo content lower than [Mo] Ｌ When we define F2 defined by formula (2) is 2.5 or less; Austenitic stainless steel alloy welded joints. F1=130B+8C+0.025Cr+0.25Mn+0.08Mo+0.6Nb+12P+7.6S+0.78Si+0.012W (1) F2 = [M] Ｈ / [M] Ｌ (2) Here, each element symbol in formula (1) is substituted with the content of the corresponding element in the weld metal in mass %.

2. 2. The austenitic stainless alloy weld joint according to claim 1, The chemical composition of the base material is B: 0.0001 to 0.0080%, Cu: 0.01-5.00%, W: 0.01-5.00%, Co: 0.01 to 1.00%, V: 0.01-1.00%, Ta: 0.01-0.20%, Hf: 0.01-0.20%, Ca: 0.001-0.010%, Mg: 0.001 to 0.010%, and Rare earth elements: 0.001-0.100%, Contains one or more elements selected from the group consisting of Austenitic stainless steel alloy welded joints.

3. The austenitic stainless steel alloy welded joint according to claim 1 or 2, The chemical composition of the weld metal is Cu: 0.01-5.00%, W: 0.01-5.00%, Co: 0.01 to 1.00%, V: 0.01-1.00%, Ta: 0.01-0.20%, Hf: 0.01-0.20%, Ca: 0.001-0.010%, Mg: 0.001 to 0.010%, and Rare earth elements: 0 to 0.100%, Contains one or more elements selected from the group consisting of Austenitic stainless steel alloy welded joints.

4. The chemical composition, in mass%, is C: 0.020% or less, Si: 0.01-1.00%, Mn: 0.20-2.00%, P: 0.030% or less, S: 0.010% or less, Cr: 16.0-25.0%, Ni: 15.0 to 40.0%, Mo: 2.5-5.0%, Nb: 0.10-2.00%, N: 0.05-0.30%, sol. Al: 0.001 to 0.100%, B: 0.0010 to 0.0050%, Cu: 0 to 5.00%, W: 0-5.00%, Co: 0-1.00%, V: 0-1.00%, Ta: 0 to 0.20%, Hf: 0-0.20%, Ca: 0-0.010%, Mg: 0 to 0.010%, Rare earth elements: 0 to 0.100%, and The balance consists of Fe and impurities. Austenitic stainless steel alloy welding material.

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