AUSTENITIC HEAT-RESISTANT STEEL WELD METAL, WELDED JOINT, WELDING MATERIAL FOR AUSTENITIC HEAT-RESISTANT STEEL, AND METHOD OF MANUFACTURING WELDED JOINT

Abstract

An austenitic heat-resistant steel weld metal with low high-temperature cracking susceptibility and good creep strength is provided. The austenitic heat-resistant steel weld metal has a chemical composition of, in mass %: 0.06% -0.14% C; 0.1%-0.6%Si; 0.1%-1.8%Mn; up to 0.025% P; up to 0.003% S; 25%-35% Ni; 20%-24% Cr; more than 4.5% and up to 7.5% W; 0.05%-0.5% Nb; 0.05%-0.4% V; 0.1%-0.35% N; up to 0.08% Al; up to 0.08% O; and 0.0005 to 0.005% B, fn1 expressed by the following Equation (1) being not less than 10:

fn1=10(Nb+V)+1.5W+20N+1500B25Si (1), where, for Nb, V, W, N, B and Si in Equation (1), the contents of the named elements in mass % are substituted.

Claims

1. An austenitic heat-resistant steel weld metal having a chemical composition of, in mass %: 06%-0.14% C; 0.1%-0.6%Si; 0.1%-1.8%Mn; up to 0.025% P; up to 0.003% S; 25%-35% Ni; 20%-24% Cr; more than 4.5% and up to 7.5% W; 0.05%-0.5% Nb; 0.05%-0.4% V; 0.1%-0.35% N; up to 0.08% Al; up to 0.08% O; 0.0005-0.005% B; 0%-0.25% Ti; 0%-4% Cu; 0%-2%Co; 0%-2% Mo; 0%-1%Ta; 0%-0.02% Ca; 0%-0.02% Mg; 0%-0.06% REM; and balance Fe and impurities, fn1 expressed by the following Equation (1) being not less than 10:
fn1=10(Nb+V)+1.5W+20N+1500B-25Si (1), where, for Nb, V, W, N, B and Si in Equation (1), the contents of the named elements in mass % are substituted.

2. The austenitic heat-resistant steel weld metal according to claim 1, wherein the chemical composition includes one or more elements selected from the group consisting of, in mass %: 0.01%-0.25% Ti; 0.01%-4% Cu; 0.01%-2%Co; 0.01%-2%Mo; 0.01%-1% Ta; 0.0005%-0.02% Ca; 0.0005%-0.02% Mg; and 0.0005%-0.06% REM.

3. A welded joint comprising: the austenitic heat-resistant steel weld metal according to claim 1; and a base material of austenitic heat-resistant steel.

4. The welded joint according to claim 3, wherein the base material has a chemical composition of, in mass %: 0.02%-0.14% C; 0.05%-1% Si; 0.1%-3% M n; up to 0.04% P; up to 0.002% S; 26%-35% Ni; 20%-26% Cr; 1%-7% W; 0.01%-1% Nb; 0.01%-1% V; 0.1%-0.6% N; 0.0005%-0.008% B; 0.003%-0.06% REM; up to 0.3% Al; up to 0.02% O; 0%-0.5% Ti; 0%-2%Co; 0%-4% Cu; 0%-4% Mo; 0%-1%Ta; 0%-0.02% Ca; 0%-0.02% Mg; and balance Fe and impurities.

5. The welded joint according to claim 4, wherein the base material has a chemical composition including one or more elements selected from the group consisting of, in mass %: 0.01%-0.5% Ti; 0.01%-2%Co; 0.01%-4% Cu; 0.01%-4%Mo; 0.01%-1% Ta; 0.0005%-0.02% Ca; and 0.0005%-0.02% Mg.

6. A welding material for austenitic heat-resistant steel having a chemical composition of, in mass %: 0.06%-0.14% C; 0.1%-0.4%Si; 0.1%-1.2%Mn; up to 0.01% P; up to 0.003% S; 28%-35% Ni; 20%-24% Cr; more than 4.5% and up to 7.5% W; 0.05%-0.5% Nb; 0.05%-0.35% V; 0.1%-0.35% N; up to 0.08% Al; up to 0.08% O; 0.0005%-0.005% B; 0%-0.25% Ti; 0%-4% Cu; 0%-2%Co; 0%-2% Mo; 0%-1%Ta; 0%-0.02% Ca; 0%-0.02% Mg; 0%-0.06% REM; and balance Fe and impurities, fn1 expressed by the following Equation (1) being not less than 10:
fn1=10(Nb+V)+1.5W+20N+1500B-25Si (1), where, for Nb, V, W, N, B and Si in Equation (1), the contents of the named elements in mass % are substituted.

7. The welding material for austenitic heat-resistant steel according to claim 6, wherein the chemical composition includes one or more elements selected from the group consisting of, in mass %: 0.01%-0.25% Ti; 0.01%-4% Cu; 0.01%-2%Co; 0.01%-2%Mo; 0.01%-1% Ta; 0.0005%-0.02% Ca; 0.0005%-0.02% Mg; and 0.0005%-0.06% REM.

8. A method of manufacturing the welded joint according to claim 4, comprising welding a base material having a chemical composition of, in mass %: 0.02%-0.14% C; 0.05%-1% Si; 0.1%-3% M n; up to 0.04% P; up to 0.002% S; 26%-35% Ni; 20%-26% Cr; 1%-7% W; 0.01%-1% Nb; 0.01%-1% V; 0.1%-0.6% N; 0.0005%-0.008% B; 0.003%-0.06% REM; up to 0.3% Al; up to 0.02% O; 0%-0.5% Ti; 0%-2%Co; 0%-4% Cu; 0%-4% Mo; 0%-1%Ta; 0%-0.02% Ca; 0%-0.02% Mg; and balance Fe and impurities. using a welding material for austenitic heat-resistant steel having a chemical composition of, in mass %: 0.06%-0.14% C; 0.1%-0.4%Si; 0.1%-1.2%Mn; up to 0.01% P; up to 0.003% S; 28%-35% Ni; 20%-24% Cr; more than 4.5% and up to 7.5% W; 0.05%-0.5% Nb; 0.05%-0.35% V; 0.1%-0.35% N; up to 0.08% Al; up to 0.08% O; 0.0005%-0.005% B; 0%-0.25% Ti; 0%-4% Cu; 0%-2%Co; 0%-2% Mo; 0%-1%Ta; 0%-0.02% Ca; 0%-0.02% Mg; 0%-0.06% REM; and balance Fe and impurities, fn1 expressed by the following Equation (1) being not less than 10:
fn1=10(Nb+V)+1.5W+20N+1500B-25Si (1), where, for Nb, V, W, N, B and Si in Equation (1), the contents of the named elements in mass % are substituted.

Description

EXAMPLES

[0249] The present invention will now be described more specifically using examples; however, the present invention is not limited to these examples. It is clear that a person skilled in the art can arrive at various variations and modifications within the scope of ideas defined by the claims, and it is understood that these variations and modifications naturally fall within the technical scope of the present invention.

[0250] [Welding Material]

[0251] Materials (steels) having the chemical compositions shown in Table 1 were molten in a laboratory to cast ingots, which were then subjected to hot forging, hot rolling, heat treatment and machining to fabricate the following two types of plates;

[0252] plate type (1) having a plate thickness of 4 mm, a width of 100 mm, and a length of 100 mm; and plate type (2) having a plate thickness of 4 mm, a width of 200 mm, and a length of 500 mm.

[0253] Further, plates of type (2) were machined to fabricate cut fillers with a thickness and width of 2 mm and a length of 500 mm.

TABLE-US-00001 TABLE 1 Chemical composition (in mass %, balance Fe and impurities) Character C Si Mn P S Ni Cr V Nb 1 0.086 0.20 0.50 <0.002 0.001 29.97 21.80 0.20 0.40 2 0.077 0.21 0.54 <0.002 0.001 28.50 21.60 0.20 0.39 3 0.079 0.23 1.01 <0.002 0.001 29.52 21.83 0.20 0.40 4 0.070 0.20 0.55 <0.002 0.001 29.06 21.70 0.20 0.29 5 0.079 0.22 0.53 <0.002 0.001 29.72 21.91 0.21 0.41 6 0.073 0.23 0.55 <0.002 0.001 28.64 21.59 0.20 0.38 7 0.098 0.40 0.42 <0.002 0.001 32.01 21.95 0.20 0.20 8 0.097 0.38 1.02 <0.002 0.001 29.87 21.98 0.20 0.38 9 0.096 0.60* 1.03 <0.002 0.001 31.81 21.98 0.21 0.40 10 0.096 0.40 1.03 <0.002 0.001 29.95 22.08 0.20 0.39 11 0.096 0.40 1.03 <0.002 0.001 29.95 22.08 0.20 0.39 12 0.085 0.30 1.05 <0.002 0.001 30.95 23.50 0.20 1.20* 13 0.076 0.23 0.56 <0.002 0.001 29.84 22.28 0.20 0.38 Chemical composition (in mass %, balance Fe and impurities) Character W B N Al O Others fn1 1 4.98 0.0018 0.16 0.005 0.007 14.37 2 4.66 0.0011 0.13 0.004 0.008 Cu: 0.02, 11.91 Co: 0.02, Ti: 0.01 3 4.92 0.0012 0.13 0.006 0.010 Cu: 0.02, 12.03 Mo: 0.01, REM: 0.01 4 5.51 0.0009 0.13 0.005 0.009 Ta: 0.01 12.18 5 4.99 0.0013 0.14 0.007 0.013 Cu: 2.95, 13.02 Ca: 0.001, Mg: 0.001 6 6.57 0.0011 0.13 0.003 0.012 Cu: 0.02 14.16 7 2.96* 0.0015 0.20 0.009 0.010 4.75* 8 5.01 * 0.22 0.008 0.011 8.16* 9 5.01 0.0015 0.23 0.007 0.009 5.43* 10 5.02 0.0007 0.25 0.005 0.014 9.38* 11 5.02 0.0053* 0.21 0.006 0.010 15.60 12 4.96 0.0009 0.13 0.004 0.009 17.95 13 5.53 * 0.15 0.005 0.008 11.35 The symbol * indicates that the associated value falls outside the range of the invention.

[0254] [Trans-Varestraint Test]

[0255] Trans-varestraint test specimens were extracted from plates of type (1). Thereafter, bead-on-plate welding was performed by GTAW with a welding current of 100 A and at a welding speed of 15 cm/min. For each specimen, when the weld pool reached the middle of the specimen as determined along the longitudinal direction, a bending deformation was applied to the specimen and an added distortion was applied to the weld metal to cause a crack. The added distortion was 2%, at which saturation is reached in terms of maximum crack length. For evaluation, the maximum crack length that had developed in the weld metal was measured and treated as an evaluation indication of the solidification cracking susceptibility of the welding material. The targeted crack length was 1.3 mm, or less, which is the maximum crack length evaluated by trans-varestraint tests of Alloy 800H weld metal, which solidifies as perfect austenite.

[0256] [Creep Rupture Test]

[0257] Cut fillers fabricated from plates of type (2) were used to perform buttering welding on the groove by manual tig welding using Ar as a shield gas, and lamination welding was then performed inside the groove to fabricate all-weld-metal specimens. For welding, the heat input was 9 kJ/cm-12 kJ/cm, and the inter-pass temperature was 150 C. or lower. No pre-weld heat treatment (pre-heating) or post-weld heat treatment was performed. Thereafter, round-rod creep-rupture specimens were extracted from the all-weld-metal portions. Creep-rupture testing was then performed at 750 C. and 127 MPa, and the specimens with rupture times above 1000 hours, which was the target under these conditions, were labeled passed, and those with rupture times not longer than 1000 hours were labeled failed.

[0258] Table 2 shows the results of the above-discussed tests.

TABLE-US-00002 TABLE 2 Determination Determination of max. crack of creep Character length strength 1 passed passed 2 passed passed 3 passed passed 4 passed passed 5 passed passed 6 passed passed 7 passed failed 8 passed failed 9 passed failed 10 passed failed 11 failed passed 12 failed passed 13 passed failed

[0259] Table 2 demonstrates that the welding materials labeled with characters 1 to 6, which have chemical compositions falling within the ranges specified by the present invention, had low weld high-temperature cracking susceptibility and satisfied the targeted creep-rupture time.

[0260] In contrast, the welding material labeled with character 7, which had a W content lower than the range of the present invention, the welding materials with characters 8 and 13, which contained no B, and the welding material labeled with character 9, which had an Si content higher than the range of the present invention, each had a creep strength below the target, while they had low high-temperature cracking susceptibilities. The welding material labeled with character 10, which had a low fn1 value even though it satisfied the ingredient ranges of the present invention, had a creep strength below the target, while it had a low high-temperature crack susceptibility. The welding material labeled with character 11, which had a B content higher than the range of the present invention, and the welding material labeled with character 12, which had an Nb content higher than the range of the present invention, had an increased high-temperature cracking susceptibility, while it had no problem in terms of creep strength.

[0261] Thus, it is clear that the welding materials satisfying the requirements of the present invention had low high-temperature cracking susceptibilities, and had sufficient creep strengths. This demonstrates that the welding material for austenitic heat-resistant steel of the present invention may provide a suitable welding material for welding high-nitrogen/high-nickel-content austenitic heat-resistant steel.

[0262] [Weld Metal and Welded Joint]

[0263] Materials having the chemical compositions shown in Table 3 were molten in a laboratory to cast ingots, which were then subjected to hot forging, hot rolling, cold rolling, heat treatment and machining to fabricate plates (plates of type (1)), each with a plate thickness of 12 mm, a width of 50 mm and a length of 120 mm. The plates of type (1) were treated as base materials for welding.

[0264] Further, materials having the chemical compositions shown in Table 4 were molten in a laboratory to cast ingots, which were then subjected to hot forging, hot rolling, heat treatment and machining to fabricate plates (plates of type (2)), each with a plate thickness of 4 mm, a width of 200 mm and a length of 500 mm. The plates of type (2) were machined to fabricate cut fillers with a thickness and width of 2 mm and a length of 500 mm.

TABLE-US-00003 TABLE 3 Chemical composition of base material (in mass %, balance Fe and impurities) Character C Si Mn P S Ni Cr V Nb W A 0.080 0.20 0.51 0.015 0.001 29.62 21.64 0.21 0.20 4.54 B 0.080 0.18 1.01 0.015 0.001 29.92 21.77 0.20 0.19 4.98 C 0.077 0.38 1.05 0.003 0.001 30.71 22.27 0.21 0.28 4.04 D 0.084 0.19 0.53 0.015 0.001 29.9 21.88 0.19 0.32 4.37 Chemical composition of base material (in mass %, balance Fe and impurities) Character B N Al O REM Others A 0.0029 0.19 0.025 0.005 0.02 Cu: 0.01 B 0.0028 0.18 0.027 0.008 0.01 C 0.0026 0.17 0.026 0.006 0.03 Ti: 0.02, Co: 0.02, Mo: 0.03 D 0.0027 0.21 0.023 0.008 0.02 Ta: 0.03, Ca: 0.001, Mg: 0.002

TABLE-US-00004 TABLE 4 Chemical composition of cut filler (in mass %, balance Fe and impurities) Character C Si Mn P S Ni Cr V Nb W B N Al O Others E 0.081 0.22 0.54 <0.002 0.001 29.86 21.75 0.20 0.39 4.92 0.0014 0.15 0.006 0.008 F 0.080 0.21 0.51 <0.002 0.001 29.52 21.46 0.20 0.35 4.98 0.0012 0.13 0.005 0.007 Cu: 0.01, Co: 0.02, Ti: 0.01 G 0.080 0.31 0.98 <0.002 0.001 31.87 21.43 0.19 0.36 5.59 0.0011 0.16 0.006 0.009 Mo: 0.01, Ta: 0.01, REM: 0.01 H 0.073 0.23 0.43 <0.002 0.001 29.95 21.89 0.20 0.39 6.51 0.0013 0.14 0.007 0.011 Cu: 0.03, Ca: 0.001, Mg: 0.001 I 0.096 0.32 0.55 <0.002 0.001 31.85 21.78 0.20 0.21 3.05 0.0015 0.12 0.005 0.013 Cu: 0.01 J 0.081 0.65 0.52 <0.002 0.001 29.56 21.59 0.21 0.41 5.05 0.0012 0.21 0.005 0.012 Cu: 0.01 K 0.075 0.31 0.54 <0.002 0.001 30.54 22.09 0.20 0.38 4.92 0.0055 0.16 0.004 0.009 L 0.081 0.28 1.02 <0.002 0.001 30.81 22.98 0.19 1.19 4.95 0.0010 0.13 0.005 0.010 M 0.08 0.51 0.56 <0.002 0.001 29.89 22.15 0.2 0.36 5.02 0.0009 0.18 0.005 0.008

[0265] For each of the plates of type (1), a V-groove with an angle of 30 and a root face of 1 mm and extending lengthwise was formed, before the plate was placed on a commercial steel plate (SM400B specified in JIS G 3160 (2008) with a thickness of 25 mm, a width of 150 mm and a length of 200 mm) and was restraint-welded along the four sides using a coated-arc-welding electrode (DNiCrFe-3 specified by JIS Z 3224 (1999)).

[0266] Thereafter, each of the fabricated cut fillers was used and lamination welding was performed within the groove by manual tig welding using Ar as a shield gas to fabricate a welded joint. For welding, the heat input was 9 kJ/cm-15 kJ/cm.

[0267] The weld metal of each of the thus obtained welded joints was cut perpendicular to the longitudinal direction to produce a cross section, which was drilled for about 1 mm at the middle as determined along the width direction and the middle as determined along the plate-thickness direction and chips were collected, and chemical analysis was conducted on the weld metal. Table 5 shows the results.

TABLE-US-00005 TABLE 5 Base Cut Chemical composition of weld metal (in mass %, balance Fe and impurities) Character material filler C Si Mn P S Ni Cr V Nb W A1 A E 0.079 0.20 0.52 <0.002 0.001 29.76 21.71 0.20 0.38 4.86 A2 F 0.075 0.22 0.52 <0.002 0.001 29.55 21.51 0.22 0.36 4.95 A3 G 0.081 0.29 0.94 <0.002 0.001 31.82 21.49 0.18 0.34 5.42 A4 H 0.071 0.21 0.42 <0.002 0.001 29.91 21.82 0.22 0.41 6.41 A5 I 0.095 0.31 0.5 <0.002 0.001 31.87 21.65 0.2 0.19 3.01* A6 J 0.074 0.62* 0.46 <0.002 0.001 29.46 21.45 0.23 0.38 4.98 A7 K 0.076 0.28 0.58 <0.002 0.001 30.47 22.18 0.21 0.34 4.91 A8 L 0.083 0.32 1.05 <0.002 0.001 30.8 22.87 0.18 1.15* 4.85 A9 M 0.078 0.49 0.55 <0.002 0.001 29.85 22.01 0.19 0.33 4.89 B1 B E 0.076 0.21 0.50 <0.002 0.001 29.86 21.73 0.19 0.37 4.88 B2 F 0.077 0.25 0.52 <0.002 0.001 29.45 21.49 0.20 0.33 4.92 B3 G 0.075 0.33 0.93 <0.002 0.001 31.85 21.35 0.22 0.35 5.44 B4 H 0.071 0.21 0.41 <0.002 0.001 29.90 21.86 0.21 0.36 6.41 B5 I 0.090 0.31 0.50 <0.002 0.001 31.75 21.72 0.20 0.22 2.94* B6 J 0.076 0.63* 0.49 <0.002 0.001 29.59 21.63 0.21 0.38 5.03 B7 K 0.068 0.29 0.52 <0.002 0.001 30.44 21.98 0.21 0.36 4.91 B8 L 0.077 0.26 0.96 <0.002 0.001 30.75 22.82 0.18 1.07* 4.87 B9 M 0.076 0.48 0.5 <0.002 0.001 29.84 22.13 0.2 0.34 4.95 C1 C E 0.076 0.21 0.56 <0.002 0.001 29.85 21.85 0.20 0.37 4.71 C2 F 0.079 0.19 0.48 <0.002 0.001 29.41 21.42 0.19 0.32 4.92 C3 G 0.078 0.28 0.92 <0.002 0.001 31.74 21.43 0.21 0.34 5.44 C4 M 0.072 0.22 0.37 <0.002 0.001 29.94 21.81 0.22 0.35 6.41 D1 D E 0.082 0.22 0.53 <0.002 0.001 29.88 21.82 0.20 0.38 4.75 D2 F 0.078 0.20 0.50 <0.002 0.001 29.39 21.46 0.19 0.34 4.95 D3 G 0.079 0.29 0.92 <0.002 0.001 30.82 21.42 0.20 0.36 5.51 D4 M 0.067 0.20 0.40 <0.002 0.001 29.84 21.85 0.22 0.38 6.49 Chemical composition of weld metal (in mass %, balance Fe and impurities) Character B N Al O Others fn1 A1 0.0011 0.12 0.005 0.008 Cu: 0.01 12.14 A2 0.0014 0.13 0.004 0.008 Cu: 0.01, Co: 0.01, Ti: 0.01 12.33 A3 0.001 0.15 0.007 0.010 Mo: 0.01, Ta: 0.01, REM: 0.01 10.50 A4 0.001 0.14 0.008 0.013 Cu: 0.02, Ca: 0.001, Mg: 0.001 14.89 A5 0.0014 0.14 0.006 0.015 Cu: 0.01 5.55* A6 0.0013 0.2 0.006 0.012 Cu: 0.01 4.04* A7 0.0053* 0.16 0.007 0.011 16.92 A8 0.0011 0.13 0.005 0.010 16.85 A9 0.0007 0.16 0.004 0.009 *4.69 B1 0.001 0.14 0.004 0.009 11.97 B2 0.0009 0.14 0.005 0.009 Cu: 0.01, Co: 0.01, Ti: 0.01 10.50 B3 0.0013 0.15 0.007 0.011 Mo: 0.01, Ta: 0.01, REM: 0.01 10.46 B4 0.0009 0.13 0.005 0.012 Cu: 0.01, Ca: 0.001, Mg: 0.001 14.04 B5 0.0010 0.13 0.004 0.014 Cu: 0.01 4.94* B6 0.0009 0.19 0.006 0.012 Cu: 0.01 2.75* B7 0.0052* 0.16 0.005 0.001 16.72 B8 0.0009 0.13 0.004 0.011 17.18 B9 0.0008 0.15 0.005 0.008 *5.03 C1 0.0011 0.13 0.005 0.008 Co: 0.01, Ti: 0.01, Mo: 0.01 11.77 C2 0.0011 0.13 0.004 0.006 Cu: 0.01, Co: 0.02, Ti: 0.02, 11.98 Mo: 0.03 C3 0.0008 0.14 0.006 0.008 Ti: 0.02, Co: 0.02, Mo: 0.01, 10.66 Ta: 0.01, REM: 0.01 C4 0.0010 0.12 0.007 0.011 Cu: 0.02, Ti: 0.01, Co: 0.01, 13.72 Mo: 0.01, Ca: 0.001, Mg: 0.001 D1 0.001 0.12 0.006 0.009 Ta: 0.01, Ca: 0.001, Mg: 0.001 11.33 D2 0.0010 0.13 0.004 0.008 Cu: 0.01, Co: 0.01, Ti: 0.01, 11.83 Ta: 0.01, Ca: 0.001, Mg: 0.001 D3 0.0011 0.14 0.006 0.009 Mo: 0.01, Ta: 0.01, Ca: 0.001, 11.07 Mg: 0.001, REM: 0.01 D4 0.0008 0.12 0.006 0.010 Cu: 0.01, Ta: 0.01, Ca: 0.001, 14.34 Mg: 0.001 The symbol * indicates that the associated value falls outside the range of the invention.

[0268] [Weld Cracking Resistance]

[0269] Specimens were extracted from five locations of the weld metal of each of the fabricated welded joints, where the observed face was provided by a transverse section (i.e. a section perpendicular to the weld bead) of the joint. The extracted specimens were mirror-face-polished and corroded before being observed by optical microscopy to determine whether there were cracks in the welded metal portion. The welded joints for which no cracks were observed in all the five specimens and the welded joints for which cracks were observed in one specimen were determined to have passed the test. The welded joints for which cracks were observed in two or more specimens were determined to have failed the test.

[0270] [Creep-Rupture Test]

[0271] Round-rod creep-rupture test specimens were extracted from the welded joints, where the weld metal was positioned at the middle of the parallel portion. Creep-rupture testing was then performed at 750 C. and 127 MPa, and those with rupture times above 1000 hours, which was about 80% of the target rupture time of the base material, were labeled passed, and those with rupture times not larger than 1000 hours were labeled failed.

[0272] Table 6 shows the results of these tests.

TABLE-US-00006 TABLE 6 Determination Base Cut Determination of creep Character material filler of weld crack strength A1 A E passed passed A2 F passed passed A3 G passed passed A4 H passed passed A5 I passed failed A6 J passed failed A7 K failed passed A8 L failed passed A9 M passed failed B1 B E passed passed B2 F passed passed B3 G passed passed B4 H passed passed B5 I passed failed B6 J passed failed B7 K failed passed B8 L failed passed B9 M passed failed C1 C E passed passed C2 F passed passed C3 G passed passed C4 M passed passed D1 D E passed passed D2 F passed passed D3 G passed passed D4 M passed passed

[0273] Table 6 demonstrates that the welded joints having the weld metals labeled with characters A1 to A4, B1 to B4, C1 to C4 and D1 to D4, having chemical compositions falling within the ranges specified by the present invention, each had a low weld high-temperature cracking susceptibility and a creep rupture time of 80% or more of the target rupture time of the base material.

[0274] In contrast, for each of the welded joints having the weld metals labeled with characters A5 and B5, the weld metal had a W content below the lower limit of the range of the present invention, i.e. more than 4.5%, and a creep strength below the target. Further, for each of the welded joints having the weld metals labeled with characters A6 and B6, the weld metal had an Si content more than the upper limit of the range of the present invention, i.e. 0.6%, and consequently had a creep strength below the target. For each of the welded joints having the weld metals labeled with characters A7 and B7, the weld metal had a B content more than the upper limit of the range of the present invention, i.e. 0.005%, and consequently had an increased weld high-temperature cracking susceptibility. For each of the welded joints having the weld metals labeled with characters A8 and B8, the weld metal had an Nb content more than the upper limit of the range of the present invention, i.e. 0.5%, and consequently had an increased weld high-temperature cracking susceptibility. For each of the welded joints having the weld metals labeled with characters A9 and B9, the value of fn1 was below 10.0, and consequently had a creep strength below the target.

[0275] Thus, the weld metals satisfying the requirements of the present invention had low high-temperature cracking susceptibilities and satisfied the creep strengths required for welded structures, and thus the properties of high-nitrogen/high-nickel-content austenitic heat-resistant steel can be sufficiently exhibited.

INDUSTRIAL APPLICABILITY

[0276] Adopting the present invention will provide an austenitic heat-resistant steel weld metal with low high-temperature cracking susceptibility and good creep strength that, when a high-nitrogen/high-nickel-content austenitic heat-resistant steel is used as a welded structure, allows that steel to fully exhibit their properties, and a welded joint having such a weld metal. Thus, the weld metal of the present invention and a welded joint having this metal are useful as a weld metal constituting part of a welded structure using high-nitrogen/high-nickel-content austenitic heat-resistant steel and used in a device used at high temperatures, such as boilers for thermal power generation, and a welded joint having such a weld metal.