Welded joint

Abstract

This welded joint comprises: a base material having a specific chemical composition; and a weld metal that joins the base material, has a specific chemical composition, and has a fcc ratio of 95% or more in the structure thereof. The yield stress YS1 of the base material is 550 MPa to 700 MPa, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base material is 0.40 to 0.90.

Description

Welded joints

[0001] The present disclosure relates to weld joints.

[0002] In recent years, due to the tightening of carbon dioxide emission regulations in response to the issue of global warming, there has been an increasing demand for hydrogen fuel, which emits less carbon dioxide than petroleum and coal, and natural gas, which also emits less carbon dioxide. Accordingly, there has been a global increase in demand for the construction of liquid hydrogen tanks, liquid carbon dioxide tanks, LNG tanks, and the like for use on ships and on land. Steel materials used in liquid hydrogen tanks, liquid carbon dioxide tanks, LNG tanks, and the like are required to ensure toughness at extremely low temperatures of −196°C, so low-temperature steels, such as Ni-based low-temperature steels containing 5 to 10% Ni, are used. These Ni-based low-temperature steels are welded using austenitic welding materials that produce weld metals with excellent low-temperature toughness. These welding materials are designed with a Ni content of, for example, approximately 70%.

[0003] For example, Japanese Patent Application Laid-Open No. 2015-171729 discloses a welded joint, which describes a welded joint consisting of an austenitic stainless steel base material and a weld metal, the chemical composition of which, by mass, contains C: 0.2% or less, Si: 2.0% or less, Mn: 5.5 to 14.5%, Cr: 13.5 to 22.0%, Ni: 3.5 to 12.5%, Cu: 1 to 5%, and N: 0.01 to 0.4%, with the balance being Fe and unavoidable impurities, and satisfies the formula (Cr = [Cr] + 1.5[Si]) and (Ni = [Ni] + 0.5[Mn] + [Cu] + 3 0([C] + [N]))) is 1.10 or less, the volume fraction of the δ ferrite phase in the weld metal is 10% or less, and the chemical composition of the base metal contains, in mass %, C: 0.1% or less, Si: 0.4 to 1.5%, Mn: 8 to 11%, Cr: 15 to 17%, Ni: 5 to 8%, Cu: 1 to 4%, and N: 0.01 to 0.3%, with the balance being Fe and unavoidable impurities.

[0004] Steel materials exposed to hydrogen environments, such as those found in liquid hydrogen tanks and pipes, are required to have high hydrogen embrittlement resistance. A welded joint has a base metal and a weld metal, as well as a fusion line (FL) at the interface between the base metal and the weld metal. The differences in chemical composition and structure of each of these components result in different hydrogen embrittlement resistance characteristics. Therefore, high hydrogen embrittlement resistance is required in the base metal, the weld metal, and the vicinity of the fusion line FL.

[0005] From the above viewpoints, an object of the present disclosure is to provide a welded joint in which hydrogen embrittlement is suppressed even when exposed to a hydrogen environment.

[0006] The means for solving the problem include the following aspects. <1> A steel sheet comprising a base metal and a weld metal joining the base metal and having an fcc fraction of 95% or more in its structure, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and a ratio of a yield stress YS2 of the weld metal to the yield stress YS1 of the base metal of 0.40 or more and 0.90 or less, and wherein the base metal has a chemical composition, in mass % with respect to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.05%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities. : 0.100% or less, S: 0.100% or less, Ni: 40.0% to 80.0%, Cr: 0% to 20.0%, Mo: 0% to 20.0%, W: 0% to 5.0%, Nb: 0% to 5.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, <2> A welded joint comprising Mg: 0% to 1.00%, Zr: 0% to 1.000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.050%, with the balance being Fe and impurities. <2> The welded joint according to <1>, wherein the base metal has a carbon equivalent Ceq represented by the following (Equation 1) of 0.14 to 0.65. Ceq = [CＢ ]+[Si Ｂ ] / 24+[Mn Ｂ ] / 6+[Ni Ｂ ] / 40+[Mo Ｂ ] / 4+[Nb Ｂ ] / 5 (Formula 1) (In Formula 1, [C Ｂ ] is the content (mass%) of C in the base material, and [Si Ｂ ] is the content (mass%) of Si in the base material, and [Mn Ｂ ] is the Mn content (mass%) in the base material, [Ni Ｂ ] represents the Ni content (mass%) in the base material, and [Mo Ｂ ] is the content (mass%) of Mo in the base material, and [Nb Ｂ] represents the Nb content (mass %) in the base material. ) <3> A weld metal is provided, which joins the base metal and has an fcc ratio of 95% or more in its structure, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and a ratio of a yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less, and the base metal has a chemical composition, in mass % with respect to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.050%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities. : 0.100% or less, S: 0.100% or less, Ni: 1.0% to 20.0%, Cr: 1.0% to 10.0%, Mo: 1.0% to 10.0%, W: 0% to 3.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.0000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V :0%~3.0000%, Ca:0%~1.000000%, The weld metal contains Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.100%, with the balance being Fe and impurities, and the content (mass%) of Mn in the weld metal is [Mn Ｗ], the content (mass%) of Ni in the weld metal is [Ni Ｗ ], [Mn Ｗ ]+[Ni Ｗ <4> The welded joint according to <3>, wherein the weld metal has a nickel equivalent Nieq, as shown in the following (Equation 2), of 25.00 to 60.00: Nieq=[Ni Ｗ ]+0.65×[Cr Ｗ ]+0.98×[Mo Ｗ ]+1.05×[Mn Ｗ ]+0.35×[Si Ｗ ]+12.6×[C Ｗ ] (Formula 2) (In Formula 2, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ ] is the content (mass%) of Mo in the weld metal, and [Mn Ｗ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ] represents the C content (mass %) in the weld metal. ) <5> A steel sheet comprising a base metal and a weld metal joining the base metal and having an fcc ratio of 95% or more in its structure, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and a ratio of a yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less, and the base metal has a chemical composition, in mass % with respect to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.050%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities, and the weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of C: more than 0.10% to 0.70%, Si: 0.05% to 1.00%, Mn: more than 20.00% to 30.00%, P : 0.100% or less, S: 0.100% or less, Ni: 0% to 14.0%, Cr: 0% to 14.0%, Mo: 0% to 5.0%, W: 0% to 5.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, A welded joint comprising: Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.200%, O: 0% to 0.100%, and the balance: Fe and impurities.<6> The welded joint according to <5>, wherein the weld metal has a stacking fault energy SFE of 10.00 or more, as expressed by the following formula (3): SFE = -7.1 + 2.8 × [Ni. Ｗ ]+0.49×[Cr Ｗ ]+2×[Mo Ｗ ]+0.75×[Mn Ｗ ]−2×[Si Ｗ ]−5.7×[C Ｗ ]−24×[N Ｗ ] (Formula 3) (In Formula 3, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ ] is the content (mass%) of Mo in the weld metal, and [Mn Ｗ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ ] is the content (mass%) of C in the weld metal, and [N Ｗ ] represents the N content (mass%) in the weld metal.

[0007] According to the present disclosure, a welded joint is provided that is inhibited from hydrogen embrittlement even when exposed to a hydrogen environment.

[0008] Fig. 1 is a schematic cross-sectional view showing a groove shape when a welded joint is produced in this example. Fig. 2 is a schematic cross-sectional view showing a position where a test piece is taken in a Charpy test. Fig. 3 is a schematic cross-sectional view showing a position where a test piece is taken in a Charpy test when a base metal is thin.

[0009] An embodiment that is an example of the present disclosure will be described below. In this specification, when a numerical range expressed using "to" is used without the prefix "greater than" or "less than," the range includes the numerical values ​​described before and after "to." Furthermore, when the prefix "greater than" or "less than" is used before and after "to," the range does not include the numerical values ​​described before or after "to." In the numerical ranges described in stages in this specification, the upper limit of a certain numerical range may be replaced with the upper limit of another numerical range described in stages, or may be replaced with a value shown in the examples. Furthermore, the lower limit of a certain numerical range may be replaced with the lower limit of another numerical range described in stages, or may be replaced with a value shown in the examples. Regarding the content, "%" means "mass %" unless otherwise specified. The content (%) of "0 to" and "0% to" means that the component is an optional component and may not be included.

[0010] <Welded Joint> A welded joint according to the present disclosure includes a base metal and a weld metal joining the base metal. The base metal has a Ni content of 5.00% or more and 10.30% or less, in mass %, relative to the total mass of the base metal, and has a chemical composition described below. The weld metal is a weld metal with an fcc fraction of 95% or more in its structure and has a chemical composition described below. The base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less.

[0011] The welded joint according to the present disclosure, due to the above-described configuration, is suppressed from hydrogen embrittlement even when exposed to a hydrogen environment. The welded joint according to the present disclosure was discovered based on the following findings.

[0012] Steel materials used in liquid hydrogen tanks and pipes are required to have excellent hydrogen embrittlement resistance to improve safety. The hydrogen embrittlement resistance of steel materials depends mainly on the composition and structure of the steel material. In other words, in welded joints, there are steel materials with different hydrogen embrittlement resistance properties between the base metal and the weld metal.

[0013] As described above, a welded joint has a base metal and a weld metal, and also has a fusion line (FL) at the interface between the base metal and the weld metal. The hydrogen embrittlement resistance of the base metal and the weld metal can be controlled by adjusting the composition of the base metal and the composition and structure of the weld metal, respectively. On the other hand, the hydrogen embrittlement resistance at the fusion line FL and its vicinity is affected by both the base metal and the weld metal. After extensive research into this point, the inventors have found that matching the yield stress of the base metal and the yield stress of the weld metal is important for the hydrogen embrittlement resistance at the fusion line FL and its vicinity. That is, they have found that excellent hydrogen embrittlement resistance can be obtained at the fusion line FL and its vicinity by controlling the yield stress YS1 of the base metal to a specific value and further controlling the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal within a certain range. This is thought to be because, when the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal (YS2 / YS1) falls outside a certain range, strain tends to concentrate in the base metal near the weld metal, causing hydrogen to accumulate locally, thereby accelerating hydrogen embrittlement.

[0014] From the above findings, it has been found that the welded joint according to the present disclosure is suppressed from hydrogen embrittlement even when exposed to a hydrogen environment.

[0015] In the welded joint according to the present disclosure, as an indicator of suppression of hydrogen embrittlement at the fusion line FL, it is preferable that the notch Charpy absorbed energy in a −196°C environment near the fusion line FL after exposure to a hydrogen environment is 27 J or more. A method for measuring the notch Charpy absorbed energy in a −196°C environment near the fusion line FL after exposure to a hydrogen environment will be described later.

[0016] Next, the physical properties of the welded joint according to the present disclosure will be described.

[0017] (Yield stress YS1 of base material) The base material has a yield stress YS1 of 550 MPa or more and 700 MPa or less. The yield stress YS1 is 550 MPa or more because the base material is used in huge structures such as liquid hydrogen tanks. If the yield stress YS1 exceeds the upper limit, the low-temperature toughness of the welded joint is poor. The yield stress YS1 is more preferably 570 MPa or more and 690 MPa or less, and even more preferably 590 MPa or more and 680 MPa or less.

[0018] The yield stress YS1 of the base material can be controlled by the composition of the base material, which will be described later.

[0019] (Ratio of Yield Stress YS2 of Weld Metal to Yield Stress YS1 of Base Metal) The ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal (YS2 / YS1) is 0.40 or more and 0.90 or less. Because it is used in huge structures such as liquid hydrogen tanks, the lower limit of YS2 / YS1 is 0.40. If YS2 / YS1 exceeds the upper limit, hydrogen embrittlement is likely to occur in the FL portion of the welded joint when exposed to a hydrogen environment. YS2 / YS1 is more preferably 0.45 or more and 0.85 or less, and even more preferably 0.50 or more and 0.80 or less.

[0020] The YS2 / YS1 ratio can be controlled by the composition of the base metal and the weld metal, which will be described later.

[0021] Measurement of Yield Stress The yield stress YS1 of the base metal and the yield stress YS2 of the weld metal are measured in accordance with JIS Z2241 (2011). The base metal test specimen is taken from the center of the thickness direction of the base metal, which will be the material for the joint, with the longitudinal direction perpendicular to the rolling direction. The weld metal test specimen is taken from the t / 4 position of the weld metal, with the longitudinal direction parallel to the weld line, so that the entire parallel portion is weld metal. If a weld metal test specimen cannot be taken at the t / 4 position, the end position of the test specimen is taken 1 mm below the surface of the weld metal. Base Metal Test Specimen - Center of the thickness direction, perpendicular to the rolling direction - Test Specimen Shape: As specified in JIS - Base metal: No. 4 test specimen, weld metal: No. A2 test specimen - May also be taken from the base metal portion of the weld joint. (In this case, the specimen should be taken from a location 100 mm or more away from the weld metal.) Welding conditions: As shown in Table 5. Taken at the t / 4 position in the direction of the weld line. If it is not possible to take a specimen at the t / 4 position, take a specimen 1 mm below the table. Take the specimen so that the entire parallel portion is weld metal. Test specimen shape: As specified in JIS

[0022] Next, the composition and structure of the base metal of the welded joint according to the present disclosure will be described.

[0023] (Base material / chemical composition) In the welded joint according to the present disclosure, a base material is used that has a Ni content of 5.00% or more and 10.30% or less, in mass %, relative to the total mass of the base material, and that has the following chemical composition. Having the chemical composition of the base material as shown below improves the hydrogen embrittlement resistance of the base material and the vicinity of the fusion line FL. In the description of the chemical composition of the base material, "%" means "mass % relative to the total mass of the base material" unless otherwise specified.

[0024] The chemical composition of the base material is, in mass%, C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, Cu: 0% to 1.00%, Co: 0% to 0.05%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, The alloy contains Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities.

[0025] C: 0.01% to 0.10% C is an element that improves the hardenability of steel and contributes to improving its strength. On the other hand, an excessive C content reduces toughness. Therefore, from the viewpoint of improving the strength and toughness of the base metal and the heat-affected zone (HAZ), the C content of the base metal is set to 0.01% to 0.10%. The lower limit of the C content of the base metal is preferably 0.015%, 0.02%, or 0.025%. The upper limit of the C content of the base metal is preferably 0.095%, 0.09%, 0.085%, 0.08%, 0.075%, or 0.07%.

[0026] Si: 0.03% to 0.50% Si is an element that increases the strength of steel. On the other hand, if the Si content is excessive, the workability and strength of the steel decrease. Therefore, the Si content of the base material is set to 0.03% to 0.50%. The lower limit of the Si content of the base material is preferably 0.05% or 0.10%. The upper limit of the Si content of the base material is preferably 0.40% or 0.30%.

[0027] Mn: 0.10% to 2.00% Mn is an element that increases the strength of steel. On the other hand, if the Mn content is excessive, workability deteriorates and toughness becomes unstable. Therefore, the Mn content of the base material is set to 0.10% to 2.00%. The lower limit of the Mn content of the base material is preferably 0.20% or 0.30%. The upper limit of the Mn content of the base material is preferably 1.70%, 1.30%, or 1.00%.

[0028] P: 0.010% or less Since P is an impurity and an element that causes embrittlement, it is preferable to reduce the P content of the base material as much as possible. Therefore, the lower limit of the P content of the base material may be 0%. However, from the viewpoint of reducing the dephosphorization cost, the P content of the base material may be 0.002% or more. On the other hand, if the P content of the base material is 0.010% or less, the adverse effect of P on embrittlement falls within an acceptable range. Therefore, the P content of the base material is set to 0.010% or less. In order to effectively suppress embrittlement, the P content of the base material is preferably 0.009% or less, 0.007% or less, or 0.005% or less.

[0029] S: 0.010% or less S is an impurity and an element that causes embrittlement. Furthermore, S forms coarse MnS in steel, which reduces the workability and strength of the steel. Therefore, it is preferable to reduce the S content of the base metal as much as possible, and the lower limit of the S content of the base metal may be 0%. However, from the viewpoint of reducing desulfurization costs, the S content of the base metal may be 0.0002% or more. On the other hand, if the S content of the base metal is 0.010% or less, the adverse effects of S, such as embrittlement, are within an acceptable range. Therefore, the S content of the base metal is set to 0.010% or less. To effectively suppress embrittlement, the S content of the base metal is preferably 0.009% or less, 0.007% or less, or 0.005% or less.

[0030] Ni: 5.00% to 10.30% Ni is an element that improves hydrogen embrittlement resistance and also contributes to improving the strength and low-temperature toughness of steel. On the other hand, if the Ni content is excessive, it is difficult to improve toughness commensurate with the increased cost, and problems may occur during pickling and hot working. Therefore, the Ni content of the base metal is set to 5.00% to 10.30%. The lower limit of the Ni content of the base metal is preferably 6.00%, 8.00%, or 10.00%. The upper limit of the Ni content of the base metal is preferably 10.00%, 9.50%, or 9.00%.

[0031] Cr: 0% to 0.60% Cr is an element that contributes to improving the strength of steel and may be contained in the base material. On the other hand, an excessive Cr content may lead to a decrease in the toughness of the steel and may cause problems during pickling or hot working. Therefore, the Cr content of the base material is set to 0% to 0.60%. The lower limit of the Cr content of the base material is preferably 0.05%, 0.10%, or 0.20%. The upper limit of the Cr content of the base material is preferably 0.55%, 0.50%, 0.45%, or 0.40%.

[0032] Mo: 0% to 0.50% Mo is an element that contributes to improving the strength of steel and may be contained in the base material. On the other hand, an excessive Mo content may lead to a decrease in the toughness of the steel and may cause problems during pickling or hot working. Therefore, the Mo content of the base material is set to 0% to 0.50%. The lower limit of the Mo content of the base material may preferably be 0.01%, 0.02%, or 0.03%. The upper limit of the Mo content of the base material is preferably 0.45%, 0.40%, or 0.35%.

[0033] Nb: 0% to 0.50% Nb is an element that forms fine carbonitrides and suppresses grain coarsening, and may be contained in the base material. On the other hand, excessive Nb content may reduce toughness and further reduce the strength of the steel. Therefore, the Nb content of the base material is set to 0% to 0.50%. The lower limit of the Nb content of the base material may preferably be 0.003%, 0.005%, or 0.010%. The upper limit of the Nb content of the base material is preferably 0.45%, 0.40%, or 0.35%.

[0034] Cu: 0% to 1.00% Cu is an element that contributes to improving the strength of steel and may be contained in the base material. On the other hand, an excessive Cu content may lead to a decrease in the toughness of the steel and may cause problems during pickling or hot working. Therefore, the Cu content of the base material is set to 0% to 1.00%. The lower limit of the Cu content of the base material is preferably 0.05%, 0.10%, or 0.20%. The upper limit of the Cu content of the base material is preferably 0.90%, 0.80%, or 0.70%.

[0035] Co: 0% to 0.05% Co is an element that contributes to improving the strength of steel, so it may be contained in the base material. On the other hand, an excessive Co content in the base material will result in a significant decrease in toughness. Therefore, the Co content of the base material is set to 0% to 0.05%. The lower limit of the Co content of the base material is preferably 0.001%, 0.003%, 0.005%, or 0.01%. The upper limit of the Co content of the base material is preferably 0.04%, 0.03%, or 0.02%.

[0036] Al: 0.0001% to 0.100% Al is an element that has a deoxidizing effect, stabilizes ferrite, and suppresses the precipitation of cementite. On the other hand, Al is easily oxidized, and an excessive Al content increases inclusions, reducing workability and the strength of the steel. Therefore, the Al content of the base material is set to 0.0001% to 0.100%. The lower limit of the Al content of the base material is preferably 0.0002%, 0.0003, 0.0005, or 0.001%. The upper limit of the Al content of the base material is preferably 0.080% or 0.060%.

[0037] N: 0.0015% to 0.0060% N is an element that increases the strength of steel. On the other hand, N is an element that forms coarse nitrides in steel and acts to deteriorate the formability of steel. Therefore, the N content of the base metal is set to 0.0015% to 0.0060%. The lower limit of the N content of the base metal is preferably 0.0020% or 0.0025%. The upper limit of the N content of the base metal is preferably 0.0055% or 0.0050%.

[0038] O: 0.0001% to 0.0030% O is an element contained in steel as an impurity. Excessive O content leads to deterioration of toughness and ductility. Therefore, the O content of the base material is set to 0.0001% to 0.0030%. The lower limit of the O content of the base material is preferably 0.0002% or 0.0003%. The upper limit of the O content of the base material is preferably 0.0025% or 0.0020%.

[0039] V: 0% to 0.060% V is an element that forms fine carbonitrides and suppresses grain coarsening, and may be contained in the base material. On the other hand, excessive V content may reduce toughness and further reduce the strength of the steel. Therefore, the V content of the base material is set to 0% to 0.060%. The lower limit of the V content of the base material may preferably be 0.001%, 0.002%, or 0.003%. The upper limit of the V content of the base material is preferably 0.055%, 0.050%, or 0.045%.

[0040] Ti: 0% to 0.020% Ti is an element that forms precipitates and refines the steel structure, and may be contained in the base material. On the other hand, if the Ti content is excessive, there is a concern that the manufacturability of the steel will decrease, cracks will occur during processing, and the strength of the steel will decrease. Therefore, the Ti content of the base material is set to 0% to 0.020%. The lower limit of the Ti content of the base material may preferably be 0.001%, 0.002%, or 0.003%. The upper limit of the Ti content of the base material is preferably 0.018%, 0.016%, or 0.014%.

[0041] B: 0% to 0.0020% B is an element that segregates at grain boundaries to increase grain boundary strength, and may be contained in the base material. On the other hand, excessive B content may reduce toughness and further reduce the strength of the steel. Therefore, the B content of the base material is set to 0% to 0.0020%. The lower limit of the B content of the base material may preferably be 0.0001%, 0.0002%, or 0.0003%. The upper limit of the B content of the base material is preferably 0.0018%, 0.0016%, or 0.0014%.

[0042] Ca: 0% to 0.0040% Ca has the function of reducing the size of sulfides and oxides, and is therefore effective in improving ductility and toughness. Therefore, Ca may be contained in the base material. On the other hand, an excessive Ca content may cause coarsening of sulfides and oxides, leading to a deterioration in the low-temperature toughness of the base material. Therefore, the Ca content of the base material is set to 0% to 0.0040%. The lower limit of the Ca content of the base material is preferably 0.0001%, 0.0002%, or 0.0005%. The upper limit of the Ca content of the base material is preferably 0.0038%, 0.0035%, or 0.0030%.

[0043] REM: 0% to 0.0050% REM is an element that forms oxides and sulfides, and contributes to the refinement of inclusions and the improvement of the toughness of steel, so it may be contained in the base material. On the other hand, if the REM content of the base material is excessive, coarse oxides are generated, increasing costs. Therefore, the REM content of the base material is set to 0% to 0.0050%. The lower limit of the REM content of the base material is preferably 0.0001%, 0.0002%, or 0.0005%. The upper limit of the REM content of the base material is preferably 0.0048%, 0.0045%, or 0.0040%.

[0044] Note that "REM" is a general term for 17 elements in total, including Sc, Y, and lanthanides, and the REM content refers to the total content of one or more REM elements. REM is generally contained in misch metal. Therefore, for example, REM may be added in the form of misch metal so that the amount of REM falls within the above range. The same applies hereinafter.

[0045] The balance in the chemical composition of the base material consists of Fe and impurities. The impurities are components that are mixed in from raw materials such as ore and scrap during industrial production of the base material, or are mixed in due to various factors in the manufacturing process, and are acceptable as long as they do not adversely affect the properties of the base material.

[0046] Carbon equivalent Ceq of base metal From the viewpoint of facilitating the enhancement of the hydrogen embrittlement resistance of the base metal, the carbon equivalent Ceq of the base metal, as shown in the following formula (1), is preferably 0.14 to 0.65. The lower limit of the carbon equivalent Ceq of the base metal is more preferably 0.16, 0.18, or 0.20. The upper limit of the carbon equivalent Ceq of the base metal is more preferably 0.60, 0.55, or 0.50. Ceq=[C Ｂ ]+[Si Ｂ ] / 24+[Mn Ｂ ] / 6+[Ni Ｂ ] / 40+[Mo Ｂ ] / 4+[Nb Ｂ ] / 5 (Formula 1) (In Formula 1, [C Ｂ ] is the content (mass%) of C in the base material, and [Si Ｂ ] is the content (mass%) of Si in the base material, and [Mn Ｂ ] is the Mn content (mass%) in the base material, [Ni Ｂ ] represents the Ni content (mass%) in the base material, and [Mo Ｂ ] is the content (mass%) of Mo in the base material, and [Nb Ｂ ] represents the Nb content (mass %) in the base material.

[0047] Next, the composition and structure of the weld metal of the weld joint according to the present disclosure will be described.

[0048] (Weld Metal / FCC Ratio) In order to improve the hydrogen embrittlement resistance of the weld metal, it is important to increase the austenite ratio in the weld metal structure. Therefore, the weld metal should have an FCC ratio of 95% or more. If the FCC ratio is less than 95%, the weld metal will have poor hydrogen embrittlement resistance. The FCC ratio of the weld metal structure is preferably 97% or more, and may be 100%. The remainder of the structure is martensite and ferrite, and the weld metal may also contain inclusions such as intermetallic compounds, oxides, carbides, and sulfides.

[0049] -Method for measuring fcc percentage The fcc percentage in the structure of weld metal is measured by the following method. That is, a ferrite scope (FERITSCOPE (registered trademark) FMP30) manufactured by Fischer Instruments Inc. is used, and a probe (FGAB 1.3-Fe) manufactured by Fischer Instruments Inc. is used as the probe of the measuring device to measure the bcc percentage. The value obtained by subtracting the bcc percentage from 100% is defined as the fcc percentage. This is an instrument that uses magnetic induction to measure the ferromagnetic content of the metal structure.

[0050] A sample for microstructural observation is taken from the center of the weld metal of a welded joint, that is, from the center of the weld metal in the width direction and at a position (t / 4 part) that is 1 / 4 of the plate thickness (however, if the weld metal protrudes higher than the surface of the steel material, at a position 1 / 4 of the plate thickness based on the surface of the steel material). A cross section of the sample in a direction perpendicular to the weld line direction (width direction) is mirror-polished. Then, for each part of the t / 4 part sample, the probe of a ferrite scope is pressed against the cross section in a direction perpendicular to the weld line direction (width direction) to measure the bcc percentage. This value is subtracted from 100%. From the above, the fcc percentage of the weld metal is determined.

[0051] (Weld Metal / Chemical Composition) The weld joint according to the present disclosure has a weld metal having the specific compositions shown in the following [First to Third Weld Metals] from the viewpoint of improving the hydrogen embrittlement resistance of the weld metal and the vicinity of the fusion line FL. In the description of the chemical composition of the weld metal, "%" means "mass % with respect to the total mass of the weld metal" unless otherwise specified.

[0052] [First Weld Metal] The first weld metal contains a large amount of Ni, 40.00% to 80.00%, from the viewpoint of improving the hydrogen embrittlement resistance of the weld metal and the vicinity of the fusion line FL, and has the chemical composition shown below. Specifically, the chemical composition of the weld metal is, in mass%, C: 0.02% to 0.30%, Si: 0.01% to 0.50%, Mn: 0.01% to 3.00%, P: 0.100% or less, S: 0.100% or less, Ni: 40.0% to 80.0%, Cr: 0% to 20.0%, Mo: 0% to 20.0%, W: 0% to 5.0%, Nb: 0% to 5.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, The alloy contains Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, Mg: 0% to 1.00%, Zr: 0% to 1.000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.050%, with the balance being Fe and impurities.

[0053] (C: 0.02% to 0.30%) C is an element that improves the strength of the weld metal. On the other hand, if the C content of the weld metal is excessive, the increase in the strength of the weld metal has a significant effect of deteriorating toughness, and the low-temperature toughness of the weld metal decreases. Therefore, the C content of the weld metal is set to 0.02% to 0.30%. The lower limit of the C content of the weld metal is preferably 0.023%, 0.025%, or 0.030%. The upper limit of the C content of the weld metal is preferably 0.25%, 0.20%, or 0.15%.

[0054] (Si: 0.01% to 0.50%) Si is a deoxidizing element. If the Si content of the weld metal is too low, the oxygen content of the weld metal increases. On the other hand, Si has low solid solubility in the austenite phase, and the greater the Si content, the more likely it is to promote hot cracking. Therefore, the Si content of the weld metal is set to 0.01% to 0.50%. The lower limit of the Si content of the weld metal is preferably 0.03%, 0.05%, or 0.10%. The upper limit of the Si content of the weld metal is preferably 0.45%, 0.40%, or 0.35%.

[0055] (Mn: 0.01% to 3.00%) Mn is an austenite-stabilizing element and improves low-temperature toughness. Mn also functions as a deoxidizer to improve the cleanliness of the weld metal. On the other hand, if the Mn content in the weld metal is excessive, solidification segregation is likely to occur in the weld metal, accelerating hot cracking. Furthermore, if the Mn content in the weld metal is excessive, the weldability during the production of a welded joint (particularly the ability to reduce fumes during welding) decreases. Therefore, the Mn content in the weld metal is set to 0.01% to 3.00%. The lower limit of the Mn content in the weld metal is preferably 0.03%, 0.05%, 0.08%, or 0.10%. The upper limit of the Mn content in the weld metal is preferably 2.50%, 2.00%, or 1.50%.

[0056] (P: 0.100% or less) P is an impurity element that reduces toughness, so it is preferable to reduce the P content of the weld metal as much as possible. Therefore, the lower limit of the P content of the weld metal may be 0%. However, from the viewpoint of reducing deP costs, the P content of the weld metal may be 0.005% or more. On the other hand, if the P content of the weld metal is 0.100%, the adverse effect of P on toughness falls within an acceptable range. Therefore, the P content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the P content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0057] (S: 0.100% or less) S is an impurity element that reduces toughness, so it is preferable to reduce the S content of the weld metal as much as possible. Therefore, the lower limit of the S content of the weld metal may be 0%. However, from the viewpoint of reducing desulfurization costs, the S content of the weld metal may be 0.0005% or more. On the other hand, if the S content of the weld metal is 0.100% or less, the adverse effect of S on toughness falls within an acceptable range. Therefore, the S content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the S content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0058] (Ni: 40.00% to 80.00%) Ni is an austenite stabilizing element and an element that enhances hydrogen embrittlement resistance. If the Ni content of the weld metal is too low, the austenitization of the weld metal becomes difficult to proceed, resulting in deterioration of low-temperature toughness and deterioration of hydrogen embrittlement resistance. On the other hand, increasing the Ni content of the weld metal increases the cost of the welded joint. Therefore, the Ni content of the weld metal is set to 40.00% to 80.00%. The lower limit of the Ni content of the weld metal is preferably 42.00%, 45.00%, 48.00%, or 50.00%. The upper limit of the Ni content of the weld metal is preferably 78.00%, 76.00%, or 75.00%.

[0059] (Cr: 0% to 20.00%) Cr is an austenite-stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal. On the other hand, if the Cr content of the weld metal is excessive, the amount of low-melting-point compounds in the molten metal increases, and the solid-liquid coexistence temperature range of the molten metal widens, making hot cracking more likely to occur. Therefore, the Cr content of the weld metal is set to 0 to 20.00%. The lower limit of the Cr content of the weld metal is preferably 1.00%, 2.00%, or 3.00%. The upper limit of the Cr content of the weld metal is preferably 18.00%, 15.00%, 13.00%, or 10.00%.

[0060] (Mo: 0% to 20.00%) Mo is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal. On the other hand, if the Mo content of the weld metal is excessive, the strength of the weld metal becomes excessive and the low-temperature toughness decreases. Therefore, the Mo content of the weld metal is set to 0% to 20.00%. The lower limit of the Mo content of the weld metal is preferably 1.00%, 2.00%, or 3.00%. The upper limit of the Mo content of the weld metal is preferably 18.00%, 15.00%, 12.00%, or 10.00%.

[0061] (W: 0% to 5.00%) W is a solid solution strengthening element and may be contained in the weld metal to improve strength. On the other hand, if the W content of the weld metal is excessive, the strength of the weld metal becomes excessive, which may result in a decrease in toughness. Therefore, the W content of the weld metal is set to 0% to 5.00%. The lower limit of the W content of the weld metal is preferably 0.10%, 0.25%, or 0.50%. The upper limit of the W content of the weld metal is preferably 4.50%, 4.00%, or 3.50%.

[0062] (Nb: 0% to 5.0%) Nb may be contained in the weld metal because it forms carbides in the weld metal and increases the strength of the weld metal. On the other hand, if the Nb content in the weld metal is excessive, there is a concern that hot cracking may occur in the weld metal. Therefore, the Nb content in the weld metal is set to 0% to 5.0%. The lower limit of the Nb content in the weld metal is preferably 0.005%, 0.008%, or 0.01%. The upper limit of the Nb content in the weld metal is preferably 4.5%, 4.0%, 3.5%, or 3.0%.

[0063] (Ta: 0% to 3.000%) Ta is a solid solution strengthening element, and may be contained in the weld metal to improve strength. On the other hand, if the Ta content of the weld metal is excessive, the strength of the weld metal becomes excessive and low-temperature toughness deteriorates. Therefore, the Ta content of the weld metal is set to 0% to 3.000%. The lower limit of the Ta content of the weld metal is preferably 0.001%, 0.003%, 0.005%, or 0.010%. The upper limit of the Ta content of the weld metal is preferably 2.500%, 2.000%, or 1.500%.

[0064] (Cu: 0% to 1.000%) Cu is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal. Cu is also an austenite stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal. On the other hand, if the Cu content in the weld metal is excessive, the above effects will saturate. Therefore, the Cu content in the weld metal is set to 0% to 1.000%. The lower limit of the Cu content in the weld metal is preferably 0.020%, 0.050%, or 0.080%. The upper limit of the Cu content in the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0065] (Co: 0% to 1.0000%) Co is an element that increases the strength of the weld metal through solid solution strengthening, and so may be contained in the weld metal. On the other hand, if the Co content of the weld metal is excessive, the ductility of the weld metal decreases and toughness cannot be ensured. Therefore, the Co content of the weld metal is set to 0% to 1.0000%. The lower limit of the Co content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Co content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0066] (Pb: 0% to 1.000%) Pb may be contained in the weld metal because it has the effect of improving the toe formability between the base steel material and the weld metal and improving the machinability of the weld metal. On the other hand, if the Pb content of the weld metal is excessive, hot cracking occurs. Therefore, the Pb content of the weld metal is set to 0% to 1.000%. The lower limit of the Pb content of the weld metal is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Pb content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0067] (Sn: 0% to 1.000%) Sn is an element that improves the corrosion resistance of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Sn content of the weld metal is excessive, there is a concern that cracks may occur in the weld metal. Therefore, the Sn content of the weld metal is set to 0% to 1.000%. The lower limit of the Sn content of the weld metal is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Sn content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0068] (Al: 0.0001% to 1.0000%) Al is a deoxidizing element and is contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Al content of the weld metal is excessive, Al may form nitrides, oxides, or intermetallic compounds in the weld metal, which may reduce the low-temperature toughness of the weld metal. Therefore, the Al content of the weld metal is set to 0.0001% to 1.0000%. The lower limit of the Al content of the weld metal is preferably 0.0003%, 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Al content of the weld metal is preferably 0.3000%, 0.2000%, or 0.1000%.

[0069] (Ti: 0% to 1.0000%) Ti is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Ti content of the weld metal is excessive, carbides may form in the weld metal, which may deteriorate the toughness of the weld metal. Therefore, the Ti content of the weld metal is set to 0% to 1.0000%. The lower limit of the Ti content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Ti content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0070] (B: 0% to 0.10000%) B is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal to improve the low-temperature toughness and strength of the weld metal. On the other hand, if the B content of the weld metal is excessive, borides will precipitate, causing a deterioration in toughness. Therefore, the B content of the weld metal is set to 0% to 0.10000%. The lower limit of the B content of the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the B content of the weld metal is preferably 0.90000%, 0.80000%, or 0.50000%.

[0071] (V: 0% to 3.0000%) V may be contained in the weld metal because it forms carbonitrides in the weld metal and increases the strength of the weld metal. On the other hand, if the V content in the weld metal is excessive, hot cracking of the weld metal may occur. Therefore, the V content in the weld metal is set to 0% to 3.0000%. The lower limit of the V content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the V content in the weld metal is preferably 2.5000%, 2.0000%, or 1.5000%.

[0072] (Ca: 0% to 1.000000%) Ca changes the structure of sulfides in the weld metal and also functions to refine the size of sulfides and oxides in the weld metal, and is therefore effective in improving the ductility and toughness of the weld metal. Therefore, Ca may be contained in the weld metal. On the other hand, an excessive Ca content in the weld metal may cause coarsening of sulfides and oxides, which may lead to a deterioration in the low-temperature toughness of the weld metal. Therefore, the Ca content of the weld metal is set to 0% to 1.000000%. The lower limit of the Ca content in the weld metal is preferably 0.000005%, 0.000010%, or 0.000020%. The upper limit of the Ca content in the weld metal is preferably 0.900000%, 0.800000%, or 0.500000%.

[0073] (Mg: 0% to 1.00%) Mg is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Mg content of the weld metal is excessive, the amount of oxides and nitrides in the weld metal increases, which may deteriorate the toughness of the weld metal. Therefore, the Mg content of the weld metal is set to 0% to 1.00%. The lower limit of the Mg content of the weld metal is preferably 0.0005%, 0.001%, or 0.002%. The upper limit of the Mg content of the weld metal is preferably 0.90%, 0.80%, or 0.50%.

[0074] (Zr: 0% to 1.000%) Zr is an element that has the effect of smoothing the bead shape of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Zr content of the weld metal is excessive, the oxygen content in the weld metal increases, which may deteriorate the low-temperature toughness. Therefore, the Zr content of the weld metal is set to 0% to 1.000%. The lower limit of the Zr content of the weld metal is preferably 0.0005%, 0.001%, or 0.002%. The upper limit of the Zr content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0075] (Hf: 0% to 1.0000%) Hf is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, an excessive Hf content in the weld metal increases costs. Therefore, the Hf content in the weld metal is set to 0% to 1.0000%. The lower limit of the Hf content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Hf content in the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0076] (REM: 0% to 0.50000%) REM is an element that stabilizes the arc during welding to obtain the weld metal, and therefore may be contained in the weld metal. On the other hand, if the REM content in the weld metal is excessive, spattering may become severe during welding to obtain the weld metal, potentially resulting in poor welding workability. Therefore, the REM content in the weld metal is set to 0% to 0.50000%. The lower limit of the REM content in the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the REM content in the weld metal is preferably 0.45000%, 0.40000%, or 0.35000%.

[0077] (N: 0% to 0.300%) N is also an interstitial solid solution strengthening element and may be contained in the weld metal to improve the strength of the weld metal. On the other hand, if the N content of the weld metal is excessive, the occurrence of blowout increases, causing welding defects. Therefore, the N content of the weld metal is set to 0% to 0.300%. The lower limit of the N content of the weld metal is preferably 0.001%, 0.0015%, or 0.002%. The upper limit of the N content of the weld metal is preferably 0.250%, 0.200%, or 0.150%.

[0078] (O: 0% to 0.050%) O is an element that can be contained in the weld metal as an impurity, and the lower limit of the O content in the weld metal is set to 0%. However, an excessive O content leads to deterioration of toughness and ductility, so the upper limit of the O content in the weld metal is set to 0.050%. On the other hand, an extreme reduction in the O content leads to an increase in manufacturing costs, so the lower limit of the O content in the weld metal is set to 0.001% or more. The lower limit of the O content in the weld metal is preferably 0.005% or 0.010%. The upper limit of the O content in the weld metal is preferably 0.045%, 0.040%, 0.035%, or 0.030%.

[0079] (Balance: Fe and impurities) The balance in the chemical composition of the weld metal consists of Fe and impurities. The impurities refer to components that are mixed in from raw materials such as ore and scrap when industrially producing the weld metal, or that are mixed in due to various factors in the production process, and are acceptable within a range that does not adversely affect the properties of the weld metal.

[0080] [Second Weld Metal] The second weld metal contains 5.00% or more Mn and Ni in total, from the viewpoint of improving the hydrogen embrittlement resistance of the weld metal and the vicinity of the fusion line FL, and has the chemical composition shown below. Specifically, the chemical composition of the weld metal is, in mass %, C: over 0.10% to 0.80%, Si: 0.05% to 1.00%, Mn: 1.00% to 20.00%, P: 0.100% or less, S: 0.100% or less, Ni: 1.0% to 20.0%, Cr: 1.0% to 10.0%, Mo: 1.0% to 10.0%, W: 0% to 3.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.0000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.100%, with the balance being Fe and impurities. The Mn content (mass%) in the weld metal is defined as [Mn Ｗ ], the Ni content (mass%) in the weld metal is [Ni Ｗ ], [Mn Ｗ ]+[Ni Ｗ ]≧5.00%.

[0081] (C: more than 0.10% to 0.80%) C is an element that improves the strength of the weld metal and ensures the strength of the weld metal. On the other hand, if the C content of the weld metal is excessive, the increase in the strength of the weld metal has a significant effect of deteriorating toughness, and the low-temperature toughness of the weld metal decreases. Therefore, the C content of the weld metal is more than 0.10% to 0.80%. The lower limit of the C content of the weld metal may preferably be 0.12%, 0.15%, 0.18%, or 0.20%. The upper limit of the C content of the weld metal is preferably 0.75%, 0.70%, 0.65%, or 0.60%.

[0082] (Si: 0.05% to 1.00%) Si is a deoxidizing element. If the Si content of the weld metal is too low, the oxygen content of the weld metal increases. On the other hand, Si has low solid solubility in the austenite phase, and the greater the Si content, the more likely it is to promote hot cracking. Therefore, the Si content of the weld metal is set to 0.05% to 1.00%. The lower limit of the Si content of the weld metal is preferably 0.06%, 0.08%, or 0.10%. The upper limit of the Si content of the weld metal is preferably 0.95%, 0.90%, 0.85%, 0.80%, 0.75%, or 0.70%.

[0083] (Mn: 1.00% to 20.00%) Mn is an austenite-stabilizing element and an element that enhances hydrogen embrittlement resistance. If the Mn content of the weld metal is too low, the austenitization of the weld metal becomes difficult, low-temperature toughness deteriorates, and hydrogen embrittlement resistance deteriorates. Mn also functions as a deoxidizer to improve the cleanliness of the weld metal. On the other hand, if the Mn content of the weld metal is excessive, microsegregation is likely to occur in the weld metal, causing significant embrittlement in the segregated areas and promoting hot cracking. Furthermore, if the Mn content of the weld metal is excessive, the weldability (particularly the ability to reduce fumes during welding) during the production of the welded joint decreases. Therefore, the Mn content of the weld metal is set to 1.00% to 20.00%. The lower limit of the Mn content of the weld metal is preferably 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, or 4.00%. The upper limit of the Mn content of the weld metal is preferably 19.00%, 18.00%, 17.00%, 16.00%, or 15.00%.

[0084] (P: 0.100% or less) P is an impurity element that reduces toughness, so it is preferable to reduce the P content of the weld metal as much as possible. Therefore, the lower limit of the P content of the weld metal may be 0%. However, from the viewpoint of reducing deP costs, the P content of the weld metal may be 0.005% or more. On the other hand, if the P content of the weld metal is 0.100%, the adverse effect of P on toughness falls within an acceptable range. Therefore, the P content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the P content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0085] (S: 0.100% or less) S is an impurity element that reduces toughness, so it is preferable to reduce the S content of the weld metal as much as possible. Therefore, the lower limit of the S content of the weld metal may be 0%. However, from the viewpoint of reducing desulfurization costs, the S content of the weld metal may be 0.0005% or more. On the other hand, if the S content of the weld metal is 0.100% or less, the adverse effect of S on toughness falls within an acceptable range. Therefore, the S content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the S content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0086] (Ni: 1.0% to 20.0%) Ni is an austenite stabilizing element and an element that enhances hydrogen embrittlement resistance. If the Ni content of the weld metal is too low, the austenitization of the weld metal becomes difficult to proceed, resulting in deterioration of low-temperature toughness and deterioration of hydrogen embrittlement resistance. On the other hand, increasing the Ni content of the weld metal increases the cost of the welded joint. Therefore, the Ni content of the weld metal is set to 1.0% to 20.0%. The lower limit of the Ni content of the weld metal is preferably 2.0%, 3.0%, 5.0%, or 7.0%. The upper limit of the Ni content of the weld metal is preferably 19.5%, 19.0%, 18.5%, or 18.0%.

[0087] (Cr: 1.0% to 10.0%) Cr is an austenite-stabilizing element and improves the low-temperature toughness of the weld metal. On the other hand, if the Cr content of the weld metal is excessive, the amount of low-melting-point compounds in the molten metal increases, and the solid-liquid coexistence temperature range of the molten metal widens, making hot cracking more likely to occur. Therefore, the Cr content of the weld metal is set to 1.0% to 10.0%. The lower limit of the Cr content of the weld metal is preferably 1.2%, 1.5%, 1.8%, 2.0%, or 2.5%. The upper limit of the Cr content of the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0088] (Mo: 1.0% to 10.0%) Mo is a precipitation strengthening element that improves the strength of the weld metal. On the other hand, if the Mo content in the weld metal is excessive, the strength of the weld metal becomes excessive and the low-temperature toughness decreases. Therefore, the Mo content in the weld metal is set to 1.0% to 10.0%. The lower limit of the Mo content in the weld metal is preferably 1.5%, 2.0%, 2.5%, or 3.0%. The upper limit of the Mo content in the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0089] (W: 0% to 3.0%) W is a solid solution strengthening element and may be contained in the weld metal to improve strength. On the other hand, if the W content of the weld metal is excessive, the strength of the weld metal becomes excessive, which may result in a decrease in toughness. Therefore, the W content of the weld metal is set to 0% to 3.0%. The lower limit of the W content of the weld metal is preferably 0.1%, 0.25%, or 0.5%. The upper limit of the W content of the weld metal is preferably 2.5%, 2.0%, or 1.5%.

[0090] (Nb: 0% to 3.0%) Nb may be contained in the weld metal because it forms carbides in the weld metal and increases the strength of the weld metal. On the other hand, if the Nb content in the weld metal is excessive, there is a concern that hot cracking may occur in the weld metal. Therefore, the Nb content in the weld metal is set to 0% to 3.0%. The lower limit of the Nb content in the weld metal is preferably 0.005%, 0.008%, or 0.01%. The upper limit of the Nb content in the weld metal is preferably 2.8%, 2.5%, 2.2%, or 2.0%.

[0091] (Ta: 0% to 3.000%) Ta is a solid solution strengthening element, and may be contained in the weld metal to improve strength. On the other hand, if the Ta content of the weld metal is excessive, the strength of the weld metal becomes excessive and low-temperature toughness deteriorates. Therefore, the Ta content of the weld metal is set to 0% to 3.000%. The lower limit of the Ta content of the weld metal is preferably 0.001%, 0.003%, 0.005%, or 0.010%. The upper limit of the Ta content of the weld metal is preferably 2.500%, 2.000%, or 1.500%.

[0092] (Cu: 0% to 1.000%) Cu is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal. Cu is also an austenite stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal. On the other hand, if the Cu content in the weld metal is excessive, the above effects will saturate. Therefore, the Cu content in the weld metal is set to 0% to 1.000%. The lower limit of the Cu content in the weld metal is preferably 0.020%, 0.050%, or 0.080%. The upper limit of the Cu content in the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0093] (Co: 0% to 1.0000%) Co is an element that increases the strength of the weld metal through solid solution strengthening, and so may be contained in the weld metal. On the other hand, if the Co content of the weld metal is excessive, the ductility of the weld metal decreases and toughness cannot be ensured. Therefore, the Co content of the weld metal is set to 0% to 1.0000%. The lower limit of the Co content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Co content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0094] (Pb: 0% to 1.000%) Pb may be contained in the weld metal because it has the effect of improving the toe formability between the base steel material and the weld metal and improving the machinability of the weld metal. On the other hand, if the Pb content of the weld metal is excessive, hot cracking occurs. Therefore, the Pb content of the weld metal is set to 0% to 1.000%. The lower limit of the Pb content of the weld metal is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Pb content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0095] (Sn: 0% to 1.0000%) Sn is an element that improves the corrosion resistance of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Sn content of the weld metal is excessive, there is a concern that cracks may occur in the weld metal. Therefore, the Sn content of the weld metal is set to 0% to 1.0000%. The lower limit of the Sn content of the weld metal is preferably 0.0050%, 0.0100%, or 0.0200%. The upper limit of the Sn content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0096] (Al: 0.0001% to 1.0000%) Al is a deoxidizing element and is contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Al content of the weld metal is excessive, Al may form nitrides, oxides, or intermetallic compounds in the weld metal, which may reduce the low-temperature toughness of the weld metal. Therefore, the Al content of the weld metal is set to 0.0001% to 1.0000%. The lower limit of the Al content of the weld metal is preferably 0.0002%, 0.0005%, 0.0008%, or 0.0100%. The upper limit of the Al content of the weld metal is preferably 0.5000%, 0.3000%, or 0.1000%.

[0097] (Ti: 0% to 1.0000%) Ti is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Ti content of the weld metal is excessive, carbides may form in the weld metal, which may deteriorate the toughness of the weld metal. Therefore, the Ti content of the weld metal is set to 0% to 1.0000%. The lower limit of the Ti content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Ti content of the weld metal is preferably 0.5000%, 0.3000%, or 0.1000%.

[0098] (B: 0% to 0.10000%) B is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal to improve the low-temperature toughness and strength of the weld metal. On the other hand, if the B content of the weld metal is excessive, borides will precipitate, causing a deterioration in toughness. Therefore, the B content of the weld metal is set to 0% to 0.10000%. The lower limit of the B content of the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the B content of the weld metal is preferably 0.90000%, 0.80000%, or 0.50000%.

[0099] (V: 0% to 3.0000%) V may be contained in the weld metal because it forms carbonitrides in the weld metal and increases the strength of the weld metal. On the other hand, if the V content in the weld metal is excessive, hot cracking of the weld metal may occur. Therefore, the V content in the weld metal is set to 0% to 3.0000%. The lower limit of the V content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the V content in the weld metal is preferably 2.5000%, 2.0000%, or 1.5000%.

[0100] (Ca: 0% to 1.000000%) Ca changes the structure of sulfides in the weld metal and also functions to refine the size of sulfides and oxides in the weld metal, and is therefore effective in improving the ductility and toughness of the weld metal. Therefore, Ca may be contained in the weld metal. On the other hand, an excessive Ca content in the weld metal may cause coarsening of sulfides and oxides, which may lead to a deterioration in the low-temperature toughness of the weld metal. Therefore, the Ca content of the weld metal is set to 0% to 1.000000%. The lower limit of the Ca content in the weld metal is preferably 0.000005%, 0.000010%, or 0.000020%. The upper limit of the Ca content in the weld metal is preferably 0.900000%, 0.800000%, or 0.500000%.

[0101] (Mg: 0% to 1.0000%) Mg is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Mg content of the weld metal is excessive, the amount of oxides and nitrides in the weld metal increases, which may deteriorate the toughness of the weld metal. Therefore, the Mg content of the weld metal is set to 0% to 1.0000%. The lower limit of the Mg content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Mg content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0102] (Zr: 0% to 1.0000%) Zr is an element that has the effect of smoothing the bead shape of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Zr content of the weld metal is excessive, the oxygen content in the weld metal increases, which may deteriorate the low-temperature toughness. Therefore, the Zr content of the weld metal is set to 0% to 1.0000%. The lower limit of the Zr content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Zr content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0103] (Hf: 0% to 1.0000%) Hf is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, an excessive Hf content in the weld metal increases costs. Therefore, the Hf content in the weld metal is set to 0% to 1.0000%. The lower limit of the Hf content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Hf content in the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0104] (REM: 0% to 0.50000%) REM is an element that stabilizes the arc during welding to obtain the weld metal, and therefore may be contained in the weld metal. On the other hand, if the REM content in the weld metal is excessive, spattering may become severe during welding to obtain the weld metal, potentially resulting in poor welding workability. Therefore, the REM content in the weld metal is set to 0% to 0.50000%. The lower limit of the REM content in the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the REM content in the weld metal is preferably 0.45000%, 0.40000%, or 0.35000%.

[0105] (N: 0% to 0.300%) N is also an interstitial solid solution strengthening element and may be contained in the weld metal to improve the strength of the weld metal. On the other hand, if the N content of the weld metal is excessive, the occurrence of blowout increases, causing welding defects. Therefore, the N content of the weld metal is set to 0% to 0.300%. The lower limit of the N content of the weld metal is preferably 0.002%, 0.005%, 0.008%, or 0.010%. The upper limit of the N content of the weld metal is preferably 0.280%, 0.250%, 0.230%, or 0.200%.

[0106] (O: 0% to 0.100%) O is an element that can be contained in the weld metal as an impurity, and the lower limit of the O content in the weld metal is set to 0%. However, an excessive O content leads to deterioration of toughness and ductility, so the upper limit of the O content in the weld metal is set to 0.100%. On the other hand, an extreme reduction in the O content leads to an increase in manufacturing costs, so the lower limit of the O content in the weld metal is set to 0.001% or more. The lower limit of the O content in the weld metal is preferably 0.005% or 0.010%. The upper limit of the O content in the weld metal is preferably 0.070%, 0.060%, or 0.050%.

[0107] (Balance: Fe and impurities) The balance in the chemical composition of the weld metal consists of Fe and impurities. The impurities refer to components that are mixed in from raw materials such as ore and scrap when industrially producing the weld metal, or that are mixed in due to various factors in the production process, and are acceptable within a range that does not adversely affect the properties of the weld metal.

[0108] (The total of the Mn content and Ni content in the weld metal ([Mn Ｗ ]+[Ni Ｗ Mn and Ni are austenite stabilizing elements, and improve the low-temperature toughness and hydrogen embrittlement resistance of the weld metal. From the viewpoint of improving the low-temperature toughness and hydrogen embrittlement resistance of the second weld metal, the manganese content in the weld metal is set to [Mn Ｗ ], the amount of nickel in the weld metal [Ni Ｗ ], it is preferable that the following formula (A) is satisfied: Ｗ ]+[NiＷ ] ≥ 5.00% ... (A) That is, the total of the Mn content and Ni content in the weld metal ([Mn Ｗ ]+[Ni Ｗ The total content of Mn and Ni in the weld metal ([Mn Ｗ ]+[Ni Ｗ ]) is more preferably 12.00% or more, 15.00% or more, or 20.00% or more.

[0109] Moreover, if Mn is excessively increased, stacking fault energy decreases and toughness deteriorates. Therefore, from the viewpoint of suppressing the cost of the weld metal and improving the low-temperature toughness of the weld metal, it is preferable that the Mn content and Ni content in the weld metal each satisfy the above-mentioned ranges, and the total Mn content and Ni content ([Mn Ｗ ]+[Ni Ｗ The total content of Mn and Ni in the weld metal ([Mn Ｗ ]+[Ni Ｗ ]) is more preferably 50.00% or less, or 40.00% or less.

[0110] Nickel equivalent Nieq of weld metal From the viewpoint of facilitating an improvement in the hydrogen embrittlement resistance of the weld metal, the second weld metal preferably has a nickel equivalent Nieq, as shown in the following (Equation 2), of 25.00 to 60.00. The lower limit of the nickel equivalent Nieq of the weld metal is more preferably 26.00, 28.00, or 30.00. The upper limit of the nickel equivalent Nieq of the weld metal is more preferably 58.00, 56.00, or 54.00. Nieq=[Ni Ｗ ]+0.65×[Cr Ｗ ]+0.98×[Mo Ｗ ]+1.05×[Mn Ｗ ]+0.35×[Si Ｗ ]+12.6×[C Ｗ ] (Formula 2) (In Formula 2, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ] is the content (mass%) of Mo in the weld metal, and [Mn Ｗ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ ] represents the C content (mass%) in the weld metal.

[0111] [Third Weld Metal] The third weld metal contains a large amount of Mn, more than 20.00% to 30.00%, from the viewpoint of improving hydrogen embrittlement resistance in the vicinity of the weld metal and fusion line FL, and has the chemical composition shown below. Specifically, the chemical composition of the weld metal is, in mass%, C: over 0.10% to 0.70%, Si: 0.05% to 1.00%, Mn: over 20.00% to 30.00%, P: 0.100% or less, S: 0.100% or less, Ni: 0% to 14.0%, Cr: 0% to 14.0%, Mo: 0% to 5.0%, W: 0% to 5.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, The alloy contains Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.200%, and O: 0% to 0.100%, with the balance being Fe and impurities.

[0112] (C: more than 0.10% to 0.70%) C is an element that improves the strength of the weld metal and ensures the strength of the weld metal. On the other hand, if the C content of the weld metal is excessive, the increase in the strength of the weld metal has a significant effect of deteriorating toughness, and the low-temperature toughness of the weld metal decreases. Therefore, the C content of the weld metal is more than 0.10% to 0.70%. The lower limit of the C content of the weld metal may preferably be 0.12%, 0.15%, 0.18%, or 0.20%. The upper limit of the C content of the weld metal is preferably 0.65%, 0.60%, 0.55%, or 0.50%.

[0113] (Si: 0.05% to 1.00%) Si is a deoxidizing element. If the Si content of the weld metal is too low, the oxygen content of the weld metal increases. On the other hand, Si has low solid solubility in the austenite phase, and the greater the Si content, the more likely it is to promote hot cracking. Therefore, the Si content of the weld metal is set to 0.05% to 1.00%. The lower limit of the Si content of the weld metal is preferably 0.06%, 0.08%, or 0.10%. The upper limit of the Si content of the weld metal is preferably 0.95%, 0.90%, 0.85%, 0.80%, 0.75%, or 0.70%.

[0114] (Mn: more than 20.00% to 30.00%) Mn is an austenite-stabilizing element and an element that enhances hydrogen embrittlement resistance. If the Mn content of the weld metal is too low, the austenitization of the weld metal becomes difficult, low-temperature toughness deteriorates, and hydrogen embrittlement resistance deteriorates. Mn is also an element that functions as a deoxidizer and improves the cleanliness of the weld metal. On the other hand, if the Mn content of the weld metal is excessive, solidification segregation is likely to occur in the weld metal, accelerating hot cracking. Furthermore, if the Mn content of the weld metal is excessive, weldability during production of a welded joint (particularly the ability to reduce fumes during welding) deteriorates. Therefore, the Mn content of the weld metal is set to more than 20.00% to 30.00%. The lower limit of the Mn content of the weld metal is preferably 20.50%, 21.00%, 21.50%, or 22.00%. The upper limit of the Mn content of the weld metal is preferably 29.50%, 29.00%, 28.50%, or 28.00%.

[0115] (P: 0.100% or less) P is an impurity element that reduces toughness, so it is preferable to reduce the P content of the weld metal as much as possible. Therefore, the lower limit of the P content of the weld metal may be 0%. However, from the viewpoint of reducing deP costs, the P content of the weld metal may be 0.005% or more. On the other hand, if the P content of the weld metal is 0.100%, the adverse effect of P on toughness falls within an acceptable range. Therefore, the P content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the P content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0116] (S: 0.100% or less) S is an impurity element that reduces toughness, so it is preferable to reduce the S content of the weld metal as much as possible. Therefore, the lower limit of the S content of the weld metal may be 0%. However, from the viewpoint of reducing desulfurization costs, the S content of the weld metal may be 0.0005% or more. On the other hand, if the S content of the weld metal is 0.100% or less, the adverse effect of S on toughness falls within an acceptable range. Therefore, the S content of the weld metal is set to 0.100% or less. To effectively suppress a decrease in toughness, the S content of the weld metal is preferably 0.080% or less, 0.060% or less, 0.040% or less, or 0.020% or less.

[0117] (Cr: 0% to 14.0%) Cr is an austenite-stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal. On the other hand, if the Cr content of the weld metal is excessive, the amount of low-melting-point compounds in the molten metal increases, and the solid-liquid coexistence temperature range of the molten metal widens, making hot cracking more likely to occur. Therefore, the Cr content of the weld metal is set to 0% to 14.0%. The lower limit of the Cr content of the weld metal is preferably 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, or 6.0%. The upper limit of the Cr content of the weld metal is preferably 13.5%, 13.0%, 12.0%, 11.0%, or 10.0%.

[0118] (Ni: 0% to 14.0%) Ni is an austenite stabilizing element and may be contained in the weld metal. On the other hand, increasing the Ni content of the weld metal increases the cost of the welded joint. Therefore, the Ni content of the weld metal is set to 0% to 14.0%. The lower limit of the Ni content of the weld metal is preferably 0.5%, 1.0%, 1.5%, or 2.0%. The upper limit of the Ni content of the weld metal is preferably 13.0%, 12.0%, 11.0%, or 10.0%.

[0119] (Mo: 0% to 5.0%) Mo is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal. On the other hand, if the Mo content of the weld metal is excessive, the strength of the weld metal becomes excessive and the low-temperature toughness decreases. Therefore, the Mo content of the weld metal is set to 0% to 5.0%. The lower limit of the Mo content of the weld metal is preferably 0.2%, 0.5%, 0.8%, or 1.0%. The upper limit of the Mo content of the weld metal is preferably 4.8%, 4.5%, 4.2%, or 4.0%.

[0120] (W: 0% to 5.0%) W is a solid solution strengthening element and may be contained in the weld metal to improve strength. On the other hand, if the W content of the weld metal is excessive, the strength of the weld metal becomes excessive, which may result in a decrease in toughness. Therefore, the W content of the weld metal is set to 0% to 5.0%. The lower limit of the W content of the weld metal is preferably 0.1%, 0.25%, or 0.5%. The upper limit of the W content of the weld metal is preferably 4.5%, 4.0%, 3.5%, or 3.0%.

[0121] (Nb: 0% to 3.0%) Nb may be contained in the weld metal because it forms carbides in the weld metal and increases the strength of the weld metal. On the other hand, if the Nb content in the weld metal is excessive, there is a concern that hot cracking may occur in the weld metal. Therefore, the Nb content in the weld metal is set to 0% to 3.0%. The lower limit of the Nb content in the weld metal is preferably 0.005%, 0.008%, or 0.01%. The upper limit of the Nb content in the weld metal is preferably 2.5%, 2.0%, 1.5%, or 1.0%.

[0122] (Ta: 0% to 3.000%) Ta is a solid solution strengthening element, and may be contained in the weld metal to improve strength. On the other hand, if the Ta content of the weld metal is excessive, the strength of the weld metal becomes excessive and low-temperature toughness deteriorates. Therefore, the Ta content of the weld metal is set to 0% to 3.000%. The lower limit of the Ta content of the weld metal is preferably 0.001%, 0.003%, 0.005%, or 0.010%. The upper limit of the Ta content of the weld metal is preferably 2.500%, 2.000%, or 1.500%.

[0123] (Cu: 0% to 1.000%) Cu is a precipitation strengthening element and may be contained in the weld metal to improve the strength of the weld metal. Cu is also an austenite stabilizing element and may be contained in the weld metal to improve the low-temperature toughness of the weld metal. On the other hand, if the Cu content in the weld metal is excessive, the above effects will saturate. Therefore, the Cu content in the weld metal is set to 0% to 1.000%. The lower limit of the Cu content in the weld metal is preferably 0.020%, 0.050%, or 0.080%. The upper limit of the Cu content in the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0124] (Co: 0% to 1.0000%) Co is an element that increases the strength of the weld metal through solid solution strengthening, and so may be contained in the weld metal. On the other hand, if the Co content of the weld metal is excessive, the ductility of the weld metal decreases and toughness cannot be ensured. Therefore, the Co content of the weld metal is set to 0% to 1.0000%. The lower limit of the Co content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Co content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0125] (Pb: 0% to 1.000%) Pb may be contained in the weld metal because it has the effect of improving the toe formability between the base steel material and the weld metal and improving the machinability of the weld metal. On the other hand, if the Pb content of the weld metal is excessive, hot cracking occurs. Therefore, the Pb content of the weld metal is set to 0% to 1.000%. The lower limit of the Pb content of the weld metal is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Pb content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0126] (Sn: 0% to 1.000%) Sn is an element that improves the corrosion resistance of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Sn content of the weld metal is excessive, there is a concern that cracks may occur in the weld metal. Therefore, the Sn content of the weld metal is set to 0% to 1.000%. The lower limit of the Sn content of the weld metal is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Sn content of the weld metal is preferably 0.900%, 0.800%, or 0.500%.

[0127] (Al: 0.0001% to 1.0000%) Al is a deoxidizing element and is contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Al content of the weld metal is excessive, Al may form nitrides, oxides, or intermetallic compounds in the weld metal, which may reduce the low-temperature toughness of the weld metal. Therefore, the Al content of the weld metal is set to 0.0001% to 1.0000%. The lower limit of the Al content of the weld metal is preferably 0.0002%, 0.0005%, 0.0008%, or 0.0010%. The upper limit of the Al content of the weld metal is preferably 0.5000%, 0.3000%, or 0.1000%.

[0128] (Ti: 0% to 1.0000%) Ti is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Ti content of the weld metal is excessive, carbides may form in the weld metal, which may deteriorate the toughness of the weld metal. Therefore, the Ti content of the weld metal is set to 0% to 1.0000%. The lower limit of the Ti content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Ti content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0129] (B: 0% to 0.10000%) B is an austenite stabilizing element and an interstitial solid solution strengthening element, and may be contained in the weld metal to improve the low-temperature toughness and strength of the weld metal. On the other hand, if the B content of the weld metal is excessive, borides will precipitate, causing a deterioration in toughness. Therefore, the B content of the weld metal is set to 0% to 0.10000%. The lower limit of the B content of the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the B content of the weld metal is preferably 0.90000%, 0.80000%, or 0.50000%.

[0130] (V: 0% to 3.0000%) V may be contained in the weld metal because it forms carbonitrides in the weld metal and increases the strength of the weld metal. On the other hand, if the V content in the weld metal is excessive, hot cracking of the weld metal may occur. Therefore, the V content in the weld metal is set to 0% to 3.0000%. The lower limit of the V content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the V content in the weld metal is preferably 2.5000%, 2.0000%, or 1.5000%.

[0131] (Ca: 0% to 1.000000%) Ca changes the structure of sulfides in the weld metal and also functions to refine the size of sulfides and oxides in the weld metal, and is therefore effective in improving the ductility and toughness of the weld metal. Therefore, Ca may be contained in the weld metal. On the other hand, an excessive Ca content in the weld metal may cause coarsening of sulfides and oxides, which may lead to a deterioration in the low-temperature toughness of the weld metal. Therefore, the Ca content of the weld metal is set to 0% to 1.000000%. The lower limit of the Ca content in the weld metal is preferably 0.000005%, 0.000010%, or 0.000020%. The upper limit of the Ca content in the weld metal is preferably 0.900000%, 0.800000%, or 0.500000%.

[0132] (Mg: 0% to 1.0000%) Mg is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, if the Mg content of the weld metal is excessive, the amount of oxides and nitrides in the weld metal increases, which may deteriorate the toughness of the weld metal. Therefore, the Mg content of the weld metal is set to 0% to 1.0000%. The lower limit of the Mg content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Mg content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0133] (Zr: 0% to 1.0000%) Zr is an element that has the effect of smoothing the bead shape of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Zr content of the weld metal is excessive, the oxygen content in the weld metal increases, which may deteriorate the low-temperature toughness. Therefore, the Zr content of the weld metal is set to 0% to 1.0000%. The lower limit of the Zr content of the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Zr content of the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0134] (Hf: 0% to 1.0000%) Hf is a deoxidizing element and may be contained in the weld metal to suppress welding defects and improve the cleanliness of the weld metal. On the other hand, an excessive Hf content in the weld metal increases costs. Therefore, the Hf content in the weld metal is set to 0% to 1.0000%. The lower limit of the Hf content in the weld metal is preferably 0.0005%, 0.0010%, or 0.0020%. The upper limit of the Hf content in the weld metal is preferably 0.9000%, 0.8000%, or 0.5000%.

[0135] (REM: 0% to 0.50000%) REM is an element that stabilizes the arc during welding to obtain the weld metal, and therefore may be contained in the weld metal. On the other hand, if the REM content in the weld metal is excessive, spattering may become severe during welding to obtain the weld metal, potentially resulting in poor welding workability. Therefore, the REM content in the weld metal is set to 0% to 0.50000%. The lower limit of the REM content in the weld metal is preferably 0.00005%, 0.00010%, or 0.00020%. The upper limit of the REM content in the weld metal is preferably 0.45000%, 0.40000%, or 0.35000%.

[0136] (N: 0% to 0.200%) N is also an interstitial solid solution strengthening element and may be contained in the weld metal to improve the strength of the weld metal. On the other hand, if the N content in the weld metal is excessive, the relative reduction of area will decrease in the third weld metal, which has a high Mn content. Furthermore, if the N content in the weld metal is excessive, the occurrence of blowout will increase, causing welding defects. Therefore, the N content in the weld metal is set to 0% to 0.200%. The lower limit of the N content in the weld metal is preferably 0.002%, 0.005%, 0.008%, or 0.010%. The upper limit of the N content in the weld metal is preferably 0.018%, 0.016%, 0.150%, 0.140%, or 0.130%.

[0137] (O: 0% to 0.100%) O is an element that can be contained in the weld metal as an impurity, and the lower limit of the O content in the weld metal is set to 0%. However, an excessive O content leads to deterioration of toughness and ductility, so the upper limit of the O content in the weld metal is set to 0.100%. On the other hand, an extreme reduction in the O content leads to an increase in manufacturing costs, so the lower limit of the O content in the weld metal is set to 0.001% or more. The lower limit of the O content in the weld metal is preferably 0.005% or 0.010%. The upper limit of the O content in the weld metal is preferably 0.090%, 0.080%, 0.060%, or 0.050%.

[0138] (Balance: Fe and impurities) The balance in the chemical composition of the weld metal consists of Fe and impurities. The impurities refer to components that are mixed in from raw materials such as ore and scrap when industrially producing the weld metal, or that are mixed in due to various factors in the production process, and are acceptable within a range that does not adversely affect the properties of the weld metal.

[0139] Stacking Fault Energy SFE of Weld Metal From the viewpoint of facilitating enhancement of the hydrogen embrittlement resistance of the weld metal, the third weld metal preferably has a stacking fault energy SFE (Stacking Fault Energy) expressed by the following (Equation 3) of 10.00 or more. The lower limit of the nickel equivalent Nieq of the weld metal is more preferably 11.00, 12.00, or 13.00. The upper limit of the nickel equivalent Nieq of the weld metal is more preferably 25.00, 20.00, 18.00, or 15.00. SFE=-7.1+2.8×[Ni Ｗ ]+0.49×[Cr Ｗ ]+2×[Mo Ｗ ]+0.75×[Mn Ｗ ]−2×[Si Ｗ ]−5.7×[C Ｗ ]−24×[N Ｗ ] (Formula 3) (In Formula 3, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ ] is the content (mass%) of Mo in the weld metal, and [MnＷ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ ] is the content (mass%) of C in the weld metal, and [N Ｗ ] represents the N content (mass%) in the weld metal.

[0140] <Method for manufacturing a welded joint> Here, a method for manufacturing a welded joint according to the present disclosure will be described. The welded joint according to the present disclosure can be manufactured by welding a steel material serving as a base metal using a welding material. As the steel material serving as the base metal, a base metal having the composition and structure described above is preferred. The thickness of the base metal in the welded joint according to the present disclosure is not particularly limited, but can be, for example, 15 mm or more and 40 mm or less.

[0141] For example, the weld joint according to the present disclosure can be obtained by gas-shielded arc welding of steel materials using a flux-cored wire. In this case, the chemical composition of the weld metal includes components derived from the flux-cored wire, which is the welding material, and the steel material, which is the base material.

[0142] The welded joint according to the present disclosure can be obtained by submerged arc welding using a solid wire and flux. For example, in submerged arc welding, a typical submerged arc welding device can be used, in which granular flux is dispersed on the weld line in advance, the solid wire is fed into the flux, and welding is performed by the arc heat generated between the solid wire and the steel material in the flux. In this case, the chemical composition of the weld metal includes components derived from the solid wire and flux, which are the welding materials, and the steel material, which is the base material.

[0143] The welded joint according to the present disclosure can be obtained by a welding method such as, for example, shielded metal arc welding, electrogas arc welding, electroslag welding, TIG welding, gas-shielded welding using a solid wire, etc. In this case, the chemical composition of the weld metal includes components derived from the welding material and the steel base material.

[0144] <Applications> Applications of the welded joint according to the present disclosure include, for example, tanks, particularly tanks for liquefied natural gas (LNG), liquefied CO ２ Examples of suitable tanks include tanks for storing one or more gases selected from the group consisting of liquefied natural gas (LNG), liquefied CO2, and liquefied hydrogen gas. ２ Tanks for storing gases such as gas and liquefied hydrogen gas are installed on ships or on land. Liquefied natural gas (LNG) tanks, liquefied CO2 tanks, etc. ２ Gas tanks and liquefied hydrogen gas tanks are required to have characteristics in low-temperature environments, particularly hydrogen embrittlement resistance at extremely low temperatures of −196° C. In response to this, by having a welded joint according to the present disclosure, the tank can be made to have excellent hydrogen embrittlement resistance.

[0145] Next, the feasibility and effects of the present disclosure will be explained in more detail using examples and comparative examples. However, the following examples do not limit the present disclosure, and any design changes that are made in accordance with the above and below spirit are all included in the technical scope of the present disclosure.

[0146] The welded joints were obtained by submerged arc welding (SAW) using a solid wire and flux.

[0147] (Steel Plate) As the base material, a steel plate having the chemical composition shown in Table 1-1 and Table 1-2 was prepared. The thickness of the base material steel plate was 20 mm.

[0148] (Production of Welded Joints) Welded joints having weld metal were produced by submerged arc welding (SAW) using a solid wire and flux for the base materials (two steel plates) listed in Tables 2-1 to 2-9. Welded joints having weld metal were produced by SAW for the base materials (two steel plates) listed in Tables 3-1 to 3-9. Welded joints having weld metal were produced by SAW for the base materials (two steel plates) listed in Tables 4-1 to 4-9.

[0149] Two steel plates (base materials 22) were butted together, and groove formation and welding were performed so that the groove shape would be an X-groove with a groove angle θ = 60° as shown in Figure 1. Specifically, after butting the two steel plates (base materials 22), a Y-shaped groove was first formed on one side, buildup welding was performed within this Y-groove, and then a back surface of the Y-groove was subjected to a chipping process to form an X-shaped groove, and buildup welding was performed within this back groove, thereby forming a weld metal 42 with an X-groove shape. The type of welding gas used in gas-shielded arc welding was Ar-20% CO ２ Gas was used. All welding currents during welding were DC, and all wire polarities were positive. The welding conditions were as shown in Table 5. The chemical composition of the weld metal was controlled to be as shown in Tables 2-1 to 2-9, 3-1 to 3-9, and 4-1 to 4-9 by selecting the base metal and adjusting the composition of the solid wire and flux (in the case of SAW).

[0150] The chemical composition, base metal yield stress YS1, weld metal yield stress YS2, ratio of weld metal yield stress YS2 to base metal yield stress YS1 (YS2 / YS1), and fcc percentage for each weld metal number are shown in Tables 1-2, 2-3, 2-6, 2-9, 3-3, 3-6, 3-9, 4-3, 4-6, and 4-9. In Tables 1-1 to 4-9, items that deviate from the requirements of the present disclosure are underlined. In the chemical compositions shown in Tables 1-1 to 4-9, the balance is Fe and impurities.

[0151] In Tables 1-1 and 1-2, comparative example base material No. 12 has a yield stress YS1 of less than 550 MPa. In Tables 2-7 to 2-9, comparative example joint No. A52 has a Ni content of less than 40.0% and a YS2 / YS1 ratio of less than 0.40. In Tables 2-7 to 2-9, comparative example joint No. A53 has a YS2 / YS1 ratio of greater than 0.90. In Tables 3-7 to 3-9, comparative example joint No. B40 has a Mo content of less than 1.0%. In Tables 3-7 to 3-9, comparative example joint No. B41 has a YS2 / YS1 ratio of greater than 0.90. In Tables 4-7 to 4-9, comparative example joint No. C49 has a Mn content of less than 20.00% and a YS2 / YS1 ratio of less than 0.40. In Tables 4-7 to 4-9, Joint No. C50, which is a comparative example, has a YS2 / YS1 ratio of more than 0.90.

[0152] <Evaluation Test> (Evaluation of Hydrogen Embrittlement Resistance Near the Fusion Line FL) The locations from which test specimens were taken are shown in Figures 2 and 3. Figure 2 shows an example of a welded joint having an X-groove with an angle θ = 60°. This welded joint has a base metal 22 (steel plate) and a weld metal 42 formed in the X-groove. Figure 3 shows the locations from which test specimens were taken when the base metal was thin. This welded joint has an X-groove with an angle θ = 60° and has a base metal 24 (steel plate) and a weld metal 44 formed in the X-groove. Charpy test specimens were taken from the obtained welded joint at the sampling position 62C shown in Figure 2. That is, when the thickness of the base metal 22 is t, the Charpy test specimens were taken from a position t / 4 from the surface of the base metal 22 in the thickness direction, with the boundary (fusion line FL) between the base metal 22 and the weld metal 42 as the center, so that the length on the base metal 22 side and the length on the weld metal 42 side were 1:1. However, when it was not possible to take a test piece centered on the t / 4 position due to the thinness of the base metal, a test piece was taken from a taking position 64C so that the edge of the test piece was aligned with a position 1 mm from the surface of the base metal 24 in the plate thickness direction and parallel to the weld line direction, as shown in Figure 3.

[0153] The shape of the groove in the welded joint is not limited to an X-groove, and may be, for example, a V-shaped groove (V-groove). Even in the case of a welded joint having a V-groove, Charpy test specimens are taken from a position that is t / 4 in the thickness direction from the surface of the base metal, where t is the thickness of the base metal. Specifically, from the obtained welded joint, Charpy test specimens are taken from a position that is t / 4 in the thickness direction from the surface of the base metal, with the boundary (fusion line FL) between the base metal and the weld metal as the center, so that the length of the base metal side and the length of the weld metal side are 1:1. However, if the base metal is too thin to take a test specimen centered at the t / 4 position, Charpy test specimens are taken from a position that is 1 mm in the thickness direction from the surface of the base metal, with the boundary (fusion line FL) between the base metal and the weld metal as the center, so that the length of the base metal side and the length of the weld metal side are 1:1.

[0154] The notch position 8 on the Charpy test specimen was the position of the fusion line FL, and three V-notch test specimens with a notch depth of 2 mm were taken. The three test specimens were exposed to 10 MPa hydrogen gas at 25°C for 48 hours, and then the test specimens were removed from the exposure environment and immersed in liquid nitrogen (-196°C) within 60 seconds, and a Charpy impact test was carried out in accordance with JIS Z2242:2005. -Evaluation criteria (hydrogen embrittlement)- A (◯): The average Charpy absorbed energy of the three test specimens was 34 J or more. B (△): The average Charpy absorbed energy of the three test specimens was 27 J or more but less than 34 J. C (×): The average Charpy absorbed energy of the three test specimens was less than 27 J.

[0155]

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[0185] As shown in Tables 2-1 to 4-9, the welded joints of the invention examples, in which the chemical compositions of the base metal and weld metal, the yield stress YS1 of the base metal, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal satisfy the requirements of the present disclosure, are less susceptible to hydrogen embrittlement and have higher Charpy absorbed energy than the welded joints of the comparative examples, even when exposed to a hydrogen environment.

[0186] 22, 24 Base metal 42, 44 Weld metal 62C, 64C Sampling position 8 Notch position

Claims

1. A weld metal joining the base metal and the fcc fraction in the structure is 95% or more, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less, and the base metal has a chemical composition, in mass% with respect to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.05%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities. : 0.100% or less, S: 0.100% or less, Ni: 40.0% to 80.0%, Cr: 0% to 20.0%, Mo: 0% to 20.0%, W: 0% to 5.0%, Nb: 0% to 5.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, A welded joint comprising: Mg: 0% to 1.00%, Zr: 0% to 1.000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.050%, with the balance being Fe and impurities.

2. The welded joint according to claim 1, wherein the base metal has a carbon equivalent Ceq of 0.14 to 0.65, as expressed by the following formula (1): Ceq = [C Ｂ ]+[Si Ｂ ] / 24+[Mn Ｂ ] / 6+[Ni Ｂ ] / 40+[Mo Ｂ ] / 4+[Nb Ｂ ] / 5 (Formula 1) (In Formula 1, [C Ｂ ] is the content (mass%) of C in the base material, and [Si Ｂ ] is the content (mass%) of Si in the base material, and [Mn Ｂ ] is the Mn content (mass%) in the base material, [Ni Ｂ ] represents the Ni content (mass%) in the base material, and [Mo Ｂ ] is the content (mass%) of Mo in the base material, and [Nb Ｂ ] represents the Nb content (mass%) in the base material.

3. A weld metal is provided, joining the base metal and having an fcc ratio of 95% or more in its structure, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less, and the base metal has a chemical composition, in mass% relative to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.050%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities. : 0.100% or less, S: 0.100% or less, Ni: 1.0% to 20.0%, Cr: 1.0% to 10.0%, Mo: 1.0% to 10.0%, W: 0% to 3.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.0000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V :0%~3.0000%, Ca:0%~1.000000%, The weld metal contains Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.300%, and O: 0% to 0.100%, with the balance being Fe and impurities, and the content (mass%) of Mn in the weld metal is [Mn Ｗ ], the content (mass%) of Ni in the weld metal is [Ni Ｗ ], [Mn Ｗ ]+[Ni Ｗ ]≧5.00%.

4. The welded joint according to claim 3, wherein the weld metal has a nickel equivalent Nieq, as shown in the following formula (2), of 25.00 to 60.

00. Nieq = [Ni Ｗ ]+0.65×[Cr Ｗ ]+0.98×[Mo Ｗ ]+1.05×[Mn Ｗ ]+0.35×[Si Ｗ ]+12.6×[C Ｗ ] (Formula 2) (In Formula 2, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ ] is the content (mass%) of Mo in the weld metal, and [Mn Ｗ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ ] represents the C content (mass%) in the weld metal.

5. A weld metal joining the base metal and having an fcc ratio of 95% or more in its structure, wherein the base metal has a yield stress YS1 of 550 MPa or more and 700 MPa or less, and the ratio of the yield stress YS2 of the weld metal to the yield stress YS1 of the base metal is 0.40 or more and 0.90 or less, and the base metal has a chemical composition, in mass% with respect to the total mass of the base metal, of C: 0.01% to 0.10%, Si: 0.03% to 0.50%, Mn: 0.10% to 2.00%, P: 0.010% or less, S: 0.010% or less, Ni: 5.00% to 10.30%, Cr: 0% to 0.60%, Mo: 0% to 0.50%, Nb: 0% to 0.50%, The weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of Cu: 0% to 1.00%, Co: 0% to 0.050%, Al: 0.0001% to 0.100%, N: 0.0015% to 0.0060%, O: 0.0001% to 0.0030%, V: 0% to 0.060%, Ti: 0% to 0.020%, B: 0% to 0.0020%, Ca: 0% to 0.0040%, and REM: 0% to 0.0050%, with the balance being Fe and impurities, and the weld metal has a chemical composition, in mass % relative to the total mass of the weld metal, of C: more than 0.10% to 0.70%, Si: 0.05% to 1.00%, Mn: more than 20.00% to 30.00%, P : 0.100% or less, S: 0.100% or less, Ni: 0% to 14.0%, Cr: 0% to 14.0%, Mo: 0% to 5.0%, W: 0% to 5.0%, Nb: 0% to 3.0%, Ta: 0% to 3.000%, Cu: 0% to 1.000%, Co: 0% to 1.0000%, Pb: 0% to 1.000%, Sn: 0% to 1.000%, Al: 0.0001% to 1.0000%, Ti: 0% to 1.0000%, B: 0% to 0.10000%, V: 0% to 3.0000%, Ca: 0% to 1.000000%, A welded joint comprising: Mg: 0% to 1.0000%, Zr: 0% to 1.0000%, Hf: 0% to 1.0000%, REM: 0% to 0.50000%, N: 0% to 0.200%, and O: 0% to 0.100%, with the balance being Fe and impurities.

6. The welded joint according to claim 5, wherein the weld metal has a stacking fault energy SFE of 10.00 or more, as expressed by the following formula (3): SFE = -7.1 + 2.8 × [Ni Ｗ ]+0.49×[Cr Ｗ ]+2×[Mo Ｗ ]+0.75×[Mn Ｗ ]−2×[Si Ｗ ]−5.7×[C Ｗ ]−24×[N Ｗ ] (Formula 3) (In Formula 3, [Ni Ｗ ] is the Ni content (mass%) in the weld metal, [Cr Ｗ ] represents the Cr content (mass%) in the weld metal, and [Mo Ｗ ] is the content (mass%) of Mo in the weld metal, and [Mn Ｗ ] is the Mn content (mass%) in the weld metal, and [Si Ｗ ] is the content (mass%) of Si in the weld metal, [C Ｗ ] is the content (mass%) of C in the weld metal, and [N Ｗ ] represents the N content (mass%) in the weld metal.

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