Weld metal, weld joint, and weld structure

Abstract

Provided is a weld metal in which chemical components thereof are, in mass percentage with reference to the total mass of the weld metal, 0.2-0.8% of C, 0.03-0.5% of Si, 5.1-20% of Mn, 0-0.05% of P, 0-0.05% of S, 0-5% of Cu, 6-20% of Ni, 0-10% of Cr, 0-10% of Mo, 0-5% of Nb, 0-5% of V, 0-5% of Ta, 0-5% of Hf, 0-5% of Ti, 0-5% of Zr, 0-1% of Co, 0-1% of Pb, 0-1% of Sn, 0-5% of W, 0-0.1% of Mg, 0.001-0.1% of Al, 0-5% of Ca, 0-0.5% of B, 0-0.5% of REM, 0-0.5% of N, and 0.001-0.15% of O, the balance being Fe and impurities. The weld metal contains greater than 1% of Nb, greater than 1% of V, no less than 0.001% of Ta, no less than 0.001% of Hf, no less than 0.1% of Ti, and / or greater than 0.5% of Zr as at least one type of element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr.

Description

Weld metals, welded joints, and welded structures

[0001] The present disclosure relates to weld metals, weld joints, and welded structures.

[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, as well as natural gas, which 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. Ni-based low-temperature steels containing 6 to 9% Ni are used for steel materials used in liquid hydrogen tanks, liquid carbon dioxide tanks, LNG tanks, and the like, due to the need to ensure toughness at extremely low temperatures (e.g., −196°C). 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 typically designed with a Ni content of 70%.

[0003] For example, as a welding material with a Ni content of 70%, Patent Document 1 describes a material with a Ni content of 35 to 70%, in which TiO ２ , SiO ２ and ZrO ２ in a total amount of 4.0 mass % or more, and further, Mn oxide is MnO ２ The content is 0.6 to 1.2 mass % in terms of TiO. ２ , SiO ２ , ZrO ２ and MnO ２ The contents of (equivalent amounts) are expressed in mass % as [TiO ２ ], [SiO ２ ], [ZrO ２ ] and [MnO ２ ], [TiO ２ ] / [ZrO ２ ] is 2.3 to 3.3, [SiO ２ ] / [ZrO ２ ] is 0.9 to 1.5, and ([TiO ２ ]+[SiO ２ ]+[ZrO ２ ]) / [MnO ２] is 5 to 13.

[0004] Japanese Patent Application Laid-Open No. 2008-246507

[0005] As mentioned above, austenitic welding materials have been used to obtain weld metals with excellent low-temperature toughness. However, austenitic welding materials have the property of being prone to hot cracking. Therefore, weld metals that suppress the occurrence of hot cracking are desired.

[0006] An object of the present disclosure is to provide a weld metal in which the occurrence of hot cracking is suppressed, a weld joint including the weld metal, and a welded structure including the weld joint.

[0007] The means for solving the problem include the following aspects. <1> The chemical composition, in mass % relative to the total mass of the weld metal, is: C: 0.20 to 0.80%, Si: 0.03 to 0.50%, Mn: 5.1 to 20.0%, P: 0 to 0.050%, S: 0 to 0.050%, Cu: 0 to 5.0%, Ni: 6.0 to 20.0%, Cr: 0 to 10.0%, Mo: 0 to 10.0%, Nb: 0 to 5.00%, V: 0 to 5.00%, Ta: 0 to 5.000%, Hf: 0 to 5.000%, Ti: 0 to 5.00%, Zr: 0 to 5.000%, Co: 0 to 1.0%, Pb: 0 to 1.0%, Sn: 0 to 1.0%, W : 0 to 5.0%, Mg: 0 to 0.10%, Al: 0.001 to 0.100%, Ca: 0 to 5.00%, B: 0 to 0.500%, REM: 0 to 0.500%, N: 0 to 0.500%, O: 0.001 to 0.150%, and the balance: Fe and impurities, and the weld metal contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the following amounts: Nb: more than 1.00%, V: more than 1.00%, Ta: 0.001% or more, Hf: 0.001% or more, Ti: more than 0.10%, Zr: more than 0.500%. <2> The weld metal according to <1>, wherein the mass ratio of the Mn content to the Ni content (Ni / Mn) is 0.33 or more. <3> The weld metal according to <1> or <2>, wherein the weld metal contains at least two elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr, each in the above-mentioned amounts. <4> The weld metal according to any one of <1> to <3>, wherein the fcc content determined by a magnetic induction method is 70% by volume or more. <5> A welded joint comprising the weld metal according to any one of <1> to <4>. <6> A welded structure comprising the welded joint according to <5>.

[0008] According to the present disclosure, there are provided a weld metal in which the occurrence of hot cracking is suppressed, a weld joint having the weld metal, and a welded structure having the weld joint.

[0009] Fig. 1 is a schematic cross-sectional view showing a base material having a groove used in Examples. Fig. 2 is a schematic cross-sectional view for explaining a test device for a FISCO cracking test. Fig. 3 is a schematic cross-sectional view for explaining a test device for a FISCO cracking test. Fig. 4 is a schematic cross-sectional view showing a welded joint sample for explaining high-temperature cracking that occurs in a weld metal portion in a FISCO cracking test.

[0010] An embodiment that is an example of the present disclosure will be described. In this specification, when a numerical range expressed using "to" is used, unless the numerical values ​​before and after "to" are followed by "greater than" or "less than," it means a range that includes these numerical values ​​as the lower and upper limits. Furthermore, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," it means a range that does not include these numerical values ​​as the lower or upper limit. In the numerical ranges described in stages in this specification, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range described in stages, or may be replaced by a value shown in an example. Furthermore, the lower limit of a certain numerical range may be replaced by the lower limit of another numerical range described in stages, or may be replaced by a value shown in an example. Furthermore, with regard to the content, "%" means "mass %." When the content (%) is "0 to," it means that the component is an optional component and may not be included.

[0011] <Weld Metal> A weld metal according to an embodiment of the present disclosure has a predetermined chemical composition and contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the content described below.

[0012] The weld metal according to the present disclosure has the above-described configuration, which suppresses the occurrence of hot cracking.

[0013] Conventionally, austenitic welding materials have been used as welding materials that can produce weld metals with excellent low-temperature toughness, and are used, for example, for steels containing 6 to 9% Ni used for LNG tanks. However, austenitic welding materials have the property of being prone to hot cracking. This is thought to be because austenitic welding materials solidify in the γ phase (face-centered cubic lattice fcc), which causes severe solidification segregation of P, S, C, Si, and the like, resulting in a decrease in the melting point of the liquid phase in the (γ phase + liquid phase) state, and tensile stress due to solidification shrinkage is applied to the liquid phase, causing hot cracking.

[0014] In response to this, the inventors focused on the crystallization of carbides in the liquid phase as a method for increasing the melting point of the liquid phase during solidification. Solidification segregation occurs as solidification progresses in the weld metal, thereby lowering the melting point of the liquid phase. P, S, C, and Si are concentrated in this liquid phase, and by crystallizing carbides in this liquid phase, the C concentration in the liquid phase can be significantly reduced. As a result, the melting point of the liquid phase increases, and hot cracking is suppressed. Therefore, the weld metal according to an embodiment of the present disclosure is configured to contain at least one element selected from the group consisting of Ti, Zr, V, Hf, Nb, and Ta, which are elements that easily form carbides, in a predetermined content. When the weld metal contains a predetermined amount of at least one element selected from the group consisting of Ti, Zr, V, Hf, Nb, and Ta, the C concentration in the liquid phase decreases due to the crystallization of carbides, thereby increasing the melting point of the liquid phase and suppressing hot cracking.

[0015] An example of an index of high-temperature cracking is the FISCO cracking test specified in JIS Z 3155 (1993), and in the weld metal according to the embodiment of the present disclosure, it is preferable that the cracking rate in the FISCO cracking test be 15% or less.

[0016] The reasons for limiting the requirements (including optional requirements) for constituting the weld metal according to the present disclosure will be specifically described below.

[0017] (Chemical Composition of Weld Metal) The chemical composition of the weld metal will be described in detail below. In the description of the chemical composition of the weld metal, "%" means "mass % relative to the total mass of the weld metal" unless otherwise specified.

[0018] The chemical composition of the weld metal is: C: 0.20 to 0.80%, Si: 0.03 to 0.50%, Mn: 5.1 to 20.0%, P: 0 to 0.050%, S: 0 to 0.050%, Cu: 0 to 5.0%, Ni: 6.0 to 20.0%, Cr: 0 to 10.0%, Mo: 0 to 10.0%, Nb: 0 to 5.00%, V: 0 to 5.00%, Ta: 0 to 5.000%, Hf: 0 to 5.000%, Ti: 0 to 5.00%, Zr: 0 to 5.000%, Co: 0 to 1.0%, Pb: 0 to 1.0%, Sn: 0 to 1.0%, W: 0 to 5.0%, Mg: 0 to 0.10%, Al: 0.001 to 0.100%, Ca: 0 to 5.00%, B: 0 to 0.500%, REM: 0 to 0.500%, N: 0 to 0.500%, O: 0.001 to 0.150%, and the balance: Fe and impurities, and the steel sheet contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the following amounts: Nb: more than 1.00%, V: more than 1.00%, Ta: 0.001% or more, Hf: 0.001% or more, Ti: more than 0.10%, Zr: more than 0.500%

[0019] (C: 0.20 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 set to 0.20 to 0.80%. The lower limit of the C content of the weld metal may preferably be 0.22%, 0.25%, 0.27%, 0.30%, 0.32%, 0.35%, 0.37%, or 0.40%. The upper limit of the C content of the weld metal is preferably 0.75%, 0.70%, 0.65%, 0.60%, 0.55%, or 0.50%.

[0020] (Si: 0.03 to 0.50%) Si is a deoxidizing element. If the Si content of the weld metal is too low, the O 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 solidification segregation occurs, resulting in hot cracking. Therefore, the Si content of the weld metal is set to 0.03 to 0.50%. The lower limit of the Si content of the weld metal is preferably 0.04%, 0.05%, or 0.08%. The upper limit of the Si content of the weld metal is preferably 0.48%, 0.45%, 0.40%, 0.35%, 0.30%, or 0.20%.

[0021] (Mn: 5.1 to 20.0%) Mn is an austenite-stabilizing element. If the Mn content of the weld metal is too low, the austenitization of the weld metal will be difficult to progress, resulting in a deterioration of low-temperature toughness. Mn is also an element that functions as a deoxidizer to improve the cleanliness of the weld metal. Mn is also an element that forms MnS, thereby rendering S in the weld metal harmless and improving the low-temperature toughness of the weld metal. In addition, Mn has the effect of preventing hot cracking. On the other hand, if the Mn content of the weld metal is excessive, it is likely to segregate in the weld metal, causing significant embrittlement in the segregated areas. Therefore, the Mn content of the weld metal is set to 5.1 to 20.0%. The lower limit of the Mn content of the weld metal is preferably 5.5%, 5.7%, 6.0%, 7.0%, 8.0%, 9.0%, or 10.0%. The upper limit of the Mn content of the weld metal is preferably 19.0%, 18.0%, 17.0%, 15.0%, or 14.5%.

[0022] (P: 0 to 0.050%) P is an impurity element that promotes hot cracking or 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 is set to 0%. However, from the viewpoint of reducing deP costs, the P content of the weld metal should be 0.003% or more. On the other hand, if the P content of the weld metal is 0.050% or less, the adverse effects of P are within an acceptable range. Therefore, the P content of the weld metal is set to 0 to 0.050%. In order to effectively suppress hot cracking or a decrease in toughness, the P content of the weld metal is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0023] (S: 0 to 0.050%) S is an impurity element that promotes hot cracking or 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 is set to 0%. However, from the viewpoint of reducing desulfurization costs, the S content of the weld metal should be 0.003% or more. On the other hand, if the S content of the weld metal is 0.050% 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 to 0.050%. In order to effectively suppress hot cracking or a decrease in toughness, the S content of the weld metal is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0024] (Cu: 0 to 5.0%) 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 5.0%. The lower limit of the Cu content in the weld metal is preferably 0.3%, 0.5%, or 0.7%. The upper limit of the Cu content in the weld metal is preferably 4.5%, 4.0%, or 3.5%.

[0025] (Ni: 6.0 to 20.0%) Ni is an austenite stabilizing element. If the Ni content of the weld metal is too low, the austenitization of the weld metal will be difficult to progress, and low-temperature toughness will deteriorate. On the other hand, if the Ni content of the weld metal is increased, the cost of the weld metal will increase. Therefore, the Ni content of the weld metal is set to 6.0 to 20.0%. The lower limit of the Ni content of the weld metal is preferably 6.5%, 7.0%, 7.5%, or 8.0%. The upper limit of the Ni content of the weld metal is preferably 19.0%, 17.0%, 15.0%, or 13.0%.

[0026] (Cr: 0 to 10.0%) 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 in the weld metal is excessive, the solid-liquid coexistence temperature range of the molten metal will be wider, making hot cracking more likely to occur. Therefore, the Cr content in the weld metal is set to 0 to 10.0%. The lower limit of the Cr content in the weld metal is preferably 1.0%, 2.0%, or 3.0%. The upper limit of the Cr content in the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0027] (Mo: 0 to 10.0%) 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 10.0%. The lower limit of the Mo content of the weld metal is preferably 1.0%, 2.0%, or 3.0%. The upper limit of the Mo content of the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0028] (Nb: 0 to 5.00%) Nb may be contained in the weld metal because it forms carbides in the weld metal and increases the strength of the weld metal. However, 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 5.00%. The lower limit of the Nb content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%. The upper limit of the Nb content in the weld metal is preferably 4.50%, 4.00%, 3.50%, 3.00%, or 2.50%. Note that when Nb is added to crystallize carbides in the liquid phase and reduce the C concentration in the liquid phase in order to suppress hot cracking, the lower limit of the Nb content in the weld metal is preferably within the range described below.

[0029] (V: 0 to 5.00%) 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 may occur in the weld metal. Therefore, the V content in the weld metal is set to 0 to 5.00%. The lower limit of the V content in the weld metal is preferably 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%. The upper limit of the V content in the weld metal is preferably 4.50%, 4.00%, 3.50%, or 3.00%. Note that when V is added to crystallize carbides in the liquid phase and reduce the C concentration in the liquid phase in order to suppress hot cracking, the lower limit of the V content in the weld metal is preferably within the range described below.

[0030] (Ta: 0 to 5.000%) Ta 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 Ta content in the weld metal is excessive, a large amount of coarse carbonitrides will precipitate, which may actually reduce the toughness of the weld metal. Therefore, the Ta content in the weld metal is set to 0 to 5.000%. The lower limit of the Ta content in the weld metal is preferably 0.001%, 0.003%, 0.005%, 0.010%, 0.020%, 0.030%, or 0.050%. The upper limit of the Ta content in the weld metal is preferably 4.500%, 4.000%, 3.500%, 3.000%, 2.000%, 1.000%, 0.500%, 0.200%, or 0.100%. When Ta is added to crystallize carbides in the liquid phase to reduce the C concentration in the liquid phase in order to suppress hot cracking, the lower limit of the Ta content in the weld metal is preferably within the range described below.

[0031] (Hf: 0 to 5.000%) Hf 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, an excessive Hf content in the weld metal may result in a decrease in the toughness of the weld metal. Therefore, the Hf content in the weld metal is set to 0 to 5.000%. The lower limit of the Hf content in the weld metal is preferably 0.001%, 0.002%, 0.005%, 0.010%, 0.020%, 0.030%, or 0.040%. The upper limit of the Hf content in the weld metal is preferably 4.500%, 4.000%, 3.500%, 3.000%, 2.000%, 1.000%, 0.500%, 0.200%, or 0.100%. When Hf is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Hf content in the weld metal is preferably within the range described below.

[0032] (Ti: 0 to 5.00%) 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, excessive Ti content in the weld metal may cause carbides to form in the weld metal, which may deteriorate the toughness of the weld metal. Therefore, the Ti content in the weld metal is set to 0 to 5.00%. The lower limit of the Ti content in the weld metal is preferably 0.003%, 0.01%, 0.02%, or 0.03%. The upper limit of the Ti content in the weld metal is preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.00%, or 1.50%. Note that when Ti is added to crystallize carbides in the liquid phase to lower the C concentration in the liquid phase in order to suppress hot cracking, the lower limit of the Ti content in the weld metal is preferably within the range described below.

[0033] (Zr: 0 to 5.000%) Zr can stabilize the bead shape during welding to obtain the weld metal, so it may be included in the weld metal. On the other hand, an excessive Zr content in the weld metal may increase the oxygen content in the weld metal, potentially deteriorating low-temperature toughness. Therefore, the Zr content in the weld metal is set to 0 to 5.000%. The lower limit of the Zr content in the weld metal is preferably 0.003%, 0.01%, 0.02%, or 0.03%. The upper limit of the Zr content in the weld metal is preferably 4.50%, 4.00%, 3.50%, 3.00%, 2.00%, 1.50%, or 1.00%. Note that when Zr is added to crystallize carbides in the liquid phase to lower the C concentration in the liquid phase in order to suppress hot cracking, the lower limit of the Zr content in the weld metal is preferably within the range described below.

[0034] (Co: 0 to 1.0%) Co is an element that increases the strength of the weld metal through solid solution strengthening, and therefore 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 1.0%. The lower limit of the Co content of the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%. The upper limit of the Co content of the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.

[0035] (Pb: 0 to 1.0%) 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 in the weld metal is excessive, hot cracking occurs. Therefore, the Pb content in the weld metal is set to 0 to 1.0%. The lower limit of the Pb content in the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%. The upper limit of the Pb content in the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.

[0036] (Sn: 0 to 1.0%) 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 1.0%. The lower limit of the Sn content of the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%. The upper limit of the Sn content of the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.

[0037] (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%, 0.2%, 0.5%, 0.8%, or 1.0%. The upper limit of the W content of the weld metal is preferably 4.8%, 4.5%, 4.3%, or 4.0%.

[0038] (Mg: 0 to 0.10%) Mg is a deoxidizing element that is effective in reducing oxygen and improving toughness, and therefore may be contained in the weld metal. On the other hand, if the Mg content in the weld metal is excessive, the arc becomes unstable during the welding operation to obtain the weld metal, increasing spatter and blowholes, and degrading welding workability. Therefore, the Mg content in the weld metal is set to 0 to 0.10%. The lower limit of the Mg content in the weld metal is preferably 0.005%, 0.01%, 0.02%, 0.03%, or 0.04%. The upper limit of the Mg content in the weld metal is preferably 0.09%, 0.08%, 0.07%, or 0.06%.

[0039] (Al: 0.001 to 0.100%) 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 or oxides 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 0.001 to 0.100%. The lower limit of the Al content of the weld metal is preferably 0.003%, 0.005%, 0.010%, 0.020%, or 0.030%. The upper limit of the Al content of the weld metal is preferably 0.090%, 0.080%, or 0.070%.

[0040] (Ca: 0 to 5.00%) 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 in the weld metal is set to 0 to 5.00%. The lower limit of the Ca content in the weld metal is preferably 0.01%, 0.02%, or 0.03%. The upper limit of the Ca content in the weld metal is preferably 4.8%, 4.5%, 4.3%, 4.0%, 3.0%, 2.0%, 1.0%, or 0.5%.

[0041] (B: 0 to 0.500%) 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, M ２３ (C, B) ６ precipitates, causing a deterioration in toughness. Therefore, the B content of the weld metal is set to 0 to 0.5000%. The lower limit of the B content of the weld metal is preferably 0.0005%, 0.001%, or 0.002%. The upper limit of the B content of the weld metal is preferably 0.480%, 0.450%, 0.430%, 0.400%, 0.300%, 0.200%, 0.100%, or 0.050%.

[0042] (REM: 0 to 0.500%) 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 of 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 of the weld metal is set to 0 to 0.500%. The lower limit of the REM content of the weld metal is preferably 0.001%, 0.002%, or 0.005%. The upper limit of the REM content of the weld metal is preferably 0.480%, 0.450%, 0.430%, 0.400%, 0.300%, 0.200%, 0.100%, or 0.050%.

[0043] (N: 0 to 0.500%) N 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, an excessive N content in the weld metal increases the occurrence of blowouts, causing weld defects. Therefore, the N content in the weld metal is set to 0 to 0.500%. The lower limit of the N content in the weld metal is preferably 0.001%, 0.005%, 0.010%, 0.020%, or 0.050%. The upper limit of the N content in the weld metal is preferably 0.450%, 0.400%, 0.350%, 0.300%, 0.200%, or 0.100%.

[0044] (O: 0.001 to 0.150%) O is contained in the weld metal as an impurity. 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 0.150% or less. 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 less. The lower limit of the O content in the weld metal is preferably 0.002% or 0.003%. The upper limit of the O content in the weld metal is preferably 0.130% or 0.100%.

[0045] (Balance: Fe and impurities) The balance of the chemical components of the weld metal is Fe and impurities. The impurities refer to components that are mixed in during industrial production of the weld metal due to raw materials such as ore or scrap, or 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.

[0046] (Nb, V, Ta, Hf, Ti, and Zr) The weld metal contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr (hereinafter simply referred to as "specific element") in the following contents. By containing the specific element in the following contents, carbides can be crystallized in the liquid phase, reducing the C concentration in the liquid phase and suppressing hot cracking. Nb: more than 1.00% V: more than 1.00% Ta: 0.001% or more Hf: 0.001% or more Ti: more than 0.10% Zr: more than 0.500%

[0047] Nb: More than 1.00% When Nb is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Nb content in the weld metal is more than 1.00%. The lower limit of the Nb content in the weld metal is preferably 1.10%, 1.20%, 1.30%, or 1.50%.

[0048] V: More than 1.00% When V is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the V content in the weld metal is more than 1.00%. The lower limit of the V content in the weld metal is preferably 1.10%, 1.20%, 1.30%, 1.50%, 1.80%, or 2.00%.

[0049] Ta: 0.001% or more When Ta is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Ta content in the weld metal is 0.001% or more. The lower limit of the Ta content in the weld metal is preferably 0.002%, 0.005%, 0.010%, 0.030%, 0.050%, or 0.060%.

[0050] Hf: 0.001% or more When Hf is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Hf content in the weld metal is 0.001% or more. The lower limit of the Hf content in the weld metal is preferably 0.002%, 0.005%, 0.010%, 0.030%, 0.040%, 0.050%, or 0.060%.

[0051] Ti: More than 0.10% When Ti is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Ti content in the weld metal is more than 0.10%. The lower limit of the Ti content in the weld metal is preferably 0.11%, 0.13%, 0.20%, 0.30%, 0.50%, 0.80%, or 1.00%.

[0052] Zr: More than 0.500% When Zr is added to reduce the C concentration in the liquid phase by crystallizing carbides in the liquid phase in order to suppress hot cracking, the lower limit of the Zr content in the weld metal is more than 0.500%. The lower limit of the Zr content in the weld metal is preferably 0.510%, 0.530%, 0.550%, 0.600%, or 0.630%.

[0053] Among the specific elements, the weld metal preferably contains at least one of Ta and Hf in the following amounts. By containing at least one of Ta and Hf, which are considered to have a higher carbide forming ability, the formation of carbides is promoted, and as a result, hot cracking can be further suppressed. Ta: 0.001% or more Hf: 0.001% or more

[0054] - Containing two or more specific elements It is preferable to contain two or more of the specific elements (i.e., elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr), each at the above-mentioned content. By containing two or more specific elements, hot cracking in the weld metal is further suppressed. This is because the formation of carbides is more promoted by containing two or more specific elements than when only one of the specific elements is added at the above-mentioned content. This is because when only one of the specific elements is added, a carbide containing that one element is formed, but the amount of carbide produced is limited due to the existence of reaction equilibrium. On the other hand, it is thought that the activity of the carbide is reduced (the activity of the carbide-forming element is increased) by containing two or more specific elements, thereby promoting the reaction.

[0055] (Total of Mn Content and Ni Content (Mn+Ni)) Mn and Ni are each an austenite stabilizing element and improve the low-temperature toughness of the weld metal. On the other hand, Ni is an expensive metal. Therefore, in order to improve the low-temperature toughness of the weld metal while suppressing the cost 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 that the total of the Mn content and Ni content (Mn+Ni) be 11.5% or more, and more preferably 12.0% or more, 13.0% or more, or 15.0% or more.

[0056] Furthermore, excessive increase in Mn reduces stacking fault energy and deteriorates toughness. 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 that the total of the Mn content and Ni content (Mn + Ni) in the weld metal is 37.0% or less. The total of the Mn content and Ni content (Mn + Ni) in the weld metal is more preferably 35.0% or less, 32.0% or less, or 30.0% or less.

[0057] (Total of Mn Content, Ni Content, and Cr Content (Mn+Ni+Cr)) Mn, Ni, and Cr are each an austenite-stabilizing element and improve the low-temperature toughness of the weld metal. On the other hand, Ni is an expensive metal. Therefore, in order to improve the low-temperature toughness of the weld metal while suppressing the cost of the weld metal, it is preferable that the Mn content, Ni content, and Cr content in the weld metal each satisfy the above-mentioned ranges, and that the total of the Mn content, Ni content, and Cr content (Mn+Ni+Cr) in the weld metal be 15.0% or more. The total of the Mn content, Ni content, and Cr content (Mn+Ni+Cr) in the weld metal is more preferably 17.0% or more, 19.0% or more, 20.0% or more, 22.0% or more, 24.0% or more, 26.0% or more, 28.0% or more, or 30.0% or more.

[0058] On the other hand, by not including an excessive Mn content, stacking fault energy does not become too low, thereby ensuring toughness. Furthermore, by not including an excessive Cr content, the amount of low-melting-point compounds in the molten metal can be reduced, and the solid-liquid coexistence temperature range of the molten metal can be prevented from widening, thereby suppressing the occurrence of hot cracking. Therefore, from the viewpoints of reducing the cost of the weld metal, improving the low-temperature toughness of the weld metal, reducing the amount of low-melting-point compounds generated in the molten metal, and suppressing the occurrence of hot cracking, it is preferable that the Mn content, Ni content, and Cr content in the weld metal each satisfy the above-mentioned ranges, and that the total of the Mn content, Ni content, and Cr content (Mn + Ni + Cr) in the weld metal be 47.0% or less. The total of the Mn content, Ni content, and Cr content (Mn + Ni + Cr) in the weld metal is more preferably 45.0% or less, 42.0% or less, or 40.0% or less.

[0059] (Mass Ratio of Mn Content to Ni Content (Ni / Mn)) Mn and Ni are each an austenite stabilizing element and improve the low-temperature toughness of the weld metal. On the other hand, Ni is an expensive metal, and if the Mn content is further increased excessively, the stacking fault energy decreases and the toughness deteriorates. Therefore, from the viewpoint of improving the low-temperature toughness of the weld metal while suppressing the cost of the weld metal, it is preferable that the mass ratio of the Mn content to the Ni content (Ni / Mn) in the weld metal be 0.33 or more. The lower limit of the mass ratio of the Mn content to the Ni content (Ni / Mn) in the weld metal is more preferably 0.50, 0.70, 1.00, 1.10, or 1.20. The upper limit of the mass ratio of the Mn content to the Ni content (Ni / Mn) in the weld metal is preferably 3.80, 3.50, 3.30, or 3.00.

[0060] (FCC Content Determined by Magnetic Induction Method) In order to improve the low-temperature toughness of the weld metal, it is preferable to increase the proportion of austenite in the structure of the weld metal. Therefore, it is preferable that the FCC content in the weld metal be 70% by volume or more. The FCC content is more preferably 80% by volume or more, or 90% by volume or more, and may be 100% by volume. The remainder of the structure is BCC.

[0061] The fcc content in the structure of weld metal can be determined by the following method: A sample is taken from the weld metal, the bcc content (volume %) is measured on the surface of the sample using a magnetic induction method, and the arithmetic mean of the measured bcc contents is determined. The obtained average bcc content is used to determine the fcc content (volume %) in the structure of the weld metal using the following formula: fcc content = 100 - bcc content Note that the sample from the weld metal is taken from the center of the weld metal so that the base metal is not included.

[0062] (Tensile Strength) The tensile strength of the weld metal is preferably, for example, 590 to 1200 MPa. The tensile strength can be measured by conducting a tensile test on the weld metal in accordance with JIS Z3111:2005.

[0063] <Welded joint and welded structure> Next, a welded joint and a welded structure according to the present disclosure will be described. A welded joint according to the present disclosure has a weld metal according to the present disclosure. For example, a welded joint according to the present disclosure includes a steel material serving as a base material and a welded portion constituted by a weld metal and a weld heat-affected zone. Furthermore, a welded structure according to the present disclosure has a welded joint according to the present disclosure.

[0064] The welded joint according to the present disclosure includes the weld metal according to the present disclosure, and therefore is inexpensive and has excellent low-temperature toughness.

[0065] Here, a method for manufacturing a welded joint according to the present disclosure will be described. Note that the manufacturing method described below is an example, and the method for manufacturing a welded joint according to the present disclosure is not limited to the following method.

[0066] The welded joint according to the present disclosure can be produced by welding a steel material as a base material using a welding material.

[0067] For example, in the method for manufacturing a welded joint according to the present disclosure, a welded joint is obtained by gas-shielded arc welding of steel materials using a flux-cored wire. In this case, the chemical components of the weld metal include components derived from the flux-cored wire, which is the welding material, and the steel material, which is the base material.

[0068] The method for manufacturing a welded joint according to the present disclosure can be achieved by submerged arc welding using a solid wire and flux. For example, in submerged arc welding, granular flux is dispersed on the weld line in advance, the solid wire is fed into the flux, and welding is performed using arc heat generated between the solid wire and the steel material in the flux. In this case, the chemical components of the weld metal include components derived from the solid wire and flux, which are the welding materials, and the steel material, which is the base material.

[0069] Furthermore, the welded joint according to the present disclosure can be obtained by a welding method such as shielded metal arc welding, simple electrogas arc welding, electroslag welding, TIG welding, and gas-shielded welding using a solid wire, etc. In this case, the chemical components of the weld metal include components derived from the welding material and the steel base material.

[0070] The type of base material of the welded joint according to the present disclosure, i.e., the steel material (weld material) used in the manufacturing method of the welded joint described above, is not particularly limited, but for example, Ni-based low-temperature steel containing 6 to 9% Ni and having a plate thickness of 20 mm or more can be suitably used.

[0071] Next, the feasibility and effects of the present disclosure will be explained in more detail using examples and comparative examples of the present disclosure. However, the following examples do not limit the present disclosure, and any design changes that are made in accordance with the intent described above and below are all included in the technical scope of the present disclosure.

[0072] Weld metals were obtained by the following methods: submerged arc welding (SAW) using a solid wire and flux, shielded metal arc welding (SMAW) using a shielded metal arc welding rod, arc welding (flux-cored arc welding (FCAW)) using a flux-cored wire, and tungsten inert gas (TIG) using a filler metal.

[0073] 1. Submerged Arc Welding (SAW) Using Solid Wire and Flux (Production of Solid Wire) Solid wire was produced by the method described below. First, steel was melted and forged, then rolled into a rod, and the rod was drawn to obtain solid wire. In this way, a solid wire with a final wire diameter of 2.4 mm was produced. After production, a lubricant was applied to the wire surface.

[0074] (Production of Welded Joint) The obtained solid wire was used to produce a welded joint having a weld metal by submerged arc welding. Specifically, submerged arc welding was performed using the solid wire in combination with NITTETSU FLUX 10H, a submerged arc welding flux manufactured by Nippon Steel Welding Co., Ltd. A steel plate (20 mm thick x 120 mm wide x 300 mm thick) having the composition shown in Table 1 was used as the steel plate (base metal) to be welded. As shown in FIG. 1 , a groove was formed in base metals 2A and 2B up to half the plate thickness so that the groove angle was 90°. The base metals 2A and 2B were butted together with the gap between them adjusted to 1 mm. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were the "submerged arc welding (SAW)" conditions listed in Table 2. In this manner, a welded joint having a weld metal was produced. The chemical composition of the obtained weld metal was controlled by adjusting the composition of the solid wire. The chemical compositions of the weld metals in the produced welded joints are shown in Tables 3-1 to 3-4 (Nos. 1 to 8, 33, 34, and 39).

[0075] 2. Shielded Arc Welding (SMAW) Using Shielded Electrodes (Manufacture of Shielded Electrodes) Shielded arc welding electrodes were manufactured by the method described below. First, a flux was applied to a core wire, and the core wire was baked at a temperature range of 300 to 500°C for 1 to 3 hours to manufacture a prototype shielded arc welding electrode. The final welding rod diameter of the obtained shielded arc welding electrode was φ6.0 mm, and the average thickness of the flux was 1.0 mm.

[0076] (Production of Welded Joints) Welded joints having weld metal were produced by shielded metal arc welding using the resulting shielded metal arc welding electrodes. A steel plate (20 mm thick x 120 mm wide x 300 mm thick) with the chemical composition shown in Table 1 was used as the steel plate (base metal) to be welded. As shown in FIG. 1 , a groove was formed in base metals 2A and 2B up to half the plate thickness to create a 90° groove angle. The base metals 2A and 2B were butted together with a gap of 1 mm between them. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were those for "shielded metal arc welding (SMAW)" listed in Table 2. In this way, welded joints having weld metal were produced. The chemical composition of the resulting weld metal was controlled by adjusting the chemical composition of the shielded metal arc welding electrodes. The chemical compositions of the weld metals in the produced welded joints are shown in Tables 3-1 to 3-4 (Nos. 9 to 16, 35, 36, and 40).

[0077] 3. Arc Welding Using Flux-Cored Wire (FCAW) (Production of Flux-Cored Wire) Flux-cored wire was produced by the method described below. First, a steel strip was fed longitudinally and formed using a forming roll to obtain a U-shaped open tube. Flux was supplied into the open tube through the opening, and opposing edges of the opening were butt-welded to obtain a seamless tube. This seamless tube was drawn to obtain a flux-cored wire without slit-like gaps. In this way, flux-cored wires with a final wire diameter of 1.2 mm were produced as prototypes. Note that during the drawing process, these flux-cored wires were annealed for 4 hours or more within a temperature range of 650 to 950°C. After the prototypes were produced, a lubricant was applied to the wire surface.

[0078] (Production of Welded Joints) Welded joints having weld metal were produced by gas-shielded arc welding using the obtained flux-cored wire. A steel plate (20 mm thick × 120 mm wide × 300 mm thick) with the chemical composition shown in Table 1 was used as the steel plate (base metal) to be welded. As shown in FIG. 1 , a groove was formed in base metals 2A and 2B up to half the plate thickness to create a 90° groove angle. The base metals 2A and 2B were butted together with the gap between them adjusted to 1 mm. Single-bead welding was performed on these base metals 2A and 2B. The welding conditions were those for "flux-cored wire (FCAW)" listed in Table 2. In this way, welded joints having weld metal were produced. The chemical composition of the obtained weld metal was controlled by adjusting the composition of the flux-cored wire. The chemical compositions of the weld metals in the produced welded joints are shown in Tables 3-1 to 3-4 (Nos. 17 to 24, 37, and 41).

[0079] <4. Gas Tungsten Arc Welding (TIG) Using Filler Metal> (Production of Filler Metal) As a filler metal, a solid wire was produced by the same method as in <1. Submerged Arc Welding (SAW) Using Solid Wire and Flux>.

[0080] (Production of Welded Joints) The resulting filler metal (solid wire) was used for gas tungsten arc welding to produce welded joints with weld metal. A steel plate (20 mm thick x 120 mm wide x 300 mm thick) with the chemical composition shown in Table 1 was used as the steel plate (base metal) to be welded. As shown in Figure 1, a groove was formed in base metals 2A and 2B up to half the plate thickness to create a 90° groove angle. The gap between base metals 2A and 2B was adjusted to 1 mm, and the base metals were butted together. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were the "tungsten arc welding (TIG)" conditions listed in Table 2. In this way, welded joints with weld metal were produced. The chemical composition of the resulting weld metal was controlled by adjusting the chemical composition of the filler metal. The chemical compositions of the weld metals in the produced welded joints are shown in Tables 3-1 to 3-4 (Nos. 25 to 32, 38, and 42).

[0081] The unit of content of the chemical components of the weld metal shown in Tables 3-1 to 3-4 is "mass % relative to the total mass of the weld metal." The remainder of the weld metal shown in Tables 3-1 to 3-4 (i.e., components other than the components shown in the tables) is iron and impurities. In Tables 3-1 to 3-4, blank spaces in the tables relating to the content of chemical components of the weld metal mean that the content of that chemical component is less than the significant digits. These chemical components may unavoidably be mixed in or generated in amounts less than the significant digits.

[0082] For the welded joints obtained in Nos. 1 to 42, the fcc content in the weld metal structure was determined by the following method. First, a sample was taken from the weld metal. The sample was taken from the center of the weld metal so that the base metal was not included. The bcc content (volume %) was measured on the sample surface by a magnetic induction method using a FERITSCOPE (registered trademark) FMP30 (manufactured by Fischer Instruments Inc.) and a Fischer Instruments Inc. probe (FGAB 1.3-Fe) as the probe of the measuring instrument. To obtain accurate measurements, the FERITSCOPE probe was placed on the sample at the center of a surface cut perpendicular to the bead longitudinal direction of the weld, and on as flat a surface as possible. The probe diameter was 7 mm. The arithmetic mean value of the measured bcc contents was calculated, and the fcc content (volume %) in the structure of the weld metal was calculated using the obtained mean bcc content value according to the following formula: fcc content = 100 - bcc content

[0083] <Evaluation Test> - FISCO Cracking Evaluation Method Hot cracking resistance was evaluated for cracking (hot cracking) occurring during solidification from the liquid phase by conducting a FISCO cracking test (JIS Z 3155 (1993): "C-type jig restraint butt weld cracking test method" (Method of FISCO test). In the FISCO cracking test, first, two steel plates 10A (base materials) were butted together and placed on the rough surfaces 122 of a C-type jig 12 as shown in FIG. 2A , and their ends were fixed with fixing bolts 14. The two steel plates 10A were placed so that the butt joints were located on the non-rough surface portions 124 in the centers of the rough surfaces 122. In this state, the butt joints were welded to form a weld metal joint 100. The welding was carried out by the above-mentioned <1. Submerged arc welding (SAW) using a solid wire and flux>, <2. Shielded arc welding (SMAW) using a shielded metal arc welding rod>, and <3. The welding was performed under the conditions described in <4. Arc welding using flux-cored wire (FCAW)> and <4. Gas tungsten arc welding (TIG) using filler metal>. When the weld metal part 100 solidifies after welding, hot cracks 110 as shown in Fig. 2B may occur in some parts. These hot cracks 110 are cracks that occur due to the application of tensile stress during solidification in the weld metal part 100, as shown in Fig. 2C.

[0084] The length of cracks occurring in the weld metal of the welded joints obtained in Nos. 1 to 42 was measured. To determine hot cracking, the weld length was taken as L (mm), the total crack length of L was taken as Lc (mm), and the crack rate R (%) was calculated using the following formula. A crack rate R≦15% was deemed to be pass, and a crack rate R>15% was deemed to be fail: R=Lc / L×100(%)

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091] The results shown in Tables 3-1 to 3-4 indicate that the weld metals of the present disclosure have excellent hot cracking resistance. On the other hand, the weld metals of the comparative examples, which do not contain the elements Nb, V, Ta, Hf, Ti, and Zr in the above-mentioned amounts, were judged to be unsatisfactory in the FISCO cracking evaluation.

[0092] The disclosure of Japanese Patent Application No. 2023-204166 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

[0093] 2A, 2B Base material 10A Steel plate (base material) 10B Welded joint sample 12 C-shaped jig 14 Fixing bolt 100 Welded metal part 110 Hot crack 122 Rough surface 124 Non-rough surface part

Claims

1. The chemical composition, expressed as mass% relative to the total mass of the weld metal, is as follows: C: 0.20-0.80%, Si: 0.03-0.50%, Mn: 5.1-20.0%, P: 0-0.050%, S: 0-0.050%, Cu: 0-5.0%, Ni: 6.0-20.0%, Cr: 0-10.0%, Mo: 0-10.0%, Nb: 0-5.00%, V: 0-5.00%, Ta: 0-5.000%, Hf: 0-5.000%, Ti: 0-5.00%, Zr: 0-5.000%, Co: 0-1.0%, Pb: 0-1.0%, Sn: 0-1.0%, W : 0-5.0%, Mg: 0-0.10%, Al: 0.001-0.100%, Ca: 0-5.00%, B: 0-0.500%, REM: 0-0.500%, N: 0-0.500%, O: 0.001-0.150%, and the balance: Fe and impurities, and the weld metal contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the following amounts: Nb: more than 1.00%, V: more than 1.00%, Ta: 0.001% or more, Hf: 0.001% or more, Ti: more than 0.10%, Zr: more than 0.500%.

2. The weld metal according to claim 1, wherein the mass ratio (Ni / Mn) of the Mn content to the Ni content is 0.33 or more.

3. The weld metal according to claim 1, containing at least two elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr, each in the above-mentioned content.

4. The weld metal according to claim 1, wherein the fcc content determined by the magnetic induction method is 70 volume percent or more.

5. A welded joint having the weld metal according to any one of claims 1 to 4.

6. A welded structure having the weld joint according to claim 5.

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