Weld metals, welded joints, and welded structures

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

[Technical Field]

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

[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 oil and coal, as well as natural gas, which also emits less carbon dioxide. Accordingly, there has also been an increasing global demand for the construction of liquid hydrogen tanks, liquid carbon dioxide tanks, and LNG tanks for use on ships and on land. Ni-based low-temperature steels containing 6-9% Ni are used for the steel materials used in liquid hydrogen tanks, liquid carbon dioxide tanks, and LNG tanks, as they must be tough at extremely low temperatures (for example, -196°C). These Ni-based low-temperature steels are welded using austenitic welding materials that provide weld metal 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 discloses "a flux-cored wire with an outer sheath made of a Ni-based alloy, the Ni content of which is 35 to 70%, the flux containing TiO2, SiO2, and ZrO2 in a total amount of 4.0 mass% or more with respect to the total mass of the wire, and further containing 0.6 to 1.2 mass% of Mn oxide calculated as MnO2, and the contents of TiO2, SiO2, ZrO2, and MnO2 (calculated) are [TiO2], [SiO2], [ZrO2], and [MnO2], respectively, in mass%, so that [TiO2] / [ZrO2] is 2.3 to 3.3, [SiO2] / [ZrO2] is 0.9 to 1.5, and ([TiO2] + [SiO2] + [ZrO2]) / [MnO2] is 5 to 13." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-246507 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

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

[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. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a base material having a groove used in the examples. [Figure 2A] FIG. 1 is a schematic cross-sectional view illustrating a test device for a FISCO cracking test. [Figure 2B] FIG. 1 is a schematic cross-sectional view illustrating a test device for a FISCO cracking test. [Figure 2C] FIG. 1 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. DETAILED DESCRIPTION OF THE INVENTION

[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 not preceded or followed by "greater than" or "less than," it means a range that includes these numerical values ​​as the lower and upper limits. When "to" is preceded or 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 present specification, the upper limit of a numerical range described in stages 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. The lower limit of a 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, regarding the content, "%" means "% by mass." The content (%) of "0 or more" means that the component is an optional component and does not need to be contained.

[0011] <Weld metal> The 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. 0060

[0013] Austenitic welding materials have traditionally been used as welding materials that can produce weld metals with excellent low-temperature toughness, such as those used for steel containing 6 to 9% Ni, which is 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, and Si, etc., which results in a lower melting point of the liquid phase in the (γ phase + liquid phase) state, and tensile stress is applied to the liquid phase due to solidification shrinkage, 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, which can lower the melting point of the liquid phase. This liquid phase contains concentrated P, S, C, and Si, 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 it is believed that 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, and the melting point of the liquid phase increases, thereby suppressing hot cracking.

[0015] An example of an indicator 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) 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 components 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: 0.20~0.80%, Si: 0.03 to 0.50% Mn: 5.1 to 20.0%, P: 0~0.050%, S: 0~0.050%, Cu: 0-5.0% Ni: 6.0 to 20.0% Cr: 0 to 10.0%, Mo: 0-10.0% Nb: 0~5.00%, V: 0~5.00%, Ta: 0 to 5.000%, Hf: 0 to 5.000%, Ti: 0~5.00%, Zr: 0 to 5.000%, Co: 0-1.0% Pb: 0-1.0% Sn: 0 to 1.0% W: 0-5.0%, Mg: 0~0.10% Al: 0.001 to 0.100%, Ca: 0-5.00%, B: 0~0.500%, REM: 0~0.500%, N: 0~0.500%, O: 0.001 to 0.150%, and The balance is Fe and impurities. The alloy contains at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the following content. Nb: More than 1.00% V: More than 1.00% Ta: 0.001% or more Hf:0.001% or more Ti: over 0.10% Zr: over 0.500%

[0019] (C: 0.20~0.80%) 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 strength of the weld metal has a large 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%) Silicon is a deoxidizing element. If the silicon content of the weld metal is too low, the oxygen content of the weld metal increases. On the other hand, Si has a 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 in the weld metal is set to 0.03 to 0.50%. The lower limit of the Si content in the weld metal is preferably 0.04%, 0.05%, or 0.08%. The upper limit of the Si content in 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 in the weld metal is too low, the austenitization of the weld metal becomes difficult, resulting in a deterioration of low-temperature toughness. Mn also functions as a deoxidizer to improve the cleanliness of the weld metal. Mn also forms MnS, which neutralizes the S in the weld metal and improves 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 in 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 in 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: 0~0.050%) 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 the dephosphorization cost, the P content of the weld metal should be 0.003% or more. On the other hand, if the P content in 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: 0~0.050%) 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 perspective of reducing the cost of desulfurization, the S content of the weld metal should be 0.003% or more. On the other hand, if the S content in 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: 0-5.0%) 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 effect becomes saturated. 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 in the weld metal is too low, the austenitization of the weld metal becomes difficult to proceed, and the low-temperature toughness deteriorates. On the other hand, increasing the Ni content of the weld metal increases the cost of the weld metal. Therefore, the Ni content of the weld metal is set to 6.0 to 20.0%. The lower limit of the Ni content in the weld metal is preferably 6.5%, 7.0%, 7.5%, or 8.0%. The upper limit of the Ni content in 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 of the weld metal is excessive, the solid-liquid coexistence temperature range of the molten metal will be widened, making hot cracking more likely to occur. Therefore, the Cr content of 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: 0-10.0%) 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 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 0 to 10.0%. The lower limit of the Mo content in the weld metal is preferably 1.0%, 2.0%, or 3.0%. The upper limit of the Mo content in the weld metal is preferably 9.0%, 8.0%, or 7.0%.

[0028] (Nb: 0 to 5.00%) Nb is an element that forms carbides in the weld metal and increases the strength of the weld metal, and therefore may be contained in 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 5.00%. 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%. 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 preferably within the range described below.

[0029] (V: 0~5.00%) V is an element that forms carbonitrides in the weld metal and increases the strength of the weld metal, and therefore may be contained in 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 of 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 of the weld metal is preferably 4.50%, 4.00%, 3.50%, or 3.00%. 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 preferably within the range described below.

[0030] (Ta: 0 to 5.000%) Ta is an element that forms carbides in the weld metal and increases the strength of the weld metal, and therefore may be contained in 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 lead to a decrease in 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 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 preferably within the range described below.

[0031] (Hf:0~5.000%) Hf is an element that forms carbides in the weld metal and increases the strength of the weld metal, and therefore may be contained in the weld metal. On the other hand, if the Hf content in the weld metal is excessive, the toughness of the weld metal may be reduced. 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, if the Ti content in 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 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%, or 3.00%, 2.00%, or 1.50%. 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 preferably within the range described below.

[0033] (Zr: 0 to 5.000%) Zr can stabilize the bead shape during the welding operation to obtain the weld metal, so it may be contained in the weld metal. On the other hand, if the Zr content in 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 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%, or 3.00%, 2.00%, 1.50%, or 1.00%. 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 preferably within the range described below.

[0034] (Co: 0-1.0%) 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 in the weld metal is excessive, the ductility of the weld metal decreases, and the toughness cannot be ensured. Therefore, the Co content in the weld metal is set to 0 to 1.0%. The lower limit of the Co content in the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%. The upper limit of the Co content in the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.

[0035] (Pb: 0-1.0%) Pb 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, and therefore may be contained in 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 in the weld metal is excessive, there is a concern that cracks may occur in the weld metal. Therefore, the Sn content in the weld metal is set to 0 to 1.0%. The lower limit of the Sn content in the weld metal is preferably 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%. The upper limit of the Sn content in the weld metal is preferably 0.95%, 0.9%, 0.85%, or 0.8%.

[0037] (W: 0-5.0%) 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 in 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 in 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 deteriorating the 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 in 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 in the weld metal is preferably 0.003%, 0.005%, 0.010%, 0.020%, or 0.030%. The upper limit of the Al content in the weld metal is preferably 0.090%, 0.080%, or 0.070%.

[0040] (Ca: 0-5.00%) Ca changes the structure of sulfides in the weld metal and also has the effect of reducing the size of sulfides and oxides in the weld metal, and is therefore effective in improving the ductility and toughness of the weld metal, so Ca may be added to the weld metal. On the other hand, if the Ca content in the weld metal is excessive, coarsening of sulfides and oxides occurs, which may lead to deterioration of 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: 0~0.500%) 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 in the weld metal is preferably 0.0005%, 0.001%, or 0.002%. The upper limit of the B content in 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 work 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 will be severe during the welding operation to obtain the weld metal, which may result 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, if the N content in the weld metal is excessive, the occurrence of blowout increases, which causes welding defects. Therefore, the N content of 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 of the weld metal is preferably 0.450%, 0.400%, or 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%. 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 remaining components in the chemical composition of the weld metal are Fe and impurities. Impurities refer to components that are mixed in during the industrial production of weld metal due to raw materials such as ores 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 the "specific element") in the following content: By containing the specific element in the following content, 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: over 0.10% Zr: over 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 set to more than 1.00%, and preferably the lower limit of the Nb content in the weld metal is 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 set to more than 1.00%, and 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 set to 0.001% or more, and preferably, the lower limit of the Ta content in the weld metal is 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 set to 0.001% or more, and preferably, the lower limit of the Hf content in the weld metal is 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 set to more than 0.10%, and 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: over 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 set to more than 0.500%, and preferably the lower limit of the Zr content in the weld metal is 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 content: 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] Contains two or more specific elements It is preferable that two or more of the specific elements (i.e., elements selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr) are contained in the above-mentioned amounts, respectively. By containing two or more specific elements, hot cracking in the weld metal is further suppressed. This is because the inclusion of two or more specific elements promotes the formation of carbides more than the addition of only one of the specific elements at the above-mentioned content. When only one of the specific elements is added, a carbide containing that element is formed, but the amount of carbide produced is limited due to the existence of reaction equilibrium. On the other hand, the inclusion of two or more specific elements is thought to lower the activity of the carbide (increase the activity of the carbide-forming element), thereby promoting the reaction.

[0055] (Total of Mn and Ni contents (Mn + Ni)) Mn and Ni are each austenite-stabilizing elements that improve the low-temperature toughness of the weld metal. On the other hand, since Ni is an expensive metal, 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] Moreover, if the Mn content is excessively increased, the stacking fault energy decreases and the 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 ranges, and that the total content of the Mn content and the Ni content (Mn + Ni) be 37.0% or less. The total content of Mn and Ni (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 austenite-stabilizing elements that improve the low-temperature toughness of the weld metal. On the other hand, since Ni is an expensive metal, 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) be 15.0% or more. The total (Mn+Ni+Cr) of the Mn content, Ni content and Cr content 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 amount of Mn, stacking fault energy does not become too low, and toughness can be ensured. Furthermore, by not including an excessive amount of Cr, the amount of low-melting-point compounds in the molten metal can be reduced, and further, 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 suppressing 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) be 47.0% or less. The total content of Mn, Ni and Cr (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 austenite stabilizing elements that improve the low-temperature toughness of the weld metal. However, Ni is an expensive metal, and if Mn is added excessively, the stacking fault energy decreases, deteriorating the toughness. 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 (Ni / Mn) of the Mn content to the Ni content 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 (Ni / Mn) of the Mn content to the Ni content 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 the 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 sample surface using a magnetic induction method, and the arithmetic mean of the measured bcc content is calculated. The obtained mean bcc content is used to calculate the fcc content (volume %) in the weld metal structure using the following formula. fcc content rate=100-bcc content rate 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 joints and welded structures> Next, the welded joint and welded structure according to the present disclosure will be described. The weld joint according to the present disclosure includes the weld metal according to the present disclosure. For example, the weld joint according to the present disclosure includes a steel material serving as a base material, and a welded portion including the weld metal and the weld heat-affected zone. Furthermore, a welded structure according to the present disclosure has the 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. It should be noted 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 (material to be welded) used in the manufacturing method of the above-mentioned welded joint, is not particularly limited, but for example, Ni-based low-temperature steel containing 6 to 9% Ni with a plate thickness of 20 mm or more can be suitably used. [Example]

[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 spirit described above and below are all included in the technical scope of the present disclosure.

[0072] The following methods are used for submerged arc welding (SAW) using solid wire and flux, shielded metal arc welding (SMAW) using covered electrodes, and arc welding using flux-cored wire (Flux Cored Wire). Arc Welding (FCAW), and gas arc welding using filler metal (Tungsten Inert Gas: TIG ) to obtain the weld metal.

[0073] <1. Submerged Arc Welding (SAW) using solid wire and flux> (Solid wire manufacturing) The solid wire was produced by the method described below. First, the 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 diameter of 2.4 mm was produced. After production, a lubricant was applied to the wire surface.

[0074] (Manufacturing of welded joints) The obtained solid wire was used to produce a welded joint having a weld metal by submerged arc welding. Specifically, the solid wire was used in combination with NITTETSU FLUX 10H manufactured by Nippon Steel Welding Co., Ltd., which is a submerged arc welding flux, to perform submerged arc welding. Steel plates (20mm thick x 120mm wide x 300mm thick) with the composition shown in Table 1 were used as the steel plates (base metals) to be welded. As shown in Figure 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 adjusted to 1mm. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were those for "submerged arc welding (SAW)" listed in Table 2. In this way, a welded joint having a weld metal was produced. The chemical compositions of the weld metals obtained were 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 Metal Arc Welding (SMAW) Using Shielded Metal Arc Welding Electrodes> (manufacturing covered metal arc welding electrodes) The covered electrodes were manufactured by the method described below. First, a covered metal arc welding rod was produced by applying flux to a core wire and firing it for 1 to 3 hours at a temperature range of 300 to 500°C. The final diameter of the obtained covered metal arc welding rod was φ6.0 mm, and the average thickness of the flux was 1.0 mm.

[0076] (Manufacturing of welded joints) The resulting covered metal arc welding rod was used to produce a welded joint having a weld metal by covered metal arc welding. Steel plates (20 mm thick x 120 mm wide x 300 mm long) with the chemical composition shown in Table 1 were used as the steel plates (base metals) to be welded. As shown in Figure 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 adjusted to 1 mm. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were those for "sheathed arc welding (SMAW)" as shown in Table 2. In this way, a welded joint with weld metal was produced. The chemical compositions of the weld metals obtained were controlled by adjusting the composition of the covered electrode. 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. Flux-cored wire arc welding (FCAW)> (Flux-cored wire manufacturing) The 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 the opposing edges of the open tube opening were butt-welded to obtain a seamless tube. This seamless tube was then drawn to obtain a flux-cored wire without slit-like gaps. In this way, a flux-cored wire with a final wire diameter of φ1.2 mm was produced. During the drawing process of these flux-cored wires, the flux-cored wires were annealed for 4 hours or more within a temperature range of 650 to 950° C. After the prototype was made, a lubricant was applied to the surface of the wire.

[0078] (Manufacturing of welded joints) The obtained flux-cored wire was used to produce a welded joint having a weld metal by gas-shielded arc welding. A steel plate (20 mm thick x 120 mm wide x 300 mm long) 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 so that the groove angle was 90°. The base metals 2A and 2B were butted together with the gap 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, a welded joint with weld metal was produced. The chemical compositions of the weld metals obtained were 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> (Filler metal manufacturing) As a filler material, a solid wire was produced by the same method as in <1. Submerged arc welding (SAW) using solid wire and flux>.

[0080] (Manufacturing of welded joints) The obtained filler metal (solid wire) was used to perform gas tungsten arc welding to produce a welded joint having a weld metal. Steel plates (20mm thick x 120mm wide x 300mm thick) with the composition shown in Table 1 were used as the steel plates (base metals) to be welded. As shown in Figure 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 adjusted to 1mm. Single bead welding was performed on these base metals 2A and 2B. The welding conditions were the same as those for "tungsten arc welding (TIG)" shown in Table 2. In this way, a welded joint having a weld metal was produced. The chemical compositions of the weld metals obtained were controlled by adjusting the 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 the 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 balance of the weld metals shown in Tables 3-1 to 3-4 (ie, components other than the components shown in the tables) is iron and impurities. In Tables 3-1 to 3-4, blanks in the tables relating to the content of chemical components in the weld metal mean that the content of that chemical component is less than the significant digits. These chemical components may be unavoidably mixed 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 structure of the weld metal 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 using a FERITSCOPE (registered trademark) FMP30 (manufactured by Fischer Instruments Inc.) and a Fischer Instruments Inc. probe (FGAB 1.3-Fe) by magnetic induction. To obtain accurate measurements, the FERITSCOPE probe was placed on the center of the surface of the sample cut perpendicular to the longitudinal direction of the weld bead, 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 rate=100-bcc content rate

[0083] <Evaluation test> FISCO crack evaluation method The hot cracking resistance was evaluated by conducting a FISCO cracking test (JIS Z 3155 (1993): "C-type jig restrained butt weld cracking test method" (Method of FISCO test)) to evaluate cracking (hot cracking) occurring when solidifying from the liquid phase. In the FISCO cracking test, two steel plates 10A (base metal) were first butted together and placed on the roughened surface 122 of a C-shaped jig 12 as shown in FIG. 2A , with each end secured with a fixing bolt 14. The two steel plates 10A were placed so that the butted portion was positioned on the non-roughened portion 124 in the center of the roughened surface 122. In this state, the butted portion was welded to form a weld metal joint 100. The welding was performed under the conditions described above for each of <1. Submerged arc welding (SAW) using a solid wire and flux>, <2. Shielded metal arc welding (SMAW) using a shielded metal arc welding rod>, <3. Arc welding (FCAW) using a flux-cored wire>, and <4. Gas tungsten arc welding (TIG) using a filler metal>. When the welded metal part 100 solidifies after welding, hot cracks 110 may occur in some parts as shown in Fig. 2B. These hot cracks 110 are cracks that occur due to the application of tensile stress when solidification occurs in the welded metal part 100, as shown in Fig. 2C.

[0084] For the weld metals of the welded joints obtained in Nos. 1 to 42, the length of cracks occurring in the weld metal was measured. To judge whether there were any hot cracks, the weld length was taken as L (mm) and the total crack length of L as Lc (mm), and the crack rate R (%) was calculated using the following formula. A crack rate R≦15% was judged as passing, and a crack rate R>15% was judged as failing. R = Lc / L × 100(%)

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3-1]

[0088] [Table 3-2]

[0089] [Table 3-3]

[0090] [Table 3-4]

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

[0092] The disclosure of Japanese Application No. 2023-204166 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0093] 2A, 2B base material 10A steel plate (base material) 10B Welded joint sample 12 C-type jig 14 Fixing bolt 100 Welded metal parts 110 Hot cracking 122 Rough surface 124 Non-rough surface area

Claims

1. The chemical composition is expressed as mass% relative to the total mass of the weld metal. C: 0.20-0.80%, Si: 0.03-0.50%, 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: 0-10.0%, Mo: 0-10.0%, Nb: 0 to 5.00%, V: 0-5.00%, Ta: 0-5.000%, Hf: 0-5.000%, Ti: 0 to 5.00%, Zr: 0-5.000%, 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: 0.001-0.100%, Ca: 0-5.00%, B: 0 to 0.500%, REM: 0-0.500%, N: 0 to 0.500%, O: 0.001 to 0.150%, and The balance is Fe and impurities. and at least one element selected from the group consisting of Nb, V, Ta, Hf, Ti, and Zr in the following content: 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: over 0.500%

2. The weld metal according to claim 1, wherein a 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, comprising 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 magnetic induction spectroscopy is 70% by volume 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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