Flux-cored wire and method for manufacturing welded joint

Abstract

To provide a flux-cored wire that can give a weld metal excelling in ultra-low-temperature toughness at low cost, and also can reduce the generation of fume and sputter, and a method for producing a welded joint using the flux-cored wire.SOLUTION: A flux-cored wire comprises a steel sheath and a flux filled into the steel sheath. The steel sheath and the wire comprise predetermined chemical components, comprising total Ti oxides in terms of TiO2, total Si oxides in terms of SiO2, total Zr oxides in terms of ZrO2, total Al oxides in terms of Al2O3, total fluorides of at least one selected from the group consisting of K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2, total Na-containing compounds of at least one selected from the group consisting of Na oxides, NaF, and Na3AlF6, and total K-containing compounds of at least one selected from the group consisting of K oxides, K2SiF6, and K2ZrF6, respectively, in specific amounts.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a flux-cored wire and a weld joint. [Background technology]

[0002] In recent years, due to the tightening of regulations on carbon dioxide emissions in response to the issue of global warming, there has been an increase in demand for hydrogen fuel, which emits no carbon dioxide compared to oil and coal, as well as natural gas, which also emits less carbon dioxide, and as a result, there has been an increase in demand worldwide for the construction of liquid hydrogen tanks and LNG tanks.The steel used for liquid hydrogen tanks and LNG tanks is Ni-based low-temperature steel containing 6-9% Ni, as it is required to ensure extreme toughness at the extremely low temperature of -196°C. Austenitic flux-cored wires are used to weld these Ni-based low-temperature steels, which produce weld metal with excellent low-temperature toughness. These flux-cored wires are typically designed with a Ni content of 70%.

[0003] For example, Patent Document 1 discloses a flux-cored wire with a Ni content of 70%, which has an Ni content of 35 to 70%, and which contains TiO2, SiO2, and ZrO2 in a total amount of 4.0 mass% or more with respect to the total mass of the wire in the flux, and further contains Mn oxides in an amount of 0.6 to 1.2 mass% calculated as MnO2, and in which, when the contents of TiO2, SiO2, ZrO2, and MnO2 (equivalent amounts) are [TiO2], [SiO2], [ZrO2], and [MnO2], respectively, the ratio [TiO2] / [ZrO2] is 2.3 to 3.3, the ratio [SiO2] / [ZrO2] is 0.9 to 1.5, and the ratio ([TiO2] + [SiO2] + [ZrO2]) / [MnO2] is 5 to 13.

[0004] However, wires designed with a Ni content of 70% to ensure low-temperature toughness of the molten metal are very expensive, and there is a demand for cheaper wires.

[0005] For example, Patent Document 2 describes a flux-cored wire having a reduced Ni content, which is "a flux-cored wire having a steel sheath and flux filled inside the steel sheath, the flux containing a predetermined fluoride, a Ti oxide, a predetermined oxide, and a carbonate in predetermined amounts, and the chemical composition of the flux-cored wire is, in mass % relative to the total mass of the flux-cored wire, C: 0.003 to 0.150%, Si: 0.35 to 1.00%, Mn: more than 2.00 and not more than 10.00%, P: The publication discloses a flux-cored wire containing 0.030% or less of Ni, 0.020% or less of S, 0.001 to 0.500% of Al, 0 to 10.00% of Ni, 0 to 5.00% of Cr, 0.10 to 0.90% of Mg, 0 to 0.10% of Ti, 0 to 0.0200% of B, 0 to 1.00% of Mo, 0 to 0.50% of Cu, 0 to 0.20% of Nb, 0 to 0.20% of V, 0 to 0.20% of Bi, 0 to 0.030% of Ca, and 0 to 0.50% of REM, with the balance being Fe and impurities. In the flux-cored wire of Patent Document 2, the chemical composition of the steel sheath is disclosed as including "C: 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0.030% or less, S: 0.020% or less, Al: 0-0.1%, and N: 0-0.030%, with the balance including iron and impurities."

[0006] Furthermore, Patent Document 3 discloses "a flux-cored wire having a steel sheath and flux filled inside the steel sheath, the flux containing predetermined amounts of predetermined fluorides, oxides, and iron powder, and the chemical composition of the flux-cored wire contains, in mass % relative to the total mass of the flux-cored wire, C: 0.003 to 0.080%, Si: 0.21 to 2.00%, Mn: 0.81 to 3.50%, P: 0.020% or less, S: 0.010% or less, Ni: 5.0 to 15.0%, with the balance being Fe and impurities." In the flux-cored wire of Patent Document 3, the chemical composition of the steel sheath is disclosed as "containing C: 0.002%, Si: 0.02%, Mn: 0.1%, P: 0.002%, S: 0.002%, and Al: 0.005%, with the balance being iron and impurities."

[0007] Furthermore, Patent Document 4 describes a flux-cored wire having a steel sheath and flux filled inside the steel sheath, the flux containing a predetermined amount of a predetermined fluoride, a Ti oxide, a predetermined oxide, and a carbonate, and the chemical composition of the flux-cored wire is, in mass % relative to the total mass of the flux-cored wire, C: 0.003 to 0.150%, Si: 0.35 to 1.00%, Mn: 0.01 to 2.00%, P: 0.030% or less, S: 0.020% or less, Cu: The publication discloses a flux-cored wire comprising: 1.00-5.00%, Ni: 0-10.00%, Cr: 10.00-20.00%, Mo: 0-5.00%, Ti: 0-0.10%, Nb: 0.001-0.500%, Al: 0.001-0.500%, Mg: 0-0.90%, B: 0-0.0200%, V: 0-0.20%, Bi: 0-0.030%, Ca: 0-0.25%, and REM: 0-0.010%, with the balance being Fe and impurities. In the flux-cored wire of Patent Document 5, the chemical composition of the steel sheath is disclosed as including "C: 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0.030% or less, S: 0.020% or less, Al: 0-0.1%, and N: 0-0.030%, with the balance including iron and impurities." [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-246507 [Patent Document 2] Patent Publication No. 2019-25524 [Patent Document 3] JP 2017-164768 A [Patent Document 4] JP 2019-48323 A Summary of the Invention [Problem to be solved by the invention]

[0009] The flux-cored wires of Patent Documents 2 to 4 can provide weld metals with excellent low-temperature toughness at -30 to 0°C. However, as mentioned above, flux-cored wires used to weld steel materials used in liquid hydrogen tanks and LNG tanks are required to ensure the toughness of the weld metal at the cryogenic temperature of −196° C. Therefore, there is a demand for flux-cored wires that can obtain weld metal with excellent cryogenic temperature toughness at −196° C. even if the Ni content is reduced.

[0010] On the other hand, expensive Ni is known as an austenite stabilizing element, but inexpensive Mn has a similar effect. Therefore, reducing the Ni content and increasing the Mn content can produce inexpensive weld metal with excellent low-temperature toughness. However, simply increasing the Mn content generates a large amount of fumes. Increased fumes reduce the visibility of the molten metal and arc, which can lead to welding defects. In addition, flux-cored wires are also required to reduce spatter.

[0011] Therefore, an object of the present invention is to provide a flux-cored wire that is inexpensive, can produce a weld metal with excellent cryogenic toughness, and can reduce the amount of fumes and spatter generated, and a method for manufacturing a welded joint using the flux-cored wire. [Means for solving the problem]

[0012] The means for solving the problem include the following aspects. <1> A flux-cored wire for welding having a steel outer sheath and flux filled inside the steel outer sheath, The chemical composition of the steel skin is, in mass% relative to the total mass of the steel skin, C: 0~0.100%, Si: 0 to 0.10% Mn: 0 to 1.00%, P: 0~0.050%, S: 0~0.050%, Al: 0 to 0.100%, Ti: 0 to 0.100%, N: 0 to 0.0100%, and The balance is Fe and impurities, and the total content of C, Si, Mn, P, S, Al, Ti, and N is 1.5000% or less, The chemical composition of the flux-cored wire, excluding oxides, fluorides, nitrides, and metal carbonates, is, in mass % based on the total mass of the flux-cored wire: C: 0.020~0.500%, Si: 0.20 to 0.80% Mn: 1.50~30.00%, P: 0~0.050%, S: 0~0.050%, Cu: 0-10.0% Ni: 5.0 to 20.0% Cr: 2.0 to 10.0%, Mo: 0-10.0% Nb: 0 to 5.0% V: 0~5.0%, W: 0-10.0%, Mg: 0-1.00% Al: 0 to 3.000%, Ca: 0 to 0.100%, Ti: 0 to 3.000%, B: 0~0.1000%, REM: 0~0.100%, Bi: 0 to 0.050% N: 0.050 to 1.000%, and The balance is Fe and impurities. The total TiO2 equivalent value of Ti oxides is 3.00 to 8.00%, The total SiO2 equivalent value of silicon oxides is 0.10 to 1.00%, The total ZrO2 equivalent value of Zr oxide is 0 to 0.80%; The total Al2O3 equivalent value of Al oxides is 0 to 0.80%, Contains one or more fluorides of K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2, the total of which is 0.10 to 2.00%, Contains one or more Na-containing compounds selected from Na oxide, NaF, and Na3AlF6, the total of which (Na oxide is calculated as Na2O) is 0.01 to 2.00%, A flux-cored wire containing one or more K-containing compounds selected from K oxide, K2SiF6, and K2ZrF6, the total of which (K oxide is calculated as K2O) is 0.01 to 2.00%. <2> The X value calculated by the following formula A is 0.10 to 160.00 <1> The flux-cored wire according to claim 1. X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO)...Formula A In formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 are the contents of the compounds represented by each chemical formula in mass% relative to the total mass of the flux-cored wire. SiO2 represents the total of silicon oxides converted into SiO2, Al2O3 represents the total of aluminum oxides converted into Al2O3, ZrO2 represents the total of zirconium oxides converted into ZrO2, MgO represents the total of magnesium oxides converted into MgO, CaO represents the total of calcium oxides converted into CaO, Na2O represents the total of sodium oxides converted into Na2O, K2O represents the total of potassium oxides converted into K2O, MnO2 represents the total of manganese oxides converted into MnO2, and FeO represents the total of iron oxides converted into FeO. In addition, the SiO2 equivalent value, the Al2O3 equivalent value, the ZrO2 equivalent value, the MgO equivalent value, the CaO equivalent value, the Na2O equivalent value, the K2O equivalent value, the MnO2 equivalent value, and the FeO equivalent value in Formula A are expressed in mass% with respect to the total mass of the flux-cored wire. <3> In the chemical composition of the flux-cored wire, the mass ratio (Mn / Ni) of the Mn content to the Ni content is 0.30 to 4.00. <1> or <2> The flux-cored wire according to claim 1. <4> The steel skin has no welds at the seams of the steel skin. <1> ~ <3> The flux-cored wire according to any one of claims 1 to 5. <5> The steel skin has welds at the seams of the steel skin. <1> ~ <3> The flux-cored wire according to any one of claims 1 to 5. <6> The surface is coated with either or both of polytetrafluoroethylene oil and perfluoropolyether oil. <1> ~ <5> The flux-cored wire according to any one of claims 1 to 5. <7> <1> ~ <6> 10. A method for manufacturing a welded joint, comprising: welding steel materials using the flux-cored wire according to any one of claims 1 to 9. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an inexpensive flux-cored wire that can produce a weld metal with excellent cryogenic toughness and reduce the amount of fumes and spatter generated, and a method for manufacturing a welded joint using the flux-cored wire. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 may be replaced by the upper limit of another numerical range, 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, 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.

[0015] <Flux-cored wire> The flux-cored wire (hereinafter sometimes simply referred to as "wire") according to the present disclosure comprises a steel sheath (hereinafter sometimes simply referred to as "sheath") and flux filled inside the steel sheath. The flux-cored wire according to the present disclosure has a steel sheath having a predetermined chemical composition, and the flux-cored wire has a predetermined chemical composition excluding oxides, fluorides, nitrides, and metal carbonates, and contains predetermined amounts of Ti oxide, Si oxide, fluoride, Na-containing compound, and K-containing compound, and is free of or contains predetermined amounts of Zr oxide and Al oxide.

[0016] The flux-cored wire according to the present disclosure has the above-described configuration, and is an inexpensive wire that can provide a weld metal having excellent cryogenic toughness and can reduce the amount of fumes and spatters generated. The flux-cored wire according to the present disclosure was discovered based on the following findings:

[0017] . The inventors have investigated a technique for obtaining a wire that can improve the cryogenic temperature toughness of the weld metal and reduce the amount of fumes and spatters generated, even when the Ni content is reduced and the Mn content is increased, and have obtained the following findings. Fumes are metal vapors generated from the molten pool that are released into the air by the arc force and solidify. Controlling this arc force can reduce the amount of fume generated. Arc force varies not only depending on the welding conditions but also on the composition of the steel sheath. Specifically, by using a mild steel sheath with a reduced Mn content, which causes fumes, the Ni content of the entire wire can be reduced, and even if the Mn content is increased, the arc force is alleviated, resulting in a weld metal with excellent cryogenic toughness and reduced fume generation. Furthermore, by using a mild steel sheath with a minimum total content of C, Si, Mn, P, S, Al, Ti, and N (especially the C content), which are factors that cause spatter, the amount of spatter generated can also be reduced. Furthermore, by including a large amount of N, which functions as a solid solution strengthening element, in addition to Ni and Mn in the wire, the strength is improved. In addition, the inventors have also investigated oxides, fluorides, Na-containing compounds, and K-containing compounds in the wire, and have found that controlling the amounts of these compounds further improves the cryogenic temperature toughness.

[0018] From the above findings, it has been found that the flux-cored wire according to the present disclosure is inexpensive, can provide a weld metal with excellent cryogenic toughness, and can reduce the amount of fumes and spatter generated.

[0019] The reasons for limiting the requirements (including optional requirements) for constituting the flux-cored wire according to the present disclosure will be specifically described below.

[0020] (Chemical composition of steel skin) The chemical composition of the steel skin will be described in detail below. In the explanation of the chemical components of the steel skin, "%" means "mass % relative to the total mass of the chemical components of the steel skin" unless otherwise specified.

[0021] The chemical composition of the steel skin is: C: 0~0.100%, Si: 0 to 0.10% Mn: 0 to 1.00%, P: 0~0.050%, S: 0~0.050%, Al: 0 to 0.100%, Ti: 0 to 0.100%, N: 0 to 0.0100%, and The balance is Fe and impurities, and the total content of C, Si, Mn, P, S, Al, Ti, and N (hereinafter, these elements are also referred to as "skin alloying elements") is 1.5000% or less.

[0022] (C: 0 to 0.100%) Carbon is an element that generates spatter. The lower the carbon content in the sheath, the better for reducing the amount of spatter. In addition, since it is necessary to reduce the total content of alloy elements in the sheath, which are the cause of spatter, it is also necessary to reduce the carbon content in the sheath. Therefore, the C content of the outer skin is set to 0 to 0.100%. The upper limit of the C content of the outer shell is preferably 0.095%, 0.090%, 0.080%, or 0.070%. The lower limit of the carbon content in the outer skin is ideally 0%, but since it is not easy to achieve 0% and the cost of removing carbon increases, 0.001%, 0.002%, or 0.003% is preferred.

[0023] (Si: 0 to 0.10%) Si is a deoxidizing element. On the other hand, since it is necessary to reduce the total content of alloy elements in the outer sheath, which causes spatter, it is also necessary to reduce the Si content in the outer sheath. Therefore, the Si content of the outer skin is set to 0 to 0.10%. The upper limit of the Si content of the outer skin is preferably 0.09%, 0.08%, or 0.07%. The lower limit of the Si content in the outer skin is ideally 0%, but since it is not easy to achieve 0% and the cost of removing silicon increases, 0.01%, 0.02%, or 0.03% is preferred.

[0024] (Mn: 0 to 1.00%) Mn is an element that causes an increase in the amount of fume generated. The lower the Mn content in the sheath, the better for reducing the amount of fume generated. In addition, since it is necessary to reduce the total content of the alloy elements in the sheath, which are the cause of spatter, it is also necessary to reduce the Mn content in the sheath. The upper limit of the Mn content in the outer shell is preferably 0.95%, 0.90%, 0.80%, or 0.70%. The lower limit of the Mn content in the outer skin is ideally 0%, but since it is not easy to achieve 0% and the cost of removing Mn increases, 0.01%, 0.02%, 0.03%, or 0.05% is preferred.

[0025] (P: 0~0.050%) Since P is an impurity element that reduces the toughness of the weld metal, it is preferable to reduce the P content of the sheath as much as possible. In addition, since it is necessary to reduce the total content of alloy elements in the sheath, which causes spatter, it is also necessary to reduce the P content of the sheath. Therefore, the P content of the outer skin is set to 0 to 0.050%. The upper limit of the P content in the outer skin is preferably 0.040%, 0.030%, 0.020%, 0.015%, or 0.010%. From the viewpoint of reducing the dephosphorization cost, the lower limit of the P content in the outer skin is preferably 0.003%.

[0026] (S: 0~0.050%) S is an impurity element that reduces the toughness of the weld metal, so it is preferable to reduce the S content of the outer sheath as much as possible. Therefore, the S content of the outer skin is set to 0 to 0.050%. The upper limit of the S content in the outer skin is preferably 0.040%, 0.030%, 0.020%, 0.015%, or 0.010%. From the viewpoint of reducing the cost of desulfurization, the lower limit of the S content in the outer skin is preferably 0.003%.

[0027] (Al: 0 to 0.100%) Al is a deoxidizing element and may be included in the sheath to prevent welding defects and improve the cleanliness of the weld metal. However, excessive Al content in the sheath can cause coarse inclusions in the steel sheath, making core processing difficult. In addition, since it is necessary to reduce the total content of alloying elements in the sheath, which can cause spatter, the Al content must be reduced even when the sheath contains Al. Therefore, the Al content of the outer skin is set to 0 to 0.100%. The lower limit of the Al content of the outer skin is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Al content of the outer skin is preferably 0.090%, 0.080%, or 0.070%.

[0028] (Ti: 0 to 0.100%) Ti is a deoxidizing element and may be included in the sheath to prevent welding defects and improve the cleanliness of the weld metal. However, excessive Ti content in the sheath can cause coarse inclusions in the steel sheath, making core processing difficult. In addition, since it is necessary to reduce the total content of alloying elements in the sheath, which can cause spatter, the Ti content must be reduced even when Ti is included in the sheath. Therefore, the Ti content of the outer skin is set to 0 to 0.100%. The lower limit of the Ti content in the outer skin is preferably 0.005%, 0.010%, 0.015%, 0.020%, or 0.030%. The upper limit of the Ti content of the outer skin is preferably 0.095%, 0.090%, 0.080%, or 0.070%.

[0029] (N: 0 to 0.0100%) N is an impurity element. On the other hand, since it is necessary to reduce the total content of alloy elements in the jacket, which causes spattering, it is also necessary to reduce the N content in the jacket. Therefore, the N content of the outer skin is set to 0 to 0.0100%. The upper limit of the N content in the outer skin is preferably 0.0095%, 0.0090%, 0.0085%, 0.0080%, or 0.0070%. From the viewpoint of reducing the cost of denitrification, the lower limit of the N content in the outer skin is preferably 0.0010% or 0.0020%.

[0030] (balance: Fe and impurities) The remaining components in the chemical composition of the exine shell are Fe and impurities. Impurities refer to components that are mixed in during industrial production of the outer sheath due to raw materials such as ore or scrap, or various factors in the manufacturing process, and are acceptable within a range that does not adversely affect the properties of the wire.

[0031] (Total content of alloying elements in the outer shell) The outer shell alloy elements (C, Si, Mn, P, S, Al, Ti, and N) are elements that cause an increase in the amount of spatter. In order to reduce the amount of spatter, the lower the total content of the outer shell alloy elements, the more advantageous it is. Therefore, the total content of alloying elements in the outer shell is set to 1.5000% or less. The upper limit of the total content of the skin alloying elements is preferably 1.4000%, 1.2000%, 1.0000%, or 0.8000%. The lower limit of the total content of the outer shell alloying elements is ideally 0%, but since it is not easy to achieve 0% and the cost of reducing the outer shell alloying elements increases, 0.0500%, 0.1000%, 0.2000%, or 0.3000% is preferable.

[0032] (Chemical composition of flux-cored wire) The chemical components of the flux-cored wire according to the present disclosure will be described below. In the description of the chemical components of the flux-cored wire, "%" means "mass % relative to the total mass of the flux-cored wire" unless otherwise specified. The chemical components of the flux-cored wire may be contained in the steel sheath or in the flux, but in order to make the chemical components of the steel sheath fall within the above range, it is preferable that most of the chemical components of the flux-cored wire are contained in the flux. In addition, when the flux-cored wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, the metal oxide may be included in the plating layer. In describing the chemical components of the flux-cored wire, "chemical components excluding nitrides, oxides, fluorides, and metal carbonates" may be simply referred to as "chemical components."

[0033] The chemical composition of the flux-cored wire according to the present disclosure, excluding oxides, fluorides, nitrides, and metal carbonates, is: C: 0.020~0.500%, Si: 0.20 to 0.80% Mn: 1.50~30.00%, P: 0~0.050%, S: 0~0.050%, Cu: 0-10.0% Ni: 5.0 to 20.0% Cr: 2.0 to 10.0%, Mo: 0-10.0% Nb: 0 to 5.0% V: 0~5.0%, W: 0-10.0%, Mg: 0-1.00% Al: 0 to 3.000%, Ca: 0 to 0.100%, Ti: 0 to 3.000%, B: 0~0.1000%, REM: 0~0.100%, Bi: 0 to 0.050% N: 0.050 to 1.000%, and The balance is Fe and impurities.

[0034] That is, in the flux-cored wire according to the present disclosure, the above-mentioned components are the contents of components contained other than oxides, fluorides, nitrides, and metal carbonates.

[0035] (C: 0.020~0.500%) 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 wire is excessive, the increase in the strength of the weld metal has a significant effect of deteriorating the toughness, and the cryogenic toughness of the weld metal is significantly reduced. Therefore, the C content of the wire is set to 0.020 to 0.500%. The lower limit of the C content of the wire is preferably 0.050%, 0.100%, or 0.200%. The upper limit of the C content of the wire is preferably 0.450%, 0.400%, or 0.350%.

[0036] (Si: 0.20 to 0.80%) Silicon improves the cleanliness of the weld metal and suppresses the occurrence of welding defects such as blowholes. On the other hand, if the wire contains too much Si, microsegregation is likely to occur in the weld metal when welding Ni steel or Ni-based alloy steel, causing significant embrittlement in the segregated area. Therefore, the Si content of the wire is set to 0.20 to 0.80%. The lower limit of the Si content of the wire is preferably 0.23%, 0.25%, 0.30%, or 0.35%. The upper limit of the Si content of the wire is preferably 0.75%, 0.70%, or 0.65%.

[0037] (Mn: 1.50 to 30.00%) Mn is an austenite stabilizing element and improves the cryogenic temperature toughness of weld metal. Mn also functions as a deoxidizer and improves the cleanliness of weld metal. Mn also neutralizes the S in weld metal by forming MnS, improving the cryogenic temperature toughness of weld metal. In addition, Mn has the effect of preventing hot cracking. On the other hand, if the wire contains an excessive amount of Mn, microsegregation is likely to occur in the weld metal when welding Ni steel or Ni-based alloy steel, and significant embrittlement occurs in the segregated area. Therefore, the Mn content of the wire is set to 1.50 to 30.00%. The lower limit of the Mn content of the wire is preferably 2.00%, 5.00%, 7.00%, or 9.00%. The upper limit of the Mn content of the wire is preferably 28.00%, 25.00%, 22.00%, or 20.00%.

[0038] (P: 0 to 0.050%) Since P is an impurity element that reduces the toughness of the weld metal, it is preferable to reduce the P content of the wire as much as possible. Therefore, the lower limit of the P content of the wire is set to 0%. However, from the viewpoint of reducing the dephosphorization cost, the P content is preferably 0.003% or more. On the other hand, if the P content of the wire is 0.050% or less, the adverse effect of P on toughness falls within an acceptable range. In order to effectively suppress a decrease in the toughness of the weld metal, the P content of the wire is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0039] (S:0~0.050%) S is an impurity element that reduces the toughness of the weld metal, so it is preferable to reduce the S content of the wire as much as possible. Therefore, the lower limit of the S content of the wire is set to 0%. However, from the viewpoint of reducing the cost of desulfurization, the S content of the wire should be 0.003% or more. On the other hand, if the S content of the wire is 0.050% or less, the adverse effect of S on toughness falls within an acceptable range. In order to effectively suppress a decrease in the toughness of the weld metal, the S content of the wire is preferably 0.040% or less, 0.030% or less, 0.020% or less, 0.015% or less, or 0.010% or less.

[0040] (Cu: 0 to 10.0%) Cu is a precipitation strengthening element and may be contained in the wire to improve the strength of the weld metal. Cu is also an austenite stabilizing element and may be contained in the wire to improve the cryogenic toughness of the weld metal. On the other hand, if the Cu content of the wire is excessive, the above effect saturates. Therefore, the Cu content of the wire is set to 0 to 10.0%. The lower limit of the Cu content of the wire is preferably 0.5%, 0.7%, 1.0%, or 2.0%. The upper limit of the Cu content of the wire is preferably 9.5%, 9.0%, or 8.0%.

[0041] (Ni: 5.0 to 20.0%) Ni is an austenite stabilizing element. If the Ni content of the wire is too low, the Ni content of the entire wire becomes insufficient, making it difficult for the weld metal to be austenitized, and resulting in a deterioration in cryogenic toughness. On the other hand, increasing the Ni content of the wire increases the cost of the wire. Therefore, the Ni content of the wire is set to 5.0 to 20.0%. The lower limit of the Ni content of the wire is preferably 6.0%, 7.0%, 10.0%, or 12.0%. The upper limit of the Ni content of the wire is preferably 19.0%, 18.0%, or 17.0%.

[0042] (Cr: 2.0 to 10.0%) Cr is an austenite stabilizing element. If the Cr content of the wire is too low, the Cr content of the entire wire will be insufficient, making it difficult for the weld metal to undergo austenitization, and resulting in a deterioration in cryogenic toughness. On the other hand, if the Cr content of the wire is excessive, the amount of low-melting point compounds in the molten metal increases, and the solid-liquid coexistence temperature range of the molten metal widens, making hot cracking more likely to occur. Therefore, the Cr content of the wire is set to 2.0 to 10.0%. The lower limit of the Cr content of the wire is preferably 2.2%, 2.5%, 3.0%, or 3.5%. The upper limit of the Cr content of the wire is preferably 9.5%, 9.0%, or 8.0%.

[0043] (Mo: 0-10.0%) Mo is a solid solution strengthening element and a precipitation strengthening element, and may be contained in the wire to improve the strength of the weld metal. On the other hand, if the Mo content of the wire is excessive, the strength of the weld metal becomes excessive and the cryogenic temperature toughness decreases. Therefore, the Mo content of the wire is set to 0 to 10.0%. The lower limit of the Mo content of the wire is preferably 1.0%, 2.0%, 2.5%, or 3.0%. The upper limit of the Mo content of the wire is preferably 9.5%, 9.0%, or 8.0%.

[0044] (Nb: 0 to 5.0%) 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 wire. On the other hand, if the Nb content of the wire is excessive, there is a concern that hot cracking may occur in the weld metal. Therefore, the Nb content of the wire is set to 0 to 5.0%. The lower limit of the Nb content of the wire is preferably 0.5%, 1.0%, or 1.5%. The upper limit of the Nb content of the wire is preferably 4.5%, 4.0%, or 3.5%.

[0045] (V: 0 to 5.0%) 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 wire. On the other hand, if the V content of the wire is excessive, hot cracking of the weld metal may occur. Therefore, the V content of the wire is set to 0 to 5.0%. The lower limit of the V content of the wire is preferably 0.5%, 1.0%, or 1.5%. The upper limit of the V content of the wire is preferably 4.5%, 4.0%, or 3.5%.

[0046] (W: 0-10.0%) W is a solid solution strengthening element and may be contained in the wire to improve the strength of the weld metal. On the other hand, if the W content of the wire is excessive, the strength of the weld metal becomes excessive, which may result in a decrease in toughness. Therefore, the W content of the wire is set to 0 to 10.0%. The lower limit of the W content of the wire is preferably 0.5%, 1.0%, 2.0%, or 3.0%. The upper limit of the W content of the wire is preferably 9.0%, 8.0%, or 7.0%.

[0047] (Mg: 0-1.00%) Mg is a deoxidizing element and is effective in reducing oxygen in the weld metal and improving the toughness of the weld metal, so it may be contained in the wire. On the other hand, if the Mg content of the wire is excessive, the arc becomes unstable, spatter and blowholes increase, and welding workability deteriorates. Therefore, the Mg content of the wire is set to 0 to 1.00%. The lower limit of the Mg content of the wire is preferably 0.02%, 0.05%, 0.10%, or 0.20%. The upper limit of the Mg content of the wire is preferably 0.90%, 0.80%, or 0.70%.

[0048] (Al: 0 to 3.000%) Al is a deoxidizing element and is effective in suppressing the occurrence of welding defects such as blowholes and improving the cleanliness of the weld metal, and therefore may be contained in the wire. On the other hand, if the Al content of the wire is excessive, Al may form nitrides or oxides in the weld metal, which may reduce the cryogenic toughness of the weld metal. Therefore, the Al content of the wire is set to 0 to 3.000%. The lower limit of the Al content of the wire is preferably 0.010%, 0.020%, or 0.050%. The upper limit of the Al content of the wire is preferably 2.800%, 2.500%, 2.000%, or 1.500%.

[0049] (Ca: 0 to 0.100%) Ca changes the structure of sulfides in the weld metal and 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 contained in the wire. On the other hand, excessive Ca content in the wire may cause coarsening of sulfides and oxides, which may lead to deterioration of the cryogenic toughness of the weld metal, and may also lead to deterioration of the weld bead shape and deterioration of weldability due to instability of the arc. Therefore, the Ca content of the wire is set to 0 to 0.100%. The lower limit of the Ca content of the wire is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Ca content of the wire is preferably 0.095%, 0.090%, or 0.085%.

[0050] (Ti: 0 to 3.000%) Ti is a deoxidizing element and is effective in suppressing the occurrence of welding defects such as blowholes and improving cleanliness, and therefore may be contained in the wire. On the other hand, if the Ti content of the wire is excessive, carbides may be formed in the weld metal, which may deteriorate the toughness of the weld metal. Therefore, the Ti content of the wire is set to 0 to 3.000%. The lower limit of the Ti content of the wire is preferably 0.005%, 0.008%, 0.020%, 0.050%, or 0.100%. The upper limit of the Ti content of the wire is preferably 2.500%, 2.000%, or 1.500%.

[0051] (B: 0 to 0.1000%) B may be contained in the wire because it has the effect of improving the hardenability of the weld metal and further increasing the tensile strength of the weld metal. On the other hand, if the B content of the wire is excessive, the B content in the weld metal will also be excessive, resulting in the formation of coarse BN or Fe. 23 It may form B compounds such as (C, B)6, which may deteriorate the cryogenic toughness of the weld metal. Therefore, the B content of the wire is set to 0 to 0.1000%. The lower limit of the B content of the wire is preferably 0.0010%, 0.0020%, or 0.0030%. The upper limit of the B content of the wire is preferably 0.0900%, 0.0700%, 0.0500%, or 0.0100%.

[0052] (REM: 0 to 0.100%) REM is an element that stabilizes the arc, and may be contained in the wire. On the other hand, if the REM content of the wire is excessive, spattering becomes severe, which may result in poor welding workability. Therefore, the REM content of the wire is set to 0 to 0.100%. The lower limit of the REM content of the wire is preferably 0.001%, 0.002%, or 0.005%. The upper limit of the REM content of the wire is preferably 0.090%, 0.080%, or 0.070%.

[0053] "REM" refers to a total of 17 elements consisting of Sc, Y, and lanthanides, and the "REM content" above refers to the total content of these 17 elements. When lanthanides are used as REMs, industrially, the REMs are contained in the form of misch metals.

[0054] (Bi: 0 to 0.050%) Bi is an element that improves the detachability of slag, and may be contained in the wire. On the other hand, if the Bi content of the wire is excessive, solidification cracking may occur in the weld metal. Therefore, the Bi content of the wire is set to 0 to 0.050%. The lower limit of the Bi content of the wire is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Bi content of the wire is preferably 0.048%, 0.045%, 0.040%, or 0.035%.

[0055] (N: 0.050~1.000%) N is an austenite stabilizing element and also an interstitial solid solution strengthening element. Furthermore, N has less adverse effect on the toughness of the weld metal due to the increase in strength of the weld metal than C. If the N content of the wire is low, the austenitization of the weld metal becomes difficult to progress, and the low-temperature toughness of the weld metal deteriorates. Furthermore, the strength of the weld metal is insufficient. On the other hand, if the N content of the wire is excessive, the occurrence of blowout increases, causing welding defects. Therefore, the N content of the wire is set to 0.050 to 1.000%. The lower limit of the N content of the wire is preferably 0.070%, 0.100%, or 0.150%. The upper limit of the N content of the wire is preferably 0.950%, 0.900%, or 0.850%.

[0056] (balance: Fe and impurities) The remaining components in the chemical composition of the wire are Fe and impurities. The remaining Fe is, for example, Fe contained in the steel outer sheath, Fe in the alloy powder contained in the flux (for example, iron powder), and the like. Further, impurities refer to components that are introduced into the wire during industrial production due to the raw materials or various factors in the production process, and are acceptable within a range that does not adversely affect the wire.

[0057] (Mass ratio of Mn content to Ni content (Mn / Ni) Mn and Ni are austenite stabilizing elements that improve the cryogenic toughness of the weld metal, but Ni is an expensive metal and Mn is an element that increases the amount of fume generated. Therefore, from the viewpoint of improving the cryogenic toughness of the weld metal and reducing the amount of fume generated while suppressing the cost of the wire, the mass ratio (Mn / Ni) of the Mn content to the Ni content in the wire is preferably 0.30 to 4.00. The lower limit of the mass ratio (Mn / Ni) of the Mn content to the Ni content in the wire is more preferably 0.40, 0.50, or 0.60. The upper limit of the mass ratio (Mn / Ni) of the Mn content to the Ni content in the wire is more preferably 3.50, 3.00, or 2.50.

[0058] (Total Ti oxides converted to TiO2: 3.00 to 8.00% by mass) Ti oxides increase the oxygen content in the weld metal, which deteriorates the cryogenic toughness. On the other hand, Ti oxide is a slag component that acts to uniformly coat the entire bead with slag. Ti oxide also stabilizes the duration of the arc and reduces the amount of spatter. Therefore, the inclusion of Ti oxide improves welding workability (especially vertical welding).

[0059] If the total Ti oxides in terms of TiO2 is less than 3.00%, the amount of slag generated is insufficient to uniformly coat the bead, and the slag will stick to the bead surface, resulting in poor bead appearance. Furthermore, if the total Ti oxides in terms of TiO2 is less than 3.00%, the effect of stabilizing the arc is lost, and the amount of spatter generated increases. Furthermore, welding workability (especially vertical welding) cannot be ensured. On the other hand, if the total Ti oxides in terms of TiO2 exceeds 8.00%, the oxygen content in the weld metal increases, making it impossible to ensure cryogenic toughness. Furthermore, if the total Ti oxides in terms of TiO2 exceeds 8.00%, the arc becomes more stable, reducing the amount of spatter generated, but the slag becomes more viscous, resulting in a thicker slag and a bulging bead toe. Furthermore, if the total Ti oxides in terms of TiO2 exceeds 8.00%, pits are more likely to occur. Slag inclusion also occurs.

[0060] Therefore, the total amount of Ti oxides converted into TiO2 is set to 3.00 to 8.00%. The lower limit of the total amount of Ti oxides converted into TiO2 is preferably 3.50%, 4.00%, or 4.50%. The upper limit of the total amount of Ti oxides converted into TiO2 is preferably 7.50%, 7.00%, or 6.50%.

[0061] The Ti oxide may be present in the flux mainly as rutile, titanium oxide, titanium slag, ilmenite, sodium titanate, potassium titanate, etc. Therefore, the Ti oxide content can be adjusted to fall within the above range mainly by controlling the Ti oxide content of the flux.

[0062] Here, the total TiO2 equivalent value of Ti oxides refers to the mass % of TiO2 relative to the total mass of the wire, when all Ti oxides contained in the wire (for example, TiO, TiO2, Ti2O3, Ti3O5, etc., added as rutile, titanium oxide, titanium slag, ilmenite, sodium titanate, potassium titanate, etc.) are converted into TiO2. The total TiO2-equivalent value of Ti oxides is then determined by analyzing the mass of Ti present in the wire as oxides using an X-ray fluorescence analyzer. Specifically, the wire is polished to expose a longitudinal cross section (a cross section parallel to the longitudinal direction of the wire: L-section) at a position halfway along the wire diameter φ, and the cross section is analyzed. For example, if TiO2, Ti2O3, and Ti3O5 are detected by analysis, the mass percentages of each Ti oxide are expressed as [TiO2], [Ti2O3], and [Ti3O5], and the total TiO2-equivalent value of Ti oxides is expressed as [equivalent TiO2], and this can be calculated using the following formula 1. [Converted TiO2]=(0.60×[TiO2]+0.67×[Ti2O3]+0.64×[Ti3O5])×1.67...Equation 1 The coefficients (0.60, 0.67, 0.64) in Equation 1 are used to calculate the amount of Ti contained in each oxide, and the multiplier (1.67) at the end is used to calculate the TiO2 equivalent value from the total amount of Ti present as oxide in the wire.

[0063] Here, we will explain how to calculate the coefficients. x O y If oxides (e.g., TiO2, Ti2O3, Ti3O5) are detected, M x O y The coefficient is calculated using the following formula 2. [atomic weight of element M] × x / ([atomic weight of element M] × x + [atomic weight of oxygen] × y) Equation 2 The 0.60, 0.67, and 0.64 in formula 1 correspond to the coefficients calculated in formula 2 above. We will also explain how to calculate the multiplier for the conversion value. a O b The multiplier for converting to (e.g., TiO2) is calculated using the following formula 3. ([atomic weight of element M] × a + [atomic weight of oxygen] × b) / ([atomic weight of element M] × a) Equation 3 The 1.67 in equation 1 corresponds to the multiplier calculated in equation 3 above. In addition, oxides can also be considered as compounds that combine two metal elements. In that case, the coefficient is calculated as follows: M x O y M 2 z (e.g., TiO3·Fe, that is, M=Ti, M 2 = oxide of Fe, x=1, y=3, z=1) is detected, the calculation is performed using the following equation 4. [atomic weight of element M] × x / ([atomic weight of element M] × x + [atomic weight of oxygen] × y + [M 2 atomic weight of element × z) Equation 4

[0064] The sum of the SiO2-equivalent values ​​of Si oxides, the sum of the ZrO2-equivalent values ​​of Zr oxides, the sum of the Al2O3-equivalent values ​​of Al oxides, the sum of the MgO-equivalent values ​​of Mg oxides, the sum of the Na2O-equivalent values ​​of Na oxides, the sum of the K2O-equivalent values ​​of K oxides, the sum of the CaO-equivalent values ​​of Ca oxides, the sum of the MnO2-equivalent values ​​of Mn oxides, and the sum of the FeO-equivalent values ​​of Ti oxides can also be calculated in the same manner as the sum of the TiO2-equivalent values. That is, a longitudinal cross section at half the wire diameter φ is analyzed using an X-ray fluorescence analyzer, and coefficients and multipliers are calculated according to the various oxides detected using Equations 2, 3, and 4, and then calculations are performed in the same manner as Equation 1. Representative oxides detected by analysis are listed below. Si oxides; SiO, SiO2, Si2O3, Si2O4 Zr oxide; ZrO2 Al oxides: AlO, Al2O3, Al3O5 Magnesium oxide; MgO, MgO2, Mg2O Na oxide; Na2O, Na2O2 K oxide; K2O, KO2 Calcium oxide; CaO, CaO2 Manganese oxides; MnO, Mn2O, MnO2 Fe oxides: FeO, Fe2O4, FeO3

[0065] (Total of Si oxides converted into SiO2: 0.10 to 1.00% by mass) Silicon oxides increase the oxygen content in the weld metal, deteriorating the cryogenic toughness. On the other hand, silicon oxide is a slag component that increases the viscosity of molten slag and improves slag removability. If the total SiO2 equivalent of silicon oxides is less than 0.10%, the slag encapsulation state is poor, slag removability is poor, the bead shape and bead appearance are poor, and welding workability (particularly vertical welding) cannot be ensured. On the other hand, if the total SiO2 equivalent value of Si oxides exceeds 1.00%, the oxygen content of the weld metal increases, making it impossible to ensure cryogenic toughness. Furthermore, if the total SiO2 equivalent value of Si oxides exceeds 1.00%, the amount of spatter increases. Furthermore, if the total SiO2 equivalent value of Si oxides exceeds 1.00%, pits and gas grooves are more likely to occur. Furthermore, slag inclusion occurs.

[0066] Therefore, the total SiO2 equivalent value of Si oxides is set to 0.10 to 1.00%. The lower limit of the total SiO2 equivalent value of Si oxides is preferably 0.15%, 0.20%, or 0.25%. The upper limit of the total amount of Si oxides converted into SiO2 is preferably 0.95%, 0.90%, or 0.85%.

[0067] The Si oxides may be present in the flux mainly as silica sand, zircon sand, feldspar, sodium silicate, potassium silicate, etc. Therefore, the Si oxide content can be adjusted to the above range mainly by controlling the Si oxide content of the flux.

[0068] (Total Zr oxide ZrO2 equivalent: 0 to 0.80% by mass) Zr oxides increase the oxygen content in the weld metal and deteriorate cryogenic toughness. Therefore, from the viewpoint of cryogenic toughness, it is preferable that Zr oxides are not contained, and the lower limit of the total Zr oxides converted into ZrO2 is set to 0%.

[0069] However, Zr oxide is a slag component and has the effect of improving slag coverage in horizontal fillet welding and smoothing the bead shape, so it may be contained from this perspective. On the other hand, if the total Zr oxide content in terms of ZrO2 exceeds 0.80%, the bead shape tends to become convex, and slag inclusion occurs.

[0070] Therefore, the total Zr oxide converted into ZrO2 is set to 0 to 0.80%. The upper limit of the total amount of Zr oxides converted into ZrO2 is preferably 0.60%, 0.40%, 0.20%, or 0.10%.

[0071] Zr oxide may be present mainly as zircon sand, zirconium oxide, etc. in the flux, and may also be contained in trace amounts in Ti oxide. Therefore, the Zr oxide content can be adjusted to the above range mainly by controlling the Zr oxide content of the flux.

[0072] (Total Al oxides converted to Al2O3: 0 to 0.80% by mass) Since Al oxides act as an oxygen source, adding Al oxides increases the amount of oxygen in the weld metal, which causes a deterioration in toughness. Therefore, from the viewpoint of cryogenic toughness, it is preferable not to include Al oxides, and the lower limit of the total Al2O3-equivalent value of Al oxides is set to 0%.

[0073] However, when forming molten slag, Al oxide improves the encapsulation of the slag, thereby preventing undercutting on the upper leg side of the fillet bead, so it may be contained from this perspective. On the other hand, if the total Al2O3 equivalent of Al oxides exceeds 0.80%, the bead toe on the lower leg side of the fillet bead will become bulged, and slag inclusion will occur. Therefore, the total Al2O3 converted value of Al oxides is set to 0 to 0.80%. The upper limit of the total Al oxide content in terms of Al2O3 is preferably 0.60%, 0.20%, or 0.10%.

[0074] In many cases, Al oxide is present in the flux mainly as a component of alumina, feldspar, etc. Therefore, the Al oxide content can be adjusted to the above range mainly by controlling the Al oxide content of the flux.

[0075] (Total fluoride: 0.10 to 2.00% by mass) K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2 (hereinafter, these fluorides may be referred to as "specific fluorides") have the effect of reducing the oxygen content in the weld metal. If the total amount of specific fluorides is less than 0.10%, the oxygen content in the weld metal becomes too high and low-temperature toughness cannot be ensured. On the other hand, if the total content of specific fluorides exceeds 2.00%, a large amount of welding fumes is generated, resulting in welding defects.

[0076] Therefore, the total content of at least one of the specific fluorides is set to 0.10 to 2.00%. The lower limit for the total of particular fluorides is preferably 0.20%, 0.30%, or 0.40%. The upper limit for the total of particular fluorides is preferably 1.90%, 1.80%, or 1.70%.

[0077] (Total of Na-containing compounds: 0.01 to 2.00% by mass) Na oxides, NaF, and NaAlF (hereinafter, these Na-containing compounds may be referred to as "specific Na-containing compounds") decompose during welding, and the Na acts as a deoxidizer to reduce the oxygen content in the weld metal, thereby improving the cryogenic toughness of the molten metal. If the total amount of the specific Na-containing compounds is less than 0.01%, the effect of reducing the oxygen content in the weld metal is small, and cryogenic toughness cannot be ensured. On the other hand, if the total content of the specific Na-containing compounds exceeds 2.00%, the solidification temperature of the welding slag becomes lower, and welding workability (particularly vertical welding ability) deteriorates.

[0078] Therefore, at least one of the specific Na-containing compounds is contained, and the total amount thereof is set to 0.01 to 2.00%. The lower limit of the total amount of the specific Na-containing compounds is preferably 0.05%, 0.15%, 0.20%, or 0.30%. The upper limit of the total amount of the specific Na-containing compounds is preferably 1.90%, 1.80%, 1.70%, or 1.50%. The content of Na oxides means the total Na2O equivalent value of Na oxides.

[0079] (Total of K-containing compounds: 0.01 to 2.00% by mass) In potassium oxide, K2SiF6, and K2ZrF6 (hereinafter, these potassium-containing compounds may be referred to as "specific potassium-containing compounds"), potassium decomposes during welding and acts as a deoxidizer, reducing the oxygen content in the weld metal, thereby improving the cryogenic toughness of the molten metal. If the total amount of the specific K-containing compounds is less than 0.01%, the effect of reducing the oxygen content in the weld metal is small, and cryogenic toughness cannot be ensured. On the other hand, if the total amount of the specific K-containing compounds exceeds 2.00%, the solidification temperature of the welding slag becomes lower, and the welding workability (particularly vertical welding ability) deteriorates.

[0080] Therefore, the total content of at least one of the specific K-containing compounds is set to 0.01 to 2.00%. The lower limit of the total amount of the specific K-containing compounds is preferably 0.05%, 0.20%, 0.30%, or 0.40%. The upper limit of the total amount of the specific K-containing compounds is preferably 1.95%, 1.90%, 1.80%, or 1.50%. The content of K oxides means the total K2O equivalent value of K oxides.

[0081] (Total of Mg-containing compounds: 0.01 to 2.00% by mass) The flux-cored wire according to this embodiment may contain, in addition to the specific Na-containing compound and the specific K-containing compound, one or more Mg-containing compounds selected from Mg oxide and MgF2. Mg oxides and MgF2 (hereinafter, these Mg-containing compounds may be referred to as "specific Mg-containing compounds") decompose during welding, and the Mg acts as a deoxidizer to reduce the oxygen content in the weld metal, thereby improving the cryogenic toughness of the molten metal. When the total content of the specific Mg-containing compounds is 0.01% or more, the effect of reducing the oxygen content in the weld metal is increased, and the cryogenic temperature toughness is further improved. On the other hand, when the total amount of the specific Mg-containing compounds is 2.00% or less, the solidification temperature of the welding slag increases, further improving the welding workability (particularly vertical welding ability).

[0082] Therefore, the total content of one or more specific Mg-containing compounds is preferably 0 to 2.00%, and when an Mg-containing compound is contained, the total content is preferably 0.01 to 2.00%. The lower limit of the total amount of the specific Mg-containing compounds is more preferably 0.20%, 0.30%, or 0.40%. The upper limit of the total amount of the specific Mg-containing compounds is more preferably 1.90%, 1.80%, or 1.70%. The content of Mg oxide means the total MgO-equivalent value of Mg oxide.

[0083] (Other reasons for including specific Na-containing compounds and specific K-containing compounds in wire) Even if the contents of the specific Na-containing compound and the specific K-containing compound are each less than 0.01% and the amount of CaF2 containing Ca, which functions as a deoxidizer, is increased, the amount of spatter increases and welding workability deteriorates.Furthermore, even if the amount of metallic Mg, which functions as a deoxidizer, is increased, metallic Mg increases the amount of diffusible hydrogen in the weld metal and deteriorates cold cracking resistance. Therefore, in order to obtain a weld metal that is excellent in welding workability (particularly vertical weldability) as well as in cryogenic toughness and resistance to cold cracking, it is necessary to include the specific Na-containing compound and the specific K-containing compound in the wire within the above-mentioned ranges. From the same viewpoint, it is also preferable that the wire contains a specific Mg-containing compound in the above range. The contents of the specific Mg-containing compound, the specific Na-containing compound, and the specific K-containing compound are expressed in mass % relative to the total mass of the flux-cored wire.

[0084] (X value calculated by formula A) In the flux-cored wire according to the present disclosure, the value of X calculated by the following formula A is preferably 0.10 to 160.00. X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO)...Formula A In formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 are the contents of the compounds represented by each chemical formula in mass% relative to the total mass of the flux-cored wire. SiO2 represents the total of silicon oxides converted into SiO2, Al2O3 represents the total of aluminum oxides converted into Al2O3, ZrO2 represents the total of zirconium oxides converted into ZrO2, MgO represents the total of magnesium oxides converted into MgO, CaO represents the total of calcium oxides converted into CaO, Na2O represents the total of sodium oxides converted into Na2O, K2O represents the total of potassium oxides converted into K2O, MnO2 represents the total of manganese oxides converted into MnO2, and FeO represents the total of iron oxides converted into FeO. In addition, the SiO2 equivalent value, the Al2O3 equivalent value, the ZrO2 equivalent value, the MgO equivalent value, the CaO equivalent value, the Na2O equivalent value, the K2O equivalent value, the MnO2 equivalent value, and the FeO equivalent value in Formula A are expressed in mass% with respect to the total mass of the flux-cored wire.

[0085] In formula A, the numerator is an index of the amount of compounds that decompose during welding, function as deoxidizers, and reduce the oxygen content of the weld metal (Ca, Mg, Na, K, Si), and fluorine, which reduces the diffusible hydrogen content of the weld metal. On the other hand, the denominator is an index of the amount of compounds containing oxygen (O), which increases the oxygen content of the weld metal.

[0086] That is, when the X value is 0.10 or more, the amount of compounds containing oxygen (O) that increase the oxygen content in the weld metal is small, the effect of reducing the oxygen content in the weld metal is large, and the cryogenic toughness is further improved. On the other hand, if the X value is 160.00 or less, the amount of fluoride is not too large, slag inclusion is less likely to occur, and a sound joint can be easily produced.

[0087] Therefore, the value of X calculated by formula A is preferably set to 0.10 to 160.00. The lower limit of the X value is more preferably 1.00, 5.00, or 10.00. The upper limit of the X value is more preferably 130.00, 100.00, 70.00, 50.00, or 20.00.

[0088] (Ceq calculated by formula B) In the flux-cored wire according to the present disclosure, Ceq calculated by formula B is preferably 0.30 to 0.75. Ceq=[C]+[Si] / 24+[Mn] / 6+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14...Formula B In formula B, the element symbols represent the content, in mass %, of each element contained as a chemical component excluding oxides, fluorides, nitrides, and metal carbonates relative to the total mass of the flux-cored wire.

[0089] Ceq affects the hardenability of the weld metal. When Ceq is high, the weld metal hardens, improving its tensile strength, but reducing its cryogenic toughness. When Ceq is 0.30% or more, the Ceq of the weld metal tends to be satisfied, and the tensile strength of the weld metal tends to be satisfactory. When Ceq is 0.75% or less, it becomes easier to prevent the Ceq of the weld metal from becoming excessive, the cryogenic temperature toughness of the weld metal is sufficient, and low-temperature cracking tends to be suppressed. Therefore, Ceq is preferably 0.30 to 0.75. The lower limit of Ceq is more preferably 0.35, 0.40, or 0.45. The upper limit of Ceq is more preferably 0.70, 0.65, or 0.60.

[0090] -Total content of other oxides: 0 to 10.00%- In the flux-cored wire according to the present disclosure, when one or more oxides selected from the group consisting of Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide are contained as oxides other than Ti oxide, Si oxide, Zr oxide, and Al oxide, the total content thereof is preferably 10.00% or less. Oxides included in the group consisting of Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide may be simply referred to as "other oxides." Furthermore, the total content of each oxide in the other oxides may be simply referred to as the "total content of other oxides."

[0091] When the flux-cored wire according to the present disclosure contains one or more of the other oxides, the total content of the other oxides is calculated as the sum of the Fe oxide (converted into FeO), the Mg oxide (converted into MgO), the Na oxide (converted into NaO), the K oxide (converted into KO), the Mn oxide (converted into MnO), and the Ca oxide (converted into CaO).

[0092] In addition, since the other oxides are not essential components in the flux-cored wire according to the present disclosure, the lower limit of the total content of the other oxides in the flux-cored wire is 0%. On the other hand, other oxides have the effect of maintaining a good weld bead shape and improving vertical weldability. Furthermore, Mg oxide, Fe oxide, and the like also have the effect of stabilizing the arc. To achieve such effects, the total content of other oxides may be greater than 0%. To further enhance these effects, the lower limit of the total content of other oxides may be set to 0.05%, 0.10%, 0.15%, or 0.20%. On the other hand, when the total content of other oxides is 10.00% or less, the occurrence of slag entrapment is suppressed, and a sound joint can be easily fabricated. Therefore, the upper limit of the total content of other oxides is preferably set to 10.00%, and may be set to 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00%, 0.50%, or 0.30%.

[0093] The content of other oxides in the flux-cored wire according to the present disclosure does not need to be limited to each type of oxide. The content of each oxide in the other oxides and the total content of the other oxides are measured by fluorescent X-ray analysis in the same manner as the content of Ti oxide described above.

[0094] (nitrides, metal carbonates) Nitrides (especially nitrides in flux) reduce the amount of diffusible hydrogen in the weld metal, significantly improving the cold cracking resistance of the weld metal. The reason for this is unclear, but one possible reason is that the N in the nitrides combines with hydrogen (H) during welding to form ammonia (NH3), which is then released outside the weld metal. Therefore, the flux-cored wire according to the present disclosure may include nitrides.

[0095] The flux-cored wire according to the present disclosure may contain, as the nitride, one or more selected from the group consisting of AlN, BN, Ca3N2, CeN, CrN, Cu3N, Fe4N, Fe3N, Fe2N, Mg3N, Mo2N, NbN, Si3N4, TiN, VN, ZrN, Mn2N, and Mn4N, for example.

[0096] Metal carbonates are ionized by the arc and generate CO2 gas, which reduces the hydrogen partial pressure in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. Therefore, the flux-cored wire according to the present disclosure may contain metal carbonate in the flux.

[0097] The flux-cored wire according to the present disclosure may contain, as the metal carbonate, one or more selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3. However, the type and composition of the metal carbonate are not limited.

[0098] The contents of nitrides and metal carbonates are measured by fluorescent X-ray analysis in the same manner as the content of Ti oxides described above.

[0099] The flux-cored wire according to the present disclosure may further include a lubricant applied to the wire surface. The lubricant applied to the wire surface has the effect of improving the wire feedability during welding. Various types of lubricants (e.g., vegetable oils such as palm oil) can be used for welding wire, but in order to suppress cold cracking of the weld metal, it is preferable to use one or both of polytetrafluoroethylene oil (PTFE oil) and perfluoropolyether oil (PFPE oil) that do not contain H. Furthermore, as described above, the flux-cored wire according to the present disclosure may further include a plating formed on the wire surface. In this case, the lubricant is applied to the surface of the plating.

[0100] The amount of hydrogen contained in the flux-cored wire according to the present disclosure is not particularly limited, but is preferably 12 ppm or less relative to the total mass of the flux-cored wire in order to reduce the amount of diffusible hydrogen in the weld metal. The amount of hydrogen in the flux-cored wire may increase due to moisture penetration into the flux-cored wire during storage. Therefore, if there is a long period of time between the wire's manufacture and its use, it is desirable to prevent moisture penetration by the means described below.

[0101] (wire shape) Next, the shape (wire structure) of the flux-cored wire according to the present disclosure will be described. Flux-cored wires are usually classified into two types: wires with a seamless shape (wires with no welds at the seams of the steel sheath) in which the seams of the steel sheath are welded, and wires with a seam shape (wires with welds at the seams of the steel sheath) in which the seams of the steel sheath are not welded and include slit-like gaps.

[0102] The flux-cored wire according to the present disclosure can have any of these shapes. However, in order to suppress the occurrence of cold cracking in the weld metal, it is preferable that the steel sheath does not have slit-like gaps. H (hydrogen) that penetrates the weld during welding diffuses into the weld metal and the material to be welded, and accumulates in areas where stress is concentrated, causing cold cracking. There are various sources of H, but when welding is performed under strict control of the cleanliness of the weld and the gas shielding conditions, moisture (HO) contained in the wire is the main source of H, and the amount of this moisture strongly affects the amount of diffusible hydrogen in the weld joint.

[0103] If the steel sheath has a seam, atmospheric moisture is likely to penetrate into the flux through the seam. Therefore, it is desirable to prevent atmospheric moisture from penetrating into the flux through the steel sheath during the period from wire production to use by removing the seam. If the steel sheath has a seam and there is a long period between wire production and use, it is desirable to vacuum-pack the entire flux-cored wire or store the flux-cored wire in a container that can keep it dry in order to prevent the penetration of sources of H, such as moisture.

[0104] (wire diameter) The diameter of the flux-cored wire according to the present disclosure is not particularly limited, but is, for example, φ1.0 to φ2.0 mm. Note that the diameter of a typical flux-cored wire is φ1.2 to φ1.6 mm.

[0105] (Filling rate) The filling factor of the flux-cored wire according to the present disclosure is not particularly limited as long as the above-mentioned conditions are satisfied. In consideration of the filling factor of a typical flux-cored wire, the lower limit of the filling factor of the flux-cored wire according to the present disclosure may be, for example, 8%, 10%, or 12%. The upper limit of the filling factor of the flux-cored wire according to the present disclosure may be, for example, 28%, 25%, 22%, 20%, or 17%.

[0106] <Method for manufacturing flux-cored wire> Next, a method for manufacturing a flux-cored wire according to the present disclosure will be described. The manufacturing method described below is an example, and the method for manufacturing the flux-cored wire according to the present disclosure is not limited to the following method.

[0107] (In the case of seamless flux-cored wire) A method for manufacturing a flux-cored wire having a seamless shape includes the steps of preparing flux, forming a steel strip using a forming roll while feeding it in the longitudinal direction to obtain a U-shaped open tube, supplying flux into the open tube through the opening of the open tube, butt-welding the opposing edge portions (both circumferential ends) of the opening of the open tube to obtain a seamless tube, drawing the seamless tube to obtain a flux-cored wire having a predetermined wire diameter, and annealing the flux-cored wire during or after the drawing step. The flux is prepared so that the content of each component of the flux-cored wire falls within the above-mentioned range. Note that the width and thickness of the steel strip that is the material of the steel sheath, as well as the flux filling rate, which is determined by the amount of flux filling, also affect the content of each component of the flux-cored wire.

[0108] The butt welding is performed by electric resistance welding, laser welding, TIG welding, or the like. During or after the wiredrawing process, the flux-cored wire is annealed to remove moisture from the flux-cored wire. In order to make the H content of the flux-cored wire 12 ppm or less, the annealing temperature is preferably 650°C or higher and the annealing time is preferably 4 hours or longer. In order to prevent deterioration of the flux, the annealing temperature is preferably 900°C or lower.

[0109] If the cross section of a butt seam welded flux-cored wire without slit-like gaps is polished and etched, the weld marks can be seen, but if it is not etched, the weld marks cannot be seen. For this reason, it is sometimes called seamless, as mentioned above. For example, in "New Edition: Introduction to Welding and Joining Technology" (2008) edited by the Japan Welding Society, Sanpo Publishing, p. 111, it is stated that a butt seam welded flux-cored wire without slit-like gaps is a seamless type wire. Even if the gaps in the steel sheath of a flux-cored wire are brazed, a flux-cored wire without slit-like gaps can be obtained.

[0110] (In the case of flux-cored wire with slit-shaped gaps) The method for producing a flux-cored wire having a slit-like gap is the same as the method for producing a seamless flux-cored wire, except that instead of butt-welding both circumferential ends of an open pipe to obtain a seamless pipe, the method for producing a flux-cored wire having a slit-like gap includes a step of forming an open pipe and butt-welding the ends of the open pipe to obtain a pipe with a slit-like gap. The method for producing a flux-cored wire having a slit-like gap may further include a step of crimping the butted ends of the open pipe. In a method for manufacturing a flux-cored wire having slit-like gaps, a tube having slit-like gaps is drawn.

[0111] <Method for manufacturing welded joints> Next, a method for manufacturing a welded joint (welding method) according to the present disclosure will be described. A method for manufacturing a welded joint according to the present disclosure includes a step of welding steel materials using the flux-cored wire according to the present disclosure described above.

[0112] In the method for manufacturing a welded joint according to the present disclosure, the welding method is preferably gas-shielded arc welding. In the method for manufacturing a welded joint according to the present disclosure, the type of steel material (welded material) that serves as the base material of the welded joint is not particularly limited. For example, CMSteel materials with high cold cracking susceptibility having a (weld crack susceptibility composition) of 0.24% or more, particularly high-strength steel plates with a tensile strength of 590 MPa to 1700 MPa and a plate thickness of 20 mm or more, can be suitably used.

[0113] The method for manufacturing a welded joint according to the present disclosure may include a step of welding steel materials using a flux-cored wire according to the present disclosure in one or more of the first to final passes. When the welding is performed in only one pass, the flux-cored wire according to the present disclosure is used in that one pass. The polarity of the flux-cored wire may be either positive or negative, since the effect on the amount of diffusible hydrogen in the weld metal and the amount of spatter generated is negligibly small, but positive is preferred.

[0114] The type of shielding gas used in the method for manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure exhibits excellent welding workability regardless of the type of shielding gas, and can obtain a welded joint having high strength, high toughness, and high fatigue strength. Commonly used shielding gases such as 100% carbon dioxide and mixed gases of Ar and 3 to 30% CO2 by volume can be preferably used as the shielding gas in the method for manufacturing a welded joint according to the present disclosure. Furthermore, the shielding gas used in welding using the flux-cored wire according to the present disclosure may contain 5% or less by volume of O2 gas. Because these gases are inexpensive, welding using these gases is advantageous for industrial use. Normally, when these gases are used in combination with a rutile-based flux-cored wire, they generate a large amount of spatter, deteriorating welding workability. However, the method for manufacturing a welded joint according to the present disclosure uses the flux-cored wire according to the present disclosure, which can sufficiently suppress the amount of spatter, and therefore, even when these gases are used as shielding gases, good welding workability can be achieved.

[0115] The welding position in the method for manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure can exhibit good welding workability (particularly vertical welding ability) regardless of the welding position, which may be a flat position, a horizontal position, a vertical position, or an overhead position.

[0116] The welded joint obtained by the welded joint manufacturing method according to the present disclosure includes a base steel material and a welded joint composed of a weld metal and a weld heat-affected zone. Because the welded joint according to the present disclosure is manufactured using the flux-cored wire according to the present disclosure, the welded joint includes a weld metal having a good bead shape. The tensile strength of the welded joint obtained is high, ranging from 590 to 1200 MPa. [Example]

[0117] Next, the feasibility and effects of the present disclosure will be explained in more detail using examples and comparative examples. However, the following examples do not limit the present disclosure, and any design changes that are made in accordance with the spirit described above and below are all included in the technical scope of the present disclosure.

[0118] (Flux-cored wire manufacturing) The flux-cored wires of the examples and comparative examples were produced by the method described below. First, a steel strip having the chemical composition of the outer sheath shown in Table 1 was fed in the longitudinal direction and formed using forming rolls to obtain a U-shaped open pipe. Flux was supplied into the open pipe through the opening, and the opposing edges of the opening of the open pipe were butt-welded to obtain a seamless pipe. The seamless tube was drawn to obtain a flux-cored wire without slit-like gaps, although some samples were drawn to tubes with slit-like gaps without seam welding. In this way, flux-cored wires with a final wire diameter of 1.2 mm were produced as prototypes. During the drawing process, the flux-cored wires were annealed at a temperature range of 650 to 950°C for 4 hours or more. After the prototypes were produced, a lubricant was applied to the wire surface. The configurations of these flux-cored wires are shown in Tables 2A to 2D.

[0119] The units of the contents of the chemical components of the sheath, the chemical components of the wire, the oxide content, the fluoride content, the Na-containing compound content, the K-containing compound content, and the iron powder content shown in Tables 1 and 2 are mass% relative to the total mass of the flux-cored wire. In the tables, "mass% relative to the total mass of the steel sheath" and "mass% relative to the total mass of the flux-cored wire" are both abbreviated to "mass%," and "chemical components of the wire excluding oxides, fluorides, nitrides, and metal carbonates" is abbreviated to "chemical components of the wire."

[0120] [Table 1]

[0121] [Table 2A]

[0122] [Table 2B]

[0123] [Table 2C]

[0124] [Table 2D]

[0125] The remainder of the steel sheath shown in Table 1 (i.e., components other than those shown in the table) and the remainder of the flux-cored wire shown in Table 2 (i.e., components other than those shown in the table) are iron and impurities. Among the flux-cored wires shown in Table 2, those marked "seamless" in the "wire structure" column have a seamless shape and are coated with palm oil as a lubricant unless otherwise specified in the "remarks" column. In addition, those marked "with slit-like gaps" in the "wire structure" column are wires with slit-like gaps, and those marked "PTFE coated" in the "remarks" column are wires coated with PTFE oil. Each element contained in the flux-cored wire shown in Table 2 is in the form of a steel sheath or metal powder. In Tables 1 and 2, values ​​outside the ranges specified in this disclosure are underlined. Furthermore, in Tables 1 and 2, blank spaces in the tables relating to the content of chemical components, compounds, etc., mean that the chemical components, compounds, etc. are not intentionally included. These chemical components, compounds, etc. may be unavoidably mixed in or generated.

[0126] [evaluation] The flux-cored wires of the examples and comparative examples were used to carry out evaluation by vertical upward gas-shielded arc welding. Specifically, the evaluation was carried out by the method described below. The steel plates used for welding were 50 mm thick and had a tensile strength of 780 MPa, and the welding gas used for the evaluation was Ar-20% CO2. Furthermore, all welding currents used for the evaluation were direct current, and all wire polarities were positive. The welding conditions for evaluation were as shown in Table 3.

[0127] [Table 3]

[0128] (Fume amount evaluation) The amount of fume produced when gas shielded arc welding was performed using the flux-cored wires of the examples and comparative examples was evaluated. The amount of fumes generated by welding was measured using a high-volume air sampler to capture the total amount in accordance with JIS Z3930:2013 (Method for measuring fume generation in arc welding). Flux-cored wires with a fume amount of 1000 mg / min or less were deemed to have "passed" the test for fume amount.

[0129] (Evaluation of spatter amount) The amount of spatter when gas shielded arc welding was performed using the flux-cored wires of the examples and comparative examples was evaluated. The amount of spatter generated by welding was measured by collecting spatter scattered from the arc point in a collection box and measuring the weight per unit time. The welding conditions applied were as shown in Table 3. Flux-cored wires with a spatter amount of 2000 mg / min or less were deemed "passed" in terms of spatter amount.

[0130] (Evaluation of cryogenic toughness) Using the flux-cored wires of the examples and comparative examples, steel plates were gas-shielded arc-welded, and three impact test specimens (V-notch test specimens with a notch depth of 2 mm) were taken from the center of the plate thickness direction of the deposited metal. The three impact test pieces were subjected to a Charpy impact test at -196°C in accordance with JIS Z2242:2005. The three impact test pieces were rated as "pass" when the average Charpy absorbed energy at -196°C was 27 J or more, and as "fail" when it was less than 27 J.

[0131] (comprehensive evaluation) If the evaluation of the amount of fume, the amount of spatter, and the evaluation of the cryogenic toughness were all "pass," the test was evaluated as "pass," and if any of them were "fail," the test was evaluated as "fail."

[0132] [Table 4]

[0133] It is clear that the flux-cored wires of the examples have small amounts of fume and spatter, and the resulting weld metal has excellent cryogenic toughness. On the other hand, the comparative examples did not satisfy any of the requirements defined in this disclosure and therefore failed in one or more evaluation items.

Claims

1. A flux-cored wire for welding having a steel outer sheath and flux filled inside the steel outer sheath, The chemical composition of the steel skin is, in mass % relative to the total mass of the steel skin, C: 0-0.100%, Si: 0 to 0.10%, Mn: 0 to 1.00%, P: 0 to 0.050%, S: 0 to 0.050%, Al: 0-0.100%, Ti: 0 to 0.100%, N: 0 to 0.0100%, and The balance is Fe and impurities, and the total content of C, Si, Mn, P, S, Al, Ti, and N is 1.5000% or less, The chemical composition of the flux-cored wire, excluding oxides, fluorides, nitrides, and metal carbonates, is, in mass % based on the total mass of the flux-cored wire: C: 0.020-0.500%, Si: 0.20-0.80%, Mn: 1.50-30.00%, P: 0 to 0.050%, S: 0 to 0.050%, Cu: 0-10.0%, Ni: 5.0 to 20.0%, Cr: 2.0-10.0%, Mo: 0-10.0%, Nb: 0 to 5.0%, V: 0 to 5.0%, W: 0-10.0%, Mg: 0-1.00%, Al: 0-3.000%, Ca: 0-0.100%, Ti: 0-3.000%, B: 0-0.1000%, REM: 0-0.100%, Bi: 0 to 0.050%, N: 0.050 to 1.000%, and The balance is Fe and impurities. Ti oxide TiO ２ The total conversion value is 3.00 to 8.00%, Si oxide SiO ２ The total of the converted values ​​is 0.10 to 1.00%, Zr oxide ZrO ２ The total of the conversion values ​​is 0 to 0.80%, Al in Al oxide ２ O ３ The total of the conversion values ​​is 0 to 0.80%, K ２ SiF ６ , K. ２ ZrF ６ , NaF, Na ３ AlF ６ , CaF ２ , and MgF ２ The total amount of any one or more fluorides is 0.10 to 2.00%, Na oxide, NaF, and Na ３ AlF ６ The total of any one or more of the following Na-containing compounds (except Na oxides): ２ O equivalent) is 0.01 to 2.00%, K oxide, K ２ SiF ６ , and K ２ ZrF ６ Contains one or more K-containing compounds (excluding K oxides) ２ The flux-cored wire has a Cr content (calculated as O) of 0.01 to 2.00%.

2. 2. The flux-cored wire according to claim 1, wherein the value of X calculated by the following formula A is 0.10 to 160.

00. X = (8 × CaF ２ + 5 × MgF ２ + 5 × NaF + 5 × K ２ SiF ６ + 5 × K ２ ZrF ６ + Na ３ AlF ６ ) / (SiO ２ + Al ２ O ３ + ZrO ２ + 0.5 × MgO + CaO + 0.5 × Na ２ O + 0.5 × K ２ O + MnO ２ + FeO) ···· Formula A In formula A, CaF ２ , MgF ２ , NaF, K ２ SiF ６ , K. ２ ZrF ６ , and Na ３ AlF ６ is the content of the compound represented by each chemical formula in mass % relative to the total mass of the flux-cored wire. ２ is Si oxide SiO ２ Indicates the total of the converted values, Al ２ O ３ is Al in Al oxide ２ O ３ The sum of the converted values ​​is ZrO ２ is Zr oxide ZrO ２ MgO represents the sum of Mg oxides in MgO equivalent values, CaO represents the sum of Ca oxides in CaO equivalent values, and Na ２ O is Na in Na oxide ２ The sum of the O conversion values ​​is shown, and K ２ O is K in K oxide ２ The total of MnO ２ is Mn oxide MnO ２ FeO indicates the total FeO converted value of Fe oxides. In addition, the SiO ２ Conversion value, Al ２ O ３ Conversion value, ZrO ２ the MgO equivalent value, the CaO equivalent value, the Na ２ O equivalent value, the above K ２ O equivalent value, the MnO ２ The converted value and the FeO converted value are expressed as mass % with respect to the total mass of the flux-cored wire.

3. 3. The flux-cored wire according to claim 1, wherein the mass ratio (Mn / Ni) of the Mn content to the Ni content in the chemical components of the flux-cored wire is 0.30 to 4.

00.

4. The flux-cored wire according to any one of claims 1 to 3, wherein the steel sheath has no welded joint at the joint of the steel sheath.

5. The flux-cored wire according to any one of claims 1 to 3, wherein the steel sheath has a welded portion at a joint of the steel sheath.

6. 6. The flux-cored wire according to claim 1, wherein the surface is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.

7. A method for manufacturing a welded joint, comprising a step of welding steel materials using the flux-cored wire according to any one of claims 1 to 6.

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