Flux-cored wire and method for manufacturing welded joint

Abstract

To provide a manufacturing method for a flux-cored cut wire and a weld joint.SOLUTION: This invention includes a welding flux-cored wire comprising a steel jacket and flux to charge the interior of the steel jacket and containing nitride in the flux, having a Ni content of 0.003-40.00% by mass% to the total mass of the flux-cored wire, and satisfying both the formula 1 and the formula 2, 0.03<[W]+[Sn]+[Sb]≤30.00 . . . formula 1, 0.05≤[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≤55.00 . . . formula 2, element symbols surrounded by angled parenthesis in the formula 1 and the formula 2 represent contents by mass% to the flux-cored wire of each element contained in the flux-coed wire.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, there has been an increasing demand for larger and lighter construction and industrial machinery, and as a result, ultra-high tensile strength steel plates such as 780MPa and 980MPa steel are being used.The reason for using these ultra-high tensile strength steel plates is that they make products lighter and reduce the amount of steel used, which reduces steel costs and transportation costs, and because the thinner steel and reduced unit weight make it easier to handle and require less welding, it is expected to shorten manufacturing times and reduce construction costs.

[0003] When welding high-strength, extra-thick steel plates, preheating is performed to prevent cold cracking, i.e., cracking that occurs in the weld after the temperature of the weld has dropped to near room temperature. Furthermore, when welding ultra-high tensile steel plates, the weld metal may also be required to have corrosion resistance and hot cracking resistance.

[0004] For example, Patent Document 1 discloses a flux-cored wire in which the flux contains metal fluoride or the like in consideration of welding workability, cold cracking resistance of the weld metal, and the like. Patent Document 2 discloses a flux-cored wire containing a predetermined amount of BaF2 or the like in consideration of welding workability and hot cracking resistance of the weld metal. Patent Document 3 discloses a flux-cored wire that takes into consideration the corrosion resistance and hot cracking resistance of the weld metal, and in which the core flux contains aluminum (Al) at a concentration of about 3% to about 20% by weight based on the total weight of the wire. Furthermore, Patent Document 4 discloses a welding wire in which the core contains Cr, Mn, Ni, and C in predetermined amounts. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-300768 [Patent Document 2] Japanese Patent Application Publication No. 2017-24032 [Patent Document 3] Japanese Patent Application Publication No. 2019-63870 [Patent Document 4] Japanese Patent Application Publication No. 2019-34340 Summary of the Invention [Problem to be solved by the invention]

[0006] As in Patent Documents 1 to 4, various flux-cored wires have been proposed that take into consideration welding workability, resistance to cold cracking of the weld metal, resistance to hot cracking, corrosion resistance, etc., but a flux-cored wire that satisfies all of these properties is desirable. Note that in order to suppress the occurrence of cold cracking and to omit or simplify the preheating process, it is effective to reduce diffusible hydrogen during welding.

[0007] The present disclosure has been made in view of the above-described circumstances, and has an object to provide a flux-cored wire and a method for manufacturing a welded joint that allows welding to be performed without preheating the steel material or with only simple preheating, provides excellent corrosion resistance to the weld metal, and is capable of suppressing cold cracking and hot cracking by reducing the amount of diffusible hydrogen in the weld metal. [Means for solving the problem]

[0008] The gist of the present disclosure is as follows. <1> A flux-cored wire for welding having a steel sheath and flux filled inside the steel sheath, A flux-cored wire containing nitrides, with an N content of 0.003 to 40.00% by mass relative to the total mass of the flux-cored wire, and satisfying both formula 1 and formula 2. 0.03<[W]+[Sn]+[Sb]≦30.00...Equation 1 0.05≦[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≦55.00...Equation 2 The element symbols enclosed in square brackets in Formula 1 and Formula 2 represent the content of each element contained in the flux-cored wire in mass % relative to the total mass of the flux-cored wire. <2> The chemical components of the flux-cored wire, excluding the nitrides, oxides, fluorides, and carbonates, are, in mass % based on the total mass of the flux-cored wire, C: 0.003 to 0.500%, Si: 0 to 3.50% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.020%, W: 0~10.00%, Sn: 0~10.00%, Sb: 0 to 10.00% Cu: 0-10.00% Ni: 0~50.00%, Cr: 0~50.00%, Mo: 0~50.00%, Nb: 0 to 0.50% V: 0~0.50%, Ti: 0 to 0.50% Al: 0-1.00%, B: 0~0.100%, Mg: 0-2.00% Ca: 0-2.00%, Zr: 0 to 0.50% REM: 0~0.50%, Bi: 0 to 0.300%, and Remainder: Fe and impurities <1> The flux-cored wire according to claim 1. <3> The flux-cored wire contains, in mass % relative to the total mass of the wire, 0.20 to 8.00% of Ti oxide and 0 to 3.0% in total of one or more oxides selected from the group consisting of Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca oxide. <1> or <2> The flux-cored wire according to claim 1. <4> The flux-cored wire contains fluoride, and the F content is 0.002 to 30,000% by mass relative to the total mass of the flux-cored wire. <1> ~ <3> 10. The flux-cored wire according to any one of the above items. <5> The flux-cored wire contains one or more carbonates selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3, and the total content of the carbonates is 5.000% or less in mass% based on the total mass of the flux-cored wire. <1> ~ <4> 10. The flux-cored wire according to any one of the above items. <6> The surface is coated with either or both of polytetrafluoroethylene oil and perfluoropolyether oil. <1> ~ <5> 10. The flux-cored wire according to any one of the above items. <7> The nitride is 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. <1> ~ <6> 10. The flux-cored wire according to any one of the above items. <8> <1> ~ <7> 10. A method for manufacturing a welded joint, comprising: gas-shielded arc welding steel materials using the flux-cored wire according to any one of claims 1 to 9. [Effects of the Invention]

[0009] According to the present disclosure, there are provided a flux-cored wire and a method for manufacturing a welded joint that allow welding to be performed without preheating the steel material or with only simple preheating, provide excellent corrosion resistance to the weld metal, and suppress cold cracking and hot cracking by reducing the amount of diffusible hydrogen in the weld metal. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram showing a cutting position A of a corrosion-resistant test piece for evaluating the corrosion resistance of a weld metal in an example. [Figure 2] FIG. 2 is a schematic diagram illustrating a corrosion test apparatus used in a general corrosion test in the examples. [Figure 3] FIG. 2 is a schematic diagram illustrating a corrosion test device used in a localized corrosion (pitting corrosion) test in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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. Furthermore, 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 necessarily need to be contained.

[0012] First, the process and mechanism leading to the completion of the flux-cored wire and the method for manufacturing a welded joint according to the present disclosure will be described. In the welding of high-strength extra-thick steel plates, preheating is performed to suppress cold cracking. In order to suppress the occurrence of cold cracking and to omit or simplify the preheating process, it is effective to reduce the diffusible hydrogen during welding. For example, it has been reported that fluoride is added to the flux or welding wire to reduce the amount of diffusible hydrogen. The mechanism is thought to be that the fluoride in the welding material is dissociated by the arc, the hydrogen partial pressure in the arc atmosphere is reduced by the fluorine, and the amount of hydrogen dissolved in the molten pool is reduced. However, if the wire contains fluoride, a large amount of fumes are generated during welding, which can lead to reduced workability. Therefore, the inventors considered using materials other than fluoride and found that wire containing nitride can achieve the same effect as fluoride. Specifically, it is presumed that nitrides in the welding material dissociate in the arc to generate nitrogen, lowering the hydrogen partial pressure in the arc atmosphere and reducing the amount of hydrogen dissolved in the molten pool. Another presumed reason is that N in the nitride combines with hydrogen (H) during welding to form ammonia (NH3), which is then released outside the weld metal. Furthermore, wire containing nitride suppresses the generation of fumes during welding.

[0013] On the other hand, in order to improve the corrosion resistance of the weld, it is effective to include elements that contribute to improving corrosion resistance (sometimes referred to as "corrosion-resistant elements" in this specification), such as W, Sn, Sb, Cu, Ni, Cr, and Mo, in the flux-cored wire. However, when flux-cored wire containing these corrosion-resistant elements is used, W, Sn, and Sb promote cold cracking and hot cracking in the weld metal (in this specification, cold cracking and hot cracking are sometimes collectively referred to as "cracks"). However, it has been found that the inclusion of nitrides in the wire also suppresses the occurrence of cracks in the weld metal. Although the mechanism is unclear, it is thought that the nitrides contained in the wire flux and the nitrogen contained in the steel sheath cause the prior austenite grain size in the weld metal to be refined, thereby suppressing the occurrence of cracks. The refinement of the prior austenite grain size in the weld metal is presumably due to the occurrence of the solute drag effect, i.e., N segregating to grain boundaries, reducing the grain boundary migration rate, and thereby refining the prior austenite grain size.

[0014] <Flux-cored wire> The flux-cored wire according to the present disclosure is a flux-cored wire for welding having a steel sheath and flux filled inside the steel sheath, and contains nitrides, with an N content of 0.003 to 40.00% by mass relative to the total mass of the flux-cored wire, and satisfies both formula 1 and formula 2. 0.03<[W]+[Sn]+[Sb]≦30.00...Equation 1 0.05≦[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≦55.00...Equation 2 The element symbols enclosed in square brackets in Formula 1 and Formula 2 represent the content of each element contained in the flux-cored wire in mass % relative to the total mass of the flux-cored wire. The content of each element in Formula 1 and Formula 2 represents the total amount of each element, including the amount of each element contained as a simple metal element and the amount of each element contained as a compound such as a nitride, oxide, fluoride, or carbonate. The reasons for limiting the requirements (including optional requirements) for the flux-cored wire according to the present disclosure will be specifically described below.

[0015] As described above, the flux-cored wire according to the present disclosure contains nitrides, has an N content of 0.003 to 40.00%, and satisfies both formula 1 and formula 2. 0.03<[W]+[Sn]+[Sb]≦30.00...Equation 1 0.05≦[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≦55.00...Equation 2 The flux-cored wire (particularly the flux) according to the present disclosure preferably contains oxides, fluorides, and / or carbonates in addition to the above. These components will be described in detail below. In the following description, "%" means "mass % relative to the total mass of the flux-cored wire" unless otherwise specified.

[0016] 0.03<[W]+[Sn]+[Sb]≦30.00...Equation 1 W, Sn, and Sb (these elements may be collectively referred to as the "first corrosion-resistant element group" in this specification) are elements that improve corrosion resistance. However, if the total content of the first corrosion-resistant element group is too small, the corrosion resistance of the weld metal cannot be sufficiently improved. Therefore, in the flux-cored wire according to the present disclosure, the total content of the first corrosion-resistant element group is set to more than 0.03% from the viewpoint of improving the corrosion resistance of the weld metal. The lower limit of the total content of the first corrosion-resistant element group may be 0.05%, 0.10%, or 0.15%. On the other hand, if the total content of the first corrosion-resistant element group is too high, hot cracking of the weld metal becomes more likely to occur. Therefore, the total content of the first corrosion-resistant element group is set to 30.00% or less. The upper limit of the total content of the first corrosion-resistant element group may be 20.00%, 15.00%, or 10.00%. In addition, the flux-cored wire according to the present disclosure preferably contains at least one of Sn and Sb from the viewpoint of ensuring corrosion resistance.

[0017] 0.05≦[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≦55.00...Equation 2 Cu, Ni, Cr, and Mo (these elements may be collectively referred to as the "second corrosion-resistant element group" in this specification) each improve corrosion resistance, although not as much as the first corrosion-resistant element group. Therefore, in the flux-cored wire according to the present disclosure, in order to further improve corrosion resistance in addition to the improvement in corrosion resistance due to the first corrosion-resistant element group, the total content of the first corrosion-resistant element group and the second corrosion-resistant element group is set to 0.05% or more. The lower limit of the total content of the first corrosion-resistant element group and the second corrosion-resistant element group may be 0.08%, 0.10%, or 0.15%. On the other hand, if the total content of the first corrosion-resistant element group and the second corrosion-resistant element group is too high, hot cracking of the weld metal becomes more likely to occur. Therefore, the total content of the first corrosion-resistant element group and the second corrosion-resistant element group is set to 55.00% or less. The upper limit of the total content of the first corrosion-resistant element group and the second corrosion-resistant element group may be 50.00%, 40.00%, or 30.00%. In order to satisfy formula 1 and formula 2, the total content of the second corrosion-resistant element group is 0% or more and less than 54.97%. The preferred contents of each element in the first corrosion-resistant element group and the second corrosion-resistant element group will be described later.

[0018] (nitrides) The flux-cored wire according to the present disclosure contains nitrides, which contribute to suppressing cracking in the weld metal. While nitrides may be contained in the steel sheath, it is preferable to contain nitrides at least in the flux, as this facilitates controlling the N content relative to the total mass of the wire within the range described below. Nitrides in the flux-cored wire (particularly in the flux) reduce the amount of diffusible hydrogen in the weld metal, significantly improving the cold cracking resistance of the weld metal. While the reason for this is unclear, it is presumed that the dissociation of nitrides in the welding material by the arc produces nitrogen, lowering the hydrogen partial pressure in the arc atmosphere and reducing the amount of hydrogen dissolved in the molten pool. Another presumed reason is that N in the nitrides combines with hydrogen (H) during welding to form ammonia (NH3), which is then released outside the weld metal.

[0019] On the other hand, the W, Sn, and Sb of the first corrosion-resistant element group contained in the flux-cored wire according to the present disclosure are elements that promote cold cracking and hot cracking. These corrosion-resistant elements have low melting points, and are difficult to solidify in the weld metal during welding work, and are prone to segregation, which is thought to be the cause of promoting cracking. However, the flux-cored wire according to the present disclosure contains nitrides, which suppress the occurrence of cold cracking and hot cracking.

[0020] Examples of nitrides that can be contained in the flux-cored wire according to the present disclosure include AlN, BN, Ca3N2, CeN, CrN, Cu3N, Fe4N, Fe3N, Fe2N, Mg3N, Mo2N, NbN, Si3N4, TiN, VN, ZrN, Mn2N, and Mn4N. When the flux-cored wire according to the present disclosure contains one or more of these nitrides and does not contain any other nitrides, the N content is represented by the following formula A. Formula A: N content=0.342×AlN+0.564×BN+0.189×Ca3N2+0.091×CeN+0.212×CrN+0.068×Cu3N+0.059×Fe4N+0.077×Fe3N+0.111× Fe2N+0.161×Mg3N+0.068×Mo2N+0.131×NbN+0.399×Si3N4+0.226×TiN+0.216×VN+0.133×ZrN+0.113×Mn2N+0.06×Mn4N Here, the chemical formula of the nitride in Formula A indicates the mass % of the nitride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficients of the chemical formula of each nitride are calculated from the chemical formula weight of each nitride. When nitrides other than those listed above are contained, the N content is calculated from the chemical formula weight of each nitride according to the above formula A.

[0021] (N:0.003~40.00%) The flux-cored wire according to the present disclosure contains 0.003 to 40.00% of N relative to the total mass of the flux-cored wire.

[0022] The amount of nitrogen contained in the flux-cored wire is measured by analysis according to JIS G1228:1997. If the total N content in the entire flux-cored wire is 0.003% or more, the amount of diffusible hydrogen in the weld metal is sufficiently reduced and the cold cracking resistance of the weld metal is improved. Therefore, the flux-cored wire according to the present disclosure contains nitrides and has an N content of 0.003% or more. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the N content may be set to 0.005%, 0.008%, 0.010%, 0.015%, 0.020%, or 0.022%. In the flux-cored wire of the present disclosure, the upper limit of the N content is not particularly limited from the viewpoint of reducing the amount of diffusible hydrogen, but considering that the inside of the steel sheath is filled with flux, the upper limit of the N content is 40.00%. The upper limit of the N content may be 35.00%, 30.00%, or 25.00%. The proportion of N contained in the steel sheath relative to the entire wire is small, and the N content in the flux-cored wire according to the present disclosure can be adjusted mainly by the type and content of nitrides contained in the flux.

[0023] In the flux-cored wire according to the present disclosure, the N content of nitrogen contained in the flux as nitrides is preferably 0.002% or more relative to the total mass of the flux-cored wire. To further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the N content of nitrogen contained in the flux as nitrides may be 0.005%, 0.008%, 0.010%, 0.015%, 0.020%, or 0.022% relative to the total mass of the flux-cored wire. Considering that the flux is filled inside the steel sheath, the upper limit of the N content of nitrogen contained in the flux as nitrides is preferably 15.00%, but may also be 10.00%, 8.00%, or 5.00% relative to the total mass of the flux-cored wire.

[0024] Next, the chemical components of the flux-cored wire according to the present disclosure, excluding nitrides, oxides, fluorides, and carbonates, will be described. The chemical components described below may be contained in the steel sheath or in the flux. Furthermore, when the flux-cored wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, the chemical components may be contained in the plating layer. In the following description, "chemical components excluding nitrides, oxides, fluorides, and carbonates" may be simply referred to as "chemical components." The chemical composition of the flux-cored wire according to the present disclosure, excluding nitrides, oxides, fluorides, and carbonates, is: C: 0.003 to 0.500%, Si: 0 to 3.50% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.020%, W: 0~10.00%, Sn: 0~10.00%, Sb: 0 to 10.00% Cu: 0-10.00% Ni: 0~50.00%, Cr: 0~50.00%, Mo: 0~50.00%, Nb: 0 to 0.50% V: 0~0.50%, Ti: 0 to 0.50% Al: 0-1.00%, B: 0~0.100%, Mg: 0-2.00% Ca: 0-2.00%, Zr: 0 to 0.50% REM: 0~0.50%, Bi: 0 to 0.300%, and The balance preferably consists of Fe and impurities.

[0025] (C: 0.003 to 0.500%) C is an important element for ensuring the yield strength and tensile strength of the weld metal through solid solution strengthening. By ensuring that the C content in the chemical composition of the flux-cored wire is 0.003% or more, the yield strength and tensile strength of the weld metal can be sufficiently ensured. On the other hand, by keeping the C content in the chemical composition of the flux-cored wire at 0.500% or less, the C content in the weld metal is kept at an appropriate level, which prevents excessive increases in the yield strength and tensile strength of the weld metal and improves the toughness of the weld metal. Therefore, in order to stably ensure all of the toughness, yield strength, and tensile strength of the weld metal, the lower limit of the C content in the chemical components of the flux-cored wire is preferably set to 0.003%, and the upper limit of the C content in the chemical components of the flux-cored wire is preferably set to 0.500%. If necessary, the lower limit of the C content may be set to 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, or 0.060%. Similarly, the upper limit of the C content may be set to 0.450%, 0.400%, 0.350%, 0.300%, or 0.250%.

[0026] (Si: 0 to 3.50%) Since Si is not an essential component, the lower limit of the Si content in the chemical components of the flux-cored wire is 0%. On the other hand, Si is a deoxidizing element and has the function of reducing the oxygen content in the weld metal and increasing the cleanliness of the weld metal. However, since a Si content of 3.50% or less can suppress a decrease in the toughness of the weld metal, this is preferably set as the upper limit. Furthermore, to stably ensure the toughness of the weld metal, the upper limit of Si may be set to 3.00%, 2.00%, or 1.00%. To achieve the above effect, the lower limit of the Si content may be set to 0.40%, 0.45%, 0.50%, or 0.60%.

[0027] (Mn: 0 to 10.00%) Since Mn is not an essential element, the lower limit of the Mn content in the chemical components of the flux-cored wire is 0%. On the other hand, Mn is an element that is effective in ensuring the hardenability of the weld metal and increasing its strength. When the Mn content in the chemical components of the flux-cored wire is 10.00% or less, the susceptibility of the weld metal to intergranular embrittlement is reduced, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Mn content is preferably set to 10.00%. More preferably, the upper limit of the Mn content is 9.50%, 9.00%, 8.00%, or 6.00%. To achieve the above effects, the lower limit of the Mn content may be set to 0.40%, 0.45%, 0.50%, or 0.60%.

[0028] (P: 0 to 0.030%) P is an impurity element, and from the viewpoint of suppressing a decrease in the toughness of the weld metal, it is preferable to reduce the P content in the flux-cored wire as much as possible. Therefore, the lower limit of the P content in the chemical components of the flux-cored wire is 0%. Furthermore, if the P content in the chemical components of the flux-cored wire is 0.030% or less, a decrease in the toughness of the weld metal can be suppressed. In order to effectively suppress solidification cracking of the weld metal, the P content in the chemical components of the flux-cored wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less.

[0029] (S:0~0.020%) S is also an impurity element, and from the viewpoint of suppressing a decrease in the toughness and ductility of the weld metal, it is preferable to reduce the S content in the flux-cored wire as much as possible. Therefore, the lower limit of the S content in the chemical components of the flux-cored wire is 0%. Furthermore, if the S content in the chemical components of the flux-cored wire is 0.020% or less, it is possible to suppress a decrease in the toughness and ductility of the weld metal. The S content in the chemical components of the flux-cored wire is more preferably 0.015% or less, 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.

[0030] (W:0~10.00%) W is an effective element for improving the corrosion resistance of the weld metal. However, as mentioned above, the total content of W, Sn, and Sb in the flux-cored wire is sufficient as long as it is in the range of more than 0.03% to 30.00%, and W is not an essential element. Therefore, the lower limit of the W content in the chemical components of the flux-cored wire is 0%. On the other hand, when the W content in the chemical components of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the W content in the chemical components of the flux-cored wire is preferably set to 10.00%. More preferably, the upper limit of the W content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the W content may be set to 0.01%, 0.03%, 0.50%, or 0.60%.

[0031] (Sn: 0 to 10.00%) Sn is an effective element for improving the corrosion resistance of the weld metal, but the total content of W, Sn, and Sb in the flux-cored wire should be in the range of more than 0.03% to 30.00%, and Sn is not an essential element. Therefore, the lower limit of the Sn content in the chemical components of the flux-cored wire is 0%. On the other hand, when the Sn content in the chemical components of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the Sn content in the chemical components of the flux-cored wire is preferably set to 10.00%. More preferably, the upper limit of the Sn content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Sn content may be set to 0.01%, 0.03%, 0.50%, or 0.60%.

[0032] (Sb: 0-10.00%) Sb is an element effective for improving the corrosion resistance of the weld metal, but it is sufficient that the total content of W, Sn, and Sb in the flux-cored wire is in the range of more than 0.03% to 30.00%, and Sb is not an essential element. Therefore, the lower limit of the Sb content in the chemical components of the flux-cored wire is 0%. On the other hand, if the Sb content in the chemical components of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the Sb content in the chemical components of the flux-cored wire is preferably set to 10.00%. More preferably, the upper limit of the Sb content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Sb content may be set to 0.01%, 0.03%, 0.50%, or 0.60%. As described above, the first corrosion-resistant element group preferably contains at least one of Sn and Sb.

[0033] (Cu: 0-10.00%) Since Cu is not an essential component, the lower limit of the Cu content in the chemical components of the flux-cored wire is 0%. On the other hand, Cu has the effect of improving the strength and toughness of the weld metal. To fully obtain this effect, it is preferable that the Cu content in the chemical components of the flux-cored wire be 0.01% or more. Cu may be contained in the plating on the surface of the steel sheath of the flux-cored wire, or may be contained in the flux as a single element or as an alloy. Cu plating also has the effect of improving rust resistance, electrical conductivity, and chip wear resistance. Therefore, the Cu content in the chemical components of the flux-cored wire is the total amount of Cu contained in the steel sheath and flux, and Cu contained in the plating on the wire surface. On the other hand, by making the Cu content of the chemical components of the flux-cored wire 10.00% or less, it is possible to suppress a decrease in the toughness of the weld metal. Therefore, it is preferable to make the Cu content 10.00% or less. The upper limit of the Cu content of the chemical components of the flux-cored wire is preferably 9.00%, 8.00%, 7.00%, 6.00%, 5.00%, 4.00%, 3.00%, or 2.00%.

[0034] (Ni: 0 to 50.00%) Since Ni is not an essential component, the lower limit of the Ni content in the chemical components of the flux-cored wire is 0%. On the other hand, Ni is an element effective for improving the toughness of the weld metal. However, by keeping the Ni content in the chemical components of the flux-cored wire at 50.00% or less, it is possible to suppress a decrease in the hot cracking resistance of the weld metal. Therefore, it is preferable to set the upper limit of the Ni content in the chemical components of the flux-cored wire at 50.00% or less. More preferably, the upper limit of the Ni content is 45.00%, 40.00%, 35.00%, or 30.00%. In order to obtain the effect of improving the toughness of the weld metal, it is preferable that the Ni content be 0.10% or more, 0.30% or more, 0.50% or more, or 1.00% or more.

[0035] (Cr:0~50.00%) Since Cr is not an essential component, the lower limit of the Cr content in the chemical components of the flux-cored wire is 0%. On the other hand, Cr is an element effective in ensuring the hardenability of the weld metal and increasing its strength. However, by limiting the Cr content in the chemical components of the flux-cored wire to 50.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Cr content is preferably set to 50.00%. More preferably, the upper limit of the Cr content is 45.00%, 40.00%, 35.00%, or 30.00%. In order to obtain the effect of increasing the strength of the weld metal, the lower limit of the Cr content in the flux-cored wire according to the present disclosure may be set to 0.01%, 0.05%, 0.10%, or 0.20%, as necessary.

[0036] (Mo: 0-50.00%) Since Mo is not an essential element, the lower limit of the Mo content in the chemical components of the flux-cored wire is 0%. On the other hand, Mo has the effect of improving the hardenability of the weld metal, and is therefore an element effective in increasing the strength of the weld metal. To achieve this effect, the lower limit of the Mo content in the chemical components of the flux-cored wire is preferably set to 0.01%, 0.05%, 0.10%, or 0.15%. On the other hand, by setting the Mo content in the chemical components of the flux-cored wire to 50.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the Mo content in the chemical components of the flux-cored wire is preferably set to 50.00% or less. The upper limit of the Mo content in the chemical components of the flux-cored wire is preferably 48.00%, 45.00%, 40.00%, 30.00%, or 10.00%.

[0037] (Nb: 0 to 0.50%) Since Nb is not an essential component, the lower limit of the Nb content in the chemical components of the flux-cored wire is 0%. On the other hand, Nb forms fine carbides in the weld metal, and these fine carbides cause precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. To fully obtain this effect, the lower limit of the Nb content in the chemical components of the flux-cored wire is preferably set to 0.005%, 0.010%, 0.015%, or 0.020%. On the other hand, when the Nb content in the chemical components of the flux-cored wire is 0.50% or less, the formation of coarse precipitates in the weld metal due to Nb is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Nb content in the chemical components of the flux-cored wire is preferably 0.50%, and more preferably 0.45%, 0.40%, 0.30%, or 0.20%.

[0038] (V:0~0.50%) Since V is not an essential element, the lower limit of the V content in the chemical composition of the flux-cored wire is 0%. On the other hand, V improves the hardenability of the weld metal and is therefore an effective element for increasing the strength of the weld metal. To fully obtain this effect, the lower limit of the V content in the chemical components of the flux-cored wire is preferably set to 0.001%, 0.01%, 0.03%, or 0.05%. On the other hand, when the V content in the chemical components of the flux-cored wire is 0.50% or less, the amount of V carbide precipitated in the weld metal does not increase too much, excessive hardening of the weld metal is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the V content in the chemical components of the flux-cored wire is preferably 0.50%, and more preferably 0.40%, 0.30%, 0.20%, 0.10%, or 0.08%.

[0039] (Ti: 0 to 0.50%) Since Ti is not an essential component, the lower limit of the Ti content in the chemical components of the flux-cored wire is 0%. On the other hand, Ti is a deoxidizing element and has the effect of reducing the amount of oxygen in the weld metal. Furthermore, Ti contained in the chemical components of the flux-cored wire remains in small amounts in the weld metal and fixes the solute N, thereby mitigating the adverse effect of the solute N on the toughness of the weld metal. Therefore, the chemical components of the flux-cored wire may contain 0.001% or more, 0.01% or more, 0.03% or more, or 0.05% or more of Ti. On the other hand, when the Ti content in the chemical components of the flux-cored wire is 0.50% or less, the formation of excessive precipitates in the weld metal is suppressed, thereby suppressing a decrease in toughness. When Ti is contained in the chemical components of the flux-cored wire, ferrotitanium (an alloy of iron and titanium) is generally contained in the flux. The upper limit of the Ti content in the chemical components of the flux-cored wire is preferably 0.50%, and more preferably 0.40%, 0.30%, 0.20%, 0.10%, or 0.08%. The flux-cored wire according to the present disclosure preferably contains 0.20 to 8.00% of Ti oxide as described later. When Ti oxide is contained, the Ti content is the content of components other than Ti constituting the Ti oxide.

[0040] (Al: 0-1.00%) Since Al is not an essential component, the lower limit of the Al content in the chemical components of the flux-cored wire is 0%. On the other hand, Al is a deoxidizing element, and like Si, it reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. However, an Al content of 1.00% or less can suppress a decrease in the toughness of the weld metal. Therefore, it is preferable that the Al content of the chemical components of the flux-cored wire be 1.00% or less. Furthermore, to stably ensure the toughness of the weld metal, the upper limit of the Al content may be 0.95%, 0.90%, 0.85%, or 0.80%. If necessary, the lower limit of the Al content may be 0.005%, 0.01%, 0.05%, 0.10%, 0.15%, or 0.20%.

[0041] (B: 0 to 0.100%) Since B is not an essential component, the lower limit of the B content in the chemical components of the flux-cored wire is 0%. On the other hand, B combines with solute N in the weld metal to form BN, which has the effect of reducing the adverse effect of solute N on the toughness of the weld metal. Furthermore, B also improves the hardenability of the weld metal, thereby improving the strength of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.0005% or more B. On the other hand, by keeping the B content of the chemical composition of the flux-cored wire at 0.100% or less, the B content in the weld metal does not increase too much, and coarse BN and Fe are prevented. 23 The formation of B compounds such as (C, B)6 can be suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the B content in the chemical components of the flux-cored wire is preferably 0.100%, and more preferably 0.050%, 0.030%, or 0.010%.

[0042] (Mg: 0-2.00%) Since Mg is not an essential component, the lower limit of the Mg content in the chemical components of the flux-cored wire is 0%. On the other hand, Mg is a deoxidizing element, and like Al, it reduces the amount of oxygen in the weld metal and improves the cleanliness of the weld metal. However, by keeping the Mg content in the chemical composition of the flux-cored wire at 2.00% or less, the amount of spatter and fumes generated by the violent reaction between Mg and oxygen in the arc can be suppressed. Therefore, it is preferable that the Mg content in the chemical composition of the flux-cored wire be 2.00% or less. The preferred lower limit of the Mg content in the chemical composition of the flux-cored wire is 0.15%, 0.20%, 0.25%, or 0.30%. The preferred upper limit of the Mg content in the chemical composition of the flux-cored wire is 1.70%, 1.60%, 1.50%, 1.40%, 1.00%, or 0.90%.

[0043] (Ca: 0-2.00%) (Zr: 0 to 0.50%) (REM: 0 to 0.50%) Since Ca, Zr and REM are not essential elements, the lower limit values of the Ca content, Zr content and REM content in the chemical components of the flux-cored wire are all 0%. On the other hand, Ca, Zr, and REM all have the function of changing the structure of sulfides in the weld metal and reducing the size of sulfides and oxides, thereby improving the ductility and toughness of the weld metal. Therefore, the Ca content in the chemical components of the flux-cored wire may be set to 0.002% or more, the Zr content in the chemical components of the flux-cored wire may be set to 0.0002% or more, and the REM content in the chemical components of the flux-cored wire may be set to 0.0002% or more. On the other hand, by reducing the Ca content, Zr content, and REM content in the chemical components of the flux-cored wire, the amount of spatter can be suppressed and weldability can be improved. Therefore, the upper limit of the Ca content in the chemical components of the flux-cored wire is preferably 2.00%, the upper limit of the Zr content in the chemical components of the flux-cored wire is preferably 0.50%, and the upper limit of the REM content in the chemical components of the flux-cored wire is preferably 0.50%. REM is a general term for 17 elements, including Sc, Y, and lanthanides, and the REM content refers to the total REM content. REM is generally contained in misch metal. Therefore, for example, misch metal may be added to the alloy to adjust the REM content to the above range.

[0044] (Bi: 0 to 0.300%) Since Bi is not an essential component, the lower limit of the Bi content in the chemical components of the flux-cored wire is 0%. On the other hand, Bi is an element that improves slag removability. To fully obtain this effect, the Bi content in the chemical components of the flux-cored wire is preferably 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, when the Bi content in the chemical components of the flux-cored wire is 0.300% or less, the occurrence of solidification cracking in the weld metal can be suppressed. Therefore, the upper limit of the Bi content in the chemical components of the flux-cored wire is preferably 0.300%. The upper limit of the Bi content in the chemical components of the flux-cored wire may also be preferably 0.200%, 0.150%, or 0.100%.

[0045] (balance: Fe and impurities) The remaining components in the flux-cored wire according to the present disclosure are Fe and impurities, such as Fe contained in the steel sheath and Fe in the alloy powder contained in the flux. Further, the term "impurities" refers to components that are introduced into the flux-cored 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 flux-cored wire according to the present disclosure.

[0046] (Ti oxide: 0.20 to 8.00%) The flux-cored wire according to the present disclosure preferably contains 0.20 to 8.00% of Ti oxide with respect to the total mass of the flux-cored wire, where the content of Ti oxide in the flux-cored wire according to the present disclosure is expressed as the amount converted to TiO2. The Ti oxide content is determined by analyzing the mass of Ti present as oxide in the flux-cored wire 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 cross section) at a position half the wire diameter φ, and the cross section is analyzed. For example, if TiO2, Ti2O3, and Ti3O5 are detected by analysis, the mass% of each Ti oxide is expressed as [TiO2], [Ti2O3], and [Ti3O5], and the total TiO2-equivalent value of the Ti oxides is expressed as [equivalent TiO2], and the content can be calculated using the following formula C1. [Converted TiO2]=(0.60×[TiO2]+0.67×[Ti2O3]+0.64×[Ti3O5])×1.67...Formula C1 The coefficients (0.60, 0.67, 0.64) in formula C1 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.

[0047] Here, we will explain how to calculate the coefficients. x O yIf oxides (e.g., TiO2, Ti2O3, Ti3O5) are detected, M x O y The coefficient for is calculated using the following formula C2. [atomic weight of element M] × x / ([atomic weight of element M] × x + [atomic weight of oxygen] × y) Equation C2 The coefficients 0.60, 0.67, and 0.64 in formula C1 correspond to the coefficients calculated in formula C2 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 formula C3 below. ([atomic weight of element M] × a + [atomic weight of oxygen] × b) / [atomic weight of element M × a] Equation C3 The 1.67 in formula C1 corresponds to the multiplier calculated in formula C3 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 formula C4. [atomic weight of element M] × x / ([atomic weight of element M] × x + [atomic weight of oxygen] × y + [M 2 atomic weight of element] × z) Formula C4

[0048] Ti oxide mainly functions as a slag former. Since oxide is not an essential component of the flux-cored wire according to the present disclosure, the lower limit of the Ti oxide content in the flux-cored wire is 0%. However, when vertical up welding is performed using a flux-cored wire with a Ti oxide content of 0.20% or more, a sufficient amount of slag can be secured to prevent the molten metal from dripping, thereby ensuring vertical weldability. Therefore, when the flux-cored wire according to the present disclosure contains Ti oxide, the lower limit of the Ti oxide content is preferably 0.20%. The lower limit of the Ti oxide content is more preferably 1.00%, and even more preferably 2.00%. To improve vertical weldability, the lower limit of the Ti oxide content may be 3.00%, 3.50%, 4.00%, or 4.50%.

[0049] On the other hand, from the viewpoint of suppressing an increase in the amount of slag and suppressing defects due to slag inclusion (a phenomenon in which slag remains in the weld metal), the upper limit of the Ti oxide content is preferably set to 8.00%. The upper limit of the Ti oxide content is more preferably 7.00%. If necessary, the upper limit of the Ti oxide content may be set to 6.70%, 6.40%, 6.20%, 6.00%, 5.90%, or 5.80%. Although Ti oxides include rutile-type titanium oxide and anatase-type titanium oxide, when the flux-cored wire according to the present disclosure contains Ti oxide, it is not limited to the rutile type and may be the anatase type.

[0050] (Total of oxides other than Ti oxide: 0 to 3.0%) The flux-cored wire according to the present disclosure may contain one or more oxides selected from the group consisting of Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide, and the total content thereof is preferably 3.0% or less. In the present disclosure, oxides included in the group consisting of Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide may be simply referred to as "specific oxides." Furthermore, the total content of each specific oxide may be abbreviated as the "total content of specific oxides." When the flux-cored wire according to the present disclosure contains only one or more oxides of FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2, K2O, and CaO as any of the specific oxides, the total content of the specific oxides is calculated as the sum of the contents of FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2, K2O, and CaO. In addition, since oxides are not essential components of the flux-cored wire according to the present disclosure, the lower limit of the total content of specific oxides in the flux-cored wire is 0%. On the other hand, oxides have the effect of maintaining a good weld bead shape and improving vertical weldability. Furthermore, Na oxide, K oxide, Mg oxide, Fe oxide, and the like also have the effect of stabilizing the arc. To achieve such effects, specific oxides may be contained, i.e., the total content of the specific oxides may be greater than 0%. To further enhance these effects, the lower limit of the total content of the specific oxides may be set to 0.05%, 0.10%, 0.15%, or 0.20%. On the other hand, by keeping the total content of the specific oxides at 3.0% or less, the occurrence of slag entrapment can be suppressed. Therefore, the upper limit of the total content of the specific oxides is preferably set to 3.0%, and may also be set to 2.0%, 1.0%, or 0.5%.

[0051] The contents of the specific oxides in the flux-cored wire according to the present disclosure do not need to be limited to each type of oxide. However, from the viewpoint of suppressing deterioration in toughness due to an excessive increase in the oxygen content in the weld metal, a composition of, for example, Si oxide: 0.08% or more and 0.95% or less, Zr oxide: 0.8% or less, and Al oxide: 0.5% or less is preferable. The content of each oxide and the total content of oxides in the flux-cored wire according to the present disclosure are measured by using fluorescent X-ray analysis, similar to the above-mentioned content of Ti oxide. The total content of specific oxides in the flux-cored wire according to the present disclosure refers to the sum of the total Fe oxide content (FeO equivalent), the total Ba oxide content (BaO equivalent), the total Na oxide content (NaO equivalent), the total Si oxide content (SiO equivalent), the total Zr oxide content (ZrO equivalent), the total Mg oxide content (MgO equivalent), the total Al oxide content (AlO equivalent), the total Mn oxide content (MnO equivalent), the total K oxide content (KO equivalent), and the total Ca oxide content (CaO equivalent).

[0052] In addition, in order to obtain the effect of maintaining a good weld bead shape and the effect of improving vertical weldability, the flux-cored wire according to the present disclosure preferably contains 0.20 to 8.00% of Ti oxide and the total content of specific oxides is preferably 0 to 3.0%.

[0053] (F content: 0.002~30.000%) The flux-cored wire according to the present disclosure does not need to contain fluoride, and therefore, in the flux-cored wire according to the present disclosure, the lower limit of the fluoride content is 0%. On the other hand, fluorides reduce the amount of diffusible hydrogen in the weld metal and significantly improve the cold cracking resistance of the weld metal. This is because when welding is performed with a flux-cored wire, the fluorine (F - ) is hydrogen (H + It is presumed that this is because F combines with fluorine to form hydrogen fluoride (HF), which is then released outside the weld metal. To obtain this effect, the total F content is preferably 0.002% or more. On the other hand, fluorides cause the generation of fumes during welding. However, the flux-cored wire according to the present disclosure contains nitrides, which suppresses the generation of fumes during welding even when it contains fluorides. The reason for this is not clear, but it is presumed that because nitrogen has a lower boiling point than hydrogen fluoride (HF) (N2: -196°C, hydrogen fluoride (HF): +20°C), nitrides are decomposed by the arc to generate nitrogen (N), which then combines as nitrogen molecules (N2), lowering the arc temperature and reducing the amount of high-temperature vapor in the arc, thereby suppressing the generation of fumes.

[0054] When the flux-cored wire according to the present disclosure contains a fluoride, the type of fluoride is not limited, but preferably the flux contains one or more fluorides selected from the group consisting of CaF, MgF, LiF, NaF, KZrF, KSiF, and NaAlF. These fluorides ionize to produce Ca, Mg, Li, Na, K, Zr, Si, and Al, which all combine with oxygen to reduce the oxygen content in the weld metal and act as deoxidizing elements. This is advantageous in terms of improving the toughness and elongation of the weld metal. When the flux-cored wire according to the present disclosure contains 0.002% or more of fluoride, the lower limit of the content of each fluoride is not particularly limited as long as the total mass percentage of the fluorides contained in the flux-cored wire (preferably flux) according to the present disclosure is 0.002% or more in terms of F content. Furthermore, since the F content indicates the amount of fluorine (F) contained in the fluoride in mass % relative to the total mass of the flux-cored wire, when the type of fluoride is the above-mentioned preferred example fluoride, the F content is calculated by the following formula B. Formula B: 0.487×CaF2+0.610×MgF2+0.732×LiF+0.452×NaF+0.402×K2ZrF6+0.517×K2SiF6+0.543×Na3AlF6 Here, the chemical formula of the fluoride in formula B indicates the mass % of the fluoride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficient of each chemical formula of the fluoride is calculated from the chemical formula weight of each fluoride. When a fluoride other than the above-mentioned preferred examples is contained, the F content is calculated from the chemical formula weight of each fluoride in accordance with the above formula B. The lower limit of the F content is preferably 0.002%, more preferably 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, or 0.030%, expressed as a mass percentage relative to the total mass of the flux-cored wire. In order to suppress the generation of fumes during welding, the preferred upper limit of the F content is 30.000%, 20.000%, 10.000%, 3.000%, 2.000%, 1.000%, 0.500%, 0.100%, or 0.050% by mass relative to the total mass of the flux-cored wire. The F content in the flux-cored wire according to the present disclosure is measured by fluorescent X-ray analysis.

[0055] (Total carbonate content: 0-5,000%) The flux-cored wire according to the present disclosure does not need to contain carbonate, and therefore, in the flux-cored wire according to the present disclosure, the lower limit of the carbonate content is 0%. On the other hand, carbonates are ionized by the arc to generate CO2 gas. CO2 gas reduces the hydrogen partial pressure in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. To achieve this effect, the flux-cored wire according to the present disclosure may contain carbonates. In particular, it is preferable that the flux of the flux-cored wire contains carbonates. The type and composition of the metal carbonate contained in the flux-cored wire according to the present disclosure are not limited, but the types of metal carbonate contained in the flux-cored wire include MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO 3、 and SrCO3 (hereinafter, carbonates included in this group may be abbreviated as "specific carbonates"). In order to obtain the above-mentioned effects, it is preferable to contain the above-mentioned specific carbonates, that is, it is preferable that the total content of the specific carbonates is greater than 0%. In order to further exert these effects, the lower limit of the total content of the specific carbonates may be set to 0.050%. On the other hand, when the content of the specific carbonate is 5.000% or less, the occurrence of sagging of the weld bead can be suppressed, thereby improving welding workability. Therefore, when the flux-cored wire according to the present disclosure contains the specific carbonate, the upper limit of the total content of the specific carbonate is preferably 5.000%. If necessary, the upper limit of the content of the specific carbonate may be 4.000%, 3.000%, 2.000%, 1.000%, or 0.500%. The content of each specific carbonate and the total content of the specific carbonates in the flux-cored wire according to the present disclosure are measured by using fluorescent X-ray analysis, similar to the content of Ti oxide described above.

[0056] 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 as lubricants for welding wires, 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. As described above, the flux-cored wire according to the present disclosure may further include a plating formed on the surface of the wire, in which case the lubricant is applied to the surface of the plating.

[0057] 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.

[0058] (steel shell) As long as the above-mentioned conditions are satisfied, the steel sheath of the flux-cored wire according to the present disclosure is not particularly limited. For example, the steel sheath may be a mild steel sheath having a chemical composition including C: 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0-0.030%, S: 0-0.020%, Al: 0-0.1%, and N: 0-0.030%, with the balance being iron and impurities. Although the steel sheath also normally contains N as an impurity, the N contained in the flux as nitrides is more effective at reducing the amount of diffusible hydrogen in the weld metal than the N contained in the steel sheath. The detailed mechanism behind this is unknown, but it is presumed that this is because the steel sheath is in contact with the shielding gas and is therefore at a lower temperature than the flux, so although the N in the steel sheath diffuses into the droplets, it is difficult for it to dissociate into the arc. From the above viewpoints, it is preferable that the flux-cored wire according to the present disclosure has an N content of nitrogen contained as nitride in the flux of 0.002% or more with respect to the total mass of the flux-cored wire. Furthermore, if the steel sheath contains a large amount of nitrogen, it may be difficult to draw the wire and may cause wire breakage. Therefore, it is generally preferable that the N content (%) in the steel sheath is low.

[0059] (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 that have a shape without slit-like gaps (seamless shape) because the seams of the steel outer sheath are welded (sometimes called seamless wires), and wires that have a shape that includes slit-like gaps because the seams of the steel outer sheath are not welded.

[0060] 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 any 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. If the steel sheath has a seam, moisture in the air is likely to penetrate into the flux through the seam. Therefore, it is desirable to prevent moisture in the air 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.

[0061] (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.

[0062] (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%.

[0063] <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.

[0064] (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 amounts of nitrides, N, first corrosion-resistant element group, second corrosion-resistant element group, and optionally fluorides, Ti oxide, specific oxides, specific carbonates, and chemical components of the flux-cored wire fall within the above-mentioned ranges. Note that the flux filling rate, which is determined by the width and thickness of the steel strip that is the material of the steel sheath, and the amount of flux filling, also affect the amounts of nitrides, fluorides, Ti oxide, specific oxides, specific carbonates, and chemical components of the flux-cored wire.

[0065] 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.

[0066] 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.

[0067] (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.

[0068] <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 gas-shielded arc welding steel materials using the flux-cored wire according to the present disclosure described above.

[0069] The flux-cored wire according to the present disclosure is applicable to welding of all kinds of steel materials, and the flux-cored wire according to the present disclosure can effectively suppress cold cracking and hot cracking without preheating or with a preheating temperature of 50°C or less, and can produce a welded joint having a corrosion-resistant weld metal. 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, CM Steel materials with high cold cracking susceptibility having a (weld cracking 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 30 mm or more, can be suitably used. Because such steel plates have high cold cracking susceptibility and hot cracking susceptibility, when these steel plates are welded by a normal weld joint manufacturing method, it is difficult to suppress the occurrence of cold cracking and hot cracking without sufficient preheating. On the other hand, the method for manufacturing a welded joint according to the present disclosure uses a flux-cored wire according to the present disclosure that can suppress cold cracking and hot cracking, and therefore when steel materials that are highly susceptible to cold cracking and hot cracking are welded by the method for manufacturing a welded joint according to the present disclosure, the occurrence of cold cracking can be suppressed without preheating or with significantly reduced preheating. Furthermore, the joint obtained by the method for manufacturing a welded joint according to the present disclosure may be an undermatched joint in which the tensile strength of the weld metal is lower than the tensile strength of the steel plate base material.

[0070] The method for manufacturing a welded joint according to the present disclosure includes a step of gas-shielded arc welding a base steel sheet 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 type of base steel sheet (base material) is not particularly limited. 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.

[0071] 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 produce a welded joint that has high strength, high toughness, and high fatigue strength in addition to corrosion resistance and crack resistance. Commonly used shielding gases such as 100% carbon dioxide and mixed gases containing 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 O2 gas by volume. Because these gases are inexpensive, welding using these gases is advantageous for industrial use.

[0072] 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 regardless of the welding position, such as a flat position, a horizontal position, a vertical position, or an overhead position.

[0073] The welded joint obtained by the method for manufacturing a welded joint according to the present disclosure includes a base steel plate (base material) and a welded joint composed of a weld metal and a weld heat-affected zone. The base material of the welded joint is not particularly limited. The welded joint according to the present disclosure is manufactured using the flux-cored wire according to the present disclosure, in which the amounts of corrosion-resistant elements, nitrides, etc. are preferably controlled, and therefore has corrosion resistance and crack resistance and includes a weld metal with a good bead shape.

[0074] By using the flux-cored wire according to the present disclosure for gas-shielded arc welding, preheating work can be omitted or simplified, and a welded joint having excellent corrosion resistance and cracking resistance can be obtained. [Example]

[0075] 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.

[0076] (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 was fed longitudinally and formed using forming rolls to obtain a U-shaped open tube. Flux was supplied into the open tube through the opening, and the opposing edges of the opening were butt-welded to obtain a seamless tube. 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 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 composition of these flux-cored wires is shown in the table below.

[0077] Tables 1 to 4 show the nitrides, chemical components (the content of each element contained as a component excluding nitrides, oxides, fluorides, and carbonates), the content of oxides, fluorides, and carbonates, and the content of iron powder. The units of these contents disclosed in Tables 1 to 4 are mass% relative to the total mass of the flux-cored wire. In the tables, "mass% relative to the total mass of the flux-cored wire" is abbreviated to "mass%," and "chemical components excluding nitrides, oxides, fluorides, and carbonates" is abbreviated to "chemical components." The "total N content in the flux" shown in Table 1 indicates the amount of nitrogen (N) contained in nitrides in the flux in mass% relative to the total mass of the flux-cored wire, and is the value (N equivalent value) calculated by the above-mentioned formula A. The "total N content in the wire" indicates the total content of nitrogen contained in nitrides in the flux and the nitrogen contained in the steel sheath in mass% relative to the total mass of the flux-cored wire. In Table 2, "the amount of elements contained as chemical components in the first corrosion-resistant element group A" and "the amount of elements contained as chemical components in the second corrosion-resistant element group B" refer to the content of each element contained as a component of the first and second corrosion-resistant element groups in the flux-cored wire, excluding nitrides, oxides, fluorides, and carbonates. "Total of first corrosion-resistant element group A" refers to the total content of all elements in the first corrosion-resistant element group in the flux-cored wire, and "Total of first and second corrosion-resistant element groups A+B" refers to the total content of all elements in the first and second corrosion-resistant element groups in the flux-cored wire. "The amount of elements contained as nitrides in the total of A+B" refers to the total content of elements in the first and second corrosion-resistant element groups in the flux-cored wire, other than chemical components (specifically, nitrides). The F content shown in Table 3 indicates the amount of fluorine (F) contained in the fluoride in the flux in mass % relative to the total mass of the flux-cored wire, and is the value (F equivalent value) calculated by the above-mentioned formula B. The total of specific oxides other than Ti oxide shown in Table 3 is the total content of FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2, KO, and CaO used as Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide, respectively.

[0078] [Table 1]

[0079] [Table 2]

[0080] [Table 3]

[0081] [Table 4]

[0082] The remainder of the flux-cored wire shown in the table (i.e., components other than the components shown in the table) is iron and impurities. Among the flux-cored wires shown in the table, 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. Also, 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 (including elements in the first corrosion-resistant element group A and the second corrosion-resistant element group B) contained as a chemical component in the flux-cored wire shown in Table 2 is in the form of a steel sheath or metal powder. In the table, values outside the ranges specified in this disclosure are underlined. Furthermore, in Tables 1 to 4, 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.

[0083] [evaluation] The flux-cored wires of the examples and comparative examples were used to carry out gas-shielded arc welding and evaluation. 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.

[0084] [Table 5]

[0085] (Evaluation of corrosion resistance of weld metal) (1) General corrosion test To evaluate the corrosion resistance of the underside of a tanker's upper deck against general corrosion, a rectangular piece (corrosion resistance test piece 11 for corrosion resistance evaluation) measuring 15 mm wide x 60 mm long x 5 mm thick was cut out from position A of the joint for evaluation in Figure 1, which was manufactured under the welding conditions shown in Table 5, so that it consisted of only the weld metal. The surface was polished with 600-grit emery paper. The underside and end faces were sealed with tape to prevent corrosion, and a general corrosion test was carried out using the corrosion test equipment shown in Figure 2. In Figure 1, the symbols 1 and 2 represent the base material (steel), 5 represents the backing material, and 7 represents the weld metal.

[0086] This corrosion test apparatus consists of a corrosion test tank 12 and a temperature control plate 13. Water 16, maintained at 36°C, is poured into the corrosion test tank 12. A gas mixture (inlet gas 14) consisting of 4 vol% O, 13 vol% CO, 0.01 vol% SO, 0.05 vol% H, S, and the remainder N is introduced into the water 16 to fill the corrosion test tank 12 with supersaturated water vapor, replicating the corrosive environment under the upper deck of a crude oil tank. Corrosion-resistant test specimens 11 placed on the top and bottom surfaces of the test tank are subjected to repeated temperature cycles of 25°C for 3 hours and 50°C for 21 hours via a temperature control plate 13 equipped with a built-in heater and cooler for 180 days, causing condensation on the surface of the corrosion-resistant test specimens 11 and resulting in general corrosion. In Figure 2, reference numeral 15 denotes exhaust gas from the test tank.

[0087] After the above test, the rust on the surface of each corrosion-resistant test piece was removed, and the mass loss due to corrosion was calculated from the change in mass before and after the test. This value was then converted into the annual thickness loss (corrosion rate on one side). The results were evaluated on a three-level scale according to the following criteria, and a corrosion rate of 0.20 mm / y or less (A or B) was evaluated as having good general corrosion resistance. A: Corrosion rate is 0.10 mm / y or less B: Corrosion rate is greater than 0.10 mm / y and less than 0.20 mm / y C: Corrosion rate is over 0.20 mm / y

[0088] (2) Localized corrosion (pitting corrosion) test In order to evaluate the corrosion resistance against pitting corrosion in the bottom plate of a tanker oil tank, a rectangular piece (corrosion resistance test piece 17 for corrosion resistance evaluation) measuring 15 mm wide, 60 mm long, and 5 mm thick was cut out from cut-out position A of the joint for evaluation in Figure 1, which was manufactured under the welding conditions in Table 5, so that it consisted of only the weld metal, and the entire surface was polished with 600-grit emery paper.

[0089] Next, a test solution was prepared by adjusting a 10 mass% NaCl aqueous solution with concentrated hydrochloric acid to a Cl ion concentration of 10 mass% and a pH of 0.85. The corrosion test specimens were hung with fishing line through a 3 mm diameter hole drilled at the top of the specimens, and each specimen was immersed in 2 L of test solution for 168 hours for a corrosion test. The test solution was preheated and maintained at 30°C, and replaced with fresh test solution every 24 hours.

[0090] The equipment used in the corrosion test is shown in Figure 3. This corrosion test equipment is a double-layered device consisting of a corrosion test tank 18 and a thermostatic chamber 19. The corrosion test tank 18 contains the test solution 20, in which a corrosion-resistant test piece 17 is immersed while being suspended by fishing line 21. The temperature of the test solution 20 is maintained by adjusting the temperature of water 22 contained in the thermostatic chamber 19.

[0091] After the corrosion test, the rust formed on the surface of the corrosion-resistant test piece was removed, and the mass difference before and after the test was calculated. This difference was then divided by the total surface area to determine the annual thickness loss (corrosion rate on both sides). The results were evaluated on a three-level scale according to the following criteria, and a corrosion rate of 0.50 mm / y or less (A or B) was evaluated as having good localized corrosion resistance. A: Corrosion rate is 0.30 mm / y or less B: Corrosion rate is greater than 0.30 mm / y and less than 0.50 mm / y C: Corrosion rate is over 0.50 mm / y

[0092] (Evaluation of diffusible hydrogen content in weld metal) The amounts of diffusible hydrogen in the weld metals obtained by gas-shielded arc welding using the flux-cored wires of the examples and comparative examples were evaluated. The welding conditions for the evaluation were as shown in Table 5. The amount of diffusible hydrogen in the weld metal was measured using gas chromatography in accordance with JIS Z 3118:2007 (Method for measuring hydrogen content in steel welds). Flux-cored wires with a diffusible hydrogen content of 1.0 ml / 100 g or less in the weld metal were rated as "passing" for diffusible hydrogen content. A was given for 0.5 ml / 100 g or less, B for over 0.5 ml / 100 g and up to 1.0 ml / 100 g, and C for over 1.0 ml / 100 g.

[0093] (Evaluation of crack resistance) (1) T-shaped weld cracking test (high temperature cracking resistance) The hot cracking resistance was evaluated by welding 50 mm thick steel plates with a tensile strength of 780 MPa under the welding conditions shown in Table 5 in a constant atmosphere controlled at a temperature of 20°C and a humidity of 60%, and then conducting tests on the welded joints obtained in accordance with JIS Z 3153-1993 (T-type weld cracking test method). Flux-cored wires in welded joints that did not develop cracks in the T-type weld cracking test were deemed to have passed the test for high-temperature cracking resistance.

[0094] (2) Y-shaped weld cracking test (low-temperature cracking resistance) The cold cracking resistance was evaluated by welding a 50 mm thick steel plate with a tensile strength of 780 MPa under the welding conditions shown in Table 5 in a constant atmosphere controlled at a temperature of 0°C and a humidity of 60%, and then conducting a test on the resulting welded joint in accordance with JIS Z 3158:2016 (Y-type weld cracking test method). Flux-cored wires in welded joints that did not experience cracks in the Y-type weld cracking test were deemed "passed" in terms of cold cracking resistance.

[0095] The test results obtained by the above-mentioned method are shown in Table 6. If all evaluation items were passed, the overall evaluation was considered to be passed, and if even one item was not passed, the overall evaluation was considered to be failed.

[0096] [Table 6]

[0097] The flux-cored wire of the embodiment can produce a weld metal having excellent corrosion resistance and excellent mechanical properties. Furthermore, as shown in the test results in Table 6, the flux-cored wires of the examples also passed the evaluation item for the amount of diffusible hydrogen in the weld metal (A or B), and weld metals having excellent mechanical properties can be produced. Furthermore, when welding was performed using the flux-cored wires of the examples, no cross-section cracks were observed in all cross sections of the T-shaped weld cracking test (hot cracks, i.e., no cross-section cracks occurred in the high temperature range during welding or cooling after welding). Therefore, the flux-cored wires of the examples have extremely high hot cracking resistance. When welding was performed using the flux-cored wire of the example, no cross-sectional cracks were observed in all cross sections of the Y-shaped weld cracking test, even if the steel material was not preheated. This means that no cross-sectional cracks occurred during cooling after welding or in the low temperature range after cooling. Therefore, the flux-cored wire of the example has extremely high resistance to cold cracking. 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. [Explanation of symbols]

[0098] 1, 2: Base material (steel), 5: Backing material, 7: Weld metal, 11, 17: Corrosion-resistant test piece, 12, 18: Corrosion test tank, 13: Temperature control plate, 14: Inlet gas, 15: Exhaust gas, 16, 22: Water, 19: Thermostatic bath, 20: Test solution, 21: Fishing line, A: Cutting position of corrosion-resistant test piece.

Claims

1. A flux-cored wire for welding having a steel outer sheath and flux filled inside the steel outer sheath, The flux-cored wire contains nitrides, and the N content is 0.003 to 40.00%, the Ti oxide content is 0 to 8.00%, the total content of oxides other than Ti oxide is 0 to 3.0%, the F content is 0 to 30.000%, and the total content of carbonates is 0 to 5.000%, in mass% relative to the total mass of the flux-cored wire; The chemical components of the flux-cored wire, excluding the nitrides, oxides, fluorides, and carbonates, are, in mass % based on the total mass of the flux-cored wire, C: 0.003 to 0.500%, Si: 0 to 3.50%, Mn: 0 to 10.00%, P: 0 to 0.030%, S: 0-0.020%, W: 0-10.00%, Sn: 0-10.00%, Sb: 0 to 10.00%, Cu: 0 to 10.00%, Ni: 0 to 50.00%, Cr: 0-50.00%, Mo: 0 to 50.00%, Nb: 0 to 0.50%, V: 0-0.50%, Ti: 0 to 0.50%, Al: 0-1.00%, B: 0 to 0.100%, Mg: 0-2.00%, Ca: 0-2.00%, Zr: 0 to 0.50%, REM: 0-0.50%, Bi: 0 to 0.300%, and The balance is composed of Fe and impurities. A flux-cored wire that satisfies both formulas 1 and 2. 0.03<[W]+[Sn]+[Sb]≦30.00...Formula 1 0.05≦[Cu]+[Ni]+[Cr]+[Mo]+[W]+[Sn]+[Sb]≦55.00...Formula 2 The element symbols enclosed in square brackets in Formula 1 and Formula 2 represent the content of each element contained in the flux-cored wire in mass % relative to the total mass of the flux-cored wire.

2. 2. The flux-cored wire according to claim 1, wherein the flux-cored wire contains, in mass % relative to the total mass of the flux-cored wire, 0.20 to 8.00% of Ti oxide and 0 to 3.0% in total of one or more oxides selected from the group consisting of Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide.

3. 3. The flux-cored wire according to claim 1, wherein the flux-cored wire contains fluoride and has an F content of 0.002 to 30.000% by mass relative to the total mass of the flux-cored wire.

4. MgCO ３ , Na ２ CO ３ , LiCO ３ , CaCO ３ , K. ２ CO ３ , BaCO ３ , FeCO ３ , MnCO ３ and SrCO ３ and a total content of the carbonates is 5.000% or less in mass% with respect to the total mass of the flux-cored wire.

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

6. The nitride is AlN, BN, Ca ３ N ２ , CeN, CrN, Cu ３ N, Fe ４ N, Fe ３ N, Fe ２ N, Mg ３ N, Mo ２ N, NbN, Si ３ N ４ , TiN, VN, ZrN, Mn ２ N, and Mn ４ The flux-cored wire according to any one of claims 1 to 5, wherein the flux-cored wire is one or more selected from the group consisting of N.

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

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