Flux-cored cut wire and method for manufacturing welded joints

Abstract

To provide a manufacturing method for a flux-cored cut wire and a weld joint which can suppress the generation of low-temperature cracks without carrying out base metal preheating work and form a weld metal having a favorite bead shape.SOLUTION: This invention includes a bevel-charging flux-cored to charge at least a part in a bevel provided among a plurality of base metals when manufacturing a weld joint by welding the plurality of base metals, a bevel-charging flux-cored cut wire which has a steel jacket and a flux to charge the interior of the steel jacket and contains nitride in the flux, and a manufacturing method for a weld joint using the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a flux-cored cut wire and a method for manufacturing 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] However, although the demand for ultra-high tensile steel has become very high, the amount of ultra-high tensile steel of 780 MPa or more used is still small compared to the total amount. The reason for this is that ultra-high tensile steel is prone to cold cracking when it is welded without preheating. Cold cracking is a general term for cracks that occur in a weld after the temperature of the weld has dropped to around room temperature after welding, and underbead cracks and toe cracks belong to this category. Cold cracking is one of the most serious welding defects because it generally results in a sharp notch. Although cold cracking can be prevented by preheating the weld during welding, the preheating process significantly increases the cost and time required for welding.

[0004] This cold cracking is caused by diffusible hydrogen in the weld metal. Therefore, adding fluoride to the flux and welding wire used in submerged arc welding can reduce the amount of hydrogen ions (H + ) to fluorine ions (F - ) to discharge the hydrogen out of the arc, thereby reducing the hydrogen concentration in the molten pool. For example, Patent Document 1 proposes a flux-cored wire for 490 to 780 MPa class high-tensile steel, in which the V content is optimized and diffusible hydrogen is absorbed by the V to improve cold cracking resistance, and the weld crack prevention preheat temperature is set to 50° C. or less. This wire contains fluoride as a slag agent.

[0005] On the other hand, when manufacturing a joint with a large heat input in submerged arc welding, in order to achieve high welding efficiency and control the penetration depth, cut wire, which is made by cutting a thin steel wire into pieces of a predetermined length, is filled into the groove. For example, Patent Document 2 discloses a cut wire in which the wire is covered with a Cu cladding layer and the surface of which is coated with oil. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-257785 [Patent Document 2] Japanese Patent Application Publication No. 9-94690 Summary of the Invention [Problem to be solved by the invention]

[0007] When fluorides are contained in the slag agent of a flux-cored cutting wire used for groove filling, a problem occurs in that a large amount of fumes is generated. Excessive fumes reduce the visibility of the molten metal and arc, which can lead to poor bead shape.

[0008] For the reasons described above, a welding consumable is desired that can suppress the occurrence of cold cracking without preheating the base metal or with only simple preheating, and can form a weld metal with a good bead shape.

[0009] The present disclosure has been made in view of the above-described circumstances, and aims to provide a flux-cored cut wire and a method for manufacturing a welded joint that can suppress the occurrence of cold cracking without preheating the base metal or with only simple preheating, and can form a weld metal having a good bead shape. [Means for solving the problem]

[0010] The gist of the present disclosure is as follows. <1> A flux-cored cut wire for groove filling, which is used to fill at least a portion of a groove provided between a plurality of base materials when welding the base materials together to produce a welded joint, A flux-cored cutting wire for groove filling, comprising a steel outer sheath and flux filled inside the steel outer sheath, the flux containing nitrides. <2> 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> The flux-cored cutting wire for groove filling according to claim 1. <3> The N content of the flux-cored cut wire is 0.003 to 15,000 mass% relative to the total mass of the wire. <1> or <2> The flux-cored cutting wire for groove filling according to claim 1. <4> The chemical composition of the flux-cored cut wire, excluding nitrides, oxides, fluorides, and carbonates, is, in mass % based on the total mass of the flux-cored cut wire, C: 0~0.500%, Si: 0 to 10.00% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.030%, Cu: 0~50.00%, Ni: 0 to 90.0% Cr: 0~90.00%, Mo: 0~90.00%, Nb: 0 to 10.00%, V: 0~10.00%, Ti: 0 to 10.00% Al: 0 to 10,000%, Mg: 0~3.000%, B: 0~10.000%, Ca: 0~3.000%, W: 0~90.00%, Sn: 0~90.00%, Sb: 0~90.00%, REM: 0 to 90.000%, Bi: 0 to 1.000%, and Remainder: Fe and impurities <1> ~ <3> 10. The flux-cored cutting wire for groove filling according to any one of claims 1 to 9. <5> At least a part of the groove formed between the base materials <1> ~ <4> 10. A method for manufacturing a welded joint, comprising: a flux-cored cut wire welding step of filling and welding with the flux-cored cut wire according to any one of the above. <6> The flux-cored cut wire welding process involves filling the groove with the flux-cored cut wire and welding in one pass. <5> A method for manufacturing the welded joint described above. <7> The flux-cored cut wire welding process includes one-layer welding in which the flux-cored cut wire is filled in the first layer in the groove and welded, or multi-layer welding in which the flux-cored cut wire is filled in the first layer and the second layer and thereafter in the groove and welded, and welding is performed at least until the temperatures of the plurality of base materials reach their respective preheat equivalent temperatures. <5> A method for manufacturing the welded joint described above. <8> The welding method is submerged arc welding or gas shielded arc welding. <1> ~ <7> 10. A method for manufacturing a welded joint according to any one of the above. <9> Each of the plurality of base materials is a high-strength steel material having a tensile strength of 780 MPa or more. <5> ~ <8> 10. A method for manufacturing a welded joint according to any one of the above. <10> Each of the plurality of base materials is a steel material having a thickness of 50 mm or more. <5> ~ <9> 10. A method for manufacturing a welded joint according to any one of the above. <11> The flux-cored cut wire welding process includes: The welding is performed using a flux-cored wire that has a steel outer sheath and flux filled inside the steel outer sheath, and contains at least one of nitride and fluoride, as a welding material wire attached to an electrode for generating an arc. <5> ~ <10> 10. A method for manufacturing a welded joint according to any one of the above. [Effects of the Invention]

[0011] According to the present disclosure, there are provided a flux-cored cut wire and a method for manufacturing a welded joint that can suppress the occurrence of cold cracking without preheating the base metal or with only simple preheating, and can form weld metal with a good bead shape. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram showing an example of a flux-cored cut wire welding process according to the present disclosure. [Figure 2] FIG. 10 is an explanatory diagram showing another example of a flux-cored cut wire welding process according to the present disclosure. [Figure 3] FIG. 2 is an explanatory diagram showing the groove shape used in the evaluation of cold cracking resistance in the examples and the state of filling with a flux-cored cutting wire. [Figure 4] FIG. 1 is an explanatory diagram showing the groove shape used in the evaluation of cold cracking resistance in the initial groove layer in the examples and the state of filling with a flux-cored cut wire. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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 need to be contained.

[0014] In the case of high-strength extra-thick steel plates, preheating is performed to prevent cold cracking. In order to prevent cold cracking and to eliminate or simplify the preheating process, it is effective to reduce the amount of diffusible hydrogen during welding. As mentioned above, the amount of diffusible hydrogen can be reduced by using a flux-cored wire containing fluoride in the flux, but this generates a large amount of fumes during welding, which hinders welding workability. In order to suppress the generation of fumes and reduce the amount of diffusible hydrogen during welding, it is conceivable to add nitrides to the flux or welding wire. However, this technique tends to cause the arc to become unstable during welding, resulting in an unstable bead shape. The reason why the addition of nitrides makes the arc unstable is thought to be due to the dissociation of the nitrides in the arc. The inventors of the present invention have proposed a solution to this problem by preventing nitrides from dissociating in the arc and allowing diffusible hydrogen and nitrogen in the molten pool to react. They then performed welding using a flux-cored cut wire containing nitrides in the flux as a filler in the groove between the base metals. They found that this reduced the amount of diffusible hydrogen in the weld metal, resulting in a welded joint with excellent cold cracking resistance and a good bead shape. Although the mechanism is unclear, it is believed that inserting a flux-cored cut wire containing nitrides in the flux as a filler in the groove between the base metals and melting the filler with the welding arc melts the nitrides while suppressing dissociation, thereby preventing the arc from becoming unstable and resulting in a good bead shape.

[0015] <Flux-cored cut wire> The flux-cored cut wire according to the present disclosure is a flux-cored cut wire for groove filling, which is used to fill at least a portion of a groove formed between multiple base materials when welding the multiple base materials together to produce a welded joint, and which has a steel outer sheath and flux filled inside the steel outer sheath, and the flux contains nitrides. The reasons for limiting the requirements (including optional requirements) for the flux-cored cut wire according to the present disclosure will be specifically described below.

[0016] First, the components contained in the flux-cored cut wire according to the present disclosure will be described. The flux-cored cut wire according to the present disclosure contains nitrides in the flux, and preferably contains predetermined alloying elements, oxides, fluorides, carbonates, etc. The flux of the flux-cored cut wire according to the present disclosure may further contain iron powder. These components are described in detail below. In the following description, "%" means "mass % relative to the total mass of the flux-cored cut wire" unless otherwise specified.

[0017] (nitrides) The flux-cored cut wire according to the present disclosure contains nitrides in the flux. The nitrides 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, one possible explanation is that N in the nitrides combines with hydrogen (H) during welding to form ammonia (NH3), which is then released outside the weld metal. Examples of nitrides that can be contained in the flux of the flux-cored cut 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 cut wire according to the present disclosure contains one or more of these nitrides and does not contain any other nitrides, the N content is expressed 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 relative to the total mass of the flux-cored cut 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.

[0018] (N:0.003~15.000%) The flux-cored cut wire according to the present disclosure preferably contains 0.003 to 15,000% N based on the total mass of the flux-cored cut wire.

[0019] The amount of nitrogen contained in the flux-cored cut wire is measured by analysis using JIS G1228:1997. If the total N content in the entire flux-cored cut 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, it is preferable that the flux-cored cut wire according to the present disclosure contains nitrides in the flux, and that the N content in the entire flux-cored cut wire is 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 in the entire wire may be set to 0.005%, 0.008%, 0.010%, 0.015%, 0.020%, or 0.022%. In the flux-cored cut wire of the present disclosure, the upper limit of the N content in the entire wire is not particularly limited from the viewpoint of reducing the amount of diffusible hydrogen. However, considering that the interior of the steel sheath is filled with flux, the upper limit of the N content in the entire wire is 15,000%, and may be 10,000%, 8,000%, or 5,000%. The proportion of N contained in the steel sheath relative to the total amount of the cut wire is small, and the N content in the flux-cored cut wire according to the present disclosure can be adjusted mainly by the type and amount of nitride contained in the flux.

[0020] In the flux-cored cut 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 cut 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 cut 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 15,000%, but may also be 10,000%, 8,000%, or 5,000% relative to the total mass of the flux-cored cut wire.

[0021] Next, components other than nitrides and N in the flux of the flux-cored cut wire according to the present disclosure will be described. The components described below may be contained in the steel sheath or in the flux. Furthermore, when the flux-cored cut wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, the components may be contained in the plating layer. In the following description, the "chemical composition excluding nitrides, oxides, fluorides, and carbonates" may be simply referred to as the "chemical composition," and the components contained in this chemical composition may be referred to as the "chemical components." The chemical composition of the flux-cored cutting wire according to the present disclosure, excluding nitrides, oxides, fluorides, and carbonates, is: C: 0~0.500%, Si: 0 to 10.00% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.030%, Cu: 0~50.00%, Ni: 0 to 90.0% Cr: 0~90.00%, Mo: 0~90.00%, Nb: 0 to 10.00%, V: 0~10.00%, Ti: 0 to 10.00% Al: 0 to 10,000%, Mg: 0~3.000%, B: 0~10.000%, Ca: 0~3.000%, W: 0~90.00%, Sn: 0~90.00%, Sb: 0~90.00%, REM: 0 to 90.000%, Bi: 0 to 1.000%, and The balance preferably consists of Fe and impurities. None of the above chemical components are essential, but the content of each chemical component will be explained below.

[0022] (C: 0 to 0.500%) Since C is not an essential element, the lower limit of the C content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, C is an important element for ensuring the yield strength and tensile strength of the weld metal through solid solution strengthening. When the C content in the chemical composition of the flux-cored cut 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 cut wire at 0.500% or less, the C content in the weld metal is maintained 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, 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 composition of the flux-cored cut wire is preferably set to 0.003%, and the upper limit of the C content in the chemical composition of the flux-cored cut 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%, 0.250%, or 0.120%.

[0023] (Si: 0 to 10.00%) Since Si is not an essential component, the lower limit of the Si content in the chemical composition of the flux-cored cut 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. Si can be contained, for example, at 10.00% or less. 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 more stably ensure the toughness of the weld metal, the upper limit of Si may be set to 3.50%, 3.00%, 2.00%, or 1.00%. If necessary, the lower limit of the Si content may be set to 0.40%, 0.45%, 0.50%, or 0.60%.

[0024] (Mn: 0 to 10.00%) Since Mn is not an essential element, the lower limit of the Mn content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Mn is an element effective in ensuring the hardenability of the weld metal and increasing its strength. When the Mn content in the chemical composition of the flux-cored cut wire is 10.00% or less, the susceptibility of the weld metal to intergranular embrittlement can be 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%.

[0025] (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 cut wire as much as possible. Therefore, the lower limit of the P content in the chemical composition of the flux-cored cut wire is 0%. Furthermore, if the P content in the chemical composition of the flux-cored cut wire is 0.030% or less, a decrease in the toughness of the weld metal can be suppressed. To effectively suppress solidification cracking of the weld metal, the P content in the chemical composition of the flux-cored cut wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less. However, since an extreme reduction in the P content leads to an increase in manufacturing costs, from the viewpoint of reducing dephosphorization costs, the P content is preferably 0.003% or more.

[0026] (S:0~0.030%) 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 cut wire as much as possible. Therefore, the lower limit of the S content in the chemical composition of the flux-cored cut wire is 0%. Furthermore, if the S content in the chemical composition of the flux-cored cut wire is 0.030% or less, a decrease in the toughness and ductility of the weld metal can be suppressed. The S content in the chemical composition of the flux-cored cut wire is more preferably 0.020% or less, 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.

[0027] (Cu: 0 to 50.00%) Since Cu is not an essential component, the lower limit of the Cu content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire be 0.01% or more. Cu may be contained in the plating on the surface of the steel sheath of the flux-cored cut 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 tip wear resistance. Therefore, the Cu content in the chemical composition of the flux-cored cut wire is the total amount of Cu contained in the steel sheath and flux, and Cu contained in the plating on the wire surface. Cu can be contained, for example, at 50.00% or less. On the other hand, when the Cu content in the chemical composition of the flux-cored cut wire is 10.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, it is preferable that the Cu content be 10.00% or less. The upper limit of the Cu content in the chemical composition of the flux-cored cut wire is more preferably 9.00%, 8.00%, 7.00%, 6.00%, 5.00%, 4.00%, 3.00%, or 2.00%.

[0028] (Ni: 0 to 90.0%) Since Ni is not an essential component, the lower limit of the Ni content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, since Ni improves the toughness and hot cracking resistance of the weld metal, the Ni content in the wire is preferably greater than 0%. To obtain the effect of improving the toughness of the weld metal, the Ni content in the flux-cored cut wire according to the present disclosure is more preferably 0.10% or more, 0.30% or more, 0.50% or more, or 1.00% or more. On the other hand, from the viewpoint of suppressing a decrease in the hot cracking resistance and toughness of the weld metal, the upper limit of the Ni content is preferably 90.0%, and may be 85.0%, 80.0%, or 75.0%.

[0029] On the other hand, when the flux-cored cut wire according to the present disclosure is a low-alloy cut wire, as described below, a Ni content of less than 55.0% can suppress a decrease in the hot cracking resistance of the weld metal. Therefore, in the case of a low-alloy cut wire, the upper limit of the Ni content is preferably less than 55.0%. The upper limit of the Ni content may also be 54.0%, 50.0%, or 45.0%.

[0030] (Cr:0~90.00%) Since Cr is not an essential component, the lower limit of the Cr content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Cr is an element that is effective in ensuring the hardenability of the weld metal and increasing the strength of the weld metal. Cr can be contained, for example, in an amount of 90.00% or less. However, by ensuring that the Cr content in the chemical composition of the flux-cored cut wire is 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 cut wire according to the present disclosure may be set to 0.01%, 0.05%, 0.10%, or 0.20%, as necessary.

[0031] On the other hand, when the flux-cored cut wire according to the present disclosure is a low-alloy cut wire, as described below, a Cr content of 10.00% or less can suppress a decrease in the toughness of the weld metal. Therefore, in the case of a low-alloy cut wire, the upper limit of the Cr content is preferably set to 10.00%. More preferably, the upper limit of the Cr content is 9.50%, 9.00%, 8.00%, or 6.00%.

[0032] (Mo: 0-90.00%) Since Mo is not an essential component, the lower limit of the Mo content in the chemical composition of the flux-cored cut 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 obtain this effect, the lower limit of the Mo content in the chemical composition of the flux-cored cut wire is preferably set to 0.01%, 0.05%, 0.10%, or 0.15%. Mo can be contained at 90.00% or less, for example. On the other hand, if the Mo content in the chemical composition of the flux-cored cut wire is 50.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the Mo content in the chemical composition of the flux-cored cut wire is preferably 50.00% or less. The upper limit of the Mo content in the chemical composition of the flux-cored cut wire is more preferably 48.00%, 45.00%, 40.00%, 30.00%, or 10.00%.

[0033] (Nb: 0 to 10.00%) Since Nb is not an essential component, the lower limit of the Nb content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire is preferably set to 0.005%, 0.010%, 0.015%, or 0.020%. Nb can be contained in an amount of, for example, 10.00% or less. On the other hand, if the Nb content in the chemical composition of the flux-cored cut wire is 0.50% or less, the formation of coarse precipitates due to Nb in the weld metal 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 composition of the flux-cored cut wire is preferably 0.50%, and more preferably 0.45%, 0.40%, 0.30%, or 0.20%.

[0034] (V:0~10.00%) Since V is not an essential component, the lower limit of the V content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire is preferably set to 0.001%, 0.010%, 0.030%, or 0.050%. V can be contained in an amount of, for example, 10.00% or less. On the other hand, if the V content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire is preferably 0.50%, and more preferably 0.40%, 0.30%, 0.20%, 0.10%, or 0.08%.

[0035] (Ti: 0 to 10.00%) Since Ti is not an essential component, the lower limit of the Ti content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire remains in small amounts in the weld metal and fixes solute N, thereby mitigating the adverse effects of solute N on the toughness of the weld metal. Therefore, the chemical composition of the flux-cored cut wire may contain 0.001% or more, 0.010% or more, 0.030% or more, or 0.050% or more of Ti. Ti can be contained in an amount of, for example, 10.00% or less. On the other hand, if the Ti content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire, ferrotitanium (an alloy of iron and titanium) is generally contained in the flux. The upper limit of the Ti content in the chemical composition of the flux-cored cut wire is preferably 0.50%, and more preferably 0.40%, 0.30%, 0.20%, 0.10%, or 0.08%.

[0036] (Al: 0 to 10,000%) Since Al is not an essential component, the lower limit of the Al content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Al is a deoxidizing element and, like Si, reduces the oxygen content in the weld metal and improves the cleanliness of the weld metal. Al may be contained, for example, at 10.000% or less. However, an Al content of 1.000% or less can prevent a decrease in the toughness of the weld metal. Therefore, the Al content in the chemical composition of the flux-cored cut wire is preferably 1.000% or less. Furthermore, to stably ensure the toughness of the weld metal, the upper limit of the Al content may be 0.950%, 0.900%, 0.850%, or 0.800%. If necessary, the lower limit of the Al content may be 0.005%, 0.010%, 0.050%, 0.100%, 0.150%, or 0.200%.

[0037] (Mg: 0-3.000%) Since Mg is not an essential component, the lower limit of the Mg content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Mg is a deoxidizing element and, like Al, reduces the oxygen content in the weld metal, improving the cleanliness of the weld metal. The Mg content can be, for example, 3.000% or less. However, by keeping the Mg content in the chemical composition of the flux-cored cut wire at 2.000% 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 cut wire be 2.000% or less. The preferred lower limit of the Mg content in the chemical composition of the flux-cored cut wire is 0.150%, 0.200%, 0.250%, or 0.300%. The preferred upper limit of the Mg content in the chemical composition of the flux-cored cut wire is 1.700%, 1.600%, 1.500%, 1.400%, 1.000%, or 0.900%.

[0038] (B: 0 to 10.000%) Since B is not an essential component, the lower limit of the B content in the chemical composition of the flux-cored cut 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 cut 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 cutting wire at 10,000% or less, the B content in the weld metal does not increase too much, and coarse BN and Fe are removed. 23 The formation of B compounds such as (C, B)6 is 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 composition of the flux-cored cut wire is preferably 8.000%, 5.000%, 1.000%, or 0.100%, and more preferably 0.050%, 0.030%, or 0.010%.

[0039] (Ca: 0-3.000%) Since Ca is not an essential component, the lower limit of the Ca content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Ca has 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 composition of the flux-cored cut wire may be set to 0.002% or more. The Ca content can be, for example, 3.000% or less. On the other hand, by reducing the Ca content in the chemical composition of the flux-cored cut wire, the amount of spatter can be suppressed and weldability can be improved. Therefore, the upper limit of the Ca content in the chemical composition of the flux-cored cut wire is preferably 2.000%.

[0040] (W:0~90.00%) Since W is not an essential element, the lower limit of the W content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, W is an element effective for improving the corrosion resistance of the weld metal, and the lower limit of the W content may be set to 0.30%, 0.50%, 1.00%, 5.00%, or 10.00%, as necessary. On the other hand, when the W content in the chemical composition of the flux-cored cut wire is 90.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the W content in the chemical composition of the flux-cored cut wire is preferably set to 90.00%. More preferably, the upper limit of the W content is 80.00%, 70.00%, 60.00%, or 50.00%.

[0041] (Sn: 0 to 90.00%) Since Sn is not an essential element, the lower limit of the Sn content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Sn is an element effective for improving the corrosion resistance of the weld metal, and the lower limit of the Sn content may be set to 0.30%, 0.50%, 1.00%, 5.00%, or 10.00%, as necessary. On the other hand, by keeping the Sn content in the chemical composition of the flux-cored cut wire at 90.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the Sn content in the chemical composition of the flux-cored cut wire is preferably set to 90.00%. More preferably, the upper limit of the Sn content is 80.00%, 70.00%, 60.00%, or 50.00%.

[0042] (Sb: 0 to 90.00%) Since Sb is not an essential element, the lower limit of the Sb content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, Sb is an element effective for improving the corrosion resistance of the weld metal, and the lower limit of the Sb content may be set to 0.30%, 0.50%, 1.00%, 5.00%, or 10.00%, as necessary. On the other hand, when the Sb content in the chemical composition of the flux-cored cut wire is 90.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, the upper limit of the Sb content in the chemical composition of the flux-cored cut wire is preferably set to 90.00%. More preferably, the upper limit of the Sb content is 80.00%, 70.00%, 60.00%, or 50.00%.

[0043] (REM:0~90.000%) Since REM is not an essential component, the lower limit of the REM content in the chemical composition of the flux-cored cut wire is 0%. On the other hand, REMs change the structure of sulfides in the weld metal and also reduce the size of sulfides and oxides, thereby improving the ductility and toughness of the weld metal. Therefore, the REM content in the chemical composition of the flux-cored cut wire may be set to 0.0002% or more. The REM content can be, for example, 90.000% or less. On the other hand, by reducing the REM content in the chemical composition of the flux-cored cut wire, the amount of spatter can be suppressed and weldability can be improved. Therefore, the upper limit of the REM content in the chemical composition of the flux-cored cut wire is preferably 0.500%. 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 1.000%) Since Bi is not an essential component, the lower limit of the Bi content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cutting wire is preferably 0.005% or more, 0.010% or more, or 0.012% or more. Bi can be contained at, for example, 1.000% or less. On the other hand, if the Bi content in the chemical composition of the flux-cored cut 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 composition of the flux-cored cut wire is preferably 0.300%. The upper limit of the Bi content in the chemical composition of the flux-cored cut wire may more preferably be 0.200%, 0.150%, or 0.100%.

[0045] (balance: Fe and impurities) The remaining components in the flux-cored cut 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, impurities refer to components that are introduced into the flux-cored cut wire during industrial production due to the raw materials or various factors in the production process, and are acceptable to the extent that they do not adversely affect the flux-cored cut wire according to the present disclosure.

[0046] (Ti oxide: 0 to 8.00%) Ti oxide mainly functions as a slag former. Since oxide is not an essential component of the flux-cored cut wire according to the present disclosure, the lower limit of the total amount of Ti oxide in the flux-cored cut wire is 0%. However, from the viewpoint of ensuring a sound bead appearance, if the flux-cored cut wire according to the present disclosure contains Ti oxide, the lower limit of the Ti oxide content is preferably set to 0.20%. When welding is performed using a flux-cored cut wire with a Ti oxide content of 0.20% or more, a sound bead appearance can be ensured. The lower limit of the Ti oxide content is more preferably 1.00%, and even more preferably 2.00%. In order to ensure a sound bead appearance, the lower limit of the Ti oxide content may be 3.00%, 3.50%, 4.00%, 4.50%, or 5.00%.

[0047] 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 set to 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%.

[0048] Furthermore, when the flux-cored cut wire according to the present disclosure is a low-alloy cut wire as described below, the Ti oxide content is preferably 0 to less than 0.20% based on the total mass. Ti oxide improves bead appearance, but reducing the Ti oxide content can also reduce the amount of diffusible hydrogen in the molten metal. When the flux-cored cut wire according to the present disclosure is a low-alloy cut wire, the Ti oxide content is preferably less than 0.20% in order to reduce the amount of diffusible hydrogen. In the case of a low-alloy cut wire, the upper limit of the Ti oxide content may be 0.15%, 0.10%, or 0.08%, or the wire may be free of Ti oxide, i.e., the Ti oxide content may be 0%.

[0049] The Ti oxide content in the flux-cored cut wire according to the present disclosure is expressed as the amount converted into TiO2. The Ti oxide content is determined by analyzing the mass of Ti present as oxide in the flux-cored cut 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 percentages of each Ti oxide are expressed as [TiO2], [Ti2O3], and [Ti3O5], and the total TiO2-equivalent value of the Ti oxides is expressed as [equivalent TiO2], and the content is 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.

[0050] 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 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 may be 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

[0051] (Total content of specific oxides other than Ti oxide: 0 to 10.0%) The flux-cored cut wire according to the present disclosure may contain oxides other than Ti oxide. For example, 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 may be included. In this specification, 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 referred to simply as "specific oxides," and the total content of each oxide may be referred to as the "total content of specific oxides." Since oxides are not essential components of the flux-cored cut wire according to the present disclosure, the lower limit of the total content of specific oxides in the flux-cored cut 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, 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, when the total content of the specific oxides is 10.0% or less, the occurrence of slag entrainment can be suppressed. Therefore, when the flux-cored cut wire according to the present disclosure contains the specific oxides, the upper limit of the total content of the specific oxides is preferably 10.0%, and may be 9.0%, 8.0%, 7.0%, 6.0%, 3.0%, 2.0%, 1.0%, or 0.5%. When the flux-cored cut 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 above oxides, the total content of the above specific oxides is calculated as the sum of the contents of FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2, K2O, and CaO.

[0052] The content of the specific oxides in the flux-cored cut wire according to the present disclosure does 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 the specific oxides in the flux-cored cut wire according to the present disclosure are measured by X-ray fluorescence analysis, similar to the above-mentioned content of Ti oxide.

[0053] (F content: 0.002% or more) The flux-cored cut wire according to the present disclosure does not need to contain fluoride, and therefore the lower limit of the fluoride content in the flux-cored cut wire according to the present disclosure 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 cut 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 cut wire according to the present disclosure contains nitrides in the flux, which suppresses the generation of fumes during welding even when it contains fluorides. The reason for this is unclear, 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). This lowers the arc temperature, reducing the amount of high-temperature vapor in the arc, thereby suppressing the generation of fumes.

[0054] When the flux-cored cut wire according to the present disclosure contains a fluoride, the type of fluoride is not limited, but the flux preferably 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 cut 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 cut wire (preferably flux) according to the present disclosure is 0.002% or more in terms of F. 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 cut wire, when the type of fluoride is one of the preferred examples described above, the F content is calculated using 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 relative to the total mass of the flux-cored cut wire. The coefficients of the chemical formula of each fluoride are 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 cut wire. In order to suppress the generation of fumes during welding, the upper limit of the F content is preferably 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 cut wire. The F content in the flux-cored cut wire according to the present disclosure is measured by fluorescent X-ray analysis.

[0055] (Total content of specific metal carbonates: 0-10,000%) The flux-cored cut wire according to the present disclosure does not need to contain metal carbonate, and therefore the lower limit of the metal carbonate content in the flux-cored cut wire according to the present disclosure is 0%. On the other hand, metal carbonates are ionized by the arc and 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 cut wire according to the present disclosure may contain metal carbonate. In particular, it is preferable that the flux of the flux-cored wire contains carbonate. The type and composition of the metal carbonate contained in the flux-cored cutting wire according to the present disclosure are not limited, but the type of metal carbonate contained in the flux-cored cutting wire is preferably one or more selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3 (hereinafter, metal carbonates in this group may be abbreviated as "specific metal carbonates"). In order to obtain the above-mentioned effects, it is preferable to contain the above-mentioned specific metal carbonates, that is, it is preferable that the total content of the specific metal carbonates is greater than 0%. In order to further exert these effects, the lower limit of the total content of the specific metal carbonates may be set to 0.050%. On the other hand, by setting the content of the specific metal carbonate to 10.000% or less, the occurrence of sagging of the weld bead can be suppressed, improving welding workability. Therefore, when the flux-cored cut wire according to the present disclosure contains specific metal carbonates, the upper limit of the total content of the specific metal carbonates is preferably 10.000%. If necessary, the upper limit of the content of the specific metal carbonates may be set to 9.000%, 8.000%, 7.000%, 6.000%, 3.000%, 2.000%, 1.000%, or 0.500%. The content of each specific metal carbonate and the total content of the specific metal carbonates in the flux-cored cut wire according to the present disclosure are measured by X-ray fluorescence analysis, similar to the Ti oxide content described above.

[0056] The components of the flux-cored cut wire according to the present disclosure have been described above, but the flux-cored cut wire according to the present disclosure may be a low-alloy cut wire or a rutile cut wire, as described below.

[0057] [I] Low alloy cutting wire When the flux-cored cut wire according to the present disclosure is a low-alloy cut wire, the content of Ti oxide is preferably 0 to less than 0.20%.Furthermore, it is preferable that the wire satisfies at least one of the compositions [I-2] to [I-6] below. [I-2] The chemical composition excluding nitrides, oxides, fluorides, and carbonates is expressed in mass% relative to the total mass of the flux-cored cut wire, C: 0.003 to 0.500%, Si: 0 to 3.50% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.030%, Cu: 0-10.00% Ni: 0 to less than 55.0% Cr: 0 to 10.00% Mo: 0~50.00%, Nb: 0 to 0.50% V: 0~0.50%, Ti: 0 to 0.50% Al: 0 to 1.000%, Mg: 0 to 2.000%, B: 0~0.100%, Ca: 0 to 2.000%, REM: 0~0.500%, Bi: 0 to 0.300%, and The balance consists of Fe and impurities. [I-3] The flux-cored cut wire contains one or more oxides selected from the group consisting of Ti oxide and specific oxides (i.e., 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 of Ti oxide and the specific oxides is 10.0% or less, in mass %, based on the total mass of the flux-cored cut wire. [I-4] The flux-cored cut wire contains fluoride, and the F content is 0.002% or more by mass based on the total mass of the flux-cored cut wire. [I-5] The flux-cored cut wire contains one or more specific metal carbonates selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3, and the total content of the specific metal carbonates is 0.050 to 10,000% by mass relative to the total mass of the flux-cored cut wire. [I-6] 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.

[0058] [II] Rutile-based cutting wire When the flux-cored cutting wire according to the present disclosure is a rutile-based cutting wire, the Ti oxide content is preferably 0.20 to 8.00% and the Ni content is preferably greater than 0 and up to 90.00%. Furthermore, it is preferable that the composition satisfies at least one of the following compositions [II-2] to [II-6]. [II-2] The chemical composition excluding nitrides, oxides, fluorides, and carbonates is expressed in mass% relative to the total mass of the flux-cored cutting wire, C: 0.003 to 0.500%, Si: 0 to 3.50% Mn: 0 to 10.00%, P: 0~0.030%, S: 0~0.030%, Cu: 0-10.00% Ni: 0.1 to 90.0%, Cr: 0~50.00%, Mo: 0~50.00%, Nb: 0 to 0.50% V: 0~0.50%, Ti: 0 to 0.50% Al: 0 to 1.000%, Mg: 0 to 2.000%, B: 0~0.100%, Ca: 0 to 2.000%, REM: 0~0.500%, Bi: 0 to 0.300%, and The balance consists of Fe and impurities. [II-3] The flux-cored cut wire contains one or more oxides selected from the group consisting of specific oxides (i.e., 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 of the specific oxides is 10.0% or less, in mass% based on the total mass of the flux-cored cut wire. [II-4] The flux-cored cut wire contains fluoride, and the F content is 0.002% or more in mass % relative to the total mass of the flux-cored cut wire. [II-5] The flux-cored cut wire contains one or more specific metal carbonates selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3, and the total content of the specific metal carbonates is 0.050 to 10,000% by mass relative to the total mass of the flux-cored cut wire. [II-6] 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.

[0059] Although the amount of hydrogen contained in the flux-cored cut wire according to the present disclosure is not particularly limited, it is preferably 12 ppm or less relative to the total mass of the flux-cored cut wire in order to reduce the amount of diffusible hydrogen in the weld metal. The amount of hydrogen in the flux-cored cut wire may increase due to moisture penetration into the flux-cored cut wire during storage. Therefore, if there is a long period between the wire's manufacture and its use, it is desirable to prevent moisture penetration by the means described below.

[0060] (steel shell) As long as the above-mentioned conditions are satisfied, the steel sheath of the flux-cored cut 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 N content of nitrogen contained as nitride in the flux of the flux-cored cut wire according to the present disclosure is 0.002% or more relative to the total mass of the flux-cored cut wire. Furthermore, if the steel sheath contains a large amount of nitrogen, it may be difficult to draw the wire and may cause breakage. Therefore, it is generally preferable that the N content (%) of the steel sheath is low.

[0061] (Cut wire size) The diameter of the flux-cored cut wire according to the present disclosure (corresponding to the diameter of the flux-cored wire before cutting) is not particularly limited, but is, for example, φ1.0 to φ2.0 mm. Note that the diameter of a typical flux-cored cut wire is φ1.2 to φ1.6 mm. The length (length in the axial direction) of the flux-cored cut wire according to the present disclosure is not particularly limited, but is approximately the same as the diameter, for example, 1.0 to 2.0 mm.

[0062] (Filling rate) The fill factor of the flux-cored cut wire according to the present disclosure is not particularly limited as long as the above-described conditions are satisfied. In consideration of the fill factor of a typical flux-cored cut wire, the lower limit of the fill factor of the flux-cored cut wire according to the present disclosure may be, for example, 8%, 10%, or 12%. The upper limit of the fill factor of the flux-cored cut wire according to the present disclosure may be, for example, 28%, 25%, 22%, 20%, or 17%.

[0063] <Method for manufacturing flux-cored cut wire> There are no particular limitations on the procedures for producing the flux-cored cut wire according to the present disclosure, but the following example can be given as a method for producing a wire filled with flux before cutting. First, a method for producing seamless flux-cored cut wire in which the seams of the steel sheath are welded and there are no slit-like gaps includes the steps of preparing the flux so that the nitrides, chemical composition, etc. fall within predetermined ranges, forming the steel strip using forming rolls while feeding it longitudinally to obtain a U-shaped open tube, supplying flux into the open tube through the opening, butt-welding the opposing edges (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 with a predetermined wire diameter, and annealing the flux-cored wire during or after the drawing step. The wire is then cut to a predetermined length to obtain the flux-cored cut wire.

[0064] Here, the butt welding is performed by electric resistance welding, laser welding, TIG welding, or the like. Furthermore, during or after the wiredrawing process, annealing is performed to remove moisture from the wire. Preferably, the annealing temperature is 650°C or higher, and the annealing time is 4 hours or longer, in order to reduce the H content in the wire to 12 ppm or less. However, in order to prevent deterioration of the flux, the annealing temperature is preferably 900°C or lower. Note that, instead of butt welding, a wire without slit-shaped gaps can also be obtained by brazing the gaps in the steel sheath.

[0065] Alternatively, the seam of the steel sheath may not be welded, and a flux-cored cut wire with a slit-shaped gap may be obtained. In this case, the method is the same as the method for manufacturing a seamless wire, except that instead of butt-welding the ends of an open pipe to obtain a seamless pipe, a process of forming an open pipe and butt-welding the ends of the open pipe to obtain a pipe with a slit-shaped gap is included. The method for manufacturing a wire with a slit-shaped gap may further include a process of crimping the butted ends of the open pipe. In the method for manufacturing a wire with a slit-shaped gap, a pipe is drawn while having a slit-shaped gap.

[0066] As described above, the flux-cored cut wire according to the present disclosure may be cut from a seamless wire in which the seams of the steel sheath are welded and there are no slit-like gaps, or from a wire in which the seams of the steel sheath are not welded and there are slit-like gaps. However, the flux-cored cut wire is preferably cut from a wire in which the steel sheath has no slit-like gaps. Hydrogen (H) that penetrates the weld during welding diffuses into the weld metal and the welded material, accumulating in areas of stress concentration and causing cold cracking. While there are various sources of H, if the cleanliness of the weld and the welding conditions are strictly controlled, moisture (HO) contained in the flux-cored cut wire can be a source of H. The amount of this moisture can affect the amount of diffusible hydrogen in the welded joint. Therefore, while a seamless wire without slit-like gaps is preferable, if the flux-cored cut wire is cut from a wire with slit-like gaps, it can be stored, for example, vacuum-packaged or in a container that can maintain a dry state.

[0067] The flux-cored cut wire according to the present disclosure may also have an oil (lubricant) applied to its surface. The lubricant applied to the surface of the cut wire has the effect of suppressing rust formation during storage. Various types of lubricants (e.g., vegetable oils such as palm oil) can be used as such lubricants, 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), which do not contain H (hydrogen). Note that when the flux-cored cut wire has a plating on its surface, the lubricant is applied to the plating surface.

[0068] <Method for manufacturing welded joints> Next, in manufacturing a welded joint using the above-described flux-cored cut wire, the present disclosure provides a flux-cored cut wire welding process in which a flux-cored cut wire is filled into at least a portion of a groove between a plurality of base materials and then welded. That is, in manufacturing a welded joint, a flux-cored cut wire according to the present disclosure is filled into the groove of the base materials and welded in at least one of the first pass through the final pass. When welding is performed in only one pass, the flux-cored cut wire according to the present disclosure is used in that one pass.

[0069] In the case of multi-layer welding, it is preferable to fill at least the first layer in the groove with the flux-cored cut wire according to the present disclosure during the flux-cored cut wire welding process. That is, by filling the first layer in the groove, where the probability of cold cracking is high, with the flux-cored cut wire according to the present disclosure, the load of the preheating work can be reliably reduced, for example, by lowering the preheating temperature to 50°C or less, or the preheating work itself can be omitted.

[0070] 1 and 2 each show an example of a flux-cored cut wire welding process according to the present disclosure. Of these, FIG. 1 shows an example in which a flux-cored cut wire 4 is filled into a portion of a groove 3 formed between base metals 1 and 2, and multi-layer welding is performed. First, as shown in FIG. 1(a), a backing material 5 is attached to the back surfaces of the base metals 1 and 2, and then the flux-cored cut wire 4 according to the present disclosure is filled into the first layer of the groove 3. Next, as shown in FIG. 1(b), a welding wire 6 (a wire as a welding material attached to an electrode for generating an arc) is placed approximately above the center of the filled flux-cored cut wire 4, and an arc is generated to perform welding.

[0071] The configuration and components of the welding wire 6 are not particularly limited, and a known solid wire or flux-cored wire can be used. The welding wire 6 preferably has a steel sheath and flux filled inside the steel sheath, and contains at least one of nitride and fluoride. By using a flux-cored wire containing at least one of nitride and fluoride as the welding wire 6 together with the flux-cored cut wire according to the present disclosure, the amount of diffusible hydrogen in the weld metal can be further reduced, further improving cold cracking resistance. In particular, the use of a flux-cored wire containing nitride can also suppress the generation of fumes during welding.

[0072] The composition of the flux-cored wire containing at least one of nitride and fluoride can have the same composition as the flux-cored cut wire according to the present disclosure described above, with respect to the N content, F content, and other components.

[0073] Here, it is preferable that the temperatures of the base metals 1 and 2 reach the preheat temperature (preheat-equivalent temperature) when the base metals 1 and 2 are preheated in advance by the welding of the first layer in FIG. 1( b). The preheat-equivalent temperature is a temperature calculated by the following method, and preferably reaches, for example, 100°C. If the temperatures of the base metals 1 and 2 reach the preheat-equivalent temperature, the risk of cold cracking is eliminated. Therefore, in the second and subsequent layers of multi-layer welding, welded joints may be produced without using the flux-cored cut wire according to the present disclosure. If the temperatures of the base metals 1 and 2 do not reach the preheat-equivalent temperature by the welding of the first layer, it is preferable that the flux-cored cut wire 4 according to the present disclosure is again dispersed on the weld metal 7 obtained by including the flux-cored cut wire 4 filled in the first layer, fill the groove 3, and then the welding wire 6 is placed to perform welding. In other words, from the viewpoint of suppressing low-temperature cracking, this process is repeated for the second and subsequent welding layers, and welding is performed by filling with the flux-cored cut wire 4 according to the present disclosure until the temperatures of the base materials 1 and 2 reach a temperature equivalent to preheating. Once the temperature equivalent to preheating is reached, welding is performed without using the flux-cored cut wire according to the present disclosure, as in the previous case. The "equivalent preheat temperature" is the preheat temperature required to prevent cold cracking, and depends on the carbon equivalent, welding conditions, chemical composition, etc. The equivalent preheat temperature in this disclosure is calculated using the welding calculation software: Welding Simulator (URL: http: / / www-it.jwes.or.jp / weld_simulator / cal4.jsp) from the Welding Information Center of the Japan Welding Engineering Society.

[0074] The example of a flux-cored cut wire welding process shown in Figure 1 is a case of multi-layer welding in which a flux-cored cut wire is filled into the first layer and the second and subsequent layers in the groove and welded. The flux-cored cut wire according to the present embodiment is filled and welded at least until the temperature of the base metal reaches a temperature equivalent to preheating (for example, until it reaches 100°C). In other words, by using a flux-cored cut wire according to the present disclosure to weld the first layer in the groove, the amount of diffusible hydrogen in the weld metal can be reduced. Moreover, because this flux-cored cut wire welding process also serves as a preheating operation, the preheating operation can be omitted or the burden of the preheating operation can be significantly reduced.

[0075] Furthermore, as shown in FIG. 2, the flux-cored cut wire welding process of the present disclosure may be performed in a single pass by filling the groove with a flux-cored cut wire according to the present disclosure. That is, as shown in FIG. 2(a), a backing material 5 is attached to the back surface of the base materials 1 and 2. Then, in the example shown in FIG. 2, a flux-cored cut wire 4 according to the present disclosure is dispersed so as to fill almost the entire groove 3, for example, approximately 80% of the groove height. Next, as shown in FIG. 2(b), a welding wire 6 is placed approximately above the center of the filled flux-cored cut wire 4, and an arc is generated to perform welding. As shown in FIG. 2(c), a welded joint is produced using a weld metal 7 containing the flux-cored cut wire 4. Note that welding is performed at least until the temperature of the base materials 1 and 2 reaches a temperature equivalent to preheating (e.g., until it reaches 100°C). In the example of the flux-cored cut wire welding process shown in FIG. 2, the amount of diffusible hydrogen in the weld metal can be reduced by using a flux-cored cut wire according to the present disclosure to fill the groove. Furthermore, since this flux-cored cut wire welding process also serves as a preheating operation, the preheating operation can be omitted or the burden of the preheating operation can be significantly reduced.

[0076] In the example of the flux-cored cut wire welding process shown in Figure 2, the flux-cored cut wire according to the present disclosure is used in almost the entire groove, so preheating work can be omitted or the burden of preheating work can be significantly reduced.

[0077] 1 and 2 show an example in which the groove between the base materials is a so-called V-groove, but the present disclosure is not limited to this groove shape, and groove shapes other than V-groove, such as I-groove, L-groove, K-groove, J-groove, X-groove, U-groove, H-groove, Y-groove, and any other groove shape, may be used. Furthermore, the present disclosure may be applied to single-sided welding as shown in FIGS. 1 and 2, or to double-sided welding. Furthermore, in the case of multi-layer welding as in the example of FIG. 1, each layer may be welded in two or more passes.

[0078] Although the welding method (welding means) used in the present disclosure is not particularly limited, submerged arc welding or gas-shielded arc welding is preferable in order to reliably melt the flux-cored cut wire filled in the groove. However, since it may be difficult to fill the groove with the flux-cored cut wire in vertical welding or overhead welding, the welding position is preferably downward or horizontal.

[0079] Furthermore, the method for manufacturing a welded joint according to the present disclosure is not particularly limited in terms of the type or shape of the base material, but is most effective when cold cracking is an issue and preheating is a burden. That is, a typical example is welding a base material made of high-strength steel with a tensile strength of 780 MPa or more (preferably with an upper limit of 1500 MPa or less). Furthermore, in the case of extra-thick steel with a thickness of 50 mm or more (preferably with an upper limit of 250 mm or less), the burden of preheating is particularly large. Therefore, it is extremely effective to apply the present disclosure when the base material is an extra-thick high-strength steel. The combination of base materials forming the groove is arbitrary, and the base materials may be the same type or different types.

[0080] Furthermore, while a typical method for manufacturing a welded joint produces a welded joint comprising a base steel plate (base material) and a welded joint consisting of a weld metal and a weld heat-affected zone, the present disclosure uses a flux-cored cut wire containing a specified nitride in the flux as a groove filler, and therefore preferably produces a welded joint having a diffusible hydrogen content in the weld metal of 1.0 ml / 100 g or less. In particular, by using a flux-cored cut wire that further contains a specified chemical component, a welded joint with high strength and high toughness can be produced.

[0081] The weld joint obtained by the weld joint manufacturing method according to the present disclosure is manufactured using the flux-cored cut wire according to the present disclosure, in which the amount of nitrides and the like are preferably controlled, and therefore has a weld metal with a good bead shape.

[0082] By performing gas-shielded arc welding using the flux-cored cut wire according to the present disclosure, preheating work can be omitted or significantly reduced, a welded joint with excellent resistance to cold cracking can be obtained, and an increase in the amount of fume generated during welding can be effectively suppressed. [Example]

[0083] 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.

[0084] (Manufacture of flux-cored cut wire) The flux-cored cut wires of the examples and comparative examples were produced by the method described below. First, a steel strip was fed in the longitudinal direction 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, except that some samples were drawn to obtain a tube with slit-like gaps without seam welding, and then the tube was drawn to obtain a wire. In this way, flux-cored wires with a final filler diameter of 1.6 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 at least 4 hours. After the prototypes were produced, a lubricant was applied to the surface of some of the wires. The produced flux-cored wires were then cut to lengths of 1.6 mm to prepare samples of flux-cored cut wire. The configurations of these flux-cored cut wires are shown in Tables 1A-1 to 1D-2.

[0085] Tables 1A-1 to 1D-2 show the nitride content in the flux, the total N content in the flux, the total N content in the cut wire, the alloy component content (i.e., each element contained as a chemical component excluding nitrides, oxides, fluorides, and carbonates), the oxide content (TiO2 and oxides other than TiO2), the fluoride content, the F content, the carbonate content, and the iron powder content. The units of these contents shown in Tables 1A-1 to 1D-2 are mass% relative to the total mass of the flux-cored cut wire. In the tables, mass% relative to the total mass of the flux-cored cut wire is abbreviated as "mass%," and the chemical composition excluding nitrides, oxides, fluorides, and carbonates is abbreviated as "alloy component" in Tables 1D-1 and 1D-2. The "amount of nitrides in the flux" of the flux-cored cut wires shown in Tables 1A-1 and 1A-2 indicates the amount of nitrides in the flux as a percentage by mass relative to the total mass of the flux-cored cut wire, and the "total N content in the flux" indicates the amount of nitrogen (N) contained in nitrides in the flux as a percentage by mass relative to the total mass of the flux-cored cut wire, and is the value (N equivalent value) calculated using the above-mentioned formula A. Meanwhile, in Tables 1D-1 and 1D-2, the "total N content in the cut wire" is the total N content relative to the total mass of the flux-cored cut wire, which is the sum of the nitrogen contained in nitrides in the flux and the nitrogen contained in the steel sheath. The "F content" shown in Table 1B-1 and Table 1B-2 indicates the amount of fluorine (F) contained in the fluoride in the flux in mass % relative to the total mass of the flux-cored cut wire, and is the value (F equivalent value) calculated using the above-mentioned formula B. The amount of "TiO2" shown in Tables 1A-1 and 1A-2 is the TiO2-equivalent content of Ti oxide. The total amount of "oxides other than TiO2" shown in Tables 1B-1 and 1B-2 is the total of the Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide contents converted into FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2, KO, or CaO.

[0086] [Table 1A-1]

[0087] [Table 1A-2]

[0088] [Table 1B-1]

[0089] [Table 1B-2]

[0090] [Table 1C-1]

[0091] [Table 1C-2]

[0092] [Table 1D-1]

[0093] [Table 1D-2]

[0094] The remainder of the flux-cored cut wires shown in Tables 1A-1 to 1D-2 (ie, components other than the components shown in the tables) is iron and impurities. In addition, wires marked "PTFE coated" in the "Remarks" column of Tables 1A-1 and 1A-2 are cut wires cut from wires coated with PTFE oil, and those marked blank are cut wires cut from wires coated with palm oil as a lubricant. In addition, wires marked "seamless" in the "wire structure" column are cut wires cut from wires having a seamless shape, and wires marked "with slit-like gaps" are cut wires cut from wires having slit-like gaps. Each element contained as an alloy component in the flux-cored cut wires shown in Tables 1D-1 and 1D-2 is in the form of a steel sheath or metal powder. Furthermore, in Tables 1A-1 to 1D-2, blank spaces in the tables relating to the content of alloying elements, compounds, etc., mean that the alloying elements, compounds, etc. are not intentionally contained. These alloying elements, compounds, etc. may be unavoidably mixed in or generated.

[0095] [evaluation] The flux-cored cut wires of the invention examples and comparative examples were evaluated by the methods described below. (i) Evaluation of cold cracking resistance Welding was performed on 50 mm thick steel sheets with a tensile strength of 780 MPa under welding condition number 1 in Table 2, and the results were evaluated. Tests were conducted in accordance with JIS Z 3157-1993 (U-shaped weld cracking test method) and JIS Z 3158:2016 (Y-shaped weld cracking test method). The groove shape was a Y-shape as shown in Figure 3, with a slit length of 300 mm. The filling thickness of the flux-cored cutting wire 4 in the groove 3 was 8 mm. Furthermore, as welding wires (filler metals), flux-cored wires a to d having the total N content and total F content shown in Table 3 were used. The total N content and total F content shown in Table 3 are the contents (mass%) relative to the total mass of the wire, and were adjusted by adding nitrides and / or fluorides as part of the flux. Flux-cored cut wires for welded joints that did not develop cracks in both the U-shaped weld cracking test and the Y-shaped weld cracking test were judged to be "passed" in terms of cold cracking resistance.

[0096] (ii) Evaluation of cold crack resistance in the first layer of the groove Welding was performed on a 50 mm thick steel sheet with a tensile strength of 780 MPa under welding condition number 2 in Table 2. The groove shape was a V-shape as shown in Figure 4, and the filling thickness of the flux-cored cut wire 4 in the groove 3 was 2 mm. Furthermore, flux-cored wires a to d having the N content and F content shown in Table 3 were used as welding wires (filler metals), and SB-41 manufactured by Nippon Steel Welding Industries Co., Ltd. was used as backing material 5. The welded joints obtained in evaluation (ii) were used for the evaluation of bead shape described later. In addition, in the welding condition numbers 1 and 2 in these evaluations (i) and (ii), the tests were carried out without preheating the base materials (steel materials) 1 and 2. In addition, in Figures 3 and 4, the reference numerals 1 and 2 indicate the steel plates that are the base materials.

[0097] [Table 2]

[0098] [Table 3]

[0099] (Bead shape evaluation) After i) evaluation of cold cracking resistance (Y-shaped weld cracking test and U-shaped weld cracking test) and ii) evaluation of cold cracking resistance in the first layer, the height difference of the bead surface was measured at 25 mm intervals along the bead length to evaluate the bead shape. In this case, both after i) evaluation of cold cracking resistance (Y-shaped weld cracking test and U-shaped weld cracking test) and after ii) evaluation of cold cracking resistance in the first layer, if the surface unevenness of the bead shape was 3 mm or less, it was evaluated as good (Y), and if it was more than 3 mm, it was evaluated as poor (N).

[0100] (Evaluation of diffusible hydrogen content in weld metal) 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.

[0101] <Comparative Example 105> Instead of using a cut wire, an austenitic stainless steel welding wire having the same composition as “S-4” described in Table 2 of JP 2003-126989 A (C: 0.011 mass%, Si: 0.40 mass%, Mn: 0.56 mass%, P: 0.001 mass%, S: 0.001 mass%, Cr: 20.2 mass%, Ni: 18.3 mass%, Mo: 6.2 mass%, Cu: 0.7 mass%, N: 0.215 mass%) was used, and welding and evaluation similar to those described above were performed under welding condition number 2 in Table 2.

[0102] The test results obtained using the above method are shown in Tables 4-1 and 4-2. If all evaluation items were passed, the overall judgment was considered to be passed, and if even one item was not passed, the overall judgment was considered to be failed.

[0103] [Table 4-1]

[0104] [Table 4-2]

[0105] When welding was performed using the flux-cored cut wire of the example, no cross-sectional cracks were observed in all cross sections in the U-shaped weld cracking test and the Y-shaped weld cracking test, even without preheating the steel material. This proves that the flux-cored cut wire of the example has extremely high resistance to cold cracking. Furthermore, as shown in the test results in Tables 4-1 and 4-2, the flux-cored cut wires of the examples also passed the evaluation of bead shape, and showed good welding workability. In addition, the flux-cored cut wire of the example also passed the evaluation item of the amount of diffusible hydrogen in the weld metal, and it was possible to produce a weld metal having excellent mechanical properties. 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.

[0106] As described above, according to the present disclosure, even when welding extremely thick high-strength steel plates, it is possible to reduce the burden of preheating work and prevent cold cracking, and it is also possible to produce welded joints with a good bead shape while minimizing problems in the working environment caused by fumes and spatter, making it possible to manufacture welded joints that are advantageous in terms of cost. [Explanation of symbols]

[0107] 1, 2: Base material (steel), 3: Groove, 4: Flux-cored cut wire, 5: Backing material, 6: Welding wire, 7: Weld metal.

Claims

1. A flux-cored cut wire for groove filling, which is used to fill at least a portion of a groove provided between a plurality of base materials when welding the base materials together to produce a welded joint, a steel outer shell and a flux filled inside the steel outer shell, the flux containing nitrides; The N content of the flux-cored cut wire relative to the total mass is 0.003 mass% or more, 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 A flux-cored cutting wire for groove filling, which is one or more types selected from the group consisting of N.

2. 2. The flux-cored cutting wire for groove filling according to claim 1, wherein the N content of the flux-cored cutting wire is 0.003 to 15,000 mass% relative to the total mass of the flux-cored cutting wire.

3. The chemical composition of the flux-cored cut wire, excluding nitrides, oxides, fluorides, and carbonates, is, in mass % based on the total mass of the flux-cored cut wire, C: 0-0.500%, Si: 0 to 10.00%, Mn: 0 to 10.00%, P: 0 to 0.030%, S: 0-0.030%, Cu: 0 to 50.00%, Ni: 0 to 90.0%, Cr: 0-90.00%, Mo: 0 to 90.00%, Nb: 0 to 10.00%, V: 0-10.00%, Ti: 0-10.00%, Al: 0-10.000%, Mg: 0-3.000%, B: 0-10.000%, Ca: 0-3.000%, W: 0-90.00%, Sn: 0-90.00%, Sb: 0 to 90.00%, REM: 0-90.000%, Bi: 0 to 1.000%, and The balance is composed of Fe and impurities. Ti oxide: 0 to 8.00%, Total of specific oxides other than Ti oxide: 0 to 10.0% F: 0 to 30.000%; 3. The flux-cored cut wire for groove filling according to claim 1, wherein the total of the specific oxides other than Ti oxide is a total of 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.

4. A method for manufacturing a welded joint, comprising: a flux-cored cut wire welding step of filling at least a portion of a groove formed between a plurality of base materials with the flux-cored cut wire according to any one of claims 1 to 3 and welding the same.

5. The method for manufacturing a welded joint according to claim 4, wherein the flux-cored cut wire welding step includes filling the groove with the flux-cored cut wire and welding in one pass.

6. 5. The method for manufacturing a welded joint according to claim 4, wherein the flux-cored cut wire welding process comprises single-layer welding in which the flux-cored cut wire is filled in the first layer in the groove and welded, or multi-layer welding in which the flux-cored cut wire is filled in the first layer and second and subsequent layers in the groove and welded, and welding is performed at least until the temperatures of the plurality of base materials reach their respective preheat equivalent temperatures.

7. The method for manufacturing a welded joint according to any one of claims 4 to 6, wherein the welding means is submerged arc welding or gas shielded arc welding.

8. The method for manufacturing a welded joint according to any one of claims 4 to 7, wherein the plurality of base materials are each a high-strength steel material having a tensile strength of 780 MPa or more.

9. The method for manufacturing a welded joint according to any one of claims 4 to 8, wherein the plurality of base materials are steel materials each having a thickness of 50 mm or more.

10. The flux-cored cut wire welding process includes:

10. The method for manufacturing a welded joint according to any one of claims 4 to 9, wherein welding is performed using a flux-cored wire that has a steel outer sheath and flux filled inside the steel outer sheath, and that contains at least one of nitride and fluoride, as a wire that serves as a welding material to be attached to an electrode for generating an arc.

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