Flux-cored wire, gas shielded arc welding method, and method for producing welded metal

Abstract

To provide a flux-cored wire that yields welded metal having excellent mechanical properties despite having a Mn content of less than 1.0 mass% in the wire.SOLUTION: A flux-cored wire comprises, in mass% based on the total mass of the wire, Mn: 0.71 mass% or more and less than 1.00 mass%, and V: 0.02 mass% or more and 0.15 mass% or less, with specified contents of C, Si, Ni, F, and the like, and has a value A, calculated by the formula (1): A=546×[C]+66×[Mn]+583×[Ni]+(-138)×[V]-183, of 71 or more and less than 150. In formula (1), [C], [Mn], [Ni], and [V] represent the contents (mass%) of each component relative to the total mass of the wire.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a flux-cored wire, a gas-shielded arc welding method using the flux-cored wire, and a method for producing a weld metal using the welding method. [Background technology]

[0002] Flux-cored wire, a type of welding material, is used in welding shipbuilding, marine structures, construction, pipes, etc. When welding the above-mentioned various structures, flux wires containing a large amount of Mn are generally used. This is because the mechanical properties of the obtained weld metal can be adjusted to a desired range by including an appropriate amount of Mn in the wire.

[0003] For example, Patent Document 1 describes an Ar-CO alloy containing, for example, 1.5 to 3.5% Mn by mass relative to the total mass of the wire. 2 A mixed gas flux-cored wire is disclosed. The flux-cored wire can provide a weld metal having appropriate strength and good toughness in a low temperature range, and can also improve welding workability.

[0004] However, when the wire contains a large amount of Mn, such as the flux-cored wire described in Patent Document 1, the Mn concentration in the fumes generated during welding is also high, which raises concerns about adverse health effects. For example, the U.S. Occupational Safety and Health Act regulates the Mn content of welding wire to limit the exposure amount of Mn in welding fumes to a certain level or less. Specifically, Title 40 of the Code of Federal Regulations, Part 63, Subpart XXXXXX, states that the Mn content of welding wire is limited to less than 1.0 wt% per total weight of wire as a requirement for Metal Fabrication Hazardous Air Pollutants (MFHAP). In Japan, welding fumes containing Mn are also designated as a specified chemical substance (Class 2 substance).

[0005] On the other hand, Patent Document 2 discloses a wire alloy composition with high Si and low Mn, which improves the slag removability after welding. 2 Patent Document 2 discloses a wire for gas-shielded arc welding using Mn as a shielding gas. In the wire described in Patent Document 2, the Mn content is specified to be 0.15 to 0.85%. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-124023 A [Patent Document 2] Japanese Patent Application Publication No. 6-182585 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in order to suppress the Mn concentration in the welding fumes, the Mn content in the wire needs to be less than 1 mass%, so the Mn concentration in the welding fumes cannot be reduced with the flux-cored wire described in Patent Document 1. Furthermore, in a situation where the Mn content of welding wire must be regulated, such as in the United States, the flux-cored wire described in Patent Document 1 cannot be used.

[0008] In addition, in the gas shielded arc welding wire described in Patent Document 2, the Mn content in the wire is less than 1%, but the mechanical properties of the weld metal, such as the tensile strength and toughness expressed by the Charpy impact test, are not sufficient. In general, when the Mn content in the wire is reduced, it is difficult to obtain the desired mechanical properties of the weld metal. Specifically, it is difficult to obtain a weld metal with excellent mechanical properties while keeping the Mn content of the welding wire less than 1.0 mass%, as specified by Title 40 of the Code of Federal Regulations, Part 63, Subpart XXXXXX.

[0009] The present invention has been made in view of the above problems, and has an object to provide a flux-cored wire capable of producing a weld metal having good mechanical properties even when the Mn content in the wire is less than 1.0 mass %, a gas-shielded arc welding method using the flux-cored wire, and a method for producing a weld metal using the welding method. [Means for solving the problem]

[0010] The above object of the present invention is achieved by the following configuration [1] relating to a flux-cored wire.

[0011] [1] A flux-cored wire in which a steel sheath is filled with flux, For the total mass of wire, C: 0.030 mass% or more and 0.090 mass% or less, Si: 0.60 mass% or more and 1.20 mass% or less, Mn: 0.71% by mass or more and less than 1.00% by mass, Ni: 0.10 mass% or more and less than 0.50 mass% V: 0.02 mass% or more and 0.15 mass% or less, F: 0.010 mass% or more and 0.200 mass% or less, Fe: 94% by mass or more, Contains Mo: 0.18% by mass or less, At the same time, When the C content in the wire is expressed as [C] in mass% relative to the total mass of the wire, the Mn content in the wire is expressed as [Mn] in mass% relative to the total mass of the wire, the Ni content in the wire is expressed as [Ni] in mass% relative to the total mass of the wire, and the V content in the wire is expressed as [V] in mass% relative to the total mass of the wire, Value A calculated by the following formula (1): 71 or more and less than 150, The flux-cored wire according to claim 1, A = 546 × [C] + 66 × [Mn] + 583 × [Ni] + (-138) × [V] - 183 Equation (1)

[0012] Moreover, a preferred embodiment of the present invention relating to the flux-cored wire relates to the following [2].

[0013] [2] When the Ni content in the wire is expressed as [Ni] in mass% relative to the total mass of the wire, the V content in the wire is expressed as [V] in mass% relative to the total mass of the wire, the Mo content in the wire is expressed as [Mo] in mass% relative to the total mass of the wire, and the F content in the wire is expressed as [F] in mass% relative to the total mass of the wire, A value B calculated by the following formula (2): 7.25 or more and 10.85 or less, The flux-cored wire according to [1], B = ([Ni] + [V] + [Mo]) / [F] Equation (2)

[0014] The above object of the present invention is achieved by the gas shielded arc welding method having the following configuration [3].

[0015] [2] A gas-shielded arc welding method, comprising carrying out gas-shielded arc welding using the flux-cored wire according to [1] or [2].

[0016] The above object of the present invention is achieved by the following configuration [3] relating to a method for producing a weld metal.

[0017] [3] A method for producing weld metal, comprising carrying out gas-shielded arc welding using the flux-cored wire according to [1] or [2] to produce weld metal. Effect of the Invention

[0018] According to the present invention, it is possible to provide a flux-cored wire capable of producing a weld metal having good mechanical properties even when the Mn content in the wire is less than 1.0 mass %, a gas-shielded arc welding method using the flux-cored wire, and a method for producing a weld metal using the welding method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present inventors have conducted extensive research to obtain a flux-cored wire capable of maintaining the mechanical properties of the weld metal within a desired range even when the Mn content in the wire is less than 1.0 mass%. In the present invention, good mechanical properties refer to a state in which the desired strength and low-temperature toughness can be obtained. As a result, the inventors have found that the above-mentioned problems can be solved by setting the Mn content in the wire to 0.71 mass% or more and less than 1.00 mass%, and in particular, by appropriately controlling the V content in the wire and controlling the value calculated by a specific formula using the C, Mn, Ni and V contents in the wire. The present invention has been made based on these findings.

[0020] Hereinafter, an embodiment for carrying out the present invention (hereinafter, referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be carried out with any modification within the scope of the gist of the present invention.

[0021] [Flux-cored wire] The flux-cored wire according to the present embodiment (hereinafter, simply referred to as "wire") is a wire in which flux is filled in a steel sheath (hereinafter, simply referred to as "sheath"). Hereinafter, the components contained in the flux-cored wire according to the present embodiment and the reasons for the numerical limitations of the components will be described in more detail.

[0022] In the present embodiment, the content means mass% relative to the total mass of the flux-cored wire unless otherwise specified. Each element contained in the flux-cored wire according to the present embodiment may be contained in either the steel sheath or the flux, or may be contained in both the steel sheath and the flux. Furthermore, unless otherwise noted, each of the above elements may be contained in the flux-cored wire in the form of a metal, in the form of a compound, or in both the form of a metal and a compound. Therefore, regardless of the form in which each of the above elements is contained in the flux-cored wire, it is defined by the converted value in terms of the elemental substance. For example, when taking Si as an example, the Si content refers to the total of the Si-converted values of metallic Si and Si compounds. Note that metallic Si includes Si single substance and Si alloys.

[0023] <C: 0.030 mass% or more and 0.090 mass% or less> C is an element that has the effect of improving the strength of the weld metal. Also, by containing C in the wire instead of Mn which has the effect of forming an austenite structure, the balance between the strength and low-temperature toughness of the weld metal can be improved. If the C content in the wire is less than 0.030 mass%, the above effects cannot be fully obtained, and the desired strength and low-temperature toughness cannot be obtained. Therefore, the C content in the wire is 0.030 mass% or more based on the total mass of the wire, preferably 0.035 mass% or more, and more preferably 0.040 mass% or more. On the other hand, if the C content in the wire exceeds 0.090 mass%, the amount of welding fume generated increases, and the strength of the weld metal becomes excessive, resulting in the inability to obtain the desired low-temperature toughness. Therefore, the C content in the wire is 0.090 mass% or less based on the total mass of the wire, preferably 0.080 mass% or less, more preferably 0.070 mass% or less, and even more preferably 0.060 mass% or less.

[0024] <Si: 0.60 mass% or more and 1.20 mass% or less> Si is an element with a deoxidizing effect. If the Si content in the wire is less than 0.60% by mass, the deoxidation of the weld metal is insufficient, and the desired low-temperature toughness cannot be obtained. Therefore, the Si content in the wire should be 0.60% by mass or more based on the total mass of the wire, preferably 0.70% by mass or more, more preferably 0.80% by mass or more, and even more preferably 0.90% by mass or more. On the other hand, if the Si content in the wire exceeds 1.20% by mass, coarse ferrite is formed, and the desired low-temperature toughness cannot be obtained. Therefore, the Si content in the wire should be 1.20% by mass or less based on the total mass of the wire, preferably 1.10% by mass or less, more preferably 1.05% by mass or less, and even more preferably 1.00% by mass or less.

[0025] <Mn: 0.71% by mass or more and less than 1.00% by mass> When the Mn content in the wire increases, the Mn concentration in the fume generated during welding also increases. In order to meet the requirements of MFHAP, the Mn content in the wire needs to be less than 1.00% by mass based on the total mass of the wire. In addition, in order to reduce the Mn concentration in the welding fume, the lower the Mn content in the wire, the better. Therefore, the Mn content in the wire is preferably 0.98% by mass or less, more preferably 0.95% by mass or less, based on the total mass of the wire. On the other hand, Mn is an element that has a deoxidizing effect and an effect of forming an austenite structure, and greatly contributes to improving the strength and low-temperature toughness of the weld metal. If the Mn content in the wire is less than 0.71% by mass, the desired strength and the desired low-temperature toughness cannot be achieved simultaneously. Therefore, from the perspective of the Mn concentration in the fume generated during welding, the lower the Mn content in the wire, the better. However, considering the compatibility of the strength and low-temperature toughness of the weld metal, the Mn content in the wire needs to be 0.71% by mass or more based on the total mass of the wire. In addition, from the perspective of the strength and low-temperature toughness of the weld metal, the Mn content in the wire is preferably 0.80% by mass or more, more preferably 0.85% by mass or more, and even more preferably 0.90% by mass or more.

[0026] <Ni: 0.10 mass% or more and less than 0.50 mass%> Ni is an element that has the effect of improving the low-temperature toughness of the weld metal. If the Ni content in the wire is less than 0.10 mass%, the desired low-temperature toughness cannot be obtained. Therefore, the Ni content in the wire is 0.10 mass% or more based on the total mass of the wire, preferably 0.20 mass% or more, more preferably 0.30 mass% or more, and even more preferably 0.35 mass% or more. Also, in order to obtain a weld metal having even more excellent mechanical properties, it is also important to suppress the variation in low-temperature toughness. As will be described later, Ni is also an element that affects the occurrence of variation in low-temperature toughness together with V, Mo, and F. Therefore, from the viewpoint of suppressing the variation in low-temperature toughness, the Ni content in the wire is even more preferably 0.36 mass% or more. On the other hand, if the Ni content in the wire is 0.50 mass% or more, the raw material cost of the wire increases and segregation occurs at the grain boundary equivalent position, and the desired low-temperature toughness cannot be obtained. Therefore, the Ni content in the wire is less than 0.50 mass% based on the total mass of the wire, preferably less than 0.45 mass%, and more preferably 0.40 mass% or less.

[0027] <V: 0.02 mass% or more and 0.15 mass% or less> V is an element that contributes to improving the strength and low-temperature toughness of the weld metal in a small amount in the component system of the wire according to the present embodiment. In the present embodiment, in order to satisfy the requirements of MFHAP, the Mn content is less than 1.0% by mass. On the other hand, by actively containing V in the wire, it is possible to achieve both the desired strength and low-temperature toughness of the weld metal. This is because by containing V in the wire, carbides and nitrides are formed in the weld metal, and thereby the grain refinement can be achieved. If the V content in the wire is less than 0.02% by mass, the above effects cannot be sufficiently obtained, and the desired strength and low-temperature toughness cannot be obtained. Therefore, the V content in the wire is 0.02% by mass or more with respect to the total mass of the wire, preferably 0.04% by mass or more, more preferably 0.06% by mass or more, and even more preferably 0.07% by mass or more. On the other hand, if the V content in the wire exceeds 0.15% by mass, the strength of the weld metal becomes excessive, and the desired low-temperature toughness cannot be obtained. Therefore, the V content in the wire is 0.15% by mass or less with respect to the total mass of the wire, preferably 0.13% by mass or less, more preferably 0.11% by mass or less, and even more preferably 0.09% by mass or less.

[0028] <F: 0.010% by mass or more and 0.200% by mass or less> F is an element having an effect of stabilizing the arc and an effect of reducing the amount of diffusible hydrogen remaining in the weld metal. If the F content in the wire is less than 0.010% by mass, the above effects cannot be sufficiently obtained. Therefore, the F content in the wire is 0.010% by mass or more with respect to the total mass of the wire, preferably 0.020% by mass or more, more preferably 0.030% by mass or more, and even more preferably 0.040% by mass or more. On the one hand, when the F content in the wire exceeds 0.200% by mass, the amount of spatter generated increases and the weldability deteriorates. Therefore, the F content in the wire should be 0.200% by mass or less, preferably 0.150% by mass or less, more preferably 0.130% by mass or less, and even more preferably 0.100% by mass or less, based on the total mass of the wire. F is preferably contained in the wire in the form of a fluoride compound. For example, it may contain NaF, K 2 SiF 6 and the like.

[0029] In addition, as the form of the fluoride compound contained in the wire, it is more preferable to contain a fluoride compound containing an element with a deoxidizing effect higher than that of Mn in the flux. Elements with a deoxidizing effect higher than that of Mn are, for example, Si, Ti, Al, Mg, Be, Ce, B, etc. It is preferable to contain a fluoride compound containing at least one of these elements in the flux. This is because the fluoride compound related to the element with a deoxidizing effect higher than that of Mn dissociates into F and a deoxidizing element near the arc, and this deoxidizing element vaporizes due to the heat of the arc to become metal vapor, and oxidizes in the air preferentially over Mn to become fume. As a result, the Mn concentration in the welding fume can be suppressed.

[0030] <Mo: 0.18% by mass or less (including 0% by mass)> By containing an appropriate amount of Mo in the wire, the strength of the weld metal can be improved while maintaining the low-temperature toughness. Therefore, when aiming to adjust the strength of the weld metal, Mo may be contained in the wire, but it is not always necessary to contain Mo in the wire, and the Mo content in the wire may be 0% by mass. When containing Mo in the wire to improve the strength of the weld metal, the Mo content in the wire is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.07% by mass or more, and even more preferably 0.09% by mass or more, based on the total mass of the wire. On the one hand, when the Mo content in the wire exceeds 0.18% by mass, the low-temperature toughness of the weld metal decreases. In other words, in this specification, the above-mentioned "appropriate amount of Mo" means that the Mo content in the wire is in the range of 0.18% by mass or less. Therefore, the Mo content in the wire shall be 0.18% by mass or less based on the total mass of the wire. Further, from the viewpoint of maintaining the low-temperature toughness of the weld metal, the Mo content in the wire is preferably 0.15% by mass or less, more preferably 0.13% by mass or less, and even more preferably 0.11% by mass or less.

[0031] <Total amount of O (oxygen): 0.20% by mass or less> The wire according to this embodiment may contain O (oxygen). When it is desired to reduce the amount of slag generated and avoid the slag removal operation after welding, the O content in the wire is preferably 0.20% by mass or less, more preferably 0.15% by mass or less, in total based on the total mass of the wire. As the O (oxygen) source contained in the wire, O (oxygen) in the steel sheath, or TiO contained in the flux 2 such as titanium oxides, Al 2 O 3 such as aluminum oxides, SiO 2 such as silicon oxides, Fe 2 O 3 such as iron oxides and the like.

[0032] <Total amount of N: 0.10% by mass or less> In the wire according to this embodiment, when N is included for the purpose of forming nitrides with V in the weld metal, the N content is preferably 0.05% by mass or less, more preferably 0.02% by mass or less, in total based on the total mass of the wire. As the N source contained in the wire, N contained in the N in the steel sheath or nitrides contained in the flux and the like can be mentioned.

[0033] <Fe: 94% by mass or more> Fe is the main component of the wire according to this embodiment. In view of the deposition amount and other component compositions, the Fe content in the wire is 94 mass% or more, preferably 95 mass% or more, and more preferably 97 mass% or more, based on the total mass of the wire. On the other hand, the Fe content in the wire is practically 98 mass% or less, and preferably 97.5 mass% or less, based on the total mass of the wire. In addition, the flux-cored wire according to this embodiment preferably contains the above-mentioned Fe, C, Si, Mn, Ni, V, F and Mo in a total content of 96 mass% or more, more preferably 97 mass% or more, and even more preferably 98 mass% or more.

[0034] <Value A calculated by formula (1): 71 or more and less than 150> C, Mn, and Ni are elements that act to form an austenite structure, and V is an element that acts to form a ferrite structure. The present inventors have found that a weld metal that can improve low-temperature toughness can be obtained by appropriately controlling the contents of each component contained in the flux-cored wire according to the present embodiment and controlling the value A obtained by the following formula (1).

[0035] If the value A calculated by the following formula (1) is less than 71 or is 150 or more, the balance of the components becomes poor, the structure is not refined, and low-temperature toughness deteriorates. Therefore, the value A calculated by the following formula (1) is set to 71 or more, preferably 80 or more, more preferably 90 or more, and even more preferably 100 or more. On the other hand, the value A calculated by the following formula (1) is set to less than 150, preferably 140 or less, more preferably 130 or less, and even more preferably 125 or less.

[0036] A = 546 × [C] + 66 × [Mn] + 583 × [Ni] + (-138) × [V] - 183 Equation (1)

[0037] In this embodiment, an index of weld metal having even more preferable mechanical properties is small variation in low-temperature toughness. By setting the relationship between V, Ni, and Mo and F in the wire as follows, the variation in low-temperature toughness of the weld metal can be suppressed, and better mechanical properties can be obtained.

[0038] <Value B calculated by formula (2): 7.25 or more and 10.85 or less> V, Ni, and Mo are elements that are relatively difficult to oxidize and are easily retained in the molten pool, so that by controlling the contents of V, Ni, and Mo, it is easy to adjust the strength and low-temperature toughness of the weld metal. However, if the molten pool is disturbed during welding due to arc instability, etc., there is a risk that the elements V, Ni, and Mo will become non-uniform, resulting in variations in low-temperature toughness depending on the position of the weld metal. On the other hand, as described above, if F is present in an appropriate amount, it has the effect of stabilizing the arc, so the inventors have found that the variation in low-temperature toughness can be controlled by the ratio of the total content of V, Ni, and Mo to the F content. That is, if the F content is appropriate, the arc is stabilized and the molten pool is stably stirred, so that the elements V, Ni, and Mo are uniformly dispersed, and the variation in low-temperature toughness at the position in the weld metal can be suppressed.

[0039] When the value B calculated by the following formula (2) is 7.25 or more and 10.85 or less, the variation in low-temperature toughness at various positions in the weld metal can be suppressed. Therefore, the value B calculated by formula (2) is preferably 7.25 or more, more preferably 7.85 or more, and even more preferably 8.30 or more. On the other hand, the value B calculated by formula (2) is preferably 10.85 or less, more preferably 10.25 or less, and even more preferably 9.85 or less.

[0040] B = ([V] + [Ni] + [Mo]) / [F] Equation (2)

[0041] In the above formulas (1) and (2), [C] is the value representing the C content in the wire as a mass % with respect to the total mass of the wire. [Mn] is the value representing the Mn content in the wire as a mass % with respect to the total mass of the wire. [Ni] is the value representing the Ni content in the wire as a mass % with respect to the total mass of the wire. [V] is the value representing the V content in the wire as a mass % with respect to the total mass of the wire. [Mo] is the value representing the Mo content in the wire as a mass % with respect to the total mass of the wire. [F] is the value representing the F content in the wire as a mass % with respect to the total mass of the wire.

[0042] <Other elements> Examples of the remainder of the flux-containing wire according to the present embodiment include Cu, Cr, Ti, Zr, Nb, B, Na, K, Li, Mg, Ca, Ba, Be, and Ce. The wire according to the present embodiment may contain each of them within the range of Cu: 0.30 mass % or less, Cr: 0.50 mass % or less, Ti: 0.04 mass % or less, Zr: 0.01 mass % or less, Nb: 0.1 mass % or less, B: 0.01 mass % or less, Na: 0.30 mass % or less, K: 0.30 mass % or less, Li: 0.30 mass % or less, Mg: 0.50 mass % or less, Ca: 0.10 mass % or less, Ba: 0.10 mass % or less, Be: 0.10 mass % or less, and Ce: 0.10 mass % or less with respect to the total mass of the wire. Naturally, these elements may also be 0 mass %.

[0043] <Total content of Ti, Zr, Mg, and Al: 0.50 mass % or less> Among the other elements listed above, in particular, the contents of strong deoxidizing elements such as Ti, Zr, Mg, and Al are preferably reduced. Generally, by precipitating elements such as Ti, Zr, Mg, and Al as compounds in the weld metal and achieving grain refinement, the low-temperature toughness can be improved. However, when the Mn content in the wire is regulated to less than 1.00% as in the present invention, if strong deoxidizing elements such as Ti, Zr, Mg, and Al are added to the wire, oxides mainly composed of strong deoxidizing elements such as Ti, Zr, Mg, and Al will appear as slag on the molten pool. At this time, since the oxides of strong deoxidizing elements such as Ti, Zr, Mg, and Al have a relatively low work function, the arc will deflect towards the generated oxides, and there is a risk of arc instability. When arc instability occurs, there may be an increase in the total amount of fume and variations in low-temperature toughness. Therefore, the total content of Ti, Zr, Mg, and Al in the wire is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.10% by mass or less. As described above, V is relatively difficult to oxidize and contributes to grain refinement in the form of carbides or nitrides. Therefore, when regulating the Mn content in the wire as in the present invention, it is preferable to regulate strong deoxidizing elements such as Ti, Zr, Mg, and Al and contain V in the wire to ensure mechanical properties.

[0044] <Remainder> The remainder of the flux-cored wire according to this embodiment is inevitable impurities such as P, S, Bi, Co, Sn, Sb, and As. Regarding the above-mentioned inevitable impurities in the wire, in total, it is preferably 0.50% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.10% by mass or less based on the total mass of the wire. In particular, P and S are preferably regulated as follows.

[0045] <P: 0.020% by mass or less> P is an impurity element that reduces the toughness of the weld metal, and the lower the P content in the wire, the more preferable. When the P content in the wire exceeds 0.020% by mass based on the total mass of the wire, the toughness of the weld metal deteriorates. Therefore, the P content in the wire should be 0.020% by mass or less based on the total mass of the wire, preferably 0.015% by mass or less, and more preferably 0.013% by mass or less.

[0046] <S: 0.030% by mass or less> S is an impurity element that reduces the toughness of the weld metal, and the lower the S content in the wire, the more preferable. When the S content in the wire exceeds 0.030% by mass based on the total mass of the wire, the toughness of the weld metal deteriorates. Therefore, the S content in the wire should be 0.030% by mass or less based on the total mass of the wire, preferably 0.020% by mass or less, and more preferably 0.015% by mass or less.

[0047] <Flux filling rate: 6% by mass or more and 10% by mass or less> In the flux-cored wire according to this embodiment, the flux filling rate, which is the mass of the flux based on the total mass of the wire, is not particularly limited as long as each component in the wire is within the above range, and can be set to any range. From the viewpoint of suppressing the amount of diffusible hydrogen, the flux filling rate is preferably 6% by mass or more and 10% by mass or less, and more preferably 7% by mass or more and 9% by mass or less.

[0048] [Manufacturing method of flux-cored wire] The flux-cored wire according to the present embodiment can be manufactured, for example, by the following method. First, the steel strip constituting the outer sheath is formed by a forming roll while being fed in the longitudinal direction to form a U-shaped open tube. Next, flux containing a predetermined amount of metal, alloy, compound, etc. so as to have a predetermined chemical composition is filled into the open tube, and then processed so as to have a circular cross section. At this time, the outer sheath can be seamless by welding or the like. Then, the wire is drawn by cold working to a wire diameter of, for example, 0.9 mm or more and 2.0 mm or less, thereby manufacturing the flux-cored wire. Annealing may be performed during the cold working.

[0049] [Gas shielded arc welding method] The gas-shielded arc welding method according to this embodiment is a method for performing gas-shielded arc welding using the flux-cored wire according to the embodiment described above. In the gas-shielded arc welding method according to this embodiment, various welding conditions are not particularly limited except for the use of the flux-cored wire according to this embodiment, and general conditions for a welding method using a flux-cored wire can be used for the type of base material, welding voltage, welding current, welding position, etc. The shielding gas is also not particularly limited, but from the viewpoint of improving the welding workability, it is preferable to use MAG welding (Metal Active Gas Welding), and 75 to 80 volume % Ar-20 to 25 volume % CO 2 It is more preferable that:

[0050] [Method of manufacturing weld metal] The method for producing a weld metal according to the present embodiment is a method for producing a weld metal by performing gas-shielded arc welding using the flux-cored wire according to the present embodiment. Various welding conditions are not particularly limited, and the gas-shielded arc welding method according to the present embodiment can be used. EXAMPLES

[0051] Hereinafter, examples of the flux-cored wire according to the present embodiment and comparative examples will be described.

[0052] [Evaluation of mechanical properties of weld metal] <Wire production> First, flux was filled into a strip-shaped steel sheath to produce flux-cored wires having various components and a diameter of 1.2 mm. The flux filling rate was adjusted to 8 mass %.

[0053] <Weld metal manufacturing> Next, using the obtained flux-cored wire, gas-shielded arc welding was performed on a base material having a plate thickness and chemical composition shown in Table 1 below under the conditions shown in Table 2 below to produce a weld metal.

[0054] <Evaluation of mechanical properties> (Collection of test specimens) In accordance with the "Tensile and impact test method for weld metal" specified in JIS Z 3111:2005, one tensile test specimen (A0 test specimen) was taken from the center of the weld metal in the plate thickness direction, and three impact test specimens (V-notch test specimens) were also taken.

[0055] (Method and criteria for evaluating tensile performance) A tensile test was carried out on the collected tensile test pieces at room temperature (about 20 to 23°C) in accordance with JIS Z 2241:2011, and the yield stress and tensile strength were measured to evaluate the tensile performance. Weld metals with a yield stress (0.2% yield strength) of 460 MPa or more were evaluated as having the desired yield stress and passed the test, while weld metals with a yield stress of less than 460 MPa were evaluated as failing the test. Furthermore, weld metals having a tensile strength of 560 MPa or more were evaluated as having the desired tensile strength and thus passed, whereas weld metals having a tensile strength of less than 560 MPa were evaluated as failing.

[0056] (Method and criteria for evaluating toughness) For each impact test piece, the test temperature was set to -30°C, and the Charpy absorbed energy (vE -30℃ ) was measured to evaluate the toughness. For the examples and comparative examples, measurements were carried out on three impact test pieces each. Those for which all the Charpy absorbed energy measurements exceeded 47 J were evaluated as having the desired low-temperature toughness and were deemed to have passed the test. Those for which even one Charpy absorbed energy measurement was less than 47 J were evaluated as failing the test.

[0057] In addition, from the measurement results of the Charpy absorbed energy for each of the three impact test pieces, the maximum and minimum values ​​were extracted for each of the invention examples and comparative examples, and the difference between the two values ​​was calculated to evaluate the variation in low-temperature toughness. In other words, the variation in low-temperature toughness is evaluated by evaluating the degree to which the measurement results of the Charpy impact energy differ depending on the position in the weld metal. In addition, for the examples and comparative examples, those in which the difference between the maximum and minimum Charpy absorbed energy was more than 20 (J) and not more than 30 (J) were judged to have suppressed variation in low-temperature toughness and to have good evaluation results. Also, those in which the difference between the maximum and minimum Charpy absorbed energy was more than 15 (J) and not more than 20 (J) were judged to have further suppressed variation in low-temperature toughness and to have excellent evaluation results. Furthermore, those in which the difference between the maximum and minimum Charpy absorbed energy was not more than 15 (J) were judged to have sufficiently suppressed variation in low-temperature toughness and to have particularly excellent evaluation results.

[0058] The chemical components of the wire used and the values ​​calculated from formulas (1) and (2) are shown in Table 3 below, and the evaluation results of the mechanical properties are shown in Table 4 below. In Table 3 below, formulas (1) and (2) are as follows.

[0059] A = 546 × [C] + 66 × [Mn] + 583 × [Ni] + (-138) × [V] + -183 Equation (1)

[0060] B = ([V] + [Ni] + [Mo]) / [F] Equation (2)

[0061] However, in the above formulas (1) and (2), [C] is the value of the C content in the wire expressed as mass% relative to the total mass of the wire. [Mn] is the value of the Mn content in the wire expressed as mass% relative to the total mass of the wire. [Ni] is the value of the Ni content in the wire expressed as mass% relative to the total mass of the wire. [V] is the value of the V content in the wire expressed as mass% relative to the total mass of the wire. [Mo] is the value of the Mo content in the wire expressed as mass% relative to the total mass of the wire. [F] is the value of the F content in the wire expressed as mass% relative to the total mass of the wire.

[0062] The remainder of the components in the wire shown in Table 3 are impurities. In addition, in the column of the content of each component in Table 3, "-" indicates that the component was not added during the production of the wire or was below the detection limit.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] [Table 4]

[0067] As shown in Tables 3 and 4 above, in Examples 1 to 6 in which the contents of each component in the wire and the value A calculated by formula (1) were within the numerical range of the present invention, weld metals excellent in both tensile performance and low-temperature toughness were obtained.

[0068] In particular, in Examples 1 to 4, the value B calculated by formula (2) was in the preferred range of 7.25 or more and 10.85 or less, so the variation in low-temperature toughness could be suppressed to 30 J or less, and the mechanical properties of the weld metal could be further improved.

[0069] On the other hand, in Comparative Example No. 1, the V content in the wire was less than the lower limit specified in the present invention, and therefore the evaluation results of the tensile performance and low-temperature toughness were poor. In Comparative Example No. 2, the value A was less than the lower limit specified in the present invention, and therefore the evaluation result of the low temperature toughness was poor. In Comparative Example No. 3, the V content in the wire was less than the lower limit of the present invention, and the value A exceeded the upper limit of the present invention, so the evaluation results of the tensile performance and low temperature toughness were poor. In Comparative Example 4, the Mn content in the wire was less than the lower limit specified in the present invention, and therefore the evaluation results of the tensile performance and low-temperature toughness were poor.

[0070] Thus, according to the present invention, even when the Mn content in the wire was less than 1.0 mass %, a weld metal having good mechanical properties could be obtained.

Claims

1. A flux-cored wire in which a steel sheath is filled with flux, For the total mass of wire, C: 0.030% by mass or more and 0.090% by mass or less, Si: 0.60% by mass or more and 1.20% by mass or less, Mn: 0.71% by mass or more and less than 1.00% by mass, Ni: 0.10 mass% or more and less than 0.50 mass%; V: 0.02% by mass or more and 0.15% by mass or less, F: 0.010% by mass or more and 0.200% by mass or less, Fe: 94% by mass or more, Contains Mo: 0.18% by mass or less, At the same time, When the C content in the wire is expressed as [C] in mass% with respect to the total mass of the wire, the Mn content in the wire is expressed as [Mn] in mass% with respect to the total mass of the wire, the Ni content in the wire is expressed as [Ni] in mass% with respect to the total mass of the wire, and the V content in the wire is expressed as [V] in mass% with respect to the total mass of the wire, Value A calculated by the following formula (1): 71 or more and less than 150, The flux-cored wire according to claim 1, A = 546 × [C] + 66 × [Mn] + 583 × [Ni] + (-138) × [V] - 183 ... formula (1)

2. When the Ni content in the wire is expressed as [Ni] in mass% with respect to the total mass of the wire, the V content in the wire is expressed as [V] in mass% with respect to the total mass of the wire, the Mo content in the wire is expressed as [Mo] in mass% with respect to the total mass of the wire, and the F content in the wire is expressed as [F] in mass% with respect to the total mass of the wire, Value B calculated by the following formula (2): 7.25 or more and 10.85 or less, The flux-cored wire according to claim 1, B = ([Ni] + [V] + [Mo]) / [F] ... formula (2)

3. 3. A gas-shielded arc welding method, comprising: carrying out gas-shielded arc welding using the flux-cored wire according to claim 1 or 2.

4. A method for producing a weld metal, comprising carrying out gas-shielded arc welding using the flux-cored wire according to claim 1 or 2 to produce a weld metal.

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