Wire for gas shield arc welding, gas shield arc welding method and weld metal manufacturing method

Abstract

To provide a wire for gas shield arc welding which can obtain weld metal having good tensile strength and toughness at low temperature.SOLUTION: There is provided a wire for gas shield arc welding, wherein with respect to the total mass of the wire, a C content is 0.040 mass% or more and 0.090 mass% or less, contents of Si, Mn, Ti, Ni, Fe, Cr, Mo and Cu are regulated, contents of each element to the total mass of the wire are represented by [C], [Si], [Mn], [Ti], [Ni], [Cr], [Mo], and [Cu] by mass%, the value A1 calculated by the following expression (1) is 4.05 or more, and the value A2 calculated by the following expression (2) is 0.45 or more. Expression (1): A1=[Mn]+[Ni], and Expression (2): A2=-[C]+[Si] / 7+[Mn] / 7+[Ti] / 4+[Ni] / 38+[Cr] / 8+[Mo] / 5+[Cu] / 15.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a gas shielded arc welding wire used for arc welding of high-tensile steel, a gas shielded arc welding method using the welding wire, and a method for manufacturing a weld metal using the welding wire.

Background Art

[0002] Welded structures such as offshore structures used in oil and gas drilling and production and offshore wind power generation, and pipelines used in oil and gas transportation, are increasing in size and operation in cold regions. Therefore, the steel plates used in these welded structures are being strengthened, and accordingly, the welding materials used are also required to have excellent properties of high strength and toughness at low temperatures.

[0003] In addition, in recent years, when manufacturing the above-described welded structures, welding is tend to be carried out under welding conditions of high current and large heat input in order to improve the efficiency of welding work. Under such conditions of large heat input, the strength of the weld metal decreases and the impact properties also deteriorate. For this reason, even when welding is carried out under severe welding conditions, the demand for technology for obtaining a welded portion having excellent properties is increasing, and in particular, the need for a welding material capable of improving the properties of the welded portion is increasing.

[0004] For example, Patent Document 1 proposes a wire containing a metal flux that defines the contents of C, Si, Mn, S, and P with respect to the total mass of the wire and defines the conversion values of metal fluoride, Na oxide, and K oxide in the flux. Patent Document 1 describes that by limiting the above components, it is possible to obtain a welding wire containing a metal flux for welding that is excellent in welding workability, excellent in weather resistance defects and crack resistance, and has good mechanical properties of the weld metal.

[0005] In addition, Patent Document 2 discloses a gas metal arc welding wire for high-tensile steel that contains C, Si, Mn, Cu, Ni, Cr, Mo, V, Nb, and Ti, restricts P, S, Al, N, and O, and regulates the total amount of Ca, Mg, and As with respect to the total weight of the wire. According to Patent Document 2, it is possible to obtain a wire with yield strength and toughness equal to or better than those of the high-tensile steel used as the base material, no defects due to sulfides, and good workability.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, when welding is carried out using the flux-cored wire described in Patent Document 1 above, the tensile strength of the weld metal is 540 to 680 MPa, and sufficient tensile strength cannot be obtained. In addition, the gas metal arc welding wire described in Patent Document 2 above contains a predetermined amount of Nb and V and also contains a large amount of Cr in order to improve strength and yield strength. Therefore, the tensile strength becomes too high, raising concerns about hot cracking, and it is difficult to obtain a weld metal with sufficient toughness.

[0008] The present invention has been made in view of such problems, and an object thereof is to provide a gas shielded arc welding wire that is suitably used for gas shielded arc welding of high-tensile steel and can obtain a weld metal with good tensile strength and toughness at low temperatures, a gas shielded arc welding method using the welding wire, and a method for manufacturing a weld metal using the welding wire.

Means for Solving the Problems

[0009] The above object of the present invention is achieved by the following configuration [1] related to a wire for gas shielded arc welding.

[0010] [1] With respect to the total mass of the wire, C: 0.040% by mass or more and 0.090% by mass or less, Si: 0.40% by mass or more and 0.90% by mass or less, Mn: 1.35% by mass or more and 2.80% by mass or less, Ti: 0.05% by mass or more and 0.40% by mass or less, Ni: 1.80% by mass or more and 3.70% by mass or less, and, Fe: 88.0% by mass or more, and contains Cr: 0.60% by mass or less (including 0% by mass), Mo: 0.90% by mass or less (including 0% by mass), Cu: 0.50% by mass or less (including 0% by mass), and When the C content with respect to the total mass of the wire is represented as [C] in % by mass, the Si content with respect to the total mass of the wire is represented as [Si] in % by mass, the Mn content with respect to the total mass of the wire is represented as [Mn] in % by mass, the Ti content with respect to the total mass of the wire is represented as [Ti] in % by mass, the Ni content with respect to the total mass of the wire is represented as [Ni] in % by mass, the Cr content with respect to the total mass of the wire is represented as [Cr] in % by mass, the Mo content with respect to the total mass of the wire is represented as [Mo] in % by mass, and the Cu content with respect to the total mass of the wire is represented as [Cu] in % by mass, the value A1 calculated by the following formula (1) is 4.05 or more, and the value A2 calculated by the following formula (2) is 0.45 or more, and a wire for gas shielded arc welding is characterized in that. A1 = [Mn] + [Ni] ··· Formula (1) A2 = -[C] + [Si] / 7 + [Mn] / 7 + [Ti] / 4 + [Ni] / 38 + [Cr] / 8 + [Mo] / 5 + [Cu] / 15 ··· Formula (2)

[0011] Further, a preferred embodiment of the present invention related to a wire for gas shielded arc welding relates to the following [2] to [6].

[0012] [2] The wire for gas shielded arc welding according to [1], wherein the value A3 calculated by the following formula (3) is 5.0 or less. A3 = [Ti] / [C] ··· Formula (3)

[0013] [3] The wire for gas shielded arc welding according to [1], wherein the value A4 calculated by the following formula (4) is 28.5 or less. A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu] ··· Formula (4)

[0014] [4] The wire for gas shielded arc welding according to [1], wherein the value A3 calculated by the following formula (3) is 5.0 or less, and the value A4 calculated by the following formula (4) is 28.5 or less. A3 = [Ti] / [C] ··· Formula (3) A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu] ··· Formula (4)

[0015] [5] Further, it contains at least one selected from Na, K, and Li, when the Na content with respect to the total mass of the wire is expressed as [Na] in mass%, the K content with respect to the total mass of the wire is expressed as [K] in mass%, and the Li content with respect to the total mass of the wire is expressed as [Li] in mass%, the wire for gas shielded arc welding according to any one of [1] to [4], wherein the value A5 calculated by the following formula (5) is 0.80 or less. A5: [Na] + [K] + [Li] ··· Formula (5)

[0016] [6] Further, F: 0.30 mass% or less, and the wire for gas shielded arc welding according to any one of [1] to [5].

[0017] Further, the above object of the present invention is achieved by the following configuration [7] related to the gas shielded arc welding method.

[0018] [7] A gas shielded arc welding method, characterized by welding using the gas shielded arc welding wire according to any one of [1] to [6].

[0019] Further, the above object of the present invention is achieved by the following configuration [8] related to the method for manufacturing a welded metal.

[0020] [8] A method for manufacturing a welded metal, characterized by manufacturing the welded metal using the gas shielded arc welding wire according to any one of [1] to [6].

Advantages of the Invention

[0021] According to the present invention, it is possible to provide a gas shielded arc welding wire that is suitably used for gas shielded arc welding of high-tensile steel and can obtain a welded metal having good tensile strength and toughness at low temperatures, a gas shielded arc welding method using the welding wire, and a method for manufacturing a welded metal using the welding wire.

Embodiments for Carrying Out the Invention

[0022] In order to obtain a weld metal with good tensile strength and toughness at low temperatures, the inventors conducted intensive studies. However, generally, toughness depends on strength, and it is difficult to achieve both high strength and toughness at low temperatures as the strength increases. Therefore, it was difficult to solve the above problems only by adjusting the content of specific elements in the wire. Thus, the inventors found that by appropriately controlling the value calculated by a specific formula using the content of elements in the wire, the desired strength of the weld metal can be maintained. Further, the inventors found that by appropriately controlling the total value of the Mn content and the Ni content in the wire, the toughness of the weld metal at low temperatures can be improved. That is, by controlling the value calculated by formula (1) described later and the total value of the Mn content and the Ni content based on the content of elements in the wire, a weld metal having both characteristics of high strength and low-temperature toughness can be obtained.

[0023] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described. Note that the present invention is not limited to the embodiment described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0024] [Wire for Gas Shielded Arc Welding] The wire for gas shielded arc welding according to the present embodiment may be a flux-cored wire or a solid wire. In this specification, these may be collectively referred to simply as a wire. The flux-cored wire is one in which a flux is filled in a steel sheath (hereinafter also simply referred to as a sheath), and its outer diameter is preferably, for example, 0.9 mm or more and 1.6 mm or less. Further, the flux filling rate can be set to any value as long as the content of each element in the wire is within the scope of the present invention. From the viewpoints of the drawability of the wire and the wire feeding property, for example, it is preferably 6% by mass or more and 20% by mass or less based on the total mass of the wire. Further, the wire is not limited in terms of the form of its joint or the shape of its cross section, such as whether it has a joint in the sheath or not.

[0025] A solid wire generally refers to a wire with a homogeneous cross-section where the wire cross-section is solid. To improve the electrical conductivity of the wire during welding, copper plating may be applied to the wire surface. In this embodiment, the outer diameter of the solid wire and the presence or absence of plating on the wire surface are not particularly limited, but the outer diameter is preferably, for example, 0.9 mm or more and 1.6 mm or less.

[0026] Hereinafter, the elements contained in the wire according to this embodiment and the reasons for limiting their contents will be described in detail. When the wire according to this embodiment is a flux-cored wire, each of the elements described below only needs to be contained in either the outer skin or the flux, and may be contained in both the steel outer skin and the flux. In this case, the content of each element in the wire is expressed as a mass percentage of the content of the element with respect to the total mass of the steel outer skin and the flux. Also, when the wire according to this embodiment is a solid wire, each of the elements described below only needs to be contained in either the bulk of the wire or the copper plating, and may be contained in both the bulk of the wire and the copper plating. In this case, the content of each element in the wire is expressed as a mass percentage of the content of the element with respect to the total mass of the bulk of the wire and the copper plating.

[0027] Furthermore, each element defined in this embodiment may be contained in the wire in the form of a metal, in the form of a compound, or in both the forms of a metal and a compound, unless otherwise noted. Therefore, regardless of the form in which each element is contained in the wire, it is defined by the conversion value converted to the elemental form. For example, when taking Si as an example, the Si content refers to the total of the Si conversion values of metallic Si and Si compounds. Note that metallic Si includes Si single body and Si alloys.

[0028] <C: 0.040 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. If the C content is less than 0.040% by mass, the desired strength of the weld metal cannot be obtained. Therefore, the C content based on the total mass of the wire is 0.040% by mass or more, preferably 0.045% by mass or more, and more preferably 0.050% by mass or more. On the other hand, if the C content exceeds 0.090% by mass, it promotes the coarsening of grain boundary carbides and reduces the toughness at low temperatures. Therefore, the C content based on the total mass of the wire is 0.090% by mass or less, preferably 0.080% by mass or less, more preferably 0.075% by mass or less, and even more preferably 0.070% by mass or less.

[0029] <Si: 0.40% by mass or more and 0.90% by mass or less> Si is an element that has the effect of ensuring the toughness of the weld metal and improving the strength. If the Si content is less than 0.40% by mass, the desired strength and toughness of the weld metal cannot be obtained. Therefore, the Si content based on the total mass of the wire is 0.40% by mass or more, preferably 0.43% by mass or more, and more preferably 0.48% by mass or more. On the other hand, if the Si content exceeds 0.90% by mass, a coarse ferrite structure is formed and the toughness of the weld metal at low temperatures cannot be stably obtained. Therefore, the Si content based on the total mass of the wire is 0.90% by mass or less, preferably 0.80% by mass or less, more preferably 0.75% by mass or less, and even more preferably 0.70% by mass or less.

[0030] <Mn: 1.35% by mass or more and 2.80% by mass or less> Mn is an element that has the effect of improving the strength and toughness at low temperatures of the weld metal. If the Mn content is less than 1.35% by mass, the desired strength of the weld metal cannot be obtained. Therefore, the Mn content based on the total mass of the wire is 1.35% by mass or more, preferably 1.50% by mass or more, more preferably 1.85% by mass or more, and even more preferably 2.00% by mass or more. On the one hand, when the Mn content exceeds 2.80% by mass, the strength of the weld metal increases excessively and the toughness at low temperatures decreases. Therefore, the Mn content with respect to the total mass of the wire should be 2.80% by mass or less. In addition, in the weld metal, in order to suppress the occurrence of intergranular fracture of the structure mainly composed of the base metal region and further improve the toughness at low temperatures, the Mn content with respect to the total mass of the wire is preferably 2.70% by mass or less, and more preferably 2.60% by mass or less.

[0031] <Ti: 0.05% by mass or more and 0.40% by mass or less> Ti is an element that forms a complex oxide mainly composed of Ti in the weld metal, and acicular ferrite is formed starting from this complex oxide, promoting the refinement of the weld metal structure. Therefore, by containing Ti in the wire, the toughness can be improved while maintaining the strength of the weld metal. If the Ti content is less than 0.05% by mass, the desired strength of the weld metal cannot be obtained. Therefore, the Ti content with respect to the total mass of the wire is 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.15% by mass or more. On the other hand, when the Ti content exceeds 0.40% by mass, the grain boundaries become brittle and the toughness decreases. Therefore, the Ti content with respect to the total mass of the wire should be 0.40% by mass or less, preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.

[0032] <Ni: 1.80% by mass or more and 3.70% by mass or less> When Ni is contained in the wire, the matrix phase is strengthened and the effect of improving the toughness of the weld metal at low temperatures can be obtained. If the Ni content is less than 1.80% by mass, the desired toughness of the weld metal at low temperatures cannot be obtained. Therefore, the Ni content with respect to the total mass of the wire is 1.80% by mass or more, preferably 2.00% by mass or more, and more preferably 2.30% by mass or more. On the one hand, when the Ni content exceeds 3.70% by mass, hot cracking is likely to occur. Therefore, the Ni content with respect to the total mass of the wire is 3.70% by mass or less, preferably 3.50% by mass or less, more preferably 3.10% by mass or less, and even more preferably 2.80% by mass or less.

[0033] <Fe: 88.0% by mass or more> Fe is the main component of the wire according to this embodiment. From the viewpoint of ensuring the welding amount of the wire, in this embodiment, the Fe content with respect to the total mass of the wire is 88.0% by mass or more, preferably 90.0% by mass or more, more preferably 92.0% by mass or more, and even more preferably 93.2% by mass or more.

[0034] <Cr: 0.60% by mass or less (including 0% by mass)> When Cr is contained in the wire, the hardenability can be increased and the effect of improving the strength of the weld metal can be obtained. In this embodiment, while adjusting the contents of other elements and controlling the value A2 calculated by the following formula (2), if the strength of the weld metal can be ensured, Cr may not be contained in the wire, or it may be 0% by mass. However, since Cr also has the effect of improving the strength of the weld metal, when Cr is contained in the wire for the purpose of improving the strength, the Cr content with respect to the total mass of the wire is preferably 0.20% by mass or more, and more preferably 0.30% by mass or more. On the other hand, when the Cr content exceeds 0.60% by mass, the strength of the weld metal rises excessively, and the desired toughness of the weld metal at low temperatures cannot be obtained. Therefore, when Cr is contained in the wire according to this embodiment, the Cr content with respect to the total mass of the wire is 0.60% by mass or less, preferably 0.55% by mass or less, and more preferably 0.50% by mass or less.

[0035] <Mo: 0.90% by mass or less (including 0% by mass)> When Mo is contained in the wire, the effect of improving the strength of the weld metal can be obtained. In the present embodiment, while adjusting the content of other elements and controlling the value A2 calculated by the formula (2) described later, if the strength of the weld metal can be ensured, Mo may not be contained in the wire, and it may be 0% by mass. However, when Mo is contained in the wire for the purpose of improving the strength of the weld metal, the Mo content with respect to the total mass of the wire is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. On the other hand, when the Mo content exceeds 0.90% by mass, the strength of the weld metal rises excessively, and the desired toughness of the weld metal at low temperature cannot be obtained. Therefore, when Mo is contained in the wire according to the present embodiment, the Mo content with respect to the total mass of the wire is 0.90% by mass or less, preferably 0.80% by mass or less, more preferably 0.40% by mass or less, and even more preferably 0.15% by mass or less.

[0036] <Cu: 0.50% by mass or less (including 0% by mass)> When Cu is contained in the wire, the strength of the weld metal can be maintained, and by strengthening the parent phase, the effect of improving the toughness at low temperature can be obtained. In the present embodiment, while adjusting the content of other elements and controlling the value A2 calculated by the formula (2) described later, if the strength of the weld metal can be ensured, Cu may not be contained in the wire, and it may be 0% by mass. However, when Cu is contained in the wire, the effect of improving the electrical conductivity during welding can be obtained. Therefore, when Cu is contained in the wire for the purpose of improving the electrical conductivity, the Cu content with respect to the total mass of the wire is preferably 0.15% by mass or more, and more preferably 0.20% by mass or more. In addition, when Cu exists in the plating layer, the electrical conductivity of the wire is further improved. Therefore, when Cu is contained in the wire according to the present embodiment, at least a part of the Cu content preferably exists in the Cu plating layer of the wire. On the one hand, when the Cu content exceeds 0.50% by mass, the risk of cracking of the weld metal due to solidification segregation increases. Therefore, when Cu is contained in the wire according to the present embodiment, the Cu content based on the total mass of the wire is 0.50% by mass or less, preferably 0.40% by mass or less, and more preferably 0.15% by mass or less.

[0037] Also, in the wire according to the present embodiment, by controlling the value calculated by a predetermined formula based on the content of the contained elements, the toughness and strength of the weld metal can be ensured. Hereinafter, the formula for ensuring the toughness and strength of the weld metal and the range of the value obtained by this formula will be described in detail. In this specification, the C content based on the total mass of the wire is [C] in % by mass, the Si content based on the total mass of the wire is [Si] in % by mass, the Mn content based on the total mass of the wire is [Mn] in % by mass, the Ti content based on the total mass of the wire is [Ti] in % by mass, the Ni content based on the total mass of the wire is [Ni] in % by mass, the Cr content based on the total mass of the wire is [Cr] in % by mass, the Mo content based on the total mass of the wire is [Mo] in % by mass, and the Cu content based on the total mass of the wire is [Cu] in % by mass. Further, although details will be described later, the wire according to the present embodiment preferably contains at least one selected from F, Na, K, and Li within a range that satisfies a predetermined formula or the content in the predetermined wire. Therefore, in this specification, the F content based on the total mass of the wire is [F] in % by mass, the Na content based on the total mass of the wire is [Na] in % by mass, the K content based on the total mass of the wire is [K] in % by mass, and the Li content based on the total mass of the wire is [Li] in % by mass.

[0038] <Value A1 calculated by formula (1): 4.05 or more> In the wire according to the present embodiment, it is also important to define the content of each of the above elements and to define the total value of the Mn content and the Ni content. That is, the inventors have found that by appropriately controlling the value A1 calculated by formula (1), which is the total value of the Mn content and the Ni content, while controlling the content of each of the above elements, the toughness of the weld metal at low temperatures can be improved.

[0039] When the value A1 calculated by formula (1) is less than 4.05, the desired toughness of the weld metal at low temperature cannot be obtained. For example, the toughness at -40°C becomes less than 62 J, which is the desired value. Therefore, the value A1 calculated by formula (1) should be 4.05 or more, preferably 4.20 or more, more preferably 4.50 or more, and even more preferably 4.70 or more. In this embodiment, the upper limit value of the value A1 calculated by formula (1) is not particularly limited. However, if the value A1 is 6.00 or less, the risk of causing cracks in the weld metal is reduced. Therefore, the value A1 calculated by formula (1) is preferably 6.00 or less, more preferably 5.50 or less, and even more preferably 5.30 or less.

[0040] A1 = [Mn] + [Ni] ··· formula (1)

[0041] <The value A2 calculated by formula (2): 0.45 or more> In the wire according to this embodiment, while defining the contents of the above elements, it is also important to control the value calculated by a formula based on the C content, Si content, Mn content, Ti content, Ni content, Cr content, Mo content, and Cu content in the wire. The inventors have found that there is a good correlation between the value A2 calculated by the following formula (2) and the strength of the weld metal based on the contents of the above elements. That is, the following formula (2) is a formula in which the relationship between the elements affecting the strength of the weld metal and the strength of the weld metal is parameterized by multiple regression analysis.

[0042] A2 = -[C] + [Si] / 7 + [Mn] / 7 + [Ti] / 4 + [Ni] / 38 + [Cr] / 8 + [Mo] / 5 + [Cu] / 15 ··· formula (2)

[0043] When the value A2 calculated by the above formula (2) is less than 0.45, the desired strength of the weld metal cannot be obtained. For example, the strength is less than 720 MPa which is the desired value. Therefore, the value A2 calculated by the above formula (2) should be 0.45 or more. Also, by setting the value A2 to 0.49 or more, the strength of the weld metal can be 780 MPa or more. Therefore, the value A2 obtained by the above formula (2) is preferably 0.49 or more, and more preferably 0.51 or more. On the other hand, in the present embodiment, although the upper limit value of the value A2 calculated by the above formula (2) is not particularly defined, considering the balance between the strength and toughness of the weld metal, it is preferably 0.70 or less.

[0044] Furthermore, for the wire according to the present embodiment, when controlling the values calculated by the following formulas (3) and (4) based on the content of each element, a weld metal with an excellent balance between strength and toughness can be obtained. A weld metal with an excellent balance between strength and toughness means that, for example, the strength is preferably 750 - 900 MPa, and the toughness is preferably 70 - 120 J.

[0045] <The value A3 calculated by formula (3): 5.0 or less> By appropriately controlling the Ti content and C content in the wire, the structure is refined in the weld metal, so that the toughness can be improved while maintaining the strength of the weld metal. When the value calculated by the following formula (3) is 5.0 or less, a weld metal can be obtained in which the toughness of the weld metal is in a more preferable range. Therefore, the value A3 calculated by formula (3) is preferably 5.0 or less, and more preferably 4.0 or less. On the other hand, in the present embodiment, although the lower limit value of the value A3 calculated by the following formula (3) is not sometimes defined, considering the Ti content and C content in the wire according to the present embodiment, it is preferably 0.556 or more.

[0046] A3 = [Ti] / [C] ··· formula (3)

[0047] <Value A4 calculated by formula (4): 28.5 or less> When the value A4 calculated by the following formula (4) is 28.5 or less, it is possible to obtain a weld metal within the above preferable range without the strength of the weld metal rising excessively. Therefore, the value A4 calculated by formula (4) is preferably 28.5 or less, and more preferably 27.0 or less. On the other hand, in the present embodiment, the lower limit value of the value A4 calculated by the following formula (4) is not particularly defined, but considering the balance between the strength and toughness of the weld metal, it is preferably 18.0 or more.

[0048] A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu] ··· Formula (4)

[0049] The present invention aims to obtain desired strength and toughness. However, toughness depends on the strength value, and depending on the target strength, the balance between strength and toughness may vary. For example, when designed for a certain strength, the toughness is good, but when the target strength is increased and redesigned, the toughness may extremely deteriorate. This is because depending on the target strength, the elements contained in the wire and the balance of the content of each element change, affecting the weld metal structure. In the present embodiment, as an index of the balance between strength and toughness, the ratio of the desired strength (720 MPa) to the desired toughness value (62 J) at -40°C of the weld metal is used. That is, when the tensile strength (TS) of the weld metal is represented as [TS] (MPa) and the impact value (IV) indicating the toughness at -40°C is represented as [IV] (J), when [TS] / [IV] is 11.6 or less, excellent toughness can be ensured with respect to the strength, and it can be determined that the balance between strength and toughness is extremely excellent.

[0050] When the value A3 calculated by the above formula (3) is 5.0 or less and the value A4 calculated by the formula (4) is 28.5 or less, [TS] / [IV] can be controlled to 11.6 or less, and while maintaining the desired strength and toughness, it is possible to obtain a weld metal with an even better balance between strength and toughness.

[0051] The wire according to this embodiment preferably further contains at least one selected from F, Na, K, and Li. Hereinafter, the preferred content of each of these elements and the reasons for the limitation will be described in detail. In this specification, when at least one selected from Na, K, and Li is contained in the wire, the Na content with respect to the total mass of the wire is [Na] in mass%, the K content with respect to the total mass of the wire is [K] in mass%, and the Li content with respect to the total mass of the wire is [Li] in mass%.

[0052] <F: 0.30 mass% or less> When F is contained in the wire, it is possible to reduce the diffusible hydrogen in the weld metal and suppress the amount of spatter generated, thereby obtaining the effect of improving arc stability. The F content in the wire may be 0 mass%, but when F is contained in the wire to improve arc stability, the F content with respect to the total mass of the wire is preferably 0.005 mass% or more, and more preferably 0.010 mass% or more. Note that depending on the elements contained in the wire, if the F content is too high, the arc may become unstable and spatter may increase. Therefore, the F content with respect to the total mass of the wire is preferably 0.30 mass% or less, and more preferably 0.15 mass% or less.

[0053] <The value A5 calculated by the formula (5): 0.80 or less> Alkali metals such as Na, K, and Li are elements that have the effect of stabilizing the arc, similar to F. Therefore, in the present embodiment, in order to improve the arc stability, it is preferable to contain at least one selected from F, Na, K, and Li in the wire. Regarding the preferable content when containing F in the wire, it is as described above. However, for Na, K, and Li, by defining the total amount thereof, the arc stability can be further improved. The content of Na, K, and Li in the wire may be 0% by mass respectively. However, when containing at least one of Na, K, and Li in the wire to improve the arc stability, the total amount thereof, that is, the value A5 calculated by the following formula (5) is preferably 0.005 or more, and more preferably 0.010 or more. Note that depending on the elements contained in the wire, if the total content of Na, K, and Li becomes too large, the arc may become unstable and sputtering may increase. Therefore, the value A5 calculated by formula (5) is preferably 0.80 or less, and more preferably 0.40 or less.

[0054] A5 = [Na] + [K] + [Li] ··· Formula (5)

[0055] In addition to the above elements, the wire according to the present embodiment may contain Al, Mg, Zr, etc. within a range that does not interfere with the effects of the present invention. The preferable ranges of the contents of these elements and the reasons for the limitations will be further described.

[0056] <Al: 0.10% by mass or less (including 0% by mass)> Al is an element that may be contained in the wire as an unavoidable impurity. However, since Al also has the effect of suppressing the deterioration of the toughness of the weld metal, in the present embodiment, Al may be intentionally contained in the wire. When it is desired to obtain the effect of Al, the Al content with respect to the total mass of the wire is preferably 0.005% by mass or more. However, since Al is a strongly deoxidizing element, if the Al content in the wire increases, it combines with oxygen in the weld metal to form coarse oxides, which may deteriorate the toughness. Therefore, when Al is contained in the wire, the Al content based on the total mass of the wire is preferably suppressed to 0.10% by mass or less.

[0057] <Mg: 0.10% by mass or less (including 0% by mass)> Mg is an element that may be contained in the wire as an unavoidable impurity. However, since Mg also has the effect of suppressing the deterioration of the toughness of the weld metal, in this embodiment, Mg may be intentionally contained in the wire. When the effect of Mg is desired, the Mg content based on the total mass of the wire is preferably 0.005% by mass or more. However, since Mg is a strongly deoxidizing element, if the Mg content in the wire increases, it combines with oxygen in the weld metal to form coarse oxides, which may deteriorate the toughness. Therefore, when Mg is contained in the wire, the Mg content based on the total mass of the wire is preferably suppressed to 0.10% by mass or less.

[0058] <Zr: 0.10% by mass or less (including 0% by mass)> Zr is an element that may be contained in the wire as an unavoidable impurity. However, since Zr also has the effect of suppressing the deterioration of the toughness of the weld metal, in this embodiment, Zr may be intentionally contained in the wire. When the effect of Zr is desired, the Zr content based on the total mass of the wire is preferably 0.005% by mass or more. However, since Zr is a strongly deoxidizing element, if the Zr content in the wire increases, it combines with oxygen in the weld metal to form coarse oxides, which may deteriorate the toughness. Therefore, when Zr is contained in the wire, the Zr content based on the total mass of the wire is preferably suppressed to 0.10% by mass or less.

[0059] <Other elements> In the wire according to this embodiment, the remainder excluding the above elements is preferably inevitable impurities. Examples of the inevitable impurities include Al, Mg, Zr, Nb, V, W, Sn, Ca, B, P, S, O, and N. The content of each of these inevitable impurities is preferably 0.0200% by mass or less, more preferably 0.0100% by mass or less, based on the total mass of the wire. Further, the total content of these inevitable impurities is preferably 0.5% by mass or less based on the total mass of the wire.

[0060] [Method for manufacturing wire for gas shielded arc welding] [Method for manufacturing flux cored wire]< When the wire according to this embodiment is a flux cored wire, the flux cored wire can be manufactured, for example, by the following method. First, the steel strip constituting the outer skin is formed into a U-shaped open tube by a forming roll while being fed in the longitudinal direction. Next, after filling the outer skin with a flux containing a metal or alloy, a compound, Fe powder, etc. so as to have a predetermined chemical composition, it is processed so that the cross section becomes circular. It is also possible to make it seamless by welding or the like at the joint of the outer skin. Then, it is drawn by cold working to have a wire diameter of, for example, 1.0 mm or more and 2.0 mm or less. Note that annealing may be performed during the cold working. If the content of each element in the wire is within the range defined in the present invention, the problems of the present invention can be solved, so the mass fraction of the flux with respect to the total mass of the wire, that is, the flux filling rate is not particularly limited. However, from the viewpoint of improving the stability of the wire components, the flux filling rate is preferably 6% by mass or more, more preferably 7% by mass or more. Further, since the wire is likely to break when the flux filling rate is high, it is preferably 20% by mass or less, more preferably 15% by mass or less.

[0061] [Method for manufacturing solid wire]< When the wire according to this embodiment is a solid wire, the solid wire can be manufactured, for example, by the method shown below. First, molten steel having a prescribed composition is melted using a converter, an electric furnace, or the like. The method of melting this molten steel is not limited to a specific technique. Next, steel materials such as billets are manufactured from the obtained molten steel by a continuous casting method, an ingot-making method, or the like. Thereafter, after heating the obtained steel material, hot rolling is performed, and further dry cold rolling and wire drawing are performed to manufacture a steel wire rod. The operating conditions of hot rolling and cold rolling are not limited to specific conditions, and may be any conditions for manufacturing a steel wire rod having a desired dimensional shape. Further, by performing annealing, pickling, wire drawing, and plating processes on the steel wire rod, a predetermined product, that is, a solid wire can be obtained.

[0062] [Type of wire] In this embodiment, when the contents of C, Si, Mn, Ti, Ni, Fe, Cr, Mo, and Cu in the wire are controlled within a prescribed range, and the value A1 calculated by formula (1) and the value A2 calculated by formula (2) are controlled within a prescribed range, the type of wire is not limited. However, generally, steel plates used for welded structures such as offshore structures and pipelines are thick plates with a thickness of about 50 to 200 mm, and multi-layer welding is the mainstream. Therefore, from the viewpoint of improving work efficiency, a welding material with extremely little welding slag and capable of reducing slag removal work is required. Therefore, it is preferable that the oxide content contained in the wire is small. Specifically, when the wire used in this embodiment is a flux-cored wire, it is preferable to use a metal-based flux-cored wire rather than a titania-based flux-cored wire. Further, from the viewpoint of increasing the welding amount and improving the welding work efficiency, it is preferable to use a metal-based flux-cored wire rather than a solid wire. When the wire used in this embodiment is a metal-based flux-cored wire, the oxygen amount relative to the total mass of the wire is preferably at the impurity level, for example, preferably 0.03 mass% or less, and more preferably 0.01 mass% or less.

[0063] Next, the gas shielded arc welding method according to this embodiment will be described.

[0064] [Gas Shielded Arc Welding Method] The gas shielded arc welding method according to this embodiment is a method of welding using the above-described wire for gas shielded arc welding. Various welding conditions other than using the wire according to this embodiment are not particularly limited, and it can be a welding method for general types of base materials. For example, it is preferable to use high-tensile steel used for operation of large equipment or in cold regions as the base material. Also, for welding voltage, welding current, welding posture, etc., general conditions in a welding method using a wire for gas shielded arc welding can be used. The welding posture is not particularly limited either. However, since the wire according to this embodiment contains strong deoxidizing elements such as Ti, deoxidation of the molten metal proceeds, an oxide film is formed on the surface of the molten metal, and the weld bead is less likely to sag. Therefore, the gas shielded arc welding method according to this embodiment can be suitably used particularly in a horizontal welding posture.

[0065] The type of shielding gas is not particularly limited either. Generally, the mechanical properties of the weld metal tend to deteriorate as the content of CO 2 or O 2 in the shielding gas increases. Thus, for example, if a weld metal satisfying desired mechanical properties can be formed in 100% CO 2 gas, it is also possible to produce a weld metal satisfying desired mechanical properties in 80% Ar - 20% CO 2 gas. On the other hand, generally, since steel plates used for welded structures such as offshore structures and pipelines are thick plates, from the viewpoint of obtaining deep penetration, it is preferable that the content of CO 2 is high. In this embodiment, by using the above-described wire, a weld metal satisfying desired mechanical properties can be produced. Considering the penetration during welding, it is preferable that the content of CO 2 in the shielding gas is high, and it is more preferable to use 100% CO 2 gas.

[0066] Next, a method for manufacturing a weld metal according to the present embodiment will be described.

[0067] [Method for manufacturing weld metal] The method for manufacturing a weld metal according to the present embodiment is a method for manufacturing a weld metal using the wire for gas shielded arc welding according to the above-described present embodiment. In the method for manufacturing a weld metal according to the present embodiment, the gas shielded arc welding method is not particularly limited, and the gas shielded arc welding method according to the above-described present embodiment can be applied.

Examples

[0068] Hereinafter, the effects of the present invention will be specifically described by giving inventive examples and comparative examples, but the present invention is not limited thereto.

[0069] [Production of wire] [Production of flux-cored wire] Using carbon steel, a tubular outer skin with a diameter of 1.2 mm was formed, and the outer skin was filled with flux to produce flux-cored wires of inventive examples and comparative examples having various compositions. Note that the mass fraction of the flux with respect to the total mass of the wire (flux filling rate) was in the range of 6% by mass or more and 10% by mass or less.

[0070] [Production of solid wire] Steel materials were produced from molten steel having various compositions, and after heating the obtained steel materials, hot rolling, cold rolling, and wire drawing were performed to produce steel wire rods. Thereafter, solid wires having various compositions were produced by performing steps such as annealing, pickling, wire drawing, and plating on the steel wire rods.

[0071] [Gas shielded arc welding] Next, gas shielded arc welding was performed using the obtained wires of the inventive examples and comparative examples. The welding conditions used during gas shielded arc welding are shown below.

[0072] · Base metal: JIS G 3106:2017 SM490A · Type and flow rate of shielding gas: 100% CO 2 , 25 liters / min · Wire diameter: 1.2 mm · Welding position: Downward · Groove shape: V-shaped · Groove angle: 20° · Groove gap: 16 mm · Welding current: 280 A ± 20 A · Arc voltage: 29 V · Welding speed: 250 - 450 mm / min · Preheat temperature: 140 - 160 °C · Interpass temperature: 140 - 160 °C

[0073] [Evaluation of Weld Metal] The mechanical properties of the weld metal obtained by the above gas shielded arc welding were evaluated. The mechanical properties of the weld metal were evaluated in accordance with the "Tensile and Impact Test Methods for Weld Deposits" specified in JIS Z 3111:2005. Tensile test specimens and impact test specimens were taken from the as-welded weld metal, and the tensile strength and Charpy absorbed energy were measured for evaluation.

[0074] [Measurement and Evaluation of Tensile Strength] For each test specimen, a tensile test was carried out at room temperature as the test temperature, and the tensile strength was measured. As the evaluation criteria for the tensile strength, when the tensile strength was 780 MPa or more, it was rated as A and evaluated as excellent. Also, when the tensile strength was 720 MPa or more and less than 780 MPa, it was rated as B and evaluated as good. Furthermore, when the tensile strength was less than 720 MPa, it was rated as C and evaluated as poor.

[0075] [Measurement of Toughness] For each test piece, an impact test was carried out at a test temperature of -40°C, and the Charpy absorption energy was measured. Three test pieces were sampled so that the notch position was at the center of the weld metal as-welded, and the Charpy absorption energy was measured for each of them, and the average was calculated. As the toughness evaluation criteria, when the Charpy absorption energy was 90 J or more, it was rated as A, indicating excellent toughness. Also, when the Charpy absorption energy was 62 J or more and less than 90 J, it was rated as B, indicating good toughness. Furthermore, when the Charpy absorption energy was less than 62 J, it was rated as C, indicating poor toughness.

[0076] In this example, those with a tensile strength evaluation of A or B and a toughness evaluation of A or B were considered qualified, and those with any evaluation of C were considered unqualified. The wire types, elements contained in each wire, and their contents in the inventive examples and comparative examples are shown in Table 1 below, and the values A1 to A5 calculated by formulas (1) to (5) and the evaluation results are shown in Table 2 below.

[0077] Note that the remainder other than the wire elements shown in Table 1 below are inevitable impurities, and neither K nor Li is contained in all the wires of the inventive examples and comparative examples. Also, in Table 1 below, "-" indicates that the corresponding element is not intentionally contained or is below the detection limit. In Table 2, "-" in formula (5) indicates that the element used in the calculation of formula (5) cannot be calculated because it is not intentionally contained or is below the detection limit.

[0078] In Table 2 below, formulas (1) to (5) are as follows. A1 = [Mn] + [Ni] ··· Formula (1) A2 = -[C] + [Si] / 7 + [Mn] / 7 + [Ti] / 4 + [Ni] / 38 + [Cr] / 8 + [Mo] / 5 + [Cu] / 15 ··· Formula (2) A3 = [Ti] / [C] ··· Formula (3) A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu] ··· Formula (4) A5: [Na] + [K] + [Li] ··· Formula (5)

[0079]

Table 1

[0080]

Table 2

[0081] As shown in Table 1 and Table 2 above, in Invention Examples No. 1 to 14, the content of each element in the wire is within the range defined in the present invention, and the values A1 and A2 calculated by Formula (1) and Formula (2) are within the range defined in the present invention. Therefore, it was possible to obtain a weld metal with good tensile strength and toughness at low temperatures. In particular, in Invention Examples No. 1 to 12 and 14, since the value A3 calculated by Formula (3) is within the preferable range in the present invention, the toughness of the weld metal became even more excellent. Also, in Invention Examples No. 1 to 13, since the value A4 calculated by Formula (4) is within the preferable range in the present invention, it was possible to suppress the tensile strength from becoming excessively high. Furthermore, in Invention Examples No. 1 to 12, since both the value A3 calculated by Formula (3) and the value A4 calculated by Formula (4) are within the preferable range in the present invention, the value of [TS] / [IV] became 11.6 or less, and it was possible to obtain a weld metal with an even more excellent balance between strength and toughness.

[0082] On the other hand, in Comparative Example No. 1 and Comparative Example No. 2, since the value A2 calculated by Formula (2) is less than the lower limit of the range defined in the present invention, the strength of the weld metal decreased. Further, in Comparative Example No. 3, since the value A1 calculated by the formula (1) is less than the lower limit of the range defined in the present invention, the Ni content in the wire is less than the lower limit of the range defined in the present invention, and thus the toughness of the weld metal is reduced.

Claims

1. With respect to the total mass of the wire, C: 0.040% by mass or more and 0.090% by mass or less, Si: 0.40% by mass or more and 0.90% by mass or less, Mn: 1.35% by mass or more and 2.80% by mass or less, Ti: 0.05% by mass or more and 0.40% by mass or less, Ni: 1.80% by mass or more and 3.70% by mass or less, and Fe: 88.0% by mass or more, and contains Cr: 0.60% by mass or less (including 0% by mass), Mo: 0.90% by mass or less (including 0% by mass), Cu: 0.50% by mass or less (including 0% by mass), and When the C content with respect to the total mass of the wire is represented as [C] in % by mass, the Si content with respect to the total mass of the wire is represented as [Si] in % by mass, the Mn content with respect to the total mass of the wire is represented as [Mn] in % by mass, the Ti content with respect to the total mass of the wire is represented as [Ti] in % by mass, the Ni content with respect to the total mass of the wire is represented as [Ni] in % by mass, the Cr content with respect to the total mass of the wire is represented as [Cr] in % by mass, the Mo content with respect to the total mass of the wire is represented as [Mo] in % by mass, and the Cu content with respect to the total mass of the wire is represented as [Cu] in % by mass, The value A1 calculated by the following formula (1): is 4.05 or more, and The value A2 calculated by the following formula (2): is 0.45 or more, A wire for gas shielded arc welding, characterized in that. A1 = [Mn] + [Ni]... Formula (1) A2 = -[C] + [Si] / 7 + [Mn] / 7 + [Ti] / 4 + [Ni] / 38 + [Cr] / 8 + [Mo] / 5 + [Cu] / 15... Formula (2)

2. The value A3 calculated by the following formula (3): is 5.0 or less, A wire for gas shielded arc welding according to claim 1, characterized in that. A3 = [Ti] / [C]... Formula (3)

3. The value A4 calculated by the following formula (4): is 28.5 or less, A wire for gas shielded arc welding according to claim 1, characterized in that. A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu]... Formula (4)

4. The value A3 calculated by the following formula (3): is 5.0 or less, and The value A4 calculated by the following formula (4): is 28.5 or less, A wire for gas shielded arc welding according to claim 1, characterized in that. A3 = [Ti] / [C]... Formula (3) A4 = 52.8×[C] + 26.3×[Si] + 0.5×[Mn] + 13.4×[Ti] + 1.1×[Ni] + 2.1×[Cr] + 0.9×[Mo] + 1.5×[Cu]... Formula (4)

5. Furthermore, it contains at least one selected from Na, K, and Li, when the Na content with respect to the total mass of the wire is expressed as [Na] in mass %, the K content with respect to the total mass of the wire is expressed as [K] in mass %, and the Li content with respect to the total mass of the wire is expressed as [Li] in mass %, the wire for gas shielded arc welding according to claim 1, characterized in that the value A5 calculated by the following formula (5) is 0.80 or less. A5: [Na] + [K] + [Li]... Formula (5)

6. Furthermore, F: 0.30 mass % or less, and characterized in that it contains the wire for gas shielded arc welding according to claim 1.

7. A gas shielded arc welding method, characterized by welding using the wire for gas shielded arc welding according to any one of claims 1 to 6.

8. A method for manufacturing a welded metal, characterized by manufacturing the welded metal using the wire for gas shielded arc welding according to any one of claims 1 to 6.

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