Flux-cored wire

Abstract

To provide a flux-cored wire which has excellent welding workability during gas-shielded arc welding and can give a welded metal having excellent toughness at low temperatures and tensile strength.SOLUTION: This flux-cored wire for gas-shielded arc welding has a sheath filled with a flux, with its chemical components adequately controlled, and θ of 10.0 or more to 30.0 or less calculated by the mathematical formula (I). (I): θ=4.1×α-3.2×γ-32.3, where α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30 and γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni], when [Si], [Cr], [Mo], [Ti], [C], [N], [Mn], [Cu], and [Ni] denote the content (mass%) of Si, Cr, Mo, Ti, C, N, Mn, Cu and Ni respectively relative to the total mass of the wire.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flux-cored wire.

Background Art

[0002] Generally, in order to improve the efficiency of transportation and storage, gas is liquefied at a low temperature and stored in a tank. Therefore, the structural members of the storage tank are required to have low-temperature toughness in the liquefaction temperature range of the stored gas. As a structural member such as a storage tank for liquefied ethylene gas, a 5% Ni steel plate having good tensile strength and low-temperature toughness is used. For the welding material of the 5% Ni steel plate, a Ni-based alloy welding material is often used, but a stainless steel welding material having a lower cost than the Ni-based alloy is also used.

[0003] Here, Patent Document 1 discloses a stainless steel flux-cored wire for a 5% Ni steel plate. This flux-cored wire aims to improve low-temperature toughness by adjusting the components of the weld metal so as to obtain a fully austenitic structure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, in a storage tank for liquefied natural gas, since toughness characteristics in a lower temperature range than that of a tank for liquefied ethylene gas are required, a 9% Ni steel plate having better low-temperature toughness and higher strength than a 5% Ni steel plate is used.

[0006] Similar to 5% Ni steel sheets, Ni-based alloy welding materials are generally used for welding 9% Ni steel sheets, but if stainless steel welding materials can be applied, costs can be reduced. However, the stainless steel flux-cored wire described in Patent Document 1 may not be suitable for 9% Ni steel plates because it may lack sufficient strength. Furthermore, to prevent hot cracking, it is desirable to have a certain amount of ferrite phase rather than a completely austenitic structure. In addition, good weldability is required for flux-cored wires during arc welding.

[0007] The present invention has been made in view of the above-described circumstances, and aims to provide a flux-cored wire that provides good weldability during gas shielded arc welding and can produce a weld metal with excellent tensile strength and low-temperature toughness. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors have found that by defining the components in flux-cored wire within a predetermined range, the ratio of austenite phase to ferrite phase in the weld metal can be controlled, and by making the solidification mode a single-phase ferrite solidification (F mode), fine Widmanstetten austenite can be precipitated, thereby improving tensile strength and low-temperature toughness. The present invention is based on these findings.

[0009] The above objective of the present invention is achieved by the following configuration [1] relating to flux-cored wire.

[0010] [1] A flux-cored wire for gas shielded arc welding, having flux filled in its outer sheath, With respect to the total mass of the wire, Fe: 40% by mass or more and 70% by mass or less, Cr: 15.0 mass% or more and 25.0 mass% or less, Ni: 5.0% by mass or more and 11.0% by mass or less, Si: 0.5% by mass or more and 3.0% by mass or less, Mn: 0.5% by mass or more and 5.0% by mass or less, Total amount of Na and K: 0.05% by mass or more and 1.0% by mass or less. TiO2: 3.0% by mass or more and 9.0% by mass or less, ZrO2: more than 1.0 mass% and 4.0 mass% or less, It contains Al2O3: 0.3% by mass or more and 2.0% by mass or less. C: Less than 0.015% by mass, Ti: 1.0% by mass or less, Mo: 2.0% by mass or less, Cu: 0.5% by mass or less, Al: 0.9% by mass or less, N: 0.040% by mass or less, F: 0.30% by mass or less, A flux-cored wire characterized in that θ, calculated by the following formula (I), is between 10.0 and 30.0. θ=4.1×α-3.2×γ-32.3 (I) However, when the Si content relative to the total mass of the wire is [Si] in mass%, the Cr content relative to the total mass of the wire is [Cr] in mass%, the Mo content relative to the total mass of the wire is [Mo] in mass%, the Ti content relative to the total mass of the wire is [Ti] in mass%, the C content relative to the total mass of the wire is [C] in mass%, the N content relative to the total mass of the wire is [N] in mass%, the Mn content relative to the total mass of the wire is [Mn] in mass%, the Cu content relative to the total mass of the wire is [Cu] in mass%, and the Ni content relative to the total mass of the wire is [Ni] in mass%, α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30 γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni] Let's assume that.

[0011] Furthermore, one embodiment relating to flux-cored wire is, With respect to the total mass of the wire, It is characterized by containing Bi: 0.001% by mass or more and 0.10% by mass or less.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a flux-cored wire that has good welding workability during gas shielded arc welding and can obtain a weld metal with excellent tensile strength and low-temperature toughness.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a graph showing the relationship between the tensile strength and θ of the inventive examples and comparative examples.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0015] [Flux-Cored Wire] The flux-cored wire according to the present embodiment (hereinafter, also simply referred to as "wire") has a flux filled in a steel outer skin. In the present embodiment, the outer diameter of the wire is not particularly limited, but for example, it is preferably 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 wire drawing property during wire manufacturing and wire feeding property, for example, it is preferably 10% by mass or more and 20% by mass or less with respect to the total mass of the wire. Furthermore, the wire is not limited in the form of its joint or the shape of its cross-section, such as whether it has a joint on the outer skin or not. The wire according to the present embodiment can be used for gas shielded arc welding using, for example, 100% by volume of CO2 gas as the shielding gas.

[0016] Hereinafter, the components contained in the flux-cored wire for gas shielded arc welding according to the present embodiment will be described in detail regarding the reasons for addition and the reasons for numerical limitation.

[0017] <Fe: 40 mass% or more and 70 mass% or less> Fe is the main component of the wire according to this embodiment. The Fe content with respect to the total mass of the wire is 40 mass% or more, preferably 45 mass% or more, and more preferably 50 mass% or more. Also, the Fe content with respect to the total mass of the wire is 70 mass% or less, preferably 67.5 mass% or less, and more preferably 65 mass% or less.

[0018] <Cr: 15.0 mass% or more and 25.0 mass% or less> Cr is an important constituent element that determines the amount of ferrite in the weld metal, and is also an important element for the oxidation resistance of the weld metal, the stability of ferrite, and the suppression of embrittlement behavior due to thermal cycles. When the Cr content with respect to the total mass of the wire is less than 15.0 mass%, it becomes insufficient to obtain a weld metal with a high ferrite structure. Therefore, the Cr content with respect to the total mass of the wire is 15.0 mass% or more, preferably 15.5 mass% or more, and more preferably 16.0 mass% or more. On the other hand, when the Cr content with respect to the total mass of the wire exceeds 25.0 mass%, the tendency to embrittle due to multiple thermal cycles during welding becomes significant. Therefore, the Cr content with respect to the total mass of the wire is 25.0 mass% or less, preferably 24.5 mass% or less, and more preferably 24.0 mass% or less.

[0019] <Ni: 5.0 mass% or more and 11.0 mass% or less> Ni, like Cr, is an important constituent element that determines the amount of ferrite in the weld metal, and is also an important element for the oxidation resistance of the weld metal, the stability of austenite, and the suppression of embrittlement behavior due to thermal cycles. When the Ni content with respect to the total mass of the wire is less than 5.0 mass%, it becomes insufficient to obtain a weld metal with a high austenite structure. Therefore, the Ni content with respect to the total mass of the wire is 5.0 mass% or more, preferably 5.5 mass% or more, and more preferably 6.0 mass% or more. On the other hand, when the Ni content exceeds 11.0% by mass with respect to the total mass of the wire, it becomes difficult to ensure the amount of ferrite considered necessary in the present invention. Therefore, the Ni content with respect to the total mass of the wire is 11.0% by mass or less, preferably 10.8% by mass or less, and more preferably 10.6% by mass or less.

[0020] <Si: 0.5% by mass or more and 3.0% by mass or less> Si is an important element as a deoxidizer for the weld metal and is a component having an effect of improving the wettability of the weld bead. When the Si content with respect to the total mass of the wire is less than 0.5% by mass, it causes insufficient deoxidation, which may cause pore defects such as blowholes or reduce the toughness of the weld metal. Therefore, the Si content with respect to the total mass of the wire is 0.5% by mass or more, preferably 0.6% by mass or more, and more preferably 0.8% by mass or more. On the other hand, although Si is a ferrite stabilizing element, if it is added excessively to the wire, the toughness decreases even with the same amount of ferrite. Therefore, the Si content with respect to the total mass of the wire is 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less. In this embodiment, the Si content represents the total Si content derived from Si alone, Si compounds, and Si alloys contained in the wire.

[0021] <Mn: 0.5% by mass or more and 5.0% by mass or less> Mn is an important element as a deoxidizer for the weld metal. When the Mn content with respect to the total mass of the wire is less than 0.5% by mass, it causes insufficient deoxidation, which may cause pore defects such as blowholes or reduce the toughness of the weld metal. Therefore, the Mn content with respect to the total mass of the wire is 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 1.5% by mass or more. |On the other hand, if the Mn content exceeds 5.0% by mass with respect to the total mass of the wire, the slag detachment property may deteriorate. Therefore, the Mn content with respect to the total mass of the wire should be 5.0% by mass or less, preferably 4.0% by mass or less, and more preferably 3.0% by mass or less.

[0022] <Total amount of Na and K: 0.05% by mass or more and 1.0% by mass or less> Na and K are components that have the effect of stabilizing the arc. By adding an appropriate amount to the wire, a good bead shape can be obtained. If the total amount of Na and K with respect to the total mass of the wire is less than 0.05% by mass, a good bead shape cannot be obtained. Therefore, the total amount of Na and K with respect to the total mass of the wire should be 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.50% by mass or more. On the other hand, if the total amount of Na and K with respect to the total mass of the wire exceeds 1.0% by mass, the low-temperature toughness deteriorates. Therefore, the total amount of Na and K with respect to the total mass of the wire should be 1.0% by mass or less, preferably 0.9% by mass or less, and more preferably 0.8% by mass or less. Note that even if both Na and K are contained in the wire, or only one of them is contained in the wire, it is sufficient as long as the total amount is 0.05% by mass or more and 1.0% by mass or less.

[0023] <TiO2: 3.0% by mass or more and 9.0% by mass or less> TiO2 is added to the wire as a slag former and is a component that has the effect of forming a slag with good enveloping property. If the TiO2 content with respect to the total mass of the wire is less than 3.0% by mass, the enveloping property of the slag deteriorates. Therefore, the TiO2 content with respect to the total mass of the wire should be 3.0% by mass or more, preferably 5.0% by mass or more, and more preferably 7.0% by mass or more. On the other hand, when the TiO₂ content with respect to the total mass of the wire exceeds 9.0% by mass, the amount of slag generated becomes excessive, and slag entrainment is likely to occur at the welded part. Therefore, the TiO₂ content with respect to the total mass of the wire should be 9.0% by mass or less, preferably 8.5% by mass or less, and more preferably 8.0% by mass or less. In this embodiment, the TiO₂ content is the TiO₂ conversion value of the Ti compound.

[0024] <ZrO₂:: More than 1.0% by mass and 4.0% by mass or less> ZrO₂ is a high melting point oxide and is a component that adjusts the viscosity and melting point of the slag. It has the effect of increasing the solidification temperature of the slag and improving the bead shape during welding. When the ZrO₂ content with respect to the total mass of the wire is 1.0% by mass or less, the bead shape deteriorates. Therefore, the ZrO₂ content with respect to the total mass of the wire should exceed 1.0% by mass, preferably 1.3% by mass or more, and more preferably 1.6% by mass or more. On the other hand, when the ZrO₂ content with respect to the total mass of the wire exceeds 4.0% by mass, the melting point of the molten slag may become excessive, and the bead appearance and bead shape may deteriorate. Therefore, the ZrO₂ content with respect to the total mass of the wire should be 4.0% by mass or less, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less. In this embodiment, the ZrO₂ content is defined as the ZrO₂ conversion value of all Zr contained in Zr metal, Zr alloy and Zr compound.

[0025] <Al₂O₃: 0.3% by mass or more and 2.0% by mass or less> Al₂O₃ is a component that has the effect of increasing the viscosity of the molten slag, improving the fluidity, and improving the bead appearance and bead shape. If the Al2O3 content relative to the total mass of the wire is less than 0.3% by mass, the bead appearance and bead shape cannot be kept good, and in particular, the workability of vertical welding deteriorates. Therefore, the Al2O3 content relative to the total mass of the wire should be 0.3% by mass or more, preferably 0.6% by mass or more, and more preferably 0.9% by mass or more. On the other hand, if the Al2O3 content relative to the total mass of the wire exceeds 2.0% by mass, the viscosity of the molten slag becomes too high and the bead shape becomes poor. Therefore, the Al2O3 content relative to the total mass of the wire should be 2.0% by mass or less, preferably 1.5% by mass or less, and more preferably 1.0% by mass or less. In this embodiment, the Al2O3 content is the value in terms of Al2O3 of the Al compound.

[0026] <C: less than 0.015% by mass> By including C in the wire, the amount of carbon in the weld metal increases and the low-temperature toughness decreases. Therefore, it is preferable to reduce the C content relative to the total mass of the wire as much as possible. When the C content relative to the total mass of the wire is 0.0l5% by mass or more, the low-temperature toughness of the weld metal decreases and the amount of spatter generated during welding increases. Therefore, the C content relative to the total mass of the wire should be less than 0.015% by mass, preferably 0.012% by mass or less, and more preferably 0.009% by mass or less.

[0027] <Ti: 1.0% by mass or less> Ti is not an essential component in the wire of this embodiment, but since it is an element having a deoxidizing action, Ti can be included in the wire as an optional component. When the Ti content relative to the total mass of the wire exceeds 1.0% by mass, due to the effect as a strong deoxidizer, the carbon in the weld metal increases and the toughness of the weld metal decreases. Therefore, the Ti content relative to the total mass of the wire should be 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less. The lower limit of the Ti content with respect to the total mass of the wire is not particularly limited and may be 0% by mass, but may also be 0.001% by mass or more. In this embodiment, the Ti content is the total amount of Ti contained in Ti alone and Ti alloys.

[0028] <Mo: 2.0% by mass or less> Mo is not an essential component in the wire of this embodiment, but Mo can be contained in the wire as an optional component for the purpose of improving the strength of the weld metal. When the Mo content with respect to the total mass of the wire exceeds 2.0% by mass, the low-temperature toughness decreases. Therefore, the Mo content with respect to the total mass of the wire is 2.0% by mass or less, preferably 1.8% by mass or less, and more preferably 1.6% by mass or less. The lower limit of the Mo content with respect to the total mass of the wire is not particularly limited and may be 0% by mass, but may also be 0.001% by mass or more.

[0029] <Cu: 0.5% by mass or less> Cu is not an essential component in the wire of this embodiment, but Cu can be contained in the wire as an optional component for the purpose of stabilizing the austenite structure. When the Cu content with respect to the total mass of the wire exceeds 0.5% by mass, the low-temperature toughness decreases. Therefore, the Cu content with respect to the total mass of the wire is 0.5% by mass or less, preferably 0.3% by mass or less, and more preferably 0.1% by mass or less. The lower limit of the Cu content with respect to the total mass of the wire is not particularly limited and may be 0% by mass, but may also be 0.001% by mass or more.

[0030] <Al: 0.9% by mass or less> Al is not an essential component in the wire of this embodiment, but since Al is an element having a deoxidizing action, Al can be contained in the wire as an optional component. When the Al content with respect to the total mass of the wire exceeds 0.9% by mass, the solidification structure of ferrite changes from columnar crystals to equiaxed crystals, and the shape of the subsequently formed austenite changes from Widmanstätten to granular, resulting in a decrease in toughness and deterioration of slag detachability. Therefore, the Al content with respect to the total mass of the wire should be 0.9% by mass or less, preferably 0.6% by mass or less, and more preferably 0.2% by mass or less. The lower limit of the Al content with respect to the total mass of the wire is not particularly limited and may be 0% by mass, or may be 0.001% by mass or more. In this embodiment, the Al content is the total amount of Al contained in elemental Al and Al alloys.

[0031] <N: 0.040% by mass or less> N is not an essential component in the wire of this embodiment, but since it is an element having the effect of improving the strength of the weld metal, reducing the surface tension, and improving the bead conformity, N can be contained in the wire as an optional component. When the N content with respect to the total mass of the wire exceeds 0.040% by mass, the surface tension of the molten metal becomes too low, spatter increases, the bead shape deteriorates, and slag detachability also deteriorates. Therefore, the N content with respect to the total mass of the wire should be 0.040% by mass or less, preferably 0.030% by mass or less, and more preferably 0.020% by mass or less. The lower limit of the N content with respect to the total mass of the wire is not particularly limited and may be 0% by mass, or may be 0.001% by mass or more.

[0032] <F: 0.30% by mass or less> F is not an essential component in the wire of this embodiment, but since it is an element having the effect of increasing the viscosity of the molten slag, improving the fluidity, and improving the bead appearance and bead shape, F can be contained in the wire as an optional component. If the F content relative to the total mass of the wire exceeds 0.30% by mass, there is a risk of increased porosity defects. Therefore, the F content relative to the total mass of the wire should be 0.30% by mass or less, preferably 0.25% by mass or less, and more preferably 0.20% by mass or less. Furthermore, there is no particular limit to the lower limit of the F content relative to the total mass of the wire; it may be 0% by mass, but it may also be 0.001% by mass or more.

[0033] <θ calculated by formula (I): between 10.0 and 30.0> In this embodiment, by appropriately controlling the content of each of the above elements and controlling θ, which is calculated by the following formula (I) based on the amount of each alloying element contained in the wire, the weld metal can be maintained at a predetermined ferrite content, and the desired strength and toughness can be obtained. If θ calculated by formula (I) is less than 10.0, the amount of ferrite will be insufficient, resulting in inadequate strength of the weld metal. Therefore, θ should be 10.0 or greater, preferably 12.0 or greater, and more preferably 24.0 or greater. On the other hand, if θ calculated by formula (I) exceeds 30.0, the amount of ferrite becomes excessive, reducing the low-temperature toughness and making it impossible to obtain the desired Charpy impact value. Therefore, θ should be 30.0 or less, and preferably 29.0 or less.

[0034] θ=4.1×α-3.2×γ-32.3 (I) However, when the Si content relative to the total mass of the wire is [Si] in mass%, the Cr content relative to the total mass of the wire is [Cr] in mass%, the Mo content relative to the total mass of the wire is [Mo] in mass%, the Ti content relative to the total mass of the wire is [Ti] in mass%, the C content relative to the total mass of the wire is [C] in mass%, the N content relative to the total mass of the wire is [N] in mass%, the Mn content relative to the total mass of the wire is [Mn] in mass%, the Cu content relative to the total mass of the wire is [Cu] in mass%, and the Ni content relative to the total mass of the wire is [Ni] in mass%, α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30 γ = 24×[C] + 28×[N] + 0.25×[Mn] + 0.5×[Cu] + 1.10×[Ni] Let it be so.

[0035] <Bi: 0.001 mass% or more and 0.10 mass% or less> The wire according to this embodiment may further contain Bi. Bi is a component having the effect of improving slag detachability. However, if it is contained excessively in the wire, Bi segregates in the final solidification region of the weld metal, and the high-temperature crack resistance of the weld metal deteriorates. When Bi is contained in the wire, if the Bi content with respect to the total mass of the wire is 0.001 mass% or more, the effect of improving slag detachability can be obtained. Therefore, the Bi content with respect to the total mass of the wire is preferably 0.001 mass% or more, and more preferably 0.01 mass% or more. On the other hand, if the Bi content with respect to the total mass of the wire is 0.10 mass% or less, deterioration of the high-temperature crack resistance of the weld metal can be suppressed. Therefore, the Bi content with respect to the total mass of the wire is preferably 0.10 mass% or less, and more preferably 0.08 mass% or less. In this embodiment, the Bi content means the total amount of Bi contained in Bi alone, Bi alloy, and Bi compound.

[0036] <Balance> The wire according to this embodiment contains inevitable impurities in the range of 2.0% or less as the balance of components other than the above. Further, Co, V, W, etc. may be contained in the balance of the wire in the range of 1.0% or less, respectively.

[0037] The wire according to this embodiment preferably contains Fe, Cr, Ni, Si, Mn, Na and K, TiO2, ZrO2, Al2O3, C, Ti, Mo, Cu, Al, N, F in total by 90 mass% or more, more preferably 93 mass% or more, still more preferably 95 mass% or more, and particularly preferably 98 mass% or more.

Example

[0038] The effects of the present invention will be specifically described below with reference to examples and comparative examples of the present embodiment, but the present invention is not limited thereto.

[0039] We prepared flux-cored wire for gas shielded arc welding with a diameter of 1.20 mm by adjusting the chemical composition of the wire to various concentrations.

[0040] <Evaluation of Mechanical Properties> Gas-shielded arc welding was performed using the prepared flux-cored wire under the welding conditions for evaluating the mechanical properties shown in Table 1 below. In this example, a test plate with symbol 1.3 as specified in JIS Z3111 was used. Two layers of buttering were applied to the groove surface using the wire to be used, and then gas-shielded arc welding was performed to produce a weld metal test specimen. The mechanical properties of the weld metal were evaluated in accordance with the "Tensile and Impact Test Methods for Weld Metal" specified in JIS Z 3111:2005. A0 tensile test specimens were taken from the weld metal test specimens and their tensile strength was evaluated by tensile testing. Additionally, V-notch test specimens were taken and their low-temperature toughness was evaluated by Charpy impact testing at -196°C. The evaluation criteria for mechanical properties were as follows: a tensile strength of 640 MPa or higher and a Charpy impact value of 25 J or higher at -196°C were rated as ○ (good), and among these, those with a tensile strength of 670 MPa or higher were rated as ◎ (excellent). Conversely, those with a tensile strength of less than 640 MPa or a Charpy impact value of less than 25 J at -196°C were rated as × (poor).

[0041] [Evaluation of welding workability] Furthermore, to evaluate the weldability, gas shielded arc welding was performed using the flux-cored wire described above, under the welding conditions for evaluating weldability shown in Table 1 below. In this embodiment, two welding positions were used: horizontal fillet welding and vertical upward fillet welding.

[0042] <Evaluation of bead shape> The bead shape was evaluated in accordance with AWS A5.22 15.2.2. The evaluation criteria for the bead shape were as follows: those that met the criteria of the AWS standard were marked with ○ (good), and those that did not meet the criteria and had a convex bead were marked with × (bad).

[0043] <Evaluation of slag detachability> The slag detachability was evaluated by applying a light impact with a hammer to the welded joint and checking for slag detachment. The evaluation criteria for slag detachability were as follows: ○ (good) indicated that the slag detached naturally or with minor impact, while × (poor) indicated that the slag was stuck to the bead surface and did not detach.

[0044] The component composition of the fabricated wire and the calculated values ​​based on specific components are shown in Tables 2 and 3 below, and the evaluation results are shown in Table 4 below. In Table 2, "Na+K" represents the total amount of Na and K content in the wire. Also, in the "Calculated value based on specific components" column in Table 3, α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30 γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni] Let θ be the value calculated by the following formula (I). θ=4.1×α-3.2×γ-32.3 (I) However, in the above formula, [Si] is the value of the Si content relative to the total mass of the wire expressed in mass%, [Cr] is the value of the Cr content relative to the total mass of the wire expressed in mass%, [Mo] is the value of the Mo content relative to the total mass of the wire expressed in mass%, [Ti] is the value of the Ti content relative to the total mass of the wire expressed in mass%, [C] is the value of the C content relative to the total mass of the wire expressed in mass%, [N] is the value of the N content relative to the total mass of the wire expressed in mass%, [Mn] is the value of the Mn content relative to the total mass of the wire expressed in mass%, [Cu] is the value of the Cu content relative to the total mass of the wire expressed in mass%, and [Ni] is the value of the Ni content relative to the total mass of the wire expressed in mass%.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] [Table 4]

[0049] As shown in Tables 2-4 above, the wires No. 1-11, which are examples of the invention, exhibit excellent mechanical properties and weldability because the wire composition and the θ obtained by formula (1) are within the range of the present invention.

[0050] On the other hand, in the comparative example wire No. 12, although the content of each component was within the range of the present invention, the low-temperature toughness decreased because θ calculated by formula (I) exceeded the upper limit of the range of the present invention.

[0051] In the comparative example, wire No. 13 showed a significant decrease in low-temperature toughness because the content of Cr, Ni, and C in the wire exceeded the upper limit of the present invention, as did θ.

[0052] In comparative examples, wires No. 14 to 16 had an Al2O3 content below the lower limit of the present invention range, resulting in poor bead shape and slag detachability in vertical upward fillet welding, as well as poor slag detachability in horizontal fillet welding. Furthermore, wire No. 16 also exhibited reduced low-temperature toughness.

[0053] In comparative examples, wires No. 17 to 20 had an Al content exceeding the upper limit of the present invention, resulting in poor bead shape and slag detachability in vertical upward fillet welding, as well as poor slag detachability in horizontal fillet welding. Furthermore, these wires also exhibited reduced low-temperature toughness.

[0054] In the comparative example, wire No. 21 exhibited reduced low-temperature toughness because its Mo content exceeded the upper limit of the present invention.

[0055] Figure 1 is a graph showing the relationship between the tensile strength (MPa) of the wires in the inventive example and comparative example and θ, with the vertical axis representing tensile strength (MPa) and the horizontal axis representing θ. The dashed lines shown in Figure 1 are approximate lines obtained by linearly approximating each point. As shown in Figure 1, it was demonstrated that the tensile strength decreases as the value of θ calculated by equation (I) decreases.

[0056] As described in detail above, the flux-cored wire for gas shielded arc welding according to this embodiment yields a weld metal with good bead shape and slag detachability, and an excellent balance between tensile strength and low-temperature toughness.

Claims

1. A flux-cored wire for gas shielded arc welding, in which flux is filled in the outer sheath, With respect to the total mass of the wire, Fe: 40% by mass or more and 70% by mass or less, Cr: 15.0% by mass or more and 25.0% by mass or less, Ni: 5.0% by mass or more and 11.0% by mass or less, Si: 0.5% by mass or more and 3.0% by mass or less, Mn: 0.5% by mass or more and 5.0% by mass or less, Total amount of Na and K: 0.05% by mass or more and 1.0% by mass or less. TiO ２ 3.0% or more by mass, 9.0% or less by mass ZrO ２ : 1.0% mass percentage exceeding 4.0% mass percentage Al ２ O ３ It contains 0.6% by mass or more and 2.0% by mass or less, C: Less than 0.015% by mass, Ti: 1.0% by mass or less, Mo: 2.0% by mass or less, Cu: 0.5% by mass or less, Al: 0.2% by mass or less, N: 0.040% by mass or less, F: 0.30% by mass or less, The total amount of Fe, Cr, Ni, Si, Mn, Na and K, and TiO ２ , the ZrO ２ , the Al ２ O ３ The C, Ti, Mo, Cu, Al, N, and F are included in total in an amount of 98% by mass or more. The remainder of the components other than those mentioned above contains unavoidable impurities in a range of 2.0% by mass or less. The following formula (I) is characterized in that θ is between 10.0 and 29.0, A flux-cored wire capable of producing weld metal with a tensile strength of 640 MPa or higher and a Charpy impact value of 25 J or higher at -196°C. θ=4.1×α-3.2×γ-32.3...(I) However, when the Si content relative to the total mass of the wire is [Si] in mass%, the Cr content relative to the total mass of the wire is [Cr] in mass%, the Mo content relative to the total mass of the wire is [Mo] in mass%, the Ti content relative to the total mass of the wire is [Ti] in mass%, the C content relative to the total mass of the wire is [C] in mass%, the N content relative to the total mass of the wire is [N] in mass%, the Mn content relative to the total mass of the wire is [Mn] in mass%, the Cu content relative to the total mass of the wire is [Cu] in mass%, and the Ni content relative to the total mass of the wire is [Ni] in mass%, α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30 γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni] Let's assume that.

2. moreover, With respect to the total mass of the wire, The flux-cored wire according to claim 1, characterized in that it contains Bi: 0.001% by mass or more and 0.10% by mass or less.

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