Flux-cored wire

Abstract

Provided is a flux-cored wire that is excellent in weldability during gas shielded arc welding and that can produce a weld metal that is excellent in tensile strength and low-temperature toughness. A flux-cored wire for gas shielded arc welding, which is filled with flux in a sheath, has each chemical component appropriately controlled and has θ, which is calculated from the following formula (I), of 10.0 or greater but 30.0 or less. θ = 4.1 x α - 3.2 x γ - 32.3... (I) where, in terms of mass %, assuming that the contents of Si, Cr, Mo, Ti, C, N, Mn, Cu, and Ni relative to the total mass of the wire are [Si], [Cr], [Mo], [Ti], [C], [N], [Mn], [Cu], and [Ni], respectively, α = 0.02 x [Si] + [Cr] + 1.20 x [Mo] + 0.3 x [Ti] + 0.30, and γ = 24 x [C] + 28 x [N] + 0.25 x [Mn] + 0.5 x [Cu] + 1.10 x [Ni].

Description

Technical Field

[0001] This invention relates to flux-cored welding wire. Background Technology

[0002] Generally, in order to improve the efficiency of gas transportation and storage, it is liquefied at low temperature and stored in storage tanks. Therefore, the structural components of the storage tanks are required to have low-temperature toughness within the liquefaction temperature range of the stored gas.

[0003] For structural components such as storage tanks used for liquefied ethylene gas, 5% Ni steel plates with good tensile strength and low-temperature toughness are used. For welding 5% Ni steel plates, Ni-based alloy welding materials are commonly used, but stainless steel welding materials, which are less expensive than Ni-based alloys, can also be used.

[0004] Here, Patent Document 1 discloses a stainless steel flux-cored welding wire for 5% Ni steel plates. This flux-cored welding wire aims to improve low-temperature toughness by adjusting the composition of the weld metal in a way that results in a fully austenitic structure.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6719217 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] On the other hand, in liquefied natural gas storage tanks, because toughness characteristics are required at a lower temperature range than those required for liquefied ethylene gas storage tanks, 9% Ni steel plates, which have better low-temperature toughness and higher strength than 5% Ni steel plates, are used.

[0010] Similar to 5% Ni steel plates, Ni-based alloy welding materials are generally used for 9% Ni steel plates. However, if stainless steel welding materials are used, the cost can be reduced.

[0011] However, the stainless steel flux-cored welding wire described in Patent Document 1 cannot be used for 9% Ni steel plates due to insufficient strength. Furthermore, to prevent hot cracking, it is desirable for the flux-cored welding wire to contain a certain degree of ferrite phase, rather than a completely austenitic structure. In addition, good weldability is also required during arc welding in flux-cored welding wires.

[0012] In view of the above circumstances, the present invention aims to provide a flux-cored welding wire that has good welding operability in gas shielded arc welding and can produce weld metal with excellent tensile strength and low-temperature toughness.

[0013] Problem-solving methods

[0014] The inventors, through dedicated research aimed at solving the aforementioned problems, discovered that by specifying the composition of the flux-cored welding wire within a defined range and controlling the ratio of austenite to ferrite phases in the weld metal, the solidification morphology becomes ferrite single-phase solidification (F-mode). This allows for the precipitation of fine Widmanstaette austenite, thereby improving tensile strength and low-temperature toughness. This invention is based on these findings.

[0015] The above-mentioned objective of the present invention is achieved by the following [1] configuration of the flux-cored wire.

[0016] [1] A flux-cored welding wire, characterized in that it is a flux-cored welding wire for gas-shielded arc welding with flux filled in its outer sheath, wherein, relative to the total mass of the welding wire, it comprises:

[0017] Fe: 40% by mass or more and 70% by mass or less

[0018] Cr: ≥15.0% by mass and ≤25.0% by mass

[0019] Ni: 5.0% by mass or more and 11.0% by mass or less

[0020] Si: ≥0.5% by mass and ≤3.0% by mass

[0021] Mn: ≥0.5% by mass and ≤5.0% by mass

[0022] Total Na and K content: ≥0.05% by mass and ≤1.0% by mass

[0023] TiO2: ≥3.0% by mass and ≤9.0% by mass

[0024] ZrO2: greater than 1.0% by mass and less than 4.0% by mass

[0025] Al2O3: ≥0.3% by mass and ≤2.0% by mass,

[0026] and satisfy

[0027] C: less than 0.015% by mass

[0028] Ti: less than 1.0% by mass

[0029] Mo: less than 2.0% by mass

[0030] Cu: less than 0.5% by mass

[0031] Al: less than 0.9% by mass

[0032] N: less than 0.040% by mass

[0033] F: less than 0.30% by mass, and,

[0034] The θ calculated by the following formula (I) is greater than or equal to 10.0 and less than or equal to 30.0.

[0035] θ=4.1×α-3.2×γ-32.3…(I)

[0036] Wherein, the Si content relative to the total mass of the welding wire is defined as [Si] (mass %), the Cr content relative to the total mass of the welding wire is defined as [Cr] (mass %), the Mo content relative to the total mass of the welding wire is defined as [Mo] (mass %), the Ti content relative to the total mass of the welding wire is defined as [Ti] (mass %), the C content relative to the total mass of the welding wire is defined as [C] (mass %), the N content relative to the total mass of the welding wire is defined as [N] (mass %), the Mn content relative to the total mass of the welding wire is defined as [Mn] (mass %), the Cu content relative to the total mass of the welding wire is defined as [Cu] (mass %), and the Ni content relative to the total mass of the welding wire is defined as [Ni] (mass %).

[0037] α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30

[0038] γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni].

[0039] In another embodiment of the flux-cored welding wire, it is characterized in that, relative to the total mass of the welding wire, it contains Bi: 0.001% by mass or more and 0.10% by mass or less.

[0040] Invention Effects

[0041] According to the present invention, a flux-cored welding wire is provided that exhibits good weldability during gas-shielded arc welding and can produce weld metal with excellent tensile strength and low-temperature toughness. Attached Figure Description

[0042] Figure 1 This is a graph showing the relationship between the tensile strength and θ of the inventive example and the comparative example. Detailed Implementation

[0043] The embodiments of the present invention will now be described in detail. However, the present invention is not limited to the embodiments described below, and can be implemented in any way without departing from the spirit of the invention.

[0044] Flux-cored welding wire

[0045] The flux-cored welding wire (hereinafter referred to as "welding wire") of this embodiment has flux filled in a steel outer sheath.

[0046] In this embodiment, the outer diameter of the welding wire is not particularly limited; for example, it is preferably 0.9 mm or more and 1.6 mm or less. Furthermore, the flux filling rate can be set to any value if the content of each element in the welding wire is within the range of this invention, but from the viewpoint of wire drawability and feedability during welding wire manufacturing, it is preferably 10% by mass or more and 20% by mass or less relative to the total mass of the welding wire. Moreover, the shape of the weld seam and the cross-sectional shape are not limited regardless of whether the welding wire has a seam or not. The welding wire of this embodiment, for example, can be used for gas-shielded arc welding with 100% CO2 gas as the shielding gas.

[0047] The following section details the reasons for adding and limiting the values ​​of the components contained in the flux-cored welding wire for gas-shielded arc welding according to this embodiment.

[0048] <Fe: 40% by mass or more and 70% by mass or less>

[0049] Fe is the main component of the welding wire in this embodiment. The Fe content relative to the total mass of the welding wire is 40% by mass or more, preferably 45% by mass or more, and more preferably 50% by mass or more. In addition, the Fe content relative to the total mass of the welding wire is 70% by mass or less, preferably 67.5% by mass or less, and more preferably 65% ​​by mass or less.

[0050] <Cr: ≥15.0% by mass and ≤25.0% by mass>

[0051] Cr is an important component that determines the amount of ferrite in weld metals, and it is also an important element for the oxidation resistance and stability of ferrite in weld metals, as well as for inhibiting embrittlement caused by thermal cycling.

[0052] If the Cr content relative to the total mass of the welding wire is less than 15.0% by mass, it becomes insufficient for obtaining a high-ferritic weld metal. Therefore, the Cr content relative to the total mass of the welding wire is 15.0% by mass or more, preferably 15.5% by mass or more, and more preferably 16.0% by mass or more.

[0053] On the other hand, if the Cr content relative to the total mass of the welding wire is higher than 25.0% by mass, the tendency for embrittlement caused by multiple thermal cycles during welding becomes significant. Therefore, the Cr content relative to the total mass of the welding wire is 25.0% by mass or less, preferably 24.5% by mass or less, and more preferably 24.0% by mass or less.

[0054] <Ni: 5.0% by mass or more and 11.0% by mass or less>

[0055] Like Cr, Ni is an important component that determines the amount of ferrite in weld metals. Furthermore, it is an important element for the oxidation resistance and austenite stability of weld metals, as well as for inhibiting embrittlement caused by thermal cycling.

[0056] If the Ni content relative to the total mass of the welding wire is less than 5.0% by mass, it becomes insufficient for obtaining a weld metal with a high austenitic structure. Therefore, the Ni content relative to the total mass of the welding wire is 5.0% by mass or more, preferably 5.5% by mass or more, and more preferably 6.0% by mass or more.

[0057] On the other hand, if the Ni content relative to the total mass of the welding wire is higher than 11.0% by mass, it is difficult to ensure the amount of ferrite considered necessary in this invention. Therefore, the Ni content relative to the total mass of the welding wire is 11.0% by mass or less, preferably 10.8% by mass or less, and more preferably 10.6% by mass or less.

[0058] <Si: 0.5% by mass or more and 3.0% by mass or less>

[0059] Si is an important element as a deoxidizer in weld metal and is a component that promotes weld fusion.

[0060] If the Si content relative to the total mass of the welding wire is less than 0.5% by mass, it will cause insufficient deoxidation, leading to porosity defects such as bubbles, or reducing the toughness of the weld metal. Therefore, the Si content relative to the total mass of the welding wire is 0.5% by mass or more, preferably 0.6% by mass or more, and more preferably 0.8% by mass or more.

[0061] On the other hand, Si is a ferrite stabilizing element, but if too much is added to the welding wire, the toughness will decrease even with the same amount of ferrite. Therefore, the Si content relative to the total mass of the welding wire is 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less.

[0062] Furthermore, in this embodiment, the term "Si content" refers to the total Si content of the welding wire, including Si monomers, Si compounds, and Si alloys.

[0063] <Mn: ≥0.5% by mass and ≤5.0% by mass>

[0064] Mn is an important element as a deoxidizer for welding metals.

[0065] If the Mn content relative to the total mass of the welding wire is less than 0.5% by mass, it will cause insufficient deoxidation, leading to porosity defects such as bubbles, or reducing the toughness of the weld metal. Therefore, the Mn content relative to the total mass of the welding wire is 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 1.5% by mass or more.

[0066] On the other hand, if the Mn content relative to the total mass of the welding wire is higher than 5.0% by mass, the slag peelability may decrease. Therefore, the Mn content relative to the total mass of the welding wire is 5.0% by mass or less, preferably 4.0% by mass or less, and more preferably 3.0% by mass or less.

[0067] <Total Na and K: ≥0.05% by mass and ≤1.0% by mass>

[0068] Na and K are components that stabilize the electric arc. By adding them to the welding wire in appropriate amounts, a good weld bead shape can be obtained.

[0069] If the total amount of Na and K relative to the total mass of the welding wire is less than 0.05% by mass, a good weld bead shape cannot be obtained. Therefore, the total amount of Na and K relative to the total mass of the welding wire is 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.50% by mass or more.

[0070] On the other hand, if the total amount of Na and K relative to the total mass of the welding wire is higher than 1.0% by mass, the low-temperature toughness decreases. Therefore, the total amount of Na and K relative to the total mass of the welding wire is 1.0% by mass or less, preferably 0.9% by mass or less, and more preferably 0.8% by mass or less.

[0071] Furthermore, the welding wire may contain both Na and K, or it may contain only either one, as long as the total amount is more than 0.05% by mass and less than 1.0% by mass.

[0072] <TiO2: 3.0% by mass and 9.0% by mass>

[0073] TiO2, when added to welding wire as a slag-forming agent, is a component that has the effect of forming slag with good coating properties.

[0074] If the TiO2 content relative to the total mass of the welding wire is less than 3.0% by mass, the coating properties of the slag deteriorate. Therefore, the TiO2 content relative to the total mass of the welding wire is 3.0% by mass or more, preferably 5.0% by mass or more, and more preferably 7.0% by mass or more.

[0075] On the other hand, if the TiO2 content relative to the total mass of the welding wire is higher than 9.0% by mass, the amount of slag generated is excessive, and slag inclusions are likely to occur in the weld. Therefore, the TiO2 content relative to the total mass of the welding wire is 9.0% by mass or less, preferably 8.5% by mass or less, and more preferably 8.0% by mass or less.

[0076] Furthermore, in this embodiment, the TiO2 content is the TiO2 conversion value of the Ti compound.

[0077] <ZrO2: greater than 1.0% by mass and less than 4.0% by mass>

[0078] ZrO2 is a high-melting-point oxide that is used to adjust the viscosity and melting point of slag. It can increase the solidification temperature of slag and improve the weld bead shape during welding.

[0079] If the ZrO2 content relative to the total mass of the welding wire is less than 1.0% by mass, the weld bead shape becomes unsatisfactory. Therefore, the ZrO2 content relative to the total mass of the welding wire is higher than 1.0% by mass, preferably 1.3% by mass or more, and more preferably 1.6% by mass or more.

[0080] On the other hand, if the ZrO2 content relative to the total mass of the welding wire is higher than 4.0% by mass, the melting point of the molten slag becomes too high, and the appearance and shape of the weld bead may deteriorate. Therefore, the ZrO2 content relative to the total mass of the welding wire is 4.0% by mass or less, preferably 3.0% by mass or less, and more preferably 2.0% by mass or less.

[0081] Furthermore, in this embodiment, the ZrO2 content is defined as the Zr content of all Zr contained in Zr monomers, Zr alloys, and Zr compounds as a ZrO2 conversion value.

[0082] <Al2O3: ≥0.3% by mass and ≤2.0% by mass>

[0083] Al2O3 is a component that increases the viscosity of molten slag, improves its fluidity, and has the effect of giving the weld bead a good appearance and shape.

[0084] If the Al2O3 content relative to the total mass of the welding wire is less than 0.3% by mass, the weld appearance and shape cannot be well maintained, especially the operability of vertical welding deteriorates. Therefore, the Al2O3 content relative to the total mass of the welding wire is 0.3% by mass or more, preferably 0.6% by mass or more, and more preferably 0.9% by mass or more.

[0085] On the other hand, if the Al2O3 content relative to the total mass of the welding wire is higher than 2.0% by mass, the viscosity of the molten slag becomes too high, and the weld bead shape will be poor. Therefore, the Al2O3 content relative to the total mass of the welding wire is 2.0% by mass or less, preferably 1.5% by mass or less, and more preferably 1.0% by mass or less.

[0086] Furthermore, in this embodiment, the Al2O3 content is the Al2O3 conversion value of the Al compound.

[0087] <C: less than 0.015% by mass>

[0088] By including carbon in the welding wire, the carbon content in the welding metal increases, and the low-temperature toughness decreases. Therefore, it is preferable to minimize the carbon content relative to the total mass of the welding wire.

[0089] If the carbon content relative to the total mass of the welding wire is 0.015% by mass or more, the low-temperature toughness of the weld metal decreases, and the amount of spatter during welding increases. Therefore, the carbon content relative to the total mass of the welding wire is less than 0.015% by mass, preferably less than 0.012% by mass, and more preferably less than 0.009% by mass.

[0090] <Ti: less than 1.0% by mass>

[0091] Ti is not an essential component in the welding wire of this embodiment; however, it is an element with deoxidizing properties, and therefore can be included in the welding wire as an arbitrary component.

[0092] If the Ti content relative to the total mass of the welding wire is higher than 1.0% by mass, the carbon content in the welding metal increases due to its effect as a strong deoxidizer, and the toughness of the welding metal decreases. Therefore, the Ti content relative to the total mass of the welding wire is 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.6% by mass or less.

[0093] Furthermore, the lower limit of Ti content relative to the total mass of the welding wire is not specifically limited; it can be 0% by mass, or it can be 0.001% by mass or more.

[0094] In addition, in this embodiment, the Ti content is the total amount of Ti contained in the Ti monomer and the Ti alloy.

[0095] <Mo: less than 2.0% by mass>

[0096] Mo is not a necessary component in the welding wire of this embodiment, but it can be included in the welding wire as an arbitrary component for the purpose of improving the strength of the weld metal.

[0097] If the Mo content relative to the total mass of the welding wire is higher than 2.0% by mass, the low-temperature toughness decreases. Therefore, the Mo content relative to the total mass of the welding wire is 2.0% by mass or less, preferably 1.8% by mass or less, and more preferably 1.6% by mass or less.

[0098] Furthermore, there is no particular limit to the lower limit of the Mo content relative to the total mass of the welding wire; it can be 0% by mass, or it can be 0.001% by mass or more.

[0099] <Cu: less than 0.5% by mass>

[0100] Cu is not a necessary component in the welding wire of this embodiment, but for the purpose of stabilizing the austenitic structure, Cu can be included in the welding wire as an arbitrary component.

[0101] If the Cu content relative to the total mass of the welding wire is higher than 0.5% by mass, the low-temperature toughness decreases. Therefore, the Cu content relative to the total mass of the welding wire is 0.5% by mass or less, preferably 0.3% by mass or less, and more preferably 0.1% by mass or less.

[0102] Furthermore, there is no specific limit to the lower limit of Cu content relative to the total mass of the welding wire; it can be 0% by mass, or it can be 0.001% by mass or more.

[0103] <Al: less than 0.9% by mass>

[0104] Al is not a necessary component in the welding wire of this embodiment, but because it is an element with deoxidizing properties, it can be included in the welding wire as an arbitrary component.

[0105] If the Al content relative to the total mass of the welding wire is higher than 0.9% by mass, the solidification structure of ferrite changes from columnar to equiaxed, and the shape of the subsequently formed austenite changes from Widmanstätten to granular, thus reducing toughness and worsening slag exfoliation properties. Therefore, the Al content relative to the total mass of the welding wire is 0.9% by mass or less, preferably 0.6% by mass or less, and more preferably 0.2% by mass or less.

[0106] Furthermore, there is no specific limit to the lower limit of the Al content relative to the total mass of the welding wire; it can be 0% by mass, or it can be 0.001% by mass or more.

[0107] Furthermore, in this embodiment, the Al content is the total amount of Al contained in the Al monomer and the Al alloy.

[0108] <N: less than 0.040% by mass>

[0109] Nitrogen (N) is not an essential component in the welding wire of this embodiment, but it is an element that increases the strength of the weld metal and reduces the surface tension, thus having the effect of good weld fusion. Therefore, it can be included in the welding wire as an arbitrary component.

[0110] If the N content relative to the total mass of the welding wire is higher than 0.040% by mass, the surface tension of the molten metal becomes too low, spatter increases, and the weld bead shape and slag peelability deteriorate. Therefore, the N content relative to the total mass of the welding wire is 0.040% by mass or less, preferably 0.030% by mass or less, and more preferably 0.020% by mass or less.

[0111] Furthermore, there is no specific limit to the lower limit of the N content relative to the total mass of the welding wire; it can be 0% by mass, or it can be 0.001% by mass or more.

[0112] <F: less than 0.30% by mass>

[0113] F is not an essential component in the welding wire of this embodiment, but it is an element that has the effect of increasing the viscosity of the molten slag, improving fluidity, and making the weld bead appearance and shape good. Therefore, F can be included in the welding wire as an arbitrary component.

[0114] If the F content relative to the total mass of the welding wire is higher than 0.30% by mass, porosity defects may increase. Therefore, the F content relative to the total mass of the welding wire is 0.30% by mass or less, preferably 0.25% by mass or less, and more preferably 0.20% by mass or less.

[0115] Furthermore, there is no specific limit to the lower limit of the F content relative to the total mass of the welding wire; it can be 0% by mass, but it can be 0.001% by mass or more.

[0116] <θ calculated according to formula (I): 10.0 or higher and 30.0 or lower>

[0117] In this embodiment, by properly controlling the content of each of the above elements and controlling θ calculated by the following formula (I) based on the amount of each alloying element contained in the welding wire, the welding metal can be maintained at a specified ferrite content and the desired strength and toughness can be obtained.

[0118] If θ calculated by formula (I) is less than 10.0, the ferrite content is insufficient, and the strength of the weld metal is inadequate. Therefore, θ is 10.0 or more, preferably 12.0 or more, and more preferably 24.0 or more.

[0119] On the other hand, if θ calculated by formula (I) is higher than 30.0, there is an excess of ferrite, resulting in reduced low-temperature toughness and preventing the attainment of the desired Charpy impact value. Therefore, θ is preferably 30.0 or less, and more preferably 29.0 or less.

[0120] θ=4.1×α-3.2×γ-32.3…(I)

[0121] Wherein, the Si content relative to the total mass of the welding wire is expressed as [Si] (mass %), the Cr content relative to the total mass of the welding wire is expressed as [Cr] (mass %), the Mo content relative to the total mass of the welding wire is expressed as [Mo] (mass %), the Ti content relative to the total mass of the welding wire is expressed as [Ti] (mass %), the C content relative to the total mass of the welding wire is expressed as [C] (mass %), the N content relative to the total mass of the welding wire is expressed as [N] (mass %), the Mn content relative to the total mass of the welding wire is expressed as [Mn] (mass %), the Cu content relative to the total mass of the welding wire is expressed as [Cu] (mass %), and the Ni content relative to the total mass of the welding wire is expressed as [Ni] (mass %).

[0122] α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30

[0123] γ=24×[C]+28×[N]+0.25×[Mn]+0.5×[Cu]+1.10×[Ni].

[0124] <Bi: ≥0.001% by mass and ≤0.10% by mass>

[0125] The welding wire in this embodiment may also contain Bi.

[0126] Bi is a component that improves the slag stripping properties, but if it is present in excess in the welding wire, it will segregate in the final solidification zone of the weld metal, thus deteriorating the weld metal's resistance to hot cracking.

[0127] When the welding wire contains Bi, if the Bi content relative to the total mass of the welding wire is 0.001% by mass or more, the effect of improving the slag peelability can be obtained. Therefore, the Bi content relative to the total mass of the welding wire is preferably 0.001% by mass or more, and more preferably 0.01% by mass or more.

[0128] On the other hand, if the Bi content relative to the total mass of the welding wire is 0.10% by mass or less, the deterioration of the hot crack resistance of the weld metal can be suppressed. Therefore, the Bi content relative to the total mass of the welding wire is preferably 0.10% by mass or less, and more preferably 0.08% by mass or less.

[0129] Furthermore, in this embodiment, the so-called Bi content refers to the total amount of Bi contained in Bi monomers, Bi alloys, and Bi compounds.

[0130] <Balance>

[0131] The welding wire of this embodiment contains unavoidable impurities in the range of 2.0% by mass or less, as a balance of components other than those described above. Furthermore, the balance of the welding wire may contain Co, V, W, etc., in the range of 1.0% by mass or less.

[0132] The welding wire of this embodiment preferably contains 90% by mass or more of Fe, Cr, Ni, Si, Mn, Na and K, TiO2, ZrO2, Al2O3, C, Ti, Mo, Cu, Al, N and F in total, more preferably 93% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more.

[0133] Example

[0134] The following examples and comparative examples of the present invention are provided to illustrate the effects of the present invention in detail, but the present invention is not limited thereto.

[0135] The chemical composition of the welding wire is prepared in various ways to produce a flux-cored welding wire with a diameter of 1.20 mm for gas shielded arc welding.

[0136] <Evaluation of Mechanical Properties>

[0137] Using the prepared flux-cored welding wire, gas shielded arc welding was performed according to the welding conditions for the mechanical property evaluation test shown in Table 1 below. Furthermore, in this embodiment, a test plate of designation 1.3 as specified in JIS Z3111 was used. Two layers of pre-surface welding were performed on its bevel surface using the welding wire used, followed by gas shielded arc welding to prepare a deposited metal test body. The mechanical properties of the deposited metal were evaluated according to the "Tensive and Impact Test Methods for Deposited Metals" as specified in JIS Z 3111:2005. Tensile test pieces (A0 number) were extracted from the deposited metal test body, and tensile strength was evaluated by tensile testing. V-notch test pieces were extracted, and low-temperature toughness was evaluated by Charpy impact testing at -196°C. As evaluation criteria for mechanical properties, a tensile strength of 640 MPa or higher and a Charpy impact value of 25 J or higher at -196°C were classified as 0 (good), with a tensile strength of 670 MPa or higher being classified as ◎ (excellent). In addition, those with a tensile strength of less than 640 MPa, or a Charpy impact value of less than 25 J at -196°C, are classified as × (poor).

[0138] [Evaluation of Welding Operability]

[0139] Furthermore, to evaluate weldability, gas-shielded arc welding was performed using the aforementioned flux-cored welding wire, according to the welding conditions for the weldability evaluation test shown in Table 1 below. Also, in this embodiment, two welding postures were employed: horizontal fillet welding and upward vertical fillet welding.

[0140] <Evaluation of Weld Bead Shape>

[0141] Evaluate the weld bead shape according to AWS A5.22 15.2.2. As the evaluation criterion for weld bead shape, those that meet the above AWS standard criteria are marked as 0 (good), and those that do not meet the above criteria, such as convex welds, are marked as × (bad).

[0142] <Evaluation of slag stripping properties>

[0143] For the welded joint, apply light tapping with a hammer to confirm the slag removal and evaluate the slag removal performance accordingly.

[0144] As an evaluation standard for slag peelability, slag peeling off naturally or after being lightly tapped is rated as 0 (good), while slag sticking to the weld surface and unable to peel off is rated as × (bad).

[0145] The composition of the produced welding 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.

[0146] Furthermore, in Table 2, "Na+K" represents the total Na and K content in the welding wire. Additionally, in the "Calculated values ​​based on specific components" column of Table 3,

[0147] α=0.02×[Si]+[Cr]+1.20×[Mo]+0.3×[Ti]+0.30

[0148] γ = 24 × [C] + 28 × [N] + 0.25 × [Mn] + 0.5 × [Cu] + 1.10 × [Ni], where θ is the value calculated according to the following formula (I).

[0149] θ=4.1×α-3.2×γ-32.3…(I)

[0150] In the above formula, [Si] represents the Si content relative to the total mass of the welding wire (in mass%), [Cr] represents the Cr content relative to the total mass of the welding wire (in mass%), [Mo] represents the Mo content relative to the total mass of the welding wire (in mass%), [Ti] represents the Ti content relative to the total mass of the welding wire (in mass%), [C] represents the C content relative to the total mass of the welding wire (in mass%), [N] represents the N content relative to the total mass of the welding wire (in mass%), [Mn] represents the Mn content relative to the total mass of the welding wire (in mass%), [Cu] represents the Cu content relative to the total mass of the welding wire (in mass%), and [Ni] represents the Ni content relative to the total mass of the welding wire (in mass%).

[0151] [Table 1]

[0152] Table 1

[0153]

[0154] [Table 2]

[0155]

[0156] [Table 3] Table 3

[0157]

[0158] [Table 4]

[0159]

[0160] As shown in Tables 2 to 4 above, welding wires No. 1 to 11, which are examples of the invention, have excellent mechanical properties and welding operability because the composition of the welding wire and θ obtained according to formula (1) are within the scope of the present invention.

[0161] On the other hand, in the comparative example of welding wire No. 12, the content of each component is within the scope of the present invention, but the θ calculated by formula (I) exceeds the upper limit of the scope of the invention, thus reducing the low-temperature toughness.

[0162] As a comparative example, welding wire No. 13 contains Cr, Ni, and C contents that exceed the upper limit of the scope of this invention, and θ also exceeds the upper limit of the scope of this invention, thus significantly reducing its low-temperature toughness.

[0163] As comparative examples, welding wires No. 14 to 16 have poor weld bead shape and slag removal properties in upward fillet welds and horizontal fillet welds because the Al2O3 content in the welding wires is lower than the lower limit of the scope of this invention. In addition, the low-temperature toughness of welding wire No. 16 is also reduced.

[0164] As comparative examples, welding wires No. 17 to 20 have poor weld bead shape and slag removal properties in upward fillet welds and horizontal fillet welds because the Al content in these wires is higher than the upper limit of the scope of this invention. In addition, the low-temperature toughness of these welding wires is also reduced.

[0165] As a comparative example, welding wire No. 21 has reduced low-temperature toughness because the Mo content in the welding wire exceeds the upper limit of the scope of this invention.

[0166] Figure 1 This is a graph showing the relationship between the tensile strength (MPa) of the welding wires in the invention example and the comparative example and θ, with the vertical axis representing tensile strength (MPa) and the horizontal axis representing θ. Also, Figure 1 The dashed lines shown are approximate straight lines that approximate the shape of each point.

[0167] like Figure 1As shown, the tensile strength decreases as the value of θ calculated according to formula (I) decreases.

[0168] As detailed above, the flux-cored welding wire for gas-shielded arc welding according to this embodiment can produce weld metal with good weld bead shape and slag peelability, and an excellent balance between tensile strength and low-temperature toughness.

[0169] The above is with reference to the appendix. Figure 1 Various embodiments have been described, but the present invention is certainly not limited to such examples. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the patent claims, and these are also understood to fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

[0170] Furthermore, this application is based on Japanese Patent Application No. 2020-210799, filed on December 18, 2020, the contents of which are incorporated herein by reference.

Claims

1. A flux-cored welding wire, characterized in that, It is a flux-cored welding wire used in gas-shielded arc welding, with flux filling its outer sheath. Relative to the total mass of the welding wire, containing Fe: 40% by mass or more and 70% by mass or less Cr: ≥15.0% by mass and ≤25.0% by mass Ni: ≥5.0% by mass and ≤11.0% by mass Si: ≥0.5% by mass and ≤3.0% by mass Mn: ≥0.5% by mass and ≤5.0% by mass Total Na and K content: ≥0.05% by mass and ≤1.0% by mass TiO2: ≥3.0% by mass and ≤9.0% by mass ZrO2: greater than 1.0% by mass and less than 4.0% by mass Al2O3: ≥0.3% by mass and ≤2.0% by mass, and meeting the following requirements C: less than 0.015% by mass Ti: less than 1.0% by mass Mo: ≥0.001% by mass and ≤2.0% by mass Cu: less than 0.5% by mass Al: less than 0.9% by mass N: less than 0.040% by mass F: less than 0.30% by mass, and, As a balance of the components other than those mentioned above, unavoidable impurities are contained in the range of less than 2.0% by mass. The θ calculated according to the following formula (I) is greater than or equal to 10.0 and less than or equal to 30.

0. θ=4.1×α-3.2×γ-32.3…(I) Wherein, the Si content relative to the total mass of the welding wire is defined as [Si] (mass %), the Cr content relative to the total mass of the welding wire is defined as [Cr] (mass %), the Mo content relative to the total mass of the welding wire is defined as [Mo] (mass %), the Ti content relative to the total mass of the welding wire is defined as [Ti] (mass %), the C content relative to the total mass of the welding wire is defined as [C] (mass %), the N content relative to the total mass of the welding wire is defined as [N] (mass %), the Mn content relative to the total mass of the welding wire is defined as [Mn] (mass %), the Cu content relative to the total mass of the welding wire is defined as [Cu] (mass %), and the Ni content relative to the total mass of the welding wire is defined as [Ni] (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].

2. The flux-cored welding wire according to claim 1, characterized in that, Relative to the total mass of the welding wire, it also contains Bi: more than 0.001% by mass and less than 0.10% by mass.

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