Method of manufacturing a flux-cored wire and a welded joint

Abstract

A flux-cored welding wire comprising a steel sheath and a flux filling the interior, comprising C: 0.02-0.8%, Si: 0.2-0.8%, Mn: 15-30%, Ni: 1-10%, N: 0.05-1%, and other optional elements in specified amounts, with the remainder being: Fe and impurities, the total amount of Ti oxides, the total amount of Si oxides, the total amount of Zr oxides, the total amount of Al oxides, the total amount of fluorides of K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2 and MgF2, the total amount of Na oxides, the total amount of Na-containing compounds of NaF and Na3AlF6, and the total amount of K oxides, K2SiF6 and K2ZrF6 containing K compounds, in specified amounts.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing flux-cored welding wire (a welding wire filled with flux) and a welded joint. Background Technology

[0002] In recent years, due to stricter carbon dioxide emission restrictions stemming from global warming, the demand for hydrogen fuel (which emits no carbon dioxide compared to oil and coal) and natural gas (which emits less carbon dioxide) has increased. Consequently, the demand for the construction of liquid hydrogen and LNG storage tanks has also risen globally. For the steel used in liquid hydrogen and LNG storage tanks, Ni-based cryogenic steels containing 6–9% Ni are used, based on the requirement of ensuring toughness at extremely low temperatures of -196°C.

[0003] Furthermore, for welding these Ni-based low-temperature steels, austenitic flux-cored wires were used to obtain weld metals with excellent low-temperature toughness. These flux-cored wires were primarily designed with a Ni content of 70%.

[0004] For example, as a flux-cored wire with a Ni content of 70%, Patent Document 1 discloses: "A flux-cored wire with a Ni content of 35 to 70%, wherein the flux contains a total of 4.0% by mass or more of TiO2, SiO2 and ZrO2 relative to the total mass of the wire, and further contains 0.6 to 1.2% by mass of Mn oxide in terms of MnO2, and when the contents of TiO2, SiO2, ZrO2 and MnO2 (converted amount) are set in mass% as [TiO2], [SiO2], [ZrO2] and [MnO2] respectively, a Ni-based alloy with [TiO2] / [ZrO2] of 2.3 to 3.3, [SiO2] / [ZrO2] of 0.9 to 1.5 and ([TiO2]+[SiO2]+[ZrO2]) / [MnO2] of 5 to 13 is used as the outer sheath."

[0005] Furthermore, Patent Document 2 discloses: "A tubular flux-cored arc welding wire, which, by weight %, contains C: 0.15-0.8%, Si: 0.2-1.2%, Mn: 15-34%, Cr: less than 6%, Mo: 1.5-4%, S: less than 0.02%, P: less than 0.02%, B: less than 0.01%, Ti: 0.09-0.5%, N: 0.001-0.3%, TiO2: 4-15%, a total of one or more selected from SiO2, ZrO2 and Al2O3: 0.01-9%, a total of one or more selected from K, Na and Li: 0.5-1.7%, one or more selected from F and Ca: 0.2-1.5%, and the remainder being Fe and other unavoidable impurities."

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-246507

[0007] Patent Document 2: Japanese Patent Application Publication No. 2017-502842 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, the welding wire designed with 70% Ni content to ensure the low-temperature toughness of the molten metal is very expensive, requiring cheaper welding wire.

[0010] Expensive Ni is well-known as an austenite stabilizing element, but inexpensive Mn has the same effect. Therefore, by reducing the Ni content and increasing the Mn content, weld metal with excellent low-temperature toughness can be obtained at a low cost. However, simply replacing Ni with Mn to increase the Mn content results in an excess of Mn, which actually reduces the low-temperature toughness.

[0011] Therefore, the objective of this invention is to provide a flux-cored welding wire that can produce weld metal with excellent low-temperature toughness at low cost, and a method for manufacturing a weld joint using the flux-cored welding wire.

[0012] Methods for solving problems

[0013] The means used to solve the problem include the following solutions.

[0014] <1> A flux-cored welding wire, comprising a steel sheath and flux filling the interior of the steel sheath, is used for welding.

[0015] The metallic composition of the flux-cored welding wire, expressed as a percentage of mass relative to the total mass of the flux-cored welding wire, is as follows:

[0016] C: 0.020~0.800%

[0017] Si: 0.20–0.80%

[0018] Mn: 15.0~30.0%

[0019] P: 0–0.050%

[0020] S: 0~0.050%

[0021] Cu: 0–10.0%

[0022] Ni: 1.0~10.0%

[0023] Cr: 0–2.0%

[0024] Mo: 0–10.0%

[0025] Nb: 0–5.0%

[0026] V: 0~5.0%

[0027] W: 0–10.0%

[0028] Mg: 0–1.00%

[0029] Al: 0–3.0%

[0030] Ca: 0–0.100%

[0031] Ti: 0~3.000%

[0032] B: 0~0.1000%

[0033] REM: 0~0.100%

[0034] Bi: 0~0.050%

[0035] N: 0.050~1.000%

[0036] O: 0–0.020%, and

[0037] Remaining components: Fe and impurities.

[0038] The oxides and fluorides in the chemical composition of the flux-cored wire, expressed as a percentage of mass relative to the total mass of the flux-cored wire, are as follows:

[0039] The total converted value of TiO2 for Ti oxides is 3.00% to 8.00%.

[0040] The total SiO2 conversion value of Si oxides is 0.10% to 1.00%.

[0041] The total ZrO2 conversion value of Zr oxides is 0–0.80%.

[0042] The total conversion value of Al oxides to Al2O3 is 0–0.80%.

[0043] Containing one or more specific fluorides selected from K₂SiF₆, K₂ZrF₆, NaF, Na₃AlF₆, CaF₂, and MgF₂, in total amounts of 0.10–2.00%.

[0044] The total amount of Na-containing compounds (where Na oxides are converted from Na₂O) is 0.01% to 2.00%, consisting of one or more of Na oxides, NaF, and Na₃AlF₆.

[0045] The total amount of K-containing compounds (where K oxide is the equivalent of K2O) is 0.01% to 2.00%.

[0046] <2> according to <1> The flux-cored wire, wherein the total content of Mg, Al and Ca in the above-mentioned metal components is 0.01% or more by mass% relative to the total mass of the flux-cored wire.

[0047] <3> according to <1> or <2> The flux-cored welding wire, wherein the Si content in the above-mentioned metal composition is Si: 0.25-0.80%.

[0048] <4> according to <1> ~ <3> The flux-cored wire according to any one of the above-mentioned metal components, wherein the mass ratio (Mn / Ni) of the Mn content to the Ni content in the above-mentioned metal composition is 1.20 or more.

[0049] <5> according to <1> ~ <4> The flux-cored wire described in any one of the following methods, wherein the value of X calculated by the following formula A is 0.10 to 160.00.

[0050] X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO) Formula A

[0051] In Formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 represent the content of each compound represented by its chemical formula, expressed as a percentage of mass relative to the total mass of the flux-cored wire. Furthermore, SiO2 represents the total SiO2 conversion value of Si oxides, Al2O3 represents the total Al2O3 conversion value of Al oxides, ZrO2 represents the total ZrO2 conversion value of Zr oxides, MgO represents the total MgO conversion value of Mg oxides, CaO represents the total CaO conversion value of Ca oxides, Na2O represents the total Na2O conversion value of Na oxides, K2O represents the total K2O conversion value of K oxides, MnO2 represents the total MnO2 conversion value of Mn oxides, and FeO represents the total FeO conversion value of Fe oxides.

[0052] Furthermore, the conversion values ​​of SiO2, Al2O3, ZrO2, MgO, CaO, Na2O, K2O, MnO2, and FeO in Formula A are expressed as mass% relative to the total mass of the flux-cored wire.

[0053] <6> according to <1> ~ <5> The flux-cored wire described in any one of the following contains one or more Mg-containing compounds selected from Mg oxide and MgF2, and the total amount of these compounds (wherein the Mg oxide is the equivalent value of MgO) is 0.01 to 2.00%.

[0054] <7> according to <1> ~ <6> The flux-cored wire described in any one of the above-mentioned steel outer sheaths does not have a welded portion at the joint.

[0055] <8> according to <1> ~ <6> The flux-cored wire as described in any one of the above-mentioned steel outer sheaths has a welded portion at the joint.

[0056] <9> according to <1> ~ <8> The flux-cored wire described in any one of the following is coated on its surface with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.

[0057] <10> A method for manufacturing a welded joint, which has the capability to use <1> ~ <9> The process of welding steel with any one of the flux-cored welding wires.

[0058] Invention Effects

[0059] According to this disclosure, a flux-cored welding wire that yields weld metal with excellent low-temperature toughness at low cost and a method for manufacturing a weld joint using the flux-cored welding wire are provided. Attached Figure Description

[0060] Figure 1 This is a cross-sectional view showing the shape of the weld edge when two steel plates are welded together using fillet welds in the embodiment. Detailed Implementation

[0061] An embodiment that is one example of this disclosure will be described.

[0062] It should be noted that, in this specification, the numerical range represented by "~" refers to the range that includes these values ​​as the lower and upper limits, unless the values ​​before and after "~" are marked with "exceeding" or "below". Conversely, the numerical range that includes "exceeding" or "below" means that these values ​​are not included as the lower or upper limits.

[0063] Within the numerical ranges described in this specification, the upper limit of a certain numerical range can be replaced by the upper limit of other numerical ranges described in different stages, or by the values ​​shown in the embodiments. Similarly, the lower limit of a certain numerical range can be replaced by the lower limit of other numerical ranges described in different stages, or by the values ​​shown in the embodiments.

[0064] In addition, regarding content, "%" refers to "mass %".

[0065] As for the content (%), "0~" means that the ingredient is optional and may not be present.

[0066] Flux-cored welding wire

[0067] The flux-cored welding wire disclosed herein (hereinafter, sometimes simply referred to as "welding wire") has a steel sheath (hereinafter, sometimes also simply referred to as "sheath") and flux filling the interior of the steel sheath.

[0068] In the flux-cored welding wire disclosed herein, the metallic components in the chemical composition of the flux-cored welding wire are a specified composition, and the oxides and fluorides in the chemical composition of the flux-cored welding wire include Ti oxide, Si oxide, fluoride, Na-containing compound, and K-containing compound in a specified amount, and do not contain Zr oxide or Al oxide, or include Zr oxide and Al oxide in a specified amount.

[0069] The flux-cored welding wire disclosed herein, through the above-described configuration, becomes a welding wire from which excellent low-temperature toughness welding metal can be obtained at low cost.

[0070] Furthermore, the flux-cored wire disclosed herein was discovered through the following understanding.

[0071] The inventors researched a technique for obtaining welding wires that improve the low-temperature toughness of weld metals even when the Ni content is reduced and the Mn content is increased. The result was the following findings.

[0072] Expensive Ni is well-known as an austenite stabilizing element, but inexpensive Mn has the same effect. Increasing the Mn content can reduce the Ni content, resulting in cheaper welding wire and weld metal with excellent low-temperature toughness. However, simply replacing Ni with Mn to increase the Mn content leads to an increase in oxygen in the weld metal due to excessive Mn, which in turn reduces low-temperature toughness. This is because Mn readily combines with oxygen to form oxides in the weld metal.

[0073] In contrast, by increasing the Mn content, and simultaneously including specific fluorides such as NaF and MgF that achieve strong deoxidation and reduce hydrogen content, the oxygen content in the weld metal can be reduced, thus ensuring low-temperature toughness.

[0074] Based on the above findings, the flux-cored welding wire disclosed herein becomes a welding wire that can inexpensively produce welding metals with excellent low-temperature toughness.

[0075] The following is a detailed explanation of the reasons for limiting the requirements (including optional requirements) that constitute the flux-cored wire of this disclosure.

[0076] [Metallic components in the chemical composition of flux-cored welding wire]

[0077] The following describes the metallic components in the chemical composition of the flux-cored welding wire disclosed herein.

[0078] It should be noted that in the description of the metal composition of flux-cored welding wire, "%" refers to "mass % relative to the total mass of the flux-cored welding wire" unless otherwise specified.

[0079] The metallic components of flux-cored welding wire can be contained in a steel sheath or in flux.

[0080] Furthermore, when the flux-cored welding wire of this disclosure has a coating on the outer surface of the steel sheath, it can also be included in the coating.

[0081] Here, the "metallic components in the chemical composition" of flux-cored welding wire refers to the components in the flux-cored welding wire other than oxides, fluorides, nitrides, and metal carbonates. Furthermore, oxides, fluorides, nitrides, and metal carbonates present in the steel sheath are not removed during testing because they are either absent or present in trace amounts. In other words, the aforementioned "components other than oxides, fluorides, nitrides, and metal carbonates" means excluding the oxides, fluorides, nitrides, and metal carbonates contained in the flux.

[0082] The metallic components in the chemical composition of the flux-cored welding wire disclosed herein are as follows:

[0083] C: 0.020~0.800%

[0084] Si: 0.20–0.80%

[0085] Mn: 15.0~30.0%

[0086] P: 0–0.050%

[0087] S: 0~0.050%

[0088] Cu: 0–10.0%

[0089] Ni: 1.0~10.0%

[0090] Cr: 0–2.0%

[0091] Mo: 0–10.0%

[0092] Nb: 0–5.0%

[0093] V: 0~5.0%

[0094] W: 0–10.0%

[0095] Mg: 0–1.00%

[0096] Al: 0–3.0%

[0097] Ca: 0–0.100%

[0098] Ti: 0~3.000%

[0099] B: 0~0.1000%

[0100] REM: 0~0.100%

[0101] Bi: 0~0.050%

[0102] N: 0.050~1.000%

[0103] O: 0–0.020%, and

[0104] Remaining components: Fe and impurities.

[0105] That is, in the flux-cored welding wire disclosed herein, the above-mentioned components are the contents of components other than oxides, fluorides, nitrides and metal carbonates.

[0106] (C: 0.020~0.800%)

[0107] C is an element that increases the strength of weld metal and is used to ensure the strength of weld metal.

[0108] On the other hand, if the carbon content of the welding wire is excessive, the increase in strength of the welding metal will have a significant effect on toughness deterioration, and the low-temperature toughness of the welding metal will be significantly reduced.

[0109] Therefore, the carbon content of the welding wire is set to 0.020–0.800%.

[0110] The lower limit of the carbon content in the welding wire is preferably 0.050%, 0.100%, or 0.200%.

[0111] The upper limit of the carbon content in the welding wire is preferably 0.750%, 0.700%, 0%, 0.650%, 0.600%, 0.550%, 0.500%, 0.450%, 0.400%, or 0.350%.

[0112] (Si: 0.20-0.80%)

[0113] Si improves the cleanliness of the weld metal and inhibits the formation of welding defects such as porosity.

[0114] On the other hand, if the Si content of the welding wire is excessive, microsegregation is easily generated in the weld metal during the welding of Ni steel and Ni-based alloy steel, resulting in significant embrittlement in the segregated areas.

[0115] Therefore, the Si content of the welding wire is set to 0.20–0.80%.

[0116] The lower limit of Si content in the welding wire is preferably 0.25%, 0.30%, or 0.35%.

[0117] The upper limit of Si content in the welding wire is preferably 0.75%, 0.70%, or 0.65%.

[0118] (Mn: 15.0~30.0%)

[0119] Mn is an austenite stabilizing element. If the Mn content in the welding wire is too low, austenitization of the weld metal becomes difficult, and low-temperature toughness deteriorates.

[0120] In addition, manganese (Mn) functions as a deoxidizer to improve the cleanliness of weld metal. Furthermore, Mn neutralizes sulfur (S) in weld metal by forming MnS, thus improving the low-temperature toughness of the weld metal. Mn also helps prevent high-temperature cracking.

[0121] On the other hand, if the Mn content in the welding wire is excessive, microsegregation is easily generated in the weld metal during the welding of Ni steel and Ni-based alloy steel, resulting in significant embrittlement at the segregated areas. Furthermore, the excessive Mn increases the oxygen content in the weld metal, which conversely reduces low-temperature toughness.

[0122] Therefore, the Mn content of the welding wire is set to 15.0%–30.0%.

[0123] The lower limit of Mn content in the welding wire is preferably 17.0%, 18.0%, 19.0%, or 20.0%.

[0124] The upper limit of Mn content in the welding wire is preferably 28.0%, 25.0%, 22.0%, or 20.0%.

[0125] (P: 0–0.050%)

[0126] Phosphorus (P) is an impurity element that reduces the toughness of the weld metal; therefore, the P content in welding wire is preferably minimized. Consequently, the lower limit for the P content in welding wire is set at 0%. However, from the perspective of reducing the cost of P removal, a P content of 0.003% or higher in welding wire is preferable.

[0127] On the other hand, if the phosphorus (P) content of the welding wire is 0.050% or less, it falls within the range where the adverse effects of P on toughness are tolerable. In order to effectively suppress the reduction in toughness of the weld metal, the P content of the welding wire is preferably 0.040%, 0.030%, 0.020%, 0.015%, or 0.010% or less.

[0128] (S: 0~0.050%)

[0129] Sulfur (S) is an impurity element that reduces the toughness of the weld metal; therefore, the S content in welding wire should be minimized. Consequently, the lower limit for the S content in welding wire is set at 0%. However, from the perspective of reducing desulfurization costs, an S content of 0.003% or higher in the welding wire is preferable.

[0130] On the other hand, if the sulfur content of the welding wire is 0.050% or less, it falls within the range where the adverse effects of sulfur on toughness are tolerable. In order to effectively suppress the reduction of toughness of the weld metal, the sulfur content of the welding wire is preferably 0.040%, 0.030%, 0.020%, 0.015%, or 0.010% or less.

[0131] (Cu: 0-10.0%)

[0132] Cu is a precipitation strengthening element, and can be included in welding wire to improve the strength of weld metal. In addition, Cu is an austenite stabilizing element, and can also be included in welding wire to improve the low-temperature toughness of weld metal.

[0133] On the other hand, if the Cu content of the welding wire is excessive, the above effect will be saturated.

[0134] Therefore, the Cu content of the welding wire is set to 0-10.0%.

[0135] The lower limit of Cu content in the welding wire is preferably 0.1%, 0.3%, 0.5%, 0.7%, or 1.0%.

[0136] The upper limit of Cu content in the welding wire is preferably 9.5%, 9.0%, or 8.0%.

[0137] (Ni: 1.0~10.0%)

[0138] Ni is an austenite stabilizing element. If the Ni content in the welding wire is too low, austenitization of the weld metal becomes difficult, leading to a deterioration in low-temperature toughness. Furthermore, to ensure the low-temperature toughness of the weld metal, it is necessary to excessively increase the Ni content in the steel outer sheath.

[0139] On the other hand, if the Ni content of the welding wire is increased, the cost of the welding wire will increase.

[0140] Therefore, the Ni content of the welding wire is set to 1.0–10.0%.

[0141] The lower limit of Ni content in the welding wire is preferably 1.5%, 2.0%, or 2.5%.

[0142] The upper limit of Ni content in the welding wire is preferably 9.5%, 9.0%, or 8.5%.

[0143] (Cr: 0-2.0%)

[0144] Cr is an austenite stabilizing element, and it can also be included in welding wire to improve the low-temperature toughness of weld metal.

[0145] On the other hand, if the Cr content of the welding wire is excessive, the amount of low-melting-point compounds in the molten metal increases, which in turn widens the solid-liquid coexistence temperature range of the molten metal, thus making it more prone to high-temperature cracking.

[0146] Therefore, the Cr content of the welding wire is set to 0-2.0%.

[0147] The lower limit of Cr content in the welding wire is preferably 0.1%, 0.2%, or 0.3%.

[0148] The upper limit of Cr content in the welding wire is preferably 1.9%, 1.8%, or 1.7%.

[0149] (Mo: 0-10.0%)

[0150] Mo is a solid solution strengthening element and a precipitation strengthening element. In order to improve the strength of weld metal, it can also be contained in the welding wire.

[0151] On the other hand, if the Mo content in the welding wire is excessive, the strength of the weld metal becomes excessive, and the low-temperature toughness decreases.

[0152] Therefore, the Mo content of the welding wire is set to 0-10.0%.

[0153] The lower limit of the Mo content in the welding wire is preferably 2.0%, 2.5%, 3.0%, or 3.5%.

[0154] The upper limit of the Mo content in the welding wire is preferably 9.8%, 9.5%, 9.0%, or 8.0%.

[0155] (Nb: 0–5.0%)

[0156] Nitrogen (Nb) is an element that forms carbides in weld metal, increasing its strength, and therefore can also be contained in welding wire.

[0157] On the other hand, if the Nb content in the welding wire is excessive, high-temperature cracking of the weld metal may occur.

[0158] Therefore, the Nb content of the welding wire is set to 0–5.0%.

[0159] The lower limit of Nb content in the welding wire is preferably 0.5%, 1.0%, or 1.5%.

[0160] The upper limit of Nb content in the welding wire is preferably 4.5%, 4.0%, or 3.5%.

[0161] (V: 0-5.0%)

[0162] V is an element that forms carbonitrides in welding metal, increasing the strength of the welding metal, and therefore can also be contained in welding wire.

[0163] On the other hand, if the V content of the welding wire is excessive, high-temperature cracking of the weld metal may occur.

[0164] Therefore, the V content of the welding wire is set to 0-5.0%.

[0165] The lower limit of the V content in the welding wire is preferably 0.5%, 1.0%, or 1.5%.

[0166] The upper limit of the V content in the welding wire is preferably 4.5%, 4.0%, or 3.5%.

[0167] (W: 0-10.0%)

[0168] W is a solid solution strengthening element, and it can also be included in welding wire to improve the strength of weld metal.

[0169] On the other hand, if the welding wire has an excessive amount of W, the strength of the weld metal becomes excessive, which may result in a decrease in toughness.

[0170] Therefore, the W content of the welding wire is set to 0-10.0%.

[0171] The lower limit of W content in the welding wire is preferably 0.5%, 1.0%, or 2.0%.

[0172] The upper limit of the W content in the welding wire is preferably 9.0%, 8.0%, 7.0%, or 6.0%.

[0173] (Mg: 0-1.00%)

[0174] Mg is a deoxidizing element that reduces the oxygen content of welding metal, thus improving its toughness. Therefore, it can also be included in welding wire.

[0175] On the other hand, if the Mg content of the welding wire is excessive, the arc becomes unstable, spatter and porosity increase, and the weldability deteriorates.

[0176] Therefore, the Mg content of the welding wire is set to 0-1.00%.

[0177] The lower limit of Mg content in the welding wire is preferably 0.02%, 0.05%, 0.10%, or 0.20%.

[0178] The upper limit of Mg content in the welding wire is preferably 0.90%, 0.80%, or 0.70%.

[0179] (A1: 0-3.0%)

[0180] Al is a deoxidizing element that is effective in inhibiting welding defects such as porosity and improving the cleanliness of weld metal. Therefore, it can also be included in welding wire.

[0181] On the other hand, if the welding wire has an excessive Al content, Al will form nitrides or oxides in the welding metal, which may reduce the low-temperature toughness of the welding metal.

[0182] Therefore, the Al content of the welding wire is set to 0-3.0%.

[0183] The lower limit of Al content in the welding wire is preferably 0.05%, 0.1%, 0.5%, or 1.0%.

[0184] The upper limit of the Al content in the welding wire is preferably 2.5%, 2.0%, or 1.5%.

[0185] (Ca: 0~0.100%)

[0186] Ca has the effect of altering the structure of sulfides in weld metal and refining the size of sulfides and oxides in weld metal, thus effectively improving the ductility and toughness of weld metal. Therefore, Ca can also be included in welding wire.

[0187] On the other hand, if the welding wire contains excessive Ca, it may lead to the coarsening of sulfides and oxides, resulting in a deterioration of the low-temperature toughness of the weld metal. In addition, it may also cause deterioration of the weld bead shape and weldability due to arc instability.

[0188] Therefore, the Ca content of the welding wire is set to 0–0.100%.

[0189] The lower limit of Ca content in the welding wire is preferably 0.010%, 0.020%, or 0.030%.

[0190] The upper limit of the Ca content in the welding wire is preferably 0.095%, 0.090%, or 0.085%.

[0191] (Total content of Mg, Al and Ca: ≥0.01%)

[0192] Mg, Al and Ca are effective for arc stability, and therefore are preferred to be contained in welding wire.

[0193] Therefore, the total content of Mg, Al and Ca in the welding wire is preferably set to 0.01% or more.

[0194] The lower limit of the total content of Mg, Al and Ca in the welding wire is preferably 0.03%, 0.10% or 0.30%.

[0195] It should be noted that the total content of Mg, Al, and Ca in the welding wire refers to the metallic Mg, metallic Al, and metallic Ca contained in the steel outer sheath and flux. From the viewpoint of arc stability, it is preferable to set the total content of metallic Mg, metallic Al, and metallic Ca in the flux to be 0.01% or more. The lower limit of the total content of Mg, Al, and Ca in the flux is preferably 0.10%, 0.30%, or 0.50%.

[0196] (Ti: 0~3.000%)

[0197] Ti is a deoxidizing element that is effective in inhibiting welding defects such as porosity and improving cleanliness, and therefore can be included in welding wire.

[0198] On the other hand, if the Ti content in the welding wire is excessive, carbides will be generated in the welding metal, which may degrade the toughness of the welding metal.

[0199] Therefore, the Ti content of the welding wire is set to 0–3.000%.

[0200] The lower limit of Ti content in the welding wire is preferably 0.020%, 0.050%, or 0.100%.

[0201] The upper limit of Ti content in the welding wire is preferably 2.500%, 2.000%, or 1.500%.

[0202] (B: 0~0.1000%)

[0203] B has the effect of improving the hardenability of weld metal and further improving the tensile strength of weld metal, so it can also be contained in welding wire.

[0204] On the other hand, if the welding wire has an excessive amount of boron (B), the boron in the welding metal will also become excessive, forming coarse BN or Fe particles. 23 Compounds such as (C, B)6 may degrade the low-temperature toughness of weld metals.

[0205] Therefore, the B content of the welding wire is set to 0-0.1000%.

[0206] The lower limit of the B content in the welding wire is preferably 0.0010%, 0.0020%, or 0.0030%.

[0207] The upper limit of the B content in the welding wire is preferably 0.0900%, 0.0700%, or 0.0500%.

[0208] (REM: 0~0.100%)

[0209] REM is an element that stabilizes the electric arc, and therefore can also be contained in welding wire.

[0210] On the other hand, if the REM content of the welding wire is excessive, spatter becomes severe, which may worsen the weldability.

[0211] Therefore, the REM content of the welding wire is set to 0–0.100%.

[0212] The lower limit of REM content in the welding wire is preferably 0.001%, 0.002%, or 0.005%.

[0213] The upper limit of REM content in the welding wire is preferably 0.090%, 0.080%, or 0.070%.

[0214] It should be noted that "REM" refers to a total of 17 elements, including Sc, Y, and the lanthanides, and the "REM content" mentioned above refers to the total content of these 17 elements. When using lanthanides as REM, REM is industrially contained in the form of mixed rare earth alloys.

[0215] (Bi: 0~0.050%)

[0216] Bi is an element that improves the peelability of slag, and therefore can also be included in welding wire.

[0217] On the other hand, if the Bi content in the welding wire is excessive, solidification cracking may occur in the weld metal.

[0218] Therefore, the Bi content of the welding wire is set to 0–0.050%.

[0219] The lower limit of Bi content in the welding wire is preferably 0.005%, 0.010%, or 0.020%.

[0220] The upper limit of the Bi content in the welding wire is preferably 0.048%, 0.045%, 0.040%, or 0.035%.

[0221] (N: 0.050~1.000%)

[0222] Nitrogen (N) is an austenite stabilizing element and also an intrusive solid solution strengthening element. Furthermore, N has less of an adverse effect on the toughness of the weld metal than carbon (C) due to the increased strength of the weld metal.

[0223] If the nitrogen content in the welding wire is low, austenitization of the weld metal becomes difficult, and the low-temperature toughness of the weld metal deteriorates. In addition, the strength of the weld metal is also insufficient.

[0224] On the other hand, if the nitrogen content in the welding wire is excessive, the occurrence of melting and breakage increases, becoming a cause of welding defects.

[0225] Therefore, the nitrogen content of the welding wire is set to 0.050–1.000%.

[0226] The lower limit of the nitrogen content in the welding wire is preferably 0.070%, 0.100%, or 0.150%.

[0227] The upper limit of the nitrogen content in the welding wire is preferably 0.950%, 0.900%, or 0.850%.

[0228] (O: 0~0.020%)

[0229] O can be present as an impurity in the metal composition of the welding wire. However, if the O content becomes excessive, it will lead to a deterioration in the toughness and ductility of the weld metal. Therefore, the upper limit for the O content in the welding wire is set at 0.020% or less.

[0230] The upper limit of the oxygen content in the welding wire is preferably 0.015%, 0.010%, or 0.005%.

[0231] On the other hand, from the viewpoint of suppressing the increase in manufacturing costs caused by the reduction of O content, the lower limit of O content in welding wire is preferably 0.0005%, 0.001% or 0.002%.

[0232] It should be noted that the "O content" mentioned here refers to the amount of oxygen contained in the metal composition of the welding wire, such as the amount of oxygen contained in the oxide film of the alloy powder. Therefore, it excludes oxygen contained in the welding wire as oxides.

[0233] (Remaining portion: Fe and impurities)

[0234] The remaining components in the metal composition of the welding wire are Fe and impurities.

[0235] The remaining Fe includes, for example, the Fe contained in the steel outer casing and the Fe in the alloy powder (e.g., iron powder) contained in the flux.

[0236] In addition, impurities refer to components that are introduced into the welding wire during industrial manufacturing from raw materials or through various factors during the manufacturing process. These components are permissible within a range that do not adversely affect the welding wire.

[0237] (Mass ratio of Mn content to Ni content (Mn / Ni))

[0238] Mn and Ni are austenite stabilizing elements, which improve the low-temperature toughness of weld metals. On the other hand, Ni is an expensive metal, and Mn is an element that contributes to increased smoke generation.

[0239] Therefore, from the viewpoint of suppressing the cost of welding wire and improving the low-temperature toughness of weld metal, the mass ratio of Mn content to Ni content in welding wire (Mn / Ni) is preferably 1.20 or higher.

[0240] The lower limit of the mass ratio of Mn content to Ni content (Mn / Ni) in the welding wire is more preferably 1.50 or 1.80.

[0241] The upper limit of the mass ratio (Mn / Ni) of Mn content to Ni content in the welding wire is preferably 28.0 or 25.0.

[0242] [Oxides and fluorides in the chemical composition of flux-cored welding wire]

[0243] Next, the oxides and fluorides in the chemical composition of the flux-cored welding wire disclosed herein will be explained.

[0244] It should be noted that in the description of oxides and fluorides in flux-cored wire, unless otherwise specified, "%" refers to "mass % relative to the total mass of the flux-cored wire".

[0245] Furthermore, the oxides, fluorides, nitrides, and metal carbonates present in the steel outer casing are either absent or present in trace amounts. Therefore, when this specification refers to the content of oxides, fluorides, nitrides, and metal carbonates, it refers to the content of oxides, fluorides, nitrides, and metal carbonates contained in the flux.

[0246] (Total TiO2 conversion value of Ti oxides: 3.00-8.00% by mass%)

[0247] Ti oxides increase the oxygen content of the weld metal, thus degrading its low-temperature toughness.

[0248] On the other hand, Ti oxides are a component of the slag, which helps to uniformly coat the weld bead with slag. Furthermore, Ti oxides help stabilize the arc and reduce spatter. Therefore, the presence of Ti oxides improves weldability, especially vertical weldability.

[0249] If the total TiO2 conversion value of Ti oxides is less than 3.00%, the amount of slag generated will be insufficient to uniformly coat the weld bead. Consequently, the slag will sinter onto the weld bead surface, resulting in a poor weld appearance. Furthermore, if the total TiO2 conversion value of Ti oxides is less than 3.00%, the arc stabilization effect will disappear, and spatter generation will increase. Additionally, weld workability (especially vertical welding) cannot be guaranteed.

[0250] On the other hand, if the total TiO2 conversion value of Ti oxides exceeds 8.00%, the oxygen content of the weld metal increases, making it impossible to ensure low-temperature toughness. Furthermore, if the total TiO2 conversion value of Ti oxides exceeds 8.00%, although spatter generation is reduced due to arc stability, the increased viscosity of the slag leads to a thicker slag, causing the weld edge to bulge. Additionally, if the total TiO2 conversion value of Ti oxides exceeds 8.00%, pits become more likely to form. Furthermore, slag inclusions are also formed.

[0251] Therefore, the total TiO2 conversion value of Ti oxides is set to 3.00–8.00%.

[0252] The lower limit of the total TiO2 conversion value of Ti oxides is preferably 3.50%, 4.00%, or 4.50%.

[0253] The upper limit of the total TiO2 conversion value of Ti oxides is preferably 7.50%, 7.00%, or 6.50%.

[0254] It should be noted that Ti oxides mainly exist in the form of rutile, titanium dioxide, titanium slag, electrolytically polished alumina products, sodium titanate, and potassium titanate in flux. Therefore, by primarily controlling the Ti oxide content in the flux, the Ti oxide content within the aforementioned range can be set.

[0255] Here, the total TiO2 conversion value of Ti oxides refers to the mass of TiO2 relative to the total mass of the welding wire when all Ti oxides contained in the welding wire (such as TiO, TiO2, Ti2O3, Ti3O5, etc., added in the form of rutile, titanium oxide, titanium slag, electrolytically polished alumina products, sodium titanate, potassium titanate, etc.) are converted into TiO2.

[0256] Furthermore, the total TiO2 conversion value of Ti oxides was calculated as follows: the mass of Ti present as oxides in the welding wire was analyzed using a fluorescence X-ray analysis device and an X-ray diffraction (XRD) device. In addition, based on the analysis of the components contained in the flux using fluorescence X-ray analysis, the molecular structure of the contained components was resolved using X-ray diffraction (XRD), thereby allowing the separate determination of the amount of Ti present as oxides and the amount of Ti contained as metallic components in the welding wire.

[0257] Specifically, firstly, flux is collected from the welding wire and analyzed using the method described above. For example, if TiO2, Ti2O3, and Ti3O5 are detected through analysis, the following formula C1 is used to calculate the total Ti oxide mass percentage as [TiO2], [Ti2O3], and [Ti3O5], and the total TiO2 conversion value of the Ti oxides as [converted TiO2].

[0258] [Conversion of TiO2] = (0.60 × [TiO2] + 0.67 × [Ti2O3] + 0.64 × [Ti3O5]) × 1.67 (Equation C1)

[0259] The coefficients (0.60, 0.67, 0.64) in Formula C1 are used to calculate the amount of Ti contained in each oxide, and the multiplier (1.67) at the end is used to calculate the TiO2 conversion value from the total amount of Ti present as oxide in the welding wire.

[0260] Here, the method for calculating the coefficients is explained. If we set it to detect M... x O y For example, oxides of TiO2, Ti2O3, Ti3O5, then M x O y The coefficients involved are calculated using the following formula C2.

[0261] [Atomic weight of element M] × x / ([Atomic weight of element M] × x + [Atomic weight of oxygen] × y) Equation C2

[0262] In equation C1, 0.60, 0.67, and 0.64 are equivalent to the coefficients obtained from equation C2 above.

[0263] Furthermore, the method for calculating the multiplier used to determine the conversion value is explained. This is used to convert to M. a O b (For example, TiO2) The multiplier is calculated by the following formula C3.

[0264] ([atomic weight of element M] × a + [atomic weight of oxygen] × b) / ([atomic weight of element M] × a) Equation C3

[0265] The 1.67 in equation C1 is equivalent to the multiplier obtained from equation C3 above.

[0266] Furthermore, the case where the oxide is a compound formed by combining with two metal elements is also considered. Regarding the method for calculating the coefficients in this case, if we assume that M is detected... x O y M 2 z (For example: TiO3·Fe, i.e., M=Ti, M) 2=Oxides of Fe, x=1, y=3, z=1, then the following formula C4 is used for calculation.

[0267] [Atomic weight of element M] × x / ([Atomic weight of element M] × x + [Atomic weight of oxygen] × y + [M 2 [Atomic weight of the element] × z) Equation C4

[0268] Furthermore, the total conversion values ​​of SiO2 for Si oxides, ZrO2 for Zr oxides, Al2O3 for Al oxides, MgO for Mg oxides, Na2O for Na oxides, K2O for K oxides, CaO for Ca oxides, MnO2 for Mn oxides, and FeO for Fe oxides are obtained through the same calculations as the total conversion values ​​of TiO2 for Ti oxides. That is, the collected flux is analyzed using a fluorescence X-ray analysis device and an X-ray diffraction (XRD) device, and the coefficients and multipliers are calculated according to the above formulas C2, C3, and C4, corresponding to the various oxides detected, and the calculations are performed in the same manner as in formula C1.

[0269] The following are representative oxides detected through analysis.

[0270] Si oxides: SiO, SiO2, Si2O3, Si2O4

[0271] Zr oxide: ZrO2

[0272] Al oxides: AlO, Al2O3, Al3O5

[0273] Mg oxides: MgO, MgO2, Mg2O

[0274] Na oxides: Na₂O, Na₂O₂

[0275] K oxides: K₂O, KO₂

[0276] Ca oxides: CaO, CaO2

[0277] Mn oxides: MnO, Mn2O, MnO2

[0278] Fe oxides: FeO, Fe2O4, FeO3

[0279] Furthermore, when analyzing various compositions such as Ti oxide, the method for separating the steel outer sheath from the flux is as follows: The steel outer sheath of the flux-cored wire is opened using pliers or similar tools, and the internal flux is collected. Then, the adhering flux is removed from the inner surface of the outer sheath, the contact area between the steel outer sheath and the flux, using a wire brush and ultrasonic cleaning. Thus, the steel outer sheath is separated from the flux.

[0280] (Total SiO2 conversion value of Si oxides: 0.10-1.00% by mass%)

[0281] Si oxides increase the oxygen content of the weld metal, which degrades its low-temperature toughness.

[0282] On the other hand, Si oxide is a component of slag and has the function of increasing the viscosity of molten slag and improving the peelability of slag.

[0283] When the total SiO2 conversion value of Si oxides is less than 0.10%, the slag coating is poor, the slag peeling property becomes poor, and the weld bead shape and appearance also become poor. In addition, weldability (especially vertical weldability) cannot be guaranteed.

[0284] On the other hand, if the total SiO2 conversion value of Si oxides exceeds 1.00%, the oxygen content of the weld metal increases, making it impossible to ensure low-temperature toughness. Furthermore, if the total SiO2 conversion value of Si oxides exceeds 1.00%, the amount of spatter increases. Moreover, if the total SiO2 conversion value of Si oxides exceeds 1.00%, pits and gas grooves become more likely to form. Additionally, slag inclusions are formed.

[0285] Therefore, the total SiO2 conversion value of Si oxide is set to 0.10 to 1.00%.

[0286] The lower limit of the total SiO2 conversion value of Si oxides is preferably 0.15%, 0.20%, or 0.25%.

[0287] The upper limit of the total SiO2 conversion value of Si oxides is preferably 0.95%, 0.90%, or 0.85%.

[0288] It should be noted that Si oxides mainly exist in the form of silica sand, zircon sand, feldspar, sodium silicate, potassium silicate, etc., in the flux. Therefore, by mainly controlling the Si oxide content in the flux, the aforementioned range of Si oxide content can be set.

[0289] (Total ZrO2 conversion values ​​of Zr oxides: 0-0.80% by mass%)

[0290] Zr oxides increase the oxygen content of the weld metal, thus deteriorating its low-temperature toughness. Therefore, from the perspective of low-temperature toughness, it is preferable to have no Zr oxides, and the lower limit of the total ZrO2 conversion value of Zr oxides is set to 0%.

[0291] However, Zr oxides are a component of slag and have the effect of improving the slag coverage in horizontal fillet welds, thus making the weld bead shape smoother. Therefore, from this point of view, it is also acceptable for them to be included.

[0292] On the other hand, if the total ZrO2 conversion value of Zr oxides exceeds 0.80%, the weld bead shape is prone to becoming convex. In addition, slag inclusions are generated.

[0293] Therefore, the total ZrO2 conversion value of Zr oxides is set to 0–0.80%.

[0294] The upper limit of the total ZrO2 conversion value of Zr oxides is preferably 0.60%, 0.40%, 0.20%, or 0.10%.

[0295] It should be noted that Zr oxide mainly exists in the form of zirconium sand and zirconium oxide in the flux. In addition, it may also be present in trace amounts in Ti oxide. Therefore, by mainly controlling the Zr oxide content in the flux, the aforementioned range of Zr oxide content can be set.

[0296] (Total Al2O3 conversion values ​​of Al oxides: 0-0.80% by mass%)

[0297] Al oxides act as an oxygen source; therefore, the addition of Al oxides increases the oxygen content in the weld metal, contributing to toughness degradation. Thus, from the perspective of low-temperature toughness, the absence of Al oxides is preferable, and the lower limit of the total Al2O3 conversion value of Al oxides is set at 0%.

[0298] However, when Al oxides form molten slag, they can prevent undercut on the upper weld leg side of the fillet weld bead by improving the slag coating properties, so they can also be included from this point of view.

[0299] On the other hand, if the total Al2O3 conversion value of Al oxides exceeds 0.80%, the weld bead edge on the lower weld leg side of the fillet weld will become a bulging weld bead shape. Furthermore, slag inclusions will occur.

[0300] Therefore, the total Al2O3 conversion value of Al oxides is set to 0-0.80%.

[0301] The upper limit of the total Al2O3 conversion value of Al oxides is preferably 0.70%, 0.60%, 0.40%, 0.20%, or 0.10%.

[0302] It should be noted that Al oxides mostly exist in the form of aluminum oxide, feldspar, and other components in the flux. Therefore, by primarily controlling the Al oxide content in the flux, the aforementioned range of Al oxide content can be established.

[0303] (Total of specific fluorides: 0.10–2.00% by mass)

[0304] K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2 (referred to as “specific fluorides” in this specification) have the effect of reducing the oxygen content of weld metal.

[0305] If the total amount of a particular fluoride is less than 0.10%, the oxygen content of the weld metal becomes high, and low-temperature toughness cannot be ensured in the welding wire of this disclosure with a high Mn content.

[0306] On the other hand, if the total amount of a particular fluoride exceeds 2.00%, a large amount of welding fumes will be generated, resulting in welding defects.

[0307] Therefore, the total amount of any one or more fluorides contained in a specific fluoride is set to 0.10 to 2.00%.

[0308] The lower limit for the total amount of a specific fluoride is preferably 0.20%, 0.30%, or 0.40%.

[0309] The upper limit for the total amount of a particular fluoride is preferably 1.90%, 1.80%, or 1.70%.

[0310] (Total Na-containing compounds: 0.01–2.00% by mass)

[0311] Na oxides, NaF, and Na3AlF6 (hereinafter, these Na-containing compounds are sometimes referred to as "specific Na-containing compounds") decompose during welding, and the resulting Na acts as a deoxidizer, reducing the oxygen content of the weld metal. As a result, the low-temperature toughness of the molten metal is improved.

[0312] If the total amount of a particular Na-containing compound is less than 0.01%, the reduction in oxygen content in the weld metal will be minimal and cannot ensure low-temperature toughness.

[0313] On the other hand, if the total amount of certain Na-containing compounds exceeds 2.00%, the solidification temperature of the weld slag will decrease, and the weldability (especially vertical weldability) will deteriorate.

[0314] Therefore, the total amount of any one or more of the specific Na-containing compounds is set to 0.01 to 2.00%.

[0315] The lower limit for the total amount of a specific Na-containing compound is preferably 0.05%, 0.15%, 0.20%, or 0.30%.

[0316] The upper limit for the total amount of a specific Na-containing compound is preferably 1.90%, 1.80%, 1.70%, or 1.50%.

[0317] It should be noted that the content of Na oxides refers to the total of the converted Na2O values ​​of Na oxides.

[0318] (Total of compounds containing potassium: 0.01–2.00% by mass)

[0319] The potassium (K) released during welding from the decomposition of potassium oxides, K₂SiF₆, and K₂ZrF₆ (hereinafter, these potassium-containing compounds are sometimes referred to as "specific potassium-containing compounds") acts as a deoxidizer, reducing the oxygen content of the weld metal. As a result, the low-temperature toughness of the molten metal is improved.

[0320] If the total amount of a particular potassium-containing compound is less than 0.01%, the reduction in oxygen content in the weld metal will be minimal and cannot ensure low-temperature toughness.

[0321] On the other hand, if the total amount of a particular K-containing compound exceeds 2.00%, the solidification temperature of the weld slag will decrease, and the weldability (especially vertical weldability) will deteriorate.

[0322] Therefore, the total amount of any one or more of the specific K-containing compounds is set to 0.01 to 2.00%.

[0323] The lower limit for the total amount of a specific K-containing compound is preferably 0.05%, 0.20%, 0.30%, or 0.40%.

[0324] The upper limit for the total amount of a specific K-containing compound is preferably 1.95%, 1.90%, 1.80%, or 1.50%.

[0325] It should be noted that the content of K oxide refers to the total K2O conversion value of K oxide.

[0326] (Total Mg compounds: 0.01–2.00% by mass)

[0327] In addition to containing specific Na-containing compounds and specific K-containing compounds, the flux-cored wire of this embodiment may also contain one or more Mg-containing compounds selected from Mg oxide and MgF2.

[0328] During welding, the Mg produced by the decomposition of Mg oxides and MgF2 (hereinafter, these Mg-containing compounds are sometimes referred to as "specific Mg-containing compounds") acts as a deoxidizer, reducing the oxygen content of the weld metal. As a result, the low-temperature toughness of the molten metal is improved.

[0329] If the welding wire contains a specific Mg-containing compound (preferably the total amount of the specific Mg-containing compound is 0.01% or more), the reduction effect of oxygen content in the welding metal becomes greater, thereby improving low-temperature toughness.

[0330] On the other hand, if the total content of certain Mg compounds is less than 2.00%, the solidification temperature of the welding slag will be higher, thereby improving the weldability (especially vertical weldability).

[0331] Therefore, the total content of any one or more Mg-containing compounds in a specific Mg-containing compound is preferably set to 0 to 2.00%, and in the case of containing Mg-containing compounds, the total content is preferably set to 0.01 to 2.00%.

[0332] The lower limit for the total amount of a specific Mg-containing compound is more preferably 0.05%, 0.20%, 0.30%, or 0.40%.

[0333] The upper limit for the total amount of a specific Mg-containing compound is more preferably 1.90%, 1.80%, or 1.70%.

[0334] It should be noted that the content of Mg oxides refers to the total of the MgO conversion value of Mg oxides.

[0335] (Other implications of the presence of specific Na-containing compounds and specific K-containing compounds in the welding wire)

[0336] Even when the contents of specific Na-containing compounds and specific K-containing compounds were set to below 0.01%, spatter increased and weldability deteriorated, even with the addition of CaF2, which contains Ca and functions as a deoxidizer. Furthermore, even with the addition of Mg, which also functions as a deoxidizer, the amount of diffusible hydrogen in the weld metal increased, leading to a deterioration in low-temperature cracking resistance.

[0337] Therefore, in order to obtain weld metal with excellent weldability (especially vertical weldability) and excellent low-temperature toughness and resistance to low-temperature cracking, it is necessary to include specific Na-containing compounds and specific K-containing compounds within the above-mentioned ranges.

[0338] From the same point of view, it is also preferable to include specific Mg-containing compounds in the welding wire within the range described above.

[0339] It should be noted that the contents of specific Na-containing compounds, specific K-containing compounds, and specific Mg-containing compounds are expressed as a percentage of mass relative to the total mass of the flux-cored wire.

[0340] (The value of X calculated using formula A)

[0341] In the flux-cored welding wire disclosed herein, the X value calculated by the following formula A is preferably 0.10 to 160.00.

[0342] X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO) Formula A

[0343] In Formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 represent the content of each compound represented by its chemical formula, expressed as a percentage of mass relative to the total mass of the flux-cored wire. Furthermore, SiO2 represents the total SiO2 conversion value of Si oxides, Al2O3 represents the total Al2O3 conversion value of Al oxides, ZrO2 represents the total ZrO2 conversion value of Zr oxides, MgO represents the total MgO conversion value of Mg oxides, CaO represents the total CaO conversion value of Ca oxides, Na2O represents the total Na2O conversion value of Na oxides, K2O represents the total K2O conversion value of K oxides, MnO2 represents the total MnO2 conversion value of Mn oxides, and FeO represents the total FeO conversion value of Fe oxides. Furthermore, the conversion values ​​of SiO2, Al2O3, ZrO2, MgO, CaO, Na2O, K2O, MnO2, and FeO in Formula A are expressed as mass% relative to the total mass of the flux-cored wire.

[0344] In Formula A, the molecule is an indicator of the amount of fluorine compounds that contain components (Ca, Mg, Na, K, Si) that decompose during welding, function as deoxidizers, reduce the oxygen content of the weld metal, and reduce the diffusivity of the weld metal.

[0345] On the other hand, the denominator is an indicator of the amount of oxygen (O) compounds that increase the oxygen content of the weld metal.

[0346] That is, if the value of X is above 0.10, the amount of oxygen (O) compounds that increase the oxygen content of the weld metal is small, the oxygen content reduction effect of the weld metal becomes greater, and thus the low-temperature toughness is improved.

[0347] On the other hand, if the X value is below 160.00, the amount of fluoride will not be excessive, making it difficult to form inclusions and making it easier to make a sound joint.

[0348] Therefore, the X value calculated by formula A is preferably set to 0.10 to 160.00.

[0349] The lower limit of the X value is more preferably 1.00, 5.00 or 10.00.

[0350] The upper limit of the X value is more preferably 130.00, 100.00, 70.00, 50.00 or 20.00.

[0351] -Total content of other oxides: 0~10.00%-

[0352] When the flux-cored wire of this disclosure contains one or more oxides selected from Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide, other than Ti oxide, Si oxide, Zr oxide, and Al oxide, the total content of these oxides is preferably 10.00% or less. Oxides contained in the group consisting of Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide are sometimes simply referred to as "other oxides." Furthermore, the total content of each of the individual oxides in the other oxides is sometimes simply referred to as the "total content of other oxides."

[0353] When the flux-cored welding wire disclosed herein contains one or more of the aforementioned other oxides, the total content of the aforementioned other oxides is calculated as the sum of the FeO conversion value of Fe oxide, the MgO conversion value of Mg oxide, the Na2O conversion value of Na oxide, the K2O conversion value of K oxide, the MnO2 conversion value of Mn oxide, and the CaO conversion value of Ca oxide.

[0354] It should be noted that in the flux-cored wire disclosed herein, other oxides are not essential components, therefore the lower limit of the total content of other oxides in the flux-cored wire is 0%.

[0355] On the other hand, other oxides have the effect of maintaining weld bead shape and improving weldability. Furthermore, Mg oxides and Fe oxides also have the effect of stabilizing the arc. To obtain the aforementioned effects, the total content of other oxides can be set to more than 0%. To further enhance these effects, the lower limit of the total content of other oxides can be set to 0.05%, 0.10%, 0.15%, or 0.20%. On the other hand, if the total content of other oxides is 10.00% or less, the formation of inclusions can be suppressed, and a sound joint can be easily formed. Therefore, the upper limit of the total content of other oxides is preferably set to 10.00%, but it can also be set to 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00%, 0.50%, or 0.30%.

[0356] The content of other oxides in the flux-cored wire disclosed herein does not need to be limited according to the type of each oxide.

[0357] In addition, the content of each oxide in other oxides and the total content of other oxides were determined by fluorescence X-ray analysis and X-ray diffraction (XRD) in the same manner as the content of Ti oxides mentioned above.

[0358] (Nitrogen compounds, metal carbonates)

[0359] Nitrides (especially those in flux) reduce the amount of diffusible hydrogen in the weld metal and significantly improve its resistance to low-temperature cracking. The reason for this is unclear, but one speculated reason is that the nitrogen in the nitride combines with hydrogen (H) during welding to form ammonia (NH3), which is then released into the weld metal.

[0360] Therefore, the flux-cored wire disclosed herein may also contain nitrides.

[0361] In the flux-cored wire disclosed herein, the nitride may include one or more selected from AlN, BN, Ca3N2, CeN, CrN, Cu3N, Fe4N, Fe3N, Fe2N, Mg3N, Mo2N, NbN, Si3N4, TiN, VN, ZrN, Mn2N, and Mn4N.

[0362] Metal carbonates are ionized by an electric arc, producing CO2 gas. The CO2 gas reduces the partial pressure of hydrogen in the welding atmosphere, thus reducing the amount of diffusible hydrogen in the weld metal.

[0363] Therefore, the flux-cored welding wire disclosed herein may also contain metal carbonates in the flux.

[0364] In the flux-cored welding wire disclosed herein, the metal carbonate may include one or more selected from MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3 and SrCO3.

[0365] However, there are no restrictions on the types and composition of metal carbonates.

[0366] In addition, the contents of nitrides and metal carbonates were determined by fluorescence X-ray analysis and X-ray diffraction (XRD) in the same manner as the contents of Ti oxides mentioned above.

[0367] The flux-cored welding wire of this disclosure may further include a lubricant coated on the surface of the welding wire. The lubricant coated on the surface of the welding wire improves the feed rate of the welding wire during welding. Various types of lubricants (e.g., vegetable oils such as palm oil) can be used as the lubricant for the welding wire, but to suppress low-temperature cracking of the weld metal, it is preferable to use one or both of hydrogen-free polytetrafluoroethylene oil (PTFE oil) and perfluoropolyether oil (PFPE oil). Furthermore, as described above, the flux-cored welding wire of this disclosure may further include a coating formed on the surface of the welding wire. In this case, the lubricant is coated on the surface of the coating.

[0368] The hydrogen content in the flux-cored welding wire disclosed herein is not particularly limited, but to reduce the diffusible hydrogen content of the weld metal, it is preferably 12 ppm or less relative to the total mass of the flux-cored welding wire. The hydrogen content in the flux-cored welding wire may increase during storage due to moisture intrusion. Therefore, in cases where the period from wire manufacturing to use is long, it is preferable to prevent moisture intrusion by the methods described later.

[0369] (Welding wire shape)

[0370] Next, the shape (wire structure) of the flux-cored welding wire disclosed herein will be described.

[0371] Generally, flux-cored welding wires are classified into any of the following types: welding wires that have a shape without slit-like gaps (seamless shape) because the joints of the steel sheath are welded (welding wires that do not have a welded portion at the joints of the steel sheath); and welding wires that have a shape containing slit-like gaps (slit shape) because the joints of the steel sheath are not welded (welding wires that have a welded portion at the joints of the steel sheath).

[0372] The flux-cored welding wire of this disclosure can be of any shape. However, to suppress low-temperature cracking of the weld metal, it is preferable that there are no slit-like gaps in the steel outer sheath. During welding, hydrogen (H) that penetrates into the weld joint diffuses into the weld metal and the materials being welded, accumulating at stress concentration points and causing low-temperature cracking. The sources of H supply vary, but when welding is performed under strictly controlled conditions of weld joint cleanliness and gas protection, the moisture (H2O) contained in the welding wire becomes the main source of H supply, and the amount of this moisture strongly affects the diffusible hydrogen content of the weld joint.

[0373] When the steel sheath has seams, atmospheric moisture can easily penetrate into the flux through these seams. Therefore, it is preferable to prevent atmospheric moisture from penetrating into the flux through the steel sheath during the period from the time the welding wire is manufactured until its use by removing the seams. When the steel sheath has seams and the period from the time the welding wire is manufactured to its use is long, to prevent the intrusion of sources of moisture, it is preferable to vacuum-pack the entire flux-cored wire or store it in a container that can maintain its dryness.

[0374] (Welding wire diameter)

[0375] The diameter of the flux-cored welding wire disclosed herein is not particularly limited, but may be, for example, φ1.0 to φ2.0 mm. It should be noted that the diameter of a typical flux-cored welding wire is φ1.2 to φ1.6 mm.

[0376] (Fill rate)

[0377] The filler ratio of the flux-cored wire disclosed herein is not particularly limited as long as the above conditions are met. Given the typical filler ratio of flux-cored wires, the lower limit of the filler ratio of the flux-cored wire disclosed herein can be set, for example, 8%, 10%, or 12%. Furthermore, the upper limit of the filler ratio of the flux-cored wire disclosed herein can be set, for example, 28%, 25%, 22%, 20%, or 17%.

[0378] In addition, the mass of the steel outer skin and the flux were measured separately when calculating the fill rate.

[0379] <Manufacturing Method of Flux-Cored Welding Wire>

[0380] Next, the manufacturing method of the flux-cored welding wire disclosed herein will be described.

[0381] It should be noted that the manufacturing method described below is an example, and the method for manufacturing the flux-cored welding wire disclosed herein is not limited to the following method.

[0382] (Case with a seamless flux-cored wire)

[0383] A method for manufacturing a flux-cored welding wire with a seamless shape includes the following steps: a step of preparing flux; a step of forming a U-shaped tube by feeding a steel strip along its length direction and forming it with a forming roller; a step of supplying flux into the tube through the opening; a step of butt welding the opposite edges (both circumferential ends) of the opening of the tube to obtain a seamless tube; a step of drawing the seamless tube to obtain a flux-cored welding wire with a specified wire diameter; and a step of annealing the flux-cored welding wire during or after the drawing process.

[0384] The flux is prepared in a manner that ensures the components of the flux-cored wire are within the aforementioned specified range. Furthermore, it should be noted that the flux filling rate, determined by the material of the steel sheath (i.e., the width and thickness of the steel strip) and the amount of flux filling, also affects the quantity of each component in the flux-cored wire.

[0385] Butt welding is performed using methods such as resistance welding, laser welding, or TIG welding.

[0386] Furthermore, during or after the wire drawing process, the flux-cored wire is annealed to remove moisture. To ensure the hydrogen content of the flux-cored wire is below 12 ppm, the annealing temperature is preferably set to 650°C or higher, and the annealing time to 4 hours or higher. Additionally, to prevent flux deterioration, the annealing temperature is preferably set to 900°C or lower.

[0387] If the cross-section of a flux-cored wire without a slit-like gap after butt welding is ground and etched, weld marks can be observed; otherwise, they are not visible. Therefore, it is sometimes referred to as seamless, as described above. For example, in the Welding Society's "New Edition of Introduction to Welding and Joining Technology" (2008), p. 111, flux-cored wire without a slit-like gap after butt welding is described as a seamless type of wire. A flux-cored wire without a slit-like gap can also be obtained by brazing the gap in the steel sheath of the flux-cored wire.

[0388] (Case of flux-cored wire with a narrow slit-like gap)

[0389] The manufacturing method of flux-cored wire with a slit-like gap has a step of forming a slit tube and butt-welding the ends of the slit tube to obtain a tube with a slit-like gap, instead of butt-welding the two circumferential ends of the slit tube to obtain a seamless tube. Apart from this step, it is the same as the manufacturing method of flux-cored wire with a seamless shape. The manufacturing method of flux-cored wire with a slit-like gap may further include a step of closing the butt-welded ends of the slit tube.

[0390] In the manufacturing method of flux-cored welding wire with a slit-like gap, a tube with a slit-like gap is drawn into wire.

[0391] <Manufacturing Method of Welded Joints>

[0392] Next, the manufacturing method (welding method) of the welded joint disclosed herein will be described.

[0393] The method for manufacturing a welded joint disclosed herein includes the step of welding steel using the flux-cored welding wire of the present disclosure described above.

[0394] In the method for manufacturing the welded joint disclosed herein, gas-shielded arc welding is a suitable welding method.

[0395] In the method for manufacturing the welded joint disclosed herein, the type of steel (the material to be welded) that serves as the base material for the welded joint is not particularly limited, but for example, P can be suitably used. CM Steels with a low-temperature cracking susceptibility of 0.24% or higher (welding cracking susceptibility component) are particularly high-strength steel plates with a tensile strength of 590MPa to 1700MPa and a thickness of 20mm or more.

[0396] In the method for manufacturing welded joints disclosed herein, it is preferable to include a process of welding steel using the flux-cored wire of this disclosure in any one or more passes, from the first pass to the final pass. When welding is performed in only one pass, the flux-cored wire of this disclosure is used in that single pass.

[0397] The polarity of the flux-cored welding wire is so small that its effect on the diffusivity of hydrogen in the weld metal and the amount of spatter is negligible; therefore, it can be either positive or negative, but positive is preferred.

[0398] In the method for manufacturing welded joints disclosed herein, the type of shielding gas used in gas-shielded arc welding is not particularly limited. Commonly used shielding gases such as 100% carbon dioxide gas and a mixture of Ar and 3-30% CO2 are preferred. Furthermore, the shielding gas used in welding with the flux-cored wire of this disclosure may also contain 5% or less O2. These gases are inexpensive, making welding using them advantageous for industrial applications.

[0399] The welding posture in the method for manufacturing the welded joint disclosed herein is not particularly limited. In the method for manufacturing the welded joint disclosed herein, the welding posture can be any one of the following: downward posture, horizontal posture, vertical posture, and upward posture.

[0400] The welded joint obtained by the method for manufacturing a welded joint disclosed herein comprises a steel base material and a welded portion consisting of weld metal and a heat-affected zone. The tensile strength of the obtained weld metal is preferably, for example, a high strength of 590 to 1200 MPa.

[0401] Example

[0402] Next, the feasibility and effects of this disclosure will be further described in detail through examples and comparative examples. However, the following embodiments do not limit this disclosure. Design changes made in accordance with the above and following principles are all included within the technical scope of this disclosure.

[0403] (Manufacturing of flux-cored welding wire)

[0404] The flux-cored welding wires of this disclosure and comparative examples are manufactured by the methods described below.

[0405] First, while conveying the steel strip along its length, a forming roller is used to form a U-shaped tube. Flux is then supplied into the tube through its opening, and the opposite edges of the opening are butt-welded to obtain a seamless tube.

[0406] The seamless tube was drawn into a wire to obtain a flux-cored wire without slit-like gaps. A portion of the samples were made into tubes with slit-like gaps without seam welding, and then drawn into wires.

[0407] By operating in this manner, a flux-cored welding wire with a final diameter of φ1.2mm was successfully produced.

[0408] Furthermore, during the wire drawing process of these flux-cored welding wires, the wires are annealed at a temperature range of 650–950°C for more than 4 hours. After trial production, a lubricant is applied to the surface of the welding wire. The composition of these flux-cored welding wires is shown in Tables 1-A to 1-F.

[0409] The metal content, oxide content, fluoride (specific fluoride) content, Na-containing compound content, K-containing compound content, and iron powder content of the welding wires shown in Tables 1-A to 1-F are expressed as a percentage of mass relative to the total mass of the flux-cored welding wire. In the tables, "percentage of mass relative to the total mass of the flux-cored welding wire" is abbreviated as "percentage of mass," and "metal content in the chemical composition of the welding wire" is abbreviated as "chemical composition."

[0410] [Table 1-A]

[0411]

[0412] [Table 1-B]

[0413]

[0414] [Table 1-C]

[0415]

[0416] [Table 1-D]

[0417]

[0418] [Table 1-E]

[0419]

[0420] [Table 1-F]

[0421]

[0422] The remaining portion of the flux-cored wires shown in Tables 1-A to 1-F (i.e., components other than those shown in the tables) consists of iron and impurities.

[0423] Among the flux-cored wires shown in the table, those marked "seamless" in the "Wire Structure" column have a seamless shape, while those marked "with slit-like gap" have a slit-like gap. Unless otherwise specified in the "Remarks" column, the wires are coated with palm oil as a lubricant, and those marked "PTFE oil" are coated with PTFE oil.

[0424] The elements contained in the flux-cored welding wires shown in Tables 1-A to 1-F are in the form of steel outer sheath or metal powder.

[0425] Furthermore, in Tables 1-A to 1-F, numerical values ​​that deviate from the range specified in this disclosure are underlined.

[0426] Furthermore, in Tables 1-A to 1-F, the blank columns in the tables relating to the content of chemical components, compounds, etc., indicate that the chemical component, compound, etc., was not intentionally present. These chemical components, compounds, etc., may also be unavoidably mixed in or generated.

[0427] [evaluate]

[0428] The evaluation was conducted by using the flux-cored welding wires of the examples and comparative examples of this disclosure, performing gas-shielded arc welding in an upward vertical welding manner. Specifically, the evaluation was conducted by the method described below.

[0429] The steel plate used for welding is 50mm thick steel with a tensile strength of 780MPa. The welding gas used in the evaluation was set to Ar-20 vol% CO2 gas. Furthermore, the welding current was set to DC for all evaluations, and the polarity of the welding wire was set to positive for all evaluations.

[0430] In addition, the welding conditions during the evaluation were set as described in Table 2.

[0431] [Table 2]

[0432] Current Voltage speed Heat input A V mm / minute kJ / mm 220 30 16 25

[0433] (Evaluation of oxygen content in weld metal)

[0434] The oxygen content of the weld metal obtained by gas shielded arc welding using the flux-cored welding wires of the present disclosure and comparative examples is evaluated.

[0435] The oxygen content of weld metal is determined by taking an analytical sample (pin) from the center of the plate thickness and the center of the weld metal width along the length of the weld joint, and measuring it using the inert gas melting infrared absorption method.

[0436] Set oxygen levels below 380 ppm as A, above 380 ppm but below 450 ppm as B, and above 450 ppm as C.

[0437] (Evaluation of low-temperature toughness)

[0438] Using the flux-cored welding wire of the present and comparative examples, a steel plate was subjected to gas-shielded arc welding, and three impact test pieces (V-notch test pieces with a notch depth of 2 mm) were collected from the center of the weld metal in the thickness direction.

[0439] For the three impact test pieces, the Charpy impact test according to JIS Z2242:2005 was carried out at -196℃.

[0440] Then, the cases where the average Charpy impact absorption energy of the three impact test pieces at -196℃ was above 34J were considered "qualified", and the cases where it was below 34J were considered "unqualified".

[0441] (Arc stability (weld bead formation))

[0442] Using the flux-cored welding wires of the examples and comparative examples of this disclosure, fillet welds were performed, and the weld bead formation was evaluated by the side angle. It should be noted that... Figure 1 This diagram illustrates the shape of the weld bead at point 8 when a fillet weld is performed with steel plate (upper plate) 6 in a T-shape (i.e., right angle) contact with steel plate (lower plate) 7. Figure 1 The definition of the side angle 5 is shown in the figure. In this specification, as... Figure 1 As shown, the angle between the steel plate (upper plate) 6 and the weld seam edge of the weld metal 8 is set as the side angle 5a, and the angle between the steel plate (lower plate) 7 and the weld seam edge of the weld metal 8 is defined as the side angle 5b. Furthermore, the case where the sum of the side angle 5a and the side angle 5b is 200 degrees or more is determined as "A", and the case where the angle is less than 200 degrees is determined as "B".

[0443] (Comprehensive judgment)

[0444] The condition that the oxygen content of the weld metal is rated as "A" or "B" and the low-temperature toughness is rated as "qualified" is considered "qualified". The condition that meets at least one of the following conditions is considered "unqualified": the oxygen content of the weld metal is rated as "C" and the low-temperature toughness is rated as "unqualified".

[0445] Furthermore, regarding the influence of the composition of the steel plate (base material) in the weld metal after welding, since the dilution rate caused by the base material composition is very low, it can be said that the influence of the base material in the evaluation test is very low.

[0446] [Table 3]

[0447]

[0448] It can be seen that, in the case of the flux-cored welding wire of this disclosure, the oxygen content of the welding metal is low, and the resulting welding metal has excellent low-temperature toughness.

[0449] On the other hand, the comparative example is deemed unqualified in more than one evaluation item because it does not meet any of the requirements specified in this disclosure.

[0450] It should be noted that the entire contents of Japanese application 2021-162397 are incorporated into this specification by reference.

[0451] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent as those documents, patent applications and technical standards specifically described therein.

[0452] Explanation of symbols

[0453] 5a, 5b Lateral angles

[0454] 6 steel plates (upper plate)

[0455] 7. Steel plate (bottom plate)

[0456] 8 Welding Metal

Claims

1. A flux-cored welding wire, comprising a steel sheath and flux filling the interior of the steel sheath, for welding. The metallic composition of the flux-cored wire, expressed as a percentage by mass relative to the total mass of the flux-cored wire, is as follows: C：0.020～0.800％、 Si: 0.20–0.80% Mn: 15.0~30.0% P：0～0.050％、 S：0～0.050％、 Cu: 0–10.0% Ni: 1.0~10.0% Cr：0～2.0％、 Mo: 0–10.0% Nb: 0–5.0% V：0～5.0％、 W：0～10.0％、 Mg: 0–1.00% Al：0～3.0％、 Ca: 0–0.100% Ti: 0~3.000% B：0～0.1000％、 REM: 0~0.100% Bi: 0~0.050% N：0.050～1.000％、 O: 0–0.020%, and Remaining components: Fe and impurities. The oxides and fluorides in the chemical composition of the flux-cored wire, expressed as a percentage by mass relative to the total mass of the flux-cored wire, are as follows: The total converted value of TiO2 for Ti oxides is 3.00% to 8.00%. The total SiO2 conversion value of Si oxides is 0.10% to 1.00%. The total ZrO2 conversion value of Zr oxides is 0–0.80%. The total conversion value of Al oxides to Al2O3 is 0–0.80%. Containing one or more specific fluorides selected from K₂SiF₆, K₂ZrF₆, NaF, Na₃AlF₆, CaF₂, and MgF₂, in total amounts of 0.10–2.00%. The total amount of Na-containing compounds, including any one or more of Na oxides, NaF, and Na3AlF6, is 0.01% to 2.00%, where Na oxides are converted from Na2O. The total amount of K-containing compounds, including K oxide, K2SiF6 and K2ZrF6, is 0.01 to 2.00%, where K oxide is the equivalent of K2O.

2. The flux-cored welding wire according to claim 1, wherein, The total content of Mg, Al and Ca in the metal composition is 0.01% or more by mass% relative to the total mass of the flux-cored wire.

3. The flux-cored welding wire according to claim 1 or claim 2, wherein, The Si content in the metal composition is 0.25-0.80%.

4. The flux-cored welding wire according to any one of claims 1 to 3, wherein, The mass ratio of the Mn content to the Ni content in the metal composition, i.e., Mn / Ni, is 1.20 or higher.

5. The flux-cored welding wire according to any one of claims 1 to 4, wherein, The value of X calculated using the following formula A ranges from 0.10 to 160.

00. X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO) Formula A In Formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 represent the content of each compound represented by its chemical formula, expressed as a percentage of mass relative to the total mass of the flux-cored wire. Furthermore, SiO2 represents the total SiO2 conversion value of Si oxides, Al2O3 represents the total Al2O3 conversion value of Al oxides, ZrO2 represents the total ZrO2 conversion value of Zr oxides, MgO represents the total MgO conversion value of Mg oxides, CaO represents the total CaO conversion value of Ca oxides, Na2O represents the total Na2O conversion value of Na oxides, K2O represents the total K2O conversion value of K oxides, MnO2 represents the total MnO2 conversion value of Mn oxides, and FeO represents the total FeO conversion value of Fe oxides. Furthermore, the conversion values ​​of SiO2, Al2O3, ZrO2, MgO, CaO, Na2O, K2O, MnO2, and FeO in Formula A are expressed as mass% relative to the total mass of the flux-cored wire.

6. The flux-cored welding wire according to any one of claims 1 to 5, wherein it contains one or more Mg-containing compounds selected from Mg oxide and MgF2, the total of which is 0.01 to 2.00%, wherein the Mg oxide is the equivalent value of MgO.

7. The flux-cored welding wire according to any one of claims 1 to 6, wherein, The steel outer skin does not have welded sections at the seams.

8. The flux-cored wire according to any one of claims 1 to 6, wherein, The steel outer skin has welded sections at the seams.

9. The flux-cored welding wire according to any one of claims 1 to 8, wherein the surface is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.

10. A method for manufacturing a welded joint, comprising the step of welding steel using any one of claims 1 to 9 with flux-cored welding wire.

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