Coated electrode, welded joint and welded metal

Abstract

Provided is a coated electrode for use in the welding of a structure in an extremely low-temperature region, said coated electrode being capable of obtaining a weld metal having excellent strength and an amount of lateral bulge equal to or greater than a desired value. Provided is a coated welding rod containing 0.001 to 0.400 mass% of Nb, 0.001 to 0.400 mass% of V, and 0.001 to 0.020 mass% of N, in which the contents of Fe, C, Cr, Ni and the like are defined with respect to the total mass of the welding rod. In addition, the value A1 is more than 0.120 and less than 0.500, and the value A2 is less than 0.10. In addition, A1 = [Nb] W + [V] W, A2 = 1.22 * ([Cr] W + [Mo] W + 0.7 * [Nb] W)-([Ni] W + 35 * [C] W + 20 * [N] W + 0.25 * [Cu] W)-10.0. In this connection, [Element] W is the value represented by mass% of the content of the element in the coated electrode.

Description

Technical Field

[0001] This invention relates to flux-coated welding electrodes, welding joints, and welding metals. Background Technology

[0002] Generally, gases are liquefied at low temperatures and stored in tanks to improve transportation and storage efficiency. Therefore, the structural components of storage tanks are required to have low-temperature toughness within the liquefaction temperature range of the stored gas. For example, Patent Document 1 discloses a low-temperature stainless steel welding electrode for welding stainless steel plates.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2-205293 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In recent years, the demand for hydrogen has increased due to environmental concerns and the consideration of using hydrogen as fuel for power generation and automobiles. Consequently, the requirements for storage tanks, specifically those capable of safely storing liquefied hydrogen, have also risen. Specifically, there is a need for operation at extremely low temperatures, such as -253°C or higher, than those typically used in liquefied hydrogen storage tanks. Therefore, there is a desire to develop a flux-coated welding electrode capable of welding structures in even lower temperature ranges. The transverse bulge value is required as an indicator of the low-temperature toughness of the weld metal used in such cryogenic storage tanks. However, the flux-coated welding electrode described in Patent Document 1 does not consider transverse bulge.

[0008] The present invention addresses these problems and aims to provide a flux-coated electrode for welding structures in extremely low temperature regions, which produces weld metal with excellent strength and a transverse bulge exceeding the expected value, as well as a weld joint and weld metal obtained using the flux-coated electrode.

[0009] Problem-solving methods

[0010] Through repeated and dedicated research, the inventors discovered that, in order to obtain weld metal exhibiting excellent strength and transverse bulge in extremely low temperature regions, it is effective to control the combined amount of Nb and V in the welding electrode, and to ensure that the values ​​obtained using the calculation formulas for Cr and Ni equivalents are within a specified range, thereby controlling the ferrite content. This invention is based on the above insights.

[0011] The above-mentioned objective of the present invention can be achieved by the following [1] configuration involving the coated welding electrode.

[0012] [1] A flux-coated welding electrode, characterized in that, relative to the total mass of the electrode, it contains:

[0013] Fe: ≥30% by mass and ≤55% by mass

[0014] C: ≥0.001% by mass and ≤0.020% by mass (excluding C from carbonates)

[0015] Cr: ≥10.0% by mass and ≤30.0% by mass

[0016] Ni: 6.0% by mass or more and 20.0% by mass or less

[0017] Nb: ≥0.001% by mass and ≤0.400% by mass

[0018] V: ≥0.001% by mass and ≤0.400% by mass, and

[0019] N: ≥0.001% by mass and ≤0.020% by mass, and

[0020] Mo: less than 4.0% by mass

[0021] Cu: less than 0.50% by mass

[0022] The value A1 calculated by the following formula (1) is: above 0.120 and below 0.500.

[0023] The value A2 calculated by the following formula (2) is less than 0.10.

[0024] A1 = [Nb] W + [V] W …Formula (1)

[0025] A2 = 1.22 × ([Cr]) W + [Mo] W +0.7 × [Nb] W )-([Ni] W +35×[C] W +20×[N] W +0.25×[Cu] W )-10.0 …Formula (2)

[0026] Among them, [Nb] W [V] is the Nb content in the coated welding electrode expressed as a percentage by mass. W This is the V content in the coated welding electrode, expressed as a percentage by mass, [Cr]. W This is the Cr content in the coated welding electrode, expressed as a percentage by mass, [Mo]. W This is the Mo content in the coated welding electrode, expressed as a percentage by mass ([Ni]).W This is the Ni content in the coated welding electrode, expressed as a percentage by mass. [C] W This is the carbon content in the coated welding electrode, expressed as a percentage by mass, [N]. W This is the nitrogen content in the coated welding electrode, expressed as a percentage by mass, [Cu]. W It is the Cu content in the coated welding electrode, expressed as a percentage by mass.

[0027] Furthermore, regarding the preferred embodiments of the present invention relating to coated welding electrodes, see [2] to [3] below.

[0028] [2] According to the flux-coated electrode described in [1], it is characterized in that, relative to the total mass of the electrode, it further comprises:

[0029] F: ≥0.50% by mass and ≤3.00% by mass

[0030] Ca: ≥3.0% by mass and ≤9.0% by mass

[0031] Mn: ≥0.1% by mass and ≤6.0% by mass

[0032] TiO2: ≥5.0% by mass and ≤25.0% by mass

[0033] Conversion values ​​for SiO2 between metallic Si and Si compounds: 3.0% by mass and 8.0% by mass.

[0034] Na: ≥0.05% by mass and ≤0.50% by mass, and

[0035] K: ≥0.05% by mass and ≤1.50% by mass, and

[0036] ZrO2 conversion values ​​for metallic Zr and Zr compounds: below 2.0% by mass

[0037] Conversion value of metallic Mg and Mg compound MgO: less than 1.0% by mass

[0038] P: less than 0.030% by mass

[0039] S: less than 0.030% by mass

[0040] Co: less than 0.30% by mass

[0041] W: less than 0.50% by mass

[0042] REM: less than 0.50% by mass

[0043] Ti: less than 1.0% by mass

[0044] Al: less than 0.3% by mass

[0045] Al2O3: less than 2.0% by mass

[0046] Li: less than 0.50% by mass.

[0047] [3] The coated welding electrode according to [1] or [2] is characterized in that,

[0048] The Ni content is 7.0% by mass or more and 10.0% by mass or less.

[0049] The Cr content is 12.0% by mass or more and 15.0% by mass or less.

[0050] The Mo content is 1.0% by mass or more and 2.0% by mass or less.

[0051] The above-mentioned objective of the present invention can be achieved by the following [4] configuration relating to the welded joint.

[0052] [4] A welded joint, characterized in that it is manufactured by welding with a stainless steel plate as the base material and using any one of the flux-coated electrodes described in [1] to [3].

[0053] The above-mentioned objective of the present invention can be achieved by the following [5] configuration involving the weld metal.

[0054] [5] A welding metal, characterized in that, relative to the total mass of the welding metal, it contains

[0055] C: ≥0.001% by mass and ≤0.040% by mass

[0056] Cr: ≥14.0% by mass and ≤22.0% by mass

[0057] Ni: ≥7.0% by mass and ≤18.0% by mass

[0058] Mn: ≥0.3% by mass and ≤3.0% by mass

[0059] Nb: ≥0.001% by mass and ≤0.400% by mass, and

[0060] V: ≥0.001% by mass and ≤0.400% by mass

[0061] N: ≥0.001% by mass and ≤0.050% by mass, and

[0062] Si: less than 1.0% by mass

[0063] Ti: less than 1.0% by mass

[0064] Mo: less than 4.0% by mass

[0065] Cu: less than 0.50% by mass

[0066] The balance consists of Fe and unavoidable impurities, and...

[0067] The value A3 calculated by the following formula (3) is: above 0.120 and below 0.500, and

[0068] The value A4 calculated by the following formula (4) is below 9.40.

[0069] A3 = [Nb] M + [V] M …Formula (3)

[0070] A4 = 1.22 × ([Cr]) M + [Mo] M +0.7 × [Nb] M )-([Ni] M +35×[C] M +20×[N] M +0.25×[Cu] M ...Equation (4)

[0071] Among them, [Nb] M [V] is the Nb content in the weld metal expressed as a percentage by mass. M This is the V content in the weld metal expressed as a percentage by mass, [Cr]. M This is the Cr content in the welding metal expressed as a percentage by mass, [Mo]. M This is the Mo content in the weld metal expressed as a percentage by mass, [Ni]. M This is the Ni content in the welding metal expressed as a percentage by mass, [C]. M It is the carbon content in the weld metal expressed as a percentage by mass, [N]. M This is the nitrogen content in the welding metal expressed as a percentage by mass, [Cu]. M It is the Cu content in the welding metal expressed as a percentage by mass.

[0072] Furthermore, regarding the preferred embodiments of the present invention relating to welded metals, see [6] below.

[0073] [6] The welding metal according to [5] is characterized in that,

[0074] P: less than 0.030% by mass

[0075] S: less than 0.030% by mass

[0076] Co: less than 0.500% by mass

[0077] W: less than 0.50% by mass

[0078] The Ni content is 12.0% by mass or more and 14.0% by mass or less.

[0079] The Cr content is 17.0% by mass or more and 19.0% by mass or less.

[0080] The Mo content is 1.7% by mass or more and 2.5% by mass or less.

[0081] The effects of the invention

[0082] According to the present invention, a flux-coated welding electrode can be provided, resulting in weld metal with excellent strength and a transverse bulge exceeding a desired value. Furthermore, according to the present invention, a weld joint can be provided that is suitable for use in extremely low-temperature environments by using the flux-coated welding electrode. Moreover, according to the present invention, a weld metal with excellent strength and a transverse bulge exceeding a desired value can be provided. Detailed Implementation

[0083] The following is a detailed description of the methods for carrying out the present invention. However, the present invention is not limited to the embodiments described below.

[0084] [Chemical Coated Welding Electrode]

[0085] The flux-coated welding electrode of this embodiment is composed of a steel core coated with flux. This flux-coated welding electrode controls the content of Fe, C, Cr, Ni, Nb, V, Mo, Cu, and N in the electrode, and controls the combined content of Nb and V, along with the value calculated using a specific formula for the content of Cr, Mo, Nb, Ni, C, N, and Cu, within a specified range.

[0086] The following is a detailed description of the components contained in the coated welding electrode of this embodiment. Also, in this specification, the coated welding electrode is sometimes simply referred to as a welding electrode.

[0087] <Fe: 30% by mass or more and 55% by mass or less>

[0088] Fe is the main component of the core of the welding electrode according to this embodiment. The Fe content in the welding electrode is 30% by mass or more, preferably 31.5% by mass or more, and more preferably 33% by mass or more. On the other hand, the Fe content relative to the total mass of the welding electrode is 55% by mass or less, preferably 50% by mass or less, and more preferably 45% by mass or less.

[0089] <C: ≥0.001% by mass and ≤0.020% by mass>

[0090] Carbon (C) is an element that increases the tensile strength of weld metal. However, it segregates in the final solidification phase of the weld metal, lowering the melting point of the molten metal and deteriorating its resistance to hot cracking. If the C content in the welding electrode is less than 0.001% by mass, weld metal with good tensile strength cannot be obtained. Therefore, the C content relative to the total mass of the welding electrode is 0.001% by mass or more, preferably 0.003% by mass or more, and more preferably 0.005% by mass or more. On the other hand, if the C content in the welding electrode is higher than 0.020% by mass, the susceptibility to hot cracking increases. Therefore, the C content relative to the total mass of the welding electrode is 0.020% by mass or less, preferably 0.016% by mass or less, and more preferably 0.013% by mass or less. Furthermore, the C content specified in this embodiment is the value excluding C contained in the welding electrode as carbonate.

[0091] <Cr: ≥10.0% by mass and ≤30.0% by mass>

[0092] Cr is a component that improves the strength of the weld metal and stabilizes the ferrite phase. When the Cr content in the welding electrode is less than 10.0% by mass, weld metal with sufficient strength cannot be obtained. Therefore, the Cr content relative to the total mass of the welding electrode is 10.0% by mass or more, preferably 11.0% by mass or more, and more preferably 12.0% by mass or more. On the other hand, if the Cr content in the welding electrode is higher than 30.0% by mass, the toughness of the weld metal deteriorates, and Cr solidification segregation is promoted, resulting in poor resistance to hot cracking. Therefore, the Cr content relative to the total mass of the welding electrode is 30.0% by mass or less, preferably 20.0% by mass or less, and more preferably 15.0% by mass or less.

[0093] <Ni: 6.0% by mass or more and 20.0% by mass or less>

[0094] Ni is a component that has the effect of stabilizing the austenitic structure. When the Ni content in the welding electrode is less than 6.0% by mass, the austenitic structure is unstable. Therefore, the Ni content relative to the total mass of the welding electrode is 6.0% by mass or more, preferably 6.4% by mass or more, more preferably 6.8% by mass or more, and even more preferably 7.0% by mass or more. On the other hand, if the Ni content in the welding electrode is higher than 20.0% by mass, the solid solubility of C and N decreases, and porosity is more likely to occur. Therefore, the Ni content relative to the total mass of the welding electrode is 20.0% by mass or less, preferably 16.0% by mass or less, more preferably 12.0% by mass or less, and even more preferably 10.0% by mass or less.

[0095] <Nb: ≥0.001% by mass and ≤0.400% by mass>

[0096] Nb is a component that generates carbides, reducing the amount of dissolved carbon and thus increasing the absorption work and transverse expansion. In this embodiment, particularly with the aim of achieving a transverse expansion of the desired value or higher, it is necessary to properly control the content of Nb and V (described later). If the Nb content in the electrode is less than 0.001% by mass, the desired transverse expansion cannot be obtained. Therefore, the Nb content relative to the total mass of the electrode is 0.001% by mass or more, preferably 0.02% by mass or more, and more preferably 0.10% by mass or more. On the other hand, if the Nb content in the electrode is higher than 0.400% by mass, the toughness of the weld metal decreases. Therefore, the Nb content relative to the total mass of the electrode is 0.400% by mass or less, preferably 0.300% by mass or less, and more preferably 0.200% by mass or less.

[0097] <V: ≥0.001% by mass and ≤0.400% by mass>

[0098] Like Nb, V is a component that reduces the amount of dissolved C by forming carbides, thus increasing the absorption work and transverse expansion. To achieve the desired transverse expansion, the V content needs to be properly controlled. If the V content in the welding electrode is less than 0.001% by mass, the desired transverse expansion cannot be obtained. Therefore, the V content relative to the total mass of the welding electrode is 0.001% by mass or more, preferably 0.050% by mass or more, and more preferably 0.080% by mass or more. On the other hand, if the V content in the welding electrode is higher than 0.400% by mass, the toughness of the weld metal decreases. Therefore, the V content relative to the total mass of the welding electrode is 0.400% by mass or less, preferably 0.300% by mass or less, and more preferably 0.200% by mass or less.

[0099] <N: ≥0.001% by mass and ≤0.020% by mass>

[0100] Nitrogen (N) is a solid solution strengthening element that improves the strength of weld metal. The N content relative to the total mass of the welding electrode is 0.001% by mass or more, preferably 0.003% by mass or more, and more preferably 0.005% by mass or more. On the other hand, if the N content is higher than 0.020% by mass, the absorbed work of the weld metal decreases. Therefore, the N content relative to the total mass of the welding electrode is 0.020% by mass or less, preferably 0.018% by mass or less, and more preferably 0.015% by mass or less.

[0101] <Mo: less than 4.0% by mass>

[0102] Like Cr, Mo is a component that improves the strength of weld metal. However, in the coated electrode of this embodiment, it is not necessary to contain Mo; it can be 0% by mass. However, when Mo is included in the electrode for the purpose of improving the strength of the weld metal, the Mo content relative to the total mass of the electrode is preferably 1.0% by mass or more, more preferably 1.7% by mass or more. On the other hand, if the Mo content in the electrode is higher than 4.0% by mass, the toughness of the weld metal deteriorates, and Mo solidification segregation is promoted, resulting in a deterioration in resistance to hot cracking. Therefore, the Mo content relative to the total mass of the electrode is preferably 4.0% by mass or less, preferably 3.1% by mass or less, more preferably 2.2% by mass or less, and even more preferably 2.0% by mass or less.

[0103] <Cu: less than 0.50% by mass>

[0104] Cu is a component that has the effect of stabilizing the austenitic structure, but in the coated electrode of this embodiment, it is not necessary to contain Cu; it can be 0% by mass. However, when Cu is included in the electrode for the purpose of stabilizing the austenitic structure, the Cu content relative to the total mass of the electrode is preferably 0.001% by mass or more, more preferably 0.005% by mass or more. On the other hand, if the Cu content in the electrode is higher than 0.50% by mass, the hot crack resistance of the weld metal deteriorates. Therefore, the Cu content relative to the total mass of the electrode is 0.50% by mass or less, preferably 0.25% by mass or less, more preferably 0.15% by mass or less.

[0105] <Value A1 calculated by equation (1): ≥0.120 and ≤0.500>

[0106] As mentioned above, Nb and V are components that significantly affect the work absorbed and transverse bulge of the weld metal. Therefore, by controlling the individual contents of Nb and V in the welding electrode and keeping the total content of Nb and V within an appropriate range, the desired transverse bulge can be obtained. If the total content of Nb and V in the welding electrode, i.e., the value A1 calculated by the following formula (1), is less than 0.120, the desired work absorbed and transverse bulge cannot be obtained. Therefore, the value A1 is 0.120 or more, preferably 0.150 or more, and more preferably 0.200 or more. On the other hand, if the value A1 calculated by the following formula (1) is greater than 0.500, the work absorbed by the weld metal decreases. Therefore, the value A1 is 0.500 or less, preferably 0.400 or less, and more preferably 0.300 or less.

[0107] A1 = [Nb] W + [V] W …Formula (1)

[0108] Among them, [Nb] W[V] is the Nb content in the coated welding electrode expressed as a percentage by mass. W It is the V content in the coated welding electrode, expressed as a percentage by mass.

[0109] <Value A2 calculated from equation (2): less than 0.10>

[0110] In this embodiment, by adjusting the parameters of the content of ferrite stabilizing elements Cr, Mo, and Nb in the welding electrode, and the content of austenite stabilizing elements Ni, C, N, and Cu, the ferrite content of the weld metal can be controlled within a desired range. More specifically, the following formula (2) is a formula that subtracts the equivalent amount of Cr (converted to chromium as a ferrite stabilizing element) and the equivalent amount of Ni (converted to nickel as an austenite stabilizing element) from the equivalent amount of Cr (converted to chromium as a ferrite stabilizing element). Therefore, by specifying the value A2 calculated by this formula (2), it is possible to prevent an excess or deficiency of ferrite content and to balance strength and toughness.

[0111] If the value A2 calculated by the following formula (2) is higher than 0.10, then there is too much ferrite, and the transverse bulge of the weld metal is reduced. Therefore, the value A2 is 0.10 or less, preferably 0 or less, more preferably -0.10 or less, and even more preferably -0.20 or less. On the other hand, the lower limit of the value A2 is not particularly limited, but it is preferably -2.0 or more, more preferably -1.2 or more.

[0112] A2 = 1.22 × ([Cr]) W + [Mo] W +0.7 × [Nb] W )-([Ni] W +35×[C] W +20×[N] W +0.25×[Cu] W )-10.0 …Formula (2)

[0113] Among them, [Cr] W This is the Cr content in the coated welding electrode, expressed as a percentage by mass, [Mo]. W This is the Mo content in the coated welding electrode, expressed as a percentage by mass, [Nb]. W This is the Nb content in the coated welding electrode, expressed as a percentage by mass. [Ni] W This is the Ni content in the coated welding electrode, expressed as a percentage by mass. [C] W This is the carbon content in the coated welding electrode, expressed as a percentage by mass, [N]. W This is the nitrogen content in the coated welding electrode, expressed as a percentage by mass, [Cu]. W It is the Cu content in the coated welding electrode, expressed as a percentage by mass.

[0114] In the coated electrode of this embodiment, if each component is within the above-mentioned content range, the problem of the present invention can be solved. Furthermore, to further improve weldability and the mechanical properties of the weld metal, the electrode preferably also contains F, Ca, Mn, TiO2, metallic Si and Si compounds, Na, and K. Additionally, it is also preferable to specify the content of metallic Zr and Zr compounds, metallic Mg and Mg compounds, P, S, Co, W, REM, Ti, Al, Al2O3, and Li in the total mass of the electrode. The preferred ranges for these contents will be explained below.

[0115] <F: 0.50% by mass or more and 3.00% by mass or less>

[0116] In this embodiment, to suppress sputtering and stabilize the arc, the welding electrode may contain fluorine (F). If the F content in the welding electrode is 0.50% by mass or more, the effects of suppressing sputtering and stabilizing the arc can be achieved. Therefore, when the welding electrode contains F, it is preferable that the F content in the total mass of the welding electrode is 0.50% by mass or more, more preferably 0.80% by mass or more. On the other hand, if the F content in the welding electrode is 3.00% by mass or less, sputtering and fumes can be suppressed. Therefore, the F content in the total mass of the welding electrode is preferably 3.00% by mass or less, more preferably 2.00% by mass or less. Furthermore, F is contained in the form of fluorides such as CaF2 or NaF.

[0117] <Ca: 3.0% by mass or more and 9.0% by mass or less>

[0118] Ca is an element contained in welding electrodes in the form of carbonates or CaF2. Therefore, when the welding electrode contains Ca, the Ca content relative to the total mass of the welding electrode is preferably 3.0% by mass or more, more preferably 3.5% by mass or more, and even more preferably 4.0% by mass or more. In addition, the Ca content in the welding electrode is preferably 9.0% by mass or less, more preferably 8.0% by mass or less, and even more preferably 7.0% by mass or less.

[0119] <Mn: ≥0.1% by mass and ≤6.0% by mass>

[0120] Mn has the effect of suppressing porosity caused by oxidizing gases through deoxidation and also has the effect of stabilizing austenite structure. Therefore, in this embodiment, the welding electrode can contain Mn. If the Mn content in the welding electrode is 0.1% by mass or more, sufficient deoxidation effect can be obtained. Therefore, the amount of Mn added in the total mass of the welding electrode is preferably 0.1% by mass or more, and more preferably 1.5% by mass or more. On the other hand, if the Mn content is 6.0% by mass or less, the solidification segregation of Mn in the final solidification zone of the weld metal can be suppressed, and the occurrence of hot cracking can be suppressed. Therefore, the Mn content in the total mass of the welding electrode is preferably 6.0% by mass or less, and more preferably 5.0% by mass or less.

[0121] <TiO2: 5.0% by mass or more and 25.0% by mass or less>

[0122] TiO2 is the main component of the slag-forming agent, and it has the effect of forming a uniform and well-coated slag, thereby improving arc stability. In addition, TiO2 also increases the melting point of the slag, resulting in a flat weld bead shape in all-position welding. If the TiO2 content in the welding electrode is 5.0% by mass or more, the above-mentioned effects can be fully obtained. Therefore, the TiO2 content relative to the total mass of the welding electrode is preferably 5.0% by mass or more, more preferably 8.0% by mass or more, and even more preferably 10.0% by mass or more. On the other hand, if the TiO2 content in the welding electrode is 25.0% by mass or less, the flux melts easily, and the formation of slag inclusions can be suppressed. Therefore, the TiO2 content relative to the total mass of the welding electrode is preferably 25.0% by mass or less, more preferably 20.0% by mass or less. Furthermore, the term "TiO2 content in the welding electrode" refers to the TiO2 conversion value of the Ti compounds contained in the welding electrode.

[0123] <Conversion value of SiO2 for metallic Si and Si compounds: ≥3.0% by mass and ≤8.0% by mass>

[0124] Si has the effect of improving the strength of weld metal and acting as a binder (water glass) for flux coating. These effects are achieved when the SiO2 conversion value in the welding electrode is 3.0% by mass or more. Therefore, the SiO2 conversion value in the total mass of the welding electrode is preferably 3.0% by mass or more, more preferably 3.5% by mass or more. On the other hand, if the SiO2 conversion value in the welding electrode is 8.0% by mass or less, it can prevent the deterioration of hot crack resistance. Therefore, the SiO2 conversion value in the total mass of the welding electrode is preferably 8.0% by mass or less, more preferably 7.0% by mass or less. Furthermore, the SiO2 conversion value is the value of SiO2 converted from the total amount of Si monomers, Si alloys, and Si compounds contained in the welding electrode.

[0125] <Na: ≥0.05% by mass and ≤0.50% by mass>

[0126] Alkali metals such as sodium (Na) are components that improve arc stability and can be contained in welding electrodes as fluorides or complex oxides. If the Na content in the welding electrode is 0.05% by mass or more, the improved arc stability can be achieved. Therefore, the Na content relative to the total mass of the welding electrode is preferably 0.05% by mass or more, more preferably 0.10% by mass or more. On the other hand, if the Na content in the welding electrode is 0.50% by mass or less, the decrease in the melting point of the slag can be suppressed, resulting in a good weld bead shape in all-position welding. Therefore, the Na content relative to the total mass of the welding electrode is preferably 0.50% by mass or less, more preferably 0.40% by mass or less. Furthermore, Na may exist in the welding electrode, for example, as Na₂O.

[0127] <K: 0.05% by mass or more and 1.50% by mass or less>

[0128] Alkali metals such as potassium (K), like sodium (Na) mentioned above, are components that improve arc stability and can be contained in welding electrodes as fluorides or complex oxides. If the K content in the welding electrode is 0.05% by mass or more, an improved arc stability effect can be obtained. Therefore, the K content relative to the total mass of the welding electrode is preferably 0.05% by mass or more, more preferably 0.5% by mass or more. On the other hand, if the K content in the welding electrode is 1.50% by mass or less, the decrease in the melting point of the slag can be suppressed, resulting in a good weld bead shape in all-position welding. Therefore, the K content relative to the total mass of the welding electrode is preferably 1.50% by mass or less, more preferably 1.20% by mass or less. Furthermore, K may exist in the welding electrode, for example, as K₂O or K₂SiF₆.

[0129] <ZrO2 conversion values ​​for metallic Zr and Zr compounds: less than 2.0% by mass>

[0130] ZrO2 is a component that accelerates slag solidification and has the effect of forming a flat weld bead shape in both vertical and overhead welding positions. However, the ZrO2 conversion value in the welding electrode can also be 0% by mass. Furthermore, if the ZrO2 conversion value in the welding electrode is 2.0% by mass or less, good slag coating and slag peeling properties can be obtained. Therefore, the ZrO2 conversion value relative to the total mass of the welding electrode is preferably 2.0% by mass or less, more preferably 1.0% by mass or less. In this embodiment, the ZrO2 conversion value is the value of all Zr contained in metallic Zr and Zr compounds converted into ZrO2. Metallic Zr refers to the total amount of Zr contained in Zr monomers and Zr alloys. Zr compounds refer to Zr oxides, etc. In the following description, "metal" means monomer or alloy, and "compound" means oxide, etc.

[0131] <Conversion value of MgO between metallic Mg and Mg compounds: less than 1.0% by mass>

[0132] Metallic Mg and Mg compounds are components that raise the solidification point of slag and improve arc stability, but the MgO conversion value in the welding electrode can also be 0% by mass. If the MgO conversion value is 1.0% by mass or less, it is possible to prevent the deterioration of the weld bead shape. Therefore, the MgO conversion value is preferably 1.0% by mass or less, more preferably 0.8% by mass or less. Furthermore, in this embodiment, the MgO conversion value is the value of all Mg contained in metallic Mg and Mg compounds converted into MgO. In addition, metallic Mg means the total amount of Mg contained in Mg monomers and Mg alloys.

[0133] <P: less than 0.030% by mass>

[0134] Phosphorus (P) is an unavoidable impurity in welding electrodes. The higher the P content in the weld metal, the lower the low-temperature toughness; therefore, the lower the P content in the welding electrode, the better. Thus, the P content relative to the total mass of the welding electrode is preferably 0.030% by mass or less, more preferably 0.025% by mass or less.

[0135] <S: less than 0.030% by mass>

[0136] Like phosphorus (P), sulfur (S) is an unavoidable impurity in welding electrodes. The higher the S content in the weld metal, the lower the low-temperature toughness; therefore, the lower the S content in the welding electrode, the better. Thus, the S content relative to the total mass of the welding electrode is preferably 0.030% by mass or less, more preferably 0.020% by mass or less.

[0137] <Co: less than 0.30% by mass>

[0138] Co is a component that adjusts the toughness of weld metal, and the presence of Co in the welding electrode can be adjusted as needed. If the Co content in the welding electrode is 0.30% by mass or less, the reduction in the strength of the weld metal can be suppressed. Therefore, the Co content relative to the total mass of the welding electrode is preferably 0.30% by mass or less, and more preferably 0.20% by mass or less.

[0139] <W: less than 0.50% by mass>

[0140] W is a solid solution strengthening element in steel, which is dissolved in the weld metal and has the effect of improving the strength of the weld metal. W can be included in welding electrodes as needed. If the W content in the welding electrode is 0.50% by mass or less, it can suppress the deterioration of toughness. Therefore, the W content relative to the total mass of the welding electrode is preferably 0.50% by mass or less, more preferably 0.1% by mass or less.

[0141] <REM: less than 0.50% by mass>

[0142] REM (rare earth elements) are deoxidizing elements, so the presence of REM in welding electrodes can be adjusted as needed. However, if the REM content in the welding electrode is 0.50% by mass or less, the reduction in weldability can be suppressed. Therefore, the REM content relative to the total mass of the welding electrode is preferably 0.50% by mass or less, more preferably 0.10% by mass or less. Furthermore, REM refers to the 15 lanthanide rare earth elements from La to Lu in the periodic table. These elements can be added individually or in combination.

[0143] <Ti: less than 1.0% by mass>

[0144] Ti is a component that improves the toughness of weld metal, and therefore, welding electrodes can be made to contain Ti as needed. If the Ti content in the welding electrode is 1.0% by mass or less, the oxygen content in the weld metal can be reduced, and the toughness of the weld metal can be adjusted to the desired range. Therefore, the Ti content relative to the total mass of the welding electrode is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. Furthermore, the term "Ti content in the welding electrode" refers to the content of Ti monomers and all metallic Ti contained in the Ti alloy contained in the welding electrode.

[0145] <Al: less than 0.3% by mass>

[0146] Al has a deoxidizing effect and stabilizes the toughness of the weld metal; therefore, welding electrodes can be made to contain Al as needed. If the Al content in the welding electrode is 0.3% by mass or less, the yield of alloying elements in the weld metal can be appropriately adjusted, suppressing excessive strength gain. Therefore, the Al content relative to the total mass of the welding electrode is preferably 0.3% by mass or less, more preferably 0.1% by mass or less. Furthermore, the term "Al content in the welding electrode" refers to the content of all metallic Al contained in the Al monomers and Al alloys within the welding electrode.

[0147] <Al2O3: less than 2.00% by mass>

[0148] Al2O3 is a slag-forming agent, a component that improves weld bead shape; therefore, it can be included in the welding electrode as needed. If the Al2O3 content in the welding electrode is 2.00% by mass or less, good slag removal properties can be obtained. Therefore, the Al2O3 content relative to the total mass of the welding electrode is preferably 2.00% by mass or less, more preferably 1.50% by mass or less. Furthermore, the term "Al2O3 content in the welding electrode" refers to the Al value of Al compounds such as Al oxides contained in the welding electrode converted to Al2O3.

[0149] <Li: less than 0.50% by mass>

[0150] Alkali metals such as Li, like Na and K mentioned above, are components that improve arc stability and can be included in welding electrodes as fluorides or complex oxides. Furthermore, if the Li content in the welding electrode is 0.50% by mass or less, it can suppress the decrease in the melting point of the slag and result in a good weld bead shape in all-position welding. Therefore, the Li content relative to the total mass of the welding electrode is preferably 0.50% by mass or less, and more preferably 0.20% by mass or less.

[0151] <Surplus of coated welding rods>

[0152] The flux-coated welding electrode of this embodiment, as an essential component, may contain Fe, C, Cr, Ni, Nb, V, and N, and also Mo and Cu. The total content of these components relative to the total mass of the electrode is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. Additionally, the electrode may also contain Si, F, Mn, TiO2, ZrO2, MgO, Na, K, P, S, Co, W, REM, Ti, Al, Al2O3, Li, etc. Furthermore, in the flux-coated welding electrode, it is preferable that these components, together with the aforementioned essential components, total 85% by mass or more, more preferably 90% by mass or more, and even more preferably 92% by mass or more. Moreover, as a balance of the aforementioned components, the flux-coated welding electrode may contain, for example, CO2 contained in carbonates such as Ba, Ta, Bi, and CaCO3. The carbonates decompose due to the heat energy during welding, generating CO2 gas. Since the CO2 component from the decomposition does not contribute to the mechanical properties of the weld metal, in this embodiment, the CO2 component from the carbonate is treated as a surplus. When the coated electrode of this embodiment contains CO2, it is preferable that the CO2 content is in the range of 0.5% by mass or more and 3.0% by mass or less relative to the total mass of the electrode.

[0153] The manufacturing method of the coated electrode in this embodiment is not particularly limited and can be manufactured by a conventional manufacturing process. There are no particular restrictions on the materials of the core and the flux coating; stainless steel or similar materials can be used. The content of each component in the total weight of the coated electrode can be controlled within the aforementioned range.

[0154] The flux-coated welding electrode of this embodiment is, for example, suitable for welding low-temperature steels such as 5% Ni steel and various austenitic stainless steels.

[0155] [Welded joint]

[0156] The welded joint of this embodiment is manufactured by welding stainless steel plate as the base material using the above-mentioned flux-coated welding rod.

[0157] [Welding metal]

[0158] The weld metal of this embodiment, for example, is formed by welding using the aforementioned coated welding electrode, and exhibits excellent strength and transverse bulge. Hereinafter, the components and their contents contained in the weld metal of this embodiment will be described in detail. Furthermore, the total amount of each element contained in the weld metal within a specified region unaffected by the composition of the base material will be defined as the content value in the total mass of the weld metal. Hereinafter, the content of each component in the weld metal of this embodiment will be explained.

[0159] <C: ≥0.001% by mass and ≤0.040% by mass>

[0160] Carbon (C) is a component in weld metal that stabilizes the austenitic phase, making it difficult for it to transform into the martensitic phase. Furthermore, C also contributes to increasing the strength of the weld metal. If the C content in the weld metal is less than 0.001% by mass, weld metal with good tensile strength cannot be obtained. Therefore, the C content relative to the total mass of the weld metal is 0.001% by mass or more, preferably 0.005% by mass or more, and more preferably 0.010% by mass or more. On the other hand, if the C content in the weld metal is higher than 0.040% by mass, the strength increases excessively, making it difficult to obtain excellent low-temperature toughness. Therefore, the C content relative to the total mass of the weld metal is 0.040% by mass or less, preferably 0.035% by mass or less, and more preferably 0.030% by mass or less.

[0161] <Cr: ≥14.0% by mass and ≤22.0% by mass>

[0162] Cr is a component in weld metal that stabilizes the ferrite phase, making it difficult for it to transform into the martensitic phase. If the Cr content in the weld metal is less than 14.0% by mass, the ferrite phase is unstable, and excellent low-temperature toughness cannot be obtained. Therefore, the Cr content relative to the total mass of the weld metal is 14.0% by mass or more, preferably 16.0% by mass or more, and more preferably 17.0% by mass or more. On the other hand, if the Cr content in the weld metal is higher than 22.0% by mass, the ferrite phase is over-stabilized, and the low-temperature toughness decreases. Therefore, the Cr content relative to the total mass of the weld metal is 22.0% by mass or less, preferably 20.0% by mass or less, and more preferably 19.0% by mass or less.

[0163] <Ni: 7.0% by mass or more and 18.0% by mass or less>

[0164] Ni is a component in weld metal that stabilizes the austenite phase, making it difficult for it to transform into the martensitic phase. If the Ni content in the weld metal is less than 7.0% by mass, the austenite phase is unstable, and the ultra-low temperature toughness decreases. Therefore, the Ni content relative to the total mass of the weld metal is 7.0% by mass or more, preferably 10.0% by mass or more, and more preferably 12.0% by mass or more. On the other hand, if the Ni content in the weld metal is higher than 18.0% by mass, the austenite phase is over-stabilized, and excellent ultra-low temperature toughness cannot be obtained. Therefore, the Ni content in the weld metal is 18.0% by mass or less, preferably 16.0% by mass or less, and more preferably 14.0% by mass or less.

[0165] <Mn: ≥0.3% by mass and ≤3.0% by mass>

[0166] Mn is an austenite stabilizing element and acts as a deoxidizer to remove oxygen from the weld metal as slag, thus improving mechanical strength. If the Mn content in the weld metal is less than 0.3% by mass, the deoxidation effect is insufficient, the oxygen content in the weld metal increases, and therefore excellent low-temperature toughness cannot be obtained. Therefore, the Mn content relative to the total mass of the weld metal is 0.3% by mass or more, preferably 0.4% by mass or more, and more preferably 0.5% by mass or more. On the other hand, if the Mn content in the weld metal is higher than 3.0% by mass, the strength of the weld metal increases excessively, and the low-temperature toughness decreases. Therefore, the Mn content relative to the total mass of the weld metal is 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less.

[0167] <Nb: ≥0.001% by mass and ≤0.400% by mass>

[0168] Nitrogen (Nb) is a component that forms carbides in the weld metal, reducing the amount of dissolved carbon (C) and thus increasing the absorbed work and transverse bulge. If the Nb content in the weld metal is less than 0.001% by mass, the desired transverse bulge cannot be obtained. Therefore, the Nb content relative to the total mass of the weld metal is 0.001% by mass or more, preferably 0.010% by mass or more, and more preferably 0.020% by mass or more. On the other hand, if the Nb content in the weld metal is higher than 0.400% by mass, the tensile strength of the weld metal decreases. Therefore, the Nb content relative to the total mass of the weld metal is 0.400% by mass or less, preferably 0.200% by mass or less, and more preferably 0.100% by mass or less.

[0169] <V: ≥0.001% by mass and ≤0.400% by mass>

[0170] Like Nb, V is a component that generates carbides in the weld metal, reducing the amount of dissolved C and thus increasing the absorbed work and transverse bulge. If the V content in the weld metal is less than 0.001% by mass, the desired transverse bulge cannot be obtained. Therefore, the V content relative to the total mass of the weld metal is 0.001% by mass or more, preferably 0.010% by mass or more, and more preferably 0.050% by mass or more. On the other hand, if the V content in the weld metal is higher than 0.400% by mass, the tensile strength of the weld metal decreases. Therefore, the V content relative to the total mass of the weld metal is 0.400% by mass or less, preferably 0.300% by mass or less, and more preferably 0.200% by mass or less.

[0171] <N: ≥0.001% by mass and ≤0.050% by mass>

[0172] Nitrogen (N) is a component in weld metal that stabilizes the austenitic phase, making it difficult for it to transform into the martensitic phase. Additionally, N contributes to the increased strength of the weld metal. Ideally, N should be 0.001% by mass or more. If the N content in the weld metal exceeds 0.050% by mass, the strength increases excessively, making it difficult to obtain excellent low-temperature toughness. Therefore, the N content relative to the total mass of the weld metal should be 0.050% by mass or less, preferably 0.040% by mass or less, and more preferably 0.035% by mass or less.

[0173] <Si: less than 1.0% by mass>

[0174] Si is a component that promotes deoxidation, but in the weld metal of this embodiment, Si may be absent or may be 0% by mass. When Si is included in the weld metal to ensure the strength and low-temperature toughness of the weld metal, the Si content in the weld metal is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, relative to the total mass of the weld metal. On the other hand, if the Si content in the weld metal is higher than 1.0% by mass, the crystal strength of the weld metal is reduced, and excellent low-temperature toughness cannot be obtained. Therefore, the Si content relative to the total mass of the weld metal is 1.0% by mass or less, preferably 0.8% by mass or less, more preferably 0.7% by mass or less.

[0175] <Ti: less than 1.0% by mass>

[0176] Ti is a component that improves the toughness of weld metal, but the weld metal in this embodiment may contain no Ti or may contain 0% by mass. On the other hand, if the weld metal contains more than a specified amount of Ti, the strength will increase excessively, resulting in a decrease in toughness. Therefore, the Ti content relative to the total mass of the weld metal is preferably 1.0% by mass or less, preferably 0.05% by mass or less, and more preferably 0.02% by mass or less.

[0177] <Mo: less than 4.0% by mass>

[0178] Mo is a component that improves the strength of weld metal, but in the weld metal of this embodiment, Mo may be absent or may be 0% by mass. When the weld metal contains Mo for the purpose of improving the strength of the weld metal, the Mo content in the weld metal is preferably 1.2% by mass or more, more preferably 1.7% by mass or more, relative to the total mass of the weld metal. On the other hand, if the weld metal contains more than a predetermined amount of Mo, the strength will increase excessively, resulting in a decrease in toughness. Therefore, the Mo content relative to the total mass of the weld metal is preferably 4.0% by mass or less, preferably 3.0% by mass or less, more preferably 2.5% by mass or less.

[0179] <Cu: less than 0.50% by mass>

[0180] Cu is a component that improves the strength of weld metal. In the weld metal of this embodiment, Cu may be absent or may be 0% by mass. On the other hand, if the weld metal contains more than a specified amount of Cu, the strength will increase excessively, resulting in a decrease in toughness. Therefore, the Cu content relative to the total mass of the weld metal is 0.50% by mass or less, preferably 0.30% by mass or less, and more preferably 0.20% by mass or less.

[0181] <The value A3 calculated by the following formula (3): 0.120 or higher and 0.500 or lower>

[0182] As mentioned above, Nb and V are components that significantly affect the work absorbed and transverse bulge of the weld metal. Therefore, by controlling the individual contents of Nb and V in the weld metal and appropriately controlling the total content of Nb and V, the desired transverse bulge can be obtained. If the total content of Nb and V in the weld metal, i.e., the value A3 calculated by the following formula (3), is less than 0.120, the desired work absorbed and transverse bulge cannot be obtained. Therefore, the value A3 is 0.120 or more, preferably 0.130 or more, and more preferably 0.150 or more. On the other hand, if the value A3 calculated by the following formula (3) is greater than 0.500, the tensile strength of the weld metal decreases. Therefore, the value A3 is 0.500 or less, preferably 0.400 or less, and more preferably 0.300 or less.

[0183] A3 = [Nb] M + [V] M …Formula (3)

[0184] Among them, [Nb] M [V] is the Nb content in the weld metal expressed as a percentage by mass. M It is the V content in the welding metal expressed as a percentage by mass.

[0185] <Value A4 calculated by the following formula (4): 9.40 or less>

[0186] In this embodiment, by adjusting the parameters of the content of ferrite stabilizing elements, namely Cr, Mo, and Nb, and the content of austenite stabilizing elements, namely Ni, C, N, and Cu, in the weld metal, the ferrite content of the weld metal can be controlled within a desired range. More specifically, the following formula (4) is a formula that subtracts the equivalent amount of Cr (converted to chromium content as a ferrite stabilizing element) and the equivalent amount of Ni (converted to nickel content as an austenite stabilizing element) from the equivalent amount of Cr (converted to chromium content as a ferrite stabilizing element). Therefore, by specifying the value A4 calculated by this formula (4), it is possible to prevent an excess or deficiency of ferrite content and to balance strength and toughness.

[0187] If the value A4 calculated by the following formula (4) is higher than 9.40, then there is too much ferrite, and the low-temperature toughness and transverse bulging of the weld metal deteriorate. Therefore, the value A4 is 9.40 or less, preferably 9.20 or less, and more preferably 9.00 or less.

[0188] A4 = 1.22 × ([Cr]) M + [Mo] M +0.7 × [Nb] M )-([Ni] M +35×[C] M +20×[N] M +0.25×[Cu] M ...Equation (4)

[0189] Among them, [Cr] M This is the Cr content in the welding metal expressed as a percentage by mass, [Mo]. M This is the Mo content in the weld metal expressed as a percentage by mass, [Nb]. M This is the Nb content in the weld metal expressed as a percentage by mass, [Ni]. M This is the Ni content in the welding metal expressed as a percentage by mass, [C]. M It is the carbon content in the weld metal expressed as a percentage by mass, [N]. M This is the nitrogen content in the welding metal expressed as a percentage by mass, [Cu]. M It is the Cu content in the welding metal expressed as a percentage by mass.

[0190] <Value A5 calculated by the following formula (5): 0.08 or less>

[0191] As mentioned above, C and N are components in weld metal that stabilize the austenitic phase and prevent it from transforming into the martensitic phase. Therefore, by controlling the content of C and N in the weld metal and ensuring that the combined content of C and N is below 0.08, the transverse bulge can be increased.

[0192] A5 = [C]M + "N"M... Equation (5)

[0193] Among them, [C] M It is the carbon content in the weld metal expressed as a percentage by mass, [N]. M It is the value of N content in the welding metal expressed as a percentage by mass.

[0194] <P: less than 0.030% by mass>

[0195] The higher the phosphorus (P) content in the weld metal, the lower its low-temperature toughness; therefore, the lower the P content in the weld metal, the better. Thus, the P content relative to the total mass of the weld metal is preferably 0.030% by mass or less, and more preferably 0.025% by mass or less.

[0196] <S: less than 0.030% by mass>

[0197] Similar to phosphorus (P), the higher the sulfur (S) content in the weld metal, the lower the low-temperature toughness; therefore, the lower the S content in the weld metal, the better. Thus, the S content relative to the total mass of the weld metal is preferably 0.030% by mass or less, more preferably 0.020% by mass or less.

[0198] <Co: less than 0.500% by mass>

[0199] Co is a component that has the effect of adjusting the toughness of weld metal, so the weld metal can be contained in it as needed. If the Co content in the weld metal is 0.500% by mass or less, the reduction in strength can be suppressed. Therefore, when Co is contained in the weld metal, the Co content relative to the total mass of the weld metal is preferably 0.500% by mass or less, more preferably 0.30% by mass or less.

[0200] <W: less than 0.50% by mass>

[0201] W is a component that improves the strength of weld metal, and therefore, the weld metal can be contained in it as needed. However, if the weld metal contains more than a specified amount of W, the strength will increase excessively, resulting in a decrease in toughness. Therefore, the W content relative to the total mass of the weld metal is preferably 0.50% by mass or less, and more preferably 0.10% by mass or less.

[0202] <Balance: Fe and unavoidable impurities>

[0203] In the welding metal of this embodiment, the balance besides the components described above is Fe and unavoidable impurities. Fe is the main component constituting the core of the coated electrode of this embodiment and remains in the welding metal. The Fe content relative to the total mass of the welding metal is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. On the other hand, the Fe content relative to the total mass of the welding metal is preferably 75% by mass or less, more preferably 72% by mass or less, and even more preferably 70% by mass or less. In addition to P and S mentioned above, unavoidable impurities include, for example, O, As, Sb, Sn, Bi, and S. The O content in the welding metal is preferably less than 0.100% by mass relative to the total mass of the welding metal. Furthermore, the total amount of unavoidable impurities other than P, S, and O in the welding metal is preferably 0.20% by mass or less relative to the total mass of the welding metal.

[0204] Example

[0205] The present invention is described in more detail below with examples, but the present invention is not limited to these examples. Modifications may be made to the present invention within the scope that can conform to the spirit of the present invention, and these modifications are all included within the technical scope of the present invention.

[0206] [Preparation of flux-coated welding electrodes]

[0207] Prepare coated electrodes with the compositions shown in Tables 1 to 3 below. The coating rate is 30 to 45% by mass. Also, in Table 1, Equation (1): A1 represents the value A1 calculated by Equation (1), and Equation (2): A2 represents the value A2 calculated by Equation (2). Equations (1) and (2) are as follows.

[0208] A1 = [Nb] W + [V] W …Formula (1)

[0209] A2 = 1.22 × ([Cr]) W + [Mo] W +0.7 × [Nb] W )-([Ni] W +35×[C] W +20×[N] W +0.25×[Cu] W )-10.0 …Formula (2)

[0210] Among them, [Nb] W [V] is the Nb content in the coated welding electrode expressed as a percentage by mass. W This is the V content in the coated welding electrode, expressed as a percentage by mass, [Cr]. WThis is the Cr content in the coated welding electrode, expressed as a percentage by mass, [Mo]. W This is the Mo content in the coated welding electrode, expressed as a percentage by mass ([Ni]). W This is the Ni content in the coated welding electrode, expressed as a percentage by mass. [C] W This is the carbon content in the coated welding electrode, expressed as a percentage by mass, [N]. W This is the nitrogen content in the coated welding electrode, expressed as a percentage by mass, [Cu]. W It is the Cu content in the coated welding electrode, expressed as a percentage by mass.

[0211] [Covered Arc Welding]

[0212] Prepare two 20mm thick carbon steel plates, machine them to a 45° bevel angle, and then use pre-coated welding electrodes to form 2-3 layers of weld overlay between the bevel surface and the backing plate surface, arranging the carbon steel plates in a V-groove configuration. Subsequently, use individual welding electrodes to weld the bevel. Welding conditions are 130A-24V, 8 layers, 20-23 weld passes for flat welding positions.

[0213] [Composition measurement of weld metal]

[0214] For the obtained weld metal, solid-state emission spectroscopy analysis was performed at the same location as the extraction position of the tensile test specimen described later, according to JISG 1253:2002, to measure the composition of each weld metal. The chemical composition content in the weld metal is shown in Tables 4 and 5. Also, in Table 4, Equation (3): A3 represents the value A3 calculated from Equation (3), and Equation (4): A4 represents the value A4 calculated from Equation (4). In Table 5, Equation (5): A5 represents the value A5 calculated from Equation (5). Equations (3) to (5) are as follows. In addition, the balance of the weld metal is Fe and unavoidable impurities.

[0215] A3 = [Nb] M + [V] M …Formula (3)

[0216] A4 = 1.22 × ([Cr]) M + [Mo] M +0.7 × [Nb] M )-([Ni] M +35×[C] M +20×[N] M +0.25×[Cu] M ...Equation (4)

[0217] A5 = [C] M + "N"M... formula (5)

[0218] Among them, [Nb] M [V] is the Nb content in the weld metal expressed as a percentage by mass. M This is the V content in the weld metal expressed as a percentage by mass, [Cr]. M This is the Cr content in the welding metal expressed as a percentage by mass, [Mo]. M This is the Mo content in the weld metal expressed as a percentage by mass, [Ni]. M This is the Ni content in the welding metal expressed as a percentage by mass, [C]. M It is the carbon content in the weld metal expressed as a percentage by mass, [N]. M This is the nitrogen content in the welding metal expressed as a percentage by mass, [Cu]. M It is the Cu content in the welding metal expressed as a percentage by mass.

[0219] [Mechanical property evaluation test]

[0220] (Pendulum impact test)

[0221] According to JIS Z 2242:2023, standard V-notch test pieces were extracted from the obtained weld metal and pendulum impact tests were performed. The test temperature for the pendulum impact test was -196℃, and the pendulum impact value (vE-196℃) and transverse bulge LE (mm) were measured. Furthermore, five test pieces each for measuring the pendulum impact value and transverse bulge were extracted from each weld metal. For both the pendulum impact value and transverse bulge, the maximum and minimum values ​​from the five test results were removed, and the average of the remaining three values ​​was calculated for evaluation.

[0222] (Tension test)

[0223] According to JIS Z 3111:2005, from the obtained weld metal, test piece A0 is extracted from the center of the test piece as the weld centerline, and a tensile test is performed. The test temperature for the tensile test is room temperature (20℃).

[0224] The pendulum impact values, transverse bulge, and tensile strength measurements obtained from the pendulum impact tests are shown in Table 5 below. In all the evaluation tests mentioned above, the average pendulum impact value was 35.0 (J / cm²). 2 A test result meeting the following criteria is acceptable: a transverse bulge of 0.53 mm or more, and a tensile strength of 498 MPa or more. Failure to meet any one of these criteria results in a failing grade. Additionally, the average pendulum impact value must be 40.0 (J / cm²). 2 Those with a transverse bulge of 0.70 mm or more and a tensile strength of 530 MPa or more are considered better.

[0225] Table 1

[0226]

[0227] Table 2

[0228]

[0229] Table 3

[0230]

[0231] Table 4

[0232]

[0233] Table 5

[0234]

[0235] As shown in Tables 1 to 5, in Invention Examples No. 1 to 14, the content of specific components in the welding electrode is properly controlled, and the values ​​A1 and A2 calculated by Equations (1) and (2) are within the range specified in this embodiment. Therefore, in the obtained weld metal, the content of each component and the values ​​A3 and A4 calculated by Equations (3) and (4) are also within the range specified in this embodiment. Therefore, weld metal with excellent mechanical properties, especially with a transverse bulge exceeding the expected value, can be obtained.

[0236] On the other hand, in Comparative Examples No. 1 and 3, the N content in the welding electrodes is higher than the upper limit value specified in this invention, and the value A1 calculated by formula (1) is lower than the lower limit value specified in this invention. In addition, in the weld metal obtained using the welding electrodes of Comparative Examples No. 1 and 3, the value A3 calculated by formula (3) is lower than the lower limit value specified in this invention, and the value A4 calculated by formula (4) is higher than the upper limit value specified in this invention.

[0237] In Comparative Example No. 2, the value A1 calculated by Equation (1) is lower than the lower limit value specified in this invention. In addition, in the weld metal obtained using the welding rod of Comparative Example No. 2, the value A3 calculated by Equation (3) is also lower than the lower limit value specified in this invention, and the value A4 calculated by Equation (4) is higher than the upper limit value specified in this invention.

[0238] Furthermore, in Comparative Example No. 4, the value A2 calculated by Equation (2) is higher than the upper limit value specified in this invention. Additionally, in the weld metal obtained using the welding electrode of Comparative Example No. 4, the value A4 calculated by Equation (4) is higher than the upper limit value specified in this invention.

[0239] Therefore, in comparative examples No. 1 to 4, the results showed low pendulum impact values ​​and low lateral bulges.

[0240] The above descriptions of various embodiments are not limited to these examples. Those skilled in the art will readily conceive of various modifications and alterations within the scope claimed by the patent claims, and these are naturally understood to fall within the technical scope of this invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

[0241] Furthermore, this application is based on Japanese Patent Application No. 2024-006773, filed on January 19, 2024, the contents of which are incorporated herein by reference.

Claims

1. A flux-coated welding electrode, characterized in that, Relative to the total mass of the welding electrode, containing Fe: ≥30% by mass and ≤55% by mass C: ≥0.001% by mass and ≤0.020% by mass Cr: ≥10.0% by mass and ≤30.0% by mass Ni: 6.0% by mass or more and 20.0% by mass or less Nb: ≥0.001% by mass and ≤0.400% by mass V： 0.001% by mass or more and 0.400% by mass or less, and N: ≥0.001% by mass and ≤0.020% by mass, and Mo: less than 4.0% by mass Cu: less than 0.50% by mass Wherein, the C does not include the C in carbonates. The value A1 calculated by the following formula (1) is: above 0.120 and below 0.

500. The value A2 calculated by the following formula (2) is below 0.

10. A1 = [Nb] W + [V] W … Equation (1) A2 = 1.22×([Cr] W + [Mo] W + 0.7×[Nb] W ) - ([Ni] W + 35×[C] W + 20×[N] W + 0.25×[Cu] W ) - 10. Among them, [Nb] W [V] is the Nb content in the coated welding electrode expressed as a percentage by mass. W This is the V content in the coated welding electrode, expressed as a percentage by mass, [Cr]. W This is the Cr content in the coated welding electrode, expressed as a percentage by mass, [Mo]. W This is the Mo content in the coated welding electrode, expressed as a percentage by mass ([Ni]). W This is the Ni content in the coated welding electrode, expressed as a percentage by mass. [C] W This is the carbon content in the coated welding electrode, expressed as a percentage by mass, [N]. W This is the nitrogen content in the coated welding electrode, expressed as a percentage by mass, [Cu]. W It is the Cu content in the coated welding electrode, expressed as a percentage by mass.

2. The flux-coated welding electrode according to claim 1, characterized in that, Relative to the total mass of the welding electrode, it also contains F: ≥0.50% by mass and ≤3.00% by mass Ca: 3.0% or more and 9.0% or less by mass Mn: ≥0.1% by mass and ≤6.0% by mass TiO2: ≥5.0% by mass and ≤25.0% by mass Conversion values ​​of SiO2 for metallic Si and Si compounds: ≥3.0% by mass and ≤8.0% by mass. Na: ≥0.05% by mass and ≤0.50% by mass, and K: ≥0.05% by mass and ≤1.50% by mass, and ZrO2 conversion values ​​for metallic Zr and Zr compounds: below 2.0% by mass. Conversion value of metallic Mg and Mg compound MgO: less than 1.0% by mass. P: less than 0.030% by mass S: less than 0.030% by mass Co: less than 0.30% by mass W: less than 0.50% by mass REM: less than 0.50% by mass Ti: less than 1.0% by mass Al: less than 0.3% by mass Al2O3: less than 2.0% by mass Li: less than 0.50% by mass.

3. The flux-coated welding electrode according to claim 1, characterized in that, The Ni content is 7.0% by mass or more and 10.0% by mass or less. The Cr content is 12.0% by mass or more and 15.0% by mass or less. The Mo content is 1.0% by mass or more and 2.0% by mass or less.

4. A welded joint, characterized in that, It is manufactured by welding stainless steel plate as the base material using any one of claims 1 to 3.

5. A welding metal, characterized in that, Relative to the total mass of weld metal, containing C: ≥0.001% by mass and ≤0.040% by mass Cr: ≥14.0% by mass and ≤22.0% by mass Ni: ≥7.0% by mass and ≤18.0% by mass Mn: ≥0.3% by mass and ≤3.0% by mass Nb: ≥0.001% by mass and ≤0.400% by mass, and V: ≥0.001% by mass and ≤0.400% by mass N： More than 0.001% by mass and less than 0.050% by mass, and Si: less than 1.0% by mass Ti: less than 1.0% by mass Mo: less than 4.0% by mass Cu: less than 0.50% by mass The balance consists of Fe and unavoidable impurities, and... The value A3 calculated by the following formula (3) is: above 0.120 and below 0.500, and The value A4 calculated by the following formula (4) is below 9.

40. A3 = [Nb] M + [V] M …Formula (3) A4 = 1.22×([Cr] M + [Mo] M + 0.7×[Nb] M ) - ([Ni] M + 35×[C] M + 20×[N] M + 0.25×[Cu] M ) … Equation (4) Among them, [Nb] M [V] is the Nb content in the weld metal expressed as a percentage by mass. M This is the V content in the weld metal expressed as a percentage by mass, [Cr]. M This is the Cr content in the welding metal expressed as a percentage by mass, [Mo]. M This is the Mo content in the weld metal expressed as a percentage by mass, [Ni]. M This is the Ni content in the welding metal expressed as a percentage by mass, [C]. M It is the carbon content in the weld metal expressed as a percentage by mass, [N]. M This is the nitrogen content in the welding metal expressed as a percentage by mass, [Cu]. M It is the Cu content in the welding metal expressed as a percentage by mass.

6. The weld metal according to claim 5, characterized in that, P: less than 0.030% by mass S: less than 0.030% by mass Co: less than 0.500% by mass W: less than 0.50% by mass The Ni content is 12.0% by mass or more and 14.0% by mass or less. The Cr content is 17.0% by mass or more and 19.0% by mass or less. The Mo content is 1.7% by mass or more and 2.5% by mass or less.

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