Coated electrode for arc welding, weld joint and weld metal

Abstract

To provide a coated electrode for arc welding that is used in welding of a structure in an ultralow temperature region, from which weld metal having excellent strength and a lateral expansion amount equal to or higher than a desired value can be obtained.SOLUTION: A coated electrode for arc welding has regulated contents of Fe, C, Cr and Ni to the total mass of the electrode, and contains 0.001 to 0.400 mass% Nb, 0.001 to 0.400 mass% V, and 0.001 to 0.020 mass% N. A value A1 is 0.120 or more and 0.500 or less, and a value A2 is 0.10 or less. A1 is [Nb]W+[V]W, and A2 is 1.22×([Cr]W+[Mo]W+0.7×[Nb]W)-([Ni]W+35×[C]W+20×[N]W+0.25×[Cu]W)-10.0. [Element]W is a value obtained by expressing the contents of the elements in the coated electrode for arc welding by mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a covered arc welding rod, a welded joint, and a weld metal.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, in consideration of the environment, it has been considered to use hydrogen as a fuel for power generation, automobiles, etc., and the demand for hydrogen has been increasing. Along with this, regarding storage tanks, the requirements for storage tanks that can safely store liquefied hydrogen have been increasing. Specifically, it is required that it can be used even in an extremely low temperature region lower than the temperature used in normal liquefied storage tanks, for example, about -253°C or higher. For this reason, the development of a covered arc welding rod that can cope with the welding of structures in an even lower temperature region is desired. As an index of the low-temperature toughness of the weld metal for such low-temperature tanks, the value of transverse swelling may be required. However, in the covered arc welding rod described in Patent Document 1, transverse swelling is not considered.

[0005] The present invention has been made in view of such problems, and is a covered arc welding rod used for welding structures in the cryogenic region, which has excellent strength and can obtain a weld metal having a lateral bulge amount equal to or greater than a desired value. An object of the present invention is to provide a covered arc welding rod, a welded joint obtained by using the covered arc welding rod, and a weld metal.

Means for Solving the Problems

[0006] As a result of intensive studies by the present inventors, in order to obtain a weld metal having excellent strength and lateral bulge amount in the cryogenic region, it is effective to control the total amount of Nb and V in the welding rod and to control the ferrite amount by setting the value obtained by the calculation formula using Cr equivalent and Ni equivalent within a predetermined range. The present invention has been made based on the above findings.

[0007] The above object of the present invention is achieved by the configuration of the following [1] relating to the covered arc welding rod.

[0008] [1] With respect to the total mass of the welding rod, Fe: 30% by mass or more and 55% by mass or less, C: 0.001% by mass or more and 0.020% by mass or less (excluding C in carbonate), Cr: 10.0% by mass or more and 30.0% by mass or less, Ni: 6.0% by mass or more and 20.0% by mass or less, Nb: 0.001% by mass or more and 0.400% by mass or less, V: 0.001% by mass or more and 0.400% by mass or less, and N: 0.001% by mass or more and 0.020% by mass or less, and contains Mo: 4.0% by mass or less, Cu: 0.50% by mass or less, The value A1 calculated by the following formula (1): 0.120 or more and 0.500 or less, The value A2 calculated by the following formula (2): 0.10 or less, characterized by a covered arc welding rod. A1 = [Nb] W + [V] W ··· Formula (1) A2 = 1.22×([Cr] W + [Mo] W + 0.7×[Nb] W ) - ([Ni] W + 35×[C] W + 20×[N] W + 0.25×[Cu] W ) - 10.0 ··· Formula (2) However, [Nb] W is the value representing the Nb content in the covered arc welding rod in mass%, [V] W is the value representing the V content in the covered arc welding rod in mass%, [Cr] W is the value representing the Cr content in the covered arc welding rod in mass%, [Mo] W is the value representing the Mo content in the covered arc welding rod in mass%, [Ni] W is the value representing the Ni content in the covered arc welding rod in mass%, [C] W is the value representing the C content in the covered arc welding rod in mass%, [N] W is the value representing the N content in the covered arc welding rod in mass%, [Cu] W is the value representing the Cu content in the covered arc welding rod in mass%.

[0009] Further, the preferred embodiments of the present invention related to the covered arc welding rod relate to the following [2] to [3].

[0010] [2] Further, with respect to the total mass of the welding rod, F: 0.50 mass% or more and 3.00 mass% or less, Ca: 3.0 mass% or more and 9.0 mass% or less, Mn: 0.1 mass% or more and 6.0 mass% or less, TiO2: 5.0 mass% or more and 25.0 mass% or less, SiO2 conversion value of metallic Si and Si compounds: 3.0 mass% or more and 8.0 mass% or less, Na: 0.05 mass% or more and 0.50 mass% or less, and K: 0.05 mass% or more and 1.50 mass% or less, are contained, ZrO2 equivalent value of metallic Zr and Zr compounds: 2.0 mass% or less, MgO equivalent value of metallic Mg and Mg compounds: 1.0 mass% or less, P: 0.030 mass% or less, S: 0.030 mass% or less, Co: 0.30 mass% or less, W: 0.50 mass% or less, REM: 0.50 mass% or less, Ti: 1.0 mass% or less, Al: 0.3 mass% or less, Al2O3: 2.0 mass% or less, Li: 0.50 mass% or less, characterized by the covered arc welding rod according to [1].

[0011] [3] The Ni is 7.0 mass% or more and 10.0 mass% or less, The Cr is 12.0 mass% or more and 15.0 mass% or less, The Mo is 1.0 mass% or more and 2.0 mass% or less, characterized by the covered arc welding rod according to [1] or [2].

[0012] The above object of the present invention is achieved by the following configuration [4] related to the welded joint.

[0013] [4] A welded joint characterized by being manufactured by welding using a covered arc welding rod according to any one of [1] to [3] with a stainless steel plate as the base material.

[0014] The above object of the present invention is achieved by the following configuration [5] related to the weld metal.

[0015] [5] With respect to the total mass of the weld metal, C: 0.001 mass% or more and 0.040 mass% or less, Cr: 14.0 mass% or more and 22.0 mass% or less, Ni: 7.0 mass% or more and 18.0 mass% or less, Mn: 0.3 mass% or more and 3.0 mass% or less, Nb: 0.001 mass% or more and 0.400 mass% or less, and V: 0.001 mass % or more and 0.400 mass % or less, N: 0.001 mass % or more and 0.050 mass % or less, and contains Si: 1.0 mass % or less, Ti: 1.0 mass % or less, Mo: 4.0 mass % or less, Cu: 0.50 mass % or less, and the balance is Fe and inevitable impurities, and the value A3 calculated by the following formula (3): 0.120 or more and 0.500 or less, and the value A4 calculated by the following formula (4): 9.40 or less. A welding metal characterized by the above. 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 ) ··· Formula (4) However, [Nb] M is the value representing the Nb content in the welding metal in mass %, [V] M is the value representing the V content in the welding metal in mass %, [Cr] M is the value representing the Cr content in the welding metal in mass %, [Mo] M is the value representing the Mo content in the welding metal in mass %, [Ni] M is the value representing the Ni content in the welding metal in mass %, [C] M is the value representing the C content in the welding metal in mass %, [N] M is the value representing the N content in the welding metal in mass %, [Cu] M is the value representing the Cu content in the welding metal in mass %.

[0016] Also, a preferred embodiment of the present invention relating to the welding metal relates to the following [6].

[0017] [6] P: 0.030 mass% or less, S: 0.030 mass% or less, Co: 0.500 mass% or less, W: 0.50 mass% or less, the above Ni: 12.0 mass% or more and 14.0 mass% or less, the above Cr: 17.0 mass% or more and 19.0 mass% or less, the above Mo: 1.7 mass% or more and 2.5 mass% or less, characterized in that it is the welding metal according to [5].

Effect of the Invention

[0018] According to the present invention, it is possible to provide a covered arc welding rod capable of obtaining a welding metal having excellent strength and a lateral bulge amount equal to or greater than a desired value. Further, according to the present invention, by using the covered arc welding rod, it is possible to provide a welded joint that can be suitably used in an extremely low temperature environment. Furthermore, according to the present invention, it is possible to provide a welding metal having excellent strength and a lateral bulge amount equal to or greater than a desired value.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

[0020] [Covered Arc Welding Rod] The covered arc welding rod according to the present embodiment is configured by covering a steel core wire with a covering agent. In this covered arc welding rod, the contents of Fe, C, Cr, Ni, Nb, V, Mo, Cu, N, etc. in the welding rod are controlled, and the total content of Nb and V, and the values calculated by specific formulas using the contents of Cr, Mo, Nb, Ni, C, N, and Cu are controlled within a predetermined range.

[0021] Hereinafter, each component contained in the covered arc welding rod according to the present embodiment will be described in detail. Note that in this specification, the covered arc welding rod may be simply referred to as a welding rod.

[0022] <Fe: 30 mass% or more and 55 mass% or less> Fe is the main component constituting the core wire of the welding rod according to this embodiment. The Fe contained in the welding rod is 30 mass% or more, preferably 31.5 mass% or more, and more preferably 33 mass% or more. On the other hand, the Fe content with respect to the total mass of the welding rod is 55 mass% or less, preferably 50 mass% or less, and more preferably 45 mass% or less.

[0023] <C: 0.001 mass% or more and 0.020 mass% or less> C is an element that improves the tensile strength of the weld metal. On the other hand, it segregates at the final solidification part of the weld metal, lowers the melting point of the melt, and deteriorates the high-temperature crack resistance. When the C content in the welding rod is less than 0.001 mass%, a weld metal having good tensile strength cannot be obtained. Therefore, the C content with respect to the total mass of the welding rod is 0.001 mass% or more, preferably 0.003 mass% or more, and more preferably 0.005 mass% or more. On the other hand, when the C content in the welding rod exceeds 0.020 mass%, the high-temperature crack sensitivity increases. Therefore, the C content with respect to the total mass of the welding rod is 0.020 mass% or less, preferably 0.016 mass% or less, and more preferably 0.013 mass% or less. Note that the C content defined in this embodiment is a value excluding C contained as a carbonate in the welding rod.

[0024] <Cr: 10.0 mass% or more and 30.0 mass% or less> Cr is a component that has the effect of improving the strength of the weld metal and stabilizing the ferrite phase. If the Cr content in the welding rod is less than 10.0% by mass, a weld metal with sufficient strength cannot be obtained. Therefore, the Cr content based on the total mass of the welding rod 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, when the Cr content in the welding rod exceeds 30.0% by mass, the toughness of the weld metal deteriorates, and the solidification segregation of Cr is promoted, resulting in deteriorated high-temperature crack resistance. Therefore, the Cr content based on the total mass of the welding rod is 30.0% by mass or less, preferably 20.0% by mass or less, and more preferably 15.0% by mass or less.

[0025] <Ni: 6.0% by mass or more and 20.0% by mass or less> Ni is a component that has the effect of stabilizing the austenite structure. If the Ni content in the welding rod is less than 6.0% by mass, the austenite structure becomes unstable. Therefore, the Ni content based on the total mass of the welding rod 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, when the Ni content in the welding rod exceeds 20.0% by mass, the solid solubility of C and N decreases, and blowholes are likely to occur. Therefore, the Ni content based on the total mass of the welding rod 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.

[0026] <Nb: 0.001% by mass or more and 0.400% by mass or less> Nb is a component that has the effect of forming carbides to reduce the amount of dissolved carbon, and improving the absorbed energy and the lateral bulging amount. In this embodiment, particularly for the purpose of making the lateral bulging amount equal to or greater than a desired value, it is necessary to appropriately control the contents of Nb and V described below. If the Nb content in the welding rod is less than 0.001% by mass, the desired lateral bulging amount cannot be obtained. Therefore, the Nb content with respect to the total mass of the welding rod 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 welding rod exceeds 0.400% by mass, the toughness of the weld metal decreases. Therefore, the Nb content with respect to the total mass of the welding rod is 0.400% by mass or less, preferably 0.300% by mass or less, and more preferably 0.200% by mass or less.

[0027] <V: 0.001% by mass or more and 0.400% by mass or less> Similar to Nb, V is a component that has the effect of forming carbides to reduce the amount of dissolved carbon, and improving the absorbed energy and the lateral bulging amount. In order to make the lateral bulging amount equal to or greater than a desired value, it is also necessary to appropriately control the V content. If the V content in the welding rod is less than 0.001% by mass, the desired lateral bulging amount cannot be obtained. Therefore, the V content with respect to the total mass of the welding rod 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 rod exceeds 0.400% by mass, the toughness of the weld metal decreases. Therefore, the V content with respect to the total mass of the welding rod is 0.400% by mass or less, preferably 0.300% by mass or less, and more preferably 0.200% by mass or less.

[0028] <N: 0.001% by mass or more and 0.020% by mass or less> N is a solid solution strengthening element and has the effect of improving the strength of the weld metal. The N content with respect to the total mass of the welding rod 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, when the N content exceeds 0.020% by mass, the absorbed energy of the weld metal decreases. Therefore, the N content with respect to the total mass of the welding rod is 0.020% by mass or less, preferably 0.018% by mass or less, and more preferably 0.015% by mass or less.

[0029] <Mo: 4.0% by mass or less> Mo, like Cr, is a component having the effect of improving the strength of the weld metal. However, in the covered arc welding rod according to the present embodiment, it is not always necessary to contain Mo, and it may be 0% by mass. However, when Mo is contained in the welding rod for the purpose of improving the strength of the weld metal, the Mo content with respect to the total mass of the welding rod is preferably 1.0% by mass or more, and more preferably 1.7% by mass or more. On the other hand, when the Mo content in the welding rod exceeds 4.0% by mass, the toughness of the weld metal deteriorates, and the solidification segregation of Mo is promoted, resulting in deterioration of the high-temperature crack resistance. Therefore, the Mo content with respect to the total mass of the welding rod is 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.

[0030] <Cu: 0.50% by mass or less> Cu is a component that has the effect of stabilizing the austenite structure. However, in the covered arc welding rod according to this embodiment, it is not necessarily required to contain Cu, and it may be 0% by mass. However, when Cu is contained in the welding rod for the purpose of stabilizing the austenite structure, the Cu content with respect to the total mass of the welding rod is preferably 0.001% by mass or more, and more preferably 0.005% by mass or more. On the other hand, when the Cu content in the welding rod exceeds 0.50% by mass, the high-temperature crack resistance of the weld metal deteriorates. Therefore, the Cu content with respect to the total mass of the welding rod is set to 0.50% by mass or less, preferably 0.25% by mass or less, and more preferably 0.15% by mass or less.

[0031] <Value A1 calculated by formula (1): 0.120 or more and 0.500 or less> As described above, Nb and V are components that greatly affect the absorbed energy and transverse bulge amount of the weld metal. Therefore, by controlling the respective contents of Nb and V in the welding rod and controlling the total value of the contents of Nb and V within an appropriate range, a desired transverse bulge amount can be obtained. If the value A1 calculated by the following formula (1), which is the total value of the contents of Nb and V in the welding rod, is less than 0.120, the desired absorbed energy and transverse bulge amount cannot be obtained. Therefore, the value A1 is set to 0.120 or more, preferably 0.150 or more, and more preferably 0.200 or more. On the other hand, when the value A1 calculated by the following formula (1) exceeds 0.500, the absorbed energy of the weld metal decreases. Therefore, the value A1 is set to 0.500 or less, preferably 0.400 or less, and more preferably 0.300 or less.

[0032] A1 = [Nb] W + [V] W ··· Formula (1) However, [Nb] W is the value representing the Nb content in the covered arc welding rod in % by mass, and [V] W is the value representing the V content in the covered arc welding rod in % by mass.

[0033] <Value A2 calculated by formula (2): 0.10 or less> In this embodiment, by adjusting the parameters using the contents of Cr, Mo, and Nb, which are ferrite stabilizing elements in the welding rod, and the contents of Ni, C, N, and Cu, which are austenite stabilizing elements, the ferrite amount of the weld metal can be controlled within a desired range. More specifically, the following formula (2) is an equation for subtracting the equivalent amount of Ni, which is the degree of austenite stabilizing element converted to the nickel amount, from the equivalent amount of Cr, which is the degree of ferrite stabilizing element converted to the chromium amount. Therefore, by defining the value A2 calculated by this formula (2), it is possible to prevent the ferrite amount from becoming excessive or insufficient, and to achieve a balance between strength and toughness.

[0034] When the value A2 calculated by the following formula (2) exceeds 0.10, the ferrite amount becomes too large and the transverse bulge amount of the weld metal decreases. Therefore, the value A2 should be 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 value of the value A2 is not particularly limited, but it is preferably -2.0 or more, and more preferably -1.2 or more.

[0035] 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) However, [Cr] W is the value representing the Cr content in the covered arc welding rod in mass%, [Mo] W is the value representing the Mo content in the covered arc welding rod in mass%, [Nb] W is the value representing the Nb content in the covered arc welding rod in mass%, [Ni] W is the value representing the Ni content in the covered arc welding rod in mass%, [C] Wis the value representing the C content in the covered arc welding electrode in mass%, [N] W is the value representing the N content in the covered arc welding electrode in mass%, [Cu] W is the value representing the Cu content in the covered arc welding electrode in mass%.

[0036] For the covered arc welding electrode according to this embodiment, if each component is within the above content range, the problems of the present invention can be solved. In addition, in order to further improve the welding workability and the mechanical properties of the weld metal, it is preferable that the welding electrode further contains F, Ca, Mn, TiO2, metallic Si and Si compounds, Na, K, etc. Also, it is preferable that the contents of metallic Zr and Zr compounds, metallic Mg and Mg compounds, P, S, Co, W, REM, Ti, Al, Al2O3, Li with respect to the total mass of the welding electrode are defined. Hereinafter, the preferable ranges of these contents will be described.

[0037] <F: 0.50 mass% or more and 3.00 mass% or less> In this embodiment, for the purpose of suppressing the amount of spatter generated and stabilizing the arc, F can be contained in the welding electrode. When the F content in the welding electrode is 0.50 mass% or more, the effect of suppressing the amount of spatter generated and stabilizing the arc can be obtained. Therefore, when F is contained in the welding electrode, the F content with respect to the total mass of the welding electrode is preferably 0.50 mass% or more, and more preferably 0.80 mass% or more. On the other hand, when the F content in the welding electrode is 3.00 mass% or less, spatter and fume can be suppressed. Therefore, the F content with respect to the total mass of the welding electrode is preferably 3.00 mass% or less, and more preferably 2.00 mass% or less. Note that F is contained in the form of fluorides such as CaF2 and NaF.

[0038] <Ca: 3.0 mass% or more and 9.0 mass% or less> Ca is an element contained in the welding rod in the form of carbonate or CaF2. Therefore, when Ca is contained in the welding rod, the Ca content based on the total mass of the welding rod 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. Also, the Ca content in the welding rod 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.

[0039] <Mn: 0.1% by mass or more and 6.0% by mass or less> Mn has an effect of suppressing blowholes caused by oxygen-based gas due to its deoxidizing effect and an effect of stabilizing the austenite structure. Therefore, in the present embodiment, Mn may be contained in the welding rod. When the Mn content in the welding rod is 0.1% by mass or more, a sufficient deoxidizing effect can be obtained. Therefore, the amount of Mn added based on the total mass of the welding rod is preferably 0.1% by mass or more, and more preferably 1.5% by mass or more. On the other hand, when the Mn content is 6.0% by mass or less, the solidification segregation of Mn in the final solidification region of the weld metal is suppressed, and the occurrence of hot cracks can be suppressed. Therefore, the Mn content based on the total mass of the welding rod is preferably 6.0% by mass or less, and more preferably 5.0% by mass or less.

[0040] <TiO2: 5.0% by mass or more and 25.0% by mass or less> TiO2 is the main component of the slag former, which can form a uniform and well-coated slag and has the effect of improving arc stability. In addition, TiO2 also has the effect of raising the melting point of the slag and flattening the bead shape in all-position welding. When the TiO2 content in the welding rod is 5.0 mass% or more, the above effects can be fully obtained. Therefore, the TiO2 content based on the total mass of the welding rod is preferably 5.0 mass% or more, more preferably 8.0 mass% or more, and even more preferably 10.0 mass% or more. On the other hand, when the TiO2 content in the welding rod is 25.0 mass% or less, the coating agent is easily melted, and the generation of slag rings can be suppressed. Therefore, the TiO2 content based on the total mass of the welding rod is preferably 25.0 mass% or less, more preferably 20.0 mass% or less. Note that the TiO2 content in the welding rod represents the TiO2 conversion value of the Ti compounds contained in the welding rod.

[0041] <SiO2 conversion value of metallic Si and Si compounds: 3.0 mass% or more and 8.0 mass% or less> Si has the effects of improving the strength of the weld metal and acting as a binder (water glass) for the coating agent. When the SiO2 conversion value in the welding rod is 3.0 mass% or more, the above effects can be obtained. Therefore, the SiO2 conversion value based on the total mass of the welding rod is preferably 3.0 mass% or more, more preferably 3.5 mass% or more. On the other hand, when the SiO2 conversion value in the welding rod is 8.0 mass% or less, the deterioration of high-temperature crack resistance can be prevented. Therefore, the SiO2 conversion value based on the total mass of the welding rod is preferably 8.0 mass% or less, more preferably 7.0 mass% or less. Note that the SiO2 conversion value is the value obtained by converting the total Si contained in elemental Si, Si alloys, and Si compounds in the welding rod into SiO2.

[0042] <Na: 0.05 mass% or more and 0.50 mass% or less> Alkali metals such as Na are components having the effect of improving arc stability and can be contained in the welding rod as fluorides or complex oxides. When the Na content in the welding rod is 0.05% by mass or more, the effect of improving arc stability can be obtained. Therefore, the Na content based on the total mass of the welding rod is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. On the other hand, when the Na content in the welding rod is 0.50% by mass or less, a decrease in the slag melting point can be suppressed, and the bead shape in all-position welding can be improved. Therefore, the Na content based on the total mass of the welding rod is preferably 0.50% by mass or less, and more preferably 0.40% by mass or less. Note that Na exists in the welding rod, for example, as Na2O or the like.

[0043] <K: 0.05% by mass or more and 1.50% by mass or less> Alkali metals such as K are components having the effect of improving arc stability in the same manner as the above-mentioned Na and can be contained in the welding rod as fluorides or complex oxides. When the K content in the welding rod is 0.05% by mass or more, the effect of improving arc stability can be obtained. Therefore, the K content based on the total mass of the welding rod is preferably 0.05% by mass or more, and more preferably 0.5% by mass or more. On the other hand, when the K content in the welding rod is 1.50% by mass or less, a decrease in the slag melting point can be suppressed, and the bead shape in all-position welding can be improved. Therefore, the K content based on the total mass of the welding rod is preferably 1.50% by mass or less, and more preferably 1.20% by mass or less. Note that K exists in the welding rod, for example, as K2O, K2SiF6 or the like.

[0044] <ZrO2 conversion value of metallic Zr and Zr compounds: 2.0% by mass or less> ZrO₂ is a component that has the effect of accelerating slag solidification and forming a flat bead shape in the vertical and upward positions. However, the ZrO₂ equivalent value in the welding rod may be 0% by mass. Also, when the ZrO₂ equivalent value in the welding rod is 2.0% by mass or less, good slag covering properties and slag peeling properties can be obtained. Therefore, the ZrO₂ equivalent value with respect to the total mass of the welding rod is preferably 2.0% by mass or less, and more preferably 1.0% by mass or less. In this embodiment, the ZrO₂ equivalent value is the value obtained by converting all the Zr contained in metallic Zr and Zr compounds into ZrO₂. Metallic Zr means the total amount of Zr contained in Zr alone and Zr alloys. Also, Zr compounds mean Zr oxides and the like. In the following descriptions as well, metal means a single substance or an alloy, and compound means an oxide or the like.

[0045] <MgO equivalent value of metallic Mg and Mg compounds: 1.0% by mass or less> Metallic Mg and Mg compounds are components that have the effect of raising the slag solidification point and improving arc stability. However, the MgO equivalent value in the welding rod may be 0% by mass. When the MgO equivalent value is 1.0% by mass or less, deterioration of the bead shape can be prevented. Therefore, the MgO equivalent value is preferably 1.0% by mass or less, and more preferably 0.8% by mass or less. In this embodiment, the MgO equivalent value is the value obtained by converting all the Mg contained in metallic Mg and Mg compounds into MgO. Also, metallic Mg means the total amount of Mg contained in Mg alone and Mg alloys.

[0046] <P: 0.030% by mass or less> P is an inevitable impurity in the welding rod. Since the lower the P content in the weld metal, the lower the extremely low temperature toughness, it is preferable that the P content in the welding rod is low. Therefore, the P content with respect to the total mass of the welding rod is preferably 0.030% by mass or less, and more preferably 0.025% by mass or less.

[0047] <S: 0.030% by mass or less> Like P, S is an inevitable impurity in the welding rod. Since the toughness at extremely low temperatures decreases as the S content in the weld metal increases, it is preferable that the S content in the welding rod be low. Therefore, the S content with respect to the total mass of the welding rod is preferably 0.030 mass% or less, and more preferably 0.020 mass% or less.

[0048] <Co: 0.30 mass% or less> Since Co is a component having the effect of adjusting the toughness of the weld metal, Co can be contained in the welding rod as necessary. When the Co content in the welding rod is 0.30 mass% or less, a decrease in the strength of the weld metal can be suppressed. Therefore, the Co content with respect to the total mass of the welding rod is preferably 0.30 mass% or less, and more preferably 0.20 mass% or less.

[0049] <W: 0.50 mass% or less> Since W is a solid solution strengthening element in steel and is a component that has the effect of dissolving in the weld metal and improving the strength of the weld metal, W can be contained in the welding rod as necessary. When the W content in the welding rod is 0.50 mass% or less, deterioration of toughness can be suppressed. Therefore, the W content with respect to the total mass of the welding rod is preferably 0.50 mass% or less, and more preferably 0.1 mass% or less.

[0050] <REM: 0.50 mass% or less> Since REM (rare earth element) is a deoxidizing element, REM can be contained in the welding rod as necessary. However, when the REM content in the welding rod is 0.50 mass% or less, a decrease in welding workability can be suppressed. Therefore, the REM content with respect to the total mass of the welding rod is preferably 0.50 mass% or less, and more preferably 0.10 mass% or less. Note that REM means 15 lanthanoid series rare earth elements from La to Lu in the periodic table. These elements may be added alone or in combination of two or more.

[0051] <Ti: 1.0 mass% or less> Since Ti is a component that has the effect of improving the toughness of the weld metal, Ti can be contained in the welding rod as needed. When the Ti content in the welding rod is 1.0 mass% or less, the oxygen content of the weld metal can be reduced, and the toughness of the weld metal can be adjusted to a desired range. Therefore, the Ti content based on the total mass of the welding rod is preferably 1.0 mass% or less, and more preferably 0.5 mass% or less. Note that the Ti content in the welding rod represents the content of all metallic Ti contained in the Ti alone and Ti alloys contained in the welding rod.

[0052] <Al: 0.3 mass% or less> Since Al is a component that has a deoxidizing effect and has the effect of stabilizing the toughness of the weld metal, Al can be contained in the welding rod as needed. When the Al content in the welding rod is 0.3 mass% or less, the yield of alloying elements into the weld metal can be appropriately adjusted, and excessive strength increase can be suppressed. Therefore, the Al content based on the total mass of the welding rod is preferably 0.3 mass% or less, and more preferably 0.1 mass% or less. Note that the Al content in the welding rod represents the content of all metallic Al contained in the Al alone and Al alloys contained in the welding rod.

[0053] <Al2O3: 2.00 mass% or less> Since Al2O3 is a slag former and is a component that has the effect of improving the bead shape, Al2O3 can be contained in the welding rod as needed. When the Al2O3 in the welding rod is 2.00 mass% or less, good slag detachability can be obtained. Therefore, the Al2O3 content based on the total mass of the welding rod is preferably 2.00 mass% or less, and more preferably 1.50 mass% or less. Note that the Al2O3 content in the welding rod represents the value obtained by converting the Al in Al compounds such as Al oxides contained in the welding rod into Al2O3.

[0054] <Li: 0.50 mass% or less> Alkali metals such as Li, like the above-mentioned Na and K, are components having the effect of improving arc stability and can be contained in the welding rod as fluorides or complex oxides. Also, when the Li content in the welding rod is 0.50% by mass or less, a decrease in the slag melting point can be suppressed and the bead shape in all-position welding can be improved. Therefore, the Li content with respect to the total mass of the welding rod is preferably 0.50% by mass or less, and more preferably 0.20% by mass or less.

[0055] <Remainder of the covered arc welding rod> The covered arc welding rod in the present embodiment contains, as essential components, Fe, C, Cr, Ni, Nb, V, and N, and may contain Mo and Cu. The total content of these components is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more with respect to the total mass of the welding rod. Further, the welding rod may further contain Si, F, Mn, TiO2, ZrO2, MgO, Na, K, P, S, Co, W, REM, Ti, Al, Al2O3, Li, etc. Note that the covered arc welding rod preferably contains these components in a total amount of 85% by mass or more, more preferably 90% by mass or more, and even more preferably 92% by mass or more in combination with the above essential components. Furthermore, the covered arc welding rod may contain, as the remainder of the above components, for example, Ba, Ta, Bi, etc., or CO2 contained in carbonates such as CaCO3. The carbonate decomposes by the thermal energy during welding to generate CO2 gas. Since the decomposed CO2 component does not contribute to the mechanical properties of the weld metal, in the present embodiment, the CO2 component derived from the carbonate is treated as the remainder. When the covered arc welding rod in the present embodiment contains CO2, it is preferably contained in the range of 0.5% by mass or more and 3.0% by mass or less with respect to the total mass of the welding rod.

[0056] The manufacturing method of the covered arc welding rod according to the present embodiment is not particularly limited and can be manufactured by general manufacturing processes. The materials of the core wire and the covering agent can be used without particular limitation such as the steel type of stainless steel, as long as the content of each component in the total weight of the covered arc welding rod is controlled within the above range.

[0057] The covered arc welding rod according to this embodiment can be suitably used, for example, for welding low-temperature steels such as 5% Ni steel and various austenitic stainless steels.

[0058] [Welded joint] The welded joint according to this embodiment is manufactured by welding using the above-mentioned covered arc welding rod with a stainless steel plate as the base material.

[0059] [Weld metal] The weld metal according to this embodiment is formed, for example, by welding using the above-mentioned covered arc welding rod, and has excellent strength and lateral bulging amount. Hereinafter, the components contained in the weld metal according to this embodiment and their contents will be described in detail. Each element is defined as a value obtained by taking the total amount of components contained in the weld metal in a predetermined region that is not affected by the composition of the base material as the content per total mass of the weld metal. The content of each component in the weld metal according to this embodiment will be described below.

[0060] <C: 0.001 mass% or more and 0.040 mass% or less> C is a component that stabilizes the austenite phase in the weld metal and makes it difficult to cause transformation to the martensite phase. Also, C is a component that contributes to an increase in the strength of the weld metal. If the C content in the weld metal is less than 0.001 mass%, a weld metal having good tensile strength cannot be obtained. Therefore, the C content with respect to the total mass of the weld metal is 0.001 mass% or more, preferably 0.005 mass% or more, and more preferably 0.010 mass% or more. On the other hand, if the C content in the weld metal exceeds 0.040 mass%, the strength excessively increases and it becomes difficult to obtain excellent cryogenic toughness. Therefore, the C content with respect to the total mass of the weld metal is 0.040 mass% or less, preferably 0.035 mass% or less, and more preferably 0.030 mass% or less.

[0061] <Cr: 14.0 mass% or more and 22.0 mass% or less> Cr is a component that stabilizes the ferrite phase in the weld metal and makes it difficult for the transformation to the martensite phase to occur. If the Cr content in the weld metal is less than 14.0% by mass, the ferrite phase becomes unstable and excellent cryogenic toughness cannot be obtained. Therefore, the Cr content with respect 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 exceeds 22.0% by mass, the ferrite phase is excessively stabilized and the cryogenic toughness decreases. Therefore, the Cr content with respect 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.

[0062] <Ni: 7.0% by mass or more and 18.0% by mass or less> Ni is a component that stabilizes the austenite phase in the weld metal and makes it difficult for the transformation to the martensite phase to occur. If the Ni content in the weld metal is less than 7.0% by mass, the austenite phase becomes unstable and the cryogenic toughness decreases. Therefore, the Ni content with respect 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 exceeds 18.0% by mass, the austenite phase is excessively stabilized and excellent cryogenic 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.

[0063] <Mn: 0.3% by mass or more and 3.0% by mass or less> Mn is an austenite stabilizing element and, as a deoxidizer, removes oxygen in the weld metal as slag, having the effect of improving mechanical strength. When the Mn content in the weld metal is less than 0.3% by mass, the deoxidation effect is insufficient and the amount of oxygen in the weld metal increases, so excellent cryogenic toughness cannot be obtained. Therefore, the Mn content based on 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, when the Mn content in the weld metal exceeds 3.0% by mass, the strength of the weld metal rises excessively and the cryogenic toughness decreases. Therefore, the Mn content based on 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.

[0064] <Nb: 0.001% by mass or more and 0.400% by mass or less> Nb is a component that forms carbides in the weld metal to reduce the amount of solid-solved C and has the effect of improving the absorbed energy and the lateral bulging amount. When the Nb content in the weld metal is less than 0.001% by mass, the desired lateral bulging amount cannot be obtained. Therefore, the Nb content based on 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, when the Nb content in the weld metal exceeds 0.400% by mass, the tensile strength of the weld metal decreases. Therefore, the Nb content based on 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.

[0065] <V: 0.001% by mass or more and 0.400% by mass or less> V, like Nb, is a component that has the effect of forming carbides in the weld metal to reduce the amount of dissolved C, and improving the absorbed energy and the lateral expansion amount. When the V content in the weld metal is less than 0.001% by mass, the desired lateral expansion amount cannot be obtained. Therefore, the V content with respect 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, when the V content in the weld metal exceeds 0.400% by mass, the tensile strength of the weld metal decreases. Therefore, the V content with respect 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.

[0066] <N: 0.001% by mass or more and 0.050% by mass or less> N is a component that stabilizes the austenite phase in the weld metal and makes it difficult to transform into the martensite phase. Also, N is a component that contributes to the increase in the strength of the weld metal. It is practical for N to be 0.001% by mass or more. When the N content in the weld metal exceeds 0.050% by mass, the strength rises excessively and it becomes difficult to obtain excellent cryogenic toughness. Therefore, the N content with respect to the total mass of the weld metal is 0.050% by mass or less, preferably 0.040% by mass or less, and more preferably 0.035% by mass or less.

[0067] <Si: 1.0% by mass or less> Si is a component that has the effect of promoting deoxidation. However, in the weld metal according to this embodiment, Si may not be contained and may be 0% by mass. When Si is contained in the weld metal for the purpose of ensuring 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, based on the total mass of the weld metal. On the other hand, when the Si content in the weld metal exceeds 1.0% by mass, the crystal strength of the weld metal decreases and excellent extremely low-temperature toughness cannot be obtained. Therefore, the Si content based on 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.

[0068] <Ti: 1.0% by mass or less> Ti is a component that has the effect of improving the toughness of the weld metal. However, in the weld metal according to this embodiment, Ti may not be contained and may be 0% by mass. On the other hand, when Ti is contained in the weld metal in an amount exceeding a predetermined amount, the strength increases excessively and the toughness decreases. Therefore, the Ti content based on the total mass of the weld metal is 1.0% by mass or less, preferably 0.05% by mass or less, more preferably 0.02% by mass or less.

[0069] <Mo: 4.0% by mass or less> Mo is a component that has the effect of improving the strength of the weld metal. However, in the weld metal according to this embodiment, Mo may not be contained and may be 0% by mass. When Mo is contained in the weld metal 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, based on the total mass of the weld metal. On the other hand, when Mo is contained in the weld metal in an amount exceeding a predetermined amount, the strength increases excessively and the toughness decreases. Therefore, the Mo content based on the total mass of the weld metal is 4.0% by mass or less, preferably 3.0% by mass or less, more preferably 2.5% by mass or less.

[0070] <Cu: 0.50% by mass or less> Cu is a component that has the effect of improving the strength of the weld metal. However, in the weld metal according to the present embodiment, Cu may not be contained and may be 0% by mass. On the other hand, when Cu is contained in the weld metal in an amount exceeding a predetermined amount, the strength increases excessively, leading to a decrease in toughness. Therefore, the Cu content with respect 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.

[0071] <Value A3 calculated by the following formula (3): 0.120 or more and 0.500 or less> As described above, Nb and V are components that greatly affect the absorbed energy and transverse bulge amount of the weld metal. Therefore, by controlling the respective contents of Nb and V in the weld metal and appropriately controlling the total value of the contents of Nb and V, a desired transverse bulge amount can be obtained. When the value A3 calculated by the following formula (3), which is the total value of the contents of Nb and V in the weld metal, is less than 0.120, a desired absorbed energy and transverse bulge amount 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, when the value A3 calculated by the following formula (3) exceeds 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. A3 = [Nb] M +「V」 M ··· Formula (3) However, [Nb] M is the value representing the Nb content in the weld metal in % by mass, and [V] M is the value representing the V content in the weld metal in % by mass.

[0072] <Value A4 calculated by the following formula (4): 9.40 or less> In this embodiment, by adjusting the parameters using the contents of Cr, Mo, and Nb, which are ferrite-stabilizing elements in the weld metal, and the contents of Ni, C, N, and Cu, which are austenite-stabilizing elements, the ferrite in the weld metal can be controlled within a desired range. More specifically, the following formula (4) is an equation for subtracting the Ni equivalent amount obtained by converting the degree as an austenite-stabilizing element into the nickel amount from the Cr equivalent amount obtained by converting the degree as a ferrite-stabilizing element into the chromium amount. Therefore, by defining the value A4 calculated by this formula (4), it is possible to prevent the ferrite amount from becoming excessive or insufficient, and to achieve a balance between strength and toughness.

[0073] When the value A4 calculated by the following formula (4) exceeds 9.40, the amount of ferrite becomes too large, and the low-temperature toughness and transverse swelling of the weld metal deteriorate. Therefore, the value A4 is preferably 9.40 or less, more preferably 9.20 or less, and even more preferably 9.00 or less.

[0074] A4 = 1.22×([Cr] M + [Mo] M + 0.7×[Nb] M ) - ([Ni] M + 35×[C] M + 20×[N] M + 0.25×[Cu] M ) ··· Formula (4) However, [Cr] M is the value representing the Cr content in the weld metal in mass%, [Mo] M is the value representing the Mo content in the weld metal in mass%, [Nb] M is the value representing the Nb content in the weld metal in mass%, [Ni] M is the value representing the Ni content in the weld metal in mass%, [C] M is the value representing the C content in the weld metal in mass%, [N] M is the value representing the N content in the weld metal in mass%, [Cu] M is the value representing the Cu content in the weld metal in mass%.

[0075] <Value A5 calculated by the following formula (5): 0.08 or less> As described above, C and N are components that stabilize the austenite phase in the weld metal and make it difficult for transformation to the martensite phase to occur. Therefore, by controlling the respective contents of C and N in the weld metal and setting the total value of the contents of C and N to 0.08 or less, the value of the transverse bulge amount can be improved. A5 = [C] M + [N] M ··· Formula (5) However, [C] M is the value representing the C content in the weld metal in mass%, and [N] M is the value representing the N content in the weld metal in mass%.

[0076] <P: 0.030 mass% or less> As the P content in the weld metal increases, the very low temperature toughness decreases. Therefore, it is preferable that the P content is low. Accordingly, the P content with respect to the total mass of the weld metal is preferably 0.030 mass% or less, and more preferably 0.025 mass% or less.

[0077] <S: 0.030 mass% or less> Similar to P, as the S content in the weld metal increases, the very low temperature toughness decreases. Therefore, it is preferable that the S content is low. Accordingly, the S content with respect to the total mass of the weld metal is preferably 0.030 mass% or less, and more preferably 0.020 mass% or less.

[0078] <Co: 0.500 mass% or less> Since Co is a component having an effect of adjusting the toughness of the weld metal, Co can be contained in the weld metal as necessary. When the Co content in the weld metal is 0.500 mass% or less, a decrease in strength can be suppressed. Therefore, when Co is contained in the weld metal, the Co content with respect to the total mass of the weld metal is preferably 0.500 mass% or less, and more preferably 0.30 mass% or less.

[0079] <W: 0.50 mass% or less> Since W is a component having the effect of improving the strength of the weld metal, W can be contained in the weld metal as needed. However, if W is contained in the weld metal in an amount exceeding a predetermined amount, the strength will increase excessively and the toughness will decrease. Therefore, the W content with respect to the total mass of the weld metal is preferably 0.50 mass% or less, and more preferably 0.10 mass% or less.

[0080] <Balance: Fe and unavoidable impurities> In the weld metal according to the present embodiment, the balance excluding the above components is Fe and unavoidable impurities. Fe is the main component constituting the core wire of the covered arc welding rod according to the present embodiment and remains in the weld metal. The Fe content with respect to the total mass of the weld metal is preferably, for example, 40 mass% or more, more preferably 50 mass% or more, and still more preferably 60 mass% or more. On the other hand, the Fe content with respect to the total mass of the weld metal is preferably 75 mass% or less, preferably 72 mass% or less, and more preferably 70 mass% or less. In addition, examples of unavoidable impurities include O, As, Sb, Sn, Bi, and S in addition to the above P and S. The O in the weld metal is preferably less than 0.100 mass% with respect to the total mass of the weld metal. Also, the total amount of unavoidable impurities excluding P, S, and O in the weld metal is preferably 0.20 mass% or less with respect to the total mass of the weld metal.

Examples

[0081] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples, and modifications can be made and implemented within the scope that conforms to the spirit of the present invention, and all of them are included in the technical scope of the present invention.

[0082] [Fabrication of Covered Arc Welding Rod] Covered arc welding rods having the compositions shown in Tables 1 to 3 below were produced. The covering rate was 30 to 45 mass%. In Table 1, formula (1): A1 indicates the value A1 calculated by formula (1), and formula (2): A2 indicates the value A2 calculated by formula (2). Formulas (1) and (2) are as follows.

[0083] A1 = [Nb] W + [V] W ··· Formula (1) A2 = 1.22×([Cr] W + [Mo] W + 0.7×[Nb] W ) - ([Ni] W + 35×[C] W + 20×[N] W + 0.25×[Cu] W ) - 10.0 ··· Formula (2) However, [Nb] W is the value representing the Nb content in the covered arc welding rod in mass%, [V] W is the value representing the V content in the covered arc welding rod in mass%, [Cr] W is the value representing the Cr content in the covered arc welding rod in mass%, [Mo] W is the value representing the Mo content in the covered arc welding rod in mass%, [Ni] W is the value representing the Ni content in the covered arc welding rod in mass%, [C] W is the value representing the C content in the covered arc welding rod in mass%, [N] W is the value representing the N content in the covered arc welding rod in mass%, [Cu] W is the value representing the Cu content in the covered arc welding rod in mass%.

[0084] [Covered arc welding] Two carbon steel plates with a thickness of 20 mm were prepared. After machining to a bevel angle of 45°, a coated arc welding rod was fabricated and used to form 2 - 3 layers of buttering layers on the surface of the beveled part and the backing material surface. The carbon steel plates were arranged to form a V - groove. Subsequently, welding was carried out on the bevel using each coated arc welding rod. The welding conditions were 130 A - 24 V, downward position, 8 layers, 20 passes to 23 passes.

[0085] [Measurement of Weld Metal Composition] For the obtained weld metal, in accordance with JIS G 1253:2002, solid - state emission spectroscopic analysis was performed at the same position as the tensile test piece sampling position described later to measure the composition of each weld metal. The contents of chemical components in the weld metal are shown in Table 4 and Table 5. In Table 4, formula (3): A3 represents the value A3 calculated by formula (3), and formula (4): A4 represents the value A4 calculated by formula (4). In Table 5, formula (5): A5 represents the value A5 calculated by formula (5). Formulas (3) - (5) are as follows. Also, the remainder of the weld metal is Fe and unavoidable impurities.

[0086] 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 ) ··· Formula (4) A5 = [C] M + [N] M ··· Formula (5) However, [Nb] M is the value representing the Nb content in the weld metal in mass%, [V] M is the value representing the V content in the weld metal in mass%, [Cr] M is the value representing the Cr content in the weld metal in mass%, [Mo] M is the value representing the Mo content in the weld metal in mass%, [Ni]M is the value representing the Ni content in the weld metal in mass%, and [C] M is the value representing the C content in the weld metal in mass%, and [N] M is the value representing the N content in the weld metal in mass%, and [Cu] M is the value representing the Cu content in the weld metal in mass%.

[0087] [Evaluation Test of Mechanical Properties] (Charpy Impact Test) In accordance with JIS Z 2242:2023, standard V-notch test pieces were taken from the obtained weld metal, and the Charpy impact test was carried out. The test temperature of the Charpy impact test was -196°C, and the Charpy impact value (vE-196°C) and the lateral expansion amount LE (mm) were measured. Note that five test pieces for measuring the Charpy impact value and five test pieces for measuring the lateral expansion amount were taken from each weld metal respectively. For the Charpy impact value and the lateral expansion amount, after deleting the maximum value and the minimum value among the five test results, the average value of the three test results was calculated and evaluated.

[0088] (Tensile Test) In accordance with JIS Z 3111:2005, in the obtained weld metal, A0 test pieces were taken from the position where the center of the test piece was the weld center line, and the tensile test was carried out. The test temperature of the tensile test was room temperature (20°C).

[0089] The Charpy impact value and the lateral expansion amount by the Charpy impact test, and the measurement results of the tensile strength are shown together in Table 5 below. In each of the above evaluation tests, those with an average Charpy impact value of 35.0 (J / cm 2 ) or more, a lateral expansion amount of 0.53 mm or more, and a tensile strength of 498 MPa or more were considered qualified. Also, those that did not achieve the reference value in any item were considered unqualified. Also, those with an average Charpy impact value of 40.0 (J / cm 2 ) or more, a lateral expansion amount of 0.70 mm or more, and a tensile strength of 530 MPa or more were evaluated as more preferable.

[0090]

Table 1

[0091]

Table 2

[0092]

Table 3

[0093]

Table 4

[0094]

Table 5

[0095] As shown in Tables 1 to 5, in Invention Examples Nos. 1 to 14, the contents of specific components in the welding rod were appropriately controlled, and the values A1 and A2 calculated by Expressions (1) and (2) were within the ranges defined in this embodiment. Therefore, also in the obtained weld metal, the contents of the respective components and the values A3 and A4 calculated by Expressions (3) and (4) were within the ranges defined in this embodiment. Accordingly, a weld metal with excellent mechanical properties, particularly with a transverse bulge amount equal to or greater than a desired value, could be obtained.

[0096] On the other hand, in Comparative Examples Nos. 1 and 3, the N content in the welding rod exceeded the upper limit value defined in the present invention, and the value A1 calculated by Expression (1) was less than the lower limit value defined in the present invention. Further, for the weld metal obtained by using the welding rods of Comparative Examples Nos. 1 and 3, the value A3 calculated by Expression (3) was less than the lower limit value defined in the present invention, and the value A4 calculated by Expression (4) exceeded the upper limit value defined in the present invention. In Comparative Example No. 2, the value A1 calculated by formula (1) was less than the lower limit defined in the present invention. Also, for the weld metal obtained using the welding rod of Comparative Example No. 2, the value A3 calculated by formula (3) was less than the lower limit defined in the present invention, and the value A4 calculated by formula (4) exceeded the upper limit defined in the present invention. Furthermore, in Comparative Example No. 4, the value A2 calculated by formula (2) exceeded the upper limit defined in the present invention. Also, for the weld metal obtained using the welding rod of Comparative Example No. 4, the value A4 calculated by formula (4) exceeded the upper limit defined in the present invention. Therefore, in all of Comparative Examples No. 1 to 4, the Charpy impact value and the transverse bulge amount were low.

Claims

1. Based on the total mass of the welding rod, Fe: 30% by mass or more and 55% by mass or less, C: 0.001% by mass or more and 0.020% by mass or less (excluding C in carbonates), Cr: 10.0% by mass or more and 30.0% by mass or less, Ni: 6.0% by mass or more and 20.0% by mass or less, Nb: 0.001% by mass or more and 0.400% by mass or less, V: 0.001% by mass or more and 0.400% by mass or less, and N: 0.001% by mass or more and 0.020% by mass or less, containing Mo: 4.0% by mass or less, Cu: 0.50% by mass or less, Value A1 calculated by the following formula (1): 0.120 or more and 0.500 or less, Value A2 calculated by the following formula (2): 0.10 or less, characterized by a covered arc welding rod. 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 ) - 10.0... Equation (2) However, [Nb] Ｗ represents the value of the Nb content in the covered arc welding electrode, expressed in mass%, and [V] Ｗ represents the value of the V content in the covered arc welding electrode, expressed in mass%, and [Cr] Ｗ represents the value of the Cr content in the covered arc welding electrode, expressed in mass%, and [Mo] Ｗ represents the value of the Mo content in the covered arc welding electrode, expressed in mass%, and [Ni] Ｗ represents the value of the Ni content in the covered arc welding electrode, expressed in mass%, and [C] Ｗ represents the value of the C content in the covered arc welding electrode, expressed in mass%, and [N] Ｗ represents the value of the N content in the covered arc welding electrode, expressed in mass%, and [Cu] Ｗ represents the value of the Cu content in the covered arc welding electrode, expressed in mass%.

2. Furthermore, based on the total mass of the welding rod, F: 0.50% by mass or more and 3.00% by mass or less, Ca: 3.0% by mass or more and 9.0% by mass or less, Mn: 0.1% by mass or more and 6.0% by mass or less, TiO ２ : 5.0% by mass or more and 25.0% by mass or less, SiO of metallic Si and Si compounds ２ Conversion value: 3.0% by mass or more and 8.0% by mass or less Na: 0.05% by mass or more and 0.50% by mass or less, and K: 0.05% by mass or more and 1.50% by mass or less, containing ZrO of metallic Zr and Zr compounds ２ Conversion value: 2.0 mass% or less MgO conversion value of metallic Mg and Mg compounds: 1.0% by mass or less, P: 0.030% by mass or less, S: 0.030% by mass or less, Co: 0.30% by mass or less, W: 0.50% by mass or less, REM: 0.50% by mass or less, Ti: 1.0% by mass or less, Al: 0.3% by mass or less, Al ２ O ３ : 2.0 mass% or less, Li: 0.50% by mass or less, characterized by the covered arc welding rod according to Claim 1.

3. The Ni: 7.0% by mass or more and 10.0% by mass or less, The Cr: 12.0% by mass or more and 15.0% by mass or less, The Mo: 1.0% by mass or more and 2.0% by mass or less, characterized by the covered arc welding rod according to Claim 1.

4. A welded joint characterized by being manufactured by welding using the covered arc welding rod according to any one of Claims 1 to 3 with a stainless steel plate as the base material.

5. Based on the total mass of the weld metal, C: 0.001% by mass or more and 0.040% by mass or less, Cr: 14.0% by mass or more and 22.0% by mass or less, Ni: 7.0% by mass or more and 18.0% by mass or less, Mn: 0.3% by mass or more and 3.0% by mass or less, Nb: 0.001% by mass or more and 0.400% by mass or less, and V: 0.001% by mass or more and 0.400% by mass or less, N: 0.001% by mass or more and 0.050% by mass or less, containing Si: 1.0% by mass or less, Ti: 1.0% by mass or less, Mo: 4.0% by mass or less, Cu: 0.50 mass% or less, with the balance being Fe and inevitable impurities, and the value A3 calculated by the following formula (3): 0.120 or more and 0.500 or less, and the value A4 calculated by the following formula (4): 9.40 or less, a weld metal characterized by this. 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) However, [Nb] Ｍ represents the Nb content in the weld metal expressed as mass%, and [V] Ｍ represents the V content in the weld metal expressed as mass%, and [Cr] Ｍ represents the Cr content in the weld metal expressed as mass%, and [Mo] Ｍ represents the Mo content in the weld metal expressed as mass%, and [Ni] Ｍ represents the Ni content in the weld metal expressed as mass%, and [C] Ｍ represents the C content in the weld metal expressed as mass%, and [N] Ｍ represents the N content in the weld metal expressed as mass%, and [Cu] Ｍ represents the Cu content in the weld metal expressed as mass%.

6. P: 0.030 mass% or less, S: 0.030 mass% or less, Co: 0.500 mass% or less, W: 0.50 mass% or less, the Ni: 12.0 mass% or more and 14.0 mass% or less, the Cr: 17.0 mass% or more and 19.0 mass% or less, the Mo: 1.7 mass% or more and 2.5 mass% or less, a weld metal according to claim 5, characterized by this.

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