Coated arc-welding rod, welded joint, and weld metal

Abstract

Provided is a coated arc-welding rod which is for use in welding a structure in an extremely low temperature range, and from which it is possible to obtain a weld metal that has excellent strength and that exhibits a lateral swelling amount equal to or more than a desired value. The coated arc-welding rod contains Fe, C, Cr, Ni, and the like in amounts specified with respect to the total mass of the welding rod, and contains 0.001-0.400 mass% of Nb, 0.001-0.400 mass% of V, and 0.001-0.020 mass% of N. In addition, value A1 is 0.120-0.500 and value A2 is 0.10 or less as determined by A1=[Nb]W+[V]W and 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. [Element]W represents a value indicating, in mass%, the amount of the element contained in the coated arc-welding rod.

Description

Covered metal arc welding electrodes, weld joints and weld metals

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

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

[0003] Japanese Patent Publication No. 2-205293

[0004] In recent years, with environmental considerations in mind, the use of hydrogen as a fuel for power generation, automobiles, and the like has been considered, and the demand for hydrogen is increasing. Accordingly, there is also a growing demand for storage tanks that can safely store liquefied hydrogen. Specifically, they are required to be usable in cryogenic temperatures, for example, at temperatures lower than those used in ordinary liquefied storage tanks, such as temperatures of about −253°C or higher. Therefore, there is a need for the development of a covered metal arc welding electrode that can be used for welding structures in even lower temperature regions. The value of lateral bulge is sometimes required as an indicator of the low-temperature toughness of the weld metal for such low-temperature tanks. However, the covered metal arc welding electrode described in Patent Document 1 does not take lateral bulge into consideration.

[0005] The present invention has been made in view of the above problems, and has an object to provide a covered metal arc welding rod used for welding structures in a cryogenic temperature range, which has excellent strength and can produce a weld metal having a lateral expansion amount equal to or greater than a desired value, and a weld joint and weld metal obtained by using the covered metal arc welding rod.

[0006] As a result of extensive research, the inventors have found that in order to obtain weld metal that exhibits excellent strength and lateral expansion in the cryogenic temperature range, it is effective to control the total amount of Nb and V in the welding rod and to control the amount of ferrite by keeping the value obtained by a calculation formula using the Cr equivalent and Ni equivalent within a predetermined range. The present invention was made based on this finding.

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

[0008] [1] A covered metal arc welding rod containing, relative 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 carbonate C), 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, Mo: 4.0% by mass or less, Cu: 0.50% by mass or less, a value A1 calculated by the following formula (1): 0.120 to 0.500, and a value A2 calculated by the following formula (2): 0.10 or less. A1 = [Nb] Ｗ + [V] Ｗ ...Formula (1) A2=1.22×([Cr] Ｗ + [Mo] Ｗ +0.7 × [Nb] Ｗ )-([Ni] Ｗ +35 x [C] Ｗ +20×[N] Ｗ +0.25 × [Cu] Ｗ ) -10.0 ... Equation (2) where [Nb] Ｗ is the Nb content in the covered electrode expressed in mass%, [V] Ｗ is the V content in the covered electrode expressed in mass%, and [Cr] Ｗ is the Cr content in the covered electrode expressed in mass%, and [Mo] Ｗ is the value of the Mo content in the covered electrode expressed in mass%, and [Ni] Ｗ is the Ni content in the covered electrode expressed in mass%, [C] Ｗ is the value of the C content in the covered electrode expressed in mass%, [N] Ｗ is the value of the N content in the covered electrode expressed in mass%, and [Cu] Ｗ is the Cu content in the covered electrode expressed in mass %.

[0009] Furthermore, preferred embodiments of the present invention relating to the covered electrode relate to the following [2] to [3].

[0010] [2] Furthermore, 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, TiO ２ : 5.0 mass% or more and 25.0 mass% or less, SiO of metal Si and Si compound ２ % or more and 8.0% or less by mass in terms of Zr content; Na: 0.05% or more and 0.50% or less by mass; and K: 0.05% or more and 1.50% or less by mass; and ２ 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, Al ２ O ３ : 2.0 mass % or less, Li: 0.50 mass % or less.

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

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

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

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

[0015] [5] The weld metal contains, relative 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, Si: 1.0 mass % or less, Ti: 1.0 mass % or less, Mo: 4.0 mass % or less, Cu: 0.50 mass % or less, with the balance being Fe and unavoidable impurities, and a value A3 calculated by the following formula (3): 0.120 or more and 0.500 or less, and A weld metal characterized in that the value A4 calculated by the following formula (4) is 9.40 or less: A3 = [Nb] Ｍ + "V" Ｍ ...Formula (3) A4=1.22×([Cr] Ｍ + [Mo] Ｍ +0.7 × [Nb] Ｍ )-([Ni] Ｍ +35 x [C] Ｍ +20×[N] Ｍ +0.25 × [Cu] Ｍ ) ...Equation (4) where [Nb] Ｍ is the Nb content in the weld metal expressed in mass%, [V] Ｍ is the value of the V content in the weld metal expressed in mass%, and [Cr] Ｍ is the Cr content in the weld metal expressed in mass%, and [Mo] Ｍ is the value of the Mo content in the weld metal expressed in mass%, and [Ni] Ｍ is the Ni content in the weld metal expressed in mass%, [C] Ｍ is the value of the C content in the weld metal expressed in mass%, [N] Ｍ is the value of the N content in the weld metal expressed in mass%, and [Cu] Ｍ is the Cu content in the weld metal expressed in mass %.

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

[0017] [6] The weld metal according to [5], characterized in that 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, and the Mo: 1.7 mass% or more and 2.5 mass% or less.

[0018] According to the present invention, a covered metal arc welding electrode can be provided that can produce weld metal having excellent strength and a lateral expansion amount equal to or greater than a desired value. Furthermore, according to the present invention, by using the covered metal arc welding electrode, a weld joint that can be suitably used in a cryogenic environment can be provided. Furthermore, according to the present invention, a weld metal having excellent strength and a lateral expansion amount equal to or greater than a desired value can be provided.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments. However, the present invention is not limited to the preferred embodiments described below.

[0020] [Coated Electrode] The coated electrode according to the present embodiment is configured by covering a steel core wire with a coating material. In this coated electrode, the contents of Fe, C, Cr, Ni, Nb, V, Mo, Cu, N, etc. in the welding electrode are controlled, and the total content of Nb and V and a value calculated by a specific formula 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 metal arc welding electrode according to the present embodiment will be described in detail. In this specification, the covered metal arc welding electrode may be simply referred to as a welding rod.

[0022] <Fe: 30% by mass or more and 55% by mass or less> Fe is the main component constituting the core wire of the welding rod according to this embodiment. The Fe content in the welding rod 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 rod is 55% by mass or less, preferably 50% by mass or less, and more preferably 45% by mass or less.

[0023] <C: 0.001% by Mass or More and 0.020% by Mass or Less> C is an element that improves the tensile strength of the weld metal. However, it segregates in the final solidification portion of the weld metal, lowering the melting point of the molten liquid and degrading hot cracking resistance. If the C content in the welding rod is less than 0.001% by mass, it is difficult to obtain a weld metal with good tensile strength. Therefore, the C content relative to the total mass of the welding rod is set to 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 rod exceeds 0.020% by mass, the hot cracking susceptibility increases. Therefore, the C content relative to the total mass of the welding rod is set to 0.020% by mass or less, preferably 0.016% by mass or less, and more preferably 0.013% by mass or less. Note that the C content specified in this embodiment excludes C contained in the welding rod as carbonate.

[0024] <Cr: 10.0% by Mass or More and 30.0% by Mass or Less> Cr is a component that improves the strength of the weld metal and stabilizes 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 relative to the total mass of the welding rod is set to 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 rod exceeds 30.0% by mass, the toughness of the weld metal deteriorates and solidification segregation of Cr is promoted, resulting in deterioration of hot cracking resistance. Therefore, the Cr content relative to the total mass of the welding rod is set to 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 relative to the total mass of the welding rod is set to 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 rod exceeds 20.0% by mass, the solid solubility of C and N decreases, making blowholes more likely to occur. Therefore, the Ni content relative to the total mass of the welding rod is set to 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 forms carbides, reduces the amount of dissolved C, and improves the absorbed energy and the amount of lateral expansion. In this embodiment, it is necessary to appropriately control the contents of Nb and V, which will be described later, particularly to achieve a desired amount of lateral expansion. If the Nb content in the welding rod is less than 0.001% by mass, the desired amount of lateral expansion cannot be obtained. Therefore, the Nb content relative to the total mass of the welding rod is set to 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 relative to the total mass of the welding rod is set to 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> Like Nb, V is a component that forms carbides, reduces the amount of solute C, and improves the absorbed energy and lateral expansion amount. Therefore, the V content must be appropriately controlled to achieve a desired lateral expansion amount or more. If the V content in the welding rod is less than 0.001% by mass, the desired lateral expansion amount cannot be obtained. Therefore, the V content relative to the total mass of the welding rod is set to 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 relative to the total mass of the welding rod is set to 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 relative to the total mass of the welding rod is set to 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 exceeds 0.020% by mass, the absorbed energy of the weld metal decreases. Therefore, the N content relative to the total mass of the welding rod is set to 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> Like Cr, Mo is a component that has the effect of improving the strength of the weld metal. However, in the covered metal arc welding electrode according to this embodiment, Mo does not necessarily need to be contained, and it may be 0% by mass. However, when Mo is contained in the welding electrode for the purpose of improving the strength of the weld metal, the Mo content relative to the total mass of the welding electrode is preferably 1.0% by mass or more, and more preferably 1.7% by mass or more. On the other hand, if the Mo content in the welding electrode exceeds 4.0% by mass, the toughness of the weld metal deteriorates and solidification segregation of Mo is promoted, resulting in deterioration of hot cracking resistance. Therefore, the Mo content relative to the total mass of the welding electrode is set to 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 metal arc welding electrode according to this embodiment, Cu does not necessarily need to be contained, and it may be 0% by mass. However, when Cu is contained in the welding electrode for the purpose of stabilizing the austenite structure, the Cu content relative to the total mass of the welding electrode is preferably 0.001% by mass or more, and more preferably 0.005% by mass or more. On the other hand, if the Cu content in the welding electrode exceeds 0.50% by mass, the hot cracking resistance of the weld metal deteriorates. Therefore, the Cu content relative to the total mass of the welding electrode 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 significantly affect the absorbed energy and lateral expansion amount of the weld metal. Therefore, a desired lateral expansion amount can be obtained by controlling the respective contents of Nb and V in the welding rod and controlling the total content of Nb and V within an appropriate range. If the value A1 calculated by the following formula (1), which is the total content of Nb and V in the welding rod, is less than 0.120, the desired absorbed energy and lateral expansion 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, if 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) where [Nb] Ｗ is the Nb content in the covered electrode expressed in mass%, [V] Ｗ is the V content in the covered electrode expressed in mass %.

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

[0034] If the value A2 calculated by the following formula (2) exceeds 0.10, the amount of ferrite becomes too large, resulting in a decrease in the amount of lateral expansion of the weld metal. Therefore, the value A2 is set to 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 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 x [C] Ｗ +20×[N] Ｗ +0.25 × [Cu] Ｗ ) -10.0 ... Formula (2) where [Cr] Ｗ is the Cr content in the covered electrode expressed in mass%, and [Mo] Ｗ is the value of the Mo content in the covered electrode expressed in mass%, [Nb] Ｗ is the Nb content in the covered electrode expressed in mass%, [Ni] Ｗ is the Ni content in the covered electrode expressed in mass%, [C] Ｗ is the value of the C content in the covered electrode expressed in mass%, [N] Ｗ is the value of the N content in the covered electrode expressed in mass%, and [Cu] Ｗ is the Cu content in the covered electrode expressed in mass %.

[0036] The covered electrode according to the present embodiment can solve the problems of the present invention if the content of each component is within the above range. In order to further improve the welding workability and the mechanical properties of the weld metal, the welding electrode may further contain F, Ca, Mn, TiO ２ , metal Si and Si compounds, Na and K, etc. Also, metal Zr and Zr compounds, metal Mg and Mg compounds, P, S, Co, W, REM, Ti, Al, Al ２ O ３It is also preferable that the content of Li relative to the total mass of the welding rod is specified. The preferred ranges of these contents will be described below.

[0037] <F: 0.50% by mass or more and 3.00% by mass or less> In this embodiment, F can be contained in the welding rod to suppress the amount of spatter generated and stabilize the arc. When the F content in the welding rod is 0.50% by 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 rod, the F content relative to the total mass of the welding rod is preferably 0.50% by mass or more, and more preferably 0.80% by mass or more. On the other hand, when the F content in the welding rod is 3.00% by mass or less, spatter and fumes can be suppressed. Therefore, the F content relative to the total mass of the welding rod is preferably 3.00% by mass or less, and more preferably 2.00% by mass or less. Note that F is CaF ２ and NaF or other fluoride forms.

[0038] <Ca: 3.0 mass % or more and 9.0 mass % or less> Ca is a carbonate or CaF ２ Therefore, when Ca is contained in the welding rod, the Ca content relative to the total mass of the welding rod is preferably 3.0 mass% or more, more preferably 3.5 mass% or more, and even more preferably 4.0 mass% or more. Furthermore, the Ca content in the welding rod is preferably 9.0 mass% or less, more preferably 8.0 mass% or less, and even more preferably 7.0 mass% or less.

[0039] <Mn: 0.1% by Mass or More and 6.0% by Mass or Less> Mn has a deoxidizing effect that suppresses blowholes caused by oxygen-based gases and stabilizes the austenite structure. Therefore, in this embodiment, Mn may be contained in the welding rod. A Mn content of 0.1% by mass or more in the welding rod can achieve a sufficient deoxidizing effect. Therefore, the amount of Mn added relative to 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, a Mn content of 6.0% by mass or less suppresses solidification segregation of Mn in the final solidification region of the weld metal, thereby suppressing the occurrence of hot cracking. Therefore, the Mn content relative to 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] <TiO ２ :5.0 mass% or more and 25.0 mass% or less>TiO ２ is the main component of the slag forming agent, and is a component that has the effect of forming a uniform slag with good encapsulation properties and improving arc stability. ２ It also has the effect of increasing the melting point of the slag and flattening the bead shape in all-position welding. ２ If the content is 5.0 mass % or more, the above-mentioned effect can be sufficiently obtained. ２ The content is preferably 5.0 mass% or more, more preferably 8.0 mass% or more, and even more preferably 10.0 mass% or more. ２ When the content is 25.0 mass % or less, the coating material becomes easily soluble, and the occurrence of slag inclusions can be suppressed. ２ The content is preferably 25.0 mass % or less, and more preferably 20.0 mass % or less. ２ The content is the TiO of the Ti compound contained in the welding rod. ２ Represents the conversion value.

[0041] <Metal Si and Si compound SiO ２Converted value: 3.0 mass % or more and 8.0 mass % or less> Si has the effect of improving the strength of the weld metal and the effect of acting as a binder (water glass) for the coating material. ２ The above effect can be obtained when the converted value is 3.0 mass % or more. ２ The converted value is preferably 3.0 mass % or more, and more preferably 3.5 mass % or more. ２ If the converted value is 8.0 mass % or less, it is possible to prevent the hot cracking resistance from deteriorating. ２ The converted value is preferably 8.0 mass % or less, and more preferably 7.0 mass % or less. ２ The converted value is the sum of all Si contained in the Si element, Si alloy, and Si compound in the welding rod, expressed as SiO ２ This is the value converted into

[0042] <Na: 0.05% by mass or more and 0.50% by mass or less> Alkali metals such as Na are components that have the effect of improving arc stability and can be contained in the welding rod as fluorides or composite 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 relative to 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, the decrease in the slag melting point can be suppressed and a good bead shape can be achieved in all-position welding. Therefore, the Na content relative to 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 can be, for example, Na ２ O and the like are present in the welding rod.

[0043] <K: 0.05% by mass or more and 1.50% by mass or less> Like Na, alkali metals such as K are components that have the effect of improving arc stability, and can be contained in the welding rod as fluorides or composite 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 relative to 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, the decrease in the slag melting point can be suppressed and a good bead shape can be achieved in all-position welding. Therefore, the K content relative to 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 can be, for example, K. ２ O and K ２ SiF ６ etc., are present in the welding rod.

[0044] Metallic Zr and Zr compound ZrO ２ Converted value: 2.0 mass% or less > ZrO ２ is a component that has the effect of accelerating slag solidification and forming a flat bead shape in both vertical and overhead positions. ２ The converted value may be 0 mass %. ２ When the converted value is 2.0 mass % or less, good slag encapsulation and slag removability can be obtained. ２ The converted value is preferably 2.0 mass % or less, and more preferably 1.0 mass % or less. ２ The converted value is calculated by dividing all Zr contained in metallic Zr and Zr compounds by ZrO. ２ The value is converted into Zr. Metallic Zr means the total amount of Zr contained in simple Zr and Zr alloys. Furthermore, Zr compounds mean Zr oxides and the like. In the following description, metal means simple Zr or alloys, and compounds mean oxides and the like.

[0045] <Metallic Mg and Mg Compounds, Equivalent to MgO: 1.0% by Mass or Less> Metallic Mg and Mg compounds are components that increase the slag solidification point and improve arc stability. However, the MgO equivalent value in the welding rod may be 0% by mass. A MgO equivalent value of 1.0% by mass or less can prevent deterioration of the bead shape. 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 refers to the total amount of Mg contained in metallic Mg and Mg compounds, converted into MgO. Furthermore, metallic Mg refers to the total amount of Mg contained in Mg alone and in Mg alloys.

[0046] <P: 0.030% by mass or less> P is an unavoidable impurity in a welding rod. Since the cryogenic toughness decreases as the P content in the weld metal increases, a lower P content in the welding rod is preferable. Therefore, the P content relative 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> S, like P, is an unavoidable impurity in a welding rod. Since the cryogenic toughness 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 relative to the total mass of the welding rod is preferably 0.030% by mass or less, and more preferably 0.020% by mass or less.

[0048] <Co: 0.30% by mass or less> Co is a component that has the effect of adjusting the toughness of the weld metal, so Co can be contained in the welding rod as necessary. If the Co content in the welding rod is 0.30% by mass or less, a decrease in the strength of the weld metal can be suppressed. Therefore, the Co content relative to the total mass of the welding rod is preferably 0.30% by mass or less, and more preferably 0.20% by mass or less.

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

[0050] <REM: 0.50% by mass or less> Because REM (rare earth element) is a deoxidizing element, REM can be contained in the welding rod as needed. However, if the REM content in the welding rod is 0.50% by mass or less, deterioration of welding workability can be suppressed. Therefore, the REM content relative to the total mass of the welding rod is preferably 0.50% by mass or less, and more preferably 0.10% by mass or less. Note that REM refers to the 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> Ti is a component that has the effect of improving the toughness of the weld metal, so Ti can be contained in the welding rod as necessary. When the Ti content in the welding rod is 1.0 mass% or less, the oxygen content in the weld metal can be reduced, and the toughness of the weld metal can be adjusted to a desired range. Therefore, the Ti content relative to 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 refers to the content of all metallic Ti contained in the Ti alloy and elemental Ti contained in the welding rod.

[0052] <Al: 0.3 mass% or less> Al is a component that has a deoxidizing effect and stabilizes the toughness of the weld metal, so 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 alloy elements in the weld metal can be appropriately adjusted, and excessive strength increase can be suppressed. Therefore, the Al content relative to the total mass of the welding rod is preferably 0.3 mass% or less, and more preferably 0.1 mass% or less. The Al content in the welding rod refers to the content of all metallic Al contained in the Al alloy and the elemental Al contained in the welding rod.

[0053] <Al ２ O ３ :2.00% by mass or less> Al ２ O ３ is a slag former and a component that has the effect of improving the bead shape, so if necessary, Al may be added to the welding rod. ２ O ３ The welding rod may contain Al. ２ O ３ When the content of Al relative to the total mass of the welding rod is 2.00 mass % or less, good slag removability can be obtained. ２ O ３ The Al content is preferably 2.00 mass % or less, and more preferably 1.50 mass % or less. ２ O ３ The content is the amount of Al in Al compounds such as Al oxides contained in the welding rod. ２ O ３ This represents the value converted into

[0054] <Li: 0.50% by mass or less> Like Na and K, alkali metals such as Li are components that have the effect of improving arc stability and can be contained in the welding rod as a fluoride or composite oxide. Furthermore, 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 a good bead shape can be achieved in all-position welding. Therefore, the Li content relative 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 Covered Metal Arc Welding Electrode> The covered metal arc welding electrode of this 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 mass% or more, more preferably 55 mass% or more, and even more preferably 60 mass% or more, based on the total mass of the welding electrode. The welding electrode may further contain Si, F, Mn, TiO ２ , ZrO ２ , MgO, Na, K, P, S, Co, W, REM, Ti, Al, Al ２ O ３ , Li, etc. The covered electrode preferably contains these components in total, together with the above essential components, at 85 mass % or more, more preferably at 90 mass % or more, and even more preferably at 92 mass % or more. Furthermore, the covered electrode may contain, as the balance of the above components, for example, Ba, Ta, Bi, etc., or CaCO ３ CO contained in carbonates such as ２ Carbonates may contain CO ２ Gas is generated. Decomposed CO ２ In this embodiment, the CO 2 derived from carbonate is used because the CO 2 does not contribute to the mechanical performance of the weld metal. ２ The CO ２ When the welding rod contains CO in a range of 0.5 mass % to 3.0 mass % based on the total mass of the welding rod, ２ It is preferred that the compound contains:

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

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

[0058] [Welded Joint] The welded joint according to this embodiment is produced by welding a stainless steel plate as a base material using the above-described covered metal arc welding electrode.

[0059] [Weld Metal] The weld metal according to this embodiment is formed, for example, by welding using the above-mentioned covered electrode, and has excellent strength and lateral expansion. The components and their contents contained in the weld metal according to this embodiment will be described in detail below. Each element is defined as the total amount of the component contained in a predetermined region of the weld metal that is not affected by the composition of the base metal, expressed as a value 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% by Mass or More and 0.040% by Mass or Less> C is a component that stabilizes the austenite phase in the weld metal, making it less likely to transform to the martensite phase. 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, it is difficult to obtain a weld metal with good tensile strength. Therefore, the C content relative to the total mass of the weld metal is set to 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 exceeds 0.040% by mass, the strength increases excessively, making it difficult to obtain excellent cryogenic toughness. Therefore, the C content relative to the total mass of the weld metal is set to 0.040% by mass or less, preferably 0.035% by mass or less, and more preferably 0.030% by mass or less.

[0061] <Cr: 14.0% by Mass or More and 22.0% by Mass or Less> Cr is a component that stabilizes the ferrite phase in the weld metal and makes it less likely to transform into the martensite phase. If the Cr content in the weld metal is less than 14.0% by mass, the ferrite phase becomes unstable, making it difficult to obtain excellent cryogenic toughness. Therefore, the Cr content relative to the total mass of the weld metal is set to 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 becomes excessively stabilized, resulting in a decrease in cryogenic toughness. Therefore, the Cr content relative to the total mass of the weld metal is set to 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 less likely to transform into the martensite phase. If the Ni content in the weld metal is less than 7.0% by mass, the austenite phase becomes unstable, resulting in reduced cryogenic toughness. Therefore, the Ni content relative to the total mass of the weld metal is set to 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 becomes excessively stabilized, making it impossible to obtain excellent cryogenic toughness. Therefore, the Ni content in the weld metal is set to 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 also a deoxidizing agent that removes oxygen in the weld metal as slag and improves mechanical strength. If the Mn content in the weld metal is less than 0.3% by mass, the deoxidizing effect is insufficient, increasing the oxygen content in the weld metal, making it impossible to obtain excellent cryogenic toughness. Therefore, the Mn content relative to the total mass of the weld metal is set to 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 exceeds 3.0% by mass, the strength of the weld metal increases excessively, resulting in a decrease in cryogenic toughness. Therefore, the Mn content relative to the total mass of the weld metal is set to 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, reduces the amount of solute C, and improves the absorbed energy and the amount of lateral expansion. If the Nb content in the weld metal is less than 0.001% by mass, the desired amount of lateral expansion cannot be obtained. Therefore, the Nb content relative to the total mass of the weld metal is set to 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 exceeds 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 set to 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> Like Nb, V is a component that forms carbides in the weld metal, reduces the amount of solute C, and improves the absorbed energy and lateral expansion. If the V content in the weld metal is less than 0.001% by mass, the desired lateral expansion cannot be achieved. Therefore, the V content relative to the total mass of the weld metal is set to 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 exceeds 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 set to 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, making it less likely to transform into the martensite phase. N is also a component that contributes to increasing the strength of the weld metal. Practically, the N content 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 cryogenic toughness. Therefore, the N content relative to the total mass of the weld metal is set to 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 Mass% or Less> Si is a component that has the effect of promoting deoxidation, but in the weld metal according to this embodiment, Si need not be contained, or may be 0 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 mass% or more, and more preferably 0.3 mass% or more, relative to the total mass of the weld metal. On the other hand, if the Si content in the weld metal exceeds 1.0 mass%, the crystal strength of the weld metal decreases, and excellent cryogenic toughness cannot be obtained. Therefore, the Si content relative to the total mass of the weld metal is set to 1.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.7 mass% or less.

[0068] <Ti: 1.0 mass% or less> Ti is a component that has the effect of improving the toughness of the weld metal, but in the weld metal according to this embodiment, Ti does not need to be contained, and it may be 0 mass%. On the other hand, if Ti is contained in the weld metal in excess of a predetermined amount, the strength increases excessively, resulting in a decrease in toughness. Therefore, the Ti content relative to the total mass of the weld metal is set to 1.0 mass% or less, preferably 0.05 mass% or less, and more preferably 0.02 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 need 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, and more preferably 1.7% by mass or more, relative to the total mass of the weld metal. On the other hand, if Mo is contained in the weld metal in an amount exceeding a predetermined amount, the strength increases excessively, resulting in a decrease in toughness. Therefore, the Mo content relative to the total mass of the weld metal is set to 4.0% by mass or less, preferably 3.0% by mass or less, and more preferably 2.5% by mass or less.

[0070] <Cu: 0.50 mass% or less> Cu is a component that has the effect of improving the strength of the weld metal, but in the weld metal according to this embodiment, Cu need not be contained, and it may be 0 mass%. On the other hand, if Cu is contained in the weld metal in excess of a predetermined amount, the strength increases excessively, leading to a decrease in toughness. Therefore, the Cu content relative to the total mass of the weld metal is set to 0.50 mass% or less, preferably 0.30 mass% or less, and more preferably 0.20 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 significantly affect the absorbed energy and lateral expansion amount of the weld metal. Therefore, a desired lateral expansion amount can be obtained by controlling the respective contents of Nb and V in the weld metal and appropriately controlling the total content of Nb and V. If the value A3 calculated by the following formula (3), which is the total content of Nb and V in the weld metal, is less than 0.120, the desired absorbed energy and lateral expansion amount cannot be obtained. Therefore, the value A3 is set to 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) exceeds 0.500, the tensile strength of the weld metal decreases. Therefore, the value A3 is set to 0.500 or less, preferably 0.400 or less, and more preferably 0.300 or less. A3 = [Nb] Ｍ + "V" Ｍ ...Equation (3) where [Nb] Ｍ is the Nb content in the weld metal expressed in mass%, [V] Ｍ is the V content in the weld metal expressed in mass %.

[0072] <Value A4 Calculated by Formula (4) Below: 9.40 or Less> In this embodiment, the ferrite content of the weld metal can be controlled within a desired range by adjusting parameters that use the contents of Cr, Mo, and Nb, which are ferrite stabilizing elements, and the contents of Ni, C, N, and Cu, which are austenite stabilizing elements, in the weld metal. More specifically, Formula (4) below is a formula for subtracting the Ni equivalent, which is calculated by converting the level of the ferrite stabilizing element into the amount of nickel, from the Cr equivalent, which is calculated by converting the level of the ferrite stabilizing element into the amount of chromium. Therefore, by specifying the value A4 calculated by Formula (4), it is possible to prevent the amount of ferrite from becoming excessive or insufficient, and to achieve a balance between strength and toughness.

[0073] If the value A4 calculated by the following formula (4) exceeds 9.40, the amount of ferrite becomes too large, deteriorating the low-temperature toughness and lateral expansion of the weld metal. Therefore, the value A4 is set to 9.40 or less, preferably 9.20 or less, and more preferably 9.00 or less.

[0074] A4=1.22×([Cr] Ｍ + [Mo] Ｍ +0.7 × [Nb] Ｍ )-([Ni] Ｍ +35 x [C] Ｍ +20×[N] Ｍ +0.25 × [Cu] Ｍ ) ...Equation (4) where [Cr] Ｍ is the Cr content in the weld metal expressed in mass%, and [Mo] Ｍ is the value of the Mo content in the weld metal expressed in mass%, [Nb] Ｍ is the Nb content in the weld metal expressed in mass%, [Ni] Ｍ is the Ni content in the weld metal expressed in mass%, [C] Ｍ is the value of the C content in the weld metal expressed in mass%, [N] Ｍ is the value of the N content in the weld metal expressed in mass%, and [Cu] Ｍ is the Cu content in the weld metal expressed 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, making 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 content of C and N to 0.08 or less, the value of the amount of lateral expansion can be improved. A5 = [C] Ｍ + "N" Ｍ ...Equation (5) where [C] Ｍ is the value of the C content in the weld metal expressed in mass%, [N] Ｍ is the value of the N content in the weld metal expressed in mass %.

[0076] <P: 0.030% by mass or less> Because the cryogenic toughness decreases as the P content in the weld metal increases, it is preferable that the P content in the weld metal be small. Therefore, 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.

[0077] <S: 0.030% by mass or less> As with P, the greater the S content in the weld metal, the more the cryogenic temperature toughness decreases, so the lower the S content in the weld metal is preferred. Therefore, the S content relative to the total mass of the weld metal is preferably 0.030% by mass or less, and more preferably 0.020% by mass or less.

[0078] <Co: 0.500 mass% or less> Co is a component that has the effect of adjusting the toughness of the weld metal, so Co can be contained in the weld metal as necessary. If 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 relative 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% by mass or less> W is a component that has the effect of improving the strength of the weld metal, so W can be contained in the weld metal as necessary. However, if the W content in the weld metal exceeds a predetermined amount, the strength increases 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.

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

[0081] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples and can be practiced with modifications within the scope of the spirit of the present invention, and all such modifications are included in the technical scope of the present invention.

[0082] [Preparation of Covered Electrodes] Covered electrodes having the compositions shown in Tables 1 to 3 below were prepared. The coverage was set to 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 x [C] Ｗ +20×[N] Ｗ +0.25 × [Cu] Ｗ ) -10.0 ... Equation (2) where [Nb] Ｗis the Nb content in the covered electrode expressed in mass%, [V] Ｗ is the V content in the covered electrode expressed in mass%, and [Cr] Ｗ is the Cr content in the covered electrode expressed in mass%, and [Mo] Ｗ is the value of the Mo content in the covered electrode expressed in mass%, and [Ni] Ｗ is the Ni content in the covered electrode expressed in mass%, [C] Ｗ is the value of the C content in the covered electrode expressed in mass%, [N] Ｗ is the value of the N content in the covered electrode expressed in mass%, and [Cu] Ｗ is the Cu content in the covered electrode expressed in mass %.

[0084] [Shielded Metal Arc Welding] Two carbon steel plates with a thickness of 20 mm were prepared and processed to have a groove angle of 45°. Then, using the fabricated shielded metal arc welding rod, two to three layers of buttering were formed on the surface of the groove and the surface of the backing material, and the carbon steel plates were arranged to form a V-groove. Then, welding was performed on the groove using each shielded metal arc welding rod. The welding conditions were 130 A, 24 V, flat position, 8 layers, 20 to 23 passes.

[0085] [Measurement of Weld Metal Composition] The obtained weld metals were subjected to solid-state emission spectroscopy analysis in accordance with JIS G 1253:2002 at the same positions as those from which tensile test specimens, described below, were taken, to measure the composition of each weld metal. The contents of chemical components in the weld metals are shown in Tables 4 and 5. In Table 4, A3 in formula (3) represents the value A3 calculated by formula (3), and A4 in formula (4) represents the value A4 calculated by formula (4). In Table 5, A5 in formula (5) represents the value A5 calculated by formula (5). Formulas (3) to (5) are as follows. The balance 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 x [C] Ｍ +20×[N] Ｍ +0.25 × [Cu] Ｍ )...Formula (4) A5=[C" Ｍ + "N" Ｍ ...Equation (5) where [Nb] Ｍ is the Nb content in the weld metal expressed in mass%, [V] Ｍ is the value of the V content in the weld metal expressed in mass%, and [Cr] Ｍ is the Cr content in the weld metal expressed in mass%, and [Mo] Ｍ is the value of the Mo content in the weld metal expressed in mass%, and [Ni] Ｍ is the Ni content in the weld metal expressed in mass%, [C] Ｍ is the value of the C content in the weld metal expressed in mass%, [N] Ｍ is the value of the N content in the weld metal expressed in mass%, and [Cu] Ｍ is the Cu content in the weld metal expressed in mass %.

[0087] [Mechanical Performance Evaluation Test] (Charpy Impact Test) Standard V-notch test pieces were taken from the obtained weld metals and subjected to a Charpy impact test in accordance with JIS Z 2242:2023. The test temperature for the Charpy impact test was -196°C, and the Charpy impact value (vE-196°C) and the amount of lateral expansion LE (mm) were measured. Five test pieces for measuring the Charpy impact value and five test pieces for measuring the amount of lateral expansion were taken from each weld metal. The maximum and minimum values ​​of the five test results were deleted, and the average values ​​of three test pieces were calculated and evaluated for the Charpy impact value and the amount of lateral expansion.

[0088] (Tensile test) A0 test piece was taken from the obtained weld metal at a position where the center of the test piece was the weld center line, and a tensile test was performed in accordance with JIS Z 3111: 2005. The test temperature for the tensile test was room temperature (20°C).

[0089] The results of the Charpy impact test, the lateral expansion amount, and the tensile strength are shown in Table 5. In each of the above evaluation tests, the average value of the Charpy impact value was 35.0 (J / cm ２ ) or more, the lateral expansion amount was 0.53 mm or more, and the tensile strength was 498 MPa or more, they were judged to have passed. In addition, those that did not achieve the standard value in any item were judged to have failed. In addition, 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]

[0091]

[0092]

[0093]

[0094]

[0095] As shown in Tables 1 to 5, in Invention Examples Nos. 1 to 14, the contents of specific components in the welding rods were appropriately controlled, and the values ​​A1 and A2 calculated by formulas (1) and (2) were within the ranges specified in this embodiment. Therefore, in the obtained weld metals, the contents of each component and the values ​​A3 and A4 calculated by formulas (3) and (4) were also within the ranges specified in this embodiment. Therefore, weld metals with excellent mechanical properties, and in particular, with a lateral expansion amount equal to or greater than a desired value, were obtained.

[0096] On the other hand, in Comparative Examples 1 and 3, the N content in the welding rod exceeded the upper limit specified in the present invention, and the value A1 calculated by formula (1) was less than the lower limit specified in the present invention. Furthermore, for the weld metal obtained using the welding rods of Comparative Examples 1 and 3, the value A3 calculated by formula (3) was less than the lower limit specified in the present invention, and the value A4 calculated by formula (4) exceeded the upper limit specified in the present invention. For Comparative Example 2, the value A1 calculated by formula (1) was less than the lower limit specified in the present invention. Furthermore, for the weld metal obtained using the welding rod of Comparative Example 2, the value A3 calculated by formula (3) was less than the lower limit specified in the present invention, and the value A4 calculated by formula (4) exceeded the upper limit specified in the present invention. Furthermore, for Comparative Example 4, the value A2 calculated by formula (2) exceeded the upper limit specified in the present invention. Furthermore, for Comparative Example 4, the value A2 calculated by formula (2) exceeded the upper limit specified in the present invention. For the weld metal obtained using welding electrode No. 4, the value A4 calculated by formula (4) exceeded the upper limit specified in the present invention. Therefore, all of Comparative Examples Nos. 1 to 4 had low Charpy impact values ​​and lateral expansion amounts.

[0097] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0098] This application is based on a Japanese patent application (Patent Application No. 2024-006773) filed on January 19, 2024, the contents of which are incorporated herein by reference.

Claims

1. With respect to the total mass of the welding rod, it contains: 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. 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. The covered arc welding rod is characterized by this. 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 % by mass, [V] Ｗ is the value representing the V content in the covered arc welding rod in % by mass, [Cr] Ｗ is the value representing the Cr content in the covered arc welding rod in % by mass, [Mo] Ｗ is the value representing the Mo content in the covered arc welding rod in % by mass, [Ni] Ｗ is the value representing the Ni content in the covered arc welding rod in % by mass, [C] Ｗ is the value representing the C content in the covered arc welding rod in % by mass, [N] Ｗ is the value representing the N content in the covered arc welding rod in % by mass, [Cu] Ｗ is the value representing the Cu content in the covered arc welding rod in % by mass.

2. Further, with respect to 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, the SiO of metallic Si and Si compounds ２ converted 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 ２ the ZrO converted value of metallic Zr and Zr compounds: 2.0% by mass or less, the MgO converted 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% by mass or less, Li: 0.50% by mass or less, characterized by the covered arc welding rod according to claim 1.

3. The covered arc welding rod according to claim 1, characterized in that Ni is 7.0% by mass or more and 10.0% by mass or less, Cr is 12.0% by mass or more and 15.0% by mass or less, and Mo 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 using the covered arc welding rod according to any one of claims 1 to 3 with a stainless steel plate as a base material.

5. With respect to 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, Si: 1.0% by mass or less, Ti: 1.0% by mass or less, Mo: 4.0% by mass or less, Cu: 0.50% by mass or less, 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. 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 weld metal in% by mass, [V] Ｍ is the value representing the V content in the weld metal in% by mass, [Cr] Ｍ is the value representing the Cr content in the weld metal in% by mass, [Mo] Ｍ is the value representing the Mo content in the weld metal in% by mass, [Ni] Ｍ is the value representing the Ni content in the weld metal in% by mass, [C] Ｍ is the value representing the C content in the weld metal in% by mass, [N] Ｍ is the value representing the N content in the weld metal in% by mass, [Cu] Ｍ is the value representing the Cu content in the weld metal in% by mass.

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

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