Solid wire and gas shielded arc welding method

Abstract

Provided is a solid wire with which it is possible to obtain a back bead having an excellent appearance without using a back shielding gas, and with which it is possible to obtain a weld metal having excellent mechanical properties. A solid wire for steel material welding in which at least one of the steel materials to be welded contains 4-10 mass% of Cr, with respect to the total mass of the wire, at least one of the steel materials to be welded being a steel material containing Cr in the amount of 4-10 mass%, with respect to the total mass of the wire. The present invention is characterized by containing 0.02 mass% to 0.11 mass% (inclusive) of C, 0.6 mass% to 1.7 mass% (inclusive) of Si, 0.2 mass% to 1.5 mass% (inclusive) of Mn, more than 0.005 mass% to 0.030 mass% (inclusive) of S, 4.0 mass% to 13 mass% (inclusive) of Cr, 0.3 mass% to 1.5 mass% (inclusive) of Mo, 0.030 mass% or less of P, 1.4 mass% or less of Ni, 0.05 mass% or less of Nb, 0.05 mass% or less of V, 0.05 mass% or less of Ti, and 0.05 mass% or less of Al, with the remainder comprising Fe and unavoidable impurities.

Description

Technical Field

[0001] The invention relates to a solid welding wire and a gas shielded arc welding method. Background Art

[0002] In the fields of oil refineries and chemical plants, steel containing Cr is used to withstand harsh environments. Generally speaking, when gas shielded arc welding is performed on steel with a high Cr content as a butt single-sided weld joint, in order to prevent the formation of high-melting-point Cr oxides on the surface of the back weld bead and cause poor appearance of the penetration weld, it is necessary to perform back protection with an inert gas during the initial welding. However, the continuous flow of back shielding gas from the back side of the steel increases costs and complicates the operation when the target steel is, for example, a pipe.

[0003] Patent Document 1 discloses a welding material capable of constructing a weld having excellent penetration performance and mechanical properties without using a back shielding gas. The welding material described in Patent Document 1 specifies the contents of C, Cr, Mo, Ni and Al, controls the relationship between the Cr and Mn contents and the Si content, the relationship between the S content and the Mn content, the total amount of the Al content and the O content, and specifies the contents of P and S among impurities.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-24388 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, for the weld metal, post-weld heat treatment (PWHT: Post Weld Heat Treatment) is performed for the purpose of improving toughness, etc. However, in the welding material described in the above-mentioned Patent Document 1, the high temperature phase transformation temperature (Ac1 phase transformation point) is not studied, and the toughness of the weld metal may not be ensured due to the temperature of PWHT. In addition, there is room for further improvement in terms of penetration performance and mechanical properties of the initial layer.

[0009] The present invention has been proposed in view of the above situation, and its object is to provide a solid welding wire and a gas shielded arc welding method that are used for welding steel materials in which at least one of the steel materials to be welded contains 4 mass % or more and 10 mass % or less of Cr, and that can obtain a back weld bead with excellent appearance without using a back shielding gas, and can obtain a weld metal with excellent mechanical properties.

[0010] Means of solving the problem

[0011] The present inventors have conducted intensive studies to solve the above problems and have found that it is particularly important to control the Si content and the S content in the solid wire in order to suppress the occurrence of defective back bead formation. The present invention has been made based on this finding.

[0012] The above object of the present invention is achieved by the following structure [1] related to the solid welding wire.

[0013] [1] A solid welding wire, characterized in that it is used for welding steel materials wherein at least one of the steel materials to be welded contains 4% by mass or more and 10% by mass or less of Cr, wherein the content of Cr is 4% by mass or more and 10% by mass or less relative to the total mass of the welding wire.

[0014] C: 0.02 mass % or more and 0.11 mass % or less,

[0015] Si: 0.6 mass % or more and 1.7 mass % or less,

[0016] Mn: 0.2 mass % or more and 1.5 mass % or less,

[0017] S: more than 0.005 mass % and less than 0.030 mass %,

[0018] Cr: 4.0 mass % or more and 13 mass % or less,

[0019] Mo: 0.3 mass % or more and 1.5 mass % or less, and

[0020] P: 0.030 mass% or less,

[0021] Ni: 1.4 mass% or less,

[0022] Nb: 0.05 mass% or less,

[0023] V: 0.05 mass% or less,

[0024] Ti: 0.05 mass% or less,

[0025] Al: 0.05 mass % or less,

[0026] The balance contains Fe and inevitable impurities.

[0027] In addition, preferred embodiments of the present invention of the solid welding wire relate to the following [2] and [3]

[0028] [2] The solid welding wire according to [1], further comprising Zr: 0.15 mass % or less relative to the total mass of the welding wire.

[0029] [3] The solid welding wire according to [1] or [2], characterized in that it also contains at least one selected from Co, Cu and N in the range of Co: 0.5 mass % or less, Cu: 0.5 mass % or less, and N: 0.02 mass % or less relative to the total mass of the welding wire.

[0030] The above-mentioned object of the present invention can be achieved by the following structure [4] involving the gas shielded arc welding method.

[0031] [4] A gas shielded arc welding method, characterized in that the solid welding wire described in any one of [1] to [3] is used to weld a steel material containing 4 mass % or more and 10 mass % or less of Cr, without using a back shielding gas.

[0032] Effects of the Invention

[0033] According to the present invention, a solid welding wire can be provided which can obtain a back weld bead with excellent appearance and a weld metal with excellent mechanical properties without using a back shielding gas, and a gas shielded arc welding method using the solid welding wire can be provided. DETAILED DESCRIPTION

[0034] Hereinafter, the mode for implementing the present invention will be described in detail. In addition, in this specification, the solid welding wire is sometimes referred to as "welding wire". In addition, the present invention is not limited to the embodiment described below, and can be arbitrarily changed without departing from the scope of the present invention.

[0035] 〔Solid welding wire〕

[0036] The solid welding wire of the present embodiment is used for welding of a steel material in which at least one of the steel materials to be welded contains Cr of 4% by mass or more and 10% by mass or less. The so-called steel materials to be welded refer to a plurality of steel materials to be welded. For example, when the solid welding wire of the present embodiment is used for welding a pair of butted steel materials, the Cr content of at least one of the steel materials in the pair of steel materials can be 4% by mass or more and 10% by mass or less. That is, any one of the pair of steel materials can contain Cr in the range of 4% by mass or more and 10% by mass or less, or the Cr content of one of the steel materials in the pair of steel materials can be 4% by mass or more and 10% by mass or less, and the Cr content of the other steel material is not particularly limited and is outside the range of 4% by mass or more and 10% by mass or less. In addition, it is preferred that the Cr content of one of the steel materials is 10% by mass or less (including 0% by mass). As a pair of steel materials, for example, the steel materials to be welded can be a combination of 9% Cr steel and 2% Cr steel, or a combination of 9% Cr steel and a welding steel material described in JIS G 3106. The solid welding wire of this embodiment can also be applied to such dissimilar material joints.

[0037] Hereinafter, steel having a Cr content of 4 mass % or more and 6 mass % or less is referred to as 5% Cr steel, and steel having a Cr content of 8 mass % or more and 10 mass % or less is referred to as 9% Cr steel. In the present embodiment, the shape of the steel material used as the welded steel material is not particularly limited, and for example, it can be applied to welding of steel plates or pipes.

[0038] The chemical components contained in the solid wire of the present embodiment will be described in detail below with respect to the reasons for their inclusion and the reasons for numerical value limitations.

[0039] <C: 0.02 mass % or more and 0.11 mass % or less>

[0040] C is an important element that combines with Cr and Mo to form carbides and has the effect of ensuring the strength of the weld metal. In addition, as an austenite-forming element, it helps to suppress the formation of delta ferrite in the weld metal. If the C content is less than 0.02% by mass relative to the total mass of the welding wire, the desired strength of the weld metal cannot be obtained. Therefore, the C content is 0.02% by mass or more, preferably 0.03% by mass or more, more preferably 0.04% by mass or more, and even more preferably 0.05% by mass or more relative to the total mass of the welding wire.

[0041] On the other hand, if the C content exceeds 0.11% by mass relative to the total mass of the welding wire, the solidification temperature of the segregated portion is greatly reduced, and hot cracks are likely to occur. In addition, the strength of the weld metal is excessive, and sulfide stress cracking may occur. In addition, the precipitation of carbides is excessive, and the toughness of the weld metal is reduced. Therefore, the C content is 0.11% by mass or less, preferably 0.105% by mass or less, and more preferably 0.10% by mass or less relative to the total mass of the welding wire.

[0042] <Si: 0.6 mass % or more and 1.7 mass % or less>

[0043] Si preferentially forms an oxide film on the back bead surface that has a low melting point and is less likely to hinder the solidification of the weld metal, and has the effect of preventing poor back bead formation caused by Cr oxidation during welding. If the Si content is less than 0.6% by mass relative to the total mass of the welding wire, the above effect cannot be fully achieved, and the back bead shape deteriorates. Therefore, the Si content is 0.6% by mass or more, preferably 0.8% by mass or more, and more preferably 0.9% by mass or more relative to the total mass of the welding wire.

[0044] On the other hand, if the Si content exceeds 1.7% by mass relative to the total mass of the welding wire, δ ferrite is excessively generated in the weld metal, and the toughness of the weld metal decreases. In addition, the amount of slag generated on the surface weld bead increases, and slag inclusions are likely to occur. Therefore, the Si content is 1.7% by mass or less, preferably 1.6% by mass or less, and more preferably 1.5% by mass or less relative to the total mass of the welding wire.

[0045] <Mn: 0.2 mass % or more and 1.5 mass % or less>

[0046] Mn is an element that acts as a deoxidizer of the weld metal and has the effect of increasing the strength of the weld metal and improving the toughness. In addition, Mn is an austenite-forming element and helps suppress the formation of delta ferrite in the weld metal. If the Mn content is less than 0.2% by mass relative to the total mass of the welding wire, insufficient deoxidation occurs, and the effect of suppressing the residual delta ferrite in the weld metal cannot be fully obtained, and the toughness of the weld metal decreases. Therefore, the Mn content is 0.2% by mass or more, preferably 0.3% by mass or more, and more preferably 0.4% by mass or more relative to the total mass of the welding wire.

[0047] On the other hand, if the Mn content exceeds 1.5% by mass relative to the total mass of the welding wire, the high temperature strength of the weld metal deteriorates. In addition, the solidification temperature of the segregated portion decreases, and the transformation point decreases, making PWHT at high temperatures difficult. In addition, complex oxides are generated together with Cr, resulting in poor back bead formation. Therefore, the Mn content is 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.1% by mass or less relative to the total mass of the welding wire.

[0048] <S: more than 0.005 mass % and less than 0.030 mass %>

[0049] S affects the convection in the molten pool, increases the penetration depth, and has the effect of improving the stability of the arc and forming a good back bead. If the S content is less than 0.005 mass % relative to the total mass of the welding wire, incomplete penetration occurs and the back bead shape deteriorates. Therefore, the S content is higher than 0.005 mass %, preferably 0.006 mass % or more, and more preferably 0.007 mass % or more relative to the total mass of the welding wire.

[0050] On the other hand, if the S content exceeds 0.030 mass % relative to the total mass of the welding wire, hot cracking may occur. Therefore, the S content is 0.030 mass % or less, preferably 0.025 mass % or less, and more preferably 0.020 mass % or less relative to the total mass of the welding wire.

[0051] <Cr: 4.0 mass % or more and 13 mass % or less>

[0052] Cr is a main element of at least one of the steel materials to be welded, that is, 5% Cr steel and 9% Cr steel, in welding using the solid welding wire of the present embodiment, and is an indispensable element for ensuring the oxidation resistance and high temperature strength of the weld metal at high temperatures. If the Cr content is less than 4.0% by mass relative to the total mass of the welding wire, the oxidation resistance and high temperature strength of the weld metal are insufficient. Therefore, the Cr content is 4.0% by mass or more, preferably 4.2% by mass or more, and more preferably 4.5% by mass or more relative to the total mass of the welding wire.

[0053] On the other hand, if the Cr content exceeds 13% by mass relative to the total mass of the welding wire, an oxide film that hinders uniform solidification of the high melting point weld metal is formed on the back bead surface even when the Si content is controlled as described above. In addition, since Cr is a ferrite-forming element, it causes residual delta ferrite to deteriorate the toughness and creep properties of the weld metal. Therefore, the Cr content is 13% by mass or less, preferably 12% by mass or less, and more preferably 11% by mass or less relative to the total mass of the welding wire.

[0054] <Mo: 0.3 mass % or more and 1.5 mass % or less>

[0055] Mo is a solid solution strengthening element and is an element having the effect of improving high temperature strength by precipitation of carbides. If the Mo content is less than 0.3 mass % relative to the total mass of the welding wire, the high temperature strength of the weld metal is insufficient. Therefore, the Mo content is 0.3 mass % or more, preferably 0.35 mass % or more, and more preferably 0.4 mass % or more relative to the total mass of the welding wire.

[0056] On the other hand, if the Mo content exceeds 1.5% by mass relative to the total mass of the welding wire, residual delta ferrite will occur, and the toughness and creep properties of the weld metal will deteriorate. Therefore, the Mo content is 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.2% by mass or less, relative to the total mass of the welding wire.

[0057] <P: 0.030 mass % or less>

[0058] P is an impurity element and a component that increases the sensitivity to hot cracking. If the P content is higher than 0.030 mass % relative to the total mass of the welding wire, hot cracking may occur. Therefore, the P content is 0.030 mass % or less, preferably 0.020 mass % or less, and more preferably 0.015 mass % or less relative to the total mass of the welding wire.

[0059] <Ni: 1.4 mass % or less>

[0060] Ni is an austenite forming element like Mn, and contributes to suppressing the formation of delta ferrite in the weld metal. In the present embodiment, the lower limit of the Ni content is not particularly limited, and may be 0% by mass. However, when Ni is contained in the welding wire for the purpose of suppressing the formation of delta ferrite in the weld metal, the Ni content is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more, relative to the total mass of the welding wire.

[0061] On the other hand, if the Ni content exceeds 1.4% by mass relative to the total mass of the welding wire, the high temperature strength of the weld metal deteriorates. In addition, the transformation point is lowered, and PWHT at high temperatures is difficult. Therefore, the Ni content is 1.4% by mass or less, preferably 1.2% by mass or less, and more preferably 1.0% by mass or less relative to the total mass of the welding wire.

[0062] <Nb: 0.05 mass % or less>

[0063] Nb is a solid solution strengthening element, but excessive inclusion in the welding wire causes precipitation of nitrides, which excessively increases the strength of the weld metal. In addition, Nb causes residual delta ferrite, which greatly deteriorates the toughness of the weld metal. If the Nb content exceeds 0.05% by mass relative to the total mass of the welding wire, the toughness of the weld metal deteriorates. Therefore, the Nb content is 0.05% by mass or less, preferably 0.03% by mass or less, and more preferably 0.02% by mass or less relative to the total mass of the welding wire.

[0064] <V: 0.05 mass % or less>

[0065] Excessive inclusion of V in the welding wire causes carbonitride precipitation, causes residual delta ferrite, and deteriorates the toughness of the weld metal. If the V content exceeds 0.05 mass % relative to the total mass of the welding wire, the toughness of the weld metal deteriorates. Therefore, the V content is 0.05 mass % or less, preferably 0.03 mass % or less, and more preferably 0.02 mass % or less relative to the total mass of the welding wire.

[0066] <Ti: 0.05 mass % or less>

[0067] Ti forms an oxide film that hinders uniform solidification of the weld metal, and deteriorates the formation of a good back bead shape. If the Ti content exceeds 0.05 mass % relative to the total mass of the welding wire, the back bead shape deteriorates. Therefore, the Ti content is 0.05 mass % or less, preferably 0.03 mass % or less, and more preferably 0.02 mass % or less relative to the total mass of the welding wire.

[0068] <Al: 0.05 mass % or less>

[0069] Both Al and Si are elements that preferentially form an oxide film on the back bead surface that has a low melting point and is less likely to hinder the solidification of the weld metal, but have a high slag generation ability, so there is a possibility of slag inclusion. If the Al content exceeds 0.05% by mass relative to the total mass of the welding wire, slag inclusion is likely to occur. Therefore, the Al content is 0.05% by mass or less, preferably 0.03% by mass or less, and more preferably 0.02% by mass or less relative to the total mass of the welding wire.

[0070] The solid welding wire of the present embodiment may contain Zr, Cu, Co, and N in addition to the above-mentioned components. The contents of the components that may be further contained in the welding wire and the reasons for their limitation are described below.

[0071] <Zr: 0.15 mass % or less>

[0072] Zr and Si are both elements that preferentially form an oxide film that does not easily hinder the solidification of the weld metal on the surface of the back bead, so in the solid welding wire of this embodiment, Zr is preferably contained as needed. If Zr is contained in the welding wire in a range of 0.15 mass% or less, the toughness will not be reduced due to excessive formation of δ ferrite, and poor back bead formation caused by Cr oxidation during welding can be prevented. Therefore, when Zr is contained in the solid welding wire of this embodiment, the Zr content is preferably 0.15 mass% or less relative to the total mass of the welding wire. When Zr is contained, it is preferably 0.005 mass% or more, and more preferably 0.010 mass% or more.

[0073] <Co: 0.5 mass % or less, Cu: 0.5 mass % or less, N: 0.02 mass % or less>

[0074] Co, Cu, and N are all austenite forming elements like Ni and Mn, and are elements that contribute to suppressing the formation of delta ferrite in the weld metal. In order to obtain the desired mechanical properties of the weld metal by suppressing the formation of delta ferrite, the solid welding wire of the present embodiment can contain at least one selected from Co, Cu, and N as needed. Therefore, it is preferred that at least one selected from Co, Cu, and N is contained in the range of Co: 0.5 mass % or less, Cu: 0.5 mass % or less, and N: 0.02 mass % or less relative to the total mass of the welding wire. In addition, the Co content is more preferably 0.40 mass % or less, and more preferably 0.30 mass % or less. The Cu content is more preferably 0.40 mass % or less, and more preferably 0.30 mass % or less. The N content is more preferably 0.015 mass % or less, and more preferably 0.010 mass % or less.

[0075] In addition, when the welding wire contains Co, the Co content is preferably 0.05 mass% or more, and more preferably 0.10 mass% or more. When the welding wire contains Cu, the Cu content is preferably 0.05 mass% or more, and more preferably 0.10 mass% or more. When the welding wire contains N, the N content is preferably 0.002 mass% or more, and more preferably 0.005 mass% or more. In addition, the welding wire of this embodiment can form a Cu plating layer, and the Cu content also includes the amount of copper plating.

[0076] <Ballast: Fe and unavoidable impurities>

[0077] The balance of the solid wire of this embodiment is Fe and inevitable impurities. The so-called inevitable impurities refer to elements that are not intentionally added to the wire, and examples of elements other than the above include B, Sn, As, Sb, etc. The content of impurities in the solid wire is preferably 0.10% by mass or less in total, and more preferably 0.05% by mass or less.

[0078] [Gas shielded arc welding method]

[0079] The gas shielded arc welding method of the present embodiment is a welding method for welding a steel material having a Cr content of 4 mass % or more and 10 mass % or less, using the above-mentioned solid welding wire and without using a back shielding gas. As mentioned above, when welding a steel material containing 4 mass % to 10 mass % of Cr, if a conventional solid welding wire is used, the back weld bead is easily oxidized, and the shape and appearance of the back weld bead are deteriorated. However, at least as welding of the initial layer, by using the above-mentioned solid welding wire of the present embodiment and without using a back shielding gas, a back weld bead with excellent penetration performance and mechanical properties can be formed.

[0080] In the gas shielded arc welding method of the present embodiment, the type of welding is not particularly limited, and in addition to tungsten inert gas (TIG) shielded welding, metal active gas (MAG) welding and metal inert gas (MIG) welding may also be used.

[0081] <Type and flow rate of shielding gas>

[0082] When welding with the solid wire of this embodiment, the shielding gas used on the surface side is not particularly limited, and for example, Ar gas, carbon dioxide, a mixed gas of Ar gas and carbon dioxide, or a mixed gas of Ar gas and oxygen can be used. The flow rate of the gas is also not particularly limited, and for example, it can be 15 to 50 L / min.

[0083] <Welding position, wire diameter>

[0084] In addition, the welding position using the solid welding wire of this embodiment is not particularly limited, and welding can be performed at various welding positions. In addition, the wire diameter (diameter) of the solid welding wire of this embodiment is not particularly limited, and it can be applied to welding wires of diameters specified in welding material standards such as AWS or JIS.

[0085] Example

[0086] Hereinafter, the effects of the present invention will be specifically described by giving examples of the present invention and comparative examples, but the present invention is not limited thereto.

[0087] [Manufacturing of solid welding wire]

[0088] Solid wires were produced so that the components contained in the wires were of various contents. The contents (mass %) of the chemical components in the total mass of the wires are shown in Tables 1 and 2 below. The remainder of the wires excluding the chemical components shown in Tables 1 and 2 below is Fe and unavoidable impurities. In Tables 1 and 2, "-" means that the component is not actively contained.

[0089] [Gas shielded arc welding (for back pass evaluation)]

[0090] Welding for evaluating the back pass was performed. Specifically, a pair of steel plates with a thickness of 19 to 25 mm, a Cr content of 9 mass%, a Mo content of 1 mass%, and a groove angle of 70° were prepared, and a primary layer was formed by TIG welding. The welding conditions are shown below.

[0091] <Welding conditions>

[0092] Welding method: TIG welding

[0093] Wire diameter: 2.4mm

[0094] Root gap: 2-3mm

[0095] Welding current: 90~110A

[0096] Arc voltage: 10~14V

[0097] Preheating: 150~300℃

[0098] Type of shielding gas, flow rate: 100% Ar, 15 L / min

[0099] Back shielding gas: None

[0100] Welding position: flat welding

[0101] [Evaluation test of back weld bead]

[0102] The weld metal obtained using each solid wire was visually observed on the back side of the weld (back bead appearance) and the cross-sectional macroscopic view of the weld metal to evaluate the back bead. On the back side of the weld, the shape of the back bead, the degree of oxidation, the presence of burn-through, and the presence of a depressed weld were observed. Regarding the cross-sectional macroscopic view, the back bead height, the depression depth of the back bead, and the shape of the boundary between the base material and the back bead were observed.

[0103] In addition, regarding the appearance of the back bead, the back bead width is uniform, there is no meandering or unevenness, there is no discoloration or unevenness due to oxidation, and no burn-through or sunken weld is confirmed, which is good (acceptable). On the other hand, the back bead width is uneven, there is severe unevenness, the back bead is discolored or uneven due to oxidation, or burn-through or sunken weld is confirmed, which is unacceptable.

[0104] In addition, in the cross-sectional macroscopic observation, the back weld bead height of 1 mm or more is qualified, and the back weld bead height of less than 1 mm is unqualified. In addition, near the width direction end of the back weld bead, there is no depression of 0.5 mm or more relative to the back of the base material, which is qualified, and the depression of 0.5 mm or more is unqualified. In addition, in the cross-sectional macroscopic observation, the shape of the boundary between the base material and the back weld bead is observed, and the shape of the boundary between the base material and the back weld bead is good (qualified), and the shape of the back weld bead is a sharp convex shape at the boundary between the base material and the back weld bead. It is poor (unqualified). In addition, for burn-through, there is a tendency for the back weld bead to be a sharp convex shape at the boundary between the base material and the back weld bead.

[0105] Then, as an evaluation of the back bead, a weld that passes all of the above items is evaluated as "A", and a weld that fails one or more of the items is evaluated as "C".

[0106] [Gas shielded arc welding (for weld metal evaluation)]

[0107] Welding for weld metal evaluation was performed. Specifically, the groove angle of SM490A steel material with a plate thickness of 12 mm and described in JIS G3106:2020 was processed to 45°, and a solid welding wire was prepared. After two or more isolation layers were welded inside the groove and on the backing plate, the root interval was 6.5 mm, and weld metal was formed by multi-layer welding by TIG welding. The welding conditions are shown below.

[0108] <Welding conditions>

[0109] Welding method: TIG welding

[0110] Wire diameter: 1.2mm

[0111] Welding current: 160~180A

[0112] Arc voltage: 10~16V

[0113] Type of shielding gas, flow rate: 100% Ar, 25 L / min

[0114] Welding position: flat welding

[0115] PWHT temperature, time: 745℃, 1 hour

[0116] [Evaluation test of mechanical properties of weld metal]

[0117] <Phase transition point measurement test>

[0118] A round rod-shaped test piece having a diameter of 8 mm and a length of 12 mm was extracted from the obtained weld metal, and the volume change of the test piece during heating by high-frequency induction heating was measured to measure the Ac1 transformation point.

[0119] In addition, when PWHT is performed at a temperature higher than the Ac1 transformation point, the weld metal undergoes reverse transformation to a structure containing primary martensite with high strength and low toughness, which deteriorates the performance of the weld joint. Therefore, the method with a high Ac1 transformation point can increase the margin of the PWHT temperature setting. Therefore, as an evaluation standard, the Ac1 transformation point is 800°C or above, and is evaluated as "A" (excellent), 760°C or above and below 800°C, and is evaluated as "B" (good), and below 760°C, It is evaluated as "C" (poor).

[0120] <Tensile strength test>

[0121] A tensile test piece with a diameter of 6 mm and a point distance of 24 mm was extracted from the center of the plate thickness of the obtained weld metal in parallel with the weld line direction, and the room temperature tensile strength (TS) of the weld metal was measured according to the metal material tensile testing method described in JIS Z 2241:2011.

[0122] In addition, if the strength of the weld metal is excessive, sulfide stress corrosion cracking may occur. In addition, if the strength of the weld metal is insufficient, a structure with the desired strength cannot be manufactured. Therefore, as an evaluation standard, the measurement result of the tensile strength test is 600MPa or more and 720MPa or less, and is evaluated as "A" (excellent), 550MPa or more and less than 600MPa, or more than 720MPa and less than 780MPa, and is evaluated as "B" (good), and less than 550MPa or more than 780MPa, and is evaluated as "C" (poor).

[0123] <Pendulum impact test>

[0124] A 2 mm V-notch pendulum impact test piece was taken from the center of the plate thickness of the obtained weld metal perpendicular to the weld line direction, and the pendulum impact value at -30°C or -40°C was measured according to the pendulum impact test method for metal materials described in JIS Z 2242:2005.

[0125] In addition, as a toughness evaluation standard based on the pendulum impact value, the measured result of the absorbed energy of the pendulum impact test at -30°C or below is divided by the original cross-sectional area of ​​the notch, and the pendulum impact value obtained is 47 (J / cm 2 ) and above are rated as "A" (excellent), 27 (J / cm 2 ) and below 47 (J / cm 2 ) were rated as "B" (good), and those below 27 (J / cm 2 ) were rated “C” (poor).

[0126] The measurement results of each evaluation test are shown in Table 3 below, and the evaluation results are shown in Table 4 below.

[0127]

Table 1

[0128]

[0129]

Table 2

[0130]

[0131]

Table 3

[0132]

[0133]

Table 4

[0134]

[0135] [Evaluation results]

[0136] As shown in Tables 1 to 4 above, in Invention Examples No. A1 to A16, since the chemical composition of the solid welding wire is within the numerical range specified in the present invention, a back weld bead with excellent appearance can be obtained without using a back shielding gas, and a weld metal with excellent mechanical properties can be obtained.

[0137] On the other hand, in Comparative Examples No. B1 and B3 to B5, the Si content in the solid wire is lower than the lower limit of the numerical range specified in the present invention, so the evaluation results of the back pass are poor. In addition, in Comparative Examples No. B2, B6, and B7, the Si content in the solid wire is higher than the upper limit of the numerical range specified in the present invention, so the evaluation results of toughness are low. In Comparative Example No. B8, the C content in the solid wire is higher than the upper limit of the numerical range specified in the present invention, so the strength of the weld metal is excessive, and the probability of sulfide stress cracking is increased.

[0138] In Comparative Example No. B9, since the C content and the Ni content in the solid wire are higher than the upper limit of the numerical range specified in the present invention, the strength of the weld metal is excessive, the toughness is reduced, and the transformation point is reduced, making PWHT at high temperatures difficult. In Comparative Example No. B10, since the C content and the Mn content in the solid wire are higher than the upper limit of the numerical range specified in the present invention, the strength of the weld metal is excessive, the toughness is reduced, and the transformation point is reduced, making PWHT at high temperatures difficult, and in addition, poor formation of the back bead occurs.

[0139] In addition, although the above-mentioned invention examples No. A1 to A16 are examples of welding between steel plates with high Cr content, which is generally difficult to form a good back weld bead, good evaluation results were obtained without using a back shielding gas by using a solid welding wire having a composition within the numerical range specified in the present invention. This shows that even if the Cr content of at least one of the steel materials to be welded is 4 mass% or more and 10 mass% or less, and the Cr content of the other steel material is, for example, 10 mass% or less (including 0 mass%), it is possible to obtain good weld metal without using a back shielding gas. In welding of steel plates with a Cr content of 5 mass% to 10 mass% or less, the poor appearance of the back weld is caused by the high Cr content of the steel plate and the welding material. Therefore, when the Cr content of one of the steel materials used as the welded steel material is less than 4 mass%, the solid welding wire as in the present embodiment can be applied.

[0140] Above, various embodiments have been described, but the present invention is certainly not limited to such examples. If it is a person skilled in the art, then it is obvious that various variations or modifications can be thought of within the scope described in the scope of the patent claims, and about these, of course, it should also be considered to belong to the technical scope of the present invention. In addition, the various constituent elements of the above-mentioned embodiments can also be arbitrarily combined without departing from the scope of the purpose of the invention.

[0141] In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2022-142294) filed on September 7, 2022, the contents of which are incorporated herein by reference.

Claims

1. A solid welding wire, characterized in that: The invention is used for welding of steel materials to be welded, wherein at least one of the steel materials to be welded is a steel material containing 4 mass % or more and 10 mass % or less of Cr, Relative to the total mass of welding wire, it contains: C: 0.02 mass % or more and 0.11 mass % or less, Si: 0.6 mass % or more and 1.7 mass % or less, Mn: 0.2 mass % or more and 1.5 mass % or less, S: more than 0.005 mass % and less than 0.030 mass %, Cr: 4.0 mass % or more and 13 mass % or less, Mo: 0.3 mass % or more and 1.5 mass % or less, and P: 0.030 mass% or less, Ni: 1.4 mass% or less, Nb: 0.05 mass% or less, V: 0.05 mass% or less, Ti: 0.05 mass% or less Al: 0.05 mass % or less, The balance contains Fe and inevitable impurities.

2. The solid welding wire according to claim 1, characterized in that: Zr is also contained in an amount of 0.15 mass % or less relative to the total mass of the welding wire.

3. The solid welding wire according to claim 1 or 2, characterized in that: Furthermore, at least one selected from Co, Cu and N is contained in the range of Co: 0.5 mass % or less, Cu: 0.5 mass % or less, and N: 0.02 mass % or less, based on the total mass of the welding wire.

4. A gas shielded arc welding method, characterized in that: Using the solid welding wire according to claim 1 or 2, welding is performed without using back shielding gas on a steel material containing at least 4 mass % and 10 mass % Cr among the steel materials to be welded.

5. A gas shielded arc welding method, characterized in that: Using the solid welding wire according to claim 3, welding is performed without using back shielding gas on a steel material in which at least one of the steel materials to be welded contains 4 mass % or more and 10 mass % or less of Cr.

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