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 welding a steel material containing 1-10 mass% inclusive of Cr, the solid wire containing, in mass% relative to the total mass of the wire, 0.05-0.15% inclusive of C, 0.8-1.7% inclusive of Si, 0.4-1.2% inclusive of Mn, 7.5-13.0% inclusive of Cr, 0.70-1.5% inclusive of Mo, 0.010-0.10% inclusive of Nb, 0.10-0.50% inclusive of V, 0.010-0.070% inclusive of N, and satisfying the following conditions: 0.030% or less of P, 0.030% or less of S, 0.80% or less of Ni, 0.025% or less of Ti, 0.020% or less of Al, and 0.70% or less of Co, with the balance being Fe and unavoidable impurities. And the balance of 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] Generally speaking, steel materials containing Nb, V, etc. added to 9Cr-1Mo steel containing 8% to 10% Cr and 0.85% to 1.20% Mo are called 9Cr-1Mo-Nb-V steel. Cr-Mo ferritic high-strength heat-resistant steel represented by such 9Cr-1Mo-Nb-V steel has excellent high-temperature properties and is used in boilers and pressure vessels for thermal and nuclear power generation.

[0003] When the steel material with high Cr content as described above is subjected to gas shielded arc welding as a butt single-side weld joint, in order to prevent the formation of high melting point Cr oxide on the surface of the back weld bead and cause poor appearance of the back weld, it is necessary to use inert gas back shielding in the initial layer welding. However, there are problems such as increased cost and complicated operation when the target steel material is, for example, a pipe.

[0004] Patent Document 1 discloses a welding material capable of constructing a weld having excellent back bead performance and mechanical properties without using 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.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 10-24388 Summary of the invention

[0008] Problems to be solved by the invention

[0009] However, for the purpose of improving toughness, etc., post-weld heat treatment (PWHT: Post Weld Heat Treatment) is sometimes performed on the weld metal of ferritic high-strength heat-resistant steel such as 9Cr-1Mo-Nb-V steel. However, in the welding material described in the above-mentioned Patent Document 1, the high-temperature transformation temperature (Ac1 transformation point) has not been studied, and the toughness of the weld metal may not be ensured according to the PWHT temperature. In addition, there is room for further improvement in the back bead performance and the mechanical properties of the initial layer.

[0010] Furthermore, Patent Document 1 does not sufficiently consider the suppression of the formation of δ-ferrite. In order to form a weld metal that can adequately cope with boilers and pressure vessels for thermal power generation and nuclear power generation, it is important to further suppress the formation of δ-ferrite.

[0011] The present invention has been proposed in view of the above-mentioned problems, and its object is to provide a solid welding wire and a gas shielded arc welding method, which are used for welding a steel material containing 1 mass % or more and 10 mass % or less of Cr, without using a back shielding gas, and can obtain a back weld bead with excellent appearance, and can obtain a weld metal with excellent mechanical properties.

[0012] Means of solving the problem

[0013] The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that it is particularly important to control the Si content in the solid welding wire in order to suppress the occurrence of defective back bead formation. In addition, the present inventors have found that by controlling the contents of Nb, V, and Co in the solid welding wire, the formation of delta ferrite can be suppressed, and a weld metal having desired mechanical properties can be obtained. The present invention has been made based on this finding.

[0014] The above object of the present invention is achieved by the following (1) structure of the solid welding wire.

[0015] (1) A solid welding wire, characterized in that it is a solid welding wire for welding a steel material containing 1 mass % or more and 10 mass % or less of Cr, wherein:

[0016] Relative to the total mass of welding wire, it contains:

[0017] C: 0.05 mass % or more and 0.15 mass % or less,

[0018] Si: 0.8 mass % or more and 1.7 mass % or less,

[0019] Mn: 0.4 mass % or more and 1.2 mass % or less,

[0020] Cr: 7.5 mass% or more and 13.0 mass% or less,

[0021] Mo: 0.70 mass % or more and 1.5 mass % or less,

[0022] Nb: 0.010 mass % or more and 0.10 mass % or less,

[0023] V: 0.10 mass % or more and 0.50 mass % or less,

[0024] N: 0.010 mass % or more and 0.070 mass % or less, and

[0025] P: 0.030 mass% or less,

[0026] S: 0.030 mass % or less,

[0027] Ni: 0.80 mass % or less,

[0028] Ti: 0.025 mass% or less,

[0029] Al: 0.020 mass % or less,

[0030] Co: 0.70 mass % or less,

[0031] The balance contains Fe and inevitable impurities.

[0032] Furthermore, preferred embodiments of the present invention of the solid welding wire relate to the following (2) and (3).

[0033] (2) The solid welding wire according to (1), further comprising Zr: 0.10 mass % or less based on the total mass of the welding wire.

[0034] (3) The solid welding wire according to (1) or (2), further comprising 0.50 mass % or less of Cu based on the total mass of the welding wire.

[0035] The above-mentioned object of the present invention is achieved by the following structure (4) related to the gas shielded arc welding method

[0036] (4) A gas shielded arc welding method, characterized in that welding is performed on a steel material containing 1 mass % to 10 mass % of Cr using the solid welding wire according to any one of (1) to (3) without using a back shielding gas.

[0037] Effects of the Invention

[0038] According to the present invention, a solid welding wire can be provided which 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, and a gas shielded arc welding method using the solid welding wire can be provided. DETAILED DESCRIPTION

[0039] 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.

[0040] 〔Solid welding wire〕

[0041] The solid welding wire of this embodiment is used for welding steel containing 1% by mass or more and 10% by mass or less of Cr. For example, the steel to be welded can be composed of a combination of 9% Cr steel and 2% Cr steel, and the solid welding wire of this embodiment can also be applied to dissimilar material joints. The solid welding wire of this embodiment is particularly preferably used for welding 9Cr-1Mo-Nb-V steel.

[0042] Hereinafter, 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 it can be applied to welding of steel plates, steel pipes, and the like, for example.

[0043] 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.

[0044] <C: 0.05 mass % or more and 0.15 mass % or less>

[0045] C is an important element that combines with Cr, Mo, V and Nb 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 0.05% 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 0.05% by mass or more, preferably 0.06% by mass or more, and more preferably 0.07% by mass or more relative to the total mass of the welding wire.

[0046] On the other hand, if the C content exceeds 0.15% 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 precipitation of carbides is excessive, and the toughness of the weld metal is reduced. Therefore, the C content is 0.15% by mass or less, preferably 0.14% by mass or less, and more preferably 0.13% by mass or less relative to the total mass of the welding wire.

[0047] <Si: 0.8 mass % or more and 1.7 mass % or less>

[0048] Si preferentially forms an oxide film on the back bead surface that has a low melting point and is unlikely 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 0.8% 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 0.8% by mass or more, preferably 0.9% by mass or more, and more preferably 1.0% by mass or more relative to the total mass of the welding wire.

[0049] 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.

[0050] <Mn: 0.4 mass % or more and 1.2 mass % or less>

[0051] 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 0.4% 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 0.4% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more relative to the total mass of the welding wire.

[0052] On the other hand, if the Mn content exceeds 1.2% 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, Mn forms a composite oxide together with Cr, causing poor back bead formation. Therefore, the Mn content is 1.2% by mass or less, preferably 1.1% by mass or less, and more preferably 1.0% by mass or less relative to the total mass of the welding wire.

[0053] <Cr: 7.5 mass % or more and 13.0 mass % or less>

[0054] Cr is a main element of a high Cr content steel material to be welded, which makes it difficult to form a good back bead 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 7.5% 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 7.5% by mass or more, preferably 7.8% by mass or more, and more preferably 8.0% by mass or more relative to the total mass of the welding wire.

[0055] On the other hand, if the Cr content exceeds 13.0% 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 13.0% by mass or less, preferably 12.5% ​​by mass or less, and more preferably 12.0% by mass or less relative to the total mass of the welding wire.

[0056] <Mo: 0.70 mass % or more and 1.5 mass % or less>

[0057] 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 0.70 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 0.70 mass % or more, preferably 0.75 mass % or more, and more preferably 0.80 mass % or more relative to the total mass of the welding wire.

[0058] 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.

[0059] <Nb: 0.010 mass % or more and 0.10 mass % or less>

[0060] Nb is an element that has the effect of improving the strength of the weld metal by solid solution strengthening and precipitation as nitride. If the Nb content is less than 0.010 mass % relative to the total mass of the welding wire, the effect of improving the strength of the weld metal cannot be fully achieved. Therefore, the Nb content is 0.010 mass % or more, preferably 0.013 mass % or more, and more preferably 0.015 mass % or more relative to the total mass of the welding wire.

[0061] On the other hand, if the Nb content exceeds 0.10% by mass relative to the total mass of the welding wire, residual delta ferrite will occur, which greatly deteriorates the toughness of the weld metal. Therefore, the Nb content is 0.10% by mass or less, preferably 0.09% by mass or less, and more preferably 0.08% by mass or less relative to the total mass of the welding wire.

[0062] <V: 0.10 mass % or more and 0.50 mass % or less>

[0063] V is an element that precipitates in the weld metal as carbonitrides and has the effect of improving the strength of the weld metal. If the V content is less than 0.10% by mass relative to the total mass of the welding wire, the effect of improving the strength of the weld metal cannot be fully obtained. Therefore, the V content is 0.10% by mass or more, preferably 0.13% by mass or more, and more preferably 0.15% by mass or more relative to the total mass of the welding wire.

[0064] On the other hand, if the V content exceeds 0.50 mass % relative to the total mass of the welding wire, residual delta ferrite occurs, and the toughness of the weld metal deteriorates. Therefore, the V content is 0.50 mass % or less, preferably 0.40 mass % or less, and more preferably 0.30 mass % or less, relative to the total mass of the welding wire.

[0065] <N: 0.010 mass % or more and 0.070 mass % or less>

[0066] N is an element that contributes to solid solution strengthening and stabilization of strength by precipitation as a nitride. In addition, it is an austenite-forming element and has the effect of suppressing delta ferrite in the weld metal. If the N content is less than 0.010 mass % relative to the total mass of the welding wire, the above-mentioned effect cannot be fully achieved, the strength is reduced, and delta ferrite is generated. Therefore, the N content is 0.010 mass % or more, preferably 0.015 mass % or more, and more preferably 0.020 mass % or more relative to the total mass of the welding wire.

[0067] On the other hand, if the N content exceeds 0.070 mass % relative to the total mass of the welding wire, pores will occur. Therefore, the N content is 0.070 mass % or less, preferably 0.065 mass % or less, and more preferably 0.060 mass % or less relative to the total mass of the welding wire.

[0068] <P: 0.030 mass % or less>

[0069] 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.

[0070] <S: 0.030 mass % or less>

[0071] S affects convection in the molten pool, increases the penetration depth, and improves the stability of the arc, which has the effect of forming a good back bead. In the present embodiment, the lower limit of the S content is not particularly limited, and may be 0% by mass. However, when S is contained in the welding wire for the purpose of further improving the back bead forming ability, the S content is preferably 0.003% by mass or more, and more preferably 0.005% by mass or more, relative to the total mass of the welding wire.

[0072] 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.

[0073] <Ni: 0.80 mass % or less>

[0074] 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.

[0075] On the other hand, if the Ni content exceeds 0.80% 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 0.80% by mass or less, preferably 0.60% by mass or less, and more preferably 0.50% by mass or less relative to the total mass of the welding wire.

[0076] <Ti: 0.025 mass % or less>

[0077] 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 0.025 mass % relative to the total mass of the welding wire, the back bead shape deteriorates. Therefore, the Ti content is 0.025 mass % or less, preferably 0.018 mass % or less, and more preferably 0.015 mass % or less relative to the total mass of the welding wire.

[0078] <Al: 0.020 mass % or less>

[0079] 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 unlikely to hinder the solidification of the weld metal, but have a high slag generation ability, so there is a possibility of slag inclusion. In addition, Al is a ferrite-generating element, and excessively generates delta ferrite in the weld metal, which reduces the toughness of the weld metal. In addition, Al preferentially forms nitrides compared to Nb and V, and thus inhibits the formation of Nb and V nitrides that have a high-temperature strength ensuring effect, resulting in a reduction in high-temperature strength. Therefore, the Al content is 0.020 mass% or less, preferably 0.015 mass% or less, and more preferably 0.012 mass% or less relative to the total mass of the welding wire.

[0080] <Co: 0.70 mass % or less>

[0081] Co is an austenite-forming element like Ni and Mn, and is an element that contributes to suppressing the formation of delta ferrite in the weld metal. By including Co in the welding wire, desired mechanical properties of the weld metal can be obtained. In the present embodiment, the lower limit of the Co content is not particularly limited, and may be 0% by mass. However, when Co is included in the welding wire for the purpose of suppressing the formation of delta ferrite in the weld metal, the Co content is preferably 0.005% by mass, more preferably 0.05% by mass or more, further preferably 0.10% by mass or more, and particularly preferably 0.15% by mass or more relative to the total mass of the welding wire.

[0082] On the other hand, if the Co content exceeds 0.70 mass % relative to the total mass of the welding wire, the transformation point decreases and PWHT at high temperature becomes difficult. Therefore, the Co content is 0.70 mass % or less, preferably 0.60 mass % or less, and more preferably 0.50 mass % or less relative to the total mass of the welding wire.

[0083] The solid wire of the present embodiment may contain one or both of Zr and Cu in addition to the above-mentioned components within the ranges shown below. The contents of the components that may be additionally contained in the wire and the reasons for their limitation are described below.

[0084] <Zr: 0.10 mass % or less>

[0085] Zr and Si are both elements that preferentially form an oxide film that is less likely to hinder the solidification of the weld metal on the back bead surface, so it is preferable to contain Zr in the solid welding wire of the present embodiment as needed. If Zr is contained in the welding wire in a range of 0.10 mass % or less, the toughness will not be reduced due to excessive formation of δ ferrite, and poor back bead formation due to Cr oxidation during welding can be prevented. Therefore, when Zr is contained in the solid welding wire of the present embodiment, the Zr content is 0.10 mass % or less, preferably 0.08 mass % or less, and preferably 0.07 mass % or less relative to the total mass of the welding wire.

[0086] On the other hand, when Zr is contained in the welding wire in order to obtain the above-mentioned effect, the Zr content is preferably 0.005 mass % or more, and more preferably 0.010 mass % or more, based on the total mass of the welding wire.

[0087] <Cu: 0.50 mass % or less>

[0088] Cu, like Ni and Mn, is an austenite-forming element and is an element that contributes to suppressing the formation of delta ferrite in the weld metal. Therefore, it is preferable to contain Cu in the solid welding wire of the present embodiment as needed. If Cu is contained in the welding wire in a range of 0.50 mass % or less, the high temperature strength of the weld metal will not be deteriorated, and a weld metal having desired mechanical properties can be obtained. Therefore, when the solid welding wire of the present embodiment contains Cu, the Cu content is preferably 0.50 mass % or less, more preferably 0.40 mass % or less, and further preferably 0.30 mass % or less relative to the total mass of the welding wire.

[0089] On the other hand, when Cu is contained in the welding wire in order to obtain the above-mentioned effect, the Cu content is preferably 0.01 mass % or more, more preferably 0.05 mass % or more, and further preferably 0.10 mass % or more relative to the total mass of the welding wire. In addition, the welding wire of this embodiment may also be plated with Cu, and the Cu content also includes the copper-plated portion.

[0090] <Ballast: Fe and unavoidable impurities>

[0091] 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, more preferably 0.05% by mass or less in total.

[0092] [Gas shielded arc welding method]

[0093] The gas shielded arc welding method of the present embodiment is a welding method for welding a steel material to be welded containing 1% to 10% by mass of Cr using the above-mentioned solid welding wire without using a back shielding gas. As mentioned above, when the Cr content of the steel material to be welded is, for example, 8% to 10% by mass, if the existing solid welding wire is used for welding, the back weld bead is easily oxidized, and the shape and appearance of the back weld bead are deteriorated. However, at least as the welding of the initial layer, by using the above-mentioned solid welding wire of the present embodiment, not only the steel material with a high Cr content that is particularly easy to oxidize the back weld bead, but also the steel material to be welded containing 1% to 10% by mass of Cr, without using a back shielding gas, a back weld bead with excellent back weld bead performance and mechanical properties can be formed.

[0094] 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.

[0095] <Type and flow rate of shielding gas>

[0096] 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.

[0097] <Welding position, wire diameter>

[0098] 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 and JIS.

[0099] Example

[0100] 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.

[0101] [Manufacturing of solid welding wire]

[0102] Solid wires were produced by making the contents of the welding wires various. The contents (mass %) of the chemical components in the total mass of the welding wires are shown in the following Table 1. The balance of the welding wires other than the chemical components shown in the following Table 1 is Fe and unavoidable impurities.

[0103] [Gas shielded arc welding (for back pass evaluation)]

[0104] Welding for evaluating the back pass was performed. Specifically, a pair of steel plates with a thickness of 19 mm, a steel type of ASTM A387 Grade 91 Class 2, and a groove angle of 70° were prepared, and a primary layer was formed by TIG welding. The welding conditions are shown below.

[0105] <Welding conditions>

[0106] Welding method: TIG welding

[0107] Wire diameter: 2.4mm

[0108] Root gap: 2-3mm

[0109] Welding current: 90~110A

[0110] Arc voltage: 10~14V

[0111] Preheating: 150~300℃

[0112] Type of shielding gas, flow rate: 100% Ar, 15 L / min

[0113] Back shielding gas: None

[0114] Welding position: flat welding

[0115] [Evaluation test of back weld bead]

[0116] <Evaluation items>

[0117] The weld metal obtained using each solid wire was visually observed on the back side of the weld (back bead appearance) and the cross-section of the weld metal was visually observed to evaluate the back bead. Regarding the appearance of the back bead, the degree of oxidation, the presence of burn-through, and the presence of a concave bead were observed. Regarding the cross-section macroscopically, the back bead height, the back bead concave depth, and the shape of the boundary between the base material and the back bead were observed.

[0118] <Evaluation Method and Evaluation Criteria>

[0119] (Appearance of the back weld)

[0120] 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 depressed bead is confirmed, which is good. On the other hand, the back bead width is inconsistent, there is severe unevenness, the back bead is discolored or uneven due to oxidation, or burn-through or depressed bead is confirmed, which is unacceptable. If it is judged to be unacceptable, the appearance state is recorded in the measurement result column.

[0121] (Height of back weld bead)

[0122] In the cross-sectional macroscopic observation, the height of the back bead is measured. In this embodiment, the back bead height of 0.5 mm or more is acceptable, and the back bead height of less than 0.5 mm is unacceptable. The back bead height is recorded in the measurement result column.

[0123] (Depth of the depression)

[0124] Observe whether there is a dent near the end of the back weld in the width direction, and measure the depth of the dent if there is one. In this embodiment, the test is acceptable if there is no dent of more than 0.5 mm relative to the back of the base material, and unacceptable if there is a dent of more than 0.5 mm. The depth of the dent is recorded in the measurement result column.

[0125] (Shape of the boundary between the base material and the back weld bead)

[0126] The shape of the boundary between the base material and the back weld bead is observed in the cross-sectional macroscopic view. The shape that is gently convex from the base material to the back weld bead is judged as good (acceptable), and the shape that is sharply convex at the boundary between the base material and the back weld bead is judged as bad (unacceptable). "Good" or "bad" is recorded in the measurement result column. In addition, for those that have burn-through, there is a tendency for the back weld bead to form a sharply convex shape at the boundary between the base material and the back weld bead.

[0127] (Comprehensive evaluation of back weld)

[0128] Then, as the evaluation of the back bead, the evaluation is "A" if all the above items are acceptable, and the evaluation is "C" if one or more items are unacceptable. The evaluation results are described in the column of the evaluation results of the back bead.

[0129] [Gas shielded arc welding (for weld metal evaluation)]

[0130] Welding for weld metal evaluation was performed. Specifically, the groove angle of SM490A steel described in JIS G3106:2020 with a plate thickness of 12 mm 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.

[0131] <Welding conditions>

[0132] Welding method: TIG welding

[0133] Wire diameter: 1.2mm

[0134] Welding current: 160~180A

[0135] Arc voltage: 10~16V

[0136] Type and flow rate of shielding gas: 100% Ar, 25 liters / minute

[0137] Welding position: flat welding

[0138] PWHT temperature and time: 760°C, 2 hours

[0139] [Evaluation test of mechanical properties of weld metal]

[0140] <Evaluation items>

[0141] For the weld metal obtained using each solid wire, the temperature setting margin of PWHT was evaluated by measuring the Ac1 transformation point, and the area ratio of delta ferrite was measured. In addition, the mechanical properties were evaluated by performing a tensile test and a pendulum impact test. The measurement results and evaluation results of each evaluation item are shown together in the following Table 2. In addition, for some test pieces with poor back welds, the mechanical properties evaluation test of the weld metal was not performed.

[0142] <Evaluation Method and Evaluation Criteria>

[0143] (Measurement of Ac1 phase transition point)

[0144] A round rod-shaped test piece with a diameter of 8 mm and a length of 12 mm was extracted from the obtained weld metal before PWHT, and the volume change of the test piece during heating by high-frequency induction heating was measured to measure the Ac1 transformation point.

[0145] 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, and the performance of the weld joint deteriorates. Therefore, the higher the Ac1 transformation point, the greater the margin of the PWHT temperature setting. Therefore, as an evaluation standard, the Ac1 transformation point is 800°C or higher, and is evaluated as "A" (excellent), 780°C or higher and lower than 800°C, and is evaluated as "B" (good), and lower than 780°C, and is evaluated as "C" (poor).

[0146] (Measurement of delta ferrite area ratio)

[0147] From the weld metal obtained before PWHT, a 12 mm square test piece with a cross section perpendicular to the welding direction including the final weld layer original part was extracted, and the microstructure of the final weld layer original part was observed after appropriate grinding and etching, and the area ratio of delta ferrite was measured in a field of view of 100 times. The area ratio was measured using the point counting method, and the area ratio was calculated based on more than 600 grid points per field of view.

[0148] In addition, delta ferrite remains without being transformed into austenite during welding, which has an adverse effect on strength and toughness, causing the performance of the welded joint to deteriorate, so the smaller the area ratio, the better. Therefore, as an evaluation standard, the area ratio of delta ferrite is less than 5%, and it is evaluated as "A" (excellent), 5% or more and less than 10%, and it is evaluated as "B" (good), and 10% or more, It is evaluated as "C" (poor).

[0149] (Tensile test)

[0150] 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.

[0151] As the evaluation criteria, a tensile test result of 720 MPa or more was evaluated as "A" (excellent), a result of 620 MPa or more and less than 720 MPa was evaluated as "B" (good), and a result of less than 620 MPa was evaluated as "C" (poor).

[0152] (Pendulum impact test)

[0153] A 2 mm V-notch pendulum impact test piece was taken from the plate thickness center of the obtained weld metal perpendicular to the weld line direction, and the pendulum impact value at 20° C. was measured in accordance with the pendulum impact test method for metal materials described in JIS Z 2242:2005.

[0154] The toughness evaluation standard based on the pendulum impact value is 60 (J / cm 2 ) or above, rated as "A" (excellent), 34 (J / cm 2 ) and less than 60 (J / cm 2 ) were rated as "B" (good), and those below 34 (J / cm 2 ) were rated “C” (poor).

[0155]

Table 1

[0156]

[0157]

Table 2

[0158]

[0159] [Evaluation results]

[0160] As shown in Tables 1 and 2 above, in Invention Examples No. A1 to A7, although they are examples of welding steel plates with a high Cr content that are usually difficult to form good back beads, the chemical composition of the solid wire used is within the numerical range specified in the present invention. Therefore, without using a back shielding gas, a back bead with excellent appearance can be formed, and a weld metal with excellent mechanical properties can be obtained. In the welding of steel plates with a Cr content of 8% to 10% by mass, the poor appearance of the back weld is due to the high Cr content of the steel plate and the welding material. Therefore, the solid wire of the present embodiment can also be applied when the Cr content of the steel to be welded is 1% or more and less than 8%. That is, when the Cr content of the steel to be welded is 1% or more and 10% or less, by using the solid wire of the present invention, a good weld metal can be obtained without using a back shielding gas.

[0161] On the other hand, in Comparative Examples No. B1 to B7, the Si content in the solid wire is lower than the lower limit value specified in the present invention. In addition, in Comparative Examples No. B5 to B7, the Ti content in the solid wire is higher than the upper limit value specified in the present invention. Therefore, the evaluation results of the back beads are poor. In addition, in Comparative Example No. B8, since the Si content in the solid wire is higher than the upper limit value specified in the present invention, the area ratio of δ-ferrite increases. In addition, in Comparative Examples No. B9 and B10, since the Si content in the solid wire is higher than the upper limit value specified in the present invention, the area ratio of δ-ferrite increases, and the evaluation results of toughness are poor.

[0162] As described above, various embodiments have been described, but the present invention is of course not limited to such examples. For those skilled in the art, it is obvious that various modification examples or alteration examples can be conceived within the scope described in the claims of the patent. Regarding these, it should of course be considered to belong to the technical scope of the present invention. In addition, within the scope not departing from the gist of the invention, the constituent elements of the above embodiments can be arbitrarily combined.

[0163] Furthermore, this application is based on a Japanese patent application (Japanese Patent Application No. 2022-176386) filed on November 2, 2022, the content of which is incorporated herein by reference.

Claims

1. A solid welding wire, It is characterized in that A solid welding wire used for welding steel containing 1 mass % or more and 10 mass % or less of Cr, wherein Relative to the total mass of welding wire, it contains: C: 0.05 mass % or more and 0.15 mass % or less, Si: 0.8 mass % or more and 1.7 mass % or less, Mn: 0.4 mass % or more and 1.2 mass % or less, Cr: 7.5 mass % or more and 13.0 mass % or less, Mo: 0.70 mass % or more and 1.5 mass % or less, Nb: 0.010 mass % or more and 0.10 mass % or less, V: 0.10 mass % or more and 0.50 mass % or less, N: 0.010 mass % or more and 0.070 mass % or less, and P: 0.030 mass% or less, S: 0.030 mass % or less, Ni: 0.80 mass % or less, Ti: 0.025 mass% or less, Al: 0.020 mass % or less, Co: 0.70 mass % or less, The balance contains Fe and inevitable impurities.

2. The solid welding wire according to claim 1, It is characterized in that Zr is also contained in an amount of 0.10 mass % or less relative to the total mass of the welding wire.

3. The solid welding wire according to claim 1 or 2, It is characterized in that Cu is further contained in an amount of 0.50 mass % or less relative to the total mass of the welding wire.

4. A gas shielded arc welding method, It is characterized in that Using the solid welding wire according to claim 1 or 2, welding is performed on a steel material containing 1 mass % or more and 10 mass % or less of Cr without using a back shielding gas.

5. A gas shielded arc welding method, It is characterized in that Using the solid welding wire according to claim 3, welding is performed on a steel material containing 1 mass % or more and 10 mass % or less of Cr without using a back shielding gas.

Images