Solid wire and gas shielded arc welding methods

Abstract

To provide a solid wire which yields a penetration bead with an excellent appearance and also creates a weld metal with excellent mechanical performance, without using back shielding gas.SOLUTION: A solid wire, designed for welding steel materials with Cr content of 1 mass% or more and 10 mass% or less, contains, in terms of mass% relative to the total mass of the wire, C: 0.05% or more and 0.15% or less, Si: 0.8% or more and 1.7% or less, Mn: 0.4% or more and 1.2% or less, Cr: 7.5% or more and 13.0% or less, Mo: 0.70% or more and 1.5% or less, Nb: 0.010% or more and 0.10% or less, V: 0.10% or more and 0.50% or less, and N: 0.010% or more and 0.070% or less, with P: 0.030% or less, S: 0.030% or less, Ni: 0.80% or less, Ti: 0.025% or less, Al: 0.020% or less, and Co: 0.70% or less, with the balance being Fe and inevitable impurities.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Generally, steel materials containing Cr: 8 mass% to 10 mass% and Mo: 0.85 mass% to 1.20 mass% etc., to which Nb, V, etc. are added, are called 9Cr-1Mo-Nb-V steel. Cr-Mo ferrite high-strength heat-resistant steel typified by such 9Cr-1Mo-Nb-V steel has excellent high-temperature characteristics and is used in boilers, pressure vessels, etc. of thermal power generation and nuclear power generation.

[0003] When gas shielded arc welding a steel material with a high Cr content as described above as a butt single-sided welded joint, in order to prevent appearance defects of the back bead due to the formation of high melting point Cr oxides on the back wave surface, a back shield with an inert gas is required for the first layer welding. However, continuously flowing the back shield gas from the back side of the steel material has problems that the cost increases and the work becomes complicated when the target steel material is, for example, a pipe material.

[0004] Patent Document 1 discloses a welding material capable of constructing a welded part having excellent back wave performance and mechanical performance without using a back shield gas. The welding material described in Patent Document 1 has the contents of C, Cr, Mo, Ni, and Al defined, and the relationships between the Cr and Mn contents and the Si content, the relationship between the S content and the Mn content, and the total amount of the Al content and the O content are controlled, and the contents of P and S in the impurities are defined.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] Incidentally, post-weld heat treatment (PWHT) is sometimes applied to the weld metal of ferritic high-strength heat-resistant steels such as 9Cr-1Mo-Nb-V steel to improve toughness and other properties. However, in the welding material described in Patent Document 1, the high-temperature transformation temperature (Ac1 transformation point) has not been considered, and depending on the PWHT temperature, it may not be possible to ensure the toughness of the weld metal. Furthermore, there was room for further improvement in the back bead performance and the mechanical performance of the first layer.

[0007] Furthermore, Patent Document 1 does not adequately consider the suppression of δ-ferrite formation. In order to form weld metal that can adequately meet the requirements for boilers and pressure vessels in thermal and nuclear power plants, it is important to further suppress the formation of δ-ferrite.

[0008] The present invention has been made in view of the above-mentioned problems, and aims to provide a solid wire and a gas-shielded arc welding method that can be used for welding steel materials containing 1% to 10% by mass of Cr, and that can produce a back bead with excellent appearance and a weld metal with excellent mechanical performance without using back shielding gas. [Means for solving the problem]

[0009] The inventors of this invention conducted intensive research to solve the above problems and found that, in particular, controlling the Si content in the solid wire is important to suppress the occurrence of defects in back bead formation. Furthermore, the inventors found that by controlling the Nb, V, and Co content in the solid wire, the formation of δ-ferrite can be suppressed, and a weld metal with desired mechanical properties can be obtained. This invention is based on this finding.

[0010] The above objective of the present invention is achieved by the following configuration (1) relating to a solid wire.

[0011] (1) A solid wire used for welding steel materials containing 1% by mass or more and 10% by mass or less of Cr, With respect to the total mass of the wire, C: 0.05% by mass or more and 0.15% by mass or less, Si: 0.8% by mass or more and 1.7% by mass or less, Mn: 0.4% by mass or more and 1.2% by mass or less, Cr: 7.5% by mass or more and 13.0% by mass or less, Mo: 0.70% by mass or more and 1.5% by mass or less, Nb: 0.010 mass% or more and 0.10 mass% or less, V: 0.10% by mass or more and 0.50% by mass or less, N: Contains 0.010% by mass or more and 0.070% by mass or less. P: 0.030% by mass or less, S: 0.030% by mass or less, Ni: 0.80% by mass or less, Ti: 0.025% by mass or less, Al: 0.020% by mass or less, Co: 0.70% by mass or less, A solid wire characterized by the remainder consisting of Fe and unavoidable impurities.

[0012] Furthermore, preferred embodiments of the present invention relating to solid wires are as follows: (2) and (3).

[0013] (2) Furthermore, with respect to the total mass of the wire, Zr: 0.10% by mass or less, The solid wire according to (1), characterized by containing the following:

[0014] (3) Furthermore, with respect to the total mass of the wire, Cu: 0.50% by mass or less, A solid wire according to (1) or (2), characterized by containing the following.

[0015] The above object of the present invention is achieved by the following configuration (4) related to the gas shielded arc welding method.

[0016] (4) A gas shielded arc welding method characterized in that welding is performed without using a back shield gas on a steel material containing 1% by mass or more and 10% by mass or less of Cr using the solid wire described in any one of (1) to (3). [Advantages of the Invention]

[0017] According to the present invention, it is possible to provide a solid wire capable of obtaining a back bead with excellent appearance and a weld metal having excellent mechanical properties without using a back shield gas, and a gas shielded arc welding method using this solid wire. [Embodiments for Carrying Out the Invention]

[0018] Hereinafter, embodiments for carrying out the present invention will be described in detail. In this specification, the solid wire may be simply referred to as "wire". Further, the present invention is not limited to the embodiments described below, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[0019] [Solid Wire] The solid wire according to the present embodiment is used for welding a steel material containing 1% by mass or more and 10% by mass or less of Cr. For example, the welded steel material can be composed of a combination of 9% Cr steel and 2% Cr steel, and the solid wire according to the present embodiment can also be applied to a dissimilar material joint. The solid wire according to the present embodiment is particularly preferably used for welding 9Cr-1Mo-Nb-V steel.

[0020] Hereinafter, those having a Cr content of 8% by mass or more and 10% by mass or less may be 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, for example, steel plates and steel pipes.

[0021] Regarding the chemical components contained in the solid wire according to this embodiment, the reasons for their inclusion and the reasons for numerical limitations will be described in detail below.

[0022] <C: 0.05 mass% or more and 0.15 mass% or less> 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. Furthermore, as an austenite-forming element, it contributes to suppressing the formation of δ-ferrite in the weld metal. If the C content relative to the total mass of the wire is less than 0.05 mass%, the desired strength of the weld metal cannot be obtained. Therefore, the C content relative to the total mass of the wire is set to 0.05 mass% or more, preferably 0.06 mass% or more, and more preferably 0.07 mass% or more. On the other hand, if the C content relative to the total mass of the wire exceeds 0.15 mass%, the solidification temperature of the segregation part decreases significantly, and hot cracking is likely to occur. Also, the precipitation of carbides becomes excessive, and the toughness of the weld metal decreases. Therefore, the C content relative to the total mass of the wire is set to 0.15 mass% or less, preferably 0.14 mass% or less, and more preferably 0.13 mass% or less.

[0023] <Si: 0.8 mass% or more and 1.7 mass% or less> Si preferentially forms an oxide film with a low melting point on the back bead surface and is difficult to inhibit the solidification of the weld metal, and has the effect of preventing poor back bead formation due to the oxidation of Cr during welding. If the Si content relative to the total mass of the wire is less than 0.8 mass%, the above effects cannot be fully obtained, and the back bead shape deteriorates. Therefore, the Si content relative to the total mass of the wire is set to 0.8 mass% or more, preferably 0.9 mass% or more, and more preferably 1.0 mass% or more. On the one hand, when the Si content exceeds 1.7% by mass with respect to the total mass of the wire, excessive δ-ferrite is generated in the weld metal, and the toughness of the weld metal decreases. In addition, the amount of slag generation on the surface bead increases, and slag entrainment is likely to occur. Therefore, the Si content with respect to the total mass of the wire should be 1.7% by mass or less, preferably 1.6% by mass or less, and more preferably 1.5% by mass or less.

[0024] <Mn: 0.4% by mass or more and 1.2% by mass or less> Mn is an element that functions as a deoxidizer for the weld metal, has the effect of improving the strength of the weld metal and enhancing the toughness. Also, Mn is an austenite-forming element and contributes to suppressing the formation of δ-ferrite in the weld metal. When the Mn content with respect to the total mass of the wire is less than 0.4% by mass, it causes insufficient deoxidation and fails to sufficiently obtain the effect of suppressing the residual δ-ferrite in the weld metal, resulting in a decrease in the toughness of the weld metal. Therefore, the Mn content with respect to the total mass of the wire should be 0.4% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more. On the other hand, when the Mn content with respect to the total mass of the wire exceeds 1.2% by mass, the high-temperature strength of the weld metal deteriorates. In addition, the solidification temperature of the segregation part decreases, the transformation point decreases, and PWHT at high temperatures becomes difficult. Furthermore, Mn forms a complex oxide with Cr, causing poor backwave formation. Therefore, the Mn content with respect to the total mass of the wire should be 1.2% by mass or less, preferably 1.1% by mass or less, and more preferably 1.0% by mass or less.

[0025] <Cr: 7.5% by mass or more and 13.0% by mass or less> Cr is a major element of the weld steel with a high Cr content for which it is difficult to form good underbead ripples in welding using the solid wire according to the present embodiment, and is an essential element for ensuring the oxidation resistance and high-temperature strength of the weld metal at high temperatures. If the Cr content with respect to the total mass of the wire is less than 7.5% by mass, the oxidation resistance and high-temperature strength of the weld metal will be insufficient. Therefore, the Cr content with respect to the total mass of the wire is set to 7.5% by mass or more, preferably 7.8% by mass or more, and more preferably 8.0% by mass or more. On the other hand, when the Cr content with respect to the total mass of the wire exceeds 13.0% by mass, even when the Si content is controlled as described above, an oxide film that inhibits uniform solidification of the high-melting-point weld metal is generated on the surface of the underbead ripple. Further, since Cr is a ferrite-forming element, it causes the remaining of δ-ferrite and deteriorates the toughness and creep performance of the weld metal. Therefore, the Cr content with respect to the total mass of the wire is set to 13.0% by mass or less, preferably 12.5% by mass or less, and more preferably 12.0% by mass or less.

[0026] <Mo: 0.70% by mass or more and 1.5% by mass or less> Mo is a solid solution strengthening element and an element having an effect of increasing the high-temperature strength by precipitation of carbides. If the Mo content with respect to the total mass of the wire is less than 0.70% by mass, the high-temperature strength of the weld metal will be insufficient. Therefore, the Mo content with respect to the total mass of the wire is set to 0.70% by mass or more, preferably 0.75% by mass or more, and more preferably 0.80% by mass or more. On the other hand, when the Mo content with respect to the total mass of the wire exceeds 1.5% by mass, it causes the remaining of δ-ferrite and deteriorates the toughness and creep performance of the weld metal. Therefore, the Mo content with respect to the total mass of the wire is set to 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.2% by mass or less.

[0027] <Nb: 0.010% by mass or more and 0.10% by mass or less> Nb is an element that has the effect of improving the strength of the weld metal by solid solution strengthening and precipitation as nitrides. If the Nb content relative to the total mass of the wire is less than 0.010% by mass, the effect of improving the strength of the weld metal cannot be fully obtained. Therefore, the Nb content relative to the total mass of the wire is 0.010% by mass or more, preferably 0.013% by mass or more, and more preferably 0.015% by mass or more. On the other hand, if the Nb content relative to the total mass of the wire exceeds 0.10%, it causes the remaining of δ-ferrite and greatly deteriorates the toughness of the weld metal. Therefore, the Nb content relative to the total mass of the wire is 0.10% by mass or less, preferably 0.09% by mass or less, and more preferably 0.08% by mass or less.

[0028] <V: 0.10% by mass or more and 0.50% by mass or less> V is an element that has the effect of improving the strength of the weld metal by precipitating as carbonitrides in the weld metal. If the V content relative to the total mass of the wire is less than 0.10% by mass, the effect of improving the strength of the weld metal cannot be fully obtained. Therefore, the V content relative to the total mass of the wire is 0.10% by mass or more, preferably 0.13% by mass or more, and more preferably 0.15% by mass or more. On the other hand, if the V content relative to the total mass of the wire exceeds 0.50%, it causes the remaining of δ-ferrite and deteriorates the toughness of the weld metal. Therefore, the V content relative to the total mass of the wire is 0.50% by mass or less, preferably 0.40% by mass or less, and more preferably 0.30% by mass or less.

[0029] <N: 0.010% by mass or more and 0.070% by mass or less> N is an element that contributes to solid solution strengthening and precipitation as nitrides to stabilize the strength. It is also an austenite-forming element and has the effect of suppressing δ-ferrite in the weld metal. If the N content relative to the total mass of the wire is less than 0.010% by mass, the above effects cannot be fully obtained, the strength decreases, and δ-ferrite is generated. Therefore, the N content relative to the total mass of the wire is set to 0.010% by mass or more, preferably 0.015% by mass or more, and more preferably 0.020% by mass or more. On the other hand, if the N content relative to the total mass of the wire exceeds 0.070% by mass, blowholes will occur. Therefore, the N content relative to the total mass of the wire is set to 0.070% by mass or less, preferably 0.065% by mass or less, and more preferably 0.060% by mass or less.

[0030] <P: 0.030% by mass or less> P is an impurity element and is a component that increases the susceptibility to hot cracking. If the P content relative to the total mass of the wire exceeds 0.030% by mass, the occurrence of hot cracking is a concern. Therefore, the P content relative to the total mass of the wire is set to 0.030% by mass or less, preferably 0.020% by mass or less, and more preferably 0.015% by mass or less.

[0031] <S: 0.030% by mass or less> S affects the convection in the molten pool, increases the penetration depth, improves the arc stability, and has the effect of forming a good bead appearance. In this 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 wire for the purpose of further improving the bead appearance forming ability, the S content relative to the total mass of the wire is preferably 0.003% by mass or more, and more preferably 0.005% by mass or more. On the other hand, if the S content relative to the total mass of the wire exceeds 0.030% by mass, the occurrence of hot cracking is a concern. Therefore, the S content relative to the total mass of the wire is set to 0.030% by mass or less, preferably 0.025% by mass or less, and more preferably 0.020% by mass or less.

[0032] <Ni: 0.80 mass% or less> Ni is an austenite forming element like Mn and contributes to suppressing the formation of δ-ferrite in the weld metal. In this embodiment, the lower limit of the Ni content is not particularly limited and may be 0 mass%, but when Ni is contained in the wire for the purpose of suppressing the formation of δ-ferrite in the weld metal, the Ni content with respect to the total mass of the wire is preferably 0.05 mass% or more, and more preferably 0.10 mass% or more. On the other hand, when the Ni content with respect to the total mass of the wire exceeds 0.80 mass%, the high-temperature strength of the weld metal deteriorates. Also, the transformation point decreases and PWHT at high temperatures becomes difficult. Therefore, the Ni content with respect to the total mass of the wire is 0.80 mass% or less, preferably 0.60 mass% or less, and more preferably 0.50 mass% or less.

[0033] <Ti: 0.025 mass% or less> Ti generates an oxide film that inhibits the uniform solidification of the weld metal and deteriorates the formation of a good back bead shape. When the Ti content with respect to the total mass of the wire exceeds 0.025 mass%, the back bead shape deteriorates. Therefore, the Ti content with respect to the total mass of the wire is 0.025 mass% or less, preferably 0.018 mass% or less, and more preferably 0.015 mass% or less.

[0034] <Al: 0.020 mass% or less> Al, together with Si, is an element that preferentially forms an oxide film with a low melting point and is difficult to inhibit the solidification of the weld metal on the back bead surface. However, due to its high slag-forming ability, there is a concern of causing slag entrainment. Also, Al is a ferrite-forming element, and excessive formation of δ-ferrite in the weld metal reduces the toughness of the weld metal. Furthermore, since Al forms nitrides preferentially over Nb and V, it inhibits the formation of Nb and V nitrides that ensure high-temperature strength, leading to a decrease in high-temperature strength. Therefore, the Al content with respect to the total mass of the wire is 0.020 mass% or less, preferably 0.015 mass% or less, and more preferably 0.012 mass% or less.

[0035] <Co: 0.70 mass% or less> Co, like Ni and Mn, is an austenite-forming element and an element that contributes to suppressing the formation of δ-ferrite in the weld metal. By including Co in the wire, the desired mechanical properties of the weld metal can be obtained. In this embodiment, the lower limit of the Co content is not particularly limited and may be 0 mass%. However, when Co is included in the wire for the purpose of suppressing the formation of δ-ferrite in the weld metal, the Co content with respect to the total mass of the wire is preferably 0.005 mass%, more preferably 0.05 mass% or more, still more preferably 0.10 mass% or more, and particularly preferably 0.15 mass% or more. On the other hand, when the Co content with respect to the total mass of the wire exceeds 0.70 mass%, the transformation point decreases and PWHT at high temperatures becomes difficult. Therefore, the Co content with respect to the total mass of the wire is set to 0.70 mass% or less, preferably 0.60 mass% or less, and more preferably 0.50 mass% or less.

[0036] The solid wire according to this embodiment may contain either one or both of Zr and Cu within the ranges shown below in addition to the above components. The content of the components that the wire may further contain and the reasons for their limitation are explained below.

[0037] <Zr: 0.10 mass% or less> Zr, together with Si, is an element that preferentially forms an oxide film that is difficult to inhibit the solidification of the weld metal on the back wave surface. Therefore, it is preferable to include Zr in the solid wire according to this embodiment as needed. When Zr is included in the wire within the range of 0.10 mass% or less, it is possible to prevent poor back wave formation due to the oxidation of Cr during welding without reducing the toughness due to excessive formation of δ-ferrite. Therefore, when Zr is included in the solid wire according to this embodiment, the Zr content with respect to the total mass of the wire is set to 0.10 mass% or less, preferably 0.08 mass% or less, and more preferably 0.07 mass% or less. On the other hand, when Zr is contained in the wire to obtain the above effects, the Zr content based on the total mass of the wire is preferably 0.005% by mass or more, and more preferably 0.010% by mass or more.

[0038] <Cu: 0.50% by mass or less> Cu is an austenite-forming element like Ni and Mn, and is an element that contributes to suppressing the formation of δ-ferrite in the weld metal. Therefore, it is preferable to contain Cu in the solid wire according to this embodiment as needed. When Cu is contained in the wire in the range of 0.50% by mass or less, a weld metal having desired mechanical properties can be obtained without deteriorating the high-temperature strength of the weld metal. Therefore, when Cu is contained in the solid wire according to this embodiment, the Cu content based on the total mass of the wire is preferably 0.50% by mass or less, more preferably 0.40% by mass or less, and even more preferably 0.30% by mass or less. On the other hand, when Cu is contained in the wire to obtain the above effects, the Cu content based on the total mass of the wire is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more. Note that the wire of this embodiment may be copper-plated, and the Cu content shall include the copper plating portion.

[0039] <Balance: Fe and inevitable impurities> The balance of the solid wire according to this embodiment is Fe and inevitable impurities. Inevitable impurities mean those that are not intentionally added to the wire, and examples of elements other than the above include B, Sn, As, Sb, etc. The total content of impurities in the solid wire is preferably 0.10% by mass or less, and more preferably 0.05% by mass or less.

[0040] 〔Gas shielded arc welding method〕 The gas shielded arc welding method according to this embodiment is a welding method that uses the above-mentioned solid wire to weld a steel material containing 1% to 10% by mass of Cr, without using back shielding gas. As described above, when welding with conventional solid wire when the Cr content of the steel material to be welded is, for example, 8% to 10% by mass, the back bead is prone to oxidation, and the shape and appearance of the back bead deteriorate. However, by using the solid wire according to this embodiment for at least the first layer of welding, it is possible to form a back bead with excellent back bead performance and mechanical performance without using back shielding gas, not only for high-Cr content steel materials where the back bead is particularly prone to oxidation, but also for steel materials containing 1% to 10% by mass of Cr.

[0041] In the gas shielded arc welding method according to this embodiment, the type of welding is not particularly limited, and in addition to TIG (Tungsten Inert Gas) welding, MAG (Metal Active Gas) welding and MIG (Metal Inert Gas) welding can also be used.

[0042] <Types and flow rates of shielding gas> In welding with solid wire according to this embodiment, the shielding gas used on the front side is not particularly limited, but for example, Ar gas, carbon dioxide, a mixture of Ar gas and carbon dioxide, or a mixture of Ar gas and oxygen gas can be used. The gas flow rate is also not particularly limited, but for example, it can be 15 to 50 L / min.

[0043] <Welding position, wire diameter> Furthermore, the welding position using the solid wire according to this embodiment is not particularly limited, and welding can be performed in various welding positions. In addition, the wire diameter (diameter) of the solid wire according to this embodiment is not particularly limited, but it can be applied to wires with diameters specified in welding material standards such as AWS or JIS. [Examples]

[0044] The effects of the present invention will be specifically explained below with reference to examples and comparative examples of the present invention, but the present invention is not limited thereto.

[0045] [Manufacturing of solid wires] Solid wires were fabricated to have varying concentrations of chemical components. Table 1 below shows the chemical content (mass %) per unit of total wire mass. The remainder of the wire, excluding the chemical components shown in Table 1, consists of Fe and unavoidable impurities.

[0046] [Gas shielded arc welding (for back bead evaluation)] Welding was performed to evaluate the back bead. Specifically, a pair of steel plates with a thickness of 19 mm, steel grade ASTM A387 Grade 91 Class 2, and groove angle of 70° were prepared, and the first layer was formed by TIG welding. The welding conditions are shown below.

[0047] <Welding conditions> Welding method: TIG welding Wire diameter: 2.4mm Root gap: 2-3mm Welding current: 90-110A Arc voltage: 10~14V Preheating: 150~300℃ Shielding gas type and flow rate: 100% Ar, 15 liters / minute Back shielding gas: None Welding position: Downward

[0048] [Reverse wave evaluation test] <Evaluation Criteria> For the weld metal obtained using each solid wire, the back side of the weld (back bead appearance) was visually observed, and the macroscopic cross-section of the weld metal was also visually observed to evaluate the back bead. For the back bead appearance, the degree of oxidation, the presence or absence of burn-through, and the presence or absence of concave beads were observed. For the macroscopic cross-section, the height of the back bead, the depth of the back bead depression, and the shape of the boundary between the base metal and the back bead were observed. The measurement results and evaluation results for each evaluation item are shown in Table 2 below.

[0049] <Evaluation Methods and Criteria> (Exterior view of Uraha) Regarding the appearance of the back bead, a good result was achieved when the back bead width was uniform, there was no meandering or unevenness, there was no discoloration or unevenness due to oxidation, and no melt-down or concave bead was observed. On the other hand, a failure was achieved when the back bead width was uneven, there was severe unevenness, the back bead was discolored due to oxidation or unevenness was observed, or melt-down or concave bead occurred. For those judged to be failures, the appearance was noted in the measurement results column.

[0050] (Height of the back wave) In the cross-sectional macroscopic observation, the height of the back wave was measured. In this embodiment, samples with a back wave height of 0.5 mm or more were deemed acceptable, and those with a back wave height of less than 0.5 mm were deemed unacceptable. The back wave height was recorded in the measurement results column.

[0051] (Depth of the depression) The presence or absence of depressions was observed near the widthwise end of the back bead, and the depth of the depressions was measured for those present. In this embodiment, materials without depressions deeper than 0.5 mm on the back surface of the base material were deemed acceptable, while those with depressions deeper than 0.5 mm were deemed unacceptable, and the depth of the depressions was recorded in the measurement results column.

[0052] (Shape of the boundary between the base material and the backing material) In the cross-sectional macroscopic view, the shape of the boundary between the base material and the back bead was observed. A smooth convex shape from the base material toward the back bead was judged as good (pass), while a sharply rising convex shape at the boundary between the base material and the back bead was judged as poor (fail). The measurement result column was recorded as "Good" or "Poor". It should be noted that in cases where melt-through occurred, the back bead tended to have a sharply rising convex shape at the boundary between the base material and the back bead.

[0053] (Overall evaluation of Uranami) For the evaluation of the back wave, those that passed all of the above items were given a rating of "A," and those that failed one or more items were given a rating of "C," and the evaluation results were recorded in the back wave evaluation results column.

[0054] [Gas shielded arc welding (for weld metal evaluation)] Welding was performed to evaluate the weld metal. Specifically, a 12mm thick SM490A steel plate, as specified in JIS G3106:2020, was machined to a 45° groove angle. Using a prepared solid wire, the groove and backing plate were buttered in two or more layers. Then, with a root gap of 6.5mm, weld metal was formed by multi-layer welding using TIG welding. The welding conditions are shown below.

[0055] <Welding conditions> Welding method: TIG welding Wire diameter: 1.2mm Welding current: 160~180A Arc voltage: 10~16V Shielding gas type and flow rate: 100% Ar, 25 liters / minute Welding position: Downward PWHT temperature, time: 760℃, 2 hours

[0056] [Mechanical performance evaluation test of weld metal] <Evaluation Criteria> For weld metals obtained using each solid wire, the tolerance of the PWHT temperature setting was evaluated by measuring the Ac1 transformation point, and the area fraction of δ-ferrite was measured. Furthermore, mechanical performance was evaluated by conducting tensile tests and Charpy impact tests. The measurement results and evaluation results for each evaluation item are shown in Table 2 below. Note that for some test pieces with poor back bead formation, mechanical performance evaluation tests of the weld metal were not performed.

[0057] <Evaluation Methods and Criteria> (Measurement of the Ac1 transformation point) From the weld metal obtained before PWHT, a round bar-shaped test specimen with a diameter of 8 mm and a length of 12 mm was taken, and the Ac1 transformation point was determined by measuring the volume change of the test specimen during heating using a high-frequency induction heating method. Furthermore, if PWHT is performed at a temperature higher than the Ac1 transformation point, the weld metal undergoes a reverse transformation, resulting in a structure containing high-strength, low-toughness fresh martensite, which degrades the performance of the welded joint. Therefore, a higher Ac1 transformation point allows for a greater margin in the temperature setting for PWHT. Accordingly, the evaluation criteria were as follows: an Ac1 transformation point of 800°C or higher was rated "A" (Excellent), a transformation point of 780°C or higher but less than 800°C was rated "B" (Good), and a transformation point of less than 780°C was rated "C" (Poor).

[0058] (Measurement of δ-ferrite area ratio) From the weld metal obtained before PWHT, a 12 mm square test specimen containing the final pass raw material in a cross-section perpendicular to the welding direction was taken. The microstructure of the final pass raw material was observed by appropriately polishing and etching, and the area fraction of δ-ferrite was measured in a 100x field of view. The area fraction was calculated using the point calculation method, with the area fraction calculated from more than 600 grid points per field of view. Furthermore, δ-ferrite remains after welding without transforming into austenite, negatively affecting strength and toughness and degrading the performance of the welded joint. Therefore, a smaller area ratio is preferable. Accordingly, the evaluation criteria were as follows: a δ-ferrite area ratio of less than 5% was rated "A" (excellent), 5% or more but less than 10% was rated "B" (good), and 10% or more was rated "C" (poor).

[0059] (Tensile test) A tensile test specimen with a diameter of 6 mm and a gauge length of 24 mm was taken from the center of the weld metal plate thickness, parallel to the direction of the weld line, and the room temperature tensile strength (TS) of the weld metal was measured in accordance with the tensile testing method for metallic materials described in JIS Z 2241:2011. The evaluation criteria were as follows: products with a tensile test result of 720 MPa or higher were rated "A" (Excellent), those with a result between 620 MPa and 720 MPa were rated "B" (Good), and those with a result below 620 MPa were rated "C" (Poor).

[0060] (Charpy impact test) A 2 mm V-notch Charpy impact test specimen was taken perpendicular to the direction of the weld line from the center of the obtained weld metal plate thickness, and the Charpy impact value at 20°C was measured in accordance with the Charpy impact test method for metallic materials described in JIS Z 2242:2005. Furthermore, the criterion for evaluating toughness using the Charpy impact value is a Charpy impact value of 60 (J / cm²) obtained by dividing the measured absorbed energy from a Charpy impact test at 20°C by the original cross-sectional area of ​​the notch. 2 Those with a score of 34 (J / cm²) or higher were given an evaluation of "A" (Excellent), and 2 ) or more 60(J / cm 2 Those with a value less than 34 (J / cm²) were rated "B" (good), and 34 (J / cm²) were selected. 2 Those that scored below ) were rated "C" (poor).

[0061] [Table 1]

[0062] [Table 2]

[0063] [Evaluation Results] As shown in Tables 1 and 2 above, although Invention Examples No. A1 to A7 are examples of welding steel plates with high Cr content, which is generally difficult to form a good back bead, the chemical composition of the solid wire used was within the numerical range specified in this invention. Therefore, it was possible to obtain a back bead with an excellent appearance and weld metal with excellent mechanical performance without using back shielding gas. In welding steel plates with a Cr content of 8 mass% to 10 mass%, poor appearance of the back bead is due to the high Cr content of the steel plate and welding material. Similarly, the solid wire according to this embodiment can be applied when the Cr content of the steel material to be welded is 1 mass% or more and less than 8 mass%. That is, when the Cr content of the steel material to be welded is 1 mass% or more and 10 mass% or less, a good weld metal can be obtained without using back shielding gas by using the solid wire according to the present invention.

[0064] On the other hand, in Comparative Examples B1 to B7, the Si content in the solid wire was below the lower limit specified in the present invention, and in Comparative Examples B5 to B7, the Ti content in the solid wire exceeded the upper limit specified in the present invention. Therefore, the evaluation results for the back wave were poor. In addition, in Comparative Example B8, the Si content in the solid wire exceeded the upper limit specified in the present invention, resulting in an increase in the area ratio of δ-ferrite. Furthermore, in Comparative Examples B9 and B10, the Si content in the solid wire exceeded the upper limit specified in the present invention, resulting in an increase in the area ratio of δ-ferrite and poor evaluation results for toughness.

Claims

1. A solid wire used for welding steel materials containing 1% by mass or more and 10% by mass or less of Cr, With respect to the total mass of the wire, C: 0.05% by mass or more and 0.15% by mass or less, Si: 0.8% by mass or more and 1.7% by mass or less, Mn: 0.4% by mass or more and 1.2% by mass or less, Cr: 7.5% by mass or more and 13.0% by mass or less, Mo: 0.70% by mass or more and 1.5% by mass or less, Nb: 0.010% by mass or more and 0.10% by mass or less, V: 0.10% by mass or more and 0.50% by mass or less, N: 0.010% by mass or more and 0.070% by mass or less, Co: Contains 0.005% by mass or more and 0.70% by mass or less. P: 0.030% by mass or less, S: 0.030% by mass or less, Ni: 0.80% by mass or less, Ti: 0.025% by mass or less, Al: 0.020 mass% or less, A solid wire characterized in that the remainder consists of Fe and unavoidable impurities.

2. Furthermore, relative to the total mass of the wire, Zr: 0.10% by mass or less, The solid wire according to claim 1, characterized in that it contains

3. Furthermore, relative to the total mass of the wire, Cu: 0.50% by mass or less, A solid wire according to claim 1 or 2, characterized by containing the following:

4. A gas shielded arc welding method characterized by welding a steel material containing 1% by mass or more and 10% by mass or less of Cr using the solid wire described in claim 1 or 2, without using a back shielding gas.

5. A gas shielded arc welding method characterized by welding a steel material containing 1% by mass or more and 10% by mass or less of Cr using the solid wire described in claim 3, without using a back shielding gas.

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