Solid wire and gas shielded arc welding method

Abstract

To provide solid wire that can obtain excellent back bead of appearance and obtain weld metal having excellent mechanical performance, without using back shield gas.SOLUTION: Solid wire, which is used in welding steel materials to be welded, at least one of which is a steel material containing 4 mass% or more and 10 mass% or less of Cr, contains 0.02 mass% or more and 0.11 mass% or less of C, 0.6 mass% or more and 1.7 mass% or less of Si, 0.2 mass% or more and 1.5 mass% or less of Mn, over 0.005 mass% and 0.030 mass% or less of S, 4.0 mass% or more and 13 mass% or less of Cr, and 0.3 mass% or more and 1.5 mass% or less of Mo, with respect to total mass of the wire, which further comprises 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, where a remainder is composed of 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 technology]

[0002] In the fields of petroleum refineries and chemical plants, steels containing chromium are used to withstand harsh environments. Generally, when high-chromium-content steels are gas-shielded to form one-side butt weld joints, back-shielding with an inert gas is required for the first layer of welding to prevent poor appearance of the back-shielding bead due to the formation of high-melting-point chromium oxides on the back-shielding surface. However, continuously flowing back-shielding gas from the back of the steel increases costs and, when the steel being welded is, for example, a pipe, makes the process complicated.

[0003] Patent Document 1 discloses a welding material that can produce welds with excellent back-sealing and mechanical properties without using back-shielding gas. The welding material described in Patent Document 1 has specified contents of C, Cr, Mo, Ni, and Al, and the relationship 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 among the impurities are specified. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-24388 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, post-weld heat treatment (PWHT) is sometimes performed on weld metal to improve toughness, etc. However, the high-temperature transformation temperature (Ac1 transformation point) of the welding material described in Patent Document 1 was not considered, and depending on the PWHT temperature, it may not be possible to ensure the toughness of the weld metal. In addition, there is room for further improvement in the back-beam performance and the mechanical performance of the first layer.

[0006] The present invention has been made in view of the above-mentioned circumstances, and has an object to provide a solid wire and a gas-shielded arc welding method that can be used in welding steel materials to be welded, at least one of which contains 4% by mass to 10% by mass of Cr, and that can provide a back-beam weld with excellent appearance and a weld metal with excellent mechanical properties without using a back-shielding gas. [Means for solving the problem]

[0007] As a result of intensive research to solve the above problems, the inventors have found that in order to suppress the occurrence of poor formation of the backside bead, it is particularly important to control the Si content and S content in the solid wire. The present invention was made based on this finding.

[0008] The above object of the present invention is achieved by the following configuration [1] relating to a solid wire.

[0009] [1] A solid wire used for welding in which at least one of the steel materials to be welded is a steel material containing 4% by mass or more and 10% by mass or less of Cr, For the total mass of the wire, C: 0.02% by mass or more and 0.11% by mass or less, Si: 0.6% by mass or more and 1.7% by mass or less, Mn: 0.2% by mass or more and 1.5% by mass or less, S: more than 0.005% by mass and 0.030% by mass or less, Cr: 4.0% by mass or more and 13% by mass or less, Mo: 0.3 mass% or more and 1.5 mass% or less, P: 0.030% by mass or less, Ni: 1.4% by mass or less, Nb: 0.05% by mass or less, V: 0.05% by mass or less, Ti: 0.05% by mass or less, Al: 0.05% by mass or less, The balance of the solid wire is Fe and unavoidable impurities.

[0010] Furthermore, preferred embodiments of the present invention relating to the solid wire relate to the following [2] and [3].

[0011] [2] Furthermore, for the total mass of the wire, Zr: 0.15% by mass or less The solid wire according to [1], characterized in that it contains

[0012] [3] Furthermore, at least one selected from Co, Cu, and N, For the total mass of the wire, Co: 0.5% by mass or less, Cu: 0.5% by mass or less, N: 0.02% by mass or less, The solid wire according to [1] or [2], characterized in that it contains in the range of

[0013] The above object of the present invention is achieved by the gas-shielded arc welding method according to the following item [4].

[0014] [4] A gas-shielded arc welding method for welding steel materials, at least one of which contains 4% by mass or more and 10% by mass or less of Cr, using the solid wire according to any one of [1] to [3], without using back-shielding gas. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a solid wire that can produce a weld metal with excellent mechanical properties and a back-shielded arc weld with excellent appearance without using a back-shielded gas, and a gas-shielded arc welding method using this solid wire. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the solid wire may be simply referred to as a "wire." The present invention is not limited to the embodiments described below, and can be modified as desired without departing from the spirit and scope of the present invention.

[0017] [Solid wire] The solid wire according to this embodiment is used for welding steel materials to be welded, at least one of which contains 4% by mass or more and 10% by mass or less of Cr. The steel materials to be welded refer to multiple steel materials to be welded. For example, when the solid wire according to this embodiment is used for welding a pair of butt-jointed steel materials, it is sufficient that the Cr content of at least one of the pair of steel materials is 4% by mass or more and 10% by mass or less. That is, both of the pair of steel materials may 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 pair of steel materials may be 4% by mass or more and 10% by mass or less, and the Cr content of the other steel material may not be particularly limited and may be outside the range of 4% by mass or more and 10% by mass or less. Note that the Cr content of the other steel material is preferably 10% by mass or less (including 0% by mass). The pair of steel materials to be welded can be, for example, a combination of 9% Cr steel and 2% Cr steel, or a combination of 9% Cr steel and a welding steel material specified in JIS G 3106. The solid wire according to this embodiment can also be applied to such dissimilar material joints.

[0018] Hereinafter, those with a Cr content of 4% by mass or more and 6% by mass or less are sometimes referred to as 5% Cr steel, and those with a Cr content of 8% by mass or more and 10% by mass or less are sometimes 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 pipes.

[0019] Regarding the chemical components contained in the solid wire according to the present embodiment, the reasons for their inclusion and the reasons for numerical limitation will be described in detail below.

[0020] <C: 0.02% by mass or more and 0.11% by mass or less> 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. 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 0.02% by 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 0.02% 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. On the other hand, when the C content relative to the total mass of the wire exceeds 0.11% by mass, the solidification temperature of the segregation part significantly decreases, and hot cracking is likely to occur. In addition, the strength of the weld metal becomes excessive, and sulfide stress cracking is a concern. Furthermore, 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 0.11% by mass or less, preferably 0.105% by mass or less, and more preferably 0.10% by mass or less.

[0021] <Si: 0.6% by mass or more and 1.7% by 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, having the effect of preventing poor back bead formation due to the oxidation of Cr during welding. When the Si content with respect to the total mass of the wire is less than 0.6% by mass, the above effect cannot be fully obtained, and the back bead shape deteriorates. Therefore, the Si content with respect to the total mass of the wire is 0.6% by mass or more, preferably 0.8% by mass or more, and more preferably 0.9% by mass or more. On the other hand, when the Si content with respect to the total mass of the wire exceeds 1.7% by mass, excessive δ-ferrite is generated in the weld metal, and the toughness of the weld metal decreases. In addition, the amount of slag generated 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 is 1.7% by mass or less, preferably 1.6% by mass or less, and more preferably 1.5% by mass or less.

[0022] <Mn: 0.2% by mass or more and 1.5% by mass or less> Mn functions as a deoxidizer for the weld metal, has the effect of improving the strength of the weld metal and improving the toughness. Also, Mn is an austenite forming element and contributes to the suppression of 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 0.2% by mass, it causes insufficient deoxidation and cannot fully obtain the effect of suppressing the residual δ-ferrite in the weld metal, and the toughness of the weld metal decreases. Therefore, the Mn content with respect to the total mass of the wire is 0.2% by mass or more, preferably 0.3% by mass or more, and more preferably 0.4% by mass or more. On the other hand, when the Mn content with respect to the total mass of the wire exceeds 1.5% 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 temperature becomes difficult. Furthermore, it forms a complex oxide with Cr and causes poor back bead formation. Therefore, the Mn content with respect to the total mass of the wire is 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.1% by mass or less.

[0023] <S: More than 0.005% by mass and 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 good bead appearance. When the S content with respect to the total mass of the wire is 0.005% by mass or less, poor penetration occurs and the bead appearance shape deteriorates. Therefore, the S content with respect to the total mass of the wire is more than 0.005% by mass, preferably 0.006% by mass or more, and more preferably 0.007% by mass or more. On the other hand, when the S content with respect to the total mass of the wire exceeds 0.030% by mass, there is concern about the occurrence of hot cracking. Therefore, the S content with respect to the total mass of the wire is 0.030% by mass or less, preferably 0.025% by mass or less, and more preferably 0.020% by mass or less.

[0024] <Cr: 4.0% by mass or more and 13% by mass or less> Cr is a main element of 5% Cr steel and 9% Cr steel, which are at least one of the steel materials of the welded steel material in the 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. When the Cr content with respect to the total mass of the wire is less than 4.0% by mass, the oxidation resistance and high-temperature strength of the weld metal become insufficient. Therefore, the Cr content with respect to the total mass of the wire is 4.0% by mass or more, preferably 4.2% by mass or more, and more preferably 4.5% by mass or more. On the other hand, when the Cr content with respect to the total mass of the wire exceeds 13% by mass, even when the Si content is controlled as described above, an oxide film that inhibits the uniform solidification of the high-melting-point weld metal is generated on the bead surface. Also, 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 13% by mass or less, preferably 12% by mass or less, and more preferably 11% by mass or less.

[0025] <Mo: 0.3% by mass or more and 1.5% by mass or less> Mo is a solid solution strengthening element and also an element that has the effect of increasing the high-temperature strength by the precipitation of carbides. If the Mo content relative to the total mass of the wire is less than 0.3% by mass, the high-temperature strength of the weld metal will be insufficient. Therefore, the Mo content relative to the total mass of the wire should be 0.3% by mass or more, preferably 0.35% by mass or more, and more preferably 0.4% by mass or more. On the other hand, if the Mo content relative to the total mass of the wire exceeds 1.5% by mass, it will cause the remaining of δ-ferrite and deteriorate the toughness and creep performance of the weld metal. Therefore, the Mo content relative to the total mass of the wire should be 1.5% by mass or less, preferably 1.3% by mass or less, and more preferably 1.2% by mass or less.

[0026] <P: 0.030% by mass or less> P is an impurity element and 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 should be 0.030% by mass or less, preferably 0.020% by mass or less, and more preferably 0.015% by mass or less.

[0027] <Ni: 1.4% by 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% by mass. However, when Ni is contained in the wire for the purpose of suppressing the formation of δ-ferrite in the weld metal, the Ni content relative to the total mass of the wire is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. On the other hand, if the Ni content relative to the total mass of the wire exceeds 1.4% by mass, the high-temperature strength of the weld metal will deteriorate. Also, the transformation point decreases, making PWHT at high temperatures difficult. Therefore, the Ni content relative to the total mass of the wire should be 1.4% by mass or less, preferably 1.2% by mass or less, and more preferably 1.0% by mass or less.

[0028] <Nb: Below 0.05 mass%> Nb is a solid solution strengthening element. However, if it is excessively contained in the wire, nitrides will precipitate, causing the strength of the weld metal to become excessively high. In addition, Nb causes the remaining δ-ferrite, greatly deteriorating the toughness of the weld metal. When the Nb content with respect to the total mass of the wire exceeds 0.05 mass%, the toughness of the weld metal deteriorates. Therefore, the Nb content with respect to the total mass of the wire should be 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less.

[0029] <V: Below 0.05 mass%> V, when excessively contained in the wire, precipitates carbonitrides, causes the remaining δ-ferrite, and deteriorates the toughness of the weld metal. When the V content with respect to the total mass of the wire exceeds 0.05 mass%, the toughness of the weld metal deteriorates. Therefore, the V content with respect to the total mass of the wire should be 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less.

[0030] <Ti: Below 0.05 mass%> Ti forms 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 0.05 mass%, the back bead shape deteriorates. Therefore, the Ti content with respect to the total mass of the wire should be 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less.

[0031] <Al: Below 0.05 mass%> 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 slag entrainment. When the Al content with respect to the total mass of the wire exceeds 0.05 mass%, slag entrainment is likely to occur. Therefore, the Al content with respect to the total mass of the wire should be 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less.

[0032] In addition to the above components, the solid wire according to this embodiment may contain Zr, Cu, Co, and N. The content of the components that the wire may further contain and the reasons for their limitations will be described below.

[0033] <Zr: 0.15 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 contain Zr in the solid wire according to this embodiment as needed. When the Zr content is contained in the range of 0.15 mass% or less in the wire, it is possible to prevent poor back wave formation due to the oxidation of Cr during welding without reducing the toughness due to the excessive generation of δ-ferrite. Therefore, when Zr is contained in the solid wire according to this embodiment, the Zr content with respect to the total mass of the wire is preferably 0.15 mass% or less. When containing Zr, it is preferably 0.0'05 mass% or more, and more preferably 0.010 mass% or more.

[0034] <Co: 0.5 mass% or less, Cu: 0.5 mass% or less, N: 0.02 mass% or less> Co, Cu, and N are all austenite-forming elements like Ni and Mn, and are elements that contribute to the suppression of the formation of δ-ferrite in the weld metal. In order to obtain the desired mechanical properties of the weld metal by suppressing the formation of δ-ferrite, at least one selected from Co, Cu, and N can be contained in the solid wire according to this embodiment as needed. Therefore, it is preferable to contain 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, N: 0.02 mass% or less, with respect to the total mass of the wire. Note that the Co content is more preferably 0.40 mass% or less, and even more preferably'0.30 mass% or less. The Cu content is more preferably 0.40 mass% or less, and even more preferably 0.30 mass% or less. The N content is more preferably 0.015 mass% or less, and even more preferably 0.010 mass% or less. Furthermore, when Co is contained in the wire, the Co content is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. When Cu is contained in the wire, the Cu content is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. When N is contained in the wire, the N content is preferably 0.002% by mass or more, and more preferably 0.005% by mass or more. Note that the wire of this embodiment may be plated with Cu, and the Cu content includes the copper plating.

[0035] <Balance: Fe and unavoidable impurities> The balance of the solid wire according to this embodiment is Fe and unavoidable impurities. The unavoidable impurities are those elements that are not intentionally added to the wire, and examples of the unavoidable impurities other than those mentioned above include B, Sn, As, and Sb. 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.

[0036] [Gas-shielded arc welding method] The gas-shielded arc welding method according to the present embodiment is a welding method for welding steel having a Cr content of 4% by mass or more and 10% by mass or less using the above-described solid wire without using back-shielding gas. As described above, when welding steel containing 4% by mass to 10% by mass of Cr, if a conventional solid wire is used, the back-shield is easily oxidized, and the shape and appearance of the back-shield deteriorates. However, by using the solid wire according to the present embodiment as at least the first layer of welding, a back-shield with excellent back-shield performance and mechanical properties can be formed without using back-shield gas. In the gas-shielded arc welding method according to the present 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.

[0037] <Type and flow rate of shielding gas> The shielding gas used on the front side during welding with the solid wire according to this embodiment is not particularly limited, but examples thereof include Ar gas, carbon dioxide gas, a mixture of Ar gas and carbon dioxide gas, and a mixture of Ar gas and oxygen gas. The gas flow rate is also not particularly limited, but can be, for example, 15 to 50 L / min.

[0038] <Welding position, wire diameter> Furthermore, the welding position using the solid wire according to the present embodiment is not particularly limited, and welding can be performed in various welding positions. Furthermore, the wire diameter of the solid wire according to the present embodiment is not particularly limited, but can be applied to wires having diameters specified in welding material standards such as AWS or JIS. [Example]

[0039] The effects of the present invention will be specifically explained below by giving examples of the present invention and comparative examples, but the present invention is not limited to these.

[0040] [Solid wire manufacturing] Solid wires were produced so that the wire contained various amounts of components. The contents (mass%) of chemical components per total mass of the wire are shown in Tables 1 and 2 below. The remainder of the wire, excluding the chemical components shown in Tables 1 and 2 below, consists of Fe and unavoidable impurities. In Tables 1 and 2, "-" indicates that the component was not intentionally included.

[0041] [Gas shielded arc welding (for back-beam evaluation)] Welding was carried out to evaluate the reverse side of the weld. 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 first layer was formed by TIG welding. The welding conditions are as follows:

[0042] <Welding conditions> Welding method: TIG welding Wire diameter: 2.4mm Root gap: 2~3mm Welding current: 90~110A Arc voltage: 10~14V Preheat: 150-300℃ Shielding gas type and flow rate: 100% Ar, 15 liters / min Back shield gas: None Welding position: Downward

[0043] [Uranami evaluation test] For the weld metal obtained using each solid wire, the back side of the weld (appearance of the back bead) was visually observed, and the cross-section of the weld metal was also visually observed to evaluate the back bead. The back side of the weld was observed for the shape of the back bead, the degree of oxidation, the presence or absence of burn-through, and the presence or absence of a concave bead. The cross-section was observed for the height of the back bead, the depth of the depression in the back bead, and the shape of the boundary between the base metal and the back bead.

[0044] Regarding the appearance of the back wave, those that had a uniform back wave width, no meandering or unevenness, no discoloration or unevenness due to oxidation, and no burn-through or concave bead were judged to be good (passed).On the other hand, those that had an uneven back wave width, severe unevenness, discoloration or unevenness due to oxidation of the back wave, or burn-through or concave bead were judged to be unsatisfactory.

[0045] In addition, in cross-sectional macro observation, a specimen with a back wave height of 1 mm or more was deemed "pass," while a specimen with a back wave height of less than 1 mm was deemed "fail." Furthermore, a specimen without a depression of 0.5 mm or more in depth relative to the back surface of the base material near the widthwise end of the back wave was deemed "pass," while a specimen with a depression of 0.5 mm or more was deemed "fail." Furthermore, the shape of the boundary between the base material and the back wave was observed macro-sectionally, and specimens with a gentle convex shape from the base material toward the back wave were deemed "good" (pass), while specimens with a sharply raised convex shape at the boundary between the base material and the back wave were deemed "bad" (fail). Furthermore, specimens with burn-through tended to have a sharply raised convex shape at the boundary between the base material and the back wave. In assessing Uranami, if all of the above items were passed, the grade was "A," and if one or more items were failed, the grade was "C."

[0046] [Gas-shielded arc welding (for weld metal evaluation)] Welding was carried out to evaluate the weld metal. Specifically, a 12mm thick SM490A steel material specified in JIS G3106:2020 was machined to a 45° groove angle, and the prepared solid wire was used to butter the inside of the groove and the backing metal in two or more layers. After that, the weld metal was formed by multi-layer TIG welding with a root gap of 6.5mm. The welding conditions are as follows:

[0047] <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 / min Welding position: Downward PWHT temperature, time: 745℃, 1 hour

[0048] [Mechanical performance evaluation test for weld metal] <Transformation point measurement test> A round bar-shaped test piece with a diameter of 8 mm and a length of 12 mm was taken from the obtained weld metal, and the Ac1 transformation point was measured by measuring the volume change of the test piece 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 will undergo reverse transformation to form a structure containing high-strength, low-toughness fresh martensite, degrading the performance of the welded joint, so a higher Ac1 transformation point allows for a greater tolerance in setting the PWHT temperature. Therefore, the evaluation criteria were as follows: an Ac1 transformation point of 800°C or higher was rated "A" (excellent), one between 760°C and 800°C was rated "B" (good), and one below 760°C was rated "C" (poor).

[0049] <Tensile strength test> A tensile test piece with a diameter of 6 mm and a gauge length of 24 mm was taken from the center of the plate thickness of the obtained weld metal parallel to the weld line direction, and the room temperature tensile strength (TS) of the weld metal was measured in accordance with the tensile test method for metallic materials described in JIS Z 2241:2011. If the strength of the weld metal is excessive, there is a risk of sulfide stress corrosion cracking. Furthermore, if the strength of the weld metal is insufficient, it is impossible to manufacture a structure with the desired strength. Therefore, the evaluation criteria were as follows: A tensile strength test result of 600 MPa or more but 720 MPa or less was rated "A" (excellent); A tensile strength test result of 550 MPa or more but less than 600 MPa, or more than 720 MPa but 780 MPa or less, was rated "B" (good); and a tensile strength test result of less than 550 MPa or more than 780 MPa was rated "C" (poor).

[0050] <Charpy impact test> A 2 mm V-notch Charpy 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 Charpy impact value at −30°C or −40°C was measured in accordance with the Charpy impact test method for metallic materials described in JIS Z 2242:2005. The evaluation standard for toughness based on the Charpy impact value is a Charpy impact value of 47 (J / cm2), obtained by dividing the absorbed energy measured by a Charpy impact test at -30°C or below by the original cross-sectional area of ​​the notch. 2 ) or higher was rated as "A" (excellent), and 27 (J / cm 2 ) or more 47(J / cm 2 ) was rated as "B" (good), and 27 (J / cm 2 ) was rated as "C" (poor).

[0051] The measurement results of each evaluation test are shown in Table 3 below, and the evaluation results are shown in Table 4 below.

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] [Table 4]

[0056] [Evaluation results] As shown in Tables 1 to 4 above, in invention examples A1 to A16, the chemical composition of the solid wire was within the numerical range specified in the present invention, so that it was possible to obtain a back-shield with excellent appearance and a weld metal with excellent mechanical properties without using a back-shield gas.

[0057] On the other hand, Comparative Examples B1 and B3 to B5 had poor evaluation results for back-strip strength because the Si content in the solid wire was below the lower limit of the numerical range specified in the present invention. Comparative Examples B2, B6, and B7 had poor evaluation results for toughness because the Si content in the solid wire exceeded the upper limit of the numerical range specified in the present invention. Comparative Example B8 had excessive weld metal strength because the C content in the solid wire exceeded the upper limit of the numerical range specified in the present invention, increasing the probability of sulfide stress cracking.

[0058] In Comparative Example No. B9, the C content and Ni content in the solid wire exceeded the upper limits of the numerical ranges specified in the present invention, resulting in excessive strength of the weld metal, reduced toughness, and a lower transformation point, making PWHT at high temperatures difficult.In Comparative Example No. B10, the C content and Mn content in the solid wire exceeded the upper limits of the numerical ranges specified in the present invention, resulting in excessive strength of the weld metal, reduced toughness, and a lower transformation point, making PWHT at high temperatures difficult, and also resulting in poor formation of back-beam.

[0059] Although the above-mentioned invention examples A1 to A16 were examples in which steel sheets with high Cr contents, which are generally difficult to form good uranami welds, were welded together, good evaluation results were obtained without using back-shielding gas by using a solid wire having a composition within the range specified in the present invention. This indicates that good weld metal can be obtained without using back-shielding gas even when the Cr content of at least one steel sheet to be welded is 4% by mass or more and 10% by mass or less, and the Cr content of the other steel sheet is, for example, 10% by mass or less (including 0% by mass). In welding steel sheets with a Cr content of 5% by mass to 10% by mass or less, poor appearance of the uranami bead is due to the high Cr content of the steel sheet and welding material. Therefore, the solid wire according to this embodiment can be used even when the Cr content of one steel sheet to be welded is less than 4% by mass.

Claims

1. A solid wire used for welding in which at least one of the steel materials to be welded is a steel material containing 4% by mass or more and 10% by mass or less of Cr, For the total mass of the wire, C: 0.02% by mass or more and 0.11% by mass or less, Si: 0.6% by mass or more and 1.7% by mass or less, Mn: 0.2% by mass or more and 1.5% by mass or less, S: more than 0.005% by mass and not more than 0.030% by mass, Cr: 4.0% by mass or more and 13% by mass or less, Mo: 0.3 mass% or more and 1.5 mass% or less, P: 0.030% by mass or less, Ni: 1.4% by mass or less, Nb: 0.05% by mass or less, V: 0.05% by mass or less, Ti: 0.05% by mass or less, Al: 0.05% by mass or less; The balance of the solid wire is Fe and unavoidable impurities.

2. Furthermore, for the total mass of the wire, Zr: 0.15% by mass or less 2. The solid wire according to claim 1, comprising:

3. Furthermore, at least one selected from Co, Cu, and N, For the total mass of the wire, Co: 0.5% by mass or less, Cu: 0.5% by mass or less, N: 0.02% by mass or less, 3. The solid wire according to claim 1, wherein the content of the Cr is in the range of 1.

4. 3. A gas-shielded arc welding method for welding steel materials, at least one of which contains 4 mass % or more and 10 mass % or less of Cr, using the solid wire according to claim 1 or 2 without using a back-shielded gas.

5. 4. A gas-shielded arc welding method for welding steel materials, at least one of which contains 4% by mass or more and 10% by mass or less of Cr, using the solid wire according to claim 3 without using a back-shielded gas.

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