Horizontal narrow gap gas shielded arc welding method

Abstract

Provided is a welding method for horizontal narrow gap welding of steel materials, which does not require a special device and which enables construction without welding defects even when the groove angle is 15° or less. In this horizontal narrow gap gas shielded arc welding method for multi-layer welding of steel materials, the composition of a welding wire, in mass %, is C: 0.02-0.15%, Si: 0.60-0.95%, Mn: 1.80-2.10%, P: 0.030% or less, S: 0.030% or less, B: 0.0003-0.0050%, REM: 0.020-0.060%, O: 0.010% or less, and N: 0.010% or less, with the balance being Fe and unavoidable impurities, and SLI obtained from formula (1) satisfies 10-46.　(1): SLI = [Si] × [Mn] × [B] × 10000 / α Where [element] is the content (mass %) of the element in the welding wire, and α is the volume ratio (0 < α ≤ 1) of CO2 gas in the shielding gas.

Description

Horizontal narrow gap gas shielded arc welding method

[0001] The present invention relates to a horizontal position narrow gap gas-shielded arc welding method, and more particularly to a horizontal position narrow gap gas-shielded arc welding method for joining narrow gap steel materials by multi-layer welding in a horizontal position.

[0002] In recent years, steel plates have tended to become thicker as steel structures such as buildings and ships have become larger. However, the thicker the plate, the larger the groove area, which increases the number of welding passes, resulting in the problem of increased labor and time required for welding. Furthermore, there is also the problem that it is becoming difficult to secure skilled welders due to the declining labor force. For these reasons, there is a demand for improved welding efficiency in the manufacturing of steel structures.

[0003] One method for improving welding efficiency is to narrow the gap. By narrowing the gap, the groove area can be reduced, which reduces the number of welding passes and shortens the construction time. However, narrow gap welding in a horizontal position is difficult to prevent welding defects such as insufficient fusion, hot cracking, and slag entrapment, and various studies are being conducted.

[0004] For example, Patent Document 1 discloses a narrow-groove welding method in which, when welding an I-groove, L-groove, or V-groove, the welding torch is angled relative to the lower and upper groove surfaces, respectively, and welding is performed with two or more passes per layer.

[0005] Furthermore, Patent Document 2 discloses a horizontal narrow-groove welding method in which, when horizontally welding a narrow-groove weld line with two electrodes, a leading wire is directed toward a lower corner of the groove and a trailing wire is directed toward an upper corner of the groove, and welding is performed while generating arcs from both wires.

[0006] Furthermore, Patent Document 3 discloses a horizontal narrow groove arc welding method in which, in an I-shaped horizontal groove welded joint, the apex of the weaving is tilted back in the opposite direction to the welding progress direction from a vertical line relative to the weld line when viewed from the front, and the welding is performed continuously at a specific weaving angle, width, and cycle.

[0007] Furthermore, Patent Document 4 discloses a horizontal carbon dioxide gas shielded arc welding method in which narrow gap horizontal multi-layer welding of steel plates having a thickness of 16 to 25 mm is performed with positive polarity using a solid wire containing 0.025 to 0.050 mass % of a rare earth element.

[0008] Japanese Patent Publication No. 53-41105 Japanese Patent Publication No. 55-19460 Japanese Patent Publication No. 58-49352 Japanese Patent No. 5051966

[0009] However, the method described in Patent Document 1 causes hot cracking in the upper bead. Furthermore, the methods described in Patent Documents 2 and 3 require specialized equipment and cannot be performed with general-purpose welding equipment. Furthermore, when the method described in Patent Document 4 is applied with a groove angle of 15° or less, welding defects such as slag inclusion and insufficient fusion are likely to occur, making it difficult to produce a joint without welding defects.

[0010] The present invention aims to solve the above problems and to provide a welding method that does not require special equipment and can perform horizontal narrow groove welding of steel materials without welding defects even when the groove angle is 15° or less.

[0011] The inventors have investigated a welding method that can be performed without welding defects using various welding wires and simple welding movements when welding horizontally positioned narrow gap steel materials with a groove angle of 15° or less, a root gap in the range of 7 to 15 mm, and a plate thickness in the range of 10 to 100 mm. The simple welding movements referred to here are a linear movement of the welding torch in the direction of the weld line and a reciprocating weaving movement in a direction perpendicular to the weld line direction, i.e., perpendicular to the horizontal plane, combined with the linear movement. After extensive research into the above welding movements, they discovered that a highly directional arc can be achieved by adding a rare earth element to the welding wire and making it positive polarity. Furthermore, the Si, Mn, and B contents in the welding wire and the CO in the shielding gas were investigated. ２ It was found that by adjusting the gas ratio, the amount of slag formed and its melting point can be controlled, and welding defects such as poor fusion and slag inclusion do not occur.

[0012] The present invention was completed based on these findings and further investigations, and the gist of the present invention is as follows. [1] A horizontal narrow gap gas-shielded arc welding method for joining steel materials having a groove angle θ of 15° or less, a root gap G in the range of 7 to 15 mm, and a plate thickness t in the range of 10 to 100 mm by multi-layer gas-shielded arc welding, wherein a welding wire having a chemical composition containing, by mass%, C: 0.02 to 0.15%, Si: 0.60 to 0.95%, Mn: 1.80 to 2.10%, P: 0.030% or less, S: 0.030% or less, B: 0.0003 to 0.0050%, rare earth elements (REM): 0.020 to 0.060%, O (oxygen): 0.010% or less, and N: 0.010% or less, with the balance being Fe and unavoidable impurities, is used, and the SLI calculated from the following formula (1) is in the range of 10 to 46. SLI = [Si] × [Mn] × [B] × 10000 / α (1) where [element] is the content (mass%) of the element in the welding wire, and α is the CO content in the shielding gas. ２ The volume ratio of the gas (0<α≦1) is 0<α≦1. [2] The horizontal narrow gap gas-shielded arc welding method according to the above item [1], wherein the chemical composition of the welding wire further contains, in mass%, at least one selected from Cu: 0.60% or less, Ni: 1.50% or less, Cr: 0.80% or less, Mo: 0.80% or less, Nb: 0.04% or less, V: 0.04% or less, Ti: 0.30% or less, Al: 0.10% or less, Sn: 0.30% or less, and Pb: 0.30% or less. [3] The horizontal narrow gap gas-shielded arc welding method according to the above item [1] or [2], wherein positive polarity welding is performed using the welding wire as a negative electrode. [4] In any one of [1] to [3] above, the gas-shielded arc welding method is a horizontal narrow-groove gas-shielded arc welding method, in which the welding current I is in the range of 240 to 360 A, the welding voltage E is in the range of 26 to 42 V, and the welding speed S is in the range of 20 to 80 cm / min.

[0013] According to the present invention, in horizontal narrow-groove gas-shielded arc welding of steel materials, no special equipment is required, and it is possible to provide a welded joint with excellent soundness and no welding defects even when the groove angle is 15° or less, thereby achieving significant industrial benefits.

[0014] 1 is a schematic cross-sectional view showing an example of a horizontal narrow groove shape, and FIG. 2 is a schematic cross-sectional view showing an example of a weld metal laminated in the horizontal narrow groove shape.

[0015] The present invention relates to a method for horizontal narrow-gap gas-shielded arc welding in which the groove angle θ of the steel material is 15° or less, the root gap G is in the range of 7 to 15 mm, and the plate thickness t of the steel material is in the range of 10 to 100 mm.

[0016] [Steel Material] First, the steel material applied in this embodiment will be described. The steel material is a thick steel plate used in steel structures such as buildings and ships. Examples of steel types include 490 MPa-class steel, 550 MPa-class steel, 590 MPa-class steel, and 780 MPa-class steel. The plate thickness t of the steel material according to this embodiment is in the range of 10 to 100 mm. If the plate thickness t of the steel material is less than 10 mm, there is no benefit to reducing the groove area by narrow gap welding. On the other hand, the plate thickness t of the steel material used for the above applications is generally limited to 100 mm. Therefore, the plate thickness t of the steel material is limited to the range of 10 to 100 mm. Preferably, the plate thickness t of the steel material is in the range of 15 to 90 mm.

[0017] Next, an example of the chemical composition of the steel material is shown below. The chemical composition of the steel material to be used preferably contains, in mass %, C: 0.04 to 0.15%, Si: 0.05 to 1.00%, Mn: 0.50 to 2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, O (oxygen): 0.010% or less, and N: 0.010% or less, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, it is preferable that the steel contains at least one element selected from the group consisting of Cu: 1.00% or less, Ni: 2.00% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.20% or less, V: 0.20% or less, Ti: 0.050% or less, Sn: 0.05% or less, Pb: 0.050% or less, REM: 0.050% or less, and B: 0.0030% or less as an optional composition. The optional composition is determined in consideration of strength, toughness, etc., according to the intended use of the steel material.

[0019] [Groove angle θ] In this embodiment, as shown in FIG. 1, the groove angle θ, which is the angle at the groove portion of the horizontally butted steel materials 1, 1, is 15° or less. If θ exceeds 15°, the welding efficiency, which is the advantage of a narrow groove, is reduced, so it is limited to 15° or less. Note that θ is 0° when the groove walls of the upper and lower steel materials 1, 1 are parallel, and this case is also covered by this embodiment. The preferred angle of θ is in the range of 0 to 10°.

[0020] [Root Gap G] As shown in FIG. 1 , the narrowest gap in the groove between the horizontally butted steel materials 1, 1 is called the root gap and is expressed in G (mm). In this embodiment, the root gap G is in the range of 7 to 15 mm. If G is less than 7 mm, it is difficult to insert a welding torch into the groove. On the other hand, if G exceeds 15 mm, the efficiency of welding, which is an advantage of a narrow groove, is diminished. For this reason, the root gap G is limited to the range of 7 to 15 mm. Preferably, the root gap G is in the range of 8 to 13 mm.

[0021] [Gas-shielded arc welding method] Next, a gas-shielded arc welding method according to the present invention will be described. Gas-shielded arc welding is the mainstream of arc welding methods, and is a welding method that uses a gas (shielding gas) to protect the arc and molten metal from oxygen and nitrogen in the atmosphere.

[0022] [Shielding gas] Carbon dioxide (CO ) is the cheapest shielding gas. ２ gas), inert gas such as Ar or He, or CO２ In this embodiment, a mixed gas of CO ２ This is a welding method that uses a shielding gas that is mainly composed of gas. Note that when selecting the composition of the shielding gas, it is necessary to take into account the SLI value, which will be described later.

[0023] [Other Welding Conditions] Next, other welding conditions will be described. <Welding Current I> In this embodiment, the welding current I is preferably set in the range of 240 to 360 A. If the welding current I is lower than 240 A, the arc pressure will be low, which may result in slag entrapment or insufficient fusion due to unmelted slag. On the other hand, if the welding current I is higher than 360 A, there is a risk of dripping due to convection of the weld metal, i.e., overlap. Therefore, the welding current I is preferably set in the range of 240 to 360 A. More preferably, the welding current I is set in the range of 260 to 340 A, and even more preferably, the welding current I is set in the range of 270 to 320 A.

[0024] <Welding Voltage E> In this embodiment, the welding voltage E is preferably set in the range of 26 to 42 V. If the welding voltage E is lower than 26 V, the arc cannot be stably maintained, which may result in unstable welding. On the other hand, if the welding voltage E is higher than 42 V, the arc will widen and the arc heat will be dispersed, making it difficult to melt the slag and making it more likely to become engulfed in slag. Therefore, the welding voltage E is preferably set in the range of 26 to 42 V. More preferably, the welding voltage E is set in the range of 28 to 40 V, and even more preferably, the welding voltage E is set in the range of 30 to 38 V.

[0025] <Welding Speed ​​S: 20 cm / min to 80 cm / min> In this embodiment, the welding speed S is preferably set in the range of 20 to 80 cm / min. If the welding speed S is less than 20 cm / min, even with the appropriate current and voltage, excessive weld metal is generated, which may result in dripping of the weld metal. On the other hand, if the welding speed S is greater than 80 cm / min, sufficient heat is not applied, which may result in the slag not being melted, which may result in slag inclusion. Therefore, the welding speed S is preferably set in the range of 20 to 80 cm / min. More preferably, the welding speed S is set in the range of 25 to 75 cm / min, and even more preferably, the welding speed S is set in the range of 28 to 72 cm / min.

[0026] [Multi-layer welding] The narrow-gap gas-shielded arc welding method according to this embodiment is applied to narrow-gap multi-layer welding using a backing metal 2 at the bottom (narrow side) of a horizontal narrow groove, as shown in Figure 2. When carrying out the narrow-gap gas-shielded arc welding method according to this embodiment, the welding conditions for each pass from the first layer to the final layer are set appropriately within the range of welding conditions described above. The number of layers of the multi-layer weld metal 3 depends on the plate thickness t of the steel material 1, the groove angle θ, the root gap G, and the like, but as described above, if the plate thickness t is in the range of 10 to 100 mm, a range of approximately 2 to 20 layers is preferable. Furthermore, the number of passes may be multiple passes per layer, and is preferably in the range of 3 to 50 passes.

[0027] [Welding Polarity] Either positive or negative polarity can be selected for welding polarity. Positive polarity increases the potential of the steel material and decreases the potential of the welding wire. On the other hand, negative polarity decreases the potential of the steel material and increases the potential of the welding wire. However, in the case of the narrow groove of this embodiment, in which the groove angle θ is small and the root gap G is small, positive polarity is preferable because it improves the efficiency of welding. The reason for this is that in a narrow groove, the arc tends to be directed toward the groove wall, making it difficult to melt the groove bottom (narrow side). Therefore, by welding with positive polarity using a wire to which REM has been added, as described below, the arc directionality is improved, the arc tends to concentrate at the groove bottom, and the groove bottom can be stably and sufficiently melted.

[0028] [Welding Wire] Next, a welding wire used in the horizontal narrow gap gas-shielded arc welding method according to this embodiment will be described.

[0029] The welding wire in this embodiment may be of various standards, such as YGW11, YGW18, G59JA1UC3M1T, G69A2UCN2M4T, and G78A2UCN4M4T, as classified in JIS Z3312:2009. The wire diameter φ is preferably in the range of 1.0 to 2.0 mm.

[0030] The chemical composition of the welding wire is, in mass %, C: 0.02 to 0.15%, Si: 0.60 to 0.95%, Mn: 1.80 to 2.10%, P: 0.030% or less, S: 0.030% or less, and B: 0.0003 to 0.0050%. The wire also contains rare earth elements (REM): 0.020 to 0.060%, O (oxygen): 0.010% or less, and N: 0.010% or less, with the balance consisting of Fe and unavoidable impurities. Furthermore, the wire is characterized in that Si, Mn, and B are contained so that the SLI calculated from the following formula (1) falls within the range of 10 to 46: SLI = [Si] × [Mn] × [B] × 10000 / α (1) where [element] is the content (mass %) of the element, and α is the CO content in the shielding gas. ２ The volume ratio of the gas (0<α≦1) is 0<α≦1. Details of SLI and α will be described later.

[0031] [Chemical Composition of Welding Wire] The reasons for limiting the chemical composition of the welding wire are as follows: Hereinafter, "%" in the chemical composition means "mass %".

[0032] [C: 0.02 to 0.15%] C is an element that contributes to improving the strength of the weld metal, and a content of 0.02% or more is required to ensure the strength of the weld metal. On the other hand, if the C content exceeds 0.15%, the weld metal hardens and its toughness decreases, so the C content is limited to 0.15% or less. Preferably, the C content is in the range of 0.03 to 0.14%, and more preferably, the C content is in the range of 0.04 to 0.13%.

[0033] [Si: 0.60 to 0.95%] Si acts as a deoxidizing element and generates slag on the weld metal surface. The generation of slag suppresses dripping of the weld metal into the groove, effectively preventing welding defects. To achieve this effect, a Si content of 0.60% or more is required. On the other hand, if the Si content exceeds 0.95%, excessive slag is generated, causing slag inclusion, so the Si content is limited to 0.95% or less. Preferably, the Si content is in the range of 0.62 to 0.92%, and more preferably, the Si content is in the range of 0.66 to 0.90%.

[0034] [Mn: 1.80 to 2.10%] Mn acts as a deoxidizing element, and the inclusion of Mn oxide (MnO) in the slag improves the fluidity of the slag and improves the compatibility between the base metal and the weld metal. To achieve this effect, a Mn content of 1.80% or more is required. On the other hand, if the Mn content exceeds 2.10%, the slag becomes excessively fluid, making it impossible to suppress dripping of the weld metal. For this reason, the Mn content is limited to the range of 1.80 to 2.10%. Preferably, the Mn content is in the range of 1.85 to 2.05%, and more preferably, the Mn content is in the range of 1.90 to 2.00%.

[0035] [P: 0.030% or less] P is an element that is inevitably mixed in. It reduces the toughness of the weld metal and further induces hot cracking, so it is preferable to reduce its content as much as possible. A P content of 0.030% or less is acceptable. Therefore, the P content is limited to 0.030% or less. However, because excessive reduction leads to increased refining costs, it is preferable to adjust the P content to 0.002% or more. More preferably, the P content is in the range of 0.003 to 0.025%.

[0036] [S: 0.030% or less] S is an element that is inevitably mixed in and induces hot cracking, so it is preferable to reduce it as much as possible. An S content of 0.030% or less is acceptable. Therefore, the S content is limited to 0.030% or less. However, since excessive reduction leads to an increase in refining costs, it is preferable to adjust the S content to 0.002% or more. More preferably, the S content is in the range of 0.003 to 0.025%.

[0037] [B: 0.0003 to 0.0050%] B acts as a deoxidizing element in the weld metal and forms B oxides (B ２ O ３ The inclusion of B has the effect of improving the fluidity of the slag, lowering the melting point, and suppressing slag entrainment. To achieve such an effect, the B content must be 0.0003% or more. On the other hand, if the B content exceeds 0.0050%, cracks occur during the wire manufacturing process, reducing manufacturability. Therefore, the B content is limited to the range of 0.0003 to 0.0050%. Preferably, the B content is in the range of 0.0008 to 0.0040%, and more preferably, the B content is in the range of 0.0012 to 0.0035%.

[0038] [Rare Earth Elements (REM): 0.020 to 0.060%] Wires containing rare earth elements (REM) have the effect of improving arc directivity when used with positive polarity. The improved arc directivity suppresses arc deflection toward the groove wall, effectively dissolving slag formed in the previous pass and preventing incomplete fusion, thereby preventing welding defects. Therefore, REM is an essential element in this embodiment. To achieve this effect, a REM content of 0.020% or more is required. On the other hand, if the REM content exceeds 0.060%, cracks occur during the wire manufacturing process, deteriorating manufacturability. Therefore, the REM content is limited to 0.060% or less. Preferably, the REM content is in the range of 0.025 to 0.055%, and more preferably, the REM content is in the range of 0.028 to 0.050%.

[0039] Here, REM is a general term for 17 elements from the fourth to sixth periods of Group 3 of the periodic table, excluding the actinides. In this embodiment, it is preferable to use 15 elements of the lanthanides with atomic numbers 57 to 71, with Ce and La being particularly suitable. Ce or La may be added alone or in combination. Note that the REM content in this embodiment is the sum of the contents of the above-mentioned REM elements.

[0040] [O (oxygen): 0.010% or less] O (oxygen) is an element that is inevitably mixed in and reduces the workability of the wire, so it is preferable to reduce its content as much as possible. An O content of 0.010% or less is acceptable. However, excessive reduction leads to an increase in refining costs, so the O content is preferably adjusted to 0.001% or more. More preferably, the O content is in the range of 0.002 to 0.008%.

[0041] [N: 0.010% or less] N is an element that is inevitably mixed in and reduces the toughness of the weld metal, so it is preferable to reduce its content as much as possible. A N content of 0.010% or less is acceptable. However, excessive reduction of N leads to increased refining costs, so the N content is preferably adjusted to 0.001% or more. More preferably, the N content is in the range of 0.002 to 0.008%.

[0042] [Optional Composition] The above-described components are the basic chemical composition of the welding wire used in this embodiment. In this embodiment, in addition to the basic chemical composition, at least one selected from the following compositions may be further included as an optional composition, if necessary. The composition is Cu: 0.60% or less, Ni: 1.50% or less, Cr: 0.80% or less, Mo: 0.80% or less, Nb: 0.04% or less, V: 0.04% or less, Ti: 0.30% or less, Al: 0.10% or less, Sn: 0.30% or less, and Pb: 0.30% or less. The optional composition is determined in consideration of the strength, toughness, corrosion resistance, and the like, depending on the intended use of the welding wire. Each optional composition will be described below.

[0043] [Cu: 0.60% or less] Cu is an element that increases the strength of the weld metal. If Cu is contained in an amount exceeding 0.60%, the weld metal will exhibit red shortness in the temperature range around 1100°C, inducing cracks on the bead surface. Therefore, the Cu content is preferably 0.60% or less. When Cu is added to increase the strength of the weld metal, it is more preferable that Cu be contained in an amount of 0.05% or more. More preferably, the Cu content is in the range of 0.08 to 0.50%.

[0044] [Ni: 1.50% or less] Ni is an element that increases the strength of the weld metal without reducing its toughness. Ni is an expensive element, and if it is contained in an amount exceeding 1.50%, it increases the wire cost. Therefore, the Ni content is preferably 1.50% or less. When Ni is added to increase the strength of the weld metal, it is more preferable that Ni be contained in an amount of 0.01% or more. More preferably, the Ni content is in the range of 0.04 to 1.40%.

[0045] [Cr: 0.80% or less] Cr is an element that improves the strength and corrosion resistance of the weld metal. If the Cr content exceeds 0.80%, the wire hardens during wiredrawing, deteriorating manufacturability. Therefore, the Cr content is preferably 0.80% or less. When Cr is added to increase the strength of the weld metal, it is more preferable that the Cr content be 0.02% or more. More preferably, the Cr content is in the range of 0.05 to 0.75%.

[0046] [Mo: 0.80% or less] Mo is an element that improves the strength and corrosion resistance of the weld metal. If the Mo content exceeds 0.80%, the wire hardens during wiredrawing, deteriorating manufacturability. Therefore, the Mo content is preferably 0.80% or less. When Mo is added to increase the strength of the weld metal, it is more preferable that the Mo content be 0.02% or more. More preferably, the Mo content is in the range of 0.04 to 0.75%.

[0047] [Nb: 0.04% or less] Nb is an element that precipitates fine carbides and increases the strength of the weld metal. If the Nb content exceeds 0.04%, the wire hardens during wiredrawing, deteriorating manufacturability. Therefore, the Nb content is preferably 0.04% or less. When Nb is added to increase the strength of the weld metal, it is more preferable that the Nb content be 0.01% or more. More preferably, the Nb content is in the range of 0.01 to 0.03%.

[0048] [V: 0.04% or less] V is an element that precipitates fine carbides and increases the strength of the weld metal. If the V content exceeds 0.04%, the wire hardens during wiredrawing, deteriorating manufacturability. Therefore, the V content is preferably 0.04% or less. When V is added to increase the strength of the weld metal, it is more preferable that V be contained in an amount of 0.01% or more. More preferably, the V content is in the range of 0.01 to 0.03%.

[0049] [Ti: 0.30% or less] Ti is an element that precipitates fine carbides and increases the strength of the weld metal. If Ti is contained in an amount exceeding 0.30%, the wire hardens during wiredrawing, deteriorating manufacturability. Therefore, the Ti content is preferably 0.30% or less. When Ti is added to increase the strength of the weld metal, it is more preferable that Ti be contained in an amount of 0.04% or more. More preferably, the Ti content is in the range of 0.05 to 0.28%.

[0050] [Al: 0.10% or less] Al has the effect of improving the yield of REM when melting the wire material. If the Al content exceeds 0.10%, the toughness of the weld metal deteriorates. Therefore, the Al content is preferably 0.10% or less. When Al is added to improve the yield of REM, it is more preferable that the Al content be 0.01% or more. More preferably, the Al content is in the range of 0.01 to 0.08%.

[0051] [Sn: 0.30% or less] Sn has the effect of improving the corrosion resistance of the weld metal. If the Sn content exceeds 0.30%, it will induce hot cracking. Therefore, the Sn content is preferably 0.30% or less. When Sn is added to improve the corrosion resistance of the weld metal, it is more preferable that Sn be contained in an amount of 0.01% or more. More preferably, the Sn content is in the range of 0.02 to 0.25%.

[0052] [Pb: 0.30% or less] Pb has the effect of improving the machinability of the weld metal. If the Pb content exceeds 0.30%, it will induce hot cracking. Therefore, the Pb content is preferably 0.30% or less. When Pb is added to improve the machinability of the weld metal, it is more preferable to add 0.01% or more Pb. More preferably, the Pb content is in the range of 0.02 to 0.25%.

[0053] [Remainder Composition] The balance other than the basic chemical composition and optional composition described above consists of Fe and unavoidable impurities. Examples of unavoidable impurities include H, Mg, Zn, Re, Co, Sb, and Bi, and a total of 0.01% or less is acceptable. Furthermore, elements other than these may be contained as long as the basic chemical composition and optional composition described above are satisfied, and such embodiments are also within the technical scope of the present invention.

[0054] [Method of Manufacturing Welding Wire] Here, a method of manufacturing welding wire will be described. Molten steel having the above-described composition is melted in a converter, electric furnace, or the like, and then the steel material produced by continuous casting, for example, a billet, is hot-rolled and then cold-rolled, for example, by wiredrawing, to form a steel wire having a diameter in the range of 1.0 to 2.0 mm. Here, the hot rolling and cold rolling are only required to produce a steel wire having a predetermined size and shape, so the setting conditions for the rolling, etc. are not particularly limited. The steel wire after rolling is sequentially subjected to the steps of annealing, pickling, Cu plating, and wiredrawing to form a welding wire having a predetermined wire diameter.

[0055] [SLI: 10-46] Next, among the compositions of the welding wire described above, the compositions (Si, Mn, B) that combine with oxygen in the wire to form slag and the CO in the shielding gas are ２The parameter [SLI] obtained from the relationship with the gas ratio will be described.

[0056] CO in shielding gas ２ The gas acts as an active gas, and the deoxidizing elements Si, Mn, and B contained in the wire are oxidized to form slag. The main components of the slag are SiO ２ -MnO. This is due to oxidation products of Si and Mn, which are contained in large amounts in the wire. When B is contained in the wire, B ２ O ３ If the melting point of the slag is too high, it cannot be melted by the arc and the slag remains between the weld beads. This causes a welding defect of slag inclusion. To prevent such welding defects, it is necessary to adjust the contents of Si, Mn, and B in the wire and to reduce the amount of CO in the shielding gas. ２ It is important to adjust the amount of slag generated by adjusting the volume ratio α of the gas. The inventors have found that the above object can be achieved by setting the SLI, expressed by the following formula (1), within an appropriate range: SLI = [Si] × [Mn] × [B] × 10000 / α (1) where [element] is the content (mass%) of the element in the welding wire, and α is the CO content in the shielding gas. ２ The volume ratio of the gas is (0<α≦1).

[0057] In addition, when α=1, CO ２ When the gas is 100% by volume and α<1, i.e., CO ２ When the gas is less than 100% by volume in the shielding gas, the remaining gas is an inert gas, and examples of the inert gas include Ar gas, He gas, etc. For example, when α=0.8, CO ２ The gas accounts for 80% by volume, and the remaining 20% ​​by volume is an inert gas (e.g., Ar gas). Note that other gases are permitted as unavoidable impurities within a range that does not affect weldability.

[0058] If the SLI is less than 10, the slag melting point is high and slag inclusion occurs, so it is essential to adjust the SLI to 10 or more. On the other hand, if the SLI exceeds 46, the slag melting point drops too much and dripping of the weld metal cannot be suppressed. For this reason, the SLI is limited to the range of 10 to 46. Preferably, the SLI is in the range of 12 to 44, and more preferably, the SLI is in the range of 15 to 40.

[0059] Two steel plates 1 of 490 to 590 MPa grade and 10 to 100 mm thick with the composition shown in Table 1 were grooved with a groove angle θ and root gap G as shown in Figure 2, and a backing metal 2 was used on the bottom of the groove to prepare a welded joint by gas-shielded arc welding. The welding gas was CO ２ A mixed gas of an inert gas, such as Ar gas, was used.

[0060]

[0061] The welding wire was prepared by melting steel ingots having the compositions shown in Table 2 and drawing them into wires having a diameter of 1.2 mm.

[0062]

[0063] The steel materials, groove shapes, welding conditions, and welding wires used in each welding test are all shown in Table 3. The welding speed was adjusted for each pass.

[0064]

[0065] Cross-sectional macrographs were taken from the resulting welded joints and the presence or absence of welding defects was evaluated. Those with no welding defects were rated "absent," while those with defects such as slag inclusion, undercut, overlap, incomplete fusion, or hot cracking were rated "present."

[0066] None of the inventive examples had any welding defects, whereas the comparative examples outside the scope of the present invention had welding defects.

[0067] 1 Steel material 2 Backing metal 3 Weld metal (multi-layer) θ Groove angle G Root gap t Steel plate thickness

Claims

1. A horizontal narrow groove gas shielded arc welding method for joining steel materials with a groove angle θ of 15° or less, a root gap G in the range of 7 to 15 mm, and a plate thickness t in the range of 10 to 100 mm by multi-layer welding of gas shielded arc welding. Using a welding wire having a chemical composition containing, in mass%, C: 0.02 to 0.15%, Si: 0.60 to 0.95%, Mn: 1.80 to 2.10%, P: 0.030% or less, S: 0.030% or less, B: 0.0003 to 0.0050%, rare earth element (REM): 0.020 to 0.060%, O (oxygen): 0.010% or less, and N: 0.010% or less, with the balance being Fe and inevitable impurities, the SLI obtained from the following formula (1) is in the range of 10 to 46. SLI = [Si] × [Mn] × [B] × 10000 / α... (1) Here, [element] is the content (mass%) of the element in the welding wire, and α is the volume ratio of CO ２ gas in the shielding gas (0 < α ≤ 1).

2. The chemical composition of the welding wire further contains at least one selected from the group consisting of, by mass%, Cu: 0.60% or less, Ni: 1.50% or less, Cr: 0.80% or less, Mo: 0.80% or less, Nb: 0.04% or less, V: 0.04% or less, Ti: 0.30% or less, Al: 0.10% or less, Sn: 0.30% or less, and Pb: 0.30% or less. The horizontal narrow groove gas shielded arc welding method according to claim 1.

3. The horizontal narrow groove gas shielded arc welding method according to claim 1 or 2, wherein the welding is performed by a straight polarity welding using the welding wire as a negative electrode.

4. In the gas shielded arc welding, the welding current I is in the range of 240 to 360 A, the welding voltage E is in the range of 26 to 42 V, and the welding speed S is in the range of 20 to 80 cm / min. The horizontal narrow groove gas shielded arc welding method according to any one of claims 1 to 3.

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