Horizontal Narrow Orifice Gas Shielded Arc Welding Method

Abstract

Provided is a horizontal narrow gap welding method for steel materials that does not require special equipment and that enables construction without welding defects even when the groove angle is 15° or less.The method is a horizontal narrow gap gas shielded arc welding method for multi-layer welding of steel materials, in which the composition of the welding wire contains, in mass %, 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 the SLI calculated from formula (1) satisfies 10-46. SLI=[Si]×[Mn]×[B]×10000 / α... (1) Here, [element] is the content (mass%) of the element in the welding wire, and α is the CO content in the shielding gas. 2 Gas volume ratio (0

Description

Technical Field

[0001] The present invention relates to a horizontal narrow groove gas shielded arc welding method, and more particularly to a horizontal narrow groove gas shielded arc welding method for joining thick steel plates in a horizontal position by multi-layer welding. In this specification, "x~y" representing a numerical range means x or more and y or less, including the boundary values.

Background Art

[0002] In recent years, with the increase in the size of steel structures such as buildings and ships, steel plates tend to become thicker. However, the larger the plate thickness, the larger the groove area, resulting in an increase in the number of welding passes and the problems of requiring labor and time for welding construction. Furthermore, there is also a problem that it has become difficult to secure welding technicians due to the decrease in the working population, and for these reasons, an improvement in the welding construction efficiency in the manufacture of steel structures is desired.

[0003] As a method for improving welding construction efficiency, groove narrowing can be mentioned. By narrowing the groove, the groove area is reduced, the number of welding passes can be reduced, and the construction time can be shortened. However, in narrow groove welding in a horizontal position, it is difficult to prevent welding defects such as poor fusion, hot cracking, and slag entrapment, and various studies have been conducted.

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

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

[0006] In addition, Patent Document 3 discloses a transverse narrow groove arc welding method for a type I transverse open groove welded joint, in which, when viewed from the front, the apex of the weaving is inclined and retreats in the direction opposite to the welding progress direction from the vertical line with respect to the welding line, and is continuously performed 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 groove transverse multi-layer build-up welding of a steel plate with a thickness of 16 to 25 mm is performed in a positive polarity using a solid wire containing 0.025 to 0.050% by mass of a rare earth element.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in the method described in Patent Document 1, hot cracks occur in the upper bead. In addition, the methods described in Patent Documents 2 and 3 require dedicated equipment and cannot be implemented with a general-purpose welding apparatus. Further, when the method described in Patent Document 4 is applied with a groove angle of 15° or less, welding defects such as slag entrapment and poor fusion are likely to occur, and there is a problem that it is not easy to produce a joint without welding defects.

[0010] An object of the present invention is to solve the above problems and provide a welding method that does not require special equipment and enables construction without welding defects even when the groove angle is 15° or less in the transverse narrow groove welding of steel materials.

Means for Solving the Problems

[0011] The inventors studied a welding method that can be constructed without generating welding defects with various welding wires and only a simple welding operation in the horizontal narrow groove welding of 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. Here, the simple welding operation refers to the operation of linearly moving the welding torch in the welding line direction and the weaving operation that reciprocates in a direction perpendicular to the welding line direction, that is, in a direction perpendicular to the horizontal plane, in combination with the above linear movement operation. As a result of intensive studies during the above welding operations, it was found that a highly directional arc can be obtained by making the welding wire contain rare earth elements and making it a positive polarity. Furthermore, by adjusting the contents of Si, Mn, and B in the welding wire and the CO 2 gas ratio in the shielding gas, it was found that the amount of slag formed and the melting point can be controlled, and welding defects such as lack of fusion and slag entrapment do not occur.

[0012] The present invention was completed through further studies based on such findings, and the gist of the present invention is as follows. 〔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, 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 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, and making the SLI obtained from the following formula (1) 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〕In the above 〔1〕, 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. This is a horizontal narrow groove gas shielded arc welding method. 〔3〕In the above 〔1〕 or 〔2〕, this is a horizontal narrow groove gas shielded arc welding method in which the welding wire is used as the negative electrode to perform straight polarity welding. 〔4〕In any one of the above 〔1〕 to 〔3〕, 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. This is a horizontal narrow groove gas shielded arc welding method.

Advantages of the Invention

[0013] According to the present invention, in the horizontal narrow groove gas shielded arc welding of steel materials, it is possible to provide a welded joint with excellent soundness without welding defects even when a special device is not required and the groove angle is 15° or less, and it has an extremely remarkable effect in the industry.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0015] Embodiments regarding the constituent elements of the present invention will be specifically described below. In the horizontal narrow groove gas shielded arc welding method according to an embodiment of the present invention, the groove angle θ of the steel material is set to 15° or less, the root gap G is in the range of 7 to 15 mm, and the gas shielded arc welding is targeted for steel materials with a plate thickness t of the steel material 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 for steel structures such as buildings and ships. Examples of the steel grade include 490 MPa grade steel, 550 MPa grade steel, 590 MPa grade steel, and 780 MPa grade steel. Also, the plate thickness t of the steel material according to this embodiment is in the range of 10 to 100 mm. When the plate thickness t of the steel material is less than 10 mm, there is no merit in reducing the groove area by narrow groove welding. On the other hand, the upper limit of the plate thickness t of the steel material used for the above applications is generally 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 contains, by 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, and the balance is preferably Fe and inevitable impurities.

[0018] Furthermore, as an optional composition, it is preferable to contain at least one selected from 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. The optional composition is determined in consideration of strength, toughness, etc. according to the purpose of use of the steel material.

[0019] [Groove angle θ] In this embodiment, as shown in FIG. 1, the present invention targets a narrow groove with a groove angle θ, which is the angle at the groove opening of the horizontally arranged steel materials 1 and 1 butted vertically, of 15° or less. If θ exceeds 15°, the advantage of the narrow groove, which is the improvement in welding efficiency, will be diminished. Therefore, it is limited to 15° or less. Note that θ being 0° means that the groove walls of the upper and lower steel materials 1 and 1 are parallel, and this case is also within the scope of this embodiment. The preferred angle of θ is in the range of 0 to 10°.

[0020] [Root gap G] Also, as shown in FIG. 1, the interval between the narrowest sides at the groove openings of the horizontally arranged steel materials 1 and 1 butted vertically is called the root gap and is represented by G (mm). The root gap G in this embodiment is in the range of 7 to 15 mm. If G is less than 7 mm, it is difficult to insert the welding torch into the groove. On the other hand, if G exceeds 15 mm, the advantage of the narrow groove, which is the improvement in welding efficiency, will be diminished. Therefore, 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, the gas shielded arc welding method according to the present invention will be described. The gas shielded arc welding method is the mainstream of the arc welding method and is a welding method that uses a gas (shielding gas) to protect the arc and the molten metal from oxygen and nitrogen in the atmosphere.

[0022] [Shielding gas] As the shielding gas, carbon dioxide gas (CO 2 gas), which is the cheapest in terms of cost, inert gases such as Ar and He, or a mixed gas obtained by mixing CO 2 gas and an inert gas are used. In this embodiment, it is a welding method using a shielding gas mainly composed of CO 2 gas. Note that it is necessary to consider the SLI numerical values described later for the composition of the shielding gas.

[0023] [Other welding conditions] Next, other welding conditions will be described. <Welding current I> In this embodiment, it is preferable that the welding current I is in the range of 240 to 360 A. If the welding current I is lower than 240 A, the arc pressure becomes low, and there is a risk of slag entrainment and poor fusion due to remaining slag. On the other hand, if the welding current I is higher than 360 A, there is a risk of sag, that is, overlap, due to the convection of the welding metal. Therefore, the welding current I is preferably in the range of 240 to 360 A. More preferably, the welding current I is in the range of 260 to 340 A, and even more preferably, the welding current I is in the range of 270 to 320 A.

[0024] <Welding voltage E> In this embodiment, it is preferable that the welding voltage E is in the range of 26 to 42 V. If the welding voltage E is lower than 26 V, it may not be possible to stably maintain the arc, and the welding may become unstable. On the other hand, if the welding voltage E is higher than 42 V, the arc spreads and the arc heat is dispersed, so the slag cannot be melted and slag entrainment is likely to occur. Therefore, the welding voltage E is preferably in the range of 26 to 42 V. More preferably, the welding voltage E is in the range of 28 to 40 V, and even more preferably, the welding voltage E is in the range of 30 to 38 V.

[0025] <Welding speed S: 20 cm / min to 80 cm / min> In this embodiment, it is preferable that the welding speed S is in the range of 20 to 80 cm / min. When the welding speed S is less than 20 cm / min, even with the appropriate current and voltage, excessive welding metal is generated, so there is a risk of sag in the welding metal. On the other hand, when the welding speed S is greater than 80 cm / min, sufficient heat is not provided and the slag cannot be melted, so there is a risk of slag entrainment. Therefore, the welding speed S is preferably in the range of 20 to 80 cm / min. More preferably, the welding speed S is in the range of 25 to 75 cm / min, and even more preferably, the welding speed S is in the range of 28 to 72 cm / min.

[0026] [Multi-layer welding] The narrow groove gas shielded arc welding method according to this embodiment is applicable to multi-layer welding of a narrow groove using a backing metal 2 at the bottom (narrow side) of a horizontally oriented narrow groove as shown in Fig. 2. When implementing the narrow groove gas shielded arc welding method according to this embodiment, the welding conditions for each pass from the first layer to the final layer are appropriately set within the range of the welding conditions described above. Regarding the number of layers of the multi-layer weld metal 3, it depends on the plate thickness t of the steel material 1, the groove angle θ, the root gap G, etc. However, as described above, when the plate thickness t is in the range of 10 to 100 mm, a range of 2 to 20 layers is preferable. Also, regarding the number of passes, there may be cases where multiple passes are made in one layer, and a range of 3 to 50 passes is preferable.

[0027] [Polarity during welding] Either the straight polarity or the reverse polarity can be selected as the polarity during welding. The straight polarity raises the potential of the steel material and lowers the potential of the welding wire. On the other hand, the reverse polarity lowers the potential of the steel material and raises the potential of the welding wire. However, in the case of the narrow groove of this embodiment where the groove angle θ is small and the root gap G is small, the straight polarity is preferable because the welding efficiency is improved. The reason is that in a narrow groove, the arc tends to face the groove wall and it becomes difficult to melt the bottom (narrow side) of the groove. Therefore, by welding with the straight polarity using a wire added with REM described later, the arc directivity is improved, the arc tends to concentrate on the bottom of the groove, and the bottom of the groove can be stably and sufficiently melted.

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

[0029] In this embodiment, welding wires of various standards can be used. For example, YGW11, YGW18, G59JA1UC3M1T, G69A2UCN2M4T, G78A2UCN4M4T, etc. classified in JIS Z3312:2009 can be mentioned. The wire diameter φ is preferably in the range of 1.0 to 2.0 mm.

[0030] Next, as the chemical composition of the welding wire, by mass%, it contains 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%. Also, it contains rare earth elements (REM): 0.020 to 0.060%, O (oxygen): 0.010% or less, N: 0.010% or less, and the balance is composed of Fe and inevitable impurities. Further, it is characterized by containing Si, Mn, and B so that the SLI obtained from the following formula (1) satisfies the range of 10 to 46. SLI = [Si] × [Mn] × [B] × 10000 / α ··· (1) Here, [element] is the content (% by mass) of the element, and α is the volume ratio of CO 2 gas in the shielding gas (0 < α ≤ 1). Regarding the details of SLI and α, they 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 "% by mass".

[0032] [C: 0.02 to 0.15%] C is an element that contributes to improving the strength of the weld metal, and it is necessary to contain 0.02% or more to ensure the strength of the weld metal. On the other hand, when the C content exceeds 0.15%, the weld metal hardens and the toughness decreases, so it 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 surface of the weld metal. The generation of slag suppresses the dripping of the weld metal in the groove and effectively acts to prevent welding defects. To obtain such an effect, Si needs to be contained at 0.60% or more. On the other hand, when the Si content exceeds 0.95%, excessive slag is generated, causing slag entrainment, so it is limited to 0.95% or less. Preferably, the Si content is in the range of 0.62 - 0.92%, and more preferably, the Si content is in the range of 0.66 - 0.90%.

[0034] [Mn: 1.80 - 2.10%] Mn acts as a deoxidizing element. When Mn oxide (MnO) is contained in the slag, it has the effect of improving the fluidity of the slag and the compatibility between the base metal and the weld metal. To obtain such an effect, Mn needs to be contained at 1.80% or more. On the other hand, when the Mn content exceeds 2.10%, the fluidity of the slag becomes excessive and the dripping of the weld metal cannot be suppressed. Therefore, the Mn content is limited to the range of 1.80 - 2.10%. Preferably, the Mn content is in the range of 1.85 - 2.05%, and more preferably, the Mn content is in the range of 1.90 - 2.00%.

[0035] [P: 0.030% or less] P is an element that inevitably mixes in. It reduces the toughness of the weld metal and further induces hot cracking, so it is preferably reduced as much as possible. If the P content is 0.030% or less, it is acceptable. Therefore, the P content is limited to 0.030% or less. However, excessive reduction leads to an increase in refining costs, so 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 - 0.025%.

[0036] [S: 0.030% or less] S is an inevitably mixed element that induces hot cracking, so it is preferably reduced as much as possible. If the S content is 0.030% or less, it is acceptable. Therefore, the S content is limited to 0.030% or less. Note that excessive reduction will lead to an increase in refining costs, so the S content is preferably adjusted to 0.002% or more. More preferably, the S content is in the range of 0.003 - 0.025%.

[0037] [B: 0.0003 - 0.0050%] B acts as a deoxidizing element in the weld metal. When B oxide (B 2 O 3 ) is contained, it has the effect of improving the fluidity of the slag and lowering the melting point, and suppressing slag entrainment. To obtain such an effect, B needs to be contained at 0.0003% or more. On the other hand, when the B content exceeds 0.0050%, cracks occur in the wire manufacturing process, and the manufacturability deteriorates. Therefore, the B content is limited to the range of 0.0003 - 0.0050%. Preferably, the B content is in the range of 0.0008 - 0.0040%, and more preferably, the B content is in the range of 0.0012 - 0.0035%.

[0038] [Rare earth elements (REM): 0.020 - 0.060%] The wire added with rare earth elements (REM) has the effect of improving the arc directivity by setting the polarity to positive. By improving the arc directivity, it suppresses the arc deflection to the groove wall, effectively acts on preventing the dissolution and fusion defects of the slag formed in the previous pass, and prevents welding defects. Therefore, it is an essential element in this embodiment. To obtain such an effect, REM needs to be contained at 0.020% or more. On the other hand, when the REM content exceeds 0.060%, cracks occur in the wire manufacturing process, deteriorating the manufacturability. Therefore, the REM content is limited to 0.060% or less. Preferably, the REM content is in the range of 0.025 - 0.055%, and more preferably, the REM content is in the range of 0.028 - 0.050%.

[0039] Here, REM is a general term for 17 elements from the 4th to 6th periods among the elements of Group 3 in the periodic table, excluding actinoids. In this embodiment, it is preferable to use 15 elements of lanthanoids with atomic numbers 57 to 71, and particularly Ce and La are preferred. 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 each element of the above-mentioned REM.

[0040] [O (oxygen): 0.010% or less] O (oxygen) is an element that inevitably mixes in, and it is preferable to reduce it as much as possible because it deteriorates the workability of the wire. The O content is acceptable if it is 0.010% or less. Note that excessive reduction leads to an increase in refining costs, so it is preferable to adjust the O content 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 inevitably mixes in, and it is preferable to reduce it as much as possible because it deteriorates the toughness of the weld metal. The N content is acceptable if it is 0.010% or less. Note that excessive reduction of N leads to an increase in refining costs, so it is preferable to adjust the N content 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-mentioned components are the basic chemical composition of the welding wire used in this embodiment. In this embodiment, in addition to the above-mentioned basic chemical composition, as an optional composition, at least one selected from the following compositions can be contained as necessary. The compositions are: 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. Note that the optional composition is determined in consideration of strength, toughness, corrosion resistance, etc., according to the purpose of use of the welding wire. Hereinafter, the optional composition will be described individually.

[0043] [Cu: Below 0.60%] Cu is an element that increases the strength of the weld metal. When Cu is contained in an amount exceeding 0.60%, it exhibits hot shortness in the temperature range near 1100°C and induces bead surface cracking. Therefore, the Cu content is preferably 0.60% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Cu content is 0.05% or more. More preferably, the Cu content ranges from 0.08 to 0.50%.

[0044] [Ni: Below 1.50%] Ni is an element that increases the strength without reducing the toughness of the weld metal. Ni is an expensive element, and when contained in an amount exceeding 1.50%, it increases the wire cost. Therefore, the Ni content is preferably 1.50% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Ni content is 0.01% or more. More preferably, the Ni content ranges from 0.04 to 1.40%.

[0045] [Cr: Below 0.80%] Cr is an element that improves the strength and corrosion resistance of the weld metal. When Cr is contained in an amount exceeding 0.80%, the wire hardens during wire drawing, deteriorating the manufacturability. Therefore, the Cr content is preferably 0.80% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Cr content is 0.02% or more. More preferably, the Cr content ranges from 0.05 to 0.75%.

[0046] [Mo: Below 0.80%] Mo is an element that improves the strength and corrosion resistance of the weld metal. When Mo is contained in an amount exceeding 0.80%, the wire hardens during wire drawing, deteriorating the manufacturability. Therefore, the Mo content is preferably 0.80% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Mo content is 0.02% or more. More preferably, the Mo content ranges from 0.04 to 0.75%.

[0047] [Nb: Below 0.04%] Nb is an element that precipitates fine carbides and increases the strength of the weld metal. When Nb is contained in an amount exceeding 0.04%, the wire hardens during wire drawing, deteriorating the manufacturability. Therefore, the Nb content is preferably 0.04% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Nb content is 0.01% or more. More preferably, the Nb content is in the range of 0.01 - 0.03%.

[0048] [V: Below 0.04%] V is an element that precipitates fine carbides and increases the strength of the weld metal. When V is contained in an amount exceeding 0.04%, the wire hardens during wire drawing, deteriorating the manufacturability. Therefore, the V content is preferably 0.04% or less. When adding for increasing the strength of the weld metal, it is more preferable that the V content is 0.01% or more. More preferably, the V content is in the range of 0.01 - 0.03%.

[0049] [Ti: Below 0.30%] Ti is an element that precipitates fine carbides and increases the strength of the weld metal. When Ti is contained in an amount exceeding 0.30%, the wire hardens during wire drawing, deteriorating the manufacturability. Therefore, the Ti content is preferably 0.30% or less. When adding for increasing the strength of the weld metal, it is more preferable that the Ti content is 0.04% or more. More preferably, the Ti content is in the range of 0.05 - 0.28%.

[0050] [Al: Below 0.10%] Al has the effect of improving the recovery rate of REM during melting of the wire material. When Al is contained in an amount exceeding 0.10%, the toughness of the weld metal deteriorates. Therefore, the Al content is preferably 0.10% or less. When adding for improving the recovery rate of REM, it is more preferable that the Al content is 0.01% or more. More preferably, the Al content is in the range of 0.01 - 0.08%.

[0051] [Sn: Below 0.30%] Sn has the effect of improving the corrosion resistance of the weld metal. When Sn is contained in an amount exceeding 0.30%, hot cracking is induced. Therefore, the Sn content is preferably 0.30% or less. When adding for improving the corrosion resistance of the weld metal, it is more preferable that Sn is 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: Below 0.30%] Pb has the effect of improving the machinability of the weld metal. When Pb is contained in an amount exceeding 0.30%, hot cracking is induced. Therefore, the Pb content is preferably 0.30% or less. When adding for improving the machinability of the weld metal, it is more preferable that Pb is added in an amount of 0.01% or more. More preferably, the Pb content is in the range of 0.02 to 0.25%.

[0053] [Remaining composition] The remainder other than the above-described basic chemical composition and optional composition consists of Fe and inevitable impurities. Examples of the inevitable impurities include H, Mg, Zn, Re, Co, Sb, and Bi, and as long as the total is 0.01% or less, it is acceptable. Also, as long as the above-described basic chemical composition and optional composition are satisfied, other elements may be contained, and such embodiments are also included in the technical scope of the present invention.

[0054] [Method for manufacturing welding wire] Here, the method for manufacturing a welding wire will be described. After melting molten steel having the above-described composition in a converter, an electric furnace, or the like, a steel material manufactured by a continuous casting method, for example, a billet, etc. is hot-rolled, and then cold-rolled, for example, wire drawing is performed to obtain a steel wire rod in the range of 1.0 to 2.0 mm in diameter. Here, since the hot rolling and cold rolling only need to manufacture a steel wire rod having a predetermined dimensional shape, the setting conditions for the rolling and the like are not particularly limited. The rolled steel wire rod is sequentially subjected to each process of annealing - pickling - Cu plating - wire drawing to obtain a welding wire having a predetermined wire diameter.

[0055] [SLI:10~46] Subsequently, regarding the parameter [SLI] obtained from the relationship between the components (Si, Mn, B) that form slag by combining with oxygen in the wire among the above-described welding wire compositions and the CO 2 gas ratio in the shielding gas, an explanation will be given.

[0056] CO 2 gas in the shielding gas acts as an active gas, and Si, Mn, and B, which are deoxidizing elements contained in the wire, are oxidized to form slag. The main components of the slag are SiO 2 -MnO. This is due to the oxidation products of Si and Mn with high contents in the wire. When B is contained in the wire, B 2 O 3 mixes into the slag, and the melting point of the slag decreases. If the melting point of the slag is too high, melting by the arc is impossible, and slag remains between the weld beads. Therefore, in order to prevent such welding defects, it is important to adjust the contents of Si, Mn, and B in the wire and to adjust the amount of slag generation according to the volume ratio α of CO 2 gas in the shielding gas. And it has been found that the above object can be achieved by setting the SLI represented by the following formula (1) within an appropriate range. 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).

[0057] Note that when α = 1, the CO 2 gas becomes 100% by volume, and when α < 1, that is, when the CO 2 gas is less than 100% by volume in the shielding gas, the remaining gas is an inert gas. Examples of such inert gases include Ar gas and He gas. For example, when α = 0.8, the CO 2The gas accounts for 80% by volume, and the remaining 20% by volume is an inert gas (for example, Ar gas). Other gases as inevitable impurities are allowed as long as they do not affect weldability.

[0058] If this SLI is less than 10, the slag melting point is high and slag entrainment occurs, so it is essential to adjust it to be 10 or more. On the other hand, if the SLI exceeds 46, the melting point of the slag drops too much and it becomes impossible to suppress the dripping of the weld metal. Therefore, 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.

Example

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

[0060]

Table 1

[0061] The welding wire was made by melting a steel ingot with the composition shown in Table 2 and drawing it into a wire with a diameter of 1.2 mm.

[0062]

Table 2

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

[0064]

Table 3

[0065] For the obtained welded joints, cross-sectional macrographs were taken to evaluate the presence or absence of welding defects. Those without welding defects were designated as "none", and those with defects such as slag entrapment, undercut, overlap, lack of fusion, and hot cracking were designated as "present".

[0066] In all of the inventive examples, no welding defects occurred. On the other hand, in the comparative examples outside the scope of the present invention, welding defects occurred.

Explanation of Signs

[0067] 1 Steel material 2 Backup plate 3 Weld metal (multi-layer) θ Groove angle G Root gap t Thickness of steel material

Claims

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, In mass percent, C: 0.02-0.15%, Si: 0.60-0.95%, 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): 0.020-0.060%, O (oxygen): 0.010% or less, and N: 0.010% or less; Optionally, 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 Contains at least one selected from A welding wire having a chemical composition with the balance being Fe and unavoidable impurities is used, A horizontal narrow gap gas-shielded arc welding method, in which the SLI calculated 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 CO content in the shielding gas. ２ The volume ratio of the gas is (0<α≦1).

2. 2. The horizontal narrow gap gas-shielded arc welding method according to claim 1, wherein positive polarity welding is performed using the welding wire as a negative electrode.

3. 3. The horizontal narrow gap gas-shielded arc welding method according to claim 1, wherein in the gas-shielded arc welding, a welding current I is in the range of 240 to 360 A, a welding voltage E is in the range of 26 to 42 V, and a welding speed S is in the range of 20 to 80 cm / min.

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