Vertical narrow-gap gas shielded arc welding method

Abstract

This invention provides a high-quality and highly efficient vertical narrow-groove gas-shielded arc welding method that enables the creation of a welded joint with high toughness, particularly excellent low-temperature toughness of the weld metal, while stabilizing the weld bead shape and preventing the occurrence of welding defects, including suppressing the dripping of molten metal, which is a problem in vertical welding. In a vertical narrow-groove gas-shielded arc welding method in which two thick steel plates with a thickness of 10 mm or more are joined by single-layer welding or multi-layer welding using weaving, a welding wire containing a predetermined amount of REM is used, and a welding torch having a bent portion and a tip portion defined by the bent portion is used to perform weaving for the first layer of welding, and at that time, when weaving with respect to the groove surface of the thick steel material, the angle θ1 of the tip of the welding torch with respect to the horizontal direction at the reference position is set to an angle greater than 45°, and the tip of the welding torch is swung toward the groove surface of the thick steel material under predetermined conditions.

Description

Technical Field

[0001] The present invention relates to a narrow-groove gas shielded arc welding method, and particularly to a vertical narrow-groove gas shielded arc welding method that can be applied to butt welding of two thick steel plates. Here, "narrow groove" means that the groove angle is 20° or less and the groove gap is 20 mm or less.

Background Art

[0002] Gas shielded arc welding used in steel welding construction is generally a consumable electrode type that uses a gas of CO2 alone or a mixed gas of Ar and CO2 for shielding the molten part. Such gas shielded arc welding is widely used in manufacturing fields such as automobiles, construction, bridges, and electrical equipment.

[0003] Recently, with the increase in the size and thickness of steel structures, the amount of welding in the manufacturing process, particularly the amount of welding in butt welding of steel plates, has increased. Furthermore, a lot of time is required for welding construction, leading to an increase in construction costs.

[0004] As a method for improving the above problems, the application of narrow-groove gas shielded arc welding, in which a groove with a small groove gap with respect to the plate thickness is multi-layer welded by an arc welding method, can be considered. This narrow-groove gas shielded arc welding is expected to reduce the amount of welding compared to normal gas shielded arc welding, achieving high welding efficiency and energy savings, and ultimately reducing construction costs.

[0005] On the other hand, for vertical high-efficiency welding, electro-slag welding is usually applied. However, it is based on one-pass large heat input welding, and in welding with a plate thickness exceeding 60 mm, there is concern about excessive heat input and a decrease in the toughness of the weld metal and the heat-affected zone of the weld. In addition, there is a limit to the plate thickness for one-pass welding, and currently, welding with a plate thickness exceeding 65 mm has not yet been technically established.

[0006] Therefore, there is a need to develop a high-quality and highly efficient welding method that applies narrow-gap gas-shielded arc welding to vertical welding. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6439882 [Patent Document 2] Patent No. 6119940 [Patent Document 3] Patent No. 5884209 [Patent Document 4] Patent No. 6119948 [Overview of the project] [Problems that the invention aims to solve]

[0008] As a welding method that applies such narrow-gap gas shielded arc welding to vertical welding, for example, the methods described in Patent Documents 1 and 2 are characterized by directing the tip of the welding torch toward the groove wall to promote melting of the groove wall and performing a U-shaped weaving along the groove wall. However, when the angle that the wire tip makes with the horizontal direction is between 10° and 45°, the welding current fluctuates greatly during the reciprocating motion due to weaving, which has the problem of reducing the low-temperature toughness of the weld metal. In addition, the methods described in Patent Documents 3 and 4 have the problem that, because there is no bend in the welding torch, when the angle of the torch becomes large, the height of the torch base becomes high and it is prone to interference with the workpiece, and the melting of the grooves on the left and right sides is insufficient.

[0009] As mentioned above, a high-quality and highly efficient vertical narrow-gap gas-shielded arc welding method that can be applied to welding thick steel materials has not yet been sufficiently developed. Meanwhile, advancements in welding automation technology (welding robots) have made it possible to weave the welding torch to suit groove shapes and welding positions, which was previously difficult. By utilizing this, it is becoming possible to perform welding operations (setting conditions) that are suitable for steel materials, groove shapes, welding positions, and welding materials (wires).

[0010] The present invention aims to provide a vertical narrow-gap gas-shielded arc welding method that enables high-quality and highly efficient welding of thick steel materials by utilizing high-performance and high-precision welding automation technology and performing precise welding torch weaving according to the groove shape and welding position. [Means for solving the problem]

[0011] The inventors conducted further investigations to solve the above problem, • Use a welding wire containing 0.015 to 0.100% by mass of REM (Rare Earth Metal), - To further control the welding conditions in the first layer welding, specifically, to perform weaving using a welding torch equipped with a bent portion and a tip portion defined by this bent portion, and in doing so, to position the tip of the welding torch at an appropriate angle to the horizontal plane when weaving against the groove surface of the thick steel material, and to oscillate the tip of the welding torch toward the groove surface of the thick steel material under appropriate conditions. As a result, we have found that even with a small groove angle, it is possible to ensure sufficient joint depth while preventing the occurrence of welding defects, stabilize the bead shape including suppressing the dripping of molten metal which is a problem in high-current vertical welding, and further improve the toughness of the welded joint, especially the low-temperature toughness of the weld metal. This invention was completed after further consideration based on the above findings.

[0012] In other words, the gist of the present invention is as follows:

[0013] 1. In a vertical narrow-groove gas shielded arc welding method in which two thick steel plates with a thickness of 10 mm or more are joined by single-layer welding or multi-layer welding using weaving, with a groove angle of 20° or less and a groove gap of 20 mm or less, A welding wire containing REM: 0.015 to 0.100% by mass is used, The weaving of the first layer of welding is performed using a welding torch having a bent portion and a tip portion defined by the bent portion, and at that time, when weaving against the groove surface of the thick steel material, the tip portion of the welding torch is swung toward the groove surface of the thick steel material, and the position where the tip portion of the welding torch is aligned with the welding line direction when viewed from the thickness direction of the thick steel material is set as the reference position, the angle θ1 of the tip portion of the welding torch with respect to the horizontal direction at the reference position is set to an angle greater than 45°, and the swing angle θ2 of the tip portion of the welding torch from the reference position is set to be between 5° and 60°. The joint depth in the initial welding layer shall be 10 mm or more. Vertical narrow-gap gas shielded arc welding method.

[0014] 2. The vertical narrow-groove gas shielded arc welding method according to paragraph 1, wherein the joint is a single-layer weld and the groove gap is 25% or less of the plate thickness of the thick steel material.

[0015] 3. The vertical narrow-gap gas shielded arc welding method according to paragraph 1, wherein the joining is performed as multi-layer welding, and the joining depth in the first layer welding is 10 mm or more and 70 mm or less.

[0016] 4. The vertical narrow-gap gas shielded arc welding method according to any one of 1 to 3, wherein, in the weaving of the first layer welding, the weaving pattern of the welding torch as viewed from the direction of the welding line is U-shaped. [Effects of the Invention]

[0017] According to the present invention, even when welding a thick steel plate with a thickness of 10 mm or more under a groove condition with a small groove angle, while suppressing the dripping of molten metal, which is a problem in vertical welding, stabilizing the bead shape and preventing the occurrence of welding defects, high-quality and high-efficiency narrow-groove gas shielded arc welding can be performed to obtain a welded joint with high toughness, particularly excellent low-temperature toughness of the weld metal. And, the welding method of the present invention has less deposition amount compared to ordinary gas shielded arc welding, and energy saving can be achieved by increasing the welding efficiency, so a significant reduction in welding construction cost becomes possible. In addition, in the welding method of the present invention, a water-cooled copper backing pressing mechanism for preventing the dripping of molten metal, such as an electro-gas arc welding device, is unnecessary, so the complication of the device can be avoided. Furthermore, since the heat input per pass can be suppressed by welding construction with multiple passes and a predetermined groove shape, it becomes easy to ensure the desired mechanical properties in the weld metal and the heat-affected zone of the steel plate.

Brief Description of the Drawings

[0018] [Figure 1] It shows examples of various groove shapes. [Figure 2] In the V-shaped groove shape, it shows the construction procedure when performing the first layer welding by the welding method of the present invention. [Figure 3] It is a schematic diagram showing the swinging state of the welding torch during weaving with respect to the groove surface of the thick steel plate. [Figure 4] In the V-shaped groove shape, it shows an example of the groove cross-section after performing the first layer welding. [Figure 5] It shows the weaving pattern of the welding torch as seen from the welding line direction during the weaving of the first layer welding.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the present invention will be specifically described. Figures 1(a) to 1(c) show examples of various groove shapes. In the figures, reference numeral 1 denotes a thick steel material, 2 denotes the groove surface of the thick steel material, and 3 denotes the groove of the lower part of the steel material (in a Y-shaped groove). The symbols θ denotes the groove angle, G denotes the groove gap, t denotes the plate thickness, and h denotes the groove height of the lower part of the steel material (in a Y-shaped groove). As shown in the figure, the groove shape targeted here can be either a V-groove (including I-grooves and L-grooves) or a Y-groove, and it is also possible to have a multi-stage Y-groove as shown in Figure 1(c). As shown in Figures 1(b) and (c), the groove angle and groove gap in the case of a Y-shaped groove are those of the groove in the lower part of the steel material. Here, the groove in the lower part of the steel material refers to the area from the steel material surface that becomes the back surface during welding (the surface on the welding equipment (welding torch) side is the front surface, and the opposite side is the back surface) up to about 20-40% of the plate thickness.

[0020] Figure 2 shows the procedure for performing the first layer welding using the welding method according to one embodiment of the present invention in a V-shaped groove. In the figure, reference numeral 4 denotes the welding torch, 5 denotes the welding wire, and 6 denotes the backing material. The weld line, molten pool, and weld bead are not shown in the figure. Here, as shown in Figure 2, this welding method is a gas-shielded arc welding method in which two thick steel plates of a predetermined thickness are butted together and joined by vertical welding using weaving, with the direction of travel being upward. During weaving against the groove surface of the thick steel plate, the tip of the welding torch is swung toward the groove surface of the thick steel plate. Here, a V-shaped groove is shown as an example, but the same applies to other groove shapes.

[0021] Furthermore, Figure 3 is a schematic diagram showing the oscillation state of the welding torch during weaving against the groove surface of a thick steel material. Figures 3(a) and (b) show the welding torch in the reference position and the state when the welding torch has oscillated at an angle of θ2, respectively, as viewed from the plate thickness direction (the back surface of the thick steel material in Figure 2 (the side with the backing material)). Figure 3(c) is a view from arrow X in Figure 3(a). The reference position is the position where the tip of the welding torch (center line, i.e., the direction in which the welding wire protrudes) is aligned with the welding line direction when viewed from the plate thickness direction, as shown in Figure 3(a). Also, in Figures 3(a) and (b), it is assumed that the groove surface of the thick steel material to be melted (not shown) is on the left side of the page. In the figure, reference numeral 7 denotes the main body of the welding torch, 8 denotes the power supply tip, 9 denotes the bent portion, and 10 denotes the tip portion. Here, the tip portion 10 is the part that is on the welding wire (not shown) side of the bent portion 9. The bent portion 9 may be provided on either the main body 7 or the power supply tip 8 that constitute the welding torch, but from the standpoint of ease of installation, it is preferable to provide it on the power supply tip 8. Furthermore, θ1 is the angle of the tip of the welding torch relative to the horizontal at the reference position, θ2 is the oscillation angle of the tip of the welding torch from the reference position, θ3 is the bending angle at the bent part of the welding torch, and l is the length of the tip of the welding torch, each of which is based on the center line of each part of the welding torch.

[0022] Figure 4 shows an example of a groove cross-section after the first layer of welding in a V-shaped groove. In the figure, reference numeral 11 denotes the weld bead, symbol D denotes the joint depth in the first layer of welding, and W denotes the weld bead width in the first layer of welding (the gap between grooves after the first layer of welding). The joint depth D in the first layer of welding is the minimum weld bead height in the first layer of welding, when the steel surface that becomes the back surface during welding is used as the starting point (the first layer weld bead height closest to the starting steel surface). Here, a V-shaped groove is used as an example, but D and W are similar for other groove shapes as well.

[0023] Next, the reasons for limiting the groove angle, groove gap, and steel plate thickness within the aforementioned ranges in the welding method of the present invention will be explained.

[0024] Bevel angle θ: 20° or less While smaller grooves in steel materials allow for faster and more efficient welding, they also increase the likelihood of defects such as poor fusion. Furthermore, welding with groove angles exceeding 20° can be performed using conventional methods. Therefore, this welding method targets groove angles of 20° or less, where conventional methods are difficult and further efficiency improvements are expected. In the case of a V-groove, a groove angle of 0° is called an I-groove, and in terms of welding volume, this 0° case is the most efficient. Therefore, a groove angle of 0° (I-groove) is acceptable. However, because the groove closes during welding due to thermal distortion, it is preferable to take this into account and set the groove angle according to the plate thickness t (however, in the case of a Y-groove, the groove height h of the lower part of the steel material). Specifically, the groove angle is preferably (0.5 × t / 20)° or greater, and more preferably (0.8 × t / 20)° or greater. Furthermore, the groove angle is preferably (2.0 × t / 20)° or less, and more preferably (1.2 × t / 20)° or less. For example, when the plate thickness t is 100 mm, the groove angle is preferably 2.5° or greater, and more preferably 4° or greater. Furthermore, the groove angle is preferably 10° or less, and more preferably 6° or less. However, when the plate thickness t exceeds 100 mm, the upper limit of the suitable range for the groove angle will exceed 10°, but in this case, the upper limit of the suitable range shall be 10°.

[0025] Bevel gap G: 20mm or less The smaller the groove of the steel material, the faster and more efficient the welding can be. Furthermore, welding with a groove gap exceeding 20 mm is difficult because the molten metal tends to drip. To address this, it is necessary to keep the welding current low, but this increases the likelihood of welding defects such as slag inclusion. Therefore, this discussion focuses on groove gaps of 20 mm or less. The groove gap is preferably 4 mm or more, and more preferably 12 mm or less. In particular, when joining by a single-layer weld consisting only of an initial weld, the groove gap is more preferably 25% or less of the plate thickness of the steel material to be welded, and even more preferably 20% or less.

[0026] Plate thickness t: 10mm or more The steel plate thickness should be 10 mm or more. If the steel plate thickness is less than 10 mm, a sound joint can sometimes be obtained while suppressing the heat input even when using conventional welding methods, such as semi-automatic CO2 arc welding with flux-cored wire. The plate thickness is preferably 15 mm or more, and more preferably 20 mm or more. In general, when dealing with rolled steel materials, the maximum plate thickness is generally 100 mm. Therefore, it is preferable that the maximum plate thickness of the steel materials covered here be 100 mm or less.

[0027] Furthermore, high-tensile steel is particularly suitable as the material to be welded (for example, extra-thick YP460MPa class steel for shipbuilding (tensile strength 570MPa class steel) or TMCP steel SA440 for construction (tensile strength 590MPa class steel)). High-tensile steel has strict limitations on welding heat input, is prone to cracking in the weld metal, and the required joint strength and toughness cannot be obtained due to the effects of welding heat. In contrast, this welding method makes it possible to weld efficiently by reducing the amount of heat input, and it is also possible to weld 590MPa class high-tensile steel plates and 590MPa class corrosion-resistant steel, which is a high-alloy type. This welding method can also be applied to mild steel without any problems.

[0028] The reasons for limiting the groove angle, groove gap, and steel plate thickness in this welding method have been explained above. In this welding method, it is preferable to use a welding wire that has a component composition that is compatible with the steel material to be welded. Furthermore, it is important to use a welding wire that contains REM. The following describes the component composition of the welding wire used in this welding method.

[0029] REM:0.015~0.100% by mass REM is an effective element for refining inclusions during steelmaking and casting, and for improving the toughness of weld metal. Furthermore, REM has the effect of further favorably suppressing arc generation on the groove surface, especially when the welding wire is positive polarity (wire negative) or when the welding current is high. This refinement of droplets and stabilization of droplet transfer suppresses spatter generation, enabling stable gas-shielded arc welding. In addition, the formation of REM oxides on the molten metal surface reduces the likelihood of weld metal sagging even when the angle of the welding torch tip relative to the horizontal is large. However, if the REM content is less than 0.015 mass%, this effect of droplet refinement and droplet transfer stabilization cannot be obtained. On the other hand, if the REM content exceeds 0.100 mass%, cracking may occur during the welding wire manufacturing process, or the toughness of the weld metal may decrease. Therefore, the REM content of welding wire should be in the range of 0.015 to 0.100 mass%. The REM content of the welding wire is preferably 0.025% by mass or more and 0.050% by mass or less.

[0030] The components of the REM mentioned above are not particularly limited and should be appropriately selected according to the type of steel to be welded. For example, when welding high-tensile steel plates as described above, in addition to the REM mentioned above, the component composition should include C: 0.10-0.20 mass%, Si: 0.05-2.5 mass%, Mn: 0.25-3.5 mass%, P: 0.05 mass% or less, S: 0.02 mass% or less, Al: 0.005-3.00 mass%, O: 0.008 mass% or less, and N: 0.008 mass% or less, with the remainder being Fe and unavoidable impurities.

[0031] Furthermore, the polarity of the welding wire used is preferably negative (positive polarity) from the viewpoint of fully obtaining the effects of droplet miniaturization and droplet transfer stabilization due to the inclusion of REM.

[0032] Furthermore, in this welding method, it is important to use a welding wire containing the aforementioned REM, and to efficiently weld while appropriately controlling the initial welding conditions with a heat input suitable for the groove shape, thereby obtaining the predetermined joint depth. The welding conditions and joint depth will be explained below.

[0033] Angle θ1 of the tip of the welding torch relative to the horizontal at the reference position: An angle greater than 45° relative to the horizontal. As shown in Figure 3, by using a welding torch equipped with a bent section and a tip defined by this bent section, and performing weaving while oscillating the tip of the welding torch toward the groove surface of the thick steel material, it becomes possible to bring the wire tip closer to the groove surface while avoiding contact between the power supply tip and the groove surface of the thick steel material. Furthermore, since the wire tip also faces the groove surface, direct melting of the groove surface by the arc becomes possible. Therefore, even when the welding heat input per pass is suppressed, the groove surface can be sufficiently melted and the occurrence of welding defects can be suppressed. In addition, by widening the arc heat input range due to the weaving of the welding torch, it is possible to suppress the dripping of molten metal and stabilize the bead shape. However, when θ1 is less than 45°, the welding current fluctuates significantly during the reciprocating motion caused by weaving, leading to unstable welding, poor shielding, and reduced low-temperature toughness of the weld metal. Therefore, θ1 should be set to an angle greater than 45°. On the other hand, when θ1 exceeds 90°, the weld metal tends to flow forward of the groove, and the angle of the bend becomes larger. Therefore, it is preferable that the suitable range for the angle θ1 of the tip of the welding torch relative to the horizontal direction be 90° or less.

[0034] The oscillation angle θ2 of the tip of the welding torch from the reference position is 5° to 60°. As described above, by using a welding torch equipped with a bent section and a tip defined by this bent section, and performing weaving while oscillating the tip of the welding torch toward the groove surface of the thick steel material, it becomes possible to bring the wire tip closer to the groove surface while avoiding contact between the power supply tip and the groove surface of the thick steel material. Furthermore, since the wire tip also faces the groove surface, direct melting of the groove surface by the arc becomes possible. Therefore, even when the welding heat input per pass is suppressed, the groove surface can be sufficiently melted to suppress the occurrence of welding defects. In addition, the widening of the arc heat input range due to the weaving of the welding torch can suppress dripping of molten metal and stabilize the bead shape. However, if θ2 is less than 5°, the above effects cannot be fully obtained, resulting in welding defects and dripping of molten metal. On the other hand, if θ2 exceeds 60°, the groove surface melts excessively, resulting in welding defects due to undercutting of the groove surface. For this reason, the oscillation angle θ2 of the tip of the welding torch from the reference position should be between 5° and 60°. Preferably, it should be 10° or more, and more preferably 45° or less.

[0035] While the bending angle θ3 at the bent portion of the welding torch and the length l of the tip of the welding torch are not particularly limited, from the viewpoint of controlling θ1 and θ2 within the above range, it is preferable to set θ3 to a range of 10 to 45° and l to a range of 10 to 50 mm.

[0036] Joint depth D in the first layer welding: 10 mm or more To weld thick steel materials, particularly those with a plate thickness of 40 mm or more, to a predetermined groove shape, the joint depth in the first layer of welding must be 10 mm or more. Furthermore, if the joint depth in the first layer of welding is less than 10 mm, welding heat will concentrate, causing molten metal to drip. Therefore, the joint depth in the first layer of welding should be 10 mm or more, preferably 25 mm or more. The upper limit of the joint depth in the first layer of welding is the same as the upper limit of the steel plate thickness, i.e., approximately 100 mm. However, when performing multi-layer welding, especially when the plate thickness of the steel material to be welded is 80 mm or more, if the joint depth in the first layer welding exceeds 70 mm, excessive heat input during welding is likely to occur, and welding defects such as hot cracking, poor fusion of the groove surface due to heat dispersion during welding, and slag inclusion may occur. Therefore, when performing multi-layer welding, the joint depth in the first layer welding is preferably 10 mm or more, more preferably 20 mm or more, and even more preferably 25 mm or more. Furthermore, the joint depth in the first layer welding is preferably 70 mm or less, more preferably 60 mm or less, and even more preferably 55 mm or less. In the case of single-layer welding, the joint depth D is more preferably 15 mm or more and 65 mm or less.

[0037] The basic conditions have been described above, but it is preferable to further satisfy the following conditions in the welding method of the present invention.

[0038] Welding torch weaving depth L in the plate thickness direction: 10mm to 70mm This welding method involves weaving the welding torch, and it is important to properly control the weaving depth L in the plate thickness direction and the maximum weaving width M in the direction perpendicular to the plate thickness and the weld line, which will be described later. Here, the weaving depth L in the thickness direction and the maximum weaving width M in the thickness direction and the direction perpendicular to the weld line for each weaving pattern are as shown in Figures 5(a) to (d). The weaving depth L and the maximum weaving width M in the plate thickness direction and the direction perpendicular to the weld line, as described later, are the weaving depth and maximum weaving width of the welding wire tip, calculated assuming that the tip of the welding torch is always at the reference position described above, without considering the oscillation of the welding torch tip. The weaving pattern, as described here, is the trajectory of the welding wire tip, assuming that the tip of the welding torch is always at the reference position described above, without considering the oscillation of the welding torch tip.

[0039] In vertical upward welding, which is the basis of this welding method, the joint depth and the weaving depth in the thickness direction of the plate are approximately the same. Therefore, if the weaving depth in the thickness direction of the plate is less than 10 mm, it becomes difficult to obtain the desired joint depth. On the other hand, if the weaving depth in the thickness direction of the plate exceeds 70 mm, not only does it become difficult to obtain the desired joint depth, but the amount of heat input for welding becomes excessive, making it difficult to obtain the desired mechanical properties in the heat-affected zone of the weld metal and steel material. In addition, welding defects such as hot cracking, poor fusion of the groove surface due to the dispersion of heat during welding, and slag inclusion are more likely to occur. Therefore, the weaving depth in the thickness direction of the plate is preferably 10 mm or more, more preferably 15 mm or more, preferably 70 mm or less, and more preferably 65 mm or less. In the case of single-layer welding, the weaving depth in the thickness direction of the plate is even more preferably 20 mm or more, and even more preferably 60 mm or less. In the case of multi-layer welding, the weaving depth in the thickness direction of the plate is even more preferably 25 mm or more, and even more preferably 55 mm or less.

[0040] The maximum weaving width M in the plate thickness direction and in the direction perpendicular to the weld line during welding torch weaving is (W-6) mm or more and W mm or less (W: weld bead width in the first layer of welding). To prevent unmelted areas on the groove surface, it is preferable to set the maximum weaving width in the direction of plate thickness and perpendicular to the weld line to (W-6) mm or more. On the other hand, if the maximum weaving width in the direction of plate thickness and perpendicular to the weld line exceeds W mm, molten metal dripping may occur, potentially making welding impossible. Therefore, the maximum weaving width in the plate thickness direction and in the direction perpendicular to the weld line is preferably in the range of (W-6) mm or more and W mm or less. More preferably it is (W-4) mm or more, and more preferably (W-1) mm or less. In the case of single-layer welding, W is the groove width on the steel surface that becomes the surface (the side facing the welding device (welding torch)) during welding.

[0041] Furthermore, the weaving pattern of the welding torch is not particularly limited and can be U-shaped, V-shaped, trapezoidal, or triangular when viewed from the direction of the welding line (which coincides with the welding direction and is usually vertical), as shown in Figures 5(a) to (d). For example, if the weaving pattern is U-shaped or trapezoidal, the weaving from point A to point B and point C to point D as shown in Figures 5(a) and (b) corresponds to weaving toward the groove surface of the thick steel material. In this case, during the weaving from point A to point B, the tip of the welding torch is swung toward the groove surface of the thick steel material on the left side of the paper, while during the weaving from point C to point D, the tip of the welding torch is swung toward the groove surface of the thick steel material on the right side of the paper. Note that during the weaving from point B to point C (including point D to point A in the case of a trapezoid), it is not necessary to swung the tip of the welding torch. In addition, in Figures 5(a) to (d), the trajectory of the welding torch at each point where the direction of the welding torch changes (points B and C in Figure 5(a)) may be angular or rounded.

[0042] However, in vertical upward welding, weaving close to the weld surface is prone to causing molten metal to drip. Also, if the welding torch movement deviates from the groove surface, uniform melting of the groove surface cannot be obtained, and welding defects such as poor fusion are likely to occur. In particular, while general trapezoidal and triangular weaving patterns that do not require reversal movements have a low load on the equipment, molten metal dripping is likely to occur due to welding torch movement close to the weld surface (point D to point A in the trapezoidal weaving pattern in Figure 5(b), and point C to point A in the triangular weaving pattern in Figure 5(d)). For this reason, from the viewpoint of suppressing molten metal dripping, it is preferable to use a U-shaped or V-shaped weaving pattern that does not involve torch movement on the weld surface side. Furthermore, with V-shaped or triangular weaving patterns, if the groove gap is large (for example, 6 mm or more), the welding torch movement may deviate from the groove surface (for example, in the movement from point A to point B in Figure 5(c), the trajectory of the welding torch tip may no longer be parallel to the groove surface (the side closer to the welding torch)), resulting in uneven melting of the groove surface and making welding defects such as poor fusion more likely. Therefore, in such cases, a U-shaped weaving pattern is optimal, as it makes it easier to operate the welding torch parallel to the groove surface.

[0043] Furthermore, the distance 'a' from the back surface of the steel material to the deepest point of the welding wire tip during weaving in the thickness direction (for example, points B and C in Figures 5(a) and (b), and point B in Figures 5(c) and (d)) is usually about 2 to 5 mm. Furthermore, when applying U-shaped weaving or trapezoidal weaving to the groove shapes described above, M1, M2, and M3 in Figures 5(a) and (b) will be approximately 2-18 mm, 0-10 mm, and 0-10 mm, respectively. Furthermore, the frequency and stopping time during weaving (the stopping time at each point, such as point A shown in Figure 5) are not particularly limited. For example, the frequency can be around 0.25 to 0.5 Hz (preferably 0.4 to 0.5 Hz), and the stopping time can be around 0 to 0.5 seconds (preferably 0.2 to 0.3 seconds).

[0044] While there is no need to specify conditions other than those mentioned above, if the average welding current is less than 270A, the molten pool will be small, and on the surface side, melting and solidification will be repeated with each torch weaving, resulting in a multi-layer welding-like state where fusion failure and slag inclusion are likely to occur. On the other hand, if the average welding current exceeds 360A, dripping of the molten (weld) metal is likely to occur, and it becomes difficult to confirm the arc point due to welding fumes and spatter, making adjustments during construction difficult. For this reason, it is preferable to set the average welding current to 270-360A. Furthermore, by setting the average welding current to 270-360A, stable penetration can be obtained while suppressing the generation of welding fumes and spatter, which is even more advantageous when implementing this welding method. Other than these conditions, standard methods should be followed. For example, welding voltage: 28-37V (increases with current), welding speed (upward): 1-15cm / min (preferably 4-9cm / min), wire protrusion length: 20-45mm, wire diameter: approximately 1.2-1.6mm. Furthermore, there are no particular limitations on the composition of the shielding gas; a gas consisting solely of CO2, or a mixture of Ar and CO2, may be used.

[0045] Furthermore, when performing multi-layer welding, it is preferable to limit the number of layers to approximately 2 to 4 layers from the viewpoint of preventing stacking defects. The welding conditions for each layer other than the first layer are not particularly limited and can be followed according to standard methods; for example, they can be the same as the welding conditions for the first layer described above. Furthermore, the welding method of the present invention is based on one pass of welding per layer. [Examples]

[0046] Two steel materials with the groove shapes shown in Table 1 were subjected to narrow-gap vertical upward gas shielded arc welding using a welding torch with a bent section on the power supply tip as shown in Figure 3 (θ3: 15°, l: 20 mm) under the welding conditions shown in Table 2. Here, all the steel materials used had a composition containing C: 0.04-0.06 mass%, Si: 0.1-0.2 mass%, Mn: 1.8-2.0 mass%, P: 0.01 mass% or less, S: 0.005 mass% or less, Al: 0.02-0.06 mass%, O: 0.003 mass% or less, and N: 0.005 mass% or less, with the remainder being Fe and unavoidable impurities. Gas cutting was used for beveling the steel materials, and no grinding or other treatment was performed on the bevel surface. Furthermore, the welding wire used was a 1.2 mmφ solid wire of a grade suitable for steel strength or one grade higher. The component composition of all welding wires other than REM shown in Table 2 contained C: 0.10~0.20 mass%, Si: 0.6~0.8 mass%, Mn: 1.8~2.0 mass%, P: 0.01 mass% or less, S: 0.005 mass% or less, Al: 0.005~0.03 mass%, O: 0.003 mass% or less, and N: 0.005 mass% or less, with the remainder being Fe and unavoidable impurities. Furthermore, the welding current was set to 260-330A, the welding voltage to 28-46V (increasing with the current), the average welding speed to 0.7-42.7cm / min (adjusted during welding), the average wire protrusion length to 30mm, and the welding length to 400mm. In all cases, CO2 alone was used as the shielding gas, and welding was performed using a separate gas shielding system from the nozzle used for normal arc welding.

[0047] For Nos. 8-15 and 17, multi-layer welding was used. In each layer except the first layer, welding was performed using gas shielded arc welding with weaving applied, with a welding current of 270-360A and a welding voltage of 28-37V. For Nos. 1-7 and 16, single-layer welding was used to finish the welded joints.

[0048] After the initial weld, the bead width and joint depth were measured at five arbitrarily selected points. For the bead width, the maximum value measured was defined as the bead width W in the initial weld, and for the joint depth, the minimum value measured was defined as the joint depth D in the initial weld.

[0049] Furthermore, the dripping of molten metal during the initial welding stage was visually evaluated as follows. ◎: No dripping of molten metal. ○: Less than 3 spots of molten metal dripping. ×: Three or more drips of molten metal, or interruption of welding.

[0050] Furthermore, ultrasonic testing was performed on the final welded joints, and they were evaluated as follows. ◎: No detection defects ○: Only acceptable defects with a defect length of 3 mm or less are detected. ×: Detects defects with a length exceeding 3 mm.

[0051] In addition, the final welded joints were subjected to Charpy impact tests in accordance with JIS Z 2242 (test temperature: -40°C) so that the center of the weld metal was at the notch position, and the absorbed energy vE-40(J) at the test temperature was measured. The low-temperature toughness of the weld metal was then evaluated according to the following criteria. ◎: vE-40(J) is 47J or higher ○: vE-40(J) is less than 47J and 27J or higher ×: vE-40(J) is less than 27J These results are listed in Table 2.

[0052] [Table 1]

[0053] [Table 2]

[0054] As shown in Table 2, in the inventive examples No. 1, 4-12, there was no molten metal dripping during the initial layer welding, or if there was, it was in two or fewer locations. Furthermore, no defects were detected in ultrasonic testing. Moreover, in all of these inventive examples, excellent low-temperature toughness was obtained in the weld metal. On the other hand, in comparative examples No. 13-17, where the groove gap was larger than 20 mm, molten metal dripping was observed in three or more places during the first layer welding, or welding could not be continued due to excessive molten metal dripping. Furthermore, in comparative examples No. 2 and 3, where the angle θ1 was not greater than 45°, ultrasonic testing detected defects with a defect length of more than 3 mm, indicating that sufficient low-temperature toughness of the molten metal could not be obtained. [Explanation of symbols]

[0055] 1:Thick steel material 2: Bevel surface of thick steel material 3: Beveling of the lower section of the steel material 4: Welding torch 5: Welding wire 6: Backing material 7: Main body 8: Power supply chip 9: Bending section 10:Tip 11: Weld bead

Claims

1. In a vertical narrow-groove gas-shielded arc welding method in which two thick steel plates with a thickness of 10 mm or more are joined by single-layer welding or multi-layer welding using weaving, with a groove angle of 20° or less and a groove gap of 20 mm or less, REM: Use a welding wire containing 0.015 to 0.100% by mass, The weaving of the first layer of welding is performed using a welding torch having a bent portion and a tip portion defined by the bent portion, and at that time, when weaving against the groove surface of the thick steel material, the tip portion of the welding torch is swung toward the groove surface of the thick steel material, and the position where the tip portion of the welding torch is aligned with the welding line direction when viewed from the thickness direction of the thick steel material is set as the reference position, the angle θ1 of the tip portion of the welding torch with respect to the horizontal direction at the reference position is set to an angle greater than 45°, and the swing angle θ2 of the tip portion of the welding torch from the reference position is set to be between 5° and 60°. The joint depth in the initial welding layer shall be 10 mm or more. Vertical narrow-gap gas shielded arc welding method.

2. The vertical narrow-groove gas shielded arc welding method according to claim 1, wherein the joining is performed as a single-layer weld and the groove gap is 25% or less of the plate thickness of the thick steel material.

3. The vertical narrow-gap gas shielded arc welding method according to claim 1, wherein the joining is multi-layer welding and the joining depth in the first layer welding is 10 mm or more and 70 mm or less.

4. The vertical narrow-gap gas shielded arc welding method according to any one of claims 1 to 3, wherein, in the weaving of the first layer welding, the weaving pattern of the welding torch as viewed from the direction of the welding line is U-shaped.

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