Hybrid welding method and method for manufacturing welded joint

Abstract

To make it possible to perform penetration welding with high efficiency and stably by utilization of a relatively low-cost and low-output laser in hybrid butt welding of a thick steel plate having a plate thickness of more than 16 mm by arc and laser.SOLUTION: When welding a butt part in such a manner that steel plates having a plate thickness of 16 mm or more are butted by use of a combination of arc welding and laser welding, a root face RF of a groove formed on the butt part is so made as to be 2 m or more and 10.5 m or less, a route gap RG is so made as to be less than 2 mm (including 0), and RF and RG satisfy the formula (RF≤4×RG+4.5), arc welding is firstly performed, laser welding is subsequently performed, and first pass welding is performed with laser output of 6 kW or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a welding method for welding thick plates by hybrid welding of arc welding and laser welding, and to a method for manufacturing a welded joint using the welding method. [Background technology]

[0002] 2. Description of the Related Art In recent years, as architectural structures, bridges, railway vehicles, and industrial machinery have become larger, the thickness of the steel plates used has been increased in order to satisfy the design stress of the structures. Multi-layer gas-shielded arc welding is mainly used for welding thick steel plates. Gas-shielded arc welding has low heat input, making it easy to ensure the mechanical properties of the base material and weld metal. However, as the plate thickness increases, the number of welding layers and passes increases, reducing the welding efficiency. In addition, it becomes difficult to stably perform full-fill welding in which the weld metal penetrates to the back surface of the steel plate without using a backing. For this reason, there is a demand for an efficient welding method that can shorten manufacturing time and reduce construction costs.

[0003] As one method to meet this demand, a method of highly efficient welding of thick plates using hybrid welding, which combines gas-shielded arc welding and laser welding, is being considered. For example, Patent Document 1 discloses a hybrid welding method that achieves excellent high-speed weldability and gap resistance by performing arc welding first and laser welding second, and welding while arranging the arc and laser on the same weld line.

[0004] Patent Document 2 discloses a hybrid welding method using arc and laser, in which a protrusion and a depression are continuously formed along the longitudinal direction of the groove on one side of a butt joint of steel plates having a thickness of 5 to 16 mm to be welded in one pool, the steel plates are positioned so that only the tip surface of the protrusion abuts the mating groove, and welding is performed with the laser light and welding wire aimed at a position on the intersection between a surface including a central region of the gap between the grooves formed by the depression and the end of the region where the protrusion and depression are formed on the side where the laser light is irradiated, thereby making it possible to easily secure a gap between the grooves.

[0005] Patent Document 3 discloses a hybrid welding method using arc and laser in which a steel plate 16 to 40 mm thick is assembled into a narrow groove shape such as an I-shape, V-shape, or Y-shape with a root gap of 2 to 7 mm and a groove angle of 0 degrees to 20 degrees, an arc welding torch is advanced, a laser irradiation point is placed behind it, the laser irradiation target position is P, the welding speed is V, and when the wire target position of the preceding gas shielded arc welding is set to the origin 0, P is set in the range of V to 4V in the direction opposite to the welding progress direction from the wire target position. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2006-224130 A [Patent Document 2] JP 2011-218362 A [Patent Document 3] JP 2017-154156 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a problem of how to weld thick steel plates, such as those having a thickness of 16 mm or more, with high efficiency and at the lowest possible cost. The techniques of Patent Documents 1 to 3 use hybrid welding to perform full penetration welding in which the butt joints of thick plates are completely penetrated from one side to the other side, but it is desirable to weld more efficiently and at lower costs.

[0008] Therefore, an object of the present invention is to provide a hybrid arc and laser butt welding method for thick steel plates having a thickness of 16 mm or more that enables highly efficient and stable full penetration welding using a relatively inexpensive low-power laser. [Means for solving the problem]

[0009] As a result of intensive research to solve the above technical problems, the inventors have discovered that by optimizing the root face of the groove formed at the butt joint of thick steel plates in accordance with the root gap, it is possible to stably perform full-penetration welding of the first layer even when using a low-power laser, and that once full-penetration welding of the first layer has been achieved, the remaining groove can be easily filled with weld metal by conventional arc welding. The gist of such the present invention is as follows.

[0010] (1) A hybrid welding method in which steel plates having a thickness of 16 mm or more are butted together and the butted portion is welded using a combination of arc welding and laser welding, The root face RF of the groove formed in the butted portion is 2 mm or more and 10.5 mm or less, the root gap RG is less than 2 mm (including 0), and the RF and RG satisfy the following formula, RF≦4×RG+4.5 A hybrid welding method characterized in that arc welding precedes laser welding, and the first layer is welded with a laser output of 6 kW or less.

[0011] (2) A method for manufacturing a welded joint, characterized in that steel plates having a thickness of 16 mm or more are butt-welded together and the hybrid welding method described in (1) above is used. Effect of the Invention

[0012] According to the present invention, the first layer welding of thick steel plate can be performed at a high welding speed of, for example, 0.8 m / min using a low-power laser, so that welded joints using thick steel plate with a plate thickness of more than 16 mm can be manufactured with significantly improved construction efficiency and construction costs. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram for explaining the hybrid welding method of the present invention. [Diagram 2] FIG. 2 is a diagram for explaining a cross section of a weld metal of a first layer formed by hybrid welding. [Diagram 3] FIG. 2 is a schematic diagram showing an example of a first layer weld metal formed by hybrid welding, in which the dimension of the root face in (b) is shorter than the dimension in (a). [Figure 4] FIG. 1 is a diagram showing the relationship between the root face and the root gap of a Y-shaped groove depending on whether the first layer welding is good or bad. [Diagram 5] FIG. 13 is a diagram for explaining the distance between the arc and the laser. [Figure 6] FIG. 2 is a diagram for explaining a root face RF and a root gap RG of a Y-shaped groove. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to a method for stably achieving full penetration welding without using a backing in the first layer welding from one side of a thick steel plate by using a hybrid welding method that combines arc welding and laser welding. Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] In hybrid arc and laser welding, which combines arc welding and laser welding, as shown in Figure 1, two steel plates 1, 1 are butted together, and a gas-shielded arc welding torch 3 is moved ahead of a groove 2 formed at the butt joint, and a laser welding torch 4 follows from behind, and the two are moved simultaneously in the direction of the arrows to weld the steel plates 1, 1 while forming a weld bead 6 in the groove.

[0016] During hybrid welding, the trailing laser is irradiated onto the molten pool 5 formed by the preceding arc welding, and the heat input from the laser is added to the heat input from the arc, forming a deeply penetrated weld metal 7 in which the root surface is welded through to the back side of the groove (the side opposite the torch), as shown in Figure 2.

[0017] The inventors have studied a means for stably performing deep penetration welding that penetrates to the back side of thick plates over 16 mm using hybrid welding that combines an arc with a low-power laser. They came up with the idea of ​​performing a first layer of welding in which the weld metal penetrates completely to the back side of the groove, and then performing welding in the remaining part of the groove, rather than performing welding in one layer. If the first layer can be fully welded, the remaining gap can be easily filled with weld metal by normal arc welding or laser-arc hybrid welding. The welding method for the first layer and the remaining gap does not have to be the same.

[0018] Therefore, the conditions under which a weld metal that penetrates to the back side of the groove can be formed in the first layer welding were examined, and the following experiment was conducted. Two steel plates with a thickness of 19 mm were prepared and butt-welded. The grooves formed between the steel plates were Y-shaped grooves with four different root face RF values ​​of 2.5mm, 4.5mm, 6.5mm, and 8.0mm, and five different root gap RG values ​​of 0mm, 0.3mm, 0.5mm, 1mm, and 1.5mm. Each was combined and temporarily assembled, and butt hybrid welding was performed, with arc welding preceded by laser irradiation. For the arc welding, a 1.2 mmφ solid wire, YM-28 (product name) manufactured by Nippon Steel & Sumikin Welding Co., Ltd., was used, and the shielding gas conditions were Ar+20% CO2 mixed gas with a flow rate of 25 L / min. A fiber laser was used for the laser welding. The distance AL between the target position of the arc and the laser irradiation point (see Fig. 5) is 2.5 mm, the angle θ between the welding torch (wire axis) and the optical axis of the laser (see Fig. 5) is 45 degrees, and the welding conditions are size The conditions in Table 1 were used depending on the As an example of full penetration welding, schematic diagrams of the cross section of the weld metal after welding for different RF are shown in Figure 3(a) and (b). In both cases, the weld metal penetrated to the back side of the groove on the root face, and a good back bead was formed.

[0019] [Table 1]

[0020] The welding results were evaluated by visually inspecting the condition of the back side of the weld. As shown in Figure 3, if the weld metal had completely penetrated to the back side of the groove (a defect-free back bead had been formed), it was marked with an O, and if it had not penetrated to the back side of the groove, it was marked with an X. Fig. 4 shows the relationship between the welding results and the combination of the root face RF and the root gap RG of the groove, with good results being obtained in the area to the right of the solid line.

[0021] As a result, it was found that when the RF and RG satisfy the following formula, full penetration welding of the first layer can be performed stably. RF≦4×RG+4.5

[0022] Furthermore, after examining the individual conditions of RF and RG, it was found that in welding the first layer of steel plate with a thickness of 16 mm or more, by making the groove a groove with a root surface such as a Y-shaped groove, making the RF and RG satisfy the above formula, and setting the RF to 2 mm or more and 10.5 mm or less, and the RG to less than 2 mm (including 0), it is possible to stably perform welding in which the weld metal completely penetrates to the back side of the groove.

[0023] By welding under the above conditions, the present invention makes it possible to obtain a first layer weld metal that penetrates to the back side of the groove with high efficiency by hybrid welding using a low-power laser in welding thick steel plates. Below, the necessary and preferable requirements for the present invention will be described in more detail.

[0024] (Basic form of hybrid welding) In the present invention, hybrid welding is performed by placing a welding torch 3 for gas shielded arc welding (hereinafter simply referred to as arc welding) in advance and a laser torch 4 behind it. By performing arc welding first, the laser beam is reliably irradiated onto the molten pool, allowing the laser to be used effectively.

[0025] The leading arc welding is preferably performed by a backward method inclined toward the welding direction (the direction of the arrow in Fig. 1) as shown in Fig. 1 and Fig. 4(a). The laser is irradiated toward the inside of the molten pool 5 formed by the arc welding from a direction inclined toward the opposite side to the welding direction. This allows the heat input from the laser to be added to the heat input from the arc, forming a deep weld metal that penetrates all the way to the back side of the groove.

[0026] The distance AL between the arc and the laser is not particularly limited as long as the heat input by the laser can be utilized, but if the distance AL is the distance between positions 10 and 11 in Fig. 5, it is preferable that the distance AL is in the range of 1 mm or more and less than 5 mm. Note that in a Y-shaped groove, a U-shaped groove, and a J-shaped groove, position 10 is the target position of the wire 8 for arc welding at the height of the upper end of the RF, and position 11 is the irradiation point position of the laser 9. The angle θ between the welding torch and the laser optical axis is not particularly limited, but is preferably between 20 and 60 degrees.

[0027] (Steel plate thickness) The thickness of the steel plate to be welded is 16 mm or more. Even if the thickness is less than 16 mm, and especially without using hybrid welding, welding can be performed with the same welding efficiency as the present invention. The upper limit of the plate thickness is preferably 80 mm or less, and more preferably 40 mm or less.

[0028] (Group shape) The shape of the groove is not important as long as it has a root surface. Examples include Y-shaped grooves, U-shaped grooves, and J-shaped grooves. For these grooves, the root surface shown by RF in Figure 6 must be 2 mm or more and 10.5 mm or less, and the root gap shown by RG must be less than 2 mm. In addition, RF (mm) and RG (mm) must satisfy the following formula. RF≦4×RG+4.5

[0029] If the root face is 10.5 mm or less, full penetration welding is possible even if the root gap RG is less than 2 mm and a low-power laser is used, regardless of the plate thickness. If the root face is more than 10.5 mm, full penetration welding using a low-power laser becomes difficult. Also, if the root face is less than 2 mm or the root gap is 2 mm or more, dripping is likely to occur and a good back bead cannot be formed. In addition, when the root face RF (mm) exceeds the upper limit calculated from the formula (4 × RG + 4.5) in relation to the root gap RG (mm), with a laser with an output of 6 kW or less, the weld metal will not reach the back side of the groove, and full penetration welding will not be possible.

[0030] The groove angle of a Y-shaped groove or a U-shaped groove is preferably 40 to 140 degrees, and more preferably 40 to 100 degrees. The groove angle of a J-shaped groove is preferably 20 to 70 degrees, and more preferably 20 to 50 degrees. With a preferred groove angle, the number of weld layers does not increase, and the welding efficiency is good.

[0031] (First layer welding) In the first layer welding by hybrid welding, the weld metal penetrates the root surface to the back side of the groove and a good back bead is formed. In order to perform such full penetration welding, the following conditions are set for each welding in hybrid welding.

[0032] Conditions for arc welding, such as current, voltage, welding speed, and heat input, can be appropriately determined according to the thickness of the steel plate, the shape of the groove, etc. There are no particular limitations on the shielding gas, but in consideration of arc stability and cost, it is preferable to use a mixed gas consisting of Ar gas and 5 to 30% CO2 gas. In addition, the laser is limited to a low-power laser with an output of 6 kW or less. Such a laser is preferably a YAG laser, a disk laser, or a fiber laser. A shielding gas for the laser is not particularly necessary because the irradiation point is close to the target position of the arc, but in order to further strengthen the shielding, a mixed gas consisting of Ar gas and 5 to 30% CO2 gas can be used. Also, O2 gas and He gas may be added as necessary.

[0033] The thickness of the first layer formed by hybrid welding in the plate thickness direction is preferably large from the viewpoint of welding efficiency, but if it is too thick, it becomes more susceptible to solidification cracking, so the lower limit is preferably the root face RF + 1.0 mm, and the upper limit is preferably RF + 6.0 mm. In addition, in the present invention, the welding speed of hybrid welding can be set to a high speed of 0.8 mm / min or more.

[0034] (welding from the second layer onwards) In the present invention, the first layer is welded by the hybrid welding described above, and the remaining inside of the groove can also be welded by laser arc hybrid welding in the same way. However, since the first layer has been fully welded, it can also be easily welded by gas shielded arc welding. For each welding step, it is desirable to employ a welding method that is as efficient as possible. EXAMPLES

[0035] Hybrid welding was performed under the conditions shown below, and the state of bead formation after welding was investigated and evaluated as described above. The steel plates used were WEL-TEN (registered trademark) 590 manufactured by Nippon Steel & Sumitomo Metal Corporation with a thickness of 19 mm. These steel plates were butt-jointed and temporarily assembled, and the first layer was welded using hybrid welding, which combines preceding gas-shielded arc welding and subsequent laser welding.

[0036] The butt joint was a Y-shaped groove with a groove angle of 60 degrees, and the root face (RF) and root gap (RG) shown in Table 2. For arc welding, the current was 240-270A, the voltage was 22-26V, and the shielding gas composition was Ar+20%CO2. For laser welding, the laser medium was fiber laser, the laser output was 4.4-4.6kW, the welding speed was 1.1-1.8m / min, the distance between the arc and the laser AL was 2.5mm, and the angle θ between the optical axis of the welding torch and the laser was 45 degrees, and hybrid welding of the root surface was performed. After welding, the specimens were cut perpendicular to the welding direction, and the cross sections were mirror-polished and etched with nital to reveal the structure. The cross sections were then observed to evaluate the quality of weld metal penetration on the back side and the presence or absence of weld backside cracks. Cases where weld metal had penetrated well to the back side and there were no weld backside cracks were marked with an ◯, and all other cases were marked with an ×. The evaluation results are also shown in Table 2.

[0037] [Table 2] [Explanation of symbols]

[0038] 1 steel plate 2 Bevel 3 Gas shielded arc welding torch 4 Laser welding torch 5. Molten Pool 6 Weld Bead 7 Welding metal 8 Welding Wire 9. Laser 10. Aim position of welding wire 11 Laser irradiation point RF groove root face RG Groove Root Gap

Claims

1. A hybrid welding method in which steel plates having a thickness of 16 mm or more are butted together and the butted portion is welded using both arc welding and laser welding, The root face RF of the groove formed in the butted portion is 2 mm or more and 10.5 mm or less, the root gap RG is less than 2 mm (including 0), and the RF and RG satisfy the following formula (excluding the case where RF is 6 mm and RG is 0.8 mm), RF≦4×RG+4.5 A hybrid welding method, characterized in that arc welding is performed first, laser welding is performed second, the laser output is set to 4.6 kW or less, the laser is irradiated to a molten pool formed by the arc welding, and a first layer of welding is performed in which the weld metal penetrates to the back side of the groove.

2. A method for manufacturing a welded joint, comprising butting together steel plates having a thickness of 16 mm or more and using the hybrid welding method according to claim 1.

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