Multi-electrode one-sided submerged arc welding method

Abstract

To provide a multielectrode one-side surface submerged-arc welding method in which slug-inclusion and high-temperature crack hardly occur and stability in height of a back bead is excellent, even in a thick plate.SOLUTION: In a multielectrode one-side surface submerged-arc welding method, one-side surfaces of two steel plates 20 butted to each other are welded to each other, using a plurality of electrodes 15. The electrode 15 includes at least three electrodes 15 of a first electrode 15a, a second electrode 15b and a third electrode 15c. The first electrode 15a is arranged at the front in a welding direction X, and then the second electrode 15b and the third electrode 15c are arranged in this order. Welding is performed under the condition that a polarity of the first electrode 15a is AC, a polarity of the second electrode 15b is AC, a phase difference in AC between the first electrode 15a and the second electrode 15b is 0°-90°or 275°-360°, and an in-electrode distance L2 between the second electrode 15b and the third electrode 15c is 210 mm-320 mm.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a multi-electrode single-sided submerged arc welding method. [Background technology]

[0002] Multi-electrode one-sided submerged arc welding is a highly efficient welding method that is used in a wide range of fields, primarily in shipbuilding, as plate welding. Various welding methods have been disclosed for this type of highly efficient multi-electrode one-sided submerged arc welding.

[0003] Generally, as steel plates become thicker, it becomes more difficult to stabilize the back bead height and the back bead tends to become pear-shaped, which makes it more susceptible to slag inclusion and hot cracking. In response to this, for example, Patent Document 1 discloses a multi-electrode single-sided single-layer submerged arc welding method characterized in that welding is performed under the following conditions: polarity of the first electrode: DC, electrode side negative, inter-electrode distance between the first and second electrodes: 80 mm or more and 160 mm or less, inter-electrode distance between the second and third electrodes: 80 mm or more and 160 mm or less, arc voltage of the first electrode: 25 to 40 V, welding current of the second electrode: 800 to 1400 A. This makes it possible to suppress hot cracking even in thick plates.

[0004] Patent Document 2 discloses a multi-electrode single-sided submerged arc welding method characterized in that the speed control method of the leading electrode, i.e., the wire feed speed, is set to constant speed control, and the power supply method of the trailing electrode is set to AC and the external characteristics are set to constant voltage characteristics, for example. This makes it possible to reduce appearance defects of the back bead. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-193444 A [Patent Document 2] JP 2015-150571 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the welding method described in Patent Document 1 is susceptible to the effects of magnetic blow because it uses direct current as the welding current for the first electrode. This magnetic blow may affect the back bead height, leaving room for improvement. In addition, the welding method described in Patent Document 2 leaves room for improvement in terms of preventing slag inclusion and hot cracking when welding thick plates.

[0007] The present invention has been made in consideration of the above, and an object of the present invention is to provide a multi-electrode one-sided submerged arc welding method in which slag inclusion and hot cracking are less likely to occur, even in thick plates, and in which the back bead height is stable. [Means for solving the problem]

[0008] In response to the above-mentioned problems, the multi-electrode single-sided submerged arc welding method according to the present embodiment uses a plurality of electrodes to join one side of two butted steel plates, the electrodes including at least three electrodes: a first electrode, a second electrode, and a third electrode, the first electrode being arranged at the front in the welding direction, followed by the second electrode and the third electrode in that order, and welding is performed under the following conditions: polarity of the first electrode: AC, polarity of the second electrode: AC, phase difference between the AC of the first electrode and the second electrode: 0° to 90° or 275° to 360°, and inter-electrode distance between the second electrode and the third electrode: 210 mm to 320 mm.

[0009] In this way, by making the polarity of the first and second electrodes AC and setting the phase difference between them within a specific range, the penetration shape is stabilized. Furthermore, by setting the inter-electrode distance between the second and third electrodes within a specific range, the influence of the third and subsequent electrodes on the back bead height can be reduced. As a result, slag inclusion and hot cracking are less likely to occur, and the back bead height can be stabilized.

[0010] In the above method, the wire diameter of the first electrode is preferably 3.2 mm to 6.4 mm.

[0011] This achieves more stable penetration and more stable back bead height. In addition, this welding method can ensure a sufficient penetration width at the root, making it more difficult for hot cracks to occur even when welding thick plates, i.e., thick steel plates.

[0012] In the above method, it is also preferable that the second electrode has a wire diameter of 4.0 mm to 6.4 mm, and the third electrode has a wire diameter of 4.0 mm to 6.4 mm.

[0013] This allows for more stable penetration and a more stable back bead height. In addition, this welding method ensures a sufficient penetration width at the root, making it more difficult for hot cracks to occur even when welding thick plates.

[0014] In the above method, it is also preferable that the inter-electrode distance between the first electrode and the second electrode is 25 mm or more and less than 80 mm.

[0015] This allows for more stable penetration and a more stable back bead height. In addition, this welding method ensures a sufficient penetration width at the root, making it more difficult for hot cracks to occur even when welding thick plates.

[0016] In the above method, it is also preferable that the power supply characteristic of the first electrode is a constant voltage.

[0017] This stabilizes the position at which the arc occurs, making the back bead height more stable.

[0018] In the above method, it is also preferable to use a flux backing method.

[0019] The flux backing method tends to be more difficult to stabilize the back bead height than the flux copper backing method. However, since the welding method according to the present embodiment has excellent stability of the back bead height, the back bead height can be stabilized even when the flux backing method is used. Effect of the Invention

[0020] By welding using the multiple-electrode one-sided submerged arc welding method of the present invention, it is possible to easily stabilize the back bead height even in thick plates, and to make it more difficult for slag inclusion and hot cracking to occur. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram for explaining a welding device used in a multi-electrode one-sided submerged arc welding method according to this embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing, from an information perspective, steel plates to be welded by the multi-electrode one-sided submerged arc welding method according to the present embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view of the periphery of a steel plate, showing a state in which multi-electrode one-sided submerged arc welding is performed by the flux copper backing method. [Figure 4] FIG. 4 is a schematic cross-sectional view of the periphery of a steel plate, showing a state in which multi-electrode one-sided submerged arc welding is performed by the flux backing method. [Diagram 5] FIG. 5 is a schematic diagram for explaining the inter-electrode distance and the like in the multi-electrode single-sided submerged arc welding method according to this embodiment. [Figure 6] FIG. 6 is a schematic diagram of the steel plate and its periphery for explaining hot cracking resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, the embodiment for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be carried out with any modification within the scope of the gist of the present invention. Furthermore, the use of "~" to indicate a range of numerical values ​​means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0023] <Welding equipment> In the multi-electrode one-sided submerged arc welding method according to this embodiment (hereinafter sometimes simply referred to as the "welding method"), for example, a welding device as shown in FIG. 1 is used, but the welding method is not limited to such a welding device. When the flux copper backing method is used, a backing device 50a as shown in Fig. 3 is placed on the stand frame 11. Backing flux 52 is spread on a backing copper plate 55 of the backing device 50a. The backing flux 52 is in contact with the bottom surface of the steel plate 20 placed on a stand (not shown). When the flux backing method is used, a backing device 50b as shown in Fig. 4 is placed on the stand frame 11. Inside the fireproof canvas 56 of the backing device 50b, underlay flux 58 is filled on a heat-resistant cover 57, and backing flux 52 is spread on top of it. The backing flux 52 is in contact with the bottom surface of the steel plate 20 placed on a stand (not shown).

[0024] The welder beam 13 moves the welder 12 along the longitudinal direction of the steel plate 20 . The welding machine 12 is disposed above the frame 11, i.e., above the steel plate 20. As shown in Fig. 2, the welding machine 12 welds the steel plate 20 from the front side of the welding groove M of the steel plate 20. The welding machine 12 is equipped with a plurality of welding torches including a plurality of electrodes 15.

[0025] The welding machine 12 moves along the welding beam 13 at a predetermined speed in the direction of the arrow in FIG. 1, while welding the steel plates 20 from the front side of the welding groove M in FIG. 2 by one-sided submerged arc welding with the electrode 15.

[0026] In the multi-electrode one-sided submerged arc welding method according to this embodiment, as shown in Figures 3 and 4, submerged arc welding is performed from the front side of a steel sheet 20 using front flux 51, and beads are simultaneously formed on the front and back sides of the steel sheet 20. In Figures 3 and 4, reference numeral 53 denotes slag, reference numeral 54 denotes weld metal, reference numeral 57 denotes a heat-resistant cover, and reference numeral 58 denotes an underlay flux.

[0027] Here, the flux copper backing method is one of the welding methods. As shown in Fig. 3, the flux copper backing method is a welding method in which backing flux 52 is spread on a backing copper plate 55, and the backing copper plate 55 is pressed from the back side of the backing copper plate 55 by a push-up mechanism, so that the backing flux 52 is adhered to the back side of the butted steel plates 20. It is preferable to spread the backing flux 52 in a layer. Also, an example of the push-up mechanism is air pressure using an air hose 59. By the above method, welding can be performed in one pass.

[0028] Another welding method is the flux backing method. As shown in Fig. 4, the flux backing method is a welding method in which a backing flux 52 contained in a fire-resistant canvas 56 is pressed by a push-up mechanism to adhere the backing flux 52 to the back surface of the butted steel plates 20. It is preferable that an underlay flux 58 is filled on a heat-resistant cover 57 in the fire-resistant canvas 56, and the backing flux 52 is scattered on top of the underlay flux 58. The above method also allows welding in one pass.

[0029] The flux backing method has an advantage that welding can be performed even when there is a difference in plate thickness or unevenness in the steel plate 20. On the other hand, compared to the flux copper backing method, it tends to be difficult to stabilize the back bead height. In contrast, by using the welding method according to this embodiment, it is possible to stabilize the back bead height even when using the flux backing method. In this way, by using the present invention together with the flux backing method, it is possible to stabilize the back bead height, which has been a problem in the past, while taking advantage of the advantages of the flux backing method. Therefore, it is preferable that the welding method according to this embodiment uses the flux backing method.

[0030] <Welding conditions> The welding method according to the present embodiment uses a welding machine which is, for example, the apparatus described above in <Welding Apparatus> and includes at least three electrodes 15 arranged in the order of a first electrode 15a, a second electrode 15b, and a third electrode 15c from the front in a welding proceeding direction X as shown in FIG. 5 . The polarity of first electrode 15a and second electrode 15b is alternating current, the phase difference therebetween is 0° to 90° or 275° to 360°, and the inter-electrode distance L2 between second electrode 15b and third electrode 15c is 210 mm to 320 mm.

[0031] (1st electrode 15a) In this embodiment, the polarity of the first electrode 15a is AC. This makes it possible to suppress the occurrence of magnetic arc blow, and therefore the back bead height is stable. On the other hand, if the polarity of the first electrode 15a is DC, magnetic arc blow is likely to occur, and the back bead height becomes unstable due to the deflection of the arc.

[0032] It is preferable that the power supply characteristics of the first electrode 15a be a constant voltage, since this stabilizes the position at which the arc is generated and therefore stabilizes the back bead height.

[0033] The arc voltage of the first electrode 15a is preferably, for example, 30 to 45 V. By setting it in this range, the arc voltage of the first electrode is not too high, and the voltage value is in an appropriate range, so that the back bead height is more stable. In addition, since the penetration width of the root can be sufficiently secured, hot cracks can be made less likely to occur even when welding thick plates. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of hot cracks, the arc voltage of the first electrode 15a is more preferably 32 V or more, and even more preferably 34 V or more. From the same viewpoint, the arc voltage of the first electrode 15a is more preferably 42 V or less, and even more preferably 40 V or less. The above is merely an example of a preferred range of values, and is not limited thereto. In other words, the arc voltage of the first electrode 15a may be set to, for example, 28 V or 48 V. Even if the arc voltage is outside the above range of values, the back bead height can be sufficiently stabilized, and high-temperature cracking can be sufficiently prevented.

[0034] The welding current of the first electrode 15a is preferably, for example, 800 to 1600 A. By setting it in this range, the welding current of the first electrode 15a is not too high, and the current value is in an appropriate range, so that the back bead height is more stable. In addition, since the penetration width of the root can be sufficiently secured, hot cracking can be made less likely to occur even when welding thick plates. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of hot cracking, the welding current of the first electrode 15a is more preferably 900 A or more, and more preferably 1000 A or more. From the same viewpoint, the welding current of the first electrode 15a is more preferably 1550 A or less, and more preferably 1400 A or less. The above is merely an example of a preferred numerical range, and is not limited thereto. That is, the welding current of the first electrode 15a may be, for example, 850 A or 1650 A. Even if the welding current is outside the above numerical range, the back bead height can be sufficiently stabilized, and hot cracking can be sufficiently prevented.

[0035] 5, the sweepback angle θ1 of the first electrode 15a is expressed as the angle between the center line of the first electrode 15a and a plane having a normal line in the welding direction X. Note that the angle perpendicular to the welding direction X is defined as 0°, and the side of the welding direction X is defined as positive. The sweepback angle θ1 of the first electrode 15a is preferably 1° or more and 15° or less, from the viewpoint of easily obtaining penetration and stably obtaining a back bead height.

[0036] The wire diameter of the first electrode 15a is preferably 3.2 mm to 6.4 mm. By setting the diameter in this range, the back bead width can be sufficiently secured, and the back bead height is stable. In addition, the penetration width of the root can be sufficiently secured, and therefore, slag inclusion and hot cracking can be prevented. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of slag inclusion, the wire diameter of the first electrode 15a is more preferably 4.0 mm or more, and more preferably 4.8 mm or less. Moreover, the wire 16a of the first electrode 15a is preferably a solid wire, since this has a deep penetration and good moisture absorption resistance.

[0037] Submerged arc welding mainly uses solid wires, whose wire diameter is limited to a specific nominal diameter, and the actual diameter is generally interpreted broadly to include a margin of error. Here, the nominal diameters of solid wires for submerged arc welding in JIS Z 3200:2005 are 3.2 mm, 4.0 mm, 4.8 mm, and 6.4 mm, with a tolerance of ±0.06 mm.

[0038] Therefore, the wire diameters specified in this embodiment also include an error of ±0.06 mm as the actual diameter. That is, for example, a wire diameter of 3.2 mm means "3.2 mm ±0.06 mm" as the actual diameter, a wire diameter of 4.0 mm means "4.0 mm ±0.06 mm" as the actual diameter, a wire diameter of 4.8 mm means "4.8 mm ±0.06 mm" as the actual diameter, and a wire diameter of 6.4 mm means "6.4 mm ±0.06 mm" as the actual diameter.

[0039] (Second electrode 15b) In this embodiment, the polarity of the second electrode 15b is AC. This makes it possible to suppress the occurrence of magnetic arc blow, and therefore the back bead height is stable. On the other hand, if the polarity of the second electrode 15b is DC, magnetic arc blow is likely to occur, and the back bead height becomes unstable due to the deflection of the arc.

[0040] The power supply characteristics of the second electrode 15b are preferably, for example, constant current or drooping, which stabilizes the welding current and therefore the penetration, making it more difficult for hot cracks to occur. It should be noted that the above is merely a preferred example and the present invention is not limited to this.

[0041] The arc voltage of the second electrode 15b is preferably, for example, 28 to 43 V. By setting it in this range, the voltage of the second electrode is not too high, and the voltage value of the arc voltage is in an appropriate range, so that the back bead height is more stable. In addition, since the penetration width of the root can be sufficiently secured, hot cracks can be made less likely to occur even when welding thick plates. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of hot cracks, the arc voltage of the second electrode 15b is more preferably equal to or higher than 30 V, and more preferably equal to or higher than 32 V. From the same viewpoint, the arc voltage of the second electrode is more preferably equal to or lower than 40 V, and more preferably equal to or lower than 38 V. The above is merely an example of a preferred range of values, and is not limited thereto. In other words, the arc voltage of the second electrode 15b may be set to, for example, 26 V or 45 V. Even if the arc voltage is outside the above range of values, the back bead height can be sufficiently stabilized, and high-temperature cracking can be sufficiently prevented.

[0042] The welding current of the second electrode 15b is preferably, for example, 600 to 1300 A. By setting it in this range, the current of the second electrode 15b is not too high, and the current value of the welding current is in an appropriate range, so that the back bead height is more stable. In addition, since the penetration width of the root can be sufficiently secured, hot cracks are less likely to occur even when welding thick plates. From the viewpoint of further stabilizing the back bead height and preventing hot cracking, the welding current of the second electrode 15b is more preferably 700 A or more. From the same viewpoint, the welding current of the second electrode 15b is more preferably 1200 A or less, and further preferably 1100 A or less. The above numerical ranges are merely examples of preferred numerical ranges, and are not limited thereto. That is, the welding current of the second electrode 15b may be, for example, 550 A or 1400 A. Even with a welding current outside the above numerical ranges, the back bead height can be sufficiently stabilized, and hot cracking can be sufficiently prevented.

[0043] As shown in FIG. 5, the sweepback angle θ2 of the second electrode 15b is expressed as the angle between the center line of the second electrode 15b and a plane having the welding proceeding direction X as its normal line. The sweepback angle θ2 of the second electrode 15b is preferably 1° or more and 15° or less. By setting the sweepback angle θ2 within this range, the molten pool formed by the second electrode 15b is less likely to be swept away in the welding proceeding direction X. As a result, the state of the molten pool formed by the first electrode 15a is not disturbed, and the back bead height can be stabilized.

[0044] The wire diameter of the second electrode 15b is preferably 4.0 mm to 6.4 mm in diameter. By setting the diameter in this range, a sufficient penetration width of the root can be ensured, and slag inclusion and hot cracking can be made less likely to occur. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of slag inclusion, the wire diameter of the second electrode 15b is more preferably 4.8 mm or more.

[0045] (3rd electrode 15c) In this embodiment, the polarity of the third electrode 15c can be either DC or AC, and in the case of DC, either DCEP, which is a DC rod positive, or DCEN, which is a DC rod negative, can be used. Among them, AC is preferred from the viewpoints of increasing the yield of the chemical components of the wire in the weld metal, making the yield of the chemical components of the weld metal more stable, and improving the mechanical properties.

[0046] The power supply characteristics of the third electrode 15c are preferably, for example, constant current or drooping characteristics, which stabilizes the welding current and therefore the penetration, making it more difficult for hot cracks to occur. The above is merely a preferred example, and is not intended to be limiting. In other words, the power supply characteristics of the third electrode 15c may be constant voltage. Even with a constant voltage, the penetration is sufficiently stable and high-temperature cracking is sufficiently unlikely to occur.

[0047] The range of the arc voltage of the third electrode 15c is not particularly limited, and welding can be performed by appropriately setting it to a conventionally known general condition. For example, the arc voltage of the third electrode 15c is 40V to 48V. However, this is merely an example of a preferable numerical range, and the present invention is not limited to this.

[0048] The range of the welding current of the third electrode 15c is not particularly limited, and welding can be performed by appropriately setting it to a conventionally known general condition. For example, the welding current of the third electrode 15c is 700 A to 1500 A. However, this is merely an example of a preferable numerical range, and the welding current is not limited to this. Moreover, by increasing the welding current of the third electrode 15c in accordance with the distance between the second electrode 15b and the third electrode 15c being set to 210 mm or more, slag inclusion can be prevented. From the viewpoint of preventing such slag inclusion, the welding current of the third electrode 15c is preferably 800 A or more, and more preferably 900 A or more.

[0049] 5, the advance angle θ3 of the third electrode 15c is expressed as the angle between the center line of the third electrode 15c and a plane having a normal line in the welding direction X. In the case of the advance angle, the side opposite to the welding direction X is considered to be positive. The advance angle θ3 of the third electrode 15c is preferably 1° or more and 15° or less. By setting the advance angle θ3 within this range, the arc of the third electrode 15c is inclined toward the welding proceeding direction X, and the slag formed by the first electrode 15a and the second electrode 15b is melted by the arc heat of the third electrode 15c, so that the wire does not collide with the slag, and the arc is stabilized.

[0050] The wire diameter of the third electrode 15c is preferably 4.0 mm to 6.4 mm in diameter. By setting the diameter in this range, a sufficient penetration width of the root portion can be ensured, and slag inclusion and hot cracking can be made less likely to occur. From the viewpoint of further stabilizing the back bead height and preventing the occurrence of slag inclusion, the wire diameter of the third electrode 15c is more preferably 4.8 mm or more.

[0051] (4th electrode 15d onwards) The electrodes 15 in the welding method according to this embodiment may include at least three electrodes, which are the first electrode 15a to the third electrode 15c, in this order from the front in the welding proceeding direction X, and any number of electrodes greater than this may be used. For example, as shown in Fig. 5, the electrodes 15 of the welding machine 12 include three electrodes, a first electrode 15a, a second electrode 15b, and a third electrode 15c, arranged in this order from the front of the welding direction X indicated by the arrow in the figure. Each electrode 15 is arranged along the welding line direction. If necessary, the electrodes 15 may further include four electrodes including a fourth electrode 15d indicated by a dashed line in Fig. 5.

[0052] By providing the fourth electrode 15d, the pool (molten pool) can be further increased. Meanwhile, since the effects of the present invention are achieved as long as the first electrode 15a, the second electrode 15b, and the third electrode 15c satisfy the above-mentioned conditions, the number of electrodes 15 can be set to three or four as desired. Moreover, the number of electrodes 15 is not limited to four, and may be five or more as desired.

[0053] The power supply characteristics of the fourth electrode 15d or the subsequent electrodes are preferably set to, for example, a constant current or drooping characteristic, which stabilizes the welding current and therefore the penetration, making it more difficult for hot cracks to occur. The above is merely a preferred example, and is not intended to be limiting. In other words, the power supply characteristics of the fourth electrode 15d and the subsequent electrodes may be constant voltage. Even at a constant voltage, the penetration is sufficiently stable and high-temperature cracking is sufficiently unlikely to occur.

[0054] The ranges of the arc voltage and welding current of the fourth electrode 15d and the subsequent electrodes are not particularly limited, and welding can be performed by appropriately setting the conventionally known general conditions. For example, general conditions for the fourth electrode include an arc voltage of 40 V to 50 V and a welding current of 700 A to 1500 A. However, these are merely examples of preferred numerical ranges and are not limited to these.

[0055] The wire diameter of the fourth electrode 15d is preferably 4.0 mm to 6.8 mm in diameter. By setting the diameter in this range, a sufficient penetration width of the root portion can be ensured, and slag inclusion and hot cracking can be made less likely to occur.

[0056] Thus, for the fourth electrode 15d and the subsequent electrodes, there are no particular limitations or preferred ranges for the wire diameter, arc voltage, welding current, polarity, etc., and welding can be performed under general conditions. These general conditions can be set, for example, as follows: wire diameter: diameter 4.0 mm to 6.8 mm, arc voltage: 40 V to 50 V, welding current: 700 A to 1500 A. Other conditions can be set as follows: wire diameter: diameter 6.4 mm, arc voltage: 46 V, welding current: 1300 A, polarity: AC or DC, etc.

[0057] (First electrode 15a and second electrode 15b) The phase difference of the AC between the first electrode 15a and the second electrode 15b is set to 0° to 90° or 275° to 360°. Note that 360° and 0° are the same. By setting the phase difference between the first electrode 15a and the second electrode 15b within the above range, the weld metal generated by the third electrode 15c and subsequent electrodes can penetrate deeply into the weld metal formed by welding using the first electrode 15a and the second electrode 15b, making it difficult for slag inclusion and hot cracking to occur. This penetration depth is thought to be due to the effect of the smooth surfaces of the weld metal and slag formed by welding using the first electrode 15a and the second electrode 15b. If the phase difference between the first electrode 15a and the second electrode 15b is more than 90° and less than 275°, the slag inclusion resistance and hot cracking resistance are deteriorated.

[0058] When the phase difference of the AC between first electrode 15a and second electrode 15b is within the range of 0° to 90°, the phase difference is preferably 80° or less, more preferably 70° or less, and even more preferably 60° or less. When the phase difference of the AC between first electrode 15a and second electrode 15b is within the range of 275° to 360°, the phase difference is preferably 280° or more, more preferably 290° or more, and even more preferably 300° or more.

[0059] The inter-electrode distance between the first electrode 15a and the second electrode 15b is the distance indicated by L1 in Fig. 5. The inter-electrode distance L1 is the distance between a point where the tip of the wire 16a protruding from the first electrode 15a contacts the steel sheet 20 when it is extended as shown by the dashed line in Fig. 5, and a point where the tip of the wire 16b protruding from the second electrode 15b contacts the steel sheet 20 when it is extended as shown by the dashed line in Fig. 5, in the arrangement of the electrodes 15 during welding.

[0060] Similarly, the inter-electrode distance L2 between the second electrode 15b and the third electrode 15c means the distance between the points where the tips of the wires 16b and 16c protruding from the second electrode 15b and the third electrode 15c, respectively, are extended and come into contact with the steel plate 20.

[0061] The interelectrode distance L1 between the first electrode 15a and the second electrode 15b is preferably, for example, 25 mm or more and less than 80 mm. By setting it in this range, the molten pool formed by the first electrode 15a and the second electrode 15b becomes one pool or semi-one pool, which inhibits the dendrites in the root from growing horizontally, making it more difficult for hot cracks to occur. From the viewpoint of further stabilizing the back bead height, the inter-electrode distance L1 is more preferably 30 mm or more, and even more preferably 45 mm or more, and from the same viewpoint, the inter-electrode distance L1 is more preferably 70 mm or less, and even more preferably 60 mm or less.

[0062] The ratio V1 / V2 of the arc voltage (V1) of the first electrode 15a to the arc voltage (V2) of the second electrode 15b is preferably 1.01 or more. This lowers the position of the arc generation point of the second electrode 15b, thereby obtaining a penetration width at the root and suppressing the occurrence of slag inclusion and incomplete fusion. The ratio represented by V1 / V2 is more preferably 1.03 or more, and further preferably 1.05 or more. The upper limit of the ratio represented by V1 / V2 is not particularly limited, but is practically 1.5 or less, and preferably 1.3 or less.

[0063] In the present embodiment, the protruding lengths A1 to A3 of the wires 16a to 16c of the first to third electrodes 15a to 15c are not particularly limited and can be set within a general range. In the case where the electrode 15 includes a fourth electrode 15d and subsequent electrodes, the same applies to the protruding length A4 of the wire 16d of the fourth electrode 15d and the protruding lengths of the wires of the subsequent electrodes. However, it is preferable that at least one of the first electrode 15a and the second electrode 15b has a wire protruding length A1, A2 of 20 mm or more. By making the wire protruding length A1, A2 20 mm or more, the wire is less likely to fuse to the tip. It is more preferable that the wire protruding length A1, A2 is 25 mm or more. Also, it is preferable that at least one of the first electrode 15a and the second electrode 15b has a wire protruding length A1, A2 of 40 mm or less. By making the wire protruding length A1, A2 40 mm or less, the wire target position is less likely to shift, and the penetration and back bead height are stabilized.

[0064] (Second electrode 15b and third electrode 15c) The inter-electrode distance L2 between the second electrode 15b and the third electrode 15c is 210 mm to 320 mm. By setting it in this range, the distance between the second electrode 15b and the third electrode 15c is appropriate, so that cooling after welding by the second electrode becomes appropriate. Specifically, welding by the third electrode 15c can be performed after the pool formed by welding by the second electrode 15b is cooled. Therefore, a back bead can be formed only by welding the first electrode 15a and the second electrode 15b, and the back bead height becomes stable.

[0065] If the inter-electrode distance L2 is less than 210 mm, the gap between the second electrode 15b and the third electrode 15c is small, so the pool formed by welding with the second electrode 15b is not cooled completely, and the arc of the third electrode 15c interferes with the pool formed by welding with the second electrode 15b. As a result, the welding by the third electrode 15c interferes with the back bead formed by welding between the first electrode 15a and the second electrode 15b, making the back bead height unstable. Furthermore, when the inter-electrode distance L2 exceeds 320 mm, the gap between the second electrode 15b and the third electrode 15c becomes too large, and the slag formed by the welding with the second electrode 15b completely solidifies and covers the weld metal formed by the welding with the second electrode 15b. Therefore, when an arc is started using the third electrode 15c, the tip of the wire of the third electrode 15c does not reach the weld metal formed by the welding with the second electrode 15b, and an arc is not generated.

[0066] The inter-electrode distance L2 may be 210 mm or more, but from the viewpoint of further stabilizing the back bead height, it is preferably 230 mm or more, and more preferably 250 mm or more. Furthermore, the inter-electrode distance L2 may be 320 mm or less, but from the viewpoint of arc start stability, it is preferably 310 mm or less, and more preferably 300 mm or less.

[0067] When the polarity of the third electrode 15c is AC, the phase difference between the second electrode 15b and the third electrode 15c is preferably 90° to 270°. The phase difference between the second electrode 15b and the third electrode 15c affects the penetration of the third electrode 15c during welding, and the hot cracking resistance is improved. The phase difference is preferably 90° or more, more preferably 110°, and even more preferably 120° or more. For the same reason, the phase difference is preferably 270° or less, more preferably 250° or less, and even more preferably 240° or less.

[0068] In the case where the electrode 15 includes the fourth electrode 15d and the polarity of the third electrode 15c and the fourth electrode 15d is AC, the phase difference between the third electrode 15c and the fourth electrode 15d is preferably 90° to 270°. By setting the phase difference between the third electrode 15c and the fourth electrode 15d to 90° to 270°, the arcs repel each other and the arc of the third electrode 15c faces forward. As a result, the slag formed by the first electrode 15a and the second electrode 15b is melted by the arc heat of the third electrode 15c, so that the wire does not collide with the slag and the arc is stable.

[0069] As described above, the wire diameters of the second electrode 15b and the third electrode 15c are preferably in the range of 4.0 mm to 6.4 mm, respectively. From the viewpoint of further stabilizing the back bead and preventing the occurrence of slag inclusion, however, it is more preferable that the wire diameters of the second electrode 15b and the third electrode 15c are both in the range of 4.0 mm to 6.4 mm, and it is even more preferable that both are 4.8 mm or more.

[0070] Furthermore, when the electrode 15 includes the fourth electrode 15d, at least one of the third electrode 15c and the fourth electrode 15d preferably has a wire protrusion length A3, A4 of 40 mm or more. By making the wire protrusion length A3, A4 40 mm or more, slag is less likely to adhere to the electrode tip, so that a good front bead shape can be obtained. The wire protrusion lengths A3, A4 are more preferably 45 mm or more. Furthermore, the upper limit of the wire protrusion lengths A3, A4 is not particularly limited, but from the viewpoint of making the front bead more stable, it is preferably 80 mm or less, more preferably 75 mm or less.

[0071] In addition to the above, conditions not described for each electrode 15 may be appropriately set according to general conditions for welding. For example, the inter-electrode distance between the third electrode 15c and the fourth electrode 15d can be set arbitrarily. The welding speed is, for example, 34 cm / min to 110 cm / min, but is not limited to this.

[0072] (Steel plate 20) The steel plate 20 is not particularly limited, but may be, for example, a steel plate for shipbuilding. In the case of a steel plate for shipbuilding, the length is, for example, 10 m to 40 m. When welding in this embodiment is performed, as shown in Fig. 2, steel plates 20 are butted against each other and intermittent or continuous in-plane tack is applied at the position of the weld groove M. Tabs 21 and 22 for treating craters are attached to the starting end 31 and the ending end 32 of the steel plate 20. It should be noted that FIG. 2 is merely one embodiment and is not intended to be limiting.

[0073] (Table flux 51) Although there is no particular limit to the type of front flux 51, a bonded flux containing iron powder is particularly preferred. By including iron powder in the front flux 51, it becomes easier to obtain a sufficient penetration depth of the weld metal, and the hot cracking resistance becomes better.

[0074] <Welding method> An outline of multi-electrode one-sided submerged arc welding to which the welding method according to the present embodiment is applied will be described with reference to Figs. 1 to 5, but the welding method is not limited to the following method.

[0075] (preparation process) In the preparation step, first, a steel plate 20 having tabs 21 and 22 attached thereto as shown in FIG. 1 and FIG. 2 and intermittently or continuously tacked in-plane is prepared. Next, backing flux 52 is supplied by a flux supplying means (not shown) to the upper surface of a backing copper plate 55 of a backing device 50a as shown in Fig. 3. Alternatively, as shown in Fig. 4, an underlay flux 58 may be supplied by a flux supplying means (not shown) to the upper surface of a heat-resistant cover 57 in a fire-resistant canvas 56 of a backing device 50b, and then backing flux 52 may be supplied on top of that.

[0076] Then, the steel plates 20 prepared above are set in the welding device 100, and the weld groove M formed by the steel plates 20 is placed above the backing device 50a or the backing device 50b. Next, a driving device (not shown) is operated to perform fine adjustment so that the backing copper plate 55 or the fireproof canvas 56 is positioned directly below the weld groove M.

[0077] It is also preferable to spray a groove filler on the groove of the steel plate 20 before welding. By using a groove filler, the effect of the tack bead can be mitigated and the back bead height can be more stable. It is particularly effective to use the groove filler in combination with the flux backing method. There is no particular limit to the type of groove filler, and examples include iron powder and cut wire made of mild steel.

[0078] Next, the backing copper plate 55 and the heat-resistant cover 57 are pressed by the pushing mechanism, and the backing flux 52 is pressed against and adhered to the back surface of the welding groove M of the butted steel plates 20. As the pushing mechanism, in Fig. 3 and Fig. 4, a method is used in which compressed air is introduced into an air hose 59 to expand it.

[0079] (Electrode adjustment process) In the electrode adjustment step, the first electrode 15a is set to an alternating current, and the inter-electrode distances L1, L2 between the first electrode 15a to the third electrode 15c are adjusted to satisfy the above-mentioned conditions. The order of the preparation step and the electrode adjustment step is not particularly limited, and either step may be performed first, or they may be performed simultaneously.

[0080] (Welding process) In the welding process, first, the welder 12 of the welding device 100 is moved to a welding start position. Next, the second electrode 15b is set to AC, a welding current is supplied under desired conditions, and the welder 12 is operated. Then, the welder 12 is moved at a predetermined speed along the welder beam 13 from the starting end 31 to the ending end 32 of the steel sheet 20 (see FIG. 2 for both), as shown by the arrow in FIG. 1, while supplying the front flux 51, thereby welding the steel sheets 20 together.

[0081] The multi-electrode single-sided submerged arc welding method according to this embodiment can be used for both single-layer welding and multi-layer welding, but from the viewpoint of work efficiency, one-pass single-layer welding is preferred. EXAMPLES

[0082] The present invention will be specifically described below with reference to test examples, but the present invention is not limited to the following examples in any way.

[0083] (Examples 1 to 7, Comparative Examples 1 to 5) Two steel plates with beveled ends were butted against each other to form a V-shaped groove. The V-shaped groove had a groove angle of 35° and a root gap of 0 mm. The length of the steel plate was 1.2 m and the thickness of the steel plate was 40 mm. The composition of the steel sheet, the composition of the wire used, and the composition of the surface flux are shown in Table 1.

[0084] [Table 1]

[0085] A welding machine equipped with four electrodes, a first electrode to a fourth electrode, was used to perform four-electrode, single-layer submerged arc welding on the above steel plate under the conditions shown in Tables 2 and 3 to prepare a welded test specimen.

[0086] Specifically, the welding device used was one having a backing device 50b as shown in FIG. The phase difference of the AC current between the first and second electrodes, the phase difference between the second and third electrodes, the phase difference between the third and fourth electrodes, and the inter-electrode distance between the second and third electrodes in each test example are as shown in Table 2. The wire diameter, external characteristics, polarity, welding current, arc voltage, torch sweep angle, advance angle, and wire extension length of each electrode, as well as the welding speed, inter-electrode distance between the first and second electrodes, and inter-electrode distance between the third and fourth electrodes were the same in all test examples, and were the conditions shown in Table 3. The conditions other than those shown in Tables 2 and 3 were conventionally known conditions, and were all the same. Of the above conditions, the torch sweep angle and advance angle are expressed as the angle between the center line of each electrode and a plane with the welding direction X as the normal line, as shown in Figure 5. Note that the angle perpendicular to the welding direction X is considered to be 0°, and for sweep angles, the side of the welding direction X is considered to be positive. For advance angles, the side opposite the welding direction X is considered to be positive.

[0087] (Evaluation: Back bead height) The stability of the back bead height of the welded test specimens obtained by each welding method was evaluated based on the height, standard deviation, and coefficient of variation. The height of the back bead was measured at 0.1 mm intervals using a laser displacement meter in the range of 600 mm to 900 mm from the starting end of the steel plate, and the average value was taken as the height. The standard deviation was determined by measuring the range of 600 mm to 900 mm from the starting edge of the steel plate at 0.1 mm intervals using a laser displacement meter. The coefficient of variation cv is a value obtained by using the back bead height and standard deviation obtained above as (standard deviation / back bead height). The stability of the back bead height was evaluated based on the coefficient of variation cv obtained above according to the following criteria. The results are shown in Table 2. ◎(Very stable): cv<0.35 ○(Stable): 0.35≦cv<0.50 ×(unstable):0.50≦cv

[0088] (Evaluation: resistance to hot cracking) As shown in FIG. 6, the weld metal formed by the welding method according to this embodiment is composed of a weld metal 60 formed by the first electrode and the second electrode, and a weld metal 61 formed by the third electrode and subsequent electrodes. The structure of the weld metal 60 formed by the first and second electrodes is susceptible to hot cracking due to the lateral growth of dendrites. Therefore, the weld metal formed by the third and subsequent electrodes penetrates deeply and melts the brittle structure, improving hot cracking resistance. Therefore, the penetration depth T of the weld metal 61 formed by the third and subsequent electrodes was measured and evaluated from the cross-sectional macrostructure. In this test example, the weld metal 61 formed by the third and subsequent electrodes refers to the weld metal formed by the third and fourth electrodes.

[0089] The hot cracking resistance was evaluated according to the following criteria based on the relationship between the plate thickness t of the steel plate 20, which corresponds to the points indicated by the symbols t and T in Figure 6, and the penetration depth T of the weld metal 61 formed by the third electrode and subsequent electrodes from the surface (upper surface) of the steel plate 20. ○(Good):{12 / (16×t)}≦T<{14 / (16×t)} ×(Defective): T<{12 / (16×t)} or T≧{16 / (16×t)}

[0090] (Evaluation: Weld metal penetration width) The slag inclusion was evaluated using the penetration width of the weld metal. The penetration width of the weld metal can be evaluated from the cross-sectional macrostructure, as in the evaluation of the hot cracking resistance described above. Specifically, the location indicated by a pair of opposing arrows in Figure 6 is an example of a position 10 mm above the bottom end of the steel plate, and the weld metal penetration width at a height of 10 mm above the bottom end of the steel plate was evaluated according to the following criteria. If the weld metal penetration width is more than 11.0 mm, slag inclusion can be prevented. On the other hand, if the weld metal penetration width is 11.0 mm or less, slag inclusion is likely to occur. ○ (Good): The weld metal penetration width is over 11.0 mm × (Fail): The penetration width of the weld metal is 11.0 mm or less.

[0091] [Table 2]

[0092] [Table 3]

[0093] As shown in Table 2, all of the welded test specimens obtained in Examples 1 to 7 were good in all evaluation items including the stability of the back bead height, the penetration width of the weld metal, and the hot cracking resistance. In particular, the welded test specimens obtained in Examples 1 to 3, 6, and 7 were very good in the stability of the back bead height, and also had very good hot cracking resistance.

[0094] In contrast, as shown in Table 2, all of the welded test pieces obtained in Comparative Examples 1 to 5 were evaluated as poor in at least one of the items. Specifically, the welded test specimens obtained in Comparative Examples 1 to 3 had an AC phase difference between the first and second electrodes outside the range of the present invention, and the hot cracking resistance and the penetration width of the weld metal were poor.

[0095] In the welded test specimen obtained in Comparative Example 4, the inter-electrode distance between the second electrode and the third electrode was less than the lower limit, and the back bead height was poor. In some cases, the back bead was not formed. In the welded specimen obtained in Comparative Example 5, the distance between the second and third electrodes exceeded the upper limit, and no arc was generated at the third electrode. Therefore, it could not be evaluated. Therefore, all the evaluation results in Table 2 are marked "-". [Explanation of symbols]

[0096] 11 Mounting frame 12 Welding machine 13 Welder Beam 15 electrodes 15a 1st electrode 15b 2nd electrode 15c 3rd electrode 15d 4th electrode 16a~16d Wire 17a~17d Chip 20 steel plate Tabs 21 and 22 31 Beginning 32 Termination 50a, 50b backing device 51 Front Flux 52 Backing Flux 53 Slug 54 Welding metal 55 Copper backing plate 56 Fireproof Canvas 57 Heat-resistant cover 58 Underlay Flux 59 Air Hose 60 Weld metal formed by the first electrode and the second electrode 61 Weld metal formed by the third and subsequent electrodes 100 Welding equipment A1~A4 Wire extension length L1, L2 distance between electrodes T is the penetration depth of the weld metal formed by the third and subsequent electrodes t Steel plate thickness

Claims

1. A multi-electrode one-sided submerged arc welding method for joining one side of two butted steel plates using a plurality of electrodes, comprising: the electrodes include at least four electrodes: a first electrode, a second electrode, a third electrode, and a fourth electrode; The first electrode is placed at the front of the welding direction, followed by the second electrode, the third electrode, and the fourth electrode in this order along the welding line direction; Polarity of the first electrode: AC, The sweepback angle θ 1 of the first electrode: 1° or more and 15° or less, Polarity of the second electrode: AC, A phase difference between the AC current of the first electrode and the AC current of the second electrode: 0° to 90° or 275° to 360°, and Distance between the second electrode and the third electrode: 210 mm to 320 mm; The power supply characteristic of the fourth electrode: constant current or drooping characteristic; A multi-electrode one-sided submerged arc welding method in which one pass and one layer welding is performed under the above conditions.

2. 2. The method for multiple-electrode single-sided submerged arc welding according to claim 1, wherein the wire diameter of the first electrode is 3.2 mm to 6.4 mm.

3. 3. The method for multiple-electrode single-sided submerged arc welding according to claim 1, wherein the wire diameter of the second electrode is 4.0 mm to 6.4 mm, and the wire diameter of the third electrode is 4.0 mm to 6.4 mm.

4. The method for multi-electrode single-sided submerged arc welding according to any one of claims 1 to 3, wherein an inter-electrode distance between the first electrode and the second electrode is 25 mm or more and less than 80 mm.

5. The method for multi-electrode single-sided submerged arc welding according to any one of claims 1 to 4, wherein the power supply characteristic of the first electrode is a constant voltage.

6. The method for multiple-electrode single-sided submerged arc welding according to any one of claims 1 to 4, wherein a flux backing method is used.

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