JP2017213569A - Submerged arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submerged arc welding method hardly generating a hot crack, having excellent shapes of a table bead and a back bead, and further having reduced slag inclusion.SOLUTION: In a submerged arc welding method, which is a submerged arc welding method for performing welding of a single-sided one layer by using many electrodes 15, welding is performed under conditions that a polarity of a first electrode 15a is set in electrode side minus in DC current, an inter-electrode distance L1 between the first electrode 15a and a second electrode 15b is 80 mm or more and 140 mm or less, an inter-electrode distance L2 between the second electrode 15b and a third electrode 15c is 10 mm or more and 100 mm or less, and a current of the second electrode 15b is 900 A or more and 1,600 A or less.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a submerged arc welding method for welding one layer on one side using a large number of electrodes.

  Multi-electrode single-sided submerged arc welding, in which single-sided single-layer welding is performed using a large number of electrodes, is a high-efficiency welding method applied to a wide range of fields, mainly shipbuilding as plate joint welding. Various multi-electrode single-sided submerged arc welding methods aiming at such high efficiency have been disclosed.

  For example, in Patent Document 1, in a submerged arc welding method in which welding is performed with a single electrode or two or more electrodes, a welding wire containing 0.01 to 1% by mass of a rare earth element is used as the first electrode. A submerged arc welding method is disclosed in which the polarity of the electrode is DC positive polarity or AC.

Further, for example, in Patent Document 2, a wire having a wire diameter of 3.2 mm or less is applied to the first electrode and the second electrode in multi-electrode welding of three or more electrodes, and the first electrode has a current of 800 A or more and is welded. current density of the current divided by the wire cross-sectional area at the first electrode 145A / mm ² or more, a multi-electrode submerged arc welding method in the second electrode is 95A / mm ² or more is disclosed.

JP 2010-212296 A JP 2007-268564 A

  However, when the welding method described in Patent Document 1 is performed with alternating current (AC), the wire feed speed is not constant, so that it becomes unstable in a high current region, and the shape stability of the back bead in the thick plate There was a problem that it was difficult to ensure. Moreover, when the welding method described in Patent Document 1 is performed with direct current electrode positive (DCEP), it is difficult to ensure the shape stability of the back bead with a thick plate because the penetration width is narrow. There was a problem of being. In the present specification, “thick plate” refers to a steel plate having a plate thickness of 30 mm or more. In addition, the welding method described in Patent Document 1 does not define the distance between the electrodes, so that hot cracking is likely to occur or the shape of the front bead may become unstable. The “hot crack” means a crack that occurs in a high temperature range during welding or cooling.

  In addition, the welding method described in Patent Document 2 has a problem that since the wire diameter of the first electrode and the wire diameter of the second electrode are thin, the penetration width of the root portion is narrowed, and hot cracking is likely to occur. . In addition, since the welding method described in Patent Document 2 does not define the distance between the electrodes, similarly to the welding method described in Patent Document 1, the case where hot cracking is likely to occur or the shape of the front bead is unstable. It may become.

Furthermore, including the above-mentioned Patent Documents 1 and 2, in the conventional multi-electrode single-sided single-layer submerged arc welding, the shape of the back bead tends to become a die as the plate becomes thicker, and the occurrence rate of hot cracking is generally increased. There is a problem of rising. Therefore, when performing multi-electrode single-sided single-layer submerged welding, the condition of sacrificing the shape of the back bead had to be adopted in order to reduce the occurrence rate of hot cracks on the thick plate side.
In addition, in the conventional multi-electrode single-sided single layer submerged arc welding, when the first electrode that is first arc-welded to the thick plate in the welding progress direction is a direct current electrode negative (DCEN), There was a problem like this. In other words, conventionally, when the first electrode is DCEN, compared with the case where the first electrode is DC plus (DCEP) or AC, the melting transition is unstable, and the weld metal formed in the groove is unstable. Since the shape becomes unstable, there is a problem that slag entrainment occurs. “Slag entrainment” means that slag remains in the weld metal.

  The present invention has been made in view of the above circumstances, and provides a submerged arc welding method in which high-temperature cracking hardly occurs, the front and back beads have good shapes, and slag entrainment is reduced. Let it be an issue.

A submerged arc welding method according to the present invention that solves the above-described problems is a submerged arc welding method that performs welding on one side of one layer using a large number of electrodes, wherein the polarity of the first electrode is DC and the electrode side is negative, The electrode distance L1 between the first electrode and the second electrode is 80 mm or more and 140 mm or less, the electrode distance L2 between the second electrode and the third electrode is 10 mm or more and 100 mm or less, and the current of the second electrode is 900 A or more and 1600 A or less. We will perform welding under the conditions.
As described above, the submerged arc welding method according to the present invention includes the polarity of the first electrode, the interelectrode distance between the first electrode and the second electrode, the interelectrode distance between the second electrode and the third electrode, The voltage of one electrode and the current of the second electrode are set as specific conditions. Therefore, hot cracking hardly occurs, the front bead and the back bead have good shapes, and slag entrainment can be further reduced.

In the submerged arc welding method according to the present invention, a value L2 / L1 obtained by dividing L2 by L1 is preferably 0.12 or more and 1.13 or less.
Thus, the submerged arc welding method according to the present invention specifies the relationship between the interelectrode distance L1 between the first electrode and the second electrode and the interelectrode distance L2 between the second electrode and the third electrode. In addition, slag entrainment can be further reduced.

In the submerged arc welding method according to the present invention, the welding speed is preferably 50 cm / min or more and 150 cm / min or less.
Thus, since the submerged arc welding method according to the present invention has a welding speed in a specific range, the shape of the back bead becomes better.

In the submerged arc welding method according to the present invention, the wire diameter of the first electrode is preferably 4.0 mmφ or more and 6.4 mmφ or less.
As described above, in the submerged arc welding method according to the present invention, since the wire diameter of the first electrode is in a specific range, stable penetration is realized and the shape of the back bead is more stable. Also, with such a welding method, the penetration width of the root portion can be sufficiently secured, so that even when a thick plate is welded, high temperature cracks can be made more difficult to occur.

In the submerged arc welding method according to the present invention, the wire diameter of the second electrode is preferably 4.0 mmφ to 6.4 mmφ, and the wire diameter of the third electrode is preferably 4.0 mmφ to 6.4 mmφ. .
Thus, the submerged arc welding method according to the present invention has a specific range for the wire diameter of the second electrode and the wire diameter of the third electrode, so that a stable penetration width can be secured and slag entrainment occurs. hard. Further, since the arc spread is large, the shape of the front bead is good.

In the submerged arc welding method according to the present invention, the current of the first electrode is preferably 1000 A or more and 1700 A or less.
Thus, since the submerged arc welding method according to the present invention sets the current of the first electrode within a specific range, stable penetration is realized and the shape of the back bead becomes better.

In the submerged arc welding method according to the present invention, the voltage of the second electrode is preferably 40V or more and 50V or less.
Thus, in the submerged arc welding method according to the present invention, the second electrode does not become a high voltage and the voltage value is in an appropriate range, so that a sufficient penetration width can be secured. Therefore, slag entrainment hardly occurs.

  The submerged arc welding method according to the present invention specifies various conditions such as the polarity of the first electrode and the distance between the electrodes, so that hot cracking is unlikely to occur, and the shape of the front and back beads is good, Furthermore, slag entrainment is reduced.

It is a schematic explanatory drawing of the welding apparatus used for the submerged arc welding method which concerns on one Embodiment of this invention. It is explanatory drawing which looked at the steel plate welded with the submerged arc welding method which concerns on one Embodiment of this invention from upper direction. It is a schematic explanatory drawing of the steel plate periphery which shows the mode at the time of performing submerged arc welding in a cross section. It is a schematic explanatory drawing of the steel plate periphery which shows the state at the time of performing a submerged arc welding, changes the structure of a backing device, and shows it. It is a schematic explanatory drawing for demonstrating the distance between electrodes and the wire protrusion length in the submerged arc welding method which concerns on one Embodiment of this invention. It is a schematic explanatory drawing around the steel plate for demonstrating the hot cracking resistance in an Example.

Hereinafter, a submerged arc welding method (hereinafter, also simply referred to as “welding method”) according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
In the welding method according to this embodiment, for example, single-sided submerged arc welding is performed using a large number of electrodes such as three or four. And the welding method concerning this embodiment specifies the polarity of an electrode, the distance between electrodes, and the electric current of an electrode, and specifies the welding speed, the wire diameter of an electrode, the polarity of an electrode, a voltage, etc. as a preferable aspect.
First, the outline of the main part of the welding apparatus used in the welding method according to the present embodiment and the steel plate will be described.

(Welding equipment)
As shown in FIG. 1, the welding apparatus 100 mainly includes a gantry frame 11, a welder 12, and a welder beam 13.
The gantry frame 11 is formed so as to form a substantially U shape in a cross-sectional view in a direction perpendicular to the longitudinal direction with a steel square frame as a frame, and the upper side is open. A backing device 50 a shown in FIG. 3 is supported inside the gantry frame 11. And the steel plates 20 and 20 are mounted on the backing copper plate 55 of the backing device 50a.
Note that a backing device 50b shown in FIG. 4 may be supported inside the gantry frame 11 instead of the backing device 50a shown in FIG. In this case, the steel plates 20 and 20 are placed on the fireproof canvas 56 of the backing device 50b.

The welder beam 13 guides the welder 12 along the weld groove portion G (see FIG. 2) of the steel plates 20 and 20.
The welding machine 12 is disposed above the gantry frame 11 (above the steel plate 20), and welds the steel plate 20 from the front side of the welding groove portion G of the steel plate 20. The welding machine 12 includes a large number of electrodes (welding torches) 15. The welder 12 welds the steel plate 20 by single-sided submerged arc welding with the electrode 15 from the front side of the welding groove G while moving along the welder beam 13 at a predetermined speed. In addition, the welding machine 12 shown in FIG. 1 operates the drive device which is not shown in figure, and welds the steel plate 20, moving from left to right as shown by the arrow in the figure.

  In the welding method according to the present embodiment, as shown in FIG. 3, an uplift mechanism such as an air hose 59 is applied to a backing flux 52 dispersed in a layered manner on a backing copper plate 55 from the abutted steel plate 20 and the back surface of the steel plate 20. Is pressed and welded in one pass.

  As described above, when the backing device 50b shown in FIG. 4 is used instead of the backing device 50a shown in FIG. 3, welding is performed as follows. That is, as shown in FIG. 4, from the abutted steel plate 20 and the back surface of the steel plate 20, the backing flux 52, the underlay flux 58, and the heat-resistant cover 57 accommodated in the refractory canvas 56 are pushed up by an air hose 59 or the like. Is pressed and welded in one pass.

  3 and 4, the welding method according to this embodiment performs submerged arc welding from the front side of the steel plate 20 using the front flux 51, and simultaneously forms beads on the front and back surfaces of the steel plate 20. When the welding method according to the present embodiment is performed, the steel plates 20 and 20 are joined together via the weld metal 54, and the slag 53 is formed on the surface of the weld metal 54.

(steel sheet)
Examples of the steel plate 20 include shipbuilding steel plates (for example, Japan Maritime Association standard mild steel and high-tensile steel). The steel plate 20 may have a cross-sectional shape that is flat, substantially L-shaped, substantially I-shaped, substantially H-shaped, substantially U-shaped, or substantially T-shaped, but is not limited thereto.
In the present embodiment, for example, as shown in FIG. 2, the steel plates 20 and 20 may be brought into contact with each other, and at the position of the welding groove portion G, intermittent or continuous in-plane provisional attachment may be welded. In addition, the tab 21 and the tab 22 for processing a crater are attached to the start end 31 and the termination | terminus 32 of the steel plate 20 shown in FIG.
The length of the steel plate 20 is, for example, 10 to 30 m. The plate | board thickness of the steel plate 20 is 10-40 mm, for example.

  Moreover, the welding method according to the present embodiment can be applied, for example, when welding a steel sheet 20 using a bond flux and having a groove shape of a Y-shaped groove. However, the welding to which the welding method according to the present embodiment can be applied is not limited to this, and may be a V-shaped groove steel plate, or a melt flux or a sintered flux was used. It may be welding.

(Flux and wire types / chemical components)
It should be noted that the flux (bond flux and melt flux) that can be used in the welding method according to the present embodiment, the type of wire and the chemical composition are not limited to specific ones, and are generally used for submerged arc welding. Anything can be applied.

(Welding method)
The welding method according to the present embodiment uses the above-described welding apparatus 100, and as shown in FIG. 5, the polarity of the first electrode 15a is DC and the electrode side minus (DCEN), and the first electrode 15a and the second electrode 15b. The inter-electrode distance L1 is 80 mm or more and 140 mm or less, the inter-electrode distance L2 between the second electrode 15b and the third electrode 15c is 10 mm or more and 100 mm or less, and the current of the second electrode 15b is 900 A or more and 1600 A or less. Weld.

  In the submerged arc welding, a solid wire is mainly used, and the wire diameter is generally limited to a specific nominal diameter such as 4.0 mmφ, 4.8 mmφ, or 6.4 mmφ. The actual diameter is generally widely interpreted as including an error range.

  For example, as shown in FIG. 5, the electrode 15 of the welding machine 12 includes three electrodes, a first electrode 15 a, a second electrode 15 b, and a third electrode 15 c, in order from the welding progress direction (the direction indicated by the arrow in the figure). I have. In addition, the electrode 15 can further be provided with four including the 4th electrode 15d shown with the dashed-two dotted line in FIG. 5 as needed. If the fourth electrode 15d is provided, the pool (melt pool) can be further increased. Whether the number of the electrodes 15 is three or four can be arbitrarily set, but the effect of the present invention is that the first electrode 15a, the second electrode 15b, and the third electrode 15c are set as described above. Can be played.

  Here, as shown in FIG. 5, the interelectrode distances L <b> 1 and L <b> 2 are obtained by extending the tips of the wires 16 a to 16 c protruding from the electrodes 15 a to 15 c in the arrangement of the electrodes 15 when performing welding, respectively. The distance of the part which touched the steel plate 20 is said. In FIG. 5, portions where the tips of the wires 16a to 16c are extended are indicated by thin broken lines.

  The protruding lengths of the wires 16a to 16d refer to the lengths A1, A2, A3, and A4 from the portions 17a to 17d where the wires 16a to 16d of the electrodes 15a to 15d protrude to the steel plate 20, respectively. The protruding length A1 of the wire 16a of the first electrode 15a in this embodiment can be set to 30 to 40 mm, for example. The protruding length A2 of the wire 16b of the second electrode 15b in the present embodiment can be set to 50 to 60 mm, for example. In addition, the protruding length A3 of the wire 16c of the third electrode 15c in the present embodiment can be set to 50 to 60 mm, for example. The protruding length A4 of the wire 16d of the fourth electrode 15d in this embodiment is not particularly limited and can be set under general conditions.

  Moreover, it is preferable that the 1st electrode 15a in this embodiment makes opening angle (theta) 1 from the steel plate with respect to a welding direction 70-90 degrees (namely, torch angle: -20-0 degrees). The second electrode 15b in the present embodiment preferably has an opening angle θ2 from the steel plate with respect to the welding direction, for example, 80 to 100 ° (that is, torch angle: −10 to + 10 °). The third electrode 15c in the present embodiment preferably has an opening angle θ3 from the steel plate with respect to the welding direction, for example, 80 to 100 ° (that is, torch angle: −10 to + 10 °). The fourth electrode 15d in the present embodiment preferably has an opening angle θ4 from the steel plate with respect to the welding direction, for example, 90 to 110 ° (that is, torch angle: 0 to + 20 °).

Hereinafter, each condition will be described.
(Polarity of the first electrode)
The polarity of the first electrode 15a in this embodiment is DCEN.
When the polarity of the first electrode 15a is DCEN, it is possible to reduce the fluctuation of the penetration depth with respect to the current change caused by the shallower penetration. Thereby, the stable penetration is realized and the shape of the back bead is stabilized. Further, if the polarity of the first electrode 15a is DCEN, the amount of wire welding at the same current is large, and the chemical component of the wire is increased in the weld metal, so that the mechanical properties (for example, impact performance) are good. become.

If the polarity of the first electrode 15a is AC, the wire feeding speed is not constant, so that it becomes unstable in the high current region, and the shape of the back bead becomes unstable.
If the polarity of the first electrode 15a is DCEP, the shape of the back bead becomes unstable because the melting width is narrow. Further, in this case, the amount of wire welding is small, and the yield of chemical components of the wire in the weld metal is reduced, so that the mechanical properties (for example, impact performance) are not improved.

(Distance L1 between the first electrode and the second electrode)
The interelectrode distance L1 between the first electrode 15a and the second electrode 15b is 80 mm or more and 140 mm or less. If the distance L1 between the electrodes is within this range, the interval between the first electrode 15a and the second electrode 15b is appropriate, so that the cooling time is appropriate, and the second electrode 15b can be welded before the pool is solidified. Therefore, it is possible to deepen the penetration of the weld metal in the welding of the second electrode 15b.
Here, in the structure of the weld metal 60 (see FIG. 6) formed by the first electrode 15a, columnar crystals grow in the lateral direction, so that high temperature cracks are likely to occur.
However, as described above, when the weld metal 61 generated in the second electrode 15b is deeply melted, the fragile structure can be melted, and the hot crack resistance is improved.

If the interelectrode distance L1 is less than 80 mm, the arc of the first electrode 15a and the arc of the second electrode 15b interfere with each other, and the shape of the back bead becomes unstable.
On the other hand, when the interelectrode distance L1 exceeds 140 mm, the interval between the first electrode 15a and the second electrode 15b is long, so that the cooling time becomes long and the pool is solidified. Therefore, the penetration becomes shallow in the welding of the second electrode 15b, and a hot crack occurs.
From the viewpoint of further stabilizing the shape of the back bead, the inter-electrode distance L1 is preferably 90 mm or more. From the viewpoint of making hot cracks less likely to occur, the interelectrode distance L1 is preferably 130 mm or less, and more preferably 120 mm or less.

(Distance L2 between the second electrode and the third electrode)
The inter-electrode distance L2 between the second electrode 15b and the third electrode 15c is 10 mm or more and 100 mm or less. When the interelectrode distance L2 is within this range, the penetration width is increased. Therefore, the first electrode 15a makes it easy to melt the slag generated at the toes of the front bead, thereby preventing the occurrence of slag entrainment.
If the interelectrode distance L2 is less than 10 mm, the arc of the second electrode 15b and the arc of the third electrode 15c interfere with each other, and the shape of the front bead becomes unstable.
On the other hand, when the interelectrode distance L2 exceeds 100 mm, since the distance between the second electrode 15b and the third electrode 15c is separated, the penetration width becomes narrow. Therefore, the first electrode 15a makes it difficult to melt the slag generated at the toe of the front bead, and slag entrainment occurs.
From the viewpoint of stabilizing the shape of the front bead, the interelectrode distance L2 is preferably 15 mm or more. From the viewpoint of making slag entanglement difficult to occur, the interelectrode distance L2 is preferably 80 mm or less, and more preferably 30 mm or less.

(Current of the second electrode)
The current of the second electrode 15b is set to 900A or more and 1600A or less. When the current of the second electrode 15b is within this range, the back bead formed by the first electrode 15a is not adversely affected, so that the shape of the back bead can be stabilized. Further, when the current of the second electrode 15b is within this range, the penetration of the weld metal can be deepened in the welding of the second electrode 15b. Therefore, when the weld metal 61 generated in the second electrode 15b is deeply melted, the fragile structure generated in the first electrode 15a can be melted, and the hot crack resistance is improved.
When the current of the second electrode 15b is less than 900 A, the welding becomes shallow in the welding of the second electrode 15b, and hot cracking occurs.
If the current of the second electrode 15b exceeds 1600 A, the welding of the second electrode 15b adversely affects the back bead formed by the welding of the first electrode 15a, and the shape of the back bead becomes unstable.
Note that the current of the second electrode 15b is preferably 950 A or more from the viewpoint of making hot cracking less likely to occur. From the viewpoint of making the shape of the back bead more stable, the current of the second electrode 15b is preferably 1550 A or less.

The welding method according to the present embodiment described above includes the polarity of the first electrode, the interelectrode distance L1 between the first electrode and the second electrode, the interelectrode distance L2 between the second electrode and the third electrode, The current of the second electrode is a specific condition. Therefore, according to the welding method according to the present embodiment, hot cracking is unlikely to occur, the front and back beads have good shapes, and slag entrainment can be reduced.
That is, conventionally, when submerged arc welding is performed on the first electrode with DCEN, the shape of the front bead becomes a mountain shape, and slag tends to bite into the toe portion, and the slag cannot be completely melted by the second electrode. Therefore, slag entrainment occurred.
However, in the welding method according to the present embodiment, by defining the welding conditions to the above-described conditions, hot cracking is difficult to occur, and the shape of not only the front bead but also the back bead is good, and the slag winding It is possible to reduce the noise.

(Other embodiments)
In the welding method according to the present embodiment, when the following mode is adopted, hot cracking is less likely to occur, the shape of the front bead and the back bead is made better, and slag entrainment is further improved. Can be reduced.

(L2 / L1)
A value L2 / L1 obtained by dividing the interelectrode distance L2 between the second electrode 15b and the third electrode 15c by the interelectrode distance L1 between the first electrode 15a and the second electrode 15b is, for example, 0.12 or more and 1.13 or less Is preferred. In this way, the arc force generated at the second electrode 15b and the third electrode 15c is strong, and a wide penetration width can be secured. In addition, since the pool generated in the first electrode 15a is not completely solidified or maintains a high temperature, it is easy to melt, so that the penetration width by the second electrode 15b and the third electrode 15c is widened, and the slag is increased. Entrainment can be further reduced.
From the viewpoint of further reducing slag entrainment, L2 / L1 is more preferably 0.16 or more, and more preferably 0.90 or less.
L2 / L1 can be set by appropriately changing the attachment positions of the first electrode 15a, the second electrode 15b, and the third electrode 15c attached to the welding machine 12.

(Welding speed)
The welding speed (electrode moving speed) is preferably, for example, 50 cm / min or more and 150 cm / min or less. If it does in this way, since the welding speed is appropriate, the shape of the back bead becomes more stable.
From the viewpoint of further stabilizing the shape of the back bead, the welding speed is more preferably 60 cm / min or more, and more preferably 140 cm / min or less.
The welding speed can be adjusted by appropriately changing the thickness of the steel plate 20, the current and voltage supplied to the electrode 15, the moving speed of the welding machine 12 that moves the welding machine beam 13, and the like.

(Wire diameter of the first electrode)
The wire diameter of the first electrode 15a is preferably, for example, 4.0 mmφ or more and 6.4 mmφ or less. If it does in this way, stable penetration will be realized and the shape of a back bead will become more stable. Also, with such a welding method, the penetration width of the root portion can be sufficiently ensured, so that even when a thick plate having a plate thickness of 30 mm or more is welded, high temperature cracks are less likely to occur. be able to.
From the viewpoint of further stabilizing the shape of the back bead and preventing the occurrence of hot cracking, the wire diameter of the first electrode 15a is preferably 4.8 mmφ or more, for example.

(The wire diameter of the second electrode, the wire diameter of the third electrode)
The wire diameter of the second electrode 15b and the wire diameter of the third electrode 15c are both preferably 4.0 mmφ or more and 6.4 mmφ or less, for example. If it does in this way, the stable penetration width can be secured and it will be hard to generate slag entrainment. Further, in this case, since the arc spread is large, the shape of the front bead becomes good.
From the viewpoint of making slag entanglement difficult and further improving the shape of the front bead, the wire diameter of the second electrode 15b and the wire diameter of the third electrode 15c are both 4.8 mmφ or more, for example. preferable.

(Current of the first electrode)
For example, the current of the first electrode 15a is preferably 1000 A or more and 1700 A or less. If it does in this way, since the 1st electrode 15a will not become a high electric current too much and an electric current value exists in the suitable range, the shape of a back bead will become more stable. In addition, with such a welding method, the penetration width of the root portion can be sufficiently ensured, so that even when a thick plate is welded, high temperature cracks can be made more difficult to occur.
In addition, from the viewpoint of further stabilizing the shape of the back bead and preventing the occurrence of hot cracking, the current of the first electrode 15a is preferably 1100 A or more, and more preferably 1150 A or more, for example. From the same viewpoint, the current of the first electrode 15a is more preferably 1650 A or less, and further preferably 1600 A or less, for example.
The range of the current value of the first electrode 15a described above is merely a preferable numerical range, and is not limited to this. The current value of the first electrode 15a can be less than 1000A (for example, 950A) or can exceed 1700A (for example, 1750A). Even in this case, the shape of the back bead is sufficiently stable, and hot cracks are not easily generated.

(Voltage of the second electrode)
The voltage of the second electrode 15b is preferably 40V or more and 50V or less, for example. If it does in this way, since the 2nd electrode 15b does not become a high voltage too much and a voltage value exists in the suitable range, the penetration width can fully be ensured. Therefore, slag entrainment is less likely to occur. Further, when the voltage of the second electrode 15b is within this range, gas blowing up is reduced, so that the shape of the front bead is further stabilized.
In addition, it is more preferable that the voltage of the 2nd electrode 15b shall be 42V or more, for example from a viewpoint which makes it difficult to generate | occur | produce slag entrainment and also stabilizes the shape of a surface bead, and it is more preferable to set it as 44V or more. Further preferred. Further, from the same viewpoint, the voltage of the second electrode 15b is more preferably 48V or less, and further preferably 46V or less, for example.
The range of the voltage value of the second electrode 15b described above is merely an example of a preferable numerical value range, and is not limited thereto. The voltage value of the second electrode 15b may be less than 40V (for example, 38V), or may exceed 50V (for example, 52V). Even if it does in this way, slag winding does not generate | occur | produce enough, and the shape of a surface bead will become stable.

(The polarity of the second electrode, the polarity of the third electrode)
The polarity of the second electrode 15b and the polarity of the third electrode 15c may be AC, for example.

(Conditions not mentioned above)
Conditions not described above can be implemented by appropriately setting general conditions. As a general condition, for example, the current value of the third electrode 15c is set to 700 A or more and 1300 A or less, and the voltage value is set to 43 V or more and 46 V or less.
Further, for example, when the fourth electrode 15d is provided, the wire diameter of the fourth electrode 15d is set to 4.0 mmφ to 6.8 mmφ, the current value is set to 700A to 1500A, and the voltage value is set to 40V to 50V. Is mentioned.
The interelectrode distance between the third electrode 15c and the fourth electrode 15d can be set arbitrarily.
There are no particular limitations or preferred ranges regarding the wire diameter, voltage value, current value, polarity, etc. of the fourth electrode 15d, and the fourth electrode 15d can be performed under general conditions. As general conditions, for example, the wire diameter may be 6.4 mmφ, the voltage value may be 46 V, the current value may be 1300 A, and the polarity may be AC, DCEN, DCEP, or the like.

(Outline of welding)
Next, an outline of multi-electrode (three electrodes in the following example) single-sided single layer submerged arc welding to which the welding method according to the present embodiment is applied will be described with reference to FIGS.

(Preparation process)
In the preparation step, first, as shown in FIG. 2, a tab 21 and a tab 22 are attached, and a steel plate 20 and a steel plate 20 that are intermittently or continuously in-plane temporarily attached are prepared.
Next, as shown in FIG. 3, the backing flux 52 is supplied to the upper surface of the backing copper plate 55 of the backing device 50a by a flux supply means (not shown).
And as shown in FIG. 1, the steel plate 20 and the steel plate 20 are set to the welding apparatus 100, and as shown in FIG. 3, the welding groove part G formed by the steel plate 20 and the steel plate 20 above the backing apparatus 50a. Arrange.
Then, a drive device (not shown) is operated to make fine adjustment so that the backing copper plate 55 is positioned immediately below the welding groove portion G.
Next, compressed air is introduced into the air hose 59 to expand it, and the backing flux 52 is pressed against the back surface of the weld groove G.

When the backing copper plate 55 shown in FIG. 4 is used instead of the backing device 50a shown in FIG. 3, the following is performed. That is, as shown in FIG. 4, the underlay flux 58 is supplied to the upper surface of the heat-resistant cover 57 in the fireproof canvas 56 of the backing device 50b by a flux supply means (not shown), and the backing flux 52 is further supplied thereon. .
And as shown in FIG. 1, the steel plate 20 and the steel plate 20 are set to the welding apparatus 100, and as shown in FIG. 4, the welding groove part G formed by the steel plate 20 and the steel plate 20 above the backing apparatus 50b. Arrange.
Then, a drive device (not shown) is operated to make fine adjustment so that the fire-resistant canvas 56 is positioned immediately below the weld groove G.
Next, compressed air is introduced into the air hose 59 to expand it, and the backing flux 52 is pressed against the back surface of the weld groove G.

(Electrode adjustment process)
In the electrode adjustment step, the polarity of the first electrode 15a and the above-described interelectrode distances L1 and L2 are adjusted to satisfy the above-described conditions. Note that the order of the preparation step and the electrode adjustment step is not particularly defined, and either step may be performed first or simultaneously.

(Welding process)
In the welding process, first, the welding machine 12 of the welding apparatus 100 is moved to the welding start position. Next, a current is supplied so that the current value of the second electrode 15b satisfies the above-described condition, and the welding machine 12 is operated. Then, as shown in FIG. 1, the surface flux 51 is supplied while moving the welding machine 12 along the welding machine beam 13 at a predetermined speed from the start end 31 to the end end 32 (both see FIG. 2) of the steel plate 20. The steel plate 20 and the steel plate 20 are welded.

Hereinafter, a confirmation experiment for confirming the effect of the present invention will be described.
About the two steel plates which formed the slope in the end surface, the end surfaces were faced to each other and abutted to form a Y-shaped groove. This Y-shaped groove has a groove angle of 45 °, 50 °, 60 °, a root face of 3 to 6 mm, and a root gap of 0 mm. In this example, the length of the steel plate was 1.2 m, and the thickness of the steel plate was 12 to 40 mm. The groove angle is 60 ° when the plate thickness is 12 mm, 45 ° when 32 mm, and 45 ° when 40 mm.
Table 1 shows the composition of the steel sheet, the composition of the wire used, and the composition of the flux.

With respect to this steel plate, No. 2 in Table 2 to Table 4. Submerged arc welding of one electrode on one side of three or four electrodes was performed under the conditions shown in 1 to 68, a weld specimen was produced, and the following evaluation was performed.
A welding apparatus having a backing apparatus 50a shown in FIG. 3 was used, and a bond flux was used as a front flux. In addition, conditions other than the conditions shown in Table 2 to Table 4 are conventionally known conditions, and all are the same conditions. “-” Regarding the fourth electrode in Table 2 and Table 4 indicates that the fourth electrode is not provided. The polarities of the second electrode and the third electrode were both AC.

(Bead shape)
The bead shape was evaluated by visually observing the shape of the front and back beads. As for the shape of the front bead and the back bead, the extra height is 2 to 6 mm, the extra height and the bead width are almost uniform (（), and the extra height is 2 to 6 mm. In addition, those with a slightly uniform height and bead width were evaluated as good (◯). Also, the front and back bead shapes are under-excessive or excessive, undercuts occur frequently, the bead width is non-uniform, and / or the bead appearance is poor. Was also judged as bad (x).

(High temperature crack resistance)
As shown in FIG. 6, the weld metal formed by the welding method under the above conditions is a weld metal 60 formed by the first electrode, a weld metal 61 formed by the second electrode, and only the third electrode, or And a weld metal 62 formed of a third electrode and a fourth electrode.
As described above, in the structure of the weld metal 60 formed by the first electrode, the columnar crystal grows in the horizontal direction, so that hot cracking is likely to occur. Therefore, the weld metal generated in the second electrode is deeply melted, and the fragile structure is melted to improve the hot crack resistance.
Therefore, the penetration depth T of the weld metal 61 and the weld metal 62 formed by the second electrode and the third electrode (or the second electrode to the fourth electrode) was measured and evaluated from the cross-sectional macrostructure. When the thickness of the steel plate 20 is t, the penetration of the weld metal 61 and the weld metal 62 formed by the second electrode and the third electrode (or the second electrode to the fourth electrode) from the surface (upper surface) of the steel plate 20. When the depth T is in the relationship of “14 / 16t ≦ T <16 / 16t”, the hot crack resistance is very good (（), and when the relationship of “12 / 16t ≦ T <14 / 16t” is satisfied. When the hot cracking resistance was good (◯) and the relationship of “T <12 / 16t” or “T ≧ 16 / 16t” was satisfied, the hot cracking resistance was judged as poor (×).

(Slag entrainment)
An X-ray transmission test was conducted for a range of 750 mm excluding the start end of 200 mm and the end of 250 mm out of the weld length of 1200 mm. The slag entrainment was very good when the slag entrainment was zero (◎), the maximum dimension of the slag entrainment ≦ t / 2 and the sum of scratches ≦ 2t is good for slag winding (◯), the maximum dimension of slag wrapping is> t / 2, and the sum of scratches is> 2t for slag winding Defective (x) (t indicates the plate thickness).

  As shown in Table 2 and Table 3, Since the weld specimens 1 to 47 satisfied the requirements of the present invention, the bead shape, hot crack resistance, and slag entrainment were excellent (Examples). Among these, No. 1, 3-5, 8, 9, 11, 12, 15, 16, 18-22, 25-28, 30-35, 38-41, 43, 44, 46, 47, the weld specimen is a bead shape. And slag entrainment was very good.

On the other hand, as shown in Table 4, no. Since the weld specimens according to 48 to 68 did not satisfy the requirements of the present invention, the bead shape, hot crack resistance, or slag entrainment was inferior (comparative example).
Specifically, no. The weld specimen according to No. 48 was inferior in hot cracking resistance because the current of the second electrode was too low.
No. Since the polarity of the 1st electrode was DCEP, the weld test body which concerns on 49,56,63 was inferior in the bead shape.
No. Since the polarity of the 1st electrode was AC, the weld test body concerning 50, 57, 64 was inferior in the bead shape.
No. The weld specimens according to 51, 58 and 65 were inferior in bead shape because the distance between the first electrode and the second electrode was too short.
No. Since the distance between the first electrode and the second electrode was too long, the weld specimens according to 52, 59 and 66 were inferior in hot crack resistance.
No. In the weld specimens according to 53, 60 and 67, the inter-electrode distance between the second electrode and the third electrode was too long, so the slag entrainment was inferior.
No. Since the distance between the second electrode and the third electrode was too short, the weld specimens according to 54, 61, and 68 were inferior in the bead shape.
No. The weld specimens according to 55 and 62 were inferior in bead shape because the current of the second electrode was too high.

15 electrode 15a 1st electrode 15b 2nd electrode 15c 3rd electrode L1, L2 Distance between electrodes

Claims (7)

A submerged arc welding method for welding one layer on one side using a number of electrodes,
The polarity of the first electrode is DC and the electrode side is negative,
The electrode distance L1 between the first electrode and the second electrode is 80 mm or more and 140 mm or less,
The electrode distance L2 between the second electrode and the third electrode is 10 mm or more and 100 mm or less,
Welding is performed under the condition that the current of the second electrode is set to 900A or more and 1600A or less.   The submerged arc welding method according to claim 1, wherein a value L2 / L1 obtained by dividing the L2 by the L1 is 0.12 or more and 1.13 or less.   The submerged arc welding method according to claim 1 or 2, wherein a welding speed is 50 cm / min or more and 150 cm / min or less.   The submerged arc welding method according to any one of claims 1 to 3, wherein a wire diameter of the first electrode is 4.0 mmφ or more and 6.4 mmφ or less. The wire diameter of the second electrode is 4.0 mmφ or more and 6.4 mmφ or less,
The submerged arc welding method according to any one of claims 1 to 4, wherein a wire diameter of the third electrode is 4.0 mmφ or more and 6.4 mmφ or less.   The submerged arc welding method according to any one of claims 1 to 5, wherein the current of the first electrode is 1000A or more and 1700A or less.   The voltage of the said 2nd electrode is 40V or more and 50V or less, The submerged arc welding method as described in any one of Claims 1-6 characterized by the above-mentioned.

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