JP2002120068A - Multiple electrode submerged arc welding method excellent in weld bead shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple electrode submerged arc welding method by which molten metal flowing to the rear part of the molten metal at high speed welding is effectively and efficiently restrained by utilizing electromagnetic action, and thus defect, etc., such as undercut, in a weld bead accompanying the speeding up of welding, is prevented. SOLUTION: In the multiple electrode submerged arc welding method using AC as welding current of at least the rearmost electrode, to non-solidified welded metal part at the rear part of the rearmost electrode, AC magnetic field having the same frequency as the welding current of the above electrode, is impressed from the vertical and the right and left direction with respect to a weld line. Further, at least one among the magnetic flux density in the AC magnetic field, the frequency phase difference between the above AC magnetic field and the welding current of the above electrode and the impressed position of the above AC magnetic field, is adjusted to obtain the excellent weld bead shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submerged welding method, and more particularly to a multi-electrode submerged welding method for manufacturing a welded steel pipe and performing various splicing of steel sheets.

[0002]

2. Description of the Related Art Conventionally, in submerged arc welding, various methods have been proposed for increasing the welding speed in order to increase the efficiency of welding work. For example, Japanese Patent Publication No. 54-32749 discloses a multi-electrode submerged arc welding method for performing high-speed welding at 3 m / min or more using two or more electrodes. In order to prevent welding bead failure due to flow, a DC reverse polarity power supply is used as the welding power supply, and the distance between the electrode axes of the leading electrode and the trailing electrode is 10 to 40 mm,
Also disclosed is a multi-electrode submerged arc welding method in which welding is performed such that the final trailing electrode axis makes an advancing angle of 20 to 40 degrees with respect to the vertical axis.

Japanese Patent Publication No. Sho 56-52672 discloses a single electrode or multi-electrode high-speed submerged arc welding method in which the shape of a welding groove is I-shaped, and the tip of a leading electrode is deeper than the surface of a non-welded object. By submerging and setting the welding current and voltage of the leading electrode to high current and low voltage, the arc heat is evenly distributed in the thickness direction, thereby melting the non-welded material in front of the joint while sufficiently melting it. There is disclosed a submerged arc welding method capable of flowing a metal while pushing it backward, thereby forming a smooth weld bead during high-speed welding.

[0004] The high-speed submerged arc welding method disclosed in Japanese Patent Publication No. 54-32749 and Japanese Patent Publication No. 56-52672 disclose the distance between electrodes, the electrode shaft angle, the groove shape, the depth of the electrode tip, and the like. In this method, the position of the welding electrode is adjusted to change the flow of the molten metal during welding to prevent a weld bead shape defect such as an undercut or a humping bead due to an increase in welding speed.

On the other hand, when performing high-speed submerged arc welding, electromagnetic force acts to change the flow of the molten metal during welding, thereby preventing the shape of a weld bead such as an undercut or a humping bead during high-speed welding. A method of doing so has also been proposed.

For example, Japanese Patent Publication No. 60-148679 relates to a single electrode or multi-electrode high-speed submerged arc welding method, in which a moving magnetic field generator is provided in parallel with a weld metal before solidification during welding, and a moving magnetic field generator is provided. And thrust (Lorentz force) forward (welding direction) to the molten metal due to the interaction with the eddy current generated in the molten metal by the interaction between the molten metal and the molten metal at the time of high-speed welding. Disclosed is a method for preventing the flow of the molten metal in the opposite direction to the welding direction and thereby the undercut defect.

However, Japanese Patent Publication No. 60-148679
In the case of high-speed submerged arc welding using two or more multi-electrodes, the welding method disclosed in Japanese Patent Application Laid-Open Publication No. H11-129455 increases the length of the molten pool (unsolidified molten metal) as described above, and thus suppresses the flow of the molten metal. In order to obtain sufficient thrust (Lorentz force), a large and expensive moving magnetic field generator is required.
In addition, during welding, the temperature around the molten metal is high,
Since there is a flux right above the molten metal, there is a limit in moving the moving magnetic field generator close to the molten metal, so that it is difficult to realize industrially.

Japanese Patent Application Laid-Open No. Hei 8-243750 discloses a two-electrode submerged arc welding method in which a very thick steel material having a thickness of 60 mm or more is welded with a low current in one pass. By applying an AC magnetic field synchronized with (AC), a Lorentz force is generated and this arc is directed in the direction of the succeeding electrode (opposite to the welding direction), resulting in the arc force generated from the succeeding electrode. A method is disclosed in which the flow of molten metal from the succeeding electrode to the preceding electrode is suppressed, and the pool of molten metal immediately below the preceding electrode is reduced, thereby improving the penetration depth of the preceding electrode. In Japanese Patent Application Laid-Open No. 8-243750, in addition to applying an AC magnetic field to an arc generated from a leading electrode, an AC magnetic field is applied to a molten metal between a leading electrode and a trailing electrode to apply a Lorentz force to the molten metal. Also disclosed is a method for obtaining the same effect as described above.

However, the invention disclosed in Japanese Patent Application Laid-Open No. H8-243750 discloses a method of performing gouging of a material to be welded by a pool of water immediately below a preceding electrode, which is a problem for one-pass welding of an extremely thick steel material having a thickness of 60 mm or more at a low current. For the purpose of eliminating the reduction in penetration, Lorentz force is applied to the arc generated from the leading electrode by applying an AC magnetic field or to the molten metal between the leading electrode and the trailing electrode. It is not possible to suppress the flow of molten metal behind (in the opposite direction to the welding direction) the molten metal after the last trailing electrode due to the increase in the length of the molten pool, and to prevent undercut defects in the weld bead.

Japanese Patent Application Laid-Open No. 60-240382 relates to a multi-electrode high-speed submerged arc welding method, which relates to an arc generated by flowing backward from a preceding electrode wire during high-speed welding in a vertical and vertical direction. A magnetic field is applied to apply a Lorentz force to the arc in a direction perpendicular to the left and right (lateral direction of the welding line), and the ratio between the welding current value (AC) and the magnetic flux density value (DC magnetic field) of the leading electrode wire is defined. Thus, a method is disclosed in which welding is performed while vibrating the arc of the preceding electrode wire in the lateral (vertical) direction of the welding line. This invention does not vibrate the lead electrode wire itself,
Only the arc of the leading electrode wire is electromagnetically vibrated in the lateral (vertical) direction of the welding line to prevent scattering of droplets at the wire tip and disturbance of the flux, etc. This is a method of dispersing and reducing the arc force on the molten metal, thereby suppressing the flow of molten metal behind the molten metal and preventing an undercut defect in a weld bead.

However, according to the experiments conducted by the present inventors, the method of electromagnetically vibrating the arc of the preceding electrode in the lateral (vertical) direction of the welding line does not provide a sufficient effect of preventing the undercut of the weld bead. Did not reach.

[0012]

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the prior art, an object of the present invention is to prevent a defect such as an undercut of a weld bead due to an increase in the speed of submerged arc welding of multiple electrodes. It is an object of the present invention to provide a method for effectively and efficiently suppressing the flow of molten metal behind the molten metal (reverse to the welding direction) during high-speed welding, which causes the molten metal, by using an electromagnetic effect.

[0013]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem, and its gist is as follows. (1) In a multi-electrode submerged arc welding method using an alternating current as a welding current for at least the most recent electrode, the unsolidified weld metal portion behind the most recent electrode is welded from the left and right vertical direction of the welding line. While applying an alternating magnetic field having the same frequency as the welding current, the magnetic flux density of the alternating magnetic field, the frequency phase difference between the alternating magnetic field and the welding current of the electrode, and the application position of the alternating magnetic field, according to the welding speed. A multi-electrode submerged arc welding method having an excellent weld bead shape, wherein at least one of the methods is adjusted. (2) The phase difference between the alternating magnetic field applied immediately below the tip of the last electrode and the frequency of the welding current of the last electrode is adjusted within a range of -10 ° to 10 °. The multi-electrode submerged arc welding method according to the above (1), which has an excellent weld bead shape. (3) In the case where the application position of the AC magnetic field is a distance L from the leading edge position of the unsolidified weld metal to the solidification end position,
The multi-electrode submerged arc welding method according to any one of the above (1) or (2), wherein the non-solidified weld metal is adjusted to a range of 0.5 L or less from the foremost position of the unsolidified weld metal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 4 shows a side view as viewed from a vertical section including a welding line, a plan view as viewed from above, and a cross-sectional view of the welded portion (A) when conventional three-electrode high-speed submerged arc welding is performed. FIG. 7 (b) is a cross-sectional view of a welding line in the width direction of the weld bead portion at the time of high-speed welding (the occurrence of an undercut defect) according to the conventional method.

In general, as shown in FIG. 4, when submerged arc welding is performed at a high speed, the unsolidified weld metal portion 14 behind the rearmost electrode (third electrode 3) is rearward (reverse in the welding direction). ) Is known to increase. That is, in FIG. 4, the distance between the foremost position 23 of the welded material fusion zone on the welding line 12 and the foremost position 18 of the unsolidified weld metal is defined as the retreat distance 17 of the unsolidified weld metal,
If the position of the weld toe where solidification starts the earliest on the surface of the weld bead (unsolidified weld metal part) is defined as the solidification start position 19 of the bead toe, the unsolidified weld metal is increased as the welding speed increases. The retreat distance 17 increases, and accordingly, the solidification start position 19 of the bead toe also retreats (moves in the opposite direction to the welding direction). As a result, the unsolidified weld metal is solidified in a small amount at the solidification start position 19 of the bead toe (welded section AA ′ cross-sectional view), and the weld bead toe 19 is solidified.
7B, an undercut defect 25 as shown in FIG.

The receding distance 17 of the unsolidified weld metal and the solidification start position 19 of the bead toe are determined by the arc force determined by the welding conditions and the melting force determined by the interfacial tension between the slag and the molten metal (solid or liquid), gravity, and the like. It is almost determined by the balance of the metal flow. Since the welding current increases to increase the welding current and the arc force tends to increase as the welding speed increases, the retreat distance 17 of the unsolidified weld metal increases and the bead increases. In order to prevent an undercut defect caused by the retreat of the solidification start position 19 at the toe, the welding speed at the time of welding must be regulated.

The present invention has intensively studied an effective method for suppressing the backward flow of the unsolidified molten metal formed behind the most trailing electrode, which tends to increase as the welding speed increases. As a result, an AC magnetic field having the same frequency as that of the AC welding current of the most posterior electrode is applied to the unsolidified weld metal portion behind the most posterior electrode from the right and left vertical direction of the welding line, and the electromagnetic action thereof is performed. The method of generating a pressing force from the top to the bottom of the unsolidified molten metal and adjusting the magnetic flux density, phase, and application position of the alternating magnetic field according to the welding speed is a method of retreating the unsolidified molten metal. Distance 17
It has been found that this is effective in preventing an undercut defect due to an increase in the size and a retreat of the solidification start position 19 at the bead toe.

The present invention has been made based on the above-mentioned findings, and as shown in FIG.
When performing submerged arc welding using No. 3, the welding electrode that is the most rearward in the left-right vertical direction of the welding line with respect to the unsolidified weld metal part behind the rearmost welding electrode (third electrode 3). An AC magnetic field having the same frequency as the AC welding current of the (third electrode 3) is applied, and the magnetic flux density of the AC magnetic field, the frequency phase difference between the AC magnetic field and the AC welding current of the electrode, and A multi-electrode high-speed submerged arc welding method characterized by adjusting at least one of a magnetic field application position.

According to the present invention, an AC magnetic field 8 applied to the unsolidified weld metal portion behind the welding electrode (third electrode 3) located at the rearmost position in the right and left vertical direction of the welding line, The Lorentz force 9 from the top to the bottom generated by the electromagnetic interaction with the welding current flowing in the direction opposite to the welding direction in the pool causes the rearward position of the rearmost welding electrode (third electrode 3). The unsolidified molten metal is pushed downward, and apparently, the leading edge position 18 and the solidification start position 19 of the unsolidified molten metal are pushed forward. As a result, the retreat distance 17 of the unsolidified weld metal increases with the increase in the welding speed, and the solidification start position 19 retreats (moves in the opposite direction to the welding direction).
Is suppressed, preventing the occurrence of undercut defects, etc.
High-speed welding can be performed while maintaining a good weld bead shape.

At this time, when the magnetic flux density of the AC magnetic field 8 to be applied to the unsolidified weld metal portion behind the rearmost welding electrode is changed according to the welding speed, for example, when the welding speed is increased, Adjustment is performed so as to increase the magnetic flux density of the AC magnetic field, and the pressing force 9 from the top to the bottom generated in the unsolidified molten metal is adjusted. As a result, the backward flow of the unsolidified molten metal can be suppressed with an increase in welding speed, and the occurrence of defects such as undercut defects in the welded portion can be suppressed. It is possible to secure the shape of the weld bead.

In order to adjust the magnetic flux density of the AC magnetic field, it is sufficient to adjust the magnetic flux density of the AC magnetic field so as to prevent the occurrence of weld bead defects while checking the occurrence of weld bead defects in the welded portion at that time. Investigate the relationship between the magnetic flux density of the AC magnetic field at speed and other welding conditions and the incidence of defects such as undercut defects in the weld, and adjust the magnetic flux density of the AC magnetic field according to this relationship so that welding defects do not occur. It is desirable.

Further, according to the present invention, as the welding current for the final rear electrode 3, an alternating current is used, which is cheaper than a direct current as compared with a direct current, can easily obtain a welding amount, and can obtain a soft arc. Therefore, as the magnetic field applied to the rear unsolidified weld metal portion of the electrode, an AC magnetic field having substantially the same frequency as the frequency of the AC welding current used for the electrode is used. This makes it possible to always generate the lower Lorentz force 9 and suppress the backward flow of the unsolidified molten metal.

In the present invention, an alternating current is used as the welding current for the final electrode 3 for the above reason. By setting the magnetic field to be applied to the solidified weld metal portion to a DC magnetic field and applying the magnetic field in the direction indicated by 8 in FIG. 1, the same effect as in the case of the AC current and the AC magnetic field can be obtained.

In the present invention, the phase difference between the AC magnetic field applied to the unsolidified weld metal portion behind the final rear electrode and the AC welding current of the final rear electrode is used to prevent the occurrence of undercut defects. It is necessary to set it from -10 degrees to 10 degrees. FIG. 6 shows Table 1 and welding speed: 2.1 m /
The relationship between the phase difference between the AC welding current of the final rear electrode and the AC magnetic field and the occurrence rate of undercut defects when submerged arc welding is performed under the welding conditions of min is shown. Here, the undercut occurrence rate is the total value of the undercut defect lengths per unit length of the weld bead.

From the results shown in FIG. 6, when the frequency phase difference between the AC welding current of the final rear electrode and the AC magnetic field is 0, a downward Lorentz force always acts on the unsolidified molten metal. As the phase difference increases from the range of 10 degrees (in absolute value of the phase), the rate at which the upward Lorentz force is generated in the unsolidified molten metal increases, and the effect of suppressing the backward flow of the unsolidified molten metal decreases. Therefore, the occurrence rate of undercut defects was found to increase. According to the results of the study by the inventors, this is because the unsolidified molten metal moves up and down due to the change in the direction of the Lorentz force due to the increase in the frequency phase difference between the AC welding current and the AC magnetic field of the final rear electrode. Vibration has been found to adversely affect particularly the bead toe solidification start position, which is believed to promote the occurrence of undercut defects.

Accordingly, in the present invention, in order to prevent an undercut defect occurring due to an increase in the frequency phase difference between the AC welding current and the AC magnetic field of the final rear electrode for these reasons, the AC welding of the final rear electrode is performed. The phase difference between the current and the alternating magnetic field is defined to be from -10 degrees to 10 degrees.

In the present invention, the position of the alternating magnetic field applied to the unsolidified weld metal portion behind the final rear electrode is
When the distance from the leading end position of the unsolidified weld metal to the solidification end position is L, it is necessary to adjust the distance from the leading end position of the unsolidified weld metal to 0.5 L or less. Here, the solidification end position is defined as a position where solidification ends most slowly on the surface of the 28 weld beads (unsolidified weld metal portion) shown in FIG.

FIG. 8 shows Table 1 and a welding speed of 2.1 m.
/ Min welding conditions, the magnetic field generating coil is placed at various positions in the range from the leading edge position of the unsolidified weld metal to the solidification end position, and an AC magnetic field is applied, and the AC magnetic field is applied when submerged arc welding is performed. The relationship between the position and the incidence of undercut defects is shown. Here, the undercut occurrence rate is the total value of the undercut defect lengths per unit length of the weld bead. Here, the magnetic generation coil installation position (%) on the horizontal axis in FIG. 8 indicates the distance from the leading end position of the unsolidified weld metal to the distance from the leading end position of the unsolidified weld metal to the solidification end position. It is shown as a ratio.

From the results shown in FIG. 8, the position of the AC magnetic field applied to the unsolidified weld metal portion behind the final rear electrode is defined assuming that the distance from the foremost position of the unsolidified weld metal to the solidification end position is L. 0.5L from the leading edge of unsolidified weld metal
In the following range, undercut defects do not occur,
If it exceeds 0.5 L, the occurrence of undercut defects cannot be reduced. This is because the welding current flowing in the unsolidified weld metal is distributed radially from the position directly below the tip of the electrode, so if the application position of the AC magnetic field is excessively far from the position directly below the tip of the electrode, the current will decrease, It is considered that this is because the Lorentz force generated by the electromagnetic action also decreases. For these reasons, in the present invention, the position to which the AC magnetic field is applied is set at 0.5 degrees from the most advanced position of the unsolidified weld metal.
It is defined in the range of L or less.

The present invention can be implemented with the device configuration shown in FIGS. The alternating magnetic field 8 is applied to a pair of magnetic field generating coils 4 having an iron core 5 disposed at the center of the axis with respect to an unsolidified weld metal portion behind the third electrode located rearmost of the three welding electrodes 1 to 3. Are arranged as shown in FIGS. 2 and 3, and the straight line connecting the tips of the pair of iron cores 5 is perpendicular to the welding line 12 and parallel to the surface of the workpiece 6.

At this time, the position of the tip of the iron core 5 is determined as shown in FIG. 2 in order to prevent a short circuit of the coil current due to the magnetic field generating coil being too close to the weld metal and to obtain a stable magnetic flux density. The three electrodes 3 are installed at a height of 20 mm or more in the width (lateral) direction of the material to be welded from the axial center of the wire 11 and at a height of 10 mm or more from the surface of the material to be welded, and as shown in FIG. Is desirably arranged so that the angle formed by the central axis of the above and the perpendicular to the surface of the material to be welded 6 is within 45 degrees.

[0032]

Embodiments of the present invention will be described below. FIG. 1 shows an example of a welding apparatus used in the present invention. In this case, FIGS. 2 and 3 show a positional relationship between a tip of a wire 11 of a third electrode and a tip of an iron core 5 arranged on a magnetic field generating coil 4. Was.

As an example of the present invention, the wire diameter, welding current, welding voltage,
The flat steel plate was welded at the welding speeds shown in Table 2 under the conditions of the groove shape and the magnetic field of the unsolidified weld metal portion, and the occurrence of undercut defects in the welded portion was evaluated. Further, in order to compare the effects of the present invention and the conventional method, a comparative example was performed under the same conditions as in Tables 1 and 2 except for the magnetic field conditions. Table 2 shows the results at that time.

[0034]

[Table 1]

[0035]

[Table 2]

FIG. 4 is a comparative example of the conventional method, in which no magnetic field is applied behind the last trailing electrode. FIG. 5 is a side view of the example of the present invention when a magnetic field is applied in each submerged arc welding. FIG. 7 shows a plan view and a cross-sectional view (AA ′ cross-section) of the welded portion, and FIG. 7 shows a cross-sectional view of the obtained weld bead portion in the width direction welding line.

As is clear from the results shown in Table 2, in the comparative example in which the magnetic field 8 was not applied to the unsolidified weld metal portion behind the wire 11 of the third electrode 3 located at the rearmost position, the welding speed was Undercut welding at a relatively low speed of 1.9 m / min did not produce undercut defects, but underhigh-speed welding at a welding speed of 2.1 m / min produced undercut defects 25 (FIG. 7B). On the other hand, in the example of the present invention, the welding speed was 1.9 m / min and 2.1 m / mi.
No undercut defect was generated in the weld bead toe 27 in any of the cases n, and the good bead 26 (FIG.
(A)) was obtained.

As shown in FIG. 4, when no magnetic field is applied behind the last trailing electrode of the conventional method (comparative example), the welding arc 13 increases due to the increase of the welding arc 13 at the welding speed of 2.1 m / min. The solidified weld metal 14 is easily flowed backward, the retreat distance 17 of the unsolidified weld metal increases, and the solidification start position 19 at the bead toe moves backward (moves in the opposite direction to the welding direction), so that the unsolidified welding is performed. When the amount of metal is small, the solidification start position 14 at the bead toe is solidified (cross-sectional view taken along the line AA ′ of the welded portion).
An undercut defect 25 as shown in FIG.

On the other hand, in the embodiment of the present invention, as shown in FIG. 5, the AC magnetic field 8 is applied to the unsolidified weld metal portion behind the wire of the electrode 3 located at the rearmost position, so that the Lorentz force 9 Is generated, and the flow of the unsolidified weld metal 14 in the direction opposite to the welding direction can be suppressed by the action. As a result, the welding speed was 2.1 m / min.
At the time of high-speed welding, the increase in the retreat distance 17 of the unsolidified weld metal is suppressed, and the solidification start position 19 at the bead toe is also suppressed.
7 can be prevented (welded section AA 'cross-sectional view), and FIG.
As shown in (a), a weld bead 28 having a good shape without undercut defects 27 was obtained.

[0040]

According to the present invention, it is possible to prevent defects such as undercuts generated in a weld bead due to high speed of submerged arc welding of multiple electrodes, and to increase a welding speed while maintaining a good weld bead. This makes it possible to improve the efficiency of welding work.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a submerged arc welding apparatus according to an embodiment of the present invention.

FIG. 2 is a front view showing an arrangement of an AC magnetic field applying device of the submerged arc welding device according to the embodiment of the present invention.

FIG. 3 is a side view showing an arrangement of an AC magnetic field applying device of the submerged arc welding device according to the embodiment of the present invention.

FIG. 4 is a side view and a plan view of a conventional method of submerged arc welding and a sectional view of the welded portion (AA ′ section).

FIG. 5 is a side view, a plan view, and a sectional view of a welded portion (AA ′) during submerged arc welding according to an embodiment of the present invention.
cross section)

FIG. 6 is a graph showing a relationship between a frequency phase difference between an alternating magnetic field and a welding current and an occurrence rate of an undercut defect in the present invention.

FIG. 7A shows an example of the present invention and FIG. 7B shows a comparative example.
Section of weld bead in high speed welding of steel

FIG. 8 is a graph showing the relationship between the application position of an AC magnetic field and the incidence of undercut defects in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 1st welding electrode 2 2nd welding electrode 3 3rd welding electrode 4 Magnet generating coil 5 Iron core 6 Workpiece 7 Welding direction 8 AC magnetic field 9 Lorentz force 10 Groove 11 Welding wire 12 Welding line 13 Welding arc 14 Not yet Solidified weld metal part 15 Solidified weld metal 16 Flux 17 Retreat distance of unsolidified weld metal 18 Most advanced position of unsolidified weld metal 19 Solidification start position of bead toe end 20 First electrode arc generation point 21 Second electrode arc generation point 22 Third electrode arc generation point 23 Most advanced position of welded material fusion zone 24 Unsolidified weld metal 25 Undercut defect 26 Welding current direction in unsolidified weld metal 27 Solidification end position from most advanced position of unsolidified weld metal Distance (L) 28 Solidification end position 29 Solidification weld metal 30 Weld bead toe

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshihiro Inmaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Tsutomu Shimazu 20-1 Shintomi, Futtsu-shi, Chiba New Japan F-term in Technical Development Division of Steel Corporation (reference) 4E001 AA03 BB05 DA01 DB01 DC05 DE01 DE03 DF01 4E082 AA06 AA15 BA01 BA02 EA01 EB11 HA03

Claims (3)

[Claims] 1. A multi-electrode submerged arc welding method using an alternating current for a welding current of at least a rearmost electrode, wherein a non-solidified weld metal portion behind the rearmost electrode is formed from a left-right vertical direction of a welding line. While applying an alternating magnetic field having the same frequency as the welding current of the electrode, the magnetic flux density of the alternating magnetic field, the frequency phase difference between the alternating magnetic field and the welding current of the electrode, and the application of the alternating magnetic field in accordance with the welding speed. A multi-electrode submerged arc welding method having an excellent weld bead shape, wherein at least one of the positions is adjusted. 2. A phase difference between a frequency of an alternating magnetic field applied immediately below a tip portion of the last electrode and a frequency of a welding current of the last electrode is adjusted within a range of -10 ° to 10 °. The multi-electrode submerged arc welding method according to claim 1, wherein the weld bead shape is excellent. 3. When the distance from the foremost position of the unsolidified weld metal to the solidification end position is L, the application position of the AC magnetic field is within a range of 0.5 L or less from the foremost position of the unsolidified weld metal. The multi-electrode submerged arc welding method according to claim 1 or 2, wherein the method is adjusted.