JP2023042183A - Submerged arc weld joint and its manufacturing method - Google Patents

Abstract

To provide a manufacturing method of a multi-electrode submerged arc weld joint.SOLUTION: Steel plates 1 are brought into abutment together, and a submerged arc weld joint is manufactured by multi-electrode submerged arc welding of two or more electrodes. In spraying of a flux 4, the flux 4 is sprayed on a welding line in front of a first electrode in the welding direction from a first flux spraying port 13. Also, at least on one side at a predetermined distance apart horizontally from the weld line from a second flux spraying port 23a, the flux 4 is sprayed in a range from a position in front of a wire tip of the first electrode in the welding direction to a position behind the wire tip of a tail end electrode in the welding direction, and thereby the multi-electrode submerged arc welding is given. As a result, the occurrence of gas blow-up is suppressed to reduce variation of a bead width, and thereby undercut is suppressed. Further, the amount of oxygen and the amount of nitrogen are reduced to predetermined ranges, and thereby the weld joint having a beautiful bead exterior appearance and weld metal with high toughness is obtained.SELECTED DRAWING: Figure 1

Description

The present invention relates to a submerged arc welded joint formed by butting together thick steel plates and welding them by a multi-electrode submerged arc welding method, and a method for manufacturing the same. It also relates to a technology for suppressing the increase in the amount of steel and improving the toughness of the weld metal.

The submerged arc welding method, which is used to weld thick steel plates, is characterized by the fact that it enables highly efficient welding by using a large current. can be improved. For example, in welding large-diameter steel pipes, multi-electrode submerged arc welding such as four-electrode and five-electrode submerged arc welding is applied (see, for example, Patent Document 1).

In the submerged arc welding method, granulated flux is dispersed on the weld line of the steel plate, a welding wire is inserted into the flux, an arc is generated in the flux, and the base metal of the steel plate, the welding wire and the flux are melted. Welding is performed, but the melted flux adjusts the bead surface shape and shields the molten metal from the atmosphere to improve the mechanical properties of the weld metal.

Normally, flux is sprayed in multi-electrode submerged arc welding from a flux spray port located in front of the first electrode in the welding direction. It is necessary to secure the flux spraying height.

In order to solve such a problem, for example, Patent Document 2 discloses that a torch is provided with a plurality of welding wire supply portions spaced apart in the running direction (welding direction), and at least in front of the torch in the running direction (welding direction). A submerged arc welding apparatus is described with flux feeders at the front and back.

Further, in Patent Document 3, an electrode torch is sandwiched between flux distribution pipes arranged in front and rear of the welding direction, so that the thickness of the flux is changed so that the rear part of the electrode torch is thicker than the front part, and the flux is distributed in a submerged arc. A welding flux distribution method is described. According to this method, submerged arc welding can be performed on uphill joints with an inclination angle of 6° or more, and good beads without molten metal flow can be obtained.

In addition, Patent Document 4 describes a flux distribution method for submerged arc welding in which the flux surface temperature is detected during welding, the rotation speed of a flux distribution screw conveyor is controlled based on the result, and the flux distribution amount is controlled. ing. According to this method, the amount of flux sprayed can be controlled regardless of the welding conditions.

Further, Patent Document 5 is characterized in that the atmospheric component between flux particles before spraying is replaced with a gas that does not contain nitrogen gas, and the area from the front edge of the flux spraying position to the rear of the molten pool is covered with a shield cover. A multi-electrode submerged arc welding process with three or more electrodes is described. According to this method, it is possible to suppress an increase in the amount of nitrogen in the weld metal in high-efficiency submerged arc welding.

Further, Patent Literature 6 describes an apparatus for supplying flux to a submerged welding arc. The flux supplying device described in Patent Document 6 includes a tank in which the flux is collected, a divider to which the flux is supplied by gravity from the tank through a passage, and a movable flux suspended from the divider by gravity. and two passages for supplying flux to the front and back of the electrode, respectively. In addition, in the apparatus described in Patent Document 6, it is assumed that the tank is mounted at a predetermined height above the welding arc, and that a vacuum device is arranged to collect excess flux behind the movable electrode and lead it to the tank. there is

Japanese Patent Application Laid-Open No. 53-119240 Japanese Utility Model Laid-Open No. 59-120072 Japanese Patent Application Laid-Open No. 56-009076 Japanese Patent Application Laid-Open No. 03-013274 Japanese Patent Application Laid-Open No. 2010-029931 JP-A-55-117594

However, according to the techniques described in Patent Documents 2 to 6, the flux distribution height around each electrode in multi-electrode submerged arc welding, especially the flux distribution height around the rear electrode, is sufficiently high. There was a problem that it could not be held stably.

Normally, flux is sprayed in multi-electrode submerged arc welding from a flux spray port located in front of the first electrode in the welding direction. Because the flux is displaced to both sides of the weld line by , the height of the flux distribution around the electrode becomes lower in the rear electrode. Moreover, since a large current is used in submerged arc welding, the arc pressure is high and the flux spraying height is low at the rear electrode, which causes strong gas blow-up, making it difficult to obtain the effect of shielding the molten metal from the atmosphere. As a result, the amount of oxygen and nitrogen in the weld metal increases, degrading the mechanical properties of the weld metal, and blowing up the gas makes it difficult to obtain a beautiful bead appearance. In particular, this tendency becomes stronger as the number of electrodes increases. In particular, when a flux with a low bulk density and a coarse particle size is used, the arc pressure cannot be suppressed by the flux, making it difficult to suppress the occurrence of gas blow-up.

The present invention solves the problems of the prior art described above, prevents the occurrence of gas blow-up, and has excellent mechanical properties that can produce a submerged arc welded joint having a beautiful bead appearance and a weld metal with low oxygen and nitrogen contents. An object of the present invention is to provide a method for manufacturing an excellent submerged arc welded joint.

In order to achieve the above-described object, the present inventor produced welded joints by butting thick steel plates together, using the multi-electrode submerged arc welding method, and variously changing the flux distribution method. During welding, the state of blown gas was observed, and the appearance of the bead and the amount of oxygen and nitrogen in the weld metal were measured for the welded joint obtained.

As a result, in addition to dispersing the flux from the first flux sprinkling port on the weld line forward in the welding direction of the preceding electrode (first electrode), a second flux sprinkling port is further provided to disperse the flux from the weld line. It occurred to me to distribute the flux at least on one side at a predetermined distance in the horizontal direction and in the installation range of the electrodes along the welding direction. This makes it possible to stably secure the desired flux distribution thickness from the vicinity of the leading electrode to the periphery of the last electrode, prevent gas blow-up during welding, have an excellent bead appearance, and keep the amount of oxygen and nitrogen within the appropriate range. It has been found that submerged arc welded joints with reduced weld metal can be obtained.

The present invention has been completed based on these findings and further studies. That is, the gist of the present invention is as follows.
[1] The weld metal of the welded joint contains 250 to 350 ppm oxygen and 30 to 60 ppm nitrogen, and the difference between the maximum and minimum bead widths of the weld metal is 3.0 mm or less. A submerged arc welded joint characterized by:
[2] When thick steel plates are butted against each other to manufacture a submerged arc welded joint by multi-electrode submerged arc welding, a flux spraying device having first and second flux spraying ports is used, and the first flux spraying port is used. Disperse the flux from the first electrode of the multiple electrodes onto the weld line ahead of the first electrode in the welding direction, and distribute the flux from the second flux spray port to at least one side that is horizontally away from the weld line by a predetermined distance. In the range from the position in front of the wire tip of the first electrode in the welding direction to the position behind the wire tip of the rearmost electrode of the multi-electrodes in the welding direction, the multi-electrode submerged arc welding is performed. A method for manufacturing a submerged arc welded joint, characterized by:
[3] The submerged arc according to [2], wherein a predetermined distance from the welding line in the horizontal direction is 20 to 100 mm from the welding line to the end of the second flux spraying port. A method for manufacturing a welded joint.
[4] The flux spraying device includes a flux storage tank for storing flux, a first flux supply pipe connected to the flux storage tank for supplying the flux, and a flux supply pipe connected to the first flux supply pipe. a first flux sprinkling port for sprinkling the flux, a second flux feeding pipe connected to the flux storage tank for feeding the flux, and a second flux feeding pipe connected to the second flux feeding pipe a second flux spraying port for spraying flux, wherein the first flux spraying port is a flux spraying port for spraying the flux onto the weld line forward in the welding direction of the first electrode; 2, the flux spraying port is a spraying port that sprays the flux on at least one side that is horizontally away from the welding line by a predetermined distance, and the second flux spraying port has a front end in the welding direction, The welding direction rear end of the second flux spray port is located forward in the welding direction from the position of the wire tip of the first electrode, and the welding direction rearward from the position of the wire tip of the rearmost electrode. The method for manufacturing a submerged arc welded joint according to [2] or [3], characterized in that the second flux spraying port is provided in the above.
[5] The method for manufacturing a submerged arc welded joint according to [4], wherein the cross-sectional area of the first flux feed pipe and the second flux feed pipe is 600 mm ² or more over the entire length. .
[6] In [4] or [5], characterized in that the inclination angle with respect to the horizontal plane of the central axes of the first flux feeding pipe and the second flux feeding pipe is 30° or more over the entire length. A method of manufacturing the described submerged arc welded joint.
[7] Manufacture of a submerged arc welded joint according to any one of [2] to [6], wherein the thick steel plate is a thick steel plate having a thickness of 20 mm or more and a tensile strength of 415 MPa or more. Method.

According to the present invention, a multi-electrode submerged arc welded joint having high-toughness weld metal that can suppress the occurrence of gas blow-up around the electrodes and fluctuations in bead width, can further reduce the oxygen content and nitrogen content to a predetermined range, and It can be done, and there is a remarkable effect in industry. Moreover, according to the present invention, it is possible to suppress the undercut by suppressing the fluctuation of the bead width.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows typically an example of the flux distribution apparatus which can be used by this invention. FIG. 4 is an explanatory diagram schematically showing an arrangement example of first and second flux spraying ports; It is explanatory drawing which shows typically the groove shape used in the Example. It is explanatory drawing which shows the sampling point of a Charpy impact test piece.

The present invention is a method for manufacturing a submerged arc welded joint in which thick steel plates are butted together and a submerged arc welded joint is obtained by multi-electrode submerged arc welding with two or more electrodes.

The obtained submerged arc welded joint is a single-layer or multi-layer welded joint depending on the plate thickness of the thick steel plate to be used, desired welding conditions, and the like.

The thick steel plate used in the present invention is preferably a steel plate having a thickness of 20 mm or more and a tensile strength of 415 MPa or more.

Next, the prepared thick steel plates are butted against each other, the butted surfaces are grooved in a predetermined shape, and multi-electrode submerged arc welding with two or more electrodes is performed using welding wire and flux to form a submerged arc welded joint. obtain.

The welding wire to be used is preferably selected from solid wires (commercially available) for submerged arc welding specified in JIS Z 3351 that are suitable for the above-described thick steel plates that are the materials to be welded, but flux cored wires are also applicable. . The welding wire to be used is preferably 2.4 mmΦ or more from the viewpoint of welding stability.

Moreover, the flux to be used is preferably selected from submerged arc welding fluxes (commercially available) specified in JIS Z 3352 that are compatible with the above-described thick steel plates. Any of molten type, fired type and sintered type can be used as the flux to be used.

In the present invention, the welding conditions for multi-electrode submerged arc welding are not particularly limited as long as a desired weld joint can be formed. Any welding conditions such as shape, current, voltage and current density can be applied. For example, the interval between adjacent electrodes is preferably 8 to 30 mm, which is the interval between wire tip positions measured on the surface of the steel plate. If the distance between the electrodes is less than 8 mm, the distance is too narrow, and the contact tips for power supply may come into contact with each other.

As for the inclination angle of each electrode, the line perpendicular to the steel plate is 0°, the inclination angle of the first electrode with respect to the welding direction is -20 to 0°, and the inclination angle of the electrodes after the second electrode is immediately before is preferably in the range of 5 to 25° with respect to the electrodes. Regarding the tilt angle, the + side means the forward angle side, and the - side means the backward angle side.

The welding speed of multi-electrode submerged arc welding does not have to be particularly limited and can be determined as needed, but it is preferably about 500 to 5000 mm/min from the viewpoint of welding workability.

In the present invention, the flux is preferably spread using a flux spreading device 100, one example of which is shown in FIG. The flux spraying device 100 used in the present invention has a first flux sprinkling port 13 surrounding a plurality of electrodes (five electrodes 31 to 35 in FIG. 2), and a first Preferably, the device is provided with two flux sprinkling ports 23a and/or 23b.

The first flux sprinkling port 13 is arranged at a predetermined position on the weld line in front of the first electrode 31 of the multiple electrodes in the welding direction so that the flux can be spread on the weld line with an appropriate width. The shape of the outlet side of the first flux sprinkling port 13 is not particularly limited, but is preferably circular, square, rectangular, or elliptical. The first flux sprinkling port to be used does not need to have a constant cross-sectional area, but preferably has a minimum cross-sectional area of 600 mm ² or more so that the flux does not clog the flux feed pipe.

Further, the second flux spraying ports 23a and 23b are, for example, as shown in FIG. ) on at least one side a predetermined distance B horizontally from the weld line so as to maintain a proper flux distribution height around the multi-electrode perimeter. In addition, as shown in FIG. 2(a), the second flux spraying port is arranged on both sides of the weld line so that the flux can be uniformly distributed in the direction perpendicular to the weld line. It is preferable from the viewpoint that a left-right symmetrical reinforcement can be formed. The "predetermined distance B" referred to here is the distance B from the welding line to the ends of the second flux distribution ports 23a and 23b, and is preferably 20 to 100 mm. If the distance B from the welding line to the end of the flux sprinkling port is less than 20mm, there is a high risk of interference between the welding torch and the flux sprinkling port. Become.

Further, the second flux spraying ports 23a, 23b are arranged such that the front end portion of the second flux spraying port in the welding direction is located forward in the welding direction from the position of the tip of the welding wire of the first electrode. are positioned rearward in the welding direction from the position of the tip of the welding wire of the rearmost electrode. This makes it possible to maintain a uniform and appropriate flux distribution height around the multiple electrodes from the first electrode to the rearmost electrode.

The outlet side shape of the second flux sprinkling ports 23a and 23b is not particularly limited, but is preferably rectangular. The second flux sprinkling port to be used does not need to have a constant cross-sectional area, but preferably has a minimum cross-sectional area of 600 mm ² or more so that the flux does not clog the flux feed pipe.

In the flux sprinkling device 100 used in the present invention, one end of the flux feeding pipe is connected to each entrance side of the flux sprinkling port described above. Further, the other end of the flux feeding pipe is connected to the flux storage tank so that the stored flux can be fed to the flux sprinkling port.

One end of a first flux feed pipe 12 is connected to the first flux sprinkling port 13, and the other end of the first flux feed pipe 12 is connected to the flux storage tank 11. can be fed to the flux spray port. Similarly, one end of the second flux feeding pipes 22a, 22b is connected to the second flux spraying ports 23a, 23b, respectively, and the other end of the second flux feeding pipes 22a, 22b A flux storage tank 21 (11) is connected to the end.

In the present invention, connection of the flux spraying port, the flux feed pipe, and the flux storage tank is not limited to the connection method described above. One flux feeding pipe is connected to the flux storage tank, and the connected flux feeding pipe is branched in the middle, and two flux sprinkling ports are connected to each branched end. may For example, the flux spraying device used in the present invention comprises a flux storage tank for storing flux, one flux feeding pipe connected to the flux storage tank for feeding the flux, and the one flux feeding pipe. A flux feeding pipe branched in the middle, a first flux spraying port connected to one end of the branched flux feeding pipe to spray the flux, and the other end of the branched flux feeding pipe and a second flux sprinkling port connected to and sprinkling the flux.

The cross-sectional shape of the flux feed pipe is not particularly limited, but a circular shape is preferable. Furthermore, the minimum cross-sectional area of the flux feed pipe is preferably 600 mm ² or more in order to prevent clogging of the flux in the feed pipe. In addition, it is more preferably 1200 mm ² or more. From the viewpoint of workability, the flux feed pipe is preferably made of a material that can be bent relatively freely, such as vinyl chloride or silicone rubber.

Further, the flux feed pipes 12, 22 extend over the entire length from the flux storage tank 11 (21) to the flux sprinkling ports 13, 23 at an angle α (°) with respect to the horizontal plane measured along the center line of the pipe, α: It is preferable to arrange it so that it is kept at 30° or more. If the angle of the flux feed pipe with respect to the horizontal plane is small, such as when α is less than 30° relative to the horizontal plane, the flux will stay inside the pipe, and the height of the flux distribution around the electrode will become smaller, making it easier for gas to blow up. Become.

The flux storage tank 11 (21) is a storage container for storing the flux 4, and is not particularly limited as long as it can store the amount of flux required for submerged arc welding. The flux storage tanks may be separately arranged for the first flux sprinkling port 13 and the second flux sprinkling port 23, but there is no problem in using them in common due to the installation location.

FIG. 1 shows only the flux spraying device 100, the plurality of electrodes (contact tips) 3, and the welding wire 2, and the welding wire supply means, welding power source, etc. connected to each electrode are omitted from the illustration. However, any conventional welding device (welding power source, control device, welding machine, etc.) can be applied. In addition, it is preferable to scatter the flux along the welding line before welding, or to scatter the flux ahead of the welding point in the welding direction in conjunction with the welding machine.

Also, for multi-electrode submerged arc welding, the proper height of flux distribution is a height sufficient to cover the contact tip of each electrode with flux, that is, approximately 30 to 40 mm from the surface of the material to be welded (steel plate). It is preferable to set it as a degree.

In the present invention, when performing multi-electrode submerged arc welding using a flux spraying device for multi-electrode submerged arc welding as shown in FIG. (Steel plate) It is preferable to adjust the height from the surface to the height described above. As a result, the arc of a plurality of electrodes can be covered with flux, there is no blow-up of gas during welding, the bead width is excellent in stability, and excellent quality weld metal can be obtained.

The submerged arc welded joint obtained by butting the above thick steel plates and by multi-electrode submerged arc welding under the above welding conditions has a composition containing 250 to 350 ppm of oxygen and 30 to 60 ppm of nitrogen, and a bead width The weld metal has a difference of 3.0 mm or less between the maximum and minimum values of

If the amount of oxygen in the weld metal exceeds 350 mass ppm or the amount of nitrogen exceeds 60 mass ppm, intergranular ferrite is formed and the toughness of the weld metal is lowered. On the other hand, when the oxygen content of the weld metal is less than 250 mass ppm and the nitrogen content is less than 30 mass ppm, bainite is formed instead of intragranular acicular ferrite, resulting in a decrease in weld metal toughness. In order to obtain such oxygen and nitrogen contents in the weld metal, it is necessary to perform stable welding without blowing up of gas. , it is necessary to adopt a flux distribution method as in the present invention.

Moreover, if the difference between the maximum and minimum values of the bead width of the weld metal exceeds 3.0 mm, an undercut with a depth of 0.5 mm or more occurs and the bead appearance deteriorates.

The present invention will be further described below based on examples.

A thick steel plate (plate thickness: 38 mm, tensile strength 590 MPa) having the chemical composition shown in Table 1 was prepared. Two (pair) test plates (length: 1200 mm) 1, 1' were sampled from the prepared thick steel plate, and as shown in Fig. 3, the angle: 70 °, groove depth: 15 mm single-sided Y opening The ends were beveled and butted together to form a test piece. Then, using these specimens, submerged arc welded joints (normal weld length: 1000 mm) were produced by multi-electrode submerged arc welding.

In addition, multi-electrode submerged arc welding is performed by five-electrode submerged arc welding with the electrode arrangement shown in Table 4, and for multi-electrode submerged arc welding having first and second flux spray ports, one example of which is shown in FIG. Flux was sprayed using a flux sprayer. As the flux, a commercially available sintered flux (bulk density: 1.2 g/ml, average particle size: 800 µm) having the composition shown in Table 2, which is specified in JIS Z 3351 and conforms to the thick steel plate, was used. used a commercially available welding wire (diameter: 4.0 mmΦ) having the composition shown in Table 3, which is specified in JIS Z 3352 and conforms to the thick steel plate.

In carrying out multi-electrode submerged arc welding, as shown in Table 5, the minimum cross-sectional area and minimum inclination angle of the flux feed pipe in the flux spraying device, and the arrangement of the flux spraying port were changed to achieve flux spraying. Conditions were varied. The arrangement of the flux sprinkling ports used was as shown in FIGS. 2(a) to 2(f).

In FIG. 2(a), the first flux spraying port 13 is arranged on the weld line, and the second flux spraying ports 23a and 23b are arranged on both sides of the weld line with a predetermined distance B in the horizontal direction. FIG. 2B shows the case where the first flux sprinkling port 13 is arranged on the weld line, and the second flux sprinkling port 23a is arranged on one side horizontally away from the weld line by a predetermined distance B. is the case. 2(a) and 2(b), the end portion of the second flux spraying port 23 forward in the welding direction is positioned forward in the welding direction from the welding wire of the first electrode 31, and the second The rear end of the flux spraying port 23 in the welding direction is positioned rearward in the welding direction from the welding wire of the rearmost electrode 35 .

Moreover, FIG. 2(c) is a comparative example in which only the first flux spraying port 13 is arranged on the weld line, and FIG. FIG. 2(e) and FIG. 2(f) show the case where only the second flux spraying ports 23a and 23b are arranged on both sides, and FIG. 2(e) and FIG. In the case where the second flux spraying ports 23a and 23b are arranged on both sides separated by a predetermined distance B in the welding direction, in FIG. is positioned forward of the welding wire of the rearmost electrode 35, and in FIG. It is a comparative example arranged so as to be in a more rearward position.

The first flux sprinkling port 13 has a circular cross section, and the cross section on the sprinkling port outlet side has a cross-sectional area equal to or larger than the minimum cross-sectional area of the flux feed pipe. The second flux sprinkling port 23a has a cross-sectional area on the outlet side of the sprinkling port that is equal to or larger than the minimum cross-sectional area of the flux feed pipe.

The cross-sectional areas of the flux feed pipes 12 and 22 are set within the appropriate range shown in Table 5 so that the flux can be fed by gravity, and the minimum inclination angle α with respect to the horizontal plane in the entire route is set to The angles shown in Table 5 were adjusted. The flux feed pipe was made of silicon rubber.

Then, multi-electrode submerged arc welding was performed. Welding conditions were as shown in Table 6. The welding speed was 1000 mm/min and the welding heat input was 9.83 kJ/mm. In welded joint No. 13, Ar gas was blown into the flux storage tank before welding to perform gas purging to drive out the air existing between flux grains.

During welding, the occurrence time of gas blow-up was measured. From the obtained occurrence time of gas blow-up, ◎ indicates that gas blow-up does not occur, ○ indicates that gas blow-up occurs continuously for less than 3 seconds, and x indicates that gas blow-up occurs continuously for 3 seconds or more. The gas blowing property was evaluated.

In addition, the bead was observed in the stationary portion of the obtained welded joint, and if there was an undercut, a sample was taken from the portion and the macroscopic shape of the cross section was observed to measure the depth of the undercut. ◎ indicates no undercut, ○ indicates that there is an undercut and the depth is less than 0.5 mm, and x indicates that there is an undercut and the depth is 0.5 mm or more. bottom.

Furthermore, for the steady portion of the obtained welded joint, the bead width was measured at intervals of 10 mm along the weld bead using a vernier caliper from the surface, the maximum and minimum values were obtained, and the difference was calculated. If the difference between the maximum and minimum values of the obtained bead width is less than 2.0 mm, the bead width stability is indicated by ◎, if it is 2.0 mm or more and 3.0 mm or less, and x if it exceeds 3.0 mm. evaluated.

Furthermore, samples for analysis were taken from the weld metal part of the obtained welded joint at intervals of 100 mm along the welding direction, and the amount of oxygen and nitrogen contained in the weld metal was analyzed using infrared absorption analysis. , the maximum and minimum values of oxygen content and nitrogen content in the welded joint were obtained.

In addition, Charpy impact test pieces (V notch) were taken from a position 2 mm below the surface layer of the steel plate at intervals of 100 mm along the welding direction so that the notch position was at the center of the weld metal from the weld metal part of the welded joint obtained. Then, a Charpy impact test was carried out at a test temperature of -30°C to determine the absorbed energy vE _-30 (J) and evaluate the impact properties. Fig. 4 shows the sampling position of the Charpy impact test piece (V notch).

Table 7 shows the results obtained.

In all of the present invention examples, no gas blow-up occurred continuously for 3 seconds or more during welding (evaluation: ⊙ and ◯), gas blow-up could be prevented, and the maximum and minimum values of the bead width of the weld metal The difference is 3.0 mm or less (evaluation: ◎ and ○), showing excellent bead width stability, and the oxygen content in the weld metal is 250 mass ppm to 350 mass ppm, and the nitrogen content is 30 mass ppm to 60 mass ppm. As shown below, the oxygen content and nitrogen content in the weld metal are reduced to within the appropriate range, and the toughness of the weld metal is improved.

Furthermore, among the examples of the present invention, the cross-sectional areas of the flux feed pipes 12 and 22 are both 600 mm ² or more over the entire length, the minimum inclination angles of the flux feed pipes 12 and 22 with respect to the horizontal plane are both 30° or more, and the second In the case of welded joints No. 6 to No. 8 satisfying the condition that the flux spraying ports 23 are provided on both sides of the weld line and the predetermined distance B in the horizontal direction from the weld line is within the range of 20 to 100 mm , there is no gas blow-up (◎), the difference between the maximum and minimum bead width is less than 2.0 mm (◎), and the bead width stability is particularly excellent. The amount of nitrogen and the amount of nitrogen are kept low within the appropriate range, and the toughness of the weld metal is improved.

On the other hand, in the comparative example in which the flux was sprayed outside the scope of the present invention, during welding, gas blow-up occurred violently, the bead width became unstable, deep undercuts occurred, and oxygen in the weld metal was reduced. The amount of nitrogen exceeds 350 mass ppm, the nitrogen content exceeds 60 mass ppm, and the Charpy impact test absorbed energy vE _-30 is less than 100 J at the test temperature: -30°C, and the weld metal toughness is reduced. In welded joint No. 13, due to gas purging, the oxygen content in the weld metal is less than 250 mass ppm, the nitrogen content is less than 30 mass ppm, and vE _-30 of the weld metal is less than 100 J, indicating that the weld metal toughness is low. .

1 thick steel plate 2 welding wire 3 contact tip (electrode)
4 Flux 7 Weld metal 8 Charpy impact test piece 11 Flux storage tank (flux hopper)
12 first flux feeding pipe 13 first flux sprinkling port 21 flux storage tank (flux hopper)
22, 22a, 22b Second flux feed pipes 23, 23a, 23b Second flux sprinkling port 31 First electrode 35 Last electrode (fifth electrode)
100 Flux spraying device for multi-electrode submerged arc welding (flux spraying device)

Claims (7)

The weld metal of the weld joint contains 250 to 350 ppm oxygen and 30 to 60 ppm nitrogen, and the difference between the maximum and minimum bead widths of the weld metal is 3.0 mm or less. submerged arc welded fittings. In manufacturing a submerged arc welded joint by butting together thick steel plates by multi-electrode submerged arc welding, a flux spraying device having first and second flux spraying ports is used, and flux is supplied from the first flux spraying port. , the first electrode of the multi-electrode is sprayed onto the weld line in front of the welding direction, and the second flux sprinkling port distributes the flux on at least one side horizontally away from the weld line by a predetermined distance, the The multi-electrode submerged arc welding is performed by dispersing in a range from a position in front of the wire tip of the first electrode in the welding direction to a position behind the wire tip of the rearmost electrode of the multi-electrodes in the welding direction. A method of manufacturing a submerged arc welded joint, comprising: 3. The submerged arc welded joint according to claim 2, wherein the predetermined horizontal distance from the weld line is 20 to 100 mm from the weld line to the end of the second flux spray port. Production method. The flux spraying device includes a flux storage tank for storing flux, a first flux supply pipe connected to the flux storage tank for supplying the flux, and a flux supply pipe connected to the first flux supply pipe for supplying the flux. further, a second flux feeding pipe connected to the flux storage tank for feeding the flux; and a second flux feeding pipe connected to the second flux feeding pipe for spraying the flux and a second flux sprinkling port, wherein the first flux sprinkling port is a flux sprinkling port for spraying the flux on the weld line ahead of the welding direction of the first electrode, and the second flux The spray port is a spray port that sprays the flux on at least one side that is horizontally away from the weld line by a predetermined distance, and the front end of the second flux spray port in the welding direction is the first flux spray port. The above-described 4. A method for manufacturing a submerged arc welded joint according to claim 2 or 3, wherein a second flux distribution port is provided. 5. The method for manufacturing a submerged arc welded joint according to claim 4, wherein the cross-sectional area of said first flux feed pipe and said second flux feed pipe is 600 mm ^<2> or more over the entire length. 6. The submerged arc welding according to claim 4 or 5, characterized in that the inclination angle of the central axes of the first flux feed pipe and the second flux feed pipe with respect to the horizontal plane is 30° or more over the entire length. Method for manufacturing fittings. The method for manufacturing a submerged arc welded joint according to any one of claims 2 to 6, wherein the thick steel plate has a thickness of 20 mm or more and a tensile strength of 419 MPa or more.

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