JP5120131B2 - Multi-electrode submerged arc welding method - Google Patents

Description

  The present invention relates to a multi-electrode submerged arc welding method and relates to a method suitable for pipe welding of large-diameter welded steel pipes used for natural gas, crude oil transportation line pipes, structural pipes and the like.

  In recent years, in order to reduce the total cost of natural gas or crude oil transportation pipelines, consideration has been given to the application of high-strength thick-walled large-diameter steel pipes that can increase the operating pressure, reduce the amount of steel used, and reduce the costs of on-site welding. Being started. Such welded steel pipes are required to have properties such as excellent weld quality, a beautiful weld bead appearance, and high-speed welding with high heat input. Generally, it is manufactured by double-sided single-layer welding from the inner and outer surfaces by submerged arc welding. However, in a welded portion of a high-strength steel plate or a thick steel pipe, the low temperature toughness is often lowered due to excessive heat input. In particular, this tendency is remarkable in high-strength welded steel pipes of X80 to X120 class.

  In order to increase the toughness of the welded part, it is known that it is effective to reduce the heat input of welding together with measures from the material side such as toughening of steel plates and welding materials. In order to reduce the welding heat input, it is necessary to reduce the amount of welding per unit weld length, and the groove cross-sectional area is also reduced as the amount of welding decreases. However, the reduction in the groove cross-sectional area is almost synonymous with thickening the root face in double-sided single-layer welding of steel pipes, so there is little to obtain a sound weld that does not remain undissolved on the root surface. Increasing the depth of penetration with the amount of heat input is an issue.

  In order to achieve this problem, a multi-electrode welding method in which a small-diameter (wire diameter of 3.2 mm or less) welding wire is applied to the first pole or the first and second poles has been proposed (for example, Patent Documents 1 and 2). It is described that deep welding, high welding amount, and higher welding speed can be achieved at the same time by combining welding current that can obtain high current density on thin wire, and as a result, welding heat input is greatly reduced. Has been.

  However, in the welding method, there is a concern that the amount of nitrogen in the weld metal increases due to the high-speed feeding of the welding wire as the welding speed increases. That is, submerged arc welding is a welding method in which the arc generating part is shielded from the atmosphere by a flux and mixing of nitrogen can be suppressed as much as possible, but a welding method in which the small-diameter welding wire as described above is fed at high speed. In this case, atmospheric components existing between the flux particles may be caught in a high flow velocity around the feeding wire and enter the arc cavity to increase the amount of nitrogen in the weld metal part. It is known that the amount of nitrogen in the weld metal is one of the factors that largely control the toughness of the weld metal portion, as is the amount of heat input by welding, and the amount of mixed nitrogen should be reduced.

  Furthermore, when high-speed welding is directed from the viewpoint of productivity improvement, the amount of nitrogen in the weld metal portion tends to increase with increasing welding speed (for example, Non-Patent Document 1). There are various theories regarding this cause, and no clear conclusion has been reached at this point, but the effect of welding speed on the denitrification phenomenon of droplets falling in the arc atmosphere and the effect on the nitrogen partial pressure fluctuation in the arc atmosphere The influence of the speed has been pointed out, and in any case, the increase in the amount of weld metal nitrogen due to the increase in the welding speed may be superimposed on the increase due to the high-speed feeding of the welding wire described above.

  On the other hand, as a technique for reducing the amount of nitrogen in the weld metal, it has been proposed to use a high-carbon welding wire (Non-Patent Document 2). The carbon contained in the wire aims at the effect of lowering the nitrogen partial pressure in the arc by generating CO gas in the high temperature atmosphere of the arc and reducing the amount of nitrogen taken into the molten metal. However, since the carbon content of the welding wire is set high, the carbon content of the weld metal is increased and the toughness is reduced. Under high-speed welding conditions, the arc passing speed is fast, and the molten pool shape becomes long. Even if an arc atmosphere with a reduced nitrogen partial pressure is obtained, it is difficult to completely shield the molten pool.

For this reason, Patent Document 3 and Non-Patent Document 3 disclose a technique in which a gas not containing N ₂ is allowed to flow in the dispersed flux or in the flux before spreading, and N ₂ is excluded from the gas components between the flux particles. It is disclosed. However, in the case of high-speed submerged arc welding using a thin wire, as described above, as the wire feed speed increases, the atmospheric components involved in the arc cavity increase, and the welding due to the increased welding speed. Since it is difficult to completely block the molten pool extending in the direction from the atmosphere, there is a concern that a sufficient shielding effect cannot be expected with the above method.
JP 2006-272377 A JP 2007-268564 A JP 50-33956 A Journal of the Japan Welding Society, Vol. 2 (1984), No. 3, P541 Outline of National Conference of Japan Welding Society, No. 21, (1977), P8 Outline of National Conference of Japan Welding Society, No. 18, (1976), P4

  As mentioned above, submerged high-speed welding using small-diameter wires can greatly reduce the amount of heat input, and is an extremely effective technology for the production of thick, large-diameter welded steel pipes with low-temperature toughness specifications that are expected to increase in future demand. It is. However, on the other hand, because it contains the concern of increased nitrogen content in the weld metal due to the construction method, it is desired to secure a more stable weld by investigating shield technology and welding materials. Yes.

  The present invention has been made in order to solve the above-mentioned problems, and while maintaining the characteristics of a high-efficiency submerged arc welding method characterized by high-speed feeding of a thin wire, the present invention is suitable for the application of the method. The purpose is to solve the increase in the amount of nitrogen without increasing the carbon content of the welding wire.

  As for the nitrogen amount in the weld metal of the welded joint by inner and outer surface single-layer welding, the present inventors use a large diameter (generally, 4.0 mm or more) wire and perform welding at a low speed and a small diameter (3 .2 mm or less) The case where welding was performed by high-speed welding using a wire was compared and the following knowledge was obtained. In addition, the weld joint was manufactured with the test material of the same board thickness with a thick wire and a thin wire.

(1) When welding is performed at a low speed using a large-diameter wire, a gas not containing N ₂ (hereinafter simply referred to as gas) is blown into the flux before welding and immediately before spraying, and atmospheric components between particles. It is an effective means for minimizing the amount of increase in nitrogen in the weld metal.

  (2) On the other hand, in the case of welding construction using a thin wire, it is necessary to increase the wire feeding speed as compared with welding with a large wire. There is a possibility of involving atmospheric components.

  (3) Further, when the welding speed is increased or when it is necessary to increase the distance between the electrodes from the viewpoint of the stability of the molten pool during multi-electrode welding, the shape of the molten pool extends in the weld line direction. In particular, the shielding effect due to the replacement gas in the flux sprayed from the front of the first electrode may disappear in the rear part of the molten pool, and nitrogen mixing may be significant in the rear part of the molten pool.

  (4) Further, since the welding heat input is small and the solidification speed of the weld metal is increased, the time for discharging nitrogen in the molten metal is short, and nitrogen remains in the solidified weld metal.

  (5) In order to solve these problems, at high welding speeds exceeding 1.0 m / min, it is necessary to take measures to shield atmospheric components from mixing up to the back of the molten pool.

  (6) Specifically, in multi-electrode welding, the welding line direction distance to be shielded reflects the shape of the molten pool extended by high-speed welding, and extends backward from the tip of the wire protruding position of the final electrode, and A length proportional to the welding speed is required.

The present invention has been made based on further studies based on the obtained knowledge, that is, the present invention
1. A multi-electrode submerged arc welding method with three or more electrodes in which the welding wire of the first and second electrodes has a wire diameter of 3.2 mm or less and a welding speed of 80 cm / min or more. A multi-electrode submerged arc welding method characterized in that the gas is replaced with a gas not containing ₂ and the shield from the front edge of the flux distribution position to the rear of the molten pool is covered with a shield cover for preventing air contamination.
2. When covering from the leading edge of the flux distribution position to the back of the molten pool with a shield cover for preventing air contamination, the distance L satisfies at least the formula (1) from the tip of the welding wire protrusion of the final electrode to the rear side. 2. The multi-electrode submerged arc welding method according to 1 above.

L ≧ 2 + 0.04 × v (1)
v: Welding speed [cm / min]
3. A shield cover attached to the flux transport pipe and the welding electrode in order to shield the welded portion of the multi-electrode submerged arc welder from the atmosphere, and the shield cover has the entire lower surface and a part of the outer peripheral surface opened. The interior is a hollow three-dimensional member, and the upper surface has a plurality of openings into which the flux transport pipe and the welding electrode can be inserted, respectively, and the outer peripheral surface is on the welding electrode side of the line connecting the centers of the plurality of openings. On the extension line, at least an opening having a width wider than the weld bead width is provided symmetrically across the extension line, and the three-dimensional member has a height higher than the height of the flux spraying port of the flux transport pipe. A shield cover characterized by having a full length in the direction.
4). A shield cover that is attached to the flux transport pipe and the welding electrode in order to shield the welded portion of the multi-electrode submerged arc welder from the atmosphere, the shield cover being hollow inside, and one of the upper and lower surfaces and the four circumferential surfaces. The rectangular parallelepiped has one surface open, and the rectangular parallelepiped has a non-open surface on the upper surface as an upper surface, an open surface of the four peripheral surfaces as a rear surface, and the upper surface has a flux transport pipe and a welding electrode on its width center line, respectively. It has a plurality of insertable openings, the rear surface is wider than at least the weld bead width, and the upper surface of the rectangular parallelepiped is above the flux spraying port when the flux transport pipe is inserted into the opening. Shield cover characterized by that.

  According to the present invention, while maintaining the characteristics of a high-efficiency submerged arc welding method characterized by high-speed feeding of a thin wire, an increase in the amount of nitrogen in the weld metal, which is a concern when the method is applied, is reduced. Can produce natural gas, crude oil transportation line pipes, structural pipes, etc., which can be solved without increasing the amount and require low temperature toughness, using welding wires with high efficiency and low carbon content This is extremely useful in industry.

The present invention is characterized by using a shield box having a shape optimized in accordance with the molten pool shape of multi-electrode submerged arc welding using a thin wire in addition to blowing N ₂ gas into the flux. Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically illustrating an apparatus configuration in the case of carrying out welding flux and gas shielding of a welded part in a four-electrode multi-electrode submerged arc welding method. In the figure, 1 is a flux hopper, 2 is flux transport Tubes, 3 are flux distribution ports, 4 and 4a are gas supply pipes, 5 is a shield box, 5a is the front surface of the shield box 5, 5b is the rear surface of the shield box 5, 6 is an electrode, and the first electrode at the top, 6a is The second electrode, 6b is the third electrode, 6c is the fourth electrode,
7 is a wire, 8 is an arc space, 9 is a molten pool, 10 is a weld metal, 11 is a solidified slag, 61 is an opening for inserting the first electrode 6 provided on the upper surface of the shield box 5, and 62 is a shield box 5 is an opening for inserting the second electrode 6 a provided on the upper surface of the shield 5, 63 is an opening for inserting the third electrode 6 b provided on the upper surface of the shield box 5, and 64 is a second opening provided on the upper surface of the shield box 5. An opening for inserting the four electrodes 6c, a indicates flux.

  The welding flux a is stored in the flux hopper 1 and supplied to the front of the first electrode 61 from the flux spraying port 3 via the flux transport pipe 2. Gas supply pipes 4 and 4a are attached to the flux hopper 1 and the flux spraying port 3, respectively, and a gas that excludes atmospheric components between the flux particles is injected from the vicinity of these tips.

  Furthermore, a shield box 5 is provided from the leading edge of the flux distribution position to the position where the final electrode, the fourth electrode 6c in this figure, is a certain distance on the rear side from the tip of the welding wire protrusion, The welded portion is covered from above, and air mixing between the front edge of the flux distribution position and the rear of the molten pool 9 is prevented. A part of the flux sprayed from the flux spraying port 3 usually circulates in the welding progress direction from the flux spraying port 3.

  FIG. 3 is a schematic diagram for explaining the configuration of the shield box 5. The shield box 5 is a rectangular parallelepiped having an opening on the bottom surface on the welded portion side and the rear surface 5b on the rear side in the welding progress direction. Flux transport so that the axial center of the flux transport tube 2 and the first electrode 6 (the second electrode 6a, the third electrode 6b, and the fourth electrode 6c are omitted in the drawing) is positioned on the center line 12 of the width W An opening into which the tube 2 is inserted, an opening 61 of the first electrode 6, an opening 62 of the second electrode 6a, an opening 63 of the third electrode 6b, and an opening 64 of the fourth electrode 6c are provided. The figure shows a state where the flux transport tube 2 and the first electrode 6 are inserted into the opening.

  The distance L1 between the flux transport pipe 2 and the first electrode 6 on the upper surface of the shield box 5 is set to a dimension that enables welding with the first electrode 6 after the height of the dispersed flux becomes substantially constant.

  The shield box 5 may be fixed to the flux transport pipe 2 and the first electrode 6, the second electrode 6 a, the third electrode 6 b and the fourth electrode 6 c, or may be fixed only to the flux transport pipe 2.

The height h ₁ of the shield box 5 is equal to or higher than the height h ₀ of the opening provided in the spray port of the flux transport pipe 2 to avoid contact with the flux, and the shield box 5 shown in the figure has a height of the opening. It is an addition to the dimensions of the height d to h _0.
The front surface 5a of the shield box 5 is made of a heat-resistant and flexible material such as leather so as not to involve air. The rear surface 5b on the rear side in the welding progress direction is opened to release the slag.

FIG. 2 is a schematic side cross-sectional view for explaining the lengthwise dimension of the shield box 5 and shows the rear side from the final electrode 6c. Shield box 5 includes a flux distribution opening 3 (not shown), to the distal end of the welding wire protruding portion of the final electrode 6c and the length of the position to which a constant distance L ₂ on the rear side. The distance L ₂ is _a distance satisfying at least L ₂ = 2 + 0.04 × v from the tip of the protruding portion of the welding wire of _the final electrode to the rear side. However, v: welding speed [cm / min].

When the distance L ₂ <2 + 0.04 × v, the shielding effect is insufficient, and therefore L ₂ ≧ 2 + 0.04 × v. L ₂ may be at least 2 + 0.04 × v, the upper limit is not particularly defined, and may be appropriately determined in consideration of operability and the like.

  An opening into which the electrode 6 is inserted is provided on the upper surface of the shield box 5, and the welding wire 7 is provided to the welded portion through the electrode 6. The opening of the shield box 5 is provided with a size or structure that does not cause a gap when the electrode 6 is inserted.

  The welding wire 7 is introduced into the weld through the electrode 6 to generate an arc and form an arc space 8. In the arc space 8, a molten pool 9 is formed by the molten flux, the molten welding wire 7, and the base metal melting portion. The weld pool 9 forms a weld metal 10 and a solidified slag 11 with the end of welding.

  The atmospheric components between the particles of the flux 3 are replaced by the gas supplied from the gas supply pipes 4, 4 a, and the atmospheric components are eliminated until the flux 3 is reached. However, if a large amount of gas is allowed to flow through the gas supply pipe 4a close to the flux spraying port 3, the sprayed flux may be scattered to the surroundings. It is desirable to keep it. The atmospheric components can be eliminated by using the gas supply pipes 4 and 4a alone. As described above, when only the gas supply pipe 4a close to the flux spraying port 3 is used, if a large amount of gas is flowed, the flux after spraying may be scattered to the surroundings, so that the flow rate is 10 liters / min or less. It is desirable to keep it at a minimum.

The multi-electrode submerged arc welding method targeted by the present invention achieves high-efficiency and high-speed welding using small-diameter wires, and thus contributes mainly to ensuring the penetration depth, and the welding wire feed speed is high. It is desirable to use a DC low-voltage power supply for the first electrode, which is the largest, to ensure stable deep penetration, and to use an AC power supply generally applied to submerged arc welding of pipes after the second electrode. According to the invention, until the molten metal is completely solidified, the increase in the amount of nitrogen in the weld metal is minimized even when a welding wire having a low carbon content is used by shielding air contamination between the flux particles. Can be achieved. Hereinafter, the effects of the present invention will be specifically described with reference to examples.

A low carbon content steel plate and welding wire shown in Tables 1 and ₂ are used, and a fusion type flux mainly composed of SiO ₂ —CaO—CaF ₂ is used as a welding flux. Bead-on-plate welding was performed under the welding conditions shown in FIG. The welding method is configured according to FIG. 1, and the apparatus will be described using the same reference numerals as those in FIG.

  As the welding power source, a DC low voltage or AC power source was used for the first electrode, and an AC power source was used for the second to fourth electrodes. Further, the welding speed was appropriately changed between 0.5 and 2.5 m / min, and the relationship between the welding speed and the carbon content in the weld metal was clarified.

The gas flow rate from the gas supply pipe 4 was set to 10 liter / min, and the gas flow rate from the gas supply pipe 4a was set to 5 liter / min. Further, the gas used contains no basic N _2, it was and applying the non-combustible industrial gas (Ar, CO _2, etc.).

As schematically shown in FIG. 3, the shield box 6 has a width W in the direction perpendicular to the welding line of 10 cm, and the length in the direction of the welding line is the distance behind the welding wire tip position of the final electrode (fourth electrode in this example). L ₂ is basically a value calculated by the calculation formula of claim 2. The distance from the base material surface, the opening provided in the flux distribution opening 3 height h ₀ or more, the height of the distribution opening in the case of this example 40 mm, the distance from the base material surface of the shield box Was 50 mm.

  Evaluation of the weld metal part nitrogen amount is a value obtained by subtracting the nitrogen amount NB introduced from the base metal and the welding wire from the quantitative value NW of the analysis sample collected from the center of the obtained weld metal part, ΔN (= NW−NB ). As ΔN is closer to zero, nitrogen contamination from atmospheric components is suppressed. When measuring the NW, analysis chips are collected from the center of the weld metal using a 3 mmφ drill and measured by a gas combustion method.

  Table 4 shows the results of compilation using ΔN as an index. Comparative Example No. 10-12 show the case where no shield gas is flowed and the shield box is not used. Although ΔN is slight under the condition of a welding speed of 50 cm / min, it is apparent that ΔN increases as the welding speed increases.

  Comparative Example No. 13 to 21 are results when gas is supplied from either or both of the gas supply pipes 4 and 4a. In this case, Comparative Example No. Although a decrease in ΔN is confirmed as compared with 10 to 12, it still exhibits a high value.

  On the other hand, the present invention example No. in which a shield box is installed between the flux spraying port and the distance L behind the last electrode is provided. Regarding 1 to 9, ΔN is kept low even under high-speed welding conditions up to 250 cm / min, and it can be seen that the shielding effect of the molten pool is remarkably obtained.

On the other hand, in Comparative Example No. In Nos. 22 to 27, it is clear that a part of the molten pool reaches the outside of the shield box, particularly under high-speed welding conditions, so that the shielding effect is not as high as that obtained in the examples. In the case of this example, the height of the spray port is 40 mm, and the height h ₁ from the base material surface of the shield box is 50 mm.

  Evaluation of the weld metal part nitrogen amount is a value obtained by subtracting the nitrogen amount NB introduced from the base metal and the welding wire from the quantitative value NW of the analysis sample collected from the center of the obtained weld metal part, ΔN (= NW−NB ).

  As ΔN is closer to zero, nitrogen contamination from atmospheric components is suppressed. When measuring the NW, analysis chips are collected from the center of the weld metal using a 3 mmφ drill and measured by a gas combustion method.

  Table 4 shows the results of compilation using ΔN as an index. Comparative Example No. Reference numerals 10 to 12 indicate ΔN when no shielding gas is supplied and no shield box is used. Although ΔN is slight under the condition of a welding speed of 50 cm / min, it is apparent that ΔN increases as the welding speed increases.

  Comparative Example No. 13 to 21 are results when gas is supplied from either or both of the gas supply pipes 4 and 4a. In this case, Comparative Example No. Although a decrease in ΔN is confirmed as compared with 10 to 12, it still exhibits a high value.

  On the other hand, the present invention example No. in which a shield box is installed between the flux spraying port and the distance L behind the last electrode is provided. Regarding 1 to 9, ΔN is kept low even under high-speed welding conditions up to 2.5 m / min, and it can be seen that the shielding effect of the molten pool is remarkably obtained.

  On the other hand, the comparative example No. whose distance L is shorter than a regulation value. In Nos. 22 to 27, it is clear that a part of the molten pool reaches the outside of the shield box, particularly under high-speed welding conditions, so that the shielding effect is not as high as that obtained in the examples.

The figure which illustrates typically the apparatus structure in the case of implementing a welding flux and the gas shield of a welding part in the multi-electrode submerged arc welding method of 4 electrodes. Diagram for explaining a welding wire tip position behind the distance L ₂ final electrode. The figure which shows an example of the structure of the shield box used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flux hopper 2 Flux transport pipe 3 Flux distribution port 4, 4a Gas supply pipe 5 Shield box 5a Front surface 5b Rear surface 6 Leading electrode (first electrode)
6a 2nd electrode 6b 3rd electrode 6c 4th electrode 7 Wire 8 Arc space 9 Weld pool 10 Weld metal 11 Solidification slag 61, 62, 63, 64 Opening part a Flux

Claims (4)

A multi-electrode submerged arc welding method with three or more electrodes in which the welding wire of the first and second electrodes has a wire diameter of 3.2 mm or less and a welding speed of 80 cm / min or more. A multi-electrode submerged arc welding method characterized in that the gas is replaced with a gas not containing ₂ and the shield from the front edge of the flux distribution position to the rear of the molten pool is covered with a shield cover for preventing air contamination. When covering from the leading edge of the flux distribution position to the back of the molten pool with a shield cover for preventing air contamination, the distance L satisfies at least the formula (1) from the tip of the welding wire protrusion of the final electrode to the rear side. The multi-electrode submerged arc welding method according to claim 1.
L ≧ 2 + 0.04 × v (1)
v: Welding speed [cm / min]   A shield cover attached to the flux transport pipe and the welding electrode in order to shield the welded portion of the multi-electrode submerged arc welder from the atmosphere, and the shield cover has the entire lower surface and a part of the outer peripheral surface opened. The interior is a hollow three-dimensional member, and the upper surface has a plurality of openings into which the flux transport pipe and the welding electrode can be inserted, respectively, and the outer peripheral surface is on the welding electrode side of the line connecting the centers of the plurality of openings. On the extension line, at least an opening having a width wider than the weld bead width is provided symmetrically across the extension line, and the three-dimensional member has a height higher than the height of the flux spraying port of the flux transport pipe. A shield cover characterized by having a full length in the direction.   A shield cover that is attached to the flux transport pipe and the welding electrode in order to shield the welded portion of the multi-electrode submerged arc welder from the atmosphere, the shield cover being hollow inside, and one of the upper and lower surfaces and the four circumferential surfaces. The rectangular parallelepiped has one surface open, and the rectangular parallelepiped has a non-open surface on the upper surface as an upper surface, an open surface of the four peripheral surfaces as a rear surface, and the upper surface has a flux transport pipe and a welding electrode on its width center line, respectively. It has a plurality of insertable openings, the rear surface is wider than at least the weld bead width, and the upper surface of the rectangular parallelepiped is above the flux spraying port when the flux transport pipe is inserted into the opening. Shield cover characterized by that.

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