JP2015223605A - Narrow groove gas-shield arc-welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a narrow groove gas-shield arc-welding method of a thick steel material, capable of effectively preventing a defect by a hot rack and a lack of fusion, and capable of also attaining an improvement in welding execution efficiency, without executing mending of a groove face, even when applying low-cost groove processing by gas cutting and plasma cutting.SOLUTION: A gas-shield arc-welding method is provided for joining a thick steel material 1 of a predetermined groove condition by multilayer welding of a narrow groove, and initial layer welding is set as multielectrode welding of two electrodes or more, and a first electrode 4 and a second electrode 5 are arranged along predetermined parallel welding lines 7, and one of welding wires 4b and 5b supplied from power supply tips 4a and 5a on the welding torch tip of the first electrode and the second electrode, is set to a wire minus (positive polarity), and the other is set to a wire plus (reverse polarity), and the welding depth in a bottom part of the thick steel material is set to 1.5 mm or more, by properly controlling relative arrangement of the first electrode and the second electrode.

Description

The present invention relates to a gas shielded arc welding method, and more particularly to a narrow gap gas shielded arc welding method for thick steel materials.
In the present invention, “narrow groove” means that the groove angle is 25 ° or less and the minimum groove width between the steel materials to be welded is 50% or less of the plate thickness of the steel material. .

The gas shielded arc welding used for welding of steel is generally a consumable electrode type using a gas of CO ₂ alone or a mixed gas of Ar and CO ₂ as a shield for a molten part. Widely used in the field of manufacturing electrical equipment and the like.

  By the way, in recent years, with the increase in the size and thickness of steel structures, the amount of welding in the manufacturing process, particularly butt welding of steel materials, has increased, and more time is required for welding work, resulting in increased construction costs. Is invited.

  As a method for improving this, it is conceivable to apply narrow gap gas shielded arc welding in which a gap having a small gap with respect to the plate thickness is subjected to multilayer welding by arc welding. This narrow gap gas shielded arc welding has a smaller amount of welding than normal gas shielded arc welding, so that it is possible to achieve higher efficiency and energy saving of welding, and consequently to reduce the construction cost.

As a technique related to such narrow gap gas shielded arc welding, Patent Document 1 discloses that the hole of the shield gas ejection port for welding is formed into an oblong (elliptical) shape to improve the diffusibility of the shield gas, and torch. Discloses a narrow groove MIG welding torch in which the hole of the contact tip is made into an oval shape and the weaving direction of the welding wire is always fixed, and a welding method using the same.
In this welding method, one-pass lamination welding is performed per layer using an inert gas. However, in such one-pass welding per layer, heat concentrates in the central portion of the groove, so that the groove surface of the steel material is insufficiently melted and the melting depth becomes small. In order to compensate for this, the welding wire has a constant weaving direction to ensure a fusion depth at the groove surface and reduce welding defects due to poor penetration.

Patent Document 2 discloses a tip for submerged welding in which one side surface of a tip end portion of a tip of a welding torch is protruded and the protruding portion is curved so as to be concave along a through hole.
This submerged welding tip uses a winding of the welding wire and feeds the welding wire in a bent state from the tip, thereby generating an arc at a position close to the groove surface and melting depth at the groove surface. To reduce welding defects due to poor penetration.

However, in the techniques described in Patent Documents 1 and 2, it is not always sufficient to melt the groove surface of the steel material. Therefore, in the techniques of Patent Documents 1 and 2, in order to effectively suppress welding defects due to poor penetration or the like, it is necessary to perform extremely high-precision and clean machining as the groove processing of the steel material.
On the other hand, in general structures such as buildings, bridges and shipbuilding, excluding high-value-added steel structures, from the viewpoint of cost, etc., groove processing by gas cutting, plasma cutting, etc. is performed and used for welding as it is. Is normal. Groove processing by gas cutting or plasma cutting is low cost and easy to construct. However, groove processing by gas cutting, plasma cutting, or the like has a tendency that the surface of the groove surface becomes rough, that is, the unevenness of the surface becomes large, and it is difficult to perform high-precision processing such as machining.
For this reason, it is difficult to apply the techniques described in Patent Documents 1 and 2 to general structures such as buildings, bridges, and shipbuilding.

JP-A-7-116852 Japanese Patent Laid-Open No. 50-67758 Japanese Patent Application No. 2012-265521 JP 2005-246478 A

  In order to solve the above problem, the inventors previously described in Patent Document 3 that “the bottom groove angle is 10 ° or less, the bottom groove gap is 7 mm or more and 15 mm or less, and the thickness is 22 mm or more. In a gas shielded arc welding method in which steel materials are joined by narrow gap multi-layer welding, the first layer welding is divided into two or more passes, and each pass is distributed to both sides of the bottom groove gap and further supplied from the power feed tip at the tip of the welding torch. Narrow groove gas shielded arc welding characterized in that the melting depth at the bottom of the thick steel material is 1.5 mm or more by controlling the wire supply angle in the range of 5 ° to 15 ° with respect to the perpendicular. Method. "

With the development of the narrow groove gas shielded arc welding method described in Patent Document 3 above, it becomes possible to ensure a melting depth of 1.5 mm or more from the groove surface at the bottom of the thick steel material. Narrow groove gas shielded arc welding that does not cause defects due to high-temperature cracking, poor fusion, etc., for general structures such as gas cutting and plasma cutting, as well as general structures such as bridges and shipbuilding It became possible to do.
However, in the technique of Patent Document 3, since the number of welding passes is large and the welding work efficiency tends to be low, improvement of this point has been desired.

  The present invention relates to an improvement of the narrow groove gas shielded arc welding method disclosed in Patent Document 3 above, and even when performing low-cost groove processing such as gas cutting or plasma cutting, Provided is a narrow gap gas shielded arc welding method for thick steel materials, which can effectively prevent defects due to hot cracking, poor fusion, etc. without performing maintenance etc., and can also improve the welding efficiency. For the purpose.

Now, in order to solve the above-mentioned problems, the inventors tried to perform the first layer welding in Patent Document 3 as multi-electrode welding in one pass.
However, if the first layer welding is simply multi-electrode welding, the arc will interfere with each other and the heat will tend to concentrate in the center of the groove, resulting in the opening at the bottom of the thick steel material. The front surface was not sufficiently melted.

Therefore, the inventors further studied the groove conditions and welding conditions that can obtain sufficient melting of the groove surface at the bottom of the thick steel material when the first layer welding is multi-electrode welding.
As a result, for the groove conditions in narrow groove gas shielded arc welding,
(a) Bottom groove angle: 25 ° or less
(b) Bottom groove gap: 7 mm or more and 18 mm or less,
In addition, for welding conditions,
(c) The first layer welding is multi-electrode welding of two or more electrodes, the first electrode and the second electrode are arranged along a predetermined parallel welding line,
(d) About the welding wire supplied from the power supply tip at the tip of the welding torch of the first electrode and the second electrode, one is a wire minus (positive polarity), the other is a wire plus (reverse polarity),
(e) Properly controlling the relative arrangement of the first electrode and the second electrode during welding construction,
We obtained the knowledge that melting depth at the bottom of thick steel material: 1.5mm or more is achieved stably and is extremely important for welding with high welding efficiency.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. In the gas shield arc welding method in which the bottom groove angle is 25 ° or less, the bottom groove gap is 7 mm or more and 18 mm or less, and the thick steel material having a plate thickness of 22 mm or more is joined by multi-pass welding of narrow grooves,
The first layer welding is multi-electrode welding of two or more electrodes, and the first electrode and the second electrode are arranged along a predetermined parallel welding line,
One of the first electrode and the second electrode is wire minus (positive polarity), the other is wire plus (reverse polarity),
Further, the distance between the tip of the welding wire supplied from the power supply tip at the tip of each welding torch of the first electrode and the second electrode is within a range of 5 mm to 16 mm, and the first electrode is perpendicular to the direction of the welding line. By controlling the angle of the straight line connecting the welding wire tips of the second electrode within a range of 45 ° or less,
A narrow groove gas shielded arc welding method in which the melting depth at the bottom of the thick steel material is 1.5 mm or more.

2. 2. The narrow groove gas shielded arc according to 1 above, wherein, in the first layer welding, a supply angle of each welding wire of the first electrode and the second electrode with respect to each bottom groove is 5 ° or more and 15 ° or less with respect to the perpendicular. Welding method.

3. In the first layer welding, the distance between the side ends of the welding wire tips of the first electrode and the second electrode at the bottom groove and the groove surface of the thick steel material is 0.5 mm or more and 3.0 mm or less. 2. The narrow groove gas shielded arc welding method according to 2.

4). The said 1st layer welding WHEREIN: As the welding wire sent to the electric power feeding chip | tip of the said 1st electrode and the said 2nd electrode, the wire curved in the range from which a curvature radius is 150 mm or more and 300 mm or less uses said 1-3. Narrow groove gas shielded arc welding method.

5. In the first layer welding, the third and subsequent electrodes are arranged in the center of the groove behind the first electrode and the second electrode. Gas shield arc welding method.

6). 6. The narrow groove gas shielded arc welding method according to any one of 1 to 5, wherein a mixed gas containing 60% by volume or more of CO ₂ gas is used as a shielding gas in the narrow groove gas shielded arc welding.

According to the present invention, even when low-cost groove processing such as gas cutting or plasma cutting is performed as the groove processing, there is no occurrence of defects due to hot cracking or poor fusion, and the welding operation efficiency is improved. High narrow gap gas shielded arc welding can be performed.
The narrow gap gas shielded arc welded joint obtained in this way is significantly less expensive to manufacture than conventional welded joints, so it is particularly applicable to general structures such as buildings, bridges and shipbuilding. And extremely useful.

The various groove shape in the welding method of this invention is shown. The V-shaped groove | channel shape shows the construction point at the time of constructing first layer welding with two electrodes by the welding method of the present invention, (a) is a front view, (b) is a top view. In the V-shaped groove shape, the groove after the first layer welding is performed with two electrodes by the welding method of the present invention is shown. It is a schematic diagram which shows the penetration state at the time of performing first layer welding with two electrodes, (a) is the case where the first electrode and the second electrode have the same polarity (wire plus-wire plus), and (b) is the first This is a case where the electrode and the second electrode have different polarities (wire minus wire plus). It is explanatory drawing of the direction of the electromagnetic force which acts on an arc. It is explanatory drawing of the maximum recessed part depth of a groove surface.

Hereinafter, the present invention will be specifically described.
FIGS. 1A to 1C show various groove shapes targeted by the welding method of the present invention. In the figure, reference numeral 1 is a thick steel material, 2 is a groove surface of the thick steel material, 3 is a bottom groove, the symbol θ is the bottom groove angle, G is the bottom groove gap, and h is the bottom groove height. , And t represents the plate thickness.
As shown in the figure, the groove shape in the welding method of the present invention can be either a V-shaped groove (including an I-shaped groove) or a Y-shaped groove, and FIG. It is also possible to use a multi-stage Y-shaped groove as shown in FIG.

Here, the bottom groove is defined as a groove in the lower part of the steel material. Moreover, the groove | channel of a steel material lower step part means the area | region from the bottom face of steel materials to about 20 to 40% of board thickness.
In relation to the definition of the bottom groove as described above, the bottom groove angle is represented by θ, the bottom groove gap is represented by G, and the bottom groove height is represented by h. In the case of a V-shaped groove, the bottom groove height h is defined as 20% of the plate thickness t.

Moreover, FIG. 2 shows the construction point at the time of constructing first layer welding with two electrodes by the welding method of the present invention in a V-shaped groove shape, (a) is a front view, (b) is a front view. It is a top view.
In the figure, reference numeral 4 is a first electrode, 5 is a second electrode, 4a and 5a are welding power tips of a welding torch, 4b and 5b are welding wires, 6 is a backing material, 7 is a welding wire, 8 is a welding bead, 9 Is a molten pool. Further, the symbol a represents the distance between the welding wire tips supplied from the power supply tips at the welding torch tips of the first electrode and the second electrode, and α represents the welding wire tips of the first electrode and the second electrode with respect to the direction perpendicular to the welding line. The angle of the straight line connecting between them, φ is the supply angle of the welding wire supplied from the power feed tip at the tip of the welding torch, and d is the distance between the side end of the tip of the welding wire at the bottom groove and the groove surface of the thick steel material Indicates.
In addition, illustration of a molten pool is abbreviate | omitted in Fig.2 (a). Moreover, about the 1st electrode and 2nd electrode in FIG.2 (b), only the welding wire tip position is shown, respectively, and illustration is abbreviate | omitted about another structure.
In addition, here, a V-shaped groove shape is shown as an example, but a, α, φ, and d are the same in other groove shapes.

Further, FIG. 3 shows a groove after first layer welding is performed with two electrodes by the welding method of the present invention in a V-shaped groove shape. In the drawing, the symbol P indicates the melting depth at the bottom of the thick steel material, and H indicates the weld height (average of the weld bead height).
Here, a V-shaped groove shape is shown as an example, but P and H are the same in other groove shapes.

  Next, the reason why the bottom groove angle, the bottom groove gap, and the plate thickness of the steel material are limited to the above ranges in the welding method of the present invention will be described.

Bottom groove angle θ: 25 ° or less The smaller the groove portion of the steel material, the faster and highly efficient welding is possible, but defects such as poor fusion tend to occur. Further, welding in the case where the bottom groove angle exceeds 25 ° can be performed by a conventional construction method. For this reason, in this invention, construction is difficult with the conventional construction method, and the bottom groove angle, which is expected to be further improved in efficiency, is 25 ° or less.
In the V-shaped groove, when the bottom groove angle is 0 °, it is called a so-called I-shaped groove. From the viewpoint of the amount of welding, this 0 ° is the most efficient. Since the groove is closed during welding, it is preferable to set the bottom groove angle corresponding to the plate thickness t (in the case of a Y-shaped groove, the bottom groove height h). .
Specifically, the bottom groove angle is preferably in the range of (0.5 × t / 20) to (2.0 × t / 20) °, more preferably (0.8 × t / 20) to (1.2 × t / 20) Range of degrees. For example, when the plate thickness t is 100 m, the bottom groove angle is preferably in the range of 2.5 to 10 °, and more preferably in the range of 4 to 6 °.
However, when the plate thickness t exceeds 100 mm, the upper limit of the preferred range exceeds 10 °. In this case, the upper limit of the preferred range is 10 °.

Bottom groove gap G: 7 mm or more and 18 mm or less The smaller the groove portion of the steel material, the faster and the high-efficiency welding is possible, but defects such as poor fusion tend to occur. Also, welding with a bottom groove gap exceeding 18 mm can be performed by a conventional construction method. For this reason, the present invention is intended for a bottom groove gap of 18 mm or less, which is difficult to construct by the conventional construction method and is expected to further improve the efficiency. On the other hand, when the bottom groove gap is less than 7 mm, it is difficult to perform first layer welding described later as multi-electrode welding of two or more electrodes. For this reason, the bottom groove gap is in the range of 7 mm or more and 18 mm or less. Preferably it is the range of 8 mm or more and 12 mm or less.

Plate thickness t: 22 mm or more The steel plate thickness should be 22 mm or more. This is because if the steel plate thickness is less than 22 mm, the groove angle is increased in the conventional lathe groove while the groove gap is decreased, and in some cases, the groove targeted in the present invention. This is because the groove cross-sectional area becomes smaller.
For example, when the plate thickness t is 20 mm, the groove sectional area is 140 mm ² in the case of an I-shaped groove having a bottom groove angle of 0 ° and a bottom groove gap of 7 mm, which is an object of the present invention. A groove shape with a groove angle of 25 ° and a groove gap of 2 mm has a groove cross-sectional area of 133 mm ² , and the groove with a groove shape is a highly efficient weld with a smaller amount of welding.
When a general rolled steel material is targeted, the upper limit of the plate thickness is generally 100 mm. Therefore, it is preferable that the upper limit of the thickness of the steel material targeted in the present invention is 100 mm or less.

In addition, as a steel type made into object by this invention, a high-tensile steel is especially suitable. This is because high-strength steel has severe welding heat input restrictions and is liable to crack the weld metal. On the other hand, in the present invention, heat input: 20 kJ / cm ² or less enables efficient welding from the first layer to the final layer, and the weld shape of each pass is almost 90 ° of fillet welding, and is difficult to crack. It is because it becomes a shape. Furthermore, welding of 780 MPa class steel is possible without preheating, and welding of 590 MPa class corrosion resistant steel, which is a high alloy system, is also possible. Of course, it goes without saying that mild steel can be handled without problems.

  As described above, in the welding method of the present invention, the reason for limiting the bottom groove angle, the bottom groove gap and the plate thickness of the steel material has been described, but in the present invention, the melt depth at the bottom of the thick steel material when these are satisfied. It is important that the thickness is 1.5 mm or more.

Melting depth at the bottom of the thick steel material: 1.5 mm or more In the groove processing of the steel material in the present invention, processing by gas cutting, plasma cutting, laser cutting or the like is performed. However, it does not exclude machining. On the other hand, the melting depth required for the groove surface in narrow groove gas shielded arc welding is mainly determined by the surface properties of the groove surface (particularly, the recess depth and cleanliness).
In the most common groove cutting by gas cutting, except for special steel and stainless steel, there is a large difference in the finish of the cut surface depending on the gas flow rate and crater selection at the time of gas cutting. For example, when the gas flow rate or crater adjustment is good, the depth of the recess on the groove surface is about 0.2 mm or less, but in special cases, for example, when the flame flow rate drops below normal due to crater wear, etc. In some cases, the depth of the recess exceeding 1 mm may occur. However, even if such a concave portion is generated, the general structure or the like is directly used for welding without care. Therefore, in order to effectively prevent defects due to hot cracks, poor fusion, etc., the groove surface during welding construction, especially the bottom of the thick steel material where the temperature during welding is low and the melting depth tends to be small, Need to melt deeper. Further, since the cut surface is covered with a thick oxide film generated by processing heat, it is necessary to melt the groove surface deeper in the welding process.
From the above, in the present invention, the melting depth at the bottom of the thick steel material is 1.5 mm or more. Preferably it is 2.0 mm or more. However, if the melting depth exceeds 4 mm, an undercut occurs on the upper portion of the weld bead on the groove surface, which causes a welding defect. Therefore, the melting depth is preferably 4 mm or less.

As described above, in the present invention, it is important that the melting depth at the bottom of the thick steel material is 1.5 mm or more. And in order to achieve this under high welding construction efficiency, it is extremely important to properly control the welding conditions of the first layer in gas shielded arc welding.
Hereinafter, the welding conditions for the first layer will be described in detail.

When the first layer welding is a multi-electrode welding of two or more electrodes, the first electrode and the second electrode are arranged along a predetermined parallel welding line. With one electrode, heat tends to concentrate in the center of the groove, so that melting on the groove surface of the steel material is insufficient, and fusion defects (cold wrap), defects due to sputtering and slag entrainment attached to the groove surface are likely to occur. In particular, in the first layer welding, since the temperature of the steel material is low and the melting depth is small, defects due to poor fusion are likely to occur. From the viewpoint of improving the welding work efficiency, it is advantageous to use multi-electrode welding with two or more electrodes.
Accordingly, the first layer welding is multi-electrode welding of two or more electrodes, and at least the first electrode and the second electrode among the electrodes are arranged along a predetermined parallel weld line. The number of electrodes is preferably 2 to 4 electrodes.

One of the first electrode and the second electrode is wire minus (positive polarity), and the other is wire plus (reverse polarity)
When the first electrode and the second electrode have the same polarity (for example, both the first electrode and the second electrode are wire plus), as shown in FIG. Therefore, sufficient melting cannot be obtained on the groove surface. In FIG. 4A, reference numeral 10 is an arc, and 11 is a droplet.
Here, when the first electrode and the second electrode have the same polarity, the reason why the respective arcs face inward is considered as follows.
That is, when the first electrode and the second electrode have the same polarity, that is, the currents have the same direction, as shown in FIG. From the direction, the electromagnetic force acts inward on each of the first electrode and the second electrode. Furthermore, since the current flowing (spreading) in the groove is opposite to the current flowing in the electrode, the magnetic field generated by the current flowing in the groove and the magnetic field generated by the current flowing in the electrode attract each other inward. Produces the electromagnetic force. As a result, they act on the respective arcs, and as a result, the arcs are strongly inward.
On the other hand, if one of the first electrode and the second electrode is wire minus (positive polarity) and the other is wire plus (reverse polarity) and the arrangement of the first electrode and the second electrode is appropriately controlled, the welding currents of each other The magnetic field generated by the magnetic field generates a strong outward electromagnetic force (see FIG. 5), and overcomes the inward electromagnetic force generated by the magnetic field generated by the current flowing in the groove surface, so that the arcs are mutually connected as shown in FIG. It will be repelled. As a result, it is possible to obtain a sufficient melting depth on the groove surface.
Therefore, regarding the welding wire supplied from the power supply tip at the tip of the welding torch of the first electrode and the second electrode, one is wire minus (positive polarity) and the other is wire plus (reverse polarity).

Distance a between welding wire tips supplied from the tip of each welding torch of the first electrode and second electrode a: 5 mm or more and 16 mm or less Welding wire supplied from the tip of the tip of each welding torch of the first electrode and second electrode The distance a between the tips (hereinafter, also simply referred to as the distance between the first and second electrodes, see FIG. 2B) needs to be controlled within a range of 5 mm to 16 mm. Here, the distance between the welding wire tips refers to the distance between the centers of the welding wire tips in each electrode.
This is because if the distance between the first and second electrodes is less than 5 mm, current (electrons) flows between the electrodes, the heat of the arc itself is reduced, and sufficient melting of the groove surface cannot be obtained. . On the other hand, when the distance between the first and second electrodes exceeds 16 mm, the outward electromagnetic force between the electrodes decreases in inverse proportion to the distance, and the arc repulsion for overcoming the inward electromagnetic force generated by the current flowing through the groove surface. Since no force is obtained, the arcs of each other face inward, and heat concentrates in the center of the groove. As a result, sufficient melting on the groove surface cannot be obtained.
Further, in narrow groove welding, it becomes a problem to suppress welding defects due to adhesion of spatter to the groove surface, but the first electrode and the second electrode are arranged along a predetermined parallel welding line, One is wire minus (positive polarity), the other is wire plus (reverse polarity), and the distance between the first and second electrodes is controlled within the range of 5 mm to 16 mm, so that the spatter is absorbed by each molten metal. The Thereby, since adhesion of the sputter | spatter to a groove surface is suppressed, it becomes possible to obtain a sound welded part.
Accordingly, the distance between the tips of the welding wires supplied from the power supply tips at the tips of the welding torches of the first electrode and the second electrode is controlled in the range of 5 mm to 16 mm. In order to obtain deeper and more stable melting of the groove surface by stronger repulsion of the arc, it is preferable to control the distance between the first and second electrodes within a range of 5 mm to 8 mm.

The angle α of the straight line connecting between the welding wire tips of the first electrode and the second electrode with respect to the direction perpendicular to the welding line α: 45 ° or less As described above, in the narrow groove gas shield arc welding method of the present invention, arc repulsion is achieved. It is used to ensure melting of the groove surface, but the angle α of the straight line connecting the tips of the welding wires of the first electrode and the second electrode with respect to the direction perpendicular to the welding line (hereinafter simply referred to as 1-2 electrode arrangement) If the angle (refer to FIG. 2B), which is also referred to as an angle, exceeds 45 °, sufficient arc repulsive force cannot be obtained, and sufficient melting cannot be obtained on the groove surface.
Therefore, the angle of the straight line connecting the welding wire tips of the first electrode and the second electrode with respect to the direction perpendicular to the welding line is controlled within a range of 45 ° or less. More preferably, it is 30 ° or less. The first-second electrode arrangement angle may be 0 °.

  Note that Patent Document 4 discloses a multi-electrode gas shielded arc welding method in which gas shielded arc welding is performed using two or more electrodes, but this is mainly intended for fillet welding and the like. The conditions for performing narrow gap welding as in the present invention are not disclosed. Therefore, the welding method disclosed in Patent Document 4 is technically completely different from the welding method of the present invention on the premise that narrow groove welding is performed.

  Although the basic conditions have been described above, in the welding method of the present invention, by further satisfying the following conditions, the melting depth from the groove surface at the bottom of the thick steel material can be obtained more deeply and stably. Become.

Supply angle of the first electrode and the second electrode with respect to each bottom groove of the welding wire: 5 ° or more and 15 ° or less with respect to the perpendicular The arc has directivity and is easily oriented in the direction indicated by the tip of the electrode (welding wire) There is. In order to effectively utilize the directivity of this arc for melting of the groove surface, it is advantageous to direct the direction pointed to by the electrode tip to the groove surface. It varies greatly depending on the supply angle of the welding wire supplied.
Here, when the supply angle with respect to the bottom groove of the welding wire supplied from the power supply tip at the tip of the welding torch is less than 5 ° with respect to the perpendicular, the current flows through a path with smaller resistance. As a result, the arc scoops up the wire which is an electrode (climbing of the arc), and it becomes difficult to maintain melting at the target groove surface, particularly at the bottom. On the other hand, when the supply angle to the bottom groove of the welding wire supplied from the power supply tip at the tip of the welding torch exceeds 15 ° with respect to the perpendicular, the arc is too directed to the groove surface, and the weld bead shape becomes convex, and the first layer In subsequent welding, arc melting is insufficient, and welding defects are likely to occur. For this reason, it is preferable that the supply angle with respect to each bottom part groove | channel of the welding wire of a 1st electrode and a 2nd electrode shall be the range of 5 degrees or more and 15 degrees or less with respect to a perpendicular. More preferably, it is 6 ° or more and 12 ° or less.
In addition, since the supply angle with respect to each bottom part groove | channel of the welding wire of a 1st electrode and a 2nd electrode becomes the same as the inclination of an electric power feeding chip, especially an electric power feeding chip front-end | tip, the supply angle of this welding wire by the inclination of this electric power feeding tip end Can be controlled.

Distance between the end of the welding wire of the first electrode and the second electrode at the bottom groove and the groove surface of the thick steel material: 0.5 mm or more and 3.0 mm or less Stabilize the melting depth deeper at the bottom of the thick steel material Therefore, it is preferable that the distance between the side end portion of the tip of the welding wire of the first electrode and the second electrode in the bottom groove and the groove surface of the thick steel material be 0.5 mm or more and 3.0 mm or less.
This is because if the distance between the side edge of the welding wire tip at the bottom groove and the groove surface of the thick steel material is less than 0.5 mm, an arc is generated between the top of the wire and the groove surface, and the bottom of the thick steel material The groove face cannot be efficiently melted. On the other hand, if it exceeds 3.0 mm, the arc is separated from the groove surface, and the groove surface cannot be efficiently melted. More preferably, it is the range of 0.5-2.0 mm, More preferably, it is the range of 0.5-1.0 mm.
In addition, the side edge part of the front-end | tip of the welding wire said here shall point out the side edge part by the side near the groove surface of the thick steel material which it is made to fuse | melt with each electrode.

Curvature radius of welding wire fed to power supply tip of first electrode and second electrode: 150 mm or more and 300 mm or less In the present invention, the supply angle of the welding wire supplied from the power supply tip of the welding torch tip of the first electrode and the second electrode In order to control this, a power supply tip with a bent tip is used. At this time, the welding wire passes through the power feed tip having a bent tip. However, in order to allow the welding wire to pass more smoothly, it is preferable to bend the welding wire in advance using a so-called three-point roller or the like.
Here, if the radius of curvature of the welding wire is less than 150 mm, the feeding resistance of the wire increases, the welding wire cannot be stably fed, and it becomes difficult to maintain the arc. On the other hand, if the radius of curvature of the welding wire exceeds 300 mm, there is no effect in reducing the feeding resistance of the wire when the tip of the feeding tip is bent. It becomes difficult to maintain.
Therefore, it is preferable that the radius of curvature of the welding wire fed to the power supply tips of the first electrode and the second electrode is 150 mm or more and 300 mm or less. More preferably, it is 175 mm or more and 275 mm or less.

Electrodes after the third electrode: disposed in the center of the groove behind the first electrode and the second electrode When the weld height exceeds the bottom groove gap, the risk of hot cracking increases. In order to avoid this, it is effective to arrange the electrodes after the third electrode in the center of the groove behind the first electrode and the second electrode. This further reduces the number of stacks and greatly reduces the risk of stacking faults in multilayer welding.
The polarity after the third electrode is not particularly limited, and may be either wire minus (positive polarity) or wire plus (reverse polarity).

In the case of two-electrode welding, by appropriately managing the weld height H per layer with respect to the bottom groove gap G, the weld bead shape including penetration becomes constant, and the groove surface It is possible to ensure stable penetration. Furthermore, higher heat input is effective to obtain deeper penetration, but if the heat input becomes too high, the weld height increases, making it difficult to evenly melt the groove surfaces on both sides. become.
Here, if the weld height per layer is less than 0.4 times the bottom groove gap G, not only the heat input becomes insufficient and it becomes difficult to deeply melt the groove surface, but the welding amount is insufficient. The weld bead shape in the case changes. On the other hand, if the weld height per layer exceeds 1.0 times the bottom groove gap G, the amount of welding becomes too large and the groove surfaces on both sides cannot be evenly melted.
Therefore, when the first layer welding is the two-electrode welding, the weld height is preferably 0.4 times or more and 1.0 times or less of the bottom groove gap G. More preferably, it is 0.5 to 0.8 times the bottom groove gap G.

  In addition, the welding conditions in the layers other than the first layer are not particularly specified, but may basically be the same as the welding conditions for the first layer described above.

Shielding gas composition: 60% by volume or more of CO ₂ gas The penetration of the weld is governed by the gouging effect by the arc itself and the convection of the weld metal in a high temperature state. When the convection of the weld metal is inward, the hot weld metal convects from the top to the bottom, so the penetration directly under the arc increases. On the other hand, when the convection of the weld metal is directed outward, the high-temperature weld metal is convected from the center in the left-right direction, the weld bead expands and the penetration of the groove surface increases. Accordingly, in order to achieve the fusion depth of 1.5 mm or more at the bottom of the thick steel material targeted in the present invention, it is preferable that the convection of the weld metal is directed outward.
For that purpose, the concentration of oxygen (O) and sulfur (S) governing the molten metal flow is preferably 400 ppm by mass or more (however, exceeding 1000 ppm by mass makes it difficult to ensure the toughness of the weld metal, 1000 ppm by mass or less).
Here, since the amount of oxygen in the weld metal is greatly influenced by the shield gas composition, the shield gas composition is a mixture containing 60% by volume or more of CO ₂ gas and the remainder as an inert gas such as Ar. It is preferable to use a gas. Particularly preferred is CO ₂ gas: 100% by volume.

  Note that conditions other than those described above do not need to be specified, and may be determined according to a regular method. For example, welding current: 280 to 360 A, welding voltage: 32 to 37 V (increase with current), welding speed: 30 to 80 cm / min, wire protrusion length: 15 to 30 mm, wire diameter: 1.2 to 1.6 mm, per pass Welding heat input: 10 to 25 kJ / cm.

Narrow groove gas shield arc welding was performed on the groove-shaped steel materials shown in Table 1 under the welding conditions shown in Tables 2 and 3.
Note that gas cutting was used for the groove processing of the steel material, and the groove surface was not subjected to maintenance such as grinding. The maximum recess depth on the groove surface was measured using a laser displacement meter.
That is, as shown in FIG. 6, two parallel lines that pass through the highest convex part and the lowest concave part of the measurement point respectively and include all the measurement points therebetween and an intermediate line thereof are drawn. Here, the concave portion is a portion lower than the intermediate line, and the concave portion depth of the groove surface is a distance between the concave portion and the intermediate line. The maximum recess depth on the groove surface is the maximum value of the recess depth.
The measurement results are also shown in Table 1.

  The welded joint thus obtained was cut out in 5 cross sections, and the melt width of the bottom portion was measured in each cross section. For each cross section, the melt depth was measured by subtracting the length corresponding to the bottom groove gap from the measured melt width and dividing this value by 2, and the average value was obtained. This value was taken as the melting depth at the bottom of the steel material.

Further, the obtained welded joint was subjected to ultrasonic flaw inspection and evaluated as follows.
A: No detected defect. O: Only a defective defect having a defect length of 3 mm or less was detected. X: A defect having a defect length exceeding 3 mm was detected. The results are also shown in Table 3.

As shown in Table 3, in Nos. 1 to 16 which are invention examples, the melting depth at the bottom of the steel material is 1.5 mm or more, and there is no detection defect even if there is an ultrasonic flaw detection inspection. The length was 3 mm or less.
On the other hand, all of Comparative Examples No. 17 to 21 had a melting depth of less than 1.5 mm at the bottom of the steel material, and a defect having a defect length of more than 3 mm was detected in the ultrasonic flaw detection inspection.

1: Thick steel material 2: Groove surface of thick steel material 3: Bottom groove 4: First electrode 5: Second electrode 4a, 5a: Feeding tip of welding torch 4b, 5b: Welding wire 6: Backing material 7: Welding Line 8: Weld bead 9: Weld pool
10: Arc
11: Droplet θ: Bottom groove angle G: Bottom groove gap h: Bottom groove height t: Plate thickness a: Welding wire tip supplied from the feeding tip of each welding torch tip of the first electrode and the second electrode Distance α: Angle of a straight line connecting the welding wire tips of the first electrode and the second electrode with respect to the direction perpendicular to the welding line φ: Supply angle of the welding wire supplied from the power feed tip at the tip of the welding torch d: Bottom groove The distance between the side end portion of the tip of the welding wire and the groove surface of the thick steel material at P: Melting depth at the bottom of the thick steel material H: Average weld height

Claims (6)

In the gas shield arc welding method in which the bottom groove angle is 25 ° or less, the bottom groove gap is 7 mm or more and 18 mm or less, and the thick steel material having a plate thickness of 22 mm or more is joined by multi-pass welding of narrow grooves,
The first layer welding is multi-electrode welding of two or more electrodes, and the first electrode and the second electrode are arranged along a predetermined parallel welding line,
One of the first electrode and the second electrode is wire minus (positive polarity), the other is wire plus (reverse polarity),
Further, the distance between the tip of the welding wire supplied from the power supply tip at the tip of each welding torch of the first electrode and the second electrode is within a range of 5 mm to 16 mm, and the first electrode is perpendicular to the direction of the welding line. By controlling the angle of the straight line connecting the welding wire tips of the second electrode within a range of 45 ° or less,
A narrow groove gas shielded arc welding method in which the melting depth at the bottom of the thick steel material is 1.5 mm or more.   2. The narrow groove gas shield according to claim 1, wherein, in the first layer welding, a supply angle of each of the first electrode and the second electrode with respect to each bottom groove of the welding wire is 5 ° or more and 15 ° or less with respect to the vertical line. Arc welding method.   2. The distance between a side end portion of a welding wire tip of the first electrode and the second electrode at a bottom groove and a groove surface of the thick steel material in the first layer welding is 0.5 mm or more and 3.0 mm or less. Or the narrow groove gas shielded arc welding method according to 2.   The said first layer welding WHEREIN: As a welding wire sent to the electric power feeding tip of the said 1st electrode and the said 2nd electrode, the wire curved in the range from which a curvature radius is 150 mm or more and 300 mm or less is used. Narrow groove gas shielded arc welding method.   5. The narrow opening according to claim 1, wherein, in the first layer welding, an electrode after the third electrode is arranged at a groove center behind the first electrode and the second electrode. Pre-gas shield arc welding method. The narrow groove gas shielded arc welding method according to any one of claims 1 to 5, wherein a mixed gas containing 60% by volume or more of CO ₂ gas is used as a shielding gas in the narrow groove gas shielded arc welding.

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