JP5884209B1 - Vertical narrow groove gas shielded arc welding method - Google Patents

Abstract

The present invention uses high-performance and high-precision welding automation technology to perform weaving of a precise welding torch according to the groove shape, welding posture, etc. An object of the present invention is to provide a high-quality and high-efficiency vertical narrow groove gas shielded arc welding method applicable to welding of thick steel materials. As a predetermined groove condition, in a gas shielded arc welding method in which two thick steel materials having a plate thickness of 40 mm or more are joined by vertical multi-layer welding using weaving, the first layer welding conditions, particularly the welding torch angle and welding heat input amount. The weaving conditions are appropriately controlled so that the joining depth in the first layer welding is 20 mm or more and 50 mm or less.

Description

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

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

  By the way, in recent years, with the increase in size and thickness of steel structures, the amount of welding in the manufacturing process, especially 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. Since this narrow gap gas shielded arc welding has a smaller amount of welding than normal gas shielded arc welding, it is expected that the efficiency and energy saving of welding can be achieved, and that the construction cost can be reduced.

  On the other hand, electroslag welding is usually applied to vertical high-efficiency welding, but 1-pass large heat input welding is fundamental, and welding with a plate thickness exceeding 60 mm causes excessive heat input and there is a concern of reduced toughness. Has been. In addition, there is a limit to the plate thickness in one-pass welding, and in particular, the technology has not yet been established for welding in which the plate thickness exceeds 65 mm.

For this reason, it is desired to develop a high-quality and high-efficiency welding method in which narrow gap gas shielded arc welding is applied to vertical welding.
As a welding method in which such narrow groove gas shielded arc welding is applied to vertical welding, for example, Patent Document 1 discloses a double-sided multi-layer welding method for a double-sided U-shaped groove joint. In this welding method, lamination welding is performed by TIG welding using an inert gas, and the use of inert gas suppresses the generation of slag and spatter and prevents the lamination defects.
However, TIG welding, which is a non-consumable electrode type, is greatly inferior in efficiency of the welding method itself as compared with MAG welding or CO ₂ welding using a steel wire as a consumable electrode.

Further, Patent Document 2 discloses a vertical welding method with a narrow groove in which weaving of a welding torch is performed in order to suppress spatter and poor fusion.
However, in this welding method, since the weaving direction of the welding torch is not the groove depth direction but the steel plate surface direction, it is necessary to weave the welding torch before the molten metal droops, and the welding current is about 150A. It is necessary to reduce the welding amount per pass (≈ heat input amount) with a low current.
For this reason, when this welding method is applied to the welding of a thick steel material having a large plate thickness, the welding becomes a small amount of multi-pass laminating, increasing the number of stacking faults such as poor penetration, and greatly reducing the welding efficiency.

Furthermore, as in Patent Document 2, Patent Document 3 discloses a vertical welding method in which weaving of a welding torch is performed in order to suppress poor fusion.
Although the surface angle (groove angle) disclosed here is as wide as 26.3 to 52 °, since the weaving of the welding torch here is also performed in the groove depth direction, It is possible to take a relatively large amount of welding.
However, since the amount of weaving in the groove depth direction is small and the composition of the weld metal and welding wire is not considered, it is necessary to suppress the amount of welding per pass (≈ heat input), and the welding depth per pass The depth is as shallow as about 10 mm.
For this reason, when this welding method is applied to the welding of a thick steel material having a large plate thickness, it is also a small amount of multi-pass laminating welding, resulting in an increase in laminating defects such as poor penetration and a reduction in welding efficiency.

Patent Document 4 discloses a two-electrode electrogas arc welding apparatus that enables one-pass welding of an extremely thick material.
Although the use of this two-electrode electrogas arc welding apparatus enables the joining of thick steel materials up to a plate thickness of about 70 mm, the amount of heat input greatly increases to about 360 kJ / cm due to the use of two electrodes. When the thermal effect is large and the joint is required to have high characteristics (strength and toughness), it is very difficult to satisfy such characteristics.
In addition, in this two-electrode electrogas arc welding apparatus, it is indispensable to provide a ceramic backing on the back surface and a water-cooled copper metal pressing mechanism on the front surface (welder side) in the groove. On the other hand, there is no concern about dripping of molten metal, but the welding apparatus becomes complicated.
Furthermore, in this two-electrode electrogas arc welding apparatus, it is indispensable to provide a copper-plating pressing mechanism on the surface (welder side), so 1-pass welding is fundamental and low-pass as multi-pass laminating welding. It is difficult to achieve heat.

JP 2009-61483 A JP 2010-115700 A JP 2001-205436 A JP-A-10-118771

As described above, a high-quality and high-efficiency vertical narrow groove gas shielded arc welding method that can be applied to welding of thick steel materials has not yet been developed.
On the other hand, as welding automation technology (welding robot) has become lighter, more functional, and more accurate, weaving of the welding torch suitable for the groove shape and welding posture, which has been difficult until now, becomes possible. Welding construction (condition setting) suitable for steel materials, groove shapes, welding postures and welding materials (wires) has become possible.

  The wood invention uses a high-function and high-precision welding automation technology to perform weaving of a precise welding torch according to the groove shape, welding posture, etc. An object of the present invention is to provide a high-quality, high-efficiency, vertical narrow groove gas shielded arc welding method applicable to welding of thick steel materials.

Now, in order to solve the above-mentioned problems, the inventors have conducted intensive research on welding conditions in the case of applying vertical narrow groove gas shielded arc welding to a thick steel material.
As a result, when performing narrow gap gas shielded arc welding of thick steel materials in the vertical direction, two or more passes are required to obtain desired mechanical properties in the weld metal and the heat affected zone, and to achieve high welding efficiency. As a multi-layer welding, it was found that it is important to suppress the welding heat input per pass and to make the joining depth (welding depth) in the first layer welding 20 mm or more and 50 mm or less.

Further, further research was conducted on the welding conditions for obtaining a predetermined joining depth in the first layer welding by suppressing the welding heat input per pass as the above-described multilayer welding of two or more passes. As a result, with the groove condition set as a predetermined condition, the welding conditions of the first layer, in particular the welding torch angle and the weaving conditions, are properly controlled to suppress the dripping of molten metal, which is a problem in vertical welding. The joining depth in the first layer welding described above could be achieved while stabilizing the bead shape included and preventing the occurrence of welding defects. Thereby, even if it was a thick steel material with a plate thickness of 40 mm or more, it was found that high-quality and high-efficiency vertical narrow groove gas shield arc welding can be performed.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. A vertical narrow gap gas shield arc welding method in which two thick steel materials having a groove angle of 25 ° or less, a groove gap of 20 mm or less, and a plate thickness of 40 mm or more are joined by vertical multilayer welding using weaving. In
During the first layer welding, the angle of the welding torch is 25 ° to 75 ° with respect to the horizontal direction, the welding heat input is 30 kJ / cm to 170 kJ / cm and the weaving depth in the plate thickness direction is 15 mm to 50 mm. Welding the torch with the maximum weaving width in the thickness direction and in the direction perpendicular to the welding line being (W-6) mm to Wmm, where W is the weld bead width in the first layer welding. ,
A vertical narrow groove gas shield arc welding method in which a joining depth in the first layer welding is 20 mm or more and 50 mm or less.

2. 2. The vertical narrow gap gas shield arc welding method according to 1, wherein the weaving pattern of the welding torch viewed from the direction of the welding line is a U-shape in the first layer welding weaving.

3. The vertical narrow groove gas shielded arc welding method according to 1 or 2, wherein the total amount of S and O of the weld metal in the first layer welding is 450 mass ppm or less and the N content is 120 mass ppm or less.

4). The vertical narrow groove gas shielded arc welding according to any one of the above 1 to 3, wherein the total amount of Si and Mn of the welding wire used in the first layer welding is 1.5% by mass or more and 3.5% by mass or less. Method.

5. The vertical narrow groove gas as described in any one of 1 to 4 above, wherein the total amount of Ti, Al and Zr of the welding wire used in the first layer welding is 0.08% by mass or more and 0.5% by mass or less. Shielded arc welding method.

6). 6. The vertical narrow groove gas shielded arc welding method according to any one of 1 to 5, wherein a gas containing 20% by volume or more of CO ₂ gas is used as the shielding gas.

7). The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 6, wherein in the first layer welding, an average welding current is in a range of 270A to 360A.

According to the present invention, even when a thick steel material having a plate thickness of 40 mm or more is welded, while preventing bead shape stabilization and weld defects including molten metal sag suppression, which is a problem in vertical welding, High quality and high efficiency narrow gap gas shielded arc welding can be performed.
The welding method of the present invention has a smaller amount of welding than ordinary gas shielded arc welding, and can achieve energy saving by increasing the efficiency of welding, so that the welding construction cost can be greatly reduced.
Further, in the welding method of the present invention, a water-cooling type copper metal pressing mechanism for preventing dripping of molten metal as in the electrogas arc welding apparatus shown in Patent Document 4 is unnecessary, so that the apparatus is not complicated. Further, since welding heat input per pass can be suppressed by multipass welding, it is easy to secure desired mechanical properties at the weld metal and steel material heat affected zone.

The various groove shape in the welding method of this invention is shown. In the V-shaped groove shape, the construction procedure when performing the first layer welding by the welding method of the present invention is shown. In the V-shaped groove shape, the groove cross section after the first layer welding is performed by the welding method of the present invention is shown. FIG. 5 shows a weaving pattern of a welding torch viewed from the direction of the welding line in the first layer welding weaving, wherein (a) is U-shaped, (b) is trapezoidal, (c) is V-shaped, and (d) is triangular. Is. In invention example (No. 7) of this invention, it is a photograph after performing first layer welding with the welding method of this invention, (a) shows the whole external appearance, (b) shows a groove cross section. is there.

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 groove in the lower part of the steel material (in the Y-shaped groove), a groove angle is denoted by symbol θ, and a groove gap is denoted by G. , T indicates the plate thickness, and h indicates the groove height of the lower part of the steel material (in the Y-shaped groove).
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 and a L-shaped groove) or a Y-shaped groove, In addition, as shown in FIG. 1C, a multi-stage Y-shaped groove may be used.
In the present invention, as shown in FIGS. 1B and 1C, the groove angle and the groove gap in the case of the Y-shaped groove are defined as the groove angle and groove at the groove of the lower steel material step. Let it be a gap. Here, the groove of the lower part of the steel material means 20 to 40% of the plate thickness from the steel material surface which becomes the back surface (the surface on the welding device (welding torch) side is the front surface and the opposite surface is the back surface) during welding. Means an area to the extent.

Moreover, FIG. 2 shows the construction point at the time of constructing the first layer welding in the welding method of the present invention in a V-shaped groove shape. In the figure, reference numeral 4 is a welding torch, 5 is a welding wire, 6 is a backing material, and φ is the angle of the welding torch with respect to the horizontal direction. In addition, about a weld line, a molten pool, and a weld bead, illustration is abbreviate | omitted.
Here, as shown in FIG. 2, the welding method of the present invention is a gas shielded arc in which two thick steel materials having a predetermined plate thickness are butted together and joined by vertical welding using weaving. It is welding and is based on upward welding with the traveling direction upward.
Here, the V-shaped groove shape is shown as an example, but the same applies to other groove shapes.

Furthermore, FIG. 3 shows a groove cross section after first layer welding is performed by the welding method of the present invention in a V-shaped groove shape. In the figure, symbol 7 is a weld bead, symbol D represents the joining depth in the first layer welding, and W represents the weld bead width (gap between the grooves after the first layer welding) in the first layer welding.
In addition, the joining depth D in the first layer welding is the minimum value of the first layer weld bead height when starting from the steel surface that is the back surface during welding (the first layer weld bead height closest (low) from the starting steel surface). S).
Here, a V-shaped groove shape is shown as an example, but D and W 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.

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 groove angle exceeds 25 ° can be performed by a conventional construction method. For this reason, in this invention, construction is difficult by the conventional construction method, and the case where groove angle: 25 degrees or less where further improvement in efficiency is expected is targeted.
In the V-shaped groove, when the groove angle is 0 °, it is called a so-called I-shaped groove, and from the viewpoint of the amount of welding, this 0 ° is the most efficient. Since the groove is closed inside, it is possible to set the groove angle according to the thickness t (however, in the case of Y-shaped groove, the groove height h of the lower part of the steel material). preferable.
Specifically, the groove angle is preferably in the range of (0.5 × t / 20) to (2.0 × t / 20) °, more preferably (0.8 × t / 20) to The range is (1.2 × t / 20) °. For example, when the plate thickness t is 100 m, the groove angle is preferably in the range of 2.5 to 10 °, 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 °, but the upper limit of the preferred range in this case is 10 °.

Groove gap G: 20 mm or less The smaller the groove portion of the steel, the faster and more efficient the welding is possible. In addition, in the case where the groove gap exceeds 20 mm, the molten metal tends to sag and is difficult to construct. As a countermeasure, it is necessary to keep the welding current low, but welding defects such as slag entrainment tend to occur. Therefore, the case where the groove gap is 20 mm or less is targeted. Preferably it is the range of 4 mm or more and 12 mm or less.

Plate thickness t: 40 mm or more The plate thickness of the steel material is 40 mm or more. This is because if the thickness of the steel material is less than 40 mm, the amount of welding heat input can be suppressed even if a conventional welding method, for example, one-pass welding such as electrogas arc welding in Patent Document 4, is used. .
For example, in the case of a V-shaped groove having a plate thickness t: 35 mm, a groove angle: 20 °, and a groove gap: 8 mm, the heat input by one-pass welding using electrogas arc welding of Patent Document 4 is about 150 kJ / cm. It becomes.
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 which is the subject of the present invention, high-strength steel (for example, ultra-thick YP 460 MPa class steel for shipbuilding (tensile strength 570 MPa class steel) or TMCP steel SA440 for architecture (tensile strength 590 MPa class steel)) is particularly used. Is preferred. This is because high-strength steel has severe restrictions on welding heat input, and cracks are likely to occur in the weld metal, and the required joint strength and toughness cannot be obtained due to the effect of welding heat. On the other hand, in the present invention, welding can be efficiently performed at a heat input of 170 kJ / cm or less, and 590 MPa class high-strength steel sheets and 590 MPa class corrosion-resistant steels that become high alloy systems can also be welded. Of course, mild steel can be handled without problems.

As described above, the reason for limiting the groove angle, the groove gap, and the steel plate thickness in the welding method of the present invention has been described. In the present invention, a thick steel material is efficiently welded with a heat input suitable for a narrow groove. For this reason, it is important to set the welding depth in the first layer welding within a predetermined range while appropriately controlling the first layer welding conditions with multilayer welding of two or more passes.
Hereinafter, the reason for limiting the joining depth in the first layer welding and the first layer welding conditions will be described.

Joining depth D in the first layer welding: 20 mm or more and 50 mm or less In order to weld a steel plate having a thickness of 40 mm or more in the present invention by multi-pass welding of two or more passes, the joining depth in the first layer welding is 20 mm or more. It is necessary to. If the joining depth in the first layer welding is less than 20 mm, the welding heat concentrates, so that dripping of the molten metal occurs. On the other hand, if the joining depth in the first layer welding exceeds 50 mm, welding heat input tends to be excessive, and welding defects such as hot cracking, poor fusion of the groove surface due to dispersion of heat during welding, slag entrainment, etc. Occurs. Therefore, the joining depth in the first layer welding is 20 mm or more and 50 mm or less. Preferably, it is 25 mm or more and 40 mm or less.

Welding torch (feed tip end) angle φ: 25 ° or more and 75 ° or less with respect to the horizontal direction The angle of the welding torch is closer to the horizontal than the vertical, so that the arc faces the back side from the surface of the weld bead and the molten metal droops. Can be suppressed. Here, if the angle of the welding torch is less than 25 ° with respect to the horizontal direction, it is difficult to form a weld bead, and if the angle of the welding torch exceeds 75 ° with respect to the horizontal direction, it is difficult to suppress dripping of the molten metal. It becomes. Therefore, the angle of the welding torch needs to be 25 ° or more and 75 ° or less with respect to the horizontal direction. Preferably they are 30 degrees or more and 45 degrees or less.

Weld heat input: 30 kJ / cm or more and 170 kJ / cm or less In multilayer welding, the number of passes can be reduced by increasing the heat input per pass (= the amount of welding), and weld stacking faults can be reduced. However, if the welding heat input becomes too large, it becomes difficult to secure the strength and toughness of the weld metal, and it becomes difficult to suppress the softening of the heat affected zone of the steel material and to secure the toughness by the coarsening of the crystal grains. In particular, when the welding heat input exceeds 170 kJ / cm, in order to secure the characteristics of the weld metal, a dedicated wire that takes into account the dilution of the steel material becomes indispensable, and even steel materials that are designed to withstand the heat input of welding become indispensable. . On the other hand, in order to secure a molten metal and obtain a welded portion having no weld defects, it is advantageous that the heat input is high, and if the weld heat input is less than 30 kJ / cm in a narrow groove, melting of the groove surface is insufficient. However, the occurrence of stacking faults is inevitable.
Therefore, the welding heat input is 30 kJ / cm or more and 170 kJ / cm or less. Preferably, it is 90 kJ / cm or more and 160 kJ / cm or less.

Weaving depth L in the thickness direction in the weaving of the welding torch: 15 mm or more and 50 mm or less The welding method of the present invention performs the weaving of the welding torch, and the weaving depth in the thickness direction in the weaving of this welding torch. It is important to appropriately control L and the maximum weaving width M in the plate thickness direction and the direction perpendicular to the weld line, which will be described later.
In addition, the weaving depth L in the plate thickness direction and the maximum weaving width M in the plate thickness direction and the direction perpendicular to the weld line in various weaving patterns are as shown in FIGS.

Here, in the vertical upward welding that is the basis of the welding method of the present invention, the welding depth and the weaving width in the plate thickness direction are approximately the same, so if the weaving depth in the plate thickness direction is less than 15 mm, It is difficult to make the joining depth in layer welding 20 mm or more. On the other hand, if the weaving depth in the plate thickness direction exceeds 50 mm, it becomes difficult not only to make the joining depth in the first layer welding 50 mm or less, but also the welding heat input becomes excessive, and the weld metal or steel material It is difficult to obtain the desired mechanical properties in the heat-affected zone, and it is easy to generate weld defects such as hot cracks, poor fusion of the groove surface due to heat dispersion during welding, and slag entrainment. .
Therefore, the weaving depth in the plate thickness direction is 15 mm or more and 50 mm or less. Preferably, it is the range of 25 mm or more and 35 mm or less.

Maximum weaving width M: (W-6) mm to W mm in the thickness direction and the direction perpendicular to the welding line in the weaving of the welding torch (W: weld bead width in the first layer welding)
In order to prevent unmelting of the groove surface, the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line needs to be (W-6) mm or more. On the other hand, when the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line exceeds Wmm, the molten metal drips and welding cannot be established.
Therefore, the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line is in the range of (W-6) mm to Wmm. Preferably, it is the range of (W-4) mm or more and (W-1) mm or less.

Further, the weaving pattern of the welding torch is not particularly limited, and as shown in FIGS. 4A to 4D, a U-shape when viewed from the welding line direction (which coincides with the welding progress direction and is usually the vertical direction). V-shaped, trapezoidal, triangular, etc. 4A to 4D, the trajectory of the welding torch at each point where the direction of the welding torch changes (point B and point C in FIG. 4A) is made square. You may make it round.
However, in vertical upward welding, weaving near the weld surface tends to cause dripping of the molten metal, and when the welding torch operation deviates from the groove surface, the groove surface is uniformly melted. Cannot be obtained, and welding defects such as poor fusion are likely to occur. In particular, a general trapezoidal and triangular weaving pattern that does not require reversal operation has a small apparatus load, but a welding torch operation at a location close to the welding surface side (point D of the trapezoidal weaving pattern in FIG. 4B) Due to the point A and the point C to the point A in the triangular weaving pattern in FIG. For this reason, from the viewpoint of suppressing dripping of the molten metal, it is preferable to use a U-shaped or V-shaped weaving pattern without a torch operation on the welding surface side.
Further, in a V-shaped or triangular weaving pattern, when the groove gap is large (for example, 6 mm or more), the welding torch operation is shifted from the groove surface (for example, from point A to point B in FIG. 4C). In operation, the locus of the tip of the welding torch is no longer parallel to the groove surface (side close to the welding torch) and the groove surface cannot be uniformly melted, and welding defects such as poor fusion are likely to occur. Therefore, in such a case, it is optimal to use a U-shaped weaving pattern capable of operating the welding torch parallel to the groove surface.

Note that the steel material at the deepest point of the welding torch tip during weaving in the plate thickness direction (for example, points B and C in FIGS. 4 (a) and 4 (b), point B in FIGS. 4 (c) and 4 (d)). The distance a from the back surface is usually about 2 to 5 mm.
When U-shaped weaving or trapezoidal weaving is applied to the groove shape targeted by the present invention, M ₁ , M ₂ , and M ₃ in FIGS. 4A and 4B are _{2 to} 18 mm, respectively. 0 to 10 mm and 0 to 10 mm.
Further, the frequency and stop time during weaving (stop time at each point such as point A shown in FIG. 4) are not particularly limited. For example, the frequency is 0.25 to 0.5 Hz (preferably 0.4 to 0.5 Hz) and the stop time may be about 0 to 0.5 seconds (preferably 0.2 to 0.3 seconds).

  Although the basic conditions have been described above, in the welding method of the present invention, by further satisfying the following conditions, dripping of molten metal, which is a problem particularly in vertical welding, is suppressed, and the bead shape is further stabilized. Can be planned.

Total amount of weld metal S and O in first layer welding: 450 mass ppm or less To achieve stable upward welding, molten metal is prevented from dripping and stable weld bead shape (no irregularities) In order to prevent the molten metal from sagging, it is important to manage the S amount and O amount that reduce the surface tension and viscosity of the molten metal at a low level.
Here, when the total amount of S and O of the weld metal exceeds 450 mass ppm (hereinafter also simply referred to as ppm), in addition to the decrease in surface tension and viscosity, the convection of the weld metal becomes outward on the surface, The high-temperature weld metal convects from the center toward the periphery, the molten metal spreads, and the dripping of the molten metal is likely to occur. For this reason, it is preferable that the total amount of S and O of the weld metal that governs the surface tension and viscosity of the molten metal and the molten metal flow is 450 ppm or less. More preferably, it is 400 ppm or less.

The welding wire usually contains S in an amount of 0.010 to 0.025% by mass for the purpose of lowering the surface tension and flattening the weld bead. In order to reduce the S amount of the weld metal, it is effective to lower the S amount in the steel material in addition to the reduction of the S amount of the welding wire itself.
Furthermore, the amount of O in the weld metal increases due to the oxidation of CO _{2 in} the shield gas. For example, when 100% CO ₂ gas is used as the shielding gas, the amount of O in the weld metal increases by about 0.040 to 0.050 mass%. In order to reduce the amount of O in such a weld metal, addition of Si and Al to the welding wire is effective in addition to the reduction of O which is usually contained in the welding wire itself by about 0.003 to 0.006 mass%. It is also effective to increase the welding current and arc voltage so that the slag metal reaction (deoxidation reaction) in the molten metal, the slag aggregation, and the surface of the weld bead are sufficiently lifted.

N amount of weld metal in first layer welding: 120 ppm or less Nitrogen (N) in the weld metal is discharged from the weld metal and becomes bubbles during solidification. Generation | occurrence | production of this bubble causes the vibration of a molten metal surface, and causes dripping of a molten metal. In particular, if the amount of N in the weld metal exceeds 120 ppm, the molten metal tends to sag. Therefore, the amount of N in the weld metal in the first layer welding is preferably 120 ppm or less. More preferably, it is 60 ppm or less.

In general, the welding wire contains nitrogen (N) as an impurity in an amount of 50 to 80 ppm. From here, the amount of N in the weld metal increases by about 20 to 120 ppm due to mixing of impurities in the shielding gas and the atmosphere. On the other hand, since the inner diameter of the nozzle for arc welding is usually about 16 to 20 mm, it is difficult to completely shield the weld metal portion having a joining depth exceeding the inner diameter of the nozzle using such a nozzle. In particular, the amount of N in the weld metal may exceed 200 ppm.
In order to prevent such an increase in the amount of N and reduce the amount of N in the weld metal in the first layer welding to 120 ppm or less, and further to 60 ppm or less, a gas shield system different from the normal arc welding nozzle is provided. It is effective to suppress the mixing of air into the weld metal.

  In addition, since S, O and N are eluted from the steel material to the weld metal by dilution of the steel material during welding, S: 0.005 mass% or less, O: 0.003 mass% or less, and N: 0.004 mass% or less It is preferable to use the steel material in order to suppress the S amount, O amount, and N amount of the weld metal in the first layer welding described above.

The total amount of Si and Mn of the welding wire used in the first layer welding: 1.5% by mass or more and 3.5% by mass or less Appropriate for preventing the above-mentioned dripping of molten metal and obtaining a stable weld bead shape appearance It is important to form an amount of slag. The slag is mainly composed of SiO ₂ and MnO, and the amount of this slag greatly depends on the total amount of Si and Mn in the welding wire.
Here, when the total amount of Si and Mn in the welding wire is less than 1.5% by mass, a slag amount sufficient to prevent dripping of the molten metal cannot be obtained. On the other hand, if the total amount of Si and Mn in the welding wire exceeds 3.5% by mass, the slag may become a lump and hinder the welding of the subsequent layers. Accordingly, the total amount of Si and Mn of the welding wire used in the first layer welding is preferably 1.5% by mass or more and 3.5% by mass or less. More preferably, it is 1.8 mass% or more and 2.8 mass% or less.

Total of Ti amount, Al amount and Zr amount of welding wire used in first layer welding: 0.08% by mass or more and 0.5% by mass or less Preventing dripping of the above-mentioned molten metal and obtaining a stable weld bead shape appearance TiO ₂ , Al ₂ O ₃ , and Zr ₂ O ₃ have a great influence on the physical properties (viscosity) of slag that play an important role in the slag.
Here, when the total of the Ti amount, Al amount, and Zr amount of the welding wire is less than 0.08 mass%, the viscosity of the slag effective for preventing dripping of the molten metal cannot be obtained. On the other hand, if the total amount of Ti, Al and Zr in the welding wire exceeds 0.5% by mass, both removal of slag and remelting become difficult, resulting in hindrance to welding in subsequent layers.
Therefore, the total of the Ti content, Al content and Zr content of the welding wire used in the first layer welding is preferably 0.08 mass% or more and 0.5 mass% or less. More preferably, it is 0.15 mass% or more and 0.25 mass% or less.

  The components of the welding wire other than those described above may be appropriately selected according to the components of the thick steel material to be welded. From the viewpoint of suppressing the amount of S, O, and N in the above-described weld metal, S : 0.03 mass% or less, O: 0.01 mass% or less, N: 0.01 mass% or less, Si: 0.05-0.80 mass%, Al: 0.005-0.050 mass %, It is preferable to use a welding wire (for example, JIS Z 3312 YGW18, JIS Z 3319 YFEG-22C).

Shielding gas composition: 20% 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. Therefore, in the vertical multi-layer gas shielded arc welding of the thick steel material targeted by the present invention, in order to suppress the dripping of the molten (welded) metal and obtain a uniform weld bead shape, the convection of the weld metal should be inward. Is preferred.
Here, from the viewpoint of reducing oxygen (O) that governs the flow of molten metal in the weld metal, it is advantageous to keep the CO ₂ gas low, but the CO ₂ gas contracts the arc itself by a dissociative endothermic reaction, There is an effect of making the convection of the weld metal more inward.
Therefore, as the shield gas composition, it is preferable that the CO ₂ gas and 20% by volume or more. More preferably, it is 60 volume% or more. Note that an inert gas such as Ar may be used for the remainder other than the CO ₂ gas. Further, CO ₂ gas: it may be 100 vol%.

  The penetration of the weld is also affected by the directivity of the arc and the gouging effect. Therefore, it is preferable that the polarity of the welding is a wire minus (positive polarity) having a higher arc directivity and a gouging effect.

Conditions other than the above need not be specified, but if the average welding current is less than 270A, the molten pool is small, and on the surface side, it becomes a state of multilayer welding that repeats melting and solidification for each torch weaving, resulting in poor fusion, slag Entrainment is likely to occur. On the other hand, if the average welding current exceeds 360 A, dripping of molten (welded) metal is likely to occur, and it becomes difficult to check the arc point by welding fume and spatter, making adjustment during construction difficult. For this reason, it is preferable that an average welding current shall be 270-360A. In addition, by setting the average welding current to 270 to 360 A, stable penetration can be obtained while suppressing generation of welding fumes and spatters, which is further advantageous in performing welding according to the present invention.
Other conditions may be determined according to a standard method, for example, welding voltage: 32 to 37 V (increase with current), welding speed (upward): 3 to 15 cm / min (preferably 4 to 9 cm / min), wire The protruding length may be about 20 to 45 mm, and the wire diameter may be about 1.2 to 1.6 mm.

The welding conditions in each layer other than the first layer are not particularly limited, and may basically be the same as the above-described welding conditions for the first layer.
Moreover, it is preferable that the number of stacks until the completion of welding is about 2 to 4 layers from the viewpoint of preventing stacking faults. The welding method of the present invention is based on the lamination welding of one pass per layer.

Narrow groove vertical multi-layer gas shield arc welding was performed on the two steel materials having the groove shape shown in Table 1 under the welding conditions shown in Table 2.
Here, all steel materials used were S: 0.005 mass% or less, O: 0.003 mass% or less, and N: 0.004 mass% or less. 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.
As the welding wire, a 1.2 mmφ solid wire of a grade for steel strength or one rank higher than that was used. In addition, as for the component composition in the used welding wire, all are S: 0.005 mass% or less, O: 0.003 mass% or less, N: 0.005 mass% or less, Si: 0.6-0.8 It was mass%, Al: 0.005-0.03 mass%.
Furthermore, the welding current is 270 to 360 A, the welding voltage is 32 to 37 V (increase with the current), the average welding speed is 3 to 15 cm / min (adjusted during welding), the average wire protrusion length is 30 mm, and the welding length Was 400 mm. No. Except for No. 11, welding was performed by providing a gas shield system different from the normal arc welding nozzle.
In addition, about the welding in each layer other than the first layer, it was set as the same heat input condition as the first layer welding fundamentally.

  After the first layer welding, the bead width and the joining depth were measured by observing the cross-sectional macrostructure at five points arbitrarily selected. In addition, about the bead width, the maximum value of the measured value was made into the first layer welding bead width W, and about the joining depth, the minimum value of the measured value was made into the first layer welding joint depth D.

Moreover, the dripping of the molten metal during the first layer welding was visually evaluated as follows.
◎: No weld metal sag ○: Weld metal sag 2 or less ×: Weld metal sag 5 or more or welding interrupted

Furthermore, the ultrasonic inspection was implemented about the finally obtained welded joint, and it evaluated as follows.
A: No detected defect O: Only a defective defect having a defect length of 3 mm or less is detected. X: A defect having a defect length exceeding 3 mm is detected. These results are also shown in Table 2.

As shown in Table 2, No. 1 is an invention example. In 1 to 14, there was no dripping of the first layer weld metal, or even two or less. Further, even in the ultrasonic flaw detection, there was no detection defect, but the defect length was 3 mm or less.
On the other hand, No. which is a comparative example. In Nos. 15 to 19, there were five or more weld metal sags, and / or a defect with a defect length of more than 3 mm was detected in ultrasonic inspection.

  Further, in FIG. 7 shows an outer appearance photograph of the table after the first layer welding (welding operation side), and FIG. From the same figure, No. which properly controlled the weaving conditions. In Example 7 of the invention, it can be seen that the desired joining depth is obtained with a joining depth D of about 28 mm in the first layer welding. At the same time, a stable weld bead shape was obtained.

1: Thick steel material 2: Groove surface of thick steel material 3: Groove of steel lower part 4: Welding torch 5: Welding wire 6: Backing material 7: Weld bead θ: Groove angle G: Groove gap h: Steel material Groove height of lower step t: Plate thickness φ: Angle of welding torch with respect to horizontal direction D: Joining depth in first layer welding W: Weld bead width in first layer welding L: Weaving depth in plate thickness direction M: Maximum weaving width in the thickness direction and in the direction perpendicular to the weld line

Claims (7)

A vertical narrow gap gas shield arc welding method in which two thick steel materials having a groove angle of 25 ° or less, a groove gap of 20 mm or less, and a plate thickness of 40 mm or more are joined by vertical multilayer welding using weaving. In
During the first layer welding, the angle of the welding torch is 25 ° to 75 ° with respect to the horizontal direction, the welding heat input is 30 kJ / cm to 170 kJ / cm and the weaving depth in the plate thickness direction is 15 mm to 50 mm. Welding the torch with the maximum weaving width in the thickness direction and in the direction perpendicular to the welding line being (W-6) mm to Wmm, where W is the weld bead width in the first layer welding. ,
A vertical narrow groove gas shield arc welding method in which a joining depth in the first layer welding is 20 mm or more and 50 mm or less.   2. The vertical narrow gap gas shield arc welding method according to claim 1, wherein the weaving of the first layer welding has a U-shaped weaving pattern of the welding torch viewed from the welding line direction.   The vertical narrow gap gas shielded arc welding method according to claim 1 or 2, wherein the total amount of S and O of the weld metal in the first layer welding is 450 mass ppm or less and the N content is 120 mass ppm or less. .   The vertical narrow gap gas shielded arc according to any one of claims 1 to 3, wherein the total amount of Si and Mn of the welding wire used in the first layer welding is 1.5 mass% or more and 3.5 mass% or less. Welding method.   The vertical narrow gap according to any one of claims 1 to 4, wherein the total amount of Ti, Al, and Zr of the welding wire used in the first layer welding is 0.08 mass% or more and 0.5 mass% or less. Gas shield arc welding method. Stand facing Narrow Gap gas shielded arc welding method according to claim 1, using a gas containing 20 vol% or more of CO ₂ gas as a shielding gas.   The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 6, wherein in the first layer welding, an average welding current is in a range of 270A to 360A.