JPWO2017094578A1 - Vertical narrow groove gas shielded arc welding method - Google Patents

Abstract

The first layer welding conditions, especially the welding torch angle, welding heat input, and weaving conditions, are controlled appropriately so that the joint depth in the first layer welding is 20 mm or more and 65 mm or less. Then, a cooling plate capable of sliding movement in the upward direction is pressed as a surface covering material for the thick steel material, and welding is performed while moving the cooling plate upward in accordance with the upward movement of the welding torch.

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 plate thickness of the steel material. .

The gas shielded arc welding used for welding of steel is generally a consumable electrode type in which a gas of CO ₂ alone or a mixed gas of Ar and CO ₂ is used as a shield for a molten portion. Such gas shielded arc welding is widely used in the fields of manufacturing automobiles, architecture, bridges, shipbuilding, 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 groove gas shielded arc welding in which a groove having a small gap with respect to the plate thickness is welded by an arc welding method. 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 may cause a decrease in 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 with a plate thickness exceeding 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 to 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. It is necessary to reduce the welding amount per pass (≈ heat input) with a low current of about 150A.
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, resulting in a large number of laminating defects such as poor penetration and a large reduction in 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 °, the weaving of the welding torch here is also performed in the groove depth direction. Therefore, in the vertical welding method of Patent Document 3, it is possible to take a relatively large amount of welding per pass.
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 10mm.
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.
By using this two-electrode electrogas arc welding apparatus, it is possible to join thick steel materials up to about 70 mm thick. However, the heat input increases significantly to about 360 kJ / cm by using two electrodes. For this reason, when the heat influence on a steel plate is large and a high characteristic (strength, toughness) is required for a joint, it becomes very difficult to satisfy such a characteristic.
In addition, in this two-electrode electrogas arc welding apparatus, the arc on the back surface side electrode becomes difficult to see, which makes it difficult to prevent welding defects. Furthermore, with this two-electrode electrogas arc welding apparatus, it is difficult to install a copper metal in the groove due to problems such as groove dimensional accuracy. Therefore, low heat input is achieved as multi-pass lamination welding. It is difficult.

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 present invention is a high-quality and high-efficiency that can be applied to welding of thick steel materials, particularly thick steel materials with a plate thickness of 40 mm or more, by utilizing high-function and high-precision welding automation technology. An object is to provide a vertical narrow gap gas shielded arc welding method.

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, in order to obtain the desired mechanical properties in the weld metal and the heat-affected zone and to achieve high efficiency in welding when performing vertical narrow gap gas shielded arc welding of thick steel materials, narrow gaps are required. It was found that it is important to suppress the welding heat input per pass and control the joining depth (welding depth) in the first layer welding within a predetermined range while reducing the welding amount.

  Therefore, the inventors have further studied the welding conditions for performing the above-described welding. 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. And this makes it possible to perform high-quality and high-efficiency vertical narrow-gap gas shielded arc welding that achieves the desired mechanical characteristics even with thick steel materials with a plate thickness of 40 mm or more. I got the knowledge.

In addition, when performing the vertical gas shielded arc welding as described above, since the problem is that the bead appearance of the finally obtained welded joint is likely to deteriorate depending on the welding conditions of the final layer welding, the inventors have found that Went further to solve this issue.
As a result, at the time of final layer welding, a cold plate that can slide in the upward direction is pressed against the thick steel material from the side of the welding torch as the surface material for the groove of the thick steel material. It was found that a beautiful bead appearance can be easily obtained by performing welding while moving the cooling plate upward.
The present invention was completed after further studies based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Vertical narrow gap gas shielded arc welding where two steel plates with 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 single-layer welding or multi-layer welding using weaving. In the method
During first layer welding, the welding torch angle is 25 ° to 75 ° with respect to the horizontal direction, the welding heat input is 30 kJ / cm to 300 kJ / cm, and the weaving depth in the plate thickness direction is 15 mm to 63 mm. Weaving the welding torch with the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line being (W-6) mm to Wmm, where W is the weld bead width in the first layer welding. The joining depth in the first layer welding is 20 mm or more and 65 mm or less,
At the time of final layer welding, a cooling plate capable of sliding movement in the upward direction is pressed against the thick steel material from the side of the welding torch as the surface contact material of the thick steel material, and in accordance with the upward movement of the welding torch Welding while moving the cooling plate upward;
Vertical narrow gap gas shielded arc welding method.

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

3. The vertical narrow gap 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 ppm by mass or less and the N content is 120 ppm by mass or less. .

4). 4. The vertical narrow groove gas shield arc welding method according to any one of 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.

5. The vertical narrow gap gas shielded arc welding according to any one of 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% by mass or more and 0.50% by mass or less. Method.

6). 6. The vertical narrow groove gas shield 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 for the first layer welding.

7). The vertical narrow groove gas shield arc welding method according to any one of 1 to 6, wherein an average welding current of the first layer welding is 270A or more and 360A or less.

According to the present invention, even when a thick steel material having a thickness of 40 mm or more is welded, while preventing bead shape stabilization and welding 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 savings by improving the efficiency of welding, so that the welding construction cost can be greatly reduced, and more easily. A beautiful bead appearance can be obtained.

Examples of various groove shapes are shown. In a V-shaped groove | channel shape, an example of the construction point at the time of constructing first layer welding with the welding method concerning one embodiment of the present invention is shown. In a V-shaped groove shape, an example of a groove cross section after first layer welding is performed by a welding method according to an embodiment of the present invention is shown. In the first layer welding weaving, an example of a welding torch weaving pattern as seen from the direction of the welding line is shown. (A) is U-shaped, (b) is trapezoidal, (c) is V-shaped, (d) is It is triangular. An example of the construction point at the time of constructing final layer welding by the welding method concerning one embodiment of the present invention is shown. In invention example (No. 7), it is a photograph after performing first layer welding, (a) shows the whole appearance, and (b) shows a groove section.

Hereinafter, the present invention will be specifically described.
1A to 1C show examples of various groove shapes. 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 target groove shape here can be either a V-shaped groove (including an I-shaped groove and a L-shaped groove) or a Y-shaped groove. As shown in FIG. 1C, a multi-stage Y-shaped groove may be used.
As shown in FIGS. 1B and 1C, the groove angle and the groove gap in the case of the Y-shaped groove are the groove angle and the groove gap in the groove of the steel lower step part. Here, the groove in the lower part of the steel material means 20 to 40% of the plate thickness from the steel material surface that 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 by the welding method according to the embodiment of the present invention in the 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 present welding method is a gas shielded arc welding in which two thick steel materials having a predetermined plate thickness are butted and these thick steel materials are joined together by vertical welding using weaving. Yes, 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 a welding method according to an embodiment of the present invention in a V-shaped groove shape. In the figure, symbol 7 is a weld bead (weld bead in the first layer welding), symbol D is the joint depth in the first layer welding, and W is the weld bead width in the first layer welding (between the grooves after the first layer welding). Gap).
In addition, the joining depth D in the first layer welding is the minimum value of the weld bead height in the first layer welding when starting from the steel surface that is the back surface during welding (closest (low) first layer welding from the starting steel surface). (Weld bead height).
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 more efficient welding is possible, but defects such as poor fusion tend to occur. In addition, welding when the 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 case where the groove angle is 25 ° or less at which higher 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 this 0 ° is the most efficient in terms of the amount of welding, and the groove angle is 0 °. (I-shaped groove) may be used, but since the groove is closed during welding due to welding thermal strain, the thickness t (however, in the case of Y-shaped groove, the lower part of the steel material) It is preferable to set a groove angle according to the groove height h).
Specifically, the groove angle is preferably (0.5 × t / 20) ° or more and (2.0 × t / 20) ° or less, more preferably (0.8 × t / 20) ° or more, (1.2 × t / 20) ° or less. For example, when the plate thickness t is 100 m, the groove angle is preferably 2.5 ° or more and 10 ° or less, more preferably 4 ° or more and 6 ° or less.
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 °.

Groove gap G: 20 mm or less The smaller the groove portion of the steel material, the faster and more efficient the welding becomes 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 they are 4 mm or more and 12 mm or less.

Plate thickness t: 40 mm or more The steel plate thickness should be 40 mm or more. This is because if the plate thickness of the steel material is less than 40 mm, even if the conventional welding method, for example, the electrogas arc welding of Patent Document 4, is used, there will be no significant problem in performance such as the strength and toughness of the joint. is there.
When a general rolled steel material is targeted, the upper limit of the plate thickness is generally 100 mm. Therefore, the thickness of the steel material is preferably 100 mm or less. In the case of single-layer welding, the thickness is preferably 65 mm or less.

  In addition, high-tensile steel (for example, ultra-thick YP460MPa grade steel for shipbuilding (tensile strength 570MPa grade steel) and TMCP steel for construction SA440 (tensile strength 590MPa grade steel)) is particularly suitable as the material to be welded. It is. 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, the welding method of the present invention enables efficient welding at a heat input of 300 kJ / cm or less, and also enables the welding of 590 MPa class high-tensile steel sheets and 590 MPa class corrosion resistant steels, which are high alloy systems. Of course, mild steel can be handled without problems.

The reason why the groove angle, the groove gap, and the steel plate thickness are limited in the welding method of the present invention has been described above. However, the welding method of the present invention is suitable for the above-described groove shape and plate thickness of the thick steel material. In order to perform welding efficiently with a large amount of heat input, it is important to set the joining depth in the first layer welding within a predetermined range while appropriately controlling the first layer welding conditions.
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 65 mm or less Thickness: 40 mm or more In order to weld a steel material of 40 mm or more, especially with multipass welding of 2 passes or more, the joining depth in the first layer welding must be 20 mm or more. is there. When the joining depth in the first layer welding is less than 20 mm, the welding heat concentrates, and dripping of the molten metal occurs. On the other hand, if the joining depth in the first layer welding exceeds 65mm, welding heat input tends to be excessive, and welding defects such as high-temperature cracking, poor fusion of the groove surface due to dispersion of heat during welding, slag entrainment, etc. Will occur. Therefore, the joining depth in the first layer welding is 20 mm or more and 65 mm or less. Preferably, it is 25 mm or more and 60 mm or less. In the case of single layer welding, the joining depth D in the first layer welding is approximately the same as the plate thickness (40 mm or more).

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 of the surface of the weld bead and the molten metal sag 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. On the other hand, when the angle of the welding torch exceeds 75 ° with respect to the horizontal direction, it is difficult to suppress the dripping of the molten metal. 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 300 kJ / cm or less In multi-layer welding, the number of passes can be reduced by increasing the heat input per pass (= 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 300 kJ / cm, a dedicated wire that takes into account the dilution of the steel material is indispensable to secure the properties of the weld metal, and even steel materials that are designed to withstand the welding heat input are required. . On the other hand, in order to secure molten metal and obtain a weld zone free from welding defects, it is advantageous that the heat input is high, and if the heat input is less than 30 kJ / cm in a narrow groove, the groove surface will melt. Insufficient stacking defects are unavoidable.
Therefore, the welding heat input is 30 kJ / cm or more and 300 kJ / cm or less. Preferably, it is 90 kJ / cm or more and 280 kJ / cm or less.

Weaving depth L in the plate thickness direction in the weaving of the welding torch: 15 mm to 63 mm This welding method performs the weaving of the welding torch. It is important to properly control 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 this welding method, the joining depth and the weaving width in the plate thickness direction are approximately the same. For this reason, if the weaving depth in the plate thickness direction is less than 15 mm, it is difficult to set the joining depth in the first layer welding to 20 mm or more. On the other hand, when the weaving depth in the plate thickness direction exceeds 63 mm, it becomes difficult to set the joining depth in the first layer welding to 65 mm or less. Furthermore, the welding heat input becomes excessive, making it difficult to obtain the desired mechanical properties in the heat-affected zone of the weld metal or steel material, as well as high-temperature cracking and groove due to the dispersion of heat during welding. Weld defects such as poor surface fusion and slag entrainment are likely to occur.
Therefore, the weaving depth in the plate thickness direction is 15 mm or more and 63 mm or less. Preferably, it is 25 mm or more and 60 mm or less.

The maximum weaving width M: (W-6) mm to Wmm (W: welding bead width in the first layer welding) in the thickness direction and the direction perpendicular to the welding line in the weaving of the welding torch
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, if the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line exceeds Wmm, the molten metal will sag and welding will not be realized.
Accordingly, 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 W mm. Preferably, it is (W-4) mm or more and (W-1) mm or less.
In the case of single-layer welding, W is a groove width on the steel material surface that becomes the surface (surface on the welding device (welding torch) side) during welding.

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 at a location close to the welding surface side tends to cause dripping of the molten metal. Further, when the welding torch operation deviates from the groove surface, uniform melting of the groove surface cannot be obtained, and welding defects such as poor fusion tend 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.
In addition, when U-shaped weaving or trapezoidal weaving is applied to the groove shape described above, M ₁ , M ₂ , and M ₃ in FIGS. 4A and 4B are 2 to 18 mm and 0 to 10 mm, respectively. It will be about 0-10mm.
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 Hz or more and 0.5 Hz or less). ), And the stop time may be about 0 to 0.5 seconds (preferably 0.2 seconds or more and 0.3 seconds or less).

  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 the first layer welding: 450 mass ppm or less To achieve stable upward welding, the molten metal is prevented from dripping and has a 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), the convection of the weld metal becomes outward on the surface in addition to the decrease in surface tension and viscosity, 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, which controls 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 lower limit is not particularly limited, but is preferably 15 ppm.

The welding wire usually contains 0.010 to 0.025 mass% of S 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 shielding gas. For example, when 100 volume% 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 that 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, when 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. The lower limit is not particularly limited, but is preferably 15 ppm.

Further, normally, 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 nozzle inner diameter of 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 nozzle inner diameter 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 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 due to the dilution of the steel material at the time of welding, it is necessary to use a steel material of S: 0.005 mass% or less, O: 0.003 mass% or less, and N: 0.004 mass% or less. It is suitable for suppressing the S amount, O amount and N amount of the weld metal in the first layer welding described above.

Total amount of Si and Mn in the welding wire used in the first layer welding: 1.5% to 3.5% by mass To prevent the molten metal from dripping and to obtain a stable weld bead appearance, an appropriate amount of slag is used. It is important to form. 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 of the welding wire.
Here, if the sum of the Si content and the Mn content of the welding wire is less than 1.5% by mass, a slag amount sufficient to prevent dripping of the molten metal may not 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 becomes a lump and may interfere with welding in the subsequent layers. Accordingly, the total amount of Si and Mn in 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 amount of Ti, Al and Zr of welding wire used in first layer welding: 0.08 mass% or more and 0.50 mass% or less Important role to prevent dripping of molten metal and to obtain stable weld bead shape appearance It is TiO ₂ , Al ₂ O _3, and Zr ₂ O ₃ that greatly affects the physical properties (viscosity) of the slag that fulfills the above.
Here, when the sum 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 of the welding wire exceeds 0.50% by mass, both removal of slag and remelting become difficult, which may hinder welding in subsequent layers.
Therefore, the total amount of Ti, Al and Zr of the welding wire used in the first layer welding is preferably 0.08% by mass or more and 0.50% by 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% (for example, JIS Z 3312 YGW18 and JIS Z 3319 YFEG-22C etc.) is preferably used.

Shielding gas composition: 20% by volume or more of CO ₂ gas The penetration of the weld is governed by the gouging effect of the arc itself and the convection of the weld metal at high temperature. 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 the oxygen (O) that governs the flow of molten metal in the weld metal, it is advantageous to keep the CO ₂ gas low. On the other hand, the CO ₂ gas has an arc by a dissociative endothermic reaction. It has the effect of constricting and making the convection of the weld metal more inward.
Therefore, the shielding gas composition is preferably 20% by volume or more of CO ₂ gas. 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, what is necessary is just to set the polarity of welding according to the characteristic of a welding material.

The 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 and Slag entrainment tends to occur. On the other hand, if the average welding current exceeds 360 A, the molten (welded) metal tends to sag, 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. Further, 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 carrying out this welding method.
For other conditions, it is sufficient to follow a regular method, for example, welding voltage: 32 to 37 V (increase with current), welding speed (upward): 2 to 15 cm / min (preferably 4 cm / min or more, 9 cm / min) Below), wire protrusion length: 20 to 45 mm, wire diameter: about 1.2 to 1.6 mm.

The first layer welding conditions have been described above. In the vertical narrow gap gas shielded arc welding method of the present invention, as shown in FIG. 5, the thick steel material 1 is connected to the thick steel material 1 from the welding torch 4 side during the final layer welding. It is important to press the cooling plate 8 that can slide and move in the upward direction as an edge of the groove of the groove, and perform welding while moving the cooling plate 8 upward in accordance with the upward movement of the welding torch 4 It is. This makes it possible to easily obtain a beautiful bead appearance. In FIG. 5, the illustration of the molten pool and the weld bead in the final layer welding is omitted.
Here, a water-cooled copper metal plate (copper metal) is suitable as the cooling plate. Further, from the viewpoint of workability, it is preferable that the length of the cooling plate in the upward direction (welding line direction) is 0.4 to 2.0 times the length of the thick steel material.

The welding conditions in each weld layer other than those described above are not particularly limited. For example, similarly to the initial layer welding, the welding may be performed by performing weaving according to the joining depth. In this case, the welding conditions such as the welding current, the welding voltage, and the wire to be used may be the same as in the first layer welding.
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. In the case of single layer welding, the first layer welding is the final layer welding.

Narrow groove vertical upward 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 mass%, Al: 0.005-0.030 mass% Met.
Furthermore, the welding current is 200 to 380A, the welding voltage is 28 to 37V (increases with the current), the average welding speed is 2.3 to 15.0cm / min (adjusted during welding), the average wire protrusion length is 30mm, and the welding length The thickness was 400 mm. Further, except for No. 11, welding was performed by providing a gas shield system different from the normal arc welding nozzle.

  In addition, No. 1 to 19 are multilayer welding, and even in each layer other than the first layer, welding current is set to 270 to 330 A, welding voltage is set to 28 to 37 V, gas shield arc welding using weaving is performed, and welding is performed. Finished the joint. No. 20 finished the welded joint as a single layer weld. Furthermore, in No. 1-14 and No. 19-20, a water-cooled type that allows sliding movement in the upward direction from the welding torch side to the thick steel material groove as a facing material for the groove of the thick steel material during final layer welding. A copper metal plate (copper metal) was pressed and welding was performed while the metal plate was moved upward in accordance with the upward movement of the welding torch. On the other hand, in Nos. 15 to 18, welding was performed without using such a water-cooled copper metal plate during final layer welding.

  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 bead width W in the first layer welding, and about the joining depth, the minimum value of the measured value was made into the joining depth D in the first layer welding.

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 3 or more and 4 or less ×: Weld metal sag 5 or more or welding interruption

Furthermore, the ultrasonic inspection was implemented about the finally obtained welded joint, and it evaluated as follows.
◎: No detected defects ○: Only defective defects with a defect length of 3 mm or less are detected ×: Defects with a defect length exceeding 3 mm are detected

In addition, the bead surface of the finally obtained welded joint was subjected to appearance inspection and evaluated as follows.
○: The unevenness of the bead surface is small and sufficiently glossy. X: The unevenness of the bead surface is large. These results are also shown in Table 2.

As shown in Table 2, in Nos. 1 to 14 and Nos. 19 to 20 which are invention examples, there was no sagging of the first layer weld metal, or even at most two places. Also in ultrasonic flaw detection, there was no detection defect or even a defect length of 3 mm or less. Furthermore, in these inventive examples, in the finally obtained welded joint, irregularities on the bead surface were small, and a beautiful bead appearance was obtained.
On the other hand, in Nos. 15 to 18 as comparative examples, there were five or more weld metal sags, or a defect with a defect length of more than 3 mm was detected in ultrasonic inspection. In No. 15-18, which was welded without using a water-cooled copper metal plate during the final layer welding, the final welded joint had large bead surface irregularities and sufficient gloss. It was not obtained.

  6A shows an appearance photograph of the front side (welding operation side) after the first layer welding of No. 7, which is an example of the invention, and FIG. 6B shows a cross-sectional macrostructure photograph. From the figure, it can be seen that, in the invention example No. 7 in which the weaving conditions and the like are appropriately controlled, 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 lower part of steel material 4: Welding torch 5: Welding wire 6: Backing material 7: Weld bead (weld bead in first layer welding)
8: Cooling plate θ: Groove angle G: Groove gap h: Groove height of steel lower step t: Plate thickness φ: Angle of welding torch with respect to horizontal direction D: Joint depth in first layer welding W: First layer Weld bead width in welding L: Weaving depth in the plate thickness direction M: Maximum weaving width in the plate thickness direction and perpendicular to the weld line

Claims (7)

Vertical narrow gap gas shielded arc welding where two steel plates with 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 single-layer welding or multi-layer welding using weaving. In the method
During first layer welding, the welding torch angle is 25 ° to 75 ° with respect to the horizontal direction, the welding heat input is 30 kJ / cm to 300 kJ / cm, and the weaving depth in the plate thickness direction is 15 mm to 63 mm. Weaving the welding torch with the maximum weaving width in the plate thickness direction and the direction perpendicular to the weld line being (W-6) mm to Wmm, where W is the weld bead width in the first layer welding. The joining depth in the first layer welding is 20 mm or more and 65 mm or less,
At the time of final layer welding, a cooling plate capable of sliding movement in the upward direction is pressed against the thick steel material from the side of the welding torch as the surface contact material of the thick steel material, and in accordance with the upward movement of the welding torch Welding while moving the cooling plate upward;
Vertical narrow gap gas shielded arc welding method.   The vertical narrow gap gas shielded arc welding method according to claim 1, wherein, in the weaving of the first layer welding, the weaving pattern of the welding torch viewed from the welding line direction is a U-shape.   The vertical narrow gap gas shielded arc welding according to claim 1 or 2, wherein the total amount of S and O of the weld metal in said first layer welding is 450 mass ppm or less and N content is 120 mass ppm or less. Method.   The vertical narrow groove gas shielded arc welding method 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.   The vertical narrow gap gas shielded arc 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 0.50 mass% or less. Welding method. The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 5, wherein a gas containing 20% by volume or more of CO ₂ gas is used as the shielding gas for the first layer welding.   The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 6, wherein an average welding current of the first layer welding is 270A or more and 360A or less.

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