CN107921569B

CN107921569B - Vertical narrow groove gas shielded arc welding method

Info

Publication number: CN107921569B
Application number: CN201680045636.5A
Authority: CN
Inventors: 片冈时彦; 早川直哉; 大井健次
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2015-09-11
Filing date: 2016-09-07
Publication date: 2020-02-14
Anticipated expiration: 2036-09-07
Also published as: JP6119940B1; JPWO2017043086A1; CN107921569A; WO2017043086A1; KR20180021893A; KR102014811B1

Abstract

The invention relates to a gas shielded arc welding method for a vertical narrow groove. In a vertical narrow groove gas shielded arc welding method for joining 2 thick steel materials (1) having a thickness of 10mm or more by single layer welding or multilayer welding using weaving under a predetermined groove condition, weaving is performed for primary layer welding using a welding torch (4) having a curved portion and a tip defined by the curved portion, and at this time, when the welding torch is weaved with respect to a groove surface (2) of the thick steel materials, the tip of the welding torch is weaved toward the groove surface of the thick steel materials under a predetermined condition.

Description

Vertical narrow groove gas shielded arc welding method

Technical Field

The invention relates to a narrow-groove gas shielded arc welding method, in particular to a vertical narrow-groove gas shielded arc welding method which can be applied to butt welding of 2 pieces of thick steel.

Here, the "narrow groove" means that the groove angle is 25 ° or less and the groove gap is 20mm or less.

Background

Gas shielded arc welding for steel welding applications typically involves the introduction of CO₂Gas alone, or Ar and CO₂The consumable electrode type in which the mixed gas of (a) is used for protecting a melting portion is widely used in the manufacturing field of automobiles, buildings, bridges, electric devices, and the like.

However, in recent years, as steel structures have become larger and thicker, the amount of welding in the manufacturing process, particularly the amount of welding by butt welding of steel materials, has increased, and further, a large amount of time is required for welding work, resulting in an increase in work cost.

As a method for improving this, application of narrow groove gas shielded arc welding in which a groove having a gap with a small plate thickness is multi-welded by an arc welding method is considered. Since the amount of deposited metal is reduced in this narrow groove gas shielded arc welding as compared with the usual gas shielded arc welding, the welding efficiency and energy saving can be achieved, and further, the reduction of the construction cost is expected.

On the other hand, electroslag welding is generally used for vertical high-efficiency welding, but 1-pass high heat input welding is fundamental, and there is a possibility that toughness is lowered due to excessive heat input in welding with a plate thickness of more than 60 mm. Further, at present, 1-pass welding has a limitation on the plate thickness, and particularly welding with a plate thickness of more than 65mm has not been established.

Therefore, it is desired to develop a high-quality and high-efficiency welding method using narrow groove gas shielded arc welding for vertical welding.

As a welding method for applying such narrow groove gas shielded arc welding to vertical welding, for example, patent document 1 discloses a double-sided multilayer welding method for a double-sided U-groove joint. In this welding method, laminate welding by TIG welding using an inert gas is performed, and the use of an inert gas suppresses the generation of slag and spatter, thereby preventing laminate defects.

However, TIG welding as a non-consumable electrode type and MAG welding using a steel wire as a consumable electrode, CO₂The welding process itself is significantly less efficient than welding.

Patent document 2 discloses a vertical welding method of a narrow groove in which a welding torch is swung to suppress sputtering and fusion failure.

However, in this welding method, since the oscillation direction of the welding torch is not the groove depth direction but the steel plate surface direction, the welding torch needs to be oscillated before the molten metal drops, and as a result, it is necessary to set the welding current to a low current of about 150A and suppress the deposition amount per 1 pass (approximately equal to the heat input amount).

Therefore, when this welding method is applied to welding of thick steel materials having large thicknesses, the number of lamination defects such as weld penetration defects increases due to a small number of passes of lamination welding, and the welding efficiency significantly decreases.

Further, patent document 3 discloses a vertical welding method in which a welding torch is swung to suppress fusion failure, as in patent document 2.

The face angle (bevel angle) disclosed here is as wide as 26.3 to 52 °, but the oscillation of the welding torch is also performed in the depth direction of the bevel. Therefore, in the vertical welding method of patent document 3, the amount of deposit can be obtained more per 1 pass.

However, since the amount of oscillation in the groove depth direction is small and the composition of the weld metal and the wire is not considered, it is necessary to suppress the deposition amount (heat input amount) per 1 pass and the weld depth per 1 pass is as shallow as about 10 mm.

Therefore, when this welding method is applied to welding of thick steel materials having large thicknesses, the number of passes of the laminate welding is still small, and thus laminate defects such as weld penetration failure increase, and welding efficiency decreases.

Patent document 4 discloses a two-electrode carbon dioxide arc welding apparatus capable of 1-pass welding of an extremely thick material.

By using the carbon dioxide arc welding apparatus with the two electrodes, the sheet thickness: joining of thick steel materials of up to about 70 mm. However, since the heat input amount is greatly increased to about 360kJ/cm by the double electric polarization, the thermal influence on the steel sheet is large, and it is very difficult to satisfy high properties (strength and toughness) when the joint is required to have such properties.

In this two-electrode carbon dioxide gas arc welding apparatus, a pressing mechanism is indispensable in which a ceramic backing plate is provided on the back side of the bevel and a water-cooled copper backing plate is provided on the front side (the side of the welding machine), and there is no risk of dripping of molten metal, but the welding apparatus is complicated.

In addition, in this two-electrode carbon dioxide gas arc welding apparatus, since a pressing mechanism for providing a copper substrate on the surface (the side of the welding machine) is indispensable, 1-pass welding is essential, and it is difficult to achieve low heat input in the form of multi-pass lamination welding.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-61483

Patent document 2: japanese patent application laid-open No. 2010-115700

Patent document 3: japanese patent laid-open No. 2001-205436

Patent document 4: japanese laid-open patent publication No. 10-118771

Disclosure of Invention

As described above, at present, a high-quality and high-efficiency vertical narrow groove gas shielded arc welding method applicable to welding of thick steel materials has not been developed yet.

On the other hand, the welding automation technology (welding robot) has been developed to be lightweight, highly functional, and highly precise, and it has been difficult to swing the welding torch suitable for the groove shape and the welding portion, and by utilizing this welding automation technology, it has become possible to adapt to welding work (condition setting) of the steel material, the groove shape, the welding portion, and the welding material (welding wire).

The invention aims to provide an upright narrow-groove gas shielded arc welding method which can weld high-quality and high-efficiency thick steel materials by utilizing a high-function and high-precision welding automation technology.

In order to solve the above problems, the present inventors have made extensive studies on welding conditions for applying vertical narrow groove gas shielded arc welding to a thick steel material.

As a result, it has been found that, when performing vertical narrow groove gas shielded arc welding of a thick steel material, it is important to suppress the amount of input of welding heat per 1 pass by multilayer welding in which the groove gap is made narrower or 2 passes or more in order to obtain desired mechanical characteristics in the weld metal and the heat-affected zone and to achieve high welding efficiency.

However, even when the amount of welding heat input per 1 pass is suppressed in this manner, it is necessary to obtain a sufficient bonding depth (welding depth) while preventing occurrence of a welding defect or the like, and particularly to obtain a sufficient bonding depth in primary layer welding. Therefore, the inventors of the present invention have further studied welding conditions that can achieve the above-described effects.

As a result, the following findings were obtained: in the swing of the primary layer welding using the welding torch having the curved portion and the tip defined by the curved portion, it is important to swing the tip of the welding torch toward the groove surface of the thick steel material under appropriate conditions when swinging the welding torch with respect to the groove surface of the thick steel material, and therefore, it is possible to secure a sufficient joint depth while sufficiently melting the groove surface to prevent the occurrence of welding defects, and further, it is possible to stabilize the bead shape including suppressing the dripping of molten metal which becomes a problem in the high-current vertical welding.

The present invention has been completed by further repeated studies based on the above findings.

That is, the gist of the present invention is as follows.

1. A vertical narrow groove gas shielded arc welding method, wherein a groove angle is set to be 25 DEG or less, a groove gap is set to be 20mm or less, 2 pieces of thick steel materials with a thickness of 10mm or more are joined by single layer welding or multilayer welding using weaving,

wherein the swing of the primary layer welding is performed by using a welding torch having a curved portion and a tip defined by the curved portion, and at this time, when swinging with respect to the bevel face of the thick steel material, the tip of the welding torch is swung toward the bevel face of the thick steel material, a position at which the tip of the welding torch coincides with a weld line direction when viewed from a plate thickness direction of the thick steel material is set as a reference position, an angle theta 1 of the tip of the welding torch with respect to a horizontal direction at the reference position is set to 10 DEG to 45 DEG, and a swing angle theta 2 of the tip of the welding torch from the reference position is set to 10 DEG to 60 DEG,

the joining depth of the primary layer welding is set to 10mm or more.

2. The gas-shielded arc welding method with a narrow vertical groove according to claim 1, wherein the joint is a single-layer weld and the groove gap is 25% or less of the thickness of the thick steel material.

3. The vertical narrow groove gas-shielded arc welding method according to claim 1, wherein the joining is multilayer welding, and a joining depth of the primary layer welding is 25mm to 60 mm.

4. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein a weaving pattern of the welding torch seen from the weld line direction in the weaving of the initial layer welding is コ -shaped.

5. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 4, wherein a total of an S amount and an O amount of the weld metal in the initial layer welding is 450ppm by mass or less and an N amount is 120ppm by mass or less.

6. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 5, wherein the total of the Si content and the Mn content of the wire used for the primary layer welding is 1.5 to 3.5% by mass.

7. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 6, wherein a total of the Ti amount, the Al amount, and the Zr amount of the wire used for the primary layer welding is 0.08 to 0.50% by mass.

8. The gas shielded arc welding method with a narrow vertical groove according to any one of 1 to 7, wherein the gas shielded arc welding method uses a gas shielded arc welding method in which the gas shielded arc welding method contains 20 vol% or more of CO₂The gas is used as a protective gas.

9. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 8, wherein an average welding current in the initial layer welding is in a range of 270 to 420A.

According to the present invention, even when a thick steel material having a thickness of 10mm or more is welded, high-quality and highly efficient narrow-groove gas shielded arc welding can be performed while stabilizing the shape of the bead including suppressing dripping of molten metal, which is a problem in vertical welding, and preventing the occurrence of welding defects.

Therefore, the welding method of the present invention can achieve energy saving due to high welding efficiency even if the deposited amount is small as compared with the usual gas shielded arc welding, and thus can significantly reduce the welding cost.

Further, in the welding method of the present invention, since a water-cooled pressing mechanism for a copper substrate for preventing dripping of molten metal, such as the carbon dioxide arc welding apparatus shown in patent document 4, is not required, the complexity of the apparatus can be avoided, and further, since the input of welding heat per 1 pass can be suppressed by performing welding work in a plurality of passes and with a predetermined groove shape, it is easy to ensure desired mechanical characteristics in the heat affected zone between the weld metal and the steel material.

Drawings

Fig. 1 is a diagram showing examples of various groove shapes.

Fig. 2 is a view showing a construction procedure in the case of performing the welding of the initial layer by the welding method according to the embodiment of the present invention in the V-groove shape.

Fig. 3 is a schematic view showing a swinging state of the welding torch when swinging with respect to the bevel face of the thick steel material.

Fig. 4 is a view showing an example of a groove cross section after initial layer welding is performed in a V-shaped groove shape.

Fig. 5 is a diagram showing a weaving pattern of the welding torch as seen from the welding line direction in weaving of the initial layer welding.

Detailed Description

The present invention will be described in detail below.

Fig. 1 (a) to (c) show examples of various groove shapes. In the figure, reference numeral 1 denotes a thick steel material, 2 denotes a bevel face of the thick steel material, 3 denotes a groove of a lower step portion of the steel material (in a Y-shaped groove), and reference numeral θ denotes a groove angle, G denotes a groove gap, t denotes a plate thickness, and h denotes a groove height of the lower step portion of the steel material (in the Y-shaped groove).

The groove shape to be used here may be any of a V-groove (including an I-groove and an レ -groove) and a Y-groove, as shown in fig. 1, or may be a multi-step Y-groove, as shown in fig. 1 (c).

As shown in fig. 1 (b) and (c), the groove angle and the groove gap in the case of the Y-groove are set to the groove angle and the groove gap in the groove of the steel lower step portion. Here, the groove of the lower steel portion is a region from the steel surface to the back surface (the surface on the welding device (welding torch) side is the front surface, and the surface on the opposite side is the back surface) to about 20 to 40% of the plate thickness during welding.

Fig. 2 is a view showing a construction procedure in the case where the welding method according to one embodiment of the present invention is used to construct the initial layer welding in the V-groove shape. In the figure, reference numeral 4 denotes a welding torch, 5 denotes a welding wire, and 6 denotes a backing material. The weld line, weld pool, and weld bead are not shown.

Here, as shown in fig. 2, this welding method is based on upward welding in which 2 thick steel materials having a predetermined thickness are butted and these thick steel materials are joined by gas shielded arc welding using weaving vertical welding, and the traveling direction is directed upward. Then, when the welding torch swings with respect to the bevel face of the thick steel material, the tip of the welding torch swings toward the bevel face of the thick steel material.

Here, the groove shape of the V shape is shown as an example, but the same applies to other groove shapes.

Fig. 3 is a schematic view showing a state of oscillation of the welding torch when the welding torch oscillates with respect to the slope surface of the thick steel material, and fig. 3 (a) and (b) are views showing a state in which the welding torch is located at a reference position and a state in which the welding torch oscillates at an angle θ 2, respectively, as viewed from the plate thickness direction (the back surface (the side having the backing plate material) of the thick steel material in fig. 2). Fig. 3 (c) is an X-direction view of fig. 3 (a). The reference position is a position where the tip (center line, i.e., the extending direction of the welding wire) of the welding torch coincides with the welding line direction when viewed from the plate thickness direction as shown in fig. 3 (a). In fig. 3 (a) and (b), a bevel surface (not shown) of the thick steel material to be melted is located on the left side of the drawing.

In the figure, reference numeral 7 denotes a main body portion, 8 denotes a power feeding tip, 9 denotes a bending portion, and 10 denotes a tip portion. Here, the tip portion 10 is a portion closer to a welding wire (not shown) than the bent portion 9. The bending portion 9 may be provided in either the main body portion 7 or the power feeding tip 8 constituting the welding torch, and is preferably provided in the power feeding tip 8 in view of workability and the like.

Further, θ 1 is an angle of the tip of the welding torch with respect to the horizontal direction at the reference position, θ 2 is a swing angle of the tip of the welding torch from the reference position, θ 3 is a bending angle of a bending portion of the welding torch, and l is a length of the tip of the welding torch, which are based on the center line of each part of the welding torch.

Fig. 4 is a view showing an example of a groove cross section after initial layer welding is performed in a V-shaped groove shape. In the figure, reference numeral 11 denotes a weld, reference numeral D denotes a joint depth of the primary layer weld, and reference numeral W denotes a weld width (gap between grooves after the primary layer weld) of the primary layer weld.

The joining depth D of the primary layer welding is the minimum value of the primary layer bead height (the primary layer bead height closest (lower) to the steel surface that becomes the starting point) when the steel surface that becomes the back surface is used as the starting point at the time of welding. Here, the groove shape of V is shown as an example, but D and W are also the same in other groove shapes.

Next, the reason why the groove angle, the 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.

Bevel angle θ: below 25 °

The smaller the bevel portion of the steel material is, the faster and more efficient welding becomes possible, while defects such as fusion failure are likely to occur. Welding at a bevel angle of more than 25 ° can also be performed by a conventional construction method. Therefore, in the present invention, the groove angle at which construction is difficult in the conventional construction method and further high efficiency is expected is: the case of 25 ° or less is targeted.

In addition, in the V-groove, the groove angle of 0 ° is called an I-groove, and from the viewpoint of the deposition amount, the most effective case of 0 ° and the groove angle may be 0 ° (I-groove), but in view of this, it is preferable to set the corresponding groove angle according to the plate thickness t (in the case of the Y-groove, the groove height h of the steel lower step portion, among others) because the groove closes during welding due to welding thermal strain.

Specifically, the groove angle is preferably (0.5 × t/20) ° to (2.0 × t/20) °, and more preferably (0.8 × t/20) ° to (1.2 × t/20) °. For example, when the plate thickness t is 100mm, the groove angle is preferably 2.5 ° to 10 °, and more preferably 4 ° to 6 °.

However, if the plate thickness t is greater than 100mm, the upper limit of the preferable range is greater than 10 °, but in this case, the upper limit of the preferable range is set to 10 °.

Groove gap G: less than 20mm

The smaller the bevel portion of the steel material is, the faster and more efficient welding is possible. In addition, when the groove gap is larger than 20mm, molten metal is liable to drip and construction is difficult. As a countermeasure, it is necessary to suppress the welding current to a low level, but welding defects such as slag inclusion are likely to occur. Therefore, the groove gap is set to 20mm or less. Preferably in the range of 4mm to 12 mm. In particular, when the welding is performed by single-layer welding consisting of only initial layer welding, the groove gap is more preferably 25% or less of the thickness of the thick steel material of the material to be welded. More preferably 20% or less.

Plate thickness t: over 10mm

The thickness of the steel material is set to 10mm or more. This is because, if the thickness of the steel material is less than 10mm, even if the conventional welding method is used, for example, semi-automatic CO using a semi-flux cored wire is used₂In arc welding, a sound joint may be obtained while suppressing the amount of welding heat input. Preferably 20mm or more, more preferably 25mm or more.

When a general rolled steel material is used, the thickness is usually 100mm as an upper limit. Therefore, the upper limit of the thickness of the steel material to be used in the present invention is preferably 100mm or less.

In addition, as the steel grade to be welded, high-tensile steel (for example, ultra-thick YP460MPa grade steel for shipbuilding (tensile strength 570MPa grade steel), and TMCP steel SA440 for construction (tensile strength 590MPa grade steel)) is particularly preferable. This is because the welding heat input of high tensile steel is strictly limited, cracks are likely to occur in the weld metal, and the required joint strength and toughness cannot be obtained due to the influence of the welding heat. In contrast, in the welding method according to the embodiment of the present invention, the heat input amount: the welding efficiency is 170kJ/cm or less, and 590MPa grade high tensile steel plate and 590MPa grade corrosion resistant steel which is a high alloy system can be welded. Of course, mild steel can also be used without problems.

The reason why the groove angle, the groove gap, and the plate thickness of the steel material are limited in the welding method of the present invention has been described above, but it is important in the welding method of the present invention to efficiently weld while appropriately controlling the welding conditions with the amount of heat input suitable for the groove shape to obtain a predetermined joint depth.

The welding conditions and the joining depth will be described below.

Angle θ 1 of the tip of the welding torch at the reference position with respect to the horizontal direction: 10-45 degree

As shown in fig. 3, the welding torch having a curved portion and a tip defined by the curved portion is used, and the tip of the welding torch is swung while swinging toward the tapered surface of the thick steel material, so that the tip of the welding wire can be brought close to the tapered surface while avoiding contact between the power feeding tip and the tapered surface of the thick steel material. Further, since the wire tip also faces the bevel surface, the bevel surface can be directly melted by the arc. Therefore, even when the amount of welding heat input per 1 pass is suppressed, the bevel surface can be sufficiently melted to suppress the occurrence of welding defects. Further, the expansion of the arc heat input range due to the oscillation of the welding torch can suppress the dripping of the molten metal and stabilize the bead shape.

However, if θ 1 is less than 10 °, the above-described effects cannot be sufficiently obtained, and welding defects and dripping of the weld metal occur. On the other hand, if θ 1 is greater than 45 °, the welding wire feed resistance at the bend of the welding torch increases, making it difficult to continue welding stably, and welding defects and dripping of the weld metal still occur. Therefore, the angle θ 1 of the tip of the welding torch at the reference position with respect to the horizontal direction is set to 10 ° to 45 °. Preferably from 15 to 30.

Oscillation angle θ 2 of the tip of the welding torch from the reference position: 10-60 degree

As described above, by using the welding torch including the curved portion and the tip defined by the curved portion, the tip of the welding torch is swung while swinging toward the tapered surface of the thick steel material, so that the tip of the welding wire can be brought close to the tapered surface while avoiding contact between the power feeding tip and the tapered surface of the thick steel material. Further, since the wire tip also faces the bevel surface, the bevel surface can be directly melted by the arc. Therefore, even when the amount of welding heat input per 1 pass is suppressed, the bevel surface can be sufficiently melted to suppress the occurrence of welding defects. Further, the expansion of the arc heat input range due to the oscillation of the welding torch can suppress the dripping of the molten metal and stabilize the bead shape.

However, if θ 2 is less than 10 °, the above-described effects cannot be sufficiently obtained, and welding defects and dripping of the weld metal occur. On the other hand, if θ 2 is greater than 60 °, the bevel surface is excessively melted, and therefore a weld defect occurs due to undercut of the bevel surface. Therefore, the oscillation angle θ 2 of the tip of the welding torch from the reference position is set to 10 ° to 60 °. Preferably from 25 to 45.

The bending angle θ 3 of the bending portion of the welding torch and the length l of the tip portion of the welding torch are not particularly limited, and from the viewpoint of controlling θ 1 and θ 2 to the above ranges, it is preferable to set θ 3 to a range of 10 to 45 ° and set l to a range of 10 to 40 mm.

Bonding depth D in primary layer welding: over 10mm

In order to weld thick steel materials to be welded in a predetermined groove shape, it is necessary to set the depth of joint in primary layer welding to 10mm or more. When the joining depth in the initial layer welding is less than 10mm, the welding heat concentrates, and therefore, the molten metal drips. Therefore, the joining depth in the primary layer welding is set to 10mm or more. Preferably 25mm or more. The upper limit of the joining depth in the initial layer welding is the same as the upper limit of the thickness of the steel material, that is, about 100 mm.

However, when multilayer welding is performed, particularly when the thickness of a steel material to be welded is 70mm or more, if the joining depth in primary layer welding is more than 60mm, welding heat input tends to become excessive, and welding defects such as fusion failure of a bevel surface and slag inclusion due to high-temperature cracking and heat generation dispersion during welding may occur. Therefore, when multilayer welding is performed, the joining depth in initial layer welding is preferably 60mm or less. More preferably 50mm or less.

While the basic conditions have been described above, in the welding method of the present invention, it is preferable that the following conditions are further satisfied.

Swing depth L of the torch in the plate thickness direction: 5mm or more

In the welding method of the present invention, the welding torch is oscillated, but it is also important to appropriately control the oscillation depth L of the oscillation of the welding torch in the plate thickness direction and the maximum oscillation width M in the direction perpendicular to the plate thickness direction and the weld line, which will be described later.

Here, the rocking depth L in the plate thickness direction and the maximum rocking width M in the direction perpendicular to the plate thickness direction and the weld line in each rocking mode are shown in fig. 5 (a) to (d).

The maximum width M of the weaving in the weaving depth L and the direction perpendicular to the weld line described later herein are the weaving depth and the maximum width of the weaving of the welding wire tip obtained assuming that the tip of the welding torch is positioned at the reference position without considering the weaving of the tip of the welding torch. The weaving pattern here is a trajectory of the welding wire tip when the welding torch tip is assumed to be always located at the reference position without considering the weaving of the welding torch tip.

Here, in the upward vertical welding which is the basis of the welding method of the present invention, since the joining depth and the swing width in the plate thickness direction are approximately the same, in the case of the multilayer welding, when the swing depth in the plate thickness direction is less than 5mm, it is difficult to set the joining depth of the initial layer welding to 10mm or more. Therefore, the rocking depth in the plate thickness direction is preferably 5mm or more. More preferably 25mm or more. Since the swing depth in the plate thickness direction does not exceed the plate thickness, the upper limit is usually about 100 mm.

However, when multilayer welding is performed, particularly when the thickness of a steel material to be welded is 70mm or more, if the rocking depth in the thickness direction is greater than 60mm, it is difficult to set the joining depth in initial layer welding to 60mm or less, and the welding heat input amount is too large, so that it is difficult to obtain the required mechanical properties in the heat affected zone of the weld metal or steel material, and in addition, welding defects such as fusion defects on the bevel face due to high-temperature cracks and heat generation dispersion during welding, and slag inclusion are likely to occur.

Therefore, the swing depth in the plate thickness direction when multilayer welding is performed is preferably 60mm or less. More preferably 50mm or less.

Maximum swing width M of the welding torch in a direction perpendicular to the plate thickness direction and the weld line direction: (W-6) mm-Wmm (W: weld width in primary layer welding)

In order to prevent the bevel surface from being non-melted, it is necessary to set the maximum swing width in the direction perpendicular to the plate thickness direction and the weld line to (W-6) mm or more. On the other hand, if the maximum swing width in the direction perpendicular to the plate thickness direction and the weld line is larger than Wmm, the molten metal may drip off, and welding may not be performed.

Therefore, the maximum swing width in the direction perpendicular to the plate thickness direction and the weld line is preferably (W-6) mm to Wmm. More preferably (W-4) mm to (W-1) mm.

The swing pattern of the welding torch is not particularly limited, and as shown in fig. 5 (a) to (d), コ -shaped, V-shaped, trapezoidal, triangular, and the like may be formed when viewed from the welding line direction (which coincides with the welding advancing direction and is generally perpendicular). For example, when the swing pattern is コ -shaped or trapezoidal, the swing of point a → point B and point C → point D as shown in fig. 5 (a) and (B) corresponds to the swing with respect to the groove surface of the thick steel material. In this case, the tip of the welding torch is swung toward the paper surface and the bevel surface of the thick steel material on the left side is swung in the swing between point a → point B, while the tip of the welding torch is swung toward the paper surface and the bevel surface of the thick steel material on the right side is swung in the swing between point C → point D. Note that, in the swing of point B → point C (including point D → point a in the case of a trapezoid), the tip of the welding torch may not be swung. In fig. 5 (a) to (d), the trajectory of the welding torch may be angular or rounded at each point (points B and C in fig. 5 (a)) where the direction of the welding torch changes.

However, in the vertical welding, the molten metal is likely to drip when the welding torch swings at a position close to the welding surface side, and further, when the welding torch moves away from the groove surface, uniform melting of the groove surface is not obtained, and welding defects such as fusion failure are likely to occur. In particular, in the typical trapezoidal and triangular weaving patterns in which the reverse operation is not required, the load on the apparatus is small, and on the other hand, the molten metal is likely to drip due to the movement of the welding torch at a position close to the welding surface side (point D → point a of the trapezoidal weaving pattern in fig. 5 (b), and point C → point a of the triangular weaving pattern in fig. 5 (D)). Therefore, from the viewpoint of suppressing the dropping of the molten metal, it is preferable to adopt an コ -shaped or V-shaped oscillation mode in which the welding torch is not moved on the welding surface side.

In the V-shaped or triangular weaving pattern, when the groove gap is large (for example, 6mm or more), the torch movement deviates from the groove surface (for example, in the movement of point a → point B in fig. 5 (c), the trajectory of the torch tip is not parallel to the groove surface (the side close to the torch) and the like), and uniform melting of the groove surface cannot be obtained, and welding defects such as fusion failure are likely to occur. Therefore, in this case, an コ -shaped swing pattern is preferable in which the welding torch can be easily operated in parallel with the bevel surface.

The distance a between the deepest point of the wire tip (e.g., points B and C in fig. 5 (a) and (B), and points B in fig. 5 (C) and (d)) and the back surface of the steel material during the swing in the thickness direction is usually about 2 to 5 mm.

When the rocking mode is applied to the groove shape, M in fig. 5 (a) and (b)₁、M₂、M₃Are respectively provided withAbout 2 to 18mm, about 0 to 10mm, and about 0 to 10 mm.

Further, the frequency and the stop time (stop time at each point such as point a shown in fig. 5) during the swing are not particularly limited, and for example, the frequency may be about 0.25 to 0.5Hz (preferably about 0.4 to 0.5Hz), and the stop time may be about 0 to 0.5 seconds (preferably about 0.2 to 0.3 seconds).

Total amount of S amount and O amount of weld metal in primary layer welding: : 450 mass ppm or less

In order to achieve stable vertical welding, it is necessary to prevent dripping of molten metal and obtain a stable bead shape (smooth bead without unevenness), and in particular, it is important to manage the amount of S and the amount of O that lower the surface tension and viscosity of molten metal to prevent dripping of molten metal to be low.

Here, if the total amount of the S amount and the O amount of the weld metal is more than 450 mass ppm (hereinafter, also simply referred to as ppm), in addition to the decrease in surface tension and viscosity, convection of the weld metal is outward on the surface, and the high-temperature weld metal is convected from the center toward the periphery to diffuse the molten metal, so that dripping of the molten metal is likely to occur. Therefore, the amount of S and the amount of O in the weld metal that govern the surface tension and viscosity of the molten metal and the flow are preferably set to 450ppm or less in total. More preferably 400ppm or less. The lower limit is not particularly limited, but is preferably 15 ppm.

In addition, the wire usually contains 0.010 to 0.025 mass% of S for the purpose of reducing surface tension and flattening a weld. In addition to the reduction of the S content of the wire itself, it is effective to reduce the S content in the steel material for the reduction of the S content of the weld metal.

Further, the amount of O in the weld metal is determined by the amount of CO in the shielding gas₂Is increased. For example, in the case of using 100% CO₂When the gas is used as a shielding gas, the amount of O in the weld metal is increased by about 0.040 to 0.050 mass%. In addition to reducing the amount of O contained in the wire itself, which is usually about 0.003 to 0.006 mass%, the amount of O in the weld metal is effectively reduced, and Si and Al are added to the wire. In addition, the welding current and the arc voltage are increased, and the welding is sufficiently performedThe slag metal reaction (deoxidation reaction) in the molten metal, the cohesion of the slag, and the floating on the weld surface are also effective.

N amount of weld metal in primary layer welding: less than 120ppm

Nitrogen (N) in the weld metal becomes bubbles released from the weld metal at the time of solidification. The generation of the bubbles causes vibration of the liquid surface, which causes dropping of the molten metal. In particular, when the N content in the weld metal is more than 120ppm, the molten metal tends to drip, and therefore the N content in the weld metal in the initial layer welding is preferably 120ppm or less. More preferably 60ppm or less. The lower limit is not particularly limited, but is preferably 25 ppm.

In addition, nitrogen (N) is generally contained in the welding wire in an amount of 50 to 80ppm as an impurity, and thus the amount of N in the weld metal is increased by about 20 to 120ppm due to the inclusion of the impurity of the shielding gas and the atmosphere. On the other hand, since the inner diameter of a nozzle in arc welding is generally about 16 to 20mm, it is difficult to completely seal a weld metal portion having a joint depth larger than the inner diameter of the nozzle using such a nozzle, and as a result, the amount of N in the weld metal may be larger than 200 ppm.

In order to prevent such an increase in the N amount and to set the N amount of the weld metal in the initial layer welding to 120ppm or less, and further to 60ppm or less, it is effective to provide a gas shield system different from a nozzle of a normal arc welding, thereby suppressing the mixing of the atmosphere in the weld metal.

Further, S, O and N are eluted from the steel material to the weld metal by the dilution of the steel material at the time of welding, and therefore S: 0.005 mass% or less, O: 0.003 mass% or less and N: the steel material of 0.004 mass% or less is preferable in terms of suppressing the S amount, O amount and N amount of the weld metal in the primary layer welding.

Total of Si amount and Mn amount of the wire used for primary layer welding: 1.5 to 3.5% by mass

In order to prevent the above-described dripping of the molten metal and obtain a stable bead-shaped appearance, it is important to form an appropriate amount of slag. The slag is mainly made of SiO₂And MnO, the amount of slag of which is mainly determined by the amount of Si in the wireTotal amount of Mn.

Here, when the total of the Si content and the Mn content of the wire is less than 1.5 mass%, a sufficient amount of slag may not be obtained although the dropping of molten metal is prevented. On the other hand, if the total of the Si content and the Mn content of the wire is more than 3.5 mass%, the slag may form lumps, which may cause obstacles to the next layer and subsequent layers of welding. Therefore, the total of the Si content and the Mn content of the wire used for primary layer welding is preferably 1.5 mass% to 3.5 mass%. More preferably 1.8 to 2.8 mass%.

Total of Ti amount, Al amount, and Zr amount of the wire used for primary layer welding: 0.08 to 0.50 mass%

TiO having a large influence on the physical properties (viscosity) of slag₂、Al₂O₃And Zr₂O₃The physical properties (viscosity) of the slag play an important role in preventing the molten metal from dripping and obtaining a stable bead-shaped appearance.

Here, when the total of the Ti amount, Al amount, and Zr amount of the wire is less than 0.08 mass%, the viscosity of the slag effective for preventing the dropping of the molten metal may not be obtained. On the other hand, if the total of the Ti content, Al content, and Zr content of the wire is more than 0.50 mass%, removal and remelting of slag may be difficult, and welding of the next layer or later may be hindered.

Therefore, the total of the Ti amount, Al amount, and Zr amount of the wire used for primary layer welding is preferably 0.08 to 0.50 mass%. More preferably 0.15 to 0.25 mass%.

The components of the welding wire other than those described above may be appropriately selected depending on the components of the thick steel material to be welded, and from the viewpoint of suppressing the S amount, O amount, and N amount in the weld metal, it is preferable to use a wire whose composition is represented by S: 0.03 mass% or less, O: 0.01 mass% or less, N: 0.01 mass% or less, and provided that Si: 0.05 to 0.80 mass%, Al: a welding wire in a range of 0.005 to 0.050 mass% (e.g., JIS Z3312 YGW18, JIS Z3319 YFEG-22C, etc.).

Protective gas composition: 20% by volume or more of CO₂Gas (es)

The penetration of the weld is affected by the gouging effect of the arc itself and the convection of the weld metal in a high temperature state. When the convection of the weld metal is directed inward, the high-temperature weld metal is convected downward from above, and therefore the penetration directly below the arc increases. On the other hand, when the convection of the weld metal is outward, the high-temperature weld metal is convected in the left-right direction from the center, the weld bead is widened, and the penetration of the bevel surface is increased. Therefore, in the vertical multilayer gas shielded arc welding of a thick steel material which is an object of the present invention, in order to suppress dripping of molten (welding) metal and obtain a uniform bead shape, it is preferable to direct convection of the welding metal inward.

In this case, from the viewpoint of reducing oxygen (O) that governs the flow of the weld metal, CO is used₂It is advantageous that the gas suppression is low, on the other hand, CO₂The gas has the effect of constricting the arc itself by dissociative endothermic reactions, causing convection of the weld metal more inward.

Therefore, as the shielding gas composition, CO is preferably used₂The gas is set to 20 vol% or more. More preferably 60% by volume or more. In addition, CO₂The rest other than the gas may be an inert gas such as Ar. In addition, it may be CO₂Gas: 100% by volume.

Input amount of welding heat: 30-170 kJ/cm

In the multi-layer welding, the number of passes can be reduced by increasing the heat input amount (deposition amount) per 1 pass, and the weld stack defects can be reduced. However, if the welding heat input amount becomes too large, it becomes difficult to ensure toughness by suppressing softening of the heat-affected zone of the steel material and coarsening of crystal grains, in addition to ensuring strength and toughness of the weld metal. In particular, if the welding heat input amount is more than 170kJ/cm, a special welding wire for diluting the steel material is indispensable for securing the characteristics of the weld metal, and further, a steel material designed to withstand the welding heat input is indispensable for the steel material. On the other hand, in order to secure molten metal and obtain a welded portion free from welding defects, it is advantageous that the welding heat input amount is high, and when the welding heat input is less than 30kJ/cm in a narrow groove, the fusion of the groove surface is insufficient, and lamination defects are likely to occur.

Therefore, the welding heat input amount is preferably set to 30kJ/cm to 170 kJ/cm. More preferably 90kJ/cm to 160 kJ/cm.

Furthermore, the penetration of the weld is also affected by the directionality of the arc and the gouging effect. Therefore, the polarity of welding is preferably wire minus (positive polarity), which is a wire negative electrode having a larger arc directivity and a larger gas-cutting effect.

Other conditions than the above are not particularly limited, and when the average welding current is less than 270A, the weld pool is small, and the surface side is in a multilayer welded state in which melting and solidification are repeated every time the welding torch swings, and fusion defects and slag inclusions are likely to occur. On the other hand, if the average welding current is more than 420A, the molten (welding) metal is likely to drop, and the arc point is difficult to confirm due to welding fumes and spatters, which makes adjustment during the work difficult. Therefore, the average welding current is preferably 270 to 420A. Further, setting the average welding current to 270 to 420A is more advantageous in performing the welding of the present invention because it is possible to obtain a stable penetration while suppressing the generation of welding fumes and spatters.

As for conditions other than these, it is sufficient as long as a conventional method is followed, for example, set as a welding voltage: 28-50V (rising with current), welding speed (up): : 0.5-50 cm/min (preferably 1.5-10 cm/min), welding wire extension length: 15-45 mm, diameter of welding wire: about 1.2-1.6 mm.

In the case of multilayer welding, the number of layers to be stacked until the end of welding is preferably about 2 to 4 layers from the viewpoint of preventing stacking defects. The welding conditions for each layer other than the initial layer are not particularly limited as long as they are in accordance with a predetermined method, and for example, they may be the same as the welding conditions for the initial layer.

In the welding method of the present invention, welding is performed by 1 pass per layer.

Examples

A welding torch (θ 3: 30 °, l: 15mm) having a bent portion on a power feeding tip shown in fig. 3 was used for 2 pieces of steel materials having a groove shape shown in table 1 under the welding conditions shown in table 2, and vertical gas shielded arc welding with a narrow groove was performed.

Here, the steel materials used were S: 0.005 mass% or less, O: 0.003 mass% or less, N: 0.004 mass% or less of YP460 MPa-grade steel. In addition, in the groove processing of steel, gas cutting is used, and the groove surface is not processed by grinding or the like.

The welding wire used was a solid wire of 1.2mm phi for steel strength or a grade 1 grade higher than that. In addition, the welding wires used were all S: 0.005 mass% or less, O: 0.003 mass% or less, N: 0.005 mass% or less, Si: 0.6 to 0.8 mass%, Al: 0.005 to 0.030 mass%.

Further, the welding current is 250 to 430A, the welding voltage is 28 to 44V (rising together with the current), the average welding speed is 1.0 to 34.9 cm/min (adjusted during welding), the average wire stick-out length is 15 to 28mm, and the welding length is 400 mm. Further, welding is performed by providing a gas shield system different from a nozzle of a general arc welding.

In addition, in nos. 2, 20, 21, and 22, 2 steel pieces were joined by single layer welding consisting of only primary layer welding, and in addition, 2 steel pieces were joined by multilayer welding.

After the initial layer welding, the bead width and the joint depth were measured by observing a cross-sectional macro structure of 5 points arbitrarily selected. The maximum value of the measured values is defined as the bead width W, and the minimum value of the measured values is defined as the joint depth D.

Further, the dripping of the molten metal at the time of primary layer welding was evaluated by visual observation as follows.

◎ No dripping of weld metal

○ dropping weld metal at a position of 2 or less

△ the dropping point of the welding metal is 3-4

X: dropping the weld metal at 5 or more spots, or interrupting the welding

Further, the welded joint finally obtained was subjected to ultrasonic flaw detection and evaluated as follows.

◎ No defects detected

○ detecting only qualified defects with a defect length of 3mm or less

X: detect defects with a defect length greater than 3mm

These results are also shown in Table 2.

[ Table 1]

[ Table 2]

As shown in Table 2, in Nos. 1 to 14 and 20 to 22, which are examples of the invention, no primary layer of the weld metal was dropped or even 2 spots or less were dropped. In the ultrasonic flaw detection, no flaw was detected, or the length of the flaw was 3mm or less, if any.

On the other hand, in comparative examples Nos. 15 to 19, there were 5 or more drops of the weld metal, and/or defects having a defect length of more than 3mm were detected in the ultrasonic flaw detection.

Description of the symbols

1: thick steel material

2: bevel face of thick steel

3: bevel of lower section of steel

4: welding torch

5: welding wire

6: backing plate material

7: main body part

8: power supply welding tip

9: bending part

10: front end part

11: weld seam

Claims

performing weaving of primary layer welding by using a welding torch having a curved portion and a tip defined by the curved portion, wherein the tip of the welding torch is rocked toward a slope surface of the thick steel material when the welding torch is rocked with respect to the slope surface of the thick steel material, a position where the tip of the welding torch coincides with a weld line direction when viewed from a thickness direction of the thick steel material is set as a reference position, an angle θ 1 of the tip of the welding torch with respect to a horizontal direction at the reference position is set to 10 ° to 45 °, and a rocking angle θ 2 of the tip of the welding torch from the reference position is set to 10 ° to 60 °,

the joining depth of the primary layer welding is set to 10mm or more.

2. The gas shielded arc welding method according to claim 1, wherein the joint is a single-layer weld and the groove gap is 25% or less of the thickness of the thick steel material.

3. The vertical narrow-groove gas-shielded arc welding method according to claim 1, wherein the joint is a multilayer weld, and a joint depth in the primary layer weld is 25mm to 60 mm.

4. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein in the weaving of the initial layer welding, a weaving pattern of the welding torch as viewed from a weld line direction is コ font.

5. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein the total of the S amount and the O amount of the weld metal in the initial layer welding is 450ppm by mass or less and the N amount is 120ppm by mass or less.

6. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein the total of the Si amount and the Mn amount of the wire used for primary layer welding is 1.5 to 3.5% by mass.

7. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein the total of the Ti amount, the Al amount, and the Zr amount of the wire used for primary layer welding is 0.08 to 0.50% by mass.

8. The gas-shielded arc welding method with a narrow vertical groove according to any one of claims 1 to 3, wherein 20 vol% or more of CO is used₂The gas is used as a protective gas.

9. The vertical narrow-groove gas-shielded arc welding method according to any one of claims 1 to 3, wherein the average welding current in the primary layer welding is in the range of 270 to 420A.