CN108290239A - Vertical narrow groove gas-shielded arc welding method - Google Patents

Abstract

Properly control the welding conditions of the first layer, especially the torch angle, welding heat input, and swing conditions, and set the joint depth in the first layer welding to be more than 20mm and less than 65mm, and when the final layer is welded, it will be able to move upward The sliding cooling plate is pressed against the thick steel material from the welding torch side as a backing plate material for the groove of 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

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 suitable for butt welding of two thick steel materials.

In the present invention, "narrow groove" means that the groove angle is 25° or less and the minimum groove width between steel materials to be welded is 50% or less of the thickness of the steel materials.

Background technique

Gas-shielded arc welding used in steel welding is usually a consumable electrode type that uses CO ₂ alone or a mixed gas of Ar and CO ₂ for shielding of the melting zone. Such gas-shielded arc welding is widely used in the manufacturing fields of automobiles, buildings, bridges, shipbuilding, and electrical equipment.

However, in recent years, along with the increase in size and thickness of steel structures, the amount of welding in the manufacturing process, especially in the butt welding of steel materials, has increased. In addition, welding construction requires a lot of time, which will lead to construction problems. Increased cost.

As a method of improving this, application of narrow groove gas shielded arc welding in which the groove of a gap relatively small to the plate thickness is welded by an arc welding method can be considered. Compared with normal gas shielded arc welding, the narrow groove gas shielded arc welding has a smaller amount of deposition, so it can achieve high welding efficiency and energy saving, and can even be expected to bring about a reduction in construction costs.

On the other hand, in vertical high-efficiency welding, electroslag welding is usually applied, but the heat input welding is basically the size of one pass, and in welding with a plate thickness exceeding 60mm, the heat input becomes too much and the toughness may be reduced. decline. Furthermore, there is a limit to the thickness of the plate in one-pass welding, and the current status of welding with a plate thickness exceeding 65 mm is not yet established technically.

Therefore, development of a high-quality and efficient welding method that applies narrow-groove gas-shielded arc welding to vertical welding is desired.

As a welding method for applying such narrow-groove gas-shielded arc welding to vertical welding, for example, Patent Document 1 discloses a double-side multilayer welding method for double-side U-groove joints. In this welding method, lamination welding of TIG welding using an inert gas is performed, and generation of slag or spatter is suppressed by using an inert gas to prevent lamination defects.

However, the efficiency of the welding method itself is greatly deteriorated in TIG welding of the non-consumable electrode type compared with MAG welding or CO ₂ welding using a steel wire as a consumable electrode.

In addition, Patent Document 2 discloses a narrow-groove vertical welding method in which a welding torch is swung in order to suppress spatter and poor fusion.

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

Therefore, when this welding method is applied to the welding of thick steel materials with a large plate thickness, it becomes lamination welding with a small number of passes, and lamination defects such as poor penetration increase, and welding efficiency is greatly reduced.

In addition, in Patent Document 3, similar to Patent Document 2, a vertical welding method is disclosed in which a welding torch is swung in order to suppress poor fusion.

The face angle (groove angle) disclosed here is relatively wide from 26.3° to 52°, but the swinging of the welding torch here is also performed with respect to the groove depth direction. Therefore, in the vertical welding method of Patent Document 3, a relatively large amount of deposition per one pass can be obtained.

However, the amount of wobble in the groove depth direction is small, and the welding metal and wire composition are not taken into consideration. Therefore, it is necessary to suppress the deposition amount (≈heat input amount) per pass, and the welding depth per pass becomes shallower. About 10mm.

Therefore, when this welding method is applied to the welding of thick steel materials with a large plate thickness, it still becomes lamination welding with a small number of passes, and lamination defects such as poor penetration increase, and welding efficiency decreases.

In addition, Patent Document 4 discloses a two-electrode carbon dioxide gas shielded welding device capable of performing one-pass welding of extremely thick materials.

By using this two-electrode carbon dioxide gas shielded welding device, it is possible to join thick steel materials up to about 70 mm in thickness. However, the amount of heat input greatly increases to about 360 kJ/cm due to polarization of the two electrodes. Therefore, the thermal influence on the steel plate is large, and when high properties (strength, toughness) are required for the joint, it becomes very difficult to satisfy such properties.

In addition, in this two-electrode carbon dioxide gas shielded welding device, since it is difficult to observe the arc of the rear side electrode, there is a problem that it is difficult to prevent welding defects. In addition, in this two-electrode carbon dioxide gas shielded welding device, it is difficult to install a copper pressure plate in the groove due to problems such as groove size accuracy, so it is difficult to achieve low heat input as multi-pass stack welding.

prior art literature

patent documents

Patent Document 1: Japanese Unexamined Patent Publication No. 2009-61483

Patent Document 2: Japanese Patent Laid-Open No. 2010-115700

Patent Document 3: Japanese Patent Laid-Open No. 2001-205436

Patent Document 4: Japanese Patent Application Laid-Open No. 10-118771

Contents of the invention

The problem to be solved by the invention

As described above, a high-quality and high-efficiency vertical narrow-groove gas-shielded arc welding method suitable for welding thick steel materials has not yet been developed.

On the other hand, the lightweight/high performance/high precision of welding automation technology (welding robot) continues to advance, and the swing of the welding torch suitable for the groove shape and welding posture that has been difficult until now has become possible. , It can be suitable for welding construction (condition setting) of steel material, groove shape, welding posture and welding material (welding wire).

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

Solution to the problem

In order to solve the above-mentioned problems, the inventors have repeatedly conducted detailed studies on welding conditions when vertical narrow groove gas shielded arc welding is applied to thick steel materials.

As a result, the following insights were obtained: In order to obtain the desired mechanical properties in the weld metal and heat-affected zone and to achieve high welding efficiency when performing vertical narrow groove gas shielded arc welding of thick steel materials, It is important to control the joint depth (welding depth) in the first layer welding to a predetermined range by setting a narrow groove to reduce the amount of deposition and suppress the welding heat input per pass.

Therefore, the inventors have further advanced studies on welding conditions for performing the above-mentioned welding. As a result, by setting the groove conditions to predetermined conditions and appropriately controlling the welding conditions of the first layer, especially the welding torch angle and swing conditions, it is possible to realize dripping of molten metal that is a problem in vertical welding. The stabilization of the bead shape and the prevention of welding defects, including the suppression of the weld, achieve the above-mentioned joint depth of the first layer of welding. In addition, it has been found that high-quality and efficient vertical narrow-groove gas-shielded arc welding can be performed to obtain desired mechanical properties even for thick steel materials with a plate thickness of 40 mm or more.

In addition, in the case of vertical gas-shielded arc welding as described above, it was also found that the appearance of the bead of the finally obtained welded joint tends to deteriorate depending on the welding conditions of the final layer welding. And further advance the research.

As a result, the following knowledge was obtained: when the final layer is welded, the cooling plate that can slide upward is used as the backing plate material of the groove of the thick steel material from the welding torch side to press the thick steel material, corresponding to welding. Welding is performed while moving the cooling plate upward without moving the torch upward, thereby making it possible to easily obtain a beautiful weld bead appearance.

The present invention is an invention completed after further studies based on the above knowledge.

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

1. A vertical narrow groove gas shielded arc welding method, the groove angle is set to be below 25°, the groove interval is set to be below 20mm, and two thick steel materials with a plate thickness of more than 40mm are passed through a swinging single Layer welding or multi-layer welding for bonding, where,

When welding the first layer, set the angle of the welding torch to 25° to 75° relative to the horizontal direction, set the welding heat input to 30kJ/cm to 300kJ/cm, and set the swing depth in the thickness direction Set to 15 mm or more and 63 mm or less, and set the maximum swing width in the direction perpendicular to the plate thickness direction and the welding line to be (W-6) mm or more when the bead width of the first layer welding is W Wmm or less, so that the swing of the welding torch is performed, the joint depth of the first layer welding is set to be more than 20 mm and less than 65 mm,

When the final layer is welded, the cooling plate that can slide upward is used as the surface pad material of the bevel of the thick steel material to press against the thick steel material from the welding torch side, corresponding to the upward movement of the welding torch On the other hand, welding is performed while moving the cooling plate upward.

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

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

4. The vertical narrow groove gas shielded arc welding method according to any one of 1 to 3 above, wherein the total amount of Si and Mn in 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-groove gas-shielded arc welding method according to any one of 1 to 4 above, wherein the total amount of Ti, Al, and Zr in the welding wire used in the first layer welding is 0.08 mass % to 0.50% by mass.

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

Invention effect

According to the present invention, even when welding thick steel materials with a plate thickness of 40 mm or more, it is possible to stabilize the shape of the bead including the suppression of dripping of molten metal which is a problem in vertical welding, and prevent welding defects, and implement high-quality and efficient narrow-groove gas-shielded arc welding.

In addition, the welding method of the present invention has less deposition amount than conventional gas-shielded arc welding, and can also achieve energy saving based on high welding efficiency. Therefore, welding construction costs can be greatly reduced, and beautiful welding can be easily obtained. road appearance.

Description of drawings

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

Fig. 2 is a diagram showing an example of construction procedure when performing welding of a first layer with a welding method according to an embodiment of the present invention in a V-shaped groove shape.

Fig. 3 is a view showing an example of a groove cross-section after performing primary layer welding in a V-shaped groove shape by a welding method according to an embodiment of the present invention.

4 is a diagram showing an example of the swing pattern of the welding torch viewed from the direction of the welding line in the swing of the first layer welding, (a) is a U-shaped case, (b) is a trapezoidal case, and (c) is a V-shaped case. In the case of a font, (d) is a case of a triangle.

FIG. 5 shows an example of a construction procedure when performing final layer welding using a welding method according to an embodiment of the present invention.

Fig. 6 is a photograph after first-layer welding in the invention example (No. 7), (a) showing the overall appearance, and (b) showing the groove cross section.

Detailed ways

Hereinafter, the present invention will be specifically described.

1( a ) to ( c ) are diagrams showing examples of various groove shapes. In the figure, number 1 is the thick steel material, 2 is the groove surface of the thick steel material, and 3 is the groove of the lower section of the steel material (at the Y-shaped groove). Use t to represent the plate thickness, and use h to represent the groove height of the lower section of the steel (at the Y-shaped groove).

As shown in this figure, the groove shape as the object here can also be set as any one of V-shaped groove (including I-shaped groove and レ-shaped groove) and Y-shaped groove, and it can also be used as shown in Figure 1 ( c) shows a multi-stage Y-shaped groove.

It should be noted that, as shown in Figure 1(b) and (c), the groove angle and groove interval in the Y-shaped groove are set to the groove angle and groove interval at the groove of the lower section of the steel material. Here, the bevel of the lower section of the steel material refers to 20 to 40 of the thickness from the surface of the steel material that will be the back surface during welding (the surface on the side of the welding device (torch) is the front surface, and the surface on the opposite side is the back surface). % around the area.

In addition, FIG. 2 is a diagram showing construction procedures when performing primary layer welding with a welding method according to an embodiment of the present invention in a V-shaped groove shape. In the figure, reference numeral 4 is a welding torch, 5 is a welding wire, 6 is a backing plate material, and φ is an angle of the welding torch relative to the horizontal direction. It should be noted that the illustration of the welding line, the molten pool, and the bead is omitted.

Here, as shown in FIG. 2, this welding method is gas-shielded arc welding in which two thick steel materials having a predetermined plate thickness are butt-jointed, and the above-mentioned thick steel materials are joined to each other by vertical welding using swinging. Upward welding with the direction of travel upward.

In addition, although the V-shaped groove shape was shown as an example here, it is the same also in other groove shapes.

Moreover, FIG. 3 is a figure which shows the cross section of the groove|groove after the welding method of one embodiment of this invention performed the initial layer welding in the groove shape of V shape. In the figure, the symbol 7 is the weld bead (weld bead of the initial layer welding), the symbol D indicates the joint depth of the initial layer welding, and W indicates the bead width of the initial layer welding (the interval between the grooves after the initial layer welding) .

It should be noted that the joint depth D of the initial layer welding is the minimum value of the bead height of the initial layer welding when the steel material surface that becomes the back side during welding is used as the starting point (the initial layer closest (lower) to the steel material surface of the starting point layer welding bead height).

Here, the V-shaped groove shape is shown as an example, but the same applies to D and W in other groove shapes.

Next, in the welding method of the present invention, the reasons for limiting the bottom groove angle, the bottom groove interval, and the plate thickness of the steel materials to the aforementioned ranges will be described.

Groove angle θ: below 25°

The smaller the groove portion of the steel material, the faster and more efficient welding can be performed, but the reverse side is more likely to have defects such as poor fusion. In addition, welding when the groove angle exceeds 25° can also be performed by conventional construction methods. Therefore, in the present invention, the case where the groove angle is 25° or less, which is difficult to construct by the conventional construction method and is expected to be more efficient, is targeted.

It should be noted that under the V-shaped groove, the groove angle of 0° is called the so-called I-shaped groove, and the situation of 0° from the surface of the deposited amount is the most effective, although the groove angle can also be 0° (I-shaped groove), but the groove is closed during welding due to welding thermal strain, so it is preferable to set the same value as the plate thickness t (wherein, in the case of Y-shaped groove, steel material The groove angle corresponding to the groove height h) of the lower section.

Specifically, the groove angle is preferably not less than (0.5×t/20)° and not more than (2.0×t/20)°, more preferably not less than (0.8×t/20)° and (1.2×t/20)° the following. For example, when the plate thickness t is 100 m, the groove angle is preferably not less than 2.5° and not more than 10°, more preferably not less than 4° and not more than 6°.

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

Groove interval G: below 20mm

The smaller the groove portion of the steel material, the faster and more efficiently the welding can be performed. Furthermore, in welding when the groove interval exceeds 20 mm, the molten metal tends to drip and construction becomes difficult. As a countermeasure against this, it is necessary to keep the welding current low, but welding defects such as slag entrainment tend to occur. Therefore, the groove interval is 20 mm or less. Preferably, it is 4 mm or more and 12 mm or less.

Plate thickness t: over 40mm

The plate thickness of the steel material is set to 40 mm or more. This is because, if the plate thickness of the steel material is less than 40 mm, even if a conventional welding method such as carbon dioxide gas shielded welding in Patent Document 4 is used, there will be no major problems in the strength and toughness of the joint.

In addition, when general rolled steel materials are used as an object, 100 mm is usually set as an upper limit about plate|board thickness. Therefore, the plate thickness of the steel material is preferably 100 mm or less. In addition, in the case of single-layer welding, it is preferable to set it as 65 mm or less.

It should be noted that, as the steel type of the material to be welded, high-tensile steel is particularly preferred (for example, very thick YP460MPa grade steel for shipbuilding (570MPa grade steel for tensile strength) or TMCP steel SA440 for construction (590MPa grade steel for tensile strength) ). This is because the welding heat input of high-tensile steel is strictly limited, the weld metal is prone to cracking, and the required joint strength or toughness cannot be obtained due to the influence of welding heat. On the other hand, in the welding method of the present invention, heat input: 300kJ/cm or less and high-efficiency welding can be performed, even 590MPa-class high-tensile steel sheets and high-alloy 590MPa-class corrosion-resistant steels can be welded. Of course, mild steel can also be handled without problems.

In the above, in the welding method of the present invention, the reasons for limiting the groove angle, the groove interval, and the plate thickness of the steel material have been explained. Therefore, it is important to properly control the welding conditions of the first layer and make the joint depth of the first layer welding within the specified range.

Hereinafter, the reasons for limiting the joint depth in the above-mentioned first-layer welding and the first-layer welding conditions will be described.

Joint depth D in initial layer welding: 20mm or more and 65mm or less

In order to weld thick steel materials having a plate thickness of 40 mm or more, especially by multi-layer welding of two or more passes, it is necessary to set the joint depth in the first layer welding to be 20 mm or more. If the joint depth in the first-layer welding is less than 20 mm, the welding heat is concentrated, so that dripping of molten metal occurs. On the other hand, if the joint depth in the first layer welding exceeds 65 mm, the welding heat input tends to become excessive, and high-temperature cracking, poor fusion of the groove surface caused by heat dispersion during welding, and slag entrainment, etc. Welding defects. Therefore, the joint depth in the first layer welding is set to be 20 mm or more and 65 mm or less. Preferably, it is 25 mm or more and 60 mm or less. In addition, in the case of single-layer welding, the joint depth D in the first-layer welding is about the same as the plate thickness (40 mm or more).

The angle φ of the welding torch (the tip of the power supply tip): 25° or more and 75° or less relative to the horizontal direction

The angle of the welding torch is closer to the horizontal than the vertical, so that the arc faces back from the bead surface, and dripping of the molten metal can be suppressed. Here, if the angle of the welding torch is less than 25° with respect to the horizontal direction, it becomes difficult to form a weld bead. On the other hand, if the angle of the torch exceeds 75° with respect to the horizontal direction, it becomes difficult to suppress dripping of 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 it is 30° or more and 45° or less.

Welding heat input: more than 30kJ/cm and less than 300kJ/cm

In multilayer welding, welding lamination defects can be reduced by reducing the number of passes by increasing the amount of heat input (=deposition amount) per pass. However, when 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 softening of the heat-affected zone of steel materials and secure toughness due to grain coarsening. Especially when the welding heat input exceeds 300kJ/cm, a special welding wire that considers the dilution of the steel material is indispensable to ensure the properties of the weld metal. In addition, the steel material needs to be designed to withstand the welding heat input. On the other hand, in order to ensure molten metal and obtain a weld without welding defects, it is advantageous to have a high welding heat input. If the welding heat input is less than 30kJ/cm at a narrow groove, the melting of the groove surface will be insufficient, and lamination defects will occur. generation is inevitable.

Therefore, the welding heat input amount shall be 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.

The swing depth L in the plate thickness direction in the swing of the welding torch: 15 mm or more and 63 mm or less

This welding method is a method of swinging the welding torch, but the swing depth L in the plate thickness direction and the swinging in the direction perpendicular to the plate thickness direction and the welding line described later in the swinging of the welding torch are appropriately suppressed to the maximum. The case of width M is critical.

It should be noted that among various wobble patterns, the wobble depth L in the thickness direction and the wobble maximum width M in the direction perpendicular to the plate thickness direction and the welding line are shown in Fig. 4 (a) to (d) .

Here, in the upward vertical welding which is the basic welding method in this welding method, the joint depth is about the same as the swing width in the plate thickness direction. Therefore, if the weaving depth in the plate thickness direction is less than 15 mm, it is difficult to make the joining depth in the first layer welding 20 mm or more. On the other hand, when the weaving depth in the plate thickness direction exceeds 63 mm, it is difficult to reduce the joint depth in the first layer welding to 65 mm or less. In addition, the amount of welding heat input becomes too much, it is difficult to obtain the desired mechanical properties in the heat-affected zone of the weld metal or steel, and high-temperature cracking, poor fusion of the groove surface caused by heat dispersion during welding, and slag are likely to occur. Involvement and other welding defects.

Therefore, the swing depth in the plate thickness direction is set to be 15 mm or more and 63 mm or less. Preferably, it is 25 mm or more and 60 mm or less.

The maximum swing width M in the swing of the welding torch in the direction perpendicular to the plate thickness direction and the welding line: (W-6) mm or more and W mm or less (W: bead width of the first layer welding)

In order to prevent non-melting of the groove surface, it is necessary to set the maximum swing width in the direction perpendicular to the plate thickness direction and the welding line to be (W-6) mm or more. On the other hand, when the maximum swing width in the direction perpendicular to the plate thickness direction and the welding line exceeds Wmm, the molten metal drips and the welding fails.

Therefore, the maximum swing width in the direction perpendicular to the plate thickness direction and the welding line is set to be in the range of (W-6) mm or more and W mm or less. Preferably, it is (W-4) mm or more and (W-1) mm or less.

In addition, in the case of single-layer welding, W is the groove width at the steel material surface which becomes the surface (the surface on the welding apparatus (torch) side) at the time of welding.

In addition, the swing pattern of the welding torch is not particularly limited, but as shown in Fig. 4(a) to (d), it can be U-shaped when viewed from the direction of the welding line (in line with the direction of welding progress, usually in the vertical direction). , V-shaped, trapezoidal and triangular, etc. It should be noted that, in Figure 4(a)-(d), the trajectory of the welding torch at each point where the direction of the welding torch changes (points B and C in Figure 4(a)) may have corners or angles. Can have rounded corners.

However, in the upward vertical welding, the wobble at the site near the welding surface side tends to cause dripping of the molten metal. Moreover, when the action of the welding torch deviates from the groove surface, uniform melting of the groove surface cannot be obtained, and welding defects such as poor fusion are likely to occur. In particular, in the general trapezoidal and triangular swinging patterns that do not require reverse movement, the device load is small, but the reverse side is due to the torch action at the position near the welding surface (point D of the trapezoidal swinging pattern in Figure 4(b)→ Point A, point C→point A of the triangular swing pattern in FIG. Therefore, from the viewpoint of suppressing dripping of the molten metal, it is preferable to use a U-shaped or V-shaped swing pattern in which the welding torch on the welding surface side does not operate.

In addition, in a V-shaped or triangular swing pattern, when the groove interval is large (for example, 6mm or more), the welding torch action deviates from the groove surface (for example, the action at point A→B in Figure 4(c) In the process, the trajectory of the front end of the welding torch is no longer parallel to the groove surface (the side close to the welding torch), etc.), uniform melting of the groove surface cannot be obtained, and welding defects such as poor fusion are prone to occur. Therefore, in such a case, it is most appropriate to use a U-shaped swing pattern that can move the welding torch in parallel to the groove surface.

It should be noted that the deepest point of the welding torch tip when swinging in the thickness direction (for example, points B and C in Fig. 4(a) and (b), and point B in Fig. 4(c) and (d) ) from the back of the steel is usually about 2 to 5 mm.

In addition, in the case where U-shaped swing or trapezoidal swing is applied to the above-mentioned groove shape, M ₁ , M ₂ , and M ₃ in Fig. ~10mm or so.

In addition, the frequency and stop time during oscillation (stop time at each point such as point A shown in FIG. 4 ) are not particularly limited, as long as the frequency is, for example, 0.25 to 0.5 Hz (preferably not less than 0.4 Hz and not more than 0.5 Hz). , The stop time may be about 0 to 0.5 seconds (preferably not less than 0.2 seconds and not more than 0.3 seconds).

The basic conditions have been described above, but in the welding method of the present invention, by further satisfying the following conditions, it is possible to suppress dripping of molten metal that is a problem particularly in vertical welding, and further stabilize the shape of the bead. .

The total amount of S and O in the weld metal in the first layer welding: 450 mass ppm or less

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

Here, if the total amount of S and O in the weld metal exceeds 450 ppm by mass (hereinafter also simply referred to as ppm), in addition to the decrease in surface tension and viscosity, the convection of the weld metal becomes outward on the surface, The high-temperature weld metal convects from the center toward the periphery, the molten metal expands, and dripping of the molten metal tends to occur. Therefore, the S amount and the O amount of the weld metal, which control the surface tension, viscosity, and melt flow of the molten metal, are preferably 450 ppm or less in total. More preferably, it is 400 ppm or less. In addition, although the lower limit is not specifically limited, It is preferable to set it as 15 ppm.

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

In addition, the O content of the weld metal increases due to the oxidation of _CO2 in the shielding gas. For example, in the case of using 100% by volume of CO ₂ gas as the shielding gas, the amount of O in the weld metal increases by about 0.040 to 0.050% by mass. In reducing 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 the welding wire itself usually containing about 0.003 to 0.006% by mass of O. Furthermore, it is also effective to increase the welding current and arc voltage to sufficiently advance the slag metal reaction (deoxidation reaction) in the molten metal, the agglomeration of the slag, and the floating to the surface of the weld bead.

The amount of N in the weld metal in the first layer welding: 120ppm or less

Nitrogen (N) in the weld metal is expelled from the weld metal and becomes bubbles during solidification. The generation of the air bubbles causes the vibration of the melt surface, which causes dripping of the molten metal. In particular, when the amount of N in the weld metal exceeds 120 ppm, dripping of the molten metal is likely to occur, so the amount of N in the weld metal in the first layer welding is preferably 120 ppm or less. More preferably, it is 60 ppm or less. In addition, although the lower limit is not specifically limited, It is preferable to set it as 15 ppm.

In addition, the welding wire usually contains 50 to 80 ppm of nitrogen (N) as an impurity, and therefore, the amount of N in the weld metal increases by about 20 to 120 ppm due to the impurities of the shielding gas and the incorporation of the atmosphere. On the other hand, generally, the inner diameter of the nozzle of arc welding is about 16 to 20 mm. Therefore, using such a nozzle, it is difficult to completely protect the part of the weld metal beyond the joint depth of the inner diameter of the nozzle. As a result, the amount of N in the weld metal may vary. Will exceed 200ppm.

In order to prevent such an increase in the amount of N and to make the N amount of the weld metal in the first layer welding to be 120ppm or less, and further to 60ppm or less, a gas shielding system different from the nozzle of ordinary arc welding is installed, thereby preventing the atmosphere from entering the weld. The case of the mixture of the metal is effective.

It should be noted that due to the dilution of the steel material during welding, S, O, and N are segregated from the steel material to the weld metal. Therefore, it is preferable to use S: 0.005% by mass or less, O: 0.003% by mass or less, and N: 0.004% by mass or less.

The total amount of Si and Mn in the welding wire used in the first layer welding: 1.5% by mass or more and 3.5% by mass or less

In order to prevent the above-mentioned dripping of the molten metal and obtain a stable appearance of the bead shape, it is important that an appropriate amount of slag is formed. The slag is mainly composed of SiO ₂ and MnO, and the amount of the slag is largely influenced by the total amount of Si and Mn in the welding wire.

Here, if the total amount of Si and Mn in the welding wire is less than 1.5% by mass, a sufficient amount of slag for preventing dripping of molten metal may not be obtained. On the other hand, when the total amount of Si and Mn in the welding wire exceeds 3.5% by mass, slag may form into agglomerates, which may hinder welding of the next layer or later. Therefore, the total of the Si content and the Mn content of the welding wire used for the primary 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.

The total amount of Ti, Al, and Zr in the welding wire used in the first layer welding: 0.08% by mass or more and 0.50% by mass or less

TiO ₂ , Al ₂ O ₃ , and Zr ₂ O ₃ have a large influence on the physical properties (viscosity) of slag that play an important role in preventing the above-mentioned dripping of molten metal and obtaining a stable bead shape appearance. .

Here, if the total amount of Ti, Al, and Zr in the welding wire is less than 0.08% by mass, the viscosity of slag effective for preventing dripping of molten metal cannot be obtained. On the other hand, when the total amount of Ti, Al, and Zr in the welding wire exceeds 0.50% by mass, slag removal and remelting become difficult, which may hinder welding of the next layer or later.

Therefore, the total amount of Ti, Al, and Zr in the welding wire used for primary 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.

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

Composition of shielding gas: make _CO2 gas more than 20% by volume

The penetration of the weld is governed 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 inward, the high-temperature weld metal convects from the top to the bottom, so the depth of penetration immediately below the arc increases. On the other hand, when the convection of the weld metal is outward, the high-temperature weld metal convects from the center to the left and right, the bead expands, and the penetration of the groove surface increases. Therefore, in the vertical multilayer gas-shielded arc welding of thick steel materials aimed at by the present invention, in order to suppress dripping of molten (weld) metal and obtain a uniform bead shape, it is preferable to make the convection flow of the weld metal inward.

Here, from the viewpoint of reducing oxygen (O) that dominates the molten metal flow of the weld metal, it is advantageous to suppress the CO ₂ gas to be low, but on the other hand, the CO ₂ gas has the function of causing the arc to dissociate and absorb heat. The effect of constricting itself and making the convection of the weld metal more inward.

Therefore, as a shielding gas composition, it is preferable to make _CO2 gas 20 volume% or more. More preferably, it is 60 volume% or more. In addition, what is necessary is just to use inert gas, such as Ar, for the remainder other than _CO2 gas. Also, CO ₂ gas may be 100% by volume.

In addition, the penetration depth of the weld is also affected by the directivity of the arc and the gouging effect. Therefore, the polarity of welding may be set according to the characteristics of the welding material.

Regarding the conditions other than the above, although there is no need to specify in particular, if the average welding current is less than 270A, the molten pool will be small, and the surface side will be in the state of multi-layer welding in which melting and solidification are repeated every time the welding torch swings, which is likely to occur. Poor fusion or slag involved. On the other hand, when the average welding current exceeds 360A, dripping of molten (welding) metal is likely to occur, and confirmation of the arc point becomes difficult due to welding fume and spatter, so adjustment during construction becomes difficult. Therefore, it is preferable to set the average welding current to 270-360A. Furthermore, by setting the average welding current to 270 to 360 A, generation of welding fume and spatter can be suppressed and stable penetration can be obtained, so it is more advantageous in implementing this welding method.

Regarding the other conditions, as long as the general method is used, for example, welding voltage: 32 to 37V (increased with the current), welding speed (upward): 2 to 15cm/min (preferably 4cm/min or more and 9cm /min or less), wire protrusion length: 20-45mm, wire diameter: about 1.2-1.6mm.

Above, the initial layer welding conditions have been described, but in the vertical narrow groove gas shielded arc welding method of the present invention, as shown in FIG. It is important that the surface pressure plate of the groove of the thick steel material 1 is pressed against the thick steel material 1 from the welding torch 4 side, and the cooling plate 8 is moved upward in response to the upward movement of the welding torch 4 . Thereby, a beautiful bead appearance can be easily obtained. It should be noted that, in FIG. 5 , the illustration of the molten pool and the bead of the final layer welding is omitted.

Here, as the cooling plate, a water-cooled copper metal plate (copper pressing plate) is preferable. Furthermore, from the viewpoint of workability, the length in the upward direction (welding line direction) of the cooling plate is preferably 0.4 to 2.0 times the length of the thick steel material.

In addition, the welding conditions of each welded layer other than the above are not specifically limited, For example, what is necessary is just to perform welding with oscillation corresponding to the joint depth similarly to initial layer welding. In this case, welding conditions such as welding current, welding voltage, and welding wire to be used may be the same as those in the case of first-layer welding.

In addition, the number of laminations until welding is completed is preferably about 2 to 4 layers from the viewpoint of preventing lamination defects. It should be noted that, in the case of single-layer welding, first-layer welding becomes final-layer welding.

Example

Two sheets of steel materials having a groove shape shown in Table 1 were subjected to upward vertical gas shielded arc welding with a narrow groove under the welding conditions shown in Table 2.

Here, the steel materials used were S: 0.005% by mass or less, O: 0.003% by mass or less, and N: 0.004% by mass or less. It should be noted that gas cutting is used for the groove processing of steel, and the groove surface is not trimmed by grinding or the like.

In addition, as the welding wire, a solid welding wire of 1.2 mmφ is used for steel material strength or one grade higher than that. In addition, the composition of the welding wire used was 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 % .

In addition, the welding current is 200-380A, the welding voltage is 28-37V (increased with the current), the average welding speed is 2.3-15.0cm/min (adjusted during welding), the average wire protrusion length is 30mm, and the welding length is 400mm. Furthermore, except for No. 11, welding was performed by installing a gas shielding system different from the nozzle of normal arc welding.

It should be noted that Nos. 1 to 19 are multi-layer welding, and in the welding of each layer other than the first layer, the welding current is set to 270 to 330A, and the welding voltage is set to the range of 28 to 37V. Oscillating gas shielded arc welding, the welded joints are finished. Also, No. 20 has finished the welded joint as a single layer weld. In addition, in Nos. 1 to 14 and Nos. 19 to 20, when the final layer is welded, a water-cooled copper metal plate (copper pressing plate) that can slide in the upward direction is used as the groove of the thick steel material. The backing material is pressed against the thick steel material from the welding torch side, and welding is performed while moving the metal plate upward in response to the upward movement of the welding torch. On the other hand, in Nos. 15 to 18, at the time of final layer welding, welding was performed without using such a water-cooled copper metal plate.

After the initial layer welding, the width of the weld bead and the joint depth were measured by observing the cross-sectional macrostructure at 5 randomly selected points. For the bead width, the maximum value of the measured values was taken as the bead width W of the initial layer welding, and the minimum value of the measured values was used as the joint depth D of the first layer welding for the joint depth.

In addition, dripping of the molten metal at the time of first-layer welding was visually evaluated as follows.

◎: No dripping of weld metal

○: The dripping of weld metal is less than 2 parts

△: Drips of weld metal are at least 3 locations and at least 4 locations

×: The dripping of weld metal is more than 5 parts or the welding is interrupted

In addition, ultrasonic flaw detection was performed on the finally obtained welded joint, and the following evaluations were performed.

◎: No defect detected

○: Only qualified defects with a defect length of 3 mm or less are detected

×: Defects with a defect length exceeding 3 mm were detected

Moreover, about the bead surface of the welded joint finally obtained, visual inspection was implemented and it evaluated as follows.

○: The surface of the bead has small unevenness and sufficient gloss

×: Large unevenness on the surface of the weld bead

The above-mentioned results are collectively described in Table 2.

[Table 1]

Table 1

[Table 2]

As shown in Table 2, in Nos. 1 to 14 and Nos. 19 to 20 of the inventive examples, there was no dripping of the primary weld metal, or even if there was, there were two or less places. Furthermore, in the ultrasonic flaw detection inspection, no defect was detected, or even if there was, the length of the defect was 3 mm or less. In addition, in the above-mentioned invention examples, in the finally obtained welded joint, the unevenness of the surface of the bead is small, and a beautiful bead appearance is obtained.

On the other hand, in Nos. 15 to 18 of Comparative Examples, there were five or more spots of dripping of the weld metal, or defects with a defect length exceeding 3 mm were detected in the ultrasonic flaw detection inspection. In addition, in Nos. 15 to 18, which were welded without using a water-cooled copper metal plate at the time of final layer welding, in the finally obtained welded joint, the unevenness of the bead surface was large, and sufficient gloss was not obtained. .

In addition, FIG. 6( a ) shows an appearance photograph of the front side (welding construction side) of No. 7 of Invention Example after welding the first layer, and FIG. 6( b ) shows a cross-sectional macrostructure photograph. As can be seen from the figure, in Invention Example No. 7 in which the weaving conditions and the like were appropriately controlled, the desired joint depth was obtained when the joint depth D in the first layer welding was about 28 mm. Moreover, a stable bead shape is obtained at the same time.

Label description

1: thick steel

2: Groove surface of thick steel

3: The groove of the lower part of the steel

4: welding torch

5: welding wire

6: Backing plate material

7: Weld bead (weld bead of initial layer welding)

8: cooling plate

θ: groove angle

G: Groove interval

h: Groove height of the lower section of the steel

t: plate thickness

φ: The angle of the welding torch relative to the horizontal direction

D: joint depth of initial welding

W: bead width of initial layer welding

L: Swing depth in the direction of plate thickness

M: The maximum swing width in the direction perpendicular to the plate thickness direction and the welding line.

Claims (7)

1. A vertical narrow groove gas shielded arc welding method, the groove angle is set to be below 25°, the groove interval is set to be below 20mm, and two thick steel materials with a plate thickness of more than 40mm are passed through a swinging single Layer welding or multi-layer welding for bonding, where, When welding the first layer, set the angle of the welding torch to 25° to 75° relative to the horizontal direction, set the welding heat input to 30kJ/cm to 300kJ/cm, and set the swing depth in the thickness direction Set to 15 mm or more and 63 mm or less, and set the maximum swing width in the direction perpendicular to the plate thickness direction and the welding line to be (W-6) mm or more when the bead width of the first layer welding is W Wmm or less, so that the swing of the welding torch is performed, and the joint depth of the first layer welding is set to be 20 mm or more and 65 mm or less, When the final layer is welded, the cooling plate that can slide upward is used as the surface pad material of the bevel of the thick steel material to press against the thick steel material from the welding torch side, corresponding to the upward movement of the welding torch On the other hand, welding is performed while moving the cooling plate upward. 2. vertical narrow groove gas shielded arc welding method according to claim 1, wherein, In the swinging of the first layer welding, the swinging pattern of the welding torch viewed from the direction of the welding line is a "U" shape. 3. The vertical narrow groove gas shielded arc welding method according to claim 1 or 2, wherein, The total amount of S and O in the weld metal in the first layer welding is 450 mass ppm or less, and the N amount is 120 mass ppm or less. 4. 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 in the welding wire used for the first-layer welding is 1.5% by mass or more and 3.5% by mass or less. 5. The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 4, wherein, The total amount of Ti, Al, and Zr in the welding wire used for the primary layer welding is 0.08% by mass or more and 0.50% by mass or less. 6. The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 5, wherein, A gas containing more than 20% by volume of CO ₂ gas is used as the shielding gas for the first layer welding. 7. The vertical narrow groove gas shielded arc welding method according to any one of claims 1 to 6, wherein, The average welding current of the said primary layer welding is 270 A or more and 360 A or less.