JPS6333941B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multi-electrode arc welding method useful for welding steel materials, particularly for welding large diameter steel pipes manufactured by the UOE method. In manufacturing large-diameter steel pipes using the UOE method, the side edges of a steel plate with bevels on opposite sides are bent slightly toward the same side, and then pressed to make the side edges face inward. The open pipe is bent into a U-shape, and then pressed into an O-shape so that the side edges abut each other to obtain an open pipe.Temporary welding is performed at the key points of the groove of this open pipe, and both ends of the open pipe are After welding a tab plate with approximately the same curvature as the open pipe so that it is located on the extension of the groove, welding of the abutting part is first performed on the inner surface, then the outer surface is made into a tube body, and then the pipe expansion process is performed. We plan to complete the process through these steps. Therefore, the inner and outer surfaces of the open pipe are welded using the submerged arc welding method, especially multi-electrode submerged arc welding, which has a large heat input, can finish each inner and outer surface with a single layer of welding, and has a beautiful bead shape. law has been adopted. However, recently there has been an increase in demand for thick-walled, large-diameter steel pipes, and there is a tendency for high-temperature toughness to be required. unable to meet the demands of In other words, due to the large amount of heat input, the welding heat affected zone [hereinafter referred to as HAZ (Heat Affected Zone)]
This is because the toughness of the steel decreases. In order to solve this problem within the technical scope of the submerged arc welding method, it is possible to perform multi-layer welding by suppressing the amount of heat input, but if such a method is adopted, the amount of heat input per layer In order to suppress this, it is necessary to reduce the number of welding electrodes and to reduce the welding speed, and furthermore, slag removal work is required each time one layer of welding is completed, resulting in a significant decrease in efficiency. For this reason, it is practically impossible to manufacture thick-walled, large-diameter steel pipes with high toughness at low temperatures by submerged arc welding. Therefore, various methods of welding open pipes have been attempted, using MIG (Metal Inert-gas) welding or a combination of MIG welding and submerged arc welding. In the former case, both the leading and trailing electrodes are MIG.
Use a welding electrode, in the latter case MIG as the leading electrode.
In this method, a submerged arc welding electrode is used as the welding electrode and the last row (final) electrode, and these electrodes are appropriately spaced apart to perform welding in one run. However, this method is not suitable for the leading electrode.
Since the direct current for MIG welding is passed through, a magnetic blow phenomenon occurs in the arc of the trailing electrode, and a good bead appearance cannot be obtained and there are many defects, making it impossible to apply it to actual products. In addition, in DC MIG welding, the arc is generally highly concentrated, resulting in deep penetration and formation of a bead with a pear-shaped cross section, and hot cracking is likely to occur in the middle of the dendrites formed on both sides of the bead. Particularly when the welding current is large, welding defects due to poor fusion tend to occur.
Methods using MIG welding are not a sufficient solution. The present invention was made against this technical background, and at least performs AC MIG welding using the leading electrode, AC MIG welding or submerged arc welding using the trailing electrode, and performs multilayer welding using a multiple pool method. As a practical example, the amount of heat input is distributed,
The purpose of this invention is to provide a multi-electrode arc welding method that can improve the toughness of HAZ without reducing efficiency. First, prior to a specific explanation of the present invention, the AC MIG welding method will be described. Originally, MIG welding was considered to be a welding method that primarily uses direct current. In other words, the discharge phenomenon itself can occur regardless of the type of AC or DC current, but in the case of MIG welding, when an AC voltage is applied between the wire that serves as the welding electrode and filler material and the workpiece that is the welding target, a predetermined Although a discharge occurs once under these conditions, the discharge phenomenon is interrupted during the zero current phase when the polarity of the discharge current alternates, and subsequent re-ignition often fails, making it impossible to expect stable and continuous arc generation. ,For this
Direct current is always used in the MIG welding method, and
MIG welding always meant DC welding. This is an attempt to combine the above-mentioned MIG welding method and submerged arc welding method, for example,
This also applies to the techniques disclosed in No. 3543 and Japanese Patent Application Laid-open No. 130242/1983. However, while taking advantage of the features of the MIG welding method (which uses direct current), there is a possibility of converting the power source to alternating current with the intention of not generating residual magnetism that causes magnetic blowout and simplifying the power supply device. As a result of various studies, we found that 1 to 15% by weight of essential ingredients.
TiO ₂ and 1 to 10% by weight alone or in total
Na ₂ O and/or K ₂ O as an arc stabilizer,
In addition, by using a composite wire containing 1 to 10% by weight of SiO ₂ as a slag forming agent, a technique that enables a stable and continuous arc even when using an AC power source, that is, AC MIG welding. I found out that the law is possible. The present invention was previously simply
Unlike direct current MIG welding, which has been called MIG welding method, AC MIG as mentioned above does not cause magnetic arc blowing by the trailing welding electrode.
The welding method is used to perform multilayer welding using a multiple pool method, in other words, multilayer welding in one run. The multi-electrode arc welding method according to the present invention can be roughly divided into two types: those using only AC MIG welding and those using a combination of AC MIG welding and submerged arc welding. The welding method is adopted, and the main part is multi-layer welding using a multiple pool method, and the purpose is to enable welding with excellent efficiency and HAZ toughness. First, the former method will be explained. The most basic implementation is AC MIG as shown in Figure 1.
Composite wires 1f and 1r for welding are arranged in tandem at a distance l ₁ apart from each other in the direction of welding progress indicated by the white arrow, and an alternating current voltage is applied between both composite wires 1f and 1r and the workpiece W. Perform AC MIG welding by applying voltage. The composite wires 1f and 1r are inserted through the welding heads 11 and 11, with their respective tips facing the workpiece W, and are fed out by feed rolls 12 and 12. A mixed inert gas consisting of helium, carbon dioxide, and argon is ejected toward the workpiece W, covering the arc generated between the composite wires 1f and 1r and the workpiece W, and further preventing the progress of welding. Composite wires 1f, 1r in the direction of the arrow mark
The points such as moving the workpiece W in a linked manner or moving the workpiece W in the opposite direction of the white arrow are different from the normal DC method.
It is similar to MIG welding and other continuous welding methods. Therefore, the separation distance l ₁ between the composite wires 1f and 1r is a value at which AC MIG welding is performed as multilayer welding in a two-pool method, that is, the composite wires 1l, 1r,
1r needs to be set to the value required to form each moleton pool independently. The value of l ₁ varies depending on welding conditions, that is, welding voltage, welding current, and welding speed, but in the range of less than 200 mm, it is 2
If a pool is not formed and the diameter exceeds 500 mm, the tab plate will become long during welding in the manufacture of large-diameter steel pipes, which will hinder work. is preferable. Next, the composite wires 1f and 1r will be explained.
The use of these composite wires 1f and 1r is of course essential for stabilizing the arc and enabling AC MIG welding, but their selection is extremely important for obtaining a good bead. As a result of repeated various experiments by the present inventors, it has been found that it is suitable to use the following composite wire as this composite wire. That is, based on the entire composite wire, 1 to 15% by weight of TiO ₂ and 1 to 10% by weight of Na ₂ O and/or K ₂ O alone or in total as arc stabilizers; % SiO ₂ as a slag forming agent. here
The reason for setting TiO ₂ to 1 to 15% by weight is that if it is less than 1%, the arc stability will be poor, and if it exceeds 15%, the restriking voltage will become too high and there is a risk of arc breakage. Also, Na ₂ O added singly or in combination,
The reason why the amount of K ₂ O is 1 to 10% by weight is because if it is less than 1%, the effect of stabilizing the arc is small, and if it exceeds 10%, blowholes are likely to occur in the bead. Further, the reason why SiO ₂ is set to 1 to 10% by weight is that if it is less than 1%, slag formation is insufficient, and if it exceeds 10%, the amount of slag becomes excessive and slag entrainment defects are likely to occur. The above-mentioned components of the arc stabilizer and slag forming agent may be incorporated as raw materials into the steel hollow body constituting the wire, or may be melted into the wire itself and incorporated integrally therewith. . This composite wire also contains MnO as a deoxidizer,
Al ₂ O ₃ and CaF ₂ , as well as Fe--Mn and Fe--Mo as strength improvers for weld metal, may be added in small amounts, one or more of each. Fig. 1 schematically shows the welding state of the workpiece W. In the figure, the white regions behind the tips of the composite wires 1f and 1r indicate the moleton pools W ₁ and W ₂ , and A leading bead W ₃ is formed by the molton pool W ₁ , and a trailing bead W ₄ is formed on the upper layer of the leading bead W ₃ by the malton pool W ₂ associated with the trailing composite wire 1r. A slag W ₅ is formed on the leading bead W ₃ in front of the trailing composite wire 1r, but since this slag W ₅ is as thin as approximately 1 mm, it is not affected by the arc of the trailing composite wire 1r. It can be melted and removed without any problem. In this way, the present invention employs a multiple pool system in which the leading and trailing beads are formed substantially simultaneously by a plurality of independent Molton pools W ₁ and W ₂ that are formed at appropriate lengths apart. Multilayer welding, that is, multilayer welding in one run, is performed. In the case of the welding method of the present invention, the heat input is distributed to each composite wire 1f and 1r, so that the low-temperature toughness of the HAZ can be improved as in the case of multilayer welding of one layer in one run. It is highly efficient because it can be done in one run. and up the advance welding
By using MIG welding, magnetic blowing phenomenon does not appear in the arc of trailing welding, and since the slag _W5 generated by preceding welding is thin, it is melted and removed by the arc of trailing welding, causing slag entrainment defects. A good bead can be obtained. Furthermore, in the method of the present invention, the use of a composite wire is essential for performing AC MIG welding, but when using a composite wire, the arc Since the concentration is weak, there is also the effect of preventing poor fusion and high temperature cracking caused by this. Next, another embodiment in which only the AC MIG welding method is used as described above will be described. In the embodiment shown in Fig. 1, the leading and trailing welding electrodes are each made of one composite wire, but one or both of them have multiple wires (in practice, 2 to 4 wires). It is also possible to use a composite wire of in this case,
A plurality of composite wires, each serving as a leading or trailing electrode, are placed in close proximity to form a single molton pool. In other words, even when using multiple composite wires as leading or trailing electrodes, the leading pool,
Only one trailing pool is formed, and as far as multilayer welding with two pools is concerned, one composite wire is equivalent to multiple composite wires arranged in close proximity as leading or trailing electrodes. be. If one or a plurality of composite wires arranged in close proximity to each other as a leading electrode, a trailing electrode, or an intermediate electrode as described later, each of which contributes to the formation of the same morton pool, is referred to as a welding electrode unit, the first
In the method shown in the figure, one composite wire is used in each of the leading welding electrode unit FU1 and the trailing welding electrode unit RU.
This means welding using 1. On the other hand, in the embodiment shown in Fig. 2, the preceding welding electrode unit
As FU2 and trailing welding electrode unit RU2,
Both are two composite wires 2f ₁ , 2f ₂ and 2r ₁ ,
_2r2 is used, and both welding electrode units are arranged in tandem. Welding electrode unit FU
2 (or RU2) of composite wires 2f ₁ , 2f ₂ (or 2
r ₁ , 2r ₂ ) dimension l ₂₁ (or l ₂₂ ) [all dimensions between tips] are the same Molton pool W ₁ (or
W ₂ ), for example, about 20 mm. When one unit includes three or more composite wires, the dimensions between adjacent wires may be similarly determined. And both welding electrode units FU2,
The dimension between RU2, that is, the separation dimension _l2 between the tip of the composite wire _2f2 on the rear side of unit FU2 and the tip of composite wire _2r1 on the front side of unit RU2 is as described above because it is necessary to keep the moleton pools of each unit independent. Same as above, the range is 200 to 500 mm.
Even when each welding electrode unit is composed of a plurality of composite wires as shown in FIG.
It goes without saying that the same effects as in the illustrated embodiment can be achieved. When the welding electrode unit is composed of a plurality of composite wires, the welding speed can be increased even when the groove is wide or deep. FIG. 3 shows an embodiment in which three welding electrode units, leading, middle, and trailing, are arranged in tandem. Each welding electrode unit
The number of composite wires for FU3, MU3, and RU3 may be set to 2 for each as shown in the figure, or 1 or 3 or more for each, as required, but the implementation of Figure 2 As in the example, the distance between the composite wires constituting the same welding electrode unit should be set to a small value of about 20 mm so that the unit as a whole forms a single morton pool, and the distance between the welding electrode units should be set to a small value of about 20 mm. The distance, that is, the tip of the composite wire on the rear side of the preceding welding electrode unit FU3 and the intermediate welding electrode unit MU3
The separation distance l ₃₁ between the front composite wire tip of the intermediate welding electrode unit MU3 and the separation distance l ₃₂ between the rear composite wire tip of the intermediate welding electrode unit MU3 and the front composite wire tip of the trailing welding electrode unit RU3 are formed by each unit. The range shall be 200 to 500 mm so that the moleton pools W ₁ , W ₀ , and W ₂ are independent. In the case of the embodiment shown in Fig. 3, the same effects as those shown in Figs. As the heat input is further distributed, the low-temperature toughness improvement effect of HAZ is even more remarkable. The number of welding electrode units arranged in tandem is not limited to 2 or 3 as in the above three examples, but may be 4 or more, depending on workpiece specifications (wall thickness, groove conditions, required low-temperature toughness), welding speed, etc. It may be selected appropriately based on the number of composite wires constituting the unit. Next, another method of the present invention, that is, a method of using AC MIG welding method and submerged arc welding method in combination will be explained. Simply stated, this method uses one or more submerged arc welding wires in place of the trailing or final welding electrode unit RU1, RU2, or RU3 shown in Figures 1 to 3, that is, the final welding electrode unit. The welding electrode unit is arranged to perform submerged arc welding using the welding electrode unit. When multiple submerged arc welding wires are used, the distance between the tips of adjacent wires is the same as in the welding electrode unit for AC MIG welding described above. A small value of about 20 mm is used to form a moleton pool, and the separation distance between the welding electrode unit for submerged arc welding, that is, the last row, and the preceding or intermediate welding electrode unit located in front of it, that is, the former. The distance between the front wire tip and the rear wire tip of the latter is set to 200 to 500 mm so that the moleton pools formed by these two welding electrode units are independent. In this case as well, a composite wire with the composition described above is used for the unit for AC MIG welding, but the wire used for the unit for submerged arc welding should be selected appropriately, and the flux used should also be selected appropriately. Bye. In short, this method performs submerged arc welding as the last line of welding, followed by AC welding using one or more welding electrode units.
MIG welding is performed. FIG. 4 schematically shows one embodiment of the welding process along with the welding progress state of the workpiece W. A composite wire 4f serving as a welding electrode unit FU4 for AC MIG welding is inserted into a welding head 41 and fed out by a feed roll 42 at the front in the welding progress direction indicated by a white arrow. An alternating current voltage is applied between the composite wire 4f and the workpiece W, and the above-mentioned mixed inert gas is ejected from the welding head 41 toward the workpiece W, whereby the composite wire 4
Covering the arc between f and workpiece W, AC MIG
Have the welding done. And welding electrode unit FU4
Behind the welding electrode unit RU4 for submerged arc welding.
Two submerged arc welding wires 4r ₁ and 4r ₂ are fed out through welding heads 43 and 43, and a flux (not shown) is placed in front of the submerged arc welding wire 4r ₁ and behind the composite wire 4f. A feeder is installed, and the flux FL supplied from this feeder
Then, the arc between the wires 4r ₁ and 4r ₂ and the workpiece W is covered, and submerged arc welding is performed in a known manner.
Note that the distance l ₄ between the tips of wires 4f and 4r ₁ is 200
Set to ~500mm. In this way, the preceding unit FU4 exchanged
When performing MIG welding and submerged arc welding in the following unit RU4, the preceding AC MIG welding first forms a moleton pool W ₄₁ , which is obtained from the preceding speed W ₄₃ , and then the subsequent AC MIG welding. A morton pool W ₄₂ is formed by the subsequent submerged arc welding, which results in a trailing bead W ₄₄ , and two-layer welding is performed in one run. In addition, slag from AC MIG welding on the preceding bead W ₄₃
W ₄₅ is formed, but since it has a thickness of about 1 mm as in the case described above, it is melted and removed by the arc of the subsequent submerged arc welding. Note that _W46 is slag formed by submerged arc welding, and most of it is recovered together with the used flux FL. Even when submerged arc welding is used in combination, AC MIG welding is performed on all but the last welding electrode unit, so trailing welding (AC MIG welding or submerged arc welding)
Since the magnetic blowing phenomenon does not appear in the arc, and the slag generated by the preceding AC MIG welding is thin, it is melted and removed by the subsequent AC MIG welding or submerged arc welding, and no slag entrainment defects occur. A bead is obtained. The heat input is also dispersed as before, improving the low-temperature toughness of the HAZ. Also, multi-layer welding is performed in one run, so efficiency is high, and the use of composite wire reduces arc concentration.
It also prevents poor fusion and high-temperature cracking, and
The same effect as with MIG welding alone can be achieved. By performing submerged arc welding last, the appearance of the bead shape became extremely beautiful.
In addition, this also provides the unique effect of eliminating the risk of stress concentration on the defective bead shape. Next, the effects of the method of the present invention will be clarified by examples. In both of the following two examples, the method shown in Fig. 4 is used, that is, AC MIG welding is performed in the preceding unit, and submerged arc welding is performed in the subsequent unit, and the number of composite wires in the former is is 1
In this case, the number of submerged arc welding wires used was two. The workpiece is as shown in Figure 5.
Taper one side of each long piece of two steel plates 100mm wide, 2000mm long, and 25mm thick to form a V-shaped groove with a depth of 9mm on each of the front and back sides, and cut a 7mm groove in the center.
The two root faces were machined to provide a root face, and the two root faces were abutted against each other. The chemical composition (weight%) of the steel plate is C: 0.12, Si: 0.28,
Mn: 1.25, P: 0.016, S: 0.005. Example 1 (1) Welding conditions: according to Table 1

[Table] Note that the distance l ₄ between wires 4f and 4r ₁ was 400 mm. (2) Chemical composition of test composite wire for AC MIG welding: according to Table 2

[Table] (Unit: Weight%)
Note that the wire with symbol a is a real wire and does not satisfy the conditions of the method of the present invention. Symbols b to d are composite wires suitable for carrying out the method of the present invention, such as TiO ₂ , K ₂ O, Na ₂ O,
It does not satisfy the component conditions for SiO ₂ . On the other hand, those with symbols e to h satisfy the above component conditions. (3) Wire and flux wire for submerged arc welding: Commercially available Si-Mn wire flux: Neutral melting type flux (4) Welding results: According to Section 3

[Table] As is clear from the results, stable AC MIG welding cannot be performed with solid wires or composite wires b to d that do not satisfy the above component conditions, and in particular, beads are not formed with solid wires. On the other hand, when using a composite wire that satisfies the above component conditions, stable AC MIG welding of the workpiece can be performed.
Furthermore, no defects occur. Note that the above example shows the results when a welding machine with a no-load voltage of 85V is used, but the welding machine has a no-load voltage of 85V.
When using a 95V wire, the arc was stable even when composite wires b to d were used, and no blowholes or slag entrainment were obtained. It is presumed that this effect is not solely dependent on the composition of the arc stabilizer and slag forming agent of the wire. Example 2 (1) Welding conditions: According to Table 1 However, the distance l ₄ between wires 4f-4r ₁ was varied variously. Also, welding was done on both the front and back sides. Moreover, the composite wire under test is of the symbol f. (2) Results of a Charpy test to examine HAZ toughness: See Table 4 Measurements were performed at three locations for each sample.

[Table] As is clear from this result, the distance between the wires is
If it was less than 200 mm (sample numbers 1 to 3), the effect of multilayer welding could not be obtained, and if it was 200 mm or more (sample numbers 4 to 7), good toughness was obtained. As described in detail above, the present invention has high production efficiency, high HAZ low-temperature toughness, and can realize welding that can form a good bead without defects. There are many areas that contribute to improvements in productivity and production efficiency. Note that the welding method according to the present invention does not need to be applied to both the front and back surfaces of a workpiece, and considerable effects can be obtained even if it is applied only to welding the surfaces to be welded later. That is, in the case of manufacturing large diameter steel pipes by the UOE method, the method of the present invention may be applied only to external welding. This is because the toughness of the exposed HAZ is largely determined by the last welding performed.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic diagrams in which all of the present invention is carried out by AC MIG welding, and Figure 4 shows the present invention in which only the last row is welded by submerged arc welding, and the rest by AC MIG welding. FIG. 5 is a perspective view of the workpiece used in Examples 1 and 2. 1f, 1r, 4f...Composite wire, 4r ₁ , 4r ₂
...submarine arc welding wire, FU1, RU1...FU4,
RU4...Welding electrode unit.

Claims (1)

[Claims] 1. 1 to 15% by weight of TiO ₂ as its essential component
and 1 to 10% by weight of Na ₂ O and/or K ₂ O alone or in total as an arc stabilizer;
A plurality of welding electrode units consisting of a single composite wire containing 10% by weight of SiO ₂ as a slag forming agent or multiple composite wires placed close together to form a single Molton pool are connected to each independent Molton pool. A multi-electrode arc welding method characterized by performing AC MIG welding with each welding electrode unit arranged in tandem and separated from each other by the distance required to form a pool. 2. The multi-electrode arc welding method according to claim 1, wherein the distance is 200 to 500 mm. 3 1-15% by weight of TiO ₂ as its essential component
and 1 to 10% by weight of Na ₂ O and/or K ₂ O alone or in total as an arc stabilizer;
One welding electrode unit is preceded by one composite wire containing 10% by weight of SiO ₂ as a slag forming agent or a plurality of composite wires arranged closely to form a single morton pool. A 1 or A multi-electrode arc welding method characterized in that a welding electrode unit consisting of a plurality of submerged arc welding wires is used as the last electrode, and submerged arc welding is performed using the welding electrode unit. 4. The multi-electrode arc welding method according to claim 3, wherein the distance is 200 to 500 mm. 5 1 to 15% by weight of TiO ₂ as its essential component
and 1 to 10% by weight of Na ₂ O and/or K ₂ O alone or in total as an arc modifier;
A plurality of welding electrode units each consisting of a single composite wire containing 10% by weight of SiO ₂ as a slag forming agent or multiple composite wires placed closely to form a single moleton pool, each independently preceded by being arranged in tandem and separated from each other by a distance required to form a malton pool;
1, which is separated from the welding electrode unit by a distance necessary to perform AC MIG using the welding electrode unit and to form a single morton pool independent of the malton pool formed by the AC MIG welding; Alternatively, a multi-electrode arc welding method characterized in that a welding electrode unit consisting of a plurality of submerged arc welding wires is used as the last electrode, and submerged arc welding is performed using the welding electrode unit. 6. The multi-electrode arc welding method according to claim 5, wherein the distance is 200 to 500 mm.