JPH0729206B2 - High-speed submerged arc welding method using multiple electrodes - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-speed submerged arc welding method suitable as a welding method for producing large-diameter welded steel pipes such as line pipes and structural pipes. is there.

<Conventional technology and its problems> In the UO mill line used for manufacturing large diameter welded steel pipe, UO
Submerged arc welding is generally applied to the main welding of the inner and outer surfaces of the steel pipe, which is carried out after the tack welding following the press, and at present, both inner and outer surface welding are combined with electrodes of 3 to 4 poles (5 for outer surface welding). Welding with multiple electrodes has been carried out. This is because the welding speed is determined by the amount of deposited metal supplied, the control of the molten pool, and the gouging force of the base metal, and these capabilities have been known to increase in proportion to the number of electrodes.

Specifically, for inner surface welding, connect a direct current (DC) or alternating current (AC) power source to the first pole, connect an AC power source to the second pole and thereafter, set the current value of each pole to 1500 A or less, and It is implemented in 5 lines, and the connection method at this time is, for example, "DC-AC-
In the case of the combination of "AC", for example, a V connection in which the third pole is delayed by 60 ° with respect to the second pole is adopted. In addition, the same electrode arrangement as in the case of the inner surface welding is applied to the outer surface welding. The connection method in this case is, for example, in the case of the combination of "DC-AC-AC-AC", the reverse V connection in which the 3rd pole is 120 ° behind the 2nd and 4th poles is adopted, and the operation is 4 lines. It is usually carried out by

However, even in high-speed submerged arc welding in which 3 to 5 electrodes are applied as described above, it is difficult to control the welding amount, gouging force, molten pool, etc. when multiple electrodes are used. Regardless, the maximum welding speed that can be secured was 3.6 m / min. In other words, if the welding speed is further increased, it is difficult to form a good bead, and undercut or necking which is a welding defect occurs, and a bad situation in welding quality such as significantly impairing the bead appearance occurs. It was inevitable.

By the way, the production efficiency of a large diameter welded steel pipe mill is mainly defined by the capacity of the welding line, and the capacity of this welding line is determined by the welding speed, idle time, and the number of lines. Therefore, in order to improve the production efficiency and reduce the production cost, it is considered that the most practical measure is to significantly increase the welding speed and reduce the number of lines. However, even if the number of electrodes is increased to 5 in order to achieve the improvement of the welding speed by means of "increasing the number of electrodes", which is very simple, the current technology limits the improved welding speed as described above. Therefore, it is not possible to dramatically improve the production efficiency of large-diameter welded steel pipe mills, and it is impossible to expect results that will lead to a reduction in the number of lines.

In this way, as the number of electrodes increases, it becomes more difficult to control the stability of the welding arc and the bead shape. Therefore, increasing the number of electrodes from the maximum practical limit of 5 poles to 6 poles or more Achieving significant improvements was said to be a long way off from the current level of technology.

However, in response to the ever-increasing demands for cost reduction and production efficiency improvement of large diameter welded steel pipe,
The object of the present invention is to find a method that can significantly improve the welding speed of submerged arc welding without degrading the product quality, and even if the number of required lines in a large diameter welded steel pipe mill is reduced, sufficient production efficiency is achieved. It was to establish the means by which the improvement of can be achieved.

<Means for Solving the Problems> The inventors of the present invention, in the process of earnestly studying to achieve the above-mentioned object, “in order to improve the welding speed at the time of submerged arc welding, it is most realistic to increase the number of electrodes used. Therefore, in order to achieve a welding speed that exceeds the current level and obtain a product of satisfactory quality, it is essential to develop a stable welding method using multiple electrodes with 6 or more electrodes. " As a result of continuing the research to prove the validity of each one by experiment while calculating the optimum one by the simulation calculation from the combination pattern of various conditions, "Using multiple electrodes of 6 poles or more in submerged arc welding" Even in this case, the welding arc can be sufficiently stabilized by devising a) electrode connection method, b) electrode angle, electrode spacing, tip height setting, c) flux used. And stable control of the bead shape is possible, good slag releasability is also secured, and high-speed welding with good internal quality and bead formation with good appearance under sufficient penetration. (The maximum welding speed of 4.5 m / min or more is achieved) ”was obtained.

The present invention has been made on the basis of the above-mentioned findings and the like. “When performing submerged arc welding, six or more electrodes are used, and a) a direct current is applied to at least the leading electrode, b) The phase difference of the AC power supply to the electrodes other than the above is set so that the force acting on the arc of the final pole is oriented in the welding advancing direction on average. Set the advancing angle respectively and set the distance between each electrode within 25mm. D) Welding current balance of n electrodes is 1st pole: 1, 2nd pole to (n-2) th pole: 0.7 each 1.10, (n-1) th poles: 0.6 to 0.80, the n poles set to 0.5 to 0.75 _{range, e) SiO 2: 5~25%} ( hereinafter,% represents the component ratio is the weight% ), Al ₂ O ₃ : 2 to 20%, MnO: 0.5 to 15%, TiO ₂ : 2 to 10%, CaO: 5 to 25%, BaO: 1 to 5%, MgO: 3 to 15%, CaF ₂ : 25-60%, B ₂ O ₃ : 2% or less, the balance consisting of unavoidable impurities, and (CaO + MgO) / SiO ₂ = 1.5-3.0, with a chemical composition of 60% or more. 100 μm (48 to 145 mesh)
By using a molten flux with a particle size that falls within the range of 1), it is possible to perform high-speed welding of high-quality products by satisfying each of the following conditions, greatly improving product production efficiency, and reducing welding lines. It has the feature that it can be implemented ”.

That is, the present invention is: (a) increase the number of electrodes to more than 6 electrodes, (b) establish an optimal connection method, (c) optimal setting of electrode angle, electrode interval, and chip height, (d) high-speed flux By solving the four technical problems of
It enables high-speed submerged arc multi-electrode welding of 4.5 m / min or more (more than 1.5 times the current level), improves efficiency and reduces the number of lines, and has a complicated 6-electrode technology or more multi-electrodes. It is not only the key point of the technology, but at the same time, it also provides the technology of controlling the flux physical properties to ensure good bead appearance, penetration, slag peeling property, internal quality, and high speed. Hereinafter, the present invention will be described in more detail along with its operation and effects with reference to the drawings.

<Operation and Effect> FIG. 1 is a conceptual diagram showing an example of the submerged arc multi-electrode welding method according to the present invention using six electrodes.

As shown in FIG. 1, in the method of the present invention, six or more electrodes are arranged, and a DC (direct current) power source is applied to at least the leading electrode to achieve proper and stable gouging, and other electrodes ( An AC (alternating current) power supply is applied to the second pole and later in the example of FIG. 1) in order to ensure industrial superiority. However, especially in multi-electrode submerged arc welding with 6 or more electrodes, the connection method controls the magnetic force acting on each pole and the direction of the arc, and is an important factor that controls the stability, bead shape and high speed of the welding arc. Becomes Therefore, the connection method was confirmed by performing simulation calculation under the following assumptions and determining and verifying the connection method on the actual line.

That is, simulation calculation 1) Generally, in multi-electrode welding, the final pole has a large effect on the bead shape, so only the force that acts on the final pole is considered. 2) The force that acts on the final pole is the welding current of each pole. , Phase difference,
It shall be determined by the distance between the electrodes, the tip height (extention), and the magnetic permeability (μ). 3) The average value of the force acting on the arc of the final pole is smoothin
It is set to about 0.1 × 20 N / m, which is considered desirable from the results of examination of g action and the appearance of the formed bead. 4) The time during which the force acting on the arc of the final pole is directed in the welding progress direction is the smoothing action and From the examination result of the appearance of the formed bead, it was clarified that it is desirable to determine the phase difference so that the time is as long as possible. 5) The force [Fn] acting on the final n-th pole is calculated by the formula Fn = Fn ₁ + Fn ₂ + ... + Fni + ... + Fnn _-1 + Fnn + Fn ₀ Based on the results of the preconditions of, and the results of the actual test, it is concluded that it is possible to apply the AC power supply to the other pole at least when using the DC power supply for the leading pole. Reached Especially, in the 6-electrode submerged arc welding shown in Fig. 1, the following magnetic pole and phase difference connection method suitably controls the magnetic force acting between the electrodes to optimize the welding arc stability and bead shape. I also confirmed that.

DC-AC-AC-AC-AC-AC 0 ° + 60 ° + 120 ° −90 ° + 120 ° (Here, + indicates the advance of phase difference, − indicates the delay, and when the second pole is used as the reference Shows the phase difference).

In addition, Table 1 shows a part of the “combination of AC pole phase difference in 6-electrode submerged arc welding and the examination result of the welding situation” from which the above conclusion was obtained. The welding conditions at this time are as follows: 1.00 inch thick bead-on-plate, welding current and voltage: 1st pole …… 1200A, 30V, 2nd pole …… 1000A, 33V, 3rd pole …… 900A, 36V, 4th pole …… 850A, 40V, 5th pole: 700A, 42V, 6th pole: 600A, 44V, welding speed: 4.0m / min.

Furthermore, from the result of welding test using this connection method with a 6-electrode submerged welding machine of a real line, the wall thickness: 0.25 ~
When welding conventional 2.00 electrode submerged arc welding for welding 2.00 inch large diameter steel pipe, welding speed is 1.0
While it was ~ 2.8 m / min, in the 6-electrode submerged arc welding according to the present invention, total current: 5000 A or more, welding speed: 3.0
It was confirmed that a stable arc and a beautiful bead appearance were obtained in the range of ~ 5.0 m / min, and its superiority and the validity of the calculation results were verified.

By the way, in the method of the present invention, the leading DC pole is provided with a receding angle and the other electrodes are provided with an advancing angle. The reason for giving the leading electrode a receding angle is that the gouging force is expanded by the leading electrode. This is because it is intended. The receding angle of the preceding DC pole should be -20 °, and the electrode capacity should be 2000A at maximum. When the leading DC pole has an advancing angle of 0 ° or more, the smoothing action promotes the flow of molten metal in the bead width direction and is effective for improving the appearance, but the digging action is significantly reduced and the penetration depth is insufficient. Therefore, a sufficient welding speed cannot be achieved. On the other hand, if the leading DC electrode has a receding angle of more than −20 °, the molten pool is agitated more than necessary, and there is a concern that welding defects may undercut or slag inclusion may occur frequently. On the other hand, the advancing angle of the trailing AC pole blocks the backward flow of the molten metal in the molten pool, and beauty is given to form a bead appearance. This advancing angle is 0 to + 45 °. The range is good.

In addition, Table 2 shows the welding test results using the bead-on-plate having a plate thickness of 1.00 inch.
It can be confirmed that good welding results can be obtained by providing the lead DC pole with a receding angle and the trailing AC pole with an advancing angle.

Here, in order to secure a sufficient deposition amount, bead appearance, and arc stability at a welding speed of 4.5 m / min, it is preferable to apply a large diameter solid wire of 4.0 to 6.4 mmφ as a welding wire.

In addition, the space between the tip of each electrode is
In the method of the present invention using d flux), it is necessary to set the distance to within 25 mm in each case, which can improve the arc stability and the prevention of welding defects. If the distance between the electrodes exceeds 25 mm, the bead appearance will deteriorate, and the slag that floats in a semi-solidified state will be interfered by the electrodes and cause slag catching, which is disadvantageous in terms of product quality and workability. Invite.

Table 3 shows a part of the results of the welding test using a bead-on-plate with a plate thickness of 1.00 inch and varying the distance between the electrodes. Is 25
It can be confirmed that good results are obtained when set within mm.

Regarding the current balance, the rigidity of the trailing electrode arc is moderated by decreasing the distribution by 0.1 to 0.05 normally as the electrode moves from the leading electrode to the trailing electrode, and high-speed welding (υ> 3m
(/ min), a wide and smooth bead appearance can be obtained. However, it has been found that, particularly when the wall thickness is thin, a better bead appearance can be obtained by increasing the current of the second pole with respect to the first pole in welding that does not require a deep penetration. And the current balance is especially 1st pole …… 1, 2nd pole …… 0.7 ～ 1.10, ・ ・ ・ ・ Same as above, ・ ・ ・ ・ Same as above, n-1 pole ・ ・ ・ 0.6〜0.80, nth pole ・ ・ ・ 0.5〜 If the distribution is set to 0.75, a good bead appearance can be secured more stably.

Even when high-speed submerged arc welding is performed under the conditions as described above, the problems of weld bead shape and weld metal performance deterioration cannot be sufficiently wiped out with high-speed welding. Therefore, the present inventors have conducted research to solve the above-mentioned problems. First, (A) by adding an appropriate amount of Al ₂ O ₃ or SiO ₂ as a flux component, an appropriate melting point in the coexistence with CaF ₂ is obtained.・ A viscous slag is generated. (B) Flux particle size Nominal dimension specified by JIS 300-
We have found that undercut and slag entrapment are reduced as much as possible when the 100 μm area is constantly maintained at 60% or more, and by taking such measures, welding speed: 5.0 m /
It was confirmed that good bead appearance and slag releasability were obtained even in min high current (high heat input) welding, and welding workability and welding defect prevention effect could be improved. Then, after further study, SiO ₂ , MnO, CaO, CaF ₂ , Al ₂ O ₃ , MgO, TiO ₂ , BaO and B ₂ O _{3 in the} Al ₂ O ₃ -SiO ₂ -CaF ₂ component system flux.
The balance of components _{SiO 2: 5~25%, Al 2} O 3: 2~20%, MnO: 0.5~15%, TiO 2: 2~10%, CaO: 5~25%, BaO: 1~5% _{, MgO: 3~15%, CaF 2} : 25~60%, B 2 O 3: 2% or less, and _{(CaO + MgO) / SiO 2} = 1.5~3.0 by controlling so as to satisfy the basicity Always kept at a high value, the effect of reducing the amount of oxygen is effectively exhibited even in welding with an increased number of electrodes, and it becomes possible to sufficiently suppress the amount of oxygen in the weld metal formed to 350 ppm or less, This is the reason why we have realized a fusion type flux for high-speed welding that can fully meet the specifications of low hardness and high toughness generally required for large diameter line pipes.

Of course, in this flux, SiO ₂ , MnO, CaO, CaF ₂ , Al ₂ O
_If the component balance of ₃ , MgO, TiO ₂ , BaO and B ₂ O ₃ is out of the above range, the above effect cannot be stably ensured.

In addition, the nominal size of the above flux specified by JIS 300-
When the area of 100 μm is less than 60%, welding defects become noticeable in multi-electrode high speed welding, undercut occurs when the coarse grain area increases, and slag inclusion occurs when the fine grain area increases. Will occur frequently.

As described above, the present invention relates to submerged arc welding in which a number of unsolved problems continue when trying to further increase the speed, and "further increase in number of electrodes", "probability of optimal connection method", By solving the difficult technical problems of "optimal setting of electrode angle, electrode interval, tip height" and "development of high-speed flux" from a comprehensive point of view, the above obstacles were overcome and a stable high-speed submerged arc welding method was achieved. Although established, the effect will be described more specifically below with reference to the examples.

<Example> Six electrodes were set as shown in FIG. 2, and the phase difference of the AC poles after the second pole was 0 °, + 60 °, +120.
Submerged arc welding tests were conducted on steel plates under the conditions shown in Table 4 for the other conditions, such as °, -90 °, and +120 °.

The flux used at this time was substantially CaO:
18.0%, MgO: 6.0%, SiO ₂ : 14.0%, CaF ₂ : 37%, Al ₂ O ₃ : 15%,
_{MnO: 3%, TiO 2:} 3%, BaO: 3% and B ₂ O _3: made of 1%, and _{[(CaO + MgO) / SiO 2} = 1.7 ] a constituent balance, the particle size is defined by JIS 6 areas with nominal dimensions of 300 to 100 μm
It included 5%. The wire used was a solid wire of 4.0 mmφ, and its composition was as shown in Table 5.

When the appearance of the weld beads was evaluated after the test, it was confirmed that all of them had a good appearance.

<Summary of Effects> As described above, according to the present invention, the maximum welding speed:
A high-speed submerged arc welding method of 4.5 m / min or more has been established, which can significantly improve the production efficiency of large-diameter welded steel pipes such as line pipes and structural pipes, and increase production even if the number of welding lines is reduced. It will be possible to achieve the extremely useful effects in the industry, such as being able to deal with.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram showing an example of a submerged arc multi-electrode welding method according to the present invention using six electrodes. FIG. 2 is a schematic explanatory view of electrode setting conditions in the example of the present invention.

Claims (1)

[Claims] 1. Use of 6 or more electrodes, and a) to
characterized in that welding is performed while satisfying the condition of e),
High-speed submerged arc welding method. a) applying a direct current to at least the leading electrode, b) setting the phase difference of the AC power supply to the electrodes other than the above so that the force acting on the arc of the final pole is oriented in the welding advancing direction on average. c) The leading electrode has a receding angle and the other electrodes have an advancing angle, and the distance between each electrode is set within 25 mm. d) The welding current balance of n electrodes is 1st pole: 1 , 2nd pole to (n-2) th pole: 0.7 to 1.10 each, (n-1) th pole: 0.6 to 0.80, nth pole: 0.5 to 0.75, e) SiO weight ratio _{2: 5~25%, Al 2 O} 3: 2~20%, MnO: 0.5~15%, TiO 2: 2~10%, CaO: 5~25%, BaO: 1~5%, MgO: 3~ 15%, CaF ₂ : 25-60%, B ₂ O ₃ : 2% or less, the balance consisting of unavoidable impurities, and a chemical composition satisfying (CaO + MgO) / SiO ₂ = 1.5-3.0. % Or more is specified by JIS Nominal size 300 to 100 μm Using melt flux having a particle size entering the area.