JPH04147770A - Submerged arc welding method at high speed by using multiple electrodes - Google Patents

Abstract

PURPOSE:To perform multiple electrode submerged arc welding at high speed and to improve efficiency by multiplying the number of electrodes, regulating the welding current balance in the specified range and specifying flux composi tion. CONSTITUTION:Six or more pieces of electrodes are used and a sweepback angle and a sweepfoward angle are provided to preceding electrodes and other electrodes, respectively and the distance between each electrode is set within 25mm. The welding current balance of n pieces of electrodes, is set in the range of 1, 0.7-1.10 each, 0.6-0.80, 0.5-0.75 for a first electrode, a second electrode-a (n-2)th electrode, a (n-1)th electrode and a nth electrode, respectively. The chemical composition of flux consists of, by weight, 5-25% SiO2, 2-20% Al2O3, 0.5-15% MnO, 2-10% TiO2, 5-25% CaO, 1-5% BaO, 3-15% MgO, 25-60% CaF2, <=2%B2O3 and the balance with inevitable impurities. The chemical composition satisfies (CaO+MgO)/SiO2=1.5-3.0 and welding type flux having the grain size in the ATSM 48/145 mesh area is used for more than 60% thereof.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a high-speed submerged arc welding method that is suitable as a welding method for manufacturing large diameter welded steel pipes such as line pipes and structural pipes. be.

<Conventional technology and its issues> The UO mill line used for manufacturing large diameter welded steel pipes
Submerged ac welding is generally applied to the main welding of the inner and outer surfaces of steel pipes, which is carried out after tack welding following UO press, and currently a combination of 3 to 4 electrodes is used for both inner and outer surface welding (for outer surface welding, Welding with multiple electrodes is being carried out (some examples use five electrodes). This is because it was known that the welding speed was determined by the amount of deposited metal supplied, the control of the molten pool, and the gouging force of the base metal, and that these capabilities increased in proportion to the number of electrodes.

Specifically, for internal welding, connect a direct current (DC) or alternating current (AC) source to the first pole, connect an AC power source to the second pole and beyond, and set various current values to 1500 A or less. ~5
This is carried out in a line operation, and the connection method at this time is, for example, in the case of a "DC-AC-AC" combination, the third pole is delayed by 60'' with respect to the second pole. Also, the same electrode arrangement as for internal welding is used for external welding, but in this case, for example, in the case of a "DC-AC-AC-AC" combination, the third pole is the second pole. Inverted V with 120° delay compared to 4-pole
A wire connection is adopted and the operation is normally carried out on four lines.

However, even with high-speed submerged arc welding that uses 3 to 5 electrodes as described above, it becomes difficult to control the amount of welding, gouging, molten pool, etc. when using multiple electrodes, so it is difficult to control the amount of welding, gouging, molten pool, etc. The maximum welding speed that can be secured is limited to 3.6 m/l lin. In other words, if you try to increase the welding speed beyond that, it will become difficult to form a good bead, resulting in welding defects such as undercuts and necking, which will significantly impair the appearance of the bead and cause unfavorable welding quality. It was unavoidable.

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 the welding line is determined by the welding speed, idle time, and number of lines. Therefore, in order to improve production efficiency and reduce production costs, it is considered that the most practical measure is to significantly increase the welding speed and reduce the number of lines. However,
Even if we try to improve welding speed by a very simple method called "increasing the number of electrodes" and increase the number of electrodes to 5, as mentioned above, there is a limit to the welding speed that can be improved with the current technology. Not only was it not possible to dramatically improve the production efficiency of large-diameter welded steel pipe mills, it was also impossible to expect results that would 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, the number of electrodes, which was considered to be the practical limit of 5 at most, has been increased to 6 or more to improve the welding speed. Achieving significant improvements was still considered to be a long way off, given the current level of technology.

However, in response to the growing demand for cost reduction and production efficiency improvement for large diameter welded steel pipes,
The purpose of the present invention is to find a method that can significantly improve the welding speed of submerged arc welding without reducing product quality, and to achieve sufficient production efficiency even when the number of lines required in a large-diameter welded steel pipe mill is reduced. The objective was to establish a means by which improvements could be achieved.

Means for Solving the Problem> In the course of intensive study to achieve the above objective, the present inventors discovered that ``increasing the number of electrodes used is the most realistic way to increase the welding speed during submerged arc welding.'' 1. 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 that uses multiple electrodes of six or more. As a result of continuing research to calculate the optimal combination pattern of various conditions through simulation calculations and verifying its validity one by one through experiments, we found that ``Multi-electrode of 6 or more electrodes in submerged arc welding'' a) How to connect the electrodes.

Mouth) Setting of electrode angle, electrode spacing, and tip height.

c) Flux used.

By devising this method, the welding arc can be sufficiently stabilized, making it possible to stably control the bead shape, as well as ensuring good slag removability, resulting in good welding under sufficient penetration. High-speed welding with bead formation with good internal quality and appearance (maximum welding speed 4.5 m/min)
The knowledge that the above) can be realized is obtained.

The present invention has been made based on the above-mentioned findings, etc., and includes the following: ``When performing submerged arc welding, six or more electrodes are used, and a) direct current is applied to at least the leading electrode, b) Set 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 directed in the direction of welding progress on average. Each electrode has its own advancing angle, and the distance between each electrode is set within 25 degrees. d) The welding current balance of the n electrodes is set to 1° for the 1st pole and 1° for the 2nd to (n-2)th poles: each Set in the range of 0.7-1.10° (n-1) pole: 0.6-0.80° n-th pole: 0.5-0.75, e) Sing: 5-25% ( (Hereinafter, percentages representing component proportions are expressed as weight percentages.)

AlzCh: 2~20%, MnO: 0.5~
15%.

TiOt: 2-10%, CaO: 5-2
5%.

BaO: 1-5%, MgO: 3-15%.

CaFt: 25-60%, BzO3:2
% or less, the remainder consists of unavoidable impurities, the chemical composition satisfies Tsuka (CaO + Mg0) / 5iOz = 1.5 to 3.0, and moreover, 60% or more is AS T M4B.
By using a molten flux with a grain size in the /145 mesh range and performing welding while satisfying the following conditions, high-speed welding of high-quality products is possible, greatly improving product production efficiency, and improving welding line efficiency. It is characterized by the fact that it has made it possible to carry out reductions.

That is, the present invention (a) Multipolarization of the number of electrodes to 6 or more.

(bl　Establishment of optimal wiring method.

(Optimal setting of C1 electrode angle, electrode spacing, and chip height.

(d) Development of high-speed flux.

By solving the following four technical issues, we have enabled high-speed submerged arc multi-electrode welding with a maximum welding speed of 4.5 m/win or more (1.5 times the current speed), improving efficiency and reducing the number of lines. It is a key point for complex 6-electrode technology or more multi-electrode technology.
At the same time, it also provides an electrode setting method to obtain good single-domain appearance, penetration, slag removability, and internal quality, and a control technology for flux physical properties to ensure high speed. The present invention will be explained in more detail along with its functions and effects with reference to the following.

Functions and Effects> 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 in order to achieve proper and stable gouging, a DC (direct current) power source is applied to at least the leading electrode, and the other electrodes ( In the example shown in FIG. 1, an AC (alternating current) power source is applied to the second and subsequent poles in order to ensure industrial superiority. However, especially in multi-electrode submerged arc welding with 6 or more electrodes, the connection method controls the various magnetic forces and arc direction, and is an important factor governing the stability, bead shape, and high speed of the welding arc. Become.

Therefore, the wiring method was determined through simulation calculations based on the following assumptions and determination and verification of the wiring method on the actual line.

That is, the simulation calculations are as follows: 1) In general, in multi-electrode welding, the final electrode greatly affects the bead shape, so only the forces acting on the final electrode are considered.

2) The forces acting on the final pole are various welding currents.

phase difference, distance between electrodes, chip height (extentio
n).

It shall be determined by magnetic permeability (μ).

3) The average value of the force acting on the arc at the final pole is ss+o
Approximately 0.0. lX2ON/m
Make it.

4) The time during which the force acting on the final pole is directed in the welding direction is the smoothing action described above.
The phase difference is determined so as to be ``as long as possible,'' which has become clear from the results of examination of the appearance of the formed bead.

5) The force (Fn) acting on the final n-th pole is calculated using the prerequisites of the formula % as an indicator, as well as the results of actual machine tests. It was concluded that it is possible to apply AC power to the poles. In particular, in the 6-electrode submerged arc welding shown in Figure 1, the following polarity and phase difference connection method optimally controls the magnetic force acting between each pole and is optimal for welding arc stability and bead shape. It was also confirmed that

DC-AC-AC-AC-AC-AC O@ +60° +120° -90"+120"
(Here, + indicates an advance in the phase difference, and - indicates a delay, indicating the phase difference when the second pole is used as a reference).

Table 1 shows a part of the "results of examination of ACC polar phase difference combinations and welding conditions in 6-electrode submerged arc welding" that led to the above conclusion.The welding conditions at this time were for the test material: 1.00 inch thick bead-on plate, welding current and voltage: 1st pole: 1200A, 30V, 2nd pole: 100OA, 33V, 3rd pole: 900A, 36V, 4th pole: 850A, 40V, 5 poles, 700A, 42V, 6th pole, 600A, 44V, welding speed: 4. Om/+in.

Furthermore, from the results of a welding test using an actual 6-electrode submerge welding machine using this connection method, the wall thickness: 0.2
When welding large diameter steel pipes of 5 to 2.00 inches, when conventional four-electrode submerged arc welding was applied, the welding speed was 61.0 to 2.8 m/sin, whereas the heather invention 6. For submerged arc welding, total current: 5000 A or more, welding speed: 3.0 to 5.0 m/si
It was confirmed that a stable arc and beautiful bead appearance were obtained within the n range, proving its superiority and the validity of the calculation results.

By the way, in the method of the present invention, the leading DC pole has a receding angle and the other electrodes have advancing angles. This is for the purpose of achieving this goal. It is preferable that the receding angle of this leading DC pole be up to 120 degrees, and that the electrode capacity be up to 2000 A at maximum.

If the leading DC pole has an advancing angle of 0'' or more, s
Moothing action promotes vortex flow in the bead width direction and is effective in improving appearance, but diggi
ngaction is significantly reduced and sufficient welding speed cannot be achieved due to insufficient penetration depth. On the other hand, if the leading DC pole has a receding angle exceeding -20@, there is a concern that the molten pool will be stirred more than necessary, and there will be a tendency for undercutting of welding defects and slag entrainment to occur frequently. on the other hand,
The advancing angle of the trailing AC pole is given to block the backward flow of molten metal in the molten pool and form a beautiful bead appearance, and this advancing angle is in the range of 0 to +456. It's good.

Note that Table 2 shows the welding test results using a bead-on plate with a plate thickness of 1.00 mm, and from this Table 2, it is also possible to determine the receding angle for the leading DC pole and the advancing angle for the trailing AC pole. It can be confirmed that good welding results can be obtained by holding it.

Here, a sufficient amount of welding was achieved at a welding speed of 4°5m/11in.

In order to ensure bead appearance and arc stability, it is preferable to use a large diameter solid wire of 4.0 to 6.4 mφ as the welding wire.

In addition, the distance between the tips of each electrode is determined by the molten flux (fu).
In the present invention method using sed flux), 25
Must be set within, this will make the arc stable,
It can be effective in preventing welding defects. If the distance between the electrodes exceeds 25cm, the appearance of the bead will deteriorate, and the slag that has floated up in a semi-solidified state will interfere with the electrodes, causing slag to get caught, resulting in poor product quality and workability. cause disadvantage.

Table 3 shows some of the results of welding tests using bead-on plates with a thickness of 1.0'04 inches and varying the distance between the electrodes. 6! Good results can be obtained when the distance between the electrodes is set within 25 m! I can recognize it.

Regarding current balance, by decreasing the distribution by approximately 0.1 to 0.05 as you move from the leading electrode to the trailing electrode, the rigidity of the trailing electrode arc is alleviated and high-speed welding (v
> 3 m/l lin), a wide and smooth bead appearance can be obtained. However, it has been found that a better bead appearance can be obtained by increasing the current in the second electrode relative to the first electrode, particularly when welding with a thin wall and not requiring a large penetration depth.

And especially the current balance 1st pole...1° 2nd pole...0.7~1.10° ...Same as above.

...Same as above.

If the distribution is set as follows: n-1st pole - 0.6 to 0.80°, nth pole...0.5 to 0.75°, it is possible to more stably ensure a good bead appearance.

Now, even when high-speed submajor arc welding is carried out under the conditions shown above, the problem of deterioration of the weld bead shape and the performance of the weld metal cannot be sufficiently eliminated as the welding speed increases. Therefore, the present inventors conducted research to solve the above problems, and first, (A) Alz Off + Si as a flux component.
When an appropriate amount of O□ is added, slag with an appropriate melting point and viscosity is produced in coexistence with CaFz.

(B) If the A S T M48/145 mesh region of flux particle size is always maintained at 60% or more, undercutting and slag entrainment are minimized.

By discovering this and taking such measures, welding speed: 5. It was confirmed that good bead appearance and slag removability were obtained even in large current (high heat input) welding at Om/min, and that welding workability and welding defect prevention effect could be improved. After further investigation, the A1zCh-Sin
g 5i02. in CaFz component flux.
MnO, Cab, CaF2. Af203. MgO.

5i composition balance of TiO□, BaO and B2O3
Oz: 5-25%, kilz Oz: 2-20
%.

MnO: 0.5-15%, Ti0z: 2-1
0%.

CaO: 5-25%, BaO: 1-5%.

Mg0=3~15%, CaFz: 25~
60%.

By controlling BzOz: 2% or less and satisfying (CaO+Mg0)/5iOz=1.5 to 3.0, the basicity is always kept at a high value, and even in welding with an increased number of electrodes, oxygen The effect of reducing the amount of oxygen is effectively demonstrated, making it possible to suppress the amount of oxygen in the weld metal to 350 ppm or less, meeting the low hardness and high toughness specifications generally required for large diameter line pipes. This means that we have realized a melting type flux for high-speed welding that can sufficiently clear the conditions.

Of course, in this flux, SiO2, MnO.

Cab, CaFx+ uzos+ MgO, TiCh,
BaO and B,0. If the component balance of is outside the above range, the above-mentioned effects cannot be stably ensured.

In addition, if the A S T M48/145 mesosch region of the above flux is less than 60%, welding defects become noticeable in multi-electrode high speed welding, and when the coarse grain region increases, undercuts and When the fine grain area increases, slag entrainment occurs frequently.

As mentioned above, the present invention relates to submerged arc welding, where many unresolved problems have arisen when attempting to further increase the speed. By solving the difficult technical issues of ``optimal setting of electrode angle, electrode spacing, and tip height'' and ``development of high-speed flux'' from a comprehensive perspective, we have overcome the above obstacles and developed a stable high-speed submerged arc welding method. has been established, and its effects will be explained in more detail below using examples.

<Example> Six electrodes were set as shown in Fig. 2, and the phase difference of the AC poles after the second pole was θ''+60°, +
A submer arc welding test was conducted on steel plates with the angles set at 120°, -90°, and +120°, and other conditions as shown in Table 4.

Note that the flux used at this time was substantially Ca
O: 18.0%, MgO: 6.0%, SiOz
: 14.0%.

CaFz: 37%, u! 03: Is%, MnO: 3
%, TiOz: 3%, BaO: 3% and Boo:
It consists of 1%, ((CaO+Mg0)/5iOz
= 1.7), and the particle size is A S T
It contained 65% of the M48/145 mesh area. In addition, the wire used is a 4.0 Tsuru φ solid wire,
Its component composition was as shown in Table 5.

Table 5 When the appearance of the weld beads was evaluated after the test, it was confirmed that all the weld beads had a good appearance.

Summary of effects> As explained 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 greatly improve the manufacturing efficiency of large-diameter welded steel pipes such as line pipes and structural pipes, and even if the number of welding lines is reduced. This brings about extremely useful effects industrially, such as making it possible to respond to increased production.

[Brief explanation of the drawing]

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. FIG. 2 is a schematic explanatory diagram of electrode safety conditions in an example of the present invention.

Claims (1)

[Scope of Claims] A high-speed submerged arc welding method, characterized in that welding is performed using six or more electrodes and satisfying the following conditions a) to e). a) Apply a DC current to at least the leading electrode; b) Set 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 electrode is directed in the direction of welding progress 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 set to 1st pole: 1 , 2nd pole to (n-2)th pole: 0.7 to 1.10 each, (nth
-1) Pole: set in the range of 0.6 to 0.80, nth pole: set in the range of 0.5 to 0.75, e) SiO_2: 5 to 25%, Al_2O_3: 2 to 20% by weight
, MnO: 0.5-15%, TiO_2: 2-10%,
CaO: 5-25%, BaO: 1-5%, MgO: 3-15%, CaF_2: 25-60%, B_
2O_3: Contains 2% or less, the remainder consists of unavoidable impurities, and has a chemical composition that satisfies (CaO + MgO)/SiO_2 = 1.5 to 3.0, and more than 60% meets ASTM48/
A molten type flux having a particle size in the 145 mesh range is used.