JPS61162272A - Narrow groove 2-electrode submerged arc welding method - Google Patents

Abstract

PURPOSE:To obtain a defectless weld zone which is stable even under low heat input conditions by converting a droplet droplet transfer state to a spray. CONSTITUTION:The inter-electrode distance in AC submerged arc welding in which a preceding electrode and succeeding electrode are longitudinally arranged in the welding advance direction is made 5-20mm and the phase difference between both electrodes is made 60 deg. or 90 deg.. The wire diameter of the respective electrodes is made 1.2-3mm and the welding heat quantity H (KJ/cm) corresponding to a groove gap width G is set for the narrow groove joint having >=8mm groove gap width G under the condition of 60-250A/mm<2> current density. More specifically, melti-layer building-up by the single layer single pass satisfying equation I in the case of <=18mm G and the single layer two pass lamination satisfying the equation II in the case of >14mm G is executed. The narrow groove 2-electrode submerged arc welding is thus executed.

Description

[Detailed description of the invention] (Industrial application field) Two-electrode submerged arc welding method (hereinafter abbreviated as TSAW)
In this specification, we describe improvements that are suitable for assembling welded structures that require high performance and quality from the standpoint of safety, such as pressure vessels and offshore structures that use extra-thick steel. The results of research and development on the narrow gap T S A W method, which reduces costs and improves efficiency one by one, are described below.

(Prior art) Regarding the prevention of welding defects in the TSIV method for extra-thick steel plates, for example, in Japanese Patent Publication No. 11312/1982, the distance between the electrodes l is set to 15 mm or less, and the arc voltage is set to be lower than that of the preceding electrode (2). It is disclosed that the transition voltage 1' is lowered and that a welding current suitable for the electrode diameter of the trailing electrode 'I' is adopted. According to this method, the wire diameter is 550A to 750A for a wire diameter of 4.8mmφ, 450A to 650A for a wire diameter of 4.0mmφ, and 450A even for a wire diameter of 3.2**φ.
As shown in A, the welding current is relatively large, so if the inside of a narrow gap is laminated using the one-layer, one-bath method, high-temperature cracks are likely to occur in the center of the weld bead, and it is difficult to weld 17 layers. These cracks cannot be completely remelted, and they remain, creating harmful defects. For this reason, Japanese Patent Publication No. 58-11312 adopts a one-layer, two-bus welding method.

In order to prevent the above defects using the 1-layer 1-panu lamination method,
Although a low current should be used, because the wire diameter is large, it is easy to cause a short circuit during welding, which may cause the welding operation to be interrupted, or the current density may become small, causing the droplet transfer mode to become short-circuit transfer, resulting in the formation of a molten pool. The temperature decreases and the stability of the weld is impaired, causing welding defects.

These welding defects include poor fusion and slag entrainment, and to prevent this, it is necessary to increase the welding heat input by -1-=, but this will deteriorate the mechanical performance of the weld. Therefore, it is undesirable.

(Problems to be Solved by the Invention) Problems to be solved by the invention, more specifically, the efficiency decreases under low current and low heat input conditions, and weld defects such as poor fusion and slag entrainment occur, resulting in damage to the weld. It is an object of the invention of a basket to advantageously overcome problems such as poor quality.

(Means for solving the problem) This invention performs cross/AE "leave merge arc welding" in which a leading electrode and a trailing electrode are arranged in tandem in the direction of welding progress. 20 mm, the phase difference between both electrodes is 60″ or 90°, and the wire diameter of each electrode is 1
．． 2-3.0 Dragon, current density 60-250 A/am2
Under the conditions, for a narrow groove joint with a groove gap width G of 8111 or more, the welding heat amount H (K, I/
cm), when G≦18 mm, one layer, one bus lamination that satisfies the following, and when G>14, one layer, two bus lamination that satisfies the following: Narrow gap two-electrode submerging. This is an arc welding method.

In the AC TSAW method, the welding power source connected to both electrodes can be connected in parallel (0 layer phase difference),
Connection (60" phase difference), Scotto!1! (90° phase difference), reverse V connection (120° phase difference), and anti-parallel connection (180° phase difference) are available, especially for narrow gaps. If the distance between the electrodes is small in parallel connection, inverted V connection, or antiparallel connection, the flow of molten steel will become unstable due to mutual interference of the arc between both electrodes, and welding defects such as undercasting, poor fusion, and slag entrainment will occur. It becomes easier.

On the other hand, if the distance between the electrodes is increased, mutual interference between the arcs GJ and Z will be weakened, but the slag of the leading electrode will interfere, making the arc of the leading electrode unstable and causing welding defects.

Therefore, according to the present invention, if the distance between the electrodes is small, the molten steel flow will be more stable than each of the above-mentioned connection methods, and a good bead shape will be easily obtained if the V-connection or Scotto connection is used, which is particularly suitable for narrow-gap welding. Based on the knowledge that this connection method is a good method, we inspected the adoption of this connection method and achieved high quality with no welding defects even under low heat input conditions in the narrow gap two-electrode welding method that was conventionally performed by merchant heat. This welding method has been developed to obtain a welded part with a high quality.

When stacking the gap tip in multiple layers using the one-layer, one-bus stacking method, the smaller the groove gap width G, the better for reducing welding material consumption, welding man-hours, and costs, but it is not too small. If it is too long, it is clearly disadvantageous in terms of slag peelability, welding defects, etc., and a groove gap width G of 8 mm or more is generally required.

The welding power source is connected to the leading electrode and the trailing electrode as described above.
For both r, use an AC power supply to avoid mutual interference of arcs, and use 3.2 to obtain high current density with low current by connecting (60'' phase difference) or Scot 1 to wiring (90'' phase difference).
Wire diameter smaller than the dragon, for example, practically 1.2 to 1.2, such as 1.2 dragon φ, 1.6 ■ seal φ, 2,41111 φ
Apply a 3.0 fl electrode rod.

Flux for welding can be fired, sintered, or melted, and its composition is generally commercially available, especially those with reduced amounts of oxygen, nitrogen, and diffusible hydrogen in the weld metal. It is preferable to use a material with improved welded shape and slag removability.

By adopting the following welding methods, welding +
AI! It is possible to reduce the number and cost of welded parts, but in order to further improve the quality and performance of welded parts, it is important to control the joining conditions, and this is the focus of this invention. .

Here, the electrode arrangement and welding heat formation process will be explained with reference to FIG. 1 as follows.

The diameter of the wire used for the leading electrode I7 and the trailing electrode is 1.2 to 3.0I11, and the welding current density for the cross-sectional area of these wires is from 6OA/+u" to 2508/ll.
Applicable within the range of I2. Imakari wire diameter 3.2m
When the current density is 60 A/fin 2 or more at φ, the welding current exceeds 482 A, and for example, when the groove gap width G = 10 m
If two-electrode SA- is carried out with one layer and one bus laminated at a welding current of 482 A on the groove of 1-m, there is a concern that high-temperature cracks may occur in the weld bead 1-'2.

Wire diameter 2.4mmψ and 1.6 smaller than 3.2va
The minimum welding current at I■φ is 121 A for a wire diameter of 166 mm, 271 A for a wire diameter of 2.4 mm, and the minimum welding current for a wire diameter of 1.6 + n is 121 A, and the minimum welding current for a wire diameter of 2.41 mm is 2.4 mm. At a current of 271^, such a low welding current does not cause high temperature cracks and a good welded joint can be obtained.

The biggest reason for limiting the current density to 60871m2 to 25OA/++12 is to use spray transfer for the droplet transfer j-r type 3□3', which lowers the temperature of the molten pool to ensure sound welding even under low heat input conditions. It is located at 7j4. As a result of examining the melt transfer using an X-ray fluoroscopic observation device and a cylinder velocity camera, it was found that if the current density was less than 6 (IA/mm2), the droplet was 3°3'
There is a large short-circuit transition, and the welding heat shape has irregular waves, making it difficult to obtain stable heat, and welding defects such as poor fusion and slag entrainment may occur. On the other hand, 25OA
/am2, the melting speed of the wire becomes faster and the arc length (Zunawaji arc voltage) becomes unstable, and the arc force becomes too strong, causing excessive movement of the molten steel flow and impairing stability. As a result, undercuts and slag entrainment may occur.

Figure 2 shows a comparison of the range of the appropriate heat input amount H relative to the groove gap width G when performing one-layer, one-bus, two-electrode submerged arc welding using the conventional method and the method of the present invention. It can be seen that the appropriate heat input can be reduced to about 273 compared to the conventional method, and furthermore, two-electrode submerged arc welding can be performed up to a groove gap width G -8 mm.

In other words, by using a wire with a wire diameter of 1.2 to 3.0+U and reducing the penetration depth under low current conditions to prevent the occurrence of high temperature cracks, and by setting a high current density, spray transfer can be achieved. As a result of improving the arc stability, increasing the molten pool temperature, and improving the bead shape, the groove gap width G can be narrowed, the consumption of welding + A I4, the number of welding man-hours, and the cost can be reduced. It is also possible to simultaneously improve mechanical performance by reducing heat input.

The center electrode distance p between the leading electrode (5) and the trailing electrode (T) should be within a range of 20 mm from the leading electrode (5). If this is smaller than 5 fins, the arcs 4, 4' generated at the leading electrode (7) and the trailing electrode (T) will interfere with each other, causing undercutting, poor fusion, and slag entrainment. on the other hand,
If it is larger than 20111, the arc 4' of the trailing electrode T becomes unstable because the slag generated by the melting of the leading electrode I becomes unstable, and slag entrainment and fusion failure are likely to occur. In this case, preferably the leading electrode I7 and the trailing electrode T
It is necessary to place the electrodes on the groove center line 5. If any electrode deviates significantly from the groove center line 5, it may cause undercuts, poor fusion, slag entrainment, etc. on the groove side walls 1, 1'. Defects are more likely to occur.

The groove gap width G in the case of laminating one layer and one bus can be applied from 811 to 18 irises, but one layer and two pass lamination is particularly suitable when the width is 14 irises or more.

Welding heat input H (MJ/m
) has an appropriate range in order to prevent welding defects.

Exists.

In the case of one-layer one-pass lamination, if m=・G −1-4<H, both groove side walls 1.1
′ may not be sufficiently melted, resulting in welding defects such as poor fusion and slag entrainment.
When G +12<H, the amount of heat input becomes excessive and an undercut occurs, deteriorating the slag releasability, and this undercut remains unmelted in the next layer welding, causing poor fusion.

On the other hand, in the case of one-layer, two-pass lamination, the heat input should be within the range of 0.8(-・G+4)>
When it becomes I+, the heat input becomes too small, and the rewelding bead does not survive near the center of the opening width G, and slag gets caught between the rewelding beads, which may result in poor fusion.
(--・G +12) <I+, the amount of heat input becomes excessive, and overflow nobuhi F is likely to occur, and this part cannot be completely melted in the next layer welding, resulting in poor fusion and slag entrainment. be.

In the case of one-layer, two-pass lamination, it is preferable that the wire is aimed at a distance of about 2+u to 6I1 m from the groove sidewall 1 or 1'. If it is too close to fin 21, it will cause undercuff I, and if it is too far from fin 6, it will tend to cause poor fusion and slag entrainment.

In addition, the welding heat input II described above is based on current, voltage,
It can be calculated based on the welding speed, but in order to achieve spray transfer and a stable wire feeding speed, the appropriate current changes depending on the wire diameter. An example of the range of welding conditions that can be employed in the method of the present invention is shown in Table 1, and the welding speed can be adjusted to provide an appropriate amount of heat input.

Table 1 Applicable welding condition range for each wire diameter Note that the wire diameters and welding conditions of the leading electrode I and the trailing electrode T can be combined as appropriate.

The angle θ of the leading electrode with respect to the welding direction and the angle θ of the trailing electrode with respect to that are the front (→
-) or (-) can be adjusted 8 times within a range of ±20°.

(Example) Steel plate with a thickness of 50 mm (0.16 χC, 0.33 χSi,
1.23χMn.

0.007χP, 0.004χS, 0.51χMo
, 0.024χA7 has the shape shown in Figure 3 (t =
A U-groove of 50mm, t+=2on, θ-26) was machined, and two-electrode SAW was performed using the welding materials in Table 2.
The occurrence of welding defects was investigated by visual inspection of each layer and by an X-ray transmission test after three-layer welding. Table 3 shows the welding conditions and the presence or absence of welding defects. In addition, the welding power source is an AC-AC 11■ combination, and as ■ connection (60° phase difference), 1 layer 1
Pass welding was performed, and the welding length was 5 cm.

Table 2? As shown in Table 3, according to the present invention, a sound welded joint is obtained with no welding defects. However, in a comparative example in which the appropriate heat input amount was outside the range of 1■, slag Entrainment, poor fusion, and high-temperature cracks occurred, and a good welded joint could not be obtained.

Large side M-η The plate thickness is 53 mm as in Example 1, and the shape (t
=50mm, t, -30++m, θ-2°), and using the welding materials in Table 2, welded a two-electrode SAW.
The occurrence of welding defects was investigated by visual inspection of each layer and by an X-ray transmission test after four-layer welding. Table 4 shows the welding conditions and the presence or absence of welding defects. In addition, the junction power supply is A.
C-AC combination, 1-node connection (90° phase difference)
One layer was welded in two passes, and the welding length was 50c1.

The results are shown in Table 4. According to the present invention, a sound welded part is obtained with no welding defects. However, in the comparative example where the proper conditions were deviated, defects such as slag entrainment and poor fusion occurred, and a good welded part was obtained. No welds were obtained.

2-Cr-IMO steel plate (0,14χC
50,22χSi, 0.48χMn, 0.003χ
P, 0.004χS, 2.26XCr.

1.00! Mo, 0.13
-3°), and the welding materials shown in Table 5 were combined to perform multilayer welding of one layer and one bath. Welding conditions are shown in Table 6.
It is as follows. The chemical composition of the weld metal is shown in Table 7, and the mechanical performance is shown in Table 8.

Table 7 Ihiso shoulder of Nji 1 Suzu genus Table 8 Results of inspection of defects in Kitachibana town *) SOCALl'hltype There are defects in the welded part of the groove gap G = 14 fin of the method of this invention and the comparative example. was not observed and was good, but the comparative example G
= 10 mm, many defects such as slag entrainment, high temperature twisting, and poor fusion occurred. In addition, as shown in Table 8, the impact value of the weld metal in the impact test piece taken from the center of the plate thickness showed low toughness in the comparative example G-14m11 due to the large heat input, but in this invention method, the impact value of the weld metal was low due to the large heat input. A reduction in the amount of heat is achieved,
Extremely excellent toughness is obtained.

(Effects of the Invention) As described above, in the past, in fields where welding was performed using a high amount of heat, when welding was carried out to improve mechanical performance, welding defects often occurred, but this invention By changing the droplet transfer mode to a spray type, a stable and sound weld can be obtained even under low heat input conditions, and the mechanical performance can also be significantly improved.

[Brief explanation of the drawing]

Fig. 1 is a front view and side view showing the electrode arrangement according to the present invention, Fig. 2 is a comparison graph of the appropriate heat input amount range with respect to the groove gap width G, and Figs. It is a sectional view showing a shape.

Claims (1)

[Claims] 1. AC submerged arc welding in which a leading electrode and a trailing electrode are arranged in tandem in the welding direction, and the distance between the electrodes is 5 to 20 m.
m, the phase difference between both electrodes is 60° or 90°, the wire diameter of each electrode is 1.2 to 3.0 mm, and the current density is 60 to 25
Under the condition of 0 A/mm^2, for a narrow groove joint with a groove gap width G of 8 mm or more, the welding heat amount H (KJ/cm) corresponding to the groove gap width G, when G≦18 mm, 8/6・G+4≦H≦8/6・G+12 One layer, 1 pass lamination that satisfies G+
12) A narrow gap two-electrode submerged arc welding method comprising applying multi-layer stacking by laminating one layer and two passes, satisfying the following.