JPS608908B2 - Narrow gap two-electrode submerged arc welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a narrow gap welding technique for welding thick steel plates with narrow joints, which enables high welding efficiency without impairing bead appearance, slag removal properties, weld defect resistance, etc. This relates to a two-haze submerged arc welding method.

The narrow joint welding method is an efficient and economical welding method that has a good track record in MIG welding and C02 welding. However, with the submerged arc welding method, there are problems such as deterioration of slag removability due to narrow grooves, high temperature cracking, and the occurrence of undercuts. There was almost no track record of pre-submerged arc welding. By first selecting welding conditions that match the groove width, the present inventors have made it possible to perform narrow joint submerged arc welding using a single-layer, single-pass stack without deteriorating welding workability or generating welding defects. We have already made a proposal regarding this, but subsequent studies have shown that when a two-electrode welding method is adopted to further improve efficiency, the appropriate voltage range is somewhat narrow, and slight voltage fluctuations can cause However, undercutting or convex bead formation may occur, resulting in deterioration in slag removability, poor fusion, or slag entrainment.

Therefore, in this two-electrode narrow gap submerged arc welding, it was necessary to monitor the welding equipment and meters particularly strictly. Therefore, the inventors of the present invention solved these problems in two-electrode narrow-gap submerged arc welding and conducted a detailed study of the welding method with the aim of improving welding efficiency. It has been found that by making the distance extremely small, the voltage range in which a concave bead with a fine waveform can be obtained without undercutting can be significantly widened, and the width of the joint that can be welded in one pass per layer can be widened.

In other words, in such narrow joint welding, it is essential to form a concave bead with a large concavity without causing undercuts in order to obtain good slag removability and a sound welded metal without weld defects. Become.

In other words, in narrow joint welding, the groove wall surface is almost vertical, so
4.Even a small undercut significantly deteriorates slag removability. In addition, if the bead is flat or convex with a small degree of indentation, the contact angle between the groove wall surface and the weld metal surface will be small, which will not only deteriorate the slag removability, but also cause the bead trace to disappear when the next layer is deposited. Poor fusion and slag entrainment are likely to occur in the parts. Figure 1 shows the wire W-1 shown in Table 1.
was combined with the flux F-1 shown in Table 2, the leading and trailing currents were 500 A, the welding speed was 60 skin/mjn, and the plate thickness was 5.
This study investigated the effects of welding voltage and interpolar distance on the bead shape of the first layer when layer-by-layer, one-pass stack welding was performed in a narrow groove with a groove width of 12 ribs.

As can be seen from this figure, the distance between the leading and trailing electrodes has a very large effect on the possible voltage range for narrow gap welding.
If the distance between poles is 15 or less, the welding voltage is 25 to 30V.
A good concave bead can be obtained over a wide range of voltage, but when the distance between poles exceeds 15 ribs, a convex bead tends to occur on the low voltage side, and the voltage range in which a concave bead can be obtained is limited. It becomes extremely narrow.

In addition, in the case of two-electrode welding with a narrow inter-electrode distance, the neck bead width is found to be wider than in the case of single-electrode welding with the same heat input; If a two-electrode welding method is used in which the distance between electrodes is narrow even when the tip width is widened, it is possible to melt one layer and one pass without increasing the amount of heat input. Note that by reducing the distance between poles, the appropriate voltage range becomes wider and the bead width tends to become wider, not only when the wire diameter is on the 3.2 side, but also when the wire diameter is on the 3.2 side, 2.4 Yanagi, 4.
A similar finding was observed on the 0 side and in the case of 4.8 skin. The present invention is based on the above findings, and its gist is as follows:
When butt welding thick steel plates with a thickness of 30 or more, the groove portion with a groove width of 8 to 3 mm and a joint angle of less than 20 degrees is positioned approximately at the center of the welding line with the leading wire and trailing wire, and The distance between the centers of the tips of both wires is 15 skins or less, and each layer is 1 layer.
It is a narrow gap two-thunder electrode submerged arc welding method that is characterized by layered welding in passes. The present invention will be described in detail below.

First, in the method of the present invention, the target is limited to butt welding of thick steel plates with a thickness of 30 mm or more, because one-pass welding on both sides is possible for plates with a thickness of less than 30 mm, and in particular, narrow gap welding is adopted. This is because there is almost no effect in terms of efficiency.

Next, in the present invention, the groove width is set to 8 ribs or more because if it is less than this, it is difficult to remove slag in two-electrode welding, no matter how welding flux and welding conditions are selected. By becoming impossible.

Also, if the width of the tip exceeds 3, the width of the tip will become too wide.
Even if the efficiency is improved by using electrodes, it is no longer possible to take advantage of the economic advantages of narrow gap welding. If the joint angle is 200 or more, the groove width becomes too wide in the case of thick plates, and the advantages of narrow groove welding cannot be utilized. The reason why the distance between the centers of the tips of the leading electrode wire and the trailing electrode wire is limited to 15 willows or less is as described above. Here, in the present invention, the groove width refers to the width of the bottom of the groove where the weld bead is to be placed, and in the second and subsequent layers it corresponds to the bead width in the previous stage, but in the first layer welding, the groove width corresponds to the width of the groove bottom where the weld bead is placed. 2 of the radius of curvature of the gap (backing groove) or the bottom of the groove
This corresponds to double (U-shaped groove).

In addition, the distance between the centers of the tips of the wire is the value measured on the weld line of the workpiece. In addition, since the method of the present invention is one-layer, one-pass stacked welding, the wire position only needs to be approximately at the center of the groove width, and there is no need to worry about shifting the wire position for each pass.

Next, the effects of the present invention will be illustrated in more detail through examples.

Example Welding wire W-2 shown in Table 1 and fluxes F-2 and F-3 shown in Table 2 were combined to form an SM with a plate thickness t=50 skin.
-1 layer 1 inside the groove shown in Figure 2, which was created using -50B steel and changing the groove angle Q and groove width W, under each welding condition.
The first layer of the pass was welded, and welding workability and the presence or absence of welding defects were investigated.

Furthermore, if there is no problem in welding workability and there are no defects, weld one pass of each layer to the plate thickness surface under the same welding conditions, and after placing a decorative bead in the final pass, we conduct an X-ray transmission test. We conducted a soundness investigation. Table 1 Table 2 Table 3 The results are shown in Table 3. In the comparative example, undercutting was likely to occur in the first layer welding, and slag swelling was slightly difficult.

Furthermore, when a low welding voltage was used to enable slag separation, a convex bead formed and the X-ray performance after the completion of layer welding was poor. On the other hand, in the welding method of the present invention, a good concave bead was obtained, so that slag was easily peeled off even inside the groove, and good results were obtained in the X-ray transmission test after the completion of layer welding.

Note that since the final pass was outside the groove, a good weld bead with an appropriate reinforcement height was obtained under all welding conditions. As described above, the method of the present invention not only enables efficient two-electrode narrow-gap latent welding in a single layer and one pass over a wide welding voltage range, but also allows for wide groove width without increasing heat input.
One-pass welding becomes possible, and a significant reduction in cost can be expected due to reductions in welding time, slag removal time, and welding materials.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between bead shape (indentation degree), welding voltage, and interpolar distance, and FIG. 2 is a diagram showing the groove shape used in the example. W: groove width, Q: groove angle, t: plate thickness. Hair 2 illustrations

Claims (1)

[Claims] 1 When butt welding thick steel plates with a plate thickness of 30 mm or more, the groove portion with a groove width of 8 to 30 mm and a groove angle of less than 20° is positioned with the leading wire and trailing wire approximately at the center of the weld line, and both A narrow gap two-electrode latent arc welding method characterized by making the distance between the centers of the tips of the wires 15 mm or less and performing layer welding in one pass per layer.