JPS6340634B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a narrow gap submerged arc welding method that can save welding materials and increase efficiency in double-sided multilayer welding of steel plates with a thickness of about 25 to 80 mm. Narrow gap submerged arc welding has recently become popular as an efficient and economical welding method. The present inventors have previously proposed a narrow-gap submerged arc welding method using one layer and one pass, but this method uses an I-shaped groove with a backing metal, a U-shaped groove, or an H-shaped groove. It has a property that the narrower the groove becomes more effective as the plate thickness increases, so it is suitable for extremely thick steel, and usually,
In the case of double-sided multi-layer welding of medium-thickness steel plates of 25 to 80 mm, which is the most frequently performed process, the bevel processing costs are high, so the conventional bevel angle that can be processed by gas cutting is required.
An X-shaped groove of about 60° was actually more economical. Therefore, with the aim of developing an economical narrow-gap submerged arc welding method for medium-thickness steel plates, the present inventors developed narrow-gap welding techniques by reducing the groove angle of the conventional X-shaped, V, or Y-shaped grooves. We considered the possibility of As a result, when welding the first layer with a groove angle of approximately 40°, it is necessary to increase the welding current considerably in order to avoid fusion failure at the bottom of the groove.
It has been found that when the first layer is welded under such welding conditions, undercuts occur, making it difficult to remove the slag, and causing pear-shaped beads and high-temperature cracks. However, at the same time, it was also discovered that by leaving an unfused portion, that is, an unfused portion, at the bottom of the groove, hot cracking and deterioration due to slag peeling are extremely unlikely to occur. In other words, Table 1 shows wire W-1 shown in Table 2 combined with flux F-1 shown in Table 3 with a plate thickness of 35 mm.
We investigated the occurrence of slag separation, hot cracking, poor fusion at the bottom of the groove, etc. when welding the first layer in a Y-shaped groove with a groove angle of 40° using SM-50A steel under various welding conditions. The results are shown below. As can be seen from this table, when high current welding conditions are used to prevent fusion failure at the bottom of the groove at the bottom of the weld metal, and when a small diameter wire is used, hot cracking or undercutting occurs without exception. On the other hand, in the case of relatively low current and low speed welding that causes fusion failure at the bottom of the groove, undercuts and hot cracks do not occur. Moreover, the slag removability is also good. Among these welding defects, hot cracking is a serious defect that can be fatal to welded structures, and undercuts also deteriorate slag removability in narrow gap welding and significantly reduce work efficiency. Otherwise, when the next layer is applied, it can cause serious defects such as poor fusion and slag entrainment at the bead toe end. On the other hand, although poor fusion at the bottom of the groove is a welding defect, it can be removed during welding on the FP (finishing pass) side by removing the back side prior to welding, or due to the welding heat of the first layer welding on the FP side. It has the property of being able to be removed by welding. However, as shown in Figure 1A, the unfused part U due to this poor fusion exists in an irregular shape at the bottom of the groove below the weld metal WM, sometimes resembling a blowhole, or containing slag. In some cases, the penetration line is extremely uneven, so to remove it, it is necessary to make the undercut extremely deep, which increases welding materials and work hours, and halves the effect of narrowing the gap. result. Therefore, with the aim of making this penetration line uniform, we conducted further studies and found that powder, granules, etc.
Alternatively, it has been found that this penetration line can be made uniform by spraying rod-shaped filler material in advance. In other words, Fig. 1B shows the bead shape and welding direction when a cut wire made by cutting a wire with the same composition as the welding wire to an appropriate length as a filler metal is sprinkled on the bottom of the groove in advance and welded in the first layer. This figure shows a sketch of the weld line shape. As you can see in this figure, the unmelted part U is the weld metal WM
It remains extremely uniform and continuous at the bottom of the groove under the groove, and the weld line can be said to be almost straight. This is thought to be due to the fact that the bottom of the groove was filled with cut wire instead of flux, so the arc was stably generated even at the bottom of the groove, and the arc heat was conducted uniformly. In addition, since filler metal reduces the melting rate of the base metal, using a filler metal with a sufficiently low C content compared to the base metal is effective in preventing the occurrence of hot cracking even when welding steel plates with a high C content. There is also. The present invention is based on the above knowledge, and its gist is that in double-sided butt welding of a joint having a V, Y, or X-shaped groove with a groove angle of 45° or less, 2.5 per 10cm welding length
Spread filler metal in excess of g in advance and apply welding current.
By setting the current to 600A or less, the first layer of welding is performed by leaving an unmelted part at the bottom of the groove, and this unmelted part is welded.
It is a narrow gap submerged arc welding method that is characterized by welding by melting the first layer weld metal on the FP side, or by removing it by chiseling before welding on the FP side. The reasons for limiting the numerical values in the present invention will be described below. First, in the method of the present invention, the groove angle is set to 45° or less because a groove angle exceeding 45° results in too large a groove cross-sectional area, making it impossible to take advantage of the economical advantages of narrow-gap welding. Depends on what you can't do. Next, the amount of filler metal sprayed was set to 2.5 g or more per 10 cm of welding length, because if it is less than 2.5 g, the amount is too small.
This is due to the fact that the effect of uniformly remaining the unmelted portion becomes almost unrecognizable. There is no particular upper limit for the amount of spraying, but from practical knowledge it is approximately 100%.
It is desirable to have a weight of up to about 100 g. In addition, the welding current in the first layer welding was set to 600A or less because the welding current was
If the current exceeds 600A, undercuts are extremely likely to occur, making it difficult to remove slag. In addition, in the method of the present invention, the filler metal is not limited to the above-mentioned cut wire, but powdered, granular, or rod-shaped steel can be used, but it is generally the same composition as the welding wire and the base steel plate. It is true. Moreover, as mentioned above, by making the C content lower than that of the base material, the effect of preventing hot cracking can be expected. As described above, the method of the present invention makes the conventional groove angle extremely small and actively generates fusion defects, which were conventionally considered to be weld defects, during first layer welding, thereby eliminating hot cracks and undercuts. By using a filler metal (cut wire, etc.), this unmelted part can be easily removed during welding on the back side (FP side), and the groove is different from the conventional one. As with the conventional method, it can be processed by gas cutting, and there is no need to provide a gap between both grooves, such as a root gap, and no backing material is required, so temporary assembly of the workpiece is easy and moderately easy as with the conventional method. It can be said that this is an extremely economical welding method for thick plates. Incidentally, the submerged arc welding in the method of the present invention is also effective with the single-electrode multi-electrode method, and by using the multi-electrode method, it is possible to increase the welding speed and further increase in efficiency can be expected. Next, the effects of the present invention will be illustrated in more detail with reference to Examples. Example Welding wire W-2 shown in Table 2 and cut wire CW were mixed with flux F-2 shown in Table 3,
Combined with F-3, length 1000mm, plate thickness 35 and 50mm
Initial layer welding was performed in the groove shown in Figure 2 using SM-50B steel under each welding condition, and the presence or absence of poor fusion and hot cracking was confirmed by X-ray transmission tests. Of these, for those with no hot cracking and good slag peeling, layer welding was performed on the BP side and FP side, and an X-ray transmission test was conducted again to confirm the soundness of the joint. The results are shown in Table 4. In the comparative example, it was difficult to remove the slag during first layer welding, hot cracks occurred in the weld metal, and the gouging depth became deep, resulting in formation of layers on the FP side. While the number increases,
In the method of the present invention, by welding the first layer while leaving an unfused portion, weld metal with good slag separation and no hot cracking was obtained. Furthermore, this unfused portion could be easily removed by gouging or FP side welding, and no defects were observed in the X-ray transmission test after the completion of layer welding.

【table】

【table】

【table】

【table】

[Table] Slag peeling ◎: Natural peeling ○: Easy peeling △: Slightly difficult to peel ×: Difficult to peel
It is possible to efficiently and economically weld medium-thickness steel plates of about 100 to 100 m thick, and cost reductions can be expected.

[Brief explanation of drawings]

Figure 1 shows the effect of cut wire scattering on the shape of the unmelted part remaining at the bottom of the groove, Figure 2
The figure is a diagram showing the groove shape and layering method used in the example. WM: weld metal, U: unfused part, CW: cut wire, G: gouging shape.

Claims (1)

[Claims] 1 In double-sided butt welding of joints with V, Y, or X-shaped grooves with a groove angle of 45° or less, BP
By spraying 2.5 g or more of filler metal per 10 cm of welding length at the bottom of the side groove in advance and reducing the welding current to 600 A or less, an unmelted portion is left at the bottom of the groove and the first layer weld is performed. A narrow gap submerged arc welding method characterized by removing and welding the part by melting the first layer weld metal on the FP side or by back chiseling prior to welding on the FP side.