JPS6312713B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a welding method in which molten metal solidifies on a downhill slope, and is capable of forming a good weld by specifying the physical properties of slag formed on molten metal. It is. In so-called downhill slope welding, molten metal and molten slag formed by welding heat tend to flow in the welding direction, that is, downhill, due to their fluidity. Therefore, the molten metal and slag in the solidification process tend to flow into the molten pool in front, and a noticeable concave portion (hereinafter referred to as a concave bead) is formed on the outer surface of the weld bead after solidification.
Overlaps, undercuts, and even slag entrainment defects occur, and these tendencies become more pronounced as the welding speed increases. Therefore, in downhill slope welding, there is a limit to the increase in welding speed, and it is thought that some kind of improvement must be made. Below, regarding this situation, we will use the manufacturing of spiral steel pipes by welding as an example. will be explained in more detail. However, the following description is not intended to limit the invention and may be applied to various downhill slope welds. Welding methods have a wide range of applications, including submerged arc welding and overlay welding performed by dispersing flux, as well as welding using flux-cored wire. The first method for manufacturing spiral steel pipes by welding is
As schematically shown in the figure, the steel strip 1 is wound in a spiral shape while being fed in the direction of the arrow, and the torch 2
The inner surface is welded using a torch 3, and then the outer surface is welded using a torch 3. When welding the inner surface, if the torch is placed on the upward slope side, concavities in the bead will not occur as much, but undercuts and slag winding tend to occur, so if the torch position is placed on the downward slope side, Undercuts are less likely to occur, but the amount of concavity in the bead increases, and overlapping tends to occur more easily. When welding the outer surface side, if the torch position is on the downward slope side, the center convexity of the bead will not occur as much, but overlap will tend to occur. There is a tendency for undercuts to increase as well. For this reason, there are various embankment plans for the arrangement of torches 2 and 3, but generally, as shown in Figure 2, torch 2 is located on the uphill slope Ai, and torch 3 is located on the downhill slope. They are arranged at the inclined part Ao. Therefore, although the former apparently is welding in an uphill inclined position and the latter is welded in a downhill inclined position, in reality, the inclinations should be considered to be completely opposite as described below. In other words, in inclined welding, not only the arc generation point is inclined, but also the molten metal formed by the arc heat is on the inclined surface, and the molten metal and molten slag covering it are solidified on the inclined surface. Welcome. Therefore, molten metal, etc. tends to flow down on an inclined surface, but when the direction of flow is toward the solidified side, new molten metal tends to be layered on top of the molten metal that is solidifying. Therefore, the amount of molten metal at the freezing point increases, especially the central protruding bead (herein referred to as a convex bead).
On the other hand, when the flow direction of the molten metal is towards the molten metal side, the molten metal always flows downward before solidification progresses, so the amount of molten metal at the solidification point is insufficient, especially in the central part. Concave beads (referred to herein as medium concave beads)
is formed. In the present invention, whether the welding is an uphill slope welding or a downhill slope welding is determined not by the direction of the slope at the arc generation point but by the direction of the slope during the solidification process of the molten metal. Welding under conditions where it is easy to form a bead is called downhill slope welding, while welding under conditions where it is easy to form a medium convex bead is called uphill slope welding. If the direction of the inclination changes during the solidification process, either one may be determined by considering the magnitude of the above-mentioned influence on the bead appearance. Therefore, reconsidering the welding of the spiral steel pipe, since the spiral steel pipe is turning clockwise in Fig. 2, the molten pool formed by arc heat at the inner weld part will reach the lowest point immediately after welding. P is reached, and this time it goes uphill while remaining unsolidified until it reaches the Bi region, where solidification progresses, so although it appears to be an uphill slope weld, it is actually a downhill slope weld. Therefore, a medium concave bead is likely to be formed. On the other hand, in the outer weld, the molten pool reaches the highest peak R immediately after welding, heads downhill while remaining unsolidified, and solidifies when it reaches the Bo area, so it appears to be a downhill slope weld. However, this is essentially an uphill slope welding, and a medium convex bead is likely to be formed. As mentioned above, the bead shape that appears in slope welding becomes medium concave or medium convex depending on the uphill or downhill slope, but downhill slope welding has more problems in terms of joint strength and weld defects. In addition, downward slope welding seems to be more difficult in terms of the frequency with which the above problems occur. Therefore, in order to prevent the above-mentioned problems from occurring, the general measure is to suppress the welding speed, and the welding speed for downhill slope welding has become extremely slow. Naturally, the speed on the outer surface side also decreases accordingly. Therefore, in the case of the above-mentioned spiral welding, it is said that there are more problems in the inner side welding, and that the main reason for not being able to improve the welding speed is the inner side welding. Figure 3 is a cross-sectional view of a spiral weld, where Mi indicates the weld metal on the inner surface and Mo indicates the weld metal on the outer surface.When the inner surface is welded at high speed, the amount of concavity in the bead at Mi increases significantly. In some cases, not only is the welding level lower than the base metal surface level, but welding defects such as overlap, undercut, and even slag entrainment become very noticeable. Such defects in the inner side welding can be avoided by adjusting the eccentricity l (Fig. 2) between the perpendicular line passing through the center point O of the spiral tube and the axis of the torch 2.
Although it can be improved to some extent by adjusting welding conditions (current, voltage, distance between electrodes in multi-electrode welding, etc.), hollows, undercuts, overlaps,
It is difficult to prevent all slag fogging and the like at the same time. For this reason, welding while increasing the slag viscosity using a high melting point flux has been considered, but at the cost of reducing the amount of hollows and overlaps, the number of defects such as slag entrainment and undercuts is increased. increased, and it was not possible to improve the welding speed of spiral pipe. The present invention was made with attention to these circumstances, and after searching for conditions that would suppress all of the above-mentioned defects and enable high-speed welding, it was found that the solidification temperature (platinum The temperature at which the viscosity becomes 1000 poise measured by the ball pulling method) is 850~
Welding speed can be improved by performing downhill slope welding at 1400℃ using a method that forms a slag with a physical property of a viscosity of 5 poise or less at 1450℃ and a slag with a viscosity of 5 poise or more at 1200℃. Also, the formation of a medium concave bead is avoided, and welding defects such as overlapping, slag entrainment, and undercuts do not occur. The welding method itself employed in the present invention is not subject to any particular restrictions as described above, but the flux that provides the slag that satisfies the above conditions may be dispersed flux, wire-filled flux, or wire-coated flux. From the manufacturing point of view, it does not matter whether the molten flux is a sintered flux or not. Furthermore, the composition of the flux can be freely set as long as it does not adversely affect the aforementioned conditions regarding solidification temperature, viscosity, etc. In the above-mentioned prior art, a proposal was made to increase the slag viscosity using a high-melting point flux, but the melting point of the flux and the viscosity of the slag do not correspond one-to-one. Further, the properties of the slag coating the molten metal can be directly indicated by the viscosity of the slag. Therefore, in the present invention, the greatest emphasis was placed on specifying the physical properties of slag. The basis for limiting the physical properties of the slag in the present invention will be explained below. As mentioned above, the solidification temperature of the slag approximately corresponds to the melting temperature of the flux. Therefore, as the solidification temperature of the slag becomes lower, the meltability of the flux, that is, the amount of slag increases, and a larger load is exerted on the molten metal, making it easier to form concave beads. Therefore, if the solidification temperature of the slag is too low, it leads to the disadvantage that it is easy to form concave beads, so it is necessary to set a lower limit, which is set at 850°C. In order to determine the solidification temperature of the slag, Stokes' platinum ball pulling method was adopted, and the temperature at which the measured viscosity reached 1000 poise was determined as the solidification temperature of the slag. In other words, when the solidification temperature of slag falls below 850°C, the amount of slag produced increases and concave beads are formed.
Defects such as overlaps have become extremely common. On the other hand, as for the upper limit, the slag viscosity increases in response to an increase in the slag solidification temperature, so welding defects such as slag entrainment and undercuts are more likely to occur, although the medium concave bead is eliminated. Therefore, we investigated the limit that would not cause these drawbacks and found that it was 1400℃. Next, we focused on the fact that the fluidity of slag during the solidification process of molten metal has a significant effect on bead shape, etc., and considered that it was necessary to limit the viscosity of slag at 1200°C and 1450°C. In other words, the temperature at which the molten metal begins to solidify is approximately 1450°C, and if the viscosity of the slag is high when the molten metal begins to solidify, it is thought that solidification will begin while the slag is still involved in the molten metal. The slag must have sufficient fluidity at this temperature. The viscosity of slag is 5 at 1450℃
If the poise is exceeded, the viscosity is too high and the frequency of occurrence of defects such as slag entrainment and undercut increases, and these defects cannot be eliminated even by adjusting the amount of eccentricity, welding conditions, etc. described above. In addition, it is approximately 1200℃ that solidification to the inside of the bead is completely completed, and it is thought that the bead shape and bead appearance are finally determined when solidification is completely completed. When the viscosity was less than 5 poise, the fluidity was too good and medium concave beads were likely to be formed. Since the present invention is configured as described above, the formation of a medium concave bead is suppressed, and overlap, undercut, and
It is possible to improve welding speed without causing welding defects such as slag entrainment. For example, the welding speed for spiral steel pipes was conventionally limited to 2.5 m/min, but with the present invention, it can be increased to 3.0 m/min or more. It also became possible. Next, examples of the present invention will be shown. Example 1 SS-41 material with a downward slope of 6 degrees (12 mm ^t ×
1000mm ^l ), and the wire (preceding electrode: US−
36, 4.8 mm〓, trailing electrode: US-36, 4.0 mm〓) and flux (Table 1; high temperature viscosity curve during melting is shown in Figure 4), and welding was carried out under the welding conditions shown in Table 2. Summer. The results were as shown in Table 1. Macro photographs of the bead cross sections for each example of flux usage are attached as reference photographs. In addition, the symbol S in each photo is 350mm from the start side, and the symbol E is from the end side.
Each cut is shown at 350mm.

[Table] Note 2 Flux consumption rate (consumed flux amount/consumed wire amount)
Note 3: The occurrence of defects was determined by X-ray tests, cross-sectional macroscopic images, and the naked eye.

[Table] In the case of using Flux A, the viscosity of the slag was too low, and the beat became concave in the middle, and overlapping and slag entrainment were observed. In the case using Flux B, the solidification temperature of the slag was appropriate, so no concavities were observed in the beets, but the uniformity and appearance of the beets were poor because the high temperature viscosity was excessive, and Entrainment and undercutting occurred. In the case of using flux C, the viscosity was similar to that of flux B, so slag entrainment and undercut were not eliminated. For those using flux D, 1200℃
Because the viscosity of the slag was too low, concavities in the bead occurred and overlapping was observed. With fluxes E and F, satisfactory results were obtained in all respects. In the case of using Flux G, the viscosity was excessive as a whole, so the bead shape was the worst, and undercuts and slag entrainment occurred frequently.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the state of welding and manufacturing a spiral pipe, FIG. 2 is an explanatory view seen from the front, FIG. 3 is a cross-sectional shape of a bead, and FIG. 4 is a high-temperature viscosity curve of slag.

Claims (1)

[Claims] 1. In a welding method on a downhill slope in which slag is formed on the molten metal and the molten metal is solidified on the downhill slope, welding is performed on the molten metal at a solidification temperature of 850 to 1400°C, A submerged arc welding method on a downhill slope characterized by forming and welding a slag having physical properties of a viscosity of 5 poise or less at 1450°C and a viscosity of 5 poise or more at 1200°C (However, Solidification temperature refers to the temperature at which the viscosity becomes 1000 poise as measured by the platinum ball pulling method).