JPS6357153B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multi-electrode tandem high-speed submerged arc welding method, and is intended to propose an improvement in submerged arc welding, which can be used particularly for seam welding of large-diameter steel pipes to obtain highly efficient and high-quality welds. For example, increasing the speed of submerged arc welding used for seam welding has a direct effect on improving the production efficiency of UO large-diameter steel pipes. It is being considered. The baked flux for high-speed welding that the inventors developed earlier has good workability at high speeds, but the weak point of this type of flux is that the arc concentration is somewhat poor, and depending on the welding conditions, Sometimes welding became unstable. In other words, in general, fired fluxes have a small bulk specific gravity, and when the flux is spread at a low height, arc blow-up occurs between the electrodes.
If this is severe, it may cause melting of the electrode tip, resulting in a decrease in welding efficiency. In addition, such unstable phenomena during welding appear as weld defects such as meandering of the bead, degrading the quality of the welded part. The basic purpose of this invention is to improve the above-mentioned weaknesses in the fired flux and to fully bring out its high-speed welding performance. The inventors have promoted the advantages of the above-mentioned fired flux for high-speed welding, which enables high-efficiency welding, and have also found that the instability seen during welding is due to the unique properties of this flux, such as its low bulk specific gravity and Since this property is the main factor contributing to high-speed welding performance, especially in relation to gas generation, we believe that there is no way to resolve the above weaknesses other than improving the arc generation conditions, and we have determined the appropriate phase difference of the electrode current. I've been considering options. As a result, among the appropriate phases found by the inventors in the four-electrode method, we found one that improves the stability and efficiency during welding of the previously described fired flux. That is, 6 to 15% by weight (hereinafter simply expressed as %)
MgO, 5-15% Al ₂ O ₃ , 5-20% TiO ₂ , and 6-15% CaF ₂ within a range that satisfies the following formulas (1) and (2) at the same time, 25-35% SiO ₂ , 4-15%
The composition contains MnO and 5 to 15% CaO, and the gas generated by thermal decomposition of these components is
It is a sintered flux of 1.5 to 3%, and the median diameter DMED, which accounts for 50% of the cumulative particle size distribution, is 500 to 30%.
Flux for multi-electrode tandem high-speed submerged arc welding in which fine particles of 800 μm and particle diameter of 295 μm or less account for 15% or less of the total.Note 1.3≦MgO/CaF ₂ +0.59・Al ₂ O ₃ /TiO ₂ ≦1.7
...(1) 0.2≦MgO/CaF ₂ ≦1.0 ...(2) This flux contributes to improving stability during welding, especially when used in the multi-electrode submerged arc welding method described below. Significantly. Note: Apply alternating current to all four electrodes arranged in a row from the front in the direction of welding: L pole, M ₁ pole, M ₂ pole, and T pole, and apply an alternating current to either the front L pole or the last T pole. The current phase difference between the three removed electrodes is 120°, and the remaining T or L pole has a current phase difference of 0°± with respect to the farthest electrode.
This is done by loading it with a 3-phase AC power source with an angle of 30°. In order to prevent undercut during high-speed welding, it is necessary to deflect the T-pole arc predominantly in the welding direction, thereby suppressing the rapid flow of molten steel backward. In order to deflect the T pole arc in the welding direction, T
It is important to control the electromagnetic force acting on the polar arc, but if you exclude either the L or T pole among the L pole, M ₁ pole, M ₂ pole, and T pole, there will be no current between the three electrodes. The phase difference of the remaining T or L poles is 120°, respectively, and the current phase difference of the remaining T or L poles is 0°± with respect to the farthest electrode.
When the angle is 30°, the electromagnetic force acting on the T-pole arc is appropriate; however, outside this condition, the T-pole arc may swing excessively in the direction of welding progress, or may swing in the opposite direction to the direction of welding progress, resulting in undercut. is likely to occur. Next, the reasons for limiting the flux composition are as follows. MgO: It is a high melting point oxide, and since a low melting point is desirable for high speed welding, it is preferable to have less. However, in order to increase basicity and toughness, it is necessary to add 6% or more, while if it exceeds 15%, high speed welding inhibit sex. Al ₂ O ₃ : Like MgO, it is a high melting point oxide, but if it is less than 5%, slag releasability deteriorates, and if it exceeds 15%, high-speed weldability is inhibited. TiO ₂ : Affects the stability of the arc. If it is less than 5%, the stability of the arc will deteriorate, and if it exceeds 20%, the beat shape will tend to become convex. CaF ₂ : It has the effect of improving the toughness of weld metal, but 6
If it is less than 15%, the effect will be small, and if it exceeds 15%, the slag viscosity will drop too much and the violent movement of molten steel will not be suppressed, resulting in deterioration of the bead appearance. In addition to the above, the relationships 1.3≦MgO/CaF ₂ +0.59Al ₂ O ₃ /TiO ₂ ≦1.7 0.2≦MgO/CaF ₂ ≦1.0 apply to fluxes of various chemical compositions.
This is an experimental formula showing a good range of welding workability. Good workability cannot be obtained outside this range of conditions. SiO ₂ : The main component of flux, which is added to adjust the basicity and slag viscosity.
If it is less than 25%, the viscosity becomes too small and high-speed weldability is impaired. If it exceeds 35%, the basicity becomes too low and the toughness of the weld metal cannot be ensured. MnO: If it is less than 4%, the slag removal property deteriorates.
If it exceeds 15%, oxygen increases due to reduction of MnO and the toughness of the weld metal deteriorates. CaO: If it is less than 5%, the toughness of the weld metal deteriorates. If it exceeds 15%, spot marks are likely to occur. The particle size of the fired flux is also a factor that affects welding workability. If the median diameter is smaller than 500 to 800 μ, it is too small and the amount of flux melted becomes excessive and the amount of gas generated increases. However, the fluidity of the flux is required, making it difficult for gas to escape, causing the cavity to blow up and becoming unstable. It becomes an arc. If it exceeds 800 μm, the flux becomes too coarse and uniform melting of the flux is not achieved, resulting in uneven gas generation. Therefore, this case also becomes unstable. Furthermore, if the proportion of fine particles with a diameter of 295 μm or less exceeds 15%, undercuts will significantly increase. Examples will be described in more detail below. Using the 4-electrode submerged arc welding equipment shown in Fig. 1, welding was carried out under the welding conditions shown in Table 2, using the fluxes A1 to A4 shown in Table 1 as test fluxes, to the steel plate with the V groove shown in Fig. 2. Summer.

【table】

[Table] Each flux of A1 to A4 is shown in the current phase relationship in Figure 3a and b, respectively, and shows two types of connections: connection C1 according to the present invention and comparative connection C2 according to the conventional method.
As shown in Table 3, the results of the workability evaluation obtained by the above method show that undercuts did not occur for any flux, regardless of the connection.
According to the connection shown in Fig. 3a, the meandering that occurs in the connection shown in Fig. 3b is suppressed, and a more stable bead can be obtained.
Further, even though the arc blow-up was noticeable, this was suppressed and no chip melting occurred.

[Table] In the above embodiment, the front L pole and the last T
Although the connection shown in Fig. 3a was used in which the poles were in the same phase, the phase difference of each current was within 0° ± 30°, and almost the same welding results were obtained. As described above, according to the present invention, it is possible to improve multi-electrode high-speed submerged arc welding with high efficiency and to obtain a high-quality welded part.

[Brief explanation of drawings]

Fig. 1 is an electrode arrangement diagram of a four-electrode welding device, Fig. 2 is a sectional view of a test groove showing the V-groove dimensions, and Figs. It is a current phase relation diagram shown.

Claims (1)

[Claims] 1. An alternating current is applied to all four electrodes arranged in a line in the order of L pole, M ₁ pole, M ₂ pole, and T pole from the front in the direction of welding progress. The current phase difference between the three electrodes excluding one of the T poles is 120°, and the current phase difference of the remaining T or L poles is 0° with respect to the farthest electrode. Loaded with a 3-phase AC power supply with ±30°; 6-15% by weight magnesia (MgO), 5-15% by weight alumina (Al ₂ O ₃ ), 5-20% by weight titania (TiO ₂ ). , and 6 to 15% by weight of fluorite (CaF ₂ ) using the following formula: 1.3MgO/CaF ₂ +0.59・Al ₂ O ₃ /TiO ₂ ≦1.7, 0.2≦MgO/CaF ₂ ≦1.0. Contains together with 25-35% by weight of silica (SiO ₂ ), 4-15% by weight of manganese oxide (MnO) and 5-15% by weight of lime (CaO) within a satisfactory range at the same time. The gas generated by decomposition is 1.5 to 3
% by weight, the median diameter dmed of particles that account for 50% by weight in the cumulative particle size distribution is 500 to 800 μm, and the particle size is
A multi-electrode tandem high-speed submerged arc welding method that combines the use of a sintered flux in which fine particles of 295 μm or less account for 15% by weight or less of the total.