JP3463333B2 - Large heat input multilayer submerged arc welding method for thick steel plate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to multi-pass submerged arc welding, and more particularly, to welding a thick steel plate such as a square joint of a steel box column from one side with high efficiency. The present invention relates to a large heat input multi-layer submerged arc welding method capable of efficiently obtaining a weld having a good bead appearance in the case of construction. 2. Description of the Related Art In recent years, the height of buildings has been increased, and box pillars having a plate thickness of 40 mm or more have been commonly used, and the efficiency of welding has become increasingly important. For the welding of box column joints, the single-pass, single-pass, large-heat-input submerged arc welding method using a flux that increases the amount of welding by adding iron powder for high efficiency is widely used. Since the amount of welding required for welding increases significantly with an increase in the plate thickness, the applicable plate thickness is limited by the current capacity of the welding machine and the like. Multi-pass welding must be performed in thick steel plate welding where it is difficult to apply one-pass welding.However, in multi-pass welding with large heat input submerged arc welding, the slag thickness increases with increasing heat input. There are problems such as deterioration in peelability and easy occurrence of solidification cracking. Various measures have been proposed to solve the problem of multi-pass submerged arc welding. For example, Japanese Patent Application Laid-Open No. 63-192593 discloses a slag stripping method containing Al ₂ O ₃ as a main component. Japanese Patent Application Laid-Open Nos. 57-64491 and 61-9979 propose a method of preventing solidification cracking by defining the chemical composition of a weld metal. ing. However, these methods have been proposed on the premise that a relatively small heat input path, which is a conventional method, is laminated on a groove of about 50 ° or more, and thus sufficient efficiency cannot be secured. [0004] Therefore, the present inventors have
For the purpose of improving the slag peelability and solidification cracking resistance, which is a problem during large heat input multi-layer construction of single-sided submerged arc welding of thick steel plates, 30% or less in JP-A-2-258191 A high-efficiency welding method was proposed in which a flux containing iron powder and having a specific composition was combined with a multi-step groove. As a result, the number of passes in multi-layer welding of thick steel plates exceeding the applicable range of the one-pass welding method can be minimized. However, the iron powder-added flux contains a large amount of iron powder in the flux and therefore has a large bulk specific gravity, so that the bead width is hardly widened, and the shape of the toe portion tends to overlap. In particular, in this method, since the groove width is widened by making the groove a multi-step groove, the condition range in which a good bead appearance can be obtained is narrowed in the final layer using the flux containing iron powder. For this reason, if the final layer is combined with a flux that can secure a sufficient bead width, and if it is not possible to perform welding with a good bead appearance with no defects by laminating one pass per layer, stable and efficient welding I can't achieve it.
An object of the present invention is to solve the above-mentioned problems and to provide a high-efficiency large heat input multilayer welding method having a good bead appearance and a high efficiency. The present inventors have conducted extensive studies on the bead width and shape in one-layer one-pass welding and found that the addition of iron powder to the flux has a great effect on the bead shape. Revealed. The present invention is based on these findings. That is, the present invention has a plate thickness of 40 mm
When multi-layer welding of the above thick steel plates, the first layer is welded using a sintering flux containing 20 to 40% by weight of iron powder with respect to the total flux, and the final layer does not contain iron powder, and A large heat input multi-layer submerged arc welding method for thick steel plates, wherein welding is performed using a flux having a composition ratio represented by the formula (1) of 1.5 or less. R = (MgO + CaO + Al ₂ O ₃ ) / (SiO ₂ + CaF ₂ ) (1) The following describes the groove shape and flux in the present invention. State the reason. First is the groove angle, but as the groove of a thick steel plate that is usually welded from one side,
V-grooves are common, and in large heat input submerged arc welding of thick steel plates, grooves with an angle of about 35-40 ° are used. The groove angle cannot be unnecessarily narrowed from the viewpoint of ensuring penetration, so that when the plate thickness is large, the groove cross-sectional area becomes large, and the welding heat input necessary for raising in one pass increases. It is the limit of one-pass welding in terms of capacity and durability. Further, the mechanical properties of the welded portion deteriorate as the heat input increases, so that the material is also restricted from this aspect. As described above, there is a limit in applying one-pass welding, and multilayer welding is applied to a thick material exceeding this limit. Regarding the flux used for the first layer, it is necessary to use a flux added with iron powder. Iron powder is a component that improves the concentration of the arc during welding, improves the welding workability in large heat input welding, and transfers to the molten pool during welding to increase the welding speed. The effect is not sufficient, and if the content exceeds 40%, the bead appearance deteriorates. Therefore, an appropriate range is set to 20 to 40%. On the other hand, it is desirable that the flux used for welding the final layer does not contain iron powder, and that the composition ratio R of the flux represented by the formula (1) be 1.5 or less. That is, in order to improve the efficiency of the multi-layer welding, it is important to reduce the number of passes as much as possible, and it is desirable to perform lamination of one pass per layer. However, as the groove width of the final layer becomes wider, the groove becomes wider. It is easy to cause unmelted residue and undercut, and the appropriate welding conditions become extremely narrow.
You will not endure practical use. One of the causes is that the arc concentrates due to the iron powder contained in the flux,
This is because as the bulk specific gravity of the flux increases, the heat capacity increases, and the bead width is hardly widened. Therefore, in principle, it is necessary that the bead width does not contain iron powder, the melting point of the slag is not too high, and the bead width is easily widened. For this reason, when the composition ratio R represented by the formula (1) is used as an index for evaluating the melting point of the slag, a sufficient bead width cannot be obtained with a flux in which this is too large, and 1.
5 is the upper limit. As described above, the present invention relates to high-efficiency submerged arc welding using iron powder-added flux for a thick steel plate, and aims to obtain a weld bead having excellent bead appearance by applying a specific flux to the final layer. It is. Here, the flux of the final layer does not contain iron powder in principle,
Iron contained in the flux from ferromagnetic iron used as a deoxidizing agent may be contained as long as it is in a normally used range. In addition, as the groove used in the present invention, a multi-step groove extending in at least two stages is preferable. In other words, in order to increase the efficiency of multi-layer welding, it is necessary to increase the heat input of multi-layer welding and to suppress the groove cross-sectional area. However, as shown in FIG. By using the groove having the following shape, the cross-sectional area of the groove can be reduced, and the shape of the weld metal can be formed into a shape in which solidification cracking hardly occurs and excellent in slag removability. Embodiments of the present invention will be described below. Welding was performed under the conditions shown in Table 3 using a steel sheet and a wire shown in Table 1 and a flux having the chemical composition shown in Table 2. [Table 1] [Table 2] [Table 3] Table 4 summarizes the welding results. [Table 4] Embodiments 1 to 4, 7 according to the present invention
When 8, 10, and 11 were used, good bead appearance was obtained under good welding workability. On the other hand, in the fluxes for the final layers indicated by symbols 5 and 9, the metallic iron content deviates from the condition of the gist of the present invention. Bead appearance was poor. As described above, by using the flux according to the present invention, welding with good bead appearance can be achieved with high efficiency.

[Brief description of the drawings] FIG. 1 is a sectional view showing a groove shape in an embodiment.

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Claims (1)

(57) [Claims] [Claim 1] When multi-layer welding of a thick steel plate having a thickness of 40 mm or more, a sintering type flux in which the first layer contains 20 to 40% by weight of iron powder with respect to the total flux. The final layer does not contain iron powder, and the composition ratio represented by equation (1) is 1.
5. A method for multi-layer submerged arc welding of thick steel plates with high heat input, wherein welding is performed using a flux having the following composition. R = (MgO + CaO + Al ₂ O ₃ ) / (SiO ₂ + CaF ₂ ) ・ ・ ・ ・ ・ (1)