JPH1058143A - Large heat input, two-electrode submerged arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large heat input, two-electrode submerged arc welding method most suitable for the single-side, one-pass welding for a corner weld joint or the like in which a steel plate of >=50mm in thickness is used without additionally providing an equipment such as a welding power source. SOLUTION: Welding is performed under the condition where the diameter of the wire of a preceding electrode is over 4.8mm to 5.6mm, the current density of the preceding electrode is 80-100A/mm<2> , the voltage of the preceding electrode is 42-55V, and the distance between the preceding electrode and a succeeding electrode is below 50-90mm. The baking type flux having the composition consisting of, by weight, 10-30% SiO2 , 5-30% MgO, 2-20% Al2 O3 , 2-10% CaO, 10-40% iron powder, and 1-10% in total of one kind or more of Si, Mn, Ti and Al as the metallic content is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-electrode submerged arc welding having a large heat input, and particularly to a submerged arc welding in which a thick steel plate such as a square joint of a steel box column is welded from one side to achieve a good energy efficiency. In addition, the present invention relates to a more efficient submerged arc welding method that can be performed without increasing the equipment such as a welding power source.

[0002]

2. Description of the Related Art In recent years, high-rise building columns have resulted in the use of extremely thick box columns. For welding of box column joints, one side using iron powder added flux
The large-pass heat input two-electrode submerged arc welding method is widely used, but the required thickness of the deposited metal increases significantly with the increase in the thickness, so the applicable thickness is limited by the current capacity of the welding machine. You. In the case of thick joints where it is difficult to apply one-pass welding, a method of performing submerged arc welding after performing underlay welding by CO ₂ welding is often used, but a great deal of labor is required for underlay welding. Therefore, there is a problem economically, and the expansion of the applicable range of the one-pass welding has been an urgent issue in order to improve the efficiency of box joint square joint welding.

The maximum usable current of a submerged arc welding machine generally used for box column corner joint welding is 2000
A, but for this current it is generally 6.
4mm wire is used. However, in this case, when the current density is small and the plate thickness becomes 50 mm or more, when performing one-pass welding, it is necessary to reduce the welding speed in order to secure the welding amount. If the welding speed is too slow, the molten metal tends to precede the welding arc, making it difficult to obtain a stable penetration, or causing problems such as a short circuit of the leading electrode with the molten metal.

Conventionally, welding wires commercially available for general submerged arc welding have a diameter of 4.0, 4.8,
6.4mm, and 4.8 and 4.
Although there is a wire with a diameter of 0 mm, with a welding wire of 4.8 mm in diameter, when the welding current exceeds about 1800 A, the feeding speed exceeds the capacity of a normal welding machine. However, there is a problem that the welding is not stable and reliable welding cannot be performed.

[0005] From the above, it is necessary to increase the thickness of the sheet exceeding 50 mm.
Pass submerged arc welding has poor reliability, and one-pass welding is generally applied up to about 50 mm. Regarding the problem of such one-pass welding of a thick corner joint, for example, Japanese Patent Publication No. Hei 6-30818 discloses a groove shape, an electrode wire diameter, a distance between a leading electrode and a trailing electrode, A submerged arc welding method for a square joint having a plate thickness of 40 mm or more, which specifies a groove shape, an electrode arrangement, and welding conditions such as a current ratio, a voltage ratio, and a wire protrusion length of a trailing electrode, has been proposed. This submerged arc welding method states that it can provide high-quality welds even if the workpiece has an inclination of the weld line due to welding heat distortion, but the penetration depth tends to be shallow at plate thicknesses of 50 mm or more. There were problems such as the inability to perform one-pass welding with a plate thickness of 60 mm or more.

Japanese Patent Publication No. 6-73757 proposes a submerged arc welding method capable of realizing one-pass welding exceeding a plate thickness of 50 mm by combining a specific flux and a welding current condition of 2000 A or more. However, this method requires a special welding machine to apply a current of 2,000 A or more, and has a problem that the applicable range is limited.

[0007]

SUMMARY OF THE INVENTION The present invention provides an optimal solution to this problem. One-sided single pass of a steel plate having a thickness of 50 mm or more can be performed without increasing the equipment such as a welding power source. An object is to propose a large heat input submerged arc welding method that enables welding.

[0008]

Means for Solving the Problems The inventors of the present invention have developed a maximum current of 2000, which is the most common as a high heat input submerged arc welding machine.
A two-electrode submerged arc welding machine A was used to study the application limits of one-pass submerged arc welding to thick steel plates. As a result, when using conventional welding materials, flux and welding conditions alone were not sufficient. It was insufficient to obtain stable penetration, and it was concluded that it was important to increase the arc force.

In order to increase the arc force, it is necessary to increase the current density of the leading electrode or to concentrate the arc force by squeezing the arc. However, it is difficult to use an optimal current with a conventionally used wire. It is difficult, and the welding conditions proposed so far lack the consideration of performing high-efficiency welding using the full capacity of the welding machine. Therefore, the present inventors have maximized the efficiency of one-pass submerged arc welding when a welding current of about 2000 A is used, and have achieved stable and reliable welding in one-pass welding of steel plates having a thickness of 50 mm or more. The necessary conditions for performing are discussed. As a result, by effectively and stably increasing the current density of the leading electrode in the relationship between the welding current and the wire diameter, that is, when the welding current is about 2000 A, the welding wire diameter is reduced by 5.0 mm.
By setting it to the level, stable penetration can be ensured, and by setting the high current density, the leading electrode voltage can be set to a high welding voltage that could not be used conventionally, ensuring stable penetration and bead appearance Has found that it can be improved.

The present invention has been made based on the above findings. The present invention relates to a large heat input two-electrode submerged arc welding method for welding a steel plate having a thickness of 50 mm or more using a leading electrode and a trailing electrode, wherein the wire diameter of the leading electrode is more than 4.8 mm to 5.6 mm. The electrode current density is 80 ~
A large heat input two-electrode submerged arc welding method characterized in that welding is performed under conditions of 100 A / mm ² , a leading electrode voltage of 42 V to 55 V, and a distance between the leading electrode and the trailing electrode of less than 50 to 90 mm. There further, flux used in the present invention, in _{weight%, SiO 2: 10~30%,} MgO: 5~30%, Al 2 O 3: 2~
A calcined flux containing 20%, CaO: 2 to 10%, iron powder: 10 to 40%, and a total of 1 to 10% of one or more of Si, Mn, Ti and Al as a metal component is preferable.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the present invention will be described in detail below. The welding method of the present invention is a large heat input two-electrode submerged arc welding method capable of performing one-pass welding of a steel plate having a thickness of 50 mm or more, preferably 60 mm or more using a leading electrode and a trailing electrode.

Wire diameter: more than 4.8 mm to 5.6 mm When the maximum welding current is 2000 A, to achieve one-pass welding of a plate thickness of 60 mm, a welding current of about 1900 A is required. Since the current density becomes too large and the melting speed of the wire increases, the feeding becomes unstable and stable welding cannot be performed. On the other hand, if it exceeds 5.6 mm, the current density becomes too small and it becomes difficult to obtain sufficient penetration. For this reason, the diameter of the wire used is over 4.8 mm to 5.
6 mm.

The current density of the leading electrode: 80 to 100 A / mm ² The current density of the leading electrode is an indispensable factor in securing penetration in large heat input one-pass welding that produces a large amount of molten metal at a low speed. For this purpose, 80 A / mm ² or more is required. On the other hand, when the current density increases the melting rate of the wire is required wire feed commensurate therewith to increase, in a typical welder when the current density exceeds 100 A / mm ² feed wires not It becomes stable and poor penetration easily occurs. Therefore, the current density of the leading electrode is 80 to 100 A / m
m ² range. In addition, it is more preferably 85 to 95 A / mm ² .

Lead electrode voltage: 42 V to 54 V Since the arc length changes depending on the voltage of the lead electrode, the shape of the penetration is significantly affected. If the voltage is less than 42 V, the stability of the leading electrode voltage is poor, the bead appearance is easily disturbed, and the penetration width is narrow, so that poor fusion is likely to occur. Meanwhile, 54
If it exceeds V, the penetration will decrease, and poor penetration may occur. For this reason, the range of the leading electrode voltage was set to 42V to 54V. The voltage is more preferably 42 to 48V.

[0015] Distance between the leading electrode and the succeeding electrode: 50 mm or more
Less than 90 mm The distance between the electrodes must be set so that the shape of the molten pool becomes a semi-one pool in order to prevent solidification cracking of the weld metal. Therefore, for a large heat input welding as in the present invention, if it is less than 50 mm, the molten pool is close to a one pool, and solidification cracks are easily generated. On the other hand, if the distance is 90 mm or more, poor fusion is likely to occur. Therefore, the distance between the leading electrode and the succeeding electrode is set to 50 mm to less than 90 mm. In addition, more preferably
It is 60-80 mm. In the present invention, the inter-electrode distance is a distance from the center of the leading electrode wire to the center of the following electrode wire on the surface of the steel plate to be welded.

The other welding conditions include a welding current ratio, a welding voltage of a trailing electrode, an inclination of an electrode, a protrusion length, and the like. These are the large heat input submerged arc welding of a normal box-column joint. The welding current ratio I ₂ / I ₁ : 0.7 to 1.0 (where,
I ₁ : leading electrode current, I ₂ : trailing electrode current), welding voltage of trailing electrode: 42 to 55 V, inclination of electrode: (leading electrode) 0 to −
10 °, (the trailing electrode) 20 to 0 °, and protrusion length: 30 to 80 mm. The welding speed is a condition that is inevitably determined as a speed necessary to fill the groove from the welding speed determined by the welding current and the welding material.
The range for performing the pass welding is preferably in the range of 12 to 30 cm / min.

The flux used in the present invention is
Iron powder added flux SiO ₂ -MgO-Al ₂ 0 ₃ system is preferred.
A preferred composition range of the flux will be described. SiO ₂ : 10 to 30% SiO ₂ is an important component as a slag-making material, but if it is less than 10%, the melting point of the generated slag is too high to obtain a good bead appearance, while if it exceeds 30%, the slag is As the amount increases, the slag removability deteriorates or the basicity decreases too much, and the toughness of the weld metal deteriorates. Therefore, the content of SiO ₂ is set in the range of 10 to 30%. In addition, it is preferably 15 to 25%.

MgO: 5 to 30% MgO is an effective component for adjusting the melting point and basicity of slag, but if it is less than 5%, this effect is poor, and if it exceeds 30%, the melting point rises too much. The bead appearance deteriorates. For this reason, MgO was set in the range of 5 to 30%. Preferably,
15-28%.

Al ₂ O ₃ : 2 to 20% Al ₂ O ₃ is an effective component for increasing the melting point without lowering the viscosity of the produced slag, but if it is less than 2%, this effect is poor. %, The melting point of the slag is too high and the bead appearance tends to deteriorate. For this reason,
Al ₂ O ₃ was in the range of 2 to 20%. In addition, preferably 5 to
15%.

CaO: 2 to 10% CaO is an effective component for adjusting the melting point and basicity of the slag, but if it is less than 2%, this effect is poor, and if it exceeds 10%, the slag removability deteriorates. . For this reason, CaO
The range was 10%. In addition, it is preferably 4 to 8%. Metal Fe (iron powder): 10 to 40% Fe is an essential component for increasing the welding speed and improving the welding workability. If it is less than 10%, the welding speed is not sufficiently improved, while it exceeds 40% If it is contained, the bead width tends to be narrow, and a good bead appearance cannot be obtained. For this reason, metal Fe (iron powder) was set in the range of 10 to 40%. In addition, it is preferably 20 to 38%.

Metal Si, Mn, Ti, Al: at least one kind in total
Addition of a metal component as a deoxidizing agent is required. If less than 1%, the effect is not sufficient and the oxygen content of the weld metal increases excessively, deteriorating the toughness, while including more than 10% in total In addition, there is a tendency that the oxygen content is too low and the toughness is rather deteriorated.
Although the composition range of the flux suitable for use in the present invention has been described above, components that are usually used in flux may be added as other components. Such components include CaF ₂ , BaO, ZrO, B ₂ O ₃ , CO _2, etc., wherein CaF ₂ , BaO, ZrO, CO ₂ is within 5% and B ₂ O ₃ is within 1%. Respectively. BaO, CaF ₂ ,
ZrO is an effective component for adjusting the basicity and melting point of slag, but addition of more than 5% impairs bead appearance and slag removability. CO ₂ is a component that is generated by decomposition of carbonate during welding and is effective in reducing the hydrogen partial pressure by reducing the hydrogen partial pressure. However, if it exceeds 5%, the bead appearance deteriorates due to the generation of gas. Becomes significant. B ₂ O ₃ is an effective component for improving the toughness of the weld metal, but if it exceeds 1%, the crack resistance of the weld metal deteriorates.

As flux and other components, Na ₂ O, which is inevitably contained as a binder and impurities of each raw material,
There are components such as K ₂ O, but these are not a problem as long as they are within the usual range.

[0023]

EXAMPLE Using a steel plate and a welding wire having a chemical composition shown in Table 1 and a flux having a composition shown in Table 2, submerged arc welding of one side and one pass under the groove shape shown in FIG. Was performed, and the internal defect and bead appearance of each joint were examined. Table 3 shows the results.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

In Examples Nos. 1 to 5 of the present invention, a welded joint having a good bead appearance and no internal defects was obtained despite the extremely thick joint. On the other hand, in Comparative Example No. 6 in which the leading electrode voltage was out of the range of the present invention, poor fusion was found, and in No. 7 in which the leading electrode voltage and the distance between the electrodes were out of the range of the present invention, poor fusion was observed. In Comparative Example No. 8 in which the current density of the electrode was out of the range of the present invention, poor penetration was observed.
Defects of poor bead appearance occurred.

[0028]

According to the present invention, a welded joint having a good bead appearance without internal defects even in single-sided one-pass welding of a thick steel plate having a thickness of 50 mm or more without increasing the equipment such as a welding power source. Can be obtained with high efficiency.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a groove shape.

Claims (2)

[Claims] 1. A large heat input two-electrode submerged arc welding method for welding a steel plate having a thickness of 50 mm or more using a leading electrode and a trailing electrode, wherein a diameter of a wire of the leading electrode is more than 4.8 mm to 5.6 mm; Current density of the leading electrode is 80-100 A / m
A large heat input two-electrode submerged arc welding method, characterized in that welding is performed under conditions of m ² , a leading electrode voltage of 42 V to 55 V, and a distance between the leading electrode and the trailing electrode of 50 mm to less than 90 mm. 2. In weight%, SiO ₂ : 10-30%, MgO: 5-5%
_{30%, Al 2 O 3:} 2~20%, CaO: 2~10%, iron powder: 10
The large heat input two-electrode submerged arc welding according to claim 1, wherein a sintered flux containing 40% and a total of 1 to 10% of at least one of Si, Mn, Ti and Al as a metal component is used. Method.