JP2947731B2 - Large heat input 2-electrode submerged arc welding method - Google Patents

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 system having a large heat input, and more particularly to a welding power source in a case where a thick steel plate such as a square joint welding of a steel box column is welded from one side with high efficiency. And a highly efficient one-pass submerged arc welding method when there is a restriction.

[0002]

2. Description of the Related Art In recent years, the height of buildings has 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. A single-pass, single-pass, large-heat-input, two-electrode submerged-arc welding method using iron powder-added flux that provides high efficiency is widely used for welding box column corner joints. Since the amount of welding increases remarkably, the applicable plate thickness is limited by the current capacity of the welding machine. When 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. However, underpass welding requires a great deal of labor, so one-pass welding is required. Increasing the scope of welding is a pressing issue.

With respect to the one-pass welding of a thick joint, improvement measures have been proposed in the past. For example, Tokuho 6-30
In Japanese Patent No. 818, the electrode arrangement and welding conditions are specified to cope with the inclination of the welding line due to the thermal distortion of the workpiece, and
A method of performing one-pass welding of 40 mm or more has been proposed,
This method is a general welding condition for two-electrode submerged arc welding. When the plate thickness is 50 mm or more, the penetration depth tends to be small, and one-pass welding with a plate thickness of 60 mm or more cannot be performed.

In addition, the present inventors have proposed in Japanese Patent Publication No. 6-73757 a method of realizing one-pass welding exceeding a plate thickness of 50 mm by combining a specific flux and a welding current condition of 2,000 A or more. In order to apply a current of 2000 A or more, a special welding machine was required, and the applicable range was limited.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present inventors
Using a two-electrode submerged arc welding machine with a maximum current of 2000 A, which is the most common as a large heat input submerged arc welding machine,
The application limit of one-pass submerged arc welding of thick steel plates was examined. When using conventional welding materials, the combination of flux and welding conditions alone was not enough to obtain stable penetration, and the arc force increased. Has been found to be important. 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, but it is difficult to use an optimal current with a conventionally used wire. Also, the conventionally proposed welding conditions lacked the consideration of performing high-efficiency welding using the full capacity of the welding machine. That is, in the two-electrode submerged arc welding under the limitation of the welding current, in order to raise the application limit of the one-pass welding, it is necessary to secure the amount of welding. Therefore, it is desirable to use both electrodes under conditions close to the limiting current. Conventionally, no method for solving this problem has been found.

The present invention proposes an optimal solution to the problem of the limitation of one-pass welding in consideration of such current limitation.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a two-electrode submerged arc welding of a steel plate having a thickness of 50 mm or more using a welding current of 2000 A or less, in which the current density of the leading electrode is 80 to 80 mm.
95A / mm ² , lead wire diameter D is 4.8mm <D ≦ 5.6m
m and the ratio of the leading pole current I ₁ to the trailing pole current I ₂ is (I ₂ /
I ₁ ) is a large heat input two-electrode submerged arc welding method characterized in that welding is performed under the conditions of ≧ 0.9 and a distance between the electrodes of 90 to 120 mm, and further, by weight%, SiO ₂ : 10 to 30%, MgO:
_{5~30%, Al 2 O 3:} 2~20%, CaO: 2~10%, iron powder:
A large heat input two-electrode submerged arc welding method characterized by using a firing flux for submerged arc welding containing 10 to 40% and 1 to 10% of at least one of Si, Mn, Ti and Al as a metal component. It is.

[0008]

The present invention will be described below in detail. The present inventors have maximized the efficiency of one-pass submerged arc welding using a two-electrode submerged arc welding machine with a maximum welding current of 2,000 A, enabling one-pass welding of a plate thickness of 50 mm or more and a plate thickness of about 60 mm. The necessary conditions for doing so were examined.

When the welding current is limited, it is necessary to reduce the welding speed in order to secure the welding amount. However, if the welding speed is too slow, the molten metal tends to precede the welding arc and is stable. It becomes difficult to obtain an improved penetration. Since such a phenomenon occurs, it is necessary to increase the welding current to increase the welding speed in order to increase the thickness of the plate applied for one-pass welding.

Therefore, when a two-electrode submerged arc welding machine with a maximum welding current of 2000 A is used, a plate thickness of 50 mm
The degree was the application limit of one-pass welding. However, the present inventors have found that by effectively and stably increasing the current density of the leading electrode, stable penetration can be ensured and one-pass welding with a plate thickness of about 60 mm can be realized.

That is, the diameter of a welding wire conventionally used for general submerged arc welding is 4,
0 4.8, 6.4 mm, and welding wires with a diameter of 4.8, 6.4 mm are generally used for large heat input welding.
Below 00 A, the current density is insufficient with a welding wire having a diameter of 6.4 mm, and it is not possible to suppress a decrease in penetration due to a decrease in welding speed. However, if the welding current of a welding wire with a diameter of 4.8 mm exceeds about 1800 A, the feed speed will exceed the capacity of a normal welding machine, so the wire feed, arc voltage and current will not be stable and will be stable. Welding cannot be performed. For this reason, the welding current has to be limited to a low value, and the welding amount is insufficient, so that pass welding with a plate thickness of 50 mm or more has been difficult.

Therefore, in order to realize the penetration and the securing of the welding speed in an optimum state, it is necessary to perform welding at an optimum current density as a relationship between the welding current of the leading electrode and the wire diameter. When the current is 2000 A, it is optimal to make the diameter of the welding wire about 5.0 mm. Further, in order to make the most of the welding speed, it is desirable that the welding current of the trailing electrode is also high, and the welding speed can be improved by optimizing the welding conditions and electrode arrangement.

The reasons for limiting the numerical values will be described below. Current density of the leading electrode: the current density of 80~95A / mm ² leading electrode is an essential factor in ensuring penetration in large heat input one-pass welding to produce large quantities 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 speed of the wire increases, so it is necessary to feed the wire accordingly.
If the current density exceeds 95 A / mm ² , the wire feeding becomes unstable in a general welding machine, and poor penetration is likely to occur. For this reason, it was set to 80 to 95 A / mm ² . -Wire diameter: 4.8mm <D ≤ 5.6mm When the maximum welding current is 2000A, to achieve one-pass welding with a plate thickness of 60mm, a welding current of about 1900A is required. Since the density becomes too high 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. Therefore, 4.8 mm <D ≦ 5.6 mm. - leading electrode current I ₁ and the trailing electrode current I _{2 ratio: (I 2 / I 1)} ≧ 0.9 trailing electrode current is used at a lower setting than the leading electrode current to prevent solidification cracking of the weld metal Many times,
A higher value is desirable for increasing the welding speed, and when the maximum welding current is 2000 A, to secure high efficiency (I ₂ /
I ₁ ) must be at least 0.9.・ Distance between poles: 90 to 120mm In general, the distance between the poles is set so that the solidification form of the molten pool becomes a semi-one pool in order to prevent solidification cracking of the weld metal. Since the pole current is set high, it must be set at a position where the solidification of the weld metal by the leading electrode has advanced further. Therefore, if the thickness is less than 90 mm, the shape tends to cause solidification cracking.
When the value exceeds, the following electrode passes through the molten pool in which the solidification of the slag of the leading electrode has progressed, so that the slag is entrained and the bead appearance is easily disturbed due to the disorder of the molten pool. For this reason, the distance between the electrodes was set to 90 to 120 mm.

The other welding conditions include welding voltage, electrode inclination, protrusion length, and the like. These may be in the range used when performing normal submerged arc welding. 33-45V, 42-55 for trailing pole
About V, the leading electrode is 0-10 °, the trailing electrode is 20-0
°, the protruding length may be 30 to 80 mm from the steel plate surface. The welding speed is a condition that is inevitably determined as a speed required to fill the groove by the welding speed determined by the welding current and the welding material, but is desirably in the range of 15 to 35 cm / min.

The flux used here is Si
O ₂ -MgO-Al ₂ 0 but _3-type iron powder added flux are preferred,
The reason for limiting the numerical values will be described below. · SiO _2: 10~30% SiO ₂ is an important component as the slag forming is not obtained a good bead appearance too elevated melting point of the product slag is less than 10%, while more than 30% If it is contained, the amount of slag increases and the slag removability deteriorates, or the basicity decreases too much and the toughness of the weld metal deteriorates. 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 and the bead appearance. Deteriorates. 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, and 20% If it is contained in excess, the melting point of the slag tends to be too high and the bead appearance tends to deteriorate. CaO: 2 to 10% CaO is an effective component for adjusting the melting point and basicity of slag. However, if it is less than 2%, this effect is poor, and if it exceeds 10%, the slag removability deteriorates. I do.・ 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 improvement of the welding speed is not sufficient, while 40% If it is contained in excess, the bead width tends to be narrow, and a good bead appearance cannot be obtained.・ Metal Si, Mn, Ti, Al: 1 to 10% or more in total It is necessary to add a deoxidizer as a metal component. On the other hand, if the content exceeds 10% in total, the amount of oxygen tends to be too low and the toughness is rather deteriorated.

The reasons for specifying the flux according to the present invention are as follows.
As described above, other components such as flux
The components used in (1) may be added. That
Such components include CaF_Two, BaO, ZrO, B_TwoO_Three, CO_TwoSuch
And CaF_Two, BaO, ZrO, CO _TwoIs less than 5%, B_TwoO_ThreeIs 1%
Each can be added within the following ranges. BaO, Ca
O and ZrO are useful for adjusting slag basicity and melting point.
Although it is an effective component, addition of more than 10%
Harms the peeling property. CO_TwoIs due to the decomposition of carbonate during welding.
To reduce the hydrogen content in the weld metal by reducing the resulting hydrogen partial pressure.
Although it is an effective component to remove gas, it generates gas when it exceeds 5%.
The deterioration of the bead appearance due to this becomes significant.

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. As described above, the present invention relates to a high-efficiency submerged arc welding using iron powder-added flux for a thick steel plate, and in order to obtain an optimal current density of the leading electrode, optimizes a welding current and a wire diameter and welding conditions. A flux suitable for use in conjunction with a welding method is proposed to realize high efficiency submerged arc welding of thick joints, which could not be conventionally performed.

[0018]

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 welding wire shown in Table 1 and a flux having the chemical composition shown in Table 2. Table 4 summarizes the welding results.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

[Table 4]

When the first to fifth embodiments according to the present invention are used,
A joint having good bead appearance without defects under good welding workability was obtained. On the other hand, in Comparative Examples 6 and 9, the wire diameter was large and the current density was lower than the proper condition of the present invention, so that sufficient penetration was not obtained. In Comparative Example 7, since the wire diameter was small and the current density was larger than the appropriate range, stable welding could not be performed, and sufficient penetration was not obtained. In Comparative Example 8, since the wire diameter was thin outside the proper range, if the current density was proper, the welding current was too low, the welding amount was insufficient, and the speed was too slow, resulting in poor penetration. In Comparative Example 10, solidification cracking occurred because the distance between the electrodes was out of the appropriate condition, and in Comparative Example 11, the bead appearance was poor because the flux was not appropriate.

[0024]

As described above, according to the welding method according to the present invention, in one-pass submerged arc welding of a plate thickness of 50 mm or more, a joint having no defect and a good bead appearance can be obtained with high efficiency.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-234369 (JP, A) JP-A-7-68380 (JP, A) JP-A-2-179392 (JP, A) JP-A-61-1986 232067 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 9/18 B23K 35/362 310

Claims (2)

(57) [Claims] 1. A plate thickness of 50 mm using a welding current of 2000 A or less.
In the above-described two-electrode submerged arc welding of a steel sheet with a large heat input, the current density of the leading electrode is 80 to 95 A / mm ² , the diameter D of the wire of the leading electrode is 4.8 mm <D ≦ 5.6 mm, and the leading electrode current I ₁ And the following pole current I ₂ is (I ₂ / I ₁ ) ≧ 0.9, and the distance between the poles is 90 to
A large-heat-input two-electrode submerged arc welding method characterized by welding under the condition of 120 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 according to claim 1, wherein a firing flux for submerged arc welding 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. Two electrode submerged arc welding method.