JP2006272377A - Submerged arc welding method of steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a submerged arc welding method of steel materials, a method that can reduce welding heat input while securing usual penetration and that can also suppress degradation of toughness in a welding heat-affected zone. <P>SOLUTION: In performing submerged arc welding on steel materials using multiple electrodes of two or more electrodes, the electric current of the first electrode is set at ≥800A and the current density at 180-400A/mm<SP>2</SP>. It is desirable that a DC power source is used for the feeding to the first electrode and/or a distance between the centers of wires of the adjacent electrodes is ≤25 mm at a position on the surface of the steel materials, and that an electrode angle α<SB>1</SB>is α<SB>1</SB>=-10 to 10° in the first electrode W<SB>1</SB>and is α<SB>1</SB>=α<SB>i-1</SB>+(5 to 20°) in each electrode W<SB>i</SB>from the second electrode onward, where α<SB>i-1</SB>is the electrode angle of the immediately preceding electrode W<SB>i-1</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a submerged arc welding method for steel materials, and more particularly to a submerged arc welding method for steel materials suitable for pipe making welding of large diameter steel pipes such as UOE steel pipes and spiral steel pipes. As an applied steel material of this invention, the thing of thickness 10-50mm is preferable.

Submerged arc welding of two or more electrodes is applied to pipe making welding (seam welding) of large diameter steel pipes. From the standpoint of improving pipe production efficiency, double-sided single-layer welding, in which the inner surface side is welded with one pass and the outer surface side with one pass, has become common, and highly efficient welding is performed (for example, Patent Documents 1 and 2).
In double-sided single-layer welding, it is necessary to ensure a sufficient penetration depth so that the inner and outer surface weld metals overlap and there is no unmelted part, and welding is generally performed by applying a large current of 1000 A or more. However, since importance is attached to efficiency and defect suppression, there is a problem that the welding heat input becomes too high, and the toughness of the welded portion, particularly the heat affected zone, deteriorates.

  In order to increase the toughness of the welded portion, it is effective to reduce welding heat input. However, unless the heat input is significantly reduced with respect to the heat input of seam welding that is usually performed, it is not possible to obtain a toughness improving effect by clearly reducing the heat input. When the heat input is lowered in such a manner, the welding amount decreases, so that it is necessary to reduce the groove cross-sectional area in accordance with the amount of welding decrease. If it does so, unless further deep penetration welding is performed, the weld metal of the inner and outer surfaces will not overlap, resulting in insufficient penetration. Therefore, it is necessary to overcome the extremely difficult problem of achieving both a significant reduction in input heat input and an increase in penetration depth.

For example, Patent Document 2 proposes a submerged arc welding method in which the penetration depth is increased by increasing the current density in accordance with the electrode diameter. However, in this method, the current and current density are insufficient, and the heat input is greatly increased. It is difficult to achieve both reduction and increase in penetration depth.
JP-A-11-138266 JP-A-10-109171

Conventionally, in pipe-forming welding of large-diameter steel pipes, seam welding has been carried out with a large current and a large heat input in order to obtain a sound weld with high efficiency and no defects. The base metal is melted not only in the plate thickness direction but also in the plate width direction. As a result, a large amount of heat energy is consumed in the melting of the base material portion that does not need to be melted. The toughness of the affected area is deteriorated.
In view of the above problems, the present inventors provide a steel submerged arc welding method capable of reducing welding heat input while ensuring the same penetration as before, and further suppressing toughness deterioration of the weld heat affected zone. For the purpose.

The present inventors have intensively studied to achieve the above-mentioned object, and by supplying arc energy in the plate thickness direction as much as possible, only the necessary penetration depth is secured and the melting of the base material in the plate width direction is suppressed. By doing so, it was found that excessive welding heat input can be omitted and that the toughness of the weld heat affected zone can be improved by the heat input reducing effect. This invention is made | formed based on this knowledge, The summary is as follows.
(Invention Item 1) In submerged arc welding of steel materials with two or more electrodes, welding is performed with the current of the first electrode being 800 A or more and the following current density of 180 to 400 A / mm ² . Submerged arc welding method.

Current density = current / wire cross-sectional area (Invention 2) A method of submerged arc welding of steel according to Invention 1, wherein a DC power source is used to supply power to the first electrode.
(Invention Item 3) The distance between the wire centers at the steel material surface position of adjacent electrodes is 25 mm or less, the following electrode angles are set to -10 to 10 ° for the first electrode, and the immediately preceding electrode for each electrode after the second electrode The electrode angle + (5 to 20 °) of the steel material according to claim 1 or 2, wherein the steel material is a submerged arc welding method.

Electrode angle: an angle formed by the electrode wire with respect to a plane perpendicular to the welding progress direction, 0 ° when the wire is on the plane, and the tip end side of the wire upstream of the rear end side in the welding progress direction A negative angle is given for the case in the case, and a positive angle is given for the opposite case.
(Invention 4) The submerged arc welding of steel according to any one of Inventions 1 to 3, wherein the steel is subjected to groove machining with a groove depth of steel material thickness x 0.3 or less. Method.
(Invention 5) When submerged arc welding is performed on both surfaces of a steel material with multiple electrodes of two or more electrodes, each side of both surfaces is welded by the welding method according to any one of Items 1-4. Submerged arc welding method for steel.

  According to the present invention, it is possible to reduce the welding heat input while maintaining the conventional penetration depth (here, the steel thickness direction component of the distance from the steel surface to the lower end of the weld metal). It becomes possible to obtain excellent toughness in the heat-affected zone. From the manufacturer's side, it becomes possible to use a low-cost steel material whose toughness was not sufficient, and the manufacturing cost can be reduced.

Hereinafter, the reasons for limiting the requirements of the present invention will be described.
As a result of repeated examination by the inventors of the multi-electrode welding experiment, the first electrode has a large current of 800 A or more and the current density (= welding current / wire cross-sectional area) is high. It has been found that welding in which melting of the base material (material to be welded) is suppressed can be performed. It is difficult to obtain deep penetration in the steel thickness direction at currents lower than 800A. In addition, when the current density is lower than 180 A / mm ² , the arc energy density is insufficient and sufficient penetration in the steel thickness direction cannot be obtained. On the other hand, if it exceeds 400 A / mm ^2, it becomes a high current condition, and the wire feeding speed becomes too high. For this reason, the wire feeding device is too burdensome and not realistic. Preferably it is the range of 180-350 A / mm < ² >. In order to perform such high current density welding, it is necessary to reduce the wire diameter. Further, in order to perform high current welding, it is difficult to weld with a normal submerged arc welding machine, and a welding machine that can feed wires at high speed. Need to use. In order to obtain the current density, it is desirable that the wire diameter is 3.2 mm or less, preferably 2.4 mm or less.

With respect to the power supply characteristics of the first electrode, a stable deep penetration can be obtained by using a direct current (constant voltage) power supply that can maintain welding conditions stably without alternation. The polarity is preferably reverse polarity (minus the base metal side) with deep penetration.
The distance between the centers of the wires at the steel material surface position of adjacent electrodes (hereinafter referred to as the distance between the poles) is preferably 25 mm or less. Further, as shown in FIG. 4, the electrode angle α _i of the i-th electrode is set to α ₁ = −10 to 10 ° for the first electrode W ₁ , and α _i = α _i for each electrode W _i after the second electrode. ₋₁ (electrode angle of the immediately preceding leading electrode W _i−1 ) + Δα may be Δα = 5 to 20 °. However, i is an integer greater than or equal to 2, and i = 2-4 is common.

  Since the first electrode performs welding with an extremely high energy density, the arc pressure is high, the molten metal behind the first electrode flows violently and vibrates the molten pool, but the distance between the electrodes is 25 mm or less. Thus, the vibration of the first electrode is set to −10 to 10 °, and the electrode angle of the succeeding electrode is set to the electrode angle of the immediately preceding preceding electrode + (5 to 20 °) (that is, the succeeding electrode). The electrode is tilted 5 to 20 degrees backward as viewed from the front end of the wire with respect to the preceding preceding electrode), thereby relaxing the flow of molten metal from the first electrode, stabilizing the movement of the molten pool, and high quality with few defects Bead.

Moreover, excessive welding heat input can be avoided by setting the groove depth of the base material to steel material thickness × 0.3 or less. If the groove depth exceeds the steel thickness x 0.3, it is necessary to reduce the groove angle in order to reduce heat input. However, welding defects such as slag entrainment and cracking are likely to occur, and penetration will occur. This is not preferable because the variation in depth also increases, resulting in insufficient penetration.
When the present invention is applied to only one side of double-sided and single-sided welding, the effect of the present invention (an effect that enables deep penetration welding) is unlikely to be exhibited.

  After applying the groove processing of the groove shape for large diameter pipe making seam welding shown in FIG. 1 and Table 2 to the steel plate having the thickness, composition and tensile properties shown in Table 1, by multi-electrode submerged arc welding Welded joints were produced by performing welding equivalent to large-diameter pipe-forming seam welding with inner and outer surface layers.

The welding conditions were set for each plate thickness, the inner surface side was constructed under the welding conditions shown in Table 3, and the outer surface side was constructed under the welding conditions shown in Table 4. Using melt flux is the flux with inner and outer surfaces consisting mainly of _{SiO 2 -CaO-CaF 2, 0.07} % in mass% on the wire C, 0.05% Si, 1.5% Mn, the steel composition containing 0.5% Mo A welding wire was applied. Tables 3 and 4 show the observation results of the welds.

All the conditions N1 to N3 on the inner surface side shown in Table 3 are examples satisfying the invention items 1 to 4, and good welding was performed.
Conditions 1 to 7 on the outer surface side shown in Table 4 are examples that satisfy the invention items 1 to 5, and good welding results were obtained. On the other hand, Condition 8 is a comparative example in which the invention items 1 to 4 are satisfied on the inner surface side but the current and current density of the first electrode are insufficient on the outer surface side, and the invention item 1 is not satisfied. Condition 9 is a comparative example in which Invention Items 1 to 4 are satisfied on the inner surface side but the current density of the first electrode is insufficient on the outer surface side and does not satisfy Invention Item 1, resulting in insufficient melting.

  Conditions 10 and 11 are embodiments in which the invention items 1 to 4 are satisfied on the inner surface side, the invention item 1 is satisfied on the outer surface side, and therefore the invention item 5 is also satisfied. However, under condition 10, since the power supply of the first electrode was an AC power supply (not satisfying the invention item 2), the current and voltage of the first electrode were not stable, the beads became irregular, and many slugs were generated. In condition 11, although the invention item 2 is satisfied, the electrode angle of the second electrode is excessive and the distance between the electrodes is long (does not satisfy the invention item 3), so that slag entrainment occurs and the bead width becomes irregular. It was.

  For joints welded under Condition 5 in Table 4, Charpy impact test piece 2 (No. 4 test piece specified in JIS Z 3111) taken from the position of the outer side bond part (shown in Fig. 3) was used. A Charpy impact test was performed in accordance with the metal material impact test method, and the absorbed energy and the ductile fracture surface ratio were determined. The result is shown in FIG. From the figure, it can be seen that very high weld heat affected zone toughness is obtained over a wide temperature range.

  The present invention is not limited to pipe-making welding of large-diameter steel pipes, but can be used in all industries in which steel materials are welded using multi-electrode submerged arc welding.

It is sectional drawing which shows the example of groove shape. It is a Charpy impact characteristic figure which shows an example of the weld joint outer surface side bond part toughness of an Example. It is sectional drawing which shows the Charpy impact test piece collection position. It is a schematic diagram which shows the suitable range of an electrode angle.

Explanation of symbols

1 Steel (base material, eg steel plate)
Electrode angle of 2 Charpy impact test piece 3 Notch 4 weld metal 5 bond portion _{W i} i-th electrode alpha _i i-th electrode

Claims (5)

A submerged arc welding method for steel, characterized in that when submerged arc welding is performed on a steel material with ^two or more electrodes, the first electrode has a current of 800A or more and the following current density is 180 to 400A / mm2.
Current density = current / wire cross-sectional area   2. The method of submerged arc welding of steel material according to claim 1, wherein a DC power source is used for feeding power to the first electrode. The distance between the wire centers at the steel surface position of adjacent electrodes is 25 mm or less, the following electrode angles are -10 to 10 ° for the first electrode, and the electrode angle of the immediately preceding electrode + ( The submerged arc welding method for steel materials according to claim 1 or 2, characterized by being set to 5 to 20 degrees.
Electrode angle: an angle formed by the electrode wire with respect to a plane perpendicular to the welding progress direction, 0 ° when the wire is on the plane, and the tip end side of the wire upstream of the rear end side in the welding progress direction A negative angle is given for the case in the case, and a positive angle is given for the opposite case.   The method of submerged arc welding of steel material according to any one of claims 1 to 3, wherein the steel material is subjected to groove processing with a groove depth of steel material thickness x 0.3 or less.   When submerging arc welding a steel material to a double-sided single layer with two or more electrodes, each side of the both surfaces is welded by the welding method according to any one of claims 1 to 4, wherein the submerged steel material is characterized in that Arc welding method.

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