JP5223369B2 - Multi-electrode submerged arc welding method for steel - Google Patents

Description

  The present invention relates to a multi-electrode submerged arc welding method for steel materials, and more particularly, to a method suitable for pipe making welding of large-diameter steel pipes such as UOE steel pipes and spiral steel pipes having a base metal thickness of 10 to 50 mm.

  For seam welding of large-diameter steel pipes, double-sided single-layer welding, in which the inner surface side is welded in one pass and the outer surface side in one pass, is generally used by multi-electrode submerged arc welding of three or more electrodes.

  Double-sided single-layer welding is a highly efficient welding method, but it is necessary to secure a sufficient penetration depth so that the inner and outer weld metals overlap and there are no unmelted parts. It is common to do.

  However, if the heat input is increased, the weld heat affected zone structure becomes coarse and toughness degradation occurs, and if the heat input is reduced, welding defects such as slag entrainment increase, so welding is possible even at low heat input. A seam welding method for large-diameter steel pipes, which is excellent in preventing the occurrence of defects, has been proposed.

  Patent Document 1 relates to a multi-electrode sommered arc welding method, in order to obtain a sufficient penetration depth and a good bead shape, a bead shape is prepared using a large-diameter wire for the last row electrode, and a DC power source is used for the preceding electrode. A method is disclosed that uses and increases the current density with a thin wire to obtain a penetration depth.

  However, in the method described in Patent Document 1, the penetration depth is obtained and the shape of the bead surface is improved, but the slag does not sufficiently float from the bottom of the weld metal deeply dug by the preceding electrode and remains as a defect. Has been pointed out.

  Patent Document 2 relates to a pipe making welding method for large-diameter steel pipes. The inner surface side welding is performed by multi-electrode submerged arc welding with small heat input, and the outer surface side welding is performed by multi-layer welding by gas metal arc welding and submerged arc welding. A method for producing a joint having high-performance weld properties while ensuring suppression and shape is described.

However, since the welding method described in Patent Document 2 requires that the inner surface side welding be a small heat input welding and the outer surface side welding be a two-layer welding, the efficiency is extremely low and it is difficult to apply to actual operation.
JP-A-52-82652 JP 58-32583 A

  As mentioned above, it is difficult to say that the seam welding method for large-diameter steel pipes, which can withstand practical use and is excellent in preventing the occurrence of welding defects even at low heat input, is not fully completed. In addition, in order to obtain a sound weld with no defects, seam welding with a large current and a large heat input is currently being carried out.

  As a result, it is becoming difficult to ensure good toughness in weld metal and weld heat affected zone with the recent increase in strength of line pipes such as realization of APIX120.

  Therefore, in view of the above problems, the present invention aims to provide a steel multi-electrode submerged arc welding method that reduces welding heat input while ensuring the conventional penetration and further suppresses the occurrence of welding defects. And

  In the case of multi-electrode submerged arc welding with 3 or more electrodes, the present inventors have already used a thin wire to obtain current and current density (= current / wire cross-sectional area) in order to obtain a penetration depth at the weld. It has been clarified that the increase is effective (for example, JP-A-2006-272377). This is because the gouging force on the base material due to the concentration of the arc is increased due to the increase in current and current density, and the effect is maximized especially when the current values and current densities of the preceding 1 and 2 electrodes are above a certain value.

  However, although deep penetration can be obtained by increasing the current and current density, since the penetration is deep, the slag generated by the slag metal reaction occurring in the weld metal is not sufficiently lifted and the incidence of defects increases. A trend was observed.

Therefore, the present inventors have intensively studied to solve the above problems, and obtained the following knowledge.
(1) When deep penetration is obtained by increasing the current density, a strong arc force generates a strong metal flow in the molten pool formed by multiple electrodes, and the turbulence causes slag entrainment during solidification.

  (2) When a high current and current density are applied to the preceding two poles and the molten pool is not a single pool but a semi-one pool, the strong flow in the molten pool becomes stable and slag entrainment during solidification is prevented. The

  (3) Furthermore, even when the amount of penetration decreases due to the metal pushed out from the trailing electrode when gouging the base material with the arc force, the penetration depth can be stably secured by using the semi-1 pool.

The present invention has been made by further study based on the above knowledge, that is, the present invention,
1. In submerged arc welding of steel materials with three or more electrodes, a DC power source is used to supply power to the first electrode, and the current density of the first electrode is set to 287 A / mm ² or more and 382 A / mm ² or less. the current density of the 154A / mm ² or more 271A / mm ² or less, 27 mm or more 30mm or less in the steel material surface position electrode distance between the first electrode and the second electrode, between the electrodes of the second electrode and the third electrode A multi-electrode submerged arc welding method for steel, wherein the distance is 15 mm or more and 18 mm or less .
2. The following current 1150A or 1300A of the first electrode, a multi-electrode submerged arc welding method for steel 1, wherein the performing the current of the second electrode 850A or 950A or less.
3. The multi-electrode submerged arc welding method for steel according to 1 or 2, wherein welding with the first electrode is performed with a wire diameter of 3.2 mm or less.
4). A multi-electrode submerged arc welding method for a steel material, wherein the inner surface and the outer surface of the steel material are each welded by multi-electrode submerged arc welding according to any one of 1 to 3.

  According to the present invention, a multi-electrode submerged arc welding method is obtained that reduces welding heat input while ensuring penetration as before, and further suppresses the occurrence of welding defects. The high-strength steel pipe can be manufactured with high productivity and is extremely useful in industry.

Hereinafter, the reasons for limiting the requirements of the present invention will be described.
[Welding power source]
In the present invention, in a multi-electrode submerged arc welding method having three or more electrodes, a DC power source is used for feeding power to the first electrode. The polarity may be either positive polarity or reverse polarity, and is not particularly defined.

When a DC power source is used for feeding power to the first electrode, a sufficient penetration depth can be obtained even with a small heat input. After the second electrode, it is desirable to use an AC power supply so that the mutual arcs do not interfere with each other.
[Welding current]
Welding with the first electrode is performed at a current density of 250 A / mm ² or more, and welding with the second electrode is performed at a current density of 150 A / mm ² or more.

  In the case of multi-electrode submerged arc welding with three or more electrodes, the penetration by the first electrode and the second electrode has a great influence on the penetration shape of the weld, so the current density (= welding current / wire cross-sectional area) of both is specified. .

When the current density of the first electrode is less than 250 A / mm ^{2 and} the current density of the second electrode is less than 150 A / mm ² , the arc energy density is insufficient and sufficient penetration in the thickness direction of the steel cannot be obtained. .

  Further, in order to perform such high current density welding, it is necessary to reduce the wire diameter. In order to obtain the current density, the wire diameter is set to 3.2 mm or less, preferably 2.4 mm or less. The welding current is desirably 1000 A or more, and the welding current of the second electrode is desirably 600 A or more.

  As the welding current increases, it is necessary to increase the wire feeding speed. As a result, a load is applied to the wire feeding device, and stable wire feeding becomes difficult. Therefore, the upper limit of the welding current is appropriately selected according to the capability of the wire feeding device of the welding machine to be used.

[Distance between electrodes]
In the present invention, one of a plurality of inter-electrode distances (distances between the centers of adjacent wires) is 23 mm or more at the steel material surface position and 20 mm or less between the remaining electrodes. For example, in the case of four electrodes, one of the three electrode distances may be 23 mm or more and the remaining two may be 20 mm or less, and the electrode distance of 23 mm or more may be the distance between the first electrode and the second electrode, -Between the third electrode and between the third electrode and the fourth electrode Since the leading electrode performs welding with extremely high energy density, the arc pressure is high and the molten metal behind the arc is intense. It flows backward, and the weld pool is vibrated to entrain slag and residue on the groove surface and cause defects.

  In view of this, in the present invention, the shape of the molten pool is a semi-1 pool in which a part of the bottom surface of the molten pool is curled and shallow so that the molten metal flows gently along the bottom surface in the molten pool. Semi 1 pool refers to a generally gourd-like shape where two molten pools are connected.

  For this reason, one of the interelectrode distances at the steel material surface position is 23 mm or more and the remaining interelectrode distance is 20 mm or less between the multiple electrodes of three or more electrodes. A semi-pool pool can be obtained, and it is possible to suppress the occurrence of defects while ensuring deep penetration.

  When the distance between all the poles is less than 23 mm, the bottom surface of the molten pool has an arc shape and defects are likely to occur, and the depth of penetration may be reduced by the flow of metal from the trailing electrode.

  On the other hand, when the distance between two or more electrodes is 23 mm or more, the weld pool becomes too large, and the solidification rate at the bottom of the weld metal becomes too fast, so that the number of defects increases remarkably.

  According to the present invention, a deeply welded bead with small heat input for pipe making is obtained, and the occurrence of defects is less than that of conventional ones. Therefore, seam welding of a high-strength steel pipe that is particularly thick and requires high toughness. This is an effective welding method for parts.

  In other words, by reducing heat input to obtain high toughness, a decrease in yield due to an increase in the occurrence of defects, and because of the fact that steel materials must be built with low components, a heat treatment with extremely poor production efficiency is required. Although it was unavoidable, the present invention made it possible to easily produce a thick material having high strength and high toughness.

  When the present invention is used for seam welding (double-sided single-layer welding) of a UOE steel pipe, the effect of the present invention (effect of enabling deep penetration welding) when applied to only one of the inner surface and the outer surface. It is preferable to apply to both sides.

  A UOE steel pipe was prepared by a normal process using steel plates having chemical components and mechanical properties shown in Table 1. The groove shape of seam welding shall be as shown in FIG.

  Seam welding was performed by three-electrode submerged arc welding and four-electrode submerged arc welding.

  Table 3 shows the welding conditions of 3-electrode submerged arc welding, the presence or absence of welding defects, and the visual results of the bead appearance. Tables 4 and 5 show the welding conditions of 4-electrode submerged arc welding, the presence or absence of welding defects, and the visual results of the bead appearance. . The presence or absence of welding defects and the penetration status were confirmed by X-ray inspection.

  The electrode angles in the table are shown in FIG. FIG. 3 shows the sampling position of the specimen 2 of the Charpy impact test for determining the FL toughness (vTrs) of the UOE steel pipe 1 in the table, and the BOND 5 of the welded part 4 on the final side (outer surface side) is set as the notch position 3. .

  In both the three-electrode submerged arc welding and the four-electrode submerged arc welding, in the example of the present invention, a good weld without slag entrainment or insufficient penetration was obtained.

  On the other hand, in the comparative example in which the distance between the electrodes and / or the current density of the first and second electrodes is outside the range of the present invention, slag entrainment and insufficient penetration were observed.

Sectional drawing which shows a groove shape. The figure explaining an electrode angle. Sectional drawing which shows the Charpy impact test piece collection position.

Explanation of symbols

1 UOE steel pipe 2 Test piece 3 Notch position 4 Welded part 5 BOND

Claims (4)

In submerged arc welding of steel materials with three or more electrodes, a DC power source is used to supply power to the first electrode, and the current density of the first electrode is set to 287 A / mm ² or more and 382 A / mm ² or less. the current density of the 154A / mm ² or more 271A / mm ² or less, 27 mm or more 30mm or less in the steel material surface position electrode distance between the first electrode and the second electrode, between the electrodes of the second electrode and the third electrode A multi-electrode submerged arc welding method for steel, wherein the distance is 15 mm or more and 18 mm or less . The following current 1150A or 1300A of the first electrode, a multi-electrode submerged arc welding method of the steel according to claim 1, wherein the current of the second electrode and performs at least 850A 950A or less.   The multi-electrode submerged arc welding method for steel according to claim 1 or 2, wherein welding with the first electrode is performed with a wire diameter of 3.2 mm or less.   A multi-electrode submerged arc welding method for a steel material, wherein the inner surface and the outer surface of the steel material are each welded by multi-electrode submerged arc welding according to any one of claims 1 to 3.

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