JP5742090B2 - Submerged arc welding method for steel with excellent toughness of weld heat affected zone - Google Patents

Description

  The present invention relates to a 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.

  Submerged arc welding of two or more electrodes is applied to pipe making welding (seam welding) of large diameter steel pipes, and double-sided single-layer welding in which the inner surface side is welded with one pass and the outer surface side is welded with one pass from the viewpoint of improving pipe production efficiency. High-efficiency welding is performed (for example, Patent Documents 1 and 2).

  In double-sided single-layer welding, it is necessary to secure a sufficient penetration depth so that the inner surface weld metal and the outer surface weld metal overlap and there is no unmelted portion, so welding is generally performed by applying a large current of 1000 A or more. However, emphasis is placed on the welding efficiency and the suppression of defects, the welding heat input becomes too high, and the toughness of the welded portion, particularly the heat affected zone, tends to deteriorate.

  In order to increase the toughness of welds, it is effective to reduce the heat input of welding, but if the heat input is not significantly reduced compared to the heat input of seam welding that is usually performed, the effect of improving the toughness is It is not clear, and if the heat input is greatly reduced, the welding amount also decreases, so the groove cross-sectional area needs to be reduced in accordance with the amount of decrease in the welding amount. For this reason, unless further deep penetration welding is performed, the weld metals on the inner and outer surfaces do not overlap, increasing the risk of insufficient penetration.

  Therefore, increasing the toughness of the welded portion requires both a significant reduction in input heat input and an increase in penetration depth, and various proposals have been made so far, but it is extremely difficult to achieve.

  For example, Patent Document 2 proposes a submerged arc welding method in which the current density is increased in accordance with the electrode diameter and the penetration depth is increased. However, the current and current density are insufficient for recent specifications. It is difficult to achieve both a significant reduction in heat input and an increase in penetration depth.

  Patent Document 3 proposes a submerged arc welding method with a high current and a further high current density. By supplying arc energy in the plate thickness direction as much as possible, only the necessary penetration depth is secured, and the steel width By suppressing the melting of the base material in the direction, excessive welding heat input is omitted, and both heat input reduction and deep penetration are achieved.

JP 11-138266 A JP-A-10-109171 JP 2006-272377 A

  However, in the submerged arc welding method described in Patent Document 3, although both heat input reduction and deep penetration can be achieved, the bead width on the steel sheet surface is small and tends to be a substantially uniform bead width from the steel sheet surface to the penetration tip. That is, since Fusion Line (hereinafter referred to as FL) is oriented in the plate thickness direction, brittle fracture in the plate thickness direction is likely to progress, and there is a problem that the toughness value tends to be lowered despite low heat input welding.

  The present invention provides a submerged arc welding method for a steel material that provides excellent toughness in the weld heat affected zone on both the inner and outer surfaces while obtaining sufficient penetration with low heat input when submerged arc welding of the steel material from the inner and outer surfaces. With the goal.

  The present inventors fabricated inner and outer surface welded joints of steel using various welding conditions in submerged arc welding, and investigated the weld metal cross-sectional shape, the weld metal cross-sectional area, and the toughness of the weld heat affected zone.

As a result, by properly controlling the weld metal cross-sectional area of the inner and outer surfaces according to the plate thickness, the bead width on the steel plate surface is expanded while obtaining sufficient penetration, and the weld heat affected zone (notch position FL) on both the inner and outer surfaces. ) Found that excellent toughness can be obtained. The present invention has been made by further study based on the obtained knowledge, and the gist thereof is as follows.
1. When the inner and outer surfaces further welding steel having a groove in submerged arc welding, satisfies the sum of the inner surface weld metal cross sectional area S ₁ and the outer surface weld metal cross sectional area S ₂ is (1), and the inner surface weld metal cross area S ₁ is (2), the outer surface weld metal cross sectional area S ₂ is excellent in toughness of the heat affected zone characterized by satisfying the expression (3), submerged arc welding method of the steel.
0.40 ≦ (S ₁ + S ₂ ) / t ² ≦ 0.80 (1)
S ₁ / t ² ≦ 0.35 (2)
S ₂ / t ² ≦ 0.45 (3)
Where t: steel plate thickness (mm), S ₁ : inner weld metal cross-sectional area (mm ² ) in a weld cross-section macro perpendicular to the welding direction, excluding a portion that overlaps with the outer weld metal after outer welding, S ₂ : Cross section area of outer surface weld metal (mm ² ) in the weld section cross-section macro perpendicular to the welding direction
A welded joint produced by the welding method described in 2.1.

  According to the present invention, a welded joint having excellent toughness in the weld heat affected zone on both the inner and outer surfaces can be obtained while obtaining sufficient penetration according to the plate thickness of the steel material, which is extremely useful industrially.

The figure explaining groove shape. The figure explaining the sampling position of a Charpy impact test piece.

In the steel submerged arc welding method according to the present invention, when welding the inner surface side and the outer surface side of the steel material, the inner surface weld metal cross-sectional area (S ₁ ) and the outer surface weld metal cross-sectional area (S ₂ ) so as not to cause insufficient penetration. Welding conditions are selected so that the sum of and satisfies equation (1).
0.40 ≦ (S ₁ + S ₂ ) / t ² ≦ 0.80 (1)
Where t: steel plate thickness (mm), S ₁ : inner weld metal cross-sectional area (mm ² ) in a weld cross-section macro perpendicular to the welding direction, excluding a portion that overlaps with the outer weld metal after outer welding, S ₂ : Cross section area of the outer surface weld metal (mm ² ) in the weld cross section macro perpendicular to the welding direction.

If the sum of the inner surface weld metal cross-sectional area (S ₁ ) and the outer surface weld metal cross-sectional area (S ₂ ) is less than 0.40 × t ² , the inner surface and / or the outer surface welding may not have sufficient penetration depth. The weld metal and the outer surface weld metal do not overlap, and a sound weld bead cannot be obtained. The preferred range is from 0.40 to 0.60.

Further, in order to prevent excessive welding heat input, the welding conditions are set so that the inner surface weld metal cross-sectional area (S ₁ ) and the outer surface weld metal cross-sectional area (S ₂ ) satisfy the expressions (2) and (3). Select.
S ₁ / t ² ≦ 0.35 (2)
S ₂ / t ² ≦ 0.45 (3)
If the inner surface weld metal cross-sectional area (S ₁ ) exceeds 0.35 × t ² , the welding heat input becomes excessive in the inner surface welding, and deterioration of the toughness of the weld heat affected zone becomes a problem. The preferred range is from 0.20 to 0.30. Note that the sum of the inner surface weld metal cross-sectional area (S ₁ ) and the outer surface weld metal cross-sectional area (S ₂ ) is 0.80 × t ² or less from the equations (2) and (3).

Similarly, if the outer surface weld metal cross-sectional area (S ₂ ) exceeds 0.45 × t ² , the welding heat input becomes excessive in the outer surface welding, and the deterioration of the toughness of the weld heat affected zone becomes a problem. The preferred range is from 0.25 to 0.40.

When carrying out the present invention, a test material having the same thickness as that of the main welding is welded under various conditions in advance, and the relationship between the heat input and the weld metal cross-sectional area is obtained, and S ₁ and S ₂ are Welding conditions that satisfy Equations (1), (2), and (3) are selected. It is desirable to apply high current density welding conditions to the leading electrode so that the inner surface weld metal and the outer surface weld metal overlap.

  Moreover, this invention is the welded joint produced with the welding method mentioned above.

  1 is applied to a steel sheet having a thickness of 28, 33, and 38.1 mm having chemical components shown in Table 1, and then the inner and outer surface one-layer welding is performed under the welding conditions shown in Table 3. Electrode submerged arc welding was performed to produce a welded joint. Table 2 shows the groove dimensions.

  A Charpy impact test piece (No. 4 test piece specified in JISZ3111) is taken from the manufactured joint, and a Charpy impact test (notch position: FL, test temperature: −30 ° C.) according to the metal material impact test method of JISZ2242. And the absorbed energy (average value of three) was determined.

  FIG. 2 shows the sampling position of the Charpy impact test piece 2. With FL5 of the welded portion 4 as a notch position, the notch 3 is parallel to the plate thickness direction, and the position of 7 mm below the surface of the steel plate 1 is the center of the Charpy impact test piece 2 for each of inner surface welding and outer surface welding. Collected. Table 4 shows the results of the Charpy impact test (upper: inner surface side, lower: outer surface side) and the observation results of the weld metal cross-sectional shape.

  In the present invention example (Condition Nos. 1 to 5), the weld metal cross-sectional area of inner and outer surface single-layer welding was controlled, so that a sound weld bead with sufficient penetration depth was obtained, and excellent toughness was obtained in the weld heat affected zone. I was able to do it.

  On the other hand, in the comparative examples (Condition Nos. 8 and 9), the sum of the weld metal cross-sectional areas of the inner and outer surface single-layer welding was small and the expression (1) was not satisfied, resulting in insufficient penetration.

  In the comparative example (condition No. 6), the inner-surface weld metal cross-sectional area did not satisfy the formula (2), and the toughness of the inner-surface weld heat-affected zone deteriorated. In the comparative example (Condition No. 7), the outer surface weld metal cross-sectional area did not satisfy the formula (3), and the toughness of the outer surface weld heat affected zone was deteriorated.

1 Steel plate 2 Charpy impact test piece 3 Notch 4 Welded part 5 FL

Claims (2)

When the inner and outer surfaces further welded steel provided with X-shaped groove in the submerged arc welding of two or more electrodes,
The sum of the inner surface weld metal cross sectional area S ₁ and the outer surface weld metal cross sectional area S ₂ satisfies the expression (1), and the inner surface weld metal cross sectional area S ₁ is (2), the outer surface weld metal cross sectional area S ₂ ( 3) satisfies the equation,
The current density of the first electrode is 265 A / mm ² or more,
The heat input is 9.9 (kJ / mm) or less,
The welding heat affected zone, wherein the Charpy impact value vE-30 of the inner surface welding heat affected zone is 143 (J) or more, and the Charpy impact value vE-30 of the outer surface welding heat affected zone is 97 (J) or more. Submerged arc welding method for steel with excellent toughness.
0.42 ≦ (S ₁ + S ₂ ) / t ² ≦ 0.77 (1)
S ₁ / t ² ≦ 0.33 (2)
S ₂ / t ² ≦ 0.44 (3)
Where t: steel plate thickness (mm), S ₁ : inner weld metal cross-sectional area (mm ² ) in a weld cross-section macro perpendicular to the welding direction, excluding a portion that overlaps with the outer weld metal after outer welding, S ₂ : Cross section area of outer surface weld metal (mm ² ) in the weld section cross-section macro perpendicular to the welding direction   A welded joint produced by the welding method according to claim 1.

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