JP5239900B2 - 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.

  Submerged arc welding with two or more electrodes is applied to pipe making welding (seam welding) of large-diameter steel pipes. From the viewpoint 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 is welded with one pass, 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, emphasizing efficiency and defect suppression, 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 is also reduced, so that the groove cross-sectional area needs to be reduced in accordance with the amount of welding reduction. 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, although the submerged arc welding method described in Patent Document 3 can achieve both heat input reduction and deep penetration, there is a problem that the bead width on the steel sheet surface becomes small and undercut is likely to occur.

  The present invention provides a multi-electrode submerged arc welding method for steel, which can provide a sound weld bead without undercut while obtaining sufficient penetration with small heat input when submerging arc welding of steel from both sides with three or more electrodes. The purpose is to do.

  The inventors made double-sided weld joints of steel under various welding conditions by submerged arc welding with multiple electrodes, and investigated the weld metal cross-sectional shape and the appearance of the beads.

As a result, it was found that by properly controlling the current of the first electrode and the last electrode, the bead width on the steel sheet surface was widened while obtaining sufficient penetration, and a healthy bead without undercut was obtained. . The present invention has been made by further study based on the obtained knowledge, and the gist thereof is as follows.
1. In submerged arc welding method for a steel material of duplex-layer welding by 4 electrodes, the current density of the first electrode is a (1), the current density of the last electrode satisfy formula (2), and first A method of submerged arc welding of steel, wherein the current of the electrode and the current of the last electrode satisfy the expression (3).
D _L ≧ 220 (1)
80 ≦ D _T ≦ 120 (2)
I _T / I _L ≧ 0.50 (3)
Here, D _L : current density of electrode of first electrode (A / mm ² ), D _T : current density of last electrode (A / mm ² ), I _L : current of first electrode (A), I _{T is} the current (A) of the last electrode, and the current density is a value obtained by dividing the welding current by the cross-sectional area of the welding wire.

  According to the present invention, a sound bead having no undercut is obtained while obtaining a sufficient penetration with a small heat input, which is extremely useful industrially. Moreover, the effect of reducing extra height by increasing a bead width is also acquired.

The figure which shows a groove shape.

  In the multi-electrode submerged arc welding method of steel materials according to the present invention, each of inner surface welding and outer surface welding in the case of performing double-sided single-layer welding on a steel material having a plate thickness of 20 mm to 40 mm with an inner and outer surface total heat input of about 70 to 160 kJ / cm. The target is characterized by adjusting welding conditions so as to prevent poor penetration at the first electrode in welding of three or more electrodes and to obtain a beautiful bead appearance at the last electrode. Conventionally, steel materials having a thickness of 20 mm to 40 mm are generally welded at a total heat input of about 80 to 200 kJ / cm on the inner and outer surfaces.

  In the present invention, the wire diameter and welding current of the first electrode and the last electrode are set so that the current density of the first electrode satisfies the equation (1) and the current density of the last electrode satisfies the equation (2). Set.

When the current density of the first electrode is less than 220 (A / mm ² ), insufficient melting occurs, so that the current density is set to 220 (A / mm ² ) or more.

  In such a case, the bead width tends to be small in the surface appearance of the bead and a humping bead tends to be formed. Therefore, the current density of the last electrode is set to satisfy the expression (2).

Further, in the present invention, in order to reliably obtain the deep penetration welding effect by the first electrode and the effect of suppressing the undercut and humping bead by the last electrode, the current of the first electrode and the current of the last electrode are obtained. Is set so as to satisfy the expression (3).
D _L ≧ 220 (1)
80 ≦ D _T ≦ 120 (2)
I _T / I _L ≧ 0.50 (3)
Here, D _L : current density of electrode of first electrode (A / mm ² ), D _T : current density of last electrode (A / mm ² ), I _L : current of first electrode (A), I _{T is} the current (A) of the last electrode, and the current density is a value obtained by dividing the welding current by the cross-sectional area of the welding wire.

After processing the groove shown in Fig. 1 on steel plates with thicknesses of 25.4 mm and 38.1 mm, multi-electrode submerged arc welding of double-sided single-layer welding was performed under various welding conditions to produce welded joints, and bead appearance And the penetration depth was investigated. Table 1 shows groove dimensions (θ1: outer surface groove angle, θ2: inner surface groove angle, 1: outer surface groove depth, 2: inner surface groove depth in FIG. 1), and Table 2 shows inner surface welding conditions. Table 3 shows the outer surface welding conditions. In Tables 2 and 3, _DL indicates the current density of the first electrode, and _DT indicates the final current density.

  Table 4 shows the results of investigating the bead appearance and penetration depth (bead cross-sectional shape in the table) in inner surface welding, and Table 5 shows the case of outer surface welding. The penetration depth was measured by measuring the distance from the steel sheet surface to the penetration tip.

  From Table 4, good bead appearance and bead cross-sectional shape are obtained under the welding conditions (inner surface welding conditions N1, N2) satisfying the provisions of the present invention.

  In Table 5, no. Nos. 1 to 5 are examples of the present invention, satisfying the formulas (1), (2) and (3), and a sound bead having no undercut was obtained while obtaining sufficient penetration with a small heat input.

  On the other hand, no. 6 to 20 are comparative examples. In 6 to 10, the current density of the first electrode was low and the formula (1) was not satisfied, and the penetration depth was insufficient. No. In Nos. 11 to 15, the current density of the last electrode was low and did not satisfy Equation (2), and undercut occurred.

  No. In 16 and 17, the current density of the last electrode was high and did not satisfy the formula (2), and humping beads were generated. No. No. 18 did not satisfy the formulas (1) and (2), and insufficient melting and undercut occurred. No. In 19 and 20, the current ratio between the first electrode and the last electrode did not satisfy the expression (3), and a humping bead occurred.

1: outer surface groove depth 2: inner surface groove depth θ1: outer surface groove angle θ2: inner surface groove angle

Claims (1)

In submerged arc welding method for a steel material of duplex-layer welding by 4 electrodes, the current density of the first electrode is a (1), the current density of the last electrode satisfy formula (2), and first A method of submerged arc welding of steel, wherein the current of the electrode and the current of the last electrode satisfy the expression (3).
D _L ≧ 220 (1)
80 ≦ D _T ≦ 120 (2)
I _T / I _L ≧ 0.50 (3)
Here, D _L : current density of electrode of first electrode (A / mm ² ), D _T : current density of last electrode (A / mm ² ), I _L : current of first electrode (A), I _{T is} the current (A) of the last electrode, and the current density is a value obtained by dividing the welding current by the cross-sectional area of the welding wire.

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