JP2009214127A - Submerged arc welding method for steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a submerged arc welding method for a steel material which is suitable to use for pipe-making welding of a large diameter steel pipe such as a UOE steel pipe and a spiral steel pipe. <P>SOLUTION: When welding the inside and the outside of a steel plate by one layer welding, in at least one side of internal welding and external welding, welding conditions are selected so that the relationship between plate thickness and bead width which is measured on the surface layer of the steel plate, satisfies expression (1): 0.40≤W<SB>1</SB>/t≤0.65 and the relationship between the plate thickness and the bead width which is measured in a position at the depth of 0.4t from the surface layer of the steel plate, satisfies expression (2): W<SB>2</SB>/t≤0.34 [wherein t is the plate thickness (mm), W<SB>1</SB>is the bead width (mm) which is measured on the surface layer of the steel plate and W<SB>2</SB>is the bead width (mm) which is measured in the position of 0.4t in the plate thickness direction from the surface layer of the steel plate]. <P>COPYRIGHT: (C)2009,JPO&INPIT

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 with two or more electrodes is applied to pipe making welding (seam welding) of large diameter steel pipes. High-efficiency 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 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 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 reduction in heat input 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, the bead width on the surface of the steel sheet becomes small, and the bead width tends to be substantially uniform from the steel sheet surface to the penetration tip. Therefore, the Charpy test piece is sampled so that the notch 3 direction and the plate thickness direction are parallel as shown in 2 of FIG. 2 and the position 7 mm below the surface of the steel plate on the outer surface welding side is at the center of the Charpy test piece to perform the Charpy test. Then, Fusion Line (hereinafter referred to as FL) is oriented in the plate thickness direction, and brittle fracture in the plate thickness direction is likely to progress, and there is a problem that the toughness value tends to be low despite low heat input welding.

  Furthermore, with such a bead shape, there is a problem that welding defects are likely to occur due to slag entrainment.

  An object of this invention is to provide the submerged arc welding method of the steel materials from which the welded joint without a weld defect is obtained, fully obtaining the effect of the welding heat-affected zone toughness improvement by welding heat input reduction.

The present inventors examined the relationship between the bead shape and the weld heat affected zone toughness for the steel submerged arc welded joint, and measured the bead width measured on the surface layer of the steel sheet, and the bead width near the penetration tip and the steel sheet. It was found that an excellent Charpy impact test result (notch position: FL) can be obtained while suppressing the slag entrainment by controlling the ratio of the thickness to the appropriate range. The present invention is based on the above-mentioned knowledge, and the gist thereof is as follows.
1. A submerged arc welding method for steel sheets in which inner and outer surface single layer welding is performed, wherein at least one of the inner surface welding and the outer surface welding, the bead width measured at the steel sheet surface layer satisfies the formula (1) and 0.4 t from the steel sheet surface layer. A submerged arc welding method for a steel sheet, characterized in that the bead width measured at the depth position satisfies the formula (2).
0.40 ≦ W ₁ /t≦0.80 (1)
However, t: board thickness (mm), W ₁ : bead width (mm) measured in the steel sheet surface layer
W ₂ /t≦0.34 (2)
However, t: plate thickness (mm), W ₂ : bead width (mm) measured at a position of 0.4 t in the plate thickness direction from the steel plate surface layer.
A welded joint produced by the welding method described in 2.1.

  According to the present invention, it is possible to obtain a weld bead having no weld defect while sufficiently obtaining the effect of improving the weld heat-affected zone toughness by reducing the welding heat input, and toughness at the weld heat-affected zone (notch position: FL). An excellent welded joint is obtained, which is extremely useful in industry.

In the steel submerged arc welding method according to the present invention, when the steel plate is welded by one-layer inner / outer surface welding, the relationship between the plate thickness and the bead width measured on the surface of the steel plate in at least one of inner surface welding and outer surface welding is as follows. The welding conditions are selected so as to satisfy the formula (1).
0.40 ≦ W ₁ /t≦0.80 (1)
Where t: plate thickness (mm), W ₁ : bead width (mm) measured on the steel sheet surface layer,
When the relationship between the plate thickness t and the bead width W ₁ measured on the surface layer of the steel plate satisfies 0.40 ≦ W ₁ /t≦0.80, slag entrainment is suppressed and a sound weld is obtained. The bead width W ₁ measured on the steel sheet surface layer refers to the bead width on the outer surface that is the surface layer.

In a weld bead where W ₁ /t>0.80, the amount of heat given to the base material is inevitably increased, and the toughness of the weld heat affected zone deteriorates.

On the other hand, in a weld bead satisfying 0.40> W ₁ / t, brittle fracture progresses in the plate thickness direction because FL is oriented in the plate thickness direction with a substantially uniform bead width from the steel plate surface to the penetration tip. It becomes easy to do and a toughness value becomes low. Also, welding defects due to slag entrainment are likely to occur.

Therefore, in addition to the definition of the expression (1), the welding conditions are further selected so as to satisfy the expression (2), and the FL is inclined with respect to the sheet thickness direction in the sheet thickness direction of the steel sheet.
W ₂ /t≦0.34 (2)
According to the formula (2), the bead width W ₂ measured at a position of a depth of 0.4 t from the steel sheet surface layer is defined as W ₂ / t being 0.34 or less. The bead width at the center of the plate thickness becomes narrow.

  The present invention can be applied to both inner surface welding and outer surface welding, and is preferably applied to both inner surface welding and outer surface welding. The welding conditions for obtaining a bead width that satisfies the provisions of the present invention are determined in advance using a test material.

  The API standard X70 grade steel plate having the thickness and composition shown in Table 1 was subjected to groove processing with the groove dimensions shown in Table 2 in the groove shape shown in FIG.

  A plurality of butt-welded joints were manufactured by performing four-electrode submerged arc welding of inner and outer surface one-layer welding under the various welding conditions shown in Table 4 on the inner surface side and various welding conditions shown in Table 4 on the outer surface side.

  About the obtained welded joint, the Charpy impact test was done based on the metal material impact test method of JISZ2242, and the toughness of the welded part was evaluated.

  The Charpy impact test piece (No. 4 test piece specified in JIS Z 3111) has a notch 3 direction parallel to the plate thickness direction and a position 7 mm below the steel plate surface on the outer surface welding side as shown in 2 of FIG. The sample was collected so as to be in the center of the test piece, and three tests were performed at −30 ° C. to determine the average value of Charpy absorbed energy. The notch position: FL was a position where the ratio of the weld metal to the base material (welding heat affected zone) at the notch bottom was 50% -50%.

  Table 5 shows the shape of the outer surface side weld, the Charpy impact test result, and the presence or absence of welding defects. Condition No. 1 to 5 are examples of the present invention, and excellent toughness could be obtained in the weld heat affected zone while obtaining a sound bead.

On the other hand, Condition No. No. 6 was W ₁ /t<0.40, and did not satisfy the formula (1) of claim 1, resulting in insufficient penetration. Condition No. Although No. 7 had no welding defects, W ₂ /t>0.34, which did not satisfy the formula (2) of claim 2 and the impact value was low. Condition No. No. 8 was W ₂ /t>0.34 and did not satisfy the formula (2) of claim 2, and slag entrainment occurred and the impact value was low. Condition No. No. 9 was W ₁ /t>0.80 and did not satisfy the formula (1) of claim 1 and the impact value was low.

The figure explaining the groove shape of an Example. The figure explaining the Charpy impact test piece collection position of an Example.

Claims (2)

A submerged arc welding method for steel sheets in which inner and outer surface single layer welding is performed, wherein at least one of the inner surface welding and the outer surface welding, the bead width measured at the steel sheet surface layer satisfies the formula (1) and 0.4 t from the steel sheet surface layer. A submerged arc welding method for a steel sheet, characterized in that the bead width measured at the depth position satisfies the formula (2).
0.40 ≦ W ₁ /t≦0.80 (1)
However, t: board thickness (mm), W ₁ : bead width (mm) measured in the steel sheet surface layer
W ₂ /t≦0.34 (2)
However, t: plate thickness (mm), W ₂ : bead width (mm) measured at a position of 0.4 t in the plate thickness direction from the steel plate surface layer.   A welded joint produced by the welding method according to claim 1.

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