JP2014073523A - Submerged arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submerged arc welding method capable of obtaining stably a high-toughness weld heat affected zone, when performing single-layer welding on both surfaces of a thick steel plate.SOLUTION: After performing tack-welding from the upper surface side, in submerged arc welding using two or more electrodes, welding on the lower surface side is performed in such a condition that the wire diameter of a first electrode is 2.4-3.2 mm and a welding current is 1,000 A or higher, and further in the submerged arc welding using two or more electrodes, welding on the upper surface side is performed in such a condition that the wire diameter of the first electrode is 4.0-6.4 mm.

Description

  The present invention relates to a submerged arc welding method for steel plates.

Submerged arc welding used when welding steel sheets is widely used as a highly efficient welding technique because it can supply a large current to increase the penetration depth and the amount of wire welding. In particular, in the submerged arc welding of thick steel plates, it is possible to employ multiple electrodes and weld the lower surface side and the upper surface side in one pass each (so-called double-sided single layer welding).
In double-sided single-layer welding of steel sheets, it is necessary to secure a depth of penetration so that the weld metal on the lower surface side and the weld metal on the upper surface side are sufficiently overlapped, and no unmelted portion is formed. Is generally performed by welding (for example, Patent Documents 1 and 2).

Further, since it is necessary to form a wide bead in order to suppress surface defects such as undercuts, adjustment of welding conditions such as increasing the voltage is also performed.
However, increasing the current or voltage causes an increase in welding heat input, resulting in a problem that the toughness of the weld heat affected zone deteriorates. In order to improve the toughness of the weld heat-affected zone with respect to such a problem, a technique for improving the characteristics of the steel sheet (for example, Patent Documents 3, 4, and 5), a technique for using a thin wire in welding construction ( For example, Patent Documents 6 and 7), techniques for controlling the bead shape (for example, Patent Documents 8 and 9), and the like have been studied.

  However, it is difficult for the techniques disclosed in Patent Documents 3 to 9 to stably increase the toughness of the weld heat affected zone. In other words, the weld heat affected zone (especially the coarse grain region) when welding the lower surface side is heated again by welding on the upper surface side. Therefore, when evaluating toughness in the Charpy impact test, The test results vary greatly depending on the positional relationship between the weld heat affected zone and the Charpy impact test piece. Therefore, even if double-sided single-layer welding of steel sheets is performed under the same welding conditions, the toughness evaluation varies in the material test after welding.

Japanese Patent Laid-Open No. 11-138266 Japanese Patent Laid-Open No. 10-109171 JP 2002-146471 A JP 2004-52104 A JP 2009-91653 A JP 2006-272377 A JP 2009-241128 JP 2010-274275 A JP 2010-274276 A

  An object of the present invention is to provide a submerged arc welding method capable of stably obtaining a high toughness weld heat-affected zone when performing butt welding of steel plates, particularly double-sided single layer welding of thick steel plates.

  The inventor conducted submerged arc welding of the steel sheet under various welding conditions, and investigated the toughness of the weld heat affected zone of the welded joint. As a result, the shape of the boundary line (hereinafter referred to as the melting boundary line) between the weld metal formed by solidification after melting and the weld heat affected zone formed on the unmelted steel sheet is referred to as the lower surface side and the upper surface side, respectively. It has been found that by controlling properly, it is possible to stably obtain excellent toughness of the weld heat affected zone by double-sided single-layer welding.

  In particular, in the case of a thick steel plate having a thickness of 30 mm or more, when both surfaces of the steel plate are welded using a wire having a large wire diameter (hereinafter referred to as a thick wire) as in the conventional case, as shown in FIG. The angle θ2 (°) formed between the boundary line 4 and a line perpendicular to the surface of the steel sheet 1 and the angle θ1 (°) formed between the molten boundary line 5 on the upper surface side and a line perpendicular to the surface of the steel sheet 1 are both small. . That is, since the lower boundary side melting boundary line 4 and the upper boundary side melting boundary line 5 are both formed substantially perpendicular to the surface of the steel plate 1, the Charpy impact test piece for evaluating the toughness of the weld heat affected zone It becomes extremely difficult to stably control the arrangement of the sampling position (that is, the notch position of the test piece) and the position of the melting boundary line. As a result, it was found that the dispersion of data obtained by the Charpy impact test became large.

  On the other hand, when a wire having a small wire diameter (hereinafter referred to as a thin wire) is used, the melting boundary line can be inclined. For example, when a thin wire is used for welding on the lower surface side, as shown in FIG. 1, the angle θ2 formed by the fusion boundary line 4 on the lower surface side and a line perpendicular to the surface of the steel sheet 1 increases. Therefore, it is possible to easily collect Charpy impact test specimens where the notch position of the test specimen intersects the melt boundary line, suppressing variations in data obtained by the Charpy impact test, and thus enabling proper evaluation of toughness. It becomes.

  However, when a thin wire is used, there is a problem that slag tends to accumulate at the deepest part of the weld metal, that is, at the tip of the lower surface side weld metal 2 in FIG. Then, after welding using a thin wire, the slag is melted by welding using a large wire. In other words, it is possible to stably improve the toughness of the heat affected zone and suppress the occurrence of defects by combining the welding with a thin wire and the welding with a large wire in double-sided single layer welding of thick steel plates. It becomes.

The present invention has been made based on such knowledge.
That is, according to the present invention, in butt welding of steel sheets having a thickness of 30 mm or more, after performing tack welding from the upper surface side, the wire diameter of the first electrode is set to 2.4 to 2 in submerged arc welding using two or more electrodes. Submerged by welding on the lower surface side at 3.2mm and welding current of 1000A or higher, and by welding on the upper surface side with a first electrode wire diameter of 4.0 to 6.4mm in submerged arc welding using two or more electrodes This is an arc welding method.

In the submerged arc welding method of the present invention, the total heat input of all electrodes of the lower surface side welding heat input and the upper surface side heat input of the steel plate is Q (kJ / cm), and the total heat input Q is the plate of the steel plate. It is preferable that the following expression (1) is satisfied with respect to the thickness t (mm). Further, it is preferable to perform welding on the lower surface side of the steel sheet so that the welding current I ₁ (A) of the first electrode and the welding current I ₂ (A) of the second electrode satisfy the following expression (2). .
Q ≦ 1.3 × t ^1.37 (1)
0.70 ≦ I ₂ / I ₁ ≦ 0.95 (2)
Here, of both surfaces of the steel plates to be welded, the surface on the side where tack welding is performed is referred to as the upper surface, and the surface facing the upper surface is referred to as the lower surface. In order to distinguish two or more electrodes from each other, an electrode arranged at the head in the welding progress direction is referred to as a first electrode, and the subsequent electrodes are sequentially referred to as a second electrode, a third electrode, and the like.

  According to the present invention, when performing butt welding of thick steel plates by submerged arc welding by double-sided single-layer welding, it is possible to stably obtain a high toughness heat-affected zone.

It is sectional drawing which shows typically the example of the welded joint formed by this invention. It is sectional drawing which shows typically the example of the welded joint formed by the conventional butt welding. It is sectional drawing which shows the example of the groove shape of a steel plate typically. It is sectional drawing which shows typically the collection position of a Charpy impact test piece.

A procedure for performing butt welding of steel plates by applying the present invention will be described below.
First, as shown in FIG. 3, a groove is processed at the end of the steel plate 1. In FIG. 1, t is the thickness (mm) of the steel plate 1, α and β are the groove angle (°), and U and V are the groove depth (mm).
The present invention is applied to a steel plate having a thickness t of 30 mm or more. Since the steel plate having a thickness of less than 30 mm has no significant problem in the evaluation of the toughness of the weld heat affected zone formed by the conventional welding method, the effect of the present invention as described above is small. On the other hand, if the plate thickness exceeds 45 mm, double-sided single layer welding may be difficult. Therefore, the thickness t of the steel plate is preferably in the range of 30 to 45 mm.

The groove angles α and β and the groove depths U and V may be set so that the weld metals are overlapped as shown in FIG. 1, and the numerical values are not particularly limited.
The groove is tack-welded from one side of the steel sheets which are processed and faced together. Hereinafter, the surface on the side where tack welding is performed is referred to as an upper surface, and the surface facing the upper surface is referred to as a lower surface.
Next, submerged arc welding on the lower surface side is performed in one pass to form the lower surface side weld metal 2 as shown in FIG. 1 in FIG. 1 is a melting boundary line on the lower surface side. Multi-layer, multi-pass welding has the problem of reduced efficiency.

  Welding on the lower surface side is performed using two or more electrodes. This is because if one electrode is used for welding, an improvement in welding speed cannot be expected. In addition, since the structure of a welding apparatus and the operation management of welding construction will become complicated when an electrode is increased excessively, five or less electrodes are preferable. Hereinafter, in order to distinguish two or more electrodes from each other, the electrode arranged at the head in the welding progress direction is referred to as a first electrode, and the subsequent electrodes are sequentially referred to as a second electrode, a third electrode, and the like.

In welding on the lower surface side, a thin wire having a wire diameter of 2.4 to 3.2 mm is used at the first electrode. If the wire diameter of the first electrode is less than 2.4 mm, the wire feeding speed becomes too fast, so that a large current cannot be applied and deep penetration cannot be obtained. On the other hand, if the thickness exceeds 3.2 mm, the lower surface side weld metal 2 that increases the angle θ2 cannot be formed, so that the toughness deteriorates.
The wire diameter after the second electrode is not particularly limited. However, a wire diameter of 3.2 mm or more is preferable because welding can be performed stably. More preferably, it is 3.2 to 4.8 mm.

The welding current I ₁ of the first electrode is 1000 A or more. When the welding current I ₁ is less than 1000 A, a sufficient penetration depth cannot be obtained, and it becomes difficult to overlap the weld metals as shown in FIG. On the other hand, if it exceeds 1400A, the wire feeding speed becomes too fast, making it difficult to stably feed the wire. Thus, the welding current I ₁ of the first electrode is preferably in the range of 1000～1400A.
The welding current after the second electrode is not particularly limited. However, it is preferable that the welding current of the second electrode is I ₂ (A) and I ₂ / I ₁ satisfies the formula (2). If I ₂ / I ₁ is less than 0.70, welding is not stable, and as a result, the bead width becomes unstable, and the shape of the lower-surface side weld metal 2 and the molten boundary line 4 may be difficult to control. On the other hand, if it exceeds 0.95, the surplus height increases, and it may be difficult to control the shape of the lower surface side weld metal 2 and the molten boundary line 4.
0.70 ≦ I ₂ / I ₁ ≦ 0.95 (2)
By performing the lower surface side welding in this way, the lower surface side weld metal 2 having a large angle θ2 can be formed. However, by using a small-diameter wire, slag entrainment may occur at the deepest innermost portion of the lower surface side weld metal 2.

Therefore, by performing submerged arc welding on the upper surface side using a large-diameter wire, as shown in FIG. 1, the upper surface side weld metal 3 is formed so as to overlap the lower surface side weld metal 2, and the slag is melted. To suppress welding defects.
The upper surface side welding is performed using two or more electrodes. This is because if one electrode is used for welding, an improvement in welding speed cannot be expected. The number of electrodes is preferably 5 or less, for the same reason as described above.

In welding on the upper surface side, a thick wire having a wire diameter of 4.0 to 6.4 mm is used at the first electrode. If the wire diameter of the first electrode is less than 4.0 mm, not only is it difficult to melt the slag in the lower surface side weld metal 2, but there is a possibility that the slag may accumulate in the deepest part of the upper surface side weld metal 3. In submerged arc welding, the wire diameter is usually up to 6.4 mm.
The wire diameter after the second electrode is not particularly limited.

As for the welding heat input of submerged arc welding, it is preferable that the total heat input Q (kJ / cm) of all the electrodes on the lower surface side and the upper surface side satisfies the following formula (1) with respect to the plate thickness t of the steel plate. When Q exceeds 1.3 × t ^1.37 kJ / cm, the welding heat input is too large and the toughness of the weld heat affected zone may deteriorate. On the other hand, if it is less than t ^1.37 kJ / cm, it is difficult to secure a sufficient penetration depth. Therefore, it is more preferable to satisfy the following expression (3).
Q ≦ 1.3 × t ^1.37 (1)
t ^1.37 ≦ Q ≦ 1.3 × t ^1.37 (3)
As described above, according to the present invention, the toughness of the weld heat affected zone can be improved. Moreover, since the melting boundary line of the lower surface side weld metal can be tilted, as shown in FIG. 4, when a Charpy impact test piece is taken, the notch of the test piece intersects the lower surface side melting boundary line. Become. Further, in the vicinity of the intersection of the melting boundary line on the lower surface side and the upper surface side, the melting boundary line on the upper surface side is also inclined, so that it intersects with the notch of the test piece. As a result, it is possible to greatly suppress the influence of the change in the sampling position of the specimen and the change in the shape of the melt boundary line on the evaluation of toughness, and stable toughness can be obtained.

  As the wire used in the present invention, either a solid wire or a cored wire can be used.

  After forming a groove having the shape shown in FIG. 3 on two types of steel plates (thickness t: 31.8 mm, 38.1 mm) having the components shown in Table 1, submerged arc welding (one pass) on the lower surface side is performed. Then, submerged arc welding (one pass) was performed on the upper surface side.

  Table 2 shows the groove shape of the steel plate 1. In Table 2, the groove angle of the lower surface is an angle β (°) shown in FIG. 3, and the groove angle of the upper surface is an angle α (°) shown in FIG. In Table 2, the groove depth on the lower surface is V (mm) shown in FIG. 3, and the groove depth on the upper surface is U (mm) shown in FIG.

  The conditions of submerged arc welding are shown in Tables 3-6. As shown in Tables 3 and 4, welding symbol 9 is welded with 3 electrodes (1 pass) for top surface welding and bottom surface welding, welding symbol 10 is welded with 5 electrodes (1 pass) for top surface welding and bottom surface welding, and all others Welding was performed with 4 electrodes (1 pass). In the currents shown in Tables 5 and 6, the first electrode was a direct current, and the second and subsequent electrodes were an alternating current. The distance between the electrodes in Tables 5 and 6 is the distance (mm) between the wire tips on the surface (lower surface or upper surface) of the steel plate 1. The distance between the base material and the electrode is the distance (mm) between the surface (lower surface or upper surface) of the steel plate 1 and the lower surface of the contact chip. The electrode angle is shown with the forward angle (°) as positive and the backward angle (°) as negative. Here, the advancing angle is an angle formed by a wire perpendicular to the steel sheet and the wire so that the wire tip is positioned in front of the welding direction with respect to the torch, and the receding angle is the wire tip. The angle between the wire and the wire perpendicular to the steel plate is such that the wire is inclined so as to be located behind the welding progress direction.

After welding under each of these conditions (welding symbols 1 to 18), the bead width is confirmed at the steady portion of the welded joint produced, the maximum value and the minimum value are measured, and the difference is obtained to obtain the bead. The stability of the width was evaluated. The results are shown in Table 7.
Furthermore, the presence or absence of slag inclusion of weld metal and the presence or absence of poor penetration were investigated by X-ray photography. The results are shown in Table 7.

Further, five welded joints were prepared by welding under each condition, and Charpy impact test pieces and cross-sectional macro test pieces were collected from the test piece collection position 6 shown in FIG.
Charpy impact test pieces were collected from each welded joint as No. 4 test pieces as defined in JIS standard Z3111 (ie, 100 pieces for each weld symbol). The Charpy impact test piece was sampled so that the notch was parallel to the plate thickness direction and the plane including the intersection of the melting boundary lines (plane parallel to the surface of the steel plate 1) was the center of the test piece in the plate thickness direction. The position of the notch was a position where the ratio of the weld metal and the weld heat affected zone at the notch bottom was 50%.

The Charpy impact test was performed in accordance with JIS standard Z2242 (test temperature: −30 ° C.), and the absorbed energy _V E _-30 (J) was measured. The results are shown in Table 7. The absorbed energy _V E _-30 in Table 7 represents the lowest value among the measured values obtained by 100 Charpy impact tests for each welding symbol.
Three cross-section macro specimens were collected from each weld joint (ie, 15 for each weld symbol). Table 7 shows the result of measuring the extra height (mm) from each cross-section macro test piece. In addition, the surplus height in Table 7 shows the average value of the measured values of 15 test pieces for each welding symbol.

  The welding symbols 1 to 10 are invention examples. The welding symbols 1 and 2 are examples in which the wire diameter of the first electrode for bottom surface welding is 2.4 to 3.2 mm, the welding current for the first electrode is 1000 A or more, and the wire diameter of the first electrode for top surface welding is 4.0 to 6.4 mm. Therefore, stable and excellent toughness was obtained, and at the same time, good weld quality was obtained. The weld symbols 3 to 6 are examples in which the total welding heat input on the lower surface side and the upper surface side satisfies the formula (1), and extremely high absorbed energy of 100 J or more was obtained. In addition, welding symbols 7 to 10 are examples in which the welding current of the first electrode and the second electrode is set so as to satisfy the expression (2) by welding on the lower surface side, and the extra height of the bead is 3 mm. Hereinafter, the difference between the maximum value and the minimum value of the bead width could be suppressed to 3 mm or less, and a bead having an excellent shape was obtained.

  The welding symbols 11 to 18 are comparative examples. In welding symbols 11 and 12, since the wire diameter of the first electrode of the bottom surface welding is less than 2.4 mm, a high welding current of 1000 A or more is set, so that stable welding cannot be performed and the bead width is not stable. The welding symbols 13 and 14 had low absorbed energy because the wire diameter of the first electrode exceeded 3.2 mm in the lower surface side welding. In welding symbols 15 and 16, a penetration failure occurred because the welding current of the first electrode of the bottom surface welding was less than 1000 A. In welding symbols 17 and 18, the wire diameter of the first electrode of top surface welding was less than 4.0 mm, and slag entrainment occurred.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Lower surface side weld metal 3 Upper surface side weld metal 4 Lower surface side melting boundary line 5 Upper surface side melting boundary line 6 Test piece sampling position

Claims (3)

  In butt welding of steel plates with a thickness of 30 mm or more, after performing tack welding from the upper surface side, the wire diameter of the first electrode is 2.4 to 3.2 mm and the welding current is submerged arc welding using two or more electrodes. The submerged is characterized in that the lower surface side is welded at 1000A or more, and the upper electrode is welded with the wire diameter of the first electrode set to 4.0 to 6.4mm by submerged arc welding using two or more electrodes. Arc welding method. The total heat input of all electrodes of the lower surface side welding heat input and the upper surface side welding heat input of the steel plate is defined as Q (kJ / cm), and the total heat input Q corresponds to the plate thickness t (mm) of the steel plate. The submerged arc welding method according to claim 1, wherein the following equation (1) is satisfied.
Q ≦ 1.3 × t ^1.37 (1) The welding of the lower surface side of the steel sheet is performed so that the welding current I ₁ (A) of the first electrode and the welding current I ₂ (A) of the second electrode satisfy the following expression (2): The submerged arc welding method according to claim 1 or 2.
0.70 ≦ I ₂ / I ₁ ≦ 0.95 (2)

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