Wrapping welding method and wrapped weld joint

Abstract

The present invention provides a wrapping welding method and a wrapped weld joint. A wrapping welding method according to the present invention involves forming a first weld bead 3a along a short side of a rectangular contact surface 2a where a vertical plate 2 contacts a main plate 1, and then welding in such a manner that the first weld bead 3a extends onto the main plate 1 from both short sides of the rectangular contact surface 2a. A weld metal damming member 4 with a rectangular base of base width MT is then placed on the main plate 1 to contact the first weld bead 3a. A second weld bead 3b and a third weld bead 3c are then formed along the long sides of the rectangular contact surface 2a, made to cover the ends of the first weld bead 3a, and then formed extending farther along the weld metal damming member 4 and on the main plate 1.

Description

Rotation welding method and rotation welding joint

[0001] The present invention relates to a box welding technique for main plates and vertical plates, particularly gussets, which is widely used when constructing steel structures, and in particular to a box welding method and box welded joint suitable for steel structures (e.g., steel bridges, ships, etc.) that require excellent fatigue properties.

[0002] Generally, steel structures have many boxing welded joints, in which the periphery of a vertical plate, e.g., a gusset, is welded to a main plate (so-called boxing weld). In boxing welded joints, a weld bead surrounds the gusset. If the weld bead develops defects (e.g., cracks) and the weld toe shape is not smoothly formed, stress concentration at the weld toe is likely to occur. As a result, the welding residual stress caused by the boxing weld and the repeated stress caused by external forces overlap, causing fatigue cracks, which then propagate and lead to fatigue failure. Note that an external force refers to a load repeatedly acting on a steel structure from the outside. For example, if the steel structure is a steel bridge, this is a load repeatedly caused by natural weather conditions (e.g., wind) or vehicle traffic, and if the steel structure is a ship, this is a load repeatedly caused by wind and waves.

[0003] In recent years, as steel structures age, damage caused by fatigue has been increasing. To prevent such damage, it is necessary to periodically inspect steel structures, monitor the progress of damage, and take measures according to the progress of damage. Therefore, technologies to improve the fatigue properties of boxing welded joints in steel structures have been investigated.

[0004] For example, Patent Document 1 proposes a method for manufacturing a boxing welded joint in which the long sides of a rectangular abutment surface where a rib plate (gusset) abuts against a main plate are fillet welded, and then, after cooling to room temperature, the short sides of the rectangular abutment surface are welded from the corners of the rectangular abutment surface. The technique described in Patent Document 1 proposes that the short sides of the rectangular abutment surface are welded so that they are at least (2 × fillet weld leg length) longer than (rib plate thickness + 2 × fillet weld leg length). This allows for stable enhancement of joint fatigue strength. However, with this technique, the weld bead formed along the short sides of the rectangular abutment surface (i.e., the short side weld bead) overlaps the weld bead formed along the long sides (i.e., the long side weld bead), and the short side weld bead extends beyond the long side weld bead onto the main plate. In this way, when the long side weld bead is welded first and then the short side weld bead is placed on top of it and welded, a gap (i.e., a space surrounded by the main plate, long side weld bead, and short side weld bead) is likely to occur where the weld beads overlap, and fatigue cracks due to stress concentration are likely to occur. It is often difficult to prevent the propagation of fatigue cracks that occur, and therefore the technology disclosed in Patent Document 1 cannot be expected to significantly improve the fatigue strength of boxing welded joints.

[0005] Patent Document 2 also proposes a boxing welding method. In the technology described in Patent Document 2, a first weld bead is formed along the short side of a rectangular abutment surface where the gusset abuts the main plate, extending from both short sides of the rectangular abutment surface onto the main plate. Next, a second weld bead and a third weld bead are welded along the long side of the rectangular abutment surface so as to cover the first weld bead and extend beyond the first weld bead onto the main plate. The distance M between the formed second and third weld beads is set to 10.0 mm or less. This prevents gaps from forming where the weld beads overlap, thereby preventing fatigue cracks regardless of the shape of the weld toe. Furthermore, by welding the short-side weld bead so that its length does not exceed the long-side weld bead, the occurrence of gaps where the weld beads overlap can be more significantly prevented. The technology described in Patent Document 2 is said to be able to use ordinary welding equipment and welding materials and to form a boxing weld joint inexpensively.

[0006] JP 8-19860 A JP 2018-158380 A

[0007] However, in recent years, there has been a demand for further improvements in the fatigue strength of welded structures. In addition, the method described in the above-mentioned Patent Document 1, in which a long side weld bead is first welded and then a short side weld bead is welded over the long side weld bead, has the problem that gaps are likely to occur where the weld beads overlap, and therefore improvement in the fatigue strength of the boxing welded joint cannot be expected.

[0008] Therefore, an object of the present invention is to provide a box welding method and a box welded joint that can inexpensively and stably improve fatigue strength, especially when the gusset plate thickness is thin.

[0009] In order to achieve the above object, the present inventors have intensively studied a boxing welding method that stabilizes the spacing between long side weld beads in a boxing weld joint and reduces variations. As a result, it has been found that a width of the bottom surface (i.e., bottom width) M that contacts the main plate is previously set on the main plate between the extending long side weld beads (i.e., the portion that becomes the spacing between the long side weld beads). Ｔ The inventors came up with the idea of ​​disposing a weld metal retaining member formed to be equal to the target spacing between the long side weld beads. By extending and welding the long side weld beads along this retaining member, the spacing between the long side weld beads can be stably and consistently formed relative to the target spacing.

[0010] Furthermore, if the weld metal blocking member is a member that does not bond with the weld metal during welding, the weld metal blocking member can be easily removed after welding, making it easy to adjust the long side weld bead spacing. Here, "a member that does not bond with the weld metal" refers to a member that has a heat capacity that is low enough to prevent it from melting during welding in a turn welding operation. Examples of materials suitable for the weld metal blocking member include copper and ceramics.

[0011] The present invention has been completed based on the above findings and further studies, and is summarized as follows: [1] A turn welding method using a weld metal blocking member for turn-welding a standing plate to a main plate, wherein the weld metal blocking member has a width M of a bottom surface that abuts against the main plate. Ta weld metal damming member is disposed on the main plate adjacent to the first weld bead, and a second weld bead and a third weld bead are sequentially formed along the long sides of the rectangular abutment surface, and the second weld bead and the third weld bead are placed on the main plate adjacent to the first weld bead, and the second weld bead and the third weld bead are extended onto the main plate along the long sides of the rectangular abutment surface, and the second weld bead and the third weld bead are placed on the main plate adjacent to the first weld bead, and the second weld bead and the third weld bead are extended onto the main plate along the weld metal damming member. [2] The box welding method according to [1], wherein the second weld bead and the third weld bead are formed so as to satisfy formulas (1) and (2). M≦Q (1) 2.0≦M≦30.0 (2) where Q: length of the short side of the rectangular abutting surface (mm), M: distance (mm) between the second weld bead and the third weld bead. [3] The box welding method according to [1] or [2], wherein the shorter distance N between the short side of the rectangular abutting surface and the tip of the second weld bead or the third weld bead is 5.0 mm or more and 100.0 mm or less. [4] The box welding method according to any one of [1] to [3], wherein the weld metal damming member is a member that does not bond to the weld metal. [5] The box welding method according to [4], wherein the weld metal damming member is made of copper or ceramics. [6] The weld metal damming member has a longitudinal length N T is 5 to 200 mm, and the bottom width M represents the width of the rectangular bottom surface that contacts the main plate in a cross section perpendicular to the longitudinal direction. T[7] The boxing welding method according to any one of [1] to [6], wherein the weld metal damming member has a trapezoidal cross-sectional shape with a width of 2.0 to 30.0 mm. [7] The boxing welding method according to any one of [1] to [6], wherein the weld metal damming member has a cross section perpendicular to the longitudinal direction, and a region in contact with the extended long side weld bead on the side surface is a curve or a line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less. [8] A boxing welded joint formed by boxing a standing plate to a main plate, comprising: a first weld bead formed along a short side of a rectangular abutment surface where the standing plate abuts against the main plate and extending from both sides of the short side of the rectangular abutment surface onto the main plate in a straight line parallel to the short side of the rectangular abutment surface, and a second weld bead and a third weld bead formed along a long side of the rectangular abutment surface and covering an end of the first weld bead and extending onto the main plate, the second weld bead and a third weld bead being extended long side weld beads, the second weld bead and the third weld bead being extended long side weld beads, the second weld bead and the third weld bead being extended long side weld beads, the second weld bead and the third weld bead being extended long side weld beads M≦Q (1) 2.0≦M≦30.0 (2) Where, Q: length (mm) of the short side of the rectangular abutment surface, M: distance (mm) between the second weld bead and the third weld bead.

[10] The boxing welded joint according to [8] or [9], wherein the shorter distance N between the short side of the rectangular abutment surface and the tip of the second weld bead or the third weld bead is 5.0 mm or more and 100.0 mm or less.

[0012] According to the present invention, poor welding of boxing welded joints can be avoided and the spacing between extended long side weld beads can be adjusted to a constant value. As a result, even when the thickness of vertical plates, particularly gusset plates, is small, such as 2 to 30 mm, the fatigue strength of boxing welded joints can be particularly improved inexpensively and stably, providing significant industrial benefits. The present invention also has the advantage of being applicable not only to the construction of new steel structures but also to the repair of deteriorated steel structures.

[0013] FIG. 1 is an explanatory diagram (plan view) that schematically shows the steps of a box welding method according to the present invention. FIG. 2 is a plan view that schematically shows an example of a weld bead formed by the box welding method according to the present invention. FIGS. 3(a) to 3(c) are perspective views that schematically show an example of the external shape of a weld metal damming member according to the present invention. FIG. 4 is a cross-sectional view that schematically shows the relationship between an elongated weld bead and a weld metal damming member after box welding according to the present invention. FIG. 5 is a plan view that shows the shape of a test piece for a box welded joint fatigue test used in an example of the present invention.

[0014] The present invention relates to a box welding method using a weld metal retaining member 4 for box welding a gusset 2, which is a vertical plate, to a main plate 1. The present invention also relates to a box welded joint obtained by this box welding method.

[0015] In the present invention, there is no particular limitation on the steel material that can be used for the main plate 1 and the gusset 2, and the effects of the present invention can be achieved with any type of steel. For steel welded structures, SM400, SM490, SM520, SM570, etc., which have a yield strength of 245 to 560 MPa, are all suitable. While the thickness of the main plate 1 is not particularly limited, it is preferable to use a steel material with a thickness of 2 to 30 mm for the gusset 2, which is a vertical plate. If the thickness of the gusset 2 is less than 2 mm, welding becomes difficult. On the other hand, if the thickness exceeds 30 mm, it is disadvantageous from the viewpoint of improving fatigue properties.

[0016] Next, the procedure of the box welding method according to the present invention for obtaining a box weld joint will be described with reference to Fig. 1. The rectangular abutment surface 2a where the gusset 2 abuts against the main plate 1 coincides with the shape of a rectangular line obtained by projecting the gusset 2 onto the main plate 1. In the following description, the shape of this rectangular line will be referred to as the rectangular abutment surface 2a.

[0017] In the example shown in Fig. 1, as a preparation step before the boxing welding step, a gusset 2 is placed on the upper surface of the main plate 1. Next, the boxing welding step described below is carried out to produce a welded joint having a weld bead as shown in Fig. 2. Note that Fig. 1 mainly shows the gusset 2 on one side of the main plate 1 and its surroundings.

[0018] First, a first weld bead 3a (hereinafter also referred to as a short-side weld bead) is formed along the short side of the rectangular abutment surface 2a. At this time, as shown in FIG. 1A , the first weld bead 3a is welded so that it extends from both ends of the short side of the rectangular abutment surface 2a onto the main plate 1. Therefore, the first weld bead 3a is longer than the short side of the rectangular abutment surface 2a. This allows the subsequent second weld bead 3b and third weld bead 3c (hereinafter also referred to as long-side weld beads) to cover the end of the first weld bead 3a. This allows the end of the first weld bead 3a to melt. Note that if the first weld bead 3a is too long, the subsequent second weld bead 3b and third weld bead 3c will not be able to completely cover the end of the first weld bead 3a. In this case, a gap surrounded by main plate 1, first weld bead 3a, and second weld bead 3b, or a gap surrounded by main plate 1, first weld bead 3a, and third weld bead 3c, is likely to occur, resulting in fatigue cracks. For this reason, it is preferable to weld first weld bead 3a by adjusting its length in advance, taking into consideration the width of the long side weld bead, so that it can be covered by the subsequent second weld bead 3b and third weld bead 3c.

[0019] Next, the weld metal damming member 4 is disposed on the main plate 1 so as to be adjacent to the first weld bead 3a (see (b) in FIG. 1). In the present invention, the bottom surface of the weld metal damming member 4 that contacts the main plate 1 is referred to as the rectangular bottom surface 4a. Preferably, the width center line X of the rectangular bottom surface 4a that contacts the main plate 1 is aligned with the plate thickness center line Y of the gusset. An error of up to 2 mm is allowed here. The structure of the weld metal damming member 4 will be described later. In FIG. 1, to make it easier to understand the relationship with the weld bead, etc., the position of the weld metal damming member 4 is shown using the shape of the rectangular bottom surface 4a when the bottom surface of the weld metal damming member contacts the main plate 1.

[0020] 1(c), second weld bead 3b is formed along the long side of rectangular abutment surface 2a, covers the end of first weld bead 3a, and extends onto main plate 1. Then, from the portion beyond gusset 2, second weld bead 3b is extended along the long side of rectangular bottom surface 4a of weld metal damming member 4 that has been arranged in advance.

[0021] 1(d), third weld bead 3c is formed along the long side of rectangular abutment surface 2a, covers the end of first weld bead 3a, and extends onto main plate 1. From the portion beyond gusset 2, third weld bead 3c is extended along the long side of rectangular bottom surface 4a of pre-installed weld metal retaining member 4. Although FIG. 1 shows second weld bead 3b on the left side of rectangular abutment surface 2a and third weld bead 3c on the right side, this may be reversed.

[0022] By welding in this order (a) to (d), first to third weld beads 3a to 3c can be formed along the rectangular abutment surface 2a of the gusset 2. Although not shown in Figure 1, weld beads can be formed around the gusset on the opposite side in a similar manner. The weld metal retaining member 4 is removed after welding is completed.

[0023] An example of weld beads formed using the above procedure is shown in Figure 2. The second weld bead 3b and the third weld bead 3c are formed to satisfy the following formulas (1) and (2): M≦Q (1) 2.0≦M≦30.0 (2) where Q is the length (mm) of the short side of the rectangular abutment surface 2a, and M is the distance (mm) between the second weld bead 3b and the third weld bead 3c extending onto the main plate. The distance M is the distance (unit: mm) between the second weld bead 3b and the third weld bead 3c extending onto the main plate 1 (i.e., the inside dimension distance between the bead toes of the second weld bead 3b and the third weld bead 3c). This inside dimension distance between the bead toes of the second and third weld beads is an actual value (i.e., an actually measured value). This is calculated based on the width M of the rectangular bottom surface 4a of the weld metal retaining member. T Approximately matches.

[0024] In the present invention, the distance M is preferably set to 2.0 mm or more and 30.0 mm or less to satisfy formula (2). If the distance between the second weld bead 3b and the third weld bead 3c extending to the main plate 1 (i.e., the distance M) exceeds 30.0 mm, the effect of the second weld bead 3b and the third weld bead 3c in suppressing stress flowing into the weld toe of the first weld bead 3a decreases. As a result, the effect of reducing stress concentration begins to decrease, and the effect of improving fatigue strength decreases. On the other hand, if the distance M is less than 2.0 mm, the second weld bead 3b and the third weld bead 3c come into contact with each other, making actual welding impossible. The distance M is more preferably set to 5.0 mm or more and more preferably set to 25.0 mm or less.

[0025] In addition to satisfying the above-mentioned formula (2), the distance M (mm) is preferably set to be equal to or less than the length (Q) (unit: mm) of the short side of the rectangular abutment surface 2 a of the gusset 2 so as to satisfy the formula (1). If the distance M (mm) exceeds the length Q (mm) of the short side of the rectangular abutment surface 2 a of the gusset 2, stress may easily flow into the gusset weld toe, raising concerns that fatigue cracks may easily occur. The above-mentioned "gusset weld toe" refers to the weld toe of the first weld bead 3.

[0026] As shown in FIG. 2 , the shorter of the distance between the short side of the rectangular abutment surface 2 a and the tip of the second weld bead 3 b and the distance between the short side of the rectangular abutment surface 2 a and the tip of the third weld bead 3 c is defined as the distance N. The "distance between the short side of the rectangular abutment surface 2 a and the tip of the second weld bead 3 b (or the third weld bead 3 c)" refers to the distance (i.e., the length) from the end of the rectangular abutment surface 2 a to the tip of the second weld bead 3 b (or the third weld bead 3 c). The distance N between the rectangular abutment surface 2 a and the tips of the second and third weld beads is an actual value (i.e., an actually measured value). The distance N is preferably 5.0 mm or greater. If the distance N is less than 5.0 mm, the length of the extended second weld bead or the extended third weld bead is too short, making fatigue cracks more likely to propagate. The distance N is more preferably 10.0 mm or greater, and even more preferably 15.0 mm or greater. On the other hand, if the gap N is too long, the welding time will be long. Therefore, the gap N is preferably 100.0 mm or less. The gap N is more preferably 50.0 mm or less, and further preferably 30.0 mm or less.

[0027] The welding method used in the box welding method of the present invention is preferably a shielded metal arc welding method or a gas metal arc welding method, but other welding methods can also be used as appropriate. In addition, either manual welding or automatic welding may be used.

[0028] Next, the weld metal blocking member 4 used in the present invention will be described. Fig. 3 shows an example of the external shape of the weld metal blocking member 4.

[0029] The weld metal damming member 4 used in the present invention has a rectangular bottom surface 4a abutting against the main plate 1 (i.e., bottom surface width) M T is formed to be equal to the target value of distance M (hereinafter also referred to as the target distance) between extended second weld bead 3 b and extended third weld bead 3 c. This allows the actual measured value of distance M between extended second weld bead 3 b and extended third weld bead 3 c to be stably the target distance.

[0030] The weld metal blocking member 4 used in the present invention has a longitudinal length N Tis 5 mm or more, and the width of the bottom surface 4a that abuts against the main plate 1 (i.e., the bottom surface width) M T The longitudinal length N of the weld metal blocking member 4 is preferably 2.0 to 30.0 mm, and the cross section perpendicular to the longitudinal direction (i.e., the length direction) is preferably approximately trapezoidal, as shown in Fig. 3(a). However, as shown in Fig. 3(b), the cross section may be approximately rectangular. T If the bottom width M is less than 5 mm, the interval N will be less than 5.0 mm when the joint is fabricated, and the length of the extended second weld bead or the extended third weld bead will be too short, making it easier for fatigue cracks to propagate. T The reason for setting the numerical range is the same as the reason for the interval M described above, and therefore will not be explained further.

[0031] In addition, the longitudinal length N of the weld metal blocking member 4 T is a length corresponding to the lengths of the second weld bead 3b and the third weld bead 3c formed extending on the main plate 1. T is set to 5 mm or more, preferably 200 mm or less, and is preferably set to be larger than the target interval N. This "target interval N" refers to the target value of the length of second weld bead 3b and third weld bead 3c formed by extending on main plate 1 (i.e., the distance N between rectangular abutting surface 2a and the tip of the second and third weld beads). Also, the width M of rectangular bottom surface 4a abutting against main plate 1 (i.e., the bottom width) T is set for each welding operation within the range of 2.0 to 30.0 mm so as to match the target gap between the extended second weld bead 3b and the third weld bead 3c.

[0032] As shown in FIGS. 3( a) and 3(b), the weld metal damming member 4 used in the present invention preferably has a curved (specifically, arc-shaped) area in contact with the extended weld bead on the side surface of the weld metal damming member 4 in a cross section perpendicular to the longitudinal direction, with the elevation angle θ from the bottom surface 4a being θ: 60° or less. Instead of a curved line, as shown in FIG. 3(c), a straight line may be used, with the elevation angle θ from the bottom surface 4a being θ: 60° or less. By using such a curved or straight line, the bead shape of the extended weld bead tends to be similarly semi-elliptical, with the elevation angle θ being 60° or less, as shown in FIG. 4. This reduces or avoids stress concentration in the extended weld bead. It is more preferable that θ be between 0° and 45°. If the elevation angle θ from the bottom surface 4a exceeds 60°, the amount of deposited weld metal increases, making it difficult to achieve a bead shape similar to the desired semi-elliptical shape. The shape of the top surface of the weld metal damming member 4 does not have to be flat. Here, the cross-sectional shapes shown in Figures 3(a) and 3(c) are referred to as trapezoidal shapes, and the cross-sectional shape shown in Figure 3(b) is referred to as rectangular shapes. This trapezoidal shape includes a shape in which one or both of the two opposing sides are arc-shaped, as in Figure 3(a). Also, for example, as in Figure 3(c), the bottom width M T On one side having a bottom width M T The shape includes a shape having straight lines connecting the ends of the trapezoid and the corners of the trapezoid.

[0033] The above-mentioned extended weld bead is a part of the second weld bead and the third weld bead, and refers to the weld bead portion formed by extending beyond the gusset 2 onto the main plate as described above.

[0034] The height H of the weld metal blocking member 4 is not particularly limited, but may be determined appropriately depending on ease of handling, and is preferably set to 30 to 100 mm.

[0035] Furthermore, it is preferable that the weld metal damming member 4 is a member that does not bond with the weld metal. By using a member that does not bond with the weld metal, the weld metal damming member 4 can be easily removed from its installed position after welding is completed. Examples of such materials include copper and ceramics. Examples of ceramics include SiO2 and Al2O3.

[0036] Next, an example of a box welded joint obtained by the box welding method of the present invention will be described. Note that the shapes, functions, and effects of the main plate 1, the gusset 2 that serves as the upright plate, the weld bead 3, and the weld metal retaining member 4 have been described in detail in the section on the box welding method described above, so will not be described here.

[0037] The boxing weld joint of the present invention has a main plate 1, a gusset 2 on the main plate, and a weld bead 3 joining the main plate and the gusset. As shown in Figure 2, the weld bead 3 is made up of a first weld bead 3a, a second weld bead 3b, and a third weld bead 3c.

[0038] In the present invention, as described above, first weld bead 3a is formed, weld metal damming member 4 is disposed adjacent to first weld bead 3a, and then second and third weld beads 3b, 3c are formed. Weld metal damming member 4 is curved or straight with an elevation angle θ of 60° or less from bottom surface 4a. Therefore, the extended weld bead portions of second weld bead 3b and third weld bead 3c of the resulting weld joint have cross sections as shown in Fig. 4. That is, the bead shapes of the extended weld beads in the weld joint are similarly close to semi-elliptical, with an elevation angle θ of 60° or less.

[0039] In the boxing weld joint of the present invention, the second weld bead 3b and the third weld bead 3c are preferably formed so as to satisfy the above-described formulas (1) and (2). Furthermore, preferably, the shorter distance N between the short side of the rectangular abutment surface 2a and the tip of the second weld bead 3b or the third weld bead 3c is 5.0 mm or more and 100.0 mm or less. The extended weld bead spacing M and the extended weld bead length N of the weld joint were measured with a vernier caliper.

[0040] According to the boxing welded joint of the present invention having such a configuration, the distance M between the extended weld beads on the main plates is stable and constant, which particularly improves the fatigue strength of the boxing welded joint.

[0041] The present invention will be further described below with reference to examples.

[0042] Steel plate A was prepared having the chemical composition and mechanical properties shown in Table 1. The thickness of steel plate A was 14 mm. This steel plate A had a stress intensity factor ΔK of 15 MPa. 1 / 2 When the fatigue crack propagation rate is 1.85 × 10 -8 This steel sheet has fatigue properties of 1000 m / cycle.

[0043]

[0044] From the prepared steel plate A, a main plate 1 (plate thickness: 14 mm, plate width: 80 mm, length: 500 mm) and a gusset 2 (plate thickness: 4 to 14 mm, plate width: 75 mm, height: 50 mm) which will become a standing plate were each taken. The gusset 2 was used by processing the prepared steel plate A so that the plate thickness Q was 4.0 to 14.0 mm. Here, the plate thickness Q is equivalent to "the length of the short side of the rectangular abutment surface 2a of the gusset 2."

[0045] A gusset 2 was placed at the center of the main plate 1. The plate thickness Q of the gusset 2 used is shown in Table 2. Next, the gusset 2 was box-welded to the main plate 1 by gas metal arc welding using a flux-cored wire, to produce a box-welded joint as shown in FIG. 5. The flux-cored wire used was MX-Z200 (wire diameter: 1.2 mm) manufactured by Kobe Steel, Ltd., and the welding conditions were 240 A and 32 V. Both the short side weld beads and the long side weld beads were welded with a target leg length of approximately 6 mm.

[0046] The box welding procedure is as follows. First, a first weld bead 3a, which is a short-side weld bead, was formed along the short side of the rectangular abutment surface 2a of the gusset 2. At this time, as shown in FIG. 1(a), the first weld bead 3a was welded so as to extend onto the main plate 1 from both sides of the short side of the rectangular abutment surface 2a. The extension length of the first weld bead 3a was set to a length that could be covered by the second weld bead 3b and the third weld bead 3c, which are long-side weld beads.

[0047] Next, a trapezoidal weld metal damming member 4 shown in FIG. 3(a) was disposed on the main plate 1 so as to be in contact with the first weld bead 3a and with the widthwise center line X of the rectangular bottom surface 4a aligned with the center line Y of the plate thickness Q of the gusset 2 (see (b) in FIG. 1). The weld metal damming member 4 used was machined to a predetermined size using an FB-B3 manufactured by Kobe Steel, Ltd. The dimensions of each part (i.e., M T , N T , θ) are also shown in Table 2.

[0048] Next, as shown in FIG. 1(c), second weld bead 3b was formed along the long side of rectangular abutment surface 2a, covering the end of first weld bead 3a, and extending onto main plate 1. From the portion beyond gusset 2, second weld bead 3b was extended along pre-installed weld metal retaining member 4.

[0049] Next, as shown in Fig. 1(d), third weld bead 3c was formed along the long side of rectangular abutment surface 2a, covering the end of first weld bead 3a, and extending onto main plate 1. From the portion beyond gusset 2, third weld bead 3c was extended along pre-installed weld metal retaining member 4.

[0050] The weld beads around the gusset were formed using the above procedure to form the box weld joint shown in Fig. 5, which was used as an example of the present invention. Note that in some box welds, second weld bead 3b and third weld bead 3c were formed without disposing weld metal retaining member 4, which was used as a comparative example.

[0051] For the obtained boxing welded joints, the distance M between the extended second weld bead 3b and the extended third weld bead 3c was measured at three locations, the average value (actual measurement value) was determined, and the difference between the average value and the target value was calculated. The obtained results are shown in the "Extended weld bead distance M" column of Table 2. In addition, the distance N between the extended second weld bead 3b and the extended third weld bead 3c was measured with a vernier caliper, and the value (actual measurement value) is shown in the "Extended weld bead distance N" column of Table 2.

[0052] A fatigue test was conducted on the obtained boxing welded joint. The fatigue test was conducted at room temperature in the atmosphere under the conditions of axial load control, stress ratio 0.1, and frequency 10 Hz, and the fatigue life was measured. Here, the "axial load control" was defined as "load application direction: longitudinal direction of the main plate." The "fatigue life" refers to the number of load repetitions until fatigue fracture occurs. The obtained fatigue life is shown in Table 2.

[0053]

[0054] In all of the inventive examples, the difference between the measured value and the target value for the spacing M between the extended second weld bead 3b and the extended third weld bead 3c (i.e., the long side weld beads) was within 0.5 mm, and the examples had good fatigue lives. On the other hand, the comparative examples, which did not use the weld metal retaining member 4, had reduced fatigue lives. For example, in a comparative example (e.g., boxing welded joint No. 13) in which the difference between the measured value and the target value for the spacing M between the long side weld beads was 1.6 mm or more, the fatigue life was reduced to less than half of that of the inventive example (boxing welded joint No. 4) with the same target value for spacing M.

[0055] REFERENCE SIGNS LIST 1 Main plate 2 Gusset (standing plate) 2a Rectangular abutment surface of gusset 3 Weld bead 3a First weld bead (short side weld bead) 3b Second weld bead (long side weld bead) 3c Third weld bead (long side weld bead) 4 Weld metal damming member 4a Rectangular bottom surface of weld metal damming member

Claims

1. A turn welding method using a weld metal blocking member for turn-welding a vertical plate to a main plate, wherein the weld metal blocking member has a width M of a bottom surface that abuts against the main plate. T and the box welding includes forming a first weld bead along a short side of a rectangular abutment surface where the upright plate abuts against the main plate and extending from both sides of the short side of the rectangular abutment surface onto the main plate in a straight line parallel to the short side of the rectangular abutment surface, then disposing the weld metal blocking member on the main plate so as to be adjacent to the first weld bead, and forming a second weld bead and a third weld bead sequentially along the long side of the rectangular abutment surface, and then covering an end of the first weld bead with the second weld bead and the third weld bead extending onto the main plate so as to be along the weld metal blocking member.

2. The boxing welding method according to claim 1, wherein the second weld bead and the third weld bead are formed so as to satisfy the following formulas (1) and (2): M≦Q (1) 2.0≦M≦30.0 (2) where Q is the length of the short side of the rectangular abutment surface (mm), and M is the distance between the second weld bead and the third weld bead (mm).

3. A turn welding method as described in claim 1 or 2, wherein the shorter distance N between the short side of the rectangular abutment surface and the tip of the second weld bead or the third weld bead is 5.0 mm or more and 100.0 mm or less.

4. A box welding method according to any one of claims 1 to 3, wherein the weld metal blocking member is a member that does not join with the weld metal.

5. The box welding method according to claim 4, wherein the weld metal blocking member is made of copper or ceramics.

6. The weld metal blocking member has a longitudinal length N T is 5 to 200 mm, and the bottom width M represents the width of the rectangular bottom surface that contacts the main plate in a cross section perpendicular to the longitudinal direction. Ｔ The box welding method according to any one of claims 1 to 5, wherein the cross section has a trapezoidal shape having a diameter of 2.0 to 30.0 mm.

7. A box welding method according to any one of claims 1 to 6, wherein the weld metal retaining member has a cross section perpendicular to the longitudinal direction, and the area in contact with the extended long side weld bead on the side is a curve or a line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

8. A boxing welded joint formed by box-welding a standing plate to a main plate, comprising: a first weld bead formed along the short side of a rectangular abutment surface where the standing plate abuts against the main plate, and extending from both sides of the short side of the rectangular abutment surface onto the main plate in a straight line parallel to the short side of the rectangular abutment surface; and second and third weld beads which are extended long side weld beads formed along the long sides of the rectangular abutment surface and formed by covering the end of the first weld bead and extending onto the main plate, wherein in a cross section perpendicular to the longitudinal direction of the extended long side weld bead, the angle of elevation θ from the main plate in the region where the extended long side weld bead and the main plate contact each other is θ: 60° or less.

9. The boxing weld joint according to claim 8, wherein the second weld bead and the third weld bead are formed so as to satisfy the following formulas (1) and (2): M≦Q (1) 2.0≦M≦30.0 (2) where Q is the length of the short side of the rectangular abutment surface (mm), and M is the distance between the second weld bead and the third weld bead (mm).

10. A boxing weld joint as described in claim 8 or 9, wherein the shorter distance N between the short side of the rectangular abutment surface and the tip of the second weld bead or the third weld bead is 5.0 mm or more and 100.0 mm or less.

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