Rotation welding method and rotation welding joint

Abstract

The present invention provides a box welding method and a box welded joint. In the box welding method of the present invention, a first weld bead 3a is formed along the short side of the rectangular abutment surface 2a where the upright plate 2 abuts against the main plate 1, and then welding is performed so that the first weld bead 3a extends onto the main plate 1 from both sides of the short side of the rectangular abutment surface 2a. Next, a bottom width M T Weld metal damming member 4 having a rectangular bottom surface is disposed on main plate 1 so as to be in contact with first weld bead 3a. Next, second weld bead 3b and third weld bead 3c are formed along the long sides of rectangular abutment surface 2a, covering the end of first weld bead 3a, and extending onto main plate 1 along weld metal damming member 4.

Description

[Technical Field]

[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. [Background technology]

[0002] Steel structures typically have many boxing welded joints, where the periphery of a vertical plate, such as a gusset, is welded to the main plate (so-called boxing weld). In boxing welded joints, the 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 external forces refer to loads repeatedly acting on a steel structure from the outside. For example, if the steel structure is a steel bridge, these loads are repeatedly caused by natural weather conditions (e.g., wind) and vehicle traffic, and if the steel structure is a ship, these loads are 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 method consistently improves 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, gaps (i.e., spaces surrounded by the main plate, long side weld bead, and short side weld bead) tend to form where the weld beads overlap, and fatigue cracks due to stress concentration tend to occur. It is often difficult to prevent the propagation of fatigue cracks that do 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 the 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 that they 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 technology described in Patent Document 2 is said to be able to form a boxing weld joint inexpensively using conventional welding equipment and welding materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 8-19860 [Patent Document 2] JP 2018-158380 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, there has been a demand for further improvements in the fatigue strength of welded structures. Furthermore, the method described in 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 tend to form where the weld beads overlap, making it difficult to expect improvements in the fatigue strength of boxing welded joints.

[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. [Means for solving the problem]

[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 was completed based on the above findings and further investigations, and the gist of the present invention is as follows. [1] A turn welding method using a weld metal blocking member for turn-welding a vertical plate to a main plate, The weld metal retaining member has a bottom surface that abuts against the main plate with a width M T a rectangular base having a In the above-mentioned turning welding, a first weld bead is formed 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; Next, the weld metal retaining member is disposed on the main plate so as to be adjacent to the first weld bead, a second weld bead and a third weld bead are sequentially formed along a long side of the rectangular abutment surface, and the second weld bead and the third weld bead are placed over an end of the first weld bead, and are further extended onto the main plate so as to be aligned with the weld metal retaining member. Turn welding method. [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 is the length of the short side of the rectangular contact surface (mm), M: The distance (mm) between the second weld bead and the third weld bead. [3] The method of turning welding described in [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] The box welding method according to any one of [1] to [3], wherein the weld metal blocking member is a member that does not join with the weld metal. [5] The turn welding method according to [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, In a cross section perpendicular to the longitudinal direction, the width of the rectangular bottom surface that contacts the main plate is represented by the bottom width M T The box welding method according to any one of [1] to [5], wherein the wire has a trapezoidal cross section with a diameter of 2.0 to 30.0 mm. [7] A turn welding method according to any one of [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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less. [8] A turn-welded joint formed by turn-welding a vertical plate to a main plate, a first weld bead formed 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; a second weld bead and a third weld bead, which are extended long side weld beads formed along long sides of the rectangular abutment surface and covering ends of the first weld bead and extending onto the main plate; A boxing welded joint, wherein in a cross section perpendicular to the longitudinal direction of the extended long side weld bead, the elevation angle 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 [8], 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 is the length of the short side of the rectangular contact surface (mm), M: The distance (mm) between the second weld bead and the third weld bead.

[10] A boxing weld joint as described in [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. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram (plan view) that schematically shows the procedure of the box welding method according to the present invention. [Figure 2] FIG. 2 is a plan view schematically showing an example of a weld bead formed by the box welding method according to the present invention. [Figure 3] 3(a) to 3(c) are perspective views each showing a schematic example of the external shape of a weld metal blocking member according to the present invention. [Figure 4] FIG. 4 is a cross-sectional view schematically showing the relationship between the elongated weld bead and the weld metal blocking member after box welding according to the present invention. [Figure 5] FIG. 5 is a plan view showing the shape of a test piece for a boxing welded joint fatigue test used in an example of the present invention. DETAILED DESCRIPTION OF THE 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. The thickness of the main plate 1 is not particularly limited, but 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 steps of the box welding method according to the present invention for obtaining a box welded joint will be described with reference to Fig. 1. The rectangular contact surface 2a where the gusset 2 contacts 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 contact 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 top surface of the main plate 1. Next, the boxing welding step described below is carried out to produce a welded joint with 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. 1(a), 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, weld metal dam member 4 is disposed on main plate 1 so as to be adjacent to first weld bead 3a (see (b) in FIG. 1). In the present invention, the bottom surface of weld metal dam member 4 that contacts main plate 1 is referred to as rectangular bottom surface 4a. Preferably, width center line X of rectangular bottom surface 4a that contacts main plate 1 is aligned with thickness center line Y of the gusset. An error of up to 2 mm is allowed here. The structure of weld metal dam 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 weld metal dam member 4 is shown using the shape of rectangular bottom surface 4a when the bottom surface of the weld metal dam member contacts 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 retaining member 4 that has been placed 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. Third weld bead 3c is then formed by extending from the portion beyond gusset 2 along the long side of rectangular bottom surface 4a of pre-installed weld metal retaining member 4. Note that 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 weld bead 3a to third weld bead 3c can be formed along rectangular contact surface 2a of gusset 2. Although not shown in FIG. 1, weld beads can be formed around the gusset on the opposite side in a similar manner. Weld metal retaining member 4 is removed after welding is completed.

[0023] Figure 2 shows examples of weld beads formed using the above procedure. Second weld bead 3b and third weld bead 3c are formed so as to satisfy the following formula (1) and formula (2). M≦Q ‥‥(1) 2.0≦M≦30.0 ‥‥(2) where Q is the length of the short side of the rectangular contact surface 2a (mm), M: 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 distance between the bead toes of the second weld bead 3b and the third weld bead 3c). This inside distance between the bead toes of the second and third weld beads is an actual value (i.e., an actually measured value). This is the width M of the rectangular bottom surface 4a of the weld metal retaining member. T Approximately matches.

[0024] In the present invention, it is preferable that the distance M is set to 2.0 mm or more and 30.0 mm or less so as to satisfy the 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 spacing M) exceeds 30.0 mm, the second weld bead 3b and the third weld bead 3c are less effective at suppressing stress flowing into the weld toe of the first weld bead 3a. This reduces the effect of reducing stress concentration, and reduces the effect of improving fatigue strength. On the other hand, if the spacing M is less than 2.0 mm, the second weld bead 3b and the third weld bead 3c come into contact, making actual welding impossible. The spacing M is more preferably 5.0 mm or more, and more preferably 25.0 mm or less.

[0025] In addition to satisfying the above-mentioned formula (2), the spacing 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 2a of the gusset 2 so as to satisfy formula (1). If the spacing M (mm) exceeds the length Q (mm) of the short side of the rectangular abutment surface 2a 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 contact surface 2a and the tip of the second weld bead 3b and the distance between the short side of the rectangular contact surface 2a and the tip of the third weld bead 3c is defined as distance N. The "distance between the short side of the rectangular contact surface 2a and the tip of the second weld bead 3b (or the third weld bead 3c)" refers to the distance (i.e., the length) from the end of the rectangular contact surface 2a to the tip of the second weld bead 3b (or the third weld bead 3c). This distance N between the rectangular contact surface 2a and the tips of the second and third weld beads is an actual value (i.e., an actually measured value). Distance N is preferably 5.0 mm or greater. If 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. 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 distance N is too long, the welding time will be long. Therefore, the distance N is preferably 100.0 mm or less. The distance 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. As shown in FIG.

[0029] The weld metal blocking 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 3b and extended third weld bead 3c. This allows the actual measured value of distance M between extended second weld bead 3b and extended third weld bead 3c to be stably formed to be the target distance.

[0030] The weld metal blocking member 4 used in the present invention has a longitudinal length N T is 5 mm or more, and the width of the bottom surface 4a abutting against the main plate 1 (i.e., the bottom surface width) M T It is preferable that the thickness of the conductive film is 2.0 to 30.0 mm, and that the cross section perpendicular to the longitudinal direction (i.e., the length direction) has a substantially trapezoidal shape as shown in Fig. 3(a). However, the cross section may have a substantially rectangular shape as shown in Fig. 3(b). Longitudinal length N of weld metal blocking member 4 T If the base width M is less than 5 mm, the interval N during joint fabrication will be less than 5.0 mm, 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 above numerical range is the same as the reason for the interval M described above, and therefore will be omitted.

[0031] In addition, the longitudinal length N of the weld metal blocking member 4 T is a length corresponding to the length 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 interval 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 a range of 2.0 to 30.0 mm so as to match the target gap between extended second weld bead 3b and 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) shape in the region of the side surface of the weld metal damming member 4 that contacts the extended weld bead in a cross section perpendicular to the longitudinal direction, such that the elevation angle θ from the bottom surface 4a is θ: 60° or less. Instead of a curved shape, a straight line may be used, as shown in FIG. 3(c), in which the elevation angle θ from the bottom surface 4a is θ: 60° or less. By using such a curved or straight line, the bead shape of the extended weld bead tends to resemble a semi-ellipse, similarly with an elevation angle θ of 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 that resembles the desired semi-ellipse. Furthermore, the shape of the top surface of the weld metal blocking member 4 does not have to be flat. Here, the cross-sectional shapes shown in Fig. 3(a) and Fig. 3(c) are referred to as trapezoidal shapes, and the cross-sectional shape shown in Fig. 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 Fig. 3(a). Also, for example, as in Fig. 3(c), one of the two opposing sides has a base width M T On one side having a base 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. 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 they will not be explained 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, 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 from bottom surface 4a of 60° or less. 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, second weld bead 3b and third weld bead 3c are preferably formed so as to satisfy the above-described formulas (1) and (2). Also preferably, the shorter distance N between the short side of rectangular abutment surface 2a and the tip of second weld bead 3b or third weld bead 3c is 5.0 mm or more and 100.0 mm or less. The extended weld bead distance 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 interval 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. [Example]

[0042] Steel plate A was prepared with 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 plate has fatigue properties of m / cycle.

[0043] [Table 1]

[0044] From the prepared steel plate A, the main plate 1 (plate thickness: 14 mm, plate width: 80 mm, length: 500 mm) and the gusset 2 (plate thickness: 4 to 14 mm, plate width: 75 mm, height: 50 mm) that will become the standing plate were each cut. 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 contact 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 using gas metal arc welding with a flux-cored wire to produce a box-welded joint as shown in Figure 5. The flux-cored wire used was Kobe Steel's MX-Z200 (wire diameter: 1.2 mm), 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 procedure for box welding is shown below. First, first weld bead 3a, which is a short-side weld bead, was formed along the short side of rectangular abutment surface 2a of gusset 2. At this time, first weld bead 3a was welded so that it extended onto main plate 1 from both sides of the short side of rectangular abutment surface 2a, as shown in FIG. 1(a). The extension length of first weld bead 3a was set to a length that could be covered by second weld bead 3b and 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 FIG. 1(b)). The weld metal damming member 4 used was machined to a predetermined size using an FB-B3 machine manufactured by Kobe Steel, Ltd. The dimensions of each part (i.e., M T , N T , θ) are also listed 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 weld metal retaining member 4 that had been placed in advance.

[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 weld metal retaining member 4 that had been placed in advance.

[0050] Using the above procedure, weld beads were formed around the gusset to form a box weld joint as 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 providing weld metal retaining member 4, which was used as a comparative example.

[0051] For the obtained boxing welded joint, 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 measured value) was calculated, and the difference between the average value and the target value was calculated. The obtained results are also shown in the "Extended weld bead distance M" column in Table 2. 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 measured value was also listed 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 carried out in room temperature and air 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" mentioned above refers to the number of load repetitions until fatigue fracture occurs. The obtained fatigue life is shown in Table 2.

[0053] [Table 2]

[0054] In all of the examples of the present invention, the difference between the measured value and the target value for the distance 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 they 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 the comparative example (e.g., boxing weld joint No. 13) where the difference between the measured value and the target value for the distance 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 example of the present invention (boxing weld joint No. 4) with the same target value for the distance M. [Explanation of symbols]

[0055] 1 Main plate 2 Gusset (standing plate) 2a Rectangular contact 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 Welded 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, The weld metal retaining member has a width M of a bottom surface that abuts against the main plate. T a rectangular base having a In the above-mentioned turning welding, a first weld bead is formed 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; Next, the weld metal retaining member is disposed on the main plate so as to be adjacent to the first weld bead, a second weld bead and a third weld bead are sequentially formed along a long side of the rectangular abutment surface, and the second weld bead and the third weld bead are placed over an end of the first weld bead, and are further extended onto the main plate so as to be aligned with the weld metal blocking member. Turn welding method.

2. 2. The box 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): Note M≦Q (1) 2.0≦M≦30.0 (2) Where Q is the length of the short side of the rectangular contact surface (mm), M: The distance (mm) between the second weld bead and the third weld bead.

3. 2. The box welding method according to claim 1, wherein a shorter distance N between a short side of the rectangular abutment surface and a 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 turn welding method as described in claim 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.

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

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

7. The weld metal blocking member has a longitudinal length N T is 5 to 200 mm, In a cross section perpendicular to the longitudinal direction, the bottom width M represents the width of the rectangular bottom surface that contacts the main plate. Ｔ The box welding method according to any one of claims 1 to 4, wherein the cross section has a trapezoidal shape having a diameter of 2.0 to 30.0 mm.

8. The weld metal damming member has a longitudinal length N T of 5 to 200 mm, The box welding method according to claim 5, wherein the cross section perpendicular to the longitudinal direction has a trapezoidal cross section with a bottom width M T representing the width of a rectangular bottom surface in contact with the main plate being 2.0 to 30.0 mm.

9. The weld metal damming member has a longitudinal length N T of 5 to 200 mm, The box welding method according to claim 6, wherein the cross section perpendicular to the longitudinal direction has a trapezoidal cross section with a bottom width M T representing the width of a rectangular bottom surface in contact with the main plate being 2.0 to 30.0 mm.

10. The box welding method according to any one of claims 1 to 4, wherein a region of the weld metal damming member that contacts the extended long side weld bead on the side surface in a cross section perpendicular to the longitudinal direction is a curve or a straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

11. A pass welding method as described in Claim 5, 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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

12. A pass welding method as described in Claim 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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

13. A pass welding method as described in Claim 7, 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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

14. A pass welding method as described in Claim 8, 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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

15. A pass welding method as described in Claim 9, 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 straight line with an elevation angle θ from the rectangular bottom surface of θ: 60° or less.

16. A turn-welded joint formed by turn-welding a vertical plate to a main plate, a first weld bead formed 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; a second weld bead and a third weld bead, which are extended long side weld beads formed along long sides of the rectangular abutment surface and covering ends of the first weld bead and extending onto the main plate; In a cross section perpendicular to the longitudinal direction of the extended long side weld bead, an elevation angle θ from the main plate in a region where the extended long side weld bead and the main plate contact each other is θ: 60° or less. Turn welded joint.

17. 17. The boxing weld joint according to claim 16, wherein the second weld bead and the third weld bead are formed so as to satisfy the following formulas (1) and (2): Note M≦Q (1) 2.0≦M≦30.0 (2) Where Q is the length of the short side of the rectangular contact surface (mm), M: The distance (mm) between the second weld bead and the third weld bead.

18. 18. The boxing welded joint according to claim 16 or 17, wherein a shorter distance N between a short side of the rectangular abutment surface and a 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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