JP2022188325A - Turning weld joint with excellent fatigue strength and turning welding method - Google Patents

Abstract

To provide a turning weld joint which can improve a fatigue strength inexpensively and stably, and a turning welding method.SOLUTION: A turning weld joint, which is obtained by turning welding a gusset 2 to a main plate, has a first weld bead 3 which is continuously heaped up so as to pass a short side from one side of a long side of the gusset 2 by fillet-welding of the gusset 2 and the main plate to reach the other side of the long side of the gusset 2, and further has: a second weld bead 4 which is so formed as to extend on the main plate along the first weld bead 3 on one side of the long side of the gusset; and a third weld bead 5 which is so formed as to extend on the main plate along the first weld bead 3 on the other side of the long side of the gusset. An interval M between an extension part of the second bead 4 and an extension part of the third bead 5 is equal to or less than a length W of the short side of the gusset. The weld joint has a striking mark 9 over a range of 50% or more of the interval M in a region that extends from a weld toe of the first weld bead 3 to a surface of the main plate and is sandwiched between the two extension parts.SELECTED DRAWING: Figure 5

Description

The present invention relates to a turn-welded joint between a main plate and a gusset and a welding method that are widely used when constructing steel structures, and is particularly suitable for steel structures such as steel bridges and ships that require excellent fatigue properties. The present invention relates to a turn-welded joint and a turn-welding method.

Generally, in steel structures, as shown in FIG. 8, there are many boxing weld joints in which the periphery of the gusset 2 is fillet welded (so-called angle boxing welding) to the main plate 1 . In this boxing welded joint, the weld bead 3 surrounds the gusset 2, and defects such as cracks occur in the weld bead 3, and the shape of the weld toe 3a between the weld bead 3 and the main plate 1 changes. If it is not formed smoothly, stress concentration tends to occur at the weld toe 3a.

On the other hand, a technique for reducing the degree of stress concentration by deforming the boundary region from the weld toe to the surface of the main plate has been put into practical use. The deformation is created by striking a hard terminal against the boundary area and is commonly referred to as peening. Peening can suppress the occurrence of fatigue cracks in welded joints caused by external forces. The external force is the load that repeatedly acts on the steel structure from the outside, and in the case where the steel structure is a steel bridge, the load that is repeatedly generated by natural weather conditions such as wind and the passage of vehicles. If the object is a ship, it is a repetitive load caused by wind and waves.

In recent years, with the aging of steel structures, there have been an increasing number of reports on damage caused by fatigue. In order to prevent such damage, it is necessary to periodically inspect steel structures, manage the progress of damage, and take countermeasures as the damage progresses. In particular, when damage caused by fatigue occurs in a steel bridge, it is possible to reduce the external force acting on the steel bridge by restricting the passage of vehicles, but it causes traffic congestion and delays in logistics. It has a great negative impact on social activities. Therefore, techniques for improving the fatigue properties of welded joints by improving the soundness of boxing welded joints of steel structures are being studied.

In Patent Document 1, a gusset contacts a main plate with a rectangular contact surface (hereinafter referred to as a rectangular contact surface). Techniques for improving the fatigue strength of are disclosed. According to this technology, fatigue strength is improved by performing peening treatment over the entire length of the boxing weld. have.

In Patent Document 2, a short-side bead is formed in boxing welding, then two long-side beads are formed along the long side of the rectangular contact surface, and an interval is provided between the long-side beads. A method is disclosed for improving fatigue strength by striking the weld toe of the steel. In this technique, since the weld bead formed along the short side of the rectangular abutment surface of the gusset is short, the start and end of the weld are present at the stress concentration points of the boxing weld joint. Weld beads at the start and end of the weld are likely to have gaps, and there is concern that fatigue cracks may start at locations other than the peened locations.

JP 2006-175512 A JP 2018-171647 A

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the prior art and to provide a rotary welded joint and a rotary welding method capable of stably improving the fatigue strength at a low cost.

In order to increase the fatigue strength of boxing welded joints, the present inventors have studied techniques for suppressing the initiation and propagation of fatigue cracks. As a result, the gusset and the main plate are fillet welded so that the bead on the short side does not become a so-called short bead. and then extending onto the main plate along the weld bead on the long side of the gusset to form a second weld bead and a third weld bead, and between the extension of the second weld bead and the extension of the third weld bead It was found that the occurrence of fatigue cracks from the weld can be suppressed by peening the area from the weld toe between the welds to the surface of the main plate.

Furthermore, when a fatigue crack occurs, the starting point of the fatigue crack exists only between the two elongated weld beads, and the propagation of the fatigue crack occurring on the main plate side is restricted between the two beads. , and eventually fatigue cracks can be prevented from propagating over a wide area.

The present invention was completed based on these findings and further studies, and the gist of the present invention is as follows.
[1] A welded joint obtained by turn-welding a gusset to a main plate, wherein the gusset and the main plate are welded together by fillet welding so that one of the long sides of the gusset passes through the short side of the gusset and the It has a first weld bead continuously heaped up to the other long side of the gusset, and further extends on the main plate along the first weld bead on one side of the long side of the gusset. a formed second weld bead; and a third weld bead formed extending on the main plate along the first weld bead on the other side of the gusset long side, wherein the second weld bead The distance M between the extending portion of and the extending portion of the third weld bead is less than or equal to the length W of the short side of the gusset (M ≤ W), and the welding of the first weld bead sandwiched between the two extending portions A boxy welded joint characterized by having an impact mark over a range of 50% or more of the distance M in a region from the toe to the surface of the main plate.
[2] A rotary welded joint according to [1], wherein the length W of the short side of the gusset is 30.0 mm or less, and the interval M is 10.0 mm or less.
[3] The boxy welded joint according to [1] or [2], wherein the interval M is 1.0 mm to 4.0 mm.
[4] The boxy welded joint according to any one of [1] to [3], wherein the maximum depth of the impact mark is 0.03 mm or more and less than 0.50 mm.
[5] In any one of [1] to [4], when the stress intensity factor range ΔK of the main plate is 15 MPa·m ^1/2 , fatigue crack propagation in the width or thickness direction of the main plate A boxy welded joint characterized by a speed of 1.75×10 ⁻⁸ m/cycle or less.
[6] In any one of [1] to [5], when the stress intensity factor range ΔK of the main plate is 15 MPa·m ^1/2 , the fatigue crack propagation rate in the plate thickness direction of the main plate is A boxy welded joint characterized by being 1.00×10 ⁻⁸ m/cycle or less.
[7] In the welding method of joining the gusset to the main plate by turn welding, the gusset and the main plate are welded together by fillet welding from one of the long sides of the gusset through the short side of the gusset. A first weld bead is formed continuously extending to the other side of the long side, and a second weld bead extends onto the main plate along the first weld bead on one side of the long side of the gusset. forming a third weld bead extending on the main plate along the first weld bead on the other side of the gusset long side, and the extension of the second weld bead and the third weld bead The distance M from the extending portion is set to be equal to or less than the length W of the short side of the gusset (M≦W), and the region sandwiched between the two extending portions and extending from the weld toe of the first weld bead to the surface of the main plate A rounding welding method characterized in that an impact mark is provided over a range of 50% or more of the distance M in the.
[8] In [7], in providing the hit mark, the length T in the direction parallel to the short side of the gusset is 1 mm to 10 mm, and the radius of curvature R in the cross section perpendicular to the short side is 1 mm to 10 mm. A round welding method characterized by using a striking terminal.
[9] The round welding method according to [8], wherein the striking terminal is driven by air pressure or high-frequency current.
[10] In any one of [7] to [9], the turning is characterized in that the length W of the short side of the gusset is 30.0 mm or less and the interval M is 10.0 mm or less. Welding method.
[11] A round welding method according to any one of [7] to [10], wherein the interval M is set to 1.0 mm to 4.0 mm.
[12] A round welding method according to any one of [7] to [11], wherein the maximum depth D of the impact mark is 0.03 mm or more and less than 0.50 mm.
[13] In any one of [7] to [12], when the stress intensity factor range ΔK of the main plate is 15 MPa m ^1/2 in performing the boxing welding, the width of the main plate or A boxing welding method, wherein a fatigue crack propagation rate in a plate thickness direction is 1.75×10 ⁻⁸ m/cycle or less.
[14] In any one of [7] to [13], when the stress intensity factor range ΔK of the main plate is 15 MPa m ^1/2 in performing the boxing welding, the thickness direction of the main plate A boxing welding method characterized in that the fatigue crack propagation rate to 1.00×10 ⁻⁸ m/cycle or less.

In the present invention, the effect can be exhibited by using the main plate and the gusset of any material. Further extension of life can be expected by applying this to the main plates and gussets with low fatigue crack growth.

The present invention can be applied not only when constructing a new steel structure but also when repairing an aged steel structure.

According to the present invention, when constructing a new steel structure or when repairing an aged steel structure, it is possible to inexpensively and stably improve the fatigue strength of boxing welded joints. It has a remarkable effect.

1 is a schematic perspective view schematically showing a boxing welded joint according to the present invention; FIG. It is a schematic plan view which shows typically the welding execution procedure of the box welding method which concerns on this invention. FIG. 3 is a schematic cross-sectional view of the boxing welded joint according to the present invention, viewed from the gusset long side. FIG. 4 is a schematic plan view showing the vicinity of the weld bead extending portion of the boxing welded joint according to the present invention; FIG. 4 is a schematic plan view showing an impact mark around the weld bead extending portion of the boxing welded joint according to the present invention. 1 is a schematic perspective view schematically showing a striking terminal used in the boxing welding method according to the present invention; FIG. FIG. 2 is a schematic plan view and a schematic right side view showing a test piece of a boxing welded joint according to the present invention; It is a schematic perspective view which shows the conventional boxing-welded joint typically.

First, the gusset and main plate to which the present invention is applied will be described.

[Gusset]
The plate thickness of the gusset is the length W of the short side of the gusset described above, and specifically, it is preferably 5.0 mm to 30.0 mm. Further, the plate length of the gusset is the length of the long side of the gusset, and specifically, it is preferably 30.0 mm to 1,000.0 mm. Furthermore, the width of the gusset is the height of the gusset, and specifically, it is preferably 50.0 mm to 1,000.0 mm.
Steel grades of the gusset include SM400, SM490, etc., and the tensile strength is preferably in the range of 400 MPa to 720 MPa.

[Main plate]
The shape of the main plate is not particularly specified, and any shape can be applied. 0 mm is preferred.

Examples of steel types for the main plate include SM400 and SM490. In particular, steel materials that require fatigue crack propagation resistance include SM490 and SM570, and the tensile strength is preferably in the range of 400 MPa to 720 MPa.

As will be described later, this fatigue crack propagation resistance is evaluated by obtaining the fatigue crack propagation rate (da/dN) corresponding to the stress intensity factor range (ΔK) by a fatigue crack propagation test conforming to ASTM E647. ing.

Next, the welded joint and construction procedure of the present invention will be specifically described with reference to the drawings.

[Construction procedure and structure of boxing welded joint]
FIG. 1 is a schematic perspective view schematically showing an example of a box-welded joint according to the present invention, and FIGS. 1 is a schematic plan view schematically shown; FIG. The construction procedure of the boxing weld joint according to the present invention will be described below with reference to FIGS. 2(a) to 2(d).

First, as shown in FIG. 2( a ), the first weld bead 3 is formed along the entire circumference of the gusset 2 . Since the first weld bead 3 is formed so as to wrap around the gusset 2, it is longer than the short side of the gusset 2, ensuring soundness of the weld bead in the peripheral region of the short side.

In addition, as shown in FIG. 3, it is preferable that the width S of the first weld bead 3 and the height H of the first weld bead 3 are substantially equal. Specifically, it is preferable to set the width-to-height ratio [S/H] in the range of 0.9 to 1.2 from the viewpoint of reducing stress concentration in the region.

Next, as shown in FIG. 2(b), a second weld bead 4 is formed along one of the long sides of the first weld bead 3 formed on the gusset 2. Next, as shown in FIG. Then, the second weld bead 4 is extended from the first weld bead 3 onto the main plate 1 to form an extension portion 4a.

Subsequently, as shown in FIG. 2C, a third weld bead 5 is formed along the other long side of the first weld bead 3 formed on the gusset 2 . Then, the third weld bead 5 is extended from the first weld bead 3 onto the main plate 1 to form an extension portion 5a.

By forming the second weld bead 4 and the third weld bead 5 in the first weld bead 3 in this way, the occurrence of defects such as voids inside the first weld bead 3 can be prevented, and the weld bead 3 can be , 4, 5 and the main plate 1, and as a result, fatigue cracks can be prevented regardless of the shape of the weld toe 3a of the first weld bead 3. .

Regarding the second weld bead 4 and the third weld bead 5, in FIGS. Although the third weld bead 5 is formed along the right side of , there is no problem even if the left and right are reversed. That is, the present invention can be applied even if the weld bead formed along the right side of the long side of the gusset 2 is the second weld bead 4 and the weld bead formed along the left side of the long side is the third weld bead 5. can be done.

After forming each weld bead 3, 4, 5 in such a procedure, it is sandwiched between the extended portion 4a of the second weld bead 4 and the extended portion 5a of the third weld bead 5 shown in FIG. 2(d). A region (hereinafter also referred to as a “boundary region”) 8 from the weld toe 3a of the first weld bead to the surface of the main plate 1 is hit (peened) and shown in FIGS. A hit mark 9 shown is provided. The range is 50% or more of the distance M between the extended portion 4 a of the second weld bead 4 and the extended portion 5 a of the third weld bead 5 . By striking a range of 50% or more, compressive residual stress is introduced into the impact mark 9 and the surrounding main plate surface, fatigue cracks can be prevented from occurring from the weld toe, and fatigue cracks can be prevented from occurring. , the crack propagation can be suppressed. If this range is less than 50% of the interval M, the range of introduction of compressive residual stress is small and the effect of preventing fatigue cracks from the weld toe is not exhibited.

[Gap between extensions M, length N]
FIG. 4 is an enlarged view showing an example in which the weld beads 3, 4 and 5 are formed and the boundary region 8 is formed by the above procedure. When the distance M between the extended portion 4a of the second weld bead 4 and the extended portion 5a of the third weld bead 5 formed by extending on the main plate 1 becomes larger than the length W of the short side of the gusset 2, the second A fatigue crack starting at the weld toe portion of the first weld bead 3 between the weld bead 4 and the third weld bead 5 is likely to occur. Therefore, the distance M is set to be equal to or less than the length W of the short side (M≦W). Here, the distance M refers to the shortest distance between the extension 4a of the second weld bead 4 and the extension 5a of the third weld bead 5.

Furthermore, the length W of the short side is 30.0 mm or less as a general example. It is preferable to: As a matter of course, when the length W of the short side is 10.0 mm or less, the interval M≤W. Furthermore, regardless of the length W of the short side, by setting the interval M to 1.0 mm to 4.0 mm, the fatigue resistance is more excellent (the effect of improving the fatigue life is greater), which is more preferable. . If the interval M=0 mm, that is, if the interval does not exist, the case-welded portion of the conventional case-welded joint is stretched, and the embodiment of the present invention cannot be implemented. Therefore, the interval M should satisfy M>0 mm. It should be noted that even if the distance M is larger than the length W of the short side, the effect of improving the fatigue life to some extent can be expected compared to a normal welded joint.

Next, the length N of the extended portions 4a and 5a of the second weld bead 4 and the third weld bead 5 is the length from the end of the first weld bead to the tip of the extended portion, as shown in FIG. If the length N exceeds 10.0 mm, it is not preferable from the viewpoint of welding work efficiency and work cost, so N is preferably 10.0 mm or less. More preferably, N is between 4.0 mm and 8.0 mm.

[Blow mark]
FIG. 5 is a schematic plan view showing a range in which compressive residual stress is introduced by the impact mark 9. As shown in FIG. Reference character Q shown in FIG. 5 indicates the length (width) of the impact mark 9 in the direction parallel to the short side of the gusset 2 . As shown in FIG. 5( a ), when the width Q and the interval M of the impact marks satisfy Q≧0.5M, the extended portion 4 a of the second weld bead 4 and the extended portion 5 a of the third weld bead 5 Compressive residual stress is introduced into the entire range sandwiched between the weld toes of the first weld bead, fatigue cracking is suppressed, and the fatigue life of the welded joint can be improved. Note that FIG. 5A is an example of Q=M. However, as shown in FIG. 5(b), when Q<0.5M, the range in which the compressive residual stress is introduced is narrow, and fatigue cracks occur from the weld toe where the compressive residual stress is not introduced. becomes an easy state. However, it should be noted that even when Q<0.5M, the effect of improving the fatigue life is obtained compared to the state in which no impact is applied.

Furthermore, as for the depth of the impact mark 9, the maximum depth is preferably 0.03 mm or more and less than 0.50 mm. This is because if the thickness is less than 0.03 mm, the effect of suppressing fatigue crack initiation is poor, and if it exceeds 0.50 mm, stress concentration associated with a local decrease in plate thickness accelerates the initiation of fatigue cracks, which is undesirable.

[Battering terminal]
As shown in FIG. 6, the striking terminal 10 preferably has a curved surface in which the lower end portion of a quadrangular prism is curved in a semi-arc shape, and the aforementioned boundary region 8 is struck with the arc-shaped curved surface. .

When the striking terminal 10 shown in FIG. 6 is used, it is preferable to arrange the striking terminal 10 so that the direction of the thickness T of the striking terminal 10 and the short side of the gusset 2 are parallel to each other, and strike the boundary region 8 . When the thickness T of the striking terminal 10 is small, fatigue cracks are likely to occur starting from the striking mark 9 . If the thickness T is too large, it will be difficult to obtain the appropriate impact marks 9 described above. Therefore, the thickness T of the striking terminal 10 is preferably in the range of 1 mm to 10 mm.

When the direction of the thickness T of the striking terminal 10 and the short side of the gusset 2 are arranged parallel to each other, the width L of the striking terminal 10 becomes parallel to the long side of the gusset 2 . The lower end of the surface defined by the width L is preferably semicircular with a radius of curvature R. If the radius of curvature R is too small, the width Q of the impact mark 9 becomes small, and fatigue cracks are likely to start. If the radius of curvature R is too large, it will be difficult to obtain the appropriate impact marks 9 described above. Therefore, the width Q of the striking terminal 10 is preferably in the range of 1 mm to 10 mm.

It is preferable that the impact mark 9 is formed by driving the impact terminal 10 with air pressure or high-frequency current. For example, a method of pneumatically actuating the semi-cylindrical tip described above and striking the weld toe is preferred. In addition, the tip of the striking terminal 10 may be spherical, rectangular, or similar in shape, and the striking point may be the base metal side of the welded portion. good. Furthermore, for the percussion device, devices with other driving force such as high-frequency current, ultrasonic waves, etc. can also be used.

In the above description, an example was described in which the second weld bead 4 and the third weld bead 5 were formed around one short side of the gusset 2. However, as shown in FIG. The present invention can be similarly applied when forming the second weld bead 6 and the third weld bead 7 around the short side.

The boxing welded joint obtained by the present invention described above can prevent the occurrence of fatigue cracks regardless of the shape of the weld toe. And when a fatigue crack occurs, it can prevent the fatigue crack from propagating over a wide area. Moreover, since it can be obtained using conventional welding equipment and welding materials, it is possible to suppress an increase in construction costs.

[Welding method]
Welding methods for carrying out box welding are mainly shielded arc welding and gas metal arc welding, but other means can also be used as appropriate, and either manual welding or automatic welding may be employed.
The present invention can be applied not only when constructing a new steel structure, but also when repairing an aged steel structure.

[Fatigue crack propagation resistance]
The fatigue crack propagation resistance properties of welded joints and steel plates (gussets, main plates) are determined by fatigue crack propagation tests conforming to the standard of ASTM E647 to determine the fatigue crack propagation rate (da/dN) corresponding to the stress intensity factor range ΔK. I am evaluating. This stress intensity factor range ΔK is ΔK=Kmax−Kmin, and represents the difference between the maximum value and the minimum value of the stress intensity factor. In addition, the fatigue crack propagation rate (da / dN) indicates that the fatigue crack propagates when a constant load is repeatedly applied to the test piece, and the rate at that time (fatigue crack propagation rate) is the crack length a and the number of repetitions N is obtained as a tangent line (da/dN) of a curve representing the relationship of

Here, in the present invention, as a welded joint and a steel plate having excellent resistance to fatigue crack propagation, when the stress intensity factor range ΔK is 15 MPa m ^1/2 , fatigue crack propagation in the plate width or plate thickness direction The speed is 1.75 × 10 ^-8 m / cycle or less, and as a welded joint and a steel plate exhibiting further excellent properties, when the stress intensity factor range ΔK is 15 MPa m ^1/2 , the plate It means that the fatigue crack propagation rate in the thickness direction is 1.00×10 ⁻⁸ m/cycle or less.

In the welded joint obtained by turn-welding the gusset to the main plate, the fatigue crack occurs in the boundary region 8 shown in FIG. Cause joint failure. Therefore, if the fatigue crack propagation in the width or thickness direction of the steel sheet is delayed, that is, if the fatigue crack propagation speed is slow, it is expected that the period until joint fracture will be extended. Welded joints were prepared from various steel plates to verify the relationship between fatigue crack propagation characteristics and rupture life of welded joints. In the welded joint of the present invention, if the fatigue crack propagation rate in the plate width or plate thickness direction is 1.75 × 10 ^-8 m / cycle or less, the rupture life is 4% compared to the welded joint of the steel plate otherwise. It was found that the above was improved. Furthermore, a welded joint whose main plate is a steel plate whose fatigue crack propagation rate in the plate thickness direction is 1.00 × 10 ^-8 m / cycle or less has a rupture life improved by 20% or more compared to a steel plate that does not satisfy the characteristics. It became clear that

Using the test piece shown in FIG. 7, the following welding experiment was conducted.
Gusset 2 (plate thickness: 25mm, plate width: 75mm, height: 60mm) was welded to main plate 1 (plate thickness: 12mm, plate width: 80mm, length: 500mm) by gas-shielded arc welding using a flux-cored welding wire. A welded joint was produced by box welding. MX-Z200 (wire diameter: 1.2 mm) manufactured by Kobe Steel, Ltd. was used as the flux-cored welding wire, and the welding conditions were aimed at a voltage of 240 V and a current of 36 A, and welding was performed so that the leg length was about 8 mm. The gusset 2 was positioned at the center of the main plate 1 in the width and length directions. The striking terminal used had a shape of T=3 to 5 mm and L=4 mm as shown in FIG. 6, and was struck at an air pressure of 6 kg/cm ² and a frequency of 90 Hz. Materials having the components shown in Table 1 were used for the main plate 1 and gussets 2 .

Steel grades A to C were used for the main plate 1, and steel grade D was used for the gusset 2. For test numbers 3, 4, 7, 8, 11, and 12, the gusset 2 was processed to have a plate thickness of 10 mm. Regarding test numbers 5 to 7, when the stress intensity factor range ΔK is 15 MPa m ^1/2 , the fatigue crack propagation speed in the plate width direction is 1.75 × 10 ^-8 m / cycle or less. Steel plate B was used as main plate 1 . For test number 8, when the stress intensity factor range ΔK is 15 MPa m ^1/2 , steel plate C having a fatigue crack propagation rate in the plate thickness direction of 1.00 × 10 ^-8 m / cycle or less is used as the main plate. used as 1. When the stress intensity factor range ΔK of steel plate A is 15 MPa·m ^1/2 , the fatigue crack propagation speed in the plate width direction is 1.92×10 ⁻⁸ m/cycle.

Table 2 shows the fatigue test results of the welded joints produced as described above.
The fatigue test was carried out by load control using a hydraulic servo pulsar and fixing both longitudinal ends of the test piece to the testing machine. A load was applied in which the load varied sinusoidally along time. One stress loading cycle is defined as the period from reaching the minimum or maximum load to reaching the minimum or maximum load again. The minimum load was set to be 0.1 times the maximum load, and the maximum load was constant in one fatigue test. The stress range is the maximum load minus the minimum load. The rupture life was defined as the number of cycles from the start of loading, i.e., 0 cycles, until the fatigue crack penetrated through the thickness and width direction of the main plate and the specimen fractured.

From the results in Table 2, it can be seen that Test Nos. 1 to 8, which are examples of the present invention, all have excellent rupture life, that is, fatigue properties. Test numbers 5 to 8 using steel plate B and steel plate C, which are excellent in the fatigue crack propagation rate in the plate thickness direction, showed particularly excellent fatigue properties.

1 main plate 2 gusset 3 first weld bead 3a weld toes 4, 6 second weld bead 5, 7 third weld bead 4a second weld bead extension 5a third weld bead extension 8 boundary region 9 impact mark 10 striking terminal

Claims (14)

A welded joint obtained by turn-welding a gusset to a main plate, wherein the gusset and the main plate are welded together by fillet welding from one side of the long side of the gusset through the short side of the gusset to the length of the gusset. It has a first weld bead continuously heaped up to the other side of the gusset, and is formed extending on the main plate along the first weld bead on one side of the gusset long side. a second weld bead; and a third weld bead formed by extending on the main plate along the first weld bead on the other side of the gusset long side, the extended portion of the second weld bead and the distance M between the extending portion of the third weld bead is less than or equal to the length W of the short side of the gusset (M ≤ W), and the weld toe portion of the first weld bead sandwiched between the two extending portions A rotary welded joint characterized by having an impact mark over a range of 50% or more of the distance M in a region from to the surface of the main plate. 2. A turn welded joint according to claim 1, wherein the length W of the short side of said gusset is 30.0 mm or less and said spacing M is 10.0 mm or less. A turn-welded joint according to claim 1 or 2, characterized in that said spacing M is between 1.0 mm and 4.0 mm. 4. The boxing welded joint according to any one of claims 1 to 3, wherein the maximum depth of said hit mark is 0.03 mm or more and less than 0.50 mm. When the stress intensity factor range ΔK of the main plate is 15 MPa·m ^1/2 , the fatigue crack propagation rate in the plate width or plate thickness direction of the main plate is 1.75 × 10 ^-8 m/cycle or less. A rotary weld joint according to any one of claims 1 to 4. When the stress intensity factor range ΔK of the main plate is 15 MPa·m ^1/2 , the fatigue crack propagation rate in the plate thickness direction of the main plate is 1.00×10 ⁻⁸ m/cycle or less. A box weld joint according to any one of claims 1 to 5. In the welding method for joining the gusset to the main plate by turning and welding, the gusset and the main plate are welded together by fillet welding, passing through the short side of the gusset from one side of the long side of the gusset, and joining the long side of the gusset. Forming a first weld bead continuously heaped up to the other side, and forming a second weld bead extending on the main plate along the first weld bead on one side of the gusset long side. forming a third weld bead extending on the main plate along the first weld bead on the other side of the gusset long side, the extension of the second weld bead and the extension of the third weld bead; The distance M is set to the length W or less of the short side of the gusset (M ≤ W), and the distance from the weld toe of the first weld bead sandwiched between the two extensions to the surface of the main plate is the distance A boxing welding method characterized by providing an impact mark over a range of 50% or more of M. In forming the impact mark, a striking terminal having a length T in a direction parallel to the short side of the gusset of 1 mm to 10 mm and a curvature radius R of 1 mm to 10 mm in a cross section perpendicular to the short side is used. The round welding method according to claim 7, characterized by: 9. The round welding method according to claim 8, wherein the striking terminal is driven by air pressure or high-frequency current. The box welding method according to any one of claims 7 to 9, wherein the length W of the short side of the gusset is 30.0 mm or less, and the distance M is 10.0 mm or less. The box welding method according to any one of claims 7 to 10, characterized in that the interval M is set to 1.0 mm to 4.0 mm. The boxing welding method according to any one of claims 7 to 11, characterized in that the maximum depth D of the impact mark is 0.03 mm or more and less than 0.50 mm. In performing boxing welding, when the stress intensity factor range ΔK of the main plate is 15 MPa·m ^1/2 , the fatigue crack propagation rate in the width or thickness direction of the main plate is 1.75 × 10 ^-8 m. /cycle or less. When performing boxing welding, when the stress intensity factor range ΔK of the main plate is 15 MPa m ^1/2 , the fatigue crack propagation speed in the plate thickness direction of the main plate is 1.00 × 10 ^-8 m/cycle. The boxing welding method according to any one of claims 7 to 13, characterized in that:

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