JP2012011462A - Welded joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welded joint which is suitable for a steel structure, such as a steel bridge, requiring excellent fatigue characteristics and of which fatigue strength is improved by introducing compression residual stress without imparting deformation, which becomes a new stress concentration part, on a welded part.SOLUTION: The steel welded joint includes an impact trace continuously formed along a welding bead on a steel material surface by hammer peening or an oscillation terminal of ultrasonic impact treatment. A tip end part of the oscillation terminal is a circular arc shape in which a top part of a perpendicular cross section in a movement direction has a curvature radius of 1-10 mm, or a shape in which a top part of a perpendicular cross section in the movement direction includes a straight line part of 0.1 mm or less and chamfered parts having a curvature radius of 0.1-2 mm on both ends of the straight line part, or a circular arc shape on a major axis side of an oval shape in which a top part of a perpendicular cross section in the movement direction is the oval shape with a minor axis of 1 mm or longer and the minor axis/the major axis≤2. The oscillation terminal has a width of 1-10 mm in the movement direction. The impact trace is formed in a region of 5 mm, preferably 0.5-5 mm, on a base material side from a weld toe part in a maximum depth of at least 0.03 mm and less than 0.50 mm.

Description

  The present invention is a welded joint suitable for steel structures that require excellent fatigue properties such as steel bridges, and improves fatigue strength by introducing compressive residual stress without deforming the welded part as a new stress concentration part. About what

  In recent years, with the aging of steel bridges, reports of damage cases due to corrosion and fatigue are increasing. In order to prevent these problems, it is necessary to establish an inspection system. In particular, in the case of fatigue damage, it is important to reduce the external force of the passing vehicle and improve the welding quality from the design and production aspects.

  If the weld has defects such as cracks, or if the shape of the toe is inadequate and becomes a stress concentrated part, the effect of welding residual stress is superimposed on the repeated stress and fatigue notches are likely to occur, resulting in fatigue failure. Therefore, proposals from various viewpoints have been made for the prevention.

  Patent Document 1 relates to a method for improving the fatigue strength of a welded portion and a welded structure using the welded portion, and is a processing device that performs plastic deformation by striking the vicinity of the weld toe while ultrasonically oscillating. It is described that the fatigue strength can be stably improved without depending on the skill level of the worker at high speed by processing under the striking condition.

  Patent Document 2 relates to a laser shock peening method, which uses a pulsed laser beam from a laser light source to instantaneously vaporize a surface thin layer or a surface coating that forms a plasma, and a part of the surface due to its explosive force. Describes a method of introducing a compressive residual stress into a fan rotor blade of a gas turbine engine by a method of locally generating a compressive force.

  Patent Document 3 relates to a method and apparatus for improving the fatigue characteristics of a welded joint, and a device for the same, and using a striking pin whose tip is a specific size, the steel plate surface is formed so that a groove having a specific size is formed at the weld toe. It is described that compressive residual stress is introduced into the weld by compressing.

  Non-Patent Document 1 relates to a method for improving the fatigue strength of a welded joint portion of high strength steel (SM570) by hammer peening and TIG treatment, and since fatigue strength may decrease when hammer peening is applied, the stress concentration at the weld toe And the results of studies on a new hammer peening method that reduces residual stress.

  Normally, hammer peening is performed by an operator holding a peening device in hand so that the tip of the tip (tip is also called a vibration terminal or chipper) hits the welding toe from an oblique upper side, and deposits the load of the peening device on the welding toe. In this way, work is reduced to reduce the workload.

  Therefore, when hammer peening is performed on the out-of-plane gusset joint in which the rib 2 is erected on the base material 1 shown in FIG. 13, a deep groove (striking mark) that becomes a stress concentration point at the weld toe by the tip of the chipper 5 of the peening apparatus. ) And a fatigue crack 7 may occur from the tip of the weld bead 3.

  Non-Patent Document 1 introduces that grinding a part of the weld toe with a grinder before hammer peening is effective in preventing the occurrence of fatigue notches, and proposes that hammer peening be performed multiple times of about 3 passes. is doing.

JP 2006-175512 A JP 2006-159290 A JP 2010-29897 A

IMPROVING FATIGUE STRENGTH OF WELDED JOINTS BY HAMMER PEENING TIG-DRESSING: Kengo ANAMI, Chitoshi MIKI, Hideki TANI, Haruto YAMActu, Str. / Earthquake Eng. , JSCE, Vol. 17, NO. 1, 57s-68s, 2000 April)

  By the way, when manufacturing a welded structure, a welding method is selected in consideration of the work environment, work efficiency, and welded joint performance. In order to improve the fatigue strength of the welded portion, the fatigue strength of the welded portion described in Patent Document 1 is improved. Although the method is applied, if the characteristics of the welded joint having excellent fatigue characteristics are clear, it is possible to select an optimal fatigue strength improving method in the same manner as the selection of the welding method.

  Patent Document 3 describes a welded structure having excellent fatigue resistance characteristics, and discloses a welded portion that is preferable as a welded part of a fatigue crack occurrence risk part. However, when applied to an actual structure, the welded part is disclosed. There are concerns about the difficulty in obtaining the equipment and the construction efficiency. Moreover, the hit | damage processing method of patent document 3 uses the hit | damage pin whose tip curvature radius is 1/2 or less of the thickness of a metal material and 2-10 mm, and the hit pin does not touch a weld metal during hitting. Although it gives an impact mark on the surface of the base metal material, it is difficult to efficiently introduce compressive residual stress.

  In addition, the ultrasonic peening method described in Patent Document 1 is expensive and difficult to obtain as compared with a conventional device that drives a chip with air pressure. The laser shock peening method described in Patent Document 2 requires pretreatment of the material, and the apparatus is expensive and large, and is difficult to apply to steel bridge manufacturing.

  Then, in order to solve the said subject, this invention aims at providing the welded joint excellent in the fatigue characteristic.

In order to improve the fatigue strength of the welded joint, the present inventors have intensively studied a method for reducing the tensile residual stress due to welding of the toe portion where fatigue cracks are likely to occur, and the hammer peening damage mark is welded to the weld toe. It has been found that the maximum compressive residual stress due to impact can be introduced into the weld toe when it is further away from the base metal side. The present invention has been made based on the above findings and further studies. Hammer peened or ultrasonic impact treated steel welded joint, having a striking trace continuously formed on the steel surface along the weld bead by the vibration terminal, the tip of the vibration terminal is advancing The apex of the cross section perpendicular to the direction is an arc shape with a radius of curvature of 1 mm or more and 10 mm or less, and has a length of 1 mm or more and 10 mm or less in the traveling direction. A welded joint having a maximum depth of 0.03 mm or more and less than 0.50 mm in a region up to 5 mm.
2. The vibration terminal has a chamfered portion with a radius of curvature of 0.1 mm or more and 2 mm or less at both ends of a linear portion whose top portion of the cross section perpendicular to the traveling direction is 3 mm or less, and a length of 1 mm or more and 10 mm or less in the traveling direction. 2. The welded joint according to 1, wherein
3. The tip of the vibration terminal has an elliptical arcuate shape with a short axis of 1 mm or more at the top of the cross section perpendicular to the traveling direction, and has a length of 1 mm or more and 10 mm or less in the traveling direction. The weld joint according to 1.
4). The weld joint according to any one of claims 1 to 3, wherein the hitting mark is formed in a region from a position 0.5 mm away from the weld toe to the base metal side to 5 mm by the vibration terminal. .

  According to the present invention, a welded joint excellent in fatigue strength of a welded portion is obtained, which is extremely useful industrially.

Schematic explaining the principle that fatigue characteristics are improved by the welded joint according to the present invention. The figure explaining the X, Y, Z direction of the vibration terminal used for the hit | damage of the welded joint which concerns on this invention It is a figure explaining the vibration terminal used for the hit | damage of the welded joint which concerns on this invention, (a) is a XZ cross section, (b) is a figure which shows the shape of a YZ cross section. It is a figure explaining the other vibration terminal used for the hit | damage of the welded joint which concerns on this invention, (a) is a XZ cross section, (b) is a figure which shows the shape of a YZ cross section. It is a figure explaining the other vibration terminal used for the hit | damage of the welded joint which concerns on this invention, (a) is a XZ cross section, (b) is a figure which shows the shape of a YZ cross section. It is a figure which shows the effect of the vibration terminal which has the shape of various front-end | tip parts, (a) is a shape of a front-end | tip part, (b) shows the relationship between the residual stress of the X direction by the FEM analysis result, and the distance from a deformation | transformation center. Figure. The top view which shows the positional relationship of a welding toe and a hit | damage trace. The top view of the test body of an Example. Example ((a) is the shape of the tip portion, (b) is a diagram showing the shape of the vibration terminal and the result of residual stress measurement). The dimensional shape of the two welded joints used in the examples and the measurement positions of the hitting marks are shown, (a) is a top view, and (b) is a side view. For two welded joints, a laser is applied from the weld metal to the base metal at the position where the cross-sectional shape in the vicinity of the rotating welded portion shown in FIG. 10 (a) is obtained (the position of the end portion in the length direction of the 75 mm long rib). It is a figure which shows the log | history of the cross section measured by 0.5 mm pitch using the displacement meter, (a), (b) shows the measurement result in each welding joint. The figure which shows the fatigue test result of the two welded joints which showed the cross-sectional shape of the welding part to Fig.11 (a), (b). The figure explaining the defect which arises in a toe by hammer peening.

  The present invention is a welded joint of steel material, and is compressed to the weld toe by continuously forming a striking trace along the weld bead on the surface of the steel material around the weld toe, excluding the weld metal and the weld toe. The residual stress is introduced. In the following description, the toe (sometimes referred to as a weld toe) is defined as the line of intersection between the surface of the member and the surface of the weld metal (the illustrated welding terminology dictionary, Nikkan Kogyo, September 20, 1971, 4th edition).

  FIG. 1 is a schematic view for explaining the principle of improving fatigue characteristics by a welded joint according to the present invention, and shows a side view of a welded joint welded by welding a rib 2 around a base material 1. The surface of the base material 1 at a distance d from the toe 4 of the weld bead 3 is plastically deformed (indicated by a dotted line) by pressing the base material surface with a tip (not shown) having a width B in a direction perpendicular to the base material surface. It is a blow mark that caused.

  The position of the impact mark on the surface of the base material 1 (specified by the distance d from the toe 4) is determined by the compressive residual stress generated in the base material 1 due to the welding of the toe 4 when the impact mark is formed by the tip having the width B. The tensile residual stress is canceled out so that the toe 4 has a compressive residual stress. Even when the hitting mark is formed in contact with the toe (distance d = 0), the compressive residual stress can be introduced into the toe, and therefore is within the scope of the present invention.

  In the welded joint according to the present invention, the base material surface is pressurized as an index of the influence of the compressive residual stress generated in the base material 1 when the impact mark is formed on the tensile residual stress at the toe 4. The shape of the vibration terminal used for forming the hitting mark on the surface and the maximum depth of the hitting mark in the region closer to the base material than the weld toe are used. In the welded joint according to the present invention, the weld bead including the weld toe is not struck in principle. However, the weld bead is temporarily deformed to such an extent that the weld bead is not subjected to plastic deformation by adjustment immediately before and after the operation. You can strike it.

  3 to 5 show the shape of the tip of the vibration terminal. FIG. 2 is a diagram for explaining the X direction and the Y direction in these drawings. The X direction is a direction perpendicular to the striking direction, and the Y direction is the striking direction.

  The vibration terminal shown in FIG. 3 has a circular arc shape with a radius of curvature (r) of 1 mm or more and 10 mm or less at the top in a cross section (XZ cross section) in which the tip of the vibration terminal is perpendicular to the traveling direction (Y direction). It has an outer periphery (FIG. 3 (a)) and has a length (b) of 1 mm or more and 10 mm or less in the traveling direction (Y direction) (FIG. 3 (b)).

  In the case of an oscillating terminal having an arcuate outer periphery at the top, if the radius of curvature of the arc is less than 1 mm, deformation that becomes a stress concentration part may be formed at the toe, whereas if it exceeds 10 mm, the contact area may be Since it becomes large and sufficient compressive residual stress cannot be applied to the toe, the radius of curvature (r) is set to 1 mm or more and 10 mm or less.

  FIG. 4 shows the shape of a vibration terminal according to another example of the present invention, and the tip of the vibration terminal is 3 mm or less at the top in a cross section (XZ cross section) perpendicular to the traveling direction (Y direction). It has an outer peripheral portion having a chamfered portion with a radius of curvature (r) of 0.1 mm or more and 2 mm or less at both ends of the linear portion a (FIG. 4A), and a length of 1 mm or more and 10 mm or less in the traveling direction (Y direction). It has a substantially bowl shape having (b) (FIG. 4 (b)). The tip of the vibration terminal of the example of the present invention is a flat rectangular portion.

  In the case of a vibration terminal having an outer peripheral portion with a straight portion a at a part of the top portion, it is necessary to provide chamfered portions on both sides to prevent the occurrence of cracks due to impact. If the radius of curvature (r) of the chamfered portion is less than 0.1 mm, the chamfered portion may form a deformation that becomes a stress concentrated portion at the toe, whereas if it exceeds 2 mm, the contact area increases, Therefore, a chamfered portion with a radius of curvature of 0.1 mm to 2 mm is used.

  Since the compressive residual stress is also applied by the chamfered portion, the length of the straight portion a of the rectangular portion is set to 3 mm or less. When the length of the straight part a of the rectangular part exceeds 3 mm, a deformation that becomes a stress concentration part is formed at the toe.

  Since the vibration terminal shown in FIG. 4 has a rectangular portion at the tip of the vibration terminal, it is possible to repeatedly hit the same place with a smaller number of hits compared to a tip or a tip having a spherical shape, which is efficient. A stable and deep impact mark shape can be obtained.

  FIG. 5 shows the shape of a vibration terminal according to another example of the present invention, and the tip of the vibration terminal has an elliptical long diameter at the top in a cross section (XZ cross section) perpendicular to the traveling direction (Y direction). And the elliptical minor axis (r1) is 1 mm or more (FIG. 5A) and has a length of 1 mm or more and 10 mm or less in the traveling direction (Y direction). It is formed in a shape (FIG. 5B).

  In the case of an oscillating terminal having an elliptical long-diameter arc-shaped outer peripheral portion at the top, if the elliptical short diameter (r1) is less than 1 mm, it is hit by the long-circular arc-shaped outer peripheral portion, and the stress concentrated portion at the toe Therefore, the elliptical minor axis (r1) is 1 mm or more.

  3 to 5 all have a length of 1 mm or more and 10 mm or less in the traveling direction (Y direction).

  If the length is less than 1 mm, compressive residual stress cannot be applied to the toe, whereas if the length is more than 10 mm, a deformation that becomes a stress concentration portion is formed at the toe, so that it is 1 mm or more. 10 mm or less.

  FIG. 6 shows the results of investigating the influence of the shape of the tip of the vibration terminal on the compressive residual stress. The tip portion is a base material (flat plate) using the vibration terminal model shown in FIG. 6 (1) (points to the circled numeral 1 in the figure, hereinafter the same), (2), (3), (4). 12 mm thick steel plate with a yield strength of 294 MPa and a tensile strength of 445 MPa) With the center axis of the vibration terminal perpendicular to the surface, a load was applied to the vibration terminal model and the base material was pushed in 0.1 mm. The stress distribution was obtained by FEM analysis by simulating the case where the load was released after the concave deformation was given to the surface side. In FIG. 6B, the horizontal axis indicates the distance from the center axis of the vibration terminal, and the vertical axis indicates the residual stress.

  The vibration terminals of (1) and (2) have an arcuate outer periphery with a radius of 4.5 mm in the XZ cross section (cross section perpendicular to the striking direction) at the top of the tip, and the YZ cross section (in the striking direction) The length of the cross section) was 1 mm for the vibration terminal and 4 mm for the vibration terminal (2).

  The vibration terminal of (3) has an outer peripheral portion with a chamfered portion having a curvature radius of 0.5 mm at both ends of a linear portion of 1 mm at the top in the XZ cross section (cross section perpendicular to the striking direction). The length of the YZ cross section (cross section in the striking direction) was 9 mm. The vibration terminal (4) has a hemispherical shape with a radius of curvature of 3 mm at the tip.

  From the figure, in the case of the vibration terminal ((1), (2), (3)), the tip is farther from the center of the deformed part (the axis center of the vibration terminal) than the hemispherical vibration terminal ((4)). A large compressive residual stress can be applied even at the position, and the residual stress at the toe (tensile residual stress) can be reduced more efficiently. In particular, the vibration terminal of (3) having a rectangular portion at its tip has the largest compressive residual stress, and it is possible to repeatedly hit the same place with a smaller number of times of hitting than a tip having a spherical or arc shape at the tip. Efficient, stable and deep strike mark shape can be obtained.

  From FIG. 6, the vibration terminals having different XZ cross-sectional shapes ((1), (2) are arc-shaped with a radius of 4.5 mm, and (3) is a chamfered portion with a radius of curvature of 0.5 mm at both ends of a linear portion of 1 mm at the top. In any case, a large compressive residual stress is generated at a position about 0.5 mm away from the end of the deformed portion (x≈0.8 mm), and the maximum value is around 2 mm from the hitting portion center, that is, at the hitting portion. It is located near 1 mm from the end (x≈0.8 mm).

  Also, from the figure, in the case where the tip is a hemispherical vibration terminal ((4)), compressive residual stress is not introduced at a position 5 mm away from the impact center (width center of the XZ cross section), but (1), ( In the case of the vibration terminals 2) and (3), it is possible to introduce a compressive residual stress of about 100 to 200 MPa even at a position 5 mm away from the hit center. Therefore, the striking trace may be formed in the region from the position where the end of the vibration terminal on the weld toe side is 0.5 mm away from the weld toe in the X direction (defined in FIG. 2) to 5 mm. preferable. In particular, considering the large range of compressive residual stress, the end of the vibration terminal on the weld toe side is 2 mm from the position 0.5 mm away from the weld toe in the X direction (defined in FIG. 2). It is preferable to form in the area up to. However, since compressive residual stress (about −50 MPa) is also generated at the end of the hitting mark (deformed portion), the present invention forms the hitting mark in a region up to 5 mm from the weld toe to the base metal side. .

  If the tip of the vibration terminal of (1), (2), (3) has an arc shape on the major axis side of an ellipse having a minor axis of 1 mm or more at the top of the traveling direction perpendicular section (XZ section), the compressive residual stress Is preferably distributed over a wide range.

  When hitting, it is preferable to hit the long side of the tip of the vibration terminal parallel to the toe. This is because the compressive residual stress is distributed in a wider range as the portion parallel to the toe becomes longer.

  The maximum hit depth is 0.03 mm or more and less than 0.50 mm. If the maximum depth to the bottom is less than 0.03 mm, sufficient compressive residual stress cannot be applied to the toe, and if it is 0.50 mm or more, the plastic deformation around the impact mark becomes excessive and a new stress concentration source This is because there is a possibility of becoming. As long as the base metal strength changes, the compressive residual stress that reduces the tensile residual stress of the weld toe and the maximum compressive residual stress at a position away from the impact mark are within the range of the impact mark depth. A distribution state is obtained.

  In the welded joint according to the present invention, the shape of the tip of the vibration terminal and the base metal side of the weld toe are 5 mm, more preferably the base of the weld toe so as not to hit the weld bead including the weld toe. The positions where the hitting marks are formed in the region from the position 0.5 mm away from the material side to 5 mm are appropriately combined.

  For example, in the case of the vibration terminals of (1) and (2), if the striking center (width center of the XZ cross section) is 0.5 mm from the weld toe to the base metal side, the vibration terminal A part of the weld toe is closer to the weld metal and covers the weld toe.

  While maintaining the shape of the top, it is possible to close the width near the top as shown in Fig. 3, but depending on the shape of the weld toe, the weld toe will be struck, so it is closer to the base metal than the weld toe. In a region of 5 mm, more preferably 0.5 mm to 5 mm from the weld toe to the base metal side, a position where the weld toe is not struck is selected and struck continuously along the weld toe.

  FIG. 7 is a plan view showing the positional relationship between the weld toe 4 and the hitting mark 6. In the present invention, if the hitting mark 6 is within 5 mm from the weld toe 4 to the base metal 1 side, the distance from the weld toe 4 is as follows. Therefore, the compressive residual stress can be introduced into the weld toe 4, so that it is possible to form the striking dent 6 linearly within the range without following the shape of the weld toe 4 in the welding direction, and the work efficiency is improved. improves.

  When hitting a position 5 mm away from the weld toe to the base metal side, the side on the base metal side of the tip of the vibration terminal is hit as the position of the base metal side 5 mm. Will be formed on the side. Even in this case, it is preferable that the long side on the base material side of the tip of the vibration terminal is the welding toe side. Further, even if the hitting mark is further formed on the base material side by the width of the hitting mark from 5 mm on the base material side, the effect of the present invention is not impaired.

  Further, it is preferable to obtain the relationship shown in FIG. 6 in advance when the amount of pushing is variously changed within the scope of the present invention, because it is easy to adjust the striking force to form a striking mark and select the striking position in actual work. .

  If the r portion is provided by grinder grinding or the like at the boundary between the toe 4 and the base material 1 before pressurizing the base material surface with the vibration terminal 5, the deformation of the base material surface does not reach the toe end 4 and is larger. It is preferable that compressive residual stress can be introduced into the toe 4. The hitting trace is preferably formed by hitting a plurality of times so that part or all of the hitting marks overlap each other. In addition, the function and effect of the present invention can be obtained by either hammer peening or ultrasonic impact treatment.

A vibration terminal (hereinafter referred to as a vibration terminal having a tip shape A) having a chamfered portion to prevent a crack from being generated on both sides of the top part is flat (straight part), and a vibration terminal having a hemispherical tip part (Hereinafter referred to as a vibration terminal having a tip shape B), a hammer peening (air pressure of about 6 kg / cm ² , frequency of 90 Hz, moving speed of 0.25 mm) on a base material (SM400) of width 150 mm × length 300 mm × plate thickness 12 mm Per second) by repeatedly striking the vibrating terminal vertically (FIG. 8).

  The specimen was subjected to residual stress measurement by X-ray. Residual stress measurement using X-rays was performed with a beam diameter of 1 mmφ. FIG. 9 shows the shape of the vibration terminal and the measurement result of the residual stress. The tip shape A vibration terminal has a residual stress on the compression side of about 4 mm, but the tip shape B vibration terminal has a residual stress on the compression side of about 1.5 mm. ing.

  Next, a welded joint was prepared, hammer peened by the method of the present invention, and then a fatigue test was performed. FIG. 10 shows the dimension and shape of the welded joint and the measurement position of the impact mark, where (a) shows a top view and (b) shows a side view. Two welded joints were produced under welding conditions of 280A-32V-25cpm.

For each welded joint, hammer peening (with an air pressure of about 6 kg / cm ² , a frequency of 90 Hz, and a moving speed of 0.25 mm / second) was repeatedly hit vertically on the vibration terminal using the vibration terminal having the tip shape A described above. The dimensions of the hitting marks were measured.

  As shown in FIG. 10 (a), the size of the impact mark is rotated from the weld metal to the base metal at a position where the cross-sectional shape in the vicinity of the welded portion is obtained (position of the end portion in the length direction of the rib having a length of 75 mm). Measurements were made at a pitch of 0.05 mm using a laser displacement meter.

  11 (a) and 11 (b) show the cross-sectional shapes of the welds obtained by the two welded joints. FIG. 12 shows the results of a fatigue test (frequency 3 to 5 Hz) for each welded joint. In the case of using the vibration terminal having the tip shape A, the fatigue life was improved as compared with the welded joint (comparative example in the figure).

DESCRIPTION OF SYMBOLS 1 Base material 2 Rib 3 Welding bead 4 Toe 5 Chipper 6 Scratch 7 Fatigue crack

Claims (4)

  Hammer peened or ultrasonic impact treated steel welded joint, having a striking trace continuously formed on the steel surface along the weld bead by the vibration terminal, the tip of the vibration terminal is advancing The apex of the cross section perpendicular to the direction is an arc shape with a radius of curvature of 1 mm or more and 10 mm or less, and has a length of 1 mm or more and 10 mm or less in the traveling direction. A welded joint having a maximum depth of 0.03 mm or more and less than 0.50 mm in a region up to 5 mm.   The vibration terminal has a chamfered portion with a radius of curvature of 0.1 mm or more and 2 mm or less at both ends of a linear portion whose top portion of the cross section perpendicular to the traveling direction is 3 mm or less, and a length of 1 mm or more and 10 mm or less in the traveling direction. The welded joint according to claim 1, comprising:   The tip of the vibration terminal has an elliptical arcuate shape with a short axis of 1 mm or more at the top of the cross section perpendicular to the traveling direction, and has a length of 1 mm or more and 10 mm or less in the traveling direction. The welded joint according to claim 1.   The said hit | damage trace is formed in the area | region to 5 mm from the position 0.5 mm away from the welding toe to the base material side by the said vibration terminal. Welded joints.