Peening method, peening apparatus, and welded structure

Abstract

To suppress shortage of peening from occurring in a weld toe and indentations of a base material from becoming excessively deep.SOLUTION: A tip portion 50 of a needle 5 in a cross section perpendicular to a longitudinal direction includes: an arc-shaped first portion 51 located on a base member 11 side of a central axis J1; and an arc-shaped second portion 52 located on a side opposite to the base member 11 of the central axis J1. A center 511 of the first portion 51 is located on the central axis J1. A center 521 of the second portion 52 is also located on the central axis J1. In the cross section, a radius R1 of the first portion 51 is smaller than a radius R2 of the second portion 52. This can suppress shortage of peening from occurring in a weld toe 34 and indentations of the base material 11 from becoming excessively deep.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a peening technique in which a weld toe, which is the boundary between the base metal and the weld metal in a welded joint, is struck with a needle. [Background technology]

[0002] Needle peening is a conventional method for reducing stress concentration at the weld toe and increasing the fatigue strength of a welded joint by striking the weld toe with a needle to plastically deform it. In needle peening, increasing the radius of the spherical tip of the needle increases the radius of the indentation formed at the weld toe, further increasing the fatigue strength after peening. On the other hand, if the radius of the needle tip is too large, the needle may not reach the boundary between the weld metal and the base metal, resulting in an unindented area (i.e., a portion that does not come into contact with the needle and is not plastically deformed), which may result in a small increase in the fatigue strength of the welded joint. Furthermore, if the radius of the needle tip is too small, the indentation in the base metal may be too deep, potentially reducing the fatigue strength.

[0003] In Patent Document 1, in a multiple peening method in which a peening process is repeated multiple times by moving a vibration terminal along a weld toe line and striking the weld toe line with the vibration terminal, the radius of curvature R of the tip of the vibration terminal used for the i-th time is i and the radius of curvature R of the tip of the vibration terminal used for the (i+1)th time. i+1 But, "R i <R i+1 ≦2R i This reduces stress concentration by increasing the radius of curvature of the weld toe without leaving overlap defects or crease defects at the weld toe, thereby improving the fatigue strength of the welded joint.

[0004] Furthermore, Patent Document 2 relates to ultrasonic impact treatment of a weld toe, and proposes a technology in which a pin with a curvature radius smaller than that of the weld toe is used to perform ultrasonic impact treatment by bringing the pin into contact with the weld toe to work-harden the surface in the vicinity of the weld toe, and then ultrasonic impact treatment is performed on the weld toe using a pin with a curvature radius larger than that of the weld toe. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4842409 [Patent Document 2] Patent No. 6756241 Summary of the Invention [Problem to be solved by the invention]

[0006] However, simply changing the radius of curvature of the tip of the vibration probe between the i-th peening process and the (i+1)-th peening process, as in the multiple peening method of Patent Document 1, may result in incomplete peening at the weld toe or excessively deep indentations in the base metal, etc. Furthermore, the multiple peening method requires performing peening two or more times using two types of vibration probes with different radius of curvature at the tip. The same applies to the ultrasonic impact treatment of Patent Document 2.

[0007] The present invention has been made in consideration of the above-mentioned problems, and has an object to suppress the occurrence of hammered remains at the weld toe and the indentation in the base metal from becoming excessively deep. [Means for solving the problem]

[0008] A first aspect of the present invention is a peening method for striking a weld toe, which is a boundary between a base metal and a weld metal in a welded joint extending in the longitudinal direction, with a needle, the method comprising the steps of: (a) positioning a rod-shaped needle centered on a central axis inclined at an inclination angle of 40° to 80° relative to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; and (b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle. The tip of the needle in the cross section perpendicular to the longitudinal direction comprises a first portion having an arc shape whose center is located on the central axis and is located on the base metal side of the central axis, and a second portion having an arc shape whose center is located on the central axis and is located on the opposite side of the central axis from the base metal side. In the cross section, the radius of the first portion is smaller than the radius of the second portion.

[0009] A second aspect of the present invention is the peening method of the first aspect, wherein the radius of the first portion in the cross section is 25% or more and 75% or less of the radius of the second portion.

[0010] A third aspect of the present invention is a peening method for striking a weld toe, which is a boundary between a base metal and a weld metal in a welded joint extending in the longitudinal direction, with a needle, the method comprising the steps of: (a) positioning a rod-shaped needle centered on a central axis inclined at an inclination angle of 40° to 80° relative to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; and (b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle. The tip of the needle in the cross section perpendicular to the longitudinal direction comprises a first portion having an arc shape whose center is on the central axis and located on the base metal side of the central axis, and a second portion having an arc shape whose center is on the central axis and located on the opposite side of the central axis from the base metal side. In the cross section, the radius of the first portion is larger than the radius of the second portion.

[0011] A fourth aspect of the present invention is the peening method of the third aspect, wherein the radius of the second portion in the cross section is 25% or more and 75% or less of the radius of the first portion.

[0012] A fifth aspect of the present invention is a peening method for striking a weld toe, which is a boundary between a base metal and a weld metal in a welded joint extending in the longitudinal direction, with a needle, the method comprising the steps of: (a) positioning a rod-shaped needle centered on a central axis inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; and (b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle. The tip of the needle in the cross section perpendicular to the longitudinal direction comprises a first portion that is located on the base metal side of the central axis and has an arc-like shape with its center located on the opposite side of the central axis from the base metal side, and a second portion that is located on the opposite side of the central axis from the base metal side and has its center located on the central axis. In the cross section, the radius of the first portion is different from the radius of the second portion.

[0013] A sixth aspect of the present invention is the peening method of the fifth aspect, wherein the smaller of the radius of the first portion and the radius of the second portion in the cross section is 25% or more and 75% or less of the larger radius.

[0014] A seventh aspect of the present invention is a peening method for striking a weld toe, which is a boundary between a base metal and a weld metal in a welded joint extending in the longitudinal direction, with a needle, the method comprising the steps of: a) positioning a rod-shaped first needle centered on a central axis inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the first needle facing the weld toe; b) performing a first peening treatment on the weld toe by striking the weld toe with the tip of the first needle; c) positioning a rod-shaped second needle centered on a central axis inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in the cross section, with the tip of the second needle facing the weld toe; and d) performing a second peening treatment on the weld toe by striking the weld toe with the tip of the second needle. The tip of the first needle in the cross section has an arc shape whose center is located on the central axis of the first needle. The tip of the second needle in the cross section has an arc shape whose center is located on the central axis of the second needle and whose radius is different from the radius of the tip of the first needle. The tilt angle of the central axis of the first needle in step a) is different from the tilt angle of the central axis of the second needle in step c).

[0015] An eighth aspect of the present invention is a peening method according to the seventh aspect, wherein the smaller of the radius of the tip of the first needle and the radius of the tip of the second needle in the cross section is 25% or more and 75% or less of the larger radius.

[0016] A ninth aspect of the present invention is a peening device comprising a rod-shaped needle centered on a central axis and an advancing / retracting mechanism that moves the needle forward and backward relative to an object to strike the object. A peening portion, which is a recess, is formed in the object by the impact of the needle, which moves along the longitudinal direction of the object. The tip of the needle in a cross section perpendicular to the longitudinal direction comprises a first portion located on one side of the central axis as a boundary, and an arc-shaped second portion located on the other side of the central axis as a boundary. The radius of the first portion and the radius of the second portion in the cross section are different.

[0017] A tenth aspect of the present invention is a welded structure comprising a weld joint extending in the longitudinal direction. A weld toe, which is a boundary between a base metal and a weld metal in the weld joint, comprises a peening portion, which is a recess formed by striking with a needle. The peening portion comprises a first recess having an arc shape that is continuous with the surface of the base metal in a cross section perpendicular to the longitudinal direction and recessed from the surface of the base metal in the thickness direction of the base metal, and a second recess having an arc shape that is continuous with the surface of the weld metal in the cross section and recessed from the surface of the weld metal toward the interior of the weld metal. The first recess and the second recess are continuous. The radius of the first recess and the radius of the second recess are different. [Effects of the Invention]

[0018] The present invention can suppress the occurrence of hammered remains at the weld toe and the indentation in the base metal from becoming excessively deep. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a perspective view showing a part of a welded structure according to a first embodiment. [Figure 2] FIG. 2 is an enlarged longitudinal cross-sectional view showing a portion of a welded joint. [Figure 3] FIG. 2 is a diagram showing the configuration of a peening device. [Figure 4] FIG. 1 is a diagram showing a flow of peening. [Figure 5]FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the tip of the needle. [Figure 6] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. [Figure 7] FIG. 10 is an enlarged vertical cross-sectional view showing the vicinity of a tip portion of a needle used in a peening method according to a second embodiment. [Figure 8] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. [Figure 9] FIG. 10 is an enlarged longitudinal sectional view showing the vicinity of a tip portion of a needle used in a peening method according to a third embodiment. [Figure 10] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. [Figure 11] FIG. 10 is an enlarged vertical cross-sectional view showing the vicinity of a tip portion of a needle used in a peening method according to a fourth embodiment. [Figure 12] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. [Figure 13] FIG. 10 is a diagram showing a flow of peening by a peening method according to a fifth embodiment. [Figure 14] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the tip of the needle. [Figure 15] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. [Figure 16] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the tip of the needle. [Figure 17] FIG. 2 is an enlarged longitudinal cross-sectional view showing the vicinity of the weld toe. DETAILED DESCRIPTION OF THE INVENTION

[0020] FIG. 1 is a perspective view showing a portion of a welded structure 1 according to a first embodiment of the present invention. The welded structure 1 is a structure in which a plurality of base materials are joined by welding. The welded structure 1 is, for example, a relatively large structure such as a floating body for a semi-submersible offshore wind power generation system or a transfer press. FIG. 1 shows a portion of a welded joint 3 in the welded structure 1, in which the lower end surface of a substantially flat base material 12 is joined by welding to the upper surface of a substantially flat base material 11. The welded joint 3 is a T-joint in which the base materials 11 and 12 are welded so that they are substantially perpendicular to each other.

[0021] In the example shown in FIG. 1 , weld metal 31 (i.e., a weld line) extending in a substantially linear manner is formed at the connection between the top surface of base metal 11 and the right side surface of base metal 12. Weld metal 31 is metal that is melted by the heat during welding and then solidifies. In the following description, the direction in which weld metal 31 extends is also referred to as the "longitudinal direction." This longitudinal direction is also the direction in which weld joint 3 extends. In weld joint 3, weld metal 31' extending in a substantially linear manner in the longitudinal direction is also formed at the connection between the top surface of base metal 11 and the left side surface of base metal 12. Weld metal 31 and weld metal 31' are also called weld beads. In weld joint 3, base metal 11 and base metal 12 are joined by weld metals 31 and 31'.

[0022] FIG. 2 is an enlarged longitudinal cross-sectional view of a portion of the welded joint 3 shown in FIG. 2. FIG. 2 shows a cross-section perpendicular to the longitudinal direction of the welded joint 3 in a region near a weld toe 34, which is the boundary between the base metal 11 and the weld metal 31. In FIG. 2, the boundary between the base metal 11 and the weld metal 31 is illustrated by a dashed line. The shape of the boundary varies depending on the degree of penetration of the weld metal 31 into the base metal 11. In the example shown in FIG. 2, the flank angle α at the weld toe 34 is approximately 120°. The flank angle α is the angle between a surface 111 of the base metal 11 and a surface 311 of the weld metal 31 in the weld toe 34, assuming that a peening portion 35 (described later) is not provided. The surface 111 of the base metal 11 is a main surface of the base metal 11 that is approximately parallel to the left-right direction in FIG. 2 and extends approximately perpendicularly in the up-down direction. The surface 311 of the weld metal 31 is the main surface of the weld metal 31 that extends diagonally upward to the left in FIG. 2 from the surface 111 of the base metal 11. The flank angle α is greater than 90° and smaller than 180°. The flank angle α is preferably greater than 100° and smaller than 140°.

[0023] In the example shown in Fig. 2, the weld toe 34 is provided with a peening portion 35, which is a recess extending approximately linearly along the longitudinal direction. The peening portion 35 is a recess provided so as to crush the boundary between the base metal 11 and the weld metal 31 by peening the weld toe 34. In this peening, a needle, which will be described later, is moved along the weld toe 34 and applies continuous impacts to the weld toe 34, thereby plastically deforming the surface layer of the weld toe 34 and forming the peening portion 35. In other words, this peening is so-called needle peening. This increases the fatigue strength of the weld toe 34.

[0024] In the cross section shown in FIG. 2 , the peening portion 35 includes a first recess 351, which is an indentation formed on the base metal 11 side, and a second recess 352, which is an indentation formed on the weld metal 31 side. The first recess 351 and the second recess 352 are continuous in the left-right direction in FIG. 2 , and the peening portion 35 is composed of the first recess 351 and the second recess 352. In FIG. 2 , the boundary between the first recess 351 and the second recess 352 is indicated by a dashed dotted line. The first recess 351 is continuous with the surface 111 of the base metal 11 and is a substantially arc-shaped recess that is recessed from the surface 111 in the thickness direction of the base metal 11 (downward in the example shown in FIG. 2 ). The second recess 352 is continuous with the surface 311 of the weld metal 31 and is a substantially arc-shaped recess that is recessed from the surface 311 toward the inside of the weld metal 31 (diagonally downward to the left in the example shown in FIG. 2 ).

[0025] Next, with reference to Figures 3 to 6, the peening device 7 that forms the peened portion 35 at the weld toe 34 and the peening process of the weld toe 34 by the peening device 7 will be described. The peening device 7 includes a needle 5, a needle holder 71, and a holder movement mechanism 74. The needle 5 is a generally rod-shaped member that is positioned with its tip 50 facing the weld toe 34, which is the boundary between the base metal 11 and the weld metal 31. The needle 5 is also called a pin or a hammer. The needle 5 is, for example, a generally cylindrical member, and the surface of the tip 50 of the needle 5 is generally spherical crown-shaped. The needle holder 71 includes a holder body 72 and an advancing / retracting mechanism 73. The holder body 72 is a generally cylindrical member that holds the needle 5. The advancing / retracting mechanism 73 is provided inside the holder body 72 and moves the needle 5 forward and backward relative to the weld toe 34. The advancing and retracting mechanism 73 is, for example, an air cylinder driven by compressed air, etc. The structure of the needle holder 71 may be modified in various ways.

[0026] The holder moving mechanism 74 includes a support portion 75, a guide rail 76, and a drive portion 77. The support portion 75 is a support block that supports the needle holder 71. The guide rail 76 extends in a substantially straight line along the longitudinal direction of the weld joint 3. The support portion 75 is attached to the guide rail 76 so as to be movable in the longitudinal direction along the guide rail 76. The drive portion 77 is a mechanism that moves the support portion 75 along the guide rail 76, thereby moving the tip portion 50 of the needle 5 in the longitudinal direction along the weld toe 34. The drive portion 77 is, for example, a hydraulic motor or an electric motor. The structure of the holder moving mechanism 74 may be modified in various ways.

[0027] When peening the weld toe 34 by the peening device 7, first the position of the needle holder 71 is adjusted and the needle 5 is placed with the tip 50 facing the weld toe 34 (step S11).

[0028] Figure 5 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50 of the needle 5, which is a rod-shaped member centered on the central axis J1. Figure 5 is a vertical cross-sectional view including the central axis J1 of the needle 5, and the central axis J1 is indicated by a dashed dotted line. Figure 5 also shows a cross-section of a region near the weld toe 34 before the peening portion 35 (see Figure 2) is formed. In the example shown in Figure 5, the intersection of the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5.

[0029] In the cross section shown in Fig. 5, the angle formed between the central axis J1 of the needle 5 and the surface 111 of the base material 11 (hereinafter also referred to as the "needle inclination angle θ") is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5 is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or less, and is 60° in the example shown in Fig. 5.

[0030] In the cross section shown in FIG. 5 , the tip portion 50 of the needle 5 includes a first portion 51 located on the base metal 11 side of the central axis J1 and a second portion 52 located on the weld metal 31 side of the central axis J1 (i.e., the side opposite the base metal 11 side). The first portion 51 is a portion of the tip portion 50 of the needle 5 located between the central axis J1 and the surface 111 of the base metal 11. The second portion 52 is a portion of the tip portion 50 of the needle 5 located between the central axis J1 and the surface 311 of the weld metal 31. In other words, the central axis J1 is located between the second portion 52 and the surface 111 of the base metal 11. The first portion 51 and the second portion 52 are smoothly connected on the central axis J1. In the example shown in FIG. 5 , a tangent to the first portion 51 and a tangent to the second portion 52 coincide at the intersection of the tip portion 50 of the needle 5 and the central axis J1.

[0031] The first portion 51 and the second portion 52 are each a substantially arc-shaped portion that is convex toward the weld toe 34. In FIG. 5 , the imaginary center of the first portion 51 is indicated by a black circle labeled 511, and the imaginary center of the second portion 52 is indicated by a black circle labeled 521. The center 511 of the first portion 51 is located on the central axis J1 of the needle 5. The center 521 of the second portion 52 is also located on the central axis J1 of the needle 5.

[0032] In a direction parallel to the central axis J1, the center 521 of the second region 52 is located farther from the tip 50 of the needle 5 than the center 511 of the first region 51. Therefore, the radius R1 of the first region 51 is smaller than the radius R2 of the second region 52. That is, the needle 5 is an asymmetric needle in which the shape of the tip 50 in the cross section is asymmetric with respect to the central axis J1. The radius R1 of the first region 51 is preferably 25% or more and 75% or less of the radius R2 of the second region 52. For example, the radius R1 of the first region 51 is 1.5 mm, and the radius R2 of the second region 52 is 3.0 mm. Furthermore, the diameter of the substantially cylindrical region of the needle 5 excluding the tip 50 (i.e., the diameter of the region in a cross section perpendicular to the central axis J1) is, for example, 3.0 mm.

[0033] Once the needle 5 is positioned in step S11, the drive unit 77 (see FIG. 3) moves the needle 5 in one longitudinal direction, while the advance / retract mechanism 73 (see FIG. 3) moves the needle 5 forward and backward approximately parallel to the central axis J1 relative to the weld toe 34. As a result, the tip 50 of the needle 5 moving in one longitudinal direction along the weld toe 34 continuously strikes the weld toe 34, performing a peening process on the weld toe 34 and forming the peened area 35 shown in FIG. 6 (step S12). Note that, in the above-mentioned continuous strikes by the needle 5 moving in the longitudinal direction, it is preferable that the needle inclination angle θ (i.e., the strike angle of the needle 5 with respect to the weld toe 34) is constant, but some variation is acceptable.

[0034] Figure 6 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a peened portion 35 has been formed by striking with the needle 5. In Figure 6, the needle 5 striking the weld toe 34 is also shown by a two-dot chain line. Of the peened portion 35, a first recess 351 is an impression formed in the surface 111 of the base metal 11 by a first portion 51 of the needle 5 (see Figure 5). A second recess 352 is an impression formed in the surface 311 of the weld metal 31 by a second portion 52 of the needle 5 (see Figure 5).

[0035] 6, the virtual center of the substantially arc-shaped first recess 351 is indicated by a black circle with reference numeral 361. The virtual center of the substantially arc-shaped second recess 352 is indicated by a black circle with reference numeral 362. The radius r1 of the first recess 351 and the radius r2 of the second recess 352 are different. In the example shown in FIG. 6, the radius r1 of the first recess 351 is smaller than the radius r2 of the second recess 352.

[0036] The radius r1 of the first recess 351 is approximately the same as the radius R1 of the first portion 51 at the tip 50 of the needle 5 (see FIG. 5). The maximum depth d1 of the first recess 351 is, for example, not less than 0.1 mm and not more than 0.5 mm. The maximum depth d1 of the first recess 351 is the distance in the thickness direction between the surface 111 of the base material 11 before the peening portion 35 is formed and the portion of the first recess 351 that is farthest from the surface 111 in the thickness direction.

[0037] The radius r2 of the second recess 352 is approximately the same as the radius R2 of the second portion 52 at the tip portion 50 of the needle 5 (see FIG. 5). The radius r1 of the first recess 351 is preferably 25% to 75% of the radius r2 of the second recess 352. The radius r1 of the first recess 351 may be approximately 10% to 20% larger than the radius R1 of the first portion 51 of the needle 5. The radius r2 of the second recess 352 may be approximately 10% to 20% larger than the radius R2 of the second portion 52 of the needle 5.

[0038] As described above, the peening method according to the first embodiment is a peening method in which the needle 5 strikes the weld toe 34, which is the boundary between the base metal 11 and the weld metal 31, in the weld joint 3 extending in the longitudinal direction. This peening method includes the steps of: (a) positioning the rod-shaped needle 5, which is centered on the central axis J1 and which is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, with the tip 50 of the needle 5 facing the weld toe 34 (step S11); and (b) performing a peening treatment on the weld toe 34 by striking the weld toe 34 with the tip 50 of the needle 5 (step S12).

[0039] The tip portion 50 of the needle 5 in a cross section perpendicular to the longitudinal direction includes an arc-shaped first portion 51 located on the base material 11 side of the central axis J1, and an arc-shaped second portion 52 located on the opposite side of the central axis J1 from the base material 11. A center 511 of the first portion 51 is located on the central axis J1. A center 521 of the second portion 52 is also located on the central axis J1. In the above cross section, a radius R1 of the first portion 51 is smaller than a radius R2 of the second portion 52.

[0040] In this peening method, in a cross section perpendicular to the longitudinal direction, the first portion 51, which has a relatively small radius R1, strikes the intersection between the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 and the portion near the intersection. This makes it possible to prevent the formation of an unstruck portion (i.e., a portion that does not come into contact with the needle 5 and is not plastically deformed) in the weld toe 34. This also makes it possible to prevent the maximum depth of the first recess 351 formed in the surface 111 of the base metal 11 by the first portion 51 from becoming excessively large. Furthermore, the second portion 52, which has a relatively large radius R2, strikes the surface 311 of the weld metal 31, making it possible to form a second recess 352 that is relatively shallow and has a gentle surface in the surface 311 of the weld metal 31. This makes it possible to suitably reduce stress concentration in the weld toe 34.

[0041] As described above, this peening method can prevent the occurrence of unhammered areas at the weld toe 34 and the indentations in the base metal 11 from becoming excessively deep, and can also suitably reduce stress concentration at the weld toe 34, thereby improving the fatigue strength of the welded joint 3. Furthermore, this peening method can form the peened area 35 having the above-mentioned cross-sectional shape by moving the needle 5, which continuously strikes the weld toe 34, only once in the longitudinal direction (i.e., by one peening process). Therefore, the time required for peening the weld toe 34 can be shortened.

[0042] As described above, in the cross section, the radius R1 of the first portion 51 is preferably 25% or more and 75% or less of the radius R2 of the second portion 52. This makes it possible to suitably prevent the occurrence of hammered-in remains at the weld toe 34 and the indentation in the base metal 11 from becoming excessively deep.

[0043] The above-described peening device 7 includes a needle 5 and an advancing / retracting mechanism 73. The needle 5 is rod-shaped and centered on a central axis J1. The advancing / retracting mechanism 73 moves the needle 5 forward and backward relative to an object (in the above example, the weld toe 34) to strike the object. A peened portion 35, which is a recess, is formed in the object by the impact of the needle 5, which is moved along the longitudinal direction of the object. In a cross section perpendicular to the longitudinal direction, the tip 50 of the needle 5 includes an arc-shaped first portion 51 located on one side of the central axis J1 (on the base material 11 side in the above example) and an arc-shaped second portion 52 located on the other side of the central axis J1 (on the opposite side from the base material 11 in the above example). In the above cross section, the radius R1 of the first portion 51 and the radius R2 of the second portion 52 are different.

[0044] As a result, as described above, it is possible to prevent the occurrence of hammered remains at the weld toe 34 and to prevent the indentation in the base metal 11 from becoming excessively deep, and it is also possible to suitably reduce stress concentration at the weld toe 34 and improve the fatigue strength of the welded joint 3. The same applies to the second to fourth embodiments described below.

[0045] The welded structure 1 described above includes a weld joint 3 extending in the longitudinal direction. A weld toe 34, which is the boundary between the base metal 11 and the weld metal 31 in the weld joint 3, includes a peening portion 35, which is a recess formed by impact with a needle 5. The peening portion 35 includes a circular-arc-shaped first recess 351 that is continuous with the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, and a circular-arc-shaped second recess 352 that is continuous with the surface 311 of the weld metal 31 in the cross section. The first recess 351 is recessed from the surface 111 of the base metal 11 in the thickness direction of the base metal 11. The second recess 352 is recessed from the surface 311 of the weld metal 31 toward the interior of the weld metal 31. The first recess 351 and the second recess 352 are continuous. A radius r1 of the first recess 351 and a radius r2 of the second recess 352 are different.

[0046] As a result, as described above, it is possible to prevent the occurrence of hammered remains at the weld toe 34 and to prevent the indentation in the base metal 11 from becoming excessively deep, and it is also possible to suitably reduce stress concentration at the weld toe 34 and improve the fatigue strength of the welded joint 3. The same applies to the second to fourth embodiments described below.

[0047] Next, a peening method according to a second embodiment of the present invention will be described. The peening method according to the second embodiment is substantially the same as the peening method according to the first embodiment (steps S11 to S12) described above, except that a needle 5a shown in Fig. 7 is used instead of the needle 5 described above (see Fig. 5). In the needle 5a shown in Fig. 7, the shape of the tip 50a is different from the shape of the tip 50 of the needle 5 described above.

[0048] When peening the weld toe 34 by the peening method according to the second embodiment, first, the position of the needle holder 71 (see FIG. 3) is adjusted, and the needle 5a is placed with the tip 50a facing the weld toe 34 (FIG. 4: step S11).

[0049] Figure 7 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50a of the needle 5a, which is a rod-shaped member centered on the central axis J1. Figure 7 is a vertical cross-sectional view including the central axis J1 of the needle 5a, and the central axis J1 is indicated by a dashed dotted line. Figure 7 also shows a cross-section of a region near the weld toe 34 before the peening portion 35a (see Figure 8, described later) is formed. In the example shown in Figure 7, the intersection of the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5a.

[0050] 7, the needle inclination angle θ of the needle 5a (i.e., the angle formed between the central axis J1 of the needle 5a and the surface 111 of the base material 11) is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5a is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or less, and is 60° in the example shown in FIG.

[0051] 7, the tip 50a of the needle 5a includes a first portion 51a located on the base metal 11 side of the central axis J1 and a second portion 52a located on the weld metal 31 side of the central axis J1 (i.e., the side opposite the base metal 11). The first portion 51a is a portion of the tip 50a of the needle 5a located between the central axis J1 and the surface 111 of the base metal 11. The second portion 52a is a portion of the tip 50a of the needle 5a located between the central axis J1 and the surface 311 of the weld metal 31. In other words, the central axis J1 is located between the second portion 52a and the surface 111 of the base metal 11. The first portion 51a and the second portion 52a are connected substantially smoothly on the central axis J1.

[0052] The first portion 51a and the second portion 52a are each a substantially arc-shaped portion that is convex toward the weld toe 34. In FIG. 7, the imaginary center of the first portion 51a is indicated by a black circle labeled 511a, and the imaginary center of the second portion 52a is indicated by a black circle labeled 521a. The center 511a of the first portion 51a is located on the weld metal 31 side of the central axis J1 of the needle 5a (i.e., the side opposite to the base metal 11 side). In other words, the central axis J1 is located between the center 511a of the first portion 51a and the surface 111 of the base metal 11. That is, the needle 5a is an eccentric needle in which the center 511a of the first portion 51a is located at a position displaced from the central axis J1. The center 521a of the second portion 52a is located on the central axis J1 of the needle 5a.

[0053] In a direction parallel to the central axis J1, the center 521a of the second portion 52a is located farther from the tip 50a of the needle 5a than the center 511a of the first portion 51a. The radius R1 of the first portion 51a is smaller than the radius R2 of the second portion 52a. That is, the needle 5a is an asymmetric needle in which the shape of the tip 50a in the cross section is asymmetric with respect to the central axis J1. The radius R1 of the first portion 51a is preferably 25% or more and 75% or less of the radius R2 of the second portion 52a. For example, the radius R1 of the first portion 51a is 1.9 mm, and the radius R2 of the second portion 52a is 3.0 mm. The diameter of the approximately cylindrical portion of the needle 5a excluding the tip 50a (i.e., the diameter of the portion in a cross section perpendicular to the central axis J1) is, for example, 3.0 mm.

[0054] Once the needle 5a is positioned in step S11, the drive unit 77 (see FIG. 3) moves the needle 5a in one longitudinal direction, while the advancing / retracting mechanism 73 (see FIG. 3) moves the needle 5a forward and backward relative to the weld toe 34. As a result, the tip 50a of the needle 5a, which moves in one longitudinal direction along the weld toe 34, continuously strikes the weld toe 34, performing a peening treatment on the weld toe 34 and forming a peened area 35a shown in FIG. 8 (step S12).

[0055] Figure 8 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a peening portion 35a has been formed by impact with the needle 5a. In Figure 8, the needle 5a striking the weld toe 34 is also shown by a two-dot chain line. In the peening portion 35a, a first recess 351a is an indentation formed in the surface 111 of the base metal 11 by the first portion 51a of the needle 5a (see Figure 7). A second recess 352a is an indentation formed in the surface 311 of the weld metal 31 by the second portion 52a of the needle 5a (see Figure 7).

[0056] The radius r1 of the substantially arc-shaped first recess 351a is substantially the same as the radius R1 of the first portion 51a at the tip end 50a of the needle 5a. The maximum depth d1 of the first recess 351a is, for example, 0.1 mm or more and 0.5 mm or less. The radius r2 of the substantially arc-shaped second recess 352a is substantially the same as the radius R2 of the second portion 52a at the tip end 50a of the needle 5a. The radius r1 of the first recess 351a is preferably 25% or more and 75% or less of the radius r2 of the second recess 352a. Note that the radius r1 of the first recess 351a may be approximately 10% to 20% larger than the radius R1 of the first portion 51a of the needle 5a. The radius r2 of the second recess 352a may be approximately 10% to 20% larger than the radius R2 of the second portion 52a of the needle 5a.

[0057] As described above, the peening method according to the second embodiment includes the steps of: positioning a rod-shaped needle 5a centered on a central axis J1 that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, with the tip 50a of the needle 5a facing the weld toe 34 (step S11); and performing a peening treatment on the weld toe 34 by striking the weld toe 34 with the tip 50a of the needle 5a (step S12). The tip 50a of the needle 5a in the cross section perpendicular to the longitudinal direction includes an arc-shaped first portion 51a located on the base metal 11 side of the central axis J1, and an arc-shaped second portion 52a located on the opposite side of the central axis J1 from the base metal 11 side. The center 511a of the first portion 51a is located on the opposite side of the central axis J1 from the base metal 11 side. The center 521a of the second portion 52a is located on the central axis J1. In the cross section, the radius R1 of the first portion 51a is smaller than the radius R2 of the second portion 52a.

[0058] According to the peening method of the second embodiment, substantially similar to the peening method of the first embodiment, it is possible to prevent the occurrence of unhammered portions at the weld toe 34 and the indentations in the base metal 11 from becoming excessively deep, and it is also possible to suitably reduce stress concentration at the weld toe 34 and improve the fatigue strength of the welded joint 3. Furthermore, according to this peening method, the peened portion 35a having the above-mentioned cross-sectional shape can be formed by moving the needle 5a, which continuously strikes the weld toe 34, only once in the longitudinal direction (i.e., by one peening process). Therefore, the time required for peening the weld toe 34 can be shortened.

[0059] As described above, in the needle 5a, the center 511a of the first portion 51a is located on the side opposite to the base material 11 side with respect to the central axis J1. This makes the tip of the first portion 51a relatively sharp at the connection between the first portion 51a and the second portion 52a. This further reduces the occurrence of residual dents at the weld toe 34. In addition, because the overall position of the first portion 51a of the needle 5a is displaced upward compared to the first portion 51 of the needle 5, it is possible to further prevent the indentation in the base material 11 from becoming excessively deep.

[0060] As described above, in the cross section, the radius R1 of the first portion 51a is preferably 25% to 75% of the radius R2 of the second portion 52a, which makes it possible to preferably prevent the occurrence of hammered-in remains at the weld toe 34 and prevent the indentation in the base metal 11 from becoming excessively deep.

[0061] Next, a peening method according to a third embodiment of the present invention will be described. The peening method according to the third embodiment is substantially the same as the peening method according to the first embodiment (steps S11 to S12) described above, except that a needle 5b shown in Fig. 9 is used instead of the needle 5 (see Fig. 5) described above. In the needle 5b shown in Fig. 9, the shape of the tip 50b is different from the shape of the tip 50 of the needle 5 described above.

[0062] When peening the weld toe 34 by the peening method according to the third embodiment, first, the position of the needle holder 71 (see FIG. 3) is adjusted, and the needle 5b is placed with the tip 50b facing the weld toe 34 (FIG. 4: step S11).

[0063] Figure 9 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50b of the needle 5b, which is a rod-shaped member centered on the central axis J1. Figure 9 is a vertical cross-sectional view including the central axis J1 of the needle 5b, and the central axis J1 is indicated by a dashed dotted line. Figure 9 also shows a cross-section of a region near the weld toe 34 before the peening portion 35b (see Figure 10, described later) is formed. In the example shown in Figure 9, the intersection of the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5b.

[0064] 9, the needle inclination angle θ of the needle 5b (i.e., the angle between the central axis J1 of the needle 5b and the surface 111 of the base material 11) is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5b is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or more, and is 70° in the example shown in FIG.

[0065] In the cross section shown in FIG. 9 , the tip end 50b of the needle 5b includes a first portion 51b located on the base metal 11 side of the central axis J1, and a second portion 52b located on the weld metal 31 side of the central axis J1 (i.e., the side opposite the base metal 11). The first portion 51b is a portion of the tip end 50b of the needle 5b located between the central axis J1 and the surface 111 of the base metal 11. The second portion 52b is a portion of the tip end 50b of the needle 5b located between the central axis J1 and the surface 311 of the weld metal 31. In other words, the central axis J1 is located between the second portion 52b and the surface 111 of the base metal 11. The first portion 51b and the second portion 52b are smoothly connected on the central axis J1. In the example shown in FIG. 9, at the intersection of the tip end 50b of the needle 5b and the central axis J1, the tangent to the first portion 51b and the tangent to the second portion 52b coincide with each other.

[0066] The first portion 51b and the second portion 52b are each a generally arc-shaped portion that convex toward the weld toe 34. In FIG. 9, the imaginary center of the first portion 51b is indicated by a black circle labeled 511b, and the imaginary center of the second portion 52b is indicated by a black circle labeled 521b. The center 511b of the first portion 51b is located on the central axis J1 of the needle 5b. The center 521b of the second portion 52a is also located on the central axis J1 of the needle 5b.

[0067] In a direction parallel to the central axis J1, the center 511b of the first portion 51b is located farther from the tip 50b of the needle 5b than the center 521b of the second portion 52b. Therefore, the radius R1 of the first portion 51b is greater than the radius R2 of the second portion 52b. That is, the needle 5b is an asymmetric needle in which the shape of the tip 50b in the cross section is asymmetric with respect to the central axis J1. The radius R2 of the second portion 52b is preferably 25% or more and 75% or less of the radius R1 of the first portion 51b. For example, the radius R2 of the second portion 52b is 1.5 mm, and the radius R1 of the first portion 51b is 3.0 mm. The diameter of the approximately cylindrical portion of the needle 5b excluding the tip 50b (i.e., the diameter of the portion in a cross section perpendicular to the central axis J1) is, for example, 3.0 mm.

[0068] Once the needle 5b is positioned in step S11, the drive unit 77 (see FIG. 3) moves the needle 5b in one longitudinal direction, while the advancing / retracting mechanism 73 (see FIG. 3) moves the needle 5b forward and backward relative to the weld toe 34. As a result, the tip 50b of the needle 5b, which moves in one longitudinal direction along the weld toe 34, continuously strikes the weld toe 34, performing a peening treatment on the weld toe 34 and forming a peened area 35b shown in FIG. 10 (step S12).

[0069] Figure 10 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a peening portion 35b has been formed by impact with the needle 5b. In Figure 10, the needle 5b striking the weld toe 34 is also shown by a two-dot chain line. Of the peening portion 35b, a first recess 351b is an indentation formed in the surface 111 of the base metal 11 by the first portion 51b of the needle 5b (see Figure 9). A second recess 352b is an indentation formed in the surface 311 of the weld metal 31 by the second portion 52b of the needle 5b (see Figure 9).

[0070] The radius r1 of the substantially arc-shaped first recess 351b is substantially the same as the radius R1 of the first portion 51b at the tip end 50b of the needle 5b. The maximum depth d1 of the first recess 351b is, for example, 0.1 mm or more and 0.5 mm or less. The radius r2 of the substantially arc-shaped second recess 352b is substantially the same as the radius R2 of the second portion 52b at the tip end 50b of the needle 5b. The radius r2 of the second recess 352b is preferably 25% or more and 75% or less of the radius r1 of the first recess 351b. Note that the radius r1 of the first recess 351b may be approximately 10% to 20% larger than the radius R1 of the first portion 51b of the needle 5b. The radius r2 of the second recess 352b may be approximately 10% to 20% larger than the radius R2 of the second portion 52b of the needle 5b.

[0071] As described above, the peening method according to the third embodiment includes the steps of: positioning a rod-shaped needle 5b centered on a central axis J1 that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, with the tip 50b of the needle 5b facing the weld toe 34 (step S11); and performing a peening treatment on the weld toe 34 by striking the weld toe 34 with the tip 50b of the needle 5b (step S12). The tip 50b of the needle 5b in the cross section perpendicular to the longitudinal direction includes an arc-shaped first portion 51b located on the base metal 11 side of the central axis J1 and an arc-shaped second portion 52b located on the opposite side of the central axis J1 from the base metal 11 side. A center 511b of the first portion 51b is located on the central axis J1. A center 521b of the second portion 52b is also located on the central axis J1. In the cross section, the radius R1 of the first portion 51b is larger than the radius R2 of the second portion 52b.

[0072] In the peening method according to the third embodiment, in a cross section perpendicular to the longitudinal direction, the second portion 52b, which has a relatively small radius R1, strikes the intersection between the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 and the portion near the intersection. This makes it possible to prevent the occurrence of an unhammered portion (i.e., a portion that does not come into contact with the needle 5b and is not plastically deformed) in the weld toe 34. Furthermore, by striking the surface 111 of the base metal 11 with the first portion 51b, which has a relatively large radius R1, it is possible to form a first recess 351b, which is relatively shallow and has a gentle surface, in the surface 111 of the base metal 11. This makes it possible to prevent the maximum depth of the first recess 351b from becoming excessively large and to suitably reduce stress concentration in the weld toe 34.

[0073] As described above, this peening method can prevent the occurrence of unhammered areas at the weld toe 34 and the indentations in the base metal 11 from becoming excessively deep, and can also suitably reduce stress concentration at the weld toe 34, thereby improving the fatigue strength of the welded joint 3. Furthermore, this peening method can form the peened area 35b having the above-described cross-sectional shape by moving the needle 5b, which continuously strikes the weld toe 34, only once in the longitudinal direction (i.e., by one peening process). Therefore, the time required for peening the weld toe 34 can be shortened.

[0074] As described above, in the cross section, the radius R2 of the second portion 52b is preferably 25% to 75% of the radius R1 of the first portion 51b, which can suitably prevent the occurrence of hammered-in parts at the weld toe 34.

[0075] Next, a peening method according to a fourth embodiment of the present invention will be described. The peening method according to the fourth embodiment is substantially the same as the peening method according to the first embodiment (steps S11 to S12) described above, except that a needle 5c shown in Fig. 11 is used instead of the needle 5 (see Fig. 5) described above. In the needle 5c shown in Fig. 11, the shape of the tip 50c is different from the shape of the tip 50 of the needle 5 described above.

[0076] When peening the weld toe 34 by the peening method according to the fourth embodiment, first, the position of the needle holder 71 (see FIG. 3) is adjusted, and the needle 5c is placed with the tip 50c facing the weld toe 34 (FIG. 4: step S11).

[0077] Figure 11 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50c of the needle 5c, which is a rod-shaped member centered on the central axis J1. Figure 11 is a vertical cross-sectional view including the central axis J1 of the needle 5c, and the central axis J1 is indicated by a dashed dotted line. Figure 11 also shows a cross-section of a region near the weld toe 34 before the peening portion 35c (see Figure 12, described later) is formed. In the example shown in Figure 11, the intersection of the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5c.

[0078] 11, the needle inclination angle θ of the needle 5c (i.e., the angle formed between the central axis J1 of the needle 5c and the surface 111 of the base material 11) is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5c is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or less, and is 60° in the example shown in FIG.

[0079] 11, the tip portion 50c of the needle 5c includes a first portion 51c located on the base metal 11 side of the central axis J1 and a second portion 52c located on the weld metal 31 side of the central axis J1 (i.e., the side opposite the base metal 11). The first portion 51c is a portion of the tip portion 50c of the needle 5c located between the central axis J1 and the surface 111 of the base metal 11. The second portion 52c is a portion of the tip portion 50c of the needle 5c located between the central axis J1 and the surface 311 of the weld metal 31. In other words, the central axis J1 is located between the second portion 52c and the surface 111 of the base metal 11. The first portion 51c and the second portion 52c are connected substantially smoothly on the central axis J1.

[0080] The first portion 51c and the second portion 52c are each a substantially arc-shaped portion that convexly extends toward the weld toe 34. In FIG. 11 , the imaginary center of the first portion 51c is indicated by a black circle labeled 511c, and the imaginary center of the second portion 52c is indicated by a black circle labeled 521c. The center 511c of the first portion 51c is located on the weld metal 31 side of the central axis J1 of the needle 5c (i.e., the side opposite to the base metal 11 side). In other words, the central axis J1 is located between the center 511c of the first portion 51c and the surface 111 of the base metal 11. That is, the needle 5c is an eccentric needle in which the center 511c of the first portion 51c is located at a position displaced from the central axis J1. The center 521c of the second portion 52c is located on the central axis J1 of the needle 5c.

[0081] In a direction parallel to the central axis J1, the center 511c of the first portion 51c is located farther from the tip 50c of the needle 5c than the center 521c of the second portion 52c. The radius R1 of the first portion 51c is greater than the radius R2 of the second portion 52c. That is, the needle 5c is an asymmetric needle in which the shape of the tip 50c in the cross section is asymmetric with respect to the central axis J1. The radius R2 of the second portion 52c is preferably 25% or more and 75% or less of the radius R1 of the first portion 51c. For example, the radius R1 of the first portion 51c is 3.0 mm, and the radius R2 of the second portion 52c is 1.5 mm. The diameter of the approximately cylindrical portion of the needle 5c excluding the tip 50c (i.e., the diameter of the portion in a cross section perpendicular to the central axis J1) is, for example, 3.0 mm.

[0082] Once the needle 5c is positioned in step S11, the drive unit 77 (see FIG. 3) moves the needle 5c in one longitudinal direction, while the advancing / retracting mechanism 73 (see FIG. 3) moves the needle 5c forward and backward relative to the weld toe 34. As a result, the tip 50c of the needle 5c moving in one longitudinal direction along the weld toe 34 continuously strikes the weld toe 34, performing a peening treatment on the weld toe 34 and forming a peened area 35c shown in FIG. 12 (step S12).

[0083] Figure 12 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a peening portion 35c is formed by impact with the needle 5c. In Figure 12, the needle 5c striking the weld toe 34 is also shown by a two-dot chain line. Of the peening portion 35c, a first recess 351c is an indentation formed in the surface 111 of the base metal 11 by a first portion 51c of the needle 5c (see Figure 11). A second recess 352c is an indentation formed in the surface 311 of the weld metal 31 by a second portion 52c of the needle 5c (see Figure 11).

[0084] The radius r1 of the substantially arc-shaped first recess 351c is substantially the same as the radius R1 of the first portion 51c at the tip end 50c of the needle 5c. The maximum depth d1 of the first recess 351c is, for example, 0.1 mm or more and 0.5 mm or less. The radius r2 of the substantially arc-shaped second recess 352c is substantially the same as the radius R2 of the second portion 52c at the tip end 50c of the needle 5c. The radius r2 of the second recess 352c is preferably 25% or more and 75% or less of the radius r1 of the first recess 351c. Note that the radius r1 of the first recess 351c may be approximately 10% to 20% larger than the radius R1 of the first portion 51c of the needle 5c. The radius r2 of the second recess 352c may be approximately 10% to 20% larger than the radius R2 of the second portion 52c of the needle 5c.

[0085] As described above, the peening method according to the fourth embodiment includes the steps of: positioning a rod-shaped needle 5c centered on a central axis J1 that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, with the tip 50c of the needle 5c facing the weld toe 34 (step S11); and performing a peening treatment on the weld toe 34 by striking the weld toe 34 with the tip 50c of the needle 5c (step S12). The tip 50c of the needle 5c in the cross section perpendicular to the longitudinal direction includes an arc-shaped first portion 51c located on the base metal 11 side of the central axis J1, and an arc-shaped second portion 52c located on the opposite side of the central axis J1 from the base metal 11 side. A center 511c of the first portion 51c is located on the opposite side of the central axis J1 from the base metal 11 side. A center 521c of the second portion 52c is located on the central axis J1. In the cross section, the radius R1 of the first portion 51c is larger than the radius R2 of the second portion 52c.

[0086] The peening method according to the fourth embodiment, similar to the peening method according to the third embodiment, can suppress the occurrence of unhammered areas at the weld toe 34 and the indentations in the base metal 11 from becoming excessively deep, and can also suitably reduce stress concentration at the weld toe 34, thereby improving the fatigue strength of the welded joint 3. Furthermore, according to this peening method, the peened area 35c having the above-mentioned cross-sectional shape can be formed by moving the needle 5c, which continuously strikes the weld toe 34, only once in the longitudinal direction (i.e., by one peening process). Therefore, the time required for peening the weld toe 34 can be shortened.

[0087] As described above, in the needle 5c, the center 511a of the first portion 51c is located on the opposite side of the central axis J1 from the base material 11 side. This causes the overall position of the first portion 51c in the needle 5c to be displaced upward compared to the first portion 51b of the needle 5b, further preventing the indentation in the base material 11 from becoming excessively deep. Therefore, the needle inclination angle θ of the needle 5c can be made smaller than the needle inclination angle θ of the needle 5b in the third embodiment.

[0088] As described above, in the cross section, the radius R2 of the second portion 52c is preferably 25% to 75% of the radius R1 of the first portion 51c, which can suitably prevent the occurrence of hammered-in portions at the weld toe 34.

[0089] In the peening methods according to the second and fourth embodiments, the tip ends 50a, 50c of the needles 5a, 5c in a cross section perpendicular to the longitudinal direction include arc-shaped first portions 51a, 51c located on the base material 11 side of the central axis J1 and arc-shaped second portions 52a, 52c located on the opposite side of the central axis J1 from the base material 11 side. Centers 511a, 511c of the first portions 51a, 51c are located on the opposite side of the central axis J1 from the base material 11 side. Centers 521a, 521c of the second portions 52a, 52c are located on the central axis J1. In the above cross sections, a radius R1 of the first portions 51a, 51c is different from a radius R2 of the second portions 52a, 52c. In addition, in the cross section, the smaller of the radius R1 of the first portions 51a and 51c and the radius R2 of the second portions 52a and 52c is preferably 25% or more and 75% or less of the larger one.

[0090] Next, a peening method according to a fifth embodiment of the present invention will be described with reference to FIGS. 13 to 17. In the peening method according to the fifth embodiment, needles 5d and 5e shown in FIGS. 14 and 16 are used instead of the above-described needle 5 (see FIG. 5), and two peening processes are performed using the needles 5d and 5e, respectively. The needles 5d and 5e shown in FIGS. 14 and 16 have different shapes of the tip portions 50d and 50e, which are also different from the shape of the tip portion 50 of the above-described needle 5. The needle 5d is a "first needle" used in the first peening process, and the needle 5e is a "second needle" used in the second peening process.

[0091] When peening the weld toe 34 by the peening method according to the fifth embodiment, first, the position of the needle holder 71 (see FIG. 3) is adjusted, and the needle 5d is placed with the tip 50d facing the weld toe 34 (FIG. 13: step S21).

[0092] Figure 14 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50d of the needle 5d, which is a rod-shaped member centered on the central axis J1. Figure 14 is a vertical cross-sectional view including the central axis J1 of the needle 5d, and the central axis J1 is indicated by a dashed dotted line. Figure 14 also shows a cross-section of a region near the weld toe 34 before the peening portion 35e (see Figure 17, described later) is formed. In the example shown in Figure 14, the intersection of the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5d.

[0093] 14, the needle inclination angle θ of the needle 5d (i.e., the angle formed between the central axis J1 of the needle 5d and the surface 111 of the base material 11) is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5d is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or less, and is 60° in the example shown in FIG.

[0094] In the cross section shown in FIG. 14, the tip 50d of the needle 5d is a generally arc-shaped portion that is convex toward the base metal 11 and the weld metal 31. The needle 5d is a symmetrical needle, with the shape of the tip 50d in the cross section being symmetrical with respect to the central axis J1. In FIG. 14, the imaginary center of the tip 50d is indicated by a black circle labeled 501d. The center 501d of the tip 50d is located on the central axis J1 of the needle 5d. For example, the radius R3 of the tip 50d is 1.5 mm. The diameter of the generally cylindrical portion of the needle 5d excluding the tip 50d (i.e., the diameter of the portion in the cross section perpendicular to the central axis J1) is, for example, 3.0 mm.

[0095] Once the needle 5d is positioned in step S21, the drive unit 77 (see FIG. 3) moves the needle 5d in one longitudinal direction, while the advancing / retracting mechanism 73 (see FIG. 3) moves the needle 5d forward and backward relative to the weld toe 34. As a result, the tip 50d of the needle 5d moving in one longitudinal direction along the weld toe 34 continuously strikes the weld toe 34, performing a first peening treatment on the weld toe 34 and forming a recess 35d shown in FIG. 15 (step S22).

[0096] FIG. 15 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a depression 35d, which is an indentation, is formed on the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 by impact with the needle 5d. In FIG. 15, the needle 5d striking the weld toe 34 is also shown by a two-dot chain line. The radius r3 of the approximately arc-shaped depression 35d is approximately the same as the radius R3 of the tip 50d of the needle 5d (see FIG. 14). Note that the radius r3 of the depression 35d may be approximately 10% to 20% larger than the radius R3 of the needle 5d. The maximum depth d3 of the depression 35d is, for example, 0.1 mm or more and 0.5 mm or less. The maximum depth d3 of the depression 35d is the distance in the thickness direction between the surface 111 of the base metal 11 before the depression 35d is formed and the portion of the lower surface of the depression 35d located below the surface 111 that is furthest from the surface 111 in the thickness direction.

[0097] When step S22 is completed, the needle 5d is removed from the needle holder 71 (see FIG. 3), and the needle 5e is attached to the needle holder 71. Then, the position of the needle holder 71 is adjusted, and the needle 5e is positioned with the tip 50e facing the weld toe 34, as shown in FIG. 16 (step S23).

[0098] Figure 16 is an enlarged cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the tip 50e of the needle 5e, which is a rod-shaped member centered on the central axis J1. Figure 16 is a vertical cross-sectional view including the central axis J1 of the needle 5e, and the central axis J1 is indicated by a dashed dotted line. Figure 16 also shows a cross-section of a region near the weld toe 34 where the above-mentioned recess 35d is formed. In the example shown in Figure 16, the intersection (see Figure 14) between the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 at the weld toe 34 is located on an extension of the central axis J1 of the needle 5e.

[0099] In the example shown in FIG. 16, the needle inclination angle θ of the needle 5e (i.e., the angle between the central axis J1 of the needle 5e and the surface 111 of the base material 11) is 40° or more and 80° or less. In other words, the central axis J1 of the needle 5e is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base material 11. The needle inclination angle θ is, for example, 65° or more, and is 70° in the example shown in FIG. 16. The needle inclination angle θ of the needle 5e in step S23 is larger than the needle inclination angle θ of the needle 5d in step S21. In other words, the inclination angle of the central axis J1 of the first needle (i.e., needle 5d) in step S21 is smaller than the inclination angle of the central axis J1 of the second needle (i.e., needle 5e) in step S23.

[0100] In the cross section shown in FIG. 16, the tip 50e of the needle 5e is a generally arc-shaped portion that is convex toward the base metal 11 and the weld metal 31. The needle 5e is a symmetrical needle, with the shape of the tip 50e in the cross section being symmetrical with respect to the central axis J1. In FIG. 16, the imaginary center of the tip 50e is indicated by a black circle labeled 501e. The center 501e of the tip 50e is located on the central axis J1 of the needle 5e. For example, the radius R4 of the tip 50e is 3.0 mm. The diameter of the generally cylindrical portion of the needle 5e excluding the tip 50e (i.e., the diameter of the portion in the cross section perpendicular to the central axis J1) is also, for example, 3.0 mm.

[0101] Once the needle 5e is positioned in step S23, the drive unit 77 (see FIG. 3) moves the needle 5e in one longitudinal direction, while the advancing / retracting mechanism 73 (see FIG. 3) moves the needle 5e forward and backward relative to the weld toe 34. As a result, the tip 50e of the needle 5e moving in one longitudinal direction along the weld toe 34 continuously strikes the weld toe 34, performing a second peening treatment on the weld toe 34 and forming a peened area 35e as shown in FIG. 17 (step S24).

[0102] FIG. 17 is a cross-sectional view perpendicular to the longitudinal direction showing the vicinity of the weld toe 34 where a peening portion 35e, which is an indentation, is formed on the surface 111 of the base metal 11 and the surface 311 of the weld metal 31 by impact with the needle 5e. In FIG. 17, the needle 5e striking the weld toe 34 is also shown by a two-dot chain line. The radius r4 of the approximately arc-shaped peening portion 35e is approximately the same as the radius R4 of the tip 50e of the needle 5e (see FIG. 16). Note that the radius r4 of the peening portion 35e may be approximately 10% to 20% larger than the radius R4 of the needle 5e. The maximum depth d4 of the peening portion 35e is, for example, 0.1 mm or more and 0.5 mm or less. The maximum depth d4 of the peening portion 35e is the distance in the thickness direction between the surface 111 of the base material 11 before the peening portion 35e is formed and a portion of the lower surface of the peening portion 35e located below the surface 111 that is the farthest in the thickness direction from the surface 111. The maximum depth d4 of the peening portion 35e may be larger or smaller than the maximum depth d3 of the recess 35d described above, or may be the same as the maximum depth d3.

[0103] In the peening method according to the fifth embodiment, after a first peening process is performed by the needle 5e in steps S21 and S22, a second peening process may be performed by the needle 5d in steps S23 and S24. In this case, the needle 5e is the "first needle" and the needle 5d is the "second needle 5."

[0104] As described above, the needle inclination angle θ of needle 5e (e.g., 70°) is greater than the needle inclination angle θ of needle 5d (e.g., 60°), so in this case, the inclination angle of the central axis J1 of the first needle (i.e., needle 5e) in step S21 is greater than the inclination angle of the central axis J1 of the second needle (i.e., needle 5d) in step S23.

[0105] In this way, even when the first needle used in the first peening process and the second needle used in the second peening process are exchanged with the needle 5d and the needle 5e, the peening portion 35e shown in FIG. 17 is formed at the weld toe 34 in substantially the same manner as above.

[0106] As described above, the peening method according to the fifth embodiment includes the steps of: (a) positioning a rod-shaped first needle (i.e., needle 5d or needle 5e) centered on a central axis J1 that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in a cross section perpendicular to the longitudinal direction, with the tip end portion (i.e., tip end portion 50d or tip end portion 50e) of the first needle facing the weld toe 34; and (b) performing a first peening treatment on the weld toe 34 by striking the weld toe 34 with the tip end portion of the first needle. (Step S22) performing the above-mentioned peening treatment on the weld toe 34; a step (Step S23) of positioning a rod-shaped second needle (i.e., needle 5e or needle 5d) centered on a central axis J1 that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface 111 of the base metal 11 in the cross section, with the tip end (i.e., tip end 50e or tip end 50d) of the second needle facing the weld toe 34; and a step (Step S24) of performing a second peening treatment on the weld toe 34 by striking the weld toe 34 with the tip end of the second needle.

[0107] The tip of the first needle in the above cross section has an arc shape whose center (i.e., center 501d or center 501e) is located on the central axis J1 of the first needle. The tip of the second needle in the above cross section has an arc shape whose center (i.e., center 501e or center 501d) is located on the central axis J1 of the second needle and whose radius is different from the radius of the tip of the first needle. The inclination angle of the central axis J1 of the first needle in step S21 is different from the inclination angle of the central axis J1 of the second needle in step S23.

[0108] According to the peening method of the fifth embodiment, the weld toe 34 is struck by a needle 5d having a tip 50d with a relatively small radius, which prevents the formation of an unstruck portion (i.e., a portion that does not come into contact with the needle 5d and is not plastically deformed) at the weld toe 34. Furthermore, the weld toe 34 is struck by a needle 5e having a relatively large radius at the tip 50e, which prevents the formation of a peened portion 35e with a relatively shallow and gentle surface at the weld toe 34. Furthermore, by making the needle inclination angle θ of the needle 5e larger than the needle inclination angle θ of the needle 5d, the depth of the recess formed by the needle 5e in the surface 111 of the base metal 11 can be reduced. Therefore, stress concentration at the weld toe 34 can be suitably reduced, and the maximum depth d4 of the peened portion 35e at the surface 111 of the base metal 11 can be prevented from becoming excessively large. As described above, according to the peening method, it is possible to prevent the occurrence of unhammered portions at the weld toe 34 and the indentation in the base metal 11 from becoming excessively deep, and it is also possible to suitably reduce the stress concentration at the weld toe 34 and improve the fatigue strength of the welded joint 3.

[0109] In the peening method according to the fifth embodiment, the smaller of the radius of the tip of the first needle and the radius of the tip of the second needle is preferably 25% to 75% of the larger radius in the cross section. This makes it possible to preferably prevent the occurrence of pounded remains at the weld toe 34 and the indentation in the base metal 11 from becoming excessively deep.

[0110] The above-described peening method, peening apparatus, and welded structure 1 can be modified in various ways.

[0111] For example, in the peening method according to the first embodiment, the peened portion 35 does not necessarily have to be formed by only one peening process (i.e., a process of moving the needle 5 in one longitudinal direction while advancing and retracting it relative to the weld toe 34), but may be formed by multiple peening processes. The same applies to the peening methods according to the second to fourth embodiments.

[0112] In the peening method according to the fifth embodiment, the peening portion 35e does not necessarily have to be formed by only two peening processes, but may be formed by three or more peening processes. In this case, the above-mentioned needles 5d and 5e may be used in another peening process performed in addition to the first and second peening processes in steps S22 and S24, or needles having a different tip radius, etc. from the needles 5d and 5e may be used. Furthermore, in the other peening process, the needle inclination angle θ may be the same as or different from the needle inclination angle θ in the first and second peening processes.

[0113] In the peening method according to the first embodiment, the radius R1 of the first portion 51 may be less than 25% and more than 75% of the radius R2 of the second portion 52. In the peening method according to the second embodiment, the radius R1 of the first portion 51a may be less than 25% and more than 75% of the radius R2 of the second portion 52a.

[0114] In the peening method according to the third embodiment, the radius R2 of the second portion 52b may be less than 25% of or greater than 75% of the radius R1 of the first portion 51b. In the peening method according to the fourth embodiment, the radius R2 of the second portion 52c may be less than 25% of or greater than 75% of the radius R1 of the first portion 51c.

[0115] In the peening method according to the fifth embodiment, the smaller of the radius of the tip of the first needle and the radius of the tip of the second needle may be less than 25% of the larger radius and may be greater than 75%.

[0116] The structure of the peening device 7 is not limited to the above-described one, and may be modified in various ways.

[0117] The weld joint 3 and the weld metal 31 do not necessarily have to be substantially straight, but may be curved. In this case, the longitudinal direction is also a direction in which the weld joint 3 and the weld metal 31 extend while curving.

[0118] The weld toe of the weld metal 31' may or may not be peened. For example, the weld toe may be peened by the peening method according to the first embodiment. Alternatively, the weld toe may be peened by another peening method.

[0119] In the welded structure 1, the number of welded joints 3 to which peening is performed by the above-described peening method may be one or two or more. Furthermore, the welded joint 3 may be various joints other than a T-joint (for example, a cross joint).

[0120] The base materials 11, 12 of the welded structure 1 do not necessarily have to be flat plate-shaped members, and base materials of various shapes may be used.

[0121] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory. [Explanation of symbols]

[0122] 1 Welded structures 3 Welded joints 5,5a~5e needle 7 Peening equipment 11,12 Base material 31,31' Weld metal 34 Weld Toe 35, 35a, 35b, 35c, 35e Peening section 50, 50a~50e (needle) tip 51,51a~51c 1st part 52,52a~52c 2nd part 111 (Base material) surface 311 (weld metal) surface 351, 351a to 351c First recess 352, 352a to 352c Second recess 511, 511a~511c (first part) center 521, 521a~521c (second part) center J1 center axis S11~S12, S21~S24 steps

Claims

1. A peening method for striking a weld toe, which is a boundary between a base metal and a weld metal, in a weld joint extending in a longitudinal direction with a needle, comprising: a) placing a rod-shaped needle having a central axis that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle; Equipped with The tip of the needle in a cross section perpendicular to the longitudinal direction is a first portion having an arc shape with its center located on the central axis and located on the base material side of the central axis; a second portion having an arc shape and a center located on the central axis, the second portion being located on an opposite side of the central axis from the base material side; Equipped with A peening method in which the radius of the first portion is smaller than the radius of the second portion in the cross section.

2. 2. The peening method according to claim 1, A peening method, wherein a radius of the first portion in the cross section is 25% or more and 75% or less of a radius of the second portion.

3. A peening method for striking a weld toe, which is a boundary between a base metal and a weld metal, in a weld joint extending in a longitudinal direction with a needle, comprising: a) placing a rod-shaped needle having a central axis that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle; Equipped with The tip of the needle in a cross section perpendicular to the longitudinal direction is a first portion having an arc shape with its center located on the central axis and located on the base material side of the central axis; a second portion having an arc shape and a center located on the central axis, the second portion being located on an opposite side of the central axis from the base material side; Equipped with A peening method in which the radius of the first portion is greater than the radius of the second portion in the cross section.

4. The peening method according to claim 3, a radius of the second portion in the cross section that is 25% or more and 75% or less of a radius of the first portion.

5. A peening method for striking a weld toe, which is a boundary between a base metal and a weld metal, in a weld joint extending in a longitudinal direction with a needle, comprising: a) placing a rod-shaped needle having a central axis that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the needle facing the weld toe; b) performing a peening treatment on the weld toe by striking the weld toe with the tip of the needle; Equipped with The tip of the needle in a cross section perpendicular to the longitudinal direction is a first portion having an arc shape and located on the base material side of the central axis and a center located on the opposite side of the central axis from the base material side; a second portion having an arc shape and located on the opposite side of the central axis from the base material side, the second portion having a center located on the central axis; Equipped with The peening method wherein the radius of the first portion of the cross section is different from the radius of the second portion of the cross section.

6. The peening method according to claim 5, a smaller one of the radius of the first portion and the radius of the second portion in the cross section being 25% or more and 75% or less of the larger one.

7. A peening method for striking a weld toe, which is a boundary between a base metal and a weld metal, in a weld joint extending in a longitudinal direction with a needle, comprising: a) placing a rod-shaped first needle having a central axis that is inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in a cross section perpendicular to the longitudinal direction, with the tip of the first needle facing the weld toe; b) performing a first peening treatment on the weld toe by striking the weld toe with the tip of the first needle; c) placing a rod-shaped second needle centered on a central axis inclined at an inclination angle of 40° or more and 80° or less with respect to the surface of the base metal in the cross section, with the tip of the second needle facing the weld toe; d) performing a second peening treatment on the weld toe by striking the weld toe with the tip of the second needle; Equipped with the tip of the first needle in the cross section has an arc shape whose center is located on the central axis of the first needle; the tip portion of the second needle in the cross section has an arc shape whose center is located on the central axis of the second needle and whose radius is different from the radius of the tip portion of the first needle; a tilt angle of the central axis of the first needle in the step a) different from a tilt angle of the central axis of the second needle in the step c).

8. The peening method according to claim 7, a peening method, wherein the smaller of the radius of the tip of the first needle and the radius of the tip of the second needle in the cross section is 25% or more and 75% or less of the larger radius of the tip of the first needle and the radius of the tip of the second needle.

9. 1. A peening apparatus comprising: a rod-shaped needle centered on a central axis; an advancing / retracting mechanism that moves the needle forward and backward relative to an object to strike the object; Equipped with a peening portion, which is a recess, is formed in the object by striking the object with the needle that is moved along the longitudinal direction of the object; The tip of the needle in a cross section perpendicular to the longitudinal direction is an arc-shaped first portion located on one side of the central axis; an arc-shaped second portion located on the other side of the central axis; Equipped with A peening apparatus in which the radius of the first portion and the radius of the second portion are different in the cross section.

10. A welded structure, a longitudinally extending weld joint; a weld toe, which is a boundary between a base material and a weld metal in the weld joint, includes a peening portion, which is a recess formed by striking with a needle; The peening unit includes: a first recess having an arc shape that is continuous with the surface of the base material in a cross section perpendicular to the longitudinal direction and that is recessed from the surface of the base material in a thickness direction of the base material; a second recessed portion having an arc shape that is continuous with the surface of the weld metal in the cross section and recessed from the surface of the weld metal toward the inside of the weld metal; Equipped with the first recess and the second recess are continuous, A welded structure in which the radius of the first recess is different from the radius of the second recess.

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