JP5919986B2 - Hammer peening treatment method and welded joint manufacturing method using the same - Google Patents

Description

  The present invention relates to a striking terminal and a hammer peening treatment method and a welded joint using the same for forming a welded joint suitable for a steel structure that requires excellent fatigue characteristics such as a steel bridge, The stress concentration is relaxed by improving the shape of the weld toe and the fatigue strength of the weld joint is improved.

  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 first establish an inspection system. Especially in the case of fatigue damage, it is not enough to reduce the external force of the passing vehicle, etc. Improvement is important.

  In addition, stress concentration tends to occur in the welded portion when defects such as cracks exist and the shape of the weld toe is inappropriate. As a result, the repeated stress and the influence of the welding residual stress are superimposed to generate a fatigue notch, which may lead to fatigue failure. Therefore, proposals have been made from various viewpoints for preventing fatigue fracture.

  For example, 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 uses a processing device that strikes and plastically deforms the vicinity of a weld toe while being ultrasonically vibrated. A technique is described in which the fatigue strength of a welded structure can be stably improved at high speed by processing the groove under predetermined hitting conditions without depending on the skill level of the operator.

  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 to explode the surface. It is described that compressive residual stress is introduced into a fan rotor blade of a gas turbine engine by a method in which a compressive force is locally generated in a part.

  Patent Document 3 describes a technique related to a fatigue treatment improving impact processing method and apparatus for a welded joint, and in particular, by using an impact pin with a tip having a specific size and forming an impact mark near the weld toe. A technique is described in which compressive residual stress is introduced into a weld by compressing the surface of a steel sheet so as to form a groove having a specific dimension.

  Normally, hammer peening is carried out by holding the peening device so that the tip of the tip (also referred to as a striking terminal) is applied obliquely from above to the weld toe and entrusting the load of the peening device to the weld toe. This reduces the workload.

  Therefore, when hammer peening is applied to the out-of-plane gusset joint in which the rib 2 is erected on the base material 1 shown in FIG. 1, a stress concentration portion is formed at the weld toe 4 by the tip of the striking terminal 5 of the peening device. In some cases, a deep groove 6 is formed, and a fatigue crack 7 is generated from the tip of the weld bead 3.

  On the other hand, in Non-Patent Document 1, regarding the improvement of the fatigue strength of the welded joint of high strength steel (SM570) by hammer peening and TIG treatment, the fatigue crack as described above occurs when hammer peening is performed. The result of examining a new hammer peening method for reducing the stress concentration at the weld toe and the residual stress is described for the problem that the fatigue strength of the welded portion decreases.

  That is, it is described that grinding a part of the weld toe in advance with a grinder and performing hammer peening a plurality of times of about three passes before hammer peening is effective in preventing the occurrence of fatigue notches.

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) Illustrated welding terminology dictionary, Nikkan Kogyo, September 20, 1971, 4th edition, page 53

  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 part, the welded part described in Patent Document 1 and the like listed above is selected. A method for improving fatigue strength is applied. In addition, if the characteristics of a welded joint having excellent fatigue characteristics are clear, it is possible to select an optimum fatigue strength improving method in the same manner as selecting a welding method.

However, the hammer peening method using ultrasonic waves described in Patent Document 1 has a problem that the device to be used is expensive and difficult to obtain compared to a conventional device that drives a terminal with air pressure.
Further, the laser shock hammer peening method described in Patent Document 2 has a problem that it is difficult to apply to the manufacture of a steel bridge because the material needs to be pretreated and the apparatus is expensive and large.

  On the other hand, Patent Document 3 describes a welded structure excellent in fatigue resistance characteristics, and discloses a welded portion that is preferable as a welded portion of a fatigue crack occurrence risk portion. An apparatus for obtaining a welded portion is difficult to obtain, and problems remain in terms of 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 In this case, the surface of the base metal material is struck, but since the tip of the impact terminal is hemispherical, it requires a large number of impacts and efficiently introduces compressive residual stress to the welded joint. It is difficult.

  Furthermore, even the technique described in Non-Patent Document 1 still has problems in terms of construction efficiency, such as requiring grinding in advance and performing hammer peening a plurality of times.

  The present invention has been developed in view of the above-described present situation, hammer hammer peening treatment, a striking terminal for improving the fatigue strength of a welded joint, a method using the same, and fatigue strength characteristics using the method An object is to provide an excellent welded joint.

In order to improve the fatigue strength of the welded joint, the inventors diligently studied the characteristics of the weld toe portion where fatigue cracks are particularly likely to occur. As a result, it is a simple device of the pneumatic vibration method by reducing the stress concentration at the weld toe and at the same time reducing the tensile residual stress due to welding, that is, the shape of the hammering terminal by hammer peening treatment is made into a substantially bowl shape Even so, it has been found that improvement of the shape of the toe portion and introduction of compressive residual stress to the weld can be realized simultaneously.
The present invention has been made based on the above findings.

That is, the gist configuration of the present invention is as follows.
1 . In a hammer peening treatment method that uses a pneumatic vibration type striking terminal and applies a blow to the weld toe to improve the fatigue strength of the welded joint,
As the striking pin, at its distal end, a traveling direction of the cross section of the striking pin trapezoidal shape, the length in the advance direction of the distal end of the terminal is at 1mm or 10mm or less, and for that direction of travel using a terminal radius of curvature in a cross section perpendicular become less arcuate 10mm or more 1 mm, and adding a shot area as the base material over the weld metal across the weld toe, weld the base material across the weld toe A hammer peening treatment method characterized by forming an impact mark having a radius of curvature of 2 mm or more with respect to a weld toe which is a region extending over a metal.

2 . 2. The hammer peening treatment method according to 1 above, wherein, when the impact is applied using the impact terminal, the impact angle is in a range of 60 ° ± 20 ° with respect to the surface of the base material.

3 . 1 or 2 characterized in that the tip of the impact terminal has an elliptical arc shape with the major axis of the ellipse as an axis, and the minor axis of the ellipse is 1 mm or more in a cross section perpendicular to the traveling direction of the impact terminal. 2. The hammer peening processing method according to 2.

4 . The hammer peening treatment method according to any one of the above items 1 to 3 , wherein the weld toe portion extends over an area of 2 mm or more on the weld metal side and 2 mm or more on the base metal side across the weld toe. .

5 . A method for manufacturing a welded joint , wherein the hammer peening treatment method according to any one of 1 to 4 is used, and a hammer is applied to the weld toe portion across the base metal and the weld metal with the weld toe interposed therebetween,
A method for manufacturing a welded joint , wherein a radius of curvature of a hitting mark formed by the hitting is 2 mm or more.

6 . 6. The method for manufacturing a welded joint according to 5 above, wherein the weld toe spans a region of 2 mm or more on the weld metal side and 2 mm or more on the base metal side across the weld toe.

  According to the present invention, even a device that drives a terminal by a conventional air pressure, such as a flux chipper, can perform an effective striking process on the weld toe. That is, the effect of improving the fatigue strength of the welded portion can be easily obtained, which is an extremely useful technique in industry.

It is a figure explaining the defect which arises in a weld toe in hammer peening. It is the schematic explaining the principle by which a toe shape is improved by the welded joint which concerns on this invention. It is a figure explaining the X, Y, Z direction of the impact terminal used for the impact of the welded joint which concerns on this invention. It is a figure explaining the hit | damage terminal used for hit | damage of the welded joint which concerns on this invention, (a) is an XZ cross section, (b) is a figure which shows the shape of a YZ cross section. It is a figure explaining the other impact terminal used for the impact 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. (a)-(b) is a figure which shows the square turn welded joint which performed the turn welding. It is a figure which shows the profile of a toe end shape. It is a figure which shows the relationship between the frequency | count of stress loading until it leads to a fracture | rupture, and a stress range.

Embodiments of the present invention will be specifically described below with reference to the drawings.
Note that the drawings used in the following description schematically show a feature portion for convenience in order to make the feature easy to understand. Therefore, the dimensional ratio of each component may differ from the actual one.

The present invention provides a welded joint portion by applying a so-called hammer peening process in which a striking terminal is moved in the weld line direction while pressing a striking terminal (hereinafter also simply referred to as a terminal) against the weld toe of the weld bead. It provides a method for improving the fatigue strength.
In the description of the present invention, the toe or the weld toe means a line of intersection between the surface of the base material and the surface of the weld metal (see Non-Patent Document 2).

  Any of the base material, rib, and weld metal used in the present invention can be applied as long as it is used in a conventionally known weld joint. In addition, the present invention can be widely applied to welded joints in which other members are attached by welding to one member, but fatigue cracks occur due to the structure and load conditions of the place of use. The effects of the present invention can be further exhibited if a welded joint having a welded part and a weld bead that are easy to perform is targeted. Examples of the welded portion described above include a welded portion between a bridge girder and a pier in a bridge, and a welded portion between a longitudinal rib member on a ship side and a side plate in a ship.

  FIG. 2 is a schematic diagram for explaining the principle that fatigue characteristics are improved by the hammer peening treatment method according to the present invention. The welded joint portion when the rib 2 is welded to the base material 1 is welded. It is the figure shown with the cross section perpendicular | vertical with respect to a line direction. From the figure, the impact mark in which the base metal and the weld metal are pressed by the terminal against the toe 4 of the weld bead 3 to cause plastic deformation (indicated by a dotted line in the figure). It turns out that it is eight.

  FIG. 3 shows the X direction when the X direction is defined as the direction perpendicular to the striking direction (direction perpendicular to the weld line direction), and the Y direction is defined as the striking direction (direction parallel to the weld line direction). It is a figure explaining a direction and Z direction, and the X direction, Y direction, and Z direction which are demonstrated below are based on this definition.

4 and 5 show the shape of the tip of the impact terminal according to the present invention.
As shown in FIG. 4, the striking terminal according to the present invention has a tip having a length of a ₁ mm in a cross section (XZ cross section) in which the tip of the striking terminal is perpendicular to the traveling direction (Y direction). The radius of curvature (r ₁ ) has an arcuate outer periphery (FIG. 4A) of 1 mm or more and 10 mm or less, and a length b ₁ mm of ₁ mm or more and 10 mm or less in the traveling direction (Y direction). It is a thing of the substantially bowl shape (FIG.4 (b)) which has. The above length _{a 1} in the range of 5~9.5mm are preferred. This is because it is possible to hit a wide range of the base material and the toe side, which is advantageous for smoothing the toe shape in the welded portion.

When the curvature radius (r ₁ ) is less than 1 mm, a deformation that easily causes stress concentration at the toe is formed. On the other hand, if it exceeds 10 mm, the contact area between the hitting terminal and the toe portion at the time of hitting becomes too large, and sufficient compressive residual stress cannot be introduced into the toe portion. Therefore, the radius of curvature (r ₁ ) is 1 mm or more and 10 mm or less.

FIG. 5 shows the shape of a striking terminal according to another example of the present invention. As shown in the figure, the tip of the striking terminal has a length a with an ellipse major axis (r ₃ ) as the axis in the cross section (XZ cross section) perpendicular to the traveling direction (Y direction). _It has an elliptical arc-shaped outer periphery of ₂ mm, has an elliptical minor axis (r ₂ ) of 1 mm or more (FIG. 5A), and is 1 mm in the traveling direction (Y direction), like the terminal shown in FIG. It is formed in a substantially bowl shape having a length b ₂ mm of 10 mm or less (FIG. 5B). The length _{a 2} of the above, the range of 5~9.5mm are preferred. This is because it is possible to hit a wide range of the base material and the toe side, which is advantageous for smoothing the toe shape in the welded portion.

In the case of the striking terminal having the elliptical arc-shaped outer peripheral portion, if the elliptical minor axis (r ₂ ) is less than 1 mm, a deformation in which a stress concentration portion is generated at the toe portion is formed. (R ₂ ) is 1 mm or more. The upper limit is not particularly limited, but is preferably about 2 mm.
Further, if the major axis (r ₃ ) of the ellipse exceeds 8 mm, it is difficult to hit the weld toe, and therefore, the major axis (r ₃ ) is preferably larger than the minor axis and about 6 mm.

4 and 5, as described above, each has a length b ₁ and b ₂ of ₁ mm or more and 10 mm or less in the traveling direction (Y direction). If each length is less than 1 mm, not only can the compressive residual stress not be applied effectively to the toe, but the force applied to the striking terminal increases and the tip tends to collapse, frequently Replacement is required. On the other hand, when the length exceeds 10 mm, not only is the deformation where a stress concentrated portion is generated at the toe, but also a large force is required to apply an effective blow to the toe, so a large scale is required. It becomes a powerful striking device. Accordingly, b ₁ and b ₂ are each in the range of 1 mm or more and 10 mm or less.
Further, b ₁ and b ₂ are preferably the same as or smaller than a ₁ and a ₂ . This is because if the contact area of the impact terminal becomes excessively large, the force applied per unit area is weakened and it is difficult to obtain a stable shape.

In the present invention, it is important to apply a blow to the weld toe at an angle of 60 ° ± 20 ° with respect to the surface of the base material.
This is because if it exceeds 80 °, it is somewhat difficult to add an effective blow to the weld metal, while if it is less than 40 °, an effective blow to the base metal is difficult. This is because there is a risk that it cannot be added.

In the present invention, the hitting angle can be adjusted by a conventionally known method. For example, a plate having an apex angle of 60 degrees just before the start of hitting and having a certain thickness in the Y direction is formed on the base material. It is only necessary to place a flux chipper on it and check the angle before hitting. Further, it is possible to strike while placing it on a table whose angle can be arbitrarily changed, or placing a transparent plastic protractor aside and having a collaborator check visually.
However, since visual confirmation during hitting is difficult and dangerous, there is no problem if the angle is checked with the tip of the hitting terminal in contact with the hitting position at the start of hitting.
That is, regarding the confirmation of the angle, it is only necessary to confirm that it is within the range at the time of the first hit in the series of operations. This is because it is difficult for the operator himself to confirm, and it is inefficient to confirm during all work.

  Further, in the present invention, the fatigue strength of the welded joint can be sufficiently improved even with a single impact on one welded portion, but the angle to be struck within the toe is within the range of the angle described above. Can be changed as appropriate. For example, when striking on the base metal side, it is possible to strike at an angle larger than 60 °, then to the vicinity of the toe, about 60 °, and on the weld metal side, it is possible to strike at an angle smaller than 60 °. it can. The hitting can be started from the base metal side or the weld metal side. In the present invention, it is sufficient that at least one of the hammering treatments is applied to the weld toe, and the other hammering is performed on either the base metal or the weld metal side. You may. However, as a result, it is necessary that striking marks are formed on both the base material and the weld metal.

In the present invention, the weld toe portion means a region extending between the base metal and the weld metal on which a hitting mark is formed across the weld toe. Further, the range is preferably determined by measuring the length to the end point (edge) of the impact mark with reference to the weld toe, and setting the region to be 2 mm or more on the weld metal side and 2 mm or more on the base metal side. This is because if each is less than 2 mm, the fatigue strength of the welded joint may not be sufficiently improved.
In addition, although there is no special restriction | limiting in the upper limit, it is about 8 mm on the weld metal side, On the other hand, it is about 10 mm on the base material side.

According to the present invention, a weld joint is formed in which the fatigue strength of the weld joint portion is improved by hitting the weld toe portion according to the respective hammer peening treatment conditions as described above.
At that time, it is essential in the present invention that the radius of curvature of the hitting mark formed by the hitting is 2 mm or more.
This is because if the radius of curvature of the hitting trace is less than 2 mm, the effect of stress concentration relaxation due to the addition of hitting cannot be sufficiently obtained. Although there is no particular limitation on the upper limit, it is preferable that the upper limit does not exceed the leg length of the weld.

  In addition, as described above, the weld joint according to the present invention preferably has a weld toe extending over a region of 2 mm or more on the weld metal side and 2 mm or more on the base metal side with respect to the weld toe.

  As the hitting terminal used in the present invention, hitherto known hitting terminals can be used in addition to the shape described above, and examples thereof include tool steel having a tensile strength of 1000 MPa or more.

  The hitting device used in the present invention can use hitherto known welding devices, but using a conventional device that drives terminals with air pressure, such as a flux chipper, reduces the cost of equipment. Desirable because it can.

An impact terminal in which the tip of the terminal has an XZ cross section (cross section perpendicular to the terminal traveling direction), a top radius of curvature of 4.5 mm, and a YZ cross section (terminal cross section in the traveling direction) length of 5 mm; In the XZ cross section (cross section perpendicular to the traveling direction of the terminal), the major axis is 6 mm, the minor axis is 3 mm, the elliptical arc is formed with the major axis as the axis, and the length of the YZ section (the cross section in the terminal traveling direction) is 9 mm. A striking terminal having a hemispherical shape with a radius of curvature of 1.5 mm was prepared for each of the striking terminals. Further, a parallel part width: 150 mm × length: 500 mm × plate thickness: 12 mm shown in FIG. 6A is turned around a 75 mm × 50 mm rib 2 (SM490Y) and welded 3 (wire MXZ200− A corner-turn welded joint with 1.2Φ, 100% CO ₂ , 240A-30V-40CPM, 10.8 KJ / cm) was prepared.
Next, hammer peening by the impact terminal is applied to the toe end of the welded joint, the air pressure is about 6 kg / cm ² , and the frequency is 90 Hz. The angle of impact on the base material (hereinafter referred to as impact angle) Was applied within a range of 45 to 70 ° (degrees). The striking angle was checked by a collaborator by placing a transparent plastic protractor aside just before the striking.
Table 1 shows the test No., the terminal shape, and the hitting angle.

The toe radius of the welded joint after the hammer peening treatment was measured by silicon rubber casting.
The number of breaks (stress range: 200 MPa) was determined by using the test body shown in FIG. 6A to chuck both ends of the base material 1 in a fatigue testing machine and repeatedly applying stress (stress) in the longitudinal direction of the rib 2. Ratio: 0.1, frequency: 5 to 10 Hz). In the present invention, the number of breaks is preferably over 10 ⁶ times in the stress range: 200 MPa.
Furthermore, the magnitude | size of the area | region (welding toe part) of the impact mark by the said impact terminal was measured. Specifically, the distance between the rib end and the weld toe is measured before hitting with a digital caliper as a reference, and the distance to the edge of the hitting mark again with the rib end as a reference after hitting. Were measured on the weld metal side and the base metal side, respectively. Thereafter, the distance from the weld toe to the edge of the impact mark was obtained by taking the difference on the weld metal side and the base metal side, respectively.
Table 1 shows the measurement results of the radius of curvature (toe radius), the number of breaks (stress range: 200 MPa), and the range of the weld toe, respectively.

From Table 1, when the angle with respect to the surface of the base material was set to 60 ° ± 20 ° using the terminal shape of the present invention, the radius of curvature of the hitting mark was 2 mm or more. In the break test, the chucking portion of the specimen (base material) broke before the weld portion broke, but the number of times until the weld portion broke was all in the stress range: 200 MPa, It can be seen that there are at least 10 ⁶ times. On the other hand, without treatment, the stress is tensile stress, and when using a hemispherical terminal with a radius of curvature of 1.5 mm, the radius of curvature of the striking scar is larger than that without treatment, but welding It was recognized that the number of breaks of the part was inferior. If the tip of the impact terminal has a hemispherical shape, the strength of the tip is not sufficient, and sufficient compressive residual stress cannot be introduced into the base material at the time of impact. Further, the tip of the 1.5 mm hemispherical terminal was crushed after hitting.

  FIG. 7 shows the profile of the toe shape as welded with the present invention. From the figure, it can be seen that the weld toe according to the present invention has a smoother shape than the welded toe. Therefore, it can be seen that the effect of stress concentration relaxation described above is manifested in the present invention due to the shape improvement effect.

Subsequently, the base material 1 ′ is used instead of the base material 1 shown in FIG. 6B, and the parallel part width: 100 to 150 mm × length: 700 mm × plate thickness: 16 mm is used as the base material 1 ′ (SM490Y). , turning the 75 mm × 50 mm ribs 2 (SM490Y) welding 3 (wire _{MXZ200-1.2Φ, 100% CO 2, 240A} -30V-40CPM, 10.8KJ / cm) a fatigue test also angular turning joint subjected to went.
About the example of an invention, the tip radius of a hitting terminal: Three types, 4.5 mm, 3 mm, and 1.5 mm, and the length: Three types, 3 mm, 5 mm, and 9 mm were prepared. On the other hand, as a comparative example, a fatigue test was performed on those subjected to the grinder treatment (Comparative Example A series) and those not subjected to the treatment after melting (as welded, Comparative Example B series).
The test results are shown in Table 2.

  FIG. 8 shows the relationship between the number of times of stress loading up to the final break and the stress range. From this figure and Table 2, it can be seen that when the stress range is 250 MPa or less and according to the present invention, the C grade of the design curve of JSSC (Japan Steel Structure Association) is sufficiently satisfied. In particular, a sufficient fatigue life is obtained even when the tip of the impact terminal has a curvature radius of 1.5 mm, because this has a sufficient length compared to the tip having a hemispherical shape. This is because the strength of the tip is high and sufficient compressive residual stress can be introduced into the toe portion. On the other hand, it was about D grade in the comparative example A series and about E grade in the comparative example B series. Therefore, it can be seen that, according to the present invention, two or more grades are improved over the welded joint, and one grade or more is improved over the conventional grinder treatment.

1,1 'base material 2 rib 3 weld metal (bead)
4 toe 5 hammering terminal (chipper)
6 groove 7 fatigue crack 8 impact mark

Claims (6)

In a hammer peening treatment method that uses a pneumatic vibration type striking terminal and applies a blow to the weld toe to improve the fatigue strength of the welded joint,
As the striking pin, at its distal end, a traveling direction of the cross section of the striking pin trapezoidal shape, the length in the advance direction of the distal end of the terminal is at 1mm or 10mm or less, and for that direction of travel using a terminal radius of curvature in a cross section perpendicular become less arcuate 10mm or more 1 mm, and adding a shot area as the base material over the weld metal across the weld toe, weld the base material across the weld toe A hammer peening treatment method characterized by forming an impact mark having a radius of curvature of 2 mm or more with respect to a weld toe which is a region extending over a metal. 2. The hammer peening method according to claim 1 , wherein when hitting is applied using the hitting terminal, the hitting angle is in a range of 60 ° ± 20 ° with respect to the surface of the base material. 3. In section perpendicular with respect to the traveling direction of the striking pin, claim 1 of the tip of the striking pin, the major axis of the ellipse and the axis and the elliptical arc shape, characterized in that the minor axis of the elliptic circle was over 1mm or hammer peening method according to. The hammer peening process according to any one of claims 1 to 3 , wherein the weld toe spans a region of 2 mm or more on the weld metal side and 2 mm or more on the base metal side across the weld toe. Method. A method for manufacturing a welded joint , wherein the hammer peening method according to any one of claims 1 to 4 is used, and a hammer is applied to a weld toe across a base metal and a weld metal with the weld toe interposed therebetween,
A method for manufacturing a welded joint , wherein a radius of curvature of a hitting mark formed by the hitting is 2 mm or more. 6. The method for manufacturing a welded joint according to claim 5 , wherein the weld toe portion extends over a region of 2 mm or more on the weld metal side and 2 mm or more on the base metal side with the weld toe interposed therebetween.

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