JP2021115612A - Welding method and welding structure - Google Patents

Abstract

To provide a welding technology capable of securing a stable long fatigue service life when forming an extension bead by using an LTT welding material on the tip side of a corner-rotating welding part.SOLUTION: A welding method for welding a gusset plate by corner-rotating welding to high tension steel, includes: a corner-rotating welding step of providing a corner-rotating welding bead by performing corner-rotating welding to a corner-rotating part end surface of the gusset plate so that an end surface corner-rotating route depth is 5 mm or more by using an ordinary corner-rotating welding metal; and an extension bead welding step of providing an extension bead by performing welding so as to cover a corner-rotating welding bead by using a welding material having a martensitic transformation starting point of welding metal of 350°C or lower in a longer direction of the gusset plate from a corner-rotating part end surface of the corner-rotating welded gusset plate.SELECTED DRAWING: Figure 16

Description

The present invention relates to a welding method for square-rotating welding a gusset plate to a flat plate-shaped main plate of high-strength steel in a welded structure using high-strength steel, and a welded structure obtained by the welding method.

In recent years, high-strength steel whose tensile strength has been increased from the conventional 500 MPa to 1000 MPa has been used for the purpose of increasing the size of welded structures such as ships, marine structures, and bridges, and the accompanying weight reduction and safety. Is becoming.

In proportion to the increase in tension, the fatigue strength represented by the fatigue life of the base metal and the fatigue limit also improves, but the fatigue strength of the welded portion does not improve as long as the conventional welding technique is used.

Specifically, for example, as shown in FIG. 23, a flat plate-shaped main plate (also referred to as “flange”) 10 and a gusset plate (also referred to as “web” or “stiffuna”) 20 are fillet welded. A corner-turning joint is provided by being joined by a bead 31 and a corner-turning weld bead 32. In the case of such a corner-turning joint, the fatigue strength is greatly reduced at the corner-turning welded portion of the gusset plate 20.

That is, the stress generated in the main plate 10 is greatest at the weld toe of the square-turning weld bead 32 at the lower toe of the gusset plate 20. Further, the gusset plate 20 expands due to heating during welding and then contracts due to cooling. However, since the degree of expansion and contraction of the main plate 10 is smaller than that of the gusset plate 20, welding between the main plate 10 and the gusset plate 20 Tension residual stress due to welding thermal stress is generated in the portion, and this tensile residual stress is also maximized at the weld toe portion of the angular rotation welding bead 32. As a result, the fatigue strength is greatly reduced at the corner-turning welded portion of the gusset plate 20, and fatigue cracks are generated at the weld toe.

Therefore, the present inventors first perform normal corner rotation welding using a normal corner rotation welding material (conventional normal welding material) with a bead length of 7 mm, which is generally called a leg length, and then perform this corner rotation. Welding material with Ms point of 350 ° C or less (hereinafter, "LTT welding") that lowers the maltensite transformation point (Ms point) of the weld metal on the tip side of the weld and causes martensite transformation expansion in the low temperature range of 350 ° C or less. Welding technology is being developed in which an elongated bead is provided using a material), and the elongated bead undergoes maltensite transformation expansion in a low temperature range to generate compressive residual stress in the elongated bead forming region (Patent Document 1, Patent Document 1, See Non-Patent Document 1).

At this time, the LTT welding material may be used for the corner rotation welding, but the LTT welding material has extremely high strength and low elongation, and does not satisfy the characteristic standard of the welded structure design when applied to the welded steel structure. Therefore, it is preferable to perform square-rotation welding using a normal welding material satisfying the welding structure design standard, satisfy the design standard such as strength, and then perform overlay welding of the LTT extension bead.

FIG. 24 is a view for explaining the overlay welding of the extension bead, in which 10 is a main plate, 20 is a gusset plate, and 31 is a fillet weld bead formed along the longitudinal side surface of the gusset plate 20. Reference numeral 32 denotes a square weld bead formed around the tip end surface T of the gusset plate 20, and reference numeral 35 denotes an extension bead formed in the longitudinal direction of the end portion of the gusset plate 20. Further, l is the length of the extension bead 35, which is the distance from the tip end surface of the gusset plate 20 to the toe end of the extension bead 35.

The extension bead 35 is laminated on the upper side of the square-turning weld bead 32, and the tip portion in the longitudinal direction is joined to the main plate 10, and the rear end portion is joined to the tip end face T of the gusset plate 20.

According to this welding technique, the tensile residual stress at the weld toe can be reduced by the compressive residual stress generated in the formed region of the extension bead 35, so that the joint is compared with a normal square rotation welded joint without an extension bead. , The fatigue life can be greatly improved up to about 10 times.

Japanese Patent No. 5881055

C. Shiga, H. Murakawa, K.K. Hiraoka et al. , "Investigation on practical application of low transformation temperature welding materials to ship hull structure made of high tensile strength steel plates for fatigue life improvement", IIW International Conference, High-Strength Materials-Challenges and Applications, 2-3July 2015, Helsinki, Finland

However, as a result of further studies by the present inventors, even if an elongated bead is formed on the tip side of the corner-turning welded portion by using an LTT welding material, the improvement in fatigue life is only about three times. It was found that further improvement is necessary to obtain a stable improvement in fatigue life.

Therefore, an object of the present invention is to provide a welding technique capable of ensuring a stable and long fatigue life when forming an extension bead using an LTT welding material on the tip end side of a corner-turning welded portion.

The present inventors have focused on the fatigue fracture starting point of the weld bead while diligently researching the solution to the above problems.

That is, as described above, in the normal corner rotation welding, fatigue cracks occur at the toe of the corner rotation welding, which leads to the breakage of the main plate, but when the extension bead is provided, the fatigue cracks occur. It is suppressed and the fatigue life is greatly improved. However, eventually, fatigue cracks occur from other positions and fracture.

At this time, one of the positions where fatigue cracks are feared is the position of the root of the gusset plate end face and the plate penetration portion. That is, since tensile stress tends to concentrate at the tip of the gusset plate and the root position of the melted portion of the main plate, the crack grows from the root position and fatigue cracks (hereinafter, also referred to as "root cracks"). Occurs.

This will be specifically described with reference to FIGS. 1 to 4. 1 is a perspective view showing a welded portion between a main plate and a gusset plate in a welded structure, FIG. 2 is a cross-sectional view taken along the line A of FIG. 1, FIG. 3 is a cross-sectional view taken along the line B of FIG. , The state before the extension bead is provided is shown. In the figure, S is the side surface of the gusset plate 20, and T is the tip end surface of the gusset plate 20. Reference numeral 21 denotes a groove portion formed on the tip end face T of the gusset plate 20, and the welding material melts into the groove portion 21 to form a penetration root portion on the end face side. Dy is the depth of the tip Ry of the penetration root portion from the tip end face T (end face angle turning root depth) in the penetration root portion on the end face side, and is from the tip end face T in the length direction of the gusset plate 20. It is shown that the weld bead 32 is melted by turning the corner to the tip Ry of the penetration root portion.

Similarly, reference numeral 22 denotes a weld penetration portion formed on the side surface S of the gusset plate 20, and the welding material melts into the weld penetration portion 22 to form a penetration root portion on the side surface side. Dx is the depth of the tip Rx of the penetration root portion from the side surface S (side fillet root depth) in the penetration root portion on the side surface side, and is the penetration root portion from the side surface S in the width direction of the gusset plate 20. It is shown that the fillet weld bead 31 is melted down to the tip Rx of the above.

Conventionally, the end face corner turning root depth Dy in normal corner turning welding has been generally set to 0 mm to less than 2 mm. If tensile stress is concentrated on the tip Ry of such a penetration root portion, root cracks will occur no matter how the extension bead is provided. We considered that there might be some relationship between the stress state generated at the tip Ry of the part and the generation / growth of cracks, and conducted experiments and studies.

Specifically, as shown in FIG. 5, first, after the main plate 10 and the gusset plate 20 are squarely welded, an extension bead is provided to a predetermined length using an LTT welding material, and a penetration route that causes cracks is generated. _{The tensile residual stress σ max} at the tip Ry of the portion was measured, and the relationship with the end face angle rotation root depth Dy was obtained.

As a result, as shown in FIG. 6, it was found that the tensile residual stress σ _max decreases as the end face angle rotation route depth Dy increases and gradually approaches a certain value.

Next, a predetermined load was repeatedly applied to the same test piece as the fatigue strength, and the number of repetitions until the crack length reached 8 mm was measured and used as an index of the fatigue crack growth rate.

As a result, as shown in FIG. 7, it was found that the number of repetitions increased and the growth rate of fatigue cracks decreased as the end face angle turning route depth Dy increased. However, it was also found that when Dy was 5 mm or more, the increase in the number of repetitions began to slow down and tended to converge to a constant value.

From the results of these experiments, the end face angle rotation root depth Dy and the stress state generated at the tip Ry of the penetration root part and the generation / propagation of root cracks are related to each other, and the Dy should be 5 mm or more. As will be described later, when Dy = 0, the growth path is short and the growth speed is fast, but when Dy = 5, the growth path is long and the growth speed is slow, so root cracks occur. It was confirmed that the progress was suppressed and that the fatigue life could be further improved in a stable manner.

However, when the end face angle turning root depth Dy is set to 5 mm or more, the starting point of fracture shifts to another next weakest position instead of from the root. Therefore, considering this point, the end face corner turning root depth Dy Even if it is made deeper, the significance for improving the fatigue life is small.

The present invention is based on the above findings, and the invention according to claim 1 is based on the above findings.
It is a welding method in which a gusset plate is welded to high-strength steel by square rotation welding.
A corner-turning welding process in which a corner-turning welding material is used to perform corner-turning welding on the end face of the corner-turning portion of the gusset plate so that the end face corner-turning root depth is 5 mm or more, and a corner-turning welding bead is provided. ,
Cover the square weld bead with a welding material having a martensitic transformation start point of the weld metal of 350 ° C. or less in the longitudinal direction of the gusset plate from the end face of the square weld of the gusset plate. It is a welding method characterized by comprising an extension bead welding step of welding to and providing an extension bead.

The welding technique described above can be applied not only to a new structure but also to reinforcement and repair of an existing structure.

That is, in the case of a new structure, the depth of the end face of the gusset plate is reached by machining shown in FIG. 8 (a) or gouging shown in FIG. 8 (b) prior to welding the main plate and the gusset plate. A groove portion 21 of 5 mm or more is formed. As a result, it is possible to form a corner-turning welded portion having an end face corner-turning root depth Dy of 5 mm or more, so that the occurrence of root cracks can be suppressed and a further improvement in fatigue life can be stably ensured.

On the other hand, when reinforcing the existing structure, the construction is carried out according to the procedure shown in FIG. In FIG. 9, the upper row is a perspective view and the lower row is a cross-sectional view (corresponding to the cross-sectional view A in FIG. 1), and the construction proceeds from the left side to the right side.

Specifically, first, the existing corner-turning weld bead 32 is deleted by machining or gouging, and a groove portion 21 having a depth of 5 mm or more is formed on the end face of the gusset plate. After that, the corner rotation welding is performed using a normal welding material (a welding material equivalent to the existing corner rotation welding bead), and the corner rotation welding bead 32 integrated with the existing fillet welding bead 31 which is the remaining portion of the construction. To form.

At this time, a large tensile residual stress is generated at the united joint, which may be the starting point for the occurrence of fatigue cracks. An extension bead 35 is provided so as to cover with. As a result, the tensile residual stress on the surface can be converted into compressive residual stress by utilizing the transformation expansion effect of LTT, so that the risk of causing fatigue cracks can be excluded, and the fatigue life can be further improved. Can be stably secured.

In addition, since a large tensile residual stress may be generated at the combined joint portion between the corner-turning weld bead 32 and the fillet weld bead 31, it may become a starting point for fatigue cracks. In addition to covering with welding, it is more preferable that the coalesced joint has a smooth joint surface so as not to cause stress concentration in the coalesced joint.

Then, when repairing the existing structure, basically, the work may be carried out according to the above-mentioned reinforcement procedure, but prior to the formation of the groove portion 21, fatigue cracks generated in the main plate 10 are formed. It needs to be repaired. Therefore, the fatigue crack generation portion of the main plate 10 is deleted by machining or gouging, and the deletion mark 11 is usually repaired by blending a welding material into the deletion mark 11, as shown in FIG. Then, after the repair, the construction is carried out according to the above-mentioned reinforcement procedure.

The inventions according to claims 2 to 6 are based on the above findings, and the invention according to claim 2 is based on the above findings.
This is a welding method in which a gusset plate is welded to high-strength steel by square welding when constructing a new structure.
The corner turning welding process
The first aspect of the present invention is the step of forming a groove portion having a depth of 5 mm or more on the end face in the longitudinal direction of the gusset plate by machining or gouging in advance, and performing angular rotation welding. Welding method.

The invention according to claim 3 is
This is a welding method in which a gusset plate is welded to high-strength steel by square welding when reinforcing an existing structure.
The corner turning welding process
By machining or gouging, the corner turning weld bead applied to the end face of the corner turning portion of the gusset plate is removed, and a groove portion having a depth of 5 mm or more is formed on the end face of the corner turning portion of the gusset plate after removal. death,
The welding method according to claim 1, wherein the step is a step of providing a square rotation welding bead by performing a new corner rotation welding on the groove portion using a normal corner rotation welding material. ..

Further, the invention according to claim 4 is
This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding when repairing an existing structure in which fatigue cracks have occurred.
The corner turning welding process
After removing the fatigue cracks by machining or gouging and repairing the deletion marks so that the normal corner-turning welding material is blended into the deletion marks.
By machining or gouging, the corner turning weld bead applied to the end face of the corner turning portion of the gusset plate is removed, and a groove portion having a depth of 5 mm or more is formed on the end face of the corner turning portion of the gusset plate after removal. death,
The welding method according to claim 1, wherein the step is a step of providing a square rotation welding bead by performing a new corner rotation welding on the groove portion using a normal corner rotation welding material. ..

Further, the invention according to claim 5 is
The extension bead welding process
The extension bead is welded so as to cover the combined joint between the square weld bead provided on the end face of the gusset plate and the fillet weld bead installed on the side surface of the gusset plate by new square weld. The welding method according to claim 3 or 4, characterized in that it is a step of providing.

Further, the invention according to claim 6 is
The corner turning welding process
The combined joint between the square weld bead provided on the end face of the gusset plate by the new square weld and the fillet weld bead installed on the side surface of the gusset plate forms a smooth joint surface. The welding method according to claim 5, wherein the process is a step of welding.

Then, the present inventors further conducted experiments and studies, and obtained the following findings.

First, the extension bead preferably has a length of 17 mm or more in the longitudinal direction of the gusset plate from the end face of the corner turning portion of the gusset plate. By setting the length to 17 mm or more, it is possible to surely generate compressive residual stress in the extension bead to alleviate the stress concentration, and to improve the fatigue strength in the corner-turning welded portion. It is possible to improve the stable fatigue life.

That is, the invention according to claim 7 is
The extension bead welding process
The method according to any one of claims 1 to 6, wherein an extension bead having a length of 17 mm or more is provided in the longitudinal direction of the gusset plate from the end face of the corner turning portion of the gusset plate. It is a welding method.

Next, even among the LTT welding materials having an Ms point of 350 ° C. or lower forming an elongated bead, a weld metal having an Ms point of 100 to 300 ° C., that is, between 100 and 300 ° C. as shown in FIG. It is preferable to use a welding material having the maximum apparent transformation expansion amount. By forming an elongation bead using such an LTT welding material, the generation of compressive residual stress due to martensitic transformation expansion in a low temperature region becomes remarkable, so that a more stable fatigue life can be improved. ..

That is, the invention according to claim 8 is
Any of claims 1 to 7, wherein in the extension bead welding step, a material that becomes a welding metal having a martensitic transformation start point of 100 to 300 ° C. is used as the welding material for forming the extension bead. The welding method according to item 1.

Furthermore, when the present inventors try to apply the present invention to repairing or reinforcing an existing welded structure, they are required to carry out the work in various postures, but it is found that further ingenuity is required for that purpose. ,Study was carried out.

That is, when repairing or reinforcing an existing welded structure, typical welding postures include a downward posture in which a weld bead is formed on a main plate in a horizontal state, and an extension with respect to a gusset plate attached toward a ceiling plate. Upward posture for bead construction, vertical improvement posture for vertical bead construction from the upper end of vertically mounted gusset plate, and downward bead construction for vertically mounted gusset plate There is a vertical downward posture to be performed, and a horizontal posture to perform extension bead construction in the horizontal and horizontal directions of the horizontally mounted gusset plate. Of these, in the downward posture, continuous welding by a weaving method or the like is possible even when forming an elongated bead having a large width and length.

On the other hand, in the case of the vertical downward posture, the horizontal posture, and the upward posture, the molten metal hangs down due to the action of gravity during welding, so that it is difficult to easily construct the extension bead, and further ingenuity is required. Is.

Therefore, the present inventors have studied a welding method that allows easy extension bead construction even in these postures.

As a result, in the case of the lateral posture and the vertical posture (standing up posture and vertical downward posture), the extension bead forming region is divided into a plurality of passes, and the welding material for forming the extension bead is formed for each pass. It was found that an intermittent extension bead construction in which a molten path is formed by melting and welding the metal and a solidification period for solidifying the formed molten path is performed and this is repeated a plurality of times is preferable. The specific solidification period is preferably 2 seconds or less in consideration of the actual construction time because sufficient compressive residual stress is not generated if it is too long.

Specifically, the extension bead is constructed according to the procedure shown in FIG. 12 in the case of the lateral posture and the procedure shown in FIG. 13 in the case of the vertical posture. In FIGS. 12 and 13, the vertical direction of the paper surface is the vertical direction, the horizontal direction is the horizontal direction, each section divided into strips indicates one path, and the horizontal arrow indicates the path formation direction. In addition, in FIG. 13, the left figure shows the normal welding direction in the vertical advance and the vertical downward movement, and the right figure shows the extension bead construction procedure in the present invention.

That is, in the case of the lateral posture, as shown in FIG. 12, in the melting path forming step, a horizontal melting path is formed in a certain direction (to the left in the figure), and from the lower end to the upper end of the extension bead forming region. Toward, the extension bead is constructed by stacking a plurality of melting paths in the entire formation region.

On the other hand, in the case of the upright posture, as shown in FIG. 13, in the melting path forming step, the horizontal melting path is formed by folding back, and a plurality of melting paths are formed from the lower end to the upper end of the extending bead forming region. Stretch beads are constructed by stacking them in the entire formation area. For this reason, in the case of the vertical downward posture, the construction is performed in the direction opposite to the normal construction from top to bottom. In consideration of construction convenience, the melting path may be formed in a certain direction instead of folding back.

In this way, by forming a horizontal melting path in the melting path forming process and stacking it from the lower end to the upper end, the extension bead construction is performed in a lateral or vertical posture with no support on the lower side. However, since the path provided in advance of the lower side serves as a restraining wall (bank) and can support the subsequent molten path on the upper side, it is possible to suppress the sagging of the molten metal.

Then, in the case of the upward posture, gravity is applied downward to the molten path, and the molten metal is more likely to hang down. Therefore, when forming the molten path, the length of one pass is shortened. FIG. 14 shows the extension bead construction procedure in the upward posture, each partitioned section indicates one path forming region, and the vertical arrows indicate the path forming direction. As shown in FIG. 14, the extension bead forming region is divided into a plurality of rows in the longitudinal direction, and each row is further divided into one or a plurality of path forming regions to reduce the length of one pass. shorten. Then, as in the case of the upright posture, the molten path is formed by folding back, and the molten path formation and the solidification period are repeated a plurality of times to perform intermittent extension bead construction. Even in the upward posture, the melting path may be formed in a certain direction instead of being folded back in consideration of the convenience of construction.

In FIG. 14, in consideration of ease of implementation, the melting path forming step and the solidification period step are repeated in the order from the row on the weld toe side to the row on the gusset plate side of the extension bead forming region. ing.

In this way, the length of one pass is shortened and the melting path forming step and the solidification period step are repeated to obtain an elongated bead (composited elongated bead) formed by a group of weld beads (passes) having a short length. If this is the case, the time difference between the formation of the preceding melting path in the adjacent row and the formation of the succeeding melting path is important, and the subsequent melting path should be formed before the temperature of the preceding path drops below the Ms point. Is a condition, it is possible to form an elongation bead that generates compressive residual stress while suppressing the sagging of the molten metal.

As for the downward posture, continuous welding can be easily performed as described above, but intermittent welding can also be performed as described above.

As a result of examination by the present inventors, etc., in the case of intermittent welding using the above-mentioned LTT welding material, relatively large irregularities are likely to occur on the surface of the elongated bead in any posture. However, even in such a case, since sufficient compressive residual stress is generated in the extension bead using the LTT welding material, cracks occur and grow, and the fatigue life is longer than in the case where there is no unevenness on the surface. There was no significant difference in the.

The inventions according to claims 9 to 12 are based on the above findings, and the invention according to claim 9 is based on the above findings.
This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, the melting path is formed in a certain direction or folded back.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. The welding method according to any one of 8.

And the invention according to claim 10
This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in a sideways posture when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, a horizontal melting path is formed in a certain direction.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. The welding method according to any one of 9.

The invention according to claim 11 is
This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in an upright position when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, a horizontal melting path is formed in a certain direction or folded back.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. The welding method according to any one of 9.

Further, the invention according to claim 12
This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in an upward posture when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
By dividing into a plurality of rows in the longitudinal direction and further dividing each row into one or a plurality of path forming regions, an extension bead forming region is formed, and welding is performed in the extending bead forming region. It includes a melt path forming step of forming a melt path of a material and a solidification period step of solidifying the melt path.
In the melting path forming step, the melting path is formed in a certain direction or folded back.
The first to ninth aspects of the present invention, wherein the extension bead is provided over the entire formation region of the extension bead while alternately repeating the melting path forming step and the solidification period step a plurality of times. The welding method according to any one item.

The inventions according to the above claims can also be grasped from the point of view of the welded structure in which the gusset plate is welded to the high-strength steel by square welding.

That is, the invention according to claim 13 is
A welded structure in which a gusset plate is welded to high-strength steel by square welding.
On the end face of the corner turning portion of the gusset plate, a corner turning welding bead is formed so that the end face corner turning root depth is 5 mm or more.
An extension bead is provided from the end face of the corner turning portion of the gusset plate in the longitudinal direction of the gusset plate so as to cover the corner turning welding bead using a welding material having a martensitic transformation start point of the weld metal of 350 ° C. or less. It is a welded structure characterized by being welded.

And the invention according to claim 14
The welded structure is a new structure and
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion.

And the invention according to claim 15
The welded structure is an existing structure that has been reinforced.
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion.

The invention according to claim 16 is
The welded structure is an existing structure in which fatigue cracks have been repaired.
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion.

Further, the invention according to claim 17
13. The welded structure described.

In the case of the invention described in each of the above claims, a mechanism capable of stably ensuring further improvement in fatigue life is considered as follows.

First, as described above, in the conventional extension bead, the end face angle turning root depth is set to be shallow, generally from 0 mm to less than 2 mm. Therefore, as shown in FIG. 15, when tensile residual stress is applied to the corner turning welding bead 32 and a crack is generated at the starting point Ry of the end face corner turning welding route, the crack grows in the direction shown by the broken line 40 and further extends. Proceed through the bead 35. Since the extension bead 35 cannot suppress the growth of the crack, the growth of the crack generated from the root causes fatigue fracture in a short period of time.

On the other hand, in the present invention, a groove portion is provided so that the end face corner turning root depth is 5 mm or more, a corner turning welding bead is provided deep into the end face of the corner turning portion of the gusset plate, and an extension bead is further provided. , A bead extending in the longitudinal direction from the end face of the corner turning portion of the gusset plate is provided. Therefore, the tensile residual stress acting on the starting point Ry of the end face angular rotation welding route is reduced and asymptotic to a certain value of the tensile residual stress, and the occurrence of cracks is suppressed. In addition, even if a tensile residual stress is applied to the corner turning welding bead 32 and a crack occurs at the starting point Ry of the end face corner turning welding route, the starting point Ry of this end face corner turning welding route is the tip end face T (corner) of the gusset plate 20. The position is deeper than the end face of the turning portion), and the extension bead 35 formed of the LTT welding material is subjected to compressive residual stress in the square turning welding bead 32. Therefore, as shown in FIG. 16, cracks are formed. It travels not in the corner-turning weld bead 32 but in the direction shown by the broken line 40, that is, in the gusset plate 20. And, unlike the extension bead 35, the gusset plate 20 can sufficiently suppress the growth of the cracks, so that the occurrence of root cracks can be suppressed and the fatigue life can be further improved.

The fatigue life is further improved by providing a groove portion corresponding to a predetermined end face corner turning root depth on the corner turning portion end face of the gusset plate and constructing a corner turning welding bead and an extension bead. The finding that it can be done is the first finding obtained by the present inventors, etc., and the improvement of the fatigue life by applying this welding technology to new structures and existing structures is a highly reliable welded structure. And can make a great contribution to the reduction of repair and reinforcement costs in the future.

Then, as described above, in the case of the lateral posture, the vertical posture, or the upward posture, welding can be easily performed by intermittent welding, and in that case, even if relatively large unevenness occurs on the surface, cracks can be formed. It does not significantly affect development, progression, and fatigue life. The same can be said for the downward posture.

According to the present invention, it is possible to provide a welding technique capable of ensuring a stable and long fatigue life when forming an extension bead using an LTT welding material on the tip end side of a corner-turning welded portion.

It is a perspective view which shows the appearance of the tip part and the peripheral part of the gusset plate of the welded structure which concerns on one Embodiment of this invention. It is sectional drawing in A cross section of FIG. It is sectional drawing in the B cross section of FIG. It is a top view of FIG. 1, and is the figure which shows the end face angle rotation root depth. It is a figure which shows the fatigue load direction of a welded structure. It is a figure which shows the relationship between the tensile residual stress and the end face angle rotation root depth. It is a figure which shows the resistance to fatigue weighting. It is a figure which shows the method of the groove of the gusset plate. It is a figure explaining the procedure of reinforcement of an existing welded structure. It is sectional drawing which shows the outline of the existing welded structure which repaired a fatigue crack. It is a figure which shows the relationship between the Ms point temperature of a weld metal, and the apparent transformation expansion amount. It is a figure which shows the welding method of the extension bead of the lateral posture. It is a figure which shows the welding method of the extension bead in an upright posture. It is a figure which shows the welding method of the extension bead of the upward posture. It is sectional drawing which shows the growth path of the root crack of the conventional welded structure. It is sectional drawing explaining the structure of the welded structure which concerns on another Embodiment of this invention, and the growth path of a fatigue crack. It is a plan view (a) and a side surface schematic (b) of the standard test product used for the fatigue characteristic evaluation test. It is a figure (a) explaining the procedure of reinforcement of an existing welded structure, and the figure (b) explaining the procedure of repair. It is a figure (a) which shows the welding bead forming method by 3 times repeated intermittent welding, and the figure (b) which shows the transition of the temperature of a welding bead. It is a figure which shows the transition of the temperature of the welding bead at the time of forming the extended bead of the lateral posture. It is a figure (a) which shows the welding method of continuous welding of an extension bead by the weaving method, and the figure (b) which shows the transition of the temperature of an extension bead. It is a figure which shows the relationship between the amplitude stress and the number of fatigue repetitions of a welded structure assuming repair / reinforcement. It is a perspective view of the corner welded part of the conventional general welded joint. It is a top view which shows the welded joint provided with the extension bead.

Hereinafter, the present invention will be described based on the embodiments. The present invention is not limited to the following embodiments. Within the same and equal scope as the present invention, various modifications can be made to the following embodiments.

1. 1. Construction procedure during reinforcement / repair First, the construction procedure during reinforcement / repair will be explained. Here, the construction procedure for reinforcing and repairing the existing angle turning joint of the vessel in service will be described as an example.

(1) Preparation of test piece FIG. 17 is a diagram for explaining a procedure for manufacturing a test piece assuming an existing angle turning joint of a vessel in service, (a) is a schematic plan view, and (b) is a schematic side view. .. In FIG. 17, gusset plates 20 are arranged on both sides of the main plate 10.

When preparing the test piece, a hull yield point of 36 kgf / mm ^{class 2} (KA36) high-strength steel plate was used for the main plate 10 (length 800 mm, width 100 mm, thickness 20 mm) and the gusset plate 20 (length 150 mm, height 50 mm). , Thickness 16 mm). Then, as the welding material, a general flux-cored wire for 550 MPa class steel certified by a commercial ship class was used.

Then, the main plate 10 and the gusset plate 20 are fillet welded in the order of (1) to (4) shown in FIG. 17, and then squarely welded in the order of (5) to (8) to perform reinforcement construction test pieces. And said. Then, fatigue cracks were generated from the toe of the corner-turning welded portion of the same test piece toward the main plate 10 to obtain a test piece for repair work.

(2) Specific construction procedure Reinforcement / repair work for each test piece shall be performed according to the construction procedure shown in FIG. In FIG. 18, (a) is a reinforcement construction procedure, and (b) is a repair construction procedure.

(A) Securing route depth (common to reinforcement and repair)
First, the corner welded portion of the test piece in the initial state is deleted by using, for example, arc gouging. At this time, the end face of the corner turning portion of the gusset plate 20 is deleted to a depth at which the end face corner turning root depth is 5 mm or more to form a groove portion.

In addition, when rewelding the corner turning part, which is a post-process, the fillet part of the end of the gusset plate 20 is linearly turned in the direction along the end face so that the turning welding is not easy. It is preferable to remove it over the welded area. As a result, the fillet root depth can be secured, so that the fatigue resistance can be further improved.

(B) Removal of fatigue cracks and repair welding (repair only)
Next, the fatigue cracks generated in the main plate 10 are completely removed by using, for example, arc gouging, and then the fatigue cracks are repaired by welding the welding material to the deleted marks.

(C) Rewelding of the corner turning part (common for reinforcement and repair)
Next, the corner turning portion is rewelded by welding including the groove portion using a normal welding material conventionally used for corner turning welding.

(D) Construction of extension beads (common to reinforcement and repair)
Finally, an extension bead of a predetermined length is overlay welded using the LTT material so as to cover the rewelded square weld bead.

Specific examples of the LTT material include welding materials such as 10Cr-10Ni and 16Cr-8Ni. Specific examples include C 0.1 wt% or less, Cr 13 to 20 wt%, and Ni 6 to. Examples thereof include welding materials having a chemical composition based on 11 wt% and having a welding metal having a Ms point temperature of 100 ° C. or higher and 250 ° C. or lower at which transformational expansion can be sufficiently obtained.

2. Effect of extension bead welding Next, the procedure of extension bead welding, that is, the effect on the generation of compressive residual stress in intermittent welding and continuous welding will be described.

19A and 19B are views for explaining a construction procedure when intermittent welding is performed three times from the tip end face of a gusset plate, FIG. 19A is a diagram showing the progress of welding, and FIG. 19B is a temperature at the time of construction. It is a figure which shows the time change of. Incidentally, A, B, C are each a temperature measuring position, A _C1 is transformation start temperature, A _C3 of the austenite from martensite is transformation finish temperature to the austenitic structure from the martensitic structure.

Here, as shown in FIG. 19B, the extension bead is formed by repeating 3 passes with the welding pass forming step causing the temperature rise and the solidification period step causing the temperature falling as one pass. ing. Then, as shown in FIG. 19B, in the first pass, the temperature is cooled from the first peak temperature to near room temperature below the Ms point temperature during the solidification period. This cooling below the Ms point temperature means the start of transformation of the welding material into the martensitic structure.

Then, when this portion is heated (reheated) again in the welding pass forming step of the second pass, the temperature rises to the second peak temperature. At this time, the second peak temperature, if beyond the A _C3, completely transformed into austenite structure, then, is transformed again into martensite by cooling the solidification period, in FIG. 19 (b) As shown, if _{it is AC3} or less, the martensite structure remains in a part. As a result, the proportion of the austenite structure is reduced, which leads to a decrease in the amount of transformation expansion accompanying the transformation to the martensite structure when cooled to the Ms point temperature or lower. Then, the remaining martensite structure no longer undergoes transformational expansion and contracts in the same manner as a normal metal, so that tensile residual stress is generated. For these reasons, if the solidification period is lengthened, it will have a negative effect on the introduction of compressive residual stress into the elongation bead.

From the above results, it can be seen that in intermittent welding, it is necessary to appropriately set the solidification period so that the temperature falls below the Ms point temperature only once by the time of final cooling. Therefore, in the above-mentioned intermittent welding work, it is preferable to form a thermal cycle with the temperature transition as shown in FIG. 20 so that the temperature does not fall below the Ms point temperature until the final cooling. Note that FIG. 20 shows the temperature transition after the second peak of the first pass.

Specifically, as shown in FIG. 20, it is preferable that the minimum temperature of the primary thermal cycle during intermediate cooling is about 250 ° C., and the minimum temperature in the subsequent thermal cycle gradually increases to a little less than 300 ° C. .. The specific solidification period is preferably within 2 seconds, more preferably about 1 second, in consideration of the actual construction time.

In order to realize the above-mentioned construction time of about 1 second, the Ms point temperature of the extended bead is preferably 100 to 250 ° C, more preferably 100 to 200 ° C. As described above, these LTT materials have the maximum apparent transformation expansion amount between 100 and 250 ° C., and are therefore preferable for the introduction of compressive residual stress accompanying the formation of the elongation bead.

When the extension beads are continuously welded in the downward posture, even an LTT material having an Ms point temperature of 350 ° C. can be used without any problem.

FIG. 21 is a diagram illustrating a construction procedure when an extension bead is continuously welded three times using a weaving method in a general downward posture, and FIG. 21A is a diagram showing the progress of welding, FIG. 21B is a diagram showing the progress of welding. Is a diagram showing a temporal change in temperature during construction. A, B, C, _AC1 and _AC3 are the same as in FIG.

As shown in FIG. 21B, when the stretch beads are continuously welded, the thermal cycle continues in the high temperature region until the end of the third pass. However, unlike the intermittent weld shown in FIG. 19, there is no time to be significantly cooled below the A _C3. Then, at the time of final cooling after the final extension bead formation is completed, the first pass to the third pass fall below the Ms point and transform from austenite to the martensite structure at almost the same time, so that the Ms point temperature It can be seen that even if the LTT material at 350 ° C. is used, the generation of compressive residual stress and the mechanical properties are not affected.

3. 3. Construction procedure in each posture Next, the construction procedure that can be welded in each posture will be described with reference to specific experimental examples.

(1) Experimental example 1
This experimental example is an experimental example of the construction procedure in the lateral attitude welding.

Specifically, using a gusset plate having a thickness (end width of the gusset plate) of 16 mm and a main plate having a thickness of 20 mm, a welding current of 140 A is used in a sideways posture, and an extension bead having a width of 30 mm and a length of 45 mm is formed. , The welding work was intermittently performed according to the procedure shown in FIG. 12 described above (total welding work time: 60 seconds).

The thermal cycle at this time was the thermal cycle shown in FIG. It should be noted that 250 ° C. in this sideways posture is the lowest value among the intermittent welding procedures in various postures, and the extension bead is formed by intermittent welding work using an LTT material having an Ms point temperature of 100 to 250 ° C. It was confirmed that a large compressive residual stress can be generated by overlay welding preferably.

(2) Experimental example 2
This experimental example is an experimental example of the construction procedure in vertical posture welding.

Specifically, using the same gusset plate and main plate as in Experimental Example 1, the welding current is set to 140 A in each of the vertical improvement posture and the vertical downward posture, and an extension bead having a width of 30 mm and a length of 45 mm is formed. Welding was performed intermittently according to the procedure shown in FIG. 13 (total welding time: 60 seconds).

As a result, sufficient compressive residual stress was obtained in both the vertical improvement posture and the vertical downward posture.

(3) Experimental example 3
This experimental example is an experimental example of the construction procedure in upward attitude welding.

Specifically, using the same gusset plate and main plate as in Experimental Example 1, in an upward posture, the welding current is set to 140 A, and an extension bead having a width of 30 mm and a length of 45 mm is formed according to the procedure shown in FIG. Welding was performed intermittently (total welding time: 70 seconds).

As a result, the degree of interruption was higher than that in the other postures, but sufficient compressive residual stress was obtained.

(4) Experimental example 4
In this experimental example, the fatigue life of the reinforcing joint and the repair joint constructed in each of the above postures was confirmed.

Specifically, as shown in FIG. 22, a _{repeated fatigue load is applied to each test piece under the condition of amplitude stress σr = 150 N / mm 2} , and the number of repeated fatigues, which is the limit of the fatigue life, is obtained. rice field. For comparison, the same experiment was performed on a normal square turning joint without an extension bead and a conventional extension bead joint.

The results are shown in FIG. From FIG. 22, it can be seen that the fatigue life of the extended bead joint of the present invention shows a large significant difference of more than 4 times as compared with the fatigue life of a normal square turning joint in both repair and reinforcement. Further, it can be seen that the fatigue life is sufficiently longer than that of the conventional joint in which the extension bead is provided by performing the corner rotation welding without providing the groove portion.

As a result, in order to secure a stable fatigue life, it is possible to confirm a remarkable effect by increasing the depth of the root portion from 0 to 2 mm in the normal square turning joint to 5 mm or more by providing the groove portion. rice field.

In addition, since various posture welding other than downward welding requires intermittent welding, it is said that the connection part with the bead welded part formed by rotary welding has a smooth shape, or even on the surface of the extended bead. It is difficult, and a step may be generated depending on the intermittent location.

However, even in the welding work where the surface is intermittent and not smooth, sufficient compressive residual stress is generated in the elongated bead, and from the results shown in FIG. 22, fatigue cracks from the stepped portion on the surface of the elongated bead. It can be seen that there was no occurrence of.

10 Main plate 11 Deletion mark 20 Gusset plate 21 Groove 22 Weld penetration 31 Fillet welding bead 32 Square turning Welding bead 35 Extension bead 40 Broken beam showing the direction of crack growth Dx Side fillet root depth Dy End face corner turning root depth L Length of extension bead Rx Tip of penetration route from side surface Ry End face angle rotation Starting point of welding route S Side surface of gusset plate T Tip end face of gusset plate

Claims (17)

It is a welding method in which a gusset plate is welded to high-strength steel by square rotation welding.
A corner-turning welding process in which a corner-turning welding material is used to perform corner-turning welding on the end face of the corner-turning portion of the gusset plate so that the end face corner-turning root depth is 5 mm or more, and a corner-turning welding bead is provided. ,
Cover the square weld bead with a welding material having a martensitic transformation start point of the weld metal of 350 ° C. or less in the longitudinal direction of the gusset plate from the end face of the square weld of the gusset plate. A welding method comprising an extension bead welding step of welding to and providing an extension bead. This is a welding method in which a gusset plate is welded to high-strength steel by square welding when constructing a new structure.
The corner turning welding process
The first aspect of the present invention is the step of forming a groove portion having a depth of 5 mm or more on the end face in the longitudinal direction of the gusset plate by machining or gouging in advance, and performing angular rotation welding. Welding method. This is a welding method in which a gusset plate is welded to high-strength steel by square welding when reinforcing an existing structure.
The corner turning welding process
By machining or gouging, the corner turning weld bead applied to the end face of the corner turning portion of the gusset plate is removed, and a groove portion having a depth of 5 mm or more is formed on the end face of the corner turning portion of the gusset plate after removal. death,
The welding method according to claim 1, wherein the step is a step of providing a square rotation welding bead by performing a new corner rotation welding on the groove portion using a normal corner rotation welding material. This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding when repairing an existing structure in which fatigue cracks have occurred.
The corner turning welding process
After removing the fatigue cracks by machining or gouging and repairing the deletion marks so that the normal corner-turning welding material is blended into the deletion marks.
By machining or gouging, the corner turning weld bead applied to the end face of the corner turning portion of the gusset plate is removed, and a groove portion having a depth of 5 mm or more is formed on the end face of the corner turning portion of the gusset plate after removal. death,
The welding method according to claim 1, wherein the step is a step of providing a square rotation welding bead by performing a new corner rotation welding on the groove portion using a normal corner rotation welding material. The extension bead welding process
The extension bead is welded so as to cover the combined joint between the square weld bead provided on the end face of the gusset plate and the fillet weld bead installed on the side surface of the gusset plate by new square weld. The welding method according to claim 3 or 4, wherein the step is a step of providing. The corner turning welding process
The combined joint between the square weld bead provided on the end face of the gusset plate by the new square weld and the fillet weld bead installed on the side surface of the gusset plate forms a smooth joint surface. The welding method according to claim 5, wherein the process is a step of welding. The extension bead welding process
The method according to any one of claims 1 to 6, wherein an extension bead having a length of 17 mm or more is provided in the longitudinal direction of the gusset plate from the end face of the corner turning portion of the gusset plate. Welding method. Any of claims 1 to 7, wherein in the extension bead welding step, a material that becomes a welding metal having a martensitic transformation start point of 100 to 300 ° C. is used as the welding material for forming the extension bead. The welding method according to item 1. This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, the melting path is formed in a certain direction or folded back.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. 8. The welding method according to any one of 8. This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in a sideways posture when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, a horizontal melting path is formed in a certain direction.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. The welding method according to any one of 9. This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in an upright position when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
It includes a melt path forming step of forming a melt path of the welding material and a solidification period step of solidifying the melt path.
In the melting path forming step, a horizontal melting path is formed in a certain direction or folded back.
Claims 1 to claim 1, wherein a plurality of melt passes are performed over the stretched bead forming region while alternately repeating the melt pass forming step and the solidification period step a plurality of times. The welding method according to any one of 9. This is a welding method in which a gusset plate is welded to high-strength steel by angular rotation welding in an upward posture when reinforcing an existing structure or repairing an existing structure in which fatigue cracks have occurred.
The extension bead welding process
By dividing into a plurality of rows in the longitudinal direction and further dividing each row into one or a plurality of path forming regions, an extension bead forming region is formed, and welding is performed in the extending bead forming region. It includes a melt path forming step of forming a melt path of a material and a solidification period step of solidifying the melt path.
In the melting path forming step, the melting path is formed in a certain direction or folded back.
The first to ninth aspects of the present invention, wherein the extension bead is provided over the entire formation region of the extension bead while alternately repeating the melting path forming step and the solidification period step a plurality of times. The welding method according to any one item. A welded structure in which a gusset plate is welded to high-strength steel by square welding.
On the end face of the corner turning portion of the gusset plate, a corner turning welding bead is formed so that the end face corner turning root depth is 5 mm or more.
An extension bead is provided from the end face of the corner turning portion of the gusset plate in the longitudinal direction of the gusset plate so as to cover the corner turning welding bead using a welding material having a martensitic transformation start point of the weld metal of 350 ° C. or less. A welded structure characterized by being welded. The welded structure is a new structure and
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion. The welded structure is an existing structure that has been reinforced.
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion. The welded structure is an existing structure in which fatigue cracks have been repaired.
The welded structure according to claim 13, wherein a groove portion is formed on the end face in the longitudinal direction of the gusset plate, and the corner-turning weld bead is formed on the groove portion. 13. The welded structure described.

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