JPWO2016143354A1 - Welded structure - Google Patents

Abstract

A fillet welded joint in which the end face of the joining member (1) is abutted against the surface of the joined member (2) having a plate thickness of 50 mm or more, and joins the joining member (1) and the joined member (2) The weld leg length (3) and the welding width (13) of the fillet welded joint exceed 16 mm, and the end surface of the joining member (1) and the joined member (2 in the fillet welded joint) ) And the surface of the fillet welded joint, the cross section of the fillet welded joint has an unwelded portion (4) of 95% or more of the thickness (tw) of the joining member (1). For the fillet weld metal (5), the Charpy impact test fracture surface transition temperature (vTrs (° C.)) of the fillet weld metal (5) and the plate thickness (tf) of the joined member (2), or further welding Between the leg length (3) and the smaller value (L) of the welding width (13), a predetermined relationship is established. To foot.

Description

  The present invention relates to a welded steel structure (welded structure) welded using a thick steel plate, such as a large container ship or a bulk carrier. In particular, the present invention is a welded structure excellent in brittle crack propagation stopping characteristics that can stop the propagation of brittle cracks generated from the base metal or welded joint of a thick steel plate before reaching the large-scale fracture of the structure. About.

  A container ship or a bulk carrier has a structure having a large opening at the upper part of the ship, for example, unlike a tanker or the like, in order to improve the loading capacity and the handling efficiency. Therefore, in container ships and bulk carriers, it is necessary to increase the strength or thickness of the hull skin, in particular.

In recent years, container ships have increased in size, and large ships of 6,000 to 20,000 TEU have been built. TEU (Twenty feet Equivalent Unit) represents the number of containers converted into a 20-foot container and indicates the load capacity of container ships. As the size of the ship increases, thick steel plates with a thickness of 50 mm or more and a yield strength of 390 N / mm grade ² or more are used for the hull outer plates.

  In recent years, a steel plate to be a hull outer plate is often butt-welded by high heat input welding such as electrogas arc welding from the viewpoint of shortening the construction period. Such large heat input welding tends to lead to a significant decrease in toughness at the weld heat affected zone, and has been one cause of the occurrence of brittle cracks at the weld joint.

  On the other hand, in the hull structure, from the viewpoint of safety, it is necessary to prevent the hull separation by stopping the propagation of brittle cracks before reaching a large-scale fracture even if a brittle fracture occurs. It is thought that there is.

  In view of this concept, Non-Patent Document 1 reports the results of an experimental study on the brittle crack propagation behavior of welds in steel plates for shipbuilding with a thickness of less than 50 mm.

  Non-Patent Document 1 experimentally investigates the propagation path and propagation behavior of brittle cracks that are forcibly generated in the weld zone. Here, there is a description that, if the fracture toughness of the weld is secured to some extent, brittle cracks often deviate from the weld to the base metal due to the effect of residual welding stress. A plurality of examples in which a brittle crack propagated along the line have been confirmed. This suggests that it cannot be said that there is no possibility that brittle fracture propagates straight along the weld.

  However, in addition to the fact that ships constructed by applying welding equivalent to the welding applied in Non-Patent Document 1 to steel sheets with a thickness of less than 50 mm have been put into service without any problems, toughness is good. Recognizing that the steel base material (shipbuilding class E steel, etc.) has sufficient ability to stop brittle cracks, the brittle crack propagation stoppage characteristics of welded steel for shipbuilding steel are especially It was not requested.

By the way, in recent large container ships exceeding 6,000 TEU, the plate thickness of the steel plate to be used exceeds 50 mm, and in addition to the decrease in fracture toughness due to the increase in plate thickness, large heat input welding with a larger welding heat input is adopted. The fracture toughness of the part tends to further decrease. In such thick-walled high heat input welded joints, it is shown that brittle cracks generated from the welded part may go straight without warping to the base metal side, and may not stop even in the steel plate base part such as aggregate. (For example, Non-Patent Document 2).
For this reason, securing the safety of the hull structure to which a thick high-strength steel plate having a thickness of 50 mm or more is applied is a big problem. In addition, Non-Patent Document 2 also points out that a thick steel plate having special brittle crack propagation stop characteristics is required in order to stop the propagation of the generated brittle cracks.

For such a problem, for example, in Patent Document 1, in a welded structure that is preferably a hull outer plate having a thickness of 50 mm or more, an aggregate is arranged so as to intersect the butt weld, and fillet welding is performed. A joined welded structure is described.
In the technique described in Patent Document 1, the aggregate has an average equivalent circular particle diameter of 0.5 to 5 μm over a thickness of 3 mm or more in the surface layer portion and the back layer portion, and is a surface parallel to the plate thickness surface (100). A steel sheet having a microstructure with an X-ray plane intensity ratio of crystal planes of 1.5 or more is used. And by adopting a structure in which the steel plate having such a microstructure is fillet welded as a reinforcing material, even if a brittle crack occurs in the butt weld joint, brittle fracture can be stopped by the aggregate as the reinforcing material, and welding It is said that it can prevent fatal damage that destroys the structure.
However, the aggregate that is a reinforcing material used in the technique described in Patent Document 1 requires a complicated process to form a steel sheet in which a desired structure is formed, and as a result, productivity is reduced, There was a problem that it was difficult to secure a steel plate having a desired structure stably.

Patent Document 2 includes a fillet welded joint obtained by fillet welding a joining member (hereinafter also referred to as a web) to a member to be joined (hereinafter also referred to as a flange), and has excellent brittle crack propagation stop characteristics. A welded structure is described.
In the welded structure described in Patent Document 2, an unwelded portion is left on the butt surface of the web in the fillet welded joint cross section with the flange, the width of the unwelded portion, and the left and right leg lengths of the fillet welded portion. The width of the unwelded portion is adjusted so that the ratio X of the web thickness and the web thickness X satisfies the special relational expression with the brittle crack propagation stopping performance Kca of the member to be joined (flange). As a result, even if the member to be joined (flange) is made of a thick material with a plate thickness of 50 mm or more, the propagation of brittle cracks occurring in the joining member (web) is stopped at the butt surface of the fillet weld at the web and flange. The propagation of brittle cracks to the member to be joined (flange) can be prevented.
However, in the technique described in Patent Document 2, since the brittle crack propagation stop property of the joining member (web) is insufficient, the brittle crack generated in the joined member (flange) is propagated by the joining member (web). It cannot be said that it is sufficient technology to stop. In Patent Document 2, no consideration is given to the brittle crack propagation stop characteristic of the joining member (web).

For such a problem, for example, in Patent Document 3,
`` At least one of the weld leg length or welding width formed by abutting the end face of the joining member against the surface of the joined member having a plate thickness of 50 mm or more and joining the joined member and the joined member by fillet welding is 16 mm or less A welded structure having a fillet welded joint, and a thickness of the joint member in a cross section of the fillet welded joint on a surface where the end face of the joined member and the surface of the joined member in the fillet welded joint face each other It has an unwelded portion of 95% or more of tw, and the Charpy impact test fracture surface transition temperature vTrs of the fillet weld metal in the fillet welded joint is related to the plate thickness tf of the joined member, vTrs ≦ −1.5 tf + 70 and / or Charpy impact test temperature of fillet weld metal: the absorbed energy vE ₋₂₀ (J) at −20 ° C. is related to the plate thickness tf of the joined member, vE ₋₂₀ ≧ 2.75 Welded structure having fillet weld metal satisfying tf-105 "
Is described.
With such a welded structure, it is said that a brittle crack generated in a member to be joined can be prevented from propagating with fillet weld metal.

Patent Document 4 discloses that
`` At least one of the weld leg length or welding width formed by abutting the end face of the joining member against the surface of the joined member having a plate thickness of 50 mm or more and joining the joined member and the joined member by fillet welding is 16 mm or less A welded structure having a fillet welded joint, and a thickness of the joint member in a cross section of the fillet welded joint on a surface where the end face of the joined member and the surface of the joined member in the fillet welded joint face each other It has an unwelded portion of 95% or more of tw, and the Charpy impact test fracture surface transition temperature vTrs of the fillet weld metal in the fillet welded joint is related to the plate thickness tf of the joined member, vTrs ≦ −1.5 tf + 90 and / or the Charpy impact test temperature of fillet weld metal: the absorbed energy vE ₋₂₀ (J) at −20 ° C. is 50 ≦ tf ≦ 53 in relation to the plate thickness tf of the members to be joined. In the case of vE ₋₂₀ ≧ 5.75, in the case of tf> 53, vE ₋₂ Welded structure comprising fillet weld metal satisfying ₀ ≧ 2.75tf-140, and additionally joining member made of steel plate with brittle crack propagation stop toughness Kca of 2500 N / mm ^2/3 or more at service temperature body"
Is described.
By setting it as such a welded structure, the brittle crack which generate | occur | produced in the to-be-joined member can stop at the fillet weld part or the base material of a joining member.

Patent Document 5 discloses that
`` At least one of the weld leg length or welding width formed by abutting the end face of the joining member against the surface of the joined member having a plate thickness of 50 mm or more and joining the joined member and the joined member by fillet welding is 16 mm or less A welded structure including a fillet welded joint, wherein both the joining member and the joined member have a butt weld joint, and the weld metal of the butt weld joint is −65 ° C. or less in vTrs, and / or , Having a toughness of 140J or more at vE- ₂₀ , butting the butted end face of the butt welded joint of the fillet welded joint to the welded part surface of the butt welded joint of the joined member Surface has an unwelded portion of 95% or more of the plate thickness tw of the joining member in the cross section of the butt weld joint of the fillet welded joint, and also the Charpy impact test fracture surface transition temperature of the fillet welded metal in the fillet welded joint vTrs is the plate of the member to be joined in relation to tf, the vTrs ≦ -1.5tf + 90, and / or a test temperature of Charpy impact test of the fillet weld metal: absorbed energy vE _-20 at -20 ° C. (J) is the plate thickness of the workpieces tf In the case of 50 ≦ tf ≦ 53, a welded structure having a fillet weld metal satisfying vE ₋₂₀ ≧ 5.75 and tf> 53 satisfying vE ₋₂₀ ≧ 2.75tf−140. body"
Is described.
By setting it as such a welded structure, the brittle crack which generate | occur | produced in the to-be-joined member can stop at the fillet weld part or the base material of a joining member. Further, by adopting such a welded structure, brittle cracks generated from the welded part of the joined member or brittle cracks generated from the welded part of the joined member can be used as a fillet welded part, a welded part of the joined member, or a joined member. It is said that propagation can be prevented at the welded part.

JP 2004-232052 A JP 2007-326147 A Japanese Patent No.5395985 Japanese Patent No.53657661 Japanese Patent No. 5408396

Japan Shipbuilding Research Association No. 147 Research Group: "Study on Brittle Fracture Strength Evaluation of High-Temperature Heat-Insulated Joints for Ships," No. 87 (February 1978), p.35-53, Japan Shipbuilding Research Association Yuya Yamaguchi et al .: "Development of ultra-large container ship-Practical use of new high-strength heavy-duty steel plate", Journal of Japan Society of Marine Science and Technology, No. 3 (2005), p.70-76, November 2005

However, in each technique described in Patent Documents 3 to 5, it is necessary to limit the weld leg length (or weld width) to 16 mm or less. Therefore, from the viewpoint of securing the strength of the fillet welded portion, the joining member (web) The plate thickness applicable to the member to be joined (flange) was 80 mm at the maximum.
In addition, even when the plate thickness of the joining member (web) and the joined member (flange) is less than 80 mm, it is desirable to ensure the strength of the fillet weld in consideration of the variation in the weld leg length in the work. Ensuring both the weld leg length and the restricting the weld leg length to 16 mm or less in order to ensure brittle crack prevention performance requires a great deal of work management. Further, there are cases where additional costs such as reworking are required, and problems remain in these respects.

In addition, recently, large container ships have become increasingly thicker, and steel materials with a thickness of 100 mm or more are being used.
However, as described above, in each technique described in Patent Documents 3 to 5, the plate thickness applicable to the joining member (web) and the joined member (flange) is 80 mm at the maximum, and the member thickness exceeding 80 mm is used. It cannot be applied to the welded structure that has it.

The present invention solves such a problem of the prior art, and even if the weld leg length and the welding width exceed 16 mm, the propagation of brittle cracks generated in the joined member (flange) to the joined member (web) is destroyed on a large scale. It aims at providing the welded structure excellent in the brittle crack propagation stop property which can stop (prevent) before reaching.
In addition, the welded structure which this invention makes object the welding provided with the fillet weld joint formed by abutting the end surface of a joining member (web) with the surface of a to-be-joined member (flange), and joining these by fillet welding. It is a structure.

In order to achieve the above-mentioned object, the present inventors diligently studied various factors affecting the brittle crack propagation stop characteristics of a welded structure having a fillet welded joint having a weld leg length (and a welding width) exceeding 16 mm.
As a result, in order to prevent (stop) the propagation of brittle cracks generated from the joined member (flange) when the weld leg length exceeds 16 mm, the joined member (flange) and joined member (web) are butted together. It has been thought that it is not sufficient that a discontinuous portion is secured on the surface and the brittle crack propagation portion is made of a member having a brittle crack propagation stopping characteristic Kca having a predetermined value or more, and having an excellent brittle crack propagation stopping property.

In particular, when the plate thickness tf (mm) of the member to be joined (flange) increases, the energy release rate (crack growth driving force) at the tip of the brittle crack increases and the brittle crack is difficult to stop. It has been conceived that it is essential to improve the toughness of fillet welds, particularly fillet weld metals, according to the plate thickness tf (mm) of (flange).
In addition, if the weld leg length and weld width of fillet welded joints are further increased to 20 mm or more, the propagation of brittle cracks becomes easier, so the toughness of fillet weld metal can be improved in accordance with the weld leg length and weld width. I found it necessary.

  Further, in the fillet welded joint, an unwelded portion, that is, a discontinuous portion is secured on the surface where the surface of the member to be joined, the joining member, and the end face are abutted, and further, the toughness of the fillet weld metal is reduced by the length of the weld leg ( mm), welding width (mm), and plate thickness tf (mm) of the member to be welded, properly controlled for the first time, with a thickness exceeding 80 mm that was difficult with conventional technology It has been found that propagation of brittle cracks generated in the member to the joining member can be prevented (stopped) by fillet weld metal.

  That is, the setting of the unwelded part as described above and the toughness of the fillet weld metal are appropriate in relation to the weld leg length (mm), the weld width (mm), and the plate thickness tf (mm) of the joined members. By controlling the thickness of the steel plate used for the joining member (web), the brittle crack generated in the joined member (flange) can be applied to the joining member (web) without specially considering the brittle crack propagation stop characteristic. It has been found that propagation can be prevented.

  Furthermore, even when the member to be joined is a butt welded joint instead of the base material, or when the joint member is a butt welded joint, the above-described configuration similarly results in a joint member having a brittle crack generated in the member to be joined. It has been found that the propagation of metal can be prevented by fillet weld metal.

  First, the experimental results that led to the present invention will be described.

Yield strength 355 to 390 N / mm grade ² steel plates having various thicknesses, various unwelded portion ratios Y (%) (= (width B of unwelded portions in fillet welded joint cross section) / (joining member) Large fillet welded joints having unwelded portions with a thickness of tw) × 100), various low temperature toughnesses and weld leg lengths were produced. The weld leg length and weld width were both adjusted to exceed 16 mm.

  In addition, a steel plate having a butt weld joint part thickness of 50 mm or more was used as a member to be joined (flange). Further, as the joining member (web), ordinary shipbuilding class D to E steels that did not consider brittle crack propagation stopping toughness Kca were used.

The butt weld joint was produced by one-pass high heat input electrogas arc welding (SEGARC or two-electrode SEGARC) or multi-layer carbon dioxide arc welding (multi-layer CO ₂ ).

Using the obtained large fillet welded joint, an ultra-large structural model test body shown in FIG. 4B was prepared, and a brittle crack propagation stop test was performed. In addition, the ultra-large-sized structural model test body welded the steel plate of the same board thickness as the flange 2 by the tack welding 8 under the to-be-joined member (flange) 2 of the large-scale fillet welded joint 9.
4B, the butt weld joint 11 of the member to be joined (flange) 2 is produced so as to be orthogonal to the joint member (web) 1, and the tip of the mechanical notch 7 is produced. Was processed to become the BOND portion of the butt weld joint portion 11.

In the brittle crack propagation stop test, a mechanical notch was hit to generate a brittle crack, and it was investigated whether the propagated brittle crack stopped at the fillet weld. All tests were performed under the conditions of a stress of 243 to 257 N / mm ² and a temperature of −10 ° C. The stress: 243 to 257 N / mm ² is a value corresponding to the maximum allowable stress of the yield strength 355 to 390 N / mm grade ² steel plate applied to the hull. Moreover, temperature: -10 degreeC is the design temperature of a ship.

  The obtained results are shown in FIGS.

  FIG. 5 shows the Charpy impact test fracture surface transition temperature of fillet weld metal when the unwelded portion ratio Y is 95% or more and L, which is the smaller value of the weld leg length and weld width, is 17 mm. The influence of the relationship between vTrs (° C.) and the plate thickness tf of the member to be joined on the propagation stop of brittle cracks in the ultra-large structural model specimen is shown. FIG. 6 shows the Charpy impact test fracture surface transition temperature vTrs (° C.) of fillet weld metal when the unwelded portion ratio Y is 95% or more and the plate thickness tf of the joined member (flange) is 75 mm. ) And L, which is the smaller value of the weld leg length and the welding width, shows the influence of brittle crack propagation stoppage in the ultra-large structural model specimen.

From the experimental results shown in FIGS. 5 and 6, the unwelded portion ratio Y is 95% or more, and the toughness of the fillet weld, that is, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, When the thickness tf of the joining member (flange) and L, which is the smaller value of the weld leg length and welding width, satisfy a specific relationship, the load stress is 243 to 257 N / mm ² However, without giving any consideration to the Kca of the joining member (web), brittle cracks occurring in the joined member (flange) can be stopped at the fillet weld metal part, and the propagation of the brittle cracks to the joining member (web) can be prevented. It can be seen that it can be stopped (stopped).
The unwelded portion ratio Y is a ratio defined by (B / tw) × 100 (%), the ratio of the width B of the unwelded portion to the thickness (tw) of the joining member (web) in the fillet welded joint cross section. .

From the above experimental results, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, the plate thickness tf of the member to be joined (flange), the welding leg length, and the welding width is the smaller value. Regarding L, the following relationship was obtained.
When L <20, vTrs ≦ −35−1.5 (tf−75) (1a)
When L ≧ 20, vTrs ≦ −5L + 65−1.5 (tf−75) (1b)
(Where, vTrs: Charpy impact test fracture surface transition temperature of fillet weld metal (° C.), tf: plate thickness of welded member (mm), L: smaller value of weld leg length and weld width (mm ))

The present invention has been completed on the basis of such findings and further studies. That is, the gist of the present invention is as follows.
(1) A welded structure provided with a fillet weld joint in which an end face of a joining member is abutted against a surface of a joined member having a plate thickness of 50 mm or more, and joins the joining member and the joined member,
The weld leg length and weld width of the fillet weld joint is over 16 mm,
An unwelded portion having a thickness of 95% or more of the thickness tw of the joining member in the cross-section of the fillet welded joint is formed on the surface of the fillet welded joint that is abutted between the end face of the joining member and the surface of the joined member Have
Furthermore, for the fillet weld metal of the fillet weld joint,
When the smaller value of the weld leg length and the welding width is L, when L is less than 20 mm, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, The thickness tf of the member to be joined satisfies the relationship of the following formula (1a),
When L is 20 mm or more, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, the plate thickness tf of the member to be joined, and L satisfy the following relationship (1b): Satisfied, welded structure.
Record
vTrs ≤ -35-1.5 (tf-75) (1a)
vTrs ≤ -5L + 65-1.5 (tf-75) (1b)
Where vTrs: Charpy impact test fracture surface transition temperature (° C) of fillet weld metal,
tf: thickness of the member to be joined (mm),
L: The smaller value of the weld leg length and weld width (mm)
(2) The welded structure according to (1), wherein the member to be joined has a butt weld joint so as to intersect with the joining member.
(3) The joining member has a butt weld joint portion, and the joining member is disposed so that the butt weld joint portion of the joint member and the butt weld joint portion of the joined member intersect. The welded structure according to (2).

  According to the present invention, a joining member of a brittle crack generated in a member to be joined (flange) having a thickness of 50 mm or more, particularly 60 mm or more, and further a thick steel plate having a thickness of more than 80 mm, which has been difficult in the past (flange) Propagation to the web) can be stopped (blocked) before large-scale destruction. For this reason, according to the present invention, it is possible to avoid the risk of large-scale brittle fracture such as hull separation of steel structures, particularly large container ships and bulk carriers, which is great in ensuring the safety of the hull structure. It brings about an effect and has a remarkable effect in the industry.

  Also, by adjusting the dimensions of the unwelded part and the toughness of the fillet weld metal during construction, it is easy to excel in brittle crack propagation stopping characteristics without using special steel plates and without sacrificing safety. There is an effect that a welded structure can be manufactured.

It is explanatory drawing which illustrates typically an example of the cross-sectional structure of a fillet welded joint. (A) shows a case where the joining member (web) 1 and the joined member (flange) 2 are orthogonal to each other, and (b) shows that the joining member (web) 1 and the joined member (flange) 2 cross each other diagonally. In this case, when (c) is a gap 14 between the joining member (web) 1 and the joined member (flange) 2, (d) is between the joining member (web) 1 and the joined member (flange) 2. This shows a case where there is a gap 14 between them and a spacer 15 is inserted in the gap 14. It is explanatory drawing which shows typically another example of a structure of a fillet welded joint. (A) is an external view, (b) is sectional drawing. It is explanatory drawing which shows typically another example of a structure of a fillet welded joint. (A) is an external view, (b) is sectional drawing. It is explanatory drawing which shows typically the shape of a super-large-sized structural model test body. (A) is a case where the joining member (web) 1 and the joined member (flange) 2 are made only of a steel plate base material, and (b) is a joining member (web) 1 made only of the steel plate base material, ) 2 has the butt weld joint 11, (c) is the case where the joining member (web) 1 has the butt weld joint 12 and the member to be joined (flange) 2 has the butt weld joint 11. . It is a figure which shows the influence which the relationship between the toughness of a fillet weld metal and a flange board thickness has on the propagation stop of a brittle crack. It is a figure which shows the influence which the toughness of a fillet weld metal and the relationship with L which is the smaller value of the welding leg length and the welding width has on the propagation stop of a brittle crack.

  In the welded structure of the present invention, the end face of the joining member (web) 1 is abutted against the surface of the joined member (flange) 2 having a thickness of 50 mm or more, and the joining member (web) 1 and the joined member (flange) ) 2 is a welded structure including a fillet welded joint that joins 2. The fillet welded joint has fillet weld metal 5, and the weld leg length 3 and the weld width 13 exceed 16 mm. Furthermore, the unwelded part 4 which becomes a structural discontinuity part exists in the butt | matching surface of the joining member (web) 1 and to-be-joined member (flange) 2 of a fillet welded joint.

  This state is shown in FIG. FIG. 1A shows a case where the joining member (web) 1 is attached upright with respect to the joined member (flange) 2, but the present invention is not limited to this. For example, as shown in FIG. 1B, the joining member (web) 1 may be attached to the joined member (flange) 2 at an angle θ. In this case, the joining member (web) plate thickness tw used when determining the ratio Y (%) of the unwelded portion is the length of the intersection between the joining member (web) and the member to be joined (flange), (tw ) / Cos (90 ° -θ). Moreover, as shown in FIG.1 (c), you may provide the clearance gap 14 between the joining member (web) 1 and the to-be-joined member (flange) 2. FIG. Further, as shown in FIG. 1 (d), a gap 14 may be provided between the joining member (web) 1 and the joined member (flange) 2, and a spacer 15 may be inserted into the gap 14.

  In addition, when providing the clearance gap 14 between the joining member (web) 1 and the to-be-joined member (flange) 2 like FIG.1 (c) and FIG.1 (d), the welding width 13 is the joining member ( Web) It is sufficient that one side satisfies a predetermined condition. In the case of FIG. 1D, the fillet weld metal 5 may be dissolved in the spacer 15.

  As described above, the welded structure of the present invention has a discontinuous structure at the abutting surface between the joining member (web) 1 and the joined member (flange) 2 in the fillet welded joint. Have In the fillet welded joint, the butt surface between the joining member (web) 1 and the member to be joined (flange) 2 becomes a propagation surface of a brittle crack, and therefore, the unwelded portion 4 is present on the butt surface. Due to the presence of the unwelded portion 4, the energy release rate (crack propagation driving force) at the tip of the brittle crack that has propagated through the member to be joined (flange) 2 is reduced, and the brittle crack tends to stop at the butt surface. Even if a brittle crack propagates from the member to be joined (flange) 2 to the fillet weld metal 5, the fillet weld metal 5 has a thickness tf, weld leg length, and weld width of the member to be joined (flange). The brittle crack does not propagate to the joining member (web) 1 and stops at the fillet weld metal 5 because it has appropriate toughness.

In addition, it is very rare that a brittle crack occurs in a steel plate base material part with few defects. Many past brittle fracture accidents have occurred in welds. Therefore, for example, in a fillet welded joint as shown in FIGS. 2A and 2B and FIGS. 3A and 3B, a joining member (web) 1 of a brittle crack generated from the butt weld joint portion 11 is used. In order to prevent the propagation to the first, it is important that the discontinuity of the structure first exists, that is, the unwelded portion 4 exists on the abutting surface between the member to be joined and the joining member in the fillet welded joint.
Here, FIG. 2A shows a steel plate in which the member to be joined (flange) 2 is joined by a butt weld joint 11, and the joining member (web) 1 is a welded portion (butt weld joint portion) 11 of the butt weld joint. It is an external view of the fillet welded joint which fillet welded so that it may cross | intersect, (b) is sectional drawing.
3 (a), the joining member (web) 1 is a steel plate having a butt weld joint portion 12, the joined member (flange) 2 is a steel plate having a butt weld joint portion 11, and the joined member ( FIG. 2 is an external view of a fillet welded joint that has been fillet welded so that a butt welded joint portion 11 of the flange) 2 and a butt welded joint portion 12 of the joining member (web) 1 intersect each other, and (b) is a cross-sectional view. .

  2A, 2B, 3A, and 3B show the case where the butt weld joint 11 and the web 1 are orthogonal to each other, but the present invention is not limited to this. Needless to say, they may be crossed diagonally. Moreover, the manufacturing method of a fillet welded joint is not particularly limited, and any conventional manufacturing method can be applied. For example, the flange steel plates and the web steel plates may be butt welded, and the resulting butt weld joint may be fillet welded to produce a fillet weld joint. In addition, a pair of web steel plates before butt welding are tack welded to the flange, then the web steel plates are butt welded together, and the resulting butt weld joint is main welded (fillet weld) to the flange to fillet weld A joint may be manufactured.

  In the welded structure of the present invention, the dimension 16 of the unwelded portion 4 (width B of the unwelded portion) in the fillet weld joint cross section is 95% or more of the web plate thickness tw in order to suppress the propagation of brittle cracks. When the dimension of the unwelded portion 4 (width B of the unwelded portion) is less than 95% of the joining member (web) plate thickness tw, the plastic deformation in the fillet weld metal is suppressed, and the brittle crack that has entered the fillet weld metal The vicinity of the crack tip becomes high stress, and the brittle crack that has entered the joining member (web) 1 side cannot be stopped (blocked). For this reason, the dimension 16 of the unwelded portion 4 (width B of the unwelded portion) is 95% or more of the joining member (web) plate thickness tw in order to suppress the propagation of brittle cracks. In addition, Preferably they are 96% or more and 100% or less.

  Also, the weld leg length and weld width of fillet welded joints exceed 16mm. If the weld leg length and weld width of the fillet welded joint is 16 mm or less, it is advantageous to ensure the ability to prevent the propagation of brittle cracks, but if the thickness of the member exceeds 80 mm, the strength of the fillet weld will be ensured. It becomes difficult. Moreover, even when the member plate thickness is 80 mm or less, the risk of reworking in the execution work becomes high. For this reason, the weld leg length and weld width of fillet welded joints exceed 16 mm. The upper limit of the weld leg length and the weld width is not particularly limited, but is usually up to 40 mm from the viewpoint of securing the construction efficiency and the arrest performance.

In the welded structure of the present invention, when the smaller value of the weld leg length and the weld width is L for the fillet weld metal in the fillet weld joint, if L is less than 20 mm, When the Charpy impact test fracture surface transition temperature vTrs (° C) of the metal weld metal and the plate thickness tf of the joined member satisfy the relationship of the following formula (1a), and L is 20 mm or more, fillet welding It is important that the metal Charpy impact test fracture surface transition temperature vTrs (° C.), the plate thickness tf of the member to be joined, and L satisfy the relationship of the following equation (1b).
Record
vTrs ≤ -35-1.5 (tf-75) (1a)
vTrs ≤ -5L + 65-1.5 (tf-75) (1b)
Where vTrs: Charpy impact test fracture surface transition temperature (° C) of fillet weld metal,
tf: thickness of the member to be joined (mm),
L: The smaller value of the weld leg length and weld width (mm)

  The fillet weld metal is related to the plate thickness tf of the member (flange) 2 to be joined, and L, which is the smaller value of the weld leg length and the weld width, and the above-described equation (1a) or (1b) By having low temperature toughness satisfying the formula, as shown in FIGS. 5 and 6, a welded structure having a member thickness (flange) 2 of 50 mm or more is welded having a desired brittle crack propagation prevention performance. It can be a structure. Since the weld leg length and weld width exceed 16 mm, the welded member (flange) 2 can be applied not only to a thickness of 50 mm or more, but also to a welded structure having a thickness of 60 mm or more and more than 80 mm. The upper limits of the weld leg length and the weld width are not particularly limited, but are usually up to 40 mm. The upper limit of the plate thickness of the member 2 (flange) is not particularly limited, but is usually up to 120 mm. If the low temperature toughness of the fillet weld metal does not satisfy the above-mentioned formula (1a) or (1b), the low temperature toughness of the fillet weld metal is insufficient, and it is generated and propagated in the joined member (flange). It becomes impossible to prevent propagation of brittle cracks at the fillet weld metal. On the other hand, if the weld leg length exceeds 40 mm and the plate thickness of the member to be joined (flange) 2 exceeds 120 mm, it is difficult to achieve both construction efficiency and securing arrest performance.

In this way, the fillet weld metal has a low temperature that satisfies the above-described conditions in relation to the plate thickness tf of the member to be joined (flange), and L, which is the smaller one of the weld leg length and the weld width. If it is a welded structure having toughness, it is possible to prevent the brittle crack generated in the joined member (flange) from propagating with the fillet weld metal.
The lower limit of vTrs is not particularly limited, but is usually −130 ° C. when a general-purpose welding material for ships is applied. In order to lower vTrs below −130 ° C., it is necessary to apply a special (expensive) welding material such as a low-temperature tank melt.
Further, L is a smaller value of the weld leg length and the weld width, and is not limited, but is usually more than 16 mm and 40 mm or less.
Further, the thickness of the joining member (web) 1 is not particularly limited, but is usually 50 to 120 mm. If the thickness of the joining member is less than 50 mm, it is not necessary to apply the present invention, and if ordinary E grade steel is applied to the joining member (web) and the joined member (flange), the propagation of brittle cracks can be prevented. . On the other hand, since the plate thickness of the main hull structural arrest steel plate stipulated in IACS UR (International Classification Rules) is 100 mm at the maximum, it is difficult to think that the plate thickness of the joining member exceeds 120 mm.

  Further, the above welded structure is provided with the above-described fillet welded joint, for example, a hull structure having a ship hull outer plate as a flange and a partition wall as a web, or a deck as a flange, and a hatch as a web. It can be applied to the hull structure.

  Examples will be described below.

  A thick steel plate having a thickness tw shown in Table 1 is used as a joining member (web), and a thick steel plate having a thickness tf shown in Table 1 is used as a member to be joined (flange). ), (B), and a large fillet weld joint 9 having an actual structure size as shown in (c) was produced. In the produced large fillet welded joint 9, the unwelded portion 4 as shown in FIG. 1 (a), (c) or (d) is not applied to the butted surface of the joining member 1 and the joined member 2. The welded portion ratio Y (= (width B of unwelded portion / bonding member (web) plate thickness tw)) was changed to be present.The member to be joined (flange) was a thick steel plate (base material only). (FIG. 4 (a)) or a thick steel plate (FIG. 4 (b), (c)) having a butt weld joint, and the joining member (web) is a thick steel plate (base material only) (FIG. 4 (a), ( b)), or a thick steel plate having a butt weld joint (FIG. 4C).

Butt welded joints were made by one-pass high heat input electrogas arc welding (SEGARC and two-electrode SEGARC) or multi-layer carbon dioxide gas welding (multi-layer CO ₂ ). The fillet welded joint was a fillet welded joint with various low temperature toughness, various weld leg lengths or weld widths by changing the welding conditions such as welding material, welding heat input and shield gas. In addition, the low temperature toughness of fillet weld metal is based on the JIS Z 2242 standard by collecting Charpy impact test pieces (10 mm thick) from butt welded joints manufactured under the same conditions as fillet weld metal or fillet welds. The fracture surface transition temperature vTrs (° C.) was determined. In some fillet welded joints, a gap 14 was formed between the joining member (web) 1 and the joined member (flange) 2. Further, in some of the fillet welded joints, a fillet welded joint was produced by inserting a spacer 15 into the gap 14 between the joining member (web) 1 and the joined member (flange) 2.

Moreover, using the obtained large fillet welded joint 9, an ultra-large structural model test body shown in FIG. 4 was produced, and a brittle crack propagation stop test was performed.
The ultra-large structural model specimen was welded with a steel plate having the same thickness as that of the member to be joined (flange) 2 by tack welding 8 below the member to be joined (flange) 2 of the large fillet welded joint 9.
4B, the butt weld joint 11 of the member to be joined (flange) 2 is produced so as to be orthogonal to the joining member (web) 1, and FIG. In the ultra-large structural model test body shown in c), the butt weld joint portion 11 of the member to be joined (flange) 2 and the butt weld joint portion 12 of the joint member (web) 1 were crossed. And the front-end | tip of the machine notch 7 was processed so that it might become the BOND part of the butt welding joint part 11, or the weld metal WM.

In the brittle crack propagation stop test, a mechanical notch was hit to generate a brittle crack, and it was investigated whether the propagated brittle crack stopped at the fillet weld. All tests were performed under the conditions of a stress of 100 to 283 N / mm ² and a temperature of −10 ° C. The stress of 100 N / mm ² is the average value of the stress that constantly acts on the hull, and the stress of 257 N / mm ² corresponds to the maximum allowable stress of the yield strength 390 N / mm class ² steel plate applied to the hull. The value, stress 283 N / mm ² is a value corresponding to the maximum allowable stress of the yield strength 460 N / mm grade ² steel plate applied to the hull. The temperature -10 ° C is the design temperature of the ship. In calculating the values on the right side of the equations (1a) and (1b), the numbers after the decimal point are rounded off.

  The obtained results are shown in Table 1.

  In each of the inventive examples, after the brittle crack propagated through the member to be joined (flange), it entered the fillet weld metal and stopped. On the other hand, in all the comparative examples, the brittle crack propagated to the joining member (flange) without stopping at the fillet weld metal, and the fillet weld metal could not prevent the propagation of the brittle crack.

1 Joining member (web)
2 Joined members (flange)
3 Welded leg length 4 Unwelded part 5 Fillet weld metal 7 Machine notch 8 Tack welding 9 Large fillet welded joint 11 Butt welded joint part 12 of joined member (flange) Butt welded joint part 13 of joined member (web) Width 14 Clearance 15 Spacer 16 Size of unwelded part (width B of unwelded part)
θ Crossing angle

Claims (3)

The end face of the joining member is abutted against the surface of the member to be joined having a plate thickness of 50 mm or more, and a welded structure including a fillet weld joint that joins the joining member and the member to be joined,
The weld leg length and weld width of the fillet weld joint is over 16 mm,
An unwelded portion having a thickness of 95% or more of the thickness tw of the joining member in the cross-section of the fillet welded joint is formed on the surface of the fillet welded joint that is abutted between the end surface of the joining member and the surface of the joined member. Have
Furthermore, for the fillet weld metal of the fillet weld joint,
When the smaller value of the weld leg length and the welding width is L, when L is less than 20 mm, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, The thickness tf of the member to be joined satisfies the relationship of the following formula (1a),
When L is 20 mm or more, the Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal, the plate thickness tf of the member to be joined, and L satisfy the following relationship (1b): Satisfied, welded structure.
Record
vTrs ≤ -35-1.5 (tf-75) (1a)
vTrs ≤ -5L + 65-1.5 (tf-75) (1b)
Where vTrs: Charpy impact test fracture surface transition temperature (° C) of fillet weld metal,
tf: thickness of the member to be joined (mm),
L: The smaller value of the weld leg length and weld width (mm)   The welded structure according to claim 1, wherein the member to be joined has a butt weld joint so as to intersect the joining member.   The joining member has a butt weld joint portion, and the joining member is disposed so that a butt weld joint portion of the joining member and a butt weld joint portion of the joined member intersect. The welded structure according to claim 2.

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