JP3811479B2 - Weld metal for welded structure having excellent brittle fracture propagation resistance, its construction method, and welded structure - Google Patents

Description

The present invention relates to a weld metal for a welded structure excellent in brittle fracture propagation resistance that prevents the propagation of a brittle crack generated in a butt welded joint, a construction method thereof, and a welded structure.
Specifically, welding for welded structures with excellent brittle fracture propagation resistance that hinders the propagation of brittle fracture that may occur in butt welded joints of welded structures to which large heat input welding is applied using thick plates The present invention relates to a metal, a construction method thereof, and a welded structure, and relates to a technique capable of improving safety of a building structure, a civil engineering steel structure, and the like.

In order to build a steel structure, it is essential to use welding, but large heat input welding is widely applied for the purpose of reducing the construction cost and improving the construction efficiency.
In particular, as the plate thickness of the steel sheet increases, the number of welding steps increases dramatically, so that there is a high demand for welding with high heat input to the limit.
However, when high heat input welding is applied, the toughness value of the weld heat affected (HAZ) portion decreases and the width of the HAZ portion also increases, so the fracture toughness value against brittle fracture tends to decrease.
Therefore, inventions such as Patent Documents 1 and 2 have been made as steel materials in which the fracture toughness of the HAZ portion is unlikely to deteriorate even when high heat input welding is applied. In these inventions, since the fracture toughness value, which is a resistance value against the occurrence of brittle fracture, has been improved, the possibility of brittle fracture in a normal use environment is extremely low, but earthquakes and collisions between structures, If a brittle fracture occurs in an emergency such as an accident or disaster, the brittle crack propagates through the HAZ part and there is a risk of large-scale fracture.

Until now, in welded joints where TMCP steel sheets with a thickness of about 25 mm have been used, even if a brittle crack occurs, the brittle crack is displaced from the welded joint to the base metal side due to residual stress in the weld. Therefore, it has been considered that if the arresting performance of the base metal is ensured, the base metal can stop the brittle crack even if a brittle crack occurs in the welded joint.
However, as steel structures become larger, steel plates with larger thicknesses are used, and thickening of the steel plates is effective for simplifying the structure, so the design stress is high. High-tensile steel thick steel plates have been used. In such a thick steel plate, depending on the degree of fracture toughness of the welded joint portion, the inventor's 8000 ton large size propagates along the heat-affected zone of the welded joint portion without deviating to the base metal. This was revealed by a large-scale destructive test using a testing machine.

According to the test relating to the brittle fracture of steel sheets by the present inventors, as shown in FIG. ), Even if a brittle crack occurs in the steel plate 1, the propagation of the brittle crack is stopped by the aggregate 3 (arrest), and the steel plate 1 often does not break.
However, as the plate thickness increases, the aggregate performance of the aggregate itself will not be sufficient, and a large toughness distribution will occur, particularly in the plate thickness direction. It propagates when it enters the aggregate through the fillet weld where a steel plate and aggregate are attached. And a brittle crack precedes and propagates in the area | region where the toughness inside a plate | board thickness is low, and propagates also to the surface layer part of a steel plate after that, and will break a steel plate. That is, for example, for thick steel plates of 70 mm or more, it has been found that even if the aggregate is attached by fillet welding, it may not function as a structural crack arrester.
That is, even in the structure in which the aggregate 3 is joined by welding, a brittle crack propagates along the HAZ portion or the weld metal portion, which may cause a large-scale fracture.
JP-A-6-88161 JP-A-60-245768

  Therefore, in the event that a brittle crack occurs in the welded joint, the present invention prevents the propagation of the brittle crack at the additional welded portion of the function-added type that can exhibit the brittle crack propagation stopping performance. It is an object of the present invention to provide a weld metal for a welded structure excellent in brittle fracture propagation resistance that can prevent a fatal fracture of the structure, a construction method thereof, and a welded structure.

  In the welded structure, the present inventor has a residual stress of a weld metal having a Ni content of 2.5% by mass or more as a chemical component in the toe or intermediate part of the butt weld, and more than half of the yield stress of the base metal. By applying multi-layer welding, which is characterized by a compressive residual stress, over the entire plate thickness or a part of it, a butt weld should cause brittle fracture, so that the fusion line of the weld or the inside of the weld metal The present invention has been completed by finding that even if a brittle crack propagates, it is possible to prevent the propagation and progress of the brittle crack in the multi-layer weld, and to prevent a fatal fracture of the welded structure. The gist of the present invention is the following contents as described in the claims.

(1) A weld metal for welded structures having excellent brittle fracture propagation resistance that prevents the propagation of brittle cracks generated in butt weld joints,
The weld metal is multi-layer welded over the whole or part of the thickness of the base metal at the end or intermediate part of the butt weld joint,
The chemical component of the weld metal has a Ni content of 2.5% by mass or more, and the residual stress σ _R in the weld metal satisfies the following (formula 1). Excellent weld metal for welded structures.
σ _R ≦ −0.5 * Yp (Formula 1)
Where σ _R : Residual stress after welding in weld metal (Mpa)
Yp: Yield stress of base metal (Mpa)
(2) A method for constructing a weld metal for welded structures having excellent brittle fracture propagation resistance according to (1),
The heat input of the multilayer welding is 5.0 kJ / mm or less, the interpass temperature is 400 ° C. or less,
An angle φ at which the butt weld joint intersects the multilayer weld is 10 degrees or more and 45 degrees or less, and a method for applying a weld metal for a welded structure excellent in brittle fracture propagation resistance.
(3) A welded structure excellent in brittle fracture propagation resistance that prevents the propagation of brittle cracks generated in a butt welded joint, wherein the welded joint of the vertical member of the welded structure intersects the welded joint of the horizontal member Brittle fracture resistance characterized by embedding the weld metal described in (1) by repair welding in a part or all of the area removed by gouging or machining. A welded structure with excellent propagation characteristics.

  According to the present invention, in the welded structure, the residual stress of the weld metal having a Ni content of 2.5% by mass or more as a chemical component at the toe or intermediate portion of the butt weld is the yield stress (Yp ) If a multi-layer weld characterized by a compressive residual stress of less than half of the thickness is applied to the entire plate thickness or a part of it, the butt weld will cause brittle fracture, and the fusion line of the weld Even if a brittle crack propagates inside the weld metal, the weld structure has excellent brittle fracture propagation resistance that prevents the propagation and progression of brittle cracks in multilayer welds and prevents fatal fracture of the welded structure. It is possible to provide a weld metal for body, a construction method thereof, and a welded structure, and there are significant industrially useful effects.

The best mode for carrying out the present invention will be described in detail with reference to FIGS.
FIG. 2 is a view showing a butt weld joint of steel plates to which the weld metal of the present invention is applied.
In FIG. 2, joint A is a butt-welded joint between vertical members 5 (base material-1), joint B is a multilayer welded joint, joint C is vertical member 5 (base material-1) and horizontal member 6 (base material-2). ) And a joint D are butt weld joints of the horizontal members 6 (base material-2).

The weld metal according to the present invention, like the joints A, C, and D in FIG. 2, is obtained by removing a part of the end or intermediate part of the butt weld part by gouging or machining, and then applying the fracture toughness to the part. It is characterized by performing multi-layer welding with an excellent welding material.
Brittle cracks generated at the butt welds propagate through the weld line.Multi-layer welding is performed at the end or middle of the butt welds with a welding material with excellent fracture toughness. It can be increased to prevent crack propagation.
The chemical component of the weld metal of the present invention is characterized in that the amount of Ni is 2.5% by mass or more and the residual stress σ _R in the weld metal satisfies the following (formula 1).
σ _R ≦ −0.5 * YP (Formula 1)
Where σ _R : Residual stress after welding in weld metal (Mpa)
Yp: Yield stress of base metal (Mpa)
When the amount of Ni is 2.5% by mass or more, the toughness of the weld metal is increased, and when the residual stress σ _R in the weld metal satisfies the following (formula 1), the weld metal has a tensile force. Even when it works, since the tensile stress can be relaxed by the compressive residual stress, the propagation of the brittle crack can be suppressed.

FIG. 3 is a view showing a butt weld joint of steel plates to which the weld metal of the present invention is applied.
In FIG. 3, joint A shows a butt weld joint, and joint B shows a multilayer weld.
Multi-layer welding used in the present invention is a part of a butt weld joint in the butt weld joint A in which a brittle crack may propagate as shown in FIG. Is removed by gouging or machining, and then repair welding is performed on the portion with a welding material having excellent fracture toughness.
The brittle crack generated in the welded joint propagates through the butt welded joint A, but after removing a part of the butt welded joint in that area by gouging or machining, the area where the brittle crack is stopped, By performing repair welding with a welding material having excellent fracture toughness on the part, it is possible to increase the toughness of this part and prevent crack propagation.
In the present invention, the depth of gouging or machining is not particularly specified, but the brittle fracture propagation resistance can be further improved by removing 1/2 or more of the plate thickness of the vertical member by gouging or machining. it can

Further, when a brittle crack that has propagated through a butt weld joint enters a multilayer weld, if the toughness of the multilayer weld is low, the crack may enter and propagate into the repair weld.
Therefore, in the present invention, by using a welding material excellent in fracture toughness containing Ni of 2.5% by mass or more in the multilayer welded portion, the fracture toughness value of the multilayer welded portion is sufficiently secured while the addition is made. Due to the influence of compressive residual stress generated around the weld metal by welding, it is possible to prevent the brittle crack from approaching the multilayer weld without entering the multilayer weld, so along the butt weld joint The propagating brittle crack can be deviated from the butt weld and led to the base material.
In the present invention, the upper limit of Ni contained in the weld metal is not limited, but the upper limit of the Ni content is preferably 10% by mass or less in order to reduce the cost of the Ni raw material.

FIG. 4 is a detailed view of a multi-layer weld used in the welding method of the present invention.
In FIG. 4, 5 is a vertical member, 6 horizontal members, joint A is a butt weld joint, and joint B is a repair weld joint by multilayer welding used in the present invention.
In the butt weld joint A in which a brittle crack may propagate, the present inventors additionally weld the part to the region where the brittle crack is stopped using a welding material having an excellent fracture toughness value. As a result of conducting various experiments, it was found that it is preferable to control the heat input amount and the interpass temperature of multilayer welding in the longitudinal direction of the butt weld joint.
That is, the heat input of multi-layer welding is set to 5.0 kJ / mm or less, and the temperature between passes is set to 400 ° C. or less, so that the toughness of the weld metal itself is maintained and improved, and the heat effect due to additional welding is minimized. In addition, by compressing the residual stress around the welded portion generated for each pass and restraining deformation, the compressive residual stress after welding can be increased.

Further, the angle φ at which the butt weld joint and the multilayer welded portion intersect with each other is preferably 10 degrees or more and 45 degrees or less.
The main object of the present invention is to prevent brittle cracks propagating along the butt weld due to the effect of compressive residual stress occurring in the multilayer weld, and to make the butt weld and the multi-layer weld close. As a result of experimenting whether a brittle crack can be deflected from a butt weld by changing the angle φ intersecting with the butt weld, if the angle φ is 45 degrees or more, a brittle crack enters the multilayer weld. In many cases, brittle cracks cannot be stopped unless the fracture toughness of the multilayer weld is sufficiently high. However, if the fracture toughness is 45 degrees or less, the brittle crack does not approach the multilayer weld and propagates to the base metal. It was found that it can be made. However, when the angle φ is 10 degrees or less, the brittle crack propagates along the boundary between the multilayer weld and the base metal, but around the position where it passes through the region of the multilayer weld, Since the distance is too close, a brittle crack may re-propagate along the butt weld again, so the lower limit was set to 10 degrees.

  In welded structures where fragile cracks such as butt welds constructed by high heat input welding may propagate along the welded joints, brittle cracks may occur in the middle of the butt welds or at the toes. We examined the method to secure the area that can prevent the propagation of the signal.

As a method, a part of the butt weld is partially removed by gouging or the like, and repair welding is applied to the part, and the repair weld exhibits performance that can prevent the propagation of brittle cracks. Various considerations were made as to whether or not this was possible.
In the examination, in order to evaluate whether or not a brittle crack that goes straight forward can be prevented, a steel plate of 2500 mm × 2500 mm × thickness is used as shown in FIG. Machining a KUBOMI whose diameter on the surface of the test piece is about the same as the plate thickness, and changing various chemical components and welding conditions in it, Test specimens with different weld metal structures were prepared.
Then, a V-shaped notch for inserting a wedge 8 at a position 200 mm from the end of the test piece to generate a brittle crack is applied to the fusion line of the butt weld (high heat input welded joint by electrogas welding). The test piece end is cooled to a low temperature of about −40 ° C., the center of the test piece is controlled to −10 ° C., a predetermined stress is applied, and a wedge is driven into the V-shaped notch. Then, a brittle crack was generated and propagated along the fusion line of the butt weld. After the propagated brittle crack reached the additional weld, it was evaluated whether or not the brittle crack propagated.

The results are shown in Table 1.
As shown in Table 1, the amount of Ni in the weld metal needs to be 2.5 mass% or more.
The (100) plane strength ratio of the base material is preferably 1.5 or more. This is because by increasing the (100) plane strength ratio of the base material, the anisotropy also increases, so that the crack does not advance straight, so that the propagation of the crack can be suppressed.
No. In Nos. 7 and 8, since the (100) plane strength ratio of the base material was less than 1.5, it was confirmed that the load stress could be arrested under conditions smaller than those of the other invention examples.
No. Nos. 9 and 10 have propagated through the butt weld because the amount of Ni in the weld metal is smaller than the predetermined value and the welding heat input and interpass temperature are both outside the predetermined range, so the residual stress in the part is small. When a brittle crack approaches the weld, the crack enters the weld and passes through the weld without stopping at the weld. Cracks propagated and led to breakage.

No. No. 11, since the amount of Ni in the weld metal is smaller than a predetermined value and the tangent angle of the intersection between the welded portion and the butt welded portion is larger than a predetermined value, a brittle crack enters the welded portion. , Which led to breakage.
No. No. 13 is that the residual stress of the part is not sufficient and φ is larger than a predetermined value, so that the part enters the welded part and is broken as it is.
No. In No. 14, since the residual stress of the part was not sufficient, when entering the welded part, a crack entered and propagated to the welded part, which resulted in breakage.
No. No. 15, since φ was smaller than a predetermined value, when entering the welded portion, a crack along the fusion line of the welded portion changed the propagation path. Propagation has led to breakage.
No. No. 16, because φ was too larger than a predetermined value, the crack propagation direction changed when entering the weld, but eventually the crack entered the weld, leading to fracture. .
No. In Nos. 17 and 18, since the residual stress of the part is insufficient and φ is too smaller than a predetermined value, the crack is almost unchanged without changing the propagation direction of the crack when entering the welded part. It went straight and a crack entered the weld, leading to fracture.

  The present invention is not limited to a hull structure, and is widely applicable to welded structures to prevent the occurrence and propagation of brittle cracks in welded joints, welded joint structures of architectural steel frames, and welded structures of offshore structures. It can be applied to bridge welding structures, floating structures called mega floats, and the like.

It is a figure which shows the welding structure which has arrange | positioned the aggregate. It is a figure which shows the butt-welding joint of the steel plate to which the weld metal of this invention is applied. It is a figure which shows the butt-welding joint of the steel plate to which the weld metal of this invention is applied. It is detail drawing of the multilayer welded joint used for this invention. It is a figure which shows the test piece used for the Example of this invention.

Explanation of symbols

1 Steel plate 2 Welded joint 3 Aggregate (reinforcing material)
4 Fillet weld 5 Vertical member (base metal-1)
6 Horizontal members (base material-2)
7 Welded part 8 Wedge 9 Notch

Claims (3)

A weld metal for welded structures excellent in brittle fracture propagation resistance that prevents the propagation of brittle cracks generated in butt weld joints,
The weld metal is multi-layer welded over the whole or part of the thickness of the base metal at the end or intermediate part of the butt weld joint,
The chemical component of the weld metal has a Ni content of 2.5% by mass or more, and the residual stress σ _R in the weld metal satisfies the following (formula 1). Excellent weld metal for welded structures.
σ _R ≦ −0.5 * Yp (Formula 1)
Where σ _R : Residual stress after welding in weld metal (Mpa)
Yp: Yield stress of base metal (Mpa) It is a construction method of the weld metal for welded structures excellent in brittle fracture propagation resistance according to claim 1,
The heat input of the multilayer welding is 5.0 kJ / mm or less, the interpass temperature is 400 ° C. or less,
An angle φ at which the butt weld joint intersects the multilayer weld is 10 degrees or more and 45 degrees or less, and a method for applying a weld metal for a welded structure excellent in brittle fracture propagation resistance. A welded structure excellent in brittle fracture propagation resistance that prevents the propagation of brittle cracks generated in a butt welded joint, wherein the welded joint of the vertical member of the welded structure intersects the welded joint of the horizontal member. The weld metal according to claim 1 is embedded by repair welding in a part or part of the entire region removed by gouging or machining, thereby improving brittle fracture resistance. Excellent welded structure.

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