JP4091893B2 - Butt weld joint excellent in brittle crack propagation resistance, method for producing the joint, and welded structure - Google Patents

Description

The present invention relates to a butt weld joint excellent in brittle crack propagation resistance that prevents propagation of a brittle crack generated in a butt weld joint, a manufacturing method thereof, and a welded structure.
Specifically, possible brittle crack propagation resistance in good butt welded joint to prevent the propagation of a brittle crack occurring butt welded joint of welded structures according to the high heat input welding with thick plate The present invention relates to a manufacturing method and a welded structure, and relates to a technology capable of improving safety of a hull structure, 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, the application of high heat input welding, the weld heat affected zone (heat affected zone, also referred to as HAZ portion.) Toughness is lowered, and the width of the HAZ portion is also increased, the fracture toughness values for brittle fracture is reduced There is a tendency.
Therefore, inventions such as Patent Documents 1 and 2 have been made as steel materials in which the fracture toughness of the HAZ portion does not easily decrease 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 ( Thermo Mechanical Control Process ) steel plates with a thickness of about 25 mm have been used, even if brittle cracks occur, the brittle cracks are caused from the welded joints by the residual stress of the welds. It has been thought 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 as long as the arrest performance of the base material is secured. .
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 steel plate, depending on the degree of fracture toughness of the welded joint, without brittle crack deviates the base material, to propagate along the heat-affected zone of the welded joint portion 8000 tons present inventors This was revealed by a large-scale destructive test using a large-scale testing machine.

According to the test relating to the brittle fracture of steel sheets by the present inventors, as shown in FIG. 1, aggregates (reinforcing plates) are applied to steel sheets having a thickness of 50 mm or less by fillet welding so as to cross the welded joints of the steel sheets. ), 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. This shows that the aggregate 3 can be used as a crack arrester.
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. Therefore, a brittle crack will appear on the hull shell as indicated by the arrow ( → ). through the fillet weld 4 that attach certain steel 1 and aggregate 3, it enters the aggregate 3, come to propagate. Then, the plate thickness inside the toughness lower region propagates preceded by a brittle crack, then, would not break the aggregate 3 and also propagates to the surface layer portion of the aggregate 3. That is, for example about 70mm or more thick steel plate, be attached to the bone material 3 in fillet welding, it has been found that there be aggregate 3 can not function as a structural crack arrester.
That is, even if a structure aggregate 3 are joined by welding, along the HAZ or weld metal, brittle crack propagates, there can lead to massive destruction.
Japanese Patent Laid-Open No. 06-088161 JP-A-60-245768

Accordingly, the present invention is the event that a brittle crack occurs in the welded joint, it is possible to prevent fatal fracture of the welded structure to prevent the propagation of brittle crack in the repair weld-out brittle It is an object of the present invention to provide a butt-welded joint excellent in crack propagation, a manufacturing method thereof, and a welded structure.

The present inventors have in the welding structure, welds the end of the welding line direction of butt welds, or the intermediate portion, the amount of Ni as a chemical component rather than 1.0% by mass or more high Ni content of the base material, and produce multi-layer welding of a packet size in equivalent circular diameter as tissue equal to or less than a predetermined size, the plate thickness throughout, or by construction over its part, the event brittle fracture to butt weld, We found that even if a brittle crack propagates in the weld line or weld metal inside the weld zone, the propagation and progression of the brittle crack can be prevented in the multi-layer welded zone, and the fatal fracture of the welded structure can be prevented. The present invention has been completed, and the gist thereof is the following contents as described in the claims.

(1) In a butt weld joint in which steel plates are joined by butt welding, the entire thickness of the welded portion or a part of the thickness direction of the welded portion is formed at the welded end portion or the intermediate portion in the weld line direction of the butt welded joint. over region, instead of the welded portion formed by butt welding of the steel sheets, multi-layer welding unit, which is a multi-layer welding is formed by repair welding, further, multilayer prime weld-out brittle crack is On the side that is supposed to propagate, on the basis of the envelope of the boundary between the adjacent butt weld and steel plate, the envelope of the boundary between the multilayer weld and steel plate is on the base metal side, The boundary is formed such that the angle on the surface of the steel sheet is deviated by an angle φ of 3 degrees or more and 10 degrees or less. The chemical composition of the weld metal of the multi-layer weld is such that the amount of Ni is greater than the amount of Ni in the base metal. 1.0% by mass or more and the multilayer The weld metal structure of the welded portion is a butt weld joint with excellent brittle crack propagation resistance, characterized in that the equivalent circle diameter and the packet dimension PS satisfy the following (Equation 1).
PS (μm) ≦ 2 × Ni (mass%) + 5 (Formula 1)
In addition, Ni (mass%) here represents content in mass% of Ni as a chemical component of the weld metal of a multi-layer weld.
(2) A method for producing a butt-welded joint having excellent brittle crack propagation properties as described in (1), wherein a welded end portion in a weld line direction of a butt-welded joint in which steel plates are joined by butt welding, or After removing a part of the welded portion formed by butt welding of the steel plates to the intermediate portion by gouging or machining, the weld removed portion is subjected to multilayer welding by repair welding, and the thickness of the base metal A welding material in which the Ni amount of the weld metal in the multi-layer welded portion is 1.0 mass% or more higher than the Ni amount of the base metal when forming the multi-layer welded portion over the entire region or a partial region in the plate thickness direction. used, the heat input of the multi-layer welding and 2.0 kJ / mm or more, the interpass temperature of 0.99 ° C. or higher, further, the shape of the multilayer overlay clad portion, assuming that the brittle crack come propagated On the side it is, With respect to the envelope of the boundary between the butt welds and the steel plate in contact, the boundary between the multilayer overlay clad portion and the steel plate envelope, the base material side, on the steel sheet surface angle 3 degrees or more than 10 degrees of A method for producing a butt-welded joint excellent in brittle crack propagation resistance, characterized in that the boundary is formed so as to deviate by an angle φ.
(3) A welded structure having at least a vertical member and a horizontal member joined by a butt weld joint, wherein the weld joint of the vertical member of the weld structure and the weld joint of the horizontal member intersect each other. The butt weld joint having excellent brittle crack propagation property described in (1) is arranged for a part or all of the butt weld joint in the region, and the butt weld joint has a brittle crack. A welded structure excellent in brittle crack propagation resistance, characterized by being able to hinder the propagation of cracks.

According to the present invention, in the welding structure, welds the end of the welding line direction of butt welds, or the intermediate portion, the amount of Ni as a chemical component rather than 1.0% by mass or more high Ni content of the base material, and a multi-layer welding, characterized in that the packet size in equivalent circular diameter as the tissue is less than a predetermined size, by construction over the plate thickness throughout, event cause brittle fracture to the butt weld, the weld fusion line or even weld metal inside the brittle crack propagation of brittle cracks in multi-layer welding unit propagation, prevent progression, fatal brittle can prevent breakage crack propagation resistance of the welded structure An excellent butt-welded joint, a manufacturing method thereof, and a welded structure can be provided, and the industrially useful remarkable effects can be obtained.

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-welded joint for steel plates to which 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 multi-layer weld joint, and joint C is vertical member 5 (base material-1) and horizontal member 6 (base material- T joint (cross joint) by butt welding with 2), joint D indicates a butt weld joint between horizontal members 6 (base material-2).

The butt-welded joint of the present invention is obtained by removing the end of the butt welded portion in the weld line direction or a part of the intermediate portion, such as joints A and D in FIG. 2, by gouging or machining. It is characterized by performing multi-layer welding with a welding material having excellent fracture toughness.
Brittle cracks generated in butt welds propagate through the weld line, but by multi-layer welding with a welding material with excellent fracture toughness at the end or middle of the butt weld in the weld line direction. The toughness of this portion can be increased to prevent crack propagation.
The chemical composition of the weld metal of the butt weld joint of the present invention is characterized in that the amount of Ni is 1.0 mass% or more higher than the amount of Ni in the base metal, and the structure of the weld metal has an equivalent circle diameter and a packet size PS. Satisfies the following (formula 1).
PS (μm) ≦ 2 × Ni (mass%) + 5 (Formula 1)
In addition, Ni (mass%) here represents content in mass% of Ni as a chemical component of the weld metal of a multi-layer weld.
When the amount of Ni is 1.0 mass% or more higher than the amount of Ni in the base metal, the structure of the weld metal is equivalent to a circle and the packet dimension PS satisfies the above (formula 1), the structure of the weld metal is made finer. To improve fracture toughness.
The basis of (Equation 1) will be described later using an example.

Figure 3 is a view showing a butt-welded joint of steel plate to apply this onset bright.
In FIG. 3, joint A shows a butt weld joint, and joint B shows a multi-layer weld.
Multi-layer welding used in the present invention is a butt weld joint in which a brittle crack can propagate as shown in FIG. After the part is removed by gouging or machining, the welded joint B is formed by performing repair welding on the part 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 at the part, a welded joint B can be formed, and the toughness of this part can be increased to prevent crack propagation.
In the present invention, the depth of gouging or machining is not particularly specified, but the brittle crack propagation resistance is further improved by removing 1/2 or more of the plate thickness of the vertical member by gouging or machining. Can do.

In addition, when a brittle crack that has propagated through a butt weld joint enters a multilayer welded portion, if the toughness of the multilayer welded portion is low, the crack may enter and propagate into the repair welded portion.
Therefore, in the present invention, a multi-layer welded portion is formed using a welding material containing Ni amount 1.0 mass% or more higher than the Ni amount of the base material, and is melted in the vicinity of the weld melting line. A concentration of Ni element which forms a region not mixed with molten metal having a high Ni content, so-called Un-mixed-zone (hereinafter referred to as UMZ), and is difficult to diffuse from the weld HAZ portion on the base metal side toward the weld metal. By forming the distribution, the Ni content is significantly deficient as compared with the weld metal and the welded HAZ portion, and a local region having a low fracture toughness value is formed. As a result, after the occurrence of a brittle crack, the brittle crack propagating along the butt weld joint does not enter the repair weld, and the propagation path of the brittle crack is changed along the UMZ at the boundary line with the repair weld. The brittle crack can be deviated from the butt weld and led to the base material portion to be arrested.

FIG. 4 is a detailed view of a multilayer pile weld used in the welding method of the present invention.
4, the vertical members 5, 6 show a repair weld joint by the horizontal members, the joint A butt welded joint, the joint B multi layer up welding.
In the butt weld joint A in which a brittle crack may propagate, the present inventors repair and weld the portion using a welding material having an excellent fracture toughness value for the region where the brittle crack is stopped. As a result of conducting various experiments, it has been found that it is preferable to control the heat input amount and the temperature between passes of multilayer build-up welding in the longitudinal direction of the butt weld joint.
In other words, by making the heat input of multilayer pile welding 2.0 kJ / mm or more and the interpass temperature 150 ° C. or more, it is possible to improve the workability of welding while ensuring the function of stopping crack propagation. it can.

In addition, the multi-layer welded portion has a boundary between the weld metal and the steel plate on the steel plate surface adjacent to the multi-layer prime weld, at least of the butt weld on the side where the propagation of a brittle crack is assumed, It is formed so as to deviate by an angle φ of 3 degrees or more and 10 degrees or less from the extension direction of the envelope of the boundary between the weld metal and the steel sheet on the surface of the steel sheet to the base metal side at an angle on the steel sheet surface. To do.
The main point of the present invention is to shift a brittle crack propagating along the butt weld from the butt weld to the UMZ due to the influence of the unmixed region ( UMZ ) formed in the vicinity of the melting line of the multi-layer weld. Oh Ru. By changing the angle φ at which the envelope of the boundary between the weld metal of the butt weld and the steel plate surface and the envelope of the boundary between the weld metal of the multilayer weld and the steel plate surface changes, a brittle crack is generated from the butt weld. As a result of experimenting whether or not the angle can be deflected, if the angle φ exceeds 10 degrees, a brittle crack often enters the multi-layer weld, so the fracture toughness of the repair weld is not sufficiently high. it is impossible to stop the brittle crack, but if 10 degrees or less was found that can be propagated along the brittle crack at the boundary between the repair weld and the base metal.
However, when the angle φ is less than 3 degrees, 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 repair 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 3 degrees.

In a welded structure where a brittle crack may propagate along the welded joint, such as a butt weld constructed by high heat input welding, in the middle of the butt weld, or at the end in the weld line direction , It was studied how to ensure an area that can block the propagation of brittle cracks.

As the method, the part of the butt weld, remove some of the welds by gouging or the like, subjected to a repair welding on that part, demonstrate the performance of the repair weld portion can prevent the propagation of brittle crack 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, as shown in FIG. 5, a steel plate of 500 mm × 500 mm × thickness is used, and the depth is set at the center of the test piece. Machining a KUBOMI that is about half the plate thickness and the diameter on the surface of the test piece is about the plate thickness, and changing the various chemical components and welding conditions in it, the chemical components of the weld metal The test piece which formed the welding part 7 which changed the structure | tissue of a weld metal was produced. And the V-shaped notch process was given to the test piece end part, and the V-groove process 8 with a depth of 7 mm and a tip curvature of 0.25 mm was given to the area | region 7 which carried out repair welding from the notch front-end | tip part. The end of the test piece is cooled to a low temperature of about −50 ° C. or lower, the center of the test piece is controlled to −10 ° C., and a predetermined stress is applied. Then, a wedge is driven into the V-notch and a brittle crack is generated. It is, along the V groove processing portion 8 and is propagated brittle crack. Brittle crack propagating along the V groove processing section 8, after reaching the repair weld 7, the brittle cracks was evaluated whether to propagate.

The results are shown in Table 1.
As shown in Table 1, the amount of Ni in the weld metal needs to be 1.0 mass% or more, and the amount of Ni dilution in the UMZ region is larger by 1.0 mass% or more than the amount of Ni in the base metal. Since it can form, it is preferable. This is because Ni is a component that is difficult to dilute during welding, and cracks are likely to propagate along the UMZ if there is a large difference in Ni content between the base metal and the weld metal.
In addition, it is preferable that the welding heat input is large because the width of the UMZ can be increased and the width for introducing the crack is increased, and the effect similar to increasing the welding heat input is also preferable when the interpass temperature is high. Is preferable. The effect became remarkable when the welding heat input was 2.0 kJ / mm or more, and the effect was recognized when the interpass temperature was 150 ° C. 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, since the anisotropy increases, the crack is difficult to travel straight, so that the propagation of the crack can be suppressed.
FIG. 6 is a diagram showing the relationship between the amount of Ni (mass%) of the weld metal and the packet diameter (μm) of the weld metal structure.
In FIG. 6, the ● mark indicates the case where the crack propagated, and the ○ mark indicates the case where the arrest was completed. As shown by the straight line in FIG. Yes,
PS (μm) ≦ 2 × Ni (mass%) + 5 (Formula 1)
It was found that a brittle crack can be stopped even if the applied stress is 200 MPa or more.
In addition, Ni (mass%) here represents content in mass% of Ni as a chemical component of the weld metal of a multi-layer weld.

The present invention not only the hull structure, the occurrence of brittle crack in the welded joint, welded joint structures of widely applicable welded structures and building steel to welded structures in order to prevent the propagation, welded structure of marine 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 diagram showing a butt-welded joint of steel plate to apply this onset bright. It is a diagram showing a butt-welded joint of steel plate to apply this onset bright. It is detail drawing of the multilayer pile-welding joint used for this invention. It is a figure which shows the test piece used for the Example of this invention. It is a figure which shows the relationship between Ni amount (mass%) of a weld metal, and the packet diameter (micrometer) of a weld metal structure.

Explanation of symbols

1 Steel plate 2 Welded joint 3 Aggregate (reinforcing material)
4 Fillet welded part 5 Vertical member (base material-1)
6 Horizontal member (base material-2)
7 Welded part 8 V groove processing 9 Notch

Claims (3)

In butt weld joints where steel plates are joined by butt welding,
To the welded portion formed by butt welding of the steel plates over the entire thickness of the welded portion or a partial region in the thickness direction of the welded portion in the weld line direction or the intermediate portion of the butt weld joint Instead, a multi-layer prime weld is formed by repair welding.
Further, multilayer prime weld the side where-out brittle crack is assumed to come propagated, based on the envelope of the boundary between the adjacent butt welds and the steel plate, and a multilayer overlay clad portion The boundary is formed so that the envelope of the boundary with the steel sheet deviates by an angle φ of 3 degrees or more and 10 degrees or less at the angle on the steel sheet surface on the base metal side,
The chemical composition of the weld metal in the multi-layer weld zone is such that the Ni content is 1.0 mass% or more higher than the Ni content of the base metal, and the weld metal structure of the multi-layer weld zone has an equivalent circle diameter and packet dimensions. A butt-welded joint excellent in brittle crack propagation resistance, characterized in that PS satisfies the following (formula 1).
PS (μm) ≦ 2 × Ni (mass%) + 5 (Formula 1)
In addition, Ni (mass%) here represents content in mass% of Ni as a chemical component of the weld metal of a multi-layer weld. A method for producing a butt-welded joint excellent in brittle crack propagation resistance according to claim 1,
Part of the welded portion formed by butt welding of the steel plates was removed by gouging or machining at the welded portion end or intermediate portion of the butt weld joint where the steel plates were joined by butt welding. Thereafter, the weld removal portion is subjected to multi-layer welding by repair welding, and when forming the multi-layer welding portion over the entire region of the thickness of the base material or in a region in the plate thickness direction,
Using a welding material such that the amount of Ni in the weld metal of the multi-layer weld is 1.0% by mass or more higher than the amount of Ni in the base material,
The heat input of the multi-layer welding is 2.0 kJ / mm or more, the interpass temperature is 150 ° C. or more,
Furthermore, the shape of the multilayer overlay clad portion, the side where-out brittle crack is assumed to come propagated, based on the envelope of the boundary between the adjacent butt welds and the steel plate, multilayer up welding It is brittle resistant, characterized in that the boundary is formed so that the envelope of the boundary between the part and the steel sheet deviates by an angle φ of 3 degrees or more and 10 degrees or less on the surface of the steel sheet to the base metal side. A method for producing a butt-welded joint with excellent crack propagation.   A welded structure having at least a vertical member and a horizontal member joined by a butt weld joint, wherein the welded structure of the welded structure intersects the welded joint of the vertical member and the welded joint of the horizontal member, or The butt-welded joint having excellent brittle crack propagation resistance according to claim 1 is provided for the entire area of the butt-welded joint, and a brittle crack is generated in the butt-welded joint. However, the welded structure is excellent in brittle crack propagation resistance, characterized in that its propagation can be hindered.

Images