CN109311126B

CN109311126B - Welded structure having excellent brittle crack propagation stopping characteristics

Info

Publication number: CN109311126B
Application number: CN201780036808.7A
Authority: CN
Inventors: 半田恒久; 伊木聪; 大井健次; 丰田昌信; 木治升
Original assignee: JFE Steel Corp; IHI Marine United Inc
Current assignee: JFE Steel Corp; IHI Marine United Inc
Priority date: 2016-06-16
Filing date: 2017-06-15
Publication date: 2021-03-26
Anticipated expiration: 2037-06-15
Also published as: JPWO2017217515A1; JP6251463B1; CN109311126A; KR20190014068A; PH12018550204A1; KR102090914B1; WO2017217515A1

Abstract

A welded structure is formed by overlapping a double member having a ratio td/Wd of a plate thickness td to a plate width Wd of less than 2 on a surface of a member to be joined having a plate thickness of 50mm or more and joining the member to be joined by fillet welding, and further joining the member to be joined by welding on the surface of the double member to be fillet welded. An unwelded portion that is 95% or more of the plate width Wd of the doubled member in a joint cross section is formed on an overlapping surface of a surface of the doubled member and a surface of the joined member. The fillet welding conditions are adjusted so that the fracture transition critical temperature vTrs (DEG C) of the fillet metal corresponds to the fillet leg length L and that the toughness of the fillet metal is adjusted so that vTrs is not more than-5L +65-1.5(tf-75) as the control item (1b) when L is not less than 20mm and that vTrs is not more than-35-1.5 (tf-75) as the control item (1c) when L is not more than 20mm in the relation with the plate thickness tf of the joined member. Thus, it is possible to provide a welded structure which can prevent propagation of a brittle crack generated from a member to be joined or a joined member by the fillet metal part and which is suitable as a hull structure and has excellent brittle crack propagation stopping characteristics.

Description

Welded structure having excellent brittle crack propagation stopping characteristics

Technical Field

The present invention relates to a welded steel structure to be welded using thick steel plates, such as a large container ship or a bulk carrier, and more particularly to a welded structure having excellent brittle crack propagation stopping characteristics, which can stop propagation of a brittle crack generated from a thick steel plate base material or a welded joint portion before the brittle crack reaches massive destruction of the structure.

Background

Unlike a tanker or the like, for example, a container ship or a bulk carrier has a structure in which a partition wall in a cabin is small and an opening in an upper part of the ship is large, in order to improve loading capacity, loading efficiency, and the like. Therefore, in a container ship or a bulk carrier, particularly, the outer hull plate of the ship needs to be reinforced or thickened.

In addition, in recent years, large-sized container ships have been enlarged, and large-sized ships such as 6,000 to 22,000 TEUs have been built. Here, teu (cargo life Equivalent unit) represents the number of containers converted to 20 feet in length, and represents an index of the loading capacity of the container ship. With such a large-scale ship, the outer hull plate of the ship has a thickness of 50mm or more and a yield strength of 390N/mm²And thick steel plates of grade or more.

In recent years, from the viewpoint of shortening the construction period, steel sheets to be used as hull plates are often butt-welded by high heat input welding such as gas welding. In such welding with large input heat, a large decrease in toughness is likely to occur in the welding heat affected zone, which becomes one cause of brittle cracks occurring from the welded joint.

In the hull structure, it has been conventionally necessary to prevent separation of the hull by stopping propagation of a brittle crack before massive fracture occurs even if brittle fracture occurs in any event from the viewpoint of safety.

In response to such a consideration, non-patent document 1 reports experimental study results on brittle crack propagation behavior of a welded portion of a steel sheet for shipbuilding having a sheet thickness of less than 50 mm.

In non-patent document 1, the propagation path and propagation behavior of a brittle crack forcibly generated in a welded portion are experimentally examined, and it is described that if fracture toughness of the welded portion is secured to a certain degree, the brittle crack often escapes from the welded portion to the base metal side due to the influence of residual welding stress, but many cases have been confirmed in which the brittle crack propagates along the welded portion. This case implies a case where it cannot be declared that the brittle fracture has no possibility of propagating straight along the welded portion.

However, in addition to the fact that a ship constructed by applying welding equivalent to the welding applied in non-patent document 1 to a steel plate having a plate thickness of less than 50mm can sail without any problem, the brittle crack propagation stop characteristic of the welded portion of the steel material for shipbuilding is not particularly required for the ship classification rule and the like, from the knowledge that a steel plate base material (e.g., steel for shipbuilding class E) having good toughness sufficiently maintains the ability to stop the brittle crack.

However, in recent large container ships with more than 6,000TEU, the steel plate used has a plate thickness of more than 50mm, and in addition to the reduction in fracture toughness due to the increase in plate thickness, the fracture toughness of the welded portion tends to be further reduced by welding with a large input heat, which is greater in the input heat of welding. In such a thick-walled large heat input welded joint, it is shown that a brittle crack generated from a welded portion may not return to the base material side and may proceed straight, and may not stop even in a steel plate base material portion such as an aggregate (for example, non-patent document 2). Therefore, in the hull structure to which the thick-walled high-strength steel plate having a plate thickness of 50mm or more is applied, securing safety becomes a big problem.

Further, non-patent document 2 also discloses a case where a thick steel plate having a special brittle crack propagation stopping property is required in order to stop propagation of a generated brittle crack.

In order to solve such a problem, for example, patent document 1 describes a welded structure in which an aggregate is preferably arranged so as to intersect a butt weld portion in a welded structure of a hull outer plate having a plate thickness of 50mm or more, and the welded structure is formed by angle welding.

In the technique described in patent document 1, as the aggregate (reinforcing material), a steel sheet having a microstructure in which the grain size corresponding to an average circle of 0.5 to 5 μm per 3mm or more of thickness of the surface layer portion and the back layer portion is used, and the X-ray surface intensity ratio of the crystal plane at (100) plane parallel to the sheet thickness plane is 1.5 or more is used. By employing such a structure in which the steel sheet having the microstructure is fillet-welded as the reinforcing material, even if a brittle crack occurs in the butt joint portion, brittle fracture can be stopped by the bone material as the reinforcing material, and fatal damage such as fracture of the welded structure can be prevented.

Patent document 2 describes a welded structure having a fillet joint formed by fillet-welding a joining member (web) to a member to be joined (flange), and having excellent brittle crack propagation stopping properties.

In the welded structure described in patent document 2, an unwelded portion remains on the abutting surface of the web and the flange in the cross section of the fillet joint, and the width of the unwelded portion is adjusted so that the ratio X of the sum of the width of the unwelded portion and the thickness of the web and the width of the left and right leg lengths of the fillet portion satisfy a particular relational expression with respect to the brittle crack propagation stopping performance Kca of the joined members (flanges). Thus, even when a thick material having a plate thickness of 50mm or more is used as the member to be joined (flange), propagation of the brittle crack occurring in the joining member (web) can be stopped at the abutting surface between the web and the flange of the fillet portion, and propagation of the brittle crack to the member to be joined (flange) can be prevented.

Patent documents 3 to 5 also describe a welded structure having a fillet joint formed by fillet-welding a joining member (web) to a member to be joined (flange), and having excellent brittle crack propagation stopping properties.

Patent document 3 describes a welded structure having a fillet length or a weld width formed by butting an end face of a joining member against a surface of a member to be joined having a plate thickness of 50mm or more and joining the joining member and the member to be joined by fillet weldingAt least one of the members is a fillet joint of 16mm or less, wherein the fillet joint has an unwelded portion that is 95% or more of a plate thickness tw of a joining member in a cross section of the fillet joint on a surface of the fillet joint that abuts an end surface of the joining member and a surface of a member to be joined, and the fillet joint further has a Charpy impact test fracture transition critical temperature vTrs of a fillet metal that satisfies vTrs ≦ 1.5tf +70 in a relationship with the plate thickness tf of the member to be joined, and/or an absorption energy vE at a Charpy impact test temperature of-20 ℃ of the fillet metal_-20(J) Satisfies vE in the relation with the plate thickness tf of the joined member_-20Fillet weld metal of not less than 2.75 tf-105.

In addition, if the welded structure is used, the propagation of a brittle crack occurring in the members to be joined can be prevented by the fillet metal before the member to be joined is broken in a large scale.

Patent document 4 describes a welded structure including a fillet joint in which at least one of a fillet length and a weld width is 16mm or less, the fillet length and the weld width being formed by abutting an end surface of a joining member with a surface of a member to be joined having a plate thickness of 50mm or more and joining the joining member and the member to be joined by fillet welding, wherein the fillet joint has an unwelded portion that is 95% or more of a plate thickness tw of a joining member in a cross section of the fillet joint on a surface of the fillet joint that abuts an end surface of the joining member and a surface of a member to be joined, and further has a Charpy impact test fracture transition critical temperature vTrs of a fillet metal in the fillet joint that satisfies vTrs (. degree. C.). ltoreq.1.5 tf +90 in relation to the plate thickness tf of the member to be joined, and/or an absorption energy vE at a test temperature of the Charpy impact test of the fillet metal of-20 ℃._-20(J) In the relationship with the plate thickness tf of the joined member, vE is satisfied when tf is 50. ltoreq. tf (mm). ltoreq.53_-20Not less than 5.75, in tf (mm)>53 satisfied vE_-20(J) 2.75tf-140 or more, and a joint member having a brittle crack propagation-stopping toughness Kca of 2500N/mm at a common temperature^2/3The steel sheet is formed as described above.

By providing such a welded structure, propagation of a brittle crack can be stopped at the fillet portion or the base material of the joined member.

Patent document 5 describes a welded structure including a fillet joint in which at least one of a fillet length and a weld width, which is formed by abutting an end surface of a joining member with a surface of a member to be joined having a plate thickness of 50mm or more and joining the joining member and the member to be joined by fillet welding, is 16mm or less, wherein both the joining member and the member to be joined are members having a butt-welding head portion, and a weld metal of the butt-welding head portion has a value of-65 ℃ or less in vTrs and/or a value of vE or less_-20The fillet weld joint has a toughness of 140J or more, wherein a weld end face of a butt weld head portion of a joining member and a weld surface of a butt weld head portion of a member to be joined are butted against each other, and the butted surfaces have an unwelded portion of 95% or more of a plate thickness tw of the joining member in a butt weld joint cross section of the fillet weld joint, and further have a Charpy impact test fracture transition critical temperature vTrs of a fillet metal in the fillet weld joint which satisfies vTrs (. degree.C.) or less-1.5 tf +90 in a relation to a plate thickness tf of the member to be joined, and/or an absorption energy vE at a Charpy impact test temperature of the fillet metal of-20 DEG C_-20(J) In the relation with the plate thickness tf of the joined members, vE is satisfied in the case of 50. ltoreq. tf (mm). ltoreq.53_-20≧ 5.75, at tf (mm)>53 satisfied vE_-20(J) Fillet weld metal of not less than 2.75 tf-140.

By providing such a welded structure, the brittle crack can be stopped at the fillet portion or the base material of the joining member.

In addition, by providing such a welded structure, propagation of a brittle crack generated from the welded portion of the members to be joined or a brittle crack generated from the welded portion of the joining members can be prevented by the fillet portion, the welded portion of the joining members, or the welded portion of the members to be joined.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 2004-232052

Patent document 2: japanese patent laid-open publication No. 2007-326147

Patent document 3: japanese patent No. 5395985

Patent document 4: japanese patent No. 5365761

Patent document 5: japanese patent No. 5408396

Non-patent document

Non-patent document 1: japan society for shipbuilding research 147 research department: "research on evaluation of brittle fracture Strength of high tensile Steel plate Large input Heat Joint for Ship's Hull", No. 87 (2.1978), p.35-53, Japan Ship building research Association

Non-patent document 2: shankouxin, etc.: development of ultra-large container ship-practical application of new high-strength extremely-thick steel plate ", journal of the oceanographic institute of ship, No. 3 (2005), p.70-76, and No. 11 months in 17 years

Non-patent document 3: the 169 th committee of the Japan Ship building research Association reports (the relevant research on the design of destruction management control of hull structures-report (1979), p.118 to 136, the 169 th committee of the Japan Ship building research Association)

Disclosure of Invention

Problems to be solved by the invention

However, since the aggregate used as the reinforcing material in the technique described in patent document 1 is a steel sheet having a desired structure formed therein, a complicated process is required, productivity is reduced, and it is difficult to stably secure a steel sheet having a desired structure.

The technique described in patent document 2 is intended to prevent a brittle crack generated in a joining member (hereinafter, also referred to as a web) by a combination of structural discontinuity and a brittle crack propagation stopping performance of a member to be joined (hereinafter, also referred to as a flange). However, as shown in non-patent document 3, it was experimentally confirmed that it is generally more difficult to stop propagation of a brittle crack generated at a joined member (flange) of a fillet joint through a joining member (web) than to stop propagation of a brittle crack generated at a joining member (web) through a joined member (flange).

The reason for this is not clearly understood, but one of the reasons is that the fracture driving force (stress expansion coefficient) when the crack is punched into the T-joint portion is increased when punching into the joining member (web) as compared with when punching into the joined member (flange).

In this case, in the technique described in patent document 2, since the brittle crack propagation stopping characteristics and the like of the joining member (web) are insufficient, it cannot be said that the propagation of the brittle crack generated in the joined member (flange) is stopped by the joining member (web). That is, the technique described in patent document 2 cannot be said to have sufficient crack propagation stopping characteristics for a case where a brittle crack occurring in a strong deck (corresponding to a flange) of a large container ship, which is assumed in the "brittle crack arrest design guideline for NK ship class" (established in 9 months 2009), propagates to a hatch edge coaming (corresponding to a web).

In the techniques described in patent documents 3 to 5, since it is necessary to limit the fillet length (or the weld width) to 16mm or less, the limit of the maximum plate thickness to which the joining member (web) and the joined member (flange) are applied is 80mm from the viewpoint of ensuring the strength of the fillet portion. However, in recent large container ships, the thickness of members has been further increased, and steel materials having a thickness of 100mm have been applied. In the case of such a thick member exceeding 80mm, there is a problem that the techniques described in patent documents 3 to 5 are hardly applicable.

Even when the thickness of the member is less than 80mm, since the variation in leg length of the fillet portion is large during actual construction on site, there is a problem that great labor is required for construction management on site and additional cost such as correction is increased while securing the strength of the fillet portion (securing the fillet length) and securing the brittle crack-arresting performance (limiting the fillet length to 16mm or less) is satisfied.

The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a welded structure having excellent brittle crack propagation stopping characteristics, in which propagation of a brittle crack occurring in a member to be joined (flange) to a joining member (web) and propagation of a brittle crack occurring in a joining member (web) to a member to be joined (flange) can be stopped (stopped) before massive fracture occurs.

Means for solving the problems

In order to achieve the above object, the present inventors have studied a measure for reducing variation in leg length of a fillet portion during the application of the fillet portion to stop brittle cracks.

As a result, it is conceivable that the basic welding structure is changed from the conventional fillet welding structure to a fillet welding structure with a double-component member in which the double-component member is provided between the joining member and the joined member, and propagation of the brittle crack is prevented by the fillet metal portion of the double-component member and the joined member. In the case of this fillet welding structure, the construction of the fillet welding portion for stopping the brittle crack can be performed in a factory. In addition, it is expected that the variation in leg length of the fillet portion is likely to fall within a predetermined range, and this is associated with a significant reduction in actual construction cost on site.

In addition, it is expected that the joining of the joining member and the double-layered member performed on the spot where the construction management is strict can butt the end face of the joining member and the surface of the double-layered member, and the joining can be performed under welding conditions (partial penetration, complete penetration, and the like) where the construction management is easy.

The present inventors have also studied various factors that affect the brittle crack propagation stopping characteristics of the fillet welded structure with the double-component.

As a result, it is thought that, in order to prevent (stop) propagation of a brittle crack occurring from a member to be joined (flange), a discontinuous portion is secured on the overlapping surface of the member to be joined (flange) and the doubled member, and in view of a case where the energy release rate (crack progression driving force) of the brittle crack tip increases when the plate thickness tf (mm) of the member to be joined (flange) increases, and the brittle crack is hard to stop, improvement of toughness of the fillet portion associated with the plate thickness tf (mm) of the member to be joined (flange) becomes necessary.

Further, since propagation of a brittle crack becomes easy when the leg length or the weld width of the fillet portion becomes long, it is expected that the toughness of the fillet metal needs to be secured in accordance with the leg length (or the weld width).

On the other hand, the following is also foreseen: the propagation of the brittle crack from the joining member (web) is often more easily stopped than the propagation of the brittle crack from the joined member (flange), but when the plate thickness td of the double member is increased by 2 times or more with respect to the plate width Wd of the double member, the propagation of the brittle crack from the joining member (web) is more difficult to stop than the propagation of the brittle crack from the joined member (flange).

The present invention has been completed through further studies based on the above findings.

That is, the gist of the present invention is as follows.

(1) A welded structure having excellent brittle crack propagation stopping characteristics, wherein the welded structure is a fillet welded structure with a doubled member, which is provided with a fillet welded joint formed by butt-welding an end face of a joining member to a surface of the doubled member and fillet-welding the doubled member to a surface of a member to be joined having a plate thickness of 50mm or more, wherein an unwelded portion that is 95% or more of a plate width Wd of the doubled member in a cross section of the fillet welded joint is provided on an overlapping surface of the doubled member and the surface of the member to be joined, and wherein a ratio td/Wd of the plate thickness td of the doubled member to the plate width Wd satisfies the following expression (1a), and wherein a fillet metal of the fillet welded joint is set to the following fillet metal: this fillet metal has a charpy impact test fracture transition critical temperature vTrs (° c) that corresponds to the fillet length or the weld width L and satisfies the following expression (1b) or the following expression (1c) in a relationship with the plate thickness tf and the fillet length or the weld width L of the joined members.

td/Wd<2‥‥(1a)

When L is not less than 20mm, vTrs is not more than-5L +65-1.5(tf-75) as storage medium (1b)

In the case that L <20mm, vTrs is less than or equal to-35-1.5 (tf-75) as storage media (1c)

Here, vTrs: the Charpy impact test fracture transition critical temperature (. degree. C.) of fillet weld metal,

tf: the plate thickness (mm) of the joined members,

td: the thickness (mm) of the plate of the member is doubled,

and Wd: doubling the board width (mm) of the member,

l: fillet length or deposition width (mm),

l is smaller one of the fillet length and the deposition width, and L is 17mm or more.

(2) The welded structure according to (1), wherein the joined member has a pair of weld heads in a direction intersecting the joining member.

(3) The welded structure according to (2), wherein the joining member has a butt weld head portion, and the joining member is provided so that the butt weld head portion of the joining member intersects with the butt weld head portion of the joined member.

Effects of the invention

According to the present invention, it is possible to stop or stop both propagation of a brittle crack to a joined member (web) which is generated in a joined member (flange) made of a thick steel plate having a plate thickness of 50mm or more and a plate thickness exceeding 80mm, which has been difficult in the past, and propagation of a brittle crack to a joined member (flange) which is generated in the joined member (web), before the brittle crack reaches massive fracture.

Therefore, according to the present invention, the risk of large-scale brittle fracture such as separation of the hull of a steel structure, particularly a large container ship, a bulk carrier, or the like, can be avoided, and a large effect can be obtained in securing the safety of the hull structure, and a special effect is exhibited industrially.

In addition, according to the present invention, the following effects are also provided: by adjusting the size of the double-component and the toughness of the fillet metal during the construction, a welded structure having excellent brittle crack propagation stopping characteristics can be easily manufactured without using a special steel plate and without impairing safety.

Drawings

Fig. 1 is an explanatory view schematically illustrating a sectional structure of a corner joint. Fig. 1(a) shows a case where the joining member (web) 1 is orthogonal to the doubling member 10 and the member to be joined (flange) 2, and fig. 1(b) shows a case where the joining member (web) 1 obliquely intersects the doubling member 10 and the member to be joined (flange) 2.

Fig. 2 is an explanatory view schematically showing another example of the structure of the corner joint. Fig. 2(a) is an external view, and fig. 2(b) is a sectional view.

Fig. 3 is an explanatory view schematically showing another example of the structure of the corner joint. Fig. 3(a) is an external view, and fig. 3(b) is a sectional view.

Fig. 4 is an explanatory view schematically showing the shape of an ultra-large-sized structure model test body for brittle cracks generated and propagated from joined members (flanges) used in the examples. Fig. 4(a) shows a case where the joined member (flange) 2 is formed only of a steel plate base material, fig. 4(b) shows a case where the joined member (flange) 2 has a butt weld head, and fig. 4(c) shows a case where the joining member (web) 1 and the joined member (flange) 2 have a butt weld head.

Fig. 5 is an explanatory view schematically showing the shape of an ultra-large-sized structure model test body for brittle cracks generated and propagated from a joining member (web) used in the examples. Fig. 5(a) shows a case where the joining member (web) 1 is composed of only a steel plate base material, fig. 5(b) shows a case where the joining member (web) 1 has a butt weld head, and fig. 5(c) shows a case where the joining member (web) 1 and the joined member (flange) 2 have a butt weld head.

Detailed Description

The present invention will be described in detail below.

A welded structure is provided with a fillet joint which is formed by butting an end face of a joining member 1 against a surface of a doubled member 10, joining the joining member 1 to the doubled member 10, overlapping the doubled member 10 with a surface of a member to be joined 2 having a plate thickness of 50mm or more, and joining the members by fillet welding. This welded structure is provided with a fillet joint having a fillet metal 5 with a fillet length 3 or a weld width 13 of Lmm, and an unwelded portion 4 serving as a structural discontinuity is present on the overlapping surface of a doubled-up member 10 and a joined member (flange) 2 of this fillet joint. In the welded structure of the present invention, the abutting surface that abuts the end surface of the joining member 1 and the surface of the doubled member 10 may include a structural discontinuity.

This state is shown in fig. 1 in the joint cross section. Fig. 1(a) shows a case where the joining member (web) 1 is attached upright to the joined member (flange) 2, but the present invention is not limited to this. For example, as shown in fig. 1(b), the joining member (web) 1 may be attached to the member to be joined (flange) 2 at an inclination angle θ.

As described above, the welded structure of the present invention has the unwelded portion 4 having a discontinuous structure at the overlapping surface of the doubled member 10 and the joined member (flange) 2. In the welded structure of the present invention, the overlapping surface of the doubled member 10 and the joined member (flange) 2 becomes a propagation surface of a brittle crack, and therefore, in the present invention, the unwelded portion 4 is present in the overlapping surface. Due to the existence of the unwelded portion 4, the energy release rate (crack progression driving force) of the tip of the brittle crack propagating through the joining member (web) 1 or the joined member (flange) 2 is reduced, and the brittle crack is likely to stop at the overlapping surface.

Therefore, in the present invention, the fillet metal 5 is formed so as to maintain the toughness at or above the predetermined level, and the brittle crack is stopped by the fillet metal 5.

It is rare that brittle cracks are generated in a steel sheet base material portion having few defects. Most of the brittle fracture accidents in the past occurred in the welded portion. Therefore, for example, in a fillet joint as shown in fig. 2 in which the member to be joined (flange) 2 is a steel plate joined by the butt joint 22 and the joining member (web) is fillet-welded so as to intersect the welded portion (pair-welded head portion) 22 of the butt joint, or in a fillet joint as shown in fig. 3 in which the joining member (web) 1 and the member to be joined (flange) 2 are both steel plates having the pair-welded

head portions

12 and 22 and the butt joint portion 22 of the member to be joined (flange) 2 intersects the pair-welded head portion 12 of the joining member (web) 1, it is important that there is a discontinuous portion of the structure in order to prevent propagation of a brittle crack generated from the butt

joint portion

12 or 22.

Therefore, in the present invention, an unwelded portion (structural discontinuous portion) 4 is present on the overlapping surface of the joined member and the doubled member of the fillet portion.

Fig. 2(a) shows the appearance of the corner joint, and fig. 2(b) shows the cross-sectional shape of the weld head portion 22. Fig. 3 shows a corner joint in which the butt weld joint portion 22 of the joined member (flange) 2 and the butt weld joint portion 12 of the joining member (web) 1 intersect each other when both the joining member (web) 1 and the joined member (flange) 2 are steel plates having the butt weld

joint portions

12 and 22. Fig. 3(a) shows the appearance of the corner joint, and fig. 3(b) shows the joint cross-sectional shape for the

weld head portions

12, 22.

In fig. 2 and 3, the butt joint part 22 is shown as being perpendicular to the web 1, but the present invention is not limited thereto. Of course, the crossing may be inclined.

The method for producing the welded structure is not particularly limited, and any common production method can be applied. For example, the welded structure may be manufactured by butt-welding steel plates for flanges and steel plates for webs, and fillet-welding the obtained butt-welded joint via a double member. Further, a welded structure may be manufactured by temporarily welding a pair of web steel plates before butt welding to a double member on the flange surface, butt welding the web steel plates to each other, and welding the obtained butt joint to the flange.

In the present invention, in order to suppress propagation of a brittle crack, the size of the unwelded portion 4 of the cross section of the fillet joint is set to 95% or more of the doubled member width Wd. If the dimension (width B)16 of the unwelded portion 4 is less than 95% of the doubled member width Wd, plastic deformation of the fillet metal is suppressed, and the vicinity of the crack tip of the brittle crack that has been punched into the fillet metal becomes highly stressed, making it difficult to stop or arrest the brittle crack. Therefore, in order to suppress propagation of the brittle crack, the dimension (width B)16 of the unwelded portion 4 is limited to 95% or more of the doubled member width Wd. It is preferable that the content is 96% or more and 100% or less.

In the present invention, the size of the doubling member is adjusted so that the ratio td/Wd of the plate thickness td of the doubling member to the plate width Wd of the doubling member satisfies the following expression (1 a).

td/Wd<2‥‥(1a)

When the plate thickness td of the double component and the plate width Wd of the double component do not satisfy the expression (1a), it is more difficult to stop or prevent propagation of the brittle crack generated from the joining member (web) than propagation of the brittle crack generated from the joined member (flange), and propagation of the brittle crack generated from the joining member (web) and the joined member (flange) cannot be stopped or prevented together.

When td/Wd is too small, there is a problem that the longitudinal rigidity of the double member decreases, and therefore the lower limit value of td/Wd is preferably set to 0.2.

Further, in the present invention, the toughness of the fillet metal is adjusted as follows: the following expression (1b) or the following expression (1c) is satisfied in the relation between the plate thickness tf and the fillet length or the welding width L of the joined members according to the fillet length or the welding width L.

(here, vTrs: Charpy impact test fracture transition critical temperature (. degree. C.) of fillet metal, tf: plate thickness (mm) of joined member, L: fillet foot length or weld width (mm))

In addition, L is smaller of the fillet length and the welding width.

The toughness of the fillet metal is related to the plate thickness tf and the fillet length L of the joined member (flange), and by satisfying the above-described expression (1b) or expression (1c), a welded structure in which the plate thicknesses of the joined member (flange) and the joined member (web) are 50mm or more can be formed as a welded structure in which a desired brittle crack propagation preventing performance is ensured. When the toughness of the fillet metal does not satisfy the above-described expression (1b) or expression (1c), the toughness of the fillet metal is insufficient, and a brittle crack generated and propagated in the joined member (flange) or the joined member (web) cannot be prevented by the fillet metal portion.

In this way, if the double-layered member satisfies the above expression (1a) and the fillet metal satisfies the above expression (1b) or (1c) in the relation with the plate thickness tf and the fillet length (weld width) L of the joined member (flange), the propagation of the brittle crack occurring in the joined member (flange) and the brittle crack occurring in the joined member (web) can be prevented at the same time by the fillet metal.

The welded structure of the present invention is provided with the above-described corner joint, and can be applied to, for example, a hull structure of a ship in which a hull outer plate is a flange and a bulkhead is a web, a hull structure of a ship in which a deck is a flange and a hatch is a web, or the like.

Examples

The present invention will be described in detail below based on examples.

Large welded structural joints having actual structural dimensions and shapes shown in fig. 4(a), (b), and (c) and fig. 5(a), (b), and (c) were manufactured by using thick steel plates having plate thicknesses shown in tables 1-1 and 1-2 as a joining member (web), a doubling member, and a member to be joined (flange). Fig. 4(a), (b), and (c) are diagrams assuming the occurrence and propagation of a brittle crack from a joined member (flange), and fig. 5(a), (b), and (c) are diagrams assuming the occurrence and propagation of a brittle crack from a joining member (web). In the manufactured corner joint, the unwelded portion 4 as shown in fig. 1(a) exists in the butt surface between the doubled member 10 and the joined member 2 by changing the ratio Y of unwelded portions (width B of unwelded portion/plate width Wd of doubled member)). No unwelded portion remains on the abutting surface of the joining member (web) and the doubled member.

In the case of fig. 4, the joined members (flanges) are made of a thick steel plate (base material only) (fig. 4 a) or a thick steel plate with a butt joint (fig. 4 b), and the joining members (webs) are made of a thick steel plate (base material only) (fig. 4 a and b) or a thick steel plate with a butt joint (fig. 4 c). Similarly, the joining member (web) in the case of fig. 5 is also a thick steel plate (base material only) (fig. 5(a)) or a thick steel plate with butt joints (fig. 5(b)), and the joined member (flange) is a thick steel plate (base material only) (fig. 5(a), (b)) or a thick steel plate with butt joints (fig. 5(b))A thick steel plate with butt joints (fig. 5 (c)). Note that the butt weld joint was subjected to 1-pass high heat input electrogas welding (1 electrode EGW, 2 electrode EGW, SEGARC, 2 electrode SEGARC) or multi-layer CO₂And welding to manufacture.

The fillet joint is formed as a fillet metal fillet joint having various toughness, various fillet leg lengths, and deposition widths by changing welding conditions such as welding materials, welding input heat, and shielding gas. The fillet leg length and the deposition width are average values of both sides. Regarding the toughness of the fillet metal, charpy impact test pieces (10mm thick) were selected from the fillet metal or a butt welded joint manufactured under the same conditions as in fillet welding, and fracture transition critical temperature vTrs (deg.c) was determined in accordance with the regulations of JIS Z2242.

Using the obtained large-sized corner joint, an ultra-large-sized structural model test body shown in fig. 4 and 5 was manufactured, and a brittle crack propagation arrest test was performed. The ultra-large-sized structural model test body of fig. 4 was welded by tack welding 8 between the members (flanges) 2 to be joined and steel plates having the same plate thickness, under the members (flanges) 2 to be joined of the double-sided large-sized corner joint 9. The ultra-large structure model test body of fig. 5 was welded by tack welding 8 to a steel plate having the same plate thickness as the joining member (web) 1 of the large fillet joint 9 with an enlarged scale under the joining member (web) 1.

Then, the tip of the mechanical notch 7 is processed into a base material of the joining member (web) 1 or the joined member (flange) 2, a fused (BOND) portion of the butt

joint portions

12 and 22, or the weld metal WM.

In the brittle crack propagation stop test, a shock was applied to the mechanical notch to generate a brittle crack, and whether or not the propagating brittle crack stopped at the fillet portion was examined.

All the tests are carried out under the test stress of 100-283N/mm²And the temperature is-10 ℃. Test stress 100N/mm²Is the average of the stresses acting stably on the hull, test stress 257N/mm²Is suitable for the yield strength of the ship body of 390N/mm²The maximum allowable stress of the grade steel sheet was measured as 283N/mm²Is suitable for the yield strength of 460N/mm of the ship body²The maximum allowable stress of the grade steel plate is equivalent. The temperature-10 ℃ is the design temperature of the ship.

The results obtained are shown in tables 2-1 and 2-2.

[ tables 1-1]

[ tables 1-2]

[ Table 2-1]

[ tables 2-2]

As shown in tables 2-1 and 2-2, in the present example, even when the brittle crack propagates from the joined member (flange) or from the joining member (web), the crack breaks into the fillet metal of the fillet portion and stops.

On the other hand, in the comparative examples which do not depart from the scope of the present invention, when a brittle crack is propagated from a joined member (flange), or when a brittle crack is propagated from a joining member (web), or both of them, the brittle crack is propagated without stopping at the fillet portion, and the propagation of the brittle crack cannot be stopped by the fillet metal.

Description of the reference symbols

1 joining member (Web)

2 joined component (Flange)

3 feet long

4 unwelded part

5 fillet weld metal

7 mechanical notch

8 temporary welding

9 large-scale angle joint with doubling member

10 doubling element

12 web butt weld joint

13 width of fusion deposit

16 width of non-deposition (B)

22 flange butt joint part

The angle of intersection theta.

Claims

1. A welded structure, wherein,

the welded structure is excellent in brittle crack propagation stopping characteristics, and is a fillet welded structure with a doubled member, which is provided with a fillet welded joint formed by butt-welding an end face of a joining member to a surface of the doubled member and fillet-welding the doubled member to a surface of a member to be joined having a plate thickness of 50mm or more,

the fillet joint has an unwelded portion that is 95% or more of a plate width Wd of the doubled member in a cross section of the fillet joint on an overlapping surface of a surface of the doubled member and a surface of the joined member, and a ratio td/Wd of a plate thickness td of the doubled member to the plate width Wd satisfies the following expression (1a), and the fillet metal of the fillet joint is set to the following fillet metal: the Charpy impact test fracture transition critical temperature vTrs DEG C of the fillet metal corresponds to the fillet leg length or the weld width L and satisfies the following expression (1b) or the following expression (1c) in the relationship with the plate thickness tf of the joined member and the fillet leg length or the weld width L,

td/Wd<2‥‥(1a)

Here, vTrs: the charpy impact test fracture transition critical temperature of fillet weld metal,

tf: the plate thickness of the joined member is mm,

td: the thickness of the plate of the component is doubled by mm,

and Wd: the width of the plate of the member is doubled by mm,

l: the length of the fillet welding foot or the deposition width is mm,

2. The welded structure according to claim 1,

the joined member has a pair of weld heads in a direction intersecting the joining member.

3. The welded structure according to claim 2,

the joining member has a butt weld head portion, and is provided so that the butt weld head portion of the joining member intersects with the butt weld head portion of the member to be joined.