CN109311127B

CN109311127B - Welded structure having excellent brittle crack propagation stopping characteristics

Info

Publication number: CN109311127B
Application number: CN201780036899.4A
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: 2021-03-09
Anticipated expiration: 2037-06-15
Also published as: JP6615215B2; CN109311127A; KR102258423B1; KR20190009414A; PH12018502635A1; WO2017217516A1; JPWO2017217516A1

Abstract

A welded structure is provided with a double-layered member (10) at the joint between a web (1) and a flange (2). The end face of the web is butted against the surface of the doubler, the web is joined to the doubler by fillet welding, the flange surface is overlapped with the surface of the doubler, and the doubler is joined by fillet welding. At this time, the ratio Y (%) of the width of the unwelded portion of the overlapping surface in the joint cross section of the fillet joint to the sum of the sheet width of the doubled member and the leg length of the right and left fillet portions, and the brittle crack propagation arrest toughness (Kca) of the doubled member at the use temperature T (. degree. C.) were set to_T(N/mm^3/2) The relation (c) satisfies that Y (%) > or more {6900-Kca }/85. Thus, propagation of a brittle crack generated from the flange can be stopped or stopped by doubling the member.

Description

Welded structure having excellent brittle crack propagation stopping characteristics

Technical Field

The present invention relates to a welded steel structure formed by welding 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 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. This case implies that it cannot be declared that the brittle fracture has no possibility of propagating straight along the weld.

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 caused by the increase in plate thickness, the weld input heat is welded with a larger input heat, so that the fracture toughness of the weld tends to be further reduced. 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 that a thick steel plate having a special brittle crack propagation stopping property is required particularly for stopping 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 joined 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) and 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) and a member to be joined (flange), and having excellent brittle crack propagation stopping properties.

Patent document 3 describes a welded structure including a fillet joint in which at least one of a fillet length and a weld width, which is obtained by butting an end surface 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 welding, is 16mm or less, wherein a surface of the fillet joint where the end surface of the joining member is butted against the surface of the member to be joined has an unwelded portion of 95% or more of a plate thickness tw of the joining member in a cross section of the fillet joint, and the fillet joint further has a charpy impact test fracture turn of fillet metal in the fillet jointThe variable critical temperature vTrs satisfies vTrs ≦ -1.5tf +70 in the relation with the sheet thickness tf of the joined member, and/or the absorption energy vE at-20 ℃ in the Charpy impact test of 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 of this type, it is possible to prevent the propagation of a brittle crack occurring in the members to be joined by the fillet metal before the large-scale failure is achieved.

Patent document 4 describes a welded structure including a fillet joint in which at least one of a fillet length and a weld width, which is obtained by butting an end surface 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 welding, is 16mm or less, wherein the fillet joint has an unwelded portion that is 95% or more of a plate thickness tw of the 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 the member to be joined, and further has a Charpy impact test fracture transition critical temperature vTrs of the 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_-20≧ 5.75, at 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 length or a weld width of 16mm or more, at least one of which is obtained by butting an end surface 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 weldingA fillet joint wherein the joining member and the member to be joined are both members having a butt weld head part, and the weld metal of the butt weld head part has a value of-65 ℃ or lower in terms of vTrs and/or a value of vE_-20The weld surface of the butt weld joint part of the joining member and the weld surface of the butt weld joint part of the joined member in the fillet joint are butted, and the butted surface has an unwelded part which is 95% or more of the plate thickness tw of the joining member in the butt weld joint cross section of the fillet joint, and the Charpy impact test fracture transition critical temperature vTrs of the fillet metal in the fillet joint satisfies vTrs (DEG C) or less-1.5 tf +90 in the relation with the plate thickness tf of the joined member, and/or the absorption energy vE at the Charpy impact test temperature-20℃ of the fillet metal_-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 joined 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 property of the web is insufficient, it cannot be said that propagation of the brittle crack generated in the flange is stopped by the 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 the fillet length (or the weld width) needs to be limited to 16mm or less, the maximum plate thickness to which the web and the flange are applied is limited to 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 established.

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 flange to a web and propagation of a brittle crack occurring in a web to a flange can be stopped or 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 in the construction of the fillet portion for stopping a brittle crack. As a result, it is conceivable that the basic welding structure is formed from the conventional fillet welding structure into the fillet welding structure with the double member in which the double member is arranged between the web and the flange, and then the double member is attached and joined by fillet welding on the flange surface in the factory. This makes it easy to bring the variation in leg length of the fillet portion within a predetermined range, and is expected to be associated with a significant reduction in actual construction cost on site.

In the joining of the web and the doubled member by fillet welding on the flange surface, which is performed in a factory, it is expected that the end surface of the web and the surface of the doubled member will be butted against each other in the joining of the web and the doubled member performed in a field where construction management is not easy, and construction can be performed by fillet welding, partial penetration, complete penetration, or the like, which is a welding condition easy in construction management, that is, a condition of foot length management or input heat management is relaxed.

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

As a result, it is thought that in order to stop or stop propagation of a brittle crack generated from the flange, it is necessary to secure a structural discontinuity in the overlapping surface of the flange and the doubling member and to improve the brittle crack propagation stopping performance (stopping performance) of the doubling member.

Furthermore, it is also expected that propagation of a brittle crack is facilitated when the length of the structural discontinuity, i.e., the unwelded width, is shortened, and therefore it is necessary to set the blocking performance of the doubling member to a performance corresponding to the length of the structural discontinuity (unwelded width).

The present inventors have also found that in order to prevent a brittle crack generated from a flange from propagating to a web and to prevent the brittle crack from propagating in a double component, the ratio Y (%) of an unwelded portion remaining on the overlapping surface of the flange and the double component and the prevention performance of the double component need to satisfy a specific relationship. The ratio Y of unwelded portions is defined by the following equation.

Y (%): { (width of unwelded portion of overlapping surface of the doubled member and the flange in the joint cross section of the fillet joint)/(sum of plate width of the doubled member and leg length of the left and right fillet portions) } × 100 and, as a specific relationship, the following expression (2) was found.

Y(％)≥{6900-(Kca)_T}/85‥‥(2)

(Here, (Kca)_T: brittle crack propagation arrest toughness (N/mm) using a doubled member at temperature T (DEG C)^3/2))

On the other hand, in order to stop or stop the propagation of the brittle crack generated from the web, it is conceivable that a structural discontinuity must be secured also at the abutting surface of the web and the doubling member, and the brittle crack propagation stopping performance (stopping performance) of the doubling member must be improved.

Furthermore, it is also expected that propagation of a brittle crack is facilitated when the length of the structural discontinuity (the width of the unwelded portion) is shortened, and therefore, it is necessary to make the performance of inhibiting the doubling member to a performance corresponding to the length of the structural discontinuity, that is, the width of the unwelded portion. It is also expected that if the performance of preventing the double component is excellent, the unwelded portion may not be necessary.

The present inventors have found that the ratio X (%) of the unwelded portion remaining at the abutting surface between the web and the doubled member and the prevention performance of the doubled member need to satisfy a specific relationship in order to prevent a brittle crack generated from the web from propagating to the flange and to prevent the brittle crack from propagating in the doubled member. The ratio X (%) of unwelded portions is defined by the following equation.

X (%): in { (width of unwelded portion of abutting surface of the doubled member and the web in the joint cross section of the fillet joint)/((sum of plate thickness of the web and leg length of the fillet portion on the left and right) } × 100, it should be noted that X (%) includes 0%.

Further, the following expression (1) was found as a specific relationship.

X(％)≥{5900-(Kca)_T}/85‥‥(1)

Further, it has been found that if the double-walled member is an austenitic steel (high Mn steel, austenitic stainless steel, etc.) or a nickel steel plate for low temperature use (3.5% Ni steel, 5% Ni steel, 7% Ni steel, 9% Ni steel), even if the above formula (1) and/or formula (2) is not satisfied, the large brittle crack propagating from the web or the flange can be stopped in the double-walled steel plate.

In the welded structure, it has been found that the grown brittle crack is more likely to be stopped by setting the height (gap) of the unwelded portion of the overlapping surface of the doubled member and the flange to 5mm or more.

The present invention has been completed based on the above findings and further research.

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

(1) A welded structure comprising a double-layered member provided at a butt joint portion between a web and a flange,

the welded structure is a welded structure having excellent brittle crack propagation stopping characteristics, which is formed by fillet-welding the doubled member to the web and the flange,

the welded structure includes a fillet joint in which the web is fillet welded to the doubled member in a butt joint manner and a non-welded portion remains on the butt joint surface, and/or the doubled member is fillet welded to the flange in an overlapping manner and a non-welded portion remains on the overlapping surface,

a ratio Y (%) of the unwelded portion defined as below remaining on an overlapping surface of the doubled member and the flange in a joint cross section of the fillet joint, and a brittle crack propagation arrest toughness (Kca) of the doubled member at a use temperature T (DEG C)_T(N/mm^3/2) Satisfies the following formula (2).

Y (%): { (width of unwelded portion of overlapping surface of doubled member and flange in joint cross section of fillet joint)/(sum of plate width of doubled member and leg length of fillet weld portion on left and right) } × 100

Y(％)≥{6900-(Kca)_T}/85‥‥(2)

Here, (Kca)_T: brittle crack propagation arrest toughness (N/mm) using a doubled member at temperature T (DEG C)^3/2)

(2) The welded structure according to claim 1, wherein the web, the flange, and the doubling member have plate thicknesses of 50mm or more.

(3) According to the welded structure of claim 1,

a ratio X (%) (including 0%) of the unwelded portion defined below remaining at a butt surface between the doubled member and the web in a joint cross section of the fillet joint, and a brittle crack propagation arrest toughness (Kca) of the doubled member at a use temperature T (DEG C)_T(N/mm ^3/2) Satisfies the following formula (1).

X (%): { (width of unwelded portion remaining at abutting surface of web and doubled member in joint cross section of fillet joint)/(sum of plate thickness of web and leg length of right and left fillet weld portion) } × 100

X(％)≥{5900-(Kca)_T}/85‥‥(1)

(4) According to the welded structure of claim 2,

a ratio X (%) (including 0%) of the unwelded portion defined below remaining at a butt surface between the doubled member and the web in a joint cross section of the fillet joint, and a brittle crack propagation arrest toughness (Kca) of the doubled member at a use temperature T (DEG C)_T(N/mm^3/2) Satisfies the following formula (1).

X(％)≥{5900-(Kca)_T}/85‥‥(1)

(5) The welded structure according to any one of claims 1 to 4, wherein the flange has a butt-welded head portion so as to intersect the web, or the web has a butt-welded head portion so as to intersect the flange.

(6) The welded structure according to claim 5, wherein the web has a butt-welded head portion, and the web is disposed so that a butt-welded joint portion of the web intersects a butt-welded joint portion of the flange.

(7) The welded structure according to the above 1 or 2, wherein the doubled member is an austenitic steel or a nickel steel sheet for low temperature use.

(8) The welded structure according to any one of claims 1 to 4, wherein a height (gap) of an unwelded portion of an overlapping surface of the doubled member and the flange is 5mm or more.

(9) The welded structure according to the above 5, wherein a height (gap) of an unwelded portion of an overlapping surface of the doubled member and the flange is 5mm or more.

(10) The welded structure according to the above 6, wherein a height (gap) of an unwelded portion of an overlapping surface of the doubled member and the flange is 5mm or more.

(11) The welded structure according to the above 7, wherein a height (gap) of an unwelded portion of an overlapping surface of the doubled member and the flange is 5mm or more.

Effects of the invention

According to the present invention, propagation of a brittle crack to a web, which has been difficult to achieve in a flange formed of a thick steel plate having a thickness of 50mm or more and a thickness exceeding 80mm, propagation of a brittle crack to a flange, which has occurred in a web, or both can be stopped or stopped before the brittle crack reaches a large-scale 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.

Further, according to the present invention, by adjusting the size of the unwelded portion remaining on the overlapping surface between the doubled member and the flange at the time of construction and selecting the doubled member having the brittle crack propagation stop characteristic corresponding to the size of the unwelded portion, it is possible to easily manufacture a welded structure having excellent brittle crack propagation stop characteristic without using a large amount of special steel plates and without impairing safety. This effect is also similar to the unwelded portion remaining on the abutting surface between the doubling member and the web.

Drawings

Fig. 1 is an explanatory view schematically illustrating a sectional structure of a corner joint. Fig. 1(a) shows a case where the web 1 is orthogonal to the doubled member 10 and the flange 2, fig. 1(b) shows a case where the web 1 obliquely crosses the doubled member 10 and the flange 2, and fig. 1(c) shows a case where the unwelded portion height (gap) 14 of the overlapping surface of the doubled member 10 and the flange 2 is 5mm or more.

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 a flange used in the examples. Fig. 4(a) shows a case where the flange 2 is formed only of a steel plate base material, fig. 4(b) shows a case where the flange 2 has a butt weld head portion, and fig. 4(c) shows a case where the web 1 and the flange 2 have a butt weld head portion.

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 web, which is used in the examples. Fig. 5(a) shows a case where the web 1 is formed only of a steel plate base material, fig. 5(b) shows a case where the web 1 has a butt weld head portion, and fig. 5(c) shows a case where the web 1 and the flange 2 have a butt weld head portion.

Detailed Description

The present invention will be described in detail below.

The welded structure of the present invention is formed by providing a double-layered member 10 at the butt joint portion between a web 1 and a flange 2. The welded structure of the present invention is a welded structure in which the surface of a doubled member 10 is overlapped with the surface of a flange 2, the doubled member 10 is joined to the flange 2 by fillet welding, the end face of a web 1 is butted against the surface of the doubled member 10, and the doubled member 10 is joined to the web 1 by fillet welding. In the welded structure of the present invention, the web 1, the flange 2, and the doubling member 10 are all made of thick steel having a thickness of 50mm or more.

The welded structure of the present invention includes a fillet joint in which a flange 2 and a double member 10 are joined by fillet welding, the double member 10 and a web 1 are joined by fillet welding, and

fillet metals

5 and 51 are provided respectively. Further, unwelded portions 4 as structural discontinuities are present on the overlapping surfaces of the flange 2 and the doubled member 10 and/or the abutting surfaces of the doubled member 10 and the web 1.

This state is shown in fig. 1 in the joint cross section. Fig. 1(a) shows a case where the web 1 is mounted upright on the flange 2, but the present invention is not limited thereto. For example, as shown in fig. 1(b), the web 1 may be attached to the flange 2 at an angle θ. As shown in fig. 1 c, the unwelded portion height (gap) 14 of the overlapping surface of the double-layered member 10 and the flange 2 may be set to 5mm or more.

In the welded structure of the present invention, the overlapping surface of the flange 2 and the doubled member 10 and the abutting surface of the doubled member 10 and the web 1 become propagation surfaces of brittle cracks. Therefore, in the present invention, the unwelded portion 4 is present on the overlapping surface of the flange 2 and the doubled member 10 and/or the abutting surface of the doubled member 10 and the web 1. The energy release rate (crack progression driving force) of the tip of the brittle crack propagating through the web 1 or the flange 2 is reduced by the presence of the unwelded portion 4, and the brittle crack is likely to stop at the overlapping surface or the abutting surface. In the present invention, the following may be the case: when the direction of the brittle crack is from the web, the unwelded portion 4 only needs to remain on the abutting surface, and when the direction of the brittle crack is from the flange, the unwelded portion 4 only needs to remain on the overlapping surface.

In the present invention, the doubling member 10 is disposed between the flange 2 and the web 1, and the unwelded portion 4 remains as described above, and the doubling member 10 is formed as a member that maintains a predetermined or more prevention performance. Thereby, the brittle crack stops at the doubling member 10.

It is rare that brittle cracks occur in a steel sheet base material portion having few defects. Most of the brittle fracture accidents in the past are generated in the welded portion. Therefore, for example, in a fillet welded joint in which the flange 2 is a steel plate formed by joining the weld head portion 11 as shown in fig. 2 and the web 1 is fillet welded so as to intersect the weld portion (the butt weld head portion) 11 of the butt welded joint, it is important that the structure is discontinuous first to prevent propagation of a brittle crack generated from the butt weld portion 11. Therefore, in the present invention, the unwelded portion 4 is present at the overlapping surface of the flange 2 and the double-walled member 10 at the fillet portion.

Fig. 2(a) shows the appearance of the corner joint, and fig. 2(b) shows the joint cross-sectional shape of the weld head portion 11.

As shown in fig. 3, in a fillet welded joint in which the web 1 is a steel plate having a butt weld head portion 12 and the flange 2 is a steel plate having a butt weld head portion 11, and fillet welding is performed so that the butt weld portion 11 of the flange 2 and the butt weld portion 12 of the web 1 intersect each other, it is important that the structure is also discontinuous in order to prevent propagation of brittle cracks generated from the butt weld portion 11 or the butt weld portion 12. Therefore, in the present invention, unwelded portions 4 are present on the overlapping surface of the flange 2 and the doubled member 10 at the fillet portion and on the abutting surface of the web 1 and the doubled member 10, respectively. However, the unwelded portion 4 between the web 1 and the doubled member 10 had a brittle crack propagation-stopping toughness of 5900N/mm in the doubled member 10^3/2The above is not essential.

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

weld head portions

11 and 12.

In fig. 2 and 3, the butt-welded joint 11 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 ordinary 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 prevent a brittle crack generated from a flange from propagating to a web and stopping the brittle crack in a doubling member, the ratio Y (%) of an unwelded portion remaining on the overlapping surface of the flange and the doubling member and the stopping performance of the doubling member are adjusted so as to satisfy the following expression (2).

Y(％)≥{6900-(Kca)_T}/85‥‥(2)

(Here, (Kca) T: brittle crack propagation arrest toughness (N/mm) of the doubled member at the use temperature T (. degree. C.))^3/2) The following expression (2)' is preferable.

Y(％)≥{7900-(Kca)_T}/85‥‥(2)′

Here, the ratio Y (%) is defined by the following formula.

Y (%): { (Width B of unwelded portion of overlapping surface of doubled member and flange in joint cross section of Angle Joint_F) /(width D of the plate of the doubled member)_WLength l of leg of left and right fillet weld_FSum) } × 100 in fig. 1, the width of the unwelded portion 4 of the overlapping surface of the doubled member and the flange in the joint cross section of the corner joint is represented by B_FThe leg length of the fillet weld portion is represented by_FAnd (4) showing.

The ratio Y (%) of unwelded portions remaining on the overlapping surface and the double component at the use temperature T (DEG C)Brittle crack propagation arrest toughness (Kca)_TIf the formula (2) is not satisfied, brittle cracks generated from the flange cannot be prevented in the double member.

Here, as the brittle crack propagation arrest toughness Kca of the doubled member used herein, the brittle crack propagation arrest toughness Kca at the use temperature T (° c) obtained by performing a temperature gradient type brittle crack propagation arrest test (ESSO test) on the doubled member (steel plate) in advance is used.

Further, as the "use temperature T", it is general to use "-10℃", which is a design temperature of the ship.

In the present invention, in order to prevent a brittle crack generated from the web from occurring in the doubling member, the ratio X (%) of the unwelded portion remaining on the abutting surface of the web and the doubling member and the prevention performance of the doubling member are adjusted so as to satisfy the following expression (1).

X(％)≥{5900-(Kca)_T}/85‥‥(1)

Here, the ratio X (%) is defined by the following formula.

X (%): { (Width B of unwelded portion of abutting surface of doubled member and web in joint cross section of Angle Joint_W) /((thickness of web t)_WLength l of leg of left and right fillet weld_WSum) } × 100

Ratio X (%) of unwelded portions remaining on the abutting surface and brittle crack propagation arrest toughness (Kca) of the doubled member at use temperature T (. degree. C.)_TIf the formula (1) is not satisfied, the brittle crack generated from the web cannot be stopped in the doubling member.

Note that, in the case of brittle cracks from the web, the double component (Kca) is used_TEven when the ratio X (%) of the unwelded portion is 0%, the formula (1) can be satisfied and the brittle crack can be stopped by the doubling member. However, in order to stop propagation of the brittle crack generated from the flange by doubling the member, it is possible toOf usable doubling members (Kca)_TThere is a limit that the ratio Y (%) of the unwelded portion needs to be increased in order to satisfy the expression (2).

Thus, if a brittle crack is generated and propagated in the web, the toughness (Kca) is stopped by the ratio X (%) of the unwelded portion and the propagation of the brittle crack of the double component_TSatisfying the formula (1), and, when a brittle crack is generated and propagated in the flange, the toughness (Kca) of the double-component member at which the propagation of the brittle crack is stopped is set to the ratio Y (%) of the unwelded portion_TWhen the adjustment is made so as to satisfy the expression (2), the brittle crack that propagates can be stopped or stopped by the doubling member.

In the actual steel structure, it is preferable to adjust the ratio X, Y of the unwelded portion and the brittle crack propagation arrest toughness (Kca) of the double member used so as to satisfy both of the expressions (1) and (2)_T。

In the present invention, the double-layered member may be an austenitic steel (high Mn steel, austenitic stainless steel, etc.) or a low-temperature nickel steel sheet (3.5% Ni steel, 5% Ni steel, 7% Ni steel, 9% Ni steel), and in this case, the above expression (1) and/or expression (2) may not be satisfied. Austenitic steels (high Mn steels, austenitic stainless steels, etc.) are crystalline structures that do not break brittle, and therefore can impede the propagation of long, brittle cracks. Details of the chemical composition are not particularly limited, but the crystal structure at the use temperature (-10 ℃) needs to be austenite. For example, the chemical composition may be 0.2 to 0.6% of C, 0.1 to 1.0% of Si, 22 to 26% of Mn, 0.03% or less of P, 0.01% or less of S, 0.01% or less of B, 0.15% or less of N, Nb + Ti + V, or the like. On the other hand, the low-temperature nickel steel sheet (3.5% Ni steel, 5% Ni steel, 7% Ni steel, 9% Ni steel) has a brittle fracture crystal structure, but has extremely high toughness at-10 ℃ which is the ship body design temperature, and can prevent the propagation of a large brittle crack. For example, a nickel steel sheet for a low-temperature pressure vessel defined in JIS G3127 may be used as the low-temperature nickel steel sheet. The steel material is extremely expensive, has a problem of cuttability, handling, etc., and is not generally used in large quantities for the main hull structure, but is not economically problematic nor constructively problematic if the use is limited to a small local quantity like the double member of the present invention.

In the present invention, in the welded structure, a height (gap) of an unwelded portion of an overlapping surface of the doubling member and the flange may be 5mm or more. By ensuring the height (gap) of the unwelded portion to be 5mm or more, the local stress concentration of the fillet metal is reduced, and the grown brittle crack is more likely to stop.

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

Examples

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

Large welded structural joints 9 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 thicknesses shown in tables 1-1 and 1-2 as web plates and flanges, and providing double members shown in tables 1-1 and 1-2 at the abutting portions of the web plates and the flanges. Fig. 4(a), (b), and (c) assume the case where a brittle crack occurs/propagates from the flange, and fig. 5(a), (b), and (c) assume the case where a brittle crack occurs/propagates from the web.

In the manufactured corner joint of the large welded structure joint 9, the unwelded width B is set_FDoubling the sheet width D of the component 10_WLeg length l of left and right fillet weld portions_FThe ratio Y of unwelded portions is changed so that unwelded portions 4 as shown in fig. 1(a) are present on the overlapping surface of the doubling member 10 and the flange 2. In addition, in the manufactured corner joint of the large welded structure joint 9, the unwelded width B is set_WThe plate thickness t of the web 1_WLeg length l of left and right fillet weld portions_WThe ratio X of the unwelded portion is changed so that the unwelded portion 4 as shown in fig. 1(a) is present at the abutting surface of the doubled member 10 and the web 1. It should be noted that, in the following description,the case where the ratio X of unwelded portions is 0% is also included.

In addition, in the manufactured corner joint of the large welded structure joint 9, (Kca) was used as the doubling member 10_-10The temperature is 2500-11000 (N/mm)^3/2) The thick steel plate of (2). In a part of the welded structure, as shown in fig. 1 c, the unwelded portion height (gap) 14 of the overlapping surface of the double-layered member 10 and the flange 2 is set to 5mm or more.

In fig. 4, the flange is made of a thick steel plate (base material only) (fig. 4(a)) or a thick steel plate having a butt joint (fig. 4(b) and (c)), and the web is made of a thick steel plate (base material only) (fig. 4(a) and (b)) or a thick steel plate having a butt joint (fig. 4 (c)). In fig. 5, the web is made of a thick steel plate (base material only) (fig. 5(a)), a thick steel plate having a butt joint (fig. 5(b) and (c)), and the flange is made of a thick steel plate (base material only) (fig. 5(a) and (b)), and a thick steel plate having a butt joint (fig. 5 (c)).

Note that the butt joint 11 is welded by 1-pass high heat input gas welding (1 electrode and 2 electrode EGW) or multilayer carbon dioxide gas shielded welding (multilayer CO)₂) To manufacture. Furthermore, the butt welded joint 12 is welded by SEGARC welding (1-electrode and 2-electrode SEGARC) or multilayer CO gas shielded welding (multilayer CO)₂) To manufacture.

In addition, fillet welding of the double member 10 to the flange 2 was carried out mainly by carbon dioxide arc welding, and the groove shape and welding conditions were changed by changing the leg length l of the fillet metal 5 as shown in tables 2-1 and 2-2_FAnd a welding width W_FVarious changes were made. In fillet welding of the doubled part 10 and the web 1, the groove shape and welding conditions were changed mainly by partial penetration of carbon dioxide gas arc welding, and the leg length l of the fillet metal 51 was set as shown in tables 2-1 and 2-2_WAnd a welding width W_WVarious changes were made. Here, the foot length and the welding width are average values on the left and right sides.

Using the obtained large welded structure joint 9, an ultra-large structure model test body shown in fig. 4 and 5 was manufactured, and a brittle crack propagation arrest test was performed. In the ultra-large structure model test body of fig. 4, a steel plate having the same thickness as that of the flange 2 is welded by tack welding 8 to the lower side of the flange 2 of the large fillet joint 9. Further, the front end of the mechanical notch 7 is processed into a fused (BOND) portion or a weld metal WM to the weld head portion 11. In the ultra-large structure model test body of fig. 5, a steel plate having the same thickness as that of the web plate 1 is welded by tack welding 8 to the lower side of the web plate 1 of the large welded structure joint 9. Also, the front end of the mechanical notch 7 is processed into a fused (BOND) portion or weld metal WM to the weld head portion 12.

In the brittle crack propagation stop test, a brittle crack was generated by striking the mechanical notch, and whether the propagating brittle crack was stopped at the fillet portion was examined.

All tests are carried out under the stress of 100-283N/mm²And the temperature is-10 ℃. Stress 100N/mm²Is the average value of the stresses acting stably on the hull, stress 257N/mm²Is suitable for the yield strength of the ship body of 390N/mm²Stress 283N/mm, which is a value corresponding to the maximum allowable stress of a grade steel sheet²Is 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 obtained results are shown in tables 3 and 4. Table 3 shows the results of the brittle crack propagation arrest test when the web is used as the crack introduction portion, and table 4 shows the results of the brittle crack propagation arrest test when the flange is used as the crack introduction portion.

[ tables 1-1]

[ tables 1-2]

[ Table 2-1]

[ tables 2-2]

[ Table 3]

[ TABLE 3]

B) BM: base metal, WM: weld metal, BOND: fusion part

[ Table 4]

[ TABLE 4]

B) BM: base metal, WM: weld metal, BOND: fusion part

As shown in tables 3 and 4, in the present example, even when a brittle crack propagates from the flange or from the web, the crack breaks into the doubled member of the fillet portion and stops.

On the other hand, in the comparative examples outside the scope of the present invention, the brittle crack propagates without stopping in the doubling member, and the propagation of the brittle crack cannot be stopped.

Description of the reference symbols

1 web plate

2 Flange

4 unwelded part

5 fillet weld metal

51 fillet weld metal

7 mechanical notch

8 temporary welding

9 Large-scale welding structure joint with doubling component (Large-scale welding joint)

10 doubling element

11 flange butt joint part

12 web butt weld joint

The angle of intersection theta.

Claims

1. A welded structure comprising a double-layered member provided at a butt joint portion between a web and a flange,

a ratio Y% of the unwelded portion defined as follows remaining on an overlapping surface of the doubled member and the flange in a joint cross section of the fillet joint, and brittle crack propagation arrest toughness Kca of the doubled member at a use temperature T DEG C_T N/mm^3/2Satisfies the following formula (2),

y%: { (width of unwelded portion of overlapping surface of doubled member and flange in joint cross section of fillet joint)/(sum of plate width of doubled member and leg length of fillet weld portion on left and right) } × 100

Y％≥{6900-Kca_T}/85‥‥(2)

Here, Kca_T: brittle crack propagation arrest toughness N/mm using a doubled component at temperature T DEG C^3/2。

2. The welded structure according to claim 1,

the plate thicknesses of the web, the flange and the doubling member are all 50mm or more.

3. The welded structure according to claim 1,

the joint surface of the doubled member and the web remaining in the joint cross section of the corner joint is defined as followsA brittle crack propagation arrest toughness Kca of the doubled member at a use temperature T DEG C and a ratio X% of 0% of an unwelded portion_T N/mm^3/2Satisfies the following formula (1),

x%: { (width of unwelded portion remaining at abutting surface of web and doubled member in joint cross section of fillet joint)/(sum of plate thickness of web and leg length of right and left fillet weld portion) } × 100

X％≥{5900-Kca_T}/85‥‥(1)

4. The welded structure according to claim 2,

a ratio X% of 0% of the unwelded portion remaining in the abutting surface between the doubled member and the web in the joint cross section of the fillet joint, the ratio being defined as follows, and brittle crack propagation arrest toughness Kca of the doubled member at the use temperature T DEG C_T N/mm^3/2Satisfies the following formula (1),

X％≥{5900-Kca_T}/85‥‥(1)

5. The welded structure according to any one of claims 1 to 4,

the flange has a butt weld head portion in a manner intersecting the web, or the web has a butt weld head portion in a manner intersecting the flange.

6. The welded structure according to claim 5,

the web has a butt-welded head portion, and is disposed so that a butt-welded joint portion of the web intersects with a butt-welded joint portion of the flange.

7. The welded structure according to claim 1 or 2,

the doubling component is austenitic steel or nickel steel plate for low temperature.

8. The welded structure according to any one of claims 1 to 4,

in the welded structure, the height of an unwelded portion of the overlapping surface of the doubled member and the flange is 5mm or more.

9. The welded structure according to claim 5,

10. The welded structure according to claim 6,

11. The welded structure according to claim 7,