PH12014501936B1

PH12014501936B1 - Welded structure

Info

Publication number: PH12014501936B1
Application number: PH12014501936A
Authority: PH
Inventors: Sadasue Teruki; Handa Tsunehisa; Igi Satoshi
Original assignee: Jfe Steel Corp
Priority date: 2012-05-10
Filing date: 2014-08-28
Publication date: 2014-11-24
Also published as: CN104271301A; KR20140126778A; CN104271301B; PH12014501936A1; WO2013168429A1; JPWO2013168429A1; BR112014025358B1; JP5408396B1; KR101504242B1

Abstract

Disclosed is a welded structure provided with a fillet weld joint in which an weld end face of a joining member having a plate thickness of 50mm or more is butted against a front face of a joined member having a plate thickness of 50 mm or more, the joining member and the joined member being joined by fillet welding, at least one of a weld leg length and a welding width being 16 mm or less, where each weld metal of the butt weld joint(s) of the joining member and/or of the joined member has a toughness at which vTrs-W (oC) is -65oC or less and/or vE_20-W (J) is 140 J or more, an unwelded portion is provided at the butting face, the unwelded portion being 95 pcnt or more of a plate thickness tw of the joining member in a cross section of the butt weld joints of the fillet weld joint, and vTrs (OC) and/or VL20 (J) of the fillet weld metal is adjusted to satisfy a predetermined relationship with a plate thickness tr of the joined member to thereby arrest propagation of a brittle crack before catastrophic fracture occurs.

Description

Lr 4

WELDED STRUCTURE ey

TECHNICAL FIELD oo

The present invention relates to a welded structure sd carriers, bulk carriers, and other such welded structures formed by welding thick steel plates, and in particular, to a welded structure that has excellent ; brittle crack arrestability and is capable of arresting the propagation of a brittle crack initiated in a weld joint before catastrophic fracture occurs in the structure. :

BACKGROUND ART

In order to increase characteristics such as carrying capacity and cargo : handling efficiency, container carriers and bulk carriers for example have few bulkheads in the hold, unlike tankers and the like, and have large upper apertures. Therefore, in container carriers and bulk carriers, it is necessary : to strengthen or increase the thickness in particular of the outer plate of the vessel’s body.

Recently, the size of container carriers has increased, and large vessels of 6,000 to 20,000 TEU (Twenty feet Equivalent Unit) are being constructed.

A TEU is an index of the carrying capacity of a container carrier represented : in terms of a number of twenty-foot long containers. Along with this increase in size of vessels, a thick steel plate with a thickness of 50 mm or more and a yield strength of 390 N/mm? or more now tends to be used as the outer plate of the vessel’s body.

From the perspective of shortening the construction timeframe, recently the steel plates that will become the outer plate of the vessel’s body : are often butt welded by, for example, large-heat input welding such as electro gas arc welding or the like. Such large-heat input welding can easily lead to a large decrease in toughness at a hecat-affected zone and therefore is one ;

cause for the initiation of a brittle crack at the weld joint. For safety’s sake, it has been considered that should a brittle fracture initiate in the hull structure, it is necessary to arrest the propagation of the brittle crack before catastrophic fracture occurs so as to prevent hull separation.

From this perspective, the 147th Research Committee of the

Shipbuilding Research Association of Japan, “Evaluation of Brittle Fracture

Toughness of Welded Joints of Ship under High Welding Heat Input”, Report

No. 87 (February, 1978), pp. 35-53, Shipbuilding Research Association of

Japan (NPL 1) reports on experimental test results regarding the propagation behavior of brittle cracks in the weld of steel plates used for shipbuilding with a plate thickness of less than 50 mm.

In NPL 1, the propagation path and propagation behavior of brittle cracks intentionally formed in the weld were examined by experiment. The document reports that when the fracture toughness of the weld was guaranteed to some degree, the brittle crack often deviated from the weld toward the base metal due to the influence of welding residual stress. It was observed, however, that in some cases the brittle crack propagated along the weld. ;

This suggests that the probability of the brittle fracture linearly propagating along the weld is not zero.

However, many ships built by welding steel plates with a plate thickness of less than 50 mm in a manner similar to that in NPL 1 have been in actual service without problems. Moreover, steel plate base metals with high toughness (e.g., E-grade steel used for shipbuilding) are considered to have a sufficient capability to arrest brittle cracks. Therefore, the brittle crack arrestability of the weld of the shipbuilding steel is not required by the Rules : and Guidance for the Survey and Construction of Steel Ships and the like.

The steel plates used for building the mega-container carriers of 6,000

TEU or more have a plate thickness of over 50 mm, however, causing the ; fracture toughness to reduce due to the increased thickness. In addition,

, since large-heat input welding with a greater welding heat input is used, the fracture toughness of the weld is further reduced. It has been shown that, with such thick large-heat input weld joints, a brittle crack initiated in the weld might propagate linearly instead of deviating toward the base metal and may not be arrested even at the steel plate base metal portion, such as a stiffener (for example, Yamaguchi et al., "Development of Mega-Container

Carrier -Practical Use of New High-Strength Heavy Gauge Steel Plate-",

Bulletin of The Japan Society of Naval Architects and Ocean Engineers, Vol. 3 (2005), pp. 70-76, Nov. 2005 (NPL 2)). Ensuring the safety of a hull structure with thick, high strength steel plates having a plate thickness of 50 mm or more is therefore a serious problem. Furthermore, according to NPL 2, thick steel plates having special brittle crack arrestability are necessary to : arrest the propagation of initiated brittle cracks.

To address this problem, for example JP 2004-232052 A (PTL 1) discloses a welded structure that is the outer plate of a ship hull and preferably has a thickness of 50 mm or more. In the welded structure, a stiffener is placed so as to cross a butting weld, and the stiffener is joined by fillet welding.

With the technique disclosed in PTL 1, a steel plate having a microstructure with a circle-equivalent average grain size of 0.5 um to 5 um over a thickness of 3 mm or more at the surface layer and back layer, and for which the X-ray plane intensity ratio in the (100) crystal plane is 1.5 or more in a plane parallel to the plane of plate thickness, is used as the stiffener.

Adopting a structure in which a steel plate having such a microstructure is fillet welded as reinforcing material can arrest the propagation of a brittle crack at the stiffener, which is the reinforcing material, even if the brittle crack is initiated in the butting weld, and can prevent disastrous damage such : as fracture of the welded structure.

Furthermore, JP 2007-326147 A (PTL 2) discloses a welded structure that has excellent brittle crack arrestability and is provided with a fillet weld joint formed by fillet welding a joining member (also referred to below as a web) to a joined member (also referred to below as a flange).

In the welded structure disclosed in PTL 2, an unwelded portion is left at the butting face between the web and the flange in a cross section of the fillet weld joint. The width of the unwelded portion is adjusted so that a ratio X of the width of the unwelded portion to the sum of a plate thickness of the web and leg lengths of the fillet weld metal at the left and right satisfies a special relational expression with the brittle crack arresting toughness Kca of the joined member (flange). As a result, even if the joined member (flange) is a thick material with a plate thickness of 50 mm or more, propagation of a brittle crack initiated in the joining member (web) can be arrested at the butting face between the web and the flange in the fillet weld metal, thus arresting the propagation of the brittle crack to the joined member (flange).

CITATION LIST

Patent Literature

PTL 1: JP 2004-232052 A

PTL 2: JP 2007-326147 A

Non-patent Literature

NPL 1: The 147" Research Committee of the Shipbuilding Research

Association of Japan, "Evaluation of Brittle Fracture Toughness of Welded

Joints of Ship under High Welding Heat Input," Report No. 87 (February, 1978), pp. 35-53, Shipbuilding Research Association of Japan

NPL 2: Yamaguchi et al., "Development of Mega-Container Carrier —Practical Use of New High-Strength Heavy Gauge Steel Plate—," Bulletin of

The Japan Society of Naval Architects and Ocean Engineers, Vol. 3 (2005), pp. 70-76, Nov. 2005

SUMMARY OF INVENTION (Technical Problem)

However, the stiffener, which is the reinforcing material, used with the technique disclosed in PTL 1 requires complex manufacturing steps in order to achieve a steel plate having the desired microstructure. Productivity thus decreases, leading to the problem of a difficulty in stably guaranteeing steel plates having the desired microstructure.

The technique disclosed in PTL 2, on the other hand, attempts to arrest the propagation of a brittle crack initiated in the joining member (web) by a combination of the discontinuousness of the structure and the brittle crack arrestability of the joined member (flange).

As indicated by the Report of the 169th Committee of the

Shipbuilding Research Association of Japan ("Report on Research Related to

Fracture Management and Control Design for Hull Structures,” (1979), pp. 118-136, Shipbuilding Research Association of Japan), however, it has been experimentally confirmed that using the joining member (web) to arrest a brittle crack initiated in the joined member (flange) of the fillet weld joint is more difficult than using the joined member (flange) to arrest a brittle crack initiated in the joining member (web).

The reason is not clearly cited, yet one possible cause is that the fracture driving force (stress intensity factor) when the crack penetrates into the T joint is greater upon penetration into the joining member (web) than upon penetration into the joined member (flange).

Based on this consideration, the technique disclosed in PTL 2 cannot © be considered sufficient to arrest a brittle crack initiated in the joined member (flange) using the joining member (web), since the brittle crack arrestability ; and the like of the joining member (web) are insufficient. ;

Note that PTL 2 does not take the brittle crack arrestability of the joining member (web) into consideration whatsoever.

In other words, the technique disclosed in PTL 2 cannot be considered to have sufficient crack arrestability with respect, for example, to the case envisioned in ClassNK’s "Guidelines on Brittle Crack Arrest Design" (established September, 2009) in which a brittle crack initiated in the strength deck (corresponding to the flange) of a large container ship propagates to the hatch side coaming (corresponding to the web).

Moreover, with the technique disclosed in PTL 2, it is necessary to increase the brittle crack arresting toughness Kca of the flange for a smaller ratio X of the width of the unwelded portion to the sum of a plate thickness of the web and leg lengths of the fillet weld metal at the left and right, so as to satisfy a particular relational expression. A larger brittle crack arresting toughness Kca, however, leads to higher rolling load for production of steel plates, lower production efficiency, and increased manufacturing costs.

In order to resolve these problems of conventional techniques, it is an object of the present invention to provide a welded structure that has excellent brittle crack arrestability and that can arrest (stop) not only a brittle crack initiated in the joined member (flange) from propagating to the joining member (web), but also a brittle crack initiated in the joining member (web) from propagating to the joined member (flange), before catastrophic fracture occurs.

Note that the welded structure targeted by the present invention is a welded structure provided with a fillet weld joint formed by a joining member (web) and a joined member (flange), each having a plate thickness of 50 mm ; or more and a butt weld joint, in which a weld end face of the butt weld joint of the joining member (web) is butted against a weld front face of the butt weld joint of the joined member (flange) to join the joining member and the : joined member by fillet welding.

(Solution to Problem)

In order to achieve the above object, the inventors thoroughly investigated the various factors behind the brittle crack arrestability in the fillet weld joint that is formed by butting the weld end face of the butt weld joint of the joining member (web) against the weld front face of the butt weld joint of the joined member (flange) to join the joining member and the joined member by fillet welding.

As a result, the inventors realized that in order to stop (arrest) propagation of a brittle crack initiated from the joined member (flange) of the fillet weld joint under such severe conditions, it does not suffice to adopt a structure that guarantees a discontinuous portion in the butting face between the joining member (web) and the joined member (flange) and has a member exhibiting excellent brittle crack arrestability by having a brittle crack arresting toughness Kca of a predetermined value or greater in the propagating portion of the brittle crack.

In particular, considering how a larger plate thickness ty (mm) of the joined member (flange) causes the energy release rate (crack growth driving force) of a brittle crack tip to increase and makes it difficult to arrest the brittle crack, the inventors concluded that in relation to the plate thickness tf (mm) of the joined member (flange), improvement in the toughness of the fillet weld metal is essential.

The inventors also discovered that since an increase in the weld leg length or welding width of the fillet weld metal facilitates propagation of a brittle crack, at least one of the weld leg length and the welding width of the fillet weld metal needs to be 16 mm or less.

Additionally, the inventors discovered that the welded structure can be : provided with the desired brittle crack arrestability by imparting toughness of a certain value or greater to each weld metal of the butt weld joint(s) of the joined member and/or of the joining member.

In other words, the inventors discovered that in a fillet weld joint formed by a joining member (web) and a joined member (flange), each having a butt weld joint, in which a weld end face of the butt weld joint of the joining member is butted against a weld front face of the butt weld joint of the joined member, propagation to the joining member of a brittle crack initiated in a thick joined member having a plate thickness of 50 mm or more can be stopped (arrested), which was difficult with conventional techniques, by guaranteeing an unwelded portion, i.e. a discontinuous portion, having a predetermined length at the butting face; setting at least one of the weld leg length and the welding width of the fillet weld joint to be 16 mm or less; further imparting such a toughness to the fillet weld metal that satisfies a predetermined relationship in relation to the plate thickness tf (mm) of the joined member; and additionally increasing the toughness of each weld metal of the butt weld joint(s) of the joining member and/or of the joined member.

Based on the aforementioned discoveries, the inventors further found that propagation of a brittle crack can also be prevented from penetrating from the joining member into the joined member.

First, the experimental results serving as a foundation for the present invention are described. :

A large fillet weld joint was prepared with a thick joining member (web) and a thick joined member (flange), each having a butt weld joint, by butting a weld end face of the butt weld joint of the joining member (web) against a weld front face of the butt weld joint of the joined member (flange) and joining the members by fillet welding.

Note that large-scale fillet weld joints were prepared with fillet weld metals having a variety of toughnesses by adjusting the material and i conditions for welding, and with unwelded portions having a variety of unwelded portion ratios Y (%) (the ratio Y equaling (width B of the unwelded portion in a cross section of the butt weld joints joined by fillet welding)/(plate thickness t,, of joining member) x 100). In addition, at least one of the weld leg length and the welding width of each fillet weld joint was set to be 16 mm or less.

Note that the joined members (flanges) were formed by steel plates having a plate thickness of 50 mm or greater, while the joining members by normal, D- to E-grade steel plates used for shipbuilding having a plate ; thickness of 50 mm or greater with no consideration for brittle crack arresting toughness Kca whatsoever. Additionally, for both the joined members and the joining members, butt weld joints were prepared by single-pass large-heat input electro gas arc welding (SEGARC or double-electrode SEGARC) or by carbon-dioxide arc welding (multilayer fill), while adjusting the material and conditions for welding so that each weld metal of the butt weld joint(s) has a toughness at which a Charpy impact test fracture appearance transition ; temperature is —65 °C or lower and/or a Charpy impact test absorbed energy at ~20 °C is 140 J or more.

Using the resulting large-scale fillet weld joint 9, the super-scale structural test model illustrated in FIG. 3(a) was prepared, and brittle crack propagation/arrest tests were conducted. In the super-scale structural test model, a steel plate with the same plate thickness as a joined member (flange) 2 of a large-scale fillet weld joint 9 was welded to the bottom of the joined member (flange) 2 with a tack weld 8.

The super-scale structural test model illustrated in FIG. 3(a) was : prepared so that a butt weld joint 11 of the joined member (flange) 2 aligns with a butt weld joint 12 of the joining member (web) 1 in a cross section of the fillet weld joint 9, and the weld lines are perpendicular to each other. In addition, a mechanical notch 7 was shaped such that a tip end thereof is positioned at the BOND section of the butt weld joint 11 of the joined member

(flange) 2.

In the brittle crack arresting test, an impact was applied to the mechanical notch 7 to generate a brittle crack, and it was observed whether or not the propagation of the brittle crack was arrested at the fillet weld metal.

The conditions for each test were a stress of 257 N/mm?” and a temperature of -10 °C.

Note that a stress of 257 N/mm’ corresponds to the maximum allowable stress of a steel plate, used in a ship’s hull, having a yield strength of around 390 N/mm?. Furthermore, a temperature of —10 °C is the design temperature of a ship.

FIGS. 4(a) and (b) show the results of the tests.

From FIGS. 4(a) and (b), it is clear that when the unwelded portion ratio Y is 95 % or more, and when the toughness of the fillet weld metal and the plate thickness tr of the joined member (flange) satisfy a specific relationship, then even if the load stress is 257 N/mm?, a brittle crack initiated in the joined member (flange) can be arrested at the fillet weld metal and propagation to the joining member (web) of the brittle crack can be stopped (arrested) without any consideration for the Kca of the joining member (web).

Note that FIGS. 4 (a) and (b) show the cases where at least one of the weld leg length and the welding width of the fillet weld metal is 16 mm or less, and each weld metal of the butt weld joint(s) of the joined member and/or of the joining member satisfies a predetermined toughness.

Note that the unwelded portion ratio Y is defined as the ratio of the width B of the unwelded portion in a cross section of butt weld joints obtained by butting a weld end face of the butt weld joint 12 of the joining member : (web) against a weld front face of the butt weld joint 11 of the joined member (flange) and joining the members by fillet welding to the plate thickness t,, of the joining member (web), i.e. (B/ty) x 100 (%).

:

These results yield the following specific relationships between the toughness of the fillet weld joint and the plate thickness tr of the joined member (flange). FIG. 4(a) yields the following relationship: vTrs (°C) £ -1.5 t¢ (mm) + 90 (1)

FIG. 4(b) yields the following relationship.

VE_20 (J) 2 2.75 t¢ (mm) -140 (2)

When the plate thickness ts of the joined member (flange) is within the range 50 < tf (mm) £ 53, however, Expression (2) becomes VE_;o (J) = 5.75.

A larger plate thickness tf (mm) of the joined member (flange) causes the energy release rate (crack growth driving force) of the brittle crack tip to increase and makes it difficult to arrest the brittle crack. With respect to this point, however, the inventors learned that by adopting a welded structure (fillet weld joint) having a structural discontinuous portion with an unwelded portion ratio Y of 95 % or more, the energy release rate of a propagated brittle crack tip reduces, making it easier to arrest the propagation of the brittle crack.

Furthermore, the inventors discovered that if the low temperature toughness of the fillet weld metal is increased to the point of satisfying

Expressions (1) and (2), a brittle crack initiated in a thick joined member (flange) with a plate thickness of 50 mm or more can be in most cases arrested within the fillet weld metal.

The inventors also discovered that even if propagation of a brittle crack cannot be stopped in the aforementioned fillet weld metal, the propagation of the brittle crack can be stopped at the weld (butt weld joint) of : the joining member (web) by setting at least one of the weld leg length and the : welding width of the fillet weld metal to be 16 mm or less, and by imparting a : predetermined low temperature toughness to each weld metal of the butt weld : ~ joint(s) of the joined member and/or of the joining member.

Based on this consideration, the inventors concluded that by taking the above measures, such as setting the unwelded portion, improving the low temperature toughness of the fillet weld metal, adjusting the weld leg length or the welding width of the fillet weld metal, and improving the low temperature toughness of each weld metal of the butt weld joint(s) of the joined member and/or of the joining member, propagation of a brittle crack initiated in the joined member (flange) can be arrested without any particular consideration for the brittle crack arresting toughness of the steel plate used in the joining member (web).

The inventors also discovered that by taking the measures as mentioned above, a brittle crack can be prevented from propagating from the joining member (web) into the joined member (flange) at the weld (butt weld joint) of the fillet weld metal or of the joined member (flange).

The inventors also discovered that increasing not only the toughness of each weld metal of the butt weld joint(s) of the joined member and/or of the joining member, but also the toughness of each heat-affected zone (HAZ) of the butt weld joint(s) of the joined member and/or of the joining member as well as the toughness of the material steel plate, is effective for improving brittle crack arrestability.

The present invention was completed through additional examination based on the above discoveries. The main features of the present invention are as follows.

[1] A welded structure provided with a fillet weld joint in which an end face of a joining member having a plate thickness of 50 mm or more is butted against a front face of a joined member having a plate thickness of 50 mm or more, the joining member and the joined member being joined by fillet welding, wherein at least one of a weld leg length and a welding width of the fillet weld joint is 16 mm or less,

both the joining member and the joined member have a butt weld joint, each weld metal of the butt weld joint(s) of the joining member and/or of the joined member has a toughness at which a Charpy impact test fracture appearance transition temperature vIrs-W (°C) is —65 °C or lower and/or a

Charpy impact test absorbed energy at —20 °C vE.20-W (J) is 140 J or more, an unwelded portion is provided at a butting face between a weld end face of the butt weld joint of the joining member and a weld front face of the butt weld joint of the joined member in the fillet weld joint, the unwelded portion being 95 % or more of a plate thickness t,, of the joining member in a cross section of the butt weld joints of the fillet weld joint, and for a fillet weld metal in the fillet weld joint, a Charpy impact test fracture appearance transition temperature vrs (°C) of the fillet weld metal and a plate thickness tf of the joined member satisfy expression (1), and/or a Charpy impact test absorbed energy vE_;o (J) at a test temperature of —20 °C in a Charpy impact test of the fillet weld metal and the plate thickness tr of the joined member satisfy expression (2): vTrs < -1.5 tr + 90 (1)

VE_20 (J) 2 5.75 (when 50 < ty (mm) < 53),

VE_20 (J) 2 2.75 tf (mm) — 140 (when tf (mm) > 53) (2) where vTrs is the Charpy impact test fracture appearance transition temperature (°C) of the fillet weld metal,

VE_y¢ is the Charpy impact test absorbed energy (J) at a test temperature of —20 °C, and tr is the plate thickness (mm) of the joined member.

[2] The welded structure according to the aspect [1], wherein each heat-affected zone of the butt weld joint(s) of the joining member and/or of the joined member has a toughness at which a Charpy impact test fracture appearance transition temperature vTrs-H (°C) is —65 °C or lower and/or a

Charpy impact test absorbed energy at —20 °C vE_,¢-H (J) 1s 140 J or more. ;

[3] The welded structure according to the aspect [1] or [2], 13 i wherein a steel plate constituting the joining member and/or a steel plate constituting the joined member has a toughness at which a Charpy impact test fracture appearance transition temperature vTrs-B (°C) is —65 °C or lower and/or a Charpy impact test absorbed energy at —20 °C vE_-B (J) 1s 140 J or more.

[4] The welded structure according to the aspect [1], wherein the weld metal of the butt weld joint(s) of the joining member and/or of the joined member preferably has a toughness at which a Charpy impact test fracture appearance transition temperature vIrs-W (°C) is —85 °C or lower and/or a

Charpy impact test absorbed energy at —20 °C vE_20-W (J) is 160 J or more.

[5] The welded structure according to the aspect [4], wherein each heat-affected zone of the butt weld joint(s) of the joining member and/or of the joined member has a toughness at which a Charpy impact test fracture appearance transition temperature vIrs-H (°C) is —85 °C or lower and/or a

Charpy impact test absorbed energy at —20 °C vE_5o-H (J) is 160 J or more.

[6] The welded structure according to the aspect [4] or [5], wherein a steel plate constituting the joining member and/or a steel plate constituting the joined member has a toughness at which a Charpy impact test fracture appearance transition temperature vTrs-B (°C) is —85 °C or lower and/or a Charpy impact test absorbed energy at —20 °C vE_5-B (J) is 160 J or more. (Advantageous Effect of Invention)

According to the present invention, propagation to the joining member (web) of a brittle crack initiated in a joined member (flange) formed from a thick steel plate having a plate thickness of 50 mm or more can be arrested (stopped) before catastrophic fracture occurs, which conventionally was difficult. As a result, the danger of a large-scale brittle fracture in a steel structure, such as hull separation in mega-container carriers, bulk carriers, or the like, can be avoided. This effect is highly advantageous in terms of guaranteeing the safety of the hull structure and is industrially quite significant. The present invention is also effective for arresting (stopping) propagation to the joined member (flange) of a brittle crack initiated in a joining member (web) formed from a thick steel plate having a plate thickness of 50 mm or more before catastrophic fracture occurs.

Furthermore, by adjusting the dimension of the unwelded portion, the toughness of the fillet weld metal at the time of construction, the weld leg length or the welding width of the fillet weld metal, each weld metal of the butt weld joint(s) of the joined member and/or of the joining member, the heat-affected zone(s) (HAZ(s)), and the low temperature toughness of the material steel plate, it is possible easily to manufacture a welded structure with excellent brittle crack arrestability without using special steel plates with high brittle crack arresting toughness and without sacrificing safety.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be further described below with reference to the accompanying drawings, wherein:

FIG. 1 schematically illustrates the structure of a fillet weld joint formed by a joining member (web) 1 and a joined member (flange) 2, each having a butt weld joint, with (a) being an external view of the fillet weld joint, and (b) schematically illustrating a cross-sectional structure of the fillet weld joint in the butt weld joint position;

FIG. 2 schematically illustrates another example of the cross-sectional structure of the fillet weld joint, showing the case of a joining member (web) 1 and a joined member (flange) 2 crossing at an inclination;

FIG. 3 schematically illustrates the shape of the super-scale structural test model used in the examples, with (a) illustrating the case of a brittle crack propagating from the joined member (flange) 2 to the joining member (web) 1, and (b) illustrating the case of a brittle crack propagating from the joining member (web) 1 to the joined member (flange) 2; and

FIG. 4 contains graphs illustrating the effects of the relationship between the toughness of the fillet weld metal and the flange plate thickness on arresting a brittle crack from propagating from the joined member (flange) 2 to the joining member (web) 1.

DESCRIPTION OF EMBODIMENTS

A welded structure according to the present invention is a welded structure formed by a joining member (web) and a joined member (flange), each having a plate thickness of 50 mm or more and a butt weld joint, in which a weld end face of the butt weld joint of the joining member is butted against a weld front face of the butt weld joint of the joined member, and the joining member and the joined member are joined by fillet welding. FIG. 1 (a) is an external view of an example of the welded structure according to the present invention. The welded structure is provided with a fillet weld joint having a fillet weld metal 5 in which at least one of a weld leg length 3 and a welding width 13 is 16 mm or less. At a butting face between the joining member (web) 1 and the joined member (flange) 2 of the fillet weld joint, an unwelded portion (length) 4 forming a structural discontinuous portion is provided.

The fillet joint cross section in the butt weld joint position in FIG. 1(b) illustrates this state. FIG. 1(b) illustrates the case of the joining member (web) 1 being attached perpendicularly to the joined member (flange) 2, yet the present invention is not limited to this case. For example, as illustrated in FIG. 2, the joining member (web) 1 may be attached at an inclination of an angle 0 with respect to the joined member (flange) 2. In this case, the plate thickness ty, of the joining member (web) used when calculating the ratio Y (%) of the unwelded portion is the length of the crossing between the joining member (web) and the joined member (flange), i.e. (ty)/cos(90° — 0).

As described above, the welded structure according to the present invention includes an unwelded portion (length) 4 forming a structural discontinuous portion at a butting face between the joining member (web) 1 and the joined member (flange) 2 in the fillet weld joint. In the fillet weld ; joint, when a brittle crack propagates from the joined member (flange) 2 to the "

joining member (web) 1, the butting face between the joining member (web) 1 and the joined member (flange) 2 becomes a propagation surface of the brittle crack, and therefore in the present invention, the unwelded portion (length) 4 is provided at the butting face. Due to the presence of the unwelded portion (length) 4, the energy release rate (crack growth driving force) of a brittle crack tip propagating in the joined member (flange) 2 is reduced, making it easier to arrest the brittle crack at the butting face.

In the present invention, the fillet weld section (fillet weld metal) 5 having a toughness of a predetermined value or more is formed. Therefore, even if a brittle crack propagates to the joining member (web) 1 side, the brittle crack is arrested more easily at the fillet weld section (fillet weld metal) 5.

It is extremely unusual for a brittle crack to be initiated in the steel plate base metal portion, which has few defects. In the majority of past brittle fracture accidents, the brittle crack was initiated in the weld. Thus, in the fillet weld joint, as illustrated in FIG. 1(a), formed by the joining member (web) 1 and the joined member (flange) 2 having the butt weld joints 12 and 11, respectively, in which the butt weld joint 11 of the joined member (flange) 2 and the butt weld joint 12 of the joining member (web) 1 are perpendicular to each other, in order to stop propagation to the joining member (web) 1 of a brittle crack initiated in the butt weld joint 11, or propagation to the joined member (flange) 2 of a brittle crack initiated in the butt weld joint 12, it is important that the structure be discontinuous. Therefore, the unwelded portion (length) 4 is provided at the butting face between the joining member 1 and the joined member 2 in the fillet weld section.

In the fillet weld joint, as illustrated in FIG. 1(b), in which the butt weld joint 11 of the joined member (flange) 2 and the butt weld joint 12 of the : joining member (web) 1 are perpendicular to each other, the unwelded portion (length) 4 is provided at the butting face between the weld front face of the butt weld joint 11 and the weld end face of the butt weld joint 12. : :

Note that the method of manufacturing the fillet weld joint need not be limited in particular, and any regular method of manufacturing may be used.

For example, steel plates may be butt welded for the flange and other steel plates may be butt welded for the web, and the resulting butt weld joints may be fillet welded to manufacture a fillet weld joint.

In the present invention, the dimension (width B) of the unwelded portion (length) 4 in a cross section of the fillet weld joint in the butt weld joint position is 95 % or more of the web plate thickness ty in order to suppress propagation of a brittle crack. As a result, plastic deformation of the fillet weld metal becomes easier, thus easing the stress around the crack tip of a brittle crack penetrating into the fillet weld metal and suppressing propagation of the brittle crack to the joining member (web) 1 side.

Therefore, the dimension (width B) of the unwelded portion (length) 4 is limited to being 95 % or more of the joining member (web) plate thickness t,.

Preferably, the dimension is at least 96 % and at most 100 % of the joining member (web) plate thickness t,,.

Furthermore, at least one of the weld leg length 3 and the welding width 13 of the fillet weld joint is 16 mm or less. As a result, the stress around the crack tip of a brittle crack propagating to the fillet weld metal is eased through plastic deformation of the fillet weld metal, and propagation of the brittle crack is mitigated. Therefore, the weld leg length or the welding width of the fillet weld joint is limited to being 16 mm or less, which is a value that allows for the high-toughness fillet weld metal to deform easily.

The value is preferably 15 mm or less. The weld leg length 3 and the welding width 13 are preferably 4 mm or more, respectively, in terms of the rigidity of the weld joint structure.

If the joined member (flange) 2 and the joining member (web) 1 have a plate thickness of over 80 mm, the weld leg length is preferably increased for guaranteeing strength, while increasing the low temperature toughness of the fillet weld metal portion. 1s

In the present invention, the fillet weld metal in the fillet weld joint is adjusted in relation to the plate thickness tr of the joined member (flange) so as to guarantee a toughness satisfying expression (1) and/or expression (2) below: vTrs £ -1.5 ts + 90 (1)

VE_0 = 5.75 (when 50 < ty (mm) < 53),

VvE_20 2 2.75 ty (mm) — 140 (when tf (mm) > 53) 2) where vTrs is the Charpy impact test fracture appearance transition temperature (°C) of the fillet weld metal, vE_,0 is the Charpy impact test absorbed energy (J) at a test temperature of —20 °C, and tr is the plate thickness (mm) of the joined member (flange).

By having the toughness of the fillet weld metal satisfy expression (1) and/or expression (2) above in relation to the plate thickness tr of the joined member (flange), a welded structure in which the plate thickness of the joined member (flange) is 50 mm or more can be formed as a welded structure in which desired brittle crack arrestability is guaranteed, as illustrated in FIG. 4.

When the toughness of the fillet weld metal satisfies neither expression (1) nor expression (2) above, the toughness of the fillet weld metal is insufficient, and a propagating brittle crack initiated in the joined member (flange) cannot be arrested at the fillet weld metal portion.

Further, in the present invention, it is necessary to form each weld metal of the butt weld joint(s) of the joined member 2 and/or of the joining member 1 while adjusting the material and conditions for welding so that the weld metal has a toughness at which a Charpy impact test fracture appearance _ transition temperature vTrs-W (°C) is —65 °C or lower and/or a Charpy impact test absorbed energy at —20 °C vE_5o-W (J) is 140 J or more.

If the weld metal of the butt weld joint of the joining member 1 has a toughness at which vTrs-W (°C) is higher than —65 °C and vE.;o-W (J) is less than 140 J, a brittle crack propagating from the weld of the joined member

(flange) cannot be stopped at the fillet weld metal or the weld of the joining member (web).

Alternatively, if the weld metal of the butt weld joint of the joined member 2 has a toughness at which vTrs-W (°C) is higher than -65 °C and

VE_20-W (J) is less than 140 J, a brittle crack propagating from the weld of the joining member cannot be stopped at the fillet weld metal or the weld of the joined member (flange).

More preferably, each weld metal of the butt weld joint(s) of the joining member and/or of the joined member preferably has a toughness at which a Charpy impact test fracture appearance transition temperature vIrs-W (°C) is —85 °C or lower and/or a Charpy impact test absorbed energy at —20 °C

VE 20-W (J) is 160 J or more.

More preferably, in the present invention, each weld metal of the butt weld joint(s) of the joined member 2 and/or of the joining member 1 has the aforementioned toughness and, furthermore, each heat-affected zone (HAZ) has a toughness at which a Charpy impact test fracture appearance transition temperature vIrs-H (°C) is —65 °C or lower and/or a Charpy impact test absorbed energy at —20 °C vE.o-H (J) is 140 J or more. More preferably, a steel plate constituting the joined member 2 and /or a steel plate constituting the joining member 1 has a toughness at which a Charpy impact test fracture appearance transition temperature vTrs-B (°C) is —65 °C or lower and/or a 256 Charpy impact test absorbed energy at —20 °C vE_5,-B (J) is 140 J or more.

This increase in toughness allows a brittle crack propagating from the weld of the joined member (flange) or a brittle crack propagating from the weld of the joining member (web) to be stopped more easily, either at the fillet weld metal or at the weld of the joining member (web) or the weld of the joined member (flange).

More preferably, each heat-affected zone (HAZ) of the butt weld joint(s) of the joining member and/or of the joined member has a toughness at which vTrs-H (°C) is —85 °C or less and/or VE20-H (J) is 160 J or more.

More preferably, the steel plate constituting the joined member and/or the joining member has a toughness at which vIrs-B (°C) is —85 °C or lower and/or VE.;0-B (J) is 160 J or more.

The welded structure according to the present invention is provided with the above fillet weld joint and butt weld joints and can, for example, be used in a hull structure in which the outer plate of the vessel’s body is the flange and a bulkhead is the web, a hull structure in which the deck is the flange and the hatch is the web, or the like.

The present invention is described below in detail based on examples.

EXAMPLES

Butt weld joints were prepared by the welding methods shown in

Tables 1 and 2, using steel plates having the plate thicknesses and low temperature toughnesses listed in Tables 1 and 2, with the welding heat inputs listed in Tables 1 and 2, and used as joined members 2 or joining members 1.

The butt welding was performed with a variety of welding materials by single-pass large-heat input electro gas arc welding (SEGARC and double-electrode SEGARC) or by multilayer CO, welding.

V-notch Charpy impact test pieces (each being 10 mm thick) were collected from the middle portions of the weld metals and from the heat-affected zones (HAZs) (BOND sections) in the butt weld joints of the joining members and of the joined members thus obtained, in such a way that the surface of each test piece is positioned 1 mm or 2 mm below the surface layer, and that the longitudinal direction of the test piece is perpendicular to the weld line and the notch is perpendicular to the weld line. Charpy impact tests were conducted in conformity with JIS Z 2242, and the fracture : appearance transition temperature vTrs (°C) and the Charpy impact absorbed energy VE 30 (J) at a test temperature of —20 °C were calculated. Note that : the Charpy impact absorbed energy VE. (J) and the fracture appearance transition temperature vTrs (°C) were also calculated for the base metal portions of the steel plates constituting the joining members and the joined members.

The results of the low temperature toughness of the base metal portions of the steel plates and the low temperature toughness of the butt weld joints are listed in Tables 1 and 2.

Then, large-scale fillet weld joints were prepared to the size of an actual structure in the shape shown in FIGS. 3(a) and (b). Each of the large-scale fillet weld joints was formed by butting the weld end face of the butt weld joint 12 of a joining member (web) 1 against the weld front face of the butt weld joint 11 of the joined member (flange) 2, and joining the members 1 and 2 by fillet welding. The fillet welding was conducted so that the resulting fillet weld joints have a variety of weld metal toughnesses and a variety of weld leg lengths or welding widths shown in Tables 3 and 4 by varying welding conditions such as the welding material, welding heat input, shield gas, and the like.

In the prepared fillet weld joints, unwelded portions (lengths) 4 as illustrated in FIG. 1(b) or FIG. 2 at the butting faces between the joining members 1 and the joined members 2 were modified to a variety of unwelded portion ratios Y (the ratio Y equaling (width B of the unwelded portion in a cross section of the butt weld joints joined by fillet welding)/(plate thickness ty of joining member (web)) x 100), as shown in Tables 3 and 4. 25:

In addition, a V-notch Charpy impact test piece (10 mm thick) was collected from the fillet weld metal of each of the large-scale fillet weld joints thus obtained, or from a butt weld joint prepared under the same conditions as the fillet weld, to determine the absorbed energy VE, (J) at a test temperature of —20 °C and the fracture appearance transition temperature vTrs (°C) in conformity with JIS Z 2242. Tables 3 and 4 show the low temperature toughnesses of the fillet weld metals 5 determined by the tests. :

Using the large-scale fillet weld joints thus obtained, the super-scale structural test models illustrated in FIG. 3 were prepared, and brittle crack propagation/arrest tests were conducted.

FIG. 3(a) shows a super-scale structural test model which was shaped such that a tip end of the mechanical notch 7 is positioned at the BOND section of the butt weld joint 11, and in which the butt weld joint 11 of the joined member (flange) 2 and the butt weld joint 12 of the joining member (web) 1 are perpendicular to each other and a brittle crack propagates from the joined member (flange) 2 to the joining member (web) 1.

FIG. 3(b) shows a super-scale structural test model which was shaped such that a tip end of the mechanical notch 7 is positioned at the BOND section of the butt weld joint 12, and in which the butt weld joint 12 of the joining member (web) 1 and the butt weld joint 11 of the joined member (flange) 2 are perpendicular to each other and a brittle crack propagates from the joining member (web) 1 to the joined member (flange) 2.

In the super-scale structural test model shown in FIG. 3(a), a steel plate with the same plate thickness as the joined member (flange) 2 of the large-scale fillet weld joint 9 was welded to the bottom of the joined member (flange) 2 with tack weld 8. In the super-scale structural test model shown in

FIG. 3(b), an auxiliary plate 6 with the same plate thickness as a the joining member (web) 1 of the large-scale fillet weld joint 9 was to welded to the bottom of the joined member (flange) 2 with partial groove weld 10, and a steel plate with the same plate thickness as the joining member (web) 1 was welded to the bottom of the auxiliary plate 6 with tack weld 8.

In the brittle crack propagation/arrest tests, an impact was applied to the mechanical notch 7 to initiate a brittle crack, and it was observed whether or not a propagating brittle crack was arrested at the fillet weld metal, the weld of the joining member (including the heat-affected zone (HAZ)) (FIG. 3(a)), or the weld of the joined member (including the heat-affected zone)

(FIG. 3(b)).

The conditions for each test were a stress from 100 N/mm’ to 283

N/mm” and a temperature of —10 °C. A stress of 100 N/mm? is the average stress routinely applied to the ship’s hull. A stress of 257 N/mm? corresponds to the maximum allowable stress of a steel plate, used in a ship’s hull, having a yield strength of around 390 N/mm’. Furthermore, a stress of 283 N/mm? corresponds to the maximum allowable stress of a steel plate, used in a ship’s hull, having a yield strength of around 460 N/mm?. A temperature of —10 °C is the design temperature of a ship.

Table 5 shows the results of the tests.

= — oo — oo ©” ~- 00 wy

E

| 2 - = o | = ~ | = 5

Z g 2 Z g 2 OQ © g g 2 CO oO g g 4 0 ” wv oo © wy wv i gS a & 8 8 = = x x & 2 ma “ ~ wn o 8 8 3 ge g15 gl1e|g|8| ¢ 3 3 # 3 3 1) = N

Teles 3 | a gla] 3 | = g | e 2 | F|S RIFIR|®|F]| 8 $ $ % $ $ ! wl 12] wv wy ny & of |2 : Solel ee > z oy 2 wy — oN — 0 0 o — Oo fey oo dg elR|B|#|F|F|F|N|F| 7 § % $ ¥

I JSEEEEEEER EEE

Slelolelul8lo g 9 Y Y 9 Q Y :

OEE EE eee 3 AEE ER g & g & & g g 8 8 & E 2 wv a 3 vy o —~ —

J © |&lald|&|la|a|8]|A]| § 8 8 2 : = 2 ¢ = 0 Fo Pa — 0 ~ en 2 : 3 Flag 85855 3 2 # 5 7 # : — > E: — E 2 i 4 : <Q 8 5 . BE oo o > ww, p Ee < £4 © E|l=|®|s 8 {3 8 e 8 2 in © : = E = = i —_ &

BEEEEEE

[8] oO OQ Q oO oo g Z| 2 & 8 & ee]

Cl] ce ©

N

2 3 g 81a — g 8 A a ks Fla = 2 wv 2 wn E © & wy

J

KR a a E Gc © eC EB zg - “ _|& a ? 7 3 3 zi £3 £ oo < 8 8

A o a g 3S g £ B

Q

§

Q Q oO oO oO Q : 28888) |fd g 8 8 ElE(E|=2 % 8 ] ] T £ s 8 hn] : o o on — wv 2 % : 8 2 g al 8] 8 g : = 8 : £2 5 i | 8 | 85 |e gis ge ¢% 5 : i ° < a E ? Eg }

- T ‘ . . » 2s z| & [2] 2 s | 2 |g |¢

N z . < je ) o © “ © © —_ 00) o — —_ of on ol : | E © 2 £ * » © © 7 2 wn wn »n £ € & “a1” z “~ & © 3 2 <S = £ 2 o os w 2 0 = = ss © g 0 “ A wv ~ ° wl ~ —_ =~ —_ — _ —- © 2 > = = = E y a ~ © «0 = wy © o 4 0 gg R S18] H 4 $ ¢ 1% 3 Id > ¥ _ . 7 g 4 §F ££ gs] =~ |glsl| = = e 2 g |e & Ss = FE 3 < <+ <+ n “ wv w wn

S = = 2

Eo PES ge ole vole ole ul & g = &, & & z gle |b |g|g|® |e |% 5|% 2|% 5% 32 z $1218 o|312]|3 S12 12 82 gl gle gf 5 2 g = © 2 g 3 I = © 3 wv = wv 2 wn 2 wn 2 © @ @ = vu © 2 s| = & 3 & 812 % 2 3 8 2 & e & se © 2 8 8 210 = a gle 3 S 2 8 3 S e wm had o~ o~ o ~ oN ol [a] o~ oy ~ oN o z|d >

EL gle m 12 D Oo < «0 wv vy oN wy = a5 o on on = oa oo = be < | 1 | 1 1 T ° > = a o & - z 1 + E 2 3 |e 2 © g Q Q =

Ps als] 8 |a|s gs | 2 | 2 | ¢ 3 b> = aN ¢ oc wy x 0 0 3 Tl = B wv gl ©0| Oj

EE LFF] OF O[F|H] TF : $ § Gi g SE . . £ £ 8 2 Zz wv [7] g 3 & 3 - z EB gl |Z] 3s |g 2 |slel a | zs | ge] es] s = < w kt 2 >

L

= 3 = 2 1 oC ~~ on © 0 Oo — a 0 — a oo vy ge [FFF [FF] A $ Hi 7 $ $|% = g = 5 § 4 § 3 8 o o © © ~ ~ o o < o © 3 3 = Eg 3 g 2 Fe = - a 3 a a a 8 2 -

U [+3 0 Q Q 3 & 3 3 3 3 2 8 2 y Q Q Q <Q O < E ul& olE ol o £

T & £ | = b 5 gE | 8 =|8 =|8 =1 8g 5 < < | < g 3 <|% <|3% <|3% Z| %

EY wo ov o © ow 5 sg | 2 2 812 2 2 | 2 22 Bs 22 2B 2 2 a @n 7] n n 3 i | w|g w|5 wul|lt «a 2 © = = a & a A a . 2 0 — Ss <r on 00 0 — “0 wr wy oN X . a 8 SR a a= { S & 8 8 & a zg i] > B 8 : £5 ; gle : <l Q — 5 Ee alg 2 2 x a = 2 IN 2 g % = ) t i ] i 1 | 1 I > = a ; 5 : 1.3 : & 32 - i 2s] © 8 8 8 g Roe - oa £ E ” 3 . E < — « wi : 8 gz a | 8 a a | « 8 8 & a 2 = & 2

7 3 i ¥ wv)

IHRE

IHR

8 0 oo << p— * ~~~ =

EQ

21 21828 $2 1% Eid: iA 8 21 2 : EERIERIE

P1% 32 32 53 tl8 28 % z - $= o § wn 7 &® 9 nv ~~ ©

Na 00 : N a > q a 5 2 oO a] 980 pi i Ss 5 vl g§ 8 = z “ IgE

Zz £35 8S § apy © 89 g Q 3 : 8 = o © “9 oof ~~ La

Tl Ha

Gt ° > 0 2 2 ga

S 2 5 8% © I) gc

S85 2 ~

Ele LE Sw

AIEEE RS 5

EERIE:

Glf E|2 Elec 212 B12 82 2 > 813 &]= z 357 a 8 SZ 280 : 22. 5 2 5 0 0 25 ;

Eo B a . § 7 lela]

. ~ . + .

Lo 2 u 2 L 2 L 2 2 2 L 2 & 2 a a. a a a a. &. a a2 a. a. j= ou a o g 5 5 5 § 5 g 5 g 5 § £ g 5 -_ » » > » »” » » we » » ® »” » »” i] o wm a a [3] wo 13} @ [} od a a o £ 2 5 £ 2 £ £ 2 £ 2 2 2 £ £ £ g § £ £ £2 £ £2 £ £ £ g £ £ =} = =} = s = =} a a g = 2 = = 8 = 8 E = = & & 8 8 = & & 8 2

In -* gE i

HE wi w w wv wr w w © . <= o £ m ©

El : i 3 0% © 2 © 0 w “ 2 2 2 @ 2 a & a = = wi w w a a A x x x @ wn wn 8 8 8h o = wo 3 2 8 2 0 wv 0 2 WS & = & Rr 2? 2 2 3 « g 2 ow tam o 0 8 e . 8 °c oh o * 3 LN = = ©» wn wn 7] » & o g ml o

Gm

FI g 9 * vy wv wy wy = wy 3 1 2 nz 2 2 re ~ = o o g FE | | | i i a £ g do

B

= [ ro

NN

LO wv “« wv wv % o ao o~ “© wn “ & aN 5 £ ] | 7 | T q T hi T ih a .£ 5 a 2 I © 3 3 L a a & & 5 5 °

Z

= g il: ©

Sa ¢ = 0 00 on on ~ 3 3 ‘ £ 8 2 a 3 5 x 2 le | a ° s| 2 ° 7 >

Ct © © 3 £53 _ 2 gE ~ ~ = a = a 2 Q 2 « «

Ys 2

Jac] gE + wv wv ~ — : 2 = - = ©

EB * 5 g 5 a & ; g St 8 = c = - § 8 » wv © © wv «n 7) © @ n @ wn » 8 2 o

E 5 £ = Bi © 4 © : ; — . to - f on 2 eo 8 : g 8 8 % E

Q § 3 3 : ° = E 3 £ » n ©» » wn ©» wn E = 3 & 2% z @ © » » » E \ = oO gi £ g§ 3 © P md = © A E = 3 : o oS 3 & g 2 — ~ - - 0 ~ wo o “ + :

~ o } . ' . <3 — . Al ® © ~~ 2 lele|e| EEC on ele lel] 2] 28

El El 5 |G 0 I z z £ £ g Em = = = = 3S S > $i °c

Qo

Oo wv © wv wv wv wn wv

Vi ~~

QO

0

Ed ~~ = a 1 & 0 2 g v = A = ~~ ; o = on ~ = = oo ~ = «= b) = 3 £ o

BE << « 3 — © = ~~

L b) = = 5S go clslslsleals|an 8 2 aq I 1 I —- ( ol g - < I) N vn 8 Al br

Q wv =

Q o — o elo lz] sl=2]|2|E 8 S ™ 5 Pn OE % <2 mM

Q & > $i: on 5 2 wn 2 L g VI = — ~~

Ne Gt

EE

Q Ne” ow § = — 0 s Vi ele|le]lels]e 2 5 2

Es g oO Bz = $= 8 2 o

Z Es: uw sl=]s|s| alsa g TC 2 Hon 8 BSN

Q QB

< w2 | = 1 - X —- ~ “i ™~) = ~~ o = _ —_ x © Sr 8 2 §85% 5% 8 El =x g = Td = as TT » » »n 2 » %] A Zo 53 ~~ NN ~~ : * * ¥ * i * * *® E h . * r ~

. v : 2 2 2 2 2 ES 2 2 2 2 2 2 L

Sa o on a. a a a. a. a a ou ao 2 el ele sel e585 sg s5|ce » » ® » » » » ” » » »” » » » Eg 4 © a a iB a a a a 8 & a a 0 3 & © © © © © ov v © © v © v © 33] £ 2 2 2 2 2 2 2 2 2 2 Zz 2 2 ° = bi = = s B® ® = 5 ws ® 2 & 5 | & 5 gE | § 5 | § § § 5 § § | % £2. a a. a. a. a on £2. a a 2 £ E £ £ E g £ g g £ E £ £ z

S c ° S c S oS © S co 8 cS 3 8 © © Oo © © oO Oo S © Oo © oO Oo e $ : * 7} wv © wv wv @n

E © « © z @ » z z z z z “ eg gE

S

Ty 8 ¢ © wv wn wv a ] nv a ~~ wy “ wy wv 3 ~ i i ! ! es : aN ~ N a 3 “ @ a 8 $g e 8 53 = = 8 2 s 8 - =| 4 = 2 2s e2le|zs 5 | 8 ss | 8 £3

B

=

LQ : = * vn wv wn wv on w vn = z Z Zz Zz z Z Zz g o gm [] g Bw = £ 3 = n= 2 hd] “ n o “ hi] hi] o “ 2 5 T 7 = ! 7 T & & 7 g } % = iT 2 o hes < wv wv 0 x o ~ — cE 21 FF] %|¢ slags «| 5 = a 8 * * cg

T > 2 & & & & -= Cc 2g : 3 = > = € =m glE % ils & 3 > wy ~~ an < alg §g Ele |= |s|2]|zs a | =| = |e |e g

EE

T 2 2 = 2 2

El 2 .

Eg Ss EF wn ; > P25 wn v » nv 2 nn 2 » © »n 2 ©» i . E g s Fé 2 s ; © ke . oe i — z 8 : x El OS 3 . o = zg 8 q & » ©» » |. re 3 gz n © wn ©» Zz wv 2 wn » »n wn » 2 : <3 2 s 8 E:

IE oS

G¢ § > $= 5 : gs |S wv 7

Vi —

Q

0 wv Ne’

S 5 5 <

TIE 8 S wv [] ol >

SEC on 5 2 "n 8 9 Vi

O = Vi

Bp oe 5 3 n

SE 5 8 & oF = Q AN

SmBEm 2 S—» > a ve us g Elxa g hx =~ 2} . - < |g =~ oo 2» Zo F5 x 5% » * ¥ 0% * * ’ - E

[Table 5]

Brittle Crack Propagation/Arrest Test Results

Test Brittle

Test Test

EEE coy | avvmm?) in i Fillet Weld Inventive 1 loined 1-15 | 100 Arrested ret ve

Member Metal Example ini Fillet Weld I ti 3 Joining 10 100 Arrested illet We nventive

Member Metal Example i Fillet Weld I ti 4 Joined 10 257 Arrested illet We nventive

Member Metal Example i Fillet Weld I ti

Joined “10 257 Arrested illet We nventive

Member Metal Example ini Fl Weld | I ti

Joining 10 257 Arrested ange We nventive

Member Metal Example i Web Weld I ti 7 Joined 10 283 Arrested e e nventive

Member Metal Example i Fillet Weld I ti

Joined “10 283 Arrested illet We nventive

Member Metal Example

Joined Web Weld I ti ome -10 283 Arrested eb we nventve

Member Metal Example

Joined Fillet Wel I i oine 10 257 Arrested illet Weld nventive :

Member Metal Example

Joined . . 11 oine “10 257 Arrested Fillet Weld Inventive

Member Metal Example

Joined i ; : oine 10 257 Arrested Fillet Weld Inventive

Member Metal Example

Joined Fi . oine 10 057 Arrested illet Weld Inventive

Member Metal Example j

Joined Ww. A 1a | Jone | _10 283 Arrested eb Weld Inventive

Member Metal Example

Joined . : 257 Arrested Fillet Weld Inventive

Member Metal Example

Joined ; .

Member Metal I:xample :

Joined i i :

Member Metal Example '

(cont'd)

Brittle Crack Propagation/Arrest Test Results

Test Brittle

Test Test

Joining Fillet Weld Inventive - ted 18 Member 10 251 Arreste Metal Example 19 -10 100 Propagated

BF EEE Example -10 257 Propagated

BF ERE Example

Joining Comparative 21 257 Propagated

Joined Comparative — P ted

BFE

Joined Comparative -10 257 P ted

Joined Comparative 24 -10 257 Propagated

Joined Cc ti ome -10 257 Propagated omparative

Member Example

Joined Comparative 26 -10 283 Propagated

Member Example

Joined Comparative 27 -10 100 Propagated

Member Example

Joined Cc 28 ome -10 257 Propagated Omparalive

Member Example

Joined 29 oine -10 257 Propagated Comparative

Member Example

Joini 3 oining 10 257 Propagated Comparative

Member Example

Joined i

Member Example

Joined i

Member Example

Joined i

Member Example :

Joined \e . 257 Arrested Fillet Weld Inventive

Member Metal Example : ] . . . g

Member Metal Example J

In all of the inventive examples where a brittle crack propagates from the joined member (flange) to the joining member (web), the brittle crack was arrested either in the fillet weld metal of the fillet weld section or in the weld of the joining member (web). In all of the inventive examples where a brittle crack propagates from the joining member (web) to the joined member (flange), the brittle crack was arrested either in the fillet weld metal of the fillet weld section or in the weld of the joined member (flange).

On the other hand, in each of the comparative examples (test models

No. 19 to 21), which are out of the ranges of the present invention in terms of both the weld leg length and the welding width, the brittle crack propagated to the joining member or to the joined member without being arrested at any of the fillet weld metal, the weld of the joining member, or the weld of the joined member, and hence propagation of the brittle crack could not be stopped (arrested).

In addition, in each of the comparative examples (test models No. 22 to 24 and 27) having unwelded portion ratios Y out of the ranges of the present invention, the brittle crack initiated in the joined member propagated to the joining member and propagation of the brittle crack could not be stopped (arrested).

Moreover, in each of the comparative examples (test models No. 26 and 28), which are out of the ranges of the present invention in terms of the low-temperature toughness of the weld metals of the butt weld joints of the joining member and of the joined member responsible for arresting propagation of a brittle crack, the brittle crack propagated from the joined member to the joining member and propagation of the brittle crack could not : be stopped (arrested).

Additionally, in each of the comparative examples (test models No. 25, 29, 30, 32, and 33), which are out of the ranges of the present invention in terms of the low-temperature toughness of the fillet welding metal, the brittle crack propagated from the joined member to the joining member or from the joining member to the joined member, and hence propagation of the brittle crack could not be stopped (arrested).

Furthermore, in the comparative example (test model No. 31), which is out of the ranges of the present invention in terms of both the unwelded portion ratio Y and the low-temperature toughness of the fillet weld metal, the brittle crack initiated in the joined member propagated to the joining member and propagation of the brittle crack could not stopped (arrested).

REFERENCE SIGNS LIST

1 Joining member (web) 2 Joined member (flange) 3 Weld leg length 4 Unwelded portion 5 Fillet weld metal 6 Auxiliary plate 7 Mechanical notch 8 Tack weld 9 Large-scale fillet weld joint 10 Partial groove weld 11 Butt weld joint of joined member (flange) 12 Butt weld joint of joining member (web) 13 Welding width 0 Cross angle

Claims

CLAIMS: ri 4

1. A welded structure provided with a fillet weld i $n Od 1 P2y3 which an end face of a joining member having a plate thickness of 50 mm to 100 mm is butted against a front face of a joined member having a plate thicknbsy 4f 50 mm to 90 mm, the joining member and the joined member being joined by fillet welding, wherein at least one of a weld leg length and a welding width of the fillet weld joint is 16 mm or less, both the joining member and the joined member have a butt weld joint, each weld metal of the butt weld joint(s) of at least one of the joining member and the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vIrs-W (°C) is -65 °C or lower and a Charpy impact test absorbed energy at -20 °C vE_2-W (J) is 140) to 1881], an unwelded portion is provided at a butting face between a weld end face of the butt weld joint of the joining member and a weld front face of the butt weld joint of the joined member in the fillet weld joint, the unwelded portion being 95% to 100% of a plate thickness t,, of the joining member in a cross section of the butt weld joints of the fillet weld joint, and for a fillet weld metal in the fillet weld joint, at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vrs (°C) of the fillet weld metal and a plate thickness tr of the joined member satisfy expression (1), and a Charpy impact test absorbed energy vE_o(J) at a test temperature of -20 °C in a Charpy impact test of the fillet weld metal and the plate thickness t; of the joined member satisfy expression (2): vTrs <-1.5 t+ 90 (1) vE_20 (J)> 5.75 (when 50 < t{(mm) < 53), vE_20 (J)> 2.75 t(mm)-140(when t{(mm)>53) (2) where vTrs is the Charpy impact test fracture appearance transition temperature (°C) of the fillet weld metal, vE_, is the Charpy impact test absorbed energy (J) at a test temperature of -20 °C, and tr is the plate thickness (mm) of the joined member.

2. The welded structure according to claim 1, wherein each heat-affected zone of the butt weld joint(s) of at least one of the joining member and the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vTrs-H (°C) is -65 °C or lower and a Charpy impact test absorbed energy at -20 °C

VE.20-H(J) is 140 J to 178 J.

3. The welded structure according to claim 1 or 2, wherein at least one of a steel plate constituting the joining member and a steel plate constituting the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vTrs-B(°C) is -65 °C or lower and a Charpy impact test absorbed energy at -20 °C vE_29-B (J) is 140 J to 263 J.

4. The welded structure according to claim 1, wherein the weld metal of the butt weld joint(s) of at least one of the joining member and the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vTrs-W(°C) is —85 °C or lower and a Charpy impact test absorbed energy at -20 °C vE_20-W(J) is 160 J to 18817. :

5. The welded structure according to claim 4, wherein each heat-affected zone of the butt weld joint(s) of at least one of the joining member and the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vTrs-H(°C) is —85 °C or lower and a Charpy impact test absorbed energy at -20°C vE.;-H(J)is 160 J to 178 J.

6. The welded structure according to claim 4 or 5, wherein at least one of a steel plate constituting the joining member and a steel plate constituting the joined member has a toughness at which at least one of the following conditions is met, a Charpy impact test fracture appearance transition temperature vTrs-B(°C) is -85 °C or lower and a Charpy impact test absorbed energy at -20 °C vE.»9-B(J) is 160 J to 263 J.