WO2022265010A1

WO2022265010A1 - Weld structure body

Info

Publication number: WO2022265010A1
Application number: PCT/JP2022/023798
Authority: WO
Inventors: 涼太長尾; 恒久半田; 聡伊木; 哲哉田川; 暁彦山内; 宏章平澤; 昇木治; 卓哉草場
Original assignee: Ｊｆｅスチール株式会社; ジャパンマリンユナイテッド株式会社
Priority date: 2021-06-15
Filing date: 2022-06-14
Publication date: 2022-12-22
Also published as: JP7293515B2; JPWO2022265010A1; CN117460594A; TW202300674A; TWI808791B; KR20240007762A

Abstract

The present invention provides a weld structure body that has excellent brittle crack arresting performance. This weld structure body: has an end face of a joined member abutted to a surface of a member to be joined that has a plate thickness of at least 50 mm; and comprises a T joint at which the joined member and the member to be joined are joined. The welded metal of the T joint has a composition comprising at least 80% austenite phase, in area%. This weld structure body can prevent the spread, to the joined member, of brittle cracks generated from a thick member to be joined, before large-scale damage occurs, by simply adjusting welding material selection or welding conditions during the welding step and, thereby, improve the safety of a boat hull structure.

Description

Welded structure

The present invention relates to welded steel structures (welded structures) that are welded using thick steel plates, such as large container ships and bulk carriers. In particular, the present invention relates to a welded structure having excellent brittle crack arrestability, which can stop the propagation of brittle cracks generated from the base material of thick steel plates or welded joints before large-scale destruction of the structure.

Unlike tankers, for example, container ships and bulk carriers have a structure with a large opening at the top of the ship in order to improve loading capacity and cargo handling efficiency. Therefore, in container ships and bulk carriers, it is necessary to increase the strength or increase the thickness of the hull panels.

In addition, container ships have become larger in recent years, and large ships of 6,000 to 24,000 TEU are being built. TEU (Twenty Feet Equivalent Unit) represents the number of containers converted into 20-foot-long containers, and is an indicator of the loading capacity of container ships. Along with the increase in size of ships, there is a tendency to use thick steel plates having a plate thickness of 50 mm or more and a yield strength of 390 N/mm ² class or more for the hull shell plates.

In recent years, the steel plates that form the hull shell are often butt welded by high heat input welding, such as electrogas arc welding, from the viewpoint of shortening the construction period. Such high heat input welding is likely to lead to a significant decrease in toughness in the weld heat-affected zone, and has been one of the causes of brittle cracking from the welded joint.

On the other hand, in the hull structure, from the viewpoint of safety, even in the event that brittle fracture occurs, it is necessary to stop the propagation of brittle cracks before they reach a large scale and prevent hull separation. It is believed that there are

Based on this idea, Non-Patent Document 1 reports the results of an experimental study on the brittle crack propagation behavior of welds in shipbuilding steel plates with a thickness of less than 50 mm.

In Non-Patent Document 1, the propagation path and propagation behavior of brittle cracks forcibly generated in welds are experimentally investigated. This document states that if the fracture toughness of the weld zone is secured to some extent, brittle cracks often diverge from the weld zone to the base metal side due to the influence of weld residual stress. Several cases of brittle cracks propagating along the This suggests that the possibility of brittle fracture propagating straight along the weld cannot be ruled out.

However, there are many achievements that ships built by applying welding equivalent to the welding used in Non-Patent Document 1 to steel plates with a thickness of less than 50 mm are in service without any problems. Based on the recognition that good steel plate base materials (e.g. shipbuilding class E steel) have sufficient ability to arrest brittle cracks, the brittle crack propagation arresting properties of welded parts of shipbuilding steel materials are It wasn't specifically requested.

In recent years, large container ships exceeding 6,000 TEU use steel plates with a thickness of more than 50 mm. The fracture toughness tends to further decrease. In such a thick-wall, high-heat-input welded joint, brittle cracks generated from the weld go straight without warping toward the base material, and there is a possibility that they may not stop at the steel plate base material such as aggregate. For example, it is shown in Non-Patent Document 2. Therefore, ensuring the safety of the hull structure using thick high-strength steel plates with a thickness of 50 mm or more has become a major issue. In addition, Non-Patent Document 2 points out that a thick steel plate having a special brittle crack arresting property is required in order to arrest the propagation of brittle cracks that have occurred.

In order to solve such a problem, for example, Patent Document 1 discloses that, in a welded structure, which is preferably a hull plate having a thickness of 50 mm or more, an aggregate is arranged so as to intersect the butt weld portion, and fillet welding is performed. Welded structures are described that are joined by In the technique described in Patent Document 1, a steel plate having a predetermined microstructure is used as a reinforcing material and fillet-welded, so that even if a brittle crack occurs in the butt welded joint, the aggregate, which is the reinforcing material, is used. It is described that brittle fracture can be stopped at and fatal damage such as destruction of the welded structure can be prevented. However, in the technique described in Patent Document 1, a complicated process is required to make the reinforcing material into a steel sheet having a desired structure, resulting in a decrease in productivity and a stable desired structure. There was a problem that it was difficult to secure a steel plate having

In addition, Patent Document 2 describes a welded structure provided with a fillet-welded joint formed by fillet-welding a joining member to a member to be joined. In the welded structure described in Patent Document 2, an unwelded portion remains on the butting surface of the member to be joined in the cross section of the fillet welded joint with the member to be joined, and the width of the unwelded portion is determined by the brittleness of the member to be joined. It is adjusted to satisfy the crack arrestability Kca and a special relational expression. As a result, even if the member to be joined (flange) is a thick material with a plate thickness of 50 mm or more, the propagation of brittle cracks generated in the member to be joined is stopped at the butt surface of the fillet weld, and the brittleness of the member to be joined is prevented. It is stated that it can prevent the propagation of cracks. However, in the technique described in Patent Document 2, since the brittle crack propagation arresting property of the joining member is insufficient, the technique is sufficient to stop the propagation of the brittle crack generated in the member to be joined at the joining member. It can not be said.

Further,

Patent Documents

3, 4, and 5 disclose a welded structure formed by abutting an end surface of a joining member against a surface of a member to be joined and joining the member to be joined and the member to be joined by fillet welding. Are listed. In the techniques described in Patent Documents 3 to 5, a non-welded portion is provided on the surface where the end face of the member to be joined and the surface of the member to be joined meet, and at least one of the weld leg length and weld width is 16 mm or less. In addition to making a welded joint, by making a fillet welded joint in which the toughness of the fillet weld metal satisfies a specific relationship with the plate thickness of the member to be joined, or further, the joint member has brittle crack arrestability By using a steel plate with excellent toughness, or by making the welded structure of the butt weld joint with high toughness, brittle cracks generated from the welded part of the joined member are suppressed at the fillet weld or at the mother of the joined member. It is stated that the propagation can be blocked at the material or at the weld of the joining member and/or the member to be joined.

However, in each of the techniques described in Patent Documents 3 to 5, it is necessary to limit the weld leg length or weld width to 16 mm or less. The maximum plate thickness that can be applied to the joining member (flange) was 80 mm.

In response to such problems, for example, Patent Document 6 discloses a fillet welded joint in which the end surface of a member to be joined is butted against the surface of a member to be joined having a plate thickness of 50 mm or more, and the member to be joined and the member to be joined are joined. A welded structure comprising: In the welded structure described in Patent Document 6, the weld leg length and welding width of the fillet welded joint exceed 16 mm, and the end surface of the member to be joined and the surface of the member to be joined in the fillet welded joint are butted against each other. The cross section of the fillet welded joint has an unwelded portion of 95% or more of the plate thickness tw of the member to be joined, and the smaller value L of the weld leg length and the weld width and the plate thickness tf of the member to be joined By using a fillet weld metal with toughness that satisfies a specific relationship between the two, even if the plate thickness of the joint member is 65 to 120 mm, the fillet weld metal prevents the propagation of brittle cracks that occur in the member to be joined. It is stated that it is possible.

In addition, Patent Document 7 describes a welded structure having a doubler member at the butted portion of the web and flange. In the welded structure described in Patent Document 7, the web is butt fillet welded to the doubler member, an unwelded portion remains on the butt surface, and the tabular member is overlap fillet welded to the flange, and the overlap is welded. Unwelded portions remain on the mating surfaces. The technique described in Patent Document 7 states that if an austenitic steel plate is used for the doubler member, propagation of long brittle cracks can be prevented by the doubler member.

Japanese Patent Application Laid-Open No. 2004-232052 Japanese Patent Application Laid-Open No. 2007-326147 Patent No. 5395985 Patent No. 5365761 Patent No. 5408396 Patent No. 6744274 Patent No. 6615215

However, the technique described in Patent Document 6 requires strict construction management during welding in order to limit the welding leg length and welding width, and there are problems such as a decrease in productivity of welding construction and an increase in construction costs. . In addition, in a structure requiring partial penetration welding with a small unwelded portion, there is a problem that sufficient brittle crack arrestability cannot be ensured. In addition, the technique described in Patent Document 7 has a problem that the construction cost increases due to doubler member processing and welding, and a problem that the material cost rises when using an expensive austenitic steel plate for the doubler member.

The present invention solves the problems of the prior art as described above, and solves the problem of brittle cracks occurring in members to be joined (flanges) with a plate thickness of 50 mm or more without requiring strict construction control during welding. An object of the present invention is to provide a welded structure excellent in brittle crack arrestability, capable of stopping propagation to (web) before reaching large-scale fracture. In addition, the welded structure targeted by the present invention is a welded structure having a T joint formed by butting the end face of the joining member against the surface of the member to be joined and joining them by fillet welding or partial penetration welding. is.

In order to achieve the above objectives, the present inventors diligently studied various factors affecting the brittle crack arrest toughness of T-joints. As a result, if the structure of the weld metal of the T-joint is mainly composed of the austenite phase, the weld metal can be made to have high toughness. It was conceived that even when partial penetration welding is used for joining, a T-joint having excellent brittle crack arrestability can be obtained. And, as a result, propagation of brittle cracks generated in the joined member (flange) to the joined member (web) without special consideration of the brittle crack propagation arresting performance of the thick steel plate used for the joined member (web). can be prevented by the weld metal of the T-joint.

The present invention has been completed by further studies on the above findings. That is, the gist of the present invention is as follows.
[1] A welded structure comprising a T joint in which the end face of a joining member is butted against the surface of a member to be joined having a plate thickness of 50 mm or more, and the member to be joined and the member to be joined are joined, ,
The welding leg length or welding width of the T-joint is 16 mm or more, and furthermore, on the surface where the end surface of the joining member and the surface of the member to be joined in the T-joint are butted, the cross-section of the joining member is There is an unwelded part of 30% or more of the plate thickness,
A welded structure, wherein the weld metal of the T-joint has a structure containing 80% or more of an austenite phase in terms of area %.
[2] The weld metal of the T joint is, in mass%, C: 0.02 to 0.06%, Si: 0.40 to 0.80%, Mn: 0.80 to 1.70%, P: 0.020% or less, S: 0.010% or less, Ni: 7.00 to 13.00% Cr: 14.00 to 24.00% Cr: 14.00 to 24.00% N: 0.150% or less O: 0.050% or less The welded structure according to [1] having a composition with the balance being Fe and unavoidable impurities.
[3] The welded structure according to [1] or [2], wherein the member to be joined has a butt-welded joint portion so as to intersect the member to be joined.
[4] The joining member has a butt-welded joint portion, and the joining member is arranged so that the butt-welded joint portion and the butt-welded joint portion of the member to be welded intersect. 3].
[5] The welded structure according to any one of [1] to [4], wherein the joining member has a plate thickness of 50 mm or more.
[6] The welded structure according to any one of [1] to [5], wherein the non-welded portion has a gap of 10 mm or less between the butting surfaces of the member to be joined and the member to be joined.

According to the present invention, it is possible to prevent the propagation of brittle cracks generated from a thick member to be joined having a plate thickness of 50 mm or more to the member to be joined before it reaches a large-scale failure. Large-scale brittle fracture such as hull separation of ships and bulk carriers can be avoided, and the effect of improving the safety of the hull structure is brought about, which is a remarkable industrial effect. In addition, according to the present invention, brittle crack propagation arrestability can be improved simply by selecting welding materials and adjusting welding conditions during welding without using special steel materials and without compromising safety. There is also an effect that an excellent welded structure can be manufactured.

FIG. 4 is an explanatory diagram schematically showing an example of the configuration of a joint cross section of a T-joint; FIG. 4 is an explanatory diagram schematically showing another example of the configuration of the T-joint; (a) is an external view, and (b) is a sectional view. FIG. 4 is an explanatory diagram schematically showing another example of the configuration of the T-joint; (a) is an external view, and (b) is a sectional view. It is explanatory drawing which shows typically the shape of a large structural model specimen. FIG. 4 is an explanatory diagram showing an example of a groove shape of a T-joint;

In the welded structure of the present invention, as illustrated in FIGS. 1 to 3, the end face of the joining member 1 is butted against the surface of the member 2 to be joined, and the member 1 and the member 2 to be welded are joined. Equipped with a T-joint. The welded structure of the present invention is, for example, a hull structure in which the hull plate of a ship is a member to be joined (flange) and a bulkhead is a member to be joined (web), or a deck is a member to be joined (flange) and a hatch is applicable to hull structures where is a joint member (web).

The material to be joined 2 is a thick steel plate with a plate thickness of 50 mm or more, preferably 60 mm or more and 120 mm or less. Moreover, the joining member 1 is preferably made of a thick steel plate having a plate thickness of 50 mm or more, preferably 60 mm or more and 120 mm or less.

It should be noted that the T-joint included in the welded structure of the present invention has weld metal 5, and its weld leg length 3 or weld width 13 is 16 mm or more. In addition, in the welded structure of the present invention, the non-welded portion 4 (the width 16 of the unwelded portion), which is a structural discontinuity that is not welded, is formed on the butting surfaces of the joining member 1 and the member to be joined 2. The T joint It is preferable that the size of the cross section is 30% or more of the plate thickness of the joining member 1 . The presence of the unwelded portion 4 makes it easier for the brittle crack that has propagated through the member to be joined 2 to stop at the butt surfaces.

A specific example of this state is shown in Fig. 1 as a cross-sectional view of the T joint perpendicular to the weld line. Although FIG. 1(a) shows a case where the member 1 to be joined is upright and joined to the member 2 to be joined, the present invention is not limited to this. For example, as shown in FIG. 1(b), the member 1 to be joined may be joined at an angle θ with respect to the member 2 to be joined. Further, as shown in FIG. 1(c), the unwelded portion 4 may have a gap 14 between the joining member 1 and the joined member 2. As shown in FIG. Furthermore, as shown in FIG. 1(d), a spacer 15 may be inserted into the gap 14. FIG. In addition, the gap 14 is preferably 10 mm or less from the viewpoint of reducing man-hours during welding. In the present invention, the size of the "gap" on the butting surfaces of the joined member and the non-joined member is the longest length at which the perpendicular line from the upper surface of the member to be joined intersects the end surface of the joined member in the cross-sectional view of the T joint perpendicular to the weld line. distance, including the spacer thickness if spacers are inserted. The same applies when the spacer is in contact with one or both selected from the end face of the joined member and the surface of the non-joined member.

It is extremely rare for brittle cracks to occur in base metal parts of steel plates with few defects, and most occur in welded parts. In a T-joint as shown in FIGS. 2 and 3, brittle cracks occur from the butt-welded joint 11 of the members to be joined. In order to prevent the generated brittle crack from propagating to the joining member 1, it is preferable to provide a structural discontinuity between the joining member 1 and the member to be joined 2. FIG. In the present invention, as a discontinuous portion of the structure, an unwelded portion 4 having a dimension of 30% or more of the plate thickness of the joining member 1 is present on the butting surfaces of the joining member 2 and the joining member 1 of the T joint. The upper limit of the width (dimension) 16 of the unwelded portion 4 is 100% of the plate thickness of the joint member 1, preferably 40% or more, more preferably 50% or more, and 99% or less of the plate thickness of the joint member 1. is preferred, and 98% or less is preferred. In the present invention, in addition to the presence of unwelded portions on the butt surfaces as structural discontinuities, the weld metal of the T-joint has excellent toughness, so that brittle crack propagation can be prevented more reliably.

In the welded structure shown in FIG. 2, the member to be joined 2 is a steel plate joined by a butt welded joint 11, and the joined member 1 is a T joint welded so as to intersect the welded portion of the butt welded joint 11. Moreover, in the welded structure shown in FIG. and the butt welded joint 11 of the member to be joined 2 are welded so as to intersect each other.

In FIGS. 2 and 3, the joint member 1 and the butt-welded joint 11 are arranged orthogonally, but the present invention is not limited to this. Needless to say, they may cross each other obliquely. Moreover, the manufacturing method of the T-joint is not particularly limited, and any conventional manufacturing method can be applied. For example, a T-joint may be manufactured by butt-welding the steel plates for the members to be joined and the steel plates for the joining members, and welding the obtained butt-welded joints. In addition, a set of steel plates for joining members before butt welding is tack welded to the members to be joined, then the steel plates for joining members are butt welded together, and the obtained butt welded joint is finally welded to the members to be joined. A T-joint may be manufactured.

In the welded structure of the present invention, the welded leg length 3 or welded width 13 of the T-joint shall be 16 mm or more. If the weld leg length 3 and the weld width 13 are less than 16 mm, it is advantageous to ensure brittle crack arrestability, but if the member plate thickness exceeds 80 mm, it becomes difficult to ensure the strength of the weld. Even if the thickness of the member is 80 mm or less, if the weld leg length 3 and the weld width 13 are less than 16 mm, there is a high risk that it will be difficult to secure the strength of the welded portion due to rework during construction. Although the upper limits of the weld leg length 3 and the weld width 13 are not particularly limited, they are preferably 30 mm or less from the viewpoint of work efficiency and the like.

In addition, in the welded structure of the present invention, the structure of the weld metal of the T joint has an austenite phase of 80% or more, preferably 84% or more, more preferably 88% or more in terms of area%. As a phase other than the austenite phase, a ferrite phase having an area percentage of 0 to 20% can be exemplified. From the viewpoint of preventing solidification cracking, it is important to adjust the amount of ferrite in the weld metal based on the composition of the weld metal, for example, using a Schaeffler structure diagram.

In addition, from the viewpoint of ensuring the strength of the welded structure, the weld metal having the above structure has a Vickers hardness of 170 to 260 HV (yield strength of 390 MPa or more, tensile strength of 490 MPa or more). It is preferred to have

By making the structure of the weld metal a structure having an austenite phase of 80% or more in terms of area %, the toughness of the weld metal is improved. Propagation of a brittle crack generated in the joint member can be stopped by the weld metal of the fillet welded joint, and propagation of the brittle crack to the joint member can be prevented.

In addition, the weld metal of the T joint having the above structure is, in mass%, C: 0.02 to 0.06%, Si: 0.40 to 0.80%, Mn: 0.80 to 1.70%, P: 0.020% or less, S: 0.010% or less. , Ni: 7.00 to 13.00%, Cr: 14.00 to 24.00%, N: 0.150% or less, O: 0.050% or less, and the balance is Fe and unavoidable impurities.

Next, the reasons for limiting the weld metal composition of the T-joint will be explained. Hereinafter, mass% in the composition is simply described as %.

C: 0.02-0.06%
C is an element that precipitates as carbides during welding and causes intergranular corrosion and pitting corrosion, which lowers corrosion resistance. In order to obtain such an effect, the content of 0.02% or more is required. However, when the content exceeds 0.06%, the corrosion resistance is lowered. Therefore, C is limited to the range of 0.02-0.06%. Incidentally, it is preferably 0.02 to 0.05%.

Si: 0.40-0.80%
Si acts as a deoxidizing agent and also contributes to increasing the strength of the weld metal. In order to obtain such an effect, the content of 0.40% or more is required. However, if the content exceeds 0.80%, it segregates during solidification and forms a liquid phase at solidification cell interfaces, resulting in a decrease in hot cracking resistance. Furthermore, the toughness is lowered. Therefore, Si is limited to the range of 0.40-0.80%. Incidentally, it is preferably 0.40 to 0.70%.

Mn: 0.80-1.70%
Mn is an element that acts as a deoxidizing agent and contributes to increasing the strength of the austenite phase, and is contained in an amount of 0.80% or more in the present invention. On the other hand, a content exceeding 1.70% causes embrittlement. Therefore, Mn is limited to the range of 0.80-1.70%. Incidentally, it is preferably 0.90 to 1.60%.

P: 0.020% or less P is an element that is unavoidably included, and segregates at grain boundaries to adversely affect hot cracking resistance, so it is desirable to reduce it as much as possible. However, excessive reduction leads to an increase in refining costs, so in the present invention P is limited to 0.020% or less. If P is 0.020% or less, a weld metal having excellent hot cracking resistance can be obtained. Incidentally, P is preferably 0.010% or less.

S: 0.010% or less S is an unavoidable element that segregates at grain boundaries and adversely affects hot cracking resistance, so it is desirable to reduce it as much as possible. However, excessive reduction leads to an increase in refining costs, so in the present invention S is limited to 0.010% or less. Incidentally, S is preferably 0.007% or less.

Ni: 7.00-13.00%
Ni is an element that stabilizes the austenite phase, and the present invention requires a content of 7.00% or more. On the other hand, if the content exceeds 13.00%, the material cost will rise. Therefore, Ni is limited to the range of 7.00 to 13.00%. Incidentally, it is preferably 7.50 to 12.50%.

Cr: 14.00-24.00%
Cr has the effect of improving the strength of the weld metal. In the present invention, if Cr is less than 14.00%, the above effects cannot be sufficiently secured. On the other hand, if the content exceeds 24.00%, the toughness and hot cracking resistance of the weld metal are lowered. Therefore, Cr is limited to the range of 14.00-24.00%. Incidentally, it is preferably 14.50 to 23.50%.

N: 0.150% or less N is an element that is unavoidably contained, but it is an element that has the effect of increasing the strength of the weld metal in a solid solution state, and it is desirable to contain 0.003% or more. On the other hand, an excessive content lowers the toughness. Therefore, N is limited to a range of 0.150% or less. Incidentally, it is preferably 0.003 to 0.120%.

O: 0.050% or less O (oxygen) is an element that is unavoidably mixed, forms Al-based oxides and Si-based oxides in the weld metal, and contributes to suppressing the coarsening of the solidified structure. Since such an effect becomes remarkable at a content of 0.003% or more, it is desirable to have a content of 0.003% or more. Therefore, O (oxygen) is limited to 0.050% or less. Incidentally, it is preferably 0.003 to 0.040%.

The above components are the basic components, but in addition to these basic components, one or two elements selected from Nb: 0.10% or less and Ti: 0.10% or less are selected for the purpose of improving strength. More than one species can be selected and contained.

The balance other than the above elements consists of Fe and unavoidable impurities.

The weld metal of the T-joint having the composition and structure described above is preferably formed by performing multi-layer welding by adjusting the welding material and welding conditions so as to obtain the composition and structure described above. .

As the welding method, the commonly used welding covered arc welding method and gas metal arc welding method are both suitable. In addition, as the welding material, commercial coated welding rods specified in JIS Z 3221, commercial solid wires specified in JIS Z 3321, and commercial flux-cored wires specified in JIS Z 3323 are all suitable. be. Needless to say, a solid wire adjusted to a desired composition may be used.

In welding, as shown in FIG. 5, the joining member 1 may be provided with a groove having a predetermined angle (for example, 40° or less).

The present invention will be further described below based on examples.

Yield strength at plate thickness tw shown in Table 2: 355 to 460 N/mm Class ² thick steel plate is used as joint member 1, yield strength at plate thickness tf shown in Table 2: 355 to 460 N/mm Class ² thick steel plate Used as the joining member 2, the end surface of the joining member 1 is butted against the surface of the member to be joined 2, and these are welded to form the shapes shown in FIGS. A large welded joint 9 was produced. The member to be joined is a thick steel plate (base material only) (Fig. 4(a)) or a thick steel plate having a butt-welded joint (Figs. 4(b) and (c)), and the member to be joined is a thick steel plate (base material). material only) (Figs. 4(a), (b)), or thick steel plates with butt weld joints (Fig. 4(c)). The butt-welded joints were produced by one-pass high-heat-input electrogas arc welding (SEGARC and two-electrode SEGARC) or multi-layer carbon dioxide gas welding (multi-layer CO ₂ ) with welding heat inputs shown in Table 2.

Welding was performed using the gas metal arc welding method (GMAW) so that the weld metal had the composition shown in Table 1, the structure and hardness shown in Table 2, and the welding width or weld leg length. Welded joints (T joints) were prepared by changing welding conditions such as heat and shield gas. The welding material was a flux-cored wire with a diameter of 1.2 mm specified in JIS Z 3323. In some welded joints, a gap 14 was provided between the joining member 1 and the member to be joined 2 . Further, in some welded joints, the joint member 1 was welded with a groove as shown in FIG.

A test piece was taken from the weld metal of the obtained T-joint, and the composition of the weld metal was determined using an emission spectroscopic analysis method. Weld metal hardness was measured using a meter (load 0.3 to 1.0 kgf). Table 2 shows the results obtained.

Next, using the obtained large welded joint 9, a super-large structural model specimen shown in Fig. 4 was produced, and a brittle crack arrest test was performed. For the ultra-large structural model specimen, a steel plate having the same thickness as the member to be joined 2 was welded below the member to be joined 2 of the large welded joint 9 by tack welding 8 .

In addition, in the ultra-large structural model specimen shown in FIG. In the structural model specimen, the butt-welded joint portion 11 of the member to be joined 2 and the butt-welded joint portion 12 of the joining member 1 were crossed. Then, the tip of the mechanical notch 7 was machined to become the bond portion BOND of the butt weld joint portion 11 or the weld metal WM.

Also, in the brittle crack arrest test, the mechanical notch 7 was hit to generate a brittle crack, and it was investigated whether or not the propagated brittle crack would stop at the weld metal. All tests were conducted under conditions of stress of 243 to 283 N/mm ² and temperature of -10°C. The stress of 243 N/mm ² is equivalent to the maximum allowable stress of 355 N/mm class ² steel plate applied to the hull, and the stress of 257 N/mm ² is the yield strength of 390 N/mm ² applied to the hull. The stress of 283N/mm ² , the value equivalent to the maximum allowable stress of class steel plates, is the value equivalent to the maximum allowable stress of 460N/mm ² class steel plates with a yield strength applied to ship hulls. Temperature: -10°C is the ship's design temperature.

Table 3 shows the results obtained.

In all of the present invention examples, after the brittle crack propagated through the joined member 2, it plunged into the weld metal 5 and stopped. On the other hand, in all of the comparative examples, the brittle crack propagated through the joined member 2 and then propagated through the joined member 1 without stopping at the weld metal 5 . That is, in the comparative example, the weld metal 5 could not prevent the propagation of brittle cracks.

1 Joined member 2 Joined member 3 Weld leg length 4 Unwelded portion 5 Weld metal 7 Machine notch 8 Tack weld 9 Large weld joint 11 Butt weld joint of joined member 12 Butt weld joint of joined member 13 Weld width 14 Gap 15 Spacer 16 Dimensions of unwelded portion (width of unwelded portion)

Claims

A welded structure comprising a T joint in which the end surface of a joining member is butted against the surface of a member to be joined having a plate thickness of 50 mm or more, and the member to be joined and the member to be joined are joined,
The welding leg length or welding width of the T-joint is 16 mm or more, and furthermore, on the surface where the end surface of the joining member and the surface of the member to be joined in the T-joint are butted, the cross-section of the joining member is There is an unwelded part of 30% or more of the plate thickness,
A welded structure, wherein the weld metal of the T-joint has a structure containing 80% or more of an austenite phase in terms of area %.
The weld metal of the T joint is, in mass%, C: 0.02 to 0.06%, Si: 0.40 to 0.80%, Mn: 0.80 to 1.70%, P: 0.020% or less, S: 0.010% or less, Ni: 7.00 to 13.00. %, Cr: 14.00 to 24.00%, N: 0.150% or less, O: 0.050% or less, and the balance being Fe and unavoidable impurities.
The welded structure according to claim 1 or 2, wherein the members to be joined have butt weld joints so as to intersect with the members to be joined.
4. The joining member according to claim 3, wherein the joining member has a butt weld joint, and the joining member is arranged such that the butt weld joint and the butt weld joint of the member to be welded intersect. welded structure.
The welded structure according to any one of claims 1 to 4, wherein the joining member has a plate thickness of 50 mm or more.
The welded structure according to any one of claims 1 to 5, wherein the non-welded portion has a gap of 10 mm or less between the butting surfaces of the member to be joined and the member to be joined.