KR20240007762A - welded structure - Google Patents

Abstract

The present invention provides a welded structure with excellent brittle crack propagation stopping performance. The welded structure is provided with a T joint in which the cross section of the joined member abuts the surface of a member to be joined with a plate thickness of 50 mm or more, and the joined member and the member to be joined are joined, and the weld metal of the T joint is, It has a structure with an austenite phase of 80% or more in area percent. In the above-mentioned welded structure, it is possible to prevent the propagation of brittle cracks generated from thick joined members to the joined members before they lead to large-scale destruction simply by selecting the welding material and adjusting the welding conditions during welding construction. , the safety of the hull structure can be improved.

Description

welded structure

The present invention relates to a welded steel structure (welded structure) constructed by welding using thick steel plates, for example, a large container ship or bulk carrier. Among them, in particular, it relates to a welded structure with excellent brittle crack propagation stopping properties that can stop the propagation of brittle cracks generated from the base material or weld joint portion of a thick steel plate before it leads to large-scale destruction of the structure.

Container ships and bulk carriers, unlike tankers, for example, have a structure with a large opening at the top of the ship in order to improve loading capacity and unloading efficiency. Therefore, in container ships and bulk carriers, it is especially necessary to increase the strength or thicken the hull shell plating.

In addition, container ships have recently become larger, and large ships such as 6,000 to 24,000 TEU are being constructed. Additionally, TEU (Twenty Feet Equivalent Unit) represents the number converted into containers with a length of 20 feet and represents an index of the loading capacity of a container ship. With the increase in the size of ships, there is a tendency to use thick steel plates with a plate thickness of 50 mm or more and a yield strength of 390 N/mm2 or more for the hull shell plating.

Recently, steel plates used as hull shells are often butt welded by large-heat input welding, such as electro gas arc welding, from the viewpoint of shortening the construction period. Such high-heat input welding tends to lead to a significant decrease in toughness in the weld heat-affected zone, and has become one of the causes of brittle cracks occurring in the welded joint portion.

On the other hand, in the hull structure, from the viewpoint of safety, it has conventionally been considered necessary to prevent hull separation by stopping the propagation of brittle cracks before they lead to large-scale failure, even if brittle fracture occurs.

Taking this line of thinking, Non-Patent Document 1 reports the results of an experimental study on the brittle crack propagation behavior of welded areas in shipbuilding steel plates with a plate 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. Here, results are described showing that when the fracture toughness of the weld zone is secured to a certain degree, brittle cracks often deviate from the weld zone toward the base material due to the influence of weld residual stress. However, there are also multiple examples of brittle cracks propagating along the weld zone. It is being confirmed. This suggests that it cannot be asserted that there is no possibility of brittle fracture propagating straight along the weld zone.

However, in addition to the many records showing that ships built by applying welding equivalent to the welding used in Non-Patent Document 1 to steel plates with a plate thickness of less than 50 mm are in service without any problems, the steel plate base material with good toughness (shipbuilding E-grade steel) etc.), the ability to stop brittle cracks is sufficiently preserved, so the brittle crack propagation stopping characteristic of welded portions of shipbuilding steel materials has not been specifically required in classification rules, etc.

In recent large container ships exceeding 6,000 TEU, the plate thickness of the steel plate used exceeds 50 mm, and in addition to the decrease in fracture toughness due to increased plate thickness, large heat input welding with larger welding heat input is adopted, and the weld zone The fracture toughness tends to further decrease. In such a thick heat input welded joint, non-patent document 2 shows, for example, that there is a possibility that a brittle crack generated from the weld zone proceeds straight without bending toward the base material side and does not stop even in the steel sheet base material portion such as aggregate. For this reason, securing the safety of hull structures using thick high-strength steel plates with a plate thickness of 50 mm or more has become a major problem. Additionally, in Non-Patent Document 2, it is pointed out that a thick steel plate having special brittle crack propagation stopping characteristics is required, especially in order to stop the propagation of brittle cracks that have occurred.

Regarding this problem, for example, Patent Document 1 describes a welded structure, preferably a hull shell plate with a plate thickness of 50 mm or more, in which aggregates are arranged to intersect the butt welds and joined by fillet welding. there is. In the technology described in Patent Document 1, by forming a structure in which a steel plate having a predetermined microstructure is fillet-welded as a reinforcing material, even if a brittle crack occurs in the butt weld joint, brittle fracture can be stopped with the aggregate as a reinforcing material, thereby forming a welded structure. It is stated that it can prevent fatal damage such as destruction. However, the technology described in Patent Document 1 requires a complicated process to turn the reinforcing material into a steel sheet with the desired structure, and as a result, productivity decreases, making it difficult to stably secure a steel sheet with the desired structure. There was a problem that it was difficult.

Additionally, Patent Document 2 describes a welded structure including a fillet weld joint formed by fillet welding a joining part to a joined part. In the welded structure described in Patent Document 2, an unwelded portion remains on the surface of the joined member in the cross section of the fillet weld joint butted 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 a special relationship with the crack propagation stopping performance (Kca). Accordingly, even if the member to be joined (flange) is made of a thick material with a plate thickness of 50 mm or more, the propagation of brittle cracks generated in the joined member is stopped at the butt surface of the fillet weld zone, thereby reducing the brittleness of the member to be joined. It is stated that it can prevent the propagation of cracks. However, the technology described in Patent Document 2 cannot be said to be a sufficient technology for stopping the propagation of brittle cracks generated in the joined members because the brittle crack propagation stopping characteristics of the joined members are insufficient.

Additionally, Patent Document 3, Patent Document 4, and Patent Document 5 describe a welded structure formed by bringing the cross section of a joined member into contact with the surface of a member to be joined and joining the joined member and the member to be joined by fillet welding. In the techniques described in Patent Documents 3 to 5, a non-welded portion is provided on the surface where the end surface of the joined member and the surface of the member to be joined are joined, and at least one of the weld leg length or weld width is a fillet of 16 mm or less. After forming a welded joint, a fillet welded joint is made that satisfies a specific relationship between the toughness of the fillet welded metal and the plate thickness of the member to be joined, or the joined member is made into a steel sheet excellent in stopping the propagation of brittle cracks. Alternatively, by forming a welded structure in which the weld metal of the butt weld joint has high toughness, brittle cracks occurring from the welded portion of the joined members can be prevented from occurring in the fillet weld zone, or in the base metal of the joined member, or of the joined member and/or the joined member. It is stated that radio waves can be blocked at welds.

However, in each of the technologies described in Patent Documents 3 to 5, it is necessary to limit the weld leg length or weld width to 16 mm or less. Therefore, from the viewpoint of ensuring the strength of the fillet weld zone, the joined member (web) and the joined member The maximum plate thickness that could be applied to (flange) was 80 mm.

Regarding this problem, for example, Patent Document 6 discloses a welding method in which the cross section of a joining member is abutted against the surface of a member to be joined with a plate thickness of 50 mm or more, and a fillet weld joint is provided for joining the joined member to the member to be joined. The structure is described. In the welded structure described in Patent Document 6, the weld leg length and weld width of the fillet weld joint exceed 16 mm, and the cross section of the fillet weld joint is formed on the surface of the joined member in the fillet weld joint and the surface of the member to be joined. has a non-bonded portion of 95% or more of the plate thickness (tw) of the joined member, and there is a specific relationship between the smaller value (L) of the weld leg length and weld width and the plate thickness (tf) of the joined member. It is described that by using a fillet weld metal with a toughness that satisfies, even if the plate thickness of the joined members is 65 to 120 mm, brittle cracks generated in the joined members can be prevented from propagating in the fillet weld metal.

Additionally, Patent Document 7 describes a welded structure including a doubler part at the butt joint between the web and the flange. In the welded structure described in Patent Document 7, the web is fillet welded against a doubler member, a non-bonded portion remains on the abutting surface, and the doubler member is overlap fillet welded to the flange, and a non-bonded portion remains on the overlapping surface. It remains. In the technology described in Patent Document 7, it is described that if an austenitic steel sheet is used for the doubler member, the propagation of a long brittle crack can be prevented by the doubler member.

Japanese Patent Publication No. 2004-232052 Japanese Patent Publication No. 2007-326147 Japanese Patent Publication No. 5395985 Japanese Patent Publication No. 5365761 Japanese Patent Publication No. 5408396 Japanese Patent Publication No. 6744274 Japanese Patent Publication No. 6615215

Japanese Association of Shipbuilding Research, Research Section 147: “Study on the evaluation of brittle fracture strength of high-strength steel plate high-heat input welded joints for hull use”, No. 87 (February 1978), p.35-53, Japan Association of Shipbuilding Kinya Yamaguchi et al.: “Development of ultra-large container ships - Practical use of new high-strength, ultra-thick steel plates -”, Journal of the Japan Society of Ship and Ocean Engineers, No. 3 (2005), p.70-76, November 2005.

However, in the technology described in Patent Document 6, strict construction management during welding is essential to limit the weld length and weld width, and there are problems such as lower productivity of welding construction and increased construction costs. In addition, in structures that require partial welding with small non-bonded areas, there was a problem that sufficient brittle crack propagation stopping performance could not be secured. Additionally, in the technology described in Patent Document 7, there is a problem that construction costs increase due to processing and welding of doubler members, and that material costs increase significantly when expensive austenitic steel sheets are used for doubler members.

The present invention solves the problems of the prior art as described above, and eliminates the need for strict construction management during welding, and solves the problem of brittle cracks occurring in joined members (flanges) with a plate thickness of 50 mm or more in joint members (webs). The purpose is to provide a welded structure with excellent brittle crack propagation stopping performance that can prevent the propagation of cracks before they lead to large-scale destruction. In addition, the welded structure to which the present invention is intended is a welded structure having a T joint formed by bringing the cross section of the joined member into contact with the surface of the member to be joined and welding them together by fillet welding or partial penetration welding.

In order to achieve the above-mentioned object, the present inventors carefully studied various factors affecting the brittle crack propagation arrest toughness of the T joint. As a result, if the structure of the weld metal of the T joint is mainly composed of austenite phase, the weld metal can be made high toughness, for example, in cases where the weld leg length or weld width of the weld metal is 16 mm or more, We realized that even when partial penetration welding is used for joining, a T joint with excellent brittle crack propagation stopping performance can be used. Accordingly, without special consideration of the brittle crack propagation stopping performance of the thick steel plate used for the joining member (web), the propagation of the brittle crack occurring in the joined member (flange) to the joining member (web) is prevented by the T joint. It was recognized that this could be prevented with weld metal.

The present invention was completed by adding additional examination to the above-mentioned knowledge. That is, the gist of the present invention is as follows.

[1] A welded structure comprising a T-joint where the cross section of a joined member abuts the surface of a member to be joined having a plate thickness of 50 mm or more, and the joined member and the member to be joined are joined,

The welding leg length or welding width of the T joint is 16 mm or more, or additionally, on the surface of the T joint in which the cross section of the bonding member and the surface of the member to be joined are in contact with each other, the bonding member is present in the cross section of the T joint. There is an unattached area of more than 30% of the plate thickness,

A welded structure, characterized in that the weld metal of the T joint has a structure containing an austenite phase of 80% or more in area percentage.

[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: The welded structure according to [1] above, which contains 7.00 to 13.00%, Cr: 14.00 to 24.00%, N: 0.150% or less, and O: 0.050% or less, with the balance being Fe and inevitable impurities.

[3] The welded structure according to [1] or [2] above, wherein the member to be joined has a butt weld joint portion so as to intersect the member to be joined.

[4] The method described in [3] above, wherein the joining member has a butt weld joint portion, and the joining member is disposed so that the butt weld joint portion intersects the butt weld joint portion of the member to be welded. Welded structure.

[5] The welded structure according to any one of [1] to [4] above, 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] above, wherein the non-bonded portion has a gap of 10 mm or less between the joining surface of the joining member and the joined member.

According to the present invention, it becomes possible to prevent the propagation of brittle cracks generated from thick joined members with a plate thickness of 50 mm or more to the joined members before they lead to large-scale destruction, especially in hulls such as large container ships and bulk carriers. Large-scale brittle fractures such as separation can be avoided, which has the effect of improving the safety of the hull structure, showing a special industrial effect. Furthermore, according to the present invention, a welded structure with excellent brittle crack propagation stopping performance can be created by simply selecting welding materials or adjusting welding conditions during welding work, without using special steel materials or compromising safety. It also has the effect of being able to be manufactured.

1 is an explanatory diagram schematically showing an example of the configuration of a joint cross section of a T joint.
Figure 2 is an explanatory diagram schematically showing another example of the configuration of a T joint. (a) is an exterior view, and (b) is a cross-sectional view.
Figure 3 is an explanatory diagram schematically showing another example of the configuration of a T joint. (a) is an exterior view, and (b) is a cross-sectional view.
Figure 4 is an explanatory diagram schematically showing the shape of a large structural model test specimen.
Figure 5 is an explanatory diagram showing an example of a groove shape of a T joint.

(Form for carrying out the invention)

As illustrated in FIGS. 1 to 3, the welded structure of the present invention has the cross section of the joining member 1 abutted against the surface of the member to be joined 2, and the joining member 1 and the member to be welded 2 are joined. Equipped with a T joint. The welded structure of the present invention is, for example, a hull structure in which the hull shell of a ship is a member to be joined (flange), the bulkhead is a member to be joined (web), or the deck is a member to be joined (flange), and the hatch is a member to be joined. Applicable to (web) hull structure.

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

In addition, the T joint provided with the welded structure of the present invention has weld metal 5, and the 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 (width 16 of the non-welded portion), which is a structural discontinuity that is not welded, is T It is desirable to have a dimension of 30% or more of the plate thickness of the joint member 1 in the cross section of the joint. Due to the presence of the non-bonded portion 4, the brittle crack that has propagated through the member to be joined 2 is likely to stop at the abutting surface.

A specific example of this state is shown in Figure 1 when viewed from a T joint cross section perpendicular to the weld line. Fig. 1(a) shows a case where the joining member 1 stands upright and is joined to the member to be joined 2, but the present invention is not limited to this. For example, as shown in FIG. 1(b), the joining member 1 may be joined at an angle θ with respect to the member to be joined 2. Additionally, as shown in FIG. 1(c), the non-bonded portion 4 may have a gap 14 between the joining member 1 and the member to be joined 2. Additionally, as shown in FIG. 1(d), a spacer 15 may be inserted into the gap 14. Additionally, the gap 14 is preferably 10 mm or less from the viewpoint of reducing the number of steps during welding. In the present invention, the size of the “gap” in the butt surface of the joined member and the non-joined member is such that the perpendicular line from the upper surface of the joined member intersects the cross section of the joined member when viewed from the T joint cross section perpendicular to the weld line. This is the longest distance, and if a spacer is inserted, it includes the spacer thickness. The same applies to the case where the spacer is in contact with one or both sides selected from the end surface of the bonded member and the surface of the non-bonded member.

Brittle cracks rarely occur in the base metal part of a steel sheet with few defects, and most of them occur in the welded area. In a T joint as shown in FIG. 2 or FIG. 3, a brittle crack occurs from the butt weld joint portion 11 of the member to be joined. In order to prevent the generated brittle crack from propagating to the joining member 1, it is desirable to provide a structural discontinuity between the joining member 1 and the joined member 2. In the present invention, as a structural discontinuity, an unattached portion 4 is present on the butting surface of the joined member 2 and the bonded member 1 of the T joint with a dimension of 30% or more of the plate thickness of the bonded member 1. I order it. The upper limit of the width (dimension) 16 of the non-bonded portion 4 is 100% of the plate thickness of the bonding member 1, preferably 40% or more of the plate thickness of the bonding member 1, and 50% or more. It is more preferable, and 99% or less is preferable, and 98% or less is preferable. In the present invention, in addition to providing a non-bonded portion on the abutting surface as a structural discontinuity, the weld metal of the T joint is made to have excellent toughness, so that the propagation of a brittle crack 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 weld joint 11, and the joined member 1 is welded so as to intersect the weld portion of the butt weld joint 11. It's a joint. In addition, in the welded structure shown in FIG. 3, the joining member 1 is a steel plate joined by a butt weld joint 12, and the member to be joined 2 is a steel plate joined by a butt weld joint 11. It is a T joint welded so that the butt weld joint 12 of the member 1 and the butt weld joint 11 of the member 2 to be joined intersect.

2 and 3, the joining member 1 and the butt weld joint 11 are arranged to be perpendicular to each other, but the present invention is not limited to this. It goes without saying that it is okay to cross them at an angle. In addition, the manufacturing method of the T joint does not need to be particularly limited, and any commercially available manufacturing method can be applied. For example, a T joint may be manufactured by butt welding steel plates for joined members and steel plates for joining members, and welding the resulting butt welded joint. In addition, before butt welding, a set of steel plates for joining members are tack welded to the members to be joined, and then the steel plates for joining members are butt welded to each other, and the resulting butt welded joint is main welded to the members to be joined to form a T joint. It may be manufactured.

In the welded structure of the present invention, the weld leg length 3 or weld width 13 of the T joint is 16 mm or more. When the weld leg length 3 and the weld width 13 are less than 16 mm, it is advantageous to ensure brittle crack propagation stopping performance, but when the member plate thickness exceeds 80 mm, it becomes difficult to secure the strength of the weld zone. . In addition, even if the member plate thickness is 80 mm or less, if the weld leg length 3 and the weld width 13 are less than 16 mm, the risk of securing the strength of the weld zone increases due to repairs during construction. In addition, the upper limits of the weld leg length 3 and the weld width 13 are not particularly limited, but are preferably set to 30 mm or less from the viewpoint of construction efficiency and the like.

Additionally, in the welded structure of the present invention, the structure of the weld metal of the T joint is a structure having an austenite phase of 80% or more in area percentage, preferably 84% or more, and more preferably 88% or more. Examples of phases other than the austenite phase include 0 to 20% ferrite phase in area percent. For the ferrite phase, from the viewpoint of preventing solidification cracks, it is important to adjust the amount of ferrite in the weld metal based on the weld metal composition using, for example, a Schaeffler diagram.

In addition, the weld metal having the above structure should have a hardness (strength) characteristic of 170 to 260 HV in terms of Vickers hardness (390 MPa or more in yield strength and 490 MPa or more in tensile strength) from the viewpoint of securing the strength of the welded structure. desirable.

By making the structure of the weld metal a structure with an austenite phase of 80% or more in area percentage, the toughness of the weld metal is improved, even when the weld leg length 3 or weld width 13 of the T joint is 16 mm or more. , the propagation of brittle cracks occurring in the joined members can be stopped by the weld metal of the fillet weld joint, and the propagation of the brittle cracks to the joined members 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, and 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 has a weld metal composition consisting of the balance of Fe and inevitable impurities.

Next, the reason 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 to 0.06%

C is an element that precipitates as carbide during welding, causes intergranular corrosion and pitting, and reduces corrosion resistance. However, it also has the effect of increasing the strength of the weld metal through solid solution strengthening. In order to obtain this effect, a content of 0.02% or more is required. However, if it contains more than 0.06%, corrosion resistance decreases. Therefore, C was limited to the range of 0.02 to 0.06%. Also, preferably, it is 0.02 to 0.05%.

Si: 0.40 to 0.80%

Si not only acts as a deoxidizer, but also contributes to increasing the strength of the weld metal. In order to obtain this effect, a content of 0.40% or more is required. However, if it contains more than 0.80%, it segregates during solidification, creates a liquid phase at the solidification cell interface, and reduces high-temperature cracking resistance. Additionally, toughness decreases. For this reason, Si was limited to the range of 0.40 to 0.80%. Moreover, it is preferably 0.40 to 0.70%.

Mn: 0.80 to 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, content exceeding 1.70% causes embrittlement. For this reason, Mn was limited to the range of 0.80 to 1.70%. Moreover, it is preferably 0.90 to 1.60%.

P: 0.020% or less

P is an element that is inevitably included, and it segregates at grain boundaries and has a detrimental effect on high-temperature cracking resistance, so it is desirable to reduce it as much as possible. However, since excessive reduction leads to an increase in refining costs, P is limited to 0.020% or less in the present invention. If P is 0.020% or less, a weld metal with excellent high-temperature crack resistance can be secured. Also, preferably, P is 0.010% or less.

S: 0.010% or less

S is an element that is inevitably included, and it segregates at grain boundaries and has a detrimental effect on high-temperature cracking resistance, so it is desirable to reduce it as much as possible. However, since excessive reduction leads to an increase in refining costs, S is limited to 0.010% or less in the present invention. Also, preferably, S is 0.007% or less.

Ni: 7.00∼13.00%

Ni is an element that stabilizes the austenite phase, and in the present invention, its content is required to be 7.00% or more. On the other hand, content exceeding 13.00% causes a high increase in material costs. For this reason, Ni was limited to the range of 7.00 to 13.00%. Moreover, 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 effect cannot be sufficiently secured. On the other hand, if it contains more than 24.00%, the toughness and high-temperature crack resistance of the weld metal decrease. For this reason, Cr was limited to the range of 14.00 to 24.00%. Moreover, it is preferably 14.50 to 23.50%.

N: 0.150% or less

Although N is an element that is inevitably contained, it is an element that has the effect of increasing the strength of the weld metal in a solid solution state, and it is preferable to contain 0.003% or more. On the other hand, if it is contained excessively, toughness decreases. For this reason, N is limited to 0.150% or less. Moreover, it is preferably 0.003 to 0.120%.

O: 0.050% or less

O (oxygen) is an element that is inevitably mixed, and forms Al-based oxides and Si-based oxides in the weld metal, contributing to suppressing the coarsening of the solidification structure. Since this effect becomes noticeable when the content is 0.003% or more, it is preferable to contain 0.003% or more. However, if it is contained in a large amount exceeding 0.050%, coarsening of the oxide becomes significant. Therefore, O (oxygen) was limited to 0.050% or less. Moreover, it is preferably 0.003 to 0.040%.

Although the above-mentioned components are basic components, in addition to these basic components, one or two or more types selected from among Nb: 0.10% or less and Ti: 0.10% or less are contained as optional elements for the purpose of improving strength. can do.

The remainder other than the above elements consists of Fe and inevitable impurities.

The weld metal of the T joint having the above-mentioned composition and the above-described structure is preferably formed by performing multiple welding by adjusting the welding material and welding conditions so that the above-described composition and structure are obtained.

As a welding method, both the commercially available shielded arc welding method and the gas metal arc welding method are suitable. Additionally, as welding materials, commercially available coated welding electrodes specified in JIS Z 3221, commercially available solid wires specified in JIS Z 3321, and commercially available flexed wires specified in JIS Z 3323 are all suitable. Additionally, it goes without saying that a solid wire adjusted to a desired composition may be used.

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

Hereinafter, the present invention will be further explained based on examples.

Example

Yield strength of the plate thickness (tw) shown in Table 2: 355 to 460 N/mm2 grade A thick steel plate is used as the joining member (1), and yield strength of the plate thickness (tf) shown in Table 2: 355 to 460 N/mm2 grade. Using a steel plate as the member to be joined 2, the cross section of the member to be joined 1 is brought against the surface of the member to be joined 2, and these are welded, as shown in Figures 4(a), (b), and (c). A large welded joint (9) of the actual structural size was manufactured. In addition, the member to be joined is a thick steel plate (base material only) (FIG. 4(a)) or a thick steel plate with a butt weld joint (FIG. 4(b), (c)), and the joining member is a thick steel plate (base material) (FIG. 4(a), (b)), or a thick steel plate with a butt weld joint (FIG. 4(c)). In addition, the butt weld joint was produced by one-pass large heat input electro gas arc welding (SEGARC and two-electrode SEGARC) or multi-carbon dioxide gas welding (multi-layer CO ₂ ) with the welding heat input shown in Table 2.

In addition, welding is performed using gas metal arc welding (GMAW) so that the weld metal has the composition shown in Table 1, the structure shown in Table 2, the hardness, and the weld width or weld length, using welding materials, welding heat input, and shielding gas. A welded joint (T joint) was produced by changing the welding conditions. The welding material was a flexed wire with a diameter of 1.2 mm specified in JIS Z 3323. Additionally, in some welded joints, a gap 14 was formed between the joining member 1 and the member to be joined 2. In addition, in some welded joints, the joining member 1 was welded with an improvement as shown in FIG. 5.

In addition, a test piece was collected from the weld metal of the obtained T joint, the weld metal composition was determined using emission spectroscopy, etc., and the weld metal structure was determined by phase analysis using EBSD (electron backscattering diffraction) method using a Vickers hardness tester (load 0.3 to 0.3). The weld metal hardness was measured using 1.0 kgf). The obtained results are shown in Table 2.

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

In addition, in the ultra-large structural model test specimen shown in FIG. 4(b), the butt weld joint portion 11 of the member to be joined 2 is manufactured so as to be perpendicular to the joining member 1, and also shown in FIG. 4(c). In the ultra-large structural model test specimen, the butt welded joint portion 11 of the joined member 2 and the butt welded joint portion 12 of the joined member 1 were crossed. Then, the tip of the machine notch 7 was processed to become the bond portion (BOND) or weld metal (WM) of the welded joint portion 11.

In addition, in the brittle crack propagation arrest test, a blow was applied to the machine notch 7 to generate a brittle crack, and it was investigated whether the propagated brittle crack stopped in the weld metal. All tests were conducted under the conditions of stress of 243 to 283 N/mm2 and temperature of -10°C. The stress of 243N/㎟ is equivalent to the maximum allowable stress of steel sheets with a yield strength of 355N/㎟ applied to the hull, and the stress of 257N/㎟ is equivalent to the maximum allowable stress of steel sheets with a yield strength of 390N/㎟ applied to the hull. The value, stress of 283N/㎟, is a value equivalent to the maximum allowable stress of a steel plate with a yield strength of 460N/㎟ applied to the hull. Temperature: -10℃ is the ship's design temperature.

The obtained results are shown in Table 3.

In all of the present invention examples, after the brittle crack propagated through the joined members 2, it entered the weld metal 5 and stopped. On the other hand, in all of the comparative examples, the brittle crack propagated to the joined member 1 without stopping at the weld metal 5 after propagating through the joined member 2. That is, in the comparative example, the propagation of the brittle crack in the weld metal 5 could not be prevented.

1: joining part
2: Joined part
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 members
12: Butt weld joint of joining members
13: Welding width
14: gap
15: spacer
16: Dimension of unwelded part (width of unwelded part)

Claims (6)

A welded structure comprising a T-joint in which the cross section of a joined member abuts the surface of a member to be joined having a plate thickness of 50 mm or more, and the joined member and the member to be joined are joined,
The weld leg length or welding width of the T joint is 16 mm or more, or additionally, the cross section of the joining member in the T joint and the surface of the member to be joined are provided on the surface of the T joint. In the cross section, an unwelded portion of 30% or more of the plate thickness of the joint member exists,
A welded structure characterized in that the weld metal of the T joint has a structure containing an austenite phase of 80% or more in area percent. According to paragraph 1,
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, and O: 0.050% or less, with the balance being Fe and inevitable impurities. According to claim 1 or 2,
A welded structure in which the member to be joined has a butt weld joint portion so as to intersect the member to be joined. According to paragraph 3,
A welded structure in which the joining member has a butt weld joint portion, and the joining member is arranged so that the butt weld joint portion intersects the butt weld joint portion of the member to be welded. According to any one of claims 1 to 4,
A welded structure in which the joint member has a plate thickness of 50 mm or more. According to any one of claims 1 to 5,
A welded structure in which the non-bonded portion has a gap of 10 mm or less on the butting surface of the joining member and the to-be-joined member.