WO2013038686A1

WO2013038686A1 - Welded structure

Info

Publication number: WO2013038686A1
Application number: PCT/JP2012/005858
Authority: WO
Inventors: 恒久半田; 聡伊木; 遠藤　茂
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2011-09-13
Filing date: 2012-09-13
Publication date: 2013-03-21
Also published as: JPWO2013038686A1; KR101427706B1; BR112014005461B1; KR20140044406A; CN103796786B; BR112014005461A2; CN103796786A; JP5365761B2

Abstract

A welded structure provided with a fillet-welded joint obtained by bringing an end surface of a bonding member into contact with the surface of a bonded member having a plate thickness equal to or greater than 50 mm and bonding the bonding member and the bonded member by fillet welding, the weld leg length and/or the welding width of the fillet-welded joint being equal to or less than 16 mm. The welded structure has, on the plane at which the end surface of the bonding member and the surface of the bonded member are brought into contact with each other, a non-welded section at which the joint cross-section is no less than 95% of the plate thickness tw of the bonding member. The fillet welding conditions are adjusted so that the fillet welding metal is such that the relationship between the fracture appearance transition temperature vTrs(°C) of the fillet welding metal and the plate thickness tf of the bonded member satisfies the expression vTrs<=-1.5tf+90, and/or the relationship between the absorption energy vE-20(J) at a test temperature of -20°C and the plate thickness tf of the bonded member satisfies vE-20 (J)>=5.75 (where 50 <= tf (mm) <= 53), and vE-20(J)>=2.75tf(mm)-140 (where tf (mm)> 53). Moreover, by constituting the bonding member from steel plating having a brittle crack propagation stopping toughness K ca of at least 2500Ｎ/mm3/2 at feed temperature, propagation of brittle cracking generated from the bonded member having a plate thickness equal to or greater than 50 mm and having a butt-welded joint section is arrested at the fillet-welded metal section.

Description

Welded structure

The present invention relates to a welded steel structure welded using a thick steel plate, such as a large container ship or a bulk carrier, and more particularly, the propagation of a brittle crack generated from a thick steel plate base material or a welded joint. The present invention relates to a welded structure excellent in brittle crack propagation stopping characteristics, which can be stopped before reaching a large-scale fracture of an object.

Container ships and bulk carriers, for example, have a structure that has few partition walls in the hold and a large opening at the top of the ship, for example, unlike tankers, 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 thickness of the hull skin, in particular.
In recent years, container ships have increased in size, and large ships of 6,000 to 20,000 TEU have been built. TEU (Twenty feet Equivalent Unit) represents the number of containers converted into a 20-foot container and represents an indicator of the loading capacity of container ships. Along with such an increase in size of a ship, a steel plate having a plate thickness of 50 mm or more and a yield strength of 390 N / mm grade ² or more tends to be used for the hull outer plate.

In recent years, a steel plate to be a hull outer plate is often butt-welded by high heat input welding such as electrogas arc welding from the viewpoint of shortening the construction period. Such large heat input welding is likely to lead to a significant decrease in toughness at the weld heat affected zone, and has been one cause of the occurrence of brittle cracks at the weld joint.
In the hull structure, from the viewpoint of safety, it is necessary to prevent the hull separation by stopping the propagation of brittle cracks before reaching a large-scale fracture even if a brittle fracture occurs. It is considered.

In view of this concept, Non-Patent Document 1 reports the results of an experimental study on the brittle crack propagation behavior of welds in steel plates for shipbuilding with a thickness of less than 50 mm.
In Non-Patent Document 1, the propagation path and propagation behavior of a brittle crack forcibly generated in a welded part are experimentally investigated. Here, there is a description that, if the fracture toughness of the weld is secured to some extent, brittle cracks often deviate from the weld to the base metal due to the effect of residual welding stress. A plurality of examples in which a brittle crack propagated along the line have been confirmed. This suggests that it cannot be said that there is no possibility that brittle fracture propagates straight along the weld.

However, in addition to the fact that ships constructed by applying welding equivalent to the welding applied in Non-Patent Document 1 to steel sheets with a thickness of less than 50 mm are in service, there is good toughness. Based on the recognition that steel plate base materials (shipbuilding class E steel, etc.) have sufficient ability to stop brittle cracks, the brittle crack propagation stop characteristics of steel welds for shipbuilding are not required by the classification rules. It was.

However, in recent large container ships exceeding 6,000 TEU, the plate thickness of the steel plate used exceeds 50 mm, and the fracture toughness decreases due to the increase in plate thickness. In addition, large heat input welding with higher welding heat input is adopted, and the fracture toughness of the welded portion tends to be further reduced. In such thick-walled high heat input welded joints, there is a possibility that the brittle cracks generated from the welded part go straight without deviating to the base metal side, and may not stop even in the steel plate base part such as aggregate. (For example, Non-Patent Document 2). Therefore, securing the safety of the hull structure using a thick high-strength steel plate with a thickness of 50 mm or more is a big problem.
In addition, Non-Patent Document 2 also points out that a thick steel plate having special brittle crack propagation stop characteristics is required in order to stop the propagation of the generated brittle cracks.

In order to solve such a problem, for example, in Patent Document 1, in a welded structure that is preferably a hull outer plate having a thickness of 50 mm or more, an aggregate is arranged so as to intersect the butt weld, and this aggregate is used. A welded structure joined by fillet welding is described.
In the technique described in Patent Document 1, this aggregate has a mean circle equivalent particle diameter of 0.5 to 5 μm over a thickness of 3 mm or more in the surface layer portion and the back layer portion, and is parallel to the plate thickness surface ( 100) A steel sheet having a microstructure in which the X-ray plane intensity ratio of crystal planes is 1.5 or more is used. By adopting a structure in which a steel sheet having such a microstructure is welded as a reinforcing material, even if a brittle crack occurs in the butt weld, the propagation of the brittle crack can be stopped by the aggregate as the reinforcing material, and welding is performed. It is said that it can prevent fatal damage that destroys the structure.

Patent Document 2 includes a fillet welded joint obtained by fillet welding a joining member (hereinafter also referred to as a web) to a member to be joined (hereinafter also referred to as a flange), and has excellent brittle crack propagation stop characteristics. A welded structure is described.
In the welded structure described in Patent Literature 2, an unwelded portion is left on the butt surface of the web in the fillet welded joint cross section with the flange. And the ratio of the width of the unwelded part and the sum of the left and right leg lengths of the fillet weld and the web plate thickness, X is a special relational expression with the brittle crack propagation stop toughness Kca of the member to be joined (flange) The width of the unwelded part is adjusted so as to satisfy the above. As a result, 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 occurring in the joining member (web) is stopped at the butt surface of the fillet weld at the web and flange. The propagation of brittle cracks to the member to be joined (flange) can be prevented.

Japanese Patent Laid-Open No. 2004-232052 JP 2007-326147 A

However, the aggregate as a reinforcing material used in the technique described in Patent Document 1 requires a complicated process in order to obtain a steel sheet having a desired structure. For this reason, there has been a problem that productivity is lowered and it is difficult to stably secure a steel sheet having a desired structure.
Moreover, the technique described in Patent Document 2 is a combination of the discontinuity of the structure and the brittle crack propagation stop characteristic of the joined member (flange), in the propagation of the brittle crack generated in the joining member (web). It is a technology that tries to prevent it.
However, it is shown in the report of the 169th Committee of the Japan Shipbuilding Research Association (“Study on the Fracture Management and Control Design of Ship Structure—Report”, (1979), p.118-136, 169th Committee of the Japan Shipbuilding Research Association). As described above, generally, stopping the propagation of a brittle crack generated in a member to be welded (flange) of a fillet welded joint in the bonding member (web) causes the brittle crack generated in the member to be bonded (web) to be bonded (flange). It has been confirmed experimentally that it is difficult compared to stopping propagation in (1).
Although the reason for this is not clearly described, as one factor, the joining driving member (stress intensity factor) when a crack enters the T-joint portion is more than the joining member (flange). (Web) It is possible that it will be larger when entering the web.

For this reason, in order to stop the propagation of brittle cracks generated in the members to be joined (flange) in the joining member (web), the technique described in Patent Document 2 is used to stop the propagation of brittle cracks in the joining member (web). Since the characteristics and the like are insufficient, it cannot be said that the technique is sufficient.
In Patent Document 2, no consideration is given to the brittle crack propagation stop characteristic of the joining member (web).
That is, the technique described in Patent Document 2 occurs on the strong deck (corresponding to a flange) of a large container ship, which is assumed in the “Brittle Crack Arrest Design Guidelines” (established in September 2009) of the NK class, for example. It cannot be said that it has sufficient crack propagation stop characteristics for the case where the brittle cracks propagated to the hatch side combing (corresponding to the web).

The present invention solves the problems of the prior art, and is brittle, capable of stopping (blocking) the propagation of brittle cracks occurring in a member to be joined (flange) to the joining member (web) before reaching a large-scale fracture. An object of the present invention is to provide a welded structure having excellent crack propagation stopping characteristics.
In addition, the welded structure which this invention makes object is a welded structure provided with the fillet weld joint formed by abutting the end surface of a joining member (web) on the surface of a to-be-joined material (flange), and joining by fillet welding It is.

In order to achieve the above-mentioned object, the present inventors diligently studied various factors affecting the brittle crack propagation stop characteristics in fillet welded joints.
As a result, in order to prevent (stop) the propagation of brittle cracks generated from the member to be joined (flange), a discontinuous portion is secured on the abutting surface between the member to be joined (flange) and the joining member (web), and brittleness occurs. It has been thought that it is not sufficient to construct the crack propagation part with a member having a brittle crack propagation stop toughness Kca of a predetermined value or more and having excellent brittle crack propagation stop characteristics.
In particular, in view of the fact that when the plate thickness t _f (mm) of the member to be joined (flange) increases, the energy release rate (crack growth driving force) at the tip of the brittle crack increases, making it difficult to stop the brittle crack. It was conceived that it is essential to improve the toughness of the fillet weld in relation to the plate thickness t _f (mm) of the member (flange).
In addition, it has also been found that since the propagation of brittle cracks becomes easier when the leg length or weld width of the fillet weld is increased, at least one of the leg length or weld width of the fillet weld must be 16 mm or less.

In the fillet welded joint, an unwelded portion, that is, a discontinuous portion is secured on the surface where the surface of the member to be joined, the joining member, and the end face are abutted, and the joining member has a brittle crack propagation of 2500 N / mm ^3/2 or more. The joining member has stop toughness Kca, the leg length or weld width of the fillet weld is 16 mm or less, and the fillet weld toughness is high enough to satisfy a predetermined relationship with the plate thickness of the joined member. It was discovered for the first time by using a tough weld that it was possible to prevent (stop) the propagation of brittle cracks generated in a thick member to be welded having a thickness of 50 mm or more to the joining member, which was difficult with the prior art. It has also been found that this is the same when the member to be joined is a thick steel plate having a butt weld joint.

First, the experimental results on which the present invention is based will be described.
Various thickness and -10 brittle crack propagation stopping toughness Kca at ℃ is 6000 N / mm ^3/2 about (5500 ~ 6700N / mm ^3/2) steel sheet used as the joining member (web), various unwelded Fillet having part ratio Y (%) (= (width B of unwelded portion in fillet welded joint cross section) / (plate thickness tw of joining member) × 100) and various low temperature toughness and leg length A large fillet weld joint consisting of welds was produced.
The member to be joined (flange) was a steel plate having a butt weld joint and having a thickness of 50 mm or more. The butt weld joint was produced by one-pass high heat input electrogas arc welding or carbon dioxide gas welding (multilayer welding).

Using the obtained large fillet welded joint, an ultra-large structural model test body shown in FIG. 3B was produced, and a brittle crack propagation stop test was performed. In addition, the ultra-large-sized structural model test body welded the steel plate of the same board thickness as the to-be-joined member (flange) 2 by the tack welding 8 below the to-be-joined member (flange) 2 of the large-scale fillet welded joint 9.
Note that the ultra-large structural model specimen shown in FIG. 3B is manufactured so that the butt weld joint 11 of the member to be joined (flange) is orthogonal to the joint member (web), and the tip of the mechanical notch 7 is It processed so that it might become the BOND part of the butt-welded joint part 11.

In the brittle crack propagation stop test, the mechanical notch 7 was hit to generate a brittle crack, and whether or not the propagation of the brittle crack stopped at the fillet weld was investigated. All tests were performed under the conditions of a stress of 257 N / mm ² and a temperature of −10 ° C.
The stress of 257 N / mm ² is a value corresponding to the maximum allowable stress of the yield strength 390 N / mm grade ² steel plate applied to the hull. The temperature –10 ° C is the design temperature of the ship.

The obtained results are shown in FIGS. 4 (a) and 4 (b).
4 (a) and 4 (b), the unwelded portion ratio Y is 95% or more, and the brittle crack propagation stop toughness Kca of the joining member (web) is about 6000 N / mm ^3/2 or more (5500 to 6700 N / mm ^{3 / 2} ) _If the relationship between the toughness of the fillet weld and the plate thickness t _f of the member to be joined (flange) satisfies a specific relationship, even if the service stress is 257 N / mm ² or more, It can be seen that the propagation of the brittle crack generated in the member to be joined (flange) to the joining member (web) can be prevented (stopped).
Incidentally, unwelded part ratio Y, the ratio of the fillet weld width B and the joining member of the unwelded part in the joint cross-section (web) thickness t _w, the value defined by _{(B / t w) × 100} (%) It is.
4A and 4B show the case where the service stress is 257 N / mm ² , but the average value of the stress that constantly acts on the hull is about 100 N / mm ² . In this case, Kca required to prevent (stop) the propagation of the brittle crack generated in the member to be joined (flange) to the joining member (web) is 6000 N / mm ^3/2 × 100/257 (≈2334 N / mm ^3/2 ), if Kca is 2500 N / mm ^3/2 or more, crack propagation is surely prevented against stress (about 100 N / mm ² ) that constantly acts on the hull. Stop).

From these results, as a specific relationship between the toughness of the fillet weld and the plate thickness t _f of the member to be joined (flange), from FIG.
vTrs (℃) ≦ -1.5t _f (mm) +90 (1)
However, from FIG.
vE _-20 (J) ≥ 2.75t _f (mm) -140 (2)
Is obtained.
However, when the plate thickness t _f of the member to be joined (flange) is in the range of 50 ≦ t _f (mm) ≦ 53, the equation (2) is vE ₋₂₀ (J) ≧ 5.75.

Also, increased plate thickness t _f (mm) is increased when the energy release rate of the brittle crack tip member to be joined (flange) (crack growth driving force), brittle crack is less likely to stop. However, regarding this point, if a welded structure (fillet welded joint) having a discontinuous portion with an unwelded portion ratio Y of 95% or more is used, the energy release rate at the brittle crack tip that has propagated decreases, and brittleness occurs. It has been found that the propagation of cracks tends to stop.
If the low-temperature toughness of the fillet weld is further increased until the above equations (1) and (2) are satisfied, brittle cracks generated in a thick member (flange) having a plate thickness of 50 mm or more are prevented. It has been found that it is easy to stop in the meat weld.
Furthermore, even if it is not possible to prevent the propagation of brittle cracks at the fillet welded portion excellent in low temperature toughness that satisfies the above formulas (1) and (2), the joining member (web) has a brittle crack propagation stopping characteristic that exceeds a predetermined level. It has been found that if it is composed of a steel plate having it, it can be blocked in the joining member (web).
On the other hand, if no measures are taken to set the unwelded part and improve the low-temperature toughness of the fillet welds, the joint material (web) is excellent (Kca exceeds 6000 N / mm ^3/2) It has also been found that even when a thick steel plate having a brittle crack propagation stopping property is applied, it is difficult to prevent the propagation of brittle cracks under the maximum allowable stress condition.

The present invention has been completed on the basis of such findings and further studies. That is, the gist of the present invention is as follows.
1. The end face of the joining member is abutted against the surface of the member to be joined having a plate thickness of 50 mm or more, and at least one of the welding leg length or welding width formed by joining the joining member and the member to be joined by fillet welding is a corner having a length of 16 mm or less. A welded structure with a meat weld joint,
Said corner said with the end face of the joining member in the weld joint surface with abutted the surface of the bonded member, unwelded portion of 95% or more of the fillet weld joint thickness t _w of the bonding member in cross-section Have
Furthermore, for the fillet weld metal of the fillet weld joint,
The Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal and the plate thickness t _f of the joined member (flange) are expressed by the following formula (1) and / or
Charpy impact test absorbed energy vE ₋₂₀ (J) at −20 ° C. for Charpy impact test of fillet weld metal and plate thickness t _{f of the} joined member satisfy the relationship of the following formula (2) ,
In addition, the joining member is composed of a steel plate having a brittle crack propagation stopping toughness Kca of 2500 N / mm ^3/2 or more at the service temperature of the welded structure.
A welded structure characterized by that.
VTrs ≤ -1.5t _f +90 (1)
vE ₋₂₀ (J) ≧ 5.75 (however, 50 ≦ t _f (mm) ≦ 53),
vE _-20 (J) ≥ 2.75t _f (mm) -140 (however, t _f (mm)> 53) (2)
Where vTrs: Charpy impact test fracture surface transition temperature (° C) of fillet weld metal,
vE _-20 : Test temperature: Charpy impact test absorbed energy (J) at -20 ° C,
t _f : Plate thickness of the member to be joined (mm)
2. 2. The welded structure according to item 1, wherein the member to be joined having a thickness of 50 mm or more has a butt weld joint so as to intersect the joining member.
3. 3. The welded structure according to

item

1 or 2, wherein the joining member is made of a steel plate having a brittle crack propagation stop toughness Kca of 6000 N / mm ^3/2 or more at the service temperature of the welded structure.

According to the present invention, propagation of a brittle crack generated in a member to be joined (flange) made of a thick steel plate having a thickness of 50 mm or more, which has been difficult in the past, to the joining member (web), before reaching a large-scale fracture, Can be stopped (blocked). This avoids the risk of large-scale brittle fracture such as steel structures, especially large container ships and bulk carriers, and has a significant effect on ensuring the safety of the hull structure. The effect of.

In addition, at the time of construction, by adjusting the dimensions of the unwelded part and the toughness of the fillet weld metal, and by applying a steel plate having an appropriate brittle crack propagation stop performance to the joining member, without using a special steel plate, In addition, there is an effect that a welded structure excellent in brittle crack propagation stopping characteristics can be easily manufactured without impairing safety.

It is explanatory drawing which illustrates typically the cross-sectional structure of a fillet welded joint. (A) shows a case where the joining member (web) 1 and the joined member (flange) 2 are orthogonal to each other, and (b) shows that the joining member (web) 1 and the joined member (flange) 2 cross each other diagonally. Show the case. It is explanatory drawing which shows typically another example of a structure of a fillet welded joint. (A) is an external view, (b) is sectional drawing. It is explanatory drawing which shows typically the shape of the ultra-large-sized structural model test body used in the Example. (A) is a case where the member to be joined (flange) 2 is made only of a steel plate base material, and (b) is a case where the member to be joined (flange) 2 has a butt weld joint. It is a graph which shows the influence of the relationship between the toughness of a fillet weld metal, and the flange plate thickness on the propagation stop of a brittle crack.

In the welded structure according to the present invention, the end face of the joining member (web) 1 is abutted against the surface of the joined member (flange) 2 having a plate thickness of 50 mm or more, and the joining member (web) 1 and the joined member (flange) 2 are joined. Is a welded structure formed by joining fillet welds. This welded structure includes a fillet weld joint having a fillet weld metal 5 having a weld leg length 3 or a weld width 12 of 16 mm or less. Moreover, the unwelded part 4 which becomes a structural discontinuity part exists in the butt | matching surface of the joining member (web) 1 and this to-be-joined member (flange) 2 of this fillet welded joint.

This state is shown in FIG. FIG. 1A shows a case where the joining member (web) 1 is attached upright with respect to the joined member (flange) 2, but the present invention is not limited to this. For example, as shown in FIG. 1B, the joining member (web) 1 may be attached to the joined member (flange) 2 at an angle θ. In this case, the joining member (web) plate thickness tw used when determining the ratio Y (%) of the unwelded portion is the length of the intersection between the joining member (web) and the member to be joined (flange), (tw ) / Cos (90 ° -θ). In the figure, 3 is a weld leg length, 4 is an unwelded portion, 5 is a fillet weld metal, and 12 is a weld width.

As described above, the welded structure according to the present invention is a non-welded portion in which the structure is discontinuous at the abutting surface between the joining member (web) 1 and the joined member (flange) 2 in the fillet welded joint. 4. In the fillet welded joint, the butt surface between the joining member (web) 1 and the member to be joined (flange) 2 becomes a propagation surface of a brittle crack. Therefore, in the present invention, the unwelded portion 4 is present on the butt surface. . Due to the presence of the unwelded portion 4, the energy release rate (crack propagation driving force) at the tip of the brittle crack that has propagated through the member to be joined (flange) 2 is reduced, and the brittle crack tends to stop at the butt surface.
Even if a brittle crack propagates to the joining member (web) 1 side, in the present invention, a fillet welded portion (fillet welded metal 5, heat affected zone (not shown in FIG. 1 is omitted) that retains toughness of a predetermined level or more. )) And the joining member is made of a steel plate having a brittle crack propagation stopping performance greater than or equal to a predetermined level, the brittle crack is caused by a fillet weld (fillet weld metal 5, heat affected zone (not shown in FIG. 1)). ) Or the base material of the joining member (web) 1.

In addition, it is very rare that a brittle crack occurs in a steel plate base material part with few defects. Many past brittle fracture accidents have occurred in welds. Therefore, for example, in FIG. 2, the member to be joined (flange) 2 is a steel plate joined by the butt weld joint 11, and the joining member (web) intersects the welded portion (butt weld joint portion) 11 of the butt weld joint. A fillet welded joint that is fillet welded is shown. Even in such a fillet welded joint, in order to prevent the propagation of the brittle crack generated from the butt weld joint part 11 to the joining member (web) 1, it is important to have a discontinuity in the structure. For this reason, even in this case, the unwelded portion 4 is present on the abutting surface between the member to be joined and the joining member in the fillet weld.
2A shows the appearance of the fillet weld joint, and FIG. 2B shows the cross-sectional shape of the butt weld joint portion 11.

In the present invention, the dimensions of the unwelded part 4 in the fillet weld joint cross section, since propagation suppression of brittle cracks, and more than 95% of the web thickness t _w. Thereby, since the fillet weld metal is easily plastically deformed, the stress near the crack tip of the brittle crack that has entered the fillet weld metal is relieved, and the propagation of the brittle crack to the joining member (web) 1 side can be suppressed. . Therefore, the dimensions of the unwelded part 4 (width B) can inhibit the propagation of brittle cracks, it is limited to 95% or more of the bonding member (web) thickness t _w. In addition, Preferably they are 96% or more and 100% or less.

Also, the weld leg length or weld width of fillet welded joints shall be 16 mm or less. Thereby, since the fillet weld metal is easily plastically deformed, the stress near the crack tip of the brittle crack propagated to the fillet weld metal is relaxed, and the propagation of the brittle crack is stopped. For this reason, the weld leg length or weld width of fillet welded joints is limited to 16 mm or less, which is easy to deform high tough fillet weld metal. Preferably it is 15 mm or less.

In the present invention, the fillet weld metal in the fillet weld joint is toughness that satisfies the following formula (1) and / or the following formula (2) in relation to the plate thickness t _f of the member to be joined (flange). Adjust to ensure
vTrs ≤ -1.5t _f +90 (1)
vE ₋₂₀ ≧ 5.75 (however, 50 ≦ t _f (mm) ≦ 53),
vE _-20 ≥ 2.75t _f (mm)-140 (however, t _f (mm)> 53) (2)
(Where vTrs: Charpy impact test fracture surface transition temperature of fillet weld metal (° C), vE _-20 : Test temperature: Charpy impact test absorbed energy (J) at -20 ° C, t _f : Member to be joined ( (Flange) thickness (mm))
When the toughness of the fillet weld metal satisfies the above-described formula (1) and / or (2) in relation to the plate thickness t _f of the member to be joined (flange), as shown in FIG. A welded structure in which the plate thickness of the member to be joined (flange) is 50 mm or more can be made into a welded structure that ensures a certain degree of brittle crack propagation prevention characteristics. If the toughness of the fillet weld metal does not satisfy either of the above formulas (1) and (2), the fillet weld metal has insufficient toughness and has been generated and propagated in the joined member (flange). Brittle cracks cannot be prevented from propagating at fillet welds.

Even if the welded structure satisfies the above-mentioned conditions, depending on the acting stress conditions, the length of the welded structure (flange) generated by the steel plate constituting the joining member (web) may be long. There are cases where the propagation of brittle cracks cannot be prevented by the joining member (web). Therefore, in the present invention, it is preferable to select the brittle crack propagation stop toughness that the steel sheet to be applied to the joining member (web) should have in accordance with the stress acting on the structure.

According to the study of the present inventor, the joining member (web) of the welded structure that satisfies the above-described conditions has, for example, arrest performance (Kca≈2500 N / mm ^3/2 ) equivalent to that of ordinary shipbuilding class E steel. When a steel plate is applied, it is possible to prevent the propagation of long brittle cracks under in-service stress conditions (stress conditions of about 100 N / mm ² ) that occur during normal operations of ships and the like.
However, in such a joining member (web), propagation of a long brittle crack is prevented under a stress condition equivalent to the maximum allowable stress that occurs rarely (stress condition of about 257 to 283 N / mm ² ) due to a storm or the like. It becomes difficult. In order to prevent the propagation of long brittle cracks even under stress conditions equivalent to the maximum allowable stress (stress conditions of about 257 to 283 N / mm ² ), the service temperature is applied to the joining member (web). The present inventors have confirmed that it is necessary to apply a steel plate having a brittle crack propagation stop toughness Kca of 6000 N / mm ^3/2 or more. This makes it possible to prevent the propagation of long brittle cracks even under stress conditions equivalent to the maximum allowable stress (stress conditions of about 257 to 283 N / mm ² ).

There is no particular limitation on the composition and manufacturing method of a steel sheet having a brittle crack propagation stop toughness Kca of 6000 N / mm ^3/2 or more at a service temperature, for example, a hull design temperature of −10 ° C.
For example, the brittle crack propagation stop characteristics described in Japanese Patent No. 4449388, Japanese Unexamined Patent Application Publication No. 2010-202931, Japanese Unexamined Patent Application Publication No. 2009-132995, Japanese Unexamined Patent Application Publication No. 2008-214654, Japanese Unexamined Patent Application Publication No. 2005-97694, etc. Any thick steel plate with excellent resistance can be applied.

The welded structure of the present invention is provided with the above-described fillet welded joint. For example, a hull structure with a ship hull outer plate as a flange and a bulkhead as a web, or a deck as a flange, and a hatch as a web. It can be applied to the hull structure.

Hereinafter, the present invention will be described in detail based on examples.

Thick steel plates with the plate thickness and brittle crack propagation stoppage characteristics (Kca at -10 ° C) shown in Table 1 are used as joining members (webs), and thick steel plates with the thicknesses shown in Table 1 are used as joined members (flanges). Then, fillet welding was performed to produce a large fillet welded joint having an actual structure size as shown in FIGS. 3 (a) and 3 (b).
In the prepared fillet welded joint, the unwelded portion 4 as shown in FIG. 1A is provided on the butt surface between the joining member 1 and the member 2 to be joined, and the ratio Y (= (unwelded) of the unwelded portion. The width B of the part / the thickness (tw) of the joining member (web) was varied.
In addition, the to-be-joined member (flange) was a thick steel plate (base material only) (FIG. 3A) and a thick steel plate having a butt weld joint (FIG. 3B). Butt welded joints were made by one-pass high heat input electrogas arc welding (SEGARC and two-electrode SEGARC) or multilayer CO ₂ welding.

Also, the fillet welded joint is a fillet welded joint having fillet weld metal with various toughness, various weld leg lengths and welding widths by changing welding conditions such as welding material, welding heat input, shield gas, etc. . As for the toughness of fillet weld metal, Charpy impact test specimens (10 mm thick) were taken from fillet weld metal, and the absorbed energy vE ₋₂₀ at a test temperature of −20 ° C. in accordance with the provisions of JIS Z 2242. J) and the fracture surface transition temperature vTrs (° C.).

Moreover, using the obtained large fillet welded joint, an ultra-large structural model test body shown in FIG. 3 was prepared, and a brittle crack propagation stop test was performed. In addition, the ultra-large-sized structural model test body welded the steel plate of the same board thickness as the to-be-joined member (flange) 2 by the tack welding 8 below the to-be-joined member (flange) 2 of the large-scale fillet welded joint 9.
3B, the butt weld joint 11 of the member to be joined (flange) is produced so as to be orthogonal to the joint member (web), and the tip of the mechanical notch 7 is butt-joined. It processed so that it might become the BOND part of the welded joint part 11, or the weld metal WM.

In the brittle crack propagation stop test, the mechanical notch was hit to generate a brittle crack, and it was investigated whether the brittle crack propagated under the following test conditions stopped at the fillet weld. All tests were performed under the conditions of stress 100 to 283 N / mm ² and temperature: −10 ° C. The stress 100 N / mm ² is an average value of stress that constantly acts on the hull. Further, the stress 257 N / mm ² is a value corresponding to the maximum allowable stress of the yield strength 390 N / mm grade ² steel plate applied to the hull. Furthermore, the stress 283 N / mm ² is a value corresponding to the maximum allowable stress of the yield strength 460 N / mm ² grade steel plate applied to the hull. The temperature –10 ° C is the design temperature of the ship.

Table 2 shows the results obtained.

In all of the examples of the present invention, the brittle crack propagated from the fillet weld metal from the member to be joined (flange) of the fillet weld, and entered the joint member (web) and stopped. On the other hand, in the comparative example outside the scope of the present invention, the brittle crack propagated without stopping at the fillet weld and the joining member (web), and the propagation of the brittle crack could not be prevented.

DESCRIPTION OF SYMBOLS 1 Web 2 Flange 3 Leg length 4 Unwelded part 5 Fillet weld metal 7 Machine notch 8 Tack welding 9 Large fillet welded joint 11 Butt weld joint 12 of flange 12 Welding width θ Crossing angle

Claims

The end face of the joining member is abutted against the surface of the member to be joined having a plate thickness of 50 mm or more, and at least one of the welding leg length or welding width formed by joining the joining member and the member to be joined by fillet welding is a corner having a length of 16 mm or less. A welded structure with a meat weld joint,
Said corner said with the end face of the joining member in the weld joint surface with abutted the surface of the bonded member, unwelded portion of 95% or more of the fillet weld joint thickness t w of the bonding member in cross-section Have
Furthermore, for the fillet weld metal of the fillet weld joint,
The Charpy impact test fracture surface transition temperature vTrs (° C.) of the fillet weld metal and the plate thickness t f of the joined member (flange) are expressed by the following formula (1) and / or
Charpy impact test absorbed energy vE −20 (J) at −20 ° C. for Charpy impact test of fillet weld metal and plate thickness t f of the joined member satisfy the relationship of the following formula (2) ,
In addition, the joining member is composed of a steel plate having a brittle crack propagation stopping toughness Kca of 2500 N / mm 3/2 or more at the service temperature of the welded structure.
A welded structure characterized by that.
VTrs ≤ -1.5t f +90 (1)
vE −20 (J) ≧ 5.75 (however, 50 ≦ t f (mm) ≦ 53),
vE -20 (J) ≥ 2.75t f (mm) -140 (however, t f (mm)> 53) (2)
Where vTrs: Charpy impact test fracture surface transition temperature (° C) of fillet weld metal,
vE -20 : Test temperature: Charpy impact test absorbed energy (J) at -20 ° C,
t f : Plate thickness of the member to be joined (mm)
The welded structure according to claim 1, wherein the member to be joined having a thickness of 50 mm or more has a butt weld joint so as to intersect the joining member.
3. The welded structure according to claim 1, wherein the joining member is made of a steel plate having a brittle crack propagation stop toughness Kca of 6000 N / mm 3/2 or more at a service temperature of the welded structure.