JP5679336B2 - Welded structure with excellent brittle crack propagation stop properties - Google Patents

Description

  The present invention relates to the propagation of brittle cracks that may occur in base materials and welded joints of structures welded using thick steel plates such as large container ships and bulk carriers, before leading to large-scale fracture. In particular, even if a brittle crack occurs in the joint member (web) of a fillet welded joint, the brittle crack in the welded member (flange) The present invention relates to a welded structure excellent in brittle crack propagation stopping characteristics for stopping propagation.

  Container ships and bulk carriers, which are welded structures, have a structure with a large upper opening in order to improve loading capacity and cargo handling efficiency. For this reason, in these ships, it is necessary to increase the thickness of the hull skin.

  In recent years, container ships have increased in size, and large ships of 6,000 to 20,000 TEU have been built, and accordingly, the hull skin used tends to be thicker than 50 mm.

  In the hull structure, it is considered necessary to stop the propagation of brittle cracks and prevent hull separation even if brittle fracture occurs from a welded part. It is described that a steel plate having a specific microstructure and excellent in brittle fracture resistance is used as a reinforcing material for the plate.

  The brittle crack propagation behavior of welded steel plate welds with a thickness of less than 50 mm has been experimentally studied by the Japan Shipbuilding Research Association No. 147 Committee.

  In the 147th committee, if the fracture toughness of the welded part is secured to some extent as a result of experimentally investigating the propagation path and propagation behavior of the brittle crack forcibly generated in the welded part, the influence of the welding residual stress As a result, brittle cracks often deviate from the weld to the base metal side, but multiple examples of brittle cracks propagating along the weld were also confirmed. This suggests that there is no possibility that brittle fracture will propagate straight along the weld.

  However, in addition to the fact that ships constructed by applying welding equivalent to the welding applied in the 147th Committee to steel sheets with a thickness of less than 50 mm are in service, there is good toughness. From the recognition that steel plate base materials (shipbuilding class E steel, etc.) have sufficient ability to stop brittle cracks, the brittle crack propagation stop property of welded steel for shipbuilding has not been required by the classification rules.

JP 2004-232052 A

  However, in recent large container ships exceeding 6,000 TEU, the plate thickness of the steel plate exceeds 50 mm and the fracture toughness is reduced due to the plate thickness effect, and the weld heat input is also increased, so the fracture toughness of the welded portion is increased. There is a tendency to further decrease.

  Recently, in such a thick-walled high heat input welded joint, an experiment has been conducted that a brittle crack generated from a welded portion may go straight without warping to the base metal side and may not stop even in a steel plate base material such as an aggregate. (Yamaguchi et al .: "Development of ultra-large container ship-practical application of new high-strength ultra-thick steel plate"), Journal of Japan Society of Marine Science and Technology, 3, (2005), P70.), Steel plate with a thickness of 50 mm or more It is a big problem in ensuring the safety of the hull structure to which is applied. In addition, it is pointed out that a steel plate having special characteristics is necessary to stop cracks.

  Therefore, an object of the present invention is to provide a welded structure that stops a brittle crack before reaching a large-scale fracture even if a brittle fracture occurs in a thick steel plate and a welded portion thereof. .

  The inventors of the present invention diligently studied to solve the above-described problems, and the bonded member (flange) is placed on the butting surface of the bonded member (web) in the joint cross section of the fillet welded portion with the bonded member (flange). By securing an unwelded part with a dimension corresponding to the brittle crack propagation stopping performance of steel, it is possible to stop the propagation of brittle cracks in thick materials with a thickness of 50 mm or more at the butt surface between the web and flange of the fillet weld I found.

Further, in the case of a steel plate in which the joining member (web) is joined by a butt weld joint, an unwelded portion having a dimension corresponding to the brittle crack propagation stopping performance of the joined member (flange) is referred to as a welded portion of the butt weld joint. It was found that the same brittle crack propagation stopping characteristics can be obtained by securing the butt face with the flange. That is, the present invention
1. A welded structure having a fillet welded joint in which a web is joined by a butt welded joint and a welded portion of the butt welded joint intersects the flange, and at least the welded part of the butt welded joint and the flange butt An unwelded portion remains on the surface, and the ratio of the width of the unwelded portion to the sum of the thickness of the intersection and the leg length of the left and right fillet welds and brittle crack propagation at the service temperature of the flange A welded structure excellent in brittle crack propagation stop characteristics, wherein the relationship of stop toughness Kca (N / mm ^3/2 ) satisfies the following formula .
X (%) ≧ {5900−Kca (N / mm ^3/2 )} / 85
2 . The unwelded portion of the fillet weld joint, the fillet weld joint section, wherein 1, characterized in that the width to be 15 to 90% of the sum of leg length of fillet welds and the left and right plate thickness of the web Welded structure with excellent brittle crack propagation stopping characteristics.

  According to the present invention, according to the brittle crack propagation stopping performance of the steel plate used as the flange, an unwelded portion having an appropriate dimension is left on the butt face of the web of the fillet welded portion, which has been difficult to achieve in the past. It is possible to stop the propagation of brittle cracks in the above thick material.

  As a result, even if brittle cracks are generated and propagated in the hull, etc., the risk of large-scale brittle fracture such as hull separation can be avoided, making a significant contribution to ensuring the safety of steel structures, especially hull structures. However, it is extremely useful in industry.

  In addition, by adjusting the dimensions of the unwelded part during construction, steel plates with different brittle crack propagation stopping performance (steel plates with different production costs) can be properly used without using special steel plates and without compromising safety. The total cost of manufacturing the welded structure can be reduced.

It is a figure explaining each part of a fillet welded joint, (a) shows the case where a web and a flange are orthogonal, (b) shows the case where a web and a flange cross diagonally. A steel plate in which a web is joined by a butt weld joint, and shows a fillet weld joint in which the butt weld joint portion intersects the flange, (a) is an external view, and (b) is a schematic view of a joint cross-sectional shape in the butt weld joint portion. FIG. The figure explaining the shape of a cross type | mold ESSO test piece, (a) is a figure which shows the case where a web consists of a base material, (b) shows the case where a web has a butt-welded joint part. The figure which shows the test result by the cross-shaped ESSO test piece of Fig.3 (a). The figure which shows the test result by the cross-shaped ESSO test piece of FIG.3 (b).

  FIG. 1 shows a joint cross-sectional shape of a fillet welded joint. (A) shows a joining member (web) 1 (hereinafter referred to as web 1) standing upright with respect to a member (flange) 2 (hereinafter referred to as flange 2). When attached, (b) shows the case where the web 1 is attached to the flange 2 at an angle.

  Each part in the following explanation of the limitation reasons of the present invention is shown in FIG. However, in the case of the fillet welded joint shown in FIG. 1 (b), the web plate thickness for obtaining the ratio X (%) described later is the length of the web 1, the flange 2, and the intersecting portion, that is, the web plate thickness. / COS (90 ° −θ) (where θ is the crossing angle between the web and the flange, θ <90 °).

  In the present invention, the unwelded portion 4 is left on the butted surface of the fillet welded joint web 1 with the flange 2. In the fillet welded joint, the abutting surface of the web 1 with the flange 2 becomes a crack propagation surface, so that the unwelded portion 4 remains on the abutting surface.

  When the unwelded portion 4 remains, the energy release rate (crack propagation driving force) at the tip of the brittle crack that has propagated through the web 1 is lowered, and the brittle crack is likely to stop at the butt surface.

  The presence of the unwelded portion 4 reduces the energy release rate (crack growth driving force) at the tip of the brittle crack. For example, even if the crack propagates to the flange 2 side, the crack can occur at any part of the fillet weld (fillet weld). Stop at the base metal of the metal 5, the heat affected zone (not shown in FIG. 1) and the flange 2.

In the joint cross section of the fillet welded joint, the dimension of the unwelded portion 4 at the butt surface of the web 1 with the flange 2 is defined in relation to the brittle crack propagation stop toughness Kca (N / mm ^3/2 ) of the flange 2. It is desirable to do.

The ratio X (%) of the width of the unwelded portion 4 in the joint cross section of the fillet weld joint to the sum of the plate thickness of the web 1 and the leg length 3 of the fillet weld metal 5 on the left and right sides, and the steel plate used for the flange 2 The relationship of brittle crack propagation stop toughness Kca (N / mm ^3/2 ) at the service temperature is set so as to satisfy the expression (1).
X (%) ≧ {5900−Kca (N / mm ^3/2 )} / 85 (1)
When the ratio X (%) decreases, the energy release rate (crack growth driving force) at the tip of the brittle crack decreases and the brittle crack hardly stops. However, if the Kca value of the steel plate used for the flange 2 is large, the brittle crack is It is possible to stop.

  Further, the width of the unwelded portion 4 in the fillet welded joint is 15 to 90% of the sum of the plate thickness of the web 1 and the leg length 3 of the left and right fillet weld metal 5 in the joint cross section of the fillet weld. It is preferable to do.

  When the width of the unwelded portion 4 is less than 15% of the sum of the plate thickness of the web 1 and the leg length 3 of the fillet weld metal 5 on the left and right of the web 1, the energy release rate (crack propagation driving force) at the brittle crack tip Is less likely to stop brittle cracks.

  Further, when the width of the unwelded portion 4 exceeds 90% of the sum of the plate thickness of the web 1 and the leg length 3 of the fillet weld metal 5 on the left and right sides of the web 1, it is difficult to ensure the joint strength. Therefore, in this invention, it is preferable to limit to 15% or more and 90% or less of range.

  Note that brittle fracture rarely occurs in a steel plate base material with few defects, and many past brittle fracture accidents have occurred in welds. FIG. 2 shows a fillet welded joint in which a welded portion of a butt welded joint portion (hereinafter referred to as a butt welded joint portion 11) intersects the flange 2 with a steel plate in which a web 1 is joined by a butt welded joint. FIG. 4B schematically shows a joint cross-sectional shape in the butt weld joint portion 11.

  In the case of the fillet welded joint shown in FIG. 2, in order to prevent the propagation of brittle cracks generated from the butt welded joint portion 11, at least the unwelded portion 4 may remain on the butt welded surfaces of the butt welded joint 11 and the flange 2. is necessary.

  As described above, if the unwelded portion 4 is left on the abutting surface between the base material of the web 1 and the flange 2, the brittle crack is likely to stop even if a brittle crack occurs in the base material portion of the web 1. The welded portion 4 may be left over the entire length of the web 1.

In the fillet welded joint, the thickness of the butt welded joint part 11 in the thickness direction of the web 1 of the unwelded part width 4 in the joint section of the joint part where the butt welded joint part 11 and the flange 2 intersect, that is , the butt joint. The ratio X (%) to the sum of the average value of the weld metal height of the welded joint portion 11 and the leg lengths of the left and right fillet weld metal 5 (same definition as in FIG. 1), and the service temperature of the steel plate used for the flange 2 The brittle crack propagation stop toughness Kca (N / mm ^3/2 ) is preferably defined so as to satisfy the above formula (1). The ratio X (%) is desirably a value obtained in the joint cross-sectional shape in the BOND part which is the most brittle part of the butt weld joint part 11.

  Further, at the intersection of the butt weld joint 11 and the flange 2, the width of the unwelded portion 4 is set to the average value of the weld metal height of the butt weld joint 11 and the left and right fillet welds in the cross section of the fillet weld joint. It is preferable to make it 15 to 90% of the sum of the leg lengths of the metal 5.

  Although FIG. 2 shows the case where the butt weld joint 11 of the web 1 and the flange 2 are orthogonal to each other, they may be crossed obliquely. The fillet welded joint shown in FIG. 2 is manufactured by first butt welding the webs and then fillet welding the obtained butt welded joint to a flange.

  The welded structure according to the present invention has the above-described fillet welded joint. For example, the hull outer plate of the ship is a flange and the bulkhead is a web, or the deck is a flange and the hatch is a web. Applicable to hull structures.

  The welded structure according to the present invention exhibits a particularly excellent effect when a thick plate having a plate thickness exceeding 50 mm is used, but the steel plate thickness may be less than 50 mm. In the conventional hull structure, there is no unwelded portion between the butt weld joint portion of the fillet weld joint web and the butt face of the flange.

Using steel plates having various plate thicknesses and brittle crack propagation stop toughness (Kca at −10 ° C.), various unwelded portion ratios X (sum of web plate thickness and leg length of left and right fillet welds of web) T-shaped fillet welded joints having a ratio of the width to the length of the unwelded portion with respect to the above were produced. T-shaped fillet welded joints were prepared for the case where the web was only the base material of the steel plate and the case where the web was a butt weld joint. The butt weld joint was produced by one-pass large heat input welding or multilayer CO ₂ welding.

  Using the obtained T-shaped fillet welded joint, a cross-shaped ESSO test piece shown in FIG. 3 was produced and subjected to a brittle crack propagation stop test (ESSO test). The cross-shaped ESSO test piece was tack welded 8 below the flange of the T-shaped fillet weld joint 9 and a steel plate having the same thickness as the web was welded.

  The cross-shaped ESSO test piece shown in FIG. 3 (a) has a web only of the base material, and the cross-shaped ESSO test piece shown in FIG. 3 (b) is prepared so that the butt weld joint 11 of the web is perpendicular to the flange. The tip of the machine notch 7 was used as the BOND part of the butt weld joint part 11, and fillet welding was carried out to a total length of 500 mm of the test piece.

In the ESSO test, the mechanical notch was hit to generate a brittle crack, and it was investigated whether the propagated brittle crack stopped at the fillet weld. All tests were conducted under the conditions of a stress of 24 kgf / mm ² and a temperature of −10 ° C. The stress 24 kgf / mm ² is the maximum allowable stress of the yield strength 36 kgf / mm ² grade steel plate frequently used in the hull, and the temperature −10 ° C. is the design temperature of the ship.

  Tables 1 and 2 show the test results together with the plate thickness and Kca of the steel plate. Moreover, the test result of Table 1 is shown in FIG. 4, and the test result of Table 2 is shown in FIG. Table 1 shows the test results using the cross-shaped ESSO test piece of FIG. 3 (a). In the invention example satisfying the formula (1), the brittle crack stopped without propagating from the web of the fillet weld to the flange.

  Table 2 shows the test results using the cross-shaped ESSO test piece of FIG. 3B, and in the invention example satisfying the expression (1), the brittle crack stopped without propagating from the web of the fillet weld to the flange. In Table 2, No. 2-0, 3-0, and 4-0 show test results when a crack penetrates because there is no unwelded portion at the intersection between the butt weld joint 11 of the web and the flange.

  The unwelded ratio X (%) of the fillet weld in Tables 1 and 2 indicates a value obtained for any one joint cross-sectional shape.

DESCRIPTION OF SYMBOLS 1 Web 2 Flange 3 Leg length 4 Unwelded part 5 Fillet weld metal 6 Separation surface 7 Machine notch 8 Tack welding 9 T-shaped welded joint 11 Butt welded joint part a Space | interval θ Crossing angle

Claims (2)

A welded structure having a fillet welded joint in which a web is joined by a butt welded joint and a welded portion of the butt welded joint intersects the flange, and at least the welded part of the butt welded joint and the flange butt An unwelded portion remains on the surface, and the ratio of the width of the unwelded portion to the sum of the thickness of the intersection and the leg length of the left and right fillet welds and brittle crack propagation at the service temperature of the flange A welded structure excellent in brittle crack propagation stop characteristics, wherein the relationship of stop toughness Kca (N / mm ^3/2 ) satisfies the following formula.
X (%) ≧ {5900−Kca (N / mm ^3/2 )} / 85 The unwelded portion in the fillet welded joint has a width that is 15 to 90% of the sum of the thickness of the web and the leg length of the left and right fillet welded joints in the cross section of the fillet welded joint. A welded structure excellent in brittle crack propagation stopping characteristics as described in 1 .

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