Thick steel plate having heavy unit weight and fabrication method thereof

Abstract

The present invention relates to a method for manufacturing a thick steel plate having a heavy unit weight, wherein the thick steel plate has a unit weight of 30 tons or more and can be formed into a shape forming at least part of a desired structure. The method comprises the steps of: s1) using at least two thick steel plates that each have a unit weight of 25 tons or less and a thickness (t0) of 60 mm or more and have a grooved end, and arranging the steel plates so that the grooved ends face each other, thereby forming a joint having a groove; s2) performing tack welding to fix the joint; s3) performing first arc welding along the groove; s4) forming a back-surface groove, along the joint, on a back surface opposite a front surface, which is the surface on which the first arc welding was performed; and s5) performing secondary arc welding along the back-surface groove.

Description

Heavy-duty steel plate and its manufacturing method

[0001] The present invention relates to a heavy-duty steel plate and a method for manufacturing the same.

[0002] Driven by factors such as carbon neutrality, the RE100 agreement, and the Carbon Border Adjustment Mechanism (CBAM), demand for renewable energy, particularly offshore wind power, is expected to steadily increase over the next 20 years. To enhance the economic viability of offshore wind power, increasing power generation per turbine is crucial. To achieve this, wind turbines have recently been increasing in capacity, leading to increased blade length and larger towers supporting the turbines and blades.

[0003] To install wind power towers offshore, fixed structures are generally erected on the seabed, and the most commonly used structure, the monopile, is also becoming larger as the weight at the top increases.

[0004] Currently, it's common to manufacture a single monopile can from two thick plates. However, with turbine capacity expected to rapidly increase to 25 MW by 2030, the number of thick plates used to manufacture a single monopile can is expected to increase to six.

[0005] Compared to small-medium thick plates, using large-medium thick plates can reduce weld seams during can manufacturing, increase production speed, and lower monopile production costs. More importantly, using large-medium thick plates can shorten the overall project construction period, significantly reducing overall capital expenditure (Capex). For these reasons, wind power developers have no choice but to prefer large-medium thick plates, and major domestic and international plate manufacturers are making large-scale facility investments to upgrade their facilities to accommodate large-medium thick plates.

[0006] One aspect of the present disclosure is to provide a method for easily manufacturing a heavy-duty steel plate weighing 30 tons or more.

[0007] Another aspect of the present disclosure is to provide a method for manufacturing a heavy-duty steel plate capable of easily manufacturing various single-duty steel plates.

[0008] Another aspect of the present disclosure is to provide a method for manufacturing a heavy-duty steel plate having excellent low-temperature impact toughness.

[0009] The objectives of the present invention are not limited to the above-described content. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall description of the present invention.

[0010] A method for manufacturing a heavy-duty steel plate according to the present invention is a method for manufacturing a heavy-duty steel plate having a unit weight of 30 tons or more and being formed into a shape forming at least a part of a desired structure, comprising the steps of S1) using at least two heavy-duty steel plates, each of which has a unit weight of 25 tons or less and a thickness (t0) of 60 mm or more and has an end portion having a groove formed therein, and forming a joint portion having a groove by arranging the groove-formed ends of the heavy-duty steel plates to face each other; S2) performing tack welding so that the joint portion is fixed; S3) performing first arc welding along the groove; S4) forming a rear groove along the joint portion on a rear surface opposite to the front surface, with the surface on which the first arc welding is performed being a front surface; and S5) performing second arc welding along the rear groove.

[0011] In one specific example, the weld bead generated by the first arc welding may be exposed to the bottom surface of the rear groove formed in the step S4).

[0012] In one specific example, the groove of the step S1) may be a front groove, and the rear groove formed in the step S4) may satisfy Equations 1 and 2.

[0013] (Formula 1)

[0014] D1+D2 > t0

[0015] (Formula 2)

[0016] 0.05 t0 ≤ │ D1+D2-t0│ ≤ 0.25 t0

[0017] In Equations 1 and 2, D1 is the groove depth of the front groove, and D2 is the groove depth of the rear groove.

[0018] In one specific example, the groove depth (D1) of the front groove may be 0.55t0 to 0.80t0.

[0019] In one specific example, the groove of the step S1) may be a front groove, the front groove may be U-shaped or V-shaped, and the rear groove may be U-shaped.

[0020] In one specific example, the groove of the step S1) may be a front groove, and the opening width (W1) / groove depth (D1) of the front groove may be 0.4 to 0.7.

[0021] In one specific example, the ratio (W2 / W1) of the width of the opening (W2) of the rear groove divided by the width of the opening (W1) of the front groove may be 0.6 to 0.9.

[0022] In one specific example, the welding may be performed by flux cored arc welding (FCAW).

[0023] In one specific example, the first arc welding and the second arc welding may each be multi-pass submerged arc welding (SAW).

[0024] In one specific example, in step S1), groove-forming ends of N (N is a natural number greater than or equal to 3) thick plates are arranged to face each other, so that grooves are formed for each N-1 joint, tack welding is performed for each joint in step S2), first arc welding is performed for each joint in step S3), rear grooves are formed for each joint in step S4), and second arc welding is performed for each rear groove in step S5).

[0025] In one specific example, the steps S1) to S5) are performed as a unit process, and the weldment obtained by the unit process can be repeatedly performed as a post-processing plate of the step S1).

[0026] The present invention includes a heavy-duty steel plate manufactured by the method for manufacturing a heavy-duty steel plate described above.

[0027] The present invention includes a heavy-duty steel plate.

[0028] The heavy-duty steel plate according to the start of work has a unit weight of 30 tons or more and a thickness of 60 mm or more, is a heavy-duty steel plate to be formed into a shape forming at least a part of a desired structure, and has a weld seam crossing the steel plate in the width direction or length direction.

[0029] In one specific example, the weld seam of a heavy-duty steel plate may include a center having a first convex region in which the weld bead protrudes toward the parent material, a concave region in which the weld bead is concave, and a second convex region in which the weld bead protrudes toward the parent material, relative to a virtual centerline crossing the center of the weld bead in the thickness direction, based on a cross-section in the thickness direction perpendicular to the weld seam of the heavy-duty steel plate.

[0030] In one specific example, based on a cross-section in the thickness direction perpendicular to the weld seam of a heavy-duty steel plate, the weld seam has a fish scale structure, but includes a first region and a second region in which the directions in which the scales cover are opposite, and may have a structure in which a part of one of the first region and the second region is embedded into the other region.

[0031] In one specific example, based on the cross-section in the thickness direction perpendicular to the weld seam of a heavy-duty steel plate, the position of the deepest recess in the internally recessed area is P1, and the boundary points where the base material and the first and second areas all meet are P2 and P3, and the length of the perpendicular at P1 to the imaginary line crossing P2 and P3 can be 0.05t0 to 0.25t0.

[0032] In one specific example, the above-mentioned heavy-duty steel plate may have a -50°C Charvy impact absorption energy value of 27 J or more at the weld zone including the weld seam and the weld heat affected zone in a roll-milled state in an arc shape so as to form a portion of a cylinder having a diameter of 6 m.

[0033] In one specific example, the above-mentioned heavy-duty steel plate may have M weld seams (M is a natural number from 2 to 9) spaced apart and parallel to each other.

[0034] In one specific example, the desired structure may be a monopile.

[0035] The present invention includes a method for manufacturing a can of a monopile.

[0036] A method for manufacturing a can of a monopile according to the invention comprises the steps of roll-forming the above-described heavy-duty steel plate; and the steps of welding the roll-formed heavy-duty steel plate to manufacture a can.

[0037] The method for manufacturing a heavy-duty steel plate according to the start of work can easily manufacture heavy-duty steel plates of various single weights by manufacturing heavy-duty steel plates by welding heavy-duty steel plates.

[0038] According to another specific example, a method for manufacturing a heavy-duty steel plate may not require development of a new process or change or addition of production equipment to manufacture a heavy-duty steel plate of a desired single weight and desired shape.

[0039] According to another specific example, a heavy-duty steel plate has a unique welding structure, so that even after the steel plate is highly formed, the welded portion can have excellent low-temperature impact toughness, and thus can be used as a steel plate for a monopile.

[0040] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0041] Figure 1 is a schematic diagram showing an example of a heavy-duty steel plate manufactured when the number of welded steel plates is 2 or 3 in a manufacturing method according to one specific example.

[0042] Figure 2 is a detailed process diagram illustrating step S1) in a manufacturing method according to one specific example.

[0043] Figure 3 is a detailed process diagram illustrating steps S4) and S5) in a manufacturing method according to one specific example.

[0044] Figure 4 is a schematic diagram showing a cross-section in the thickness direction perpendicular to the weld seam of a heavy-duty steel plate according to one specific example.

[0045] Figure 5 is another schematic diagram showing a cross-section in the thickness direction perpendicular to the weld seam of a heavy-duty steel plate according to one specific example.

[0046] Figure 6 is an optical photograph of a heavy-duty steel plate manufactured according to one specific example.

[0047] Figure 7 is a photograph of a welded section of a heavy-duty steel plate manufactured according to one specific example.

[0048] Figure 8 is an optical photograph observing a process of roll forming a heavy-duty steel plate manufactured according to one specific example into an arc shape with a diameter of 6 m or 8 m.

[0049] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0050] In addition, the embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the relevant technical field.

[0051] The shape and size of elements in the drawing may be exaggerated for clearer explanation.

[0052] In describing the embodiments of the present invention, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the present invention, such detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terminology used in the detailed description is only for the purpose of describing the embodiments of the present invention and should in no way be limiting. Unless clearly defined otherwise, expressions in the singular form include plural meanings.

[0053] In this description, expressions such as “including” or “having” are intended to indicate certain features, numbers, steps, operations, elements, portions or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, portions or combinations thereof other than those described.

[0054] Unless otherwise specified in the specification of the present invention, the % unit means weight %.

[0055] Additionally, throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

[0056] Below, the present invention will be described in detail through each embodiment or example of the present invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may be combined with other embodiments or examples. Therefore, the citation of a claim in the patent claims is only an example of an embodiment, and the technical concept of the present invention should not be interpreted solely as a combination with the cited claim, and combinations with various claims also fall within the scope of the technical concept of the present invention.

[0057] The terms used herein are for the purpose of describing the invention and are not intended to limit the invention. Furthermore, the singular forms used herein also include the plural forms, unless the relevant definition clearly indicates a contrary meaning.

[0058] The meaning of 'comprising' as used in the specification is to specify a configuration and not to exclude the presence or addition of other configurations.

[0059] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in the dictionary are to be interpreted to have meanings consistent with the relevant technical literature and the present disclosure.

[0060] The present invention is intended to solve the problem of having to rebuild production facilities and develop production conditions at an astronomical investment cost every time the unit weight of thick steel plates required in the industry increases.

[0061] In detail, the present invention provides a method for producing a steel plate having a desired high weight using a steel plate having a lower unit weight than the desired unit weight.

[0062] In addition, the present invention provides a method for producing a heavy-duty steel plate having various required unit weights, even when the unit weight of the heavy-duty steel plate required in the industry increases or decreases.

[0063] A method for manufacturing a heavy-duty steel plate according to the invention is a method for manufacturing a heavy-duty steel plate having a unit weight of 30 tons or more and being formed into a shape forming at least a part of a desired structure.

[0064] In detail, the method for manufacturing a heavy-duty steel plate includes the steps of S1) using at least two steel plates, each of which has a unit weight of 25 tons or less and a thickness (t0) of 60 mm or more and has grooved ends, and forming a joint having a groove by arranging the grooved ends of the steel plates to face each other; S2) performing tack welding so that the joint is fixed; S3) performing first arc welding along the groove; S4) forming a rear groove along the joint on a rear surface opposite the front surface, with the surface on which the first arc welding is performed as the front surface; and S5) performing second arc welding along the rear groove.

[0065] As described above, the manufacturing method according to the start of work can manufacture a target heavy steel plate by welding a steel plate having a smaller single weight than the target single weight.

[0066] Hereinafter, in order to clearly distinguish between the intended heavy-duty steel plate and the steel plate used for welding, the steel plate used for welding is collectively referred to as a “thick plate.” In addition, for the sake of clarity, one of the two thick plates, in which the groove-forming ends are arranged to face each other to form a groove, is collectively referred to as a “first thick plate,” and the other thick plate is collectively referred to as a “second thick plate.” However, in the present invention, the number of thick plates in step S1) in which the groove-forming ends are arranged to face each other is not limited to two, and it goes without saying that three or more thick plates may be used in step S1) and the groove-forming ends of each of the thick plates may be arranged to face each other. In addition, the content described simply as a “thick plate,” without being limited to the “first thick plate” or the “second thick plate,” may be interpreted as content corresponding to “each of the first thick plate and the second thick plate.”

[0067] The unit weight of the thick plate may be 25 tons or less, specifically 5 to 25 tons, or more specifically 10 to 25 tons. Thick plates with a unit weight of 5 to 25 tons are light to medium-heavy thick plates, which are actively produced and sold by most major thick plate manufacturers, with established production facilities and processes.

[0068] The thick plate may refer to a steel plate having a thickness of 60 mm or more. In one embodiment, the thickness of the thick plate may be 60 mm to 200 mm, specifically 60 mm to 150 mm, and more specifically 60 mm to 120 mm. The thick plates to be welded may have the same thickness. It goes without saying that the thickness of the thick plate may correspond to the thickness of the heavy-duty thick steel plate to be manufactured.

[0069] The unit weight (UWH) of the manufactured heavy-duty steel plate is equal to the product of the unit weight (UWL) of the welded plate and the number (N) of welded plates (UWH = UWL x N). Accordingly, even if the range of UWH required by the industry varies, the heavy-duty steel plate that satisfies the required UWH can be manufactured by changing the UWL or N, or by changing both the UWL and N.

[0070] The UWH may be 30 tons or more. Considering the various uses of the super heavy steel plate, the unit weight (UWH) of the super heavy steel plate according to one embodiment may be 30 to 150 tons, specifically 30 to 100 tons, and more specifically 30 to 80 tons.

[0071] For example, the number of thick plates to be welded (N) is fixed, the unit weight (UWL) of the thick plates to be welded is increased, and a heavy thick plate satisfying the required UWH can be manufactured. In one embodiment, the UWL may be 25 tons or less, specifically 5 to 25 tons, more specifically 10 to 25 tons, and even more specifically 15 to 25 tons.

[0072] For example, a heavy-duty steel plate can be manufactured by fixing the unit weight of the thick plate, increasing the number of welded thick plates, and satisfying the required UWH. Accordingly, there is no upper limit to N, and N can be any natural number greater than or equal to 2. As a practical example considering the various uses of heavy-duty steel plates, N can be a natural number less than or equal to 10, a more practical example less than or equal to 6, and even more practical examples are natural numbers such as 5, 4, 3, or 2.

[0073] For example, N may be 2, in which case two thick plates may be welded to produce a heavy-duty steel plate. For another example, N may be 3, in which case three thick plates may be welded to produce a heavy-duty steel plate.

[0074] The shape in which N thick plates (N is a natural number greater than or equal to 2) are welded (i.e., the overall shape of the heavy-duty thick steel plate) is sufficient as long as it is a shape suitable for the purpose of use of the heavy-duty thick steel plate, taking into consideration the purpose of use.

[0075] Fig. 1 is a schematic diagram showing an example of a heavy-duty steel plate manufactured when N is 2 or 3. As shown in the example shown in Fig. 1, each of the thick plates (110) forming the heavy-duty steel plate (100) is arranged so that each end faces the other in the longitudinal or transverse direction, and a weld seam (120) that crosses the heavy-duty steel plate in the longitudinal or transverse direction may be provided at the joint between the thick plates (110).

[0076] Considering the purpose of a monopile, a long, strip-shaped, heavy-duty steel plate is required. Considering the purpose of a monopile, a heavy-duty steel plate is formed by N thick plates arranged so that their ends face each other in the length direction (i.e., the ends of the thick plates corresponding to the width are arranged so that they touch each other), and (each) joint can be welded.

[0077] According to one embodiment, when three or more (N) thick plates form a heavy-duty thick plate, that is, a heavy-duty thick plate with two or more weld seams (M = N-1), can be manufactured by the following two methods depending on the size, weight, etc. of the heavy-duty thick plate.

[0078] In the first method, three or more (N) thick plates are all placed together in step S1), tack welding is performed joint by joint (N-1 joints) in step S2), first arc welding is performed joint by joint (N-1 joints) in step S3), back grooves are formed joint by joint in step S4), and second arc welding is performed joint by joint in step S5), so that a large-weight thick plate can be manufactured through a single S1) to S5) process.

[0079] The second method is to use steps S1) to S5) as a unit process, and the weldment obtained by the unit process can be used as a post-process plate of step S1) so that the unit process can be repeatedly performed.

[0080] In the S1) process of the first method or by repeating the unit process in the second method, it goes without saying that the plates whose ends come into contact with each other may be plates having grooves formed at each of the ends that come into contact with each other. In other words, the plate that is interposed between the two plates may have grooves formed at each of the ends that come into contact with each of the two plates.

[0081] However, the present invention is not limited to the first method and the second method, and a heavy-duty steel plate can be manufactured by appropriately combining the first method and the second method. For example, when a heavy-duty steel plate is to be manufactured with five thick plates, as instructed in the first method, a first weldment is manufactured with three thick plates, a second weldment is manufactured with two thick plates, and then, as instructed in the second method, the first weldment and the second weldment are used as the two thick plates in step S1) to manufacture a heavy-duty steel plate.

[0082] The manufactured heavy-duty steel plate can be formed into a shape that forms at least part of the intended structure. This means that the heavy-duty steel plate is formed to suit the intended application in each industry. The heavy-duty steel plate itself is a simple plate shape without any intentional forming. Considering the use of monopiles, the heavy-duty steel plate itself is a rectangular plate (a slab shape) that is elongated in one direction.

[0083] Hereinafter, each step S1) to S5) will be described in detail with reference to FIGS. 2 and 3. For clarity of understanding, steps S1) to S5) will be described with a focus on welding of two thick plates (first thick plate and second thick plate), but the number of thick plates used to manufacture a heavy-duty thick plate is not limited to two.

[0084] Step S1) is a step of forming a joint having a groove (hereinafter collectively referred to as a front groove) by arranging the groove-forming ends of the thick plates (which are the welding targets) so that they face each other (opposite arrangement). At this time, the joint means an area where the two ends are in close contact with each other due to the opposite arrangement.

[0085] Before the opposing arrangement, grooves can be formed on each end of the rear plates to be joined together, so that when the two grooves are joined together, a front groove can be formed. Alternatively, after the opposing arrangement, a front groove can be formed along the joint.

[0086] Fig. 2 is a detailed process diagram illustrating step S1) in a manufacturing method according to one specific example. Fig. 2 is an example in which, after forming one-end grooves (211, 212) of each of the rear plates (210, 220) facing each other for welding, a front groove (230) is formed at the joint (240) by facing each other. At this time, the surface where the front groove is located is referred to as the front surface (FS), and the surface opposite the front surface (FS) is referred to as the back surface (BS).

[0087] Figure 2 illustrates an example of forming a V-shaped front groove (230), but is not limited thereto. The front groove may be V-shaped or U-shaped. The grooves of each rear plate may be formed in a shape that allows the desired shape of the front groove to be formed by opposing arrangements. The grooves may be formed through conventional processing such as milling or grinding.

[0088] After step S2) is performed, tack welding of step S3) may be performed to fix the joint (fix between grooves), and then, as the main welding, first arc welding may be performed along the front groove (230). The tack welding may be flux cored arc welding (FCAW), and the first arc welding may be multi-pass submerged arc welding (SAW). FCAW and multi-pass SAW may be performed using FCAW welding materials and SAW welding materials that are commonly used for welding thick steel plates having a thickness exceeding 60 mm.

[0089] By performing the tack welding with FCAW and the main welding of the front groove with multi-pass SAW, the weld joint can have improved mechanical properties.

[0090] Welding using FCAW can be performed with a heat input of 0.5 to 2.0 kJ / mm and can be performed continuously (zero gap).

[0091] Main welding using multi-pass SAW can be performed with 10 to 50 passes, specifically 15 to 40 passes, and more specifically 20 to 35 passes, at a heat input (heat input per pass) of 3 to 7 kJ / mm and a welding speed of 0.2 to 2 m / min.

[0092] Figure 3 is a detailed process diagram illustrating steps S4) and S5) in a manufacturing method according to one specific example.

[0093] As shown in the example in Fig. 3, after welding is performed on the front groove by the first arc welding, for example, multi-pass SAW, and the front groove is filled with a welding bead (250), a turn-over can be performed in which the first rear plate (210) and the second rear plate (220) that are integrally formed by welding are turned over so that the rear surface (BS) is on top and the rear surface is exposed.

[0094] After the first rear plate (210) and the second rear plate (220) are turned over, a rear groove (260) can be formed along the joint (240) on the rear surface (BS). The rear groove (260) can also be formed through conventional processing such as milling or grinding.

[0095] After performing welding on the front groove (230), by forming the rear groove (260), the welding bead (250) formed on the front (FW) can be exposed to the bottom surface of the rear groove (260).

[0096] After the formation of the rear groove (260), a second arc welding can be performed along the rear groove (260). By performing the second arc welding on the rear groove (260), a heavy-duty steel plate (300) can be manufactured in which a weld seam (310) is formed across the steel plate in the width direction or length direction.

[0097] As described above based on FIG. 3, the rear groove (260) may be formed so that the weld bead (250) generated by the first arc welding, specifically the multi-pass SAW, is exposed to the bottom surface of the rear groove. To increase the area of ​​the weld bead (250) exposed to the bottom surface, the rear groove (260) may be U-shaped.

[0098] The second arc welding of the rear groove (260) having the surface where the weld bead is exposed may be multi-pass SAW, as shown in the detailed process diagram of Fig. 3. The rear welding using multi-pass SAW may be performed with a heat input of 3 to 7 kJ / mm, a welding speed of 0.2 to 2 m / min, and 5 to 35 passes, specifically 7 to 25 passes, and more specifically 9 to 20 passes.

[0099] In step S4), the weld bead (250) formed on the front surface (FW) is exposed to the bottom surface of the rear groove (260), and in step S5), second arc welding, specifically multi-pass SAW, can be used for rear welding. By performing rear welding using multi-pass SAW, the weld bead filling the rear groove (260) can be firmly combined with the weld bead (250) on the front surface, and the weld including the finally formed weld seam (310) and the weld heat-affected zone can have excellent mechanical properties, and in particular, can have excellent low-temperature impact toughness.

[0100] As described above, when first arc welding, specifically multi-pass SAW, is performed on the front surface, and then a rear groove is formed so that the front surface weld bead is exposed, and then second arc welding, specifically multi-pass SAW, is performed on the rear surface, a heavy-duty steel plate satisfying the low-temperature impact toughness required for the use of a monopile can be manufactured.

[0101] In one specific example, the front groove of step S1) and the rear groove of step S4) can satisfy Equations 1 and 2 so that the weld including the weld core (310) and the weld heat affected zone can have a Charvy shock absorption energy value (CVN value) of 27 J or more, specifically a CVN value of 50 J or more, more specifically a CVN value of 100 J or more, and even more specifically a CVN value of 150 J or more at -50°C, which is required for the use of the monopile.

[0102] (Formula 1)

[0103] D1+D2 > t0

[0104] (Formula 2)

[0105] 0.05 t0 ≤ │ D1+D2-t0│ ≤ 0.25 t0

[0106] In Equations 1 and 2, D1 is the groove depth of the front groove, and D2 is the groove depth of the rear groove.

[0107] Equation 1 satisfies the condition that the combined length of the groove depth of the front groove and the groove depth of the rear groove is greater than the thickness of the rear plate, and by satisfying Equation 1, the welding bead can be exposed to the bottom surface of the rear groove.

[0108] Equation 2 is an equation related to the area occupied by the weld bead on the groove surface forming the rear groove, i.e., the degree to which the weld bead is exposed through the rear groove.

[0109] The condition of Equation 2 is a condition that a weld seam having a center (CA) in which a first convex region where the weld bead protrudes toward the base material side, a concave region where the weld bead is concave, and a second convex region where the weld bead protrudes toward the base material side are sequentially formed in the direction from the front to the rear, based on a cross-section in the thickness direction perpendicular to the weld seam of a heavy-duty steel plate (hereinafter, the steel plate cross-section).

[0110] By means of a weld seam having a center (CA) of a first convex region - a concave region - a second convex region, even after a heavy-duty steel plate is formed into an arc shape through roll forming, etc., the weld can not only satisfy the low-temperature impact toughness required for a steel plate for a monopile, but also have a remarkably high low-temperature impact toughness value.

[0111] In one specific example, since the weld seam is formed by a multi-pass SAW, the weld seam may have a fish scale structure, based on a cross-section in the thickness direction perpendicular to the weld seam of the heavy-duty steel plate. In addition, since the multi-pass SAW is performed on the front side and then turned over to perform the multi-pass SAW on the back side, the first convex region and the second convex region may have opposite directions in which the scales are covered.

[0112] In addition, in one specific example, after welding is performed on the front groove, a rear groove is formed to satisfy Equations 1 and 2, and in addition, multi-pass SAW is performed on each of the front groove and the rear groove, so that a structure can be formed in which scales belonging to one of the first convex region and the second convex region are embedded into the other convex region. The degree of embedding of the scales can be controlled by Equation 2.

[0113] The weld seam may have the above-described shape, but in terms of securing excellent mechanical properties of the weld, │D1+D2-t0│ may be 0.05t0 to 0.25t0, specifically 0.05t0 to 0.20t0.

[0114] While satisfying the above-described Equations 1 and 2, the groove depth (D1) of the front groove (230) may be 0.55t0 to 0.80t0, specifically 0.55t0 to 0.75t0, and more specifically 0.60t0 to 0.75t0. When these condition(s) are satisfied, the concave region of the weld seam may be located in a region 0.55 to 0.75t0 in the thickness direction of the heavy-duty steel plate from the front surface.

[0115] As described above, according to one specific example, when a multi-pass SAW is performed on a front groove, a rear groove is formed so that the weld bead formed by the front welding is exposed, and a multi-pass SAW is performed again on the rear groove to manufacture a heavy-duty steel plate, even after the heavy-duty steel plate is formed into an arc shape so as to form a portion of a cylinder having a diameter of 6 m, which requires a very large forming based on a monopile can, the weld may have a CVN value of 27 J or more, specifically 50 J or more, more specifically 100 J or more, and even more specifically 150 J or more at -50°C. The actual upper limit of the CVN value may be 200 J, but is not limited thereto.

[0116] In addition, in order to have better low-temperature impact toughness (CVN value at -50℃) after forming of the heavy-duty steel plate, the ratio of the opening width (W1) / groove depth (D1) of the front groove (230) may be 0.40 to 0.70, specifically 0.45 to 0.70, and more specifically 0.50 to 0.65, while satisfying the above-described Equations 1 and 2. In addition, the ratio of the widths (W2 / W1) obtained by dividing the opening width (W2) of the rear groove by the opening width (W1) of the front groove may be 0.60 to 0.90, specifically 0.65 to 0.90, and more specifically 0.70 to 0.90, while satisfying the above-described Equations 1 and 2.

[0117] It is sufficient for the heavy-duty steel plate to have a composition that exhibits properties suitable for its intended use. For example, when considering the intended use of a monopile, the heavy-duty steel plate may contain, in wt%, C: 0.04 to 0.08%, Si: 0.1 to 0.35%, Mn: 1.4 to 1.8%, Sol.Al (acid-soluble Al): 0.01 to 0.035%, Ni: 0.2 to 0.5%, Cr: 0.1 to 0.3%, Mo: 0.05 to 0.15%, Nb: 0.015 to 0.035%, Ti: 0.005 to 0.02%, N: 0.002 to 0.006%, P: 0.01% or less, S: 0.003% or less, the remainder iron (Fe) and other unavoidable impurities, but is not necessarily limited thereto. Another example of heavy-duty steel plate usable for monopile purposes, in wt%, C: 0.08% or more and 0.15% or less, Mn: 1.70% or more and 1.85% or less, Si: 0.2% or more and 0.4% or less, Al: 0.005% or more and 0.015% or less, Ni: 0.01% or more and 0.02% or less, Cr: 0.02% or more and 0.05% or less, Cu: 0.04% or more and 0.08% or less, Mo: 0.002% or more and 0.03% or less, Ti: 0.02% or more and 0.04% or less, Nb: 0.002% or more and 0.004% or less, N: 50ppm or more and 80ppm or less, P: 0ppm or more and 200ppm or less, S: 0ppm or more and 50ppm or less, and the remainder May contain iron (Fe) and other unavoidable impurities.

[0118] The present invention includes a heavy-duty steel plate manufactured by the method for manufacturing a heavy-duty steel plate described above.

[0119] The present invention includes a heavy-duty steel plate.

[0120] A heavy-duty steel plate according to the start of work is a heavy-duty steel plate having a unit weight of 30 tons or more and a thickness of 60 mm or more, and is a heavy-duty steel plate to be formed into a shape forming at least a part of a desired structure, and has a weld seam crossing the steel plate in the width or length direction.

[0121] The heavy-duty steel plate may have one weld seam extending across the steel plate in the width or length direction, or may have M weld seams (M is a natural number of 2 to 9, specifically 2 to 5, and more specifically 2 to 3) spaced apart from each other across the steel plate in the width or length direction. In terms of the manufacturing method, the heavy-duty steel plate having M spaced apart weld seams is manufactured by arranging N (wherein N is M+1) thick plates facing each other in the length or width direction and then welding them to form a single plate.

[0122] The unit weight (UWH) of the super heavy steel plate can be 30 tons or more, and considering the various uses of the super heavy steel plate, the UWH can be 30 to 150 tons, practically 30 to 100 tons, and more practically 30 to 80 tons.

[0123] The thickness (t0) of the heavy-duty steel plate may be 60 mm to 200 mm, specifically 60 mm to 150 mm, and more specifically 60 mm to 120 mm.

[0124] The heavy-duty steel plate can be formed into a shape that forms at least a portion of the desired structure. That is, the heavy-duty steel plate can be in the form of a rectangular plate (float shape) that is long in one direction and not formed by mechanical force.

[0125] Figure 4 is a schematic diagram showing a cross-section (cross-section of the thick plate) in the thickness direction perpendicular to the weld seam (310) of a heavy-duty thick plate (300) according to one specific example.

[0126] As illustrated in an example in FIG. 4, with respect to a virtual centerline (illustrated by a single-dotted line in FIG. 4) that crosses the center of the weld bead in the thickness direction based on the cross-section of the thick plate, the weld seam may include a center (CA) having a first convex region (311) in which the weld bead protrudes toward the base material, a concave region (312) in which the weld bead is concave, and a second convex region (313) in which the weld bead protrudes toward the base material. In the center (CA), the first convex region (311), the concave region (312), and the second convex region (313) may be sequentially and continuously positioned in the thickness direction of the thick plate (300). At this time, as shown by the arrow in the schematic diagram of Fig. 4, protruding toward the base material side means protrusion in the direction of the plate's plane based on the center line of the weld seam in the cross-section of the thick plate, and the welding bead being concave means sinking in the direction of the plate's plane based on the center line of the weld seam in the cross-section of the thick plate.

[0127] Fig. 5 is another schematic diagram illustrating a cross-section (thickness plate cross-section) in the thickness direction perpendicular to the weld seam (310) of a heavy-duty steel plate (300) according to one specific example. As in the example of Fig. 5, based on the thickness plate cross-section, the weld seam may have a fish scale structure. In terms of the manufacturing method, the fish scale structure may be formed by multi-pass SAW. The weld bead produced by one pass may form one scale (314) in the cross-section, and as the passes progress, these scales may form layers, and a fish scale structure in which one scale layer covers a portion of another scale layer may be formed.

[0128] In addition, the weld seam (310) may include a first region and a second region in which the directions of the scales are opposite (as shown by arrows in Fig. 5) based on the cross-section of the thick plate. In this case, the center region described above is a region divided based on the shape at the boundary between the weld seam and the base material, and the first region and the second region are regions divided by the direction of the scales. Accordingly, it goes without saying that a part belonging to the first region may also belong to the convex region or concave region of the center region.

[0129] Among the two surfaces (plate surfaces) of the steel plate (300), an area having a direction in which scales are covered toward the center of the steel plate (300) on one surface and having a relatively larger area is defined as the first area, and an area having a direction in which scales are covered toward the center of the steel plate (300) on the other surface of the two surfaces and having a relatively smaller area is defined as the second area.

[0130] As illustrated in an example in Fig. 5, based on the cross-section of the rear plate, the weld seam (310) may have a structure in which a portion of the second region is embedded into the first region. Specifically, the scale(s) belonging to the second region may have a structure in which the scale(s) belonging to the second region are embedded into the first region.

[0131] Based on the cross-section of the steel plate, the position where the deepest part of the second region embedded within the first region is set as P1, and the boundary points where all three parts of the parent material, the first region, and the second region meet are set as P2 and P3, and the length of the perpendicular at P1 to the imaginary line (BL) crossing P2 and P3 can be defined as the embedded depth. The embedded depth can be 0.05t0 to 0.25t0, specifically 0.05t0 to 0.20t0.

[0132] At this time, the first region may include 10 to 50 scales, specifically 15 to 40 scales, and more specifically 20 to 35 scales. The second region may include a smaller number of scales than the first region, and may include 5 to 35 scales, specifically 7 to 25 scales, and more specifically 9 to 20 scales.

[0133] Based on the cross-section of the thick plate, the ratio (W4 / W3) of the width of the second region (W4) on the surface of the heavy thick plate divided by the width of the first region (W3) on the surface of the thick plate may be 0.60 to 0.90, specifically 0.65 to 0.90, and more specifically 0.70 to 0.90.

[0134] The heavy-duty steel plate having the above-described weld seam can have extremely excellent low-temperature impact toughness in the weld joint even after being formed by mechanical force to suit the purpose.

[0135] The heavy-duty steel plate having the above-described weld seam, in a roll-milled state in an arc shape so as to form a portion of a cylinder having a diameter of 6 m, may have a Charvy shock absorption energy value (CVN value) of -50°C of the weld including the weld seam and the weld heat affected zone of 27 J or more.

[0136] The present invention includes a method for manufacturing a monopile can using the above-described heavy-duty steel plate.

[0137] A method for manufacturing a monopile can according to the invention comprises the steps of: roll-forming the above-described heavy-duty steel plate; and welding the roll-formed heavy-duty steel plate to manufacture a can.

[0138] A method for manufacturing a monopile can according to another invention is a method for manufacturing a heavy-duty steel plate described above, comprising the steps of: manufacturing a heavy-duty steel plate; roll-forming the manufactured heavy-duty steel plate; and welding the roll-formed heavy-duty steel plate to manufacture a can.

[0139] In the method for manufacturing a monopile can, roll forming can be performed so that the formed large-weight steel plate can form a portion of a cylinder having a diameter of 6 m to 20 m. In addition, when manufacturing the can, the roll-formed large-weight steel plates can be welded to each other, and one roll-formed large-weight steel plate can be welded to any other steel plate.

[0140] (Example 1)

[0141] Three thick plates, each weighing 25 tons and 80 mm thick, were placed face to face so that their ends were in contact with each other, and tabs were welded to both ends for fixation. Each of the thick plates was grooved at each end so that a U-shaped groove (front groove) was formed at each joint when placed face to face, with a groove depth (D1) of 50 mm and a ratio of opening width (W1) / groove depth (D1) of 0.55.

[0142] For each joint, tack welding was performed using FCAW at a heat input of 1.5 kJ / mm, and then main welding was performed using multi-pass SAW. Multi-pass SAW was performed 25 passes at a heat input of 5 kJ / mm and a welding speed of 1 m / min.

[0143] After the main welding, the three integrated plates were turned over, and a U-shaped groove was formed at each joint. The groove depth of the U-shaped groove (rear groove) was 40 mm, and the ratio of the opening width (W2) of the rear groove to the opening width (W1) of the preceding front groove was 0.8. After the groove formation, welding was performed at each joint using a multi-pass SAW. The multi-pass SAW for the rear groove was performed 13 times at a heat input of 5 kJ / mm and a speed of 1 m / min.

[0144] After welding was completed, the tabs were removed and the surfaces of the welded joints were ground to make them smooth.

[0145] Figure 6 is an optical photograph of a manufactured heavy-duty steel plate, and the dark gray portion corresponds to the welded joint.

[0146] Fig. 7 is a photograph of a cross-section of a weld joint of a manufactured heavy-duty steel plate. It was confirmed that the weld seam had a fish-scale structure by multi-pass SAW and had two regions with opposing scale-covering directions. Specifically, in Fig. 7, the region in the direction where the scales are covered from the upper part toward the center of the steel plate is the region where the upper groove is filled with weld beads (region 1), and the region in the direction where the scales are covered from the lower part toward the center of the steel plate is the region where the lower groove is filled with weld beads (region 2). In Fig. 7, the point where the second region is most deeply embedded into the first region is indicated as P1, and the points where the base material (steel) and the first and second regions all meet are indicated as P2 and P3. Thereafter, the length of the perpendicular to P1 was measured with respect to the straight line passing through P2 and P3, and the length of the perpendicular (embedding depth) was approximately 6 mm. As the groove depth of the front groove is 50 mm and the groove depth of the rear groove is 40 mm, the depth at which the second region is embedded into the first region reaches 10 mm. However, when measuring the embedded depth using a cross-sectional photograph, the embedded depth calculated from the length of the perpendicular was measured to be smaller than the actual depth as P2 and P3 were used. In addition, as the rear groove is formed so that the first region is exposed to the surface, it can be confirmed that a concave region in which the welding bead is concave is created near P2 and P3 in Fig. 7, and convex region(s) that protrude toward the base material are created on both sides centered on the concave region.

[0147] (Example 2)

[0148] A heavy-duty steel plate was manufactured in the same manner as Example 1, except that the groove depth of the rear groove was set to 31 mm and multi-pass SAW was performed 9 times for the rear groove.

[0149] (Example 3)

[0150] A heavy-duty steel plate was manufactured in the same manner as Example 1, except that the groove depth of the rear groove was 35 mm and multi-pass SAW was performed 11 times for the rear groove.

[0151] (Example 4)

[0152] A heavy-duty steel plate was manufactured in the same manner as Example 1, except that the groove depth of the rear groove was set to 45 mm and multi-pass SAW was performed 15 times for the rear groove.

[0153] (Example 5)

[0154] A heavy-duty steel plate was manufactured in the same manner as Example 1, except that the groove depth of the rear groove was set to 50 mm and multi-pass SAW was performed 18 times for the rear groove.

[0155] The manufactured heavy-duty steel plates were roll-formed into an arc shape with a diameter of 6 m or 8 m (see Fig. 8), and after forming, an impact test was performed on the welded section including the weld seam and the weld heat-affected zone at -50°C. Specifically, JIS No. 4 standard test pieces were taken in the rolling direction at points 1 / 4t0, 1 / 2t0, and 3 / 4t0 in the thickness (t0) direction of the roll-formed heavy-duty steel plates, and the CVN value was measured by performing an impact test at -50°C. The impact test was measured three times at each point, and the CVN value measured at each point was averaged.

[0156] The measurement results confirmed that all test specimens exceeded the low-temperature CVN value required for monopile use. Specifically, the large-weight steel plates manufactured in Examples 1, 3, and 4 had a CVN value of the welded portion of 170 J or more at -50°C even when roll-formed into a 6-m diameter arc shape, and the large-weight steel plate manufactured in Example 2 had a CVN value of the welded portion of 50 J at -50°C when roll-formed into a 6-m diameter arc shape. The large-weight steel plate manufactured in Example 5 had a CVN value of the welded portion of 120 J at -50°C when roll-formed into a 6-m diameter arc shape.

[0157] The above embodiments are merely examples and the present invention is not limited thereto. Anything that has substantially the same configuration and achieves the same operational effects as the technical concepts described in the claims of the present invention is included within the technical scope of the present invention.

Claims

A method for manufacturing a heavy-duty steel plate having a unit weight of 1.30 tons or more and being formed into a shape forming at least a part of a desired structure. S1) A step of using at least two steel plates, each of which is a steel plate having a weight of 25 tons or less and a thickness (t0) of 60 mm or more and having ends with grooves formed therein, and forming a joint having a groove by arranging the ends of the steel plates with the grooves formed therein to face each other; S2) A step of performing a tack welding so that the above joint is fixed; S3) A step of performing a first arc welding along the above groove; S4) A step of forming a rear groove along the joint on the rear surface opposite to the front surface, with the surface on which the first arc welding is performed as the front surface; and S5) A method for manufacturing a heavy-duty steel plate, comprising the step of performing a second arc welding along the rear groove.

2. In paragraph 1, A method for manufacturing a heavy-duty steel plate, wherein a welding bead produced by the first arc welding is exposed to the bottom surface of a rear groove formed in the above step S4).

3. In paragraph 1, A method for manufacturing a heavy-duty steel plate, wherein the groove of the above step S1) is a front groove, and the rear groove formed in the above step S4) satisfies Equations 1 and 2. (Formula 1) D1+D2 > t0 (Formula 2) 0.05 t0 ≤│D1+D2-t0│ ≤ 0.25 t0 (In Equations 1 and 2, D1 is the groove depth of the front groove, and D2 is the groove depth of the rear groove.) 4. In paragraph 3, A method for manufacturing a heavy-duty steel plate having a groove depth (D1) of the front groove of the above-mentioned front groove of 0.55t0 to 0.80t0.

5. In paragraph 2, A method for manufacturing a heavy-duty steel plate in which the groove of the above step S1) is a front groove, the front groove is U-shaped or V-shaped, and the rear groove is U-shaped.

6. In paragraph 3, A method for manufacturing a heavy-duty steel plate having an opening width (W1) / groove depth (D1) of the front groove of the above-mentioned case being 0.4 to 0.

7.

7. In paragraph 3, A method for manufacturing a heavy-duty steel plate, wherein the ratio (W2 / W1) of the width of the opening (W2) of the rear groove divided by the width of the opening (W1) of the front groove is 0.6 to 0.

9.

8. In paragraph 1, The above welding is a method for manufacturing a heavy-duty steel plate by performing flux cored arc welding (FCAW).

9. In paragraph 8, The above first arc welding and second arc welding are each multi-pass submerged arc welding (SAW) methods for manufacturing a heavy-duty thick steel plate.

10. In paragraph 1, A method for manufacturing a very heavy steel plate, wherein in step S1), groove-forming ends of N (N is a natural number greater than or equal to 3) thick steel plates are arranged to face each other, grooves are formed for each N-1 joint, tack welding is performed for each joint in step S2), first arc welding is performed for each joint in step S3), rear grooves are formed for each joint in step S4), and second arc welding is performed for each rear groove in step S5).

11. In paragraph 1, A method for manufacturing a heavy-duty steel plate, wherein the above steps S1) to S5) are performed as unit processes, and the unit processes are repeated with the weldment obtained by the above step S1) as a steel plate after the step S1). It is a heavy-duty steel plate having a unit weight of 12.50 tons or more and a thickness of 60 mm or more, and is formed into a shape that forms at least a part of the intended structure. A heavy-duty steel plate having a weld seam running across the steel plate in the widthwise or lengthwise direction.

13. In paragraph 12, A heavy-duty steel plate having a center portion having a first convex region in which the weld bead protrudes toward the parent material side, a concave region in which the weld bead is concave, and a second convex region in which the weld bead protrudes toward the parent material side, with respect to an imaginary centerline crossing the center of the weld bead in the thickness direction in a cross section perpendicular to a weld seam of the heavy-duty steel plate.

14. In paragraph 12, A heavy-duty steel plate having a weld seam having a cross-section in the thickness direction perpendicular to the weld seam of the heavy-duty steel plate, the weld seam having a fish-scale structure, but including a first region and a second region in which the scales cover in opposite directions, and a structure in which a part of one of the first region and the second region is embedded into the other region.

15. In paragraph 14, A heavy-duty steel plate, wherein, based on a cross-section in the thickness direction perpendicular to a weld seam of the heavy-duty steel plate, the deepest embedded position in the region embedded in the interior is designated as P1, and the boundary points where the base material, the first region, and the second region all meet are designated as P2 and P3, and the length of the perpendicular at P1 to an imaginary line crossing P2 and P3 is 0.05t0 to 0.25t0.

16. In paragraph 15, The above-mentioned heavy-duty steel plate is a heavy-duty steel plate, in a state of being roll-milled into an arc shape so as to form a portion of a cylinder having a diameter of 6 m, in which the -50 ℃ Charvy impact absorption energy value of the weld including the weld seam and the weld heat affected zone is 27 J or more.

17. In paragraph 12, The above-mentioned heavy-duty steel plate is a heavy-duty steel plate having M weld seams (M is a natural number from 2 to 9) spaced apart and parallel to each other.

18. In paragraph 12, The structure for the above purpose is a monopile, a heavy-duty steel plate.

19. A method for manufacturing a can using a monopile, comprising: a step of roll-forming a heavy-duty steel plate according to any one of claims 12 to 17; and a step of welding the roll-formed heavy-duty steel plate to manufacture a can.

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