KR20150026581A

KR20150026581A - Thick steel plate having excellent bend property for tower of wind power generator and method of manufacturing the same

Info

Publication number: KR20150026581A
Application number: KR20130105638A
Authority: KR
Inventors: 김기혁; 조승재; 최우남; 김혁; 왕지언; 박병규; 이대식; 박명수
Original assignee: 동국제강주식회사
Priority date: 2013-09-03
Filing date: 2013-09-03
Publication date: 2015-03-11

Abstract

The present invention relates to a steel sheet for a tower of a wind turbine generator having excellent bending properties with improved stopping properties of cracks occurring at the time of bending, and a method for manufacturing the same. A method of manufacturing a steel sheet for a wind turbine tower excellent in bendability according to an embodiment of the present invention includes: 0.08 to 0.18% of C, 0.1 to 0.45% of Si, 1.0 to 1.6% of Mn, V: more than 0% to 0.05%, Ni: more than 0% to 0.05%, Cu: more than 0% to 0.05%, P: 0% (Ceq) of 0.36 to 0.42, a content of C (0 to 30%), a content of S (0 to less than 0.02%, a content of S of more than 0 to 0.008%, a content of N of more than 0 to 0.004% and a balance of Fe and inevitably included impurities) Pcm) of 0.21 to 0.23% at a heating time of 1 minute per 1 mm thickness of the slab at 1050 to 1200 占 폚; The slab reheated is extracted at 1140 to 1160 ° C., and controlled rolling is performed at a temperature of Ar 3 or more at a cumulative rolling reduction of 30% or more to complete the rolling at 820 ° C. or less, followed by air cooling to room temperature.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for a wind turbine tower having excellent bendability,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for a wind turbine tower having excellent bendability and a method for manufacturing the same, and more particularly, to a steel sheet for a tower of a wind turbine having excellent bendability, .

The wind power industry is expected to continue to grow by 2040 due to global interest in renewable energy such as changes in energy policies in different countries and smart grid planning in Europe. Therefore, it is expected that the production of wind power generators will be continued.

In recent years, as the size of the welded structure has been increased, safety has been further demanded. Therefore, steels for manufacturing wind turbine towers are also designed to have high strength and high toughness.

In general, the steel sheet tends to have an increased carbon equivalent as the high strength and thickening progress, making it difficult to secure toughness. In order to secure the strength of the steel sheet, the conventional technique is to add an alloy component for improving the hardenability, instead of limiting the content of carbon (C). Especially, a high alloy such as Ni (nickel) Phosphorus) and S (sulfur).

On the other hand, welded structural steels with a yield strength of 355N / ㎟ or more and a thickness of 30mm or more, which are applied to the tower part of a wind turbine generator, are additionally required to secure the performance for the SEP1390 guarantee test of German steel. SEP1390 is a weld bead bend test whose purpose is to determine the crack resistance of steel. SEP1390 describes how well cracks generated in weld metal are absorbed in the heat affected zone and base metal when a sudden load is applied to a large bend specimen with low heat input weld beads However, there are few case reports of technical data due to the capacity limit of conventional bending test equipment.

On the other hand, Japanese Laid-Open Patent Publication No. 1-172258 discloses a method of manufacturing a steel sheet having a yield strength in the range of 315 to 390 N / mm 2. However, in order to prevent the problem of increasing the carbon equivalent, there is a problem in that the cost competitiveness is reduced by adding an expensive alloy element instead of reducing the C content. In addition, the characteristics of large specimen weld bead bending, which is evaluated by a 200-ton grade bending facility due to enlargement of the specimen, is not mentioned.

Korean Patent Publication No. 2012-0063200 discloses a steel material excellent in strength and impact toughness and a method for producing the same. Here, a method of producing a steel material excellent in strength with a tensile strength of 500 N / mm 2 or more, strength of 150 J or more at a low temperature of -50 캜 and general charpy impact toughness is provided, but the securing of SEP 1390 characteristics is not mentioned.

Therefore, there is a need for a manufacturing method that can obtain a base structure having excellent resistance to bending crack propagation of the steel sheet.

SUMMARY OF THE INVENTION [0006] In order to solve the above problems, the present invention provides a steel plate for a tower of a wind turbine generator having excellent bending properties with improved stopping properties of cracks occurring at the time of bending, and a method for manufacturing the same.

In one embodiment of the present invention, there is provided an aluminum alloy comprising 0.08 to 0.18% of C, 0.1 to 0.45% of Si, 1.0 to 1.6% of Mn, 0.01 to 0.05% of Al, 0.005 Ni: more than 0% to 0.05%, Cu: more than 0% to 0.05%, P: more than 0% to less than 0.02%, N: more than 0% : More than 0% to not more than 0.008%, N: not more than 0% to not more than 0.004%, and the balance of Fe and inevitably contained impurities, the carbon equivalent (Ceq) is 0.36 to 0.42%, the cracking sensitive composition (Pcm) 0.23% at a heating time of 1 minute per 1 mm of the slab thickness at 1050 to 1200 占 폚; Cooling the slab to a temperature of 1140 to 1160 占 폚 and performing control rolling at a temperature of Ar3 or higher to achieve a cumulative rolling reduction of 30% or more at a temperature of 820 占 폚 or less, followed by air cooling to room temperature; A method of manufacturing a steel plate for a wind power generator tower is provided.

According to another aspect of the present invention, there is provided a method of manufacturing a steel sheet for a wind turbine tower, the steel sheet having a tensile strength ranging from 490 to 620 N / mm 2, The present invention provides a steel sheet for a wind turbine tower excellent in bendability having a range of 355 to 470 N / mm 2, an elongation of 25 to 35%, and a yield ratio of 0.68 to 0.89%.

According to an embodiment of the present invention, it is possible to manufacture a post-steel sheet excellent in bending property satisfying the SEP1390 standard through controlled rolling without an additional heat treatment step.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

FIG. 1 is an exemplary view showing a control rolling condition of a slab in a method of manufacturing a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
2 is a view illustrating an example of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
3 is a sectional view taken along the line AA in Fig.
4 is a sectional view taken along line BB of Fig.
5 is a photograph of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
6 is a photograph showing a bending test of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
7 is a photograph showing a shape of a welded specimen after bending test using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
8 is a photograph showing a cracked portion after a bending test of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.
9 is an enlarged photograph of the portion " C " in Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

A method of manufacturing a steel sheet for a wind turbine tower excellent in bendability according to the present invention is characterized by comprising 0.08 to 0.18% of C, 0.1 to 0.45% of Si, 1.0 to 1.6% of Mn, 0.01 to 0.05% of Al, Ni: more than 0% to 0.05%, Cu: more than 0% to less than 0.05%, P: more than 0%, Ti: not more than 0.005 to 0.02% 0.02% or less, S: more than 0% to 0.008% or less, N: more than 0% to 0.004% and the balance being Fe and inevitably included impurities, carbon equivalent (Ceq) of 0.36 to 0.42% Pcm) of 0.21 to 0.23% at a heating time of 1 minute per 1 mm thickness of the slab at 1050 to 1200 DEG C, extracting the reheated slab at 1140 to 1160 DEG C, And performing a controlled rolling at a cumulative rolling reduction of 30% or more to complete the rolling at a temperature of 820 占 폚 or less and then air cooling to room temperature. Thus, So that the properties desired to be obtained on the plate can be realized.

Hereinafter, the chemical composition and limitations of the method for manufacturing a steel sheet for a wind turbine tower having excellent bendability according to the present invention will be described. In the following, the content unit of the constituent alloy is expressed as% by weight.

C (carbon) is not effective in obtaining a desired high strength when the element or content effective for increasing the strength is low, but is effective for increasing the strength, but deteriorates in toughness and ductility, and is preferably limited to 0.08 to 0.18%.

Si (silicon) is an element essential for deoxidation of steel, and is an element effective for increasing the strength. However, if the content is 0.1% or less, desired high strength can not be obtained. Moreover, if it exceeds 0.45%, toughness and ductility will be lowered. Therefore, the Si content is preferably limited to a range of 0.1 to 0.45%.

Mn (manganese) has an effect of increasing the strength at the time of heat treatment, and it is also an element added for the compensation of the strength due to the limited amount of C added. However, when the amount of Mn is too low, the effect of improving the fineness is little, and when it exceeds the above range, the weldability is lowered and the risk of cracks is increased, so that it is preferable to limit the Mn to 1.0 to 1.6%.

Al (aluminum) is an element that acts as a deoxidizer for removing oxygen by reacting with oxygen present in molten steel. When the amount is too large, however, a large amount of oxide inclusions are formed to inhibit impact toughness of the material. %. &Lt; / RTI >

Ti (titanium) plays a key role in improving the low temperature toughness through grain refinement. Therefore, it is preferable to add at least 0.005% in order to sufficiently obtain the above effect. However, if the amount is too large, the impact toughness at low temperature deteriorates. Therefore, the upper limit is preferably limited to 0.02%. Therefore, Ti is preferably limited to 0.005 to 0.02%.

Nb (niobium) improves the strength of the base material and the welded portion. However, if the amount of Nb is too large, the possibility of causing brittle cracks in the edge of the steel increases. Therefore, it is preferable to limit the content to more than 0% and not more than 0.03%.

V (vanadium) precipitates in the weld heat affected zone and has an effect of preventing the strength from being lowered. However, if the amount is too large, the strength may be lowered. Therefore, the content is preferably limited to more than 0% and not more than 0.05% .

Ni (nickel) is an element added to secure the corrosion resistance of the material itself, and also helps to improve strength and impact toughness. However, if the amount is too large, a structure such as bainite or martensite may be formed. Therefore, it is preferable to limit the content to more than 0% and not more than 0.05%.

Cu (copper) is an element capable of minimizing toughness deterioration of a base material and at the same time increasing its strength. However, when the amount is too large, surface quality is greatly deteriorated.

P (phosphorus) is an impurity which deteriorates the weldability and hinders impact toughness, and it is desirable to suppress as much as possible. However, since it is an impurity inevitably contained in the manufacturing process, it is preferable to limit the content to more than 0% and not more than 0.02%.

S (sulfur) is an element which deteriorates the ductility, impact toughness and weldability of steel, and is particularly preferably controlled to be as low as possible because it forms MnS inclusions in combination with Mn to lower the abrasion resistance of steel. .

N (nitrogen) helps improve the toughness and strength of the steel, but if it is too much, there is N in the solid state, which adversely affects the toughness of the steel. Therefore, its content is limited to more than 0% and not more than 0.004% .

In the present invention, two slabs having a range of alloy composition as described above were prepared, and Table 1 shows the alloy composition of the two slabs.

division C Si Mn Al Ti Nb V Ni Cu P S N Ceq
(%) Pcm
(%) Example 1 0.15 0.43 1.48 0.025 0.015 0.025 0.040 0.040 0.045 0.018 0.005 0.003 0.42 0.23 Example 2 0.15 0.32 1.48 0.032 0.015 0.020 0.015 0.041 0.042 0.017 0.002 0.003 0.40 0.21

As shown in Table 1, the present invention produced a slab having an alloy composition satisfying the above alloy composition range. The slab of Example 1 had a carbon equivalent (Ceq) of 0.42%, a crack-susceptible composition (Pcm) of 0.23%, a slab of Example 2 had a carbon equivalent of 0.40% and a crack-susceptible composition of 0.21%. These values satisfy the carbon equivalent range of 0.36 to 0.42% and the crack susceptibility composition range of 0.21 to 0.23%. If the carbon equivalent or the crack susceptibility is less than the above-mentioned criteria, the strength of the post-steel base material may be lowered in the rolling process. If the carbon equivalent or the crack susceptibility is less than the above-mentioned criteria, the maximum hardness of the welded portion during the SEP- Therefore, it is preferable that the carbon equivalent and the crack susceptibility composition are controlled to satisfy the above-mentioned range. Here, the carbon equivalent (Ceq) can be determined by the following equation: carbon equivalent (Ceq) = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5, ) Can be obtained from the formula of the crack susceptibility composition (Pcm) = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 +

The slabs of Examples 1 and 2 thus prepared were reheated at a temperature of 1050 to 1200 占 폚 for a heating time of 1 minute per 1 mm of the slab thickness, and were extracted at 1150 占 폚. Here, reheating at a heating time of 1 minute per 1 mm of slab thickness means reheating at a level of 1 minute per 1 mm thickness when reheating a slab having a thick thickness. For example, when a slab having a thickness of 250 mm is reheated in a heating furnace, the reheating time may be 250 minutes, if the reheating is performed at a heating time of 1 minute per 1 mm thickness of the slab as described above. At this time, in the reheating, it can be regarded that the center portion of the slab is uniformly heated.

FIG. 1 is an exemplary view showing a control rolling condition of a slab in a method of manufacturing a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention. As shown in FIG. 1, The slab of Example 2 was subjected to controlled rolling at a cumulative rolling reduction of 30% or more at a temperature of Ar3 or higher. The controlled rolling was performed at a temperature of Ar3 or higher and subjected to roughing mill (RM) and finishing mill (FM). After completion at 820 ℃ or lower, air cooling was performed to room temperature. At this time, the thickness of the slab was 260 mm, and the finishing temperature of the control rolling was 800 캜 in Example 1 and 750 캜 in Example 2. Here, Ar3 (占 폚) can be obtained by the formula of Ar3 (占 폚) = 910-273C-74Mn-56Ni-16Cr-Mo-5Cu.

After being manufactured through these processes, the steel sheet has a tensile strength in the range of 490 to 620 N / mm 2, yield strength in the range of 355 to 470 N / mm 2, elongation in the range of 25 to 35%, and elongation in the range of 0.68 to 0.89% Lt; / RTI > range.

Table 2 shows the mechanical properties of the steel sheet after being manufactured through the above-described processes.

division The tensile strength
(N / mm2) Yield strength
(N / mm2) Elongation
(%) Yield ratio
(%) EN10025 Part2
(40 < t < = 63) 470-630 335 or more 21 or more - Example 1 559 387 26 0.68 Example 2 565 418 28 0.74

As shown in Table 2, the steel sheets of Example 1 and Example 2, each having a thickness of 50 mm, had tensile strengths of 559 N / mm 2 and 565 N / mm 2 and 490 ~ 620 N / It satisfied the range of 470 ~ 630N / ㎟ which is the tensile strength standard of European standard EN10025 Part2 of the rolled steel sheet. The steel sheets of Examples 1 and 2 each have a yield strength of 387 N / mm 2 and 418 N / mm 2 and a range of 355 ~ 470 N / mm 2, thereby satisfying the range of 335 N / mm 2 or more, which is the yield strength standard of EN 10025 Part 2 Respectively. In addition, the steel sheets of Examples 1 and 2 have elongation ratios of 26% and 28%, respectively, which are in the range of 25 to 35%, and thus have an excellent elongation of 21% or more on the elongation basis of EN10025 Part2. The yield strengths of the steel sheets of Examples 1 and 2 were 0.68 to 0.89% and 0.68 to 0.74%, respectively.

division Sample thickness Test temperature Absorbed energy (vE)
(J) EN10025 Part2
(t < = 100) t / 4 vE -20 ° C 40 or more Example 1 t / 4 vE -20 ° C
116 Example 2 184

Further, as shown in Table 3, the Charpy impact test (CVN Impact test) was performed on the steel sheets of Example 1 and Example 2 which were made to have a thickness of 50 mm. The test conditions were tested under the test conditions of EN10025 Part2 with a thickness of 100 mm or less. That is, the thickness of the sample was t (the thickness of the steel sheet after Examples 1 and 2) / 4 and the test temperature was -20 ° C. As a result, the steel sheets of Examples 1 and 2 showed absorption energy of 116 J and 184 J, respectively, which were more than 40 J, which is the absorbed energy (vE) of EN 10025 Part 2, respectively. It can be seen that the toughness of the steel sheet is large due to the excellent absorption energy.

2 is a cross-sectional view taken along the line AA in Fig. 2, Fig. 4 is a cross-sectional view taken along the line BB in Fig. 2, and Fig. And FIG. 5 is a photograph of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention.

2 to 5, a groove 20 is formed on the surface of the steel plate 10 after the steel plate 10 is manufactured, and the groove 20 is welded. The welding was performed by manual metal arc welding, and the generated weld bead 30 was made to be a single pass bead. Table 4 shows the welding conditions applied to the steel strips 10 of Examples 1 and 2.

division thickness
(mm) polarity electric current
(A) Arc voltage
(V) Welding speed
(CPM) Preheating temperature (℃) Heat input (kJ / cm) Bead height
(mm) Example 1 50 DC 235 34 22 20 21 One Example 2 50 DC 235 34 22 20 21 One

As shown in Table 4, the same conditions were applied to the first and second steel sheets 10 and 10 used in the manufacture of the steel sheet welding specimen 50, respectively. That is, the thickness T of the rear steel plate 10 was 50 mm, the length L1 of the rear steel plate 10 was 500 mm, and the width W of the rear steel plate 10 was 200 mm. At the time of welding, direct current (DC) was used, the current was 235A, and the arc voltage was 34V. The welding speed was 22 CPM (cm / min), the preheating temperature was 20 ° C and the heat input was 21 KJ / cm. The height H of the weld bead 30 was 1 mm, and the length L2 of the weld bead 30 was 240 mm, which was 220 mm or more. On the other hand, the maximum hardness (Hmax) of the welded portion through the passive metal arc welding with the heat input quantity of 21 KJ / cm was less than 350.

FIG. 6 is a photograph showing a bending test of a welded specimen using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention, wherein (a) is a photograph before a bending test of a steel sheet after bending test, and ) Is a photograph after the bending test of the steel sheet weld test. Table 5 shows the bending test conditions.

division sample Groove
radius
(mm) Weld bead length
(mm) Tester Setup Length
(mm) width
(mm) thickness
(mm) Punch diameter
(mm) Roller Spacing
(mm) standard 500 200 Less than 50 4 220 or more 150 280 Example 1 500 200 50 4 240 150 280 Example 2 500 200 50 4 240 150 280

6 and Table 5, the bending test machine 100 which carried out the bending test of the steel plate welding specimen 50 had a punch 110 diameter of 150 mm and an interval between the rollers 120 of 280 mm.

2) is 200 mm, the thickness (T, see Fig. 3) is 50 mm, and the groove radius (R, Fig. 4 4) and the length of the weld bead (L2, see Fig. 2) was 240 mm.

FIG. 7 is a photograph showing a shape of a welded specimen after a bending test using a steel sheet for a wind turbine tower having excellent bendability according to an embodiment of the present invention. FIG. 9 is a photograph showing a crack portion after a bending test of a welded specimen using a steel plate for a wind power generator tower, and FIG. 9 is an enlarged photograph of a portion "C" in FIG. Here, the photographs of Figs. 7 to 9 are photographs of Example 1. Fig. Table 6 shows the results of the bending test.

division Bending angle (°) Crack number Maximum length of crack (mm) standard 60 or more 1 or more Below 80 Example 1 62 5 16 Example 2 62 3 11

As shown in Fig. 6 (b), the bend angle A1 of the post weld steel specimen after bending test was 62 degrees, which exceeded the SEP1390 standard of 60 degrees.

As shown in Table 6 and Figs. 7 to 9, the number of cracks in the weld bead was 5 and 3, respectively, and satisfied one or more requirements of SEP1390. In addition, the maximum length of the cracks was 16 mm and 11 mm, which satisfied the requirements of SEP1390 of 80 mm or less. This indicates that the length of bending crack propagation to the heat affected zone (HAZ) and the base material (BM) is 4 times longer than the standard standard.

In particular, as shown in FIG. 9, the cracks started from the welded portion WM are propagated to the heat affected portion (HAZ) and progressed in the base material BM of the steel sheet after being restrained. At this time, The length was about 10mm, and the crack stopping property was excellent.

As described above, the steel sheet manufactured by the manufacturing method according to one embodiment of the present invention can secure quality that satisfies the standard of SEP1390 through control rolling without an additional heat treatment step.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

10: After steel plate
20: Groove
30: weld bead
50: Post welded steel plate specimen

Claims

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.08 to 0.18% of C, 0.1 to 0.45% of Si, 1.0 to 1.6% of Mn, 0.01 to 0.05% of Al, 0.005 to 0.02% of Ti, More than 0% to 0.05%, Ni: more than 0% to 0.05%, Cu: more than 0% to 0.05%, P: more than 0% And the balance being Fe and inevitably contained impurities and having a carbon equivalent (Ceq) of 0.36 to 0.42% and a crack-susceptible composition (Pcm) of 0.21 to 0.23% at a temperature of 1050 to 1200 占 폚, Reheating at a heating time of 1 minute per minute; And
The slabs are reheated at 1140 to 1160 ° C and subjected to control rolling at a temperature of Ar 3 or more at a cumulative rolling reduction of 30% or more to complete the rolling at 820 ° C or lower, followed by air cooling to room temperature. A method of manufacturing a steel plate for a generator tower.

A steel sheet according to claim 1, wherein the tensile strength is in the range of 490 to 620 N / mm 2, the yield strength is in the range of 355 to 470 N / mm 2, the elongation is in the range of 25 to 35% Is 0.68 ~ 0.89%, which has excellent bendability.