Low-cost 500mpa offshore wind tower steel and method of manufacturing the same

Abstract

This invention discloses a low-cost 500MPa offshore wind turbine tower steel and its manufacturing method. The chemical composition of the offshore wind turbine tower steel, by mass percentage, is as follows: carbon: ≤0.14%, silicon: 0.32-0.38%, manganese: 1.0%-1.7%, chromium: 0.04%-0.08%, nickel: 0.03%-0.05%, sulfur: ≤0.0013%, phosphorus: ≤0.02%, with the remainder being Fe and unavoidable impurities; the CEV range is 0.31-0.44%. The manufacturing method includes steelmaking, continuous casting of steel billets, heating of steel billets, rolling of steel billets, ACC water cooling, and quenching and tempering heat treatment. This invention reduces the cost per ton of steel by lowering the precious metal content; through the quenching and tempering heat treatment process, it improves the yield strength of the wind turbine tower steel while achieving overall lightweighting of the wind turbine and extending the fatigue life of the wind turbine tower.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, specifically relating to a low-cost 500MPa offshore wind turbine tower steel and its manufacturing method. Background Technology

[0002] With the continuous development of the offshore wind power industry, and to meet the demands of expanding offshore wind farm scale and extending fatigue life, thick-film Q500-grade wind power steel will become the mainstream offshore wind power material in the future. In practical applications, it is generally used to manufacture the support structures of wind turbine equipment, such as towers and jackets. These applications require the steel to withstand significant loads and wind forces, and the safety of the material in low-temperature environments must be considered; therefore, the material must meet high strength and high / low temperature toughness requirements. However, the performance and internal quality assurance of thick-film Q500-grade wind power steel are difficult to guarantee due to factors such as insufficient compression ratio and poor deformation penetration, which greatly limits the application and promotion of the product.

[0003] Patent application CN 116536580 A discloses an easy-to-weld, high-strength and tough 500MPa grade wind power steel plate and its preparation method. Although this structural steel has good welding performance, the addition of a large amount of precious metal elements such as Mo and Ni to its chemical composition system results in high alloy cost per ton of steel. At the same time, the impact energy Akv2 at -40℃ is ≥75J, indicating poor low-temperature performance.

[0004] Patent application CN 119800232 A discloses a 500MPa grade bridge steel and its manufacturing method. Although the yield strength of this structural steel reaches the 500MPa level, its yield strength ratio is 0.86, resulting in poor toughness of the steel plate.

[0005] Therefore, it is of great significance to develop a low-cost chemical composition system for alloying elements, simple process control, good plate shape, low yield strength ratio, high straightness, and a thickness of ≥40mm for 500MPa offshore wind turbine tower steel and its manufacturing method. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost 500MPa offshore wind turbine tower steel and its manufacturing method. Based on a simple component ratio, the invention solves the problems of low yield strength, poor toughness, difficulty in ensuring low-temperature impact toughness, and high alloy cost of existing wind turbine tower steel by using a simple and efficient controlled rolling and cooling process and a tempering heat treatment process.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A low-cost 500MPa offshore wind turbine tower steel has the following chemical composition by mass percentage: carbon: ≤0.14%, silicon: 0.32-0.38%, manganese: 1.0%-1.7%, chromium: 0.04%-0.08%, nickel: 0.03%-0.05%, sulfur: ≤0.0013%, phosphorus: ≤0.02%, with the remainder being Fe and unavoidable impurities; CEV range is 0.31-0.44%. This composition system does not contain Mo (precious metal) and has a low Ni content, which greatly reduces the alloy cost per ton of steel.

[0008] The formula for calculating the carbon equivalent (CEV) is: CEV(%) = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

[0009] The steel used for offshore wind turbine towers described in this invention has a thickness of ≥40mm.

[0010] The microstructure of the steel used for offshore wind turbine towers described in this invention is ferrite + bainite.

[0011] The steel used for offshore wind turbine towers described in this invention has a yield strength ReH≥510MPa, tensile strength Rm≥750MPa, elongation after fracture A≥17%, yield strength ratio≤0.74, and impact energy KV2≥110J at -40℃.

[0012] The flaw detection of the steel used in offshore wind turbine towers described in this invention meets the Class I flaw detection requirements in GB / T 2970-2016 standard.

[0013] The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to the present invention includes steel smelting, continuous casting of steel billets, heating of steel billets, rolling of steel billets, ACC water cooling, and quenching and tempering heat treatment.

[0014] Furthermore, the steelmaking process described in this invention involves: molten iron being desulfurized and slag-removed before entering a converter for smelting, followed by refining in an LF furnace and VD vacuum treatment; the vacuum treatment time is ≥15 min; calcium treatment is performed before tapping; and argon blowing time is ≥15 min after wire feeding.

[0015] Furthermore, the continuous casting of steel billets described in this invention involves a billet thickness ≥ 250 mm, maintaining a constant casting speed during the casting process, with a casting speed range of 0.8 to 1.2 m / min, and employing electromagnetic stirring (EMS) to refine grains and light reduction techniques to prevent center segregation.

[0016] Furthermore, the billet heating method of the present invention involves using a walking beam furnace to heat the slab in sections to a uniform heating temperature of 1190-1240°C. The total heating time of the slab in the furnace is 2-4 hours, which ensures that the billet is fully austenitized while avoiding overheating.

[0017] Furthermore, the billet rolling process of the present invention adopts a two-stage controlled rolling and controlled cooling process, with the roughing rolling temperature at 1140℃~1170℃ and the total reduction rate at 40~75%; and the finishing rolling temperature at 840~870℃ and the total reduction rate at 10~20%.

[0018] Furthermore, the ACC water cooling described in this invention utilizes an ACC cooling system to perform weak water cooling to 480–520°C after rolling, with a water cooling pressure of 2.3–2.6 bar, followed by air cooling to room temperature after the temperature rises to 560–600°C.

[0019] Furthermore, the quenching and tempering heat treatment described in this invention includes: a quenching temperature of 900–930°C, a holding time of 2–2.5 min / mm from the quenching process to the warm loading of the furnace; a tempering temperature of 550–590°C, a holding time of 2.5–3 min / mm from the quenching process to the warm loading of the furnace, and natural air cooling to room temperature after the steel plate is removed from the furnace.

[0020] The inventive principle of this invention lies in:

[0021] The low-cost 500MPa offshore wind turbine tower steel rolling process provided by this invention adopts the TMCP process. This process achieves grain refinement through austenite hardening state regulation and phase transformation process control, thereby improving the strength and toughness of the steel. It can make the steel plate reach the strength level of 420MPa without adding precious metals such as Ni and Mo. The subsequent tempering heat treatment of the steel plate can further improve the hardness and toughness of the material, and significantly improve the yield strength and tensile strength, so that the steel plate reaches the strength level of 500MPa, which greatly extends the service life of the steel plate.

[0022] The beneficial technical effects of this invention are as follows:

[0023] This invention, through a suitable and economical composition system and a low carbon equivalent design, adds alloying elements Ni and Mn, and employs controlled rolling and cooling processes and optimized quenching and tempering processes, can stably produce quenched and tempered steel plates with a thickness ≥40mm and a strength of 500MPa for wind turbine towers that meet the low-temperature impact requirements of -40℃. The steel plates have good internal quality, and flaw detection meets the Class I flaw detection requirements in GB / T 2970-2016 standard. The microstructure after quenching and tempering heat treatment is ferrite + bainite. Attached Figure Description

[0024] Figure 1 The microstructure of steel for low-cost 500MPa wind turbine towers is shown in Example 1. Detailed Implementation

[0025] The present invention will be further described in detail below through embodiments. Example 1

[0026] The steel used for the offshore wind turbine tower in this embodiment has a thickness of 55mm and a chemical composition of: carbon: 0.14%, silicon: 0.38%, manganese: 1.0%, chromium: 0.08%, nickel: 0.03%, sulfur: 0.0013%, phosphorus: 0.01%, with the remainder being Fe and unavoidable impurities; the CEV is 0.32; and its production method includes the following steps: (1) Steel smelting: The molten iron is desulfurized and slag removed before entering the converter for smelting, and then refined in the LF furnace and treated with VD vacuum. The vacuum treatment time is 20 min. Calcium treatment is carried out before tapping the steel, and argon is blown statically for 18 min after wire feeding.

[0027] (2) Continuous casting of steel billets: The superheat of molten steel is 21℃, the thickness of the billet is 250mm, the casting speed is 0.8m / min, and electromagnetic stirring is used to refine the grains and light reduction technology to prevent center segregation.

[0028] (3) Steel billet heating: the temperature of the soaking zone is 1200℃, and the total heating time of the slab in the heating furnace is 180min; (4) Steel billet rolling and ACC water cooling: A two-stage controlled rolling and controlled cooling process is adopted. The roughing rolling start temperature is 1140℃, and the roughing rolling is carried out in 9 passes with a reduction of 182mm and a reduction of 35mm for thicker billets. The intermediate billet thickness is 68mm and the total reduction rate of the roughing rolling is 72.8%. The finishing rolling start temperature is 840℃, and the finishing rolling is carried out in 3 passes with a total reduction rate of 19%. The final rolling temperature is 780℃. Water cooling is carried out using the ACC cooling system. After rolling, the steel plate is cooled to 510℃ with weak water and the water cooling pressure is 2.5 bar. After the steel plate is heated to 580℃, it is air-cooled to room temperature.

[0029] (5) Quenching and tempering heat treatment: Quenching temperature 920℃, quenching process until warm loading into the furnace, holding time is 80min. Tempering temperature 590℃, tempering process until warm loading into the furnace, holding time is 100min. After the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

[0030] The microstructure of the steel plate obtained in this embodiment is shown below. Figure 1 ;Depend on Figure 1 It can be seen that its microstructure is ferrite + bainite. The microstructure of the steel plates in the other embodiments is the same as that in Embodiment 1, and will not be provided one by one.

[0031] The mechanical properties of the steel plate obtained in this embodiment are as follows: yield strength 510MPa, tensile strength 752MPa, yield ratio 0.68, elongation 22%, and impact energy at -40℃ 210J; the steel plate meets the Class I flaw detection requirements in GB / T 2970-2016 standard. Example 2

[0032] In this embodiment, the steel used for the offshore wind turbine tower is 58mm thick, and its chemical composition is: carbon: 0.1%, silicon: 0.36%, manganese: 1.2%, chromium: 0.04%, nickel: 0.05%, sulfur: 0.0008%, phosphorus: 0.01%, with the remainder being Fe and unavoidable impurities; CEV is 0.31; its production method includes the following steps: (1) Steel smelting: The molten iron is desulfurized and slag removed before entering the converter for smelting, and then refined in the LF furnace and treated with VD vacuum. The vacuum treatment time is 18 min. Calcium treatment is carried out before tapping the steel, and argon is blown statically for 18 min after wire feeding.

[0033] (2) Continuous casting of steel billets: The superheat of molten steel is 22℃, the thickness of the billet is 250mm, the casting speed is 1 m / min, and electromagnetic stirring is used to refine the grains and light reduction technology to prevent center segregation.

[0034] (3) Steel billet heating: the temperature of the soaking section is 1190℃, and the total heating time of the slab in the heating furnace is 240min.

[0035] (4) Steel billet rolling and ACC water cooling: A two-stage controlled rolling and controlled cooling process is adopted. The roughing rolling start temperature is 1160℃, and the roughing rolling is carried out in 9 passes with a reduction of 185mm and a reduction of 36mm for thick billets. The intermediate billet thickness is 65mm and the total reduction rate of the roughing rolling is 74%. The finishing rolling start temperature is 870℃, and the finishing rolling is carried out in 3 passes with a total reduction rate of 10.7%. The final rolling temperature is 800℃. Water cooling is carried out using the ACC cooling system. After rolling, the steel plate is cooled to 480℃ by weak water with a water cooling pressure of 2.4 bar. After the steel plate is heated to 560℃, it is air cooled to room temperature.

[0036] (5) Quenching and tempering heat treatment: Quenching temperature 900℃, quenching process until warm loading into the furnace, holding time is 80min. Tempering temperature 580℃, tempering process until warm loading into the furnace, holding time is 100min. After the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

[0037] The mechanical properties of the steel plate obtained in this embodiment are as follows: yield strength 538MPa, tensile strength 765MPa, yield ratio 0.70, elongation 19.5%, and impact energy at -40℃ 182J; the steel plate meets the Class I flaw detection requirements in GB / T 2970-2016 standard. Example 3

[0038] The steel used for the offshore wind turbine tower in this embodiment has a thickness of 55mm and a chemical composition of: carbon: 0.12%, silicon: 0.34%, manganese: 1.2%, chromium: 0.05%, nickel: 0.04%, sulfur: 0.0009%, phosphorus: 0.01%, with the remainder being Fe and unavoidable impurities; the CEV is 0.33; and its production method includes the following steps: (1) Steel smelting: The molten iron is desulfurized and slag removed before entering the converter for smelting, and then refined in the LF furnace and treated with VD vacuum. The vacuum treatment time is 15 min. Calcium treatment is carried out before tapping the steel, and argon is blown statically for 18 min after wire feeding.

[0039] (2) Continuous casting of steel billets: The superheat of molten steel is 22℃, the thickness of the billet is 250mm, the casting speed is 0.9m / min, and electromagnetic stirring is used to refine the grains and light reduction technology to prevent center segregation.

[0040] (3) Steel billet heating: the temperature of the soaking zone is 1240℃, and the total heating time of the slab in the heating furnace is 120min; (4) Steel billet rolling and ACC water cooling: A two-stage controlled rolling and controlled cooling process is adopted. The roughing rolling start temperature is 1150℃, and the roughing rolling is carried out in 9 passes with a reduction of 182mm and a reduction of 35mm for thicker billets. The intermediate billet thickness is 68mm and the total reduction rate of the roughing rolling is 72.8%. The finishing rolling start temperature is 850℃, and the finishing rolling is carried out in 3 passes with a total reduction rate of 19%. The final rolling temperature is 790℃. Water cooling is carried out using the ACC cooling system. After rolling, the steel plate is cooled to 500℃ by weak water with a water cooling pressure of 2.6 bar. After the steel plate is heated to 570℃, it is air-cooled to room temperature.

[0041] (5) Quenching and tempering heat treatment: Quenching temperature 910℃, quenching process until warm loading into the furnace, holding time is 80min. Tempering temperature 570℃, tempering process until warm loading into the furnace, holding time is 100min. After the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

[0042] The mechanical properties of the steel plate obtained in this embodiment are as follows: yield strength 573MPa, tensile strength 776MPa, yield ratio 0.74, elongation 18.8%, and impact energy at -40℃ 151J; the steel plate meets the Class I flaw detection requirements in GB / T 2970-2016 standard. Example 4

[0043] The steel used for the offshore wind turbine tower in this embodiment has a thickness of 58mm and a chemical composition of: carbon: 0.13%, silicon: 0.34%, manganese: 1.1%, chromium: 0.05%, nickel: 0.03%, sulfur: 0.0010%, phosphorus: 0.01%, with the remainder being Fe and unavoidable impurities; the CEV is 0.32; and its production method includes the following steps: (1) Steel smelting: The molten iron is desulfurized and slag removed before entering the converter for smelting, and then refined in the LF furnace and treated with VD vacuum. The vacuum treatment time is 20 min. Calcium treatment is carried out before tapping the steel, and argon is blown statically for 15 min after wire feeding.

[0044] (2) Continuous casting of steel billets: The superheat of molten steel is 23℃, the thickness of the billet is 250mm, the casting speed is 1.2m / min, and electromagnetic stirring is used to refine the grains and light reduction technology to prevent center segregation.

[0045] (3) Steel billet heating: the temperature of the soaking zone is 1220℃, and the total heating time of the slab in the heating furnace is 180min; (4) Steel billet rolling and ACC water cooling: A two-stage controlled rolling and controlled cooling process is adopted. The roughing rolling start temperature is 1170℃, and the roughing rolling is carried out in 9 passes with a reduction of 185mm. The reduction of the thick billet is 35mm. The intermediate billet thickness is 65mm and the total reduction rate of the roughing rolling is 72.8%. The finishing rolling start temperature is 860℃, and the finishing rolling is carried out in 3 passes with a total reduction rate of 10.7%. The final rolling temperature is 820℃. Water cooling is carried out using the ACC cooling system. After rolling, the steel plate is cooled to 520℃ by weak water with a water cooling pressure of 2.3 bar. After the steel plate is heated to 600℃, it is air cooled to room temperature.

[0046] (5) Quenching and tempering heat treatment: Quenching temperature 930℃, quenching process until warm loading into the furnace, holding time is 80min. Tempering temperature 560℃, tempering process until warm loading into the furnace, holding time is 100min. After the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

[0047] The mechanical properties of the steel plate obtained in this embodiment are as follows: yield strength 578MPa, tensile strength 780MPa, yield ratio 0.74, elongation 18.3%, and impact energy at -40℃ 129J; the steel plate meets the Class I flaw detection requirements in GB / T 2970-2016 standard. Example 5

[0048] In this embodiment, the steel used for the offshore wind turbine tower is 60mm thick, and its chemical composition is as follows: carbon: 0.14%, silicon: 0.32%, manganese: 1.7%, chromium: 0.08%, nickel: 0.05%, sulfur: 0.0011%, phosphorus: 0.01%, with the remainder being Fe and unavoidable impurities; the CEV is 0.44; its production method includes the following steps: (1) Steelmaking: Molten iron is desulfurized and slag removed before entering the converter for smelting, and then refined in the LF furnace and treated with VD vacuum. The vacuum treatment time is 15 min. Calcium treatment is performed before tapping the steel, and argon is blown statically for 15 min after wire feeding. (2) Continuous casting of steel billets: The superheat of molten steel is 21℃, the thickness of the billet is 250mm, the casting speed is 1.1m / min, and electromagnetic stirring is used to refine the grains and light reduction technology to prevent center segregation.

[0049] (3) Steel billet heating: The temperature of the heating soaking section is 1240℃, and the total heating time of the slab in the heating furnace is 120min; (4) Steel billet rolling and ACC water cooling: A two-stage controlled rolling and controlled cooling process is adopted. The roughing rolling start temperature is 1150℃, and the roughing rolling is carried out in 9 passes with a reduction of 182mm and a reduction of 35mm for thick billets. The intermediate billet thickness is 68mm and the total reduction rate of the roughing rolling is 72.8%. The finishing rolling start temperature is 850℃, and the finishing rolling is carried out in 3 passes with a total reduction rate of 13%. The final rolling temperature is 810℃. Water cooling is carried out using the ACC cooling system. After rolling, the steel plate is cooled to 490℃ by weak water with a water cooling pressure of 2.6 bar. After the steel plate is heated to 560℃, it is air-cooled to room temperature.

[0050] (5) Quenching and tempering heat treatment: Quenching temperature 900℃, quenching process until warm loading into the furnace, holding time is 80min. Tempering temperature 550℃, tempering process until warm loading into the furnace, holding time is 100min. After the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

[0051] The mechanical properties of the steel plate obtained in this embodiment are as follows: yield strength 583MPa, tensile strength 794MPa, yield ratio 0.73, elongation 17.2%, and impact energy at -40℃ 116J; the steel plate meets the Class I flaw detection requirements in GB / T 2970-2016 standard through UT flaw detection.

Claims

1. A low cost 500 MPa offshore wind tower steel, characterized in that: Its chemical composition by mass percentage is as follows: carbon: ≤0.14%, silicon: 0.32-0.38%, manganese: 1.0%-1.7%, chromium: 0.04%-0.08%, nickel: 0.03%-0.05%, sulfur: ≤0.0013%, phosphorus: ≤0.02%, with the remainder being Fe and unavoidable impurities; CEV range is 0.31-0.44%.

2. A low cost 500 MPa offshore wind tower steel according to claim 1, characterized in that: Its metallographic structure consists of acicular ferrite and bainite.

3. A low cost 500 MPa offshore wind tower for use in a steel tower according to claim 1, characterized in that: The steel used for offshore wind turbine towers has a yield strength ReH≥510MPa, tensile strength Rm≥750MPa, elongation after fracture A≥17%, yield strength ratio≤0.74, and impact energy KV2≥110J at -40℃; UT testing meets the Class I testing requirements in GB / T 2970-2016 standard.

4. A method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to any one of claims 1-3, characterized in that: This includes steel smelting, continuous casting of steel billets, heating of steel billets, rolling of steel billets, ACC water cooling, and quenching and tempering heat treatment.

5. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The steelmaking process involves the following steps: molten iron is desulfurized and slag removed before entering a converter for smelting, followed by refining in an LF furnace and VD vacuum treatment. The vacuum treatment time is ≥15 min. Calcium treatment is performed before tapping, and argon blowing is carried out for ≥15 min after wire feeding.

6. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The continuous casting of steel billets: the billet thickness is ≥250mm, and a constant casting speed is maintained during the casting process, with a casting speed range of 0.8~1.2m / min.

7. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The billet heating process involves using a walking beam furnace to heat the slab in sections to a uniform temperature of 1190–1240°C. The total heating time of the slab in the furnace is 2–4 hours.

8. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The steel plate rolling process adopts a two-stage controlled rolling and controlled cooling process. The rough rolling start temperature is 1140℃~1170℃, and the total reduction rate is 40~75%; the finish rolling start temperature is 840~870℃, and the total reduction rate is 10~20%.

9. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The ACC water cooling system utilizes the ACC cooling system to perform weak water cooling to 480–520°C after rolling, followed by red-hot cooling to 560–600°C and then air cooling to room temperature.

10. The method for manufacturing low-cost 500MPa offshore wind turbine tower steel according to claim 4, characterized in that, The quenching and tempering heat treatment is as follows: the quenching temperature is 900-930℃, the quenching process is carried out until the furnace is warm, and the holding time is 2-2.5 min / mm; the tempering temperature is 550-590℃, the quenching process is carried out until the furnace is warm, and the holding time is 2.5-3 min / mm; after the steel plate is taken out of the furnace, it is naturally air-cooled to room temperature.

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