High-strength bainite wind power steel plate easy to weld and preparation method thereof

Abstract

The invention relates to a high-strength bainite wind power steel plate easy to weld, which comprises the following components in percentage by mass: 0.05 to 0.09 percent of C, 0.08 to 0.35 percent of Si, 1.5 to 1.9 percent of Mn, 0.12 to 0.45 percent of Ni, 0.15 to 0.45 percent of Cr, 0.02 to 0.07 percent of Nb, 0.012 to 0.035 percent of Ti, 0.008 to 0.035 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.55 percent of carbon equivalent Ceq, less than or equal to 0.25 percent of welding crack sensitivity index Pcm and the balance of Fe and inevitable impurity elements. According to the steel plate, the low-C Nb-containing microalloying technical thought is utilized, and on the premise that precious elements such as Mo, Cu and B are not added, preparation of the high-strength easily-welded wind power steel plate with the bainite structure as the main part is achieved through the TMCP rolling technology. The thickness specification of the prepared steel plate is 14-20 mm, the yield strength of the steel plate is larger than or equal to 550 MPa, the tensile strength is larger than or equal to 650 MPa, the percentage elongation after fracture is larger than or equal to 18%, the ballistic work of a steel plate matrix at the temperature of 60 DEG C below zero is larger than or equal to 200 J, and the ballistic work of a simulated post-welding heat affected zone at the temperature of 60 DEG C below

Description

Technical Field

[0001] The present invention relates to the field of high-performance alloy functional materials, and particularly to a high-strength and weldable bainite wind power steel plate and a preparation method thereof. Background Art

[0002] In recent years, with the vigorous development of wind power generation in China, the installed capacity of single units on land and at sea has been increasing. On land, the units are developing towards 6 MW, and at sea, the units are developing towards over 10 MW. The large-capacity development of single units has promoted the rapid development of the wind power industry chain. Among them, the safety skeleton tower barrel of the unit is required to have a greater load-bearing capacity, which is accompanied by higher requirements for the strength and service performance standards of the steel used for the tower barrel. Currently, for safety reasons, 355 MPa grade wind power steel is still mainly used for offshore wind turbines, and its use thickness increases with the increase in installed capacity. However, 420 MPa grade wind power steel plates have begun to be used on land-based wind turbines on a large scale, and the 500 MPa grade wind power steel recently developed by Shandong Iron and Steel Group has achieved tower hoisting in Hami, Xinjiang, refreshing the new record of the strength grade of steel plates used for tower structures globally. Baosteel has also successively launched 500 MPa grade wind power steel, which has laid a good foundation for the development of high-strength wind power steel in China.

[0003] Currently, wind power steels with a yield strength below 500 MPa mainly adopt a ferrite + pearlite dual-phase structure and are mostly delivered in the normalized state. As the yield strength grade increases to 500 MPa, it is difficult to meet the strength index requirements by regulating the ferrite + pearlite dual-phase structure. Therefore, microalloying with Nb and Mo is proposed to regulate the bainite-based matrix structure to meet the requirements of higher strength indexes.

[0004] CN 116536580 A discloses an easily weldable high-strength and tough 500 MPa grade wind power steel plate and a preparation method thereof. The organizational structure is bainite + acicular ferrite + reversed austenite, and it can achieve a yield strength ≥ 500 MPa, an elongation after fracture ≥ 15%, an impact energy at -60 °C ≥ 130 J, and a post-weld heat simulation impact energy at -60 °C ≥ 95 J.

[0005] CN 117721370 A discloses an anti-fatigue and corrosion-resistant 500 MPa grade marine wind power steel plate and a preparation method thereof. It also adopts a bainite (60%) + acicular ferrite (30%) + retained austenite tissue regulation technology, and can achieve a yield strength ≥ 500 MPa, a tensile strength of 600 - 760 MPa, an elongation after fracture ≥ 17%, an impact energy at the core at -30 °C ≥ 120 J. After the steel plate is welded by submerged arc welding with a heat input ≥ 35 kJ / cm, the tensile strength of the welded joint ≥ 600 MPa, and the impact energy at -30 °C ≥ 80 J; under the condition of a stress ratio of 0.5, the axial loading fatigue limit of the welded joint after 10 7 axial loading fatigue limit ≥ 450 MPa in weeks.

[0006] The above two patented technologies respectively adopt the composition systems of low C (0.02 - 0.05%) + Nb + Mo + B and high C (0.10% - 0.12%) + Nb + Cu, and are both prepared by the TMCP + annealing or tempering process. They have excellent properties, but the corresponding manufacturing costs are significantly higher than those of ferritic + pearlitic structure wind power steel. Except for the above two publicly disclosed patents related to 500MPa grade wind power steel, other related wind power steel patents do not involve bainite structure. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to adopt the design concept of low C and Nb microalloying without adding precious elements such as Mo, Cu, B, etc., and combine with the TMCP process to realize the preparation of high-strength and weldable wind power steel plates dominated by bainite structure, and meet the yield strength ≥ 550MPa on the basis of economy.

[0008] A high-strength and weldable bainite wind power steel plate includes the following components by mass percentage: C: 0.05 - 0.09%, Si: 0.08 - 0.35%, Mn: 1.5 - 1.9%, Ni: 0.12 - 0.45%, Cr: 0.15 - 0.45%, Nb: 0.02 - 0.07%, Ti: 0.012 - 0.035%, Al: 0.008% - 0.035%, P ≤ 0.015%, S ≤ 0.008%, and control the carbon equivalent Ceq ≤ 0.55% and the welding crack sensitivity index Pcm ≤ 0.25%. The rest are Fe and inevitable impurity elements. Preferably, the steel plate does not contain Mo, Cu, B. Preferably, control the carbon equivalent Ceq of the steel plate ≤ 0.49% and the welding crack sensitivity index Pcm ≤ 0.21%.

[0009] Among them: Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15;

[0010] Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B;

[0011] In the formula, the element symbols represent the mass percentage content of the corresponding elements in the steel plate.

[0012] Preferably, the high-strength and weldable bainitic wind power steel plate comprises the following components by mass percentage: C: 0.06 - 0.08%, Si: 0.1 - 0.3%, Mn: 1.6 - 1.8%, Ni: 0.15 - 0.4%, Cr: 0.2 - 0.4%, Nb: 0.03 - 0.06%, Ti: 0.015 - 0.03%, Al: 0.01% - 0.03%, P ≤ 0.01%, S ≤ 0.005%, and the carbon equivalent Ceq is controlled to be ≤ 0.49%, and the welding crack sensitivity index Pcm is ≤ 0.21%. The balance is Fe and unavoidable impurity elements.

[0013] The functions of the main components in the high-strength and weldable bainitic wind power steel plate are as follows:

[0014] C: The basic strengthening element in steel can significantly improve the strength of steel, but also has a decisive impact on welding performance. The present invention adopts a low-carbon design to control the carbon equivalent (Ceq) and the welding crack sensitivity index (Pcm) below 0.49% and 0.21% respectively while ensuring the strength of the steel plate, so as to ensure that the steel plate is easy to weld. Therefore, the C content in the present invention is set to be controlled at 0.06 - 0.08%, preferably 0.06 - 0.07%.

[0015] Mn: The austenitizing stabilizing element in steel can expand the austenite phase region and significantly improve the strength of steel. However, too high Mn content is likely to cause center segregation in the steel plate and affect welding performance. Therefore, the Mn content in the present invention is set to be controlled at 1.6 - 1.8%, preferably 1.6 - 1.7%.

[0016] Ni: It can increase the hardenability of steel, improve the strength and low-temperature toughness of steel at the same time, especially has a significant effect on improving the low-temperature impact toughness in the heat-affected zone of welding. However, too high Ni content will increase the tendency of cold cracking after welding and is not conducive to welding performance. Therefore, the Ni content in the present invention is set to be controlled at 0.15 - 0.4%, preferably 0.15 - 0.25%.

[0017] Cr: It can improve the strength and corrosion resistance of steel at the same time and has an improvement effect on the oxidation resistance of steel. However, too high Cr will reduce the tissue uniformity and plasticity. Therefore, the Cr content in the present invention is set to be controlled at 0.2 - 0.4%, preferably 0.2 - 0.3%.

[0018] Nb: It can effectively refine austenite and ferrite grains and also play a role in precipitation and solid solution strengthening. At the same time, the precipitation phase of Nb during welding can play a role in pinning grain boundaries and inhibiting the coarsening of austenite grains in the coarse-grained heat-affected zone of welding. However, considering the relatively high alloy cost of Nb element and its certain solubility limit in steel, the Nb content in the present invention is set to be controlled at 0.03 - 0.06%, preferably 0.03 - 0.05%.

[0019] Ti: It can refine the grain size and play a role in precipitation strengthening, and can significantly improve the low-temperature impact toughness of the steel plate. A small amount of Ti can fix N and exist in the form of precipitation phases during welding to pin the grain boundaries. However, too high Ti content is likely to induce coarse TiN inclusions, which is not conducive to low-temperature impact toughness and corrosion resistance. Therefore, in the present invention, the Ti content is controlled within 0.015 - 0.03%, preferably 0.015 - 0.02%.

[0020] P and S: Impurity elements in the steel, which will increase the cold cracking tendency of the steel plate and are not conducive to welding performance. At the same time, they have adverse effects on the fatigue, low-temperature impact and corrosion resistance of the steel plate. Therefore, in the present invention, the contents of P and S are respectively controlled below 0.01% and 0.005%, and more preferably controlled below 0.008% and 0.004%.

[0021] Ceq and Pcm: Control the carbon equivalent and cold crack sensitivity coefficient of the steel within a lower range to ensure the weldability and post-weld service performance of the steel plate. In the present invention, Ceq ≤ 0.49% and Pcm ≤ 0.21% are controlled, and more preferably Ceq ≤ 0.47% and Pcm ≤ 0.20% are controlled.

[0022] The present invention also provides a method for preparing the high-strength weldable bainitic wind power steel plate, including the following steps: feeding according to the set composition → hot metal desulfurization → converter smelting → LF refining + RH refining → slab continuous casting → slab reheating → TMCP rolling (rough rolling + finish rolling) → the steel plate is taken off the production line and stacked for cooling → ultrasonic flaw detection.

[0023] The specific steps are as follows:

[0024] Step (1): Configure the steel grade according to the set steel plate composition (mass percentage), carry out hot metal smelting, and perform desulfurization treatment by the KR method to control the S content in the hot metal below 0.01%;

[0025] Step (2): Send the hot metal to the converter and add scrap steel for molten steel smelting; further carry out LF refining and RH vacuum treatment on the molten steel to achieve dehydrogenation, deoxidation and denitrification; finally, the continuous casting billet of the above-mentioned wind power steel plate is cast through a slab continuous caster to obtain a 240 mm thick casting billet;

[0026] Step (3): Reheat the 240 mm thick casting billet, and then through rough rolling, intermediate billet waiting temperature cooling, finish rolling, steel plate cooling and taking off the production line and stacking for cooling, realize the preparation of a 14 - 20 mm thick steel plate;

[0027] Step (4): Carry out ultrasonic flaw detection on the steel plate to remove the unqualified steel plates.

[0028] As a further preference of the present invention, in step (3), during the reheating stage of the slab, the heating temperature is controlled at 1100 - 1220 °C, the time in the furnace is ≥ 1.2 min / mm, and the total time in the furnace is ≥ 200 min, so as to make the core temperature and surface temperature of the slab the same and achieve sufficient austenitization.

[0029] As a further preference of the present invention, in step (3), during the rough rolling stage, the starting temperature of rough rolling is always controlled at 1120 - 1160 °C, the number of rough rolling passes is set to ≤ 8 passes, and the finishing temperature is controlled at 1050 - 1100 °C; the thickness of the intermediate billet after rough rolling is 4 - 5 times the thickness of the finished steel plate.

[0030] As a further preference of the present invention, in step (3), during the finish rolling stage, the starting temperature of finish rolling is always controlled at 860 - 900 °C, the finishing temperature is controlled at 825 - 850 °C, and the cumulative reduction ratio in the finish rolling stage is ≥ 75%.

[0031] As a further preference of the present invention, in step (3), during the cooling stage of the steel plate, after finish rolling, the steel plate is spray-cooled, the finishing cooling temperature is always controlled at 520 - 550 °C, after the steel plate is slowly cooled on the cooling bed to 280 - 320 °C, it is taken off the line for stacking and cooled to room temperature, and finally a fine bainite structure is obtained.

[0032] The application of the wind power steel plate in a wind turbine, the thickness of the steel plate is 14 - 20 mm, the organizational structure is a single-phase bainite structure, the yield strength is ≥ 550 MPa, the tensile strength is ≥ 650 MPa, the elongation after fracture is ≥ 18%, the impact energy of the steel plate matrix at - 60 °C is ≥ 200 J, and the impact energy of the simulated heat affected zone after welding at - 60 °C is ≥ 120 J.

[0033] The present invention has the following beneficial technical effects: The present invention adopts the design concept of low-C Nb microalloying and combines with the TMCP rolling process. When the thickness of the steel plate is more than 15 mm, the preparation of a wind power steel plate with a yield strength reaching 550 MPa is realized. The composition system is simple and highly economical, the preparation process is simple and stable, the carbon equivalent and the cold crack sensitivity coefficient are controlled within a low range, it is easy to weld and the impact energy of the simulated heat affected zone after welding at - 60 °C is ≥ 120 J. More preferably, for the wind power steel plate of the present invention, when the thickness of the steel plate is 18 mm, a yield strength of 575 MPa can be achieved, and the impact energy of the simulated heat affected zone after welding at - 60 °C is ≥ 150 J. Description of the Drawings

[0034] Figure 1 It is the metallographic diagram of the microscopic structure of the high-strength weldable bainite wind power steel plate in Example 1 of the present invention;

[0035] Figure 2 It is the SEM diagram of the microscopic structure of the high-strength weldable bainite wind power steel plate in Example 1 of the present invention. Detailed Embodiments

[0036] To better understand the technical solution of the present invention, the content of the present invention includes but is not limited to the specific embodiments hereinafter, and similar technologies and methods should be regarded as within the scope of protection of the present invention. To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] The following further describes the present invention in detail by way of specific embodiments.

[0038] Example 1: The steel plate thickness specification is 20 mm.

[0039] A preparation method for high-strength and weldable bainitic wind power steel plates, the main process route is: configuring the steel grade composition → hot metal desulfurization → converter smelting → LF refining + RH refining → slab continuous casting → slab reheating → TMCP rolling → the steel plate is taken off the production line and stacked for cooling → ultrasonic flaw detection. Among them, the melting composition of Example 1 is shown in Table 1 by mass percentage, and each component meets the design range of the present invention.

[0040] Table 1

[0041] C Si Mn Ni Cr Nb Ti Al P S 0.07 0.25 1.72 0.26 0.29 0.04 0.019 0.02 0.008 0.003

[0042] First, a 240-mm-thick continuous casting billet is obtained, and then the billet is rolled and cooled according to the following process to obtain a 20-mm-thick steel plate. The specific rolling process is as follows: the 240-mm-thick billet is heated to 1200 °C and held in the furnace for 210 min to completely austenitize the billet. Then, the TMCP process is used for rough rolling and finish rolling of the billet. Among them, the rough rolling starting temperature is controlled at 1150 °C, there are 6 rough rolling passes, the rough rolling ending temperature is controlled at 1080 °C, and the thickness of the intermediate billet after rough rolling is 100 mm; then finish rolling is carried out. The finish rolling starting temperature is controlled at 890 °C, the finish rolling ending temperature is controlled at 830 °C, and the cumulative reduction of finish rolling is 80%. Finally, laminar cooling is used to spray water and cool the steel plate after finish rolling. The final cooling temperature is controlled at 525 °C, and then it is slowly cooled to 300 °C through the slideway and further stack-cooled to room temperature.

[0043] The optical morphology and SEM morphology of the microstructure of the steel plate after rolling in Example 1 are as Figure 1 and Figure 2 shown, which is a typical bainite structure. The mechanical properties of the steel plate after rolling are: the yield strength is 585 MPa, the tensile strength is 667 MPa, the elongation after fracture is 25.5%, and the impact energy at -60 °C is 267 J. The impact energy at -60 °C in the simulated heat affected zone of welding under the condition of a heat input of 20 kJ / cm is 159 J.

[0044] Example 2: The steel plate thickness specification is 18 mm.

[0045] Preparation method of high-strength weldable bainite wind power steel plate, the main process route is: configuring steel grade composition → hot metal desulfurization → converter smelting → LF refining + RH refining → slab continuous casting → slab reheating → TMCP rolling → steel plate off-line stacking and cooling → ultrasonic flaw detection. Among them, the melting composition of Example 2 is shown in Table 2 by mass percentage, and each component meets the design range of the present invention.

[0046] Table 2

[0047] C Si Mn Ni Cr Nb Ti Al P S 0.066 0.28 1.68 0.25 0.31 0.038 0.017 0.016 0.007 0.003

[0048] First, a 240-mm-thick slab is obtained by continuous casting, and then the slab rolling and cooling are carried out according to the following process to obtain an 18-mm-thick steel plate. The specific rolling process is as follows: the 240-mm-thick slab is heated to 1200 °C and kept in the furnace for 220 min to completely austenitize the slab. Then, the TMCP process is used for rough rolling and finish rolling of the slab. Among them, the rough rolling starting temperature is controlled at 1150 °C, there are 7 rough rolling passes, the rough rolling ending temperature is controlled at 1070 °C, and the thickness of the intermediate slab after rough rolling is 85 mm; then finish rolling is carried out. The finish rolling starting temperature is controlled at 880 °C, the finish rolling ending temperature is controlled at 830 °C, and the cumulative reduction of finish rolling is 78.8%. Finally, laminar cooling is used to spray water and cool the steel plate after finish rolling. The finish cooling temperature is controlled at 530 °C, and then it is slowly cooled to 300 °C through the slideway and further stack-cooled to room temperature.

[0049] The microstructure of the steel plate after rolling in Example 2 is also a typical bainite structure, and its mechanical properties are: yield strength is 576 MPa, tensile strength is 675 MPa, elongation after fracture is 21.6%, and impact energy at -60 °C is 218 J. The impact energy at -60 °C in the simulated heat-affected zone of welding under the condition of a heat input of 20 kJ / cm is 172 J.

[0050] Example 3: The steel plate thickness specification is 14 mm.

[0051] Preparation method of high-strength weldable bainite wind power steel plate, the main process route is: configuring steel grade composition → hot metal desulfurization → converter smelting → LF refining + RH refining → slab continuous casting → slab reheating → TMCP rolling → steel plate off-line stacking and cooling → ultrasonic flaw detection. Among them, the melting composition of Example 3 is shown in Table 3 by mass percentage, and each component meets the design range of the present invention.

[0052] Table 3

[0053] C Si Mn Ni Cr Nb Ti Al P S 0.062 0.25 1.62 0.21 0.28 0.032 0.017 0.017 0.008 0.002

[0054] The 240-mm-thick slab is first obtained by continuous casting, and then the slab rolling and cooling are carried out according to the following process to obtain a 14-mm-thick steel plate. The specific rolling process is as follows: The 240-mm-thick slab is heated to 1200 °C and held in the furnace for 220 min to completely austenitize the slab. Then, the TMCP process is used for rough rolling and finish rolling of the slab. The rough rolling starting temperature is controlled at 1160 °C, with 8 passes of rough rolling. The rough rolling ending temperature is controlled at 1060 °C, and the thickness of the intermediate slab after rough rolling is 65 mm. Subsequently, finish rolling is carried out. The finish rolling starting temperature is controlled at 870 °C, the finish rolling ending temperature is controlled at 835 °C, and the cumulative reduction of finish rolling is 78.5%. Finally, laminar cooling is used to spray water for cooling the steel plate after finish rolling. The final cooling temperature is controlled at 540 °C, and then it is slowly cooled to 300 °C through a slideway and further stack-cooled to room temperature.

[0055] The microstructure of the steel plate after rolling in Example 3 is also a typical bainite structure, and its mechanical properties are as follows: the yield strength is 558 MPa, the tensile strength is 665 MPa, the elongation after fracture is 19.8%, and the impact energy at -60 °C is 221 J. The impact energy at -60 °C in the simulated heat affected zone under the condition of a heat input of 20 kJ / cm is 154 J. In Example 3, due to the relatively small thickness specification, a lower alloy composition design system is adopted, and its yield and tensile strengths are slightly lower than those of Examples 1 and 2. However, the comprehensive mechanical properties and the simulated welding low-temperature impact toughness of the three examples are all excellent and within the design scope of the present invention. Considering comprehensively, the alloy composition system of the high-strength wind power steel plate can be optimized according to the thickness specification, which can not only achieve excellent comprehensive mechanical properties but also achieve the best economy.

[0056] It should be clear that the embodiments described in the present invention are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the scope of protection of the present invention.

Claims

1. A high-strength and easily welded bainite wind power steel plate, comprising the following components by mass percentage: C: 0.05-0.09%, Si: 0.08-0.35%, Mn: 1.5-1.9%, Ni: 0.12-0.45%, Cr: 0.15-0.45%, Nb: 0.02-0.07%, Ti: 0.012-0.035%, Al: 0.008%-0.035%, P≤0.015%, S≤0.008%, and the carbon equivalent Ceq is controlled to be ≤0.55%, the welding crack sensitivity index Pcm is ≤0.25%, and the rest is Fe and unavoidable impurity elements; in: Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B; The element symbols in the formula represent the mass percentage of the corresponding elements in the steel plate.

2. The wind power steel plate according to claim 1, characterized in that The steel plate contains the following chemical components in weight percentage: C: 0.06-0.08%, Si: 0.1-0.3%, Mn: 1.6-1.8%, Ni: 0.15-0.4%, Cr: 0.2-0.4%, Nb: 0.03-0.06%, Ti: 0.015-0.03%, Al: 0.01%-0.03%, P≤0.01%, S≤0.005%, and the rest are Fe and unavoidable impurity elements.

3. The wind power steel plate according to claim 1, characterized in that: Control the steel plate carbon equivalent Ceq≤0.49% and the welding crack sensitivity index Pcm≤0.21%.

4. A method for preparing a wind power steel plate according to any one of claims 1 to 3, characterized in that The process includes the following steps: feed material configuration according to set composition → molten iron desulfurization → converter smelting → LF refining + RH refining → slab continuous casting → slab reheating → TMCP rolling (rough rolling + finishing rolling) → steel plate offline stack cooling → ultrasonic flaw detection; The specific steps are as follows: Step (1): configuring the steel type according to the set steel plate composition, smelting molten iron, and performing desulfurization treatment by KR method to control the sulfur content in the molten iron to be less than 0.01%; Step (2): sending the molten iron to a converter and adding scrap steel to smelt the molten steel; further subjecting the molten steel to LF refining and RH vacuum treatment to achieve dehydrogenation, deoxidation and denitrification; and finally, casting the above-mentioned wind power steel plate continuous casting slab through a slab continuous casting machine to obtain a 240 mm thick slab; Step (3): reheating the 240 mm thick ingot, and then preparing a 14-20 mm thick steel plate through rough rolling, intermediate billet cooling, finishing rolling, steel plate cooling and offline stack cooling; Step (4): Perform ultrasonic testing on the steel plates and remove the unqualified steel plates.

5. The method according to claim 4, characterized in that: In step (3), during the reheating stage of the ingot, the heating temperature is controlled at 1100-1220°C, the time in the furnace is ≥1.2min / mm, and the total time in the furnace is ≥200min, so that the core and surface temperatures of the ingot are the same and austenitization is sufficient.

6. The method according to claim 4, characterized in that: In step (3), during the rough rolling stage, the rough rolling start temperature is always controlled at 1120-1160°C, the rough rolling passes are set to ≤8 passes, and the final rolling temperature is controlled at 1050-1100°C; the thickness of the rough rolling thick intermediate billet is 4-5 times the thickness of the finished steel plate.

7. The method according to claim 4, characterized in that: In step (3), during the finishing rolling stage, the starting temperature of the finishing rolling is always controlled at 860-900°C, the final rolling temperature is controlled at 800-850°C, and the cumulative reduction in the finishing rolling stage is ≥75%.

8. The method according to claim 4, characterized in that: In step (3), during the steel plate cooling stage, after the finish rolling, the steel plate is sprayed with water for cooling, and the final cooling temperature is always controlled at 520-550°C. After the steel plate is slowly cooled to 280-320°C on the cooling bed, it is stacked off the line and cooled to room temperature.

9. Application of the wind power steel plate according to any one of claims 1 to 3 or the wind power steel plate prepared by the method according to any one of claims 4 to 8 in a wind turbine, characterized in that: The thickness of the steel plate is 14-20mm, and the microstructure is a typical bainite single-phase structure.

10. The use according to claim 9, characterized in that: The yield strength of the steel plate is ≥550MPa, the tensile strength is ≥650MPa, the elongation after fracture is ≥18%, the impact energy of the steel plate matrix at -60°C is ≥200J, and the impact energy of the simulated heat affected zone after welding at -60°C is ≥120J.

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