Q500ME high-strength, high-toughness, easy-to-weld and fatigue-resistant steel plate for wind power tower drum

Abstract

The invention discloses a Q500ME high-strength, high-toughness, easy-to-weld and fatigue-resistant steel plate for a wind power tower drum. The Q500ME high-strength, high-toughness, easy-to-weld and fatigue-resistant steel plate comprises the following chemical components in percentage by weight: 0.10 to 0.13 percent of C, 0.20 to 0.30 percent of Si, 1.50 to 1.65 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.040 to 0.050 percent of Nb, 0.035 to 0.045 percent of V, 0.012 to 0.022 percent of Ti, 0.20 to 0.30 percent of Cr, 0.020 to 0.035 percent of Als and the balance of iron and impurities. The Q500ME wind power steel plate with the thickness of 14-50 mm is obtained through the procedures of converter smelting, LF refining, RH vacuum treatment, continuous casting, slow cooling, heating, hot mechanical rolling and the like. The steel plate is excellent in mechanical property, easy to form and weld and good in fatigue resistance.

Description

Technical Field

[0001] The invention relates to the technical field of steel production for wind power, and in particular to a Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind power towers. Background Art

[0002] As one of the important directions for the development and utilization of renewable energy, wind power generation has played an important role in promoting the transformation of my country's energy structure and undertaking the task of upgrading environmental protection. The country is comprehensively promoting the large-scale development and high-quality development of wind power generation. The capacity of onshore wind turbines has increased to 10MW or even 13MW, requiring the tower to provide a higher bearing capacity. The steel used for wind power has been increased from Q355 to Q500, and the high strengthening of steel plates can reduce the weight of the tower by 12-14%. To this end, on the basis of 420MPa wind power steel, 500MPa wind power steel has also gradually begun to be used. Baosteel, Xianggang, Laigang and other steel companies have developed Q500ME wind power steel and achieved demonstration applications.

[0003] Q500ME steel for wind power is a grade in GB / T1591-2018 "Low Alloy High Strength Steel Plate", which requires yield strength ≥500MPa, tensile strength 610-770MPa, elongation after fracture ≥17%, impact energy at -40℃ ≥31J, and qualified bending performance. At the same time, it has strict requirements on harmful elements and gas content.

[0004] Chinese patent CN 108531816 B discloses "a 500MPa grade engineering machinery steel and its manufacturing method". The chemical composition is as follows: C: 0.12-0.23%, Si: 0.10-0.60%, Mn: 0.80-1.90%, P: <0.018%, S: <0.010%; and one or more selected from Cr: 0-0.50%, Ni: 0-0.60%, Mo: 0-0.45%, Cu: 0-0.40%, Nb: 0-0.060%, V: 0-0.15%, Ti: 0-0.12%, B: 0-0.0030%, Al: 0.010-0.050%; the balance is Fe and unavoidable impurities. Its metallographic structure is a uniform and fine martensitic high temperature tempered structure, so it has good mechanical properties and fatigue properties. The shortcomings are: first, the high carbon content and high carbon equivalent deteriorate the welding performance; second, the tempering process is still used in production, which increases the cost.

[0005] Chinese patent CN 112210719 A discloses "a low-cost high-performance Q500 bridge steel and production method", whose chemical composition and mass percentage are as follows: C≤0.035%, Si: 0.31%~0.40%, Mn: 1.71%~1.80%, P≤0.015%, S≤0.0030%, Nb: 0.030%~0.050%, V: 0.020%~0.050%, Ti: 0.010%~0.018%, Cr: 0.70%~0.80%, Ni: 0.10%~0.20%, residual Mo≤0.05%, Cu: 0.10%~0.20%, B≤0.0005%, N≤0.0005%, Al: 0.020%~0.050%. The yield strength is reduced while the tensile strength of the product is improved, effectively reducing the yield strength ratio of the product. The shortcoming is that the patent adopts an ultra-low carbon + alloy composition design, with a high alloy addition amount, high cost, and high requirements for cooling equipment.

[0006] Chinese patent CN 108624744 B discloses "A Q500qE bridge steel plate and its production method". The chemical composition is as follows: C: 0.045-0.07%, Si: 0.20-0.40%, Mn: 1.6-1.8%, P: ≤0.018%, S: ≤0.006%, Cr: 0.25-0.35%, Nb: 0.02-0.04%, Cu: 0.15-0.25%, Ni: 0.15-0.25%, Mo: 0.15-0.25%, Ti: 0.01-0.25%, Als: 0.015-0.045%, CEV carbon equivalent: 0.44-0.48%, Pcm welding crack sensitivity coefficient ≤0.23, the remainder is Fe and unavoidable impurities; after the controlled rolling is completed, the steel plate is relaxed for 10-160 seconds after the rolling is completed, and then enters the laminar cooling area and is cooled to 300-650°C at a cooling rate greater than 20°C / s. The shortcomings are that the patent adopts an ultra-low carbon + alloy composition design, which has a high alloy addition amount, high cost, and high requirements for cooling equipment. Second, the relaxation control technology is used, which is difficult to control and is not suitable for all thick plate production lines. Summary of the invention

[0007] The purpose of the present invention is to provide a Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind power towers, which has the following properties: yield strength ≥500MPa, tensile strength 610-770MPa, elongation after fracture ≥17%, -40°C impact energy ≥100J, and has the characteristics of easy welding, easy forming, fatigue resistance, etc. It can be used to manufacture high-strength wind power towers.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The invention discloses a Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for a wind power tower. The chemical composition of the steel plate is C: 0.10-0.13%, Si: 0.20-0.30%, Mn: 1.50-1.65%, P: ≤0.015%, S: ≤0.005%, Nb: 0.040-0.050%, V: 0.035-0.045%, Ti: 0.012-0.022%, Cr: 0.20-0.30%, Als: 0.020-0.035%, CEV≤0.46%, Pcm≤0.23%, and the balance is Fe and unavoidable impurities. The main steps and process parameters of the manufacturing method thereof include:

[0010] S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured;

[0011] S2 converter smelting: The converter smelting stage uses molten iron and high-quality scrap steel that have been pre-treated with desulfurization as raw materials. The molten iron temperature is ≥1260℃. The phosphorus and carbon content are reduced through efficient top and bottom double blowing technology to ensure that the molten steel P≤0.010%, S≤0.004%;

[0012] S3 LF refining outside the furnace: During the refining stage outside the furnace, the composition of the molten steel is precisely controlled, deoxidation and alloying are carried out, and non-metallic inclusions and harmful impurities in the molten steel are further reduced, S≤0.004%, and clean molten steel is obtained;

[0013] S4 RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas contents in molten steel, and reduce the adverse effects of harmful gases on steel quality; the vacuum degree is less than 90Pa, the vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm;

[0014] S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7.5 mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency of 5 Hz, and current of 350 A; water volume on the wide side of the crystallizer is 4500 L / min, water volume on the narrow side is 370 L / min, crystallizer inlet water temperature is 36±2°C, crystallizer inlet water temperature is 38±1°C, secondary cooling water temperature is 22~25°C, and water quality indicators must meet process requirements; protective casting is used, and the argon pressure of the long water inlet seal is greater than 0.3M Pa, flow rate 130~160L / min; argon pressure of tundish immersion water inlet sealing is greater than 0.2MPa, flow rate 15~20L / min; continuous casting superheat 20~30℃, tundish liquid level is not less than 30 tons when changing tundish; constant pulling speed is adopted, and the pulling speed is stable at 1.0m / min; the straightening temperature of the billet is controlled at 950~1000℃, and the temperature difference of the billet along the width direction shall not exceed 50℃; finally, 250mm thick continuous casting billet is produced, the low-multiple center segregation of the billet is controlled below Class C 3.0, and the billet is pile-cooled or pit-cooled for more than 36 hours after it comes off the line;

[0015] S6 Heating: The slab is heated in a walking beam heating furnace, and the atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab, the heating temperature is 1210℃~1250℃; the total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure sufficient solid solution of alloy elements and uniform slab temperature;

[0016] S7 rolling and cooling: rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing rolling stage. Rough rolling is carried out on a 3800mm rough rolling mill, with a start rolling temperature of more than 1170℃ and a single-pass relative reduction rate controlled at more than 15% for at least two passes. The torque is set to 2280k N·m during the first stage of rolling. The deformation of each pass is strictly controlled during finishing rolling, with a start rolling temperature of ≤900℃ and a final rolling temperature of ≤800℃. The torque is set to 2320k N·m during the second stage of rolling. After the steel plate is rolled, laminar cooling is carried out, with a water temperature of 17-20℃ and a final cooling temperature of 600-630℃. The head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, and the edge is shielded by 0-2.0m. The overall temperature difference after the steel plate returns to red is controlled to be ≤50℃. The steel plate is stacked and slowly cooled for 12 hours before sampling and inspection.

[0017] Furthermore, the chemical composition of the steel plate is C: 0.11%, Si: 0.24%, Mn: 1.56%, P: 0.012%, S: 0.003%, Nb: 0.042%, V: 0.039%, Ti: 0.013%, Cr: 0.25%, Als: 0.021%, and the remainder is Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the steel plate is C: 0.11%, Si: 0.24%, Mn: 1.57%, P: 0.013%, S: 0.002%, Nb: 0.045%, V: 0.040%, Ti: 0.015%, Cr: 0.24%, Als: 0.021%, and the balance is Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the steel plate is C: 0.11%, Si: 0.26%, Mn: 1.57%, P: 0.012%, S: 0.004%, Nb: 0.046%, V: 0.042%, Ti: 0.015%, Cr: 0.25%, Als: 0.020%, and the balance is Fe and unavoidable impurities.

[0020] Furthermore, the chemical composition of the steel plate is C: 0.12%, Si: 0.25%, Mn: 1.58%, P: 0.011%, S: 0.002%, Nb: 0.047%, V: 0.040%, Ti: 0.013%, Cr: 0.26%, Als: 0.022%, and the remainder is Fe and unavoidable impurities.

[0021] Furthermore, the chemical composition of the steel plate is C: 0.12%, Si: 0.27%, Mn: 1.58%, P: 0.011%, S: 0.002%, Nb: 0.045%, V: 0.042%, Ti: 0.016%, Cr: 0.24%, Als: 0.022%, and the remainder is Fe and unavoidable impurities.

[0022] Furthermore, the chemical composition of the steel plate is C: 0.12%, Si: 0.25%, Mn: 1.60%, P: 0.012%, S: 0.003%, Nb: 0.048%, V: 0.041%, Ti: 0.013%, Cr: 0.25%, Als: 0.022%, and the remainder is Fe and unavoidable impurities.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] (1) According to GB / T 1591-2018, the present invention adopts a low carbon-niobium-vanadium-titanium-chromium alloying composition design, and adopts thermomechanical rolling technology to produce a 14-50mm thick Q500ME wind power steel plate, the steel plate has a yield strength of ≥500MPa, a tensile strength of 610-770MPa, an elongation after fracture of ≥17%, and an impact energy of ≥100J at -40°C. It also has the characteristics of easy welding, easy forming, and fatigue resistance.

[0025] (2) The present invention ensures the strength and low-temperature impact toughness of the steel plate by controlling the start rolling temperature and the final rolling temperature and coordinating the cooling process.

[0026] (3) The present invention obtains a bainite-based microstructure with a grain size of 11-12 by controlling the rolling temperature and cooling process.

[0027] (4) The present invention improves the segregation of the ingot through electromagnetic stirring and dynamic soft reduction, reduces the harm of the banded structure, avoids the accumulation of harmful elements and hard phase structure in the core, and improves the product's flaw detection pass rate and the stability of welding performance;

[0028] (5) The present invention adopts a relatively high final cooling temperature and steel plate stack cooling, which effectively improves the shape of the steel plate and solves the problem of uneven internal stress of the product.

[0029] (6) The steel plate of the present invention has good welding performance, and all properties of the welded joint meet the technical requirements.

[0030] (7) The ultimate fatigue stress of the steel plate welded joint of the present invention is about 285 MPa, and when the survival rate is 97.7%, the ultimate fatigue stress is about 261 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below in conjunction with the accompanying drawings.

[0032] Figure 1 This is a low-magnification photograph of the ingot corresponding to the steel plate of the embodiment of the present invention.

[0033] Figure 2 This is the optical metallographic structure diagram of the near surface of the steel plate in Example 3 of the present invention.

[0034] Figure 3 This is a low-magnification morphology image of the impact fracture of the steel plate of Example 3 of the present invention.

[0035] Figure 4 This is a high-magnification morphology image of the impact fracture of the steel plate of Example 3 of the present invention.

[0036] Figure 5 These are the cold-bending specimens of the steel plates of Examples 1-3 of the present invention.

[0037] Figure 6 This is the SN fatigue curve of the steel plate welded joint in Example 3 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is described in more detail below with reference to the accompanying drawings using examples. These examples are merely descriptions of the best mode of carrying out the present invention and do not impose any limitation on the scope of the present invention.

[0039] The chemical composition of the steel plate of the present invention is C: 0.10-0.13%, Si: 0.20-0.30%, Mn: 1.50-1.65%, P: ≤0.015%, S: ≤0.005%, Nb: 0.040-0.050%, V: 0.035-0.045%, Ti: 0.012-0.022%, Cr: 0.20-0.30, Als: 0.020-0.035%, CEV≤0.46%, Pcm≤0.23%, and the balance is Fe and unavoidable impurities. In addition, the present invention also provides a method for manufacturing the steel plate. The main steps and process parameters are as follows:

[0040] S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured;

[0041] S2 converter smelting: In the converter smelting stage, molten iron and high-quality scrap steel that have undergone desulfurization pretreatment are used as raw materials. The molten iron temperature is ≥1260℃. The phosphorus and carbon content are reduced through efficient top and bottom blowing technology to ensure that the molten steel P≤0.010% and S≤0.004%.

[0042] S3 LF refining outside the furnace: During the refining stage outside the furnace, the composition of the molten steel is precisely controlled, deoxidation and alloying are carried out, and non-metallic inclusions and harmful impurities in the molten steel are further reduced, S≤0.004%, and clean molten steel is obtained.

[0043] S4 RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas content in molten steel, and reduce the adverse effects of harmful gases on steel quality. The vacuum degree is less than 90Pa, the vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm.

[0044] S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7.5 mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency of 5 Hz, and current of 350 A; water volume on the wide side of the crystallizer is 4500 L / min, water volume on the narrow side is 370 L / min, crystallizer inlet water temperature is 36±2°C, crystallizer inlet water temperature is 38±1°C, secondary cooling water temperature is 22~25°C, and water quality indicators must meet Process requirements: adopt protective pouring, the argon pressure of the long nozzle seal is greater than 0.3MPa, and the flow rate is 130-160L / min; the argon pressure of the tundish immersion nozzle seal is greater than 0.2Mpa, and the flow rate is 15-20L / min; the continuous casting superheat is 20-30℃, and the liquid level of the tundish is not less than 30 tons when changing tundishes; adopt a constant pulling speed, and the pulling speed is stable at 1.0m / min; the straightening temperature of the billet is controlled at 950-1000℃, and the temperature difference of the billet along the width direction shall not exceed 50℃. Finally, a 250mm thick continuous casting billet is produced, the low-multiple center segregation of the billet is controlled below Class C 3.0, and the billet is pile-cooled or pit-cooled for more than 36 hours after it comes off the line.

[0045] S6 Heating: The slab is heated in a walking beam heating furnace, and the atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab, and the heating temperature is 1210℃~1250℃. The total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure that the alloy elements are fully dissolved and the slab temperature is uniform.

[0046] S7 rolling and cooling: rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing stage. Rough rolling is carried out on a 3800mm rough rolling mill, with a start rolling temperature of more than 1170℃, and the relative reduction rate of a single pass is controlled at more than 15% for at least two passes. The torque is set to 2280k N·m during the first stage of rolling. During finishing rolling, the deformation of each pass is strictly controlled, the start rolling temperature of finishing rolling is ≤900℃, and the final rolling temperature is ≤800℃. The torque is set to 2320k N·m during the second stage of rolling. After the steel plate is rolled, laminar cooling is carried out, the water temperature is 17-20℃, the final cooling temperature is 600-630℃, the head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, and the edge is shielded by 0-2.0m. The overall temperature difference after the steel plate returns to red is controlled to be ≤50℃. Samples are taken for inspection after the steel plate stack is slowly cooled for 12 hours.

[0047] The present invention is described in detail below in conjunction with practical embodiments.

[0048] Table 1 lists the chemical composition of the examples, and Table 2 lists the rolling process parameters of the examples.

[0049] Table 1 Chemical composition of the present invention (wt%)

[0050] Example C Si Mn P S Nb V Ti Cr Als 1 0.11 0.24 1.56 0.012 0.003 0.042 0.039 0.013 0.25 0.021 2 0.11 0.24 1.57 0.013 0.002 0.045 0.040 0.015 0.24 0.021 3 0.11 0.26 1.57 0.012 0.004 0.046 0.042 0.015 0.25 0.020 4 0.12 0.25 1.58 0.011 0.002 0.047 0.040 0.013 0.26 0.022 5 0.12 0.27 1.58 0.011 0.002 0.045 0.042 0.016 0.24 0.022 6 0.12 0.25 1.60 0.012 0.003 0.048 0.041 0.013 0.25 0.022

[0051] Table 2 Rolling process parameters of the embodiment of the present invention

[0052]

[0053] The mechanical properties, low temperature impact properties and cold bending properties of the steel plate of the embodiment of the present invention were tested, and the results are shown in Table 3.

[0054] Table 3 Mechanical properties of steel plates according to the present invention

[0055]

[0056]

[0057] The present invention adopts reasonable chemical composition combined with a specific process flow to produce a 14-50mm thick thermomechanical controlled rolled Q500ME wind power steel plate, the steel plate has a yield strength of ≥500MPa, a tensile strength of 610-770MPa, a post-break elongation of ≥17%, and an impact energy of ≥100J at -40°C, and has the characteristics of easy welding, easy bending and forming, and fatigue resistance. It can be used to manufacture high-strength wind power towers.

[0058] According to customer requirements and combined with the actual tower load-bearing method, the fatigue test uses the axial force control method to perform a pull-pull loading method, the stress ratio is set to 0.5, that is, the ratio of the minimum loading stress to the maximum loading stress is 0.5, and the stress cycle uses a sine wave. The fatigue limit is determined by the lifting method, and the cycle base is set to 10 7 The fracture position of the specimens was at the weld toe.

[0059] The SN curve obtained by fitting the test data is:

[0060] lgN=16.4303-4.4177lg(S-157)

[0061] Plotting the test data and the PSN curves corresponding to different survival rates on the same coordinate axis can better show the relationship between them. The higher the survival rate, the lower the fatigue limit stress. Under the set loading method, the ultimate fatigue stress of the Q500ME submerged arc welding joint is about 285MPa; when the survival rate is 97.7%, the ultimate fatigue stress is about 261MPa, that is, under the set loading conditions, 97.7% of the samples will have an ultimate fatigue stress higher than 261MPa.

[0062] The welded joints obtained by gas shielded welding process have tensile strengths of 686MPa and 679MPa, both of which are broken at the base material outside the fusion line. The tensile strength of the entire weld is 701MPa, and the elongation after fracture is 23.0%. The average value of the impact energy of the standard sample at -40℃ in the weld zone (89\102\106) is 99J, and the average value of the impact energy of the standard sample at -40℃ in the heat affected zone (91 / 87 / 100) is 93J, which is much higher than 31J. D=3a180° bending performance is intact. The weld microstructure is proeutectoid ferrite, acicular ferrite and granular bainite, the microstructure of the coarse-grained heat affected zone is bainite, and the microstructure of the fine-grained heat affected zone is ferrite and granular bainite, with fine and uniform grains.

[0063] Vickers hardness tests were carried out on the upper surface, middle and weld toe of the weld joint. The test results are shown in Table 4. The maximum hardness HV10 of the heat affected zone is 273, which is much lower than 350, indicating that the weld joint has a low tendency to cold cracks.

[0064] Table 430mm steel plate welding joint hardness

[0065]

[0066] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind power towers, characterized by: The chemical composition of the steel plate is C: 0.10-0.13%, Si: 0.20-0.30%, Mn: 1.50-1.65%, P: ≤0.015%, S: ≤0.005%, Nb: 0.040-0.050%, V: 0.035-0.045%, Ti: 0.012-0.022%, Cr: 0.20-0.30%, Als: 0.020-0.035%, CEV≤0.46%, Pcm≤0.23%, and the balance is Fe and unavoidable impurities; The main steps and process parameters of the manufacturing method include: S1 Hot metal pretreatment: After the hot metal is desulfurized and dephosphorized by KR stirring method, S≤0.005% and P≤0.015% are ensured; S2 converter smelting: The converter smelting stage uses molten iron and high-quality scrap steel that have been pre-treated with desulfurization as raw materials. The molten iron temperature is ≥1260℃. The phosphorus and carbon content are reduced through efficient top and bottom double blowing technology to ensure that the molten steel P≤0.010%, S≤0.004%; S3LF refining outside the furnace: During the refining stage outside the furnace, the composition of the molten steel is precisely controlled, deoxidation and alloying are carried out, and non-metallic inclusions and harmful impurities in the molten steel are further reduced, S≤0.004%, and clean molten steel is obtained; S4RH vacuum treatment: This treatment mode is used to significantly reduce the hydrogen, oxygen and nitrogen gas content in molten steel, and reduce the adverse effects of harmful gases on steel quality; the vacuum degree is less than 90Pa, the vacuum time is maintained for more than 20 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6ppm, the oxygen content is ≤30ppm, and the nitrogen content is ≤50ppm; S5 slab continuous casting: dynamic light pressure is used during continuous casting, with light pressure positions at 8, 9, and 10, and a total pressure reduction of 7.5 mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at 3-stage outlet and 4-stage inlet, electromagnetic stirring frequency of 5 Hz, and current of 350 A; water volume on the wide side of the crystallizer is 4500 L / min, water volume on the narrow side is 370 L / min, crystallizer inlet water temperature is 36±2°C, crystallizer inlet water temperature is 38±1°C, secondary cooling water temperature is 22~25°C, and water quality indicators must meet process requirements; protective casting is used, and the argon pressure of the long water inlet seal is greater than 0.3M Pa, flow rate 130~160L / min; argon pressure of tundish immersion water inlet sealing is greater than 0.2MPa, flow rate 15~20L / min; continuous casting superheat 20~30℃, tundish liquid level is not less than 30 tons when changing tundish; constant pulling speed is adopted, and the pulling speed is stable at 1.0m / min; the straightening temperature of the billet is controlled at 950~1000℃, and the temperature difference of the billet along the width direction shall not exceed 50℃; finally, 250mm thick continuous casting billet is produced, the low-multiple center segregation of the billet is controlled below Class C 3.0, and the billet is pile-cooled or pit-cooled for more than 36 hours after it comes off the line; S6 Heating: The slab is heated in a walking beam heating furnace, and the atmosphere in the furnace is strictly controlled to ensure the heating temperature and heating time of the slab, the heating temperature is 1210℃~1250℃; the total time in the furnace is greater than 270min, of which the heating section time is greater than 120min and the soaking section time is greater than 30min, to ensure sufficient solid solution of alloy elements and uniform slab temperature; S7 rolling and cooling: rolling adopts two-stage controlled rolling, usually called rough rolling stage and finishing rolling stage. Rough rolling is carried out on a 3800mm rough rolling mill, with a start rolling temperature of more than 1170℃ and a single-pass relative reduction rate controlled at more than 15% for at least two passes. The torque is set to 2280k N·m during the first stage of rolling. The deformation of each pass is strictly controlled during finishing rolling, with a start rolling temperature of ≤900℃ and a final rolling temperature of ≤800℃. The torque is set to 2320k N·m during the second stage of rolling. After the steel plate is rolled, laminar cooling is carried out, with a water temperature of 17-20℃ and a final cooling temperature of 600-630℃. The head is shielded by 0-2.0m, the tail is shielded by 0-2.5m, and the edge is shielded by 0-2.0m. The overall temperature difference after the steel plate returns to red is controlled to be ≤50℃. The steel plate is stacked and slowly cooled for 12 hours before sampling and inspection.

2. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.11%, Si: 0.24%, Mn: 1.56%, P: 0.012%, S: 0.003%, Nb: 0.042%, V: 0.039%, Ti: 0.013%, Cr: 0.25%, Als: 0.021%, and the balance is Fe and unavoidable impurities.

3. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.11%, Si: 0.24%, Mn: 1.57%, P: 0.013%, S: 0.002%, Nb: 0.045%, V: 0.040%, Ti: 0.015%, Cr: 0.24%, Als: 0.021%, and the balance is Fe and unavoidable impurities.

4. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.11%, Si: 0.26%, Mn: 1.57%, P: 0.012%, S: 0.004%, Nb: 0.046%, V: 0.042%, Ti: 0.015%, Cr: 0.25%, Als: 0.020%, and the balance is Fe and unavoidable impurities.

5. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.12%, Si: 0.25%, Mn: 1.58%, P: 0.011%, S: 0.002%, Nb: 0.047%, V: 0.040%, Ti: 0.013%, Cr: 0.26%, Als: 0.022%, and the balance is Fe and unavoidable impurities.

6. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.12%, Si: 0.27%, Mn: 1.58%, P: 0.011%, S: 0.002%, Nb: 0.045%, V: 0.042%, Ti: 0.016%, Cr: 0.24%, Als: 0.022%, and the balance is Fe and unavoidable impurities.

7. The Q500ME high-strength, high-toughness, easy-to-weld, fatigue-resistant steel plate for wind turbine tower according to claim 1 is characterized by: The chemical composition of the steel plate is C: 0.12%, Si: 0.25%, Mn: 1.60%, P: 0.012%, S: 0.003%, Nb: 0.048%, V: 0.041%, Ti: 0.013%, Cr: 0.25%, Als: 0.022%, and the balance is Fe and unavoidable impurities.

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