Wind power structure steel with excellent welded joint fatigue performance and manufacturing method thereof

Abstract

The invention discloses steel with excellent welded joint fatigue performance for a wind power structure and a manufacturing method of the steel. The steel comprises the following components in percentage by weight: 0.05-0.12% of C, 0.10-0.60% of Si, 1.6-2.2% of Mn, less than or equal to 0.010% of P, less than or equal to 0.0020% of S, 0.10-0.60% of Cr, 0-0.8% of Ni, less than or equal to 0.40% of Mo, less than or equal to 0.5% of Cu, 0.01-0.06% of Al, 0.04-0.08% of Nb, 0.005-0.03% of Ti, 0.0005-0.0030% of Mg, 0.0015-0.0040% of N and the balance of Fe and inevitable impurities. Ni is larger than or equal to 0.006 t%, t is the thickness of the steel plate, and the unit is mm; and 6.0 < = alpha < = 11. The steel plate not only has excellent toughness performance, but also has good fracture performance and welding joint fatigue performance, the yield strength of the steel plate is larger than or equal to 520 MPa, the tensile strength ranges from 610 MPa to 770 MPa, the ductility is larger than or equal to 20%, the impact energy at the temperature of-60 DEG C is larger than or equal to 280 J, the CTOD at the temperature of-60 DEG C is larger than or equal to 1.2 mm, the NDTT is smaller than or equal to-60 DEG C, and the fatigue limit mean value of a sample welding joint with surplus height is larger than or equal to 203 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-alloy high-strength steels, and particularly relates to a steel for wind power structures with excellent fatigue performance of welded joints and a manufacturing method thereof. Background Art

[0002] With the international community's attention to issues such as energy security and carbon neutrality, vigorously developing green and renewable energy has become the consensus of all countries. Wind energy is a renewable clean energy. As one of the most widely applied and fastest-developing new energy power generation technologies, wind power has achieved unprecedented development and wide attention worldwide, and it is the new energy power generation technology with the largest increase in installed capacity. The proportion of wind power generation in many countries in the world is already very high. For example, the proportion of wind power generation in Denmark reaches 48%, and those in the UK and Germany both exceed 20%.

[0003] Currently, wind turbines are developing towards large-scale and large-capacity, which puts forward requirements for large thickness and high strength of the steel used for wind power support structures. At the same time, due to the special high-rise structure design of wind power towers, higher requirements are put forward for the fatigue performance of steel plates and welded joints while the strength is improved.

[0004] Chinese Patent CN114277315A discloses "a super-thick building steel plate with a yield strength of 460 MPa and a low yield ratio and a manufacturing method thereof". The chemical composition of the steel plate in this patent is by weight percentage: C: 0.13 - 0.17%, Si: 0.35 - 0.45%, Mn: 1.45 - 1.60%, Nb: 0.025 - 0.040%, Al: 0.025 - 0.045%, Ti: 0.01 - 0.02%, Ni: 0.30 - 0.50%, Cr: 0.10 - 0.20%, V: 0.05 - 0.07%, Cu ≤ 0.10%, N ≤ 0.01%, Mo ≤ 0.001%, P ≤ 0.012%, S ≤ 0.005%, and the rest is iron Fe and unavoidable impurities. A steel plate for wind power with a thickness greater than 90 mm is obtained, with a yield strength ≥ 400 MPa, a tensile strength ≥ 520 MPa, a fatigue resistance strength ≥ 400 MPa, and an impact energy at -40°C at the slab core ≥ 100 J. However, it uses a normalizing process, with relatively high energy consumption. Secondly, the strength level of the steel plate is relatively low and cannot meet the development trend of large-scale wind turbines.

[0005] Chinese Patent CN113969372A discloses "A Low-carbon Fatigue-resistant Steel Plate for Wind Power and Its Preparation Method". The chemical composition of the steel for construction described in this patent is as follows by weight percentage: C: 0.08 - 0.12%, Si: 0.25 - 0.35%, Mn: 1.45 - 1.60%, Nb: 0.02 - 0.03%, Al: 0.03 - 0.05%, Ti: 0.01 - 0.02%, Ni: 0.10 - 0.20%, V: 0.02 - 0.03%, Cr ≤ 0.10%, N ≤ 0.008%, P ≤ 0.012%, S ≤ 0.005%, O ≤ 0.002%, and the rest is iron and inevitable impurities. By reducing the carbon content and the content of precious metal elements such as Cr, and combining with the TMCP process and temper heat treatment process, the yield strength and fatigue strength of the steel are improved. However, it requires a tempering process, has a relatively high energy consumption, and the steel plate also does not meet the welding fatigue performance.

[0006] Chinese Patent CN116254468A discloses "A 420MPa-grade High-toughness Steel Plate for Wind Power and Its Preparation Method". The weight percentage of the chemical composition of the steel plate is: C: 0.02 - 0.04%, Si: 0.15 - 0.25%, Mn: 1.00 - 1.20%, Mo: 0.15 - 0.25%, Cr: 0.10 - 0.30%, Nb: 0.04 - 0.06%, Ni: 0.20 - 0.40%, Ti: 0.01 - 0.02%, Alt: 0.02 - 0.04%; N ≤ 0.005%, P ≤ 0.01%, S ≤ 0.006%, and the rest is Fe and inevitable impurities. It adopts a composition design of ultra-low carbon, low manganese, niobium microalloying, and nickel-molybdenum-copper alloying to obtain a wind power steel with a yield strength of 430MPa grade. However, its carbon content is relatively low, production is not easy to control, and it is prone to softening during welding, and it cannot well meet the usage requirements of thick wind power steel plates.

[0007] Chinese Patent CN103741024A discloses "Low-cost High-performance Steel Plate for Wind Power and Its Production Method". The weight percentage of the chemical composition of the steel plate is: C: 0.06 - 0.10%, Si: 0.20 - 0.35%, Mn: 1.27 - 1.40%, P ≤ 0.015%, S ≤ 0.005%, Nb: 0.015% - 0.030%, Als: 0.020 - 0.040%, and the rest is Fe and inevitable impurities. Adopting a low-carbon and low-manganese composition system, the fatigue performance of the invented steel plate is above 300MPa. CEV is controlled below 0.32%, and the steel plate has good welding performance. However, the strength level of the steel plate base material is relatively low, and it does not have good welding joint fatigue performance, and it cannot well meet the future development of the wind power industry.

[0008] At present, the fatigue performance of welded joints is not considered in the design and development of wind power steel, which restricts the development of large-scale wind power. Summary of the Invention

[0009] The object of the present invention is to provide a steel for wind power structures with excellent fatigue performance of welded joints and a manufacturing method thereof. This steel plate not only has excellent strength and toughness properties, but also has good fracture properties and fatigue performance of welded joints. Its yield strength is ≥520 MPa, the tensile strength is 610 - 770 MPa, the elongation is ≥20%, the impact energy at -60°C is ≥280 J, the CTOD at -60°C is ≥1.2 mm, NDTT ≤ -60°C, and the average fatigue limit of the welded joint with reinforcement specimen is ≥203 MPa. It is particularly suitable for the construction of onshore towers, offshore pile foundations and towers, meets the development trend of large-scale wind power, improves the safe operation of wind turbines, and can also be used for the construction of steel structures such as ocean engineering, bridges, ships, and buildings.

[0010] To achieve the above object, the technical solution of the present invention is:

[0011] A steel for wind power structures with excellent fatigue performance of welded joints, the chemical composition of which is in weight percentage: C: 0.05 - 0.12%, Si: 0.10 - 0.60%, Mn: 1.6 - 2.2%, P ≤ 0.010%, S ≤ 0.0020%, Cr: 0.10 - 0.60%, Ni: 0 - 0.8%, Mo ≤ 0.40%, Cu ≤ 0.5%, Al: 0.01 - 0.06%, Nb: 0.04 - 0.08%, Ti: 0.005 - 0.03%, Mg: 0.0005 - 0.0030%, N: 0.0015 - 0.0040%, and the balance includes Fe and other inevitable impurities; and it needs to satisfy simultaneously:

[0012] Ni ≥ 0.006t%, where t is the thickness of the steel plate, unit: mm;

[0013] 6.0 ≤ α ≤ 11,

[0014] Further, the balance is Fe and other inevitable impurities.

[0015] The microstructure of the steel for wind power structures of the present invention is quasi-polygonal ferrite and bainite, and the proportion of quasi-polygonal ferrite is 8 - 15%.

[0016] The yield strength of the steel for wind power structures of the present invention is ≥520 MPa, the tensile strength is 610 - 770 MPa, the elongation is ≥20%, the impact energy at -60°C is ≥280 J, the CTOD at -60°C is ≥1.2 mm, NDTT ≤ -60°C, and the average fatigue limit of the welded joint with reinforcement specimen is ≥203 MPa.

[0017] In the composition design of the steel for wind power structures according to the present invention:

[0018] C: The present invention adopts an ultra-low carbon design. On the one hand, by utilizing the interstitial strengthening and precipitation strengthening effects of carbon, the steel plate of the invention is ensured to have appropriate strength; on the other hand, excessive carbon content is prevented from reducing the low-temperature toughness and welding performance of the steel plate. Therefore, the C content in the present invention is controlled at 0.05 - 0.12%.

[0019] Si: Si is a common weak deoxidizing element in steelmaking and has a certain solution strengthening effect. However, when Si exceeds 0.6%, it intensifies the decarburization on the steel plate surface and reduces the plasticity and toughness of the steel. Therefore, the Si content in the present invention is controlled at 0.10 - 0.60%.

[0020] Mn: It is the most basic alloying element in low-alloy high-strength steel grades. It improves the strength of the steel through solution strengthening to compensate for the strength loss caused by the reduction of C content in the steel. However, too high Mn content is prone to cause segregation at the center position of the steel plate and reduce the low-temperature toughness. Therefore, the Mn content in the present invention is 1.6 - 2.2%.

[0021] P: It is an inevitable harmful impurity element in steel. Phosphorus is unevenly distributed in the steel and concentrated at the grain boundaries, affecting the grain boundary structure and being prone to cold brittleness at low temperatures. Therefore, the present invention controls P ≤ 0.010%.

[0022] S: It is an inevitable harmful impurity element in steel, which is prone to form defects such as segregation and inclusions, deteriorating the welding performance, impact toughness and fatigue performance of the steel plate. Therefore, the present invention controls S ≤ 0.0020%, and through inclusion modification technology, the inclusion morphology is spheroidized, the size is refined and the distribution is uniform to reduce its influence on toughness and corrosion resistance.

[0023] Cr: It can improve the corrosion resistance of the steel, but Cr is a precious metal element. Considering the cost, the Cr content in the present invention is controlled at 0.10 - 0.60%.

[0024] Ni: It can improve the low-temperature toughness of the steel plate. At the same time, it also has a great effect on improving the corrosion resistance of the steel in the marine environment, inhibiting the reverse effect of corrosion and the pitting corrosion tendency. However, when the Ni content is too high, it is easy to generate scale with high viscosity on the surface of the slab, which is difficult to remove, affecting the surface quality and fatigue performance of the steel plate, and the cost is relatively high. Therefore, the present invention controls the Ni content at 0 - 0.8%.

[0025] Mo: It can improve the hardenability of the steel and enhance the uniformity of properties in the thickness direction. However, too much Mo will increase the cold cracking tendency of the steel plate and also increase the cost. Therefore, the Mo content in the present invention is controlled ≤ 0.40%.

[0026] Copper Cu: Appropriately increasing the hardenability of steel can improve the steel's resistance to atmospheric corrosion. However, excessive Cu will deteriorate the steel's weldability. Therefore, in the present invention, the Cu content is controlled to be ≤0.50%.

[0027] Al: It is an element added to the steel for deoxidation. After complete deoxidation, it reduces the oxygen content in the material and improves the aging performance. In addition, an appropriate amount of Al is beneficial to refining the grains and improving the strength and toughness of the steel. Therefore, in the present invention, the Al content is controlled within 0.01 - 0.06%.

[0028] Nb: Nb is a strong carbide and nitride forming element with a strong grain refinement effect. In the present invention, an appropriate amount of Nb is added to obtain a uniform grain size, prevent excessive growth of some grains during the heating process, form mixed crystal structures, and deteriorate the strength, toughness, and corrosion resistance. Therefore, in the present invention, the Nb content is controlled at 0.04 - 0.08%.

[0029] Ti: It is a strong nitrogen-fixing element that inhibits the adverse effects of excessive N content on the steel's properties. At the same time, the formation of TiN precipitation phases can inhibit excessive grain growth in the slab and steel plate during the heating process. Therefore, in the present invention, the Ti content is controlled within 0.005 - 0.03%.

[0030] Mg: It can improve the morphology of sulfides, refine inclusions, and enhance the corrosion resistance of the steel plate. If the Mg content is too low, it cannot play the role of inclusion modification, and if it is too high, it is easy to form excessive MgO and MgS, blocking the nozzle. Therefore, in the present invention, the Mg content is controlled at 0.0005 - 0.0030%.

[0031] N: It is an impurity element in the steel grade, but it can form nitrides or carbonitrides with Ti, Al, Nb, etc., refine the grains, and improve the strength of the steel. However, excessive nitrogen will deteriorate the impact toughness and surface quality of the steel. Therefore, in the present invention, the N content is controlled at 0.0015 - 0.0040%.

[0032] In addition, the chemical composition should meet the following requirements: Ni ≥ 0.006t% (t is the thickness of the steel plate, unit: mm). To ensure the balance of alloy element content and obtain good strength, toughness, and fatigue performance of the welded joint. Controlling the Ni content can improve the low-temperature impact toughness of the steel plate, especially for thick steel plates. Controlling the α value can make full use of the precipitation strengthening effect of Al, Ti, and Nb to enhance the strength of the steel plate. However, too high an α value has limited improvement in strength but will significantly increase the cost of the steel plate.

[0033] The present invention also provides a manufacturing method for the wind power structure steel with excellent welded joint fatigue performance, including the following steps:

[0034] 1) Smelting and continuous casting

[0035] Smelt according to the above components and cast into billets;

[0036] 2) Reheat

[0037] Slab heating temperature Unit: °C;

[0038] 3) Controlled rolling

[0039] Adopt two-stage controlled rolling. The starting rolling temperature T in the first stage sr ≤0.95T rt , unit: °C; The finishing rolling temperature T fr1 ≥θ + 50 °C, θ = 887 + 464*C + 712*Ti + 290*Al - 286*Si + 5156*Nb - 644*SQRT(Nb*0.80), unit: °C;

[0040] The starting rolling temperature T in the second stage sr2 ≤θ - 50 °C; The finishing rolling temperature T fr2 ≥β + 10 °C, β = 910 - 310*(C + (Mn + Mo) / 3.875 + Cu / 15.5 + Cr / 20.67 + Ni / 5.636) + 8.89*(t / 25.4 - 0.315), unit: °C; t is the thickness of the steel plate, unit: mm;

[0041] 4) Controlled cooling

[0042] The starting cooling temperature ≥β, the cooling rate is 3 - 15 °C / s, the surface temperature of the steel plate after cooling is 350 - 400 °C, and the surface temperature after the steel plate is fully reheated is 400 - 450 °C.

[0043] Furthermore, in step 1), hot metal pretreatment, smelting, LF refining, RH refining, inclusion beneficial treatment and continuous casting are carried out in sequence. Among them, in the inclusion beneficial treatment stage, a composite inclusion with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S is formed. The size of the composite inclusion is 0.2 - 2.0 μm, and the number of composite inclusions in this size range accounts for more than 95% of the total number of inclusions. The number of inclusions with a size of 2 - 5 μm is not more than 5%; the proportion of inclusions with an aspect ratio ≤2 is greater than 85%, and the proportion of inclusions with an aspect ratio of 2 - 3 is less than 15%.

[0044] Even further, in step 1), in the hot metal pretreatment desulfurization stage, ensure that the sulfur content in the hot metal ≤0.0035%; in the LF refining stage, control the sum of the mass percentages of FeO and MnO in the slag <1%, and control the basicity R of the slag >9, R = (CaO + MgO + MnO) / (SiO 2 +P 2 O 5), and the mass percentage content of each substance in the formula is substituted; during the RH refining stage, vacuum treatment is carried out, and the vacuum treatment time is ≥ 22 min; during the inclusion beneficial treatment stage, Mg wire is added in the form of cored wire, and the wire feeding speed is 200 - 300 m / min.

[0045] Preferably, in step 3), in the first stage, the reduction rate per single pass is ≥ 7%, the reduction rate of the last two passes is ≥ 12%, and the cumulative reduction amount is ≥ 60%.

[0046] Preferably, in step 3), in the second stage, the reduction rate of the first two passes is ≥ 15%, the reduction rate of the remaining passes is 8 - 10%, and the cumulative reduction amount is ≥ 50%.

[0047] In the manufacturing method of the present invention:

[0048] During tapping from the converter with slag blocking, the oxidability of the slag in the ladle is reduced, preventing the increase of oxygen activity, reverse phosphorus of molten steel, and facilitating subsequent white slag making and inclusion modification treatment.

[0049] In LF, a reducing slag is made, and the basicity R of the slag > 9, R = (CaO + MgO + MnO) / (SiO 2 +P 2 O 5 ), and the setting of the basicity R ensures that the slag has good dephosphorization and desulfurization capabilities.

[0050] For the inclusion modification treatment setting, the Mg content is controlled according to the above target, and the setting of the wire feeding speed ensures 75% of the depth of the wire inserted into the molten steel for full reaction. Finally, mainly composite inclusions with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S are formed, so that the inclusion size is between 0.2 - 2 um, and the number of inclusions in this size range > 95%. The number of inclusions with a size of 2 - 5 um is not more than 5%. The aspect ratio of inclusions ≤ 2 accounts for more than 85%, and the aspect ratio of inclusions of 2 - 3 accounts for less than 15%. To ensure that the steel plate has good fatigue performance.

[0051] The slab heating temperature Trt is not lower than and not higher than 1250 °C.

[0052] The setting of the slab reheating temperature is to ensure the full solution of microalloyed carbonitrides and promote the homogenization of alloying elements, reducing macro and micro segregation in the steel.

[0053] The starting rolling temperature in the first stage is not higher than 0.95T rt, this is mainly to ensure that the steel plate is rolled at a relatively high temperature in the recrystallization zone to fully recrystallize and form uniform equiaxed austenite grains. The finishing temperature of the first stage is not lower than θ + 50 °C to ensure that the steel plate is rolled above the non-static recrystallization temperature, prevent mixed grains and non-uniform grains; secondly, ensure that there is enough temperature drop space during the rolling process.

[0054] The reduction rate per pass in the first stage is not lower than 7%, the reduction rate of the last two passes is greater than 12%, and the total reduction rate is greater than 60%. This is mainly to ensure that the steel plate has enough recrystallization driving force in each pass, and at the same time has enough rolling passes to homogenize the grains of the steel plate, meeting the requirement of the original austenite grain size of 25 - 30 μm after rolling.

[0055] The starting rolling temperature of the second stage is not higher than θ - 50 °C. This is mainly to fully elongate the austenite grains and transform them into fine quasi-polygonal ferrite structure during subsequent cooling.

[0056] The finishing temperature of the second stage is not lower than β + 10 °C to prevent the steel plate from being rolled in the two-phase region and reduce the impact toughness.

[0057] The reduction rate of the first two passes in the second stage is greater than 15%, the reduction rate of the remaining rolling passes is controlled at 8 - 10%, and the total reduction rate is greater than 50%. This is mainly to make the deformation fully penetrate into the core. At the same time, elongate the original austenite grains and form fine quasi-polygonal ferrite grains during subsequent cooling. Ensure the strength and toughness properties and fracture arrest properties of the core.

[0058] The starting cooling temperature is not lower than β to avoid the ferrite phase transformation before the steel plate is cooled and reduce the strength.

[0059] The cooling rate is 3 - 15 °C / s, the surface temperature after cooling is 350 - 400 °C. After the steel plate finishes cooling, the surface temperature is relatively low and the core temperature is relatively high. Subsequently, the surface will have a temperature rise. After the temperature rise, the surface temperature of the steel plate is 400 - 450 °C. This is to ensure that the steel plate forms quasi-polygonal ferrite and bainite structures, and the proportion of quasi-polygonal ferrite is 8 - 15%. The steel plate has good strength and toughness property matching.

[0060] Compared with the prior art, the present invention has the following advantages:

[0061] Currently, most wind power steels adopt high-carbon and low-manganese designs, with insufficient utilization of microalloying elements, resulting in relatively low strength of the steel plate, poor toughness and weldability.

[0062] In the composition design of the present invention, a composition system design of low C, medium Mn, Nb, Ti microalloying and Cr-Ni-Mo-Cu alloying is adopted, fully utilizing the fine grain and dislocation strengthening effects of Mn-Nb. At the same time, control Ni ≥ 0.006t%, where t is the thickness of the steel plate, unit: mm; 6.0 ≤ α ≤ 11, Make full use of the precipitation strengthening effects of Al, Ti, Nb, and V to enhance the strength of the steel plate and obtain good strength and toughness properties and welded joint fatigue properties under a low-cost system.

[0063] Based on the composition design, the present invention adopts technologies such as pure steel smelting and beneficial inclusion control, high-performance large reduction rolling manufacturing process design, steel quality homogenization, grain size control, and microstructure regulation technologies, and can produce steel plates with a yield strength greater than 520 MPa, a tensile strength of 610 - 770 MPa, good low-temperature impact toughness, and good welded joint fatigue properties. The production process is simple and the production efficiency is high.

[0064] The yield strength of the steel for wind power structures described in the present invention is ≥520 MPa, the tensile strength is 610 - 770 MPa, the elongation is ≥20%, the impact energy at -60°C is ≥280 J, the CTOD at -60°C is ≥1.2 mm, the NDTT ≤ -60°C, and the average fatigue limit of the welded joint of the specimen with reinforcement is ≥203 MPa; it is particularly suitable for the construction of onshore tower barrels, offshore pile foundations, and tower barrels, meets the development trend of large-scale wind power, improves the safe operation of wind turbines, and can also be used for the construction of steel structures such as ocean engineering, bridges, ships, and buildings. Specific Embodiments

[0065] The following further illustrates the present invention in conjunction with embodiments.

[0066] The chemical composition of the steel in the embodiments of the present invention is shown in Table 1, and the balance includes Fe and inevitable impurities; the specific process parameters of the embodiments of the present invention are shown in Table 2.

[0067] Tensile tests and Charpy V-notch impact tests were carried out on the finished steel plates obtained in the present invention. The performance results of the steel plates in the embodiments and comparative examples of the present invention are shown in Table 3.

[0068] The comparative example is the commonly used steel for wind power tower barrels at present.

[0069] The present invention adopts a unique chemical composition and process design. The manufactured steel plates have excellent strength and toughness properties, a low yield ratio, and an obvious yield plateau, and can produce steel plates for building structures with a thickness specification of ≤120 mm. The thick steel plates produced by the present invention can be used for key components of wind power structures, meet the current development needs of steel for wind power structures in China, and have broad application prospects.

[0070]

[0071]

[0072]

Claims

1. A steel for wind power structures with excellent fatigue performance of welded joints, the chemical composition of which is in weight percentage: C: 0.05 - 0.12%, Si: 0.10 - 0.60%, Mn: 1.6 - 2.2%, P ≤ 0.010%, S ≤ 0.0020%, Cr: 0.10 - 0.60%, Ni: 0 - 0.8%, Mo ≤ 0.40%, Cu ≤ 0.5%, Al: 0.01 - 0.06%, Nb: 0.04 - 0.08%, Ti: 0.005 - 0.03%, Mg: 0.0005 - 0.0030%, N: 0.0015 - 0.0040%, and the balance includes Fe and other inevitable impurities; and it needs to satisfy simultaneously: Ni ≥ 0.006t%, where t is the thickness of the steel plate, unit: mm; 6.0≤α≤11， 2. The steel for wind power structures with excellent fatigue performance of welded joints as described in claim 1, characterized in that, the balance is Fe and other inevitable impurities.

3. The steel for wind power structures with excellent fatigue performance of welded joints as described in claim 1 or 2, characterized in that, the microstructure of the steel is quasi-polygonal ferrite and bainite, and the proportion of quasi-polygonal ferrite is 8 - 15%.

4. The steel for wind power structures with excellent fatigue performance of welded joints as described in claim 1 or 2 or 3, characterized in that, the yield strength of the steel ≥ 520 MPa, the tensile strength is 610 - 770 MPa, the elongation ≥ 20%, the impact energy at -60°C ≥ 280 J, the CTOD at -60°C ≥ 1.2 mm, NDTT ≤ -60°C, and the average fatigue limit of the welded joint with a specimen with reinforcement ≥ 203 MPa.

5. The manufacturing method of the steel for wind power structures with excellent fatigue performance of welded joints as described in any one of claims 1 - 5, characterized in that, it includes the following steps: 1) Smelting and continuous casting Smelt according to the composition described in claim 1 or 2, and cast into slabs; 2) Reheating Slab heating temperature Unit: °C; 3) Controlled rolling Adopt two-stage controlled rolling. The starting rolling temperature is T sr1 ≤0.95T rt , in °C; the finishing rolling temperature is T fr1 ≥θ + 50°C, where θ = 887 + 464*C + 712*Ti + 290*Al - 286*Si + 5156*Nb - 644*SQRT(Nb*0.80), in °C; The starting rolling temperature T in the second stage sr2 ≤θ - 50°C; the finishing rolling temperature T fr2 ≥β + 10°C, where β = 910 - 310*(C + (Mn + Mo) / 3.875 + Cu / 15.5 + Cr / 20.67 + Ni / 5.636) + 8.89*(t / 25.4 - 0.315), in °C; t is the thickness of the steel plate, in mm; 4) Controlled cooling The starting cooling temperature ≥ β, the cooling rate is 3 - 15°C / s, the surface temperature of the steel plate after cooling is 350 - 400°C, and the surface temperature is 400 - 450°C after the steel plate is fully reheated.

6. The manufacturing method as described in claim 5, characterized in that, In step 1), hot metal pretreatment, smelting, LF refining, RH refining, inclusion beneficial treatment, and continuous casting are carried out in sequence. Among them, in the inclusion beneficial treatment stage, a composite inclusion with MgO + Al 2 O 3 as the core and coated with (Ca, Mn)S is formed. The size of the composite inclusion is 0.2 - 2.0 um, and the number of composite inclusions in this size range accounts for more than 95% of the total number of inclusions. The number of inclusions with a size of 2 - 5 um is not more than 5%. The proportion of inclusions with an aspect ratio ≤ 2 is greater than 85%, and the proportion of inclusions with an aspect ratio of 2 - 3 is less than 15%.

7. The manufacturing method as described in claim 6, characterized in that, in step 1), during the desulfurization stage of hot metal pretreatment, ensure that the sulfur content of hot metal ≤ 0.0035%; In the LF refining stage, control the sum of the mass percentages of FeO and MnO in the slag to be < 1%, and control the basicity R of the slag to be > 9, where R = (CaO + MgO + MnO) / (SiO 2 +P 2 O 5 ), and substitute the mass percentages of each substance in the formula; carry out vacuum treatment during the RH refining stage, the vacuum treatment time ≥ 22 min; during the inclusion beneficial treatment stage, add Mg wire in the form of cored wire, and the wire feeding speed is 200 - 300 m / min.

8. The manufacturing method as described in claim 5, characterized in that, in step 3), in the first stage, the single-pass reduction rate ≥ 7%, the reduction rate of the last two passes ≥ 12%, and the cumulative reduction ≥ 60%.

9. The manufacturing method as described in claim 5, characterized in that, in step 3), in the second stage, the reduction rate of the first two passes ≥ 15%, the reduction rate of the remaining passes is 8 - 10%, and the cumulative reduction ≥ 50%.

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