Cast iron material suitable for large-size thin-wall high-strength wind power hub as well as preparation method and application of cast iron material

Abstract

The invention discloses a cast iron material suitable for a large-size thin-wall high-strength wind power hub and a preparation method and application of the cast iron material, and belongs to the technical field of materials and casting technologys.By optimizing alloy component design and combining the synergistic effect of trace rare metal elements of barium (Ba), antimony (Sb) and bismuth (Bi) and rare earth elements (RE), the high-strength wind power hub is obtained; and by adding a three-phase SiC / SiO2 / TiC nano-particle reinforced phase, pearlite formation is inhibited, graphite nodules are refined, the spheroidization rate is larger than or equal to 95%, and the ferrite content is larger than or equal to 90%. And by adding a nano-particle reinforced phase and controlling the proportion of alloy elements such as Ni < = 0.8%, the corrosion resistance of the material is further improved. The ductile cast iron material with high spheroidization rate, excellent mechanical property, low-temperature impact resistance and corrosion resistance is prepared by using the low-temperature-resistant and high-strength casting process and the intelligent temperature-controlled and cold-controlled casting process, and the requirements of light weight, high strength, corrosion resistance and high reliability of 18MW-grade offshore wind power hubs are met.

Description

Technical Field

[0001] The present invention relates to a cast iron material suitable for large-sized thin-walled high-strength wind power hubs, its preparation method and application, belonging to the technical field of materials and casting processes, and specifically relates to a cast iron material suitable for large-sized, high-strength wind power hubs with a sphere diameter of more than 6 m and a wall thickness range of 30-450 mm, and its preparation method. Background Art

[0002] As a key component of a wind turbine generator set, the offshore wind power hub needs to withstand complex alternating loads and harsh environmental conditions. Therefore, extremely high requirements are imposed on the strength, toughness, corrosion resistance and dimensional stability of the material. Traditional ductile cast iron has insufficient corrosion resistance and low-temperature toughness and is difficult to adapt to complex environments. At present, although traditional ductile cast iron has good toughness, its strength and low-temperature resistance cannot meet the requirements, and problems such as spheroidization recession and graphite floating are likely to occur in thick and large-section castings.

[0003] Chinese Patent with Application No. CN 102851609 B discloses a manufacturing process for materials and workpieces used in offshore wind power equipment. The chemical composition of the material is 0.08 wt% - 0.16 wt% carbon, 0.20 wt% - 0.60 wt% silicon, 0.30 wt% - 0.70 wt% manganese, phosphorus ≤ 0.02 wt%, sulfur ≤ 0.015 wt%, 0.80 wt% - 1.30 wt% chromium, 0.90 wt% - 1.20 wt% nickel, 0.50 wt% - 0.80 wt% molybdenum, 0.06 wt% - 0.12 wt% vanadium, 0.50 wt% - 0.80 wt% copper, and 0.02% - 0.07 wt% rare earth, with the balance being iron and inevitable impurities. Chinese Patent with Application No. CN 115213360 B discloses a preparation method for ductile cast iron used in wind turbine hubs. The chemical composition of the ductile cast iron material is 3.80 - 3.95 wt% C, 1.19 - 1.39 wt% Si, Mn ≤ 0.20 wt%, P ≤ 0.050 wt%, S ≤ 0.015 wt%, 0.030 - 0.045 wt% Mg, Re ≤ 0.019 wt%, Sb ≤ 0.005 wt%, 0.20 - 0.40 wt% Cu, 0.10 - 0.60 wt% Ni, 0.020 - 0.080 wt% Sn, with the balance being Fe. The tensile strength of the ductile cast iron is ≥ 360 MPa, the yield strength is ≥ 223 MPa, and the elongation at break is ≥ 21.7%. The preparation method improves the traditional one-package molten iron casting to 3 - 5 packages of different molten iron castings.

[0004] In the prior art, although adding alloying elements (such as Cu, Cr, Mo) can improve strength, it may sacrifice toughness or increase cost. At the same time, it will form carbides or promote the formation of pearlite, deteriorating the low-temperature brittleness of the material. Conventional casting processes have insufficient control over the temperature field, resulting in difficult feeding during solidification and low density of castings. Therefore, there is an urgent need for a cast iron material suitable for large-size thin-walled high-strength wind power hubs, as well as its preparation method and application. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cast iron material suitable for large-size thin-walled high-strength wind power hubs.

[0006] At the same time, the present invention provides a preparation method for a cast iron material suitable for large-size thin-walled high-strength wind power hubs. By optimizing the alloy composition design, combining the synergistic effects of trace rare metal elements barium (Ba), antimony (Sb), bismuth (Bi), and rare earth elements (RE), and by adding a three-phase SiC / SiO 2 / TiC nanoparticle reinforcement phase to inhibit the formation of pearlite and refine graphite balls, with a spheroidization rate ≥ 95% and a ferrite content ≥ 90%. By adding a nanoparticle reinforcement phase and controlling the proportion of alloying elements such as Ni ≤ 0.8%, the corrosion resistance of the material is further improved. And through an intelligent temperature control and cooling casting process, a ductile iron material with high spheroidization rate, excellent mechanical properties, low-temperature impact resistance, and corrosion resistance is prepared, meeting the requirements of 18 MW-class offshore wind power hub for lightweight, high strength, corrosion resistance, and high reliability.

[0007] At the same time, the present invention provides an application of a cast iron material suitable for large-size thin-walled high-strength wind power hubs.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A cast iron material suitable for large-size thin-walled high-strength wind power hubs, its chemical composition by mass percentage is: C: 3.55% - 3.85%, Si: ≤ 2.3%, Ni: ≤ 0.8%, Mn: ≤ 0.15%, Mg: ≤ 0.06%, Nb: ≤ 0.06%, V: ≤ 0.02%, P: ≤ 0.015%, S: ≤ 0.015%, rare element barium (Ba): 0.0050% - 0.0150%, rare element antimony (Sb): 0.0020% - 0.0050%, rare element bismuth (Bi): 0.0010% - 0.0020%, rare earth elements (Y / La / Ce / Sc / Nd): 0.010% - 0.025%, and the rest is Fe and unavoidable impurities.

[0010] The rare earth elements include any one or two of Y and La, and the rare earth elements also include any one or several of Ce, Sc, and Nd.

[0011] A preparation method of a cast iron material suitable for large-sized thin-walled high-strength wind power hubs, comprising the following steps:

[0012] (1) Raw material preparation: Prepare raw materials such as pig iron (the balance), high-quality scrap steel (10-20%), ferrosilicon (0.5%-1.5%), ferrovanadium (0.2%-0.4%), ferromanganese (0.1%-0.2%), ferrocolumbium (0.1%-0.2%), nickel plate (0.2%-0.8%), nano-particle reinforcing phase (2%-4%) etc. according to the proportion. Select low-sulfur and low-phosphorus pig iron (S≤0.02%, P≤0.035%), and high-quality scrap steel (removing the coating and alloy pollution). Allocate alloys and particles such as ferrosilicon (FeSi75), ferrovanadium, ferrocolumbium (FeNb60), ferromanganese (FeMn), pure nickel plate etc. according to the proportion.

[0013] (2) Melting: Add the raw materials into an intermediate frequency induction furnace for melting, control the melting temperature at 1450°C - 1550°C, and introduce argon for protection.

[0014] (3) Spheroidizing and in-furnace inoculation treatment: After the raw materials are completely melted, add rare earth magnesium alloy for spheroidizing treatment. Place a rare earth magnesium alloy spheroidizing agent with a particle size of 6-32 mm (Si 40-45%, Mg 5.5-6.5%, Ca 1.5-2.5%, Ba 1.5-2.5%, RE 0.2-2.0%, the rest is Fe) at the bottom of the ladle, and the addition amount of the spheroidizing agent accounts for 1.0-1.8% of the total molten iron mass. Cover the surface of the spheroidizing agent with a barium ferrosilicon inoculant with a particle size of 2-8 mm (Si 65-70%, Ba 2-3%, Bi 0.1-0.2%, the rest is Fe), and the addition amount accounts for 0.2-0.4% of the total molten iron mass. The spheroidizing reaction lasts for more than 2 minutes after the molten iron is poured in, and the molten iron treatment temperature is 1365-1375°C.

[0015] Ca easily reacts with S and O, so its content is very low or not visible.

[0016] (4) Microalloying: After spheroidizing and inoculation treatment, add Sb (using calcium silicide alloy as the carrier, where Si 40-65%, Ca 15-35%, Sb 0.5-1%, the balance is iron), and the addition amount is 0.5%-1.5%, stir for 5-8 minutes until the composition is uniform to increase the number of graphite balls and improve the low-temperature impact toughness of ductile iron.

[0017] (5) Pouring and instantaneous inoculation treatment: Pouring is completed within 20 minutes after spheroidizing, inoculating, and microalloying. The molten metal is poured into a resin sand mold preheated to 50 - 300 °C. During the pouring process, an inoculant of rare earth modified barium ferrosilicon with a particle size of 0.2 - 0.8 mm (Si 65 - 70%, Ba 2 - 5%, rare earth oxide 2 - 5%, the rest is Fe) is added with the flow. The addition amount accounts for 0.1 - 0.3% of the total mass of the molten iron. The tapping temperature is controlled at 1450 ± 10 °C, the pouring waiting time is 1 minute, and the pouring temperature is 1365 °C ± 5 °C.

[0018] (6) Intelligent temperature control and cooling casting: Adopt a precise temperature control system for the casting process based on intelligent sensing and feedback control. Use distributed thermocouples (Omega) and infrared thermal imagers (FLIR) to monitor the temperature field distribution in the cavity in real time. Adjust the cooling rate through the PID (Proportional-Integral-Derivative) algorithm. Use ProCAST / MAGMA software to simulate the solidification process, optimize the layout of chill blocks, and achieve sequential solidification of the molten metal from thick walls to thin walls. The final cooling stage time is controlled within 2 hours.

[0019] Temperature control range: Pouring 1365 - 1450 °C, thick wall area (100 - 450 mm): lower temperature (1365 - 1420 °C) to avoid shrinkage defects. Thin wall area (30 - 100 mm): higher temperature (1420 - 1450 °C) to ensure complete filling.

[0020] Cooling control range: Eutectic stage 1140 - 1160 °C, final cooling 200 - 400 °C; The cooling rate in the thick wall area is controlled at 10 - 15 °C / min, and the cooling rate in the thin wall area is controlled at 15 - 20 °C / min to ensure sequential solidification; Time range: Final cooling stage ≤ 2 hours, solidification stage 30 - 90 minutes.

[0021] Eutectic stage: The stage in the solidification process of cast iron where the liquid metal undergoes eutectic reaction. At this time, austenite and graphite are simultaneously precipitated in the cast iron, which is a key part of the solidification process.

[0022] The solidification stage of the present invention includes the eutectic stage. The casting cooling process can be divided into three stages: liquid cooling stage, solidification stage, and final cooling stage. The solidification stage refers to the time required from the start of solidification to complete solidification.

[0023] (7) Post-treatment: Ultrasonic flaw detection is used to detect internal defects to ensure that the density of the casting is ≥ 99%. After turning mechanical processing, a zinc-aluminum coating (85% zinc and 15% aluminum) is cold-sprayed on the surface to further improve the corrosion resistance.

[0024] In step (1), the nano-particle reinforcement phases are SiC, SiO 2 and TiC, SiC, SiO 2The mass ratio of [substance] to TiC is 1.2:0.8:0.5.

[0025] In step (3), in the rare earth magnesium alloy spheroidizing agent, the rare earth elements include one or two of Y / La, etc.

[0026] In step (3), the preparation method of the rare earth magnesium alloy spheroidizing agent is as follows: Add raw materials in the order of melting point: First, melt silicon and calcium, and then add magnesium, Ba, rare earth alloy, and Fe. The melting temperature is controlled at 1400 - 1450 °C to avoid excessive volatilization of magnesium. Pour the molten alloy into ingot or rod shape, and after cooling, crush it into particles of 6 - 32 mm for use.

[0027] In step (5), in the rare earth modified barium ferrosilicon inoculant, the rare earth elements include one or several of Ce / Sc / Nd.

[0028] The preparation method of the rare earth modified barium ferrosilicon inoculant is as follows: The rare earth modified barium ferrosilicon inoculant is mainly based on silicon-based materials, and rare earth, barium (Ba), etc. are added. The raw material components include ferrosilicon (FeSi75): 70 - 80% (matrix material), rare earth oxide (such as CeO 2 , Sc 2 O 3 or Nd 2 O 3 one or several of them): 2 - 5%, barium: 2 - 5%. Use an electric arc furnace to melt ferrosilicon, and add rare earth oxide and barium alloy in proportion in turn, and fully react at 1500 - 1550 °C. Ensure the uniformity of components through electromagnetic stirring to avoid rare earth segregation. Atomize the molten alloy into fine particles (0.2 - 0.8 mm) by high-pressure gas (nitrogen) for standby.

[0029] In step (6), through the precise temperature control and cooling system, sequential solidification and feeding of the molten metal in the cavity are realized, improving the dimensional stability and reliability of the lightweight product.

[0030] Through the above composition design and process design, the number of ferrite in the cast iron material is ≥90%, the spheroidization rate of ductile iron is ≥95%, and the mechanical properties meet: yield strength (Rp0.2) ≥263 MPa, tensile strength (Rm) ≥392 MPa, elongation (δ) ≥16.1%, fracture toughness (J / cm 2 ) ≥20, low-temperature impact toughness (-30 °C) ≥11.2 J. The thinning amount in the 25-year life cycle under the simulated marine environment (specific conditions as described in the subsequent on-site coupon test) ≤2.11 mm.

[0031] The present invention has the following beneficial effects:

[0032] The present invention provides a cast iron material and a preparation method thereof for large-size and high-strength offshore wind power hubs with a sphere diameter of more than 6 m and a wall thickness range of 30-450 mm. Through the synergistic effect among the added trace elements Ba, Sb, Bi and rare earth elements Y / La / Ce / Sc / Nd, and by adding a three-phase SiC / SiO 2 / TiC nanoparticle reinforcing phase, the formation of pearlite is inhibited and the graphite spheres are refined, so that the spheroidization rate is ≥95% and the ferrite content is ≥90%. By adding the nanoparticle reinforcing phase and controlling the proportion of alloying elements such as Ni≤0.8%, the corrosion resistance of the material is further improved. By adopting an intelligent temperature control and cooling and controlled cooling casting process, the comprehensive performance of the material and the dimensional stability of the casting are improved. A ductile iron material with a high spheroidization rate, a high ferrite content, excellent mechanical properties and corrosion resistance is prepared to meet the requirements of large MW offshore wind power hubs for light weight, high strength, corrosion resistance and high reliability.

[0033] The present invention optimizes the microstructure of cast iron by adding trace rare elements barium, antimony, bismuth and rare earth elements, significantly improves the ferrite content and spheroidization rate, and simultaneously improves the mechanical properties and corrosion resistance of the material. Combined with an intelligent temperature control and cooling casting process, the sequential solidification and feeding of the molten metal in the cavity are realized, and the dimensional stability and reliability of the casting are improved. Compared with the prior art, the present invention has the following beneficial effects:

[0034] The ferrite content is ≥95% and the spheroidization rate is ≥90%, which significantly improves the toughness and ductility of the material.

[0035] The yield strength is ≥263 MPa, the tensile strength is ≥392 MPa, and the elongation is ≥16.1%, meeting the high-strength requirements of large MW wind power hubs.

[0036] The fracture toughness is ≥20 J / cm 2 , and the low-temperature impact toughness (-30 °C) is ≥11.2 J, improving the impact resistance of the material.

[0037] By adding Ni≤0.8%, the electrode potential of the matrix during corrosion is increased, the corrosion current density of ductile iron is significantly reduced, and the corrosion rate is reduced; by adding nanoparticles, the corrosion potential and charge transfer resistance of ductile iron are increased. The corrosion resistance of the material is further improved and it is suitable for harsh marine environments. The thinning amount in the 25-year life cycle under the simulated marine environment (specific conditions are as described in the subsequent on-site coupon test) is ≤2.11 mm.

[0038] The intelligent temperature control and cooling casting process effectively reduces casting defects and improves the dimensional stability and reliability of products. The present invention adopts a precise temperature control system for the casting process based on intelligent sensing and feedback control to accurately control the casting temperature and the insulation temperature of resin sand, realize the sequential solidification and feeding of molten metal in the cavity, and effectively improve the dimensional stability and reliability of lightweight products. The cast iron material and its preparation method of the present invention can meet the stringent requirements of large-size thin-walled high-strength wind power hubs and have broad application prospects. Description of the Drawings

[0039] Figure 1 The metallographic diagram of the cast iron prepared in Example 1;

[0040] Figure 2 The metallographic diagram of the cast iron prepared in Example 1 after the corrosion test;

[0041] Figure 3 The metallographic diagram of the cast iron prepared in Example 2;

[0042] Figure 4 The metallographic diagram of the cast iron prepared in Example 2 after the corrosion test;

[0043] Figure 5 The metallographic diagram of the cast iron prepared in Example 3;

[0044] Figure 6 The metallographic diagram of the cast iron prepared in Example 3 after the corrosion test;

[0045] Figure 7 The metallographic diagram of the cast iron prepared in Comparative Example 1;

[0046] Figure 8 The metallographic diagram of the cast iron prepared in Comparative Example 1 after the corrosion test;

[0047] Figure 9 The metallographic diagram of the cast iron prepared in Comparative Example 2;

[0048] Figure 10 The metallographic diagram of the cast iron prepared in Comparative Example 2 after the corrosion test. Detailed Embodiments

[0049] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0050] Example 1

[0051] A preparation method of a cast iron material suitable for large-sized thin-walled high-strength wind power hubs, comprising the following steps:

[0052] 1. Raw material preparation: Prepare raw materials according to the ratio of pig iron (balance), high-quality scrap steel (10%), ferrosilicon (0.5%), ferrovanadium (0.2%), ferromanganese (0.1%), ferroniobium (0.1%), nickel plate (0.2%) and three-phase nanoparticle reinforcing phase (SiC 1.2% + SiO 2 0.8% + TiC 0.5%).

[0053] 2. Melting: Add the raw materials into an intermediate frequency induction furnace for melting, control the melting temperature at 1510°C, and introduce argon for protection.

[0054] 3. Spheroidization and in-furnace inoculation treatment: After the raw materials are completely melted, place the rare earth magnesium alloy spheroidizing agent (Mg 5.5%, Si 40%, La 0.2%, Ca 1.5%, Ba 1.5%, the rest is Fe) at the bottom of the ladle. The addition amount of the rare earth magnesium alloy spheroidizing agent accounts for 1.2% of the total molten iron mass. Cover the surface of the rare earth magnesium alloy spheroidizing agent with a barium-silicon-iron inoculant (Si 65%, Ba 2%, Bi 0.1%, the rest is Fe) with a particle size of about 2 mm. The addition amount of the barium-silicon-iron inoculant accounts for 0.2% of the total molten iron mass. React for 120 seconds after the molten iron is poured in, and the molten iron treatment temperature is 1365°C.

[0055] 4. Microalloying: After spheroidization and inoculation treatment, add 0.5% of silicon-calcium alloy (Si 40%, Ca 15%, Sb 0.5%, the balance is iron), stir for 5 minutes until the composition is uniform, to increase the number of graphite balls and improve the low-temperature impact toughness of ductile iron.

[0056] 5. Pouring and instantaneous inoculation treatment: Complete pouring within 20 minutes after spheroidization, inoculation and microalloying. Pour the molten metal into a resin sand mold preheated to 300°C. During the pouring process, add a rare earth-modified barium-silicon-iron inoculant (Si 65%, Ba 2%, CeO 2 2%, the rest is Fe) with a particle size of about 0.2 mm. The addition amount of the rare earth-modified barium-silicon-iron inoculant accounts for 0.1% of the total molten iron mass. Control the tapping temperature at 1450°C, the pouring waiting time is 1 minute, and the pouring temperature is 1365°C.

[0057] 6. Intelligent temperature control and cooling casting: After pouring, the intelligent temperature control and cooling system controls the cooling rate of the thick-walled area at 15°C / min and the thin-walled area at 20°C / min to ensure sequential solidification.

[0058] Specifically, intelligent temperature control and cooling in casting: An accurate temperature control system for the casting process based on intelligent sensing and feedback control is adopted. Distributed thermocouples (Omega) and infrared thermal imagers (FLIR) are used to monitor the temperature field distribution in the cavity in real time. The cooling rate is adjusted through the PID (Proportional-Integral-Derivative) algorithm. The ProCAST / MAGMA software is used to simulate the solidification process, optimize the layout of chill blocks, and achieve the sequential solidification of the molten metal from the thick wall to the thin wall. The cooling time in the final cooling stage is controlled within 2 hours.

[0059] Temperature control range: Pouring temperature is 1365 - 1420 °C. For the thick wall area (about 100 mm), a lower temperature (1365 °C) is used to avoid shrinkage defects. For the thin wall area (about 30 mm), a higher temperature (1420 °C) is used to ensure complete filling.

[0060] Cooling control range: Eutectic stage is 1140 °C, final cooling is 200 °C. The cooling rate in the thick wall area is controlled at 15 °C / min, and the cooling rate in the thin wall area is controlled at 20 °C / min to ensure sequential solidification. Time range: Final cooling stage ≤ 2 hours, solidification stage is 30 minutes.

[0061] 7. Post-treatment: Ultrasonic flaw detection is used to detect internal defects to ensure that the density of the casting is ≥ 99%. After turning machining, a zinc-aluminum coating (85% zinc and 15% aluminum) is cold-sprayed on the surface to further improve the corrosion resistance.

[0062] The preparation method of the rare earth magnesium alloy spheroidizing agent is as follows: The raw materials are added in the order of melting point: First, silicon and calcium are melted, and then magnesium, Ba, rare earth alloy, and Fe are added. The melting temperature is controlled at 1400 °C to avoid excessive volatilization of magnesium. The molten alloy is cast into ingot or rod shape, and after cooling, it is crushed into particles about 6 mm in size for use.

[0063] The preparation method of the rare earth modified barium ferrosilicon inoculant: The rare earth modified barium ferrosilicon inoculant is mainly based on silicon-based materials, with the addition of rare earth and barium (Ba). The raw material components include ferrosilicon (FeSi75): 96% (matrix material), rare earth oxide (CeO 2 ) : 2%, barium: 2%. The ferrosilicon is melted in an electric arc furnace, and the rare earth oxide and barium alloy are added in proportion in sequence, and fully reacted at 1500 °C. Electromagnetic stirring is used to ensure uniform composition and avoid rare earth segregation. The molten alloy is atomized into fine particles (about 0.2 mm) by high-pressure gas (nitrogen) for standby.

[0064] A cast iron material applicable to large-size thin-wall high-strength wind power hubs obtained in this embodiment, its chemical composition is by mass percentage: C: 3.55%, Si: 2.3%, Ni: 0.8%, Mn: 0.15%, Mg: 0.06%, Nb: 0.06%, V: 0.02%, P: 0.015%, S: 0.015%, rare element barium (Ba): 0.0050%, rare element antimony (Sb): 0.0020%, rare element bismuth (Bi): 0.0010%, rare earth element: 0.010%, and the rest is Fe and inevitable impurities.

[0065] Application of a cast iron material applicable to large-size thin-wall high-strength wind power hubs obtained in this embodiment in large-megawatt offshore wind power hubs. The large megawatt is 18 MW; the large size is a spherical diameter of 6 m; the thin wall is a wall thickness of 30 - 100 mm.

[0066] Example 2

[0067] A preparation method of a cast iron material applicable to large-size thin-wall high-strength wind power hubs, comprising the following steps:

[0068] 1. Raw material preparation: Prepare raw materials according to the ratio of pig iron (the balance), high-quality scrap steel (20%), ferrosilicon (1.5%), ferrovanadium (0.4%), ferromanganese (0.2%), ferroniobium (0.2%), nickel plate (0.8%) and three-phase nanoparticle reinforcing phase (SiC 0.96% + SiO 2 0.64% + TiC 0.4%).

[0069] 2. Melting: Add the raw materials into an intermediate frequency induction furnace for melting, control the melting temperature at 1520 °C, and introduce argon for protection.

[0070] 3. Spheroidizing and in-furnace inoculation treatment: After the raw materials are completely melted, place a rare earth magnesium alloy spheroidizing agent (Mg 6.5%, Si 45%, Y 2.0%, Ca 2.5%, Ba 2.5%, and the rest is Fe) at the bottom of the ladle. The addition amount of the rare earth magnesium alloy spheroidizing agent accounts for 1.4% of the total molten iron mass. Cover the surface of the rare earth magnesium alloy spheroidizing agent with a barium-silicon-iron inoculant with a particle size of about 8 mm (Si 70%, Ba 3%, Bi 0.2%, and the rest is Fe). The addition amount of the barium-silicon-iron inoculant accounts for 0.3% of the total molten iron mass. React for 130 seconds after the molten iron is poured in, and the molten iron treatment temperature is 1365 °C.

[0071] 4. Microalloying: After spheroidizing and inoculation treatment, add 1.0% of silicon-calcium alloy (Si 65%, Ca 33%, Sb 1%, and the balance is iron), stir for 7 minutes until the composition is uniform to increase the number of graphite balls and improve the low-temperature impact toughness of ductile iron.

[0072] 5. Pouring and Inoculation Treatment: Pouring is completed within 20 minutes after spheroidizing, inoculating, and microalloying. The molten metal is poured into a resin sand mold preheated to 200 °C. During pouring, a rare-earth modified barium-silicon-iron inoculant with a particle size of about 0.8 mm (Si 70%, Ba 5%, Nd 2 O 3 5%, and the rest is Fe) is added with the flow. The addition amount of the rare-earth modified barium-silicon-iron inoculant accounts for 0.2% of the total mass of the molten iron. The tapping temperature is controlled at 1440 °C, the pouring waiting time is 1 minute, and the pouring temperature is 1360 °C.

[0073] 6. Intelligent Temperature and Cooling Control Casting: After pouring, the intelligent temperature and cooling control system controls the cooling rate in the thick-wall area at 15 °C / min and in the thin-wall area at 20 °C / min to ensure sequential solidification.

[0074] Specifically, for intelligent temperature and cooling control casting: A precise temperature control system for the casting process based on intelligent sensing and feedback control is adopted. Using distributed thermocouples (Omega) and infrared thermal imagers (FLIR), the temperature field distribution in the cavity is monitored in real time. The cooling rate is adjusted through the PID (Proportional-Integral-Derivative) algorithm. The ProCAST / MAGMA software is used to simulate the solidification process, optimize the layout of chill blocks, and achieve sequential solidification of the molten metal from the thick wall to the thin wall. The cooling time in the final cooling stage is controlled within 2 hours.

[0075] Temperature Control Range: Pouring temperature is 1420 - 1450 °C. For the thick-wall area (about 450 mm): lower temperature (1420 °C) to avoid shrinkage defects. For the thin-wall area (about 100 mm): higher temperature (1450 °C) to ensure complete filling.

[0076] Cooling Control Range: Eutectic stage is 1160 °C, final cooling is 400 °C; the cooling rate in the thick-wall area is controlled at 10 °C / min, and in the thin-wall area at 15 °C / min to ensure sequential solidification; Time Range: The final cooling stage ≤ 2 hours, and the solidification stage is 90 minutes.

[0077] 7. Post-treatment: Ultrasonic flaw detection is used to detect internal defects to ensure that the density of the casting is ≥ 99%. After turning machining, a zinc-aluminum coating (85% zinc and 15% aluminum) is cold-sprayed on the surface to further improve corrosion resistance.

[0078] The preparation method of the rare-earth magnesium alloy spheroidizing agent is as follows: Add raw materials in the order of melting point: First, melt silicon and calcium, and then add magnesium, Ba, rare-earth alloy, and Fe. The melting temperature is controlled at 1450 °C to avoid excessive magnesium volatilization. The molten alloy is cast into ingot or rod shape, and after cooling, it is crushed into particles of about 32 mm for use.

[0079] The preparation method of the rare earth modified barium ferrosilicon inoculant is as follows: The rare earth modified barium ferrosilicon inoculant is mainly based on silicon-based materials, and rare earth and barium (Ba) are added. The raw material components include ferrosilicon (FeSi75): 90% (matrix material), rare earth oxide (Nd 2 O 3 ): 5%, barium: 5%. Ferrosilicon is melted in an electric arc furnace, and rare earth oxide and barium alloy are added in proportion in turn, and fully reacted at 1550 °C. Electromagnetic stirring is used to ensure uniform composition and avoid rare earth segregation. The molten alloy is atomized into fine particles (about 0.8 mm) by high-pressure gas (nitrogen) for standby.

[0080] A cast iron material applicable to large-size thin-wall high-strength wind power hubs obtained in this example, its chemical composition by mass percentage is: C: 3.85%, Si: 2.0%, Ni: 0.5%, Mn: 0.10%, Mg: 0.05%, Nb: 0.05%, V: 0.01%, P: 0.01%, S: 0.005%, rare element barium (Ba): 0.0150%, rare element antimony (Sb): 0.0050%, rare element bismuth (Bi): 0.0020%, rare earth element: 0.025%, and the rest is Fe and inevitable impurities.

[0081] The application of a cast iron material applicable to large-size thin-wall high-strength wind power hubs obtained in this example in large-megawatt offshore wind power hubs. Large megawatt is 18 MW; large size is the sphere diameter of 8 m; thin wall is the wall thickness of 100 - 450 mm.

[0082] Example 3

[0083] A preparation method of a cast iron material applicable to large-size thin-wall high-strength wind power hubs, comprising the following steps:

[0084] 1. Raw material preparation: Prepare raw materials according to the ratio of pig iron (the balance), high-quality scrap steel (15%), ferrosilicon (1.0%), ferrovanadium (0.3%), ferromanganese (0.15%), ferroniobium (0.1%), nickel plate (0.5%) and three-phase nanoparticle reinforcement phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%).

[0085] 2. Melting: Add the raw materials into an intermediate frequency induction furnace for melting, control the melting temperature at 1450 °C, and introduce argon for protection.

[0086] 3. Spheroidization and in-furnace inoculation treatment: After the raw materials are completely melted, place the rare earth magnesium alloy spheroidizing agent (Mg 6.0%, Si 42%, La 0.5%, Y 0.5%, Ca 2.0%, Ba 2.0%, the rest is Fe) at the bottom of the ladle. The addition amount of the rare earth magnesium alloy spheroidizing agent accounts for 1.0% of the total molten iron mass. Cover the surface of the rare earth magnesium alloy spheroidizing agent with a barium-silicon-iron inoculant (Si 68%, Ba 2.5%, Bi 0.15%, the rest is Fe) with a particle size of about 5 mm. The addition amount of the barium-silicon-iron inoculant accounts for 0.4% of the total molten iron mass. After the molten iron is poured in, react for 140 seconds, and the molten iron treatment temperature is 1375 °C.

[0087] 4. Microalloying: After spheroidization and inoculation treatment, add 1.5% of silicon-calcium alloy (Si 50%, Ca 35%, Sb 0.8%, the balance is iron), stir for 8 minutes until the composition is uniform to increase the number of graphite balls and improve the low-temperature impact toughness of ductile iron.

[0088] 5. Pouring and instantaneous inoculation treatment: Pouring is completed within 20 minutes after spheroidization, inoculation and microalloying. Pour the molten metal into a resin sand mold preheated to 50 °C, and add a rare earth-modified barium-silicon-iron inoculant (Si 68%, Ba 3%, Sc 2 O 3 4%, the rest is Fe) with a particle size of about 0.5 mm during the pouring process. The addition amount of the rare earth-modified barium-silicon-iron inoculant accounts for 0.3% of the total molten iron mass. The tapping temperature is controlled at 1460 °C, the pouring waiting time is 1 minute, and the pouring temperature is 1370 °C.

[0089] 6. Intelligent temperature control and cooling casting: After pouring, the intelligent temperature control and cooling system controls the cooling rate of the thick-wall area at 15 °C / min and the thin-wall area at 20 °C / min to ensure sequential solidification.

[0090] Specifically, intelligent temperature control and cooling casting: Adopt a precise temperature control system for the casting process based on intelligent sensing and feedback control, use distributed thermocouples (Omega) and infrared thermal imagers (FLIR) to monitor the temperature field distribution in the cavity in real time. Adjust the cooling rate through the PID (Proportional-Integral-Derivative) algorithm, use ProCAST / MAGMA software to simulate the solidification process, optimize the layout of chill blocks, and achieve sequential solidification of the molten metal from the thick wall to the thin wall. The cooling time in the final cooling stage is controlled within 2 hours.

[0091] Temperature control range: Pouring at 1400 - 1440 °C, thick-wall area (about 200 mm): lower temperature (1400 °C) to avoid shrinkage defects. Thin-wall area (about 80 mm): higher temperature (1440 °C) to ensure complete filling.

[0092] Controlled cooling range: eutectic stage at 1150°C, final cooling at 300°C; cooling rate in thick-wall area controlled at 15°C / min, and in thin-wall area at 20°C / min to ensure sequential solidification; time range: final cooling stage ≤ 2 hours, solidification stage 60 minutes.

[0093] 7. Post-treatment: Ultrasonic flaw detection is used to detect internal defects to ensure that the density of the casting is ≥ 99%. After turning machining, a zinc-aluminum coating (85% zinc and 15% aluminum) is cold-sprayed on the surface to further improve corrosion resistance.

[0094] The preparation method of the rare earth magnesium alloy spheroidizing agent is as follows: Add raw materials in the order of melting point: first melt silicon and calcium, and then add magnesium, Ba, rare earth alloy and Fe. The melting temperature is controlled at 1430°C to avoid excessive magnesium volatilization. The molten alloy is cast into ingots or rods, and after cooling, it is crushed into particles about 20 mm for use.

[0095] The preparation method of the rare earth modified barium ferrosilicon inoculant is as follows: The rare earth modified barium ferrosilicon inoculant is mainly based on silicon-based materials, and rare earth and barium (Ba) are added. The raw material components include ferrosilicon (FeSi75): 93% (matrix material), rare earth oxide (Sc 2 O 3 ) : 4%, barium: 3%. Ferrosilicon is melted in an electric arc furnace, and rare earth oxide and barium alloy are added in proportion in turn, and fully reacted at 1525°C. Electromagnetic stirring is used to ensure uniform composition and avoid rare earth segregation. The molten alloy is atomized into fine particles (about 0.5 mm) by high-pressure gas (nitrogen) for standby.

[0096] A cast iron material suitable for large-size thin-wall high-strength wind power hubs obtained in this example, its chemical composition by mass percentage is: C: 3.70%, Si: 1.0%, Ni: 0.2%, Mn: 0.05%, Mg: 0.04%, Nb: 0.03%, V: 0.01%, P: 0.005%, S: 0.005%, rare element barium (Ba): 0.01%, rare element antimony (Sb): 0.003%, rare element bismuth (Bi): 0.0015%, rare earth element: 0.02%, and the rest is Fe and inevitable impurities.

[0097] Application of a cast iron material suitable for large-size thin-wall high-strength wind power hubs obtained in this example in large-megawatt offshore wind power hubs. Large megawatt is 20 MW; large size is the sphere diameter of 10 m; thin wall is the wall thickness of 80 - 200 mm.

[0098] Example 4

[0099] The difference between this embodiment and Embodiment 1 is only as follows: the melting temperature in Step 2 is 1550 °C. The addition amount of the rare earth magnesium alloy spheroidizing agent in Step 3 accounts for 1.8% of the total mass of the molten iron. In Step 5, in the preparation method of the rare earth modified barium ferrosilicon inoculant, the added rare earth oxide is CeO with a mass ratio of 1:1 2 and Sc 2 O 3 .

[0100] Comparative Example 1

[0101] The difference between this comparative example and Embodiment 3 is only as follows:

[0102] In Step 5, barium ferrosilicon inoculant is added instead of rare earth modified barium ferrosilicon inoculant.

[0103] Barium ferrosilicon inoculant (Si 68%, Ba 3%, the rest is Fe)

[0104] Comparative Example 2

[0105] The difference between this comparative example and Embodiment 3 is only as follows: the three-phase nanoparticle reinforcing phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a single-phase SiC nanoparticle reinforcing phase (4%).

[0106] Comparative Example 3

[0107] The difference between this comparative example and Embodiment 3 is only as follows: the three-phase nanoparticle reinforcing phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a single-phase SiO 2 nanoparticle reinforcing phase (4%).

[0108] Comparative Example 4

[0109] The difference between this comparative example and Embodiment 3 is only as follows: the three-phase nanoparticle reinforcing phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a single-phase TiC nanoparticle reinforcing phase (4%).

[0110] Comparative Example 5

[0111] The difference between this comparative example and Embodiment 3 is only as follows: the three-phase nanoparticle reinforcing phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a two-phase nanoparticle reinforcing phase (SiC 2.4% + SiO 2 1.6%).

[0112] Comparative Example 6

[0113] The difference between this comparative example and Example 3 is only that: the three-phase nanoparticle reinforcement phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a two-phase nanoparticle reinforcement phase (SiC 2.82% + TiC 1.18%).

[0114] Comparative Example 7

[0115] The difference between this comparative example and Example 3 is only that: the three-phase nanoparticle reinforcement phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a two-phase nanoparticle reinforcement phase (SiO 2 2.46% + TiC 1.54%).

[0116] Comparative Example 8

[0117] The difference between this comparative example and Example 3 is only that: the three-phase nanoparticle reinforcement phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a three-phase nanoparticle reinforcement phase (SiC 2.08% + SiO 2 1.28% + TiC 0.64%). That is, in this comparative example, the mass ratio of SiC, SiO 2 and TiC is 1.3:0.8:0.4.

[0118] Comparative Example 9

[0119] The difference between this comparative example and Example 3 is only that: the three-phase nanoparticle reinforcement phase (SiC 1.92% + SiO 2 1.28% + TiC 0.8%) is replaced by a three-phase nanoparticle reinforcement phase (SiC 1.76% + SiO 2 1.28% + TiC 0.96%). That is, in this comparative example, the mass ratio of SiC, SiO 2 and TiC is 1.1:0.8:0.6.

[0120] Comparative Example 10

[0121] The difference between this comparative example and Example 3 is only that:

[0122] In step 6, after pouring, the intelligent temperature control and cooling system controls the cooling rate of the thick-walled area at 18 °C / min and the thin-walled area at 25 °C / min.

[0123] Comparative Example 11

[0124] The difference between this comparative example and Example 3 is only that:

[0125] In step 6, the temperature control range: thick-walled area: (1350 °C), thin-walled area: (1470 °C).

[0126] Comparative Example 12

[0127] The difference between this comparative example and Example 3 is only that:

[0128] In step 6, the temperature control range: thick-walled area: (1450 °C), thin-walled area: (1410 °C).

[0129] The mechanical property test results of the cast iron materials prepared in Examples 1-4 and Comparative Examples 1-12 of the present invention are shown in Table 1 below. The corrosion property results of the cast iron materials are shown in Table 2 below.

[0130] Table 1 Test Results of Cast Iron Mechanical Properties

[0131]

[0132]

[0133] Table 2 Results of Cast Iron Specimen Corrosion Properties

[0134]

[0135]

[0136] Metallographic corrosion test: After the specimen is ground and polished to a mirror surface (i.e., Ra ≤ 0.04), the surface is rinsed twice with alcohol and dried with a hair dryer. Then, a 4% nitric acid alcohol solution is dropped on its surface, and it is corroded for 20-35 seconds (the surface becomes dark). After that, it is rinsed with clean water, dried with a hair dryer, and placed on a metallographic microscope for observation.

[0137] In the hanging piece time, a represents year.

[0138] Figure 1 It is the metallographic diagram of the cast iron prepared in Example 1; Figure 2 It is the metallographic diagram of the cast iron prepared in Example 1 after the corrosion test. It can be seen from the figure that the nodular graphite effect is good, the nodularity grade is 2, the graphite size is 7, the matrix nodularization rate is 95%, the ferrite content is 90%, and the physical and chemical properties are excellent.

[0139] Figure 3 It is the metallographic diagram of the cast iron prepared in Example 2; Figure 4 It is the metallographic diagram of the cast iron prepared in Example 2 after the corrosion test. It can be seen from the figure that the nodularization effect is good, the nodularity grade is 2, the graphite size is 7, the matrix nodularization rate is 95%, the matrix ferrite content is 90%, and compared with Example 1, there is no obvious improvement in the physical and chemical properties (the tensile strength and yield strength increase slightly, the elongation at break decreases, the average -30 °C impact energy increases, and the corrosion resistance improves).

[0140] Figure 5 The metallographic diagram of the cast iron prepared in Example 3; Figure 6 The metallographic diagram of the cast iron prepared in Example 3 after the corrosion test. It can be seen from the figure that the spheroidization effect is good, the spheroidization grade is 2, the graphite size is 7, the matrix spheroidization rate is 97%, the matrix ferrite content is 95%, and the physical and chemical properties are significantly improved compared with those in Example 1 (the tensile strength and yield strength are significantly increased, the average -30°C impact energy is increased, and the corrosion resistance is significantly improved).

[0141] Figure 7 The metallographic diagram of the cast iron prepared in Comparative Example 1; Figure 8 The metallographic diagram of the cast iron prepared in Comparative Example 1 after the corrosion test. It can be seen from the figure that the spheroidization effect is average, the spheroidization grade is 3, the graphite size is 6, the matrix spheroidization rate is 80%, the matrix ferrite content is 90%, and the physical and chemical properties are significantly lower than those in Example 3, and the mechanical properties and corrosion resistance are significantly decreased.

[0142] Figure 9 The metallographic diagram of the cast iron prepared in Comparative Example 2; Figure 10 The metallographic diagram of the cast iron prepared in Comparative Example 2 after the corrosion test. It can be seen from the figure that the spheroidization effect is better, the spheroidization grade is 2, the graphite size is 7, the matrix spheroidization rate is 90%, the matrix ferrite content is 80%, and the physical and chemical properties are significantly lower than those in Example 3, and the mechanical properties and corrosion resistance are significantly decreased.

[0143] In summary, through the synergistic effect between the added trace elements and rare earth elements, and by adding the three-phase nano-particle reinforcement phase, the formation of pearlite is inhibited and the graphite balls are refined, so that the spheroidization rate ≥ 95% and the ferrite content ≥ 90%. By adding the three-phase nano-particle reinforcement phase and controlling the proportion of alloying elements such as Ni ≤ 0.8%, the corrosion resistance of the material is further improved. By adopting the intelligent temperature control and cooling and controlled-cooling casting process, the comprehensive properties of the material and the dimensional stability of the casting are improved. The prepared ductile iron material has a high spheroidization rate, excellent mechanical properties, low-temperature impact resistance and corrosion resistance, meeting the requirements of 18 MW-class offshore wind power hub for light weight, high strength, corrosion resistance and high reliability.

[0144] It should be understood that, in order to streamline the present disclosure and assist in understanding one or more of the various inventive aspects, in the foregoing description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment or the description thereof. However, the disclosed method should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected by the claims, the inventive aspects lie in less than all of the features of the foregoing disclosed embodiments. Thus, the claims following the detailed description hereby expressly incorporate the detailed description, where each claim itself serves as a separate embodiment of the present invention.

[0145] Although the present invention has been described in terms of a limited number of embodiments, those skilled in the art within the present technical field will appreciate, upon the foregoing description, that other embodiments can be contemplated within the scope of the present invention thus described. In addition, it should be noted that the language used in this specification has been principally selected for readability and instructional purposes and not for the purpose of explaining or limiting the subject matter of the present invention. Thus, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure of the present invention is illustrative, not restrictive, and the scope of the present invention is defined by the appended claims.

[0146] The foregoing are only the preferred embodiments of the present invention, and it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A cast iron material suitable for large-size, thin-walled, high-strength wind turbine hubs, characterized in that: Its chemical composition by mass percentage is: C: 3.55%-3.85%, Si: ≤2.3%, Ni: ≤0.8%, Mn: ≤0.15%, Mg: ≤0.06%, Nb: ≤0.06%, V: ≤0.02%, P: ≤0.015%, S: ≤0.015%, rare element barium Ba: 0.0050%-0.0150%, rare element antimony Sb: 0.0020%-0.0050%, rare element bismuth Bi: 0.0010%-0.0020%, rare earth elements: 0.010%-0.025%, and the rest is Fe and unavoidable impurities.

2. The cast iron material suitable for large-size, thin-walled, high-strength wind turbine hub according to claim 1, characterized in that: The rare earth elements include any one or two of Y and La, and the rare earth elements also include any one or more of Ce, Sc and Nd.

3. The cast iron material suitable for large-size, thin-walled, high-strength wind turbine hub according to claim 1, characterized in that: In cast iron materials, the amount of ferrite is ≥90%, the spheroidization rate of ductile iron is ≥95%, and the mechanical properties meet the following requirements: yield strength ≥263MPa, tensile strength ≥392MPa, elongation ≥16.1%, fracture toughness ≥20J / cm 2 , -30℃ low temperature impact toughness ≥11.2J, 25-year life cycle thinning amount in simulated marine environment ≤2.11mm.

4. A method for preparing a cast iron material suitable for a large-size, thin-walled, high-strength wind turbine hub according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Raw material preparation: 10-20 wt% of high-quality scrap steel, 0.5-1.5 wt% of ferrosilicon, 0.2-0.4 wt% of ferrovanadium, 0.1-0.2 wt% of ferromanganese, 0.1-0.2 wt% of ferroniobium, 0.2-0.8 wt% of nickel plate, 2-4 wt% of nanoparticle reinforcement phase and the balance of pig iron are prepared in proportion; (2) Melting: Add the raw materials into a medium frequency induction furnace for melting, control the melting temperature to 1450°C-1550°C, and introduce argon gas for protection; (3) Spheroidization and pre-furnace inoculation treatment: After the raw materials are completely melted, rare earth magnesium alloy spheroidizer is added for spheroidization treatment; the rare earth magnesium alloy spheroidizer is placed at the bottom of the ladle, and the amount of rare earth magnesium alloy spheroidizer added is 1.0-1.8% of the total molten iron mass; the surface of the rare earth magnesium alloy spheroidizer is covered with barium ferrosilicon inoculant, and the amount of barium ferrosilicon inoculant added is 0.2-0.4% of the total molten iron mass; after the molten iron is poured in, the spheroidization reaction lasts ≥2 minutes, and the molten iron treatment temperature is 1365-1375°C; (4) Microalloying: After spheroidization and inoculation, add Sb complex in an amount of 0.5-1.5wt% of the total molten iron mass and stir for 5-8 minutes until the composition is uniform; (5) Pouring and instantaneous inoculation treatment: After spheroidization, inoculation and microalloying, pouring is completed within 20 minutes; The molten metal liquid is poured into the resin sand mold preheated to 50-300°C, and rare earth modified barium ferrosilicon inoculant is added during the pouring process, and the amount of rare earth modified barium ferrosilicon inoculant added accounts for 0.1-0.3% of the total molten iron mass. The furnace temperature is controlled at 1450±10°C, the pouring waiting time is at least 1min, and the pouring temperature is 1365°C±5°C; (6) Temperature and cold controlled casting: A precise temperature control system based on intelligent sensing and feedback control is used for the casting process. Distributed thermocouples and infrared thermal imagers are used to monitor the temperature field distribution in the cavity in real time. The cooling rate is adjusted through the PID algorithm. ProCAST / MAGMA software is used to simulate the solidification process, optimize the chiller layout, and realize the sequential solidification of the molten metal from thick walls to thin walls. The cooling time of the final cooling stage is controlled within 2 hours. (7) Post-processing: Ultrasonic flaw detection is used to detect internal defects to ensure that the density of the casting is ≥99%; after mechanical processing, the surface is cold-sprayed with zinc-aluminum coating.

5. The preparation method according to claim 4, characterized in that: In step (1), Pig iron is low sulfur and phosphorus pig iron, where S≤0.02% and P≤0.035%; High-quality scrap steel refers to scrap steel that has been freed of plating and alloy contamination; The nanoparticle reinforcement phases are SiC, SiO2 and TiC, and the mass ratio of SiC, SiO2 and TiC is 1.2:0.8:0.

5.

6. The preparation method according to claim 4, characterized in that: In step (3), the rare earth magnesium alloy spheroidizer has the following chemical compositions by mass percentage: Si 40-45%, Mg 5.5-6.5%, Ca1.5-2.5%, Ba 1.5-2.5%, rare earth element RE 0.2-2.0%, and the rest Fe; the rare earth element RE includes one or two of Y / La; The preparation method of rare earth magnesium alloy spheroidizer is as follows: raw materials are added in order of melting point: silicon and calcium are melted first, and magnesium, Ba, rare earth elements and Fe are added later; the smelting temperature is controlled at 1400-1450°C to avoid excessive volatilization of magnesium, the molten alloy is cast into ingots or rods, and after cooling, it is crushed into 6-32mm particles for use.

7. The preparation method according to claim 4, characterized in that: In step (3), the chemical composition of the barium ferrosilicon inoculant is as follows by mass percentage: Si 65-70%, Ba 2-3%, Bi 0.1-0.2%, and the remainder is Fe; the particle size of the barium ferrosilicon inoculant is 2-8 mm; In step (4), the Sb composite uses silicon-calcium alloy as a carrier, wherein Si is 40-65wt%, Ca is 15-35wt%, Sb is 0.5-1wt%, and the balance is iron.

8. The preparation method according to claim 4, characterized in that: In step (5), the rare earth modified barium ferrosilicon inoculant has the following chemical compositions by mass percentage: Si 65-70%, Ba 2-5%, rare earth element RE 0.5-2.0%, and the rest Fe; the rare earth element RE includes one or more of Ce / Sc / Nd; The preparation method of rare earth modified barium ferrosilicon inoculant is as follows: the raw material components include ferrosilicon FeSi75: the balance, rare earth oxide: 2-5%, and barium: 2-5%, ferrosilicon is smelted in an electric arc furnace, rare earth oxide and barium are added in proportion in sequence, and fully reacted at 1500-1550°C, electromagnetic stirring is used to ensure uniform composition and avoid rare earth segregation, and the molten alloy is atomized into 0.2-0.8mm fine particles by high-pressure nitrogen for standby use.

9. The preparation method according to claim 4, characterized in that: In step (6), the temperature control range is: pouring 1365 ~ 1450 ° C, thick wall area: lower temperature 1365 ~ 1420 ° C, to avoid shrinkage defects; thin wall area: higher temperature 1420 ~ 1450 ° C, to ensure complete filling; The wall thickness of the thick-walled area is 100-450mm; The wall thickness of the thin-walled area is 30-100mm; Cooling control range: 1140-1160℃ in eutectic stage, 200-400℃ in final cooling; cooling rate in thick-walled area is controlled at 10-15℃ / min, and cooling rate in thin-walled area is controlled at 15-20℃ / min to ensure sequential solidification; time range: final cooling stage ≤2 hours, solidification stage 30-90 minutes.

10. Application of the cast iron material suitable for large-size, thin-walled, high-strength wind turbine hub according to any one of claims 1 to 3 in large-megawatt offshore wind turbine hubs, characterized in that: Large megawatt is >18MW; large size is a sphere with a diameter of more than 6m; thin wall is a wall thickness range of 30 to 450mm.

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