A method for manufacturing a low-carbon alloy steel plate for a non-quenched fan blade

Abstract

The application provides a quenching-free manufacturing method of a low-carbon alloy steel plate 15MnNiCrMoV for high-speed fan blades with high strength and plasticity and good processing and welding performance.The low-carbon alloy steel plate 15MnNiCrMoV for fan blades is manufactured by an electric furnace + external refining + mold casting, ingot blooming + hot rolling + tempering heat treatment method, and the process route is as follows: electric furnace -> LF -> VD -> flat ingot mold casting, red delivery ingot soaking -> blooming rolling -> post-rolling cold stacking + finishing, cold billet reheating -> descaling -> rolling -> tempering heat treatment.The 15MnNiCrMoV alloy steel plate for fan blades without quenching has the characteristics of high strength and plasticity, high hardness, excellent welding and processing performance and the like; compared with a conventional quenching and tempering process, the 15MnNiCrMoV alloy steel plate for fan blades without quenching has higher production efficiency and lower manufacturing cost while ensuring the quality requirements of the steel for blades.

Description

Technical Field

[0001] This invention relates to the field of low-carbon alloy steel manufacturing technology for blades. Specifically, this invention relates to a method for manufacturing 15MnNiCrMoV high-strength alloy steel plate for wind turbine blades. More specifically, this invention relates to a method for manufacturing 15MnNiCrMoV alloy steel plate for wind turbine blades that is free from quenching and has high strength, plasticity, and good weldability. Background Technology

[0002] 15MnNiCrMoV is widely used in the manufacture of high-speed impellers and blades for blowers and centrifugal turbines. Due to its high strength and hardness, it can withstand the centrifugal forces during high-speed operation while ensuring blade stability, thereby improving blower efficiency and service life. Strict purity requirements and significant challenges in controlling surface quality and internal properties make it difficult to produce. This steel grade is typically manufactured using processes such as die casting, electroslag remelting, forging, rolling, and quenching and tempering. The finished product exhibits high strength and plasticity, good hardenability and weldability, as well as high wear resistance and heat resistance, meeting the requirements of high-speed impeller blade operation.

[0003] Besides its application in manufacturing high-speed impeller blades for blowers, 15MnNiCrMoV can also be used in other fields such as manufacturing high-precision products that withstand high-speed rotation, and medical devices. 15MnNiCrMoV is a high-strength structural steel with excellent comprehensive performance, but its production cost is relatively high.

[0004] The typical process for 15MnNiCrMoV steel plates includes electric furnace smelting, ladle refining, ingot casting, electroslag remelting, billet preparation, rolling, quenching, and tempering. The method of this invention eliminates the traditional electroslag remelting and quenching processes, significantly improving production efficiency while ensuring the quality of the blade steel.

[0005] This invention provides a suitable hot-rolling and tempering heat treatment method for the production of 15MnNiCrMoV low-carbon alloy steel plates. This method, achieved through electric furnace-LF-VD vacuum smelting-in-mold casting, ensures high steel purity and uniform microstructure. It yields strength, ductility, and toughness comparable to quenching and tempering, with a suitable hardness range of HB280-310. The tensile strength is 900-1000 MPa, yield strength 750-850 MPa, and elongation 14-17%. It also exhibits excellent weldability, meeting the requirements for manufacturing and using steel products for blades. Furthermore, it eliminates the need for electroslag remelting of steel ingots and quenching of steel plates, significantly reducing production costs. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by providing a method for manufacturing low-carbon alloy steel plates for wind turbine blades that do not require quenching.

[0007] The objective of this invention is achieved as follows: A method for manufacturing low-carbon alloy steel plates for non-quenching fan blades, comprising the following steps: Step 1: Electric furnace smelting: employing a hot charging and molten oxygen combined process, with an iron charging rate of 50-75%, slag formation and dephosphorization in advance during the melting period, uniform boiling at 1500-1600℃ during the oxidation period, and an oxygen blowing rate of 4000-4500 m³ / h during the oxidation period. 3During the tapping process, alloys are added with the steel stream according to the middle and lower limits of the chemical composition mass percentage: Al: 0.02-0.04%, Mo: 0.35-0.42%, Mn: 1.2-1.35%, Ni: 1.10-1.30%, ensuring that the tapped steel has P ≤ 0.010% and C: 0.09-0.15%. The electric furnace smelting cycle is 40-60 minutes, and the tapping temperature is 1640-1680℃. Step 2: LF refining: Argon is blown at the LF station at a flow rate of 100-300 L / min, with argon blowing throughout the process. Calcium carbide-based weak calcium carbide slag and deoxidizer are added evenly into the furnace. The amount of calcium carbide-based weak calcium carbide slag added is 120-15%. 0 kg, deoxidizer, i.e. aluminum shot, added in amounts of 100-150 kg. After the reducing slag forms, fine-tune the alloy composition for 10-15 minutes. After fine-tuning the alloy composition, maintain the white slag for 25-40 minutes. Step 3: VD refining: Maintain under vacuum of ≤67 Pa for 20-30 minutes, with weak argon stirring for 15-25 minutes. After breaking the vacuum, determine the hydrogen [H] ≤2 ppm. The weak stirring intensity is 30-100 NL / min, based on the condition that the slag surface shows obvious creep and the molten steel is not exposed. The tapping temperature is 1570-1590℃. Step 4: Ingot casting: When the tapping temperature reaches 1540-1560℃, perform ladle casting. Add 1.3-1.8 kg / t of protective slag to the casting head. When the casting head is 1 / 4-1 / 3 full, add 1.0-1.5 kg / t of heating agent. Cast into flat ingots with an ingot size of 400-550 mm. After casting, remove the cap and loosen the ingot for 3.5-7.0 hours. Step 5: Profile billet making: Heat the steel ingot to 1260-1300℃ and hold for 3.0-4.0 hours. Then perform the first rolling to form a slab. The final rolling temperature of the first rolling is 1000-1100℃. After the first rolling, perform a second reheating at 1220-1260℃. Hold the slab for 2.5-3.5 hours. After the second reheating, it is the initial rolling. The billet is then stacked and cooled, and the surface is ground with a grinding wheel at room temperature. The thickness of the billet and the finished product are 4 to 23. Step 6: Hot rolling of the billet: The billet is sent to the hot rolling line for heating at a temperature of 1240±10℃ for 9-11 min / mm. The heated billet is descaled by high-pressure water in the roughing mill to remove the iron oxide scale generated on the surface of the billet. The hot rolling process is used to roll it into a steel plate of a length with a final rolling temperature of 850-900℃. The plate is then naturally cooled to room temperature on a cooling bed for flaw detection. Step 7: Tempering heat treatment: Tempering is carried out in a nitrogen radiant tube protected heating furnace at a temperature of 590±20℃ for 20±2 min.

[0008] The chemical composition (by mass percentage) of the low-carbon alloy hot-rolled steel plate for quench-free fan blades is as follows: C: 0.13–0.18%, Si: 0.17–0.37%, Mn: 1.20–1.50%, Al: 0.020–0.060%, P: ≤0.015%, S: ≤0.010%, Cr: 0.70–1.00%, Mo: 0.35–0.50%, Ni: 1.10–1.50%, V: 0.05–0.10%, Cu: ≤0.25%, with the balance being Fe and unavoidable impurity elements.

[0009] The beneficial effects of this invention are: 1. This invention achieves high steel purity and uniformity by rationally applying the electric furnace smelting-LF+VD ladle refining-mold casting process; it designs and develops steel ingot billet opening, rolling cooling and tempering heat treatment processes, and realizes a quench-free manufacturing method for low carbon alloy steel plate 15MnNiCrMoV for wind turbine blades.

[0010] 2. The 15MnNiCrMoV low-carbon alloy steel plate for wind turbine blades of the present invention has the characteristics of high strength, high plasticity, high hardness and good processing and weldability. Its tempered yield strength is Rel: 750-850MPa, tensile strength Rm: 900-1000MPa, elongation A: 14-17%, and hardness HB 280-310, which meets the processing and use requirements of steel for wind turbine blades.

[0011] 3. The low-carbon alloy steel plate 15MnNiCrMoV for wind turbine blades of the present invention is produced by hot rolling and tempering process, and the tempered microstructure is bainite and pearlite.

[0012] 4. The quench-free manufacturing method of low-carbon alloy hot-rolled steel plate for wind turbine blades of the present invention, compared with the conventional quenching and tempering process, ensures the quality requirements of the steel for blades while having higher production efficiency and lower manufacturing cost. Detailed Implementation

[0013] The typical process for 15MnNiCrMoV steel plates includes electric furnace smelting, ladle refining, ingot casting, electroslag remelting, billet preparation, rolling, quenching, and tempering. This invention eliminates the traditional electroslag remelting and quenching processes, providing a quench-free manufacturing method for low-carbon alloy hot-rolled steel plates used in wind turbine blades. This significantly improves production efficiency and substantially reduces costs while ensuring the quality and performance requirements of the steel used in the blades.

[0014] This invention achieves high steel purity and uniformity by rationally applying the electric furnace smelting-LF+VD ladle refining-ingot casting process; it designs and develops steel ingot billet opening, rolling cooling and tempering heat treatment processes to obtain a tempered microstructure of bainite and pearlite.

[0015] The 15MnNiCrMoV low-carbon alloy steel plate for wind turbine blades produced by this manufacturing method has the characteristics of high strength, high plasticity, high hardness and good processing and weldability. Its tempered yield strength Rel: 750-850MPa, tensile strength Rm: 900-1000MPa, elongation A: 14-17%, and hardness HB 280-310, which meets the processing and use requirements of steel for wind turbine blades.

[0016] This invention relates to a method for manufacturing low-carbon alloy steel plates for wind turbine blades that have high strength, plasticity, and good processing and weldability, specifically a method for manufacturing 15MnNiCrMoV low-carbon alloy steel plates for high-speed wind turbine blades without quenching.

[0017] To achieve the above objectives, this invention provides a heat treatment method for low-carbon alloy steel plates (15MnNiCrMoV) for wind turbine blades, involving electric furnace refining, ladle refining, ingot casting, ingot billet preparation, hot rolling, and tempering. The specific process flow is as follows: electric furnace → LF → VD → ingot casting flat ingots, hot-rolled ingot homogenization → billet rolling → post-rolling cooling and finishing, cold billet reheating → descaling → rolling → tempering heat treatment. This method yields high strength and ductility with a moderate hardness of HB 280-310, exhibiting excellent weldability and meeting the requirements for manufacturing high-speed wind turbine blades. It eliminates the need for electroslag remelting of ingots and quenching of steel plates, significantly reducing production costs. The achievable dimensions are: steel strip thickness 6.0–50.0 mm, width 1600–4000 mm.

[0018] This invention provides a method for manufacturing low-carbon alloy hot-rolled steel plates for wind turbine blades. The chemical composition of the steel grade, in terms of mass percentage (%), is as follows: C: 0.13-0.18; Si: 0.17-0.37; Mn: 1.20-1.50; Al: 0.020-0.060; P: ≤0.015; S: ≤0.010; Cr: 0.70-1.00; Mo: 0.35-0.50; Ni: 1.10-1.50; V: 0.05-0.10; Cu: ≤0.25; with the balance being Fe and unavoidable impurity elements.

[0019] During the electric arc furnace smelting process, a hot charging and molten oxygen combined process is adopted. The amount of molten iron charged is controlled at 50-75%, and the electric arc furnace capacity is 70-80 tons. The amount of molten iron charged is 50-75% of the electric arc furnace capacity (the lower limit specified by Taiyuan Iron & Steel Group, usually the amount of molten iron charged is ≥70%). Foam slag is used for desulfurization and dephosphorization. During the tapping process, lime, ferromolybdenum, nickel plate, and deoxidizer are added with the steel stream. After tapping, the molten steel is stirred with a large amount of argon gas for 1-3 minutes to ensure that the P content of the tapped steel is ≤0.010% and the C content is 0.09-0.13%.

[0020] Argon is blown at the LF station, and calcium carbide-based weak calcium carbide slag and deoxidizer are added evenly into the furnace. The amount of calcium carbide-based weak calcium carbide slag added is 120-150 kg, and aluminum shot is added at 100-150 kg. After the reduction slag is formed, the alloy composition is finely adjusted and held for 25-40 minutes.

[0021] During VD treatment, maintain a vacuum of ≤67Pa for 20-30 minutes, followed by argon-fueled soft stirring for 15-25 minutes. When the tapping temperature reaches 1540-1560℃, perform ladle casting. Add 1.3-1.8 kg / t of composite protective slag during the ladle casting process. When the ladle is filled to 1 / 4-1 / 3 of its capacity, add 1.0-1.5 kg / t of exothermic agent and cast into a flat ingot. After casting, allow 3.5-7.0 hours for removing the ladle cap and loosening the ingot.

[0022] This method involves heating the steel ingot to 1260–1300℃, holding the slab at this temperature for 3.0–4.0 hours, and maintaining the slab at 1260–1300℃ for 30–40 minutes; the initial final rolling temperature is 1000–1100℃; the secondary reheating temperature is 1220–1260℃, holding the slab at this temperature for 2.5–3.5 hours, and maintaining the slab at 1220–1260℃ for 30–50 minutes; rapid rolling is then performed at a final rolling temperature of 850–900℃, followed by natural cooling on a cooling bed. The tempering temperature is 560–620℃, and the tempering time is ≤30 minutes. The ratio of initial rolled slab thickness to finished product thickness is 4–23.

[0023] Through a process control involving electric furnace smelting, ladle refining, ingot casting, ingot roughing, hot rolling, and tempering, high-purity, high-strength, ductile, and well-processed and weldable hot-rolled steel sheets are obtained. Producible sizes include steel strips with thicknesses of 6.0–50.0 mm and widths of 1600–4000 mm. The microstructure consists of bainite and pearlite.

[0024] Its tempered mechanical properties are as follows: yield strength Rel: 750-850MPa, tensile strength Rm: 900-1000MPa, elongation A: 14-17%, hardness HB280-310, which meets the processing and use requirements of steel for high-speed wind turbine blades.

[0025] The technical features are as follows: During the electric arc furnace smelting process, a hot charging and molten oxygen combined process is adopted, with a hot iron charging rate of 50-75%. Foamy slag is used for desulfurization and dephosphorization. During the tapping process, lime, ferromolybdenum, and deoxidizer are added with the steel stream. After tapping, the molten steel is stirred with a large amount of argon gas for 1-3 minutes to ensure that the tapped steel has a P content of ≤0.010% and a C content of 0.09-0.13%. Argon is blown at the LF station, and calcium carbide is evenly added into the furnace to create a weak calcium carbide slag and deoxidizer. The amount of calcium carbide added is 120-150 kg, and aluminum shot is added at 100-150 kg. After the reducing slag forms, the white slag is maintained for 25-40 minutes after fine-tuning the alloy composition for 10-15 minutes. During the VD treatment, the process is maintained under a vacuum of ≤67 Pa for 20-30 minutes, with argon gas soft stirring for 15-25 minutes. When the tapping temperature reaches 1540-1560℃, ladle casting is performed. Add 1.3-1.8 kg / t of composite protective slag during the hanging process. When the cap is poured to 1 / 4-1 / 3, add 1.0-1.5 kg / t of exothermic agent and mold it into a flat ingot. After steel pouring is completed, the cap removal and ingot loosening time is 3.5-7.0 hours.

[0026] The steel ingots are sent to the profile mill for homogenization to 1260–1300℃, and the slabs are held at this temperature for 3.0–4.0 hours. They are then subjected to initial rolling, with a final rolling temperature of 1000–1100℃. The initial rolled slabs are then stacked and cooled, followed by surface grinding. The initial rolled slabs are then heated to 1220–1260℃ for 9–11 minutes per mm (thickness 110–200 mm). They are then rapidly rolled at a final rolling temperature of 850–900℃ and allowed to cool naturally on a cooling bed. The tempering temperature is 560–620℃, and the tempering time is ≤30 minutes.

[0027] This invention provides a method for manufacturing 15MnNiCrMoV alloy steel plates for wind turbine blades without quenching by designing and controlling electric furnace smelting, ladle refining, die casting, and hot rolling + tempering processes of the initial rolled billet, thereby obtaining ideal microstructure and properties that meet the requirements of high-speed blade steel processing.

[0028] The specific embodiments of the present invention are described in detail below with reference to examples, but the specific embodiments of the present invention are not limited to the following examples. Example 1

[0029] The technical features of the 15MnNiCrMoV alloy steel plate for quench-free fan blades of the present invention are described in detail below with reference to this embodiment. The mass percentage (%) of the chemical composition of the steel ingot in this embodiment is as follows: C: 0.16, Si: 0.24, Mn: 1.28, P: 0.007, S: 0.003, Al: 0.035, Cr: 0.72, Mo: 0.36, Ni: 1.26, V: 0.06, H: 0.5ppm; the balance is Fe and unavoidable impurity elements.

[0030] In this embodiment, the middle plate is 12.0 mm thick, 1800 mm wide, and 7000 mm long.

[0031] Its tempered yield strength is 777 MPa, tensile strength is 973 MPa, elongation is 15.5%, average hardness is 300 HB, and impact toughness is 44 J, which meets the processing and manufacturing requirements of blade steel.

[0032] This embodiment was carried out in conjunction with the ladle refining, hot rolling medium and heavy plate line, and tempering line of Taiyuan Iron & Steel Group's 80-ton electric arc furnace. It includes the following sequential steps: 1. Electric arc furnace smelting: A hot charging and molten oxygen combined process is adopted, with a molten iron charging rate of 65%. Slag formation and dephosphorization are performed in advance during the melting period. High-temperature uniform boiling is achieved during the oxidation period. During tapping, a portion of the alloys, calculated according to the lower limit of the composition, is added with the steel stream: Al: 0.025%, Mo: 0.36%, Mn: 1.26%, Ni: 1.12%. This ensures that the tapped steel contains P ≤ 0.010% and C: 0.09-0.13%.

[0033] 2. LF Refining: Argon is blown at the LF station, and calcium carbide is added evenly to the furnace to form weak calcium carbide slag and deoxidizer. The amount of calcium carbide added is 130 kg, and the amount of aluminum shot added is 140 kg. After the reduction slag is formed, hold for 10-15 minutes. After the alloy composition is finely adjusted, the holding time is 30 minutes.

[0034] 3. VD refining: Maintain a vacuum of ≤67 Pa for 25 min, followed by argon-fueled gentle stirring for 18 min. The gentle stirring should be sufficient to achieve noticeable creep on the slag surface without exposing the molten steel. After breaking the vacuum, determine the hydrogen concentration; [H] ≤2 ppm.

[0035] 4. Ingot Casting: When the tapping temperature reaches 1540-1560℃, pour the ingot using a ladle. Add 1.5 kg / t of composite protective slag during the pouring process. When the ladle is filled to 1 / 4-1 / 3 of its capacity, add 1.2 kg / t of exothermic agent. Cast the ingot into a 7.2-ton flat ingot with a diameter of 400-550 mm. After casting, remove the ladle cap and loosen the ingot for 4.0 hours.

[0036] 5. Section billet preparation: The steel ingot is sent to the section mill for homogenization to 1290±10℃, and the slab is kept warm for 200 minutes; the billet is rolled, the initial rolling thickness is 135mm, and the final rolling temperature is 1120℃; the initial rolling slab is stacked and cooled, and the surface is ground with a grinding wheel.

[0037] 6. Hot Rolling of the Preliminary Billet: The preliminary billet is sent to the hot rolling line for heating at a temperature of 1240±10℃. The heated billet is then descaled using high-pressure water in the roughing mill to remove the iron oxide scale formed on the surface of the billet. A rapid rolling process is employed to roll it into a 12*1800*7000mm long steel plate at a final rolling temperature of 867℃, followed by natural cooling on a cooling bed. The steel plate then undergoes flaw detection inspection.

[0038] 7. Tempering heat treatment: Tempering is carried out in a nitrogen-protected radiant heating furnace at a tempering temperature of 590±20℃ and a tempering time of 20±2min.

[0039] After quality and performance testing, the test results of this embodiment are as follows: its tempered yield strength is 777 MPa, tensile strength is 973 MPa, elongation is 15.5%, average hardness is 300 HB, and impact toughness is 44 J. Packaging markings must be affixed and the product placed in the warehouse before leaving the factory.

[0040] Other embodiments

[0041] The components of other embodiments are shown in Table 1.

[0042]

[0043] The above embodiments of the present invention are not intended to limit the present invention. The present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing low-carbon alloy steel plates for wind turbine blades without quenching, characterized in that: Includes the following steps: Step 1: Electric furnace smelting: A hot charging and molten oxygen combined process is adopted. The molten iron charge is 50-75%. Slag formation and dephosphorization are carried out in advance during the melting period. Uniform boiling is required at 1500-1600℃ during the oxidation period, and the oxygen blowing rate during the oxidation period is 4000-4500 m³ / h. 3 During the tapping process, alloys are added with the steel stream according to the middle and lower limits of the chemical composition mass percentage: Al: 0.02-0.04%, Mo: 0.35-0.42%, Mn: 1.2-1.35%, Ni: 1.10-1.30%, ensuring that the tapped steel has P ≤ 0.010% and C: 0.09-0.15%; the electric furnace smelting cycle is 40-60 minutes, and the tapping temperature is 1640-1680℃; Step 2: LF Refining: Argon is blown at the LF station at a flow rate of 100-300 L / min. Argon is blown throughout the process. Calcium carbide-based weak calcium carbide slag and deoxidizer are added evenly into the furnace. The amount of calcium carbide-based weak calcium carbide slag added is 120-150 kg, and the amount of deoxidizer, i.e., aluminum shot, is 100-150 kg. After the reduction slag is formed, the alloy composition is fine-tuned 10-15 min. After the alloy composition is fine-tuned, the white slag is maintained for 25-40 min. Step 3: VD refining: Maintain a vacuum of ≤67Pa for 20-30 minutes, with weak argon stirring for 15-25 minutes. After breaking the vacuum, the hydrogen concentration [H] should be ≤2ppm. The weak stirring intensity should be 30-100NL / min, with the slag surface showing obvious creep and the molten steel not exposed. The tapping temperature should be 1570-1590℃. Step 4: Ingot casting: When the tapping temperature reaches 1540-1560℃, pour the ingot using a ladle. Add 1.3-1.8 kg / t of protective slag while the ladle is suspended. When the ladle is filled to 1 / 4-1 / 3, add 1.0-1.5 kg / t of exothermic agent. Cast the ingot into a flat ingot with a diameter of 400-550 mm. After the ingot is cast, remove the ladle cap and loosen the ingot for 3.5-7.0 hours. Step 5: Profile blanking: Heat the steel ingot to 1260-1300℃ and hold for 3.0-4.0 hours. Then, perform the first rolling to form a slab. The final rolling temperature of the first rolling is 1000-1100℃. After the first rolling, perform a second reheating at 1220-1260℃ and hold the slab for 2.5-3.5 hours. After the second reheating, the slab is the initial rolled slab. Then, the initial rolled slab is stacked and cooled. The surface is then ground with a grinding wheel at room temperature. The ratio of initial rolled slab thickness to finished product thickness is 4-23. Step Six: Hot Rolling of the Initial Rolled Billet: The initial rolled billet is sent to the hot rolling line for heating at a temperature of 1240±10℃ for 9-11 min / mm. The heated billet is then descaled by high-pressure water in the roughing mill to remove the iron oxide scale generated on the surface of the billet. A rapid rolling process is then used to roll it into a steel plate of a length. The final rolling temperature is 850-900℃. The plate is then naturally cooled to room temperature on a cooling bed for flaw detection. Step Seven: Tempering Heat Treatment: Tempering is carried out in a nitrogen-radiant tube protected heating furnace at a tempering temperature of 590±20℃ for 20±2 min. The chemical composition (by mass percentage) of the low-carbon alloy hot-rolled steel plate for quench-free fan blades is as follows: C: 0.13–0.18%, Si: 0.17–0.37%, Mn: 1.20–1.50%, Al: 0.020–0.060%, P: ≤0.015%, S: ≤0.010%, Cr: 0.70–1.00%, Mo: 0.35–0.50%, Ni: 1.10–1.50%, V: 0.05–0.10%, Cu: ≤0.25%, with the balance being Fe and unavoidable impurity elements.

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