A method for controlling the cleanliness of molten steel for a cast steel part of a deep sea floating wind power platform

Abstract

This application relates to the field of metal smelting technology, specifically to a method for controlling the cleanliness of molten steel in cast steel parts for deep-sea floating wind power platforms. The method includes EAF smelting: using Grade A briquetted scrap steel as the main material, impurities are removed after melting and cleaning through slag removal and decarburization boiling, with the endpoint controlled at P ≤ 0.005%; during tapping, a silicon-calcium-barium-rare earth composite deoxidizer, refining slag agent, and active lime are added in batches along with the flow for pre-deoxidation and slag washing; LF refining: deoxidation, desulfurization, and alloying are performed, maintaining high-alkalinity white slag refining, and controlling L... The total refining time is ≥80 min, ensuring that the oxide inclusions in the molten steel before VD are T[O]≤30ppm, N≤60ppm, and S≤0.005%; VD refining: deep degassing is performed for ≥20 min under vacuum ≤67Pa; after vacuum breaking, the steel is transferred to LF for heating, during which no ferroalloys are added, and soft blowing is performed to promote the floating of inclusions; casting: argon is blown into the mold cavity for ≥20 min before casting, and an argon blowing ring device is used for sealing protection during casting. This application effectively improves the metallurgical quality of key cast steel components for deep-sea wind power.

Description

Technical Field

[0001] This application relates to the field of metal smelting technology, and more specifically, to a method for controlling the cleanliness of molten steel in cast steel parts for deep-sea floating wind power platforms. Background Technology

[0002] As a crucial direction for the future development of offshore wind power, deep-sea floating wind power relies on key cast steel components such as mooring systems, towers, and node connectors, which operate under extreme marine environments characterized by high salt spray, strong corrosion, and immense alternating loads. These critical components are not only enormous in size and have uneven wall thicknesses, but also place extremely high demands on the materials' low-temperature impact toughness, fatigue resistance, and weldability. The cleanliness of the molten steel, particularly the content of harmful elements such as phosphorus and sulfur, as well as gases and non-metallic inclusions, directly determines the internal density and mechanical stability of the cast steel components, making it a core element for ensuring the safe operation of deep-sea wind power equipment.

[0003] Currently, the conventional smelting process for producing such large cast steel parts in China typically employs an electric arc furnace (EAF) for primary refining, an LF refining process, and a vacuum degassing process (VD). While this process provides basic deoxidation, desulfurization, and degassing capabilities, significant technical bottlenecks remain in achieving the ultimate cleanliness control required for ultra-low phosphorus, ultra-low sulfur, and extremely low inclusion content during actual production. Particularly when dealing with large, thick-walled castings for ultra-high-power wind turbines exceeding 16MW, conventional processes often struggle to guarantee the uniformity of the core microstructure, leading to inclusion accumulation or internal cracks caused by excessive gas levels.

[0004] Therefore, a new method for controlling the cleanliness of molten steel is urgently needed to solve the above problems. Summary of the Invention

[0005] This application achieves coordinated control of molten steel cleanliness throughout the entire process from tapping to casting. This method effectively solves the steel contamination problems caused by residual deoxidation products, secondary oxidation, and gas absorption during casting in traditional processes. It significantly reduces the content of phosphorus, sulfur, gases, and non-metallic inclusions in the steel, ultimately resulting in a substantial improvement in the internal density, low-temperature impact toughness, and fatigue resistance of key cast steel components for deep-sea floating wind power platforms, ensuring the service safety of large cast steel components in extreme marine environments.

[0006] A method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform includes the following steps: EAF smelting: using Grade A briquetted scrap steel as the main material, after melting and cleaning, impurities are removed by slag flow and decarburization boiling, with the final control P≤0.005%; during tapping, silicon-calcium-barium-rare earth composite deoxidizer, refining slag agent and active lime are added in batches along with the flow for pre-deoxidation and slag washing. LF refining: Deoxidation, desulfurization, and alloying are carried out to maintain high-basicity white slag refining. The total LF refining time is controlled to be ≥80 min, and the oxide inclusion content in the molten steel before VD is ensured to be T[O]≤30ppm, N≤60ppm, and S≤0.005%. VD refining: Deep degassing is performed for ≥20 minutes under vacuum degree ≤67Pa; after breaking the vacuum, it is transferred to LF for heating, during which no iron alloy is added, and soft blowing is performed to promote the floating of inclusions; Pouring: Before pouring, blow argon into the mold cavity for ≥20 minutes, and use an argon blowing ring device for sealing protection during pouring.

[0007] Preferably, in the EAF smelting step, the proportion of recycled material of the same steel grade added is ≤20%; during the oxygen blowing decarburization process, ≥90% of the oxide slag is discharged through the inclined furnace door to ensure that the decarburization amount is ≥0.40%; and the endpoint control is C>0.05%.

[0008] Preferably, in the EAF smelting step, 1~3 kg / t of silicon-calcium-barium-rare earth composite deoxidizer, 1~2 kg / t of refining slag agent and 4~6 kg / t of active lime are added with the steel during tapping; half of the silicon-calcium-barium-rare earth composite deoxidizer is added when 1 / 3 of the steel is tapped, and the remaining part is added before 2 / 3 of the total amount of molten steel is added.

[0009] Preferably, in the LF refining step, after the oxygen activity of the molten steel is ≤10ppm, ferrosilicon, electrolytic manganese, or high-carbon ferromanganese is added to adjust the Si and Mn element content.

[0010] Preferably, in the VD refining step, the slag layer thickness is controlled at 150~250mm, and the free space of the ladle is 1000~1200mm.

[0011] Preferably, in the soft blowing operation after vacuum breaking in the VD refining step, the argon flow rate is controlled at 80~150NL / min, and the soft blowing time is ≥20min, so that the molten steel is slightly agitated without breaking the slag surface.

[0012] This application employs key technologies such as the batch-addition of a silicon-calcium-barium rare-earth composite deoxidizer, strict control over the addition of alloys after vacuum breaking in VD (Vacuum Deoxidation), and argon gas sealing protection throughout the casting process. These technologies achieve coordinated control of molten steel cleanliness throughout the entire process, from tapping to casting. This method effectively solves the steel contamination problems caused by residual deoxidation products, secondary oxidation, and gas absorption during casting in traditional processes. It significantly reduces the content of phosphorus, sulfur, gases, and non-metallic inclusions in the steel, ultimately resulting in a substantial improvement in the internal density, low-temperature impact toughness, and fatigue resistance of key cast steel components for deep-sea floating wind power platforms, ensuring the service safety of large cast steel components in extreme marine environments. Attached Figure Description

[0013] Figure 1This is a flowchart illustrating the method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform provided in this application embodiment. Detailed Implementation

[0014] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0015] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "top," "bottom," "end," "top," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0017] Please refer to Figure 1 , Figure 1 This is a flowchart illustrating the method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform provided in this application embodiment.

[0018] The following describes the method for controlling the cleanliness of molten steel in key cast steel components of the deep-sea floating wind power platform provided in this application, with reference to specific embodiments. In this embodiment, ASTM A148 90-60 material is selected as an example, and the specific chemical composition is shown in Table 1: standard ≤0.18 ≤0.60 ≤1.8 ≤0.025 ≤0.010 ≤0.50 ≤0.30 element O% N% Al% Cu% Sb% Ti% Sn% standard ≤80ppm ≤0.0150 ≤0.030 ≤0.25 ≤0.001 ≤0.025 ≤0.015 element V% Nb% V+Nb% As% standard ≤0.05 ≤0.025 ≤0.10 ≤0.025 The control method in this embodiment adopts a process flow of "ultra-high power electric arc furnace (EAF) primary refining → LF ladle refining → VD vacuum degassing → casting". The specific steps are as follows: S1: EAF smelting.

[0019] EAF employs an oxidation smelting process. The furnace charge primarily consists of rust-free, oil-free, and paint-free Grade A compressed scrap steel, with a ≤20% proportion of recycled steel of the same grade added. The content of residual elements such as Sb, Sn, Pb, and As is controlled. 5-8% lime, 1-2 kg / t fluorite, and 1.0-1.5% carburizing agent are added with the initial charge. After the charge is melted and cleared, samples are taken to analyze the C and P content. Low-temperature dephosphorization and high-temperature decarburization operations are performed sequentially. During oxygen blowing decarburization, the furnace door should be tilted to remove more than 90% of the oxide slag. The decarburization rate during the oxidation period should be ≥0.40%. The purpose is to utilize the boiling of the molten steel formed by the decarburization reaction to achieve degassing and inclusion removal. After oxygen blowing, samples are taken to analyze the C and P content, controlling the endpoint C>0.05% and P≤0.005%. Subsequently, 2-4% lime is added again to cover the molten steel, reducing the steel's gas absorption (H / N) and phosphorus reversion. The steel is then tapped at 1600-1650℃. Before tapping, a slag-closing operation is performed. During tapping, 1-3 kg / t of silicon-calcium-barium-rare earth composite deoxidizer, 1-3 kg / t of refining slag agent, and 4-6 kg / t of quicklime are added to the ladle. When 1 / 3 of the steel has been tapped, 1 / 2 of the silicon-calcium-barium-rare earth composite deoxidizer is added first, and the remainder is added in 2-3 batches before 2 / 3 of the total steel volume is reached. When 1 / 2 of the steel has been tapped, the refining slag agent and quicklime are added to the ladle in 2-3 batches, and these are added as much as possible before 2 / 3 of the total steel volume is reached to ensure sufficient time for melting and reaction in the ladle. After all the slag and reducing agent have been added, the argon pressure should be increased appropriately. Argon gas stirring is used to ensure that the argon gas fully contacts and reacts with the molten steel, which is beneficial for the flotation of inclusions and the removal of gases.

[0020] S2: LF Refined.

[0021] The main tasks of this process are deoxidation, desulfurization, and alloying. After the ladle undergoes LF (sulfurization-free annealing), the oxygen activity of the molten steel is first measured using an oxygen analyzer. Then, depending on the situation, 1-2 kg / t of aluminum, 1-2 kg / t of aluminum-calcium alloy balls, and an appropriate amount of carbon powder are added for deoxidation. Next, 20-40 kg / t of active lime and 3-8 kg / t of fluorite are added to adjust the slag basicity to between 3.0 and 6.0. The refining time for high-basicity white slag is maintained at ≥15 min, controlling S ≤0.005% and [Al]s 0.020-0.040%. When the molten steel temperature is ≥1580℃ and the oxygen activity is ≤10 ppm, samples are taken for chemical composition analysis. After the molten steel has been fully deoxidized, ferrosilicon, electrolytic manganese, or high-carbon ferromanganese is added to adjust the Si and Mn element content to prevent the formation of large amounts of non-metallic inclusions SiO2 and MnS that are difficult to remove from the steel. The entire refining time in the LF furnace must be ≥80 min.

[0022] S3: VD Refined.

[0023] Before VD refining, the steel contains T[O]≤40ppm, N≤100ppm, and S≤0.008%. After the chemical composition is adjusted to meet the requirements, the molten steel is heated to 1650~1720℃ and then transferred to VD refining (T[O] can generally be used to indirectly evaluate the amount of oxide inclusions in the steel).

[0024] During VD refining, the slag layer thickness should be controlled at 200-400 mm. Increasing the slag thickness hinders the removal of H, N, and O from the steel. The slag should not be too sticky or too thin; high viscosity weakens its ability to adsorb non-metallic inclusions, while excessively thin slag easily corrodes the ladle refractory material. Furthermore, ensure a free space of 1000-1200 mm in the ladle. During vacuuming, simultaneously adjust the vacuum level using a Roots pump and adjust the argon supply intensity to prevent severe slag overflow. When the vacuum degree is ≤67Pa, maintain the high vacuum time for ≥20min to improve the degassing and inclusion removal capabilities. After breaking the vacuum, measure the temperature and take samples for full element analysis. Then transfer to LF for power supply and heating. During this period, no ferroalloys should be added. If carbon is insufficient, electrodes can be used to increase carbon. Control the argon flow rate to 80~200NL / min for soft blowing operation for ≥20min to promote the full floating of non-metallic inclusions in the steel. During the process, control the argon pressure in the ladle to not be too high, mainly to make the molten steel tumble slightly without breaking the slag surface, to prevent the molten steel from violently rolling and absorbing gas. After confirming that the chemical composition and molten steel temperature meet the process requirements, the steel can be tapped and poured. After vacuum degassing (VD) treatment, the H, O, and N contents in the molten steel are reduced, achieving H≤2ppm, N<40ppm, and T[O]≤20ppm.

[0025] S4: Pouring.

[0026] Inclusions formed by secondary oxidation of molten steel during the pouring process have a significant impact on the internal quality of the casting. Before the molten steel is transferred to the pouring site, the casting cavity should be purged with argon for at least 20 minutes. During the pouring process, an argon ring should be used to protect the molten steel and prevent secondary oxidation. Simultaneously, the size of the tundish nozzle should be adjusted promptly according to the molten steel flow to prevent backflow and ensure a smooth pouring process.

[0027] This application effectively improves the quality of crude steel produced in the electric arc furnace (EAF) by using high-quality raw materials, increasing decarburization during the oxidation period, controlling the final carbon content (>0.05%) and phosphorus content (≤0.005%), and implementing nitrogen prevention measures. During tapping, a silicon-calcium-barium-rare-earth composite deoxidizer is used for pre-deoxidation, and refining slag washing further treats the crude steel. This reduces oxygen activity in the molten steel and facilitates the removal of non-metallic inclusions, improving smelting efficiency and metallurgical quality in the subsequent LF refining furnace. Furthermore, through VD… Vacuum treatment reduces the H, N, and O content in steel, ultimately achieving high cleanliness indicators such as P≤0.003%, S≤0.0004%, T[O]≤20ppm, N<40ppm, H≤2ppm, inclusion area content ≤0.06%, and inclusion grade coarse series ≤0.5 and fine series ≤1.0. This solves the technical difficulty of simultaneously meeting the requirements of low phosphorus, low sulfur, low gas, and low inclusions, satisfying both customer technical specifications and the company's production technical challenges.

[0028] Using the technical solution provided in this application, the phosphorus and sulfur content of the molten steel is extremely low, the gas content (H, N, O) is significantly lower than that of the comparative example, and the area content of non-metallic inclusions is greatly reduced. This indicates that this application, through cleanliness control throughout the entire process, especially the composite deoxidation of EAF, alloy-free heating after VD, and soft blowing process, effectively improves the metallurgical quality of key cast steel components for deep-sea wind power, meeting the requirements for use under extreme operating conditions.

[0029] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0030] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform, characterized in that, Includes the following steps: E AF smelting: using Grade A briquetted scrap steel as the main material, after melting and cleaning, impurities are removed by slag flow and decarburization boiling, with the final control P≤0.005%; during tapping, silicon-calcium-barium-rare earth composite deoxidizer, refining slag agent and active lime are added in batches along with the flow for pre-deoxidation and slag washing. LF refining: Deoxidation, desulfurization, and alloying are carried out to maintain high-basicity white slag refining. The total LF refining time is controlled to be ≥80 min, and the oxide inclusion content in the molten steel before VD is ensured to be T[O]≤30ppm, N≤60ppm, and S≤0.005%. VD refining: Deep degassing is performed for ≥20 minutes under vacuum degree ≤67Pa; after breaking the vacuum, it is transferred to LF for heating, during which no iron alloy is added, and soft blowing is performed to promote the floating of inclusions; Pouring: Before pouring, blow argon into the mold cavity for ≥20 minutes, and use an argon blowing ring device for sealing protection during pouring.

2. The method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform according to claim 1, characterized in that, In the EAF smelting process, the proportion of recycled material of the same steel grade added is ≤20%; during the oxygen blowing decarburization process, ≥90% of the oxide slag is discharged through the inclined furnace door to ensure that the decarburization amount is ≥0.40%; the endpoint control is C>0.05%.

3. The method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform according to claim 1, characterized in that, In the EAF smelting step, 1~3 kg / t of silicon-calcium-barium-rare earth composite deoxidizer, 1~2 kg / t of refining slag agent and 4~6 kg / t of active lime are added with the steel during tapping; half of the silicon-calcium-barium-rare earth composite deoxidizer is added when 1 / 3 of the steel is tapped, and the remaining part is added before 2 / 3 of the total amount of molten steel is added.

4. The method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform according to claim 1, characterized in that, In the LF refining step, after the oxygen activity of the molten steel is ≤10ppm, ferrosilicon, electrolytic manganese or high-carbon ferromanganese are added to adjust the Si and Mn element content.

5. The method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform according to claim 1, characterized in that, In the VD refining step, the slag layer thickness is controlled at 150~250mm, and the free space of the ladle is 1000~1200mm.

6. The method for controlling the cleanliness of molten steel in key cast steel components of a deep-sea floating wind power platform according to claim 1, characterized in that, In the soft blowing operation after breaking the vacuum in the VD refining step, the argon flow rate is controlled at 80~150NL / min, and the soft blowing time is ≥20min, with the molten steel slightly agitated without breaking the slag surface.

Images