A thin slab continuous casting method

Abstract

The application provides a thin slab continuous casting method and belongs to the field of continuous casting. The method comprises the following steps: casting molten steel, and determining the type of the protective slag according to the casting speed of the caster during the casting process; when the casting speed of the caster is less than 4.5 m / min, the protective slag is a first protective slag; the viscosity of the first protective slag at 1300 DEG C is 0.10 Pa.s-0.20 Pa.s; when the casting speed of the caster is greater than or equal to 4.5 m / min, the protective slag is a second protective slag; the viscosity of the second protective slag at 1300 DEG C is 0.04 Pa.s-0.08 Pa.s. By adding the protective slag in two stages, the lubrication and heat transfer effect at low casting speed can be met, and the consumption of the protective slag, heat transfer and the thickness of the liquid slag layer at high casting speed can be met. Thus, the lubrication performance and heat transfer performance of the protective slag at different casting speeds can be effectively balanced, and the surface quality of the cast slab is improved.

Description

Technical Field

[0001] This application relates to the field of continuous casting technology, and in particular to a method for continuous casting of thin slabs. Background Technology

[0002] Shougang's thin slab continuous casting and rolling equipment is a world-first third-generation thin slab continuous casting and rolling production line built on the existing second-generation TSCR technology, integrating the most cutting-edge technologies in continuous casting and rolling. It features multiple production modes: single-slab production, semi-endless production, and fully endless production. This production line uses endless rolling, primarily producing high-quality, high-strength, and ultra-thin products; it achieves hot rolling instead of cold rolling, enabling the production of high-end thin-gauge hot-rolled products, while also producing products with high surface quality, good shape, and uniform and stable properties in all directions. It mainly includes three categories: thin-gauge hot-rolled coils, hot-rolled pickled plates, and hot-dip galvanized plates. The fully endless rolling specifications range from 0.8-4.0mm, and the varieties include: automotive structural steel, high-strength steel, weathering steel, pickled substrate, two-dimensional steel, high-expansion steel, medium-manganese steel, martensitic steel, and cold-rolled base materials. The casting machine is a straight-arc type with an arc radius of 5.5m. The ladle and tundish capacities are 200t and 70t respectively. The crystallizer is a long funnel type, and the billet size ranges from (900~1600)×(110~123)mm, with a metallurgical length of 26.567m. It employs a dual-mode fusion pressing technology, namely, fan-shaped 0-1 stage liquid core pressing and light pressing at the solidification end, to achieve the purpose of thinning and improving internal quality.

[0003] However, due to the small cross-sectional thickness of the crystallizer in the thin slab continuous casting and rolling production line, the liquid level fluctuation intensifies as the casting speed increases, which can easily cause problems such as crystallizer adhesion alarm, slag entrapment defects in the cast slab, and surface cracks in the cast slab. Summary of the Invention

[0004] This application provides a method for continuous casting of thin slabs to solve the following technical problem: how to improve the surface quality of the cast slab.

[0005] This application provides a method for continuous casting of thin slabs, the method comprising:

[0006] Molten steel is poured into the casting machine, and during the pouring process, the type of protective slag is determined according to the casting machine speed.

[0007] When the casting machine speed is <4.5m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300℃ is 0.10Pa·s~0.20Pa·s;

[0008] When the casting machine speed is ≥4.5m / min, the protective slag is a second protective slag; the viscosity of the second protective slag at 1300℃ is 0.04Pa·s~0.08Pa·s.

[0009] Optionally, the chemical composition of the first protective slag, by mass fraction, includes: CaO: 25.0%–35.0%, SiO2: 24.0%–28.0%, Al2O3: 4.0%–8.0%, MgO: 5.0%–9.0%, MnO: 1.0%–3.0%, NaO2+K2O: 5.0%–9.0%, LiO2<5.0%, C: 4.0%–6.0%, with the balance being unavoidable impurities.

[0010] Optionally, the melting point of the first protective slag is 1000℃~1100℃.

[0011] Optionally, the basicity of the first protective slag is 1.05 to 1.15.

[0012] Optionally, the chemical composition of the first protective slag, by mass fraction, is as follows: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, with the balance being unavoidable impurities; the melting point of the first protective slag is 1038℃, the viscosity of the first protective slag at 1300℃ is 0.10 Pa·s, and the basicity of the first protective slag is 1.10.

[0013] Optionally, the chemical composition of the second protective slag, by mass fraction, includes: CaO: 30.0%–35.0%, SiO2: 25.0%–30.0%, Al2O3: 4.0%–8.0%, MgO: 6.0%–8.0%, MnO: 0.05%–0.20%, NaO2+K2O: 6.0%–10.0%, LiO2<5.0%, C: 4.0%–6.0%, with the balance being unavoidable impurities.

[0014] Optionally, the melting point of the second protective slag is 950℃~1050℃.

[0015] Optionally, the basicity of the second protective slag is 1.25 to 1.35.

[0016] Optionally, the chemical composition of the second protective slag, by mass fraction, is as follows: CaO: 32.9%, SiO2: 27.2%, Al2O3: 6.4%, MgO: 5.9%, MnO: 0.10%, NaO2+K2O: 8.2%, LiO2: 0.88%, C: 5.23%; the melting point of the second protective slag is 1005℃, the viscosity of the second protective slag at 1300℃ is 0.06 Pa·s, and the basicity of the second protective slag is 1.29.

[0017] Optionally, the molten steel is molten steel for low-carbon steel.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art:

[0019] This application provides a method for continuous casting of thin slabs, comprising: casting molten steel, and during the casting process, determining the type of protective slag according to the casting machine speed; when the casting machine speed is <4.5 m / min, the protective slag is a first protective slag; the viscosity of the first protective slag at 1300℃ is 0.10 Pa·s to 0.20 Pa·s; when the casting machine speed is ≥4.5 m / min, the protective slag is a second protective slag; the viscosity of the second protective slag at 1300℃ is 0.04 Pa·s to 0.08 Pa·s. By adding the protective slag in two stages, both the lubrication and heat transfer effects at low casting speeds and the consumption, heat transfer, and slag layer thickness of the protective slag at high casting speeds can be satisfied. This effectively balances the lubrication and heat transfer performance of the protective slag at different casting speeds, thereby improving the surface quality of the cast slab. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart of a thin slab continuous casting method provided in an embodiment of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0025] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0027] High-speed thin slab continuous casting has attracted significant attention and widespread interest in the steel industry due to its outstanding advantages such as shorter process, lower investment, lower cost, and green energy conservation and environmental protection. To achieve higher efficiency in thin slab continuous casting and rolling, the need to improve casting machine efficiency is even more urgent. A stable increase in casting speed will provide crucial support for the economic benefits of thin slab continuous casting and rolling production lines.

[0028] The mold flux for thin slab continuous casting crystallizers differs significantly from that of conventional slab continuous casting machines. This is mainly reflected in the fact that thin slab continuous casting has a higher casting speed, lower mold flux consumption, a smaller slag film thickness, and greater friction between the crystallizer and the slab. At the same time, the heat flux of the crystallizer is also significantly greater than that of conventional slab continuous casting machines at high casting speeds. Therefore, thin slab continuous casting places higher demands on the metallurgical properties of the mold flux, especially its lubrication and heat transfer properties. The performance requirements of the protective slag vary depending on the casting speed in thin slab continuous casting. Field analysis revealed that when casting low-carbon steel at a casting speed ≥4.5 m / min, the slag layer thickness significantly decreases. Traditional processes often use a single type of protective slag from the start of casting until the end, without considering the slag layer thickness and slag consumption at different casting speeds. This patent employs a two-stage low-carbon steel protective slag based on the casting speed, achieving reasonable control over the slag's melting rate, melting point, viscosity, slag layer thickness, and crystallization properties within a reasonable range. This allows the slag to flow stably into the slag film channel, ensuring lubrication and improving heat transfer, providing important guidance for increasing the casting speed of thin slabs.

[0029] Please see Figure 1 This application provides a method for continuous casting of thin slabs, the method comprising:

[0030] S1. The molten steel is poured, and during the pouring process, the type of protective slag is determined according to the casting machine speed.

[0031] This application can effectively balance the lubrication and heat transfer properties of protective slag by using protective slag with different properties at different casting speeds, thereby reducing problems such as crystallizer sticking alarms and surface cracks on the billet during the casting process, and ensuring smooth production.

[0032] In some embodiments, the molten steel is molten steel for low-carbon steel.

[0033] In the embodiments of this application, the casting process specifically involves: customizing the secondary cooling water distribution system and crystallizer vibration parameters based on the characteristics of low-carbon steel to achieve uniform cooling and reduce internal cracks. The superheat of the tundish is strictly controlled between 20 and 35°C to ensure that the liquidus temperature is stable at 1531°C, laying the foundation for subsequent high-quality billet production. Before formal casting, meticulous tundish preparation work is carried out. By checking the slag discharge in the ladle, the appropriate amount of slag is ensured, and then the ladle slide is opened, allowing the molten steel to smoothly transition to the tundish. To prevent oxidation of the molten steel in the tundish, a high-basicity low-carbon steel covering agent is added at the stopper rod position when the molten steel volume reaches 24 tons. When the tundish volume reaches 30 tons, formal casting is started, and the molten steel is slowly poured into the crystallizer. In the initial stage, a slow pouring speed of 0.8 m / min is adopted and maintained for 3 seconds to ensure the stable formation of the initial slag film. As the casting process progresses, the casting speed is increased directly from 0.8 m / min to 3.5 m / min and stabilized at this speed until the first shearing is completed. During this stage, the casting speed is increased at a rate of 1.5 m / min², aiming to quickly reach the target casting speed while ensuring that the quality of the cast billet is not affected. After the casting speed stabilizes at 4.5 m / min, it is further increased to the target casting speed of 5.6 m / min according to production needs.

[0034] S2. When the casting machine speed is <4.5m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300℃ is 0.10Pa·s~0.20Pa·s;

[0035] In some implementations, the first protective slag is added when the casting machine speed increases from 0 to 0.8 m / min.

[0036] In some embodiments, the chemical composition of the first protective slag, by mass fraction, includes: CaO: 25.0%–35.0%, SiO2: 24.0%–28.0%, Al2O3: 4.0%–8.0%, MgO: 5.0%–9.0%, MnO: 1.0%–3.0%, NaO2+K2O: 5.0%–9.0%, LiO2 < 5.0%, C: 4.0%–6.0%, with the balance being unavoidable impurities.

[0037] In some embodiments, the melting point of the first protective slag is 1000℃~1100℃.

[0038] In some embodiments, the basicity of the first protective slag is 1.05 to 1.15.

[0039] This application achieves good lubricity, melting temperature, and viscosity of the first protective slag through a rationally designed chemical composition. Good lubricity remains crucial under low casting speed conditions (<4.5 m / min) to reduce friction between the billet and the crystallizer, preventing adhesion and cracking. At lower casting speeds, the protective slag has more time to contact the molten steel, effectively absorbing non-metallic inclusions and improving billet purity. The melting temperature of the protective slag should not be too high to ensure rapid and uniform slag film formation, while maintaining a moderate viscosity for good coverage and protection. Basicity (CaO / SiO2) primarily controls crystallization performance. At high casting speeds, increased friction necessitates reducing the risk of slag entrapment while ensuring lubrication and appropriately controlling heat transfer. The basicity of the first protective slag described in this invention is achieved by increasing the CaO content, thereby raising the crystallization temperature and the proportion of crystalline phases, and suppressing heat transfer. For example, the content of CaO can be 25.0%, 27.0%, 29.0%, 30.0%, 32.0%, 34.0%, 35.0%, etc.; the content of SiO2 can be 24.0%, 25.0%, 26.0%, 27.0%, 28.0%, etc.; the content of Al2O3 can be 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, etc.; and the content of MgO can be 5.0%, 6.0%, 7.0%, 8.0%, etc. The content of MnO can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc., the sum of NaO2 and K2O content can be 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, etc., the content of LiO2 can be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc., and the content of C can be 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, etc. The viscosity of the first protective slag at 1300℃ can be 0.10 Pa·s, 0.12 Pa·s, 0.14 Pa·s, 0.16 Pa·s, 0.18 Pa·s, 0.20 Pa·s, etc.; the melting point of the first protective slag can be 1000℃, 1020℃, 1040℃, 1060℃, 1080℃, 1100℃, etc.; and the basicity of the first protective slag can be 1.05, 1.07, 1.09, 1.10, 1.12, 1.14, 1.15, etc.

[0040] In some embodiments, the chemical composition of the first protective slag, by mass fraction, is as follows: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, with the balance being unavoidable impurities; the melting point of the first protective slag is 1038℃, the viscosity of the first protective slag at 1300℃ is 0.10 Pa·s, and the basicity of the first protective slag is 1.10.

[0041] S3. When the casting machine speed is ≥4.5m / min, the protective slag is a second protective slag; the viscosity of the second protective slag at 1300℃ is 0.04Pa·s~0.08Pa·s.

[0042] In some embodiments, the chemical composition of the second protective slag, by mass fraction, includes: CaO: 30.0%–35.0%, SiO2: 25.0%–30.0%, Al2O3: 4.0%–8.0%, MgO: 6.0%–8.0%, MnO: 0.05%–0.20%, NaO2+K2O: 6.0%–10.0%, LiO2 < 5.0%, C: 4.0%–6.0%, with the balance being unavoidable impurities.

[0043] In some embodiments, the melting point of the second protective slag is 950°C to 1050°C.

[0044] In some embodiments, the basicity of the second protective slag is 1.25 to 1.35.

[0045] This application achieves lower melting temperature, excellent fluidity, and low viscosity in the second protective slag through a rationally designed chemical composition. Under high casting speeds (4.5 m / min to 6.0 m / min), the protective slag must possess a lower melting temperature and excellent fluidity to rapidly cover the crystallizer surface and form a stable slag film to cope with more severe liquid surface disturbances. At high casting speeds, the protective slag must maintain a low viscosity and be uniformly distributed within the crystallizer to avoid cracks and steel adhesion caused by localized overheating or uneven cooling. For example, the content of CaO can be 30.0%, 31.0%, 32.0%, 33.0%, 33.5%, 34.0%, 35.0%, etc.; the content of SiO2 can be 25.0%, 26.0%, 27.0%, 28.0%, 29.0%, 30.0%, etc.; the content of Al2O3 can be 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, etc.; and the content of MgO can be 6.0%, 6.5%, 7.0%, 7.0%, etc. The content of MnO can be 0.05%, 0.08%, 0.10%, 0.15%, 0.20%, etc.; the sum of the contents of NaO2 and K2O can be 6.0%, 7.0%, 8.0%, 9.0%, 10.0%, etc.; the content of LiO2 can be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc.; and the content of C can be 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, etc. The viscosity of the second protective slag at 1300℃ can be 0.04 Pa·s, 0.05 Pa·s, 0.06 Pa·s, 0.07 Pa·s, 0.08 Pa·s, etc.; the melting point of the second protective slag can be 950℃, 980℃, 1000℃, 1020℃, 1040℃, 1050℃, etc.; and the basicity of the second protective slag can be 1.25, 1.27, 1.29, 1.30, 1.32, 1.34, 1.35, etc.

[0046] In some embodiments, the chemical composition of the second protective slag, by mass fraction, is as follows: CaO: 32.9%, SiO2: 27.2%, Al2O3: 6.4%, MgO: 5.9%, MnO: 0.10%, NaO2+K2O: 8.2%, LiO2: 0.88%, C: 5.23%; the melting point of the second protective slag is 1005℃, the viscosity of the second protective slag at 1300℃ is 0.06 Pa·s, and the basicity of the second protective slag is 1.29.

[0047] In some embodiments, the preparation methods of the first and second protective slags include steps such as batching, melting, cooling, and crushing. First, various raw materials, such as base slag, flux, and regulators, are accurately weighed according to the required performance indicators. Then, the mixed raw materials are placed in a melting furnace and heated to a high temperature to completely melt and uniformly mix them. Next, the molten protective slag is rapidly cooled to control its crystal morphology and glass content. Finally, the cooled protective slag is crushed and sieved to a specified particle size to meet the requirements for use in high-speed continuous casting of thin slabs.

[0048] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0049] Example 1

[0050] This embodiment employs a two-stage addition of the protective slag. The chemical composition of the first protective slag, by mass fraction, is as follows: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, with the balance being unavoidable impurities. The melting point of the first protective slag is 1038℃, its viscosity at 1300℃ is 0.10 Pa·s, and its basicity is 1.10. The chemical composition of the second protective slag, by mass fraction, is as follows: CaO: 32.9%, SiO2: 27.2%, Al2O3: 6.4%, MgO: 5.9%, MnO: 0.10%, NaO2+K2O: 8.2%, LiO2: 0.88%, C: 5.23%; the melting point of the second protective slag is 1005℃, the viscosity of the second protective slag at 1300℃ is 0.06 Pa·s, and the basicity of the second protective slag is 1.29.

[0051] Based on the aforementioned protective slag, this embodiment also provides a thin slab continuous casting method, including the following steps: continuous casting of low-carbon SPHC steel; secondary cooling water supply using a low-carbon steel water supply system; crystallizer vibration parameters using low-carbon steel vibration parameters; tundish superheat control at 20-35℃ (liquidity 1531℃); tundish preparation before casting; ladle slag discharge detection at 20% opening; ladle slide opening; molten steel flowing from the ladle into the tundish; after casting starts at 24 tons in the tundish, adding a high-basicity low-carbon steel covering agent at the stopper rod; starting the tundish at 30 tons; pouring molten steel from the tundish into the crystallizer, i.e., the process from casting start to the casting speed increasing to 0.8 m / min; pushing in the first protective slag; when the casting speed increases to 0.8 m / min, maintaining it for 3 seconds, then directly increasing from 0.8 m / min to 3.5 m / min and stabilizing until the shearing ends; the casting speed increase rate is 1.5 m / min. 2 When the casting speed is increased to 4.5 m / min, the slag layer of the protective slag is ideally 11 mm. When the casting speed is greater than 4.5 m / min, the casting speed is further increased to 5.8 m / min and a second protective slag is used. The thickness of the slag layer is well controlled throughout the casting process and can still be maintained at the ideal 10 mm. The liquid surface fluctuation of ±3 mm is good. The surface quality of the final product is good and no slag entrapment defects are found.

[0052] Comparative Example 1

[0053] This comparative example uses a one-stage addition of the protective slag. The chemical composition of the protective slag, by mass fraction, is as follows: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, with the balance being unavoidable impurities. The melting point of the protective slag is 1038℃, the viscosity at 1300℃ is 0.10 Pa·s, and the basicity is 1.10.

[0054] Based on the aforementioned protective slag, this embodiment also provides a thin slab continuous casting method, including the following steps: continuous casting of low-carbon SPHC steel; secondary cooling water supply using a low-carbon steel water supply system; crystallizer vibration parameters using low-carbon steel vibration parameters; tundish superheat control at 20-35℃ (liquidity 1531℃); tundish preparation before casting; ladle slag discharge detection at 20% opening; ladle slide opening; molten steel flowing from the ladle into the tundish; after casting begins, when the tundish reaches 24 tons, adding a high-basicity low-carbon steel covering agent at the stopper rod. The 30-ton tundish is started, and molten steel is poured into the crystallizer. This process, from start-up to reaching a casting speed of 0.8 m / min, involves introducing protective slag. When the casting speed reaches 0.8 m / min, it is held for 3 seconds, then rapidly increased to 3.5 m / min and stabilized at this speed until the first shearing is completed. The speed increase rate during this stage is 1.5 m / min², aiming to quickly reach the target casting speed while ensuring the billet quality remains unaffected. When the casting speed reaches 4.5 m / min, the protective slag exhibits its excellent performance, maintaining the molten slag layer thickness at the ideal 11 mm. After the casting speed stabilized at 4.5 m / min, the casting speed was further increased to the target speed of 5.6 m / min to meet production needs. The above-mentioned protective slag was still used. However, its relatively high viscosity and specific melting point range were no longer applicable under high-speed casting conditions. As a result, it was difficult to maintain the ideal 10 mm thickness of the liquid slag layer. The thickness of the liquid slag layer was only 8 mm, the liquid surface fluctuation increased, and the difficulty of surface quality control increased, which affected the surface quality of the billet and reduced the yield and product quality.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1 is that, by mass fraction, the chemical composition of the second protective slag is: CaO: 33.0%, SiO2: 25.5%, Al2O3: 8.5%, MgO: 8.0%, MnO: 0.25%, NaO2+K2O: 7.0%, LiO2: 2.0%, C: 6.5%, with the balance being unavoidable impurities;

[0057] The melting point of the second protective slag is 1040℃, the viscosity of the second protective slag at 1300℃ is 0.11 Pa·s, and the basicity of the second protective slag is 1.29.

[0058] When the casting speed reaches 4.5 m / min, the first protective slag exhibits excellent performance, maintaining the liquid slag layer thickness at the ideal 11 mm. After the casting speed stabilizes at 4.5 m / min, to meet production demands, the casting speed is further increased to the target speed of 5.6 m / min, and a second protective slag is used. However, its viscosity is 0.11 Pa·s, which is outside the range of 0.04–0.08 Pa·s, making it difficult to maintain the ideal 10–12 mm thickness of the liquid slag layer. The liquid slag layer thickness is only 8 mm, resulting in poor lubrication, increased frictional resistance, and negative impacts on the surface quality of the cast billet, reducing the yield and product quality.

[0059] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0060] In this embodiment of the invention, by adding low-carbon steel protective slag in two stages, the lubrication and heat transfer effect can be satisfied at a casting speed of <4.5m / min, while the consumption, heat transfer and liquid slag layer thickness of the protective slag can be satisfied at a casting speed of ≥4.5m / min. This can ensure smooth continuous casting and improve product quality, while also ensuring efficient production line production and product quality.

[0061] The thin slab continuous casting method provided in this embodiment of the invention is crucial for ensuring smooth continuous casting and improving product quality, while also guaranteeing efficient production line operation and high product quality. It has high technological application value, is easy to operate, and ensures stable improvement in slab quality in thin slab continuous casting machines.

[0062] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for continuous casting of thin slabs, characterized in that, The method includes: Molten steel is poured, and during the pouring process, a two-stage low-carbon steel protective slag is used depending on the pouring speed. When the casting machine speed is <4.5m / min, the protective slag is the first protective slag; the viscosity of the first protective slag at 1300℃ is 0.10Pa·s~0.20Pa·s; When the casting machine speed is ≥4.5m / min, the protective slag is a second protective slag; the viscosity of the second protective slag at 1300℃ is 0.04Pa·s~0.08Pa·s; The first protective slag is added when the casting machine speed increases from 0 to 0.8 m / min. Once the pulling speed reaches 0.8 m / min, continue at 1.5 m / min. 2 The rate of increase will raise the pulling speed to 3.5 m / min.

2. The method according to claim 1, characterized in that, The chemical composition of the first protective slag, by mass fraction, includes: CaO: 25.0%~35.0%, SiO2: 24.0%~28.0%, Al2O3: 4.0%~8.0%, MgO: 5.0%~9.0%, MnO: 1.0%~3.0%, NaO2+K2O: 5.0%~9.0%, LiO2<5.0%, C: 4.0%~6.0%, with the balance being unavoidable impurities.

3. The method according to claim 2, characterized in that, The melting point of the first protective slag is 1000℃~1100℃.

4. The method according to claim 3, characterized in that, The basicity of the first protective slag is 1.05~1.

15.

5. The method according to claim 2, characterized in that, The chemical composition of the first protective slag, by mass fraction, is as follows: CaO: 30.0%, SiO2: 25.5%, Al2O3: 5.8%, MgO: 6.8%, MnO: 1.63%, NaO2+K2O: 7.1%, LiO2: 0.66%, C: 5.65%, balance being unavoidable impurities; the melting point of the first protective slag is 1038℃, the viscosity of the first protective slag at 1300℃ is 0.10 Pa·s, and the basicity of the first protective slag is 1.

10.

6. The method according to claim 1, characterized in that, The chemical composition of the second protective slag, by mass fraction, includes: CaO: 30.0%~35.0%, SiO2: 25.0%~30.0%, Al2O3: 4.0%~8.0%, MgO: 6.0%~8.0%, MnO: 0.05%~0.20%, NaO2+K2O: 6.0%~10.0%, LiO2<5.0%, C: 4.0%~6.0%, with the balance being unavoidable impurities.

7. The method according to claim 6, characterized in that, The melting point of the second protective slag is 950℃~1050℃.

8. The method according to claim 7, characterized in that, The basicity of the second protective slag is 1.25~1.

35.

9. The method according to claim 6, characterized in that, The chemical composition of the second protective slag, by mass fraction, is as follows: CaO: 32.9%, SiO2: 27.2%, Al2O3: 6.4%, MgO: 5.9%, MnO: 0.10%, NaO2+K2O: 8.2%, LiO2: 0.88%, C: 5.23%; the melting point of the second protective slag is 1005℃, the viscosity of the second protective slag at 1300℃ is 0.06 Pa·s, and the basicity of the second protective slag is 1.

29.

10. The method according to claim 1, characterized in that, The molten steel is low-carbon steel.

Images