Method for improving castability of aluminum-containing steel in continuous casting process

Abstract

The invention discloses a method for improving castability of aluminum-containing steel in a continuous casting process, which comprises the following steps of: S1, controlling components of molten steel, and accurately controlling the content of acid-soluble aluminum in molten steel of a continuous casting ladle to be 0.020-0.060% according to mass percent; s2, calcium treatment is conducted on the molten steel, and the calcium-aluminum ratio is controlled to range from 0.10 to 0.15; s3, continuous casting process control is conducted, specifically, the superheat degree of tundish molten steel is stably controlled to range from 15 DEG C to 30 DEG C, meanwhile, constant pulling speed operation is adopted, and the pulling speed fluctuation range is controlled within + / -0.1 m / min; and S4, the content of SiO in the casting powder is reduced to be smaller than or equal to 20%, and meanwhile, the alkalinity R of the casting powder is 1.5-2.0. The continuous casting process is ensured to be smooth, nozzle nodulation and casting blank surface defects are effectively prevented, and the production efficiency and the product quality are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology in iron and steel metallurgy, and in particular to a method for improving the castability of continuous casting processes for aluminum-containing steel. Background Technology

[0002] Aluminum, as an important alloying element in steel, plays a crucial role in deoxidation, grain refinement, and improving the strength and corrosion resistance of steel. Therefore, the demand for aluminum-containing steel (especially high-strength steel and high-grade electrical steel) is increasing in the market.

[0003] However, a well-known technical challenge has always existed in the continuous casting production of aluminum-containing steel: poor castability. Specifically, this manifests as follows: 1. Nodule formation at the submerged entry nozzle (SEN): Acid-soluble aluminum [Al]s in the molten steel undergoes the following reduction reaction with SiO2 in the protective slag: 4[Al] + 3(SiO2) = 2(Al2O3) + 3[Si] The Al2O3 inclusions generated by the reaction deposit on the inner wall of the nozzle, gradually clogging the nozzle and causing instability in the molten steel flow field, fluctuations in casting speed, and even forced shutdown of casting.

[0004] 2. Deterioration of the protective slag properties: The Al2O3 generated in the reaction enters the protective slag, causing drastic changes in its chemical composition and physical properties (such as viscosity, melting point, and crystallization properties). The original protective slag loses its functions of lubrication, heat insulation, and inclusion absorption, leading to increased friction between the billet and the copper wall of the crystallizer, resulting in serious accidents such as sticking and leakage, and causing defects such as pits and cracks on the surface of the billet.

[0005] Existing technologies typically address this issue by optimizing the nozzle material (such as using ZrO2-C or BN coating) or increasing the nozzle's inner diameter, but these methods have limited effectiveness and are costly. Another approach is to develop low-reactivity protective slags, reducing the SiO2 content to decrease the reaction driving force at its source. However, simply reducing SiO2 can lead to excessively high basicity in the protective slag, increased melting point, and weakened glass transition tendency, which can conversely cause poor lubrication in the crystallizer.

[0006] Therefore, there is an urgent need for a comprehensive solution that can systematically address the problem of the castability of aluminum-containing steel. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for improving the castability of aluminum-containing steel in continuous casting processes.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for improving the castability of aluminum-containing steel in continuous casting includes the following steps: S1. Steel composition control: The acid-soluble aluminum content in the molten steel of the continuous casting ladle is precisely controlled within 0.020% - 0.060% by mass percentage. S2. Calcium treatment is applied to the molten steel to control the calcium-aluminum ratio between 0.10 and 0.15. S3. Continuous casting process control: The superheat of molten steel in the tundish is stably controlled at 15-30℃. At the same time, constant casting speed operation is adopted, and the casting speed fluctuation range is controlled within ±0.1 m / min. S4. Reduce the SiO2 content in the protective slag to ≤20%, and at the same time, the basicity R of the protective slag is 1.5~2.0.

[0009] The chemical composition of the protective slag, by mass percentage, is as follows: CaO: 35%–45%, SiO2: ≤ 20%, Al2O3: ≤ 5%, MgO: 3%–8%, Na₂O + K₂O: 8% ~ 15%, F: 5%~10%, Li2O: 1% ~ 3%, Free carbon form of C: 2%–5%, Unavoidable impurities: ≤ 2%.

[0010] The SiO2 content in the protective slag is 15% to 20%.

[0011] The protective slag contains 2% to 4% Al2O3.

[0012] The beneficial effects of this invention are: 1. This invention precisely controls the acid-soluble aluminum content in the molten steel of the continuous casting ladle to 0.020%-0.060% by mass percentage, which can meet the performance requirements of the final product and avoid excessive aluminum content from aggravating the reaction with the protective slag.

[0013] 2. This invention performs calcium treatment on molten steel, controlling the calcium-to-aluminum ratio (Ca / [Al]s) between 0.10 and 0.15. This ratio ensures the formation of liquid calcium aluminate (12CaO•7Al2O3), transforming high-melting-point Al2O3 and CaO•Al2O3 inclusions into low-melting-point, easily floating liquid inclusions, fundamentally reducing the source of nozzle nodules.

[0014] 3. The present invention stably controls the superheat of molten steel in the tundish at 15-30℃. The lower superheat is conducive to the formation of equiaxed crystals and reduces central segregation. At the same time, the stable temperature helps the protective slag to form a uniform molten structure and reduce performance fluctuations.

[0015] 4. By reducing the SiO2 content in the protective slag to ≤20%, the driving force and reaction amount of the reduction reaction with [Al] in molten steel are fundamentally reduced.

[0016] 5. Through precise calcium treatment, solid Al2O3 inclusions are transformed into liquid calcium aluminate, making them less likely to adhere to the inner wall of the nozzle. They float to the surface with the steel flow and are removed, greatly alleviating nozzle nodule formation.

[0017] 6. In the protective slag of the present invention, the addition of low SiO2, high basicity, Li2O and MgO ensures that even after absorbing a certain amount of Al2O3, the protective slag can still maintain a low melting point (1050-1150℃), a suitable viscosity (0.10-0.25 Pa•sat 1300℃) and a good glass transition tendency, providing continuous and stable lubrication and heat insulation for the crystallizer.

[0018] 7. The synergistic effect of steel composition control, process parameter optimization, and protective slag design forms a complete and closed technical solution, which systematically solves the problem of castability of aluminum-containing steel and significantly improves continuous casting operation rate, billet yield, and product surface quality. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0020] Example 1 The target composition for producing a certain grade of aluminum-containing high-strength steel is: C: 0.08%, Si: 0.10%, Mn: 1.20%, P: ≤0.015%, S: ≤0.005%, Als: 0.040%.

[0021] Molten steel treatment: 1. After refining in the LF furnace, the [Al]s of the molten steel in the ladle was measured to be 0.045%.

[0022] 2. A Ca-Si wire is fed into the ladle using a wire feeder for calcium treatment. Based on the steel volume and [Al]s content, the wire feeding speed and length are controlled to ensure that the Ca content of the treated steel reaches approximately 50 ppm, resulting in a Ca / [Al]s ratio of approximately 0.12.

[0023] 3. During continuous casting, the superheat of the molten steel in the tundish should be controlled at 20±5℃.

[0024] Applications of protective slag: The protective slag provided by this invention has the following specific components: CaO: 40%, SiO2: 18%, Al2O3: 3%, MgO: 5%, Na2O: 10%, F⁻: 8%, Li2O: 2%, C: 4%. The alkalinity R = 40 / 18 ≈ 2 (Note: Actual calculations require the use of effective CaO and SiO2; this is just an example).

[0025] Implementation results: Throughout the entire 8-heat continuous casting process, the casting speed remained stable at 0.1 m / min, and no significant nodule formation was observed in the submerged entry nozzle. The liquid level in the crystallizer was stable, and the protective slag was in good melting condition. After casting, the surface quality inspection pass rate of the billet reached 99.5%, with no obvious surface depressions or cracks. Compared with the use of traditional protective slag, the steel throughput of the nozzle increased by more than 3 times, and the number of heats cast in a single continuous process was significantly increased.

[0026] Example 2 A method for improving the castability of aluminum-containing steel in continuous casting includes the following steps: S1. Steel composition control: The acid-soluble aluminum content in the molten steel of the continuous casting ladle is precisely controlled at 0.020% by mass percentage. S2. Calcium treatment is applied to the molten steel to control the calcium-aluminum ratio between 0 and 10. S3. Continuous casting process control: The superheat of the molten steel in the tundish is stably controlled at 15℃. At the same time, constant casting speed operation is adopted, and the casting speed fluctuation range is controlled within ±0.1 m / min. S4. Reduce the SiO2 content in the protective slag to ≤20%, and at the same time, the basicity R of the protective slag is 1.5.

[0027] The chemical composition of the protective slag, by mass percentage, is as follows: CaO: 35%, SiO2: 15%, Al2O3: 2%, MgO: 3%, Na₂O + K₂O: 8% F: 5%, Li2O: 1%, C in the form of free carbon: 2%, Unavoidable impurities: ≤ 2%.

[0028] Example 3 A method for improving the castability of aluminum-containing steel in continuous casting includes the following steps: S1. Steel composition control: The acid-soluble aluminum content in the molten steel of the continuous casting ladle is precisely controlled at 0.060% by mass percentage. S2. Calcium treatment is applied to the molten steel to control the calcium-aluminum ratio between 0.15 and 0.15. S3. Continuous casting process control: The superheat of the molten steel in the tundish is stably controlled at 30℃. At the same time, constant casting speed operation is adopted, and the casting speed fluctuation range is controlled within ±0.1 m / min. S4. Reduce the SiO2 content in the protective slag to ≤20%, and at the same time, the basicity R of the protective slag is 2.0.

[0029] The chemical composition of the protective slag, by mass percentage, is as follows: CaO: 45%, SiO2: 20%, Al2O3: 5%, MgO: 8%, Na₂O + K₂O: 15%, F: 10%, Li2O: 3%, C in free carbon form: 5%, Unavoidable impurities: ≤ 2%.

[0030] Example 4 The protective slag contains 4% Al2O3, and the remaining steps and methods are the same as in Example 3.

[0031] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for improving the castability of aluminum-containing steel in continuous casting process, characterized in that, Includes the following steps: S1. Steel composition control: The acid-soluble aluminum content in the molten steel of the continuous casting ladle is precisely controlled within 0.020% - 0.060% by mass percentage. S2. Calcium treatment is applied to the molten steel to control the calcium-aluminum ratio between 0.10 and 0.

15. S3. Continuous casting process control: The superheat of molten steel in the tundish is stably controlled at 15-30℃. At the same time, constant casting speed operation is adopted, and the casting speed fluctuation range is controlled within ±0.1 m / min. S4. Reduce the SiO2 content in the protective slag to ≤20%, and at the same time, the basicity R of the protective slag is 1.5~2.

0.

2. The method for improving the castability of aluminum-containing steel in continuous casting process according to claim 1, characterized in that, The chemical composition of the protective slag, by mass percentage, is as follows: CaO: 35%–45%, SiO2: ≤ 20%, Al2O3: ≤ 5%, MgO: 3%–8%, Na₂O + K₂O: 8% ~ 15%, F： 5%～10%， Li2O: 1% ~ 3%, Free carbon form of C: 2%–5%, Unavoidable impurities: ≤ 2%.

3. The method for improving the castability of aluminum-containing steel in continuous casting process according to claim 2, characterized in that, The SiO2 content in the protective slag is 15% to 20%.

4. The method for improving the castability of aluminum-containing steel in continuous casting process according to claim 2, characterized in that, The protective slag contains 2% to 4% Al2O3.