A continuous casting method for controlling narrow side concave and crack defects of high aluminum steel casting blank

Abstract

The application discloses a continuous casting method for controlling narrow side concave and crack defects of high-aluminum steel casting blank, and adopts the following control process: (1) N in the cast molten steel is less than or equal to 0.005%, and Mn / Si is 4-6; (2) the crystallizer protecting slag adopts low-silicon high-calcium composite protecting slag, the alkalinity is 1.1-1.5, the melting point is 1150-1230 DEG C, and the viscosity is 0.1-0.16 Pa.s; (3) the control casting speed of the first furnace is 0.8-0.9 m / min, the control casting speed of the subsequent furnace is 0.95-1.4 m / min, the crystallizer liquid level fluctuation amplitude is controlled within ±3 mm, and slag is salvaged during casting; (4) when the crystallizer liquid level fluctuation amplitude is greater than or equal to ±5 mm, the casting speed is immediately reduced; the Al2O3 content and viscosity of the protecting slag are detected after each furnace is started to cast. The method can significantly inhibit the reaction strength of slag and steel, the Al2O3 accumulation amount in the protecting slag is reduced by more than 60%, and the slag ring generation rate is reduced to less than 10%.

Description

Technical Field

[0001] This invention relates to the field of metallurgical continuous casting technology, and in particular to a continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets. Background Technology

[0002] High-aluminum steel, through the targeted addition of alloying elements such as aluminum, manganese, and silicon, combined with appropriate heat treatment processes, can significantly improve the strength of steel (tensile strength ≥780MPa) while ensuring good formability. It is a key material for achieving a synergistic improvement in automotive lightweighting and collision safety, and is widely used in core automotive structural and safety components such as door anti-collision beams, A / B / C pillars, sill beams, bumpers, and seat frames. Currently, this steel has been commercially applied in high-end models such as the Audi A8 and BMW 7 Series. However, the research and development of high-aluminum steel automotive sheets in China started relatively late and is currently still in the small-batch trial production stage, without yet forming a large-scale, stable production model.

[0003] Especially when the carbon content in high-alumina steel is in the peritectic reaction range (C=0.10%~0.16%), the δ-Fe→γ-Fe peritectic transformation occurs during solidification. This transformation is accompanied by a 3%~5% volume shrinkage, which directly causes the billet shell to not adhere tightly to the mold wall, creating conditions for defects to occur. At the same time, the high content of active Al in the steel (0.4%~0.75%) easily reacts violently with SiO2 in the mold flux to generate a high-melting-point Al2O3 phase (melting point ≥1520℃), which leads to an increase in the degree of crystallization of the flux and a deterioration in its fluidity, forming a periodically distributed hard slag ring on the narrow face of the mold. The slag ring mechanically compresses the initial billet shell, forming a narrow side depression with a depth of 3-8 mm. Due to the heat insulation effect of the slag ring, the cooling rate in the depression area is 30%-40% lower than that of the surrounding area. The austenite grains are coarse, and network proeutectoid ferrite precipitates at the grain boundaries, significantly reducing the crack resistance. During continuous casting bending and straightening processes, it is easy to crack along the grain boundaries, forming deep cracks with a length of up to 50 mm, which seriously damages the quality of the cast billet.

[0004] In current high-alumina steel production, the narrow-side depression defect rate of the cast billet is as high as 80%. To avoid cracks in the rolled steel plate, the cast billet needs to undergo deep machine cleaning (cleaning depth ≥3mm) and secondary flame grinding. This process not only significantly reduces the yield of continuously cast metal and increases production costs, but also seriously affects the contract delivery schedule. Existing technologies have conducted relevant control research on the aforementioned narrow-side depression and crack defects in high-alumina steel cast billets, resulting in some patented technologies. For example, Chinese Patent Publication No. CN116140568A discloses a method for controlling subsurface longitudinal cracks in peritectic high-alumina steel continuously cast billets. This method controls the Al content in the steel to 0.4–0.5%, designs a special protective slag (CaO 37.5–45.5%, Al2O3 3.0–6.0%), optimizes the argon blowing flow rate (70–90 L / min), casting speed (≤1.4 m / min), and secondary cooling weak cooling water distribution process (specific water volume 0.58 kg / L). Simultaneously, it employs a special slag removal process for the crystallizer and controls the insertion depth of the immersion nozzle (130–150 mm), effectively reducing the influence of Al2O3 inclusions and the transformation rate of the protective slag, thus improving the subsurface longitudinal crack defect. However, this control method primarily addresses the causes of crack defects but does not propose specific technologies for controlling the morphology of narrow-sided depressions. Furthermore, its effect on defect control at high casting speeds (>1.4 m / min) is limited, failing to meet the demands of high-efficiency production.

[0005] Regarding narrow-face concavity control, Chinese Patent Publication No. CN120828115A discloses a method for achieving narrow-face concavity in continuously cast slabs. By optimizing the structure of the crystallizer outlet foot roller and adjusting the arc parameters (0.5-2.7mm), a single-sided concavity of 9-12mm is achieved at high casting speeds (1.35-1.4m / min). Although this solves the problem of low casting speed limitation, this solution is mainly for ordinary steel grades (such as Q355 and AH36) and does not consider the reaction characteristics of high-alumina steel and the influence of alumina inclusions on the uniformity of concavity formation. When applied to the production of high-alumina steel, problems such as concavity depth fluctuations are likely to occur. In addition, Chinese Patent Publication No. CN117139575A discloses a method for controlling the narrow face morphology and corner transverse cracks of a narrow-face concave continuous casting billet. It proposes to achieve narrow-side concave forming of the billet by changing the narrow-face copper plate of the crystallizer to a convex structure. However, this method has the problems of large equipment modification and poor applicability. It is only applicable to low-speed casting machines and cannot meet the production needs of high-alumina steel high-efficiency continuous casting.

[0006] In addition, the first prize of the 2022 China Metallurgical Science and Technology Award, announced on the official website of the China Iron and Steel Association in August 2022, was awarded to Shougang Group Co., Ltd. and Beijing University of Science and Technology through industry-university-research cooperation for the development and application of key technologies for continuous casting of high-alumina steel and microalloy steel. This technology clarified the influence law of the slag ring in the crystallizer on transverse depressions and cracks, and adopted the billet shell uniform control technology of "electromagnetic stirring + large-angle nozzle" and non-sinusoidal small negative slip vibration mode to reduce the crack incidence rate to 0.1% and increase the casting speed to over 1.2m / min. However, this technology focuses on optimizing the flow and vibration parameters in the crystallizer, and does not propose a systematic control scheme for key factors affecting the formation of depressions, such as the uniformity of cooling on the narrow side of the secondary cooling section and the pressure distribution of the foot roll and the billet. As a result, the systematic control effect of narrow side depressions and crack defects has not yet reached the requirements of industrial stable production standards.

[0007] In summary, existing technologies either focus on the single control of crack defects or are designed for narrow-faced indentation forming of ordinary steel grades, lacking a comprehensive control scheme for narrow-side indentation-crack system tailored to the dual characteristics of peritectic reaction and Al2O3 inclusions in high-alumina steel. Furthermore, existing technologies suffer from insufficient defect control stability under high casting speeds (>1.4 m / min), high equipment modification costs, and high process complexity, making it difficult to balance production efficiency and product quality. Therefore, developing a process suitable for the compositional characteristics of high-alumina steel, requiring no major equipment modifications, and capable of simultaneously controlling narrow-side indentation and crack defects has become a pressing technical challenge in the field of high-alumina steel continuous casting. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned shortcomings of the prior art and provide a continuous casting method for controlling narrow side depressions and cracks in high-alumina steel billets, so as to achieve joint control of narrow side depressions and cracks in high-alumina steel, ensuring product quality while taking into account production efficiency, without the need for large-scale modification of existing equipment, and adaptable to industrial-scale production scenarios.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention employs the following control process: (1) The molten steel being poured contains N≤0.005% and Mn / Si ratio of 4~6; (2) The mold flux is a low-silicon, high-calcium composite mold flux with an alkalinity of 1.1 to 1.5, a melting point of 1150 to 1230 °C, and a viscosity of 0.1 to 0.16 Pa·s; (3) The casting speed for the first furnace is controlled at 0.8 to 0.9 m / min, and the casting speed for subsequent furnaces is controlled at 0.95 to 1.4 m / min. The fluctuation range of the liquid level in the crystallizer is controlled within ±3 mm, and slag is removed during casting. (4) When the fluctuation range of the liquid level in the crystallizer is ≥ ±5 mm, immediately reduce the casting speed; after each furnace is started casting, take a sample to test the Al2O3 content and viscosity of the protective slag. When the Al2O3 content is ≥ 12% and / or the viscosity is ≥ 1.3 Pa·s, add new slag; when the fluctuation range of the liquid level in the crystallizer is ≥ ±4 mm and the duration exceeds 3 min, immediately reduce the casting speed and start adding new slag and adjust the slag removal frequency.

[0010] Furthermore, in the process (2), the SiO2 content in the protective slag is 29% to 36%, and the CaO content is 40% to 44%.

[0011] Furthermore, the Al2O3 content in the protective slag is ≤1.3%.

[0012] Furthermore, the main chemical components and their mass fractions of the protective slag are as follows: SiO2 29%–36%, CaO 40%–44%, MgO 0.5%–1.1%, Al2O3 0.5%–1.3%, Li2O 0.4%–1.2%, Na2O 5%–9%, ​​and CaF2 11%–15%.

[0013] Furthermore, in the process (3), slag is removed once every 25 to 35 minutes of pouring.

[0014] Furthermore, in the process (4), when the fluctuation amplitude of the liquid level in the crystallizer is ≥ ±4 mm and the duration exceeds 3 min, the pulling speed is immediately reduced by 0.05 to 0.1 m / min and new crystallizer protective slag is added and the slag removal frequency is increased.

[0015] Furthermore, in the process (4), when the fluctuation range of the liquid level in the crystallizer is ≥ ±5 mm, the pulling speed is immediately reduced.

[0016] Furthermore, when the fluctuation range of the liquid level in the crystallizer is ≥±5mm, the pulling speed should be immediately reduced by 0.05~0.1m / min.

[0017] Furthermore, in the process (4), samples are taken 18-22 minutes after each furnace is started to test the Al2O3 content and viscosity of the protective slag.

[0018] The design concept of this invention is as follows: Controlling the chemical composition of molten steel mainly involves controlling the nitrogen content to ≤0.005%, thus cutting off the source of defects at the chemical composition level and directly reducing the formation of AlN inclusions at high temperatures. This prevents inclusions from precipitating at grain boundaries and causing embrittlement and cracking of the billet shell. Optimizing the Mn / Si ratio to 4–6 not only ensures the strength performance of high-aluminum steel but also significantly improves the fluidity and cleanliness of molten steel, reducing the problem of uneven slag adhesion on the billet shell during casting. It also enhances the high-temperature toughness of the billet shell and reduces the risk of stress cracking during cooling and straightening.

[0019] The control of the mold flux composition mainly focuses on the characteristics of high-alumina steel, specifically preventing the inclusion of Al2O3 from the high-alumina steel in the mold flux, which could lead to abnormal melting point and viscosity of the slag system. A design of "low-silicon, high-calcium + composite alkaline earth metal oxides" is adopted, with a fixed basicity of 1.1–1.5 and control of key physicochemical parameters, such as melting point 1150–1230℃ and viscosity 0.1–0.16 Pa·s. This ensures uniform melting of the mold flux, forming a stable liquid slag film and preventing depressions caused by adhesion between the billet shell and the mold. Furthermore, the initial Al2O3 content is limited to ≤1.3%, thus reserving redundant space for the slag system to accommodate Al2O3 and slowing down the failure rate of the slag system.

[0020] The stability control of continuous casting process mainly focuses on the uniform solidification of the initial billet shell. This is achieved through refined control of process parameters to reduce stress concentration. A slow-start, stable operation, and gradual acceleration control path is adopted. For the first heat, a slow casting speed of 0.8–0.9 m / min is used to ensure uniform thickness of the initial billet shell. Subsequent heats (including the second heat) maintain a stable casting speed of 0.95–1.4 m / min, achieving a balance between production efficiency and billet shell quality. Strict control of the liquid level fluctuation in the crystallizer within ±3 mm ensures uniform shell thickness growth and avoids slag entrapment and uneven shell thickness caused by excessive liquid level fluctuations. Simultaneously, manual slag removal at regular intervals (25–35 minutes per cycle) promptly removes floating slag and high-melting-point Al2O3 inclusions from the crystallizer, preventing slag ring accumulation that disrupts the continuity of the liquid-slag film and reducing the occurrence of narrow-sided depressions from a process perspective.

[0021] Dynamic control of the casting process, combined with the complex working conditions in industrial production, establishes a multi-parameter collaborative early warning and control mechanism: In the liquid level fluctuation early warning stage, when the liquid level fluctuation amplitude in the crystallizer is ≥±5mm, the casting speed is immediately reduced and the slag removal operation is strengthened to quickly restore casting stability; In the protective slag status monitoring stage, after each furnace casting begins, samples are taken to test the Al2O3 content and viscosity of the protective slag. When the Al2O3 content is ≥12% and / or the viscosity is ≥1.3Pa·s, only new slag is added, and there is no need to adjust the slag removal frequency; When the liquid level fluctuation amplitude in the crystallizer is ≥±4mm and the duration exceeds 3min, comprehensive control measures are activated, namely, immediately reducing the casting speed, adding new slag, and adjusting the slag removal frequency, to ensure strict correspondence with the process steps in the claims and achieve precise prevention of defects.

[0022] The beneficial effects of adopting the above technical solution are as follows: This invention, through the synergistic optimization of protective slag composition design and steel composition control, can significantly suppress the slag-steel reaction intensity, reduce the accumulation of Al2O3 in the protective slag by more than 60%, and reduce the slag ring formation rate to below 10%, thus fundamentally avoiding billet shell compression and depression; This invention is compatible with existing slab continuous casting machines, requiring no large-scale equipment modification, is easy to operate, highly stable, and can achieve 15 heats of continuous casting without defects, meeting the needs of large-scale production; After adopting this method, the narrow side depression defect rate of the obtained billet is ≤7.5%, the average depression depth is ≤1.5mm, and the crack defect rate is ≤0.3%, which greatly improves the quality of the billet, reduces the machine cleaning and flame grinding processes, increases metal yield, reduces production costs, and ensures contract delivery schedule. Attached Figure Description

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 Image of the narrow-side concave morphology of a high-alumina steel billet obtained by conventional process; Figure 2 This is a narrow side morphology diagram of the cast billet obtained in Example 1; Figure 3 This is a narrow side morphology diagram of the cast billet obtained in Example 2; Figure 4 This is a narrow side morphology diagram of the cast billet obtained in Example 3; Figure 5 This is a narrow side morphology diagram of the cast billet obtained in Example 4. Detailed Implementation

[0025] The high-alumina steel for which this continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel slabs is applicable has the following chemical composition (mass fraction): C 0.10%–0.16%, Si 0.25%–0.45%, Mn 1.5%–2.5%, Als 0.4%–0.75%, N ≤ 0.005%, with the balance being Fe and unavoidable impurities. The high-alumina steel production process is as follows: hot metal pretreatment → converter smelting → LF refining → RH refining → slab continuous casting. The control process of this invention can be directly adapted to conventional production routes without the need for additional process steps.

[0026] The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets employs the following control process: (1) Precise control of the chemical composition of molten steel: mainly to strictly control the N content of molten steel to ≤0.005wt%, reduce the formation of AlN inclusions, avoid grain boundary embrittlement and intergranular cracking; adjust the Mn / Si ratio to 4 to 6, under the premise of ensuring strength, significantly improve the fluidity and cleanliness of molten steel, reduce slag on the billet shell, unevenness and local thinness, and improve the high temperature toughness and crack resistance of the billet shell.

[0027] (2) Control of mold flux composition: The mold flux adopts a low-silicon, high-calcium composite mold flux, with the following main chemical components and their mass fractions: SiO2 29%–36%, CaO 40%–44%, MgO 0.5%–1.1%, Al2O3 0.5%–1.3%, Li2O 0.4%–1.2%, Na2O 5%–9%, ​​CaF2 11%–15%; the basicity (CaO / SiO2) of the mold flux is controlled at 1.1–1.5, the melting point is 1150–1230℃, and the viscosity (1300℃) is 0.1–0.16 Pa·s. The mold flux is added after the molten steel is poured into the mold. Its main functions are to keep the surface of the molten steel warm, isolate the air to prevent secondary oxidation of the molten steel, absorb inclusions in the molten steel, lubricate the billet shell and improve the heat transfer efficiency between the billet shell and the mold wall, and ensure uniform solidification of the billet shell.

[0028] (3) Stability control of casting process: This mainly refers to the dynamic matching of casting speed control: "low speed start-stable operation-gradient speed increase" strategy. The casting speed is controlled at 0.8 to 0.9 m / min for the first furnace to ensure uniform thickening of the initial billet shell. The casting speed is stabilized at 0.95 to 1.4 m / min for subsequent furnaces (including the second furnace) to meet the needs of high-efficiency production. The fluctuation range of the liquid level in the crystallizer is controlled within ±3 mm to avoid slag entrapment and uneven billet shell. Manual slag removal is carried out every 25 to 35 minutes to remove floating slag and high melting point Al2O3 inclusions in the crystallizer, avoid slag ring accumulation that damages the continuity of the liquid slag film, and reduce narrow side depression defects.

[0029] (4) Process control of casting parameters: During the casting process, the fluctuation of the liquid level in the crystallizer, the position of the stopper rod, and the melting state of the protective slag are tracked in real time. When the fluctuation of the liquid level in the crystallizer is ≥ ±5 mm, the casting speed is immediately reduced by 0.05 to 0.1 m / min. When the fluctuation of the liquid level in the crystallizer is ≥ ±4 mm and lasts for more than 3 minutes, the casting speed is immediately reduced and new slag is added and the slag removal frequency is increased by 0.05 to 0.1 m / min. The slag removal frequency is adjusted to be once every 15 to 20 minutes to ensure timely removal of slag rings and floating slag and to ensure casting stability. 18 to 22 minutes after the start of each furnace casting, samples are taken to test the Al2O3 content and viscosity of the protective slag. When the Al2O3 content is ≥ 12% and / or the viscosity is ≥ 1.3 Pa·s, new crystallizer protective slag is added, that is, the low-silicon high-calcium composite protective slag mentioned in (2) above is added. The amount of crystallizer protective slag added is 0.8 to 1.2 kg / ton of steel.

[0030] (5) After adopting the above method, 15 heats can be continuously cast in each pour, and the narrow side depression defect rate of the resulting billet is ≤7.5%, the average depth of the depression is ≤1.5mm, and the crack defect rate is ≤0.3%, which greatly improves the quality of the billet, reduces the subsequent cleaning process, reduces production costs, and meets the needs of large-scale production.

[0031] Example 1: This example was carried out on a 230mm×2150mm slab continuous casting machine. The main chemical composition (mass fraction) of the high-aluminum steel was: C 0.10%, Si 0.25%, Mn 1.5%, Als 0.4%, N 0.0050%, with the remainder being Fe and unavoidable impurities.

[0032] Controlling the process: Steel chemical composition control: Mn / Si=6, N=0.50%; The main components of the mold flux for continuous casting are: SiO2 29%, CaO 44%, MgO 1.1%, Al2O3 1.3%, Li2O 1.2%, Na2O 9%, CaF2 11%; basicity 1.5, melting point 1150℃, viscosity 0.16 Pa·s at 1300℃; During continuous casting production: the initial casting speed is 0.80 m / min, which stabilizes at 0.95 m / min after the second heat; the liquid level fluctuation in the crystallizer is ±3 mm; slag is manually removed every 35 minutes. During the casting process, the parameters and process control are as follows: the fluctuation range of the liquid level in the crystallizer is ±1.9mm. After casting starts, samples are taken 22 minutes later to test the Al2O3 content and viscosity of the protective slag. The Al2O3 content is 12% and the viscosity is 1.3Pa·s. New slag is added immediately without adjusting the slag removal frequency.

[0033] Production results: The narrow side depression defect rate of the cast billet was 7.2%, the average depression depth was 1.3 mm, and the crack defect rate was 0.25%, all of which met the process control requirements of this invention.

[0034] Example 2: This example was carried out on a 230mm×1350mm slab continuous casting machine. The main chemical composition (mass fraction) of the high-alumina steel was: C 0.16%, Si 0.45%, Mn 2.5%, Als 0.75%, N 0.0030%, with the remainder being Fe and unavoidable impurities.

[0035] Controlling the process: Chemical composition control of molten steel: Mn / Si=5.5, N=0.30%; The main components of the mold flux for continuous casting crystallizer are: SiO2 36%, CaO 40%, MgO 0.5%, Al2O3 0.5%, Li2O 0.4%, Na2O 7%, CaF2 15%; basicity 1.11, melting point 1230℃, viscosity at 1300℃ 0.10 Pa·s; Parameters and processes during casting: initial casting speed 0.90 m / min, stabilizing at 1.4 m / min after the second furnace; liquid level fluctuation in the crystallizer ±2.5 mm; manual slag removal every 25 minutes; Process monitoring: Samples were taken and tested on the protective slag 18 minutes after each furnace was started. The Al2O3 content was stable at 9-12% and the viscosity was 0.15 Pa·s. No new slag was needed, and the original slag removal frequency was maintained.

[0036] Production results: The narrow side depression defect rate of the cast billet was 6.8%, the average depression depth was 1.0 mm, and the crack defect rate was 0.18%, which is better than the control requirements of this invention.

[0037] Example 3: This example was carried out on a 230mm×1550mm slab continuous casting machine. The main chemical composition (mass fraction) of the high-alumina steel was: C 0.15%, Si 0.30%, Mn 1.5%, Als 0.60%, N 0.0040%, with the remainder being Fe and unavoidable impurities.

[0038] Controlling the process: Chemical composition control of molten steel: Mn / Si=5, N=0.40%; The main components of the mold flux for continuous casting crystallizer are: SiO2 30%, CaO 40%, MgO 0.8%, Al2O3 0.9%, Li2O 0.8%, Na2O 8%, CaF2 14%; basicity 1.33, melting point 1150℃, viscosity at 1300℃ 0.1 Pa·s; During continuous casting production: the initial casting speed is 0.85 m / min, which stabilizes at 1.35 m / min after the second heat; the liquid level fluctuation in the crystallizer is ±2 mm; slag is manually removed every 30 minutes. Process monitoring: When the liquid level fluctuation range is 5.5mm, immediately reduce the casting speed from 1.35m / min to 1.25m / min and start the slag removal operation; 20 minutes after the start of casting, take a sample to test the Al2O3 content and viscosity of the protective slag. The Al2O3 content is 10% and the viscosity is 0.8Pa·s, so no new slag needs to be added.

[0039] Production results: The narrow side depression defect rate of the cast billet was 3.5%, the average depression depth was 0.9 mm, and the crack defect rate was 0.12%, showing significant defect control effect.

[0040] Example 4: This example was carried out on a 230mm×1800mm slab continuous casting machine. The main chemical composition (mass fraction) of the high-aluminum steel was: C 0.12%, Si 0.35%, Mn 2.0%, Als 0.55%, N 0.0045%, with the remainder being Fe and unavoidable impurities.

[0041] Controlling the process: Steel chemical composition control: Mn / Si=4, N=0.0045%; The main components of the mold flux for continuous casting are: SiO2 33%, CaO 42%, MgO 0.7%, Al2O3 0.7%, Li2O 0.6%, Na2O 6%, CaF2 12%; basicity 1.27, melting point 1190℃, viscosity at 1300℃ 0.13 Pa·s; During continuous casting production: the initial casting speed is 0.82 m / min, which stabilizes at 1.2 m / min after the second heat; the fluctuation range of the liquid level in the crystallizer is initially controlled within ±2.8 mm; slag is manually removed every 32 minutes. Process monitoring: During the casting process, the fluctuation range of the liquid level in the crystallizer increased to ±4.2mm and lasted for 4 minutes. The casting speed was immediately reduced by 0.08m / min, and new slag was added (1.2kg / ton of steel). The slag removal frequency was adjusted to once every 15 minutes. After 19 minutes of casting, the protective slag was sampled and tested. The Al2O3 content was 11% and the viscosity was 1.1Pa·s. No additional new slag was required. Subsequently, the liquid level returned to a stable level of ±2.5mm. The adjusted slag removal frequency was maintained until the casting was completed.

[0042] Production results: The narrow side depression defect rate of the cast billet was 4.1%, the average depression depth was 1.1 mm, and the crack defect rate was 0.21%, showing significant defect control effect.

[0043] Figure 1 This is a morphology image of the narrow-side concave defect in the cast billet before mechanical cleaning, obtained using existing conventional processes. Figures 2-5 The images show the narrow side morphology of the cast billets obtained in Examples 1-4, respectively; through... Figures 1-5 It can be seen that this method can effectively suppress narrow-side depressions and cracks in high-alumina steel billets. Compared with the existing technology, the narrow-side surface of the billet is flat, without obvious depressions (depth ≤ 1.5 mm) and visible cracks. The defects are significantly improved, meeting the requirements of industrial production.

Claims

1. A continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets, characterized in that, The following control process is adopted: (1) The N in the molten steel is ≤0.005% and the Mn / Si ratio is 4 to 6; (2) The mold flux is a low-silicon, high-calcium composite mold flux with an alkalinity of 1.1 to 1.5, a melting point of 1150 to 1230 °C, and a viscosity of 0.1 to 0.16 Pa·s; (3) The casting speed for the first furnace is controlled at 0.8 to 0.9 m / min, and the casting speed for subsequent furnaces is controlled at 0.95 to 1.4 m / min. The fluctuation range of the liquid level in the crystallizer is controlled within ±3 mm, and slag is removed during casting. (4) When the fluctuation range of the liquid level in the crystallizer is ≥ ±5 mm, immediately reduce the casting speed; after each furnace is started casting, take a sample to test the Al2O3 content and viscosity of the protective slag. When the Al2O3 content is ≥ 12% and / or the viscosity is ≥ 1.3 Pa·s, add new slag; when the fluctuation range of the liquid level in the crystallizer is ≥ ±4 mm and the duration exceeds 3 min, immediately reduce the casting speed and start adding new slag and adjust the slag removal frequency.

2. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 1, characterized in that: In process (2), the SiO2 content in the protective slag is 29% to 36%, and the CaO content is 40% to 44%.

3. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 2, characterized in that: The Al2O3 content in the protective slag is ≤1.3%.

4. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 3, characterized in that, The main chemical components and their mass fractions of the protective slag are as follows: SiO2 29%–36%, CaO 40%–44%, MgO 0.5%–1.1%, Al2O3 0.5%–1.3%, Li2O 0.4%–1.2%, Na2O 5%–9%, ​​and CaF2 11%–15%.

5. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 1, characterized in that: In the process (3), slag is removed once every 25 to 35 minutes of pouring.

6. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 1, characterized in that: In the process (4), when the fluctuation of the liquid level in the crystallizer is ≥ ±4 mm and lasts for more than 3 min, the pulling speed is immediately reduced by 0.05 to 0.1 m / min and new protective slag is added to the crystallizer and the slag removal frequency is increased.

7. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 1, characterized in that: In process (4), when the fluctuation range of the liquid level in the crystallizer is ≥ ±5 mm, the pulling speed is immediately reduced.

8. The continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to claim 7, characterized in that: When the fluctuation range of the liquid level in the crystallizer is ≥±5mm, immediately reduce the pulling speed by 0.05~0.1m / min.

9. A continuous casting method for controlling narrow-side depressions and cracks in high-alumina steel billets according to any one of claims 1-8, characterized in that: In process (4), samples are taken 18-22 minutes after each furnace is started to test the Al2O3 content and viscosity of the protective slag.

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