A continuous casting method of high-aluminum carbon steel and a preparation method thereof

Abstract

The application relates to the technical field of steelmaking continuous casting, in particular to a high-aluminum carbon steel slab continuous casting method and a preparation method thereof. The continuous casting method comprises the following steps: transferring molten steel from a tundish to a crystallizer, and controlling the depth of an immersed water nozzle inserted into the molten steel and the argon blowing flow of a stopper and an upper water nozzle; adding a protective slag to the molten steel in the crystallizer, continuously casting, and controlling the chemical composition and consumption of the protective slag to obtain a casting blank. The application realizes the stability of the heat transfer and lubrication of the crystallizer after the denaturation of the protective slag, the high-aluminum carbon steel casting blank is free of surface defects such as longitudinal cracks, transverse cracks and depressions, and higher speed production is realized.

Description

Technical Field

[0001] This application relates to the field of steelmaking continuous casting technology, and in particular to a method for continuous casting of high-alumina carbon steel slabs and its preparation method. Background Technology

[0002] High-alumina carbon steel has a carbon content of 0.09-0.25% by weight, an aluminum content of 0.5-2.0% by weight, and a silicon content of less than 0.5% by weight. Due to the high Al content in the molten steel, it reacts with SiO2 in the protective slag, resulting in a decrease in SiO2 and a significant increase in Al2O3 in the protective slag, causing the protective slag to deteriorate.

[0003] Currently, after the protective slag undergoes changes, high-alumina carbon steel billets develop surface defects such as longitudinal cracks, transverse cracks, and depressions, requiring manual or machine cleaning, and in severe cases, they are forced to be scrapped. Summary of the Invention

[0004] This application provides a continuous casting method for high-alumina carbon steel slabs and its preparation method to solve the technical problem that existing high-alumina carbon steel slabs are prone to surface defects such as longitudinal cracks, transverse cracks, and depressions.

[0005] In a first aspect, this application provides a continuous casting method for high-alumina carbon steel, the method comprising:

[0006] The molten steel is transferred from the tundish to the crystallizer, and the depth of the submerged nozzle inserted into the molten steel and the argon flow rate of the stopper rod and the top nozzle are controlled.

[0007] A protective slag is added to the molten steel in the crystallizer for continuous casting, and the chemical composition and consumption of the protective slag are controlled to obtain a cast billet.

[0008] Optionally, the chemical composition of the protective slag includes: CaO, SiO2, Al2O3, MgO, Na2O, F, and Li2O; wherein the content of Al2O3 is <1.0 wt%, the content of MgO is <1.0 wt%, and the content of Na2O is <2.0 wt%.

[0009] The weights of CaO, SiO2, and Al2O3 satisfy the following relationship:

[0010] [CaO] / ([CaO]+[SiO2]+[Al2O3])%=55%-60%

[0011] In the formula, [CaO] represents the weight of CaO, [SiO2] represents the weight of SiO2, and [Al2O3] represents the weight of Al2O3.

[0012] Optionally, the chemical composition of the protective slag includes CaO content of 35.0 wt%-50.0 wt%, SiO2 content of 25.0 wt%-40.0 wt%, F content of 5.0 wt%-15.0 wt%, and Li2O content of 0.5 wt%-4.5 wt%.

[0013] Optionally, the alkalinity of the protective slag is 1.2-1.5.

[0014] Optionally, the immersion nozzle is inserted into the molten steel to a depth of 150mm-180mm.

[0015] Optionally, the consumption of the protective slag is 0.4 kg / m³. 2 -0.6kg / m 2 .

[0016] Optionally, the argon flow rate of both the stopper rod and the upper water inlet is 0.

[0017] Optionally, a protective slag is added to the molten steel in the crystallizer for continuous casting, and the chemical composition and consumption of the protective slag are controlled to obtain a cast billet, including:

[0018] A protective slag is added to the molten steel in the crystallizer, and continuous casting is performed. The chemical composition, consumption, and physical parameters of the protective slag are controlled to obtain a cast billet.

[0019] The physical parameters of the protective slag include its melting point and viscosity.

[0020] Optionally, the melting point of the protective slag before use is 900℃-1100℃, and the viscosity of the protective slag before use is 0.04Pa·s-0.08Pa·s, and / or;

[0021] The melting point of the protective slag after use is ≤1200℃, and the viscosity of the protective slag after use is ≤0.15Pa·s.

[0022] Secondly, this application provides a method for preparing high-alumina carbon steel, the method comprising the method described in any embodiment of the first aspect.

[0023] The technical solutions provided in this application have the following advantages compared with the prior art:

[0024] The continuous casting method for high-alumina carbon steel provided in this application avoids the formation of large, high-melting-point crystals such as calcium aluminum feldspar, magnesium aluminum spinel, and nepheline in the slag film of the protective slag by controlling the chemical composition of the protective slag; it also ensures uniform heat transfer within the crystallizer by controlling the consumption of the protective slag; it stabilizes the performance of the protective slag by controlling the insertion depth of the submerged entry nozzle; and it avoids argon blowing at the stopper rod and the upper nozzle to ensure stable lubrication and heat transfer within the crystallizer. In summary, this method achieves stable heat transfer and lubrication in the crystallizer after the protective slag has been modified, prevents surface defects such as longitudinal cracks, transverse cracks, and depressions in the high-alumina carbon steel billet, and enables higher casting speeds. Attached Figure Description

[0025] 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.

[0026] 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.

[0027] Figure 1 A schematic flowchart of a continuous casting method for high-alumina carbon steel provided in this application embodiment;

[0028] Figure 2 A CaO-SiO2-Al2O3 ternary phase diagram is provided as a comparative example in this application;

[0029] Figure 3 A CaO-SiO2-Al2O3 ternary phase diagram is provided for an embodiment of this application. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" 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 one" 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.

[0033] 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.

[0034] Firstly, this application provides a continuous casting method for high-alumina carbon steel; please refer to [link to relevant documentation]. Figure 1 The method includes:

[0035] S1. Transfer the molten steel from the tundish to the crystallizer, and control the depth of the submerged nozzle inserted into the molten steel and the argon flow rate of the stopper rod and the top nozzle;

[0036] S2. Add protective slag to the molten steel in the crystallizer, perform continuous casting, and control the chemical composition and consumption of the protective slag to obtain a cast billet.

[0037] High-alumina carbon steel has a carbon content of 0.09-0.25% by weight, an aluminum content of 0.5-2.0% by weight, and a silicon content of less than 0.5% by weight. Due to the high Al content in the molten steel, it reacts with SiO2 in the protective slag, resulting in a decrease in SiO2 and a significant increase in Al2O3 in the protective slag, causing the protective slag to deteriorate.

[0038] After the protective slag undergoes modification, its melting point and viscosity increase significantly, resulting in coarser slag strands in the crystallizer and a sharp decrease in slag consumption. This affects the stable inflow of protective slag, increases friction in the crystallizer, causing poor lubrication and disrupting the thermocouple curves. In severe cases, this can lead to adhesion alarms, shutdowns, or steel leakage, limiting the increase in casting speed for high-alumina steel. Furthermore, the Al2O3 content in the protective slag increases significantly after modification, shifting from the pseudo-wollastonite region in the CaO-SiO2-Al2O3 ternary phase diagram to the calcium aluminum feldspar region. This results in the formation of a large number of high-melting-point, coarse crystals such as calcium aluminum feldspar, magnesium aluminum spinel, and nepheline in the slag film within the crystallizer, causing unstable heat transfer. The changes in the phase diagram region before and after the reaction are as follows: Figure 2 As shown, after the protective slag undergoes modification, the lubrication and heat transfer inside the crystallizer deteriorate, causing surface defects such as longitudinal cracks, transverse cracks, and depressions in the high-alumina carbon steel billet. These defects require manual or machine cleaning, and in severe cases, the billet must be scrapped.

[0039] To address the aforementioned issues, the continuous casting method for high-alumina carbon steel provided in this application controls the chemical composition of the protective slag to prevent the formation of large, high-melting-point crystals such as calcium aluminum feldspar, magnesium aluminum spinel, and nepheline in the slag film within the crystallizer; controls the consumption of the protective slag to ensure uniform heat transfer within the crystallizer; controls the insertion depth of the submerged entry nozzle to stabilize the performance of the protective slag; and avoids argon blowing at the stopper rod and upper nozzle to ensure stable lubrication and heat transfer within the crystallizer. In summary, this method achieves stable heat transfer and lubrication in the crystallizer after the protective slag has been modified, prevents surface defects such as longitudinal cracks, transverse cracks, and depressions in the high-alumina carbon steel billet, and enables higher casting speeds.

[0040] In some embodiments, the chemical composition of the protective slag includes: CaO, SiO2, Al2O3, MgO, Na2O, F, and Li2O; wherein the content of Al2O3 is <1.0 wt%, the content of MgO is <1.0 wt%, and the content of Na2O is <2.0 wt%.

[0041] The weights of CaO, SiO2, and Al2O3 satisfy the following relationship:

[0042] [CaO] / ([CaO]+[SiO2]+[Al2O3])%=55%-60%

[0043] In the formula, [CaO] represents the weight of CaO, [SiO2] represents the weight of SiO2, and [Al2O3] represents the weight of Al2O3.

[0044] The positive effects of controlling the Al2O3 content to <1.0 wt% include: preventing the formation of high-melting-point coarse crystals such as calcium aluminum feldspar, magnesium aluminum spinel, and nepheline in the protective slag film within the crystallizer, which would worsen heat transfer and lubrication in the crystallizer; and preventing excessive increases in viscosity and melting point after the protective slag has changed, as well as excessive decreases in the amount of protective slag consumed, which would also worsen heat transfer and lubrication in the crystallizer. Specifically, this content can be 0.9 wt%, 0.8 wt%, 0.7 wt%, etc.

[0045] The positive effects of controlling the MgO content to <1.0 wt% include: preventing the formation of large, high-melting-point magnesium aluminum spinel crystals in the protective slag film within the crystallizer, which would worsen heat transfer and lubrication in the crystallizer. Specifically, this content can be 0.9 wt%, 0.8 wt%, 0.7 wt%, etc.

[0046] The positive effects of controlling the Na₂O content to <2.0 wt% include: preventing the formation of large, high-melting-point nepheline crystals in the protective slag film within the crystallizer, which would worsen heat transfer and lubrication in the crystallizer. Specifically, this content can be 1.9 wt%, 1.8 wt%, 1.7 wt%, etc.

[0047] Controlling the weights of CaO, SiO2, and Al2O3 to satisfy the above relationship has the positive effect of placing the original composition of the protective slag in the pseudo-wollastonite and wollastonite interface region or the wollastonite region of the CaO-SiO2-Al2O3 ternary phase diagram. (See also...) Figure 3 The modification of the protective slag prevents it from entering the calcium aluminum feldspar region of the CaO-SiO2-Al2O3 ternary phase diagram, instead directing it into the wollastonite region. This avoids the formation of high-melting-point coarse crystals such as calcium aluminum feldspar, nepheline, and magnesium aluminum spinel in the slag film, achieving a slag film with lanceolate as the main crystalline phase. This stabilizes heat transfer and lubrication in the crystallizer and prevents a significant increase in melting point and viscosity after modification. If the above ratio is too high, the CaO content in the protective slag will be too high, affecting the amount of solvent added and making it difficult to control the viscosity and melting point of the protective slag. If the above ratio is too low, the protective slag will enter the calcium aluminum feldspar region of the CaO-SiO2-Al2O3 ternary phase diagram after reaction, making it difficult to meet stable heat transfer and lubrication requirements within the crystallizer. Specifically, this ratio can be 55%, 60%, 57%, etc. The above ratio is set as K.

[0048] In some embodiments, the chemical composition of the protective slag includes 35.0 wt%-50.0 wt% CaO, 25.0 wt%-40.0 wt% SiO2, 5.0 wt%-15.0 wt% F, and 0.5 wt%-4.5 wt% Li2O.

[0049] The positive effects of controlling the CaO content to 35.0%-50.0% by weight are: avoiding excessively strong or insufficient crystallization performance of the protective slag. If the content is too high, it will, to some extent, increase the crystallizer performance of the protective slag, worsen crystallizer lubrication, and increase the incidence of billet sink marks and transverse cracks; if the content is too low, it will, to some extent, reduce the crystallizer performance of the protective slag, causing excessively rapid heat transfer in the crystallizer and increasing the incidence of longitudinal cracks in the billet, while failing to meet the desired performance. Specifically, this content can be 35.0% by weight, 40.0% by weight, 45.0% by weight, etc.

[0050] The positive effects of controlling the SiO2 content to 25.0 wt%-40.0 wt% include avoiding excessively strong or insufficient crystallization performance of the protective slag. If the content is too high, it will reduce the crystallizer performance of the protective slag to some extent, leading to excessively rapid heat transfer in the crystallizer and increasing the incidence of longitudinal cracks in the cast billet. If the content is too low, it will increase the crystallizer performance of the protective slag to some extent, worsening the lubrication of the crystallizer and increasing the incidence of sink marks and transverse cracks in the cast billet. Specifically, this content can be 30.0 wt%, 35.0 wt%, 40.0 wt%, etc.

[0051] The positive effects of controlling the F content to 5.0 wt%-15.0 wt% include: avoiding excessively strong crystallization properties in the protective slag. If the content is too high, it will increase the precipitation ratio of slag film gun crystals to some extent, worsening the lubrication of the crystallizer and increasing the incidence of billet sink marks and transverse cracks; if the content is too low, it will increase the viscosity of the protective slag to some extent, failing to meet the viscosity requirements. Specifically, this content can be 5.0 wt%, 10.0 wt%, 15.0 wt%, etc.

[0052] The positive effects of controlling the Li₂O content to 0.5 wt%–4.5 wt% include: avoiding excessive use of Na₂O and F. If the content is too high, it will increase costs to some extent; if the content is too low, Na₂O and F will not be able to effectively control the melting point and viscosity of the protective slag. Specifically, the content can be 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, etc.

[0053] In some embodiments, the alkalinity of the protective slag is 1.2-1.5.

[0054] "Balance of the protective slag" refers to the weight ratio of CaO to SiO2. Controlling the basicity of the protective slag to 1.2-1.5 has the positive effects of controlling its viscosity and melting point. If the basicity is too high, it will affect the amount of solvent added to the protective slag, making it difficult to control the viscosity and melting point; if the basicity is too low, it will lead to insufficient heat control capacity of the protective slag, making the first furnace head billet prone to longitudinal cracking. Specifically, the basicity can be 1.2, 1.3, 1.4, 1.5, etc. The basicity of the above-mentioned protective slag is set as R.

[0055] In some embodiments, the immersion nozzle is inserted into the molten steel to a depth of 150mm-180mm.

[0056] The positive effects of controlling the immersion depth of the submerged nozzle into the molten steel to 150mm-180mm include: ensuring stable melting of the protective slag and reducing its degradation. If the immersion depth is too high, it may lead to insufficient heat from the molten steel flowing into the upper part of the mold, affecting the melting of the protective slag. If the immersion depth is too low, it may cause the molten steel flow within the mold to become more active at the slag-steel interface, exacerbating the reactivity and degradation of the interface, worsening the viscosity, melting point, and other properties of the protective slag, leading to unstable lubrication and heat transfer within the mold. Specifically, the immersion depth can be 150mm, 160mm, 170mm, 180mm, etc.

[0057] In some embodiments, the consumption of the protective slag is 0.4 kg / m³. 2 -0.6kg / m 2 .

[0058] The consumption of protective slag is 0.4 kg / m³. 2 -0.6kg / m 2 The positive effects include preventing severe deformation or uneven heat transfer of the protective slag. Excessive consumption can lead to uneven heat transfer within the mold, increasing the risk of longitudinal cracks in the cast billet. Conversely, insufficient consumption can affect the reactivity and deformation of the slag-steel interface within the mold, impacting the stability of the protective slag's performance. Specifically, the recommended consumption is 0.4 kg / m³. 2 0.5kg / m 2 0.6kg / m 2 wait.

[0059] In some embodiments, the argon flow rates of both the stopper rod and the upper water inlet are 0.

[0060] The positive effects of controlling the argon blowing flow rate at both the stopper rod and the upper water inlet to be 0 are: ensuring stable slag-steel interface reaction within the crystallizer and avoiding uneven heat transfer. The negative effects of performing argon blowing at the stopper rod and upper water inlet are: argon blowing exacerbates the reactivity and denaturation of the slag-steel interface within the crystallizer, worsens the viscosity, melting point, and other properties of the protective slag, leading to unstable lubrication and heat transfer within the crystallizer.

[0061] In some embodiments, a protective slag is added to the molten steel in the crystallizer for continuous casting, and the chemical composition and consumption of the protective slag are controlled to obtain a cast billet, including:

[0062] A protective slag is added to the molten steel in the crystallizer, and continuous casting is performed. The chemical composition, consumption, and physical parameters of the protective slag are controlled to obtain a cast billet.

[0063] The physical parameters of the protective slag include its melting point and viscosity.

[0064] Viscosity is an important indicator for measuring the lubrication performance of protective slag. The melting point of protective slag is mainly affected by factors such as its composition, alkalinity, and Al2O3 content. If the melting temperature is too high, the lubrication effect will be poor and uneven.

[0065] In some embodiments, the melting point of the protective slag before use is 900℃-1100℃, the viscosity of the protective slag before use is 0.04Pa·s-0.08Pa·s, and / or;

[0066] The melting point of the protective slag after use is ≤1200℃, and the viscosity of the protective slag after use is ≤0.15Pa·s.

[0067] The positive effects of controlling the melting point of the protective slag before use to 900℃-1100℃ include: ensuring the melting performance and stable heat transfer of the protective slag. If the melting point is too high, it can lead to uneven heat transfer within the crystallizer, making longitudinal cracks in the cast billet more likely; if the melting point is too low, it can cause the protective slag to segregate, affecting its stable melting. Specifically, the melting point can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, etc.

[0068] The positive effects of controlling the viscosity of the protective slag before use to 0.04 Pa·s-0.08 Pa·s include ensuring that the viscosity of the modified slag meets the lubrication requirements of the crystallizer. If the viscosity is too high, the modified slag may exceed 0.15 Pa·s, leading to insufficient slag consumption, increased slag-steel reaction within the crystallizer, and failure to meet stable heat transfer and lubrication requirements. Conversely, if the viscosity is too low, excessive slag consumption during the casting of the first furnace head billet may occur, potentially causing uneven heat transfer and longitudinal cracking of the billet. Specifically, this viscosity can be 0.04 Pa·s, 0.05 Pa·s, 0.06 Pa·s, 0.07 Pa·s, 0.08 Pa·s, etc.

[0069] The positive effects of controlling the melting point of the protective slag after use to ≤1200℃ include: ensuring stable lubrication of the protective slag; if the melting point of the protective slag after use is too high, it will, to some extent, increase the thickness of the solid slag film or the insufficient thickness of the liquid slag film in the crystallizer, affecting the lubrication of the crystallizer. Specifically, this melting point can be 1200℃, 1190℃, 1180℃, etc.

[0070] The positive effects of controlling the viscosity of the protective slag after use to ≤0.15 Pa·s include: ensuring a stable consumption of protective slag in the crystallizer and maintaining heat transfer and lubrication in the crystallizer; if the viscosity of the protective slag is too high after use, it will reduce the consumption of protective slag to some extent, increase slag-steel reaction and deformation, and worsen heat transfer and lubrication in the crystallizer. Specifically, this viscosity can be 0.15 Pa·s, 0.14 Pa·s, 0.13 Pa·s, etc.

[0071] Secondly, this application provides a method for preparing high-alumina carbon steel, the method comprising the method described in any embodiment of the first aspect.

[0072] The preparation method of this high-alumina carbon steel is based on the continuous casting method of the above-mentioned high-alumina carbon steel. The specific steps of the continuous casting method of the high-alumina carbon steel can be referred to the above embodiments. Since the preparation method of this high-alumina carbon steel adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0073] 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 national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0074] Table 1 Chemical composition of protective slag

[0075]

[0076] Table 2 Chemical composition (wt%) of high-alumina carbon steel

[0077]

[0078]

[0079] Table 3. Process parameters for continuous casting of high-alumina carbon steel

[0080]

[0081]

[0082] Table 4 Quality Results of High-Aluminum Carbon Steel

[0083] Serial Number Longitudinal cracks + transverse cracks + sink mark index of cast billet Example 1 0.5 Example 2 0.4 Example 3 0.2 Example 4 0.6 Example 5 0.3 Comparative Example 1 15.0 Comparative Example 2 18.2

[0084] The continuous casting method of this application improves the casting speed, stabilizes the thermocouple curve of the crystallizer, and reduces the longitudinal crack + transverse crack + depression index of the billet. While improving the casting speed of high-alumina carbon steel, the billet machine cleaning and manual cleaning rates are significantly reduced.

[0085] 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 continuous casting method for high-alumina carbon steel, characterized in that, The method includes: The molten steel is transferred from the tundish to the crystallizer, and the depth of the submerged nozzle inserted into the molten steel and the argon flow rate of the stopper rod and the top nozzle are controlled. Add protective slag to the molten steel in the crystallizer, perform continuous casting, and control the chemical composition and consumption of the protective slag to obtain a cast billet; The chemical composition of the protective slag includes: CaO, SiO2, Al2O3, MgO, Na2O, F, and Li2O; wherein, The content of Al2O3 is <1.0 wt%, the content of MgO is <1.0 wt%, and the content of Na2O is <2.0 wt%. The weights of CaO, SiO2, and Al2O3 satisfy the following relationship: [CaO] / ([CaO]+[SiO2]+[Al2O3])%=55%-60% In the formula, [CaO] represents the weight of CaO, [SiO2] represents the weight of SiO2, and [Al2O3] represents the weight of Al2O3; The immersion nozzle is inserted into the molten steel to a depth of 150mm-180mm; The argon blowing flow rates of both the stopper rod and the upper water inlet are 0. The consumption of the protective slag is 0.4 kg / m³. 2 -0.6kg / m 2 .

2. The method according to claim 1, characterized in that, The chemical composition of the protective slag includes: The content of CaO is 35.0 wt%-50.0 wt%, the content of SiO2 is 25.0 wt%-40.0 wt%, the content of F is 5.0 wt%-15.0 wt%, and the content of Li2O is 0.5 wt%-4.5 wt%.

3. The method according to claim 1 or 2, characterized in that, The alkalinity of the protective slag is 1.2-1.

5.

4. The method according to claim 1, characterized in that, Adding protective slag to the molten steel in the crystallizer, performing continuous casting, and controlling the chemical composition and consumption of the protective slag to obtain a cast billet, comprising: A protective slag is added to the molten steel in the crystallizer, and continuous casting is performed. The chemical composition, consumption, and physical parameters of the protective slag are controlled to obtain a cast billet. The physical parameters of the protective slag include its melting point and viscosity.

5. The method according to claim 4, characterized in that, The melting point of the protective slag before use is 900℃-1100℃, and the viscosity of the protective slag before use is 0.04Pa·s-0.08Pa·s, and / or; The melting point of the protective slag after use is ≤1200℃, and the viscosity of the protective slag after use is ≤0.15Pa·s.

Images