Continuous casting protective slag for casting high-aluminum steel molten steel and preparation method and application thereof

Abstract

The application provides a continuous casting protective slag for casting high-aluminum steel liquid steel and a preparation method and application thereof, and the mass percentage of the composition of the continuous casting protective slag is as follows: CaO: 20-26%, SiO2: 32-38%, Al2O3: 1-3%, Na2O: 7-12%, F: 6-10%, MnO: 2-4%, carbonaceous material: 3-5%, Li2O: 4-6%, and the rest is other inevitable impurities; wherein, the basicity of the continuous casting protective slag is 0.55-0.70, and the carbonaceous material is a mixture of graphite and carbon black with a mass ratio of 1:1.5-2.5. The continuous casting of high-aluminum steel is carried out by using the continuous casting protective slag, so that the problem of slag strip hypertrophy can be effectively reduced, and the continuous casting can be smoothly carried out.

Description

Technical Field

[0001] This application relates to the field of iron and steel metallurgy, specifically to a continuous casting protective slag for casting high-alumina steel molten steel, its preparation method, and its application. Background Technology

[0002] In the continuous casting process of high-alumina steel, the molten steel contains a high content of the strong reducing element Al, which easily reacts with the silica in the continuous casting protective slag, causing changes in the composition of the protective slag and affecting the smooth progress of high-alumina steel continuous casting.

[0003] Currently, many continuous casting protective slags are used to cast high-alumina steel molten steel. However, these low-reactivity continuous casting protective slags are difficult to produce, costly, have high alkalinity, poor lubrication performance, and are prone to producing large slag bars during casting, causing adhesion alarms and affecting the smooth progress of continuous casting.

[0004] Therefore, there is a need to provide a continuous casting protective slag for casting high-alumina steel that can reduce the problem of slag bar enlargement. Summary of the Invention

[0005] This application provides a continuous casting protective slag for casting high-alumina steel, its preparation method, and its application. Using this continuous casting protective slag for continuous casting of high-alumina steel can effectively reduce the problem of slag bar enlargement and facilitate the smooth progress of continuous casting.

[0006] In a first aspect, this application provides a continuous casting protective slag for casting high-alumina steel molten steel, the composition of which is as follows by mass percentage:

[0007] CaO: 20%–26%

[0008] SiO2: 32%–38%,

[0009] Al2O3: 1%–3%,

[0010] Na2O: 7%–12%,

[0011] F: 6%–10%,

[0012] MnO: 2%–4%,

[0013] Carbonaceous materials: 3%–5%,

[0014] Li2O: 4%–6%,

[0015] The remainder consists of other unavoidable impurities;

[0016] The basicity of the continuous casting protective slag is 0.55–0.70.

[0017] The carbonaceous material is a mixture of graphite and carbon black in a mass ratio of 1:1.5 to 2.5.

[0018] In the technical solution of this application, by controlling the mass percentage of each component of the continuous casting protective slag, a low-viscosity, low-melting-point continuous casting protective slag is obtained. This continuous casting protective slag can react slowly with aluminum in molten steel, preventing excessive precipitation of calcium aluminum feldspar. At the same time, by reducing the content of sodium oxide and fluorine, and using a certain mass ratio of graphite and carbon black as carbonaceous materials, the formation of high-melting-point phases and the occurrence of segregation can be reduced, thereby effectively reducing the problem of slag bar enlargement and facilitating the smooth continuous casting of high-alumina steel.

[0019] In some embodiments of this application, the melting point of the continuous casting protective slag is 850–950°C;

[0020] Optionally, the viscosity of the continuous casting protective slag at 1300℃ is 0.05~0.2Pa·s.

[0021] In some embodiments of this application, the raw materials of the continuous casting protective slag include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, semi-reinforcing carbon black, and flake graphite.

[0022] Secondly, this application provides a method for preparing continuous casting protective slag, comprising the following steps:

[0023] S10: Providing raw materials formulated according to the composition of the continuous casting protective slag according to any one of claims 1 to 3;

[0024] S20: The raw materials are mixed, pre-melted, cooled, and ground to obtain a powder;

[0025] S30: The grinding material is granulated to obtain the continuous casting protective slag.

[0026] In the technical solution of this application, a pre-melting method is used to prepare a continuous casting protective slag with the chemical composition of any embodiment of the first aspect. The continuous casting protective slag obtained in this way has good melting uniformity, fast slag formation speed, and reduces the occurrence of segregation phenomenon. The continuous casting protective slag obtained by this method is more conducive to the smooth progress of the continuous casting process.

[0027] Thirdly, this application provides a method for preparing a high-alumina steel billet, comprising the following steps:

[0028] High-alumina steel billets are obtained by continuously casting molten high-alumina steel using the continuous casting protective slag prepared according to any embodiment of the first aspect or the preparation method described in any embodiment of the second aspect.

[0029] In the technical solution of this application, the continuous casting protective slag prepared by the method of any embodiment of the first aspect or the preparation method of any embodiment of the second aspect is used to continuously cast high-alumina steel molten steel. The occurrence rate of sticking alarm and emergency speed reduction and the occurrence rate of steel leakage are low during the continuous casting process, which is conducive to the smooth continuous casting of high-alumina steel and the production efficiency is higher.

[0030] In some embodiments of this application, the mass percentage of aluminum in the molten high-aluminum steel is 3.5% to 5%.

[0031] In some embodiments of this application, during the continuous casting process, the specific water volume for secondary cooling is 0.6 to 0.8 L / kg, and the taper of the crystallizer is 0.8% to 1.2%.

[0032] In some embodiments of this application, during the continuous casting process, argon is blown onto the stopper rod and the upper nozzle, argon is used to seal the long nozzle, and argon is used to pour steel between plates.

[0033] The argon flow rate of the stopper rod is 1-3 L / min, the argon flow rate of the upper water inlet is 0.5-2 L / min, and the back pressure of the argon sealing gas at the long water inlet and the argon between the plates is >0 MPa.

[0034] In some embodiments of this application, during the continuous casting process, the thickness of the liquid slag layer of the continuous casting protective slag is 8-12 mm, and the consumption of the continuous casting protective slag is 0.3-0.4 kg / t of molten steel.

[0035] In some embodiments of this application, during the continuous casting process, the liquid slag basicity of the continuous casting protective slag is ≤1.8 and the mass percentage of alumina is ≤30%. Detailed Implementation

[0036] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0037] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0039] The smooth operation of the continuous casting process for high-alumina steel has always been a crucial factor affecting its production efficiency. Because high-alumina steel contains a high content of strongly reducing aluminum, when using traditional CaO-SiO2-based protective slag during continuous casting, the aluminum in the molten steel readily reacts with SiO2. This leads to a sharp increase in Al2O3 in the protective slag, a dramatic rise in the viscosity of the slag layer, deterioration of the protective slag's lubrication function, and a significant reduction in heat transfer between the billet shell and the mold. This imbalance between lubrication and heat transfer performance hinders the smooth progress of continuous casting.

[0040] Existing technologies include low-reactive or non-reactive continuous casting fluxes that reduce or eliminate the SiO2 content in the flux and replace it with amphoteric oxide components such as Al2O3 to inhibit or eliminate the reaction between Al and SiO2 in the flux. However, because the non-reactive flux changes from the traditional silicate structure to an aluminate structure, and the amphoteric oxide Al2O3 makes the flux structure complex and variable, its basic properties are extremely unstable, making the development of non-reactive fluxes extremely difficult. In practical applications, low-reactive CaO-SiO2-Al2O3 fluxes exhibit phenomena such as difficulty in melting, large slag strands, and uncoordinated lubrication and heat transfer, resulting in serious billet defects and making it impossible to achieve continuous casting in multiple furnaces, thus still failing to guarantee the smooth progress of continuous casting.

[0041] To address this issue, the inventors chose to improve the composition of a CaO-SiO2-based protective slag. Specifically, they optimized the composition of the protective slag to reduce the size of slag streaks during the continuous casting process of high-alumina steel, thus facilitating smoother casting. Furthermore, to further optimize the continuous casting process of high-alumina steel based on this protective slag, the inventors also further optimized the continuous casting process for high-alumina steel.

[0042] In a first aspect, this application provides a continuous casting protective slag for casting high-alumina steel molten steel, the composition of which is as follows by mass percentage:

[0043] CaO: 20%–26%

[0044] SiO2: 32%–38%,

[0045] Al2O3: 1%–3%,

[0046] Na2O: 7%–12%,

[0047] F: 6%–10%,

[0048] MnO: 2%–4%,

[0049] Carbonaceous materials: 3%–5%,

[0050] Li2O: 4%–6%,

[0051] The remainder consists of other unavoidable impurities;

[0052] The basicity of the continuous casting protective slag is 0.55–0.70.

[0053] The carbonaceous material is a mixture of graphite and carbon black in a mass ratio of 1:1.5 to 2.5.

[0054] In the technical solution of this application, by controlling the mass percentage of each component of the continuous casting protective slag, a low-viscosity, low-melting-point continuous casting protective slag is obtained. This continuous casting protective slag can react slowly with aluminum in molten steel, preventing excessive precipitation of calcium aluminum feldspar. At the same time, by reducing the content of sodium oxide and fluorine, and using a certain mass ratio of graphite and carbon black as carbonaceous materials, the formation of high-melting-point phases and the occurrence of segregation can be reduced, thereby effectively reducing the problem of slag bar enlargement and facilitating the smooth continuous casting of high-alumina steel.

[0055] The following details the design concept of each component in the continuous casting protective slag provided in this application.

[0056] Firstly, to promote the consumption of the protective slag and achieve a balanced and stable performance, the greater the consumption of protective slag, the greater the replenishment of new protective slag at the steel-slag interface. Since the amount of SiO2 consumed by the steel-slag reaction per unit mass of protective slag is reduced, the basic physicochemical properties of the protective slag may not change significantly. Therefore, by reducing the basicity and viscosity of the continuous casting protective slag, the consumption of the protective slag is increased, allowing for rapid replacement of the molten slag in contact with the high-alumina steel. This controls the deterioration of the protective slag's physicochemical properties caused by the steel-slag reaction within a certain range, ensuring that the protective slag after the steel-slag reaction still meets the requirements of continuous casting. Furthermore, a low-basicity protective slag can increase the proportion of the glass phase during solidification, slowing down the formation of slag streaks. Therefore, in this application, the mass percentages of CaO and SiO2 in the continuous casting protective slag can be controlled at 20%–26% and 32%–38%, respectively, while its basicity can be controlled within the range of 0.55–0.70. Preferably, the basicity of the continuous casting protective slag can be 0.6–0.7.

[0057] Secondly, Na₂O, F, MnO, and Li₂O in continuous casting protective slag mainly function as fluxes and fluxes, reducing the viscosity and melting point of the protective slag, thereby ensuring the consumption of protective slag and reducing the impact of steel slag reaction on continuous casting. However, through extensive experiments and analysis, the inventors discovered that while increasing the content of the above components in existing continuous casting protective slag can effectively reduce the viscosity and melting point, it also leads to excessively large slag bars. Excessively large slag bars result in an excessively narrow slag channel at the meniscus, affecting the inflow of protective slag. Furthermore, it may cause sintered agglomerates to flow into the slag channel with the molten slag, potentially causing blockage and hindering the smooth inflow of the molten slag layer, thus reducing the consumption of protective slag and affecting the smooth operation of continuous casting. The inventors analyzed that the enlarged slag bars might be due to three factors. Firstly, the components in the continuous casting protective slag react to form high-melting-point phases. Simultaneously, the low viscosity of the protective slag leads to rapid mass transfer, promoting the precipitation of these high-melting-point phases. Secondly, an excessive content of low-melting-point components in the protective slag can easily cause segregation, with the low-melting-point components forming liquid slag at lower temperatures, while the high-melting-point portions are bound together to form sintered products. Thirdly, improper composition of carbonaceous materials in the protective slag can increase the thickness of the sintered layer during casting, resulting in enlarged slag bars.

[0058] Based on the above analysis, in order to reduce the problem of slag bar enlargement, the inventors further optimized the content of Na₂O, F, MnO, and Li₂O in the continuous casting protective slag while ensuring that it has a low melting point and viscosity. Through analysis of the slag bar composition, the inventors discovered that it contains high-melting-point gun crystals. Analysis of the gun crystal production process revealed that it is mainly related to the Na₂O and F content in the continuous casting protective slag. Therefore, in the continuous casting protective slag provided in this application, the Na₂O and F content is appropriately reduced to decrease gun crystal formation, with the Na₂O and F contents controlled at 7%–12% and 6%–10%, respectively. Preferably, the mass percentages of Na₂O and F can be 8%–10% and 9%–10%, respectively.

[0059] In addition to lowering the melting point, MnO can preferentially react with SiO2 and Al in molten steel during continuous casting, thus protecting SiO2 in the continuous casting flux. However, its effect on lowering the melting point and viscosity of the flux is less effective than that of Na2O and Li2O. Therefore, the MnO content is controlled at 2%–4%. Li2O has a good effect on lowering the melting point and viscosity of the flux and has no significant effect on the slag bars. However, due to the high cost of Li2O, the Li2O content is controlled at 4%–6% in this application.

[0060] In this application, a mixture of graphite and carbon black in a mass ratio of 1:1.5 to 2.5 is used as the carbonaceous material. Because carbon black has a larger specific surface area, it provides better coating for the protective slag and stronger inhibition of sintering, thus significantly reducing the thickness of the sintered layer and consequently reducing the problem of slag growth. However, since carbon black is easily combustible at high temperatures, its effect on inhibiting slag growth weakens at high temperatures. Graphite, on the other hand, has a higher combustion temperature than carbon black and can persist at higher temperatures, continuing to inhibit the sintering of the protective slag. Furthermore, the inventors discovered that because graphene has a smaller specific surface area than carbon black, its sintering inhibition effect is not as strong. A sintered layer and a semi-molten layer appear in the protective slag. The presence of the semi-molten layer increases the ability of the molten layer to provide liquid slag, thus helping to maintain a thicker liquid slag layer. Through numerous experiments, the inventors discovered that when a mixture of graphite and carbon black in a mass ratio of 1:1.5 to 2.5 is used as the carbonaceous material, and the mass percentage of the carbonaceous material in the continuous casting protective slag is 3% to 5%, the continuous casting protective slag not only effectively inhibits sintering and reduces the problem of slag bar enlargement, but also helps maintain a thicker liquid slag layer, providing good lubrication for continuous casting, thus facilitating the smooth progress of continuous casting.

[0061] In some embodiments of this application, the melting point of the continuous casting protective slag is 850–950°C;

[0062] Optionally, the viscosity of the continuous casting protective slag at 1300℃ is 0.05–0.2 Pa·s.

[0063] In some of the above embodiments, the melting point of the continuous casting protective slag was found to be 850–950°C, and its viscosity at 1300°C was 0.05–0.2 Pa·s. It should be noted that the melting point of the protective slag in this application refers to its hemispherical point temperature. Low melting point and low viscosity are beneficial for increasing the thickness of the slag layer, improving slag consumption during continuous casting, and increasing the slag renewal rate. This prevents a sharp increase in melting point and viscosity due to a large increase in alumina content and a large decrease in silica content in the slag caused by prolonged steel-slag reaction. Simultaneously, the lower viscosity and melting point can offset the effects of steel-slag reaction to a certain extent. Even after a short period of steel-slag reaction, the protective slag can still meet the requirements of continuous casting, thus facilitating the smooth progress of continuous casting.

[0064] In some embodiments of this application, the raw materials for continuous casting protective slag include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, semi-reinforcing carbon black, and flake graphite.

[0065] In some of the above embodiments, the raw materials are commonly used in the preparation of continuous casting protective slag. The pre-melted material is the main raw material for the protective slag, serving as the primary source of SiO2, CaO, Na2O, and F. Glass powder provides SiO2 and Al2O3, manganese carbonate provides MnO, fluorite, sodium fluoride, and cryolite provide F, and lithium carbonate provides Li2O. Semi-reinforcing carbon black and flake graphite are used in the carbonaceous materials. The continuous casting protective slag is obtained by proportioning the above raw materials according to the chemical composition of the protective slag. Semi-reinforcing carbon black has a larger specific surface area than ordinary carbon black, resulting in better coating of the protective slag, better inhibition of sintering, and greater resistance to slag growth. Flake graphite has a better inhibition of sintering than ordinary graphite; more preferably, the particle size of the flake graphite is 100–500 mesh.

[0066] In some embodiments of this application, the raw materials for continuous casting protective slag, by mass percentage, include:

[0067] The composition includes: 60.0%–70.0% premelted material, 5.0%–9.0% fine glass powder, 2.0%–4.0% manganese carbonate, 10.0%–15.0% fluorite, 12.0%–15.0% lithium carbonate, 12.0%–15.0% sodium fluoride, 2.0%–4.0% cryolite, 1.5%–3.5% semi-reinforcing carbon black, and 0.8%–1.5% flake graphite.

[0068] The chemical composition of the pre-melted material is as follows by mass percentage: SiO2: 30%–35%, CaO: 18%–24%, Na2O: 7.5%–13%, F: 8%–8.5%, with the balance being other unavoidable impurities.

[0069] In some of the above embodiments, the raw materials for continuous casting protective slag are calculated based on the chemical composition of the required continuous casting protective slag and the types of each raw material. The raw materials are then proportioned accordingly to obtain continuous casting protective slag for casting high-alumina steel molten steel.

[0070] Secondly, this application provides a method for preparing continuous casting protective slag, comprising the following steps:

[0071] S10: Provide raw materials prepared according to the composition of the continuous casting protective slag according to any embodiment of the first aspect;

[0072] S20: Mix and pre-melt the raw materials, cool them, and grind them to obtain a powder;

[0073] S30: Granulate the grinding material to obtain continuous casting protective slag.

[0074] In the technical solution of this application, a pre-melting method is used to prepare a continuous casting protective slag with the chemical composition of any embodiment of the first aspect. The continuous casting protective slag obtained in this way has good melting uniformity, fast slag formation speed, and reduces the occurrence of segregation phenomenon. The continuous casting protective slag obtained by this method is more conducive to the smooth progress of the continuous casting process.

[0075] In some embodiments of this application, step S20 specifically includes:

[0076] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are pulverized to 100-150 mesh, dried at 200-250℃, and then mixed. The mixed raw materials are pre-melted at 1400-1460℃ and held for 20-30 minutes to obtain pre-melted raw materials. After cooling the pre-melted raw materials, they are mixed with semi-reinforcing carbon black and flake graphite and ground to obtain a powder with a particle size of 1-5 μm.

[0077] In some embodiments of this application, step S30 specifically includes:

[0078] The ground material is fed into a spray granulation tower to obtain hollow particles with a particle size of 60-100 mesh, which are used as continuous casting protective slag.

[0079] In some of the above embodiments, the hollow structure of the continuous casting protective slag has a better heat insulation effect, can spread well on the surface of molten steel, and thus gives the protective slag a good heat insulation effect and can prevent the molten steel from being oxidized by air.

[0080] Thirdly, this application provides a method for preparing a high-alumina steel billet, comprising the following steps:

[0081] High-alumina steel billets are obtained by continuously casting molten high-alumina steel using a continuous casting protective slag prepared according to any embodiment of the first aspect or the preparation method of any embodiment of the second aspect.

[0082] In the technical solution of this application, the continuous casting protective slag prepared by the method of any embodiment of the first aspect or the preparation method of any embodiment of the second aspect is used to continuously cast high-alumina steel molten steel. The occurrence rate of sticking alarm and emergency speed reduction and the occurrence rate of steel leakage are low during the continuous casting process, which is conducive to the smooth continuous casting of high-alumina steel and the production efficiency is higher.

[0083] In some embodiments of this application, the mass percentage of aluminum in the molten high-aluminum steel is 3.5% to 5%.

[0084] In some of the above embodiments, in the prior art, when continuously casting high-alumina steel with the aforementioned aluminum content, it is easy to encounter crystallizer sticking alarms, emergency speed reductions, and steel leakage. The method provided in this application is particularly suitable for casting high-alumina steel molten steel. By optimizing the composition of the continuous casting protective slag, it achieves a lower melting point and viscosity while inhibiting slag bar growth, ensuring the thickness of the liquid slag layer during continuous casting, and improving the slag layer renewal rate. This reduces the impact of steel-slag reaction on the liquid slag layer, ensuring that the continuous casting protective slag still meets the continuous casting requirements after the steel-slag reaction. Therefore, crystallizer sticking alarms, emergency speed reductions, and steel leakage are less likely to occur during continuous casting, facilitating smooth continuous casting. This method has excellent effects on the continuous casting of high-alumina steel with various aluminum contents.

[0085] In some embodiments of this application, during continuous casting, the specific water volume for secondary cooling is 0.6 to 0.8 L / kg, and the taper of the crystallizer is 0.8% to 1.2%.

[0086] In some of the above embodiments, the viscosity of the liquid slag in continuous casting increases sharply after reacting with the steel slag, resulting in poor fluidity and reduced ability to fill the voids between the solidified billet shell and the mold wall. To address this, the specific water volume for secondary cooling is controlled at 0.6–0.8 L / kg. This stronger secondary cooling increases the solidification thickness of the billet shell and enhances its shrinkage. Simultaneously, the taper of the mold is controlled at 0.5%–1.2%. The taper of the mold has a well-known definition in the art, calculated as: (mold top width - mold bottom width) / mold top width × 100%. The smaller taper of the mold compared to typical continuous casting molds effectively widens the voids between the mold wall and the billet. Therefore, by controlling the specific water volume for secondary cooling and the taper of the mold, the inflow channel of the liquid slag layer in continuous casting is expanded, ensuring that the high-viscosity liquid slag layer still maintains a significant thickness. This increases slag consumption and the renewal rate of the liquid slag layer, thus facilitating smooth continuous casting.

[0087] In some embodiments of this application, during continuous casting, argon is blown onto the stopper rod and the top nozzle, argon is used to seal the long nozzle, and argon is used to pour steel between plates.

[0088] The argon flow rate of the stopper rod is 1-3 L / min, the argon flow rate of the upper water inlet is 0.5-2 L / min, and the back pressure of the argon sealing gas at the long water inlet and the argon between the plates is >0 MPa.

[0089] In some of the above embodiments, during continuous casting, argon is blown through the stopper rod and the top nozzle, argon is used for sealing the long nozzle, and argon is used for pouring steel between plates. This is to prevent the slag from reacting excessively to produce too much alumina, causing the alkalinity to rise too quickly and deteriorate the lubrication performance of the protective slag. At the same time, the argon flow rate of the stopper rod is controlled at 1-3 L / min, the argon flow rate of the top nozzle is 0.5-2 L / min, and the back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0 MPa. These conditions can reduce the fluctuation range of the liquid surface in the crystallizer during continuous casting, thereby relatively reducing the intensity of the slag reaction, stabilizing the performance of the protective slag as much as possible, preventing its viscosity and alkalinity from rising too quickly, and ensuring the lubricity of the slag layer in the continuous casting protective slag.

[0090] In some embodiments of this application, during continuous casting, the thickness of the liquid slag layer of the continuous casting protective slag is 8-12 mm, and the consumption of the continuous casting protective slag is 0.3-0.4 kg / t of molten steel.

[0091] In some of the above embodiments, through measurement and calculation, by using the continuous casting protective slag provided in the first and second aspects, and in conjunction with optimized continuous casting process, it can be ensured that the thickness of the liquid slag layer of the continuous casting protective slag is 8-12 mm during continuous casting. At the same time, the consumption of the continuous casting protective slag is 0.3-0.4 kg / t of molten steel, which can ensure the slag renewal rate, prevent the alkalinity and viscosity of the liquid slag layer from being too high, and ensure good lubricity of the liquid slag layer with a thicker liquid slag layer, reducing the occurrence of crystallizer sticking alarms, emergency speed reduction and steel leakage, which is conducive to the smooth progress of continuous casting.

[0092] In some embodiments of this application, during the continuous casting process, the liquid slag basicity of the continuous casting protective slag is ≤1.8 and the mass percentage of alumina is ≤30%.

[0093] In some of the above embodiments, due to the characteristics of continuous casting of high-alumina steel, although the silica in the continuous casting protective slag reacts with the aluminum in the molten steel, the alkalinity and alumina content in the slag layer of the continuous casting protective slag will continuously increase, leading to a decrease in the thickness and lubricity of the slag layer. Through extensive experiments, the inventors have found that when using the continuous casting protective slag provided in this application to cast high-alumina steel, when the alkalinity of the slag exceeds 1.8 or the mass percentage of alumina exceeds 30%, a crystallizer adhesion alarm and emergency speed reduction are easily triggered. Therefore, during the continuous casting process, the alkalinity and alumina content in the slag layer of the continuous casting protective slag can be detected. By skimming and replacing the slag, the alkalinity can be controlled below 1.8 and the mass percentage of alumina below 30%.

[0094] Specifically, during continuous casting, if two crystallizer sticking alarms and speed reductions occur within 10 minutes, the liquid slag is scooped out and protective slag is added again to ensure the smooth progress of continuous casting.

[0095] The following examples illustrate in more detail the continuous casting protective slag for casting high-alumina steel and its application, but this application is by no means limited to these examples.

[0096] Example 1

[0097] Preparation method of continuous casting protective slag for casting high-alumina steel:

[0098] Weigh out the following components by mass percentage: 66.4% premelted material, 4.0% fine glass powder, 4.0% manganese carbonate, 6.0% fluorite, 3.0% sodium fluoride, 3.0% cryolite, 11% lithium carbonate, 1.8% semi-reinforcing carbon black, and 0.8% flake graphite as raw materials.

[0099] The chemical composition of the pre-melted material is as follows (mass percentage): CaO 24.0%, SiO2 35.0%, Na2O 12.9%, F 8.5%, with the balance being other unavoidable impurities.

[0100] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are crushed to 120 mesh, dried at 220℃, mixed evenly, pre-melted at 1420℃, held for 30 minutes, cooled, and then mixed and ground with semi-reinforcing carbon black and flake graphite to a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer, with a particle size of 80 mesh.

[0101] The protective slag for crystallizer has an basicity of 0.62, a viscosity of 0.08 Pa·s at 1300℃, and a melting point of 920℃. The mass percentage of its components is as follows:

[0102] CaO: 24.8%,

[0103] SiO2: 37.5%,

[0104] Al2O3: 2.5%,

[0105] Na2O: 9.5%,

[0106] F: 9.2%,

[0107] MnO: 3%,

[0108] Carbonaceous materials (a mixture of flake graphite and semi-reinforcing carbon black in a mass ratio of 1:2.25): 3.2%, Li₂O: 5.1%,

[0109] The remainder consists of other unavoidable impurities.

[0110] The above-mentioned continuous casting protective slag is used to cast high-alumina steel with an aluminum content of 4wt%. The secondary cooling water flow rate is 0.6–0.8 L / kg, the crystallizer taper is 1.1%, the stopper rod argon flow rate is 1–3 L / min, the upper nozzle argon flow rate is 0.5–2 L / min, the long nozzle is sealed with argon, and argon is used for casting between plates. The back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0 MPa. The maximum dimensions of the slag bars are 52 mm in length and 28 mm in width, and the continuous casting capacity can reach 660 tons.

[0111] Example 2

[0112] Preparation method of continuous casting protective slag for casting high-alumina steel:

[0113] Weigh out the following components by mass percentage: 66.8% premelted material, 4% fine glass powder, 4.0% manganese carbonate, 6.0% fluorite, 3.0% sodium fluoride, 2.5% cryolite, 11% lithium carbonate, 1.8% semi-reinforcing carbon black, and 0.9% flake graphite as raw materials.

[0114] The chemical composition of the pre-melted material is as follows (mass percentage): CaO 23.0%, SiO2 36.0%, Na2O 12.5%, F 8.0%, with the balance being other unavoidable impurities.

[0115] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are crushed to 100 mesh, dried at 220℃, mixed evenly, pre-melted at 1400℃, held for 20 minutes, cooled, and then mixed and ground with semi-reinforcing carbon black and flake graphite to form a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer, with a particle size of 80 mesh.

[0116] The protective slag for crystallizer has an basicity of 0.66, a viscosity of 0.12 Pa·s at 1300℃, and a melting point of 882℃. The mass percentage of its components is as follows:

[0117] CaO: 25.2%,

[0118] SiO2: 37.2%,

[0119] Al2O3: 2.2%,

[0120] Na2O: 8.8%,

[0121] F: 9.8%,

[0122] MnO: 2.2%,

[0123] Carbonaceous material (a mixture of flake graphite and semi-reinforcing carbon black in a 1:2 mass ratio): 3.5%, Li₂O: 5.0%.

[0124] The remainder consists of other unavoidable impurities.

[0125] The above-mentioned continuous casting protective slag is used to cast high-alumina steel with an aluminum content of 4.1 wt%. The secondary cooling water flow rate is 0.6–0.8 L / kg, the crystallizer taper is 1.1%, the stopper rod argon flow rate is 1–3 L / min, the upper nozzle argon flow rate is 0.5–2 L / min, the long nozzle is sealed with argon, and argon is used for casting between plates. The back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0 MPa. The maximum length and width of the slag bars are 56 mm and 29 mm, respectively, and the continuous casting capacity can reach 656 tons.

[0126] Example 3

[0127] Preparation method of continuous casting protective slag for casting high-alumina steel:

[0128] Weigh out the following by mass percentage: 66.5% premelted material, 4% fine glass powder, 4.0% manganese carbonate, 6.0% fluorite, 4.0% sodium fluoride, 2.0% cryolite, 11.0% lithium carbonate, 1.7% semi-reinforcing carbon black, and 0.8% flake graphite as raw materials;

[0129] The chemical composition of the pre-melted material is as follows (mass percentage): CaO 23.0%, SiO2 35.0%, Na2O 11.8%, F 8.2%, with the balance being other unavoidable impurities.

[0130] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are crushed to 120 mesh, dried at 250℃, mixed evenly, pre-melted at 1410℃, kept at that temperature for 20 minutes, cooled, and then mixed and ground with semi-reinforcing carbon black and flake graphite to form a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer, with a particle size of 80 mesh.

[0131] The protective slag for crystallizer has an basicity of 0.62, a viscosity of 0.10 Pa·s at 1300℃, and a melting point of 905℃. The mass percentage of its components is as follows:

[0132] CaO: 25.0%,

[0133] SiO2: 38.0%,

[0134] Al2O3: 2.1%,

[0135] Na2O: 9.2%,

[0136] F: 9.2%,

[0137] MnO: 2.1%,

[0138] Carbonaceous material (a mixture of flake graphite and semi-reinforcing carbon black in a mass ratio of 1:2.215): 3.4%,

[0139] Li2O: 5.2%,

[0140] The remainder consists of other unavoidable impurities.

[0141] The above-mentioned continuous casting protective slag is used to cast high-alumina steel with an aluminum content of 4.2 wt%. The secondary cooling water flow rate is 0.6–0.8 L / kg, the crystallizer taper is 1.1%, the stopper rod argon flow rate is 1–3 L / min, the upper nozzle argon flow rate is 0.5–2 L / min, the long nozzle is sealed with argon, and argon is used for casting between plates. The back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0 MPa. The maximum length and width of the slag bars are 57 mm and 27 mm, respectively, and the continuous casting capacity can reach 652 tons.

[0142] Comparative Example 1

[0143] Preparation method of continuous casting protective slag for casting high-alumina steel:

[0144] Weigh out the following by mass percentage: 66.4% premelted material, 4.0% fine glass powder, 4.0% manganese carbonate, 6.0% fluorite, 3.0% sodium fluoride, 3.0% cryolite, 11% lithium carbonate, 1.3% semi-reinforcing carbon black, and 1.3% flake graphite as raw materials;

[0145] The chemical composition of the pre-melted material is as follows (mass percentage): CaO 24.0%, SiO2 35.0%, Na2O 12.9%, F 8.5%, with the balance being other unavoidable impurities.

[0146] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are crushed to 120 mesh, dried at 220℃, mixed evenly, pre-melted at 1420℃, held for 30 minutes, cooled, and then mixed and ground with semi-reinforcing carbon black and flake graphite to a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer, with a particle size of 80 mesh.

[0147] The protective slag for crystallizer has an basicity of 0.62, a viscosity of 0.08 Pa·s at 1300℃, and a melting point of 920℃. The mass percentage of its components is as follows:

[0148] CaO: 24.8%,

[0149] SiO2: 37.5%,

[0150] Al2O3: 2.5%,

[0151] Na2O: 9.5%,

[0152] F: 9.2%,

[0153] MnO: 3%,

[0154] Carbonaceous material (a mixture of flake graphite and semi-reinforcing carbon black in a 1:1 mass ratio): 3.2%, Li₂O: 5.1%.

[0155] The remainder consists of other unavoidable impurities.

[0156] The above-mentioned continuous casting protective slag is used to cast high-alumina steel with an aluminum content of 4.1 wt%. The secondary cooling water flow rate is 0.5–0.7 L / kg, the crystallizer taper is 1.1%, the stopper rod argon flow rate is 1–3 L / min, the upper nozzle argon flow rate is 0.5–2 L / min, the long nozzle is sealed with argon, and argon is used for casting between plates. The back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0.5 MPa. The maximum length and width of the slag bar are 190 mm and 65 mm, respectively, and the continuous casting capacity can reach 216 tons.

[0157] Comparative Example 2

[0158] Preparation method of continuous casting protective slag for casting high-alumina steel:

[0159] Weigh out the following components by mass percentage: 66.1% premelted material, 4.0% fine glass powder, 4.0% manganese carbonate, 7.0% fluorite, 5.0% sodium fluoride, 3.0% cryolite, 8% lithium carbonate, 1.9% semi-reinforcing carbon black, and 0.9% flake graphite as raw materials.

[0160] The chemical composition of the pre-melted material is as follows (mass percentage): CaO 24.0%, SiO2 35.0%, Na2O 12.1%, F 8.5%, with the balance being other unavoidable impurities.

[0161] The raw materials, excluding semi-reinforcing carbon black and flake graphite, are crushed to 120 mesh, dried at 225℃, mixed evenly, pre-melted at 1410℃, kept at that temperature for 30 minutes, cooled, and then mixed and ground with semi-reinforcing carbon black and flake graphite to form a powder with a particle diameter of 1-3 μm. The powder is then fed into a spray granulation tower to form hollow particles, thus producing the protective slag for the crystallizer, with a particle size of 80 mesh.

[0162] The protective slag for crystallizer has an basicity of 0.62, a viscosity of 0.11 Pa·s at 1300℃, and a melting point of 917℃. The mass percentage of its components is as follows:

[0163] CaO: 24.8%,

[0164] SiO2: 37.5%,

[0165] Al2O3: 2.5%,

[0166] Na2O: 12.5%,

[0167] F: 10.8%,

[0168] MnO: 3%,

[0169] Carbonaceous materials (a mixture of flake graphite and semi-reinforcing carbon black in a mass ratio of 1:2.11): 3.3%, Li₂O: 3.1%,

[0170] The remainder consists of other unavoidable impurities.

[0171] The above-mentioned continuous casting protective slag is used to cast high-alumina steel with an aluminum content of 4.2 wt%. The secondary cooling water flow rate is 0.5–0.7 L / kg, the crystallizer taper is 1.1%, the stopper rod argon flow rate is 1–3 L / min, the upper nozzle argon flow rate is 0.5–2 L / min, the long nozzle is sealed with argon, and argon is used for casting between plates. The back pressure of the argon sealing gas at the long nozzle and the argon between plates is >0.5 MPa. The maximum length and width of the slag bar are 169 mm and 63 mm, respectively, and the continuous casting capacity can reach 214 tons.

[0172] By comparing the results of each embodiment and the comparative example, it can be seen that when using the continuous casting protective slag prepared in each embodiment to cast high-alumina steel molten steel, the maximum length and width of the slag bars are relatively small, which is conducive to the smooth continuous casting of high-alumina steel molten steel, and a maximum continuous casting capacity of 660t of molten steel can be achieved. In contrast, in Comparative Example 1, the slag bars are large, and the continuous casting capacity can only reach 216t. In Comparative Example 2, the slag bars are also relatively large, and the continuous casting capacity can only reach 214t. The carbonaceous material used in the continuous casting protective slag of Comparative Example 1 is different from that of Embodiment 1. The Na2O, F, and Li2O content in the continuous casting protective slag of Comparative Example 2 is significantly different from that of the embodiment, which leads to the large slag bars, which is not conducive to the smooth continuous casting process. For specific possible reasons, please refer to the above.

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a high-alumina steel billet, characterized in that, Includes the following steps: High-alumina steel billets are obtained by continuous casting of high-alumina steel molten steel using continuous casting protective slag. The aluminum content in the high-alumina steel molten steel is 3.5%-5% by mass. The slag layer thickness of the continuous casting protective slag is 8-12 mm, and the consumption of the continuous casting protective slag is 0.3-0.4 kg / t of molten steel. During the continuous casting process, the basicity of the molten slag is ≤1.8, and the alumina content by mass is ≤30%. The mass percentage of the components of the continuous casting protective slag is as follows: CaO: 20%–26% SiO2: 32%–38%, Al2O3: 1%–3%, Na2O: 7%–12%, F：6％～10％， MnO: 2%–4%, Carbonaceous materials: 3%–5%, Li2O: 4%–6%, The remainder consists of other unavoidable impurities; The basicity of the continuous casting protective slag is 0.55–0.

70. The carbonaceous material is a mixture of graphite and carbon black in a mass ratio of 1:1.5 to 2.5; The melting point of the continuous casting protective slag is 850–950℃; the viscosity of the continuous casting protective slag at 1300℃ is 0.05–0.2 Pa·s.

2. The preparation method according to claim 1, characterized in that, The raw materials for the continuous casting protective slag include: pre-melted material, glass powder, manganese carbonate, fluorite, sodium fluoride, cryolite, lithium carbonate, semi-reinforcing carbon black, and flake graphite.

3. The preparation method according to claim 1, characterized in that, The continuous casting protective slag is prepared by the following method: S10: Providing raw materials formulated according to the composition of the continuous casting protective slag as described in claim 1 or 2; S20: The raw materials are mixed, pre-melted, cooled, and ground to obtain a powder; S30: The grinding material is granulated to obtain the continuous casting protective slag.

4. The preparation method according to claim 1, characterized in that, During the continuous casting process, the specific water volume for secondary cooling is 0.6–0.8 L / kg, and the taper of the crystallizer is 0.8%–1.2%.

5. The preparation method according to claim 1, characterized in that, During the continuous casting process, argon is blown into the stopper rod and the upper sprue, argon is used to seal the long sprue, and argon is used to pour steel between plates. The argon flow rate of the stopper rod is 1-3 L / min, the argon flow rate of the upper water inlet is 0.5-2 L / min, and the back pressure of the argon sealing gas at the long water inlet and the argon between the plates is >0 MPa.