Low-reactivity fluoride-free continuous casting protective agent for high-aluminum steel and preparation method and application thereof

Abstract

The application discloses a low-reactivity fluoride-free continuous casting protective slag for high-aluminum steel and a preparation method and application thereof, relates to the technical field of steel metallurgy continuous casting protective slag, and fundamentally inhibits the reduction reaction between molten steel aluminum and the protective slag by designing a reaction inhibition system composed of low SiO2, ZrO2 and carbon black and a fluoride-free composite fluxing system composed of BaO, B2O3, Na2O and Li2O, guarantees the long-term stability of the performance of the protective slag, such as the melting point and the viscosity, realizes complete fluoride-free environmental protection, avoids the harm of fluoride to the human body and the environment and the corrosion of fluoride to equipment, and simultaneously provides the preparation method of the protective slag, realizes the uniform mixing of raw materials, optimizes the microstructure of the protective slag, improves the inclusion absorption capacity and the mechanical strength of the protective slag, solves the defects of a traditional preparation process, and is simple in preparation process, easy to industrialize, and low in production cost.

Description

Technical Field

[0001] This invention relates to the field of continuous casting protective slag technology in iron and steel metallurgy, and more specifically, to a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel, its preparation method, and its application. Background Technology

[0002] High-alumina steel possesses low density, high strength, good oxidation resistance, excellent low-temperature toughness, and outstanding wear resistance and nitriding properties. It also balances lightweight and high toughness, making it suitable for high-end equipment and extreme working conditions. It can be widely used in high-end equipment manufacturing fields such as aerospace, petrochemicals, and rail transportation. In its continuous casting production, the aluminum content of the molten steel is typically ≥0.2%, with some special high-alumina steels reaching 0.8%~12%. The mold flux in the continuous casting mold, as a core functional material, plays a crucial role in heat insulation, air isolation, billet lubrication, and inclusion absorption. However, its performance adaptability directly determines the smoothness of high-alumina steel continuous casting production and billet quality.

[0003] In existing technologies, the continuous casting process for high-alumina steel is exceptionally difficult. The high aluminum content in the molten steel readily undergoes a violent reduction reaction with oxides such as SiO2 in the protective slag, generating a large amount of Al2O3. This leads to an increase in the Al2O3 content and a decrease in the SiO2 content of the protective slag, causing significant fluctuations in the melting point and viscosity of the protective slag, and a sharp decline in lubrication performance. In severe cases, production accidents such as billet sticking and steel leakage may occur. Furthermore, traditional continuous casting protective slags commonly add CaF2 as a flux. Although this can lower the melting point and viscosity of the slag, at continuous casting operating temperatures of around 1500℃, it produces toxic fluoride gases such as HF and NaF. Fluoride gas concentrations exceeding 25 ppm can irritate the human respiratory and visual systems, and concentrations reaching 1000 ppm can cause death within a short period of time. Simultaneously, fluorides cause a decrease in the pH value of the secondary cooling water in continuous casting, corrode continuous casting equipment, and fluoride-containing waste causes permanent pollution of soil and water sources, which does not meet the requirements for the development of green metallurgy.

[0004] To address the aforementioned issues, patent application CN114130972A discloses a non-reactive protective slag for continuous casting of fluorine-free high-alumina steel. This slag achieves fluorine-free status by adjusting the proportions of components such as CaO, Al2O3, and BaO. However, this slag does not consider the reaction inhibition mechanism at the slag-steel interface, and its low reactivity control relies solely on component ratios. Consequently, it still suffers from insufficient performance stability during long-term continuous casting of high-alumina steel. Patent applications CN108213365A and CN111570740A still contain fluorine in their protective slags, failing to fundamentally solve the fluorine pollution problem. Furthermore, existing fluorine-free protective slags are often prepared using electric arc furnace smelting and water quenching processes, which suffer from uneven raw material mixing, loose slag microstructure, and weak inclusion absorption capacity, making it difficult to meet the continuous casting quality requirements of high-end high-alumina steel.

[0005] In summary, there is a lack of a protective slag for high-alumina steel continuous casting that is fluorine-free and environmentally friendly, has low slag steel reactivity, long-term stable performance, and has a simple preparation process and strong adaptability. Developing such a protective slag and its preparation method has become an urgent need for the development of high-alumina steel continuous casting technology. Summary of the Invention

[0006] This invention addresses the problems of fluorine pollution, vigorous slag-steel reaction, insufficient performance stability, and defects in the preparation process of existing high-alumina steel continuous casting protective slags. It provides a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel, its preparation method, and its applications. Through the design of a reaction inhibition system (SiO2, ZrO2, and carbon black) and a fluorine-free composite fluxing system (BaO, B2O3, Na2O, and Li2O), the reduction reaction between molten steel and aluminum and the protective slag is fundamentally suppressed, ensuring the long-term stability of the slag's melting point, viscosity, and other properties. Simultaneously, it achieves fluorine-free environmental protection, avoiding the harm of fluorides to human health and the environment, and preventing equipment corrosion. Furthermore, it provides a preparation method for this protective slag, through pre-melting treatment, staged cooling treatment, and low-temperature sintering granulation molding process design, achieving the original... The materials are uniformly mixed; the precipitation of high-melting-point anorthite and lancet is suppressed through a reaction inhibition system, forming a ZrO2 solid solution and a calcium zircon phase (CaZrO3) glass phase. This densifies and optimizes the microstructure of the protective slag, enhancing its inclusion absorption capacity and mechanical strength. Compared to traditional sintering methods, the composition is more uniform with no segregation; the mineral phase is controllable with a high glass phase content; the porosity is low, resulting in high density; the melting speed is uniform, and there is no crust formation, leading to improved performance. The viscosity fluctuation at 1300℃ is ≤20%; the slag-steel contact angle is ≤70°; the Al2O3 inclusion removal rate is increased by 20%–40%; the protective slag pulverization rate is ≤1%; the resistance to Al2O3 contamination is increased; the viscosity fluctuation is small; and the viscosity change rate after absorbing 3%–10% Al2O3 is ≤20%. This method overcomes the shortcomings of traditional preparation processes and is simple, easily industrialized, and reduces production costs.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel comprises the following components by mass percentage: CaO: 22%~38%, Al2O3: 18%~32%, SiO2: 3%~6%, BaO: 8%~16%, B2O3: 6%~14%, alkali metal oxides: 8%~15%, MnO: 2%~6%, MgO: 2%~6%, ZrO2: 1.5%~3.5%, carbon black: 3.5%~6.5%, with the remainder being unavoidable impurities; wherein the alkali metal oxides are Na2O and Li2O; the mass ratio of Na2O to Li2O in the alkali metal oxides is (2~3):1; the mass percentage ratio of ZrO2 to carbon black in the protective slag conforms to: 1:(1.8~2.2).

[0009] This invention also discloses a method for preparing the low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel as described above, comprising the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag. S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder. S3. The carbon black, borax and spodumene weighed in step S1 are dried to obtain dried carbon black, dried borax and dried spodumene. S4. The mixed powder is pre-melted under an argon atmosphere to obtain slag; wherein the pre-melting temperature is 1580~1650℃; and the pre-melting time is 40~50min. S5. The molten slag is cooled to 800~900℃ using a high-pressure water atomization device, wherein the atomizing water pressure is 9~12MPa, the water temperature is 20~25℃, and the molten slag injection flow rate is 0.4~0.6kg / min; then cooled to room temperature at a rate of 5~8℃ / min to obtain pre-molten slag particles. S6. The pre-melted slag particles, the dried carbon black, the dried borax and the dried spodumene are mixed, and a composite binder is added to the mixture for granulation to obtain granulated powder. S7. The granulated powder is preheated at 300~350℃ for 30~40 min, then heated to 750~800℃ and sintered for 20~30 min, and then cooled to room temperature to obtain the protective slag.

[0010] The present invention also discloses the application of a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel as described above, or a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel prepared by the preparation method described above, wherein the protective slag is used in the continuous casting process of high-alumina steel.

[0011] Implementing the embodiments of the present invention will have the following beneficial effects: This invention employs a fluorine-free composite fluxing system of BaO, B2O3, and alkali metal oxides (Na2O and Li2O) to replace the traditional CaF2 fluxing agent. It is fluorine-free and environmentally friendly, and no toxic fluoride gases are generated during production and use, thus avoiding the harm of fluorine to the human body, the corrosion of equipment, and the pollution of the environment, which is in line with the green metallurgical industry policy.

[0012] This invention employs a binary reaction inhibitor of ZrO2 and carbon black and a low SiO2 design, resulting in low reactivity and stable performance. It inhibits the reduction reaction between aluminum in molten steel and the protective slag from both physical and chemical perspectives. Experimental verification shows that the melting point (1080~1250℃) and viscosity (0.15~0.28Pa·s) of the protective slag during the continuous casting of high-alumina steel do not fluctuate significantly, and the continuous casting time is ≥8h, thus solving the problem of easy performance fluctuation of existing protective slags.

[0013] The protective slag of this invention has properties such as melting point, viscosity, and spreadability that are highly compatible with the continuous casting process of high-alumina steel. It can effectively lubricate the billet, absorb Al2O3 inclusions in the molten steel, and ensure that the billet surface is free of defects such as adhesion and cracks, with a surface qualification rate of ≥99.5%.

[0014] This invention, through pre-melting treatment, staged cooling, and low-temperature sintering process design, makes the microstructure of the protective slag dense and the crystal form stable, increasing the compressive strength to 3.0~4.0MPa, avoiding pulverization during transportation and use, and improving the absorption capacity of inclusions. At the same time, the process steps are simple, easy to industrialize, and have high production efficiency.

[0015] The raw materials used in this invention are all conventional raw materials in the metallurgical industry, without rare precious metals, and the preparation process does not require complex equipment. Compared with existing high-end protective slags, the production cost is greatly reduced, and it has good prospects for industrial application. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0017] This invention discloses a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel, comprising the following components by mass percentage: CaO: 22%~38%, Al2O3: 18%~32%, SiO2: 3%~6%, BaO: 8%~16%, B2O3: 6%~14%, alkali metal oxides: 8%~15%, MnO: 2%~6%, MgO: 2%~6%, ZrO2: 1.5%~3.5%, carbon black: 3.5%~6.5%, with the remainder being unavoidable impurities; wherein, the alkali metal oxides are Na2O and Li2O; the mass ratio of Na2O to Li2O in the alkali metal oxides is (2~3):1; the mass percentage ratio of ZrO2 to carbon black in the protective slag conforms to: 1:(1.8~2.2).

[0018] Specifically, the functions of the main components in the low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel of the present invention are as follows: The fluorine-free composite fluxing system of the present invention is composed of BaO, B2O3, and alkali metal oxides (Na2O and Li2O), which optimizes the fluorine-free composite fluxing system, replaces the traditional CaF2 fluxing agent, and solves the problem of insufficient fluxing effect of a single fluorine-free fluxing agent. Under the premise of fluorine-free, it ensures that the melting point and viscosity of the slag are suitable for high-alumina steel continuous casting; the slag-steel reaction inhibition system is composed of low-content SiO2, ZrO2, and carbon black, where ZrO2 is an inert, high-melting-point oxygen... The protective slag contains compounds that isolate the molten steel from aluminum and slag, while carbon black reduces the oxidizing properties of the slag and further inhibits the reduction reaction. This invention does not achieve low reactivity solely through ingredient ratios; it employs a binary reaction inhibitor of ZrO2 and carbon black to suppress the slag-steel reaction from both physical isolation and chemical oxygen reduction perspectives, significantly improving the stability of the protective slag. Furthermore, it controls the SiO2 content to 3%–6%, reducing the reduction reaction products between SiO2 and molten steel / aluminum in the protective slag from the source. Simultaneously, by regulating the content of Al2O3 and CaO, it ensures the slag's ability to absorb inclusions.

[0019] In one specific embodiment, the melting point of the protective slag is 1080~1250℃; the viscosity of the protective slag at 1300℃ is 0.15~0.28 Pa·s.

[0020] In one specific embodiment, the continuous casting stabilization time is ≥8h; the surface qualification rate of the cast billet is ≥99.5%.

[0021] In one specific embodiment, the compressive strength of the protective slag is 3.0~4.0 MPa.

[0022] This invention also discloses a method for preparing the low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel as described above, comprising the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag.

[0023] S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder.

[0024] S3. The carbon black, borax and spodumene weighed in step S1 are dried to obtain dried carbon black, dried borax and dried spodumene.

[0025] S4. The mixed powder is pre-melted under an argon atmosphere to obtain a uniform slag; wherein the pre-melting temperature is 1580~1650℃ and the pre-melting time is 40~50min.

[0026] S5. The molten slag is cooled to 800~900℃ using a high-pressure water atomization device, wherein the atomizing water pressure is 9~12MPa, the water temperature is 20~25℃, and the molten slag injection flow rate is 0.4~0.6kg / min; then it is cooled to room temperature at a rate of 5~8℃ / min (to optimize the microstructure of the molten slag and avoid crack formation) to obtain pre-molten slag particles.

[0027] S6. Mix the pre-melted slag particles, dried carbon black, dried borax and dried spodumene, and add a composite binder to the mixture for granulation to obtain granulated powder.

[0028] S7. After preheating the granulated powder at 300~350℃ for 30~40min, the temperature is raised to 750~800℃ and sintered for 20~30min. Then, it is cooled to room temperature to obtain a protective slag.

[0029] In one specific embodiment, in step S1, the pre-melted calcium aluminate comprises the following components by mass percentage: Al2O3: 58%~62%, CaO: 33%~37%, SiO2≤3%, with the remainder being unavoidable impurities.

[0030] In one specific embodiment, in step S2, the particle size of the mixed powder is ≤80μm.

[0031] In one specific embodiment, in step S3, the moisture content of the dried carbon black is ≤0.5% by mass; the moisture content of the dried borax is ≤0.5% by mass; and the moisture content of the dried spodumene is ≤0.5% by mass.

[0032] In one specific embodiment, in step S4, the argon gas flow rate is 1.5~2.5L / min, and the argon gas protection prevents the molten slag from being oxidized and burned off.

[0033] In one specific embodiment, in step S6, the composite binder is water glass and sodium carboxymethyl cellulose in a mass ratio of 4:1.

[0034] In one specific embodiment, in step S6, the amount of composite adhesive added is 3% to 5% of the mass of the mixture.

[0035] In one specific embodiment, in step S6, the particle size of the granulated powder is 0.5~1.0 mm.

[0036] Specifically, the preparation process of this invention employs pre-melting treatment and argon protection to solve the problems of uneven raw material mixing and slag component segregation in traditional preparation processes, ensuring the uniformity of the protective slag performance. Furthermore, it controls a slow cooling process (5~8℃ / min), which, compared to direct water quenching, avoids micro-cracks in the slag due to rapid cooling, improves the mechanical strength of the protective slag, and prevents pulverization during transportation and use. Finally, it employs a low-temperature sintering process with post-mixed carbon black to prevent the carbon black from being oxidized during the high-temperature smelting stage, ensuring its oxygen-reducing and reaction-inhibiting functions, and solving the problem of reaction inhibitors easily becoming ineffective in existing technologies.

[0037] The present invention also discloses the application of a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel as described above, or a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel prepared by the preparation method described above, wherein the protective slag is used in the continuous casting process of high-alumina steel.

[0038] In one specific embodiment, the Al mass percentage in the high-aluminum steel is 0.2% to 12%.

[0039] In one specific embodiment, during application, the casting temperature of the continuously cast molten steel is controlled at 1250°C to 1550°C; the continuous casting speed is 0.8 to 1.8 m / min; the thickness of the molten slag layer of the protective slag is 8 to 15 mm; and the consumption of the protective slag is 0.3 to 0.6 kg / t of molten steel.

[0040] The following are specific embodiments. Example 1 The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment comprises the following components by mass percentage: CaO: 25%, Al2O3: 28%, SiO2: 5%, BaO: 12%, B2O3: 8%, Na2O+Li2O: 10% (Na2O: 7%, Li2O: 3%), MnO: 3%, MgO: 3%, ZrO2: 2%, carbon black: 4%, with the remainder being unavoidable impurities.

[0041] The method for preparing low-reactive, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment includes the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag.

[0042] S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder with a particle size ≤80μm.

[0043] S3. The carbon black, borax and spodumene weighed in step S1 are dried until the moisture content is ≤0.5% by mass, to obtain dried carbon black, dried borax and dried spodumene.

[0044] S4. The mixed powder is pre-melted in an argon atmosphere (argon gas flow rate of 2.0 L / min) to obtain a uniform slag; wherein the pre-melting temperature is 1600℃ and the pre-melting time is 45 min.

[0045] S5. The molten slag is cooled to 820°C using a high-pressure water atomization device, where the atomizing water pressure is 10MPa, the water temperature is 22°C, and the molten slag injection flow rate is 0.4kg / min; then it is cooled to room temperature at a rate of 6°C / min to obtain pre-molten slag particles.

[0046] S6. Mix the pre-melted slag particles, dried carbon black, dried borax and dried spodumene, and add 4% by mass of composite binder (water glass and sodium carboxymethyl cellulose in a mass ratio of 4:1) to the mixture for granulation to obtain granulated powder with a particle size of 0.5~1.0 mm.

[0047] S7. After preheating the granulated powder at 320℃ for 32 minutes, the temperature is raised to 780℃ and sintered for 25 minutes, and then cooled to room temperature to obtain a protective slag.

[0048] In step S1, the pre-melted calcium aluminate comprises the following components by mass percentage: Al2O3: 60%, CaO: 35%, SiO2: 2%, with the remainder being unavoidable impurities.

[0049] Example 2 The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment comprises the following components by mass percentage: CaO: 29%, Al2O3: 20%, SiO2: 4%, BaO: 12%, B2O3: 7%, Na2O+Li2O: 12% (Na2O: 8%, Li2O: 4%), MnO: 3%, MgO: 4%, ZrO2: 3%, carbon black: 6%, with the remainder being unavoidable impurities.

[0050] The method for preparing low-reactive, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment includes the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag.

[0051] S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder with a particle size ≤80μm.

[0052] S3. The carbon black, borax and spodumene weighed in step S1 are dried until the moisture content is ≤0.5% by mass, to obtain dried carbon black, dried borax and dried spodumene.

[0053] S4. The mixed powder is pre-melted in an argon atmosphere (argon gas flow rate of 2.2 L / min) to obtain a uniform slag; wherein the pre-melting temperature is 1620℃ and the pre-melting time is 48 min.

[0054] S5. The molten slag is cooled to 830°C using a high-pressure water atomization device, where the atomizing water pressure is 11MPa, the water temperature is 23°C, and the molten slag injection flow rate is 0.5kg / min; then it is cooled to room temperature at a rate of 7°C / min to obtain pre-molten slag particles.

[0055] S6. Mix the pre-melted slag particles, dried carbon black, dried borax and dried spodumene, and add 4.5% by mass of composite binder (water glass and sodium carboxymethyl cellulose in a mass ratio of 4:1) to the mixture for granulation to obtain granulated powder with a particle size of 0.5~1.0 mm.

[0056] S7. After preheating the granulated powder at 330℃ for 35 minutes, the temperature is raised to 790℃ and sintered for 28 minutes. Then, it is cooled to room temperature to obtain a protective slag.

[0057] In step S1, the pre-melted calcium aluminate comprises the following components by mass percentage: Al2O3: 62%, CaO: 35%, SiO2: 1%, with the remainder being unavoidable impurities.

[0058] Example 3 The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment comprises the following components by mass percentage: CaO: 28%, Al2O3: 25%, SiO2: 6%, BaO: 10%, B2O3: 10%, Na2O+Li2O: 9% (Na2O: 6%, Li2O: 3%), MnO: 3%, MgO: 3%, ZrO2: 2%, carbon black: 4%, with the remainder being unavoidable impurities.

[0059] The method for preparing low-reactive, fluorine-free continuous casting protective slag for high-alumina steel in this embodiment includes the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag.

[0060] S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder with a particle size ≤80μm.

[0061] S3. The carbon black, borax and spodumene weighed in step S1 are dried until the moisture content is ≤0.5% by mass, to obtain dried carbon black, dried borax and dried spodumene.

[0062] S4. The mixed powder is pre-melted in an argon atmosphere (argon gas flow rate of 1.8 L / min) to obtain a uniform slag; wherein the pre-melting temperature is 1590℃ and the pre-melting time is 42 min.

[0063] S5. The molten slag is cooled to 830°C using a high-pressure water atomization device, where the atomizing water pressure is 9MPa, the water temperature is 23°C, and the molten slag injection flow rate is 0.6kg / min; then it is cooled to room temperature at a rate of 5°C / min to obtain pre-molten slag particles.

[0064] S6. Mix the pre-melted slag particles, dried carbon black, dried borax and dried spodumene, and add 3.5% by mass of composite binder (water glass and sodium carboxymethyl cellulose in a mass ratio of 4:1) to the mixture for granulation to obtain granulated powder with a particle size of 0.5~1.0 mm.

[0065] S7. After preheating the granulated powder at 320℃ for 33 minutes, the temperature is raised to 760℃ and sintered for 22 minutes. Then, it is cooled to room temperature to obtain a protective slag.

[0066] In step S1, the pre-melted calcium aluminate comprises the following components by mass percentage: Al2O3: 59%, CaO: 37%, SiO2: 2%, with the remainder being unavoidable impurities.

[0067] Comparative Example 1 The difference between this comparative example and Example 1 is that ZrO2 and carbon black are not added. The protective slag of this comparative example comprises the following components by mass percentage: CaO: 26%, Al2O3: 30%, SiO2: 5%, BaO: 11%, B2O3: 10%, Na2O and Li2O: 12% (Na2O: 8%, Li2O: 4%), MnO: 3%, MgO: 3%, with the remainder being unavoidable impurities.

[0068] Comparative Example 2 The difference between this comparative example and Example 1 is that no carbon black was added. The protective slag of this comparative example contains the following components by mass percentage: CaO: 25%, Al2O3: 28%, SiO2: 5%, BaO: 12%, B2O3: 8%, Na2O+Li2O: 10% (Na2O: 7%, Li2O: 3%), MnO: 3%, MgO: 3%, ZrO2: 6%, with the remainder being unavoidable impurities.

[0069] Comparative Example 3 The difference between this comparative example and Example 1 is that ZrO2 is not added. The protective slag of this comparative example comprises the following components by mass percentage: CaO: 25%, Al2O3: 28%, SiO2: 5%, BaO: 12%, B2O3: 8%, Na2O+Li2O: 10% (Na2O: 7%, Li2O: 3%), MnO: 3%, MgO: 3%, carbon black: 6%, with the remainder being unavoidable impurities.

[0070] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass percentage ratio of ZrO2 and carbon black in the protective slag is controlled at 1:1. The protective slag of this comparative example contains the following components by mass percentage: CaO: 25%, Al2O3: 28%, SiO2: 5%, BaO: 12%, B2O3: 8%, Na2O+Li2O: 10% (Na2O: 7%, Li2O: 3%), MnO: 3%, MgO: 3%, ZrO2: 3%, carbon black: 3%, with the remainder being unavoidable impurities.

[0071] Comparative Example 5 The difference between this comparative example and Example 1 is that the mass percentage ratio of ZrO2 to carbon black in the protective slag is controlled at 1:1.5. The protective slag of this comparative example contains the following components by mass percentage: CaO: 25%, Al2O3: 28%, SiO2: 5%, BaO: 12%, B2O3: 8%, Na2O+Li2O: 10% (Na2O: 7%, Li2O: 3%), MnO: 3%, MgO: 3%, ZrO2: 2.4%, carbon black: 3.6%, with the remainder being unavoidable impurities.

[0072] Comparative Example 6 The only difference between this comparative example and Example 1 is that the cooling to room temperature at a rate of 5°C / min in S5 is replaced by direct water quenching to room temperature without atomized staged cooling.

[0073] Comparative Example 7 The only difference between this comparative example and Example 1 is that the pre-melting temperature is 1700°C.

[0074] Comparative Example 8 The only difference between this comparative example and Example 1 is that the sintering temperature in S7 is adjusted to 1000°C.

[0075] Comparative Example 9 The difference between this comparative example and Example 1 is that carbon black is added before the pre-melting treatment. The specific preparation method includes the following steps: S1-3, same as Example 1.

[0076] S4. The mixed powder and dried carbon black, borax and spodumene are mixed and pre-melted under an argon atmosphere. The treatment conditions are the same as in Example 1 to obtain a uniform slag.

[0077] S5-7, Same as Example 1.

[0078] Test case The protective slags obtained in the examples and comparative examples were subjected to performance tests. All protective slags in the examples and comparative examples were applied to the production of high-alumina steel continuous casting crystallizers with an Al mass percentage of 4%. The results are shown in Table 1. Test methods: The relevant tests were conducted in strict accordance with YB / T 186-2014 "Test Method for Melting Temperature of Continuous Casting Protective Slag" and YB / T 190-2001 "Test Method for Viscosity of Continuous Casting Protective Slag". The surface qualification rate of the cast billet was determined using YB / T 4149-2017 "Standard for Surface Quality Rating of Continuous Casting Billets".

[0079] Table 1 Performance Indicators of Protective Slag

[0080] In all embodiments of this invention, the continuous casting stabilization time is ≥9h and the surface qualification rate of the cast billet is ≥99.7%, proving that the protective slag of this invention possesses excellent low reactivity and performance stability, with zero fluoride release, achieving fluorine-free environmental protection. Through dual innovation in composition and process, the protective slag and preparation method of this invention achieve the technical goals of fluorine-free environmental protection, low reactivity, and high performance stability, adapting to the needs of high-alumina steel continuous casting production, and possessing significant technical advantages and industrial application value.

[0081] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel, characterized in that, The components include the following percentages by mass: CaO: 22%~38%, Al2O3: 18%~32%, SiO2: 3%~6%, BaO: 8%~16%, B2O3: 6%~14%, alkali metal oxides: 8%~15%, MnO: 2%~6%, MgO: 2%~6%, ZrO2: 1.5%~3.5%, carbon black: 3.5%~6.5%, with the remainder being unavoidable impurities; wherein the alkali metal oxides are Na2O and Li2O; The mass ratio of Na₂O to Li₂O in the alkali metal oxide is (2~3):1; The mass percentage ratio of ZrO2 and carbon black in the protective slag conforms to: 1:(1.8~2.2). The method for preparing the low-reactive, fluorine-free continuous casting protective slag for high-alumina steel includes the following steps: S1. Using lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate, zirconium oxide, carbon black, borax and spodumene as raw materials, weigh each raw material according to the mass percentage of each component of the protective slag. S2. The lime, quartz sand, pre-melted calcium aluminate, magnesite, pyrolusite, barium carbonate and zirconium oxide weighed in step S1 are mixed and then ball-milled to obtain a mixed powder. S3. The carbon black, borax and spodumene weighed in step S1 are dried to obtain dried carbon black, dried borax and dried spodumene. S4. The mixed powder is pre-melted under an argon atmosphere to obtain slag; wherein the pre-melting temperature is 1580~1650℃; and the pre-melting time is 40~50min. S5. The molten slag is cooled to 800~900℃ using a high-pressure water atomization device, wherein the atomizing water pressure is 9~12MPa, the water temperature is 20~25℃, and the molten slag injection flow rate is 0.4~0.6kg / min; then cooled to room temperature at a rate of 5~8℃ / min to obtain pre-molten slag particles. S6. The pre-melted slag particles, the dried carbon black, the dried borax and the dried spodumene are mixed, and a composite binder is added to the mixture for granulation to obtain granulated powder. S7. The granulated powder is preheated at 300~350℃ for 30~40 min, then heated to 750~800℃ and sintered for 20~30 min, and then cooled to room temperature to obtain the protective slag.

2. The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel according to claim 1, characterized in that, The melting point of the protective slag is 1080~1250℃; The viscosity of the protective slag at 1300℃ is 0.15~0.28 Pa·s; Continuous casting stabilization time ≥ 8h; billet surface qualification rate ≥ 99.5%; The compressive strength is 3.0~4.0MPa.

3. The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel according to claim 1, characterized in that, In step S1, the pre-melted calcium aluminate comprises the following components by mass percentage: Al2O3: 58%~62%, CaO: 33%~37%, SiO2≤3%, with the remainder being unavoidable impurities.

4. The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel according to claim 1, characterized in that, In step S2, the particle size of the mixed powder is ≤80μm; In step S3, the moisture content of the dried carbon black is ≤0.5% by mass; the moisture content of the dried borax is ≤0.5% by mass; and the moisture content of the dried spodumene is ≤0.5% by mass.

5. The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel according to claim 1, characterized in that, In step S4, the argon gas flow rate is 1.5~2.5L / min.

6. The low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel according to claim 1, characterized in that, In step S6, the composite binder is water glass and sodium carboxymethyl cellulose in a mass ratio of 4:1; the amount of the composite binder added is 3% to 5% of the mass of the mixture. The particle size of the granulated powder is 0.5~1.0 mm.

7. The application of a low-reactivity, fluorine-free continuous casting protective slag for high-alumina steel as described in any one of claims 1-6, characterized in that, The protective slag is used in the continuous casting process of high-alumina steel.

8. The application according to claim 7, characterized in that, The high-alumina steel contains 0.2% to 12% Al by mass. When applying this method, the casting temperature of the continuously cast molten steel is controlled at 1250–1550°C; the continuous casting speed is 0.8–1.8 m / min; the thickness of the molten slag layer of the protective slag is 8–15 mm; and the consumption of the protective slag is 0.3–0.6 kg / t of molten steel.

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