Fluorine-free non-reactive continuous casting covering slag for high-titanium steel and preparation method of fluoride-free non-reactive continuous casting covering slag

Abstract

The invention discloses fluoride-free non-reactive continuous casting covering slag for high-titanium steel. The fluoride-free non-reactive continuous casting covering slag comprises, by mass, 18%-28% of CaO, 18%-28% of Al2O3, 5%-15% of BaO, 6%-10% of Na2O, 1%-4% of Li2O, 2%-4% of MgO, 6%-10% of B2O3, 1%-5% of SiO2, 4%-12% of TiO2, smaller than or equal to 2% of Fe2O3, 4%-12% of carbon materials and the balance impurities. According to the method, the SiO2 content is remarkably reduced, the TiO2 proportion is reasonably increased, the steel slag interface reaction is effectively inhibited, and the stability of components and performance of the casting powder in the high-titanium steel casting process is ensured. And by adding BaO, Na2O, Li2O and other fluxing agents, the melt structure is adjusted and optimized, the physical and chemical properties of the casting powder are effectively improved, and it is guaranteed that continuous casting of the high-titanium steel is smooth and the surface quality of a casting blank is good. In addition, the fluoride-free formula design eliminates the hidden danger of fluorine pollution from the source, and accords with the industrial green and environment-friendly development trend. The invention further provides a preparation method of the fluoride-free non-reactive continuous casting covering slag for the high-titanium steel.

Description

Technical Field

[0001] This invention belongs to the field of steel industry technology, specifically a fluorine-free non-reactive continuous casting protective slag for high-titanium steel and its preparation method. Background Technology

[0002] High-titanium steel is widely favored as a low-cost, high-value-added product. However, the steel-slag interface reaction leads to a drastic change in the composition of the protective slag, deteriorating its physical and chemical properties, causing surface defects in the cast billet, and limiting its efficient and high-quality development. The CaO-Al2O3-TiO2-CaF2 system of protective slag can inhibit the steel-slag interface reaction, but F is introduced to optimize performance. - Fluorine pollution ensues. Therefore, the fluorine-free treatment of protective slag is imperative.

[0003] Application CN105642849A discloses a mold flux for continuous casting of titanium-containing steel, comprising the following components in wt%: CaO: 15-35%, SiO2: 7-15%, Al2O3: 10-30%, F... - The slag composition is as follows: SiO2 content 3-15%, Li2O content 3-10%, BaO content 5-20%, Mn2O3 content 5-20%, C content 2-12%, MgO ≤1.5%, and Fe2O3 ≤2%. Compared to traditional slag systems, this invention has a lower SiO2 content and a higher Al2O3 content. While a certain amount of Mn2O3 is added as a strong oxidant, the SiO2 content remains high, and the slag system lacks TiO2, leading to interfacial reactions between steel and slag during the casting of high-titanium steel. Furthermore, this invention contains fluorides, posing a fluoride pollution problem.

[0004] Application CN118595409A discloses a high-oxidizing continuous casting protective slag suitable for high-titanium steel, with the following composition: CaO: 20-45%, SiO2: 25-50%, Al2O3: 0-4%, BaO: 0-10%, F... - The composition of the protective slag is as follows: CaO: 5-12%, Na2O: 3-12%, MgO ≤ 5%, Fe2O3: 5-15%, MnO2: 5-15%, TC: 3-15%, 0.6 ≤ (CaO / SiO2) ≤ 1.3, with the remainder being impurities. Although highly oxidizing components are added to this protective slag, the activity of SiO2 remains high, and interfacial reactions between the steel and slag are still possible. Furthermore, the presence of fluorides makes fluorine contamination unavoidable.

[0005] Application CN113751681B discloses a continuous casting protective slag suitable for high-titanium steel, with the following composition: CaO: 28-32%, SiO2: 10-18%, MgO: 2-4%, TiO2: 6-12%, Al2O3:

[0006] 16-20%, B2O3+Na2O+Li2O: 8-10%, C: 2-4%, with the balance being unavoidable impurities. However, it contains a high amount of SiO2, and this invention is still reactive, unable to completely suppress the steel-slag interface reaction between high-titanium steel and protective slag.

[0007] Applications with publication numbers CN108127094A, CN113102702B, and CN113953472B disclose three types of protective slags for high-titanium steel, the components of which contain F respectively. - 8-15%, F - 5-10%, F - :

[0008] The levels of fluorine pollution are 3-10%, inevitably leading to problems.

[0009] Therefore, the design of the aforementioned high-titanium steel protective slag has certain shortcomings. On the one hand, the slag remains reactive, and the problems caused by the steel-slag interface reaction between the high-titanium steel and the slag cannot be effectively avoided. On the other hand, the addition of fluorides to optimize the physicochemical properties of the slag leads to fluorine pollution. Therefore, to promote the green and environmentally friendly development of continuous casting protective slags and to achieve high-quality and high-efficiency production of high-titanium steel, the development of fluorine-free, non-reactive high-titanium steel protective slags is particularly important. Summary of the Invention

[0010] The purpose of this invention is to provide a fluorine-free non-reactive continuous casting protective slag for high-titanium steel and its preparation method in order to solve the problems mentioned above.

[0011] The technical solution adopted in this invention is as follows: a fluorine-free non-reactive continuous casting protective slag for high-titanium steel, comprising: CaO: 18-28%, Al2O3: 18-28%, BaO: 5-15%, Na2O: 6-10%, Li2O: 1-4%, MgO: 2-4%, B2O3: 6-10%, SiO2: 1-5%, TiO2: 4-12%, Fe2O3≤2%, carbon materials 4-12%, and the balance being impurities.

[0012] In a preferred embodiment, a method for preparing a fluorine-free non-reactive continuous casting protective slag for high-titanium steel includes the following steps:

[0013] S1: Select and pre-treat raw materials, including CaO: 18-28%, Al2O3: 18-28%, BaO: 5-15%, Na2O: 6-10%, Li2O: 1-4%, MgO: 2-4%, B2O3: 6-10%, SiO2: 1-5%, TiO2: 4-12%, Fe2O3 ≤2%, and carbon materials. Remove impurities and dry to a moisture content ≤0.5%.

[0014] S2: Weigh the pretreated raw materials by mass percentage, with the mass ratio of CaO to Al2O3 being 0.8 to 1.2.

[0015] S3: Place the weighed raw materials into the mixer and mix at a speed of 100-300 rpm for 10-30 minutes to obtain a uniformly mixed material.

[0016] S4: Send the mixture into a high-temperature furnace and melt it at 1300-1500℃ for 2-4 hours, stirring it 2-3 times during the process to make the melt composition uniform.

[0017] S5: The molten material is removed from the furnace and cooled to room temperature by water quenching or air atomization to form a glassy or microcrystalline solid.

[0018] S6: Add the required carbon material to the cooled solid, put it into a crusher to crush and mix it, and obtain coarse particles with a particle size ≤5mm.

[0019] S7: Feed the coarse particles into a ball mill for fine grinding, and pass them through a 100-200 mesh sieve to obtain fine powder with a particle size distribution that meets the requirements.

[0020] S8: The fine powder is subjected to component analysis, viscosity, melting point and crystallization performance testing. After passing the test, it is packaged to obtain the fluorine-free non-reactive continuous casting protective slag for high titanium steel.

[0021] In a preferred embodiment, in step S1, mechanical impurities with a particle size greater than 0.5 mm are removed by sieving, and iron-containing impurities are separated by magnetic separation to ensure that the metallic iron content in the raw material is less than 0.1%. The treated raw material is then fed into a drying device and dried continuously at a temperature of 80–120°C for 2–4 hours. During this period, a hot air circulation system is used to keep the material heated evenly until the moisture content of the raw material is reduced to below 0.5%, in order to avoid melt splashing or composition fluctuations caused by moisture evaporation during the subsequent melting process.

[0022] In a preferred embodiment, in step S2, an electronic scale with an accuracy of 0.1g is used to weigh each pretreated raw material component. During the weighing process, hygroscopic components such as Na2O and Li2O are weighed quickly and stored in a sealed container to prevent weighing errors from exceeding ±0.5% due to moisture absorption.

[0023] In a preferred embodiment, in step S3, all weighed raw materials are sequentially added to a horizontal twin-shaft mixer. The mixer is first started and pre-mixed at 100 rpm for 5 minutes to initially disperse the light raw materials and heavy oxides. Then, the speed is increased to 200-300 rpm, and mixing continues for 15-25 minutes. During this time, the material state is monitored through the observation window at the top of the mixer to ensure there is no obvious clumping or stratification. After mixing, 3-5 samples are taken from different locations in the mixer for component uniformity testing to ensure that the relative standard deviation of each component does not exceed 2%, thus avoiding localized component segregation during subsequent melting.

[0024] In a preferred embodiment, in step S4, the uniformly mixed material is continuously fed into a vertical electric arc furnace via a screw conveyor. The furnace power is controlled to gradually raise the furnace temperature to 1300–1500°C, with the heating rate maintained at 50–100°C / minute to prevent premature volatilization of low-melting-point components (such as Na₂O and B₂O₃) due to localized overheating. After reaching the target temperature, the temperature is maintained at a constant level for 2–4 hours. During this period, manual stirring is performed every 30–60 minutes using a graphite stirring rod, with the stirring depth reaching 2 / 3 of the melt height to ensure uniform temperature and composition within the melt. During the melting process, volatiles are collected through a tail gas treatment system to reduce the loss of components such as Na₂O.

[0025] In a preferred embodiment, in step S5, after melting is complete, the melt is continuously discharged from the guide port at the bottom of the furnace and cooled by water quenching: the melt flows into a high-pressure water stream (pressure 0.3-0.5 MPa) at a flow rate of 5-10 kg / min, is broken into particles with a diameter of 1-5 mm, and then enters a vibrating dewatering screen to remove surface moisture, followed by hot air drying (temperature 100-150℃) to remove residual moisture. If air atomization cooling is used, the melt is atomized into fine droplets by compressed air (pressure 0.6-0.8 MPa), and then naturally cooled to room temperature in the air to form spherical glass particles. Both cooling methods require controlling the cooling rate at 100-200℃ / second to suppress crystal precipitation and obtain an amorphous or microcrystalline structure.

[0026] In a preferred embodiment, in step S6, the required carbon material is added to the cooled solid (water-quenched particles or atomized particles) and fed into a jaw crusher for coarse crushing. The discharge gap of the crusher is adjusted to 3-5 mm to crush the material into coarse particles with a maximum particle size not exceeding 5 mm. During the crushing process, any metal impurities that may be mixed in are removed by an iron remover, and the crushed material is screened. The material oversizes (particle size > 5 mm) is returned to the crusher for re-crushing, while the material undersizes enters the next process, ensuring uniform particle size and reducing energy consumption in subsequent fine grinding.

[0027] In a preferred embodiment, in step S7, the coarse-particle material is fed into a ball mill for fine grinding. The ball mill is filled with alumina ceramic balls with a diameter of 5-10 mm, the ball-to-material ratio is controlled at 3:1-5:1, the mill speed is set to 150-200 rpm, and the grinding time is adjusted to 2-4 hours according to the target particle size. After grinding, the material is sieved through a 100-200 mesh standard sieve. The undersized fine powder is collected for later use, while the oversized coarse powder is returned to the ball mill for further grinding. The particle size distribution requirement for the fine powder is: particles smaller than 0.074 mm account for ≥80%, ensuring that the protective slag has good spreading and melting speed during continuous casting.

[0028] In a preferred embodiment, in step S8, the finely ground protective slag powder undergoes comprehensive performance testing: X-ray fluorescence spectrometry is used to analyze the main components, ensuring the content of each oxide is within the design range; a rotational viscometer is used to measure the viscosity at 1300℃, requiring the viscosity value to be controlled between 0.05 and 0.8 Pa·s; a fully automatic slag melting point and melting rate meter is used to determine the melting point of the protective slag, ensuring the melting point is between 950 and 1200℃; and a single-wire device is used to determine the crystallization performance of the protective slag, ensuring the crystallization temperature is controlled between 1100 and 1350℃ and the crystallization rate is between 40% and 100%. After all test items pass, the product is packaged into kraft paper bags lined with plastic bags, each bag weighing 25 kg net, sealed, and stored in a dry and ventilated warehouse to prevent moisture absorption and clumping. This completes the entire protective slag preparation process.

[0029] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] 1. This invention effectively suppresses the steel-slag interface reaction between high-titanium steel and protective slag in the crystallizer by significantly reducing the SiO2 content and reasonably increasing the TiO2 ratio. This reduces the enrichment and oxidation of titanium elements at the interface, ensuring the stability of the composition and performance of the protective slag. As a result, it reduces the probability of defects such as surface cracks and inclusions on the billet, and improves the surface quality and yield of high-titanium steel billets.

[0031] 2. This invention overcomes the adverse effects of the complex structure of the Al2O3 and TiO2 amphoteric oxide slag system on its physicochemical properties by adding fluxes such as BaO, Na2O, and Li2O, and through the coordinated control of multiple fluxes. This achieves microstructural control over macroscopic properties, thereby effectively improving the physicochemical properties of the protective slag. It not only meets the continuous casting process requirements of high-titanium steel but is also applicable to peritectic steel and other steel grades sensitive to the properties of the protective slag, broadening its application range and providing a reliable material guarantee for steel enterprises to achieve efficient and high-quality production.

[0032] 3. The fluoride-free formulation design of this invention eliminates the potential for fluoride pollution at the source, avoiding equipment corrosion, environmental pollution and health hazards caused by the release of hydrogen fluoride and other gases by traditional fluorine-containing protective slag at high temperatures. This not only reduces subsequent processing costs, but also promotes the green and environmentally friendly development of the steel industry. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the process principle of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Reference Figure 1 .

[0036] Example 1:

[0037] A fluorine-free non-reactive continuous casting protective slag for high-titanium steel comprises: CaO: 20%, Al2O3: 24%, SiO2: 5%, TiO2: 12%, BaO: 15%, Na2O: 6%, Li2O: 2%, B2O3: 6%, MgO: 4%, Fe2O3: 2%, carbon materials: 4%, and the balance being impurities.

[0038] A method for preparing a fluorine-free, non-reactive continuous casting protective slag for high-titanium steel includes the following steps:

[0039] S1: Select and pre-treat raw materials, including CaO: 20%, Al2O3: 24%, SiO2: 5%, TiO2: 12%, BaO: 15%, Na2O: 6%, Li2O: 2%, B2O3: 6%, MgO: 4%, Fe2O3: 2%, and carbon materials: 4%. Remove impurities and dry to a moisture content of ≤0.5%.

[0040] S2: Weigh the pretreated raw materials by mass percentage, with the mass ratio of CaO to Al2O3 being 0.8.

[0041] S3: Place the weighed raw materials into the mixer and mix at a speed of 100-300 rpm for 10-30 minutes to obtain a uniformly mixed material.

[0042] S4: Send the mixture into a high-temperature furnace and melt it at 1300-1500℃ for 2-4 hours, stirring it 2-3 times during the process to make the melt composition uniform.

[0043] S5: The molten material is removed from the furnace and cooled to room temperature by water quenching or air atomization to form a glassy or microcrystalline solid.

[0044] S6: Add the required carbon material to the cooled solid, put it into a crusher to crush and mix it, and obtain coarse particles with a particle size ≤5mm.

[0045] S7: Feed the coarse particles into a ball mill for fine grinding, and pass them through a 100-200 mesh sieve to obtain fine powder with a particle size distribution that meets the requirements.

[0046] S8: The fine powder is subjected to component analysis, viscosity, melting point and crystallization performance testing. After passing the test, it is packaged to obtain the fluorine-free non-reactive continuous casting protective slag for high titanium steel.

[0047] In step S1, mechanical impurities with a particle size greater than 0.5 mm are removed by sieving, and iron-containing impurities are separated by magnetic separation to ensure that the metallic iron content in the raw material is less than 0.1%. The treated raw material is then sent to a drying device and dried continuously at a temperature of 80–120°C for 2–4 hours. During this period, a hot air circulation system is used to keep the material heated evenly until the moisture content of the raw material is reduced to below 0.5%, in order to avoid melt splashing or composition fluctuations caused by moisture evaporation during the subsequent melting process.

[0048] In step S2, each pretreated raw material component is weighed using an electronic scale with an accuracy of 0.1g. During the weighing process, hygroscopic components such as Na2O and Li2O are weighed quickly and stored in a sealed container to prevent weighing errors from exceeding ±0.5% due to moisture absorption.

[0049] In step S3, all weighed raw materials are added sequentially to a horizontal twin-shaft mixer. The mixer is first started and pre-mixed at 100 rpm for 5 minutes to initially disperse the light raw materials and heavy oxides. Then, the speed is increased to 200–300 rpm, and mixing continues for 15–25 minutes. During this time, the material state is monitored through the observation window at the top of the mixer to ensure there is no obvious clumping or stratification. After mixing, 3–5 samples are taken from different locations in the mixer for component homogeneity testing to ensure that the relative standard deviation of each component does not exceed 2%, thus avoiding localized component segregation during subsequent melting.

[0050] In step S4, the uniformly mixed material is continuously fed into a vertical electric arc furnace via a screw conveyor. The furnace power is controlled to gradually raise the furnace temperature to 1300–1500°C, with the heating rate maintained at 50–100°C / minute to prevent premature volatilization of low-melting-point components (such as Na₂O and B₂O₃) due to localized overheating. After reaching the target temperature, the temperature is maintained at a constant level for 2–4 hours. During this period, manual stirring is performed every 30–60 minutes using a graphite stirring rod, with the stirring depth reaching 2 / 3 of the melt height to ensure uniform temperature and composition within the melt. During the melting process, volatiles are collected through a tail gas treatment system to reduce the loss of components such as Na₂O.

[0051] In step S5, after melting is complete, the melt is continuously discharged from the guide port at the bottom of the furnace and cooled using a water quenching method: the melt flows into a high-pressure water stream (pressure 0.3–0.5 MPa) at a flow rate of 5–10 kg / min, where it is broken into particles with a diameter of 1–5 mm. The particles then enter a vibrating dewatering screen to remove surface moisture, and are subsequently dried with hot air (temperature 100–150 °C) to remove residual moisture. Alternatively, if air atomization cooling is used, compressed air (pressure 0.6–0.8 MPa) atomizes the melt into fine droplets, which then cool naturally to room temperature in the air, forming spherical glassy particles. Both cooling methods require controlling the cooling rate at 100–200 °C / s to suppress crystal precipitation and obtain an amorphous or microcrystalline structure.

[0052] In step S6, the cooled solidified material (water-quenched particles or atomized particles) is added to the required carbon material and fed into a jaw crusher for coarse crushing. The discharge gap of the crusher is adjusted to 3-5 mm to crush the material into coarse particles with a maximum particle size of no more than 5 mm. During the crushing process, a magnetic separator removes any metal impurities that may be mixed in, and the crushed material is screened. The material that passes through the screen (particle size > 5 mm) is returned to the crusher for re-crushing, while the material that passes through the screen enters the next process, ensuring that the coarse particles are of uniform size and reducing the energy consumption of subsequent fine grinding.

[0053] In step S7, the coarse-particle material is fed into a ball mill for fine grinding. The ball mill is filled with alumina ceramic balls with a diameter of 5-10 mm, and the ball-to-material ratio is controlled at 3:1-5:1. The mill speed is set to 150-200 rpm, and the grinding time is adjusted to 2-4 hours according to the target particle size. After grinding, the material is sieved through a 100-200 mesh standard sieve. The undersized fine powder is collected for later use, while the oversized coarse powder is returned to the ball mill for further grinding. The particle size distribution requirement for the fine powder is: particles smaller than 0.074 mm account for ≥80%, ensuring that the protective slag has good spreading and melting speed during continuous casting.

[0054] In step S8, a comprehensive performance test is performed on the finely ground protective slag powder: X-ray fluorescence spectrometry is used to analyze the main components to ensure that the content of each oxide is within the design range; the viscosity is measured at 1300℃ using a rotational viscometer, which is 0.49 Pa·s; the melting point of the protective slag is measured using a fully automatic slag melting point and melting rate meter, which is 1086℃; and the crystallization performance of the protective slag is measured using a single-wire device, with a crystallization temperature of 1310℃ and a crystallization rate of 92%. After all test items pass, the product is packaged into kraft paper bags lined with plastic bags, each bag weighing 25 kg net, sealed, and stored in a dry and ventilated warehouse to prevent moisture absorption and clumping. This completes the entire preparation process of the protective slag.

[0055] Example 2:

[0056] A fluorine-free non-reactive continuous casting protective slag for high-titanium steel comprises: CaO: 28%, Al2O3: 28%, SiO2: 2%, TiO2: 4%, BaO: 5%, Na2O: 10%, Li2O: 4%, B2O3: 8%, MgO: 3%, Fe2O3: 1%, carbon materials: 7%, and the balance being impurities.

[0057] A method for preparing a fluorine-free, non-reactive continuous casting protective slag for high-titanium steel includes the following steps:

[0058] S1: Select and pre-treat raw materials, including CaO: 28%, Al2O3: 28%, SiO2: 2%, TiO2: 4%, BaO: 5%, Na2O: 10%, Li2O: 4%, B2O3: 8%, MgO: 3%, Fe2O3: 1%, and carbon materials: 7%. Remove impurities and dry to a moisture content of ≤0.5%.

[0059] S2: Weigh the pretreated raw materials by mass percentage, with the mass ratio of CaO to Al2O3 being 1.0.

[0060] S3: Place the weighed raw materials into the mixer and mix at a speed of 100-300 rpm for 10-30 minutes to obtain a uniformly mixed material.

[0061] S4: Send the mixture into a high-temperature furnace and melt it at 1300-1500℃ for 2-4 hours, stirring it 2-3 times during the process to make the melt composition uniform.

[0062] S5: The molten material is removed from the furnace and cooled to room temperature by water quenching or air atomization to form a glassy or microcrystalline solid.

[0063] S6: Add the required carbon material to the cooled solid, put it into a crusher to crush and mix it, and obtain coarse particles with a particle size ≤5mm.

[0064] S7: Feed the coarse particles into a ball mill for fine grinding, and pass them through a 100-200 mesh sieve to obtain fine powder with a particle size distribution that meets the requirements.

[0065] S8: The fine powder is subjected to component analysis, viscosity, melting point and crystallization performance testing. After passing the test, it is packaged to obtain the fluorine-free non-reactive continuous casting protective slag for high titanium steel.

[0066] In step S1, mechanical impurities with a particle size greater than 0.5 mm are removed by sieving, and iron-containing impurities are separated by magnetic separation to ensure that the metallic iron content in the raw material is less than 0.1%. The treated raw material is then sent to a drying device and dried continuously at a temperature of 80–120°C for 2–4 hours. During this period, a hot air circulation system is used to keep the material heated evenly until the moisture content of the raw material is reduced to below 0.5%, in order to avoid melt splashing or composition fluctuations caused by moisture evaporation during the subsequent melting process.

[0067] In step S2, each pretreated raw material component is weighed using an electronic scale with an accuracy of 0.1g. During the weighing process, hygroscopic components such as Na2O and Li2O are weighed quickly and stored in a sealed container to prevent weighing errors from exceeding ±0.5% due to moisture absorption.

[0068] In step S3, all weighed raw materials are added sequentially to a horizontal twin-shaft mixer. The mixer is first started and pre-mixed at 100 rpm for 5 minutes to initially disperse the light raw materials and heavy oxides. Then, the speed is increased to 200–300 rpm, and mixing continues for 15–25 minutes. During this time, the material state is monitored through the observation window at the top of the mixer to ensure there is no obvious clumping or stratification. After mixing, 3–5 samples are taken from different locations in the mixer for component homogeneity testing to ensure that the relative standard deviation of each component does not exceed 2%, thus avoiding localized component segregation during subsequent melting.

[0069] In step S4, the uniformly mixed material is continuously fed into a vertical electric arc furnace via a screw conveyor. The furnace power is controlled to gradually raise the furnace temperature to 1300–1500°C, with the heating rate maintained at 50–100°C / minute to prevent premature volatilization of low-melting-point components (such as Na₂O and B₂O₃) due to localized overheating. After reaching the target temperature, the temperature is maintained at a constant level for 2–4 hours. During this period, manual stirring is performed every 30–60 minutes using a graphite stirring rod, with the stirring depth reaching 2 / 3 of the melt height to ensure uniform temperature and composition within the melt. During the melting process, volatiles are collected through a tail gas treatment system to reduce the loss of components such as Na₂O.

[0070] In step S5, after melting is complete, the melt is continuously discharged from the guide port at the bottom of the furnace and cooled using a water quenching method: the melt flows into a high-pressure water stream (pressure 0.3–0.5 MPa) at a flow rate of 5–10 kg / min, where it is broken into particles with a diameter of 1–5 mm. The particles then enter a vibrating dewatering screen to remove surface moisture, and are subsequently dried with hot air (temperature 100–150 °C) to remove residual moisture. Alternatively, if air atomization cooling is used, compressed air (pressure 0.6–0.8 MPa) atomizes the melt into fine droplets, which then cool naturally to room temperature in the air, forming spherical glassy particles. Both cooling methods require controlling the cooling rate at 100–200 °C / s to suppress crystal precipitation and obtain an amorphous or microcrystalline structure.

[0071] In step S6, the cooled solidified material (water-quenched particles or atomized particles) is added to the required carbon material and fed into a jaw crusher for coarse crushing. The discharge gap of the crusher is adjusted to 3-5 mm to crush the material into coarse particles with a maximum particle size of no more than 5 mm. During the crushing process, a magnetic separator removes any metal impurities that may be mixed in, and the crushed material is screened. The material that passes through the screen (particle size > 5 mm) is returned to the crusher for re-crushing, while the material that passes through the screen enters the next process, ensuring that the coarse particles are of uniform size and reducing the energy consumption of subsequent fine grinding.

[0072] In step S7, the coarse-particle material is fed into a ball mill for fine grinding. The ball mill is filled with alumina ceramic balls with a diameter of 5-10 mm, and the ball-to-material ratio is controlled at 3:1-5:1. The mill speed is set to 150-200 rpm, and the grinding time is adjusted to 2-4 hours according to the target particle size. After grinding, the material is sieved through a 100-200 mesh standard sieve. The undersized fine powder is collected for later use, while the oversized coarse powder is returned to the ball mill for further grinding. The particle size distribution requirement for the fine powder is: particles smaller than 0.074 mm account for ≥80%, ensuring that the protective slag has good spreading and melting speed during continuous casting.

[0073] In step S8, a comprehensive performance test is performed on the finely ground protective slag powder: X-ray fluorescence spectrometry is used to analyze the main components to ensure that the content of each oxide is within the design range; the viscosity is measured at 1300℃ using a rotational viscometer, which is 0.27 Pa·s; the melting point of the protective slag is measured using a fully automatic slag melting point and melting rate meter, which is 980℃; and the crystallization performance of the protective slag is measured using a single-wire device, with a crystallization temperature of 1120℃ and a crystallization rate of 48%. After all test items pass, the product is packaged into kraft paper bags lined with plastic bags, each bag weighing 25 kg net, sealed, and stored in a dry and ventilated warehouse to prevent moisture absorption and clumping. This completes the entire preparation process of the protective slag.

[0074] Comparative Example 1: Traditional Fluorine-Containing Protective Slag

[0075] Comparative Example 1: Detailed Introduction of Preparation Method

[0076] Formula composition (percentage by weight)

[0077] CaO: 32%, Al2O3: 5%, SiO2: 30%, CaF2: 12%, Na2O: 8%, MgO: 4%, TiO2: 1%, carbon materials: 8% (excluding BaO, Li2O, and B2O3, containing fluoride CaF2 and with a significantly higher SiO2 content than in this invention).

[0078] Preparation steps

[0079] Raw material pretreatment: Mechanical impurities were removed only by sieving through a 1mm mesh screen; magnetic separation was not used to separate iron-containing impurities. The metallic iron content in the raw material was approximately 0.3%. The drying process was carried out in a 60℃ forced-air drying oven for 1 hour. No hot air circulation system was used, resulting in uneven heating of the material. The moisture content after drying was 1.0%.

[0080] Raw material weighing: Each component was weighed using a standard electronic scale with an accuracy of 1g. No sealing measures were taken for the hygroscopic Na2O, and the weighing process was exposed to air for about 10 minutes, which caused Na2O to absorb moisture and increase in weight. The actual weighing error reached ±1.2%.

[0081] Material mixing: A vertical single-shaft mixer was used. All raw materials were added at once and mixed directly at a speed of 150 rpm for 10 minutes without a premixing stage. As a result, the light carbon materials and heavy oxides separated into layers. After mixing, the samples were tested and the relative standard deviation of some components reached 5.3%.

[0082] High-temperature melting: The mixture is put into an intermittent resistance furnace, heated to 1200℃ and held for 1 hour without stirring. The temperature difference between the upper and lower layers of the melt reaches 80℃, and unmelted solid particles appear in some areas, resulting in poor melting uniformity.

[0083] Melt cooling: After melting, the melt is poured directly from the furnace opening into a cast iron mold and allowed to cool naturally to room temperature. The solid product is in a fully crystalline state and has no glassy structure.

[0084] Crushing and grinding: The cooled crystalline solid is crushed to a particle size of ≤10mm by a jaw crusher and then directly fed into a Raymond mill for fine grinding. It is then passed through an 80-mesh sieve, and the proportion of fine powder passing through the sieve is about 65% (particles smaller than 0.074mm account for only 58%, which is coarser than the requirements of this invention).

[0085] Testing and Packaging: The contents of CaO, SiO2, and CaF2 were tested using chemical analysis. The melting point was 1156℃, the viscosity was 0.68 Pa·s, the crystallization temperature was 1238℃, and the crystallization rate was 72%. The product was directly packed into open woven bags without any moisture-proof measures.

[0086] Comparative Example 2: (Fluorine-free but compositionally unbalanced protective slag) Detailed preparation method

[0087] Formula composition (percentage by weight)

[0088] CaO: 21%, Al2O3: 24%, SiO2: 18%, Na2O: 10%, MgO: 5%, TiO2: 15%, Carbon materials: 7% (excluding BaO, Li2O, and B2O3; CaO / Al2O3 = 0.88; TiO2 content exceeds the upper limit of 4% to 12% of this invention).

[0089] Preparation steps:

[0090] Raw material pretreatment: Sieving removed impurities with a particle size >0.5mm, but magnetic separation was not performed to remove iron, resulting in a metallic iron content of 0.25% in the raw material. Drying was carried out at 90℃ for 2 hours. A malfunction in the hot air circulation system caused localized overheating of the material, resulting in a moisture content of 0.8% after drying.

[0091] Raw material weighing: An electronic scale with an accuracy of 0.1g was used, but no rapid weighing measures were taken for hygroscopic components such as Li2O.

[0092] Material mixing: A horizontal twin-shaft mixer was used, but no staged premixing was performed. The mixture was directly mixed at 200 rpm for 15 minutes. During the mixing process, due to the high density of Al2O3, sedimentation and stratification occurred with the lightweight carbon materials. The relative standard deviation of the mixing uniformity was 4.1%.

[0093] High-temperature melting: The melting temperature was set at 1300℃ and the holding time was 2 hours. No stirring was performed during the process. An oxide film was formed on the surface of the melt, and bubbles were present inside. After cooling, TiO2 was found to be locally enriched.

[0094] Melt cooling: Air atomization cooling is used, but the compressed air pressure is only 0.4MPa, the atomized droplet size is uneven, the cooling rate is about 80℃ / second, and some particles form microcrystalline structures due to slow cooling.

[0095] Crushing and grinding: The atomized and cooled particles are directly fed into the ball mill with a ball-to-material ratio of 2:1 and a grinding time of 2 hours. After passing through a 100-mesh sieve, particles smaller than 0.074mm account for 72%.

[0096] Testing and Packaging: The contents of CaO, SiO2, and CaF2 were tested using chemical analysis. The melting point is 1192℃, the viscosity is 1.2 Pa·s, the crystallization temperature is 1386℃, and the crystallization rate is 97%. Packaging uses ordinary plastic bags, which are not sealed.

[0097] The experimental results are compared in the table below:

[0098]

[0099]

[0100] The data shows that:

[0101] Analysis of beneficial effects:

[0102] Fluorine-free and environmentally friendly: The original formula does not contain fluorine (fluorine content = 0), avoiding the equipment corrosion and environmental pollution problems caused by fluorides in Comparative Example 1, which is in line with the trend of green metallurgy.

[0103] Viscosity and crystallization properties are well-matched: The original formula, through the synergistic regulation of BaO, Li2O, and B2O3, stabilizes the viscosity at 0.27–0.5 Pa·s at 1300℃ (Comparative Example 2, lacking flux, has a viscosity of 1.2 Pa·s, a crystallization temperature of 1386℃, and a crystallization rate of 97%, exhibiting strong crystallization ability, which is unfavorable for lubricating the cast billet). The crystallization temperature is 1120–1310℃, a relatively wide range, expanding the application range of steel grades, such as peritectic steel.

[0104] Non-reactive properties and titanium stability: The original formula was optimized with TiO2 (4-12%) and SiO2 (1-5%). The TiO2 reaction rate was only 0.1%, which effectively inhibited the reaction between titanium in steel and protective slag (the reaction rate of Comparative Example 1 was 42%, and the reaction rate of Comparative Example 2 was 15%, which easily caused changes in the composition of protective slag, deteriorated its physical and chemical properties, and led to surface defects of the billet).

[0105] Spreadability and surface quality: The original formula is finely ground to 100-200 mesh, and combined with a reasonable melting process, the spreading area reaches 85cm². 2 The surface defect rate of the steel billet is less than 0.5% (Comparative Example 1 has a defect rate of 85% due to excessive reactivity; Comparative Example 2 has a defect rate of 89% due to poor performance of the protective slag).

[0106] As can be seen from the comparison of the examples and comparative examples, the fluorine-free non-reactive protective slag of the present invention is significantly superior to the traditional fluorine-containing formula or the fluorine-free formula with unbalanced composition in terms of environmental protection, viscosity control, melting point and crystallization stability, reactivity and billet quality, and has industrial application value.

[0107] In summary, this invention effectively suppresses the interfacial reaction between steel and slag by significantly reducing the SiO2 content and reasonably increasing the TiO2 proportion, ensuring the stability of the protective slag composition and performance during the casting of high-titanium steel. Furthermore, by adding fluxes such as BaO, Na2O, and Li2O, the melt structure is adjusted and optimized, effectively improving the physicochemical properties of the protective slag and ensuring smooth continuous casting of high-titanium steel and good surface quality of the cast billet. The fluoride-free formulation design eliminates the risk of fluorine pollution at the source, aligning with the trend of green and low-carbon industrial development. It avoids the equipment corrosion, environmental pollution, and health hazards caused by the release of hydrogen fluoride and other gases from traditional fluorinated protective slags at high temperatures, while also reducing subsequent processing costs.

[0108] In this invention, a unique fluorine-free CaO-Al2O3-TiO2 system inhibits the interfacial reaction between steel and slag, ensuring the stability of the protective slag composition and properties during the casting process of high-titanium steel. This reduces the probability of defects such as surface cracks and inclusions in the cast billet, thereby improving the surface quality and yield of the high-titanium steel billet. The physicochemical properties of this protective slag are highly adaptable, meeting not only the continuous casting process requirements of high-titanium steel but also applicable to peritectic steel, which is highly sensitive to cracking. This broadens its application range and provides a reliable material guarantee for steel enterprises to achieve efficient and high-quality production.

[0109] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising" or any other variations thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0110] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A non-fluoride and non-reactive continuous casting protective mold flux for high titanium steel, characterized by comprising: Comprise: CaO: 18-28%, Al2O3: 18-28%, BaO: 5-15%, Na2O: 6-10%, Li2O: 1-4%, MgO: 2-4%, B2O3: 6-10%, SiO2: 1-5%, TiO2: 4-12%, Fe2O3≤2%, carbon material 4-12%, the balance is impurities.

2. The method for preparing a non-fluorine and non-reactive continuous casting protective slag for high titanium steel according to claim 1, characterized in that: The method comprises the following steps: S1: selecting and pretreating raw materials, including CaO: 18-28%, Al2O3: 18-28%, BaO: 5-15%, Na2O: 6-10%, Li2O: 1-4%, MgO: 2-4%, B2O3: 6-10%, SiO2: 1-5%, TiO2: 4-12%, Fe2O3≤2% and carbon material, removing impurities and drying to moisture content≤0.5%; S2: taking the pretreated raw materials according to mass percentage, and the mass ratio of CaO to Al2O3 is 0.8-1.2; S3: putting the weighed raw materials into a mixer, mixing at a speed of 100-300 revolutions per minute for 10-30 minutes to obtain uniformly mixed mixture; S4: sending the mixture into a high-temperature furnace, melting at 1300-1500°C for 2-4 hours, stirring 2-3 times during the process to make the melt composition uniform; S5: guiding the molten melt out of the furnace, and cooling to room temperature by water quenching or air atomization to form a glass body or a microcrystalline solid; S6: adding the required carbon material to the cooled solid, putting it into a crusher to crush and mix uniformly to obtain coarse particles with a particle size≤5mm; S7: sending the coarse particles into a ball mill for fine grinding, passing through a 100-200 mesh sieve to obtain fine powder with a particle size distribution meeting the requirements; S8: testing the composition, viscosity, melting point and crystallization performance of the fine powder, and packaging after passing the test to obtain a non-fluorine non-reactive continuous casting protective slag for high-titanium steel.

3. The method for preparing a non-fluoride and non-reactive continuous casting protective slag for high titanium steel according to claim 1, characterized in that: In the step S1, the mechanical impurities with a particle size greater than 0.5mm are removed by screening method, and the iron-containing impurities are separated by magnetic separation process to ensure that the content of metallic iron in the raw material is less than 0.1%; the treated raw material is sent into a drying equipment, and continuously dried at a temperature of 80-120°C for 2-4 hours, during which the material is uniformly heated by a hot air circulation system, until the moisture content of the raw material is reduced to below 0.5%, to avoid splashing or composition fluctuation of the melt due to water evaporation in the subsequent melting process.

4. The method of producing a non-fluoride and non-reactive continuous casting protective slag for high titanium steel according to claim 1, characterized in that: In the step S2, the pretreated raw material components are weighed by an electronic scale with a precision of 0.1g, and the moisture-prone Na2O, Li2O and other components are quickly weighed and sealed to prevent weighing error caused by moisture absorption exceeding±0.5%.

5. The method of producing a non-fluoride and non-reactive continuous casting protective shell for high titanium steel according to claim 1, characterized in that: In the step S3, all the weighed raw materials are sequentially added into the horizontal double-shaft mixer. The mixer is started to premix for 5 minutes at a speed of 100 rpm to preliminarily disperse the light raw materials and heavy oxides. Then, the speed is increased to 200-300 rpm, and the mixing is continuously performed for 15-25 minutes. During the mixing, the material state is monitored through the observation window on the top of the mixer to ensure that there is no obvious caking or stratification. After the mixing, 3-5 samples are taken from different positions of the mixer for composition uniformity detection to ensure that the relative standard deviation of each component is not more than 2% to avoid local component segregation in the subsequent melting process.

6. The method of producing a non-fluoride and non-reactive continuous casting protective shell for high titanium steel according to claim 1, characterized in that: In the step S4, the uniformly mixed material is continuously fed into the vertical electric arc furnace through the screw conveyor. The furnace power is controlled to gradually increase the temperature in the furnace to 1300-1500℃ at a rate of 50-100℃ / min to prevent the low-melting-point components from volatilizing due to local overheating. After reaching the target temperature, the temperature is kept constant for 2-4 hours. During this period, manual stirring is performed every 30-60 minutes through the graphite stirring rod to a depth of 2 / 3 of the melt height to ensure the uniformity of the internal temperature and composition of the melt. During the melting process, the volatile components are collected through the tail gas treatment system to reduce the loss of components such as Na2O.

7. The method for preparing a non-fluoride and non-reactive continuous casting protective slag for high titanium steel according to claim 1, characterized in that: In the step S5, after the melting is completed, the melt is continuously discharged from the flow guide at the bottom of the furnace and cooled by water quenching. The melt flows into the high-pressure water flow at a flow rate of 5-10 kg / min and is broken into particles with a particle size of 1-5 mm. Then, the particles enter the vibrating dehydration screen to remove surface moisture and then pass through the hot air drying to remove residual moisture. If air atomization cooling is used, the melt is atomized into fine droplets by compressed air, and the droplets are naturally cooled to room temperature in the air to form spherical glass particles. In both cooling methods, the cooling rate needs to be controlled at 100-200℃ / s to suppress the crystallization and obtain amorphous or microcrystalline structure.

8. The method for preparing a non-fluoride and non-reactive continuous casting protective shell for high titanium steel according to claim 1, characterized in that: In the step S6, the cooled solid is added with the required carbon material, and fed into the jaw crusher for coarse crushing. The discharge gap of the crusher is adjusted to 3-5 mm to crush the material to coarse particles with a maximum particle size of not more than 5 mm. During the crushing process, the iron remover is used to remove possible metal impurities, and the crushed material is screened. The oversize material is returned to the crusher for re-crushing, and the undersize material enters the next process to ensure the uniformity of the coarse particle size and reduce the energy consumption of the subsequent fine grinding.

9. The method of producing a non-fluoride and non-reactive continuous casting protective shell for high titanium steel according to claim 1, characterized in that: In the step S7, the coarse particle material is fed into the ball mill for fine grinding. The ball mill is loaded with alumina ceramic balls with a diameter of 5-10 mm, and the ball-to-material ratio is controlled at 3:1-5:

1. The mill speed is set at 150-200 rpm, and the grinding time is adjusted to 2-4 hours according to the target particle size. After the grinding is completed, the material is screened through a 100-200 mesh standard screen. The fine powder is collected for use, and the coarse powder is returned to the ball mill for further grinding. The particle size distribution of the fine powder is required to be: the proportion of particles below 0.074 mm is ≥80% to ensure that the mold powder has good spreading property and melting speed in the continuous casting process.

10. The method of producing a non-fluoride and non-reactive continuous casting protective shell for high titanium steel according to claim 1, characterized in that: In the step S8, the fine ground protective slag powder is subjected to overall performance detection: the main components are analyzed by X-ray fluorescence spectrometer to ensure that the content of each oxide is within the design range; the viscosity is measured at 1300 DEG C. by using a rotary viscometer, and the viscosity value is required to be controlled within 0.05-0.8 Pa·s; the melting point of the protective slag is measured by using a full-automatic slag melting point and melting speed instrument to ensure that the melting point is within 950-1200 DEG C.; the crystallization performance of the protective slag is measured by using a single filament device to ensure that the crystallization temperature is controlled within 1100-1350 DEG C. and the crystallization rate is 40-100%; after all the detection items are qualified, the product is packed into kraft paper bags with plastic inner liner, each bag has a net weight of 25 kg, and after being sealed, is stored in a dry and ventilated warehouse to prevent moisture absorption and caking, thus completing the whole preparation process of the protective slag.

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