Low-alkalinity high-crystallization casting powder for pen point steel

Abstract

The invention relates to the technical field of casting powder, in particular to low-alkalinity high-crystallization casting powder for nib steel, which comprises the following raw materials: a pre-melting material, aluminum activated wollastonite, modified fluorite, cryolite, carbon nanotube composite graphite, sodium carboxymethyl cellulose and magnesia. According to the method, the modified fluorite is calcined to generate the composite fluoride, F <-> is gradually released at high temperature, and sudden viscosity reduction caused by rapid fluorine release of traditional fluorite is avoided, so that the thickness of a slag lubricating layer is stabilized, and the steel breakout risk is reduced; meanwhile, the introduced Na < + > serves as a strong network regulator, a network structure formed by silica tetrahedrons is effectively broken, the melt polymerization degree is reduced, and therefore the viscosity and the melting point of the slag are reduced; the activity of CaO in the molten slag is indirectly influenced, and the actual alkalinity of a slag system can be reduced; in addition, K < + > in the muscovite is removed through acid pickling, active Al < 3 + > is released, and the active Al < 3 + > reacts with wollastonite to generate low-melting-point calcium aluminosilicate, so that the content of effective CaO is reduced, and the alkalinity of a slag system is reduced.

Description

Technical Field

[0001] This invention relates to the field of protective slag technology, and more specifically, to a low-alkalinity, high-crystallization protective slag for pen tip steel. Background Technology

[0002] As the core material for manufacturing high-end writing instrument nibs, pen tip steel must possess high carbon content, ultra-fine grain structure, excellent hardness uniformity, and extremely high purity. Its continuous casting process places stringent requirements on the performance of the protective slag. The protective slag must simultaneously achieve the isolation and oxidation of the molten steel surface, precise lubrication between the crystallizer wall and the billet, adsorption and purification of inclusions in the molten steel, and melting and spreading characteristics suitable for the low-speed continuous casting process of pen tip steel, directly affecting the surface quality of the billet and its subsequent processing performance.

[0003] Existing protective slags for pen tip steel have unreasonable basicity and melting point design. Excessive basicity can easily cause the protective slag to react with inclusions in the molten steel to form a hard and brittle phase, resulting in defects such as scratches and inclusions on the surface of the pen tip steel. In view of this, we propose a low-basicity, high-crystallization protective slag for pen tip steel. Summary of the Invention

[0004] The purpose of this invention is to provide a low-basicity, high-crystallization protective slag for pen tip steel, in order to solve the problem mentioned in the background art that the existing pen tip steel protective slag has unreasonable design of basicity and melting point. Excessive basicity can easily cause the protective slag to react with inclusions in the molten steel to form a hard and brittle phase, resulting in defects such as scratches and inclusions on the surface of the pen tip steel.

[0005] To achieve the above objectives, the present invention provides a low-alkalinity, high-crystallization protective slag for pen tip steel, comprising the following raw materials: pre-melted material, aluminum-activated wollastonite, modified fluorite, cryolite, carbon nanotube composite graphite, sodium carboxymethyl cellulose, and magnesia. The aluminum-activated wollastonite is prepared by a solid-phase reaction between acid-washed muscovite and wollastonite. Modified fluorite is prepared by high-temperature calcination of sodium fluorosilicate and fluorite.

[0006] Preferably, the premelted material comprises 50-60 parts by weight, aluminum-activated wollastonite 8-10 parts by weight, modified fluorite 12-15 parts by weight, cryolite 5-8 parts by weight, carbon nanotube composite graphite 4-6 parts by weight, sodium carboxymethyl cellulose 2-4 parts by weight, and magnesia 2-3 parts by weight.

[0007] As a preferred embodiment, the modified fluorite is prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 800-900℃ for 2-3 hours. After calcination, the mixture is cooled by water quenching, ball-milled at 1500-2000 rpm for 10-15 minutes, washed with dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 120-150℃ for 4-6 hours to obtain the modified fluorite.

[0008] The calcination process of modified fluorite is carried out in a closed tubular rotary furnace. The furnace body adopts a double-layer water-cooled jacket structure and is lined with silicon nitride ceramic material. When the calcination temperature is 800-900℃, a slight negative pressure (-50~-100Pa) is maintained inside the furnace. The exhaust gas is introduced into the condensation and recovery system by an induced draft fan.

[0009] By calcining fluorite and sodium fluorosilicate at high temperatures, complex fluorides can be generated; these complex fluorides gradually decompose at high temperatures, releasing F. - This avoids sudden increases in local fluorine concentration and stabilizes the viscosity of the slag; at the same time, Na + As a network modifier, it reduces the degree of polymerization of silicate networks, further reducing slag viscosity and improving lubricity; by controlling calcination conditions (such as temperature and time), some SiF4 volatilizes, reducing the content of free SiO2 in the system and indirectly reducing basicity.

[0010] Preferably, the concentration of the dilute hydrochloric acid is 3-5%.

[0011] Preferably, the modified fluorite has a particle size of 80-100 μm.

[0012] Preferably, the preparation method of the aluminum-activated wollastonite is as follows: soaking muscovite in hydrochloric acid for 1-2 hours; then washing with deionized water until the washing solution is free of Cl. - The process involves mixing deionized mica and wollastonite at a mass ratio of 1:3-5 and calcining at 1250-1350℃ for 3-4 hours. After calcination, the mixture is cooled to room temperature and pulverized at 1500-2000 rpm for 10-15 minutes to obtain aluminum-activated wollastonite.

[0013] After acid washing, muscovite produces soluble salt KCl, which can be removed by washing with deionized water; the wastewater after acid washing is neutralized with lime to pH=7 before being discharged.

[0014] The potassium in muscovite was extracted through a high-temperature solid-state reaction between acid-washed muscovite and wollastonite. + The Al-OH group is removed, forming an active structure rich in Al-OH, while Al... 3+ Entering the silicate structure reduces the effective CaO content and directly reduces the basicity of the slag; this process generates a ternary low-melting-point phase of CaO-Al2O3-SiO2, which optimizes the fluidity of the slag and the matching of crystallization temperature; the crystallization tendency of aluminosilicate is mild, forming fine and uniform grains, reducing stress concentration in the slag layer and reducing crack sensitivity.

[0015] Preferably, the concentration of the hydrochloric acid is 5-10%.

[0016] Preferably, the particle size of the aluminum-activated wollastonite is 50-100 μm.

[0017] As a preferred embodiment, the preparation method of the low-alkalinity, high-crystallization protective slag for pen tip steel is as follows: S1.1 Weigh the following raw materials in parts by weight: 50-60 parts by weight of premelted material, 8-10 parts by weight of aluminum-activated wollastonite, 12-15 parts by weight of modified fluorite, 5-8 parts by weight of cryolite, 4-6 parts by weight of carbon nanotube composite graphite, 2-4 parts by weight of sodium carboxymethyl cellulose and 2-3 parts by weight of magnesia. S1.2. Stir the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 200-300 rpm for 30-40 min to obtain a dry mixture. S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2, stir at 300-400 rpm for 15-30 min, then add carbon nanotube composite graphite and sodium carboxymethyl cellulose, and continue stirring at 300-400 rpm for 1.5-2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0018] Preferably, in step S1.4, the inlet air temperature of the spray dryer is 180-200℃, the outlet air temperature is 80-90℃, and the pressure is 0.2-0.4MPa.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this type of pen tip steel, a low-alkalinity, high-crystallization protective slag is used to generate a composite fluoride through calcination of modified fluorite, which gradually releases F at high temperatures. - This avoids the sudden drop in viscosity caused by the rapid fluorine release of traditional fluorite, thus stabilizing the thickness and uniformity of the slag lubrication layer. It is suitable for low-speed continuous casting processes for pen tip steel, ensuring the smoothness of the cast billet surface and reducing scratch defects. Simultaneously, the introduction of Na... + As a strong network modifier, it can effectively break the network structure composed of silicon-oxygen tetrahedra, reduce the degree of melt polymerization, and thus reduce the viscosity and melting point of the slag. This indirectly affects the activity of CaO in the slag, helps to reduce the actual basicity of the slag system, avoids slag inclusions and internal cracking tendencies on the surface of the pen tip steel, and ensures its hardness uniformity. In addition, the thermal stability of the composite fluoride is higher than that of pure CaF2, which reduces the volatilization of fluorine in the form of SiF4. It retains the fluxing effect of fluorine, reduces the impact of fluorine pollution on the purity of pen tip steel composition, and reduces environmental pollution.

[0020] 2. In this type of pen tip steel, a low-alkalinity, high-crystallization protective slag is used to remove potassium (K) from muscovite through acid washing. + Release active Al 3+It reacts with wollastonite to form low-melting-point calcium aluminosilicates, thereby reducing the effective CaO content and slag basicity, avoiding the formation of the high-melting-point hard and brittle calcium silicate phase, and reducing the risk of surface scratches and internal cracks in pen tip steel; at the same time, the introduction of Al2O3 to form low-melting-point aluminosilicates improves slag fluidity and lowers the crystallization temperature, avoiding uneven heat transfer caused by excessively thick solidification layers; Al 3+ The silicon-oxygen network structure is strengthened, which promotes the formation of granular structure in the slag, improves the uniformity of hardness and processing performance of the pen tip steel, reduces the internal stress of the slag layer, enhances the density of the slag layer, effectively isolates air to reduce secondary oxidation of the molten steel, ensures the extremely high purity of the pen tip steel, and meets the performance requirements of high-end pen tip precision machining. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a low-alkalinity, high-crystallization protective slag for pen tip steel, comprising the following raw materials: pre-melted material, aluminum-activated wollastonite, modified fluorite, cryolite, carbon nanotube composite graphite, sodium carboxymethyl cellulose, and magnesia. The aluminum-activated wollastonite is prepared by a solid-phase reaction between acid-washed muscovite and wollastonite. Modified fluorite is prepared by high-temperature calcination of sodium fluorosilicate and fluorite.

[0023] Preparation method of pre-melted material: Calcium oxide, silicon dioxide and magnesium oxide are mixed in a mass ratio of 45:45:10, melted at 1400-1500℃, and then ground at 2000-3000rpm for 15-20min to obtain pre-melted material with a particle size of less than 1mm.

[0024] Preparation method of carbon nanotube composite graphite: Natural graphite with a fixed carbon content of more than 98% is pulverized to a particle size of less than 20 μm; mixed with multi-walled carbon nanotubes at a mass ratio of 10:1, polyethylene glycol and anhydrous ethanol at a mass ratio of 0.5% of the mixture are added, ultrasonically dispersed at a power of 200W for 30 min, and heat-treated at 900-1000℃ for 2 h under argon protection to obtain carbon nanotube composite graphite.

[0025] Example 1: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 50 parts of premelted material, 8 parts of aluminum-activated wollastonite, 12 parts of modified fluorite, 5 parts of cryolite, 4 parts of carbon nanotube composite graphite, 2 parts of sodium carboxymethyl cellulose and 2 parts of magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0026] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0027] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:3 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0028] Example 2: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials in parts by weight: 55 parts by weight of premelted material, 9 parts by weight of aluminum-activated wollastonite, 13 parts by weight of modified fluorite, 7 parts by weight of cryolite, 5 parts by weight of carbon nanotube composite graphite, 3 parts by weight of sodium carboxymethyl cellulose and 2.5 parts by weight of magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0029] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0030] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:4 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0031] Example 3: A low-alkalinity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 60 parts of premelted material, 10 parts of aluminum-activated wollastonite, 15 parts of modified fluorite, 8 parts of cryolite, 6 parts of carbon nanotube composite graphite, 4 parts of sodium carboxymethyl cellulose and 3 parts of magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0032] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0033] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:5 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0034] Example 4: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 55 parts premelted material, 9 parts aluminum-activated wollastonite, 15 parts modified fluorite, 7 parts cryolite, 5 parts carbon nanotube composite graphite, 3 parts sodium carboxymethyl cellulose and 2.5 parts magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0035] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0036] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. -The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:4 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0037] Example 5: A low-alkalinity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 55 parts premelted material, 9 parts aluminum-activated wollastonite, 12 parts modified fluorite, 7 parts cryolite, 5 parts carbon nanotube composite graphite, 3 parts sodium carboxymethyl cellulose and 2.5 parts magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0038] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0039] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:4 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0040] Example 6: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 55 parts premelted material, 8 parts aluminum-activated wollastonite, 13 parts modified fluorite, 7 parts cryolite, 5 parts carbon nanotube composite graphite, 3 parts sodium carboxymethyl cellulose and 2.5 parts magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0041] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0042] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:4 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0043] Example 7: A low-alkalinity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials by weight: 55 parts premelted material, 10 parts aluminum-activated wollastonite, 13 parts modified fluorite, 7 parts cryolite, 5 parts carbon nanotube composite graphite, 3 parts sodium carboxymethyl cellulose and 2.5 parts magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0044] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0045] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:4 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0046] Example 8: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials in parts by weight: 55 parts by weight of premelted material, 9 parts by weight of aluminum-activated wollastonite, 13 parts by weight of modified fluorite, 7 parts by weight of cryolite, 5 parts by weight of carbon nanotube composite graphite, 3 parts by weight of sodium carboxymethyl cellulose and 2.5 parts by weight of magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0047] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0048] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. -The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:3 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0049] Example 9: A low-basicity, high-crystallization protective slag for pen tip steel is prepared through the following steps: S1.1 Weigh the following raw materials in parts by weight: 55 parts by weight of premelted material, 9 parts by weight of aluminum-activated wollastonite, 13 parts by weight of modified fluorite, 7 parts by weight of cryolite, 5 parts by weight of carbon nanotube composite graphite, 3 parts by weight of sodium carboxymethyl cellulose and 2.5 parts by weight of magnesia. S1.2. Mix the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 300 rpm for 30 min to obtain a dry mixture; S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2 and stir at 400 rpm for 30 min. Then add carbon nanotube composite graphite and sodium carboxymethyl cellulose and continue stirring at 400 rpm for 2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.4. Spray dry the slurry with an inlet air temperature of 190℃, an outlet air temperature of 85℃, and a pressure of 0.3MPa to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

[0050] The modified fluorite was prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 900℃ for 3 hours. After calcination, the mixture was cooled by water quenching, ball-milled at 2000 rpm for 15 minutes, washed with 4% dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 130℃ for 6 hours to obtain modified fluorite with a particle size of 80 μm.

[0051] The preparation method of aluminum-activated wollastonite is as follows: Muscovite is soaked in 8% hydrochloric acid for 2 hours; then washed with deionized water until the washing solution is free of Cl. - The mica washed with deionized water was mixed with wollastonite at a mass ratio of 1:5 and calcined at 1300℃ for 4 hours. After calcination, the mixture was cooled to room temperature and pulverized at 2000 rpm for 15 minutes to obtain aluminum-activated wollastonite with a particle size of 70 μm.

[0052] The performance indicators and testing standards of a low-basicity, high-crystallinity protective slag for pen tip steel were obtained by adding modified fluorite and aluminum-activated wollastonite. The contents of CaO and SiO2 in the protective slag were determined by X-ray fluorescence spectrometry (XRF), and the basicity (R=CaO / SiO2) was calculated based on the mass percentage of CaO and SiO2. Low basicity usually corresponds to a lower melting point and viscosity, which allows the protective slag to melt rapidly at the continuous casting temperature, forming a uniform liquid slag film, reducing friction between the billet and the mold, and lowering the risk of steel leakage. After optimizing the fluidity, the slag film can better fill the tiny gaps between the molten steel and the mold, suppressing crack defects.

[0053] The protective slag is ground to a particle size of less than 45 μm, pressed into tablets, and then subjected to X-ray diffraction (XRD) testing. The ratio of crystalline phase to glassy phase is analyzed by XRD pattern, and the proportion of crystalline phase is quantitatively calculated by Rietveld full-spectrum fitting or internal standard method. The slag film with high crystallinity has a more stable crystal structure at high temperature, which can resist temperature fluctuations during continuous casting, reduce slag film cracking or peeling, and reduce the risk of surface cracks in the billet.

[0054] The low-alkalinity, high-crystallization protective slag for pen tip steel prepared in Examples 2 and 4-9 were tested according to the above standards, and the data obtained are shown in Table 1: Table 1 Performance data of low-basicity, high-crystallization protective slag for pen tip steel in Examples 2 and 4-9

[0055] Examples 2 and 4-5 show that: when other components in the low-basicity, high-crystallization protective slag for pen tip steel remain constant, as the weight percentage of modified fluorite increases, the basicity of the protective slag continuously decreases and the crystallization rate continuously increases; increasing the amount of modified fluorite is equivalent to diluting the CaO concentration in the system, further reducing the basicity; F - Disruption of the silicate network structure enhances melt fluidity and promotes crystal nucleation and diffusion; F - With Ca 2+ The combination generates low-melting-point fluorides, providing crystallization nuclei and accelerating crystal phase growth; the fluorosilicates in the modified fluorite decompose at high temperature to generate active Si-OF units, which react with CaO in the system to form highly crystalline phases such as gun crystals; gun crystals are typical high-temperature stable crystalline phases, and their formation improves the crystallization rate of the protective slag.

[0056] Furthermore, comparing Examples 2 and 6-7 shows that when other components remain unchanged in the low-alkalinity, high-crystallization protective slag for pen tip steel, and the weight percentage of aluminum-activated wollastonite continuously increases, the alkalinity of the protective slag continuously decreases and the crystallization rate continuously increases. Aluminum-activated wollastonite is produced by the reaction of wollastonite and acid-washed muscovite, and its main components are a CaO-SiO2-Al2O3 system. Wollastonite itself contains a high proportion of SiO2. As the amount of aluminum-activated wollastonite increases, the total amount of SiO2 in the protective slag increases, and the CaO concentration in the system is relatively diluted, leading to a decrease in basicity. Al2O3 has amphoteric characteristics in the melt and can partially replace the network structure of SiO2, but it does not increase the contribution of basic oxides, thus maintaining the low basicity characteristics. The Al in aluminum-activated wollastonite... 3+ Entering the silicate structure, it forms aluminum-doped calcium silicate, which reduces the lattice energy, enhances the stability of the crystal at high temperatures, and promotes the nucleation and growth of crystal phases. In the melt, Al2O3 combines with CaO and SiO2 to form high-melting-point crystal phases such as calcium aluminum feldspar. These crystal phases preferentially precipitate at continuous casting temperatures, which improves the crystallization rate of the protective slag.

[0057] Furthermore, comparing Examples 8, 2, and 9 reveals that during the preparation of aluminum-activated wollastonite, as the mass ratio of acid-washed muscovite to wollastonite decreases (i.e., the relative amount of wollastonite increases), the alkalinity of the final protective slag shows a decreasing trend (from 0.93 to 0.84), while the crystallization rate continuously increases (from 55% to 64%).

[0058] Under high-temperature calcination conditions of 1250-1350℃, the Al2O3 provided by acid-washed muscovite undergoes a solid-state reaction with the CaO and SiO2 provided by wollastonite. When the mass ratio of muscovite to wollastonite is relatively low, the relatively abundant CaO and SiO2 in the system can react more fully with Al2O3 to generate the desired high-melting-point, highly crystalline phases such as calcium aluminum feldspar, thereby more effectively fixing the free CaO (reducing basicity) and increasing the crystallinity due to the formation of a large number of stable crystal nuclei. Conversely, when the proportion of muscovite is too high (e.g., 1:3), Al2O3 is relatively excessive while CaO and SiO2 are insufficient, resulting in incomplete reaction, generating more low-melting-point amorphous glass phases or residual unreacted substances, thus leading to higher basicity and lower crystallinity.

[0059] Based on the above test experiments, Example 4 is considered the optimal example. Comparative Example 1: The difference between this comparative example and Example 4 is that modified fluorite was not used; fluorite was used directly.

[0060] Comparative Example 2: The difference between this comparative example and Example 4 is that aluminum-activated wollastonite was not used; wollastonite was used directly.

[0061] Comparative Example 3: This comparative example differs from Example 4 in that no carbon nanotube composite graphite was added.

[0062] Table 2 Performance data of low-basicity, high-crystallization protective slag for pen tip steel in Examples 4 and Comparative Examples 1-3

[0063] A comparison of Example 4 and Comparative Example 1 shows that: when fluorite is used directly without modified fluorite, the crystallization rate of the protective slag decreases; the fluorosilicate in the modified fluorite decomposes to generate active F. - The Si-OF composite structure promotes rapid crystallization of gunmetal at low temperatures; in contrast, ordinary fluorite only releases free F. - Its ability to promote crystallization is relatively weak, and it readily reacts with Ca. 2+ The combination generates low-melting-point CaF2, which inhibits crystal phase growth, thus leading to a decrease in crystallinity.

[0064] A comparison of Example 4 and Comparative Example 2 shows that when wollastonite is used directly without aluminum-activated wollastonite, the alkalinity of the protective slag increases and the crystallization rate decreases.

[0065] Aluminum-activated wollastonite reacts with acid-washed muscovite to produce calcium silicate containing Al2O3, with a lower SiO2 content than ordinary wollastonite. When the amount of ordinary wollastonite increases, the total SiO2 in the system rises, while CaO remains unchanged, leading to an increase in alkalinity. The Al content in aluminum-activated wollastonite... 3+ Al enters the silicate structure, forming a stable aluminum-doped crystalline phase and increasing the crystallinity; ordinary wollastonite does not contain Al. 3+ The inability to form such a stable crystalline phase leads to a decrease in crystallization rate; Al2O3 in aluminum-activated wollastonite can react with CaO and SiO2 to form calcium aluminum feldspar, which has better high-temperature stability than calcium silicate formed by ordinary wollastonite; in the ordinary wollastonite system, the main crystalline phase is low-melting-point calcium silicate, resulting in a lower crystallization rate.

[0066] A comparison of Example 4 and Comparative Example 3 shows that: without the addition of carbon nanotube composite graphite, the crystallization rate of the protective slag decreases; carbon nanotubes have a high specific surface area and a unique one-dimensional structure, which can serve as a crystal nucleus carrier, accelerating the nucleation and growth of the crystal phase, thereby improving the crystallization rate; in addition, graphite particles can reduce the viscosity of the molten slag, promote the uniform flow of the melt, and provide conditions for the orderly arrangement of the crystal phase; without the addition of graphite, the viscosity of the molten slag increases, crystal diffusion is hindered, the proportion of the glass phase increases, resulting in a decrease in the crystallization rate.

[0067] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low-basicity, high-crystallization protective slag for pen tip steel, characterized in that, Including the following raw materials: Pre-melted material, aluminum-activated wollastonite, modified fluorite, cryolite, carbon nanotube composite graphite, sodium carboxymethyl cellulose and magnesia; The aluminum-activated wollastonite is prepared by a solid-phase reaction between acid-washed muscovite and wollastonite. Modified fluorite is prepared by high-temperature calcination of sodium fluorosilicate and fluorite.

2. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 1, characterized in that, The pre-melted material consists of 50-60 parts by weight, aluminum-activated wollastonite 8-10 parts by weight, modified fluorite 12-15 parts by weight, cryolite 5-8 parts by weight, carbon nanotube composite graphite 4-6 parts by weight, sodium carboxymethyl cellulose 2-4 parts by weight, and magnesia 2-3 parts by weight.

3. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 2, characterized in that, The modified fluorite is prepared by mixing fluorite and sodium fluorosilicate at a mass ratio of 3:1 and calcining at 800-900℃ for 2-3 hours. After calcination, the mixture is cooled by water quenching, ball-milled at 1500-2000 rpm for 10-15 minutes, washed with dilute hydrochloric acid to remove unreacted substances, washed with deionized water until neutral, and dried at 120-150℃ for 4-6 hours to obtain the modified fluorite.

4. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 3, characterized in that, The concentration of the dilute hydrochloric acid is 3-5%.

5. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 3, characterized in that, The modified fluorite has a particle size of 80-100 μm.

6. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 2, characterized in that, The preparation method of the aluminum-activated wollastonite is: soaking muscovite with hydrochloric acid for 1-2 h; then washing with deionized water until the washing liquid is free of Cl - detection; mixing the muscovite washed with deionized water with wollastonite at a mass ratio of 1:3-5, calcining at 1250-1350°C for 3-4 h; after calcination, cooling at room temperature, and crushing at a speed of 1500-2000 rpm for 10-15 min to obtain aluminum-activated wollastonite.

7. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 6, characterized in that, The concentration of the hydrochloric acid is 5-10%.

8. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 6, characterized in that, The particle size of the aluminum-activated wollastonite is 50-100 μm.

9. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 2, characterized in that, The preparation method of the low-alkalinity, high-crystallization protective slag for pen tip steel is as follows: S1.1 Weigh the following raw materials in parts by weight: 50-60 parts by weight of premelted material, 8-10 parts by weight of aluminum-activated wollastonite, 12-15 parts by weight of modified fluorite, 5-8 parts by weight of cryolite, 4-6 parts by weight of carbon nanotube composite graphite, 2-4 parts by weight of sodium carboxymethyl cellulose and 2-3 parts by weight of magnesia. S1.

2. Stir the pre-melted material, modified fluorite, aluminum-activated wollastonite, cryolite and magnesia at 200-300 rpm for 30-40 min to obtain a dry mixture. S1.3 Add water to the dry mixture at a solid-liquid ratio of 1:2, stir at 300-400 rpm for 15-30 min, then add carbon nanotube composite graphite and sodium carboxymethyl cellulose, and continue stirring at 300-400 rpm for 1.5-2 h until the viscosity is less than 0.5 Pa·s to obtain a slurry. S1.

4. Spray dry the slurry to obtain a low-alkalinity, high-crystallization protective slag for pen tip steel.

10. The low-alkalinity, high-crystallization protective slag for pen tip steel according to claim 9, characterized in that, In step S1.4, the inlet air temperature of the spray dryer is 180-200℃, the outlet air temperature is 80-90℃, and the pressure is 0.2-0.4MPa.

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