A low-viscosity stable type of protecting slag suitable for high-speed continuous casting of Q355B steel

Abstract

The application discloses a low-viscosity stable type of protective slag suitable for high-speed continuous casting of Q355B steel, and belongs to the technical field of protective slag preparation, and is used for solving the technical problem that the melting performance and operation stability of the existing continuous casting protective slag need to be further improved in the use process; the application introduces lithium-boron-aluminum-silicon glass precursor powder, oxygen-nitrogen crystal control micro-nucleus powder and calcium-magnesium-phosphorus-boron viscoelastic powder into the continuous casting protective slag in cooperation, carries out systematic configuration on the preparation and batching process, builds a multi-level cooperative structure organization path covering the whole process of melting starting, liquid slag forming and slag film evolution, and the technical scheme makes the protective slag keep appropriate viscosity, lower melting temperature and shorter melting time, realizes the cooperative evolution of liquid phase generation and slag film formation, shows relatively stable interface behavior and structure response in actual continuous casting operation, and thus is favorable for reducing the occurrence tendency of defects such as pinhole bubbles, honeycomb bubbles and intermediate cracks on the surface of the Q355B steel continuous casting billet.

Description

Technical Field

[0001] This invention relates to the field of protective slag preparation technology, specifically to a low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel. Background Technology

[0002] Under high-speed continuous casting conditions for Q355B steel, the continuous casting protective slag, as a key functional auxiliary material in the crystallizer, directly affects the heat transfer, lubrication, and surface quality control of the molten steel-crystallizer interface. With the continuous increase in continuous casting speed, the heat flux density in the crystallizer increases and the molten slag renewal rate accelerates, placing higher demands on the protective slag to complete melting and form a stable molten slag layer in a short time. Existing low-viscosity protective slags suitable for this type of steel are mostly based on silicate or borosilicate systems. By adjusting the proportions of alkali metal oxides, alkaline earth metal oxides, and fluxing components, the matching of melting temperature, viscosity range, and slag film structure characteristics can be achieved. Under different production rhythms and operating conditions, the melting behavior, rheological characteristics, and operational stability of the protective slag exhibit different performances. Related technical research and applications mainly focus on the optimization of the composition system and the adaptation to the continuous casting process.

[0003] In practical applications, existing protective slag systems for high-speed continuous casting of Q355B steel often rely on a single glass phase or a few fluxing components to complete the melting and liquid slag formation process. The solid-to-liquid transition often occurs within a local temperature range, and there is a phased disconnect between the melting start-up and the establishment of liquid phase continuity. In the early stages of continuous casting or under fluctuating operating conditions, the formation rate and structural integrity of the liquid slag layer are easily affected, making it difficult to achieve stable coverage in a short period of time.

[0004] Furthermore, under the combined effects of crystallizer cooling and periodic vibration, existing protective slags often lack effective coordination in the solid phase crystallization position, slag film structure distribution, and liquid slag layer stability during slag film formation and liquid slag flow. The transition state between the slag film and liquid slag is discontinuous. Under continuous shearing and interface renewal conditions, the liquid slag layer is prone to local thinning or uneven flow, posing a certain challenge to the control of the interface state between the inner wall of the crystallizer and the surface of the billet.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a low-viscosity, stable protective slag suitable for high-speed continuous casting of Q355B steel, in order to solve the technical problem that the low viscosity and stability of protective slags used in high-speed continuous casting of steel need to be further improved in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions: A low-viscosity, stable protective slag suitable for high-speed continuous casting of Q355B steel comprises the following raw materials in parts by weight: 32 parts calcium oxide, 26 parts silicon dioxide, 8-10 parts lithium boron aluminum silicon glass precursor powder, 0.4-0.6 parts oxygen-nitrogen crystal-controlling micro-nucleation powder, 2-4 parts calcium magnesium phosphorus boron viscoelastic powder, and 24 parts auxiliary materials. Furthermore, the auxiliary material is obtained by mixing alumina, magnesium oxide, sodium oxide, lithium oxide and carbon black in a ratio of 6g:4g:5g:2g:7g.

[0008] The preparation method of the lithium boron aluminum silicon glass precursor powder is as follows: aluminum boron synergistic bridging sol is added to a reaction vessel, lithium acetate is added under stirring, and after mixing evenly, it is concentrated under reduced pressure to obtain a concentrate. The concentrate is then transferred to a drying oven at 110°C and vacuum dried for 8-12 hours. After heat treatment, the material is taken out and cooled to room temperature, then crushed through a 200-mesh sieve to obtain the lithium boron aluminum silicon glass precursor powder.

[0009] The reaction principle for preparing lithium boron aluminum silicon glass precursor powder is as follows: In the sol system, the silicon-oxygen-aluminum-oxygen-boron-oxygen network units formed by the aluminum-boron synergistic bridging sol are in a dynamic condensation and coordination equilibrium state. After the introduction of lithium salt, lithium ions enter the inorganic network structure through charge compensation and coordination regulation, interact with oxygen coordination groups, and thus change the local bonding environment. As the solvent is gradually removed, the hydroxyl condensation reaction in the system is further promoted, and the inorganic network transforms from a sol state to a highly cross-linked solid structure. Finally, after thermal excitation treatment, the residual organic groups and weak coordination structures are eliminated, and multiple oxygen coordination polyhedra rearrange to form an inorganic amorphous structure with silicon, aluminum, and boron as the main components and lithium participating in regulation. Its structural characteristics are manifested as a short-range ordered network state with multiple elements coexisting, thereby preparing lithium boron aluminum silicon glass precursor powder.

[0010] Furthermore, in the preparation of lithium boron aluminum silicon glass precursor powder, the ratio of the aluminum boron synergistic bridging sol to lithium acetate is 100-120 mL: 3-4 g, wherein the concentrate has a rotational viscosity of 6000-8000 mPa·s at 25°C and a solid content of 55-65 wt%, and the heat treatment operation is as follows: the material is transferred to a tube furnace at a temperature of 900-1050°C and held for 1-2 hours.

[0011] Furthermore, the aluminum-boron synergistic bridging sol solution is prepared by the following method: A1. Add tetraethyl orthosilicate and anhydrous ethanol to the reaction vessel and stir. After mixing evenly, add deionized water in ten equal batches with an interval of 5 minutes between additions. Then heat the reaction vessel to 30-35℃ and keep it warm and stir for 2-3 hours to obtain the silica bone sol precursor solution. A2. Add the silica sol precursor solution and the modification solution to the reaction vessel and stir. After mixing evenly, add deionized water and boric acid, and heat the reaction vessel to 35-45℃. Keep it warm and stir for 1-2 hours to obtain the aluminum-boron synergistic bridging sol solution.

[0012] The reaction principle for preparing aluminum-boron synergistic bridging sol is as follows: In an alcohol-water mixture, tetraethyl orthosilicate undergoes hydrolysis and condensation equilibrium in the presence of water, gradually forming an inorganic sol framework with silicon-oxygen tetrahedra as the basic structural units. During this process, ethoxy groups are replaced by hydroxyl groups, accompanied by rearrangement of silicon-oxygen bonds. After the introduction of an aluminum-containing modification solution, aluminum species participate in network construction in the sol system in a coordinated manner, forming connections with silicon-oxygen structures through aluminum-oxygen bonds, giving the inorganic framework a multi-center coordination characteristic. Subsequently, the added boric acid is converted into boron-oxygen structural units under thermal excitation conditions and is embedded in the silicon-oxygen-aluminum-oxygen network in a bridging manner, forming a composite inorganic sol system composed of silicon, aluminum, and boron. Its microstructure exhibits a continuous network state with multiple oxygen coordination environments coexisting, ultimately preparing an aluminum-boron synergistic bridging sol solution.

[0013] Furthermore, in step A1, the ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water is 25-30 mL: 100 mL: 35-45 mL. Furthermore, in step A2, the ratio of the silica bone sol precursor solution, the modifying solution, the deionized water and the boric acid is 100-120mL:30-40mL:10-15mL:3-4g, wherein the modifying solution is obtained by mixing aluminum isopropoxide and anhydrous ethanol in a ratio of 6-8g:30-40mL.

[0014] Furthermore, the preparation method of the oxygen-nitrogen controlled crystal micronucleus powder is as follows: silicon dioxide, aluminum oxide, calcium oxide and carbon black are added to a stirred tank and mixed evenly, then transferred to a tube furnace. Under the protection of nitrogen, the tube furnace is heated to 1100℃ and held for 1 hour. Then, the tube furnace is heated to 1350-1500℃ and held for 2-3 hours. The oxygen-nitrogen controlled crystal micronucleus powder is obtained after post-processing.

[0015] The reaction principle for preparing oxygen-nitrogen controlled crystal micronucleus powder is as follows: In a high-temperature nitrogen atmosphere, the oxide system composed of silicon dioxide, aluminum oxide, and calcium oxide undergoes solid-phase diffusion and structural rearrangement under thermal drive, forming an inorganic network framework with silicon-oxygen and aluminum-oxygen polyhedra as basic units. Carbon black participates in the local deoxygenation process of the oxide as a reducing medium under high temperature conditions, which changes the oxygen coordination environment. At the same time, nitrogen combines with the active sites in the system under thermal excitation conditions, partially replacing oxygen into the framework structure, thereby forming a mixed covalent network structure containing both oxygen and nitrogen coordination bonds, and thus preparing oxygen-nitrogen controlled crystal micronucleus powder.

[0016] Furthermore, in the process of preparing oxygen-nitrogen controlled crystal micronucleus powder, the ratio of silicon dioxide, aluminum oxide, calcium oxide and carbon black is 8-10g:6-8g:4-5g:1-2g, wherein the heating rate of the tube furnace is 2-3℃ / min, and the post-processing includes: after the reaction is completed, the material is cooled to room temperature and pulverized through a 200-mesh sieve to obtain oxygen-nitrogen controlled crystal micronucleus powder.

[0017] Furthermore, the calcium magnesium phosphorus boron viscoelastic powder is prepared by the following method: B1. Add deionized water and 85wt% phosphoric acid aqueous solution to the reactor and stir. After mixing evenly, add the composite powder in ten batches with a 5min interval between additions. Then raise the reactor temperature to 40-50℃ and keep it warm while stirring for 1-2 hours. Post-processing yields calcium magnesium phosphate precursor. B2. Add calcium magnesium phosphate precursor and boric acid to a stirring tank and stir until they are evenly mixed. Then, perform segmented heat treatment. After the heat treatment is completed, post-treatment is performed to obtain calcium magnesium phosphate boron viscoelastic powder.

[0018] The reaction principle for preparing calcium magnesium phosphorus boron viscoelastic powder is as follows: In an aqueous system, phosphoric acid undergoes ion dissociation and coordination recombination with calcium hydroxide and magnesium hydroxide to form phosphate structural units with calcium and magnesium as charge compensation centers. In this structure, phosphorus-oxygen tetrahedra form short-range ordered inorganic aggregates by sharing oxygen atoms. After dehydration, the remaining hydroxyl groups and phosphorus-oxygen bonds in the system further condense, making the phosphate network more stable. Subsequently, boric acid is introduced and heat-treated. Boron species participate in the rearrangement process of the original phosphorus-oxygen network under thermal excitation conditions. Some boron-oxygen structures are embedded in the phosphate framework in a bridging manner to form a multi-element inorganic network system containing calcium, magnesium, phosphorus and boron, thereby preparing calcium magnesium phosphorus boron viscoelastic powder.

[0019] Further, in step B1, the ratio of deionized water, 85wt% phosphoric acid aqueous solution and composite powder is 100mL:25-30mL:16-18g, wherein the composite powder is obtained by mixing calcium hydroxide and magnesium hydroxide in a ratio of 5-6g:2-3g. The post-processing includes: after stirring, reducing the pressure and distilling until no liquid is collected, transferring the obtained material to a drying oven at 60℃ and drying for 6 hours, pulverizing it through a 100-mesh sieve to obtain the calcium magnesium phosphate precursor; Further, in step B2, the ratio of the calcium magnesium phosphate precursor to boric acid is 18-20g:3-4g. The segmented heat treatment operation is as follows: the material is transferred to a tube furnace, the tube furnace is heated to 110°C at a heating rate of 5°C / min, and held for 8-10 hours. Then, the tube furnace is heated to 550-650°C at a heating rate of 2-3°C / min and held for 2-3 hours. The post-treatment includes: after the material cools to room temperature, it is crushed through a 200-mesh sieve to obtain calcium magnesium phosphate boron viscoelastic powder.

[0020] The present invention has the following beneficial effects: The continuous casting protective slag of this invention is composed of lithium boron aluminum silicon glass precursor powder, oxygen-nitrogen crystal-controlled micronucleus powder, and calcium magnesium phosphorus boron viscoelastic powder. The glass precursor system serves as the continuous phase basis, undergoing structural relaxation and forming a liquid phase framework during the heating process. The oxygen-nitrogen crystal-controlled micronucleus powder is dispersed in the system in the form of solid microstructures, participating in local structural stability in the early stage of liquid phase formation. The phosphorus-oxygen and boron-oxygen structures in the calcium magnesium phosphorus boron viscoelastic powder are gradually embedded into the glass network during the melting process. The three types of materials participate in structural rearrangement simultaneously in the melting initiation stage, so that the solid-to-liquid transition process does not depend on a single component, but is promoted under the synergistic effect of multiple structural units. During this process, liquid phase formation, solid phase retention, and viscoelastic structure intervention occur simultaneously, giving the liquid slag continuous and structurally constrained characteristics from the formation stage.

[0021] Under the cooling conditions of the crystallizer, the molten protective slag gradually transforms into a slag film structure. Among them, the lithium boron aluminum silicon glass network, as the main continuous phase, undergoes local densification and phase adjustment with the temperature gradient. Oxygen-nitrogen controlled crystal micronucleus powder provides a stable distribution of solid phase units at the slag film formation interface. Its surface structure participates in the spatial constraint of the initial stage of crystallization, allowing the solid phase structure to form preferentially in a predetermined position. Calcium magnesium phosphorus boron viscoelastic powder forms a transition structure between the glass phase and the crystalline phase. Its dispersed existence mode allows the interior of the slag film to maintain continuous connection in a solid-liquid coexistence state. The three types of materials respectively play the roles of continuous phase construction, nucleation guidance, and structural buffering in the formation and evolution of the slag film, so that the slag film gradually adjusts its internal structural distribution as it operates, maintaining the continuity of the overall evolution path under changing thermal conditions.

[0022] Under the conditions of billet descent and periodic vibration of the crystallizer, the protective slag system is in a dynamic environment of continuous shearing and interface renewal. The liquid phase formed by the lithium boron aluminum silicon glass precursor system plays the role of the main flow medium between the inner wall of the crystallizer and the surface of the billet. The oxygen-nitrogen controlled crystal micronucleus powder is fixed on the crystallizer side along with the slag film structure, forming a relatively stable boundary of the liquid slag layer. The calcium magnesium phosphorus boron viscoelastic powder exists in the liquid slag layer in a dispersed structure. Its viscoelastic properties buffer and regulate the flow of the liquid phase under shearing action. During dynamic operation, the three types of materials participate in liquid slag flow, interface constraint and deformation response at the same time, so that the liquid slag layer remains continuously distributed during operation and changes synergistically with the slag film structure, thereby affecting the evolution of the contact state between the inner wall of the crystallizer and the surface of the billet. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a SEM image of the lithium boron aluminum silicon glass precursor powder prepared in Example 3 of the present invention; Figure 2 This is a SEM image of the calcium magnesium phosphorus boron viscoelastic powder prepared in Example 6 of the present invention; Figure 3 This is a SEM image of the oxygen-nitrogen controlled crystal micronucleus powder prepared in Example 9 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The carbon black used in this application was purchased from Shanghai McLean Biochemical Technology Co., Ltd., with product number C914875.

[0027] Example 1 This embodiment provides a method for preparing lithium boron aluminum silicon glass precursor powder, including the following steps: Step I: Preparation of silica bone sol precursor solution Weigh out 25.0 mL of tetraethyl orthosilicate and 100.0 mL of anhydrous ethanol and add them to the reaction vessel. Stir until the mixture is homogeneous. Then add deionized water in ten equal batches at 5 min intervals. The total amount of water added is 35.0 mL. Then heat the reaction vessel to 30°C and keep it at that temperature for 2 h with stirring to obtain the silica bone sol precursor solution.

[0028] Step II: Preparation of aluminum-boron synergistic bridging sol solution Weigh out 6.0 g of aluminum isopropoxide and mix with 30.0 mL of anhydrous ethanol to obtain the modified solution; Weigh 100.0 mL of silica bone sol precursor solution and 30.0 mL of modification solution and add them to the reaction vessel. Stir until the mixture is homogeneous, then add 10.0 mL of deionized water and 3.0 g of boric acid. Heat the reaction vessel to 35 °C and keep it at that temperature for 1 h to obtain aluminum-boron synergistic bridging sol solution.

[0029] Step III: Preparation of lithium boron aluminum silicon glass precursor powder Weigh 100.0 mL of aluminum boron synergistic bridging sol and add it to the reactor. Add 3.0 g of lithium acetate under stirring. After mixing evenly, concentrate under reduced pressure until the rotational viscosity at 25 °C is 6000 mPa·s and the solid content is 55 wt%. The concentrate is then transferred to a drying oven at 110 °C and vacuum dried for 8 h. The material is then transferred to a tube furnace at 900 °C and kept at that temperature for 1 h. After the treatment is completed, the material is removed and cooled to room temperature. It is then pulverized through a 200-mesh sieve to obtain lithium boron aluminum silicon glass precursor powder.

[0030] Example 2 This embodiment provides a method for preparing lithium boron aluminum silicon glass precursor powder, including the following steps: Step I: Preparation of silica bone sol precursor solution Weigh out 30.0 mL of tetraethyl orthosilicate and 100.0 mL of anhydrous ethanol and add them to the reaction vessel. Stir until the mixture is homogeneous. Then add deionized water in ten equal batches at 5 min intervals. The total amount of water added is 45.0 mL. Then heat the reaction vessel to 35°C and keep it at that temperature for 3 h to obtain the silica bone sol precursor solution.

[0031] Step II: Preparation of aluminum-boron synergistic bridging sol solution Weigh out 8.0 g of aluminum isopropoxide and mix with 40.0 mL of anhydrous ethanol to obtain the modified solution; Weigh 120.0 mL of silica bone sol precursor solution and 40.0 mL of modification solution and add them to the reaction vessel. Stir until the mixture is homogeneous, then add 15.0 mL of deionized water and 4.0 g of boric acid. Heat the reaction vessel to 45 °C and keep it at that temperature for 2 h to obtain aluminum-boron synergistic bridging sol solution.

[0032] Step III: Preparation of lithium boron aluminum silicon glass precursor powder Weigh 120.0 mL of aluminum boron synergistic bridging sol and add it to the reaction vessel. Add 4.0 g of lithium acetate under stirring. After mixing evenly, concentrate under reduced pressure until the rotational viscosity at 25 °C is 8000 mPa·s and the solid content is 65 wt%, to obtain the concentrate. Transfer the concentrate to a drying oven at 110 °C and vacuum dry for 12 h. Then transfer the material to a tube furnace at 1050 °C and heat-treat for 2 h. After treatment, remove the material and let it cool to room temperature. Then crush it through a 200-mesh sieve to obtain lithium boron aluminum silicon glass precursor powder.

[0033] Example 3 This embodiment provides a method for preparing lithium boron aluminum silicon glass precursor powder, including the following steps: Step I: Preparation of silica bone sol precursor solution Weigh out 27.0 mL of tetraethyl orthosilicate and 100.0 mL of anhydrous ethanol and add them to the reaction vessel. Stir until the mixture is homogeneous. Then add deionized water in ten equal batches at 5 min intervals. The total amount of water added is 40.0 mL. Then heat the reaction vessel to 35°C and keep it at that temperature for 3 h to obtain the silica bone sol precursor solution.

[0034] Step II: Preparation of aluminum-boron synergistic bridging sol solution Weigh out 7.0 g of aluminum isopropoxide and mix with 35.0 mL of anhydrous ethanol to obtain the modified solution; Weigh 110.0 mL of silica bone sol precursor solution and 35.0 mL of modification solution and add them to the reaction vessel. Stir until the mixture is homogeneous, then add 12.0 mL of deionized water and 3.5 g of boric acid. Heat the reaction vessel to 40 °C and keep it at that temperature for 2 h to obtain aluminum-boron synergistic bridging sol solution.

[0035] Step III: Preparation of lithium boron aluminum silicon glass precursor powder Weigh out 110.0 mL of aluminum boron synergistic bridging sol and add it to the reactor. Add 3.5 g of lithium acetate under stirring. After mixing evenly, concentrate under reduced pressure until the rotational viscosity at 25 °C is 7000 mPa·s and the solid content is 60 wt%. The concentrate is then transferred to a drying oven at 110 °C and vacuum dried for 10 h. The material is then transferred to a tube furnace at 1000 °C and kept at that temperature for 2 h. After the treatment is completed, the material is removed and cooled to room temperature. It is then pulverized through a 200-mesh sieve to obtain lithium boron aluminum silicon glass precursor powder.

[0036] Example 4 This embodiment provides a method for preparing calcium magnesium phosphorus boron viscoelastic powder, including the following steps: Step (1): Preparation of calcium magnesium phosphate precursor Weigh out 10.0g of calcium hydroxide and 6.0g of magnesium hydroxide and mix them to obtain a composite powder; Weigh out 100.0 mL of deionized water and 25.0 mL of 85 wt% phosphoric acid aqueous solution and add them to the reaction vessel. Stir until the mixture is uniform. Then add the composite powder in ten batches with an interval of 5 min between additions. The total amount added is 16.0 g. Then raise the temperature of the reaction vessel to 40℃ and keep it at this temperature for 1 h. After stirring, reduce the pressure and distill until no liquid is collected. Transfer the obtained material to a drying oven at 60℃ and dry for 6 h. Crush it through a 100-mesh sieve to obtain the calcium magnesium phosphate precursor.

[0037] Step 2: Preparation of calcium magnesium phosphorus boron viscoelastic powder Weigh out 18.0g of calcium magnesium phosphate precursor and 3.0g of boric acid and add them to a stirring vessel. After mixing evenly, transfer the material to a tube furnace and heat the tube furnace to 110℃ at a heating rate of 5℃ / min. Hold the temperature for 8 hours, then heat the tube furnace to 550℃ at a heating rate of 2℃ / min and hold for 2 hours. After the heat treatment is completed, let the material cool to room temperature, pulverize it through a 200-mesh sieve to obtain calcium magnesium phosphate boron viscoelastic powder.

[0038] Example 5 This embodiment provides a method for preparing calcium magnesium phosphorus boron viscoelastic powder, including the following steps: Step (1): Preparation of calcium magnesium phosphate precursor Weigh out 12.0g of calcium hydroxide and 6.0g of magnesium hydroxide and mix them to obtain composite powder; Weigh out 100.0 mL of deionized water and 30.0 mL of 85 wt% phosphoric acid aqueous solution and add them to the reaction vessel. Stir until the mixture is uniform. Then add the composite powder in ten batches with an interval of 5 min between additions. The total amount added is 18.0 g. Then raise the temperature of the reaction vessel to 50℃ and keep it at that temperature for 2 h. After stirring, reduce the pressure and distill until no liquid is collected. Transfer the obtained material to a drying oven at 60℃ and dry for 6 h. Crush it through a 100-mesh sieve to obtain the calcium magnesium phosphate precursor.

[0039] Step 2: Preparation of calcium magnesium phosphorus boron viscoelastic powder Weigh out 20.0g of calcium magnesium phosphate precursor and 4.0g of boric acid and add them to a stirring vessel. After mixing evenly, transfer the material to a tube furnace and heat the tube furnace to 110℃ at a heating rate of 5℃ / min. Hold the temperature for 10h, then heat the tube furnace to 650℃ at a heating rate of 3℃ / min and hold for 3h. After the heat treatment is completed, let the material cool to room temperature, pulverize it through a 200-mesh sieve to obtain calcium magnesium phosphate boron viscoelastic powder.

[0040] Example 6 This embodiment provides a method for preparing calcium magnesium phosphorus boron viscoelastic powder, including the following steps: Step (1): Preparation of calcium magnesium phosphate precursor Weigh out 11.0g of calcium hydroxide and 6.0g of magnesium hydroxide and mix them to obtain composite powder; Weigh out 100.0 mL of deionized water and 27.0 mL of 85 wt% phosphoric acid aqueous solution and add them to the reaction vessel. Stir until the mixture is uniform. Then add the composite powder in ten batches with an interval of 5 min between additions. The total amount added is 17.0 g. Then raise the temperature of the reaction vessel to 45℃ and keep it at this temperature for 2 h. After stirring, reduce the pressure and distill until no liquid is collected. Transfer the obtained material to a drying oven at 60℃ and dry for 6 h. Crush it through a 100-mesh sieve to obtain the calcium magnesium phosphate precursor.

[0041] Step 2: Preparation of calcium magnesium phosphorus boron viscoelastic powder Weigh out 19.0g of calcium magnesium phosphate precursor and 3.5g of boric acid and add them to a stirring vessel. After mixing evenly, transfer the material to a tube furnace and heat the tube furnace to 110℃ at a heating rate of 5℃ / min. Hold the temperature for 9 hours, then heat the tube furnace to 600℃ at a heating rate of 3℃ / min and hold for 3 hours. After the heat treatment is completed, let the material cool to room temperature, pulverize it through a 200-mesh sieve, and obtain calcium magnesium phosphate boron viscoelastic powder.

[0042] Example 7 This embodiment provides a method for preparing a low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel, including the following steps: Step 1: Preparation of oxygen-nitrogen controlled crystal micronucleus powder Weigh out 8.0g of silicon dioxide, 6.0g of aluminum oxide, 4.0g of calcium oxide and 1.0g of carbon black and add them to a stirred tank. Mix them evenly and then transfer them to a tube furnace. Under nitrogen protection, heat the tube furnace to 1100℃ at a heating rate of 2℃ / min and hold for 1 hour. Then heat the tube furnace to 1350℃ and hold for 2 hours. After the reaction is complete, let the material cool to room temperature and crush it through a 200-mesh sieve to obtain oxygen-nitrogen controlled crystal micro-nucleus powder.

[0043] Step 2: Preparation of continuous casting protective slag Weigh out 6.0g of aluminum oxide, 4.0g of magnesium oxide, 5.0g of sodium oxide, 2.0g of lithium oxide and 7.0g of carbon black and mix them to obtain the auxiliary material; By weight, 32 parts of calcium oxide, 26 parts of silicon dioxide, 8 parts of lithium boron aluminum silicon glass precursor powder prepared in Example 1, 0.4 parts of oxygen nitrogen crystallization micro-nucleus powder, 2 parts of calcium magnesium phosphorus boron viscoelastic powder prepared in Example 4, and 24 parts of auxiliary materials were weighed and added to a stirring tank and mixed evenly to obtain continuous casting protective slag.

[0044] Example 8 This embodiment provides a method for preparing a low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel, including the following steps: Step 1: Preparation of oxygen-nitrogen controlled crystal micronucleus powder Weigh out 10.0g of silicon dioxide, 8.0g of aluminum oxide, 5.0g of calcium oxide and 2.0g of carbon black and add them to a stirred tank. Mix them evenly and then transfer them to a tube furnace. Under nitrogen protection, heat the tube furnace to 1100℃ at a heating rate of 3℃ / min and hold for 1 hour. Then heat the tube furnace to 1500℃ and hold for 3 hours. After the reaction is complete, let the material cool to room temperature and crush it through a 200-mesh sieve to obtain oxygen-nitrogen controlled crystal micro-nucleus powder.

[0045] Step 2: Preparation of continuous casting protective slag Weigh out 6.0g of aluminum oxide, 4.0g of magnesium oxide, 5.0g of sodium oxide, 2.0g of lithium oxide and 7.0g of carbon black and mix them to obtain the auxiliary material; By weight, 32 parts of calcium oxide, 26 parts of silicon dioxide, 10 parts of lithium boron aluminum silicon glass precursor powder prepared in Example 2, 0.6 parts of oxygen nitrogen crystal-controlled micro-nucleus powder, 4 parts of calcium magnesium phosphorus boron viscoelastic powder prepared in Example 5, and 24 parts of auxiliary materials were weighed and added to a stirring tank and mixed evenly to obtain continuous casting protective slag.

[0046] Example 9 This embodiment provides a method for preparing a low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel, including the following steps: Step 1: Preparation of oxygen-nitrogen controlled crystal micronucleus powder Weigh out 9.0g of silicon dioxide, 7.0g of aluminum oxide, 4.5g of calcium oxide and 1.5g of carbon black and add them to a stirred tank. Mix them evenly and then transfer them to a tube furnace. Under nitrogen protection, heat the tube furnace to 1100℃ at a heating rate of 3℃ / min and hold for 1 hour. Then heat the tube furnace to 1450℃ and hold for 3 hours. After the reaction is complete, let the material cool to room temperature and crush it through a 200-mesh sieve to obtain oxygen-nitrogen controlled crystal micro-nucleus powder.

[0047] Step 2: Preparation of continuous casting protective slag Weigh out 6.0g of aluminum oxide, 4.0g of magnesium oxide, 5.0g of sodium oxide, 2.0g of lithium oxide and 7.0g of carbon black and mix them to obtain the auxiliary material; By weight, 32 parts of calcium oxide, 26 parts of silicon dioxide, 9 parts of lithium boron aluminum silicon glass precursor powder prepared in Example 3, 0.5 parts of oxygen nitrogen crystallization micro-nucleus powder, 3 parts of calcium magnesium phosphorus boron viscoelastic powder prepared in Example 6, and 24 parts of auxiliary materials were weighed and added to a stirring tank and mixed evenly to obtain continuous casting protective slag.

[0048] Comparative Example 1 The difference between this comparative example and Example 9 is that the lithium boron aluminum silicon glass precursor powder used in step two is replaced with lithium acetate in preparation step III.

[0049] Comparative Example 2 The difference between this comparative example and Example 9 is that the calcium magnesium phosphorus boron viscoelastic powder is omitted in step two.

[0050] Comparative Example 3 The difference between this comparative example and Example 9 is that the lithium boron aluminum silicon glass precursor powder, oxygen nitrogen crystal-controlled micronucleus powder, and calcium magnesium phosphorus boron viscoelastic powder are omitted in step two.

[0051] Performance testing: Refined and qualified Q355B molten steel is poured into the tundish from the ladle. The superheat of the molten steel in the tundish is controlled at 15°C, and the temperature fluctuation is no more than 5°C. The molten steel is then steadily poured into the crystallizer through a submerged entry nozzle. The liquid level in the crystallizer is controlled within 3mm above and below the target liquid level. During continuous casting, the crystallizer vibration frequency is set to 150 times / min, the amplitude is 8mm, and the billet pulling speed is controlled at 1.6m / min. During the crystallizer pouring process, the continuous casting protective slag prepared in Examples 7-9 and Comparative Examples 1-3 is continuously added to the surface of the molten steel. The slag layer with a thickness of 30mm is controlled to form a stable slag layer on the surface of the molten steel, so that the protective slag forms a continuous slag film between the copper plate of the crystallizer and the primary billet shell. After the billet exits the crystallizer, it enters the secondary cooling zone and adopts a weak and uniform cooling regime. The secondary cooling water volume is controlled at 0.45L / kg. The billet is continuously pulled out through the straightening section and cut into billets to obtain Q355B steel continuous casting billets. The viscosity of the continuous casting protective slags prepared in Examples 7-9 and Comparative Examples 1-3 was tested in accordance with the standard YB / T 185-2017 "Test Method for Viscosity of Continuous Casting Protective Slag". The melting temperatures of the continuous casting protective slags prepared in Examples 7-9 and Comparative Examples 1-3 were tested in accordance with the standard YB / T 186-2014 "Test Method for Melting Temperature of Continuous Casting Protective Slag". The melting time of the continuous casting protective slags prepared in Examples 7-9 and Comparative Examples 1-3 was tested in accordance with the standard YB / T 6283-2024 "Test Method for Determination of Melting Time of Continuous Casting Protective Slag". The pinhole bubble diameter grade, honeycomb bubble width grade, and intermediate crack length grade of the surface of Q355B steel continuous casting billet prepared using the continuous casting protective slag prepared in Examples 7-9 and Comparative Examples 1-3 were tested with reference to the standard YB / T 4003-2016 "Low-magnification structural defect rating chart of continuous casting steel slab". See Table 1 for specific data; Table 1 - Performance Test Data for Each Sample Viscosity / Pa·s 0.36 0.35 0.35 0.41 0.47 0.56 Melting temperature / °C 1045 1044 1042 1063 1079 1111 Melting time / s 68s 67s 65s 76 88 108 Pinhole bubble diameter grade 0.5 0.5 0.5 1.0 1.5 2.5 Honeycomb bubble width levels 0.5 0.5 0.5 1.0 1.5 2.5 Intermediate crack length grade 0.5 0.5 0.5 1.0 1.5 2.5 Data Analysis: Comparative analysis of the data in Table 1 reveals that the continuous casting protective slag prepared in this invention has a viscosity of 0.35 Pa·s, a melting temperature of 1042℃, and a melting time of 65 s. Furthermore, the Q355B steel continuous casting billet prepared using this slag exhibits pinhole bubble diameter grade of 0.5, honeycomb bubble width grade of 0.5, and intermediate crack length grade of 0.5. All these data are superior to the comparative example. This indicates that… In Comparative Example 1, the removal of lithium acetate in step III caused the precursor powder's structural construction process to change from a network rearrangement involving multiple ions to a single framework evolution path dominated by silicon, aluminum, and boron structures. This resulted in the precursor phase losing its early embedding basis for subsequent structural synergy during the formation stage. This structural change caused the interaction between the glass precursor phase and other functional components during the melting start-up process to change from embedded synergy to subsequent contact superposition, which in turn affected the synchronous relationship between liquid phase generation, solid phase constraint, and structural buffering. Due to the shift in the overall evolution path of the system, the structural continuity and interfacial synergy of the slag film and liquid slag layer during operation were reduced, making it difficult for multiple mechanisms to work together within the same operating window, ultimately resulting in a decrease in composite performance. In Comparative Example 2, the introduction of viscoelastic structural units was eliminated during the batching and mixing stage. This caused the system to lose the structural transition mechanism connecting the continuous phase and the solid phase units during operation. The overall structural coupling changed from ternary synergy to binary coexistence. This change made the phase adjustment process more dependent on instantaneous thermal conditions when the molten state transformed into the slag film structure. The lack of internal structure buffering and guiding effect on the evolution path led to a reduction in the continuity between the glass phase and the crystalline phase. Furthermore, under dynamic shear and interface renewal conditions, the structural response changed from synergistic adjustment to independent evolution. The interface adaptability weakened with the operation process, making it difficult for the system to maintain a stable operating state, thus causing an overall decline in composite performance. In Comparative Example 3, multiple synergistic structural units were simultaneously eliminated during the batching and mixing stage, causing the system to lose the pre-constructed multi-level structural organization path. The operation mainly relied on the spontaneous phase change behavior of conventional oxide components under the action of the thermal field. Due to the lack of synergistic mechanisms such as precursor network construction, interface positioning and transition connection, it was difficult to form a stable correspondence between liquid phase generation and solid phase retention during the melting start-up stage. The initial position and evolution direction of the structure during slag film formation showed a large degree of dispersion. Under the dynamic conditions of crystallizer vibration and billet downward movement, the response of each structural unit to the thermal field and shear was inconsistent, causing the overall evolution of the system to change from synergistic regulation to non-synergistic operation, thereby causing a significant decrease in composite performance. Ultimately, it is demonstrated that the changes in system performance are closely related to the integrity of the synergistic structure formed during the preparation and operation of the material. In Comparative Example 1, by changing the formation path of the precursor phase, the structural embedding mode of the material during the melting initiation stage changes, and its interaction with other components changes from synchronous evolution to staged superposition, resulting in a more dispersed structural evolution. In Comparative Example 2, the lack of transitional connection between the continuous phase and the solid phase during operation leads to phase transformation and interface renewal relying more on external thermal field conditions, weakening the internal structural adjustment capability. In Comparative Example 3, the multi-level structural organization path is further weakened, causing the material's operating behavior to mainly exhibit the spontaneous evolution characteristics of a conventional oxide system. Under the above configuration, the synergistic consistency in liquid phase generation, slag film formation, and dynamic response gradually decreases, and the structural evolution path changes from controlled to discrete, showing an overall tendency of declining composite behavior.

[0052] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0053] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0054] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A low-viscosity, stable protective slag suitable for high-speed continuous casting of Q355B steel, characterized in that, The raw materials consist of the following parts by weight: 32 parts calcium oxide, 26 parts silicon dioxide, 8-10 parts lithium boron aluminum silicon glass precursor powder, 0.4-0.6 parts oxygen nitrogen crystal-controlled micro-nucleus powder, 2-4 parts calcium magnesium phosphorus boron viscoelastic powder and 24 parts auxiliary materials. The preparation method of the lithium boron aluminum silicon glass precursor powder is as follows: aluminum boron synergistic bridging sol is added to the reaction vessel, lithium acetate is added under stirring, and after mixing evenly, it is concentrated under reduced pressure to obtain a concentrate. The concentrate is then transferred to a drying oven at 110°C and vacuum dried for 8-12 hours. After heat treatment, the material is taken out and cooled to room temperature, then crushed through a 200-mesh sieve to obtain lithium boron aluminum silicon glass precursor powder. The aluminum-boron synergistic bridging sol solution was prepared by the following method: A1. Add tetraethyl orthosilicate and anhydrous ethanol to the reaction vessel and stir. After mixing evenly, add deionized water in ten equal batches with an interval of 5 minutes between additions. Then heat the reaction vessel to 30-35℃ and keep it warm and stir for 2-3 hours to obtain the silica bone sol precursor solution. A2. Add the silica bone sol precursor solution and the modification solution to the reaction vessel and stir. After mixing evenly, add deionized water and boric acid, and heat the reaction vessel to 35-45℃. Keep it warm and stir for 1-2 hours to obtain aluminum-boron synergistic bridging sol solution. The modification solution is obtained by mixing aluminum isopropoxide and anhydrous ethanol at a ratio of 6-8g:30-40mL. The preparation method of the oxygen-nitrogen controlled crystal micronucleus powder is as follows: silicon dioxide, aluminum oxide, calcium oxide and carbon black are added to a stirred tank and mixed evenly, then transferred to a tube furnace. Under the protection of nitrogen, the tube furnace is heated to 1100℃ and held for 1 hour. Then the tube furnace is heated to 1350-1500℃ and held for 2-3 hours. The oxygen-nitrogen controlled crystal micronucleus powder is obtained after post-processing. The calcium magnesium phosphorus boron viscoelastic powder is prepared by the following method: B1. Add deionized water and 85wt% phosphoric acid aqueous solution to the reactor and stir. After mixing evenly, add the composite powder in ten batches with a 5min interval between additions. Then raise the reactor temperature to 40-50℃ and keep it warm while stirring for 1-2 hours. Post-processing yields calcium magnesium phosphate precursor. B2. Add calcium magnesium phosphate precursor and boric acid to a stirring tank and stir until they are evenly mixed. Then, perform segmented heat treatment. After the heat treatment is completed, post-treatment is performed to obtain calcium magnesium phosphate boron viscoelastic powder.

2. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, The auxiliary material is obtained by mixing alumina, magnesium oxide, sodium oxide, lithium oxide and carbon black in a ratio of 6g:4g:5g:2g:7g.

3. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, In the preparation of lithium boron aluminum silicon glass precursor powder, the ratio of aluminum boron synergistic bridging sol to lithium acetate is 100-120 mL: 3-4 g. The concentrate has a rotational viscosity of 6000-8000 mPa·s at 25°C and a solid content of 55-65 wt%. The heat treatment operation is as follows: the material is transferred to a tube furnace at a temperature of 900-1050°C and held for 1-2 hours.

4. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, In step A1, the ratio of tetraethyl orthosilicate, anhydrous ethanol, and deionized water is 25-30 mL: 100 mL: 35-45 mL; in step A2, the ratio of silica bone sol precursor solution, modifying solution, deionized water, and boric acid is 100-120 mL: 30-40 mL: 10-15 mL: 3-4 g.

5. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, In the process of preparing oxygen-nitrogen controlled crystal micronucleus powder, the ratio of silicon dioxide, aluminum oxide, calcium oxide and carbon black is 8-10g:6-8g:4-5g:1-2g, and the heating rate of the tube furnace is 2-3℃ / min.

6. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, In step B1, the ratio of deionized water, 85wt% phosphoric acid aqueous solution and composite powder is 100mL:25-30mL:16-18g, wherein the composite powder is obtained by mixing calcium hydroxide and magnesium hydroxide in a ratio of 5-6g:2-3g.

7. The low-viscosity stable protective slag suitable for high-speed continuous casting of Q355B steel according to claim 1, characterized in that, In step B2, the ratio of calcium magnesium phosphate precursor to boric acid is 18-20g:3-4g. The segmented heat treatment operation is as follows: the material is transferred to a tube furnace, the tube furnace is heated to 110°C at a heating rate of 5°C / min, and held for 8-10 hours. Then, the tube furnace is heated to 550-650°C at a heating rate of 2-3°C / min and held for 2-3 hours.

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