Low consumption continuous casting protective mold based on porous magnesium oxide and its preparation method

Abstract

The present application relates to the technical field of protecting slag, in particular to a low-consumption continuous casting protecting slag based on porous magnesium oxide and a preparation method thereof, which comprises the following components: the protecting slag comprises base glass slag powder, porous magnesium oxide, polyvinyl butyral ester solution and magnesium stearate; wherein the porous magnesium oxide is prepared from magnesium oxide powder, polystyrene microspheres, nano calcium carbonate and zirconia fiber; taking the magnesium oxide powder as a matrix, by introducing the polystyrene microspheres, forming through macro-pores after high-temperature decomposition, providing a molten slag penetration channel, the nano calcium carbonate decomposes to generate nano calcium oxide and micropores, increasing the specific surface area and exposing active sites, the multi-level pore synergistic effect significantly improves the adsorption efficiency, the zirconia fiber as a reinforcing phase, through the fiber bridging and grain boundary pinning effect to inhibit crack propagation, improve the skeleton strength, stabilize the pore structure at high temperature, reduce sintering collapse, retain the pore, thereby effectively improving the adsorption capacity of unit mass of the protecting slag, achieving the purpose of low consumption.

Description

Technical Field

[0001] This invention relates to the field of protective slag technology, and more specifically, to a low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method. Background Technology

[0002] In the continuous casting process of steel, protective slag is a key material for ensuring smooth production and billet quality. It is made from a precise ratio of various oxides, carbonaceous materials, and other additives using a special process, possessing multiple unique functions. Protective slag provides thermal insulation, reducing heat radiation and convection as it covers the surface of molten steel, maintaining a suitable temperature, ensuring good fluidity, and preventing defects such as cold shuts and cracks caused by rapid temperature drops. It also reduces the probability of secondary oxidation in the molten steel, improving the purity of the steel. Simultaneously, it has excellent lubricating properties; the carbonaceous materials selectively ablate at high temperatures to form a liquid slag film, reducing friction between the billet and the inner wall of the crystallizer, preventing surface scratches and cracks, and improving production efficiency and billet quality. Furthermore, protective slag can absorb and dissolve non-metallic inclusions in the molten steel, purifying it. With the development of the steel industry and the increasing demands for steel quality and production efficiency, the research and application of protective slag face new challenges and opportunities.

[0003] However, existing protective slags have limited absorption capacity for inclusions, making it difficult to effectively adsorb and dissolve them. As a result, unabsorbed inclusions accumulate at the molten steel-slag interface or in the crystallizer. These inclusions disrupt the uniformity of the protective slag layer, weakening its core functions such as lubrication and heat insulation. To maintain process requirements, it is usually necessary to increase the amount of protective slag added to compensate for performance loss, which in turn significantly increases the consumption of protective slag. In view of this, we propose a low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a low-consumption continuous casting protective slag based on porous magnesium oxide, the protective slag comprising basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution and magnesium stearate.

[0006] Porous magnesium oxide is made from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers.

[0007] Preferably, the porous magnesium oxide is prepared by the following method:

[0008] Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres, and zirconium oxide fibers are added to a ball mill jar, followed by a 3-5 wt% polyvinyl alcohol solution. The mill is operated at 300-500 rpm with a ball-to-material ratio of 5:1 for 3-4 hours to obtain a slurry. The slurry is then injected into a mold and pressed into a green body at 20-25 MPa. The green body is vacuum dried at 80℃ for 10-12 hours, then heated to 440-450℃ at 3-5℃ / min and held for 1-1.5 hours. The temperature is then further increased to 900-950℃ at 1-3℃ / min and held for 2-3 hours. After natural cooling to room temperature, the green body is transferred to a high-temperature atmosphere furnace and heated to 1450-1500℃ at 5℃ / min and held for 3-4 hours. After cooling to 200℃ in the furnace, the green body is removed, crushed into granules, and used to obtain porous magnesium oxide.

[0009] Polystyrene microspheres and nano-calcium carbonate are used to gradually decompose and form pores in magnesium oxide particles at high temperatures. Simultaneously, the mixture is held at 1450-1500℃ for 3-4 hours to ensure complete decomposition of the polystyrene microspheres, preventing residue formation after sintering. The large pores provide the main channels for slag liquid permeation, slowing down heat transfer, while the micropores increase active sites and capillary adsorption. Zirconia fibers are also incorporated, inhibiting abnormal growth of magnesium oxide grains through fiber bridging and grain boundary pinning, forming a three-dimensional framework to prevent pore collapse and closure, and improving structural strength. The resulting porous magnesium oxide, due to its micron-sized pores, can mechanically trap inclusions such as alumina in the molten steel. The porous structure increases the contact area between magnesium oxide and inclusions, improving the reaction rate and enhancing chemical adsorption, thereby effectively reducing the consumption of protective slag.

[0010] Preferably, the composition comprises 65-70 parts by weight of magnesium oxide powder, 13-17 parts by weight of nano-calcium carbonate, 8-10 parts by weight of polystyrene microspheres, 3-5 parts by weight of zirconium oxide fiber, and 1-2 parts by weight of polyvinyl alcohol solution.

[0011] Preferably, the polystyrene microspheres have a diameter of 30-40 μm, and the magnesium oxide powder has a particle size of 2-5 μm.

[0012] To prevent porous magnesium oxide from having its pores blocked and its interior filled by base glass slag powder, which would affect the porous effect of the porous magnesium oxide and hinder the interaction between the base glass slag powder and molten steel.

[0013] Preferably, the solid content of the slurry is controlled at 65%-70%.

[0014] Preferably, the porous magnesium oxide has a particle size distribution of 180-200 μm.

[0015] On the other hand, the present invention provides a method for preparing a low-consumption continuous casting protective slag based on porous magnesium oxide, for use in any one of the above-mentioned low-consumption continuous casting protective slags based on porous magnesium oxide, comprising the following steps:

[0016] Calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500-1550℃ for 25-30 minutes, then water-quenched to form glass slag, which is then crushed to obtain basic glass slag powder.

[0017] The basic glass slag powder, porous magnesium oxide, and magnesium stearate are mixed for 20-25 minutes, granulated by high-speed shearing at 700-800 rpm, and sprayed with a 1-2 wt% polyvinyl butyral solution to form wet granules. These granules are then filled into a mold, pressed, demolded, and allowed to stand for 24-48 hours. The temperature is then increased to 1000℃ at 5℃ / min and held for 1 hour to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

[0018] The low-residue binder polyvinyl butyral is completely decomposed after heat treatment at 1000℃ for 1 hour, effectively avoiding the impact of residual substances on the performance of the protective slag.

[0019] Preferably, the composition comprises 42-46 parts by weight of calcium oxide, 30-34 parts by weight of silicon dioxide, 7-9 parts by weight of aluminum oxide, 5-7 parts by weight of sodium carbonate, 1-2 parts by weight of boron oxide, 2-3 parts by weight of calcium fluoride, 1.5-2.5 parts by weight of graphite, and 0.4-0.6 parts by weight of cerium oxide.

[0020] Preferably, the particle size of the basic glass slag powder is 120-150 μm.

[0021] Preferably, the composition includes 81-83 parts by weight of basic glass slag powder, 12-14 parts by weight of porous magnesium oxide, 3.5-3.7 parts by weight of polyvinyl butyral solution, and 0.3-0.5 parts by weight of magnesium stearate.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] In this low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, the porous magnesium oxide uses magnesium oxide powder as the matrix. Pore formation and reinforcement are achieved by adding polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers. After sintering, a three-dimensional interconnected pore structure is formed. Its porous network can adsorb non-metallic inclusions in molten steel and purify the molten steel through a dual mechanism of mechanical retention and chemical reaction, significantly improving the cleanliness of the cast billet. The efficient inclusion adsorption capacity extends the service life of the protective slag, allowing a unit mass of protective slag to process more molten steel, reducing the consumption of protective slag and minimizing the need to replenish it due to performance fluctuations, thus achieving a low-consumption effect. Detailed Implementation

[0024] 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.

[0025] The present invention relates to a low-consumption continuous casting protective slag based on porous magnesium oxide. The protective slag comprises basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; wherein the porous magnesium oxide is prepared from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers.

[0026] Example 1: Low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, comprising the following steps:

[0027] The protective slag includes basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; wherein, the porous magnesium oxide is made from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers;

[0028] 65 parts by weight of magnesium oxide powder, 13 parts by weight of nano-calcium carbonate, 8 parts by weight of polystyrene microspheres, 3 parts by weight of zirconium oxide fiber, and 2 parts by weight of polyvinyl alcohol solution.

[0029] The mixture comprises 42 parts by weight of calcium oxide, 30 parts by weight of silicon dioxide, 7 parts by weight of aluminum oxide, 5 parts by weight of sodium carbonate, 1 part by weight of boron oxide, 2 parts by weight of calcium fluoride, 1.5 parts by weight of graphite, and 0.4 parts by weight of cerium oxide; 81 parts by weight of basic glass slag powder, 14 parts by weight of porous magnesium oxide, 3.5 parts by weight of polyvinyl butyral solution, and 0.5 parts by weight of magnesium stearate, wherein the particle size of the magnesium oxide powder is 5 μm;

[0030] Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres with a diameter of 40 μm, and zirconium oxide fibers were added to a ball mill jar, followed by the addition of a 5 wt% polyvinyl alcohol solution. The milling process was carried out at 300 rpm with a ball-to-material ratio of 5:1 for 3 hours to obtain a slurry. The solid content of the slurry was controlled at 70%. The slurry was injected into a mold and pressed into a green body at 25 MPa. The green body was vacuum dried at 80℃ for 12 hours, then heated to 450℃ at 5℃ / min and held for 1.5 hours. The temperature was then increased to 950℃ at 3℃ / min and held for 3 hours. The green body was then allowed to cool naturally to room temperature and transferred to a high-temperature atmosphere furnace. The temperature was increased to 1500℃ at 5℃ / min and held for 4 hours. After cooling to 200℃ in the furnace, the green body was removed, crushed into particles, and prepared for use, yielding porous magnesium oxide with a particle size distribution of 200 μm.

[0031] Calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500℃ for 30 minutes. The mixture is then water-quenched to form glass slag, which is then crushed to obtain basic glass slag powder with a particle size of 150μm.

[0032] Basic glass slag powder, porous magnesium oxide, and magnesium stearate were mixed for 25 min, granulated by high-speed shearing at 800 rpm, and sprayed with a 2 wt% polyvinyl butyral solution to form wet granules. The granules were then filled into a mold, pressed, demolded, and allowed to stand for 24 h. The temperature was then increased to 1000℃ at 5℃ / min and held for 1 h to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

[0033] Example 2: Low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, comprising the following steps:

[0034] The protective slag includes basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; wherein, the porous magnesium oxide is made from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers;

[0035] 65 parts by weight of magnesium oxide powder, 15 parts by weight of nano-calcium carbonate, 9 parts by weight of polystyrene microspheres, 4 parts by weight of zirconium oxide fiber, and 2 parts by weight of polyvinyl alcohol solution.

[0036] The mixture comprises 42 parts by weight of calcium oxide, 30 parts by weight of silicon dioxide, 7 parts by weight of aluminum oxide, 5 parts by weight of sodium carbonate, 1 part by weight of boron oxide, 2 parts by weight of calcium fluoride, 1.5 parts by weight of graphite, and 0.4 parts by weight of cerium oxide; 81 parts by weight of basic glass slag powder, 14 parts by weight of porous magnesium oxide, 3.5 parts by weight of polyvinyl butyral solution, and 0.5 parts by weight of magnesium stearate, wherein the particle size of the magnesium oxide powder is 5 μm;

[0037] Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres with a diameter of 40 μm, and zirconium oxide fibers were added to a ball mill jar, followed by the addition of a 5 wt% polyvinyl alcohol solution. The milling process was carried out at 300 rpm with a ball-to-material ratio of 5:1 for 3 hours to obtain a slurry. The solid content of the slurry was controlled at 70%. The slurry was injected into a mold and pressed into a green body at 25 MPa. The green body was vacuum dried at 80℃ for 12 hours, then heated to 450℃ at 5℃ / min and held for 1.5 hours. The temperature was then increased to 950℃ at 3℃ / min and held for 3 hours. The green body was then allowed to cool naturally to room temperature and transferred to a high-temperature atmosphere furnace. The temperature was increased to 1500℃ at 5℃ / min and held for 4 hours. After cooling to 200℃ in the furnace, the green body was removed, crushed into particles, and prepared for use, yielding porous magnesium oxide with a particle size distribution of 200 μm.

[0038] Calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500℃ for 30 minutes. The mixture is then water-quenched to form glass slag, which is then crushed to obtain basic glass slag powder with a particle size of 150μm.

[0039] Basic glass slag powder, porous magnesium oxide, and magnesium stearate were mixed for 25 min, granulated by high-speed shearing at 800 rpm, and sprayed with a 2 wt% polyvinyl butyral solution to form wet granules. The granules were then filled into a mold, pressed, demolded, and allowed to stand for 24 h. The temperature was then increased to 1000℃ at 5℃ / min and held for 1 h to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

[0040] Example 3: Low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, comprising the following steps:

[0041] The protective slag includes basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; wherein, the porous magnesium oxide is made from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers;

[0042] 65 parts by weight of magnesium oxide powder, 17 parts by weight of nano-calcium carbonate, 10 parts by weight of polystyrene microspheres, 5 parts by weight of zirconium oxide fiber, and 2 parts by weight of polyvinyl alcohol solution.

[0043] The mixture comprises 42 parts by weight of calcium oxide, 30 parts by weight of silicon dioxide, 7 parts by weight of aluminum oxide, 5 parts by weight of sodium carbonate, 1 part by weight of boron oxide, 2 parts by weight of calcium fluoride, 1.5 parts by weight of graphite, and 0.4 parts by weight of cerium oxide; 81 parts by weight of basic glass slag powder, 14 parts by weight of porous magnesium oxide, 3.5 parts by weight of polyvinyl butyral solution, and 0.5 parts by weight of magnesium stearate, wherein the particle size of the magnesium oxide powder is 5 μm;

[0044] Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres with a diameter of 40 μm, and zirconium oxide fibers were added to a ball mill jar, followed by the addition of a 5 wt% polyvinyl alcohol solution. The milling process was carried out at 300 rpm with a ball-to-material ratio of 5:1 for 3 hours to obtain a slurry. The solid content of the slurry was controlled at 70%. The slurry was injected into a mold and pressed into a green body at 25 MPa. The green body was vacuum dried at 80℃ for 12 hours, then heated to 450℃ at 5℃ / min and held for 1.5 hours. The temperature was then increased to 950℃ at 3℃ / min and held for 3 hours. The green body was then allowed to cool naturally to room temperature and transferred to a high-temperature atmosphere furnace. The temperature was increased to 1500℃ at 5℃ / min and held for 4 hours. After cooling to 200℃ in the furnace, the green body was removed, crushed into particles, and prepared for use, yielding porous magnesium oxide with a particle size distribution of 200 μm.

[0045] Calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500℃ for 30 minutes. The mixture is then water-quenched to form glass slag, which is then crushed to obtain basic glass slag powder with a particle size of 150μm.

[0046] Basic glass slag powder, porous magnesium oxide, and magnesium stearate were mixed for 25 min, granulated by high-speed shearing at 800 rpm, and sprayed with a 2 wt% polyvinyl butyral solution to form wet granules. The granules were then filled into a mold, pressed, demolded, and allowed to stand for 24 h. The temperature was then increased to 1000℃ at 5℃ / min and held for 1 h to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

[0047] Example 4: Low-consumption continuous casting protective slag based on porous magnesium oxide and its preparation method, including the following steps:

[0048] The protective slag includes basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; wherein, the porous magnesium oxide is made from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers;

[0049] 65 parts by weight of magnesium oxide powder, 17 parts by weight of nano-calcium carbonate, 10 parts by weight of polystyrene microspheres, 5 parts by weight of zirconium oxide fiber, and 2 parts by weight of polyvinyl alcohol solution.

[0050] The mixture comprises 42 parts by weight of calcium oxide, 30 parts by weight of silicon dioxide, 7 parts by weight of aluminum oxide, 5 parts by weight of sodium carbonate, 1 part by weight of boron oxide, 2 parts by weight of calcium fluoride, 1.5 parts by weight of graphite, and 0.4 parts by weight of cerium oxide; 81 parts by weight of basic glass slag powder, 14 parts by weight of porous magnesium oxide, 3.5 parts by weight of polyvinyl butyral solution, and 0.5 parts by weight of magnesium stearate, wherein the particle size of the magnesium oxide powder is 5 μm;

[0051] Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres with a diameter of 40 μm, and zirconium oxide fibers were added to a ball mill jar, followed by the addition of a 5 wt% polyvinyl alcohol solution. The milling process was carried out at 300 rpm with a ball-to-material ratio of 5:1 for 3 hours to obtain a slurry. The solid content of the slurry was controlled at 70%. The slurry was injected into a mold and pressed into a green body at 25 MPa. The green body was vacuum dried at 80 °C for 12 hours, then heated to 450 °C at 10 °C / min and held for 1.5 hours. The temperature was then increased to 950 °C at 10 °C / min and held for 3 hours. After natural cooling to room temperature, the green body was transferred to a high-temperature atmosphere furnace and heated to 1500 °C at 10 °C / min and held for 4 hours. After cooling to 200 °C in the furnace, the green body was removed, crushed into particles, and prepared for use to obtain porous magnesium oxide with a particle size distribution of 200 μm.

[0052] Calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500℃ for 30 minutes. The mixture is then water-quenched to form glass slag, which is then crushed to obtain basic glass slag powder with a particle size of 150μm.

[0053] Basic glass slag powder, porous magnesium oxide, and magnesium stearate were mixed for 25 min, granulated by high-speed shearing at 800 rpm, and sprayed with a 2 wt% polyvinyl butyral solution to form wet granules. The granules were then filled into a mold, pressed, demolded, and allowed to stand for 24 h. The temperature was then increased to 1000℃ at 5℃ / min and held for 1 h to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

[0054] Comparative Example 1: The method of Example 3 was used directly with magnesium oxide powder, without preparing porous magnesium oxide.

[0055] Comparative Example 2: The method of Example 3 was used directly with magnesium oxide powder and polystyrene microspheres, without the addition of nano-calcium carbonate for modification.

[0056] Comparative Example 3: The method of Example 3 was used directly with magnesium oxide powder and nano-calcium carbonate, without the addition of polystyrene microspheres for modification.

[0057] Comparative Example 4: The method of Example 3 was used directly with magnesium oxide powder, polystyrene microspheres and nano-calcium carbonate, without the addition of zirconium oxide fibers for modification.

[0058] This invention relates to a low-consumption continuous casting protective slag based on porous magnesium oxide, prepared using porous magnesium oxide. The performance indicators and testing standards for the continuous casting protective slag are as follows:

[0059] The protective slag sample was dried to a constant weight m0, then vacuum-impregnated with ethanol for 2 hours. After saturation, the wet weight m1 was measured. The saturated sample was then suspended in water and weighed for buoyancy m2. The total porosity was calculated as [1 − (m0 / m1 − m2)] × 100%. 5 g of protective slag and 20 g of simulated molten steel were placed in a crucible. The temperature was increased to 1550℃ at 10℃ / min and held for 30 min. After rapid cooling, the protective slag and molten steel were separated. The changes in alumina and silica concentrations in the molten steel were determined by ICP-OES, and the adsorption efficiency was calculated as η = (C0 − C t ) / C0×100%; In a small continuous casting simulation device, the mold size is 50mm×200mm, the initial thickness of the protective slag is 5mm, the temperature of the molten steel is 1550℃, the flow rate of molten steel is 0.1t / h, the initial protective slag is pre-dried to constant weight (m0), and the operation is stopped after 2 hours. The residual protective slag in the mold is collected and weighed (m1). ΔW=m0−m1, and the slag consumption (kg / t steel)=ΔW / (molten steel flow rate×2h).

[0060] The continuous casting protective slags prepared in Examples 1-4 and Comparative Examples 1-4 were tested according to the above standards, and the data obtained are shown in Table 1:

[0061] Table 1 Performance data of Examples 1-4 and Comparative Examples 1-4

[0062]

[0063] The above data fully demonstrate that, compared with Comparative Examples 1-4, Examples 1-4 clearly show the effect of porous magnesium oxide on the performance of continuous casting protective slag in terms of total porosity, adsorption efficiency, and slag consumption.

[0064] Because this invention uses porous magnesium oxide to prepare continuous casting protective slag, the performance of the continuous casting protective slag is effectively improved through porous magnesium oxide, as detailed below:

[0065] As can be seen from Examples 1-3, with the continuous increase of the proportion of nano-calcium carbonate, polystyrene microspheres and zirconia fiber components, the total porosity, adsorption efficiency and slag consumption of the continuous casting protective slag gradually increase. The carbon dioxide generated by the high-temperature decomposition of nano-calcium carbonate forms uniform micropores, which synergistically form a multi-level pore structure with polystyrene microspheres. Calcium oxide and magnesium oxide form a solid solution, which enhances the grain boundary bonding energy. Zirconia fibers form a three-dimensional network structure in the matrix, which enhances the skeleton support through pinning effect and crystal bridging effect. The pore distribution is uniform and the fiber reinforcement effect is significant. The high porosity and surface activity enhance the adsorption capacity of the protective slag per unit mass, reducing the amount of slag required to achieve the same metallurgical effect.

[0066] As can be seen from Examples 3 and 4, with the increase of the billet heating rate, the total porosity, adsorption efficiency, and slag consumption of the continuous casting protective slag significantly decrease. Rapid heating leads to the violent decomposition of polystyrene microspheres and nano-calcium carbonate, releasing a large amount of gas in a short time, forming interconnected macropores. The sudden increase in local gas pressure causes the pore walls to rupture, weakening the continuity of the matrix, deteriorating the pore structure, and introducing interface defects. Furthermore, rapid heating causes the rapid growth of magnesium oxide grains in the matrix, and the pores are swallowed up by the grains. Zirconia fibers do not have enough time to inhibit pore shrinkage through grain boundary pinning, and some pores are sintered and densified, resulting in a decrease in total porosity. Consequently, the adsorption effect deteriorates, the purification capacity of the protective slag per unit mass decreases, and the deterioration of the pore structure leads to a decrease in the heat insulation effect and an acceleration of heat loss from the molten steel. Therefore, it is necessary to increase the thickness of the protective slag to compensate for the loss, which increases the slag consumption.

[0067] Based on the above test experiments, it can be seen that the low-consumption continuous casting protective slag based on porous magnesium oxide prepared according to Example 3 has the best performance. Therefore, Example 3 is regarded as the best example.

[0068] A comparison of Example 3 with Comparative Examples 1-4 shows that:

[0069] Comparative Example 1 directly uses magnesium oxide powder without preparing it into porous magnesium oxide. The lower the overall porosity, adsorption efficiency, and slag consumption of the continuous casting protective slag, the worse the effect. Ordinary magnesium oxide powder, without pore-forming treatment, forms a dense structure after sintering, with tight intergranular bonding. Therefore, the specific surface area of ​​ordinary magnesium oxide powder is drastically reduced compared to porous magnesium oxide. It lacks pore channels and active sites, and cannot effectively adsorb inclusions in liquid slag. The low adsorption efficiency leads to a decrease in the cleanliness of the molten steel. It is necessary to increase the amount of protective slag to meet the purity requirements of the steel grade.

[0070] Comparative Example 2 directly used magnesium oxide powder and polystyrene microspheres without adding nano-calcium carbonate for modification. The overall porosity, adsorption efficiency, and slag consumption of the continuous casting protective slag were worse. Only the polystyrene microspheres formed large-sized main pores, lacking the micropores generated by the decomposition of nano-calcium carbonate. The resulting single-pore material was not as effective as the multi-level pore structure in terms of thermal insulation performance. This is because heat transfer between different pore sizes is more hindered, and small pore sizes can effectively increase specific surface area and capillary adsorption, thereby enhancing the reactivity with impurities. Therefore, without nano-calcium carbonate, the adsorption efficiency and slag consumption of the continuous casting protective slag were significantly reduced.

[0071] Comparative Example 3 directly used magnesium oxide powder and nano-calcium carbonate without adding polystyrene microspheres for modification. The overall porosity, adsorption efficiency, and slag consumption of the continuous casting protective slag were worse. Because large pores can enhance the permeability of the protective slag, provide a rapid penetration path for the molten protective slag, promote the formation of a continuous lubricating film between the molten slag and the molten steel, reduce friction, and make the molten slag more evenly distributed between the molten steel and the crystallizer during continuous casting, reducing local adhesion or blockage. However, only nano-calcium carbonate forms micropores, which are small and have poor connectivity, making them difficult to penetrate and easy to be blocked, thus losing the effect of the porous structure. Therefore, the adsorption efficiency and slag consumption performance are greatly reduced.

[0072] Comparative Example 4 directly used magnesium oxide powder, polystyrene microspheres, and nano-calcium carbonate without adding zirconium oxide fibers for modification. The performance of the continuous casting protective slag was worse in terms of total porosity, adsorption efficiency, and slag consumption. The toughness was improved through bridging, and edge support was provided when the polystyrene microspheres decomposed to form macropores, preventing macropore collapse. It also provided buffering for the micropores formed by the decomposition of nano-calcium carbonate, preventing micropore closure. Grain boundary pinning inhibited the growth of magnesium oxide grains and maintained the structural stability of porous magnesium oxide at high temperatures. Therefore, the dual decrease in adsorption efficiency and structural stability led to an increase in slag consumption.

[0073] In summary, using magnesium oxide powder as the matrix, polystyrene microspheres are introduced, which form interconnected macropores after high-temperature decomposition, providing slag penetration channels. Nano-calcium carbonate decomposes to generate nano-calcium oxide and micropores, increasing the specific surface area and exposing active sites. The synergistic effect of multi-level pores significantly improves the adsorption efficiency. Zirconia fibers, as the reinforcing phase, inhibit crack propagation and improve the skeleton strength through fiber bridging and grain boundary pinning. They stabilize the pore structure at high temperatures, reduce sintering collapse, and retain pores, thereby effectively improving the adsorption capacity of protective slag per unit mass and achieving the goal of low consumption.

[0074] 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 claimed invention.

Claims

1. A low-consumption continuous casting mold flux based on porous magnesium oxide, characterized in that: The raw materials for the protective slag include basic glass slag powder, porous magnesium oxide, polyvinyl butyral solution, and magnesium stearate; Among them, calcium oxide, silicon dioxide, aluminum oxide, sodium carbonate, boron oxide, calcium fluoride, graphite and cerium oxide are mixed and melted in an electric arc melting furnace at 1500-1550℃ for 25-30 minutes, then water-quenched into glass slag, and crushed to obtain basic glass slag powder. Porous magnesium oxide is prepared from magnesium oxide powder, polystyrene microspheres, nano-calcium carbonate, and zirconium oxide fibers. The preparation method of the porous magnesium oxide is as follows: Magnesium oxide powder, nano-calcium carbonate, polystyrene microspheres, and zirconium oxide fibers are added to a ball mill jar, followed by a 3-5 wt% polyvinyl alcohol solution. The mill is operated at 300-500 rpm with a ball-to-material ratio of 5:1 for 3-4 hours to obtain a slurry. The slurry is then injected into a mold and pressed into a green body at 20-25 MPa. The green body is vacuum dried at 80℃ for 10-12 hours, then heated to 440-450℃ at 3-5℃ / min and held for 1-1.5 hours. The temperature is then further increased to 900-950℃ at 1-3℃ / min and held for 2-3 hours. After natural cooling to room temperature, the green body is transferred to a high-temperature atmosphere furnace and heated to 1450-1500℃ at 5℃ / min and held for 3-4 hours. After cooling to 200℃ in the furnace, the green body is removed, crushed into granules, and used to obtain porous magnesium oxide.

2. The low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 1, characterized in that: The composition includes 65-70 parts by weight of magnesium oxide powder, 13-17 parts by weight of nano-calcium carbonate, 8-10 parts by weight of polystyrene microspheres, 3-5 parts by weight of zirconium oxide fiber, and 1-2 parts by weight of polyvinyl alcohol solution.

3. The low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 1, characterized in that: The polystyrene microspheres have a diameter of 30-40 μm, and the magnesium oxide powder has a particle size of 2-5 μm.

4. The low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 1, characterized in that: The solid content of the slurry is controlled at 65%-70%.

5. The low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 1, characterized in that: The porous magnesium oxide has a particle size distribution of 180-200 μm.

6. A method for preparing a low-consumption continuous casting protective slag based on porous magnesium oxide, used to prepare the low-consumption continuous casting protective slag based on porous magnesium oxide as described in any one of claims 1-5, characterized in that: Includes the following steps: The basic glass slag powder, porous magnesium oxide, and magnesium stearate are mixed for 20-25 minutes, granulated by high-speed shearing at 700-800 rpm, and sprayed with a 1-2 wt% polyvinyl butyral solution to form wet granules. These granules are then filled into a mold, pressed, demolded, and allowed to stand for 24-48 hours. The temperature is then increased to 1000℃ at 5℃ / min and held for 1 hour to obtain a low-consumption continuous casting protective slag based on porous magnesium oxide.

7. The method for preparing low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 6, characterized in that: The composition includes 42-46 parts by weight of calcium oxide, 30-34 parts by weight of silicon dioxide, 7-9 parts by weight of aluminum oxide, 5-7 parts by weight of sodium carbonate, 1-2 parts by weight of boron oxide, 2-3 parts by weight of calcium fluoride, 1.5-2.5 parts by weight of graphite, and 0.4-0.6 parts by weight of cerium oxide.

8. The method for preparing low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 6, characterized in that: The particle size of the basic glass slag powder is 120-150 μm.

9. The method for preparing low-consumption continuous casting protective slag based on porous magnesium oxide according to claim 6, characterized in that: The composition includes 81-83 parts by weight of basic glass slag powder, 12-14 parts by weight of porous magnesium oxide, 3.5-3.7 parts by weight of polyvinyl butyral solution, and 0.3-0.5 parts by weight of magnesium stearate.

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