Magnesite-carbon brick for refining ladle of aluminum-containing steel and its preparation method

Abstract

The application relates to a magnesium-carbon brick for refining ladle containing aluminum steel and a preparation method thereof. The magnesium-carbon brick is prepared from the following raw materials in parts by weight: 50 parts of inactive fused magnesite, 3 parts of alpha-alumina micro powder, 12 parts of 195 graphite, 1 part of aluminum powder, 2 parts of high-temperature pitch powder, 2 parts of silicon powder and 3.3-3.5 parts of thermosetting phenolic resin. In a high-temperature state, the magnesium-carbon brick can effectively prevent harmful components in steel liquid from invading the inside of the product, so as to protect the graphite. The addition of the high-temperature pitch powder can effectively seal the capillary pore channels generated in the product in a high-temperature state, so as to prevent the invasion of harmful gases in the steel liquid.

Description

Technical Field

[0001] This invention relates to the field of magnesium-carbon brick production technology, specifically to a magnesium-carbon brick for aluminum-containing steel refining ladles and its preparation method. Background Technology

[0002] The refining process of plain carbon steel is mild, and conventional magnesia-carbon bricks can meet the requirements. However, the smelting of aluminum-containing steel is subjected to multiple corrosive effects, including high temperature, long-term strong stirring, repeated temperature changes and strong chemical corrosion, which greatly accelerates the damage rate of the lining. The aluminum alloy added during the smelting process has a low density and easily floats on the surface of the molten steel. To achieve alloy homogenization, it is necessary to increase the argon pressure and continuously stir. The refining temperature is more than 30°C higher than that of ordinary carbon steel, and the smelting cycle is extended by about 10 minutes. The brick body is subjected to high-intensity heat load for a long time. Fluorite is added during slag formation to adjust the slag fluidity and form low-basicity dilute slag. The turbulent flow of molten steel and slag generated by bottom blowing argon continuously washes the slag line of the ladle and the inner wall of the molten pool. After long-term use, the lining is prone to scouring grooves of varying depths. After refining, there is no external heating source. In order to remove the flocculent alumina inclusions inside the molten steel, it is necessary to carry out long-term killing, argon blowing, wire feeding, and calcification modification treatment. The lining is repeatedly subjected to sudden changes in high and low temperatures, and the thermal stress continuously induces brick body cracks and surface peeling. The flocculent alumina inclusions generated by the reaction of aluminum in steel with dissolved oxygen can not only accumulate and block the continuous casting nozzle, causing turbulent flow and casting interruption, but also react with the highly active magnesium oxide in the brick body to continuously corrode the brick body matrix.

[0003] Current industry-standard magnesia-carbon bricks are designed only for plain carbon steel applications. Their raw materials, formulations, and mixing processes are not adapted to the unique corrosive environment of aluminum-containing steel, resulting in multiple cascading defects. To reduce costs, some fused magnesia manufacturers shorten the isothermal crystallization process, leading to incomplete magnesia grain development. This results in continuous recrystallization at high temperatures, reacting with alumina and acidic slag, exacerbating trench wear. Traditional formulations do not include... Micronized powder cannot form a magnesium aluminum spinel protective phase at high temperatures, lacking an aggregate protective film and matrix bridging structure, resulting in insufficient resistance to erosion and corrosion. Conventional antioxidants can only isolate surface oxygen for a short period of time, failing to form a stable gas barrier balance within the brick. Furthermore, they lack pore-sealing components, allowing harmful media to penetrate into the graphite oxide along capillary pores, causing the brick to become loose and damaged. Traditional mixing involves adding all materials at once, which easily leads to powder agglomeration, graphite stratification, uneven aggregate coating, and an unbalanced distribution of green body components. The inner lining is eroded first in certain areas, resulting in significant differences in overall service life.

[0004] Conventional magnesia-carbon bricks used in aluminum-containing steel refining ladles can only be used for about 70 heats, resulting in frequent maintenance. Localized erosion grooves in the slag line and molten pool cause refractory materials to not be consumed synchronously, leading to significant material waste. Furthermore, frequent blockages of the nozzles by refractory spalling and alumina inclusions cause casting stoppages. This results in a combination of costs, including refractory procurement, ladle hot repairs, and production shutdowns / reductions, significantly increasing the expenses of special steel smelting. In summary, existing ordinary magnesia-carbon bricks cannot meet the harsh operating conditions of aluminum-containing steel, which involve high temperatures, strong erosion, chemical corrosion, and alternating hot and cold temperatures. The industry urgently needs improved, long-lasting, specialized magnesia-carbon bricks to fundamentally solve prominent problems such as lining grooves, low ladle life, and poor production continuity.

[0005] In summary, existing ordinary magnesia-carbon bricks cannot adapt to the complex working conditions of aluminum-containing steel, such as high temperature, strong stirring, alumina chemical corrosion, and frequent temperature changes. There is an urgent need for a magnesia-carbon brick for aluminum-containing steel refining ladles and its preparation method to solve core problems such as lining grooves, short service life, and poor production continuity. Summary of the Invention

[0006] To address the technical shortcomings of existing conventional magnesia-carbon bricks used in aluminum steel refining ladles, such as short lining life, easy formation of grooves in the molten pool, severe brick spalling and erosion, easy blockage and difficulty in cleaning of the slits in the bottom-blown argon permeable core, and easy turbulence and interruption of casting at the continuous casting nozzle, this invention provides a magnesia-carbon brick for aluminum steel refining ladles and its preparation method.

[0007] The technical solution of the present invention is implemented as follows: A magnesium-carbon brick for aluminum steel refining ladle is prepared from the following raw materials in parts by weight: 50 parts of inactive fused magnesia, 3 parts of α-alumina micro powder, 12 parts of 195 graphite, 1 part of metallic aluminum powder, 2 parts of high-temperature asphalt powder, 2 parts of metallic silicon powder, and 3.3 to 3.5 parts of thermosetting phenolic resin.

[0008] Furthermore, the particle size classification of the inactive fused magnesium sand is as follows: 35 parts of 3mm to 6mm granules, 20 parts of 1mm to 3mm granules, and 15 parts of fine powder ≤1mm.

[0009] Furthermore, the particle size of the high-temperature asphalt powder is <0.1mm.

[0010] Furthermore, the α-alumina micro powder is of d50 grade with high activity. Micronized powder.

[0011] Furthermore, the particle size of both the aluminum powder and the silicon powder is 120 mesh.

[0012] A method for preparing magnesia-carbon bricks for aluminum steel refining ladles as described above includes the following steps: S1. After accurately weighing the above materials according to the proportion, mix them in a forced mixer. The order of adding the materials is large, medium and small particles. After dry mixing for 1 to 2 minutes, add α-alumina micro powder, then dry mix for 2 minutes, then add thermosetting phenolic resin, then mix for 3 to 5 minutes, then add 195 graphite and mix for 5 to 8 minutes, and finally add mixed fine powder. Continue mixing for no less than 20 minutes to obtain a uniform mud. S2. Molding: The mixed clay is fed into a CNC press to press and shape the bricks, controlling the three-dimensional dimensions of the bricks. The shaped brick blanks are then placed on the kiln car. S3. Drying: Send the kiln car loaded with brick blanks into the 18m far-infrared drying kiln and dry it at a constant temperature of 180℃ to 200℃ for 12 hours. S4. Finished Product Processing: After drying and ensuring the products are qualified, stack, label, and package them, then put them into the warehouse for shipment.

[0013] The present invention has the following positive effects: 1. In the initial stage of use, the product of this invention exhibits the formation of a third phase—spinel phase—which improves the product's impact resistance, enhances its erosion resistance, and effectively prevents the coupling of highly reactive MgO with harmful components in the slag and molten steel. The slight volume changes that occur during spinel formation offset the expansion and contraction of the product under rapid heating and cooling conditions. The addition of the metal component effectively prevents harmful components in the molten steel from penetrating into the product's interior at high temperatures, thus protecting the graphite. The addition of high-temperature pitch powder effectively seals the capillary pores generated in the product at high temperatures, preventing the intrusion of harmful gases from the molten steel.

[0014] 2. This invention reduces the reactivity of fused magnesia (MgO) through a vacuum hydration process, preventing continuous chemical reactions between MgO and alumina and acidic slag at high temperatures, and eliminating defects in the molten pool grooves. Micronized powder, formed at high temperatures, creates a magnesium-aluminum spinel-reinforced framework, simultaneously improving erosion and thermal shock resistance. Metallic antioxidants create internal air barriers, while high-temperature asphalt powder seals capillary pores, forming a dual barrier of gas and solid phases to prevent the intrusion of oxygen, slag, and alumina. Furthermore, optimized feeding sequence and mixing time ensure uniform dispersion of materials, tight bonding between aggregates and matrix, and significantly improved product performance stability. No additional high-temperature firing process is required; only far-infrared low-temperature drying and curing are used, allowing existing magnesia-carbon brick production lines to be put into operation directly, with controllable production costs.

[0015] 3. This invention increases the service life of the ladle by 58% to 67%, reduces the frequency of ladle hot repairs, lowers refractory material consumption, and eliminates downtime losses caused by alumina clogging the nozzle. When the resulting magnesia-carbon bricks are used as ladle linings in aluminum-containing steel refining furnaces, the service life of the ladle can be increased from approximately 70 cycles to over 110 cycles. Simultaneously, it effectively solves the problem of grooves appearing in the molten pool of the ladle, significantly reducing steelmaking costs and saving refractory material consumption.

[0016] 4. This invention incorporates The micronized powder allows the product to first react with the white alkali residue produced on the surface of the fused magnesia particles during hydration treatment at high temperatures. This alkali residue is actually Mg(OH)₂, which can react with active... Micronized powder reacts to form spinel, which can effectively adhere to the surface of fused magnesia particles to form a protective film. At the same time, it is coupled with the fine fused magnesia powder in the matrix, which improves the erosion resistance of magnesia-carbon bricks and enhances the performance of the products. Detailed Implementation

[0017] A magnesia-carbon brick for aluminum-containing steel refining ladles is prepared from the following raw materials in parts by weight: 50 parts of inactive fused magnesia, 3 parts of α-alumina micro powder, 12 parts of 195 graphite, 1 part of metallic aluminum powder, 2 parts of high-temperature pitch powder, 2 parts of metallic silicon powder, and 3.3 to 3.5 parts of thermosetting phenolic resin. The inactive fused magnesia is graded as follows: 35 parts of 3mm to 6mm granules, 20 parts of 1mm to 3mm granules, and 15 parts of fine powder ≤1mm. The high-temperature pitch powder has a particle size <0.1mm. The α-alumina micro powder is a d50 grade high-activity powder. Micronized powder. The particle size of both the aluminum powder and the silicon powder is 120 mesh.

[0018] Specifically, inactive fused magnesia is used as the main aggregate in the matrix. After hydration and passivation, the high-temperature chemical activity of MgO is greatly reduced, thereby reducing the corrosion reaction between MgO and acidic slags such as alumina and fluorite from the source and inhibiting the continuous chemical loss of the brick.

[0019] The addition of micronized powder allows the molten steel to preferentially react with Mg(OH)2 and matrix MgO generated by the hydration of magnesia surface at a high temperature of 1600℃, forming a third phase of magnesium aluminum spinel in situ. The spinel uniformly coats the magnesia aggregate to form a dense protective film, while bridging the aggregate particles and the fine powder matrix, significantly improving the high-temperature strength, toughness, and erosion resistance of the product. The formation of spinel is accompanied by a slight volume expansion, which offsets the shrinkage stress generated by the thermal cycle of the brick and reduces the occurrence of cracks.

[0020] 195 graphite enhances the thermal shock resistance of products, blocks the penetration of molten slag liquid phase, optimizes the internal thermal conductivity structure of bricks, and alleviates damage from rapid cooling and heating.

[0021] Metallic aluminum powder and metallic silicon powder vaporize at high temperatures to generate a protective inert gas phase, forming a stable gas barrier inside the brick and establishing a solid-gas phase balance. Moderate internal stress will not damage the brick's microstructure, effectively preventing harmful gases from the molten steel from penetrating inward and avoiding graphite oxidation and failure. This type of metallic powder does not participate in destructive physicochemical reactions, thus maintaining the integrity of the brick structure over a long period.

[0022] High-temperature asphalt powder fills the capillary pores and microcracks generated during the molding and use of bricks, blocking harmful media such as alumina, fluorides, and oxygen from eroding inwards, and forming a dual protection system in conjunction with metal antioxidants.

[0023] Thermosetting phenolic resin is a room-temperature molding and bonding medium that ensures the plasticity of the clay, improves the molding strength of the green body, and forms a continuous carbon bond network after drying.

[0024] In the specific preparation process, the order of adding materials and the duration of segmented mixing must be strictly followed. The micro-powder must be added slowly, evenly, and continuously; large-scale addition at once is prohibited. First, add all graded magnesia aggregates (large, medium, and small particles) and dry mix for 1 to 2 minutes. Then, slowly add α-alumina micro-powder and continue dry mixing for 2 minutes to ensure the micro-powder evenly coats the aggregate surface. Next, add thermosetting phenolic resin and mix for 3 to 5 minutes to ensure complete impregnation of all aggregates. Then, add 195% graphite and mix for 5 to 8 minutes to ensure uniform dispersion of graphite without any floating layer. Finally, add the mixed fine powder and continue mixing for at least 20 minutes to obtain a uniform clay with a consistent color, no dry powder agglomeration, and no graphite stratification. Only then can it be discharged from the mill for use.

[0025] The mixed clay is fed into a CNC press to shape the bricks, controlling their three-dimensional dimensions. The shaped brick blanks are then stacked in kiln cars. The kiln cars loaded with the brick blanks are then sent into an 18m far-infrared drying kiln, where they are dried at a constant temperature of 180℃ to 200℃ for 12 hours. After drying, the qualified products are stacked, labeled, packaged, and stored for shipment.

[0026] Implementation Case 1: In this implementation case, the aluminum content of the steel produced by Jitai Steel's 50t steel ladle is 96%, and the average service life reaches 108 times, which is 67% higher than the service life of the ordinary magnesia-carbon bricks they used before.

[0027] Case Study 2: This case study involves the production of steel in a 120T steel ladle at a factory in Gansu Province. The steel contains 79% aluminum and 7% silicon, with an average service life of 118 cycles, which is 58% longer than that of ordinary magnesia-carbon bricks. However, the ventilated bricks used by this factory only have a service life of less than 20 cycles, mostly between 16 and 18 cycles. Frequent replacement of the ventilated bricks caused the lining refractory material to be repeatedly affected by rapid heating and cooling. Otherwise, the service life would have been even higher.

[0028] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A magnesia-carbon brick for aluminum-containing steel refining ladles, characterized in that, It is prepared from the following raw materials in parts by weight: 50 parts of inactive fused magnesia, 3 parts of α-alumina micro powder, 12 parts of 195 graphite, 1 part of metallic aluminum powder, 2 parts of high-temperature asphalt powder, 2 parts of metallic silicon powder, and 3.3 to 3.5 parts of thermosetting phenolic resin.

2. The magnesia-carbon brick for aluminum-containing steel refining ladles according to claim 1, characterized in that, The particle size classification of the inactive fused magnesium sand is as follows: 35 parts of 3mm to 6mm granules, 20 parts of 1mm to 3mm granules, and 15 parts of fine powder ≤1mm.

3. The magnesia-carbon brick for aluminum-containing steel refining ladles according to claim 1, characterized in that, The high-temperature asphalt powder has a particle size of <0.1mm.

4. The magnesia-carbon brick for aluminum-containing steel refining ladles according to claim 1, characterized in that, The α-alumina micro powder is of d50 grade with high activity. Micronized powder.

5. The magnesia-carbon brick for aluminum-containing steel refining ladles according to claim 1, characterized in that, The particle size of both the aluminum powder and the silicon powder is 120 mesh.

6. A method for preparing magnesia-carbon bricks for aluminum-containing steel refining ladles as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. After accurately weighing the above materials according to the proportion, mix them in a forced mixer. The order of adding the materials is large, medium and small particles. After dry mixing for 1 to 2 minutes, add α-alumina micro powder, then dry mix for 2 minutes, then add thermosetting phenolic resin, then mix for 3 to 5 minutes, then add 195 graphite and mix for 5 to 8 minutes, and finally add mixed fine powder. Continue mixing for no less than 20 minutes to obtain a uniform mud. S2. Molding: The mixed clay is fed into a CNC press to press and shape the bricks, controlling the three-dimensional dimensions of the bricks. The shaped brick blanks are then placed on the kiln car. S3. Drying: Send the kiln car loaded with brick blanks into the 18m far-infrared drying kiln and dry it at a constant temperature of 180℃ to 200℃ for 12 hours. S4. Finished Product Processing: After drying and ensuring the products are qualified, stack, label, and package them, then put them into the warehouse for shipment.