Magnesite-carbon brick for stainless steel refining ladle and preparation method thereof

Abstract

The present application relates to a kind of magnesium-carbon bricks for stainless steel ladle and its preparation method;It is prepared from the following weight parts of raw materials:35 parts of inactive fused magnesia, 10 parts of 195 graphite, 35 parts of converter hydrated treatment of waste and old magnesium-carbon brick, 18 parts of RH or AOD waste and old magnesium-calcium brick, 1.5 parts of high-temperature pitch powder, 0.5 parts of nitride powder and 3.3 to 3.5 parts of phenolic resin binder;Completely solve the frequent groove, solution hole damage defects in the lower part of traditional magnesium-carbon brick in stainless steel ladle, improve the service life of ladle refractory from conventional 85 to 90 times to more than 150 times, fundamentally reduce the major safety hazard of ladle leakage, the service life of product is greatly improved.

Description

Technical Field

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

[0002] The reasons for the appearance of cavities in the refractory lining of the refined steel ladle during the production of NCr13 are as follows: During the production of 1Cr13, 2Cr13, 3Cr13, 4Cr13, 5Cr13, and 6Cr13, the addition of refractory heavy metals such as high-chromium alloys (chromium has a melting point of 1857℃±20℃ and a boiling point of 2672℃) leads to insufficient alloying in the molten steel, resulting in a large amount of solid solution of refractory alloys, such as Cr and Cr2. 1- Cr 2- Cr + Cr 2+ Cr 3+ Cr 4+ Cr 5+ Cr 6+ Because chromium reacts with alkalis to form acids and with acids to form bases, its solid solution accumulates and sinks at high temperatures. When it reaches the lower part of the ladle, it is propelled towards the working lining by the eddy current of the molten steel stirred by strong argon blowing, and adheres to the refractory surface. At this point, the Cr in the solid solution reacts chemically with the Mg in the magnesia-carbon bricks. As the amount of heavy metal in the solid solution increases, it begins to sink. During this sinking process, continuous chemical etching causes grooves to appear in the magnesia-carbon bricks. When the grooves reach a certain depth, the solid solution chemically etches into the interior of the magnesia-carbon bricks, forming cavities.

[0003] Furthermore, during the production of fused magnesia, manufacturers, in order to save energy, reduce manufacturing costs, and maximize profits, require three electrodes to be continuously energized and kept at a constant temperature for a certain period after the magnesite in the electric furnace melts, to promote MgO crystallization and allow the grains to grow and mature. To save costs, fused magnesia manufacturers shorten the isothermal period, resulting in poor MgO crystallization, small grains, and immature development in the fused magnesia. When these products are used in steel plants, due to the poor crystallization, small grains, and immature development of the fused magnesia, under the high-temperature conditions of converters, electric arc furnaces, and refining ladles, the MgO in the fused magnesia continues to refine its crystallization until the grains mature. This process makes the MgO in the fused magnesia highly chemically active. At this point, if acidic oxides or acidic ions are present in the molten steel, the highly active MgO can easily react with them, accelerating product damage and reducing its service life.

[0004] Therefore, when conventional magnesia-carbon bricks are used in NCr13 stainless steel refining ladles, their service life is only 85 to 90 cycles, resulting in a low ladle life, high consumption of refractory materials, high smelting production costs, and easy occurrence of grooves and cavities in the molten pool lining of the ladle, posing a safety hazard of ladle leakage. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a magnesia-carbon brick for stainless iron refining ladles, which has a long service life, completely solves the defects of molten pool cavities and groove erosion, reduces the safety risk of ladle leakage, can recycle and reuse recycled refractory waste, effectively saves costs, reduces the frequency of ladle hot repairs, reduces the total consumption of refractory materials and the overall smelting cost, and has a simple and easy-to-operate preparation method.

[0006] The technical solution of the present invention is implemented as follows: A magnesia-carbon brick for stainless steel refining ladle is prepared from the following raw materials in parts by weight: 35 parts of inactive fused magnesia, 10 parts of 195 graphite, 35 parts of waste magnesia-carbon bricks treated by converter hydration, 18 parts of RH or AOD waste magnesia-calcium bricks, 1.5 parts of high-temperature asphalt powder, 0.5 parts of nitride powder, and 3.3 to 3.5 parts of phenolic resin binder.

[0007] Furthermore, the particle size classification of the inactive fused magnesium sand is as follows: 15 parts of 3mm to 6mm granules, 15 parts of 1mm to 3mm granules, and 5 parts of fine powder ≤0.088mm.

[0008] Furthermore, the particle size classification of the waste magnesia-carbon bricks treated by the converter hydration process is as follows: 20 parts of 1mm to 6mm granules, 10 parts of 0.1mm to 1mm granules, and 5 parts of fine powder ≤0.088mm.

[0009] Furthermore, the particle size classification of the RH or AOD waste magnesium-calcium bricks is as follows: 12 parts of 0.1mm to 1mm granular material and 6 parts of ≤0.088mm fine powder.

[0010] Furthermore, the high-temperature asphalt powder has a particle size of <0.1mm; the nitride powder has a particle size of less than 120 mesh; and the inactive fused magnesia is obtained by vacuum hydration and drying passivation of ordinary fused magnesia.

[0011] A method for preparing magnesia-carbon bricks for stainless steel refining ladles as described above includes the following steps: Raw material pretreatment: Inactive fused magnesia, hydrated converter waste magnesia-carbon bricks and RH or AOD waste magnesia-calcium bricks are crushed and screened to obtain aggregates of different particle sizes. The remaining 0mm to 1mm aggregates are processed into powder by a 4R Raymond mill according to the proportion requirements. The powder is mixed with high-temperature asphalt powder and nitride powder to obtain mixed fine powder. S2. Segmented mixing: Add aggregates of different particle sizes to a forced mixer and mix for 1 to 2 minutes. Then add phenolic resin binder and mix for 3 to 5 minutes. Then add 195 graphite and mix for 5 to 8 minutes. Finally, add mixed fine powder and continue mixing for no less than 20 minutes to obtain uniform mud. S3. 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. S4. 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. S5. Finished Product Processing: After drying and ensuring the products are qualified, stack, label, and package them, then put them into the warehouse for shipment.

[0012] The present invention has the following positive effects: 1. The magnesia-carbon brick for stainless steel refining ladles of this invention uses inactive fused magnesia treated with vacuum hydration passivation as the core aggregate, which completely eliminates the high chemical activity problem caused by insufficient constant temperature time and immature MgO grain development in ordinary fused magnesia during the production stage. It fundamentally avoids the spontaneous reaction between active MgO and acidic chromium ions in molten steel at high temperatures, and significantly inhibits the continuous chemical corrosion of the brick body by chromium-based solid solutions. It completely solves the groove and cavity damage defects that frequently occur in the lower part of stainless steel refining ladles of traditional magnesia-carbon bricks, and increases the service life of ladle refractory materials from the conventional 85 to 90 times to more than 150 times, fundamentally reducing the major safety hazard of ladle leakage, and greatly improving the service life of the product.

[0013] 2. This invention relates to magnesia-carbon bricks for stainless steel refining ladles. The formula incorporates waste magnesia-carbon brick particles stabilized by converter hydration and RH or AOD waste magnesia-calcium brick components. This achieves the recycling of refractory waste while, with precise particle size distribution, the recycled aggregates and virgin aggregates form a densely packed structure. This ensures the overall high-temperature strength and erosion resistance of the brick, and also achieves high-value recycling of waste refractory materials, significantly reducing the consumption of natural mineral resources such as fused magnesia. Simultaneously, the introduction of the magnesia-calcium component can form a high-melting-point stable phase in situ within the brick, continuously generating gas resistance during use, thus increasing the internal stress of the magnesia-carbon brick during high-temperature use. This stress neither damages the microstructure of the magnesia-carbon brick nor allows it to be harmed by external substances or gases, achieving a balance between the internal and external phases of the refractory material, and between the gas and solid phases.

[0014] 3. The preparation method of the magnesia-carbon brick for stainless steel refining ladles of the present invention adopts a segmented gradient mixing process. First, the aggregate and phenolic resin binder are fully impregnated and coated. Then, 195 flake graphite is added to achieve uniform dispersion. Finally, mixed fine powder is added to complete the matrix filling. This ensures the tightness of the bonding of each phase material, so that the key indicators such as the bulk density and apparent porosity of the finished brick reach the optimal match. The thermal shock stability and resistance to molten steel eddy current erosion of the product are significantly improved compared with conventional magnesia-carbon bricks with the same carbon content, making it suitable for long-term use in the stainless steel refining process.

[0015] 4. The preparation method of magnesia-carbon bricks for stainless steel refining ladles of this invention does not involve any chemical or physical reactions. It plays a role in protecting the integrity of magnesia-carbon bricks, thereby extending their service life. There is no need to add an additional high-temperature firing process; the product can be cured simply by drying in a far-infrared drying kiln. The production energy consumption is low, the overall process is simple and controllable, and it can be directly implemented in existing magnesia-carbon brick mass production lines without the need for large-scale equipment modifications. Detailed Implementation

[0016] 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.

[0017] A type of magnesia-carbon brick for stainless steel refining ladles is prepared from the following raw materials in parts by weight: 35 parts of inactive fused magnesia, 10 parts of 195 graphite, 35 parts of waste magnesia-carbon bricks treated by converter hydration, 18 parts of RH or AOD waste magnesia-calcium bricks, 1.5 parts of high-temperature asphalt powder, 0.5 parts of nitride powder, and 3.3 to 3.5 parts of phenolic resin binder. The particle size distribution of the inactive fused magnesia is as follows: 15 parts of 3mm to 6mm granules, 15 parts of 1mm to 3mm granules, and 5 parts of fine powder ≤0.088mm. The particle size distribution of the waste magnesia-carbon bricks treated by converter hydration is as follows: 20 parts of 1mm to 6mm granules, 10 parts of 0.1mm to 1mm granules, and 5 parts of fine powder ≤0.088mm. The particle size distribution of the RH or AOD waste magnesia-calcium bricks is as follows: 12 parts of 0.1mm to 1mm granules and 6 parts of fine powder ≤0.088mm. The high-temperature asphalt powder has a particle size of <0.1mm; the nitride powder has a particle size of less than 120 mesh; and the inactive fused magnesia is made from ordinary fused magnesia through vacuum hydration and drying passivation.

[0018] The specific raw material formula is shown in the table below:

[0019] A method for preparing a magnesia-carbon brick for stainless steel refining ladles includes the following steps: Raw material pretreatment: Inactive fused magnesia, hydrated converter waste magnesia-carbon bricks and RH or AOD waste magnesia-calcium bricks are crushed and screened to obtain aggregates of different particle sizes. The remaining 0mm to 1mm aggregates are processed into powder by a 4R Raymond mill according to the proportion requirements. The powder is mixed with high-temperature asphalt powder and nitride powder to obtain mixed fine powder. S2. Segmented mixing: Add aggregates of different particle sizes to a forced mixer and mix for 1 to 2 minutes. Then add phenolic resin binder and mix for 3 to 5 minutes. Then add 195 graphite and mix for 5 to 8 minutes. Finally, add mixed fine powder and continue mixing for no less than 20 minutes to obtain uniform mud. S3. 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. S4. 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. S5. Finished Product Processing: After drying and ensuring the products are qualified, stack, label, and package them, then put them into the warehouse for shipment.

[0020] This invention addresses the problem of short service life of refining ladles used in the production of NCr13 stainless steel. Experiments have shown that after hydration treatment and drying in a vacuum container, the MgO in fused magnesium loses its activity, allowing it to react with the solid solution Cr and Cr in the molten steel. 1- Cr 2- Cr + Cr 2+ Cr 3+ Cr 4+ Cr 5+ Cr 6+ There is essentially no chemical reaction; after being used at high temperatures, the MgO in the waste magnesia-carbon bricks from the converter has lost its activity and reacts with the solid solution Cr and Cr in the molten steel. 1- Cr 2- Cr + Cr 2+ Cr 3+ Cr 4+ Cr 5+ Cr 6+ There is essentially no chemical reaction; the MgO and CaO in the waste magnesia-calcium bricks after RH or AOD use also lose their activity, and react with the solid solution Cr and Cr in the molten steel. 1- Cr 2- Cr + Cr 2+ Cr 3+ Cr 4+ Cr 5+ Cr 6+ There is basically no chemical reaction.

[0021] Adding nitrides to the product generates inert gas during high-temperature use. This inert gas exists within the capillary pores of the product, forming a gas barrier that effectively blocks and isolates chromate ions from adhering to the surface of the magnesia-carbon bricks, achieving a three-phase equilibrium of gas, solid, and liquid phases, thus preventing chemical corrosion. When the finished magnesia-carbon bricks are used as linings for 70-ton and 80-ton stainless steel refining ladles using conventional methods, their service lives are as follows: For the 70-ton ladle, used in a stainless steel plant in Guangxi, the average service life is over 170 cycles, approaching 200 cycles in destructive testing. For the 80-ton ladle, used in a stainless steel plant in Jiangsu, the average service life is over 150 cycles, reaching 160 cycles in extreme tests.

[0022] In order to improve the practicality and service life of the magnesia-carbon bricks for stainless steel refining ladles of this invention, the permeable bricks, nozzle seat bricks, and slag lines should be replaced once during use.

[0023] Case Study 1: This case study involves a 70-ton stainless steel refining ladle from Guangxi Wuzhou Xinfeng. The ladle bottom is 350mm long, the wall is 200mm long, and the slag line is 220mm long. The permeable bricks and nozzle seat bricks were replaced once during the process, achieving a service life of over 170 cycles. After dismantling, the remaining thickness of the ladle is: bottom 170mm, wall 120mm, and slag line 90mm, which is more than 30mm thicker than the remaining thickness of ordinary magnesia-carbon brick ladle with a service life of around 90 cycles.

[0024] Case Study 2: This case study involves an 80-ton steel ladle from Jiangsu Huale Alloy. The ladle bottom is 400mm long, the wall is 180mm long, and the slag line is 200mm long. The permeable bricks and nozzle seat bricks were replaced once during operation, achieving a service life of 150 cycles. After 150 cycles, it was deemed unusable and forcibly dismantled. The remaining brick lengths after dismantling were: bottom greater than 180mm, wall greater than 100mm, and slag line greater than 75mm, all longer than the remaining thickness of ordinary magnesia-carbon bricks.

[0025] 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 stainless steel refining ladles, characterized in that, It is prepared from the following raw materials in parts by weight: 35 parts of inactive fused magnesia, 10 parts of 195 graphite, 35 parts of waste magnesia-carbon bricks treated by converter hydration, 18 parts of RH or AOD waste magnesia-calcium bricks, 1.5 parts of high-temperature asphalt powder, 0.5 parts of nitride powder, and 3.3 to 3.5 parts of phenolic resin binder.

2. The magnesia-carbon brick for stainless steel refining ladles according to claim 1, characterized in that, The particle size classification of the inactive fused magnesium sand is as follows: 15 parts of 3mm to 6mm granules, 15 parts of 1mm to 3mm granules, and 5 parts of fine powder ≤0.088mm.

3. The magnesia-carbon brick for stainless steel refining ladles according to claim 1, characterized in that, The particle size classification of the waste magnesia-carbon bricks treated by the converter hydration process is as follows: 20 parts of 1mm to 6mm granules, 10 parts of 0.1mm to 1mm granules, and 5 parts of fine powder ≤0.088mm.

4. The magnesia-carbon brick for stainless steel refining ladles according to claim 1, characterized in that, The particle size classification of the RH or AOD waste magnesium-calcium bricks is as follows: 12 parts of 0.1mm to 1mm granular material and 6 parts of fine powder ≤0.088mm.

5. The magnesia-carbon brick for stainless steel refining ladles according to claim 1, characterized in that, The high-temperature asphalt powder has a particle size of <0.1mm; the nitride powder has a particle size of less than 120 mesh; and the inactive fused magnesia is obtained by vacuum hydration and drying passivation of ordinary fused magnesia.

6. A method for preparing magnesia-carbon bricks for stainless steel refining ladles as described in any one of claims 1-5, characterized in that, Includes the following steps: Raw material pretreatment: Inactive fused magnesia, hydrated converter waste magnesia-carbon bricks and RH or AOD waste magnesia-calcium bricks are crushed and screened to obtain aggregates of different particle sizes. The remaining 0mm to 1mm aggregates are processed into powder by a 4R Raymond mill according to the proportion requirements. The powder is mixed with high-temperature asphalt powder and nitride powder to obtain mixed fine powder. S2. Segmented mixing: Add aggregates of different particle sizes to a forced mixer and mix for 1 to 2 minutes. Then add phenolic resin binder and mix for 3 to 5 minutes. Then add 195 graphite and mix for 5 to 8 minutes. Finally, add mixed fine powder and continue mixing for no less than 20 minutes to obtain uniform mud. S3. 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. S4. 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. S5. Finished Product Processing: After drying and ensuring the products are qualified, stack, label, and package them, then put them into the warehouse for shipment.

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