Spinel-graphite-metal composite material for a core nozzle

Abstract

This invention belongs to the field of refractory materials technology, specifically relating to a spinel-graphite-metal composite material for core nozzles. First, a high-porosity resin-carbon bonded spinel-graphite preform is obtained by cold isostatic pressing followed by heat treatment in a protective atmosphere. Then, metallic silicon particles are used to embed the resin-carbon bonded spinel-graphite preform, which is then heat-treated in a vacuum sintering furnace. As metallic silicon permeates into the high-porosity resin-carbon bonded spinel-graphite preform, it continuously reacts with the resin-carbon and graphite, forming a dense silicon carbide layer from the surface to the interior, followed by a dense metallic silicon bonded spinel-graphite layer. With the formation of the dense silicon carbide layer on the surface, the permeation reaction ends, leaving a porous spinel-graphite layer in the core of the material. This invention avoids excessive thermal stress causing severe thermal shock that could lead to core nozzle fracture and failure, further optimizing the thermal shock resistance of the core nozzle.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials technology, specifically relating to a spinel-graphite-metal composite material for core nozzles. Background Technology

[0002] With the continuous advancement of my country's industrialization and urbanization, and the ongoing upgrading of its consumption structure, energy demand is experiencing rigid growth, and resource and environmental problems are becoming increasingly severe. Energy conservation and emission reduction have become a top priority in the national development strategy. The steel industry is a major energy consumer and carbon emitter, and the effectiveness of energy conservation and emission reduction is crucial to achieving my country's "carbon peaking" and "carbon neutrality" strategic goals and to environmental governance. Exploring simple and efficient manufacturing processes is an important technological path for achieving green manufacturing and ecological development in the steel industry, as well as a key technological route for the industry's green manufacturing and ecological development, and also a direction for the industry's innovative development. Near-net-shape manufacturing refers to manufacturing technologies that make the dimensions and shapes of products closer to the final use requirements. Compared with traditional manufacturing technologies, its manufacturing process is simpler and more efficient, with significant energy conservation and emission reduction effects, making it a typical green manufacturing technology.

[0003] Near-net-shape manufacturing technologies in the metallurgical process manufacturing field mainly include thin slab continuous casting and rolling and thin strip casting and rolling. Compared with thin slab continuous casting and rolling, thin strip continuous casting and rolling is a more compact hot-rolled strip steel production process. It integrates continuous casting and rolling, directly casting molten steel into near-net-shape thin strip steel with a thickness of 1-25mm. Among them, the most researched and fastest-developing technology is the twin-roll thin strip continuous casting and rolling technology. The twin-roll thin strip continuous casting and rolling technology uses rotating rolls as crystallizers, relying on the surface of the twin rolls to cool the liquid steel and solidify it to produce thin strip steel. Its characteristic is that the liquid metal is subjected to pressure processing and plastic deformation while crystallizing and solidifying, completing the entire process from liquid to solid thin strip in a very short time. The twin-roll thin strip continuous casting and rolling greatly shortens the process flow. The time required from casting to coiling is no more than 15 minutes, and its production line length is about 50m.

[0004] Uniform distribution of molten steel within the molten pool is a core technology in thin strip continuous casting and rolling. This requires both uniform distribution across the width of the crystallizing roll and ensuring the stability of the molten pool's meniscus. Current industrial processes employ a three-stage molten steel distribution system: the tundish, the primary transition ladle, and the core nozzle, distributing the molten steel to the thin strip continuous casting crystallizing roll. The tundish and primary transition ladle function similarly to the ladle and tundish in traditional continuous casting processes, maintaining a stable molten steel level within the crystallizer through a rational structure and flow control. In thin strip continuous casting and rolling, the working layers of both the tundish and primary transition ladle utilize existing, mature, and stable magnesia-based dry materials or coatings. The lining material can withstand the erosion and scouring of high-temperature molten steel. The core nozzle functions similarly to the submerged entry nozzle in traditional continuous casting processes, distributing molten steel secondary within the crystallizer and maintaining a reasonable and stable flow field. The core nozzle uses a spinel-graphite composite material, a traditional "three major components" of continuous casting. While spinel-graphite composites possess excellent thermal shock resistance and resistance to molten steel scouring, they also exhibit high apparent porosity. During service, the oxidation of graphite and residual air within the pores form microbubbles in the molten pool. Furthermore, the rapid solidification rate within the molten pool of thin-strip continuous casting and rolling reaches 10... 3 K*s -1 Tiny air bubbles cannot rise to the surface and be expelled in time, forming micro-defects in the thin steel strip and seriously affecting the surface quality of the steel strip. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a spinel-graphite-metal composite material for core nozzles.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A spinel-graphite-metal composite material for core nozzles, comprising a dense surface layer of silicon carbide-bonded spinel, an intermediate transition layer of dense silicon metal-bonded spinel-graphite, and an inner core of porous spinel-graphite. First, a resin-carbon bonded spinel-graphite preform with high porosity is obtained by cold isostatic pressing and heat treatment in a protective atmosphere. The resin-carbon bonded spinel-graphite preform is then embedded with silicon metal particles and heat-treated in a vacuum sintering furnace. The silicon metal particles are then subjected to 1... Under conditions of 500-1800℃, metallic silicon with suitable viscosity is formed and penetrates into a highly porosity resin-carbon bonded spinel-graphite preform. As metallic silicon penetrates into the highly porosity resin-carbon bonded spinel-graphite preform, it continuously reacts with resin-carbon and graphite. A dense silicon carbide layer and a dense metallic silicon bonded spinel-graphite layer are formed sequentially from the surface to the interior of the highly porosity resin-carbon bonded spinel-graphite preform. With the formation of the dense silicon carbide layer on the surface, the penetration reaction ends, and a porous spinel-graphite layer is maintained in the core of the material.

[0007] The raw material composition and weight percentage of the resin-carbon bonded spinel-graphite preform are as follows: 15-30% 0.6-0.2mm spinel, 10-20% 0.2-0mm spinel, 15-30% 325 mesh spinel, 5-15% grade 199 flake graphite, 10-20% 599 flake graphite, and 10-15% phenolic resin.

[0008] The spinel contains 65-75% aluminum oxide and 25-35% magnesium oxide.

[0009] The fixed carbon content in the flake graphite is greater than 98.5%.

[0010] The particle size of the embedded silicon metal particles is 3-1 mm and 5-3 mm; the mass fraction of the 3-1 mm silicon metal particles is 40-50%, the mass fraction of the 5-3 mm silicon metal particles is 50-60%, and the silicon content in the silicon metal particles is greater than 99%.

[0011] The embedding amount of the silicon metal particles is 10%-50% of the mass fraction of the resin-carbon bonded spinel-graphite preform itself.

[0012] The phenolic resin has grades 5405, 9202, and 5016, and a residual carbon content of 40-55%.

[0013] The molding pressure of the resin-carbon bonded spinel-graphite preform is 40 MPa to 120 MPa.

[0014] The protective heat treatment atmosphere for the resin-carbon bonded spinel-graphite preform is a carbon-embedded atmosphere, a nitrogen atmosphere, or an argon atmosphere.

[0015] The resin-carbon bonded spinel-graphite preform undergoes a protective heat treatment at 750-950℃.

[0016] The vacuum sintering furnace operates under a vacuum or protective atmosphere, with the graphite body generating heat at a working temperature of 1500-2000℃.

[0017] This invention provides a spinel-graphite-metal composite material for core nozzles. Using this method, a smaller temperature gradient can be quickly achieved between the inside and outside of the material during the preheating stage and the initial casting process of thin strip continuous casting. This avoids excessive thermal stress causing severe thermal shock that could lead to core nozzle fracture and failure. Simultaneously, the composite metallic phase in this material exhibits a certain degree of toughness under hot conditions, which can offset the thermal expansion of the spinel and graphite materials, further optimizing the thermal shock resistance of the core nozzle. The intermediate transition layer of this spinel-graphite-metal composite material can continuously produce a dense carbide layer through in-situ reaction during heat treatment and service. This dense carbide layer prevents the oxidation of the graphite material on one hand, and isolates the air in the pores of the inner spinel-graphite material from contact with the molten steel on the other, preventing the formation of microbubbles in the molten pool. Detailed Implementation

[0018] The present invention will be described in detail with reference to specific embodiments: Example 1:

[0019] According to the material composition in Table 1, weigh out 2.5 kg of 0.6-0.2 mm spinel, 1.5 kg of 0.2-0 mm spinel, 1.5 kg of 325 mesh spinel, 1.0 kg of 199 graphite, 2.0 kg of 599 graphite, and 1.5 kg of phenolic resin. Mix them evenly in a high-speed granulator and set aside. Dry the spinel-graphite preform at 60℃ until the volatile content is 1.5-1.7%, and then form it in a cold isostatic press at 80 MPa. After forming, the preform is heat-treated at 850℃ under carbon embedding conditions to obtain an apparent porosity of 28%. Place the porous spinel-graphite preform into a graphite crucible. Using 1 kg of 3-1 mm metallic silicon and 1.5 kg of 5-3 mm metallic silicon as cladding, a dense silicon carbide layer with a thickness of 1 mm is formed after holding at 1600℃ for 5 hours in a vacuum heat treatment furnace. The core nozzle is composed of a spinel-graphite-metallic silicon composite material consisting of a 4 mm metallic silicon bonded spinel-graphite layer and a 10 mm porous spinel-graphite layer.

[0020] Table 1. Composition of porous spinel-graphite preform material Example 2:

[0021] According to the material composition in Table 2, weigh out 2.5 kg of 0.6-0.2 mm spinel, 2.0 kg of 0.2-0 mm spinel, 2.0 kg of 325 mesh spinel, 1.2 kg of 199 graphite, 1.0 kg of 599 graphite, and 1.3 kg of phenolic resin, mix them evenly in a high-speed granulator, and set aside. Dry the spinel-graphite preform at 60°C until the volatile content is 1.0-1.2%, and then form it in a cold isostatic press at 120 MPa. After molding, the blank is heat-treated at 750℃ under carbon embedding conditions to obtain an apparent porosity of 25%. The porous spinel-graphite blank is placed in a graphite crucible, and 1.5kg of 3-1mm metallic silicon and 2.0kg of 5-3mm metallic silicon are embedded in the porous spinel-graphite blank. After being held at 1800℃ for 3 hours in a vacuum heat treatment furnace, a dense silicon carbide layer with a thickness of 3mm is formed. The core nozzle is composed of a spinel-graphite-metallic silicon composite material consisting of a 4mm metallic silicon bonded spinel-graphite layer and an 8mm porous spinel-graphite layer.

[0022] Table 2 Composition of Porous Spinel-Graphite Preform Material Example 3:

[0023] According to the material composition in Table 3, weigh out 2.5 kg of 0.6-0.2 mm spinel, 1.5 kg of 0.2-0 mm spinel, 3.0 kg of 325 mesh spinel, 0.5 kg of 199 graphite, 1.5 kg of 599 graphite, and 1.0 kg of phenolic resin, and mix them evenly in a high-speed granulator for later use. The spinel-graphite preform is dried at 60℃ until the volatile content is 0.6-0.8%, and then formed in a cold isostatic press at 120 MPa. After forming, the preform is heat-treated at 750℃ under carbon embedding conditions to obtain an apparent porosity of 35%. A porous spinel-graphite preform is placed in a graphite crucible, and 2.0 kg of 3-1 mm metallic silicon and 2.0 kg of 5-3 mm metallic silicon are used to embed the preform. After holding at 1650℃ for 6 hours in a vacuum heat treatment furnace, a dense silicon carbide layer with a thickness of 2 mm is formed. The core nozzle is composed of a spinel-graphite-metallic silicon composite material consisting of a 3 mm metallic silicon bonded spinel-graphite layer and a 10 mm porous spinel-graphite layer.

[0024] Table 3 Composition of Porous Spinel-Graphite Preform Material .

Claims

1. A spinel-graphite-metal composite material for core nozzles, characterized in that: The surface dense layer of the spinel-graphite-metal composite material is a silicon carbide-bonded spinel layer, the intermediate transition layer is a dense metal silicon-bonded spinel-graphite layer, and the inner core is a porous spinel-graphite layer. First, a resin-carbon-bonded spinel-graphite preform with high porosity is obtained by cold isostatic pressing and heat treatment in a protective atmosphere. The resin-carbon-bonded spinel-graphite preform is then covered with metal silicon particles and heat-treated in a vacuum sintering furnace. The metal silicon particles form metal silicon with suitable viscosity at 1500-1800℃ and penetrate into the high-porosity resin-carbon-bonded spinel-graphite preform. As metallic silicon permeates into the highly porous resin-carbon bonded spinel-graphite preform, the metallic silicon continuously reacts with the resin-carbon and graphite. From the surface to the interior, a dense silicon carbide layer and a dense metallic silicon bonded spinel-graphite layer are formed sequentially. With the formation of the dense silicon carbide layer on the surface, the permeation reaction ends, and a porous spinel-graphite layer is maintained in the core of the material.

2. The spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The raw material composition and weight percentage of the resin-carbon bonded spinel-graphite preform are as follows: 15-30% 0.6-0.2mm spinel, 10-20% 0.2-0mm spinel, 15-30% 325 mesh spinel, 5-15% grade 199 flake graphite, 10-20% 599 flake graphite, and 10-15% phenolic resin.

3. The spinel-graphite-metal composite material for core nozzles as described in claim 2, characterized in that: The spinel contains 65-75% aluminum oxide and 25-35% magnesium oxide.

4. The spinel-graphite-metal composite material for core nozzles as described in claim 2, characterized in that: The fixed carbon content in the flake graphite is greater than 98.5%.

5. The spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The particle size of the embedded silicon metal particles is 3-1 mm and 5-3 mm; the mass fraction of the 3-1 mm silicon metal particles is 40-50%, the mass fraction of the 5-3 mm silicon metal particles is 50-60%, and the silicon content in the silicon metal particles is greater than 99%.

6. The spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The embedding amount of the metallic silicon particles is 10-50% of the mass fraction of the resin-carbon bonded spinel-graphite preform itself.

7. The spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The molding pressure of the resin-carbon bonded spinel-graphite preform is 40 MPa to 120 MPa.

8. The spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The protective heat treatment atmosphere for the resin-carbon bonded spinel-graphite preform is a carbon-embedded atmosphere, a nitrogen atmosphere, or an argon atmosphere.

9. A spinel-graphite-metal composite material for core nozzles as described in claim 1, characterized in that: The resin-carbon bonded spinel-graphite preform undergoes a protective heat treatment at 750-950℃.

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