Anti-blocking submerged entry nozzle for special steel continuous casting and preparation method thereof

Abstract

The application discloses a special steel continuous casting anti-blocking submerged nozzle and a preparation method thereof. The special steel continuous casting anti-blocking submerged nozzle comprises a main body which is composed of a heat-conducting layer and a heat-insulating layer connected in sequence from inside to outside, and the heat-conducting layer is in contact with molten steel. The heat-conducting layer is prepared from raw materials with the following weight percentages: 60-80% of fused alumina, 4-11% of silicon carbide, 14-25% of aluminum nitride and 2-4% of boron nitride. A bonding agent is added into the heat-conducting layer. The heat-insulating layer is prepared from raw materials with the following weight percentages: 65-75% of fused alumina, 5-8% of mullite, 6-11% of glass fiber and 14-16% of silicon nitride. A binding agent is added into the heat-insulating layer. Through cooperation of the heat-conducting layer and the heat-insulating layer, the anti-nodular performance of the submerged nozzle can be significantly improved, and the number of continuous casting furnaces for titanium-containing steel materials can be up to 16 or more.

Description

Technical Field

[0001] This application relates to the field of refractory materials technology, and more specifically, it relates to an anti-clogging submersible nozzle for continuous casting of special steel and its preparation method. Background Technology

[0002] Refractory materials for continuous casting are generally used to manufacture functional components such as submerged entry nozzles. Submerged entry nozzles serve functions such as guiding molten steel flow and are crucial components of continuous casting units. The main materials used for domestically produced submerged entry nozzles are fused silica, alumina-carbon, and zirconium-carbon.

[0003] Currently, the main body of the zirconium-carbon submerged entry nozzle used in domestic continuous casting mainly adopts Al2O3-C composite material, while the slag line section adopts ZrO2-C composite material. Because the Al2O3-C main material contains both C and SiO2 in high amounts, alumina easily forms on the inner wall of the nozzle, accelerating clogging.

[0004] In particular, the smelting of titanium-containing specialty steels requires more frequent nozzle replacements. Titanium-containing specialty steels contain nitrogen and titanium, resulting in molten steel containing CaO·TiO2 inclusions or CaO-TiO2-MgO-Al2O3 composite inclusions rich in CaO·TiO2. As the molten steel passes through the initial cooling layer, these inclusions accumulate and grow on the rough surface, forming dendritic blockages rich in CaO·TiO2.

[0005] Meanwhile, as the volume of the dendritic blockage increases, large-diameter gaps are formed in the blockage, causing the molten steel to stay briefly in the gaps. This allows TiN in the molten steel to precipitate out. The TiN-containing molten steel cools and solidifies on the surface of the blockage, resulting in severe blockage of the nozzle, molten steel flow deviation, and the entrainment of adhering materials, causing defects such as inclusions. Furthermore, the erosion caused by the protective slag added to the crystallizer results in significant melting loss.

[0006] Regarding the aforementioned technologies, traditional zirconium-carbon submerged entry nozzles can only ensure that the nozzles do not clog under the premise of continuously casting 3-4 heats of titanium-containing special steel with a throughput not exceeding 1000 tons. Therefore, how to improve the efficiency of continuous casting of titanium-containing special steel, especially given the limited number of heats and the tendency for submerged entry nozzles to clog, is a problem that urgently needs to be solved in this industry. Summary of the Invention

[0007] To address the issues of limited number of furnaces for continuous casting of titanium-containing special steels using submerged entry nozzles and the tendency for these nozzles to become clogged, this application provides an anti-clogging submerged entry nozzle for continuous casting of special steels and its preparation method.

[0008] Firstly, the anti-clogging submersible nozzle for continuous casting of special steel provided in this application adopts the following technical solution: A special steel continuous casting anti-clogging submersible nozzle includes a main body, which is composed of a heat-conducting layer and a heat-insulating layer connected sequentially from the inside to the outside, and the heat-conducting layer is in contact with the molten steel. The thermally conductive layer is made from the following raw materials by weight percentage: The material comprises 60-80% fused alumina, 4-11% silicon carbide, 14-25% aluminum nitride, and 2-4% boron nitride; a binder is added to the thermally conductive layer, and the binder accounts for 10-15% of the total weight of the thermally conductive layer materials. The insulation layer is made from the following raw materials by weight percentage: The insulation layer contains 65-75% fused alumina, 5-8% mullite, 6-11% glass fiber, and 14-16% silicon nitride; a binder is added to the insulation layer, and the binder accounts for 10-15% of the total weight of the insulation layer raw materials.

[0009] By adopting the above technical solution, the submerged entry nozzle, through the combination of its main structure and materials, can reduce the possibility of cold steel layer formation in the early stage of continuous casting and extend the formation time of cold steel layer in the later stage of continuous casting. The specific principle is as follows: The main body of the submerged entry nozzle is made into a double-layer structure. The layer in contact with the molten steel is a heat-conducting layer. Before use, the heat-conducting layer is preheated, and it evenly transfers heat to the inner wall of the main body, making the heat uniform. The insulation layer allows the inner wall of the main body to maintain a stable high temperature over a long period of time, and the temperature is close to that of the molten steel. When the molten steel comes into contact with the nozzle, the temperature difference between the two is small, and the molten steel is not easily cooled on the inner wall of the nozzle.

[0010] The heat-conducting layer is modified with silicon carbide, aluminum nitride, and boron nitride. Silicon carbide has a high thermal conductivity, enabling rapid and uniform heat distribution, resulting in a more uniform temperature throughout the heat-conducting layer. Simultaneously, aluminum nitride can sinter with alumina in a nitrogen atmosphere to form an aluminum oxynitride phase. This phase enhances the heat resistance of the heat-conducting layer, increases the preheating temperature of the nozzle, maintains a high temperature at the nozzle, and reduces the likelihood of TiN, TiO2, and complex titanium oxides precipitating upon cooling. The presence of aluminum oxynitride and boron nitride in the heat-conducting layer effectively reduces the wettability of molten steel, thus mitigating the adhesion of alumina, titanium oxide, and composite inclusions. This further reduces the possibility of inclusions adhering and forming nodules on the inner wall of the nozzle. After melting at high temperatures, boron nitride forms low-melting-point boron oxide, which further fills some unsealed pores, further preventing inclusions in the molten steel from adsorbing onto the inner wall of the nozzle.

[0011] The insulation layer is made of mullite, glass fiber, and silicon nitride modified corundum. The insulation layer has a low thermal conductivity and plays a good role in heat insulation. It can effectively reduce the possibility of heat loss from the heat-conducting layer. When combined with the heat-conducting layer, it can prolong the time for molten steel to condense and form nodules.

[0012] In addition, the choice of mullite, glass fiber, and silicon nitride for the insulation layer enhances the bonding strength between the thermally conductive and insulating layers. Secondly, the alumina nitride phase formed by aluminum nitride and alumina improves the pore structure between silicon carbide particles, thus compensating for the strength reduction caused by high silicon carbide addition levels, resulting in superior thermal shock resistance of the thermally conductive layer. Simultaneously, during high-temperature sintering, the mullite and silicon carbide particles undergo rearrangement and bonding at high temperatures, with liquid phase filling the spaces between the mullite particles, leading to increased density of the insulation layer upon cooling. Therefore, the overall thermal shock resistance of the submerged gate is significantly improved.

[0013] In summary, this application has improved the structure and materials of the main body, giving the submersible gate excellent anti-clogging and thermal shock resistance characteristics.

[0014] Preferably, the weight percentages of each raw material in the heat-conducting layer are as follows: fused alumina 65-67%, silicon carbide 6-10%, aluminum nitride 20-25%, and boron nitride 3-4%.

[0015] Preferably, the weight percentages of the raw materials in the insulation layer are as follows: fused alumina 65-70%, mullite 6-7%, glass fiber 8-10%, and silicon nitride 15%.

[0016] By adopting the above technical solution and optimizing the ratio of the heat-conducting layer and the insulating layer, the anti-nodulation performance and thermal shock resistance of the immersion nozzle can be significantly improved.

[0017] Preferably, the aluminum nitride particle size in the thermally conductive layer is 3-5 μm.

[0018] By adopting the above technical solution and selecting aluminum nitride with a suitable particle size, it can be well dispersed and fully dispersed in the raw materials, thereby further improving the thermal shock resistance of the submerged nozzle.

[0019] Preferably, the amount of adhesive added is 12-13%, and the amount of binder added is 12-13%.

[0020] By adopting the above technical solution, the adhesive and binder in this application can be the same or different. The selection of adhesive and binder includes, but is not limited to, one or more of phenolic resin and dextrin. This application optimizes the addition amount of adhesive and binder to ensure uniform mixing of raw materials without reducing the bonding strength between the thermally conductive layer and the thermally insulating layer.

[0021] Preferably, the thickness ratio of the heat-conducting layer to the heat-insulating layer is 1:(2-3).

[0022] Secondly, this application provides a method for preparing an anti-clogging submersible nozzle for continuous casting of special steel, using the following technical solution: A method for preparing an anti-clogging submersible nozzle for continuous casting of special steel includes the following steps: Prepare the raw materials for the heat-conducting layer and the heat-insulating layer. Grind and crush the raw materials to below 150 mesh and sieve them for later use. The above raw materials are mixed according to the formula to obtain a heat-conducting layer and a heat-insulating layer. Then, an adhesive is added to the heat-conducting layer according to the formula, and an adhesive is added to the heat-insulating layer. The mixture is then pressed into a brick blank under a pressure of 50-100 MPa. The brick blanks are heated to 600-700℃ in a nitrogen atmosphere and fired once for 2-3 hours; then heated to 1660-1800℃ and fired a second time for 2-4 hours to obtain the submerged sprue finished product.

[0023] By adopting the above technical solution, the preparation method of the submerged nozzle in this application is simple. The submerged nozzle can maintain a high temperature during the preheating stage, reduce the possibility of nodule formation on the inner wall of the nozzle in the early stage, and extend the number of continuous casting furnaces.

[0024] Preferably, the secondary calcination temperature of the brick blank is 1700-1750℃, and the calcination is maintained at this temperature for 2-3 hours.

[0025] By adopting the above technical solution, the calcination temperature and calcination time in this application are optimized so that most of the aluminum nitride is transformed into nitrogen-rich aluminum oxide phase, thereby further improving the anti-clogging performance of the submersible nozzle.

[0026] In summary, this application has the following beneficial effects: In this application, the submerged nozzle is made into a double-layer structure, in which the heat-conducting layer in contact with the molten steel conducts heat rapidly, and the heat-insulating layer can prolong the heat dissipation time, so that the inner wall of the submerged nozzle can maintain a high temperature for a long time after preheating treatment, which can prolong the time for the molten steel to cool and form nodules. Detailed Implementation

[0027] Currently, submerged entry nozzles (SINs) for continuous casting of special steels are generally made of zirconium-carbon composite material, specifically using Al2O3-C composite material as the main material and ZrO2-C composite material for the slag line. This zirconium-carbon SIN material is unsuitable for smelting titanium-containing special steels because titanium-containing special steels contain CaO·TiO2 inclusions or CaO-TiO2-MgO-Al2O3 composite inclusions rich in CaO·TiO2, which easily deposit on the inner wall material of the SIN. Furthermore, TiN in the molten steel can precipitate during casting, leading to severe nozzle blockage. Experiments have shown that traditional zirconium-carbon SIN nozzles can only be used for 3-4 continuous casting heats, with a throughput not exceeding 1000 tons.

[0028] To address the aforementioned issues, the applicant conducted research on the structure, materials, and preparation methods of submerged entry nozzles. The findings revealed that the main body of the submerged entry nozzle is constructed with a double-layer structure. The layer in contact with the molten steel is a heat-conducting layer. Before use, the heat-conducting layer is preheated, uniformly transferring heat to the inner wall of the main body, ensuring uniform heat distribution. The insulating layer allows the inner wall of the main body to maintain a stable high temperature over a long period, closely matching the temperature of the molten steel. When the molten steel contacts the nozzle, the temperature difference between them is small, making it difficult for the molten steel to cool on the inner wall of the nozzle. This reduces the likelihood of cold steel layer formation in the early stages of continuous casting and prolongs the formation time of the cold steel layer in the later stages of continuous casting.

[0029] The thermally conductive layer is modified with silicon carbide, aluminum nitride, and boron nitride. These three materials have a synergistic effect in terms of anti-clogging and thermal shock resistance. Silicon carbide has a high thermal conductivity, which can quickly and evenly distribute heat, resulting in a more uniform temperature throughout the thermally conductive layer. At the same time, aluminum nitride can sinter with alumina in a nitrogen atmosphere to form an aluminum oxynitride phase. The aluminum oxynitride phase can improve the heat resistance of the thermally conductive layer, increase the preheating temperature of the gate, keep the gate at a high temperature, and reduce the possibility of TiN, TiO2, and complex titanium oxides precipitating when cooled.

[0030] Secondly, the alumina oxynitride phase, being granular, effectively fills the pores between the long, whisker-like silicon carbide particles and the lamellar boron nitride particles, thus compensating for the strength reduction caused by high additions of silicon carbide and boron nitride, resulting in superior thermal shock resistance. Furthermore, the presence of alumina oxynitride and boron nitride in the thermally conductive layer effectively reduces the wettability of molten steel on this layer, thereby mitigating the likelihood of alumina, titanium oxide, and composite inclusions adhering to it. This further reduces the possibility of inclusions adhering and forming nodules on the inner wall of the nozzle.

[0031] Finally, boron nitride melts at high temperature to form low-melting-point boron oxide, which further fills some unsealed pores, thus further preventing inclusions in the molten steel from adsorbing onto the inner wall of the nozzle.

[0032] The insulation layer is made of mullite, glass fiber, and silicon nitride to modify corundum. The combined effect of mullite, glass fiber, and silicon nitride enhances the adhesion strength between the heat-conducting layer and the insulation layer. At the same time, the thermal conductivity of the insulation layer is significantly reduced, providing better heat insulation and effectively reducing the possibility of heat loss from the heat-conducting layer. In conjunction with the heat-conducting layer, it can prolong the time for molten steel to solidify and form nodules.

[0033] Secondly, during high-temperature sintering of mullite and silicon carbide, the high temperature promotes the rearrangement and bonding between particles, and the liquid phase fills the spaces between mullite particles, increasing the density of the insulation layer upon cooling. Simultaneously, the fibrous structure of glass fiber provides numerous stress dispersion points within the insulation layer, enabling the main material to possess superior toughness and excellent thermal shock resistance.

[0034] Therefore, this application successfully solves the technical problem. It also successfully improves the thermal shock stability of submersible nozzles.

[0035] Unless otherwise specified, the Al2O3 content of fused alumina in the following examples and comparative examples is ≥99%; Aluminum nitride powder is available in the following three specifications: Particle size 3-5μm, brand name Destek040M; Particle size 40-80 nm, grade XT-AlN; Particle size 15μm, grade XC-1083; Fiberglass: Grade A, Item No. 210; Boron nitride is hexagonal boron nitride with a particle size of 5–15 μm; Both the adhesive and the binder are phenolic resins, purchased from Jinan Dahui Chemical Technology Co., Ltd., brand name 2123. Example

[0036] Example 1 A special type of anti-clogging submersible nozzle for continuous casting of steel, the formula of which is as follows: The total weight of the thermal conductive layer raw materials is calculated as 100 parts, of which 60 parts are fused alumina, 11 parts are silicon carbide, 14 parts are aluminum nitride, and 22 parts are boron nitride; the amount of phenolic resin added as the adhesive is 8 parts. The total weight of the insulation layer raw materials is calculated as 100 parts, including 65 parts of fused alumina, 8 parts of mullite, 11 parts of glass fiber, and 16 parts of silicon nitride; the amount of phenolic resin added as the adhesive is 11 parts.

[0037] It is prepared according to the following method: The fused alumina, silicon carbide, aluminum nitride, boron nitride, mullite, and silicon nitride were all ground and crushed until the particle size of each raw material was below 150 mesh. Among them, aluminum nitride XC-1083 was selected and sieved for later use. According to the formula of the heat-conducting layer, select raw materials and mix them to obtain the heat-conducting layer material; after weighing, calculate the weight of the adhesive according to the proportion, add the adhesive to the main material, stir and mix to obtain the pre-formed heat-conducting layer; According to the insulation layer formula, select raw materials and mix them to obtain insulation layer material; after weighing, calculate the weight of adhesive according to the proportion, add adhesive to the insulation layer material, stir and mix to obtain pre-formed insulation layer. The pre-formed heat-conducting layer and the pre-formed heat-insulating layer are bonded together at a thickness ratio of 1:1, then placed in a mold and pressed into a brick blank under a pressure of 100MPa. The brick blanks are heated to 600℃ and calcined for 3 hours in a nitrogen atmosphere; then heated to 1660℃ and calcined for 4 hours to obtain the submerged sprue finished product.

[0038] Examples 2-7 A special steel continuous casting anti-clogging immersion nozzle differs from Example 1 in that the raw material composition of the insulation layer and the heat-conducting layer are different, as shown in Table 1 below.

[0039] Table 1. Composition of the main body Example 8 A special steel continuous casting anti-clogging submersible nozzle differs from Example 5 in that it uses an equal weight of aluminum nitride with a particle size of 3-5 μm to replace aluminum nitride with a particle size of 15 μm.

[0040] Example 9 A special steel continuous casting anti-clogging immersion nozzle differs from Example 5 in that it uses an equal weight of aluminum nitride with a particle size of 40-80 nm to replace aluminum nitride with a particle size of 15 μm.

[0041] Examples 10-12 A special type of anti-clogging submersible nozzle for continuous casting of special steel differs from Example 8 in that the amount of adhesive and binder added is different, as detailed below: In Example 10, the amount of both adhesive and binder added was 12 parts; In Example 11, the amount of both adhesive and binder added was 13 parts; In Example 12, the amount of adhesive and binder added was 15 parts each.

[0042] Examples 13-15 A special type of anti-clogging submersible nozzle for continuous casting of special steel differs from Example 11 in that the processing parameters are different, as detailed below: In Example 13, the brick blank was heated to 600°C and held at that temperature for 3 hours under a nitrogen atmosphere; then heated to 1700°C and held at that temperature for 3 hours to obtain the submerged sprue finished product. In Example 14, the brick blank was heated to 600°C and held at that temperature for 3 hours under a nitrogen atmosphere; then heated to 1750°C and held at that temperature for 2 hours to obtain the submerged sprue finished product. In Example 15, the brick blank was heated to 700°C and held at that temperature for 2 hours under a nitrogen atmosphere; then heated to 1800°C and held at that temperature for 2 hours to obtain the submerged sprue finished product. Examples 16-18 A special steel continuous casting anti-clogging submersible nozzle differs from Example 14 in that the thickness ratio of the heat-conducting layer and the insulation layer is different, as detailed below; In Example 16, the thickness ratio of the heat-conducting layer to the heat-insulating layer is 1:2; In Example 17, the thickness ratio of the heat-conducting layer to the heat-insulating layer is 1:3; In Example 18, the thickness ratio of the heat-conducting layer to the heat-insulating layer is 1:4.

[0043] Comparative Example Comparative Example 1 The difference between this type of submerged entry nozzle for continuous casting of special steel and Example 1 is that it uses an insulation layer of equal thickness instead of a heat-conducting layer.

[0044] Comparative Example 2 The difference between this type of submersible nozzle for continuous casting of special steel and Example 1 is that a heat-conducting layer of equal thickness is used instead of an insulation layer.

[0045] Comparative Examples 3-8 A special steel continuous casting submersible nozzle differs from Example 1 in that the raw material composition of the insulation layer and the heat-conducting layer are different, as shown in Table 2 below: Table 2. Composition of the main body Performance testing 1. Under normal temperature and pressure conditions, the mechanical properties of the immersion nozzle samples prepared in Examples 1-18 and Comparative Examples 1-8 were tested.

[0046] 2. Application tests were conducted on the special steel production line of a steelmaking plant. Submerged nozzle samples prepared using the examples and comparative examples of this application were used, while the blank control sample was a conventional zirconium-carbon nozzle (the main body was made of Al2O3-C composite material, and the slag line part was made of ZrO2-C composite material).

[0047] The following steel grade was tested: 20MnTiB.

[0048] Test results Table 3. Mechanical properties of immersed nozzle samples Application testing: Different submerged nozzle samples were used for casting 20MnTiB steel with a throughput of 1000 tons: Table 4. Casting performance of immersion nozzle samples " / " indicates that the water inlet cannot be detected or is completely blocked.

[0049] Test results This application performs a single comparison of Example 1, Comparative Examples 1-8, and the blank control group, and in conjunction with Tables 3-4, the following results can be obtained: First, the test results of Example 1, Comparative Examples 1-2 and the blank control group show that the use of a thermally conductive layer and an insulating layer in this application can achieve better internal heat conduction and external heat insulation, thereby increasing the number of continuous casting furnaces of the submerged nozzle. After 10 continuous casting furnaces, the average thickness of the nodule is no more than 3.07 mm. Second, comparing the test results of Example 1, Comparative Examples 3-5 and the blank control group, it can be seen that the thermal conductive layer material of this application is modified by a combination of silicon carbide, aluminum nitride and boron nitride, which can also have a synergistic effect in improving the thermal shock resistance and anti-nodulation performance of the immersion gate. Third, the test results of comparing Example 1, Comparative Examples 6-8 and the blank control group show that the use of mullite, glass fiber and silicon nitride in the insulation layer material of this application can significantly improve its thermal shock resistance.

[0050] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A special steel continuous casting anti-clogging submersible nozzle, comprising a main body, characterized in that: The main body consists of a heat-conducting layer and a heat-insulating layer connected sequentially from the inside out. The heat-conducting layer is in contact with molten steel. The heat-conducting layer is made from the following raw materials by weight percentage: 60-80% fused alumina, 4-11% silicon carbide, 14-25% aluminum nitride, and 2-4% boron nitride. A binder is added to the main body material, and the binder accounts for 10-15% of the total weight of the heat-conducting layer raw materials. The heat-insulating layer is made from the following raw materials by weight percentage: 65-75% fused alumina, 5-8% mullite, 6-11% glass fiber, and 14-16% silicon nitride. An adhesive is added to the heat-insulating layer, and the adhesive accounts for 10-15% of the total weight of the heat-insulating layer raw materials.

2. The anti-clogging submersible nozzle for continuous casting of special steel according to claim 1, characterized in that: The weight percentages of each raw material in the heat-conducting layer are as follows: fused alumina 65-67%, silicon carbide 6-10%, aluminum nitride 20-25%, and boron nitride 3-4%.

3. The anti-clogging submersible nozzle for continuous casting of special steel according to claim 1, characterized in that: Fused alumina 65-70%, mullite 6-7%, glass fiber 8-10%, silicon nitride 15%.

4. The anti-clogging submersible nozzle for continuous casting of special steel according to claim 2, characterized in that: The aluminum nitride particles in the thermally conductive layer have a particle size of 3–5 μm.

5. The anti-clogging submersible nozzle for continuous casting of special steel according to claim 1, characterized in that: The amount of adhesive added is 12-13%, and the amount of binder added is 12-13%.

6. The anti-clogging submersible nozzle for continuous casting of special steel according to claim 1, characterized in that: The thickness ratio of the heat-conducting layer to the heat-insulating layer is 1:(2-3).

7. A method for preparing an anti-clogging submersible nozzle for continuous casting of special steel according to any one of claims 1-6, characterized in that: The process includes the following steps: Prepare the raw materials for the heat-conducting layer and the insulation layer. Grind and crush the raw materials to below 150 mesh and sieve them for later use. Mix the above raw materials according to the formula to obtain the heat-conducting layer and the insulation layer respectively. Then, add the binder to the heat-conducting layer and the adhesive to the insulation layer according to the formula, and press them into brick blanks under a pressure of 50-100 MPa. The brick blanks are heated to 600-700℃ in a nitrogen atmosphere and calcined once for 2-3 hours. Then, they are heated to 1660-1800℃ and calcined a second time for 2-4 hours to obtain the submersible sprue finished product.

8. The method for preparing an anti-clogging submersible nozzle for continuous casting of special steel according to claim 7, characterized in that, The secondary calcination temperature of the brick blank is 1700-1750℃, and the calcination is maintained at this temperature for 2-3 hours.

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