Castable refractory composition and manufacturing method

Abstract

The manufacturing method of accessories made of basic refractories in a steel tundish includes a preparation step, a mixing step, a mold filling step, and a forming step. The mixing step is to mix dead-burned magnesia sand, olivine sand, and a binder prepared in the preparation step according to a specific ratio to obtain a castable refractory composition. The mold filling step is to mix the castable refractory composition and water according to a specific ratio for molding and fill the mold. Finally, the forming step is to demold and dry to obtain a refractory unit.

Description

Technical Field

[0001] The present invention relates to castable refractory compositions, shaped refractory units, sintered refractory units and related manufacturing methods and uses, and in particular to a method for manufacturing accessories using basic refractories in a steel tundish.

Background Art

[0002] A steel tundish is known to be an essential and important container in the continuous casting process of molten steel. The steel tundish is mainly used to stabilize the flow of molten steel and to realize the functions of dividing the flow of molten steel and ensuring the continuous casting of molten steel without interruption of the flow. Generally, refractory units such as slag retaining walls are prepared in the steel tundish. The refractory unit makes the temperature of the molten steel uniform, changes the flow direction of the molten steel, promotes the floating, collision and aggregation of inclusions, thereby reducing the inclusion uptake into the steel billet, bloom or slab, and thereby improving the cleanliness of the molten steel. Since the refractory unit needs to be immersed in the high-temperature molten steel for a long time, it must have good supporting ability and erosion resistance.

[0003] Currently, common refractory units are mainly manufactured from aluminosilicates. However, after actual use, the above aluminosilicate units are easily eroded by the slag in the steel tundish, and as a result, it can be seen that inclusions are easily formed by the aluminosilicate units during the working process and taken into the cast steel (for example, steel billet, bloom or slab). This causes contamination of the molten steel by the aluminosilicate units, leading to the defect of insufficient cleanliness of the molten steel. When the aluminosilicate unit is directly exposed to erosion by high-temperature molten steel and strong thermal stress, the possibility of deformation, perforation, cracking or collapse increases, so this truly needs to be improved.

Summary of the Invention

Problems to be Solved by the Invention

[0004] One object of the present invention is to improve the supporting ability and erosion resistance of refractory units. Another object of the present invention is to provide a refractory unit that can effectively absorb impurities such as alumina particles, thereby improving the cleanliness of molten steel.

[0005] Another object is to provide a method for manufacturing accessories using basic refractories in a steel tundish. By this manufacturing method, the supporting ability and erosion resistance of magnesia refractory units are significantly improved, and the magnesia refractory units can effectively absorb aluminum, thereby improving the cleanliness of molten steel.

Means for Solving the Problems

[0006] According to a first aspect, the castable refractory composition contains 30 to 50% by weight of dead-burned magnesia sand, 40 to 60% by weight of olivine sand, and 2.5 to 10% by weight of a binder. It should be understood that the total weight of the castable refractory composition is 100% by weight or less.

[0007] The castable refractory composition can contain 35 to 45% by weight or 37 to 43% by weight or 40 to 50% by weight or 40 to 45% by weight or 45 to 50% by weight of dead-burned magnesia sand. Dead-burned magnesia sand is sometimes known as dead-burned magnesia or dead-burned magnesite (i.e., dead-burned MgO). The dead-burned magnesia sand can have a purity of about 90 wt% or more of MgO. The dead-burned magnesia sand can have a particle size of 400 mesh or less or 200 mesh or less. The dead-burned magnesia sand can have a particle size of 10 mesh or more or 14 mesh or more.

[0008] The castable refractory composition can contain 40 to 50% by weight of olivine sand, for example, 42 to 48% by weight of olivine sand. The olivine sand can have a particle size of about 10 mm or less, for example, about 5 mm or less. The olivine sand can have a particle size of about 500 μm or more, for example, about 1 mm or more.

[0009] The castable refractory composition can contain 2.5 to 7.5 wt% of a binder or 5 to 10 wt% of a binder. The binder can be a hydration binder, a chemical binder, an organic binder, an adhesive binder or a ceramic binder. The binder can be a cement-based binder or a cement-free binder. The binder can be a magnesium-based binder (e.g., magnesium sulfate or magnesium phosphate), a calcium-based binder (e.g., calcium aluminate), a sodium-based binder (e.g., sodium silicate), a potassium-based binder (e.g., potassium silicate) or an aluminum-based binder (e.g., aluminum phosphate or aluminum sulfate). The binder can be a phosphate (e.g., magnesium phosphate or aluminum phosphate), a sulfate (e.g., magnesium sulfate) or a silicate (e.g., potassium silicate or sodium silicate), or can contain these. In some examples, the binder is magnesium sulfate. In some examples, the binder is fumed silica. In some examples, the binder contains aluminum sulfate, boric acid and citric acid.

[0010] The castable refractory composition can include a deflocculant. A deflocculant may also be known as a dispersant or a plasticizer. The deflocculant can assist in the subdivision and / or dispersion of particles when the castable refractory composition is mixed with water in the forming process. Thus, the use of a deflocculant can enable effective subdivision of the micropowder during the mixing process, and the fine particles can be filled into the pores by the mixing process, thereby reducing the surface pores of the resulting refractory unit. This can not only significantly improve the support capacity and erosion resistance of the refractory unit, but also enable the magnesia refractory unit to effectively absorb aluminum during the working process, thereby improving the cleanliness of the molten steel. The deflocculant can be a sulfate such as magnesium sulfate or a phosphate such as sodium hexametaphosphate. The castable refractory composition can include less than 1 wt%, for example less than 0.5 wt%, of the deflocculant. In some examples, the castable refractory composition includes at least about 0.01 wt%, for example, 0.01 - 1 wt% or 0.01 - 0.5 wt%, of the deflocculant. In other examples, the castable refractory composition is essentially free of the deflocculant. For example, the castable refractory composition can include at most about 0.01%, for example, at most about 0.005 wt%, of the deflocculant.

[0011] In some examples, the binder can function as a deflocculant. For example, magnesium sulfate can function as both a binder and a deflocculant. In such examples, only a portion of the binder may function as a deflocculant. For example, a sufficient portion of the binder may function as a deflocculant such that the entire composition can be considered to contain less than 1 wt% of the deflocculant.

[0012] The castable refractory composition can include a water hydration inhibitor. The water hydration inhibitor can act to coat the particles of the castable refractory composition to reduce (e.g., prevent) water absorption. In particular, the water hydration inhibitor can act to reduce water absorption by MgO. The water hydration inhibitor can be a carboxylic acid (such as oleic acid, stearic acid, citric acid, or lactic acid) or a salt of a carboxylic acid. For example, the water hydration inhibitor can be a lactate such as aluminum lactate. The castable refractory composition can include less than 1 wt%, for example less than 0.5 wt%, of the water hydration inhibitor. In some examples, the castable refractory composition can include at least about 0.01 wt%, for example, 0.01 - 1 wt% or 0.01 - 0.5 wt% of the water hydration inhibitor. In other examples, the castable refractory composition is essentially free of the water hydration inhibitor. For example, the castable refractory composition can include at most about 0.01%, for example, at most about 0.005 wt% of the water hydration inhibitor.

[0013] In addition to dead-burned magnesia sand and olivine sand, the castable refractory composition can further include one or more refractory aggregate materials. The one or more refractory aggregate materials can include one or more of alumina, bauxite, spinel, granite, basalt, emery, chamotte, morokite, sillimanite, gibbsite, vermiculite, diatomaceous earth, and perlite. For example, the one or more refractory aggregate materials can include alumina, bauxite, and / or spinel. The alumina can be reactive alumina or semi-reactive alumina. The castable refractory composition can include up to about 20 wt% or up to about 10 wt% of the one or more refractory aggregate materials. The castable refractory composition can include at least about 1 wt% or at least about 5 wt% of the one or more refractory aggregate materials. The castable refractory composition can include 1 - 20 wt%, for example, 1 - 10 wt% or 5 - 10 wt% of the one or more refractory aggregate materials.

[0014] The castable refractory composition can further include one or more additives in addition to the deflocculant and / or water prevention agent described above in this specification. For example, the castable refractory composition can include one or more drying aids, such as fibers like organic fibers and / or metal fibers that can melt, decompose, and / or react at a temperature of less than about 150 °C or less than about 100 °C. It will be understood that the fibers can assist in achieving heating of the refractory without cracking. After melting and / or decomposition of the fibers, the pore network structure can remain to facilitate the transport and evaporation of water from the refractory (e.g., MgO).

[0015] The aluminum oxide (Al2O3) contained in the castable refractory composition can be less than 10% by weight. The castable refractory composition can include 45 - 75% magnesium oxide (MgO), 25 - 35% silicon dioxide (SiO2), less than 8% aluminum oxide (Al2O3), less than 5% iron(III) oxide (Fe2O3), and 1.5% or less calcium oxide (CaO).

[0016] The castable refractory composition can be a basic (i.e., alkaline) refractory composition.

[0017] According to a second aspect, a method for manufacturing a refractory unit sequentially includes a preparation step, a mixing step, a mold filling step, and a forming step. In the preparation step, dead-burned magnesia sand, olivine sand, and a binder are prepared. In the mixing step, 30 - 50% by weight of dead-burned magnesia sand, 40 - 60% by weight of olivine sand, and 2.5 - 10% by weight of the binder are mixed to obtain a castable refractory composition. In the mold filling step, the above castable refractory composition and 5 - 10% by weight of water are poured into a mold. In the forming step, demolding and drying are performed to obtain a refractory unit.

[0018] The castable refractory composition can have any of the features (e.g., components and relative amounts of components) described above in this specification with respect to the first aspect.

[0019] The mixing step may include uniformly mixing the components to obtain a castable refractory composition.

[0020] Drying of the refractory unit can be carried out at a temperature above 300 °C. After drying, the refractory unit can be sintered. Sintering of the refractory unit can be carried out at a temperature above 1300 °C.

[0021] The refractory unit can be a refractory unit for use in a tundish for steelmaking. For example, the refractory unit can be a retaining wall (e.g., a dam or a weir), a flow nozzle, or a corner brick. The refractory unit may also be known as a magnesia refractory unit.

[0022] According to a third aspect, a method for manufacturing an accessory using a basic refractory in a steel tundish of the present invention sequentially includes a preparation step, a mixing step, a mold filling step, and a forming step. In the preparation step, dead-burned magnesia sand, olivine sand, a binder, a deflocculant, and a water repellent are prepared. In the mixing step, 30 to 50 wt% of dead-burned magnesia sand, 40 to 60 wt% of olivine sand, 5 to 10 wt% of the binder, less than 1 wt% of the deflocculant, and less than 1 wt% of the water repellent are uniformly mixed to obtain a magnesia castable refractory, and the aluminum oxide (Al2O3) contained in the magnesia castable refractory is less than 10 wt%. In the mold filling step, a mold is prepared and the magnesia castable refractory and 5 to 10 wt% of water are poured into the mold for forming. In the forming step, demolding and drying are carried out to obtain a magnesia refractory unit.

[0023] Thus, the particles are coated with the water repellent, the micropowder is effectively subdivided by the deflocculant during the mixing process, the fine particles are filled into the pores by the mixing process, thereby reducing the surface pores of the magnesia refractory unit. As a result, not only is the support capacity and erosion resistance of the magnesia refractory unit significantly improved, but the magnesia refractory unit can effectively absorb aluminum during the working process, thereby improving the cleanliness of the molten steel.

[0024] According to a fourth aspect, there is provided a shaped refractory unit obtainable or obtained by the method according to the second or third aspect. The shaped refractory unit may be dried (i.e., it may be a dried refractory unit), but generally is not sintered. The shaped refractory unit may be in a state where it can be used, for example, in a tundish during steelmaking.

[0025] According to a fifth aspect, there is provided a sintered refractory unit obtainable or obtained by sintering the shaped refractory unit according to the fourth aspect. The sintered refractory unit may be in a state where it can be used, for example, in a tundish during steelmaking.

[0026] According to a sixth aspect, there is provided the use of a shaped refractory unit according to the fourth aspect or a sintered refractory unit according to the fifth aspect as a refractory accessory such as a slag retaining wall in a tundish during steelmaking to improve the cleanliness of molten steel. By using the shaped refractory unit or the sintered refractory unit, the cleanliness of the molten steel can be improved compared to the molten steel treated in the tundish using corresponding refractory units made from different refractory compositions not according to the present invention. The shaped refractory unit or the sintered refractory unit can be used to absorb impurities such as alumina from the steel.

[0027] According to a third aspect, the subject matter described in the following numbered paragraphs is provided. 1. A method for manufacturing an accessory made of basic refractory in a steel tundish, comprising: a preparation step of preparing dead-burned magnesia sand, olivine sand, a binder, a deflocculant, and a water repellent; A mixing step of uniformly mixing 30 to 50% by weight of dead-burned magnesia sand, 40 to 60% by weight of olivine sand, 5 to 10% by weight of a binder, less than 1% by weight of a deflocculant, and less than 1% by weight of a hydration inhibitor to obtain a magnesia castable refractory, wherein the aluminum oxide (Al2O3) contained in the magnesia castable refractory is less than 10% by weight. As a result, the particles are coated with the hydration inhibitor, the micropowder is subdivided by the deflocculant during the mixing process, and the fine particles are filled into the pores by the mixing process, thereby reducing the surface pores. A mold filling step of preparing a mold and pouring the magnesia castable refractory and 5 to 10% by weight of water into the mold for molding. A molding step of performing demolding on the mold to obtain a magnesia refractory unit, allowing the magnesia refractory unit to stand and dry, and installing it in a steel tundish for use. A manufacturing method including the above steps. 2. A method for manufacturing an accessory using a basic refractory in a steel tundish according to paragraph 1, wherein the main chemical composition of the magnesia castable refractory is 45 to 75% magnesium oxide (MgO), 25 to 35% silicon dioxide (SiO2), less than 8% aluminum oxide (Al2O3), less than 5% iron(III) oxide (Fe2O3), and 1.5% or less calcium oxide (CaO). 3. A method for manufacturing an accessory using a basic refractory in a steel tundish according to paragraph 1, wherein the magnesia refractory unit can be a retaining wall, a flow nozzle, or a corner brick.

[0028] Those skilled in the art will understand that, unless mutually exclusive, the features described in connection with any one of the above aspects can be applied to any other aspect with the necessary modifications. Further, unless mutually exclusive, any feature described in this specification can be applied to any aspect and / or combined with any other feature described in this specification.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0030] The above and other technical contents, features, and effects of the present invention will become clear from the following detailed description of the preferred embodiments with reference to the drawings.

[0031] As shown in FIG. 1, an exemplary embodiment of a method for manufacturing accessories made of basic refractories in the steel tundish 3 of the present invention includes a preparation step 31, a mixing step 32, a mold filling 33, and a forming step 34. In the preparation step 31, dead-burned magnesia sand, olivine sand, a binder, a deflocculant, and a hydration inhibitor are prepared. In the mixing step 32, 49% by weight of dead-burned magnesia sand, 45% by weight of olivine sand, 5% by weight of a binder, less than 1% by weight of a deflocculant, and less than 1% by weight of a hydration inhibitor are uniformly mixed to obtain 100% by weight of a magnesia castable refractory. The chemical composition of the magnesia castable refractory by ratio is such that the aluminum oxide (Al2O3) contained in the magnesia castable refractory is less than 10% by weight, with 45 - ⑦5% magnesium oxide (MgO), 25 - 35% silicon dioxide (SiO2), less than 8% aluminum oxide (Al2O3), less than 5% iron(III) oxide (Fe2O3), and 1.5% or less calcium oxide (CaO).

[0032] Next, in the mold filling step 33, a mold whose shape can be adjusted according to the shape of the unit to be formed is prepared. Then, the magnesia castable refractory obtained in the mixing step 32 and 6.2% by weight of water are mixed, and poured into the mold so that the magnesia castable refractory and water are mixed, and formed. Finally, in the forming step 34, demolding is performed on the above mold, and a magnesia refractory unit is obtained after taking it out of the mold.

[0033] It should be noted that there seems to be an error in the "⑦5%" in the original text. It is likely a typo and should be something like "75%". This translation has been done based on the provided text as accurately as possible.The magnesia refractory unit may be an accessory that is provided in the steel tundish and needs to come into contact with the molten steel, such as a retaining wall, a flow nozzle or a corner brick, and the magnesia refractory unit can be installed in the steel tundish for use after drying.

[0034] In an exemplary embodiment in which the fire resistant composition includes a peptizer and a hydration inhibitor, the d 50 The micropowder (having a particle size of about 0.1 mm) is effectively pulverized by the peptizer during the mixing process, the particles are completely coated with the anti-hydration agent, and the fine particles (having a particle size of about 0.1 mm) are filled into the pores during the mixing process, thereby reducing the surface pores of the magnesia refractory unit after molding. As a result, the erosion resistance of the magnesia refractory unit is greatly improved. Furthermore, the magnesia refractory unit does not have cracks after drying, is easily demolded, and has good processability and strength. Furthermore, after testing and evaluation, as well as pre-casting, filling, and molding, mass production of magnesia refractory units can be made feasible, thereby further increasing market competitiveness. Furthermore, the magnesia refractory unit can be hung and installed after completion, and can be used in very good condition.

[0035] After completion, the magnesia refractory unit was subjected to a fracture test (MOR) and a compression test (CCS). The fracture test showed a fracture strength of 7.0 N / mm 2 The compression test was 30.0N / mm 2 That is, the magnesia refractory unit has a high early strength.

[0036] After the crucible test of the magnesia refractory unit, the results show that the erosion rate is 2.1% and the permeability is 8.9%, which is better than the results of the crucible test of the conventional aluminosilicate refractory unit (erosion rate 18.9%, permeability 16.1%), which indicates that the magnesia refractory unit has better erosion and infiltration resistance capabilities.

[0037] In the hydration test, the magnesia refractory unit was completely immersed in water, covered, and then left at a constant temperature of 80 °C for 240 hours. The results showed that the weight gain rate of the magnesia refractory unit was 2.3%, the breaking test increased by 3.7%, the compression test increased by 16.4%, and the magnesia refractory unit had no cracks after the hydration test, that is, the magnesia refractory unit had good anti-hydration ability and was very stable. Furthermore, after the magnesia refractory unit was dried at 110 °C for 24 hours and then stored at room temperature for 40 days, there was no obvious change in strength. The test results are as follows.

[0038]

Table 1

[0039] The enlarged photograph of the magnesia refractory unit is shown in Figure 2. The residual massive components and composition analysis of the magnesia refractory unit are as follows.

Table 2

[0040]

Table 3

[0041] From the above, it can be seen that before use, the magnesia refractory unit initially contains less than 8 wt% aluminum oxide (Al2O3), but the aluminum oxide (Al2O3) content in both the slag line area and the molten steel area is higher than 8 wt%. Thereby, the magnesia refractory unit can effectively absorb aluminum (Al) during the working process, and as shown in the above magnified photograph, it is further proved that magnesium aluminum spinel (MgAl2O4) is formed. Furthermore, the inclusion uptake into the steel billet is significantly reduced, thereby further improving the cleanliness of the molten steel, and the magnesia refractory unit has good erosion resistance and support capacity. Moreover, the magnesia refractory unit can be effective in reducing the defect rate of steel products. The cost of the magnesia refractory unit is slightly high, but by reducing the thickness of the magnesia refractory unit and further reducing the overall cost while maintaining sufficient support capacity and erosion resistance, the market competitiveness can be enhanced.

[0042] In short, according to the method for manufacturing accessories with basic refractories in the steel tundish of the present invention, in the preparation step, dead-burned magnesia sand, olivine sand, a binder, an optional deflocculant, and an optional anti-hydration agent are prepared. In the mixing step, 30 - 50 wt% of dead-burned magnesia sand, 40 - 60 wt% of olivine sand, and 2.5 - 10 wt%, for example, 5 - 10 wt% of the binder, less than 1 wt% of the optional deflocculant, and less than 1 wt% of the optional anti-hydration agent are uniformly mixed to obtain a magnesia castable refractory, where the aluminum oxide (Al2O3) contained in the magnesia castable refractory is less than 10 wt%. In the mold filling step, a mold is prepared, and the above magnesia castable refractory and 5 - 10 wt% of water are mixed and poured into the mold. Finally, in the forming step, demolding and drying are performed to obtain a magnesia refractory unit. In this way, the erosion resistance of the magnesia refractory unit is significantly improved, and the magnesia refractory unit has better support capacity. On the other hand, the magnesia refractory unit can effectively absorb aluminum during the working process, thereby further improving the cleanliness of the molten steel.

[0043] However, the above description only gives preferred embodiments of the present invention and is not intended to limit the scope of the present invention. All simple equivalent variations and modifications made according to the claims of the present invention and the content of the description related to the present invention should still be included within the scope of the claims of the present invention.

[0044] Description of Reference Signs (The present invention) 3: Method for manufacturing accessories with basic refractories in a steel tundish 31: Preparation step 32: Mixing step 33: Mold filling step 34: Forming step

Claims

1. A castable fire-resistant composition comprising 30 to 50% by weight of heavy-fired magnesia sand, 40 to 60% by weight of olivine sand, and 2.5 to 10% by weight of a binder.

2. A castable fire-resistant composition according to Claim 1, wherein the castable fire-resistant composition comprises 40 to 50% by weight of the heavy-fired magnesia sand and 40 to 50% by weight of the olivine sand, the binder is sulfate or silicate, and the composition contains less than 10% by weight of Al₂O₃.

3. A castable fire-resistant composition according to claim 1, comprising 5 to 10% by weight of a binder.

4. A castable fire-resistant composition according to any one of claims 1 to 3, comprising a decontaminant and / or a hydration inhibitor.

5. A castable fire-resistant composition according to Claim 4, comprising less than 1% by weight of the dissolving agent and / or less than 1% by weight of the hydration inhibitor.

6. A castable fire-resistant composition according to claim 4, wherein the deconverter is sulfate.

7. A castable fire-resistant composition according to any one of claims 1 to 3, further comprising one or more fire-resistant aggregate materials such as alumina, bauxite and / or spinel, for example, a castable fire-resistant composition comprising about 20% by weight or less or about 10% by weight or less of the one or more fire-resistant aggregate materials.

8. A castable fire-resistant composition according to any one of claims 1 to 3, further comprising one or more drying aids.

9. A castable fire-resistant composition according to claim 8, wherein the drying aid is a fiber.

10. A method for manufacturing refractory units, Preparation steps include preparing calcined magnesia sand, olivine sand, and a binder, A mixing step to obtain a castable fire-resistant composition by mixing 30 to 50% by weight of the heavy-fired magnesia sand, 40 to 60% by weight of the olivine sand, and 2.5 to 10% by weight of the binder, A mold filling step in which the castable fire-resistant composition and 5 to 10% by weight of water are poured into a mold, A molding step in which the mold is demolded to remove the refractory unit from the mold and the refractory unit is dried. A method that includes this.

11. A method according to Claim 10, wherein a castable refractory composition is obtained by mixing 40 to 50% by weight of the heavy-fired magnesia sand, 40 to 50% by weight of the olivine sand, and 2.5 to 10% by weight of the binder, wherein the binder is a sulfate or silicate, and the composition contains less than 10% by weight of Al₂O₃.

12. A method according to claim 10, wherein the castable fire-resistant composition comprises 5 to 10% by weight of the binder.

13. A method according to claim 10 or 11, wherein the castable fire-resistant composition comprises a desorbent and / or a hydration inhibitor.

14. A method according to claim 13, wherein the castable fire-resistant composition comprises less than 1% by weight of the desorbent and / or less than 1% by weight of the hydration inhibitor.

15. The method according to claim 13, wherein the reconstituter is sulfate.

16. A method according to claim 10 or 11, wherein the castable fire-resistant composition further comprises one or more fire-resistant aggregate materials such as alumina, bauxite and / or spinel, for example, the castable fire-resistant composition further comprises about 20% by weight or less or about 10% by weight or less of the one or more fire-resistant aggregate materials.

17. A method according to claim 10 or 11, wherein the castable fire-resistant composition further comprises one or more drying aids.

18. The method according to claim 17, wherein the drying aid is a fiber.

19. The method according to claim 10, wherein the castable refractory composition contains aluminum oxide (Al ２ O ３ A method in which ) is less than 10% by weight.

20. The method according to claim 19, wherein the castable refractory composition comprises 45 to 75% magnesium oxide (MgO), 25 to 35% silicon dioxide (SiO₂), less than 8% aluminum oxide (Al₂O₃), less than 5% iron(III) oxide (Fe₂O₃), and 1.5% or less calcium oxide (CaO).

21. A method according to claim 10 or 11, wherein the refractory unit is a retaining wall, a flow nozzle, or a square brick.

22. A molded refractory unit obtained or obtainable by the method described in claim 10.

23. A sintered refractory unit obtained or obtainable by sintering the molded refractory unit described in claim 22.

24. The use of a molded refractory unit according to claim 22 or a sintered refractory unit according to claim 23 as a refractory accessory such as a slag-holding wall in a tundish during steelmaking, for improving the cleanliness of molten steel.

25. A method for manufacturing accessories using basic refractory materials in a steel tundish, Preparation steps include preparing calcined magnesia sand, olivine sand, a binder, a resolving agent, and a hydration inhibitor. A mixing step to obtain a magnesia castable refractory by uniformly mixing 30 to 50% by weight of the heavy calcined magnesia sand, 40 to 60% by weight of the olivine sand, 5 to 10% by weight of the binder, less than 1% by weight of the dissolving agent, and less than 1% by weight of the hydration inhibitor, wherein the magnesia castable refractory contains aluminum oxide (Al ２ O ３ The amount is less than 10% by weight, and as a result, the particles are coated with the hydration inhibitor, the micropowder is subdivided by the dissolving agent during the mixing process, and the fine particles fill the pores by the mixing process, thereby reducing surface pores in the mixing step, A mold filling step involves preparing a mold and pouring the magnesia castable refractory and 5-10% by weight of water into the mold for molding. A molding step is performed to release the mold to obtain magnesia refractory units, and the magnesia refractory units are allowed to stand and dry and then placed in the steel tundish for use. A manufacturing method that includes this.

26. A method for manufacturing accessories made of basic refractories in a steel tundish according to claim 25, wherein the main chemical composition of the magnesia castable refractory is 45 to 75% magnesium oxide (MgO), 25 to 35% silicon dioxide (SiO ２ ), less than 8% aluminum oxide (Al ２ O ３ ), less than 5% iron (III) oxide (Fe ２ O ３ ), and 1.5% or less calcium oxide (CaO).

27. A method for manufacturing an accessory made of a basic refractory material in a steel tundish according to claim 25, wherein the magnesia refractory material unit may be a retaining wall, a flow nozzle, or a square brick.

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