Flux and spraying materials

Abstract

To provide a flux to be applied or sprayed to an outer surface of an RH immersion tube, or a flux contained in a spray material for repairing an RH immersion tube, which is applied or sprayed to the outer surface of an RH immersion tube, capable of suppressing nitrogen absorption due to air intrusion from the RH immersion tube.SOLUTION: Provided flux is a flux to be applied or sprayed to an outer surface of an RH immersion tube or a flux contained in a spray material applied or sprayed to an outer surface of an RH immersion tube, in which the liquid phase exists at a temperature of 700°C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a flux and a spraying material, and more particularly to a flux to be applied or sprayed onto the outer surface of an RH immersion tube, or a flux contained in a spraying material for repairing an RH immersion tube to be applied or sprayed onto the outer surface of an RH vacuum tube, and a spraying material containing this flux. [Background technology]

[0002] RH vacuum degassing is a process in which molten steel is circulated in a vacuum vessel to remove gases such as nitrogen from the molten steel. During this process, air can enter the molten steel through a refractory tube (hereinafter referred to as the "RH submerged tube" or simply the "submerged tube") immersed in the molten steel in the ladle, causing nitrogen to be absorbed into the molten steel. This makes it difficult to achieve extremely low nitrogen content in molten steel.

[0003] To suppress this nitrogen absorption, Japanese Utility Model Application Publication No. 60-147659 describes forming a dense coating layer on the surface of the dip tube, and Japanese Patent Application Laid-Open Publication No. 10-8127 describes forming a low-melting point compound layer on the outer surface of the dip tube.

[0004] A method is also known in which the inside of an immersion tube is filled with Ar to block the intrusion of air. Japanese Patent Application Laid-Open No. 2005-200696 describes a method in which a plurality of arc-shaped gas-permeable refractories are embedded in the immersion refractory of the immersion tube, and an inert gas such as Ar gas is supplied into the immersion refractory at a pressure equal to or higher than atmospheric pressure from a gas supply pipe connected to the gas-permeable refractory.

[0005] However, since the alumina castable immersion tube (particularly the outer part) is repeatedly and intermittently immersed in the molten steel and slag in the ladle, it is prone to cracking due to thermal shock, etc. If a crack occurs, air can easily penetrate into the molten steel through the crack. Therefore, the supply of Ar gas must be greatly increased to prevent the penetration of air, resulting in a significant increase in costs.

[0006] To repair these cracks, a spraying material made of a magnesia-based aggregate mixed with a binder is sprayed onto the portion of the submerged pipe to be repaired.

[0007] Japanese Patent Publication No. 277415 / 1996 describes a hot repair method for immersed pipes in an RH-type vacuum degassing device, in which an aqueous solution of aluminum phosphate is first applied or sprayed onto the area to be repaired, and then a spraying material containing sodium silicate as a binder is sprayed onto the area.

[0008] Japanese Patent Application Laid-Open No. 2-74552 describes a spraying repair method for molten metal immersion pipes, in which a spraying powder containing 100% refractory aggregate, 0.1 to 2.0% by weight of hardening accelerator and 0.1 to 2.0% by weight of metal powder, and a sodium silicate solution consisting of 4 to 6% by weight of Na2O and 17 to 20% by weight of SiO2 are sprayed at a ratio of 18 to 25% by weight relative to 100% by weight of the spraying powder while being mixed in an injection section just before the nozzle.

[0009] Japanese Patent Application Laid-Open No. 10-212169 describes a sprayable monolithic refractory material in which powdered sodium silicate and weakly acidic sodium phosphate are added to a refractory aggregate in a specific ratio.

[0010] JP 2021-169393 A describes a refractory raw material for spraying that contains a refractory raw material as a main component, silica fume and calcined alumina as secondary components, and is substantially free of alumina cement, in which the total content of silica fume and calcined alumina is 0.8 to 22 mass% relative to 100 mass% of the refractory raw material for spraying, and the mass ratio of calcined alumina to silica fume is 0.4 to 2.5. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Publication No. 60-147659 [Patent Document 2] Japanese Patent Application Publication No. 10-8127 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-200696 [Patent Document 4] Japanese Patent Application Publication No. 8-277415 [Patent Document 5] Japanese Patent Application Publication No. 2-74552 [Patent Document 6] Japanese Patent Application Publication No. 10-212169 [Patent Document 7] Japanese Patent Publication No. 2021-169393 Summary of the Invention [Problem to be solved by the invention]

[0012] The sprayed material is usually used with a moisture content of about 13%, and as a result, the porosity of the sprayed material after it is attached to the immersion pipe and dried is high at about 24%, which means that it is not possible to sufficiently suppress nitrogen absorption due to atmospheric intrusion.

[0013] The object of the present invention is to provide a flux that can be applied or sprayed onto the outer surface of an RH immersion pipe, or a flux that can be contained in a spraying material for repairing an RH immersion pipe that can be applied or sprayed onto the outer surface of an RH immersion pipe, which can suppress nitrogen absorption by molten steel due to atmospheric air entering through the RH immersion pipe. [Means for solving the problem]

[0014] The flux according to one embodiment of the present invention is a flux that is applied or sprayed onto the outer surface of an RH immersion pipe, or a flux contained in a spraying material for repairing an RH immersion pipe that is applied or sprayed onto the outer surface of the RH immersion pipe, and which exists in a liquid phase at temperatures below 700°C.

[0015] One embodiment of the present invention relates to a spraying material for repairing RH submerged pipes, which is made by mixing the above-mentioned flux with an aggregate mainly composed of magnesia, and the concentration of the flux in the spraying material is 10% by mass or more. [Effects of the Invention]

[0016] According to the present invention, nitrogen absorption into molten steel due to air intrusion from the RH submerged pipe can be suppressed. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present inventors have investigated methods for suppressing nitrogen absorption in molten steel due to air intrusion through the RH submerged pipe, and have obtained the following findings.

[0018] As mentioned above, the porosity of the sprayed material used for repairing submerged pipes is high, at around 24% after drying, and it is not possible to sufficiently suppress nitrogen absorption into molten steel due to atmospheric intrusion. However, if part of the sprayed material melts and blocks the pores at the outer surface temperature of the submerged pipe during RH treatment (approximately 600°C), it is thought that nitrogen absorption can be suppressed.

[0019] Phosphates form a liquid phase at around 600°C, and among them, P2O5 and CaO melted and then solidified are suitable as binders for spraying materials. Hereinafter, the melted and solidified CaO and P2O5 will be referred to as "CaO and P2O5 premelt material" or simply "premelt material."

[0020] The appropriate composition of the premelt material of CaO and P2O5 is a composition such that P2O5 / (P2O5+CaO) x 100 is 90 to 98 mass %. Also, the appropriate concentration of the binder in the spraying material is 10 mass % or more.

[0021] The present inventors further conducted extensive research into a multi-component flux that can produce a liquid phase at approximately 600°C, and as a result, they found that the following fluxes (A) and (B) have a liquid phase at temperatures of 700°C or less. (A) A flux having a composition, in mass %, of Al2O3: 20 to 28%, B2O3: 1.5 to 9%, P2O5: 35 to 45%, F: 1.5 to 7%, K2O: 4 to 14%, Na2O: 7 to 13%, ZnO: 0 to 5%, CaO: 0 to 4%, and the remainder: impurities; and (B) A flux having a composition, in mass %, of BiO: 78 to 83%, B2O3: 6 to 9%, SiO2: 3.5 to 5.5%, ZnO: 3.5 to 5.5%, and the remainder: impurities.

[0022] The above-mentioned premelt material and flux (hereinafter collectively referred to as "flux") can be used not only as a binder to be added to the spray material for repairing RH-immersed pipes, but also by applying or spraying it directly onto the RH-immersed pipes.

[0023] The present invention has been completed based on the above findings. A flux and a spraying material according to one embodiment of the present invention will be described in detail below.

[0024] [Flux] The flux according to one embodiment of the present invention is a flux that is applied or sprayed onto the outer surface of an RH immersion pipe, or a flux contained in a spraying material for repairing an RH immersion pipe that is applied or sprayed onto the outer surface of an RH immersion pipe, and which exists in a liquid phase at temperatures below 700°C.

[0025] If the flux applied or sprayed onto the outer surface of the RH immersion pipe, or the flux contained in the spraying material for RH immersion pipe repair applied or sprayed onto the outer surface of the RH immersion pipe, has a liquid phase at temperatures below 700°C, part of the flux will melt at the outer surface temperature of the immersion pipe during RH treatment and block the pores in the immersion pipe, thereby suppressing nitrogen absorption by molten steel due to air entering through the immersion pipe.In addition, the flux generating a liquid phase and having fluidity can suppress the occurrence of cracks due to thermal shock, etc.

[0026] The flux preferably has a liquid phase even at a temperature of 650° C. or less, more preferably has a liquid phase even at a temperature of 600° C. or less, and even more preferably has a liquid phase even at a temperature of 550° C. The lower limit of the temperature at which the liquid phase exists is not particularly limited, but is, for example, 200° C.

[0027] Examples of fluxes that exist in a liquid phase at temperatures of 700°C or less include, but are not limited to, the following fluxes (A) and (B). (A) A flux having a composition, in mass %, of Al2O3: 20 to 28%, B2O3: 1.5 to 9%, P2O5: 35 to 45%, F: 1.5 to 7%, K2O: 4 to 14%, Na2O: 7 to 13%, ZnO: 0 to 5%, CaO: 0 to 4%, and the remainder: impurities; and (B) A flux having a composition, in mass %, of BiO: 78 to 83%, B2O3: 6 to 9%, SiO2: 3.5 to 5.5%, ZnO: 3.5 to 5.5%, and the remainder: impurities.

[0028] The amount of F (fluorine) in the flux can be measured, for example, as follows: The sample is thermally decomposed and burned in a mixed carrier gas of Ar and O2. The halogens in the sample become hydrogen halide or halogen gas, and the sulfur becomes sulfur oxide. These components are collected in an absorption liquid and converted into halide ions and sulfate ions. This absorption liquid is then injected into an ion chromatograph for analysis.

[0029] A powder of a premelt material of CaO and P2O5 may be used as a flux that exists in a liquid phase at temperatures of 700°C or less. This premelt material may contain components other than CaO and P2O5 (e.g., SiO2). The concentration of components other than CaO and P2O5 in this premelt material is preferably 10% by mass or less, and more preferably 5% by mass or less.

[0030] The composition of the premelt material containing CaO and P2O5 is such that P2O5 / (P2O5 + CaO) × 100 is 90 to 98 mass%. Here, the masses of P2O5 and CaO are substituted for the respective masses. If the purity of P2O5 is too high, it is undesirable because it reacts with moisture and generates intense heat. Furthermore, the melting point of the CaO and P2O5 composition is lowest (approximately 490°C) when P2O5 / (P2O5 + CaO) × 100 is approximately 93 mass%. Therefore, a certain liquid phase fraction can be obtained at 600°C if the composition is such that P2O5 / (P2O5 + CaO) × 100 is 90 to 98 mass%. The lower limit of P2O5 / (P2O5 + CaO) × 100 is preferably 91 mass%, more preferably 92 mass%. The upper limit of P2O5 / (P2O5+CaO)×100 is preferably 97% by mass, and more preferably 96% by mass.

[0031] These fluxes can be used by coating or spraying them onto the outer surface of the RH immersion tube. Specifically, for example, these fluxes can be mixed with water and then coated or sprayed onto the outer surface of the RH immersion tube.

[0032] Because molten slag adheres to the RH submerged tube below the point where it comes into contact with the slag, almost no air penetrates below the point where it comes into contact with the slag. Therefore, when applying or spraying flux to the outer surface of the RH submerged tube, it is acceptable to apply or spray it only to the part above the point where it comes into contact with the slag. Specifically, before using the RH submerged tube, that is, before or after heat drying, when it is new, it is acceptable to apply or spray flux only to the part above the point where it comes into contact with the slag. The part above the point where it comes into contact with the slag is only subjected to heat history during the RH treatment, so it is not lost due to melting.

[0033] The above-mentioned fluxes that exist in a liquid phase at temperatures below 700°C can also be used as binders to be added to spraying materials for RH submerged pipe repair. More specifically, the above-mentioned fluxes can also be used as binders to be added to spraying materials having a magnesia-based aggregate.

[0034] [Spraying material] The spraying material according to one embodiment of the present invention is a spraying material for repairing RH submerged pipes, which is made by mixing the above-mentioned flux as a binder with an aggregate mainly made of magnesia. The concentration of the flux in the spraying material is 10 mass% or more.

[0035] Aggregates commonly used in this field can be used. The aggregate may be any that is primarily composed of magnesia, and may also contain other materials besides magnesia. The aggregate is produced by firing MgCO3, but some MgCO3 may remain unfired. The proportion of magnesia in the aggregate is preferably 90% by mass or more. Preferably, the remainder of the aggregate is MgCO3 and impurities.

[0036] The flux to be mixed with the aggregate may be any flux that exists in a liquid phase at a temperature of 700° C. or less. Examples of fluxes that exist in a liquid phase at a temperature of 700° C. or less include the above-mentioned fluxes (A) and (B) and the above-mentioned premelt material of CaO and P2O5.

[0037] The flux concentration in the spraying material ((mass of flux / mass of spraying material) x 100) should be 10 mass% or more. If the flux concentration in the spraying material is less than 10 mass%, the amount of liquid phase will be insufficient and the pore blocking rate will be insufficient. The lower limit of the flux concentration in the spraying material is preferably 12 mass%, and more preferably 14 mass%.

[0038] On the other hand, if the flux concentration in the spraying material is too high, the fluidity of the entire spraying material will be too high, making it more likely to flow off during RH treatment and increasing the rate of corrosion of the submerged tube. The upper limit of the flux concentration in the spraying material is preferably 25 mass%, more preferably 23 mass%, and even more preferably 21 mass%. However, as will be described later, the problem of corrosion can be avoided by using a conventional spraying material in the region of the submerged tube below the part that comes into contact with the slag, and then using the spraying material of this embodiment in the region above the part that comes into contact with the slag.

[0039] The spraying material may contain components other than aggregate and flux. The concentration of components other than aggregate and flux in the spraying material is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0040] The spraying material according to this embodiment is used for repairing an RH submerged pipe. It is used, but not limited to, for hot repair of an RH submerged pipe. For example, the spraying material according to this embodiment is mixed with compressed air and water in a nozzle and sprayed onto the portion of the RH submerged pipe to be repaired.

[0041] From the viewpoint of suppressing corrosion, it is preferable to use a conventional spraying material in the area below the part of the immersion tube that comes into contact with the slag, and then use the spraying material according to this embodiment in the area above the part that comes into contact with the slag. This is because the spraying material according to this embodiment has a high liquid phase ratio of the flux and therefore is more likely to react with the slag.

[0042] The flux and spray material according to one embodiment of the present invention have been described above. The flux and spray material according to this embodiment can suppress nitrogen absorption in molten steel due to air intrusion from the RH immersion pipe. [Example]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0044] [Comparative Example 1] After 100 tonnes of molten steel in a ladle was subjected to a vacuum denitrification treatment for approximately 20 ch in an RH vacuum degassing system equipped with a new alumina castable immersion tube, a spraying material consisting of approximately 70 mass% MgO and approximately 30 mass% SiO2 was sprayed to a thickness of approximately 20-30 mm onto the entire outer surface of the immersion tube. Subsequently, a vacuum denitrification treatment (Ar was blown into the immersion tube at approximately 800 NL / min to reflux the molten steel) was carried out for 10 ch on the Al-killed molten steel (average Al concentration approximately 0.03 mass%, average nitrogen concentration approximately 28 mass ppm, 100 tonnes / ch). Average nitrogen concentration in the molten steel after treatment [N] M The average nitrogen concentration in the molten steel after treatment [N] (mass%) was measured and used as the standard for the following evaluation. M The content (mass %) was determined by sampling the molten steel after treatment and conducting chemical analysis.

[0045] Comparative Example 2 After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing system equipped with a new submerged tube made of alumina castable, a compound containing 45 mass % CaO and 55 mass % SiO2 was sprayed onto the entire outer surface of the submerged tube in the form of a layer 5 to 8 mm thick. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by multiplying the average nitrogen concentration [N] in Comparative Example 1 by the average nitrogen concentration [N] in Comparative Example 1. M The index normalized by ([N] / [N] M ) was almost 1.

[0046] Comparative Example 3 A spraying material was prepared by mixing magnesia aggregate with flux having the following composition as a binder, with the concentration of flux (binder) in the spraying material being 8 mass %. Al2O3: 25% by mass, B2O3: 8% by mass, P2O5:43% by mass, F: 4% by mass, K2O: 6% by mass, Na2O: 7% by mass, ZnO: 4% by mass, and CaO: 3% by mass.

[0047] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing facility equipped with a new alumina castable immersion tube, the above-mentioned spraying material was sprayed onto the entire outer surface of the immersion tube to a thickness of approximately 20 to 30 mm. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by multiplying the average nitrogen concentration [N] of Comparative Example 1 by the average nitrogen concentration [N] of Comparative Example 1. M The index normalized by ([N] / [N] M ) was almost 1.

[0048] [Example 1] A spraying material was prepared by mixing magnesia aggregate with flux of the following composition as a binder, with the concentration of flux (binder) in the spraying material being 10 mass %. Al2O3: 26% by mass, B2O3: 3% by mass, P2O5: 40% by mass, F: 6% by mass, K2O: 13% by mass, and Na2O: 12% by mass.

[0049] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing facility equipped with a new alumina castable immersion tube, the above-mentioned spraying material was sprayed onto the entire outer surface of the immersion tube to a thickness of approximately 20 to 30 mm. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by multiplying the average nitrogen concentration [N] of Comparative Example 1 by the average nitrogen concentration [N] of Comparative Example 1. M The index normalized by ([N] / [N] M ) was 0.80 to 0.90.

[0050] [Example 2] A flux having the following composition was prepared. Al2O3: 25% by mass, B2O3: 8% by mass, P2O5:43% by mass, F: 4% by mass, K2O: 6% by mass, Na2O: 7% by mass, ZnO: 4% by mass, and CaO: 3% by mass.

[0051] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing system equipped with a new alumina castable immersion tube, the above flux was applied to the entire outer surface of the immersion tube to a thickness of approximately 1 to 10 mm. Specifically, a mixture of the above flux with water was applied and dried to a thickness of approximately 1 to 10 mm. Subsequently, a 10 Ch vacuum denitrification treatment was performed under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after the treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by dividing the average nitrogen concentration [N] by the average nitrogen concentration [N] in Comparative Example 1. M The index normalized by ([N] / [N] M ) was 0.81 to 0.93.

[0052] The results of Comparative Examples 1-3 and Examples 1 and 2 are shown in Table 1.

[0053] [Table 1]

[0054] Comparative Example 4 A spraying material was prepared by mixing magnesia aggregate with flux having the following composition as a binder, with the concentration of flux (binder) in the spraying material being 8 mass %. BiO: 81% by mass, B2O3: 7.5% by mass, SiO2: 4.5% by mass, ZnO: 4.3% by mass, Remainder: impurities.

[0055] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing facility equipped with a new alumina castable immersion tube, the above-mentioned spraying material was sprayed onto the entire outer surface of the immersion tube to a thickness of approximately 20 to 30 mm. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by multiplying the average nitrogen concentration [N] of Comparative Example 1 by the average nitrogen concentration [N] of Comparative Example 1. M The index normalized by ([N] / [N] M ) was almost 1.

[0056] [Example 3] A spraying material was prepared by mixing magnesia aggregate with flux of the following composition as a binder, with the concentration of flux (binder) in the spraying material being 10 mass %. BiO: 81% by mass, B2O3: 7.5% by mass, SiO2: 4.5% by mass, ZnO: 4.3% by mass, Remainder: impurities.

[0057] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing facility equipped with a new alumina castable immersion tube, the above-mentioned spraying material was sprayed onto the entire outer surface of the immersion tube to a thickness of approximately 20 to 30 mm. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by multiplying the average nitrogen concentration [N] of Comparative Example 1 by the average nitrogen concentration [N] of Comparative Example 1. M The index normalized by ([N] / [N] M ) was 0.81 to 0.92.

[0058] [Example 4] A flux having the following composition was prepared. BiO: 81% by mass, B2O3: 7.5% by mass, SiO2: 4.5% by mass, ZnO: 4.3% by mass, Remainder: impurities.

[0059] After approximately 20 Ch of vacuum denitrification treatment of 100 t of molten steel in a ladle was performed in an RH vacuum degassing facility equipped with a new alumina castable immersion tube, the above flux was applied to the entire outer surface of the immersion tube to a thickness of approximately 1 to 10 mm. Subsequently, vacuum denitrification treatment was performed for 10 Ch under the same conditions as in Comparative Example 1, and the average nitrogen concentration [N] in the molten steel after treatment was measured in the same manner as in Comparative Example 1. The average nitrogen concentration [N] was calculated by dividing the average nitrogen concentration [N] by the average nitrogen concentration [N] in Comparative Example 1. M The index normalized by ([N] / [N] M ) was 0.83 to 0.94.

[0060] The conditions and results of Comparative Examples 1 and 4 and Examples 3 and 4 are shown in Table 2.

[0061] [Table 2]

[0062] Comparative Example 5 A spraying material was prepared by mixing magnesia aggregate with a premelt material of CaO and P2O5 (P2O5 / (P2O5+CaO) x 100 = 45% by mass) as a binder, with the binder concentration in the spraying material set to 8% by mass. This spraying material was sprayed to a thickness of approximately 20 to 40 mm onto the entire outer surface of an RH immersion pipe made of alumina castable after 100 t of molten steel had been subjected to a reduced pressure denitrification treatment at approximately 20 ch.

[0063] After that, the Al-killed molten steel (average Al concentration: approximately 0.03 mass%, average nitrogen concentration: approximately 28 mass ppm, 100 t / Ch) was subjected to a reduced pressure denitrification treatment (Ar was blown in from the immersion tube at approximately 800 NL / min to reflux the molten steel) for 10 Ch. The average nitrogen concentration in the molten steel after treatment [N] M (mass%) and the average corrosion rate of the immersion tube V M The average nitrogen concentration in the molten steel after treatment [N] (mm / Ch) was measured and used as the standard for the following evaluation. M The average corrosion rate of the submerged tube, V (mass%), was determined by sampling the molten steel after treatment and conducting chemical analysis. M(mm / Ch) was calculated by calculating the difference between the diameter before and after treatment at any five points on the immersion tube, dividing the difference by 2, averaging the difference, and then dividing this difference by the number of vacuum denitrification treatments (Ch).

[0064] Comparative Example 6 The spraying material was prepared in the same manner as in Comparative Example 5, except that P2O5 / (P2O5+CaO) x 100 was 85% by mass and the binder concentration in the spraying material was 15% by mass. As in Comparative Example 5, this spraying material was sprayed to a thickness of approximately 20 to 40 mm onto the entire outer surface of an RH submerged pipe after 100 t of molten steel had been subjected to a reduced pressure denitrification treatment for approximately 20 ch. Thereafter, a reduced pressure denitrification treatment was carried out for 10 ch under the same conditions as in Comparative Example 5, and the average nitrogen concentration [N] in the molten steel after treatment and the average corrosion rate V of the submerged pipe were measured in the same manner as in Comparative Example 5. The average nitrogen concentration [N] was calculated by dividing the average nitrogen concentration [N] by the average nitrogen concentration [N] in Comparative Example 5. M The index normalized by ([N] / [N] M ) was almost 1, and no nitrogen absorption suppression effect was observed. M Normalized index (V / V M ) was also almost 1.

[0065] Comparative Example 7 The spraying material was prepared in the same manner as in Comparative Example 5, except that P2O5 / (P2O5+CaO) x 100 was 93% by mass and the binder concentration in the spraying material was 8% by mass. As in Comparative Example 5, this spraying material was sprayed to a thickness of approximately 20 to 40 mm onto the entire outer surface of an RH submerged pipe after 100 t of molten steel had been subjected to a reduced pressure denitrification treatment for approximately 20 ch. Thereafter, a reduced pressure denitrification treatment was carried out for 10 ch under the same conditions as in Comparative Example 5, and the average nitrogen concentration [N] in the molten steel after treatment and the average corrosion rate V of the submerged pipe were measured in the same manner as in Comparative Example 5. [N] / [N] M was almost 1, and no inhibitory effect on nitrogen absorption was observed. M was also almost 1.

[0066] [Example 5] The spraying material was prepared in the same manner as in Comparative Example 5, except that P2O5 / (P2O5+CaO) x 100 was 93% by mass and the binder concentration in the spraying material was 30% by mass. As in Comparative Example 5, this spraying material was sprayed to a thickness of approximately 20 to 40 mm onto the entire outer surface of an RH submerged pipe after 100 t of molten steel had been subjected to a reduced-pressure denitrification treatment for approximately 20 ch. Thereafter, a reduced-pressure denitrification treatment was carried out for 10 ch under the same conditions as in Comparative Example 5, and the average nitrogen concentration [N] in the molten steel after treatment and the average corrosion rate V of the submerged pipe were measured in the same manner as in Comparative Example 5. [N] / [N] M The V / V was 0.86, and the effect of inhibiting nitrogen absorption was observed. M The value was 1.5, and the corrosion resistance was reduced.

[0067] [Examples 6-10] The spraying materials were prepared in the same manner as in Comparative Example 5, except that P2O5 / (P2O5+CaO) x 100 was set to 90-98% by mass and the binder concentration in the spraying materials was set to 10-25% by mass. As in Comparative Example 5, these spraying materials were sprayed to a thickness of approximately 20-40 mm onto the entire outer surface of the RH submerged pipe after 100 t of molten steel had been subjected to a reduced pressure denitrification treatment for approximately 20 ch. Thereafter, a reduced pressure denitrification treatment was carried out for 10 ch under the same conditions as in Comparative Example 5, and the average nitrogen concentration [N] in the molten steel after treatment and the average corrosion rate V of the submerged pipe were measured in the same manner as in Comparative Example 5. [N] / [N] M The V / V M was 1.0.

[0068] Table 3 shows the conditions and results of Comparative Examples 5-7 and Examples 5-10.

[0069] [Table 3]

[0070] The embodiments of the present invention have been described above. The above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and carried out without departing from the spirit of the present invention.

Claims

1. A spraying material for RH submerged pipe repair, which is a mixture of flux and aggregate mainly made of magnesia, The flux has a liquid phase at a temperature of 700°C or less, The composition of the flux is, in mass %, Al2O3: 20-28%, B 2 O 3: 1.5-9%, P 2 O 5: 35-45%, F: 1.5 to 7%, K 2 O: 4-14%, Na 2 O: 7-13%, ZnO: 0 to 5%, CaO: 0 to 4%, The remainder: impurities, and A spraying material in which the concentration of the flux in the spraying material is 10 mass% or more.

2. A spraying material for RH submerged pipe repair, which is a mixture of flux and aggregate mainly made of magnesia, The flux has a liquid phase at a temperature of 700°C or less, The composition of the flux is, in mass %, BiO: 78-83%, B 2 O 3: 6-9%, SiO 2 :3.5-5.5%, ZnO: 3.5-5.5%, The remainder: impurities, and A spraying material in which the concentration of the flux in the spraying material is 10 mass% or more.

3. A spraying material for RH submerged pipe repair, which is a mixture of flux and aggregate mainly made of magnesia, The flux has a liquid phase at a temperature of 700°C or less, The flux is a powder of a premelt material of CaO and P 2 O 5 , and P 2 O 5 / (P 2 O 5 +CaO)×100 is 90 to 98 mass %, A spraying material in which the concentration of the flux in the spraying material is 10 mass% or more.

4. The spray material according to any one of claims 1 to 3, A spraying material in which the concentration of the flux in the spraying material is 25 mass% or less.

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