Presumption method

Abstract

To evaluate a dissolution loss speed of a refractory in a relatively simple method.SOLUTION: This invention relates to an estimation method for estimating a ratio of dissolution loss speeds at a slag line of two immersion nozzle refractories, wherein: the two immersion nozzle refractories each contain 80 mass% or more and 97 mass% or less of zirconium dioxide, 3 mass% or more and 20 mass% or less of carbon, and 6 mass% or less of other components. The estimation method includes the steps of: identifying an apparent porosity PA of a first immersion nozzle refractory and an apparent porosity PB of a second immersion nozzle refractory; identifying an apparent specific gravity GA of the first immersion nozzle refractory and an apparent specific gravity GB of the second immersion nozzle refractory; and calculating, based on the following formulae (1), (2), and (3), a ratio γ of a dissolution loss speed VB of the second immersion nozzle refractory to a dissolution loss speed VA of the first immersion nozzle refractory.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the ratio of the erosion rates in the slag line of two refractories for submerged entry nozzles. [Background technology]

[0002] In continuous casting of steel, molten steel in a tundish is introduced into a mold through a submerged nozzle. The molten steel in the mold solidifies due to the cooling action of the mold, and is continuously drawn out by rolls to produce a steel billet.

[0003] Mold powder is continuously scattered on the surface of the molten steel during casting to prevent atmospheric oxidation of the surface of the molten steel in the mold and to ensure lubrication between the solidified shell and the mold. As the scattered powder moves down, it begins to melt near the surface of the molten steel and eventually melts completely, forming a molten slag. The molten slag (powder slag) flows into the gap between the solidified shell and the mold, forming a slag film that serves as a lubricant and controls heat transfer.

[0004] The portion of the SEN that comes into contact with the powder slag during continuous casting is called the slag line. Because the slag line is subject to erosion from both the powder slag and molten steel during casting, it undergoes erosion more rapidly than other portions of the SEN. When erosion exceeds a certain level, problems such as SEN fracture occur, making it necessary to halt continuous casting production. On the other hand, replacing the SEN when the degree of erosion is still minor avoids the above-mentioned problems, but requires frequent replacement. In other words, whether the SEN is used for an excessively long or insufficient period reduces production efficiency. Therefore, if the corrosion resistance of the SEN can be evaluated and its lifespan predicted, the SEN can be used to the fullest extent within its lifespan, greatly contributing to maximizing continuous casting production efficiency.

[0005] A conventional method for predicting such a life span involves conducting laboratory-scale experiments to evaluate the corrosion resistance of a refractory material. For example, Japanese Patent No. 7060831 (Patent Document 1) discloses a method for evaluating the corrosion resistance of a refractory material by adding powder slag to molten steel in which a test piece of the refractory material to be evaluated is immersed, rotating the test piece for two hours, and then measuring the thickness of the erosion of the test piece. Furthermore, Japanese Patent Laid-Open No. 2022-63736 (Patent Document 2) discloses a method for evaluating the corrosion resistance of a refractory material by adding molten steel and mold powder to a drum lined with the test piece, rotating the drum, and then measuring the area of ​​wear of the test piece. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7060831 [Patent Document 2] Japanese Patent Publication No. 2022-63736 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the evaluation methods involving experiments as described in Patent Documents 1 and 2 sometimes required a long time to obtain evaluation results. Furthermore, since the number of experiments increases in proportion to the number of samples to be evaluated, it may require a lot of resources to find an optimal composition from among many refractory compositions. Furthermore, the results of the experimental evaluation may not match the phenomena occurring in the field of continuous casting.

[0008] Therefore, it is desirable to develop a relatively simple estimation method for evaluating the corrosion rate of refractories. [Means for solving the problem]

[0009] The estimation method according to the present invention is a method for estimating a ratio of the corrosion rates in a slag line of two refractories for use in an SEN, the two refractories both containing 80% by mass or more and 97% by mass or less of zirconium dioxide, 3% by mass or more and 20% by mass or less of carbon, and 6% by mass or less of other components, and the apparent porosity P A and the apparent porosity P of the refractory for the second submerged entry nozzle B and a step of determining the apparent specific gravity G of the first refractory material for a submerged entry nozzle. A and the apparent specific gravity G of the second refractory material for the submerged nozzle B and a step of determining a corrosion rate V of the first refractory material for a submerged entry nozzle. A The corrosion rate V of the second refractory for the submerged entry nozzle B and calculating the ratio γ based on the following formulas (1), (2), and (3).

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[0010] According to this configuration, the corrosion rate can be evaluated in a relatively simple manner without conducting an experiment in which the refractory material is actually corroded.

[0011] Preferred embodiments of the present invention will be described below, but the scope of the present invention is not limited to the preferred embodiments described below.

[0012] In one aspect of the estimation method according to the present invention, it is preferred that the first refractory for an immersion nozzle is a refractory that has been subjected to continuous casting in the past, and the second refractory for an immersion nozzle is a refractory that has not yet been subjected to continuous casting.

[0013] According to this configuration, the rate of corrosion of a newly manufactured submerged entry nozzle can be estimated, which contributes to quality control and improvement of the submerged entry nozzle.

[0014] In one aspect of the estimation method according to the present invention, it is preferred that the first refractory for an immersion nozzle is a refractory that has been used in continuous casting in the past, and the second refractory for an immersion nozzle is a refractory for an immersion nozzle that is currently being used in continuous casting.

[0015] According to this configuration, the life of the submerged entry nozzle currently being used in continuous casting can be estimated, and therefore the timing for replacing the submerged entry nozzle can be appropriately determined.

[0016] Further features and advantages of the present invention will become more apparent from the following description of exemplary and non-limiting embodiments, which is given with reference to the drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a submerged nozzle. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of an estimation method according to the present invention will be described with reference to the drawings.

[0019] [Structure and usage of submerged entry nozzle] In this embodiment, the immersion nozzle 1, which uses the refractory for an immersion nozzle for which the corrosion rate ratio is to be estimated, is a cylindrical refractory member used, for example, to inject molten steel M into a mold 2 in continuous steel casting (FIG. 1). FIG. 1 shows, as an example, a state in use in which the immersion nozzle 1 is connected to a tundish 4 via a slide plate 3. The molten steel M is discharged into the mold 2 from the discharge port 11 of the immersion nozzle 1. In the mold 2, the surface of the molten steel M is covered with powder slag S to prevent the molten steel M from coming into contact with the air and oxidizing.

[0020] The slag line 12, which is the portion of the immersion nozzle 1 that comes into contact with the powder slag S, is a location of the immersion nozzle 1 that is particularly susceptible to corrosion. The estimation method according to this embodiment estimates the corrosion rate ratio for refractories for the immersion nozzle arranged in the slag line 12. The refractories for the immersion nozzle, the corrosion rate ratio of which is to be estimated, may be arranged locally in the slag line 12, or may also be arranged in locations other than the slag line 12.

[0021] [Composition and manufacturing method of refractory for submerged entry nozzle] In this embodiment, the two refractories for submerged entry nozzles, the corrosion rate ratio of which is estimated, each contain 80% by mass or more and 97% by mass or less of zirconium dioxide (ZrO2), 3% by mass or more and 20% by mass or less of carbon (C), and 6% by mass or less of other components. These refractories for submerged entry nozzles belong to a type of refractory generally known as a zirconia-carbonaceous refractory. Although zirconia-carbonaceous refractories are relatively expensive, they have higher corrosion resistance than other refractories such as alumina-carbonaceous refractories, making them suitable for use in slag lines. The carbon blended into zirconia-carbonaceous refractories has a lower thermal expansion coefficient than other components, resulting in zirconia-carbonaceous refractories having good spalling resistance.

[0022] The refractory for a submerged entry nozzle according to this embodiment can be obtained, for example, through a mixing step of mixing a zirconia raw material and a carbon raw material to obtain a mixture, a preforming step of forming a preform from the mixture, and a firing step of firing the preform to obtain the refractory for a submerged entry nozzle. In the mixing step, additives may be mixed in addition to the zirconia raw material and the carbon raw material.

[0023] The zirconia raw material may be a known zirconia raw material used as a raw material for refractories for submerged entry nozzles. That is, the zirconia raw material may be substantially pure zirconium dioxide (e.g., baddeleyite) or a composition containing zirconium dioxide (zirconium dioxide-containing composition). Examples of zirconium dioxide-containing compositions include, but are not limited to, stabilized zirconia raw materials containing zirconium dioxide and a stabilizer, and natural minerals containing components other than zirconium dioxide (e.g., zircon sand). A mixture of pure zirconium dioxide and a zirconium dioxide-containing composition may also be used. The stabilizer is a component that can inhibit the disintegration of zirconium dioxide particles due to phase transformation at high temperatures, and examples thereof include, but are not limited to, calcium oxide, magnesium oxide, and yttrium (III) oxide.

[0024] The carbon raw material may be a known carbon raw material used as a raw material for refractories for submerged entry nozzles. That is, the carbon raw material may be, but is not limited to, scaly graphite, carbon black, tar, pitch, resin charcoal, etc. Furthermore, the carbon raw material may be one type or multiple types.

[0025] The additive may be a known additive used as a raw material for refractories for submerged entry nozzles. For example, borides, carbides, metals, etc. may be added as additives to improve oxidation resistance. More specifically, non-limiting examples of the additive include boron carbide, zirconium boride, silicon carbide, and silicon.

[0026] Among the components of the refractory for a submerged entry nozzle, zirconium dioxide is derived from zirconium dioxide contained in the zirconia raw material. Carbon is derived from the carbon raw material. The other components are derived from components other than zirconium dioxide (stabilizers, impurities, etc.) in the zirconia raw material and additives. Therefore, when producing the refractory for a submerged entry nozzle according to this embodiment, the ratios of the zirconia raw material, carbon raw material, and additives to be mixed in the mixing step are determined taking into consideration the composition of the zirconia raw material used (the respective contents of zirconium dioxide and other components) so that the components that ultimately constitute the refractory for a submerged entry nozzle satisfy the conditions of 80% by mass to 97% by mass of zirconium dioxide (ZrO2), 3% by mass to 20% by mass of carbon (C), and 6% by mass or less of other components.

[0027] Composition is one of the dominant factors affecting the corrosion resistance of refractories. Zirconia-carbon refractories are one of the compositions with excellent corrosion resistance, which is one of the reasons why zirconia-carbon refractories are suitable for use in slag lines. However, because the corrosion resistance of a refractory is influenced by factors such as its microstructure, even zirconia-carbon refractories with the same composition may have different corrosion resistances. Because the microstructure of a refractory can vary in complex ways depending on factors such as the particle size of the raw materials, the amount of binder used that generates volatiles at high temperatures, and the refractory manufacturing conditions, it is difficult to manufacture refractories with precise control of the microstructure. In other words, it is difficult to manufacture refractories with good reproducibility in terms of corrosion resistance, which makes it difficult to predict the refractory's lifespan.

[0028] [Estimation method] The estimation method according to this embodiment is a method for estimating the ratio of the corrosion rates in the slag line of two refractories for a submerged entry nozzle. The estimation method according to this embodiment does not involve an experiment in which the refractories are actually subjected to corrosion, and therefore can be carried out relatively easily. Hereinafter, the two refractories for a submerged entry nozzle that are the subject of estimation will be referred to as the first refractory for a submerged entry nozzle and the second refractory for a submerged entry nozzle, respectively.

[0029] The estimation method according to this embodiment includes a first step of specifying the apparent porosities of the two refractories for a submerged entry nozzle, a second step of specifying the apparent specific gravities of the two refractories for a submerged entry nozzle, and a third step of estimating the ratio between the corrosion rates of the two refractories for a submerged entry nozzle.

[0030] In the first step, the apparent porosity P of the refractory for the first submerged entry nozzle is A and the apparent porosity P of the refractory for the second submerged entry nozzle B The apparent porosity of the refractory material for an immersion nozzle can be determined, for example, by the measurement method described in JIS R2205:1992.

[0031] In the second step, the apparent specific gravity G of the refractory for the first submerged nozzle is A and the apparent specific gravity G of the refractory for the second submerged entry nozzle B The apparent specific gravity of the refractory material for an immersion nozzle can be determined, for example, by the measurement method described in JIS R2205:1992.

[0032] In the third step, the erosion rate V of the refractory for the first submerged entry nozzle is measured. A The corrosion rate V of the refractory for the second submerged entry nozzle B The ratio γ (i.e., γ = V B / V A ) is calculated based on the following equations (1), (2), and (3). Note that α, β, and γ are all dimensionless quantities.

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[0033] Equation (1) specifies the apparent porosity ratio α of the two refractories for the submerged entry nozzle. A and P B is the apparent porosity P determined in the first step A and P B is.

[0034] Equation (2) specifies the ratio β of the apparent specific gravity of the two refractories for the submerged entry nozzle. The variable G in Equation (2) A and GB is the apparent specific gravity G determined in the second step A and G B is.

[0035] Equation (3) is an equation for determining the corrosion rate ratio γ using the apparent porosity ratio α and the apparent specific gravity ratio β as variables. Equation (3) was discovered through experimental studies by the inventors, which will be described below.

[0036] The inventors recovered 30 SENs that had actually been used in continuous steel casting and measured the thickness of the erosion in the slag line for each SEN. The measured erosion thickness was divided by the duration of use of each SEN to calculate the erosion rate for each SEN. Furthermore, the composition of the refractory material constituting the slag line, as well as various physical properties such as apparent porosity, apparent specific gravity, strength, elastic modulus, and thermal expansion coefficient, were measured for each SEN. The composition of the refractory material constituting the slag line for each SEN was in the range of 83-93% by mass zirconium dioxide, 6-12% by mass carbon, 1-3% by mass calcium oxide, and 0-2% by mass silicon carbide. The apparent porosity was in the range of 11-20%, the apparent specific gravity was in the range of 4.2-4.9, and the erosion rate of the nozzle slag line was in the range of 5-12 mm per hour.

[0037] For the 30 data points related to the 30 submerged entry nozzles, regression analysis was performed using various measured physical property values ​​(apparent porosity, apparent specific gravity, bulk specific gravity, bending strength, elastic modulus, thermal expansion coefficient, average particle size, etc.) as candidate explanatory variables and the erosion rate V as the response variable. One data point selected from the 30 data points was used as the reference data, and the logarithmic ratios of each physical property value and erosion rate V of the remaining 29 data points to the reference data were calculated. The correlation between the logarithmic ratios of each physical property value and the logarithmic ratio of the erosion rate V was analyzed using a conventional regression analysis method. Spreadsheet software (Microsoft Excel) was used as the analysis tool. As a result of the regression analysis, when apparent porosity P and apparent specific gravity G were used as explanatory variables, the coefficient of determination R 2was found to be the highest, and the following equation (4) was derived as the regression equation. The definitions of α, β, and γ in equation (4) are as described above. The coefficient of determination R 2 was 0.8, and it was confirmed that the derived regression equation had sufficient estimation accuracy for practical use. Equation (3) was derived by transforming equation (4). The coefficient of determination R 2 Similarly, the relative error was 0.8. The average relative error was 1.5%, and the maximum was 8.0%.

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[0038] The estimation method according to this embodiment can be used to estimate the ratio of the erosion rates in the slag line of any two refractories for a submerged entry nozzle. A , apparent specific gravity G A , and corrosion rate V A If the apparent porosity P of the other refractory for the submerged entry nozzle is known, B and apparent specific gravity G B By specifying the ratio of the erosion rates γ, the ratio of the erosion rates V A By multiplying by , the corrosion rate V of the refractory for the second submerged entry nozzle B can be estimated.

[0039] For example, the estimation method according to this embodiment can be applied to the application of estimating the corrosion resistance of a manufactured submerged entry nozzle before use. In this case, the refractory for a submerged entry nozzle that was manufactured in the past and subjected to continuous casting is designated as the first refractory for a submerged entry nozzle, and the refractory for a newly manufactured submerged entry nozzle that has not yet been subjected to continuous casting is designated as the second refractory for a submerged entry nozzle. The apparent porosity P A , apparent specific gravity G A , and corrosion rate V A The apparent porosity P of a newly manufactured second refractory material for a submerged entry nozzle can be measured, for example, by using a sample of the submerged entry nozzle that has been collected after use. B and apparent specific gravity G Bcan be measured using a completed new submerged entry nozzle as a sample. From these measurements, the ratio of the erosion rates γ and the erosion rate V of the refractory for the second submerged entry nozzle can be calculated. B According to the above method, the corrosion rate, i.e., the corrosion resistance, of a newly manufactured submerged entry nozzle can be estimated, which contributes to quality control and improvement of the submerged entry nozzle.

[0040] As another example, the estimation method according to this embodiment can be applied to the application of estimating the lifespan of an SEN currently being used in continuous casting. In this case, the SEN refractory constituting the SEN manufactured in the past and used in continuous casting is designated as the first SEN refractory, and the SEN refractory constituting the SEN currently being used in continuous casting is designated as the second SEN refractory. As described above, the apparent porosity P A , apparent specific gravity G A , and corrosion rate V A is known. In addition, the apparent porosity P B and apparent specific gravity G B Since the erosion rate ratio γ and the erosion rate V of the refractory for the second submerged entry nozzle do not change even after the submerged entry nozzle has been used, or the change can be substantially ignored, the values ​​measured at the time of manufacturing the refractory for the second submerged entry nozzle can be used. B The allowable amount of corrosion can be estimated by the corrosion rate V of the refractory for the second submerged entry nozzle. B The estimated useful life can be calculated by dividing the estimated useful life by the estimated value of the service life of the submerged entry nozzle (SEN) that is currently being used in continuous casting. The above method makes it possible to estimate the useful life, i.e., the service life of the SEN currently being used in continuous casting, and therefore makes it possible to appropriately determine when to replace the SEN. This makes it easy to prevent production problems that would be caused by continuing to use the SEN until excessive corrosion has progressed, as well as a decrease in production efficiency that would be caused by replacing the SEN when its useful life is still remaining.

[0041] Other Embodiments Regarding other configurations, it should be understood that the embodiments disclosed in this specification are illustrative in all respects and that the scope of the present invention is not limited thereby. Those skilled in the art will easily understand that appropriate modifications are possible without departing from the spirit of the present invention. Therefore, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention. [Example]

[0042] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0043] Example 1 The corrosion rate was measured for a submerged entry nozzle in a continuous slab casting machine with a mold size of 230 mm x 1600 mm. The steel type produced was ultra-low carbon steel, and the casting speed was 1.8 m / min. The slag powder composition was 37.6 mass% CaO, 37.4 mass% SiO, 7.3 mass% NaO, 5.7 mass% LiO, 5.8 mass% AlO, and 6.2 mass% F. The casting time was 2.3 hours.

[0044] Two submerged entry nozzles were used: one with a slag line made of material A1 and one with a slag line made of material B1. Material A1 had a composition of 84% by mass zirconium dioxide, 13% by mass carbon, and 3% by mass other components, with an apparent porosity of 14.7% and an apparent specific gravity of 4.57. Material B1 had a composition of 88% by mass zirconium dioxide, 9% by mass carbon, and 3% by mass other components, with an apparent porosity of 10.8% and an apparent specific gravity of 4.64. In both materials A1 and B1, the other components were primarily calcium oxide, which was included as a stabilizer in the zirconia raw material.

[0045] For the used SENs, the thickness of the erosion at the slag line was measured and divided by the casting time (2.3 hours) to determine the erosion rate. The erosion rate for Material A1 was 7.8 mm per hour, and the erosion rate for Material B1 was 6.6 mm per hour. Therefore, the measured erosion rate ratio was 0.85.

[0046] The estimated ratio of the corrosion rate calculated based on the apparent porosity and apparent specific gravity of materials A1 and B1 and equations (1), (2), and (3) was 0.87. The relative error of the estimated value to the measured value was 2.8%.

[0047] Example 2 The corrosion rate was measured for a submerged entry nozzle in a continuous slab casting machine with a mold size of 250 mm x 1500 mm. The steel type produced was low carbon steel, and the casting speed was 1.6 m / min. The slag powder composition was 35.3 mass% CaO, 30.2 mass% SiO, 13.2 mass% NaO, 2.2 mass% AlO, 7.0 mass% MgO, and 12.2 mass% F. The casting time was 2.0 hours.

[0048] Two submerged entry nozzles were used: one with a slag line made of material A2 and one with a slag line made of material B2. Material A2 had a composition of 87% by mass zirconium dioxide, 10% by mass carbon, and 3% by mass other components, with an apparent porosity of 19.1% and an apparent specific gravity of 4.71. Material B2 had a composition of 87% by mass zirconium dioxide, 10% by mass carbon, and 3% by mass other components, with an apparent porosity of 11.1% and an apparent specific gravity of 4.64. In both materials A2 and B2, the breakdown of the other components was 2% by mass calcium oxide and 1% by mass magnesium oxide, both of which were derived from stabilizers in the zirconia raw material.

[0049] For the used submerged entry nozzles, the thickness of the erosion at the slag line was measured and divided by the casting time (2.0 hours) to determine the erosion rate. The erosion rate for material A2 was 7.2 mm per hour, and the erosion rate for material B2 was 6.0 mm per hour. Therefore, the measured erosion rate ratio was 0.83.

[0050] The estimated ratio of the corrosion rate calculated based on the apparent porosity and apparent specific gravity of materials A2 and B2 and equations (1), (2), and (3) was 0.82. The relative error of the estimated value to the measured value was 2.0%.

[0051] Example 3 The corrosion rate was measured for a submerged entry nozzle in a bloom continuous casting machine with a mold size of 380 mm x 420 mm. The steel type produced was medium carbon steel, and the casting speed was 0.85 m / min. The slag powder composition was 18.5 mass% CaO, 43.1 mass% SiO, 7.1 mass% NaO, 2.1 mass% LiO, 17.8 mass% AlO, 3.2 mass% MgO, and 8.2 mass% F. The casting time was 2.0 hours.

[0052] Two submerged entry nozzles were used: one with a slag line made of material A3 and one with a slag line made of material B3. Material A3 had a composition of 81% by mass of zirconium dioxide, 16% by mass of carbon, and 3% by mass of other components, with an apparent porosity of 17.5% and an apparent specific gravity of 4.42. Material B3 had a composition of 89% by mass of zirconium dioxide, 8% by mass of carbon, and 3% by mass of other components, with an apparent porosity of 11.2% and an apparent specific gravity of 4.66. In both materials A3 and B3, the breakdown of the other components was 2% by mass of calcium oxide and 1% by mass of yttrium (III) oxide, both of which were derived from stabilizers in the zirconia raw material.

[0053] For the used SENs, the thickness of the erosion at the slag line was measured and divided by the casting time (2.0 hours) to determine the erosion rate. The erosion rate for material A3 was 10.2 mm per hour, and the erosion rate for material B3 was 8.4 mm per hour. Therefore, the measured erosion rate ratio was 0.82.

[0054] The estimated ratio of the corrosion rate calculated based on the apparent porosity and apparent specific gravity of materials A3 and B3 and equations (1), (2), and (3) was 0.79. The relative error of the estimated value to the measured value was 3.8%.

[0055] Example 4 The corrosion rate was measured for a submerged entry nozzle in a billet continuous casting machine with a mold size of 220 mm x 220 mm. The steel type produced was high carbon steel, and the casting speed was 1.4 m / min. The slag powder composition was 26.4 mass% CaO, 40.0 mass% SiO, 11.5 mass% NaO, 6.6 mass% AlO, 7.1 mass% MgO, and 8.4 mass% F. The casting time was 2.5 hours.

[0056] Two submerged entry nozzles were used: one with a slag line made of material A4 and one with a slag line made of material B5. Material A4 had a composition of 78% zirconium dioxide by mass, 18% carbon by mass, and 4% other components by mass, with an apparent porosity of 15.9% and an apparent specific gravity of 4.25. Material B4 had a composition of 84% zirconium dioxide by mass, 12% carbon by mass, and 4% other components by mass, with an apparent porosity of 17.8% and an apparent specific gravity of 4.58. In both materials A4 and B4, the breakdown of the other components was 1% calcium oxide by mass, 1% magnesium oxide by mass, and 2% yttrium (III) oxide by mass, all of which were derived from stabilizers in the zirconia raw material.

[0057] For the used submerged entry nozzles, the thickness of the erosion at the slag line was measured and divided by the casting time (2.5 hours) to determine the erosion rate. The erosion rate for material A4 was 6.0 mm per hour, and the erosion rate for material B4 was 5.6 mm per hour. Therefore, the actual erosion rate ratio was 0.93.

[0058] The estimated ratio of the corrosion rate calculated based on the apparent porosity and apparent specific gravity of materials A4 and B4 and equations (1), (2), and (3) was 0.97. The relative error of the estimated value to the measured value was 3.9%.

[0059] Example 5 The corrosion rate was measured for a submerged entry nozzle in a round billet continuous casting machine with a mold size of 260 mm in diameter. The steel type produced was stainless steel, and the casting speed was 1.6 m / min. The slag powder composition was 37.8 mass% CaO, 30.8 mass% SiO, 9.5 mass% NaO, 37.8 mass% AlO, 1.7 mass% MgO, 1.1 mass% LiO, 2.1 mass% MnO, and 9.2 mass% F. The casting time was 4.0 hours.

[0060] Two submerged entry nozzles were used: one with a slag line made of material A5 and one with a slag line made of material B5. Material A5 had a composition of 85% by mass zirconium dioxide, 10% by mass carbon, and 5% by mass other components, with an apparent porosity of 15.8% and an apparent specific gravity of 4.51. The other components were 2% by mass calcium oxide derived from the stabilizer in the zirconia raw material and 3% by mass silicon carbide added as an additive. Material B5 had a composition of 85% by mass zirconium dioxide, 12% by mass carbon, and 3% by mass other components, with an apparent porosity of 11.1% and an apparent specific gravity of 4.62. The other component was calcium oxide derived from the stabilizer in the zirconia raw material.

[0061] For the used submerged entry nozzles, the thickness of the erosion at the slag line was measured and divided by the casting time (4.0 hours) to determine the erosion rate. The erosion rate for material A5 was 8.2 mm per hour, and the erosion rate for material B5 was 7.1 mm per hour. Therefore, the measured erosion rate ratio was 0.87.

[0062] The estimated ratio of the corrosion rate calculated based on the apparent porosity and apparent specific gravity of materials A5 and B5 and equations (1), (2), and (3) was 0.85. The relative error of the estimated value to the measured value was 2.2%.

[0063] [Summary] In Examples 1 to 5, the relative error of the estimated corrosion rate ratio to the actually measured value was 3.9% at most, which revealed that the estimation method according to the present invention has sufficient estimation accuracy for practical use. [Industrial Applicability]

[0064] The present invention can be applied to, for example, estimating the lifespan of a submerged entry nozzle. [Explanation of symbols]

[0065] 1: Submerged nozzle 11:Discharge port 12: Slug line 2: Mold 3: Slide plate 4: Tundish M: Molten steel S: Powder slug

Claims

1. A method for estimating a ratio of corrosion rates in a slag line of two refractories for a submerged entry nozzle, comprising: each of the two refractories for a submerged nozzle contains 80% by mass or more and 97% by mass or less of zirconium dioxide, 3% by mass or more and 20% by mass or less of carbon, and 6% by mass or less of other components; Apparent porosity P of the refractory material for the first immersion nozzle Ａ and the apparent porosity P of the second refractory material for the submerged nozzle Ｂ and Apparent specific gravity G of the first refractory material for the immersion nozzle Ａ and the apparent specific gravity G of the second refractory material for the submerged nozzle Ｂ and The corrosion rate V of the first refractory material for the immersion nozzle Ａ The corrosion rate V of the second refractory for the submerged nozzle Ｂ and calculating the ratio γ based on the following equations (1), (2), and (3). [Equation 1]

2. the first refractory for an immersion nozzle is a refractory for an immersion nozzle that has been used in continuous casting in the past, 2. The method according to claim 1, wherein the second refractory for an immersion nozzle is a refractory for an immersion nozzle that has not yet been subjected to continuous casting.

3. the first refractory for an immersion nozzle is a refractory for an immersion nozzle that has been used in continuous casting in the past, 2. The method according to claim 1, wherein the second refractory for an immersion nozzle is a refractory for an immersion nozzle that is currently being used in continuous casting.

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