JP7774206B2 - Estimation method - Google Patents

Description

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.

In continuous steel casting, molten steel in a tundish is introduced into a mold through an immersion 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 cast steel billet.

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, eventually melting completely to form molten slag. The molten slag (powder slag) flows into the gap between the solidified shell and the mold, forming a slag film that serves the roles of lubrication and heat transfer control.

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 suffers from particularly rapid corrosion compared to other portions of the SEN. When corrosion exceeds a certain level, problems such as SEN rupture can occur, making it necessary to halt continuous casting production. On the other hand, replacing the SEN when the corrosion 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 SENs can be evaluated and their lifespan predicted, SENs can be used to the fullest extent within their lifespan, greatly contributing to maximizing continuous casting production efficiency.

A conventional method for predicting such life spans involves conducting laboratory-scale experiments to evaluate the corrosion resistance of refractories. For example, Japanese Patent No. 7060831 (Patent Document 1) discloses a method for evaluating the corrosion resistance of refractories by adding powder slag to molten steel in which a test piece of the refractory 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 Publication No. 2022-63736 (Patent Document 2) discloses a method for evaluating the corrosion resistance of refractories 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 on the test piece.

Patent No. 7060831 Japanese Patent Application Laid-Open No. 2022-63736

However, evaluation methods involving experiments, such as those described in Patent Documents 1 and 2, can take a long time to obtain evaluation results. Furthermore, because the number of experiments increases in proportion to the number of samples to be evaluated, it can require a lot of resources to find the optimal refractory composition from among the many available. Furthermore, the results of experimental evaluations sometimes do not match the phenomena occurring in the continuous casting field.

Therefore, it is desirable to develop a relatively simple estimation method that can evaluate the corrosion rate of refractories.

The estimation method according to the present invention is a method for estimating the ratio of the erosion rates in a slag line of two refractories for use in a submerged entry nozzle, each of which 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, and is characterized in that it comprises the steps of: specifying the apparent porosity _PA of the first refractory for use in a submerged entry nozzle and the apparent porosity _PB of the second refractory for use in a submerged entry nozzle; specifying the apparent specific gravity _GA of the first refractory for use in a submerged entry nozzle and the apparent specific gravity _GB of the second refractory for use in a submerged entry nozzle; and calculating the ratio γ of the erosion rate _VB of the second refractory for use in a submerged entry nozzle to the erosion rate VA of the _first refractory for use in a submerged entry nozzle based on the following formulas (1), (2), and (3):

This configuration allows the corrosion rate to be evaluated in a relatively simple manner without the need for experiments that actually cause refractory corrosion.

Preferred embodiments of the present invention are described below. However, the scope of the present invention is not limited to the preferred embodiments described below.

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

This configuration makes it possible to estimate the rate of corrosion of newly manufactured submerged entry nozzles, contributing to quality control and improvement of submerged entry nozzles.

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

This configuration makes it possible to estimate the service life of the submerged entry nozzle currently being used in continuous casting, allowing for appropriate determination of when to replace the submerged entry nozzle.

Further features and advantages of the present invention will become more apparent from the following description of exemplary, non-limiting embodiments, which proceeds with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of a submerged nozzle.

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

[Structure and usage of submerged entry nozzle]
In this embodiment, the submerged entry nozzle 1, which uses the submerged entry nozzle refractory material 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 submerged entry 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 submerged entry 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.

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 on the immersion nozzle 1 that is particularly susceptible to corrosion. The estimation method according to this embodiment estimates the corrosion rate ratio for the immersion nozzle refractories arranged in the slag line 12. Note that the immersion nozzle refractories for which the corrosion rate ratio 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.

[Composition and manufacturing method of refractory for submerged entry nozzle]
In this embodiment, the two refractories for submerged entry nozzles, the ratio of corrosion rates of which is to be estimated, each contain 80% by mass or more and 97% by mass or less of zirconium dioxide (ZrO ₂ ), 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 the type of refractories generally known as zirconia-carbonaceous refractories. 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 the other components, and therefore zirconia-carbonaceous refractories have good spalling resistance.

The refractory for a submerged entry nozzle according to this embodiment can be obtained, for example, through a mixing step in which a zirconia raw material and a carbon raw material are mixed to obtain a mixture, a preforming step in which a preform is formed from the mixture, and a firing step in which the preform is fired to obtain the refractory for a submerged entry nozzle. In addition to the zirconia raw material and the carbon raw material, additives may also be mixed in during the mixing step.

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.

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, flaky graphite, carbon black, tar, pitch, resin charcoal, etc. Furthermore, the carbon raw material may be one type or multiple types.

The additives may be known additives used as raw materials 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 additives include boron carbide, zirconium boride, silicon carbide, and silicon.

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 (ZrO 2 ), 3% by mass to 20% by mass of carbon (C), and 6% by mass or less of other components.

Composition is one of the dominant factors that determine 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 ideal 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 can 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 volatile matter at high temperatures, and the refractory manufacturing conditions, it is difficult to manufacture refractories with precise control over 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.

[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.

The estimation method according to this embodiment includes a first step of determining the apparent porosity of two refractories for submerged entry nozzles, a second step of determining the apparent specific gravities of the two refractories for submerged entry nozzles, and a third step of estimating the ratio of the corrosion rates of the two refractories for submerged entry nozzles.

In the first step, the apparent porosity P _A of the first refractory for a submerged entry nozzle and the apparent porosity P _B of the second refractory for a submerged entry nozzle are determined. The apparent porosity of the refractory for a submerged entry nozzle can be determined, for example, by the measurement method described in JIS R2205:1992.

In the second step, the apparent specific gravity _G of the first refractory for a submerged entry nozzle and the apparent specific gravity _G of the second refractory for a submerged entry nozzle are determined. The apparent specific gravity of the refractory for a submerged entry nozzle can be determined, for example, by the measurement method described in JIS R2205:1992.

In the third step, the ratio γ of the erosion rate _VB of the second refractory for the submerged entry nozzle to the erosion rate _VA of the first refractory for the submerged entry nozzle (i.e., γ = _VB / _VA ) is calculated based on the following formulas (1), (2), and (3), where α, β, and γ are all dimensionless quantities.

Equation (1) is an equation for determining the apparent porosity ratio α of two refractories for a submerged entry nozzle. The variables P _A and P _B in equation (1) are the apparent porosities P _A and P _B determined in the first step.

Equation (2) is an equation for determining the ratio β of the apparent specific gravities of two refractories for a submerged entry nozzle. The variables _G and _G in equation (2) are the apparent specific gravities _G and _G determined in the second step.

Equation (3) determines 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, as described below.

The inventors recovered 30 submerged entry nozzles that had actually been used in continuous steel casting and measured the thickness of the erosion damage in the slag line for each submerged entry nozzle. The measured erosion thickness was divided by the length of time each submerged entry nozzle was used to calculate the erosion rate for each submerged entry nozzle. Furthermore, the composition of the refractory material making up 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 submerged entry nozzle. The composition of the refractory material making up the slag line for the 30 submerged entry nozzles 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.

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 corrosion rate V as the response variable. One arbitrary data point selected from the 30 data points was used as the reference data, and the logarithmic ratios of each physical property value and corrosion 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 corrosion rate V was analyzed using a conventional regression analysis method. Spreadsheet software (Microsoft Excel) was used as the analysis tool. The regression analysis revealed that the coefficient of determination ^R2 was highest when the apparent porosity P and apparent specific gravity G were used as explanatory variables, leading to the following regression equation: (4). The definitions of α, β, and γ in equation (4) are as described above. The coefficient of determination ^R2 of equation (4) was 0.8, confirming that the derived regression equation had sufficient estimation accuracy for practical use. By transforming equation (4), equation (3) was derived. The coefficient of determination ^R2 of equation (3) was also 0.8. The relative error was 1.5% on average and 8.0% at maximum.

The estimation method according to this embodiment can be used to estimate the ratio of the corrosion rates in the slag line of any two refractories for a submerged entry nozzle. Furthermore, if the apparent porosity P _A , apparent specific gravity G _A , and corrosion rate V _A of a first refractory for a submerged entry nozzle are known, the ratio γ of the corrosion rates can be estimated by specifying the apparent porosity P _B and apparent specific gravity G _B of the other refractory for a submerged entry nozzle. The corrosion rate V _B of a second refractory for a submerged entry nozzle can be estimated by multiplying the corrosion rate V _A of the first refractory by this γ.

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 previously manufactured 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 _PA , apparent specific gravity _GA , and erosion rate _VA of the first refractory for a submerged entry nozzle can be measured, for example, using a sample of a submerged entry nozzle that has been recovered after use. The apparent porosity _PB and apparent specific gravity _GB of a newly manufactured second refractory for a submerged entry nozzle can be measured using a completed new submerged entry nozzle. Therefore, the erosion rate ratio γ and the erosion rate _VB of the second refractory for a submerged entry nozzle can be estimated from these measurements. 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 submerged entry nozzles.

As another example, the estimation method according to this embodiment can be applied to the estimation of the service life of a submerged entry nozzle (SEN) currently being used for continuous casting. In this case, the SEN refractory constituting the SEN manufactured in the past and used for continuous casting is designated as the first SEN refractory, and the SEN refractory constituting the SEN currently being used for continuous casting is designated as the second SEN refractory. As described above, the apparent porosity _PA , apparent specific gravity _GA , and erosion rate _VA of the first SEN refractory are known. Furthermore, the apparent porosity _PB and apparent specific gravity _GB of the second SEN refractory do not change or are substantially negligible even after use of the SEN. Therefore, the values measured at the time the second SEN refractory was manufactured can be used. Therefore, the erosion rate ratio γ and the erosion rate _VB of the second SEN refractory can be estimated from these measured values. The estimated service life can then be calculated by dividing the allowable amount of corrosion by the estimated value of the corrosion rate _VB of the second refractory for the immersion nozzle. The above-described method makes it possible to estimate the service life, i.e., the lifespan, of the immersion nozzle currently being used in continuous casting, and therefore makes it possible to appropriately determine the timing for replacing the immersion nozzle. This makes it easy to prevent production problems that would otherwise occur if the immersion nozzle were to continue to be used until excessive corrosion had occurred, as well as a decrease in production efficiency that would result from replacing the immersion nozzle when its service life is still remaining.

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.

The present invention will be further explained below with reference to examples. However, the present invention is not limited to these examples.

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% by mass of CaO, 37.4% by mass of _SiO2 , 7.3% by mass of _Na2O , 5.7% by mass of _Li2O , 5.8% by mass _{of Al2O3} , and 6.2% by mass of F. The casting time was 2.3 hours.

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 is included in the zirconia raw material as a stabilizer.

After use, the thickness of the erosion at the slag line of the submerged entry nozzle 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 actual erosion rate ratio was 0.85.

The estimated ratio of the corrosion rates 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 compared to the actual measured value was 2.8%.

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 composition of the slag powder was 35.3 mass% CaO, 30.2 mass% _SiO2 , 13.2 mass% _Na2O , _2.2 mass% _Al2O3 , 7.0 mass% MgO, and 12.2 mass% F. The casting time was 2.0 hours.

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% zirconium dioxide by mass, 10% carbon by mass, and 3% other components by mass, with an apparent porosity of 19.1% and an apparent specific gravity of 4.71. Material B2 had a composition of 87% zirconium dioxide by mass, 10% carbon by mass, and 3% other components by mass, 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% calcium oxide by mass and 1% magnesium oxide by mass, both of which were derived from stabilizers in the zirconia raw material.

After use, the thickness of the erosion at the slag line of the submerged entry nozzle 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 actual erosion rate ratio was 0.83.

The estimated ratio of the corrosion rates 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 compared to the actual measured value was 2.0%.

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% by mass CaO, 43.1% by mass _SiO2 , 7.1% by mass _Na2O , 2.1% by _{mass Li2O} , 17.8% by mass _Al2O3 , 3.2% by mass MgO, and 8.2% by mass F. The casting time was 2.0 hours.

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 zirconium dioxide, 16% by mass carbon, and 3% by mass 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 zirconium dioxide, 8% by mass carbon, and 3% by mass 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 calcium oxide and 1% by mass yttrium (III) oxide, both of which were derived from stabilizers in the zirconia raw material.

After use, the thickness of the erosion at the slag line of the submerged entry nozzle 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 actual erosion rate ratio was 0.82.

The estimated ratio of the corrosion rates 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 compared to the actual measured value was 3.8%.

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 composition of the slag powder was 26.4 mass% CaO, 40.0 mass% _SiO2 , 11.5 mass% _Na2O , _6.6 mass% _Al2O3 , 7.1 mass% MgO, and 8.4 mass% F. The casting time was 2.5 hours.

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.

After use, the thickness of the erosion at the slag line of the submerged entry nozzle 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.

The estimated ratio of the corrosion rates 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 compared to the actual measured value was 3.9%.

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 composition of the slag powder was 37.8% by mass of CaO, 30.8% by mass of _SiO2 , 9.5% by mass of _Na2O , _7.8 % by mass of _Al2O3 , 1.7% by mass of MgO, 1.1% by mass of _Li2O , 2.1% by mass of MnO, and 9.2% by mass of F. The casting time was 4.0 hours.

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% zirconium dioxide by mass, 10% carbon by mass, and 5% other components by mass, with an apparent porosity of 15.8% and an apparent specific gravity of 4.51. The other components were 2% calcium oxide by mass, derived from the stabilizer in the zirconia raw material, and 3% silicon carbide, added as an additive. Material B5 had a composition of 85% zirconium dioxide by mass, 12% carbon by mass, and 3% other components by mass, 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.

After use, the thickness of the erosion at the slag line of the submerged entry nozzle 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 actual erosion rate ratio was 0.87.

The estimated ratio of the corrosion rates 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 compared to the actual measured value was 2.2%.

[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. It was clear that the estimation method according to the present invention has sufficient estimation accuracy for practical use.

This invention can be applied, for example, to estimating the lifespan of an immersion nozzle.

1: Submerged nozzle 11: Discharge port 12: Slag line 2: Mold 3: Slide plate 4: Tundish M: Molten steel S: Powder slag

Claims (3)

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;
specifying an apparent porosity P _A of the first refractory material for a submerged entry nozzle and an apparent porosity P _B of the second refractory material for a submerged entry nozzle;
specifying an apparent specific gravity G _A of the first refractory material for a submerged entry nozzle and an apparent specific gravity G _B of the second refractory material for a submerged entry nozzle;
calculating a ratio γ of a corrosion rate _VB of the second refractory for a submerged entry nozzle to a corrosion rate _VA of the first refractory for a submerged entry nozzle based on the following formulas (1), (2), and (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 has not yet been subjected to continuous casting. 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.