Method for estimating the actual flow rate of inert gas supplied to molten steel in a submerged entry nozzle

Abstract

To provide a method for estimating a real flow rate of an inert gas fed to a molten steel in an immersion nozzle upon continuous casting of the molten steel.SOLUTION: A method for estimating a real flow rate of an inert gas fed to a molten steel in an immersion nozzle when the molten steel is fed from an intermediate container to a mold via a sliding gate and an immersion nozzle at a time of continuous casting of the molten steel, and, when an inert gas is blown into the immersion nozzle, includes: previously obtaining a relation between the real flow rate of the inert gas fed to the molten steel in the immersion nozzle and an opening degree of the sliding gate in accordance with the throughput of the molten steel; and estimating the real flow rate of the inert gas fed to the molten steel in the immersion nozzle from the opening degree of the sliding gate, the throughput of the molten steel and the previously obtained relation at the time of continuous casting of the molten steel.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present application discloses a method for estimating the actual flow rate of inert gas supplied to molten steel in an immersion nozzle when molten steel is supplied from a tundish to a mold via a sliding gate (hereinafter sometimes abbreviated as "SG") and an immersion nozzle during continuous casting of molten steel, and when inert gas is blown into the immersion nozzle. [Background technology]

[0002] Patent Document 1 discloses a method for adjusting the flow rate of inert gas blown into the submerged entry nozzle by controlling a valve that adjusts the flow rate of the inert gas based on a change in the opening degree of the sliding gate, when molten steel is supplied from a tundish to a mold via a sliding gate and a submerged entry nozzle during continuous casting of molten steel and an inert gas is blown into the submerged entry nozzle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-031413 Summary of the Invention [Problem to be solved by the invention]

[0004] In continuous casting machines, inert gas leaks occur from the fitting between the refractory material and the inert gas injection mechanism, etc. However, the actual amount of leakage is unknown, and it is currently impossible to measure the actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle. Therefore, even if the flow rate of the inert gas injected into the submerged entry nozzle is adjusted using the method disclosed in Patent Document 1, it is not possible to know whether the inert gas is being supplied to the molten steel in the submerged entry nozzle at the desired flow rate. In this regard, a method is needed to estimate the actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle. [Means for solving the problem]

[0005] As one of the means for solving the above problems, the present application provides: During continuous casting of molten steel, While maintaining a height between the level of the molten steel in the intermediate vessel and the level of the molten steel in the mold, From the intermediate vessel through the sliding gate and submerged nozzle The aforementioned A method for estimating an actual flow rate of an inert gas supplied to the molten steel in the submerged entry nozzle when the molten steel is supplied to a mold and the inert gas is blown into the submerged entry nozzle, comprising: For each value of the throughput of the molten steel, The relationship between the actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle and the opening degree of the sliding gate. Predict Seeking, and estimating an actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle from the opening degree of the sliding gate, the throughput of the molten steel, and the previously determined relationship during continuous casting of the molten steel; A method including Disclose 。

[0006] In the method of the present disclosure, the relationship may be determined in advance by a model experiment using a low-melting-point metal. [Effects of the Invention]

[0007] According to the technique of the present disclosure, it is possible to estimate the actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows a schematic diagram of a state in which molten steel is supplied from an intermediate vessel to a mold through a sliding gate and an immersion nozzle during continuous casting of molten steel, and an inert gas is blown into the immersion nozzle. [Figure 2] 1 illustrates the flow of the method of the present disclosure. [Figure 3]10 is a diagram illustrating the relationship between the opening degree of the sliding gate and the supply flow rate of the inert gas at a predetermined molten steel throughput. [Figure 4] The diagram shows a schematic configuration of a model experimental device using low-melting-point metal. [Figure 5] FIG. 10 is a schematic diagram for explaining measurement of pressure loss. [Figure 6] 10 is a schematic diagram for explaining the concept of a method for estimating the actual flow rate of an inert gas supplied to a flow path. FIG. [Figure 7] 10 is a schematic diagram for explaining the concept of a method for estimating the actual flow rate of an inert gas supplied to a flow path. FIG. [Figure 8] The relationship between the SG opening and pressure loss, and the relationship between the inert gas flow rate and pressure loss are shown. [Figure 9] FIG. 10 is a diagram for explaining an example of a change in SG opening degree due to inert gas injection. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1, the method of the present disclosure is a method for estimating the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 when the molten steel 10 is supplied from an intermediate vessel 20 to a mold 50 via a sliding gate 30 and a submerged entry nozzle 40 and the inert gas 60 is blown into the submerged entry nozzle 40 during continuous casting of the molten steel 10. As shown in FIG. 2, the method S10 of the present disclosure includes: determining in advance the relationship between the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 and the opening degree of the sliding gate 30 in accordance with the throughput of the molten steel 10 (step S1); and estimating the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 during continuous casting of the molten steel 10 from the opening degree of the sliding gate 30, the throughput of the molten steel 10, and the previously determined relationship (step S2).

[0010] 1.Process S1 In step S1, the relationship between the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 and the opening degree of the sliding gate 30 is determined in advance according to the throughput of the molten steel 10. The "actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle" is the flow rate of the inert gas blown into the submerged entry nozzle minus the amount of gas leaking out of the submerged entry nozzle, and refers to the flow rate actually supplied to the molten steel in the submerged entry nozzle.

[0011] 1 and 3(A), in continuous casting of molten steel 10, the opening degree of the sliding gate 30 can be controlled so that the throughput TP of the molten steel 10 becomes a target value while maintaining a height H between a level M1 of the molten steel 10 in an intermediate vessel (e.g., a tundish) 20 and a level M2 of the molten steel 10 in a mold 50. For example, by maintaining the opening degree of the sliding gate 30 while maintaining the height H, the throughput TP of the molten steel 10 can be kept constant. When it is desired to increase the throughput TP of the molten steel 10, the opening degree of the sliding gate 30 is increased while maintaining the height H, and when it is desired to decrease the throughput TP of the molten steel 10, the opening degree of the sliding gate 30 is decreased while maintaining the height H.

[0012] 3(B), when the inert gas 60 is injected into the submerged entry nozzle 40, a pressure loss occurs corresponding to the amount of the inert gas 60 that is actually supplied to the molten steel 10 without leaking to the outside. That is, when the inert gas 60 is injected into the submerged entry nozzle 40, in order to maintain the throughput TP of the molten steel 10, it is necessary to increase the opening degree of the sliding gate 30 to overcome the pressure loss caused by the inert gas 60 supplied to the molten steel 10. In other words, there is a predetermined correlation between the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 and the opening degree of the sliding gate 30, depending on the throughput TP of the molten steel 10.

[0013] The relationship between the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged nozzle 40 and the opening degree of the sliding gate 30 may be determined through various model experiments, numerical calculations, etc. In particular, this relationship may be determined in advance through model experiments using low-melting-point metals (metals with a melting point lower than that of steel, such as Sn or Sn alloys with a melting point of 300°C or less). In model experiments using low-melting-point metals, it is possible to match dimensionless numbers such as the Froude number, Reynolds number, and Weber number with those in a molten steel system (Patent No. 6750533), and this can be said to accurately simulate the flow conditions of gases and molten steel in a molten steel system. Furthermore, the equipment used in the model experiments can create an ideal state in which there is virtually no leakage of inert gas. This makes it possible to determine the relationship between the flow rate of the inert gas actually supplied to the low-melting-point metal in the submerged entry nozzle (= the flow rate of the inert gas injected into the submerged entry nozzle) and the opening degree of the sliding gate. By converting this to a molten steel system, it is possible to determine the relationship between the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 and the opening degree of the sliding gate 30. This relationship may be expressed by a mathematical formula as a function of the opening degree of the sliding gate 30 and the actual flow rate of the inert gas. Specific forms of model experiments using low-melting-point metals will be described in detail in the Examples.

[0014] 2.Process S2 In step S2, during continuous casting of the molten steel 10, the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged nozzle 40 is estimated from the opening degree of the sliding gate 30, the throughput of the molten steel 10, and the above-mentioned relationship determined in advance.

[0015] According to the method S10 of the present disclosure, the actual flow rate of the inert gas 60 supplied to the molten steel 10 in the submerged entry nozzle 40 can be estimated simply by obtaining information related to the opening degree of the sliding gate 30 and information related to the throughput TP of the molten steel 10 during continuous casting of the molten steel 10. The opening degree of the sliding gate 30 and the throughput TP of the molten steel 10 can be measured or determined directly or indirectly by known methods that are obvious to those skilled in the art.

[0016] For example, if the opening degree of the sliding gate 30 required to maintain a predetermined molten steel throughput TP during continuous casting of molten steel 10 without injecting inert gas ( FIG. 3(A) ) is assumed to be the "initial opening degree," then when inert gas is injected while maintaining the throughput TP, the opening degree of the sliding gate 30 can be increased by a predetermined amount from the initial opening degree in response to the actual flow rate of the inert gas supplied to the molten steel 10 in the submerged entry nozzle 40 ( FIG. 3(B) ). Furthermore, if the actual flow rate of the inert gas supplied to the molten steel 10 in the submerged entry nozzle 40 changes due to a change in the amount of inert gas injected or leakage, the opening degree of the sliding gate 30 also changes in accordance with the change in the actual flow rate. In other words, according to the method S10 of the present disclosure, the actual flow rate of the inert gas supplied to the molten steel 10 in the submerged entry nozzle 40 and the amount of change therein can be estimated from the opening degree of the sliding gate 30 and the amount of change therein while maintaining the throughput TP of the molten steel 10. That is, "estimating the actual flow rate" in the present application includes not only a form of estimating the actual flow rate itself, but also a form of estimating the amount of change in the actual flow rate.

[0017] 3. Supplementary Information The continuous casting machine and continuous casting conditions employed in the method S10 of the present disclosure may be the same as those employed in the conventional continuous casting machine. The type (steel grade) of the molten steel 10 is not particularly limited, as long as it is an alloy containing iron. Furthermore, the configurations of the intermediate vessel 20 (e.g., a tundish), the sliding gate 30, the submerged entry nozzle 40, and the mold 50 are not particularly limited. The mechanism and injection position of the inert gas 60 are also not particularly limited. For example, a flow path (hole) for introducing the inert gas may be provided in the side wall of the sliding gate 30 or the submerged entry nozzle 40, and the inert gas 60 may be injected through this path. Alternatively, the inert gas may be injected upstream of the sliding gate 30. The type of inert gas is also not particularly limited, and may be, for example, argon (Ar). According to the method S10 of the present disclosure, the actual flow rate Q can be estimated without introducing any new equipment into a conventional continuous casting machine. [Example]

[0018] The present invention will be further explained below with reference to model experiments using low-melting-point metals, but the present invention is not limited to the following examples. The present invention allows various conditions to be adopted as long as the object is achieved without departing from the gist of the invention.

[0019] 1. Model experiments using low-melting-point metals 1.1 Experimental conditions Figure 4 shows an overview of the equipment used in the model experiment. The position of the sliding gate (SG), the submerged entry nozzle, and the mold vessel shape were modeled after those of an actual continuous casting machine. In the experiment, the entire equipment shown in Figure 4 was heated and maintained with a heater. A vacuum was drawn inside the simulated tundish (supply tank), filling it with molten tin (melting point 231.9°C). The pressure was maintained constant by operating the suction of the vacuum pump VP via a manual valve. The molten tin was circulated using an electromagnetic pump MP, and the circulating flow rate was measured with an electromagnetic flow meter MFM. The molten tin level in the simulated mold was measured with a laser level meter LL, and the molten tin level in the simulated mold was maintained constant by operating various manual valves. The pressure in the circulation system was measured with a pressure gauge. The molten tin level in the circulation system was measured with a microwave level meter ML.

[0020] Argon (Ar) was blown into the SG structure from an inlet above the immersion nozzle. The SG structure reproduced a flow path with the SG opening fixed at a constant SG opening condition (%), as described below.

[0021] Here, the "SG opening" can be determined based on the stroke amount of the middle sliding plate among the three plates, as shown in FIG. 3, for example. Specifically, if the stroke rate of the sliding plate is SR (see formula (I) below), the SG opening (%) can be determined as 100-SR. That is, when the circular hole in the sliding plate is fully open to the flow path, the stroke rate is 0% and the SG opening is 100%. When the circular hole in the sliding plate is fully closed to the flow path, the stroke rate is 100% and the SG opening is 0%. Similarly, for example, when the stroke rate is 75%, the SG opening is 25%. In this experiment, the SG opening was determined based on the stroke rate. However, the SG opening may also be determined based on the area opening. That is, the SG opening may be determined as the ratio (a / A × 100%) of the area a of the portion facing the flow path (the portion functioning as an opening) to the total area (A) of the circular hole in the sliding plate. SR=X / D0×100% …(I) D0: Diameter of the circular hole in the sliding plate (mm) X: The stroke amount (mm) of the sliding plate, which is 0 when fully open and D0 when fully closed.

[0022] Eight 0.5 mm diameter holes were evenly spaced around the circumference of the inner wall of the tube above the SG structure. An air storage chamber was installed outside the submerged entry nozzle so as to cover all of the 0.5 mm diameter holes. After filling the air storage chamber, Ar was blown into the tube evenly through each hole without a break. The Ar flow rate was kept constant using a mass flow controller.

[0023] The circulation flow rate, pressure in the tundish, and molten metal surface height in the tundish and mold were measured while changing the SG opening, the Ar flow rate, and the electromagnetic pump output.

[0024] 1.2 Measurement of pressure loss In the above experimental system, the state before the electromagnetic pump is operated is as shown in Figure 5(A). The pressure inside the tundish at this time is p, and the height difference between the molten metal surface in the tundish and the molten metal surface in the mold is h. Next, Figure 5(B) shows the state after the electromagnetic pump is operated. The circulation flow rate of Sn circulated by the pump is Q, and the representative speed calculated from this is v. The increase / decrease in the pressure inside the tundish at this time is Δp, and the increase / decrease in the height difference is Δh. Using Bernoulli's equation with a focus on the tundish-mold relationship, the fluid energy E can be expressed as in the following equation (1).

[0025] E=(1 / 2) ρ v 2 +Δp+ρgΔh+ε0(v) (1)

[0026] where ρ is the density of the fluid, g is the acceleration due to gravity, and ε0 is the pressure loss caused by the flow path structure, such as elbows, expansions and contractions, and wall friction, and is generally expressed as a function of velocity v.

[0027] Next, when the SG is closed or Ar is being blown in, the following equation (2) shows the case where the same circulation flow rate Q (i.e., the same representative velocity v) as in equation (1) is maintained. As an example, the state when the SG is closed is shown in Figure 5(C).

[0028] E+ΔE=(1 / 2) ρ v 2 +Δp'+ρgΔh'+ε0(v) ···(2)

[0029] In this case, the pressure loss due to SG or Ar injection is taken into account, so the required fluid energy increases by ΔE. Therefore, the increase or decrease in pressure and the increase or decrease in height difference may not match the values ​​shown in equation (1). Therefore, the respective notations are Δp' and Δh'. Considering the difference between equations (1) and (2), the increase in fluid energy, i.e., the pressure loss, can be expressed as equation (3) below.

[0030] ΔE=Δp-Δp'+ρg(Δh-Δh') ···(3)

[0031] In the above experimental system, all values ​​on the right side of equation (3) are known or measurable, so it is possible to measure the pressure drop due to SG or Ar injection.

[0032] 2. Concept of the method for estimating the actual flow rate of Ar supplied to the flow path The actual flow rate of Ar in an actual machine can be estimated using the pressure loss due to SG and Ar injection calculated by the above formula (3). In an actual continuous casting machine, the mold and tundish are both open to the atmosphere, so the pressure is always constant. In this state, the throughput TP and the molten metal surface position in the mold and the molten metal surface position in the tundish are kept constant by automatic control of the SG opening. In other words, the only variable term in the above formula (2) is the pressure loss term, and if the other terms are constant, the pressure loss term will also be constant. In this case, for example, if the pressure loss due to the SG is ΔE sg = a [kPa] (Fig. 6, left side). Here, the same pressure loss ΔE ar Consider a situation where Ar is injected, causing a pressure drop of 0.01kPa. In this case, the SG is expected to be fully open due to automatic control of the SG opening to keep the throughput TP, the molten metal level in the mold, the molten metal level in the tundish, and pressure loss constant (right side of Fig. 6).

[0033] Next, let us consider a case where the actual flow rate of Ar supplied is unknown, similar to the actual situation in an actual machine. When a certain throughput TP is maintained and the SG opening is 50%, the pressure loss due to the SG is ΔE sg Let us assume a casting situation where the pressure is equal to a [kPa] (Fig. 7, left side). Here, we consider a situation where an unknown amount of Ar is injected. As a result, the SG opening is changed to 25% by automatic control. At this time, the pressure loss due to the SG is ΔE sg ' = c [kPa], the pressure loss due to the Ar blown in is ΔE ar= ac [kPa]. In other words, the Ar flow rate corresponding to this pressure loss was injected as the actual flow rate (right side of Figure 7). Note that the above approach to estimating the actual flow rate requires the SG opening and pressure loss due to Ar injection at each throughput as reference values, but this can be achieved by measuring the pressure loss under each condition in a model experiment.

[0034] 3. Experimental Results 3.1 Pressure loss due to SG opening and Ar injection measured in the experimental system Based on the above idea, the pressure loss due to SG opening and Ar injection was measured in the above model experiment. The results are shown in Figures 8(A) and (B). As shown in Figures 8(A) and (B), for both SG opening and Ar injection, the pressure loss was on the order of several kPa to several tens of kPa, which is within a comparable numerical range for each pressure loss.

[0035] As an example of applying the above concept, Figure 9 shows the predicted change in SG opening when Ar is injected at 0.3 NL / min under the initial conditions (throughput TP = 4.9 ton / min and SG opening = 45%). The values ​​in the figure are based on the measurement results shown in Figures 8(A) and 8(B). In the initial state, the pressure loss is only 20 kPa due to the SG opening (Figure 9(1)). From this, it can be seen that if the throughput TP and the molten surface position between the tundish and the mold are maintained by automatic control even after Ar injection, the pressure loss in the system will be maintained at 20 kPa (Figure 9(2)). On the other hand, the pressure loss due to an Ar flow rate of 0.3 NL / min is 9 kPa (Figure 9(3)). Consequently, the SG opening is changed to 52% (Figure 9(4)), resulting in a pressure loss of 11 kPa, so that the total pressure loss due to the SG opening and Ar injection becomes 20 kPa.

[0036] 3.2 Summary As described above, model experiments using low-melting-point metals enable the measurement of pressure loss during SG operation and Ar injection. This is because the experimental system allows accurate measurement of the molten metal level in the tundish, the molten metal level in the mold, the pressure in the tundish, the Ar flow rate, and the SG opening. Furthermore, the pressure loss during Ar injection from near the top of the SG was measured in the model experiments, as well as the pressure loss of the SG alone. The results showed that there was no significant difference in the order of pressure loss due to SG opening and Ar injection. However, the SG pressure loss was significant depending on the SG opening, demonstrating the validity of estimating the actual Ar flow rate as described above. When these results are applied to an actual process, the actual Ar flow rate supplied to the molten steel in the SEN can be estimated from the change in SG opening during Ar injection. This is based on the idea that the pressure loss in the system is maintained constant by controlling the SG opening in the actual process. Reference values ​​for the SG opening and pressure loss due to Ar injection should be determined in advance, such as through model experiments using low-melting-point metals.

[0037] 4. Study on actual equipment The validity of the above estimation of the actual Ar flow rate was indirectly confirmed by conducting a continuous casting test in an actual machine.

[0038] First, prior to the continuous casting test, a molten metal model experiment (using the above-mentioned low-melting-point metal) was conducted to simulate the continuous casting test, and the relationship between the Ar flow rate and the sliding gate opening degree at each throughput was clarified.

[0039] Next, a continuous casting test was conducted using an actual machine corresponding to the above model experiment. Here, Ar was injected only through the three-plate sliding gate during continuous casting. The actual flow rate of Ar injected from the sliding gate into the molten steel in the SEN was estimated based on the SG opening and the relationship obtained from the above model experiment. The results of (1) nozzle clogging and (2) the amount of pore defects on the slab surface were investigated for cases where Ar injection was controlled so that the estimated value was a predetermined value, and cases where such control was not performed.

[0040] In the following continuous casting tests, Ar was injected at a rate of 10 NL / min at a casting speed of Vc = 1.5 m / min, and the estimated actual flow rate of Ar was 1 NL / min, which was used as the "reference." Note that the Ar injection flow rate (10 NL / min) here refers to the flow rate set as a constant flow rate by a mass flow controller installed upstream of the Ar injection unit. The same applies below.

[0041] (1) Nozzle blockage After the completion of continuous casting, the inner wall of the submerged nozzle was observed, and the thickness was converted into an index, where the thickness of the layer adhering to the inner wall in the above-mentioned "criteria" was assigned a value of "1" and the absence of a layer adhering to the inner wall was assigned a value of "0," and this was evaluated as the "clogging index."

[0042] (2) Pore defects on the surface of the slab In the above "standard," the number of cellular defects present in the surface 10 mm of the cast piece obtained after continuous casting was indexed as "1," and the absence of any cellular defects was indexed as "0," and this was evaluated as the "cellular defect index."

[0043] 4.1 Example 1 This is an example of the "reference" mentioned above. In the above continuous casting test, when Ar was injected at 10 NL / min for a casting speed of Vc = 1.5 m / min, the estimated actual flow rate of Ar was 1 NL / min. In other words, it was estimated that only 1 / 10 of the injected amount of Ar was actually injected.

[0044] 4.2 When sealing performance is reduced 4.2.1 Example 2 After intentionally reducing the Ar sealing property in the continuous casting machine, a continuous casting test was conducted in the same manner as in Example 1. In this case, when Ar was injected at 10 NL / min at a casting speed of Vc = 1.5 m / min, the estimated actual flow rate of Ar was 0.5 NL / min. In other words, it was estimated that Ar was only injected at half the actual flow rate of Example 1. Continuous casting was conducted while maintaining this condition.

[0045] 4.2.2 Example 3 In a continuous casting machine similar to that of Example 2, the Ar flow rate was increased to optimize the estimated value of the actual Ar flow rate. By increasing the Ar flow rate to 15 NL / min, the estimated value became 1.0 NL / min. Continuous casting was continued while maintaining the estimated value at 1.0 NL / min.

[0046] 4.3 When sealing performance is improved 4.3.1 Example 4 After intentionally strengthening the Ar sealing performance in the continuous casting machine, a continuous casting test was conducted in the same manner as in Example 1. In this case, when Ar was injected at 10 NL / min at a casting speed of Vc = 1.5 m / min, the estimated actual flow rate of Ar was 2 NL / min. In other words, it was estimated that Ar was being injected at an actual flow rate twice that of Example 1. Continuous casting was conducted while maintaining this condition.

[0047] 4.3.2 Example 5 In a continuous casting machine similar to that of Example 4, the Ar injection flow rate was reduced to optimize the estimated value of the actual Ar flow rate. By reducing the Ar injection flow rate to 5 NL / min, the estimated value became 1.0 NL / min. Continuous casting was continued while maintaining the estimated value at 1.0 NL / min.

[0048] 4.4 Evaluation results Table 1 below shows the evaluation results of the clogging index and the bubble defect index for Examples 1 to 5.

[0049] [Table 1]

[0050] As is clear from the results shown in Table 1, regardless of the sealing performance of the Ar in the continuous casting machine, by changing the set flow rate of Ar injection so that the estimated value of the actual Ar flow rate was 1 NL / min, the same results as in Example 1, which was the reference, were obtained for both the blockage index and the bubble defect index (Examples 3 and 5). This proves that the estimation of the actual Ar flow rate was valid.

[0051] On the other hand, in Example 2, where the estimated value of the actual Ar flow rate was maintained at 0.5 NL / min, the bubble defect index decreased and the blockage index increased compared to the reference Example 1. This can be said to be the result of a decrease in the actual flow rate of Ar supplied to the molten steel, which reduced the number of bubbles in the molten steel while also reducing the effectiveness of floating and removing inclusions, etc., and can be said to prove that the estimation of the actual Ar flow rate was valid.

[0052] In addition, in Example 4, where the estimated value of the actual Ar flow rate was maintained at 2 NL / min, the clogging index decreased but the bubble defect index increased compared to the reference Example 1. This can be said to be the result of an increase in the actual flow rate of Ar supplied to the molten steel, which improved the effect of floating and removing inclusions, etc., while also increasing the number of bubbles in the molten steel, and it can be said to prove that the estimation of the actual Ar flow rate was valid.

[0053] From the above results, it can be said that by determining in advance the relationship between the actual flow rate of the inert gas supplied to the molten steel in the SEN and the SG aperture depending on the throughput of the molten steel based on low-melting-point metal model experiments, etc., it is possible to obtain a reasonable estimate of the actual flow rate of the inert gas supplied to the molten steel in the SEN from the previously determined relationship between the SG aperture, the throughput of the molten steel, and the actual continuous casting operation. In this way, the technology disclosed herein makes it possible to appropriately estimate the actual state of inert gas injection into the molten steel in the SEN, enabling appropriate injection depending on, for example, the use of the cast slab, the conditions of continuous casting, etc. [Explanation of symbols]

[0054] 10 Molten Steel 20 Intermediate container 30 Sliding Gate 40 Submerged Entry Nozzle 50 Mold 60 Inert Gas

Claims

1. A method for estimating an actual flow rate of an inert gas supplied to the molten steel in the submerged entry nozzle during continuous casting of molten steel, in which the molten steel is supplied from the intermediate vessel to the mold through a sliding gate and a submerged entry nozzle while maintaining a height between a level of the molten steel in the intermediate vessel and a level of the molten steel in the mold, and the inert gas is blown into the submerged entry nozzle, comprising: determining in advance a relationship between an actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle and an opening degree of the sliding gate for each value of the throughput of the molten steel; and estimating an actual flow rate of the inert gas supplied to the molten steel in the submerged entry nozzle from the opening degree of the sliding gate, the throughput of the molten steel, and the previously determined relationship during continuous casting of the molten steel; A method comprising:

2. The relationship is determined in advance by a model experiment using a low-melting-point metal. The method of claim 1.

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