JPWO2020045544A1 - How to start continuous steel casting - Google Patents

Abstract

In order to efficiently and easily reduce the oxygen concentration in the atmosphere inside the tundish before injecting molten steel, when injecting molten steel into the tundish, the atmosphere is changed through the replacement of the gas in the atmosphere inside the tundish before the start of injection. When injecting molten steel with the oxygen concentration reduced and starting continuous casting, in addition to the holes for injecting molten steel from the ladle in the lid of the tundish, to replace the atmospheric gas in the tundish. One or more gas discharge holes are provided, and the distance between the molten steel injection hole and the gas discharge hole is arranged so as to satisfy a certain relationship with the long side length of the tundish. A method for starting continuous casting of steel, in which an inert gas for atmosphere replacement is supplied so as to satisfy a predetermined flow rate with respect to the volume V in the tundish.

Description

The present invention relates to a method for starting continuous casting of steel, particularly a method for starting continuous casting after an appropriate replacement treatment of atmospheric gas in a tundish prior to the start of pouring into a mold.

In recent years, the demand for quality and properties of steel materials has been increasing year by year, and a technique for producing steel with higher cleanliness is required. In particular, non-metallic inclusions (hereinafter referred to as "inclusions") in steel materials have a great influence on quality and properties, and therefore their reduction is required. Although inclusions present in steel include sulfides and nitrides, most of them are oxides produced in the deoxidizing process of the steelmaking process.

Therefore, in the past, various technological developments have been made in the secondary refining process in order to remove inclusions generated in the deoxidation process. As a result, even in materials that require high cleanliness, such as bearing steel, those with an oxygen level in steel of about single ppm can be stably produced.

On the other hand, the molten steel after secondary refining passes through a tundish for dispensing into a continuous casting mold, but if there is air in the tundish before injecting the molten steel, the injected molten steel and the atmosphere Since it reacts with oxygen to form oxide-based inclusions, there is a problem that the inclusions in the steel are reduced during the secondary refining, but the tundish is recontaminated.

Conventionally, in Patent Document 1, the inside of the tundish is purged with an inert gas, and when the oxygen concentration in the tundish becomes 1 vol% or less, molten steel is injected into the tundish. Suggesting a way to get started.

Japanese Patent No. 3642284 (Japanese Unexamined Patent Publication No. 2002-254148)

However, the above-mentioned prior art has the following problems. That is, in the technique disclosed in Patent Document 1, the specific method for reducing the oxygen concentration in the tundish to 1 vol% is unclear, and depending on the flow rate of the inert gas and the form of the tundish at that time, the atmosphere may be affected. There was a problem that it took a long time to lower the oxygen concentration and the operation efficiency was poor.

The present invention has been developed in view of the above problems of the prior art, and an object of the present invention is to efficiently adjust the oxygen concentration in the atmosphere in the tundish before injecting molten steel in the continuous casting process. Moreover, the present invention is to propose a method that can be easily reduced.

The method according to the present invention developed to solve the above problems is
When injecting molten steel into the tundish interposed between the ladle holding the molten steel and the continuous casting mold of the molten steel, the oxygen concentration in the atmosphere was reduced by replacing the gas in the atmosphere in the tundish before the start of injection. When injecting molten steel in the state and starting continuous casting,
In addition to the molten steel injection hole from the ladle, the lid of the tundish is provided with one or more gas discharge holes for replacing the atmospheric gas in the tundish, and the molten steel injection hole and the gas discharge hole are provided. The distance L from the hole is arranged so as to satisfy the following equation (1), and the atmosphere replacement inert gas is introduced into the space inside the tundish from one or more supply pipes installed around the molten steel injection hole. This is a method for starting continuous casting of steel, characterized in that the flow rate Q is supplied so as to satisfy the following equation (2) with respect to the total area A of the gas discharge holes and the volume V in the tundish.
Record
W / 4 ≤ L ≤ 2 W / 3 ... (1)
2.0 ≤ Q ² / (AV) ・ ・ ・ (2)
However,
W: Inner length (m) of the long side of the tundish,
L: The shortest distance (m) between the center of the molten steel injection hole and the center of the atmosphere replacement gas discharge hole,
Q: Total blowing flow rate (Nm ³ / min) of inert gas for atmosphere replacement per unit time
A: Total area of gas discharge holes (m ² )
V: Volume inside the tundish (m ³ ).

Regarding the above method according to the present invention, further, the shortest distance from the center of the molten steel injection hole provided in the lid of the tundish to the center of the gas discharge hole of the atmosphere replacement gas is within the range of the above equation (1). When represented by L that satisfies, the inert gas is blown from at least one position in the range of 2 L / 3 or less, apart from the inert gas blown from the periphery along the molten steel injection hole of the lid of the tundish. In addition, the inert gas blowing angle may be blown toward the gas discharge hole with an inclination of 10 to 80 °, which may be a more preferable embodiment.

Further, in the above method according to the present invention, it is more preferable to start injecting the molten steel in the ladle into the tundish after the oxygen concentration in the tundish atmosphere satisfies the following equation (3). Can be.
Record
0.3 × M / V ≧ (O ₂ ) ・ ・ ・ (3)
M: Amount of molten steel (ton) when the tundish is full
V: Volume inside the tundish (m ³ )
(O ₂ ): Oxygen concentration in a tundish atmosphere (vol%)

According to the method for starting continuous casting of steel according to the present invention having the above-described configuration, the installation position of the gas discharge hole for the atmosphere replacement gas provided on the lid of the tundish, the total area of the gas discharge hole, and the inertness. By appropriately controlling the gas blowing angle, etc., it is possible to effectively prevent contamination of molten steel due to reoxidation, and to provide an extremely effective method especially for continuous casting of high-clean steel. Can be done.

(A), (b), (c), and (d) are schematic diagrams showing examples of tundish morphology. It is a partial cross-sectional view of a tundish. It is a schematic diagram of a tundish for explaining an inert gas blowing angle.

The inventors have described the various forms (a) to (d) of the Tundish 1 as shown in FIG. 1 in advance by using an inert gas as an atmosphere replacement gas in the Tundish 1 as a treatment prior to continuous casting. The preferred method for preventing contamination of molten steel by reoxidation by blowing was investigated. 2 and 3 show the specifications (type I) of the tundish used as the premise of this experiment. In these various tundishes, sampling holes for gas were installed, and the oxygen concentration in the tundish atmosphere was measured by a gas oxygen concentration meter using a vibration type suction pump and an electrochemical oxygen sensor. At the stage of this study, the inventors determined that the presence or absence of the gas discharge hole 3 for the atmospheric replacement gas in the tundish 1, its size and installation position, the blowing angle of the replacement inert gas, and the blowing flow rate. , It was confirmed that the replacement time for lowering the oxygen concentration in the atmosphere in Tandish 1 changed. As the inert gas for replacing the atmosphere in the tundish, argon gas, nitrogen gas or the like can be used.
A weir for controlling the flow of molten steel for promoting the floating of inclusions may be installed in the tundish 1, but especially when the weir plate 6 is installed downward from the tundish lid 1t, the tundish 1 is installed. Between the weir plate 6 and the tundish lid 1t so that the flow of gas in the tundish 1 is not obstructed even if the amount of molten steel stored in the inside is increased and the lower end of the weir plate 6 is immersed in the molten steel. It is desirable to provide a gap at least partially so as to communicate with the space inside the tundish 1 before and after the weir plate 6.

According to the experiment conducted by the inventor at this time, the inert gas used for atmosphere replacement is simply blown in, and if the gas discharge hole for properly discharging the gas is not provided, the blown inert gas is not provided. Etc. remain in the tundish 1 and are eventually discharged from the molten steel injection hole 2. As a result, the gas unexpectedly moves or stays in the tundish 1 and the oxygen concentration decreases. On the contrary, it turned out that it did not proceed, resulting in the result that it took a long time to replace the atmosphere.

On the other hand, the gas discharge hole 3 for discharging the atmosphere-replacement gas is provided at an appropriate position on the tundish lid 1t, that is, the gas discharge is performed on the tundish lid 1t at a position under the condition satisfying the following equation (1). When one or more holes 3 are provided, a stable flow is formed in a certain direction without stagnation of the gas flow from the position where the inert gas is blown for atmosphere replacement to the gas discharge hole 3. It was found that the atmosphere inside the tundish can be replaced with a low oxygen concentration in a short time.

(Number 1)
W / 4 ≤ L ≤ 2 W / 3 ... (1)
here,
W is the inner length (m) of the long side of the tundish,
L is the shortest distance (m) between the center of the hole for injecting molten steel and the center of the hole for discharging the atmosphere replacement gas.
The center of the hole for injecting molten steel and the center of the hole for discharging the atmosphere-replacement gas are the positions of the centers of gravity of the respective tundish lid openings in the horizontal plane shape.

In the present invention, when the gas discharge hole 3 for the atmosphere replacement gas is provided at a position other than the condition of the above formula (1), that is, when L <W / 4, the inert air blown for the atmosphere replacement is provided. The gas does not reach the entire area of the tundish 1, and the short-circuit gas flow toward the gas discharge hole 3 increases. Therefore, it is preferable that L ≧ W / 4. On the other hand, when L> 2W / 3, the installation position of the gas discharge hole 3 for discharging the atmosphere replacement gas is on the tundish end side (outside), and there is a possibility that an appropriate opening area cannot be secured. , L ≦ 2W / 3.

Further, in the present invention, it is effective to control the total flow rate of the inert gas for atmosphere replacement blown into the tundish 1 per unit time. That is, the flow rate of the inert gas supplied into the tundish from one or more supply pipes installed around the molten steel injection hole per unit time shall satisfy the condition of the following equation (2). is required. The reason is that it is necessary to efficiently replace the atmosphere in the tundish before casting, especially when replacing the ladle during continuous casting, in a limited time. That is, in order to replace the atmosphere from the atmospheric atmosphere to the low oxygen concentration within a short time, particularly within a few minutes, the gas discharge hole area and the volume inside the tundish should satisfy the following equation (2). This is because it is necessary to supply the flow rate of the inert gas per unit time into the tundish. If, according (2) out of the condition of formula, Q 2 ^/ becomes the ^(A · V) <2.0, with respect to the hole total area and tundish volume for gas discharge, the inert gas used in an atmosphere substituted In addition to the insufficient flow rate of the gas, the outflow rate of the inert gas in the gas discharge hole cannot be secured, which causes the inflow of the atmosphere and the influence thereof becomes large, so that the atmosphere replacement does not proceed efficiently.

(Number 2)
2.0 ≤ Q ² / (AV) ・ ・ ・ (2)
here,
Q is the total flow rate (Nm ³ / min) of the inert gas for atmospheric replacement per unit time.
A is the total area of the gas discharge holes (m ² )
V is the volume inside the tundish (m ³ ).
In addition, ^{N of Nm 3} represents the standard state of gas.

The reason for limiting the total blowing flow rate of the inert gas atmosphere replacement, in order to achieve sufficient atmosphere replacement, it is necessary to satisfy the ^{Q 2 / (A · V)} ≧ 2.0 ^{preferably, Q 2 / (a · V} ) is ≧ 6.0, So, place the installation of the pipe 4 blowing one or more inert gas which will be described later is valid.

If the gas discharge hole 3 of the inert gas for atmosphere replacement satisfies the above equation (1), not only the tundish lid 1t but also the overflow gutter opening 5 used in an emergency (FIG. 1 (d)). ) Etc. may be substituted. In this case, L indicates the distance between the molten steel injection hole 2 and the overflow gutter opening 5. Further, in an actual tundish, there may be a gap between the lid and the lid or between the lid and the tundish iron skin, etc., which causes atmospheric inflow or the inert gas blown in from the gap. The effect of the present invention may not be sufficiently obtained because the gas flows out and an appropriate gas flow cannot be formed. Therefore, it is desirable to carry out curing with a heat-resistant sheet or an amorphous refractory before casting. When the overflow gutter opening 5 is not used as a discharge hole, it is desirable to cure it with a heat-resistant sheet or the like so as not to obstruct the flow of molten steel in an emergency.

Next, the inventors have described how to blow the inert gas into the tundish 1, particularly one or a plurality of the inert gas blowing pipes 4 provided separately from the blowing of the inert gas along the molten steel injection hole 2. The blowing angle (θ) of the was also examined. As a result, for example, in the example shown in FIG. 2, the oxygen concentration in the atmosphere can be made more efficient by giving a predetermined inclination toward the gas discharge hole 3 of the atmospheric gas (inert gas) from at least one place. Could be reduced to. Here, as shown in FIG. 3, the blowing angle θ of the inert gas is based on the straight line ab in a plane passing vertically through the inert gas blowing point a and the center b of the gas discharge hole 3. It is a downward angle toward the gas discharge hole 3. Basically, the inert gas is blown downward, but a part of the inert gas is inclined toward the gas discharge hole 3 by 10 to 80 ° to make the gas flow in the tundish 1. Propulsion is given, and the atmosphere can be adjusted (gas replacement) more efficiently.

The reason why the blowing angle of the inert gas from the blowing pipe 4 at this time is tilted by 10 to 80 ° is that when the blowing angle is less than 10 ° (θ), the blown gas is in the tundish 1. It flows along the lid and does not work effectively. On the other hand, if the blowing angle is larger than 80 °, it flows almost directly downward, which is also not effective from the viewpoint of imparting propulsive force. Further, depending on the blowing position, it acts so as to obstruct the flow of the inert gas blown from around the molten steel injection hole 2, so it is preferable to set the inclination angle to be smaller than 80 °.

Further, the position of the inclined inert gas blowing pipe 4 is set when the shortest distance between the center of the molten steel injection hole 2 of the tundish lid 1t and the center of the atmosphere replacement gas gas discharge hole 3 is L. It is desirable to install it within 2 L / 3 from the center of the molten steel injection hole 2. If the installation location is larger than 2L / 3, the gas discharge hole 3 is used before the propulsive force is applied to the inert gas blown through the inert blowing pipe 4'from around the molten steel injection hole 2. Since it is discharged from the gas, the expected effect cannot be obtained.

Therefore, in the range within 2 L / 3 from the center of the molten steel injection hole 2 of the tundish lid 1t, the inert gas blowing pipe is introduced from at least one place separately from the inert gas blown from around the molten steel injection hole 2. The inert gas is blown through 4. Further, the effect of the present invention can be obtained as long as the horizontal component of the inert gas blowing is within 20 ° to the left and right with respect to the straight line ab.

In the above description, the opening area of the gas discharge hole 3 of the atmosphere replacement gas provided in the tundish lid 1t is not particularly defined, but the opening area of the gas discharge hole 3 is π (H / 4). ^If it is made larger than 2, the influence of atmospheric inflow becomes large. Therefore, in order to carry out the present invention more efficiently, it is preferable that the opening area of the gas discharge hole 3 is π (H / 4) ² or less. Here, H is the inner length (m) on the short side of the tundish. At this time, when the emergency overflow gutter provided in the tundish 1 is used as one of the gas discharge holes 3, the same effect is obtained if the ^{opening area is π (H / 4) 2 or less.} It is possible to obtain.

Furthermore, as a result of various experiments and studies, it was found that the amount of reoxidation of molten steel is affected by the oxygen concentration in the tundish, the weight of the molten steel in the tundish when it is full, and the volume inside the tundish. That is, when the oxygen concentration in the tundish at the start of injecting the molten steel in the ladle into the tundish satisfies the following equation (3), the increase in oxygen in the molten steel due to reoxidation can be greatly reduced, and the oxygen concentration in the molten steel. The amount of increase can be lower than 1 mass ppm. On the other hand, if the equation (3) is not satisfied, the oxygen concentration in the tundish atmosphere has a large effect on the molten steel, and there is a possibility that inclusions due to reoxidation will increase.
Therefore, it is better to start the molten steel injection from the ladle into the tundish when the oxygen concentration in the tundish atmosphere satisfies the equation (3).

(Number 3)
0.3 × M / V ≧ (O ₂ ) ・ ・ ・ (3)
M: Amount of molten steel (ton) when the tundish is full
V: Volume inside the tundish (m ³ )
(O ₂ ): Oxygen concentration in a tundish atmosphere (vol%)
Here, "full" means the case where the amount of molten steel contained in the tundish is the maximum during the steady casting of the continuous casting machine.

Furthermore, as a result of various experiments and studies, it was found that the amount of reoxidation of molten steel is affected by the oxygen concentration in the tundish, the weight of the molten steel in the tundish when it is full, and the volume inside the tundish. That is, when the oxygen concentration in the tundish at the start of injecting the molten steel in the ladle into the tundish satisfies the following equation (3), the increase in oxygen in the molten steel due to reoxidation can be greatly reduced, and the oxygen concentration in the molten steel can be significantly reduced. The amount of increase can be lower than 1 mass ppm. On the other hand, if the equation (3) is not satisfied, the oxygen concentration in the tundish atmosphere has a large effect on the molten steel, and there is a possibility that inclusions due to reoxidation will increase.
Therefore, it is better to start the molten steel injection from the ladle into the tundish when the oxygen concentration in the tundish atmosphere satisfies the equation (3).

(Number 4)
0.3 × M / V ≧ (O ₂ ) ・ ・ ・ (3)
M: Amount of molten steel (ton) when the tundish is full
V: Volume inside the tundish (m ³ )
(O ₂ ): Oxygen concentration in a tundish atmosphere (vol%)

Hereinafter, examples of the present invention will be described in comparison with comparative examples. This example is given as a representative of high-cleanliness steel through each process of converter-ladle smelting furnace-RH vacuum degassing furnace-continuous casting in an actual machine with a molten steel amount of about 200 tons per charge. This is an example of manufacturing a bearing steel. The composition of the bearing steel is as follows: carbon concentration 0.90% by mass or more and 1.10% by mass or less, silica concentration 0.15% by mass or more and 0.25% by mass or less, manganese concentration 0.45% by mass or less, phosphorus concentration. 0.020% by mass or less, sulfur concentration 0.0050% by mass or less, aluminum concentration 0.030% by mass or less, chromium concentration 1.4% by mass or more and 1.7% by mass or less, nitrogen concentration 0.0050% by mass or less Is. In each method, after heating and stirring in a ladle smelting furnace, RH vacuum degassing, and then a tundish from the ladle, a curved continuous casting machine (without a vertical part directly under the mold) is used to draw out bloom slabs. A cross-sectional dimension perpendicular to the direction (thickness 300 mm × width 400 mm) was cast at a slab drawing speed of about 0.70 m / min. At this time, tundishes of various forms (T type in FIG. 1 (a) and I type in FIGS. 1 (b), (c), (d)) were used and first provided at a heating position on the casting bed. The inside of the tank was heated to about 1000 ° C. with a flame obtained by burning coke oven gas with a burner. Next, the burner was extinguished, the tundish was moved to the casting position, and the inert gas was started to be blown into the tundish through a gas blowing pipe provided separately from the one from the molten steel injection hole. After that, injection of molten steel into the tundish in the ladle was started through a long nozzle attached to the sliding nozzle on the bottom of the ladle. In addition, the index of the total oxygen concentration in the slab when the sum of the total oxygen concentration in the molten steel before the tundish injection, that is, the dissolved oxygen concentration and the oxygen concentration corresponding to the inclusions is 1, is shown. The sample for total oxygen analysis was taken from the thickness 1/4 position of the center of the width in the top side cross section of the bottommost part of the slab cut at the position corresponding to about 3 tons from the casting start end, and the inert gas was melted. It was subjected to analysis according to the infrared absorption method.

Table 1 shows the form of the tundish, the total flow rate of the inert gas, and the oxygen concentration in the tundish atmosphere 3 minutes after the start of the blowing of the inert gas for the examples of the present invention and the comparative examples.

As shown in Table 1, in each of the examples of the present invention, the oxygen concentration in the atmosphere inside the tundish at the start of injection into the tundish was reduced to 2 vol% or less, and almost no reoxidation occurred even after the injection of molten steel. Along with reaching the level, the total oxygen concentration in the slab was also good. On the other hand, when a test was conducted using a tundish without a gas discharge hole for the atmosphere replacement gas, the oxygen concentration at the start of molten steel injection into the tundish was as high as 2.9 vol to 6.2 vol%. .. Further, even when the gas discharge hole is used, the distance between the molten steel injection hole and the gas discharge hole of the inert gas is shorter than the condition of the present invention, or the total flow rate of the inert gas blown is the tundish volume or the gas. When the discharge hole area was insufficient, the oxygen concentration at the start of injection of the molten steel into the tundish was 3 vol% or more, which did not reach a level at which the reoxidation of the molten steel could be suppressed. As a result, the total oxygen concentration in the slab was higher than that before the tundish injection, and good results could not be obtained.

Similar to Example 1, in an actual machine with a 1-charge molten steel amount of about 200 tons, the composition is the same as that of Example 1 in each step of converter-ladle smelting furnace-RH vacuum degassing furnace-continuous casting. Manufactured bearing steel. At this time, injection of molten steel into the tundish was started using various forms of tundish defined by L and W.
Table 2 shows the tundish form, the weight of the molten steel when the tundish is full, the total flow rate of the inert gas blown into the tundish, and the oxygen concentration in the tundish atmosphere at the start of injection of the molten steel into the tundish. In addition, the index of the total oxygen concentration in the slab when the sum of the total oxygen concentration in the molten steel before the tundish injection, that is, the dissolved oxygen concentration and the oxygen concentration corresponding to the inclusions is 1, is shown. The sampling position of the slab sample for the total oxygen concentration and the analysis method are the same as in Example 1.

As shown in Table 2, in all of the examples of the present invention, the oxygen concentration in the atmosphere inside the tundish at the start of injecting molten steel into the tundish is reduced to 2 vol% or less, and the total oxygen concentration in the slab is also good. Results were obtained. In Examples 15 to 18 of the present invention in which the gas discharge holes for the inert gas were appropriately installed and the inert gas was properly injected, the oxygen concentration in the tundish atmosphere at the start of injection of molten steel into the tundish was not inclined. It was possible to reduce the amount more stably than in the case of. Further, in addition to the inclined blowing, the oxygen concentration in the tundish atmosphere at the start of molten steel injection into the tundish is 0.3 × M / V (M: molten steel weight (ton) when the tundish is full, V: volume inside the tundish). (M ³ )) In Examples 19 to 22 of the present invention satisfying the following, the oxygen concentration in the atmosphere inside the tundish is reduced to 1 vol% or less, and the total oxygen concentration in the slab is also about about before the tundish injection. Very good results were obtained with 70% or less.

The effect of the present invention is not limited by the composition and concentration of the steel, and the present invention can be applied to steels of any composition system.

1 Tandish 1t Tundish lid 2 Molten steel injection hole 3 Gas discharge hole 4 Inert gas injection pipe 5 Overflow gutter opening 6 Weir

Claims (3)

When injecting molten steel into the tundish interposed between the ladle holding the molten steel and the continuous casting mold of the molten steel, the oxygen concentration in the atmosphere was reduced by replacing the gas in the atmosphere in the tundish before the start of injection. When injecting molten steel in the state and starting continuous casting,
In addition to the holes for injecting molten steel from the pan, the lid of the tundish is provided with one or more holes for discharging gas for replacing the atmospheric gas in the tundish, and the holes for injecting molten steel and the holes for discharging gas. The distance L from the hole is arranged so as to satisfy the following equation (1), and an atmosphere replacement inert gas is introduced into the space inside the tundish from one or more supply pipes installed around the molten steel injection hole. A method for starting continuous casting of steel, which comprises supplying a flow rate Q so as to satisfy the following equation (2) with respect to the total area A of the gas discharge holes and the volume V in the tundish.
Record
W / 4 ≤ L ≤ 2 W / 3 ... (1)
2.0 ≤ Q ² / (AV) ・ ・ ・ (2)
However,
W: Inner length (m) of the long side of the tundish,
L: The shortest distance (m) between the center of the molten steel injection hole and the center of the atmosphere replacement gas discharge hole,
Q: Total blowing flow rate (Nm ³ / min) of inert gas for atmosphere replacement per unit time,
A: Total area of gas discharge holes (m ² )
V: Volume inside the tundish (m ³ ). When the shortest distance from the center of the molten steel injection hole provided on the lid of the tundish to the center of the gas discharge hole of the atmosphere replacement gas is represented by L satisfying the range of the above equation (1), it is within 2L / 3 In addition to the inert gas blown from around the molten steel injection hole of the lid of the tundish, the inert gas is blown from at least one position, and the inert gas blowing angle is set to the gas discharge. The method for starting continuous casting of steel according to claim 1, wherein the gas is blown into the hole with an inclination of 10 to 80 °. The start of continuous casting of the steel according to claim 1 or 2, wherein the molten steel in the ladle is started to be injected into the tundish after the oxygen concentration in the tundish atmosphere satisfies the following equation (3). Method.
Record
0.3 × M / V ≧ (O ₂ ) ・ ・ ・ (3)
M: Amount of molten steel (ton) when the tundish is full
V: Volume inside the tundish (m ³ )
(O ₂ ): Oxygen concentration in a tundish atmosphere (vol%)

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