JP2023067010A - System for supplying molten steel and continuous casting method of steel - Google Patents

Abstract

To provide a system for supplying molten steel, in which, when molten steel is supplied from one vessel to another vessel through a nozzle, bubbles introduced into the molten steel in the nozzle can be prevented from leaving the nozzle, and the generation of bare hot water in the other vessel can be suppressed.SOLUTION: In a system of supplying molten steel 105 from a first vessel 101 to a second vessel 102 through a nozzle 110, the nozzle has an inlet 110a on the upstream side of the first vessel and an outlet 110b on the downstream side of the second vessel, and extends downward from the upstream side to the downstream side. The outlet of the nozzle is located below the liquid level of the molten steel supplied to the second vessel and above a bottom surface 102a of the second vessel. In the supply system, a flow rate Q (ton/min) of molten steel flowing inside the nozzle, the minimum inner diameter of the nozzle D1 (mm) upstream from the outlet, and the inner diameter of the nozzle D2(mm) at the outlet satisfy a prescribed relational expression.SELECTED DRAWING: Figure 3

Description

The present application discloses a molten steel supply system and a method for continuous casting of steel.

In continuous steel casting processes, a tundish is used as an intermediate vessel for feeding molten steel from a molten steel ladle to a mold. The tundish has (1) a function to stabilize the amount of molten steel supplied to the mold, (2) a function to distribute molten steel to multiple molds, and (3) a function to continuously perform continuous casting using multiple molten steel ladles. It has multiple functions such as a buffer function and (4) a non-metallic inclusion removal function. In particular, (4) the function of removing non-metallic inclusions is extremely important for the efficient production of high-grade steel products with high cleanliness.

Non-metallic inclusions in molten steel are mainly derived from impurities in steel such as oxides, nitrides, sulfides, and bubbles generated during the steelmaking process. It is known that when such non-metallic inclusions remain in the final product, they become starting points of fracture due to stress concentration, and deteriorate the material quality of the final product. In the steelmaking process itself, non-metallic inclusions adhere and accumulate on the inner wall of the refractory flow path, causing narrowing and blockage of the flow path. Occasionally, defects can occur both on the surface and inside of the base material, reducing product yields and lowering manufacturing costs. Therefore, in many cases, it is necessary to remove non-metallic inclusions from molten steel in a limited number of steps from secondary refining, in which the components of molten steel are finally adjusted, to casting.

In order to remove non-metallic inclusions from molten steel, the difference in specific gravity between the molten steel and the non-metallic inclusions is generally used to float the non-metallic inclusions in the molten steel, and then an oxide called flux is removed. However, it is known that the smaller the non-metallic inclusion, the lower the floating speed in this case, and the longer it takes to collect it in the flux layer. Therefore, in reducing nonmetallic inclusions in molten steel, it is effective to lengthen the residence time of nonmetallic inclusions in the tundish in order to secure the time necessary for the nonmetallic inclusions to surface. Conceivable.

In general, molten steel is supplied from a molten steel ladle to a tundish through a sliding nozzle that has a flow rate adjustment function and a long nozzle that is a cylindrical refractory that is used by immersing the lower end in the molten steel of the tundish. It is done by using energy to make it flow down. However, when the high-speed discharge flow from the long nozzle collides with the bottom of the tundish, a short-circuit flow toward the mold called a short pass can be formed (see FIG. 6), so the residence time of the molten steel in the tundish is Ensuring is not always easy. A common countermeasure to this problem is to install a weir inside the tundish to divert the flow of molten steel. In addition, there is a space in the vicinity of the weir that has almost no flow and does not contribute to the removal of floatation. no help In particular, small inclusions have little buoyancy and tend to follow the flow of molten steel, so the detouring effect is likely to be limited to removal of large inclusions.

Also, in the steelmaking process, attention must be paid to the unintentional increase of nonmetallic inclusions due to reoxidation of molten steel. In general, from the viewpoint of avoiding difficulty in stable casting due to gas generation accompanying a drop in molten steel temperature, molten steel subjected to continuous casting is subjected to deoxidation treatment in the refining process to reduce the soluble oxygen concentration to It is in a state where it is very easy to absorb oxygen. When air or lower oxides come into contact with molten steel, the molten steel absorbs oxygen and combines with elements that have a higher affinity for oxygen than molten steel (such as Al and Si dissolved in the molten steel). A reoxidation phenomenon in which inclusions are generated occurs. Therefore, in the molten steel ladle and the tundish, the oxygen concentration in the tundish is reduced by replacing the atmosphere with an inert gas, or the molten steel is made using a low-reactive flux with a low content of low-grade oxides. It is necessary to shield the molten steel from the atmosphere by coating the surface. However, when the molten steel is supplied to the tundish by the long nozzle, the flow of molten steel discharged from the nozzle is very high speed as described above. The flux covering the molten steel surface is pushed aside, and the molten steel surface is directly exposed to the open air as bare metal, and a reoxidation phenomenon occurs in which the molten steel absorbs oxygen in the atmosphere (see FIG. 6). In addition, if there is a connection failure (misalignment) at the fitting part of the nozzle, or if the airtightness of the flow path is impaired due to poor molding or wear of the refractory, outside air will be introduced into the nozzle by the ejector. (see FIG. 6). When the outside air introduced into the nozzle follows the flow of the molten steel and penetrates into the tundish, it forms a strong upward flow around the long nozzle, making the generation of bare metal more pronounced.

The above problem can occur in any process of supplying molten steel from one container to another container, and various means have been proposed to solve the problem. For example, Patent Literature 1 discloses a continuous casting method using an injection pipe in which an injection flow is blocked from the outside air by a refractory cylindrical body having an inner diameter of 300 mm or more. According to the technique disclosed in Patent Document 1, the injection flow dropped from the nozzle hits the gas inside the pipe against the liquid surface inside the pipe, introducing a large number of bubbles into the molten steel, and the large buoyancy of the bubbles increases the injection flow velocity. It could be reduced to create a gentle upward flow in the tundish. In addition, since solid inclusions have poor wettability with molten steel and easily adhere to bubbles, they are expected to be removed at high speed due to the large buoyancy of the bubbles. On the other hand, in the above injection pipe, in order to prevent the molten steel from absorbing oxygen and nitrogen from the gas phase, the inside of the pipe must be filled with a large amount of inert gas. operating costs are relatively high. In addition, when splashes of molten steel discharged from the nozzle or splashes generated by hitting the bath surface adhere to the inner wall of the pipe, the large diameter of the pipe removes heat remarkably from the adherents, and the adherents solidify and accumulate, leading to clogging. easy. Furthermore, if the bubbles introduced into the molten steel escape outside the injection pipe, the bubbles may reach the liquid surface of the molten steel in the tundish and cause reoxidation of the molten steel. refractory cost reduction is limited.

Patent Literature 2 discloses a nozzle provided with a flow control portion in the body portion in order to prevent exposure of bare water to occur due to the reversed upward flow at the bottom of the tundish. However, in the technique disclosed in Patent Document 2, it is necessary to take separate countermeasures against the occurrence of short paths, which increases the manufacturing cost. In addition, since the weight of the nozzle increases, the load on the device for gripping the nozzle increases, and there is a possibility that the nozzle cannot be supported during casting.

In Patent Document 3, a gas space of inert gas is formed inside the injection nozzle, and the inert gas is involved in the injection flow on the steel bath surface in the nozzle, and in a stirring box installed on the bottom of the tundish A continuous casting method and a continuous casting apparatus are disclosed in which agitation of the injection stream promotes aggregation of inclusions and bubbles in the molten steel. In the technology disclosed in Patent Document 3, the gas space is stably formed because the injection nozzle of the continuous casting apparatus has a discharge hole with a sufficiently large inner diameter. On the other hand, in the technique disclosed in Patent Document 3, all the air bubbles entrained in the injection flow refloat into the injection nozzle and the stirring action in the stirring box is not sufficiently exhibited. It is characterized by setting the inner diameter of the nozzle to a predetermined value or less, but the air bubbles floating on the surface of the molten steel in the tundish when the injection nozzle is removed can cause reoxidation as described above. In addition, the aspect of the gas-liquid multiphase flow in the nozzle depends on the flow velocity and dispersion state of each phase, and is generally represented by the cross-sectional void fraction. There is a risk that inclusions will flow out to the mold or re-oxidize by disturbing the flow in the tundish.

Japanese Patent No. 6575355 Japanese Patent Publication No. 2020-530813 JP 2011-235339 A

The present application can suppress the separation of bubbles introduced into the molten steel in the nozzle from the nozzle when molten steel is supplied from one container to another container through the nozzle, and the Discloses a technology capable of suppressing the occurrence of

As one means for solving the above problems, the present application provides
A system for supplying molten steel from a first vessel to a second vessel through a nozzle,
The nozzle has an inlet on the upstream side of the first container, an outlet on the downstream side of the second container, and extends downward from the upstream side to the downstream side. cage,
the outlet of the nozzle is positioned below the liquid surface of the molten steel supplied to the second container and above the bottom surface of the second container;
A flow rate Q (ton/min) of the molten steel flowing inside the nozzle, a minimum nozzle inner diameter D ₁ (mm) upstream of the outlet, and a nozzle inner diameter D ₂ (mm) at the outlet satisfies the following relations (1) to (3),
Disclosed is a molten steel supply system.

In the system of the present disclosure,
The nozzle may have an enlarged diameter portion between the inlet and the outlet,
In the enlarged diameter portion, the inner diameter of the nozzle may expand from the upstream side toward the downstream side.

The system of the present disclosure may have a blowing mechanism for blowing inert gas into the interior of the nozzle.

In the system of the present disclosure,
The nozzle may have a first nozzle section and a second nozzle section,
The first nozzle portion may be provided upstream of the second nozzle portion,
The first nozzle portion and the second nozzle portion may be connected to each other,
The second nozzle portion may include the outlet,
The second nozzle section may include a long nozzle section.

In the system of the present disclosure,
The first nozzle section may have a flow rate adjustment mechanism.

The system of the present disclosure may have a blowing mechanism for blowing an inert gas into the interior of the nozzle,
A position where the inert gas is blown by the blowing mechanism may be within a range of 100 mm from a connecting portion between the first nozzle portion and the second nozzle portion.

In the system of the present disclosure,
The first container may be a steel ladle and the second container may be a tundish.

As one means for solving the above problems, the present application provides
A method for continuous casting of steel using the system of the present disclosure, comprising:
blowing an inert gas into the nozzle so that the pressure of the gas inside the nozzle is 0.9 atm or more and 1.1 atm or less;
A method for continuous casting of steel is disclosed, comprising:

According to the technology of the present disclosure, when molten steel is supplied from one container to another container via a nozzle, it is possible to prevent the bubbles introduced into the molten steel in the nozzle from leaving the nozzle, and It is possible to suppress the generation of bare hot water in the container.

An example of the positional relationship of the 1st container in a supply system of molten steel, a 2nd container, and a nozzle is shown roughly. An example of the section composition of the nozzle in the supply system of molten steel is shown roughly. An example of the molten steel supply state in a molten steel supply system is shown schematically. The dashed arrows indicate the flow of molten steel. The apparatus configuration used for the water model experiment is shown schematically. 2 shows experimental results for the relationship between Q and D ₂ /D ₁ . ○ indicates the case where the predetermined effect was exhibited, and Δ and x indicate the case where the predetermined effect was not exhibited. It shows a problem in the prior art. The dashed arrows indicate the flow of molten steel.

1. Molten Steel Supply System Figures 1 to 3 show an example of the structure of a molten steel supply system. As shown in FIG. 1 , a molten steel supply system 100 is a system that supplies molten steel 105 from a first container 101 to a second container 102 via a nozzle 110 . As shown in FIGS. 2 and 3, in the system 100, the nozzle 110 has an inlet 110a on the first container 101 side, which is the upstream side, and an outlet 110b on the second container 102 side, which is the downstream side. and extends downwardly from the upstream side to the downstream side. The outflow port 110b of the nozzle 110 is located below the liquid surface 105a of the molten steel 105 supplied to the second container 102 and above the bottom surface 102a of the second container 102. . In the system 100, the flow rate Q (ton/min) of the molten steel 105 flowing inside the nozzle 110, the minimum nozzle inner diameter D ₁ (mm) upstream of the outlet 110b, and the outlet 110b satisfies the following relationships ( ₁ ) to (3).

1.1 First Container The first container 101 is a container from which the molten steel 105 is supplied to the second container 102 . As shown in FIGS. 1-3, in system 100, a first vessel 101 has a bottom surface 101a and side walls 101b to hold molten steel 105. As shown in FIG. The first container 101 may further have a lid (not shown). The first container 101 may have a shape and material capable of holding the molten steel 105 . Further, the first container 101 may be provided with an outflow port 101ax in a part of the bottom surface 101a so that the molten steel 105 can flow out from the outflow port 101ax. The outflow port 101ax may be provided with an opening/closing mechanism for controlling the amount of outflow of the molten steel 105 . A nozzle 110 may be directly or indirectly connected to the outlet 101ax of the first container 101 . The form of connection between the first container 101 and the nozzle 110 is not particularly limited, and can be connected by fitting, for example. The first container 101 and the nozzle 110 may be connected via some kind of intermediate member.

The first container 101 may be any container that can hold the molten steel 105, and various forms are assumed. The effect becomes even more remarkable.

1.2 Second Container The second container 102 is a container to which the molten steel 105 is supplied from the first container 101 . As shown in FIGS. 1-3, the second container 102 has a bottom surface 102a and side walls 102b and holds molten steel 105 supplied from the first container 101. As shown in FIG. The second container 102 may further have a lid 102c. The second container 102 may have any shape and material that can hold the molten steel 105 . As shown in FIG. 1, a part of the bottom surface 102a of the second container 102 may be provided with an outlet 102ax, from which the molten steel 105 can flow out to another container (eg, mold). may be configured. The outflow port 102ax may be provided with an opening/closing mechanism for controlling the amount of outflow of the molten steel 105 . A nozzle 120 may be directly or indirectly connected to the outflow port 102ax of the second container 102 . The form of connection between the second container 102 and the nozzle 120 is not particularly limited, and can be connected by fitting, for example. The second container 102 and the nozzle 120 may be connected via some kind of intermediate member.

The second container 102 may be any container capable of holding the molten steel 105, and various forms are assumed. The second container 102 may be, for example, a tundish, a steel ladle, or a mold (in this case, the first container 101 may be a tundish). , a furnace for adjusting the composition of the molten steel 105 . In particular, when the second container 102 is a tundish, the effect of applying the technology of the present disclosure becomes even more remarkable.

As shown in FIG. 3, a floating layer 106 containing flux may be present on the liquid surface 105a of the molten steel 105 supplied to the second vessel 102 . A known flux may be used as the flux. By coating the liquid surface 105a of the molten steel 105 with flux in this manner, the molten steel 105 can be shielded from the outside air. In addition, non-metallic inclusions in the molten steel 105 can be recovered by the flux. As will be described later, according to the system 100, the reversal upward flow caused by the collision of the molten steel 105 flowing out of the nozzle 110 with the bottom surface 102a of the second container 102 can be suppressed to a small level, and the liquid surface 105a of the molten steel 105 can be reduced. Disturbance is less likely to occur, and the flux is less likely to be pushed aside or interrupted due to disturbance of the liquid surface 105a, so that the problem of reoxidation due to bare hot water is less likely to occur.

1.3 Nozzle The nozzle 110 distributes the molten steel 105 from the first container 101 to the second container 102 . That is, the nozzle 110 has an inlet 110a on the first container 101 side, which is the upstream side, and an outlet 110b on the second container 102 side, which is the downstream side. The nozzle 110 extends downward from the upstream side toward the downstream side. The nozzle 110 may be, for example, a cylindrical body (cylindrical single-hole nozzle) extending downward from the upstream side toward the downstream side. Specifically, the nozzle 110 may be a cylindrical body having a central axis in the vertical direction. As shown in FIG. 2, nozzle 110 has a minimum nozzle inner diameter _D1 upstream of outlet 110b and a nozzle inner diameter _D2 at outlet 110b. In the present application, the "nozzle inner diameter" refers to the inner diameter of the nozzle portion below the flow rate adjusting mechanism 114 when there is a mechanism for adjusting the flow rate of the molten steel 105 (flow rate adjusting mechanism 114 such as a sliding gate). means the inner diameter of the nozzle portion between the first container 101 and the second container 102 when the flow rate adjusting mechanism 114 is not provided. The channel diameter in the mechanism 114 is not included in the "nozzle inner diameter".

As shown in FIG. 3, the outlet 110b of the nozzle 110 is located below the liquid surface 105a of the molten steel 105 supplied to the second container 102 and above the bottom surface 102a of the second container 102. there is That is, the nozzle 110 is immersed in the molten steel 105 in the second container 102 at its downstream end. As shown in FIG. 3, the system 100 may have a distance h ₁ between the liquid level 105a of the molten steel 105 in the second vessel 102 and the outlet 110b of the nozzle 110, and the outlet of the nozzle 110 There may be a distance _h2 from 110b to the bottom surface 102a of the second container 102 . The specific values of _h1 and _h2 and the relationship between _h1 and _h2 are not particularly limited. For example, _h1 may be 100 mm or more and 500 mm or less, _h2 may be 300 mm or more and 900 mm or less, and the ratio _h1 / _h2 between _h1 and _h2 is 0.2 or more and 0.7 or less. and the ratio D ₂ /h ₂ between the nozzle inner diameter D ₂ (see FIG. 2) and h ₂ at the outlet 110b may be 1.0 or more and 3.0 or less. By adjusting h ₁ and h ₂ , it becomes easier to suppress detachment from the nozzle 110 of the air bubble 105 x generated by a mechanism described later.

As shown in FIGS. 2 and 3, the nozzle 110 may have an enlarged diameter portion 110c between the inlet 110a and the outlet 110b. The inner diameter of the nozzle may be expanded toward it. The diameter expansion rate of the diameter expansion portion 110c is not particularly limited. In the enlarged-diameter portion 110c, the inner diameter of the nozzle may be linearly enlarged from the upstream side to the downstream side (increased monotonically), or may be curvedly enlarged. Moreover, in the enlarged diameter portion 110c, the inner diameter of the nozzle may expand continuously from the upstream side to the downstream side, or may expand intermittently. Also, the ratio of the length of the enlarged diameter portion 110c to the entire length of the nozzle 110 is not particularly limited. As shown in FIGS. 2 and 3, in the nozzle 110, the nozzle inner diameter at the lower end of the enlarged diameter portion 110c and the nozzle inner diameter _D2 at the outlet 110b may be substantially the same or different from each other. may be

As shown in FIGS. 2 and 3, the nozzle 110 may have a first nozzle section 111 and a second nozzle section 112 , the first nozzle section 111 being upstream of the second nozzle section 112 . The first nozzle portion 111 and the second nozzle portion 112 may be connected to each other, the second nozzle portion 112 may include the outlet 110b, and the second nozzle Portion 112 may include a long nozzle portion. That is, the nozzle 110 may be configured by connecting a first nozzle and a second nozzle having different shapes to each other via the connecting portion 113 . The form of connection between the first nozzle and the second nozzle in this case is not particularly limited, and for example, they may be connected by fitting. In addition, a "long nozzle part" means the part comprised by a long nozzle. The long nozzle portion may have a shape that satisfies the above relationships (1) to (3). For example, the long nozzle portion may have the enlarged diameter portion 110c described above. As shown in FIGS. 2 and 3, the nozzle part is installed independently of the second container 102 and need not be fixed to the second container 102 . In this respect, the injection pipe installed and fixed to the lid of the second container is clearly different in configuration from the nozzle section (nozzle) referred to in the present application.

As shown in FIGS. 2 and 3 , when the nozzle 110 has the first nozzle portion 111 and the second nozzle portion 112 , the first nozzle portion 111 may have the flow rate adjustment mechanism 114 . A specific example of the flow control mechanism 114 is a sliding gate as shown in FIGS. 2 and 3, for example. That is, the first nozzle part 111 may be a part configured by a sliding nozzle. In the sliding gate, at least one slide plate 114a having a flow port is slid in a direction crossing the flow direction of the molten steel 105, thereby changing the flow channel diameter. Alternatively, the flow rate adjustment mechanism 114 may be an opening/closing mechanism other than the sliding gate. Since the form of the flow rate adjusting mechanism 114 in the nozzle 110 is known, further explanation is omitted here. Incidentally, as described above, the diameter of the flow path in the flow rate adjusting mechanism 114 is not included in the inner diameter of the nozzle referred to in relations (1) and (2).

1.4 Other Mechanisms The molten steel supply system 100 may include other mechanisms in addition to the above configurations. For example, as shown in FIGS. 2 and 3, the system 100 may have a gas blowing mechanism 116 that blows inert gas into the interior of the nozzle 110 . As described above as the background art, when molten steel is supplied from one container to another container through a nozzle, outside air may be taken into the nozzle from the nozzle fitting portion or the like by an ejector. Alternatively, 100 may employ a mechanism 116 that intentionally blows inert gas into the interior of nozzle 110 . As will be described later, in the system 100 of the present disclosure, the relationships (1) to (3) are satisfied while the molten steel 105 is being supplied, so that the gas space 115 can be maintained inside the nozzle 110, and the nozzle 110 At the liquid surface 105a of the molten steel 105 inside the , gas is drawn into the molten steel 105 from the gas space 115 as the molten steel 105 flows, and various large and small bubble groups can be generated in the molten steel 105. Having the mechanism 116 for blowing inert gas into the nozzle 110 in the system 100 makes it easier to maintain the gas space 115 inside the nozzle 110 . Examples of inert gas include Ar. Although the pressure of the inert gas in the gas space 115 is not particularly limited, it may be, for example, 0.9 atm or more and 1.1 atm or less.

A specific form of the mechanism 116 for blowing inert gas into the nozzle 110 is not limited. For example, the blowing mechanism 116 can be configured by connecting an inert gas supply source (such as a container filled with a high-pressure inert gas) and the nozzle 110 with a pipe or the like. Alternatively, the inert gas supply source may be connected to a position upstream of the nozzle 110 (for example, the first container 101) so that the molten steel 105 blown with the inert gas flows into the nozzle 110. . However, it is easier to control the amount of inert gas blown into the nozzle 110 when the inert gas supply source and the nozzle 110 are connected.

As shown in FIGS. 2 and 3, when the nozzle 110 has the first nozzle portion 111 and the second nozzle portion 112, the positions to which the inert gas is blown by the blowing mechanism 116 are the first nozzle portion 111 and the second nozzle portion 112. It may be within a range of 100 mm from the connection portion 113 with the second nozzle portion 112 . Within this range, the blowing mechanism 116 described above can be easily installed in the nozzle 110 . In addition, by blowing the inert gas into this range, it becomes easier to form the gas space 115 inside the nozzle 110 .

1.5 Relationships (1) to (3)
In the molten steel supply system 100, the flow rate Q (ton/min) of the molten steel 105 flowing inside the nozzle 110 as described above, the minimum nozzle inner diameter D ₁ (mm) upstream of the outlet 110b, The nozzle inner diameter D ₂ (mm) at the outflow port 110b must satisfy the above relationships (1) to (3).

In the above relationship (3), the flow rate Q is 1.0 ton/min or more and 15.0 ton/min or less. The flow rate Q may be 1.5 ton/min or more, 2.0 ton/min or more, 2.5 ton/min or more, or 3.0 ton/min or more, and 14.0 ton/min or less to 13.0 ton/min or less. , 12.0 ton/min or less, 11.0 ton/min or less, or 10.0 ton/min or less. The flow rate Q may be 7.0 ton/min or more and 12.0 ton/min or less from the viewpoint of being particularly well adopted in actual operation and obtaining a particularly high effect.

In relation (2) above, the minimum nozzle diameter _D1 is 30 mm or more and 140 mm or less. The minimum nozzle diameter _D1 may be 35 mm or more, 40 mm or more, 45 mm or more, or 50 mm or more, and may be 130 mm or less, 120 mm or less, 110 mm or less, or 100 mm or less. The minimum nozzle diameter _D1 may be 70 mm or more and 120 mm or less from the viewpoint of being particularly well adopted in actual operation and obtaining a particularly high effect.

In the molten steel supply system 100, on the premise that the above relationships (2) and (3) are satisfied, furthermore, the above relationship (1) is satisfied, so that a predetermined effect described later is exhibited. In the system 100, the flow rate Q may be adjusted according to the nozzle diameters _D1 and _D2 so that the relationship (1) is satisfied, or an optimum nozzle flow rate may be selected according to the target flow rate Q. The geometry (nozzle diameters D ₁ and D ₂ ) may be selected.

1.6 Functions and Effects As shown in FIG. 3, in the system 100, by expanding the inner diameter of the nozzle 110 on the outflow port 110b side, A distinct gas phase (gas space 115) is formed within the nozzle 110 (while introducing an inert gas). On the liquid surface 105a in the nozzle 110, the gas space 115 is involved in the injected flow as a group of bubbles 105x on the order of submillimeters to millimeters. Of these, the larger the bubble diameter, the greater the lift acting in the horizontal direction, and the buoyancy of the bubble 105x slows down the downward flow velocity of the injection flow, especially the flow at the center of the nozzle 110, which has a high flow velocity, and the flow field is easily made uniform. Become. When the above relationships (1) to (3) are satisfied, it is easy to generate and maintain the gas space 115 and the bubble group 105x, and the bubbles 105x flowing out of the nozzle 110 are collected inside the nozzle 110. easier to be The bubbles 105x collected inside the nozzle 110 either function as the gas space 115 described above, or remain inside the nozzle 110 as bubbles 105x. In this way, in the system 100, the bubble 105x is suppressed from leaving the inside of the nozzle 110, thereby maintaining the effect of decelerating the injection flow described above and reversing the upward flow after colliding with the bottom surface 102a of the second container 102. becomes smaller. This makes it difficult for the bubbles 105x to push away the flux floating on the liquid surface 105a of the molten steel 105 in the second container 102, thereby exposing the molten steel 105 to the outside air (problem of reoxidation due to bare metal). . Furthermore, by uniforming the discharge flow velocity from the nozzle 110, the molten steel flow in the second container 102 becomes close to a plug flow toward the outlet, so a short pass is formed in the second container 102. is prevented, and the risk of flux and inclusions being brought into the next process is reduced. In addition, as a secondary effect, the bubble group 105x hit by the liquid surface 105a in the nozzle 110 is restrained in the nozzle 110, and the gas phase rate in the nozzle 110 increases, so that the bubbles 105x are trapped in the intervening portion. By adhering, inclusions can be efficiently floated and removed.

2. Steel Continuous Casting Method The technology of the present disclosure also has an aspect as a steel continuous casting method. That is, the continuous steel casting method of the present disclosure is characterized by using the system 100 of the present disclosure. Here, the steel continuous casting method of the present disclosure includes blowing an inert gas into the nozzle 110 so that the gas pressure inside the nozzle 110 is 0.9 atm or more and 1.1 atm or less. You can The details of the mechanism for blowing the inert gas into the nozzle 110 are as described above. In the continuous casting method of the present disclosure, for example, the first vessel 101 may be a steel ladle and the second vessel 102 may be a tundish, in which case the continuous casting method of steel is cast from the steel ladle through the nozzle 110. It may include feeding molten steel 105 to a tundish, feeding molten steel 105 from the tundish to a mold (not shown) through a nozzle 120, and continuously withdrawing a billet from the mold. In the steel continuous casting method of the present disclosure, typical continuous casting conditions may be employed, except that the system 100 described above is employed.

The gas pressure inside the nozzle 110 can be measured by various methods. For example, by connecting a member having a space for pressure measurement to a part of the nozzle 110 and communicating the gas space 115 inside the nozzle 110 with the space of the member, the pressure in the space of the member can be measured by the pressure of the nozzle 110. The pressure of the gas inside the nozzle 110 can be measured by measuring the pressure in the space of the member substantially the same as the gas space 115 inside.

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention can adopt various conditions as long as it achieves its purpose without departing from the gist thereof.

It is generally known that observation of a system containing molten steel is extremely difficult due to the extremely high temperature and opaqueness of the object to be observed, the presence of dust, and the like. Therefore, visualization is usually attempted by reproducing flow and heat transfer using computational fluid dynamics. Since the shape of σ changes greatly over time, it takes an enormous amount of time to accurately calculate its behavior. Therefore, the present inventors found the Fr number represented by the following formula (4), which is the ratio of the inertial force to the buoyant force, and the We number, which is the ratio of the surface tension to the inertial force and is represented by the following formula (5). However, we decided to investigate the behavior of the gas phase in molten steel by utilizing the fact that the 1/2 scale water model at room temperature is roughly consistent with the molten steel system.

ここで、v：代表流速(m/s)、g：重力加速度(m/s²)、l：代表長さ(m)、ρ：密度(kg/m³)を表す。

Here, v: representative flow velocity (m/s), g: gravitational acceleration (m/s ² ), l: representative length (m), ρ: density (kg/m ³ ).

FIG. 4 schematically shows the configuration of the apparatus used in the water model experiment. To facilitate observation, the nozzle and water receiving container were made of acrylic material, and water was continuously supplied from above at a predetermined flow rate via a pump and a mass flow controller. In addition, the water receiving container is provided with drain ports at the four corners of the bottom surface, and each drain port is equipped with a throttle mechanism. The tip on the outflow port side of was immersed for 100 mm. After confirming that the water level in the water receiving container has stabilized, the gas space is formed inside the nozzle by temporarily opening the gas inlet until the water surface inside the nozzle and the water level in the water receiving container roughly match. bottom.

1. Observation and evaluation of bubbles Observation and evaluation of bubbles by changing the amount of water supplied (can be converted to flow rate Q of molten steel) and the shape of the nozzle (minimum nozzle inner diameter D ₁ , nozzle inner diameter D ₂ at the outlet) did For each condition, since the gas space was formed inside the nozzle as described above, bubbles were generated downward from the liquid surface inside the nozzle due to entrainment by the water flow, and at least a part of the bubbles flowed out from the outlet of the nozzle. also flowed downwards. Whether the air bubbles flowing out from the nozzle are collected inside the nozzle under each condition (whether the generated air bubbles return to the inside of the nozzle again without leaving the nozzle and rising to the liquid surface of the water receiving container outside the nozzle) ) was visually checked for 10 minutes, and almost all of the bubbles were recovered (disappearance of the gas space was less than 50% by volume) with “○”, and a small amount of bubbles were removed (gas space 50% by volume or more and less than 80% by volume have disappeared) is "△", and most of the bubbles are separated from the nozzle and almost all of the gas space has disappeared (80% by volume or more of the gas space has disappeared) is " x” was evaluated. The results are shown in Table 1 and FIG. The throughput in Table 1 is a molten steel system value converted so that the flow at the nozzle inlet satisfies the Fr number approximation. That is, the value obtained by converting the amount of water supply in the water model experiment into the flow rate Q of molten steel in the molten steel system is shown.

As shown in Table 1 and FIG. 5, the following relationships (1) to ( When 3) was satisfied, almost all of the air bubbles flowing out from the nozzle were collected inside the nozzle. On the other hand, if the following relationship (1) is not satisfied, immediately after the gas inlet is closed, air bubbles caught in the air-liquid interface in the nozzle are entrained in the discharge flow, and the gas space in the nozzle remains for only a short time. Almost all the gas was discharged out of the nozzle in several seconds to several tens of seconds. That is, when the following relationships (1) to (3) are satisfied, it is possible to suppress the arrival of bubbles to the liquid surface of molten steel outside the nozzle, and it is possible to suppress the problem of reoxidation of molten steel due to bare metal.

2. Evaluation of Flow Velocity In order to confirm the effect of suppressing the generation of short paths due to the formation of bubbles, the flow velocity was measured with an electromagnetic current meter at a point of 300 mm from the water surface on the center axis of the nozzle for each condition. As a result, when the above relationship (1) was satisfied, the discharge flow velocity on the central axis was clearly lower than when the above relationship (1) was not satisfied. That is, when the relationships (1) to (3) are satisfied, the effect of suppressing short pass can be expected, the effect of suppressing reverse upward flow can be expected, and the effect of preventing reoxidation of molten steel due to bare metal can be expected. .

REFERENCE SIGNS LIST 100 Molten steel supply system 101 First container 101a Bottom surface 101b Side wall 102 Second container 102a Bottom surface 102b Side wall 102c Lid 105 Molten steel 105x Bubbles (bubble group)
110 Nozzle 110a Inlet 110b Outlet 110c Expanded Diameter Portion 111 First Nozzle Portion 112 Second Nozzle Portion 113 Connection Portion 114 Flow Control Mechanism (Sliding Gate)
114a slide plate 115 gas space 116 gas injection mechanism 120 nozzle

Claims (8)

A system for supplying molten steel from a first vessel to a second vessel through a nozzle,
The nozzle has an inlet on the upstream side of the first container, an outlet on the downstream side of the second container, and extends downward from the upstream side to the downstream side. cage,
the outlet of the nozzle is positioned below the liquid surface of the molten steel supplied to the second container and above the bottom surface of the second container;
A flow rate Q (ton/min) of the molten steel flowing inside the nozzle, a minimum nozzle inner diameter D ₁ (mm) upstream of the outlet, and a nozzle inner diameter D ₂ (mm) at the outlet satisfies the following relations (1) to (3),
Molten steel supply system.

the nozzle has an enlarged diameter portion between the inlet and the outlet;
In the enlarged diameter portion, the inner diameter of the nozzle expands from the upstream side to the downstream side,
The system of claim 1. Having a blowing mechanism for blowing an inert gas into the nozzle,
3. A system according to claim 1 or 2. The nozzle has a first nozzle section and a second nozzle section,
The first nozzle portion is provided upstream of the second nozzle portion,
the first nozzle portion and the second nozzle portion are connected to each other,
the second nozzle section includes the outlet,
wherein the second nozzle portion includes a long nozzle portion;
The system according to any one of claims 1-3. The first nozzle part has a flow rate adjustment mechanism,
5. The system of claim 4. having a blowing mechanism for blowing an inert gas into the nozzle;
A position where the inert gas is blown by the blowing mechanism is within a range of 100 mm from a connection portion between the first nozzle portion and the second nozzle portion,
6. System according to claim 4 or 5. wherein said first vessel is a molten steel ladle and said second vessel is a tundish;
A system according to any one of claims 1-6. A method for continuous casting of steel using the system according to any one of claims 1 to 7,
blowing an inert gas into the nozzle so that the pressure of the gas inside the nozzle is 0.9 atm or more and 1.1 atm or less;
A method for continuous casting of steel, comprising:

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