Tundish

Abstract

To provide a technique for stably supplying inert gas into a tundish.SOLUTION: A tundish for continuous casting, the tundish including an accommodating portion that stores molten steel, the accommodating portion including a molten steel outflow port through which the molten steel flows out, and a weir that is disposed on an upstream side of the molten steel with respect to the molten steel outflow port and is formed in a hollow cylindrical shape, the tundish further including a first gas supply portion that supplies an inert gas to an internal space of the weir, the first gas supply portion has a first porous portion in which a plurality of pores are formed throughout, a support portion which supports the first porous portion and is provided on the wall portion of the accommodating portion, and a first pipe which is provided on the wall portion of the weir between the support portion and the bottom portion of the weir and discharges the inert gas, and a third pipe which is connected to the first pipe or extends from the first pipe is disposed along the wall portion of the accommodating portion and is separated from the molten steel by a refractory brick.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tundish for relaying molten metal poured from a ladle to a mold in a continuous casting process, and to a tundish capable of efficiently removing non-metallic inclusions from the molten metal poured into the tundish. [Background technology]

[0002] To produce high-quality steel materials, further improvements in molten steel cleanliness technology are required. In the steelmaking process, after oxidative refining of molten steel in a converter or electric furnace, various refining agents are added during ladle refining to remove impurities from the molten steel. In addition, during ladle refining, the molten steel may also be degassed using a vacuum treatment. The molten steel, with improved purity, is then poured from the ladle into a tundish and into a continuous casting mold for continuous casting. However, as the molten steel passes through the tundish, it comes into contact with atmospheric gases and refractories, making it susceptible to contamination through gas absorption and refractory leaching. Furthermore, non-metallic inclusions, such as Al2O3, formed during the refining reaction remain in the molten steel supplied from the ladle to the tundish.

[0003] Non-metallic inclusions in molten steel clog the submerged entry nozzle during casting, making the casting process more unstable. Furthermore, non-metallic inclusions such as Al2O3, a deoxidation product, in molten steel can cause surface defects after rolling and internal defects in the plate if they are carried into the continuously cast slab. Therefore, they must be separated and removed as much as possible before casting. Inclusion reduction technology is crucial for obtaining high-quality slabs in continuous casting.

[0004] Patent Documents 1 to 3 disclose a technique of injecting an inert gas into the bottom of a tundish to float and separate nonmetallic inclusions efficiently and inexpensively within the tundish. Patent Document 1 uses a precast refractory material applied to the wall of the tundish to protect the piping through which the inert gas is injected. Patent Documents 2 and 3 describe that the piping arranged along the wall of the tundish is covered with a refractory coating material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2023 / 210201 [Patent Document 2] International Publication No. 2024 / 053290 [Patent Document 3] International Publication No. 2024 / 053291 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques have the following problems. In the technology described in Patent Document 1, depending on the dimensions and size of the precast refractory material, it was difficult to manage the storage area, and there was room for improvement in construction workability. In addition, when the weight was large, it had to be transported by hanging, and there was room for improvement in shortening the construction time.

[0007] The techniques in Patent Documents 2 and 3 do not specifically describe how to apply the pipe covering material, particularly the refractory material, and there is room for improvement in terms of whether the pipe can be adequately protected from molten steel. In other words, it is necessary to establish a technique for protecting the pipe so that it does not melt due to the heat of molten steel.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technology for stably supplying an inert gas into a tundish during casting without causing the piping to melt due to the heat of molten steel. [Means for solving the problem]

[0009] A tundish according to the present invention for solving the above problems is a tundish for continuous casting having a container section for storing supplied molten steel, the container section including one or more molten steel outlets for discharging the molten steel, and a hollow cylindrical weir arranged upstream of the one or more molten steel outlets in the direction of the molten steel, the tundish also including a first gas supply section for supplying an inert gas to an internal space of the weir, the first gas supply section including a first porous section having a plurality of pores formed throughout, a support section for supporting the first porous section and provided on a wall of the container section, and and a first pipe provided on the wall of the weir between the support portion and the bottom of the weir and discharging the inert gas, and optionally a bottom refractory having a second gas supply portion at the bottom of the tundish between the weir and the molten steel outlet, the second gas supply portion having a second porous portion and a second pipe connected to the second porous portion, and a third pipe connected to the first pipe or the second pipe or extending from the first pipe or the second pipe, arranged along the wall of the accommodation portion and separated from the molten steel by refractory bricks.

[0010] The tundish according to the present invention is (a) the weir has a bottom, a wall extending from the bottom, a canopy provided at one end of the wall to cover the periphery and facing the bottom of the weir, and a first gas supply section that supplies an inert gas to an internal space surrounded by the wall and the bottom; (b) having an adjusting means for adjusting the flow rate of the inert gas supplied to the first gas supply unit and the second gas supply unit; (c) the third pipe is installed along the wall of the storage section that is connected to the wall of the weir, or along a corner formed by the wall of the storage section and an upper weir that is connected to the wall of the storage section; This may be a more preferable solution. [Effects of the Invention]

[0011] In the tundish according to the present invention, the piping for supplying inert gas is protected by refractory bricks, so that a device for injecting gas from a porous portion installed at the bottom of the weir or the bottom of the tundish can be easily installed. Furthermore, the inert gas can be stably supplied during continuous casting. Therefore, the floating and separation of nonmetallic inclusions from the molten steel in the tundish is promoted, and high-cleanliness steel can be stably and easily produced. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically illustrating a tundish according to one embodiment of the present invention. [Figure 2] 2A and 2B are schematic cross-sectional views of the tundish according to the embodiment, where (a) is a cross-sectional view taken along line BB in FIG. 1, and (b) is a cross-sectional view taken along line CC. [Figure 3] 1A and 1B are schematic perspective views showing the construction status of the tundish according to the embodiment, in which (a) shows the vicinity of the pouring portion from the ladle, and (b) shows the upper weir. [Figure 4] 1A and 1B are schematic diagrams showing the procedure for protecting piping with firebricks during construction of a tundish according to the embodiment, in which (a1) and (a2) are a front view and a plan view, respectively, showing the first layer of brickwork, (b1) and (b2) are a front view and a plan view, respectively, showing the second layer of brickwork, and (c1) and (c2) are a front view and a plan view, respectively, showing the state after curing. [Figure 5] FIG. 2 is a plan view schematically showing an example of construction of piping near an upper weir of the tundish according to the embodiment. [Figure 6]1 is a graph showing the time transition of the temperature and back pressure of the gas injection pipe of the tundish constructed in the example of the invention, where (a) shows the temperature measured by the thermocouple, and (b) shows the back pressure of the injected gas. [Figure 7] 10 is a graph showing the time course of the back pressure of the gas injection pipe of the tundish constructed in the comparative example.

[0013] The following describes in detail embodiments of the present invention. Note that the drawings are schematic and may differ from the actual embodiments. Furthermore, the following embodiments exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0014] A tundish according to one embodiment of the present invention is shown schematically in FIGS. 1 and 2. FIG. 2(a) is a cross-sectional view taken along line BB in FIG. 1, and FIG. 2(b) is a cross-sectional view taken along line CC in FIG. 1. The tundish 1 of this embodiment is an intermediate vessel used in continuous casting of steel when pouring molten steel from a ladle into a continuous casting mold. The tundish 1 is, for example, a vessel having a generally rectangular parallelepiped shape with an open top. Molten steel is supplied from a ladle (not shown) through a pouring nozzle 2. In the example of FIG. 1, the stored molten steel is supplied to a mold (not shown) from two molten steel outlets 3 provided at the bottom.

[0015] In this embodiment, a weir 4 is provided between the molten steel pouring section 2a, where the molten steel pouring flow from the ladle collides with the tundish bottom section 1a, and the molten steel outlet 3 from the tundish 1 to the mold. The weir 4 has a wall section 4a extending upward from the tundish bottom section 1a, surrounding the molten steel pouring section 2a from all four sides, and an eave-shaped section 4b protruding horizontally from the upper end of the wall section 4a toward the molten steel pouring section 2a. The weir 4 may, for example, have one or more continuous notches extending from the wall section 4a to the eave-shaped section 4b. The weir 4 has a first porous section 4d in a refractory bottom section 4c surrounded by the wall section 4a, and a first piping 5a connected to the first porous section 4d within the weir and the refractory including the first porous section 4d. The first porous section 4d preferably occupies 15% or more of the total area of ​​the refractory bottom section 4c surrounded by the wall section 4a of the weir 4. Although there is no upper limit, it is preferable not to install the first porous portion 4d near the impingement point of the molten steel poured from the ladle. The first porous portion 4d is supported by a support portion provided on the wall portion 1b of the tundish, which is the portion containing the molten steel.

[0016] This configuration suppresses the short-circuiting flow of molten steel poured from the ladle through the tundish bottom 1a and redirects the flow upward, promoting the floating and separation of inclusions. Furthermore, by blowing inert gas through the first porous section 4d, non-metallic inclusions are captured by inert gas bubbles, further promoting the floating and separation. By providing the first porous section 4d in the refractory bottom 4c of the molten steel pouring section 2a, the gas bubbles escaping the first porous section 4d are refined by the shear force of the high-speed poured flow that collides with the refractory bottom 4c and moves horizontally, thereby increasing the probability of capturing inclusions.

[0017] Inert gas is supplied to the first porous region 4d through a third pipe 5c connected to a first pipe 5a provided in the weir 4 or extending from the first pipe 5a. In this embodiment, the third pipe 5c is arranged along the wall 1b of the tundish and separated from the molten steel by refractory bricks 6. This simplifies the application of refractories to the tundish and prevents the pipe 5 from being damaged by the heat of the molten steel or metal penetration, resulting in poor gas injection. This allows for the stable production of clean steel.

[0018] In this embodiment, a refractory 7 having a second porous portion 7a and a second pipe 5b connected to the second porous portion 7a is preferably provided at the bottom 1a of the tundish between the weir 4 and the molten steel outlet 3. Inert gas is blown through a third pipe 5c connected to the second pipe 5b or extending from the second pipe 5b. In this embodiment, the third pipe 5c is arranged along the wall 1b of the tundish and separated from the molten steel by refractory bricks 6. The refractory 7 is preferably installed across the entire bottom 1a of the tundish in a direction perpendicular to the flow of molten steel poured from the ladle toward the molten steel outlet 3 into the mold. Similar to the lower weir, the refractory 7 can generate a flow toward the tundish surface, promoting the floating and separation of inclusions. Additionally, as shown in FIG. 1, an upper weir 8 may be installed upstream of the refractory 7 having the second porous portion 7a, i.e., on the side receiving steel from the ladle. The upper weir can prevent inclusions floating on the receiving steel side from flowing out to the casting side of the mold. In this case, it is preferable that the third piping 5c ​​is arranged along the connecting corner of the wall 1b of the tundish and the upper weir 8. This configuration simplifies the installation of refractories in the tundish and prevents the piping 5 from being damaged by the heat of molten steel or metal penetration, resulting in poor gas injection. This allows for the stable production of clean steel.

[0019] Figure 3(a) shows a schematic diagram of the construction of the tundish refractory near the ladle pouring point 2a, viewed from above. Figure 3(b) shows a schematic diagram of the construction of the bottom refractory 7 installed at the tundish bottom 1a, facing the upper gate. Figure 4 is a schematic diagram illustrating the brickwork procedure for protecting the third piping 5c. The piping used for injection into the porous bricks must be protected from contact with molten steel. Refractory bricks, which have excellent heat resistance and corrosion resistance, are effective. Furthermore, considering the melting point of the piping itself, a certain distance must be maintained between the molten steel and the piping, and physical protection is required to prevent contact with the molten steel. Therefore, the piping was protected by stacking two layers of bricks instead of one. In this case, the joints between the bricks, which are the contact surfaces of the bricks, were subject to potential pre-existing corrosion and molten steel penetration, so the brick surfaces were cured with a basic, unformable refractory material with excellent corrosion resistance. The third pipe 5c is connected to an inert gas supply device (not shown) via a pipe 5 as shown in FIG.

[0020] First, as shown in Figures 4(a1) and (a2), the first layer of refractory bricks 6 is laid so as to sandwich the third piping 5c. Next, the second layer of refractory bricks 6 is laid so as to hide the piping from the molten steel (Figures 4(b1) and (b2)). In Figures 4(c1) and (c2), the gaps between the refractory bricks 6 and between the refractory bricks 6 and the work refractory 1c of the tundish wall are filled with insulating material 6b, and the surface is covered with a monolithic refractory material such as mortar 6a. As shown in Figure 5, when the third piping 5c ​​is arranged along the corner between the upper weir 8 and the work refractory 1c, two layers of refractory bricks 6 and insulating material 6b are laid in the same way, and the surface is cured with mortar 6a or the like.

[0021] The first porous portion 4d and the second porous portion 7a can be produced by firing an aggregate of spherical particles primarily composed of alumina at 1600°C or higher. The average pore diameter of the first porous portion 4d and the second porous portion 7a is preferably 20 to 120 μm. The average pore diameter can be determined, for example, by mercury porosimetry in accordance with JIS R 1655:2003. By setting the average pore diameter within this range, the diameter of bubbles injected into the molten steel can be controlled within a predetermined range, which is effective in suppressing slag entrainment.

[0022] The pipe 5 connected to the third pipe 5c is preferably provided with an adjusting means (not shown) for adjusting the flow rate of the inert gas. A valve equipped with a flow rate adjusting mechanism can be used as the adjusting means. The adjusting means may adjust the flow rate manually, or may be configured to automatically adjust the opening based on instructions from the control unit. Examples of inert gases include Ar, N2, and CO2. [Example]

[0023] 300 tons of molten steel was oxygen-blown in a converter and vacuum-degassed in an RH-type vacuum degasser. The molten steel was poured from the ladle into a mold via a tundish 1 shown in Figure 1 and continuously cast.

[0024] Continuous casting was performed while injecting Ar as an inert gas through the tundish bottom refractory located downstream of the weir and upper weir. For this example, the direction of the molten steel outlet 2 on the left side, based on the molten steel inlet 2a in Figure 1, is defined as the first stage, and the direction of the molten steel outlet 2 on the right side is defined as the second stage. Similarly, the left upper weir 8, the left first porous section 4d, and the second porous section 7a are also referred to as the first stage. The right upper weir 8, the right first porous section 4d, and the right second porous section 7a are also referred to as the second stage. The third piping 5c ​​on the first stage was constructed with two layers of refractory bricks using the insulating material shown in Figures 4 and 5 for heat protection. The second stage was constructed with the same two layers of refractory bricks as the first stage, except that no insulating material was used. Temperature changes during casting were measured using a thermocouple embedded near the third piping 5c. The inert gas back pressure changes were also measured using a pressure gauge installed along the piping route. The results are shown in Figure 6. The casting conditions were a single tundish with 10 charges of molten steel from the ladle, a casting time of 300 min, and a mass of molten steel per charge of 300 t. In Figure 6, MP represents the melting point of the inert gas injection piping. Pre represents the time when preheating of the refractory material in the tundish began. Sta represents the time when casting began. End represents the time when casting ended. As can be seen from Figure 6, no sudden decrease in inert gas back pressure was observed during casting, and the measured temperature was significantly below the melting point of the piping. Furthermore, visual inspection of the protected areas of the piping after casting revealed no evidence of brick melting or falling off.

[0025] As a comparative example, casting was performed under the same conditions as in the above-mentioned invention example, except that the third piping 5c ​​on the first side was protected with precast refractory material, and the third piping 5c ​​on the second side was protected with a pipe cover and cured with mortar. The transition of the inert gas back pressure is shown in Figure 7. The results are summarized below. a) Pipe 5 next to the upper weir on the 1st side maintained a back pressure of about 0.08 MPa until the end of the casting time. b) The back pressure in the piping 5 of the 1st side injection section was about 0.10 MPa for 90 minutes after the start of casting, but then it suddenly decreased and the back pressure could no longer be maintained. c) The back pressure in the piping 5 of the 2nd-side injection section dropped immediately after the start of casting, and the back pressure could not be maintained thereafter. d) The back pressure in piping 5 next to the upper weir on the 2nd st side dropped immediately after the start of casting, and could not be maintained thereafter. In addition, after casting, the protected pipes were dismantled and inspected, and it was found that all pipes except for pipe 5 next to the upper weir on the 1st side had melted due to the intrusion of molten steel. [Explanation of symbols]

[0026] 1 tundish 1a (Tundish) Bottom 1b (Tundish) wall 1c (Tundish) Work Refractory 2 injection nozzle 2a Molten steel injection section 3 Molten steel outlet 4 Weir 4a wall 4b Eaves 4c Refractory bottom 4d (first) porous section 5 Piping 5a (1st) Piping 5b (Second) Piping 5c (Third) Piping 6 Firebrick 6a Mortar 6b Insulation 7 (Bottom) Refractory (including porous part) 7a (Second) Porous section 8 Upper Weir

Claims

1. A tundish for continuous casting having a storage portion for storing supplied molten steel, The container has one or more molten steel outlets through which the molten steel flows out; a weir that is disposed upstream of the one or more molten steel outlets in the direction of the molten steel and that is formed in a hollow cylindrical shape, a first gas supply unit that supplies an inert gas to the internal space of the weir; the first gas supply unit has a first porous portion having a plurality of pores formed throughout, a support portion that supports the first porous portion and is provided on a wall portion of the accommodation unit, and a first pipe that is provided on a wall portion of the weir between the support portion and a bottom portion of the weir and discharges the inert gas; Optionally, a bottom refractory having a second gas supply at the bottom of the tundish between the weir and the molten steel outlet; the second gas supply unit has a second porous portion and a second pipe connected to the second porous portion; a third pipe connected to the first pipe or the second pipe or extending from the first pipe or the second pipe, the third pipe being arranged along a wall of the accommodation section and separated from the molten steel by refractory bricks;

2. 2. The tundish according to claim 1, wherein the weir has a bottom, a wall extending from the bottom, an eave portion provided at one end of the wall so as to cover the periphery and facing the bottom of the weir, and a first gas supply portion that supplies an inert gas to an internal space surrounded by the wall and the bottom.

3. 3. The tundish according to claim 1, further comprising an adjusting means for adjusting the flow rate of the inert gas supplied to the first gas supply section and the second gas supply section.

4. 3. The tundish according to claim 1, wherein the third piping is installed along a wall portion of the storage section that is connected to a wall portion of the weir, or along a corner formed by an upper weir that is connected to the wall portion of the storage section and the wall portion of the storage section.

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