Stopper for continuous casting

Abstract

To suppress adhesion of an inclusion near a mating part of a stopper and to prevent a tip area of the stopper from being broken or exfoliated due to lack of strength.SOLUTION: In a stopper 1 for continuous casting having a cavity 11 for gas flow on a vertical center part, in at least a part in a vertical cross section in a tip side part area C, a porous refractory 12 having gas permeability is arranged on the outer peripheral surface side, and a refractory 13 having higher strength than the porous refractory 12 is arranged on the inner peripheral surface side.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a stopper for continuous casting having a gas injection function, which controls the flow rate of molten steel by fitting from above into a nozzle installed at the bottom of a tundish, mainly when discharging molten steel from a tundish into a mold in continuous casting of molten steel. [Background technology]

[0002] Conventionally, there has been a problem of inclusions such as alumina adhering to the vicinity of the fitting portion of the stopper and the nozzle. For example, when inclusions adhere to the vicinity of the fitting portion of the stopper during casting and the adhered inclusions peel off, the gap between the stopper and the nozzle instantly becomes large and a large amount of molten steel is supplied, causing fluctuations in the molten steel surface in the mold. This causes problems such as powder entrapment in the mold, powder and inclusions being entrapped in the slab, and defects and flaws caused by the inclusions in the product. For this reason, it was necessary to suppress the adhesion of inclusions to the vicinity of the fitting portion of the stopper.

[0003] As a technique for suppressing adhesion of inclusions near the fitting portion of the stopper, a technique in which a part of the tip region of the stopper is made of a porous refractory material is known (see, for example, Patent Document 1). Also known is a configuration in which a through hole is provided in the tip region of the stopper (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2-6040 [Patent Document 2] Japanese Patent Application Publication No. 3-110048 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, as shown in FIG. 4 of Patent Document 1, when the tip of the stopper is configured with a porous tip portion 76, the gas is blown only from the porous tip portion 76, so that the adhesion of inclusions near the fitting portion of the stopper cannot be suppressed. Also, as shown in FIG. 3 of Patent Document 1, a configuration is known in which the porous tip portion 66 is sandwiched between low-permeability refractory materials in the vertical direction of the tip region of the stopper, but in this case, when viewed in a horizontal cross section of the stopper, the entire surface is made of a porous material (porous tip portion 66), so the structural strength is insufficient. Therefore, there is a possibility that the porous tip portion 66 may crack or peel off due to impacts or vibrations during control during casting.

[0006] On the other hand, as shown in Patent Document 2, in the configuration in which a through hole is provided in the tip region of the stopper, it is necessary to provide a large number of through holes (for example, a large number of through holes as shown in FIG. 5) in order to suppress adhesion of alumina inclusions. This causes a problem that the manufacturing becomes complicated and the manufacturing cost increases. In addition, the bubbles coming out of the through holes are not fine bubbles like the bubbles coming out of the porous refractory material, and there is also a problem that the adhesion of inclusions cannot be suppressed. In addition, in a configuration in which a through hole is generally provided, the hole diameter of the through hole is large, 2 to 5 mm. In this case, the bubble diameter becomes large, and the effect of suppressing the adhesion of inclusions cannot be exhibited. In addition, boiling is likely to occur in the mold, and powder entrainment is likely to occur.

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to suppress adhesion of inclusions near the fitting portion of the stopper, and to prevent the tip region of the stopper from cracking or peeling due to insufficient strength. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a stopper for continuous casting. A stopper for continuous casting having a cavity for gas flow in a vertical center portion, A stopper for continuous casting, in which, in at least a portion of the vertical cross section of the tip side region, a porous refractory material having gas permeability is arranged on an outer peripheral surface side, and a refractory material having higher strength than the porous refractory material is arranged on an inner peripheral surface side. Effect of the Invention

[0009] According to the present invention, bubbles generated by the gas blown into the molten steel from the porous refractory material arranged on the outer peripheral surface side of the tip side region of the stopper are drawn into the vicinity of the fitting portion of the stopper by the molten steel. As a result, bubbles are supplied to the vicinity of the fitting portion of the stopper, and adhesion of inclusions such as alumina near the fitting portion of the stopper can be suppressed. In addition, bubbles generated by the gas blown into the molten steel from the porous refractory material are finer than bubbles generated by the gas blown into the molten steel from the through holes. Therefore, adhesion of inclusions can be suppressed more than in the configuration in which gas is blown into the molten steel from the through holes. Furthermore, since a refractory material having a higher strength than the porous refractory material is arranged on the inner peripheral surface side of the tip side region of the stopper, it is possible to prevent the tip region of the stopper, particularly the tip side region, from cracking or peeling due to insufficient strength. [Brief description of the drawings]

[0010] [Figure 1] 1 is a vertical cross-sectional view of a stopper for continuous casting according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, showing one embodiment of the arrangement of a porous refractory material. [Diagram 3] 2 is a cross-sectional view taken along the line AA in FIG. 1, showing another embodiment of the arrangement of the porous refractory material. FIG. [Figure 4] Graph showing the results of a water model test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] FIG. 1 shows a vertical cross section of a stopper for continuous casting (hereinafter simply referred to as "stopper") 1 according to one embodiment of the present invention. FIG. 2 shows a cross section taken along the line AA in FIG. 1. Here, the vertical cross section of the stopper 1 refers to a vertical cross section passing through the vertical central axis B of the stopper 1. FIG. 1 also shows a virtual nozzle 2 into which the stopper 1 fits from above. This nozzle 2 is specifically a nozzle (upper nozzle) installed at the bottom of a tundish.

[0012] The stopper 1 has a cavity 11 for gas flow in the vertical center. In at least a part of the vertical cross section of the tip side region C of the stopper 1, a gas permeable porous refractory 12 is arranged on the outer peripheral surface side, and a refractory material (hereinafter referred to as "high-strength refractory material") 13 having higher strength than the porous refractory material 12 is arranged on the inner peripheral surface side.

[0013] Here, the tip side region C of the stopper 1 refers to the tip region above the engaging portion 14 of the stopper 1 with the nozzle 2, and in this specification, this tip side region C and the region below the engaging portion 14 of the stopper 1 are collectively referred to as the tip region D of the stopper.

[0014] In the present invention, the porous refractory material 12 is disposed on the outer peripheral surface side in at least a part of the vertical cross section of the tip side region C, and specifically, the porous refractory material 12 is preferably disposed in a region 10 mm to 250 mm above the fitting portion 14 of the stopper 1. This is based on the results of a water model test described below.

[0015] The results of the water model test are shown in Figure 4. In the water model test, the position of the porous refractory 12, i.e., the distance from the fitting part 14 to the porous refractory 12, was changed by fitting the stopper 1 and the nozzle 2 (the upper nozzle installed at the bottom of the tundish) as shown in Figure 1, and the rate at which the bubbles emerging from the porous refractory 12 rise into the tundish (TD) was measured. In the water model test, the water flow rate was 0.42 m 3The gap between the fitting portion 14 of the stopper 1 and the fitting portion 21 of the nozzle 2 was adjusted so that the water flow rate was 0.42 m 3 / min corresponds to a casting amount of 3 t / min. The flow rate of the gas injected into the water from the porous refractory 12 was 5 L / min, and the diameter of the bubbles coming out of the porous refractory 12 was about 0.3 to 1 mm. The distance from the fitting portion 14 to the porous refractory 12 refers to the distance from the fitting portion 14 to the lower end of the porous refractory 12.

[0016] As shown in FIG. 4, as the distance from the fitting portion 14 to the porous refractory 12 increases, the rate at which the bubbles from the porous refractory 12 rise into the tundish increases. A high rate of rising into the tundish means that fewer bubbles are supplied to the vicinity of the fitting portion 14. Therefore, from the viewpoint of suppressing adhesion of inclusions near the fitting portion 14, it is preferable that the distance from the fitting portion 14 to the porous refractory 12 is small. According to the water model test results of FIG. 4, when the distance from the fitting portion 14 to the porous refractory 12 is about 250 mm or less, the rate at which the bubbles rise into the tundish can be suppressed to less than about 80%, so it is preferable that the distance from the fitting portion 14 to the porous refractory 12 is 250 mm or less. In other words, the front end side region C in which the porous refractory 12 is arranged in this embodiment refers to a region up to about 250 mm above the fitting portion 14. From the viewpoint of lowering the rate at which the bubbles coming out of the porous refractory 12 rise into the tundish and increasing the number of bubbles supplied to the vicinity of the fitting portion 14, the distance from the fitting portion 14 to the porous refractory 12 is more preferably 150 mm or less, and even more preferably 100 mm or less. On the other hand, the lower limit of the distance from the fitting portion 14 to the porous refractory 12 is not particularly limited, but from the viewpoint of ensuring the strength of the fitting portion 14, the distance from the fitting portion 14 to the porous refractory 12 is preferably 10 mm or more.

[0017] Next, the arrangement of the porous refractory 12 will be described. In one embodiment of the present invention, as shown in FIG. 2, the porous refractory 12 is arranged on the entire circumference of the outer peripheral surface side in at least a part of the vertical cross section of the tip side region C. By arranging the porous refractory 12 on the entire circumference of the outer peripheral surface side in this manner, bubbles caused by the gas blown from the porous refractory 12 can be uniformly supplied to the vicinity of the fitting portion 14 of the stopper 1. In addition, instead of arranging the porous refractory 12 on the entire circumference of the outer peripheral surface side, as shown in FIG. 3, the porous refractory 12 may be arranged in a dispersed state adjacent to the high-strength refractory 13 on the outer peripheral surface side of the vertical cross section of the tip side region C. Even when the porous refractory 12 is arranged in a dispersed state in this manner, bubbles caused by the gas blown from the porous refractory 12 can be almost uniformly supplied to the vicinity of the fitting portion 14 of the stopper 1. Furthermore, when the porous refractory material 12 is arranged in a dispersed state, the high-strength refractory material 13 is arranged on the outer peripheral surface side, so that the effect of preventing the tip side region C from cracking or peeling due to insufficient strength can be significantly achieved compared to when the porous refractory material 12 is arranged around the entire outer peripheral surface side. 3, the porous refractory 12 is divided into eight parts and arranged in a dispersed state, but the number of divisions of the porous refractory 12 is not limited to this. In other words, from the viewpoint of uniformly supplying bubbles caused by the gas blown from the porous refractory 12 to the vicinity of the fitting portion 14 of the stopper 1, it is better to divide the porous refractory 12 into a larger number of parts, but as the number of parts increases, the manufacturing becomes more complicated and the manufacturing costs increase, so the number of parts of the porous refractory 12 may be appropriately determined by taking these factors into consideration. In this embodiment, as shown in Figure 1, the porous refractory material 12 is arranged in one row in a part of the vertical cross section of the tip side region C. However, for example, another row of the porous refractory material 12 can be arranged on top of the row of the porous refractory material 12 in Figure 1, as shown in Figure 2 or Figure 3, or the porous refractory material 12 can be arranged on the entire outer circumferential surface side of the vertical cross section of the tip side region C.

[0018] Next, the materials and physical properties of the porous refractory 12 and the high-strength refractory 13 will be described. First, the material of the porous refractory 12 can be alumina and graphite, which are typical materials for stoppers. Then, the gas permeability (air permeability) and pore size can be adjusted by adjusting the particle size composition of the raw material blend and the content of volatile matter in the raw material blend. The air permeability of the porous refractory 12 is in the range of 2×10 -15 M 2 ~5×10 -14 M 2 It can be about that. Here, the thickness of the porous refractory 12 (the horizontal dimension in the vertical cross section of the tip side region C (FIG. 1)) is preferably 5 mm or more. By making the thickness of the porous refractory 12 5 mm or more, the porous refractory 12 becomes less likely to peel off. In addition, since the thickness of the porous refractory 12 can be sufficiently ensured, there is also an effect that it is easy to manufacture. The thickness of the porous refractory 12 is more preferably 10 mm or more. Moreover, the height of the porous refractory 12 (the vertical dimension in the vertical cross section of the tip side region C (FIG. 1)) is preferably 15 mm or more. By making the height of the porous refractory 12 15 mm or more, a sufficient amount of gas can be injected from the porous refractory 12 into the molten steel.

[0019] In this embodiment, the high-strength refractory 13 is used in a portion other than the porous refractory 12, and as the material thereof, alumina-graphite, which is a typical material for a stopper, can be used as described above. The room-temperature bending strength of the high-strength refractory 13 is preferably 105 or more, where the room-temperature bending strength of the porous refractory 12 is taken as 100. That is, by making the room-temperature bending strength of the refractory disposed on the inner peripheral surface side of the porous refractory 12 105 or more, where the room-temperature bending strength of the porous refractory 12 is taken as 100, the effect of preventing the tip side region C from cracking or peeling due to insufficient strength can be significantly exhibited. The room-temperature bending strength of the high-strength refractory 13 is more preferably 110 or more, where the room-temperature bending strength of the porous refractory 12 is taken as 100. The upper limit of the room-temperature bending strength of the high-strength refractory 13 is not particularly limited, but in reality, the upper limit is about 300, where the room-temperature bending strength of the porous refractory 12 is taken as 100. In this embodiment, the permeability of the porous refractory 12 is higher than that of the high-strength refractory 13. Specifically, the permeability of the porous refractory 12 can be 300 or more when measured based on JIS-R2115, with the permeability of the high-strength refractory 13 being set to an index of 100. The upper limit of the permeability of the high-strength refractory 13 is not particularly limited, but in reality, the upper limit is about 9000, with the permeability of the high-strength refractory 13 being set to an index of 100.

[0020] Next, the gas injection function of the stopper 1 will be described. As described above, the stopper 1 has a cavity 11 for gas flow in the vertical center, and the gas supplied to the cavity 11 is injected from the porous refractory 12 into the molten steel. For this reason, the stopper 1 has a gas passage 15 for flowing gas from the cavity 11 to the porous refractory 12. In this embodiment, the gas passage 15 is composed of a slit-shaped gas pool 15a provided between the inner peripheral surface of the porous refractory 12 and the outer peripheral surface of the high-strength refractory 13, and a through hole 15b connecting the cavity 11 to the gas pool 15a. In this embodiment, the through holes 15b are provided in two stages as shown in FIG. 1, and 8 through holes 15b are provided per stage, totaling 16 through holes 15b, as shown in FIGS. 2 and 3. That is, the gas supplied to the cavity 11 is supplied to the porous refractory 12 via the 16 through holes 15b and the gas pool 15a, and is injected from the porous refractory 12 into the molten steel. Although not shown in Figures 1 to 3, the gas pool 15a has a bridging portion that partially bridges between the inner surface of the porous refractory material 12 and the outer surface of the high-strength refractory material 13. 1 to 3, the configuration of the gas passage 15 is not limited to the configuration shown in Fig. 1 to 3, and for example, the gas can be supplied directly to the porous refractory 12 from the through holes 15b without providing the gas pool 15a. However, from the viewpoint of uniformly supplying the gas to the porous refractory 12, it is preferable to provide a slit-shaped gas pool on the inner peripheral surface side of the porous refractory 12. The amount of gas blown from the stopper can be in the range of 1 L / min to 15 L / min.

[0021] Such a stopper 1 can be obtained by arranging the clay for forming the porous refractory 12 and the clay for forming the high-strength refractory 13 at predetermined positions in a molding frame, arranging the material that disappears by heat treatment to form the gas passage 15 so as to have the shape of the gas passage 15, and then performing heat treatment after molding. In this way, by integrally molding the clay for forming the porous refractory 12 and the clay for forming the high-strength refractory 13, at least the boundary between the porous refractory 12 and the high-strength refractory 13 in the vertical direction becomes a continuous structure without joints, as shown in FIG. 1. This makes it possible to significantly prevent the tip side region C from cracking or peeling due to insufficient strength. In addition, it is possible to prevent the base metal from entering between the porous refractory 12 and the high-strength refractory 13.

[0022] As described above, according to this embodiment, bubbles generated by the gas blown into the molten steel from the porous refractory 12 arranged on the outer peripheral surface side of the tip side region C of the stopper 1 are drawn into the vicinity of the fitting portion 14 of the stopper by the molten steel. As a result, bubbles are supplied to the vicinity of the fitting portion 14 of the stopper, and adhesion of inclusions such as alumina near the fitting portion 14 of the stopper can be suppressed. In addition, bubbles generated by the gas blown into the molten steel from the porous refractory 12 are finer than bubbles generated by the gas blown into the molten steel from the through holes. Therefore, adhesion of inclusions can be suppressed more than in the configuration in which gas is blown into the molten steel from the through holes. Furthermore, since the high-strength refractory 13 is arranged on the inner peripheral surface side of the tip side region C of the stopper, it is possible to prevent the tip region D of the stopper, especially the tip side region C, from cracking or peeling due to insufficient strength. EXAMPLES

[0023] A continuous casting test was carried out by controlling the flow rate of molten steel using the stoppers of the examples and comparative examples shown in Table 1, and the state of the tip area of ​​the stopper and the adhesion state of inclusions near the fitting part of the stopper were evaluated. The continuous casting test was carried out under the condition of 6ch of casting charge. Other casting conditions (casting speed, casting size, etc.) were general conditions.

[0024] The porous refractory and the high-strength refractory used in the stoppers of the examples and the comparative examples were made of alumina and graphite. The porous refractory on the outer peripheral side of the stoppers of the examples 1 to 3 was disposed in an area 20 to 50 mm above the fitting portion of the stopper. That is, the height of the porous refractory on the outer peripheral side of the stoppers of the examples 1 to 3 was 30 mm. On the other hand, the thickness of the porous refractory on the outer peripheral side of the stoppers of the examples 1 to 3 is as shown in Table 1. Here, the thickness of the porous refractory on the outer peripheral side of the stoppers of the examples 1 to 3 differs in the height direction, but the minimum thickness is shown in Table 1. The room temperature bending strength of the porous refractory on the outer peripheral side and the high-strength refractory on the inner peripheral side of the stoppers of the examples 1 to 3 was measured based on JIS-R2213 using a test piece of 20×20×70 mm. In Table 1, the room-temperature bending strength of the high-strength refractory material on the inner peripheral surface side is expressed as an index, with the room-temperature bending strength of the porous refractory material being set at 100.

[0025] In the evaluation of the continuous casting test, the state of the tip region of the stopper was evaluated by visually checking the state of the tip region of the stopper after the continuous casting test. Also, the adhesion state of the inclusions near the fitting portion of the stopper was evaluated by measuring the adhesion thickness near the fitting portion of the stopper of each example after the continuous casting test. In Table 1, the adhesion thickness near the fitting portion of the stopper of Comparative Example 1 is expressed as an index of 100.

[0026] [Table 1]

[0027] The stoppers of Examples 1 to 3 are stoppers that fall within the scope of the present invention, and no cracks or peeling were observed in the tip region even after 6-channel continuous casting, and the adhesion of inclusions near the mating portion was significantly reduced compared to the stopper of Comparative Example 1.

[0028] The stopper of Comparative Example 1 has a porous refractory material disposed only at the tip of the stopper as shown in Fig. 4 of the above-mentioned Patent Document 1. The effect of suppressing adhesion of inclusions near the fitting part of the stopper was not obtained, and adhesion of inclusions near the fitting part of the stopper increased. The stopper of Comparative Example 2 was one in which no high-strength refractory material was arranged on the inner peripheral side of the porous refractory material as shown in Fig. 3 of the above-mentioned Patent Document 1. Since the structural strength was insufficient, the porous refractory material broke and the tip of the stopper fell off during 6-channel continuous casting. As a result, continuous casting had to be stopped, and the adhesion of inclusions near the fitting part of the stopper could not be evaluated. [Explanation of symbols]

[0029] 1 Stopper 11 Cavity 12 Porous refractories 13 High strength refractories 14 Fitting part 15 Gas passage path 15a Gas pool (gas passage) 15b Through hole (gas passage) 2 Nozzle (Upper Nozzle) 21 Fitting part B Vertical center axis of stopper C Tip side area of ​​stopper D Stopper tip area

Claims

1. A stopper for continuous casting having a cavity for gas flow in a vertical center portion, A stopper for continuous casting, in which, in at least a portion of the vertical cross section of the tip side region, a porous refractory material having gas permeability is arranged on an outer peripheral surface side, and a refractory material having higher strength than the porous refractory material is arranged on an inner peripheral surface side.

2. 2. The stopper for continuous casting according to claim 1, wherein the room-temperature bending strength of the refractory material arranged on the inner peripheral surface side is an index of 105 or more, with the room-temperature bending strength of the porous refractory material being 100.

3. 3. The stopper for continuous casting according to claim 1, wherein in at least a part of a vertical cross section of the tip side region, the porous refractory is disposed around the entire circumference of the outer circumferential surface side, or is disposed in a dispersed state adjacent to a refractory having a strength higher than that of the porous refractory on the outer circumferential surface side.

4. The stopper for continuous casting according to claim 1 , wherein the porous refractory material has a thickness of 5 mm or more in at least a part of a vertical cross section of the tip side region.

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