JP2020078810A - Tundish for continuous casting, and apparatus and method for continuous casting - Google Patents

Abstract

To provide a tundish for continuous casting adapted to effectively prevent the production of an inclusion by preventing a re-oxidation reaction between a molten steel or in-molten-steel aluminum and an in-tundish oxygen while suppressing the inclusion in the molten steel from being brought into a mold by a short path.SOLUTION: A tundish for continuous casting, for pouring a molten steel poured from a ladle, has a steel receiving unit that receives the molten steel, a discharge unit that discharges the molten steel into the mold, and a runner 20c that communicates and couples between the steel receiving unit and the discharge unit. The tundish for continuous casting is configured such that an inlet area of the runner 20c closer to the steel receiving unit is smaller than an outlet area of the runner 20c closer to the discharge unit, and in a vertical cross-section including an axis connecting between an in-figure center on an inlet plane of the runner 20c and an in-figure center on an outlet plane of the runner 20c, an angle α defined between the axis and an inner wall of the runner 20c satisfies the following expression (1). 0°<α<12°...(1)SELECTED DRAWING: Figure 3

Description

  The present application discloses a tundish for continuous casting having a specific runner shape, and a continuous casting apparatus and a continuous casting method using the tundish.

  In the continuous casting process of steel, molten steel whose components and temperature have been adjusted in the refining process is transported to a continuous casting machine for carrying out the continuous casting process while being stored in a ladle which is a refractory container. The transported molten steel is poured into the mold of the continuous casting machine. Here, if the molten steel is directly injected into the mold from the ladle, it is difficult to control the flow rate of the molten steel. In addition, in order to perform continuous casting, it is necessary to replace the ladle and continuously supply molten steel to the mold. Therefore, in general, molten steel in a ladle is injected into an intermediate container called a tundish located below the ladle through an injection nozzle attached to the bottom surface of the ladle, and the flow rate is adjusted in the tundish. Then, it is fed into the mold.

  The tundish has the function of supplying molten steel to the mold while controlling the flow rate as described above, and also includes non-metallic inclusions such as slag that are inevitably mixed during refining of steel, etc. It has the function of floating and separating in the tundish by utilizing the fact that it is smaller than the specific gravity. As a result, it is possible to prevent the non-metallic inclusions existing in the molten steel from being directly supplied into the mold, to prevent the non-metal inclusions from mixing into the slab, and to cause the non-metal inclusions. It is possible to suppress flaws and cracks during rolling. For example, in Patent Documents 1 and 2, by optimizing the shape of the tundish, an upward flow is generated in the molten steel in the tundish, and inclusions present in the molten steel are brought into the mold by a short path. And the inclusions existing in the molten steel are floated and removed.

The molten steel in the tundish is added with aluminum or the like to suppress the amount of dissolved oxygen so that the components do not generate as a gas during solidification. On the other hand, on the molten steel surface of the tundish, reoxidation due to lower oxides in the slag and the atmosphere, that is, oxidation reaction of aluminum in the molten steel, is inevitably generated. Oxidized aluminum becomes alumina inclusions and remains in the slab, deteriorating the quality. The surface level of molten steel is a factor that determines the reoxidation reaction rate. Non-Patent Document 1 describes the reaction rate between lower oxides such as SiO ₂ and MnO in slag and aluminum in molten steel, and the metal-side mass transfer coefficient increases in proportion to the 1.5th power of the molten steel flow rate. , The movement of the molten steel surface of aluminum is promoted, and the reoxidation rate increases. Non-Patent Document 2 describes the reaction rate between oxygen in the atmosphere and aluminum in molten steel. When molten steel flows, the oxide film present on the surface of the molten steel breaks and the reoxidation rate increases. Is shown.

Japanese Patent No. 5527980 Japanese Patent No. 5527981

Katsuhiro Sasai, Yoshimasa Mizukami: Iron and Steel, 81 (1995), 1139. Yoshihiko Higuchi, Yukari Tako, Koji Takatani, Shin Fukagawa: Iron and Steel, 84 (1998), 333.

  As disclosed in Patent Documents 1 and 2, when an ascending flow is generated in molten steel in a tundish, the flow velocity of the molten steel surface increases, and the oxygen existing in the atmosphere or slag existing in the molten metal and the molten steel However, there is a problem in that the aluminum-based inclusions react with aluminum to increase the amount of alumina-based inclusions. In consideration of this point, in the tundish, while suppressing inclusions existing in the molten steel from being brought into the mold by a short path, the reoxidation reaction between the molten steel or aluminum in the molten steel and oxygen in the tundish can be prevented. New technology is needed to prevent and effectively prevent the formation of inclusions.

The present application is, as one of the means for solving the above problems, a tundish for continuous casting, injecting molten steel injected from a ladle into a mold, and a steel receiving portion for receiving the molten steel, and the molten steel Has a discharge part for discharging to the mold, and a runner connecting the steel receiving part and the discharge part in communication with each other, and the inlet area of the runner on the steel receiving part side is the hot water. In a vertical cross section that is smaller than the outlet area of the outlet on the side of the discharge portion and includes a shaft connecting the centroid of the inlet surface of the runner and the centroid of the outlet surface of the runner, Disclosed is a tundish for continuous casting in which an angle α with an inner wall satisfies the following expression (1).
0°<α<12° (1)

In the continuous casting tundish of the present disclosure, the angle α may satisfy the following expression (2).
3°<α<12° (2)

In the continuous casting tundish of the present disclosure, an angle β formed by the shaft and the inner wall of the runner may satisfy the following expression (3) in a cross section including the shaft and orthogonal to the vertical cross section.
0°<β<12° (3)

In the continuous casting tundish of the present disclosure, the angle β may satisfy the following expression (4).
3°<β<12°・・・(4)

  In the continuous casting tundish of the present disclosure, the distance between the centroid of the inlet surface of the runner and the centroid of the outlet surface of the runner may be 50 cm or more and 200 cm or less.

In the continuous casting tundish of the present disclosure, the inlet side minimum area including at least a part of the inlet contour is A ₁ among the flow passage areas of the runner, and the outlet side including at least a part of the outlet contour. When the minimum area is A ₂ , A ₁ /A ₂ may be 0.4 or more and 0.8 or less.

  The present application discloses, as one of means for solving the above problems, a continuous casting apparatus including the continuous casting tundish of the present disclosure.

The present application is, as one of the means for solving the above problems, a continuous casting method of injecting molten steel in a ladle into a tundish, and then injecting the molten steel into a mold, wherein the tundish is the molten steel. A steel receiving part for receiving the molten steel, a discharging part for discharging the molten steel to the mold, and a runner for connecting the steel receiving part and the discharging part to each other for connection. A vertical cross section in which the inlet area on the part side is smaller than the outlet area on the discharge part side of the runner, and which includes an axis connecting the centroid of the entrance surface of the runner and the centroid of the exit surface of the runner In, a continuous casting method is disclosed in which an angle α formed by the shaft and the inner wall of the runner satisfies the following expression (1).
0°<α<12° (1)

In the continuous casting method of the present disclosure, the angle α may satisfy the following expression (2).
3°<α<12° (2)

In the continuous casting method of the present disclosure, the angle β formed by the shaft and the inner wall of the runner may satisfy the following formula (3) in the cross section including the shaft and orthogonal to the vertical cross section.
0°<β<12° (3)

In the continuous casting method of the present disclosure, the angle β may satisfy the following expression (4).
3°<β<12°・・・(4)

  In the continuous casting method of the present disclosure, the distance between the centroid of the entrance surface of the runner and the centroid of the exit surface of the runner may be 50 cm or more and 200 cm or less.

In the continuous casting method of the present disclosure, in the flow passage area of the runner, an inlet-side minimum area including at least a part of the inlet contour is A ₁ , and an outlet-side minimum area including at least a part of the outlet contour. When the area is A ₂ , A ₁ /A ₂ may be 0.4 or more and 0.8 or less.

  According to a new finding of the present inventor, a tundish is divided into a steel receiving part for receiving molten steel and a discharging part for injecting molten steel into a mold, and a hot water for connecting the steel receiving part and the molten steel discharging part in communication. By increasing the average flow velocity of molten steel in the tundish, while preventing passage of inclusions existing in molten steel into the mold by a short path by providing a passage and setting the shape of the runner to the predetermined shape described above. It is possible to suppress the reoxidation reaction between the molten steel or aluminum in the molten steel and oxygen in the tundish, thereby effectively preventing the formation of inclusions.

It is a schematic diagram for explaining a continuous casting device and a continuous casting method using a tundish. It is a schematic diagram for explaining an example of a physical relationship among a steel receiving part, a discharge part, and a runner in a tundish. It is a schematic diagram for explaining an example of the shape of the runway of a tundish. It is a schematic diagram for explaining an example of the shape of the runway of a tundish. The shape of the runner in a vertical cross section including the axis X is schematically shown. It is a schematic diagram for explaining an example of the shape of the runway of a tundish. The shape of the runner is schematically shown in a cross section including the axis X and orthogonal to the vertical cross section. It is a schematic diagram for supplementary explanation about a technical idea of this indication. It is a schematic diagram for explaining an example of the shape of the runway of a tundish. The shape of the runner in a vertical cross section including the axis X is schematically shown. It is a figure which shows the conditions of calculation case (1). It is a figure which shows the conditions of calculation case (2). It is a figure which shows the relationship between the angle (alpha) and the average flow velocity of molten steel. It is a figure which shows the calculation result in case the angle (alpha) is 15 degrees. It is a figure which shows the relationship between the angle (alpha) and the backflow rate of molten steel. It is a schematic diagram for explaining the shape of the H type tundish used in the examples. It is a figure which shows the evaluation result of an Example and a comparative example.

  A tundish of the present disclosure, and a continuous casting device and a continuous casting method using the tundish will be described with reference to FIGS. 1 to 7. As shown in FIG. 1, in continuous casting, after the molten steel 1 in the ladle 10 is poured into the tundish 20, the molten steel 1 is poured into the mold 30. The forms of the ladle 10 and the mold 30 and the positional relationship between the ladle 10, the tundish 20 and the mold 30 are obvious in the field of continuous casting, and therefore detailed description thereof is omitted here.

1. Tundish for Continuous Casting As shown in FIG. 1, a tundish 20 is a tundish for continuous casting in which the molten steel 1 injected from a ladle 10 is injected into a mold 30 and is a steel receiving plate that receives the molten steel 1. It has a portion 20a, a discharge portion 20b for discharging the molten steel 1 to the mold 30, and a runner 20c for connecting and connecting the steel receiving portion 20a and the discharge portion 20b. The steel receiving portion 20a, the discharging portion 20b, and the runner 20c may be made of a known refractory material as a material for the tundish 20.

  FIG. 2 schematically shows an example of the positional relationship among the steel receiving portion 20a, the discharging portion 20b, and the runner 20c in a top view. The tundish 20 shown in FIG. 2 corresponds to an H-shaped tundish in which the steel receiving portion 20a, the discharging portion 20b, and the runner 20c are integrally formed, but the shape of the tundish 20 is not limited to this. Instead, it may have any shape as long as it has the steel receiving portion 20a, the discharging portion 20b, and the runner 20c. For example, although not shown, a weir that separates the steel receiving portion and the discharging portion is provided inside a normal tundish, and a runner that connects the steel receiving portion and the discharging portion with a hole is formed in at least a part of the weir. The form provided may be sufficient. As shown in FIG. 2, the molten steel 1 poured from the ladle 10 into the steel receiving portion 20a of the tundish 20 always passes through the runner 20c before reaching the discharging portion 20b of the tundish 20. Thus, the average flow velocity of the molten steel 1 and the like can be controlled through the runner 20c.

  3 and 4 schematically show an example of the shape of the runner 20c of the tundish 20. In FIG. 3, the overall shape of the runner 20c is shown in perspective. FIG. 4 shows the shape of the runner 20c in a vertical cross section including the axis X described later. 3 and 4 show a configuration in which the inlet surface and the outlet surface of the runner 20c are inclined with respect to the vertical direction in accordance with the general shape of the side wall of the tundish 20. The form of the entrance and the exit of the runner is not limited to this. For example, the surface of the inlet and/or the outlet of the runner 20c may be along the vertical direction.

  As shown in FIGS. 3 and 4, it is important that the inlet area of the runner 20c of the tundish 20 on the steel receiving portion 20a side is smaller than the outlet area of the runner 20c on the discharging portion 20b side. That is, the runner 20c has a flow passage area that increases from the inlet to the outlet. In this way, by making the inlet area of the runner 20c smaller than the outlet area, the average flow velocity of the molten steel 1 flowing through the runner 20c can be reduced. The ratio between the inlet area and the outlet area of the runner 20c is not particularly limited as long as the angle α described below is satisfied. The "entrance area" of the runner 20c refers to the maximum area when the region surrounded by the contours forming the entrance of the runner 20c is projected on a flat surface (when it is regarded as a flat surface). The “exit area” refers to the maximum area when the area surrounded by the contours forming the exit of the runner 20c is projected on a plane (when it is regarded as a plane).

As shown in FIGS. 3 and 4, in the vertical cross section including the axis X connecting the centroid of the entrance surface of the runner 20c of the tundish 20 and the centroid of the exit surface of the runner 20c, the axis X and the runner 20c are shown. It is important that the angle α formed with the inner wall of the above satisfies the following formula (1). In other words, the runner 20c of the tundish 20 has an angle α′ (α1+α2 in FIGS. 3 and 4) between the upper inner wall and the lower inner wall in the vertical cross section including the axis X of more than 0° and less than 24°. Become. Alternatively, it can be said that the runners 20c of the tundish 20 are tapered at an angle of more than 0° and less than 24° from the inlet to the outlet (the flow passage area is enlarged).
0°<α<12° (1)

  "The centroid of the entrance surface of the runner" means that when the area surrounded by the contours that form the entrance of the runner is regarded as a plane, that position is taken as the fulcrum among any points on that plane. The point at which the plane is in balance. The same applies to the “centroid of the exit surface of the runway”. The position of the centroid of the entrance surface of the runner can be specified as follows, for example. That is, the first moment of area is calculated with an arbitrary point on the plane corresponding to the above-mentioned "inlet area" (the plane when the area surrounded by the contours forming the inlet of the runner 20c is regarded as a plane). Then, the value obtained by dividing the calculated first moment of area by the entrance area is the distance from the origin to the centroid. Since a method for specifying the position of the centroid in a specific plane figure is known, further description is omitted here.

When the angle α in the runner 20c is more than 0°, the flow path of the runner 20c can be expanded from the inlet to the outlet, and the average flow velocity of the molten steel 1 flowing through the runner 20c is reduced. be able to. From the viewpoint of further reducing the average flow velocity, it is preferable that the angle α satisfies the following expression (2).
3°<α<12° (2)

  On the other hand, according to a new finding of the present inventor, when the angle α is increased to 12° or more, the backflow rate of the molten steel 1 flowing through the runner 20c is greatly increased. From the viewpoint of further suppressing backflow, the angle α is preferably 10° or less, more preferably 9° or less.

  3 and 4, the angle α1 formed by the upper inner wall of the runner 20c and the axis X and the angle α2 formed by the lower inner wall and the axis X may be the same value or different values. Good. Both of the angles α1 and α2 may be within the range of more than 0° and less than 12°.

In the above description, the angle formed by the inner wall of the runner 20c in a predetermined vertical cross section has been described. On the other hand, in the tundish 20, it is preferable that the runner 20c has a flow passage area increasing from the inlet to the outlet not only in the vertical direction (vertical direction) but also in the horizontal direction. FIG. 5 schematically shows an example of the shape of the runner 20c of the tundish 20. FIG. 5 shows the shape of the runner 20c in a section including the axis X and orthogonal to the vertical section (substantially the same as the shape of the runner 20c in a top view). As shown in FIG. 5, in the tundish 20 including the axis X and a cross section orthogonal to the vertical cross section, it is preferable that an angle β formed by the axis X and the inner wall of the runner 20c satisfies the following expression (3). Thus, not only in the vertical direction, but also in the direction orthogonal to the vertical direction, by making the shape of the runner 20c thicker at a specific angle from the inlet to the outlet, the molten steel flowing through the runner 20c The average flow velocity of 1 can be reduced more appropriately.
0°<β<12° (3)

The preferable range of the angle β is the same as that of the angle α. That is, it is more preferable that the angle β satisfies the following expression (4). Further, from the viewpoint of further suppressing backflow, the angle β is preferably 10° or less, and more preferably 9° or less.
3°<β<12°・・・(4)

From the viewpoint of exerting a more remarkable effect, the tundish 20 has the shape of the inner wall of the runner 20c not only in the above-described vertical (vertical) cross section and in the left-right cross section, but also in the cross-sections in all directions. The shape is preferably such that the flow path expands from the to the outlet at a predetermined angle. That is, in the tundish 20, in any cross section including the axis X, the angle γ formed by the axis X and the inner wall of the runner 20c preferably satisfies the following expression (5), and may satisfy the following expression (6). More preferable. The more preferable range of the angle γ is the same as the angle α and the angle β.
0°<γ<12° (5)
3°<γ<12° (6)

  The length of the runner 20c of the tundish 20 is not particularly limited, but if it is too short or too long, the effect tends to be small. For example, from the viewpoint of more appropriately reducing the average flow velocity of the molten steel 1, it is preferable that the distance between the centroid of the inlet surface of the runner 20c and the centroid of the outlet surface of the runner 20c is 50 cm or more and 200 cm or less. ..

  The ratio of the inlet side flow passage area and the outlet side flow passage area of the runner 20c of the tundish 20 is not particularly limited as long as the above angle is satisfied. Normally, the opening area of the inlet surface or the outlet surface of the runner 20c can largely change depending on the inclination angle (the inclination with respect to the vertical direction) of the inlet surface or the outlet surface (see FIG. 6). In this respect, it is difficult to appropriately reduce the average flow velocity of the molten steel 1 only by specifying the area ratio between the inlet surface and the outlet surface of the runner 20c. On the other hand, in the tundish 20, not only is the inlet area of the runner 20c smaller than the outlet area, but the runner 20c is tapered at a predetermined angle from the inlet to the outlet. It is possible to appropriately reduce the average flow velocity of the molten steel 1.

In addition, as shown in FIG. 7, when there is a difference between the inclination angle θ ₁ of the inlet surface of the runner 20c and the inclination angle θ ₂ of the outlet surface, of the flow passage area of the runner 20c, The minimum area on the inlet side including at least a part of the contour of is preferably specified as the “inlet area”. Further, among the flow passage areas of the runner 20c, the outlet-side minimum area including at least a part of the outlet contour may be specified as the "outlet area". Here, in the tundish 20, among the flow passage areas of the runner 20c, the inlet-side minimum area including at least a part of the inlet contour is A ₁ , and the outlet-side minimum area including at least a part of the outlet contour is When A ₂ is set, A ₁ /A ₂ is preferably 0.4 or more and 0.8 or less. In consideration of the preferred length of the runner 20c, it is preferable that the inlet side minimum area _{A 1} is 80 cm ² or more 2000 cm ² or less, it is preferable that the outlet side minimum area _{A 2} is 100 cm ² or more 5000 cm ² or less . Although FIG. 7 exemplifies the shape of the runner 20c in the vertical cross section including the axis X, the shape of the runner 20c in the cross section including the axis X and the cross section orthogonal to the vertical cross section similarly has the inlet surface and the outlet surface. It is preferable to consider the inclination angle of.

  In the tundish 20, the opening shape on the inlet side and the outlet side of the runner 20c (the shape of the runner 20c in a cross section orthogonal to the flowing direction of the molten steel 1 in the runner 20c) is a realistic and general shape. It may have any shape. For example, a polygonal opening, a round opening, or the like can be adopted. From the viewpoint that the runner can be formed more easily, a substantially square shape or a substantially round shape is preferable, and a substantially square shape is more preferable.

  In the above description, the tundish 20 is provided with only one runner 20c, but the number of runners 20c is not limited to one. Further, in the above description, in the cross-sectional shape, the inner wall of the runner 20c is described as being linear from the inlet to the outlet, but the inner wall surface of the runner 20c is not limited to the linear shape, and It may be curved in a range satisfying the angle.

2. Continuous Casting Device In the above description, the aspect of the tundish for continuous casting of the techniques of the present disclosure has been described. On the other hand, the technique of the present disclosure also has a side face as a continuous casting device. That is, the continuous casting apparatus of the present disclosure includes the tundish 20 for continuous casting of the present disclosure described above.

  In the continuous casting apparatus of the present disclosure, the preferable form of the tundish 20 and the like are as described above, and thus detailed description thereof is omitted here. Further, in the continuous casting apparatus of the present disclosure, the configuration other than the tundish 20 is obvious in the present technical field, and thus detailed description thereof will be omitted here.

3. Continuous casting method In the above description, the aspects of the tundish for continuous casting and the continuous casting apparatus among the techniques of the present disclosure have been described. On the other hand, the technique of the present disclosure has an aspect as a continuous casting method. That is, the continuous casting method of the present disclosure is a continuous casting method in which the molten steel 1 in the ladle 10 is poured into the tundish 20 and then the molten steel 1 is poured into the mold 30. A steel receiving portion 20a for receiving the molten steel 1, a discharging portion 20b for discharging the molten steel 1 to the mold 30, and a runner 20c for connecting the steel receiving portion 20a and the discharging portion 20b for communication. The entrance area on the steel receiving portion 20a side is smaller than the exit area on the discharge portion 20b side of the runner 20c, and the axis X connecting the centroid of the entrance surface of the runner 20c and the centroid of the exit surface of the runner 20c. In a vertical cross section including, the angle α formed by the axis X and the inner wall of the runner 20c satisfies the following formula (1).
0°<α<12° (1)

  In the continuous casting method of the present disclosure, the preferable form and the like of the tundish 20 are as described above, and thus detailed description thereof is omitted here. Further, in the continuous casting method of the present disclosure, configurations other than the tundish 20 are obvious in the present technical field, and therefore detailed description thereof will be omitted here.

  In the continuous casting method of the present disclosure, the flow rate (flow rate) of the molten steel 1 injected from the ladle 10 into the tundish 20 and the flow rate (flow rate) of the molten steel 1 discharged from the tundish 20 into the mold 30 are particularly limited. However, if the flow rate is a general flow rate, the effect of the continuous casting method of the present disclosure is exhibited. From the viewpoint of exerting a more remarkable effect, in the continuous casting method of the present disclosure, the average flow velocity of the molten steel 1 at the inlet of the runner 20c is 0.1 m/s or more and 1 m/s or less, and the average velocity of the molten steel 1 at the outlet is It is preferable to adjust the flow rates of the molten steel 1 injected into the tundish 20 and the molten steel 1 discharged from the tundish 20 so as to be not less than 0.05 m/s and not more than 0.5 m/s.

  Hereinafter, effects of the tundish of the present disclosure will be described with reference to examples.

1. Examination by Computational Fluid Analysis Computational fluid analysis was carried out using fluid analysis software FLUENT. Specifically, as shown in FIG. 8, the molten steel is flown at a condition of calculation case (1) (0.1 mm/s from the area of 600 mm×600 mm, and the shape of the inlet side is a square cross section of 300 mm×300 mm, and In the case where molten steel was circulated in a runner having a cross-sectional area larger than that of the inlet side and having a length of 1000 mm), the steady-state calculation of the molten steel flow velocity at the runner outlet side cross section was performed. Here, the angle formed by the axes passing through the centroids of the inlet surface and the outlet surface and the inner wall of the runner was defined as the runner inlet/outlet inclination angle α (see FIGS. 3 and 4). The turbulent flow model was k-ω, and the molten steel had a density of 7000 kg/m ³ and a viscosity of 0.006 Pa·s. It should be noted that thermal convection is not calculated since it is considered that the temperature distribution due to heat removal from the nozzle wall surface has a small effect on the flow.

  Further, depending on the shape of the tundish, it may not be possible to expand the runner at the same angle in the left-right direction. Assuming this case, regarding the condition of calculation case (2) shown in FIG. 9 (when the upper and lower sides of the runner and only the inner wall surface on one side are enlarged and the runner entrance/exit angle is set to 0° on the other side), Steady-state calculation of molten steel flow velocity in the runway exit side section was performed.

  FIG. 10 compares the runner inlet/outlet inclination angle α and the molten steel flow velocity on the outlet side cross-section of the runner with the average flow velocity of the flow from the inlet to the outlet. In both calculation cases (1) and (2), the molten steel flow velocity decreases as the runner entrance/exit gradient angle α increases. That is, it was found that even when the shapes of the runners were different as in calculation cases (1) and (2), the average flow velocity of the molten steel flowing through the runners could be arranged by the angle α.

  From the result of FIG. 10, when the runner entrance/exit inclination angle α is 2°, it is preferable that the angle α is more than 3° from the viewpoint of reducing the decrease in average flow velocity and securing a more remarkable effect. I understand. It is considered that there was almost no molten steel flow near the inner wall surface of the runner due to the effect of viscosity. Further, especially, when the runner entrance/exit gradient angle α was up to about 9°, there was an effect of decreasing the molten steel flow velocity in accordance with the increase of the angle α, but there was a tendency to saturate above that.

  The following examination confirmed that the effect of reducing the molten steel flow velocity was saturated when the runner entrance/exit gradient angle α was large. FIG. 11 shows the flow around the outlet cross section when the runner inlet/outlet inclination angle α is 15° in the calculation case (1). In this case, it is understood that the molten steel is partially sucked and flows back into the runner. If there is such backflow, the quality of molten steel may be deteriorated by entraining the slag on the surface of the molten metal in the tundish and the atmosphere, so it is preferable to reduce the flow velocity within the range in which backflow does not occur as much as possible.

  In FIG. 12, the percentage of the area in which the molten steel flows backward with respect to the area of the exit side section is defined as the backflow rate. It was found that the backflow rate was 0 when the runner inlet/outlet angle α was 9°, and the backflow rate was significantly increased when the runner inlet/outlet angle α was more than 10° and 12° or more. When such a flow occurs, the flow velocity at the outlet of the runner does not decrease, and the slag floating near the surface of the molten metal in the tundish may be sucked in to increase the inclusions in the molten steel.

  From the above results, it is necessary to set the range of the angle α to 0°<α<12°, and it is preferable to set 3°<α<12° where the flow velocity reducing effect becomes larger.

2. Actual machine test The molten steel that had been subjected to the converter-secondary refining process was poured into an H-shaped tundish, and then cast by a vertical bending continuous casting machine to obtain a slab with a width of 1600 mm and a thickness of 250 mm. As the molten steel, an aluminum killed steel having a C concentration of 0.2 mass% was used. A sample was taken from a position where the width of the slab corresponding to the steady portion between the ladle exchanges was 1/4, and the thickness from the upper surface, that is, the L surface at the time of horizontal casting was 20 mm. The obtained sample was subjected to measurement of total oxygen concentration (TO) in order to evaluate the concentration of oxide-based inclusions such as Al ₂ O ₃ . The total oxygen concentration (TO) was determined by melting the collected sample in a graphite crucible and reacting oxygen in the steel with carbon in the crucible to form carbon monoxide gas, which was then detected by an infrared absorption detector. Was found. The hollow runner shape connecting the steel receiving portion and the molten steel discharging portion of the H-shaped tundish was rectangular, and the runner length (distance between the inlet side centroid and the outlet side centroid) was 0.7 m.

In the comparative example, the shape of the runner connecting the first tank and the second tank of the H-shaped tundish was the same 34.6 cm square at the inlet and outlet, and in the example, the outlet was expanded vertically to 49.0 cm square and left and right. (See FIG. 13). At this time, the cross-sectional area of the inlet of the runner was the same as 0.12 m ^{2 under} both conditions, and the cross-sectional area of the outlet was 0.12 m ^{2 in the} comparative example and 0.24 m ^{2 in the} example. At this time, the runner entrance/exit gradient angle α was 0° in the comparative example and about 6° in the example.

  FIG. 14 shows the measurement result. The vertical axis represents the T.I. measured in the comparative example. It is a value normalized with the value of O as 1. As shown in FIG. 14, in the embodiment, the T. O decreased. That is, the shape of the runner that connects the steel receiving portion and the discharging portion of the tundish is tapered at a predetermined angle from the inlet to the outlet so that the inclusions present in the molten steel are short-passed. Inhibits the increase in the average flow rate of molten steel in the tundish while suppressing the introduction into the mold, and suppresses the reoxidation reaction between molten steel or aluminum in molten steel and oxygen in the tundish to form inclusions. It can be said that it can be prevented.

  The slab cast by the continuous casting method of the present disclosure can be used as a raw material for various steel products.

1 molten steel 10 ladle 20 tundish 20a steel receiving part 20b discharging part 20c runner 30 mold

Claims (13)

A tundish for continuous casting in which molten steel injected from a ladle is injected into a mold,
A steel receiving portion that receives the molten steel, a discharging portion that discharges the molten steel to the mold, and a runner that connects the steel receiving portion and the discharging portion in communication with each other,
The inlet area of the runner on the steel receiving portion side is smaller than the outlet area of the runner on the discharge portion side,
In a vertical section including an axis connecting the centroid of the inlet surface of the runner and the centroid of the outlet surface of the runner, the angle α between the axis and the inner wall of the runner is expressed by the following formula (1). Fulfill,
Tundish for continuous casting.
0°<α<12° (1) The angle α satisfies the following expression (2),
The tundish for continuous casting according to claim 1.
3°<α<12° (2) In a cross section including the axis and orthogonal to the vertical cross section, an angle β formed by the axis and the inner wall of the runner satisfies the following expression (3):
The tundish for continuous casting according to claim 1 or 2.
0°<β<12° (3) The angle β satisfies the following expression (4),
The tundish for continuous casting according to claim 3.
3°<β<12°・・・(4) The distance between the centroid of the entrance surface of the runner and the centroid of the exit surface of the runner is 50 cm or more and 200 cm or less,
The tundish for continuous casting according to any one of claims 1 to 4. If the inlet side minimum area including at least a part of the inlet contour is A ₁ and the outlet side minimum area including at least a part of the outlet contour is A ₂ among the flow passage areas of the runner, A ₁ /A ₂ is 0.4 or more and 0.8 or less,
The tundish for continuous casting according to any one of claims 1 to 5. A tundish for continuous casting according to any one of claims 1 to 6,
Continuous casting equipment. After injecting the molten steel in the ladle into the tundish, a continuous casting method of injecting the molten steel into the mold,
The tundish has a steel receiving portion that receives the molten steel, a discharging portion that discharges the molten steel to the mold, and a runner that connects the steel receiving portion and the discharging portion in communication with each other,
The inlet area of the runner on the steel receiving portion side is smaller than the outlet area of the runner on the discharge portion side,
In a vertical section including an axis connecting the centroid of the inlet surface of the runner and the centroid of the outlet surface of the runner, the angle α between the axis and the inner wall of the runner is expressed by the following formula (1). Fulfill,
Continuous casting method.
0°<α<12° (1) The angle α satisfies the following expression (2),
The continuous casting method according to claim 8.
3°<α<12° (2) In a cross section including the axis and orthogonal to the vertical cross section, an angle β formed by the axis and the inner wall of the runner satisfies the following expression (3):
The continuous casting method according to claim 8 or 9.
0°<β<12° (3) The angle β satisfies the following expression (4),
The continuous casting method according to claim 10.
3°<β<12°・・・(4) The distance between the centroid of the entrance surface of the runner and the centroid of the exit surface of the runner is 50 cm or more and 200 cm or less,
The continuous casting method according to any one of claims 8 to 11. If the inlet side minimum area including at least a part of the inlet contour is A ₁ and the outlet side minimum area including at least a part of the outlet contour is A ₂ among the flow passage areas of the runner, A ₁ /A ₂ is 0.4 or more and 0.8 or less,
The continuous casting method according to any one of claims 8 to 12.