JP2012045583A - Method for manufacturing high-cleanliness steel cast slab by continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably perform floatation of inclusion as compared with that of a conventional one when performing continuous casting by using a tundish in which a weir including a wall part extending upward from a tundish bottom part, and a canopy-like part oriented to a molten steel injection part side on an upper end part of the wall part is installed.SOLUTION: In continuous casting of steel, a tundish is used which is provided, between a molten steel injection part 5 and molten steel outflow parts 6 of the tundish 1, with a weir 7 including a wall part 8 extending upward from a tundish bottom part by surrounding the molten steel injection part from four directions, and a canopy-like part 9 horizontally projected by being oriented to the molten steel injection part side at the upper end part of the wall part, wherein an opening area D×H of cutouts 10 penetrating the wall part and the canopy-like part and a volume V of a space surrounded by the weir satisfy the expression (1) 0.5≤V/(D×H)≤250, and a steel cast slab 14 is continuously cast while controlling a molten steel injection flow rate so that a molten injection flow rate Q from a ladle satisfies the relationship of the expression (2) 0.18≤Q/A≤6.8 with respect to an upper opening area A of the weir.

Description

  The present invention relates to a method for producing a high cleanliness steel slab by continuous casting. More specifically, the tundish promotes the floating separation of oxide-based non-metallic inclusions such as deoxidation products to improve the cleanliness of molten steel. It relates to how to increase.

  In continuous casting of steel, the molten steel in the ladle is once poured into the tundish, and with a predetermined amount of molten steel retained in the tundish, the molten steel is poured into the mold from the tundish to produce a slab. ing. The tundish not only has the function of supplying molten steel at the time of ladle replacement when continuing continuous casting of multiple heats and the function of distributing molten steel to multiple molds, but also provides a predetermined amount of molten steel in the tundish. The amount of molten steel flowing out of the tundish from the mold to the mold is accurately controlled by the retention, and further, oxide-based nonmetallic inclusions such as deoxidation products suspended in the molten steel (hereinafter simply referred to as “inclusions”). )), And the like. In particular, due to the recent demand for high-quality steel materials, a technique for efficiently levitating and separating inclusions in tundish is widely used.

  As a method for floating and separating inclusions in a tundish, a method is generally used in which a weir is installed in the tundish and the flow of molten steel is controlled by the weir. For example, in Patent Document 1, a weir that has a through hole in the lower part and extends from the bottom of the tundish to the surface of the molten steel in the tundish is placed inside the tundish with the molten steel injection site from the ladle interposed therebetween. There is disclosed a tundish that is disposed so as to be opposed to two places, and the inside of the tundish is separated into a steel receiving region and a steel quasi-static region, and the inclusions are separated and floated in the steel quasi-static region.

  In Patent Document 2, the inside of the tundish is separated into the receiving steel side and the outgoing steel side by a weir having two through holes in contact with the bottom of the tundish, and a dam-like weir ( And the ratio L / W between the long side length L and the short side length W of the tundish is 2 to 7, and the volume ratio on the steel receiving side is 10 to 40% of the whole. A tundish is disclosed.

  Patent Document 3 discloses a tundish collision pad formed from a heat-resistant composition, the pad having a collision surface, and extending upward from the base and receiving the flow of the molten metal. An endless outer side wall that completely surrounds the internal space with the upper opening, and the outer side wall has an annular shape with at least a first portion extending inward and upward toward the opening A tundish impact pad including an inner surface is disclosed.

  A technique for improving the technique of Patent Document 3 has also been proposed. Patent Document 4 describes the flow of molten metal in a tundish that is installed in a portion where a molten metal flow injected from a ladle collides with the bottom of the tundish. A control pad having a wall portion extending upward from the bottom of the tundish surrounding the collision portion of the molten metal flow, and a hook-shaped portion extending from the upper end portion of the wall portion toward the surrounding wall center. The flow control pad which has a notch in the wall part on the side facing the long side inner wall of the tundish is disclosed.

  Further, in Patent Document 5, since the collision pad of Patent Document 3 is a refractory having an integral structure, a tank is formed relative to the molten metal flow from the ladle to the tundish so as to be a weir instead of the collision pad. A flow control weir having a wall portion extending upward from the bottom of the dish and a hook-like portion extending from the upper end portion of the wall portion toward the molten metal flow, wherein the wall portion has a height h and a hook-like shape. A weir is disclosed in which the width d of the portion satisfies the relational expression of 0.1 ≦ d / h ≦ 1.0.

Further, Patent Document 6 discloses that a portion of the molten steel flow from the ladle to the tundish collides with the bottom of the tundish, a wall portion surrounding the collision portion of the molten steel flow and extending upward from the bottom of the tundish; Using a tundish in which a flow control pad having a bowl-shaped portion extending from the upper end portion of the wall portion toward the surrounding center of the wall portion was used, the molten steel injection rate Q (m ³ / min) and the bowl-shaped portion were removed. An area S1 (m ² ) on the top surface of the flow control pad and an area S2 (m ² ) on the bottom surface of the flow control pad have a relational expression of 0.5 <(Q / S2) × (S1 / S2) <5.0. A method of manufacturing a highly clean steel slab that is continuously cast under satisfactory conditions is disclosed.

JP-A-53-6231 Japanese Patent Laid-Open No. 10-216909 JP-T 9-505242 JP 2004-1077 A JP 2004-98066 A JP 2004-154803 A

  By patent documents 1-6, the floating separation of the inclusion in a tundish was improved significantly, and the cleanliness of the molten steel improved significantly compared with the case where a weir is not installed. In particular, in Patent Documents 3 to 6, “an annular inner surface extending inward and upward toward the opening portion” or “a hook-shaped portion extending from the upper end portion of the wall portion toward the surrounding center of the wall portion”. The molten steel injection flow from the ladle to the tundish is agitated so as to return to the molten steel injection site side, so that the molten steel injection flow is decelerated and the floating separation of inclusions is hindered. In addition, the high-speed flow is eliminated and the inclusions are lifted.

  However, Patent Documents 3 to 6 still have room for improvement. That is, taking Patent Document 4 as an example, the molten steel injection flow from the ladle changes the flow direction by colliding with the wall portion extending upward from the bottom of the tundish, and further exists on the wall portion. It is agitated so as to return to the molten steel injection site side by a bowl-shaped part extending from the upper end part of the wall toward the wall enclosing center, but the volume of the space surrounded by the weir having this bowl-shaped part and the notch provided in the wall part When the molten steel injection flow rate from the ladle is not appropriate for the shape of the weir with the bowl-shaped portion, the molten steel injection flow from the ladle is uniformly decelerated. In other words, the effect of the weir cannot be obtained, and the promotion of the floating separation of inclusions in the tundish cannot be expected.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a wall portion extending upward from the bottom of the tundish between the molten steel injection site of the tundish and the molten steel outlet, and the wall. When continuously casting using a tundish equipped with a weir having a bowl-like part that protrudes in the horizontal direction facing the molten steel injection site side at the upper end part of the part, the shape of the weir having the bowl-like part is optimized In addition, by controlling the flow rate of molten steel injected into the tund according to the shape of the weir, the floating separation of inclusions can be performed more reliably than before, and as a result, product defects caused by inclusions can be reduced. To provide a method for producing a high cleanliness steel slab by continuous casting, which can be greatly reduced.

A method for producing a high cleanliness steel slab by continuous casting according to the first invention for solving the above-mentioned problem is as follows: molten steel deoxidized with aluminum is once poured into a tundish from a ladle, and then cast from the tundish to a mold. In the continuous casting of the steel slab by injecting into the molten steel, between the molten steel injection site where the molten steel injection flow from the ladle collides with the bottom of the tundish and the molten steel outlet from the tundish to the mold, the molten steel injection site A weir having a wall extending from the bottom of the tundish upward from the four directions, and a hook-like portion protruding in the horizontal direction toward the molten steel injection site at the upper end portion of the wall, A tundish in which a weir is arranged in which the opening area of the notch penetrating the wall and the bowl-shaped portion and the volume of the space surrounded by the weir satisfy the relationship of the following expression (1): Use and ladle The steel slab is adjusted while controlling the flow rate of molten steel injected from the ladle to the tundish so that the flow rate of molten steel injected into the tundish satisfies the following relationship (2) with respect to the upper opening area of the weir. It is characterized by continuous casting.
0.5 ≦ V / (D × H) ≦ 250 (1)
0.18 ≦ Q / A ≦ 6.8 (2)
However, in the formulas (1) and (2), V is the volume of the space (m ³ ) surrounded by the weir having the hook-shaped part, D is the opening width (m) of the notch, and H is the weir of the weir Height (m), Q is the molten steel injection flow rate from the ladle to the tundish (m ³ / min), and A is the upper opening area (m ² ) of the weir having the bowl-shaped portion.

In the method for producing a high cleanliness steel slab by continuous casting according to the second invention, in the first invention, the weir has a surface on the molten steel injection site side of the wall portion and a surface on the lower surface side of the bowl-shaped portion. It is a shape connected by an arc having a radius R, and the radius R of the arc satisfies the relationship of the following expression (3) with respect to the protrusion length of the bowl-shaped portion.
R ≦ 3Y (3)
However, in the formula (3), R is a radius (m) of an arc connecting a surface of the wall portion on the molten steel injection site side and a surface on the lower surface side of the bowl-shaped portion, and Y is a projection length (m ).

  According to the present invention, the shape of the weir having the bowl-shaped portion is optimized, and furthermore, the injection flow rate of the molten steel from the ladle to the tundish is controlled to the injection flow rate according to the shape of the weir. Floating separation of objects is promoted, the cleanliness of molten steel injected into the mold is improved, the cleanliness of continuously cast steel slabs is improved, and product defects caused by inclusions are greatly reduced. The

It is a figure which shows embodiment of this invention, Comprising: It is the cross-sectional schematic which looked at the part of the tundish and casting_mold | template of a continuous casting installation from the front. It is a top view of the tundish shown in FIG. It is a side view of the tundish shown in FIG. It is an expanded sectional view of the weir arrange | positioned at the tundish shown in FIG. It is a figure which shows the investigation result of the influence of the ratio (V / (DxH)) which acts on the defect generation density resulting from the inclusion in a steel plate. It is a figure which shows the investigation result of the influence of ratio (Q / A) which acts on the defect generation density by the inclusion in a steel plate. It is a figure which shows the investigation result of the influence of the radius R on the defect generation density by the inclusion in a steel plate.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 1 is a diagram showing an embodiment of the present invention, and is a schematic front sectional view showing a tundish and a mold part of a continuous casting facility, FIG. 2 is a plan view of the tundish shown in FIG. FIG. 2 is a side view of the tundish shown in FIG. 1.

  1-3, reference numeral 1 is a tundish, 2 is a mold, 3 is a long nozzle attached to the bottom of a ladle (not shown), 4 is an immersion nozzle attached to the bottom of the tundish, While the molten steel 13 deoxidized with aluminum and accommodated in the ladle is poured into the tundish 1 through the long nozzle 3, a predetermined amount of molten steel 13 is retained in the tundish. Molten steel 13 is injected into the mold 2 through the immersion nozzle 4 to produce a steel slab 14. These drawings are diagrams in which two slab slabs are continuously cast with two molds 2.

  As shown in FIGS. 1 to 3, the tundish 1 used in the present invention has a molten steel injection flow injected into the tundish 1 from the ladle (not shown) through the long nozzle 3 at the bottom of the tundish 1. Between the molten steel injection | pouring site | part 5 which is a collision position, and the molten steel outflow port 6 from the tundish 1 to the casting_mold | template 2, the wall part 8 extended in the perpendicular direction upward from the bottom part of the tundish 1, and the upper end part of the wall part 8 A weir 7 having a hook-like portion 9 facing the molten steel injection site side and protruding in the horizontal direction is disposed. An enlarged view of the longitudinal section of the weir 7 is shown in FIG. As shown in FIG. 4, the weir 7 has a shape in which the surface on the molten steel injection site side of the wall portion 8 and the surface on the lower surface side of the bowl-shaped portion 9 are smoothly connected by a concave arc whose radius is R. It has become. More specifically, it passes through the intersection P of the vertical line Z passing through the lower end point C of the surface of the wall 8 on the molten steel injection site side and the horizontal line X passing through the lower end point E of the tip of the bowl-shaped portion 9, The surface of the wall portion 8 on the molten steel injection site side and the bottom surface of the bowl-shaped portion 9 are formed by an arc having a radius R that places the center position O on the bisector of the angle CPE formed by the points C, P, and E. A side surface is formed. In addition, although the circular arc of radius R may touch the vertical line Z and the horizontal line X, it does not reach the inner surface side of the weir 7 beyond the vertical line Z and the horizontal line X. By setting it as such a shape, the stress concentration in the boundary of the wall part 8 and the bowl-shaped part 9 can be prevented, and the lifetime of the weir 7 can be extended. However, in the present invention, it is not an essential condition to provide a circular arc portion, and the surface of the wall 8 on the molten steel injection site side and the surface of the lower surface side of the bowl-shaped portion 9 may be orthogonal to each other. Absent. That is, the radius R may be zero. In FIG. 4, the symbol Y indicates the protruding length of the bowl-shaped portion 9.

  The weir 7 is also arranged on the long side surface side of the tundish 1 so as to surround the molten steel injection site 5. That is, the molten steel injection | pouring site | part 5 is enclosed from the four directions by the weir 7 whose outer shell of a planar shape is a square or a rectangular quadrangle. However, the weir 7 is provided with at least one notch 10 penetrating the wall portion 8 and the bowl-shaped portion 9, and the molten steel 13 in the space surrounded by the weir 7 is notched at the end of casting. 10 is configured to be discharged toward the molten steel outlet 6. In the tundish 1 shown in FIGS. 1 to 3, the notches 10 are arranged in two places, but there may be three or more places. In FIG. 2, the notch 10 is installed on the long side surface side of the tundish 1, but the installation position of the notch 10 is not limited to the long side surface side of the tundish 1. You may install in the surface which faced the short side surface side. Here, if the opening width of the notch 10 is less than 0.5 mm, the flow rate of the molten steel passing through the notch 10 is too small, and the molten steel 13 may remain in the space surrounded by the weir 7. It is preferable to secure an opening width of 0.5 mm or more.

  After the molten steel 13 injected into the molten steel injection site 5 through the long nozzle 3 collides with the molten steel injection site 5, it flows in four directions along the bottom surface of the tundish 1 due to the falling energy of the molten steel injection flow. 7 and collides with the wall portion 8 in the upward direction, and further flows toward the molten steel injection site 5 by the flange 9 at the upper end of the weir 7. Flows coming from four directions facing the molten steel injection site 5 collide with each other and consume kinetic energy and decelerate. That is, the high-speed molten steel flow injected through the long nozzle 3 is greatly decelerated by the weir 7, and at the same time, the molten steel flow in the tundish is made uniform. Thereby, the short circuit flow and the high-speed flow in the tundish are eliminated, and the inclusions flowing out from the molten steel outlet 6 to the mold 2 are reduced accompanying these flows. That is, the floating separation of inclusions in the tundish 1 is promoted.

  However, in order to obtain the action and effect of the weir 7, it has been found that it is necessary to inject molten steel at a flow rate corresponding to the shape of the weir 7 at the same time as optimizing the shape of the weir 7.

That is, in the tundish 1 where the weir 7 is disposed, the volume of the space surrounded by the weir 7, the opening area of the notch 10, the flow rate of molten steel injected from the ladle into the tundish 1, and the steel cleanness of the upper opening area of the weir 7 As a result of investigating the influence on crystallization, in particular, the ratio of the volume of the space surrounded by the weir 7 and the opening area of the notch 10, the flow rate of molten steel injected from the ladle into the tundish 1, and the upper opening of the weir 7 It has been found that the ratio with the area greatly affects the cleanliness of the molten steel 13. The volume of the space surrounded by the weir 7 is V (m ³ ), the opening area of the notch 10 is B (m ² ), the molten steel injection flow rate from the ladle to the tundish 1 is Q (m ³ / min), and the weir 7 The results of the investigation will be described below with the area of the upper opening of A being A (m ² ). The opening area B of the notch 10 is expressed as B = D × H, where D (m) is the opening width of the notch 10 and H (m) is the height of the weir 7. This opening width D is the total value of the opening widths of all the notches 10. The volume V of the space surrounded by the weir 7 is the volume of the space surrounded by the bottom surface of the tundish 1, the wall portion 8 of the weir 7, and the lower surface of the bowl-shaped portion 9 of the weir 7. The upper opening area A is an area in a range surrounded by the hook-shaped portion 9 on all four sides.

FIG. 5 shows the spatial volume that affects the density of defects due to inclusions in the steel sheet under the condition that the ratio (Q / A) of the molten steel injection flow rate Q to the upper opening area A is 3.3. The result of investigating the influence of the ratio (V / (D × H)) between V and the notch opening area B (= D × H) is shown. As shown in FIG. 5, it has been found that when V / (D × H) satisfies the relationship of the following formula (1), the occurrence of inclusion physical defect is reduced. That is, in order to obtain the above-mentioned action / effect by the weir 7, the weir 7 to be arranged has a relationship between the spatial volume V and the notch opening area B (= D × H) in the following formula (1). The shape must be satisfactory.
0.5 ≦ V / (D × H) ≦ 250 (1)
V / (D × H) is a factor indicating the degree of momentum attenuation in the internal space of the weir 7 of the injected molten steel 13, and can be considered as a measure of inclusion floating separation by the weir 7. When V / (D × H) is less than 0.5, the ascending flow speed of the molten steel 13 from the notch 10 becomes too large, and the molten steel surface in the tundish is roughened and exists on the molten steel surface. On the other hand, when V / (D × H) exceeds 250, the attenuation of molten steel momentum in the weir becomes small, and the floating separation effect of inclusions becomes poor.

FIG. 6 shows the relationship between the molten steel injection flow rate Q and the upper opening area A on the density of defects caused by inclusions in the steel sheet under the condition that the ratio (V / (D × H)) is constant at 30. The result of having investigated the influence of ratio (Q / A) is shown. As shown in FIG. 6, it has been found that when Q / A satisfies the relationship of the following formula (2), the occurrence of inclusion physical defect is reduced. That is, in order to obtain the above-described action / effect by the weir 7, the molten steel injection flow rate Q from the ladle to the tundish 1 satisfies the following relationship (2) with respect to the upper opening area A of the weir 7. Thus, it is necessary to control the molten steel injection flow rate from the ladle to the tundish 1.
0.18 ≦ Q / A ≦ 6.8 (2)
Q / A is a factor indicating the degree of rise of the injected molten steel 13 from the inside of the weir, and is a factor indicating a measure of the ease with which the inclusions in the molten steel rise. Like V / (D × H), the weir 7 It can be thought of as a measure of inclusion flotation separation. When Q / A is less than 0.18, since the attenuation of molten steel momentum in the weir is small, the floating separation effect of inclusions is poor, and molten steel with high cleanliness cannot be obtained. On the other hand, when Q / A exceeds 6.8, the ascending speed from the inside of the weir becomes too large, and the molten steel surface in the tundish may be roughened, and the slag existing on the molten steel surface may be involved. There is.

  Here, the weir 7 is a weir on the assumption that the molten steel 13 exists above, and therefore the height of the weir 7 is at least less than the molten steel depth in the tundish at the position where the weir 7 is disposed. Is necessary. Preferably, the height of the weir 7 is not more than ½ of the molten steel depth in the tundish at the position where the weir 7 is disposed. On the other hand, if the height of the weir 7 is too low, the effect of the weir 7 cannot be obtained. Therefore, the height of the weir 7 is preferably secured to 100 mm or more.

  In addition, the actual molten steel injection site 5 is not a “point” but has a certain area, and such a molten steel injection site is surrounded from all sides, and at the same time, the absolute amount of the space surrounded by the weir 7 is ensured. For this purpose, the length of the upper opening of the weir 7 in the tundish longitudinal direction is at least equal to the inner diameter of the lower end of the long nozzle 3, preferably more than that. In addition, in FIG. 1, the center position of the molten steel injection | pouring site | part which has an area is displayed as the molten steel injection | pouring site | part 5. FIG.

  Moreover, in the tundish 1 used in the present invention, an upper weir 11 having an opening portion is disposed between the weir 7 and the molten steel outlet 6, and further, the upper weir 11 and the molten steel outlet 6 In the middle, lower weirs 12 having openings at the top are arranged on both sides of the molten steel injection site 5 of the tundish 1.

  Using the tundish 1 having the weir 7 and the upper weir 11 and the lower weir 12 having the above shape, the molten steel 13 is controlled while controlling the molten steel injection flow rate so that the molten steel injection flow rate Q satisfies the relational expression (2). When continuous casting is performed, inclusions in the molten steel injected from the long nozzle 3 obtain an upward flow by the weir 7 and float and separate to the molten steel surface in the tundish. The inclusions that have not floated on the molten steel surface then ride on the molten steel flow and reach the wall near the molten steel surface of the upper weir 11, and the molten steel flow is separated into upward and downward flows by the upper weir 11. . Inclusions in the upward flowing molten steel float on the surface of the molten steel, while inclusions in the downward flowing molten steel flow out from the opening near the bottom of the tundish of the upper weir 11 toward the molten steel outlet 6. Thereafter, the lower weir 12 on the outer side of the upper weir 11 causes the flow of the molten steel to be directed upward, and promotes the floating of inclusions on the molten steel surface. That is, the weir 7, the upper weir 11 and the lower weir 12 promote the floating separation of inclusions in the molten steel. However, the installation of the upper weir 11 and the lower weir 12 is not an essential condition for carrying out the present invention, and even if only the weir 7 is used, the floating separation of inclusions is promoted.

Here, the radius R of the concave arc connecting the surface of the wall portion 8 on the molten steel injection site side and the surface on the lower surface side of the bowl-shaped portion 9 greatly affects the momentum attenuation of the molten steel 13 injected into the weir. . That is, the flow velocity of the molten steel 13 varies greatly depending on the size of the radius R, which greatly affects the floating separation of inclusions. Accordingly, the radius (R) is set such that the ratio (Q / A) is constant at 3.3, the ratio (V / (D × H)) is constant at 30, and the protrusion length Y of the flange 9 is constant at 0.12 m. The effect of the radius R on the density of defects due to inclusions in the steel sheet was investigated. The survey results are shown in FIG. As shown in FIG. 7, when the radius R of the arc satisfies the relationship of the following expression (3) with respect to the protrusion length Y of the bowl-shaped portion 9, that is, the radius R is not more than three times the protrusion length Y. In this case, it was found that the occurrence of inclusion physical defect is reduced. However, in the following formula (3), R is the radius (m) of the arc connecting the surface of the wall 8 on the molten steel injection site side and the surface of the bottom surface of the flange 9, and Y is the flange 9 Is a protrusion length (m) (see FIG. 4).
R ≦ 3Y (3)
When the radius R exceeds 3 times the protrusion length Y, the effect of damping the molten steel momentum in the weir is significantly reduced, which is not preferable. That is, it is preferable to determine the shape of the weir 7 so that the radius R of the arc and the protruding length Y of the bowl-shaped portion 9 satisfy the relationship of the above expression (3).

  As described above, according to the present invention, the shape of the weir 7 having the bowl-shaped portion 9 is optimized, and the injection flow rate of the molten steel 13 from the ladle to the tundish 1 is set according to the shape of the weir 7. Since the injection flow rate is controlled, the floating separation of inclusions in the tundish 1 is promoted, the cleanliness of the molten steel 13 injected into the mold 2 is increased, and the cleanness of the continuously cast steel slab 14 is improved. It is possible to significantly reduce product defects due to inclusions.

  About 250 tons of aluminum-killed ultra-low carbon steel melted by decarburization and refining of hot metal in the converter and subsequent vacuum degassing and refining in the RH vacuum degassing unit, is a tundish with a capacity of 70 tons having the configuration shown in FIG. A test for continuously casting a slab slab of steel using a slab continuous casting machine having a slab was carried out.

  At that time, the ratio (V / (D × H)) of the volume V of the space surrounded by the weir 7 and the opening area D × H of the notch, the flow rate Q of molten steel from the ladle to the tundish and the weir 7 Casting was performed by changing the ratio (Q / A) with the upper opening area A (levels 1 to 9). The upper weir 11 and the lower weir 12 were installed in the same location on the tundish in all test castings. In all tundishes, the protrusion length Y of the hook-shaped portion was 0.12 m, and the radius R of the arc connecting the wall portion and the hook-shaped portion was 0.06 m. For comparison, a casting test was also performed using the same tundish as in the test casting except that no weir 7 was installed (level 10: conventional example). After casting, the number of inclusions in the slab was examined by ultrasonic flaw detection.

  Table 1 shows the shape of the tundish weir 7 used, the molten steel injection flow rate, the ratio (Q / A), and the slab inclusion investigation results. Here, the inclusion investigation result was indexed and displayed based on the measurement value of level 10 using a tundish in which no weir 7 was arranged. In addition, the opening width D of the notch shown in Table 1 is the total value at the notch installed in two places. Further, in the remarks column of Table 1, tests in the scope of the present invention are indicated as “examples of the present invention” at levels 1 to 9, and “comparative examples” are indicated otherwise.

  As shown in Table 1, it was confirmed that the number of inclusions in the slab slab can be significantly reduced by applying the present invention. That is, by applying the present invention, it has been confirmed that the floating effect of inclusions in the tundish can be greatly promoted.

DESCRIPTION OF SYMBOLS 1 Tundish 2 Mold 3 Long nozzle 4 Immersion nozzle 5 Molten steel injection | pouring site 6 Molten steel outlet 7 Weir 8 Wall part 9 Ridge part 10 Notch 11 Upper weir 12 Lower weir 13 Molten steel 14 Steel slab

Claims (2)

When molten steel deoxidized with aluminum is once poured into the tundish from the ladle and then poured into the mold from the tundish to continuously cast the steel slab, the molten steel pouring stream from the ladle collides with the bottom of the tundish. Between the molten steel injection portion and the molten steel outlet from the tundish to the mold, a wall portion surrounding the molten steel injection portion from four directions and extending upward from the bottom of the tundish, and the molten steel at the upper end portion of the wall portion A weir having a flange-like portion that faces the injection site side and protrudes in the horizontal direction, and an opening area of a notch that penetrates the wall portion and the saddle-like portion, and a volume of a space surrounded by the weir, However, using a tundish in which a weir having a shape satisfying the relationship of the following equation (1) is used, the flow rate of molten steel injected from the ladle to the tundish is as follows with respect to the upper opening area of the weir: (2) Seki So as to satisfy the, characterized by continuously casting a steel slab at a controlled molten steel injection flow to the tundish from a ladle, a manufacturing method of a high cleanliness steel slabs by continuous casting.
0.5 ≦ V / (D × H) ≦ 250 (1)
0.18 ≦ Q / A ≦ 6.8 (2)
However, in the formulas (1) and (2), V is the volume of the space (m ³ ) surrounded by the weir having the hook-shaped part, D is the opening width (m) of the notch, and H is the weir of the weir Height (m), Q is the molten steel injection flow rate from the ladle to the tundish (m ³ / min), and A is the upper opening area (m ² ) of the weir having the bowl-shaped portion. The weir has a shape in which a surface on the molten steel injection site side of the wall portion and a surface on the lower surface side of the bowl-shaped portion are connected by an arc having a radius R, and the radius R of the arc is a protrusion of the bowl-shaped portion. The method for producing a high cleanliness steel slab by continuous casting according to claim 1, wherein the relationship of the following expression (3) is satisfied with respect to the length.
R ≦ 3Y (3)
However, in the formula (3), R is a radius (m) of an arc connecting a surface of the wall portion on the molten steel injection site side and a surface on the lower surface side of the bowl-shaped portion, and Y is a projection length (m ).

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