JP2013035001A - Method for manufacturing high-cleanliness steel cast slab by continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reliably and effectively levitate and separate inclusions by using a tundish provided with a wall and a weir having a horizontally protruding hook-like portion at the upper end portion of the wall compared to the conventional one To do.
SOLUTION: Between a molten steel injection portion 5 and a molten steel outlet 6, a wall portion 8 that surrounds the molten steel injection portion from four directions and extends upward, and toward an upper end portion of the wall portion toward the molten steel injection portion side in a horizontal direction And a tundish 1 having at least one notch and a weir 7 having a rectangular outer shape, an upper opening area S1 of the weir, an opening of the notch For the area S2, the volume V of the space surrounded by the weir, the long side length X of the rectangular outer shape of the weir, and the short side length Y of the rectangular outer shape of the weir, the injection flow rate Q of the molten steel 11 into the tundish and the tundish The steel slab is continuously cast while controlling the molten steel injection into the tundish so that the initial velocity U of the molten steel injection flow into the tank satisfies the following relationship (1). 0.03 ≦ (Q × U) × [(S1 + S2) / V] × (X / Y) ≦ 0.35 (1)
[Selection] Figure 1

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 locations, 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 section toward the wall enclosing center is disposed, the molten steel injection rate q (m ³ / min) and the bowl-shaped portion are excluded. The relational expression that the area A1 (m ² ) of the top surface of the flow control pad and the area A2 (m ² ) of the bottom surface of the flow control pad is 0.5 <(q / A2) × (A1 / A2) <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 5 as an example, the molten steel injection flow from the ladle changes the direction of the flow by colliding with the wall portion extending upward from the bottom of the tundish, and further exists on the wall portion. It is stirred 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 enclosure center, but the upper opening area of the weir, the opening area of the notch provided in the wall part, and the bowl-shaped part If the volume of the space surrounded by the weir and the planar shape of the weir is not an appropriate shape according to the molten steel injection flow rate from the ladle to the tundish and the flow rate of this molten steel injection flow, the molten steel from the ladle The injection flow cannot be uniformly decelerated, that is, the effect of the weir cannot be sufficiently 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. In continuous casting using a tundish provided with a weir having a bowl-like part horizontally 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 By optimizing according to the molten steel injection flow rate to the dish and the flow rate of the molten steel injection flow, the inclusions can be separated and floated more reliably and effectively than the conventional products. It is an object of the present invention to provide a method for producing a high cleanliness steel slab by continuous casting which can greatly reduce defects.

The gist of the present invention for solving the above problems is as follows.
(1) When deoxidized molten steel is once poured into a tundish from a ladle and then poured into a mold from the tundish to continuously cast a steel slab,
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 is surrounded from four directions and upward from the bottom of the tundish. A weir having an extending wall portion and a hook-like portion protruding in the horizontal direction facing the molten steel injection portion side at an upper end portion of the wall portion, and continuous from the wall portion to the hook-like portion Use a tundish with one or more cutouts and a weir with a rectangular outer shape,
For the upper opening area of the weir, the opening area of the notch, the volume of the space surrounded by the weir, the long side length of the rectangular outer shape of the weir, and the short side length of the rectangular outer shape of the weir. Inject the molten steel from the ladle into the tundish so that the flow rate of molten steel from the ladle into the tundish and the initial velocity of the molten steel flow from the ladle to the tundish satisfy the following relationship (1): A method for producing a high cleanliness steel slab by continuous casting, wherein the steel slab is continuously cast while being controlled.
0.03 ≦ (Q × U) × [(S1 + S2) / V] × (X / Y) ≦ 0.35 (1)
However, in the formula (1), Q is the flow rate of molten steel injected from the ladle to the tundish (tons / second), U is the initial velocity (m / second) of the molten steel injection flow from the ladle to the tundish, S1 is the upper opening area (m ² ) of the weir having the hook-shaped portion, S2 is the opening area (m ² ) of the notch, and V is the volume of the space surrounded by the weir having the hook-shaped portion (m ³⁾ ), X is the long side length (m) of the rectangular outer shape of the weir, and Y is the short side length (m) of the rectangular outer shape of the weir.
(2) The method for producing a high cleanliness steel slab by continuous casting as described in (1) above, wherein the opening width of the notch is 0.02 m or less.

  According to the present invention, the shape of the weir having the hook-like portion is optimized based on the casting conditions, and further, according to the shape of this weir, the flow rate of molten steel from the ladle to the tundish and the ladle to the tundish Since the initial velocity of the molten steel injection flow to the inside is controlled within a predetermined range, the floating separation of inclusions in the tundish is promoted, the cleanliness of the molten steel injected into the mold is improved, and the steel slab that is continuously cast is cleaned The degree is improved, and it is realized that product defects due to inclusions are greatly reduced.

It is a front cross-sectional schematic diagram which shows the part of the tundish and casting_mold | template of the continuous casting equipment used by this invention. It is a top view of the tundish shown in FIG. It is a side view of the tundish shown in FIG. It is a figure which shows the result of having investigated the influence of (Q * U) * [(S1 + S2) / V] * (X / Y) which has on the occurrence density of the defect resulting from the inclusion in a steel plate. It is a figure which shows the result of having investigated the influence of the opening width of a notch on the generation density of the defect resulting from the inclusion in a steel plate. It is a figure which shows the investigation result of the number of inclusions in a slab in comparison with an example of the present invention, a comparative example, and a conventional example.

  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 1, A predetermined amount of molten steel 11 is introduced into the tundish while the molten steel 11 previously deoxidized with a deoxidizing material such as aluminum, silicon, titanium, etc. and is poured into the tundish 1 through the long nozzle 3. In the state of being retained, the molten steel 11 in the tundish is injected into the mold 2 through the immersion nozzle 4 to produce a steel slab 12. 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 rectangular projection shape on the horizontal plane of the wall 8 is disposed, which has a bowl-shaped portion 9 that faces the molten steel injection site side and protrudes in the horizontal direction. As shown in FIG. 1, 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 an arc. The surface on the molten steel injection site side of the portion 8 and the surface on the lower surface side of the bowl-shaped portion 9 may be orthogonal to each other.

  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 from four directions. That is, the molten steel injection | pouring site | part 5 is enclosed from four directions by the weir 7 whose projection external shape to a horizontal surface is a square or a rectangular rectangle. However, the weir 7 is provided with at least one notch 10 continuous from the wall portion 8 to the bowl-shaped portion 9, and at the end of casting, the molten steel 11 in the space surrounded by the weir 7 is It passes through the notch 10 and 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. However, when the notch 10 is installed on the surface facing the short side of the tundish 1, a short-circuit flow toward the molten steel outlet 6 may be formed and the floating of the inclusion may be impaired. The notch 10 is preferably installed on the long side surface side of the tundish 1.

  After the molten steel 11 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, the shape of the weir 7 is optimized according to the casting conditions, and at the same time, the molten steel 11 is injected into the tundish 1 at a flow rate and an initial speed according to the shape of the weir 7. There is a need to.

  That is, in the tundish 1 in which the weir 7 is arranged, the upper opening area of the weir 7, the opening area of the notch 10, the volume of the space surrounded by the weir 7, the long side length of the rectangular outer shape of the weir 7, For cleaning the steel slab 12 of seven factors consisting of the short side length of the rectangular outer shape, the flow rate of the molten steel 11 injected from the ladle into the tundish 1, and the initial velocity of the molten steel injected flow from the ladle into the tundish 1 As a result of investigating the influence, the shape of the weir 7 is determined in accordance with the injection flow rate of the molten steel 11 from the ladle to the tundish 1 and the initial velocity of the molten steel injection flow from the ladle to the tundish 1. 7 was installed, and it was found that it was necessary to inject the molten steel 11 into the tundish 1 in accordance with the casting conditions used for determining the shape of the weir 7.

The flow rate of molten steel 11 from the ladle to the tundish 1 is Q (tons / second), the initial velocity of the molten steel flow from the ladle to the tundish 1 is U (m / second), and the upper opening area of the weir 7 S1 (m ² ), the opening area of the notch 10 is S2 (m ² ), the volume of the space surrounded by the weir 7 is V (m ³ ), and the long side length of the rectangular outer shape of the weir 7 is X (m) The results of the investigation will be described below with the short side length of the rectangular outer shape of the weir 7 being Y (m).

  The upper opening area S1 of the weir 7 is an area in the range surrounded by the hook-shaped portion 9 on all sides, and the opening area S2 of the notch 10 is the opening width of each notch 10 and the weir 7 The total value of all the cutouts 10 for each opening area obtained by multiplication with the height of. 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 long side length X of the outer shape is the longer length of the projected rectangular outer shape on the horizontal plane (in FIG. 2, the length of the wall portion 8 perpendicular to the long side surface of the tundish 1). The short side length Y of the external shape is the shorter length of the projected rectangular external shape on the horizontal plane (the length of the wall portion 8 parallel to the long side surface of the tundish 1 in FIG. 2). The initial velocity U of the molten steel injection flow from the ladle to the tundish 1 is that the flow rate of the molten steel 11 flowing down the long nozzle 3 is controlled by a sliding nozzle (not shown) provided above the long nozzle 3. This is the molten steel flow velocity at the time when the flow is controlled by the sliding nozzle and flows down.

  In FIG. 4, the horizontal axis is (Q × U) × [(S1 + S2) / V] × (X / Y), the vertical axis is the defect number density due to inclusions in the steel sheet, and the inclusions in the steel sheet The result of investigating the influence of (Q × U) × [(S 1 + S 2) / V] × (X / Y) on the defect generation density is shown. FIG. 4 shows the results when the opening widths of the two notches 10 are each 0.030 m. (Q × U) indicates the magnitude of the drop energy of the molten steel injection flow into the tundish 1. [(S1 + S2) / V] is the ratio of the opening area of the weir 7 to the volume in the weir. The degree of rise of the molten steel 11 injected into the weir from the inside of the weir is shown, and a measure of the ease with which the inclusions in the molten steel rise, (X / Y) is the rise from the top of the weir It can be considered to indicate the uniformity of the flow velocity and represents a measure of the floating separation of inclusions in the molten steel.

As shown in FIG. 4, the injection flow rate Q of the molten steel 11, the initial velocity U of the molten steel injection flow, the upper opening area S1 of the weir 7, the opening area S2 of the notch 10, the volume V of the space surrounded by the weir 7, the weir When the long side length X of the rectangular external shape 7 and the short side length Y of the rectangular external shape of the weir 7 satisfy the following expression (1), it is found that the occurrence of defects due to inclusions in the steel sheet is reduced. It was.
0.03 ≦ (Q × U) × [(S1 + S2) / V] × (X / Y) ≦ 0.35 (1)
When the value of (Q × U) × [(S1 + S2) / V] × (X / Y) is less than 0.03, the molten steel ascending flow rate from the weir 7 becomes too fast and disturbs the molten steel surface in the tundish. If the value of (Q × U) × [(S1 + S2) / V] × (X / Y) exceeds 0.35, the tundish slag on the molten steel surface may be caught. The molten steel ascending flow rate from 7 is slow and the floating separation of inclusions is insufficient. Therefore, the value of (Q × U) × [(S1 + S2) / V] × (X / Y) needs to be within the range of the above equation (1).

  Further, FIG. 5 shows that the opening width of the notch 10 is changed under the condition that (Q × U) × [(S1 + S2) / V] × (X / Y) is constant at 0.095, and the intervening in the steel plate is performed. It is a figure which shows the result of having investigated the influence of the opening width of the notch 10 on the generation density of the defect resulting from an object. As shown in FIG. 5, it was found that when the opening width of the notch 10 is 0.02 m or less, the occurrence of defects due to inclusions is further reduced. This is because when the opening width of the notch 10 becomes 0.02 m or less, the molten steel 11 flowing out of the weir through the notch 10 decreases, the ratio of the upward flow from the weir 7 increases, and the inclusion floats up. This is because separation is promoted. 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 11 may remain in the space surrounded by the weir 7. It is preferable to secure 0.5 mm or more.

  Here, the weir 7 is a weir on the premise that the molten steel 11 exists above. 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.

  Based on the planned injection flow rate Q of the molten steel 11 and the initial velocity U of the molten steel injection flow, the upper opening area S 1 of the weir 7, the opening area S 2 of the notch 10, the volume V of the space surrounded by the weir 7, The shape of the weir 7 is determined so that the long side length X of the rectangular outer shape and the short side length Y of the rectangular outer shape of the weir 7 satisfy the above formula (1). To the tundish 1 so that the injection flow rate Q of the molten steel 11 into the tundish 1 and the initial velocity U of the molten steel injection flow satisfy the relational expression (1). By continuously casting while controlling the injection of molten steel 11, inclusions in the molten steel injected from the long nozzle 3 obtain upward flow by the weir 7 and float to the molten steel surface in the tundish. To do. That is, the levitation and separation of the inclusions in the molten steel are promoted by the weir 7, and the clean steel slab 12 can be manufactured.

  As described above, according to the present invention, the shape of the weir 7 having the bowl-shaped portion 9 is optimized based on the casting conditions, and the flow rate of the molten steel 11 from the ladle to the tundish 1 and the ladle Since the initial velocity of the molten steel injection flow into the tundish 1 is controlled within a predetermined range according to the shape of the weir 7, the floating separation of inclusions in the tundish 1 is promoted, and the molten steel 11 injected into the mold 2 The cleanliness is improved, the cleanliness of the continuously cast steel slab 12 is improved, and it is realized that product defects due to inclusions are greatly reduced.

  About 250 tons of aluminum-killed ultra-low carbon steel melted by decarburization and refining of hot metal in a converter and subsequent vacuum degassing and refining in an RH vacuum degassing unit, is composed of two strands with a capacity of 70 tons having the configuration shown in FIG. Using a slab continuous casting facility with a tundish system, the molten steel casting speed into the mold is 5.0 tons / minute per strand, and the molten steel injection rate from the ladle to the tundish is 10.0 tons / total for the two strands. Min (Q = 0.167 ton / sec), a test of continuous casting on a steel slab slab was carried out.

  At that time, the initial velocity U of the molten steel injection flow from the ladle to the tundish, the upper opening area S1 of the weir, the opening area S2 of the notch, the volume V of the space surrounded by the weir, the long side of the rectangular outer shape of the weir A test (invention examples 1 to 7) that satisfies the scope of the present invention by casting by changing the length X and the short side length Y of the rectangular outer shape of the weir, and a test that does not satisfy the scope of the present invention (comparison) Examples 1 to 6) were carried out. The initial speed U was adjusted by changing the opening diameter of the sliding nozzle disposed above the long nozzle. Further, in all tundishes, the protruding length of the hook-shaped portion (= the protruding length from the inner wall surface of the wall portion) was 0.12 m, and the radius of the arc connecting the wall portion and the hook-shaped portion was 0.06 m.

  For comparison, a casting test using the same tundish as the test casting was performed except that no weir was installed (conventional example). Table 1 shows the condition of pouring molten steel into the tundish (= Q × U), the shape of the weir of the tundish used, and the condition of pouring the molten steel and the weir shape (Q × U) × [(S1 + S2) / V] × (X / Y). In addition, the opening width of the notch shown in Table 1 is each opening width of the notch installed in two places.

  After casting, the number of inclusions in the slab was examined by ultrasonic flaw detection. FIG. 6 shows the result of investigation of the number of inclusions in the slab. In FIG. 6, the inclusion measurement values in the conventional example using the tundish without the weir are indexed and displayed as a reference (= 1.0).

  As shown in FIG. 6, it was confirmed that the number of inclusions in the slab cast 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 Molten steel 12 Steel slab

Claims (2)

When the deoxidized molten steel is once poured into the tundish from the pan, and then poured into the mold from the tundish to continuously cast the steel slab,
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 is surrounded from four directions and upward from the bottom of the tundish. A weir having an extending wall portion and a hook-like portion protruding in the horizontal direction facing the molten steel injection portion side at an upper end portion of the wall portion, and continuous from the wall portion to the hook-like portion Use a tundish with one or more cutouts and a weir with a rectangular outer shape,
For the upper opening area of the weir, the opening area of the notch, the volume of the space surrounded by the weir, the long side length of the rectangular outer shape of the weir, and the short side length of the rectangular outer shape of the weir. Inject the molten steel from the ladle into the tundish so that the flow rate of molten steel from the ladle into the tundish and the initial velocity of the molten steel flow from the ladle to the tundish satisfy the following relationship (1): A method for producing a high cleanliness steel slab by continuous casting, wherein the steel slab is continuously cast while being controlled.
0.03 ≦ (Q × U) × [(S1 + S2) / V] × (X / Y) ≦ 0.35 (1)
However, in the formula (1), Q is the flow rate of molten steel injected from the ladle to the tundish (tons / second), U is the initial velocity (m / second) of the molten steel injection flow from the ladle to the tundish, S1 is the upper opening area (m ² ) of the weir having the hook-shaped portion, S2 is the opening area (m ² ) of the notch, and V is the volume of the space surrounded by the weir having the hook-shaped portion (m ³⁾ ), X is the long side length (m) of the rectangular outer shape of the weir, and Y is the short side length (m) of the rectangular outer shape of the weir.   The method for producing a high cleanliness steel slab by continuous casting according to claim 1, wherein the opening width of the notch is 0.02 m or less.

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