JP5673162B2 - Continuous casting method and continuous casting apparatus - Google Patents

Description

  The present invention relates to a continuous casting method and a continuous casting apparatus, and more particularly to an apparatus capable of efficiently levitating and separating oxide-based nonmetallic inclusions in molten steel injected into a tundish.

  In continuous casting of steel, while supplying the molten steel in the ladle to the tundish through a long nozzle (also called “injection nozzle”) installed at the bottom of the ladle, a predetermined amount of molten steel stays in the tundish. The molten steel in the tundish is distributed and injected into each mold through molten steel outflow holes installed at the bottom of the tundish to produce slabs. In the molten steel, oxide-based non-metallic inclusions such as alumina originating from the deoxidation product (hereinafter referred to as “inclusions”) are suspended, and the inclusions are contained in the solidified layer when the molten steel solidifies. If it is taken in, it will cause defects in inclusion physical properties in the final product such as thin steel plate. Therefore, the tundish is also required to have a function of floating and separating inclusions.

  In general, when the molten steel flow is controlled so that the molten steel flow in the tundish is a uniform flow and no short-circuit flow from the injection point to the outflow hole occurs, the floating separation of inclusions in the tundish is maximized. Based on such a concept, a method of controlling a molten steel flow in the tundish by installing a weir in the tundish has been used, and it has become possible to manufacture a slab with few inclusions. However, a high quality material is required to have a very high cleanliness, and an excellent inclusion separation method is required.

  Various tundishes have been proposed so far to promote the floating and separation of inclusions. For example, Patent Document 1 has at least two weirs between a molten steel injection point from a long nozzle and a molten steel outflow hole into a mold, and the first weir is on one side of the molten steel bath in the tundish. And the second dam is on the other side wall side of the molten steel bath in the tundish and blocks the molten steel flow at the upper part of the molten steel bath. A continuous casting tundish is disclosed in which both the first and second weirs can allow the molten steel to circulate on the side wall opposite to the weir.

  Patent Document 2 has a plurality of through holes for passing molten steel between a molten steel injection point for injecting molten steel from a ladle to a tundish and a molten steel outflow hole to a mold. Tundish for continuous casting in which the total area is 50% or less of the cross-sectional area of the molten steel channel in the tundish, and furthermore, a plurality of porous weirs in which the positions of the through holes are alternated in the length direction of the tundish Is disclosed.

JP 2005-103567 A JP 2005-28376 A

  However, the above prior art has the following problems. That is, Patent Document 1 is a method of preventing a molten steel flow injected from a long nozzle from flowing out directly from a molten steel outflow hole by installing a weir and ensuring a residence time sufficient for inclusions to float and separate. . Moreover, patent document 2 is a method of making the uniform flow of molten steel by arranging the weir which has a several through-hole multistage, and preventing the short circuit flow of the molten steel from a molten steel injection | pouring point to a molten steel outflow hole. These inventions are a method of locating a weir in a tundish to lengthen the time (residence time) that the molten steel stays in the tundish and promote the floating separation of inclusions.

  However, since Patent Documents 1 and 2 use a weir provided with a large number of small openings, there is a problem that opening clogging is likely to occur, and operation management and maintenance are difficult. Also, providing a large number of weirs is not preferable from the viewpoint of running cost.

  An object of this invention is to provide the continuous casting method and the tundish for continuous casting which solve the said subject.

The object of the present invention can be achieved by the following means.
1. A continuous casting method for supplying molten steel from a ladle to a continuous casting tundish with a single injection nozzle and supplying molten steel from the continuous casting tundish to a mold with a single molten steel discharge nozzle, the continuous casting In the tundish, the setting position of the molten steel injection point of the injection nozzle for injecting molten steel from the ladle, and the injection nozzle of the ladle so that the molten steel depth at the molten steel injection point satisfies the following equation: A continuous casting method characterized by controlling a relative position of the continuous casting tundish and an amount of molten steel in the continuous casting tundish.

2 × H <L1 + L2 + L3 <4 × H
Here, L1 is the distance from the side wall surface opposite to the molten steel outflow nozzle as viewed from the molten steel injection point on the bottom surface of the continuous casting tundish to the position directly below the molten steel injection point, and L2 is the molten steel injection The length immersed in the molten steel on the side wall opposite to the molten steel outflow nozzle as viewed from the point, L3 is the distance from the center line of the molten steel injection nozzle to the side wall surface on the molten steel surface (bath surface) of the molten steel, H Is the depth of the molten steel at the center line of the injection nozzle. 2. The continuous casting method according to 1, wherein the horizontal distance between the molten steel injection point and the molten steel outflow point satisfies the following formula.

2 × H <L4 <4 × H
Here, L4 is the distance from the center line of the injection nozzle to the center line of the molten steel outflow nozzle, and H is the depth of the molten steel at the position of the center line of the injection nozzle. A continuous casting apparatus comprising a ladle, a continuous casting tundish, a continuous casting mold, and a molten metal surface control device for controlling the molten metal surface height in the continuous casting tundish,
The positional relationship between the ladle and the continuous casting tundish, and the dimensional shape of the continuous casting tundish, when the molten steel depth at the molten steel injection point by the molten metal level control device is H, A continuous casting machine characterized by satisfaction.
2 × H <L1 + L2 + L3 <4 × H
Here, L1 is the distance from the side wall surface opposite to the molten steel outflow nozzle as viewed from the molten steel injection point on the bottom surface of the continuous casting tundish to the position directly below the molten steel injection point, and L2 is the molten steel injection The length immersed in the molten steel on the side wall opposite to the molten steel outflow nozzle as viewed from the point, L3 is the distance from the center line of the molten steel injection nozzle to the side wall surface on the molten steel surface (bath surface) of the molten steel, H Is the depth of molten steel at the center line of the injection nozzle. 4. The continuous casting apparatus according to 3, wherein a positional relationship between the ladle and the continuous casting tundish and a shape dimension of the continuous casting tundish satisfy the following expression.
2 × H <L4 <4 × H
Here, L4 is the distance from the center line of the injection nozzle to the center line of the molten steel outflow nozzle, and H is the depth of the molten steel at the position of the center line of the injection nozzle.

  According to the present invention, since the flow in the tundish is made uniform and the time required for the floating separation of inclusions can be secured, there are few inclusions in the steel and excellent cleanliness without providing many weirs. Continuously cast slabs and various steel materials using the same can be obtained and are extremely useful in industry.

The figure explaining the positional relationship of the molten steel injection | pouring nozzle of a ladle and the tundish for continuous casting in the continuous casting method which concerns on this invention. The schematic diagram which shows the flow of the molten steel in the tundish for continuous casting by this invention. Comparative example: Schematic explaining the flow of molten steel in the tundish for continuous casting. Comparative example: Schematic explaining the flow of molten steel in the tundish for continuous casting. The schematic diagram explaining the side wall dimension in the case of applying this invention to the tundish for continuous casting which has the curved side wall. Example (a figure showing a numerical fluid simulation result).

The present invention relates to a relative positional relationship between an injection nozzle for injecting molten steel from a ladle into a continuous casting tundish and a molten steel outflow nozzle for supplying molten steel from the inside of the continuous casting tundish to a mold. It is specified in relation to the depth of molten steel in the dish.
Hereinafter, the present invention will be specifically described with reference to the drawings.

  FIG. 1 shows the positional relationship between a molten steel injection nozzle of a ladle and a tundish for continuous casting in the continuous casting method according to the present invention. In the figure, 1 is a tundish for continuous casting, 2 is an injection nozzle for a ladle (not shown), 3 is a molten steel outflow nozzle, 4 is molten steel, 4a is a molten steel surface (bath surface), and 5 is the center of the molten steel outflow nozzle. 6 is a center line of the injection nozzle 2, 11 and 12 are side walls of the tundish 1 for continuous casting, 11a and 12a are side walls of the side walls 11 and 12, 13 is a bottom of the tundish 1 for continuous casting, and 13a is a bottom. The bottom surface of 13, 14 is an injection point at the position of the center line 6 at the tip of the injection nozzle 2, 15 is the outflow point at the position of the center line 5 of the molten steel outflow nozzle 3 on the bottom surface 13 a, and L 1 is the tundish 1 for continuous casting. The distance from the side wall surface 12a on the bottom surface 13a opposite to the molten steel outflow nozzle 3 when viewed from the molten steel injection point 14 to the position directly below the molten steel injection point 14, L2 is the molten steel viewed from the molten steel injection point 14. Leaked nose L3 is the length immersed in the molten steel 4 of the side wall 12 opposite to the steel plate 3, L3 is the distance from the center line 6 of the molten steel injection nozzle 2 to the side wall surface 12a on the molten steel surface (bath surface) 4a of the molten steel 4 , L4 is a distance from the center line 6 of the injection nozzle 2 to the center line 5 of the molten steel outflow nozzle 3 (L4 may be referred to as a horizontal distance between the molten steel injection point 14 and the molten steel outflow point 15), and H is the injection nozzle 2 The molten steel depth at the position of the center line 6 (H may be referred to as molten steel depth) is shown.

  In the present invention, molten steel 4 is supplied to the continuous casting tundish 1 from the ladle with one injection nozzle 2, and the molten steel 4 is provided on the bottom surface 13a from the continuous casting tundish 1 to a mold (not shown). The case where it supplies with one molten steel outflow nozzle 3 is made into object.

  In the present invention, the relative positional relationship between the injection nozzle 2 and the molten steel outflow nozzle 3 is defined using the molten steel depth H at the center line 6 of the injection nozzle 2 so as to satisfy the expression (1). The relative positional relationship between the injection nozzle 2 and the molten steel outflow nozzle 3 can be achieved, for example, by moving the ladle relative to the continuous casting tundish.

2 × H <L1 + L2 + L3 <4 × H (1)
Here, L1: distance from the side wall surface 12a opposite to the molten steel outflow nozzle 3 when viewed from the molten steel injection point 14 on the bottom surface 13a of the continuous casting tundish to the position b immediately below the injection point 14, L2. : The length immersed in the molten steel of the side wall 12 opposite to the molten steel outflow nozzle 3 when viewed from the molten steel injection point 14, L3 is the molten steel injection nozzle 2 on the molten steel surface (bath surface) 4a of the molten steel 4 The distance H from the center line 6 to the side wall surface 12a, H indicates the molten steel depth at the position of the center line 6 of the injection nozzle 2. Adjustment of the relative positional relationship between the injection nozzle 2 and the molten steel outflow nozzle 3 can be performed, for example, by moving the ladle with respect to the tundish for continuous casting.

  FIG. 2 is a schematic view showing the flow of the molten steel 4 in the continuous casting tundish 1 according to the present invention. The molten steel flowing into the continuous casting tundish 1 from the injection point 14 of the molten steel is mainly 2 in FIG. It flows to the molten steel spill nozzle 3 (molten steel spill point 15) through the kinds of paths 7 and 8.

  The path 7 is a flow (bottom flow) along the bottom surface 13a of the tundish directly toward the mold (not shown), and the path 8 is a flow (inverted flow) that reverses at the side wall surface 12a and passes through the bath surface 4a. According to the present invention, the path 7 (bottom flow) and the path 8 (reversal flow) flowing on the bath surface have the same strength, and the molten steel flow in the tundish becomes a uniform flow. Inclusions are more easily levitated and separated as the molten steel flow approaches a uniform flow, so that the removal performance of inclusions in the tundish can be improved.

  Since the path 8 (reversal flow) flows along the bottom surface 13a, the side wall surface 12, and the bath surface 4a, the bath surface flow velocity attenuates and decreases as the distance of L1 + L2 + L3 increases.

When the value of L1 + L2 + L3 is four times as large as H (FIG. 3), the molten steel flow distribution in the tundish is strong at the bottom surface 13a and weak at the bath surface 4a, and a short-circuit flow is generated at the bottom of the tundish, resulting in inclusions. Floatability is deteriorated.
On the other hand, when the value of L1 + L2 + L3 is less than twice H (FIG. 4), the reversal flow is not formed well, all the molten steel flowing from the injection point 14 flows along the tundish bottom, and a short-circuit flow is generated at the tundish bottom. Occurring and the floating separation characteristics of inclusions deteriorate.

Furthermore, when improving the floating separation property of inclusions, the horizontal distance L4 and the molten steel depth H between the molten steel injection point 14 and the molten steel outflow point 15 are preferably set so as to satisfy the equation (2).
2 × H <L4 <4 × H (2)
Since the floating separation of inclusions occurs mainly in the part where the flow is uniform, if the horizontal distance L4 between the molten steel injection point 14 and the molten steel outflow point 15 is smaller than twice the depth H, the floating of the inclusions Separation becomes insufficient, and inclusions flow out into the mold. On the other hand, as L4 is larger, the floating separation of inclusions is promoted. However, when L4 is four times or more than H, inclusion separation ability does not change even if L4 is increased. Further, when L4 is increased, cooling from the tundish bath surface 4a is strengthened and the temperature of the molten steel 4 is decreased. Therefore, considering the deterioration of the slab quality and the heating cost due to the temperature decrease, L4 has a depth H. Is preferably less than 4 times.

  In the drawings used for the above description, the side wall and bottom of the continuous casting tundish were both linear, but the side wall 12 located on the opposite side of the molten steel pouring point 15 from the molten steel pouring point 14 is It may not necessarily be vertical, and may be an inclined side wall or a curved side wall. When the sidewall is curved, the length of the sidewall surface 12a along the curvature of the sidewall is set to L2 as shown in FIG. The same applies to the bottom.

  In addition, since it has been clarified from past experiments and simulations that the molten steel flow state is the same between the tundish of similar shapes, in the present invention, the optimum values of L1, L2, L3, and L4 are set to the molten steel. Is given as a ratio to the depth H.

  The apparatus according to the present invention is a continuous casting apparatus provided with a ladle, a continuous casting tundish, a continuous casting mold, and a molten metal surface control device for controlling a molten metal surface height in the continuous casting tundish. The positional relationship between the ladle and the continuous casting tundish, and the dimensional shape of the continuous casting tundish, when the molten steel depth at the position of the pouring nozzle of the ladle by the molten metal surface control device is H Further, in the continuous casting apparatus satisfying the above formula (1), the positional relationship between the ladle and the continuous casting tundish and the shape dimension of the continuous casting tundish are the above (2). ) Is a continuous casting device that satisfies the formula.

  The effect of the present invention was verified by numerical fluid simulation. The simulation used the finite volume method, and used the k-epsilon turbulence model for the turbulence model. The boundary condition of the tundish wall surface was a standard wall function, and the bath surface was a slip wall condition. Then, using the particle tracking method for the flow field obtained by the simulation, inclusion particles having a diameter of 50 μm were introduced from the molten steel injection point, and the motion trajectory was calculated. The inclusion particles that reached the bath surface were calculated to disappear, and the number of inclusions finally flowing out from the molten steel outflow nozzle was counted for evaluation.

  Tundish has a molten steel capacity of 55 tons and does not use a weir. The molten steel depth H in the molten steel injection nozzle was 1250 mm and 950 mm. Table 1 shows the dimensions of each part defined in FIG. 1 for each simulation model.

  FIG. 6 shows the number of inclusion outflows for each simulation model in Table 1. The number of inclusion outflows is represented by an index where the number of inclusion outflows in Example 1 is 1.

  Examples 1, 2, 3, 7, 8, 9, 10, and 11 are cases where both of the expressions (1) and (2) are satisfied, and Comparative Example 4 is a condition that does not satisfy the expression (1), that is, the position of the side wall. And the value of L1 + L2 + L3 is made smaller than the lower limit of the expression (1), and Comparative Example 5 is a condition made larger than the upper limit of the expression (1). Comparative Example 6 is a condition in which only Expression (1) is satisfied and Expression (2) is not satisfied, L1 + L2 + L3 is an appropriate value, and only L4 is smaller than the lower limit of Expression (2). In Comparative Example 12, L1 + L2 + L3 is an appropriate value, and only L4 is larger than the upper limit of the expression (2).

  6 that Examples 1, 2, 3, 7, 8, 9, 10, and 11 show that the outflow of inclusions is reduced from about 1/2 to about 1/3 of Comparative Examples 4 and 5. Although Comparative Example 6 was able to reduce the inclusion outflow index compared to Comparative Examples 4 and 5, it was confirmed that Examples 1, 2, and 3 showed even better inclusion outflow characteristics. From the above, it was confirmed that the floating separation characteristics of inclusions were improved in the inventive examples. Further, Comparative Example 12 is a condition in which L4 is further increased from the range of the present invention, and shows a decrease in inclusion index equivalent to that of the Example, but the inclusion index is the same as that of Examples 7 and 9 of the present invention. Degree. Even if L4 is made larger than the range of the present invention, no further inclusion removal effect is obtained. On the other hand, it is preferable to make L4 smaller from the viewpoint of preventing the steel temperature from falling, so L4 is within the range of the present invention. It is best to do.

1 Tundish for continuous casting 2 Injection nozzle 3 Molten steel outflow nozzle 4 Molten steel 4a Molten steel surface (bath surface)
5, 6 Center lines 7, 8 Path 9 Flow distribution of molten steel 11, 12 Side wall 11a, 12a Side wall surface 13 Bottom portion 13a Bottom surface 14 Injection point 15 Outflow point

Claims (2)

A continuous casting method for supplying molten steel from a ladle to a continuous casting tundish with a single injection nozzle and supplying molten steel from the continuous casting tundish to a mold with a single molten steel discharge nozzle, the continuous casting in use Tan in the dish, and setting the position of the molten steel injection point of the injection nozzle for injecting molten steel from the ladle, the molten steel depth in the molten steel injection point is less than the lower Symbol of (1), further, horizontal distance is Suyo meet (2 ') below, the injection nozzle of the ladle and the relative position between the continuous casting tundish, continuous casting between the molten steel outflow point and the molten steel injection point continuous casting method and controlling the a molten steel quantity in use tan the dish.
2 × H <L1 + L2 + L3 <4 × H (1)
3.0 × H ≦ L4 <4 × H (2 ′)
However, in the formulas (1) and (2 ′) , L1 is a bottom surface of the tundish for continuous casting, directly below the molten steel injection point from the side wall surface opposite to the molten steel outflow nozzle as viewed from the molten steel injection point. L2 is the length immersed in the molten steel on the side wall opposite to the molten steel outflow nozzle when viewed from the molten steel injection point, L3 is the molten steel injection nozzle on the molten steel surface (bath surface) of the molten steel distance from the centerline to the sidewall surface on the opposite side of the molten steel flow nozzle, L4 is the distance from the center line of the injection nozzle to the center line of the molten steel flow nozzle, H is in the molten steel depth at the position of the center line of the injection nozzle is there. A continuous casting apparatus comprising a molten metal surface control device for controlling the melt-surface height ladle and a continuous casting tundish and the continuous casting mold in the continuous casting Tan in the dish,
The positional relationship between the ladle and the continuous casting tundish, the size and shape of the tundish for continuous casting, molten steel depth in the molten steel injection point by the melt-surface control device when a H, lower A continuous casting apparatus satisfying the following formula (1) and the following formula (2 ′) .
2 × H <L1 + L2 + L3 <4 × H (1)
3.0 × H ≦ L4 <4 × H (2 ′)
However, in the formulas (1) and (2 ′) , L1 is a bottom surface of the tundish for continuous casting, directly below the molten steel injection point from the side wall surface opposite to the molten steel outflow nozzle as viewed from the molten steel injection point. L2 is the length immersed in the molten steel on the side wall opposite to the molten steel outflow nozzle when viewed from the molten steel injection point, L3 is the molten steel injection nozzle on the molten steel surface (bath surface) of the molten steel distance from the centerline to the sidewall surface on the opposite side of the molten steel flow nozzle, L4 is the distance from the center line of the injection nozzle to the center line of the molten steel flow nozzle, H is in the molten steel depth at the position of the center line of the injection nozzle is there.

Images