JP2005334948A - Immersion nozzle for continuous casting and continuous casting method for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve productive efficiency by effectively suppressing the sticking of alumina to the vicinity of discharge holes, thereby effectively preventing the clogging of a nozzle. <P>SOLUTION: The immersion nozzle is a gas blowing type immersion nozzle 11 for continuous casting having confronted two discharge holes 11a at the bottom, and is used in the case the quality Q of molten steel into the immersion nozzle 11 to be fed is ≤10 ton/min. In the immersion nozzle, porous refractories 7 disposed in a gas blowing part has a length L (mm) in the flowing-down direction of molten steel controlled to a value defined by the inequality of 0.05×Q≤L/L0≤0.20×Q, and further, the porous refractories 7 are each arranged at a position where the distance L1 between the lower end of each porous refractory 7 and the upper end of each discharge hole 11a reaches ≤50 mm; in the inequality, L0 is the length (mm) in the flowing-down direction of molten steel from the upper attaching end of the immersion nozzle to the upper end of each discharge hole. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas blowing type immersion nozzle having two discharge holes facing the bottom, and a steel continuous casting method using this immersion nozzle, which are used in a steel continuous casting method.

  Usually, in continuous casting, as shown in FIG. 4, the molten steel 1 in the ladle is cast into the mold 6 from the tundish 2 through the immersion nozzle 5, but the sliding gate plate 4 is placed at the bottom of the tundish 2. The nozzle opening degree can be adjusted. Therefore, in continuous casting using the immersion nozzle 5, if operation is continued for a long time, alumina adheres to the inner wall of the nozzle hole 5a of the immersion nozzle 5 and nozzle clogging is likely to occur. In FIG. 4, 3 is an upper nozzle provided at the bottom of the tundish 2, and 5 b is two discharge holes provided facing the bottom of the immersion nozzle 5.

  When nozzle clogging occurs, the molten steel flow discharged from the discharge hole of the immersion nozzle into the mold fluctuates, adversely affecting the quality of the slab, and the replacement frequency of the immersion nozzle increases, resulting in a reduction in production efficiency. .

Therefore, as a technique for suppressing the nozzle clogging of the immersion nozzle, as shown in FIG. 5, a porous refractory (inner hole body) 7 is inserted into the immersion nozzle 5, and from the inner wall of the porous refractory 7, It has been proposed that Ar or other inert gas is blown into the nozzle hole 5a and that the inert gas film prevents alumina from adhering to the inner wall of the nozzle hole 5a.
Japanese Utility Model Publication No. 5-84454 JP-A-6-106313

Further, in the gas blown immersion nozzle as in Patent Documents 1 and 2, at least the inner wall material near the discharge hole is made of ZrO ₂ —CaO—C, and by the reaction between alumina and CaO adhering to the vicinity of the discharge hole, A technique has been proposed in which a low melting point compound is formed and alumina is prevented from adhering to the vicinity of the discharge hole.
JP-A-5-318059

  However, as described later, the pressure changes from negative pressure to positive pressure in the middle of the molten steel flow direction in the nozzle hole of the immersion nozzle. In the vicinity, gas blowing becomes difficult due to the high fluid pressure, and it is impossible to effectively suppress the adhesion of alumina near the discharge hole. In addition, when the flow rate of the inert gas is increased in order to improve the ability to suppress nozzle clogging, a large amount of the inert gas blown into the mold is trapped at the solidification interface, resulting in a slab as a defect. May remain.

  Moreover, in the technique of the said patent document 3, when the low melting-point compound to produce | generate is taken in in a slab, there exists a possibility of leading to a quality defect.

  The problem to be solved by the present invention is that the conventional nozzle clogging suppression technology that simply inserts a porous refractory can effectively suppress alumina adhesion near the discharge hole. Or the inert gas to suppress the adhesion of alumina and the low melting point compound to be generated to prevent the adhesion of alumina are taken into the solidification interface in the mold, leading to a quality defect of the slab. is there.

  The inventor, when the molten steel supply amount Q into the immersion nozzle is 10 ton / min or less, the inert gas blowing into the immersion nozzle is actively carried out as before, and further clogging prevention effect is obtained. As a result of repeated experiments and simulations on the length of the molten steel flow-down porous refractory (hereinafter simply referred to as “length”) and the installation position of the optimum gas blasting porous refractory for exhibiting Was established.

That is, the immersion nozzle for continuous casting of the present invention is
In order to suppress the nozzle clogging of the immersion nozzle and improve the quality of the slab by suppressing the quality defect of the slab, the optimum length and installation position of the porous refractory were clarified.
A gas-blowing type continuous casting immersion nozzle used in the case where two opposing discharge holes are provided at the bottom and the molten steel supply amount Q into the nozzle is 10 tons / min or less,
The length of the porous refractory that corresponds to the gas blowing part is defined as the length defined by the following equation,
The main feature of the porous refractory is that the distance between the lower end of the porous refractory and the upper end of the discharge hole is 50 mm or less.
0.05 × Q ≦ L / L0 ≦ 0.20 × Q
L: Length of porous refractory (mm)
L0: Length of molten steel flowing from the upper end of the immersion nozzle to the upper end of the discharge hole (mm)

  In the immersion nozzle for continuous casting of the present invention, the porous refractory is disposed at a position where the distance between the lower end and the upper end of the immersion nozzle discharge hole is 50 mm or less. When it is provided at a position exceeding 50 mm from the upper end of the discharge hole, the inert gas blown out from the porous refractory does not reach the vicinity of the discharge hole where nozzle clogging is likely to occur, and nozzle clogging cannot be suppressed. is there.

  In the present invention, the reason why the length L of the porous refractory is defined by the above formula is that when L / L0 is smaller than 0.05 × Q, the length L of the porous refractory is This is because the range in which the inert gas is blown out is too narrow due to being too short, and the range in which the nozzle clogging is suppressed on the inner surface of the nozzle hole is narrowed. On the other hand, when L / L0 is larger than 0.20 × Q, the length L of the porous refractory becomes too long, and most of the inert gas blows out from the negative pressure portion above the nozzle hole, resulting in nozzle clogging. This is because it becomes difficult to blow out the inert gas from the vicinity of the discharge holes that are easily generated.

  When molten steel is cast in a mold using the immersion nozzle for continuous casting according to the present invention, nozzle clogging of the immersion nozzle can be effectively suppressed, and during operation, the replacement frequency of the immersion nozzle is reduced and the production efficiency is improved. To do. This is the steel continuous casting method of the present invention.

  Since the present invention can effectively prevent nozzle clogging even in the vicinity of the discharge hole in the positive pressure region where inert gas blowing is difficult and nozzle clogging is likely to occur in a gas blowing type immersion nozzle. There is an advantage that efficiency is improved.

Hereinafter, the best mode for carrying out the present invention will be described with reference to FIGS.
The inventor has conducted various experiments and simulations for the practical use of a submerged nozzle for gas blowing type continuous casting with a molten steel supply amount Q of 10 ton / min or less. The optimum length and installation position of the porous refractory corresponding to the gas blowing portion for exhibiting the quality improvement effect are found, and the present invention as a method for solving these problems is completed. It was.

  That is, in the case of an immersion nozzle, it is known from a water model experiment that there is a pressure gradient on the inner wall of the nozzle hole in the vertical direction (downstream of the molten steel). An example is shown in FIG. 1. From FIG. 1, the immersion nozzle has (1) a pressure gradient from the upper part of the inner wall of the nozzle hole that becomes negative pressure to the lower part of the inner wall that becomes positive pressure, and (2) It can be seen that the branch point from the negative pressure to the positive pressure changes depending on the supply amount Q of molten steel in the nozzle (the black mark is 5.0 tons / min and the ◯ mark is 4.0 tons / min).

  Therefore, when an inert gas is blown into the nozzle hole of the immersion nozzle, even if the length of the porous refractory inserted into the nozzle is increased, the inert gas is not generated in the negative pressure region above the inner wall of the nozzle hole. While it was easy to blow out, it was estimated that it was difficult to blow out the inert gas at the lower part of the inner wall of the nozzle hole where adhesion was most due to high fluid pressure.

Based on this knowledge, the inventor constructed a method that can most effectively suppress nozzle clogging by paying attention to the length and installation position of a porous refractory for gas blowing.
Fig.2 (a) is a longitudinal cross-sectional view which shows the immersion nozzle 11 of this invention. Here, the length of the porous refractory 7 having its lower end positioned 50 mm or less directly above the discharge hole 11a of the immersion nozzle 11 is L, and the molten steel flows down from the upper end of the attachment of the immersion nozzle 11 to the upper end of the discharge hole 11a. When the directional length is defined as L0, in the present invention, the length of the porous refractory 7 which is the gas blowing portion of the immersion nozzle 11 is defined by the above formula according to the molten steel supply amount in the immersion nozzle 11. Set the length range.

Hereinafter, the installation position of the porous refractory and the experimental example that resulted in the above formula in the present invention will be described.
A low carbon steel molten steel with a component system of [C] = 0.04 mass% is a gas blown immersion nozzle (porous) having an outer diameter of 150 mm, an inner diameter of 80 mm, a discharge hole width of 80 mm, and a height of 90 mm. The distance L1 between the lower end of the refractory material and the upper end of the discharge hole is 37 mm), so that the molten steel supply rate Q is 3.0 tons / min in a mold having an internal dimension of 1250 mm in width and 230 mm in thickness. And cast.

  Then, during the casting, the thickness of the alumina adhered to the inner wall of the nozzle when the length of the gas blasting porous refractory was changed was investigated. The results are shown in Table 1 below. Moreover, the nozzle clogging speed | velocity | rate in each position of the immersion nozzle in invention example C and comparative example G in following Table 1 is shown in FIG.

  Nozzle clogging evaluation in Table 1 below means that 1300 tons (casting time: about 8 hours) of the molten steel ([C] = 0.04 mass% low carbon steel) was passed through the immersion nozzle to finish casting. Later, the inside of the nozzle was observed to measure the thickness of alumina adhered to the inner wall of the nozzle, and the nozzle clogging rate (mm / min) per unit time was determined and evaluated.

  In this 1300-ton casting test, there was no hindrance to casting due to nozzle clogging, and the nozzle clogging speed required for stable casting was 0.04 mm / min or less. Therefore, in the evaluation of the following Table 1, the nozzle clogging speed was classified as “◯” when the nozzle clogging speed was 0.04 mm / min or less, and “x” when the nozzle clogging speed exceeded 4 mm / min.

  Invention Examples A to D satisfy Claims 1 and 2, the distance between the lower end of the porous refractory and the upper end of the discharge hole is 50 mm or less, and the length of the porous refractory is L / L0 is within 0.05 × Q and 0.20 × Q with respect to the molten steel supply amount Q, that is, the length of the porous refractory is within the predetermined length range, so nozzle clogging occurs. Ar gas was effectively blown at a position near the discharge hole where it was easy to perform, and there was no operation hindrance due to nozzle clogging.

  On the other hand, in Comparative Examples E to G, L / L0 exceeds 0.20 × Q, and in Comparative Example H, L / L0 is smaller than 0.05 × Q. The blowing of Ar gas to be carried became inadequate, and the operation was hindered due to nozzle clogging.

  Of course, the present invention is not limited to the above-described example, and even if it is other than the above-described example, only the effects of the configuration added to or reduced from the above-described example are added or reduced. Needless to say.

  The present invention described above can be applied to any type of continuous casting such as a curved type and a vertical type as long as it is a continuous casting using an immersion nozzle.

(A) is a figure which shows the pressure distribution measurement result in the immersion nozzle by water model experiment, (b) is a figure explaining the measurement position of (a). (A) is the longitudinal cross-sectional view explaining the gas blowing type immersion nozzle of this invention, (b) is the figure which looked at the discharge hole part of (a) figure from the side surface. It is a figure which shows the nozzle clogging suppression effect using the gas blowing type immersion nozzle of this invention. It is a figure explaining the continuous casting method. It is a schematic explanatory drawing of the gas blowing type immersion nozzle used for a continuous casting method.

Explanation of symbols

7 Porous refractories 11 Immersion nozzle 11a Discharge hole

Claims (2)

A gas-blowing type continuous casting immersion nozzle to be used when two opposing discharge holes are provided at the bottom and the molten steel supply amount Q into the nozzle is 10 tons / min or less,
The length of the molten steel flow direction of the porous refractory that corresponds to the gas blowing part is defined as the length defined by the following equation,
An immersion nozzle for continuous casting, wherein the porous refractory is disposed at a position where the distance between the lower end of the porous refractory and the upper end of the discharge hole is 50 mm or less.
0.05 × Q ≦ L / L0 ≦ 0.20 × Q
L: Length of porous refractory in the molten steel flow direction (mm)
L0: Length of molten steel flowing from the upper end of the immersion nozzle to the upper end of the discharge hole (mm) A continuous casting method for steel, wherein molten steel is cast into a mold using the immersion nozzle for continuous casting according to claim 1.

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