JP2005028387A - Immersion nozzle for continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably control molten steel flowing speed spouted from a spouting hole by suitably forming the shape of an immersion nozzle and also, to reduce large inclusion in a cast billet by preventing drifting-flow and uniformizing the molten steel flowing. <P>SOLUTION: The immersion nozzle for continuous casting, is provided with a bottom wall 3 at the lower end of the straight tube part of the nozzle and spouting holes 2 upward at the right and the left of the lower part. For the spouting hole, the hole shape from the inside to the outside end is similar and the widening angle θ is formed in the direction from the inside to the outside in the cross sectional surface, wherein the ratio of the width w at the outside end in the spouting hole to the average hole diameter D of the straight tube part, satisfies 1.1≤w/D≤1.6 and the ratio of the length L of the spouting hole to the average hole diameter D of the straight tube part, satisfies 0.3≤L/D≤0.7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２２】
本発明例では本発明の浸漬ノズルを使用することにより、非金属介在物個数は１０個／１００ｋｇ未満であった。
【００２３】
比較例Ｎｏ．７では吐出孔の広がり角θが０であり吐出孔は内側から外側で広がりを有していないため、吐出流速が大きく、偏流が発生したために非金属介在物個数が多くなっている。
【００２４】
比較例Ｎｏ．８ではｗ／Ｄ及びＬ／Ｄが本発明の範囲を低めに外れており吐出流速が大きいため、吐出流の攪拌効果が大き過ぎて非金属介在物の凝集粗大化が促進され、また、吐出流の局所的な淀みが発生して溶鋼中の非金属介在物が凝固シェルに捕捉され、非金属介在物個数が増大した。
【００２５】
比較例Ｎｏ．９ではｗ／Ｄが本発明の範囲を高めに外れているため吐出流速が小さくなって溶鋼中の非金属介在物が凝固シェルに捕捉され、また、Ｌ／Ｄが本発明の範囲を高めに外れているため、吐出流の攪拌効果が大き過ぎて非金属介在物の凝集粗大化が促進され、非金属介在物個数が増大した。
【００２６】
【発明の効果】
本発明の連続鋳造用浸漬ノズルにより、吐出流速を適正化し、さらには吐出流を均一化することで、非金属介在物の凝集粗大化を防止し、さらには非金属介在物の凝固シェルへの捕捉を防止できるので非金属介在物の極めて少ない鋳片を安定して製造することが可能となる。
【図面の簡単な説明】
【図１】本発明による浸漬ノズルの例を示す図であり、（ａ）は軸心に沿う縦断面図、（ｂ）は（ａ）のＡ−Ａ線断面図である。
【図２】吐出孔外側端の幅ｗと直管部の平均孔直径Ｄの比ｗ／Ｄとスラブの非金属介在物個数の関係を示す図である。
【図３】吐出孔の長さＬとノズル直管部の平均孔直径Ｄの比Ｌ／Ｄとスラブの非金属介在物個数の関係を示す図である。
【符号の説明】
１ 本発明の浸漬ノズル
２ 浸漬ノズルの吐出孔
３ 浸漬ノズルの底壁
４ 浸漬ノズルの直管部
θ 吐出孔の広がり角
ｗ 吐出孔出口端の幅
Ｄ 直管部の平均孔径
Ｌ 吐出孔の長さ[0001]
BACKGROUND OF THE INVENTION
The present invention makes it possible to improve the quality of the slab by uniformizing the molten steel flow discharged from the discharge hole of the immersion nozzle and appropriately controlling the discharge flow rate in continuous casting of the slab, particularly slab slab. The present invention relates to an immersion nozzle for continuous casting.
[0002]
[Prior art]
In continuous casting of slab slabs (hereinafter also simply referred to as slabs), when pouring molten steel from a ladle into a mold, the molten metal is usually poured into the tundish once from the ladle, and then the mold is poured from the tundish through an immersion nozzle. The cast slab is continuously produced by pouring into
[0003]
In continuous casting, the discharge flow rate changes due to a change in the balance between the hole cross-sectional area of the submerged nozzle straight pipe part and the cross-sectional area of the discharge hole, and the discharge flow is biased. If the discharge flow rate is too large or too small, nonmetallic inclusions in the molten steel are trapped by the solidified shell, and nonmetallic inclusions in the slab increase. Also, if drift occurs due to excessive discharge flow rate, nonmetallic inclusions in the molten steel are trapped by the solidified shell due to local stagnation, and powder on the molten metal surface is swallowed into the molten steel, causing non-containment in the slab. Metal inclusions increase, and further, vertical cracks occur in the slab due to uneven solidification, causing product defects.
[0004]
Therefore, the conventional continuous casting has been developed with a focus on appropriately controlling the discharge flow rate and preventing the drift by changing the dimensional balance between the straight pipe portion of the immersion nozzle and the discharge hole. For example, in Patent Document 1, the ratio of the average hole diameter of the nozzle straight pipe portion to the average diameter of the discharge hole is 1.0 or more, and the length of the discharge hole, the average hole diameter of the nozzle straight pipe portion, and the discharge hole An immersion nozzle having a ratio to the length of 0.8 or more is described. However, with this immersion nozzle, the drift in the molten steel cannot be sufficiently suppressed, powder penetration occurs, and nonmetallic inclusions in the molten steel are trapped by the solidified shell, resulting in defects due to inclusions. It turns out that there is a case.
[0005]
Further, in Patent Document 2, the relationship between the outer diameter x of the nozzle straight pipe portion and the thickness t of the inner die of the mold satisfies “40 (mm) ≦ t−x ≦ 120 (mm)”, and the nozzle straight pipe portion. An immersion nozzle is described in which the ratio of the hole cross-sectional area to the total cross-sectional area of the discharge holes is 1.0 or less. However, it has been found that the maximum discharge flow rate is too large with this immersion nozzle, so that powder penetration due to fluctuations in the molten metal surface occurs and breakout easily occurs.
[0006]
Further, in Patent Document 3, the ratio of the vertical length a to the horizontal length b of the discharge hole of the immersion nozzle satisfies “0.3 ≦ a / b ≦ 1.0” and the nozzle straight An immersion nozzle is described in which the ratio of the hole cross-sectional area of the pipe portion to the total cross-sectional area of the discharge holes is 1.2 to 2.6. Although no uneven flow occurs in this immersion nozzle, it has been found that the average discharge flow rate in the mold is small and nonmetallic inclusions in the molten steel are trapped by the solidified shell, so that defects due to inclusions occur.
[0007]
[Patent Document 1]
JP 54-8117 A [Patent Document 1]
JP-A-5-154625 [Patent Document 1]
JP 2001-129645 A
[Problems to be solved by the invention]
In view of the above-mentioned problems of the prior art, the present invention provides an immersion nozzle for continuous casting that enables the production of a slab with few quality defects by appropriately controlling the discharge flow rate and preventing the uneven discharge flow. It is to provide.
[0009]
[Means for Solving the Problems]
According to the present invention, the shape of the immersion nozzle is appropriately formed to appropriately control the speed of the molten steel flow discharged from the discharge hole, and the quality of the molten steel flow is prevented and uniformed by preventing the uneven flow of the molten steel flow. It has been clarified that a slab can be produced, and the gist thereof is as follows.
(1) A bottom wall 3 is provided at the lower end of the nozzle straight pipe part, and upward discharge holes (2, 2) are provided on the left and right sides of the lower part. The discharge holes are similar in shape from the inner end to the outer end. And has a breadth in the direction from the inside to the outside in the cross section, and the ratio of the width w of the outer end of the discharge hole to the average hole diameter D of the straight pipe portion is 1.1 ≦ w / D ≦ 1 The continuous casting immersion nozzle characterized by satisfying the relationship .6.
(2) A bottom wall 3 is provided at the lower end of the nozzle straight pipe part, and upward discharge holes (2, 2) are provided on the left and right sides of the lower part. The discharge holes are similar in shape from the inner end to the outer end. And has a spread in the direction from the inside to the outside in the cross section, and the ratio of the length L of the discharge hole to the average hole diameter D of the straight pipe portion is 0.3 ≦ L / D ≦ 0.7 An immersion nozzle for continuous casting characterized by satisfying
(3) The continuous casting immersion nozzle according to (1) or (2) above, wherein a spread angle θ of the discharge hole is 40 to 70 °.
(4) The continuous casting immersion nozzle according to any one of (1) to (3), wherein the discharge hole is upward and the upward angle α is 5 to 40 °.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The continuous casting immersion nozzle of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing an example of an immersion nozzle for continuous casting according to the present invention. FIG. 1 (a) is a longitudinal sectional view along the nozzle axis, and FIG. 1 (b) is a transverse sectional view taken along line AA in FIG. It is.
[0011]
The immersion nozzle 1 has a bottom wall 3 at the lower end of the straight pipe portion 4, and discharge holes 2, 2 on the left and right sides of the lower portion of the straight pipe portion 4. The discharge holes 2 and 2 have a similar hole shape from the inner end to the outer end, and the hole shape may be any of a true circle, a horizontally long ellipse, a square, a horizontally long rectangle, and the like. The discharge holes 2 and 2 are widened in the direction from the inside to the outside in the cross section taken along the line AA in FIG. 1, and the discharge holes have a spread angle so that the discharge flow velocity can be dispersed and attenuated. it can.
[0012]
The spread angle (θ) of the discharge hole is desirably in the range of 40 ° to 70 °. If it is out of this range, fluctuations in the molten metal surface and drift will occur, and powder may be trapped and non-metallic inclusions may be trapped in the solidified shell.
[0013]
The direction of the discharge holes 2 and 2 is preferably upward, and the upward angle α is preferably 5 to 40 °. If the upward angle α is less than 5 °, the cast slab will be vertical due to non-uniform solidification by shell washing, and if the upward angle α exceeds 40 °, the powder will be entrained by the undulation of the molten metal surface.
[0014]
FIG. 2 shows the ratio w / D between the width w of the outer end of the discharge hole and the average hole diameter D of the straight pipe portion when the slab is continuously cast using the immersion nozzle shown in FIG. The relationship with the number of inclusions is shown. In addition, the width w of the discharge hole outer end is a diameter when the hole shape of the discharge hole outlet end is a circle, a long diameter when it is a horizontally long ellipse, and a long side when it is a horizontally long rectangle. .
[0015]
The mold cross-sectional shape is a result of casting SUS304 steel at a casting speed of 0.75 m / min with a slab having a thickness of 200 mm and a width of 1000 mm. If w / D is less than 1.1, the discharge flow rate is too high and the stirring effect due to the discharge flow becomes too great to promote agglomeration of non-metallic inclusions. As a result, uneven flow occurs in the discharge flow and local flow stagnation occurs, so that the nonmetallic inclusions are captured by the solidified shell and the number of nonmetallic inclusions in the slab increases. On the other hand, when w / D exceeds 1.6, the discharge flow rate is too small, and the nonmetallic inclusions in the molten steel are trapped by the solidified shell and the number of nonmetallic inclusions increases. Preferably 1.2 ≦ w / D ≦ 1.5.
[0016]
The width w of the outer end of the discharge hole is preferably larger than the average diameter d of the outlet of the discharge hole. Thereby, the damping effect of the discharge flow rate is increased, and since no drift occurs, defects such as vertical cracks are less likely to occur due to powder intrusion and uneven solidification due to the drift. The average diameter d of the discharge hole outlet can be obtained from the area of the discharge hole outlet as S (cm ² ) and the length a (cm) around the discharge hole outlet as d = 4 S / a as an average diameter.
[0017]
FIG. 3 shows the ratio L / D between the length L of the discharge hole and the average hole diameter D of the straight pipe portion when the slab is continuously cast using the immersion nozzle shown in FIG. The relationship of the number of objects is shown. The cross-sectional shape of the mold is for a slab having a thickness of 200 mm and a width of 1000 mm, and is a result of casting SUS304 steel at a casting speed of 0.75 m / min. When the L / D is less than 0.3, the deviation of the discharge flow becomes intense, and the discharge flow can be locally stagnated. Therefore, the nonmetallic inclusions in the molten steel are trapped by the solidified shell, and the number of nonmetallic inclusions is Increase. On the other hand, when L / D exceeds 0.7, the spread of the discharge flow in the horizontal plane becomes small, and the effect of the discharge flow rate attenuation due to the discharge flow hole spreading from the inside to the outside becomes small, and the discharge flow rate is excessive. Since the agitation effect is too great and the coarsening of nonmetallic inclusions is promoted, the number of nonmetallic inclusions increases. Preferably, 0.35 ≦ L / D ≦ 0.6.
[0018]
As described above, according to the immersion nozzle for continuous casting of the present invention, an appropriate discharge flow rate can be ensured and uneven flow can be prevented, so that a slab of good quality can be manufactured stably.
[0019]
【Example】
The effects of the present invention will be described below based on examples. The mold is a result of casting SUS304 steel for a slab having a cross-sectional shape of 200 mm thickness-width 1000 mm. Table 1 summarizes the investigation results of the shape of the immersion nozzle and the slab quality.
[0020]
The obtained slab was examined for the number of non-metallic inclusions. The investigation of non-metallic inclusions cuts out a 30x30x5mm thick block from the slab surface to 5mm at the center of the width of the slab where stagnation of the molten steel flow is likely to occur and sag of the steel plate is likely to occur Then, the block was immersed in an iodine alcohol solution, large inclusions of 50 μm or more were extracted, and the number of inclusions was measured with an optical microscope. The number of non-metallic inclusions was expressed as the number of inclusions per 100 g of steel dissolved in iodine alcohol.
[0021]
[Table 1]

[0022]
In the present invention example, the number of non-metallic inclusions was less than 10/100 kg by using the immersion nozzle of the present invention.
[0023]
Comparative Example No. In No. 7, the spread angle θ of the discharge hole is 0, and the discharge hole does not expand from the inside to the outside. Therefore, the discharge flow rate is large, and the number of non-metallic inclusions increases because of the occurrence of drift.
[0024]
Comparative Example No. In No. 8, w / D and L / D are out of the range of the present invention, and the discharge flow rate is large. Therefore, the stirring effect of the discharge flow is too great, and the aggregation and coarsening of nonmetallic inclusions is promoted. Local stagnation of the flow occurred, and nonmetallic inclusions in the molten steel were trapped by the solidified shell, increasing the number of nonmetallic inclusions.
[0025]
Comparative Example No. In No. 9, w / D is out of the range of the present invention, so the discharge flow rate is reduced and non-metallic inclusions in the molten steel are captured by the solidified shell, and L / D increases the range of the present invention. As a result, the agitation effect of the discharge flow is too great, which promotes the agglomeration and coarsening of nonmetallic inclusions, and increases the number of nonmetallic inclusions.
[0026]
【The invention's effect】
By the immersion nozzle for continuous casting of the present invention, the discharge flow rate is optimized, and the discharge flow is made uniform to prevent the non-metallic inclusions from agglomerating and coarsening, and further to the solidified shell of the non-metallic inclusions. Since the capture can be prevented, it is possible to stably produce a slab with very few non-metallic inclusions.
[Brief description of the drawings]
1A and 1B are diagrams showing an example of an immersion nozzle according to the present invention, in which FIG. 1A is a longitudinal sectional view along an axis, and FIG. 1B is a sectional view taken along line AA in FIG.
FIG. 2 is a diagram showing the relationship between the width w of the outer end of the discharge hole and the ratio w / D of the average hole diameter D of the straight pipe portion and the number of non-metallic inclusions in the slab.
FIG. 3 is a diagram showing the relationship between the ratio L / D of the discharge hole length L and the average hole diameter D of the nozzle straight pipe portion and the number of non-metallic inclusions in the slab.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Immersion nozzle discharge hole 3 Immersion nozzle bottom wall 4 Immersion nozzle straight pipe portion θ Discharge hole spread angle w Discharge hole outlet end width D Straight tube portion average hole diameter L Discharge hole length The

Claims (4)

There is a bottom wall at the lower end of the nozzle straight pipe part, and there are discharge holes on the left and right sides of the lower part. The continuous is characterized in that the ratio of the width w of the outer end of the discharge hole and the average hole diameter D of the straight pipe portion satisfies 1.1 ≦ w / D ≦ 1.6. Immersion nozzle for casting. There is a bottom wall at the lower end of the nozzle straight pipe part, and there are discharge holes on the left and right sides of the lower part. For continuous casting, characterized in that the ratio of the length L of the discharge hole and the average hole diameter D of the straight pipe portion satisfies 0.3 ≦ L / D ≦ 0.7. Immersion nozzle. 3. The continuous casting immersion nozzle according to claim 1, wherein a spread angle [theta] of the discharge hole is 40 to 70 [deg.]. The immersion nozzle for continuous casting according to any one of claims 1 to 3, wherein the discharge hole is upward and the upward angle α is 5 to 40 °.

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