JP2004098127A - Method for continuously casting high quality stainless steel cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously casting a high quality stainless steel cast slab by which a descended stream formed at the lower part of a mold is restrained by making slow spouted stream of molten steel from an immersion nozzle, and the heat conduction into a meniscus is made satisfactory, and the cast slab having excellent quality can stably be produced at high speed casting by preventing the defects caused by blow hole and inclusion developed on the surface of the cast slab and inclusion defect in the inner part of the cast slab, when the molten stainless iron is cast. <P>SOLUTION: In the method for continuously casting the molten stainless steel by using a vertical-bending type continuous caster for pouring the molten steel in a tundish into the mold via the immersion nozzle, the immersion nozzle having a spouting hole enlarged from the inside to the outside to the axial center is dipped into the mold to pour the molten steel. This poured molten steel quantity is made to be 0.6-5.0 ton/min to perform the casting. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a high-quality cast slab with a small number of bubbles and inclusions when the molten steel is cast using a vertical bending type continuous casting machine when the discharge flow of the immersion nozzle is set to a slow flow when casting molten stainless steel. The present invention relates to a continuous casting method for quality stainless steel slabs.
[0002]
[Prior art]
Conventionally, molten stainless steel produced in a refining furnace such as a converter or electric furnace is cast from a tundish into a mold through an immersion nozzle, and cooled by the mold and a cooling zone arranged below the mold. A method of manufacturing a slab using a so-called continuous casting apparatus that performs continuous casting while casting is adopted. (Cited Document 1), (Cited Document 2) However, inclusions such as oxides and slag in molten stainless steel (molten steel), mold powder, and the like are captured by a solidified shell during the solidification process of the slab. This is a factor that causes a surface defect of the slab, a surface flaw in a product, a crack during processing, and the like.
[0003]
In addition, when molten steel is poured from a tundish into a mold, inclusions adhere to the interior of the immersion nozzle, causing a change in the pouring amount, interruption of the pouring due to nozzle clogging, and the like. In order to prevent the inclusion of inclusions inside the immersion nozzle, casting is performed while blowing an inert gas such as argon gas into the immersion nozzle. However, the injected argon gas, etc., is discharged from the discharge port of the immersion nozzle into the mold, forming bubbles of various sizes, large ones float, and small fine bubbles accompany the discharge flow of molten steel. To the depth of the slab, or to be trapped by the solidified shell (solidified shell), which is solidifying and increasing its thickness, to generate cellular defects. Further, oxide inclusions accompanying the discharge flow also penetrate deep into the slab, and are caught by the solidified shell or form an accumulation zone inside, which causes surface or internal defects.
[0004]
As a countermeasure, as described in Patent Document 3, the casting condition of a molten stainless steel is adjusted by using a vertical bending type continuous caster and adjusting the casting conditions by changing the angle of the discharge port of the immersion nozzle upward from 5 ° to downward. °, the immersion depth is 150 to 300 mm below the meniscus and poured into the mold, and casting is performed at a casting speed of 0.8 to 1.8 m / min, resulting from inclusions and argon gas bubbles. It has been proposed to improve productivity by high-speed casting while preventing such defects.
[0005]
[References]
(A) Reference 1 (Japanese Patent Publication No. 61-39144)
(B) Reference 2 (Japanese Patent Application Laid-Open No. 3-174962)
(C) Reference 3 (Japanese Unexamined Patent Publication No. 6-262302)
[Problems to be solved by the invention]
However, in the method described in Patent Literature 3, the shape of the discharge port of the immersion nozzle, which is a casting condition, is a cylindrical shape having the same diameter from the inside to the outside of the immersion nozzle, and has an upward direction of 5 degrees to a downward direction of 35 degrees. Since the temperature range is satisfied, a molten steel flow (discharge flow) having a strong flow downward from the center of the discharge port or from the center is formed. As a result, a strong discharge flow causes fluctuations in the molten metal surface and entrainment of powder, and furthermore, bubbles and inclusions enter the deep portion of the slab accompanying this discharge flow, thereby impairing the quality of the slab. There is.
[0007]
In addition, the casting operation is performed by pouring molten stainless steel into the tundish and then pouring the molten metal into the mold from the immersion nozzle, a low-speed range immediately after pouring and pulling out, and a low-speed range at the end of casting. Non-stationary regions always occur. In the low speed region, in the early casting stage or the last casting stage, or in the unsteady part where slow casting is performed such as breakout or minor equipment trouble during casting, the discharge flow of molten steel from the immersion nozzle decreases, There is a problem that the shell washing effect on the inner surface of the solidified shell due to the flow is small, and that the solidified shell is more likely to capture bubbles and inclusions, thereby deteriorating the quality of the slab.
[0008]
On the other hand, even in the area where casting is stable, the gap between the mold and the immersion nozzle becomes narrower around the immersion nozzle immersed in the mold, causing stagnation in the flow of molten steel. There is a disadvantage that the temperature is lowered easily and the shell washing effect is reduced, and the inclusion of inclusions and bubbles of argon gas in the thin portion (surface layer portion) of the solidified shell increases.
[0009]
Further, when casting a stainless steel slab by casting a stainless steel molten steel using a vertical bending type continuous casting apparatus, if m / min corresponding to the drawing speed is used as an index, the molten steel from the discharge port of the immersion nozzle depends on the size of the mold. And the discharge flow fluctuates. When the mold size is large, the shell washing effect due to the molten steel discharge flow tends to decrease. On the other hand, when the mold size is small, the discharge flow of the molten steel becomes strong, and due to the formation of a strong downward flow, there are problems such as bubbles and inclusions penetrating deep into the slab and deteriorating the quality of the slab. .
[0010]
The present invention has been made in view of such circumstances, and when casting stainless steel, suppresses a downward flow and an upward flow formed by slowing the discharge flow of molten steel from an immersion nozzle, and applying heat to the meniscus. It is possible to stably produce high quality slabs by high-speed casting by preventing defects caused by bubbles and inclusions generated on the surface of the slab and inclusion defects inside the slab. It is an object of the present invention to provide a continuous casting method for high quality stainless steel slabs.
[0011]
[Means for Solving the Problems]
A method for continuous casting of a high-quality stainless steel slab according to the present invention, which meets the above-mentioned object, comprises a vertical bending station in which molten steel in a tundish is poured into a mold through an immersion nozzle using a bending-type continuous casting machine having a vertical portion. In the casting method of stainless steel molten steel using a casting machine, a molten steel is poured by immersing a molten steel into a mold by dipping a dip nozzle whose discharge port is widened from inside to outside with respect to the axis of the dip nozzle. Casting is performed at 5.0 ton / min or less.
[0012]
According to this method, the discharge port of the immersion nozzle is widened and the amount of molten steel to be poured satisfies 5.0 ton / min or less. It is possible to suppress bubbles and inclusions that enter the deep portion of the slab accompanying powder entrainment or downward flow due to the molten steel discharge flow.
When the pouring rate exceeds 5 ton / min, the discharge flow of molten steel from the discharge port becomes strong, and bubbles and inclusions that penetrate deep into the slab due to entrainment and downward flow of powder increase. Impairs the quality of the slab.
[0013]
Here, it is preferable that the discharge port of the immersion nozzle is a wide-angle discharge port within an angle range of 15 degrees upward to 45 degrees downward with respect to the axis of the immersion nozzle.
This makes it possible to suppress the upward flow or the downward flow in which the discharge flow from the immersion nozzle hits the solidification shell and inverts the flow, thereby making the flow slower, resulting in powder entrainment and fluctuations in the molten metal surface, and accompanying the molten steel. Bubbles and inclusions can be suppressed from penetrating into the deep part of the slab, and defects occurring on the surface layer and inside of the slab can be prevented.
[0014]
If the angle of the discharge port of the immersion nozzle exceeds 15 degrees upward, the upward flow increases, and this upward flow causes powder entrainment. On the other hand, when the angle of the discharge port exceeds 45 degrees downward, the downward flow increases and bubbles and inclusions accompanying the molten steel penetrate into the deep part of the slab, causing bubbles and inclusions on the surface layer and inside of the slab. The resulting defects are likely to occur. For this reason, it is more preferable that the angle is 10 degrees upward to 35 degrees downward.
The wide-angle discharge port of the immersion nozzle has a divergent angle from the inside to the outside with respect to the axis of the immersion nozzle, and for example, has a trumpet-like spread.
[0015]
Further, the immersion depth of the immersion nozzle can be set to 100 to 350 mm below the meniscus, and the immersion nozzle can be poured into the mold. Thereby, it is possible to suppress the fluctuation of the molten metal surface due to the discharge flow of the immersion nozzle, the entrainment of the powder, or the penetration of bubbles and inclusions into the deep part of the slab. When the immersion depth of the immersion nozzle is less than 100 mm, the molten metal discharge flow causes a change in the molten metal surface and the entrainment of the powder, which impairs the quality of the slab. On the other hand, when the immersion depth exceeds 350 mm, the downward flow formed by reversing the discharge flow becomes strong, and the number of bubbles and inclusions accompanying the downward flow increases, thereby impairing the quality of the slab.
[0016]
Preferably, the ratio of the inner diameter D of the immersion nozzle to the diameter d of the discharge port is 1.0 to 1.5. Thereby, the discharge flow velocity of the molten steel from the discharge port can be reduced, and the drift of the discharge flow during casting can be suppressed. Further, when the deposit is generated at the discharge port, the drift of the discharge flow can be reduced.
If the ratio (D / d) of the inner diameter D of the immersion nozzle to the diameter d of the discharge port is less than 1.0, the discharge port becomes too large, and the molten steel flow stagnates above the discharge port, resulting in downward discharge. The flow increases, and air bubbles and inclusions enter the deep portion of the slab along with the discharge flow, causing a defect of the slab. On the other hand, heat supply to the vicinity of the molten metal surface in the mold is insufficient, and deckle is likely to occur.
[0017]
Further, when the ratio (D / d) of the inner diameter D of the immersion nozzle to the diameter d of the discharge port exceeds 1.5, the discharge port becomes too small, and drift due to clogging of the immersion nozzle easily occurs. As a result, biased drift tends to occur, and bubbles and inclusions are liable to penetrate into a deep portion of the air bubbles and inclusions, and powder level and molten metal level change due to an upward flow are likely to occur.
Furthermore, if the inner diameter D of the immersion nozzle is increased to increase the size of the discharge port, the entire immersion nozzle becomes large, which hinders the replacement of the immersion nozzle and increases the cost of the refractory.
[0018]
Furthermore, it is preferable that at least 50% or more of the outer circumference of the discharge port of the immersion nozzle has an angle of widening outward with respect to the axis of the immersion nozzle. Thereby, since the widening angle of the discharge port is at least 50% or more, the processing of the discharge port of the immersion nozzle is facilitated, the discharge speed of the molten steel can be reduced, and the drift of the discharge flow during casting is suppressed. It is possible to suppress the increase in the diameter of the immersion nozzle and reduce the cost of the refractory used. In addition, when the range having the angle of widening in the outward direction is less than 50% of the outer peripheral line of the discharge port, the effect of slowing the flow of the discharge flow is reduced, and when the discharge port is clogged, the molten steel is melted. Drift easily occurs.
[0019]
Further, it is preferable that the molten steel poured into the mold is electromagnetically stirred. As a result, a swirling molten steel flow is formed around the inner periphery of the mold to eliminate the stagnation near the immersion nozzle, enhance the shell washing effect on the inner surface of the solidified shell, and generate air bubbles and intercalation trapped in the inner surface layer of the solidified shell. An object can be removed and a cast piece having a surface layer of good quality can be manufactured.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention.
FIG. 1 is an explanatory view of a continuous casting apparatus used for a continuous casting method of a high-quality stainless steel slab according to an embodiment of the present invention, FIG. 2 is a sectional view of the immersion nozzle, and FIG. FIG. 4 is a graph showing the relationship between d and the product inconsistency index, and FIG. 4 is a graph showing the relationship between the pouring amount and the product incompatibility index. As shown in FIG. 1, the continuous casting apparatus 1 is provided with a tundish 3 for pouring and storing a molten steel (molten steel) 2 from a ladle (not shown), and an immersion nozzle 4 attached to a lower portion of the tundish 3. I have.
[0021]
Further, a mold 7 for cooling the molten steel 2 poured from the immersion nozzle 4 and flowing out of the discharge port 5 to form a solidified shell 6 and a slab 8 whose inside cooled by the mold 7 is in a molten state are supported. The support segment 9 is provided with a plurality of watering nozzles for spraying water on the slab to cool the slab. The slab 8 is drawn out at a predetermined speed by a pinch roll (not shown) while increasing the solidification thickness by cooling. Is Powder 10 is added to the mold 7 on the meniscus (fluid surface), a part of which forms a molten layer due to the heat of the molten steel 2 flowing out from the discharge port 5, and a gap is formed between the mold 7 and the solidified shell. It flows in and lubricates well.
[0022]
Outside the mold 7, electromagnetic stirring devices 11a and 11b for stirring the molten steel 2 in the mold are provided. As shown in FIG. 2, the immersion nozzle 4 has two discharge ports 5 symmetrically below the immersion nozzle, and the angle Q of the discharge ports 5 is 15 ° above the axis x of the immersion nozzle 4. It is formed in a wide angle shape or a trumpet shape in which the condition is satisfied within a range of about 45 ° downward and the diameter increases from the inside to the outside with respect to the axis x. The supply of the argon gas to the immersion nozzle is blown from an upper nozzle arranged above the immersion nozzle 4 (not shown).
[0023]
Next, a continuous casting method for a high-quality stainless steel slab according to an embodiment of the present invention will be described using a continuous casting apparatus.
Pour stainless steel molten steel (molten steel) 2 into tundish 3 and when molten steel 2 in tundish 3 has accumulated about 20 to 25 tons, attach it to the bottom of tundish 3 while continuing pouring from a ladle. The pouring from the dipped nozzle 4 to the mold 7 is started. Then, when a predetermined molten steel is poured into the mold 7, the molten steel 2 is poured into the mold 7 while holding for about 1 minute to form a sufficiently solidified shell, and then starting to pull out the dummy bar. Then, the meniscus of the molten steel 2 is raised to a position about 100 mm below the upper end of the mold 7 to perform casting.
[0024]
Since the molten metal is poured into the mold 7, the discharge port of the immersion nozzle is widened and the amount of molten steel to be poured satisfies 5.0 ton / min or less. It can suppress the discharge flow to a slow flow, and by forming a good discharge flow, bubbles and inclusions that enter the deep part of the slab accompanying powder entrainment and downward flow due to molten steel discharge flow Can be suppressed. If the pouring rate is more than 5 tons / min, the discharge flow of molten steel from the discharge port becomes too strong, and bubbles and inclusions that enter the deep part of the slab accompanying powder entrainment and downward flow are generated. Increases and impairs the quality of the slab.
[0025]
Further, the angle of expansion of the discharge port of the immersion nozzle is within an angle range of 15 degrees upward to 45 degrees outward with respect to the axis of the immersion nozzle, and at least 50% of the outer periphery of the discharge port is expanded. By making the immersion depth (L) 100 to 350 mm, the discharge flow from the immersion nozzle becomes a uniform and slow flow, and furthermore, the solidified shell is inverted. It is possible to suppress the strong upward flow or downward flow, and to suppress the entrainment of powder and fluctuation of the molten metal level, and the intrusion of bubbles and inclusions accompanying the molten steel into the deep part of the slab, Defects that occur on the surface layer and inside of the slab can be prevented.
[0026]
FIG. 2 shows the immersion nozzle used in the present embodiment, in which the discharge port has a trumpet shape in which the entire outer periphery of the discharge port is widened from the inside to the outside with respect to the axis x of the immersion nozzle 4. The angle Q was set in a range from 15 degrees upward to 45 degrees downward. The ratio D / d of the diameter (inner diameter) D of the main body of the immersion nozzle to the diameter d of the discharge port is set to be 1.0 to 1.5, and the molten steel passing through the inside of the immersion nozzle is discharged from the discharge port to the inside of the mold. The molten steel flow flowing out into the mold can be made uniform and slow, eliminating the drift of the molten steel flow into the mold, suppressing the excessive flow of the molten steel flow to the meniscus, To prevent the generation of
[0027]
In addition, by suppressing the formation of an excessive downward flow, it is possible to prevent bubbles and inclusions from entering the deep portion of the slab, thereby preventing the surface and internal defects of the slab. Here, if the angle of the discharge port of the immersion nozzle exceeds 15 degrees upward, the upward flow becomes strong, and this upward flow causes the entrainment of powder. On the other hand, if the angle of the discharge port exceeds 45 degrees downward, the downward flow becomes strong and bubbles and inclusions accompanying the molten steel penetrate into the deep part of the slab, causing bubbles and inclusions on the surface layer and inside of the slab. The resulting defects are likely to occur.
[0028]
Further, when the immersion depth (L) is smaller than 100 mm, the fluctuation of the molten metal level and the entrainment of the powder due to the discharge flow increase. On the other hand, when the immersion depth (L) exceeds 350 mm, the downward flow becomes strong and the air bubbles accompanying the molten steel increase. And inclusions penetrate deep into the slab.
For these reasons, it is more preferable to set the immersion depth to 10 degrees upward to 30 degrees downward and the immersion depth to 150 to 300 mm. In addition, the discharge port for widening the immersion nozzle may be any as long as it forms a widening from the inside to the outside with reference to the axis of the immersion nozzle, and the main body of the immersion nozzle is generally used. A split type or an integrated type attached to a tundish can be used.
[0029]
Further, in continuous casting, poor lubrication of the powder 10 and the level of the molten metal surface occur during the period from the start of casting until the steady speed is reached, or during casting at a steady casting speed of 1.2 to 5 ton / min or less. If there is a danger of breakout due to fluctuations, etc., the pouring rate should be reduced as much as possible, or the pouring rate should be less than 0.6 ton / min. In such a case, it is necessary to perform casting with an extremely low pouring amount from the immersion nozzle 4 in relation to the ladle replacement time.
[0030]
On the other hand, even during casting at a steady casting speed, a drift may occur in the flow of the molten steel 2 on the left and right sides of the discharge port 5 of the immersion nozzle 4, and this discharge flow makes the flow in the mold 7 unstable. In particular, in the vicinity where the immersion nozzle 4 is immersed, since the gap between the immersion nozzle 4 and the inner wall is narrow, the flow of the molten steel 2 at this portion is reduced, and the uniformity of the slab 8 in the width direction is reduced. In any case where flow is not obtained and stagnation occurs due to fluctuations in flow, there is a concern that the quality of the slab 8 may be impaired.
[0031]
Therefore, in order to produce a higher quality cast slab, the electromagnetic stirrers 11a and 11b are energized in any of a range of 200 to 350 mm below the meniscus formed in the mold 7 and the The flow of the molten steel 2 that swirls around the peripheral wall is formed. The flow of the molten steel 2 can clean the inner surface of the solidified shell with the flow of the molten steel 2, prevent bubbles and inclusions from being captured, and form a good solidified shell with few bubbles and inclusions. can do.
[0032]
Further, it is also possible to blow argon gas into the immersion nozzle 4, in which case the argon gas blown from the upper nozzle disposed above the immersion nozzle 4 can be blown, and the amount is 4 NL / min or less. In addition, it is possible to suppress the inclusion of inclusions inside the immersion nozzle 4 and to promote the floating of the inclusions mixed in the molten steel 2 in the mold 7. When the blowing amount of the argon gas exceeds 4 NL / min, the number of bubbles of the argon gas increases, and the number of bubbles captured by the solidified shell 6 also increases, thereby impairing the quality of the slab 8.
[0033]
Further, in the present embodiment, an immersion nozzle in which the content of either or both of carbon and silica is reduced to zero or less than 5% by mass, or a dolomite component (a main component of which is CaO-MgO) is used. Nozzles can be used. In the case of this hardly adhering immersion nozzle, since there is little adhesion of inclusions on the inner surface of the immersion nozzle and the clogging of the discharge port 5 does not occur, it is possible to perform casting without blowing argon gas, which is caused by argon gas. Since bubble defects can be prevented, more preferable results can be obtained.
[0034]
【Example】
Next, an example of a continuous casting method for a high-quality stainless steel slab according to an embodiment of the present invention will be described.
In a mold having a thickness of 250 mm and a width of 1200 mm, a discharge port having a size of 60 ° is used as a wide-angle discharge port, and the inner diameter D of the immersion nozzle / the diameter of the discharge port is within a predetermined range. It was immersed, and casting was performed in a case where an output of 0.4 Mw was given to an electromagnetic stirring device (MD-EMS) and in a case where electromagnetic stirring was not performed. As a result, as shown in FIG. 3, when the diameter D / d of the immersion nozzle and the discharge port is in the range of 1.0 to 1.5, the product is formed by the effect of the slow formation of the discharge flow by using the wide-angle discharge port. The inconsistency index is good, and the combined inconsistency index is further greatly improved by using an electromagnetic stirrer (MD-EMS) in combination, and a high quality cast piece can be manufactured. In addition, the use of immersion nozzles with different angles of immersion nozzle discharge ports and the angle of divergence of discharge ports immersed in a mold and casting while pouring molten steel, and using electromagnetic stirring (MD-EMS) together It carried out about the case where it did.
[0035]
As a result, as shown in FIG. 4, when the immersion nozzle having the conventional discharge port without using the widening of the discharge port was used (×), the product mismatch occurrence index was 0.4 or more regardless of the pouring amount. And the variation became large, resulting in a bad result. However, when casting is performed with the discharge port widened and the D / d of the immersion nozzle in the range of 1.0 to 1.5 (○), the product inconsistency index may be 0.3 or less. As a result, a high quality cast slab could be produced.
[0036]
Further, even when casting is performed with the outer circumference of the discharge port widened by 50% and the D / d of the immersion nozzle in the range of 1.0 to 1.5 (▲), the product mismatch index is 0.25 or less. And a high quality cast slab could be produced. When the discharge port is widened, the D / d of the immersion nozzle is set in the range of 1.0 to 1.5, and the molten steel in the mold is subjected to electromagnetic stirring (MD-EMS) and cast (●), In addition, there was no occurrence of internal defects, and it was possible to manufacture a cast piece in which the occurrence of product inconsistency was stably prevented, and the quality of the steel material processed from the cast piece was good.
[0037]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and all changes in conditions without departing from the gist are within the scope of the present invention.
For example, in addition to the electromagnetic stirrer that stirs the molten steel in the mold, the electromagnetic stirrer arranged in the mold may be arranged on the support segment of the slab to stir the unsolidified molten steel. Further, the discharge port of the immersion nozzle may be a circular one or a rectangular one such as a square or a rectangle.
[0038]
【The invention's effect】
As described above, in the method for continuously casting high-quality stainless steel slabs according to claims 1 to 6, the molten steel in the tundish is cast into a mold through a dipping nozzle using a bending-type continuous casting machine having a vertical portion. In the casting method of molten stainless steel using a vertical bending continuous caster for pouring, the immersion nozzle whose discharge port is widened from the inside to the outside with respect to the axis of the immersion nozzle is immersed in the mold and poured. Since the casting is performed at the pouring rate of 0.6 to 5.0 tons / minute, the flow of molten steel is suppressed from becoming strong, the flow of molten steel is made uniform in the width direction of the mold, and powder due to the discharge flow of molten steel is formed. Bubbles and inclusions that enter the deep part of the slab accompanying the entrainment and downward flow of the slab can be suppressed, and the quality of the slab can be improved.
[0039]
In particular, in the continuous casting method for a high-quality stainless steel slab according to the second aspect, the outlet of the nozzle is widened within an angle range of 15 degrees upward to 45 degrees downward with respect to the axis of the immersion nozzle. Therefore, it is possible to make the discharge flow slow, and to suppress the drift of the discharge flow of the molten steel caused by clogging of the discharge port to produce a better quality slab without surface and internal defects. can do.
[0040]
In the continuous casting method for a high-quality stainless steel slab according to the third aspect, the immersion depth of the immersion nozzle is set to 100 to 350 mm downward from the meniscus and the molten metal is poured into the mold. Entrapment of powder or intrusion of bubbles or inclusions into the deep portion of the slab can be suppressed, and the quality of the slab can be improved.
In the continuous casting method for a high quality stainless steel slab according to claim 4, since the ratio of the inner diameter D of the immersion nozzle to the diameter d of the discharge port is 1.0 to 1.5, the molten steel is discharged from the discharge port. The flow velocity can be reduced, and the drift of the discharge flow during casting can be suppressed, and defects of the slab due to the drift of the discharge flow can be prevented.
[0041]
In the continuous casting method for a high-quality stainless steel slab according to claim 5, since at least 50% or more of the discharge ports of the immersion nozzle have a widening angle in the outward direction with respect to the axis of the immersion nozzle, the discharge port is formed. Is increased to at least 50%, the discharge flow velocity of the molten steel can be reduced, the drift of the discharge flow during casting can be suppressed, and the overall strength of the immersion nozzle can be prevented from lowering.
In the continuous casting method of high quality stainless steel slab according to claim 6, since the molten steel poured into the mold is electromagnetically stirred, a swirling molten steel flow is formed around the inner periphery of the mold to form the vicinity of the immersion nozzle or the solidified shell. Can enhance the shell-washing effect on the inner surface of the steel, remove bubbles and inclusions trapped in the solidified shell, and produce a slab having a high quality surface layer.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a continuous casting apparatus used for a continuous casting method of a high-quality stainless steel slab according to an embodiment of the present invention.
FIG. 2 is a sectional view of an immersion nozzle used in a continuous casting apparatus.
FIG. 3 is a graph showing a relationship between an inner diameter D of an immersion nozzle / an inner diameter d of a discharge port and a product mismatch index.
FIG. 4 is a graph showing a relationship between a pouring amount and a product incompatibility index.
[Explanation of symbols]
1 Continuous casting equipment 2 Stainless steel molten steel (molten steel)
Reference Signs List 3 tundish 4 immersion nozzle 5 discharge port 6 solidified shell 7 mold 8 slab 9 support segment 10 powder 11a, 11b electromagnetic stirring device D inner diameter of immersion nozzle d inner diameter of discharge port

Claims (6)

In a casting method of stainless steel molten steel using a vertical bending continuous caster in which molten steel in a tundish is poured into a mold through an immersion nozzle by using a bending type continuous casting machine having a vertical portion, a discharge port is connected to an axis of the immersion nozzle. A high-quality stainless steel characterized by casting molten steel by pouring molten steel by dipping a dipping nozzle whose angle is widened from the inside to the outside with respect to the core, and pouring the molten steel at a rate of 5.0 tons / min or less. A continuous casting method for slabs. 2. The continuous casting method for a high-quality stainless steel slab according to claim 1, wherein the discharge port of the immersion nozzle has an angle of 15 degrees upward to 45 degrees downward with respect to the axis of the immersion nozzle. A continuous casting method for high quality stainless steel slabs, characterized by having a discharge port. 3. The high quality stainless steel slab according to claim 1, wherein the immersion depth of the immersion nozzle is 100 to 350 mm below the meniscus and poured into the mold. Continuous casting method. The continuous casting method for a high-quality stainless steel slab according to any one of claims 1 to 3, wherein a ratio of an inner diameter D of the immersion nozzle to a diameter d of the discharge port is 1.0 to 1.5. Features a continuous casting method for high quality stainless steel slabs. 5. The continuous casting method for a high-quality stainless steel slab according to claim 1, wherein at least 50% or more of the outer circumference of the discharge port of the immersion nozzle expands outward with respect to the axis of the immersion nozzle. A continuous casting method for high quality stainless steel slabs, characterized by having an angle. The method for continuously casting high-quality stainless steel slabs according to any one of claims 1 to 5, wherein the molten steel poured into the mold is electromagnetically stirred.

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