JPH11123509A - Immersion nozzle for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the clogging of a nozzle caused by stickiness of alumina and to restrain the drift of molten steel in the nozzle by specifying the diameters or cross sectional areas in the inner hole at each part of the nozzle having the stepping structure and formed of a refractory containing a specific content of graphite based on the molten steel passing quantity. SOLUTION: A part of the nozzle body 2 being in contact with the molten steel is formed of the refractory containing 5-40 wt.% graphite. Further, such conditions that the min. inner diameter D (mm) of a part having no stepping structure in the inner hole part of the nozzle to the molten steel passing quantity M (ton/min) is 30D<=100, 1<=M<=7.5 and 6.25M+12.5<=D<=6.25M+65 or this min. cross sectional area S1 (cm<2> ) is 2.66<=S1 <=8.86, 1<=M<=7.5 and 0.55M+1.11<=S1 <1/2> <=0.55M+5.76, are satisfied. Furthermore, such conditions that the area ratio S2 (cm<2> ) of the discharging hole of the nozzle to the molten steel passing quantity M (ton/min) is 60<=S2 <=180, 1<=M<=7.5 and 21.25M-67.50<=S2 <=21.25M+28.75, are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for continuous casting (hereinafter simply referred to as "immersion nozzle"), and more particularly, to preventing clogging of alumina and suppressing drift of molten steel in the immersion nozzle. The present invention relates to a stepped immersion nozzle capable of improving cast slab quality.

[0002]

2. Description of the Related Art An immersion nozzle is a refractory used by being connected to a mold from a tundish, and has functions of preventing oxidation of molten steel, controlling the flow rate of molten steel in the mold, and preventing slag from being involved. Conventionally, alumina-graphite or alumina-fused quartz-graphite refractory materials have been generally used for these immersion nozzles.

[0003] However, when aluminum killed steel is cast using an immersion nozzle made of such a refractory material, there is a phenomenon that oxide-based inclusions in molten steel adhere to and accumulate on the inner surface of the immersion nozzle and are often blocked. It is a major obstacle to continuous casting operations.

[0004] In general, the flow rate control when pouring molten steel from a ladle into a mold is often performed using a slide gate. This slide gate is not always used fully open, it is usually used in a squeezed state, in such a case, drift of molten steel occurs at the bottom of the slide gate,
This molten steel drift is not eliminated even in the immersion nozzle.
When such molten steel drift occurs, a one-sided flow phenomenon occurs in the molten steel flow from the discharge hole of the nozzle, which has an adverse effect on the flow in the mold, resulting in an increase in slab defects and an operation hindrance such as breakout. In addition, when the molten steel drift occurs, the adhesion of alumina also easily occurs.

Various measures have been taken to prevent such blockage of the immersion nozzle and drift of molten steel. For example, the most effective for preventing the adhesion of alumina is gas blowing from an immersion nozzle, an upper nozzle, or the like, which is widely used. However, this method has a disadvantage that a pinhole defect due to gas bubbles easily occurs.

[0006] As the alumina deposition preventing measures a material surface, a method of disposing a CaO-ZrO ₂ -C system material in the hole portion immersion nozzle are common. This is a method of reacting alumina in molten steel with CaO in calcium zirconate to form a low melting point compound to prevent adhesion. For example, Japanese Patent Publication No. 23494/1990 discloses that the weight ratio of Ca
O and 16-35 wt% of calcium as a main component CaZrO ₃ selected from oxides of Group III elements of the Periodic Table, one or more of 0.5 to 5 wt%, as the mineral composition zirconate ZrO ₂ —CaO characterized in that an organic binder is added to a mixture comprising 20 to 95% by weight of a catenate-based clinker, 5 to 50% by weight of graphite, and 1% by weight or less of metallic silicon, molded, and then fired in a non-oxidizing atmosphere. A method for producing a continuous casting submerged nozzle is disclosed. The immersion nozzle obtained by the method described in the publication also has an effect on preventing alumina adhesion, but has drawbacks such as large erosion of the inner hole and weakness to thermal spall.

Recently, a technique has been developed in which a refractory material containing no carbon is provided in the inner hole to prevent alumina from adhering. For example, JP-A-3-243258 discloses that one or both inner surfaces of an immersion nozzle for continuously injecting molten steel in a tundish into a mold and an intermediate nozzle connected to the upper part of the immersion nozzle include (a) A carbon-less high alumina refractory not containing more than 5% by weight of SiO ₂ and containing not less than 90% by weight of Al ₂ O ₃ ; (b) not containing more than 5% by weight of SiO ₂ and containing not less than 90% by weight of MgO Carbonless high magnesia refractories; (c) more than 5% by weight of Si
Disclosed is a continuous casting nozzle comprising a refractory material that does not contain O ₂ and contains at least one of carbonless high zirconia refractories having a ZrO ₂ content of 90% by weight or more.

Japanese Patent Application Laid-Open No. 5-154628 discloses an alumina clinker having an alumina content of 99% by weight or more, having an alumina content of 70% by weight or more, a carbon content of less than 1% by weight, and a silica-containing material. 1% by weight
Disclosed is a continuous casting nozzle bore having a refractory composition of less than 0.2% and a particle size of 0.21 mm or less occupying 20 to 70%.

Further, Japanese Patent Application Laid-Open No. 8-57601 discloses that
The body is formed from a refractory material containing a carbon source,
In a continuous casting nozzle in which a portion through which molten steel passes and a portion that comes into contact with molten steel are coated with a refractory material not containing a carbon source, a portion coated with the refractory material not containing the carbon source has a straight body portion in the inner hole and a lower bottom portion in the inner hole. A discharge hole portion and an outer peripheral portion immersed in molten steel, wherein the coating portion is formed by a cylindrical body of a refractory material containing no carbon source,
And the said cylindrical body is 0.5-2.0 mm in the said straight body part.
Disclosed is a continuous casting nozzle characterized in that the nozzle is provided with a joint having a thickness of 1 to 5 mm via a joint having a thickness of 1 to 5 mm at the bottom and the bottom of the inner hole and the discharge hole.

The immersion nozzles disclosed in these publications suppress the generation of acidified gas due to the reaction between carbon and the refractory material by removing or minimizing carbon from the refractory material constituting the immersion nozzle. However, it suppresses the oxidation of Al in the steel to prevent the formation of Al ₂ O ₃ . These immersion nozzles are also effective in preventing Al ₂ O _{3 from} adhering, and their use in actual furnaces is increasing. However, even if these immersion nozzles are used, there is a drawback that non-clean steel having a large amount of inclusions in the molten steel is cast, or Al ₂ O ₃ adheres when the continuous casting is advanced.

Further, from a structural point of view, there is a technique for preventing alumina from adhering by using an immersion nozzle having a stepped inner hole. For example, Japanese Utility Model Publication No. 59-22913 discloses that the inner diameter of the lower nozzle is larger than the inner diameter of the upper nozzle,
An immersion nozzle for continuous casting is disclosed, which has a step surface of 30 mm and is provided with a material containing boron nitride over the entire inner wall portion of the nozzle and / or the entire immersion portion of the molten metal.

Also, Japanese Utility Model Publication No. 7-23091 discloses that
A plurality of steps are provided in the molten steel flow hole of the continuous casting immersion nozzle, and the molten steel flow hole has an inner diameter d ₁ > d ₂ > d ₃ > d ₄ with respect to an inner diameter d of the main pipe, and the step There is disclosed an immersion nozzle with a plurality of steps for continuous casting in which a main pipe inner diameter d is disposed between each of the parts d _{1 to} d ₃ .

Although these immersion nozzles are also effective in preventing adhesion of alumina, they may not be effective depending on the type of molten steel and casting conditions.

[0014]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent the immersion nozzle from being blocked by the adhesion of alumina, which cannot be solved by the prior art as described above, and to reduce the drift of molten steel in the immersion nozzle. An object of the present invention is to provide an immersion nozzle that can be suppressed.

[0015]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that, in a continuous casting immersion nozzle having one or more steps in the nozzle bore, the molten steel passage amount M (ton / ton) is obtained. Min), the minimum inner diameter D (mm) of the portion of the nozzle inner hole portion having no step structure, the minimum cross-sectional area S1 (cm ² ) of the portion of the nozzle inner hole portion having no step structure, and the sectional area S2 (cm ² ) of the discharge hole. It has been found that the above problem can be solved by optimizing the range of ()).

That is, the stepped continuous casting immersion nozzle of the present invention comprises a refractory material constituting a portion in contact with molten steel containing more than 5% by weight and not more than 40% by weight of graphite. Alternatively, in a continuous casting immersion nozzle having a plurality of step structures, the following condition (1) and / or
It is characterized by satisfying (2): (1) The minimum inner diameter D (mm) of the portion having no step structure in the nozzle bore portion with respect to the molten steel passing amount M (ton / min) has the following relationship. thing:

## EQU4 ## 30 ≦ D ≦ 100 1 ≦ M ≦ 7.5 6.25M + 12.5 ≦ D ≦ 6.25M + 65 (2) The stepped structure of the nozzle inner hole with respect to the molten steel passing amount M (ton / min) The minimum cross-sectional area S1 (cm ² ) of the non-existing part has the following relationship:

(Equation 5)

[0017]

FIG. 1 shows an embodiment of a stepped immersion nozzle according to the present invention. The stepped immersion nozzle of the present invention,
It is composed of a powder line section (1) and a nozzle body (2). When a step structure is provided in the inner hole of the immersion nozzle as shown in FIGS. 1 (a) and 1 (b), uneven flow in the inner hole of the immersion nozzle is prevented by the effect of the step structure, and the flow velocity in the pipe is made uniform. Therefore, the portion where the flow velocity is extremely low is eliminated. In addition, in a straight immersion nozzle, the flow velocity on the side surface side is generally slow, and the adhesion of alumina tends to proceed in that portion. However, the provision of the step structure can prevent such adhesion of alumina. Here, in FIGS. 1 (a) and 1 (b), the step structure has one-stage and two-stage immersion nozzles, but the number of the step structures is not particularly limited, and three or more stages are used. It is possible to form with. In order to enhance the drift prevention effect and the alumina adhesion prevention effect, it is preferable to provide a plurality of step structures.

Conventionally, a refractory material (for example, an alumina-graphite refractory or the like) constituting a nozzle body of an immersion nozzle is conventionally used.
When the step structure is formed by the method, particularly when the flow rate of the molten steel is small or the flow rate of the molten steel is low, the effect of the step structure is small, and even when the stepped immersion nozzle is used, alumina may be attached.

According to the present invention, in order to solve this problem, in a continuous casting immersion nozzle having one or more steps in the nozzle inner hole, the nozzle inner hole with respect to the molten steel passage amount M (ton / min) is used. Minimum inner diameter D of part without step structure
(mm), the range of the minimum cross-sectional area S1 (cm ² ) of the portion of the nozzle inner hole having no step structure, and the cross-sectional area S2 (cm ² ) of the discharge hole were optimized.

In the stepped immersion nozzle of the present invention, the inner diameter d (mm) of the portion having the step structure is represented by D (mm) when the minimum inner diameter of the portion of the inner hole portion of the immersion nozzle without the step structure is D (mm).

## EQU6 ## It is desirable that the value be in the range of D-24 ≦ d ≦ D-6.

In the case where a plurality of step structures are provided, the inner diameter of each step structure is determined from the step structure on the upper side of the immersion nozzle.

D ≧ d ₁ ≧ d ₂ ≧... ≧ d _n , more preferably

D> d ₁ > d ₂ >...> D _n

At this time, the minimum inner diameter D (mm) of the portion of the inner hole of the immersion nozzle having no step structure has a correlation with the amount of molten steel passing through the immersion nozzle M (ton / min), and it is necessary to increase M. In some cases, D also needs to be increased, and when M can be small, D can also be decreased. In this case, if D is too large with respect to M, the alumina tends to adhere. This is remarkable in a straight immersion nozzle having no step structure, but the same can be said when a stepped immersion nozzle is used. If D is too large, the effect of preventing alumina adhesion is significantly reduced.

The inventors of the present invention have conducted intensive studies. As a result, in the case of a submerged nozzle having a stepped structure in the inner hole of the submerged nozzle, when M and D are in a range satisfying the following formula, the nozzle adhered to alumina is used. It has been found that the effect of preventing occlusion is further enhanced:

[Mathematical formula-see original document] 30 ≦ D ≦ 100 1 ≦ M ≦ 7.5 6.25M + 12.5 ≦ D ≦ 6.25M + 65 When this condition is satisfied, the uniformity of the flow velocity in the pipe of the immersion nozzle increases, and the effect of preventing alumina adhesion is improved. Get higher. At this time, the conditions of D <30, D> 100, M <1 and M> 7.5 are not realistic and are not suitable as the scope of the present invention.

In the shape of the stepped immersion nozzle of the present invention, the cross section of the inner hole does not necessarily have to be circular. For example, the cross section of the upper part of the immersion nozzle is circular and the cross section of the lower part is transverse. A structure having an elliptical surface or another shape may be used. Further, the cross-sectional shape of the entire inner hole of the immersion nozzle may be non-circular. In such a case, it is preferable that the minimum lateral cross-sectional area S1 (cm ² ) of the portion having the step structure of the inner hole of the immersion nozzle satisfies the following relationship:

(Equation 10) When this condition is satisfied, the uniformity of the flow velocity in the pipe of the immersion nozzle is increased, and the effect of preventing alumina adhesion is enhanced. At this time,

[Equation 11] Is not realistic and is not suitable as the scope of the present invention. And, when the minimum inner diameter in the cross-sectional direction of the portion having no step structure of the inner hole portion of the immersion nozzle is D (mm), the inner diameter d (mm) of the portion having the step structure is

It is desirable that the range of D−24 ≦ d ≦ D−6 be satisfied.

In the above case, since the cross-sectional shape is non-circular, the inner diameters D and d represent the numerical values of the longest part in each cross-section.

Also, in the stepped immersion nozzle of the present invention, the adhesion of alumina can be greatly reduced by optimizing the cross-sectional area of the discharge hole with respect to the flow rate of molten steel M (ton / min). In general, the adhesion of alumina to the immersion nozzle is characterized not only by the straight body of the inner hole of the immersion nozzle, but also by a large amount of adhesion around the discharge hole, and in many cases, the adhesion to this part is rate-limiting. . This is thought to be because the flow velocity of the molten steel decreases near the discharge hole at the lower end of the immersion nozzle, causing stagnation or drifting of the molten steel. Generally, the larger the cross-sectional area of the discharge hole, the more remarkable the adhesion of alumina.

In the stepped immersion nozzle of the present invention,
When the cross-sectional area S2 (cm ² ) of the discharge hole is set so as to satisfy the following relationship, the alumina adhesion can be greatly reduced:

(Equation 13) When this condition is satisfied, the uniformity of the discharge flow rate from the discharge holes is increased, and the effect of preventing alumina adhesion is enhanced. At this time, S2
The ranges of <60, S2> 180, M <1 and M> 7.5 are not practical and are outside the scope of the present invention.

The sectional area S2 of the discharge hole in the present invention
(cm ² ) indicates the cross-sectional area (cross-sectional area at AA ′) in a plane perpendicular to the axial direction of the discharge hole as shown in FIG.
When there are a plurality of discharge holes, it indicates the total sum of the cross-sectional areas of the respective discharge holes. In the case where the discharge hole has a shape that expands outward, as shown in FIG. 2B, the area (the cross-sectional area at BB ′) at the portion having the largest cross-sectional area in the axial direction is obtained. ). FIG. 2 (b) is a view of a stepped immersion nozzle having a discharge hole having a shape expanding outward, as viewed from the lower end.

Here, the sectional shape of the discharge hole may be square or round, but is not particularly limited.

Further, in the stepped immersion nozzle of the present invention, the length of the portion having the step structure and the disposition position are not particularly limited.
The disposition position is preferably the center of the immersion nozzle.

Further, the shape of the bottom of the immersion nozzle is not particularly limited, but a commonly used mountain shape or pool shape can be suitably used.

As the refractory material constituting the stepped immersion nozzle of the present invention, a conventionally used graphite-alumina material or graphite-fused quartz material can be suitably used. Of course, materials other than graphite include not only alumina and fused quartz but also mullite, zirconia,
It is also possible to use oxides such as spinel and zirconia-mullite. Further, silicon carbide, boron carbide, metal Si, or the like may be added as a small amount of additive. In the refractory material constituting the stepped immersion nozzle of the present invention,
Graphite is more than 5% by weight and not more than 40% by weight, preferably 10% by weight.
３５35% by weight.

Next, the method for producing the stepped immersion nozzle of the present invention is not particularly limited, but can be produced, for example, as follows. First, a binder is added to a refractory material composed of an oxide, graphite or the like, and kneaded using a mixer such as a wet pan to obtain a kneaded material for molding. Next, these kneaded materials are filled in a molding frame, and thereafter, molding is performed by CIP molding, mechanical press, or the like. The resulting compact is dried and subsequently fired in a non-oxidizing atmosphere. After firing, it is processed as necessary to obtain a final shape.

[0034]

Next, the present invention will be further described with reference to examples and comparative examples of the present invention, but it should be understood that the present invention is not limited to the following examples. Example 1 Immersion nozzles of the product of the present invention and the comparative product described in Table 1 below were manufactured, and a casting test was performed in an actual furnace. FIG. 3 shows the shape of the manufactured immersion nozzle. 3A shows the shape of the product 1 of the present invention, and FIG. 3B shows the products 2 and 3 of the present invention and the comparative product 2
3 (c) shows the shape of the comparative product 1. FIG. The refractory material of the nozzle body (2) used was a material having a composition of 50% by weight of alumina, 30% by weight of graphite and 20% by weight of fused quartz, and 85% by weight of zirconia and A refractory material having a composition of 15% by weight of graphite was used.

[0035]

[Table 1]

In Table 1, d1 and h1 represent the inner diameter and length of the upper step structure, and d2 and h2 represent the inner diameter and length of the lower step structure.

After a casting test was performed using the immersion nozzles of the products 1 to 3 of the present invention and the comparative products 1 and 2, the immersion nozzles were recovered and the state of adhesion of alumina was confirmed. The continuous caster used for the casting test was a single strand type, and the average composition of the cast steel was C: about 0.01% by weight, Mn: about 0.03% by weight, Al: about 0.04% by weight, N: about 0.003% by weight. Moreover, in the continuous casting machine which performed the casting test, the molten steel passage amount M was 3.5 ton / min on average,
In order to prevent alumina adhesion even with this amount of molten steel passing,
The minimum inner diameter D of the portion of the immersion nozzle of the present invention having no step structure was set. On the other hand, in the comparison product immersion nozzle,
Comparative product 1 had a configuration without the step structure, and comparative product 2 was set such that the minimum inner diameter D of the immersion nozzle was out of the range of the present invention. Further, the cross-sectional area S2 of the discharge hole was set so that the product of the present invention and the comparative product were within the scope of the present invention. The recovered immersion nozzle is cut in the vertical direction, and E shown in FIGS.
The alumina adhesion thickness was measured at four points of F, G and H. Table 2
Shows the casting test conditions and the alumina adhesion thickness.

[0038]

[Table 2]

As a result of the casting test, it was confirmed that the adhered amount of alumina of the stepped immersion nozzle of the present invention was very small and the effect was large. Moreover, in the case of the straight type immersion nozzle of the comparative product 1, the amount of adhered alumina increased over the entire inner hole. Also, M and D as in comparative product 2
When the relationship was out of the range of the present invention, the alumina adhesion amount was increased.

Example 2 The immersion nozzles of the product of the present invention and the comparative product described in Table 3 below were manufactured and subjected to a casting test in an actual furnace. FIG. 4 shows the shape of the manufactured immersion nozzle. The product 4 of the present invention has a two-step structure as shown in FIG. 4 (a), and a lower part of the inner hole is a stepped immersion nozzle having a non-circular cross-sectional shape [FIG. 4A is a sectional view taken along the line AA ′ of FIG. 4A, and FIG.
FIG. 4B is a sectional view taken along line BB ′ of FIG. 4. The product 5 of the present invention has a one-step structure as shown in FIG. 4B, and the lower part of the inner hole is an immersion nozzle having an elliptical shape [FIG. 4 (e) is A- of FIG. 4 (b).
4A is a cross-sectional view, and FIG. 4F is a BB ′ cross-sectional view of FIG. The comparative product 3 has the same shape as the product 5 of the present invention, but the minimum cross-sectional area S1 of the immersion nozzle with respect to the amount of molten steel passing M is out of the range of the present invention. The refractory material of the nozzle body (2) has a composition of 62% by weight of alumina, 14% by weight of zirconia-mullite and 24% by weight of graphite, and the refractory material of the powder line part (1) includes: One having a composition of zirconia 83% by weight and graphite 17% by weight was used.

[0041]

[Table 3]

In Table 3, d1 and h1 represent the inner diameter and length of the upper step structure, and d2 and h2 represent the inner diameter and length of the lower step structure.

After performing a casting test using the immersion nozzles of the products 4 and 5 of the present invention and the comparative product 3, the immersion nozzle was recovered and the state of adhesion of alumina was confirmed. The continuous caster used in the casting test was a single strand type. The average composition of the cast steel was as follows: C: about 0.02% by weight, Mn: about 0.2% by weight, Al: about 0.04% by weight %, N: 0.003% by weight. The collected immersion nozzle was cut in the vertical direction, and the thickness of the adhered alumina was measured at three points I, J, and K shown in FIGS. 4 (a) and 4 (b). Table 4 shows the casting conditions and the measurement results of the alumina adhesion thickness.

[0044]

[Table 4]

The amount of alumina adhered to the inner hole of the immersion nozzles of the products 4 and 5 of the present invention is small, and even when the inner hole has a non-circular cross-sectional shape, the alumina adhesion of the stepped immersion nozzle of the present invention can be prevented. The effect was found to be high. on the other hand,
It was confirmed that when the relationship between the molten steel passage amount M and the minimum cross-sectional area S1 is out of the range of the present invention as in the immersion nozzle of the comparative product 3, the effect of preventing alumina adhesion is small.

Example 3 Immersion nozzles of the product of the present invention and the comparative product described in Table 5 below were manufactured and subjected to a casting test in an actual furnace. FIG. 5 shows the shape of the manufactured immersion nozzle. The shape of the immersion nozzle is the same as that of the product 2 of the present invention used in Example 1, but the shape of the comparative product 4
The cross-sectional area of the discharge port is outside the range of the present invention. 52% by weight of alumina, silica 1
A refractory material having a composition of 8% by weight, 29% by weight of graphite and 1% by weight of silicon carbide was used, and a refractory material having a composition of 83% by weight of zirconia and 17% by weight of graphite was used as a refractory material in the powder line portion. In Table 5, d1 and h1 represent the inner diameter and length of the upper step structure, and d2 and h2 represent the inner diameter and length of the lower step structure. After performing a casting test using the immersion nozzles of the inventive products 6 and 7 and the comparative product 4,
The immersion nozzle was recovered to check the state of alumina adhesion. The continuous caster used for the casting test is a single strand type,
The average composition of the cast steel is C: about 0.03% by weight, M
n: 0.2% by weight, Al: 0.04% by weight, N: 0.00
It had 3% by weight. The collected immersion nozzle was cut in the longitudinal direction, and the alumina adhesion thickness was measured at each point of L, M, N, and O shown in FIG. 5 and at points P and Q around the discharge hole shown in FIG. Table 6 shows the casting conditions and the results of measurement of the thickness of the adhered alumina.

[0047]

[Table 5]

[0048]

[Table 6]

[0049]

According to the present invention, it is possible to provide a stepped immersion nozzle capable of preventing clogging of alumina, suppressing the drift of molten steel in the immersion nozzle, and improving the slab quality.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a stepped immersion nozzle according to the present invention, wherein (a) shows an immersion nozzle having a single-step structure, and (b)
Represents an immersion nozzle having a two-step structure.

FIG. 2 is a diagram illustrating a sectional area S2 (cm ² ) of a discharge hole.

3A and 3B are diagrams showing the shape of the immersion nozzle manufactured in Example 1, wherein FIG. 3A shows the shape of the product 1 of the present invention, and FIG.
And 3 and the shape of the comparative product 2, and (c) shows the shape of the comparative product 1.

4A and 4B are diagrams showing the shape of the immersion nozzle manufactured in Example 2, (a) shows the shape of the product 4 of the present invention, and (b) shows the shape of the product 5 of the present invention.
And (c) represent A- of (a).
It is A 'sectional drawing, (d) is BB' sectional drawing of (a), (e) is AA 'sectional drawing of (b), (f) is B of (b) FIG. 14 is a sectional view taken along the line B-B '.

FIG. 5 is a view showing the shapes of immersion nozzles of the products 6 and 7 of the present invention and the comparative product 4 manufactured in Example 3.

[Explanation of symbols]

 1 powder line 2 nozzle body

Claims (2)

[Claims] 1. A refractory material constituting a portion in contact with molten steel contains more than 5% by weight and 40% by weight or less of graphite,
A continuous casting immersion nozzle having a step or a plurality of steps in an inner hole of a nozzle, characterized by satisfying the following conditions (1) and / or (2): (1) ) The minimum inner diameter D (mm) of the portion of the nozzle inner hole portion having no step structure has the following relationship with the molten steel passage amount M (ton / min): 30 ≦ D ≦ 100 1 ≦ M ≦ 7.5 6.25M + 12.5 ≦ D ≦ 6.25M + 65 (2) The minimum cross-sectional area S1 (cm ² ) of the part having no step structure in the nozzle inner hole portion with respect to the molten steel passing amount M (ton / min). In the following relationship: 2. A sectional area S2 (cm ² ) of a nozzle discharge hole with respect to a molten steel passing amount M (ton / min) satisfies the following condition.
An immersion nozzle for continuous casting with a step according to claim 1: