CA1263216A - Molten steel pouring nozzle - Google Patents

Abstract

MOLTEN STEEL POURING NOZZLE

ABSTRACT OF THE DISCLOSURE

A molten steel pouring nozzle having along the axis thereof an inner bore through which molten steel flows. At least a part of the molten steel pouring nozzle is formed with a refractory consisting essentially of at least 30 wt.% calcium oxide and at least one of magnesium oxide and aluminum oxide; and the refractory contains at least one of the magnesium oxide and the aluminum oxide so that the melting point of the refractory falls within the region of at least 2,200°C
in the CaO-MgO-Al2O3 ternary phase diagram.

Description

~ ~;3 2~

~IELD OF THE INVENTION
The present invention relates to a molten steel pouring noz~le, which is secured to a molten steel receiving vessel such as a tundi~h or a laclle.
BRIEF DESCRIPTION OF THE DRAWINGS
.
Fig. 1 is a ~chematic vertical sectional view illustrating a tundish provided with a conventional molten stee]
pouring nozzle as a tundish nozzle and a conventional molten steel pouring nozzle as an immersion nozæle;
E'ig. 2 is a schematic vertical ~ectional view illustrating a tundish provided with another conventional molten steel pouring nozzle as an immersion nozzle;
Fig. 3 is a schematic vertical sectional view illustrating a tundish provided with still another conventional molten steel pouring nozzl.e as an immersion nozzle;
Fig~ 4 is a schematic vertical sectional view illustrating a tundish provided with a conventional molten steel pouring nozzle as a tundi~h nozzle having an inert gas ejecting function and a conventional molten ~teel pouring nozzle as an immersion nozzle;
Fig. 5 is a schematic vertical sectional view illustrating a tundish provided with another conventional molten steel pouring nozzle as a tundi.sh nozzle hav ng an inert gas ejecting funct:~on and a conventional molten steel pouring nozzle aB an immersion nozzle;
Fig. 6 is a CaO-MgO-A1203 ternary phase diagram illustrating the chemical composition of the refractory forming the molten steel pouring nozzle of the preæen~ invention;

, ~ jm:sks Fig. 7 is a schematic vertical sectional vie~,7 illustrating a fir~t embodiment of the molten Rteel pouring nozzle a~ a tundish n~zzle or a ladle nozzle of the present invention;
Fig~ 8 i~ a schematic vertical sectional vie-~illustrating a second embodiment of the molten steel pouring nozzle or a ladle nozzle of the present invention;
Fig. 9 iF, a schematic vertical sectional vie~
illustrating a third embodiment o the molten steel pouring nozzle as a tundish nozzle or a ladle nozzle of the present invention;
Fig. 10 i6 a ~chema~ic vertical sectional view illustrating a fourth embodiment of the molten s~eel pouring nozzle of the present invention;
Fig. 11 is a schematic vertical sectional view illustrating a fifth embodiment of the molten steel pouring nozzle as an immersion nozzle o~ the present invention; and Fig. 12 is a schematic vertical sectional view illustrating a sixth embodiment of the molten steel pouring nozzle as a through-hols of the present invention, which is horizontally fitted in each of vertical weirq arranged in a tundi~h.
BAC~GROUND OF THE INVEMTION
-Continuous casting of molten ^~teel is carrie~ out, for example, by pouring molten steel, received from a ladle into a tundi~h, through a molten steel pouring nozzle secured to the bottom wall of the tundish, into a vertical mold arranged below the molten steel pouring nozzle to form a cast steel strand, and jw:sks 3~

continuously withdrawing the thus formed cast steel strand into a single long strand.
Fig. 1 is a schematic vertical sectional view illustrating a tundish provided with a conventional molten ~teel pouring nozzle as a tundish nozzle and a conventional molten steel pouring nozzle as an immer6ion nozzle. As shown in fig. 1, a molten steel pouring nozzle 3 a~ a tundish nozzle, having along the axi~ thereof an inner bore 4 through which molten steel flows, is ~ecured in the bottom wall 2 of a tundish 1. A molten q~eel pouring nozzle S as an immersion nozzle, having along the axi~ thereof an inner bore 6 through which molten - 2a -jm:sks ~ 26~

steel flcws, is fitted to the lower end of the molten steel pouring nozzle 3 as the tundish nozzle so as to project vertically and downwardly. The molten steel pouring nozzle 5 as the immersion nozzle has a length sufficient to allow the lower end portion thereof to be immersed into molten steel in a mold not shown during operation. ~he inner bore 4 of the molten steel pouring nozzle 3 as the tundish nozzle communicates with the inner bore 6 of the molten steel pouring nozzle 5 as the immersion nozzle.

The conventional molten steel pouring nozzle 3 as the tundish nozzle and the conventional molten steel pouring nozzle 5 as the immersion nozzle as described above are formed with any refractory excellent in erosion resistance against molten steel such as zirconia refractory, silica refractory, zirconia-silica refractory, alumina-graphite refractory or alumina silica refractory.

Fig. 2 is a schematic vertical sectional view illustrating a tundish provided with another conventional molten steel pouring nozzle as an immersion nozzle. As shown in Fig. 2,arnolten steel pouring nozæle 7 as an immersion nozzle, having along the axis thereof an inner bore 8 through which molten steel flows, is secured to the bottom wall 2 of a tundish 1 so as to project vertically and downwardly. The upper portion 7a of the molten steel pouring nozzle 7 as the immersion nozzle is forMed with a refractory particularly excellent in thermal shock resistance, and the remaining portion 7c other than the upper portion 7a is formed with any refrac-tory excellent in erosion resistance against molten steel as described above.

Fig. 3 is a schematic vertical sectional view illustrating a tunidsh provided with still another conventional molten steel pouring nozzle as an immersion nozzle. As shown in Fig. 3, a molten steel pouring nozzle 7 as an immersion nozzle, having along the axis thereof an inner bore 8 through which molten steel flows, is secured to the bottom wall 2 of a tundish l so as to project vertically and downwardly. The upper portion 7b of the inner surface portion of the molten steel pouring nozzle 7 as the immersion nozzle, which forms the inner bore 8, is formed with a refractory particularly excellent in thermal shock resistance, and the remaining portion 7c other than the upper portion 7b of the inner surface portion is formed with any refractory excellent in erosion resistance against molten steel as described above.

When pouring molten steel received in the tundish into a moll through any one of the above-mentioned conventional molten steel pouring nozzles, there may occur the problem that fine aluminum oxide present in ~3~~L6 molten steel deposits and accumulates onto the inner surface of the molten steel pouring nozzle, which forms the inner bore, and clogs up the inner bore. Such a problem occurs also when molten steel received in the ladle is poured into the tundish or the mold through the above-mentloned molten steel pouring nozzle as the ladle nozzle secured in ~he bottom wall of the ladle.

Causes of the presence of aluminum oxide in molten steel are as follows:

(1) Aluminum oxide contained in the lining bricks of a molten steel receiving vessel such as a tundish or a ladle is entangled into molten steel in the molten steel receiving vessel along with erosion of the lining bricksO

(2) In the case o aluminum-killed steel, aluminum added to molten steel produces aluminum oxide through reaction with oxygen in molten steel.

(3) In the case of aluminum-killed steel, aluminum added to molten steel produces aluminum oxide through reaction with iron oxide in the molten slag floating on the molten steel surface.

(4) Aluminum present in molten steel produces aluminum oxide through reaction with oxygen in the air.

~;263Z~G

While part of aluminum oxide entangled or produced b~y thecauses as described above floats on the molten steel surface and is separated from molten steel, most of aluminum oxide remains in molten steel in the state of ~ine particles with a size of several microns. Consequently, when molten steel in a molten steel receiving vessel is poured, for example, into a mold through the conventional molten steel pouring nozzle, aluminum oxide present in molten steel deposits and acc~,ul~tes onto the inner surface of the molten steel pouring nozzle, which forms the inner bore, and clogs up the inner bore.

As the method for preventing clogging up of the inner bore of the conventional molten steel pouring nozzle caused by aluminum oxide present in molten steel, the following methods are known:

(1) Preventing aluminum present in molten steel from reacting with oxygen in the air to produce aluminum oxide, by preventing molten steel from contacting with the air when molten steel in a ladle is poured into a tundish, and when molten steel in the tundish or the ladle is poured into a mold.

(2) Preventing temperature decrease of molten steel flowing through the inner bore of a molten steel pouring nozzle by heating the molten steel pouring,nozzle, to prevent aluminum oxide present in molten steel from precipitating and depositing onto the inner surface of the molten steel pouring nozzle, which forms the inner bore.

(3) Ejecting an inert gas from the inner surface of the molten steel pouring nozzle, which forms the inner bore, toward molten steel flowing through the inner bore, to prevent aluminum oxide present in molten steel from depositing and accumulating onto the inner surface.

Figs. 4 and 5 are schematic vertical sectional views each illustrating a tundish provided with a conventional molten steel pouring nozzle as a tundish nozzle having such an inert gas ejecting function and a conventional molten steel pouring nozzle as an immersion nozzle.

As shown in Fig. 4, a molten steel pouring nozzle 9 as a tundish nozzle, having along the axis thereof an inner bore 10 through which molten steel flows, is securea in the bottom wall 2 of a tundish 1. The molten steel pouring nozzle 5 as the immersion nozzle identical to that shown in Fig. 1 is fitted to the lower end of the molten steel pouring nozzle 9 as the tundish nozzle so as to project vertically and downwardly. The molten steel pouring nozzle 9 as the tundish nozzle is provided with an annular cavity 11, near the inner bore 10 thereof, for ejecting inert gas toward molten steel flowing through the inner bore 10. Inert gas introduced through an inert gas supply pipe 12 into the annular cavity 11 is ejected toward molten steel flowing through the inner bore 10, thereby preventing aluminum oxide from depositing onto the inner surface of the ~2~3~6 molten steel pouring nozzle 9 as the tundish nozzle, which forms the inner bore 10. A molten steel pouring nozzle 9 as a tundish nozzle shown in Fig. 5 is formed with a porous refractory. Inert gas introduced through an inert gas supply pipe 12 into the molten steel pouring nozzle 9 made of porous refractory as the tundish nozzle, is ejected toward molten steel flowing through the inner bore 10, thereby preventing aluminum oxide from depositing onto the inner surface of the molten steel pouring nozzle 9 as the tundish nozzle, which forms the inner bore 10.

(4) Removing aluminum oxide present in molten steel received in a tundish within the tundish by the steps of:
arranging in the tundish at least one vertical refractory weir which has a plurality of horizontal molten steel pouring nozzles as through-holes for passing molten steel therethrough; rectifying the flow of molten steel while t~"J,~, molten steel poured from a ladle into the ~ ~ passes through the plurality of horizontal molten steel pouring nozzles as the tnroug~-holes of the at least one weir;
and causing aluminum oxide present in molten steel to deposit onto the inner surfaces of the plurality of horizontal molten steel pouring nozzles as the through-holes, the~eby removing aluminum oxide from molten steel.

However, when continuously casting molten aluminum-killed steel containing at least 0.003 wt.

~ ~i32~6 Sol.Al into a cast steel strand of a small cross-sectional area having a side of up to 200 mm by the use of a small-diameter conventional molten steel pouring nozzle as the tundish nozzle or the immersion nozzle having inner bore diameter of from 10 to 20 mm, it is impossible, even by any of the above-mentioned methods (1) to (4), to prevent aluminum oxide present in molten steel from depositing onto the inner surface of the conventional molten steel pouring nozzle as the tundish nozzle or the immersion nozzle, and hence to prevent clogging up of the inner bore of the conventional molten steel pouring nozzle caused by aluminum oxide deposited and accumulated onto the inner surface of the molten steel pouring nozzle. It has therefore conventionally been believed impossible to continuously cast molten alumlnum-killed steel as described above into a cast steel strand of a small cross-sectional area by the use of the above-mentioned small-diameter conventional molten steel pouring nozzle as the tundish nozzle or the immersion nozzle.

Under such circumstances, there is a strong demand for the development of a molten steel pouring nozzle as a tundich nozzle oran immersion nozzle, which permits pre~ention of clogging up of the inner bore of the molten steel pouring nozzle caused by the deposition of aluminum oxide present in molten steel flowing through the inner ~i32~

bore, even when molten aluminum-killed steel having a high Sol.Al content is poured into a mold through the inner bore of a small diameter of the molten steel pouring nozzle.
However, such a molten steel pouring nozzle has not as yet been proposed.

SUMMARY OF THE IN~ENTION

A principal object of the present invention is therefore to provide a molten steel pouring nozzle as a tundish nozzle or an immersion nozzle, which permits prevention of clogging up of the inner bore of the molten steel pouring nozzle caused by the deposition of aluminum oxide present in molten steel flowing through the inner bore, even when molten aluminum-killed steel having a high Sol.Al content is poured into a mold through the inner bore Of a small diameter oE the molten steel pouring nozzle.

Another object of the present invention is to provide a molten steel pouring nozzle as a through-hole, which is fitted in a vertical refractory weir arranged in a tundish, and which permits removal of aluminum oxide present in molten steel flowing through the inner bore of the molten steel pouring nozzle.

In accordance with one of the features of the present invention, there is provided a molten steel pouring ~ ',f~
nozz]e having along the axis thereof an inner bore through which molten steel flows, characterized by comprising:
an upper half portion as ~ chemical reaction zone, which forms an upper part of the inner bore, the upper half portivn being formed with a refractory consi3ting e~sentially of calcium oxide of at least 30 wt.%, magnesium oxide and aluminum oxide, which refractory reacts with alu~inum oxide pre~ent in molten steel to produce low-melting-point compound and mixture, and a melting point of the refractory falling within the region of at least 2,200C in the CaO-MgO-A1203 ternary pha~e diagram, and a lower half portion as a molten steel flow rate controlling zone, which is provided on the lower end of the upper half portion and forms a lower part of the inner bore, the lower half portion being formed with any of zirconia refractory, silica refractory, zirconia-~ilica refractory, alumina-graphite refractory and alumina-silica refractory.

From the above-mentioned point of view, we carried out extensive studies to develop a molten ~teel pouring nozzle as a tundi~h nozzle or an immersion nozzle, which permits prevention of clogging up of the :~nner bore of the molten steel pouring nozzle cau~ed by the deposition of . ~, ~.~, jm:sks ~32~

aluminum oxide present in molten steel flowing through the inner bore, even when molten aluminum-killed steel having a high Sol.Al content is poured into a mold through the inner bore of a small diameter of the molten steel pouring nozzle.

As a resultt we obtained the following finding:
a refractory which consists essentially of at least 30 wt.~ calcium oxide and at least one of magnesium oxide and aluminum oxide and which contains at least one of said 10 magnesium oxide and said aluminum oxide so that the melting point of the refractory falls within the region of at least 2,200C in the CaO-MgO-A12O3 ternary phase diagram, produces a compound of a low melti.ng point, a eutectic mixture of a low melting point and a mixture of compounds of a low melting point (hereinafter referred to as the "low-melting-point compound and mixture") listed below on the interface between the refractory and molten steel through reaction with aluminum oxide present in molten steel~

(1) mCaO nA1203 compound;
(2) Eutectic mixture of ~gO and mCaO nA12O3;
(3) Mixture of MgO, CaO and mCaO-nA12O3;
(4) Mixture of MgO, MgO-A12O3 and mCaO nA12O3;

(5) Mixture of MgO-A12O3 and mCaO~nA12O3;

(6) Mixture of CaO and mCaO nA12O3; and ~z~

(7) Mixture of a plurality of mCaO-nA1203 with different m and n values.

Table 1 shows the molecular Eormula, the chemical composition and the melting point of the above-mentioned low-melting-point compound and mixture.

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~v~ o - - - - o o o -- o o -O O In t'~ ~ ~ U~ t- L~ t" C~ O a~
.,~ _, ~ ~ In t~ t~ ~ ~ U~ U~ tr) ~ L~l ~ o ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
_ tr) _ _ O ~D ~ C~ t- tX1 ~ ~r t~ o o o In ~ ~r t~l t- t~ ~ ~ ~ ~ ~ o ~ ~o o~ ~ ~D Lr) tr~ ~r Ln ~r In ~D ~r u~ u~ ~D
~ - --O t~ I_ ~ a~ r ~ l l l . ~ . .

td .1 ~& __ _ _ t~ _ O ~r co ~ O u~ n ~ ~ o o o u~
t~ ~ td . . . . . . . . . . .
O C) Ln t- t~l ~ ~ ~ ~ ~ ~ o t-O t~ t~ ~r ~ ~r ~ ~~r t~tll t~l~t~ t~
~1 _ __ _ _ . 0 E~ t'~ ~
~ 0~ Ot~ O
~ ,1 t~ tr) td ~ ~ l¢ Ot~ O 0~)~ t~
O . . ~1 + t'l O O
O O ~ tr) ~1 t~ t~
Sl t tt~ 0~ O 0~ ~C ~
td 1~1 ~ t~ td ~1 . . In ~1 O C~ ~ ~ td td O
) O t~ . t~ O O t') 10 td a) t~ ~1 O O tdt~ ~rl + C ) ~¢ td t`J t~ ~1 + r~ t~
O O ~ I¢t~) O ~1 + f~ t~) O +
t~ t-`J O . . (~) I¢ ~) . O t'`l O ~ t~l O O + ~ O O ~ ~ O
C~J ~ r~td td O O t~ td ~1 ~ ~1 O td ts ~ ~ ~ t`~) ~J
~ O O ~ 11-) ~,) ~ ~ t+ O O ~C
O ~d td O O O O O O td t~ O
tt) ~ O ~ t~ ~ ~ tJ~ td O C ) td ~ 1~ ~ ~ ~ ~ ~ ~ C.)tr~ LO ~
_ _ O
æ ~ c~ t~, ~ Ln ~D t- t~ a~ O ~
_ ~1 ~
_ _ _ _ ~2~32~

In the CaO-MgO-A1203 ternary phase diagram shown in Fig. 6, C represents the point of 100 wt.% CaO, M represents the polnt of 100 wt.% MgO, and A represents the point of 100 wt.% A12O3. The region E including the point C is the crystallization region of lime; the region B including the point M is the crystallization region of periclase; and the region D including the point A is the crystallization region of spinel. The line G is the eutectic line of lime and periclase, and the line F is the eutectic line of periclase and spinel. The dotted lines are melting isothermal lines drawn at intervals of 100C.

As is known from the above, in a molten steel pouring nozzle having along the axis thereof an inner bore through which molten steel flows, and formed wi-th a refractory which consists essentially of at least 30 wt.%
calcium oxide and at least one of magnesium oxide and aluminum oxide and which contains at least one of said magnesium oxide and said aluminum oxide so that the melting point of the refractory falls within the region of at least 2,200C in the CaO-MgO-A1203 ternary phase diagram, even when aluminum oxide present in molten steel deposits OIltO
the inner surface of the molten steel pouring nozzle, which forms the inner bore, the refractory having the above-mentioned chemical composition reacts with said aluminum oxide to produce the low-melting-point compound and mixture J~

on the interface between the refractory and molten steel, whereby the deposited aluminum oxide easily dissolves.

The present invention was made on the basis of the above-mentioned findings. At least a part of the molten steel pouring nozzle of the present invention is formed with a refractory which consists essentially of at least 30 wt.~ calcium oxide and at least one of magnesium oxide and aluminum oxide, and the refractory contains at least one of said magnesium oxide and said aluminum oxide r e f~a c 1~or~
so that the melting point of the ~r~crer~ falls within the region of at least 2,200C in the CaO-MgO-A12O3 ternary phase diagram.

The reasons why the chemical composition of the reEractory which forms the molten steel pouring nozzle of the present invention is defined as mentioned above are described below.

With a calcium oxide content under 30 wt.%, it is re ~rO cfar~
impossible forthe ~y~forming the molten steel pouring nozzle to react with aluminum oxide present in molten steel, and to quickly produce the low-melting-point compound and mixture mentioned above on-the interface between t~e refractory and molten steel.

On the other hand, when the content of at least one of magnesium oxide and aluminum oxide is outside /~;

~i3~

the region in the CaO-MgO-A12O3 ternary phase diagram in which the melting point of the refractory is at least 2,200C, the refractory forming the molten steel pouring nozzle tends to be easily eroded through contact with molten steel and can not bear operations for a long period of timeO

The shadowed portion in the CaO-MgO-A12O3 ternary phase diagram as shown in Fig. 6 represents the range of the chemical composition of the refractory forming the molten steel pouring nozzle of the present invention.

Table 2 shows examples of the chemical composition and melting point of the refractory forming the molten steel pouring nozzle of the present invention.

~Z63~

Table 2 _ No Chemic,al,compos,i,tion ,(wt.,~) Melting . poin t ( C ) CaO MgO A~i~03 . _ ~
1 40.5 40.5 19.0 2,300 2 44.5 44.5 11.0 2,400 3 75.5 10.5 14.0 2,200 ~ 50.0 45.0 5.0 ~,430 45.0 50.0 5.0 2,480 6 80.0 10.0 10.0 2,320 7 85.0 10.0 5.0 2,420

8 84.5 15.5 _ 2~480

9 50.0 50.0 _ 2,470 88.0 _ 12.0 2,400 11 70.0 30.0 ~ 2,410 .. ... ... , The materials for the refractory forming the molten steel pouring nozzle of the present invention may be any of:

(1) a mixture of calcium oxide and at least one of magnesium oxide and aluminum oxide;

(2) a premelt product prepared by melting a mixture of calcium oxide and at least one of magnesium oxide and aluminum oxide, solidifying by cooling the resultant molten mixture, and then pulverizing the solidified mixture; and J~

~2~;3~

(3) a natural ore comprising calcium oxide and at least one of magnesium oxide and aluminum oxide.

When manufacturing the molten steel pouring nozzle of the preseht inventicn, it is desirable to Eorm the refractory comprising any of the above-men-tioned rnaterials into a molten steel pouring nozzIe having.a prescribed shape by a kncwn methcd, and then fire the formed body thus obtained.

Uses of the molten steel pouring nozzle of the present invention are as follows:

(1) the use as a tundish nozzle which is secured in the bottom wall of a tundish, for pouring molten steel in the tundish into a mold;

(2) the use as an immersion nozzle which is fitted to the lower end of the above-mentioned molten steel pouring nozzle as the tundish nozzle so as to project vertically and downwardly, for pouring molten steel in the tundish into a mold;

(3) the use as a ladle nozzle which is secured in the bottom wall of a ladle, for pouring molten steel in the ladle into a tundish or a mold; and (4) the use as through-holes which are horizontally provided in each of vertical weirs arranged in a tundish, for passing molten steel therethrough.

32~6~

No-~, the molten steel pouring nozzle of the present invention is described with refe~ence to the drawings.

Fig. 7 is a schematic vertical sectional view illustrating a first embodiment of the molten steel pouring nozzle of the present invelltion. A molten steel pouring nozzle 13 of the first embodiment is used as a tundish nozzle which is secured in the bottom wall of a tundish or as a ladle nozzle which is secured in the bottom wall of a ladle. As shown in Fig. 7, the entirety of the molten steel pouring nozzle 13 as the tundish nozzle or the ladle nozzle, having along the axis thereof an inner bore 14 through which molten steel flows, is formed with a refractory having the chemical composition as described above, which produces the low-melting-point compound and mixture.

Accordinqly, when the molten steel ~ourinq nozzle 13 is used as the tundish nozzle or the ladle nozzle of the first embodiment, aluminum oxide present in molten steel never deposits onto the inner surface of the molten steel pouring nozzle 13, which forms the inner bore 14. Wnen the inner bore 14 may be expanded by the production of the low-melting-point compound and mixture, it is desir2ble to provide a publicly known control apparatus of molten steel flow rate such as a sliding nozzle at the lo~er end of the 327~6 molten steel pouring nozzle 13.
Fig. 8 is a schematic vertical sectional view illustrating a second embodiment of the molten steel pouring nozzle of the present invention. A molten steel pouring nozzle 13 of the second embodiment is also used as the tundish nozzle or the ladle nozzle. As shown in Fig. 8, the molten steel pouring nozzle 13 as the tundish nozzle or the ladle nozzle, having along the axis thereof an inner bore 14 through which molten steel flows, comprises an upper half portion 13a forming the upper part 14a of the inner bore 14 and a lower half portion 13b forming the lower part 14b of the inner bore 14. The upper half portion 13a is secured onto the uppermost end of the lower half portion 13b. The upper half portion 13a onto which aluminum oxide present in molten steel tends to deposit, is formed with a refractory having the chemical composition as described above, which produces the low-melting-point compound and mixture, whereas the lower half portion 13b, onto which aluminum oxide relatively hardly deposits, is formed with any of the publicly known refractories excellent in erosion resistance against rnolten steel, having the following chemical composition:
(1) for exarnple, zirconia refractory comprising 95 wt.% ZrO2 ~2) for example, silica refractory comprising 99 wt. % SiO2 (3) for example, zirconia-silica refractory comprising rn/rm ~`
la.

32~

.. . . . . . . .. .. ..

33 wt.~ sio2, 1.5 wt.~ A12O~ and 65 wt.~ ZrO2;
(4) for e~mple, alumina-graphit~ refractory comprisin~
60 wt.~ A12O3 and 33 wt.~ C; and (5) for example, alumina-silica refractory comprising 572 wt.~ A12O3 and 24 wt.% SiO2.

Accordinqly, when the molten steel pourinq nozzle 13 is used as the tundish nozzle or the ladle nozzle of the second embodment, aluminum oxide present in molten steel never deposits onto the inner surface of the upper half portion 13a of the molten steel pouring nozzle 13, which forms the upper part 14a of the inner bore 14, onto which the aluminum oxide tends to easily deposit. In addition, even when the upper part 14a of the inner bore 14 is expanded by the production of the low-meltiny~point compound and mixture, the lower part 14b of the inner bore 14 is relatively hardly expanded, since the lower half portion 13b of the molten steel pouring nozzle 13 is formed with a refractory excellent in erosion resistance against molten steel, and it is thus possible to keep constant the flow rate of molten s-teel flowing thrc,ugh the inner bore 14. When the upper part 14a of the inner bore 14 has a funnel shape as shown in Fig. 8, the lower.portion of.the upper part 14a of the inner bore 14 should have the same diameter as that of the lower part 14b of the inner bore 14.

25Since the molten steel pouring nozzle 13 as the ~6~$o6 tundish nozzle or the ~adle nozzle of the second embodiment has the lower half portion 13b formed with the refractory excellent in erosion resistance ayainst molten steel, it is possible to keep constant the flow rate of molten steel flowiny through the inner bore 14, even when the lower end of the molten steel pouring nozzle 13 is not provided with a publicly known control apparatus of molten steel flow rate such as a sliding nozzle.
Fig. 9 is a schematic vertical sectional view illustrating a third embodiment of the molten steel pouring nozzle of the present invention. A molten steel pouring nozzle 13 of the third embodiment is also used as the tundish nozzle or the ladle nozzle. As shown in Fig. 9, the molten steel pouriny nozzle 13 of the third embodiment, having along the axis thereof an inner bore 14 through which molten steel flows, comprises, as in the molten steel pouring nozzle 13 of the second embodiment, an upper half portion 13a forming the upper part 14a of the inner bore 14, and a lower half portion 13b forming the lower part 14b of the inner bore 1~. The only difference between the second embodiment and the third embodiment, is that, in the third embodiment, the upper half portion 13a is fitted into a recess 13c formed in the upper end portion of the lower half portion 13b, whereas, in the second embodiment, the upper half portion 13a is secured onto the uppermost end of the lower half portion 13b.
Accordingly when the molten steel pouring noæzle 13 is used as the tundish nozzle or the ladle nozzle of the third rn/rm !f/
, -2-~-embodiment, as in the molten steel pouring nozzle of the second embodiment described with reference to Fig. 8, aluminum oxide present in molten steel never deposits onto the inner surface of the upper hal~ portion of the molten steel pouring nozzle 13, which forms the upper part 14a of the inner bore 14, onto which the aluminum oxide tends to easily deposit. In addition, even when the upper part 14a of the inner bore 14 is expanded by the production of the low-melting-point compound and mixture, the lower part 14b of the inner bore 14 is relatively hardly expanded, since the lower half portion 13b of the molten steel pouring nozzle 13 is formed with a refractory excellent in erosion resistance against molten steel, and it is thus possible to keep constant the flow rate of molten steel flowing through the inner bore 14. When the upper part 14a of the inner bore 14 has a funnel shape as shown in Fig. 9, the lower portion of the upper part 14a of the inner bore 14 should have the same diameter as that of the lower part 14b of the inner bore 14.
Since the molten steel pouring nozzle 13 as the tundish nozzle or the ladle nozzle of the third embodiment has the lower half portion 13b formed with the refractory e~cellent in erosion resistance against molten steel, it is possible to keep constant the flow rate of molten steel flowing through the inner bore 14, even when the lower end of the molten steel pouring nozzle 13 is not provided with a publicly known control apparatus of molten steel flow rate such as a sliding nozzle. In addition, the molten steel rn/~

!~

~32~L~
-pouring nozzle 13 of the third embodiment has an advantage that, even when part of the junction between the upper half portion 13a and the lower half portion 13b is eroded by molten steel, the lower half portion 13b hardly falls off from the upper half portion 13a.
Fig. 10 is a schematic vertical sectional view illustrating a fourth embodiment of the molten steel pouring nozzle of the present invention. A molten steel pouring nozzle 15 of the fourth embodiment is used as an immersion nozzle which is fitted to the lower end of a molten steel pouring nozzle 3 as the tundish nozzle so as rn/rm 632~i to project vertically and downwardly. It is needless to say that the molten steel pouring nozzle 3 as the tundish nozzle may be any one of the molten steel pouring nozzles 13 as the tundish nozzles of the first to the third embodiments described above. As shown in Fig. 10, the molten steel pouring nozzle 15 as the immersion nozzle has along the axis thereof an inner bore 16 through which molten steel flows. The downstream end of the inner bore 16 branches off into a plurality of substantially horizontal clischarge holes 17. The molten steel pouring nozzle 15 comprises an upper part 15a of the inner sllrface portion of the molten steel pouring nozzle 15, which forms the upper part 16a of the inner bore 16, and the remainirg portion 15c other than the above-mentioned upper part 15a, which forms the lower part of the inner bore 16. The upper part 15a onto which aluminum oxide present in molten steel tends to deposit, is formed with a refractory having the chemical composition as described above, which produces the low-melting-point compound and mixture, whereas the remaining portion 15c other than the upper part 15a, onto which aluminum oxide relatively hardly deposits, is formed with any of the publicly known refractories excellent in erosion resistance against molten steel, having the chemical composition as described concerning the second embodiment of the molten steel pouring nozzle.
æ~
-~2~2~i Accordinqly, when the molten steel pourinq nozzle ~ is used as the immersion noz~le of the fourth embodiment, alumin~n oxide present in molten steel never deposits onto the upper part 15a of the inner surface portion of the molten steel pouring nozzle 15, which forms -the upper part 16a of the inner bore 16, onto which the aluminum oxide tends to easi]y deposit.

Fig. 11 is a schematic vertical sectional vie~J
illustrating a fith embodiment of the molten steel pouring nozzle of the present invention. A molten steel po~ring nozzle 15 of the fifth embodiment is also used as a~
immerslon nozzle which is fitted to the lower end ~f a molten steel pouring nozzle 3 as the tunidsh nozzle so as to project vertically and downwardly~ It is ~edless to say that the molten steel pouring nozzle 3 as the~ tundish nozzle may be any one of the molten steel pouring nozzles 13 as the tundish nozzles of the first to the third embodiments descxibed above. As shown in Fig. 11, ~he molten steel pouring nozzle 15 as the immersion nozzle has along the axis thereof an inner bore 16 through which molten steel flows. The downstream end 16b of the inner bore 16 branches off into a plurality of substantia~ly horizontal discharge holes 17. The molten steel pouring nozzle 15 comprises a lower part 15b of the inner surface portion of the molten steel pouring nozzle 15, which forms ~-.~ 6'i~7 ii32~

the downstream end 16b of the inner bore 16 includiny the plur~lity of discharge holes 17, and the remaining portion 15c other than the above-mentioned lower part 15b, ~hich forms the upper part of the inner bore 16. The lo~"er part lSb onto which aluminum oxide present in molten steel tends to deposit, is formed with a refractory having the chemical composition as described above, which produces the P~w-meltiny-point compound and mixture, whereas the remai.ning . portion 15c other than the lower part 15b, on-to whic~
aluminum oxide relatively hardly deposits, is forme~ with any of the publicly known refractories excellent in erosion resistance against molten steel, having the chemical composi-tion as described concerning the second emb~diment of -the molten steel pouring nozzle~

Accordinqly, when the molten steel pourinq nozzle 15 ls used as the immersion nozzle of the fifth embodiment, alumi~m oxide present in molten steel never deposits onto the low~ part 15b of the inner surface portion of the molten steel pouring nozzle 15, which forms the downstream end 16b of the inner bore 16 including the plurality oE discharge holes P7j onto which the aluminum oxide tends to easily deposit.

Yig. 12 is a schematic vertical sectional view illustrating a si~th embodiment of the molten steel pouring nozzle as a through-hole of the ?rcsent invention,-which is horizontally fitted in each of vertical weirs ar~anged .~ ~

3~
1~ .

~32~

in a tundish. A molten steel pouring nozzle l9 of the sixth embodiment is used as a through-hole which is horlzontally provided in each of vertical weirs arranged in a tundish. As shown in Fig. 12, two vertical refrac-tory weirs 18 are arranged at a prescribed distance -there-between in a tundish l. The num~er of the weir 18 may be one or more. A plurality of molten s-teel pouring nozzles l9 as the through-holes, each having along the axis thereof an inner bore 20 through which molten steel passes, are horizon-tally secured in each of the two weirs 18. The entirety of the molten steel pouring nozzles 19 as the through-hole is formed wi-th a refractory having the chemical composition as described above, which produces the low-melting-point compound and mixture.

Accordinal~, when the molten s-teel pouring nozzle l9is used as the through-hole o the sixth embodiment, the flow of molten steel received from a ladle not shown into the tundish l is rectified while passing through the inner bores 20 of the plurality of molten steel pouring nozzles 19 as the through-holes secured in each of -the two vertical weirs 18. In addition, aluminum oxide present in molten steel reacts with the refractory formins the molten steel pouring nozzles l9 as -the through-holes to produce the low-melting-point compound and mi~ture ~Thich f 102 _ Up on the surface of molten steel. Therefore, it is possible B ~ `

~2~3~

to substantially remove aluminum oxide present in molten steel received in the tundish l. Furthermore, since the inner bore 20 of each of the plurality of molten steel pouring nozzles 19 is never clogged up by the deposition of aluminum oxide, the flow of molten steel can be surely rectified. The inner bore 20 of the molten steel pouring nozzle l9 as the through-hole may be zigzag, apart from the linear shape as shown in Fig. 12.

Now, the molten steel pouring nozzle of the present invention is described further in detail by means of an example.

EXAMPLE

Three kinds of molten steel pouring nozzles as the tundish nozzle of the first embodiment shown in Fig.
7, formed with respective refractories having chemical compositions Nos. 5, 7 and 11 shwon in Table 2 above and having an-inner bore with a diameter of 16 mm were prepared. Then, for each of the thus prepared three kinds of molten steel pouring nozzles as the tundish nozzle, four nozzles were secured in the bottom wall of a res-pective tundish, and molten aluminum-killed steel having the chemical composition shown in the following Table 3 was continuously cast, for each of the three kinds of molten steel pouring nozzles, into four cast steel strands, ~2~3~

each haviny a rectangular cross-section with a side of 140 mm. Continuous casting of 154 tons of the above-mentioned molten steel required a time of 120 minutes, and clogging of the innPr bores of the molten steel pouring nozzles as the tundish nozzle was never caused by the deposition of aluminum oxide present in molten steel.

Table 3 (wt.%) ¦ C ¦ Si ¦ P ¦ S ¦ Cu ¦ Sol.Al _ 0.12 0.15 0.015 0.013 0.28 0.012 For comparison purposes, on the other hana, four conventional molten metal pouring nozzles as the tundish nozzle formed with a zirconia refractory comprising 95 wt.% ZrO2 and having an inner bore with a diameter of 16 mm were secured in the bottom wall of a tundish, and molten aluminum-killed steel containing 0.012 wt.% Sol.Al was continuously cast into four cast steel strands, each having a rectangular cross-section with a side of 140 mm.
After the lapse of about 10 minutes from the start of casting, deposition of aluminum oxide present in molten steel began to impair the flows of molten steel passing through the inner bores of the molten steel pouring nozzles as the tundish nozzle, and after the lapse of B
i3~ --~32~

about 18 minutes from the start of casting, all the inner bores of -the mol-ten steel pouring nozzles were substan-tially clogged up, thus making it impossible to continue continuous casting any further.

According to the molten steel pouring nozzle as the tundish nozzle or the immersion nozzle of the present invention, as described above in detail, it is possible to prevent clogging up of the inner bore of the molten steel pouring nozzle as the tundish nozzle or the immer-sion nozzle caused by the deposition of aluminum oxide present in molten steel flowing through the inner bore, even when molten aluminum-killed steel having a high Sol.Al content is poured into a mold through the molten steel pouring nozzle having a small-diameter inner bore. It is thus possible to continuously cast molten aluminum-killed steel having such a high Sol.Al content into a cast steel strand of a small cross-section. Furthermore, according to the molten steel pouring nozzle as the through-hole of the present invention, which is horizontally fitted in the vertical weir arranged in the tundish, it is possible to remove aluminum oxide present in molten steel flowing through the inner bore of the molten steel pouring nozzle as the through-hole, thus providing industrially useful effect.

_

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A molten steel pouring nozzle (13) having along the axis thereof an inner bore (14) through which molten steel flows, characterized by comprising:

an upper half portion (13a) as a chemical reaction zone, which forms an upper part (14a) of said inner bore (14), said upper half portion (13a) being formed with a refractory consisting essentially of calcium oxide of at least 30 wt.%, magnesium oxide and aluminum oxide, which refractory reacts with aluminum oxide present in molten steel to produce low-melting-point compound and mixture, and a melting point of said refractory falling within the region of at least 2,200°C in the CaO-MgO-Al2O3 ternary phase diagram; and a lower half portion (13b) as a molten steel flow rate controlling zone, which is provided on the lower end of said upper half portion (13a) and forms a lower part (14b) of said inner bore (14), said lower half portion (13b) being formed with any one of zirconia refractory, silica refractory, zirconia-silica refractory, alumina-graphite refractory and alumina-silica refractory.

2. The molten steel pouring nozzle as claimed in Claim 1, characterized in that:

said upper half portion (13a) is secured onto the uppermost end of said lower half portion (13b).

3. The molten steel pouring nozzle as claimed in Claim 1, characterized in that:

said upper half portion (13a) is fitted into a recess (13c) formed in the upper end portion of said lower half portion (13b).