FIELD OF THE INVENTION
[0001] The present invention relates to a process for continuously casting a double-layered
slab whose surface layer and internal layer are composed of steel compositions different
from each other, wherein two kinds of molten steels having compositions different
from each other are poured into an upper molten steel pool and a lower molten steel
pool, respectively, both pools being separated by a direct current magnetic field
zone provided within a mold or at a lower site thereof.
BACKGROUND OF THE INVENTION
[0002] The present inventors have heretofore proposed and practiced a process for producing
a double-layered slab whose surface layer and internal layer are composed of steel
compositions different from each other, wherein the strand pool for continuous casting
is separated into an upper pool and a lower pool by applying various types of direct
current magnetic fields, and two kinds of molten steels having compositions different
from each other are poured into the two pools through separate immersion nozzles,
whereby mixing of the two kinds of steels is minimized.
[0003] For example, the present inventors have proposed processes for producing slabs by
using the following techniques: a technique of applying a magnetic flux zone having
a uniform density in the slab width direction from one of the long sides thereof to
the other as disclosed in KOKAI (Japanese Unexamined Patent Publication) No. 63-108947;
a technique of applying a magnetic flux zone in the direction parallel to the drawing
direction of the slab as disclosed in KOKAI (Japanese Unexamined Patent Publication)
No. 63-100549; a technique wherein a direct current magnetic field is applied to a
slab cross section vertical to the drawing direction in such a manner that a magnetic
flux flows out from the center of the cross section to the periphery thereof, or on
the contrary the magnetic flux is absorbed to the center thereof from the periphery
thereof as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 4-309436.
[0004] However, in these processes, a double-layered slab is produced in principle by the
following procedures: two kinds of molten steels are prepared by such an equipment
having a function for adjusting the compositions of the steels as a converter, an
electric furnace, a ladle and a vacuum degassing equipment; these steels are separately
transported to a continuous casting machine, and poured into two tundishes, respectively;
the two kinds of steels are fed into an upper molten steel pool and a lower molten
steel pool within a mold, respectively, through two nozzles separately provided to
the two tundishes; and a slab is drawn after the step of continuous casting.
[0005] The preparation of two kinds of molten steels separately as described above often
brings about marked lowering of production efficiency in production mills which have
been constructed to produce a single- layered continuously cast slab and variously
improved. The efficiency lowering has become a fatal problem of the process, and a
essential improvement has been required.
[0006] To solve the problem, the present inventors have already proposed a method for adjusting
a molten steel composition in a molten steel pool by feeding a wire thereto in KOKAI
(Japanese Unexamined Patent Publication) No. 63-108947. However, the resultant molten
steel has not always had a uniform composition in this case.
[0007] To improve the problem, a technique has been proposed in KOKAI (Japanese Unexamined
Patent Publication) No. 3-243245 wherein solutes added to molten steel from a wire
is stirred and mixed by an electromagnetic stirrer to make the solute concentration
uniform.
[0008] In general, when solutes are added to molten steel in the form of a wire without
further processing or wire covered with a metal such as iron from the molten steel
surface within a mold, and when the wire passes through a powder layer 16 or the molten
portion of the powder layer 16 within the mold 1 without taking any measures, as shown
in Fig. 7, a portion of the powder is expected to adhere to the wire 12A, to become
molten powder 22, to be drawn into molten steel pools of molten steels 13A, 15, and
to form defects within the slab. In addition, the reference numeral 21 designates
a solidified layer of steel adhering around powder 20.
[0009] As shown in Fig. 8, a guide tube 23 made of a refractory material may be placed at
the location of the molten steel surface from which the wire 12A enter the molten
steel, and the wire 12A may be fed without being directly contacted with the powder
layer 16. Practically, since the temperature of the molten steel around the guide
tube 23 is lowered, the molten steel is solidified and adheres thereto, and as a result
casting operation is sometimes hindered.
[0010] Furthermore, even if the problem of the powder layer 16 has been solved, there cannot
be produced a double-layered slab homogeneous both in the peripheral direction and
in the longitudinal direction thereof when the concentration of the wire component
cannot be sufficiently homogenized after melting the wire 12A.
[0011] Though it is not impossible to make the component concentration homogeneous by electromagnetic
stirring as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 3-243245
described above as means for overcoming the problem, there may arise a case that the
component separation cannot be successfully performed when stirring is practiced at
a site where the direct current magnetic field zone is affected.
[0012] On the other hand, a technique of feeding a treating agent in a wire-form within
a teeming nozzle to a molten steel to be teemed into a mold is disclosed in Japanese
Unexamined Patent Publication (KOKAI) No. 51-32432. For the purpose of adding a deoxidant,
etc., to the constrained flow of molten metal flowing from a ladle to a mold and preventing
retardation of the continuous casting operation caused by disadvantageous deposition
of high melting-point oxides formed from the added treating agents, this technique
is used in feeding the treating agents in a wire-form in the nozzle of the ladle by
passing the agents through the central through-hole of the stopper rod.
[0013] Since the flow rate of the molten metal passing through the nozzle is great, the
contact time of the materials constituting the nozzle and the following reaction products
are short: a reaction product between a molten metal at the time of adding the wire
and enriched solutes formed by the wire addition, and a reaction product between the
materials constituting the nozzle and the enriched solutes formed thereby. It is therefore
concluded that the deposition of these reaction products on the nozzle wall is not
significant.
[0014] Since the molten metal flow flows out from the pouring end of the short nozzle and
falls through the air onto the molten steel surface in the mold, the dissolution amount
of the wire-form treating agent in the molten metal flow and the time for dissolving
and mixing the treating agent are restricted. Accordingly, it is not possible to feed
a large amount of the treating agent and to have a uniform dissolution concentration
thereof.
DISCLOSURE OF THE INVENTION
[0015] The present invention has been achieved in view of the problems described above.
An object of the present invention is to provide a process for casting a double-layered
slab which makes the composition adjustment of molten metal such as molten steel used
for the process simple, and which reduces the production cost thereof and improves
the quality thereof.
[0016] A further object of the present invention is to provide a process for casting a double-layered
slab which is capable of casting, continuously and without interruption, a slab having
an outer layer and an internal layer each having a uniform composition distribution.
[0017] To achieve the objects as described above in the present invention, molten steel,
for example, is first poured into a molten metal pool formed by a mold and a dummy
bar from a short nozzle and a long nozzle provided at the lower site of a tundish,
and a direct current magnetic field zone which acts on the entire slab width is imposed
by a magnet provided at a lower site of the mold a predetermined distance apart from
the meniscus in the casting direction to separate the molten steel into an upper and
a lower portion, continuous casting strand pools thus being formed. Accordingly, the
front end of the short nozzle and that of the long nozzle are immersed in the two
pools, respectively.
[0018] Subsequently, an alloy wire for composition adjustment is fed within one or both
of the immersion nozzles, sufficiently melted therewithin and mixed with the molten
steel to adjust the molten steel to have a predetermined composition.
[0019] The resultant molten steels each having a uniformly adjusted composition are each
poured into respective pools, rapidly cooled, and solidified to cast a double-layered
slab having a surface layer and an internal layer each composed of the respective
metals having uniform compositions.
[0020] It is necessary to carry out the following procedures in casting the double-layered
slab of the present invention:
(1) a molten steel of a single composition is placed in the tundish;
(2) molten steel is separated into an upper pool and a lower pool within the mold
by providing a direct current magnetic field zone to the mold;
(3) a long immersion nozzle and a short immersion nozzle are used for pouring molten
steels into respective pools; and
(4) desired additive alloys for forming double-layer compositions are sufficiently
melted and mixed within the respective immersion nozzles so that the molten steels
within the respective immersion nozzles have respective uniform additive alloy concentrations;
and it is important to observe the following procedure to surely practice the present
invention:
(5) an inert gas is injected into the immersion nozzle.
[0021] An inert gas such as Ar is blown into the molten metal flow within the nozzle from
a wire insertion opening at the stopper top end or from the upper portion of the nozzle
wall, and finely dispersed within the fluid, whereby there are inhibited the adhesion
and deposition along the entire length of the immersion nozzle, of reaction products
of dissolved substances and the molten metal within the nozzle and mutual reaction
products of nozzle constituent materials and these materials. As a result, an increase
in the internal flow resistance of the nozzle is prevented.
[0022] As in the process of the present invention wherein the nozzle is long, the lower
portion of the nozzle is immersed in the molten metal, and in addition the direction
of the flow path is changed at the nozzle front end, the flow resistance of the molten
metal within the entire nozzle is increased, and pouring steel into the pools is liable
to be hindered. Blowing an inert gas into the immersion nozzles exerts extremely significant
effects on continuous casting operation over a long period of time.
[0023] In addition, to adjust smoothly the rate of molten metal flow into each of the pools
in the present invention, two tundishes into which the same molten metal is poured
may be arranged, and a short nozzle and a long nozzle may be provided to the respective
tundishes.
[0024] In this case, different molten metals may naturally be poured into respective tundishes,
and additive alloy wires are further fed into respective immersion nozzles connected
to respective pools requiring composition adjustment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025]
Fig. 1 is an entire schematic view, which is partially sectional, showing one embodiment
of the present invention.
Fig. 2 is a partially enlarged sectional view of Fig. 1.
Fig. 3 is a sectional schematic view showing a major portion in another embodiment
of the present invention.
Fig. 4 is a sectional schematic view showing a major portion of another embodiment
of the present invention.
Fig. 5 is a sectional schematic view showing a major portion of another embodiment
of the present invention.
Fig. 6 is a sectional schematic view showing a major portion of another embodiment
of the present invention.
Fig. 7 is a sectional schematic view showing a major portion of a conventional embodiment.
Fig. 8 is a sectional schematic view showing a major portion of another conventional
embodiment.
Fig. 9 is a graph showing the concentration distribution of Ti on a slab section in
the present invention.
Fig. 10 is a graph showing the concentration distribution of Ti on a slab section
in a conventional embodiment.
Fig. 11 is a mold section showing locations where Ti concentrations are measured.
BEST MODE FOR PRACTICING THE PRESENT INVENTION
[0026] The present invention will be illustrated below in detail.
[0027] Fig. 1 schematically shows the entire equipment for practicing the present invention,
wherein a magnet 2 is placed at a lower site of a mold 1. A direct current magnetic
flux is applied in the direction vertical to the casting direction (A), namely, in
the direction crossing the thickness of the mold, by the magnet to form a static magnetic
field zone 2A, whereby an upper molten metal pool 1A and a lower molten metal pool
1B are formed within the mold. A tundish 3 in which, for example, a molten steel 13
is stored is arranged above the mold 1. To the bottom portion of the tundish are provided
a short immersion nozzle 4 open to the upper pool 1A and a long immersion nozzle 5
open to the lower pool 1 B.
[0028] Fig. 1 shows a situation where an additive alloy wire 12 is fed into the short nozzle
4 to adjust the composition of molten steel to be poured into the upper pool 1. The
reference numeral 6 in Fig. 1 designates a tundish stopper for the short nozzle 4.
It has a through-hole 6A for the alloy wire 12 as shown in Fig. 2 in detail, and opens
and closes a tundish opening 3A. To the top of the stopper 6 is provided a sealing
mechanism 8 consisting of an inert gas sealing chamber 8A, a labyrinth seal 8B, etc.
The reference numerals 9, 10 and 11 designate a straightening machine for wire drawing,
an alloy wire feeder and a coiler, respectively.
[0029] As shown in Fig. 2, the short nozzle 4 is formed at the tundish opening 3A in such
a manner that the short nozzle 4 and the tundish bottom become an integral body. If
necessary, a porous refractory material 17 connected to an inert gas injection hole
18 is provided.
[0030] In the equipment as described above, a molten steel pool is formed between the mold
1 and a dummy bar (not shown), and the stopper is opened to pour the molten steel
13 in the tundish 3 into the molten steel pool. When the molten steel in the pool
has a predetermined depth, the static magnetic field zone 2A is generated to form
the upper molten steel pool 1A and the lower molten steel pool 1B. The alloy wire
12 is then fed into the short nozzle 4. The alloy wire 12 is melted and mixed within
the short nozzle 4 to have a predetermined concentration, and the resultant molten
steel is poured into the upper molten steel pool 1A.
[0031] To form a molten steel 14 whose additive alloy concentration has been adjusted in
the upper pool 1A, namely, to form a molten steel for the surface layer, relationships
represented by the following formulas should be satisfied:
wherein f is an average melting rate of the alloy wire 12, d is a diameter of the
wire, V is a feed rate of the wire, L
M is a distance from the front end of the stopper 6 which is in the state of closing
the tundish opening to a meniscus 14B within the mold, L
N is a distance from the front end of the stopper 6 to an immersion nozzle pouring
hole 4A, and L is a distance from the meniscus 16 to a central position 2B of the
direct current magnetic field zone.
[0032] In addition, the length of the long nozzle 5 for teeming a molten steel 13A for the
internal layer, namely, the distance from the front end of a stopper 7 to a nozzle
pouring hole 5A should be longer than the distance L of the central position 2B of
the static magnetic field zone.
[0033] When the molten steel 13 is teemed into the mold 1 as described above, the molten
steel 14 for the surface layer in the upper pool is solidified to form a solidified
shell 14A, and subsequently the molten steel 13A for the internal layer is also solidified
to form a solidified shell 13B. Finally, from the mold is drawn a double-layered slab
composed of the outer layer 14A and the internal layer 13B each having a uniform concentration
distribution.
[0034] The inert gas, for example Ar, is blown into the teeming nozzle desirably at a rate
of 0.1 to 15.0 liter/min. That is, stabilized casting becomes possible over a long
period of time if the inert gas is blown in the range mentioned above.
Fig. 3 shows an embodiment using the equipment in Fig. 1, wherein the alloy wire 12
is fed into the long nozzle 5 through the stopper 7 to form a molten steel 15 for
the internal layer containing the additive alloy at a uniform concentration, and a
double-layered slab composed of a surface layer 13B and an internal layer 15A containing
the added alloy is produced.
Fig. 4 shows an embodiment wherein an alloy wire 12 and an alloy wire 12A are fed
into a short nozzle 4 and a long nozzle 5, respectively, through respective stoppers
6, 7 to form a molten steel 14 for the surface layer and a molten steel 15 for the
internal layer each containing respective additive alloys at a uniform concentration,
and a double-layered slab composed of a surface layer 14A and an internal layer 15A
each containing the respective added alloys is produced.
Fig. 5 and Fig. 6 show embodiments wherein the tundish is separated into a tundish
3A for storing a molten steel 13a and a tundish 3B for storing a molten steel 13b,
and a short nozzle 4 and a long nozzle 5 are provided to the tundish 3A and the tundish
3B, respectively. Fig. 5 shows an embodiment of forming a molten steel 15 for the
internal layer by feeding an alloy wire 12 to the molten steel 13b. Fig. 6 shows an
embodiment of forming a molten steel 14 for the surface layer and a molten steel 15
for the internal layer by feeding an alloy wire 12 and an alloy wire 12A into the
molten steel 13a and the molten steel 13b, respectively. The alloy wire may naturally
be fed only into the molten steel 13a.
[0035] When each of the molten steel layers is provided with a tundish separately from the
other tundish as described above, the amounts of molten steels fed into the respective
molten metal pools can be more effectively adjusted. Moreover, in the case of pouring
molten metals different from each other being poured into respective molten metal
layers, this procedure is convenient.
[0036] In addition, in the embodiments of Fig. 5 and Fig. 6, an inert gas may also be blown
into the molten steel from the opening for alloy wire feeding at the top end of the
stopper or from the nozzle wall in the same manner as in the embodiment of Fig. 1,
and finely dispersed thereinto. As a result, the deposition amount of adhering material
on the internal wall of the nozzle is decreased, and there can be stably produced
a double-layered slab having a uniform concentration distribution in the slab peripheral
direction and the slab casting direction.
EXAMPLES
Example 1
[0037] As shown in Fig. 1, a molten steel having an internal layer composition as listed
in Table 1 and stored in a tundish was poured into a molten steel pool formed by a
continuous casting-machine copper mold 1200 mm in long side and 250 mm in short side
and a dummy bar to have a predetermined depth. A direct current magnetic field having
a uniform magnetic flux density of 5000 G in the width direction of the slab was applied
at a site 0.63 m (distance L) apart from a meniscus 14B within the mold in the downward
direction to form a direct current magnetic field zone 2A (central position of the
direct current magnetic field being referred to as 2B). The molten steel pool was
thus separated into an upper portion and a lower portion in the casting direction.
[0038] To form a surface layer having a thickness D of 25 mm, the drawing rate (casting
rate) Vc of the slab was determined to be 0.4 m/min from the following formula:
[0039] To carry out such casting, the flow rates of each of the molten steels were controlled
by adjusting the opening degree of each of the stoppers in such a degree that the
flow rate of the molten steel for the surface layer and that of the molten steel for
the internal layer became 3.36 kg/sec and 11.04 kg/sec, respectively. The molten steel
for the surface layer was passed through a short immersion nozzle 4 while an alloy
wire containing 70% of AI was being fed into the nozzle at a rate of 1.44 g/sec. As
a result, the AI content of the slab thus obtained became 0.032% by weight as shown
in Table 1.
[0040] Moreover, Ag gas was fed into the short nozzle at a rate of 0.5 liter/min during
feeding the AI wire.
[0041] The double-layered slab could be stably cast for 120 minutes. The AI concentration
of the surface layer was uniform both in the slab peripheral direction and slab longitudinal
direction, and no powder inclusion was recognized.
Example 2
[0042] A direct current magnetic field was applied at the lower site of a continuous casting
copper mold for casting a slab having a long side of 1500 mm and a short side of 200
mm, whereby the molten steel pool within the continuous casting strand was separated
into an upper pool and a lower pool in the casting direction. The slab which was solidified
was drawn while the same molten ultra low carbon steel was being fed into each of
the pools through respective nozzles different from each other in length. The molten
steel to be fed into the pools was stored in two tundishes, and a wire (Ti content
of 70%) in which Ti alloy was sealed was fed at a rate of 38.9 g/sec into a nozzle
for pouring the molten steel into the lower pool corresponding to the internal layer
through a stopper 7 having a through-hole and a sealing mechanism as shown in Fig.
5.
[0043] The central position 2B of the direct current magnetic field is 60 cm apart from
a meniscus 13C in the downward direction. The magnetic flux was applied in the thickness
direction of the slab, and the magnetic flux density at the central position was 5500
G. The slab was cast at a rate of 1 m/min while the opening degree of the stoppers
6, 7 were controlled in such a manner that the molten steel for the surface layer
and that for the internal layer were teemed into the mold at a rate of 7.75 kg/sec
and 27.25 kg/sec, respectively. When the molten steel was solidified at the rates
as mentioned above within the mold of the continuous casting machine, the boundary
between the upper and the lower pool was located at the central position of the direct
current magnetic field zone, and the surface layer thickness reached 20 mm.
[0044] Ar was fed into the molten steel at a rate of 1 liter/min together with the wire
from the front end of the stopper for the nozzle into which the wire was fed. Casting
was stably carried out for 120 minutes, and all the molten steel was completely cast.
[0045] The Ti concentration distribution in the slab peripheral direction of the internal
layer of the slab thus cast was 0.1% as shown in Fig. 9, which agreed with the concentration
estimated from the casting conditions as mentioned above. Moreover, the Ti concentration
distribution was constant in the longitudinal direction.
[0046] In addition, Fig. 11 shows the locations at which the Ti concentration distribution
in a slab section was measured.
Example 3
[0047] Casting a slab was carried out under the same conditions as in Example 2 except that
Ar was not fed. As a result, the feed rate of the molten steel from the nozzle for
the internal layer through which the Ti wire was fed was lowered about 55 minutes
after starting to cast, and the maintenance of the feed rate of 27.25 kg/sec became
difficult. As a result, mixing the upper pool and the lower pool took place. The Ti
concentration of the slab internal layer varied from 0.03 to 0.21% after the mixing
took place, though the internal layer had a uniform Ti concentration of 0.1% for about
55 minutes from starting to cast the slab. The casting was interrupted 80 minutes
after starting to cast because feeding the molten steel for the internal layer became
impossible. After casting, reaction products of the nozzle refractory material and
Ti were observed to adhere to and deposit on the nozzle wall surface when the interior
of the nozzle was examined.
Comparative Example 1
[0048] Casting a slab was carried out under the same conditions as in Example 2 except that
the wire was fed into the pool for the internal layer from the powder layer within
the mold without passing the wire through the stopper as shown in Fig. 7. The wire
was covered with iron and adjusted in such a manner that it started to be melted within
the pool for the internal layer.
[0049] Though casting a slab was stably carried out and completed, a marked variation of
the Ti concentration in the internal layer was observed in the slab peripheral direction
as shown in Fig. 10 when the slab was examined subsequent to casting.
[0050] Moreover, there was detected within the slab a large amount of powder which seemed
to have been entrapped by the meniscus during feeding the wire.
[0051] The locations at which the Ti concentration was measured were as shown in Fig. 11,
and the wire was added at a location designated by the reference numeral 24.
POSSIBILITY OF UTILIZATION IN THE INDUSTRY
[0052] As described above in detail, in continuous casting a double-layered slab, the present
invention provides a process wherein a molten steel having a base composition is prepared
without preparing two kinds of molten steels having compositions different from each
other, a wire or two wires are fed from the stopper or stoppers of a tundish or two
tundishes during teeming a molten steel for the internal or surface layer, or both
molten steels for the respective internal and the surface layer into a mold, the wire(s)
is (are) melted and uniformly mixed within a nozzle or two nozzles, and the resultant
molten steel(s) is (are) poured into a predetermined molten pool or two molten pools.
As a result, molten steels having desired compositions can be readily prepared. In
addition, since no powder inclusion is observed and casting can be stably carried
out over a long period of time, the production cost of the double-layered slab can
be reduced, and the quality thereof can be improved.
[0053] The explanation of the reference numerals are as follows:
1: a mold,
2: a magnet
2A: a static magnetic field zone,
3: a tundish,
4: a short immersion nozzle,
5: a long immersion nozzle,
6, 7: tundish stoppers,
8: a sealing mechanism,
12: an alloy wire,
13: a molten steel,
13A: a molten steel for the internal layer,
14: a molten steel for the surface layer, and
18: an inert gas injection hole.
1. A process for producing a double-layered slab comprising a surface layer and an
internal layer by feeding molten metal into an upper molten metal pool and a lower
molten metal pool which are separated by a direct current magnetic field zone provided
within a continuous casting mold or at a lower site thereof,
wherein a short immersion nozzle and a long immersion nozzle are provided to a tundish
for continuous casting arranged above the mold, a molten metal is fed into the upper
molten metal pool through the short immersion nozzle, a molten metal is fed into the
lower molten metal pool through the long immersion nozzle, a through-hole is provided
to the central portion of either of the two tundish stoppers detachably provided to
the two respective molten metal-pouring holes of the tundish, an alloy wire is inserted
in the through-hole to be melted therewithin whereby a molten metal having a desired
composition is prepared in one of the molten metal pools, and a molten metal is fed
into the other molten metal pool from the other molten metal-pouring hole of the tundish
through the immersion nozzle.
2. The process according to claim 1, wherein a through-hole is provided in the central
portion of both tundish stoppers, two different kinds of alloy wires to be added are
inserted in the respective through-holes, and melted within the respective immersion
nozzles, whereby molten metals of desired compositions are prepared in the respective
molten metal pools.
3. The process according to claim 1 or claim 2, wherein an inert gas is fed into the
immersion nozzle(s) in which the alloy wire(s) is (are) inserted.
4. A process for producing a double-layered slab comprising a surface layer and an
internal layer by feeding molten metal into an upper molten metal pool and a lower
molten metal pool which are separated by a direct current magnetic field zone provided
within a continuous casting mold or at a lower site thereof,
wherein two molten metals of the same kind are separately poured into two respective
tundishes for continuous casting arranged above the mold, the molten metal in either
one of the two tundishes is fed into the upper molten metal pool through a short immersion
nozzle, the other molten metal in the other tundish is fed into the lower molten metal
pool through a long immersion nozzle, a through-hole is provided at the central portion
of either of the two tundish stoppers detachably provided to two respective molten
metal-pouring holes of the two respective tundishes for continuous casting, an alloy
wire is inserted in the through-hole to be melted therewithin whereby a molten metal
having a desired composition is prepared in one of the molten metal pools, and the
other molten metal is fed into the other molten metal pool from the molten metal-pouring
hole of the other tundish through the immersion nozzle.
5. The process according to claim 4, wherein molten metals having compositions different
from each other are separately poured into the two respective tundishes for continuous
casting.
6. The process according to claim 4, wherein molten metals having compositions different
from each other are separately poured into the respective two tundishes, a through-hole
is provided to the central portion of each of the two tundish stoppers provided to
the respective tundishes for continuous casting, and two different kinds of alloy
wires to be added are inserted in the respective through-holes and melted within the
respective immersion nozzles, whereby molten metals having desired compositions are
prepared in the respective molten metal pools.
7. The process according to claim 4, claim 5 or claim 6, wherein an inert gas is fed
into the immersion nozzle(s) in which the alloy wire(s) is (are) inserted.