Note: Descriptions are shown in the official language in which they were submitted.
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Description
METHOD OF CONTINUOUS STEEh CASTING
<Technical Field>
The present invention relates to a method of continuous
steel casting. More particularly, the invention relates to
a method of continuous steel casting characterized by using
a combination of a specific mold powder and an immersion nozzle
constituted of a refractory material comprising alumina as
the main component (e.g., an alumina refractory and/or an
alumina-carbon refractory).
<Background Art>
In continuous steel casting, an immersion nozzle
employing an alumina/graphite material containing and/or not
containing fused silica as a main-body material and further
employing a zirconia/graphite material and/or
zirconia/calcia/graphite material as a powder line material
a.s generally used in combination with a mold powder containing
a fluorine ingredient.
The technique using a combination of the immersion
nozzle materials and the mold powder material (hereinafter
referred to as "related-art technique 1") is accompanied by
the inclusion into the steel of impurities attributable to
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the refractories and/or attributable to themoldpowdermaterial .
For avoiding this inclusion, the following techniques have
been disclosed.
With respect to immersion nozzles, a technique for
preventing carbon pickup or mold powder suction is known which
comprises blowing an inert gas into the molten steel through
an immersion nozzle to prevent the molten steel from coming
into contact with the nozzle (see JP-A-8-57613 and
JP-A-62-130?54) (hereinafter referred to as "related-art
technique 2-1").
Furthermore, an immersion nozzle is known in which
a refractory material comprising spinel or a refractory material
comprising spinel and periclase is disposed in the part which
comes into contact with a molten steel, e.g., low-carbon
A1-killed steel, high-oxygen steel, high-Mn steel, stainless
steel, or Ca-treated steel, so as to combine unsusceptibility
to fusion loss and unsusceptibility to clogging and thereby
diminish inclusions attributable to refractories (see
JP-A-10-305355) (hereinafter referred to as "related-art
technique 2-2").
With respect to mold powders, on the other hand,
"fluorine ingredient-containing materials", such as fluorite,
capable of forming cuspidine (3Ca0~2Si02~CaF2) crystals are
generally used as ones serving as a flux for flowability
enhancement and/or contributing to heat abstraction control
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(hereinafter referred to as "related-art technique 3").
However, fluorine ingredients accelerate the fusion
loss of the immersion nozzle and indirectly make it difficult
to produce clean steel castings. It is hence necessary to
use mold powders free of fluorine or having a minimized fluorine
ingredient content.
Known techniques concerning the mold powders free of
fluorine, among those mold powders, include:
a technique in which the pH' s of spray cooling water
for cooling the casting, secondary cooling water for use after
the cooling, and machine-cooling water are kept at a neutral
value for the purpose of prolonging the lives of metallic
structures, including the pipings in the casting machine main
body, and of the concrete facilities (JP-A-58-125349);
~ a technique in which the pH' s of spray cooling water
for cooling the casting, secondary cooling water for use after
the cooling, and machine-cooling water are likewise kept at
a neutral value for the purposes of preventing the casting
machine main body, pipings, etc. from corroding and of
maintaining flowability and conversion into slag
(JP-A-51-93728);
a technique for preventing the generation of fluorine,
which is harmful to men and beasts (JP-A-50-86423);
a technique for preventing environmental pollution,
preventing the corrosion of facilities disposed around the
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continuous-casting machine, and preventing immersion nozzle
damage (JP-A-5-208250); and
a technique for preventing the silicon tetrafluoride
formed by reaction with a silicate from impairing the working
atmosphere or contaminating the secondary cooling Water
(JP-A-51-67227). (Hereinafter, these are referred to as
"related-art technique 3-1".)
Known techniques concerning the mold powders having
a minimized fluorine ingredient content include:
~ a technique for preventing immersion nozzle damage
(JP-A-5-269560); and
a technique for preventing environmental pollution
(JP-A-51-132113). (Hereinafter, these are referred to as
"related-art technique 3-2".)
Incidentally, in the case of casting with an existing
immersion nozzle (see the related-art technique 1), the inner
tube and powder line part of the immersion nozzle suffer a
fusion loss due to the molten steel, inclusions in the molten
steel, mold powder, and slag. This fusion loss changes the
shape of the immersion nozzle and disturbs the flow of the
molten steel within the mold, resulting in defects in the casting.
In addition to this "shape change of the immersion
nozzle" , a change in the thermal conductivity of the immersion
nozzle occurs during casting due to the low-melting and
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high-melting compounds formed by the reaction of immersion
nozzle materials with elements dissolved in the molten steel
and/or with the mold powder and slag. Due to this change in
thermal conductivity, the quantity of heat abstracted from
the molten steel through the immersion nozzle cannot be kept
constant . This has resulted in uneven formation of a solidified
shell and caused defects in the casting.
Attempts have been made to overcome those problems
by means of a mold powder. Specifically, as stated above,
"amoldpowderwhich forms crystals of cuspidine (3Ca0~2Si02~CaF2)
as a fluorinated mineral" has been used for controlling the
quantity of heat abstracted (see the related-art technique
3) . However, the fusion loss in the powder line part is increased,
rater than reduced, due to the fluorine ingredient in the mold
powder and a sufficient effect has not been obtained so far.
Application of a mold powder containing no fluorine
ingredient or having a low fluorine ingredient content was
attempted for the purpose of diminishing the fusion loss in
the powder line part (see the related-art techniques 3-1 and
3-2) . However, use of this mold powder has made heat abstraction
control impossible and caused defects in the casting. Thus,
there has been no perfect measure for resolution.
Although the various measures in continuous steel
casting described above have been taken for producing a clean
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steel casting, these measures also have failed to produce a
sufficient effect as will be described below.
In the related-art technique 2-1, which is "a technique
comprising blowing an inert gas into the molten steel through
a nozzle to prevent the molten steel from coming into contact
with the nozzle" , it is necessary to highly precisely control
the rate of inert-gas blowing, blowing angle, size of bubbles,
etc. In case where these factors are not controlled, the
molten-steel flow is deflected and collides against Bart of
the nozzle, rather than being prevented from contacting the
nozzle, leading to a local fusion loss or alumina deposition.
Furthermore, the mold powder and slag which have been
sucked, due to fluctuations in melt surface level caused by
the bubbling, into the molten steel filling the mold are caught
by the inert gas blown into the molten steel. However, in
case where the inert-gas flow is not in a properly controlled
state, the nozzle suffers a considerable fusion loss, rather
than being prevented from suffering the loss. In this case,
since the powder line part is not always in contact With the
mold powder, the ordinary nozzle material parts including the
nozzle orifice part and inner tube part suffer a fusion loss .
Once the nozzle suffers a fusion loss, the flow of
the inert gas blown through the nozzle is deflected further
and this accelerates the fusion loss of the nozzle and/or alumina
deposition. The fusion loss of the nozzle results in steel
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contamination.
The nozzle according to the related-art technique 2-2,
which is "an immersion nozzle in which a refractory material
comprising spinel or a refractory material comprising spinel
and periclase is disposed in the part which comes into contact
with a molten steel" , shows better unsusceptibility to fusion
loss in molten steels than alumina/graphite nozzles in ordinary
use . A detailed explanation will be given below in this respect .
The present inventors revealed that the
alumina/graphite materials in ordinary use as immersion nozzle
materials generally undergo the following reactionswith molten
steels and are hence undesirable materials for use in producing
clean steel castings. Namely, since the molten steel has an
exceedingly low carbon concentration, the graphite (C (s) : solid
graphite) in the alumina/graphite nozzle material rapidly
dissolves in the molten steel through the following reaction .
C (s) ~ C Scheme (1)
Furthermore, (Fe0) penetrates into the alumina (A1203)
in the alumina/graphite material through the following reaction.
Fe(1) + O ~ (Fe0) Scheme (2)
Elements dissolved in the molten steel likewise penetrate.
For example, in the case of Mn as one of the dissolved elements,
(Mn0) penetrates into the alumina through the following reaction .
Mn + O ~ (Mn0) Scheme (3)
2 5 ( In schemes ( 2 ) and ( 3 ) , O and Mn represent oxygen and manganese
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dissolved in the molten steel, and Fe(1) represents an iron
ingredient in the molten steel).
The "A1203-Fe0" and "A1203-Mn0" yielded as a result of
the penetration of those substances react with inclusions in
the molten steel, such as, a , g . , "Fe0-Mn0" , to yield a liquid
slag comprising "A1203-Fe0-Mn0" . Namely, the alumina suffers
a fusion loss due to a combination of the two factors.
For enhancing spalling resistance, a technique is being
generally employed which comprises incorporating fused silica
into an alumina/graphite nozzle material. However, this
technique is undesirable because fused silica also suffers
a fusion loss in a degree equal to or higher than that for
alumina.
In the case of spinel, on the other hand, the amount
of (Fe0), (Mn0), or the like penetrating thereinto is small
and, even when inclusions such as Fe0-Mn0 deposit thereon,
the spinel retains its solid phase without forming a liquid
phase. Namely, the nozzle in which spinet is disposed in the
part coming into contact with a molten steel suffers a reduced
fusion loss and, hence, brings about a diminution in molten-steel
contamination.
However, production in which the part coming into contact
With a molten steel, the main body part, and the powder line
part are constituted by disposing different materials leads
to an increase in production cost. Furthermore, the use of
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a spinel material is ineffective in mitigating the fusion loss
of the immersion nozzle caused by a powder slag. This is
attributable to the fluorine ingredient in the powder slag.
A technique which is thought to be effective for
eliminating those problems is to use a mold powder free of
any fluorine ingredient or having a low fluorine ingredient
content (see the documents shown above with regard to the
prior-art techniques 3-1 and 3-2, i.e., JP-A-58-125349,
JP-A-51-93728, JP-A-50-86423, JP-A-5-208250, JP-A-51-67227,
JP-A-5-269560, and JP-A-51-132113).
However, since these mold powders contain no fluorine
ingredient or are mold powders having a low fluorine ingredient
content, they have poor suitability for viscosity regulation
and crystallization temperature regulation and often arouse
troubles such as steel breakout and casting cracking, making
stable casting impossible. Those mold powders have not been
put to practical use so far.
It can be seen from the above that it is difficult
to obtain a clean steel unless the fusion loss of the powder
line material of an immersion nozzle is eliminated.
In view of the above-described problems of prior-art
techniques, the present inventors proposed "a specific mold
powder (mold powder having a fluorine content lower than 3$
by weight and a viscosity at 1,300°C of from 4 P to 100,000
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P) " and developed an invention which is "a method of continuous
steel casting comprising using the specific mold powder in
combination with a specific immersion nozzle (immersion nozzle
comprising: spinel and/or spinel/carbon which constitutes Bart
or all of that part of the immersion nozzle which comes into
contact with a molten steel ; a powder line material constituting
the part which comes into contact with the mold powder and/or
a slag; and a main body material constituting the other part) "
(see JP-A-2001-113345).
The present inventors made further intensive
investigations after the development of that invention. As
a result, they have surprisingly found that even when "an
immersion nozzle which is constituted of a refractory material
comprising alumina as the main component" and in which the
powder line part also is cans tituted of the refractory material
is used, then use of the specific mold powder described above
enables the nozzle to suffer little fusion loss and no alumina
deposition and makes it possible to stably produce a clean
steel casting without the need of using this mold powder in
combination with the specific immersion nozzle described above .
The invention has thus been completed.
Accordingly, an object of the invention is to provide
a method of continuous steel casting which prevents steel
contamination due to refractories and makes it possible to
stably produce a highly clean steel casting and which further
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has an effect from the standpoint of immersion nozzle production
that the nozzle can be produced exceedingly easily because
the same "refractory material comprising alumina as the main
component" is used.
<Disclosure of the Invention>
The present inventors made intensive investigations
in order to overcome the problems described above and to
accomplish the object. As a result, based on that finding,
the inventors have invented "amethodof continuous steel casting
which comprises continuously casting a steel while feeding
a molten steel into a casting mold through an immersion nozzle
and supplying a mold powder into the casting mold, characterized
by using a combination of a mold powder having a fluorine content
lower than 3~ by weight and a viscosity at 1,300°C of from
4 P to I00, 000 P and an immersion nozzle constituted of a refractory
material comprising alumina as the main component".
It has hitherto been essential to use a "fluorine
ingredient" for reducing the viscosity of a mold powder and
for heat abstraction control. However, the inventors have
found that when a slag film having evenness in properties and/or
thickness is formed between the mold and a solidified shell,
then there is no need of relying on a fluorine ingredient.
Namely, i.t has been found that increasing the viscosity of
a mold powder enables the formation of an even slag film and
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this slag film performs the function of cuspidine
(3Ca0~2Si02~CaF2) (heat abstraction control) .
It has further been found that when the mold powder
has a rupture strength at 1,300°C of 3.7 g/cm2 or higher, a
continuous slag film can be formed and continuous casting is
possible . The mold powder to be used in the invention preferably
is one having a chemical composition comprising from 5 to 25$
by weight A1203, from 25 to 70~ by weight Si02, from 10 to 505
by weight CaO, up to 205 by weight MgO, and from 0 to 2~S by
weight F (unavoidable impurity).
The immersion nozzle to be used in combination with
the mold powder is an immersion nozzle constituted of a refractory
material comprising alumina as the main component. For example,
the refractory material comprises an alumina refractory and/or
an alumina-carbon refractory. It has been further found that
the immersion nozzle can be one in which the refractory "contains
one or more members selected from silica (Si02) , silicon carbide
(SiC) , boron carbide (84C) , silicon nitride (Si3N4) , aluminum
nitride (AlN) , zirconiumboride (ZrB2) , magnesiumboride (Mg3B2) ,
zirconium sulfate (ZrSOq), silicon (Si), and aluminum (Al)".
The molten steel to be cast may be any of all kinds
of steels, such as,e.g.,aluminum-killed steel, silicon-killed
steel, high-oxygen steel, stainless steel, steel for
electromagnetic steel sheets, calcium-treated steel,
high-manganese steel, free-cutting steel, boron steel, steel
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cord, case hardening steel, or high-titanium steel.
<Brief Description of the Drawings>
Fig. 1 is a view illustrating an example of the structure
of the immersion nozzle of the type having orifice parts which
a.s to be used in Examples according to the invention (and in
Comparative Examples).
Fig. 2 is a view illustrating another example of the
structure of the immersion nozzle of the type having orifice
parts which is to be used in Examples according to the invention
(and in Comparative Examples).
Fig. 3 is a view illustrating an example of the straight
type immersion nozzle having no orifice part which is to be
used in Examples according to the invention (and in Comparative
Examples).
In the figures, numeral 1 denotes an immersion-nozzle
inner tube part, which comes into contact with a molten steel,
2 an immersion-nozzle orifice part, which comes into contact
with a molten steel, 3 an immersion-nozzle powder line part,
which comes into contactwith amoldpowder, 4 an immersion-nozzle
main body part, and 5 a straight type immersion-nozzle tip
part, Which comes into contact with a molten steel.
<Best Mode for Carrying Out the Invention>
2 5 Modes for carrying out the invention will be explained
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below. The mold powder to be used in the invention is one
having a fluorine content lower than 3$ by weight and a viscosity
at 1,300°C of from 4 to 100,000 P, as stated above.
In case where the fluorine content in the mold powder
is 3~ by weight or higher, the immersion nozzle suffers an
increased fusion loss especially in the powder line part and
the refractory ingredients which have come into the steel
contaminate the molten steel, making it impossible to obtain
a clean steel.
Viscosities of the mold powder (viscosities at 1, 300°C)
lower than 4 P are undesirable because an uneven mold powder
flow generates and crystals of dicalcium silicate, tricalcium
silicate, and the like grow in the molten mold powder, resulting
in increased temperature fluctuations of the mold copper plates
and in unstable heat abstraction . On the other hand, viscosities
thereof exceeding 100,000 are undesirable because the powder
shows poor fusibility and a slag bear generates, making stable
casting impossible.
In the invention, the viscosity can be regulated, for
example, withAl203, Ca0/Si02, or the like. When theAl203 content
is high or the Ca0/Si02 content is low, the viscosity can be
regulated so as to be high.
The mold powder to be used in the invention preferably
further has a rupture strength at 1, 300°C of 3 . 7 g/cm2 or higher,
provided that the "rupture strength of the melted mold powder"
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is defined as the maximum load as measure at the time when
a cylindrical platinum rod with a diameter of 7 mm which is
being pulled out of the melt at a constant rate separates from
the liquid surface and the liquefied mold powder breaks into
droplets. Rupture strengths lower than 3.7 g/cm2 are
undesirable because the liquid layer in a slag film is apt
to break.
The mold powder to be used in the invention can be
produced from a base raw material such as portland cement,
wollastonite, or synthetic calcium silicate, an Si02 source
such as perlite or fly ash, an Na20, KzO, or Li20 source such
as a carbonate, glass powder, or frit powder, an Mg0 source
such as magnesium carbonate, Mg0 powder from seawater, or
dolomite powder, a B203 source such as borax, colemanite, glass
powder, or frit powder, and a carbonaceous raw material such
as coke powder, flaky graphite, or carbon black. However,
fluorides such as NaF and CaF2 are not included.
Specifically, themoldpowdercanbeproducedbysuitably
adding the Si02, Na20, K20, Li20, MgO, and B203 sources and the
carbonaceous raw material to the basic raw material and
regulating the viscosity With A1203, Ca0/Si02, or the like as
stated above . For example, the raw materials are mixed together
in such a proportion as to result in a chemical composition
which comprises from 5 to 25~ by Weight A1203, from 25 to 70~
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by weight Si02, from 10 to 50~ by weight CaO, from 3 to 20~
by weight one or more members selected from the group consisting
of Na20, LizO, and K20, up to 20$ by weight MgO, up to 3$ by
weight fluorine ingredient as an unavoidable impurity, and
from 0.5 to 8$ by weight carbon and in which the Ca0/Si02 weight
ratio is in the range of from 0.2 to 1.5. Thereafter, this
mixture is homogenized with a mixer to thereby obtain the mold
powder.
It is also possible to use the mold powder a.n a granular
form prepared by adding a liquid (e. g., water) to the powder
optionally together with an organic binder or inorganic binder
and granulating the mixture by a technique such as extrusion
granulation, stirring granulation, rolling granulation, flow
granulation, or spray granulation.
Material embodiments of the immersion nozzle to be
used in combination with the mold powder described above will
be explained next.
The material constituting the immersion nozzle in the
invention is a refractory material comprising alumina as the
main component. A preferred embodiment thereof is an alumina
refractory and/or an alumina-carbon refractory.
The alumina refractory and alumina-carbon refractory
may be ones which contain one or more members selected from
silica (Si02), silicon carbide (SiC), boron carbide (B4C),
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silicon nitride (Si3N4), aluminum nitride (A1N), zirconium
boride (ZrB2) , magnesium boride (Mg38z) , and zirconium sulfate
(ZrS04). Such a wide range of materials can be used.
In another preferred embodiment, the refractories
contain one or more of silicon (Si) and aluminum (Al) . As
a result of the incorporation of such a metal, the metal reacts
with the refractory material in especially the powder line
part of the immersion nozzle and/or with a component of the
air during use at high temperatures to yield a metal reaction
product. This metal reaction product strengthens the powder
line part and contributes to an improvement in life. In the
case where the powder line part contains carbon, the metal
functions also as an antioxidant for the carbon. Thus, by
incorporating the metal, an excellent immersion nozzle can
be provided. The content of silicon (Si) and aluminum (A1)
is preferably from 0.1 to 15~ by weight, more preferably from
1 to 8$ by weight. Contents thereof lower than 0.15 by weight
are undesirable because those effects of the metal cannot be
obtained. Contents thereof exceeding 155 by weight are
undesirable because a metal reaction product is yielded in
a large amount and this leads to destruction of the refractory
structure by the resultant volume increase and to the loss
of effects of the main component of the refractory material.
In the invention, the powder line part and main body
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part of the immersion nozzle can be made of the same material.
The reason for this is that the specific mold powder according
to the invention (mold powder having a fluorine content lower
than 3~ by weight and a viscosity at 1,300°C of from 4 P to
100,000 P) is used.
Hitherto, a zirconia/carbon material has been mainly
used as a material having high unsusceptibility to fusion loss
by mold powders containing a fluorine ingredient. Compared
to general refractory materials, this material is costly.
In addition, even with this material, the powder line part
suffers a considerable fusion loss and there have been cases
where this fusion loss is a factor determining the life of
the immersion nozzle.
However, according to the invention, use of the
high-viscosity mold powder containing almost no fluorine
ingredient or containing no fluorine ingredient has eliminated
the fusion loss by a fluorine ingredient almost completely
or completely. Because of this, there is no need of using
a zirconia/carbon material for constituting the powder line
part and the material described above (refractory material
comprising alumina as the main component) can be freely used
for the powder line part. As a result, it has become possible
to use the same material as that constituting the main body
part.
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<Examples>
The invention will be explained below in detail by
reference to Examples and Comparative Examples , but the invention
should not be construed as being limited to the following
Examples.
The structures of immersion nozzles usable in the
following Examples and Comparative Examples will be explained
below by reference to Figs . 1 to 3 . Fig. 1 is a view illustrating
an example of immersion nozzle structures of the type having
orifice parts, and Fig. 2 is a view illustrating another example
of immersion nozzle structures also having orifice parts.
Fig . 3 is a view illus trating an example of straight type immersion
nozzles having no orifice part.
The immersion nozzle shown in Fig. 1 is an immersion
nozzle of the type having orifice parts. In Fig. l, 1 denotes
an immersion-nozzle inner tube part, which comes into contact
with a molten steel; 2 denotes an immersion-nozzle orifice
part, which also comes into contact with a molten steel; 3
denotes a powder line part, which comes into contact with a
mold powder and/or a slag; and 4 denotes a main part of the
immersion nozzle.
As shown in Fig. 1, this immersion nozzle has a structure
in which the orifice parts 2 have been united with the main
body part 4 to constitute that region 2a of the immersion nozzle
orifice part which comes into contact with a molten steel.
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The immersion nozzle shown in Fig. 2 is an immersion
nozzle of the type having orifice parts like the immersion
nozzle shown in Fig. 1. However, this nozzle does not have
the united structure such as that shown in Fig. 1 (see "region
2a" in Fig. 1) , but is an immersion nozzle having a structure
in which that region 2b of the immersion-nozzle orifice parts
2 which comes into contact with a molten steel is made of the
same material . In Fig . 2 , numerates 1 to 4 have the same meanings
as shown above, i . a . , 1 denotes an inner tube part, 2 an orifice
part, 3 a powder line part, and 4 a main body part.
The immersion nozzle shown in Fig. 3 is a straight
type immersion nozzle having no orifice part unlike the immersion
nozzles shown in Figs. 1 and 2. In Fig. 3, numeral 5 denotes
a nozzle tip part, which comes into contact With a molten steel,
and the other numerals have the same meanings as shown above,
i . a . , 1 denotes an inner tube part, 3 a powder line part, and
4 a main body part.
The chemical compositions of the mold powders (sample
Nos. 1 to 7) used a.n the following Examples are shown in Table
l, and the chemical compositions of comparative mold powders
(sample Nos. 8 to 21) are shown in Table 2. In Tables 1 and
2 are further shown the "fluorine ingredient" , "viscosity (at
1,300°C)", and "rupture strength (at 1,300°C)" of each mold
2 5 powder .
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Incidentally, the mold powders of sample Nos. 1 to
7 , 8 to 10 , and 13 to 17 shown in Tables 1 and 2 are "powdered
products" obtained by mixing by means of a mixer so as to result
in the given chemical compositions. The other mold powders,
i . a . , sample Nos . 11, 12 , and 18 to 21, were "granulated products"
obtained by mixing raw powders, subsequently adding a solution
consisting of 90~ by weight water and 10$ by weight sodium
silicate thereto in an amount of from 20 to 30$ by weight to
produce a slurry, and spray-granulating and drying the slurry.
These granulated products have been regulated so as to finally
have the given chemical compositions.
Table 1. Chemical compositions of mold powders used in Examples
_ Sample 1 2 3 4 5 6 7
No.
Si02 36 39 50 49 48 31 31
Chemical A1z03 7 21 10 10 18 7 7
composi- Ca0 36 35 20 19 16 43 43
tion of Mg0 4 1 10 10 B 6 8
mold Na20+LizO+K20 5 2 6 8 6 8 6
powder, Mn0+Ba0+Sr0+B203 8 0 1 1 1 0 0
wt~ F 1 0 0 0 0 2 2
Total carbon amount3 2 3 3 3 3 3
Ca0 SiOZ 1.00 0.900.40 0.39 0.33 1.401.40
(weight ratio)
Fluorine 1 0 0 0 0 2 2
ingredient
(wt~)
Viscosity 30 20 40 50 100 5 5
(at 1300
C) (P)
Rupture 5 8 10 3.7 5 6 5
strength
(at 1300C)
(g/cm2)
Table 2(1). Chemical compositions of comparative mold powders
Sample No. ~ 8 ~ 9 10 11 12 13 14
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Si02 25 26 34 32 27 29 29
Chemical A1z03 9 5 3 3 2 12 11
composi- Ca0 28 27 38 37 32 30 32
tion of Mg0 7 9 10 12 10 11 7
mold Na20+LizO+K20 21 20 3 3 10 6 5
powder, Mn0+Ba0+Sr0+Bz03 0 0 0 0 1 1 4
wt~ F 5 8 8 10 12 8 9
Total 5 5 4 3 6 3 3
carbon
amount
Ca0/Si02 1.121.04 1.12 1.16 1.191.05 1.10
(weight
ratio)
Fluorine ient (wt~) 5 8 B 10 12 8 9
ingred
Viscosity 2.0 1.5 1.5 0.5 1.2 2.0 1.0
(at 1300
C) (P)
Rupture 3.5 3.0 3.2 1.0 2.5 3.0 2.0
strength
(at 1300"C)
(g/cm2)
Table 2(2). Chemical compositions of comparative mold powders
Sample 15 16 17 18 19 20 21
No.
Si02 30 30 29 27 26 25 22
Chemical A1z03 10 7 5 9 8 7 4
composi- Ca0 34 36 38 40 42 42 38
tion of Mg0 6 8 3 5 5 0 8
mold Na20+Li20+K20 8 6 10 3 2 5 6
powder, Mn0+Ba0+Sr0+8203 0 0 0 0 0 0 0
wt~ F 9 10 11 13 15 18 19
Total carbon amount3 3 4 3 2 3 3
Ca0 Si02 1.121.20 1.30 1.50 1.60 1.651.70
(weight ratio)
Fluorine 9 10 11 13 15 18 19
ingredient
(wt~)
Viscosity 1.8 1.3 1.0 0.9 0.8 0.3 0.2
(at 1300
C) (P)
- Rupture 2.7 2.4 2.8 1.3 1.5 0.7 0.5
strength
(at 1300"C)
( g/ cmz
)
(EXAMPLES 1 TO 17 AND COMPARATIVE EXAMPLES 1 TO 6)
Examples 1 to 17 are shown in Tables 3 and 4, and
Comparative Examples 1 to 6 are shown in Table 5.
In each of the following Examples 1 to 17 and Comparative
Examples 1 to 6, continuous casting was conducted while feeding
a molten steel ( "Kind of steel" in the tables) into a casting
mold through a nozzle and simultaneously supplying a mold powder
into the casting mold. The structure of the nozzle used in
each Example or Comparative Example is shown in the table in
22
. CA 02454946 2004-O1-23
terms of figure number. The mold powders used in the Examples
and Comparative Examples had the chemical compositions of sample
Nos . 1 to 21 shown in Tables 1 and 2 , and the respective sample
Nos . are shown in Tables 3 to 5 . Only the "fluorine ingredient" ,
"viscosity (at 1,300°C)", and "rupture strength (at 1,300°C)"
of each mold powder used are shown therein. In the tables,
"~" for the material in each nozzle part in the tables means
"~ by weight".
In each of the Examples and Comparative Examples , "s table
casting" , "nozzle fusion loss or alumina deposit amount (fusion
loss of each of inner tube, orifice part inside, and powder
line)", "steel cleanness", and "percentage of steel defects"
Were evaluated in the following manners, and the results of
the evaluations are shown in Tables 3 to 5.
Evaluation of Stable Casting
"Stable casting" indicates whether stable casting is
possible or not. The case in which no BO warning [method of
evaluation employing a system which foresees the occurrence
of B.O (breakout) based on a continuous measurement of the
mold surface temperature] was given during casting and in which
the immersion nozzle had no fusion rupture accident [accident
in which the immersion nozzle breaks during casting due to
a fusion loss of the powder line and/or a part in contact with
the molten steel] is indicated by "possible" , while the other
23
CA 02454946 2004-O1-23
cases are indicated by "impossible".
Evaluation of Nozzle Fusion Loss
"Nozzle fusion loss [mm/ (steel ton) ] " is given in terms
of the dimension of the nozzle fusion loss per ton of the steel
cast. As the nozzle fusion loss increases, not only the nozzle
life becomes short, but also the amount of impurities coming
into the steel as a result of the fusion loss increases and
the steel a.s more contaminated accordingly.
Alumina Deposit Amount
The amount of alumina deposited when aluminum-killed
steel was cast is shown. Alumina deposition occurs on the
inner tube and/or orifice inside in the nozzle. Large alumina
deposit amounts make stable casting impossible. In some cases,
the deposit prevents the molten steel from passing through
the nozzle, resulting in casting stoppage. Consequently, the
less the alumina deposition, the better the nozzle.
Evaluation of Steel Cleanness
"Steel cleanness" was evaluated in terms of the degree
of sliver mars. Index "100" indicates the case in which the
steel has no sliver defects, while index "0" indicates the
case in which the steel cannot be a commercial product due
to sliver defects. Indexes between these values were
statisticlly graded for the evaluation.
Evaluation of Percentage of Steel Defects
"Percentage of steel defects" was evaluated based on
24
CA 02454946 2004-O1-23
surface cracks. The case in which the steel has negligible
surface cracks is indicated by "~", the case in which the
steel cannot be a commercial product due to surface cracks
is indicated by "X", and the case in which the steel can be
a commercial product by processing the steel surface is indicated
by .. 0 .. .
CA 02454946 2004-O1-23
Table 3(1). Examples 1-5
Example
1 2 4 5
Noz- truc- (Fig. (Fig. (Fig. (Fig. (Fig.
1) 2) 1) ) 1)
zle ure
part Materia
A1203 80 70 0 60 65
InnerC 20 30 10 30 30
tube SiOZ 0 0 0 10 5
part Kind
of
additive- - -
Additive
amount - - - - _
AlZO, 80 70 90 6 65
NozzleOri- C 20 30 10 30 30
fice Si02 0 0 0 10 5
part Kind
of
additive- - -
Additive
amount - - - - _
Pow- A120, BO 70 9 5
der C 20 30 10 30 30
line Si0= 0 0 0 10 5
part
and Kind - - - - _
of
main additive
body Additive- - - - -
part amount
Samp [5 1 ] 4] 1]
a
No.
Fluorine
Mold ingredient 0 1 2 0 1
(wt%)
pow- viscosity
der (at 100 30 5 50 30
1300C)
(P)
Rupture
strength
(at 5.0 5.0 5.0 3.7 5.0
1300C)
(g/cm=)
Kin Al-ki A -kil -ki Al-kil Al-ki
of led a a ed led
atee
St possib poasi possiblepossib possible
a a a a
casting
NozzleInner
fusiontube 0 0 0 0 0
loss Orifice
or
Evalu-alumi-inside 0 0 0 0 0
ation na Powder
de-
posi-line 0 0 0 0 0
tion
Steel 10 10 1 1 0
c
eanness
Percentage
of
steel p O O O W
defects
26
CA 02454946 2004-O1-23
Table 3(2). Examples 6-10
Example
6 7 B 9 0
Noz- truc- (Fig. (Fig. (Fig. (Fig. (Fig.
1) 2) 1) 2) 1)
zle ure
part Materia
A1z03 70- 45 70 60 100
InnerC 30 35 30 25 0
tube SiOz 0 20 0 15 0
part Kind
of
additive SiC:H,C Si:SiC Si~N,:A1AlN:ZrBzMg3Hz:A1
Additive
amount 3:3 2:5 3:2 5:4 2:3
A1z03 70 45 70 60 100
NozzleOri- C 30 35 30 25 0
five SiOz 0 20 0 15 0
part Kind
of
additive SiC:H,C Si:SiC Si3N,:A1AlN:ZrHzMg3Bz:A1
Additive
amount 3:3 2:5 3:2 5:4 2:3
Pow- AlzO, 70 45 70 60 100
der C 30 35 30 25 0
line SiOz 0 20 0 15 0
part
and Kind SiC:H,C Si:SiC Si3N,:A1AlN:ZrHzMg3Hz:A1
of
main additive
body Additive 3:3 2:5 3:2 5:4 2:3
part amount
Sample ] ] (1] ( ] (2
No.
Fluorine
Mold ingredient 2 0 1 2 0
(wt%)
pow- W
scosity
der (at 5 40 30 5 20
1300C)
(P)
Rupture
strength
(at 6.0 10 5.0 6.0 B.0
1300C)
(g~~z)
high- stainlessSi-killedelectro-Ca-
Kind oxygen steel steel magnetictreated
of
steel
steel steel steel
sheet
St possib poasib possiblepossiblepossib
a a a a
casting
Nozzle Inner
fusion tube 0 0 0 0 0
loss Orifice
or
Evalu-alumi- inside0 0 0 0 0
ationna Powder
de-
poai- line 0 0 0 0 0
tl0n
Steel 10 10 1 10 1
cleanness
Percentage
of
steel ~ Q O O CJ
defects
27
CA 02454946 2004-O1-23
Table 9. Examples 11-17
Example
11 12 13 14 15 16 17
Noz- truc- (Fig. (Fig. (Fig. (Fig. (Fe (Fe
. . (
g g g.
zle ure 2) 2) 2) 2) 2) 2) 2)
part Materia
A120, 65 100 1 100 100 0 100
Inner C 30 - - - - _ _
tube Si02 5 - - - _ _
part Kind
of
additiveZrSiO,- Zr02 - - -
Additive
amount 5 - 20 - - -
A120, 65 idU 75 0 9
NozzleOri- C 30 - 30 30 25 20 10
fice Si02 5 - - - _ _ -
part Kind
of
additiveZrSiO,- Zr02 - - - -
Additive
amount 5 - 20 - _ _ _
-
Pow- AlzO, 6~ 1 0 1 70 75 80 90
der C 30 - - 30 25 20 10
line SiOa 5 - - - _ - _
part
and Kind
of
main additiveZrSiO,- - - _ _ _
body Additive
part amount 5 - - - _ - _
Samp No. ~ 7 [77 [4 [ [ 5 [
a
Fluorine
Mold ingredient 1 2 0 0 0 0 0
(wt%)
Pow- viscosity
der (at 30 5 50 50 40 100 20
1300C)
(P)
Rupture
strength
(at 5.0 5 3.7 10 5 8 1
1300C) 0
(g/cmz) .
high- oase A - Ca- elec- stain-steel
Mn hard- killedtreat-tro- less cord
Kind steel ening ed mag- steel
of
steel
steel steel netic
steel
sheet
St posse-posse-posse-posse-posse-posse-possi-
a
casting
ble ble ble ble ble ble ble
NozzleInner
fusiontube 0 0 0 0 0 0 0
Evalu-loss Orifice
or
ation alumi-inside 0 0 0 0 0 0 0
na Powder
de-
pose- line 0 0 0 0 0 0 0
tion
Steel 1 1 100 100 10 0 100
c
eanness
Percentage
of
steel ~ O O O O O
defects
28
CA 02454946 2004-O1-23
Table 5. Comparative Examples 1-6
Comparatme
Example
1 2 4 5
Noz- truc- (Fig. (Fig. (Fig. (Fig. (Fig. (Fig.
1) 2) 2) 2) 2) 1)
zle ure
part Materia
A1z03 100 100 100 70 80 100
InnerC - - - 30 20 -
tube SiOz - - - - - -
part Kind
of
additive - - - - - -
Additive
amount - - - _ _ _
z03 100 70 90- 70 80 100
Noz- Ori- C - 30 10 30 20 -
zle five SiOz - - - - -
part Kind
of
additive - - - - - -
Additive
amount - - - - - -
Pow- A1z03 ~0 70 90 60 70 50
der C - 30 10 20 20 20
line SiOz - - - - 10 -
part
and Kind -
of
main additive - - ZrOz - ZrOz
body Additive -
part amount - - 20 - 30
Sample [8] [10 [1 ] [ ] [1 [ 1]
No.
F
uorine
Mold ingredient 5 8 12 18 B 10
(wt%)
pow- Viscosity
der (at 2 1.5 1.2 0.3 2.0 0.5
1300C)
(P)
Rupture
strength
(at 3.5 3.2 2.5 0.7 3.0 1.0
1300C)
(g/cmz)
elec- Ca- steel Al- stain- high-
tro- treatedcord killed less oxygen
Kind mag- steel steel steel
of
steel
netic
steel
sheet
Stable impos- impos-impos- impos- impos- impos-
casting
sible sible sible aible aible aible
Nozzle Inner
fusion tube 0.02 0.03 0.04 0.01 0.05 0.02
Evalu-loss Orifice
or
ation alumi- inside0.07 0.05 0.08 0.04 0.09 0.03
na Powder
de-
posi- line 0.50 0.30 0.60 0.20 0.60 0.40
tion
Stee 4 40
c
eanness
Percentage
of
steel X X X X X X
defects
29
CA 02454946 2004-O1-23
Tables 3 to 5 show the following. When the mold powders
specified in the invention Were used, "evaluation of stable
casting" was "possible", i.e., stable casting was possible,
even with each of the immersion nozzles in which the inner
tube part, orifice parts , powder line part, and main body part
were all made of an alumina/carbon refractory (Examples 1 to
11) and the immersion nozzle in which these parts Were all
made of an alumina refractory (Example 12), i.e., even with
the same refractory. Moreover, even when the powder line part
and the main body part were made of the same material as in
Examples 1 to 17, stable casting was likewise possible.
Furthermore, the "nozzle fusion loss or alumina
deposition" was "0" in each case and the "steel cleanness"
was "100". The "percentage of steel defects" also Was "O"
in each case and the surface cracks in each steel were negligible .
In contrast, in each of Comparative Examples 1 to 6,
in which the mold powder specified in the invention was not
used, "stable casting" was "impossible" , i . a . , the steel could
not be stably cast, as apparent from Table 5. The Comparative
Examples were inferior also in "nozzle fusion loss", "steel
cleanness", and "percentage of steel defects". Furthermore,
even the nozzles in which the inner tube part was made of the
same material as in Examples were inferior. This is because
during casting, a flow in a direction opposite to the direction
of the flow of the molten steel occurs simultaneously. Because
" ~ CA 02454946 2004-O1-23
of this, the powder is carried by the reverse flow and comes
into contact with the inner tube part to cause a fusion loss,
etc., giving the poor results shown in Table 5.
A comparison between the evaluation results for
Comparative Examples 1 to 6 and the evaluation results for
Examples 1 to 17 according to the invention shows the following.
Stable casting was possible only when the mold powders specified
in the invention were used. Since the nozzles suffered an
extremely reduced fusion loss, the nozzle life was improved.
Furthermore, almost no sliver defects were observed and the
steels had negligible surface cracks.
The immersion nozzles of Figs . 1 and 2 used in Examples
1 to 17 given above (the immersion nozzle of Fig. 3 also is
usable of course) and the mold powders shown in Table 1 are
mere examples for the invention . The invention is not limited
to such constitutions, and various combinations within a range
specifying the invention can be used.
<Industrial Applicability>
As described above in detail, the invention is
characterized by a method of continuous steel casting in Which
a mold powder containing virtually no fluorine ingredient,
which enhances fusion loss, is used in combination with an
immersion nozzle constituted of a refractory material comprising
31
r
CA 02454946 2004-O1-23
alumina as the main component.
Due to this constitution, the following marked effects
are produced. Impurities attributable to refractory
ingredients are prevented from coming into the molten steel
and alumina deposition within the nozzle is inhibited.
Consequently, stable casting is possible and an ultraclean
steel can be obtained. In addition, since defects in the casting
which are attributable to a refractory have been considerably
diminished, the yield of castings is improved.
The immersion nozzle to be used in the invention suffers
almost no fusion loss and, hence, can have an improved nozzle
life. It has high performance and is inexpensive due to a
reduced wall thickness and a reduced weight. The use of this
immersion nozzle a.n combination with the mold powder specified
in the invention produces an industrially exceedingly highly
valuable effect that the combination is applicable to all kinds
of steels such as, e.g., aluminum-killed steel, silicon-killed
steel, high-oxygen steel, stainless steel, steel for
electromagnetic steel sheets, calcium-treated steel,
high-manganese steel, free-cutting steel, boron steel, steel
cord, case hardening steel, or high-titanium steel.
Furthermore, from the standpoint of immersion nozzle
production, the nozzle has an advantage that it can be produced
exceedingly easily because the same "refractory material
comprising alumina as the main component" is used.
32
