TITLE OF THE INVENTION
Castable refractory material
TECHNICAL FIELD
[0001]
The present invention relates to a castable refractory material
using an organic binder as a binder.
BACKGROUND ART
[0002]
The following description will be made by taking, as a non-limiting
example of a castable refractory material, a coating material for
use in forming a coating layer of a tundish.
[0003]
A tundish for use in continuous casting of steel has a structure
in which a refractory lining is provided on an interior side of a
shell. In some cases, a coating layer is formed on a surface of the
refractory lining, for the purpose of facilitation of treatment for
residual steel, protection of the refractory lining, etc. The
coating layer is made of a coating material which is a castable
refractory material.
[0004]
As disclosed in the following Patent Document 1, the coating
material comprises a refractory powder consisting of a coarse particle
fraction having a particle size of 1 mm or more and a fine particle
fraction having a particle size of less than 1 mm, and a binder, as
with other castable refractory materials. As the refractory powder,
it is common to use a magnesia-based raw material. Known examples
of the binder include an inorganic binder such as sodium silicate,
and an organic binder such as phenolic resin.

LIST OF PRIOR ART DOCUMENTS
[PATENT DOCUMENTS]
[0005]
Patent Document 1: JP 2006-007317A
Patent Document 2: JP 2000-176612A
Patent Document 3: JP 04-130066A
Patent Document 4: JP 4273099B
SUMMARY OF THE INVENTION
[TECHNICAL PROBLEM]
[0006]
During use of the tundish, the coating layer receives heat from
molten steel and reaches a temperature of greater than 1000°C.
[0007]
An inorganic binder is a low-melting-point material. Thus, while
the inorganic binder is effective in imparting strength, in an
intermediate temperature range, for example, of 600 to 1000°C, it
becomes a factor causing deterioration in strength and corrosion
resistance, in a high temperature range, for example, of greater than
1000°C.
[0008]
In the course of a temperature rise up to 1000°C, an organic binder
is formed into a carbon bond while undergoing dissipation of a volatile
matter contained therein. The carbon bond is less wettable to slag,
and is not a low-melting-point material, so that it (organic binder)
is superior to the inorganic binder, in terms of an effect of imparting
strength and corrosion resistance in the high temperature range of
greater than 1000°C.

[0009]
However, even in the carbon bond, stability of strength in the
high temperature range of greater than 1000°C is far from satisfactory.
The carbon bond is apt to undergo degradation in a high temperature
range due to oxidation.
[0010]
The problem with degradation of the carbon bond in a high
temperature range is true, not only for the coating material, but
also for any castable refractory material using an organic binder
as a binder, in general.
[0011]
In particular, the degradation of the carbon bond is more likely
to occur under an oxidation atmosphere. However, even under a
non-oxidation atmosphere, the carbon bond can undergo decomposition
or dissipation in a high temperature range. Therefore, there is a
need for a castable refractory material having excellent stability
of strength in a high temperature range, irrespective of whether it
is used in an oxidation atmosphere or in a non-oxidation atmosphere.
[0012]
As a result of researches, the inventors of this application found
that, even under the condition of using an organic binder, stability
of strength in a high temperature range can be enhanced by adding
calcined olivine to a fine particle fraction having a particle size
of less than 1 mm, in a refractory powder. This is probably because
calcined olivine having a particle size of less than 1 mm is more
likely to be sintered due to the fine particle size, so that it is
moderately sintered in a high temperature range where the carbon bond
is liable to be damaged, thereby contributing to imparting strength.
[0013]

In the technical field of refractory materials, olivine has
heretofore been known as a refractory powder. However, there have
not been found any cases where olivine having a particle size of less
than 1 mm and preliminarily calcined is combined with an organic binder.
This will be specifically described below.
[0014]
The Patent Document 2 discloses an example where olivine is used
for a castable refractory material serving as a coating material (see
Table 1 of the Patent Document 2) . However, it is uncertain whether
the olivine in the Patent Document 2 is a preliminarily-calcined type.
Even supposing that the olivine is a preliminarily-calcined type,
it is used only in a coarse particle fraction having a particle size
of 1 mm or more. Thus, this olivine is less likely to be sintered,
so that it is difficult to contribute to imparting strength in a high
temperature range.
[0015]
The Patent Document 3 discloses an example where olivine having
a particle size of less than 1 mm is added to a castable refractory
material for use in a cast application to a molten metal vessel.
However, olivine in the Patent Document 3 must be a non-calcined type.
During use of the refractory material, non-calcined olivine undergoes
volume expansion to thereby form cracks in a microstructure of the
refractory material, while releasing crystal water (see line 2, upper
left column to line 5, upper right column, page 3 in the Patent Document
3) . Therefore, strength development in the refractory material is
rather suppressed. Strength development by sintering of olivine is
brought out only if olivine is a preliminarily- calcined type.
[0016]
The Patent Document 4 discloses an example where calcined olivine

having a particle size of less than 1 nun is used in a castable refractory
material for use in spray repair of a steelmaking electric furnace
(see Tables 2 and 3 in the Patent Document 4) . However, in the Patent
Document 4, a binder is entirely composed of an inorganic binder.
Therefore, an absolute amount of usage of the inorganic binder is
naturally increased, and a large amount of low-melting-point material
derived from the inorganic binder will exist in a high temperature
range, so that it becomes impossible to thoroughly bring out the
strength development effect by sintering of calcined olivine.
[0017]
It is an object of the present invention to provide a castable
refractory material which is less likely to undergo deterioration
in strength in a high temperature range, for example, of greater than
1000°C, even though an organic binder is used as a binder.
[SOLUTION TO THE TECHNICAL PROBLEM]
[0018]
According to one aspect of the present invention, there is provided
a castable refractory material which comprises: a refractory powder
consisting of a coarse particle fraction having a particle size of
1 mm or more and a fine particle fraction having a particle size of
less than 1 mm; and an organic binder, wherein calcined olivine is
added to the fine particle fraction, and an amount of usage of the
organic binder is in the range of 1 mass% to 20 mass%, with respect
to and in addition to 100 mass% of the refractory powder.
[EFFECT OF THE INVENTION]
[0019]
In a high temperature range where a carbon bond derived from the

organic binder is liable to undergo degradation, the calcined olivine
having a particle size of less than 1 mm is moderately sintered to
enhance strength of a resulting applied body. This makes it possible
to suppress the deterioration in strength in the high temperature
range, even under the condition of using an organic binder.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
FIG. 1 is a schematic fragmentary sectional view of a tundish.
DESCRIPTION OF EMBODIMENTS
[0021]
A castable refractory material of the present invention will now
be described in detail, based on one embodiment thereof. A castable
refractory material according to this embodiment is formed by adding
at least an organic binder to a refractory powder.
[0022]
The refractory powder consists of a coarse particle fraction
having a particle size of 1 mm or more, and a fine particle fraction
having a particle size of less than 1 mm. While a mass ratio between
the coarse particle fraction and the fine particle fraction is not
particularly specified, it will be naturally set based on common
technical knowledge in the art, in view of allowing a particle size
composition to provide a particle structure closer to a close-packed
structure, thereby obtaining practical corrosion resistance, etc.
Typically, it is preferable that the refractory powder (100 mass%)
consists of 25 to 65 mass% of the coarse particle fraction, and 35
to 75 mass% of the fine particle fraction.
[0023]

As used in this specification, the term "particle size of d or
more" means sizes of particles which are to be left over a sieve having
an opening size of d, defined in JIS-Z8801, and the term "particle
size of less than d" means sizes of particles which can pass through
the sieve.
[0024]
It is essential that calcined olivine is added to the fine particle
fraction.
[0025]
As used in this specification, the term "calcined olivine" means
a material obtained by calcining peridotite as a natural product,
at 800°C or more. Peridotite is a complex primarily consisting of
olivine, and can partially accompany a serpentinized peridotite.
[0026]
Peridotite comprises primary mineral phases, such as forsterite
(2MgO • SiO2), enstatite (MgO • SiO2) , firelight (2FeO • SiO2) , and
serpentine (3MgO • 2SiO2 • H2O).
[0027]
In peridotite, a decomposition reaction, for example, as expressed
by the following formulas (1) and (2), is started from about 800°C:
2FeO • SiO2 + O2 - Fe2O3, Fe3O4 + SiO2 ---(1)
3MgO • 2SiO2 • 2H20 - Mg2SiO4 + SiO2 + H2O ---(2)
[0028]
The formula (2) represents release of crystal water. If the
release of crystal water occurs during use of the refractory material,
strength development in the refractory material is suppressed. On
the other hand, calcined olivine obtained by preliminarily calcining
peridotite at 800°C or more has already been subjected to release
of crystal water, so that it does not substantially contain crystal

water, or contains crystal water in an amount less than that in the
original peridotite. This prevents deterioration in strength which
would otherwise be caused by the release of crystal water.
[0029]
Table 1 presents one specific example of a chemical composition
of calcined olivine. In Table 1, Igloss represents ignition loss.
[0030]
TABLE 1
[0031]
As presented in Table 1, calcined olivine is made up mostly of
MgO. A melting point of MgO is as high as 2850°C. However, in the
remainder, calcined olivine contains SiO2 and Fe2O3 in the free state,
because the decomposition reaction expressed by the formulas (1) and
(2) has already been done. As a result, a melting point of calcined
olivine is a eutectic point of the components, so that it becomes
significantly lower than the melting point of MgO. For example,
calcined olivine has a melting point of 1600 to 1800°C.
[0032]
For the purpose of ensuring removal of crystal water contained
in peridotite, and ensuring formation of the free SiO2 and Fe2O3, a
calcination temperature of peridotite is preferably equal to or
greater than 1000°C, more preferably equal to or greater than 1200°C.
[0033]
The calcined olivine added to the fine particle fraction is more
likely to be sintered, because it has a particle size which is as
fine as of less than 1 mm. The term "sintering" means a phenomenon

that particles are joined together through a solid-phase reaction
at a temperature less than a melting point, without the interposition
of a liquid phase. The calcined olivine having a particle size of
less than 1 mm can undergo sintering, for example, at a temperature
of about 1000 to 1200°C or a temperature lower than the range, and
the sintering state will be maintained until at least the melting
point of the calcined olivine.
[0034]
Therefore, the calcined olivine having a particle size of less
than 1 mm has an advantageous effect of being able to enhance strength
of a resulting applied body through sintering, in at least a
temperature range from a lower limit of about 1000 to 1200°C to an
upper limit of about 1600 to 1800°C. This temperature range is a
temperature range where a carbon bond derived from the organic binder
is liable to undergo degradation.
[0035]
That is, the castable refractory material according to this
embodiment can add strength in at least the above temperature range,
by means of sintering of calcined olivine, so that it becomes possible
to suppress deterioration in strength due to the degradation of the
carbon bond, even under the condition of using an organic binder.
[0036]
In contrast, an inorganic binder such as sodium phosphate is
already in a liquid state at 1000°C due to its excessively low melting
point, so that it has difficulty in bringing out a strength imparting
effect at a temperature around 1000°C. Further, even if a refractory
powder other than calcined olivine, such as a magnesia-based raw
material, an alumina-based raw material or a silica-based raw material,
is added to the fine particle fraction, it has difficulty in undergoing

sintering at a temperature around 1000°C due to its excessively high
melting point. Sintering in the above temperature range where the
carbon bond is liable to undergo degradation is a unique effect
obtainable when calcined olivine is used in the fine particle
fraction.
[0037]
A lower limit of a ratio of calcined olivine to the fine particle
fraction is not particularly limited. However, in view of improving
sureness of the strength imparting effect of calcined olivine,
calcined olivine preferably accounts for 4 mass% or more of the fine
particle fraction.
[0038]
An upper limit of the ratio of calcined olivine to the fine particle
fraction is not particularly limited, but calcined olivine may account
for the whole of the fine particle fraction, or an additional
refractory powder other than calcined olivine may be contained in
the fine particle fraction. However, the ratio of calcined olivine
to the fine particle fraction may be limited to 53 mass% or less.
This makes it possible to suppress excessive sintering of calcined
olivine and maintain good thermal spalling resistance.
[0039]
In the case where an additional refractory powder other than
calcined olivine is contained in the fine particle fraction, a type
of the additional raw material is not particularly limited. For
example, it is possible to use one or more selected from the group
consisting of: a magnesia-based raw material, such as magnesia clinker
or fused magnesia; a dolomite-based raw material, such as dolomite
clinker; a calcia-based raw material, such as calcia clinker; an
alumina-based raw material, such as fused alumina or bauxite; a

spinel-based raw material, such as spinel clinker; other oxide raw
materials; a carbon-based raw material, such as carbon black; a
silicon carbide-based raw material; a silicone nitride-based raw
material; other non-oxide raw materials; and a used refractory waste
comprising a primary component consisting of at least one of them.
[004 0]
In the case where an additional refractory powder other than
calcined olivine is contained in the fine particle fraction, the
remainder other than calcined olivine is preferably composed of a
raw material having a melting point greater than that of calcined
olivine. This makes it possible to suppress excessive sintering in
a matrix area made of the fine particle fraction and achieve an
improvement in thermal spalling resistance. Commonly-used
refractory powders, at least the above exemplified raw materials,
have a melting point greater than that of calcined olivine. Among
them, a magnesia-based raw material has a relatively high melting
point, and comprises a primary component consisting of MgO as with
calcined olivine, so that it contributes to enhancing microstructural
unity or continuity of the matrix area made of the fine particle
fraction.
[0041]
A raw material making up the coarse particle fraction is not
particularly limited. For example, it is possible to use one or more
of the above exemplified raw materials, in the same manner as that
in the fine particle fraction.
[0042]
Preferably, calcined olivine is also added to the coarse particle
fraction. In this case, it becomes possible to achieve enhanced
corrosion resistance. This is because calcined olivine functions to

increase a viscosity of slag through dissolution of SiO2 component, and
form a viscous protective film on a surface of the refractory material
according to this embodiment, so as to exert an effect of preventing
penetration of slag. In the present invention, calcirred olivine is
essentially added to the fine particle fraction. Thus, the addition
of calcined olivine to the coarse particle fraction makes it possible
to enhance microstructural unity or continuity in the coarse and fine
particle fractions, thereby contributing to enhancement in strength
and corrosion resistance.
[0043]
In view of improving sureness of such an effect, 35 mass% or more
of the coarse particle fraction is preferably composed of calcined
olivine. The coarse particle fraction has a particle size which is
as coarse as 1 mm or more, so that it is less likely to be sintered
as compared to the fine particle fraction. Thus, even if a large
amount of calcined olivine is used in the coarse particle fraction,
the problem of excessive sintering never occurs.
[0044]
Preferably, the coarse particle fraction comprises particles
having a particle size of 3 mm or more. In this case, supposing that
crack occurs in the refractory material according to this embodiment,
crack propagation can be blocked by the particles . A maximum particle
size of the coarse particle fraction is not particularly limited.
For example, it is preferably equal to or less than 10 mm or less,
more preferably equal to or less than 8 mm or less.
[0045]
It is essential that an amount of usage of the organic binder is
in the range of 1 mass% to 20 mass%, with respect to and in addition
to 100 mass% of the refractory powder. This is because, if the amount

is less than 1 mass%, it becomes impossible to ensure minimum strength
in a resulting applied body. On the other hand, if the amount is
greater than 20 mass%, crack occurs due to deterioration in volume
stability. The amount of the organic binder is preferably in the range
of 2 mass% to 10 mass%, more preferably in the range of 3 mass% to
6 mass%, with respect to and in addition to 100 mass% of the refractory
powder.
[0046]
As the organic binder, it is possible to use one or more selected
from materials each capable of forming a carbon bond under a hot
condition, for example, resin, sugar, and bitumen such as pitch and
tar. Examples of the resin include a phenolic resin, a furan resin,
an epoxy resin, a melamine resin and a terpene resin. A hardening
agent, such as hexamethylenetetramine, may be used in combination
with the resin. In this case, the hardening agent is encompassed
within a concept of the organic binder. Examples of the sugar include:
monosaccharides, such as glucose, fructose, galactose and mannose;
and disaccharides, such as sucrose, maltose, lactose, cellobiose and
trehalose. The pitch and tar may be a petroleum-derived type or may
be a coal-derived type. A solvent, such as a polyalcohol-containing
solvent, may be used in combination with the resin or pitch. In this
case, the solvent is encompassed within the concept of the organic
binder. In the case where the pitch and the resin are used in
combination, it is preferable to use a solvent compatible with both
of them.
[0047]
An inorganic binder may be used in combination with the organic
binder. For example, as the inorganic binder, it is possible to use
one or more selected from the group consisting of silicate salt,

phosphoric salt, boric acid, borate salt, borax, frit and cement.
Examples of the silicate salt include sodium silicate, potassium
silicate and calcium silicate. Examples of the phosphoric salt
include sodium hexametaphosphate, sodium pyrophosphate, sodium
tetrapolyphosphate, odium tripolyphosphate, sodium ultraphosphate,
potassium phosphate, lithium phosphate, magnesium phosphate, and
aluminum phosphate. Examples of the cement include alumina cement,
magnesia cement and Portland cement. The frit is a glass powder
obtained by subjecting a starting raw material comprising one or more
selected from the group consisting of silicate salt, phosphoric salt,
lithium carbonate, sodium fluoride and borate salt, to melting, rapid
cooling, and pulverization, and examples thereof include
borosilicate-based glass and zircon-based glass.
[0048]
The inorganic binder has a melting point of less than 1000°C,
typically, of 300 to 900°C, i.e., cannot maintain the form of a bond
by itself in a high temperature range of greater than 1000°C, so that
it hardly exhibits the strength imparting effect.
[0049]
In this embodiment, the inorganic binder is used to promote
sintering of calcined olivine, instead of being used to form a bond.
That is, the use of the inorganic binder causes lowering of interface
energy between calcined olivine particles in the fine particle
fraction, thereby allowing the calcined olivine to undergo sintering
from a relatively low temperature, for example, of about 700 to 800°C.
This expands a temperature range where strength is imparted by the
calcined olivine in the fine particle fraction. Therefore, it
becomes possible to suppress deterioration in strength, even in a
situation where degradation of a carbon bond can be started from 1000°C

or less, for example, where the refractory material according to this
embodiment is used in an oxidation atmosphere.
[0050]
In the case where the inorganic binder is used to promote sintering
of calcined olivine, an amount of usage thereof may be equal to or
less than 50 mass% in terms of a ratio with respect to the entire
binders. As long as it is added in the above amount, deterioration
in corrosion resistance due to formation of a low-melting-point
material is negligibly small.
[0051]
The castable refractory material according to this embodiment may
consist only of the refractory powder and the organic binder (or the
organic and inorganic binders). Alternatively, it may further
comprise an additional additive.
[0052]
For example, as the additional additive, it is possible to use
one or more selected from the group consisting of organic fiber, metal
fiber, metal powder, viscosity regulator, and dispersant. Examples
of the organic fiber include vinylon fiber, polyethylene fiber,
polypropylene fiber, and pulp fiber. The organic fiber can
effectively facilitate thermal insulation and stress relaxation under
a hot condition, while enhancing work efficiency. Examples of the
metal fiber include stainless-steel fiber, Fe fiber, Cu fiber, Al
fiber, and Ni fiber. Examples of the metal powder include Fe powder,
Cu powder, Al powder, metal Si powder, and Fe-Si alloy powder.
Examples of the viscosity regulator include: coal- or
petroleum-derived oil, such as kerosene, heavy oil, creosote oil,
and anthracene oil; vegetable oil; animal oil; ethers; lactams, such
as caprolactam; acetanilides, such as acetanilide and

acetoacetanilide; and alkylphenols, such as butylphenol. The
viscosity regulator can effectively prevent dust generation and
promote fluidity. In this connection, the aforementioned solvent to
be used in the binder is excluded from a concept of the viscosity
regulator. Examples of the dispersant include anionic modified
lignin sulfonate, and β-naphthalene sulfonate.
[0053]
A tundish dry coating process using the above castable refractory
material as a coating material will be described below.
[0054]
FIGS. 1(a) to 1(d) are schematic fragmentary sectional views of
a tundish. This tundish has a structure in which a refractory lining
2 is provided on an interior side of a shell 1.
[0055]
First of all, as illustrated in FIG. 1(a), a castable refractory
material 4 is placed on the entire bottom surface of the tundish,
while maintaining a powder form without adding any water thereto,
and evened out. Then, a core 3 is inserted into the tundish. The
core 3 is formed, for example, using a metal plate such as an iron
plate, as a hollow container-like member having an outer surface with
a configuration corresponding to that of an inner surface of the
tundish.
[0056]
Then, as illustrated in FIG. 1(b), the castable refractory
material 4 is packed into an interspace defined between a sidewall
of the tundish and the core 3, while maintaining a powder form without
adding any water thereto. Preferably, during the packing of the
castable refractory material 4, vibration is imparted to the castable
refractory material 4 to allow the castable refractory material 4

to be closely packed while filling the interspace.
[0057]
As above, a preparatory state has been completed in which the
castable refractory material is packed between the core 3 inserted
in the tundish and the refractory lining 2 of the tundish, while
maintaining a powder form without adding any water thereto.
[0058]
In the case where a coating layer is formed only on the sidewall
of the tundish, the placement of the castable refractory material
on the entire bottom surface of the tundish illustrated in FIG. 1(a)
is unnecessary.
[0059]
Then, as illustrated in FIG. 1(c), the castable refractory
material 4 is heated up to 100 to 400°C, from an inside of the core
3 through the core 3. The heating is performed, for example, using
a burner and a hot-air blower. A heating time may be set, for example,
in the range of 2 to 20 minutes. Based on this heating, the organic
binder in the castable refractory material 4 is softened to exhibit
shape retainability.
[0060]
Then, as illustrated in FIG. 1(d), the core 3 is removed from the
tundish. In this manner, a coating layer 5 is obtained.
[0061]
Then, the tundish is actually used. During use of the tundish,
the coating layer 5 receiving heat from molten steel reaches a
temperature of greater than 1000°C. This causes the organic binder
in the coating layer 5 to be formed into a carbon bond, thereby
imparting strength to the coating layer 5.
[0062]

However, the carbon bond is apt to undergo degradation in a high
temperature region of greater than 1000°C, due to oxidation.
Moreover, the coating layer 5 has a thickness which is as small as
about 5 to 100 mm. Thus, in the coating layer 5, it is particularly
important to achieve stabilization in strength. In this regard,
calcined olivine having a particle size of less than 1 mm and
constituting the coating layer 5 is sintered in a temperature range
where oxidation of the carbon bond is more likely to occur, thereby
imparting strength to the coating layer 5, so that it becomes possible
to achieve stabilization in strength of the coating layer 5.
[0063]
Then, when the coating layer 5 is worn out due to continuous usage
of the tundish, a coating layer is formed again. For this purpose,
after stopping the use of the tundish, residual steel and a residue
of the previously formed coating layer 5 are removed from a surface
of the refractory lining 2, and the aforementioned process will be
repeated again.
[0064]
A process for applying the castable refractory material according
to this embodiment, to the refractory lining of the tundish, is not
particularly limited to the aforementioned dry coating process. For
example, it is possible to add water to the castable refractory
material, and apply resulting slurry onto the refractory lining by
spraying or troweling.
[0065]
However, in use for a coating layer, when water is used for
application, the castable refractory material and the refractory
lining adhere excessively tightly to each other during application,
baking of the castable refractory material onto the refractory lining

is liable to become excessive. Moreover, the castable refractory-
material according to this embodiment contains easily-sinterable
calcined olivine having a particle size of less than 1 mm, so that
the baking is much more liable to become excessive.
[0066]
Differently from general repairing castable refractory materials
such as a bake repair material, it is desired that baking of the coating
layer onto a backing layer, i.e., the refractory lining is suppressed
to some extent in view of ease of a removal work therefor. In the
case where the castable refractory material according to this
embodiment is used to form a coating layer, the dry coating process
can be employed to prevent a degree of adhesion between the castable
refractory material and the refractory lining from becoming
excessively high. Thus, even though easily-sinterable calcined
olivine having a particle size of less than 1 mm is contained, it
becomes possible to suppress excessive baking onto the refractory
lining 2.
[EXAMPLES]
[0067]
Compositions and evaluation results of castable refractory
materials in Inventive Examples and Comparative Examples are
presented in Tables 2 to 4. The calcined olivine presented in Table
1 was used as calcined olivine in fine and coarse particle fractions
in Tables 2 to 4.
[0068]
Evaluation items in Tables 2 to 4 will be described below.
[0069]
Hot Strength: A castable refractory material was packed into a

form having an internal size of 30 × 30 × 120 mm, and dried at 200°C.
Subsequently, after removal of the form, a resulting dried castable
refractory material was evaluated. Specifically, a bending strength
under a hot condition at 1200°C and with a span of 100 mm was measured,
and, based on the measured hot bending strength, a relative evaluation
was performed on a 4-level scale of double circle, o, ∆, and ×. In
the relative evaluation on the 4-level scale, the double circle, o,
∆, and × indicate that a result of the evaluation becomes better in
a direction from × to double circle.
[0070]
Thermal Spalling Resistance: A castable refractory material was
packed into a form, and solidified by heating at 1000°C for 10 minutes.
A resulting sample was subjected to a repetitive cycle consisting
of immersion into molten steel at 1500°C and leaving at room
temperatures, and the number of cycles before the sample reaches
breakup was measured. Based on the measured number of cycles, a
relative evaluation was performed on a 4-level scale of double circle,
o, ∆, and ×. In the relative evaluation on the 4-level scale, the
double circle, o, ∆, and × indicate that a result of the evaluation
becomes better in a direction from × to double circle.
[0071]
Corrosion Resistance: A castable refractory material was packed
into a form, and solidified by heating at 1000°C for 10 minutes. A
resulting sample was subjected to a corrosion test using a
high-frequency induction furnace. A mixture of converter slag and
billet combined at a mass ratio of 1 : 1 was used as a corrosive agent,
and the sample was corroded at 1500°C for 3 hours. Then, an average
wear size was measured. Based on the measured average wear size, a
relative evaluation was performed on a 4-level scale of double circle,

o, ∆, and ×. In the relative evaluation on the 4-level scale, the
double circle, o, ∆, and × indicate that a result of the evaluation
becomes better in a direction from × to double circle.
[0072]
TABLE 2

[0073]
Table 2 presents evaluation results of samples obtained by
variously changing a ratio of calcined olivine to the fine particle
fraction.
[0074]
Sample 1 is Comparative Example in which no calcined olivine is
added to the fine particle fraction. As can be seen in Sample 2, even
when the ratio of calcined olivine to the fine particle fraction is
as small as 4 mass%, an effect of improving the hot strength at 1200°C
can be observed as compared to Sample 1. As can be seen in Samples
3 to 6, when the ratio of calcined olivine to the fine particle fraction
is equal to or greater than 18 mass%, the effect of improving the
hot strength at 1200°C becomes prominent.
[0075]
When the ratio of calcined olivine to the fine particle fraction
is equal to or greater than 18 mass%, the corrosion resistance is
also improved as compared to the case where he ratio of calcined
olivine to the fine particle fraction is 0 mass% and 4 mass%. This
is probably because calcined olivine functions to increase a viscosity
of the corrosive agent through dissolution of SiO2, and form a viscous
protective film on a surface of the refractory material, so as to
exert an effect of preventing penetration of the corrosive agent.
[0076]
However, as seen in Sample 6, when the ratio of calcined olivine
to the fine particle fraction is greater than 53 mass%, the thermal
spalling resistance is deteriorated. This is probably because
sintering of calcined olivine in the fine particle fraction becomes
excessive. Considering the above results in a comprehensive manner,
the ratio of calcined olivine to the fine particle fraction is

preferably set in the range of 4 mass% to 53 mass%.
[0077]
TABLE 3

[0078]
Table 3 presents evaluation results of samples obtained by
variously changing an amount of usage of each of organic and inorganic
binders, based on Sample 3 in Table 2.
[0079]
As can be seen in Sample 7, when the organic binder is contained
in an amount of less than 1 mass%, with respect to and in addition
to 100 mass% of the refractory powder, an amount of formation of carbon
bond is excessively small, so that the hot strength at 1200°C is
deteriorated, and the thermal spalling resistance and the corrosion
resistance are deteriorated.
[0080]
In Sample 7 where the binder is entirely composed of the inorganic
binder, the effect of improving the hot strength at 1200°C is not
observed at all, even though calcined olivine is contained in the
fine particle fraction. This is probably because a large amount of
liquid phase derived from a low-melting-point material isf prmed under
a hot condition, so that calcined olivine fails to thoroughly bring
out the strength development effect by sintering thereof.
[0081]
Sample 19 is a castable refractory material in which the organic
binder is contained in an amount of 25 mass%, with respect to and
in addition to 100 mass% of the refractory powder. In this case, an
amount of the organic binder is relatively increased as compared to
the case where the organic binder is contained in an amount of 20
mass% or less, with respect to and in addition to 100 mass% of the
refractory powder, volume stability is deteriorated due to shrinkage
or expansion during carbonization or decomposition, thereby causing
the occurrence of crack.

[0082]
As above, in view of the results in Table 3, it is essential that
the organic binder is contained in the range of 1 mass% to 20 mass%,
with respect to and in addition to 100 mass% of the refractory powder.
This is because, if the content is less than 1 mass%, it becomes
impossible to ensure minimum strength in a resulting applied body.
On the other hand, if the content is greater than 20 mass%, crack
undesirably occurs. The ratio of the organic binder is preferably
in the range of 2 mass% to 10 mass%, more preferably in the range
of 3 mass% to 6 mass%, with respect to and in addition to 100 mass%
of the refractory powder.
[0083]
TABLE 4

[0084]
Table 4 presents evaluation results of samples obtained by
variously changing a ratio of calcined olivine to the coarse particle
fraction, based on Sample 11 in Table 3.
[0085]
When 35 mass% or more of the coarse particle fraction is composed
of calcined olivine, an effect of further improving the corrosion
resistance is observed. This is probably because calcined olivine
in the coarse particle fraction forms a highly-viscous silicate film
through dissolution of SiO2 to thereby exhibit an effect of suppressing
penetration of the corrosive agent into a matrix area.
[0086]
Although the present invention has been fully described based on
a specific embodiment, it is to be understood that the present
invention is not limited thereto, but various changes and
modifications will be apparent to those skilled in the art.
INDUSTRIAL APPLICABILITY
[0087]
The castable refractory material of the present invention is
widely usable for formation or repair of linings of not only a tundish
but also a converter, an AOD furnace, a VOD furnace, a vacuum degassing
furnace such as an RH type and a DH type, other refining furnaces,
an electric furnace, a ladle, a molten iron pan, a molten iron runner,
and other molten metal vessels.
[0088]
In the castable refractory material of the present invention, a
usage environment after application may be an oxidation atmosphere
or a non-oxidation atmosphere. In particular, a significance of the

present invention is in that it is suitably used under an oxidation
atmosphere where a carbon bond is more likely to undergo degradation.
[0089]
The castable refractory material of the present invention can be
usable in both of a warm application and a hot application. As used
in this specification, the term "hot application" means an application
to be performed under a condition that a temperature of a target
surface is equal to or greater than 600°C, and the term "warm
application" means an application to be performed under a condition
that a temperature of a target surface is in the range of normal
temperature to less than 600°C.
[0090]
Examples specific to a warm application process include a dry
coating process which comprises the steps of: preliminarily setting
a state in which a castable refractory material is packed into an
interspace defined between a core inserted into a molten metal vessel
and a refractory lining of the molten metal vessel, in the form of
a power without adding any water thereto; and heating the packed
castable refractory material through the core, and then removing the
core from the molten metal vessel. The examples specific to the warm
application process further include troweling, stamping and ramming.
[0091]
Examples specific to a hot application process include a process
of packing the castable refractory material into a combustible bag
such as a flexible container bag or a vinyl bag; and throwing the
combustible bag into a target region.
[0092]
Examples common to the hot and worm application processes include
a spray application process of sending the castable refractory

material into a hollow pipe to convey the castable refractory material
on airflow and spray the castable refractory material onto a target
surface. In the spray application process, water may be added to the
castable refractory material within the hollow pipe and/or within
a nozzle connected to a distal end of the hollow pipe. Even in the
case where water is used during the application, such water is excluded
from a component of the castable refractory material of the present
invention. Further, an inorganic binder may be added to the castable
refractory material within the hollow pipe and/or within a nozzle
connected to a distal end of the hollow pipe, as an optional component
of the castable refractory material of the present invention.
[0093]
A form of the castable refractory material of the present invention
is not particularly limited. The castable refractory material may
be prepared in powder form, for example, by using a powdered binder,
such as a powdered phenolic resin. Alternatively, the castable
refractory material may be prepared in wet form to an extent capable
of being conveyed on airflow, for example, by using a liquid binder
as a part of the binder, or by using a small amount of viscosity
regulator in combination. Alternatively, the castable refractory
material may be prepared in slurry or rammed-earth form by using a
liquid binder, or by using a viscosity regulator in combination with
a powdered binder. It is apparent to those skilled in the art that
the form of the castable refractory material is adjustable depending
on the application process.
EXPLANATION OF CODES
[0094]
1: shell

2: refractory lining
3: core
4: castable refractory material
5: coating layer

We Claim:
1. A castable refractory material comprising: a refractory powder
consisting of a coarse particle fraction having a particle size of
1 mm or more and a fine particle fraction having a particle size of
less than 1 mm; and an organic binder, wherein calcined olivine is
added to the fine particle fraction, and an amount of usage of the
organic binder is in the range of 1 mass% to 20 mass%, with respect
to and in addition to 100 mass% of the refractory powder.
2. The castable refractory material as defined in claim 1, wherein
calcined olivine is also added to the coarse particle fraction, and
wherein 35 mass% or more of the coarse particle fraction is composed
of calcined olivine.
3 . A tundish comprising a coating layer formed by a dry coating process
using the castable refractory material as defined in claim 1 or 2.