CA 03037462 2019-03-19
DESCRIPTION
TITLE OF INVENTION
A REFRACTORY MATERIAL FOR SLIDING NOZZLE PLATE AND A METHOD
FOR PRODUCING THE SAME
TECHNICAL FIELD
[0001]
The present invention relates to a refractory material for a sliding nozzle
plate (hereinafter,
also referred to as "plate") for use in opening and closing control and flow
rate control during
operation of discharging molten steel, particularly molten steel having a low
concentration of free
oxygen, from a vessel such as a ladle or a tundish, in a steelmaking process,
and a method for
producing the refractory material.
BACKGROUND ART
[0002]
A surface roughening of a sliding surface, which is one main type of damage of
a plate,
is a phenomenon that a structure of the sliding surface serving as an
operating surface during
casting is embrittled, leading to the occurrence of secondary phenomena such
as abrasion, wear,
and spalling. This surface roughening is considered to be caused by exertion
of a complex
influence of several factors such as chemical factors and physical factors. It
is considered that
oxidation and decarburization often serve as a trigger of the surface
roughening, wherein oxidation
is caused by gas-phase oxidation due to oxygen in atmospheric air and liquid-
phase oxidation due
to oxygen in molten steel, and decarburization is caused by elution of carbon
into molten steel. It
is also considered that molten steel, or components in the molten steel, such
as inclusions and slag,
infiltrate in, adhere to, or react with the structure of the operating surface
embrittled by oxidation
and decarburization, and further the resulting infiltrated or adhered layer
causes spalling of the
structure, leading to acceleration of the surface roughening.
[0003]
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Meanwhile, recently, oxidation and decarburization mechanisms different from
simple
gas-phase oxidation, liquid-phase oxidation due to oxygen in molten steel and
decarburization due
to elution of carbon into molten steel have been reported.
For example, in the following Non-Patent Document 1, based on a test in which
three
types of steel consisting of extremely-low carbon Al-killed steel (carbon
concentration: 20 ppm),
low-carbon Al-killed steel (carbon concentration: 410 ppm) and ultralow carbon
Si-killed steel
(carbon concentration: 20 ppm) were placed in an electric furnace and
subjected to reaction with
a simple system-type sample composed of an alumina fine powder and carbon,
under a temperature
condition of 1560 C in an Ar atmosphere replaced under vacuum, evaluation and
consideration
of an interfacial structure of the sample are made. As a result of the
reaction with the extremely-
low carbon Al-killed steel (carbon concentration: 20 ppm), formation of an
embrittled layer having
a thickness of about 200 um on the operating surface of the sample, i.e.,
disappearance of carbon
and A1203 grains, was ascertained. Similarly, in
the low-carbon Al-killed steel (carbon
concentration: 410 ppm), formation of the embrittled layer having a thickness
of about 100 IIM
from which carbon and A1203A1 grains disappeared was ascertained.
Further, in the following Non-Patent Document 2, after undergoing operation of
pouring
molten steel, such as Al-killed steel, having a low concentration of free
oxygen, a sliding surface
of a plate was observed to ascertain formation of an embrittled layer from
which carbon and A1203
grains disappeared.
[0004]
As above, during the operation of pouring molten steel, such as Al-killed
steel, having a
low concentration of free oxygen, an embrittled layer is considered to be
formed in a part of the
sliding surface of the plate in contact with the molten steel or in a surface
of the plate exposed to
an inner bore space (this surface will hereinafter be referred to as
"operating surface") of the plate,
thereby leading to the occurrence of the surface roughening phenomenon.
However, a detailed
mechanism, an improvement method, etc., for the surface roughening have not
been sufficiently
studied.
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CITATION LIST
[NON-PARENT DOCUMENT]
[0005]
Non-Patent Document 1: Proceedings of the 1st Iron and Steel Refractories
Committee,
November 21, 2013, p. 180 ¨ p. 187
Non-Patent Document 2: Proceedings of the 3rd Iron and Steel Refractories
Committee,
November 26, 2015, p. 167 ¨ p. 174
SUMMARY OF INVENTION
[TECHNICAL PROBLEM]
[0006]
A technical problem to be solved by the present invention is to provide a
refractory
material for a plate, capable of allowing a sliding surface of the plate to
become less likely to
undergo surface roughening during operation of pouring molten steel such as Al-
killed steel, and
a method for producing the refractory material for the plate.
Further, the technical problem to be solved by the present invention is to
provide a
refractory material for a plate, which is suitable for the operation of
pouring molten steel having a
low concentration of free oxygen, and a method for producing the refractory
material for the plate.
[Solution to Technical Problem]
[0007]
As a result of various researches of the inventor about the mechanism of
surface
roughening on the sliding surface during the operation of pouring molten steel
such as Al-killed
steel, particularly molten steel having a low concentration of free oxygen, it
was found that the
aforementioned embrittled layer in which carbon and Al2O3 grains has
disappeared is formed by
the occurrence of oxidation-reduction reaction between carbon and oxide, etc.
in the refractory
material, and surface roughening accelerates by damage of the embrittled
layer.
[0008]
More specifically, carbon in the refractory material is oxidized by oxygen (0)
in an Al2O3
component, a SiO2 component, a ZrO2 component, etc., which are main components
in the
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refractory material, and becomes gas phase as CO gas and disappears, and
thereby decarburization
is caused. Further, an A1203 component, a SiO2 component, a ZrO2 component,
etc. are reduced
by carbon to generate gas phase species such as Al gas, A120 gas, SiO gas, and
carbide such as
ZrC, SiC, etc. Many of the generated gas phase species are considered to
migrate to an operating
surface and elute into the molten steel. Also, it is considered that a part of
the SiO gas forms SiC
in the refractory structure, and similarly to the generation of ZrC, when the
carbide is generated
from the oxide, its volume shrinks and many voids are generated in the
refractory structure
adjacent to the operating surface to form an embrittled layer.
[0009]
Further, in an inner bore of the plate during casting of molten steel, when
the degree of
opening of the inner bore is reduced, i.e., the opening is narrowed, a region
where the molten steel
is not filled is generated. In this region, the degree of the narrowing
becomes larger, the degree
of pressure reduction becomes larger. Thus, generally, a casting time will be
extended. It was
also found that, in some cases, as compared to a sliding surface of a lower
plate member of the
plate, a sliding surface of an upper plate member of the plate to be exposed
to such pressure
reduction for a longer time is more significantly roughened, because, in a
structure adjacent to the
sliding surface of the upper plate member, an embrittled layer from which
carbon, A1203 grain and
the like disappeared becomes thicker, and the depth of infiltration of the
molten steel or the like
becomes larger.
[0010]
From these facts, the inventors found that formation of the embrittled layer
or the surface
roughening phenomenon described above is influenced by temperature, time, and
pressure of the
inner bore space in addition to oxygen concentration in molten steel. Then,
the inventors found
that when the free oxygen concentration in molten steel is 30 ppm or less, the
higher the
temperature, the longer the time, and the greater the extent of the negative
pressure in the inner
bore space, the greater the degree of formation of the embrittled layer or
surface roughening.
[0011]
More specifically, in the refractory structure around the operating surface,
in addition to
Al2O3 grains, aggregate grains such as A1203 - ZrO2 based raw material and
ZrO2 - mullite added
4
as a low thermal expandable raw material have also been observed to suffer
significant
alteration. And it was also ascertained that this alteration also tended to be
larger in the
upper plate than in the lower plate under the throttling pouring condition for
a long time.
Further, it was ascertained that in the A1203 - ZrO2 based raw material, the
ZrO2 grains
in the raw material are altered into ZrC, whereas in the ZrO2 - mullite, the
SiO2
component in the mullite region of the particle disappears, only A1203
remains, and the
SiO2 component gasifies and migrates on the surface layer of the ZrO2 -
mullite particle
to exist as SIC. Moreover, it was confirmed that not only the 5i02 component
of the
mullite region but also the A1203 component disappears as the alteration
progresses.
Further, as for the ZrO2 grains, it was confirmed that the ZrO2 grains were
altered to ZrC
similarly to the ZrO2 grains in the A1203 - ZrO2 raw material.
[0012]
All of these phenomena are caused mainly by the reduction action of carbon in
the refractory structure, and under negative pressure conditions, the
reduction reaction
of the oxide components such as 5i02, ZrO2, and A1203 in the refractory
structure for
the plate with carbon progresses even more.
[0013]
These mechanisms can mainly be represented by the reactions shown by the
following formulas 1 to 5.
5i02 (s) + 3C (s) =SiC (s) +2C0 (g) Formula 1
3A1203.2Si02 (s) +12C (s) = 3A1203 (s) +2SiC (s) +4C0 (g) +12C (s) Formula 2
ZrO2 (s) +3C (s) =ZrC (s) +2C0 (g) Formula 3
A1203 (s) +3C (s) =2A1 (g) +3C0 (g) Formula 4
A1203 (s) +2C (s) =A120 (g) +2C0 (g) Formula 5
Date recue/Date Received 2020-08-20
[0014]
As the result of calculating the reactions of these Formulas 1 to 5 under a
temperature condition of 1550 C using thermodynamic calculation software Fact
SageTM, it was found that the reactions prone to progress more under the
negative
pressure condition. In addition, it was found that the reactions are more
likely to
progress more in the order of (1)> (2)> (3)> (4) P-- (5), and the raw
materials for general
use in the above-mentioned refractory material for the plate are prone to
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alter in the order of mullite, ZrO2 - mull ite > A1203 - Zr02 > A1/03.
Further, according to this
calculation, it was found that although the reduction reactions (4) and (5) by
the carbon of A1203
do not progress at a normal pressure of 1 atm, in the case where a small
amount of a SiO2
component is contained, a reaction occurs in a very small amount from 1 atm.
This shows that
when the SiO2 component is contained, the above-mentioned reduction reaction
occurs also on the
sliding surface in a region which becomes atmospheric pressure or positive
pressure during casting
to form the embrittled layer, causing surface roughening.
[0015]
From these findings, the refractory material for the sliding nozzle plate of
the present
invention is constructed mainly based on the following policies.
(1) The amount of carbon component should be kept to the minimum necessary.
(2) The amount of the SiO2 component and the amount of the ZrO2 component
should be
kept to the minimum necessary.
(3) The amount of a metal Al component should be kept to the minimum
necessary.
(4) The refractory structure should be densified.
Here, the above-mentioned "minimum necessary" means approximately the minimum
relative amount/degree necessary in consideration of balancing of strength,
thermal shock
resistance, corrosion resistance, etc., after employing other alternative
means.
[0016]
In addition, the refractory material for the sliding nozzle plate of the
present invention
contains an A1203 component as a main component in addition to an A1404C
component. The
A1903 component, in particular, corundum, has the required properties in the
most balanced
manner such as corrosion resistance, abrasion resistance, heat resistance,
thermal expansion
property, etc. necessary as a sliding nozzle plate. Therefore, the refractory
material for the sliding
nozzle plate of the present invention also contains corundum as an A1203
component as a main
component.
[0017]
On the other hand, when the amount of the carbon component described above (1)
is
reduced, formation of the embrittled layer can be suppressed. However, the
thermal shock
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resistance deteriorates due to an increase in elastic modulus or the thermal
expansion coefficient,
the progress of sintering by heat receiving during casting, etc., and edge
chipping of the plate,
radial cracks, etc., occur, which also cause deterioration of durability. In
addition, when the
amount of the SiO2 component and the amount of the ZrO2 component described
above (2) is
reduced, formation of the embrittled layer can be suppressed, but then the
thermal shock resistance
is lowered, and edge chipping of the plate, radial cracks, etc., occur, which
also cause deterioration
of durability.
[0018]
Therefore, in the present invention, the thermal shock resistance is increased
by
containing an A1404C component in an amount of 15 to 45 mass% which has a
lower thermal
expansion than corundum. The A1404C component is a main component of an
aluminum
oxycarbide composition and has a thermal expansion coefficient of about 4 x 10-
6 K, which is
about half of that of a corundum, and thus has a high effect of reducing the
thermal expansion
coefficient. In addition, the A1404C component is reduced under coexistence of
carbon as shown
in the following formula 6.
2A1404C (s) + 3C (s) = 2A1203 (s) +A14C3(s) + 2C0 (g) Formula 6
And according to the calculation under the temperature condition of 1550 C
using Fact
Sage, it was found that the reaction of this formula 6 occurs even at 1 atm.
[0019]
On the other hand, as a result of observing the structure around the operating
surface after
actually using a plurality of plates to which the aluminum oxycarbide
composition is applied, it
was ascertained that a small altered layer having a thickness of about several
tens of micrometers
is formed only around the surface of the aluminum oxycarbide grains and the
deeper structure
remains less altered. From this, it was found that the reaction represented by
the above Formula
6 occurs only in the surface layer of the aluminum oxycarbide composition on
the surface of the
operating surface. Further, from the above Formula 6, the above altered layer
is considered to be
composed of Al2O3 and Al4C3, and both A1203 and A1IC3 are more stable than
Zr02 and SiO2
under coexistence of carbon, and thus they are considered to function as a
protective layer for the
aluminum oxycarbide composition. From these, it was found that the aluminum
oxycarbide
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=
composition has higher stability under a reducing atmosphere at high
temperature than a
composition of Al2O3 - ZrO2 based composition, ZrO2 - mullite, and A1203 -
SiO2 based
composition, and is capable of sustaining low thermal expansion property for a
long time, and thus
it is difficult for the embrittlement of the structure due to the alteration
of the composition itself to
progress.
[0020]
Although the metal Al component in the above (3) mainly hasP an effect of
increasing the
strength by oxidation, it also has strong reducing action. The amount of the
metal Al component
should be kept to the minimum necessary to inhibit the reaction such as mainly
excessive oxidation
to suppress deterioration of the thermal shock resistance and to inhibit
formation of the embrittled
layer due to the reduction of the oxide.
[0021]
The aforementioned mechanisms (reactions) progress through pores in the
refractory
material, and thus increasing the denseness of the refractory structure
contributes to suppression
of formation of the embrittled layer or surface roughening. However, the pores
are necessary to
some extent and cannot be eliminated entirely from the viewpoint of production
because the pores
are also responsible for mitigation functions of thermal and mechanical stress
of the refractory
structure. Therefore, the densification of the refractory structure in the
above (4) needs to be
adjusted mainly in terms of balancing with thermal shock resistance.
[0022]
It is a widely common practice to impregnate with tar, pitch or a
thermosetting resin to
reinforce a carbon source and perform the densification. However, the carbon
added to the
refractory structure in this way is active and excess carbon is present, which
is thus likely to
accelerate formation of the embrittled layer. Further, with respect to such
densification, it can be
realized by other means, and thus in the present invention, it is preferable
free of such impregnating
step.
[0023]
8
Based on the above findings, the present invention is a refractory material
for a
sliding nozzle plate and a method for producing the refractory material for
the sliding
nozzle plate in the following embodiments 1 to 5.
1. A
refractory material for a sliding nozzle plate for use in casting of steel,
the
refractory material containing an A1404C component in an amount of 15 to 45
mass%, a
free carbon component in an amount of 2.0 to 4.5 mass%, a SiO2 component in an
amount of 0.5 to 4.0 mass%, and a metal Al component in an amount of 1.0 mass%
or
less (including zero), with the remainder including an A1203 component as a
primary
component, wherein the refractory material includes a surface serving as a
sliding
surface, and has a gas-permeability of 5x10-17 m2 to 40x10-17 m2, as measured
for said
refractory material including said surface and in a direction perpendicular to
said
surface, according to J1S-R2115 (2008), and an apparent porosity of 8.0% to
11.0 %, as
measured according to J1S-R2205.
2_ The refractory material according to embodiment 1, which has a thermal
expansion coefficient of 0.5 to 0.6 A as measured in a nitrogen atmosphere at
1000 C
by a non-contact method as described in J1S-R2207-1, and a bending strength of
15
MPa to 40 MPa as measured at room temperature according to J1S-R2213 (1995).
3. The refractory material according to embodiment 1 or 2, wherein the steel
has
a free oxygen concentration of 30 ppm or less as measured in a molten state of
the
steel during the casting.
4. A method for producing the refractory material as defined in any one of
embodiments 1 to 3, the method comprising the steps of:
shaping a mixture containing a metal Al or an Al-containing alloy, wherein a
total
amount of a metal Al component in the metal Al or the Al-containing alloy is
2.0 to 10.0
mass%, with respect to 100 mass% of the mixture; and
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Date recue/Date Received 2020-08-20
subjecting the mixture to heat treatment in a non-oxidizing atmosphere at 1000
C or more to adjust the content of the metal Al component in the refractory
material to
become 1.0 mass% or less (including zero).
5. The method according to embodiment 4, which is free of a step of
impregnating the refractory material with tar, pitch, or a thermosetting
resin.
[0024]
9a
Date recue/Date Received 2020-08-20
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In the present invention, the term ''free oxygen in molten steel" means
dissolved oxygen
in molten steel and does not include oxygen contained in inclusions in molten
steel present in the
form of oxide. Also, in the present invention, the term "free carbon
component" means a carbon
component that is present alone and excluding carbon components present in the
form of a
compound with other elements, regardless of crystallinity, shape, etc.
[EFFECT OF THE INVENTION]
[0025]
The present invention can significantly reduce a surface roughening on a
sliding surface
of a sliding nozzle plate in casting of steel such as Al-killed steel,
particularly even when the
opening degree is small and the degree of throttling is large or when casting
for a long time. This
makes it possible to obtain stable high durability.
In particular, in casting of steels having a free oxygen concentration in
molten steel of 30
ppm or less, in which has heretofore tended to become large in damage, the
present invention can
significantly reduce a surface roughening on a sliding surface of a sliding
nozzle plate. This makes
it possible to obtain stable high durability.
DESCRIPTION OF EMBODIMENTS
[0026]
A refractory material for a plate of the present invention contains an A1404C
component
in an amount of 15 to 45 mass%. If the content of the A1404C component is less
than 15 mass%,
the refractory material has a low effect of reducing the thermal expansion
coefficient and has
insufficient thermal shock resistance. If the content of the A1404C component
exceeds 45 mass%,
the thermal expansion amount of the refractory material for the plate becomes
relatively smaller
than the thermal expansion amount of a metal band shrink-fitted to an outer
periphery of the
refractory material, resulting in reduction in the binding force of the
refractory material for the
plate, so that cracks is more likely to occur or expand. In addition, due to
shifting of the metal
band, and particularly during reusing of the plate, problems of deterioration
in workability and
safety during handling such as detaching of the plate, are likely to occur.
[0027]
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The refractory material for the plate of the present invention contains a free
carbon
component in an amount of 2.0 to 4.5 mass%. If the content of the free carbon
component is less
than 2.0 mass%, the refractory material becomes easily wettable with oxides
such as slag, so that
oxide inclusions and slag in molten steel are more likely to adhere to and
infiltrate into an operating
surface of the plate and facilitate surface roughening. In addition, the
effect of suppressing
sintering between oxides to inhibit decrease or increase in elastic modulus is
deteriorated, so that
the thermal shock resistance is deteriorated, and cracks is more likely to
occur or expand. If the
content of the free carbon component exceeds 4.5 mass%, the embrittlement of
the structure is
accelerated by disappearance of carbon due to oxidation in the portion exposed
to the outside air.
Furthermore, according to the above Formulas 1 to 5, oxides constituting the
refractory material
also disappear together with carbon in the refractory structure. As a result,
the embrittlement of
the structure is more likely to progress, and surface roughening is easily
facilitated.
[0028]
The refractory material for the plate of the present invention contains a SiO2
component
in an amount of 0.5 to 4.0 mass%. The SiO2 component contributes to
improvement in refractory
strength and densification of the structure depending on its starting material
or its existence form.
Further, although the metal Al component contributes to improvement of
corrosion resistance and
oxidation resistance, densification of the structure, it generates A14C3 due
to heat receiving,
particularly, during casting, and this Al4C3 hydrates to break up the
structure in some cases. For
suppressing hydration of Al4C3, the SiO2 component is effective. In order to
suppress the
hydration of A14C3, it is necessary that the SiO2 component is contained in an
amount of 0.5 mass%
or more, and If the content is less than 0.5 mass%, it is impossible to
achieve a sufficient hydration
suppressing effect. On the other hand, as shown in Formulas 1 and 2, the SiO2
component reacts
partly with carbon under a high temperature condition and precipitates as SiC
and disappears as
SiO (g). However, alteration to SiC is accompanied by a decrease in volume,
and thus it is also
one factor that deteriorates the structure. Further, as described above,
according to the calculation
using Fact Sage, although the reduction reactions shown in Formulas (4) and
(5) by the carbon of
A1203 do not progress at 1 atm which is a normal pressure, in the case where a
small amount of a
SiO2 component is contained, a reaction occurs in a very small amount from 1
atm. The reduction
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= CA 03037462 2019-03-19
reaction of A1203 is one factor that facilitates embrittlement of the
refractory structure. In order
to suppress the deterioration of the structure due to the reduction reaction
or disappearance of the
SiO2 component and the A1203 component, the content of the SiO2 component
needs to be 4.0
mass% or less.
[0029]
In the refractory material for the plate of the present invention, the content
of the metal
Al component is set to 1.0 mass% or less (including zero). If the content of
the metal Al component
is 1.0 mass% or less, the refractory material contributes the effect of
suppressing oxidation of free
carbon component or A1404C component in the refractory structure, improvement
of corrosion
resistance, densification of refractory structure, etc., without largely
changing the refractory
structure due to heat receiving at the time of use. However, If the content of
the metal Al
component exceeds 1.0 mass%, it is difficult to ensure the stability of the
refractory structure
depending on the casting time, the kind of steel, the number of uses, etc.,
and rather, causing
deterioration in durability.
[0030]
The remainder of the refractory material for the plate of the present
invention other than
the above-mentioned components is mainly composed of an Al2O3 component as a
corundum.
This is because Al2O3 as corundum has a melting point of 2060 C, which is
excellent in heat
resistance, and has excellent corrosion resistance against foreign ingredients
such as FeO. Further,
in addition to the A1203 component, the remainder can contain, for the purpose
of preventing
oxidation, carbide components such as small amounts of SiC, B4C, Al4C3, etc.,
nitride components
such as Si3N4, BN, AIN, etc., and a metal component such as metallic Si, Mg in
the Al alloy, etc.
These components also deteriorate denseness of the refractory structure,
corrosion resistance, etc.,
due to oxidation, alteration, etc., so that the total amount of them is
preferably about 7.0 mass% or
less.
[0031]
In the refractory material for the plate of the present invention, denseness
of the structure
is an important factor as well as specifying the components as described
above. In particular, it is
important that the structure of the sliding surface side of the plate,
particularly the portion serving
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as an operating surface, is dense, which is on the high temperature side and
is easily affected by
the foreign components and has a large degree of alteration such as reduction
reaction.
This denseness can be evaluated or specified by a gas-permeability as measured
for said refractory
material including the surface serving as the sliding surface, and in a
direction perpendicular to
said surface, and an apparent porosity. Thus, it is necessary that the
refractory material for the
plate of the present invention includes a surface serving as a sliding
surface, and has a gas-
permeability of 40x10-17 m2 or less as measured for said refractory material
including said surface
and in a direction perpendicular to said surface, and the apparent porosity of
11.0 % or less. If the
gas-permeability exceeds 40x1017 m2 or if the apparent porosity exceeds 11.0%,
decomposition
gas from an inside of the refractory material becomes easy to migrate, further
infiltration of the
foreign component easily progresses, so that deterioration of the refractory
structure and damage
of the sliding surface (surface roughening) are accelerated. However, if the
refractory structure is
excessively densified, there is a possibility that the elastic modulus will
rise and the thermal shock
resistance will be deteriorated, so that, preferably, the lower limit value of
the gas-permeability is
x 10 -17 m2, and the lower limit value of the apparent porosity is 8.0 %.
[0032]
Preferably, the refractory material for the plate of the present invention has
a thermal
expansion coefficient of 0.5 to 0.6 % as measured in a non-oxidizing
atmosphere at 1000 C. In
the refractory material for the sliding nozzle plate, high temperature molten
steel passes through
the inner bore, and thus thermal shock resistance is required. Particularly
when the refractory
material for the sliding nozzle plate is set in a sliding nozzle device and
used under constraint
conditions by a pushing metal member, etc., in order to reduce the thermal
stress generated during
casting, it is important to reduce the thermal expansion coefficient of the
refractory material for
the sliding nozzle plate. Generally, the larger the shape of the plate, the
higher the possibility of
destruction tendency due to the thermal stress becomes. However, from the
experience of the plate
having generally largest shape heretofore, if the thermal expansion
coefficient at 1000 C is about
0.6 % or less, remarkable destruction is avoided. On the other hand, if the
amount of thermal
expansion of the refractory material for the sliding nozzle plate during
casting is too small, the
restraining force by the metal band in the outer circumferential direction of
the plate decreases,
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and when it is smaller than the thermal expansion amount of the metal band,
the restraining force
disappears. Then, in the refractory material for the sliding nozzle plate,
problems are likely to
occur; for example, cracks is likely to occur, cracks is likely to expand, and
when detaching the
plate after casting, the metal band greatly shifts and disassembling operation
becomes difficult.
For these reasons, the thermal expansion coefficient at 1000 C is preferably
about 0.5 % or more.
[0033]
Preferably, the refractory material for the plate of the present invention has
a bending
strength of 15 to 40 MPa as measured at room temperature. The refractory
material for the sliding
nozzle plate is set in a sliding nozzle device, and restraint by surface
pressure is applied in the
thickness direction, and restraint by and restraint by surface pressure is
applied in the thickness
direction, and restraint by the restraining hardware, etc., is applied from
the surroundings. When
the mechanical strength of the refractory material for the sliding nozzle
plate restrained in this way
is low, destruction is caused by the binding force. If the bending strength of
the refractory material
for the plate of the present invention as measured at room temperature is less
than 15 MPa, the
inventors have found from the experience that cracks are likely to occur at
the time of setting or
fixing into the sliding nozzle device, or at the time of the surface pressure
loading. Therefore, the
bending strength at room temperature is preferably 15 MPa or more. On the
other hand, if the
bending strength at normal temperature increases, the elastic modulus also
increases, which is a
factor of deterioration of the thermal shock resistance. If the bending
strength of the refractory
material for the plate of the present invention as measured at room
temperature exceeds 45 MPa,
the inventors have found from the experience that the elastic modulus is
likely to be excessively
high, and cracks due to thermal shock are likely to occur. Therefore, the
bending strength at room
temperature is preferably 15 to 40 MPa.
[0034]
A method for producing the refractory material for the plate of the present
invention will
be described below.
[0035]
Generally, the refractory material for the sliding nozzle plate can be
produced by a
production method including the following steps.
14
CA 03037462 2019-03-19
(A) A prescribed amount of raw material to be each component source of the
refractory
material for the sliding nozzle plate is blended and mixed together to obtain
a raw material blend.
(B) A resin which forms a carbon bond after the heat treatment and can be used
as a
regulator for wet state of a mixture at the time of shaping and further, if
necessary, a solvent, etc.,
are added and kneaded to the raw material blend to obtain a mixture.
(C) The mixture is subjected to pressure forming under an arbitrary method and
any
pressure to obtain a shaped body of the mixture.
(D) The shaped body is subjected to drying and heat treatment (burning) in a
non-
oxidation atmosphere.
(E) If necessary, polishing, winding of metal band, etc. are performed.
[0036]
In such method for producing the general refractory material for the sliding
nozzle plate,
a method for producing a refractory material for the plate of the present
invention is characterized
in that the method comprises the steps of:
adjusting the content of the metal Al component in the mixture to be in an
amount of 2.0
to 10.0 mass%;
shaping the mixture; and
subjecting the mixture to heat treatment the mixture in a non-oxidizing
atmosphere at
1000 C or more to obtain the refractory material in which the content of the
metal Al component
is 1.0 mass% or less (including zero).
[0037]
If the content of the metal Al component in the mixture is less than 2.0
mass%, the
densified structure after the heat treatment cannot be obtained. In other
words, if a shaped body
of the mixture containing the metal Al component in an amount of 2.0 mass% or
more is heat-
treated at 1000 C or more in a non-oxidizing atmosphere, the metal Al
component in the shaped
body reacts with the other components to produce reaction products such as
AIN, A14C3, A120C,
A1404C, Al2O3, etc., causing densification of the structure due to volume
expansion accompanying
reaction products. The shape of the metal Al as a metal Al component source
(raw material) can
CA 03037462 2019-03-19
be atomized grains, flake grains, fibers, or the like. In addition to metal Al
alone, an alloy of Al -
Si, Al - Mg, etc. can also be used.
[0038]
On the other hand, If the content of the metal Al component in the mixture
exceeds 10.0
mass%, the amount of the metal Al component in the refractory material
(refractory material for
the plate as a product) is highly likely to exceed 1.0 mass%. Even If the
content of the metal Al
component in the mixture is in an amount of 2.0 to 10.0 mass%, depending on
the heat treatment
conditions and the form of metal Al or an Al alloy as a metal Al component
source (raw material),
etc., the metal Al component is likely to not remain in the refractory
material after heat treatment.
Including such cases, in the present invention, the content of the metal Al
component in the
refractory material after the heat treatment is set to 1.0 mass% or less
(including zero).
[0039]
The melting point of the metal Al is 660 C. However, for example, in the case
where
the form of the metal Al is atomized grains in which the surface layer of the
grains are covered
with an oxide film or in the form of a fiber having a relatively large shape,
even the heat treatment
temperature is not lower than the melting point of the metal Al, a large
amount of metallic Al
component is likely to remain at a temperature of less than 1000 C.
Therefore, it is necessary to
firing at a high temperature of 1000 C or more to sufficiently react the
metal Al component with
other components in order to densify the structure.
[0040]
Further, the heat treatment needs to be performed in a non-oxidizing
atmosphere. However, as
a heat treatment in a non-oxidizing atmosphere, in addition to a nitrogen
atmosphere, an argon
atmosphere, and a CO atmosphere in which heat treatment is performed by
embedding in a coke,
it is also possible to be subjected to heat treatment in a simple CO
atmosphere in which a shaped
body is placed inside a container made of metal such as SiC or SUS and heated
from outside the
container with a burner or the like. On the other hand, when subjecting to
heat treatment in an
oxidizing atmosphere such as in an ambient atmosphere, not only carbon of the
shaped body is
oxidized but also AIN, A14C3, A120C, A1404C, etc., are not formed, and then it
is not possible to
densify the structure.
16
CA 03037462 2019-03-19
[0041]
In the present invention, in order to obtain the gas-permeability of 40x 10-12
m2 or less as
measured for the refractory material including the surface serving as the
sliding surface, and in a
direction perpendicular to said surface, constitution of various raw
materials, etc., as described
above, particularly morphology and amount of metal Al and further the heat
treatment conditions
may be adjusted. In the heat treatment condition, burning is performed in a
non-oxidizing
atmosphere at a temperature of 1000 C or more (for example, a temperature of
1200 C or more
under a nitrogen atmosphere having an oxygen concentration of 100 ppm or
less). At that time, a
method of finely adjusting the oxygen concentration for each temperature
region, the partial
pressures of nitrogen and CO, etc., is also effective.
In addition, with respect to each raw material, it is possible to adopt a
method of selecting
as dense as possible and shaping with oil press or friction press at a
pressure of 100 MPa or more,
such as, for example, using an A1404C-containing raw material produced by the
arc melting
method.
Further, the gas-permeability can be matched with the above-mentioned value by
methods
such as decreasing the diameter of the fine particle fraction, adjusting the
structure ratio of large,
medium, and small particle size fractions, increasing the pressure applied
during shaping,
increasing the number of tightening, adjusting the speed at pressurizing, etc.
in such a way as to
make the particle size composition of the mixture, especially the fine
particle fraction a tendency
of tight-packed structure.
Adjustment of the apparent porosity is also similar to these techniques.
In addition, there are aspects that cannot accurately grasp and express
denseness of
structure only with apparent porosity, and thus it is necessary to judge
denseness by comprehensive
evaluation with apparent porosity and gas-permeability.
[0042]
A specific method in which the shaped body of the adjusted mixture such that
the content
of the metal Al component is 2.0 to 10.0 mass% is heat treated to obtain the
refractory material
containing the metal Al component in an amount of 1.0 mass% or less, includes
optimally adjusting,
17
CA 03037462 2019-03-19
for example, temperature, gas components such as oxygen partial pressure, gas
supply rate, etc.,
for each of the above-mentioned techniques.
[0043]
As described above, in the production of the refractory material for the
sliding nozzle
plate, it is a widely common practice to impregnate with tar, pitch or a
thermosetting resin in order
to perform densification of the structure, etc. However, in the method for
producing the refractory
material for the plate of the present invention, a step of impregnating with
tar, pitch or
thermosetting resin is not necessarily required.
[0044]
Each of tar, pitch and thermosetting resin finally leaves residual carbon.
Among them,
the thermosetting resin forms a continuous rigid amorphous carbon structure
and is effective in
improving the strength. However, it is likely to cause a reduction in thermal
shock resistance. On
the other hand, tar and pitch are solid at room temperature, soften in a
temperature of several
tens C to a hundred and several tens C to form a liquid, and have a high
carbonization rate when
heat treated at high temperature and become crystalline carbon after heat
treatment. Therefore,
impregnation of the refractory material for the sliding nozzle plate under a
predetermined
temperature condition with tar or pitch has a densification effect of greatly
lowering the gas-
permeability and the apparent porosity, and maintains denseness even after
carbonization,
resulting in crystalline soft carbon. Thereby, the increase in elastic modulus
is suppressed, and
the adverse effect of lowering the thermal shock resistance is small. However,
when impregnated
with tar, pitch or thermosetting resin, carbon will be present so as to fill
the voids in the refractory
structure. Accordingly, the amount of free carbon component in the refractory
material becomes
high, and a large amount of carbon exists around the oxide raw material such
as Al2O3 grains. As
a result, the oxide material such as A1203 particle, ZrO2, mullite, etc., will
be reduced in a so-called
high efficiency under long casting conditions. From this, it becomes easier to
form an embrittled
layer by disappearance or alteration of these oxide materials, etc., in the
vicinity of the operating
surface, which is likely to further accelerate damage to the sliding surface.
Therefore, according
to the method for producing the refractory material for the plate of the
present invention, it is
preferable not to impregnate with tar, pitch or thermosetting resin.
18
CA 03037462 2019-03-19
[EXAMPLES]
[0045]
Table 1 presents Inventive Examples and Comparative Examples. In Inventive and
Comparative Examples in Table 1, raw materials were weighted and mixed so as
to have respective
given raw material compositions and given particle distributions, and an
organic binder was added
and kneaded to the mixed raw materials to obtain a mixture, which was uniaxial
pressed into a
plate-shaped body under predetermined shaping conditions. The shaped body was
subjected to
heat treatment at a predetermined temperature and atmosphere to form a
refractory material for a
sliding nozzle plate. And bulk specific gravity, apparent porosity, gas-
permeability, bending
strength, elastic modulus and thermal expansion coefficient were evaluated,
and for the evaluation
of chemical components, A1404C component, Al2O3 component, SiO2 component and
free carbon
were quantified. In addition, a reaction test with molten steel and a reaction
test with molten pig
iron were performed using a high frequency induction furnace to evaluate
formation of embrittled
layer. Furthermore, thermal shock resistance was also evaluated using the high
frequency
induction furnace. Methods of these evaluations are as follows.
[0046]
The bulk density and the apparent porosity were measured according to JIS
R2205.
Samples for use in measuring the bulk density and the apparent porosity had a
shape of 40 mm x
40 mm x 40 mm including a surface serving as the sliding surface of the
refractory material for
the sliding nozzle plate and cut out as measured in a direction perpendicular
to the surface serving
as the sliding surface of the refractory material for the sliding nozzle
plate. When the shape of the
refractory material for the sliding nozzle plate is small, it is possible to
evaluate samples cut out in
the similar shape of 30 mm x 30 mm x 30 mm.
[0047]
The gas-permeability was measured according to JIS R2115 (2008). The samples
for use
in measuring the gas-permeability was those having a size of cp50 mm including
a surface serving
as the sliding surface of the refractory material for the sliding nozzle plate
and cut out into a shape
with a thickness of 20 mm in the direction perpendicular to the surface
serving as the sliding
surface. In this sample, the surface serving as the sliding surface and a
surface of the 20 mm thick-
19
CA 03037462 2019-03-19
side were parallel. The gas-permeability of this sample in the direction
perpendicular to the surface
serving as the sliding surface was measured.
[0048]
The bending strength was measured, using a sample cut into a shape of 20 mm x
20 mm
x 80 mm, according to JIS-R 2213 (1995).
[0049]
Elastic modulus was measured by an ultrasonic method. Specifically, terminals
were
placed at both ends of a sample cut into a shape of 20 mm x 20 mm x 80 mm to
measure an
acoustic velocity, and the elastic modulus was calculated by calculating a
formula between the
acoustic velocity and The bulk density measured according to 11S-R2205.
[0050]
The thermal expansion coefficient was measured up to 1000 C in a nitrogen
atmosphere
by a non-contact method described inJIS-R2207-1.
[0051]
Among the chemical components, A1404C component, Al2O3 component and metal Al
component were quantified by Rietveld method using X-ray diffraction. If there
is a standard
sample, quantification can also be performed by the internal standard method
similarly by X-ray
diffraction method. In the analysis by ordinary X-ray fluorescence or wet
method, it is very
difficult to separate and quantify A1404C and Al2O3, and thus it is preferable
to quantify by X-ray
diffraction method. Likewise, with respect to the quantification of the metal
Al component, when
containing A1404C component, it is practically impossible to separate and
quantify the A1404C by
analyzing using atomic absorption, ICP , etc., by a wet method.
The SiO2 component was quantified by fluorescent X-ray diffraction method
according
to JIS-R 2216.
The free carbon component (expressed as "F.C." in Table I) was quantified
according to
the method prescribed in JIS-R2011.
[0052]
Formation of the embrittled layer was evaluated by a reaction test with molten
steel and
a reaction test with molten pig iron, using a high-frequency induction
furnace, as described above.
CA 03037462 2019-03-19
Specifically, the surface serving as the sliding surface of the refractory
material for the
sliding nozzle plate was lined in the high-frequency induction furnace so as
to be the inner surface
of the furnace of the high-frequency induction furnace, and the embrittled
layer formed by the
reaction test with molten steel or molten pig iron was evaluated.
As to the evaluation method of the embrittled layer on the sliding surface of
the plate due
to the oxygen in the molten steel (oxidation and decarburization is mainly
caused for molten steel),
SS400 is used as the molten steel and adjustment was made by adding Si and
carbon so that the
free oxygen concentration during the test was in the range of 30 to 50 ppm.
As to the evaluation method of the embrittled layer formation mainly due to
the reduction
reaction inside the refractory material, it was ascertained that when the
molten pig iron containing
almost no in-steel oxygen and having a carbon content of about 4 mass% was
used, the oxygen
concentration during the evaluation was stably 5 ppm or less.
The reaction tests were performed at 1600 C for 3 hours. After the reaction
test, the
lining of the high-frequency induction furnace was disassembled and the
thickness of the
embrittled layer formed on the surface serving as the sliding surface of the
refractory material for
the sliding nozzle plate (the inner surface of the furnace of the high-
frequency induction furnace)
was measured. In Table 1, the thickness of the embrittled layer is expressed
as an index with the
thickness of the embrittled layer of Example being 100. The smaller the index
is, the thinner the
embrittled layer is, and the better the surface roughness resistance. As
described in Non-Patent
Document 2, the reaction test with molten pig iron can well reproduce the
structure of the sliding
surface during the operation of pouring molten steel having a low
concentration of free oxygen
such as Al-killed steel.
[0053]
The thermal shock resistance was evaluated by a so-called immersion thermal
shock test,
in which a sample was immersed in the molten pig iron in a high-frequency
induction furnace and
the degree of cracking of the sample after cooling was evaluated.
Specifically, a sample of 40 mm
x 40 mm x 180 mm was cut out from the plate refractory, and a series of tests
was repeated three
times in which the sample was immersed in molten pig iron at 1600 C for 3
minutes and then air-
cooled for 30 minutes. After the test, the degree of cracking of the sample
was observed.
21
CA 03037462 2019-03-19
[0054]
In addition, some examples and comparative examples were applied to an actual
machine
test (actual operation). In the actual machine test, by pouring two kinds of
molten steel, i.e., molten
steel of high oxygen content steel (steel having a free oxygen concentration
in molten steel of more
than 30 ppm) and molten steel of low oxygen content steel (steel having a free
oxygen
concentration in molten steel of 30 ppm or less), samples were evaluated from
damaged state of
the refractory material for the sliding nozzle plate, etc., in three stages of
o (Excellent), A (Good)
and x (NG) in total.
[0055]
[Table 1]
Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example
8 Example 9 Example Example
10 11
Chemical component/mass%
AlsO4C 150 300 45.0 300 300 30.0 30.0 300
30.0 300 295
Alz0z (corundum) 75.0 60.0 45.0 60.0 600 60.0 60.0
60.0 60.0 600 58.7
SiOz 2.0 20 2.0 2.0 20 0.5 4.0 2.0 20
/0 1.9
F.C. 3.0 3.0 30 2.0 4.5 3.0 3.0 3.0 30
3.0 4.5
Al <1.0 <1.0 <1.0 <1.0 < 1.0 <1.0 <1.0
<1.0 <1.0 <(.0 <1.0
Total 95.0 95.0 95.0 940 965 93.5 970 950
95.0 950 94.6
C' r r P r I r P r P. I
Content of metal Al component in
5 5 5 5 5 5 5 5 7 5
mixtureimass% a I)
Normal Normal Normal Normal Normal Normal Normal High- High- Normal Normal
Shaping condition (shaping pressure)
forming forming forming forming forming forming forming Pt.:7'7g pressure
forming forming
forming
Heat treatment temperatu reit (highest
120002 120002 120002 120002 (20002 1200t 120002 120002 120002 I000 C 1200 C
temperature, non-oxidizing atmosphere)
With/Without impregnation of pitch, etc. Without Without
Without Without, Without Without Without Without Without Without With
Evaluation
Bulk density 3.10 3.00 2.95 3.02 2.92 303 294 3.03
3.02 2.96 3.05
Apparent porosity/% 85 8.5 8.5 9.0 10 0 , 8.2 95 79
70 11.0 4.5
00s-penneability/le7m2 18 20 23 23 28 (8 27 12 8
35 5
Bending strength/MPa 26 25 24 27 20 22 20 30 35
21 32
Mastic modulus/Gila 47 45 44 50 38 48 40 55 60
42 60
Themial evansion coeflicient/% 0.58 052 0.46 0.53 0.50 053
0.50 054 0.56 0.55 054
Reaction test with molten
100 91 7 86 105 86 95 88 60 98 90
steel (Ernb riffled layer thickness/Index)
Reaction test with molten pig
100 89 67 94 122 67 Ill 85 55 III 135
iron (Emb titled layer thickness/Index)
Small Small micro Small Small Medium Small Medium
Medium Small Small
Thermal shock resistance
, crack crack crack crack crack crack crack crack
crack crack crack
Result of actual machine test (High 0 Mediu Mediu
0 0 0 0 0
oxygen content steel) rn crack m crack
Result of actual machine test (Low oxygen 0 Mediu Mediu
0 0 0 A
content steel) in crack m crack
22
CA 03037462 2019-03-19
Comparati Comparati Comparati Comparati Comparati Comparati Comparati Compared
ve ve ye ye ve ye ve ve
Example 1 Example 2 Example 3 Example 4 Example 5 Exainple 6 Example 7 Example
8
Chemical component/mass%
AMC 130 48.0 30.0 30.0 30,0 300 30.0 30,0
Alc03 75.0 45.0 60.0 60.0 600 60,0 60.0 60.0
SiO2 2.0 2.0 2.0 20 0.0 4.5 , 2.0 2.0
F.C. 3.0 3.0 1.0 5.0 3.0 3.0 , 3,0 3.0
Al <1.0 <1.0 <1.0 <10 < 1,0 <1.0 2.5 <1.0
Total 930 98.0 93.0 97.0 93.0 965 95.0 95.0
P P V r pP
Content of metal Al component in P
mb2uremass%*1)
High- Low-
Normal Normal Normal Normal Normal Normal
Shaping condition (shaping pressure)
forming fomling foiming forming forming forming pressurefom,in g pressurefo ng
Heat treatment temperaturerC (highest
1200 C 1200t 12000/ 1200T3 1200Y3 1200 C 900<C 1200t
temperature, non-oxidizing atmosphere) .
With/Without of impregnation of pitch,
Without Without Without Without Without Without Without Without
etc, .
Evaluation
Bulk density 3.12 2.93 3,04 2.90 , 3.04 , /90 2.97
2.85
Apparent porosityt% 9.0 8.4 8.4 10.4 8.1 9.6 , 12.0
12.1
Gas-permeahilityllem2 17 24 21 29 17 28 39 43
Bending strength/MPa 27 23 42 18 23 ., 18 IS 14
Elastic modulus/(a 48 43 78 , 33 54 38 31 28
Thermal expansion coefficient% 0.62 042 054 049 0.55 049
0,54 0,50 ,
Reaction test with moften
109 75 80 123 82 98 123 127
steel (Emb rittled laver thickness/Index) . . -
Reaction test with molten pig
lIX) 83 89 150 67 172 178 189
iron (Embrittled layer thiclai es s/Index)
Large Small Large Small Large Small Medium Small
Thermal shock resistance
crack crack crack crack crack crack crack
crack
<Shift of
Result of actual machine test (High <Peculiar
metal <Slaking <
oxygen content steel) band crack
<Shift of <Surface <Surface
Result of actual machine test (Low oxygen
metal <Slaking roughenin roughenin
content steel)
band g g
*1 :The total amount of the metal Al
component contained in mixute
[0056]
In Table 1, in Examples 1 to 3, the content of A1404C component is in the
range of 15.0
to 45.0 mass%, the content of a SiO2 component is in the range of 2.0 mass%,
the content of free
carbon component is in the range of 3.0 mass%, and the content of the metal Al
component is in
the range of 1.0 mass% or less, each of which falls within the scope of the
present invention, and
properties such as an apparent porosity, gas-permeability, a bending strength,
thermal expansion
coefficient also fall within the scope of the present invention. Therefore, as
the result of the
reaction test with molten steel and the reaction test with molten pig iron,
formation of the
embrittled layer was negligible and evaluation of thermal shock resistance was
good. As a result
of testing the materials of Examples 1 to 3 with an actual machine, good
durability was obtained.
On the other hand, in Comparative Example 1, the content of the A1404C
component was
as low as 13.0 mass%, and the effect of reducing the thermal expansion
coefficient was low. Thus,
23
CA 03037462 2019-03-19
as a result of evaluation of thermal shock resistance, a large crack occurred
and good durability
cannot be expected.
In Comparative Example 2, the content of A1404C component was as high as 48.0
mass%,
and thus the thermal expansion coefficient became remarkably low. As the
result, when detaching
the plate from the sliding nozzle device after actual use, the shrink-fitted
band (HB) on the outer
periphery of the plate shifted and the dismantling property was bad. Further,
cracks also developed,
which made it difficult to recycle and it was evaluated as NG.
[0057]
In Examples 4 and 5, the contents of the free carbon component were,
respectively, 2.0
mass%, and 4.5 mass%, the content of the A1404C component was 30.0 mass%, the
content of the
SiO2 component was 2.0 mass%, and the content of the metal Al component is 1.0
mass% or less,
each of which falls within the scope of the present invention, and properties
such as an apparent
porosity, gas-permeability, a bending strength, thermal expansion coefficient
also fall within the
scope of the present invention.
Therefore, as the result of the reaction test with molten steel and the
reaction test with
molten pig iron, formation of the embrittled layer was negligible and
evaluation of thermal shock
resistance was good.
On the other hand, in Comparative Example 3, the content of the free carbon
component
was as low as 1.0 mass%, and thus the elastic modulus became high. As the
result, Comparative
Example 3 was evaluated as being inferior in terms of the thermal shock
resistance. Thus, even in
actual machine, good durability cannot be expected.
Further, in Comparative Example 4, the content of the free carbon component
was as high
as 5.0 mass%, and thus as the result of the reaction test with molten steel
and the reaction test with
molten pig iron, formation of the embrittled layer was became thick. Thus,
even in actual machine,
good durability cannot be expected.
[0058]
In Examples 6 and 7, the contents of the SiO2 component were, respectively,
0.5 mass%
and 4.0 mass%, the content of the AUK component was 30.0 mass%, the content of
the free
carbon component was 3.0 mass%, and the content of the metal Al component is
1.0 mass% or
24
=
CA 03037462 2019-03-19
less, each of which falls within the scope of the present invention, and
properties such as an
apparent porosity, gas-permeability, a bending strength, thermal expansion
coefficient also fall
within the scope of the present invention. Therefore, as the result of the
reaction test with molten
steel and the reaction test with molten pig iron, formation of the embrittled
layer was negligible
and evaluation of thermal shock resistance was good.
On the other hand, Comparative Example 5 does not contain the SiO2 component,
and
thus slaking occurred at the time of processing and after processing for
recovering and recycling
after actual use, it could be recycled. Further, in Comparative Example 6, the
content of the SiO2
component was as high as 4.5 mass%, and thus formation of the embrittled layer
was remarkable
in the reaction test with molten pig iron.
[0059]
In Examples 8 and 9, the content of the A1404C component was 30.0 mass%, the
content
of the SiO2 component was 2.0 mass%, the content of the free carbon component
was 3.0 mass%,
and the content of the metal Al component was 1.0 mass% or less, each of which
falls within the
scope of the present invention, and properties such as an apparent porosity,
gas-permeability, a
bending strength, thermal expansion coefficient also fall within the scope of
the present invention.
However, Examples 8 and 9 were produced by high-pressure forming, and thus in
Example 8, the
apparent porosity was as low as 7.8%, whereas in Example 9, the apparent
porosity was as low as
7.0% and the gas-permeability was as low as 8 x 1017 tn2, both of which have
high elastic modulus.
Therefore, although the formation of the embrittled layer was extremely slight
in the reaction test
with molten steel and the reaction test with molten pig iron, the thermal
shock resistance tended
to deteriorate somewhat Also in the actual machine test, although the damage
on the sliding
surface was slight, the radial crack from a nozzle hole tended to be somewhat
larger.
Comprehensively, however, better results could be obtained than the
comparative conventional
product.
[0060]
In Example 10, the heat treatment temperature was 1000 C, the content of the
A1404C
component was 30.0 mass%, the content of the SiO2 component was 2.0 mass%, the
content of
the free carbon component was 2.0 mass%, and the content of the metal Al
component was 1.0
= CA 03037462 2019-03-19
mass% or less, each of which falls within the scope of the present invention,
and properties such
as an apparent porosity, gas-permeability, a bending strength, thermal
expansion coefficient also
fall within the scope of the present invention. Therefore, as the result of
the reaction test with
molten steel and the reaction test with molten pig iron, formation of the
embrittled layer was
negligible and evaluation of thermal shock resistance was good.
On the other hand, in Comparative Example 7, a burning temperature is as low
as 900 C,
and thus despite the high-pressure forming, the reaction of the metal Al
during the heat treatment
was small. Further, the densification was insufficient, and the content of the
metal Al component
was more than 1.0 mass%. Therefore, as the result of the reaction test with
molten steel and the
reaction test with molten pig iron formation of embrittlement layer was also
remarkable, even in
the actual machine test, remarkable surface roughening occurred, and good
durability could not be
obtained.
[0061]
In Comparative Example 8, the shaping pressure at the time of shaping of the
refractory
material for the sliding nozzle plate was adjusted and the bulk density was
set low. For this reason,
in Comparative Example 8, the burning temperature was 1200 C, the content of
AUK
component was 30.0 mass%, the content of a SiO2 component was 2.0 mass%, the
content of free
carbon component was 2.0 mass%, and the content of the metal Al component is
1.0 mass% or
less, each of which falls within the scope of the present invention. However,
the apparent porosity
is 12.1 %, and the gas-permeability is 43 x 10-17 m2, and thus the
densification is insufficient. Also,
the bending strength is as low as 14 MPa. Therefore, as the result of the
reaction test with molten
steel and the reaction test with molten pig iron formation of embrittlement
layer was also
remarkable, even in the actual machine test, good durability could not be
expected. In addition,
due to insufficient strength, in the actual machine test, a peculiar crack
different from radial cracks,
etc., caused by normal thermal stress occurred, and the durability was
deteriorated.
[0062]
In Example 11, pitch impregnation performed, which falls within the scope of
the present
invention. However, the content of free carbon component became high, and the
carbon
component is uniformly present in the refractory structure. Therefore, in the
reaction test with
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molten pig iron, the reduction reaction in the refractory structure progress
and the formation of the
embrittled layer tended to be slightly thick. On the other hand, as the result
of the reaction test
with molten steel, formation of the embrittled layer was negligible. In the
actual machine test,
after the operation of pouring molten steel of high oxygen content steel,
damage to the sliding
surface was negligible, whereas after the operation of pouring molten steel of
low oxygen content
steel, damage to the sliding surface tended to be slightly larger.
Comprehensively, however, better
results could be obtained than the comparative conventional product.
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