D E C L A R A T I O N
I, MATSUDA, Atsuhiro , c/o Seiwa Patent & Law,
Toranomon 37 Mori Bldg., 5-1, Toranomon 3-chome,. Minatoku,
Tokyo, Japan, hereby verify that I am the translator
of the attached translation of International Application
2011/051679
No. PCT/ JP and that I believe the attached
translation is a true and accurate translation of the
same.
This 11th day of July,. , 2012
MATSUDA, Atsuhiro
- 1 -
DESCRIPTION
Title of Invention
MOLD POWDER FOR CONTINUOUS CASTING USE OF STEEL
5
Y802
Technical Field
[0001 ] The present invention relates to mold powder
for continuous casting use which is used added to the
inside of a casting mold at the time of continuous
10 casting of steel.
Background Art
[0002] When continuously casting molten steel, mold
powder (hereinafter sometimes described as "powder") is
15 added to the top of the molten steel surface inside of
the casting mold. The powder is required to have the
following characteristics.
[0003] 1) The melted powder layer which is formed on
the top of the molten steel surface by melting of powder
20 and the unmelted powder layer on top of that should cover
the molten steel surface so as to cut off contact with
the air and thereby have the effect of preventing
reoxidation of the molten steel and maintaining heat.
[0004] 2) The melted powder must infiltrate between
25 the casting mold and the solidifying shell and acct as a
lubricant, so the powder should constantly be supplied in
a suitable amount and have a melting speed giving a
suitable pool thickness of melted powder matched with the
speed of consumption of the powder.
30 [0005] 3) The melted powder layer should absorb nonmetallic
inclusions which float up in the molten steel
and should have little change in physical properties
(viscosity, melting temperature, solidification
temperature, etc.)
35 [0006 ] 4) The melted powder should infiltrate between
the casting mold and solidifying shell to form a uniform
powder film and the powder film should have a lubricating
action between the casting mold and the solidifying
shell.
5) The melted powder should have a suitable viscosity
and interfacial tension and the melted powder should not
5 be entrained in the molten steel.
[0007] In a continuous casting operation, local
fluctuations in the melt surface and the flow behavior of
molten steel which is formed by the flow of molten steel
which is injected into the casting mold disturb the
10 interface between the powder and molten steel whereby
melted powder sometimes is entrained in the molten steel.
[0008] Further, when continuously casting molten steel
which contains Al or Ti, since the melted powder and
molten steel touch, the following reactions occur between
15 the Al or Ti in the molten steel and the main component
in the powder, that is, Si02.
4[Al]+3(Si02)-*2(A1203)+3[Si] ...(1)
[ Ti ] + (Si02) -> (Ti02)+[Si] ... (2)
Here, [ ] indicates an composition in the molten steel,
20 while ( ) indicates an composition in the melted powder.
When the above such reactions occur between the molten
steel and the melted powder interface, the interfacial
tension between the molten steel and the melted powder
greatly falls and the entrainment of powder in molten
25 steel more easily occurs.
[0009] The majority of the melted powder which is
entrained in molten steel floats back up, but sometimes
part of it is trapped in the solidifying shell and
remains in the cast slab. The powder which remains at the
30 surface layer in the steel becomes sliver defects of the
product surface. Further, the powder which remains at the
inside becomes causes press cracking. These occur
particularly at the time of high speed casting. At the
time of medium and low speed casting as well, these often
35 become problems for tin plate, steel sheets for
automobile, and other steel with high quality demands.
[0010 ] For this reason, as a measure for prevention of
- 3 -
entrainment of powder in molten steel, entrainment
resistant powder which has a high viscosity and high
surface tension which is shown in PLT 1, entrainment
resistant powder which has a high interfacial tension
5 which is shown in PLT 2, powder which suppresses reaction
between the Al or Ti in the molten steel and the Si02 in
the powder to prevent a large drop in the interfacial
tension between the molten steel and melted powder,and
thereby suppress the entrainment of powder molten steel
10 which is shown in PLT 3, etc. have been developed.
[0011] On the other hand, when the infiltration of the
melted powder to between the casting mold and the
solidifying shell is obstructed and the lubricating
action of the melted powder is impaired, inside the
15 casting mold, the heat extraction between the solidifying
shell and the casting mold becomes unstable. As a result,
the solidification of the cast slab becomes uneven,
cracking of the cast slab is invited, and in turn
breakout occurs. Breakout not only causes stoppages of
20 operation and reduction in the amount of production, but
also inflicts serious damage to the continuous casting
facility. Accordingly, to raise the uniformity of
solidification of the cast slab in the casting mold so as
to prevent cracking and breakout, stable control of the
25 heat extraction in the casting mold is extremely
important. Thus, as shown in PLT 4, powder has been
developed which satisfies the requirements for high
viscosity and high basicity while causing precipitation
of stable crystals in the powder film and stably
30 controlling heat extraction.
[0012] Further, in steel containing Al, due to the
precipitation of the high melting point crystal gehlenite
in the powder, there is also the problem of poor
lubrication and unstable heat extraction in the casting
35 mold. Thus, as shown in PLT 5, powder has been developed
which prevents contamination of the molten steel by the
reactions of the molten steel and powder and adds Li20 or
- 4 -
F so as to prevent precipitation of the high melting
point crystal gehlenite.
[00131 PLT 6 proposes powder which raises the
viscosity of the powder in the melted state so as to
5 reduce and even out the infiltration of powder to between
the casting mold and solidifying shell and which decrease
the crystallization tendency so as to make the slag film
uniform in state and thereby make heat extraction in the
casting mold uniform.
10 [00141 Furthermore, PLT 7 proposes powder which
contains at least one type of oxide among Zr02, Ti02, and
Cr203 and makes heat extraction in the casting mold
uniform.
15 Citations List
Patent Literature
[0015] PLT 1: Japanese Patent Publication (A) No. 2-
25254
PLT 2: Japanese Patent Publication (A) No. 2000-071051
20 PLT 3: Japanese Patent Publication (A) No. 2008-264791
PLT 4: Japanese Patent Publication (A) No. 2005-040835
PLT 5: Japanese Patent Publication (A) No. 2006-110578
PLT 6: International Publication W000/33992 pamphlet
PLT 7: Japanese Patent Publication (A) No. 8-33962
25
Summary of Invention
Technical Problem
[00161 However, to respond to the demands for further
high speed casting and improved quality, with just
30 changing the powder composition to make the viscosity
higher so as to prevent entrainment like with the powder
which is described in PLT 1, a suitable infiltration of
the powder to between the casting mold and the
solidifying shell cannot be secured and the lubricity
35 cannot be maintained. Further, the possibility of
inviting breakout also cannot be completely eliminated.
[0017 ] In the powder which is described in PLT 2, the
CaO/SiO2 ratio is an extremely high one of 7 or more, so
the solidification temperature becomes higher, a suitable
amount of infiltration of powder cannot be secured, and
the lubricity between the casting mold and the
5 solidifying shell cannot be maintained. Accordingly, the
possibility of inviting breakout also cannot be
completely eliminated. Further, the amount of Si02 in the
powder is small and the amount of A1203 is large, so the
high melting point crystal gehlenite is liable to
10 precipitate and thereby obstruct lubrication and
destabilize heat extraction in the casting mold.
(0018] In the powder which is described in PLT 3, the
viscosity is high, so uniform infiltration to between the
casting mold and the solidifying shell is impaired and
15 sufficient lubricity can no longer be maintained.
Accordingly, the possibility of inviting breakout cannot
be completely eliminated. Further, to secure the
viscosity, A1203 is included in a large amount, so the
high melting point crystal gehlenite is liable to
20 precipitate and heat extraction to become unstable.
[0019 ] In the powder which is described in PLT 4, the
high melting point crystal gehlenite etc. are
intentionally made to precipitate, so the infiltration
and lubricity of the powder are liable to be obstructed
25 and the high melting point crystal is liable to
destabilize the heat extraction inside the casting mold.
[0020] In the powder which is described in PLT 5,
precipitation of the high melting point crystal gehlenite
is suppressed, but the Li20 which is contained in the
30 powder reacts with the Al or Ti in the molten steel to
lower the interfacial tension and may result in easy
entrainment of powder in the molten steel.
[0021] In this way, in the powder which is described
in PLT's 1 to 5, achievement of both prevention of
35 entrainment of powder into the molten steel and stable
control of heat extraction inside the casting mold is
extremely difficult.
- 6 -
[0022] Further, in the powder which is described in
PLT 6, the F content is reduced to raise the viscosity.
Therefore, there is the problem that this can only be
applied to the casting of blooms and billets where the
5 amount of infiltration of melted powder need only be
small.
[0023 ] Further, the powder which is described in PLT 7
is made to contain ZrO2, TiO2, and Cr2O3 so as to inhibit
the radiative heat transfer in the liquid phase of the
10 melted powder and thereby scatter or absorb heat emitted
in the liquid phase. Therefore, there is the problem that
the heat extraction inside the casting mold is not
stable.
[0024] The present invention was made in consideration
15 of this situation and has as its object the provision of
powder for continuous casting of steel which suppresses
the reaction between molten steel and the powder so as to
suppress entrainment of the powder in the molten steel
and thereby give a high grade product free of defects due
20 to powder and which stabilizes the heat extraction
inside the casting mold so as to prevent productivity
from being obstructed.
Solution to Problem
25 [0025] The gist of the present invention for solving
the above problem is as follows:
[0026] (1) Mold powder for continuous casting use
which is used for continuous casting of steel which
contains at least one of Al or Ti, said mold powder for
30 continuous casting of steel characterized by comprising
CaO/SiO2, by mass ratio, of 1.0 to 1.5, SiO2 of 15 mass%
to 30 mass%, CaO of 30 mass% to 40 mass%, A1203 of 3 mass%
to 25 mass%, Na2O of 2 mass% to 6 mass%, an F content
which is added by CaF2 or NaF of over 2 mass% to 10 mass%,
35 B2O3 of 1 mass% to 4 mass%, where a sum of the mass% of
SiO2, Na2O, and B2O3 is 20 mass% to 40 mass%, and a balance
of unavoidable impurities and by having a viscosity at
- 7 -
1300°C of 0.5 poise to 8 poise, where, CaO is value
converting all of Ca which is contained in powder to CaO.
[0027] (2) Mold powder for continuous casting use as
set forth in (1), characterized by further containing one
5 or more of Zr02 of 2 mass% to 10 mass% and SrO of 2.5
mass% to 10 mass%.
Advantageous Effects of Invention
[0028] According to the present invention, it is
10 possible to provide powder for continuous casting of
steel which suppresses the reactions between molten steel
and powder even when using molten steel which contains Al
or Ti for continuous casting and thereby suppresses
entrainment of powder in the molten steel to obtain a
15 product of a high grade which is free of defects due to
powder and which stabilizes heat extraction inside the
casting mold and does not impair productivity.
Description of Embodiments
20 [0029] Along with the faster casting speeds,
entrainment of powder in molten steel is increasing and
defects arising due to powder such as sliver defects and
press cracking occur, so use of powder which is more
resistant to powder entrainment is desired. However, with
25 the above-mentioned powder oriented toward resistance to
entrainment, there was the problem that precipitation of
high melting point crystal resulted in sufficient
lubricity not being able to be maintained between the
casting mold and solidifying shell and heat extraction
30 becoming unstable.
[0030] Thus, the inventors engaged in intensive
research to prevent the entrainment of powder in molten
steel at the time of continuous casting using molten
steel which contains Al or Ti and enable stable control
35 of heat extraction inside the casting mold.
[0031] As a result, the inventors newly discovered
that if intentionally including the F content in the
8 -
powder to a predetermined amount, the melting point of
the powder falls and the activity of the Si02 falls.
Further, the inventors newly discovered that due to the
drop in the activity of Si02, the reactions between the
5 molten steel and Si02 expressed by the above formula (1)
and formula (2) do not occur and entrainment of powder
becomes difficult.
[0032 ] Further, the inventors newly discovered that if
introducing a predetermined amount of B203 into the
10 powder, formation of high melting point crystal can also
be suppressed, destabilization of the heat extraction due
to high melting point crystal is eliminated, and heat
extraction is made stable.
[0033] In particular, the inventors studied MnO, B203,
15 S'r0, BaO, Ti02, Fe203, etc. as ingredients in addition to
the main component of powder of CaO, Si02, and Na20 and as
a result newly discovered that only B203 has the effect of
suppressing formation of high melting point crystal.
[0034 ] Below, the content of the invention will be
20 explained in detail.
[0035] In the present invention, "CaO" means the value
of all of the Ca which is contained in the powder
converted to CaO.
[0036] The mold powder of the present invention is
25 given a viscosity at 1300°C of 0.5 poise to 8 poise. If
the viscosity is less than 0.5 poise, entrainment of
powder in the molten steel cannot be sufficiently
reduced. Preferably, the viscosity is 2 poise or more. On
the other hand, if the viscosity is larger than 8 poise,
30 the uniformity of infiltration to between the casting
mold and the solidifying shell becomes insufficient.
Preferably, the viscosity is 4 poise or less.
[0037] As the method for measurement of the viscosity
of the mold powder, the rotating cylinder method is
35 preferable. The mold powder being measured is inserted
into a crucible, premelted at 1400°C for 10 to 15 minutes,
then placed in a vertical type tubular furnace (elema
furnace). The rotor of an E-type viscometer is immersed
in the melted powder and allowed to stabilize there at
1300°C for 30 minutes. After that, the rotor is made to
turn to measure the torque due to the viscous resistance
5 and thereby find the viscosity. Note that with an E-type
viscometer, it is important to calibrate it in advance by
the standard viscosity solution.
[0038] The mold powder of the present invention is
given, based on mass, a CaO/SiO2 ratio (hereinafter
10 sometimes described as "basicity") of 1.0 to 1.5. If the
basicity is less than 1.0, the amount of Si02 becomes
greater and the effect of prevention of entrainment by
suppression of the reaction cannot be obtained. The
effect of Si02 on entrainment will be explained later. On
15 the other hand, if the basicity is larger than 1.5, the
melting point of the powder becomes too high and the high
melting point crystal gehlenite is formed in the powder,
so the flowability of the melted powder remarkably
deteriorates and the infiltration and lubricity become
20 difficult to secure and also the heat extraction inside
the casting mold becomes unstable:
[ 0039 ] Next, the powder contents will be explained.
[0040] As the main components of the powder, there are
CaO and Si02. It is important to maintain the basicity
25 CaO/SiO2 in the powder at 1.0 to 1.5 as mentioned before.
[0041 ] In the powder composition of the present
invention, it is important that the Si02 in the powder be
15mass% to 30 mass%, the Na20 be 2 mass% to 6 mass%, the
B2O3 be 1 mass% to 4 mass%, and the sum of the contents of
30 Si02, Na20, and B203 be 20 mass% to 40 mass%.
[0042 ] Here, SiO2 is the main component forming the
powder and is an content necessary for adjusting the
melting temperature, viscosity, and other physical
properties. Further, the inventors newly discovered that
35 Na20 and B203 have the functions of raising the glassiness
and suppressing the formation of high melting point
crystal including A1203 and that by jointly using Na20 and
-- 10 -
B203, that effect is remarkably exhibited.
[0043 ] However, with all of Si02, Na20, and B203, if the
content is too large, reaction will easily occur with the
molten steel, so it was learned that there was a problem
5 of entrainment of powder in the molten steel.
[0044] Therefore, it was learned that, in addition to
the contents of the components of Si02, Na20, and B203, the
sum of the contents of Si02, Na20, and B203 also has, to be
prescribed.
10 [0045] Thus, the inventors discovered the optimum
ranges of the contents of the components of Si02, Na20,
and B203 and the sum of the contents of Si02, Na20, and
B203. This will be explained in detail below.
[0046 ] If the Si02 content its less than 15 mass%,
15 adjustment of the melting temperature, viscosity, and
other physical properties is difficult, so the content
has to be 15 mass% or more. However, if over 30 mass%,
the effect of inhibition of reaction between the powder
and molten steel is difficult to obtain, so the
20 resistance to entrainment deteriorates. The powder of the
present invention, as explained above, is intentionally
made to contain a predetermined amount or more of the F
content, so the activity of Si02 is low. Therefore, even
if the upper limit of Si02 is 30 mass%, the reactions
25 between the powder and molten steel can be suppressed.
[0047] As opposed to this, conventional powder in
which a predetermined amount or more of the F content is
not intentionally included has a high activity of Si02, so
even if the upper limit of Si02 is made 30 mass%, the
30 reactions between the powder and molten steel cannot be
suppressed.
[0048 ] Na20 is added for adjusting the melting point
and for raising the glass forming property and
suppressing the formation of high melting point crystal
35 containing A1203, but if the Na20 content is less than 2
mass%, that effect cannot be obtained. Further Na20 easily
reacts with the Al or Ti in molten steel, so if the Na20
- 11 -
content is over 6 mass%, the effect of prevention of
entrainment by inhibition of reactions cannot be
obtained. The more preferable range of the Na2O content is
3 mass% to 4 masso.
5 [0049] B203 is added for adjusting the melting point
and for raising the glass forming property and
suppressing the formation of high melting point crystal
containing A12O3 so as to stabilize the heat extraction in
the casting mold, but if the B2O3 content is less than 1
10 mass%, this effect cannot be obtained. Further, B203
easily reacts with the Al or Ti in molten steel, so if
the B203 content exceeds 4 mass% , the effect of prevention
of entrainment by inhibition of reactions cannot be
obtained. The preferable range of the B203 content is 2
15 mass% to 4 mass%. The more preferable lower limit of B203
is 2.5 mass%.
[0050 ] In addition to this, if the total of the
contents of the SiO2, Na2O, and B203 in the powder is less
than 20 mass%, adjustment of the melting temperature,
20 viscosity, and other physical properties becomes
difficult and the properties which inherently should be
possessed by the above-mentioned powder cannot be
satisfied. On the other hand, if the total of the
contents of SiO2, Na2O, and B203 in the powder exceeds 40
25 mass%, inhibition of the reactions between the powder and
molten steel becomes difficult and the effect of
prevention of entrainment by inhibition of reactions
cannot be obtained. The more preferable range of the
total of the contents of the SiO2, Na2O, and B2O3 is 30
30 mass% to 40 mass%.
[0051] Incidentally, as explained above, by jointly
using Na2O and B2O3, the effect of provision of the
function of raising the glass forming property and
suppressing the formation of high melting point crystal
35 containing A12O3 is remarkably exhibited. Due to this,
good heat extraction can be stably performed, so breakout
and other operational abnormalities will not occur and
- 12 -
stable operation will become possible, it was newly
discovered by experiments. The mechanism for this is
unclear, but is believed to be due to some sort of
synergistic effect caused by joint use of Na2O and B2O3.
5 [0052] The powder composition of the present invention
has a CaO content of 40 mass% or less. If the CaO content
exceeds 40 mass%, the solidification temperature becomes
higher and the infiltration and lubricity are easily
damaged.
10 [0053] On the other hand, if CaO is too small, the
viscosity rises and the lubricity falls, so this is not
preferred. Further, adjustment of the melting point
becomes difficult. Therefore, CaO is preferably made 30
mass% or more.
15 [0054] The powder composition of the present invention
has an A1203 content of 3 mass% to 25 mass%. A12O3 is added
for adjustment of the. solidification temperature and
viscosity, but if the content of A1203 in the powder is
less than 3 mass%, the effect of adjustment of the
20 solidification temperature etc. is small, while, further,
if over 25 mass%, the viscosity becomes too large, so the
infiltration and lubricity are damaged and the heat
extraction behavior becomes unstable.
[0055] In the composition of the powder of the present
25 invention, it is necessary to intentionally add CaF2 or
NaF so as to make the content of the F 10 mass% or less.
The F content lowers the powder solidification
temperature and lowers the activity of SiO2. Further, it
lowers the powder viscosity. If the F content in the
30 powder exceeds 10 mass%, the viscosity falls too much and
powder infiltration becomes excessive, so the quality of
the cast slab deteriorates. Further, CaF2 and other
crystal precipitates resulting in the heat extraction
behavior becoming unstable. The preferable content of the
35 F content is 9 mass% or less.
[0056 ] On the other hand, if the content of the F
content in the powder is too small, that is, the content
- 13 -
of the F in the powder is 2 mass% or more, the activity
of SiO7 does not drop. Further, reactions shown by the
above formula (1) and formula (2) occur between the Al
and Ti in the molten steel and the SiO2. As a result, the
5 surface tension between the molten steel and the melted
powder greatly falls and entrainment of powder into the
molten steel easily occurs.
[0057] In addition, if the content of the F in the
powder is 2 mass% or less, adjustment of the viscosity
10 becomes difficult and poor lubrication results.
[ 0058] The preferable content of the F is 2.4 mass%.
More preferably, it is 3 mass% or less.
[ 0059] Note that, "F" may take any form as a compound.
The content of F above indicates the entire content of F.
15 [0060] By making the powder the composition which have
been explained up to here, the powder of the present
invention is particularly suitable when used for casting
a slab with a high speed casting. This is because the
melted powder easily infiltrates to between the casting
20 mold and the solidifying shell.
[0061] The above summarized the component required for
the powder of the present invention and their contents.
Furthermore, the following content may be included.
[0062] In the powder composition of the present
25 invention, [.he ZrO2 content is preferably 2 mas.% to 10
mass%. ZrO2 is added in 2 mass% or more so as to secure
the viscosity. On the other hand, if the ZrO2 content in
the powder exceeds 10 mass%, the viscosity rises too much
and the lubricity falls. The more preferable range of the
30 ZrO2 content is 4 mass% or less.
[0063 ] In the powder composition of the present
invention, the SrO content is preferably 2.5 mass° to 10
mass%. By making SrO 2.5 mass% or more, it is possible to
suppress changes in the solidification temperature,
35 viscosity, and other physical property values with
respect to changes in the powder composition. On the
other hand, if the SrO content exceeds 10 mass%, the
- 14 -
production costs rise. The more preferable range of the
SrO content is 4 mass% or less.
[0064 ] Furthermore, the powder of the present
invention preferably suitably contains carbon black or
5 coke powder, graphite, and other carbons or fibers,
resins, or other organics. These carbons or organics
enable adjustment of the melting speed and have the
effect of maintaining the temperature of the molten steel
surface. Further, there is also the function as a binder
10 etc. for molding purposes.
[0065] For the composition of the powder, values
obtained by analysis by fluorescent X-rays or chemical
analysis may be used.
[0066] In the powder of the present invention, 50
15 mass% or more of the same is preferably formed from a
premelt. The "premelt base materials" are part of the raw
materials of the powder which have been melted in advance
at a high temperature. Usually, a powder starting
material is heated to 1000 to 1400°C to melt it. The
20 premelt base materials are basically comprised of CaOAl203-
Si02 with which Na20, B203, F, etc. are mixed and
which is melted and solidified at the above temperature.
50 mass% or more is made the premelt so as to make the
powder uniformly melt at the surface of the molten steel
25 in the casting mold. The form of the powder of the
present invention may be a powder or granular matter.
Further, hollow granular matter, which is superior in
terms of environmental conservation and which is superior
in the heat insulation capacity and covering ability of
30 the molten steel, is more preferable.
[006°7 ] Further, inhibition of the reaction between the
powder and molten steel has both the effects of reducing
the concentration of A1203 and Ti02 in the powder and
preventing changes in viscosity and thereby enable
35 infiltration and lubricity to be secured.
[0068 ] Here, as the reference value for suppressing a
reaction between powder and molten steel, the interfacial
i5 -
tension of the powder may be used as an indicator. The
upper limit value of the interfacial tension between the
molten steel and powder is not particularly limited, but
a higher value is preferable. As the adjustable value in
5 actual operations, 1.7N/m or so at 1550°C becomes the
general rule. Here, the interfacial tension is made the
value at 1550°C because this is a temperature which is
close to the temperature of the molten steel which'is
provided for actual continuous casting.
10 [0069] Here, the interfacial tension can be measured
by a method similar to the one which is described in
"Hiroshi Ooi, Tsutomu Nozaki, and Yutaka Yoshii_: Tetsu to
Hagane 58(1972), p. 830".
[0070] That is, in 1550°C melted powder. which has been
15 melted in a crucible, steel samples are quietly added to
make the steels melt. The shape of the molten steel in
the melted powder is captured from the side by an X-ray
photograph. It is possible to measure the shape of the
iron and find the interfacial tension from this X-ray
20 photograph.
[0071] The types of steel which the powder of the
present invention can be effectively used for are not
particularly limited so long as the molten steel contains
at least one of Al or Ti. A type of steel with a low
25 carbon concentration, for example, a type of steel with a
carbon concentration of 0.0005 to 0.05 mass%, is
susceptible to defects arising due to the powder in the
steel sheets. Therefore, the powder of the present
invention is suitable for such a type of steel.
30 [0072] Further, in the present invention, the content
of the Al or Ti in the molten steel is not limited. That
is, the content of at least one of Al and Ti is 0.1 mass%
or less. Even when using the powder of the present
invention for molten steel with a relatively low content
35 of Al or Ti, the effect of the present invention can be
sufficiently obtained.
-- 16 -
[0073] The powder of the present invention is
particularly preferably applied to the continuous casting
of an ultra low carbon steel with a concentration of Ti
in the molten steel of 0.01 to 0.07 mass%. This type of
5 steel is applied severe deformation, so it is preferable
to reduce the inclusions in the steel as much as
possible.
[0074] Further, the powder of the present invention is
particularly preferably applied to the continuous casting
10 of ultra low carbon steel with a concentration of Al in
the molten steel of 0.01 to 0.07 mass%. This type of
steel is applied severe deformation, so it is preferable
to reduce the inclusions inthe steel as much as
possible.
15 [0075] Further, the powder of the present invention is
particularly preferably applied to continuous casting of
high Al content steel where the concentration of Al in
the molten steel is over 0.1 mass%. This is because with
this type of steel, inclusions easily remain in the
20 steel.
Examples
[0076] Below, examples will be given to explain the
present invention in detail.
25 [0077] Molten steel, in 300 tons, obtained by smelting
in a converter was adjusted by a vacuum refining furnace
(RH) to predetermined concentrations to obtain ultra low
carbon steel. The molten steel was cast through a tundish
and immersion nozzle by a vertical bent type continuous
30 casting machine to obtain cast slabs of a thickness of
250 mm and a width of 1600 mm. The casting speed was 1.8
m/min.
[0078] The compositions and physical property values
of the powder and the concentrations of Al and Ti in the
35 molten steel are shown in Table 1 and Table 2
(continuation of Table 1). The Powder Nos. 1 to 21 and 50
are invention examples, while Nos. 22 to 41 and 51 are
- 17 -
comparative examples.
[0079 ] Note that, the viscosity of the powder is the
value at 1300°C and was measured using the above method.
[0080]
Table 1
Chemical compositions of powder (mass %)
Visco-
Steel compositions
( mass %)
Operability
Quality
No.
CaO SiO2 A1203 Na20 B203 F ZrO2 SrO
SiO2+Na2O
B203
CaO/
Sio
sity
(poise] C T Al Ti
Operating
abnormalities
Surface
defects
M
Press
cracking
($)
Overall
evaluation
1 22.8 15.2 12.5 5.9 3.7 9.2 4.2 6.0 24.8 1.50 7.2 0.003 0.03 0.05 G 0.2 0.1 G
2 36.5 27.5 3.8 3.9 4.0 3.1 3.0 3.2 35.4 1.33 2.9 0.002 0.04 0.02 G 0.1 0 VG
3 38.4 29.8 4.2 4.1 3.7 3.5 3.0 3.0 37.6 1.29 3.1 0.001 0.02 0.05 G 0 0 VG
4 32.4 27.5 6.8 2.1 3.4 4.1 2.1 3.1 33.0 1.18 6.2 0.003 0.02 0.04 G 0.2 0.1 G
5 36.8 28.3 3.2 4.0 3.1 2.6 3.1 3.0 35.4 1.30 2.9 0.003 0.04 0.02 G 0.2 0.1 G
6 34.5 27.4 5.5 5.9 3.7 5.1 3.0 3.3 37.0 1.26 2.5 0.001 0.03 0.02 G 0.3 0.1 G
7 32.4 27.6 4.8 4.0 1.0 6.4 3.0 3.0 32.6 1,17 2.5 0.002 0.02 0.04 G 0.3 0.1 G
8 34.8 27.9 5.5 5.9 2.8 5.1 3.1 3.1 36.6 1.25 2.4 0.003 0.04 0.04 G 0.2 0 VG
9 35.2 28.3 3.9 3.8 4.0 3.8 3.1 2.9 36.1 1.24 3.4 0.002 0.02 0.03 G 0.1 0.1 VG
10 n 34.8 28.1 5.5 5.9 2.8 4.9 0.0 3.0 36.8 1.24 2.6 0.003 0.04 0.02 G 0.2 0 VG
11 ° 35.2 28.2 3.8 3.9 3.8 3.8 3.1 0.0 35.9 1.25 3.4 0.002 0.04 0.02 G 0.1 0.1 VG
12
e
27.6 26.5 9.2 3.1 1.2 8.3 0.0 0.0 30.8 1.04 7.1 0.004 0.03 0.03 G 0.2 0.1 G
13
x
24.6 16.5 10.2 3.1 1.2 8.3 4.5 6.4 20.8 1.49 5.1 0.002 0.02 0.05 G 0.1 0 VG
14
-
38.2 29.8 4.8 5.8 3.9 4.5 2.9 3.0 39.5 1.28 2.5 0.003 0.04 0.03 G 0.2 0 VG
T5 29.1 28.2 3.8 3.8 3.9 4.1 4.2 4.1 35.9 1.03 6.0 0.003 0.02 0.04 G 0.2 0.1 G
16 38.6 28.5 3.9 4.8 3.4 2.4 3.0 3.0 36.7 1.35 2.6 0.001 0.02 0.04 0 0.1 0 VG
17 39.8 26.7 5.2 5.2 3.6 5.1 3.0 3.0 35.5 1.49 1.8 0.003 0.03 -0.02 G 0.1 0.1 VG
18 36.2 24.9 3.1 5.1 3.2 6.7 4.2 4.3 33.2 1.45 0.8 0.002 0.03 0.03 G 0.3 0.1 G
19 36.4 28.7 3.5 4.1 2.5 5.1 3.0 2.9 35.3 1.27 2.4 0.002 0.05 0.02 G 0.2 0.1 G
20 39.1 27.5 6.2 3.2 2.5 3.4 3.1 3.0 33.2 1.42 2.8 0.003 0.04 0.02 G 0.1 0 VG
21 35.4 29.5 10.3 2.4 1.9 5.0 3.3 3.4 33.8 1.20 7.8 0.001 0.03 0.04 G 0.2 0.1 G
50 34.8 27.9 5.5 5.9 2.8 5.1 3.1 3.1 36.6 1.25 2.4 0.002 0.70 -0.01 G 0.2 0.1 VG
[0081] Table 2
Chemical compositions of powder (mass%)
Visco-
Steel compositions
(mass%)
Operability
Quality
No.
aO i02 1203 a2O 203 F r02 rO
Si Oz+NazO
+3 03
CaO/
Si02
sity
[poise] C l i
Operating
abnormalities
Surface
defects
(%)
Press
cracking
(%)
Overall
evaluation
22 48.0 29.8 5.2 3.6 2.9 4.1 1.5 1.5 36.3 1.61 1.7 0.004 0.02 0.03 P 0.3 0.2 P
23 19.0 12.7 12.8 5.8 3.9 9.8 6.8 7.8 22.4 1.50 8.0 0.002 0.04 0.02 P 0.3 0.1 P
24 38.7 38.1 3.2 7.3 2.5 3.6 1.7 3.1 47.9 1.02 4.0 0.003 0.02 0.05 G 1.8 0.5 P
25 35.6 29.8 0.3 6.2 1.8 4.1 3.0 3.0 37.8 1.19 2.3 0.001 0.03 0.05 P 1.5 0.5 P
26 23.3 20.9 35.4 5.6 2.3 6.7 1.8 2.4 28.8 1.11 20.5 0.003 0.05 0.04 1 P 0.3 0.3 P
27 32.5 27.1 6.9 0.0 2.5 3.3 3.9 4.5 29.6 1.20 7.9 0.003 0.03 0.04 P 0.4 0.1 P
28 33.5 28.1 7.2 1.1 2.1 3.0 4.5 5.1 31.3 1.19 7.8 0.002 0.03 0.03 P 0.4 0.1 P
29 C 37.2 27.3 5.8 6.7 2.1 3.4 3.0 3.0 36.1 1.36 1.4 0.002 0.04 0.04 P 1.7 0.6 P
30 ° 36.2 24.5 3.4 3.5 0.0 5.9 3.3 3.1 28.0 1.48 2.3 0.003 0.02 0.04 P 0.2 0.1 P
31 m 36.7 25.4 3.1 3.5 0.3 6.1 3.2 2.9 29.2 1.44 1.4 0.001 0.02 0.04 P 0.5 0.2 P
32 p 36.4 28.5 4.1 3.5 5.5 3.9 2.8 3.0 37.5 1.28 4.2 0.001 0.03 0.02 G 1.8 0.6 P
33
e
34.5 25.1 5.8 3.4 2.5 15.2 3.0 3.0 31.0 1.37 1.0 0.003 0.04 0.02 P 1.5 0.4 P
34 x 33.2 26.1 5.2 2.8 2.8 3.9 13.0 3.0 31.7 1.27 4.3 0.003 0.04 0.05 P 0.4 0.2 P
35 31.3 25.9 3.8 5.1 3.4 6.8 3.0 15.1 34.4 1.21 2.1 0.002 0.02 0.02 P 0.3 0.3 P
36 22.6 15.1 12.5 2.0 1.1 9.8 7.2 9.2 18.2 1.50 7.9 0.002 0.03 0.04 P 0.4 0.2 P
37 21.5 27.5 7.8 5.2 3.8 9.1 1.5 3.0 36.5 0.78 7.3 0.001 0.04 0.02 G 1.8 0.5 P
38 39.5 17.2 12.3 4.2 3.7 2.8 3.0 3.0 25.1 2.30 3.9 0.003 0.02 0.05 P 1.3 0.4 P
39 33.5 15.0 3.0 5.9 1.1 9.8 0.9 6.7 22.0 2.23 0.2 0.003 0.02 0.02 G 2.1 0.5 P
40 36.0 26.5 15.8 2.9 1.3 5.1 1.5 2.1 30.7 1.36 20.9 0.001 0.04 0.02 P 0.4 0.2 P
41 41.0 29.0 12.0 2.3 0.0 1.0 0.0 0.0 31.3 1.41 5.0 0.001 0.03 0.02 P 1.1 0.6 P
51 22.6 15.1 12.5 2.0 1.1 9.8 7.2 9.2 18.2 1.50 7.9 0.002 0.60 0.01 P 1.2 0.7 P
-- 20 -
[0082] The cast slabs which were obtained by casting
were hot rolled, pickled, cold rolled, and annealed by
ordinary methods to obtain steel sheet for automobile
use. The surfaces were observed so as to investigate
5 surface defects. The sheets were press formed to inspect
for the occurrence of cracking. The quality of the steel
sheets were evaluated by the rates of occurrence of
surface defects and press cracking.
[0033] Further, the operability was evaluated placing
10 a thermocouple in the casting mold, continuously
measuring the trends in temperature, and judging the case
where the trend in temperature was stable as "G (Good)"
and the case where the trend in temperature was unstable
or the case where breakout and, other operational
15 abnormalities occurred as "P (Poor)".
[0084] Further, regarding the overall evaluation, the
case where there were no operational abnormalities and,
in quality, the sum of the surface defects and press
cracking was 0.2% or less was evaluated as "VG (Very
20 Good)", the case where there were no operational
abnormalities and, in quality, the sum of the surface
defects and press cracking was greater than 0.2% to 0.4%
as "G (Good)", and the case where operational
abnormalities occurred or, in quality, the sum of the
25 surface defects and press cracking was greater Lhan 0.4%
as "P (Poor)".
[0005] As a result, as shown in Table 1 and Table 2,
in continuous casting using the present invention, no
breakout alarms due to unstable infiltration or breakout
30 or other operational abnormalities could be seen at all,
while in the comparative examples, these operational
abnormalities were often seen.
[0005] In particular, if viewing the three component
of Si02, Na20, and B203, Nos. 27 and 28 of the comparative
35 examples are the case where Na20 is not contained or the
case where it is smaller in amount than the range of the
present invention. Even if the contents of the remaining
- 21 -
Si02 and B203 and the sum of the contents of Si02, Na20,
and B203 are in the ranges of the present invention,
operating abnormalities occurred.
[0087] Further, Nos. 30 and 31 of the comparative
5 examples are the case where B203 is not contained or the
case where it is smaller in amount than the range of the
present invention. Even if the contents of the remaining
Si02 and Na20 and the sum of the contents of Si02, Na20,
and B203 are in the ranges of the present invention,
10 operating abnormalities occurred.
[0088] As opposed to this, in Nos. 1 to 21 and No. 50
of the invention examples in the range of the present
invention, in each case, no operational abnormalities
could be seen at all.
15 [0089] This is because, in the comparative examples,
the contents of Na20 and B203 were outside the range of
the present invention, so formation of high melting point
crystal could not be sufficiently suppressed and the heat
extraction deteriorated, while in the invention examples,
20 in each case, it is believed that the formation of high
melting point crystal could be sufficiently suppressed
and good heat extraction could be realized.
[0090] Further, in the product sheets using the steel
slabs of the invention examples, the rate of occurrence
25 of surface defects due to powder and the rate of
occurrence of cracks at the time of press forming were
greatly reduced compared with the conventional examples.
[0-091] This time, a vertical bending type continuous
casting facility was used, but similar effects are
30 confirmed even in a curved type and vertical type
continuous casting facility. Further, in the present
embodiment, the example relating to production of a cast
slab for steel sheet for automobile use was explained,
but the gist of the present art is to stabilize heat
35 extraction in the casting mold and prevent defects caused
by powder entrainment. The effects are confirmed in the
case of producing cast slabs for steel sheet for can use,
- 22 -
steel pipe, and other steel as well.
[0092 ] Note that, the above explanation only
illustrates embodiments of the present invention. The
present invention can be changed in various ways in the
5 scope of the claims.
Industrial Applicability
[0093 ] As explained above, according to the present
invention, it is possible to produce a high grade steel,
10 free of defects caused by powder, by a high productivity.
Therefore, the present invention is high in value of
utilization in industry.

CLAIMS
Claim 1. Mold powder for continuous casting use which is
used for continuous casting of steel which contains at
least one of Al or Ti, said mold powder for continuous
5 casting of steel characterized by comprising CaO/SiO2, by
mass ratio, of 1.0 to 1.5, Si02 of 15 mass% to 30 mass%,
CaO of 30 mass% to 40 mass%, A1203 of 3 mass% to 25 mass%,
Na20 of 2 mass% to 6 mass%, an F content which is added by
CaF2 or NaF of over 2 mass% to 10 mass%, B203 of 1 masso
10 to 4 mass%, where a sum of the mass% of Si02, Na20, and
B203 is 20.mass%'to 40 mass%, and a balance of unavoidable
impurities and by having a viscosity at 1300°C of 0.5
poise to 8 poise.
where, CaO is value converting all of Ca which is
15 contained in powder to CaO.
Claim 2. Mold powder for continuous casting use as set
forth in claim 1, characterized by further containing one
or more of Zr02 of 2 mass% to 10 mass% and SrO of 2.5
20 mass% to 10 mass%.