Note: Descriptions are shown in the official language in which they were submitted.
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~ETHOD AND AGE,NTS FO~ PE~ODUC~NG CLEA~I STI:EL.
Background of the Invention
Technical Field:
This invention rela-tes to a method and agents Eor pro-
ducing exceptionally clean s-teel ~or continuous casting and
the like.
Description oC the Prior Art:
The prior art me-thods and agents heretoEore used Eor
the cleansing oE steel of non-metallic inclusions are
represented by U.S. Paten-ts 2,Z21,784, 4,036,635, 4 J Z17,134,
4,238,227 and 4,290,173.
Patent 2,221,784 discloses the use of additive agents
containing silicon, calcium, aluminum and at least one metal
selected from the group consisting of titanium and zirconium,
the additive being added -to the molten steel in the ladle.
Patent 4,036,635 discloses a steel melt formed under
an iron oxide containing slag held back while the steel mel-t
is tapped and subjected to deoxidation with silicon or
aluminum plus an af-ter treatment with a calcium containing
substance such as calcium silicon or calcium carbide.
Patent 4,217,134 discloses -the use of compositions
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comprising lime, fluorspar, ancl ground a:Luminum used in a
method of desulphurizing molten s-teel by adding the composi-
tions to the steel in -the :Ladle or injec-ting the composition
in particulate form in-to the molten s-teel.
Paten-t No. 4,238,227 discloses the use of a high amoun-t
of aluminum added -to the tap ladle be:Eore the -firs-t one-third
volume of steel is tapped and -then adding conventional
deoxidizers while the final two-thirds volume of steel is
tapped. Argon gas is subsequently blown through -the steel.
Patent 4,490,173 disc]oses -the use of additi.ve composi-
tions for flux solubilization, desulphuriza-tion and -the
removal of inclusions. The addi-tive composition includes
lime and a compound selected from the group consisting of
bauxite and mix-tures of calcium alimunate and bauxite.
The present invention eliminates the several problems
generally associated with the prior art methods and addi-tives
used in at-tempting to produce a clean s-teel particularly
suited for use in a continuous caster and incidentally
reduces the amount of aluminum as a deoxidizing agent to
approximately one-half of the amount heretofore believed
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necessary.
Summary O e the Invent.ion
A method and agents for producing excep-tionally clean
s-teel results in floa-ting all available non-me-tallic inclusions
to the surface of the s-teel being treated in a ladle where
they engage and are absorbed by a ladle covering compound,as
disclosed in my Paten-t 4,462,834,which contains burnt lime,
aluminum dross, fluorspar, and acid -treated graphite. The
method begins when the steel is first poured into the ladle
from the source, such as a conver-ter, electric furnace, etc.,at
which time a desulphurizing composi-tion is added simultaneously
with the molten steel; the desulphurizing material comprising
calcium eluoride, sodium carbona-te, and calcium hydroxide J
followed by the addition of a deoxidizing agent when about
one-third of the volume of steel has been added to the ladle,
the deoxidizing agent comprising metallic aluminum; this is
followed by the addition of a slag conditioning composition
when the ladle is approximately oDe-half full, the slag
conditioning composition comprising calcium oxide and calcium
and aluminum in an alloy including a small percentage of
magnesium, adding an expandable ladle cover and immediately
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followed by the in-troducti.on of ~rgon gas into the lower portion
of -the mel-t in suf-ficien-t volume and a-t a rate of introduction
sufficien-t to cause desirable turbulence in -the mol-ten metal
comprising the melt. The final step in the method is the
addition of a fina~ deoxidizing additive comprising metallic
aluminum. The -total amount of metallic aluminum as deoxidizing
agents introduced in separate and dis-tinc-t s-teps is approxi-
mately one-half the amount of metallic aluminum heretofore
believed necessary in deoxidizing mol-ten s-teel.
Description of the Preferred Embodiment
Those skilled in the art relating to producing steel
will recognize the desirable resul-ts of the presen-t invention
which produces exceptionally clean steel which may be any
grade of steel with -the leas-t non-metallic content. The
method is preferably practiced in a ladle to which molten
steel from a conventional source, such as a converter, electric
~urance and the like, is tapped. The ladle may be of any
size from 30 tons -to 300 tons capacity and the s-teel intro-
duced into the ladle may beat 3000F. or it may vary 200 F.
ei-ther way.
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The firs-t step of the method disclosed herein comprises
the positioning in -the l.adle O:e a desulphurizing agent
comprising a first additi.ve compound consisting of equal
amounts of calcium fluoride, sodium carbonate, and calcium
hydroxide followed by the in-troduction of molten s-teel in-to
the ladle or alternately addi.ng the :Eirst additive compound
-to the first s-teel introduced in-to the ladle. The second
step in the method is performed when the ladle is half full
of molten s-teel and comprises the introduction of a second
additive consisting of one-half of the normal metallic
aluminum additi.on used in deoxidizing steel together with
the addition of a third addi-tive comprising a slag condition-
ing compound consisting of equal amounts of calcium oxide and
calcium and an aluminum alloy comprising 95% aluminum
and 5% magnesium. The fourth step in the method
comprises -the addition of an expandable ladle cover w~ich
includes burnt lime, aluminum dross, fluorspar, and acid
treated graphite-which forms a slag-like layer on the molten
metal for absorbing the non-metallic inclusions,simul-taneously
creating a stirring and/or similar desirable turbulence in -the
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molten metal as by the injec-tion Oe Argon gas -through a
bottom ladle plug replacement or a hollow re-Eractory lance,
the amount and rate of fiow of -the ~rgon gas being sufficient
-to result in the desired turbulence. The introduction Oe
-the metallic aluminum addi-tive and the slag conditioning
compound results in a chemical reaction tha-t forces the
aluminum to disperse to -the ultimate degree withou-t becoming
alloyed -to ei-ther the free floating molten refractory in -the
molten steel or any of the soluable non-metallics that have
been libera-ted from their various alloys.
Those skilled in the art will observe that the non-
metallic inclusions normally found in molten steel may be
traced to the refractory materia] present as a liner in the
converter, electric furnace, etc. and/or the ladle in which
the molten me-tal -is received.
Oxygen an,d sulphur in the molten metal are responsible
for most of the non-metallic inclusions as sulphur is soluable
in steel at all temperatures above the mel-ting point and
oxygen is present in steels which are not comple-tely de-
oxidized.The deoxidizers, such as aluminum, when added to the
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ladle form oxides wl-th the dissolved oxygen in the steel.
The introduc-tion o~ -the slag conditionirlg compound herein-
be~ore se-t Eorth and the expanding ladle cover as hereinbe~ore
set forth together with -the induced -turbulence forces chemically
and physical con-tact of all of -the insoluable non-metallics
and the -rree sulphur and free aluminum oxide to rise to the
-top o-f the steel in the ladle and contact and be absorbed in
the expanding ladle cover compound. The expanding ladle
cover compound herein referred -to expands i-ts volume between
50% and 100% and this expansion of volume results in the
absorption of the non-metallics that are forced -to the top
o~ the molten s-teel by -the induced turbulence.
The products absorbed by the expanding ladle cover
compound are held in the cover compound until the molten
steel is removed irom the bo-t-tom of the ladle and they do
not revert into the molten metal.
The materials in the first additive comprising the
calcium fluroide, the sodium carbonate, and the calcium
hydroxide are present in equal amounts, the amount o~ each
ingredient being between 5 lbs. and 15 lbs. per -ton of molten
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s-teel. The metallic aluminum added when -the ladle is hal~
full is approximately one-fourth the amount o~ aluminum used
as a deoxidizer in the prior art. It is the usual prac-tice
of adding deoxidizers such as aluminum during tapping to
control the amount of aluminum in direct portion to the
steel's oxygen conten-t. Since -the oxygen content of the
liquid steel is not usually measured, -the aluminum addition
is usually de-ter~ined approximately in inverse propora-tion
to the carbon content. A curve relating total product oxygen
and carbon conten-t oE the liquid steel has been used to
determine the optimum amoun-t of aluminum needed to react
with the particularly amount of oxygen a-t each carbon content,
for example, molten s-teel having a carbon content of 0.10%
is usually treated with 165 lbs. of aluminum per 100 tons of
i5 steel or approximately one and three-quarter lbs. per ton.
In practicing the present invention, the amount of
metallic aluminum added to the ladle when the same is one-
third full and after adding the desulphurizing compound
may be an amount between three-quarter of a lb. and one and
one-quarter lbs. per ton of molten steel.
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The second addi.tive compound comprising -the slag conditioner
which is added to the ladle immedia-tely af-ter the metallic
aluminum or when the ladle is half full comprises the calcium
oxide and calcium in equal amounts and wherein -the amount
- 5 of each of -the ingredien-ts is between 5 and 15 lbs. per -ton
of molten metal. The introduction o~ ~rgon gas in suiflcient
quan-tities and at a ra-te to create a desirable turbulence
and/or stirring motion of the molten me-tal results in a
chemical reaction that forces the me-tallic aluminum to disperse
the ultimate degree withou-t becoming alloyed to either the
free -Floa-ting molten refrac-tory or any of the insoluable
non-metallics tha-t have been liberated from their various
alloys in the steel.
Those skilled in -the art will observe that the desulphurizer
compound plus the slag conditioner and -the metallic aluminum
-to which any other required alloys needed to meet the desired
aim chemistry are all in the molten bath and the same is slag-
-Cree or containsaminimum amount o~ furnace slag and that
the expanding ladle cover compound over the complete mol-ten bath
forces chemical and physical contact of all of the insol.uable
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non-metallics ancl the Eree sulphu:r and -the Eree meta:llic
aluminum tha-t are being subjec-ted to -the turbul.ence to rise
to the -top o-~ -the steel ba-th and come in con-tact and be
absorbed by the expancling ladle cover compound.
Those skilled in the ar-t will recognize that the
cleansing o:E -the steel requires time and temperature control
as -the additives cause a rapid heat 105s over an extended
period oE time during the tapping cycle which is the time i-t
-takes for -the -Eurnace to discharge its molten metal in-to the
receiving ladle.
The present invention enables a more accurate and complete
control o-E the time of the cleaning cycle and therefore
con-trols the temperature by preventing the otherwise rapid
heat loss.
A-t a predetermined time and/or predetermined -temperat-ure,
the ladle carrylng the clean steel is moved to a trim
station and a small additional quantity oi metallic aluminum
added as a final deoxidizing agent. The amount o~ the metallic
aluminum Einally added to the molten s-teel at the trim station
is an amount subs-tantially the same as -tha-t initially added
and it will occur to those skilled in the art that the -to-tal
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of the metallic a:Luminum added in -the two s-tages is approxi-
mately one-hal-f the metallic aluminum heretofore used as
deoxidizers in the cleansi.ng of stee]. by the me-thods hereto-
fore known in the ar-t.
It will occur to.those skilled in the art that the
required turbulence and/or s-tirring o-f the molten steel
may be readily achieved -through the use o:E a gas in-troducing
plug in the bottom of the ladle and/or through the use o-f a
hollow lance arranged to discharge the gas at or adjacen-t
its lower end and it will -further occur to those skilled in
the art -that the additives including -the desulphurizing
material and the slag conditioning compound and the metallic
aluminum may be introduced in small particle size along with
the Argon gas.
Al-though but one embodiment of the present invention
has been described in the foregoing specification, it will
be apparent to those skilled in the art -that various
modiEications may be made therein without ~eparting ~rom
the spirit O-e the invention and having thus described my
invention, what I claim is:
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