Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Field of the In~ention
The present invention relates to the treat~
ment of steel melts and, mora particularly, to the
treatment of steel melts wi~h alXaline-earth-metal
trea~ing agents.
Back round of the Invention
,g ~
It ha~ been known heretofore in steel
mQ~allurgy to treat s~eel melts in a deoxidized
or nondeoxldized sta~ with treating agents con-
taining alkaline-earth me~als. Gcnerally the
all~line-earth metals are ~he elem~ntal or pure
m~tals or are provided in mixtures, compounds or
alloys.
The moBt com~on alkaline-ea~th metals used
for this purpose ar~ calcium and m~gnesium and typicaL
treatmen~ agents include calcium carbide, calclum-
-silicon (CaSi) or calcium ferrosilicon which consists
o 30% by weight calcium, 60~/o by w~ight silicon and
10~/o by weigh~ iron.
Other trestment agents include in addi~ion
~o the calcium or magnesium and apart from silicon,
substances such as aluminum and manganeseO
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The treatm~nt agent is generally blown lnto the
melt at a depth of 2000 mm or more to increase the degree
o effec~i~eness and the reaction of the ~rea~ing agent
with the 1.nelt~
The treatment serves to purify the melt by re-
ducing the oxygen content and the content of oxidic im-
purities, improves the elimination of sulfides which may
remain aftsr desulfurization, etc.
For the mDst part the treatment quantities are
the ~oichiometric requirement and substan~ially ~o excess
unreacted alkaline-earth-metal treat~ent agent remains in
the meltO
In the conventional systems, substantially only
deoxidized steal m~l~s are treated to obtain m~xlmum utilization .-
o~ the all~line-car~h treating agentO Howeve~, it has been
recognized that the introduction of the entire quantity of
the alkaline-earth treating agent into ~he mel~ in a single
administration results in volatillzation of this agent and
hence it has been proposed to control the ra~e of addition ~:
so that at any instant in time the quantity which is added
is equal to the quantity which reactsO The reac~ion speed
depends on the thermodynamic and reaction-kinetic paramet~rs
of the total system. With this approach one is able to
achieve excellent utllization of the alkaline-eartll treating
agen~9 effective ductility and elongation to brealc and the
like. However, it is not possible to furtller improve the
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~hrinkage and viscosity characteristics~ -
Ob ects of the Inv ntion
It is the principal object of the present in-
ven~ion to provide a method of or process for treating
a steel melt with an all~line-earth treating agent which
o~
i5 applicable to deoxldized4nondeoxidized steel melts and
which improv~ the ductllity and break contraction char-
acteristics of the steel and is also capable o improving
the i80tropy 0~ the systemO
Descript~on of the Inventlon
Thi~ object and other which will become apparsnt
her~ina~ter ar~ attained, in accordance w~th th& invention, ..
by a process for introducing allcaline-earth treating agents
into a steel melt whereby the st~el melt ~in a deoxidized
or nondeoxidized state) i~ introdu¢sd into a casting ladle
with a siliceou -oxlde-~ree lining, is covered with a
synthetlc slliceous-oxide~ree slag, and is ~rea~ed with
the requisite quan~ity of alkaline-earth metal treating
agent in finely divided form by blowing the treating agent
in a neutral carrier gas (e.g. argon~ into the steel m~lto
The i~vention resides in that the necessary quanti~y
_
of allualine-earth treating ag~nt is introduced in deficit
or in reduced amount below that dictated by reaction
equilibrium and over a longer period ~han i~ otherwi~e
requiredO In oth~r words if the quantity Q of the trea~lng
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agent is stoichiometrically required by the melt and the
quantity i9 introduced at a rate R ~ which corresponds
~o the rate at ~Jhich the treating agenS is capable of
reacting with the sy~tem under the thermodynamic and
r&action-kinetic condltions mentioned abo~e, the rate R
corresponds ~o the customary rate of addltionO The trea~-
ment tim~ t will then be determined by the ralation~hip
t-Q/Ro According to the invention, however, the ~reating
agent i8 added at a rat2 R'<R and over a period t'~t~ - :
Pre~erably ~ 5 minutes and R'~ 0.6 kg
of Ca pe~ ~on of steel. The "breal~ contraction" referred ~o
hereina~ter is the percent reduction in a linesr dimension a~
break caused by the application o tensile stressO Thus
(break contraction) : ~ar~ x 100% in percen~ where d is
the linear dim~nsion (e~g. thiclcness) prior to application :~
of tensile ~tres~ and d' is the same dimension a~ter brealc.
More specifically, th~ deficit supply of
the all;aline-ear~h treating agent or agen~s m~ans tha~ the
reaction rate is limi~ed by the rats of supply which is less
than the maximum po~sible reaction rate under the thermodynamic : :.
peram~ters and reaction kinetic parameters and therefore
substantially smaller than the rate at w~ich the treating
agsnt has been supplied heretoforeO The tarm "prolonged'~
when u~ed herein to refer to the treatment time thu~ means a
~ime substantially grea~er than the treatment ~lme used for
the same quantity per ton of similar trea~ing agents heretofore~
Preferably the rate R' of the addition of the treating agent
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in accordance with the present invention is less than
0~5R where R is the rate of addition corresponding to the
maximum rate of reaction as de~ined above and the period
o~ addition t according to ~he invention is at least
equal to 2t where t is the addition rate for a given
quantity Q o~ the treating agent which is necessary to .!
maintain the ra~e of addition R.
Surprisingly, by the deficit and prolonged
addition ~f the alumin-~m earth treating agent, the
ductility characteristics can be increased and it is
pos~ible to lmprove substantially th~ constriction of
the r~sulting metal body at break (break contraction)
to 5O~/O or greater. The isotropy of th~se characteris~ics
is also improvedO
It has been ~ound that the introductlon of the
alkaline-earth ~rea~ing agent shouLd take place at a
depth in excess of ~000 mm, preferably about 2700 mm, in
the steel melt uslng lan~es or the likeO An important
advantage of the invention is that it can be carried out
with nondeoxidized steel melts as well 8S with deoxidized
me~ts~
When the reaction is carried out wi~h nondeoxidized
melts, the alkaline-earth treatlng agent is introduced prior
to and up to the ~ermination o~ deoxidation in the melt~
When the treatment is carried out with deoxidized ~teel
melts, the reactlon is carried out until ~he deoxidized
but yet sul~ur-containing melt has reached a desul~urizatlon
degree of 60%~
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Deoxidation and desulfuriza~ion otherwise can
be carried out by any of the conventional processes.
0~ course the trea~men~ according ~o the present in-
vention can be carried out as part o the dooxida~ion
or desulfuriza~ion process or both so that the lat~ar
treatment and the alkaline-earth treatment according to
ehe inven~ion can o~erlap. The processes may b~ con- ~ .
trolled in terms of the degree of desulfurization as .
indicat0d earlier.
~leC :
A 120 ~ons nondeoxidi~d sS~el melt has a com-
position by weigh~ of:
0.17~/~ carbon ~C~
0.01% s~licon (ST3 ~ ;
0080% mangane~e (Mn~
0~01~/o phosphorous (P) ~ :
0~017% 8ulfur (S)
0.002% aluminum (Al)
Balance iron tFe)
The melt in a dolomlte-line casting ladle is
covered with 500 kg of synthetic ~lag consisting of 80%
by weighS lime (CaO) and 20% by weight calcium fluorid~
(CaF2 ) ~
The treatlng agent was 400 kg of c~lcium-silicon
(30% by welght calcium, 60% by weight ~ilicon, 3% by
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weight aluminum, balance iron) and was introduced in ~.
powder ~orm using aluminum as a carrier gas and through
lances to a depth oE about 2600 mm below the sur~ac~ of
the melt over a period of over twelv~ minutesO
The composition of the melt af~er inj2ction
of the calcium silicon wa6
0.17% by weight carbon
0.21% by weight silicon
0.~8Vb by weight manganese
0.012% by weig~t phosphorous
0.006% by weight sulfur
0.010% by weight aluminum ..
balance iron
The steel mel~ was cast into ingots and rolled
into 50 mm thick sheets. The break contraction-in the
thi~kness direction of the sheets was 65 ~o 68O9%o
. . . ~
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110 tons of a deoxidiæed steel melt has a com-
position of
0013% by w~ight carbon
0.41% by weigh~ silicon
1~45% by w~ight manganese
0.025% by weight phosphorous
0.017% by w2ight sulfur
0.068% by weight aluminum
balance iron.
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In a casting ladle a3 deqcribed in Example I,
the steel ~elt was covered ~ith 450 kg of a synthetic
slag consis~ing o 80% by weigh~ calcium oxide and 20%
by weight calcium fluorideO
10 kg of magnesium powder and 100 kg of
ma~ne~ium ox~de powder are blown in argon into the steel .:
melt at a depth of about 2700 mm over a period of ~en
minutes~
~ er the ~reatmen~ the composition of ~he
melt is:
.
0013% carbon
0~40% silicon
1~45% manganese ..
00024% phosphorou~
0.007% sulfur
00045% aluminum
balance iron
After the steel has been rolled as described in
Example 1, the breal~ge contra~tion was 50% or reO
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