Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
There is known method and means for melting solid ma-
terials bearing iron, such as scrap metal, with heat produced
by the combustion of a fuel and essentially pure oxygen. It
is also known to add reagents to the melt stream or the melt
receiving vessel for controlling the steel melt composition and/or
refining the steel.
It is always a desideratum in the steel industry to
reduce the cost of producing steel. Considerable effort is and
has been made toward the development of techniques for direct
- melting of steel on a continuous basis and toward eliminating
any processinc, steps.
It is known in the electric furnace steelmaking art to
segregate steel scrap and to select the grades of scrap which
together contain the constituents necessary to make the desired
heat. In the electric furnace pra~tice there are involved the
melt-down and/or oxidizing period and the refining period.
The electrodes in the basi~ electric furnace melt the
charge portion directly beneath the electrodes and eventually a
pool of collected molten metal is formed on the furnace hearth.
~he pool provides a source of radiant heat for assisting in
melting the remainder of the charge. During the melting process,
a slag is formed on the surface of the pool.
In a single slag process, the slag is first oxidized
and then rendered reducing by adding the required materials during
the refining period; in a double slag process, the initially
formed slag is removed through the charging door and then a second
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slag is formed by adding materlals.
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It will be apparent that both the single slag and the
double slag processes are batch or intermittent type operations as
opposed to continuous melting operations wherein raw materials are
being continuously fed to and discharged from the meltîng vessel.
OBJRCTS AND SUMMARY OF THE I~VENTION
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It is an object oE this invention to provide a method
Eor the production of steel which obviates the need for refining
the molten metal after melting.
It is another object of this invention to provide an
- 10 improved method for the continuous melting of iron bearing material
in solid form and directly producing a steel having the desired
end chemistry.
In one particular aspect the present invention provides
a continuous process for producing steel, which comprises providing
in an oxy-fuel fired melting vessel a charge of solid steel of
; - preselected composition containing the principal elements and in
proportions corresponding substantially to those of the desired
steel end product, and melting and tapping said charge at a temper-
ature of at least 2800F, and converting the resultant liquid metal
2-0 to a solid form in the absence of a refining step and a slag removal
step.
~dditions from a separate or auxiliary melter may be
; added to make up for any chemical ingredient deficiencies in the
melt as received from the primary melter. This invention also
contemplates a tap temperature from the melting vessel of at least
2800F in order to deter "skulling" in the ~ollection vessel.
Auxiliary heating means may be provided to achieve this or greater
temperatures, if necessary, to maintain such temperatures and may
be in the form of supplemental burners.
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DESCRIPTION OF PREFERRED EMBODIMENT
This invention contemplates the melting of iron bearing
materials in solid form on a continuous basis, which is contra-
distinct to intermittent or batch type operations. The iron
bearing material is preferably in the form of selected scrap
steel, i.e., steel which has been previously refined. The end
product chemical speciflcations will dictate the type of scrap
which will be employed, e.g., if the desired end product con-
templates low sulfur and low phosphorus contents, the scrap charge
should comprise material having correspondingly low sulfur and
phosphorus. Contingent upon such specifications, the scrap metal
selection may be made from one or from a combination of types
or grades.
If it is desired to produce alloy steels from (or make
allo~ additions to) carbon steel scrap charges, non-consumable
additions are made directly in the melting furnace as part of
the charge. Such additions may be in the form of alloy scrap
containing the desired alloying elements. In order to obtain
better control of the dispersion of the desired alloying element,
it is preferred that alloy additions be made in the form of ferro-
alloys. Some of the common alloy addition agents include molyb-
denum, copper, nickel,chromium. ~ agents which are easily
susceptible to oxldatlon, and thus may be termed "consumable"
a~e not usuall~ added during the melting operatlon but lnstead
are added as required in the recelving vessel.
In an exemplary embodiment for pxoduclng automotive
quality steel, the scrap charge may comprlse a No. l bundle* class
~f scrap, whlch one would expect to have the chemical composition
*Designations of the Institute of Scrap Iron and Steel, Inc.
as shown in its yearboo~ publication "Facts", copyright 1970
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as shown in the included table.
In another exemplary embodiment for producing steel
having higher permissible sulfur, phosphorus, and other residual
contents, a lower quality steel scrap charge, such as No. 2
bundles* may be used. The end product steel might be used in
the production of seamless pipe, electric weld pipe, plates,
bars, etc.
In other embodiments, such as in the production of re~
sulfurized steels, the scrap charge may be comprised of scrap
turnings. The expected chemical composition is shown in the table.
Expected maximum %,
(by weight)
Chemical Ingredients No. 1 No. 2 Turnings
(in addition to iron-FE) Bundle Bundle
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Carbon (C) .15 .60 .60*
Sulfur (S) .03 .10 .20
Copper (Cu) .04 .70 .20
Nickel (Ni) .02 .15 .40
Chromium (C-) .02 .20 O40
Molybdenum (Mo) .01 .10 .20
Tin (Sn) ,009 .10 .025
Phosphorus (P) .010 .05 .04
Lead (Pb) nil .lO .05
* Contingentupon source, some turnings may contain as high as 2.0% C.
These compositions are to be considered general in nature
and any deyiations ~rom actual scrap used do not necessarily re-
strict ~heir use, as other grades of scrap are available and
usable in the process.
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In other embodiments two or more classes of scrap may
be melted, preferably each in a separate furnace, and the melts
collected in a common ladle, or receiving vessel. Alloy addi-
tions may be made by melting alloy scrap in a separate or auxili-
ary melting furnace and adding the resultant melt to the melt
of the primary grade of scrap, or by melting the alloy constitu-
- ents directly with the basic charge material in the primary melt-
ing vessel.
The process of the present invention contemplates the
feeding of a charge which is primarily scrap metal, i.e., metal
which has heen previously refined, into an oxy~fuel fired melting
vessel. The high temperature ~lame is directed toward,the bottom
of the feed stack and the exhausting products of combustion ascend
through the stack to preheat the metal before it reaches the
flame'target area. As the charge is rendered molten at the bottom
of the feed stack, the feed column descends to provide a substan-
tially continuous target of solid metal charge for the flame.
Preferably, the melt is immediately discharged through one or more
tap holes at the bottom of the melting vessel.
2~ The preselected scrap is charged on a continuous basis,
continuously melted, and immediately tapped so as not to accumu-
late on the hearth of the melting vessel. Thus, there is no re-
servoir of molten metal in the melting vessel, and a transition
from a non-alloy heat to an alloy composition can occur immedi-
ately by incorporating the desired alloy additions in the charge.
One of the advantages of the present invention is the
ability to s~itch from one end product composition to another
without a loss in melted materials because of the transition.
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In prior art continuous melting practices the metal accumulates
as a bath to which alloy additions may be made. In the event of
an end product composition change, there is a transition stage
during which the volume of the bath is "flushed out" before the
desired composition of the subsequent product composition is
reached. Alternatively, if the entire bath is not flushed before
- the desired subsequent composition is attained, the alloying
a~ents must be added to the receiving vessel. Such practice re-
quires the provision of excess temperatures and hence additional
heat, or else limits the type of end product chemical compositions
that can be produced, e.g., it would be difficult if not impos-
sible to produce high manganese content steel. In contrast, the
present invention provides a process which eliminates the txansi-
tion stage. It can be established, by trial, the transit period
of the feed, i.e., the time it takes for solid material, iNtro-
duced at the top of the charge column in the melting vessel, to
reach the tap hole or discharge port. Thus, in switching from
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one product to another, one determines the start of the change
in feed charge chemistry at the top o~ the feed column and as the
established transit period-elapses, the melt is transferred to
another collection vessel.
Xn some cases, dependent upon the charge composition and/or
flame conditions, it may be necessary to supplement the carbon
constituent of the charge in order to produce a liquid product
having at least 0.01~ ~arbon. It is felt that such carbon level
is necessary to minimize the degree of iron oxidation that might
occur due to the severe oxidizing flame produced by oxy-fuel
burners. The carbon level may be maintained or supplemented through
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the addition of materials which have a relatively high carbon
content, e.g., pig iron, cast iron, coke, coal, etc.
It will become apparent from a reading of the foregoing
disclosure that the present invention eliminates the need for the
refining step of the ordinary steelmaking processes; the liquid
melt may be converted to a solid form in the absence of a re-
- fining step; that there is no transitory stage between melting
of the charge and the formation of the desired end chemistry metal;
the chemistry change occurs in the melting vessel; and that no
slag removal steps in the melting vessel are required.
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