Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR PRODUCING VANADIUM-CONTAINING ALLOYS
The present invention relates to metallurgy, and more
specifically to a process for producing vanadium-containing alloys.
At present, in alloying steel use is preferably made of
ferrovanadium which is produced in an electric furnace by the
sillicoalumothermal method. The melting process generally compri-
se two stages: reduction and refining. After the reduction of
vanadium from oxides thereof, first an alloy containing up to 35
wt.% of vanadium and 9-12 wt.% of silicon is obtained, then slag
containing about 0.35 wt.% of vanadium oxides is drained. After
the draining of slag, the alloy is refined in the same furnace
after adding thereto vanadium pentoxide and lime. Thus, ferrova-
nadium is produced containing from 35 to 50 wt.% of vanadium,
from 0.5 to 0.7 wt.% of carbon and up to 2 wt.% of silicon, as
well as slag containing up to 14 wt.% of vanadium oxides to be
used in a charge for a next melting cycle.
However, when using this method, vanadium is reduced
form oxides thereof concurrently with the melting of the charge
so that difficu3tly reducible lower vanadium oxides are formed
which are bound into silicates from which vanadium can be reduced
only with difficulty as well. In addition, the reduction of va-
nadium takes place only at the metal-slag interface. This metal-
slag interface has àn insufficient surface area so that the reduc-
tion reaction proceeds at a low rate.
Due to a long residence t`ime of the metal being reduced
in an electric furnace and its contact with the electrodes an
alloy thus obtained has a high content of carbon, Average tempe-
rature in the furnace reaches 1650 C because both melting of the
charge and reduction of vanadium from oxides thereof concurrently
take place in the furnace. This temperature is insufficient to
obtain an alloy containing more than 50 wt.% of vanadium.
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Furthermore, slags deleterious to the lining are formed
in the furnace during the reduction of vanadium from oxides
thereof.
Known in the art is an aluminothermal non-furnace meth-
od of producing vanadium-containing alloys. This method permits
obtaining alloys containing up to 80 wt.% of vanadium and up to
0.1 wt.% of carbon.
This method requires, however, to use expensive vanadium
pentoxide and high-grade aluminium with a low content of impurities.
This method is deficient in a low productivity inherent in all
non-furnace aluminothermal processes, and the resulting alloy is
costly due to such a low productivity. In addition, a low degree
of vanadium extraction into the alloy also contributes to a high
cost of the resulting alloy.
A growing demand for vanadium-containing alloys for
alloying steel and low-carbon alloys with high percentage of vana-
dium poses the problem of the provision of an economically reaso-
nable and highly productive process for producing such alloys.
The main object of the invention is to provide a process
for producing vanadium-containing alloys containing more vanadium
than with known silicothermal processes for producing alloys in
electric furnaces.
Another not least important object of the invention is
t~ reduce the production cost of said alloy.
A~ important object of the invention is also to reduce
the content of carbon in said alloy from 0.03 wt.% to 0.005 wt.%.
Still another object of the invention is to prolong the
service life of the furnace lining and to improve the productivi-
ty of the furnace used to melt a charge for said alloy due to
the reduction of vanadium from oxides thereof in a melt outside
the furnace.
These and other objects are accomplished by the
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provision of a process for producing vanadium-containing alloys
comprising the steps of melting in a furnace a charge containing
vanadium and calcium oxides and xeducing vanadium from oxides
thereof in a melt with silicon, wherein, according to the inven-
tion the process comprises melting a charge ensuring the content
of vanadium oxides in the melt from 25 to 35 wt.%, discharging
said melt from the furnace into a receptacle, and reducing vana-
dium with silicon in said receptacle by adding silicon in an
amount sufficient to reduce vanadium from the oxides thereof con-
taining in said melt.
The extrafurnace reduction of vanadium from oxides the-
reof provides for a lower carbon content in the resulting alloy
which is from 0.005 to 0.03 wt.% due to the elimination of a
contact of the reduced melt with the furnace electrodes.
; Where vanadium is reduced from oxides thereof in a melt,
rather than in a solid charge, the rate of reduction is increased,
and the content of vanadium in the resulting alloy is also increas-
ed.
Since the furnace is used only to melt the charge, and
the reduction is effected outside the furnace, vanadium oxides
are present in a single valency state only, and namely in the ~-
form of V205 along with calcium oxides, whereby the furnace lining
is not damaged.
We have found that the melt containing the above-speci-
fied quantities of vanadium oxides is the optimal one. A charge
providing a content of vanadium oxides in a melt of less than 25
wt.% is high-melting so that the electric power consumption for
melting the charge is increased. Where the content of vanadium
oxides in a melt is more than 25 wt.%, the heat capacity of the
melt becomes sufficient for effecting the reduction.
The reducing agent may be added to the melt in the mol-
ten state.
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As a result, during the melting, solid material rnay be added io
the melt, such as wastes produced during the casting of the
alloy, and if necessary, iron may be added so as to increase the
yield of the alloy or modify its composition.
The above-specified reducing agent may be added to the
melt in the form of lumps of a size not exceeding 80 mm. The
heat released during the reduction is sufficient to melt the
reducing agent and to ensure a high rate of reduction with the
above-specified size of lumps.
Vanadium is preferably reduced from oxides thereof in
the melt to obtain slag containing from 1 to 10 wt.% of vanadium
oxides, whereafter,the slag is drained into another receptacle,
and vanadium is reduced in that receptacle from oxides thereof in
this slag.
Thus, the content of vanadium in the slag to be dispo-
sed of may be lowered to 0.5 wt.% and lower.
During the reduction of vanadium from oxides thereof
additional amount of vanadium oxides are preferably added to
said melt sufficient to oxidize the residual silicon.
This permits to reduce the content of silicon in the
alloy and to improve the yield of the final product.
A charge containing vanadium oxides may comprise
vanadium convertor slag preliminarily calcinated with carbon
at from 900 to 1000 C from which iron is withdrawn during the
melting.
Enriched convertor slag is less expensive than vanadium
pentoxide, but the content of vanadium in the resulting alloy
will be somewhat when using such slag.
The invention will now be described with reference to
specific embodiments of the process.
EXAMPLE 1
The process oDmprised melting in a furnace a charge
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providing for obtaining a melt containing 30 wt.% of vanadium
pentoxide, as well as calcium oxides (lime).
The melt was poured from the furnace into a ladle,
weighed, and then 350 kg of liquid ferrosilicon containing 75 wt.%
of silicon were added per 2 tons of the melt. Subsequently 200 kg
of a mixture containing vanadium pentoxide and 100 kg of metal
scrap were added to the melt.
535 kg of ferrovanadium were thus obtained containing
about 70 wt.% of vanadium and 0.015 wt.% of carbon. Slag contai-
ned less th~n 1.0 wt.% of vanadium oxides.
EXAMPLE 2
A melt of vanadium oxides and lime was poured into a
ladle from a furnace. 320 kg of liquid ferrosilicon per 2 tons
of vanadium pentoxide melt were added to obtain an alloy contain-
ing 58 wt.% of vanadium, 0.02 wt.% of carbon, and slag containing ~-
5 wt.% of vanadiwm oxides. This slag was poured into another fur-
nace, which has been used to melt ferrosilicon. In this furnace
ferrosilicon was obtained containing 1 wt.% of vanadium and slag
containing less than 0.3wt.% of vanadiwm oxides. The resulting -
ferrosilicon was used for reducing vanadium during the next melt-
ing cycle.
EXAMPLE 3
The process was conducted as described in Example 1,
but liquid ferrosilicon was replaced by solid crushed ferrosilicon
of a particle size not exceeding 50 mm.
EXAMPLE 4
400 kg of ferrosilicon containing 75 wt.% of silicon s
were added per 2 tons of melt to obtain 490 kg of an alloy con-
taining 75 wt.% of vanadiw~ and 4.2 wt.% of silicon. Slag was
then drained, and a mixture containing vanadium pentoxide and
lime was added to the metal, As a result of reaction of the
mixture and metal, the content of silicon in the metal was lowered
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to 1 wt.%.
EXAMPLE 5
300 kg of ferrosilicon were added per 2 tons of melt,
ferrosilicon being used in pumps of a size up to 80 mm. Thus,
slag containing up to 8 wt.% of vanadium oxides was obtained to
be used for producing ferrovanadium by the silicothermal method
in an electric furnace, and ferrovanadium containing 57 wt.% of
vanadium and 0.01 wt.% of carbon.
There it is desired to obtain alloys containing chromium,
manganese, nickel, tungsten, molybdenum, niobium in addition to
vanadium, products containing oxides of such metals may be also
added to the charge.
In addition to the above examples, a charge providing
the content of vanadium oxides in the melt from 25 to 35 wt.% may
also be melted. In that case, the content of the silicon reduc-
ing agent should be either greater than that given in Example 1,
when more than 30 wt.% of vanadium oxides are formed in the melt,
or smaller than that given in Example 1, when less than 30 wt.%
of the reducing agent are formed in the melt.
T~e amount of the reducing agent is calculated by the
reaction
2V2O5+5Si = 4V + 5SiO2 -
in the stoichiometric ratio.
The effective utilization of silicon in the reducing
agent is 100%.
In accordance with the process of the invention vanadium
is reduced from oxides thereof in the melt to obtain slag contain-
ing from 1 to 10 wt.% of vanadium oxides, whereafter the slag is
drained into another receptacle, and vanadium is reduced from
oxides thereof in that receptacle in this slag.
; A charge containing vanadium oxides compris~s vanadium
convertor slag preliminarily calcinated with carbon at from 900
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to loOOQC, iron being eliminated from the slag during the melting.
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