Note: Descriptions are shown in the official language in which they were submitted.
106'~0~ 6
BACKGROUND OF THE INVENTION
In the iron and steel industry, it is necessary to
treat the ferrous base metals while in the molten state with
a desulfurizing agent to reduce the sulphur content of the
metal product. Magnesium metal is a powerful deoxidizer
and desulfurizer. However, magnesium metal boils at a low
temperature and therefore, the sudden increase in volume
which is produced when metallic magnesium is added to the
molten iron, may result in violent reactions as the
magnesium metal is vaporized.
Various methods have been used to reduce this
violent activity by slowly introducing the magnesium metal
into molten ferrous metal under rigidly controlled systems.
One of these methods for reducing the violence is to impregnate
porous bodies with magnesium metal and to introduce these
magnesium impregnated porous bodies into the molten ferrous
metal Under these conditions, the impregnated magnesium
metal is released at a slow enough rate that the violence -
is held to minimum.
Among the known porous bodies which have been
used with limited success for this purpose are: porous `
coke, carbon, graphite and ceramic bodies such as quicklime,
lump limestone or dolomite and the like.
In addition, magnesium has been infiltrated
into porous iron bodies. Among these prior art iron bodies
is sponge iron in which the iron particles are very small
and are sintered together to fiorm a porous structure.
Sponge iron itself is expensive to produce and to use.
The cost of forming large porous structures from sponge
iron is also an expensive procedure.
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Since the pores of the sponge iron are excessively
small, they tend to release the magnesium too slowly when
immersed into the molten iron, and the release may be ,too
quiescent for optimum operation. Sponge iron also may
contain oxides which may form a violent reaction with the
magnesium which may also impair the efficiency.
Another method used by the prior art to produce
iron briquettes containing magnesium is to dry-press together
iron particles and magnesium particles, both of which
preferably are from 4-60 mesh.
When these compressed iron and magnesium particles
are used to desulfurize molten iron, the remaining iron
structure becomes decidedly weak as the magnesium melts
and, therefore, the magnesium may be released too quickly
and therefore may cause a violent reaction.
In contrast to these prior art products, the
instant invention prepares a network of ferrous metal
pieces, particularly steel turnings, compressed together
which forms a body having a low density, high porosity,
and high strength which may be infiltrated with large
quantities of magnesium metal.
The voids in the metal network are sufficiently
large to release the magnesium at a desirable rate, i.e.,
fast enough to provide rapid treatment, but not too fast
so that the treatment is unduly violent.
It has been found that the porous ferrous metal
network of the instant invention possesses advantages
which are not present in the prior art porous bodies.
SU~MARY OF THE INVENTION
-
A new composition of matter has been prepared
comprising a mass of scrap ferrous metal pieces compressed
~ 1062016 : ~
together in random orientation, forming a network of
interlocking pieces, said mass having a density of 1.2 to
6.3 g/cc, a porosity of 20% to 85%, and a short transverse
tensile strength of at least 2.0 psi, preferably at least
2.5 psi.
Within these broad limits, it has been found that
these limits may be divided into two types of products, -~
each product is useful for its own particular purpose.
It has been discovered that the compressed scrap metal
bodies impregnated with magnesium metal are particularly
useful for desulfurizing molten iron metal when the scrap -
bodies contain the following properties:
network of ferrous metal scrap pieces compressed
to form the metal network having a density of 1.2 to
4.0 g/cc;
porosity of 50% to 85~;
short transverse tensile strength of at least 2 psi;
impregnated with from 18% to 55% magnesium metal.
This metal scrap network impregnated with 18% to 55% magnesium
metal and the process for preparing this product is claimed
in Copending Application Serial No. 454,951, and Parent
Application Serial No. 385,584.
Compressed scrap metal bodies impregnated with
magnesium metal which fall within these limitations when
used to desulfurize molten iron releases the magnesium
metal at a rapid rate without producing a violent reaction.
Although this product may also be used successfully to
produce nodular iron, it has been found that the magnesium
infiltrated metal network containing less magnesium metal
is generally more efficient and causes less fuming. This
product possesses the following properties:
the network of iron pieces compressed to form
the body has a density of 6.5 down to 4.0 g/cc,
a porosity of 20% up to 50%, a short transverse
tensile strength of at least 2.0psi and is
impregnated with from 5% up to, but not including
18% magnesium metal
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When this product is used to produce nodular iron,
the reaction of the magnesium is slower and, therefore the `
utilization efficiency of the magnesium values is high,
since a very small amount of the magnesium is lost by
volatilization.
These masses of porous ferrous metal networks
contains a labyrinth of interstices in the voids between
the compressed interlocking metal pieces. These interstices
may be filled with magnesium metal by immersing the ferrous
metal network in molten magnesium metal, and solidifying
the molten metal impregnated throughout the interstices of
the porous metal network. The amount of magnesium which
may be impregnated into the ferrous metal mass may be from
5% to 55% by weight of the impregnated body. This product
is useful for treating ferrous melts, for example, for
desulfurizing the melts and also for producing nodular iron.
Normally about 3/4 to 1-1/2 pounds of magnesium metal
are used to desulfurize 1 ton of molten iron. About 2 to
4 more pounds of magnesium are used to form one ton of
nodular iron, which therefore requires a total of from 2-3/4
to 5-1/2 pounds of magnesium for each ton~of nodular iron.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This composition of matter is produced by selecting
scrap metal pieces, particularly steel turnings which fall
within the following size ranges:
length 1/8 to 9 inches
width 1/64 to 1 inch
thickness 1 to 100 mils
Scrap metal pieces within this size range usually
have a bulk density of from 0.1 to 1.0 g/cc.
In the instant application these metal pieces
are then compressed to form a ferrous metal network having
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a density of from 6.3 down to 4.0 g/cc. As stated previously,
the porosity of the network is 20% to 50% and it has a short
transverse tensile strength of at least 2.0 psi.
This ferrous metal network is then immersed into - :
molten magnesium metal and held in the molten metal for a
few minutes to impregnate the interstices of the metal
network. The impregnated body is removed from the molten
magnesium and it is cooled to solidify the molten magnesium.
The impregnated metal is cooled, preferably in
the absence of an oxidizing atmosphere. One preferred method
of cooling the impregnated compressed metal body is to
immerse the impregnated body into an oil bath.
The final Product comprises a porous composition
of matter comprising a compacted metal network impregnated
with magnesium metal. The composition contains from 5
up to but not including 18% magnesium metal by weight of
the total impregnated metal body.
The porous ferrous metal network composition of
the instant invention when impregnated with magnesium is
superior to the porous bodies of the prior art. The
instant porous body, not only may take up and retain magnesium
in the desired amounts, but in addition, when used to -
desulfurize iron or to form nodular iron, the porous body
releases the magnesium metal over a short period of time
without creating a violent reaction. It also has a struc- ;
tural strength which is retained as the magnesium is being
released. This is advantageous, since the maintenance of
: ,,
the structural strength is necessary to prevent a violent
reaction from taking place, for the magnesium is released
in a controlled manner. In addition it is also advantageous
to employ this particular type of magnesium infiltrated
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: - ., , - - . .
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" 106Z016
porous body over other types of magnesium impregnated bodies,
since the residual ferrous metal in the porous body may
be dissolved in the molten metal without having to remove
the residual carrier. It has also been found that this
particular type of ferrous metal body possessès sufficient
strength to withstand handling prior to infiltration, while
at the same time possesses a porosity which will hold the -
desired amount of magnesium metal.
In addition to producing a product which has all
of these advantages, the porous body of the instant material
may be made with raw materials, which are readily available.
The density of the compacted ferrous metal network
before impregnation in the instant application is from 6.3
down to 4.0 g/cc, while the density of the scrap metal
pieces before compaction was 0.1 to 1.0 g/cc. Metal porous
bodies containing amounts of magnesium metal from 5% up to,
but not including 18% may be produced by this process.
Reproducible products are also readily obtained.
If the density of the compressed ferrous metal
body is above 6.3 g/cc, the amount of magnesium which will
infiltrate the compressed body will be below 5% by weight.
When the magnesium content is below S~, a large amount
of scrap metal is added with the magnesium to the molten
iron, and the molten metal may be cooled substantially. ;~
This cooling effect may be undesirable. As previously
stated, the amount of magnesium infiltrated in the scrap
iron body, preferably, should be less than 18~ when used to
produce nodular iron. Above this amount the reaction is very
rapid, yet not violent. Within this range the reaction
is still rapid, but slow enough to prevent the magnesium
values from volatilizing excessively.
1062016
The scrap metal pieces useful in the instant -
invention include ductile iron and the like, but more
preferably steel. The scrap metal pieces, as previously
stated, must fall within the size ranges specified above.
If the scrap pieces used in this invention lie outside
the specified size range, difficulties may be encountered
in infiltrating the metal network and/or the rate of -
release of the magnesium may not be desirable.
The most desirable type of scrap metal are those
which are irregular in shape and have a variety of sizes
which fall within the sizes specified. Fine metal turnings,
short shovelings and the like are the most desirable.
The compacted metal porous bodies prepared in the --
instant invention also may be impregnated with alloys.
Alloys particularly desirable to use are magnesium alloys
containing alkaline earth ~etals, aluminum, silicon, and
rare earth metals such as cerium, lanthanum, or rare earth
alloys, such as "Misch Metal" and mixtures of these metals.
The term "magnesium" hereinafter referred to is meant to
include magnesium metal and alloys of magnesium metal.
The alloy must occupy the same volume as the 5% up to but
not including 18% by weight~
The magnesium infiltrated compacted porous steel
network structure produced in the instant invention possesses
the following combined advantages over the prior art:
1) have a range of porosities and therefore are
capable of retaining the desired quanti~ies of
magn~sium metal;
2) the impregnated bodies produced are structurally
strong and c~pable of withstanding high temp-
eratures until the magnesium has been released
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during subsequent treatment of molten iron.
3) the impregnated bodies which contain from 5~
up to, but not including 18% magnesium, when
used to form nodular iron, produces reaction
which is still rapid, but slow enough to
prevent excessive volatilization of the
magnesium values. Reaction times to release
the magnesium metal from the impregnated
bodies may range from 1/2 to 10 minutes.
4) the magnesium infiltrated bodies made by the
instant invention are uniform in composition,
and when they are used to treat molten iron,
reproducible results are obtained.
5) the addition of the particular type of magnesium
impregnated body employs iron or steel as the
carriers to the molten iron which subsequently
do not have to be removed from the molten iron.
6) the scrap metal may melt after the magnesium
has been released, thus contributing iron to
! 20 the melt and eliminating the necessity of
~- removing the carrier after the treatment.
:
Scrap metal generally contains a coating of oil.
This coating may be removed before infiltration, if desired.
One method of degreasing is by heating the scrap to burn-
off the oil. This heating may be done before or after
: compressing. It is economically advantageous, however, to
compress the scrap metal, then heat the compressed metal
to remove the oil, and to preheat the metal at the same
time before it is introduced into the molten magnesium
for infiltration.
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~` 106Z016
If the compressed metal is preheated before ~ -
introduction into molten magnesium, care should be taken -
to prevent the scrap metal from oxidizing excessively.
The oxide present can react with magnesium metal, and may
contribute to the violence during the subsequent treatment
of the ferrous melts and may consume a significant amount
of magnesium, thus lowering the efficiency.
It has been found that the weight gain of the
scrap metal compressed network due to oxidation should not
exceed about 3~ and, preferably, not exceed about l~ during
the preheatina step.
The amount of oxidation may be held within the
limits specified, if the preheating temperature in air is
held between about 500F and 1000F. Temperatures up to
about 1200F. may also be employed, if the time of preheatin~
is held to no more than about one hou~
Obviously, the preheating temperature upper limits
are not critical, if the preheating is carried out in a
non-oxidizing atmosphere.
Care should also be taken in the storage of the
magnesium infiltrated bodies to avoid reaction of the
magnesium with moisture. This may be readily accomplished
by sealing the infiltrated bodies in a suitable container
or placing the infiltrated bodies with a drying agent in
a metal can having a tight fitting lid.
In order to describe the instant invention more
fully, the following examples are presented:
E X A M P L E
In th.s exam~le a scrap steel briquette was
prepared using a roll briquetting machine. The machine
specifications were as follows:
^ 106Z~)16
Roll Diameter - 12"
Number of Briquettes - 32
Roll Motor - 20 Horsepower
Feeder Motor - 5 Horsepower
The roll separation was adjusted to give a density in the
briquettes of 6.2 g/cc.
The steel turnings used in this example were 5
to 10 mils thick, l/8 to 7/16" in width, and 3/8 to 2"
in length.
The steel turnings were fed into the worm gear
type feeder and the roll motor speed was adjusted tc 6 RPM.
The finished briquettes were 1-3/4" length by 3/4" wide
by 1/2" deep. Each briquette weighed approximately 46 g.
An accurate measurement of the volume was made by the mercury
displacement method. The volume was 7.4 cc. After burning
off the oil in an oven at 900F, the briquettes were immerged
in molten magnesium. The average weight gain due to the
infiltration of magnesium metal was found to be 6~. ;
E X A M P L E 2
Using the procedure described in Example 5, the
roll separation was increased with shimstock to yield a
lower density of 5.1 g/cc of the briquettes. The briquettes
weighed 38 g. and the volume was determined to be 7.5 cc.
The finished briquettes were again immerged in molten
magnesium and the average weight gain was found to be 12%.
E X A M P L E 3
The 6~i magnesium containing products as prepared
' in Example 1 were used to prepare ductile iron. The amount
of iron treated was 2400 lbs. at 2650F. The amount of
produot added was 54 lbs. This amounted to an addition of
magnesium of 2.7 lbs. per ton of metal treated. The initial
sulphur in the iron was 0.035~. The release time of
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106Z0~6
magnesium was determined to be approximately 50 seconds. --
The final sulphur in the iron was determined to be 0.007%.
. -:
The iron produced was ductile. The residual magnesium
was measured at various times after treatment as follows:
TIME RESIDUAL MAGNESIUM
0 ~ 0.035%
1 min. 30 sec. 0.034%
3 min. 0.033~ .
4 min. 30 sec. 0.033%
6 min. 0.033% -
E X A M P L E 4
The 12% magnesium product as prepared in Example 2
was used to prepare ductile iron. The amount of metal
treated was 2400 lbs. at 2680F. Thirty lbs. of the ~-
product were added. This is equivalent to the magnesium
addition of 3 lbs, per ton of metal treated. The initial
sulphur in the iron was 0.037%. Time of reaction was
approximately 1 min. The final sulphur in the iron was
determined to be 0.010%. The iron produced was ductile.
Residual magnesium as a function of time is tabulated below:
TIME RESIDUAL MAGNESIUM
0 0.035%
1 min. 30 sec. 0.035%
3 min. 0-033%
~0 4 min. 30 sec. 0.033%
6 min. 0.034g6
E X A M P L E 5
In this example steel turnings of the same size
as those described in Example 1 were used.
78.5 grams of the above turnings were inserted
in a compaction chamber (1-3/4" dia. x 3" high). The
turnings were compacted at 24 tons/in. to produce a
briquette 1.858" dia. x . 315" high. The density of the
briquette was 5.61 g/cc.
The compacted briquette was preheated at 960F
for 10 min. which allowed all oil on the turnings to burn
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106Z016 -
, , ,
off. The briquette was reweighed and found to weigh 77.5
g. The oil removed was 1.3% by weight.
The briquette was then immersed in molten Mg at
1400 F for 10 min. After the infiltration the briquette
was removed from the molten Mg and cooled, thè briquette
was reweighed. It was found to weight 88.0 g and contained
11.9~ Mg metal by weight.
E X A M P L E 6
In this example 167 grams of the same steel turnings
were compacted in a compaction chamber which was 1-3/4"
dia. and 6" high at 50 tons per sq. in. The briquette
was 1.8" dia. and 0.653" high. The density of this briquette
was 6.13 g/cc.
The compacted briquette was preheated at 960 F
for 10 min. which allowed all oil on the turnings to burn
of~. The briquette was reweighed and found to weigh 153.0 g.
The oil removed was 8.4~ by weight.
The briquette was then immersed in molten Mg at -
1400F for 10 min. After the infiltration the briquette
was removed from the molten Mg. and cooled, the briquette
was reweighed. It was found to weigh 171.0 g. and contained
10.5% Mg. metal by weight.
When the briquettes prepared in Example 5 and 6
were used to treat molten iron, it was found that the release
of the magnesium metal was rapid but excessive loss of
magnesium did not occur.
In the following examples, alloys of magnesium
were used to infiltrate the scrap metal network instead of
using magnesium metal alone.
E X A M P L E 7-8
In these runs, the steel turnings described in
Example 1 were inserted into a compaction chamber (1-3/4"
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` 10~16 -
diameter x 3" high) at a compaction pressure of 11.0 tons
per sq. in. The briquettes produced measured 1.86" diameter
x 0.36" high. The density of the briquettes were 4.6 g/cm3.
The compacted briquettes in Example 7 were then
preheated to 800F for 30 minutes which allowed the oil
on the turnings to burn off. After preheating, the compacted -~
briquettes in Example 7 were immersed in a melt of an alloy
of magnesium metal containing 50% "Misch Metal" for 10
minutes and the briquettes contained 17.7% magnesium -
~isch Metal by weight.
In Example 8 briquettes having a density of 4.96
g/cm3 were employed. The preheated briquettes were immersed
in a melt of magnesium metal containing 16% by weight calcium
metal for 10 minutes and the infiltrated briquette contained
15.0% magnesium-calcium metal by weight.
These briquettes prepared in Examples 7-8 which
contained "Misch Metal" and calcium in addition to the
magnesium metal may be used in the same manner as the
briquettes prepared in the previous examples for treating
molten iron metal.
From the above description and by the examples
; presented, a superior type of product has been produced
which comprises a ferrous metal network having high strength
which may be infiltrated with the desired percentages of
magnesium metal.
Such a product is superior to prior art products
when used to produce nodular iron.
While this invention has been described and
; lllustrated by the examples shown, it is not intended to
be strictly limited thereto, and other variations and
modifications may be employed within the scope of the
following claims.
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