Agent for the treatment of metal melts

The invention concerns an agent for treating metal melts in the form of a cored wire comprising a metallic sheath of steel or iron and a filling which contains a compound that splits off gas at the temperature of the metal melt and is based on an organic polymer in amounts of 0.2 to 20 g per meter cored wire. The invention also concerns the use of the agent for homogenizing, refining and homogeneously cooling as well as alloying metal melts.

FIELD OF THE INVENTION 
The invention concerns an agent for the treatment of metal melts in the 
form of a cored wire sheathed with metal. 
BACKGROUND OF THE INVENTION 
An object of metallurgical processes is to set a homogeneous analysis and 
temperature of the metal melt in the casting ladle. The convective 
currents in the ladle due to differences in density proceed too slowly and 
in practical operation have to be accelerated by introduction of inert 
flushing gases. An improved intermixing is often carried out by blowing in 
argon or nitrogen through porous bed stones or via lances. 
Even in the well-known pneumatic lance-injection process e.g. for 
desulphurization of pig iron, the carrier gas not only provides the 
pneumatic transport of the fine-grained solids but at the same time also 
results in a homogeneous dispersion of the additives in the melt. 
The development of the cored wire technique in secondary metallurgy has 
replaced pneumatic injection in some areas. The absence of a gas which 
generates turbulence is a disadvantage for many applications in particular 
for the injection of materials which do not develop their own vapor 
pressure. The homogenization of the melt occurs too slowly. Concentration 
peaks occur in the vicinity of the wire as it dissolves which lead to 
undesired reaction products or even to reductions in yield. 
In German Offenlegungsschrift No. 41 03 197 A1 a process is described for 
the rapid cooling of a metallurgical melt with a wire which is suitable 
for this that is composed of a metal sheath made of a low-carbon steel 
sheet for example and a filling made of a granulate in which the melt, 
wire sheath and wire filling are comprised of essentially the same 
material. Although the introduction of this wire onto the bottom of the 
ladle causes a rapid release of the granulate particles in the lower 
region of the melt, however, the small particle size of 0.2 to 0.5 mm 
results in a rapid melting of the granulate particles and thus the main 
cooling effect is restricted to the vicinity of the ladle bottom. The 
cooled parts of the melt are only more or less homogeneously dispersed by 
the normal movement of the bath. 
In this process the dispersion of the components of the wire filling in the 
melt thus depend exclusively on the thermal movement of the bath or on the 
vapor pressure of the filling materials of the wire. Since in leads to 
materials being introduced into the melt the cored wire injection which 
have a low or no vapor pressure, an additional dispersing effect by gas 
generation does not take place when porous gas purge stones are not 
present which is a disadvantage for a number of practical applications. 
Addition of substances to metal melts that split off gas is also known. Of 
the known gas releasers that are possible for this purpose, limestone and 
flame coal lead to detrimental changes in the quality of the melts. 
Limestone thermally splits off carbon dioxide and due to these oxidizing 
conditions influences for example the steel analysis by burning of 
aluminum; also reactions with other additives cannot be ruled out. Flame 
coal also alters the steel analysis by carburizing processes; natural 
flame coal in addition always contains undesired amounts of oxygen. 
The use of polyethylene as a solid compound which splits off ethene is 
already described in German Patent 22 52 796. However, it is there used as 
one of several components of a desulfurization composition for raw iron 
and ferro-alloy melts, which is introduced into the melt bath with the aid 
of the above mentioned lance process by means of a carrier gas stream. The 
main object of the polyethylene in this case is the creation of reducing 
conditions in the iron melt. 
OBJECT OF THE INVENTION 
The object of the invention is to create an agent of the above-mentioned 
type with a wire filling whose special admixtures split off gas at the 
application temperatures and thus cause the formation of turbulence in the 
metal bath which leads to a homogenization of the melt without having a 
detrimental effect on the composition of the melt.

DESCRIPTION OF THE INVENTION 
This object is achieved according to the present invention by providing a 
wire filling which contains a compound that splits off gas based on an 
organic polymer in amounts of 0.2 to 20 g per meter filler wire. 
The agent according to the present invention preferably contains 
polyethylene, polypropylene or/and polystyrene as the organic polymers. 
The organic polymer is preferably present in a granular form. The particle 
size is 0.1 to 10 mm, particularly preferably &lt;2.0 mm and is enclosed by 
the cored wire sheath. The wire sheath is comprised of a metallic coating 
of steel or iron. In addition to the gas-releasing compound, the wire 
filling preferably also contains non-decomposable inorganic materials 
which are introduced as oxides of alkaline-earth metals or/and aluminum, 
oxides or/and nitrides of silicon or as metals or metal oxides of group 
VIII of the periodic system of the elements. Quicklime, magnesium oxide 
and lime aluminates are particularly preferred additives. 
A preferred embodiment of the agent according to the present invention is a 
cored wire for iron and steel melts comprising an iron sheath which 
encloses a filling of 0.1 to 10% by weight polyethylene and 90 to 99.9% by 
weight filler material such as e.g. iron powder. 
The use according to the present invention of one of the aforementioned 
organic polymers already provides the necessary amount of gas when added 
in amounts of only 1 to 2% by weight to the wire filling material. A 
larger or smaller addition of polymers in the cored wire depends on the 
geometry of the available ladles or the type of use of the cored wire. The 
amounts of carbon and hydrogen introduced by the thermal decomposition of 
the organic polymers are uncritical in the form according to the present 
invention since the metal melt analysis is not negatively changed by them. 
The amounts of released gas increase the turbulence flow of the metal melt 
and have a favorable effect on the bath movement. Primary or secondary 
reactions with the other filler additives can be ruled out. 
The agent according to the present invention is primarily used for 
homogenizing, refining and short-term cooling of metal melts. Melts of 
iron and steel come into consideration as the metal melts. 
The agent according to the present invention is also suitable for alloying 
metal melts by introducing microalloying elements such as titanium, 
molybdenum, boron and others. For this type of application, these 
elements, or compounds which release these elements under the melting 
conditions, are provided in the wire filling. 
The cored wire according to the present invention generally has a diameter 
of about 5 to 16 mm, preferably of 9 to 13 mm. The wall thickness is 
between 0.1 and 0.8 mm, preferably 0.4 to 0.6 mm. The corresponding core 
diameter is 4.8 to 15.8 mm, preferably 8.2 to 11.8 mm. 
The cored wire can be manufactured according to known methods such as those 
described for example in German Patent 41 03 197, column 3, lines 49-58 
and 64-68 as well as in FIGS. 2 and 3. 
In experiments with the agent according to the present invention it 
surprisingly turned out that the application of organic polymers in cored 
wires can be very versatile. The following examples are intended to 
further elucidate this. 
EXAMPLE 1 
Flushing a Ladle 
In cases of impeded gas escape due to the flushing stones shifting on the 
base of the ladle, the application can for example be comprised of a 
simple stirring; the introduction of the agent according to the present 
invention in the form of a wire prevents a qualitative degradation of the 
affected batches. 
Cored wire with iron as a coating material, diameter 13 mm, wall thickness 
0.4 mm, core diameter 12.2 mm, with 4 g polyethylene (PE) per meter and a 
particle size between 0.5 and 1.0 mm (remaining filler core: inert 
material quicklime) was injected at a rate of 200 meters per minute. Since 
1 g polyethylene splits off 0.86 N1 ethene, 688 N1 gas per minute are 
released in this process which corresponds to the output of the argon bed 
flushing stones. The flushing time for an 80 ton ladle is 3 minutes, 
afterwards the melt is homogeneous. 
EXAMPLE 2 
Refining of Steel Melts 
A cored wire containing a filling mixture of calcium-aluminate refining 
slag and 3% PE is injected into a melt of high-carbon tool steel in a 
ladle. The slag particles in the lower ladle region are dispersed 
uniformly in the melt by strong turbulence. As a result the ascending 
liquid particles wash out finely suspended non-metallic inclusions 
(aluminum oxide) which collect in the slag. The degree of purity can be 
improved reproducibly from the initial value of Ko 60 to Ko&lt;10 according 
to the steel-iron test paper. 
EXAMPLE 3 
When steel is continuously cast it is often necessary to cool the melts 
that are too hot within a short time to the target temperature for 
casting. 
In order to cool homogeneously, the agent according to the present 
invention in the form of an iron cored wire with PE additive is introduced 
into a steel melt. 
In order to cool a 100 ton batch by 10.degree. C. in a short time, cored 
wire with an iron powder filling (as cooling agent) and an additive of 1% 
by weight PE with a particle size of 1.5 mm is used. For 66=10.degree. C. 
and 100 ton melt weight, 750 m Fe wire with a diameter of 13 mm, 
corresponding to 700 kg iron, is injected. This amount is introduced in 3 
minutes. Afterwards the melt is cooled homogeneously by 10.degree. C., and 
can be cast immediately. 
Results analogous to the 3 examples were obtained by replacing polyethylene 
by a polypropylene additive (1.5-fold weight) or polystyrene additive 
(3.7-fold weight relative to polyethylene) which generate the same amount 
of gas.