Addition agent for molten metals

An addition agent for the inoculation of a molten metal bath consists essentially of 50 to 90% by weight of a metal selected from the group consisting of alkali metal and alkaline earth metal having a particle size greater than 3 mm. but no more than 10 mm., 5 to 49% by weight of an inert porous material selected from the group consisting of semi-coke, coke, coke breeze and graphite, the porous material having a particle size greater than 3 mm. but no more than 20 mm., and 1 to 10% by weight of a binder which secures the metal particles and porous material particles together in a briquette, and can be coal pitch, coal bitumen, petroleum pitch, petroleum asphalt, or phenolic or furanic resin.

The present invention relates to composite bodies containing reactive 
metals, to be added to metal baths, the composite bodies being supported 
by porous physically inert substances which are suitably chemically inert 
to the conditions of use. 
The invention is an improvement on that of U.S. Pat. No. 3,918,963, Nov. 
11, 1975. Compared to the invention of that earlier patent, the present 
invention provides composite bodies with superior mechanical and chemical 
properties, suitable for use not only for desulfurizing pig iron baths, 
but also for steel deoxidation and desulfuriztion and for controlling the 
type and size of inclusions trapped in steel in all portions of the 
steelmaking plants, for example, in continuous casting tundishes. 
That earlier patent dealt with the problem of adding to metal baths, 
metallic elements which were highly volatile and/or easily oxidizable 
and/or violently reactive in the bath. The problem was solved in that 
earlier patent, by preparing a mixture of active metal powder and powdered 
inert support material, homogenizing the mixture, dry compacting and 
briquetting the mixture with the aid of an appropriate binder in order to 
form briquettes, heating the briquettes to activate the setting properties 
of the binder, and, if necessary, baking the briquettes. 
More particularly, the earlier patent provided a composition of the 
following weight percent: 
active metal: 5-50% 
inert material: 50-80% 
binder: 10-25% 
The material was homogenized and briquetted, that is, shaped and compacted, 
at a temperature between 80.degree. C. and 130.degree. C. Then the 
briquettes were heated to a temperature between 150.degree. C. and 
250.degree. C. for 15 to 90 minutes. If necessary, the briquettes were 
subsequently baked at a temperature between 250.degree. C. and 900.degree. 
C. 
The active metal, in the earlier patent as in the present invention, could 
be an alkali metal or an alkaline earth metal, or, more generally, any 
metal which was to be added to the bath and which was highly volatile 
and/or easily oxidizable and/or strongly reactive with the bath. The metal 
in the earlier patent was in powdered form and had a grain size between 
0.1 and 3 mm. 
The inert material, there as here, could be coke, coke breeze, semi-coke or 
graphite, or, more generally, any substance or compound having the 
required porosity and mechanical strength. The grain size of the inert 
material ranged from 0.1 to 3 mm. in the earlier patent. 
The binders of the earlier patent could be coal pitch, coal bitumen, 
petroleum pitch, petroleum asphalt or a mixture thereof. The active metal 
and inert material and binder were then homogenized at a temperature not 
higher than 50.degree. C. above the softening point of the binder. 
According to the present invention, quite unexpectedly, it has been found 
that the technical results previously obtained are improved by the present 
invention, by altering not only the proportions of the material, but more 
importantly their particle size. Thus, according to the present invention, 
addition agents in the form of composite bodies having superior mechanical 
and chemical properties as compared to those produced by the 
above-identified patent, consist essentially of more than 50% but not more 
than 90% of a metal selected from the group consisting of alkali metal and 
alkaline earth metal having a particle size greater than 3 mm. but not 
more than 10 mm., 5 to 49% by weight of a porous material having a 
particle size greater than 3 mm. but not more than 20 mm. and selected 
from the group consisting of semi-coke, coke, coke breeze and graphite, 
and 1 to 10% by weight of a binder which secures the metal particles and 
porous material particles together in a compact, which can be referred to 
as a briquette. The binder can be coal pitch, coal bitumen, petroleum 
pitch, petroleum asphalt or a mixture thereof, or a phenolic or furanic 
resin. 
The product thus obtained can be baked in an oxidizing, reducing or neutral 
atmosphere (independently or after briquetting at a temperature between 
80.degree. C. and 250.degree. C.) for less than 24 hours at a temperature 
higher than 250.degree. C. up to the melting point of the active 
substances included in the mixture. The active substances themselves can 
for example be sodium, magnesium, calcium, lithium, potassium, rubidium, 
cesium, beryllium, strontium or barium or a mixture thereof, or a compound 
of such active elements which is easily reduced by the support materials, 
such as oxides or chlorides. 
To facilitate the release of alkali and/or alkaline earth elements from 
such compounds, elements having a high affinity for oxygen, such as 
aluminum or silicon, can be included in the mixture in quantities not 
greater than 20% by weight. 
The present invention, as compared to the addition agent of the earlier 
patent, has increased resistance to disintegration under the static load 
of the overlying head of molten metal. This makes the skeleton support 
which is extracted from the bath after consumption of the metallic 
components thereof, dimensionally unaltered even when the overlying head 
of molten metal is several inches deep or more. 
Furthermore, an addition agent according to the present invention releases 
the active elements at a very slow rate with a corresponding increase in 
the efficiency of the active elements.

To enable those skilled in the art to practice the invention, the following 
illustrative examples are given: 
EXAMPLE 1 
A mixture consisting of 9% by weight pitch, 40% by weight coke breeze 
having a particle size range greater than 3 mm. but no more than 5 mm., 
and 51% by weight of particulate magnesium having a size range greater 
than 3 mm. but not greater than 10 mm., was heated at 90.degree. C. and 
compacted in small batches under a pressure of 500 Kg/cm.sup.2. These 
small compacted masses were then immersed in a pig iron bath contained in 
a 100 ton torpedo car in the proportion of 0.5 Kg of compacted material 
per ton of pig iron. The entire magnesium content of the immersed 
composites was released in the space of five minutes. The sulfur content 
of the pig iron bath was initially 0.024% by weight but was reduced to 
0.010% by weight by this treatment. The magnesium yield was 50%. 
EXAMPLE 2 
The same mixture was heated for several hours at 350.degree. C. and then 
used in a torpedo car as described in Example 1. The sulfur content of the 
bath was initially 0.032% by weight, but fell to 0.014% by weight as a 
result of the treatment described in Example 1. Again, the magnesium yield 
was 50%. 
EXAMPLE 3 
Example 2 was repeated, but in connection with a bath whose initial sulfur 
content was 0.022%. The final sulfur content was 0.002%; and the magnesium 
yield was 60%. 
EXAMPLE 4 
Example 1 was repeated, except that, instead of 51% by weight of magnesium 
particles, 25% by weight of calcium and 26% by weight of magnesium was 
used, the composition and granulometry being otherwise the same as in 
Example 1. Comparable desulfurization and magnesium and calcium yield 
results were obtained. 
EXAMPLE 5 
The composite material of Example 4 was pretreated at 350.degree. C. for 
several hours and was used, in the proportion of 500 g of desulfurizing 
agent per ton of molten steel, for desulfurizing a steel bath in the 
ladle. The initial sulfur content of the bath was 0.020% which was reduced 
to 0.010%. The magnesium and calcium yield was 50%. 
EXAMPLE 6 
Example 5 was repeated, except that 5% by weight pitch, 40% by weight coke 
breeze, 25% by weight sodium chloride and 30% by weight magnesium was 
used. The initial sulfur content of the bath was 0.025% by weight, which 
fell to 0.012% by weight. The yield of the sodium chloridemagnesium system 
was 70%, which is the sum of that which is consumed in the course of 
desulfurization plus the magnesium that is retained in the steel, the 
balance joining the slag as various salts. 
Although the present invention has been described and illustrated in 
connection with preferred embodiments, it is to be understood that 
modifications and variations may be resorted to without departing from the 
spirit of the invention, as those skilled in this art will readily 
understand. Such modifications and variations are considered to be within 
the purview and scope of the present invention as defined by the appended 
claims.