Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1981-12-17
1982-12-21
Rosenberg, P. D.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 53, C21C 702
Patent
active
043647715
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new product for the desulphurization of forge pigs and foundry pig irons, and of steels, and for the nodularization of foundry pig irons, the product being particularly suitable for direct injection, using a nozzle, in a current of carrier gas into the liquid cast iron or steel, and constituted of magnesium base shot combined with slag granules.
It is well known to treat cast iron and steel with magnesium or with magnesium base compositions, particularly for their desulphurization. However, this treatment is complicated by the low boiling point and the low density of this metal. When solid magnesium is added in various forms to the liquid cast iron or liquid steel, abrupt volatilization of this metal occurs, burning the surface and producing liquid cast iron spray. The reaction can be very violent. The technique of blowing magnesium into the liquid metal in which the magnesium which has been reduced into powder or sufficiently fine particles and is carried along by a current of carrier gas is also well known. It has the advantage of reducing the violence of the reaction and the spray while allowing the duration of addition to be increased as much as necessary. However, it does have the following problems which limit its use: (1) the very constant control of the very small flow of powdered magnesium is technically difficult to achieve; (2) the handling of magnesium powder either during transportation, or particularly in the injection apparatus, is unsafe due to the risk of sudden ignition; and (3 ) finally, the yield of the addition in the liquid metal is unstable. It can be seen that it is difficult to achieve uniform dissolution of the magnesium by this method.
A certain number of solutions which can be grouped into three categories have been proposed for overcoming these disadvantages.
In the first category, the magnesium is absorbed on a porous support such as coke (French Pat. No. 1,417,474 of American Cast Iron Pipe Company), or a porous ceramic material (French Pat. No. 1,357,511 of Foseco Trading A.G. or on an iron sponge (French Pat. No. 1,568,576 of Jarn foradling).
In the second category, the magnesium is mixed with a diluent which can also play a part in the desulphurization process such as lime (French Pat. Nos. 1,125,154; 1,168,646; 1,168,750 of the l'Institut de Recherches de la Siderurgie).
Finally, in the third category, the magnesium is coated with an inert substance (metallic oxides, halogenated salts).
These various processes have further disadvantages and they are not considered as completely satisfactory by steel manufacturers. Their disadvantages can be summed up as follows:
(i) irregularity and non-reproducibility of results; (ii) frequent blockage of the injection nozzles; (iii) violent reactions which are sometimes poorly controlled; (iv) environmental pollution if the magnesium shot is coated with chlorides; (v) difficult handling of the fine magnesium powder; (vi) very poor yield in the case of coated shot, because the coating usually disappears only at the moment when the magnesium comes to the surface of the cast iron where it burns without having reacted.
The present invention quite satisfactorily solves the problem of injecting magnesium into a bath of liquid cast iron or steel and ensures the safety of the personnel, the uniformity of operation and a minimal sulphur content yield, and simplifies handling.
It relates to a product for the desulphurization of cast irons and steels in the liquid state by injection through a nozzle in a carrier gas current, characterized in that it contains, in combination, from 10 to 90% of magnesium base shot and from 90 to 10% of granulated slag and preferably from 20 to 80% of magnesium base shot and from 80 to 20% of granulated slag, these percentages being expressed by weight.
The granulated slag can be obtained by granulation of slags of a particular composition, either by casting the molten slag into water optionally followed by a drying treatment then sifting, or by granulation in a jet of gas or "ball-
REFERENCES:
patent: 2971833 (1961-02-01), Artru
patent: 3953198 (1976-04-01), Easwaran
patent: 3957502 (1976-05-01), Cull
patent: 3969105 (1976-07-01), Ott
patent: 3998625 (1976-12-01), Koros
patent: 4190434 (1980-02-01), Bonfils
Cordier Jean
Demange Michel
Idier Jean
Rosenberg P. D.
Societe Francaise d'Electrometallurgie "Sofrem"
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