LU83694A1 - IMPROVEMENTS IN CAST REFINING PROCESSES - Google Patents

Description

(* »5. h 50¾ -ίο 2159/8110.

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Improvements to the refining processes of cast iron.

The present invention relates to a method for refining pig iron, in particular hematite pig iron, in a top blown oxygen converter.

The refining process consisting in injecting industrially pure oxygen onto the surface of a cast iron bath has been known for a long time by means of a lance introduced into a full-bottom converter.

However, in addition to numerous advantages, this method has the disadvantage, also well known, of giving rise to the phenomenon of foaming of the slag. In some cases, this phenomenon can lead to slag overflows, if y / appropriate measures are not applied quickly. * j (Jf! 1 - - 2 -

We have proposed different means, either to monitor the evolution of foaming and thus be able to intervene at the appropriate time to avoid an overflow, or to reduce or even virtually eliminate the phenomenon.

One of the means recently proposed for controlling the foaming of -1 slag, in the case of refining of phosphorous cast iron, is the blowing of neutral gas under the surface of the melt bath through passage members, for example porous bricks placed at the bottom of the converter. This technique causes a mixing of the metal-slag system which also makes it possible to improve the quality of the metal produced.

We also know that, under current economic conditions, it is advantageous to use the largest possible volume of scrap in the converter. However, it is important not to increase the energy consumption necessary for the melting of this scrap. In this regard, it is also known to burn, in the converter itself, all or part of the CO released by refining and thus recover its heat, both sensitive and latent, to ensure the preheating and / or the melting of scrap. The combustion of CO takes place all the more easily when the oxygen lance is lowered less deeply into the converter. However, the use of a high lance promotes oxidation and therefore foaming of the slag.

As mentioned above, the foaming of the slag can in the case of phosphorous melts, be controlled by the blowing of neutral gas under the surface of the bath.

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The applicant has however noted that in the case of non-phosphorous cast irons, called hematite cast irons, the blowing of neutral gas through the bottom of the converter was not sufficient to * * f -.:¾ prevent foaming of the slag.

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This is a serious drawback, since hematite cast irons represent a large part of the volume of cast irons intended for refining.

The subject of the present invention is a method making it possible to remedy this drawback.

The process which is the subject of the present invention makes it possible to refine cast irons with a low phosphorus content, while ensuring good combustion of the CO released and therefore allowing a high scrapping of scrap, and while practically removing any risk of foaming the slag.

The process for refining cast iron with a low phosphorus content in a solid-bottom converter, which is the subject of the present invention, into which is blown on the one hand, an oxidizing gas, preferably industrially pure oxygen , on the surface of the bath and on the other hand a neutral gas under the surface of the bath, and in which at least part of the CO is burned off by the refining reactions by means of oxygen introduced above the bath, is essentially characterized in that the lime necessary for the formation of the slag is added, at least in part, in the form of powder.

Powdered lime can be added in bulk, in particular by means of an existing converter loading device, for example a scrap loading bucket. In this case, it is particularly advantageous to add the lime at the same time as the scrap.

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It can also, and this is a particularly advantageous implementation of the method of the invention, be transported by a stream of oxygen and introduced into the converter / by means of the blowing lance. y,; fif i - 4 - f

Different parameters can influence the quantity of lime to be introduced into the converter / in particular the particle size of the powdered lime, the silicon content of the pig iron and the specific volume of the converter.

The applicant has found that it is particularly advantageous, within the framework of the process of the invention, to use powdered lime having a particle size such that at least 95% of the grains have a dimension of less than 160 microns.

Still in the context of the present invention, the applicant has found that it was very advantageous to add the lime powder before the start of the refining operation or at the very beginning of it, but preferably before the start of ripening. This procedure makes it possible to avoid the lime being entrained by the conversion gases and therefore contributes to the economy of the process.

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Claims (5)

1. Process for refining low phosphorus pig iron in a solid-bottom converter, into which an oxidizing gas, preferably industrially pure oxygen, is blown on the surface of the bath and on the other hand, a neutral gas under the surface of the bath, and in which at least part of the CO released by the refining reactions is burned by means of oxygen introduced above the bath, characterized in that one adds the lime necessary for the formation of the slag, at least partly in the form of powder. 2. A refining method according to claim 1, characterized in that all of the added lime is in powder form. 3. Method according to either of Claims 1 and 2, characterized in that at least part of the powdered lime is introduced through the nozzle of the converter. 4. Method according to either of claims 1 and 2, characterized in that at least part of the powdered lime is introduced by the oxygen lance. 5. Method according to either of claims 1 to 4, characterized in that the powdered lime has a particle size such that at least 95% of the lime grains have a size less than 160 microns. * Drawings; ....... vd— boards —b. paoss dent / race cc ie .. 1 t '. '~ w *' "....... À ...... γ. - ·· ne oc claims —a ^ .egé descriptive Luxent Lockt,! sf 2 oh- *? üf Le mafi / à & jh: ^ // m