Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1980-08-11
1982-10-19
Andrews, M. J.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 80, 75129, 75134M, 75135, C22B 4700
Patent
active
043548687
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a process for the desiliconization by means of carbon dioxide of manganese alloys and in particular ferromanganese alloys, in the liquid state.
Manganese alloys which are intended for siderurgical uses are produced by two broad types of process:
When carbon-saturated alloys are to be produced, manganese ore is treated in an electric furnace or in a blast furnace, with one or more carbon-bearing reducing agents.
When the alloys to be produced are not carbon-saturated, a manganese and silicon alloy is reacted on a manganese ore in the presence of lime. These reactions may be carried out in an electric furnace similar to those used in steel marking or in a ladle in which the manganese-silicon alloy is reacted with a molten mixture of lime and manganese ore.
In these two production processes, the resulting product is a ferromanganese which has a greater or lesser silicon content and whose silicon content is in equilibrium with the residual content of manganese oxide slag. In accordance with the mass action law, applied to the reaction: content of the final metal falls.
In order to comply with the requirements made by those in the siderurgical industry, attempts have been made to reduce the amount of silicon in manganese-base addition alloys. Many studies have been carried out and published, all of which aimed to reduce the losses in respect of manganese in the slag, for a given silicon content in the commercial alloy. The most effective process consisted of increasing the basicity number of the slag by increasing its proportion of lime. This method suffers from disadvantages since, on the one hand, it contributes to increasing the volume of the slag and on the other hand it increases its melting temperature, that is to say, it results in the operating temperature of the metallurgical apparatus being higher and the losses of manganese due to volatilization being higher.
Another solution to the problem of low silicon content comprises producing alloys which are not carbon-saturated by injecting oxygen into a carbon saturated base alloy which therefore has a low silicon content. This process of decarbonization with pure oxygen, as described in particular in French Pat. Nos. 2,167,520 and 2,317,369 in the name of Gesellschaft fur Elektrometallurgie NBH, suffers from the disadvantage of causing severe losses of manganese by volatilization and does not make it possible to achieve very low final carbon proportions, under economically satisfactory conditions.
The present invention concerns a novel process for producing manganese alloys with a very low silicon content, which is applied to all manganese alloys whether carbon-saturated or not.
This process comprises treatment in the liquid state of the manganese alloy which is to be desiliconized by carbon dioxide which reacts on the silicon which is to be removed with sufficiently moderate exothermicity for the degree of volatilization of the manganese to remain very low. Besides the substantial advantage which this process provides by reducing the manganese losses due to volatilization, this process also makes it possible to limit the losses of manganese in the desiliconization scoria as the carbon monoxide produced by the reaction: Si+2CO.sub.2 .fwdarw.SiO.sub.2 +2CO provides for intense mixing as between the metal and the scoria which accordingly are in almost perfect chemical equilibrium.
According to the stoichiometry, 44.8 liters of CO.sub.2 are required to oxidize 28 grams of silicon, that is to say, 1.6 m.sup.3 of CO.sub.2 per kg of silicon. In practice, we use from 1 to 3 times and preferably from 1 to 2 times the stoichiometric amount of CO.sub.2, and 0.5 times and preferably 0.7 times the stoichiometric amount of CO.sub.2 when a gas capable of oxidizing silicon is used in combination with the CO.sub.2 to make up the balance.
The invention can be carried into effect in any chamber whatever, which we shall refer to hereinafter generally as a "reactor." The walls of the reactor are formed by a refractory cladding, preferably of the
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Demange Michel
Septier Louis
Andrews M. J.
Societe Francaise d'Electrometallurgie-SOFREM
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