SU1724714A1 - Mixture for cast iron carburization at smelting in the electric furnace on the oxidized charge - Google Patents

Abstract

The invention relates to mixtures for carburizing pig iron in smelting in electric furnaces on an oxidized charge. The purpose of the invention is to increase carbon sequestration, stabilize the carbon content in the smelted iron, and reduce the cost of the iron. The mixture contains 2-8 wt.% Silicocalcium, the rest is pitch coke. The use of the proposed graphitizing mixture makes it possible to increase the degree of carbon assimilation up to 79.6-90%, stabilize the content of elements — carbon, silicon, and manganese in the iron; 2 tab. WITH S

Description

The invention relates to ferrous metallurgy, and more specifically to the composition of a mixture for carburizing cast iron in its smelting in electric furnaces using a large amount of steel scrap in the mixture.

A known mixture for carburizing cast iron, in which various carbonaceous materials are used: graphite chips, graphite strikes, coke breeze or pitch coke, etc.

The disadvantage of all carbonaceous materials is that the magnitude and stability of carbon assimilation from them by the cast iron during smelting significantly depend on the oxidation of the charge. The more oxidized steel scrap and, accordingly, the pig iron alloy, the more carbon is lost to the iron deoxidation and the less it goes to the carburization of the melt. Since the degree of oxidation of steel scrap (and other

The metallic components of the charge are unstable and not controlled due to the lack of control methods, the absorption of carbon by iron from a carburizing additive is unstable, as a result of which, after melting, an adjustment of the carbon content in the iron is required, which lengthens the melting.

A known mixture for the treatment of cast iron, consisting of carbon-containing components and slag-forming calcium-containing components, has a composition, in wt.%: Calcium carbide 75-90; ash coke shale 10-25.

A known mixture having a composition, wt.%: Lime 40-50; fine graphite 50-60.

However, these mixtures are unsuitable for carburizing cast iron during smelting in acid lining furnaces. Entering them in the quantity required to obtain in the iron specified J ihO i-few XI

J

Its carbon content means the introduction of a quantity of lime or calcium carbide equal to or greater than carbon. These calcium-containing components form the main slag, which destroys the acid lining of the furnace, which is unacceptable. In addition, a large amount of slag is formed, the removal of which is laborious.

The closest to the technical essence of the invention is a carbon-containing additive (graphite, carbon breakage, etc.), which is used to carburize cast iron. In this method, the oxidation of components (carbon monoxide) is reduced by optimizing the temperature of the input of ferroalloys, but this increases carbon carbon, i.e. its consumption increases.

The purpose of the invention is to increase the absorption of carbon from the carburizing mixture, the stability of the carbon content in the iron and the efficiency in the smelting of iron in electric furnaces from a mixture containing a large amount of oxidized steel scrap.

This goal is achieved by the addition of silicocalcium to the carburizing mixture consisting of carbon-containing substances, and pitch coke is used as a carbon-containing substance in the following ratio, wt.%: Silicocalcium 2-8; pitch coke 92-98.

When smelting pig iron in an electric furnace with acid lining on an oxidized charge, during the melting of the charge, the oxides transfer to the melt. The silicocalcium contained in the mixture deoxidizes the iron: calcium binds oxygen and its oxides pass into the slag. As the melt overheats, carbon from the pitch coke begins to dissolve in it. If the amount of silicocalcium in the mixture is less than 2 wt.%, It is not enough to bind all the oxygen, and the oxygen in the melt reacts when the melt is heated with carbon of pitch coke. Therefore, less carbon remains to carburize the pig iron, and the carbon absorption factor of the pig iron is reduced.

If the amount of silicocalcium in the mixture is more than 8 wt.%, The basicity of the slag increases greatly, the slag corrodes the acid lining of the furnace.

Since the content of silicocalcium in a mixture of 8 wt.% Is already enough to deoxidize the iron, with a larger amount of carbon absorbed from the mixture does not increase.

Incorporation into a mixture for carburizing pitch coke instead of graphite has an advantage for a number of reasons. Pitch coke contains 0.2–0.6% sulfur, which goes into cast iron and improves the efficiency of its modification due to the formation of manganese sulfides in the iron, which are graphitization centers. Pitch coke is not dusty, which improves the environment when it is loaded into the furnace, has, with the same graininess, greater porosity and specific surface area, which contributes to accelerating the dissolution of carbon in cast iron, in addition, it is 3-5 times cheaper than graphite.

Compared to other carbonaceous materials (anthracite, coal, foundry coke), pitch coke has lower ash content, more carbon and ash and carbon content varies within narrower limits (Table 1).

The narrower limits of carbon content in the material provide less variation in the carbon content of the smelted iron. The limits of the content of pitch coke are determined by the limits of the content of silicocalcium.

The use of the proposed carburizing mixture allows to increase the content of steel scrap in the charge during the electric smelting of cast iron and to ensure stable production of a specified carbon content in the iron regardless of the oxidation level of scrap, reduce the consumption of carbonaceous material, reduce the amount of dust to the environment when loading into the furnace a carburizing mixture.

Table 2 presents data on the chemical composition of cast iron and the assimilation of carbon by cast iron during smelting on an oxidized charge in an acid-lined induction electric furnace using the proposed carburizing and known mixture.

The composition of the mixture is as follows, wt%: oxidized steel scrap 97; ferrosilicon 3; a carburizing mixture of 4.5.

From the presented data, it is clear that the absorption of carbon is higher from the proposed mixture than from the known (79.6-81.8% compared to 71.4-75.04%), higher and the stability of the carbon content in the pig iron (the difference in carbon content in swimming trunks, respectively, no more than 0.05 and 0.08%). In addition, the proposed mixture does not cause intensive destruction of the furnace lining.

Claims (1)

Invention Formula A mixture for carburizing cast iron in smelting in electric furnaces on an oxidized charge, containing carbon-containing substances, characterized in that, in order to increase the absorption of carbon, to stabilize the carbon content in the smelted iron and reduce the cost of iron, it additionally contains silicocalcium, and as a carbon-containing substance pitch coke in the following ratio, wt.%: silicocalcium 2-8; pitch coke 92-98. Table 1 Table 2