US2586315A - Treatment process for hypereutectic cast irons - Google Patents

Description

product.

Patented Feb. 19, 1952 UNITED STAT TREATMENT PROCESS FOR HYPEREU- TECTIC CAST IRONS Eugene Eyt,

Pamicrs, Ariege, and Lonce Reygagne, Decazeville, Aveyron, France, assignors to Societe Anonyme .de Commentry, Fourchambault & Decazeville, Paris, France, a

company of France No Drawing. Application Fe'bruary'17f1950, Serial No. 144,845. In France March 30, 1949 2 Claims.

In conventional industrial practice, and in the case of most blast-furnaces, the range of compositions of raw cast-irons which may be produced with acceptable technical and economical conditions, is quite narrow. However, these cast-irons are not always the most appropriate as regards the requirements of consumers. Moreover, it has seldom been contemplated to improve or alter the composition of blast-furnace raw cast-iron considered as a starting The present invention particularly concerns hypereutectic cast-irons, for instance those which may be obtained according to the U. S. patent application Serial No. 111,905 filed August 23, 1949. It relates to a process enabling to alter the composition and properties of these cast-irons by lowering their carbon content and if needs be their silicon content.

It further concerns cast-irons obtained there- Although in the present specification, only blast-furnaces and blast-furnace cast-irons will be referred to for the sake of simplification, the invention concerns cast-iron of any kind, of any origin and of any preparation, whether it be of first fusion produced in any apparatus or of second fusion, 1. e. resmelted in any apparatus: e. g. cupola, electric furnace, reverberatory furnace, etc.

It is known that the solidification point of hypereutegtic cast-iron decreases as its carbon content decreases, contrarily to the phenomenon occuring in the case of hypoeutectic castiron whose solidification point increases when the carbon content decreases. Thus this point drops from about 1800 C. for a carbon content of 6.67% (cementite FesC) to 1135 C. for the eutectic content which is 4.30% in the iron-carbon system; a similar variation but of different absolute value, occurs in the case of cast-irons containing other constituents. On the contrary, the solidification point increases when the carbon content drops below the eutectic value.

According to the invention, the calories are used which are made available owing to the drop in solidification point corresponding to the correction to be applied to the carbon content of hypereutectic cast-irons discharged by a blastfurnace, for melting iron or steel in a relatively divided state (light scrap-iron, steel turnings, etc. whether previously heated or not, whether oxidized or not, for the purpose of lowering by dilution and/or by oxidation, the initial carbon content. The addition of metallie or oxidized iron must be proportionedaccording to the desired reduced carbon content which may be either greater or lower than the eutectic content; obviously, it is necessary to take into account the rise in the solidification point. of cast-iron which accompanies the'decrease in the carbon content below that eutectic content, and as a rule to proportion the addition of. iron so that the temperature of cast-iron, after addition, remains high enough above its solidification point, this temperature margin being determined according to the subsequent treatment to which cast-iron is to be subjected.

This proportioned addition of iron or steel, oxidized or not, which may be carried out in the ladle into which the hypereutectic cast-iron is poured, causes not only the carbon content to be adjusted, but also to act in a favorable way on the structure by homogenizing the thickness of graphite flakes and their distribution. This homogenization results in an improvement of the mechanical properties of cast-iron. Moreover, the amount of coke per unit weight of cast-iron eventually obtained is decreased by the increase in production due to the conversion of added iron or steel to cast-iron, owing to the calories recovered within cast-iron.

In order to decrease the silicon content, the excess silicon may be burnt by oxygen contained in iron oxide which is-obt'ained at the surface of the iron or steel in a divided state added to cast-iron as described above, by previously heating these substances by means of an oxidizing flame. It is also possible to replace iron or steel in the divided state and superficially oxidized as stated, by iron oxides such as scale, granular or powdery ores, etc.

A fraction of the oxygen content of the oxides burns a part of the carbon content of cast-iron into carbon monoxide and carbon dioxide; another fraction reacting with silicon, evolves an amount of heat greater than that required by the decomposition of the oxides. These calories together with the heat due to the difference between the actual temperature of cast-iron and that necesary for its pouring, are available for melting ferrous metallic substances after reduction of the oxides which they possibly contain. Lastly, a portion of the addition is scorified together with the oxidation products of cast-iron (MnO, S102, etc.). By a convenient predetermined addition of the mixture of iron in the divided state and of granular or powdery iron oxide, a decrease in the carbon and silicon contents is achieved, and a slag is formed whose properties determine the form of graphitization 0f cast-iron.

According to the cases, the proportions between the additions of iron or steel and of iron oxides may vary within very wide limits. These additions may be eifected either in a sprue, or in a convenient vessel, whether fixed or movable,

heated or non-heated, and into which cast-iron is poured. They may be effected in a continuous way in the sprue or in the vessel, or by mass additions once or several times.

It is also possible to lower the silicon and carbon contents while obtaining a rise in temperature of the metallic bath, "by blowing in a predetermined amount of oxygen.

What we claim is:

1. In a treatment process for lowering the carbon content and the silicon content or raw hypereutectic iron, the pouring of said hypereutectic iron from a blast-furnace; the addition to said liquid hypereutectic iron of a mixture of low carbon iron and iron oxide in a relatively divided state; and the melting of said mixture by the heat which is contained in excess in said hypereuteotic iron owing to the lowering of its solidification point when its carbon content decreases.

2. In a treatment process for lowering both the carbon content 'ahd 'the silicon content of raw hypereutectic iron, the steps which comprise taking low-carbon fironin'a relatively 'dividecl state, oxidizing superficially and heating said low-carbon iron by subjecting it to the action of an oxidizing flame, pouring molten hypereutectic iron from a furnace and adding to it when in liquid state said partially oxidized and heated low-carbon iron only in an amount adapted to the melting of said low-carbon iron by the heat contained in excess in the hypereuteotic iron owing to the lowering of the solidification point of the latter when its carbon content decreases.

EUGENE EYT.

LEONCE REYGAGNE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 77,469 Ellershausen May 5, 1868 90,926 Chubb June 8, 1869 173,159 Carpenter Feb. '8, 1876 FOREIGN PATENTS Number Country Date 3,631 Great Britain of 1868 111,522 Australia Sept. 26,1940

OTHER REFERENCES Cast Iron, page 31, edited by Hatfield.

Published in 1912 by Charles Griffin and Co., London, England.

Claims (1)

1. IN A TREATMENT PROCESS FOR LOWERING THE CARBON CONTENT AND THE SILICON CONTENT OF RAW HYPEREUTECTIC IRON, THE POURING OF SAID HYPEREUTECTIC IRON FROM A BLAST-FURNACE; THE ADDITION TO SAID LIQUID HYPEREUTECTIC IRON OF A MIXTURE OF LOW CARBON IRON AND IRON OXIDE IN A RELATIVELY DIVIDED STATE; AND THE MELTING OF SAID MIXTURE BY THE HEAT WHICH IS CONTAINED IN EXCESS IN SAID HYPEREUTECTIC IRON OWING TO THE LOWERING OF ITS SOLIDIFICATION POINT WHEN ITS CARBON CONTENT DECREASES.