US1853229A - Ferro-aluminum-silicon alloy - Google Patents

Description

Patented Apr. 12, 1932 UNITED STATES PATENT OFFICE ."BYRAMJ I SAKLAT'WALLA, OF GRAFTON, PENNSYLVANIA, ASSIGNOR TO VANAIDIUM CORPORATION OF AMERICA, 0F BRIDGEVILLE, PENNSYLVANIA, A CORPORATION OF DELAWARE FERROALUMINUM-SILICON ALLOY N0 Drawing. I

This invention relates to an alloy containing aluminum, silicon and iron, and especially to an alloy suitable for addition to molten steel for the purpose of obtaining sound, dense ingots when such steel solidifies.

The use of metallic aluminum for the purpose of scavenging molten steel is very well known and is more or less universally used in steel manufacturing practice. Its use, however, is combined with very marked deficiencies so that, while the aluminum frees the molten steel of impurities, such as iron oxide, by chemically reacting with it, the product formed from such reaction, namely, alumina, remains entrapped in the steel, thus imparting to it several objectionable qualities. Moreover, the amount of alumina remaining entrapped in the steel is not always the same and consequently ingots are obtained which have varying physical qualities, such as ductility, although of the same chemical composition. The presence of alumina in aluminum-treated steel can be always detected by means of the microscope and it is.

well recognized that the aluminum content found in such steel is not in the form of metallic aluminum but chemically combined with oxygen as alumina. If any metallic aluminum were residually present, it would be very helpful in densifying the steel and its presence would be a full assurance of the perfect scavenging action of the balance of the aluminum added? Metallic aluminum for the purpose of addition to steel further has the disadvantage of being very light in weight and, therefore, not being able to enter into the body of-the molten steel, and also its reaction with oxides and with atmospheric oxygen at high temperatures takes place extremely rapidly, more or less instantaneously. Due to this rapid action, considerable of the aluminum added is inefiectually burned up.

To remedy these deficiencies, it has been suggested to use ferro-aluminum or a ferroaluminum-silicon alloy. Such products have long been on the market but have not been utilized by the steel industry on account of certain characteristic deficiencies of the products heretofore made. The ferro-alloys thus produced contain appreciable quantities of 'in excess of the aluminum content.

Application filed February 6, 1929. Serial No. 338,037.

carbon from approximately .50% to about 1.7%. This carbon content is present in these alloys in the form of carbides, either a silicon carbide, or aluminum carbide, or mixed carbides of silicon and aluminum, or of silicon, aluminum and iron. As is well known in the case of the ferro-silicon alloys, the presence of impurities such as carbides, tends to disintegrate such alloys, making them unfit for addition to molten steel. It is by reason of the presence of these carbides in the ferroaluminum or ferro-aluminum-silicon alloys and their consequent disintegration that their commercialnse in the steel industry has been prevented. Disintegration of such alloy is alsodependent on the percentage of silicon. It has been found that, above certain percentages of silicon, the alloy becomes disintegrating even irrespective of the carbon contents.

My improved alloy contains aluminum, silicon and iron, with a minimum of carbon so as to be substantially carbide free. The aluminum content may vary from 5% to 30%,

preferably 15% to 25%. The silicon content may vary from 10% to 50%, preferably between 35% and 45%. The silicon content is The remainder is principally iron, although usual impurities or perhaps small quantities of other alloying metals may be present. The carbon should be kept to a minimum, not over 4% and preferably less than .l5%.

The alloy may be made by the addition of metallic aluminum into a bath of ferro-silicon of the suitable composition in the ordinary electric furnace used for the manufacture of ferro-silicon. The conditions under which a bath of molten ferro-silicon exists in such a furnace are such as to avoid contamination of the alloy produced by carbon.

This alloy, which is substantially free from carbides, and which does not contain silicon in excess of 50%, and preferably not over 45%, can be kept in solid non-disintegrating lumps or masses suitable for addition to molten steel. It has been ascertained that alloys containing over 45% or 50% of silicon are diflicult to keep ina non-disintegrating i condition, irrespective of their contents of impurities. This alloy also has a specific gravity approximately twice that of metallic con about 10% to 48.5%, the silicon being in excess of the aluminum, the balance being principally iron, and carbon not over about aluminum and on account of the low silicon .157

oxides and other impurities present in the .47

steel in such an instantaneous and violent manner as does metallic aluminum, but descends into the molten steel and interacts gradually, allowing the non-metallic impurities formed by the reaction to rise to the surface of the steel. Further, formed by the oxidation of the aluminum and silicon alloy together is an aluminum silicate, which has a very much lower melting point than aluminum and therefore by the exothermic reaction between the ferro-silicon-aluminum and the molten steel, finds sufficient temperature to melt and rise to the surface through the body of the molten steel. Also, this alloy does not have the objectionable feature of introducing carbides into the steel, to thereby raise its carbon content, as would be the case with the carbide containing ferro-aluminum-silicon alloys heretofore used.

My alloy also has the advantage that by its addition to steel a residual content of metallic aluminum in predetermined quantity, preferably from about .02% to 1%, can be more easily obtained in the steel. It is generally recognized that to obtain a steel containing a predetermined quantity of aluminum in the finished state by the use of pure metallic aluminum is a difficult operation. The aluminum in my alloy does not burn up quickly, but its oxidation reaction takes place gradually and slowly, thus bringing about the above result.

My alloy further has the advantage over those containing high percentages of silicon in that it can be produced at a very much cheaper cost. The cost of production of alloys containing silicon over or increases very much and not in any direct proportion to the silicon content, the power requirements for the reduction of high percent silicon alloys being abnormal.

While I have described my alloy in its preferred composition, it is to be understood that the invention is not so limited, but may be otherwise embodied within the scope of the following claims.

I claim:

1. steel densifying and scavenging alloy, containing aluminum about 5% to 30%, silicon about 10% to 48.5%, the silicon being in excess of the aluminum, the balance being principally iron, and carbon not over about 2. A steel densifying and scavenging alloy,

containing aluminum about 5% to 30%, silithe product I O. 3. A steel densifying and scavenging alloy, containing aluminum about 15% to 25%, silicon about 35% to 45%, the balance being principally iron, and carbon not over about 0- 4. A steel densifying and scavenging alloy, containing aluminum about 15% to 25%, silicon about 35% to 45%, the balance being prigcipally iron, and carbon not over about .15 o. v

In testimony my hand.

BYRAMJ I D. SAKLATWALLA.

whereof I have'hereunto set