US1508083A - Manufacture of steel - Google Patents

Description

reamed sea 9, 924.

' silica in unimportant proportions.

My 3 of making steel and particularly chromium v P ma-En sures;

I 1,508,083 PATENT OFFICE.

mm a. arm, on NEW YORK, N. Y.

" murnc'runn or STEEL.

In Drawing.

of the city, county, and State of New ,York,

have inventedcertain new and useful Improvements in the Manufacture .of Steel, of which the following is a specification.

invention aims to provide a process steel and steel alloys by which such steel or steel, alloys can be produced of great purity. v

The process is performed in a basic lined furnace, preferably an electric furnace of the Heroult arc type. A thorough deoxidation of the bath is secured by the use of a: highly siliceous slag, this stage of the process being followed by, the use of a slag lowerv in silica, A. specific example of the processis as follows-An ordinary cold charge, consisting generally of steel scra is put into a basic electric furnace an under the usual basic oxidizing slag to dephosphorize it. Such a slag, for example, comprises lime to 60%, iron oxid 15 to 20%, and the balance magnesia, alumina and The use of this slag, while it serves to remove phosphorous, leaves the bath with a certain percentage of oxides in it which are objectionable; particularly in the making of chromium steel and similar steels. often contain defects caused rimarily by oxides of chromium or other a oying metal; which oxides are reduced only with great difiiculty in the bath. The next step of the process, therefore, is directed to the thorough deoxidation of the bath.

When the dephosphorization has been completed or carried to the desired extent, this first slag isremoved and replaced by a highly siliceous slag, the principal purpose of which is to thoroughly deoxidize the ath. Such a slag, for example, may contain 35 to silica (siO with the balance chiefly lime and with small quantities of magnesia and alumina. Under this slag thetemperature of the bath should be increased, say from 1525 degrees centigrade to above 1575 degrees and repeated layers of coke dust should be added on the slag until the deoxidation is substantially complete. The total quantity of coke dust will probably average fifteen pounds to the ton of steel and in special cases may run up to fifty pounds.

a there melted These steels such a slag to finish Application filed December 10, 1920; Serial No. 431,294.

The carbon in the added coke dust 'andin the bath reacts with the silica of the slag, reducing silicon therefrom, and the latterserves to deoxidize the bath. The quantity of silicon reduced from the slag varies with the quantity of silica present in the slag. The time required for the reduction of the silicon is shortened as larger quantities of silica are use in the slag. A certain percentage of silicon is required in the finished steel, about 0.20% in ordinary chromium steel. silica in the slag and the length of time. this stage of the process should be such as to thoroughly deoxidize the bath and in addi- The percentage of v tion to ield the silicon content required in dinary basic slag, containing up to 25% silica with the balance essentially lime. The smaller the percentage of silica in this finishing slag, the greater the sulphur-carrying capacity of the slag. A good example will be aslag containing about 10% sil1ca.

The presence of silica in reducing slags decreases the sulphur-carrying capacity but is of material advantage in deoxidizing. By my process I first use the slag best adapted for deoxidizing, and follow this by the slag best adapted for reducing the sulphur content of the bath.

,In my process thehighly siliceous slag does not come into contact with hearth except at the slag line, and, therefore, does not substantially scorify the hearth. It would be disadvantageous to use the heat because when the heat is poured or tapped a portion of the slag settles over the entire hearth and would quickly cut it out. By removing this slag from the bath and finishing the metal under a highly basic slag, I secure the advantage of the high silica slag without serious injury to the furance. i

The process is ap licable not only to makin steel from col refining of a molten charge such as molten Bessemer steel or molten acid or basic open hearth steel.

scrap, but also to the the basic Where it is not necessary to remove phosphorous first fromthe bath, as in treating asic open hearth steel which has already been sufiiciently dephosphorized, the basic oxidizing slag above referred to is not necessary, and the process may be commenced with the highly siliceous slag added immediately after the metal is poured into the furnace.

In making the alloy steels referred to it is customary to add the alloying metal to the bath after dephosphorizing. For example, ferro-chrome isadded to a dephosphorized steel bath to produce chromium steel analyzing usually 1% or more of chromium. In such addition, under the old practice, oxides of chromium are produced when the term-chrome is added and are reduced with great dificulty, or if not reduced are the cause of defects in the steel. According to my process, the alloying metal is added after the highly siliceous slag has been used to remove the oxygen left in the bath by the dephosphorizlng operation, and removal of such slag.

'Iheprincipal function of the silica in the finishing slag is to increase its fluidity; and it may be replaced inwhole or in part by fluorspar and other materials which are known to accomplish the same purpose.

Though I have described with great particularity of detail certain specific processes embodying my invention, yet it is not to be understood therefrom that the invention is restricted to the specific embodiments deincense which comprises holding it molten on a basic hearth under an oxidizing slag for removal of phosphorous, replacing said deoxiolizin slag by a highly siliceous deozridizing s ag and finally by a slag lower in silica.

3. In the making of alloy steel the process which comprises, first, holding the steel molten under a highly siliceous deoxiding slag, second, removing said deoxidizing slag, third, adding the alloying ingredient and fourth, replacing said deoxidizing slag by a slag lower in silica.

4. In the making of alloy steel the process which comprises holding the steel molten on a basic hearth under a highly siliceous deoxidizing slag, adding the allo ing in. redient after the use of said deoxi 'zing s ag, and replacing said deoxidizing slag by a slag lower in silica.

In Witness whereof, I have hereunto signed my name.

FRANK E. CIJMRK.