US3325278A

US3325278A - Alloy purification process

Info

Publication number: US3325278A
Application number: US365778A
Authority: US
Inventors: Melvin L Mcclellan
Original assignee: Union Carbide Corp
Current assignee: Elkem Metals Co LP
Priority date: 1964-05-07
Filing date: 1964-05-07
Publication date: 1967-06-13
Anticipated expiration: 1984-06-13

Description

United States Patent 3,325,278 ALLOY PURIFICATION PROCESS Melvin L. McClellan, Grand Island, N.Y., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed May 7, 1964, Ser. No. 365,778 2 Claims. (Cl. 7560) The present invention relates to the purification of alloys. More particularly, the present invention relates to a process for the removal of impurities from molten metals by the oxidation of the impurities.

Many metals and alloys, by virtue of their method of manufacture, contain minor amounts of impurities which detrimentally affect their performance in. their intended use. 1

For example, ferrosilicon which is used in the treatment of steel, often contains small percentages, e.g. up to 2 percent each of aluminum and calcium.

In many instances, for example in the production of special electrical steels containing silicon the presence of such amounts of aluminum and calcium is highly undesirable since these elements interfere with the electrical properties of the steel.

It has been proposed to remove these impurities by melting the alloy under a high silica slag or holding the alloy molten under such a slag in an arc furnace. However .this type of procedure is costly and requires relatively expensive equipment.

It has also been proposed to treat aluminum and calcium containing ferrosilicon with gaseous oxygen while in the molten state to oxidize and thus remove these materials.

This approach has not been entirely successful due .to the fact that as the aluminum and/or calcium contents are lowered, substantial oxidation of silicon begins and relatively large amounts of silicon, e.g. up to 5 percent and more are lost.

Moreover, as the silicon is oxidized, it forms a fluid slag on the surface of the molten metal which has the effect of retarding further oxidation of the calcium and aluminum impurities and results in the inefiicient usage of oxygen and also causes slag separation problems.

It is therefore an object of the present invention to provide an improved process for removing impurities from molten metal through the use of gaseous oxygen.

Other objects will be apparent from the following description and claims.

A process in accordance with the present invention comprises providing a molten bath of the metal to be purified; contacting the surface of the molten metal with a stream of gaseous oxygen; and introducing inert gas into the lower portion of the molten metal bath to provide agitation thereof to thereby promote oxidation of the oxidizable impurities therein.

In the practice of the present invention impurity-containing metal for example ferrosilicon (74 to 76 percent Si) containing 0.45 percent Al and 0.20 percent Ca is provided in the molten state.

Molten ferrosilicon or other metal can be concurrently obtained by .tapping from the furnace in which it is produced into a ladle or similar device.

With the metal bath at a convenient temperature, e.g. 1350 to 1700 C. a stream of oxygen is directed at the surface of the molten metal while concurrently an inert gas, e.g. argon is introduced into the lower portion of the bath. The argon introduction can suitably be accomplished by means of a tuyere located in the bottom of the ladle containing the molten ferrosilicon. It has been found that the rate of argon introduction is preferably no greater than the rate of oxygen flow, in order to permit effective removal of aluminum and calcium. For best results, the oxygen flow should be about 1 to 2 times the rate of argon flow.

Also, the oxygen flow should be limited to a value which avoids the oxidation of metal other than the impurities to be removed. That is to say, the oxygen rate is limited so that there is no substantial slag formation on the surface of the metal.

By way of a more specific description of an embodiment of the presentinvention, a batch of molten ferrosilicon (75.8% Si, 0.20% Ca, 0.45% Al bal. Fe) is placed in a If a slag begins to form, the oxygen flow rate is suit-.

ably decreased to avoid further oxidation of silicon. It has been found that with the equipment and materials aforedescribed an oxygen flow rate of about 360 c.f.h. and an argon flow rate of about 225 c.f.h. can provide a reduction of the aluminium and calcium content to below about 25% and .06% respectively, without any significant loss of silicon, i.e. the silicon loss is less than 1 percent.

It is to be noted that in the present invention, the inert gas cannot be merely mixed with the oxygen since under these circumstances only dilution is achieved and little if any improvement in impurity removal is obtained.

In order to determine the effectiveness of the deoxidizing process of the present invention, melts of percent ferrosilicon were produced under lime-alumina slag. The slag was frozen in place and the metal was poured into a ladle having a 30 inch ID. and equipped with a tuyere inch in diameter centrally located at the bottom. The depth of the alloy in each case was about 22 inches. Argon was introduced through the tuyere and bubbled through the melt and a stream of oxygen was blow onto the surface of the molten metal through a water cooled lance. This treatment was continued in each instance until the aluminum content of the alloy was decreased to about 1.0 percent and the calcium content to about 0.5 percent. The calcium and aluminum contents of the starting alloy were about 1.7 percent and 1.6 percent, respectively.

The results obtained are shown in Table I.

TABLE I Weight of O2 Argon Slag Temp. at Starting Rate, Rate, Time, Forma- End of Alloy, lbs. c.f.h. c.i.h. minutes tion Treatpient,

I 1,590 720 225 15 Heavy 2,880 II, 1,750 360 225 25 None 2, 685

1 Silicon oxidation.

treatment of manganese, chromium, and iron base alloys.

What is claimed is:

1. A process for removing aluminum and calcium impurities from ferrosilicon which comprises:

(1) providing a molten bath of ferrosilicon (2) contacting the surface of the molten metal with a stream of gaseous oxygen and (3) introducing inert gas into the lower portion of the molten ferrosilicon bath .to provide agitation thereof to thereby promote oxidation of the calcium and aluminum impurities therein.

2. A process for removing aluminum and calcium impurities from ferrosilicon which comprises:

(1) providing a molten bath of ferrosilicon at a temperature in the range of about 1350 C. to about 1700 C.; l

(2) contacting the surface of the molten ferrosilicon with gaseous oxygen by directing a stream of oxygen at the surface of the molten ferrosilicon;

(3) introducing inert gas into the molten ferrosilicon below the surface of the molten bath and at the lower portion thereof, the rate of flow of inert gas being sufficient to cause vigorous agitation of the molten bath by bubbles of inert gas; and

(4) adjusting the rate of How of oxygen and inert gas so that the oxygen flow rate is between about 1 and 2 times the inert gas flow rate and so that there is no substantial formation of slag on the surface of the molten ferrosilicon.

References Cited UNITED STATES PATENTS 1,968,917 8/ 1934 Soldatoff 7560 2,866,701 12/1958 Strauss 7560 3,169,058 2/1965 Nelson 75-59 3,201,226 8/1965 Spolders et al 7560 FOREIGN PATENTS 872,995 7/1196 1 Great Britain. 878,386 9/ 1961 Great Britain.

BENJAMIN HENKIN, Primary Examiner.

Claims

1. A PROCESS FOR REMOVING ALUMINUM AND CALCIUM IMPURITIES FROM FERROSILICON WHICH COMPRISES: (1) PROVIDING A MOLTEN BATH OF FERROSILICON (2) CONTACTING THE SURFACE OF THE MOLTEN METAL WITH A STREAM OF GASEOUS OXYGEN AND (3) INTRODUCING INERT GAS INTO THE LOWER PORTION OF THE MOLTEN FERROSILICON BATH TO PROVIDE AGITATION THEREOF TO THEREBY PROMOTE OXIDATION OF THE CALCIUM AND ALUMINUM IMPURITIES THEREIN.