US2058494A - Production of ferro-alloy - Google Patents

Description

Oct. 27, 1936. 1 N OSTRQFSKY 2,058,494

PRODUCTIONOF FERRO ALLOY original Filed July 2o, 1955 ff f" Patented. Oct. 27, 1935 PRODUCTION or FERRO-ALLOY James N. Ostrofsky, Baltimore, Md., assignor, by mesne assignments, to Rnstless Iron and Steel Corporation of America, Baltimore, Md., a corporation of Delaware original application July zo, 193s, serial No. 681,371. Divided and this application October 27, 193s, serial No. 695,549

6 Claims.

This invention is divided out from` my copending application Serial Number 681,371, filed July 20, 1933, entitled Ferro-alloy and relates to ferro-alloys, moreparticularly to iron-chromium alloys. and to an art of producing the same.

One of the objects of my invention is the production of. an iron-chromium alloy of high chromium and nitrogen contents which readily lends itself tol an ease of, handling and wide range of application in the production of rustless iron and steel.

Another object is the production of a high grade alloy of the class indicated in a simple, reliable, and thoroughly practical manner at maximum efficiency and minimum expense.

ments and arrangement of parts, and in the several steps and the relation of each of the same to one or more of the others as described herein and the scope of the application of which is indicated in the following claims.

In the single figure of the accompanying drawing there is illustrated, in vertical section, electric furnace apparatus for carrying out the practice of my invention.

Referring now more particularly to the practice of my invention, a suitable electric furnace,

(see the accompanying drawing) for example, a 2-ton single-phase electric arc furnace, rated 60 cycle, 200 kw. at 110-180 volts, and having two carbon electrodes projecting downwardly into a magnesite lined furnace shell isprepared for the reception of a charge of raw materials. Conveniently an open-top furnace having a metal shell Ill, a magnesite lining I I and electrodes I2 and I3 is used, although it will be understood that a furnace having a lid whichgives an enclosed furnace chamber may be employed `vvhere desired. As a matter of convenience'the furnace is mounted on a suitable foundation I4 to permit the furnace tap-hole I-5 being positioned at a convenient height above the floor of the melt-shop. The furnace electrodes are supported in any suitable manner, not shown, to permit desired adjustment.

Power is supplied the furnace from an electrical transformer (not shown), with voltage control apparatus, connected to a suitable source of electrical energy. Conveniently, electrical energy is applied to. the furnace electrodes I2 and I3 respectively byL exible cables I6 and I1 connected to desired transformer and control apparatus.

In preparing thelfurnace for the reception of a charge of raw materials, power is applied and an arc struck from the furnace electrodes to a small amount of crushed ferrochrome strung along the furnace bottom between the projected electrodes. When the furnace bottom and side walls are thoroughly heated, chrome ore together with a suitable reducing agent, such as coke, and desired fluxing agents, lime and fluorspar, are added as rapidly as furnace conditions permit. The proportion of the charge rst added melts down under the action of the intense heat of the electric furnace arcs to form a slag containing the oxides of iron and chromium `which overlies the small pool of metal on the furnace bottom. The reducing agent added along with the initial charge of ingredients is in part clistributed throughout the slag and serves to effect a reduction of the oxides of iron and chromium. The reduced metals gravitate through the slag j into the underlying pool of metal formed upon the furnace bottom.

In order to achieve an iron-chromium alloy of high nitrogen content, an inexpensive nitrogen containing gas such as ammonia, is preferably directly introduced into the slag during the reduction of the oxides of iron and chromium contained therein. The ammonia gas readily dissociates into the component gases hydrogen and nitrogen. While the 'former gas, in a manner, serves as a reducing agent to aid in the reduction of the reducible oxide content of the slag, and so permit a decrease in the amount of the reducing agent employed, the latter gas is actively absorbed by the nascent iron and chromium formed during the reduction of the oxides of these metals contained in the slag. This nitrogen is then carried into the metal beneath the slag. The incidental absorption of hydrogen gas by the nascent metals is, in most instances, unobjectionable in the production of ferro-alloys of the class indicated. Best results in the production of a ferrochrome of high nitrogen content isachieved by introducing nitrogen containing gas directly into those regions of the slag where the reductionof the oxides is most actively going on. Ordinarily this is within the regions adjacent the furnace electrodes.

With the continued application of power and further introduction of the raw materials, chrome ore, coke, lime and fluorspar into the furnace, more and more of the molten metal containing iron, chromium and nitrogen is formed. This metal may be tapped out of the furnace through a suitable tap hole inthe furnace wall adjacent the bottom while further operation of the furnace continues, or the furnace may be tapped after the `preparation of a heat of metal is substantially pounds 'of lime and 300 pounds of uorspar.

These ingredients'are preferably mixed prior to charging into the furnace so that the reducing agent., coke, and the uxing agents, lime and fluorspar, are distributed throughout the charge of chrome ore. The entire charge of ingredients is added in several batches, one batch following another as rapidly as furnace conditions permit.

Under theaction of the intense heat of the electric arc, (see the accompanying drawing) the rst batch of ore, reducing agent, and ux commences generally indicated at I8 to fuse and forms a slag denoted I9 containing oxides of iron and chromium through which -is distributed the carbonaceous reducing agent.- As the ingredients fuse and become fluid, a reaction takes place between the reducing agent and the oxides of iron and chromium containedv in the slag I9. These oxides are reduced and the metals formed thereby gravitate toward the bottom of the furnace forming thereon a bath of metal 20 while the gases formed as a result of this reaction escape upward, through the ingredients in the furnace, and theninto the atmosphere.

Additions of the remaining batches of raw materials are made as permitted by the impoverishment of the slag through the reduction of the reducible oxide constituents thereof, as more particularly indicated above, and the complete or partial removal of this impoverished slag.

An iron-chromium alloy of desired nitrogen content is achieved as indicated above, by directly introducing a nitrogen containing gas, such as ammonia, into those portions of the slag where the reduction of the oxides of iron and chromium are taking place. For example, a gentle ow of ammonia gasis directly introduced into the slag adjacent the lowermost portions of the furnace electrodes through one or more refractory pipes throughout the entire process or any part thereof as desired. For the illustrative embodiment set forth above good results are achieved by introducing ammonia gas from a suitable source (not shown) through a. flexible tube 2I and a ,refractory pipe 22, having an inner diameter of about M2", positioned between electrodes `I2 and I3 and extending beneath the bottom level of slag I9. Pipe 22 is maintained in proper position for example, by means of parallel spaced angle irons 23 and 24 resting on the top of the furnace shell I0 and engaging an adjustable collar 25 secured to the pipe. The lower end of the" refractory pipe is conveniently provided Awith a number of small openings 22a. to permit escape of the nitrogencontaining gas out into the surrounding slag.

Preferablythe introduction of ammonia is continued throughout the entire period of theto form nitrides of iron and chromium. When.

substantially all of the metal is recovered from thev reducible oxides contained in the. chrome ore charged into the furnace (as evidenced by the appearance of the slag) the heat -of metal is-tapp'ed and allowed to cool after which the metal is crushed to a desired lump size ready for shipment and use. The heat of metal weighs 5,300 pounds and analyzes approximately 59%chromium, 5% carbon, 2% nitrogen, with the balance principally iron. The metal is hard and brittle, which, when crushed, lends itself to an ease of handling and furnacing in the production of, for example, rustless irons and steels of desired nitrogen contents, the proportions of which are directly controlled.

Thus it will be seen that there has been provided in this invention a ferro-alloy of high nitrogen content and an art of producing the' same in which the various objects hereinbefore noted together ,with many thoroughly practical advantages are successfully achieved. It will be seen that the process lends itself to the production of inexpensive nitrogen containing iron-chromium alloys of desired nitrogen content which maybe controlled within commercial limits.

While, for purposes of illustration, a nitrogen containing ferrochrome .of high nitrogen content is obtained it will be understood that by limiting the ow of the nitrogen containing gas into the molten ingredients during the reduction thereof, either in quantity per unit time (as by decreasing the pressure or by employing a smaller pipe) or for the total time during which nitrogen is introduced into the slag, the nitrogen content of the tapped metal may be decreased to l per cent or even lower (0.5% for example) as de' sired. So, also, by increasing the ow of nitrogen into the slag and distributing this nitrogen containing gas so as to effect a moreintixnate ass'ociation between the gas and the nascent metals as by directing a plurality of streams of nitrogen 'containing gas into those regions of the slag where the reduction of the reducible oxide is most active, the nitrogen content of the tapped metal may be increased considerably even to a value approaching 15% corresponding to a complete conversion of the chromium oxide to chromium nitride (CrN). The proportion of chromium andiron vary in accordance with the proportions of these ingredients found in the particular chrome ore employed. For-example, the chromium content of the metal may vary between about and 72% depending upon the raw materials used although, ordinarily, the chromium content varies between and 69%. pends upon the amount of carbon in the mix (this is usually in excess of the chemically equivalent amount required to achieve a reasonably high recovery of metal from the ores) and to a lesser extent upon the type and condition of the furnace employed as well as The carbon content largely deupon the rapidity with which the process is carried out; 4a rapid practice 1% although the carbon content ordinarily amounts to about 5%.

While'in the embodiment of my invention illustratively set forth above a nitrogen containing gas is directly introduced into the slag containing the oxides of iron and chromium, and preferably into those regions of the slag where the reduction of these oxides 'is most active, good results are achieved wherethe reduction of the metallic oxides is carried out in an enveloping atmosphere of nitrogen containing gas.

Likewise while the introduction of ammonia gas gives excellent results and permits the production of an iron-chromium alloy, the nitrogen content of which is readily controllable within commercial limits, good results 7are achieved where nitrogen gas is employed, as from commercial bottled nitrogen.

As many possible embodiments may be made of my invention and as many changes in the embodiment hereinbefore set forth it will be understood that all matter described herein is to be interpreted as illustrative, and not in a limiting sense.

I claim: 1.- In the production of an iron-chromium alloy of high nitrogen content, the art which includes,

reducing chrome ore, in the immediate presence of a nitrogen containing gas bubbling into and through the region undergoing reduction.

l agent and passing nitrogen gas into and through -a slag containing oxides of iron and chro- Vn iium which are reduced by said agent forming thereby the metals iron and chromium. and bubbling nitrogen gas through said slag during the reduction of the oxides contained therein whereby nitrogen is absorbed by and combines with the metals resulting therefrom.

5. In the production of an iron-chromium alloy of high nitrogen content, the art which includes, continuously melting down chrome ore in the presence of a carbon reducing agent to form a slag containing oxides of iron and chromium which are reduced by said agent thereby giving nascent iron and chromium, and passing ,am-

monia into said slag during the reduction of the 4 oxides containedtherein whereby nitrogen is absorbed by said nascent metals.

6. In the production of an iron-chromium alloy of high nitrogen content, the art which includes, melting down chrome ore in an electric arc furnace having carbon electrodes to form a slag containing the oxides of iron and chromium, reducing the oxides contained in said slag by a suitable reducing agent, and passing nitrogen containing gas into said slag adjacent said furnace elec- .trodes whereby nitrogen gas is absorbed by the metals resulting from the reduction of the oxides contained in said slag.

JAMES N. os'rRoFsiY.

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