US2070185A - Making reagents for metal alloys - Google Patents

Description

Feb. 9, 1937. G, E. SEIL.

MAKING REAGENTS FOR METAL ALLoYs Filed Jan. 18, 1936 2 Sheets-Shet l Snventor Gttoneg GILBERT E.SE|L

Feb. 9,1937. G. E. SEIL 2,070,185

MAKING REAGENTS FOR METAL ALLOYS Filed Jan. 18, 1956 2 Sheets-Sheet 2 F|G.2. 'Il 3 f /////;/////;///ff////////// Snventor @H BERT ssen.

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(Ittorneg Patented Feb. 9,V 1937 MAKING nEAGEN'rs ron METAL ALLoYs Gilbert E. Seil, Cynwyd, Pa., assignor, by mesne assignments, to Buffalo Electric Furnace Corporation, Buffalo, N. Y., a corporation of New York application .ranary is, 193s, serial N. 59,691 lin Canada August 19, 1935 6 Claims.

' This invention relates to the refining of metals, metallic material, or metal alloys. More particularly, it deals with the control of the ultimate content of desirable and undesirable constituents of metals and metal alloys, and the scope of the invention is broad enough to contain within its purview not only novel processes, but products resulting from practicing such processes and possibly furnace structures in which such processes can be carried out.

The general objectof thisinvention is to refine lmetallic material and/or metal alloys especially those containing a desirable constituent such as chromium, in a simple and readily controlled manner by which there isl facilitated, to an extent not' heretofore practicable the elimination from the metal or alloy to be refined, of the impurities or undesirable constituents therein by selective oxidation thereof.

Another object of this invention is to bring about this oxidation of impurities under condi tions as nearly ideal therefor as possible both as to speed ofrreaction and eiiciency thereof ,namely with the reactive materials in miscible solution .and thoroughly mingled. A further .object is to Vcarry out this reacting of materials in solution in the presence of a carbon monoxide superatmospheric pressure to assure absence of air.

And a further very important object of the invention is to form in a heated reaction zone and exteriorly of the bath of metallic material to be manned, a highly concentrated oxidizing reagent with the oxide solute whereby there is exposed to y the oxide surrounding the metal globules, abnormally large surfaces per unit of Weight, for thus facilitating the dissolving of the oxide in the metal. And a further object of this invention is to retain or confine and prolong close contact of the reagent forming materials in the reaction zone suiiiciently for the mass of material tobe forced to temperatures (1) above which the reducing reaction takes place to convert some of the-metal oxide tometal, and (2) above the melting pointv cf the metal at which the solubility of the Ioxide in the metal increases to a point Where a substantial quantity of the oxide goes .into solution in the metal. To this end, another object is to (Cl. 'l5-10) vary in some easy manner the ratios or proportions of the reactive and slag forming components in the zone where the reagent is formed. Still another object is to produce a metal rening oxidizing reagent which can be sold as such and for other purposes. A still further object is to correct the bath so that when the oxidizing reagent is added to the bath, the reagent will selectively oxidize the carbon or other oxidiaable im purity in the bath with substantially no net concurrent oxidation of desirable metal present, such as chromium.

` The manner in which this invention may be essentially practiced comprises carrying it out lin an electric furnace having a hearth and a hollow electrode or electrodes adapted to have charges or burdens of comminuted reagent forming material, preferably formed into briquettes or cores, forced through the electrode toward the arc end thereof. In the hollow electrode a reducingreaction is caused to take place under controlled conditions for forming a highly concentrated reagent having as its essential components a reduced metal and a metal-oxide uniformly dispersed or dissolved therein. On the furnace hearth there is charged the metallic material 'or metal alloy to berened where it is melted into a. moltenmass or bath whose essential components are a slag and a metal containing one or more oxidizable impurities (such as carbon sulphur, silicon, phosphorous, or manganese, or possible combinations thereof) desired to be removed from the metallic material of the molten bath. The reagent which is in liquid form and is hotter than the molten bath drops repetitively to the bath where the miscibility of the liquid reagent and the molten bath permits a rapid and extensive dispersion of the reagent throughout the bath. This dispersion results in the oxide of the reagent being reduced by the carbon or other oxidizable impurity in solution in the bath of metal or alloy to be rei-ined. The reduction of the oxide' frees the metal of the oxide 'to be added as increments thereof as metal to the molten alloy and the oxidation of the voxidizable impurities converts them into a gas, for instance carbon into carbon monoxide, and oxides such as SiOz, MnO, etc., which may enter the slag. This carbon monoxide gas and the carbon monoxide from the hollow electrode, and an intensely oxidizing reaction is taking place in the bath on the hearth, and both of these zones are in one furnace, they are independently situated and each is out of the range of influence of the other. Correctives may be supplied to and used in the bath on the hearth for changing its reactive characteristics or for assuring the permeability of the slag to the reagent discharging into the bath from the arc end of the electrode. The refined metal or reconstituted alloy is recovered by separating it from its slag in the usual manner. Alloys are readily made by this pr-ocess because the oxides of different metals can be fed to the electrode, or various metals can be melted on the hearth.

The formation of the reagent comprising metallic oxide uniformly dispersed in metalis effected. by rst having present in the charge forced through the hollow electrode a quantity of carbon or other reducing agent, so that only a portion of the metal oxide present is reduced to metal: second, confining or detaining the molten metal with its unreduced oxide in the electrode until the charge has been super-heated or heated to a temperature enough higher than the melting point of the metal so that the operator can be assured that a quantity of oxide present has been disseminated into the metal or has gone into solution in the metal: third, controlling the mobility or flowability of the coacting charge in the electrode so that the more fluid coactive material thereof as it becomes molten does not ow away from the unmelted material with which it is desired to have the melted material coact, or to discharge from the electrode until the desired disseminating or saturation of the reduced metal with the oxides takes place. This control is effected by feeding to the electrode'along with the other starting materials certain substances called herein correctives. Various correctives can be used for this purpose and they may be used either to retard the mobility of the reacting mass Within the electrode, or to accelerate it, as the casemay be. In the embodiment of the invention shown and described herein, the oxidizing reagent is used for refining a bath of metal on the hearth of the same electric furnace wherein the reagent is formed, but it is possible to form the liquid reagent in one furnace, solidify it by cooling (preferably rapidly) and then use it for refining metal in another furnace by supplying the reagent to the molten bath of metal to be refined.

The invention possesses other objects and features of advantage, some of whichI with the foregoing will be set forth in the following description. In the accompanying drawings there has been illustrated the best embodiment of the invention known at present, but such embodiment is to be regarded as typical only of many possible embodiments, and the invention is not to be limited thereto. In the drawings, Figure 1 shows diagrammatically how the invention may be carried out essentially. Fig. 2 is a vertical sectional view of a more preferred form of furnace for carrying out this invention. Fig. 3 shows a vertical sectional View taken along the line 3-3 in Fig. 2.

Eig. 1 is self-explanatory and is intended to make visually identifiable the various features described herein. In the arrangement shown more completely in Figs. 2 and 3, I I) represents the furnace, having a top II, side walls I2 and a hearth' I 3`made of suitable refractory material, the nature of which will vary according to the use to which it is desired to put the furnace. The furnace is desirably heated by means of electrical on the hearth I3 of the furnace.

energy and to this end there is provided an electrode or electrodes I4 which project through the side Walls of the furnace in a substantially horizontal position, although the position of the electrodes may be changed. The electrodes are desirably formed with an axial passage or bore therethrough so that the electrode is hollow and thereby is adapted to receive and permit passage therethrough at a predetermined rate of charges or cores or cartridges C of predetermined composition; under predetermined heat conditions; and surrounded by an atmosphere of predetermined nature.

The arc section of the hollow interior or bore I5 of the electrode forms a reaction chamber or reagent forming zone as the electrode itself constitutes an electric furnace since the arc can be used to heat the arc section of the electrode to reaction temperatures. The reagent-forming raw material is preferably in molded form such as cores C and these cores are fed to the electrode individually. For automatically feeding these cores to the electrode, one after another there is in existence an apparatus which carries out that function. Pairs of abutting electrodes are preferably used which may be of any desired composition such as graphite, carbon, or other suitable refractory material, for thus eflicaciously providing the heating and reduction chamber or zone wherein the reagent of this invention is formed. A molten oxidizing material constituting the reagent I'I dropping from the electrode is collected I6 indicates the molten bath of metallic material or alloy to be refined or reconstituted which is on the hearth I3 and this constitutes the refining zone of this invention. 4This bath is made up of metal or metallic material -I8 having oxidizable impurities such as carbon therein, and slag I9. 20 indicates the furnace tap-hole, 2I indicates a draw-olf or flue which may be used, if necessary, for conducting gases from the furnace, although it is normal to maintain a super-pressure in the furnace.

The components of one or a group of cores C forcibly supplied to the electrode I comprise the reagent-forming materials including reactable reagents, correctives, and a binder for holding the components in core form. The reactable reagents include oxides of one or more metals (which may be in the form of ore containing gangue material) and a reducing agent composed of one or more such reagents as carbon, carbonaceous material, silicon, silicon-carbide or the like, the correctives are hereinafter described in detail.

As the charge is forced through the electrode and the heated zone thereof is encountered, the materials ofthe charge while confined therein and exposed to a suflciently high temperature undergo two changes, namely, a chemical reaction takes place between that predetermined amount of reducing agent present and as much of the oxide present as finds its chemical requirement in the reducing agent. That is, it is arranged in advance so that there will be only enough reduclng agent present to reduce a portion of the oxide to metal, leaving a quantity of the oxide unreduced. The reaction products are reduced metal and an oxide. Also aphysical change occurs,'

namely, the chemically formed metal fuses or melts and subsequently as increased temperatures are encountered lying above the melting point. of the reduced metal the metal becomes an active solvent in which the unreducedv oxide dissolves. After reaction between the reducing agent and the oxide has occurred, increments of metal are formed or released from the oxide and larger amounts of both oxide and reducing agent will dissolve. So with this in mind, the oxides selected for the' reagent forming material fed to the electrode are chosen by considering whether or not these increments of metal released from the oxide to the bath are to be of the same metal or metals of the bath or different ones. Oxides usable for this purpose either alone or in combination are those oxides which are reducible by carbon such as manganese oxide, chromium oxide, iron oxide, silicon oxide and thelike.

As the charge is in an open-ended electrod that part of the charge which melts rst tends to run out of the electrode, or at least to ilow away from the place of its liquefaction. To overcome this, the presence of a corrective material in the charge is eiiective when it has the property of controlling, such as either retarding or accelerating as the case may be, the rate of 4flow of the Y entire mass. If the corrective is for confining or holding in place the components of the mass having lower melting points, as the temperature of the mass is increased, there is no escape of the more uid components untilthe reducing reaction and the physical coaction or solution have been realized and the entire mass becomes fluid. Such a corrective for this purpose might be calledK an anti-ilux, and include magnesia, lime, clayaluminum-oxide, comminuted slag from previous runs, or mixtures of such slags. If thecorrective is used for accelerating the mobility of the mass, its function is to maintain the relative positions of the reduced metal and the residue from the cores until a predetermined temperature is reached, whereupon the mass, as a whole, flows from the electrode. These may be termed fluxes and may consist ofrsilica, calcium silicate,-luor spar, slags, etc.

For instance, if a unitary charge were made up of 3MnO+SiO2|6C practically no reduction would take place because the MnO.SiOz has such a low melting point that the manganese silicate would flow out from the hollow electrode at a temperature below which neither the MnO or the SiOz can be reduced with carbon. Thus, the temperature at which the mass flows may preclude the reduction of the oxide. However, if one core is fed to the reaction zone made up of 3MnO+4Cf- Mn3C-l-3CO, and then if another core is fed to vthe reaction zone made up of SiO2-|-2C Si+2CO, the reduction takes place as indicated because the temperature at which the mass ilows is high enough to induce reduction of the metal oxide with the carbon. Or, conversely, where highly, infusible material is present in the reaction zone, a flux can be added which by lowering the melting point of the refractory material will tend to permit the mass to iiow instead of permitting selective Vflowing of the diierent materials. f

This tendency of some materials to melt and iiow prematurely can be anticipated by analyzing the ingredients of 'the charge and referring to melting points of its various components and their combinations as given in the International Critical Tables. From these tables it can be determined readily what ingredient to add and what quantity thereof is necessary to control to the desired figure the melting or rather the flow point of the mass as a whole.

The melting of the reduced metal is insuflicient to cause the metal oxide to dissolve therein. The temperature of the molten metal must be raised above its melting point to increase the solubility function or characteristics thereof to a point where the metal oxide is soluble therein, which is done by the use of a corrective which controls the point at which the mass in the electrode becomes uid and thus detains the molten metal in the heated zone of the electrode until its vtemperature is raised high enough to permit the metal oxide to dissolve therein, whereupon the liquid mass escapes or flows from the electrode.

The melting point of the metal to be formed in the electrode is known. It is known that at this temperature, the solvent action of the metal for the oxide is substantially zero. Therefore, depending upon the rate and/or temperature at .which the desired reduction and dissolution is to thereof 'to metal. The optimum temperature depends upon the melting point of the metal or alloy being reduced from the metal oxide material and the rate at which dissolution of the oxide in the metal is desired to take place.

It is dicult to state definite temperatures in view of the many variables. It is a case of trial and error because it is impossible to know precisely what temperature is being attained in the electrode, the test being whether or not thelmass g flowing from or released from coniinement in the electrode contains metal and is in liquid condition, for reduction `of the metal must take place. lf solid material comes from the electrode, it shows that the cores are being forced through the electrode and its heated zone too rapidly so the rate of feed of the cores is varied until liquid only drops or discharges from the electrode'. ln general, the optimum temperature is approximatelyV not less than 3200 F.l and may go to 3600 F. or even above.

The solubility of the metal oxide in the reduced metal solvent varies at different temperaturcs. So the extent of solubility is the function of the difference between the melting point of the metal and the temperature at which the metal acts as or exhibits characteristics of a solvent. Usually a temperature of from 400 to 600 F. above the melting point of the reduced metal, or alloy of metals, is required to have they metal function satisfactorily as a solvent for the metal- That is, it is desirable to use a constant linear speed of the charge through the electrode. Also it becomes necessary 'to pass a constant weight of starting materials per minute through the electrode. Yet as the cores used contain various components having different specic gravitie's, it becomes desirable to changeur lessen the weight of cores whose 'principal component is heavy with reactive materials through the hollow electrode.

' or refiners.

some leaven which while lightening the specific gravity of thecore will have no harmful effect in the reagent forming zone. Any method of increasing porosity or of decreasing apparent gravity may be used. A simple method is to use sawdust as a source of carbon for the reduction reaction as this also lessens the specific gravity of the charge.

So from the reaction or reagent forming zone of the electrode, there is obtained a highly concentrated reagent formed under conditions favorable to dissolving substantial amounts of metal oxides therein, which reagent comprises a metaloxide or mixtures of metal oxides in solution in a reduced metal or in a mixture of reduced metals in liquid form, and this reagent is prepared exteriorly of the bath I8. It comprises an oxidizing reagent formed while actually reducing metal and when solidified may be sold as an article of commerce to such users thereof as alloy makers This reagent I'I is then ready to be used in the refining operation in the refining zone I3. In the refining zone, or hearth I3, there has been previously charged the metal or alloyed metal to Abe refined, and melted into a bath I6, which bath consists essentially of the metal or metallic material to be refined and an oxidizable impurity such as carbon, or impurities which are to be removed from the metal. This involves the physical action of melting the metal to a point where its impurity or undesirable constituent such as carbon goes into liquefaction or solution therein. As can be seen from Fig. 1, the reagent drops a little at a time but continuously from the electrode into this bath. Each drop is believed to comprise a globule of metal surrounded by slag. The reagent and the bath of metal to be refined being liquid and miscible permit a rapid and extensive dispersion of the reagent in the bath which results in a molten mixture of metal-oxide, metal, and carbon. Upon this mixing, a chemical reaction takes place between the carbon of the bath and the oxide of the reagent by virtue of which there is formed carbon monoxide and additional metal. As the electrodes become very hot in the forming therein of the active reagent and the produced reagent is at a very high temperature (usually from 400 F. to 600 F. above the temperature of the molten metal of the bath), a violent reaction occurs when the reagent enters the molten bath causing terrific turbulence when the carbon monoxide is liberated by the reaction. This turbulence increases the surface contact between the reacting materials. With low carbons, almost all of the carbon reduction can be accounted for through a reaction with the reagent emanating from the electrodes. Thus there is effected in the refining zone an intensely oxidizing action. This refining action results in the rearranging or reconstituting of the metal or a metal alloy of the bath to decrease the carbon content thereof. The slag coming into the rening zone with the reagent from the electrode and any slag I9 rising from the bath I6 floats and the resulting refined metal I8 can be readily separated therefrom by known means. l

The significance of this refining step may be explained by showing that for the molten bath of alloy to be refined on the hearth by treatment with the reagent from the electrode, there can be used scrap or waste metal having an excess of an impurity or undesirable element therein which is oxidizable such as carbon and the like, because the refining reagent having some reducible material therein, in being mingled in liquid phase with the bath having an oxidizable element produces a reaction that oxidizes the undesirable element or impurity which in its combined form with oxygen escapes from the metal mixture. If the thus produced oxide is not a gas but of the type of S102, P205 and MnO, it may become a component of the slag. If it is a gas of the type of CO, it becomes a part of the atmosphere of the furnace. Such gas, together with the gas generated in the electrode causes a super-atmospheric pressure of substantially pure carbon monoxide in the furnace, and this pressure causes gas leaving the furnace to permeate through the electrode burden and out from the hollow electrode in a direction opposite to that of the core feed. There is substantially no nitrogen and carbon-dioxide in the atmosphere in the furnace. So, by using the control taught by this invention, there can be effected a decrease in the metallic material or alloy being refined of undesirable constituents such as manganese, silicon or carbon by the use of chromic oxide (CrzOa) in the reagent and of such constituents as chromium, manganese, silicon or carbon by the use of iron oxide (FeO) in the reagent. Carbon can be decreased in quantity in alloys of iron and manganese by a reagent comvposed of an iron-manganese alloy having manganese-oxide in solution therein.

In a furnace embodying this invention, electrodes were used that were 8" in diametei' which had a bore of 3%. The cores used were from 25/8 to 3" in diameter and either 81/2" or 17 long. The cores were fed through the electrode, depending upon the furnace temperature and the material of the cores, at speeds ranging from 2 to 8 per minute. The 81/2" cores weighed from 3 to 41/2 pounds depending upon the material from which they are made. The reagent forming zone in this furnace was found to be in the electrodes within ten inches from the arc end thereof.

The oxidizing reagent of this invention may be made in one furnace and used elsewhere in a refining furnace. In such an event, the reagent must obviously be cooled to solidication so it can be transported from the place of its formation to the place of its use so this invention contemplates such a solidied electric furnace product as an article of commerce. If the reagent of this invention is solidified, it is found to comprise essentially a metal having uniformly dispersed therein crystals of an oxide of one of the alloyed metals. If a quantity of this reagent is chilled or cooled quickly, the crystals of chromium oxide are found to be needle-like and disposed in the metal in parallel formation or each oriented in the same direction. If however the reagent is cooled slowly the crystals are found to be of varying concentration or non-uniformly distributed in the metal.

As can be seen from Figs. 1 and 2, the reagent formed in the reaction zone drips or drops into the bath, but in order to get into the bath, the drops of reagent I'I must pass through or penetrate the floating oxidizing slag I9. To that end this slag must be maintained in a condition to permit such penetration, for otherwise the slag may be too thick or too rigid or viscous for the free flow of the drops therethrough. Retardation of the Contact;l or mixing of the reagent drops with the metal of the bath tends to produce a harmful change of temperature and of the constitution of the reagent. That is, this delay in its travel from the electrode outlet to the metal bath may cause a change in the equilibrium in the amantes reagent and a disturbance in the value of the meetc.

. tion of the refined metal. For instance in makiducing atmosphere in the furnaces.

tallic components thereof.

Another requirement of the slag is that it shall contain an oxide to insure against the harmful stripping or removal of the metal oxide from the reagent as it passes through the slag. Accordingly, cores containing correctives for the slag of thel bath to correct the physical constants and chemical properties thereof may be either fed through the electrode or added directly to the bath on the furnace hearth. Such correctives include cores either in whole or in part of lime, magnesia, burned dolomite, silica, magnesium silicates, calcium silicates, sodium silicate, uorspar, feldspar, salts, slags from previous runs, and any mixtures of these correctives, one essential compound being an oxide of a metal, such as iron, manganese or chromium, since it is necessary to have an oxide of a metal for oxidizing the carbon. y

In connection with the use of these correctives, it is pointed out that the reaction in the reagent forming zone may require a basic slagwhile the refining reaction may require an acid slag or vice versa. Therefore, it is possible that one core used for furnishing ferro-chrome to the bath may furnish it with an acid slagwhile an alternate core may keep alkaline the slag on the bath. For instance, in order to get Ia good yield of ferrochrome from the ore, it is necessary to add sufcient silica to certan ores to increase the mobility of the mixture in the electrode to release the chrome from the chromite. The bath itself requires a slag rich in lime under certain conditions. So, cores composed entirely of lime would be used in some definite ratio with-the cores containing chrome ore and silica.

In practical operation, the furnace is rst preheated e. g. with oil to bring it to a temperature of about 2000 to -2500 F. The electrodes are then inserted and the furnace heated up to operating temperatures. Cores r of the starting materials .such as chromite (chromium oxide) and carbony are started through the electrodes to insure a 'I'his prents the oxidation of any of the values in the charge., So, as soon as CO is generated in the furnace, the metal charge of colds'crap, or other metallic material to be reiined, is then added to the furnace hearth. This scrap may be in the form of discarded ingots which failed to meet customers specications, or in the form of refuse such as strip trimmings, punchings, turnings, The temperature of the furnace and its electrodes is regulated by current input. The rate of core feed is regulated so that the desired reducing and dissolving actions take place. in the electrode whereby no non-fiuid material issues therefrom, andr cores continue to be fed until the scrap is entirely melted. l

Samples of the slag and molten metal are taken from the bath on the hearth at stated intervals, such as every 15 minutes to determine the condiinga chrome alloy if the chrome content thereof is below the desired gure, chrome ore cores are fed until the carbon content of the metal from the hearth is reduced to the desired point and the chrome has been raised to the desired point.

If the carbon has not been reduced sufficiently when the chrome is up to the maximum limit are iron oxide cores with theoretical amounts of reducing agent such asv carbon. The feeding of these iron oxide containing' cores lcontinues until the carbon content Vof the molten bath has reachedthe specified minimum. Alsothe slag is examined regularly to determine what correctives may be necessary to keep it inthe desired condition. reachedthe desired analysis, it is tapped into a ladle and is allowed to cool until it has reached a pouring temperature. It is then pouredv into molds either for ingots or for other purposes.

After the material has been cast, the electrodes are partially withdrawn from the furnace and a new charge of scrap is added; the electrodes again put in place and the current turned on and the above described steps are repeated.

For making chrome alloys it should be considered that chrome ore is composed of two components. The primary component is the mineral chromite which comprises approximately to of the ore and has the following formulaz- (Fem-lungo)xnizoaaicrzons.

In this component the molecular sum of the bases (A+B) is always equal tothe molecular sum of the acids (C-l-D)., A portion of this component can be reduced at a definite temperature by such reducing agents as carbon or silicon.

The second component of the chrome ore; (usually termed the gangue) comprises approximately 20% to 10% of the ore and consists of (MgO)x(SiO2)Y. The proportions of magnesium oxide and silicon dioxide vary between the formulas (MgO)2(SiOz 3 and (MgO)3(SiO2)2. This second component xis notreduced by reducing agents .such as carbon or silicon under usual conditions.

When the rst component is partially reduced to metal by the process of thisinvention, the

After the metal of theI bath has iron oxide of the base and the chromium oxide nate, has a particularly high melting point, and, therefore, does not ow readily in the furnace.` f

The magnesium-aluminum silicate, however, has ya melting point of 2600 F. and by itself makes a good slag. If it is desirable to correct the meltingv point of this residual material Afrom the chrome ore the addition of silica will gradually decrease the melting point to the desired degree. y

If, however, the melting point is not suciently high for the reaction and equilibrium which is required in the reagent in the hollow electrode,

it is then possible to add tothe electrode as correctives either magnesium oxide or calcium oxide to increase the refractoriness or melting.

point of this'residual material. Upon the addition of magnesia or lime the residual material,-

after the reduction of the iron oxide and chromium to metal, will have a melting point in accordance with predetermined calculations.

At least a part of the carbon in the metal is removed by the reagent formed in the electrode. Probably the percentage of carbon removed by the slag to the percentage removed by the reagent varies inversely with the percentage of carbon in the metallic bath on the furnace hearth. In other words, when the carbon in the metallic bath is relatively high, there is an appreciable reaction between the oxides in the slag and the carbon in the metal. This reaction is -a function of the surface contact between the slag and the metal. This surface contact is increased to a great extent by the turbulence caused when the dissolved metal-oxides in the reagent drop into the metallic bath and through reaction with the carbon therein, evolve CO. With low carbons almost all of the carbon decrease can be accounted for through a reaction between the carbon and the reagent emanating from the electrodes.

In considering the reactions between oxides and metals in the bath, it must be borne in mind that the order of the reactions between the oxides and the metals varies with the temperature. Silicon and manganese are more easily removed by oxidation than carbon when the temperature of the alloy is slightly above the melting point. At higher temperatures, it is more difficult to remove silicon and manganese than carbon. At low temperatures FeO will oxidize metallic chromium from the metal, converting it into CrzOa which goes into the slag without materially changing the carbon content of the bath. At higher temperatures, the ratio of chromium to carbon removed by FeO favors the carbon removal.

The recovery of materials which cannot be comminuted economically such as stainless steels of varying composition can be effected by melting the materials on the hearth of the furnace and correcting this waste material to a predetermined specication as to desirable constituents suchV as chromium and nickel, and undesirable constituents suchas carbon by feeding the cores of proper material through the electrode.

Example I.--To make low carbon ferro-manganese three methods may be usedz-l. The low carbon ferro-manganese can be produced by feeding as reagent-forming materials to the electrode cores containing manganese ore, carbon and the proper corrective. The initial material formed in the refining zone will contain carbon in appreciable quantities but as the refining action progresses andthe metal bath increases in mass due to increments thereto of metal released from the reagent as the oxide thereof is reduced to metal by oxidation of the carbon of the bath, the carbon content of the bath will obviously decrease to an exceedingly loW point. This method requires considerable time-2. In

a furnace of the type described a charge of high l carbon ferro-manganese is charged through the door into the hot furnace. Before the metal is charged cores have been fed through the electrodes until the furnace atmosphere is composed of carbon monoxide. This prevents the oxidation of the manganese. If a high manganese product is desired then cores composed of manganese ore, carbon and corrective material such as lime or magnesiaare supplied to the electrode until the resulting reagent from the electrode causes the carbon of the bath toi be decreased to the desired point- 3. Slags rich in manganese or manganese ore may be melted in the hearth or refining zone of the furnace. Cores composed of SiOz with a theoretical amount of carbon are fed to the electrode to form a re. agent containing silicon metal. The silicon of the reagent reduces the manganese in the slag of the bath on the hearth to a metallic manganese. A metal substantially free from silicon carbon may be obtained if this reaction is stopped at the point Where all the manganese is reduced from the slag but no increments of silicon from the reagent have been added to the metal. If Silico-manganese is to be made the silica-carbon cores are fed to the electrode until the desired percentage of silicon is obtained in the molten metallon the hearth.

Eample II.-Stainless steels- 1000 lbs. of stainless steel are charged into the heated hearth of the furnace. Power is admitted through the hollow electrode until the charge partially melts. Cores made from chrome ore and the theoretical amount of carbon calculated to bring about a partial reduction of the metallic oxides are fed through the electrodes at the rate of 21/2" per minute until sufficient reagent from the electrodes has caused the chromium content of the bath to reach a predetermined percentage. At this point the carbon is probably reduced to the predetermined p ercentage. If a furnace sample taken from the bath shows that the carbon is not sufciently reduced, but that the chromium is high enough,iron oxide cores Which have the theoretical amount of carbon are supplied to the electrode at the proper rate until the resulting reagent has caused the carbon to be reduced to the predetermined gure.

In this example it is sometimes necessary, depending upon the composition of the chromium cre from which the cores are made, to add enough silica to the core mixture so that the melting point of the residual gangue in the electrode will be about 3200 F. This can be accomplished by consulting any of the standard melting. point curves found in the Critical Tables. This melting point is not the proper melting point for the slag floating on the metal in the bath and for that reason cores containing silica (SiOz) can be fed 'to the electrode alternately with the chrome ore cores at a set ratio, whereby the melting point of the slag on the bath can be corrected to a predetermined figure, in this case 2850 F. to 2900 F. Although this silica may be added through the door of the furnace, it is preferable to add it through the hollow electrode so that a` permeable slag condition will be maintained on thesurface of the metal.

Example IIL-Another example for the preparation of stainless steel is to use 1000 lbs. of steel scrap, preferably with low phosphorus content, without paying any attention to inclusions of oxides, sulphur or silicon content, and melting the scrap on the hearth of the furnace. Cores containing chrome ore and the theoretical percentage of carbon for the reduction of the metallic oxides are fed to the electrodes for caus- 'Eng the oxidizing reagent to drop onto the hearth and into the melted steel scrap until the chrome Example I V.-For the manufacture of so-called carbon-free iron, it has been found successful to melt low phosphorus scrap on the hearth of the furnace. Then to treat the molten scrap with a reagent formed by supplying to the electrode vcores consisting of Very low phosphorus iron ore 'with careful control of other impurities in accordance with the specifications of the finished product, and insulcient 'carbon to reduce all of the metallic oxide contained in the ore fed to the electhe treatment with a novel oxidizing reagent of intermediate metallurgical' trode. The cores are added to the electrode until the reagent therefrom oxidizes the carbon of the molten scrap until the carbon content has reached the predetermined allowable percentage. Carbon free iron can also be made by supplying such cores to the electrode and omitting from the hearth any starting scrap as the reagent itself from the electrode will form the refined metal on the hearth.

Specifically then, this invention is directed to highly concentrated products, such as pig iron, ferro-silicon, cast iron, high-carbon ferrochrome, high-carbon ferromanganese, silicon manganese, silicon chromium, and any metallurgical products containing a percentage of either alone or in combination of carbon, silicon, sulfur phosphorus, and the like oxidizable impurities or undesirable constituents. In this invention the advantages of the undesired presence'of these reducing agents in the intermediate metallurgical products is utilized for the reduction of the oxide of the novel reagent by which `the metallic alloy is substantially rid of its impurities.

This patent issues from a patent application which constituted a continuation in part of patent application Ser. No. 724,024, led May 5, 1934 which in turn was a continuation in part of patent application Ser. No. 597,399 led March 7, 1932.

I claim:

1. The process of forming an oxidizing reagent for use in the rening of metallic material which comprises supplying to a heated zone in a substantially horizontal hollow electrode a comminuted mixture formed into cores containing essentially a metallic-oxide and a reducing agent insufficient in quantity for reducing all of the oxide, heating the mixture in the electrode to a temperature above that at which reduction of the oxide takes place and above the melting point of the reduced metal,l confining the mixture in the electrode during said heating, and effecting release thereof from the electrode in liquid condition as the desired reagent.

2. The process according to claim l in which the conning and release is effected and controlled by a mobility thereof when heated in the electrode.

3. The procees according to claim l in which the conning and release is controlled by a corrective substance added to the mixture for retarding the normal flowability of the lower melting point constituents of the mixture when heated in the electrode.

4. The process according to claim 1 in which the conning and release is controlled by a corrective substance added to the mixture for raising the otherwise normal melting point of the mixture when heated in the electrode.

5. The process according to claim l in which cores of the mixture are fed repetitively to the electrode, and there drops repetitively from the electrode in liquid condition a quantity of metal and u nreduced oxide.

6. The process according to claim 1 in which the reagent-forming mixture in the electrode is heated to a temperature substantially from 400 F. to 600 F. above the melting point of the metal reduced in the electrode.

GILBERT E. SEIL.

substance in the mixture for modifying the

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