US2094969A - Reagent for metal alloys - Google Patents

Description

@ct 5, 1937. GE. sElLv REAGENT FOR METAL ALLOYS 2 sheets-sheet 1 Filed Jan. 18, 1936 WMZPQMEKOO Stivenfor GILBERT E. SEIL Patented @et 5, i537 i attinto assomme ron Marsi. more A Gilbert lE. Seil, Cynwyd, Pa., assignor, by mesne assignments, to Buffalo Electric Furnace .Corporation, Bualo, N. Y., a corporation of New York Application llianuary 18, 1936, Serial No. 59,692 ln Great Britain December 13, 1935 (Cl. 'Z5-56) is to vary in some easy manner the ratios or proportions of the reactive and slag forming coml Claim.

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 inY Which such processes 0 can be carried out.

The general object of this invention is to rene metallic material and/or metal alloys especially those containing a desirable constituent such as chromium, in a simple and readily controlled manner by which there is 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 conditions as nearly ideal therefor as possible both as to speed of reaction and eiciency thereof, namely with the reactive materials in miscible solution and' thoroughly mingled. A further object is to carry out this reacting of materials in solution in the presence of a carbon monoxide super-atmospheric pressure to assure absence of air.

And a further very important object of the in.

vention is to form ina heated reaction zone and exteriorly of the bath of metallic material to be refined, a highly concentrated oxidizing reagentponents in the 4zone Where the reagent is formed. Still another object is to produce a metal refining 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 isv added to the bath, the reagent will selectively oxidize the carbon or other oxidizable impurity 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 in an electric furnace having a hearth and a hollow is a metal-oxide, an object is to effect rst the ref duction of a quantity of the metal oxide (which may be in the form of ore) into metal, and second the dissolution in the thus formed metal as a solt vent, of a quantity f the oxide present. Another object is to contact globules of the metal solvent with the oxide solute whereby there is exposed to the oxide surrounding the metal globules, ab-

' normally large Vsurfaces per unit of weight, for

thus facilitating the dissolving of the oxide in the' And a further object of this invention metal.

to retain or confine and prolong close contact of 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 reducing reaction 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 furnacehearth there is charged the metallic material or metal alloy to be refined Where it is melted into a molten mass or bath Whose essential components are a slag, and a metal containing one or more oxidizable impurities (such as carbon sulphur, silicon, phosphorus, or manganese, or possible combinations thereof) desired to be removed from themetallic-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 refined. The .reduction of the oin'de frees the metal of the oxide to be added as increments thereof as metal to the molten alloy and the oxidation of the oxidiz- This carbon monoxide gas and the carbonmonmetal oxide to metal, and (2)- above the melting pointof the metal at which the solubility of the cxide.- in Vthe metal increases to a point where a substantial quantity of the oxide goes into solution in the metal. To this end, another object oxide from the hollow electrode are evolved 'to such an extent that a-super-atmospheric pressure is attained in the furnace for keeping out of the furnace any air. 'I'hese steps or reactions can be carried oncontinuously or repetitively foreven though an intensely reducing reaction is taking place in the electrode, and an intensely' oxidizing W l 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 reagentdischarging 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 process 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 metal is effected by first 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 orowability of the coacting charge in the electrode so that the more fluid coactive material thereof as it becomes molten does not flow 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. 'Ihis 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 massy within the electrode, or to accelerate it, as the case may be. In the embodiment of the invention shownl and described herein, the oxidizing reagent is used for rening 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 vthe molten bath of metal to be refined.l

The invention possesses other objects and features of advantage, some of which with the foregoing will be set forth in the following description. In the accompanying drawings .there has been illustrated the bestembodiment 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 inventionmay be carried out essentially. Fig. 2 is a vertical sectional view of a more preferred form offurnace for carrying out this invention. Fig. 3 shows a vertical .sectional View taken along the line 3-3 in Fig. 2.

.energy and to this end there is provided an ele@- vI5 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 abuttingelectrodes are preferably used which may be of any desired composition such as graphite, carbon, orother suitable refractory material, for thus eicaciously providing the heating and reduction chamber or zone wherein the reagent of this invention is formed. Aniolten oxidizing material constituting the reagent I'Ivdro'pping from. the electrode is collected on the hearth I3 of the furnace. 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. This 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 drawoif or flue which may be used, if necessary, for

v conducting gases from the furnace, although it is normal to maintain a super-pressure in the furnace. l The components of one or a group of cores C forcibly supplied to the electrode I4 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 of the charge while confined therein and exposed to a sufficiently 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 arcreased temperaturesare encountered lying above the melting point of the reduced metal the metal becomes an active solvent in which the unreduced oxide dissolves. Afterreaction. 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 m2:-

fterial fed to the electrode are chosen by considerv Vchromium oxide, iron oxide, silicon oxide and the like. l

As the charge is in an open-ended electrode, that part of the charge which melts irst tends to run out of the electrode, or at least to iiow away from the place of its liquefaction. To over-v come this, the presence of a corrective material in the charge is effective when it has the property of controlling, such as either retarding or accelerating as the case may be, .the rate of flow of the entire mass. If the corrective is for conning 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 until the 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 called an anti-ux, and include magnesia, lime, clay, aluminum-oxide, comminuted slagfrom previous runs, or mixtures o'f such slags. If the corrective 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, ows from the electrode. These may be termed fluxes and may consist of silica, calcium silicate, uorspan slags, etc.

. For instance, if a. unitary charge were made up of 3MnO-l-SiOz-i-6C practically no reduction would take-place because the MnOLSiOz has such a low melting point that the manganese silicate would ow out fromthe hollow electrode at a temperature below which neither the MnO or the S102 can be reduced with carbon. Thus, the temperature at which themass ows may preclude the reduction of the oxide, However, if one core is fed to the reaction zone made up of 3MnO+4C Mn3C|3CO, and then if another core is .fed to the reaction zone made up f SiOz-l- 2C Si+2CO, the reduction takes place as indicated because the temperature at which the mass ows 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 ux can be added which by lowering the melting point of the refractory material will tend to permit the mass to iiow instead of 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 thev desired figure the melting or rather the iiow (point of the mass as a whole.

The melting of the reduced metal is insufcient to cause the metal'oxide to dissolve therein. The

temperature of the molten metal must be raised solvent.

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 temperature 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 tor the oxide is substantially zero. Therefore, depending upon the rate and/or temperature at which the desired reduction and dissolution is to take place, is determined what corrective materials are to be used and fed to the. electrodedn the cores of starting material. Theminimum temperature to which the mass in. the electrode must be raised is above that at which carbon or other reducing agent reacts with the other Y I 3 I reactiver materials such as the oxides to reduce electrode contains metal and is in liquid condition, for reduction of the metal must take place. If 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. 1n general, the optimum temperature is approximately not less than '3200 F. and may go to 3600 F. or even above.

The solubility of the metal oxide in the reduced metal solvent varies at diierent temperatures. So the extent of solubility isthe function ofthe difference between the melting point of l the metal and the temperature at which the metal acts as or exhibits characteristics of a Usually a temperature of from to 600 F. above the melting point of the reduced metal, or alloy of metals, is required to have the metal function satisfactorily as a solvent for the metal-oxide present in the electro-de or reagent zone. The fact that this temperature is usually well below'the melting point of the metal-oxide vis an indication that the oxide does go into solution rather than into suspension, although the uniform dispersion and the formation of the needle-like crystals in the chilled or quickly cooled reagent mak it quite clear that solution has taken place, as was determined in the case of chromium' alloys and chromium oxide.

Anotherphase yof operation .that is to be controlled is the uniform speed of passage of the reactive materials through the hollow electrode.

That is, it isdesirable to use a constant linear speed of the charge through the electrode.. Also it becomes necessary to pass a constant weight of starting materials iper-minute through the electrode. Yet as the cores used 'contain various components having different specific gravitieait becomes desirable to changefor lessen the weight of cores whose principal component is heavy with some leaven which while lightening the specific gravity of the core will have noy harmful eiect in the reagent forming zone. Any method of increasing porosity or of decreasing apparent gravity may be used. A simple method is to use saw-dust as a source of carbon for the reduction reaction as this also lessens the specific gravity of the charge.

Sor 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 loxides in solution in a reduced metal or in a mixture of reduced metals in liquid form, and this reagent is prepared exteriorly of the bathv it. vt comprises an oxidizing reagent formed while actually reducing metal and when solidified may be sold as an article of commerce to such 'users'thereof vas alloy makers or refiners. This reagent il! is then ready to bel 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 be refined, and melted into a bath i6, which bath consists vessentially of the. metal or metallic material to be refined and an oxidizable impurity such as carbon, or impurities which ar'eto bev removed'from vthe metal.

This involves the physical action of melting the i metal to' a point where its impurity or undesirable constituent vsuch as carbon goes into liquefaction or solution therein. As can be seen from Fig. l, 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 toy be rened being liquid an-d miscible permit a rapid and extensive dispersion of the reagent in the bath which results in a molten mixture of metal-oxide, metal, and carbop. 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 hightemperature (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 lis 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 refining 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. Y

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 metalmixture. 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. Ifit is a gas of the type of CO, it becomes a partmf 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 isl substantially no nitrogen and carbon-dioxide in the atmosphere in the furnace. So, by using the control taught by this invention, there can beeffected a rdecrease 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, man.- ganese, silicon or carbon by the use of iron oxide (F'eO)v in thereagent. Carbon can be decreased in quantity in alloys of iron and manganese by a reagent composed of an iron-manganese alloy having manganese-oxide in solution therein.

n a furnace embodying this invention, electrodes were used that were 8" inl diameter which hada bore yof 3%.". The cores used were from 2% to 3 in diameter and either 81/2" 'or 17" long. The cores were fed through the electrode, depending upon the rfurnace temperature and the material of the cores, at speeds ranging from 2" v I ing zone in this furnace was found to be in the l 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 solidification so it can be transported vfrom the place of its formation to the place of its use so this inventioncontemplates such a solidified electric furnace product as an article of commerce. If the reagent of this invention is solidied, 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 A: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 l1 must pass through or penetrate the floating oxidizing slag I9. To that end this slag must be maintained in a condition to lis stitution 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 reagent and a disturbance in the value of the metallic components thereof. y

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 the 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 vice versa. Therefore, it is possible that one core used for furnishing ferro-chrome to the bath may furnish it with an acid slag while an alternate core may keep alkaline the slag on the bath. For instance, in order to get a good yield of ferrochrome from the ore, it is necessary to add sufcient silica to certain 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. 'I'he electrodes are then inserted and the furnace heated up to oper-ating temperatures. Cores of the starting materials such as chromite (chromium oxide) and carbon are started through the electrodes to insure a l reducing atmosphere in the furnaces. This preventsthe oxidation of any of the values in the charge. So, as soon as CO is generated in the furnace, the metal charge of .cold scrap, or other metallic material to be refined, is then added to the furnace hearth. This scrap may be in the -form of discarded ingots which failed to meet customers specifications, or in the formpof refuse such as strip trimmings, punchings, turnings, etc. f The temperature of the furnace and its electrodes fed until the carbon content of the metal from e 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 Alimit of the specications, no further chrome cores are fed to the electrode but substituted for them are iron oxide cores with theoretical amounts of reducing agent such as carbon. The feeding of these iron oxide containing cores continues until the carbon content of the molten bath has reached the specified minimum. Also the slag is examined regularly to determine what correctives may be necessary to keep it in the desired condition. After the metal of the bath has reached the desired analysis, it is tapped intoa ladle and is allowed to'cool until it has reached a pouring temperature. It is then poured 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 lturned on and the above described steps are repeated.

For making chrome alloys it should'be considered that chrome ore is composedof two components. The prim-ary component is the mineral chromite which comprises approximately 80% to 90% of the ore and has the following formula:-

(F80) A. (MgO) B. (A1203) c. (CrzOs) D 'In this component the molecular sum of the bases (A+B) is always equal to the molecular sum of the acids (C-l-D).I 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 is not reduced by reducing agents such as carbon or silicon under usual conditions.

When the first component is partially reduced to metal by the process of this invention, the iron oxide ofthe base and the chromium oxide (CraOa) of the acid of the primary component are reduced forming an alloy of metallic iron and metallic chromium while in the residual material of the primary component the magnesium oxide and aluminum oxide react and combine with the. secondary component magnesium 'silicate to form spinel and magnesium-aluminum silicate. The spinel, which consists of magnesium aluminate, has a particularly high melting point, and, therefore, does not iiow readily in the furnace. The

magnesium-aluminum silicate, however, has a melting -point of 2600 F. and by itself makes a good slag. If it is desirable to correct the melting point of this residual material from the chrome ore the\addition of .silica will gradually decrease the melting point to the desired degree. If, however, the melting point is not sufficiently high for the reaction and equilibrium which is required in the reagent in the hollow electrode, it is then possible to add to the electrode as correctives either magnesium oxide or calcium oxide. to inf crease the refractoriness or melting point of this residual material. Upon' the addition of magnesia or lime the residual material, afterthe reduction 'of the -iro'n oxide and chromium to met-a1, win

have a melting point in accordance with predetermined calculations. v

At least a part of the carbon in'the metal is removed by the reagent formed in the electrode.

Probably the percentageof carbon removed by vtion of the manganese.

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 diicult to remove silicon and manganese than carbon. At low temperatures FeO will oxidize metallic chromium from the metal, converting it into CrzOs 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 specification as to desirable constituents such as chromium and nickel, and undesirable constituents such as carbon by feeding the cores of proper material through the electrode.

Eample I.'Io make low carbon ferro-manganese three methods may be used:-1. The 10W carbon ferro-manganese can be produced by feeding as reagent-forming materials to the electrode cores containingmanganese ore, carbon and the proper corrective. The initial material formed in the rening zone will contain carbon in appreciable quantities but as the refining action progresses and the 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 carbon ferro-manganese isi 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 composedy of carbon monoxide. This `prevents the oxida- If a high manganese product is'desired then cores composed of manganese ore, carbon and corrective material such a3 lime or magnesia are supplied to the electrode Y until the resulting reagent fromthe electrode ofSiOz with-a theoretical amount of carbon are fed to the electrode to form a reagent 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 and carbon may be f agent have been added to the metal.

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 re- If silicomanganese is to be made the silicacarbon cores are fed to the electrode untilthe desired percentage of silicon is obtained in the molten metal on the hearth.

Example II.-Stainless steels.l,000 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 ofvcarbon calculated to bring about a partial reduction of the metallic oxides are fed through the electrodes at the rate of 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 percentage. If a furnacesample taken from the bath shows that the carbon is not sufficiently 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 figure.

In this example it is sometimes necessary, den pending upon the composition of the chromium ore 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 inthe 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 gure, in this case 2850 F. to 2900 F. Athough 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 the surface 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 meltying the scrap on the hearth of the furnace.

and into the melted steel scrap until the chrome I,

content of the' bath has reached thel desired proportion due to increments of chromium to the bath from the reagent and from reaction between the reagent rand the carbon of the bath. At this point, if any nickel is to be added, it may be added through the ,door of the'furnace or by cores, through the electrode. When this method for the preparation of stainless steel is followed, asubstantially carbon free product is obtained.

Example IV.-,For the manufacture of socalled carbon-free iron, it has' been found successful Ito y melt low phosphorus scrap 'onthe hearth of the furnace. 'Ihen to treat the molten scrap with a reagent formed by supplying to the electrode cores consisting of very low phosphorus in accordance with the specifications of the linished product, and insufficient carbon to reduce all of the metallic oxide contained in the ore fed to the electrode. 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 the treatment with a novel highly concentrated oxidizing reagent of intermediate metallurgical 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 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:

A reagent, useful in the reningof metallic material, such as ferrov alloys, for oxidizing oxidizable impurities therein, which comprises essentially a solid chromium containing alloy having uniformly dispersed therein uncombined chromic oxide.

' GILBERT E. SEIL.

Images