US2049091A - Manufacture of metallic alloys - Google Patents

Description

Patented July 28, 1936 STATEd TEN? MANUFACTURE OF METALLIC ALLOYS Robert Wicker-sham Stimson, New York, N. Y.

9 Claims.

This invention relates to the manufacture of metallic alloys in which any number of metals suchas cobalt copper chromium manganese molybedenum nickel titanium tungsten uranium vanadium and zirconium and metalloids may be contained in any proportions with the elementiron and is directed to production of alloys that are substantially free from sonims solid foreign substances and occluded gases.

As to the state of the art it has been proposed to produce ferruginous alloys that are low in or free from carbon and silicon by reducing ores compounds oxides or mixtures thereof of nonferrous metals (either with or without other metalliferous material) in the presence of fluxes such as lime limestone fluorspar borax and the like by means of metallic reducing agents such as aluminium magnesium and silicon or mixtures of or compounds or alloys containing aluminium silicon and the like a suitable furnace or reaction chamber being employed for the purpose. It has also been proposed to associate the reactive materials with an iron or steel bath and cause them to react in a manner whereby alloy elements are directly added to the ferrous bath.

The various proposals may be placed in two classes as regards the chemical reaction by which extraction of metal is effected, namely:--(1) those in which sufiicient heat is evolved by the reaction as to be self-sustaining once the reaction is started such as processes wherein the reactive materials are submerged in liquid steel or fed upon a reception slag which supplies heat needed to start the reaction, and (2) those in which the furnace supplies heat required to maintain and accomplish and, it may be, to start the reduction action. Or the proposals may be classified according to the location in the furnace or furnace charge at which reduction of the material .containing an alloy element takes place, namely:-(1) on the hearth of the furnace (if desired the metallic reaction product usually called ferro-alloy" may then be added to or diluted with iron or steel either in the same or any other furnace) (2) inthe body of the metal-bath (3) at the surface of contact between the metal-bath and slag (4) in the body of the slag and (5) on top of a special or reception slag.

All processes relevant to either or both of the above mentioned methods of classification are included in the ambit of the present invention which may be considered as a means of enlarging the scope of their uses to include production of alloys of the previously defined special qualities.

As regards metallic alloys of the special qualities to which the invention is directed that is to say homogeneous deoxidized desulphurized and 5 degasified alloys which may also be more or less free from any but not all of the elements silicon titanium manganese phosphorus and carbon they are generally obtainable as crucible or pot melting products; or they may be produced by melt- '10 ing-down and excessively over-oxidizing pig iron by means of ore and the oxidizing flame of a high-powered open-hearth furnace, incorporating solid ferro-alloy additions in the metal-bath and deoxidizing and degasifying the product by means of relatively large quantities of aluminium; or a sealed basic electric furnace of suitable type is used wherein is heated pure or refined iron and/or alloy steel in the presence of metallic deoxidizing agents, such as ferro-chrome and ferrosilicon, and basic fluxes with or without carbon, slow boiling the metal by addition of an oxidant, subsequently removing partof the slag formed, adding a deoxidant (carbon) and materials to form a reducing and refining slag, continuing the heating until the molten metal has attained the desired degree of purity as regards sulphur and phosphorus, adjusting the composition of the metal, and finally adding aluminium as a quieter.

The object of the invention is to provide an improved and economical process whereby metallic alloys that are substantially free from sonims solid foreign substances and occluded gases may be produced and wherein desired nonferrous metals and metalloids may be largely or wholly obtained by direct reduction of oxygencontaining materials of the kind and class that constitutes their sources such as appropriate ores metalliferous aggregates and metallic compounds also wherein an iron or a steel bath of carbon or alloy type may be employed when a ferrous solvent or diluent is required for the metallic reaction product. In this connection it may be stated that when operating processes wherein ore of an alloy element (e. g. chromite) is reduced in the presence of a ferrous bath it is difficult to produce final metal that is on the one hand sufficiently free from the reducing agent and other undesirable elements without on the other hand causing it to absorb and contain harmful quantities of gases and solid non-metallic matter such for example as compound silicates of iron and chromium whereas according to this invention both metals that are rich in alloy elements and alloys that are rich in iron may be produced 55 in a remarkably clean and sound condition while the alloy elements when desired may be largely or wholly obtained directly from ores concentrates aggregates of compounds or compounds in which they are contained.

In the specification of my co-pending application No. 756,552 filed Dec. 17, 1924 for U. S. Letters Patent is described a process for the production of alloy steels that contain more than 50% of a metal or metals of the iron group, i. e., iron nickel and cobalt, together with more than 3% of other metal or metals and metalloids the characteristic quality of the metallic products being substantially the same as that to which the present invention is directed. The process of manufacture includes reduction of material such for example as iron ore or mixtures containing a substantial quantity of iron ore in the presence of at least a basic flux by means of furnace applied heat and a silicon-iron reducing agent which also contains an alloy element-the reduction reactions occurring at or below 1600 C. The process further provides for the use of a special'ferrous diluent comprising carbon or alloy steel of characteristic composition, also for special purification of the metallic products by means of a specific calcium carbide containing deoxidizing and desulphurizing slag metallic bath additions and killing or dead-melting the final alloy steel.

It has now been found that metals having the compositionsand characteristic qualities to which the invention is directed may be produced by modifications of this process and its thermal conditions. Preferably I prepare a crude alloy for further treatment by causing chemical reactions to take place between various ingredients of an assemblage of solid reactive materials comprising any number of oxygen-containing metalliferous components of the kind and class that constitutes a source of desired non-ferrous metals and metalloids at least a basic flux and any number and kind of non-carbonaceous reducing agents, and when desired the metallic reaction product is united with steel of carbon or alloy type. Thus by using heat supplied by a tilting non-carbonaceous and preferably basic lined direct-arc electric furnace having amorphous or graphitized carbon electrodes and the means disclosed herein I may clarify and purify: (a) rich metallic alloys produced by other methods, either before or after they have been dissolved in or diluted with steel, also (b) ferruginous alloys produced with the sole use of and by smelting the reactive materials specified in my copending application No. 756,552 which alloys are clarified and purified after they have been diluted with steel of appropriate. carbon or alloy type in the same or any other furnace, dilution being effected in any manner other than by the so-called direct method, also (0) alloys produced by the direct method wherein the enriching element is provided by reduction of material that constitutes a source of the alloy element whilst-the reducible material is associated with ferrous bath in such manner that the metallic reaction product is directly added thereto. Also when using the direct method to enrich a ferrous bath a variety of reducing agents that either do or alloy with at least a basic flux for the purpose of extracting metal from oxygenous material that constitutes a source of cobalt copper chromium manganese molybdenumnickel titanium tungsten uranium vanadium or zirconium or metalloids.

My researches suggest that at least one of the carbides of, for example, chromium is not dissociated by means of an oxidizing slag at usual working temperatures but remains dissolved in the metal-bath also that preponderance of such carbides may account in a measure for occasionally observed imperfect homogeneity and areas of segregation. It is a feature of the invention therefore that metals such as chromium are not given an avoidable opportunity to unite with carbon except under conditions which at least are not known to be favorable to chemical The invention comprises two salient features either one or both of which may be necessary and used in any process of manufacturing alloys wherein an ore or compound of an alloy element is metallified or wherein metal comprising an alloy element is dissolved in or diluted with iron or steel of appropriate carbon or alloy 'type or wherein alloy metal is prepared for further treatment by admixing or uniting and heating solid or liquid metal comprising an alloy element or alloy elements with appropriate carbon or alloy steel.

It is well known that a calcium carbide containing reducing slag deoxidizes and desulphurizes a metal-bath also that it adds carbon to the bath. My experiments indicate that when treating liquid metal with calcium carbide containing slags of the particular compositions hereinafter specified the phosphorus-content of the metalbath as-well as its carbon-content is increased.

It has now been found that a calcium carbide containing slag as hereinafter defined and specified may be employed, without appreciable formation of metallic carbides, to deoxidize and desulphurize, i. e., clarify and purify,,a liquid complex metal or alloy as for example a steel bath subsequent to the addition of alloy elements such as chromium provided the slag does not contain more than 2% of carbon in the form of CaC: and preferably the metal-bath contains less carbon also phosphorus than is permissible in the final metal. In order to avoid excessive recarburation and rephosphorization the basic slag is not maintained in a reducing condition anylonger gasifying' additions such as ferro-silicon ferrotitanium and aluminium also the metal-bath may be further benefited by being killed or deadmelted, i. e., held in a fluid state under a liquid neutral or non-oxidizing basic covering until the tendency to evolve gases is diminished or exhausted and non-metallic inclusions pass into the covering and form slag.

According to the invention any type or grade of iron or steel may be used when the purpose is to enrich it with an alloy element or alloy elements. However it is desirable that the task of the reducing slag shall be as light as possible and it has been found that if steel of appropriate carbon or alloy type is prepared by melting-down solid steel in the presence of a manganese-containing oxidant-by means 'of a basic lined furnace and in the manner hereinafter illustrated 7 whereby its phosphorus-content is brought below the maximum quantity of this element allowable in the final alloy whilstthe sum of the percentages of silicon manganese and carbon contained therein exceed the sum of the minimum percentages of these elements to be present in the final metallic product a steel is produced which during enrichment or when being used to dilute ferruginous alloys that are rich in an alloy element or alloy elements does not as readily absorb and dissolve gases and other harmful elements and compounds as may otherwise be expected.

It is obvious therefore that in the production of alloys of certain types and grades use of the special calcium carbide containing slag may be dispensed with and the novel carbon or alloy steel solvent or diluent may be employed either with or without the addition of purifying and scavenging metallic bath additions and finally killing the melt; however when the object is to produce alloys of the highest quality treatment with the reducing slag is not omitted.

The preferred complete process according to the invention may comprise the following actions or steps:

((2) Either smelting the reactive materials and fluxes on the hearth of a pre-heated basic lined furnace which may contain lime and a liquefying fiux such as fluorspar borax or manganese oxide, or when desired.

(b) Preparing and associating and smelting the reactive materials and fluxes with an iron or steel bath in such manner that the metallic reaction product is added directly to the ferrous bath. In cases of this kind and when the complex metal is produced by mixing or diluting lowcarbon ferro-alloys with ferrous metal the alloy elements are preferably but not essentially dissolved in or mixed or diluted with steel of appropriate carbon or alloy type which has been prepared in the specific manner and is of the special composition herein disclosed.

(c) Thereafter replacing the non-metallic reaction product or slag which may have been de metalized in the well known way either with a covering consisting of non-oxidizing or neutral basic fluxes or with a deoxidizing-desulphurizing basic slag containing CaCz or with one of these after the otherheat being applied in either or both cases.

(d) Making solid metallic bath additions and applying heat subsequent to removing or altering the character of the slag or slags containing metallic oxides irrespective of the purposes for which they may be employed such as correcting the composition of or recarburizing or deoxidizing or degasifying the metal-bath.

(e) Maintaining the chemical character of the non-oxidizing or the deoxidizing basic slag by additions of lime carbonaceous matter fluorspar borax or silica and keeping the slag in a liquid state by applying thermal energy and adding liquefying fluxes thereto, and

(f) Removing non-metallic inclusions and diminishing the evolution of g ses or substantially completing degasification by killing the metalbath either before teeming or before tapping the melt or at both of these periods.

When a steel bath is employed to be enriched with an alloy element it may consist of openhearth carbon or alloy steel which is transferred to a basic lined electric arc furnace in which it may be enriched and further purified or using a basic lined furnace to provide the required thermal energy it may be prepared by melting-down appropriate solid materials such for example as low phosphorus and sulphur carbon or alloy steel scrap or mixtures thereof with or without pig iron or other ferrous metal preferably manganese ore or manganese ore and titanic concentrates and an abundance of lowsilica basic flux being employed during the operation. During the melting-down operation the bath temperature may be controlled by regulating the current, density and voltage within the range that effects the oxidation and. removal of phosphorus until this element is below the maximum limit allowable in the final metal whereupon the phosphorated slag is completely removed preparatory to further treatment of the metal which preferably is given in a basic lined electric arc furnace.

Another accomplishment of this practice and feature of the invention is that metallic manganese or manganese and titanium are introduced into the metal-bath, it having been found that the presence of manganese therein resists and retards the removal by oxidation of final I small quantities of carbon. Further purposes of this metallic addition are to enhance the liquidity of the metal-bath during the alloying period when its carbon-content tends to become undesirably low also to cause it to resist the absorption of gases and oxygen-containing substances that otherwise take place during the alloying period and thereby increase the quantities of occlusions and inclusions to be removed during the clarifying and final purifying stages of the process.

The following example will serve to illustrate one manner of operating the process according to the invention wherein a steel bath is employed as a solvent it being understood that no limitations or restrictions are implied thereby:

Clean medium carbon open-hearth steel scrap (phosphorus averaging 0.030% to 0.035%) with a small quantity of manganese steel scrap was melted-down in a tilting basic-lined direct are electric furnace (having graphitized carbon electrodes) containing crushed burnt lime and manganese ore of good grades the former in sufficient quantity to ensure a strongly basic calcareous slag and the latter in slight excess of the amount required to oxidize the silicon and phosphorus but not all of the carbon contained in the charge. When suflicient molten steel had accumulated under the electrodes high-power input was applied until conditions favored pushing in the semi-molten scrap that adhered to the furnace banks which was done after a little lime had been added. From then on until heating up to a suitable slagging temperature the bath was carefully controlled at 1300-1350 C. and by means of fluxing with ore low-silica lime and low-sulphur fluorspar the slag was kept in a fluid oxidizing state surcharged with free or uncombined CaO. When a preliminary bath analysis showed that phosphorus had been worked down to 0.010% lime was added the bath temperature was increased and when it had reached 1625-1675 C. the phosphorated slag was completely poured and skimmed off including the small quantity of lime that was finally added to wash the metal-bath and furnace banks and the hot bath upon being covered with a protective layer of lime and one fifth its weight of fluorspar was ready for the alloying operation. Test anal- 9 that contained not more than 20% of SiO2 with materials having been beneficiated and agglomerated were then used: (a) ferro-silicon having 91.10%-silicon (b) chromite containing 53.15%-

chromic oxide and (c) burnt lime (maxima 2.0%- SiOz and 0.080%-S) slightly in excess of the quantity required to coalesce with the oxidated silicon. As rapidly as possible without dangerously chilling the bath this reaction mixture was shovelled in the furnace was luted to avoid loss of heat, and high-power applied, care being exercised to elevate the electrodes and keep them out of physical contact with the metallic oxide containing slag; also when needed, lime and borax and liquefying fluxes such as fluorspar and iron, manganese and titanic ores were added so that a fusible slag was produced by the reaction CaO from 40% to 60%, FeO from 5% to 20% and MnO from 5% to 15%, which slag compositions have been found to accompany satisfactory recoveries of metal. After the bath had been stirred and final analysis samples taken a small quantity of powdered coke was fed upon the slag and shortly thereafter it was poured and raked off and a non-oxidizing layer of lime and fiuorspar was formed in its place. Test analyses at this stage showed: 0.009%-pho'sphorus,, 0.09%- m a n g a n e s e, 0-.07%-carbon, 0.005%-silicon, 0.033 -sulphur and 1 1.28 -chromium.

The bath being hot because of the rapidity with which the slag had been replaced by a covering of lime and fiuorspar the deoxidizing-desulphurizing slag forming mixture was hurriedly shovelled in followed by powdered coke to deoxidize the atmosphere, power was applied, and the furnace door cracks sealed with fireclay. A fairly powerful deoxidizing and desulphurizing slag, that is one containing about 1.20-1.35% of carbon in the form of calcium carbide, being desired, which slag when free from metallic oxides has a medium or slightly dark gray instead of light gray or white color, the slag forming mixture had been prepared as follows: 60 units of low-silica burnt lime and 20 units each of low-sulphur fiuorspar and petroleum coke all of which being crushed or powdered were intimately admixed. As soon as the slag was completely freed from oxygen a ferro-manganese bath addition was made for the purpose of assisting deoxidization, the bath and slag were stirred slag and metal tests were taken, the slag composition was corrected as required with lime fluorspar and borax, a little coke was fed in and the furnace re-sealed. With the exception that ferro-silicon, to partly degasify the bath, was added in the place of ferro-manganese this procedure was repeated until the bath was killed and samples of the metal rested quietly and without pufling in the moulds after which final temperature and metal tests were taken and the bath was held in a dead-melted or quiescent state for about twenty minutes before tapping. Prior to tapping the bath temperature was increased 100 C. or more by increasing the current density and voltage to provide for another and briefer dead-rest in the crucible and both when tapping and when teeming the utmost care was exercised to avoid the introduction of slag into the final metal. The ingot analyses showed: 0.014%-phosphorus, 0.09%-manganese, 0.12%-

carbon, trace-silicon, 0.010%-sulphur and 11.14% chromium.

It will be understood that the scope oi. the invention includes the production of metals that do not require the employment of a previously pre- 8 pared steel bath also that the reducible materials may consist of a mixture of ores or compounds such as chromite and wolframite or an iron ore may be included provided it does not exceed in quantity 10% of the aggregate of metalyielding materials. When a previously prepared metal-bath is employed the materials that comprise the reduction reaction mixture are, of course, added to such a bath in a manner that is appropriate to the character of the reducing agent that is being employed; and when desired the metal-bath may be recarburized by means of powdered carbonaceous matter such as petroleum coke broken electrodes and the like but it is preferred to use materials such as washed metal suitable pig iron and when an increase in the phosphorus-content is permissible, by prolonged use of the CaCz containing reducing slag. Any type of electric or high-powered open-hearth or other suitable type or kind of furnace may be employed to supply heat throughout the process or two or more furnaces of the same or different kind or kinds may be used. And whether a pre-- viously prepared bath is or is not employed in the process the reducing agent may act as a vehicle for and contain non-ferrous metals that are components of the final alloy metals-4m example of such a reducing agent being an iron-chromiumsilicon alloy-which may be employed singly or 35 with other similar alloys or any reducing agent or agents specified herein. And in all cases the reducing agents may be employed in the quantities theoretically required as indicated by the chemical equations ofv the reduction reactions or any quantities differing therefrom. It will be understood that the metalliferous materials may be beneficiated or dressed in any suitable manner,

I claim:--

1. In a metallurgical process of manufacturing metallic alloys that are substantially free from sonims, solid foreign substances and occluded gases, which comprehends preparing a crude alloy-for further treatmentby associating the reactive materials in a solid state and causing chemical reactions to occur between ingredients of an assemblage comprising: (a) any number of metalliferous substances of the kind and class that constitute sources of non-ferrous metals and metalloids; (b) at least a basic flux; and (c) any number of the various non-carbonaceousreducing agents wherein a crude alloy is prepared for further treatment the step of preparing steel, of carbon or alloy type, to be united with the metallic reaction product in the preparation of the crude u alloy which comprehends melting-down solid steel in the presence of a manganese-containing oxidant and under'conditions which add metallic manganese to the steel.

2. In a metalhirgical process of manufacturing .5 metallic alloys -that are substantially free from sonims,- solid foreign substances and occluded gases, which comprehends preparing a crude al- -metalloids;- (b). at least a basic flux; and (c) any n number of the various non-carbonaceous reducing agents wherein a crude alloy is prepared for further treatment the step of preparing steel, of carbon or alloy type, to be united with the metallic reduction product in the preparation of the crude alloy which comprehends removing phosphorus from the steel through the instrumentality of a slag formed while melting-down the steel in the presence of a titanium-containing oxidant.

3. In a metallurgical process of manufactur ing metallic alloys that are substantially free from sonims, solid foreign substances and occluded gases, which comprehends preparing a crude alloy-for further treatment-by associating the reactive materials in a solid state and causing chemical reactions to occur between ingredients of an assemblage comprising: (a) any number of metalliferous substances of the kind and class that constitute sources of non-ferrous metals and metalloids; (b) at least a basic flux; and (c) any number of the various non-carbonaceous reducing agents the step of preparing steel, of carbon or alloy type,to be united with the metallic reaction product in the preparation of the crude alloy which comprehends meltingdown solid steel in the presence of a manganesecontaining oxidant under chemical and thermal conditions favouring the oxidation of phosphorus and then removing the phosphorated slag therefrom.

4. In a process of producing ferruginous alloys, the steps of melting and treating a ferruginous metal with a mangenese-containing oxidant, then adding any number of'alloying elements to the liquid metal and subsequently treating the resultant liquid alloy with a reducing slag that contains not more than 2% of carbon in the form of calcium carbid.

5. In a process of producing ferruginous alloys, the steps of melting and treating a ferruginous metal with an oxidant of an alloying metal, then adding any number of alloying elements to the liquid metal and subsequently treating the resultant liquid alloy with a reducing slag that contains not more than 2% of carbon in the form of calcium carbide, and stopping" the action of the reducing slag before undesired recarburation and rephosphoration of the liquid metal has taken place.

6. In a process of preparing ferruginous alloys, the step of subjecting a liquid ferruginous metal to which titanium in amount less than 1% has been added, to a direct alloying treatment whereby a foreign alloying element is added to the liquid metal.

'7. In a process of preparing ferruginous alloys, the step of subjecting a liquid ferruginous metal to which titanium and manganese in amount less than 1% have been added, to a direct alloying treatment whereby a foreign alloying element is added to the liquid metal.

8. In a process of refining a chromium-containing ferruginous alloy having a phosphorus content below the maximum quantity of this element allowable in the final metal, while the sum of the percentage of silicon, manganese and carbon thereof exceeds 0.45%, the step of treating such metal while in liquid condition with a reducing slag that contains not more than 2% of carbon in the form of calcium carbide, and stopping the action of the reducing slag before undesired recarburation and rephosphoration of the 30 liquid metal has taken place.

9. A process of refining a ferruginous alloy having a phosphorus content below the maximum quantity of this element allowable in the final metal, while the sum of the percentages of silicon, manganese and carbon thereof exceeds 0.45%, which comprises treating said ferruginous alloy while in liquid condition with a reducing slag that contains not more than 2% of carbon in the form of calcium carbide, and stopping the action of the reducing slag before undesired recarburation and rephosphoration of the liquid metal has taken place.

ROBERT WICKERSHAM STIMSON.