US2176688A - Chromium metallurgy - Google Patents

Description

Oct. 17, 1,939.

M. J. UDY

CHROMIUM METALLURGY Filed Sept. 7, 1958 ramz'le, calca/m i Imm/@aule eagen I urnace Crucible; INVENTOR MdL/@Cile (o man MARvxN J. UDY :imma/m,- earm BY WVM-ian ATTORNEYS Patented Oct. 17, 1939.

UNITED STATES PATENT oFFicE 45 Claims.

This invention relates to chromium metallurgy and has for an object the provision of certain improvements relating to chromium-bearing products and methods of producing such products. More particularly, the invention contemplates the production of improved chromiumbearing materials and improved composite reagents for use in producing ferrochromium and for use in incorporating chromium in iron and steel, the provision of improved methods of producing chromium-bearing materials and improved composite reagents for such uses and the provision of improved methods of producing ferrochromium and chromium-bearing iron and steell products. A further object of the invention is to provide certain improvements in methods of utilizing high-carbon ferrochromium in the production of low-carbon ferrochromium and chromium-bearing iron and steel products. The invention further contemplates the provision of composite reagents of various compositions suitable for effective and efficient use in operations characterized as to type by performance in electric furnaces, combustion furnaces, foundry ladies, crucibles and other types of equipment.

As hereinafter employed and as employed in the claims, the term ferrochromiurn, as used to define metallic productsl subjected to oxidation treatments, unless qualified, includes all products containing iron and chromium and which also contain carbon in undesirable amounts relatively to the chromium contents, Which amounts-can be reduced effectively by means of the oxidizing treatments to provideproducts more suitable than the original material for use in forming metallic products containing chromium; and the meaning of the term roasting, unless qualified, is re`-` stricted to cover oxidizing operations in which the materials undergoing treatment are subjected, in the solid state, to the action of oxidizing gases, such as air, at elevated temperatures.

The invention deals with the difficult problem of carbon elimination and suppression faced by chromium metallurgists, and it provides an effective and efficient solution for that problem.

In the production of alloys containing chromium and iron, control of carbon is an important factor. Many of the more important alloys must contain carbon in amounts notexceeding very low percentages. Chromium for use in producing (Cl. 'l5-27) such alloys is obtained initially by reduction of natural chromium-bearing ores which also contain iron. Such ores commonly are reduced by carbon, for economic reasons, and.'because o! the great amnity of chromium for carbon, and because iron is reduclble at chromium reduction temperatures, the reduction products are metals in the form of alloys or mixtures of iron and chromium (ferrochromium) contaminated with considerable amounts of carbon. The 1 amounts of carbon contained in ferrochromium products resulting from carbon reduction make all of such products unsuitable for direct use in the productionof many alloys containing iron and chromium and elimination of the carbonl therefore is necessary in many instances.

For the same reason that it is diillcult or imv possible to exclude carbon from ferrochromium in reduction with carbon, complete elimination of carbon from carbon-bearing ferrochromium after 0 production has been dimcult or impossible.

Many procedures have been proposed for reducing the carbon in ferrochromium, and for utilizing reducing agents other than carbon to avoid its incorporation in the ferrochromium in 25 the first instance, in order to produce ferrochromium products suitable for direct use in producing low-carbon alloys containing iron and chromium. Many of the procedures proposed heretofore can be operated successfully technically, .but are economically unsound.

In industrial operations, for the most part, ferrochromium of the very low carbon content required in the production of low-carbon alloys containing iron and chromium (for example, chromium steels containing .06 per cent to .20 per cent C) has been secured by replacement of the carbon in high-carbon ferrochromium with silicon followed by removal of the silicon by oxidation, as by treatment with more chromium-bear- 40 ing ore. The present invention provides another, more effective and more denitely controllable method of removing carbon from high-carbon ferrochromium. The method of the invention accomplishes carbon removal by oxidation of the metal and carbon of the ferrochromium to produce a. concentrated oxidized chromium product from which the chromium can be reduced again readily by means of silicon, or a similar noncarbonaceous reducing agent. According to this l0 invention an agent like silicon-is utilized indirectly for aiding in obtaining low-carbon chromiumproducts from chromite ores; The controlled oxidation of silicon in accordance with the invention distinguishes the method of the invention from the prior art method and makes the method of the invention more eiiective and more economical. 1

'Ihis invention is based on my discovery that products resulting from controlled oxidation of ferro-chromium are particularly well adapted for use in the production of exothermic mixtures capable of reacting within themselves to produce metallic chromium at temperatures normally employed in operations designed for the production of alloys o! chromium and iron.

The improved products of my invention are produced by subjecting carbon-bearing ferrochromium to controlled oxidizing treatments to form products containing oxides of iron and chromium, free or substantially free of metal and containing carbon in an amount less than that contained in the ferrochromium employed. 'I'he ierrochromium may be oxidized either in the molten state or in the solid state, and the oxidation treatment may be controlled to eect any desired degree of carbon elimination. 'I'he degree of carbon elimination effected in any oxidation treatment will depend upon the carbon specication o! the chromium-bearing product to be produced through the use ot the particular material of the oxidation treatment.

The ferrochromium may be subjected to the oxidizing treatment alone or in the presence of one or more addition agents such as lime or soda ash which serve as oxidation promoters and which react with the oxides resulting from oxidation of the iron and chromium. When the .ferrochromiurn is subjected to the oxidizing treatment alone in the ilrst instance the product of such oxidizing treatment may be subjected to a iurther oxidizing treatment in the presence of one or more agents of the aforementioned type to accomplish further oxidation, to bind the oxides chemically, or to accomplish both of these objectives.

The composite reagents o! my invention comprise iron and chromium oxide-bearing products resulting from the oxidation of ferrochromium and one or more solid, non-carbonaceous reducing agents such as aluminum or silicon or an alloy of aluminum or silicon with one or more other elements. The oxide-bearing material and the non-carbonaceous reducing agent are ilnely divided and intimately mixed. The degree of subdivision and intimacy of mixing of components of the mixture preferably are such that every particle of reducing material contained in the mixture is in direct and substantially complete contact with particles of reducing agent. I have found that such intimate contact requires a degree o! comminution such that a large proportion of the oxide-bearing material and the reducing agent consists of particles sumciently small to pass a 100-mesh screen (Tyler series) and grinding of the materials in contact, or together.

The products o! oxidation treatments of terrochromium are admirably suited for grinding to the degree ot tlneness necessary for the required intimate mixing and contact. Such products can be ground readily in an ordinary ball mill substantially to impalpable powders.

The products o! oxidation, also, are admirably suited for use in forming exothermic mixtures,

and oxidation is readily controlled to form products containing suillcient oxygen to support combustion of reducing agents which may be substantially complete, if desired. The iron of the ferrochromium is converted readily to ferrie oxide (Fez-Ox), and the chromium is converted readily to chromic oxide (CrzOs) Oxidation may be iurther controlled to convert a large proportion of the chromium to chromic anhydride (CrOs) Depending upon the conditions under which the various composite reagents are to be employed, they may contain additional oxygen-containing substances to provide additional heat for melting the metal and slag produced.

Any of the common oxidizing agents such, for example, as sodium nitrate, sodium chlorate and manganese dioxide may be employed for promoting oxidation of silicon with the resultant production of additional heat. Such oxidizing agents are required, for example, when the reaction mixtures contain large amounts of inert materials such as slag-forming materials, and they are employed in amounts suillcient to produce enough heat to melt the metal and slag produced and give the slag the desired iluidity. The addition of such oxidizing agents requires additional silicon, when silicon is employed for reduction, and the total amounts of silicon and available oxygen are so proportioned as to provide about the theoretical amount of silicon for combining with the available oxygen. I! excess silicon is used, the excess will enter the metal produced, control of this being eil'ected in the use oi improved oxidation products.

The products resulting from the roasting of ferrochromium in the solid state to eilect a high degree ot elimination of carbon are particularly well adapted for the production of a nely divided product by grinding. Therefore, the invention will be described more particularly hereinaiter with reference to the production and use of such products.

Roasting in the solid state to eiIect a high degree of carbon elimination requires preliminary ilne grinding of the carbon-bearing ferrochromium. I have i'ound products in which the major portion of the particles are minus 100 mesh to be most suitable for effective removal of carbon by roasting. The roasting of the iinely divided particles results in the production oi' particles of the resulting oxidized compounds of the same general order of size as the particles ot ferrochromium treated. 'I'hese particles appear to consist of agglomerates of even smaller particles formed as a result of oxidation of the individual atoms of the components of the ferrochromium. Roasting of the ilnely divided` ferrochromium tends to produce separated particles approaching the molecular sizes of the compounds formed, and, while the achievement of this objective is impossible, the character of the smaller particles produced, as indicated by the ease with which the particles may be disrupted, indicates that the tendency is not arrested entirely. The roastedi product as discharged or withdrawn from the roasting equipment will not necessarily be in the form of a powder as ne as the ferrochromium powder employed in its production. Usually, it will contain a large proportion of agglomerates of particles of the size of and smaller than the particles of ferrochromium employed in its production. 'Ihe particles comprising the agglomerates are relatively loosely bound together and they may be separated readily by grinding.

Grinding of the roasted product breaks up the agglomerates readily and effectively and results in the production of a finely divided product which is an extremely desirable material for mixing with solid non-carbonaceous reducing agents to produce composite reagents for use in producing chromium-bearing metal products. Simple grinding to produce a product in which ninety per cent of the particles are minus 100- mesh results in' conversion of more than fty per cent of the product to an\impalpable powder, a powder in which more than fifty per cent of the material (by weight) consists of particles small enough to pass a 200-mesh screen. The extremely finely divided particles readily coat and tenaciously adhere to particles of solid non-v carbonaceous reducing agent with which they may be mixed and thus provide the intimate contact required for reduction to a very high degree with controlled oxidation.

In practicing my invention, advantage may be taken of the effect of roasting in facilitating regrinding by subjecting the ferrochromium to a preliminary roasting operation in a relatively coarse state of division to accomplish fractional oxidation and subsequently re-grinding and reroasting one or more times, if necessary, to accomplish the desired degree of oxidation. For example, the ferrochromium may be ground in the first instance to form a product, the major portion of which consists of particles not sub-` stantially smaller than required to pass through a (i5-mesh or equivalent screen (Tyler series). After roasting of this relatively coarse product to accomplish eiiicient oxidation in view of its relatively coarse nature,l the roasted product may 4be subjected to a grinding operation to form a product, the major portion of which consists of particles small enough to pass a 1D0-mesh screen. 'I'he resulting more finely divided material may be roasted to effect a further degree of oxidation.

Preliminary roasting (followed by re-grinding and re-roastlng) may be carried out with ferrochromium ground intially to any desired pa'rticle size. Double or multiple roasting (preliminary roasting followed by re-grinding and reroasting) may be advantageous for several reasons. For example, the grinding of high carbon ferrochromium to produce a product of which a large proportion consists of particles small enough to pass a 10o-mesh screen is a relatively simple matter, Therefore, the problem of securing an ultimate oxidized product comprising particles of the most desirable small sizes can be simplified by combining the advantages which can be derived as a result oi the grinding characteristics of high carbon ferrochromium with advantages which can be derived as a result of the grinding characteristics of the oxidized product.

Multiple roasting may be carried out with or without the presence of oxidation promoters in any stage, or, when any stage of roasting is carried out in the presence of one or more of such agents, additional amounts may be added to the product of that stage of roasting before subjecting it to the next stage of roasting. Thus, for example, when chromate formation is desired, I prefer to first roast finely divided ferrochromium at a relatively high temperature above 1000 C. in the presence of suiiicient lime to form calcium chromite with all of the chromium in the ferrochromium and subsequently roast the product obtained by such roasting treatment at a temperature below 1000" C. in the presence of auflicient additional lime and soda ash to provide a total amount of calcium' oxide and sodium oxide to combine with all of the chromic oxide remaining unchanged to form chromate and chromite of calcium and sodium.

l Roasting operations may be facilitated by selection of the ferrochromium to be treated. Highcarbon ferrochromium products grind more readily and can be converted to desirably small particles more easily than low-carbon ferrochromium. Thus, -for example, ferrochromium containing 8 to 10 per cent or more carbon can be reduced to the form of a powder comprising very small particles quite easily; ferrochromium containing 6 to 8 per cent carbon is more dinicultly reducible to particles of desirablyA small sizes; and ferrochromium containing less 'than about 6 per cent carbon can be reduced to particles desirably small in size only with considerable difficulty relatively to the difficulties encountered in finely dividing ferrochromium products containing more than 6 per cent carbon.

The .grinding of relatively low-carbon ferrochromium is facilitated if the ferrochromium also contains silicon. Thus, for example, ferrochromium containing about 4 to 6 per cent carbon and amounts of silicon up to about 3 per cent can be ground quite readily.

In practicing my invention, I prefer to employ ferrochromium as nearly saturated as possible with carbon, or, alternatively, ferrochromium containing smaller amounts of carbon, but containing, also, sufiicient silicon to compensate, in its influence upon grinding characteristics, for the carbon deficiency. When I produce the ferrochromium for roasting by reduction treatments of chromium-bearing materials, I prefer to employ sufficient carbon to incorporate in the resulting ferrochromium as much carbon as possible, and, if the conditions of operation are not -such as to permit the production of products of the higher carbon content, I operate the `reduction process ,under conditions 'such as to reduce silicon from silica contained in the charge and form a product containing, preferably, about 1 to 3 per cent of silicon. Larger quantities of silicon improve the grinding characteristics of the ferrochromium produced, but they are objectionable because they increase the bulk of the slag producedin the ultimate reduction of the oxidized products of the invention.

In forming the composite reagents of the invention, the roasted product and the solid` noncarbonaceous reducing agent maybe ground separately and mixed together subsequently or` the two products may' be ground together. I prefer to grind the two products together at least in the preparation of the final composite reagent, as grinding of the twoproducts together results in thorough mixing and aids in lcoating of the larger particles of each product with the extremely iine particles of the other product, thus producing the most desirable type of intimate contact. Grinding and mixing etliciencies are improved when the solid non-carbonaceous reducing agent is ground preliminarily-,to a finely divided condition. In employing silicon containing reducing agents, according to my preferred practice, Iemploy a 4reducing agent ground initially to such an extent that a--large proportion consists of particles small enough to pass a 10o-mesh screen.

In the preferred composite reagents of my invention', the majority of the particles of the roasted material and non-carbonaceous reducing agent combined are small enough to pass a 1D0-mesh screen. Substantial amounts consist of particles small enough to pass a 150-mesh screen and of particles small enough to pass a 20D-mesh screen. Substantially all of the particles may be small enough to pass a 20G-mesh screen, and this type of product is most desirable when the composite reagent is to be used for the direct production of a metal product containing iron and chromium in the proportions in which these elements are present in the components of the composite reagent. When the composite reagent is to be employed on the surface of a molten metalA bath for incorporating chromium in the metal such a ne state of division of the components of the composite reagent is not so essential tothe securing of good results.

The products of my invention may be em- Y ployed in any suitable manner for producing chromium-bearing alloys. The oxidized products. for example, may be added to the furnace either alone or in admixture with the reducing agent when reduction is to be carried out in an electric furnace where ample heat is available. When reduction is to be carried out in combustion furnaces or in crucibles, the oxidized product preferably is mixed intimately with the reducing agent before being charged into the furnace or crucible. The intimate mixture may be employed in a loose condition, or it may be employed in a compact condition, as. for example, in the form of briquettes, or tightly packed in combustible bags or metal containers. In adding the intimate mixture of oxidized material and reducing agent to a combustion furnace, I prefer to employ it in the form of a compact mass, as in the form of briquettes or agglomerates.

When the composite reagents are to be formed into briquettes or packed in containers, it is desirable to employ particles of different sizes in the ranges 80 to 100 mesh; 100 to 150 mesh; 150 to 200 mesh; and minus 200 mesh. Substantial amounts of the material will consist of particles within these size ranges when grinding is carried out under conditions designed to accomplish subdivision of about to 10 per cent of the materials to minus 200 mesh particles. The use of various sized particles provides for an effective degree of interlocking of particles which tends to produce strong briquettes capable of withstanding rough handling in shipping and which also tends to aid in securing the desirable intimate contact of particles of roasted material with particles of reducing agent. The use of various sized particles also provides for tight packing of the materials in containers.

In producing oxidized products from molten alloys of iron and chromium, oxidation may be carried out in any suitable manner. For example, a molten bath of the alloy may be blown with air or subjected to the action of an oxide of iron. Oxidation preferably is carried out in the presence of a base like calcium oxide to produce a workable slag. When lime is employed the chromium oxidized to chromic oxide enters into chemical combination with the calcium oxide of the lime, forming calcium chromite. Lime in the oxidized product is not objectionable, as it functions to flux the oxidized reducing agent in reducing operations to which the oxidized product is subjected ultimately. Lime may be employed in any suitable amount, but, when the oxidized product is to be stored for any considerable period of time, it preferably is used in a restricted or controlled amount such that the oxidized product will contain no uncombined calcium oxide. Free or uncombined calcium oxide absorbs moisture and carbon dioxide from the atmosphere which may cause dangerous explosions (or carbon contamination of the metal after in connection with the procedures for oxidizing alloys containing chromium and iron at temperatures below their melting points.

When alloys containing iron and chromium are oxidized in the solid state, any suitable temperatures below their melting points may be employed. Preferably, the lowest temperatures capable of effecting the desired degree of oxidation are employed.

I have discovered that oxidation of the iron, chromium and carbon proceeds rapidly and effectively when alloys containing these elements are heated, in a fine state of division, to temperatures substantially higher than 1200" C., but below the melting points of the alloys. At temperatures below 1000 C., oxidation proceeds more slowly, and oxidized products containing less than about 0.30 per cent of carbon (by weight) are diilcult to obtain. Even at temperatures as high as 1200" C., products containing less than 0.20 per cent by weight of carbon are diilcult or impossible to produce with many hours of roasting under oxidizing conditions. At temperatures substantially higher than 1200 C., products containing not more than about 0.10 per cent by weight of carbon and containing even as little as a trace of carbon can be produced by roasting under oxidizing conditions for periods of time shorter than two hours. In roasting to eilect a high degree of carbon elimination, I prefer to employ temperatures in excess of 1250 C. or even in excess of 1300 C. Operating at temperatures above 1300 C., in the range 1300u C. to 1350 C., with and without oxidation promoters, I have obtained oxidized products entirely free of carbon, products in which the presence of carbon could not be detected by the usual analytical methods.

In carrying out roasting of ferrochromium in accordance with my invention, I may produce oxidized products entirely free of carbon or products substantially free of carbon such, for example, as products containing not more than about 0.02 per cent or which contain less than about 0.05 per cent of carbon. I may produce, also, oxidized products containing carbon in amounts up to 0.10, 0.20, 0.30 per cent or more.

Materials consisting of particles larger than those which will pass a 1D0-mesh screen can be roasted indefinitely at temperatures around 1000 C. without total elimination of carbon being effected. Particle size is an important factor bearing on the matters of times and temperatures required for oxidation and degrees of carbon elimination accomplished. In general, coarser products require longer periods of treatment and the use of higher temperatures than finer products.

vless than one per cent of soda ash in the roast- Complete oxidation of ground ferrochromium by roasting at low temperatures-in one-operation is diillcult to accomplish, kbut substantially complete oxidation may be obtained by roasting in the presence of lime and a little soda. l In using lime there are, in any event, several advantages. In subsequent reaction with silicon or ferro-silicon, lime is available for slagging the produced silica and accelerating its production. Ordinarily, in roasting in the presence of admixed lime, I prefer to use about equal amounts of lime and of ferrochromium. This may or may not be enough in relation to the silica produced in subsequent reduction of the oxidized material with silicon-containing reducing agents. It, however, does give a, composition not subject to change in the air and therefore advantageous for shipping. More lime can be physically admixed before the exothermic action if it be wanted. Another advantage in roasting in the presence of lime is that oxidation may be readily carried beyond the CraOa point with production of CrOs. In reaction with silicon, CrOa produces considerably more heat than CraOz.

If desired, the roasting may convert substantially all the chromium to chromate. But it is usually better to .have in the roasted product a considerable percentage of CraOa. The reaction of CrOa with silicon is, as stated, more highly exothermic than that of CrzOa; that is, for equal quantities of chromium more heat is developed, the proportion of oxygen in CrOs being double that of CrzOa and theexcess being, so to speak, loosely bound. However, more slag is formed per unitl of chromium as CrOa, more silicon being oxidized to silica. The yield of chromium metal per unit of silicon used in reduction is greater from CrzOa than from CrOs. It has been found advantageous in some cases to carry the roasting of ferrochromium so far as to give onlya minor proportion of the chromium as chromate. However, in other cases the proportion may be higher. Equal proportions of chromium in the two forms give a useful product. Any desired content of oxygen within limits can be put into the product in roasting to chromate. When the oxidized material is to be used for adding molten chromium to small bodies of metal, as for example in a foundry ladle, a higher oxygen content as CrO; in the material gives more heat and a higher temperature to the molten chromium addition. Larger-operations, as in open hearth steel practice, require less oxygen. Thus, in roasting ferrochromium, the oxygen content is made to suit the particular purpose for which the product is to be utilized, the chromium content being inverse to the oxygen added in roasting.

In the roasting with lime the proportion of lchromate in the product can be controlled by the roasting temperature, and also by the relative amount of soda in the roasting mixture. temperature of roasting also aifects the elimination of carbon, as hereinbefore pointed out, higher temperatures being conducive to quicker elimination of carbon, and to smaller chromate content, with higher chromite.

Roasting ferrochromium at temperatures well under 1000 C. with somewhat less than 100 per cent by weight of lime with no soda ash or with ing charge converts the chromium mostly to chromate without complete oxidation and elimination of carbon from the ferrochrome metal in a reasonable length of time. Above 1000" C. the

The`

carbon-is eliminated but the chromate breaks regulation of the tem" rature to control theratio of chromate to chromite (CrOa to CraOa) in the oxidized product, and thus of the oxygen content and exothermicity. I have found, for example, that addition to a roasting mix of ferrochromium and lime of soda ash (NazCOa) in the amount of about 2 to'5 per cent by Weight of the ferrochromium metal results in about 50 per cent conversion of the chromium to chromate in a short time with elimination of a substantial amount of carbon and oxidation of metal when the temperature of roasting is held around l000 C.; the remaining chromium being oxidized largely to chromic oxide (CrzOa). A small amount of the chromium will be present as metallic chromium which functions to bind the residual carbon. With more lime or more soda the proportions of chromate is increased. A 50-50 oxidation of chromium to chromite and chromate gives an oxidized material' capable of a highly exothermic reaction with silicon alloys. Such a compound of CaO, FezOs, CrzOa and CrOz containing a small amount of NazO from the soda ash and made from ferrochromium by roasting in air, is a highly advantageous material for exothermic production of chromium-iron metal. A fully chromated material containing CaO, NazO,

FezOs and CrOa in chemical combination can readily be made. It contains less chromium but is more exothermic.

It is however possible to oxidize highv carbonl ferrochromium completely by roasting it in finely divided form without the presence of lime or other oxidation promoter; roasting being in two or more stages and the material being re-ground between the roasting stages. This shortens the time and fuel required. Oxidation of ferrochromium containing 6 to 10 per cent carbon is a vigorous exothermic action which starts at about 600 to 700 C., the temperature rising automatically to 1000 C. or higher. But substantially complete elimination of metal and of carbon requires heating of the material for a time after the exothermic action has spent itself` and this time is materially shortened by the presence of a base or other oxidation promoter with the ferrochromium. Double roasting has the advantage of facilitating grinding to a greater iineness than is usually possible for the unroasted metal. The lime and soda are omitted with advantage in the first roasting and added in subsequent regrinding and re-roasting.

When roasting in two stages, the temperature may Well be carried considerably above 1000D C. in the first. stage. 1350 C. for example, to substantially completely eliminate carbon and oxidize the Cr to CraOa and after re-grinding with lime and soda a second roasting at 700 to 1000 C. puts a good percentage of CrOa in the product, a proportion which can be above per cent of the total contained chromium. It is often advantageous in practice to roast to 100 per kcent CrO: and mix the fully chromated productwith chromite obtained by roasting at higher temperature for shorter time.

-sired for the subsequent exothermic action.

Oxidation can be accelerated by raisingV the partial pressure of oxygen in well understood ways. by the use of oxygen itself, or a compound capable of releasing oxygen at the roasting temperature, such as sodium chlorate. sodium nitrate, sodium bichromate, chromium trioxide, manganese dioxide. or the like. The use of oxygen, by raising the owgen content of the roasting atmosphere to a point above the ordinary concentration of oxygen in air, naturally facilitates oxidation. A small quantity of one of the oxygen-releasing 'compounds mentioned, present along with the lime, also shortens the roasting time, such compound serving when so used as an effective promoter of oxidation, while relying upon the air as the main source of oxygen.

The roasting step may in fact be conducted, with or without lime, in the presence of a sumcient quantity of one of the oxidizing agents or oxygen-releasing compounds mentioned hereinabove to furnish owgen for oxidation of most or all of the metal. When this is done, the oxidation becomes strongly exothermic and is completed in a few minutes.

However. in the ordinary practice of the present invention, air and lime, with a little soda, are relied on. Instead of lime, strontia or baryta may be used but their molecular weights are higher and their cost greater. Potash may be used instead of soda. The bases may be used in the fox-m of carbonates. Magnesia or dolomitic lime may be used.

'I'he roasting can be done in a roasting or calcining furnace of suitable type such as an open hearth or reverberatory furnace with mechanical rabbling or in a rotary kiln. stirring during roasting aids oxidation. Fine grinding of the mixture in a pebble or ball mill before roasting is good practice.

'Ihe color of the roasted product is from black to gray to yellow. depending upon the CaO content and the CrO: content. Complete oxidation of ferrochromium is 'attended with loss of magnetism and the fully roasted material is non-magnetic. In the roasting, oxidation of the metal and of the carbon proceed together, with loss of magnetic power as the metal and carbon are eliminated with formation of FezO; and without formation of FeO. The magnetic test may be used to measure the elimination of metal, of- P'eO and of carbon, the roasting being stopped when the material becomes non-magnetic.

If the synthetic chromite is insuiilciently high in CrtFe ratio, it may be next beneilciated by replacement of iron with lime and preferential reduction of iron. in the manner described in my Patent No. 2,098,176. Or the ore may be beneiiciated before reduction to high carbon ferrochromium. Whether or not such beneiiciation is practiced. the resultant chromite, which may be calcium ferrichromite or a calcium chromite, or a chromated chromite, is then exothermically reducible with a non-carbonaceous reducing agent, such as ferrosilicon, ferrochrome silicon, aluminum, or the like. This reduction results in the production of an iron-chromium alloy low in carbon; e. g. chromium steel", low carbon ferrochromium, or even (where iron has been selectively reduced and removed) a chromium metal of high purity. Low grade, high iron, materials are, however, advantageous in making chrome alloy steel and iron.

As a carbon-free reducing agent, any of the alloys of aluminum or silicon. .or magnesium, may be used. Calcium, magnesium and aluminum silicides are effective. Where nickel is wanted in the final alloy, nl'ckel silicide may form a component of the reducing agent. Ferrochrome silicon is useful in adding chromium with the heat developed in exothermic reduction of roasted ferrochrome by the silicon.

In accordance with one aspect of my invention, roasted ferrochromium is mixed with ferrosilicon or'ferrochrome silicon, both as fine powders, in such quantity as to supply sufllcient silicon to reduce the chromium and iron oxides to metal. To make a good exothermic mixture reacting completely and quickly, it is necessary that the mixing be exceptionally complete. It is a useful expedient. after making the mixture to ball mill it for a time. The mixture is next introduced into a steel bath, as in the open hearth steel furnace, in such relative quantity as to supply the desired chromium content in the final steel product. This step may be the final step in standard open hearth steel manufacture; that is, the step when exothermic action is initiated and completed with production of molten metal which enters the steel, while the SiO: formed, as well as any BiO: present in the mixture added, combines with the CaO present in the chromite to form a non-refractory slag; this slag being free-running at the steel-making temperature, and not objectionable either in amount or in character. In making this addition to molten iron or steel. there is no local chilling. As a matter of fact. with the usual exothermic mixtures, there is an increase in temperature. The exothermic mixture adds molten chromium to the steel. The mixture can be such as to add no silicon or a desired amount of silicon to the steel.

The advantage of tine particle size and intimate contact of the particle, particularly in the manufacture of low carbon ferrochrome where the allowable silicon content may be from 1 to 1.5 per cent, may be illustrated by the following examples, of small Vscale tests.

A mix of roasted ferrochrome and ferrochrome silicon, 30.6 per cent being plus 100 mesh, 65 per cent minus 100 mesh and plus 150 mesh, 4.1 per cent minus 150 mesh and plus 200 mesh and 0.3 per cent minus 200 mesh gave a metal, when the mix was ignited and the exothermic reaction allowed to proceed to completion, which contained 6.2 per cent Si. The same mix when ground to completely pass a 200 mesh screen gave a metal containing l per cent Si, which is within the specified range for Si in low carbon ferrochrome.

Silicon control was not accomplished at the expense of chromium recovery. In fact the advantage of silicon control was supplemented by an advantage of additional or increased recovery of chromium. The recovery in the second example above, employing the iiner material. was approximately seven per cent better than the recovery in the first example, employing the coarser material. Recoveries achieved in large scale operations usually exceed ninety per cent.

'Ihe control of silicon in the metal in one step is different from the prior art and is accomplished by the use of a roasted ferrochrome which has had the gangue of the ore removed and a product produced of controlled oxygen content which allows the use of a high lime slag in the exothermic reaction and still produces molten metal and molten slag. Such conditions are conducive to the silicon control in metal. This saves a refining operation to remove the silicon from the metal which is the. general practice in common use.

The same eiliciency of silicon control in the metal can be accomplished in the electric steel furnace or open hearthfurnacein making chrome steels if the same degree of fine grinding and contacting is practiced, with the advantage of a saving in time of making the heat and in power used, as compared to the usual practice of using ferrochrome metal in making chromium steels. Coarser mixes can of course be used with varying degrees of economy particularly in 'furnaces like the electric furnace where additional heat is readily available to produce the high temperatures needed. Under such conditions the time of reacting is prolonged.

In a modiiied embodiment of the invention, a chromium steel is produced entirely by exothermic reaction. In this method of operation, no steel bath is necessary, all of the iron needed for the subsequent steel over that reduced from thev synthetic chromite being supplied through the ferrosilicon or ferrochrome silicon used, the amount of chromium put into the steel being correspondingly high. An oxygen-carrying compound such as sodium nitrate, sodium chlorate, sodium bichromate, or the like, may be added with the roasted ferrochromium, and the amount of silicon added in the reducing agent is made sumcient to supply silicon for oxidation by this `added material and to give suiicient heat in being oxidized to melt the .whole of the mix,vin addition to that required for reducing the metal oxides of the chromite. Iron ore may be used in the silicothermic mixture and steel of a desired composition made by the exothermic reaction-of iron oxide and ferrosilicon. As in the method previously described, enough' lime should ordinarily be presentV in the exothermic mixture to form, with the resultant silica, as well as-any silica present as such in the chromite. a slag having a lime-silica ratio of approximately 1.5:1 by weight. Where somewhat higher or lower slag ratios are desirable in the steel-making operation, the lime and silicon may be adjusted accordingly.

When it is not advisable to incorporate in the composite reagents or reaction mixtures sufficient lime to form, with the silica formed by oxidation of silicon employed for reduction and with any silica present in the mixtures before reduction, a slag of the desirable compositori, the additional lime required may be acquired by the silica from a highly basic slag with which the mixture may be placed in contact in the reduction receptacle. Thus, forlexample, in employing composite reagents or reaction mixtures deficient in lime (calcium oxide), I prefer to place them in contact with slag layers containing lime in excess of that required to form a tri-calcio silicate with the silica present therein. Slag layers containing lime and silica in the ratio of four calcium oxide to one silica and higher have been employed satisfactorily. The silica produced extracts calcium oxide from the highly basic slag immediately surrounding the zone of reaction.

The composite reagents in briquetted form function admirably when placed on slag layers overlying molten metal layers. They extend down through the slag layer and iioat on the surface of the metal layer. Reaction takes place at the contact surfaces, and the brlquettes appear lor composite reagents preferably should not conto dissolve or melt away smoothly and uniformly, from the bottom up, with the solid upper portion descending uniformly until entirely' submerged and consumed.

In forming the various reaction mixtures or 5 composite reagents for various uses, varying amounts of lime may be incorporated. For steelmaking, for example, lime sufllcient to provide a ratio of lime toA silica inthe range of from 1: 1 to 1.5:1 may be provided, and for low-carbon or carbon-free ferrochromium production, lime suiiicient to provide a ratio of lime to silica in the range of from 1.5:1 to 2:1 may be employed. As hereinbefore pointed out, the reaction mixtures 16 tain free or uncombined lime. All lime present preferably should be chemically bound with compounds such as iron oxide, chromium oxide, silica and alumina present in the mixture. The mixture may contain suflicient lime to combine with all of such substances present, or the lime present may be insuflicient for this purpose. If the reaction mixture or composite reagent is to be formed and employedsubstantially immediately, or within a short time after the oxidized material is produced, any desired amount of lime in exeess of that required to bambine with the eempounds in the oxidized material may be employed. In using oxidized ferrochromium as described for making chrome steel inthe open hearth furnace an advantageous procedure is to mix it in powdered form with finely divided ferrochrome silicon to form a Silico-thermic mixture capable of converting itself by exothermic reaction into molten chromium-iron metal and lime silicate slag; then igniting the mixture in an insulated furnace, allowing the reaction to complete itself and pouring the metal into the open hearth steel bath, with or without the silicate slag. This procedure effects addition of molten low carbon ferrochromium to the open-hearth refined steel. The amount of chromium thus put into the steel is that required for the desired alloy composition.

In utilizing oxidizedferrochromium as the oxidant and ferrosilicon as the reducing agent in the exothermic mixture, all of the silicon can be. oxidized. With a small excess of silicon over this amount, some silicon will enter the metal.

Following are examples showing specicl embodiments of my invention.

Example I A low grade chromite ore was reduced with carbon in a submerged arc electric furnace to obtain ferrochromium metal containing substantially all the chromium and iron of the ore. This metal was ground with lime in a ball mill to a fineness of 100 mesh and roasted for about one hour and a half at a maximum temperature of 1350 C. with stirring in a reverberatory furnace to obtain complete oxidation of .the metal and contained carbon. An artificial chromite, calcium ferrichromite, was obtained. It contained only a trace of carbon. This roasted product was ground together with ferrosilicon toa neness of 100 mesh and the mixture was fed in packages to a bath of molten steel in an electric furnace. 'I'he mixture underwent a smooth exothermic reaction deliver-ing molten metal in the form of globules and the feeding was stopped when suilicient chromium was added to the steel. The alloy formed contained 18.7 per cent chromium and carbon under 0.1 per cent; this carbon coming partly from that in the steel and partly from the ferrosilicon.

In the above example the low grade chrome ore analyzed:

= Per cent CnO; 13.85 Iron oxides (calculated as FeO) 12.00 MgO 21.18 S105 35.70 A110; 2.02 CO; (ignition loss) 14.30

nl The ferrochromium obtained in melting this ore was 42 per cent chromium, 48 per cent iron, 7 per cent carbon and 3 per cent silicon. Roasting this metal. ground and mixed with about equal weight oi' limel produced'au artificial chromate of the following composition:

Per cent CnO; 26 FezO: 29 CaO 42 S: 2.7 Carbon Trace In utilising this low carbon roasted product (containing per cent available oxygen) for making .E 18 per cent chromium steel, 236 parts of the I.' weight) and 2.2 per cent CrzOn. 'Ihe chromium recovery from the ferrochromium metal was about 94 per cent.

Example II 0. To make chromium steel from roasted ferrochromium and ferrosilicon alone, the 42:48 ferrochromium obtained from low grade chrome ore as in Example I was ground in a proportion of 100 parts with 434 parts lime and roasted in a gas-fired rotary kiln at l300 C. to form 563 parts of carbon-free calcium ferrichromate. This was ground lwith 264 parts ferrosilicon (50 per cent Si) and mixed with 269 parts powdered sodium chlorate. The mixture was ignited in a refractory container by a small thermite charge. A smooth and vigorous exothermic action took place, the mixture converting itself into 218 parts of molten chrome-iron metal containing 17.4 per cent Cr and a lime silicate slag in which the CaO-SiOz ratio was around l.5:l. The slag contained less than l per cent CrzOa.

In this operation, the amount of ferrosilicon vwas suilicient to reduce all the iron and chromium of the roasted chromite and to react with the NaClOx of the mixture, forming NaCl which was volatilized in the reaction. 'Ihe silicon in the chrome steel product was less than 0.5 per cent and the carbon less than 0.1 per cent.

Example III A high carbon ferrochromium made by total reduction of a substandard chrome ore, and containing 61 per cent Cr, 8 per cent C, 3 per cent Si and approximately 28 per cent Pie, was ground and mixed with lime and soda ash in a proportion of 132 parts lime and 5 parts soda per 100 parts metal and the mixture was roasted on an open hearth for about an hour at a temperature of about 750 to 875 C. The roasted product was a j chromated chromite, substantially carbon-free,

containing 28 per cent CrOa, 10 per cent CrzOa, 14 per cent FezOa, 44 per. cent CaO, 1 per cent NazO and 2 per cent S102. AThis material contains 22 per cent chromium, about 10 per cent iron and 20 per cent available oxygen as CrOa. CrnO: and FezOg. The roasting converted some 69 per cent of the chromium to chromate and 31 per cent to' chromite. When this oxidized material is ground and mixed with 35 per cent by weight of 50 per cent ferrosilicon and the mixture ignited, it converts itself into a low-carbon metal,

44 per cent Cr and 55 per cent Fe and a lime silicate slag; one hundred parts of oxidized ferrochromium and 35 parts ferrosilicon becoming about 50 parts metal and 85 parts slag. In adequate quantity the mixture produces freerunning molten metal and slag.

'Ihe exothermic mixture' of Example IlI may be ignited by adding it to a bath of molten iron or steel in relative quantity such as to dilute the chromium content to that wanted in the finished alloy. Or the mixture may be reacted in a separate furnace and the molten metal product run into the steel furnace. In a particular instance a chromated chromite admixed with ferrochromesilicon was added in steel drums to a 65 ton open hearth steel heat after the carbon elimination. About 20 minutes after addition of 6800 pounds of the chromite mixture, the steel was tapped with a chromium content of 1.2 per cent, representing a recovery of 85 per cent of the chromium contained in the Silico-thermic mixture. Any desired quantity of such mixture may be added without raising the silicon content of the steel.

I have also utilized a material composed of roasted ferrochromium and ferrochrome silicon in intimate admixture for putting chromium into cast iron in a 50 pound foundry ladle, at the same time diluting the'carbon and silicon contents of the cupola metal and also raising the temperature of the metal somewhat, which facilitated the casting operation. Increasing the strength of the cast iron by some 43 per cent was an important result. making is possible to vary the castings by ladle additions. The diluting action of the hot ferro-metal added by exothermic action is a function of the iron oxide formed in roasting ferrochromium as well as of the iron in the silicon alloy. For this function, a roasted low grade ferrochromium high in iron is particularly adapted, further dilution being effected.' if desired, by iron oxide and ferrosilicon added to the exothermic mixture.

The reaction mixtures or composite reagents of the invention employing oxidation products produced through the use of soda ash as an oxygen promoter may be formed into very strong briquettes merely by wetting the material with water in an amount equal to about 6 per cent of the weight of materials of the reaction mixture, forming the desired shapes, and baking 'the shapes at temperatures in the range 200 C. to 600 C. to drive off the water. The sodium chromate formed by reaction of the soda ash with chromic anhydride produced during the oxidizing treatment appears to form the elective bonding agent. Apparently, the sodium chromate picks up water of crystallization which enters crystals as elimination of water proceeds in baking, which crystals form interlocking structures briefly during baking and are dehydrated subsequently. leaving, in eilect, a rigid sintered mass.

The oxidized products and the composite reagents'of the invention may be used in producing u.

alloys containingiron and steel ot any composition which can be produced through the use of such products and reagents.

Following are some of the various alloys which may be produced through the use of the products and reagents of the invention:

(1) High chromium steels:

18-8 type Maximum carbon 0.25. Minimum carbon 0.08. Ball-bearing type 1.0% (II-17% Cr. Cutlery type .55.'?5% 0,-15-18 Cr.

2) cnromiummickemron '(austenmc) C si Mn ci Ni ou max.

0.25 1.25 0.75 8.60 0.20 0.50 4.00 10.00 0. 20 0. 50 0. 40 18. 00 0.25 2.50 0. 80 Z100 0. 20 0. 50 0. 60 20.00 0. 20 0. 50 0. 00 25. il) 0. 20 2.00 0. 60 25.00

(3) MISCELLANEOUS Elements in percentage of steel Type C Si Mn Cr Ni Al V 3% chromium .05-.25 .35 .40 4- 6 Turbine type .l2 .20 .40 l2-l3 .40 Cutlery type .35 .20 .35 12-13 Cutlery modliled type .70 .40 .45 16-17 Ball-bearing 1.05 .45 .40 16-17 P t alve t ter Ff?. .w 2.75 P t alve t iif2- l .c .90 l8% Cr iron l0 50 28% Criron.. .l5 .50 18-8 stainless .06. 20 50 This application is a continuation-in-part .of my prior copending applications Serial No. 165,417, filed September 23, 1937 and a continuation-in-part of application Serial No. 221,003, filed July 23, 1938. The production of chromate in accordance with my invention is described and claimed in my co-pending application Serial No. 256,559, filed February 15, 1939.

In the accompanying drawing, I have shown for purposes of illustration only, and not for purposes of limitation, a flow sheet illustrating several of the possible chromium recovery processes which may be carried out in employing the principles of the invention. Heavy lines have been employed to outline a complete chromium recovery process commencing with the treatment of chrornite ore initially and indicating the production ultimately of desirable chromiumbearing metal products. By means of broken lines, I have illustrated alternative oxidizing operations, and, in light lines, I have indicated the use of various oxidizing agents, other than those produced directly in the oxidizing operations, in forming reaction mixtures in accordance with the invention. The basic material and oxidation promoter employed in the oxidation operations may be added at any or all of the points indicated by the heavy solid lines.

What I claim is:

l. rihe method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms, and mixing the oxidized product in the solid state with a solid non- '-'arbonaceous reducing agent capable of reducing the oxidized forms of iron and chromium i'n the oxidized product to metallic iron and metallic chromium.

2. The method of producing a composite reagent suitable i'or use in the production of chromium alloys which comprises oxidizingcarbonbearing ferrochromium in a solid. finely divided condition and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms, and mixing the oxidized product with a solid, finely divided, non-carbonaceous reducing agent capable of reducing the oxidized forms ot iron and chromium in the oxidized product to metallic iron and metallic chromium.

3. The method of producing a composite reagent suitable ior use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, iinely divided condition and forming an oxidized product low in carbon and containing ferric oxide and chromic oxide, and mixing the oxidized product with a. solid, finely divided silicon-containing reducing agent and oxidizing material capable of developing by reaction with silicon a temperature higher than those resulting from reaction of ferric oxide and chromic oxide with silicon.

4. The method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, iinely divided condition and forming an oxidized product low in carbon and containing ferric oxide and chromic oxide, and forming a mixture containing (1) the ferrie oxide and chromic oxide of the oxidized product, (2) solid, ilnely divided ferro-silicon and-(3) oxidizing material capable of developing by reaction with silicon a temperature higher than those resulting from reaction of ferrie oxide and chromic oxide with silicon.

5. 'I'he method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, nely divided condition and in the presence of lime and forming an oxidized product low in carbon and containing calcium oxide in chemical combination with chromium oxide, and mixing the oxidized product with a solid, finely divided non-carbonaceous reducing agent capable of reducing the chromium oxide of the oxidized product to metallic chromium.

6. The method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, nely divided condition and in the presence of lime and forming an oxidized product low in carbon and containing calcium oxide in chemical combination with chromium oxideand forming a mixture containing the oxidized product and a solid, finely divided non-carbonaceous reducing agent whose oxidation reaction product is amphoteric or acid and which is capable of reducing the chromium oxide of the oxidized product to metallic chromium.

7. 'Ihe method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, nely divided condition and forming an oxidized product low in carbon and containing oxidized chromium a substantial amount of which is in the form of chromium trioxide, and mixing the oxidized product with a solid, finely divided, non-carbonaceous reducing agent capable of reducing the oxidized chromium to metallic chromium.

13.-The method of producing a composite reagent suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, finely divided condition and in the presence of lime and forming an oxidized product low in carbon and containing calcium oxide in chemical combination with oxidized chromium a substantial amount of which is in the form of chromium trioxide, and mixing the oxidized product with a solid, ilnely divided, non-carbonaceous reducing agent capable of reducing the oxidized chromium to metallic chromium.

9` 'I'he method of producing a composite reagent suitable for use in the production of chromium alloys which comprisessubjecting carbonbearing ferrochromium in separate operations to oxidizing treatments at elevated temperatures in the presence of lime to form (1) a product low in carbon and containing oxidized chromium largely in the form of calcium chromite and (2) a product low in carbon and containing oxidized chromium largely in the form oi calcium chromate, and mixing the chromite and chromate products in the solid state with a solid, non-carbonaceous reducing agent capable of reducing the chromite and chromate to metallic chromium.

10. The method of producing a composite reagent suitable for use in the production of chromium alloys which comprises subjecting carbonbearing ferrochromium to an oxidizing treatment and forming an oxidized product low in carbon and in which chromium is present largely in the form of chromic oxide, subjecting the oxidized product to a low-temperature oxidizing treatment in the presence of calcium oxide and soda ash to form a product containing chromate, and mixing the chromate-bearing product with a solid, finely divided, non-carbonaceous reducing agent capable of reducing to the metallic state the chromium contained in the chromate-bearing product.

11. A composite reagent suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, iinely divided condition produced by oxidizing carbonbearing ferrochromium and forming a product low in carbon and containing iron and chromium in oxidized forms and (2) a solid, non-carbonaceous reducing agent capable of reducing the oxidized forms of iron and chromium to metallic iron and metallic chromium.

12. A composite reagent suitable for use in the production of chromium Valloys which comprises (l) oxidized ferrochromium in solid, finely divided condition produced by oxidizing carbonbearing ferrochromium in solid, finely divided condition and forming a product low in carbon and containing iron and chromium in oxidized forms and (2) a solid, non-carbonaceous redu'cing agent capable oi' reducing the oxidized forms of iron and chromium to metallic iron and metallic chromium.

13. A composite reagent suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, finely divided condition produced by oxidizing carbonbearing ferrochromium in solid, finely divided condition and forming a product low in carbon and containing ferrie oxide and chromic oxide, (2) a solid, nnely divided silicon-containing reducing agent and (3) oxidizing material capable of developing by reaction with silicon a temperaananas condition and forming a product low in carbon and containing ferrie oxide and chromic oxide,

(2) solid, finely divided ferrosilicon and (3) oxidizing material capable of developing by reaction with silicon a temperature higher than those resulting from reaction of ferric oxide and chromic oxide with silicon.

15. A composite reagent suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, ilnely divided iorm produced by oxidizing carbon-bearing ferrochromium in solid, iinely divided condition and in the presence of lime and forming a product low in carbon and containing calcium oxide in chemical combination with chromium oxide and (2) a solid, finely divided, non-carbonaceous reducing agent capable of reducing the chromium oxide to metallic chromium.

16. A composite reagent suitable for use in the production of chromium alloys which comprises (1) oxidized ferrochromium in solid, finely divided form produced by oxidizing carbon-bearing ferrochromium in solid, finely divided condition and in the presence of lime and forming a product low in carbon and containing calcium oxide in chemical combination with chromium oxide and (2) a solid, finely divided, non-carbonaceous reducing agent whose oxidation reaction product is amphoteric 0r acid and which is capable of reducing the chromium oxide to metallic chromium.

17. A composite reagent suitable .for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, finely divided form produced by oxidizing carbon-bearing ferrochromium and forming a product low in carbon and containing iron oxide, chromic oxide and a substantial amount of chromium trioxide and (2) a solid, finely divided, non-carbonaceous reducing agent capable of reducing the oxides of iron and chromium to metallic iron and metallic chromium.

18. A composite reagent suitable for use in the production of chromium alloys which comprises (1) oxidized ferrochromium in solid, finely divided form produced by oxidizing carbon-bearing ferrochromium in solid, finely divided condition and in the presence of lime and forming a product low in carbon and containing calcium oxide in chemical combination with chromium oxide in which a substantial amount of the chromium is present in the form of chromium trioxide and (2) a solid, non-carbonaceous reducing agent capable of reducing the chromium oxide to metallic chromium.

19. A composite reagent suitable for use in the production of chromium alloys comprising (l) a product containing oxidized chromium in which the chromium is present largely as calcium chromate, (2) a. product containing oxidized chromium in which the chromium is present largely as calcium chromite, said products containing calcium chromate and calcium chromite being products resulting from oxidation treatments of carbon-bearing ferrochromium, and (3) a solid, noncarbonaceous reducing agent capable oi reducing the chromite and chromate to metallic chromium.

20. A composite reagent suitable for use in the production of chromium alloys, formed by grinding a non-carbonaceous reducing agent in the presence of oxidized ferrochromium produced by oxidizing carbon-bearing ferrochromium at a in and being substantially free of uncombined.,

calcium oxide, the non-carbonaceous reducing agent being capable of reducing the iron oxide and the chromium oxide to metallic iron and metallic chromium and being present in an amount about suiiicient to reduce all of the chromium and iron present.

21. A composite reagent suitable for use in the production of chromium alloys, formed by grinding a non-carbonaceous reducing agent in the presence of oxidized ferrochromium produced by oxidizing carbon-bearing ferrochromium at a temperature below its melting point and forming a product containing iron oxide and containing calcium oxide in chemical combination with chromium oxide, said productcontaining an amount of calcium oxide sufclent t0 combine with all of the chromium oxide contained therein and being substantially free of uncombined calcium oxide, the non-carbonaceous red-ucing agent being capable of reducing the iron oxide and the chromium oxide to metallic iron and metallic chromium and being present in an amount about sufficient to reduce all of the chromium and iron present, and the major portion of said composite reagent consisting of particles small enough to pass a 10D-mesh screen.

22. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium chromate intimately mixed with a solid, nely divided, non-carbonaceous reducing agent capable of reducing to 4the metallic state the chromium of the calcium chromite and calcium chromate.

23. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite, calcium chromate and sodium chromate intimately mixed with a solid, nnely divided, non-carbonaceous reducing agent capable of reducing to the metallic state the chromium of the chromite and chromate compounds.

24. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium chromate intimately mixed with a solid, nely divided silicon-containing reducing agent.

25. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium chromate intimately mixed with a finely divided, solid, non-carbonaceous reducing agent, the amount of chromium present in the mixture in the form of chromate being not substantially greater than the amount of chromium present in the mixture in the form of chromite.

26. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium chromate intimately mixed with a ilnely divided, solid, silicon-containing reducing agent, the amount of chromium present in the mixture in the form of chromate being not substantially greater than the amount of chromium present in the mixture in the form of chromite.

27. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, whichcomprises calcium chromite. calcium chromate, and sodium chromate intimately mixed with a finely divided, solid, non-carbonaceous reducing agent, the amount of chromium present in the mixture in the form of chromate being not substantially greater than the amount of chromium present in the mixture in the form of chromite.

28. A composite reagent suitable for use in the production of a metallic chromium-bearing product by exothermic reaction which consists essentially oi' calcium oxide, ferric oxide, sodium oxide, chromic oxide and chromium trioxide intimately mixed with a silicon-containing reducing agent, the amount of chromium present in the mixture in the form of chromium trioxide being not substantially greater than the amount of chromium present in the mixture in the i'orm of chromic oxide:

29. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium `chromate intimately mixed with a nely divided silicon-containing, reducing agent, the amount of chromium present in the mixture in the form of. chromate being not substantially greater than the amount of chromium present in the mixture in the form of chromite and the silicon and the oxygen available for reaction with the silicon being present in such amount and proportion that the mixture is capable upon ig-- nition of converting itself by exothermic reaction into molten chromium-bearing metal and molten calcium silicate slag.

30. A composite reagent suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite, calcium chromate and sodium chromate intimately mixed with a finely divided silicon-containing reducing agent, the amount of chromium present in the mixture in the form of chromate being not substantially greater than the amount of chromium present in the mixture in the form of chromite and the silicon and the oxygen available for reaction with the silicon being present in such amount and proportion that the mixture is capable upon ignition of converting itself by exothermic reaction into molten chromium-bearing metal and molten calcium silicate slag.

3l. A product suitable for use in the production of metallicl chromium comprising calcium chromite and calcium chromate and containing an amount of chromium in the form of chromate not substantially in excess of the amount present in the form of chromite.

32; A product suitable for use in the production of metallic chromium comprising calcium chromite, sodium chromate and calcium chromate and containing an amount of chromium in the form of chromate not substantially in excess of the amount present in the form of chromite.

33. A product suitable for use in the production of a metallic chromium-bearing product, consisting essentially of calcium oxide, ferric oxide. sodium oxide, chromic oxide and chromium trioxide and containing an amc-unt of chromium in the form of chromium trioxide not substantially in excess of the amount present in the for of chromic oxide.

34. The method of producing a metallic alloy containing iron and chromium which comprises igniting a compositereagent comprising (l) a product 1o the 'solid omo produced by oxidizing carbon-bearing ferro-chromium and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms and (2) a solid, non-carbonaceous reducing agent capable of reducing the oxidized forms of iron and chromium in the oxidized product to metallic iron and metallic chromium. l

35. The method of producing a metallic alloy containing iron and chromium which comprises igniting a composite reagent comprising (1) a product in the solid state produced by oxidizing carbon-bearing ferro-chromium and forming an oxidized product low in carbon and containing calcium oxide and iron and chromium in oxidized forms and (2) a solid, finely divided, silicon-containing reducing agent.

36. The method of producing a metallic alloy containing iron and chromium which comprises igniting in contact with molten metal a composite reagent comprising (l) a product in the solid state produced by oxidizing carbon-bearing ferrochromium and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms and (2) a solid, non-carbonaceous reducing agent capable of reducing the oxidized forms of iron and chromium in the oxidized product to metallic iron and metallic chromium.

37. The method of producing a metallic alloy containing iron and chromium which comprises igniting in contact with molten metal a composite reagent comprising (l) a product in the solid state produced by oxidizing carbon-bearing ierrochromium and forming an oxidized product low in carbon and containing calcium oxide and iron and chromium in oxidized forms and (2) a solid, ilnely divided, silicon-containing reducing agent.

38. In a process of producing a low-carbo chrorniferous metal, the steps which comprise oxidizing a high-carbon ferrochromiumalloy to get rid of carbon and convert the metal content thereof to oxide form, thereby producing a ferrous chromite product, selectively reducing iron oxide therefrom in thev presence of lime to form a product containing calcium chromite, and reducing the calcium chromite product with a non-carbonaceous reducing agent.

39. Areaction mixture comprising (l) asilicon- -containing reducing agent, (2) oxidized ferrochromium produced by oxidizing carbon-bearing ferrochromium in solid, iinely divided condition and forming a product low in carbon and containing iron and chromium inoxidized forms and (3) lime in an amount such u to provide about 1.5 to 2.0 molecules of calcium oxide for each atom of silicon in the mixture.

40. The method oi' producing an alloy containing iron and chromium which comprises smelting chromium-bearing ore with carbon to produce high-carbon ferrochromium, oxidizing the highcarbon ferrochromium and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms, and reducing to the metallic state the iron and chromium of the oxides oi' iron and chromium contained in the oxidized product with a non-carbonaceous reducing agent to produce a metallic alloy containing iron and chromium.

41. The method of producing an alloy containing iron and chromium which comprises smelting chromium-bearing ore with carbon to produce high-carbon ferrochromiurn, oxidizing the high-carbon ferrochromium and forming an oxidized product low in carbon and containing iron and chromium in oxidized forms, and reducing to the metallic state the iron and chromium oi the oxides of iron and chromium contained in the oxidized product with a silicon-containing reducing agent to produce a metallic' alloy containing iron and chromium.

42. The method of producing an alloy containing iron and chromiuml which comprises smelting chromium-bearing ore with carbon to produce high-carbon ferrochromium, oxidizing the highcarbon ferrochromium and forming an oxidized product low in carbon and containing iron and chromium-in oxidized forms, and reducing to `the metallic state the iron and chromium of the oxides oi.' iron and chromium vcontained in the oxidized products with an aluminum-containing reducing agent to produce a metallic alloy containing iron and chromium.

43. 'I'he method of producing an alloy containing iron and chromium which comprises smelting chromite ore to eiect selective reduction of iron contained therein with the production of a metal product high in iron and low in chromium and a benetlciated ore product high in chromium and low in iron, smelting the beneciated ore product with carbon to produce high-carbon terrochromium, oxidizing the high-carbon ferro'- chromium and forming an oxidized product low in carbon and containing oxides oi' iron and chromium, and reducing to the metallic state the iron and chromium of the oxides of iron and chromium contained in the oxidized product with a non-carbonaceous reducing agent to produce a metallic alloy containing iron and chromium.

44. The method of producing an alloy containing iron and chromium which comprises smelting chromite ore to eiIect selective reduction of iron contained therein with the production of a metal product high in iron and low in chromium and a benenciated ore product high in chromium and low in iron, smelting the beneflciated ore product with carbon to produce high-carbon ferrochromium, oxidizing the high-carbon ferrochromium and forming an oxidized product low in carbon and containing oxides oi iron and chromium, and reducing to the metallic state the iron and chromium oi' the oxides of iron and chromium contained inthe oxidized product with a silicon-containing reducing agent to produce a metallic alloy containing iron and chromium.

45. 'Ihe method o! producing an alloy containing iron and chromium which comprises smelting chromite ore to efi'ect selective reduction of iron contained therein with the production of a metal product high in iron and low in chromium and a benetlciated ore product high in chromium and low in iron, smelting the beneilciated ore product with carbon to produce Vhigh-carbon ferrochromium, oxidizing the high-carbon ferrochromium and forming an oxidized product low in carbon and containing oxides of iron and chromium, and reducing to the metallic state the iron and chromium of the oxides of iron and chromium contained in the oxidized product with an'aluminum-containing reducing agent to produce a metallic alloy containing iron and chromium.

MARVIN J. UDY.

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