US2986459A - Metallurgical process - Google Patents

Description

y 30, 1961 M. c. UDY 2,986,459

METALLURGICAL PROCESS Filed Dec. 4, 1959 Chromite Ore or Concentrate or Blended Iron Oxide-Chromite h ro m }je Qrg Reduction Burden Hon (ire Essential Carbonaceous i Fluxes Reductant i I Calcining and I Calcining and {I Calcining and I: Pre-Reduction Pre-Reduction Pre-Reduction l Umt Umt Umt l l Stabilized, Free- Stabilized, Free- Stabilized, Free- Flowing Sinter Flowing Sinter Flowing Sinter Carbonaceous Carbonaceous Reductant Smelting Smelting Reductant Furnace Furnace Waste High- Carbon Low- Carbon Chromium Waste Slag Iron-Chrome Metallic Oxide Slag Alloy lron Slag Holding or Blending Furnace Chromium-Iron Master Steel Alloy Low C and Si Oxygen or Non-Carbonaceous oxide Reductant Steel Refining (return of oxidized Furnace chromium or manganese v Alloying to metallic phase) l l Adjustments Finished Slag to 'NVENTQR Steel to M|ll Waste Murray C. Udy

United States Patent 2,986,459: METALLURGICAL PROCESS Murray C. Udy, Niagara Falls, N.Y., assignor to Strategic-Udy Metallurgical and Chemical Processes, Ltd., Hamilton, Ontario, Canada- Filed Dec. 4, 1959, Ser. No. 857,293 9 Claims. CI. 75-40 This invention relates in general to'metallurgy and has ior its principal object the provision of a' new and improved process for producing chrome-iron alloys of con trolled silicon-carbon contents and special grades of finished steels directly from chromite ores and concentrates, including conventional high-grade ores,-m-arginal and low: grade chromite ores of chromium-toiron ratios as low as 0.5 to 1.0, and various physical mixtures or blends of iron oxideand chromium oxide-bearing materials as shown by the accompanying flow sheet. Specifically, the invention involves the provision of a unique carbothermic reduction of either raw or previously concentrated materials of the general class'defined for the production and recovery of valuable low-carbon chrome-iron master alloys which can be processed to provide a wide variety of finished steels including, by way of illustration, straight ferritic or maltensitic chromium steels of the Series 400 and .5 types, austenitic nickel-chromium stainless steels of the so-called Strauss or Series 300 types, such as the popular 18-8 stainless steel, modified chromium-nickel .steels such as the silicon-containing Rezistal type of :austenitic alloys, low-chromium and chromium-vanadium toolsteels, manganese-chromium steels, and the like.- The accompanying flow sheet shows various modifica- .tions of the invention.-

Heretofore, it has been considered axiomatic that the processing of chromite ores and particularly low chromium-to-iron ratio oxidic reduction burdens should proceed via various preliminary beneficiation operations aimed at attaining intermediate products of chromium-to-iron ratios within ther-ange of from 3 to 5 parts chromium to each part iron, namely, products which are amenable .to

2,986,456 Patented May 30, 1961 2 chromium alloy of oil-grade or relatively low-chromium content,and a molten slag product of relatively enriched chromium oxide content containing iron in any desired proportion lower than that of the original raw charge material. In essence, in accordance with the process of said copending application, the initial smelting operation is conducted to adjust the chromeziron ratio within the slag to any j desired value according to the exact nature of the ferrochrome alloy sought to be recovered within a subsequent smelting operation or openations conducted with the chromium-enriched, i.e., iron degrade'd, slag recovered from the first stage, while at the same time placing the residual chromium oxide values present in the slag in con-- dition for substantially complete reduction and settlingout or recovery 'of' the metallic chromium from the ultimate wasteslag product produced in said subsequent treatment by existing methods for the production of high have been directed to methods for rendering thelow-gradechromites amenable for treatment via techniques developed and adopted by industry in conjunction with the processing of high-grade chromite ores to steelmaking ferroalloys. For example, .in copending United States application Serial Number 731,993, which was filed by.

Marvin I. Udy on April 30, 1958, now Patent No. 2,934,- 422, granted April 26, 1960, there are described and claimed a series of related processes which are directed to the multi-stage smelting of chromite-bearing materials for the production and recovery'of so-called standard grades of ferrochromium. In accordance with the proc-.

esses of said copending application, a natural chromite ore or concentrate of relatively low Cr-zFe ratio is beneficiated for ultimate use in the production of ferrochromium alloys by an initial carbothermic smelting operation, conducted for the selective reduction and removal of ex-.

cess iron present in the ore or concentrate, with the production and recovery of low-carbon metallic iron of controlled low-chromium content or a high-carbon ferrosmelting operation or operations. In processing the residual chrome-enriched slag from the first stage forthe production of high-carbon and medium-carbon ferrocliromium products, a second smelting operation is required whereas, if the enriched slag is to be processed to low carbon ferrochromium, two or even three additional stages any attempted .direct or even selective carbothermic re-.

duction type of operation.

It has been postulated that non-carbonaceous reductants such as ferrosilicon or ferrochrornium siliconcan be employed to maintain carbon specifications within tolearble boundaries, but experience demonstrates that when low-silicon contents are also desired, aswould be the case in most any steehn-aking operation since the silicon content of the melt must be oxidized into the slag before decarburiza-tion can be effected, this type of reductant must be employed in deficient amounts, i.e., in quantities less than the stoichiometric requirements of the contained iron oxide and chromium oxide contents of the starting ma-.

terial, with the result that a consequent sacrifice in the yield of metal obtained becomes necessary. Needless to say, such a sacrifice becomes impossible, economically, when one is concerned with the marginal or low-grade chrome-iron starting materials.

In order to understand the full significance of the process of my invention, it is essential to understand current industrial practices with respect to. the production of,

stainless steels. Thus, with very few exceptions the production of ferroalloys employed in steelmak-ing is effected.

independently of the steelmaking operation, per -se, but in any event, the ferroalloy producer devotes considerfor use in the production of Series 300 steels. plained hereinbefore, much of the expense incidental to the production of these steelmaking alloys exists with respect to the simple procurement of raw materials which are suitably deficient in iron or at least favorably constituted for the elimination of excess iron, but this fac tor is actuallyof no basic importance since the steel maker must ultimately introduce iron into his melt to produce any of the commercially important stainless steels. That is to say, while the ferroalloy producer goes to considerable added effort and expense to provide relatively low-iron alloys of base constitution corresponding to the alloying metals chromium and nickel, for example,

the steelmakers ultimate use of these alloys is predicated upon iron dilution practices which almost invariably reestablish their end-products as iron base alloys.

Considering the faetthat the cost of the contained chromium in low-carbon .ferrochromium, for example, currently ranges from about 3.71m 41 cents per pound, and the cost of contained nickel in equivalent ferroniclirel alloys currently ranges from about 60 cents to over one dollar per pound, it becomes abundantly clear why the production of stainless steels by existing methods represents such a costly undertaking. In addition to these initial production costs, it is customary for the steelmaker to'oxidize substantial carbon out of the steel melt by means of ore or oxygen which results in oxidation of appreciable chromium into the slag phase. To recover these values following decarburization and refining of the melt, the steelmaker must then use various expensive deoxidizing or reducing agents such as silicon metal, ferrosilicon, aluminum, etc. The combined efiectof the use of high-grade starting materials, strict adherence to socalled standard alloys, and the extensive refining and post-refining reduction operations practiced by. the steelmaker hasbrought the most common stainless steels to current price levels within the range of from 350 to 600 dollars per' net ton, even in semi-finished slab or billet forms.

It its broadest aspect, the process of my invention is directed to the provision of a unique tandem stage reduction technique for the treatment of chromite ores or admixed chromite and iron oxide-bearing materials of virtually any chrome-iron ratio to derive a low-carbon stainless steel master alloy of predetermined iron and chrocontents corresponding substantially to the precise proportion of these metals desired in aparticular grade of finished steel. In other aspects, and particularly those pertaining to the utilization of extremely low chrome-toir'on ratio starting materials, the invention departs from existing conventions which dictate that these materials must- -be processed initially to standard grades of ferrochromium, and provides via a tandem reduction smelting arrangement "a chromium-iron alloy which may be processed directly within aiconventio'nal steelmaking furnace to produce virtually any type offinished steel. Common to all aspects 'of my invention is the utilization of a unique tandem reduction technique in whichl a portion of a combined oxidic'reduction burden of chromium and iron is subjected to c arbothermic reduction to derive an ironchromium alloy of relatively high-carbon content, whereias the remainder of said reduction burden is simultaneously subjected to carhothe-rmic reduction to derive metallic iron of low-carbon content and a chrome-rich slag for recycle to the iron-chromium alloy-production stage of the tandem reduction cycle. The metallic products of the two furnaces are'then recombined in molten form to provide arelatively low-carbon master alloy of iron and chromium which may be processed directly by stand:

ard procedure sor refining to produce stainless steel "of:

any desired composition;

Essentially, the process of the invention is based, ,at

least in part, on the observation that whereas carbon control isdiflicult to achieve under. conditions involving the simultaneous directreduction of bothchromium oxide and iron oxide and generally necessitates sacrificing a portion of the total available" chromiumto the slag phase, carbon control to extremely low values can be read} ily maintained in the selective, reduction of iron only from such a mixed oxidic reduction burden. In accordance with a preferred process of the invention, the aforementioned phenomena are utilized toipermit.maximumfchromium re duction with iron from one fraction of a mixed chromium oxide-iron oxide reduction burden of natural or. synthetic t n dlf igin; w thout r ga d. o c on mam,

subjected to selective carbothermic reduction to produce low-carbon metallic iron or semi-steel. The metallic products of the tandem direct and selective reduction operations are then recombined in proper proportions to yield a controlled carbon content master alloy of chromium and iron ratio approximately equivalent to the precise proportions desired in the final steel product, namely, alloys ranging from .60-90 percent iron and 10- 40 percent chromium. The reconstituted master alloy requires only mild refining and alloying additions, as desired, to yield virtually any grade of'finished steel. To provide a balanced, closed system with respect to total incoming chromium values, the chromiumrich slag produced in the iron production phaseof the tandem reduction operation is'recycled, preferably in molten form, to the direct reduction stage for addition to its fraction in the production of further quantities of the high-carbon iron-chromium alloy.

It is believed that the foregoing process measures may behest understood by reference to the following detailed description of specific embodiments of the invention taken in conjunction with the accompanying drawing, wherein the single figure constitutes a schematic flow diagram or flow sheet illustrating the exact sequence of steps or operations involved in the processing of a typical iron oxidechromiurn oxide reduction burden to a finished stainless or corrosion-resistant steel.

In the practice of the process of my invention, a

- chromite ore or concentrate, or such a material blended necessary fluxing additions, and the combined mass is tion of the resulting iron-chromium product produced,

this the smea s. its sites was use i then calcined to produce a substantially stabilized reduction burden of predetermined base-acid ratio. In either event, I prefer to follow the unique fluxing techfliql es described in the above-mentioned US. Patent to Marvin I. Ucly, although the base-acid ratios of the slag systems of the present invention may be constituted at optimum values anywhere within the range of from one to twoand-one-quarter (LO-2.25) parts by weight base (calculated as MgO and excluding iron oxide) to each part by weight of silica, and entirely satisfactory results are obtained.

l The iiuxed charge is calcined by heating within any suitable apparatus, such as a rotary kiln, for example, to establish it at. the maximum possible temperature for a free-flowing consistency, without overheating to the extent that the charge will form rings within the kiln. Ordinarily, this can be accomplished quite readily by heating the charge to a temperature within the range of from 1100to 1300 C. Of course, the split char ges can be melted directly within the tandem electric furnaces, but

I find that the use of a kiln with gas, oil, coal or even waste gases from an electric furnace, provides a more economical operation as compared with theuseof. electrical energy exclusively. Furthermore, I prefer to operate within the successive smelting and refining stages of the process of the invention with molten charge from a preceding stage in order to further economize on power consumption by avoiding the necessity for remelting these materials I also find it to be advantageous to practicesorne pre -reduction. within the kiln by the direct addition of .a portion of the overallcarbonaceous reducan the k n a e nsistsat lfr e, ith the p mary objective of maintaining through-put the kiln for supplying the tandem electric furnaces or equivalent smelting units on a conti ous basis. Breredu ti n f chmmium O i lihq f l,

but it is found that from 33-60% oxygen removal can be eifected in the kiln while maintaining good throughput and avoiding any significant reduction of the chromium oxides contained in a reduction burden. 1

The hot, free-flowing partially reduced material discharged from the kiln is subdivided into two approximately equal-weight fractions. This subdivision and, in turn, the respective loads on the tandem furnaces can be regulated in accordance with the chrome-iron ratio of the original material, as modified to the extent that any blending is practiced in the formation of the iron oxidechromium oxide charge material. The fraction to be treated by direct and substantially total reduction for" the production ofthe iron-chrome alloy is charged to the smelting zone of one of the tandem electric furnaces maintained at a temperature within the range -offrom 1450-1750 0., together with additional quantitiesofa -carbonaceous reductantinan amount suflicient to effect reduction to the metallic state of all of the-chromium oxide and iron oxide contained therein. The resulting metal product will have a chromium-iron ratio corresponding to that of the original ore or blended ores, but upgraded with respect to chromium content to any desired extent by reason of the additional chromium oxide values recycled from the tandem furnace operating on the selective reduction cycle for low-carbon iron. In view of the fact that the former furnace is operated for maximum chromium recovery in the metal phase, the carbon content in the iron-chrome alloy recovered will normally range upwards to 6 percent. Where justified for any specific starting material, a lower carbon content can be achieved in the iron-chrome alloy by leaving a portion of the chromium oxide content in the residual waste slag produced in this furnace. In general, however, by reasons of the ease of carbon control attained through practice of the dilution technique of the invention, I prefer to effect maximum chromium reduction in thisphase of the tandem operation.

The remaining fraction of the kiln sinter is supplied to the smelting zone of the second tandem furnace, which is also maintained at a temperature within the range of from l450l750 C., together with a controlled quantity of carbonaceous reductant sufiicient to effect the selective reduction to the metallic state of the major. portion of the iron contained therein. In this connection, it is to be noted that in a reduction operation of the class. described the metallic phase product can be maintained .substantially free of carbon contamination until the e uaLirQn in. the Pha t fi hsaa is?! equivalen tna proximatq 6 w e er te c n i reduction of the charge under action of a carbonaceous reducing agent results in slight gradual carbon contamination of the metal until a residual level of approximately 3 4 percent iron-is reached in the slagphase, but attempted carbonaceous reduction beyond this 3-4; percent iron residue results in. rapid carbon contamination of the metal. Within the range 3-8 percent iron unreduced in the slag, it is generally found that the major portion of the chromium is likewise retained in oxide form within the slag. At the upper limits of this range, namely, 6-8 percent residual iron, it is possible to achieve carbon control within the range of from 0.2 to 0.5 percent, with a simultaneous low-chromium content within the metallic iron phase product. Of course, provided the full production of the tandem iron furnace is to be utilized for dilution of the carbon content in the highcarbon iron-chrome alloy from the other tandem furnace, it is relatively immaterial whether the iron product also contains a portion of the chromium in metallic form and, under these circumstances, the selective reduction is simply continued to the maximum possible limit consist- .ent with the.carbon..level :desired in the metal phase.

On" the .otherhand, .it sometimes proves desirable to -.bleed a portion of the total iron productionout of the system for marketing or for use in theproduction of car-hon steel and, under'such circumstances, it is equally desirable tomaintain alow-chromi'um content in the output'product fromthe selective reduction or-iron tandem furnace.- These objectives" can be obtained by operating the iron-furnace at-yarious residual iron levels within the range'f'rom' 3 to 8 percent, in that, both the carbon'and chromium contents of the iron can be ex pected to increase as the reduction is carried below the upper-limits of this range. a

The metallic phase products from the tandem furnaces, or any portion of theseproducts, are 'brought togetherin molten form in theprecise ratio desired in the final steel product soughtto be produced. ;-'Ihis blending or carbon dilution operation will generally result in the production of a composite master alloy-of carboncontent within the range of from 0.3 to 1 .5 percentyand a silicon content within the range'of from 0. 1 to 0.5 percent. Thus, since the high-carbon chromium-iron alloy is diluted to an ironbase alloy, in lieu of the conventional chromium-base alloys presently used in steel making, it is entirely possible to reduce the carbon content in the composite master alloy to mediumand low-carbon values. Preferably, the'blending or'dilution operation is conducted within an intermediate holdingfurnace or directly within-the steel refining unit of the system. 1 1 i The master alloy recovered from the holding furnac or formed 'in'situ in a refining furnace of the electric, open-hearth or converter types, is blended with any alloy ing additions, i.e., nickelfferronickel, manganese, etc., required in accordance withthe particular type of steel being produced. The refining or finishing unit is operated in conventional fashion to effect decarburization of the metal and adjustments are made for silicon content, Where desired, and the like. Undesirable constituents can be removed during the refining melt or other constituents maybe added to obtain the desired grade specifications for the steel produced. Chromium adjustments can be made directly during the finishing heat by oxidizing any excess chromium into the slag. On the other hand, assuming a correct chromium balance has been obtained in the initial smelting and blending operations conducted towards the production of the master alloy, it is desirable, following completion of the oxygen decarburization in the finishing furnace, to treatthe melt with a small quantity of 'a noncarbonaceous reducing agent to return to the steel any, chromium oxidized into the slag phase during the oxidation reactions. Thefinished steel is then recovered from the steel furnace and is treated by conventional working methods for conversion to consumer products.

As will be readily-appreciated,; in lieu of the alloying additions to the refining furnace, any alloying metals other than the iron and chromium contents of the master alloy required in' the finished steel could be carried into the master alloy in whole or in part by direct reduction from .an oxidic additive to. the original oreor blended-ore frac; tion charged to the iron-chrome smelting furnace. For example, if a nickel-chromium stainless steel is' desired, a nickel-iron or nickel ore could be blended with the chrome-iron fraction chargedto the allow-furnace as a combined source of nickel and iron. The nickel would be reduced initially to form a ferro nickel'alloy, whereas continued reduction would provide a metal phase product or crude high-carbon alloy of combined iron, nickel and chromium contents for ultimate blending with the lowcarbon iron produced in the secondtandem furnace. The resulting crude alloy would then be subjected'to the same treatment as'described hereinbefore in connection withthe basichigh-carbon iron-chromium alloyr componentof the invention. g g

' In the operation of the tandem smelting stages of the process of the invention, .I prefer to, employ a carbonaceousreducing agent suchas bituminous or anthracite coals, lignites or lignite chars; coke' breeze, or coke, etc. The carbonaceous reductants need not beI-;.pr.0cesed t0. any

-7 particular o m and... tart. fine t und. o. be admin ably su ted tor-u e n he p oces L While' he aromas can bepra iaed; incqninn tion with y yp o smel n equ n en 'I; p f t mp y a e n: e ect ic fu nace ope ted-unde cond ons, o co b ned. arc-re istance a d; .s a r ie i tane he asl ev dth on h the m ntenance Qfirelat e y sh r r s s u kto. the; sur ace the nol er ag ba or by positioning the electrode tips in s-lightly submerged relaon h p w thin. h slag ha h... incomi harsemater i uppl d t h j ur ceo thefslag h around the peripher l po ions, o theufn t a c am n. order to maintain, he ar .z neas bstantia ly fr e o a mu ate charge, andhe tenters the. calci d char e d c ly from the heat d s ag a hincoutaat herew h.

In utiliz ng he ch om um xid s a r the o car on iron furnace to upgrade he o i fraction harged. to the hig a bona oy furna pr e o. a e ag n mol en torm r y. o he. e t na e. and t e a d. esi ter rac 'Qn nd'rer u ta necessary for the production of the iron-chromium metal.

- It will be read ly ppare to a y ki le metallurgist that; for particular types of chromite charge materials, it may. p e ben ficia to m ntain t hr mi n n ores separate through the tandem reduction phases of the process, bringing the endproducts of the two smelting furnaces together for the first time, in the blending of the l w-c rbon m ster. al oyhuseepa e e k ln n e utilized to feed one furnace with a sintered chromite ore and the other with a sintered iron ore, the first furnace operating on' total direct reduction. for the production of a high carbon chrome-iron alloy, with the second furnace also operating on direct reduction for the production of low-carbon iron or semi-steel. These products would then be blended to dilute the carbon content of the alloy with the production of the desired low-carbon master alloy. Under these conditions of operation, it becomes possible to eliminate the necessity for recycling the slag from the iron furnace to the alloy furnace. The exact sequence of steps involved in this type of operation has been indicated by the dotted line showing contained on the flowsheet. 7

It is believed that the proeess of the invention will be best understood by reference to the following specific examples str i t pp cat on o he foregoing P ciples and procedures to the. production of stainless steels from a typical low-grade oxidic starting material.

EXAMPLE I Charge analyses Chromite Concentrate, percent Iron Ore,

A chromite concentrate of the foregoing analysis, in amount 4540 pounds, was blended thoroughly with 4280 pounds of iron ore of the foregoing analysis and charged to a rotary kiln together with 1100 pounds of coal of about 70 percent fixed carbon content. The charge was preheated and prereduced in the kiln to provide a free-flowing sinter at 2250. F. which analyzed 11.2 percent chromium and 33.3 percent iron, with a carbon content of about 5.0%.

This sinter, in total amount 79l0 pounds, was. divided into two separate charges ot 27-10 pounds and 5200 pounds, respectively.

Metal (17851135.): j Percent Cr 31.1

C 6.0 Si 1.0 Fe Bal.

Slag (2848 lbs.):

Cr. 1.0 ,Fe 1.2

The second fraction of the kiln discharge, Weighing 5200 pounds was smelted in a second are electric furnace in the presence. of 250 pounds of'coal of 70 percent fixed carbon content to produce 2460 pounds of iron of 1,0 percent carbon content and a recyclable chromium oxide slag containing about 1.0 percent residual iron.

The 1785 pounds of high-carbon chrome-iron from the first tandem furnace and the 2460 pounds of low: carbon iron from the second tandem furnace were recombined in a steel refining furnace with a lime flux and blown with oxygen to produce 4080pounds of a stand- 'ard grade steel containing 19.7 percent chromium and 0.03. percent carbon.

EXAMPLE n Metal (1665 lbs): Percent Cr 52.0 C 6.0 Si 1.0 Fe Bal.

Slag (2140 lbs.)

Cr 1.7 Fe 1.0

A second kiln was charged with 4400 pounds of iron ore of the foregoing analysis, 600 pounds. of lime, and 900 pounds of coal (70% F .C.). The hot kiln discharge, in amount 4230 pounds, analyzing 57 percent iron and 5 percent carbon, was charged to a second electric furnacetogether with 290 pounds of coal (70% RC.) and smelted therein with the production of 2520 pounds of semi-steel of 0.5 percent carbon.

The 1665 pounds of chrome-iron from the first furmace and the 2520 pounds of semi-steel from the second furnace were combined in a steel refining furnace and blown with oxygen to provide 4050 pounds of steel of the following analysis:

"ffI-Iaving'thus described the subject inatter of'm-yin- Yentionjwhat it"'is"desired to secure byL'ettersPatent is: 1 Process for the'production'of alloyed steel from ores of; chromium oxide and iron oxide that; comprises, subj'ecting a firstore fraction ofmixedchromium and iron oxide contents tc-reduction smelting in the presence of a carbonaceous reducing agent in an amount suificient to efifect reduction to the metallic state'of substantially alloftheiron oxide and chromium oxide contained therein with the production of a crude high-carbon iron-chromium alloy and a waste slag product, subjecting a second ore fraction containing a predominant proportion of iron oxide to reduction smelting in the presence of a carbonaceous reducing agent in an amount controlled to effect the selective reduction to the metallic state of the major portion of the iron oxide content thereof with the production of low-carbon metallic iron, blending said highcarbon iron-chromium alloy with said low-carbon metallic iron to provide a master alloy of controlled intermediate carbon content, and refining said master alloy as necessary for the production and recovery of a chromiumalloyed steel product.

2. The process as claimed in claim 1, wherein said first ore fraction is a chromite ore and said second ore fraction is an iron ore.

3. The process as claimed in claim 1, wherein said first and second ore fractions are each formed by blending a chromite ore with an iron oxide ore, there being recovered a chromium oxide-containing residual slag from said reduction smelting of the second ore fraction, and said slag is recycled to the reduction smelting operation conducted on said first ore fraction.

4. Process for the production of alloyed steel from a complex material comprising iron oxide and chromium oxide that comprises fluxing said material to form a composite reduction charge, subjecting a first fraction of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount sufficient to effect reduction to the metallic state of substantially all of the iron oxide and chromium oxide contained therein with the productionof a crude high-carbon ironchromium alloy and a waste slag product, subjecting a second fraction of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount controlled to effect the selective reduction to the metallic state of the major portion of the iron oxide content thereof with the production of low-carbon metallic iron and a chromium oxide-containing molten slag product, recycling said chromium oxide-containing molten slag to the reduction smelting stage operating on the first fraction of said charge, blending said high-carbon iron-chromium alloy with said low-carbon metallic iron to provide a master iron-chromium alloy of controlled intermediate carbon content, and refining said master alloy as necessary for the production and recovery of a chromium-alloyed steel product.

5. Process for the production of alloyed steel from a complex material comprising iron oxide and chromium oxide that comprises fluxing said material to form a composite reduction charge, subjecting a first fraction of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount suflicient to effect reduction to the metallic state of substantially all of the iron oxide and chromium oxide contained therein with the production of a crude high-carbon ironchromium alloy and a waste slag product, subjecting a second fraction of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount controlled to effect the selective reduction to the metallic state of the major portion of the iron oxide content thereof with the production of low-carbon metallic iron and a chromium oxide-containing molten slag product, recycling said chromium oxide-containing molten slag to the reduction smelting stage operating on the first fraction of said charge, blending said high'carbon v. a r 10 s iron-chromium alloy with said'low-carbon metallic iron to provide a master. iron-chromium alloy of controlled intermediate carbonjcontent, refining said master alloy within a refining furnace in the presence of a'fnon-carbonaceous refining agent for the production and recovery of a chromium-alloyed steel product.

6. The process as claimed in claim 5, wherein said master alloy is subjected'to refining within the refining furnace together with alnickel, alloying additive for. the production and recovery. of a nickel-chromiumfalloy ed steelproduct.

7. Process for the recovery of iron and chromium in alloyed form from a complex material comprising iron oxide and chromium oxide that comprises fluxing said material to form a composite reduction charge, subjecting a first portion of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount sufiicient to effect reduction to the metallic state of substantially all of the iron oxide and chromium oxide contained therein with the production of a crude high-carbon iron-chromium alloy of predetermined ironchromium ratio and a waste slag product, subjecting a second portion of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount controlled to effect the selective reduction to the metallic state of the major portion of the iron oxide content thereof with the production of lowcarbon metallic iron and a chromium oxide-containing molten slag product, recycling said chromium oxide-containing molten slag product to the reduction smelting stage operating on said first charge portion, and blending said high-carbon iron-chromium alloy and said low carbon metallic iron to provide an iron-chromium alloy of predetermined iron-chromium ratio and intermediate carbon content.

8. Process for the recovery of iron and chromium in alloyed form from a complex material comprising iron oxide and chromium oxide that comprises fluxing said material to form a composite reduction charge, subjecting a first'portion of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount sufiicient to effect reduction to the metallic state of substantially all of the iron oxide and chromium oxide contained therein with the production of a crude high-carbon iron-chromium alloy of predetermined ironchromium ratio and a waste slag product, subjecting a second portion of said composite charge to reduction smelting in the presence of a carbonaceous reducing agent in an amount controlled to effect the selective reduction to the metallic state of that portion of the iron in excess of 38% of the total iron content of said second charge portion with the production of low-carbon metallic iron and a chromium oxide-containing molten slag product, recycling said chromium oxide-containing molten slag product to the reduction smelting stage operating on said first charge portion, and blending said high-carbon ironchromium alloy and said low carbon metallic iron to provide an iron-chromium alloy of predetermined ironchromium ratio and intermediate carbon content.

9. Process for the production of alloyed steel from chrome-iron ores that comprises, subjecting a first ore fraction to reduction smelting in the presence of a carbonaceous reducing agent in an amount sufiicient to elfect reduction to the metallic state of substantially all of the iron oxide and chromium oxide contained therein with the production of a crude high-carbon iron-chromium alloy and a waste slag product, subjecting a second ore fraction to reduction smelting in the presence of a carbonaceous reducing agent in an amount suflicient to effect the selective reduction to the metallic state of the major portion of the iron oxide content thereof with the production of a low-carbon metallic iron and a residual slag containing the chromium oxide content and the remainder of the iron content thereof, recycling said slag to a reduction smelting operation conducted on said first ore 1 lfractiqn, blending said high-carbon i1,qzan-chnmaiwam alloy with Said low-carbon metallie iron to provide a master alley; Of conti'olled intermediate carbon content, and rej-I fining said master alloy as. necessary forfthe'producltien' arid feeovery of, a chromium-alloyed steel product.

Becket et a Feb. 17 I931 Gustafsson 14, 1933 170' J ourna1 of 12 Udy Nov. 2, 1937 Udy Feb. 212. 193$, Fei1;1 19.4!

e f 1 1,. 1 1 1111; 2.91. 958; A em-mum ER R E RE CES Metal s, Febr uary 1949-, page; '9-I- 9 5 re1iedj

Claims (1)

1. PROCESS FOR THE PRODUCTION OF ALLOYED STEEL FROM ORES OF CHROMIUM OXIDE AND IRON OXIDE THAT COMPRISES, SUBJECTING A FIRST ORE FRACTION OF MIXED CHROMIUM AND IRON OXIDE CONTENTS TO REDUCTION SMELTING IN THE PRESENCE OF A CARBONACEOUS REDUCING AGENT IN AN AMOUNT SUFFICIENT TO EFFECT REDUCTION TO THE METALLIC STATE OF SUBSTANTIALLY ALL OF THE IRON OXIDE AND CHROMIUM OXIDE CONTAINED THEREIN WITH THE PRODUCTION OF A CRUDE HIGH-CARBON IRON-CHROMIUM ALLOY AND A WASTER SLAG PRODUCT, SUBJECTING A SECOND ORE FRACTION CONTAINING A PREDOMINANT PROPORTION OF IRON OXIDE TO REDUCTION SMELTING IN THE PRESENCE OF A CARBONACEOUS REDUCING AGENT IN AN AMOUNT CONTROLLED TO EFFECT THE SELECTIVE REDUCTION TO THE METALLIC STATE OF THE MAJOR PORTION OF THE IRON OXIDE CONTENT THEREOF WITH THE PRODUCTION OF LOW-CARBON METALLIC IRON, BLENDING SAID HIGHCARBON IRON-CHROMIUM ALLOY WITH SAID LOW-CARBON METALLIC IRON TO PROVIDE A MASTER ALLOY OF CONTROLLED INTERMEDIATE CARBON CONTENT, AND REFINING SAID MASTER ALLOY AS NECESSARY FOR THE PRODUCTION AND RECOVERY OF A CHROMIUMALLOYED STEEL PRODUCT.

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