US2176687A - Chrome alloy making - Google Patents

Description

oct; 17, 1939. M J. um 2,176,687

CHROME ALLOY MAKING Filed Jan. 22, 1938 @Eff lNvENToR MARWA/ J. 05)

ATTORN EY Oct. 17, 1.939. M. J; UDY A 2,176,687

CHROME ALLOY MAKING Filed Jan. 22, 1938 `2 Sheets-Sheet 2 flied/"6 .f2/7226299 /edacz'oz w//lz Carbon zzz presence af [ame if i .ferma 70mm/72 5a!! 272i!! 0f pfef fzmizng armi/rang dev/ce ATTORN EYS Patented Oct. 17', 1939 UNITED sTATEs PATENT ori-ICE CHROME ALLOY MAKING Marvin J. Udy, Niagara FallsrN'. Y. Application January 22, 1938, Serial No. 186,466

31 Claims.

This invention or discovery relates to chrome alloy making; and it comprisesvmanufacture of a composition for use in making chrome iron alloys. said composition being a mixture of pulverulent 6 substantially carbon-free and `completely oxidized ferrochromium with pulverulent ferrochrome metal low in carbon and high in silicon, in proportions enabling the composition to undergo internal exothermic reactions forming low carbon 10 ferrochromium metal to be supplied to a steel or iron bath in any ratio; and it further comprises a method of utilizing chromite ores of any grade in making alloy steels wherein ferrochromium metal made from chromite by total reduction with carbon and rich in carbon is subjected to ah oxidizing roast in the presence of lime thereby eliminating carbon, the oxidized product in pulverulent form is admixed with a pulverulent metal containing chromium, iron and silicon in 90 high proportion, said metal being formed by re smelting ferrochromium with silica and carbon and the admixture is added to molten iron or steel to form the desired alloy; all as more fully hereinafter set forth and as claimed.

g5 Chromium alloys of iron and steel have reached great commercial importance for various purposes, particularly as corrosion-resistant or rustless iron or stainless steel and as oxidation-resistant and high str-ength ferrous metals generally. For the most part the chromium in these alloys is supplied by ferrochromium made from chromite ores and diluted, so to speak, with iron; other alloying metals, nickel, vanadium, molybdenum, tungsten, etc., being often added in small quantities. The chromium content may range from a fraction of a per cent to above per cent; iron being the major component of the alloy. Processes have been proposed for making chrome steel direct from chromite ores. For various reasons such direct" processes have not proved successful. In practice, for the most part, the ore is first reduced to ferrochromium as an intermediate allo-y supplying chromium for the finished steel or iron alloy.

In utilizing ferrochromium as source of chro-A mium for these alloys, a large problem in the industry arises from a requirement that the alloy shall be extremely low in carbon content; a usual maximum oi tolerance being 0.2 per cent. Carbon lower than 0.05 per cent of the alloy is often desirable. Generally speaking, for most technical uses, the lower the carbon content, the better is the quality of the alloy. Ferrochromium always carries carbon.` To meet the low carbon `g requirement in the finished alloy, n ot only must the steel or iron forming the major part of the alloy be carefullyreiined but means must be found 1to avoid carbon being carried into the steel by the ferrochromium serving as source of chromium for the alloy..

Carbon elimination in chromium metallurgy entails great expense. The industry is forced in great measure to use a special low carbon ferrochromium madeby reducing chromite ores with non-carbonaceous reducing agents; in which the 10 cost per unit of chromium is double that for chromium in the high carbon .grades of ferrochromium produced by the usual electric smelting of chromite ores with carbon (coke) as a reducing agent. It has also been considered necessary 15- to use ferrochromium ofthe highest possible chromium content as Wellasslow in carbon; the 'present standard being 'l0 per cent chromium or a ratio-of chromium to iron' of 2.33: l. For this it has been necessary to comb the globe for high ,20 grade or low iron chromites, leaving unutilized plentiful supplies, both domestic and foreign, of -good ores too high in iron to yield standard marketable ferrochromium; metal with the high chromium content considered necessary in ferro- 5 chromium used to supply chromium for the alloy steel and iron. The industry, to avoid carbon in the iinal alloy, has to use a low carbon high grade ferrochromium made from the rare highgrade ores and then to dilute this metal with iron in .30 making commercial alloys carrying minor per- 'centages of chromium. So the industry labors under the fundamental economic disadvantage of vstanding the cost of a 70 per cent chromium low carbon metal which is diluted with liron to an .35 alloyv containing usually less than 30 per cent chromium.

In my Patent 2,098,176, November 2, 1937, I have described and claimed manufacture of a synthetic chromite ore containing calcium chro- =40 mite replacing ferrous chromite of the natural ore, by selective reduction of iron from ferrous chromite ore in the presence of lime. By the invention of said patent substantially complete control is afforded of the chromium-iron ratio in .45 chromite ores and thus in the ferrochromium subsequently produced. This permits utilizing in chromium metallurgy for making marketable high grade ferrochromiuxn, the low grade (high iron) chromite ores hitherto unavailable for such use.

In the present invention I depart from the practice oi making commercial chrome steels by directly adding commercial ferrochromium of the .highest possible grade to molteniron or steel. I6

Instead, I add to the molten bath a particular two-component mixture oi.' oxides withmetal containing silicon in prportion' iumcient to reduce the oxides by exothermie action, giving a subannually carbon-free mm1- sonwnmg cmomium and iron. The oxidized component oi' the mixture is made by roasting metal produced by total reduction oi a chrcsnite ore with carbon. In roasting the carbon disappears and oxides of chromium and iron are reproduced. This roasted material is one component oimy mixture. The other component is a metal rich in silicon'and low in carbon produced by resmelting a similar total-reduction metal, resmelting being with silica and carbon. The two components are mixed in such proportions that the silicon in one component reduces the oxides oi iron and chromium in the other with evolution oi heat. Such a composition on mixture with molten ironfundergoes reaction with the production of a chromium iron alloy of any ratio of chromium to iron desired in commercial alloys. In the chromite ore .used in producing the two components, the ratio ot chromium to iron is, within limits, immaterial.

Other things being equal, the heat evolution in the two component mixture increases with an increase in the proportion ot iron in the oxide component and vice versa. Therefore low grade ores with a high ratio oi iron to chromium are desirable in making the oxide component.

In practice the exothermic mixture contains as a third component enough lime to form a basic silicate slag with the silica formed from the silicon in the reaction. The lime containing composition when added to a molten steel bath supplies chromium in any desired ratio and at the same time contributes heat to the bath. The silica formed in the action combines with the lime to form a low melting basic slag which can be oi relatively low volume in relation to the iron-chromium metal formed in the action. 'I'he lime combining with sillcu adds somewhat to the heat of evolution. By proper proportioning of the mixture components, the heat ci' the exothermic reaction may contribute a great part or all oi the heat required to bring to fusion both the lime silicate slag and the metal which are products o! the reaction. The conversion oi silicon to vsilica may be complete. with uumclent lime in admixture to form a silicate containingiime in excess of an equimolecular ratio to the silica." A ratio oi 1.5:?. -Ior example, eilects completion of the exothermic reaction. VWith @nO/B102 ratios between 1 and 2 'the Si content of the metal product is under sulstantlally 'complete control.

In utilizing the exothermic mixture for making alloy steel, it is possible to ignite the mixture in c. hot furnace and toadd label-lot' products of the silico-thermic reaction to a bath oi reilned molten Vsteel in an open hearth furnace.

According'tothe invention there is provided from low grade chromiteores a composition useful as' an'intermediute materiel for making chromium alloy steels in the open hearth furnace. ,The intermediate mayv carry into the steel from 90 to 95 per cent oi the total chromium oi the ores used; the silicon ln the exothermic mixture being inV proportion to reduce' boththe chromium and the iron o( the oxidized component; the proportion of lime in the mixture 'sumcient to form a basic silicate slag contributing as I have found, to substantially complete reduction ot the oxides without more than a slight excess oi.' silicon going vinto the nished alloy steel. In a short period of time the basic slag rennes silicon out of the metti.

Commercial alloyed steel (iron) is made diluting with molten iron the metal product oi the Y internal exothermic reaction; the added iron being sumcient to establish the desired chromium ratio in theilnished alloy.

In a copending application Serial No. 165,417, illed September 23, 1937, I describe methods ci' oxidizing ierrochromium to calcium iron chromite. This oxidation oi the metal results in substantially complete elimination oi' the carbon contained therein and is advantageously carried on in the presence oi a relatively large quantity oi lime. The oxidation product composed of lime, ferric oxide and chromic oxide which is conveniently termed calcium ierrichromite, may be used tc great advantage as the oxidized component oi the stated composition. It is advantageous ii it contains the amount of lime required to form a basic silicate. as described, with the silica produced from the second component. Basicity aids the oxidation oi' 8i to S102.

In roasting ierrochromium with lime and a little soda ash to total oxidation ci the metals and elimination oi' carbon, as described in my acknowledged prior application, I have found it advantageous to oxidize a substantial proportion of the chromium to CrO: and to leave in the oxidized material a substantial content of chromate. So doing, a mixture of the chromate-containing calcium ierrichromite with siliconized ferrochromium may be made to convert itself into molten ierrochrome metal and molten basic silicate slag.

It is possible to fully roast ferrochromium in the presence oi a base to ferric oxide and chromate of the base. This is described in my copending application Serial No. 177,365, filed November 30, 1937. With lime alone serving as the base the oxidation of chromium to chromate requires several hours of roasting, but with soda present in adequate amount the conversion to chromate may be complete in half an hour at or somewhat below l000 C. It is possible to control the rate and degree of conversion to chromate in roasting chromium and lime by the quantity of soda present and by regulation of the temperature.

Roasting at temperatures well under 1000 Cx with no soda ash or less than one per cent oi sodo. in'theroesting charge converts the chromium mostly to calcium chromate without complete oxidation and elimination of carbon from the ierrochrome metal in a reasonable length oi' time. Above 1G00" the carbon is eliminated but the 'chromate breaks down to chromite. As the soda is increased the temperature can be raised without breaking down the chromate and the carbon can be completely eliminated without raising the temperature. Additions o! soda in amounts above one per cent oi' the charge or two per cent of the metal permits regulation of the temperature to control the ratio of'chromate to chromlte (Cros to CrzOa) in the oxidized product. I have found for example that addition to a roasting mix oi' ferrochromium and lime of soda ash (Na2CO3) in the amount of 5 to 10 per cent by weight of the ferrochromium metal results in 50 per cent conversion to chromate in a short time with total elimination of carbon and oxidation of all the metal when the temperature of roasting is held at 1 D00 C.; the remaining chromium being oxidized to CrzOa appearing as calcium chromite. This StL-5 0 oxidation of chromium to chromite and chromate gives an oxidized material capable of a highly exothermic reaction with siliconized ferrochrOmium. Such a compound of CaO, Feroe.,

CrzO; and CrOa containing a small amount of 'l5 amasar Nago from the soda ash and made from terrochromium by roasting in air, is a highly advantaseous material to be' adxnixed with ferrosilicon or ierrochrome silicon to form the exothermic or "sllico-thermic material of the present invention.

The roasting operation can be carried on in an4 openhearth or reverberatory furnace with mechanical rabbling or in a rotary kiln. Limestone may be used in the roasting mix to supply lime. A little soda, in the order of 2 to i0 per cent oi the metal, besides controlling the conversion to chromate greatly promotes the oxidation of the chromium to chromite. The soda may be added to the roasting mix in the form oi sodium chromate. The roasting may be made to yield' any desired ratio of Cro: to CrzOa-in the oxidizedproduct.

For siliconizing high carbon ierrochromium, a mixture of crushed or granular metal with silica rock (quartzite)l and'coke may be charged continuously into a submerged arc electric iurnace and a metal siliconized to a' low carbon content is tapped from the furnace; high silicon content in the tapped metal replacing the carbon content oi the charged ferrochromium. The silicon content may be as high as desired, up to per cent, for example. This operation is similar to that of making ferrosilicon; the high carbon ferrochrome taking the place of scrap iron.

An exothermic mixture of calcium ferrichromite containing chromate with i'errochrome-silicon containing a slight excess of silicon over the quantity required to reduce the iron and chromium oxides is a highly advantageous material for supplying to molten refined steel the chromium required for a finished alloy. A calcium ferricliromite made by total oxidation ot high carbon ferrochromium in the presence o! much lime and some soda, the latter serving as a wetting agent for the Ierrochromlum undergoing oxidation, as described in the companion application, is substantially free of carbon. And a ierrochrome-silicon made by sm'elting high carbon ferrochromium with silica and carbon to a g high silicon content may also be substantalll' free of carbon. A mixture of the two within the purview of the present invention, added to a steel bath, supplies substantially carbon-free ironchromium metal together .with heat to be used for melting the lime silicate slag and metal formed in reduction by silicon. Thus chromium is supplied to the steel with substantially coin-1 plete elimination oi the carbon of ierrochroe mium.

In adding a two-eomponent mixture of oxi dized and siliconized ferrochrorniuxn to the steei bath, as described, it is possible to so proportion the two reagents as to minimize the accompanying slag production., 'I'he amount of slag relative to the metal chromium is dependent upon the proportion of irons oxide introduced with the chromium oxides in the oxide component and reduced by the silicon oi the other component.

This in turn depends upon thechromium-iron ratio in the oxidized ferrochromium and in the chrornite ores from which it is made by total reduction. While the higher grade materials (of lower iron ratios) give oxidized and siliconized products involving smaller slag additions to the steel furnace, it has been found thatthe larger slag additions per unit of chromium associated with the use of low grade chromltes and 'ferruchromiums of high iron ratios are by nomeans prohibitive. In fact, it is' possible to'use the lowest grade orcs as source o! the ferrochromium,

both thatv which is oxidized and that which is siiiconized. I Vhave even used, for example, chromiierous ironores'with 2 to 3 per cent chro-l mium content; with a ratio to the iron content ot 1:20. This is described in an accompanying application.

Using chromite ores of with total reduction to high carbon ierrochromium followed by portional :oxidation and siliconizing of the ferrochromium, the proportions of oxidized and siliconized product finely divided and admixed for introduction into the steel iurnace determine the ratio of slag added with the iron-chromium metal. A major proportion of the oxidized product admixed 'with 'a minor 4proportion of the siliconized product gives excellent results. 'Ihis proportioning permits addition of silicon to terrochroxnium in a ratio sufilcient for nearly complete absence of carbon from the ierrochrome silicon. The lower the proportion in the siliconized product of the total iron and chromium in the mixture. the higher is the percentage of silicon in this4 product required to reduce the iron and chromium oi the oxidized product. However, it has been found in utilizing low grade ores that the lower chromium content oi' the high carbon ferrochromium permits complete carbon removal with addition of a smaller percentage of silicon to the metal than is required for higher grade i'errochromium. For example, a. ierrochromium o! a Cr-Fe ratio less than 1:1, as I have found, has the carbon content lowered to less than 0.10 per cent by smelting with silica and carbon, to a silicon content of 40 per cent in the ferro'chrome silicon product. This compares with considerably higher percentages ot silicon required to lower the carbon content below 0.10 per cent in ierrochrome alloys having standard Cr-Fe ratios above 2:1. There is thus an incidental advantage in using sub= standard ierrochromium made from low grade chromites.

In utilizing mixtures oi oxidized and siliconized ierrochromium made from low grade,ores of chromium-iron ratios between i and 2 to 1, exothermic actions in the mixture may be exemplii'led in chemical equations:

Equation 1 represents action in a mixture oi oxidized and siliconized ierrochromdum both having a Cr-Fe ratio less than 1:1; the proportions of oxidized and siliconized ferrochrornium taking part in the reaction being 1:1.5 or 40:60 per cent of the original 1:1 ferrochromium, 40 per cent being oxidized and combined with lime as calcium ierrichromite and 60 per cent being siliconized to a 20 per cent silicon content; the products being low carbon ferrochromium and a calcium silicate slag containing 4Ca0 to 3810: and in a weight ratio of '15 per cent of the ferrochromium; the heat developed in the reaction being estimated from available data as 109,000,

calories or 2590 centigrade units per pound silicon oxidized. Ihere is an ample margin of heat over that required to melt the slag; (something under 5 pounds slag per pound silicon). The production oi.' metal in the reaction is over 8 pounds per pound silicon oxidized.

sub-standard grade Uil In Equation 2 the chromium-iron ratio of the oxidized and siliconized ferrochromium is..1.85, the proportion of oxidized and siliconized ferrochromium is '73:27 and the silicon content of the ferrochrome silicon in the mixture is 51 per cent. The slag to metal ratio is 1.37. The heat set free in the reaction may be estimated at 144,700 calories, or 2300 centigrade units per pound of silicon oxidized; an amount ot heat ample for raising pounds slag per pound of silicon to the temperature of a steel furnace. The production of metal is nearly 3.5 pounds per pound Si.

Equation 3 illustrates silico-thermic reduction of calcium chromate by ierrochrome silicon (50 per cent Si) with production of 2.20 pounds metal and 4 pounds slag per pound silicon with an estimated heat evolution of 4000 centigrade units; which appears in excess by some 60 per cent over the heat used in melting the metal and slag products ot the reaction. 'I'he equation illustrates the quantitative eliect of chromate contained in the oxidized component in supplying heat for making the reacting admixture with the siliconized component fully exothermic when ignited in a hot furnace or when added to a bath of molten steel asin an open hearth steel furnace.

If in roasting ferrochromium to make the oxidized or oxygenated component of the silicothermic mixture, all or the greater part ci the chromium is converted to chromate the heat of the reaction is greatly increased and the silicon content of the siliconized component may be lessened. However, the excess heat may be utilized in adding to the heat of the steel bath.

While a lower silicon content in the siliconized low carbon ferrochromium permits a higher proportion of this product in adrnixture with oxidz'zed errochromlum,'it is sometimes advantageous to lower the proportion of ierrochromesilicon in the mixture and to increase the silicon percentage, thus supplying additional silicon for reduction of the higher proportion of oxides in the mixture. This eii'ects additional heat development when the mixture is fed to the steel furnace, the additional heat being accompanied by an increased slag ratio. There is a net gain of heat delivered to the furnace by the internal exotherrnic reaction of which the mixture is capable, the delivery oi' heat per unit Weight of the material being in direct proportion to the percentage content of reducible oxides and the equivalent silicon for reduction.

an important advantage of the invention as described is that it results in being able to prepare in the open hearth steel furnace alloy1 steels of greater chromium content than has heretofore been practicable. These alloys carrying from 12 to 18 per cent chromium and above can now be made in the open hearth, utilizing the present invention. For making such relatively high chromium alloys the electric furnace is no longer necessary. But it may be used, when desired.

The exothermic mixture may be ignited in -a separate furnace and molten metal and slag run into the open hearth. The eiect is that of adding molten low carbon ferrochromium.

Another advantage of the method is that alloying metals, other than chromium, may be added as oxides to the exothermic mixture or in metallio form to the ferrochrome silicon component. As an example oi the latter modification, nickel silicate ore may be utilized as source of silica for aimee? siliconizing high carbon ferrochromium, this incorporating nickel in the metal in addition to iron and chromium as nickel-ferrochrome silicon. Oxides of nickel, vanadium, molybdenum, etc., may be made part of the oxidizedcomponent of the mixture fed to the steel bath, and thus be reduced by silicon to metal which is thus added to the steel with the chromium supplied by the mixture.

In practice o! the invention, a number of modifications are possible. The exothermic mixture of -oxidized and siliconized ferrochromlum may b so compounded as to form the equivalent of i'errochromium having any desired carbon content .within the usual commercial ranges. The mixture of oxidized and siliconized ferrochromium can be so made as to yield a substantially carbon-free metal. By adding into the mixture a proportion of finely ground high carbon ferrochromium the metal product can be made to contain a. corresponding percentage of carbon. As I have found, it is desirable to have in the mixture silicon equivalent to the chromium and iron oxides therein. Then addition to the mixture of high carbon ferrochromium puts carbon into the metal. With suiiicient lime present to convert the silica formed in the reduction into calcium silicates, little or no silica is reduced by carbon. This aiords complete control of the carbon content of the metal product. In a chromate mixture with silicon insumcient for the reduction, residual carbon in the siliconized metal is oxidized and removed by A reduction of the oxide component; heat absorbed in this reduction being supplied by the silicon reaction.

In siliconizing high carbon ierrochromium at 1500 to 1600 C. in a submerged arc electric furnace, a comparatively small amount oi' carbon in the metal is replaced by adding a much larger amount of silicon. In this operation, as above noted, it is advantageous to have a relatively low chromium-iron ratio in the metal. A high carbon ferrochromium made from low grade ores requires a relatively small addition of silicon to eliminate carbon. In utilizing low grade ores it is possible to control the carbon content of the nished steel by varying the silicon percentage added to the ferrochromium so as to leave more or less carbon in the metal component of the silico-thermic mixture added to the steel.

In another mocliiication of the Silico-thermic mixture the silicon content is sulilcient tdrcduce the chromium oi the oxidized ierrochromlum component and iron oxide in 'this component is reduced by carbon either in high carbon ferrochromium added to the mixture or present as residual carbon in the siliconized component.

If desired, an oxidizer such as sodium chlorate or nitrate may be incorporated in the mixture with excess silicon to be oxidized for additional thermicity.

As a general rule it is advantageous, as stated, to utilize the lower grade chromite ores for making both the oxidized and the siliconized ferrochromium in the silice-thermic mixture. How.- ever, any desired grade of ore may be used for making either component. It may be desirable for example, to siliconize a low grade ferrochromium and to oxidize a high chromium metal to chromate and FeaOs, in making the silicothermic mixture.

In siliconizing fernochromium, and particu- ,larly the lower grade materials to relatively low "arnesi" Ina-specinc embodiment of my inventionl have made a mixture of oxidized with siliconised NazCO: and this iinely ground mixture war roasted in a gas fired rotary furnace at temperatures from 700 to 1100 C. The roasted product was a chromated calcium ferrlchromite analyzing as follows:

Per cent 14.6 22.9 13.4

The-proportion of chromium as chromate is 54 per cent.

The above high carbon ferrochrome metal was siliconized by smelting in a submerged arc furnace with quartzite and coke to a silicon content of per cent with 35 per cent Cr and 15 Fe. 117

parts oi' this ferrochrome silicon (equivalent to 63 parts of the original metal) were pulverized and intimately admixed with the271 parts of ferrichromate produced by oxidation as abovev described of 100 parts of high carbon metal and with 'l2-parts of lime in a ball mill.

This mixture was quickly fed to a red hot steel furnace and thereby ignited. The mixture reacted exothermically and converted itself to 146 parts of low carbon ferrochromium molten metal analzing per cent chromium, 0.05 per cent carbon and silicon under 1 per cent with approximately 312 parts molten calcium silicate slagl containing lime and silica in a ratio of 1.5 tov 1 and 1.6 per cent chromium. The recovery of chromium from the original high carbon metal was per cent.

Molten iron can be added to this low carbon metal in any ratio to make a finished alloy of desired chromium content.

In a speciilc exampleof my invention utilizing a low grade ore analzing as follows Per cent Crz01 13.75 Iron oxides as FeO 12.00 M30 21.18 A1201 2.02 B102- 35170 CO2 14.30

I smelt this ore in a submerged arc furnace in continuous operation by the process described in my copending application Serial No. 165,954, and produce a metal of the following composition:

somewhat under 1000 C. for a time and then at a temperature of 1000 to 1100 C. From this roast. 236.4 parteci calcium ferrichromite are obtained analysing follows f Per cent Crack 25.9 Fes0- 29.0 SiO: 2.7 CsO 42.2 C .02

I smelt 36 parts of the above metal with silica and coke in a submerged arc furnace and produce 72 parts ierrochromesilicon containing 50 per cent Si, 23.4 percent Cr, 26.6 per cent Fe with 0.04 per cent carbon.

For making low metal I mix or briquette for reaction on a steel bath. or for separate` reaction to produce low carbon ferrochrome, the 236.4 parts of calcium ferrichromite and 72 parts of the 50 per cent ferrochrome silicon ground to 100 mesh or nner. Intlseinternsl reaction ofthis mixture there is produced 126 parts of metal analzing 46.5 per c ent Cr and 53.4 Der cent Fe. with less than 0.10 per cent carbon. With this metal there is produced in the reaction 166 parts of calcium' silicate slag containing about 5 per cent CrsOs. If made on the steel bath the metal enters the steel to supply chromium in the ratio desired. It reacted to produce ferrochrome, excesssiliccnmaybeusedinthemixture withsodium nitrate or chlorate to produce additional heat., In this example.92 per cent of the original ferrochrnium appears 'in the metal product of the exothermic reaction.

If I wish to produce,- for example. the equivaient of `1.5 to 2 per cent carbon grade ferrochrome. I mix and react the 236 pounds of ferrichromite. 72 pounds of irrochrome silicon and 35 pounds of the original high carbon ferrochromium containing 7 per cent carbon and produced from the ore as described. I thus make 160.9 pounds of metal containing 46 per cent chromium and 5i per cent iron with 0.65 per cent Si and 1.52 per cent C.- In a third example ci' the invention, two different ores are used having the following anal- YS5 Ore No 1 Ore No. 2

Porb P- Pet- Percent cont cent cent C1101... 38.40 OL... 22.95 0h01... 43.00 Cr 29.5 Fe0 12.61 Fe.-.. 9.85 FeO-.-- 25.00 Fe 19.4 CsO 1.90 Cs0..-. Trace Mg0 14.31 Mg 10.60 A1101... 22.95 Alion... 15.60 8101..-.- 6.50 8102..... 3.80

The or/Fe mxo in ors No. 1 is 2.34 and in om Na. 2 s 1.52.

I first beneflciate parts of No. 2 ore by replacement oi FeO with CaO as described in my Patent No. 2,098,176, and produce 27.7 parts of metal analyzing 31.7 per cent Cr, 63.2 per cent Fe and 5 per cent C, together with something less than 100 parts of calcium chromite ore containing 20.7 parts chromium and 1.94 parts iron.

I next smelt the altered calcium chromite ore with 100 parts of ore No. 1 in a submerged arc furnace and produce 59 parts of metal analyzing Cr 70 per cent, Fe 19.9 per cent, C 7 per cent and Si 3 per cent. The slag goes to waste carrying with it the ore gangue refractories, MgO and A1203, out of the system.

I roast 59 parts of this metal with 59m of lime to produce 139.6 parts calcium ferrichromite analyzing:

Per cent CD03 FeaOu 7 11.9 CaO 45.0 Carbon, less than 0.02

I- smelt 20 parts of the 27 parts of metal obtained in altering No. 2 ore with silica and coke in a submerged arc furnace and produce 38 parts of ferrochrome silicon analzlng 50 per cent Si, 16.7 per cent Cr. 32.2 per cent Fe and 0.04 per cent C. I then mix this ferrochrome silicon with the 139 parts of calcium ierrochromite t0 produce by exothermic reaction approximately 70 parte oi low carbon ierrochromium analyzing per cent Cr and 34.8 per cent Fe. This metal runs about 0.03 per cent in carbon content.

If to the 139 parte of ferrichromite and 3u ports ferrochrome silicon the remaining 'l parte of high carbon chrome iron metal from the beneilciating step were to be added, there would be an exotliermic mixture capable of producing 'I7 parts of ierrochrome analyzing 61.7 per cent chromium and 0.49 per cent carbon.

In reacting any of the described mixtures of oxidized and siliconized metal, a chrome-iron metal is formed in minute droplets which readily diuse into a steel bath.

In the accompanying drawings, I have shown i'or purposes of illustration only, and not for purposes of limitation, dow sheets illustrating several of the possible chromium recovery processes which may be carried out in employing the principles of the invention. The flow sheets illustrate complete chromium recovery processes. cornmencing with the treatment of chrornite ore initially and indicating the production ultimate-D ly of desirable chromium-bearing metal products. lAlternative methods oi producing high-carbon ierrochromlum are illustrated. Fig. 1 illustrates a process in which high-carbon ierrochromium is produced by direct reduction of the iron and chromium of chromite ore. Fig. 2 illustrates a process in which iron is selectively reduced from chromite ore with the production of a high-iron, low-chromiumA metal product and a mneficiated ore product, and the residual iron and chromium of the beneficiated ore product are reduced with carbon to produce high-carbon ferrochromium. in the process illustrated in Fig. l, ferrochrome silicon is produced by smelting a portion of the lu'gh-carbon ferrochromium with carbon and silica, While in the process illustrated in Fig. 2, ferrochrome silicon is produced by smelting the high-iron, low-chromium metal product with carbon and silica. In dotted lines, I have suggested modiiled procedures which may employ oxidizing materiels such as chromate, chlorate and nitrate compounds and alloying elements such as nickel, vanadium and molybdenum.

What I claim is:

l. A material made from chromite ore comprising oxidized ferrochromium substantially free of carbon in finely divided admixture with low carbon ferrochrome-slicon of a silicon content suficient to reduce the metal oxides of said oxidized ferrochromiurn.

2. A silico-thermic material comprising in nnely divided admixture oxidized ferrochromium substantially free of carbon, low carbon ferro` chrome-silicon metal containing silicon in amount sufncient to reduce said oxidized ferrochromium to metal and lime in amount required to form a basic silicate with the silica formed in said reduction.

3. A synthetic material composed of lime, ferric oxide, chromic oxide and chromium trioxide finely divided and in intimate admixture with ierrochrome silicon, said mixture being capable oi undergoing internal reactions converting itself to chromium-iron metal and lime silicate slag.

4. A manufactured material useful in production of nickel-chromium-iron alloys by exothermic action which comprises a mixture oi (l) a product in solid finely divided form mainly composed of oxides oi iron and chromium in chemical combination with lime and formed by roesting carbon-bearing ferrochromium in the presence of lime to oxidize the metals and carbon o1 the ferrochromium wd (2) solid finely divided nickel-ferrochrcme siilcon inquantity to reduce iron and chromium oxides contained in the roasted ierrochromiurn with formation or c liniesilicate slag.

5. A material manuiactured from lorv grade chromite ore and comprising oxidized ferrochromium containing lime in chemical combination with chroinic oxide and' chromium trioxide in finely divided admixture with low carbon ferrochrome silicon of e chromium-iron ratio less than l and a silicon content about #i0 per cent or less.

6. The method oi producing e material suitable for use in the manufacture oi alloys containing chromium and iron which comprises grinding a mixture of ferrochrome silicon and a product containing oxid'med chromium formed by subjecting a carbon-bearing alloy containing iron end chromium to en oxidizing treatment, thereby to eiiect intimate mixing of iinely divided particles of the ierrochrome silicon and nely divided particles or' the product containing oxidized chromium.

7. A product suitable for use in the production of alloys containing chromium and iron comprising an intimate mixture of finely divided ferrochrome silicon und o. product containing oxidized chromium formed by subjecting a carbon-bearing alloy containing iron and chromium to an oxidizing treatment, said intimate mixture being a product formed by grinding together the ierrochrome silicon and the product containing oxidized chromium.

8. The method oi producing a reaction mixture suitable for use in the production of chromium alloys which comprises oxidizing carbon-bearing i'errochromium 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 solid, finely divided ierrochrome silicon.

9. The method oi producing a reaction mixture suitable for use in the production of chromium alloys which comprises oxidizing carbon-bearing ierrochromium 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 solid, ilnely divided ferrochrome silicon.

10. The method of producing a reaction mixture 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 ferrie oxide and chromic oxide, and forming a mixture containing (1) the ferrie oxide and chromic oxide of the oxidized product, (2) solid, ilnely divided ferrochrome silicon and (3) oxidizing material capable of deo arrasar f 7l veloplng by reaction with silicon a temperature higher than those resulting trom reaction o! l ferrie oxide and chromic' oxide with silicon.

ll. The method of producing `a reaction mixture suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ierrochromium in a solid, nnely divided condition and in the presence oi lime and iorm.

ing an oxidized product llow in carbon and containing calcium oxide in chemical combination with chromium oxide, and mixing the oxidized product with solid, ilnely divided ierrochrome siliwn.

l2. The method of producing a reaction mixture suitable for use in the production of chromium alloys which comprises oxidizing carbonbearing ferrochromium in a solid, iinely dividedcondition and forming an oxidized product low in carbon and containing oxidized chromium a substantial amount oi which is in the. form of chromium trioxide, and mixing the oxidized product with solid, finely divided ierrochrome silicon.

13. The method oi producing a reaction mixture 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 solid, iinely divided ferrochrome silicon.

14. A reaction mixture suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, finely divided condition produced by oxidizing carbon-bearing ierrochromium and forming a product low in carbon and containing iron and chromiumv in oxidized forms and (2) solid ferrochrome silicon.

l5. A reaction mixture suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, nely divided condition produced by oxidizing carbonbearing ferrochromium in solid, nely divided condition and forming. a productlow in carbon and containing iron and chromium in oxidized forms and (2) solid ferrochrome silicon.

16. A reaction mixture suitable for use in the production of chromium alloys which comprises (l) oxidized ferrochromium in solid, finely divided condition produced by oxidizing carbonbearlng ferrochromium in solid, finely divided condition and forming a product low in carbon and containing ferrie oxide and chromic oxide, (2) solid, finely divided ferrochrome silicon and (3) oxidizing material capable oi developing by reaction with silicon a temperature higher than those resulting from reaction of ferric oxide and chromic oxide with silicon.

17. A reaction mixture suitable for use in the production of 'chromium alloys which comprises (l) oxidized ferrochromium in solid, iinely divided form produced by oxidizing carbon-bearing ferrochromium in solid, ilnely 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) solid, ilnely divided ferrochrome silicon.

18. A reaction mixture suitable for 'use in the production of chromium alloys which comprises (1) oxidized 'ferrochromium in solid, ilnely 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 trioxided and (2) solid. iinely divided ierroohrome silicon.

' 19. A reaction mixture suitable for use in the production o! chromium alloys which comprises (l) oxidized ferrochromium in solid, finely divided form produced by oxidizing carbon-bearing ferrochromium in solid. i'inely divided cofndie I tion and inthe presence of lime and iorminza mixed with solid, finely vdivided ferrochrome' silicon.

. 22. A reaction mixture 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 ierrochrome silicon. 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.

23. A reaction mixture 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, solidferrochrome silicon, the amount oi chromium present in the mixture in the form of chromate being not substantially greater than the amount of chromium I present in the mixture in the form of chromite.

24. A reaction mixture suitable for use in the production of a metallic chromium-bearing product by exothermic reaction which consists essentially of calcium oxide, ferrie oxide, sodium oxide. chromic oxide and chromium trioxide intimately mixed with ferrochrome silicon, 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 form of chromic oxide. f 25. A reaction mixture suitable for use in the production of metallic chromium by exothermic reaction, which comprises calcium chromite and calcium chromate intimately mixed with ilnely divided ferrochrome silicon, 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.

26. A reaction mixture suitable for use in the production oi metallic chromium by exothermic reaction, which comprises calcium chromite, calcium chromate and sodium chromate intimately mixed with ilnely divided ferrochrome silicon, 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 und the silicon and the oxygen available for reaction with the silicon being present in auch mount and proportion that the mixture il capable upon iznition of converting itself by exothermic reaction into molten chromium-bearing metal ond molten calcium silicate slag.

27. The method or producing a metallic alloy containing iron and chromium which comprises igniting a reiiiction mixture comprising (i) l. product in tho .solid state produced by oxidizing carbon-bemin@ fcrrcchromium and forming: an oxidized product iow in carbonv and containing iron and chromium in oxidized forms and (2) Solid ierrhrofmc silicon.

2S. The nicifiiod of producing a metallic aiioy containing` i. and chromium which comprises ignitlnc in co ict with molten metoi o roction mixtixrc mg (1) o. product in the solid sit-lote orario by oxidizing carton-benino Ierrochrcmium ui forming on oxidized product low in corno no containing iron omi chromiiun in oxidized is sind (2) :Solid ierrochrome oili in i forms, @melting high-carbon ferrochromii u: h carbon in the presence oi Silico, to proff lowcorbon inno-chromo siii mme? con, and mixing the oxidized product and the ferrochrome silicon in finely divided forms.

30. A method of producing a reaction mixture suitable for use in the production of chromium alloys which comprises reducing ohromite ore with carbon to produce high-carbon ferrochromium, oxidizing a. portion of the ferrochromium in solid, finely divided condition and forming an oxidized product iow in carbon und containing iron and chromium in oxidized forms, smelting another portion of the ferrochromium with oarilon in the presence of silica to produce lowcarbon Ierrochrome oiiicon, and mixing the oxidized product and the tc.rochrome silicon in iinciy divided forms.

31. A method oi producing o reaction mixture suitable for me in the production oi' chromium aiioys which comprises emciting ferrous chi-omite orc in the presence oi limo ond o iiioited amount of carbon to soloctiveiy rcduco iron and produce (i) o metoi product higii in iron and low in chromium und (2) c. benccioted product low in iron omi high in chromium, omcltihg the beneiiciatefi ore product with cochon to produce highwerbon icrrochromiuo iron iow-ciiromium prouct with carbon in the presence of silica. to produce lowwchromium lowcorbon fcrrochrome silicon, oxidizing: the high carbon forrochromium in eolici, ihieiy divided condition and forming on oxidized product iow in carbon ond containing? iron chromium in oxidized formo, amd mixing the ierrochrome silicon und 'the oxidized product in. iinely divided forms. A

orneiting the high A fifi

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