US1857779A - Method of producing iron or steel alloys - Google Patents

Description

Patented May' 10, 1932 UNITED STATES PATENT. OFFICE nnnmne GUSTAV nonm AND EMIL GUSTAF monvnnzo sosrnrsson, or s'rocxnonnr,

. swnnnn METHOD or PRODUCING men on. STEEL ALLOYS The present invention, which is a contion Serial No. 7 56,823, filed June 24, 1926, relates to a method for producing alloys of metals belonging to the iron group, and especially alloys of iron, directly out of oxide ores of said metal and oxide ores of the al loy constituents, with the use of carbon as a reducing agent. The carbon, if desired, may

be partly replaced by other reducing agents such as ferro-silicon, ferro-manganese o aluminium.

The expression alloys of iron comprises all alloys containing iron, ranging from, on the one hand, alloys in which iron is the main constituent, that is to say, iron or steel which in addition to the iron contains one or more other metals which impart special desirable properties to the iron, such properties being such as are not possessed by carbon-iron or carbon-steel alone; to, on the other hand, alloys in which iron ispresent to a relatively less extent as in, for example, ferro-manganese, ferro-chromium, ferro-manganesesilicon, or the like. I a e In iron works it often happens that in one heat or smelting an alloyed iron or steel containing a certain percentage of, for instance, chromium, is to be produced and that in a following heat an alloyed iron or steel containing a different percentage of chromium will have to be manufactured. In such cases it has been necessary, prior to our invention disclosed in said copending application and prior to the present invention, to make up a special charge for every different percentage of chromium in the alloyed metal, which, of course, requires several corresponding charges of difierent compositions. It has also been proved to be rather difiicult to regulate the percentage of alloy constituent within narrow limits by simply varying the composition of the charge.

The method disclosed in our copending application, Serial No. 7 56,823, of which this No Drawing. n Application filed July 26, 1929, Serial No. 381,382, and in Sweden September 24, 1924.

is a continuation, obviated the above inconvenience to such extent that it represented a distinct advance in the art. The method consisted chiefly in making up separate mixtures of finely ground portions of each one of the oreswith carbonaceous material of a quantity proportioned to the reduction of the ore and to the desired percentage of carbon in the final product, and'melting these mixtures in a furnace, with the quantities of the mixtures so proportioned to' each other as to obtain an alloy of the desired composition.

Now it is well known that chromium ore,

when reduced by carbonaceous reducing agents, always produces a product which is more or less contaminated with carbon, so that further refinement iswnecessary. For this reason, inventors and experts in the metallurgical art have, prior to our inventions, found it necessary first to produce a highcarbon product, and thereafter to remove the excess carbon by the addition of ore or by other means. These two-stage processes are necessarily costly and result in. a considerable loss of alloying metal.

It is the principal object of the present invention to perfect the process disclosed in our application, Serial No. 756,823 and briefly described above so that the foregoing disadvantages will be entirely obviated. This we have done and we are able at will to produce predetermined low carbon alloys directly while using a carbonaceous reducing agent. 'Our improved process will now be described in detail.

The invention comprises forming separate mixtures of the oxide ore of the base metal, forinstance, iron, and of the oxide ore of the alloy constituent together with carboncontaining reducing agent of a quantity pro portioned to the reduction of the ore and to the desired percent-age of carbon in the metal therefrom and reducing and melting said mixtures 'whilst floating on top of or in a slag bath in an electric furnace whilst pro- 35* I -1 ing a more solid adhesion of the grains, ad-

'- quantity ofcarbon useful for the reduction portioning the quantities of the'mixtures to each other so as to obtain an alloy of the desired percentage of the alloy constituent.

The expression carbon-containing reduc ing agen is understood to comprise, on the one hand, all sorts of carbon, for instance, char-coal, pit-coal, anthracite, coke or the like; on the other hand, however, also any mixture of carbon with another reducing- I agent'or agents, such as ferro-slhcon, ferromanganese, ferro-aluminium-silicon, aluminium or the like, provided such other reducing agent be added only in such proportion, that the carbon is the main constituent and that the process will remain endothermic.

While the mixtures may consist of finely ground and intimately mixed loose material,

we prefer to transform each of "them into a solidified state by mixing tge-corresponding oxide ore in a finely divi ed state with carbon-containing reducing agent in a finely divided state and transforming said mixture into. briquettes or any other'form of bodies in known manner. The smaller the size. of the grains of the ore and particles of the reducing agent, such as carbon, that is to say, the closer the size of the grains approaches the molecular size the better the method is effected. .In the briquettes the particles of the reducing agent and the grains l of the ore should be distributed as unifor mly as possible and the mass should be of such consistency as will prevent segregation of its constituents.

v If required or found suitable for obtainhesive's of known kind may be used in the process of transforming the materials into solidified state but in such case, provided carbonaceous adhesives are used, thetotal 1n the various kinds of charge should be so adapted. that the desired percentage of carbon is obtained in the final product. p In some instances the charges or briquettes are dried prior to being introduced into the electric furnace, in'air or some other atmosphere,

.for instance, an atmosphere-containing'carhome acid, when usmghme or lime-white as an adhesive and areagent. Thus, if liq- 'uid'carbonaceous reducing material or liquid adhesive has been added, the mass will be dried so that these'materials become solid and keep the particles of the ore and those of the reducing agent together in fixed relation. By the drying process any contents of water that may be present are expelled,

so that bursting of the briquettes or bodies through steam developed by the heat in the furnace cannot take place.-

If, to facilitate a very intimate mixing of the particlesof the ore with those of the reducing agent and any adhesive added,-a

certain percentage of water has to be added, it may be preferred only to partially dry the mixture prior to the briquetting process which is best carried out with a certain percentage of water in the mixture.

Obviously, if a plurality of metals are to be alloyed with the iron, separate charges,

preferably in the form of solidified bodies, may be prepared from the ores of each of said metals, or a charge may be prepared from a suitable mixture of these ores.

Y The charge of the base metal, for instance, iron ore, may be reduced'and melted in ad-v sition of the final productand it will then be found easy during working to take tests to ascertain whether the desired proportions have been obtained, andiby an increased addition of the one or the other kind of charge to control the final composition of the product. Y

' Of course, such afurnace practice may also be applied when reducing and melting an admixture of different kinds of charge. Thus, by controlling the quantity fed in of each kind of charge, alloys having different percentages of the alloyin metal or metals may be readily produced wit out varying the composition of each kind of charge. If only a small quantity of other metal is to be alloyed with the base metal, it is preferred first to reduce the base 'metal out of the base metal charge in the manner set forth, and then to reduce the metal or metals to be allo ed with the base metal out of the alloy 0 arge or charges. Withgreater percentages of alloying metal that order is used between the different kinds of charge which is found most advanta eous in each individual case.

In or inary cases .deoxidizing of iron or 1 steel is effected by the addition of deoxidizing metals, generally ferro-manganese or ferrosilicon or both, in a metallic state, and such deoxidation may be applied also to our present process at any desired time during a smelting. It is preferred, however, to prepare bri uettes or other bodies in the-manner previous y set forth, out. of oxide ore of a metaladapted to be used as a deoxidizing agent, especiallymanganese, such briquettes a being reduced and melted on the slag bath in the furnace when deoxidation of metal orslag or both is to be effected. The deoxidizing metal reduced in this process then removes from the alloy previously obtained in the furnace aigreater or smaller part of its oxygen, and is transferred into the slag bottom of the furnace. In producing, for in stance,so called rustless iron andv steel holding 9-16% Cr and below 0.7% 0., the consumption of chromium charge for a given quantity of alloy will be considerably smaller if reduction is effected in the manner set forth. 7 Ifnot, such reduction will take place with the chromium first reduced out of the chromium charge, which chromium is thus lost in the slag. As the chromium ore is much more expensive per unit of oxygen absorbed tric resistance heat developed in the slag,

from the slag than is; for instance, manganese ore, a considerable .saving will be attained in this manner.

'The reduction and melting should preferably take place with the electrode or electrodes out of contact with the charge or charges, especially'when using carbon electrodes, and by the aid, at least in part, of eleift. e charge or charges being reduced and melted whilst floating on or in said slag as is more fully described in our Patent No. 1,686,206. The present invention takes the process of that application several steps further, in that, instead of one charge, two or more charges are used, for example, an iron charge and a chromium charge, and these two charges are so proportioned to each other as to produce the desired alloy directly. Our success in producing these alloys, particularly the lower carbon alloys, such as stainless iron, directly, where prior inventors have failed, appears to be due in great part to the fact that in the present process the charge is reduced and melted while floating on the top of or in a slag bath .in an electric furnace .with the aid, at least in part, of electric resistance'heat developed in the slag and that the particles of ore and carbon are mixed in correct proportions in intimate contact with one another, which contact is maintained during the course of the reaction.

In reducing and melting the different kinds of chargein succession, it is preferred in some cases, after one kind of charge has been reduced and melted wholly or partly to draw off the slag thus formed out of'the furnace,

before treatment of the next kind of charge is commenced. The reasons for this are different. In ores of comparatively expensive metals, a considerable saving may be attained in this manner, owing to slagging of the expensive metal to a less extent, in that a smaller quantity of slag than otherwise'is saturated in the furnace with oxides of this metal. If

some or more of the oxide ores holdsulphur' to such an extent that the-percentage of sulphur in the metal produced would be higher than desirable, it is preferred first to reduce and to melt the charge or charges containing this ore or these ores respectively, and then wholly or partly to draw ofi the slag obtained for removing the sulphur absorbed in the same. Prior to tapping the slag the same may be deoxidized in the manner hereinabove set forth, or in some other way, for instance, by the addition of lime and carbon and by working with the electric arc, so that carbide of calcium is formed, in order to reduce the percentage of-metal of the slag, and to increase its capability of absorbing sulphur. By tapping the slag intervening with the melting of the diiferent kinds of charge, the phosphorus transferred into the slag may also be removed from the furnace, before the same would, perhaps, be reduced. and absorbed. in the metal in the treatment of the other kind of charge. By controlling the total percentage of carbon in the different kinds of charge, a product having thedesired percentage of carbon may be produced directly. The desired percentage of carbon in the product may also, however, be obtained by controlling the percentage of carbon in the kind of charge out of which a metal havinga low percentage of carbon may be most readily produced, thus, for example, in the iron ore charge,- so that a metal having a low percentage 0 carbonis first obtained, that is to sa iron, in the example given, and by then ad ing the other kind or kinds of charge having a percentage of carbon so adapted that the final product will have the desired percentage of carbon. If, however, products having difierent percentages of carbon areto be produced, it is more simple to use chargesdn which the total quantity of carbon has been adapted so that a product of alloyed iron or steel or an alloy as low in carbon as possible is obtained which is then carburized to the desired percentage of carbon in the furnace or outside the same. Preferably this carburization may also be effected.

by introducing into the furnace and by reducing and melting, in'a final process, a certain furnace, either in the furnace or outside the same, for instance in a ladle or another furnace. In the same manner, an iron alloy or the like having approximately the proper percentage of the desired alloy substances,

such iron alloy beingproduced directly out of oxide ores according to the invention,

may preferably beadmixedwith such alloy substances in a metallic state in known manduced at a much lower cost than in the meth ods heretofore practised for the production of such alloyed'irons and steels. In order not to attain too high percentages of carbon in the final product, the alloy substances, as a matter of fact, hitherto had to be added to the iron in the form of very expensive low- 'rustless.

carbon alloys of these substances, With the application of this method, for example, so called rustless iron or steel, that is to 'say an iron having a rather high percentage 0 chromium or about 916%, and a rather low percentage of carbon, or below 0.7%, may be produced directly. No difliculty will be experienced with this method in directly roducing an iron holding, for instance, a out 14% Cr and below 0.1% C.which,without further treatment may directly be regarded as In the production of such rustless iron it has been found particularly suitable to use lime-white as anadhesive, either in the iron ore charge or in the chromium ore charge, or in both kinds of charge. The reason for this is that the chromium ores contain, as ..a rule, a large quantity of magnesia, which makes the slag produced viscous unless'a com- %aratively large quantityzoflime is added. y the addition of lime-white, an almost complete desulphurization of the metals 'is obtained at the same time while reducing and melting the charges of the two kinds of ore,

inasmuch as the lime' covering'thegrains as a film absorbs the sulphur while forming sillphideof calciumwhich is absorbed in the s ag.

' In order to form a suitable slag in the fur?- nace for the reduction and the melting of the diflerent kinds of charge, requisite fluxes may be admixed either in a finely divided state in preparing thedifierent kinds ofcharge, or, such fluxes may be directly'introduced into process. 4

The followingis a specific example of the proportioning of the charges in accordance with our invention for the production of socalled rustless iron, it being understood, how'- ever, that the invention is not limited to the composition of the to herein. For the production of rustless iron, an iron charge and a chromium charge are used hav difi'erent charges referred the following composition in part by The charges are both prepared of finely divided ore, preferably of such a grading as to be able to pass a sieve having at least 550 meshes per cmF, and finely divided charcoal of the same rading; The lime is preferably used in the orm of lime-white and act s as a binding agent. After the materials have been accurately mixed and the mixture brought into briquettes or other pieces, the charges are carefully dried. The iron charge is 'then fed into the electric furnace and reduced and melted whilst floating on or in a slag bath in saineby the aid, at least in part, of electric resistance heat developed in said slag bath, an iron 'very low in carbon being then obtained on the bottom of the furnace, whereas the slag becomes rather rich in ferrous oxide. The greater part oftheslag is then ta ped ofi and the sla may be deoxidize for instance by intro ucing into the furnace. briquettes or other bodies of man-v ganese ore and carbonaceous material, for the purpose of saving chromium. The chromium charge is then fed into the furnace and reduced and melted in the same manner as the iron charge. In order to utilize chromium oxlde contained in the slag, a suitable quantity of a thermal reducing agent, preferably ferro-silicon, may be added to the slag. By suitably adapting the quantity of the chromi- 11m charge'in relation to that of iron char e, an iron having the content of chromium e slred will directly obtained. 3

If, on the other hand, stainless steel is to' be produced, the carbon content in one of the tended contentsof chromium and carbon.

the furnace. Preferably, the admixture 'of flux is then adapted so that a slag is obtained which is suited to each separatereduction:

. from oxide ore of said metaland oxide ore- What we claim is:--- i g 1. A method of producing an alloy of a metal belonging to the iron group directly of the alloy constituent or constituents, which, in a group ofstep'sfincludesforming separate mixtures ofach 'ofsaidores with an amount of carbon-containing reducingagent propor-,

tioned to the'reductionof the ore and'to the v desired percentage of carbon in'the, alloyobt aihed erefrom, briquetting said mixtures separately, '-and reducing and melting said i briquettes on a slag both an-clectric furnace whilst proportioning the quantity of briquettes of each kind so as to obtain an alloy of the desired composition.

7 2. A method of producing an alloy of a metal belonging to the iron group directly from oxide ore of said metal and oxide ore of the alloy constituent or constituents,

which, in a group of steps, includes forming separate mixtures of each of said ores with anamount of carboncontaining reducing agent proportioned to the reduction of the ore and to the desired percentage of carbon in the alloy obtained therefrom, briquetting said mixtures separately and reducing and melting on a slag bath in an electric furnace briquettes of each kind one after the other in order to provide for adapting the working conditions of the furnace to each kind of dif ferent'ores whilst proportioning the quantity of briquettes of each kind so as to obtain an.

alloy of the desired composition.

3. A. method of producing an alloy of a metal belonging. to the iron group directly from oxide ore of said metal and oxide ore of the alloy constituent or constituents, which, in a, group of steps, includes forming separate mixtures of each of said ores with an amount of carbon-containing reducing agent proportioned to the reduction of the ore and to the desired percentage of carbon in the alloy obtained therefrom, briquetting said mixtures separately, reducing and melting said briquettes on a slag bath in an electric furnace whilst proportioning the quantity of briquettes'of each kind in order to produce an alloy of the desired composition and deoxidizing the alloy produced and the slag by reducing and melting in the presence thereof briquettes containing an intimate mixture of finely divided oxide ore of a deoxidizing metal and finely divided carbonaceous material, this latter being added in a quantity proportioned to the reduction of said ore.

4. A method of producing an alloy of a metal belonging to the iron group directly from oxide ore of said metal and oxide ore of the alloy constituent, which, in a group of steps,includes forming separate mixtures of each of said two ores with an amount of carbon-containing reducing agent proportioned to the reduction of the ore and to the desired percentage of carbon in the alloy obtained therefrom, briquetting said mixtures separately, reducing and melting first only one kind of briquettes on a slag bath in an electric furnace, tapping the slag formed during said redu'ction process and adding, reducing and melting the other kind of briquettes Whilst proportioning the quantity of briquettes of steps, includes forming separate mixtures of each of said two ores wlth an amount of carbon-containing reducing agent proportioned briquettes of either one or the other kind andthereby provide the exact percentage of metal contents in the final product.

6. A methodof producing rustless iron or stainless steel directly from iron oxide ore and chromium oxide ore, which, in a group of steps, includes forming separate mixtures of each bf said two ores with an amount of earbon-containing reducing agent proportioned to the reduction requirements of the ore and to the desired percentage of carbon in the alloy obtained therefrom, briquetting said mixtures separately and reducing and melting said briquettes on a slag bath in an electric furnace whilst proportioning the quantity of briquettes of each kind in order to provide an iron alloy containing the desired percentage of chromium.

7. A method of producing an alloy of a metal belonging to the iron group directly from oxide ore of said metal and oxide ore of the alloy constituent or constituents, which, in a group of steps, includes forming separate mixtures of each of said ores with a carhon-containing reducing agent, the percentage of carbon in the mixture containing the ore of the main alloy constituent being proportioned so that the percentage of carbon in the metal reduced from this mixture will be lower than the percentage of carbon in the final product, briquetting said mixtures separately, reducing and melting said briquettes on a slag bath in an electric furnace whilst proportioning the quantity of briquettes of each kind in order to provide an alloy of the desired composition and carburizing the mixture, whereby to obtain the desired percentage of carbon in the final product.

In testimony whereof, we have hereunto set our signatures.

HENNING GUSTAV FLODIN. EMIL GUSTAF TORVALD GUSTAFSSON.

each kind in order to produce an alloy of the 1 desired composition.

5. A method of producing an alloy of a metal belonging to the iron group directly from oxide ore of said metal and oxide ore of the alloy constituent, which, in a group of