Process of producing substantially pure iron

Abstract

Claims

PatentedApr. 28, 1925. ' UNITED STATES PATENT OFFICE. ARTHUR P. HOLLOWAY AND SAMUEL PEACOCK, F WHEELING. WEST VIRGINIA, AS- SIGNORS TO WHEELING STEEL CORPORATION, OF WHEELING, WEST VIRGINIA, A CORPORATION OF WEST VIRGINIA. PBZOOESS OF PRODUCING SUBSTANTIALLY PURE IRON. ll'o Drawing. To aZZ whom it may concern: Be it known that we, ARTHUR P. Hen- LOWAY and SAMUEL PEACOCK, both citizens of the United States, residing, respectively, 3 at Wheeling, in the county of Ohio and State of West Virginia, have invented certain new and useful Improvements in Processes of Producing Substantially Pure Iron; and we do hereby declare the following to be a full, clear, and exact de-. scription of the invention, such as will en able others skilled in the art to which it appertains to make and use the same. This invention relates to a process ofi producing a substantially pure iron product and has for its object to improve the procedures heretofore proposed. With these and other objects in view the invention consists in the novel steps and combination of steps constituting the procsee all as will be more fully hereinafter disclosed and particularly pointed out in the claims. In order'that the invention may be the more clearly understood it is said: As is well known, blast furnace pig iron is a crude iron alloy ,mixture containing say from 60 to 70 per cent free elemental iron and from to 40 per cent o1 various so eutectoids and alloys of iron with carbon, sulphur, phosphorous, silicon and manganese. The well known usual operation of making from such a crude mixture of al But in all such processes the iron is oxidized by the air treatment to an objectionable extent if the metalloids are removed to per cent, and therefore ferroalloys are commonly later employed to rein the form of molten slags or gaseous, Application filed June 12, 1924. Serial No. 719,582. duce oxides. In the case of employment of term-silicon for this reduction the following reaction may take place: The silica, SiO thus produced has a melting point above that of the bath, and can be removed by contact with a" base such as an iron or a calcium oxide with either of which it forms a relatively low melting point silicate. But this latter procedure has its disadvantages as will presently appear. That is, if we consider specifically the open. hearth process with which this invention is more directly concerned, its refining process is largely one of the oxidation of the iron by means of air; its controlling factors consist or time, a high temperature and a fluid slag capable of seizing and holding to itself the oxides and impurities present. The contact between the impurities in the molten and rather crude alloy mixture and the oxidizing reagents is always variable, uncertain and incomplete, so that when one attempts to carry the open hearth process to such an extreme as to cause the elimination of the metalloid impurities down to say below per cent it is inevitable that a more or less large proportion of 'the iron is oxidized to such an extent, that there will be present insulh- Further, when continuing the contact between the molten metal and the various gases present over a long period .of time as is necessary in the prior procedures in order to search out and burn out the diminishing proportions of metallo'id impuritles with, considerable liberation of reaction gases within the metal, as especially is the case when the iron carbide present'is converted into elemental iron and carbon monoxide, a relatively large proportion of gases such as hydro en, nitrogen, carbon. monoxide, etc., are issolved into or are adsorbed by the molten metal. This latter action is 'very objectionable, indeed, for it entails undesirable later procedures to get rid of these gases. The presence, of such dissolved or occluded gas s in the final product is also highly detrimental to the metal when fur ther worked in various industrial procedures. In fact, it may be said that crude pig iron cannot nave its total metalloid con tent reduced below of one per cent by either the Bessemer or the open hearth process and at the same time escape a highly injurious oxidation and gaseous occlusion in the body of the metal. By the term metalloid above employed, is meant carbon, sulphur, phosphorus and silicon. It is further well known to steel masters, that iron may be heavily oxidized and gassed in removing metalloids, and that by means of a succeeding treatment, in the furnace, ladle, or even in the ingot mold, said iron may be deoxidized by various means. Ferroalloys are sometimes used for this purpose as illustrated by the following equation: A similar e nation illustrates the use of ferro-silicon. ut these operations are further well known to never be completeunless an excess of the ferro-alloy is employed, and in such cases, the metalloid silicon may be left in the metal in undesirable proportions and the same may be true of the metal manganese. Accordingly these alloys are employed in restricted proportions. It is also a fact that no matter how efficient is such ferro-alloy treatment, it does not eliminate the dissolved, the adsorbed nor the occluded gases present. It is also well known that calcium or aluminum are sometimes added to the molten metal, and thatv they deoxidize the latter very thoroughly, but they again fail to remove all the occluded or adsorded gases that may be present. They are further objectionable in their d'eoxidizing effects as may be illustrated by the following equation: That is, in such eases,vthere remains in the metal an oxide of the aluminum, or calcium, and these oxides melt only at several hundred degrees above the temperature of the molten iron. It results that as these oxides cannot dis-- solve, they remain in the metal as disseminated microscopic impurities'giving all sorts of trouble later, and especially serving as nuclei for corrosion growths; It is also now believed that the iron-ferrous oxide eutectoid which is more commonly known as burnt iron is the fundamental cause of perhaps 60 per cent of iron and steel failures in industrial applications, and that this eutectoid depends for its formation on the nascent iron oxide in contact with metallic iron which is inevitably produced in the prior procedures. In other words, it is believed that while the simple admixture'of iron and ferrous oxide at very high temperatures forms such eutectoid very slowly, if ,at all, yet iron at the instant/of its oxidation when in contact with an unoxidized iron readily forms such eutectoids at lower temperatures and even at temperatures far below the melting point of either. The process of this invention, on the other hand,largely avoids the foregoing objections and produces a clean and substantially pure iron product containing less than r 0 per cent of carbon, silicon, sulphur and hosphorous when taken together, and said clean iron product possesses a minimum of dissolved or adsorbed or occludedgases because of the relatively short time of contact with high temperature gases when in the quiescent state. Said clean iron product in addition to the above is not subjected at any stage to a deoxidizing treatment in the cleansing procedure, and hence it is substantially free of oxide disseminations and eutectoids. The process of this invention therefore, consists simply in working down the silicon, the sulphur and the phosphorus present in the melt by any of the well known open hearth or Bessemer processesfor the production of substantially pure iron, but with this important difference; care is taken to not permit the operation to go through the usual decarburizing phase The molten metal is tapped into a suitable electric furnace, and the temperature is brought up to approximately 1750 degrees (1., keeping such metal covered with a suitable low viscosity basic. slag, preferably containing from two to six per cent sodium oxide in the form of a sodium silicate adniixed with calcium or other silicate. Next, one introduces-iron oxide to said bath below said slag in small proportions and only until the molten iron no longer reacts with the iron oxide to produce carbon monoxide. In the meantime the molten-metal is kept thoroughly stirred in any suitable manner as for example by the motor action of the electric current embeen oxidized to an objectionable extent as in the prior processes and having never been gassed as in said prior procedures, does not need to be later degassed nor even deoxidized. The electric furnace serves to keep the melt up to the required temperature for metalloids to react while being 'fractionally treated with iron oxide,-but the iron not being. at the same time in contact at very -ployed. .The resulting metal having never hightempdratures with oxidizing gases as in the prior procedures, there is found to be no need to subject the metal to adeoxidizing, nor to degassing actions in order to produce a substantially pure iron, roduct. It will now be clear that t e process of this invention difl'er's radially from the prior prdcedures in thefollowing particulars; The molten bath of crude iron is subjected to a refining process in any suitable-and well known fuel fed furnace and in a well known way, but care is t-aken'to so control the air blown into or over the molten mass during the refining as to not produce an objectionable oxidation of the iron. In fact, the refining action in the fuel fed furnace is stopped as soon as the molten mass shows that the iron is practicall freed from silicon, and before it is oxidized. Noattempt remaining iii the mass, the molten metal is next passed from the fuel fed furnace into an electrically heated furnace, Where only sufficient iron oxide is added to the molten bath that is now raised to a high tempera ture and constantly stirred, to reduce the carbon present as desired. The iron product thus produced will be found to be slagless and to have an exceptional purity in that the amount of gases contained therein after treatment in the electric furnace will be substantially zero or at most not more than 0.01 per cent. The - amount of metalloids can readily be reduced to below 0.10 per cent andbr inarily will not be higher than 0.11 per cent. The amount of other impurities will not exceed .03 per cent, so that the entire product can be easily made to contain 99.85 per cent pure IIOIl. What is claimed is z 1. The process of producing an iron product exceeding 99- per cent pure iron, which consists in refining said iron with the aid of air in a suitable fuel fed furnace; stopping said refining action when said iron begins to show signs of decarburization; transferring said iron to an electrically heated furnace; raising the temperature in said last named furnace when out of contact with air to a point higher than is practicable in a v 60 fuel-fed furnace sufficiently for any carbon present to reduce any iron oxide present; and agitating the molten mass and feeding iron oxide thereto sufficient for the metalloids present to be reduced to less than 0.15 per cent. 2. The rocess of producing an iron product excee ing 99.4 per cent pure iron, which consists in refining said iron with the aid of air in a suitable fuel fed furnace, only until sald iron begins to show signs of decarburizat-ion; cutting 01f said air and transferring said iron to an electrically heated furnace: raising the temperature of said.- iron in said electric furnace out of contact withair to a a degree sulficient for any carbon present to reduce any iron oxide present; agitating the molten mass; and feeding iron oxide thereto sutlicient for the .metalloids present to be reduced to less than 0.13 per cent. 3. The process ofproducing an iron prodnot containing more than 99.5 per cent pure "iron which consists in refining in a fuel fed furnace a molten bath of crude iron with the aid of air; shutting off said air when said iron begins to decarburize; transferring the treated iron in its non-oxidized condition to 13.11 electric furnace and raising its temperature above 1600 0.; agitating the molten 4. The process of producing an iron pfodnot containing more than 99.7 per cent pure iron which consistsin refining in a fuel fed furnace a molten bath of crude iron containing substantially no gases; stopping said refining action before said iron begins to decarburize; transferring the treated iron in its non-oxidized condition to an electric furnace and raising its temperature above 1650 C.; a itating the molten bath thus produced; and ceding iron oxide to said last named bath only in suflicient quantities to react with the carbon and other impurities present. 5. The process of producing an iron product containing more than 99.8 per cent iron, and less than 0.12 per cent of metalloids, which .consists in providing a molten bath of iron in a fuel fed furnace; refining said iron until it shows signs of decarburization; stopping said refining action before said iron is decarburized; passing the semirefined iron into an electrically heated furnace; raising the temperature of said iron in said last named'furnace out of contact with air above,1700 (1; agitating the thus heated iron; and gradually adding iron oxide ,to said iron until its metalloid impurities are reduced, below 0.11 per cent. 6. The process of producing an iron prodnot containing more than.99.5 per cent pure iron which consists in refining in a fuel fed furnace a molten bath of crude iron; stopping said refining action before said iron' is decarburized; transferring the treated iron in its non-oxidized condition to an electric molten bath in said last named furnace; and feeding iron oxide to said last named bath only in sufficient quantities to react with the impurities present. 7. The process of producing an iron product containing more than 99.8 per cent iron and less than 0.12 per cent of metalloids, which consists in providing a molten bath of iron in a fuel fed furnace; refining said iron in said furnace: stopping said refining action before said iron is oxidized; passing the treated iron into an electrically heated furnace; covering said iron in said last named furnace with a basic slag; raising the tem erature of said iron out of contact with air above 1700 0.; agitating the thus heated iron; and gradually adding iron oxide to said iron until its metalloid impurities are reduced below 0.12 per cent. 8. The herein described slagless substantially pure decarburized iron product, the same containing more than 99% iron; less than 0.15% metalloids; and substantially all of the gases present ,befone decarburization. , 9. The herein described slagless substantially pure decarburized iron product, the same containing more than 99.4% iron; less than 0.13% metalloids, substantially all of its gases gresent before decarburization; and said pro not being of a character adapted to enhance the corrosion resisting qualities of ure iron. 10. T e herein described slagless substantially pure decarburized iron product the same containing more than 99.7% iron: less than 0.11% metalloids; substantially all of the gases that were present prior to its decarburization; and substantially no compounds enhancing the corrosion of the product. In testimony whereof we afix our signatures. ARTHUR P. HOLLOWAY. SAMUEL PEACOGK.

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Cited By (3)

    Publication numberPublication dateAssigneeTitle
    US-3188197-AJune 08, 1965Surahammars Bruks AktiebolagMethod of refining hot metal in an electric arc furnace
    US-3472649-AOctober 14, 1969Canada Steel Co, Metallgesellschaft Ag, Pickands Mather & CoElectric-arc steelmaking
    US-3472650-AOctober 14, 1969Canada Steel Co, Metallgesellschaft Ag, Pickands Mather & CoElectric-arc steelmaking