US2590843A - Steelmaking process - Google Patents

Description

April"1, 1952 F. CREMER 2,590,843

STEEL MAKING PROCESS Filed March 19, 1948 2 SHEETSSHEET 1 rick Oremer Q\ \WMMNNNAAAA,

A ril 1, 1952 I F. CREMER STEEL MAKING PROCESS Filed March 19, 1948 2 SHEETSSHEET 2 [raven 2%) fiederich Cremer' fgeni.

Patented Apr. 1, 1952 UNITED STATES PATENT ()FFICE STEELMAKING PROCESS Frederick Cremer, Chicago, Ill. 7 Application March 19, 1948, Serial No. 15,853

' Claims. 1

This is a continuation-in-part of my copending application for patent on Steel Making Process, Serial No. 537,184, filed May 24, 1944, now abandoned.

In addition to the subject matter of the abovenoted application, this application includes as new subject matter improvements in the nature of refinements of the process originally disclosed which have been developed during the pendency of thefirst application; and this application also includes in its disclosure apparatus for expediting the originally disclosed process and the refinements thereto disclosed in this application.

One major object of the processes of" this application is to produce as an end product steels which are free from contaminating substances particularly excess of oxygen and/or oxidizing agents, which I have found to be a major cause of erratic behaviors of steel during rolling and in ultimate service.

Another important object of my invention is to provide a melting stock of exactly predetermined characteristics which may wholly or in major part serve as a substitute for presently utilized charges in steel producing furnaces.

Yet another important object of my invention is the production of a melting stock which can utilize for fine steel making pig irons which for any reason at all are seriously variant from desired specifications.

Yet another important object of my invention is the production of a non-molded melting stock in nodule form, these nodules being of relatively small size, hence capable. of stock pile storage, like coal, and easily handled for charging the furnace.

How the foregoing and still other objects and advantages of the invention are achieved is set forth in the detailed description which follows and shown on the accompanying drawings in which:

Fig. 1 is a diagrammatic longitudinal cross section of a type of furnace in which certain steps in my process may typically be accomplished;

Fig. 2 is a transverse cross section of the furnace of Fig. 1 taken substantially alongthe line 2-2 of Fig. 1;

Fig. 3 is a transverse cross section of the furnace of Fig. 1 taken substantially along the line 33 of Fig. 1; and

Fig. 4 is a diagrammatic medial cross section of an electric furnace of the induction type showing the use of nodules of my invention for steel production and the recovery for certian important uses of the gases produced during reduction of the nodules. v

At best, pig irons have always contained impurities which have presented many problems to the steel-making industry. The blast furnace production of pig iron invariably leaves in'the iron a carbon content far in excess of any reasonable requirement of steel. This carbon residue comes wholly from the coke and its reduction to desirable amounts in the finished steel has been a time-consuming and expensive process.

Pig irons also contain a certain amount of sulphur which aside from a few instances is considered highly undesirable in a finished steel. This sulphur, like the carbon, comes wholly from the coke and the problem is increasingly complicated by the-necessity of the industry to use cokes of consistently higher sulphur content as the low sulphur bearing coke-forming coals are exhausted.

Another substance generally considered undesirable in steel making but invariably present in pig iron is phosphorus, which in major part is present in the ore and remains in the iron reduced therefrom, and in minor part is picked up from the coal to further add to the ore-produced phosphorus content.

Additionally, pig irons contain silicon, which like the other above noted substances, is considered highly undesirable if present in any marked quantity in finished steel. This silicon comes both from the gangue material in th ore and from the coke ash.

These present-in-excess or undesirable factors in pig iron are not usually present in the pure elemental form described for them immediately hereinabove but are present in the forms of carbides of iron, sulphides of iron, phosphides of iron and silicides of iron.

Having in mind the production on a commercial basis of a melting stock of this optimum characteristic, namely, metallic iron of extremely low carbon content and for all practical purposes free from contamination with compounds of sulphur, phosphorus and silicon, and capable of reduction to a point of oxygen freedom not heretofore capable of accomplishment, I will describe the process and apparatus by which this may be done.

The first step inthe process is, of course, the determination of the analysis of the pig iron with which I am to work. A typical analysis might be, say, carbon 4.0%, silicon 1.0%, phosphorus .10% and sulphur .05%.

A quantity of the molten pig iron is brought to my mixing furnace Hi, Fig. 1, later herein more fully described, in a ladle (not shown) and slowly discharged from the ladle into the open receiving form of carbon dioxide, and precipitating metallic iron. The converted calcium sulphide floats on the top of the iron associated with the lime powder dross and is caught by another ladle (not shown) into which the mixing furnace may discharge through its discharge end l2.

When the last-mentioned ladle is filled, it is transferred to the receiving end [I of the mixing furnace, the powdery material (consisting of calcium sulphide and calcium oxide) is skimmed off and this ladle is then slowly discharged into the mixing furnace for the second passage therethrough of the iron.

The next step is that of incorporating into the furnace and on the surface of the molten metal a charge of metal-cleansing compound such as calcium ferrite. In using calcium ferrite the charge may be varried according to whether it is desired to remove from the molten iron only the silicides or whether it is desired to also remove therefrom the phosphides. As in the case of the lime, the calcium ferrite is placed on the metal in the form of a finely divided, non-cohesive powder.

Assuming the desire to remove only the silicon from the iron, only a sufiicient amount of calcium ferrite would be added to react with the silicides, a matter capable of relatively accurate determination with the analysis of the iron and the calcium ferrite known (as for instance a calcium ferrite comprised of, say, 75% ferric oxide and calcium oxide and iron of, say, 1% silicon and .10% phosphorus).

The addition of the calcium ferrite starts a heat-producing reaction in which the major iron content of the calcium ferrite becomes metallic iron, the silicon of the iron silicides and the calcium of the calcium ferrite reacting to produce a calcium silicate slag with possible traces therein of calcium phosphate and minor quantities of ferrous oxide.

If it is desired to remove from the iron the phosphorus in addition to the silicon the amount of calcium ferrite added to the metal in the mixing furnace is increased by that amount calculated to react with the phosphorus substantially coincident with the calcium ferrite-iron silicide reaction. The reaction of the silicon and calcium ferrite produces a floating calcium silicate slag and there will thus be added to the calcium silicate slag, resulting from the previously desired reaction, a calcium phosphate slag.

In either of the aforementioned instances this slag, whether it be one principally containin calcium silicate (where the silicides only are removed from the iron) or one containing also calcium phosphate (where the phosphides are also removed from the iron), will float on top of the iron as it is caughtby a ladle when discharged from the mixing furnace and may readily be skimmed off and disposed of.

By the above-described reactions, I remove all but traces of the undesirable metaloids, the sulphides, silicides and phosphides, and for purposes of differentiation from pig iron containing 4 them I call this washed iron uncontaminated pig iron.

' Up to this point in my process little cooling will be found to have taken place in the metal inasmuch as radiation losses are compensated for by the reactions described hereinabove which are of an exothermic nature.

The poured out metal now having been twice passed through the mixing furnace is now returned for its third and final passage therethrough.

The molten metal ladle is again poured into the receiving end ll of the mixing furnace and I now add to the metal a pre-determined amount of an iron oxide such, for instance, as roll scale. The amount I add to the metal in this stage of the process is carefully computed to represent an amount of iron oxide compound the oxygen content of which is sufficient to react with that amount of the carbon in the iron representing an excess over that amount desired to be permitted to remain in the finished or end product. It is pointed out that rarely, if ever, would one wish to add an amount of oxide suificient to wholly reduce the carbon content of the iron.

In this instance I use the term end product as alternatively generic to (1) nodules of the type and formed in the manner hereinafter described or (2) a steel made from these nodules whether mixed, as hereinafter described, or used without mixture with other nodules of different reduction characteristics.

Suffice to say that, however the end product of the reaction about to be described is used, I form my material into masses of relatively small, generally spheroid shape which I term nodules.

It will be obvious that by varying the iron oxide ratio to that of the pig iron carbon content, I can produce a reaction mixture in which any desired final carbon content of the finished product can be provided. Were it desirable to do so I can produce a nodule which, upon being heated, would reduce to a steel having a carbon content of, say, 25% or by reducing the oxide added to the iron I could produce a steel having a carbon content of 1.25%.

The roll scale when added to the molten metal is at about room temperature, thus from the moment of its addition, it being in relatively large ratio on a poundage basis to the iron, a cooling effect is immediately produced by reason of the temperature differentials of the mixed materials which reduces the iron to a temperature not far above that at which incipient crystallization starts.

The roll scale, like the lime or calcium ferrite of the previously described steps, is added to the metal in finely comminuted non-cohesive form. At the beginning of the mixing of the metal and scale in the mixing furnace the scale floats on the surface of the metal and becomes thoroughly admixed therein as will be apparent from the description of the mixing furnace contained hereinafter.

As the mixing of iron oxide and metallic iron continues, some of the oxygen in the oxide reacts with some of the carbon in the iron and an endothermic reaction in the mass begins to take place. As the mixing furnace rotates, the oxide soon thoroughly permeates the mass of metal and as the endothermic reaction continues the crystallization temperature of the iron is soon reached. As this crystallization temperature-is approached the mass tends to solidify in localized spots surrounding the minute roll scale particles and the continued rotary action of the mixingfurnace forms these masses into pelletlike formations or nodules.

In the event of a shortage of good roll scale or other similar iron-oxide-bearing compound it is possible to produce in the mixing furnace of Fig. 1, which it will be noted has a socalled basic lining or internal refractory material, iron oxide from the pig iron itself. This may be done by training into the mixing furnace and over the metal in the first weirs thereof a sharp flame containing an excess of air overthat required for flame production. As this flame passes over the shallow pools of transient fluid pig iron in the furnace the flame gases will create on the top of the iron a floating ferrous oxide which will react in oxidizing the silicon and phosphorus and will also react to some degree with the carbon in the iron to form carbon monoxide. There will thus be created a cooling reaction sufficient, under the rotation of the mixing furnace, to induce nodulization.

As the nodules descend toward the outlet end of the mixing furnace they will continue to give off carbon monoxide which may readily be collected for production of the sharp flame having the air excess required for ferrous oxide production.

The freely-tumbling, descending mass of porous nodules in the reaction indicated hereinabove generate on their surfaces and to some degree within their pores, by reason of their exposure to combustion gases and the excess air, a very pure iron oxide scale equivalent to the finest uncontaminated roll scale.

It needs be said that while most careful control must be exercised in this method of producing the nodule to arrive at the desired quantity of carbon-reducing oxide it is possible by this method to produce a suflicient and exact quantity of such oxide to bring down the carbon content of the finished steel to desired specification.

In that form described up to this point these nodules are chiefly comprised of a conglomerate mixture of metallic iron and oxides 'of highly carboniferous iron in an intimate admixture .of porous, almost cinder-like consistency in which the iron oxide particles are thoroughly and evenly dispersed. The latent heat of fusion released as the iron approaches its crystallization temperature slows down the hardening of the materials effectively causing the nodules to form to desired size as the mixing furnace is rotated. Up to this time I have described the preparation of a nodule which in its final form has removed from it the silicon, phosphorus and sulphur formerly in the pig iron. This nodule has in it, by addition, only that percentage of oxides sufiicient to reduce its own carbon content to an ultimate level at which it is desired to produce a steel made wholly from such nodule. This nodule would be free from slag-forming constituents and upon being placed in a melting furnace would rely upon the carbon monoxide atmosphere formed within itself, and by which it would be enveloped, as a protection against oxidization in the melting furnace. For the purposes of complete differentiation from nodules prepared as described hereinafter, I call the nodule contain ing only iron oxide a slag-free nodule.

I now wish to make it clear that I can produce nodules from pig iron which is not preliminarily put through the steps of sulphur,

silicon and phosphorus removal. While not possessing every advantage which may be had from the more thoroughly treated nodules, for some purposes the nodules hereinafter described are completely adequate. By reason of their size, consistency and intimate admixture of their constituents these less refined nodules will produce many results in steel manufacture of a highly beneficial character as will be hereinafter apparent.

In all the steps of my process described immediately hereinafter, it is assumed that the pig iron about to be nodulized contains carbon, silicon and sulphur in those amounts commonly encountered in an average pig iron, say, for example, carbon 4%, silicon 1%, phosphorus .l0% and sulphur .05%. such pig iron contaminated pig iron.

In the steps of my process about to be described, let it be assumed that the mixing furnace and the reactions taking place therein seek in this case only to produce a nodule, which is utilizable in the open hearth process, as a melting stock, the major portion of the reactions,

- aside from addition of carbon-reducing oxides and nodule formation, taking place in the open hearth furnace.

As above indicated, while the nodule devoid of silicon, phosphorus and sulphur would in the melting furnace form a slag-free melting stock, nodules prepared as hereinafter described would form a slag in the open hearth furnace. For purposes of differentiation of the last mentioned nodules from those described hereinabove, I call them slag-bearing nodules.

A differentiation is made between the "melting furnace for the slag free nodule which could be the open hearth furnace (used for melting purposes only) or that shown in Fig. 4 of the drawings, or in fact, any known melting furnace type and the open hearth furnace which latter is particularly adapted for handling slag-containing or slag-requiring melting stock.

I can prepare in the mixing furnace of Figs. 1 through 3 nodules from molten contaminated .pig iron into a melting stock having great utility (l) by adding directly thereto a suflicient quantity of oxides only for reaction to desired limits with the iron-held carbon, or (2) producing by inherent oxidation by a flame a sufficient amount of oxides, or (3) I can also add to the pig iron oxides and a sufficient quantity of silicon and phosphorus-reactive chemicals such as lime (CaO), calcium carbonate (CaCOs) and/or calcium ferrite which will produce in the open hearth furnace a free floating slag. When calcium ferrite is used in the reaction mixture of my nodule of this type it should preferably contain about 75% iron oxide and 25% of lime.

In forming contaminated pig iron into slag forming nodules having self carbon-reducing properties by incorporating therein only iron oxides I utilize the same methods as have been described hereinbefore with respect to producing, from non-contaminated pig iron, nodules having self carbon-reducing properties. That is to say that I may put into the molten metal in the mixing furnace of Fig. 1, as an additive, a sufficient quantity of iron oxide, in any desirable form, the oxygen content of which has been computed to be sufficient to reduce the carbon content of the iron to desired amounts in the finished steel; or I may carefully oxidize the iron, by a flame having an excess of air, to an oxide content sufficient to reduce the carbon to desired limits.

For clarity let us call In using the nodule-forming method described above it will be noted that no attempt whatsoever has been made to induce change in character of the iron-contaminating silicides, phosphides and sulphides. In this case their removal is left to be wholly a reaction performed in the open hearth furnace.

It is occasionally desirable to form nodules of my invention from contaminated pig iron not only with the carbon-reducing oxide present but also having incorporated therein slag-forming reaction components to insure the early formation of slags of desirable viscosity characteristics. I have found calcium compounds such as lime (CaO), limestone (CaCOg) or calcium ferrite (CaOFezOa) ideal for these purposes.

When lime is used as a metal-cleansing, slagforming reaction component I add to the metal in the mixing furnace the quantity of iron oxide required for carbon removal and also a quantity of lime, both additives being in finely divided non-cohesive form.

As contrasted to the hereinafter described use of limestone as a slag-formant, lime will be found to be only a mild coolant so that it should be added only when the iron is relatively cool, say, 2400" F., to prevent, during nodulization, undesirable lumpy solidification prior to equalization of heat throughout the mass and prior also to incipient solidification of the mixture into nodules.

The lime-iron oxide admixture to the molten iron is adjusted so that the added quantity of lime is sufficient to convert the iron silicides and iron phosphides into calcium silicates and calcium phosphates, which are formed upon reaction with a certain amount of the iron oxide, sufficient to oxidize the silicon into iron silicate, the phosphorus into iron phosphate, the sulphides into sulphur dioxide and a certain amount of carbon into carbon monoxide. phur dioxide and carbon monoxide, being gaseous, will be released. The manipulation in the mixing furnace would be the same as described herein with respect to other reaction mixtures and, of course, the ultimate form of discharge of the mixing furnace would be the nodule-type reaction product forming the nucleus of my invention.

Instead of lime-reaction products as a slag forming metal-cleansing component of my nodule I can also use limestone. In using limestone it is powdered to non-cohesive consistency and added to the molten pig iron together with the carbon-reducing iron oxide. Care must be exercised to set into the mixture only enough limestone to react with the silicon, phosphorus and sulphur in the manner hereinafter described, because the addition of the limestone creates a rapid cooling action which is desirable in case the metal in the mixing furnace should be quite hot. This cooling action is caused by absorption of heat consumed through the dissociation of the limestone into lime and carbon dioxide, the latter tending to oxidize some metallic iron into ferrous oxide, which latter compound, coming into contact with the iron silicides and iron phosphides, oxidizes them into iron silicates and iron phosphates. These iron silicates and iron phosphates in the presence of lime attempt to become converted into calcium silicates and calcium phosphates or calcium-iron-silicates and calciumiron-phosphates. The cooling action commented upon hereinabove is designed to regulate the Both the sul-.

rate of solidification and nodule formation before the oxidization of the silicon and phosphorus is complete, a matter which would only change to some degree the physical chemistry of the resultant nodule and the above-described reactions delayed until the nodule was again brought to reaction temperature in the open hearth furnace. The sulphur would be disposed of predominantly in the open hearth furnace when the iron sulphides on contact with the oxidizing slag-forming constituents would be converted into sulphur dioxide and burned away.

The nodule produced in the immediately hereinabove described manner would be much more a conglomerate than any other described herein in that it would contain metallic pig iron, possibly several oxides of iron (this resulting from both the added oxide and the reaction of the limestone-borne oxides), lime and limestone, and

silicates and phosphates.

Another method of forming a slag-forming type of nodule which closely parallels those utilizing lime or limestone, in addition to carbonreducing iron oxide in the form of roll scale, utilizes the calcium ferrite series as a metalcleansing, slag-forming additive possessing the ability to accelerate the early removal of silicon, phosphorus and sulphur from the pig iron, and to avoid formation of slags of high viscosity characteristics later on. As previously mentioned I prefer that the calcium ferrite be of a composition on the order of about iron oxide and 25% calcium oxide (lime). The roll scale being at room temperature has a slight cooling effect on the molten metal and the addition of the calcium ferrite in fine powdered form i quickly incorporated in the metal by the rotation of the mixing furnace and institutes an exothermic reaction readily overcoming the cooling effects of the roll scale. The mixture of roll scale and calcium ferrite temporarily inhibits formation of a fluid slag and maintains throughout the noduleforming mass a condition of non-cohesiveness readily permitting equalization of heat in the furnace-held mass and, in consequence, the ready formation of nodules when the crystallization temperature of the nodule-forming material is reached.

Referring now to the drawings, in this instance particularly to Figs. 1 through 3, there is therein shown a mixing furnace well adapted to proper production of the nodule of my invention. The mixing furnace i0 is considerably elongated in contrast to its diameter. As best shown in Figs. 2 and 3, the furnace throughout its length is of rectangular cross section twisted convolutely. That is to say that it is comprised of four side walls l3, l4, l5, I6 connected along adjacent edges and the structure formed by the walls being so twisted throughout its length that there is defined between the juncture of any pair of walls taken in a cross sectional plane at one point and in a cross sectional plane at another point not too remote therefrom (for instance, in that portion between the planes at which Figs. 2 and 3 are taken) convolutely arcuate portions typically indicated by reference numeral 11.

As best shown in Fig. 1 the mixing furnace is tilted slightly to a lower level at that point adjacent its discharge end 12 than at its intake or charge-receiving end H. At spaced intervals throughout its length I provide partial bafiles I8 of semi-convolute configuration which extend into the mixing furnace to retard the flow of materials therethrough.

Holding, as it must, metal in its liquid and high temperature form the interior of the furnace will, of course, be formed of suitable refractory material l9 which should be basic as contrasted to "acid materials. This refractory material is held within an appropriate steel shell 20. Positioned along the shell 20 are a plurality of annular supports, each indicated 2i, borne by appropriate rollers 22 (Fig. 2).

A ring gear 221' mounted on shell 20 driven by a drive gear 23 furnishes rotation to the furnace. Gear 23 is mounted on a suitable shaft on the opposite end of which is a variable speed pulley 24 driven by a belt 25 connected to a reversing mechanism 26.

It will be obvious that the above described structure provides a mixing furnace capable of being rotated in either clockwise or counterclockwise direction at variable speeds. This is of great importance when it is considered that the I rate of flow of the materials therethrough and the amount of rotational agitationgiven them can seriously affect the chemical reactions taking place within the furnace and also the formation of the nodules. It will also be obvious that the configuration of the furnace is such as to give to the materials passing therethrough during rotation of the furnace alternate spreading out and contraction of the exposed upper surface with corresponding change in the depth of the materials, all of which is of utmost importance in handling the powdery, light, non-cohesive reaction component added to the iron While therein and producing that intimate admixture of such reaction components which is essential'to getting the greatest benefit that may be had from the nodules of my invention.

Referring now to Fig. 4, there is therein shown an electrical induction furnace comprising a crucible-like lining llll reposing in a refractory material III with the water-bearing induction coils H2 helically entwined therearound. The upper lip H3 of the lining H] is outwardly flared, as shown, to abutting'ly receive the annular lip lid of an inverted and vertically movable inverted hood H5. Surrounding hood H5 is an annular hopper H6 which upon having material placed therein will discharge into the furnace upon lifting of hood H5. At the top of hood H5 is an outlet tube Ii] to which is connected a flexible gas-conveying tube I 18.

The induction furnace of Fig. 4 finds utility only in using my slag-free nodule for steel production. A charge of slag-free nodules may be placed in this furnace and when suificient heat has been generated the carbon-oxygen reaction between the oxides and carbon content of the nodule will begin to take place. The steel now at desired carbon content will begin to accumu; late in the bottom of the furnace and the carbon monoxide generated during the reduction process will be driven upwardly ultimately finding its way into hood I I5 and finding outlet through tube I I! into flexible tube I IS.

The steel may be drawn off as desired through drain 3 19. The carbon monoxide may be utilized by addition thereto to oxygen to form fuel for an appropriately designed internal combustion engine or for production of carbon dioxide in any of its commercially desirable forms and part of this gas may, if desired, be trained across the steel-receiving ladle to prevent oxidation of the steel as it is withdrawn from the furnace in which it was produced.

As hereinbefore to some degree indicated, by

10 carefully proportioning the oxide additive to the nodule to the known carbon content of the incorporated iron, whether the nodules be of the slagfree or slag-bearing type, it is possible to regulate the ultimate carbon content of the steel resulting from reheating the nodule in the open I hearth furnace, where nodules alone are used as the melting stock.

I will now describe a method of utilizing the nodules, preferably those of the slag-free type, for production of a steel of any desired range of carbon content and metallic content in addition to iron including all the metal oxides that are reducible by carbon, iron carbides, silicon carbides, aluminum carbides, iron silicides and iron aluminum alloys, I refer particularly to the oxides of manganese, chromium, nickel, cobalt, molyb denum and tungsten and silicon. By making reducible metallic oxides a part of the reaction mixture of my nodules, I am able to substitute the oxygen of iron oxide by oxygen of the metallic oxide to be reduced, and obtain thereby a ferrous alloy wherein the iron is obtained from the metallic iron contained in either the contaminated or uncontaminated pig iron, and the alloy metal or combination of alloy metals is obtained from the respective metallic oxide or combination of metallic oxides. To illustrate, the addition of manganese dioxide (M1102) to obtain an alloy of iron and manganese. Two chemical equivalents of MnOz contain the same amount of oxygen as one chemical equivalent of roll scale represented by the chemical equivalent symbol F6204.

So called low alloy content steels can be produced in a like manner by mixing into the reaction mixture for the nodules equivalent amounts of respective metallic oxides.

Knowing the carbon content of the pig iron, I

. prepare a quantity of nodules which will produce a steel, say, of a carbon content of 1.25% and stock-pile them. I then prepare ga quantity of nodules which have sufiicient oxides therein to produce thereof a steel containing, say, .10% and correspondingly stock-pile them. Itwill be obvious that if it were necessary to produce a steel to a specification of, say, 575% carbon, a -50 mixture of such nodules placed in the open hearth furnace would produce a steel having this carbon content. likewise, the percentage of each of the high and low carbon content nodules can be varied to produce an ultimate steel of any desired content between the indicated limit values of carbon. This production of steel can be well accomplished in the electric furnace or in the open hearth furnace which in this case are required to serve only for melting and tapping.

The slag-bearing nodules used alone as a furnace charge are susceptible of similar treatment and handling to that described above, but in this case some of the slag produced during the heating of the nodules in the open hearth furnace might necessarily have to be run off in the same manner as is done at present where the open hearth furnace is charged with scrap steel and pig iron plus slag-forming and oxiding agentsin such amount that it becomes necessary to draw off some run-oil slag to lower the slag level in the furnace.

Both the slag-forming nodules and the slagfree nodules find utility as a substitute for scrap steel when this latter material is in short supply. While the slag-containing nodule willproduce in the open hearth furnace somewhat more slag than is present when steel scrap alone is used as a supplement to conventionally used pig iron, the slags will be formed early and with a low iron content due to reduction by carbon and may be easily disposed of in the conventional manner of slag flushing.

The slag-free nodules when used as a substitute for scrap steel will result in less slag in the open hearth furnace than present therein under present methods of scrap steel-pig iron steel production. Still other uses of nodules, which could be readily prepared b my process, would be that of preparing them to have an oxide ratio in excess of their own carbon removal requirements, the excess oxides permitting use of the nodules as a substitute for relatively silica-free open hearth lump ore used to increase in the slags the oxide ratio; and' the converse use of nodules prepared with short oxide contents which could be used as a substitute for pig iron as a reagent --for blocking the heat by decreasing the oxide ratio in the slags. The reason that nodules would better serve these opposite purposes than the lump ore or the pig iron being that the well distributed nodules would float in the slag by reason of their gas-exuding characteristics under heat, hence be available, where most desired, for the specific purpose of controlling the slag chemistry, a matter which is not true with respect to lump ore or pig iron.

One matter which has been briefly mentioned hereinbefore but which deserves greatest emphasis is that the nodules of my invention, whether slag-free or slag-bearing, in use as a 100% melting stock, produce a practically oxygen-free steel.

I attribute the ability of my nodules to produce fine quality, accurate-to-carbon specification relatively oxygen free steels to physical and chemical properties possessed by them which I will now discuss.

In the first place, it is to be realized that in putting my reaction substances into the molten pig iron in the melting furnace, in every instance they are put therein in a highly comminuted, powdery, non-cohesive form. Only a non-drafty furnace, such as that shown on the drawings, will suffice to handle these products in this airdispersable form. Most furnaces including particularly open hearth furnaces operate under draft conditions making use of powdered reducing agents impossible. The continuous roll-over, expansion-contraction type of rotational agitation imparted to the metal and powders by my mixing furnace assures their thorough and uniform commingling. Thus each particle of the undesirable sulphides, silicides, and phosphides in the pig iron (in the case of the slag-bearing nodule) is put into close juxtaposition to a particle of a substance which will, either directly or by chain reaction, react with it.

In the cases of both the slag-bearing and slagfree nodules the carbon-reducing iron oxide is likewise added to the molten pig iron in finely divided, powdery, non-cohesive form. The carbides, like the other metalloids in the iron mass are relatively uniformly distributed, and thus, carbide particles are placed in close juxtaposition to an oxide particle of sufficient potency to react therewith producing metallic iron and carbon monoxide gas.

It will be further helpful at this point to note that the reaction materials are in closely arranged molecular juxtaposition and the nodule itself is not a solid, but on the contrary, a spongelike but cohesive mass having much the appearance of a common cinder. This is due to the fact that during its formation at the temperature of crystallization thereof, a considerable gas production due to reaction between its components is reached.

Thus when a nodule is reheated to that degree at which the formerly interrupted reaction which was taking place therein at the time of its forma tion, can again take place, the resultant carbon monoxide gas finds ready egress through naturally preformed outlet channels facilitating rather than impeding the reaction and releasing from each nodule its own re-oxydization-preventing atmosphere.

To sum up, it will be obvious that by bringing the particle size and ratio of the oxide as nearly as may be .done to correspond to the particle size and ratio of the carbide with which it is to react and by distributing the reducing agent thoroughly throughout the mass of the iron and by providing natural outlets for the gaseous reaction products, not only will the reaction due to reheating be facilitated, but it is obviously bound to be thoroughly complete, assuming, of course, that the percentage of oxide has been properly computed.

Thus there is no residual remainder of un-reacted iron oxide left to contaminate the steel.

There is one additional factor which contributes to the presence of oxygen in steel as presently made, namely, the fact that at the temperatures at which steels are made (2600 F. and upwards) in order to reduce the carbon content some of the oxides actually go into solution in the steel, and this temperature is so high that it is above the optimum thermal range at which the carbon in its lower concentrations will react sufficiently with the oxides, whereby a commercial steel may be made. This condition is the result of the chemical equilibrium phenomenon controlling the reversible chemical reactions involved.

The optimum temperature range for reaction of iron carbides and iron oxide have found to be in the range from about 1800 F. to about 2650 F. and the optimum from the standpoint of speed for each steel is that rangeysay, about 50 prior to its meeting its melting temperature. It will be realized that the higher the carbon content of the finished steel the lower will be its meltin temperature.

While the above temperatures are optimum for the reaction it will be found that in using nodules of the type described herein, the ignition temperature of these reactions is around 1500 F. Thus when a furnace is charged wholly with nodules and these are brought to about 1500 F. the carbon-iron oxide reaction will actually begin. The top layer in the open hearth furnace will first start to give off carbon monoxide gas, then as lower layers in the furnace reach ignition temperature the reaction will start therein and so on. As the temperature in the furnace-held mass increases, the reaction will be accelerated and continue until that temperature slightly under melting temperature is reached. Assuming, for instance, a relatively high carbon steel having a melting temperature of, say, 2600 F. the reaction will be found to reach completion, as evidenced by the absence of exuding carbon monoxide gas, in a temperature range immediately therebelow. Now, in the case of use of the non-slag forming nodules it is necessary that a cover, hereinafter described, be provided for the material to prevent re-oxydation during that period when the steel is brought to the tapping heat by the furnace flame. The tapping heat is considerably above .ishing slag is developed thereon While the steel is brought to tapping heat.

It will thus be apparent that the carbon-reducing reaction in nodules of the type constituting my invention takes place in a temperature range below that of the melting point of the steel in consequence of which the oxides are entirely reduced by the excess of carbon'remaining in the steel at temperatures so low that there is not the slightest opportunity for any of such oxides to go into solution in the steel. By the time the steel becomes fluid the oxides are completely reduced.

By being heated under a protective blanket of carbon monoxide gas and by being further blanketed by a slag cover as the melting temperature isreached, this slag cover being self-generated in the case of the slag-bearing nodules, or, in the case of the non-slag bearing nodules this slag cover being produced by the addition into the furnace of a neutral silicate and. fluorspar containing slag, the steel is well prevented from reoxydation during that further heating required to bring the steel to the tapping temperature.

While I have hereinabove given the practical facts with respect to nodules of the type herein described I have evolved a theory which seemingly further explains my ability to produce steels which are oxygen-[free to a degree not attainable by conventional methods using melting stocks which differ from nodules. This theory also seemingly accounts for the ability of the iron carbides to reduce by approximately complete reaction the oxides in the pig iron prior to achievement of the melting point thereof. This theory assumes that the so-called solid state of iron-carbon alloys existing below their respective melting points may more scientifically be defined as a crystallized state in which all matter therein down to the smallest particle is arranged in a symmetrical order, a definite internal structural pattern having a, regular fixed arrangement of atoms in a space lattice. This concept is in sharp contrast to the molten state of the iron-carbon alloy wherein my theory envisions the matter in the liquid as being in an amorphous condition, the particles forming being arranged in a haphazard, random mobile relationship.

Now it is a well known fact that carbon in the form of carbide of iron has the property of diffusing in a metallic iron matrix at a relatively fast rate, the speed of diffusion depending on the carbide concentration differential in different parts of the reaction system and temperature.

. the carbide in the orderly arrangement of matter in the crystallized state.

' Thus under temperature conditions below the melting point of the matrix which may be highly favorable to carbide diffusion, the oxide is yet held in a relatively fixed condition, unable, so to speak, to escape contact with the diffusing carbide and being reduced by contact'with the carbide to metallic iron and oxygen, the latter combining with the carbon in the carbide to produce carbon monoxide which passes off as a gas, and producing also metallic iron. The production of the metallic iron, temporarily devoid of carbide content, induces a temporary carbide concentration differential soon brought to equilibrium as more diffusing carbide seeks to overcome this differential, this reaction continuing until each carbide particle that can do so has sought out and reduced such oxide as it can find until a point is reached where the carbides in excess of the oxides can no longer find oxides with which to react.

My theory with respect to the inability to completely de-oxydize steel when this is attempted, as in conventional practice, by melting stocks not in nodule form, at high temperatures, say, above the melting point of steel, even though exactly the same components were used and in exactly the same proportions as I would use in the nodule of my invention, is as follows: a

I propound the theory that the carbon monoxide resulting from the reaction of the carbides and the oxides, each reacting particle of each of which is in a mobile state in the molten matrix, has a reaction-inhibiting effect particularly as the low concentration point of the oxides is reached. My theory in that regard assumes that when a particle of diffusing iron carbide meets a mobile and diffusing iron oxide particle the explosive formation of the carbon monoxide gas propels the particles apart by a jet-like action, terminating the reaction short of full completion, producing in the seemingly deoxydized mass of steel a pseudo-equilibrium by reason that the mobile oxides to a degree can escape from complete reduction by the carbides. This would inevitably result in the presence of oxygen in the steel unless reduction thereof were continued for extremely long and completely unfeasible periods.

From a time saving standpoint I Wish to point out that by using nodules of the type hereinabove described it is possible to increase the production of each open hearth furnace from 10 to 50%. Typically, under present practice the ela sed tap- V to-tap time is from about 10 to 11 hours whereas under my methods the tap-to-tap time may be reduced to as little as from about 7 to 9 /2 hours. This is due to the accelerated rate at which the furnace may be charged with nodules as contrasted to filling the furnace with scrap and pi iron and the accelerated rate of carbon-removal reaction which is possible by the use of nodules.

Still another additional savings factor reposes in the fact that at the continuous high temperatures at Which conventional open hearth furnaces must operate, they soon burn out. The lower reaction temperatures at which the nodule of my invention may be melted to produce steel of desired characteristics considerably lengthens furnace life.

Yet another factor worthy of consideration is the fact that, being substantially oxygen free due to inherent factors, de-oxydizing agents in short supply, manganese in particular, may be reduced to a minimum to take care of teeming.

From the foregoing it will be apparent that nodules made in accordance with my above-described process and apparatus represent a marked advance in the steel-making industry.

Having described and shown my inventions in considerable detail, I do not wish this exactness of disclosure to be taken in a limiting but rather in-an illustrative sense, desiring to be limited only as I may be by the scope of the appended claims. a

I claim:

1. The method of producing an unmolded porous nodule comprising a homogeneous mixture of pig iron and iron oxide for the production of steel of a desired carbon content, said method comprising introducing pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in l a molten state into an elongated rotary furnace having a basic refractory lining of non-circular cross-section which is twisted longitudinally, introducing onto the surface of the molten pig iron powdered iron oxide in an amount such that the oxygen content of the said oxide is suiiicient to react with some but not all of the carbon content in the iron, rotating the furnace on its longitudinal axis to subdivide the molten pig iron and the said oxide into a succession of closely spaced, shallow pools and to effect an alternate increase of the surface areas and a decrease of the depths and a decrease of the surface areas and an increase of the depths of the said pools and to simultaneously pass the pools successively through the furnace, thus effecting an intimate and uniform mixture of the said oxide and the molten pig iron, coincidentally and progressively cooling the mixture to a crystalline state, continuing the said movement of the furnace until the homogeneous mixture forms into discrete porous nodules, and discharging the nodules from the furnace.

2. The method of producing a homogeneous mixture of pig iron and iron oxide for the production of steel of a desired carbon content, said method comprising introducing pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into an elongated rotary furnace having a basic refractory lining of noncircular cross-section which is twisted longitudinally, introducing onto the surface of the molten pig iron powdered iron oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, rotating the furnace on its longitudinal axis to subdivide the molten pig iron and the said oxide into a succession of closely spaced, shallow pools andto effect an alternate increase of the surface areas and a decrease of the depths and a decrease of the surface areas and an increase of the depths of the said pools and to simultaneously pass the pools successively through the furnace, thus effecting an intimate and uniform mixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

3. The method of producing a homogeneous mixture of pig iron and a carbon-reducible metal oxide for the production of steel of a desired carbon content, said method comprising introducing pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into an elongated rotary furnace having a basic refractory lining of non-circular cross-section which is twisted longitudinally, introducing onto the surface of the molten pig iron a powdered carbon-reducible metal oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, rotating the furnace on its longitudinal axis to subdivide the molten pig iron and the said oxide into a succession of closely spaced, shallow pools and to effect an alternate increase of the surface areas and a decrease of the depths and a decrease of the surface areas and an increase of the depths of the said pools and to simultaneously pass the pools successively through the furnace, .thus effecting an intimate and uniform mixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

4. The method of producing an unmolded porous nodule comprising a homogeneous mixture of pig iron and iron oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into a rotary furnace having a basic refractory lining of non-circular cross-section to form a pool therein, introducing onto the surface of the molten pool of pig iron powdered iron oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, rotating the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface area and increase of depth of the pool and thus effect an intimate and uniform admixture of the iron oxide and the molten pig iron, coincidentally and progressively cooling the mixture to a crystalline state, continuing the said movement of the furnace until the homogeneous mixture forms into discrete porous nodules, and discharging the nodules from the furnace.

5. The method of producing a homogeneous mixture of pig iron and iron oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into a rotary furnace having a basic refractory lining of non-circular cross-section to form a pool therein, introducing onto the surface of the molten pool of pig iron powdered iron oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, rotating the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface area and increase of depth of the pool and thus effect an intimate and uniform admixture of the iron oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

6. The method of producing a homogeneous ixture of pig iron and a carbon-reducible metal oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into a rotary furnace having a basic refractory lining of non-circular crosssection to form a pool therein, introducing onto the surface of the molten pool of pig iron a powdered, carbon-reducible metal oxide in an' amount such that the oxygen content of the said oxide is suflicient to react with some but not all of the carbon content in the iron, rotating the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface. area and increase of depth of the 17 pool and thus effect an intimate and uniform admixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

7. The method of producing a homogeneous mixture of pig iron and a carbon-reducible metal oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron which is substantially free from objectionable amounts of sulfur, phosphorus and silicon for steel making, in a molten state into a furnace having a basic refractory lining of non-circular cross-section to form a pool therein, introducing onto the surface of the molten pool of pig iron a powdered, carbonreducible metal oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, moving the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface area and increase of depth of the pool and thus effect an intimate and uniform admixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

8. The method of producing an unmolded por ous nodule comprising a homogeneous mixture of pig iron and a carbon-reducible metal oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron in a molten state into a furnace having a basic refractory lining of non-circular cross-section to form a pool therein, introducing onto the surface of the molten pool of pig iron a powdered, carbon-reducible metal oxide in an amount such that the oxygen content of the said oxide is sufiicient to react with some but not all of the carbon content in the iron, moving the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface area and increase of depth of the pool and thus effect an intimate and uniform admixture of the said oxide and the molten pig iron, coincidentally and progressively cooling the mixture to a crystalline state, continuing the said movement of the furnace until the homogeneous mixture forms into discrete porous nodules, and discharging the nodules from the furnace.

9. The method of producing a homogeneous mixture of pig iron and a carbon-reducible metal oxide for the production of steel of a desired carbon content, said method comprising introducing a mass of pig iron in a molten state into a furnace having a basic refractory lining of non-circular cross-section to form a pool therein, introducing onto the surface of the molten pool of pig iron a powdered, carbon-reducible metal oxide in an amount such that the oxygen content of the said oxide is sufiicient to react with some but not all of the carbon content in the iron, moving the said furnace to effect alternate increase of surface area and decrease of depth and decrease of surface area and increase of depth of the pool and thus effect an intimate and uniform admixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

10. The method of producing a homogeneous mixture of pig iron and iron oxide for the production of steel of a desired carbon content, said method comprising treating an impure pig iron in a molten state to remove therefrom objectionable amounts of sulfur, phosphorus and silicon, introducing said purified pig iron in a molten state into an elongated rotary furnace having a basic refractory lining of non-circular cross-section which is twisted longitudinally, introducing onto the surface of the molten pig iron powdered iron oxide in an amount such that the oxygen content of the said oxide is sufficient to react with some but not all of the carbon content in the iron, rotating the furnace on its longitudinal axis to subdivide the molten pig iron and the said oxide into a succession of closely spaced, shallow pools and to effect an alternate increase of the surface areas and a decrease of the depths and a decrease of the surface areas and an increase of the depths of the said pools and to simultaneously pass the pools successively through the furnace, thus effecting an intimate and uniform mixture of the said oxide and the molten pig iron, and coincidentally and progressively cooling the mixture to a crystalline state.

FREDERICK CREMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 84,053 Ellershausen Nov. 17, 1868 85,053 Blair Dec. 22, 1868 91,901 Blair June 29, 1869 860,922 Lash July 23, 1907 885,248 Hibbard Apr. 21, 1908 1,180,994 Ford Apr. 25, 1916 1,475,762 Ford Nov. 27, 1923 1,477,135 Lash Dec. 11, 1923 1,527,536 Byrnes Feb. 24, 1925 1,590,730 Evans June 29, 1926 1,590,739 Evans June 29, 1926 1,815,946 Langer July 28, 1931 1,865,183 Gaus June 28, 1932 1,897,647 Hart Feb. 14, 1933 1,907,782 Gaines May 19, 1933 2,079,848 Francis May 11, 1937 2,111,344 Weitzenkorn Mar. 15, 1938 2,159,977 Nicholas 1- May 30, 1939 2,302,999 OBrien Nov. 24, 1942 FOREIGN PATENTS Number Country Date 12,950 Great Britain of 1901 550,927 Great Britain Feb. 1, 1943

Claims (1)

1. THE METHOD OF PRODUCING AN UNMOLDED POROUS NODULE COMPRISING A HOMOGENEOUS MIXTURE OF PIG IRON AND IRON OXIDE FOR THE PRODUCTION OF STEEL OF A DESIRED CARBON CONTENT, SAID METHOD COMPRISING INTRODUCING PIG IRON WHICH IS SUBSTANTIALLY FREE FROM OBJECTIONABLE AMOUNTS OF SULFUR, PHOSPHORUS AND SILICON FOR STEEL MAKING, IN A MOLTEN STATE INTO AN ELONGATED ROTARY FURNACE HAVING A BASIC REFRACTORY LINING OF NON-CIRCULARCROSS-SECTION WHICH IS TWISTED LONGITUDINALLY, INTRODUCING ONTO THE SURFACE OF THE MOLTEN PIG IRON POWDERED IRON OXIDE IN AN AMOUNT SUCH THAT THE OXYGEN CONTENT OF THE SAID OXIDE IS SUFFICIENT TO REACT WITH SOME BUT NOT ALL OF THE CARBON CONTENT IN THE IRON, ROTATING THE FURNACE ON ITS LONGITUDINAL AXIS TO SUBDIVIDE THE MOLTEN PIG IRON AND THE SAID OXIDE INTO A SUCCESSION OF CLOSELY SPACED SHALLOW POOLS AND TO EFFECT AN ALTERNATE INCREASE OF THE SURFACE AREAS AND A DECREASE OF THE DEPTHS AND A DECREASE OF THE SURFACE AREAS AND AN INCREASE OF THE DEPTHS OF THE SAID POOLS AND TO SIMULTANEOUSLY PASS THE POOLS SUCCESSIVELY THROUGH THE FURNACE, THUS EFFECTING AN INTIMATE AND UNIFORM MIXTURE OF THE SAID OXIDE AND THE MOLTEN PIG IRON, COINCIDENTALLY AND PROGRESSIVELY COOLING THE MIXTURE TO A CRYSTALLINE STATE, CONTINUING THE SAID MOVEMENT OF THE FURNACE UNTIL THE HOMOGENEOUS MIXTURE FORMS INTO DISCRETE POROUS NODULES, AND DISCHARGING THE NODULES FROM THE FURNACE.

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