USRE23778E - Method of fluidizing slag in the - Google Patents

Description

Feb. 9, 1954 J J BOWDEN Re. 23,778

METHOD OF FLUIDIZINOSLAG IN THE MANUFACTURE OF STEEL BY OPEN HEARTH AND ELECTRIC FURNACE PROCESSES.

Original Filed Feb. 26, 1949 I INVENTOR Jane-a J Bar/051v gma- 4 ATTORNEY Reissued Feb. 9, 1954 METHOD OF FLUIDIZING SLAG IN THE' MANUFACTURE OF STEEL BY OPEN HEARTH AND ELECTRIC FURNACE PROCESSES James J. Bowden, Warren, Ohio Original No. 2,597,851, dated May 27, 1952, Serial No. 78,506, February 26, 1949. Application for reissue June 16, 1953, Serial No. 362,175

Matter enclosed in heavy brackets II appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

Claims.

This invention relates. to themanufacture of iron and steel by the open hearth and electric furnace processes, but more particularly to that part of theseprocesses which relates to the proper conditioning of the slag, which floats upon the molten metal.

Itis well known to those skilled inthe art in themanufacture of steel by. the open hearth of the afore-designated processes that in one of the standard methods of operation the furnace is charged with limestone or lime, iron ore, steel scrap and pig iron. in that sequence, and that the metallic charge is then melted by theheat of an extraneous fuel. such as oil or gas or electricity. And it is also known that when the metal has become molten, the lime, which had been charged on the bottom of the furnace, tends to rise into the slagwhich. is mainly a liquid overlying the steel bath. Iron ore is by no means. always employed. Large tonnage of steel is also made by charging limestone, scrap and pig iron in this designated order.. Or where burned. lime is used theoperator charges small amounts of scrap onto the bottom of the furnace, then burned lime, then the. balance of. the scrap, and finally pig iron. Since the electric furnace process is conventional, it is not described in detaz'l.

The constituents of .this initial slagv in the open hearth process are normally an iron and manganese silicate, but later when suflicient lime comes up into the slag, the principal constituents are dicalcium. silicate, calcium aluminoferrites, calcium ferrites, calcium phosphates and free lime; these salts are formed in that sequence.

These slags, through a constantly changing state of oxidation, normally increase their con centration. of the iron oxide phase, and simultaneously decrease. the concentration of the free lime (CaO) in the slag.

TABLEIOF INCIDENCE AND DISPOSITION or LIME IN THE'NORMAL ORDER OF MINERAL FORMATION IN OPEN'HE'ARTH'SLAG Now, as .is: also well' known in: this technological branch off-science",v the slag as delineated here 2. above is the key to the rate of production of steel ingots, for it is necessary to have a properly conditioned slag to have properly made quality steels. And coincidental with this feature we know that a properly conditioned slag cannot behad until the lime is in solution in the slag; or as-mineralogists say, the slag should be mature. to properly control the manufacture of the steel.

Now as the lime, which is charged on the bottom of the furnace or composes the layer overlying the small amount of scrap on the bottom,

is finally released when the metallic charge is melted, the lime, because of itslower specific gravity, rises through the metal and into the iron manganese silicate slag.

The lumps of lime as they go up through this iron manganese silicate slag are coated. by the slag therewith. But because of the superior afiinity of lime for silica, the manganese and iron in this coating are replaced by the calcium, resulting in a coating (2CaOSiOz) around the lumps of lime floating in the slag bath.

Because of its properties, dicalcium silicate--- seals oil the further calcination or solution of the lime thus encased. The reason for this is that dicalcium silicate has a melting point of 2130* 0. which is roughly some 500 C. higher than the operating temperature of the open-hearth furnace practice.

nace is only suitable for operation at temperatures not in excess of 1650 C.-1700 C. Hence, some other means than a high temperature alone is necessary to dissolve the limestone or lime, and

get it into solution in the slag by reaction, since the furnace structure will not stand up under the temperature necessary to melt dicalcium silicate.

Normally, this is accomplished by-the oxidation of the iron in the charge which thencombines with the lime in the slag to eventually form.

by reason of the law of eutectics, it dissolves the coating of dicalcium silicate from around the lumps of lime, after which the-remaining.

lime is again coated with dicalcium silicate from the slag and the process repeated until'all the. lime is in solution or present as excess uncom---- In the normal practice this bined free lime.

waiting for such oxidizing reaction which forms dicalcium ferrite is too slow, so the'furnace'op erator commonly resorts to the" use: 'of fluorsparr of dicalcium silicate.

For the open hearth furnace is made up mainly of silica brick, and such a fur additions to speed up the solubilizing reaction of the lime. The fluorspar, because of its lower melting point (1360 C.) and the law of eutectics, and its other properties, speeds up the fluxing and fiuidizing process of the lime. However, fiuorspar in some cases is detrimental to the steel quality, unless precisely used, by tending to increase the concentration of FeO in the slag.

The principal object of the present invention is to condition open hearth and electric furnace steel slags containing calcium oxide and calcium silicates, and particularly to fiuidizing such slags by adding a mineral having certain percentage relations to each other of CaO, A1203 and F8203 as explained below and a melting point of 05- 14.35 C. to the slag, which has been formed by heating a charge of metallic iron and a source of calcium oxide.

Another object is to decrease the time necessary to fluidize such slags and thus increase the production of steel i. e. tons per furnace hour, as compared with the employment of fluorspar.

A still further object is to make the slag more effective in removing sonims (solid non-metallic impurities or inclusions) from molten steel by more effectively dissolving lime in the slag.

An additional object is to secure a greater ingot yield from the same melted charge than has been attainable when fiuorspar has been added to assist. The explanation for this appears below.

One other object is the saving of lime in the charge because of more eflicient use, which in turn speeds up production. The lower the lime charge, the faster is the heat time.

Other objects will became obvious or apparent hereinafter from reading the disclosure, more especially with recourse to the accompanying drawing.

For a better understanding of the present invention reference should be made to the accompanying drawing, which depicts a triaxial diagram, the three components of which are, reading clockwise on the triangle, A1203, F6203 and CaO.

Referring to the drawing, the upper points represent 100% A120; and each horizontal line (designated xx, the primes denoting decreases of this component) toward the base a progressive decrease of 10% in the A1203 content. Accordingly, the heavy line parallel to and close to the base of the triangular diagram denotes a content of 1.5% A1203, Whereas the heavy line intermediate the fourth and fifth horizontal line denotes 56% A1203.

The lower right apex of the triangular diagram denotes 100% F8203; and each line y-y (the primes denoting 10% decrease of this component) a progressive decrease of 10% in the F6203 content. Accordingly, the short heavy line, i. e. the third away from the lower right apex, denotes 70% F8203, whereas the much longer heavy line paralleling it but further away from that apex and near the left leg of the triangle denotes 5.0% F6203.

The lower left apex of this triangular diagram denotes 100% CaO; and each line z--z (the primes denoting 10% decrease of this component) a progressive decrease of 10% in the CaO content. Accordingly, the heavy line, the fourth away from the lower left apex, denotes 60% CaO; and the heavy line parallel therewith further away denotes 25% CaO.

These six lines, consisting of the three sets of parallel lines just described form a hexagon which has the following boundaries (read ng from top clockwise), expressed in terms of components The mineral compositions of the present invention fall within the areas identified as E, D, and C in the order of preference recited, each of which areas is within this hexagon.

In accordance with the present invention a mineral, whose components of initial formation are calcium oxide, alumina and iron oxide, combined in accordance with percentages of each which fall within area E, D or 0 shown in the drawing with the preference in that sequence, and which has been formed by melting these components, is added to the partly formed slag and after the metal in the charge has become liquid due to melting. It is to be understood that the operation to which reference has been made is that of the manufacture of steel by the open hearth or electric furnace processes. The charge, consisting of iron to be converted to steel, iron oxide and limestone or other source of calcium oxide, is heated until the iron has become melted. The iron oxide need not be used except where pig iron is plentiful enough to use in higher percentages; At this stage the slag has lime floating therein, on the surface of which lime particles there is a coating of dicalcium disclosed, it is possible to rapidly flux and com-' bine the dicalcium silicate coating surrounding the lumps of lime as well as fluxing the lime itself. This puts them into solution, thus completing the formation of the slag. There is thus secured a mature slag which is liquid, fluid and by its nature endowed with activity to combine with and remove from the underlying metal the impurities which are deleterious to the quality of the metal itself. This slag is capable of removing such impurities as oxides, silicates and sulfides from the molten steel which is thereby refined and brought to the desired end point.

This synthetic mineral additive which functions in the role of accelerating the fluidizing of the slag is formed by intimately mixing the components in the correct proportions, then melting them together. This forms the desired mineral composition; after which the molten mineral is cast, cooled, crushed, and screened to size.

The amount of my preferred composition minerals that will be necessary to add to the slag to facilitate the solution of the lime will vary from one-half pound to ten pounds per ton of steel in the melt. The amount necessary to add will vary; it will depend upon the percentage of' pmccssiint-this iirventionaanetcvbe-iound"onztheae drawing in er-easel D.: and-.=C anddndicatetki T. Ta blesa-=-"l-.an.d 2.-, Butfoncommerciakreasons wlllmotebeypossible to use pure materials-inatheinr manufacture 2 because; ot; the exce ssiv,ei-.-costs of pure materials; Therefore,impuritiesewhiclr are: carriedvinthe raw materials that. are-.used== willt. be-.;present in-the mixture from which the-minenalis-made. -.andthe latter Willzbfi influenceitcrthat; 1 extent: by them .7; Although-the; commerciala-taw'r materialsz do-hayer components other thanvalume ina, lime and iron oxide, it is these threevlcome ponents and their percentagel-of:.11e1ationship to each; othen as. brought:- out; above: thatds: cant: Following:the;-guide above;;;the preference: Wi11'1.b&.;130 select compositions, approaching thosee imthezrguidethaving the lowest melting point: that ares.-.-p ossible :otatta-inment, with raw materials; that: arerainailable and; economically suitable;

The; miner-alsof. the; type: which-phavelbeenaa discussed-henna when: introduced. intu t-the:- open:- hearthlor" electric furnace slag; systemmy-willl firstr melt and then unite with one or more ofythew components that are presentin the slag, namely thesilicates of lime; the oxides of lime, calcium ferrites, calcium alumi'no fe'rrites, by reason: of

' the-low melting pointsgofthe addedfmineral,

Andyasin-accordance with the law ofentectlc mlxturesgthey will form a product of even: lower...

melting point. These twoaccomplishments iwill'f speed upgthe reaction ofputting the undissolved'" lime-and =calcium components into the fluid state in' the slags;

Tetra calcium alumina ferrite (4CaOA1203F9203) and idicalcium ferrite (ZCa'OFeZOa'), form ,a .complete series of'solid solutions; area Einsthedrawing is' composed ofthem. This is. also true; for: tetra calcium aluminoferrite with penta. calcium. tri aluminate (5CaO3;Al20's).; area. C inzthedrawing is so composed; An eutectic mixture, .witha... specimen composition of '47 %'i lime, 43% alumina. and iron oxide, which melts at. 1335f. (1;. forms a-soli'd solution. Calcium aluminate.-

(GwOAlzOa) takes upwabout'. %:ncalcium ferrite--(Cal0Fe20e) in: solid? solution and? the lattertakes up-about- 10%wofirthe,=f.ormer in solid-solution; A-- compoofr' 281%"; Ca()', 13% AI2O3- and '59 -FezOi-' meltszapprcximately at- 1205?" C;-

The following table shows the crystalline phases having quadruple and quintuplepoints" together -with'- their approximate analyses and. melting points 7 Composition. M It e s Approx.-

CBQ. A110: F2203.

Within area E are the solid solutionsot tetra calciun'e-alum-inoterrite E(4a0P-A1z0aFe20a) wAlzflsEezOfl. andcalcium. ferrites including hexagflnphaunded iby these. series of points, expressed in terms of the components CaO, A1203,

andv 81639; reading-gcleckwise -vtrom its topmost 1 Area.-

isedefineda as,- the ,irregular six sided p lstgq nbounded-by these six. points. .(starting at the. upnermostgpoint and. reading, clockwise) Aneaisqis .definedgas, aiour sideldfleurebounded bystheseflpointsl. .(stantin at theuppermost point.

The..ccnst.itiientsoi;minerals within or substanwitliinz ltherz areas-E D; and-.0, by weight percentages of CaO, A1203, and Form, the corresponding point numbers and approximate melting-"- points are to be found set out in Table '2." Within the preferred area E, or the less.pre-

ferred areas D and C, I naturally favor the selec':

tion of minerals having lower inelting points,'al-

the pulverized components into I a continuous mass by heating to a temperature considerably below fusion; union between the particles results from surface cohesionno fusion .isinvolved.

That my invention will be more fully'un'derstood, the more detailed practice thereof is illusf trated by the following example:

EXAMPLE The furnace (open hearth or electric) charged with limestone, steel scrap and pig iron.

It may or may not contain iron oxide ore. The

charge is melted using any suitable heat source sg.

oil, gas or electricity. When lime has risen up into the slag or is coming up into it, one of the.

preferred minerals in a. uniform, pulverized c-ondition is added and well incorporated therein-IP That composition containing 13% A1203, 28% CaO and 59% F8203, and having a M.-P. of 1205 C. is one of the best.

When added mineral melts'it combines with the dicalcium silicate coating on-the lumps of lime floating in the slag, putting it in solution, and also with the free lime. In this manner speeding up of the solution of the lime isz-accomplished. I

The use of synthetic minerals of areas EyD and C in the drawing and of predetermined melting points within the range substantially 1205-1435" C. possesses advantages not to be secured by using fluorspar in conditioning open hearth and electric furnacesteel slags. When fiuorspar is used to thin the slag, the formation of dicalcium ferrite in the slag is enhanced, which dicalcium ferrite will dissociate giving oif FeO. But when alumina-containing minerals such as I propose to use are added, tetra calcium aluminoferrite is formed in the slag, and in contrast it does not dissociate to give up oxygen as an oxide of iron. This means that there is a somewhat lower content of FeO in the slag;

in consequence there is more iron in the bath.

when FeO in the slag is lower.

There has been pointed ,out supra that, in

addition to an increased ingot yield forthe" reason just explained, there may be a saving of lime charged. There is a lower lime charge NC. and whose components of initial formation claims. The abbreviation M. P." has its cus-" tomary meaning of melting point. In the claims the term mineraP embraces preferably the preformed product formed by melting, cooling and crushing, but also is intended to cover the product formed by sintering. In the claims the term calcium oxide has been used in reference to a component in the formation of the slag. It is intended, of course, to embrace calcium carbonate and other precursors of calcium oxide, such concept being clear from the specification.

I claim:

1. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435 C. and whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation to each other as shown in the area of the accompanying drawing "bounded substantially by the following points:

45% CaO 50% A1203 5% F6203 42% 021.0 40% A1203 1.8% F6203 38%. 08.0 36% AlzOc 1 26% F6203 34% CaO 27% A; 39% F6203 25% 08.0 5% A120; 70% F6203 28.5% CaO 1.5% A1203 70% F620: 41.5% .CaO 1.5% A1203 57% F8203 53% 09.0 6% A1203 41% F6203 57% CaO 17% A1203 26%Fe203'. 52% CaO 26% A1203 22% F8203 55% CaO 36% A1203 9% F8203 47% CaO 43% A1203 10% F8203 49% CaO 46% A1203 5% F8203 which slag has been formed by heating a charge of metallic iron to be converted and calcium oxide, employing substantially one-half to ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above theM. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fluidizing the slag by melting of the mineral which then combines with components of the slag.

2. The method of conditioning open hearth and electric furnace slags in steel manufacture,

which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435 C. and whose components of initial formation were lime, alumina and iron oxide,

and having the percentage relation to each other as shown in area 0 of the accompanying drawing,

"but below the M. P. of dicalcium silicate, the

addition of the mineral fluidizing the slag by melting of the mineral which then combines with components of the slag.

3. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435 were lime, alumina and iron oxide, and having "ea-m ing substantially one-half to ten pounds of the aforesaid mineral per "ton of total'iron melted, the temperature of the furnace beingabove the M. P. of the charge' an'd' still"further ab'ove the M. P. of theaforesaid mineral but below the M. P. of dicalcium silicate, the addition -of the mineral gfhiidizingthe slag by meltingof the mineral which then'combines with components of the slag.

'4. The method of conditioningopen hearth and electric furnace slags in-steelmanufacture, which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435" ("Jma'in'd whose components "of initial formation "were lime, alumina ahd iron'o'xide, and having the percentage relation to each other as shown in area E of the-accompanying drawing, which slag has been formed by heating a charge of metallic iron to be converted and calcium'oxide, "employing substantially 'one half to ten pounds "ofthe aforesaid 'mineralper ton of total iron 'm'elte'd, the tem erature of the furnace being 'above 'the M. P. of the charge and "still further above the M. Poi the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fluidizing the slag by melting of" the mineral which then combines with components of the slag.

5. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435 C. and whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation to each other as shown in area E. of the accompanying drawing, which slag has been formed by heating a charge of metallic iron and iron oxide ore to be converted, and calcium oxide, employing substantially onehalf to ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above the M. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fluidizing the slag by melting of the mineral which then combines with components of the slag.

6. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral having a M. P. of substantially 1205-1435" C. and whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation to each other as shown in area D of the accompanying drawing, which slag has been formed by heating a charge of metallic iron and iron oxide ore to be converted, and calcium oxide, employing substantially one-half to ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above the M. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fluidizing the slag by melting of the mineral which then combines with components of the slag.

'7. The method of conditioning open hearth and electric furnace slags in steel manufacture, which sl'ags contain-dicalcium silicatean'd free lime, "comprisingthegsteps of adding to the slag a mineral havin'g a'M. P. of substantially 1205-1435? "C. and whose components or initial formation werelime, alumina-and iron oxide, and having the percentage "relation to each other as shown in area C of the accompanying drawing, which slag has beenformed by heating a charge of metallic iron and-iron oxide ore to be converted, and calcium oxide,-employing substantially onehalf to 'ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the chargeand still further above the P. of the aforesaid "mineral-but below the M. P. -of dicalcium silicate, the addition of the mineral fluidizing the slag by melting of the mineral which then combines with components of the slag.

-8. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain a dicalcium silicate and free lime, comprising the steps of adding to the slag a mineral'having a M. P. of substantially 1205-1435 C. and whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation'to each'other-as'shown in the area of the accompanying drawing bounded substantially by the following points:

45% C30 50% A1203 5% F8203 42% 02.0 40% A1203 18% Fe203 33% CaO 36% A1203 26% F6203 34% CaO 27% A1203 39% F6203 25% CaO 5% A1203 70% F6203 28.5% CaO 1.5% A1203 70% F203 41.5% CaO 1.5% A1203 57% F6203 53% C20 6% A1203 41% F6203 57% (33,0 17% A1203 26% F6203 52% 03.0 26% A1203 22% F8203 55% C30 36% A1203 9% F6203 47% C210 43% A1203 10% FezOa 49% C310 46% A1203 5% F6203 which slag has been formed by heating a charge of metallic iron and iron oxide ore to be converted, and calcium oxide, employing substantially one-half of ten pounds of the aforesaid mmeral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above the M. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fluioizlng the slag by melting of the mineral which then combines with components of the slag.

9. The method of conditioning open hearth and electric furnace slags in steel manufacture, which slags contain a calcium silicate and free lime, comprising the steps of adding to the slag, a mineral having an M. P. of substantially 1205- 1435 0., whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation to each other as shown in area E of the accompanying drawing, which slag has been formed by heating a charge of metallic iron to be converted and calcium oxide, employing substantially one-half to ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above the M. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition of the mineral fiuidizing the slag by melting of the mineral which then combines with components of the slag.

10. The method of conditioning open hearth and electric furnace slags in steel manufacture,

which slags contain a calcium silicate and free lime, comprising the steps of adding to the slag a mineral having an M. P. of substantially 1205- 1435 C., whose components of initial formation were lime, alumina and iron oxide, and having the percentage relation to each other as shown in the area of the accompanying drawing bounded substantially by the following points:

45 CaO 50 A1203 F6203 42% CaO 40 A1203 18 F8203 38% C20 36 A1203 26 F9203 34% CaO 27% A1203 39 Fe203 25 C210 5 A1203 70 F6203 28.5 CaO 1.5 A1203 '70 F9203 41.5 03.0 1.5 A120: 57 F8203 53 CaO 6 A1203 41 Fe203 57% CaO 17% A1203 26 F6203 52 CaO 26 A1203 22 F6203 55% Geo 36% A1203 9 F8203 47% Geo 43 A1203 F8203 49 C210 46% A1203 5 F9203 which slag has been formed from a charge of metallic iron to be converted and calcium oxide, employing substantially one-half to ten pounds of the aforesaid mineral per ton of total iron melted, the temperature of the furnace being above the M. P. of the charge and still further above the M. P. of the aforesaid mineral but below the M. P. of dicalcium silicate, the addition 12 01' the mineral fluidizing the slag by melting 'of the mineral which then combines with components of the slag. JAMES J. BOWDEN,

References Cited in the file of this patent or the original patent UNITED STATES PATENTS Number Name Date 687,029 Hughs Nov. 19, 1901 1,890,485 Amsler Dec. 13, 1932 2,159,977 Nicholas May 30, 1939 2,198,625 Koppers Apr. 30, 1940 2,283,622 Bowden et a1 May 19, 1942 FOREIGN PATENTS Number Country Date 4,642 Great Britain of 1877 4,625 Great Britain of 1879 535,245 Great Britain Apr. 2, 1941 OTHER REFERENCES Open Hearth Proceedings of 1946, pages 47 to 56. Published by the A. I. M. E., New York, N. Y. Open Hearth Proceedings of 1948, pages 194 to 205. Published by the A. I. M. E., New York, N. Y. Journal of the American Chemical Society, vol.

50, pages 396 to 406. Published in 1928 by the Society at Easton, Pa.

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