AMERICAN INSTITUTE OF MINING AND RlETALLURGICAL ENGINEERS

Technical Publication No. 1108 (CL.ASS c!. IRON AND STEEL DIVISION. NO. 133)

DISCUSSION O F THIS PAPER 18 INVITED. Discussion in (3 copies) may he sent to the Sec.ret.ar.v, Alnerican lnstitute of Mining and RIetallurgical Engineers. 29 West 39th Street. New York. N. T. Unless special arraligenlent is made, discussion of this pnper s i l l close Dee. 31, 1939. Any disrussion nffered illereafter should preferably he in the form of a new paper.

Effect of the Volunle alicl Properties of Bosli a i d Hearth Slag on Quality of Iron

(Cle\~t.lan<l RIaeting, April 1939)

THE st,11~1y of the possibility of effecting a lower cost in the manu- fnct,ure of pig irc111 reveals the iml~ort~ance of the ever preselit cluestion of slag chemistry and volume.

Factors that cleter~nille slag chemistry and volunle are the iinpurities in the ore available, the ash-sulphur co~l te~l t of the coke, aacl a flus rn:tterial necessary to promote reinoval of sulphur. Of these, the ores present by Snr t,he m:tjor source of impurities and what may prove to he t,lle lowest pract,ical slag volume \vit,li desired cl~emist~ry in one locality mny be conaiderecl low or 1lig.h in some other center of iron manuf:tcture. The C;hicago district is not only blessecl wit,h ores of high cluality, but wit11 excellent coke nilcl flus m:tterials as ~vell. It is the intent of this paper t,o discuss slag probleills a t tlle South Works only, \\-here burclens consist of Mesalji ores, Michig:zn stone, anclcoke ranging from 7 to 9 per cent nsh mlcl ~ollt~aillillg ail average of 0.57 per cent sulphur.

Early in t,he clevelopment of moclenl blast-furnace prhctice, the con- sicleration of slags was secont1:iry to the many acljustnients of mechanics1 clifficulties, such as furnace lines, stock dist~ribut.ioii, stove clesign for ol~tnining higher blast temperatures, i~llpl.ovecl clle~nical ~egregat~ioa ant1 size of ram m:zt,erin.ls. Furnace operators, after making these improve- nlenbs, turned their att,eiltioll to the study of other ref in en lent,^ in practice, of 1~11ich slit$ clleillistry appeared t'o be the nlost important,.

I t is oidy ~vithin the last two decades that operators have become I'nmilinr wit,ll the various aspects of slag compositions. The inclust,ry, \vhile r:tt,l~er slow in its recognition, is intlebted to such investigators as R a l ~ k i n , ~ \3Trigl~t,1 Feilc1,"oyster12 RlcCaffery,~Iiini~ey,~oloU~rook~~i~cl .Joseph,"vhose researches concerning the eliilliilatioll of sulphur within tllr bln.qt funlace ailcl the effect of slag col~~positioil upon melting poi~it', \riscosity, and clesulpl~urizi~~g power 11ave established crit.eria for tlie selection of slags of the requisit,e cluality.

Large slag vollllnes result in higher coke consumption and cost of disposal. Any att,empt to lower slag quantity must Ije accomplishecl

ILI:~nuscr~pt received at the ofice of the Institute May 2, 1939. * Soutll Works, Cernegie-Illinois Steel Corporation, Chicago, 111. Bec:l~ne :I

lne~nber of the A.I.M.E. in July 1939. References are a t the end of the paper.

Copyright, 1939, by the American Institute of Mining and hletallnrgicsl Engineers, Inc. ~IETALS TECENOLOGY, September 1939. Printed in U. S. A.

2 EFFEC'Y O F VO1,UhIE AND PROPERTIES O F SLAG ON IBON

by n careful adjnst,ment of slag quality in order t,o produce iron within specificat,ions.

To det,errnine t,he proper slag quality it, is necessnry to keep in mind t,hat all blast furnaces in t,he process of making iron produce two clist,inc~t t,ypes of slng \\.it,hin t,he furnace-t1i:tt ~vIlic.11 is m:ttle above the tuyeres, :111d t,ll:tt, \vlii(*l~ is for~lled aft,er fusing \vit,ll t,lie coke ash belo\v the t,uyeres. 'l'lle slag above t,he tuyeres coiit~ai~ls, ~i:tt,u~.ally, :t higher proportioti of I):tstts, :tt~tl slroriltl possess u low viscosity and ~ilelti l~g poilit to ensure ~.eglll;tr fu1.11nce movemrl~t and lo\\, fuel consiuii~pt,ioii. The more acid slag belo\r the tuyeres should possess enough c:ilcium oxide a t temper- ntures t'o warrallt sufficielit sul~erheat,, :tnd n viscosity of ample con- sisbency to ensure a rlesiretl clesulpliuriznt~io~i. Fro111 this it call be seen that t,he opt,immm slag for t.he zone aljove the tuyeres ~ n a y not prove drsiral~le for the remo~-:tl of sulphur Ijelow tlie tuyeres and, as a conse- quence, a corn1)romise in slng c.omposit.ioi1 n ~ u s t be effect,ecl. I n cases of estreme v:triat,ion between opt,imurn compositions for the two functions, it has proved acl\.allt.ageor~s t,o 1,rocluc.e a slng of mininlum melting point and viscosit,y \vit,Ii no regard t,o t,lie su lp l l~~r cont.ent of the iron, \vIlich is clesulphurizetl by subsecluent treat,ment,. The pursvance of this practice a t t,he Corljy plant,, ill -England, lins result,etl in an improved fur- nace operat,iol~ aticl eco~ion~ies t1i:tt. consiclerably exceed t,he cost of, external clesulplluriz~t~ion.

At South Works :t b:~l:tncecl slag con~lit~ion is possible, i\~hich permits ;

smoot,h operation alitl sat.isf:tct,ory desulphuriza,t,ion withill the furnace. Whether or not we are pursuing the 111ost ecolloll~ical methocl oiily actual t,rial will prove.

Table 1 shows :tvcrnge slag analyses 2nd volmnes carried in the pro-. cl~~ction of Bessemrr alld basic grades of iron clwing t,lie last sis months of 1937. These slags will hereafter be referred to as "nonaal slags." I11 the plot,tillg of these i ~ o r ~ ~ l n l slags on tlie temperat,~ue n~icl viscosity iliagrams of t,he syst,eill CaC)-A1..0:,-Si02 the act,ual average a~lalyses of t'lie osicles \\err proport,io~ied t,o t,otn,l 100 per cent,. Compensat,ion \\-as 11lnt1e for lime equivale~lt t,o calcium sulphicle by axs~u~iing tha t all the m:tnganrse c.sist,ecl as nlangnliese sulphitle and t,he reliini~iii~g sulphnr as cnlciium sulphitle. Tlre result,s of t.liese aclj~st~ecl slag coiilposit,ioils are plot,t,ed on Fig. I , tlle t,elnper:lt,rlre cliagrnm, :t~ltl Figs. 2 and 3, t,lle \ris(rosit.y tlingrnms. :~t. poirits -4 n ~ i d B, desigtiat,ing the Besse111er nncl l)nsic lie:irt,h sI:tgs, i.c~spect,ively. These point.s.revea1 th:l,t major changes in melt,ing point,, viscosit,y aricl mineralogical cori~positioii are reaclily effected by sliglrt changes .in the chemist,ry of tlie burden. Vnriat,ions of only 2 pel. cent ill lirne or silica result in n clifferelice of npI,rosim:tt,ely 200" F. in t.he ~nelt~ing poi~its of t'hese normal slags. Both points nre also near phase-bounclary lines, causing cont,inuous l~i i~ieral clia~lges between calciium orthosilicate, tricalciuln clisilicate and Gehlenite. T11e

TABLE 1 .- dverage Norn~al Practice LAST SIX MONTHS OF 1937

Analyses 1 No . 6 Furnace . B e u m e r I No . 8 Furnnce . Standard 1 Iron . Per Cent Basic Iron.'Per Cent

Slag volume (excluding scrap). 111 ....... Sinter in burden. per cent . . . . . . . . . . . . . Scr:tp charged per ton nlet:~l pl.oduct.d, lb . Coke rate. Ib . per ton rnet.~l . . . . . . . . . . . Blast temperature. cleg . F . . . . . . . . . . . . .

Actual slag a~~alys i s : SiOa . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1203 . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . . S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Corrected slag analysis: Hearth slag:

SiO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . A120 ., . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bosh slag: . SiOz. . . . . . . . . . . . . . . . . . . . . . . . . . . . A1208 . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . RIgO . . . . . . . . . . . . . . . . . . . . . . . . . . .

Blast . pressure. lh . per sq . in . . . . . . . . . . . Bases-silica ratio: (actual slng) . . . . . . . . Average iron .~nnlysis, pcr cent:

Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . Sl~lphur . . . . . . . . . . . . . . . . . . . . . . . . .

35.5 10.8 4 7 . 6

1 . 5 1 . 1 1

30 .6 11 .1 47 .8

1 . 5

37.6 7 . 0

54.2 1 . 2

per cent S in slag l{at.io: per cellt ,net..tl . . . . . . . . . . . . . . 1 40

OTHER D.IT.~

0 . 9 2 0 .030

37

100 per cent basic Grc~tle of iron tnnde . . . . . . . . . . . . . . . . . . . Proaluct.ion:

Daily t.ollr~ngc . . . . . . . . . . . . . . . . . . . Percent. nge of r.~.tell 11 ..~pncit y. . . . . . .

\.al.i:\t,ions in vis;;cosit.y. as noted on Figs . 2 ancl 3. are of equal magnitude. I'or in t.l~is 1oc:tlity the iso-viscosity lines are estre~llely close together . -4 slag. \vl~c~)se properties are so greatly iilflueilcecl by these slight changes in t. he cllemistry of the burden. may lose its effective~less in the elilni- 11.1t. ion of sulpliur .

The theoretical Bessenler ancl basic bosh slag compositions1 indicatetl upcn~ Figs . 1 . 2 :tnd 3 as cr.' ancl b'. respecti\~ely. \Irere calc~lat~ed by cleilucting oxides in'the consumed coke from the'oxides present in the actual slags and balancing to 100 per 'cent after conlpellsating for a

100 per cent Bessemer

777 9 4 . 2

4 EFFECT O F VOLUME AND PROPERTIES O F SLAG ON IRON

nletal siliconization of 75 per cent of normal. As pointecl out by McCaffery,"l~e hosh s1:tgs nlay contain a consiclerable amount oi iron oxides, which probably occur as calcium ferrites mlcl iron silicates. The compositiolns of t,he bosh slags, as inclicat-ecl in our calcul:ttions, are not

1007. S10r

( + i a m ~ as monrx d r 0ja.j FIG. 1.-LOCI OF NORMAL AND TEST PR.Il:TICE HLAi;R.

. .Isot,hen~ls are jn Cent.igmcle unit,s.

to be const,rued :IS t,hose of the actual slags but are merely to I)c used :is guides in est,ini,zting the relative thermal ailil physical cll:tr:~ct,erist,ics.

An examination of 'the locatioiis of these slags, \rhich :tpprosimate the composition esisting above the tuyere zone, indicates that they possess rnelti~lg points approximately 570" F. higher .than t l ~ e corre-:

G . E. STEUDEL 5

sponcling hearth slags. Viscosities in this region :ire estremely high (Figs. 2 and 3 ) .

Operating under these slag conclitions, s~ilall variations in chemistry esert a decidecl influence up6n slag properties and cause wide swiligs in iron analyses. Such circunlstallces force the operator to reduce l~urdens ill orcler to broadcn the n1:trgin of blast-heat reserve, which leads to lower production and illcreased coke consumption.

CODE:- c0DZ:-

A. = NORPW/. BCSSE~PR HCRRTY SLPB. AX = ULERCO *BCSSLLICR NC~RTN SLRO

a'.. .,- ~ O S M ,, a h - ,. a- BOSY . (* samE 4s ~ u r r , 1938)

F I G . ~ . - ~ I S C O S I T I E S OF NORMAL AND TEST PRACTICE SLAGS.

To cleternline the potentialities of an alt,eration in slag, our first step was the calculation of 25 per cent, 50 per cent and 75 per cent reductions in the amount of limestone from a normal basic burden. This study was interesting because it followed closely the lines of the much publicized Corby practice in England.

The theoretical slag con~positions and pertinent data concerning the stone reductions to the normal burden are listed in Table 2. The . nomenclature of the slags, whose loci are plotted on Figs. 4 and 5,- is given a t the end of Table 2.

Giving consicler:tt,ion first to the bosh slags for the various st,one recluctions, we not'e that c' lies in 3, region where melting point and viscosity are much more clesir:thle tl1n.n those of the nonnnl slng b'. Fig. 4 ilitli~nt~es tlmt s1n.g c' hits n ~nelting'point npproximately 775" F. lower than slag b' alicl Fig. 5 inclic:ttes n clecidecl irnpro\~ement in vis- c:ouit,y. ' The tlesiral~ility of a s1n.g of this type o\.el. t,lle normnl hosh sla,R h:ts been frecluently pro~lcrl in nct,unl practice by smoother furnnce mow- ment a,nd lower coke consumpt,ioll ~v l~e l l oper:l.ting \vitJl lean slags as

80. do#*la~ ~ n s l c ~ ~ a a r x S L ~ G BX = ALTF~PO* aastc x ~ ~ R T N SLAG

A'. . ,. sosw ,, dko: ,, aosr

C * s n n ~ AS ~ L Y , /93a) FIG. 3.-\'ISCOSITIES OF NORXfAL A N D TEST PRACTICE SLAGS.

comparecl to the'irreguIar liloverllelit alicl high coke consumption associ- nt,ecl ~vit,h limey slags.

Bosh s1:tgs for the higher stone recluctions d' and e' Iinve melting temperatures comp:trable to that of c'. The viscosity of slng d' is approximately eight poises higher than c'; :tnd e' with the 5 5 per cent stone reduction is in a Irery viscous region. Slag cl', like c' , sllo\vs merit,

. in that i t shoulil be a desir:thle bosh sl:tg. These 11osh sl:tgs possess superior char:tc'teristics over the normal bosh slag and may I:)c espectetl to produce iron with a favorable recluction in coke consumption. How- . -

G . E. S T E U D E L

TABLE 2.-Stmndard Basic Iron

. . . . . . . . . . . . . . . . Tl~eoretical stone.. . . . . . . . . . . . . . . . . . . . . . 4,750 Theoretical manganese.. 1.51 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theoretical pig. . . . . . . . . . . . . . . . . . . . . . . . . 7 . 0 2 Fa:C. . I . 27

Theoretical phosphorus.. . . . . . . . . . . . . . . . . 0 . 1 6 1 Slag volume.. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.004

Composition, Per Cent I RIaterial Slag,

Gary coke.. . . . . . . . . . . . . . . . . . . . . C;rorlp 3 . . . . . . . . . . . . . Group 7 . .

Scale . . . . . . . . . . . . . . . . Open-heart.h slag.. . . . Bessemer slag.. . . . . . . St.one . . . . . . . . . . . . . . . .

Total . . . . . . . . . . . . . .

Slag C:on- stituent

Stone.

12,000 19.000 9,600

500 1,400

300 4,750

30,800

Normal *lag 1 25 Per Cent 50 Per Cent Theoret~cal Stone R e d r ~ c t i o ~ ~ Stone Reduction

Lh. Lh. Ye I P Lln 1 SiO; bl?Oz C a 0 1 hIgO ~

Oxirles. Oxides, Oxides.

Theoretical hearth slag 1

Theoretical hosh slag

Slag vol~~rne , Ih.. . . . . . . . . . . . . . . 1,004 813 Est in~ated sulphur it1 metal prod-

uct, per cent. . . . . . . . . . . . . . . . . 0.030 0 .066 0.144 I I I

Nomenclature. Loci plotted on Figs. 4 and 5.

Burden Hearth Slag

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Normal 25 per cent, stone reduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 per cent stone reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 per cent stone reduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Bosh Slag

ever, calcul,zt,ions I~asecl o n the Holbrook ancl Joseph cliagram of relat,ive clesulphurizing power (Fig. 6) i n t 1 i r a t . e t,hat the c o r r e s p o l l t l i l l g hearth slags C, D n.nd E clo not possess sufficient desulphurizing power t,o pro- cluce i r o l l \ \ . i tshin p r e s e l l t open-hearth specific;ations. The estimatetl sulphur cont,entu of t.lie iron are as follo\vs:

25 per cent stone recluction. . . . . . . . . . . 0.066 per cent sulphur in iron 50 per cent stone reduct , io~~. . . . . . . . . . . 0 14-1 per cent sulphur in iron 75 per cent stone reduction. . . . . . . . . . . 0.313 per cent sulphur in iron

8 EFFECT OF VOLUME AND PROPERTIES OF SLAG ON IRON

Because of the small amount of resesrch in these partictllar fielcls witli nct,ual furnace slags, t,lir rstinlnt,ed sulpliur contents nre to be t.tzken only nu an ilitlicnt'ioll of n-\~nb might be espect,ecl.

FIG. 4.-SLAGS AT VARIOUS LIMESTONE REDUCTIONS I N A B.ISIC BURDEN. I Whether or not the savings ohtaiiiecl wit11 the suggested method for

improving bosh slags woulcl be enough to justify external desulphuri- zation, we are not in a positio~l t o state without further investigation. The study of leaner slags did, however, lead to a proposal that appears to have possibilities. This co~lsists of the inject io~~ of preheated calcium oside into the hearth or lower part of the bosh in a manner similar to the Heskanip flue-dust injection process. A remoral of approxinlately 25 per cent stone fro111 the burden and the compensati~lg addition of an

G . E. STEUDEL 9

equivalent alllolint of calciulll oxide to the heart11 ~\rould retain the advantageous chart~cteristics of the leaner bosh slag and eliminate the necessity for es ten~nl desulphurization. Cdculnt~ions indicate tbat if the calcium osicle \irere preheated to n temperature of 1700' F. the heat necessary to bring the osicle to that of the llornlal hearth t e n - peratures ~vould hc supplied by ml nclclitio~l of approsin~ately 22' F. )>last temperature.

CODE: - C0OE:-

C.: HraaTd - } z 5 z J n d ~ ~ E ~ u c 7 ~ e ~ ~ Bu*oed. c i s aosw .. e'e. eosv - FIG. .5.-VISCOSITIES OF SLAGS AT VARIOUS STONE REDUCT1C)NB M BURDEN.

Because mill conclitions did not perrnit any of the clrastic changes in practice clescrihecl ahove, our attention was diverted to a more con- servative esperimental plan in which available materials nrld ecluipnle~lt coulcl be utilizecl.

Having locateel the normal Besserner ant1 basic slags, A and B, upon the diagram (Fig. l), slag location may be irnprovecl by moving to the right, that is, to a position within the upper area of the Gehlenite field.

10 EFFECT O F \'OI,UhIE AND PROPERTIES OF SLAG ON IRON

The atta.inment of :t sl:~g approsininting such a position requirecl an increase in t,he a.luminn content. To achieve this, we I ~ a d hut one alter- native, which, fortunat,ely, served n t,wofold Since approsi-' mately ha.lf t.he alumina in the I~urclen colnes from t . 1 ~ coke, i t n-ns apparent that if t,he slag volumes were redt~ced the alumil~n ~voulcl illcrease. Theoretical slig compositions were calculateil for I~urtlens in u~hicli the siliceous ores were elimi11:tt~ed. The compositions of such slngs :~.pprosi- mate tllose plotted upoil Figs. 1, 2 anti 3 a t point's .FIX, B:r, c~':r n.nd bl.r.

FIG. 6.-DESULPHURIZINC~ PO\VER O F S L A G S \\.ITH REDU(.I.:D STONE I N B U R D E N .

The locat,ions of t,hesc slngs are a clccitlecl i~ill)rovcmc~~it. over t,llosc of the ~zornlal slags. The meltsing tem1)er:ttures the viscoaitir:s of t,lic. hearth slngs are much less subject to r:lpicl cl~nngcs clue to slight vnri- ntiorls in burden chemistry. The isother~ns intlicatsc tlhat cll:~,nges of nlIout, 5 per cent in hearth-slag compositions :ire requirecl to cause a tlifforc!~ic:e in rnelt,ing t,emperatures of approsimtttely 200' F., \vhere:ts the same tem- perature difference is effect,ed by a c l ln~~ge of b u t 2 per cent, in tlie 11c)rlnnl slag co~ilposition. AH previously mentionecl, the essential tliffc:rc~ic.e between tile slags is in tllcir a1runin:i cont,ent,. Slag Bz contains :tpprosi- mately 16 per cent aluminn,, while t,lle normal basic slags cont,ain 1.4 11c.r cent or less. I n t,hc normal Besseme.r practice the n l ~ ~ m i n a is rn.rely above 11 per cent;, but with the reduced slag volume and t,he clinrging of an additional 200 Ib. of producer ash it \ins possible t,o'obtnin s1:tgs approximating 16 per cent alumina'.

Tlle bosh-slag locations, which npl-)rosimat,c those of thc altered .pmctick-slag compositiol~s, illtlicntc . . re1:ttively 'lit.t.le improi~ement. ill

TABLE 3.-l'e-st Practice, No . 6 Blast Furnace. Bessemer

Feb . hlarch April Mas June July 1 1938 I 1938 ( 1938 / 1938 / 1938 1 1938

SiO? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1203 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

SiO? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1203 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Slag volrrtnc (cscluding scrap), 111 . . . . . . . . . . . . Sirlt, er in hr~rtlen, per cent . . . . . . . . . . . . . . . . . . Scrap chnrgetl, Ih . per ton n~c ta l 11roduced . . . . Coke ra.t.e, lb . per t, or1 of 111etal . . . . . . . . . . . . . . Blast t,empcr.itnre, cleg . F . . . . . . . . . . . . . . . . . . Bl:~stpressuic at . blowingengirlcs, 11, . pcr srl . in .

per cent . 8 in slag Ratio: per ccllt in nletal . . . . . . . . . . . . . . . . . .

Bares Ratio: %, (actual slng) . . . . . . . . . . . . . . . . . . .

6 1 1

Iron analysis : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silicon

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8ulp1111r

I1n.y~ on vclrious gritcles of iron : Basic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13essemer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ingot ~lioltl . . . . . . . . . . . . . . . . . . . . . . . . . . . hlalleahle . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Number of ch:~tlgcs in ~ K L ( . I ( J of it.011 ~>r~.)rlucccl . Proclt~ct, ion.

Dailyt, orln.rge . . . . . . . . . . . . . . . . . . . . . . . . . Percerlt, age of rat, ed capnt.it+ . . . . . . . . . . . .

37.57 13.82 44.77 2.00 1.14

921 10.6

12 1771 1132 16.8

48

1.25

1.47 0.024

0 12 16 0 1

671 81.3

1.74 2.02 1 . 3 5 1 . 3 7

37.9337.2536.9737.3035.6s 13 .7813 .66 l5 .0714 .2615 .72 44.6245.7844.7745.1645.00

1.60 1.27

1.93 1.15

1.83 1.21

770 0.3 232

1676 1210 17.4

51

1.25

1.40 0.0290.0190.0250.0270.02~

0 0 0 0 6 20 0

5 4 6 6 7

868 105.2

881 1 .8

9 1807 1155

. 16.8

40

1.23

1.52

19 12 0

690 83.6

12.2 lj8 62.2

------ 861 1.0 267

1693 1125 17.8

63

1.28

1.46

20 10 0

5-12 101 . 9

. 738 0.0

12 1790 1235 l 5 . 6

-50

1.29

1.53

26 0

2

732 88.6

2 . 0.

767 0 . 0

78 1776 1147 1.5 ..5

33

1.32

. 1.38

22 0 3

753 91 . 1

12 EFFECT O F VOL.UhIE .4 ND PROPERTIES O F SLAG ON IRON

TABLE 4.-Test Practice

Feb . March April h. lay June July / 1938 1 1938 / 1938 1 1938 1 1038 1 1938

SiOi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Al?Oi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49.8

35.30 15.89

3.20 1.27

CORRECTED SLAG COLIPOSITION. HEARTH- SLAG. PER CENT

SiO?... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AlrOa . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

36.58 13.91

3.94 1.07

35.84 14.56 43.15 4.05 1.14

36.6 16.5 43.6 3 .3

SiO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A1203 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CaO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MgO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MgO'. . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Slag volume (excluding scrap), lb . . . . . . . .,. . . . Sintek in burden, per cent . . . . . . . . . . . . . . . . . . Scrap charged per ton metal protluced . . . . . . .

. Coke rate, lb per ton metal . . . . . . . . . . . . . . . . Blast temperature, cleg . F . . . . . . . . . . . . . . . . . . Blsst pressure a t hlo\\ring engines, 11)s . per sq .

in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . per cent 9 in slag

liatio: per cent in . . . . . . . . . . . . . . . . . .

: Bases . . Ratio: -- silica (actual slag) . . . . . . . . . . . . . . . . . . .

Iron analysis: Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulphur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Days on varior~s grades of iron: Basic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bessemer . . . . . . . . . . . . . . . . : . . . . . . . . . . . . Ingotmold . . . . . . . . . . . . . . . . . . . . . . . . . . . Malleable . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Nunlber of clisnges in grades of iron produced Production:

Daily tonnnge . . . . . . . . . . . . . . . . . . . . . . . . . Percentage of rat.ed capacity . . . . . . . . . . . .

37.1 15.1 43.6 4 . 2

981 11.9 112

1732 1003

17.5

41 .

35.80 15.57

3.08 1.18

36.18 13.96

3..71 1.08

1.32

0.91 0.028

2S 0 0 0 0

980 98.0

35.75 14.75

43.3543.7744.4043.2043.2s 2.84 1.12

938 15.2 113

1697 1024

17.9

40

37.1 16.1 43.6 3 .2

37.7 14.4 43.8 4 . 1

1.29

0.90

31

1066 106.6

...... 915 3 .8 SO

1753 1109

18.4

42

37.4 14.5 44.3 3.S

1.28

0.89

30

1071 107.1

36.9 15.3 44.9 2 . 9

824 3 .7 75

1748 1020

17.9

45

1.25

0.93 0.0270.0260.0250.0250.024

31 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1076 107.6

786 0 .0 84

1734 1046

17.0

47

314 778 0 .0 117

1667 1155

17.9

53

1.29

0 . 9 1

30

1041 104.1

1.32

0.94

31

1129 112.9

physical or thermal properties over the rlorlnal slags. Being aware of the estrenlely viscous condition of the slags in the bosll zone, ~ v e felt assured that a reducecl quantity of slag ~vould considerably improve gas penetration and furnace movement.

As a result of the foregoing considerations, it was decided to esperi- nlent with slag compositions in progressive steps of reduced slag volunle on one Bessenler and one basic furnace. The first steps of the six-month test were taken in the month of FeLruary 1938.

The pertinent data for the period of the experiment are shown on Tables 3 and 4. Althougl~ practice in No. 6 furnace is referred to as " Bessenler " it lnacle ingot-mold grade iron for a consiclerable portion of the periocl, as \\Tell as merchant and standard basic over short clurations, as indicated in the tables.

TABLE ~ . - C O . ? ~ ~ ~ C L T ~ S O H of Slag Volt~nles a:nd Coke Rates

Bessemer : . . . . . . . . . . . . . . . . . . . . . . . Slag volu~ne. .

Coke rate.. . . . . . . . . . . . . . . . . . . . . . . . . . . Pounds scrap charged per ton nletnl pro-

duced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per cent sinter in 1,t~rtlen.

Basic: Slag volu~ne. . . . . . . . . . . . . . . . . . . . . . . . . Cokemte . . . . . . . . . . . . . . . . . . . . . . . . . . . Pounds scrap charged per ton of 111et:ll

produced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Per cent sinter in hurclen.

In comparing the nornlal practice with that of the test period, it will l ~ e notecl that in the practice on the basic furnace a monthly average slag voli~nle of 778 lb. was attained, whieh was as low as the materials available would permit. In previous practice slag volumes of less than 1050 lb. had never been regularly used. The average nlonthly slag volume in the Besseiner practice was reducecl to as low as 738 lb., whereas in the nornlal practice 950 lb. was considered n~inimum.

The improvement of coke rates in the test period is evident. Table 5 sllo\vs a cornparisoll of the average slag volumes and coke rates for average llorinnl practice with those of the average for the last two months of the test periocl, during \~~hich the lowest slag volumes were carried. \\7hile lower coke rates were attainecl during the test period than those of the two months hhown here, those low rates were accumpanietl, as es:imin:ition of the previously tabulated data reveals, by higher

amounts of acr:ip allcl sinter in the burdens.' Tlle coke r&tluced pelr 100 111. slag volr~me for the Bessemcr pr:tct,icc \vns . ;

100 X l.:io; \\. l~icl~ g i \ w 55.6 11,. p(:r t,o11 lllet,:il (illcluilillg scrap).

Assuming tbat 300 11). of cwkc is requircd to melt 2240 Ih. of sc.rnp in the 1jl:ist funlncc, t,lrc melt,illg o f 27 I t ) . of scrnp require.:

, . 1.11e coke snvillg in tile Besscmer pract,ic tallen 1,cc:omes: . .

scrap) for enc.11 100 lb. rcbcluc:tiol~ ill slag 1-olrlme.

Tllc saving eff'cutecl in t,hc Ijn~ic! prnct.ice, cdculsted in the s:tme mnllner, is 1S.4 111. of' coke per toll of luc?t,:tl protl~~cetl -jt!scluclil~g scrnp) for each 100-111. rec.luct,iol~ ill slag volulnc. I t is il~t~ercsting tl~:it a sull- st,ant.inl rt;cluct,iol~ i l l coke c~ollsunlpt,ion was effect,c:rl i l l t l ~ e l)nsic pr:~:cticc in sliit,e of t,Ilc 12.6 per cent sinter ri:tluctioll i l l t,l~tr Ijt~rclel~.

Froln these d:\,t,:c, i t :t,ppears that, t,he :tver:lgc ~9\'illp ill coke, nftcr ;~cljust,mc-.trt for scr:~p? m:ty I,(! s:iicl to bc approsim:ttc.ly 50 11,. per ton of me td for e\.ery 100 It>. of slag volrlme reclucetl. . .

Blast pressures (luring the test periocl \rrcre tlt!fi~ritcly lo~vcr ancl Inore . . . .

~iniforln. 'J'here is littale tloubt t,lr:tt this, \\::IS ' C I ; I ~ t,o tllc sm:tllcr :~rnoullt. of visc~ous sl:tg in tho I>oslr clrlri~~g t,he lo\\: s1:l.g volu~ncb l)rn,t:tict:.

'The cffect of t,llc :tlt,erecl slag chemistry and the sing \.olr~lnc rlporl s~noot,li fur11:tce ol)er:~t,io11 \v:is \ ~ r y m:lrked; as s l lo\ \ :~~ .l,y Figs. 7 to 10. \\'llile t,lid Imsic pi:ict,ice s!-~o\\:s :t general im1)rovelncnt i l l H I I I I - ) I I I I ~ 111li-

formitfly ib iron t,o t,lle c?st,el~t, of t,h& lo\\:c!s! sl:ig \,c~)lirmes ~ ~ r r i ~ d , t,ll(, Bessemcr ;~)rnc?tice intlic:it,es it11 ol,timurn degree of s11lp1111r ulliI'ormit,y at, n slag vol~lmr of nl)prosimntctly 820 11). l 'l~is, Ilo\\:~:\.er, ~ I I O I I I ( I trot, I N cl6nsi;lcretl c\litlence :ig:tilrst t l ~ c lo\\.er slag volr~mcs, as t,hr frecluel~cy ol' ,l~urtlen cllnlrges rocluirecl hy ;.ariat,ions in sbt1cific:ntiulls of i rol~ t o meet, illill dt:tll:~llds increaskcl over the latter molrt,hs. Tlrl~o11g11 necessity, t.hc test \V~KI.IIII ~ ~ ~ l d e r ' n c t , ~ ~ : i l dl,er:ttiilg ~ondit~ions and Ijecnuse of t h e lo\\: steel c lekl~cls during' t,he first hnlf of 193s t,he hurc-lcn on the Bessemcr fwnncc \V:LS chn.ngetl frc~m four t,o sevc.11 times p(.r luont.h. n,ncl nlt.lloug.11 thc ljurtlel~ on t . 1 ~ l:)nsik funiacrt rcmninctl t,he snlnc!, t,llc \\.ill11 \vns rod~~c;ctl or illcrenscd 6000 to 7000 co. l't,. per initlutc from onc ~veck to :LI~(.,~II(-I..

~nil'orln'it~y in silicon on I~ot~lr t , l~e Bcsserrler anil b:csic practice like- .\\.is(' SII(;IVS ii grntlu:tl improvelne~~t,. Hcrc! ngnil~, t,111! ct~t.\,c.s t,encl t,o t,r~rn 1111\\::1rcl :tt the lower slug volumes, :tpl,arr~rt,ly ,for tJ~u s:t.mc I.cnsolis 3s 1'(.)1. the trend i l l the sulphur uniformitmy curves. . Thc most out,st:tnding oper:ttirlg :tclvsnt,age i n t,his practice is t,he coilsist,ent,ly 11igI1 cj,~n,lity of t.hc r n ~ t a l prc:,cluct,, \\,hich \vns common

t l l ro~tgl io~~t t,he range of t,he slags carried cluring tho: six-mollth pcriotl of the (:sj,erimr:nt. During t,his periocl the Bessemcr furnaces operated for ovcr three rnont,hs nncl the basic fr~rnace for over five months without making n cast containing more than 0.050 per cent sulpllur. We attrihut,e t,his improvelnent clirectly t o the slowlless of furnace ''s\\-i~lgs" charac-

t,eriat,ic of the tcst practice, \\~hic;ll gave opport,unit,y for t,lle :tl~plicjnt,ion of n tlegrcc of cont,rol not heretofore rcalized. The clistll.ihution clata 011

sulphur nlid silicon analyses is t,abulttted in T:thles 8 :tncl 9. Curves depicting comparisons beti\reen t,he average quality of metal during the normal periocl and that of the test perioil are sl~o\i.n on Figs. 11 and 12.

16 EFFECT OF V O L U ~ ~ E AND PROPERTIES OF SLAG ON IRON

At the beginning of the esperiment, there was some cloubt as to the practical linlit to \vhich slag \rolumes, even with alterecl chemistry, coulcl he reclucecl \vithout cletri~i~ellt to the cluality of the iron. The attnin- ment of a mliform, high-cluality product was not accomplishecl without some change in operating practice. To further promote removal of

//oo

/do0

2

900 s X R \

BOO Q

B \1: 0

700 Q

sulphur fro111 the iron wit11 lower slag ~~olumex, only one flush \\.its m:tcle I~efore the cast, ancl care was taken not to blo\v the ful.nnce a t cast time, l ~ u t rather to leave as much of the slag in tlie furnace as practicable. In t,his itray the average time of the slag in the hearth was lengthened, ancl opportu~lity for slag-metal contact increased, with the result that the

masimunl clesulphurizing power of the slag IVW nppronched. The marked diffel.cnce in the sulphur cont,ents of the slags on the Besselncr :tnd basic furnnces might be attrihutecl t)o the fact that, on the Bessemer furnace, \\~hich is equipped with n remote-control mutl gun, t,he flow of

f MAR. APR M A V JUNE JULY /VbmAL 58 38

BEJSEMPR 38 38 38 38

PRHCVCE b- ~ $ ~ < ~ A & ~ & ~ E - ~ FIG. 9.-CAST-TO-CAST SILICON VARIATION IN B E S S E ~ ~ E R IRON.

slag from tlle tn.pping hole a t cast n7:ts Illore easily regulated, whereas in the basic furnace, nrhich does not have n remote-cont1.01 gun, as mucll sl:ig c.oulc1 not safely I)e retnillecl in the flirnace a t cast time.

A comparison of the clesulphurizing ratio of the slags dill-iag the test periotl \vith that of the llorlllnl periocl is illnstrsted in Fig. 13. The results prove coi~clusively tha t tbe limit of sulpllur d)sorption of the slags was not reached.

To .continue the pr:tctice of low slag volumes iiecessnrily eliminates the use of high-silic:t ores. \Vh:tt t,lie cost woultl be to rccluce the silic:~. in these ores to permit. lo\\ sl:tg volumes has not heen cletcrmincil. The

f . MRR RPR. /WHY JUNE J&Y NRMRL 8HS0C

38 58 38 38 p ! C T / C 6 h- 7E5T PRRCZ'CE .-!

(BAJ/C J FIG. 1 0 . - C . i s . ~ . - ~ r c , - c ~ $ ' r SILI(.!ON V A K l A T I O N IN I(;\$IC: IKOS.

~.cmovnl of the cliffcrenc(-..s ill silic:t : t ~ ~ t l stone l~c~t,\vc.cn t,lic burclcns low nncl high i l l slag restilt,s i l l n suIjst,ant,ial s:tving in the freight rates alone.

As t)lle sing \rolumes are reduced by tlie elimin:tt,ion of tlie siliceous orcs, t,he oxides originating from the coke have n nieasural~ly increased

---effect, upon the perceiitage of total vsicles in t,he slag. .For t,his reason,

it is esse~it,i:il t h a t tlie ash in the coke I)e kcl.)t uniform so t,lint ma.simum I3erlefits may accrue from the altered slag pract,icc.

PERCENT SULPHUR /N //?OM FIG. 1 ~ . - ~ I S T R ~ B I ~ T I ~ N OF SULPHUIt ANALYSIS.

Tlie test, \\.bile 11:tmperecl by many ch:tngcs in burden nnd \\fincl, w:ts I 1111clcr regular operating coliclitio~ls \\it11 thc Furn:ices averaging from

20 EFFECT OF VOLUME AND PROPERTIES OF SLAG ON IRON

92 to 105 per cent of their ratecl capacity. The changes were not con- ducive to unifortn operation or to low coke practice. This, llo\vever, \v:ts

partly offset by the more uniform ash content in the coke usually attend- :tnt with a loiv rate of mill operation.

The fact that furnace mo\rement was not at any time disturbed by these many changes is conr-incing evidence that the lolver slag volu~nes impro~ed collclitio~i of the hosli slag.

Sulpliur nbsorption in the slag was illcreased approximutely 20 per cent by the retention of more slag in the furnace, particularly at cast

G . E. STEUDEL 21

time, thereby nlaking possible ~nai~ltena~lce of a deeper bed and per- mitting longer contact betn~een iron and slag.

To state any of the cost reductions in dollars and cents tvould be confusing, as the cost of rani materials varies so widely, owing, primarily, to shipping rates; practice that R-ould lead to a substantial saving at one plant might be less importarlt a t another iron-manufacturing center.

F I G . 13.-DESULPHURIZING RATIOS, NORMAL A N D TEST PRACTICE.

The savings t.hst can be directly attributed to the revised practice are iteinizecl as follo\vs: (1) reduced alnouut of slag for disposal, (2) reclucecl coke consumpt,ion, (3) reduced stone consumption, (4) reduced cost of ore transportntion per iron unit effected by elimination of high-silica ore, (5) reclucecl flue-dust procluction, (6) lower blowing-engine pressures.

To these should be added an illdirect saving in a inore uniform product for the open hearths, and the ease with which furnace practice can be adjusted to conform with mill production.

22 EI"I.'ISC'r 01" VOI .URIE A N D PROPERTIES O F SJ.AG O N lltOh'

'

The aUthor wishes to express his npprecin.t,iot~ to i\4cssrs. R.. D. Beck nllcl C.'G. Hogberg, melnbers'of the Sout,h Works blast,-furnncc c~rga~li- znt,ion, 'fo'r t,heir- genr:rous assistance in the pr~'~a.r:i.t,ic-,~~ of this pnpcr. Hc .tzlso \visIies to t,hnnk Mr. H. A. Stxnin, Assist,ant Ge11cr:tl Superint'g~~clcnt,, Sout,l~ Works, n.ncl klr. H. 131. . lnl~r~son, Sl~pcrillt,endelit, of Blnst Furt~:~c;c:s, Il~lnlicl Stecl Co., for tllcir kindly c.~.itic.ism t3nc.l sr~ggest,io~)s.

REFE~KNCES 1. C;. A . lk~llkin allil P. 1':. \\'rigllt,: Tcru:try 8yste111 C:IO-AI~O~-S~O.. :Itttcr. -1tt l .

Sci. (1915). 2. A . S. Peiltl nnrl P. H. Itoyst,cr: SI:tg Viscosity Tnhlcs for U1:tst Pr~r~l:icc M'ork.

U. S. Bur. Mincs 7'cclr. I'nper 187 (1918). 3. It. S. McC:lffery :111tl Co-tvorkers: Viscosity of H1:lst-furn:~cc 81:igs. 7'r(!tts.

A.I.M.E. (1933) 100. 4. S. P. I<inr~ey: Co1111)osit.iolt O F Materials from Various Elevat,iona in :ill 1ro11 I3l:lst.

Fr~rnace. U. S. I3r1r. Mit~cs Teclr. P a p c r 397 (1926). 5. 11'. F. Holl.,rook :il l11 T. 1,. Joseph: Reln.tive Desulphurizi~~g Po\vcr of 13l:ist-

furn:~ce Slngs. 7'rntis. A . I . M . E . (1936) 120, 99. A. 11. S. McC:rffery: A St,lltly of Blast-furn:lcc Slngs. Blnsl l.'rrrrioce ancl Slccl I'lrrttl.

(July 1935).