By James T. MacKenzie, Chief Chem ist, American Cast Iron Pipe Company, Birm ingham , Ala.
[American Exchange Paper.]
S teel sc ta p in cu p o la m ix tu re s h a s challenged th e a tte n tio n of fo u n d ry m e n every w h ere for a n u m b er of y ears. M an y p a p e rs h av e been p re
sen ted in th e te c h n ic a l P re s s an d before th e vario u s te c h n ic a l societies d e a lin g w ith th e s tr e n g th of irons o b ta in e d from such m ix tu res, an d i t is alm o st u n iv e rsa lly accep ted t h a t steel scrap does in crease th e s tr e n g th of th e iro n q u ite o u t of p ro p o rtio n to its effect on th e chem ical analysis. T he re c e n t w ork of P iw o w arsk i o n th e influence of g ra p h ite nu clei h a s p ro v id ed a v a lu able th eo ry as a basis fo r f u tu r e in v e s tig a tio n and m ay serve to assist in th e in t e r p r e ta tio n of some h e re to fo re anom alous re s u lts . A ccu rate th e rm a l d a ta m ay be e x p ected in th e fo u n d ry lite r a tu r e of th e f u tu r e , because th e d evelopm ent of th e o p tic a l p y ro m e te r h as placed w ith in th e reach of everyone th e m ean s of o b serv in g an d re c o rd in g te m p e ra tu re . R e c e n t in v e s tig a tio n has shown t h a t th e d is a p p e a rin g filam en t ty p e of p y ro m e te r is a c c u ra te , w ith in v ery sm all lim its, fo r all ty p e s of f o u n d r y ' iro n s a n d th e quickness w ith w hich re a d in g s m ay be m ade, e v en by an in ex p erien ced o bserver, is re m a rk a b le . M an y of th e conflicting re s u lts o b ta in e d by th e use of steel scrap a re d u e u n d o u b ted ly to differences in m e ltin g c o n d itio n s, of w hich th e te m p e ra tu re is pro b ab ly th e m ost im p o rta n t. “ H o t ir o n ” is a n in d e fin ite te r m an d m ay m ean one th i n g w hen spoken by th e sto v e -p la te fo u n d e r an d so m e th in g e n tire ly d iffe re n t w hen spoken by th e m a n u f a c tu r e r of heavy c a stin g s.
A n o th e r cause of m is u n d e rs ta n d in g in discus
sions of steel h as b e e n t h e confusion of te s t b ar a n d c a s tin g . T h e iro n t h a t w ill m ake th e s tro n g e s t te s t b a r of say 1.25 in . din. an d 15 in.
le n g th w ill c e rta in ly m ake a p oor r a d ia to r , if i t will m ake i t a t all, an d will be alm o st as u n s u it
able fo r a v ery heav y c a stin g . T his is one of th e
reasons w hy v ario u s sta te m e n ts e x is t as to th e m ax im u m perm issible p erc e n ta g e of steel scrap in th e c h a rg e , w hich, if m em ory fails n ot, v aries from zero to 10 0 p e r cent.
In e x tric a b ly associated w ith th e te m p e ra tu re of m e ltin g a n d th e chem ical com position of th e m elt, is th e problem of o x id a tio n . W ith steel in th e m ix tu re , th e low er th e m eltin g te m p e ra tu re , th e g r e a te r th e o x id a tio n , th e lower will be th e carbon, silicon, an d m anganese, an d th e h ig h e r will be th e fre e z in g p o in t an d th e gas co n ten t. Conse
q u e n tly th e p ra c tic a l fluidity, or “ co u lab ilite ” as G u ille t an d P o rte v in call it, is ra p id ly reduced.
T his p a p e r is concerned chiefly w ith th e to ta l carb o n absorbed by steel scrap when m elted w ith th e v ario u s cokes of a n u n u su a l collection, n o t com plete, b u t well re p re se n ta tiv e and co n tain in g th e ex trem es likely to be encountered. The cupola used was a N u m b er 0 W h itin g w ith a 27-in. shell, lin e d to 18 in . w ith clay brick, w ith 2 tuyeres 17 in . above th e m a n te l p la te an d 70 in. below th e c h a rg in g door. T he lin in g was s tr a ig h t from m a n te l to c h a rg in g door. The tu y e re s m easured 9 in. by 3 in . a t th e lin in g ; an d th e blast, sup
plied by a fa n , w as fa irly c o n sta n t a t 4 oz. p er sq.
in . I n some of th e e a rly h e a ts th e volume in creased as th e stock fell in th e stack, b u t th e p ra c tic e w as changed as soon as th is was noted a n d th e r e a f te r th e sta c k was k e p t fu ll of coke th ro u g h o u t th e m e ltin g period. N one of th e h eats re p o rte d h e re w as affected by th is to a g re a t e x te n t, th o u g h in several h e a ts a slig h t drop in c arb o n on th e la s t ta p or so m ay be n oted. The cupola w as lig h te d in th e u su al way an d th e wood allowed to b u rn aw ay by n a tu r a l d ra f t, coke being p u t on to h av e th e bed a t 30 in . above th e tuyeres w hen th is was accom plished. T he w ind was then p u t on fo r five m in u te s to h e a t th e ta p hole and b a sin , a f te r which th e bed was b u ilt to 40 in. w ith fresh coke, th e b re a s t stopped in , th e charges quickly p u t in an d th e b la s t p u t on as soon as th e sta c k was filled (ab o u t 5 m in .). The first ta p was m ade in 25 m in ., w hen u su a lly 25 to 75 lb. of iron w ere o b ta in e d , a f t e r w hich m e ltin g proceeded a t th e r a t e of ap p ro x im a te ly 1,000 lb. p er h r. A sh a n k lad le of 200 lb, c a p a c ity was used for h a n d lin g th e m o lte n iro n w hich was poured in to pigs o n ^ th e first tw o o r th r e e ta p s and th e n in to
well blacked a n d d rie d te s t m oulds, g iv in g th e 2 x l x 2 8 - i n . b a rs c a s t v e rtic a lly . C harges were 100 lb. w ith sufficient 50 p e r cen t, ferro-silicon a n d 80 p e r c e n t, fe rro -m an g an ese to give th e in d ic a te d com position. These w ere placed on to p of th e steel in th e c e n tre of th e cupola. The coke c h a rg e w as k e p t c o n s ta n t a t 25 lb., except in th e case of th e h ig h v o la tile p etro leu m cokes, P a rc o , W ic h ita F a lls, a n d Shell. No fluxing was a tte m p te d , b u t th e r e was u su a lly a th in liquid slag w hich was allow ed to r u n in to th e ladle and was skim m ed off before p o u rin g . T he a m o u n t of th is slag v a rie d p ra c tic a lly w ith th e ash co n ten t of th e coke, fo r i t seems t h a t th e h ig h e r th e ash th e g r e a te r th e o x id a tio n of th e steel an d th e p ro p o rtio n of fe rro u s oxide to silicon dioxide is th u s a u to m a tic a lly m a in ta in e d . T h ere w as very little c u ttin g of th e lin in g e x c e p t in th e m elts w ith th e v ery h ig h -ash cokes.
T ab le I shows th e re s u lts fo r to t a l carb o n which a re c a lc u la te d fro m th e d e ta ile d d a ta of T ab le I I . The base was ta k e n as 2.00 silico n ; 0.10 phos
p h o ru s ; a n d 0.50 p e r c e n t, m an g an e se. P u re iro n holds 4.3 p e r cen t, c arb o n in so lu tio n ; 80 per cen t, m an g an ese, a b o u t 6.7 p e r c e n t, c a rb o n ; and 21 p e r cen t, silicon (F e2Si), o r 15.6 p e r cen t, phosphorus (F e sP ), th ro w th e c arb o n to zero.
T h erefo re th e co rrectio n s a re as fo llo w s: — F o r each p e r c e n t, v a ria tio n in m an g an e se (3 .4 /8 0 ), 0.04 p e r c e n t. C.
F o r each p e r cen t, v a r ia tio n in silicon (4 .3 /2 1 ), 0.21 p e r c e n t. C.
F o r each p e r c e n t, v a r ia tio n in phosphorus (4 .3 /1 5 .6 ), 0.28 p e r c en t. C.
T he c alc u latio n s a re a d m itte d ly d o u b tfu l, b u t th e sum of all th r e e c o rrectio n s is less th a n 0.20 p e r c e n t, in n e a rly all cases, an d i t seem s th e only hope of re d u c in g all th e m elts to a comm on basis.
T able I I is given to e n a b le anyone to m ak e a d e ta ile d stu d y of th e a c tu a l re s u lts o b ta in e d u n d is
tu r b e d by th e a ssu m p tio n of th e a u th o r.
T u rn in g a g a in to T able I , i t seem s t h a t 'in th e beehive cokes th e carbon rises as th e ash falls, b u t in no re g u la r w a y ; w hile in th e p u re cokes th e sam e th in g is n o te d in re g a r d to v o la tile m a tte r . I t is a t once a p p a r e n t t h a t th e s tr u c tu r e of th e coke is of fu n d a m e n ta l im p o rta n c e an d
A ctual analysis.
o
m ay c o u n te r a c t to a co n sid erab le e x te n t th e effect of th e com position. T he tw o h ig h -ash cokes have li tt le d ifference in s tr u c tu r e a n d li tt le in carb o n ab so rp tio n . The B ra d fo rd is m u ch so fte r th a n th e F ir e O reek (w hich is e x tr a o rd in a rily h a r d an d d ense), an d so c a rb u rise s to a n e x te n t n o t w ar
r a n te d by th e difference in ash. C om ing to th e p u re cokes, th e B a r r e t t is h a r d a n d dense (really a tr u e coke), th e B ay o n n e q u ite c ellu lar, a n d th e o th e rs h ighly c ellu lar. I n fa c t, th e W ic h ita F a lls b u rn e d along th e cell w alls so ra p id ly t h a t sm all pieces w ere blow n o u t of th e s ta c k in a v e rita b le show er, w hich no d o u b t a cco u n ted fo r its fa ilu re to m elt. T he P a rc o was m u ch b e tte r , an d gave few sp a rk s of th is n a tu r e , b u t re q u ire d an in o rd i
n a te ly long tim e to begin m e ltin g , -and th e n m elted v ery slowly. The fu rn a c e w as 70 m in u te s in b la s t before an y iro n m elted , a n d th e n i t cam e slowly b u t h o t, th ro w in g o u t g r e a t q u a n titie s of
“ k ish ” as i t w as being p o u red . The S hell coke was so b ro k en up in its lo n g jo u rn e y in bags from th e P acific C o a st t h a t i t was alm o st useless to t r y it, b u t u n d e r th e h e a t i t m elted dow n to a soft, gum m y mass, so no d ed u ctio n s could be m ad e from its o rig in a l s tru c tu r e . W hile i t is n o t th o u g h t t h a t th e v o latile m a tte r h a s an y in flu en ce p e r se, on escap in g i t pro b ab ly leaves th e coke in a m ore porous c o n d itio n th a n o rig in ally .
I n a n able p a p e r p u b lish ed by M r. F . H u d so n in Th e Fo u n d r y Tr a d e Jo u r n a l, D ecem ber 1 1 , 1 9 2 4 , e n title d “ The M e ltin g an d C a s tin g of H ig h D u ty I r o n s ,” th e fo u r p o in ts in flu en cin g th e a b so rp tio n o f c arb o n a re s t a te d as fo llo w s: — (1) T e m p e r a tu re in th e m e ltin g z o n e ; (2) tim e in th e m e ltin g z o n e ; (3) atm o sp h ere of com bus
tio n ; a n d (4) in itia l an aly sis of m a te ria l m elted . T h a t th ese a re t r u e th e r e is no d o u b t, fo r th e first two' a n d la s t a re sp ecial s ta te m e n ts of th e f u n d a m e n ta l law s o f so lu tio n , v iz., te m p e ra tu re , tim e of c o n ta c t, an d c o n c e n tra tio n . T he th ir d , based on th e know n c h em istry of th e iro n -carb o n - oxygen system , is pro b ab ly b e tte r fixed in th e m in d s of fo u n d ry m en th a n th e o th e r th r e e . The a u th o r w ould, how ever, q u estio n th e re s tric tio n im plied in th e w ords “ m e ltin g zo n e,” fo r he is convinced t h a t a b so rp tio n can an d o fte n does co n tin u e in th e h e a r th follow ing e x a c tly th e law s
s ta te d above. R u n n in g only 15 p er cen t, steel on A iB O coke he h as observed a c o n sta n t d iffer
ence in to t a l c arb o n of 0 .10 p e r cen t, when ta p p in g in te r m itte n tly as a g a in s t co n tinuous flow, th e l a t t e r b ein g a b o u t 3.50 p e r c en t, an d th e fo rm e r 3.60 p e r c e n t .; th is o n th e la rg e foundry cupolas ru n n in g h e a ts of 10 hours.
S in ce o n ly th e m e ltin g o f steel scrap is being considered, w h ere th e o rig in a l m a te ria l is n early th e sam e in all cases, th ese p rin cip les m ay be r e s ta te d a s : — (1) T e m p e r a tu re ; (2) tim e of con
t a c t w ith ccirhon; a n d (3) atm osphere of com bus
tio n . L o o k in g a t th e problem solely from th e s ta n d p o in t of th e coke, th e case m ay be s t a t e d : —T h a t th e te m p e r a tu r e d ep en d s on th e p u r ity , re a c tiv ity an d size o f th e coke in th e m e ltin g zone an d b elo w ; t h a t th e tim e of c o n ta c t dep en d s on th e p u r ity an d size of th e coke, fo r th e h ig h e r th e ash th e m o re will be th e te n d en c y to cover up th e carb o n by slag an d p re v e n t c o n ta c t w ith th e m e t a l ; an d t h a t th e atm o sp h ere of com bustion d ep en d s o n th e p u r ity , re a c tiv ity , an d size of th e coke. S ince th e re a c tiv ity dep en d s on th e p u rity an d p hysical s tr u c tu r e , an d since th e effective size of th e coke dep en d s on th e s tru c tu r e , one m ay assum e t h a t th e e x te n t of c a rb u risa tio n dep en d s on th e p u r ity an d s tru c tu r e of th e coke.
U n fo rtu n a te ly , th e te s tin g of coke h a s n o t re ach ed th e p la n e o f tr u e science, an d , although i t ican be ta k e n fo r g r a n te d t h a t th e re a c tiv ity is a fu n c tio n of s tr u c tu r e , no one is y e t sure of a t e s t t h a t will in d ic a te th e r ig h t s tr u c tu r e fo r m a x im u m re a c tiv ity . I t w ould a p p e a r t h a t for c a rb u ris a tio n , coke should n o t be e ith e r ex trem ely dense o r e x tre m e ly p o ro u s ; t h a t i t should be n e ith e r too h a r d n o r too s o f t ; an d t h a t i t should be n e ith e r very h eav y n o r v ery lig h t. A h a rd , dense, heav y coke w ill te n d to allow oxygen to p e rs is t a long d istan ce above th e tu y eres, and th e m o lten m e ta l w ill flow ov er a c o m p arativ ely sm all s u rfa c e o f coke on its w ay th ro u g h th e m e ltin g zone, w here m ost of th e c a rb u ris a tio n ta k e s place.
J u s t as rock candy is h a r d e r to dissolve th a n lo af su g a r, so is th e dense carbon m ore difficult to dissolve th a n th e lig h t, th o u g h tim e o f c o n ta c t is p robably th e e x p la n a tio n of b o th . On th e
o th e r h a n d , a so ft, ¡porous, lig h t coke will b u rn alm ost e n tire ly to carbon m onoxide close to th e tu y e re s, w ith conseq u en tly low te m p e ra tu re , and i t will easily cru sh dow n a n d e ith e r s h u t off th e b la s t o r blow o u t of th e s ta c k as d id th e W ic h ita F a lls. U n d o u b ted ly , if h ig h te m p e ra tu re can be o b ta in e d w ith a so ft, p u re coke, th e m e ta l can easily be s a t u r a te d beyond th e e u te c tic . A m edium s tr u c tu r e w ould a p p e a r in g e n e ra l to give th e m ax im u m c a rb u ris a tio n , even if te m p e r a tu r e is som ew hat sacrificed, fo r th e h ighest te m p e ra tu re s o b ta in e d w ere w ith th e F ir e Creek a n d B a r r e t t yokes, b u t n e ith e r gives th e best c a rb u ris a tio n fo r its class. B y in c re a sin g th e am o u n t of B a r r e t t to 35 lbs. p e r ch arg e, o r th e sam e ra tio as th e P a rc o h e a t of 5 /2 /2 5 , carbons of n e a rly 4 p e r c en t, w ere o b ta in e d a t te m p e ra tu re s a p p ro x im a tin g 1,600 deg.
T his is mot tr u ly c o m p a ra tiv e , since 35 lbs. of P a rc o coke c o n ta in e d only 30 lbs. of c arb o n , and th e B a r r e t t c o n ta in e d alm o st 35 lb s., b u t th e te s t is illu m in a tin g as a n illu s tra tio n of th e effect of h ig h e r te m p e ra tu re a n d g r e a te r tim e of c o n ta c t u sin g th e sam e coke th u s e lim in a tin g th e effect of all o th e r v ariab les.
The m elts w ith unbroken A B C coke show clea rly th e effect of th e coke size on th e carb o n ab so rp tio n . F o r all o th e r te s ts on th is cupola, th e coke w as c a re fu lly b ro k en u p so t h a t no piece w ould sta y on a tw o-inch s c r e e n ; b u t in th e se th r e e te s ts la rg e lum ps of coke, n o n e of w hich would pass a tw o-inch screen, w ere used th r o u g h o u t an d th e carb o n d ro p p ed 0.3 p e r c e n t, from th e a v erag e fo r th e b roken coke in s p ite o f th e sam e te m p e ra tu re o b ta in e d u n d e r b o th c o n d itio n s (1,500 deg. C.).
The e x p e rim e n t w ith W ic h ita F a lls an d A B C , 50 p e r c en t, each, above a bed of A B C is in te r e s t
ing, T able I I — h e a t of 8 /2 9 /2 5 . H e re a co rrected carb o n of 3.04 p e r cen t, w as o b ta in e d fro m th e m ix tu r e , th o u g h th e te m p e r a tu r e given w as r a t h e r low (1,450 deg. C .). T hus by m ix in g a coke (or pro b ab ly p itc h w ould be m ore a c c u ra te ) of h ig h r e a c tiv ity w ith one of good s tr u c tu r e , re s u lts m ay be o b ta in e d n o t possible w ith e ith e r alone.
As m ost of th ese m elts w ere m ade on m ild steel scrap of n o n d e sc rip t c h a ra c te r an d w ith a con
sid e ra b le v a ria tio n in size from t h a t desired (1 in.
ro u n d ), i t a p p e a re d w o rth w hile to ru n some te s ts to see if o rd in a ry v a ria tio n s in size h a d any effect on th e c arb o n a b so rp tio n . A 500 lb. le n g th of 3.25 in . ro u n d m ild steel (0.16 p e r cen t. C, 0.06 p er cen t. P , 0.43 p e r cen t. M n, an d 0.038 p e r cen t. S) was c u t in to 8-in. le n g th s an d m elted (h e a t of 1 /2 1 /2 7 ). T he n e x t d ay a sim ilar te s t was ru n w ith 0.75 in . ro u n d of th e sam e analysis c u t to 8 ins. T he h e a t of 1 /2 9 /2 7 w as ru n on th in s trip s of th e sam e steel, v a ry in g in th ick n ess from \ to i in ., a n d in w id th from 1 to 2 ins., as th e r e was n o t sufficient of o n e p a rtic u la r size in stock to m ak e up a com plete m elt. The larg e steel was h e a v ie r th a n a n y th in g used in th e se te s ts, and th e th i n s trip s w ere lig h te r th a n a n y th in g used in th e m , w hile th e J in . ro u n d would alm ost re
p re s e n t th e average. I t is e v id e n t t h a t th e c a r
bon ab so rp tio n does n o t depend on th e size, for th e a v erag e of th e la rg e b ars an d th e th in s trip s is th e sam e. F o r som e reason th e te m p e ra tu re of th e J in. ro u n d m e lt was fully 50 deg. h ig h er th a n th e o th e r tw o, a n d th e c arb o n is 15 p o in ts h ig h er.
These te s ts prove t h a t carbon is n o t absorbed to a n y ap p reciab le e x te n t by th e solid steel though th e rev erse m ay b e n o ted on th e su lp h u r, which seem s to be absorbed m uch m ore read ily bv th e sm all stuff. A n o th e r in te re s tin g confirm ation of th is is th e m elt of 8 /5 /2 5 . T his steel h ad been in th e cupola fo r over a n h o u r u n d e r blast, tr y in g to m e lt i t w ith th e Shell coke. W hen th e te s t was ab an d o n ed an d th e b o tto m dropped, th e whole body of th e steel was som ewhere betw een 900 and 1,200 deg. C ., b u t only a few pieces showed th e s lig h te st signs of m e ltin g . To te s t th e question of carb o n a b so rp tio n , th e a u th o r exam ined several o f th ese u n d e r th e m icroscope, finding th e m erest film of carbon, so i t w as decided to m e lt i t w ith A B C coke as a f u r th e r te s t on th is p o in t. The c arb o n on th e m elt, 2.56 p er c e n t., is ju s t 0.06 p er cen t, above th e a v e ra g e fo r th is coke on new steel, an d is well below some o th e r m elts, so i t is th o u g h t th e r e is no d o u b t of th e accuracy of th e g e n e ra lis a tio n , w hich was also m ade by M r. H udson (loc. c it.).
T able I I I shows th e equalised carbons on five m elts w hich w ere rem elted w ith s lig h t a d d itio n s of
silicon a n d m anganese, using th e sam e coke. The m e ta l from th e first m e lt was la rg e ly in pigs, an d th e r e fo re co n sid erab ly h e a v ie r in section th a n th e steel. The av erag e was a p p ro x im a te ly 2 x 3 x 8 ins. w ith some few pieces as larg e as 4 x 4 ins
Ta b l e. IIT .
Coke. Carbon,
1st melt.
Carbon, 2nd melt.
Carbon absorption,
2nd melt.
Dayton 1.80 2.23* 0.43
Sewanee 1.80 2.57 0.77
Bradford 2.81 3.33 0.52
A B C 2 . 18f 2.93 0.75
Barrett 3.85 4.25 0.40
* Cold melt. f Scaffolded.
The o rig in a l A B C h e a t scaffolded a f t e r th e second ta p , because of som e rods a little too long in th e charge, so t h a t i t is n o t tr u ly r e p r e s e n ta tiv e of th e m elts of th is coke, b u t th e re m e lt w ent off in g r e a t shape. T he re m e lt on th e D a y to n coke was sluggish, p robably d u e to o x id a tio n a n d high s u lp h u r, th o u g h th e silicon w as ab n o rm ally in creased in a n tic ip a tio n of th is r e s u lt. I t was difficult to g e t a n a c c u ra te re a d in g on it, b u t i t w as e stim a te d t h a t th e te m p e r a tu r e w as a b o u t 1.400 deg. fro m th e cupola, w hich is close to th e
The o rig in a l A B C h e a t scaffolded a f t e r th e second ta p , because of som e rods a little too long in th e charge, so t h a t i t is n o t tr u ly r e p r e s e n ta tiv e of th e m elts of th is coke, b u t th e re m e lt w ent off in g r e a t shape. T he re m e lt on th e D a y to n coke was sluggish, p robably d u e to o x id a tio n a n d high s u lp h u r, th o u g h th e silicon w as ab n o rm ally in creased in a n tic ip a tio n of th is r e s u lt. I t was difficult to g e t a n a c c u ra te re a d in g on it, b u t i t w as e stim a te d t h a t th e te m p e r a tu r e w as a b o u t 1.400 deg. fro m th e cupola, w hich is close to th e