On the Genesis of lVidmanst(Itten Structure in Meteo~,'Ites and in Iron-nickel and Iron-carbon Alloys-20-104-173

8/13/2019 On the Genesis of lVidmanst(Itten Structure in Meteo~,'Ites and in Iron-nickel and Iron-carbon Alloys-20-104-173

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173

On the genesis o f lVid m an st(itten stru ctu re in meteo~, itesand in iron-nickel and iron-carbon alloys.

B y Colonel N. T. Br LAIEW, C.B. , F.C .S.

[ Read Novem ber 6, 1928.]

I . [ n t , o d u e t i o n .

~N A pr i l 190 9 a pa l~er on a r t i fi c ia l rep rod uc t ion of meteor ic s t r uc tu rein a ll oys o f i r on aud c a rbon was r ead by t he au tho r be fo re t he

R us sia n :Minera logical So cie ty (t~eferenee 1, see below, p. 183 ). I n th,~tpape r spec i a l r e f e r e l l ee was made t o t he work o f Sorby, who , t o c i t e h i s(~w n w o r d s , f o r m o r e t h a n t w e n t y y e a r s . . , c o m m e n ce d t o c a re f u ll y~tud y the microseoi )ieal s t ruc ture of i ron an d s tee l in o rder, i f possib le , to

th ro w l i gh t on t he o r ig in o f me teo r i c . i r on (2 ). A b r i e f su rvey o f t hew o r k o f S t o d a r t a n d F a r a d a y, o f O s m o n d , R i n n e , a n d B e r w e r t h w a sa l so g iven and , subsequen t l y, t he s t ruc tu re o f a ca rbon- s t ee l con t a in ing0 .5 5 Z ca rbon w i th pe r f ec t l y deve loped W idmans t~ i tt en f i gu re s wasdescr ibed .

Th i s a l l oy be longed t o a s e r ie s o f ca rbon-s t ee ls p r ep a red i n 1907 an d1908 , a t t he au th or s r eques t , a t d i f fe r en t Russ i an s t ee l -works un de rcond i t i ons o f ex t r eme s lowness o f coo li ng . These r e sea rches were und e r-t a k e n b y t h e a u t h o r ia o r d e r to b r i n g i h to c lo s er h a r m o n y th e p r o c e s se so f c rys t a l l iza t i on wi th t he va r ious a r eas o f t he equ i l i b r i um d i ag ram .T h e a u t h o r w a s d e e p ly i m p r e s s e d b y t il e w o r k o f S o r b y o n m e t e o r i t e sl ind by t ha t o f Auosso ff on damascene s tee l, and , s t a r t i ng und e r t hegu id anc e o f h i s t eache r P ro fe s so r Tschernoff , he d i r e c t e d h i s ea r l ye ffo r ts t owa rds ob t a in in g l a rge s t ruc tu re s ea s i l y d is ce rn ib l e w i th a nak ed~ye (3) .

Fol low ing Anosso ff s p r ecep ts , t he s tee l a l loys were me l t ed i n c ruc ib le s ,ove r-he a t ed fo r a ce r t a in pe r iod o f t ime , and t hen a l lowed t o coo l downs lo w l y i n t h e c r u c i b le s t o g e t h e r w i th th e f a r n a c e. A b o u t t w e n t y a ll oy sw i t h c a r b o n - c o n t e n t v a r y i n g b e t w e e n 0 . 4 0 Z a n d 2 . 3 0 Z w e r o p r e p a r e dun de r cond i t ions o f und i s tu rbe d and v e ry s low coo l ing , t he i n t e rva lb e t w e e n 1 , 5 0 0 ~ a n d 2 9 0 ~ C . t a k i n g f o r m o s t o f t h e m a s m u c h a s s i x tyhour s .


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1 7 4 N T B E L A I E W ON

U nd er t hese cond i t ions a l l the a l l oys deve loped a ve ry f ine m ac ro -

scop i c c rys t a l li ne s t ruc tu re and supp l i ed t he au th or w i th a vas t f ie ld o fr e se a r ch . P a r t i c u l a r l y b e a u t i f u l w e r e th e c r y s t a ll i n e a g g r e g a t e s o n t h eou t e r c rus t s o f t he a l loys nos . 1 , 2 , 5 , and 6 , and t he i r eo r r e spo nd ingm acro s t rue tu re s (4 ) ; t he r ea l puzz l e, howeve r, was o ffe r ed by t he a l l oyno . 8 . The f i r st spec imen o f t ha t a l l oy t o r each t he au th or w as posses sedof a cha rac t e r i s t i c s t r uc tu r e o f wh i t e pa ra ll e l bands . A f ir s t i n fe r ence t obe made was t ha t t h i s s t r u c tu r e m igh t be a mac roscop i c eu tec t ic s t ruc -tu r e , l i ke t ha t o f ce r t a in g r an i t e s and o the r rocks . As t h i s pa r t i cu l a rl i ne o f r e sea rch seemed to open vas t ho r izons , a ca r e fu l s t udy was madeof t he w ho le a l loy, bu t , t o t he au th or s d i s appo in tme n t , an en t i r e ly newst ruc ture was re ve a led : t r i angles , equ i la te ra l an d isosce les, qu adra ngles ,pen t agons , and va r ious o the r conf igu ra t i ons , bu t on ly excep t i ona l l y i nse t s o f pa r a l l e l l ine s, l ~a ther r e luc t an t l y, t h i s hypo thes i s o f a m ac ro -scop ic eu t ec t ic had t o be aband one d and ano the r one subs t i t u t ed ; i t tookthe a u tho r a cons ide rab l e t ime be fo re he r ea l ized t ha t i n h i s hands wasa p e r f e c t e x a m p l e o f s y n t h e t i c a l l y r e p r o d u c e d m e t e o r ic s t r u c tu r e a n d t h a tt he va r ious geome t r ica l m ark ings were , i n f ac t, t he f am ous W idmans t~ t tt en

f igures . A s soon as th i s wa s rea l ized i t becam e necessa iT t o co r r e l a t eth i s s t r uc tu re wi th r e f e r ence t o t he o the r c rys t a l l ine s t ruc tu re s o f t hei ron -ca rb on a ll oys , t he n e tw ork s t ruc tu re and t he s t ruc tu re o f l a rgec rys t a ls . Thu s was evo lved t he hypo thes is o f t he t r i ad o f s econda rys t ruc tu re s , v i z. t he ne tw ork s t ruc tu re , t he s t ruc tu re o f l a rge c rys t a l s,and t he Widmans t i i t t en s t ruc tu re (5 ) .

I n a s ub s e q u e n t p a p e r, p r e s e n t e d h y t h e a u t h o r i n t h e e a r l y p a r t o f1 9 1 4 t o t h e I n s t i t u t e o f M e t a ls ( 6) , a f u r t h e r s te p f o r w a r d w a s u n d e r -

t a k e n a n d t he , so t o s a y, u n i v e r s a l it y o f t h e W i d m a n s t ~ t t e n s t r u c t u r ewas shown and i t s occur r ence i n va r ious me ta l s an d a l l oys dem ons t r a t ed .M ore r ecen t l y, i n a second pap e r t o the s ame Ins t i t u t e (7 ), t he au tho rr e t u r n e d t o t h e m o r p h o l o g i c a l a s p e c t o f t h e ~ Tid m a n st~ it te n s t r u c t u r eand t he re l a t ion o f t ha t s t r uc tu r e t o the i nne r s t ru c tu re o f t he c rys t a l l i neg r a i n .

Th ere rem ains , s t il l, to fo l low up, s tep b y s tep , the genes i s of theW i d m a n s t i it te n s t r u c t u r e i n a ll oy s o f i r o n a n d c a r b o n a n d i n t h o se o fi ron and n i cke l, Suc h a s t udy wi l l enab l e us , i t i s hoped , t o t h row somel ight a l so on the gen es i s of W idmans t~ i tt en s t r uc ture in meteor i t es .

I I . The tr iad o f secondary structures in alloys o f iron an d steel

L e t u s c o n s id e r t h e e q u i l ib r i u m d i a g r a m o f i r o n a n d c a r b o n a l lo y s(fig . 1 ). On t h is d i ag ram t em pera tu re s a r e p lo t t ed a s o rd ina te s , and t he


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T I t E G E N E S I S O F W 1 D , ~ I A N S T ~ T T E N S T B , U C T U R E . ] 7 5

percentage of carbon as abscissae. The various curves may be int erpr eted

as showing graphically at what temperat ure a new constituent appears orvanishes i n an alloy of a certain concentration. In other words, theequUib rium diagram shows at a glance what changes occur in an alloyand at what temperature they occur.

The first change to be taken into consideration is the solidification or,what m~ght be called, primary crystallization. This t ransformation fromthe fluid to the solid state is not instantaneous, but gradual and spreadsover a certain int erva l of temperatures. There are, therefore, on thediagram two curves instead of one : AC and A E showing the beginnin g

~ t~oo2-- ,~-/---4-- ~E .~ ,, ~_ I - I,ook - I _,L--I

. . . . . - + - - - - - I2 - - - - - i - t /0 I 2 3 4 6

F ~ i

~

800

.t~ bOO

50U

2 ino

.,'/Tck ~ 2

FI(~. 2.

Fio. 1. Equilibrium diagram of iron-carbon alloys. (After H. C. tt . Car-

penter, 1904.)Fro. 2. Equilibrium diagram of iron-nickel alloys. (After F. Osmond, 1904.)

and the end of solidification. The area between these two curves maybe called the area of solidification or of pri mar y crystallization. Thiscrystallization consists in the formation o f den dri tes of a solid solutionof iron and carbon, and all steels a fter solidification will be bui lt up ofjuxtaposed and interlocked dendrites mutually limiting each other.Every dendrite is a chemical as well as a crystallographical unit and

continues as such, un ti l a new phenomenon of a crystallographical or ofa chemical nature talees place.

After solidification every alloy enters the area AESOG(fig. 1), which maybe called the granulationarea. In this area the crystallographic uni ty ofthe dendr ites is destroyed by the formation of the new grains or granulae


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176 ~ . T. I~: ELAI EW ON

o f 7 - ir o n , a n d t h e p r o c e ss c o n t in u e s t i l l t h e w h o l e m a s s o f t h e a l l o y i s

c o n v e r t e d i n t o s u c h n e w g r a i n s o r g r a n u ] a e , m u t u a l l y l i m i t i n g e a c h o t h e r.A s t h e a l l oy s c o o l d o w n t h e y re a c h a n e w c r i t i c a l r a n g e w h e r e a

c h e m i c al c h a n g e - - t h e d e c o m p o s i t io n o f t h e s o l id s o l u t i o n - - t a k e s p l a ce .Th e p r o c e s s c o ,~s is ts f i r s t in t h r o w i n g o u t o f t h e e x c e s s o f o n e o f t h ec o m p o n e n t s a n d , a f te r w a , ' d s , i na e u t e c t o i d t r a n s f o r m a t i o n a t a c o n s t a n tt e m p e r a t u r e o f 6 9 5 ~ C ., w h e n t h e r e m a i n i n g s a t u r a t e d s o l id s o lu t io n o ft h e c o m p o s i t i o n 0 9 0 Z c arb o,1 is w h o l l y c o n v e r t e d i n to a m i n u t e a g g r e g a t eo f a l t e r n a t i n g f ih n s o r J a m e l l a e o f t h e t w o c o m p o n e n t s, f c r r i t e ( p u r e ir o n )a n d c e m e n t i t e ( F e sC ) . T h i s a g g r e g a t e w a s c a l l e d b y S o r h y t h e ' p e a r l yc o n s t i t u e n t ' , a n d i s n o w k n o w n a s ' p e a r l i t e '.

T h e p r o c e s s j u s t d e s c r i b e d o f c h e m i c a l d e c o m p o s i t i o n o f t h e s o li ds o l u t i o n m a y b e c a l l e ds e c o n d a r y c r y s t a l l i z a t i o n .I t o c c u r s i n a m a s sb u i l t u p o f a n u m b e r o f g r a n u l a e , w h i c h a r e a l lo t r io m o r p h i c c r y s ta l s .E a c h g r a n u l a p o s s es s es i t s ow n c r y s t a l l o g r a p h i c o r i e n t a t i o n a n d i s ad i s t i n c t c r y s t a l l o g r a p h i c u n i t. W h e n t h c p r o c cs s o f c h e m i c a l d e c om -p o s i t i o n s t a r t s t h e r e i s n o r e a s o n w h y i t s h o u l d s t a r t i n a n y p o i n t o f t h eg r a n u l a in p r e f e r e n c e t o a n y o th e r. O , f l y w h e r e d i f f e r e n t g r a i n s m e e t is

t h e r e a k i n d o f n e u t r a l z o n e - - a ' n o m a n ' s l a n d ' - - w h e r e t h e c r y s ta l l i n em a t t e r c a n n o t a s s um e th e o r i e n t a t io n o f e i t h e r o f th e g r a i n s . T h i s t h i nl a y e r i s, s o t o s a y, p r e d e s t i n e d t o f a c i l i t a t e t h e e j e c t io n o f t h e f i r s tp a r t i c l e s o f t h e c r y s t a l l i z i n g e l e m e n t . G i v e n s u f fi c ie n t t i m e a n d o t h e rs u i t a b l e c o n d i t i o n s , t im w h o l e o f t h e e x c e ss e l e m e n t w o u l d b e e j e c te d t ot h e p e r i p h e r y o f th e g r a i n , f o r m i n g a m e m b r a n e o r a s h e ll of a c e r t a i nt h i c k n e s s . O n a p l a n e s e c t i o n s u ch s t r u c t u r e w o u l d a p p e a r a s a c e l l u l a ro r n e t w o r k s t r u c t ~ r e .

I f t h e i n t e r v a l o f s e c o n d a r y c r y s t a l l iz a t i o n i s c o v e re d r a t h e r r a p i d l y,a c e r t a i n a m o u n t o f t h e e x c e ss e l e m e n t w i l l b e fo r c e d t o c r y s t a l l i z e o u t' o n t h e s p o t ' , t h a t i s, n o t o n t h e b o u n d a r y, b u t i n t h e m i d d l e o f t h eg r a i n . S u c h s e p a r a t i o n w i l l n e c e s s a r i l y f o ll ow t h e c r y s t a l l o g r a p h i c p l a n e so f t h e c r y s t a l l i n e m a t t e r. A s i r o n a n d s t ee l i n t h e i r ~/ -s tu te a r e a r r a n g e di n a f a c e - c e n t r e d c u b i c l a t t ic e , t h e s e p la n e s w i l l b e t h e f o u r p a i r s o f t h eo c t a h e d r a l p l a n e s . T h e s e p a r a t i o n o f t h e e x c e s s e l e m e n t w i l l f o ll o w i ns p a c e t h e s e p l a n e s . O n a s e c a n t p l a n e s u c h o c t a h e d r a l s e c ti o n s w i l la p p e a r a s Wi e l m a n s t d ~ t e n j T g u r e s ( 7 , p .3 8 0 ) . S u c h f i g u re s w i l l b e a ra d i s t i n c t c h a r a c t e r i n e v e r y g r a in . T h e c o m b i n a ti o n o f m e s h e s w i t ht h e s e f i g u re s , a s s u g g e s t e d b y t h e a u t h o r, m i g h t b e c a l le dJ Vid , m a n s td l t e ns t r u c t u r e , a s d i s t i n c t f r o m t h e Wi d m a n s t K i t e n f i g u r e s t h e m s e l v e s .

A t h i r d t y p e o f s t r u c t u r e m i g h t b e a n t i c i p a t e d if , f o r o n e r e a s o n o ro t h e r, th e g r a n u l a t i o n p r o c e s s n o t h a v i n g t a k e n p la ce ~ t h e s e c o n d a r y


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TII E GENESIS OF WIDMA NSTATTEN STRUCTURE 177

depos i ts were t o a r r an ge t hemse lves pa ra ll e l t o ti de dendr i t i c axes . Suc h

a s t ruc tu re usua l l y occur s i n i so l a t ed c rys t a l s and was ca l l ed by t hea u t h o r t h estructure o f large crystals.

These t h r ee m a in t yp es o f s econda ry depos it s, t he ne tw ork s t ruc tu re ,t hc s t ruc tu re o f l a rge c rys t a l s , and t he Widmans t i i t t en s t ruc tu re , cons t i -t u t e t he t r i ad o f s econda ry s t ruc tu re s 48). The Widmans t~s s t ruc tu re ,t he l a s t -nam ed o f t he t r i ad , has a pa r t i cu l a r impor t anc e t o us , be ing t hes t ruc tu re o f t he c la s s o f me teo r i c i r ons ca ll ed oc t ahedr i t e s .

I I I . Equilibrium diagram of iron-nickel alloys.The equ i l i b r i um d i ag ram o f i r on -n i cke l a l loys is based , i n t he f i rs t

i n s tance , on t he Osm ond ' s hypo thes i s , t h a t w i th a ve ry s l ow coo l ing t het r ans fo rm a t ions r e su l t i ng i n t he decom pos i t ion o f t he so li d so lu t ionwou ld occur a t t he s ame t emp era tu re s a s t he r eve r se p roces s occur s o nhea t i ng (9) . O n t he bas i s o f t he rm a l cu rves on hea t i ng and , t o a s t i l ll a rg e r d e g re e , o n t h a t o f t h e m a g n e t ic t r a n s f o rm a t i o n s , O s m o n d d r e w u pa d i ag ram g iven on fig . 2 . The a r ea cove red by t h i s d i ag r am r ep re sen t s ,b road ly speak ing , t he p rocesses wh ich i n t he i r on -ca rbo n a ll oys we red e s i g n a te d a s ' s e c o n d a r y c r y s t a l l i z a t io n ' . T h e c o m p l e x o f t h e c u r v e sAE AB BCDa n d F C D imp l ie s t ha t a dec omp os i t ion o f t he so li d so lu -t i on t akes p l ace w i th in t he a r easA E B a n d JBFCDC. T h e p r o d u c t s o ft h i s decom pos i t i on wou ld be two n i cke l i f e rous f e r ri te s ; one t o t he l e f t o ft h e d i a g r a m w i t h a b o u t 7 o f n i c ke l , a n d t h e o t h e r i n t h e r i g h t - h a n ds ide con t a in ing up t o abou t 50 Z . I n me teo r i te s such p rodu c t s a r ea c t u a l ly m e t w i t h : t h e y a r e t h e w e l l- k n o w n k a m a c i t e a n d t a c n i te .

A t t em pt s t o p roduce such dup l ex s t ruc tu re s i n a r t i fi c ia l a l l oys werefo r a ve ry l on g time w i thou t r e su l t ( 10 ) . I n 1910 , howeve r, Dr. Ca r lB e n e d ic k s s u cc e ed e d i n b r i n g i n g o u t th e d u p l e x m e t e o r i ti c s t r u c t u r e i nan a l l oy con t a in ing 11 .7 Z o f n i cke l 410 i ). Fo r a wh i l e t he conc lus ive -n e ss o f t h es e e x p e r i m e n t s w a s c o n te s te d b y F r a e n k e l a n d Ta m m a n n 4 1 0 h ),bu t i t wa s subsequen t l y s t r en g thene d i n Dr. Bcn ed i cks ' s l a t e r pap e r (11 ) ,a n d f u r th e r p r o v e d i n D . a n d H . H a n s o n ' s p a p e r 4 1 0 j ) . T h e H a n s o nd iag ram s l igh t l y d iffe rs f rom tha t o f Osm ond in t ha t the F F ' o r t aen i t el ine i s p laced , no t a t ab ou t 50 ~o, bu t a t abo ut 32 of n icke l . In a l lessentia ls , how ever, bo th d iag ram s are qu i te s im i la r (ef t f igs. 2 and 4) .

T h e O s m o n d ' s d i a g r a m w a s a d o p t e d t b r m e t e o r it e s b y F. R i n n e i n1905 412). H e even sugg es t ed t ha t t he c l a s si fi ca ti on o i me t eo r i c i r onsm igh t be based on such a scheme , and he i n t roduced t h e t h r ee g rou ps o f' l a cun it e s ' , ' s ub l acu n i t e s ' , and ' supe r l acun i t e s ' ; t he f i r s t g roup ro ug h ly

~ 2


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17 8 1~-. T. um , A I~ w OX

com pr i s i ng t he hexahed r i t e s , t he ~econd t he oe t ahedr i te s , and t he t h i rd

t h e n i c k e l- r ic h a ta x it e s. H e a ls o s u g g e s te d t h e w o r d e u t r o p i e f o r t h ot ransf orm at ion s in the so l id s ta te w hie il in t echn ica l a l loys a re ca l l ede u t e c t o i d t r a n s f o r m a t i o n s ; t h u s 1 R i n n e b r o u g h t f o r w a r d a g a i n t h e

ana logy be twe en t he eu t ec to id pea r l i t e and t he p l e s s it e o f me teo r i c i r ons.H e f u r t h e r a d d e d t o th e O s m o n d s d i a g r a m t h e t h e n h y p o t h e t ic a l li n e so f p r im ary c rys t a l l i za ti on , and t hus mad e t he two d i ag ram s a s s im i l a r a spossibl e. A f t e rward s t hese cu rves were expe r im en ta l l y de t e rm ined byG u e r t l e r a n d Ta m m a n n ( 13 ) , a n d q u i t e r e c e n t l y co n t r m e d a n d s u b -s t a n t ia t e d b y D . I t a n s o n a n d J . R . F r e e m a n ( 1 4 ). T h e l a t te r s d i a g r a mis r ep roduc ed i n fig . 4 . The an a log y o f t he l e f t pa r t s o f the d i ag ram s o ff ig . 1 ( i ron-c arb on a l loys) and of f ig . 4 ( i ron -nick e l a l loys) is ve ry rem ar k-ab l e : i n bo th d i ag ram s t he re a r e the l i nes o f p r im ary c rys t a l l iza t i on andthe cu rves o f t r ans fo rma t ions i n the so l id s t a t e - - t h e s econda ry c rys t a l li za -t ion . In each ease these two are~*s a re sep ara te d b y a reas of so l id so lu-t i o n s - t h e g r a n u l a t i o n zo ne s. T h e a n a l o g y is f u r t h e r s tr e n g t h e n e d b ythe im po r t an t f ac t t ha t bo th t he i r on -ca rbo n and i ron -n i cke l a l l oysc rys t a l li ze i n t he r egu l a r sys t em ; i t is to be no t ed more pa r t i cu l a r l y

tha t i n bo th k inds o f a l l oys t he so l i d y - so lu t i ons o f t he g r anu l a t i on zonecrys ta l l i ze in the face-cent red cubic l a t t i ce .

The re fo re , i n bo th k inds o f a l loys we m us t expec t t he occur r ence o fs imi l a r s t r uc tu re s unde r s im i l a r c i r cums tances , and , more pa r t i cu l a r l y,t he appea rance , un de r su i t ab le cond i t ions , o f t he W idmans ti~ tt en s t ruc -ture . I l l s t ee l s, as previou s ly shown, th i s s t ru c tu re reg ula r ly appe arsunde r f avourab l e t r ea tmen t , wh i l s t i n me teo r i c i r ons i t ha s l ong beenrecogn i zed a s a ch a rac t e r i s ti c f ea tm e .

1V. Gr anu lation hylJothesis an d 3 iron.

Le t us now cons ide r m ore ch )se ly t he m orpho logy o f t he Widm ans t i it t ens t ruc tu re . Th i s s t ruc tu re is cha rac t e r i zed by ~ com bina t i on o f a ne tw orkand of W idmans t~ i tt en f igures , both ti le f igures and th e ne tw ork be ingseconda ry depos i ts o f an exces s e l em en t i n a so li d c rys t a l l i ne med ium.As the Widmans t :~ t ten f igures a re oc tahedra l sec t ions , the f i r s t funda-m en ta l cond i t ion fo r t he i r appea rance will be t he oc t ahed ra l c lTs ta l li za -t ion of the so l id so lu t ion (6 , p . 48) ; in o ther words , the so l id c rys ta l l inem a t r i x w h e r e t h e s e c o n d a ry c o n s ti tu e n t s a r e d e p o s it e d m u s t b e a r r a n g e din space i a the f i t ce-cent rcd cubic l a t t i ce (7 , p . 398) .

Th e second se l f -ev iden t f unda me n ta l cond i t ion wi l l be t he occur r enceof t he s cconda tT crys ta l l i za t ion , as i t is the secon dary depos i t s whichbr ing t b rwa rd t he oc t ahed ra l cha rac t e r o f t he c rys ta l l ine ma t r i x . Th i s


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T H E G E N E S I S O F W I D M A N S T A T T E N S T R U C T U R E 1 7 9

s e c o n d c o n d i t io n i m p l i e s , t h e r e fo r e , t h e p r e s e n c e i n t h e e q u i l i b r i u m

d i a g r a m o f t h e c o m p l e x o f c u r v e s o f se c o n d a r y c r y s ta l li z a ti o n . B u t , a ss h o w n a b o v e in s e c ti o n I I , t h e s e c o n d a ry d e p o si ts m a y l o dg e t h e m s e l v e sn o t o n l y a s W i d m a n s t i i t te n f ig u r e s i n s id e t h e g r a n u l a e , b u t m i g h ts e g r e g a t e c o m p l e t el y r o u n d t h e g r a n u ] a e a s e n v e lo p e s ; i n t h e a b s e n c e o fg r a n u l a t i o n t h e y m i g h t e v e n lo d g e t h e m s e l v e s p a r a l l e l to t h e a x e s ofp r i m a r y d en d r i te s , as i n th e s t r u c t u r e o f l a rg e c r y s t al s . O n l y i n t h ef ir s t in s t a n c e w i l l t h e W i d m a n s t ~ t t e n S t r u c tu r e a p p e a r ; t h e r e f o r e a t h i r dc o n d it io n is to b e a d d e d t o t h e t w o f ir s t f u n d a m e n t a l o n e s - - n a m e l y, t h eo c c u r r e n c e o f g r a n u l a t i o n a n d s u c h v e lo c i t y o f t r a n s f o r m a t i o n a s t o l e a dt o t h e s e p a r a t i o n , o f a p a r t a t l e a s t, o f t h e s e c o n d a r y d e p o s i t i n s i d e t h eg r a n u l a e .

Ac3.9000~4~ Ar3=88 ~

4OO

6

Z@ ~ ro

P e r G e n t C ~.

Fro 3. EIO. 4.FIG. 8 . Equ i l ibr ium diagram o f i ron-carbon a l loys .Fro. 4 . Eq ui l ibr ium diagra m of i rbn-f iickel a lloys.

J. 1~. Fr eem an , 1923.)

(After K. Honda, 1922.)(Af t e r D . H anson and

T h e g r a n u l a t i o n p r o c e s s o c c u r s a f t e r t h e s o l i d i f i c a t i o n h a d b e e n a c c o m -p l is h e d , i . e . in a so li d s t a te . I t i s g o v e r n e d b y Ta m m a n n s l a w s o fs p o n t a n e o u s c r y s t a l l i z a t io n a n d o f t h e l i n e a r v e l o c i ty o f c r y s t a l li z a t i o n .A s s u g g e s t e d b y t h e a u t h o r i n a p r e v i o u s p a p e r ( 4, 1 9 2 0 , io. 1 6 ; 5 , p . 3 7 9 ) ,t h i s p r o c es s m i g h t b e l i n k e d u p a n d e v e n ca u s e d b y t h e a l lo t r o p ie c h a n g ei n i r o n , i . e . b y t h e a p p e a r a n c e o f a n e w p h a s e .

A s t h e g r a n u l a t i o n a r e a i s t h e t r u e 7 -z o ne , t h e r e m u s t e x i s t i n th es o l id i f ic a t io n r a n g e a n o t h e r a l l o tr o p i e m o d i fi c a ti o n . T h i s i s g i v e n b y t h e3 - ir 0 n , w h i c h h a s b e e n b r o u g h t i n t o e v i d e n c e i n t h e i r o n - c a r b o n s e r ie s


8/13

1 80 1~-. T. BE LA IEW O~"

b y R u e r a n d K l e s p e r ( 1 5 ). I u i ro n - n i c k e l a l lo y s t h e s a m e 8 - t r a n s f o r m a -

t i o n h a s b e e n q u i t e r e c e n t l y e s ta b li sh e d b y t[ a n s o n a n d F r e e m a n (1 4 ).The i r d i ag ram is r ep rodu ced i n f ig . 4 , whe re , in t he l e f t -hand t o p co rne r,t he 8 -7 tr ans fo rm a t ion i s c l ea r l y shown . In fig . 3 i s r ep roduced one o ft he l a t e s t i r on -ca rbon d i ag ram s , t ha t o f l :r onda , wh ich a lso shows 8 - ironl ines (16) . The co m par i son of these tw o d i~Jgrams br ing s ou t ver y c lear lythe s im i la r i ty of t il e processes in stee l s and in n icke l - i rons . In bothcases the re i s a gra nu la t ion zone , and in both cases to( ) there i s the8 t r ans fo rma t ion .

As p rev ious ly men t ioned , t he au tho r sugg es t ed the neces s it y o f ad -m i t t i ng such a t r ans fo rm a t ion i n t he i r on -ca rbon a ll oys . H e a lways f e lt ,howeve r, t ha t un t i l a s im i la r t r an s fo rm a t ion was de t ec t ed i n t he i r on -n i cke l a ll oys , t he g r anu l a t i on t he o ry i n i ts ap p l i ca t i on t o t he W idm an-s t~ itten f igures of m eteo r i t es w ould n ot be on a sure bas is , l i e t akes ,t he r e fo re , t h i s opp or tu n i t y o f d ry,wing a t t en t i on t o ] ) r. Hanson ' s pape r.

Le t u s cons ide r now the i n fl uence o f t he r a t e o f coo l i ng on t heoccur r ence o f t he W idm ans t i i t t en s t ruc tu re . Le t u s suppose t ha t thefun dam enta l condi t ions , a l rea dy enu m era ted , a re coral) lied wi th , i . e . tha t

the a l loys in ques t ion :(1 ) c rys t a l l i ze i n t he f ace -cen t r ed cub i c l a t t i ce ;(2) the y a re sub jec t to t raHsfo rma t ion in a so l id s ta te , i. c . to secon dary

crys ta l l i za t ion ;( 3 ) t h is s e c o n d a r y c r y s ta l l iz a t i o n o c c u rs i n a n a l r e a d y ' g r a n u l a t e d '

al loy.Then , a s p r e v ious ly m en t ioned , two com ses wou ld be open t o t he

seconda ry depo s i t s : e i t he r t o s eg rega t e a t t he bounda r i e s, o r t o s epa ra t e

inside t he g r a ins a s we ll. I f t he w ho le o f t he s eco nda ry depos it ha st ime t o s eg rega t e round t he g r anu]ae , t hen a pu re ne twork ~ t rue tu rewo u ld ensue . I f , on the o the r hand , t he p roces s were t o p roceed a ta more acce l e r a ted pace , a c e r t a in p ropor t i on o f t he depos i t wou ld beibrced to c rys ta l l i ze ou t ' on the spot ' , i. c . no t a t the bound~r ies , bu t inthe midd l e o f t he g r~Sns. The acce le r a ti on o f t he r a t e a t w h ich t heseco nda ry phases a re be ing d epos i ted usua l ly r( sults f rom a cer ta ininc rease i n t i le ve loc i t y o f coo l i ng ; t he r e fo re , con t r a ry t o wh a t w asp r e v i o u s ly t h o u g h t ( 1 0 f ) , t h e r a t e o f c o olin g t h r o u g h t h e a r e a o fseconda ry c rys t a l l i za t i on need no t be exceed ing]y s l ow.

A c t ing on t he p r ev ious hypo thes i s o f ve ry s l ow coo li ng , t he au tho rsubjec ted the f i r st se r ies o f h i s a l loys to as long a cool ing as was pra c-t i ca ll y poss ib le . I n eve ry ca se t il e s t r uc tu re was r em arka b ly we lldeve loped , hu t , wh i l s t t he hype r- eu t ec io id a l l oywit 1'80 ,~/ of carbon


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TH E GENESI S OF ~ VIDMANSTATTEN STRUC TURE . 181

had the s t ructur e o f large crystals , the other one with 0.60 carbon

exhibitecl a macroscopic networ k ~tructure w ith ve ry large meshes, butwith only faint s igns of i ll -defiued W idm an s~ t te n f igures . On the otherhand, the al loys of the second series , and par t icular ly the al loy 'no . 8 'wi th 0 '55 Z carbon, showed a rema rkahly developed Widm anst i i tteu 'structure (fig. 5).

Chemical co mposit ion and th e size of the gran ulae of the two lash-named al loys ( 'nos . 5 and 8 ' ) a t 'e the same; therefore we may inferthat the condi t ions of cooling throug h the granulat ion zone were the

Fio . 5. Fro. 6.Fla. 5. Widm~nst~ttten figures showx~ by a carbon-steel contain ing 0'55~/o

carbon (alloy 'no. 8') . 9.Fie.. 6. Widmanst~itten figures shown by the Tazowell (Tennessee) meteoric

iron (con taining 14.82 ~ nickel).

same. On the o ther h and, the al loys of the second series were tak enout of the furnace earl ier than those of the first series, presm nably beforethe secondary crystall ization had started. Th at difference in the eondi-.t iolJs of cooling might account for the difference in the separation of thedeposi ts and for the occurrence of the Widm anst~t ten s t ructure .

In t lie exper iments of Dr.Car l Benedicks (10 i ) a procedure was adoptedto avoid the dendrit ic crystall ization and thus, so to say, to 'prepare the:


10/13


11/13

TIIE G):N]~S]S OF ~A'IDMA NST~.'rT~N STIiUCTUI~F,. 18 3

a r e a s o f p r i m a r y a n d s e c o n da r y, c r y s t a l l i z a t i o n , a n d o f g r a n u l a t i o n , b u t

t h e l a t e s t r e s ea r c h e s h a v e s h o w n t h a t t h e ~ - t r a n s f o r m a t i o n a ls o o c c u r s i nbo th cases .

( 4 ) F r o m t h e c h a r a c t e r o f t h e e q u i l i b r i u m d i a g r a m o f t h e i r o n - c a r b o na n d i r o n - n i c k e l a l l o y s i t is t o be p r e s u m e d t h a t u n d e r s u it a l) l c c o n d i t i o n st h e Wi d m a n s t ~ i t te n s t r u c t u r e m a y o c c u r i n b o t h i n st a n c es . A s i t h a p p e n s ,t h e W i d m a n s t ~ t t e n s t r u c t u r e i s o f u s u a l o c c u r r e n c e i n i r o n - c a r b o n a l lo y s ,a n d t h e W i d m a n s t ~ t t e n f i g u r e s a re a c h a r a c t e r i s t i c f e a t u r e a f m e t e o r i cl rof l s .

( 5 ) A s a , 'a t e o f c o o l in g w h i c h w o u l d c a u s e t h e l a rg e s t p o s si b le g r a n u l a -t i o n a n d , a f t e r w a r d s , t h e q u i c k e s t ~ e p a r a t i o n o f c o n s t i t u e n ts , w i l l b e a l so

t h e m o r e f a v o u r a b l e t o o b t a i n t h e W i d m a u s t ~ it te n s t r u c t u r e , i t m a y b ei n f e r re d t h a t s u c h o r l i k e c o n d i t i o n s w e r e , a p p a r e n t l y, r e a l iz e d in m e t e o r i ci r o n s ; ~ ,iz. a v e r y h i g h t e m p e r a t u r e o f t h e m a s s b e l o w t h e t e m p e r a t u r eo f f u s io n , a r e s u l t i n g l a rg e g r a n u l a t i o n , a n d , t h e n , a r c l a t i v e l y r a p i dc o o l i n g , r e s u l t i n g i n a q u i c k s e p a r a t i o n o f t h e k a m a c i t e a n d t a e n i t e .

i ~ I~EFE:RENCES.

(1) N . T. BELAIFW (]I . T. F ,~IeB~ ,),~ t u d e s s u r l a st r uc t u, e d e W i d m a n s f f i t t e n .1 . S u r l a re p ro d u c t io n a r t if i ei e ll e d e l a s tr u c tu r e d e W id m a n s f f i t t e n d a n s l a c i e r a u c a rb o ne .Zap isk i Im p. ~d in . Obsh . St . Pe te rsbu rg (Verh . Russ . ) I in . Gese l l . ) , 19099ser. 2 , vo l . 47 , pp . 209-231. (Russ ian w i th Fr en ch rdsum~.)

(2) Iff. C. So nny , Onthe microscop ica l s t r~ te tu re o f i ron an d s teel .J o u r n . I r o n a n dSteel Inst., 1887, no. 1, vol. 30, pp. 255-288.

(3 ) N.T. BELAI]~W,C ry s t a l l i s a t i o n o f me ta l s . Lo ndo n, 1923~ p. 18. [Min. Abs tr. ,vol. 2, p. 87.]

(4) 1N. T . EZl.AXEw,C~Tlstull isati~n, s tr uc tur e a nd prol~ert ies of s teel on slow cooling.Thes i s , Pe t rog rad , 190 9 . (Russi an wi th G erm an r4sum6 . ) See a lsoS u r l ac r i s t a l l is a t i o n e t s t r u e lu r e d e s a c i e r s r e f ro id i s l e n t e me n t ,l~evue de ~4t a l lu rg i e , 1912 ,vol . 9 , p . 321; andThe s t ruc tu r e o f s tee l. J o u r n . I n s t . Ae r o n a u t i c a l E n g i n e e r s ,1920, vol. 1, pp. 14-23.

(5) ~ l. T. BE ~IEW , Thesis , 1939 ; and fo l low ing papers as in (4 ) . See a lsoSeeo~ula ry s t ruc tu res in s tee l .Chem ica l and Meta l lu rg i ca l Eng ine e r ing , 1923, vo l . 28,pp. 537-540.

(6) N. T. BEI.AIEW,T h e Wi d m a n s t ~ t t e n s ~ r u ct u re i n v a r i o u s a ll o ys a ~ w l m e t a l s .Jou rn . Ins t . M eta ls, 1914, no .2 , vol . 12, pp. 45-49.

(7) IN. T. BEr.AIEW , Thei n n e r s t r u c tu r e o f t h e c ry s t a l g r a in a s r e v e a l e d b y me te o r i te sa n d Wi d m a n s t ( ~ t t e n f i g u r e s . Jo ur n. In st . M etals , 1923, no. 1 , vol . 29, pp. 379-403.

(8) See Ref . (4 ) and (5) , and mo re par t icu lar ly (3), pp . 64-71 .(9) F. Os~o,~D an d G. C,~TAVV,S u r les fe rs ~fftdoriep~es. R e v u e d e ~ d t a l l u rg i e ,

1904, vol. 1~ p. 69.(10) Fo r ea r ly e ffo r ts t o rep roduce and im i t a t e t h e me teo r i c s t ruc tu re s i n

a l l oys o f i ron and n i cke l see :a) .T. STODA]RTand M. FARADAY,E x p e r i m e n t s o n th e a l lo y s o f st ee l, ~ a d e w i t h a

v i e w to i t s imp ro v e me n t . Qu art . Jo ur n. S ci , 1820, vol . 9 , pp. 319-330.


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1 8 4 ~ T B E L A I E W O N

(b) P. Ah'OSSOrF, 0 Bu la t a kh . [ O n da ma sc e n e s te el.7Gorny J'ournal, 1841,vel. 1, p. 162 (Russ.) 9 the s ame in Fre nch in An nua ire du Jou rna l des Minesde Russie, 184:3, St. P6ter sbou rg ; and in Ge rm an : Er ma nn , A r c h l y f i i r d iew i s s en s c h a ft ll e h e K u n d e y o n t ~ a s s l a n d Ivol. 9, p. 510. On Anossof f see : N. T.BELA IEV, yThe Ru ss ia n co nt r ibu t ion .in the n ine teen th ce nh t ry to the me ta l lu rgy of s tee l.Jo ur n. R. Soc. Art s, 19217 vol. 59, pp. 833-836.

(c) H. C. Son~y~ On the microscopica l s t ruc ture o f meteor i tes an d meteor ic i ron .Prec. R. Soc. Londony 1865, vol. 13, p. 333 ; and On the microscopica l s truc ture o li ron and steel . See Ref. (2)1 par tic ula rly the par agr aph on p. 286, und er thetitle im i t a t i o n o f me te o r ic i r on .

(d) A. DAUnn]~E Expdr iences synthdl lqaes re la t ives a ux mdtdori les.Paris (DunodEd.), 1868.

(e) S. ~,[EV~'IEn~ lm ih d io n sy nlM liqu e d es . f~rs nickeh;s m (itdoril lq~tes.Bull. See.Min. France, 1880, vol. 31 pp. 158-155.

(f) g. E. STUArt Discuss ion ors Ber wcr th 's paper. Jo ur n. Ir on and SteelInst.~ 1907, no. 31 vol. 751 p. 48.

(g) F. BJ : r tWEHTH, S tee l and meteor ic i ron .Jou rn. Ir on a nd S[eel Ins t ~ 1907~no. 3, vol. 757 pp. 37-~6.

(h) W. FRA~N~EL an d G. TA~. ~,t ~, ULer metcor i sehes Eisen . Zeits. Anorg.Chemie, 1908, vol. 60, pp. 416-435.

(i) C. BENEDICKS Synlh~ se du fe r mdt~;or ique.Nova Acta Regiae Societ,~tisSc ie nt ia ru m Up sal ien sis , 1910, ser. 4, no. 101 vol. 2, pp. 1- 26 ; and E i n eSyn the se c on Me te o r e i s e n . Inter nationa ler Kongress fii r Bergbau, Hii t tenwesenu.s.w., Diisseldorf 1 1910, Ab te ih mg 21Vor trag 24, 7 pp. 1-3. Berl in (Verlag yonJ. Springer).

(j ) D. HA,~SON an d Hi ld a E. HA.~SeN, ~he c ons t i tu t ion e f the n icke l - i ron a lloys~Jo ur n. Ir on "rod Steel Ins t. , 1920~ no. 21 vol. 102~ pp. 39-60. At th e end ofthis paper a bibliography of papers dealing with the constitution of the iron-nickel alloys is appe nded . See also E. C()HE~ 7 Me te o r i l e nkunde ,Stuttgart ,1905, pp. 78-8 5; an d L. FLL'rcJ[En~ A n in t rod uc t io n to the s tud y of meteori tes,1914~ pp. 35-42.As to the r eprodu ction of Widma nstS tten str uctu re in iron-carbon alloys, see :

(k) F. OS~O~D 1 S~ r l a c r i st a ll og r a ph ie du f e r. Pa ris 7 1900~ p. '247 an d figs. -04

and 25 ; and F. OsMo~n an d G. CAnTAvn~ On the c rys ta l logra phy of i ron .TheMet al log raphi st , 19011 vol. 4, p. 119.

(7) J. O. ARNOLD and A. McWILLIA)I, The thermal t ransfor~ ,a t ions of ca tboa tsteels. Jo ur n. I ro n an d St(.el I n s t , 1905t no. 2, vol. 68, p. 35, and fig. 6 ; andNature7 1904, v(,l. 71~ p. 32.

(m) N.T. B~LA~EW The~is, 1909 (I{ef. 4) ; and Sur la reproduction ar t i . f ie iel le deh~ s t ruc ture de TVidm a~st / i t t en dar t s l ac ie r aa carbone .Revue de MPtallurg ie 7 1910~vol. 7, p. 510 ; and Ref. (1":.(11) C. BE~EDICKS 7 Su r les fe r s mdldor@~es n a ture l s e t mjn thgl iques e t l eur eonduc-

tibilitd dlecb~ique. Ark iv fl'ir Matematik, Ast ro nom i och Fysik, Stock hohn, 1917,no. 17, vol. 121 pp. 1-11.

(1 ~ F. RLn.~E, l~hys ika l i seh-chemlsche Bem evk u~g en i iber l eeh~isches u n d me/eori sches.Eis(n. Neues Ja hrb. Min 7 19051 vo). 1, pp. 12'2-158.

(13) W. (;U~;RT~.Ea and G. TA~II~I.*.NI~'~ {?bet die Tr~.rbind~ng~ n des l ,. isens m it.~ i l i e ium. Zeits. AnGry. Chem., 1905. vol. 47, pp. 163-179.

(14) D. ]JANseN and J. R. Fs~E ~nx, Ju n. , T he c ons t i tu t i on o f a l loys ( ~ i r on a ~ dnicke l . Jo ur n. I,' on and Sfeel I n s t , 1923, no. 1, vol. 1077 pp. 301-314.


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THE GEN ESIS OF WIDMANSTATTEN STI~UCTURE. 1 85

(15) R . I~UER un d R . KSESPER,D i e G a m m a - D e l t a U m w a n d l u n g d es r e i n e~ E i s e n su n d i h re B e e i n f l u s s u ~ g d u r c h C S i C o u n d C u.F e r r u m , 1 91 4, v o l . 2 , p . 2 5 7 .

(16 ) K. HO~DA~O n the c ons t it u t iona l d i a g r a m o f t he i r on - c a r bon a l loys .J o u r n .I r o n a n d S t e e l I n s t , 1 9 22 , n o . 17 v o l . 1 0 5, p p . 38 1 - 3 9 0 .

(1 7) T h e m e t e o r i c i r o n s a re u s u a l l y ' u n i g r a n ' , b u t i t is n o t u n c o m m o n t of i n d m e t e o r i t e s w i t h s e v e r a l g r a n u l e s . S e e f o r i n s t a n c e : . H IM ~ELBA UER~Orien t ie rung Yon Schni t t f lSchen an Meteore i sen .Ts c h e r m a k s M i n . P e t r . M i t t. , 1 90 9,v o l. 2 8, p p . 1 5 3- 16 9 . ( R e f e r e n c e i s t h e r e m a d e to t h e m e t e o r i t e s o f L a u r e n sC o u n t y , o f M u k e r o p , a n d o f B e t h a n y. )

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On the Genesis of lVidmanst(Itten Structure in Meteo~,'Ites and in Iron-nickel and Iron-carbon Alloys-20-104-173