By Professor E- Piwowarsky, Dr.Eng., A ix-la-Chapelle.
A f a ir ly e x te n s iv e li te r a tu r e a lre a d y e x ists on th e effect of nickel a n d c h ro m iu m a d d itio n s on th e p ro p e rtie s of c a st ir o n .1 F ro m th e se w orks, an d also fro m t h e r e p o r ts a n d co m m u n icatio n s of n u m ero u s m a n u f a c tu r in g a n d consum ing concerns, i t is a p p a r e n t t h a t even a nickel a d d itio n of fro m 0.5 to 3.0 p e r c e n t, a p p re c ia b ly in creases th e u n i
fo rm ity an d d e n sity of th e s tr u c tu r e , en su re s v ery good m a c h in a b ility e v e n in h a rd ty p e s of iron, p re v e n ts th e a p p e a ra n c e o f h a r d spots, a n d in creases th e re sista n c e to corrosion a n d w ear, etc.
I t is also know n t h a t a m o d e ra te a d d itio n of chrom ium in c a st iro n w ith a nick el c o n te n t has a p a rtic u la rly beneficial effect in im p ro v in g th e s tr u c tu r e a n d in c re a sin g th e re s is ta n c e to w ear a n d th e lia b ility to “ g ro w .” M o st o f th e s e ch em ico -m etallu rg ical a n d physical a d v a n tag es are p re s e n t— an d f a r to o little r e g a r d is p a id to th is fa c t—even w hen th e m ech a n ical te s t shows scarcely any, o r only a m o d e ra te in crease in th e s tr e n g th figures. I n p o in t of fa c t, in d eed , th e in crease of s tr e n g th fo u n d by n u m ero u s in v e s tig a to rs (C am pion, H u r s t, M oldenke, P iw o w arsk y an d B aver, Sm alley, M e ric a , W ick e n d en , Y a n ic k , etc .) in p e a rlitic c a st iro n as a re s u lt of a llo y in g w ith nickel a n d chrom ium , as a ru le h a rd ly exceeds 30 p e r c e n t. So long, th e re fo re , as th e m ech
an ic a l p ro p e rtie s o b ta in e d by alloying do n o t e x ceed th ese lim its , w hich a re such as c a n he o b ta in e d in unalloyed c a st iro n by su ita b ly m ix in g th e c h a rg e a n d by p a y in g re g a rd to th e m o re re c e n t refin in g processes (e.g ., a b n o rm al s u p e r
h e a tin g of th e liq u id iro n 2), th e r e is obviously no occasion to ad d nick el and ch ro m iu m to th e m e ta l m erely fo r th e p u rp o se of in c re a sin g its s tr e n g th . M oreover, i t is by no m eans c e r ta in a t p re s e n t
1 Cf . t h e b ib lio g r a p h y in th e B u lte tin o f t h e B r it is h C a st Iron R esea rch A ss o c ia tio n , N o . 8, A p r il, 1925, p . 5.
2 G erm an P a t e n t s , u nd er G. 63,543 V I/1 8 b ., F e b r u a r y 21, 1925.
w h eth er th e re s u lts so f a r o b ta in e d m increasing th e m echanical p ro p e rtie s of c a st iro n by nickel a n d chrom ium a d d itio n s m ay n o t be m ainly a t t r i b u ta b le to causes w hich— as, fo r exam ple, th e re finem ent of th e g ra p h ite — could be o b tain ed by c h e a p e r an d sim p ler m eans (d eoxidation, su p er
h e a tin g th e m o lten m etal, e tc .). I t ap p eared necessary, th e re fo re , to in v e s tig a te th e influence of th ese tw o m ost im p o rta n t alloying elem ents, which u n q u e stio n a b ly o p e ra te beneficially in re g a rd to th e i r p h y sico -m etallu rg ical re a c tio n , on c a st iro n to w hich th e b est m echanical q u alities, as fa r as te c h n ic a l ju d g m e n t could a n tic ip a te , h a d been im p a rte d by su ita b le tr e a tm e n t.
T h e course was th e re fo re ado p ted of b rin g in g v ery h o t m o lten iro n to a s t a te of solidification, a t first m ain ly w hite, an d of g ra p h itis in g i t only by su b seq u en t a n n e a lin g so t h a t i t c o n ta in e d : —
(1) T he p rim a ry carbon in th e finest an d m ost fav o u rab le a rra n g e m e n t possible, an d (2) as fine
g ra in e d a so rb itic -p e a rlite gro u n d mass as pos
sible.
A t th e sam e tim e i t was in te n d e d to pay special a tte n tio n to th e effect of nickel an d chrom ium on th e th e rm a l s ta b ility of th e m etal. The charge of th e m e lts h a d , th e re fo re , to be a d ju ste d so t h a t by accelerated solidification a n d cooling th e iron solidified p re p o n d e ra tin g ly w hite, h u t n ev erth e
less c o n ta in e d sufficient silicon to re n d e r probable th e com plete dissociation of th e h y p er-eu tectic carb o n by m eans of as sh o rt as possible a subse
q u e n t a n n e a lin g a t n o t too h ig h a te m p e ra tu re , fo r a long p eriod of an n ealin g , p a rtic u la rly a t too hig h a te m p e ra tu re , m ig h t possibly have elim i
n a te d a g a in th e ad v a n ta g e s of th e fine p rim a ry s tru c tu r e . I t was necessary, how ever, t h a t th e silicon c o n te n t should n o t be so h ig h as to p erm it of la rg e q u a n titie s o f f e r r ite m ak in g th e ir a p p e a r
ance d u rin g th e cooling w hen th e a n n ealin g h ad been effected. T his could be secured if a grey to m o ttle d ch arg e w ere caused to solidify m o ttled to grey by artificially accelerated cooling.
F o r th e te s ts in q u estio n tw o m ain series of e x p e rim e n ts w ere a rra n g e d , viz., one w ith high carbon a n d low silicon iro n (in d ic a te d by A), and one w ith low carb o n an d h ig h silicon m e ta l (indi
cate d by B).
W ith in th e se tw o series h e a ts w ere c a rr ie d o u t w ith o u t nickel, as well as h e a ts w hich w ere a d ju s te d to 1 a n d 3 p e r c en t, n ick el an d 3 p e r c en t, nickel + 0.5 p e r c e n t c h ro m iu m in th e final p ro d u ct. A ch arg e of G erm an h e m a tite a n d in g o t iro n (d ead m ild steel) was used as ra w m a te r ia l in all th e h e a ts . A b o u t 10 p e r c e n t, of Sw edish p ig -iro n w as used in th e ch a rg e of h e a t 1 only.
T he in crease o f th e silicon a d d itio n in series B was effected by a d d in g h ig h p e rc e n ta g e ferro -silico n to th e finished h e a t. T he w eig h t of all th e casts in th e te s ts was a b o u t 25 kg. (55 lbs.). T hey w ere c a rrie d o u t in a g r a p h ite crucible lin e d w ith m ag
nesite, a n d in a n o il-h e a te d fu rn a c e . T he te m p e r a tu r e of th e h e a t w as in all cases ra ise d to a b o u t 1,550 deg. C., w hen th e cru cib le was ta k e n o u t of th e fu rn a c e , an d th e h e a t p o u red w hen th e te m p e ra tu re h a d fa lle n to 1,400 deg. T he te m p e r a tu r e w as m easu red o p tic a lly (by th e H olborn- K u rlb a u m p y ro m e te r) an d by in s e rtin g p la tin u m a n d p la tin u m -rh o d iu m th erm o -e lem en ts in th e h e a ts to check th e m easu re m e n ts. F ro m each h e a t fo u r te s t b a rs a b o u t 33 m m . in d ia m e te r an d 700 mm . in le n g th w ere c a st, tw o of th e s e b ein g p o u red in to a n iro n chill, lin ed fa irly th ic k ly w ith clay, w hich was in each case p re h e a te d to 100 deg.
T h e la s t tw o b a rs w ere e a s t in a d ry s a n d m o u ld .3 Top c a s tin g was em ployed th ro u g h o u t. T he b a rs c a s t in chills w ere ra p id ly h e a te d in a g as muffle fu rn a c e to a b o u t 925 to 950 deg. C. As soon as th e y h a d re ach ed th is te m p e ra tu re th e fu rn a c e was s h u t off an d th e sam ples w ere le f t to cool. H a lf of th e se ch ill b a rs w ere th e re u p o n re h e a te d to 20 to 30 deg. above th e A3 p o in t a n d quenched in oil. The h a rd e n in g te m p e r a tu r e v a rie d , accord
ing to th e com position of t h e sam ples, fro m 820 to 850 deg. T h e quenched sam ples w ere k e p t a t 650 deg. fo r h a lf a n h o u r, w hen th e y w ere a g a in quenched in o il; th e y w ere th e n re h e a te d to 450
3 T h e b a rs c a s t in s a n d sh o w ed th r o u g h o u t a e u t e c t ic to tem p er-c a rb o n -lik e s tr u c tu r a l fo r m a tio n , a n d h a d a tr a n s v e r s e s t r e n g t h o f 48 to 65 k g /m m 2 w it h a t e n s ile s tr e n g t h o f 28 t o 36 k g /m m 2 (17.8 to 20.3 to n s p er sq . in .) . A s th e s e h e a t s h a d n ot been d e o x id ise d a n d c o n s e q u e n tly d id n o t a p p r o a ch th e b e st v a lu e s h ith e r to re a ch ed in sa n d c a s t in g b y su p e r h e a t in g t h e m elt [u p t o a b o u t 75 k g /m m 2 tr a n s v e r s e s tr e n g t h a n d 36 to 42 k g /m m 2 (22.8 t o 26.6 to n s p er s q . in .) t e n s ile s tr e n g th ) th e y h a v e b een o m itte d from c o n s id e r a tio n in t h e t r e a t m e n t o f th e p r e s e n t P a p e r .
cleg, fo r 15 m in u te s fo r th e rem oval of any h a rd ness stresses, a n d th e n le f t to cool.
F o r m echanical te s tin g all th e b ars w ere tu rn e d to a d ia m e te r of 30 mm. T he resu lts of th e re se a rc h a re su m m arised in T able 1. These show t h a t as a re s u lt o f th e th e rm a l an d m e ltin g pro
cess h e re em ployed u n u su ally h ig h b en d in g s tre n g th s w ere in fa c t a tta in e d . * These m ig h t pos
sibly h av e been ev en h ig h er if m ore care h a d been devoted to th e process of d eo x id atio n an d to over
com ing th e o ccu rren ce of p ip in g , to which f u r th e r re fe re n c e is m ad e la te r. Series o f te s ts o n th is p o in t a re in p re p a ra tio n . I t should be noted t h a t v e ry h ig h deflection values are p ecu liar to h ig h tra n s v e rs e stre n g th s . W hen i t is considered t h a t in th e n o rm al tra n sv e rs e te s t, w ith a b a r d ia m e te r of 30 mm. an d a d istan ce betw een th e su p p o rts e q u a l to 20 tim es th e d iam eter, deflec
tio n s of 10 to 15 m m . are u sual an d norm al, th e deflection values of 20 to ab o u t 45 mm. m u st be c h a ra c te rise d as ex cep tio n ally high. They dem on
s t r a t e th e g r e a t to u g h n ess1 .and e la s tic ity of th e m a te ria l. I n th ese te s ts , u n fo rtu n a te ly , i t was n o t as y e t possible, as h as alread y been sta te d , e n tire ly to e lim in a te th e p ip in g fav o u red by th e w h ite o r m o ttle d solidification an d th e large d ia m e te r of th e b ars. S u itab le signs are accord
in g ly in s e rte d in colum n 5 of Table 1 to in d icate w h eth er th e f r a c tu r e w as found fau ltless, or showed a slig h t or a serious p ipe. W hen i t is con
sid ered t h a t only a few of th e values a re in d icated as fre e from p ip in g i t is s u rp ris in g t h a t n o tw ith s ta n d in g th is o ccurrence of defects such h ig h tr a n s verse v alu es w ere still o b tain ed . No doubt th e reaso n of th is is t h a t in th e tra n sv e rs e te s t th e n eu t r a l fibre plays a re la tiv e ly sm all p a r t in s tra in ing th e m a te ria l, w hile th e p ip e is generally dis
posed c e n tra lly (see F ig . 1, w hich shows th e fra c tu r e of c e rta in b a rs in w hich th e size of th e p ip e is red u ced ). On th e o th e r h a n d , th e effect of the p ipe becam e all th e m ore u n p le a sa n tly observable in th e ten sile te s t. F o r th is te s t, however, th e b roken pieces fro m th e tra n sv e rs e te s t were used.
4 T h e sp ecific sh o c k e n e r g y o f th e a llo y e d sa m p les w as tw o to th r e e t im e s t h e v a lu e s h ith e r to ob served in o rd in ary g r e y c a s t ir o n . F or e x a m p le , h e a t 5 show ed 1.39 m k g /c m 2 ; h e a t 12, 1.05 m k g /c m 2.
Ta b l e
1 2 3
H eat Type of
Chemical Composition.
No. Heat.
Gr. C.C. Si. Mn. P. S. Ni. Cr.
1 CA I
\ A I V \
/ 0.28 1.98 1.57 0.76 0.068 0.014 — —
2 r a i i
\ A I I V \
/ 0.14 2.70 1.88 0.62 0.092 0.027 — —
3 / A II I
\ A I I I v \
/ 0.21 2.38 1.74 0.60 0.076 0.025 0.89 —
4 r a IV
\ A IV V \
/ 0.59 2.48 1.61 0.56 0.083 0.025 2.73 —
5 / A V
\ A V v \
/ 0.19 2.88 1.40 0.75 0.052 0.015 2.86 —
6 r A VI
\ A VI V \
/ 0.26 2.60 1.74 0.60 0.084 0.024 3.10 0.80
7 f B I
\ B I y \
/ 0.37 1.98 2.58 0.60 0.040 0.020 — —
8 I B I I
\ B I I y \
/ 0.23 2.03 2.49 0.53 0.092 0.03 0.86 —
9 f B I I I
\ B I I I v \
/ 0.33 1.99 0.96 0.48 0.060 0.032 3.02 —
10 r B IV
\ B IV V \
/ 1.54 1.38 2.09 0.55 0.072 0.028 3.17 —
] r B V
\ B V v \
/ 0.35 2.13 2.06 0.52 0.04 0.026 2.80 0.50
12 / B VI
\ B VI V
\
/ 0.37 2.05 1.70 0.68 0.06 0 .0 1 6 2.69 0.47
O= Perfect fracture. *= S m all pipe. **= L arge pipe.
I.
4 5 6 7
Composition after
Heat Treatment. Transverse Test. Tensile Test.
Jsnnell Hardness Number.
Gr. c .c . kg/mm2. Deflection
in mm. fracture. kg/mm2. lia. of bars.
mm.
fracture.
/ 2.34 0.69 87.0 39.5 * 4 4 .5t 5 * 240
\ 1.78 0.60 90.5 32.3 ** 51.7 20 * 249
/ 2.07 0.73 85.6 38.8 0 30.9 ? 20 *** 238
\ 2.37 0.45 — — — 36.9 ? 20 *** 167
/ 1.98 0.58 90.3 38.8 0 24.3 ? 20 *** 263
\ 1.94 0.73 75.8 19.0 ** 26.8 ? 20 *** 255
/ —
_ _ _ _
31.7 ? 20 *** —\ - — 93.4 22.5 ** 57.2 5 ** —
r 2.18 0.71 90.2 24.2 * 40.7 ? 20 *** 2.63
\ - — 87.4 23.5, ** 42.8 ? 20 *** 2.73
r i.8 5 0.97 100.0 30.2 * 69.4 5 * 300
\ - — 102.0 15.6 * 71.4 5 0 300
/ 1.43 0.85 99.25 43.2 * 38.5 20 ** 238
\ 1.43 0.82 90.7 26.0 * 28.8 20 ** 233
/ 1.38 0.78
_ _
—. — — — —\ 1.50 0.70 104.0 28.5 0 33.5 20 ** 225
/ 1.43 0.58 58.3 ? 109 ? ** — — — 257
\ 1.77 0.47 106.0 32.0 ** 37.4 20 *** 246
/ 2.72 0.20 81.8 8.0 ? ** 39.4 20 * 218
\ - 71.7 15.6 * 33.7 20 ** 183
f —
__
75.7 5 * 292\ ~ — 102.3 27.5 * 67.3 5 * 285
r 1.46 0.95 119.6 28.7 0 60.0 5 * 303
\ - — 128.6 37.2 * 56.7 5 * 316
***=V ery large pipe, t To convert kg/mm* to tons/sq. in. multiply by 0.63.
A VI B V v A III Fig. 1— FractureofSeveralTransverseTestPiecestotheDiminishingSizeofFire.
174
T hey h ad been tu r n e d to a d ia m e te r of 20 m m . in o rd e r t h a t th e te n s ile te s t b ars m ig h t h av e conical e n la rg e m e n ts a t th e ir ends. The m a jo rity of th e ten sile b a rs conseq u en tly show m uch to o low values, fo r n o tw ith s ta n d in g th e w eak en in g ow ing to th e p ip e th e m ax im u m load was in re la tio n to
F i g . 2 .— A p p e a r a n c e o f T u r n i n g s s h o w i n g E l a s t i c i t y — N a t u r a l S i z e .
th e e n tir e cross section. The figures of ten sile s tr e n g th n ev erth eless show t h a t w ith to le ra b ly good b ars one c a n c o u n t on te n sile s tr e n g th s of over 50 k g /m m .s (31.7 to n s p e r sq. in .). To p ro v e th is , sm all te n s ile te s t b ars, 5 mm. in d ia m e te r (also
w ith conical e n la rg e m e n ts a t th e ends) w ere m ad e from c e r ta in b a rs in w hich th e p ip e fo rm a tio n was less pron o u n ced , th e sides w hich w ere fre e fro m d e fe c t b ein g used fo r th e p u rp o se. I t will
»o’
X
«>
H<
63 PC
%c
ccta tam ota
£ mH HK
ta02
ccK 02>
2<
HC
taw
ocs
«
be seen fro m T able 1 t h a t th e se b a rs showed te n sile stre n g th s u p to a b o u t 75 k g ./m m.2 (47.6 to n s p e r sq. in .) , even in cases w here th e s e sm all b a rs still showed a s lig h t d e fe c t in th e fr a c tu r e .
More-over, a n e lo n g a tio n of 2 to 4 p e r c e n t, w as no ted in m o st o f th ese sm all te n s ile sam ples.
T h e B rin e ll h a rd n e s s o f alm o st all th e alloys is fa irly h ig h . I t v a rie s betw een a b o u t 200 a n d ’300.
N o tw ith s ta n d in g th e se h ig h h a rd n e s s figures all th e b a rs w ere fo u n d to be easily m ach in ed w ith o rd in a ry t u r n i n g ’tools, a n d showed n o appreciable in crease in sh e a rin g s tr e n g th com pared w ith o r d in a ry c a s t iro n . C o n tin u o u s tu r n in g s 3 to 5 m.
in le n g th w ere o b ta in e d on m ach in in g , an d these w ere m a in ta in e d even w hen th e feed was increased.
F ig s . 2 a n d 3 show th e a p p e a ra n c e of th ese tu r n ings. F ro m th e tr a n s v e rs e s tre n g th figures, and in p a r t also fro m th e te n s ile s tr e n g th figures of th e d iffe re n t sam ples, i t is a p p a re n t t h a t a nickel a d d itio n clea rly exercises a beneficial, a lth o u g h n o t a v ery g ro a t, effect o n th e m ech a n ical p ro p e r tie s ; w hile o n th e o th e r h a n d , nickel in con
ju n c tio n w ith chrom ium is capable of in creasin g th e m ech a n ical p ro p e rtie s even of th is h ig h -g rad e iro n by 1 0 t o 20 p e r cen t, in th e high-carbon se rie s A a n d by 10 t o 30 p e r c en t, in th e low- carb o n series B. T he tr e a te d sam ples, how ever, in d ic a te d in colum n 2 of T able I by th e le tte r v, do n o t show an y n o te w o rth y im p ro v em en t in th e m echanical p ro p e rtie s com pared w ith th e u n tr e a te d sam ples. T his is in itse lf re m a rk a b le , b u t i t m ay be e x p la in e d as fo llo w s: T he g ra in of th e g ro u n d m ass a n d th e s tru c tu r e of th e p rim a ry carbon lib e ra te d by th e a n n e a lin g process are so fine, ow ing to th e th e rm a l tr e a tm e n t m e n tio n e d , t h a t a su b s e q u e n t alloying process is incapable of re n d e rin g th e g r a in s till finer. As a m a t te r of fa c t, in th e sam ples c a s t in s a n d a n in crease of s tre n g th o f a b o u t 10 to 15 p e r c e n t was observed as a re s u lt of such tr e a tm e n t. A lthough n o t la rg e , th e in crease w as c e rta in ly p re s e n t. A m ong th e bars c a s t in chill m oulds, on th e o th e r h a n d , only th e m elts c o n ta in in g chrom ium an d nickel showed a s lig h t in c re a se in th e figures re la tin g to m ech an i
cal p ro p e rtie s as a r e s u lt o f th e a d ju s tin g process (c/. m e lts 6 a n d 12 in T able I).
The s tr u c tu r e of th e f r a c tu r e in a la rg e n u m b er of th e h e a ts —p a rtic u la rly those c o n ta in in g nickel a n d chrom ium —w as so fine in g ra in t h a t th e m a te ria l could be d istin g u ish e d fro m h ard en ed tool steel only by a p ra c tise d eye. F ig . 4 shows,
by w ay of exam ple, tw o fra g m e n ts w hich were chip p ed off in th e f r a c tu r e , w hich to o k th e fo rm of a cu p o r b asin , of a tra n s v e rs e te s t b a r in h e a t 12. T h e fineness of g r a in resem bles, in fa c t, t h a t seen in th e f r a c tu r e of h ig h -g ra d e tool steel.
A t th e o u ts e t of th is P a p e r i t was s ta te d t h a t th e th e rm a l a f t e r - t r e a t m e n t w as so a d ju s te d t h a t a so rb itic -p e a rlite g ro u n d m ass w ith fin ely -d
istri-4. * »
■*y, ■'
■*-*»-•*- >• *
*
* *
*
• 4 •
* ■ *.
* „ «
% ■' * * * *•"
J • * : * *
:
t*
* r
F i g . 5 a . — G r a p h i t e S t r u c t u r e f r o m H e a t A V I x 100.
b u te d p rim a ry c a rb o n m u s t m a k e its a p p e a ra n c e . All th e m icros, in f a c t, show ed in th e u n e tc h e d s t a t e a s t r u c tu r e o f p rim a ry c arb o n in a n a rr a n g e m e n t as re g a rd s m a g n itu d e such a s is show n in F ig . 5a, m agnified 100 tim es. Only a sin g le h e a t, nam ely, N o. 10, in w hich th r o u g h an o v e rs ig h t th e carb o n c o n te n t tu r n e d o u t to o h ig h , show ed even in th e final c o n d itio n , to g e th e r w ith con
sid e ra b le q uantities of ferrite, very fine-grained
e u te c tic g ra p h ite , w hich could scarcely be dis
tin g u is h e d w hen m agnified 100 tim es. The u n e tc h e d m icro, of th i s h e a t h a d th e re fo re to be rep ro d u ced (F ig . 5b) m agnified 500 tim es. Some of th e b ars show ed in p a rts , to g e th e r w ith th e p rim a ry , as show n in F ig . 5a m agnified 100 tim es, also p rim a ry carb o n —d is trib u te d v ery uniform ly o v e r th e s o rb itic -p e a rlite g ro u n d m ass—of such a
Fi g. 5b.— Gr a p h i t e St r u c t u r e p r o m
B I v x 500.
h ig h d egree o f fineness t h a t i t h a d to be m agnified 500 tim e s t o be id en tified . T his is a p p a re n t from F ig . 6 (a an d b). These illu s tra tio n s reproduce th e s tr u c tu r e o f h e a t 7 m agnified 500 an d 1,000 tim es. I t will be seen t h a t h ere also one h as to d o w ith a so rb itic -p e a rlite g ro u n d mass, fo r even when m agnified 1,000 tim es i t was still impossible to d is tin g u is h c e rta in p e a rlite fields, w hich, how
ever, could be done in th e case of th e h e a ts
con-ta m in g chrom ium an d nickel. The illu s tra tio n s c a n d d of F ig . 6 show th e s tr u c tu r e of th e sam e
h e a t a f t e r th e a d ju s tin g process, n am ely, a t those p o in ts w here th e c o arsest s e p a ra tio n "of te m p e r
carb o n w as fo u n d , so t h a t a com parison of th e illu s tra tio n s a a n d d shows th e u p p e r an d low er
lim it values in th e fo rm a tio n of th e elem en tary carbon in re sp e c t of m a g n itu d e . I t is a p p a re n t,
(c) x 1,000. (d) x 1,000. Fig. 6.—StructureopHeatVII, aandbBeforeandcanddAfterTreatment.
m oreover, t h a t by th e a d ju s tin g process th e s o rb itic -p e a rlite g ro u n d m ass h a s been c o n v e rte d in to ex cep tio n ally fine g r a n u la r p e a rlite o f th e c o ag u la ted c e m e n tite . I n th is co n n ectio n re f e r ence sh o u ld also be m a d e to F ig . 7, w hich shows th e s t r u c tu r e in th e rm a lly -re g u la te d sa n d -c a st iro n , 7a b ein g t h a t in o r d in a ry g rey c a s t iro n , w hile t h a t in F ig s . 7b a n d 7c is fro m th e sam ples
(a)
Fi g. 7 .— St r u c t u r e o e He a t- Tr e a t e d Ca st Ir o n s, x 5 00.
o f sa n d -c a st iro n m e n tio n e d a t th e b e g in n in g of th is P a p e r, th e g ra p h ite c o n te n t o f w hich w as caused to solidify in th e fo rm of a fine s tr u c tu r e by th e r m a l s u p e rh e a tin g of th e m elt. I t h a d s tru c k th e a u th o r t h a t in o rd in a ry , o r s u p e rh e a te d unalloyed g rey c a s t iro n , th e rm a l tr e a tm e n t fr e q u e n tly produces a s t r u c tu r e w hich in its fo rm a tio n resem bles b lu n t needles o f m a r te n s ite , b u t
w h i c h i n r e a l i t y h a s a l s o a p r e p o n d e r a t i n g l y g r a n u l a r - p e a r l i t i c g r o u n d m a s s , w h i c h , h o w e v e r , b e a r s a n apparent r e s e m b l a n c e t o m a r t e n s i t e — a s t r u c t u r a l p h e n o m e n o n w h i c h i s a l s o o b s e r v a b l e i n t h e h a r d e n i n g a n d t e m p e r i n g o f s t e e l , a n d w h i c h h a s l e d H a n e m a n t o e s t a b l i s h a n e w t h e o r y o f h a r d e n i n g 5 o n a m e t a l l o g r a p h i c b a s i s .
W h i l s t i t f o l l o w s f r o m t h e s e , t e s t s t h a t a n i c k e l
(6)
F i g . 7.— Continued.
a d d i t i o n , p a r t i c u l a r l y i n c o m b i n a t i o n w i t h a m o d e r a t e c h r o m i u m c o n t e n t , i s v e r y w e ll a d a p t e d t o p r o d u c e a n o t e w o r t h y i n c r e a s e i n t h e m e c h a n i c a l p r o p e r t i e s , e v e n w i t h t h e b e s t f o r m a t i o n o f t h e e l e m e n t a r y c a r b o n , i t i s f u r t h e r a p p a r e n t ,
5 W erk sto ffau ssch u ss-B erich t des V .D .E. (R e p o rt of th e M a te ria ls C om m ittee of th e G erm an E n g in ee rs’ A ssociation), No. 61.
(e)
F i g . 7 .—C o n t i n u e d .
a c c e le ra te d cooling (p o u rin g in chill m oulds o r in w e t m o u l d s ). T his ty p e o f c h a rg e re q u ire s, acco rd i n g to th e carb o n c o n te n t, silicon c o n te n ts of a b o u t 1.4 to a b o u t 2.2 p e r c e n t. T h ese sm all
6 K . E m m el h a s a lr e a d y p u b lis h e d so m e fig u re s o f th e sa m e ord er o f m a g n it u d e b a se d u p o n a s im ila r p ro ce ss ( cf. S ta h l u n d E is e n , 1 9 2 5 , I I , p a g e 1 4 6 9 ) . P . B a rd en h eu er a ls o o b ta in e d a p p r o x im a t e ly s im ila r fig u re s ( c /. S ta h l u n d E isen , 1927, p a g e 857).
even fro m th e te s ts so f a r c a rrie d o u t, t h a t i t is possible to o b ta in by th e m eth o d s h e re a d o p te d a special ty p e o f m alleable c a s t ir o n6 w ith w hich s tre n g th s h ith e r to u n re a c h e d w ill be asso ciate d . H e re i t is sim ply a q u estio n , in c o n tr a d is tin c tio n to th e know n m alleab le-iro n p rocess, t o cause a m e ta l of w hich th e ch a rg e is g rey to m o ttle d , to solidify w h ite to m o ttle d by m ean s o f artificially
-V 'T-'V
castin g s, p o u red w hite or m o ttle d , can be com
p letely g ra p h itis e d w ith in a few m in u tes. The
a u th o r succeeded, in fa c t, in com pletely an d u n i
form ly g ra p h itis in g sm all castin g s w ith a wall
th ick n ess up to 35 mm . as quick ly as 10 m ins. by im m ersin g th e m in a s a lt b a th a t a te m p e ra tu re of 925 to 950 d eg . C ., w hen th e g ro u n d m ass show ed a s o rb itic -p e a rlite s t r u c tu r e w ith a m uch
th ick n ess up to 35 mm . as quick ly as 10 m ins. by im m ersin g th e m in a s a lt b a th a t a te m p e ra tu re of 925 to 950 d eg . C ., w hen th e g ro u n d m ass show ed a s o rb itic -p e a rlite s t r u c tu r e w ith a m uch