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THE cC-^y CONVERSION IN IRON-NICKEL ALLOYS 
' UNDER HIGH PRESSURE 



W. Jellinghaus and O. Schmidt 



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ff653 July 65 



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Translated from Archiv fur das Eisenhiittenwesen, 
Vol. 36, No. 1, pp. 47-51, 1965. 



NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON NOVEMBER 1965 



: ■ * . "^ 

^^ -^ fl 

^rosL I ^chiT fur das EisaJEihutteCTresan (ArohJTes of Metallor^ ) 1965^ 
Vol. 36, to* i, pp. 4T-5i.J^ 

THB «->7 COSVEBSIOH II IHDN-IICEEL ALLOYS UHDBl HIGH TmSSUM 
W* JelliBghaus and 0* Sdhaidt^ Ifax-Planok: Institute for Iron iesearch, Dusseldori"* 

Abstracts y-a comrersion of iron allos^s containing 30-35% nickel by coollpg t^ 
loir tettperatnres* ]>«t«nixMLtion of the amounts of the ^ phase re«f ora^d Iqr heatii^ 
through Aeasurenent of electrical resistance and ai^ne^e property. Experiments more 
carried out under noxmal pressure and pressures of 5»0(X)*10»000 kg/cm • s^ort^-interral 
experiments were carried out by heating to Z50« 3{K}, 350, or 400 C without ax^ es« 
sential change in oonoentration* Sicperiments at 430^ C were performed under normal 
pressure and also under higher pressures and for prolonged internals* The authors 
demonstrated changes of concentration. 

Of using high pressure^ the tenperatis*es of the ptose equilibria can by displaced. 
In phase comreraicm from unbalanced states » pressure msy also inf luenee the rate and 
completeness of the coxnrersion^ especially if the connrersiosi is acocmpaniod by changea 
of volume. f^^^^ 

During the isothermal decomposition of the deep-^cooled austenite, i.e.^ of a cubic 
faoe«-cenbered mixed crystal of iron and carbon^ a slight increase of Tolio&e occurs. 
W« Jellinghaus and H* Friedewold (1) found a considerable reduction of the rate of 
conrersion at temperatures between Jt50 and 350^ C and pressures of 4,000 and 5,000 
kg/on as comiMtred with the beharior under customary pressure. As & consequence of 
the incr^ise of pressure, they found an increase of the rate, in the elimination of 
carbide from austenitic isanganese steel, where this process results in a reduction 
of volume. However, this example was not very convincing as proof for the favoring 
or accelerating action of high pressures in the case of reduction of volume because 
the amount 4af the carbide created during elimination represents only a small fraction 

(1) Ar^* BLsenhuttenwes. 31 (1960 ?• 309/17 (Mitt. Max-Planck-Inst . gisenfarsch., 
I^eatise 848, and l^rkstoffaussch. 12E8), 

•1- 



of the total mass idiereas, 1& tha d9C0Bi|K>sitioii of austeaite, tho ooirrersioii auff ects 
either the tefcal mass or an appreoiable part of the latter* For the inhibiting action 
of pressure in the deoonposition of austenite linked with an increase of Toltate^ data 
haTe also been adduoed lay £, sc^idtaftasa, w* Biernann and H. Sohenok (2). Further 
experiments on the inflmenoe of pressure seemed desirable for reaotions aooon^uiied 
bgr reduction of rolvme* 

Sacaaples mere seleeted in which a large part of the total mass is affected and 
the reactions take place preferably in substituted mixed orystals and not in inter*^ 
ealated mixed oryvtals (e.g., austenitio manganese steel)* ihere the inereased 
pressure appreciabl;f influences the diffusion of the alloyed partners^ it was to be 
expected that this influence is not so easily obscured for reactions in substituted 
mixed crystals Igr the influence of the magnitude and of the sign of the chaise of 
Tolume* AUays of iron aad nickel eaajtslning 25-5d^ nidtel appeared suitable for euoh 
experimeacte* Ihis oonaerns eabstituted mixed crystals whidt earn be tramsfermed 
extensirely into the bod^^oentered oubie crystal form and should produce a reduction 
of Tol«e upon return to the faoe^centered form* The a -^7 oonTeraion starts partly 
alreac^ immediately abore 200^ C« This circumstance is Tesry useful from the metal«» 
lurgical riewpoint because contizmcus neasureaients in a high-pressure ressel abore 
400^ C are rather difficult* In regard to diffusion^ it should be kept in mimd that 

the adjustment of the phase equilibria between <^- and v - mixed crystals below 

o 
500 C requires prolonged interrals* 

The y- « o^rrersion in the irom-ai^el wy^mtmm has been inrestigated in detail 

Iqt maay researchers* per our present task^ it is sufficient to know that the twe«phase 

e 
field d< +)rhas an appreciable width already at 500 C idiich further increases with 

lower temperatures* the ccnrerslon inertia of the f^ce^centwed Y^Hsixed crystals 

is sufficiently great ^ howoTor^ to preserre the composition of the mixed crystals 

(2) Arch* Eisenhuttesires* 32 (1961) P* 843/50 (Werkstoffaussch* 1302)* -rAlso Dr*- 
Ing* Dise* (Extract) by W* Biermann, lechn* Hochsoh. Aachen* 

- 2 - 



unohax^ed byr quenohing to 20 or C* Upon deep-oooling in liquid air or other agonts^ 
deodjcing also does not need to be expected* fhB faoe-*aentered mixed oiystals quenched 
to 20 C are supersaturated with iron in regard to the phase equilihriim* The body** 
centered mixed oxystals with 2S««35 % niokel obtained l3gr loir«temperature cooling are 
supersaturated with niokel* On the basis of the balanced system, there i^ould be 
present simultaneously^ both at 20 and at 400^ 0, body^centered mixed crystals with 
a low coateat of nickel and faee'-ceatered mixed crystals with a high content of 
nickel* According to £• A» Oven and T» H* Liu (3), tiie body-*centered limit mixed 
crystal contains 6*6 % nickel and the faee-centered crystal cantains 43 % nickel at 
400^ C* In an all^ with 35 % nickel, thecH-^^ conrersi^i allegedly does not become 
o<mplete below 450^ C under customary pressure* The reaaining ^Hsixed crystals are 
said to contain less and the newly formed ^ <«ixed crystals more than 35 % nickel* 
Our task consisted in transforming the crystals without demixing into the bod^^oem^ered 
crystal form and, upon heatiag of the ^ «mixed crystals supersaturated with ni^el 
to measure the formation of ^ -mixed crystals in consideration of temperature, 
quantity, time and nickel content both under customary as well as high pressure* 
Saaple Preparation, Pressure Apparatus and 
Measurement Procedure 
The samples were prepared by mixing, compacting and sintering of powdered carboxisrl 
iron and carboz^l nickel* From data of the manufacturer, carboxayl nickel contains 
not less than 99*B % nickel and not more than 0*05 % iron, and carboziyl iron contains 
not less than 99*7 % iron and not more than 0*04 % nickel* After sintering^ Hlb 
content of carbon was 0*002 %• Sintering was carried out at 1,3S09 C for 48 hours* 
Tne samples were cooled in the furnace and subsequently cut into cylinders witii a 
diameter of 4*5 am and a length of 35 m* Upon measurement of the electric resistance 
in the ^-state, the samples were oonrerted through deep^cooling in liqidd nitrogen 
into a primarily ferritic state* 

(3) J* Iron Steel Inst. 163 (1949) p#132/37 & 1 table; see esp* p* I36. 

- 3 - 





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For the experifteixts usdar high pressure^ we utilised the high-»presaure apparatus 
described lay U* Jelliiighaus and H* Priedevold (1)« A hollow oylix^erj^ closed at one 
end, of tasQipered chrone-nickel-^aolybdenum steel with a tensile strezigth of 100 kg/m 
serTed as high-pressure Tessel. The effeetire working space has a diameter of 25 na 
and a lezigth of 100 aoa with a wall thickness of 28 am* Pressure Is produced )9y 
a two-stage high«*pr assure pump enployii^ as pressure fluid **silioon«*oil* with a ris- 
cosity of S oSt at rooK temperature* The apparatus if oapable of pressures up to 
6,000 kg/ca • pressure is controlled with a steel-tube spring<»pressure gauge* The 
pressure Tessel is heated to the startii^ teaiperature by a rartically adjustable 
furnace and temperature is measured with a nickel-chrome/nickel thermoeot^le element 
whose h0t*soldered junction is located in a bore, 12 am deep* in tke middle of t^ 
cylinder wall, AM automatic ri^ulator was utilized for the isothermal experiments 

which maintains taaperature oonstcuit with dl 2^ C* About two hours are required to 

o 
heat the unit from room temperature to 400 C« 

Die o(->2foon7ersion was obserred primarily by measur^ient of eleot^ie resistance* 
power leads and potential terminals consisting of copper wire with a diameter of 
0«4 mm were silver-soldered at the extremities of the samples* The samples and the 
electric leads were isolated ty i?eramio tubes. In order to seal the bushings of the 
measuring wires from the high-pressure vessel to the outside, we utilised the methcKi 
of Ebert and Gielessen (4)* A Thomson bridge served for measurement of resistance* 

For the ccmiplementary magnetic measurements as far as deteradnation at room 
temperature was concernedj^ we utilised an electrotfignet with axially drilled poles 
as developed by Stablein and Schroeter (5)* Concentration of nickel in the ^« mixed 
crystal with the aid of the Curie temperature was determined by a magnetic scale 
according to Hathieu (6)* Further uses of the scale will be described later* 

Experimental Findings 

o(-^>( Conversion UP to 4Q0" C 
Upon heating, an increase of electrio resistance occurs which is due in part 

(4) Ann* I^s., 6* Polge, 1 (1947) P* 229/40. see esp* P. 230 

(5) Z. anorg. allg* Cham* 174 (1928 P. 193/215 . 

(6) Arch* Bisenhifbtenwes. 16 (1942/43) p. 416/23* 

- S - 



to the increased temperature but in part also due to thffpf^Y P^^se oozrrersion* 
This non-reTerrible part of the increase of resistance is found abore 236° C for the 
alley with 34*8 % nickel* If heating is arrested br^ transition to a constant temper-- 
ature^ the increase of resistance is also praetioally arrested* In seireral ezperi- 
nents with constant t^aperatures between 250 and 400^ C* no appreciable increase of 
resistanoe was foimd after 20 hoinrs. Durix^ coolings resistance decreases but ^e 
decrease is less than the increase upon heating due to the non-reversible ^-^^ 
eonrersion* 

^ble 1 groups the Talues of electric resistance measured at room temperature 
before and after the eocperiment* These measiir^ients were also made for the samples 
heated under high pressure without stress* The conditions of measurement consequently 
concord for both groups of annealing experiments (at pressures of 1«000 and 5^000 kg/cm | 
ref* 2)* 

fhe quantitatire proportion of the newly formed X phase was caloulatod from the 
ehanges of resistance* Us assumed here that elastic stresses in the mixture of the 
two iypes of orystals did not have a,rxy appreciable influence on electric resistanoe* 
On this assumption, the volume ratio x of the ^ •phase was oalculated according 

to the mxxiK rule ^ ^ * (1) 

f roffi t^e specdfic resistances of 1^ pure c(-.phase f^oo^^ ^^ ^^® phase jsixture Pxeg* 

The specific resistanoe of tiie pure c{«phase of the iron alloy with 34*8 % 
niokel was eoctrapolated according to measturements Iqr Shirakawa (7) from the resis- 
tances of alloys with 25 and with 30 % ni<dcel* Jn the experiments performed under 
high pressures^ the Increases in the quantitatire ratio of the )f -phase are 2 to S 
times as high as in experiments under customary pressin^e^ figure 1 shows the increase 
of the speoific electric resistance under annealing* The curves extrapolated from 
low annealing temperatures intersect in the vicinity of the iiiitial resistanoe* 



(7) Sd. Isp. Tohoku Univ. 27 (1939) P, 485/531. 



• 6 - 



Aa appreciable infliaaBce of pressure on the teaperatiire at thb st&r t of non- 
reTersible ohajiges can aot be observed . 

SS 




i2s iw m. 



m m JSff m m 



^ ) Aniaptempepstar m ^C 

Fig« I * Increase of electric resistance due to inconplete re^-fonuition of c/^^phase 
into "^^plsase in iron allegre vith 29*9 asd 34.8^ nickel under cuetenazy and vaader 
high pressure* 

Legend: a) specific electric resistance in •••! b) content of ^ ^fbjBLse in initial 
state 19^1 e) pressiure in kg/cK^; d) allay coatent:.**! e) initial resistaneei ^ 
f) content of ^ «phase in initial state 3*9^; g) annealing tenperatiare in C« 

Measuramects of magnetic saturation can be utilised in the same Banner for the 

determination of the quantitative ratio^of the j^y^phase if the saturation Talues are 

knoim for o(^ IQO % and K= 100 %. :^ey were carried out for the iron alloys with 

-^^^.,, . J. J.* mtj.1. J *ij 4 :t Joo, 100% « — 4 ?g Joo, uz^ 
29*9 % nickel, looording to formula I, there is ralid a; = - — TZTIZZ * 

For the 29*9 % nickel allegr^ it is difficult to find a saturation ralue in 

literature irtiioh can be ascribed reliably to a state of the alley completely free of 

austenite* The saturation ralue required in formula 2 for the pure bod^-centered 

state was therefore provisionally derived through calculation }sy assuming as kncmm^ 

from the measurements of resistance in the same alloy, the ratio of the ^«»phase in 

the deep-cooled state. Tor the further treatment of the 29*9 % nickel alloy^ tiiere 

resulted approximately the same increases in the share of the )^ -phase as from the 



(2) 



- 7 - 



the xeasuresieBts of resistance (cf, Table 2)* 

Table 2-^-Measuraaents of magsetization for determinixag ^^)f cozrrerslon of 
29.9 %^^nxckel alloy. 



iieat treatnezits 



] pressure in | magnetisation ^Jt* ratio of 
kg/oa^j I Iooat20^C^»2 | ^-phase; 

I in Gauss; j aeasured; ^ 

i ■■] 7ol^^ 



oaloulatedi 
from pesobajnii 



I. pare t^ -phase, 13§0° C, 


.— 


19370 ' 





-«■— 


48 kours, rumaee 










oooling; 




4800 


100 






11. 1 / IS aiB deep- 


.».. 


1M«) 


9^ 




18830 


3,9 


0,35 






18810 


4.1 


0,5 


nr. I / 11 / anneaUng 


1 


17640 


11.9 


8,8 


at 350«> C, 




(18840) 








5000 


16610 
(18830) 


18,9 


16.1 


Ty* 1 / 11-/ aonealiog 


1 


16S10 


21,0 


18,3 


at 400° C, 19 hours. 




(18830) 






furnace eooliag. 


5000 


14300 
(18810) 


34,8 


32,5 



(I) pressure^ 1 leg/am t (2) data in parentheses: Talues aeasxured in initial 
statei (5) 4Tf S 0O tot ek-state froa Peschard - 18^880| (4) in liquid 

nitrogen* 

Table 2 furti^r lists the toIuim ratios of l^e ^ --phase obtained if we intro- 



duce 18^880 G^uss for ^^Joo,i^%ac as basis for calculation in accordance with 
Pesehard (8)* Since this ralue is lower bjr 490 Gauss than the one ealculated from 
f onnula 2 with a given x« there results a oorrespondingly lower Tolune ratio of the ^^ 
phase* 

Subsequent to the annealing treatment, temperatiare/sagnetisatlon eunres were 
plotted froB samples of both alloys and the Curie-taaperatures detenained were ooa- 
pared with the Curie«*tffl&peratures of the pure "^-^phase* There were found cmly minor 
dlYergenees* The concen tration of nickel in the re-foraed ^^djced czystal is 
consequently still app roximately the sasie as earlier in the initial hcmogeneous 
austenitic state* S inoe» aocordiog to Pesehard (9), the Ci^trie temperature rises« 

(8) aov. Metallurg., Mcti., 22 (1925) P. 490/614, 581/609 and 663/85; cf* esp p* 670* 

(9) cf* ref* 8. p. 594. 



^ 8 - 



at aboat 30 ^ nickel « ly ^ C per 1 % nioUl^ the iacreases founci cf 8^ C (pressure 

2 
s 1 kg/am ) ajid 10^ C (pressure = 5,00) kg/as^) and under 400*^ C trealasei* of the 

29*9 % nickel allojr can be equated with an increase of the nickel cozstenfe bgr 0*3 and 

0*4 %• Aocording to the equilibriusi^ we should have feund, at 4(X) C» an increase 

to 43 %, i.e*« an increase ta 13.1 ^ nickel* 



Table 3 « Measta^eoiesfes of hardness on sables of 29*9 ^nickel allqr* 



heat treatment I 



pressure in kg/as ; j hardness, H7 10; 



ToluDie ratio 
of J^-phase 



(I) 



in 



I. 1300 C, 48 hours, 

furnaee eooliagj . . 

IX. I / IS Bin deep-oooling ^ ] 

TIT, 1 / 11 / annealing at 350° C, 

20 hovurs, cooling to 20*^ C« 

T?. 1 / 11 / annealing at 400** C, 

. 19 hours* cooling to 20° C. 



125 





200 


1 


197 


5000 


20T 


1 


204 


5000 


183 



100 

11,9 
18,9 
21,0 
54,8 



(1) s calculated on the basis of measizrements of magnet izat ion i (2) « in liqidd nitrogen* 

In allaying the iron with 29*9 ^ nickel, we also seasiired the Tickers hardness 
on samples with different pro^-aod/or annealing treatment (Table 3)* Jjnder oonrersion 
frc^ \ to <a{ , an increase of hardness occurs upon cooling to low temperatures* 
Annealing treatment at 350 C did not yet produce any measurable diminution of 
hardness*vHowerrer^ :afterlanmeaMng at 400^ C ni^ increased pressure^ hardness has 
beoome appreoiably reduced* 

prolonged experiments at 400^ C for o(-» if Conner si on 

At higher temperatures and appreciably longer duraticm of annealings the 
expectance for coming closer to equilibrium is greater* Experiments on an iron alloy 

with 29*7 % nirtel were earried eut at 430° C for 528 hours (22 days), both under 

/ 2 
customary pressure and under a pressure of lO^OOO kg/om * The pressure was created 

in this case through heating of the sanple in a closed steel Tossel filled with mer<- 



9 - 



crxrj (!)• Accordiog to the diagrfia of oquililiriia of 9mx aod Liu (3), we should 
h&Te ohtainedf at 450^ C, a Toluae ratio of the ^ -phase of 71 % axad nickel 
concezrtration of about 39 % for a sample with a nickel content of 29*1 %* Subsequently^ 
there was fouxxi a ratio of the ^phase of 19 % under custcnary pressure and a ratio 
of 31 % under high pressure* On the basis of quaixtity, eqxailibrium is far from 
being reached* Tram the tesperatureHttgnetlzation curres, there resulted Curie-Joints 
of the 5f -Jhase of 518** C f^ P = 1 kg/<»^ and 2T2® C for p r 10,000 kg/oa . 
Since^ aeofnrding to Pesohard (8), the Curie point for the hoRc^eneous mixed crystal 
with 29.7 % nickel lies at 120 C* the nickel concentrations of the ^''-^phase hare, 
under these eomiitions^ iacr^ised appreciably in the direction of the equilibrium* 
Aocording to Pesohard^ we calculate^ from the Curie temperatures, the nickel content 
of the y--phase as about 30 % in the experiment under customaiy pressure and as 
36*2 % for the experimeiKt under high pressure* consequently, the quantity of the 
"^ ^phase is higher under high pressure but the adaptation of the concentration to 
equilibrium is less complete. 




f m Tosim^s^ m m m . 



r«L^ m ^ m m m m ¥m^s^ 
-^f Mefifemperatur m *r 

pig. 2»«>Temperature'-magnetisation curres for determining nickel concentration of c(^ 

and V^-phase after prolonged annealing at 430^ C under customary and under high 

pressure* 

Legend: a) magnetisation in ogs/gi b) pressure:*«*| o) initial state with 

predominant share of c<-phase; d) after annealing for 528 hours at 430 Ci 

e) austenitie state; f) measureing temperature in C* 



- 10 - 





After prolonged treatment at 430 C, a change of the nickel content can also 
be noted in the o(«.phase« Tonperature- Buignetixation ciu^es were plotted as demon** 
etration (fig. 2). The oonTersion of the o<*|jaa8e which is still constant at 430** C» 
to the ^ •phase at higher t^iperatures can be determined from the regression of the 
speoifio magnetisation* The comparison of the respeetlTe temperatures with the actual 

diagram furnishes mean Talues for the nickel content of the o( -mixed crystals* These 

o 2 2 

temperatures (530 C at p » 10,000 kg/om and 560^ C at p ^ 1 kg/on ) o«xe^o3ad to 

a nickel content of 26*S and/or 24.5 %^ fh0 nickel content has therefore dropped bat 

o 
still lies far abore the eontent of equilibriim of S*3 % nickel yalid for 430 C* 

T«ro brief -interral experiments at 450 C for 2*5 hours of the same alloy 
resulted in a 7olame ratio of the lS*phase of 27^ ui»ier high pressure and in a ratio 
of 16 % imder customary pressure* fhe Curie temperatures in both oases were the same 
as for the initial homogeneous austenitic alloy so that the nickel ooncentrations 
oensequexAly did net ohaoge appreciably* These findings correspond to expectations* 
The <4^)^ eenrersion has occurred in greater part alrea<j^ duristg heating* On the 
other hand^ the composition of the mixed crystals has not undergone any appreciable 
change at the teiminal temperature of the experiment after 2*5 hours. 

Discussion of Findings 

The experiments performed at low temperatures piroduced a re^-f ormation, farored 
ly pressure, of the f aoe-ceatered from the bofll^«*centered crystals* This did not 
ohaoge the nickel concentration* The result canseguemtly was an instable state in 
iriiich the quaatitatiTO ratio of the ^-phase was increased* The changes ef oencen-' 
tration demanded by the diagram of equilibrium, homoTer, had not occurred* Apparently, 
there exists for tsmperattires belflw 400^ C only the possibility of a displac^aent 
conTorsion bwt not the possibility of adaptation of the concentration to the equili- 
brium* It is notewoi^hy that the displacement comrersion from <;^to g^ starts at 
spproximately the same temperature, regardless of whether customary or highly inoreased 



• 11 - 



pressure is enployed. According to the Cl&usius-ClapeiyTaii equation, there should 
have beesi a drop of the equilifaritim temperature for the coHlrerslon aoccapanied by 
reduction of toIuko* a corresponding drop of the o(-^ )^ conrersion teffiperatures 
through pressure vms obserred in the iron^chrone ^stea \^ KaufnanUt Leyexsaar and 
Barv^ (10)* I^ ^^^ iron-niokel systen, the same autk<»:s iirrestigated an alloy vith 
9*5 ^-aton (10*5 ^-to1«) niokel and found a drop of the coxnrersion temperature of 
2 X 10 C^^lkg/ma at pressures up to 60,000 k^om^* At p - 1 kg/am , the starting 

tesq>erature of the cK-^z oomrersion lies at 680 C* 

If we did not flnd^ in our aim experiments on iron^oidcel alleys, az^ differenoe 
in the teoBperaturea at ivhioh the^^^^oenrersion starts, then there must be a special 
reason for this* The reaction of the iron**nickel allor/s in a ^-> <4 connrersion still 
corresponds approximately to the theoretical requirements that the **^s^ --tamper ature^ 
i#e,^ the temperature of tke start of cozrrersion, is reduced ly high pressure as 
obserred Ty patel and Cohen (U)* Ifta^ does this not ooour in the c^ -^ ^oonrersion? 
The initial state in the^J^-^c^ c^irersion, i«e«jtke homogeneous austenitio mixed 
crystal, should mecihanically still havs been in an isotropic state of stress* In the 
nickel-ciartensite and/or the mixture of mickel-aartensite and residual austenite 
which represents the initial state for the <?V-^ 6 conversion^ no further mention is 
made of a low-^strass or isotropic state. In the displacement conversion from V" 
toward ^ , the atom distances ai^ shortened in certain directions in the crystal 
lattice but lengthened in other directions* The increase of volume leads to anisd* 
tropic state because a uniform hydrostatic pressure in all directions would increase 
the pressure in all directions would increase the pressure stresses in some directions 
but more or less equalise the existing tensii stresses in other directions* However 
this Isads^ at least for pressure stresses, niiich lie in the same order of magnitude 
as the internal stresses existing in the material, only to a changed spatial distri- 

(13) Kaxifiaan, L«t A» Leyenaar and J* S« Harvey: progress in very high pressure 

reasearch* Hew York 1961 
(11) Acta metallurg*, Hev York, 1 (1953) p* 631/38* 



- 12 - 



buction of the stresses bixt not jet to a state with a uziiform aaount of stress in 
arbitrar/ directions, ne are also justified in reoailixig that Ute ciausius-^Clapeyron 
equation vas derired froa the states of stress of gases sind liquids^ i»e«« fron 
relations in which anisotropjr of the stresses does not occur* 

At the ti!&e of completing this ceamuni cation, there was published a report tagr 
Melniko7^ Sokolor and Stregulin (12) which discusses the influence of |H*e8sure on 

the tem^rature ef the cL^ ^oonTsrsion in an alloy with 27. 6 % nickel and 0.046 % 

2 

•arbon* It p « 1 kg/oK ^ this temperature lies at 465^ C* Sxperiaents with pressures 

2 o , 

of 1, 10,000« 20^000 aikl 30,<XX) kg/as showed a displaceaent by 0*0025 C/at p ? 

2 
30,000 kg/ca • This finding consequently differs considerably froa the result «f the 

present investigation in which we found an appreciable difference between the 

quantities conTerted with or without pressure but no notable displacement of the 

stazi; of conrersion* 

Howerer^ the deviation is entirely justifiable both liy the lower nickel and higher 

carbon content of the alley employed hy the gussian investigators (12) whioh inereases 

the oonversion temperature Isy about 160 C as compared to the alloy with 29*9 % nickel 

utilised la^ us and because of the considerably higher pressures employed by them* 

It is understandable that 20,000 kg/ cm are superior to the internal stresses 

. 2 

whereas 5,000 kg/cm do not yet produce axqr appreoiable effect* 

Ihe experiments at 430^ C have d^scnstrated that changes of concentration are 

o 

effected by increase of temperature and duration which do not oecur at 400 C and 

with brief intervals. However, the high niokel content ef the <X nsixed crystals 

o 

after the prolonged experiment at 430 C is still very f^r from the state of equili^ 

brium* This is understandable inasmuch as the composition of the alloy with 29*7 % 
niokel lies appreciably closer to the nickel contexxt of the '^•^liait mixed crystal 
(according to the equilibrium, 38*8 % nickel) than to that of the c< -limit mixed 
crystal iriiioh allegedly contains only 6*3 % nickel* In order to reach the eonoen«» 

(12) Mel'nikoVf L* A*» B* !• Sololov and A* I* Stregulin: Phys* Metals Metallog^. 
5 (1933) Ir. 3, ?. 31/36. 

- 13 - 



lKra:tion of ertiailibrium in the o( --phase, there is consequeiattly necessary a mudi 
more extenslTe diffusion* The experiments produced a lesser change of concentration 
in the V ^uLxed crystal lander high pressure than imder custaaaiy pressure* It 
would be premature to attempt to interpret this finding* Wd might oonoeiTe both 
of an inhibition of diffusion throiigh pressure as veil as a displacemexst of the line 
of eijuilibrium of the X*^^^^ crystal towaird lower temperatures or lesser niokei 
content* 

Suaaary 

The c<-^ 2r conversion of two non^rsTersible alloys of iron with 29*7 and/or 

o 
54*8 % nickel is obserred at temperatures Mp to 430 C and customary pressure and 

,2 
under pressure of 5,000 kg/cm • In both cases, conrersion begins during steady 

heating at approocimately the seme temperatiires* If heating is arrested at 250, 300, 



o 
350» or 400 C« we then find in the experiments \mder pressure 2 to 3 times ths amount 

of newly fomed V -phase* Continuation at the temperatures indicated beyond 20 

hours does not produce any increase of the ^ -»phase and the ooncentrations of the 

mixed crystals remain almost unchanged* Diffusion can be demonstrated at 430^ C 

after continuation for 22 days* In the experiment xmder custoaary pressure, the 

nickel contents come closer to the value required by the diagram of state than in the 

experiment under high pressure. HowoTer, in both cases the nickel content of the 

c^ -mixed crystals remains higher than required l^^ the equilibrium* fhe start 

of «^"^ "JS conTersion at the same temperature independently of the amount of pressure 

is explained hy the highly stressed initial state* 



.'L