THE INFLUENCE OF PHASE TRANSFORMATION ON THE TEMPERATURE SPECTRUM OF INTERNAL FRICTION IN N18 K10M5T AND H10N7K10M5 STEELS

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THE INFLUENCE OF PHASE TRANSFORMATION ON THE TEMPERATURE SPECTRUM OF

INTERNAL FRICTION IN N18 K10M5T AND H10N7K10M5 STEELS

W. Chomka, J. Pastor

To cite this version:

W. Chomka, J. Pastor. THE INFLUENCE OF PHASE TRANSFORMATION ON THE TEMPER- ATURE SPECTRUM OF INTERNAL FRICTION IN N18 K10M5T AND H10N7K10M5 STEELS.

Journal de Physique Colloques, 1983, 44 (C9), pp.C9-211-C9-215. �10.1051/jphyscol:1983927�. �jpa-

00223374�

JOURNAL DE PHYSIQUE

Colloque C9, supplement au n012, Tome 44, d6cembre 1983 page C9-211

THE INFLUENCE OF PHASE TRANSFORMATION ON THE TEMPERATURE SPECTRUM OF INTERNAL FRICTION I N N18KlOM5T AND HlON7KlOM5 STEELS

W. Chomka and J . Pa'stor

I n s t i t u t e of Physics, TechnicaZ University of Gdalisk, 80-952 Gdarisk, Poland

Kc'sum6

-

Nous p r 6 s e n t o n s l e s r 6 s u l t a t s de 1' a p p l i c a t i o n de

-

l a metode du f r o t t e m e n t i n t e ' r i e u r pour 1' Q t u d e de l a t r a n s f o r m a t i o n m a r t e n s i t i q u e dans deux a c i e r s i n d u s t r i e l s f a b r i q u e s en Polonge: I

-

N181<10E45T, 11

-

HlON7KlOM5. Les t e n p e r a t u r e s c a r a c t 6 r i s t i q u e s o n t 6 t 6 trouve'es. Nous avons L t a b l i que l a t r a n s f o r m a t i o n atherme e s t dans 1' a c i e r I e t l a t r a n s f o r m a t i o n i z o t h e r m dans 1' a c i e r 11,

A b s t r a c t

-

I n t h e p r e s e n t n o t e t h e a p p l i c a t i o n o f t h e i n t e r n a l f r i c t i o n method t o t h e i n v e s t i g a t i o n o f phase t r a n s f o r m a t i o n s i n tt.to t y p e s o f P o l i s h commercial s t e e l s /I

-

N18KJ.0M5Tt I1

-

HlON71<10M5/ i s presented. Our measurements a l f o n e d t o e v a l u a t e t h e c h a r a c t e r i s t i c

t e m p e r a t u r e s /M,, t'1#

,

kc,, ACS

/

o f phase t r a n s f o r m a t i o n s i n b o t h s t e e l s , as ell as t o i n d i c a t e d i f f e r e n c e s beetwen a t h e r m a l m a r t e n s i t e t r . a n s f o r m a t i o n L n s t e e l I and i s o t h e r m a l i n s t e e l 11.

iNTi<ODUCTION

The N18KlOM5T s t e e l / s t e l l I/ b e l o n g s t o t h e g r o u p o f c l a s s i c a l maraging s t e e l s

[ill

and HlON7K101.15 s t e e l s t e e l X I / i s t h e

s e m i a u s t e n i t i c maraging s t a i n l e s s s t e e l

(1.

The t h e r m a l t r e a t m e n t o f b o t h s t e e l s , l e a d i n g t o h i g h m e c h a n i c a l p r o p e r t i e s , i s s i m i l a r and c o n s i s t s o f a u s t e n i z i n g , m a r t e n s i t e t r a n s f o r m a t i o n /MT/ and ageing. There a r e homever d i f f e r e n c e s i n t h e k i n e t i c s o f MT. The s t e e l I undergoes a t h e r m a l MT, w h i l e t h e k i n e t i c s o f MT i n s t e e l I1 s h o u l d be i s o t h e r m a l due t o t h e c o n t e n t o f Cr / 1 0 , 5 v [3],

I t i s known t h a t d u r i n g phase t r a n s f o r m a t i o n an anomalous b e h a v i o u r o f i n t e r n a l f r i c t i o n

/Q-'/

i s observed /e.g. [4,5]/.

P a r t i c u l a r l y , i n t h e most i n v e s t i g a t e d case o f I-IT, when Q' s h o u l d be p r o p o r t i o n a l t o t h e q u a n t i t y o f m a t e r i a l w h i c h t r a n s f o r m s per u n i t t e m p e r a t u r e change

/

dm/dT [5'1/, t h e t e m p e r a t u r e dependence o f

Q-'

s h o u l d r e v e a l maximum.

EXPERIMENTAL

I n t e r n a l f r i c t i o n a p p a r a t u s : Measurements o f i n t e r n a l f r i c t i o n /Q-'/, f r e e v i b r a t i o n f r e q u e n c y / f / and s e l f t w i s t i n g o f t h e sample / & / were performed on t h e i n v e r t e d t o r s i o n pendulum w i t h t h e

e l e c t o n i c equipment r e c e n t l y produced i n t h e I n s t i t u t e [6]. The specimens i n t h e shape o f m i r e / d i a m e t e r 0,8mm, u s e f u l l e n g h t 70mn/

viere mounted i n t h e pendulum and heated o r c o o l e d i n t h e range o f temperatures from 1231< to10931<, u s u a l l y ~ i t h t h e r a r e o f 3i</min The s t r a i n amp1 it u d e d u r i n g t h e measurements was l e s s t h a n &=lo-%

and t h e t e s t f r e q u e n c y was about iHz.

[ . ; a t e r i a l : A c c o r d i n g t o t h e s t e e l ' s c e r t i f i c a t e s , t h e c o m p o s i t i o n and t h e c h a r a c t e r i s t i c t e m p e r a t u r e s a r e as f o l l o w / > % e i g h t ;.;/:

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983927

JOURNAL DE PHYSIQUE

-

s t e e l I: C-0,Ol; 1"I-0,05; Si-0,02; P-0,003; S-0,008; Ni-16,s;

Ti-0,56; No-4,9; Co-8,s; C1-0,05; fi&=4581<; ; P.$ =343K;

t\,,=8931<;

%,=

1053K,

-

s t e e l 11: C-0.02; Mn-0.03;Si-0,03; P-0,002; 5-0,Ol.; Cr-10,5;

Ni-7,5; Pio-5,7; Co-3,8; A1-0,08; Cu-0,08; iV1,=403K;

Pi,

-

below room t e m p e r a t u r e ; k,=9231<; A,, = I 0 7 3 K.

A f t e r squeezing g r i p s t o t h e ends o f samples and b e f o r e

mounting i n t h e pendulum, t h e samples were anealed a t 1093iC f o r

1

hour and quenched i n a i r .

EXPEKIElENTAL RESULTS AN9 OISCUSSIQt\l

F i g . l a and l b show a t y p i c a l b o h a v i o u r o f T f a n d f' / f % ~ , G

-

shear modulus/ f o r t h e samples, of NlSKlOM5T and WlON7I<lOM5 s t e e l , r e s p e c t i v e l y , i n t h e whole range o f t e m p e r a t u r e s from 1231< t o 1093 K. T h i s b e h a v i o u r f o r b o t h s t e e l s i s s i m i l a r , i.e. d u r i n g h e a t i n g a h i g h t e m p e r a t u r e maximum o f U" c o r e l a t e d w i t h minimum o f f2 i s obser\/ed, D u r i n g c o o l i n g t h i s maximum does n o t e x i s t and t h e l e v e l o f h i g h t e m p e r a t u r e background i s lower. D u r i n g subsequent c o o l i n g t h e l o w t e m p e r a t u r e maximum appears s i m u l t a n e o u s l y w i t h t h e decrease i n shear modulus.

150 CI

1.6 9

X

130 1.4

- ⁵

110

:

110

1,22

* '290 _1.0- " 90

.. '

⁷⁰ _0.8 ⁷⁰

50 5 0

3 0 3 0

10 10

(a)

I" T I K I 900 1

(6)

^{T l K l}

Fig. 1. Temperature dependence o f i n t e r n a l f r i c t i o n

/Q-Y

and f r e q u e n c y square / f z / o f : a/N18l:lOM5T s r e e l /I/ ; b/ HlON71ClOE45 s t e e l /II/. H e a t i n g / c o o l i n g r a t e : 3K/min.

The h i g h t e m p e r a t u r e maxima o f

Q-'

i n b o t h s t e e l s a r e due t o t h e m a r t e n s i t e t o a u s t e n i t e t r a n s f o r m a t i o n and can be e x p l a i n e d as t h e r e s u l t o f changes i n g r a i n b o u n d a r i e s m o b i l i t y . The f a c t t h a t t h e h i g h t e m p e r a t u r e background f o r a u s t e n i t e i s s h i f t e d towards h i g h e r t e m p e r a t u r e s i n r e s p e c t t o t h a t f o r m a r t e n s i t e s u g g e s t s t h a t t h e m o b i l i t y o f a u s t e n i t e - a u s t e n i t e i n t e r f a c e s i s l o w e r t h a n o f

m a r t e n s i t e - m a r t e n s i t e i n t e r f a c e s , s o t h e maximum d u r i n g m a r t e n s i t e t o a u s t e n i t e t r a n s f o r m a t i o n i s t h e r e s u l t o f two concurent

processes: i n c r e a s e o f i n t e r n a l f r i c t i o n backgroud n i t h t e m p e r a t u r e and decrease o f t h i s background ~ v i t h t h e i n c r e a s i n g c o n t e n t of a u s t e n i t e . A l t h o u g h a b e g i n n i n g o f t h i s second p r o c e s s i s d i f f i c u l t t o see i n f i g . 1, i t is p o s s i b l e t o e s t i m a t e t h e c h a r a c t e r i s t i c temperatures o f m a r t e n s i t e t o a u s t e n i t e t r a n s f o r m a t i o n :

-

f o r s t e e l

I

: A,; = 900K, A;, =1050K;

-

f o r s t e e l I S : gc, = 915K, Ar(cS=1070K;

I n t h e t e m p e r a t u r e 1093 K b o t h s t e e l s were i n a u s t e n i t i c phase, b u t t h e processes o f s o l u t i o n h e a t t r e a t m e n t and r e c r y s t a l i z a t i o n

had n o t been ended, because t h e r e was t h e i s o t h e r m a l decrease i n 9-*

and i n c e r a s e o f f Z .

D u r i n g c o o l i n g i n t h e range o f

MT

t e m p e r a t u r e s t h e U" maxima &ere observed i n b o t h s t e e l s . As t h e r e a r e d i f f e r e n c e s i n t h e b e h a v i o u r o f t h e s e maxima f o r b o t h s t e e l s , t h e y w i l l be d i s c u s s e d s e p a r a t e l y .

S t e e l I: The l o w t e m p e r a t u r e maximum o f (1-'in s t e e l I i s

observed o n l y d u r i n g c o o l i n g from t e m p e r a t u r e o f a u s t e n i z i n g . D u r i n g r e h e a t i n g o n l y h i g h l e v e l o f i n t e r n a l f r i c t i o n background /6xlo'*/is observed. T h i s maximum, p r e s e n t e d i n f i g . l a i s exposed w i t h

d e t a i l s i n f i g . 2a. T a k i n g i n t o account measurements o f few samples it i s p o s s i b l e t o d i s t i n g u i s h f o u r r e p e t i t i v e peaks r-i B C D i n t h i s e r r a t i c and complex maximum. The n e x t f i g . 2b shows s i m i l a r

maximum f o r sample aged a t 623K f o r 3 h o u r s and a u s t e n i z e d f o r 1 5 m i n a t 1053 /i.e. a t t e m p e r a t u r e 40K l o w e r t h a n before/. The main peak S i n t h i s case i s l o w e r , whereas t h e o t h e r elements o f t h e s t r u c t u r e o f t h i s maximum a r e more d i s t i n c t .

The presence o f peaks A and B can be e x p l a i n e d a s t h e r e s u l t o f PIT i t s e l f , a c c o r d i n g t o t h e gheory [5J/ ~ - L d m / d ~ / . The e x i s t e n c e o f d i s t i n c t peak A i n t h e cas8 samples aged and a u s t e n i z e d i n l o b e r t e m p e r a t u r e s may be r e l a t e d t o t h e n u c l e a t i o n o f m a r t e n s i t e i n some c o n v e n i e n t p o i n t s o f n o t c o m p l o t l y homogenized s t r u c t u r e o f

a u s t e n i t e /e.g. i n a r e a s r e a c h i n Co [7]/.

Peaks C and D a r e p r o b a b l y r e l e v a n t t o t h e i n t e r a c t i o n between h i g h number o f m o b i l e d i s l o c a t i o n s , c r e a t e d d u r i n g MT /phase work- hardening/ and c h a r a c t e r i s t i c f o r a " f r e s h " m a r t e n s i t e and such d e f e c t s o f t h e s t r u c t u r e as i n t e r m e t a l i c compouds n o t - c o m p l e t e l y s o l u t e d d u r i n g a u s t e n i z i n g i n l o v i e r t e m p e r a t u r e s / f i g . 2b compared w i t h f i g . 2a/.

From p r e s e n t e d measurements t h e M, and Pif t e m p e r a t u r e s f o r s t e e l 1 a r e e v a l u a t e d ;

- ^{M L}

=470 K, i.e. t h e t e m p e r a t u r e o f i n c r e a s e o f ( 1 " g i v i n g b i r t h t o t h e main peak B f o r t h o sample a u s t e n i z e d a t 1093K / f i g . 2a/; f o r t h e sample a u s t e n i z e d a t 1053K t h i s t e m p e r a t u r e i s 4 K because o f t h e e x i s t e n c e o f peak A / f i g . 2b/; % i g h e r

-

^ki;= 3301<, t h i s t e m p e r a t u r e i s o b t a i n e d by e x t r a p o l a t i o n o f 10s;

t e m p e r a t u r e s l o p e o f peak B t o t h e l e v e l o f t h e

background, t h i s e x t r a p o l a t i o n i s necessary because t h e C and D peaks p r o b a b l y a r e n o t d i r e c t l y connected w i t h

34

26

*I

0 .

218

-

1

-

.-

^-.-1,4

-

>I0 b 6 2 - B

'

- - -

. . 6) .,. . ..,...

^'.,"

^,

^{, , ,}

-

?4

-

in 18

", 14 -1.2

0

100 300 500 100 200 300 400 500

T [ K I TCK l

Fig. 2. Q-' and f 2 v s . t e m p e r a t u r e f o r s t e e l

I

i n t h e range o f MT t e m p e r a t u r e s ; a/ sample c o o l e d from 1093K / p a r t o f f i g , l a / ; b/sample c o o l e d f r o m 1053K a f t e r 3 hour's a g e i n g i n 623 K.

**.'..

... _...

_"

_,....,,

:-*""..

-

-

1.3 -1.2

-

- 1 3 -

J O U R N A L DE PHYSIQUE

a )

²⁰⁰ T C K I ^{300 400}

Fig. 3 a/ ~ : f ' a n d & v s . t e m p e r a t u r e f o r s t e e l II d u r i n g : c o o l i n g from 1093K tol231:/aa a

,

p a r t o f f i g . l b / r e h e a t i n g / O O 0

/

t o 363 I< and subsequent

c o o l i n g t o 123 K

/

l a/

..

b/ V ' i n t h e range o f PIT t e m p e r a t u r e s i n t h e t i m e o f c o o l i n g d u r i n g t h e r m a l c y c l i n g o f s t a b i l i z e d sample of s t e e l 11.

m a r t e n s i t e t r a n s f o r m a t i o n and a r e t h e r e s u l t o f phase work- hardening.

S t e e l 11: F i g . 3a exposes t h e p a r t o f f i g . l b , i.e. maximum o f

Q-'

and r e l a t e d b e h a v i o u r o f f 2 d u r i n g c o o l i n g f r o m 1093Kto 123 K. I n a d d i t i o n , t h e same f i g . 3a shows s e l f - t w i s t i n g o f t h e sample / t h e z e r - o i n t movement o f t h e pendulum, expressed i n t h e u n i t s o f sheap s t r a i n & / as w e l l as t h e r e s u l t s o f

Q-' , f

and 6 measurements d u r i n g t h e r e h e a t i n g from 123K t o 363K and d u r i n g t h e subsequent c o o l i n g t o 123 K.

T h i s l o w t e m p e r a t u r e maximum o f Q-' i s fevl t i m e s l o w e r t h a n t h a t f o r s t e e l I what may be e x p l a i n e d as a r e s u l t o f i s o t h e r m a l I'iT n h i c h is s l o w e r t h a n a t h e r m a l flT as i n s t e e l I / c o o l i n g r a t e 3t</min

/.

Due t o t h e isothermal, PiT, w h i c h o c c u r s n o t o n l y d u r i n g c o o l i n g b u t a l s o d u r i n g r e h e a t i n g , r h e maximum o f Q-'appears a g a i n d u r i n g r e h e a t i n g and even, though i n r e s i d u a l form, d u r i n g t h e subsequent c o o l i n g .

E v e r y t i m e i n t h e range o f t e m p e r a t u r e s o f Q-'maximum t h e decrease i n shear modulus i s observed / s m a l l e r i n c l i n a t i o n of f2/T/

d u r i n g c o o l i n g and b i g g e r d u r i n g reheating w i t h r e s p e c t t o n o r m a l t e m p e r a t u r e dependence o f f z

/.

T h i s may be e x p l a i n e d i n f r i s t o r d e r a p p r o x i m a t i o n as t h e r e s u l t o f g r o w i n g c o n t e n t o f l e s s packed m a r t e n s i t e /BCC/ i n more packed a u s t e n i t e m a t r i x /FCC/ [8].

The s e l f

-

t w i s t i n g o b s e r v e d f o r t h e samples o f b o t h s t e e l s can be u n d e r s t o o d as t h e r e s u l t o f i n t e r n a l s t r e s s e s i n t r o d u c e d d u r i n g MT. E x i s t e n c e o f t h i s phenomenon i n t h e case o f s t e e l I 1 /iig.3a/, n o t o n l y d u r i n p c o o l i n g b u t d u r i n g r e h e a t i n g and each t i m e i n t h e v i c i n i t y o f U' naxzmun a l l o w e d t o v e r i f y o u r f o r m e r h y p o t h e s i s t h a t t h e

Q-'

maximum i s due t o a k i n d o f r e l a x a t i o n process [9]

.-

^No

r e l a x a t i o n process can i n v o l v e such macroscopic changes, b u t phase t r a n s f o r m a t i o n can do i t . So vie c o n c l u d e t h a t Q"maximum observed d u r i n c o o l i n g and r e h e a t i n i s t h e d i r e c t r e s u l t o f i s o t h e r m a l KT and t i e r e i s no M maximum o%served by P r i o u e t

al.

i n Fe.Ni-C [19

The h i g h d e s t a b i l i t y o f t h e s h a p e a n d h e i g h t o f t h e l o w t e m p e r a - t u r e maximum

i s

o b s e r v e d . T h e c h a n g e s d e p e n d o n t h e number o f

t r a n s f o r a t i o n c y c l e s i n w h i c h s a m p l e s o f s t e e l T i w e r e i n v ~ f k ; ~ d u r i n g m e a s u r e m e n t s a s w e l l a s o n t h e p e r i o d o f time from q u e n c h i n g

t i l l .

m e a s u r e m e n t s , F i g . 3 b i l u s t r a t e s t h i s b e h a v i o u r .

The m e a s u r e d s a m p l e had b e e n h e l d i n room t e m p e r a t u r e f o r

5

m o n t h s s i n c e q u e n c h i n g a n d t h e n mounted i n t h e p e n d u l u m a n d m e a s u r e d d u r i n g s u b s e q u e n t t h e r m a l c y c l e s . E a c h t h e r n a l c y c l e a a s c o n s i s t e d o f h e a t i n g / 1 0 I < / ~ i n / t o

1 0 9 3 K ,

a u s t e n i z i n g f o r

2

h o u r s . , c o o l i n g /15K/min/ c o

650K

a n d f u r t h e r c o o l i n g / 3i</min/ t o 123K, d u r i n g ~ h i c h

t h e m e a s u r e m e n t s p r e s e n t e d w e r e d o n e .

D u r i n g t h e f i r s t c c l e t h e Q-' maximum kxas v e r y l o w , T h e h e i g h t s f t h i s maximum r a d u a l l i n c r e a s e s w i t h t h e number o f c y c l e . B a g i n n i n g f r o m t8e f o u r t i c y c l e t h e maxima a r e s i m i l a r . B e c a u s e Q-'-

dm/dT, s o t h i s b e h a v i o u r o f Q - ' c a n b e i n t e r p r e t e d a s t h e r e s u l t o f s t a b i l i z a t i o n o f a u s t e n i t e

/ 5

m o n t h s i n room t e m p e r a t u r e / w h i c h i s g r a d u a l l y removed o n l y

~y

f o u r c y c l e s o f a u s t e n i z i n g i n 1093K. The e f f e c t o f s t a b i l i z a t i o n O F a u s t e n i t e d u r i n g l o n g h o l d i n g

of

s a m p l e s i n room t e m p e r a t u r e was o b s e r v e d f o r s i m i l a r s t e e l s [ l o , 111 , b u t

i t i s s t i l l

n o t c o m p Z e t e l y u n d e r s t o o d .

I t

i s s u p p o s e d t h a t t h e p o s s i b l e mechanism

0.:

t h i s phenomenon

i s

t h e d i f f u s i o n o f i n t e r s t i t i a l s t o t h e p o t e n t i a l p o i n t s o f m a r t e n s i t e n u c l e a t i o n .

T h e l a s t 6 - t h c y c l e was p e r f o r m e d i n d i f f e r e n t

w a y :

- ^{i n}

t e m p e r a t u r e s o f

3 3 3 K ,

293K,

233#,

203K t h e c o o l i n g

rbas s t o p e d f o r

1 0 m i n u t e s a n d t h e i s o t h e r m a l b e h a v i o u r o f Q - ' w a s o b s e r v e d . T h e t o t a l d e c r e a s e o f

^Q-I

w a s r e s p e c t i v e l y

40, 5 ,

3 6 a n d 20% / m a r k e d by d a s h e d l i n e o n f i g .

3b/.

P a r t i c u l a r & o r t h t o u n d e r l i n e i s t h e i s o t h e r m a l r u n o f

^Q-I

a t

293 K.

~ n tKis c a s e

0-'

rras i c r e a s i n g d u r i n g t h e F i r s t

5

m i n u t e s o f a n n e a l i n g a n d o n l y t h e n s t a r t e d t o d e c r e a s e s o t h e t o t a l e f f e c t w a s

5%

d e c r e a s e o f Q-' , s e e n i n F i g . 3b. T h i s i s a d i r e c t e v i d e n c e t h a t MT i n s t e e l

I1

i s i s o t h e r m a l .

B e c a u s e t h e

bi,

a n d

MC

t e m p e r a t u r e s o f i s o t h e r m a l Elf s t r o n g l y d e p e n d o n t h e r a t e o f c o o l i n g s o g i v i n t h e

1.1;

a n d

f$

t e m p e r a - t u r e s ,

A e

u n d e r l i n e t h a t t h e y h a v e b e e n e v a q u a t o d i n t h e c o n d i t i o n o f c o n t i n u o u s c o o l i n g w i t h

t h e

r a t e o f liK/min. U s i n t h e r e s u l t s

p r e s e n t e d i n f i g .

30,

vie o b t a i n e d

~ ; = 4 5 0 ~

a n d

M;

= 1 8 5 ~ by e x t r a p o l a - t i o n , r e s p e c t i v e l y , h i h- a n d loby- t e m p e r a t u r a s l o p e o f t h e

9''

maximum t o t h e l e v e l o f t h e b a c k g r o u n d .

CONCLUSION

The i n t e r n a l f r i c t i o n method may b e u s e d n o t o n l y t o e v a l u a t e t h e c h a r a c t e r i s t i c t e m p e r a t u r e s o f p h a s e t r a n s f o r m a t i o n s i n m a r a g i n g s t e e l s , b u t

i t

a l s o a l l o w s t o i n d i c a t e t h e d i f f e r e n c e s b e e t w e n a t h e r m a l a n d i s o t h e r m a l

fviT.

P a r t i c u l a r y o u r m e a s u r e m e n t s show t h a t :

- a t h e r m a l t r a n s f o r m a t i o n i n s t e e l

I

d e v e l o p e s more r a p i d l y t h a n i s o t h e r m a l o n e i n s t e l l

11,

- i n s t e e l

1

t h e e f f e c t o f e a r l i e r n u c l e a t i o n o f m a r t e n s i t e a n d t h e e f f e c t o f p h a s e w o r k - h a r d e n i n g i s o b s e r v e d ;

-

t h e i s o t h e r m a l CiT i n s t e e l I I o b s e r v e d by i n t e r n a l f r i c t i o n method

h a s a l l c h a r a c t e r i s t i c f e a t u r e s o f t h i s t r a n s f o r m a t i o n , i.e.

i t

r u n s i n i s o t h e r m a l c o n d i t i o n s a s w a l l a s d u r i n c o o l i n g a n d r e h e a - t i n g o f t h e s a m p l e s . Eioreover t h e e f f e c t o f s t a g i l i z a t i o n e x i s t s .

-

he work w a s s u p p o r t e d by P o l i s h Academy o f S c i e n c e w i t h i n t h o f r a m e o f

I"li?i 24

P r o b l e m ,

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