THE NEW COLD-WORK PEAKS IN LOW CARBON AND INTERSTITIAL-FREE STEELS

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THE NEW COLD-WORK PEAKS IN LOW CARBON AND INTERSTITIAL-FREE STEELS

H. Chen, T. Chou

To cite this version:

H. Chen, T. Chou. THE NEW COLD-WORK PEAKS IN LOW CARBON AND

INTERSTITIAL-FREE STEELS. Journal de Physique Colloques, 1987, 48 (C8), pp.C8-149-C8-154.

�10.1051/jphyscol:1987819�. �jpa-00227123�

JOURNAL DE PHYSIQUE

Colloque C8, supplhment au n012, Tome 48, dbcembre 1987

THE NEW COLD-WORK PEAKS IN LOW CARBON AND INTERSTITIAL-FREE STEELS

H.B. CHEN and T. S. CHOU

Research and Development Department, C h i n a S t e e l C o r p . , Kaohsiung, Taiwan, C h i n a

ABSTRACT

A new peak a t 210'220 K ('1 Hz) f o r a low carbon s t e e l and an i n t e r s t i t i a l f r e e s t e e l and a n o t h e r peak a t 170K ('1 Hz) f o r t h e i n t e r s t i t i a l f r e e s t e e l were o b s e r v e d f o r heavy p l g s t i c - d e f o r m e d specimens. n o s e peaks e x h i b i t an anomalous dependence o f s t r a i n a m p l i t u d e and an a g i n g e f f e c t . The main c h a r a c t e r i s t i c s o f t h e s e p e a k s a r e i n t e r p r e t e d i n t e r m s o f i n t r i n s i c motion o f h i g h d i s l o c a t i o n d e n s i t y due t o h i g h i n t e r n a l r e s i d u a l s t r e s s .

I . I n t r o d u c t i o n

There a r e many i n v e s t i g a t i o n s on i n t e r n a l f r i c t i o n o f p l a s t i c a l l y deformed p u r e i r o n s and s t e e l s . Some r e l a x a t i o n peaks s u c h a s a - p e a k (30K a t 1Hz o r 50K a t 1OOK Hz), y-peak (300K a t 1Hz) were found. These p e a k s were b e l i e v e d t o b e a s s o c i a t e d w i t h i n t r i n s i c motion o f d i s l o c a t i o n s ( 1 - 4 ) . I n a d d i t i o n t o t h e s e p e a k s such a s Snoek-Koster(S-K) peak was c o n s i d e r e d a s due t o t h e i n t e r a c t i o n between d i s l o c a t i o n s and i n t e r s t i t i a l atoms ( 5 , 6 ) . I n t h i s s t u d y , a new c o l d work peak was o b s e r v e d a t 210-220 K ( a t '1 Hz) i n both o f t h e 70% c o l d - r o l l e d low carbon and i n t e r s t i t i a l f r e e s t e e l s , and a s m a l l peak a t 170K was found f o r t h e a s c o l d r o l l e d i n t e r s t i t i a l f r e e s t e e l .

The new p e a k s i n t h i s s t u d y seem t o b e s i n g l e r e l a x a t i o n p e a k s , and were d i m i n i s h e d a f t e r a g e i n g a t 498K and 448K f o r 10 m i n u t e s f o r 220K peak and 170Kpeak r e s p e c t i v e 1 y .

I t i s i n t e r e s t i n l : t h a t t h e new p e a k s e x h i b i t anomalous s t r a i n a m p l i t u d e depen- dence. Such an a m p l i t u d e dependence w i l l be d i s c u s s e d a s due t o an a n n i h i l a t i o n e f f e c t o f t h e k i n k p a i r s d u r i n g i n t e r n a l f r i c t i o n measurement when t h e s t r a i n a m p l i t u d e was i n c r e a s e d . The a p p e a r a n c e o f s u c h p e a k s may b e a t t r i b u t e d t o t h e i n t r i n s i c motion o f d i s l o c a t i o n s w i t h h i g h k i n k - p a i r d e n s i t y u n d e r h i g h r e s i d u a l s t r e s s which was i n t r o d u c e d by heavy c o l d r o l l i n g .

1 1 . Experimental Method

The m a t e r i a l was m e l t e d i n a vacuum f u r n a c e . The c h e m i c a l c o m p o s i t i o n i s shown i n T a b l e 1. The m a t e r i a l A is a low carbon s t e e l and m a t e r i a l B had been t r e a t e d u s i n g Nb s u c h t h a t t h e f e r r i t e m a t r i x i s i n t e r s t i t i a l f r e e .

The specimens f o r i n t e r n a l f r i c t i o n measurement were p r e p a r e d by h o t r o l l i n g i n a p i l o t r o l l i n g m i l l t h e n c o l d r o l l e d t o t h e f i n a l t h i c k n e s s . m e t o t a l reduc- t i o n i n c o l d r o l l i n g was 70%. Some o f t h e c o l d r o l l e d specimens were s u b s e q u e n t l y n o r m a l i z e d a t 9 2 0 ° c ( 1 1 9 3 ~ ) and c o o l e d i n vacuum. 'Ihe n o r m a l i z a t i o n t r e a t m e n t was c a r r i e d o u t f o r t h e z o ~ p a r i s o n o f s o l u t i o n c o n d i t i o n s o f C and N i n low carbon s t e e l and i n t e r s t i t i a l f r e e s t e e l . A f t e r n o r m a l i z i n g , some o f t h e s e specimens were s t r a i n e d i n a t e n s i l e t e s t i n g machine f o r 20 and 30%, r e s p e c t i v e l y . Some i n t e r s t i t i a l f r e e specimens were aged a t v a r i o u s t e m p e r a t u r e s and t h e n t e s t e d i n i n t e r n a l f r i c t i o n t e s t i n g machine t o s e e t h e e f f e c t s o f a g i n g .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987819

C8-150 JOURNAL DE PHYSIQUE

An a u t o m a t i c i n v e r t e d t o r s i o n pendulum a p p a r a t u s was used t o measure t h e i n - t e r n a l f r i c t i o n from 120K t o 500K w i t h a h e a t i n g r a t e o f ZK/min and v i b r a t i o n f r e q u e n c y around 1 Hz i n vacuum o f t o r r .

111. E x p e r i m e n t a l R e s u l t s 111-1 New Cold Work Peaks

A s shown i n F i g . 1, i n t h e low carbon s t e e l , t h e Snoek and t h e S-K peak can b e s e e n f o r t h e a s - n o r m a l i z e d and 20% t e n s i l e s t r a i n e d specimens. For t h e a s c o l d - r o l l e d specimens a new peak around 220K ('1 Hz) was o b s e r v e d and t h e Snoek peak was d i s a p p e a r e d .

I n t h e i n t e r s t i t i a l f r e e s t e e l , n e i t h e r t h e Snoek peak n o r t h e S-K peak was o b s e r v e d f o r t h e a s n o r m a l i z e d and a s t e n s i l e s t r a i n e d specimens. I t i t t h e r e f o r e c e r t a i n t h a t no s o l u t e C and N i s p r e s e n t i n t h e m a t r i x o f t h i s s t e e l i n d e e d . On t h e o t h e r hand, i n t h e a s - c o l d - r o l i e d i n t e r s t i t i a l f r e e s t e e l , two p e a k s were o b s e r v e d a t 170K and 220K r e s p e c t i v e l y , a s shown i n Fig. 2. These two p e a k s can b e s e e n c l e a r l y when background i s s u b t r a c t e d and p l o t t e d , a s d e m o n s t r a t e d i n Fig. 3.

The o c c u r r e n c e o f t h e s e p e a k s h a s n o t been r e p o r t e d y e t . I t s e e m t h a t t h e heavy c o l d work i s a n e c e s s a r y c o n d i t i o n t o cause t h e s e new p e a k s .

1 1 1 - 2 A c t i v a t i o n Energy

The a c t i v a t i o n e n e r g i e s f o r e a c h o f t h e new peaks o f i n t e r s t i t i a l f r e e s t e e l were c a l c u l a t e d u s i n g E q u a t i o n (1).

2 4 1 1

H=kfln (

I / ( %

-

-1

(1)

where k i s t h e Boltzmalln c o n s t a n t , T l and T2 a r e t h e t e m p e r a t u r e s a t

I h e c a l c u l a t e d r e s u l t s a r e shown i n Tabie 2.

I n Fig. 3 t h e d o t s show the e x p e r i m e n t a l d a t a and t h e s o l i d c u r v e s were p l o t t e d u s i n g t h e d a t a c a l c u l a t e d by E q u a t i o n ( 2 ) .

1 1

Q

.

Sech (H/k

(T

- f))

where T i s t h e peak t e m p e r a t u r e P P

I t can b e s e e n t h a t b o t h o f t h e p e a k s e x p r e s s a s s i n g l e r e l a x a t i o n p e a k s (Debye p e a k s ) .

111-3 Amplitude E f f e c t

F i g . 3 shows t h e i n t e r n a l f r i c t i o n c u r v e s measured u n d e r d i f f e r e n t s t r a i n a m p l i t u d e f o r t h e a s - c o l d - r o l l e d i n t e r s t i t i a l f r e e specimens. The peaks show t h e anomalous dependence o f s t r a i n a m p l i t u d e . ' h e v a r i a t i o n o f t h e peak h e i g h t d e t e r - mined a t ~ r a r i o u s s t r a i n a m p l i t u d e i s shown i n F i g . 4. As can be s e e n i n t h i s f i g u r e t h e peak h e i g h t o f t h e 220K peak d e c r e a s e s w i t h an i n c r e a s i n g s t r a i n a m p l i t u d e i n t h e r a n g e from 2 . 9 5 x 1 0 - ~ t o 1 . 8 7 ~ 1 0 - 4

.

However t h e h e i g h t o f 170K peak i n c r e a s e s i n i t i a l l y t h e n d e c r e a s e s w i t h t h e i n c r e a s i n g s t r a i n a m p l i t u d e . 111-4 Aging E f f e c t

F i g . 5 shows t h e I F s p e c t r u m o f t h e a s - c o l d - r o l l e d and . t h e aged specimens. I t can b e s e e n c l e a r l y from t h i s f i g u r e t h a t t h e peak h e i g h t o f 220K peak d e c r e a s e s w i t h t h e i n c r e a s i n g a g i n g t e m p e r a t u r e . F o r t h e 170K peak, a s i m i l a r e f f e c t w a s a l s o o b s e r v e d which can n o t be s e e n a s c l e a r a s t h a t o f 220K peak shown i n t h i s f i g u r e . From t h i s f i g u r e i t can a l s o be n o t i c e d t h a t t h e peak t e m p e r a t u r e o f t h e 220K and 170K p e a k s i n c r e a s e s w i t h an i n c r e a s i n g a g i n g t e m p e r a t u r e .

?he peak h e i g h t and peak t e m p e r a t u r e o f t h e s e specimens were p l o t t e d a s a f u n c t i o n o f a g i n g t e m p e r a t u r e a s shown i n F i g . 6 a and Fig. 6b, r e s p e c t i v e l y . I t

can b e s e e n from F i g u r e 6 a t h a t t h e peak h e i g h t a p p r o a c h e s t o z e r o a s a g i n g t e m p e r a t u r e was i n c r e a s e d up t o 498K f o r 220K peak and 448K f o r 170K peak. The peak t e m p e r a t u r e o f b o t h two peaks i n c r e a s e s w i t h i n c r e a s i n g a g i n g t e m p e r a t u r e a s shown i n F i g . 6h.

I V . D i s c u s s i o n

So f a r , few d i s c u s s i o n s have b e e n made i n t h e e a r l i e r p u b l i s h e d a r t i c l e s on t h e 170K and 220K peaks which were found i n t h e p r e s e n t s t u d y . I t can b e s e e n from F i g s . 1 through 3 t h a t t h e r e is almost no new peak f o r t h e as-normalized and t h e a s - t e n s i l e - s t r a i n e d specimens, b u t , pronounced new peaks e x i s t i n t h e 70% c o l d - r o l l e d specimens. I t means t h a t t h e heavy p l a s t i c d e f o r m a t i o n i s n e c e s s a r y t o g e t t h i s k i n d o f new p e a k s .

Some i m p o r t a n t f a c t o r s s u c h a s t h e w e l l - d e v e l o p e d d i s l o c a t i o n c e l l s , t h e c o l d - r o l l e d t e x t u r e , t h e h i g h i n t e r n a l r e s i d u a l s t r e s s a n d / o r o t h e r d e f e c t s g e n e r a t e d i n t h e h e a v i l y deformed m a t e r i a l s h o u l d b e c o n s i d e r e d b e f o r e a f u l l u n d e r s t a n d i n g is e s t a b l i s h e d . However, t h e g e n e r a t i o n mechanisms o f t h e s e new p e a k s s h o u l d b e d i f f e r e n t from t h e S-K p e a k , s i n c e t h e new peaks d i d a p p e a r i n t h e i n t e r s t i t i a l - f r e e specimens i n which no Snoek peak and no S-K peak were o b s e r v e d , s e e F i g . 2 . I t means t h a t t h e i n t r i n s i c motion o f d i s l o c a t i o n s can be r e s p o n s i b l e f o r t h e new p e a k s .

I n o r d e r t o e x p l a i n t h e main c h a r a c t e r i s t i c s o f t h e s e new p e a k s , t h e g e n e r a - t i o n mechanisms a r e c o n s i d e r e d i n t e r m s o f t h e i n t r i n s i c motion o f d i s l o c a t i o n s by which h i g h d e n s i t y o f k i n k p a i r s were a c t e d by h i g h i n t e r n a l r e s i d u a l s t r e s s , which can b e d i s c u s s e d a s f o l l o w s :

1) The Anomalous Amplitude E f f e c t s

Some kink p a i r s can b e a n n i h i l a t e d w i t h o t h e r k i n k p a i r s d u r i n g t h e I F mea- surement due t o t h e a c t i o n o f t h e a p p l i e d s t r e s s . S i n c e t h e d i s t a n c e among t h e k i n k s can be v e r y s m a l l u n d e r t h e c o o r p e r a t i v e a c t i o n o f t h e h i g h i n t e r n a l r e s i d u a l s t r e s s and t h e a p ~ l i e d s t r e s s . The q u a n t i t i e s o f t h e a n n i h i l a t e d k i n k s s h o u l d be i n c r e a s e d when t h e s t r a i n a m p l i t u d e i s

i n c r e a s e d d u r i n g t h e I F measurement, meanwhile, t h e r e l a x a t i o n s t r e n g t h i s d e c r e a s e d .

2) A c t i v a t i o n Energy and Aging E f f e c t

According t o t h e t h e o r y o f S e e g e r ( 7 ) , t h e k i n k - p a i r f o r m a t i o n e n t h a l p y (tikp) i s d e t e r m i n e d by,

where Hk i s t h e a c t i v a t i o n e n e r g y f o r a s i n g l e k i n k formation, a is t h e h e i g h t o f a s i n g l e k i n k , b i s t h e d i s l o c a t i o n s t r e n g t h , SZ1 i s t h e p r e l o g a - r i t h m i c f a c t o r o f t h e e l a s t i c p a r t o f t h e d i s l o c a t i o n l i n e - t e n s i o n and t h e a is t h e s h e a r s t r e s s . The a can be c o n s i d e r e d a s t h e sum o f i n t e r n a l r e s i d u a l s t r e s s and t h e a p p l i e d s t r e s s . I n a d d i t i o n t o t h e i n t e r n a l r e s i - d u a l s t r e s s , some s p e c i a l d i s l o c a t i o n c o n f i g u r a t i o n may a l s o he produced d u r i n g heavy p l a s t i c d e f o r m a t i o n , t h e r e f o r e , t h e k i n k - p a i r f o r m a t i o n e n t h a l p y can be d i f f e r e n t from t h a t o f a-peak and y-peak.

I t can be n o t i c e d t h a t , a c c o r d i n g t o E q . ( 3 ) , t h e i n c r e a s e s w i t h de- c r e a s i n g a . 7 h e r e f o r e . one can e x p e c t t h a t t h e a g i n g t r e a t m e n t o f t h e s p e c i - mens will reduce the^ and t h u s i n c r e a s e t h e Hkp and t h e peak t e m p e r a t u r e s , a s shown i n F i g s . 5 and 6 ( b ) .

There a r e s t i l l some q u e s t i o n s l e f t b e h i n d t h e mechanisms proposed above; s u c h a s t h e v a l u e s o f p r e e x p o n e n t i a l t i m e c o n s t a n t ( r ), s e e Table 1 , a r e q u i t e h i g h f o r t h e k i n k - p a i r f o r m a t i o n i n m e t a l s . B e s i d e s , t h e O e f f e c t s o f s u b s t i t u t i o n a l atoms a n d / o r c o l d r o l l e d t e x t u r e on t h e d i s l o c a t i o n motion were n o t d i s c u s s e d i n t h i s p a p e r . I t would be i n t e r e s t i n g t o c l a r i f y t h e e f f e c t s o f t h e s e f a c t o r s on t h e mechanisms o f new peaks r e p o r t e d i n t h i s s t i ~ d y i n t h e f u t u r e .

JOURNAL

DE

PHYSIQUE V. Conclusion

( 1 ) A new peak a t 212K (-1.OHz) f o r low carbon s t e e l and two p e a k s a t 170K and 220K ('1.3Hz) f o r i n t e r s t i t i a l f r e e s t e e l were o b s e r v e d .

(2) These k i n d s o f peaks a p p e a r e d o n l y i n t h e c o n d i t i o n t h a t specimens were heavy cold-worked s u c h a s r o l l i n g f o r 70% r e d u c t i o n .

( 3 ) Both peaks a r e s i n g l e r e l a x a t i o n p e a k s , t h e a c t i v a t i o n e n e r g y o f 170K peak and 220K peak f o r i n t e r s t i t i a l f r e e s t e e l a r e 0.21ev and 0.28ev r e s p e c - t i v e l y by o u r measurement.

(4) Both p e a k s o f i n t e r s t i t i a l f r e e s t e e l e x h i b i t anomalous dependence o f s t r a i n a m p l i t u d e .

(5) Both peaks o f i n t e r s t i t i a l f r e e s t e e l e x h i b i t an a g i n g e f f e c t , t h e peaks a r e d i s a p p e a r e d a f t e r aged a t 498K and 448K f o r t h e 220K peak and t h e 170K peak r e s p e c t i v e l y . The peak t e m p e r a t u r e s s h i f t t o h i g h e r t e m p e r a t u r e s i d e w i t h i n c r e a s i n g a g i n g t e m p e r a t u r e s

( 6 ) The c h a r a c t e r s o f t h e s e peaks can be i n t e r p r e t e d i n t e r m s o f

i n t r i n s i c motion o f d i s l o c a t i o n w i t h h i g h kink p a i r d e n s i t y u n d e r a c t i o n o f h i g h r e s i d u a l s t r e s s .

R e f e r e n c e s

1 . R. H. Chamber, P h y s i c a l A c o u s t i c s , Vol. i I I A , Academic P r e s s , New York (1966) p . 123.

2. G. F a n t o z z i and I . G. R i t c h i e , J. P h y s i q u e , 4 2 (1981), C5-3.

3 . A. S e e g e r and B. S e s t a k , S c r i p t a M e t a l l . ,5 (1971), p . 875.

4. M. Shimada and K. Sakamoto, S c r i p t a M e t a l l . , 1 3 (1979), p . 1177.

5 . T. S. KC, S c r i p t a M e t a l l . , l 6 (1982), p.225.

6 . Schoek G . , S c r i p t a M e t a l l . , l 6 (1982). p . 233.

7. A. S e e g e r , J . P h y s i q u e , 42 (1981), C5-201.

Table 1 Chemical c o m p o s i t i o n (wt%, Fe: b a l a n c e )

Temperature ( K )

F i g . 1 I n t e r n a l f r i c t i o n f o r d i f f e r e n t t r e a t e d specimens o f low carbon s t e e l .

( s t r a i n amp1 i t u d e = 2 . 7 5 ~ 1 0 - ~ )

F i g . 2 I n t e r n a l f r i c t i o n f o r

d i f f e r e n t t r e a t e d specimens o f i n t e r s t i t i a l f r e e s t e e l .

( s t r a i n a m p l i t u d e = 2 . 9 5 x 1 0 - ~ )

T a b l e 2. A c t i v a t i o n e n e r g y and peak t e m p e r a t u r e of t h e new p e a k s

TEMPERATURE,

K

TEMPERATURE.

K

Tp (K)

CU

* u,

...

a

N

L a - *..-.

^{. e....- em-.... L (U}

-....-.

.. _...

< 4 <

- by Equ. (2)

0

-

(3

-3 9

O N -

-

x

9 ' " -

7 X

...

v . . . . . . .

.

...

- "...

_..*..-*.

."- ..

-

by Equ.<2)

-

120 170 220 2iU 320 120 170 220 270 320

TEMPERATURE

.

^K TEMPERATURE ^I

K

(C) (0)

E ( e v ) 0 . 2 3 0 . 2 8

p e a k - 1 o f A a l l o y 170

'07

-

'i ^{0 - -}

120 170

220

270 120 170 220 270 320

X

N ' J - c u -

*.

<

(3

w 0 - a -

x 7 0 - -

F i g . 3 I n t e r n a l f r i c t i o n a n d o s c i l l a t i o n f r e c l u e n c i e s o f i n t e r s t i t i a l f r e e s t e e l _ 5 measured a t d i f f e r e n t s t r a i n ampl5tutle. (A) s t r a i n a m p l i t u d e = 2 . 9 5 x 10

( B ) s t r a i n a m p l i t u d e = 4.70 x 10- ( C ) s t r a i n a m p l i t u d e = 9.37 x lo-' (D) s t r a i n a m p l i t u d e = 1 . 8 7 x 10-4

-

-

peak-2 o f A a l l o y 220

..-... _.... ....

.I.. ......a.

... ... _{-.. .-.}

- by Equ.(2)

-

CU

=? -

N

L Z -

<

0

"$a

-

^X

lo -

... .... ... ... ... - .. ... .... _{.... ...}

<

- by Equ. (2)

- -

-

C8-154 JOURNAL DE PHYSIQUE

30

0 4 8 12 16 20

Strain Amplitude ( x lo4 )

I . the l70K peak

2. the 220 K peak

2 *

I 4

F i g . 4 V a r i a t i o n o f Peak h e i g h t w i t h d i f f e r e n t s t r a i n a m p l i t u d e f o r i n - t e r s t i t i a l f r e e s t e e l

F i g . 5 E f f e c t o f a g i n g tempera- t u r c on t h e I F s p e c t r u m f o r i n t e r s t i t i a l f r e e s t e e l .

Fig. 6 E f f e c t o f a g i n g t e m p e r a t u r e on (.I) t h e ~ e a k h e i g h t and ( b ) t h e peak tem- p e r a t u r e o f 220K and 170K p c a k s f o r i n t e r s t i t i a l f r e e s t e e l .