. /

/ \

\\I

B U C K I N G C O l ~ P I C K U P C O I L

S A M P L E

T H E R M O C O U P L E

..,,,_ l ,.m,ol fl M

fl M A G N E T

T

R E C O R D E R

Fig. 1 - E x p e r i m e n t a l a p p a r a t u s . Magne t i s a w a t e r - c o o l e d c o p p e r so leno id , 28.5 m m b o r e , c a p a b l e of p r o d u c i n g 130 kOe a t 9000 A, 400 V.

placed in a pickup coil in the cen te r of a high-f ie ld magnet , and the magnet ic field was set to a p rede- t e r m i n e d value. The in tegra ted output of the pickup coil, which is a d i rec t m e a s u r e of the magne t iza t ion of the sample and hence the amount of m a r t e n s i t e formed, was plotted d i rec t ly agains t the sample t em- p e r a t u r e dur ing the cooling. The magne t iza t ion axis was ca l ib ra ted us ing a sample of pure i ron . A set of expe r imen ta l curves for 410 s t a in l e s s is shown in Fig. 2. The M s t e m p e r a t u r e for each run was de t e r - mined by ext rapola t ing the l i nea r port ion of the curve to 0 pct m a r t e n s i t e . Fig. 3 shows the M s t em- pe ra tu r e s , de t e rmined in this way, as a funct ion of the applied field for both a l loys . It is c l ea r f rom the f igure that the effect of magnet ic field on the M s t em- pe ra tu r e is l i nea r up to at l eas t 130 kOe. (The de- magne t iz ing field co r r ec t ion is about 1 kOe max i mum and has been neglected. Eq. [4] of Sa tyanarayan e t al ,

which apparen t ly a t tempts to account for the demag- ne t iz ing field, is not co r r ec t when the applied field is large compared to the demagni t i z ing field). It is i nhe ren t in the m e a s u r i n g method used here that the

IO0

75

5o

25 0-

0 I 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0

T E M P E R A T U R E ( ~

F i g . 2 - - P e r c e n t m a r t e n s i t e v s t e m p e r a t u r e for 410 s t a i n l e s s s t e e l in v a r i o u s f i e l d s . C u r v e s t r a c e d d i r e c t l y f r o m x - y r e - c o r d e r p lo t s .

T a b l e I I , S u m m a r y o f Resu l ts

Magnetization* AT ~ I H cal

Alloy 4~cM, Gauss /, emu/mol M s, ~ AH' kOe AT' mol-K

Comp. 2 20.600 11,600 321 0.28 1.0 Comp. t 21,300 12,100 lO! 0.31 0.9 52100 21,300 12,100 121 0.34 0.8

410 17,700 10,000 342 0.15 1.6

*Martensite magnetizatio n assumed equal to the corresponding ferdte.

3 7 0

3 6 0

350

3 4 0 o LLJ W 17'0

I--

160 uJ 13_

1 5 0 t.iJ I--

1 4 0

1 3 0

1 2 0 0

I I I I [ 1

- e

J

. y I I 1 I

2 0 4 0 6 0 8 0

F I E L D , KOe

I I I 0 0 1 2 0 140

Fig. 3--Effect of m a g n e t i c f ie ld on the m a r t e n s i t e s t a r t ~14 s ) t e m p e r a t u r e of two a l l o y s t e e l s .

1 4 - *

1.2 �9

I.O --

I O 2O

I I I l I

4 1 0

l I

e - -

I I I L I I 4 0 6 0 8 0 I 0 0 1 2 0 1 4 0

F I E L D , K O e

Fig . 4 - - R a t e of f o r m a t i o n of m a r t e n s [ r e in 410 s t a i n l e s s s t e e l v s m a g n e t i c f ie ld .

z o I- < 2 . 0

~ ~o

I I I J

J J -- / * Re f . 6 --

/ /

/ Ref. I /

-- comp. 2 o/" " / R e f I * 4 1 0

/ comp. / . /

/ /

/ /

/ /

/

/ I I I 0 0 0 5 1.0 1 5 2 . 0

$--a E N T R O P Y OF T R A N S F O R M A T I O N /kS ,cal/moI-K

F ig . 5 - -Ra te of f o r m a t i o n of m a r t e n s i t e v s e n t r o p y of t r a n s - f o r m a t i o n . Un labe l l ed point is f r o m Ref. 6, for a s t e e l con- t a i n i n g 0.6 C, 4 Cr , 8 Ni, 3 Si, and 1 Mo.

720-VOLUME 7A, MAY 1976 METALLURGICAL TRANSACTIONS A

. /

/ \

\\I

B U C K I N G C O l ~ P I C K U P C O I L

S A M P L E

T H E R M O C O U P L E

..,,,_ l ,.m,ol fl M

fl M A G N E T

T

R E C O R D E R

Fig. 1 - E x p e r i m e n t a l a p p a r a t u s . Magne t i s a w a t e r - c o o l e d c o p p e r so leno id , 28.5 m m b o r e , c a p a b l e of p r o d u c i n g 130 kOe a t 9000 A, 400 V.

placed in a pickup coil in the cen te r of a high-f ie ld magnet , and the magnet ic field was set to a p rede- t e r m i n e d value. The in tegra ted output of the pickup coil, which is a d i rec t m e a s u r e of the magne t iza t ion of the sample and hence the amount of m a r t e n s i t e formed, was plotted d i rec t ly agains t the sample t em- p e r a t u r e dur ing the cooling. The magne t iza t ion axis was ca l ib ra ted us ing a sample of pure i ron . A set of expe r imen ta l curves for 410 s t a in l e s s is shown in Fig. 2. The M s t e m p e r a t u r e for each run was de t e r - mined by ext rapola t ing the l i nea r port ion of the curve to 0 pct m a r t e n s i t e . Fig. 3 shows the M s t em- pe ra tu r e s , de t e rmined in this way, as a funct ion of the applied field for both a l loys . It is c l ea r f rom the f igure that the effect of magnet ic field on the M s t em- pe ra tu r e is l i nea r up to at l eas t 130 kOe. (The de- magne t iz ing field co r r ec t ion is about 1 kOe max i mum and has been neglected. Eq. [4] of Sa tyanarayan e t al ,

which apparen t ly a t tempts to account for the demag- ne t iz ing field, is not co r r ec t when the applied field is large compared to the demagni t i z ing field). It is i nhe ren t in the m e a s u r i n g method used here that the

IO0

75

5o

25 0-

0 I 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0

T E M P E R A T U R E ( ~

F i g . 2 - - P e r c e n t m a r t e n s i t e v s t e m p e r a t u r e for 410 s t a i n l e s s s t e e l in v a r i o u s f i e l d s . C u r v e s t r a c e d d i r e c t l y f r o m x - y r e - c o r d e r p lo t s .

T a b l e I I , S u m m a r y o f Resu l ts

Magnetization* AT ~ I H cal

Alloy 4~cM, Gauss /, emu/mol M s, ~ AH' kOe AT' mol-K

Comp. 2 20.600 11,600 321 0.28 1.0 Comp. t 21,300 12,100 lO! 0.31 0.9 52100 21,300 12,100 121 0.34 0.8

410 17,700 10,000 342 0.15 1.6

*Martensite magnetizatio n assumed equal to the corresponding ferdte.

3 7 0

3 6 0

350

3 4 0 o LLJ W 17'0

I--

160 uJ 13_

1 5 0 t.iJ I--

1 4 0

1 3 0

1 2 0 0

I I I I [ 1

- e

J

. y I I 1 I

2 0 4 0 6 0 8 0

F I E L D , KOe

I I I 0 0 1 2 0 140

Fig. 3--Effect of m a g n e t i c f ie ld on the m a r t e n s i t e s t a r t ~14 s ) t e m p e r a t u r e of two a l l o y s t e e l s .

1 4 - *

1.2 �9

I.O --

I O 2O

I I I l I

4 1 0

l I

e - -

I I I L I I 4 0 6 0 8 0 I 0 0 1 2 0 1 4 0

F I E L D , K O e

Fig . 4 - - R a t e of f o r m a t i o n of m a r t e n s [ r e in 410 s t a i n l e s s s t e e l v s m a g n e t i c f ie ld .

z o I- < 2 . 0

~ ~o

I I I J

J J -- / * Re f . 6 --

/ /

/ Ref. I /

-- comp. 2 o/" " / R e f I * 4 1 0

/ comp. / . /

/ /

/ /

/ /

/

/ I I I 0 0 0 5 1.0 1 5 2 . 0

$--a E N T R O P Y OF T R A N S F O R M A T I O N /kS ,cal/moI-K

F ig . 5 - -Ra te of f o r m a t i o n of m a r t e n s i t e v s e n t r o p y of t r a n s - f o r m a t i o n . Un labe l l ed point is f r o m Ref. 6, for a s t e e l con- t a i n i n g 0.6 C, 4 Cr , 8 Ni, 3 Si, and 1 Mo.

720-VOLUME 7A, MAY 1976 METALLURGICAL TRANSACTIONS A

z e r o - f i e l d value of M, mus t be obtained by ex t r apo la - tion, s ince the m a r t e n s i t e wi l l not be magne t i zed and wi l l give no s ignal at z e r o f ie ld .

The e x p e r i m e n t a l r e su l t s , e x p r e s s e d both as in- c r e a s e in M s per kOe of f ie ld and as I H / L x T , a re given in Table II, along with o ther r e l evan t data. The equivalent data f rom Satyanarayan e t al is included in the table; the a g r e e m e n t is good. F o r c o m p a r i s o n of these r e s u l t s with o ther magne t ic expe r imen t s , and with va r ious e s t i m a t e s of AGe, To, and AGo, see the d i scuss ion of Sa tyanarayan e t a l .

The data below M s for the 410 s t a in l e s s w e r e ade- quate to d e t e r m i n e the ra te of m a r t e n s i t e fo rmat ion . The amount of m a r t e n s i t e i n c r e a s e d l inea r ly with de- c r e a s i n g t e m p e r a t u r e f rom about 10 to 50 pct m a r - t ens i t e . The ra te of fo rma t ion of m a r t e n s i t e was in- dependent of magne t ic field, as shown in Fig . 4, and in a g r e e m e n t with a t h e o r e t i c a l t r e a t m e n t as out l ined by Magee 4 which equates the ra te of nuclea t ion of m a r t e n s i t e to the f r ee energy d i f fe rence between aus ten i te and m a r t e n s i t e . Sa tyanarayan e t a l give a

�9 !

plot of m a r t e n s l t e fo rma t ion ra te v s ~xS3'-a for t h r ee al loy s t ee l s , which conf i rms the t h e o r e t i c a l p r ed i c - t ion by Brooks , Entwis t le , and Ib rah im 5 of a l inea r r e l a t ionsh ip . T h e i r graph is r ep roduced as F ig . 5, with an added point for the new data on 410 s t a in l e s s s t ee l . The new point c l e a r l y fa i l s to l ie on the l ine.

CONC LUSIONS

We have found that the m a r t e n s i t e s t a r t t e m p e r a - t u re i n c r e a s e s l inea r ly with f ie ld up to 130 kOe in two al loy s t e e l s . The r a t e of fo rma t ion of m a r t e n s i t e is not inf luenced by magne t ic f ield. N u m e r i c a l va lues fo r the entropy of t r a n s f o r m a t i o n have been obtained, and a r e in r easonab le a g r e e m e n t with o ther de t e rmina t i ons and e s t i m a t e s .

ACKNOWLEDGMENTS

P. J . F l a n d e r s helped us g rea t ly with the e x p e r i - men ta l a r r a n g e m e n t s , and the L abo ra to ry fo r R e s e a r c h on the S t ruc tu re of Mat t e r , U n ive r s i t y of Pennsylvania , p rov ided a c c e s s to the h igh- f ie ld equipment . The L a b o r a t o r y is suppor ted by the National Science Foundat ion. SKF Inc. of Ph i lade lph ia kindly provided s a m p l e s of 52100 s t ee l .

R E F E R E N C E S

1. K. R. Satyanarayan, W. Eliasz, and A. P. Miodownik: ActaMet., 1968, vol. 16, p. 877.

2. A. B. Greninger and A. R. Troiano: Trans. ASM, 1940. vol. 28, p. 537. 3. E. I. Estrin: Phys. Metals Metallogr., 1965. vol. 19. no. 6, p. 117. 4. C. L. Magee: in Phase Transformations, p. 118, ASM, Metals Park, Ohio, 1970. 5. R. Brook, A. R. Entwistle, and E. F. lbrahim: J. Iron Steellnst., 1960,

vol. 195. p. 292. 6. L. V. Voronchikhin and 1. G. Fakidov: Phys. Metals Metallogr., 1966, vol. 21,

no. 3. p. 119.

METALLURGICAL TRANSACTIONS A VOLUME 7A, MAY 1976-721