FERROMAGNETIC TRACES IN AUSTENITIC STAINLESS STEELS AT 4.2 K

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FERROMAGNETIC TRACES IN AUSTENITIC STAINLESS STEELS AT 4.2 K

K. Pieterman, A. Ketting, J. Geerse

To cite this version:

K. Pieterman, A. Ketting, J. Geerse. FERROMAGNETIC TRACES IN AUSTENITIC STAIN- LESS STEELS AT 4.2 K. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-625-C1-631.

�10.1051/jphyscol:19841127�. �jpa-00223597�

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JOURNAL DE PHYSIQUE

Colloque C1, suppl6ment au n o 1, Tome 45, janvier 1984 page Cl-625

FERROMAGNETIC TRACES IN AUSTENITIC STAINLESS STEELS AT

4 , 2

K

X. Pieterman, A. Ketting and J. Ch. Geerse

Dept. f o r Applied Physics, D e l f t University of TechnoZogy, Lorentzweg 1, 2628 CJ D e l f t , The netherlands

Resume

-

Dans c e t a r t i c l e , sont d e c r i t e s des mesures magnetiques q u i se r a p p o r t e n t m r s a c i e r s inoxydables de l a s e r i e ALSI 300

1

4,2

K.

I 1 a 6 t 6 examine j u s q u ' i i

quel p o i n t l e comportement magnetique des d i f f e r e n t $ types, 6 t a i t i n f l u e n c e p a r soudage ou p a r frequents r @ f r o i d i s s e m e n t s , j u s q u ' i i 4,2 K. De plus, l ' i n f l u e n c e de d i f f e r e n t e s a d d i t i o n s s u r l a s t a b i l i t e de l a s t r u c t u r e a u s t e n i t i q u e a e t 6 conside- ree. Des preparations examinees, une grande p a r t i e (303, 304, 310, 316L, 316Ti, 321) semblait montrer une c e r t a i n e forme de comportement ferro-magnetique, t a n d i s que seulement peu d ' a u t r e s (X6CrNi 1811,316LN) r e s t a i e n t compl6tement paramagnetiques 1 4,2

K.

A b s t r a c t

-

This paper describes magnetisation experiments on austeni t i c s t a i n l e s s s t e e l s o f A I S I 300 s e r i e s a t 4.2

K.

The i n f l u e n c e o f welding and c y c l i c c o o l i n g on t h e i r magnetic behaviour was studied, as was t h e i n f l u e n c e o f t r a c e a d d i t i o n s f o r s t a b i l i z i n g t h e p r o p e r t i e s o f s t a i n l e s s s t e e l . A l a r g e number o f samples has been studied, most o f them showed ferro-magnetic t r a c e s a t 4.2 K (303, 304, 310, 316L, 316Ti, 321). Only a few remain f u l l y paramagnetic (X6CrNi 1811, 316LN) a t 4.2 K.

INTRODUCTION

The s t a b i l i t y o f a u s t e n i t i c s t a i n l e s s s t e e l s has been s t u d i e d e x t e n s i v e l y i n t h e pastl ' 2 ' 3 '4'5'

.

I t i s w e l l known t h a t most o f them are unstable below room tem- p e r a t u r e f o r t h e t r a n s i t i o n i n t o t h e m a r t e n s i t i c phase. Because t h e a u s t e n i t i c phase i s paramagnetic and t h e m a r t e n s i t i c phase i s ferromagnetic, t h e magnetic c h a r a c t e r o f t h e s t e e l w i l l change. Whether such a t r a n s i t i o n occurs depends very c r i t i c a l l y on t h e chemical composition o f the s t e e l , so d i f f e r e n t heats o f t h e same type o f s t a i n l e s s steeT may show u n l i k e magnetic behaviourl. When using s t a i n l e s s s t e e l s i n t h e neighbourhood o f magnetic f i e l d s i t i s important t o know t h e i r magnetic beha- v i o u r , e s p e c i a l l y when h i g h homogeneities are r e q u i r e d .

I n t h a t respect i t i s a l s o necessary t o know t h e i n f l u e n c e o f welding on t h e magnetic c h a r a c t e r o f t h e s t a i n l e s s s t e e l . I n t h i s paper maqnetisation measurements a r e r e p o r t e d on welded and unwelded samples o f t h e types

AISI

303, 304, 304N, 310, 310S, 316, 3161, 316LN, 316Ti and 321 a t 4.2

K.

PREPARATION OF THE SAMPLES

The samples were machined o u t o f bars received from d i f f e r e n t manufacturers i n t o c y l i n d e r s o f 10 mm diameter and 10 mm long. For each type o f s t a i n l e s s s t e e l a l s o two c y l i n d e r s o f 10 by

5

mm were machined and bounded together by fusion-welding. Welded and unwelded samples were machined o u t o f the same bar. Chemical ana- l y s i s of each specimen was c a r r i e d out; t h e r e s u l t s a r e l i s t e d i n t a b l e

l.

Out o f t h e 32 samples used i n t h i s study 22 were annealed a t 1 0 8 0 ~ ~ f o r 90 minutes and quenched i n water. The magnetisation o f 3 samples was measured b e f o r e and a f t e r heat treatment. The amount o f ferromagnetism was reduced, b u t o n l y one o f them (316) was f u l l y paramagnetic a f t e r heat treatment, i n d i c a t i n g a pure a u s t e n i t i c s t r u c t u r e

(see t a b l e

2 ) .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841127

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C1-626 JOURNAL

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PHYSIQUE

Table 1. Chemical a n a l y s i s o f the measured s t a i n l e s s s t e e l samples.

(Compositions i n w t %)

A l l o y n a m e

C C r

Ni Mn Mo T i S i Cu

S

303 0.062

304

(a)

0.055 3 0 4 ( b ) 0.067

304

N

' 0.075

310 0.066

310

S

0.062

316

(a)

0.070 316

(b)

0.034 316

( c )

0.044

316 L 0.033

316 LN 0.032

316

T i

0.055

X6CrNi

1811 0.072 321

(a)

0.066 321 ( b ) 0.057

Table

2.

Magnetic s u s c e p t i b i l i t y and s a t u r a t i o n magnetisation o f d i f - f e r e n t specimens a f t e r f i r s t c o o l i n g a t

4.2

K

A1 1 oy name ~ o n d i

t i

onX xo

X,

h a t

(kA/m)

303

AWQ

14.5 5.5

1.1

304

(a) AM

22.7 4.2 1.5

304

(b) AM

7.1 7.1 0

304

( c j

304 N 310 310 S 316

(a)

316 ( 6 ) 316

( c j

316

( c j

316 L 316 LN 316

T i

323

(a)

321

( a )

321

(b)

"AM =

As machined

AWQ

=

annealed a t

1 0 8 0 ~ ~

f o r

90

minutes, then water quenched

EXPERIMENTAL

PROCEDURE

Measurements concerning t h e magnetic s u s c e p t i b i l i t y x

=

( ) T . have been made aM a t

4.2 K

i n magnetic f i e l d s up t o 1 T. The specimens were moungd ~ n s i d e a sample h o l d e r t h a t f i t s i n an ac magnetometer surroundedby a superconducting magnet.

The sample holder c o u l d be e a s i l y taken o u t o f t h e c r y o s t a t f o r quick changing t h e

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sample. Cool-down time f o r t h e samples was t y p i c a l l y

2

minutes, they were h e l d a t l i q u i d helium temperature f o r about

15

minutes t o sweep the magnetic f i e l d t o

1

T and back and measure t h e magnetic s u s c e p t i b i l i t y . Afterwards t h e samples were a l - lowed t o warm up t o room temperature i n a i r .

C y c l i c c o o l i n g e f f e c t s were s t u d i e d on

13

samples by c o o l i n g them down once every day d u r i n g a p e r i o d o f

14

days. Holding t i m e i n l i q u i d helium was

15

minutes each time.

RESULTS

N o n - l i n e a r i t y o f t h e magnetisation curves i n d i c a t e s ferromagnetic t r a c e s i n t h e s t a i n l e s s s t e e l . I n t h e case o f t h e unwelded samples t h i s i s caused by t h e f o r - mation o f a' martensite. The s a t u r a t i o n magnetisation Msat o f t h e ferromagnetic p a r t i n d i c a t e s t h e amount o f a' m a r t e n s i t e . I n t h e case o f t h e welded samples, f e r - romagnetism i s caused by m a r t e n s i t e formation on c o o l i n g and welding by 6 - f e r r i t e and carbide formation induced by t h e welding process. Ferromagnetism induced by welding o n l y can be found by s u b s t r a c t i n g t h e measured Msat values (Msatw

-

Msatu

i n t a b l e

3).

Table

3.

Magnetic s u s c e p t i b i l i t y and s a t u r a t i o n magnetisation o f d i f f e r e n t specimens a f t e r welding a t

4.2

K.

A1 l o y name Condition

xo X,

Msat Msatw- Msatu ~ t a b i l

i

tyX

(kA/m) (kA/m) on welding

303 25.1 7.4 1.7 0.6 +

304

(a)

AM 47.3 6.4 3.3 1.8 +

304

(b) AM

22.2 7.2 1.3 1.3 +

304

( c ) AM

93.2 9.6 6.1 -5.5 +

304

N A WQ

8.2 6.8 0.1 0 +++

3 10

AWQ

246 37.0 22.0 1.2 +++

310

S AM

92.0 20.0 14.2 4.4 ++

316

(a) AM

14.5 9.7 0.3 0.3 +

316

(b) AWQ

16.7 16.7 0 0 ++++

316

( c )

13.0 13.0 0 0 ++++

316

L AWQ

45.6 12.3 2.2 -0.2 ++

316

LN

11.8 11.8 0 0 ++++

316

T i A

WQ 31.0 12.9 1.6 -0.3 ++

X6CrNi

1811

AWQ

9.9 9.9 0 0 ++++

321

( a ) AWQ

25.0 15.1 2.4 -2.9 +

321

(b)

A WQ 38.7 14.9 2.5 -0.2 ++

+

⁼^poor

++

= reasonable

+++

= good

++++

= excel l e n t

FERROMAGNETIC TRACES AT FIRST COOLING

The r e s u l t s o f t h e magnetisation o f t h e unwelded samples on f i r s t c o o l i n g t o

4.2 K

are l i s t e d i n t a b l e

2; x0

i s the magnetic s u s c e p t i b i l i t y a t zero a p p l i e d f i e l d , X , a t maximum f i e l d where t h e ferromagnetic p a r t i s s a t u r a t e d and

M s a t

i s t h e s a t u r a t i o n magnetisation. Out o f

16

measured specimens o n l y

6

showed f u l l y paramag- n e t i c behaviour on f i r s t cooling. Important i s t h a t a l l o f t h e untraced

316

type specimens remain f u l l y a u s t e n i t i c , where o n l y one o f t h e

304

samples showed no ferromagnetism. Also t h e

316LN

specimen and t h e s p e c i a l composite

X6CrNil811

r e - mained a u s t e n i t i c . The

304N

type shows a s l i g h t l y n o n - l i n e a r behaviour, although i t i s r e p o r t e d t o be f u l l y paramagnetic i n t h e The r e s u l t s i n d i c a t e

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'21-628 JOURNAL

DE PHYSIQUE

t h a t i n t h e case of t h e 304 type t h e o c c u r r i n g o f y

-

a' t r a n s f o r m a t i o n i s more c r i - t i c a l l y dependent o f t h e chemical composition than i n t h e case o f t h e 316 type o f s t a i n l e s s s t e e l . Comparing t h e chemical analyses w i t h t h e magnetic behaviour o f t h e 304 specimens one may conclude t h a t a low carbon t o g e t h e r w i t h a h i g h chromium con- t e n t enhance m a r t e n s i t e formation. Also t h e i n f l u e n c e o f t h e a u s t e n i t e s t a b i l i z i n g Mn a d d i t i o n i s important as i s seen i n t h e case o f sample 304(c) w i t h a h i g h value f o r MSat and a low Mn content.

FERROMAGNETIC TRACES INDUCED BY WELDING

Table 3 shows t h e r e s u l t s o f t h e measurements o f t h e welded samples. The chemi- c a l composition i s t h e same as f o r t h e unwelded samples. A f t e r welding t h e number o f specimens t h a t remained f u l l y paramagnetic decreased t o f o u r (316(b), 316(c),

X6CrNi 1811 and 316LN). The f i r s t t h r e e showed a s l i g h t decrease i n magnetic suscep- t i b i l i t y (resp.

5,

4 and 2%) and o n l y t h e 316 LN type o f s t a i n l e s s s t e e l showed no d i f f e r e n c e whatsoever. A l a r g e increase of t h e ferromagnetic p a r t was found f o r t h e samples 303 and 304 whereas sample 304(c) showed a l a r g e decrease o f t h e ferromag- n e t i c p a r t .

T h i s i n d i c a t e s again t h e r a t h e r u n s t a b l e c h a r a c t e r o f these types o f s t a i n l e s s s t e e l and t h e l a r g e dependence o f t h e magnetic c h a r a c t e r on thermal h i s t o r y and chemical composition. Only t h e 304N type may be regarded as f a i r l y s t a b l e w i t h and w i t h o u t welding.

With one exception (303) a l l o f t h e annealed samples showed decreasing magnetisation a f t e r welding. Only i n one case (304(c)) o f t h e "as-machined" samples, i n d i c a t e d i n t a b l e 3 by AM ("as-machined"), showed decreasing magnetisation. Table 3 a l s o gives t h e s t a b i l i t y on welding o f t h e d i f f e r e n t types o f s t a i n l e s s s t e e l w i t h r e s p e c t t o t h e changes i n magnetisation. The Mo s t a b i 1 is e d types 316 have excel l e n t p r o p e r t i e s i n t h i s r e s p e c t except f o r sample 316(a) which may g i v e b e t t e r r e s u l t s when annealed.

The low carbon s t e e l 316L i s s t a b l e on welding b u t i t showed ferromagnetism on f i r s t c o o l i n g .

S u r p r i s i n g l y t h e X6CrNi 1811 sample w i t h o u t Mo a d d i t i o n showed very good r e s u l t s . It remains f u l l y paramagnetic and has e x c e l l e n t s t a b i l i t y .

The so c a l l e d weldable s t e e l s w i t h T i a d d i t i o n o f t h e types321 and 316Ti showed l e s s s t a b i l i t y than t h e 316 and 316LN types. Even a f t e r annealing they showed ferromagne- t i c t r a c e s and must be regarded as u n s t a b l e as was s t a t e d i n r e f .

7 .

Fig.

1

shows some t y p i c a l l y magnetisation curves f o r welded and unwelded specimens.

FERROMAGNETIC TRACES ON CYCLIC COOLING

C y c l i c c o o l i n g e f f e c t s have been s t u d i e d on 13 d i f f e r e n t specimens: 304(d), 304N, 310, 310S, 316(a), 316(b), 316(c), 316L, 316LN, 316Ti, X6CrNi 1811, 321(a), 321(b). O f t h e measured specimens f o u r showed i n c r e a s i n g ferromagnetism on c y c l i c c o o l i n g namely: 304(d), 304N, 310 and 321(b). The r e s u l t s a r e shown i n f i g u r e 2.

The t h r e e types o f s t a i n l e s s s t e e l specimens showed d i f f e r e n t behaviour on c y c l i c cooling. Both 304 types showed no e f f e c t on t h e f i r s t f o u r cooldown runs t o 4.2 K.

A f t e r t h a t a sharp r i s e i n M

at

was detected. 304 was r e p o r t e d unstable1, b u t c y c l i c c o o l i n g e f f e c t s on 304N sampfes are n o t published as f a r as we know. I n r e f . 2, 4, 6 and 8 304N was r e p o r t e d s t a b l e . Again we must conclude t h a t t h e magnetic character o f these s t e e l s i s u n p r e d i c t a b l e because o f t h e wide commercial composition l i m i t s . Sample 310 shows a s l i g h t increase o f ferromagnetism from t h e f i r s t c o o l i n g c y c l e onwards which remains t h e same a f t e r 10 cycles. The e f f e c t i s r a t h e r small, o n l y a

2%

increase o f Msat a f t e r 10 cycles. I n r e f . 2 i t was r e p o r t e d s t a b l e .

Sample 321(b) shows a l a r g e increase o f M s a t between the f i r s t and t h e second cooldown and a s l i g h t f u r t h e r increase i n t h e n e x t 9 cooldown runs. This e f f e c t was a l s o r e p o r t e d i n r e f . 2. The o t h e r specimen o f t h i s type o f s t e e l (321(a)) showed no e f - f e c t s on c y c l i c c o o l i n g as was r e p o r t e d i n r e f .

1.

The d i f f e r e n c e between these two samples c o u l d be explained by l o o k i n g a t t h e chemical composition: sample 321(a) c o n t a i n s t w i c e as much of t h e a u s t e n i t e s t a b i l i s i n g Mn as sample 321(b). T h i s was e x a c t l y t h e case w i t h t h e samples o f L a r b a l e s t i e r and King2 (Mn0.77, u n s t a b l e ) and o f Reed and M i k e s e l l ' (Mn2.0, s t a b l e ) .

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Fig. 1 - Magnetisation curves of d i f f e r e n t s t a i n l e s s s t e e l samples. Straight l i n e -

before welding, dotted l i n e - a f t e r welding.

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DE

PHYSIQUE

Fig. 2 - Magnetisation of d i f f e r e n t specimens as function of the num- ber of cooling cycles N between room temperature and

4.2

K. Table

4.

Summary of r e s u l t s

A1 1 oy name ferromagnetic traces

on f i r s t cooling on welding on c y c l s cooling

303

+ + x

304

( a ) + + x

304

( b ) - +

^f

304

( c ) + +

x

304N

+ - +

310

+

^t

+

310s

+ + -

316

( a ) - + -

316

(b) - - -

316

( c ) - - -

316L

+ + -

316LN

- - -

316Ti

+ + -

X6CrNi 1811

- - -

321

( a ) + + -

321

(b) + + +

+

=

detected

-

⁼

not detected

x =

nbt tested

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CONCLUSIONS

Table 4 summarizes t h e r e s u l t s o f t h e magnetisation measurements on 16 d i f f e - r e n t types o f s t a i n l e s s s t e e l . Four samples remained paramagnetic under a l l circum- stances: 316(b), 316(c), 316LN and X6CrNi 1811. These types may be regarded as s t a b l e a u s t e n i t i c s t a i n l e s s s t e e l s . Sample 316(a) showed some ferromagnetism on welding probably due t o t h e low Mo content.

I n t h e case o f t h e 303, 304 and 321 samples

we

can conclude t h a t one cannot be sure about t h e i r magnetic c h a r a c t e r i n advance. The knowledge o f t h e chemical composition c o u l d be h e l p f u l t o p r e d i c t whether ferromagnetic t r a c e s w i l l occur, b u t i n general when magnetic behaviour i s c r i t i c a l one should n o t use these types o f s t a i n l e s s s t e e l unless exact magnetisation measurements has been done.

I n t h e case o f t h e 310 specimens a b s o l u t e magnetisation i s f a i r l y l a r g e . There i s a p o s s i b i l i t y o f a ferromagnetic t r a n s i t i o : i n t h e a u s t e n i t i c phase caused by t h e l a r g e amount o f Ni i n these types o f s t e e l

.

That leaves o n l y t h e 316LN type o f s t e e l t o be p e r f e c t l y s t a b l e (no evidence o f t h e c o n t r a r y i s known i n t h e l i t e r a t u r e ) and t h e t y p e X6CrNi 1811, o f which we a r e n o t aware o f any r e s u l t s published before.

ACKNOWLEDGEMENT

The authors wish t o thank P r o f .

H.

Postma f o r h i s advice and encouragement.

They a r e a l s o g r a t e f u l t o Mr. G.J. Maanenschijn and M r . P.F. C o l i j n o f t h e Metal- l u r g i c a l Department f o r analyzing t h e samples and h e l p f u l discussions. The t e c h n i c a l assistance o f Mr. W. den Braver a t t h e p r e p a r a t i o n o f the experimental set-up i s g r a t e f u l l y acknowledged.

REFERENCES

1.

REED R.P. and MIKESELL R.P., Adv. Cryog. Eng. 4 (1960) 84.

2. LARBALESTIER D.C. and KING H.W., Cryogenics 13-(1972) 160.

3. WARNES L.A.A. and KING H.W., Cryogenics 16 ( m 7 6 ) 473.

4. COLLINGS

E.W.,

Adv. Cryog. Eng. 26 (1979737.

5.

WARNES L.A.A. and KING H.W., C r y G e n i c s 21 (1982) 729.

6. COLLINGS E.W. and HART S.C., Cryogenics

2

(197 9) 521.

7. KING H.W.. CIM B u l l e t i n J u l y 1981.

8. GEYARI C.; Vacuum

26

(1976) 587.