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JOURNAL DE PHYSIQUECol loqu e C1, suppl6m ent au no 1, Tome 45, janv ier 1984 page Cl -62 5

FERROMAGNETIC TRACES IN AUSTENITIC STAINLESS STEELS AT 4 , 2 K

X Pieterman A Ketting and J Ch GeerseDept. fo r Applied Phys ics De lf t Unive rs it y of TechnoZogy Lorentzweg 12628 J Del f t The netherlands

Resume - Dans c e t a r t i c le , son t de c r i t e s des mesures magnet iques qu i se rap po r te n tm r s c i e r s i n o x yd a b l e s de l a s e r i e ALSI 300 1 4,2 K I 1 a 6 t 6 e xa min e j u s q u ' i iq u e l p o i n t l e c om po rte me nt m a gn e ti qu e des d i f f e r e n t t yp e s , 6 t a i t i n f l u e n c e p a rsoudage ou pa r f req uen ts r@ f ro id i s sem en ts , j us qu ' i i 4,2 K De p l u s , l ' i n f l u e n c e ded i f f e r e n t e s a d d i t i o n s su 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 te n i t i q u e a e t 6 c on sid e-ree . Des pr ep ar at io ns examinees, une grande p a r t i e (303, 304, 310, 316L, 3 16Ti,321) se mb la i t mon t rer une ce r t a in e forme de comportement fer ro-magnet ique, ta nd isque seulement peu d 'a u tr e s (X6CrNi 1811,316LN) r e s t a i e n t compl6tement paramagnet iques4,2 KA b s t r a c t - T h i s p a p e r d e s c r ib e s m a g n e t i s a t i o n ex p e ri m en t s o n a u s t e n i t i c s t a i n l e s ss t e e l s o f A I S I 3 00 s e r i e s a t 4 .2 K The i n f l u e n c e o f w e l di n g and c y c l i c c o o l i n go n t h e i r m a g ne t ic b e h a vi o u r was s t u d i e d , 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 sf o r s t a b i l i z i n g t h e p r o p e rt i es o f s t a i n l e s s s t e e l . A la rge number o f samples hasbeen s tud ie d, mos t o f them showed fer ro-m ag ne t ic t ra ce s a t 4 .2 K (303, 304, 310,316L, 316Ti, 321). Only a few rema in f u l l y paramag net ic (X6CrNi 1811, 316LN) a t4.2 KINTRODUCTION

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 h as been s t u d i e d e x t e n s i v e l y i nt h e pastl2 3 4 5 . t i s we l l known th a t mos t o f t hem are uns ta b le be low 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 p hase. Because t h e a u s t e n i t i c phasei s p a r am a gn e ti c a nd t h e m a r t e n s i t i c p ha se i s f e r ro m a g n et ic , t h e m a g ne ti c c h a r a c t e ro f th e s t e e l w i l l c hange. W heth er su ch a t r a n s i t i o n o c cu rs depends v e r y c r i t i c a l l yon t h e c h e m ic a l c o m p o s i ti o n o f t h e s t e e l , so d i f f e r e n t h e a ts o f t h e same ty p e o fs t a i n l es s s teeT may show un l i ke magne t i c behav iourl . When us ing s ta in le ss s te e ls i nt h e n e i gh b ou rh o od o f m ag n e ti c f i e l d s i t s i m p o r t a n t t o know t h e i r m a g n e t ic b eh a-v i o u r , e s p e c i a l l y when h i g h h o m og e n ei ti e s a r e r e q u i r e d .I n t h a t r es pe ct i t s a l s o n e ce ss ar y t o know t h e i n f l u e n c e o f w e ld i n g o n t h em a g n et ic 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 p a p er m a q n e t i s a t i o n m easurem entsar e r ep or te d on welded and unwelded samples o f t h e types S 303, 304, 304N, 310,310S, 316, 3161, 316LN, 316T i and 32 1 a t 4.2 K.PREPARATION OF THE SAMPLES

The samples were mach ined ou t o f ba rs r ece ive d f rom d i f f e re n t m anu fac tu re rsi n t o c y l i n d e r s o f 1 0 mm d i am e t e r a nd 10 mm l o n g. F o r each t y p e o f s t a i n l e s s s t e e la l s o tw o c y l i n d e r s o f 1 0 b y 5 mm were machined and bounded tog et he r by fu s io n- we l-din g. Welded and unwelded samples were machined ou t o f t he same ba r. Chemical ana-l y s i s o f each specimen was c a r r i e d o u t; 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 lO ut o f t h e 32 samples u se d i n t h i s s tu d y 22 were a nn ea le d a t 1 0 8 0 ~ ~o r 9 0 m i n u t e sand quenched i n water . The mag ne t isa t ion o f 3 samples was measured bef or e and a f t e rhe at t reatm ent . The amount o f fer romagnet ism was reduced, b u t on ly one o f them (316)was f u l l y p a ra ma gn eti c a f t e r h e a t t re a tm e nt , i n d i c a t i n g a pu re a u s t e n i t i c s t r u c t u r e( s e e t a b l e 2) .

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

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Tab le 1 Chemical ana l ys i s o f t he measured s t a i n le ss s te e l samples.( Com posi ti ons i n w t )A l l o y n a m e C C r N i Mn Mo T i S i Cu S303 0.062304 (a) 0.0553 0 4 ( b ) 0 . 0 6 7304 N 0.075310 0.066310 S 0.062316 (a ) 0.070316 (b) 0.034316 ( c ) 0.044316 L 0.033316 LN 0.032316 T i 0.055X6CrNi 1811 0.072321 (a) 0.0663 2 1 ( b ) 0.057

Tab le 2. M ag ne tic 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 m a g n et is a ti o n o f d i f -f e r e n t s pecimens a f t e r f i r s t c o o l i n g a t 4.2 KA1 1o y name ~ o n d ii nX xo X h a t

(kA/m)303 AWQ 14.5 5.5 1 1304 (a ) AM 22.7 4.2 1.5304 b) M 7.1 7.1 0304 ( c j304 N310310 S316 (a )316 6 )316 ( c j316 ( c j316 L316 LN316 T i323 (a )321 ( a )321 (b )AM = As machinedAWQ = annea led a t 1 0 8 0 ~ ~o r 90 min utes , then wa ter quenched

EXPERIMENTAL PROCEDUREaMeasurements concern ing the magnet i c suscept i b i l i t y x = ( )T. have been madea t 4.2 K i n magne tic f i e l d s up t o 1 T. The specimens were moun gd ~ n s i d e sampleho ld er t h a t f i t s i n an ac magnetometer sur roundedby a superconduc t i ng magnet .The sample ho l de r c ou l d be eas i l y t aken ou t o f t he c r yos t a t f o r qu i ck chang ing t he

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sample . Cool-down t ime f o r the samples was ty p i c a l l y 2 min u te s , t h e y were h e ld a tl i q u i d h e li u m te m pe ra tu re f o r a bo ut 15 m i n ut e s t o sweep t h e m ag n et ic f i e l d t o 1 Tand back and measure the magne tic su s c e p t i b i l i t y . A f te rwards the samples were a l -lowed t o warm up t o room tempera tu re 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 cooling them down once everyd a y d u r i n g a p e r i o d o f 14 d ays . H o l d i n g t i m e i n l i q u i d h e l iu m was 15 minutes eacht ime.RESULTS

N o n - l i n e a r i t y o f t h e m a g n e t i s a ti o n c ur ve s i n d i c a t e s f e rr o m ag n e ti c t r a c e s i nt h e s t a i n l e s s s t e e l . I n t h e ca se o f t h e u nw elde d sam ples t h i s i s caused b y t h e f o r -m a ti on o f a m a r t e n s i te . The s a t u r a t i o n m a g n e t i s a ti o n M s at o f t h e f e r r o m a g n e t i cp a r t i n d i c a t e s t h e am ount o f a ma r te n s i t e . I n t h e c a se o f t h e we ld ed sa mp le s, f e r -r omag ne ti sm i s cau se d b y ma r te n s i t e f o rma t i o n on c o o l i n g an d w e ld i n g by - f e r r i t eand carb id e for ma t ion induced by th e wel d in g process. Ferromagnetism induced bywe ld in g o n l y can be found by su bs t rac t in g the measured Msat values Msatw Msa tui n t a b le 3 .

Tab le 3. M a gn et ic 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 m a g n et i sa t io n o f d i f f e r e n tsp ec imen s a f t e r w eld i ng a t 4.2 K.A1 l o y name Co nd it io n xo X Msat Msatw- Msatu ~ t a b i l yX

kA/m) kA/m) on we ld in g303 25.1 7.4 1.7 0.6304 a) M 47.3 6.4 3.3 1.8304 b ) AM 22.2 7.2 1.3 1.3304 c ) AM 93.2 9.6 6.1 -5.5304 N A 8.2 6.8 0.1 03 10 AWQ 246 37.0 22.0 1.2310 S AM 92.0 20.0 14.2 4.4316 a ) AM 14.5 9.7 0.3 0.3316 b) AWQ 16.7 16.7 0 0316 c ) 13.0 13.0 0 0316 L AWQ 45.6 12.3 2.2 -0.2316 LN 11.8 11.8 0 0316 T i A 31.0 12.9 1.6 -0.3X6CrNi 1811 AWQ 9.9 9.9 0 0321 a ) AWQ 25.0 15.1 2.4 -2.9321 b ) 38.7 14.9 2.5 -0.2

= poor= reasonable+++ = good++++ = e x ce l e n t

FERROMAGNETIC TRACES AT FIRST COOLINGThe r e s u l t s o f t h e m a g n e t i s a ti o n o f t h e u nw eld ed sam ples o n f i r s t c o o l i n g t o4.2 K are l i s t e d i n t ab l e 2; x0 i s t h e ma gn et ic s u s c e p t i b i l i t y a t z ero a p p l i e df i e l d , X a t maximum f i e l d where t h e f e r r o m a g n et i c p a r t i s s a t u r a t e d a nd M s a t i s t h es a t u r a t i o n m a g n e t i s a t i o n . Out o f 16 measured specimens only 6 showed f u l l y paramag-

n e t i c b e ha vi ou r on f i r s t c o ol in g . I m po rt an t i s t h a t a l l o f t h e un tr ac e d 316 t y p esp ec imens re main f u l l y a u s t e n i t i c , w here o n l y o ne o f t h e 304 samples showed nofe r romagne t ism. A lso the 316LN spec imen and the spec ia l compos i te X6CrNil811 r e -main ed a u s te n i t i c . The 304N t y p e shows a s l i g h t l y n o n - l i n e a r b e ha v io u r, a l t h ou g h ti s r e p or t ed t o b e f u l l y param agnetic 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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t h a t i n t h e case of t h e 304 t y pe t h e o c c u r r i n g o f y - a t r a ns f o rm a t i on i s more c r i -t i c a l l y d ep en de nt o f t h e c he mi ca l c o m p o si ti o n t h a n i n t h e ca se o f t h e 3 16 t y p e o fs t a i n l es s s t e e l . C om pa ring t he c hem i c al ana l ys es w i t h t h e m agne ti c behav iou r o f t he304 specimens one may conc lude t h a t a low carbon to ge th er w i t h a h i gh chromium con-t e n t e nhance m a r t e n s it e f o rm a t io n . A l so 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 gMn a d d i t i o n i s i m p o r t a n t as i s seen i n t h e c ase o f s am ple 3 0 4 ( c) w i t h a h i g h v a l u ef o r MSat and a lo w Mn co nt en t.

FERROMAGNETIC TRACES INDUCED BY WELDINGTab le 3 shows th e r e s u l t s o f t he measurements o f th e welded samples . The chemi-c a l c om pos i t i on i s t he same as f o r t h e unwe lded samp les. A f t e r w e l d i ng t he num ber o fs pecim ens t h a t r em a ined f u l l y pa r am agne ti c decr eased t o f o u r ( 316 ( b ), 316 ( c ) ,X6CrN i 1811 and 316LN). The f i r s t th re e showed a s l i g h t decrease i n magnet i c suscep-t i b i l i t y ( re sp . 5, 4 and 2%) and on l y t he 316 LN t y pe o f s t a i n l e s s s t ee l showed nod i f f e r en c e w ha ts oeve r. A l a r ge i nc r eas e of t he f e r r om ag ne t i c pa r t was found f o r t hesamples 303 and 304 whereas sample 304 (c) showed a l a r g e decrease o f th e ferromag-n e t i c p a r t .T h i s i n d i c a t e s a g a i n 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 t h es e ty p es o f s t a i n l e s s s t e e land the la rg e dependence o f the magnet ic cha rac te r on therma l h i s to r y and chem ica lc om pos i ti on . O n ly t he 304N t y pe may be r ega r ded as f a i r l y s t ab l e w i t h and w i t ho u tweld ing.Wi th one exce p t ion (303) a l l o f the annea led samples showed dec reas ing magn et i sa t io na f t e r w e l d i ng . O n l y i n one c as e ( 304 ( c ) ) o f t he as- mach ined samp les, i nd i c a t e d i nta b le 3 by AM ( as -mach ined ) , showed dec reas ing magn et i sa t ion . Tab le 3 a l so g ive st h e s t a b i l i t y on w e ld in g o f t h e d i f f e r e n t ty pe s o f s t a i n l e s s s te e l w i t h r e s pe c t t ot he changes i n m agne t i s a t i on . The Mo s t ab i 1 s ed t ypes 316 have ex c e l l e n t p r o pe r t i e si n t h i s r e s pe c t exc ep t f o r s am ple 316 (a ) w h i c h may g i v e b e t t e r r e s u l t s when annealed.The l ow ca r bon s t e e l 316L i s s t a b l e on w e l d i ng b u t i t showed fe r romagnet i sm on f i r s tc 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 th ou t Mo ad d i t i o n showed very good r e su l t s . tre ma in s f u l l y p a ra ma gn eti c and ha s e x c e l l e n t s t a b i l i t y .The s o c a l l e d w e l d ab l e 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 t y p e s 3 21 and 3 16 Ti showed l e s ss t a b i l i t y t han t h e 316 and 316LN t y pes . E ven a f t e r annea l i ng t hey s how ed fe rr om agne -t i c t r a c e s a nd m u st be r e g a rd e d as u n s t a b l e as was s t a t e d i n r e f . 7 . F i g . 1 showssome t y p i c a l l y magne t i sa t io n curves f o r we lded and unwe lded specimens.FERROMAGNETIC TRACES ON CYCLIC COOLING

C y c l i c c oo l i n g e f f e c t s have been s t ud i ed on 13 d i f f e r e n t s pecim ens: 304 (d ) ,304N, 310, 310S, 31 6( a) , 316 (b), 316 (c), 316L, 316LN, 316T i, X6CrNi 1811, 321 (a),321(b) . O f t he measured spec imens four showed inc reas ing fe r romagnet i sm on cyc l i ccoo l ing namely: 304(d) , 304N, 310 and 321(b) . The re su l t s a re shown i n f i g u r e 2.The t h r e e t y p e s o f s t a i n l e s s s t e e l sp ec im en s showed d i f f e r e n t b e h a vi o u r o n c y c l i cc oo l i ng . B o t h 304 t y pes showed no e f f e c t on t he f i r s t f o u r c ooldow n r uns t o 4 .2 K.A f t e r t h a t a s harp r i s e i n M at was de tec ted . 304 was rep or t ed uns tab le1 , b u t c y c l i cco o l in g e f f e c ts on 304N sampfes a re n o t pub l i she d as f a r as we know. I n r e f . 2, 4 ,6 and 8 304N was re po r te d s ta bl e. Again we must conc lude th a t th e magnet ic chara c te ro f t h e se s t e e l s i s u n p r e d i c t a b l e b ecau se o f t h e w i d e c om mercial c om p o si ti on l i m i t s .Sample 310 shows a s l i g h t i n c r e a s e o f f e rr om a g ne ti sm f ro m t h e f i r s t c o o l i n g c y c l eonw ards w h i c h rem ai ns t he same a f t e r 10 c y c l es . The e f f e c t i s r a t he r sm a l l , on l y a2% i nc re a se o f Msa t a f t e r 10 c yc le s . I n r e f . 2 i t was r ep o r t ed s t ab l e .Sample 321(b) shows a la r g e inc rease o f s a t betw een t he f i r s t and t he s econd c oo l -down and a s l i g h t f u r t h e r i nc re a se i n t h e n e x t 9 c oo ldow n r uns . T h i s e f f e c t was a l s or e p o rt e d i n r e f . 2. The o t he r s peci men o f t h i s t y pe o f s t e e l ( 321 ( a ) ) showed no e f -f e c t s o n 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 fe re n ce be tween these twosamples co u ld be exp la ined by lo ok i ng a t the chem ica l compo s i t i on : sample 321(a)c on t a i ns t w i c e as much o f t h e au s t e n i t e s t a b i l i s i n g Mn as s am p le 321 (b ) . T h i s wasex ac t l y t he c ase w i t h t he s amp les o f La r b a l es t i e r and K i ng2 (Mn0.77, uns t ab l e ) ando f Reed and M ik es e l l ' (Mn2.0 , s t ab le ) .

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Fig. Magnetisation curves of di ffe re nt st ai nl es s ste el samples. S trai ght l in ebefore welding dotted li n e a ft e r welding.

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Fig. Magnetisation of d if fe re nt specimens as func tion of th e number of cooling cycles N between room temperature and 4.2 K

Table 4. Summary of r e su l t sA1 1oy name ferromagnetic traceson f i r s t cooling on welding on c y c l s cooling303304 a )304 b)304 c )304N310 t310s316 a )316 b)316 c )316L316LN316T iX6CrNi 1811321 a )321 b)

= detected= not detected= nbt tested

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CONCLUSIONSTab le 4 summar izes th e r es u l ts o f t he mag ne t isa t ion measurements on 16 d i f f e -r e n t t y p es o f s t a i n l e s s s t e e l . F ou r sa mple s r emaine d p ara mag n e ti c u nd er a l l c i r c um-

sta nc es : 31 6 b), 31 6 c), 316LN and X6CrNi 1811. These types may be regarded asst ab le au s te n i t ic s t a i n l es s s t ee ls . Sample 316 a) showed some fer romagnet ism onwe ld in g p robab ly due t o th e low Mo con ten t .I n th e case o f t he 303, 304 and 321 samples we can conc lude that one cannot be sureabou t th e i r magne tic cha r ac t e r i n advance . The know ledge o f th e chemica l compos i t ionc o u l d be h e l p f u l t o p r e d i c t wh eth er f e rr o m a gn e ti c t r a c e s w i l l o c cu r, b u t i n ge ne ra lwhen m ag ne ti c b eh a v io u r i s c r i t i c a l one s ho u ld n o t us e th e s e t yp e s o f s t a i n l e s sst ee l un less exa ct m agn et is a t io n measurements has been done.I n th e case o f t h e 310 s pecim ens a b so l u t e m a g n et i sa t io n i s f a i r l y l a r g e . T here i sa p o s s i b i l i t y o f a f e r r om a g n e t i c t r a n s i t i o : i n t h e a u s t e n i t i c p hase caused b y t h el a r g e am ount o f N i i n th e s e ty pe s o f s t e e lT h at l ea ve s o n l y t h e 316LN t y p e 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 n o e vi de nc e o f t h ec o n t r a r y i s known i n t h e l i t e ra tu re ) a nd t h e t y p e X6CrNi 1811, o f wh ic h we a re n o taware o f a ny r e s u l t s p u b l i sh e d b e f o r e .ACKNOWLEDGEMENT

The au tho rs w ish t o thank P ro f . H. Postma f o r h i s adv ice and encouragement.They a re a l so g r a t e f u l t o Mr. G .J. Maanenschi jn and M r . P.F. C o l i j n o f t h e M et al -l u r g i c a l D e pa rtme nt f o r a n a l y z i n g t h e sa mp le s an d h e lp fu l d i s c u s s io n s . The t e c h n i c a la s s i s ta n c e o f M r. W den B r a v e r a t t h e p r e p a r a t i o n o f t he e x p e ri m e nt a l s e t -u p i sg ra te fu l l y a c k n o w le d g e d .REFERENCES1 REED R.P. and MIKESELL R.P., Adv. Cryog. Eng. 4 1960) 84.2. LARBALESTIER D.C. and KING H.W., Cry oge nics 13- 1972) 160.3. WARNES L.A.A. and KING H.W., C ry ogenic s 16 m 7 6 ) 473.4. COLLINGS E.W. Adv. Cryog. Eng. 26 1 97 97 37 .5. WARNES L.A.A. and KING H.W., C ry G e n i c s 21 19 82 ) 729.6. COLLINGS E.W. and HART S.C., Cry ogenic s 19 7 9 ) 521.7. KING H.W.. CIM B u l l e t i n J u l y 1981.8. GEYARI C.; Vacuum 6 1976) 587.