Comparative Study of Fracture in Pressure Vessel Steels A533B and a 508

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B.A. Gurovich et a l. /Jou rna l of Nuclear Materials 228 1996) 330 -337 331

T h e c h e m i c a l c o m p o s i t i o n o f t h e i n v e s t i g a t e d A m e r -i c a n s t e el s is p r e s e n t e d i n Ta b l e 1 . I t s h o u l d b e n o t e dt h a t t h e c o n t e n t o f i r r tp u r it ie s , d e f i n i n g t h e t e n d e n c y o fp r e s s u r e v e s s e ls t o r a d i a t i o n e m b r i t t l e m e n t ( P a n d C u ) ,i s c o n s i d e r a b l y h i g h e r i n w e l d m e t a l J W Q t h a n i n J W P.A s t h e p h o s p h o r u s a n d c o p p e r c o n t e n t w a s lo w o r h ig h

s imu l t aneous ly, i t wa, ; impo ss ib l e t o s epa ra t e t h e i n f lu -e n c e o f t h e s e e l e m e n t s .C h a r p y s a m p l e s w e re p r e p a r e d a n d i r r a d i a te d a f t e r

t h a t . S u m m a r y d a t a o n i r r a d i a t io n , a n n e a l i n g co n d i -t i o n s a n d r e - i r r a d i a t i o n a r e p r e s e n t e d i n Ta b l e 2. T h es a m p l e s la b e l e d J R Q a n d J W P w e r e i r r a d i a t ed i n th ep o w e r r e a c t o r o f t h e A r m e n i a n N N P - 2 ( V V E R - 4 4 0 ,Russ i a ) , t he s ample ., ; JW Q in t he powe r r eac to r o fN o v o v o r o n e z h N P P - 5 ( V V E R - 1 0 0 0 , R u s s i a ). I n a llc a s e s t h e s a m p l e s w e r e i r r a d i a t e d i n m o d e r n i z e d c o n -t a ine r a s se mbl i e s i n channe l s fo r su rve i l l ance s ample s .B e f o r e t h e i r i n s e r t i o n i n t o t h e r e a c t o r , t h e s a m p l e sw e r e c o v e r e d w i t h a s p e c i a l n i ck e l c o r r o s io n - p r e v e n t i v e

f i lm ( th ickne ss 5 ixm) .T h e e m b r i t t l e m e n t o f th e s p e c i m e n s a f t e r i r r a d i a -

t i o n w a s e v a l u a t e d b y th e D B I T s h i ft a n d d e c r e a s e o ft h e u p p e r s h e l f e n e rg y i n i m p a c t t e s t s o f C h a r p y s p e c i -m e n s w i t h V- n o t c h . I n t h e i n i ti a l s t a te , b o t h C h a r p yand subs i ze Cha rpy spec im ens (5 x 5 x 27 .5 r am) weret e s t ed .

T h e r a n g e o f t h e c h e m i c a l c o m p o s i t i o n o f t h e i n v e s -t i g a t e d R u s s i a n s t e e l s is p r e s e n t e d i n Ta b l e 1 .

T h e R u s s i a n b a se m e t a l ( 1 5 K H 2 M FA ) w a s h e a tt r ea t ed a f t e r f o rging; und e r t he fo l l owing cond i t i ons :quench in g : 1000°C - 10 h , o i l coo l ing ; t emp er ing : 700°C

1 6 h, a i r c o o l in g . P o s t w e l d h e a t t r e a t m e n t f o r t h eR u s s i a n w e l d m e t a l ( S V- 1 0 K H M F T ) : h o l d i n g 1 5 h a t665°C , fu rnace coo l ing up t o 300°C , t hen a i r coo l ing .

F r a c t o g r a p h i c r e s e a r c h w a s c a r r ie d o u t o n h a l v es o fC h a r p y s p e c i m e n s , w h i c h w e r e t a k e n a n d e v a c u a t e dj u s t a f t e r t h e t e s t s , i n o r d e r t o p r e s e r v e t h e f r a c t u r e

su r f aces . Th e f r ac tu re su r f aces we re i nves t i ga t ed w i tht h e X - r a y m i c r o a n a l y z e r S X R - 5 0 , r a d i o a c t i v e v e r s i o n( ' C a m e c a ' ) , t h a t w a s i n s t a l l e d i n a p r o t e c t i v e c h a m b e r.T h e i m a g e s o f th e f r a c t u r e s w e r e o b t a i n e d w i t h s e c -o n d a r y e l e c t r o n s a t a n a c c e l e r a t in g v o l ta g e o f 2 0 k Va n d a p r o b e c u r r e n t o f 0 . 8 n A w i t h m a g n i f i c a t i o n int h e r a n g e 5 0 - 3 5 0 0 t i m e s . T h e q u o t a o f d i f f e r e n t t y p e so f f r ac tu re (du c t i l e , i n t e r c rys t a l l i ne , c l eavage and qua -s i d e a v a g e ) i n t h e t o t a l f r a c t u r e s u r f a c e a f t e r t h e t e s tsa t d i f f e r e n t t e m p e r a t u r e s w a s e v a l u a t e d u s i n g t h eG l a g o l e v m e t h o d [1 ]. T h e a b s o l u t e e r r o r o f m e a s u r e -m e n t s a t 9 5 c o n f i d e n c e l e v e l d i d n o t ex c e e d 3 .Te s t i n g t e m p e r a t u r e s f o r e a c h m a t e r i a l c o r r e s p o n d e dt o t h e u p p e r s h e lf , th e d u c t i l e - b r i t t l e t r a n s i t io n t e m -p e r a t u r e a n d t h e l o w e r s h e lf i n t h e t e m p e r a t u r e d e p e n -d e n c e o f t h e i m p a c t e n e rg y.

T h e i m a g e s h a v e b e e n a n a l y z e d u si n g t h e I m a g eA n a l y s i s S y s te m I B A S - 2 0 0 0 w i t h s u b s e q u e n t c a l c u la -t i o n o f d i m e n s i o n d i s t r i b u t i o n h i s to g r a m s f o r t h e f r a c -t u r e d u c t i l e c o m p o n e n t ' d i m p l e s ' , u s in g s p e c i a l ly d e v e l -o p e d e v a l ua t io n p r o c e d u r e s a n d c o m p u t e r p r o g r am s .I n t h i s ca s e t h e i n a c c u r a c y o f t h e m e a n d i m e n s i o nd e t e r m i n a t i o n w a s 1 0 f o r t h e 9 0 c o n f i d e n c e l e v el .D u c t i l e c o m p o n e n t s a l o n g t h e p e r i m e t e r a n d i n t h ec e n t e r h a v e b e e n a n a l y z e d s e p a r a t e l y. A s t h e i m p a c t

Table 1Chemical Com position of investigated pr essure vessel materials

Labe l ASTM wt

code Si Mn P S Cu Ni Cr Mo C V

JRQ A 533Bclass 1 0.24 1.42 0.017 0.004SteelPlate

JWP A 533Bclass 1 0.33 1.18 0.009 0.004

WeldedJoint

JWQ A 508class 3 0.3 1.29 0.026 0.005WeldedJoint

15KH2MFA 0.27 0.39 0.0 11 0.012

0.37 0.48 0.016 0.018SV-10KHM FT 0.15 0.97 0.029 0.012

0.35 1.03 0.036 0.013

0.14 0.84 0.12 0.51 0.19 0.003

0.03 0.9 0.06 0.03 0.09 0.002

0.26 1.1 0.04 0.48 0.09 0.002

0.12 0.19 2.52 0.64 0.13 0.25

0.14 0.27 3.00 0.71 0.18 0.310.15 0.09 1.37 0.43 0.05 0.19

0.21 0.29 1.58 0.50 0.07 0.23

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B.A. Gurovich et a l. /Jou rna l o f Nuclear Mater ials 228 1996) 330 -33 7

Ta b l e 3S u m m a r y d a t a o n f r a c t o g r a p h i c a n al y si s o f C h a r p y s p e c i m e n s f o r m a t e r i a ls a f t e r i r r a d i a ti o n , a n n e a l i n g a n d r e i r r a d i a ti o n

333

L a b e l M a t e r i a l C c m d i t io n s T t e s t C h a r p y P o s i t io ntype a ( °C) ene rg y on cu rve

( J ) (KCV -T) b

Q u o t a o f d i f f e re n t fr a c t u r e m o d e s ( % ) c

Duc t i l e In t e rc rys t a l l ine Quas ie l eavage C lea -v a g e

JR Q BM i r r ad . 100 83 .1 DB T 50 10 -

JR Q BM i r t. + anne a l . 40 93 .3 DB T 55 10 -

JR Q BM 100 19 .6 LS 30 10 -J R Q B M r e - i r ra d . 1 40 5 5 .7 D B T 4 0 1 0 -JR Q BM 220 108.2 US 100 - -

JW P W M - 40 16 .5 LS 5 - 30JW P W M re - i r r ad . - 20 26 .7 DB T 15 - 35JW P W M 20 152.9 US 85 - 15

J W Q W M 4 0 4 . 7 L S 5 2 0 7 5J W Q W M r e - ir r a d . 1 20 5 5 .7 D B T 5 5 2 0 2 5J W Q W M 2 0 0 1 27 U S 1 0 0 - -

4 0

35

6050

655 0

a B M - b a s e m e t a l ; W M - w e l d m e t a l .b L S - l o w e r s h e lf r a n g e ; U S - u p p e r s h e l f r a n g e ; D B T -c _ Q u o t a o f t h i s m o d e l e s s t h a n 5 % .

duc t i l e to b r i t t l e t r ans i t ion r ange .

T h e m a i n g o a l o f t h e p r e s e n t r e s e a r c h i s t o f in dc o r r e l a ti o n s b e t w e e n t h e q u o t a s o f th e a r e a s w i t h d if -f e r e n t ty p e s o f f r a c t u r e i n t h e f r a c t u r e s u r f a c e a n dc h a r a c t e ri s ti c s o f it s e m b r i t t l e m e n t ( i m p a c t e n e r g y a n dD B T r ) .

Ta b l e 2 p r e s e n t s t h e d a t a o n i r r a d ia t i o n c o n d i t io n so f th e s p e c i m e n s , r e c o v e r y a n n e a l i n g c o n d i t io n s , D B T Ti n al l s t a t e s a n d c o r r e s p o n d i n g s h i f ts o f t h e t e m p e r a -t u r e .

T h e r e s u l t s o f t h e f r a c t o g r a p h i c a n a l y s is o f A m e r i -c a n b a s e m e t a l s t e e l a n d w e l d s a r e s u m m a r i z e d i nTa b l e 3 .

A c o m p a r i s o n o f t h e r e s u lt s p r e s e n t e d i n Ta b l e 3r e v e a ls s o m e f e a t u r e s i n t h e c h a r a c t e r o f f r a c tu r e s i nt h e s e s t ee l s. F r o m o u r s t a n d p o i n t , t h e d e t e c t i o n o f th ei n t e r c r y s t a U i n e f r a c t u r e i n t h e f r a c t u r e s u r f a c e s o f b o t hb a s e a n d w e l d m e t a l s , d i s c o v e re d a t t e m p e r a t u r e s , c o r -r e s p o n d i n g w i t h t h e l o w e r s h e l f a n d D B T ' F, i s o f p a r -

t i c u l a r i n t e r e s t . B e f o r e , t h e r e w a s n o i n f o r m a t i o n o nt h e e x i s t e n c e o f i n t e r c r y s t a l li n e c o m p o n e n t s i n fr a c -t u r e s o f A m e r i c a n s te e ls . I t sh o u l d b e n o t e d t h a t s u c hi n f o r m a t i o n i s o f f u n d a m e n t a l i m p o r t a n c e , b e c a u s e i t i sp o i n t e d o u t t h a t f o r t h e s e s t e e l s , t h e r a d i a t i o n e m b r i t -t l e m e n t is d e fi n e d n o t o n l y b y st e e l h a r d e n i n g u n d e ri r ra d i a t io n , b u t b y t h e p r o c e s s o f r e v e r si b l e t e m p e rb r i t t l e n e s s a s w e l l .

I n t h i s c o n n e c t i o n t h e m e c h a n i c a l c h a r a c t e r i st i c s o f

t h e s t e e l A 5 3 3 B h a v e b e e n s t u d i e d b y t h e k i n e t i ch a r d n e s s m e t h o d . T h e m e a s u r e m e n t s h a d b e e n d o n ef o r t h e s t e e l J R Q s p e c i m e n s i n t h e i n it i a l s t a t e a f t e ri r r a d ia t i o n a n d i r r a d ia t i o n w i t h s u b s e q u e n t r e c o v e r ya n n e a l i n g ( ir r a d i a ti o n c o n d i t i o n s a n d r e c o v e r y a n n e a l -i n g c o n d i t io n s a r e g i v e n in Ta b l e 2 ). M e c h a n i c a l p r o p -e r t i e s o f t h e s p e c i m e n s a r e g i v e n in Ta b l e 4 . I t s h o u l db e n o t e d t h a t t h e u n i f o r m s t ra i n , o b t a i n e d b y t h ist e s ti n g m e t h o d , c o r r e l a te s w i t h u n i f o r m e l o n g a t i o n .

Ta b l e 4M e c h a n i c a l p r o p e r t i e s o f t h e b a s e m e t a l J R Q b y t h e k i n e t ic h a r d n e s s m e t h o d ( b a l l d i a m e t e r 2 .5 r a m )

S t a t e H a r d n e s s A H A H a Te n s i le A R m A R m b Yi e ld A R p o A R p o 2 c U n i f o r m S h i f tH ( k g / m m ) ( % ) s tr e ss ( M P a ) ( % ) s tr e ss ( M e a ~ ( % ) s t ra i n D B Tr( k g / m m 2 ) R m R p o ~ A m AT

( M e a ) ( M P a ) ( % ) ° C )

( % )

Ini t ia l 203 616 481 21Irrad . 228 25 704 88 591 110 10 65I r r a d +annea l . 212 9 36 681 65 74 536 55 50 10 20 31

a U n r e c o v e r e d p a r t r a d i a t i o n i n d u c e d i n i ti a l h a r d n e s s .b U n r e c o v e r e d p a r t r a d i a t i o n i n d u c e d i n i ti a l R m .c U n r e c o v e r e d p a r t r a d i a t i o n i n d u c e d y i e ld s t r es s .d U n r e c o v e r e d p a r t r a d ia t io n i n d u c e d A D B Tr s h if t.

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334 B.A. Gurovich et a l. /Jou rna l o f Nuclear M aterials 228 1996) 330 -33 7

It is commonly supposed that the yield stress is ofprimary concern in the studies of hardening to radia-tion embrittlement of pressure vessel materials underirradiation and that the hardness, correlating with theformer, is less interesting. Analysis of the data given inTable 4 indicates that:

uniform strain (elongation) of the steel JRQ doesnot correlate with DBTT shift, because DBTI rever-sion in annealing takes place without any change ofthis magnitude. Numerous studies, relating to re-versible brittleness, point out that the development ofreversible brittleness does not correlate neither withvariatio n in uniform strain no r with total el ongation [8].In the case of brittleness, resulting from hardening, therelation between DBTr shift and elongation has notbeen studied sufficiently.

ultimate tensile strength slightly correlates withDBTT shift (unrecovering of ultimate strength afterrecovery annea ling is 74%, as compar ed with 31%unrecovery of DBTT);

- also the yield stress weakly correlates with DBTTshift (unrecovering of yield stress after recovery anneal-ing is 50%, while D BT r unrecov ering is 31%);

- the best correlati on is observed between theDBTT shift and the hardness (hardness unrecoveringafter recovery annealing is 36%, while DB Tr unrecov-ering is 31%).

Thus the results obtained for the mechanical prop-erties of the steel JRQ indicate that no correlation canbe observed between DBTT recovery and yield stressafter annealing . Consequentl y, it is impossible to come

to an exact conclusion that radiation embrittle ment isdetermined mainly by the steel hardeni ng under irradi-ation. Also it indicates that there are some othermechanisms contributing to radiation embrittlement.

The area with prevailing intercrysta lline fracture i nthe fracture surface of the base metal JRQ and weldmetal JWQ are shown in Figs. la and lb respectively.

Comparison of fractographic analysis data for thewelds with different cont ent of unfavorable impuritiesindicates that the m ain distinction in the fracture char-acter is the lack of intercrystalline component in thefractures of the weld with low content of Cu and PJWP).

Fig. 1. Areas with prevailing intercrystalline fracture of (a)re-irradiated base metal JRQ (Ttest = 100°C), (b) reirradiatedweld metal JWQ (Ttest = 40°C).

In all cases the quota of intercrystalline compo nentin the fracture remains unaffected with temperaturedecrease from the transient region to the low shelftemperature and is equal to 10% and to 20% for thebase and weld metal, respectively.

The analysis of Tables 1 and 2 indicates that anincrease of the transition temperature shift after irradi-ation is enforced by an unfavorably high impurity con-tent in spite of the fact that in the case of the weldwith lower content of phosphorus and copper (JWP)the neutr on fluence was higher.

Table 5Summary data on fractographic analysis of subsize Charpy specimens for base metal JRQ before irradiation

h a r p y T t e s t Position Quota of different fracture modes (%) a

energy (°C) on curve Ductile Intercrystalline Quas ic leavage Cleavage(J) (KCV-T)

1 1 0 0 L S 1 0 0

3 - 25 DBT 15 - - 8522 100 US 100 - - -

a _ Quota of this mode less than 5%.

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B.A. Gurovich et aL /Journal of Nuclear Materials 228 1996) 330-337 335

2 0 . 0 0 -

e

- - 1 2 . 0 0 -m, . i , .o

G ) 8 . o o -i

ra3 4 00

¢

/• ~ - R u M m i a n R P V - ~ t e e l 6

0 . 0 0 ~ ~ 1 ' I ' I ' Is o o l z 0 o l s o o 2 0 0 0 0 2 4 0 0 2 a 0 o

Tka n n- Tk 0 C

Fig. 2. Correlat ion between the unrecovered part of DBTIshift and the intercrystall ine quota of fractures in Am ericanand R ussian (base metals after annealing 475°C - 150 h)pressu re vessel steels. T ka,n - DBT T after irradiation andannealing, Tk 0 - DBqSr in initial state.

A f r a c t o g r a p h i c sl tu d y o f t h e b a s e m e t a l J R Q b e f o r ei r r a d i a t i o n ( Ta b l e 5 ) , a f t e r i r r a d i a t io n , a n n e a l i n g a n dre - i r r a d i a t i o n (Tab le: 3 ) ha s i nd i ca t ed t ha t t he i n t e r-c r y s t a ll i n e c o m p o n e n t a r i se s a t t h e i r r a d i a t i o n s t a g e,a n d i t s q u o t a r e m a i n s p r a c t i c a l ly u n a f f e c t e d a f t e r r e -c o v e ry a n n e a l i n g a n d r e - i r r a d i a t i o n .

T h e i n v e s t ig a t i o n s l e a d t o t h e c o n c l u s i o n t h a t t h ep r e s e n c e o f a n i n t e r c r y s ta l l i n e c o m p o n e n t i n t h e f r a c -t u r e c o r r e l at e s w i th t h e u n r e c o v e r e d p a r t o f D B T rs h if t a f t e r r e c o v e r y a n n e a l in g a t t e m p e r a t u r e s , c o i n c id -i n g w i t h t h o s e o f t e m p e r b r i t t l e n e s s g r o w t h ( T- - 4 5 0 -470°C) (see Fig . 2) .

T h e i n t e r c r y s t a ll i n e c o m p o n e n t i n f r a c t u r e s u r f a c es h o u l d b e t a k e n i n t o a c c o u n t b o t h i n e v a l u a t i o n o fr a d i a t i o n e m b r i t t l e m e n t d e g r e e a n d i n d i s c u s s i o n sa b o u t a d v i s ab i l it y o f p r e s s u r e v e s s e l r e co v e r y a n n e a l -ing .

T h e o t h e r b r i t t l e c o m p o n e n t s o f f ra c t u r e s u r f a c e -

c l e a v a g e a n d q u a s i e l e a v a g e - h a v e b e e n o b s e r v e d ( F ig s .3 a n d 4 ) . It s h o u l d b e n o t e d t h a t t h e q u o t a o f c l e a v a g ei s v e r y h ig h ( u p t o 6 5 % i n t h e i r r a d i a t e d s t a t e a n d u pt o 1 0 0 % i n t h e b a s e m e t a l b e f o r e i r r a d i a t i o n ) . I t d e -c r e a s e s w i th t e s t i n g t e m p e r a t u r e i n c r e a s e a n d i s p r a c t i -c a l ly a b s e n t a t t e m p e r a t u r e s , c o r r e s p o n d i n g w i t h t h eu p p e r s h e lf . R e l a t i v e l y h i g h c l e a v a g e q u o t a o n t h es u r f a c e f r a c t u r e o f t h e s u b s i z e C h a r p y s p e c i m e n s b e -f o r e i r r a d i a t i o n m a y b e c a u s e d b y l o w t es t t e m p e r a t u r ec o r r e s p o n d i n g w i th t h e l o w e r s h el f ; t h e r a d i a t i o n d e -f e c t s a b s e n c e ; t h e d i f f e r e n c e o f t h e d e f o r m a t i o n r a t ed u r i n g t h e s u b s iz e C h a r p y s p e c i m e n s t e s t .

Fig. 3. The area with bri t t le fracture by cleavage (irradiatedbase me tal JR Q, Ttest = 100*C).

I t i s wo r th no t ing t ha t i n Russ i a n s t ee l s t he quas i -c l e a v a g e f r a c t u r e i s m o r e c h a r a c t e r i s t ic t h a n t h e c l e av -a g e f r a c t u r e . T h i s f a c t ca n b e p r o b a b l y e x p l a i n e d b yt h e p r e s e n c e o f n u m e r o u s p r e c i p i t a t e s in t h e s e s t e e ls .

N u m e r o u s i n v e s ti g a t io n s o f R u s s i a n w e l d s p e c i m e nf r a c t u r e s u r f a c e s f o r V V E R - 4 4 0 a n d f e w e r o n e s f o rV V E R - 1 0 0 0 i n d i c a t e t h a t t h e i n t e r c ry s t a l li n e f r a c t u r e ,a s a ru l e , is p r ac t i ca l l y absen t i n t he who le r ang e o ft e s t in g t e m p e r a t u r e s , i r r a d i a t i o n c o n d i t i o n s a n d i m p u -r i t y c o n t e n t s ( s o m e t i m e s t h e p h o s p h o r o u s c o n t e n t c a nr e a c h 0 . 0 5 % ) . A t t h e s a m e t i m e , t h e i n t e r e r y s t a l l i n ef r a c t u r e i s p r e s e n t i n t h e b a s e m e t a l s p e c i m e n s , c h a r a c -

t e r i z e d b y l o w e r c o n t e n t o f u n f a v o r a b l e i m p u r i t i e s ,t h a n i n th e w e l d s , at t e s ti n g t e m p e r a t u r e s , c o r r e s p o n d -i n g w i t h t h e l o w e r s h e l f a n d D B T I ' . To e x p l a i n t h i s f ac ti t i s neces sa ry t o ca r ry ou t add i t i ona l i nves t i ga t i ons .

T h e a n a l ys i s o f Ta b l e 3 l e a d s t o t h e c o n c l u s i o n t h a ti n a l l c as e s t h e i m p a c t e n e rg y c o r r e l a t e s o n l y w i th t h e

Fig. 4. The area with brittle fracture by quasieleavage (re-irradiated weld me tal JWQ, Ttest= 40°C).

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336 B.A. Gurovich et al. /Jou rna l of Nuclear Materials 228 1996) 330-3 37

100.00

.E~ 8 0 0 0

4 60.00

E 40. 0

~ 20 00

0.00

• J a=

• ~ vQ ~ /

; % . - /_ _ _ ' %

÷

I I ~ I I I

0 0 0 2 0 . 0 0 4 0 . 0 0 6 0 . 0 0 8 0 , 00 100 00

D u c t i l e q u o t a i n a f r a c t u r e ,

Fig. 5. Correlation between the normalized impact energy

A / A u s ) and the ductile part in the fracture surface ofAmerican and Russian pressure vessel steels. Aus - Impactenergy in the upper shelf region.

quota of ductile fracture in the total fracture surface.This conclusion is true for the fractures of Russiansteels as well.

Fig. 5 shows the normalized value of the impactenergy versus total quota of ductile fracture for Charpyspecimen fractures for different steels, irradiation con-ditions and testing temperatures. In this curve, thenormalized impact energy A / A u s ) had been taken

equal to the relation of the impact energy at fixedtemperature to its value at the temperature, corre-sponding to the upper shelf of the curve KCV-TtesrFig. 5 summarizes the data on fractographic and C harpyinvestigations of Amer ican steels A533 and A508 andRussian steels: 15KH2MFA (base metal) and SV-10KHMFT (weld). It can be seen from Fig. 5 that therelation between the values is linear. But an experi-mental relation of so simple type can exist only ifdimple sizes are unaffected by testing or irradiationconditions.

The fact that the impact energy correlates exclu-sively with the ductile quota in the fractures of thespecimens looks reasonable. It follows from the factthat the impact energy per unit area of the fracturewith the ductile fracture type at the upper shelf area ismore than one order of magnitude higher than that ofthe brittle fracture type at the lower shelf area. Thisresult points out to possibility of experimental mea-surement of quantitative relation between parametersof ductile fracture and impact energy.

In the consecutive studies, particular emphasis hasbeen given to the ductile component distribution onthe fracture surfaces and to characteristics of the duc-tile component as a function of testing temperatures.

Fig. 6. Typical section with ductile 'dimple'-type character ofthe fracture (reirradiated base metal JRQ, Ttest = 140°C).

The fractures obtai ned in impact testing are character-ized by the presence of a ductile 'belt' along theperimeter of the fracture zone and also of areas withductile fracture in the central part of the fracture.Ductile sections along the perimeter constitute a con-tinuous zone, while in the central part of the fracturethe ductile and brittle components are mixed and dis-crete. The belt is visible owing to its topography dis-tinction and the fact that the medium sizes of dimplesvary. Moreover, it has been noted that more than 50of the ductile fracture is concentrated in the ductilebelts with smaller size of the dimples than in thecenter.

A typical section with ductile, dimple-type characterof the fracture is given in Fig. 6. The results of quanti-tative processing of the dimples size histograms, usingthe weld JWQ as an example, are presented in Table 6.

Table 6Summary data on image analysis results of Charpy specimensfor weld metal JWQ after reirradiation

Ttest Charpy Position Analyzed place d D°C energy on curve (~m)

(J) KCV-T a40 4.7 LS under notch 1.6

periphery 1.2center 1.5

120 55.7 DBT under notch 1.6periphery 1.2center 1.7

200 127 US under notch 1.4periphery 1.2center 1.7

a L S lower shelf range; US - upper shelf range; DBT -ductile to brittle transition range.

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B.A. Gurovich et al. /Jo urn al o f Nuclear Materials 228 1996) 33 0-3 37 337

1 6 0 . 0 0 -. -

~

4 ) 1 2 0 . 0 0 •rq )

0q )

~ 8 0 . 0 0 -0ffl

40.00

+

4 -

=in Rus sian PV steels

~[ ubsizt specimens

++

, +

4 'e

0 . 00 I ' i ' I ~ i

0 . 0 0 1 . 0 0 2 . 0 0 3 . 0 0 4 . 0 0

Dim ple s izes , I~mFig. 7. The absorbed energy vs. dimple sizes in the center of

the fractures for the American (JWQ) and Russian pressurevessel steels (base and w eld metals) after the different irradia-tion and test conditions.

T h e a n a l ys i s l e a d s t o t h e c o n c l u s i o n t h a t t h e d i m p l es i ze s o n t h e d u c t i l e a r e a s o f f r a c t u r e p r a c t i c a l l y d o e sn o t d e p e n d o n t h e t e s t t e m p e r a t u r e a n d t h e a b s o r b e de n e rg y v a lu e . A n a l o g o u s r e s u lt s w e r e o b t a i n e d f o r R u s -s i an s t ee l s a s we l l . Nu me rou s i nves t i ga t i ons o f t hed u c t i l e f r a c t u r e p a r a m e t e r s o f R u s s i a n s t e e l s s h o w t h a ta l s o d im p l e s i z e s d o n o t d e p e n d o n i r r a d i a t i o n a n d t e s tc o n d i t i o n s, t h e s a m p l e s i ze a n d c h e m i c a l c o m p o s i t i o no f p r e s su r e ve s se l s t ee l s ( s ee F ig . 7 ). Ho weve r, t hei n f l u e n c e o f s i ze a n d q u a n t i t y o f t h e n o n m e t a l l i c in c l u -s ions on t he d imp le s i ze s and va r i a t i on i n s i ze s can beo b s e r v e d .

4 . C o n c l u s i o n

C o m p a r a t i v e r e s e a r c h o f t h e f r a c t u r e s u r f a c e s o f t h es p e c i m e n s a f t e r i m p a c t t e s t s c a r r i e d o u t f o r A m e r i c a na n d W e s t E u r o p e a n p r e s s u r e v e s s el s t e el s , A 5 3 3 B C l a s s1 ( s t ee l p l a t e an d w e lde d j o in t ) , A508 C la s s 3 ( s t ee lw e l d e d j o i n t ) , a n d a l s o R u s s i a n s t e e ls , 1 5 K H 2 M FA

( b a s e m e t a l ) , 1 0 K H M F T ( w e l d ) , h a s r e v e a l e d t h e f o l -l owing r egu l a r i t i e s :

( 1 ) T h e i m p a c t e n e rg y c o r r e l a t e s o n l y w i t h t h e q u o t ao f t h e d u c t i l e fr a c t u r e c o m p o n e n t i n t h e f r a c t u r e s u r -face .

( 2 ) I r r a d i a t i o n i n d u c e s i n t e r c r y st a l l in e f r a c t u r e i nR u s s i a n a n d A m e r i c a n b a s e m e t a l s .

( 3 ) I r r a d i a t i o n i n d u c e s i n t e r c r y st a l l in e f r a c t u r e i nA m e r i c a n w e l d w i t h h i g h c o n t e n t o f r e s i d u a l e l e m e n t s

P a n d C u . A t t h e s a m e t i m e , ir r a d i a t i o n o f R u s s i a nw e l d s w i t h P c o n t e n ts u p t o 0 . 0 5 d o e s n o t in d u c e a nin t e r c rys t a l l i ne f r ac tu re , a s a ru l e .

( 4 ) H i g h c o n t e n t s o f P a n d C u i n i r r a d i a t e d s t e e lsl e a d t o s ig n i f ic a n t s h i ft o f D B T I ' a n d i n c o m p l e t e D B T rrecove r ing a f t e r annea l ing .

( 5 ) T h e c o r r e l a t i o n e x is t s b e t w e e n D B T I ' u n r e c o v -e r i n g a n d i n t e r c ry s t a l li n e f r a c t u r e c o m p o n e n t i n t h ef r a c t u r e o f i r r a d i a t e d s t e e l sp e c i m e n s a f t e r r e c o v e r ya n n e a l i n g a t t e m p e r a t u r e s , c o i n c i d i n g w i t h t e m p e r a -t u r e s o f t e m p e r b r i t t l e n e s s g r o w t h .

( 6 ) F o r t h e b a s e m e t a l o f t h e s t e e l A 5 3 3 B , c o n s i d -e r a b l y l o w e r r e c o v e r y o f t h e y i e l d s tr e s s a f t e r r e c o v e r ya n n e a l i n g i s f o u n d o u t , a s c o m p a r e d w i t h D B T T. T h i sf a c t p o i n t s o u t t o t h e n o n d o m i n a t i n g c o n t r i b u t i o n o fr a d i a t i o n h a r d e n i n g t o t h e s t e e l e m b r i t t l e m e n t u n d e ri r r ad i a t i on .

A c k n o w l e d g e m e n t s

T h e a u t h o r s a r e t h a n k f u l t o Yu . K o r o l e v f o r h iscon t r i bu t ion t o t he impac t t e s t i ng , M. Bak i rov, V.P o t ap o v, G . Z h a r o v o i ( V N I I A E S ) f o r t h e d e t e r m i n a -t i o n o f m e c h a n i c a l p r o p e r t i e s b y t h e k i n e t i c h a r d n e s sm e t h o d , K . P r i k h o d k o f o r t h e i m a g e a n a l ys i s. T h i sw o r k w a s p e r f o r m e d i n t h e R e a c t o r M a t e r i a l s D i v i s i o no f t h e R u s s i a n R e s e a r c h C e n t e r ' K u r c h a t o v I n s t i tu t e ' .

R e f e r e n c e s

[1] S.A. Saltykov, Stereometricheskay a Metallografiya (M etal -lurgiya, Moscow, 1976) pp. 139-144.

[2] M .B. Baldrov, Kon trolle 10 (1994) 50.[3] Standards for Strength Calculations of Components and

Piping o f Nuclear Power Plants (Energatomizdat, Moscow,1989) pp. 193-198.

[4] Radiation E mbrit t lemen t of Re actor Vessel M aterials ,Regulatory Guide 1.99, Task M E 305-4 rev. 2, US N uclearRegulatory Commission (US NRC , Washington, 1988) pp.1.99-1-1.99-10.

[5] N.N. Alekseenko, A.D. Amaev, I .V. Gorynin and V.A.

Nikolaev, Russ. Radia tsionn oe Povrezhdenie S talei Kor-pusov Vodovodyanykh Reaktorov (Energatomisdat ,Moscow, 1981) pp, 20-91.

[6] G.R. Odette, Scripta Metall. 17 (1983) 1183.[7] J.R. Hawtho rne, in: Okhrupch ivanie K onstruktsionnykh

Stalei i Splavov, eds. C .L Briant, S.K. Banergy (Metal-lurgiya, Moscow, 1988) pp. 423-480.

[8] L.M. Utevski, E.E., Glicman and G.S. Kark, ObratimayaOtpusknaya Khrup kost ' Stalei i Splavov Zheleza (M etal-lurgiya, Moscow, 1987) pp. 10-49.