On the influence of cyclic hardening and crack opening displacement (COD) on crack advance during fatigue
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Service at Eie~,ated TemperaPuresm Nuclear,Paver Ge#eratton. " A, O.
Schaefer,ed, pp, 1-30,ASME,New York, 3975, 6. R K. Bhargava Ph.D.DlssertaUon,Umver,~tyof CmcmnatL 1975. 7. D, L Mtche},L Moteff,and A, L LoveIl"A~'~aMet., 1973~voL 21~pp t269-77, 8, P,, K, Bha~ava,J. Moteff,and K W. Swmdeman Proceedings ofa ~'mb~mum on "Stracmrat Materials .for Service at Elevated Temperatures in Nuclear Power Genemdon, "A, O, Schaefer,elL,pp. 33-54, ASME,NewYo~k, 1975, 9, K, D, Chailengerand J. Moteff,Met. Trans,, 1972,voL 3, pp. 1675-78.
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NORMALIZED SHEAR ST~,,,~, o~,/~ Fig, 5--Deformation mechanism map for 304 Stainless Steel with the corresponding microstructural feature fields, The field designated A represents the region of strong carbidedislocation interaction which tends to prevent the normal formation of subgrains.
v e t o p e d a s a r e s u l t of d e f o r m a t i o n in the v a r i o u s f i e l d s of the d e f o r m a t i o n m e c h a n i s m map is o u tl in e d . A l s o shown is t h e r e g i o n w h e r e the c o m p l e x c a r b i d e s of MzaC6 type i n t e r a c t s t r o n g l y w i t h the d i s l o c a t i o n s an d t h e r e b y p r e v e n t t h e i r r e a r r a n g e m e n t i n t e cell.s o r s u b g r a i n s . T h i s p r e l i m i n a r y i n f o r m a t i o n is b a s e d on the t r a n s m i s s i o n e l e c t r o n m i c r o s c o p e e v a l u a t i o n of the s u b s t r u c t u r e of a s e l e c t e d s e t of s p e c i m e n s . T a b l e I I s u m m a r i z e s in a q u a l i t a t i v e m a n n e r t h e c h a r a c t e r i s t i c s of the d i s l o c a t i o n s u b s t r u c t u r e and the c a r b i d e s . One o b v i o u s e f f e c t of th e p r e s e n c e of c a r b i d e s is the l o s s of d u c t i l i t y , T h i s c i r c u m s t a n c e c l e a r l y s u g g e s t s t h a t f o r c e r t a i n m e t a l s t h e f o r m a t i o n of c e l l s ancL/or s u b g r a i n s i s a n a t u r a l and r e q u i r e d o c c u r r e n c e in the n o r m a l d e f o r m a t i o n p r o c e s s e s and c o n t r i b u t e s to the ductility. T h e f o r m a t i o n of M~C~ t y p e c a r b i d e s in 304 an d 316 s t a i n l e s s s t e e l has been well established. The influe n c e of t h e i r p r e s e n c e on the high t e m p e r a t u r e s t r e n g t h has b e e n s t u d i e d by B i s s e t al, ~4 E t i e n n e e t ed ~ and T a n a k a and S h i n o d a } ~ H o w e v e r , the i n f l u e n c e of t h e p r e s e n c e of c a r b i d e s on the d e f o r m a t i o n c h a r a c t e r i s t i c s and f r a c t u r e m o d e s of AISI 304 s t a i n l e s s s t e e l at e l e v a t e d t e m p e r a t u r e s n e e d s to be f u r t h e r i n vestigated. This information is all the m o r e d e s i r a b l e in v i e w of the i n v o l v e m e n t of 304 s t a i n l e s s s t e e l in t h e s t r u c t u r a l c o m p o n e n t s of the liquid m e t a l f a s t b r e e d e r reactor, R e s e a r c h w a s s p o n s o r e d by the U. S. E n e r g y R e s e a r c h and D
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