Influence of grain orientation on the dislocation substructure in austenitic stainless steel
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Table I. Alloy Composition (Wt Pct)
C
Mn
Si
P
S
Cr
Ni
Mo
Fe
0,08
1.78
0.48
0.026
0,010
18.9
8.6
0.46
Bal
S. N. MONTEIRO AND H . - J . K E S T E N B A C H E l e c t r o n m i c r o s c o p y s t u d i e s of d i s l o c a t i o n s u b s t r u c t u r e d e v e l o p e d d u r i n g p l a s t i c d e f o r m a t i o n of p o l y c r y s t a l l i n e m a t e r i a l a r e u s u a l l y r e s t r i c t e d to the o b s e r v a tion of t w o - d i m e n s i o n a l s e c t i o n s of the s p e c i m e n . This r e s t r i c t i o n is unfortunate in v i e w of l a r g e d i f f e r e n c e s in s u b s t r u c t u r e which have s o m e t i m e s b e e n o b s e r v e d in the s a m e m a t e r i a l or e v e n the s a m e g r a i n . l ' 2 It m a y then be difficult to d e c i d e w h e t h e r such d i f f e r e n c e s a r e r e a l o r m e r e l y a r i s e f r o m d i f f e r e n t v i e w s of the s a m e s t r u c t u r a l f e a t u r e s , a d i s t i n c t i o n which b e c o m e s r e l e vant when s t r u c t u r a l v a r i a b l e s , such as d i s l o c a t i o n c e l l s i z e , a r e to be c o r r e l a t e d with m e c h a n i c a l p r o p e r t i e s . In this c a s e , it m a y be w o r t h w h i l e to s e a r c h for s o m e c r y s t a l l o g r a p h i c r e g u l a r i t y in the d i s l o c a t i o n d i s t r i b u tion b e c a u s e , if this r e g u l a r i t y e x i s t s , a t h r e e - d i m e n s i o n a l v i e w of the s u b s t r u c t u r e m a y be c o n s t r u c t e d f r o m s u i t a b l y o r i e n t e d t w o - d i m e n s i o n a l s e c t i o n s . The p u r p o s e of this note is to r e p o r t on such c r y s t a l l o g r a p h i c r e g u l a r i t i e s o b s e r v e d in the d i s l o c a t i o n s u b s t r u c t u r e of an a u s t e n i t i c s t a i n l e s s s t e e l a f t e r p l a s t i c d e f o r m a t i o n at i n t e r m e d i a t e t e m p e r a t u r e s . It will be shown that, in this m a t e r i a l and under the p a r t i c u l a r e x p e r i m e n t a l conditions which c o r r e s p o n d to the dyn a m i c s t r a i n aging i n t e r v a l , an e q u i a x e d c e l l s t r u c t u r e is f o r m e d . This s t r u c t u r e , h o w e v e r , p r e v i o u s l y obs e r v e d in a s i m i l a r alloy, s r e p r e s e n t s only one a s p e c t of a g e n e r a l l y quite i n h o m o g e n e o u s d i s l o c a t i o n d i s t r i bution. The p r e s e n t i n v e s t i g a t i o n was p e r f o r m e d on p o l y c r y s t a l l i n e AISI-304 s t a i n l e s s s t e e l s t r a i n e d to f a i l u r e in t e n s i o n at t e m p e r a t u r e s b e t w e e n 400 and 600~ The c h e m i c a l c o m p o s i t i o n of the a l l o y is given in Table I, and the a v e r a g e g r a i n s i z e of the a n n e a l e d m a t e r i a l was a p p r o x i m a t e l y 40 ~m. Round t e n s i l e s p e c i m e n s with a gage s e c t i o n of 4 m m in d i a m and 24 m m in length w e r e tested under vacuum at a strain rate of 3.5 • 1
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