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Martensite

Austenite Crystal Orientation

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K_S/ ~ "~- Retoined N-W Austenite F i g . 5--Schematic showing the abeyance of both K - S and N-W orientation r e l a t i o n s within the s a m e lath m a r t e n s i t e packet corresponding t o the diffraction pattern of F i g . 2 .

t h e c o m p o s i t i o n . T h e s e o b s e r v a t i o n s do not s u p p o r t e a r l i e r p r e d i c t i o n s f o r a n o r i e n t a t i o n r e l a t i o n w h i c h is exactly intermediate b e t w e e n K-S and N-W relations. M o r e s i g n i f i c a n t l y , it i s i d e n t i f i e d i n t h i s s t u d y that austenite//martensite p h a s e s can obey both K-S and N-W orientation relations alternating amongst the m a r t e n s i t e l a t h s o f t h e s a m e p a c k e t ( F i g . 5) f o r s o m e a l l o y s t e e l c o m p o s i t i o n s . T h e r e is n o a p r i o r i r e a s o n w h y t h i s c a n not h a p p e n . O n t h e o t h e r h a n d , a h y p o t h e s i s c a n be a d v a n c e d t o e x p l a i n t h i s o n t h e b a s i s that t h e two o r i e n t a t i o n r e l a t i o n s g i v e b e t t e r f l e x i b i l i t y in t e r m s of i n c r e a s e d v a r i a n t s a v a i l a b l e d u r i n g m a r t e n s i t e n u c l e a t i o n . 4's B a s e d on l i m i t e d d a t a p r e s e n t e d h e r e , it s e e m s also possible to h a v e o r i e n t a t i o n r e l a tions o t h e r than K-S or N-W alternating amongst the l a t h s of the s a m e p a c k e t . I n a d d i t i o n , t h e s e o b s e r v a t i o n s p o i n t o u t the e x t r e m e c a u t i o n t o be e x e r c i z e d i n the u s e o f i n d i r e c t m e t h o d s of c r y s t a l l o g r a p h i c a n a l y s i s for lath martensite transformation which a l s o p r o b a b l y a c c o u n t s f o r t h e wide s c a t t e r4,s i n t h e h a b i t p l a n e a n a l y s i s of t h i s t e c h n o l o g i c a l l y i m p o r t a n t transformation. T h e a u t h o r a c k n o w l e d g e s NSF ( C o n t r a c t N o . D M R 720 3 2 6 9 A 0 1 ) f o r f i n a n c i a l s u p p o r t a n d the D i v i s i o n o f B a s i c E n e r g y S c i e n c e s , U.S. D e p a r t m e n t o f E n e r g y through the M a t e r i a l s and M o l e c u l a r R e s e a r c h Division of t h e L a w r e n c e B e r k e l e y L a b o r a t o r y f o r p r o v i d i n g l a b o r a t o r y f a c i l i t i e s . It is a p l e a s u r e to acknowledge t h e c o n t i n u e d e n c o u r a g e m e n t of P r o f e s s o r G. T h o m a s in t h i s p r o g r a m .

1. B. V. Narasimha Rao, J. Y. Koo, and G. Thomas: EMSA Proceedings, p . 30, Claitors Publishing Division, Baton Rouge, 1975. 2. G. Thomas: Battelle Colloquiumon Fundamental Aspects o f Structural Alloy Design, R. I. Jaffee andB. A. Wilcox,eds., Plenum, 1977. 3 . G. Thomas: Met. Trans. A, 1978, vol. 9A, p . 439. 4 . G. Thomas andB. V. N. Rao: International