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b a s e alloys has b e e n studied by s e v e r a l i n v e s t i g a t o r s . L e s l i e e t al 1 r e p o r t e d a g r a i n size dependence of the DBTT of 6 ~ -1/2 in an F e - T i alloy while a s l i g h t l y l a r g e r g r a i n s i z e dependence was o b s e r v e d by Bucher and Goddenow e and Gupta 3 in F e - T i - A 1 a l l o y s . R e c e n t l y Jin et a l 4,5 w e r e able to s u p p r e s s the t r a n s i t i o n t e m p e r a t u r e of a t i t a n i u m - g e t t e r e d f e r r i t i c F e - 1 2 Ni alloy to below liquid h e l i u m t e m p e r a t u r e by o b t a i n i n g an u l t r a f i n e g r a i n size through t h e r m a l cycling. The r e p o r t s on the effect of r e t a i n e d a u s t e n i t e on the m e c h a n i c a l p r o p e r t i e s of f e r r i t i c (or m a r t e n s i t i c ) s t e e l s a r e s o m e w h a t c o n t r a d i c t o r y . A b e n e f i c i a l effect of r e t a i n e d a u s t e n i t e on t e n s i l e d u c t i l i t y in m a r a g i n g type s t e e l s has b e e n r e p o r t e d . 6'7 Rack and Kalish 8 and P a m p i l l o and Paxton, 7 however, found little benefit in i m p a c t toughness f r o m r e t a i n e d a u s t e n i t e . In 9-Ni s t e e l ~ and 6-Ni steel, m the s u p r e s s i o n of the DBTT and the i m p r o v e d l o w - t e m p e r a t u r e toughness w e r e a t t r i b u t e d to the p r e s e n c e of r e t a i n e d a u s t e n i t e f o r m e d d u r i n g t e m p e r i n g . R e c e n t l y Hwang ~ o b s e r v e d a cons i d e r a b l e i n c r e a s e in t e n s i l e d u c t i l i t y and i m p a c t toughness by i n t r o d u c i n g r e t a i n e d a u s t e n i t e into a f i n e g r a i n e d F e - N i - T i c r y o g e n i c alloy, but l i t t l e i m p r o v e m e n t was found in f r a c t u r e t o u g h n e s s . In m a n y of the p r e v i o u s s t u d i e s the a c c o m p a n y i n g effect of r e d u c e d s t r e n g t h d u r i n g the f o r m a t i o n of r e tained a u s t e n i t e has been neglected. This paper exa m i n e s the influence of g r a i n s i z e and r e t a i n e d a u s t e n i t e at s i m i l a r s t r e n g t h l e v e l s on the t e n s i l e d u c t i l i t y and the d u c t i l e - b r i t t l e t r a n s i t i o n of a t i t a n i u m g e t t e r e d F e - 8 Ni-2 Mn-0.15 Ti alloy. MATERIALS AND E X P E R I M E N T A L PROCEDURE

positions a r e shown in Table I. The ingots w e r e hom o g e n i z e d u n d e r v a c u u m at 1200~ for 24 h o u r s and f u r n a c e cooled, and then upset c r o s s - f o r g e d at l l 0 0 ~ to 10 cm wide by 1.3 cm thick p l a t e s . These p l a t e s w e r e a n n e a l e d at 900~ for 1 hour u n d e r a r g o n gas to r e m o v e p r i o r d e f o r m a t i o n s t r a i n and a i r cooled. This a n n e a l e d m a t e r i a l has a g r a i n size of 38 ~ m d i a m e t e r and is d e s i g n a t e d as A N . Optical m e t a l l o g r a p h y and 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 y w e r e p e r f o r m e d by s t a n d a r d l a