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D. A N T O L O V I C H

The low c y c l e fatigue (LCF) b e h a v i o r of a high s t r e n g t h , m e t a s t a b l e a u s t e n i t i c s t e e l c a l l e d T R I P s t e e l h a s b e e n s t u d i e d . High s t r a i n L C F e x p e r i m e n t s on c y l i n d r i c a l , w e l l - p o l i s h e d s p e c i m e n s u n d e r d i a m e t r a l s t r a i n c o n t r o l w e r e c a r r i e d out. To s t u d y the effect of a m i x e d a u s t e n i t e - m a r t e n s i t e m a t r i x , L C F t e s t s w e r e a l s o done on the T R I P s t e e l a f t e r inducing s i g n i f i c a n t a m o u n t s of m a r t e n s i t e in the a u s t e n i t e m a t r i x b y m e a n s of a v e r y high u n i d i r e c tional p r e s t r a i n . To e s t a b l i s h the r o l e p l a y e d b y the m a r t e n s i t e t r a n s f o r m a t i o n , t e s t s w e r e a l s o run above the M D. The amount of m a r t e n s i t e induced was m a g n e t i c a l l y m e a s u r e d by m e a n s of a " p e r m e a m e t e r " b u i l t s p e c i f i c a l l y for this p u r p o s e . It was found that the L C F llfe of the T R I P s t e e l , both a t r o o m t e m p e r a t u r e (in the p r e s e n c e of m a r t e n s i t i c t r a n s f o r mation) and at 200~ (in the a b s e n c e of the t r a n s f o r m a t i o n ) , was r e l a t e d to the p l a s t i c s t r a i n r a n g e , E p R , b y the M a n s o n - C o f f i n law. E i t h e r c y c l i c h a r d e n i n g o r softening o c c u r r e d at r o o m t e m p e r a t u r e , depending p r i m a r i l y upon the p l a s t i c s t r a i n r a n g e used in cycling. H a r d ening was o b s e r v e d below 3 p c t p l a s t i c s t r a i n r a n g e . F o r L C F t e s t s at 200~ c y c l i c s o f t e n ing was Observed in a l l c a s e s . The h a r d e n i n g and softening b e h a v i o r has been found to d e pend on the m a r t e n s i t i c t r a n s f o r m a t i o n taking p l a c e in t h e s e s t e e l s d u r i n g cycling. Howe v e r , the L C F life c o r r e l a t e d b e s t to the p e r c e n t r e d u c t i o n in a r e a , independent of the e x t e n t of the m a r t e n s i t e t r a n s f o r m a t i o n . A c l a s s of m e t a s t a b l e a u s t e n i t i c s t e e l s c a l l e d T R I P s t e e l s h a s b e e n r e p o r t e d to have an e x c e l l e n t c o m b i n a tion of s t r e n g t h , d u c t i l i t y , and t o u g h n e s s , t-5 The high t o u g h n e s s and d u c t i l i t y a s s o c i a t e d with t h e s e s t e e l s have b e e n a t t r i b u t e d to a s t r e s s - o r s t r a i n - i n d u c e d t r a n s f o r m a t i o n of m e t a s t a b l e a u s t e n t t e to m a r t e n s i t e d u r i n g the t e n s i l e t e s t i n g at t e m p e r a t u r e s below M D.x-B The t r a n s f o r m a t i o n to m a r t e n s l t e s t r e n g t h e n s the d e f o r m e d r e g i o n and f o r c e s the s u b s e q u e n t d e f o r m a t i o n into a d i a c e n t m a t e r i a l . T h i s i n h i b i t s n e c k i n g and e