T r a ns f or ma 11 on s .
One p a r t i c u l a r a s p e c t r e q u i r i n g f u r t h e r work
c o n c e r n s what h a s been termed r e c o v e r y a s s i s t e d m a r t e n s i t e and which was found to o ccu r i n th e and 6y. manganese a l l o y s . An u n d e r sta n d in g o f th e t r a n s f o r m a t io n mechanism would be a id e d by a more d e t a i l e d s tu d y o f th e t i m e f temperature* t r a n s f o r m a t io n behaviour* s o t h a t th e k i n e t i c s o f i t s t r a n s f o r m a t io n c o u ld be used to g a i n a b e t t e r id e a o f t h e r a t e c o n t r o l l i n g s t e p . Other im p ortan t a s p e c t s a r e such f e a t u r e s a s t h e p r e s e n c e or a b se n c e o f s u r f a c e t i l t s * the r e l a t i o n s h i p between growth and p r io r a u s t e n i t e g r a i n boundaries* and e r y s t a l l o g r a p h i c o r i e n t a t i o n
r e l a t i o n s h i p s . The ir o n manganese system however d oes not seem to l e n d i t s e l f v ery w e l l t o t h i s typ e o f o b s e r v a t io n s * owing t o the problems o f s u r f a c e v o l a t i l i s a t i o n . An ir o n n i c k e l a l l o y w i t h i n the range 5> to 10yi n i c k e l may t h e r e f o r e prove to be more u s e f u l i f th e r e c o v e r y a s s i s t e d m a r t e n s it e r e a c t i o n can be made to o c c u r .
P r o p e r t i e s .
U ndoubtedly th e major problem t o be s o lv e d i n t h e i r o n manganese system i s t h a t o f b r i t t l e n e s s . The p r e s e n t work has shown t h a t t h i s i s l i k e l y to be due t o a temper b r i t t l e n e s s e f f e c t * but th e im p u r ity r e s p o n s i b l e h a s not been i s o l a t e d . F u rth er work i s t h e r e f o r e needed not o n ly t o i d e n t i f y th e im p u r ity but a l s o to d eterm ine the c o n d i t i o n
purpose a f u r t h e r s e r i e s o f a l l o y s a re b ein g prepared and c o n s i s t e s s e n t i a l l y o f an 8# manganese a l l o y w it h t h e f o l l o w i n g a d d i t i o n s or m o d i f i c a t i o n s .
( i ) Very low carbon h ig h p u r i t y a l l o y i n which s p e c i a l p r e c a u t i o n s have been taken to minimize both th e s i l i c o n and phosphorus l e v e l s . ( i i ) As above* but w it h an a d d i t i o n o f 0 . 1 # Ti to t i e up i n t e r s t i t i a l e le m e n t s . ( i i i ) S p l i t m e lt s o f 8 # manganese c o n t a i n i n g v a r i a b l e ( a ) n i t r o g e n (b) carbon ( c ) s i l i c o n . By s tu d y in g th e e f f e c t s o f t h e s e i m p u r i t i e s on the temper b r i t t l e n e s s s u s c e p t i b i l i t y o f the i r o n manganese system* i t i s hoped t h a t the source o f e m b r itt le m e n t may be
i d e n t i f i e d and an a n t i d o t e found.
In a d d i t i o n t o t h e above*work i s a l r e a d y underway w i t h in t h e department t o s tu d y th e e f f e c t s o f molybdenum a d d i t i o n s bn the b r i t t l e n e s s problem.
R K F