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I. INTRODUCTION T H E F e - C r - C o a l l o y s y s t e m has r e c e i v e d m u c h a t t e n t i o n d u r i n g the p a s t s e v e r a l y e a r s b e c a u s e of the d u c t i l i t y and e x c e l l e n t p e r m a n e n t m a g n e t p r o p e r t i e s the s y s t e m offers.l-12 While m o s t of the m a g n e t a l l o y r e s e a r c h and d e v e l o p m e n t e f f o r t h a s b e e n d e v o t e d to F e - C r - C o a l l o y s containing a d d i t i o n a l f e r r i t e f o r m i n g e l e m e n t s (such a s Si, A1, Ti, Mo, V, Nb, and so forth), m o r e r e c e n t w o r k I~ d e m o n s t r a t e s that a s i m p l e t e r n a r y c o m p o s i t i o n s u f f i c e s to allow c o n v e n i e n t a l l o y p r o c e s s i n g a s w e l l a s to a c h i e v e high e n e r g y p e r m a n e n t m a g n e t p r o p e r t i e s . C o m m e r c i a l a p p l i c a t i o n s of t h e s e a l l o y s have a l r e a d y t a k e n p l a c e , n The o r i g i n of the p e r m a n e n t m a g n e t i s m in the F e C r - C o a l l o y s y s t e m is a t t r i b u t e d to the e x t r e m e I y fine s c a l e t w o - p h a s e s t r u c t u r e o b t a i n e d by s p i n o d a l d e c o m p o s i t i o n of the i r o n r i c h b c c ~ - p h a s e within the (oct + c~2) m i s c i b i l i t y g a p . 8'9 W h i l e t h e s e F e - C r - C o b a s e a l l o y s a r e known a s " d u c t i l e p e r m a n e n t m a g n e t s " , it should be c l e a r I y u n d e r s t o o d that t h e y a r e , in m o s t c a s e s , ductiIe in the s o l u t i o n a n n e a l e d and quenched o~-state r a t h e r than in the fully d e c o m p o s e d s t a t e . The d e c o m p o s i t i o n to a c h i e v e d e s i r a b l e m a g n e t p r o p e r t i e s often l e a d s to a s e v e r e e m b r i t t l e m e n t . D e c o m p o s i t i o n could a l s o o c c u r d u r i n g p r e l i m i n a r y a l i o y p r o c e s s i n g , e . g . , d u r i n g c o o l i n g to r o o m t e m p e r a t u r e a f t e r hot w o r k i n g or a n n e a l i n g , thus d e t e r i o r a t i n g the d u c t i l i t y n e c e s s a r y f o r s u b s e q u e n t cold r o l l i n g o r f o r m i n g . The r e c e n t l y d e v e l o p e d " d e f o r m a r i o n - a g i n g " t e c h n i q u e ~~ which i n t r o d u c e s s t r o n g m a g n e t i c a n i s o t r o p y and a S. JIN and S. MAHAJAN are Members of Technical Staff, and D. BRASEN is Associate Member of Technical Staff, Bell Laboratories, Murray Hill, NJ 07974. Manuscript submitted April 30, 1979. METALLURGICAL TRANSACTIONS A

high e n e r g y p r o d u c t in F e - C r - C o a l l o y s without m a g netic field heat treatment, requires plastic deformation a s a m e c h a n i s m for inducing m a g n e t i c a n i s o t r o p y . Hence the d u c t i l i t y of the a l l o y i s e s s e n t i a l in a c h i e v i n g d e s i r a b l e p e r m a n e n t m a g n e t p r o p e r t i e s by t h i s t e c h n i q u e . In view of the s i g n i f i c a n c e of m e c h a n i c a l p r o p e