Influence of heat treatments on microstructures in an Fe-Co-V alloy
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a p r e v i o u s s t u d y on low v a n a d i u m a l l o y (nominal c o m p o s i t i o n : 2.7 wt p c t V and F e = Co), the p h a s e e q u i l i b r i a and t r a n s f o r m a t i o n s have b e e n i n v e s t i g a t e d b y o p t i c a l m e t a l l o g r a p h y and s c a n n i n g e l e c t r o n m i c r o s c o p y - m i c r o p r o b e a n a l y s i s . 1 It is o b s e r v e d that, b y quenching the a l l o y into i c e d - b r i n e o r a i r c o o l i n g f r o m the high t e m p e r a t u r e s i n g l e - p h a s e y f i e l d [ s e e F i g . l(a)a], v a n a d i u m can b e r e t a i n e d in a s u p e r s a t u r a t e d s o l i d s o l u t i o n ; t h i s o b s e r v a t i o n is c o n s i s t e n t with the p r e v i o u s work, s-s and t h i s p h a s e h a s b e e n d e s i g n a t e d a s ~a. D u r i n g the p r e c e d i n g t r e a t m e n t , the phase undergoes a structural transformation, namely ffcc) ~ ~2 (bcc). On a n n e a l i n g ~2 in the t w o - p h a s e ~ + y f i e l d b e t w e e n 900 and 950~ [ s e e Fig. l(b)], d e c o m p o s i t i o n into v a n a d i u m - r i c h (N-fcc) and v a n a d i u m p o o r ( ~ - b c c ) r e g i o n s o c c u r s . Subsequently, on q u e n c h ing into i c e d - b r i n e o r a i r cooling, the y r e g i o n s a g a i n u n d e r g o the fcc ~ b c c (aa) t r a n s i t i o n . On a g i n g this m a t e r i a l at 600~ ~2 d e c o m p o s e s into ~ (bcc) m a t r i x and s t a b l e y p r e c i p i t a t e s [ s e e F i g . l(c)], and f a v o r a b l e m a g n e t i c p r o p e r t i e s of the a l l o y have b e e n a t t r i b u t e d to t h e s e p r e c i p i t a t e s . 6 Below ~ 730~ the ~1 p h a s e o r d e r s into a B a s u p e r l a t t i c e , and the k i n e t i c s of l o n g - r a n g e o r d e r i n g a r e e x t r e m e l y r a p i d ; 7 the o r d e r e d - v a r i a n t was d e n o t e d a s rv'~.4 It i s a p p a r e n t f r o m F i g . l ( c ) t h a t t h e a l l o y s c o n t a i n i n g 2 . 5 - 3 . 0 wt p c t V, 35-50 wt p c t Co and b a l a n c e F e m a y o r d e r on a n n e a l i n g at 600~ It is a l s o known that t h e p r e s e n c e of l o n g - r a n g e o r d e r h a s d e l e t e r i o u s e f f e c t s on y i e l d s t r e n g t h a s w e l l a s on d u c t i l i t y , a - n T h e r e f o r e , in o r d e r to c o r r e l a t e the o b s e r v e d m e c h a n i c a l p r o p e r t i e s with m i c r o s t r u c t u r e s p r o d u c e d b y v a r i ous h e a t t r e a t m e n t s , 8 it is e s s e n t i a l to know the s t a t e
S. MAHAJAN, member technical staff, Bell Laboratories, Murray Hill, N. J. 07974. M. R. PINNEL, and J. E. BENNETT are members, technical staff, Bell Laboratories, Colombus, Ohio 43213. Manuscript submitted October 8, 1973. METALLURGICAL TRANSACTIONS
of o r d e r of d i f f e r e n t m i c r o s t r u c t u r a l f e a t u r e s . It {s a l s o not c l e a r w h e t h e r the y ~ 2 t r a n s f o r m a t i o n can be categorized as massive or martensitic: English's 4 r e s u l t s a r e c
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