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p r o g r e s s in c l a r i f y i n g the Mn-C s y s t e m was made by Kuo and P e r s s o n * who e s t a b l i s h e d the e x i s t e n c e and t e m p e r a t u r e r a n g e of s t a b i l i t y of five b i n a r y p h a s e s one of which was new. T h e i r r e s u l t s differ s t r i k i n g l y f r o m the e a r l i e r phase d i a g r a m s r e p o r t e d by Vogel and DSring z and Isobe s i n d i c a t i n g a need for a s y s t e m a t i c r e i n v e s t i g a t i o n of the e n t i r e phase d i a g r a m . The r e s u l t s r e p o r t e d h e r e a r e p a r t of those which we have obtained in an i n v e s t i g a t i o n u n d e r t a k e n to i n t e r p r e t and c o r r e l a t e t h e r m o d y n a m i c data on the F e - M n - C system. 4 EXPERIMENTAL Materials Alloys were made with Specpure m a n g a n e s e (Johnson Matthey C h e m i c a l s ) and National Spectroscopic graphite e l e c t r o d e s (Union C a r b i d e C o r p o r a t i o n , C a r bon P r o d u c t s Division). Weighed q u a n t i t i e s of the e l e m e n t s were m e l t e d together in ZrOa c r u c i b l e s in an a r g o n a t m o s p h e r e by induction h e a t i n g and then c a s t into 6 m m d i a m s i l i c a t u b e s . Samples of t h r e e of the alloys (Nos. 4, 7, and 8) w e r e a n a l y z e d by m e m b e r s of the M.I.T. Analytical L a b o r a t o r y and the r e s u l t s a r e given in p a r e n t h e s e s along with the n o m i n a l c o m p o s i t i o n s in Table L Procedure Samples of the v a r i o u s alloys were s e a l e d in a p a r tial a t m o s p h e r e of a r g o n in Vycor t u b e s . These were e q u i l i b r a t e d for p e r i o d s r a n g i n g f r o m 14 d at 700~ to 2 d at 800 ~ and 900~ to 4 h at 1000~ to ~h* at 1100~ and quenched by b r e a k i n g the c a p s u l e s under w a t e r . P r o d u c t p h a s e s w e r e identified in s a m p l e s by m i c r o s c o p i c e x a m i n a t i o n and f r o m X - r a y d i f f r a c t i o n powder p a t t e r n s obtained with a D e b y e - S c h e r r e r type c a m e r a and V - f i l t e r e d c h r o m i u m r a d i a t i o n . The powd e r s a m p l e s of s p e c i m e n s c o n s i s t i n g of the y - p h a s e w e r e obtained as f i l i n g s . All the other powder s a m p l e s were c r u s h e d and ground in a n a l u n d u m m o r t a r and p e s t l e . ROBERT BENZ, formerly with the Research Staff, Massachusetts Institute of Technology, Cambridge, Mass. 02139, is presently with Technical Information Group, University of California, Los Alamos Scientific Laboratory, Los A/amos, N. M. 87544. JOHN F. ELLIOTT, Fellow of TMS, and JOHN CHIPMAN, Fellow of ASM and of TMS, are Professor and Professor Emeritus, respectively, Department of Metallurgy and Materials Science, Massachusetts lntsitute of Technology. Manuscript submitted August 18, ] 972. METALLURGICALTRANSACTIONS

RESULTS The Mn-C phase d i a g r a m s e e n in Fig. 1 is b a s e d upon a) X - r a y d i f f r a c t i o n m e a s u r e m e n t s of m a n g a n