Thermodynamics of the fcc Fe-Mn-C and Fe-Si-C alloys
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M A N G A N E S E and s i l i c o n a r e the m o s t c o m m o n of the a l l o y i n g e l e m e n t s in s t e e l , yet t h e i r b i n a r y s y s t e m s with i r o n have been studied I only i n c o m p l e t e l y . The t e r n a r y s y s t e m F e - M n - C was s u b j e c t to a n u m b e r of e a r l y i n v e s t i g a t i o n s2-4 a s a r e s u l t of which the p h a s e d i a g r a m i s known at l e a s t up to 14 wt pct Mn. E a r l y work on F e Si-C has b e e n s u m m a r i z e d by G r e i n e r , M a r s h , and Stoughton. 5 The a c t i v i t y of c a r b o n in each of t h e s e t e r n a r y s y s t e m s at 1000~ was d e t e r m i n e d by Smith. 6 The p u r p o s e of this p a p e r is to extend S m i t h ' s m e a s u r e m e n t s over a r a n g e of t e m p e r a t u r e s and to higher m a n g a n e s e c o n c e n t r a t i o n s . The excellent a g r e e m e n t at 1000~ p e r m i t s i n c o r p o r a t i o n of both s e t s of data into a definitive t h e r m o d y n a m i c t r e a t m e n t . E X P E R I M E N T A L PROCEDURE Materials The F e - M n a l l o y s w e r e p r e p a r e d by induction m e l t i n g u n d e r an a r g o n a t m o s p h e r e e l e c t r o l y t i c i r o n and s p e c t r o s c o p i c a l l y s t a n d a r d i z e d m a n g a n e s e of J o h n s o n Matthey Company. A l u m i n a c r u c i b l e s w e r e u s e d for a l l o y s c o n t a i n i n g l e s s than 30 pct Mn. F o r higher conc e n t r a t i o n s z i r c o n i a c r u c i b l e s w e r e used. The m e l t s w e r e cast by suction into 5 m m ID v y c o r t u b e s and then r o l l e d into 0.25 m m s h e e t s . F e - S i a l l o y s containing 1.86 and 3.71 pct Si w e r e s i m i l a r l y p r e p a r e d u s i n g highp u r i t y s i l i c o n (99.99 pct) in s i l i c a c r u c i b l e s and r o l l e d to 0.3 m m s h e e t s . Alloys of 4.51, 5.14, and 6.94 pct Si w e r e sucked into 1.5 m m c a p i l l a r i e s and u s e d a s r o d s . C o m p o s i t i o n v a r i a t i o n s w e r e checked by X - r a y m i c r o a n a l y s i s and found to be l e s s than the l i m i t s of d e t e c tion, • pct Si. Two a l l o y s containing 3.28 and 3.97 pct Si w e r e 10 m i l s h e e t s of the c o m m e r c i a l h i g h - p u r i t y a l l o y s u s e d by Sakao and Elliott 7 for m e a s u r e m e n t s of TSUGUYASUWADA,formerly of the Research Staff, Massachusetts Institute of Technology, Cambridge, Mass., is now a Staff Metallurgist, Climax Molybdenum Co., Ann Arbor, Michigan. HARUE WADA,formerly of the Research Staff, MIT, Cambridge, is now a Research Assistant, University of Michigan,Ann Arbor. JOHN F. ELLIOTT, Fellow of The MetallurgicalSociety of AIME, is Professor, Department of Metallurgy and Materials Science, MIT, Cambridge. JOHN CHIPMAN, Fellow of The MetallurgicalSociety of AIME and of The American Society for Metals, is Professor Emeritus, Department of Metallurgy and Materials Science, MIT, Cambridge, Manuscript submitted September 14, 1971. METALLURGICALTRANSACTIONS
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