Thermodynamics and solubility of carbon in ferrite and ferritic Fe-Mo alloys
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p r i m a r y o b j e c t i v e of the m a j o r i t y of i n v e s t i g a t i o n s that have b e e n m a d e on the i r o n - c a r b o n s y s t e m in the p a s t was the d e t e r m i n a t i o n of the bounda r i e s between the v a r i o u s p h a s e s . M o r e o v e r , the b u l k of t h e s e s t u d i e s have b e e n c o n c e r n e d with the d e t e r m i n a t i o n of the p h a s e b o u n d a r i e s of the a u s t e n i t e region. Thermodynamic quantities calculable from the a f o r e - m e n t i o n e d d a t a w e r e a l m o s t a l w a y s r e s t r i c t e d to the d e t e r m i n a t i o n of the enthalpy of s o l u tion of c a r b o n in the r e s p e c t i v e i r o n p h a s e s . N e v e r t h e l e s s , t h e s e i n v e s t i g a t i o n s have p r o v i d e d an i m p o r t a n t s t e p p i n g s t o n e for f u r t h e r e x p e r i m e n t a t i o n to o b t a i n the t h e r m o d y n a m i c p r o p e r t i e s of c a r b o n d i s s o l v e d i n t e r s t i t i a l l y in the h o m o g e n e o u s p h a s e s of the s y s t e m . H a n s e n and A n d e r k o , 1 Benz and E l l i o t t , 2 E l l i o t t , 3 and Shunk, 4 have m a d e c r i t i c a l r e v i e w s of the p u b l i s h e d d a t a on the i r o n - c a r b o n s y s t e m . A l l of the t h e r m o d y n a m i c s t u d i e s involved e q u i l i b r a t i o n of an i r o n s a m p l e with c a r b u r i z i n g a t m o s p h e r e s . CO//CO2 and C H J H z gas m i x t u r e s a r e the most commonly used carburizing media. Following e q u i l i b r a t i o n , the c a r b o n content of the s a m p l e i s d e t e r m i n e d . Thus, a r e l a t i o n s h i p b e t w e e n c a r b o n content and c a r b o n p o t e n t i a l i s o b t a i n e d and i s u s e d in the c a l c u l a t i o n of v a r i o u s t h e r m o d y n a m i c p r o p e r t i e s p e r t a i n i n g to the s y s t e m . C h i p m a n 5 has r e c e n t l y r e v i e w e d and e v a l u a t e d the d a t a , and c o n s t r u c t e d a p h a s e d i a g r a m in which the b o u n d a r i e s a r e c o n s i s t e n t with the m e a s u r e d p r o p e r t i e s of the p h a s e s involved and with the laws of t h e r m o d y n a m i c s . Dunwald and W a g n e r 6 w e r e p i o n e e r s in the s t u d y of f e r r i t e f r o m a t h e r m o d y n a m i c viewpoint. T h e y u s e d JOSEPH A. LOBO is Technical Manager, Gait Malleable Iron Co., Brentford, Ontario. GORDON H. GEIGER is Head and Professor of Metallurgical Engineering, University of Arizona, Tucson, AZ 85721. Both authors were associated with the Materials Engineering Department, University of Illinois at Chicago Circle when this work was conducted. Manuscript submitted June 5, 1974. METALLURGICAL TRANSACTIONS A
a CO//CO2 g a s m i x t u r e a s the c a r b u r i z i n g m e d i u m and obtained t h r e e e q u i l i b r i u m c a r b o n contents at 800~ S m i t h 7 m a d e a m o r e e x t e n s i v e s t u d y u s i n g CHJH2 g a s m i x t u r e s and r e p o r t e d d
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