The rate of decarburization of liquid iron by CO 2 and H 2
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T H E r a t e of d e c a r b u r i z a t i o n of liquid F e - C a l l o y s by COs and O ~ h a s b e e n the s u b j e c t of n u m e r o u s i n v e s t i g a t i o n s . 1-~ D e s p i t e the i m p o r t a n c e of t h e s e r e a c t i o n s in s t e e l m a k l n g t h e r e s t i l l e x i s t s s o m e u n c e r t a i n t y a s t o the r a t e c o n t r o l l i n g m e c h a n i s m . Many i n v e s t i g a t o r s , particularly those studying levitated drops, concluded that m a s s t r a n s f e r t h r o u g h the g a s f i l m b o u n d a r y l a y e r n e a r the s u r f a c e of the liquid i s c o n t r o l l i n g the r a t e . W o r k b y the a u t h o r s is h a s shown that the r a t e of d e c a r b u r i z a t i o n of s o l i d i r o n in CO-CO2 m i x t u r e s is p r i m a r i l y c o n t r o l l e d b y g a s diffusion at t e m p e r a t u r e s g r e a t e r than 1400K. However, s o m e i n v e s t i g a t o r s 5'6 c o n c l u d e d that a slow c h e m i c a l r e a c t i o n is c o n t r o l l i n g the r a t e s f o r liquid i r o n . In p a r t i c u l a r at low c a r b o n c o n t e n t s when oxygen c o v e r a g e on the s u r f a c e is high the r a t e m a y b e c o n t r o l l e d b y a slow c h e m i c a l r e a c tion. It i s the p u r p o s e of the p r e s e n t w o r k to r e s o l v e t h i s d i s c r e p a n c y and to r e - e x a m i n e the i n t e r p r e t a t i o n of the r e s u l t s of p r e v i o u s i n v e s t i g a t o r s who c o n c l u d e d that a c h e m i c a l r e a c t i o n i s influencing the r a t e . Since, g a s p h a s e m a s s t r a n s f e r m a y b e the r a t e c o n t r o l l i n g m e c h a n i s m , the m a s s t r a n s f e r r e l a t i o n s h i p s f o r the experimental geometries used were also investigated. This was done b y m e a s u r i n g the t r a n s p o r t c o n t r o l l e d r a t e of o x i d a t i o n of a d e n s e - c a r b o n b l o c k in CO-CO2 m i x t u r e s a t 1800 K. The r a t e of d e c a r b u r i z a t i o n of F e - C - S a l l o y s in CO-CO2 m i x t u r e s and of F e - C a l l o y s in h y d r o g e n w a s a l s o d e t e r m i n e d . If m a s s t r a n s f e r i s c o n t r o l l i n g the r a t e of d e c a r b u r i z a t i o n of liquid i r o n in CO-CO2 g a s m i x t u r e s , the r a t e is equal to the flux of CO, to the s u r f a c e (Jco2). F o r m o s t e x p e r i m e n t a l c o n d i t i o n s the e q u i l i b r i u m C O , p r e s s u r e is s m a l l and the flux is given b y ~
Jco2 = ~TT in (1 + Pco2)
[1]
R. J. FRUEHAN and L. J. MARTONIK are Senior Scientist and Research Metallurgical Analyst, respectively, Research Laboratory, U. S. Steel Corporation, Monroeville, Pa. 15146. Manuscript submitted August 23, 1973. METALLURGICAL TRANSACTIONS
w h e r e m is the a v e r a g e m a s s t r a n s f e r c o e f f i c i e n t . The a v e r a g e m a s s t r a n s f e r c o e f f i c i e n t h a s b e e n r e l a t e d to the p r o p e r t i e s o f the g a s s t r e a m f o r s e v e r a l e
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