Desulfurization of liquid steel containing aluminum or silicon with lime
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THE
o v e r a l l d e s u l f u r i z a t i o n r e a c t i o n s of F e - C , F e - S i , and Fe-A1 a l l o y s with CaO can be r e p r e s e n t e d by S + CaO + C = CaS + CO
[1]
S + 2CaO + ~Si = CaS + ~CaeSiO4
[2]
3S + 4CaO + 2A1 = 3CaS + CaA1204.
[3]
As d i s c u s s e d in p r e v i o u s p u b l i c a t i o n s , ~-3 the r e a c t i o n s as w r i t t e n r e p r e s e n t the o v e r a l l r e a c t i o n ; to u n d e r s t a n d the d e s u l f u r i z a t i o n m e c h a n i s m the i n d i v i d u a l s t e p w i s e r e a c t i o n s should be c o n s i d e r e d . F o r e x a m p l e , Eq. [2] has a m i n i m u m of t h r e e p h a s e s p r e s e n t , a s s u m i n g that the CaO is i m p r e g n a t e d with liquid s l a g . F o r this case t h e r e is only a line of contact b e t w e e n the t h r e e p h a s e s which is not f a v o r able for r a p i d d e s u l f u r i z a t i o n . It has b e e n p r o p o s e d that an i m p o r t a n t step in the d e s u l f u r i z a t i o n of F e - S i m e l t s is the f o r m a t i o n of the v a p o r s p e c i e s SiS and that the CaO m e r e l y acts as a getter for the s u l f u r b e a r i n g g a s e s . It is one of the p u r p o s e s of the p r e s e n t work to p r o v e this h y p o t h e s i s . The d e s u l f u r i z a t i o n of F e - A 1 m e l t s m u s t p r o c e e d by m e a n s of a n o t h e r type of m e c h a n i s m s i n c e t h e r e is no s i g n i f i c a n t a l u m i n u m s u l f u r v a p o r s p e c i e s . The m e c h a n i s m of d e s u l f u r i z a tion of Fe-A1 alloys with CaO will a l s o be e x a m i n e d . It has b e e n r e c e n t l y p r o p o s e d by T u r k d o g a n 4 that liquid s t e e l c a n be d e s u l f u r i z e d e f f i c i e n t l y by i n j e c t i n g CaO with A1 or Si. By doing so a l a r g e CaO7 l i q u i d - m e t a l s u r f a c e a r e a is p r o v i d e d and a l o c a l l y high A1 or Si content at the i n t e r f a c e will e x i s t , both of which a r e f a v o r a b l e for r a p i d d e s u l f u r i z a t i o n . The p r e s e n t work was u n d e r t a k e n to d e t e r m i n e whether the d e s u l f u r i z a t i o n r e a c t i o n s a r e fast enough to make this p r o p o s e d p r o c e s s f e a s i b l e .
RESULTS AND DISCUSSION
EXPERIMENTAL T o d e m o n s t r a t e the e f f e c t i v e n e s s of s u l f u r t r a n s f e r f r o m l i q u i d - i r o n a l l o y s to CaO via the gas phase, a s e r i e s of e x p e r i m e n t s was made with F e - 3 . 0 pct CR. J. FRUEHAN is with U.S. Steel Research Laboratory, Monroeville, PA 15146 Manuscript submitted October 5, 1977. METALLURGICALTRANSACTIONS B
Si-S alloys at 1400~ About 8 g of the a l l o y was cont a i n e d in a ZrO2 c r u c i b l e (1.7 c m ID) and 1 g of g r a n u l a r CaO p a r t i c l e s w e r e s u s p e n d e d above the m e l t in a p l a t i n u m b a s k e t at a p r e d e t e r m i n e d d i s t a n c e (x) of 0.3, 0.8, or 2.5 c m above the m e l t . The s a m p l e s w e r e heated in a
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