Inclusion precipitation diagram for the Fe-O-Ca-AI system
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M. FAULRING
AND
S. RAMALINGAM
The i n c l u s i o n p r e c i p i t a t i o n d i a g r a m for the F e - O - C a - A 1 s y s t e m at 1823 K was developed in t e r m s of H e n r i a n a c t i v i t i e s f r o m t h e r m o d y n a m i c data. In the d i a g r a m , s t a b i l i t y s u r faces s e p a r a t e the O-Ca-A1 s a t u r a t e d and u n s a t u r a t e d v o l u m e s and the location of a point r e p r e s e n t s the c h e m i s t r y of the s t e e l . By allowing the c h e m i s t r y of the s t e e l to change by the f o r m a t i o n of r e a c t i o n products, the sequence of p r e c i p i t a t i o n of the i n c l u sion phases can be p r e d i c t e d . F r o m the i n c l u s i o n p r e c i p i t a t i o n d i a g r a m , p r o j e c t i o n s of i n t e r p h a s e b o u n d a r i e s on the Ca-A1, Ca-O and A1-O p l a n e s and the s t a b i l i t y l i n e s for c o n s t a n t a l u m i n u m contents, it was concluded that 1) the C a R 1 r a t i o in liquid i r o n d e t e r m i n e s the identity of the i n c l u s i o n p h a s e s , 2) the c a l c i u m and a l u m i n u m contents can v a r y over a n a r r o w r a n g e for each c a l c i u m a l u m i n a t e phase, 3) in s t e e l s containing a l u m i n u m with an a c t i v i t y >0.01, c a l c i u m has little effect as a d e o x i d i z e r , and 4) close c o n t r o l of the c a l c i u m and a l u m i n u m contents is r e q u i r e d to obtain a s p e c i f i c c a l c i u m a l u m i n a t e i n c l u s i o n phase. A c t i v i t y coefficients a r e hypothesized that r e l a t e the r a t i o s of the c a l c i u m and a l u m i n u m contents of liquid steel, the identity of the p r e c i p i t a t i n g i n c l u s i o n p h a s e s and the c a l c u l a t e d a c t i v i t y r a t i o s hCa/hA1.
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the p r o d u c t i o n of killed s t e e l s , deoxidation with a l u m i n u m is the most p r a c t i c a l method of p r e v e n t i n g pinhole p o r o s i t y . Its use, however, is l i m i t e d by the p r e c i p i t a t i o n of a l u m i n a g a l a x i e s and Type II sulfides and, in s o m e continuous casting o p e r a t i o n s , by nozzle blockage. The d e t r i m e n t a l effects of the n o n m e t a l l i c i n c l u s i o n s a s s o c i a t e d with a l u m i n u m deoxidation a r e well d o c u m e n t e d in the l i t e r a t u r e . As a r e s u l t , an a l t e r n a t i v e deoxidation p r a c t i c e using c a l c i u m in conj u n c t i o n with a l u m i n u m is f r e q u e n t l y employed to modify the n o n m e t a l l i c i n c l u s i o n s found in a l u m i n u m killed s t e e l s . In o r d e r for an e l e m e n t to be an effective d e o x i d i z e r , it must be soluble in liquid s t e e l and when used with a l u m i n u m it m u s t have an equal or g r e a t e r affinity for oxygen than a l u m i n u m . The free e n e r g y of f o r m a tion for c a l c i u m oxide and published s o l u b i l i t y data ~'2 show c a l c i u m m e e t s both of these r e q u i r e m e n t
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