Sulfides and oxides in Fe-Mn alloys: Part III. Formation of oxysulfides during freezing of steel
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E. T. TURKDOGAN
The p r e v i o u s study of the p h a s e r e l a t i o n s ( P a r t I) is now e x t e n d e d to the s o l i d - l i q u i d r e g i o n s of F e - M n - S and F e - M n - S - O s y s t e m s . The d i f f e r e n t i a l t h e r m a l a n a l y s i s m e a s u r e m e n t s m a d e with 1 to 5 p c t M n - F e a l l o y s containing s u l f u r and oxygen s u b s t a n t i a t e d the p o s i t i o n s of the u n i v a r i a n t c u r v e s in p c t Mn v s T p l o t s d e r i v e d f r o m o t h e r a v a i l a b l e d a t a and t h e o r e t i c a l c o n s i d e r a t i o n s . It i s found that if s u f f i c i e n t oxygen and s u l f u r a r e p r e s e n t in the F e - M n a l l o y s , t h e r e m a y be a liquid oxysulfide p h a s e p r e s e n t at t e m p e r a t u r e s above 900%2, depending on the m a n g a n e s e content. T h e h i g h e r the m a n g a n e s e content in s o l u t i o n , the h i g h e r i s the t e m p e r a t u r e below which no liquid p h a s e is p r e s e n t , e.g. for 10 p p m , 900~C and for 10 p c t Mn, -1200~ The f o r m a t i o n of o x i d e s , s u l f i d e s , and liquid o x y s u l f i d e s in the i n t e r d e n d r i t i c r e g i o n s d u r i n g s o l i d i f i c a t i o n , a s p r e d i c t e d f r o m the p h a s e r e l a t i o n s in the F e - M n - S - O s y s t e m , w a s v e r i f i e d by m i c r o s c o p i c e x a m i n a t i o n u s i n g s c a n n i n g e l e c t r o n m i c r o s c o p y and m e t a l l o g r a p h i c t e c h n i q u e s .
I N P a r t I of this s e r i e s of p a p e r s , T u r k d o g a n and K o r ~ d i s c u s s e d p h a s e r e l a t i o n s in the F e - M n - S - O s y s t e m d e r i v e d f r o m the a v a i l a b l e d a t a by applying the M o r e y W i l l i a m s o n t h e o r e m on u n i v a r i a n t c u r v e s i n t e r s e c t i n g a t an i n v a r i a n t point. T h e p r e v i o u s study i s now e x tended to the s o l i d - l i q u i d r e g i o n s of F e - M n - S and F e M n - S - O s y s t e m s . Some of the c a l c u l a t e d u n i v a r i a n t e q u i l i b r i a w e r e t e s t e d by d i f f e r e n t i a l t h e r m a l a n a l y s i s (DTA) of F e - M n a l l o y s containing s u l f u r and oxygen. Using these phase equilibria some consideration is given to the f o r m a t i o n of sulfide and o x y s u l f i d e i n c l u s i o n s d u r i n g s o l i d i f i c a t i o n of s t e e l .
r e g i o n of the F e - M n and F e - S b i n a r y s y s t e m s r e s p e c tively. ii) The m a n g a n e s e d i s t r i b u t i o n r a t i o b e t w e e n 5 - i r o n and the liquid f o r the F e - M n s y s t e m z a p p l i e s a l s o to the F e - M n - S s y s t e m , thus [~Mn ]s
= 0.74
[2 ]
T h e e q u i l i b r i u m c o n s t a n t for the Mn-S g e a c t i o n in the liquid p h a s e i s r e p r e s e n t e d by ioz
PHASE EQUILIBRIA F o r the p r e s e n t p u r p o s e it is c o n v e n i e n t to show the p h a s e r e l a t i o n s in the F e - M n - S and F e
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