Growth of the solid-liquid region during one-dimensional solidification of binary alloys. Part II
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has b e e n e s t a b l i s h e d f r o m t h e r m a l m e a s u r e m e n t s 1-3 that d u r i n g f r e e z i n g of ingots s o l i d i f i c a t i o n of s t e e l o c c u r s over a finite r e g i o n (mushy zone) where both s o l i d and liquid coexist. T h e s e m e a s u r e m e n t s a l s o show that the width of t h i s r e g i o n may v a r y f r o m a f r a c t i o n of an inch to s e v e r a l i n c h e s , depending on solute c o n c e n t r a t i o n in the m o l t e n alloy and the cooling r a t e . More r e c e n t s t u d i e s 4-6 and e x p e r i e n c e in d e a l ing with p r a c t i c a l p r o b l e m s in solidification of s t e e l s i n c r e a s i n g l y point to a c r u c i a l role played by the " m u s h y z o n e " in f r e e z i n g of a l l o y s . The p h y s i c a l and c h e m i c a l p r o c e s s e s o c c u r r i n g within the s o l i d - l i q u i d r e g i o n d u r i n g s o l i d i f i c a t i o n a r e r e s p o n s i b l e for the f o r m a t i o n of i n c l u s i o n s , p o r o s i t y , and d e v e l o p m e n t of m i c r o - and m a c r o s e g r e g a t i o n in ingots. T h e s e p r o c e s s e s also d e t e r m i n e the scale of d i s p e r s i o n of s e g r e g a t e in a s - c a s t s t e e l s . An i n i t i a l effort in this d i r e c t i o n is d e s c r i b e d in s e v e r a l r e c e n t p a p e r s by the a u t h o r s . 7"9 In P a r t 17 an a p p r o x i m a t e m a t h e m a t i c a l a n a l y s i s was given for the p r o c e s s of s o l i d i f i c a t i o n of a finite slab of b i n a r y alloy for the case where the d e n s i t i e s of solid and liquid alloys a r e equal and the s u r f a c e t e m p e r a t u r e of the slab i s constant. The two s y s t e m s c o n s i d e r e d were F e - C and F e - P . The r e s u l t s showing the effects of solute type; of solute c o n c e n t r a t i o n and of the cooling r a t e on the s o l i d i f i c a t i o n of b i n a r y a l l o y s were p r e s e n t e d in this p r e v i o u s p a p e r . ~ The p r e s e n t paper i s a c o n t i n u a t i o n ( P a r t II) of the paper m e n t i o n e d above. 7 The p u r p o s e of this study is to explore the s o l i d i f i c a t i o n b e h a v i o r of two other b i n a r y s y s t e m s of p r a c t i c a l i n t e r e s t , n a m e l y F e - S and F e - S i . These two s y s t e m s and the F e - P s y s t e m d i s c u s s e d p r e v i o u s l y 7 a r e e x a m p l e s of alloy s y s t e m s in which the solute d i s t r i b u t i o n r a t i o s differ c o n s i d e r a b l y and hence give a c o m p r e h e n s i v e p i c t u r e of the effect of alloy p a r a m e t e r s on c e r t a i n s o l i d i f i c a t i o n c h a r a c teristics. The alloy p a r a m e t e r s that a r e s i g n i f i c a n t f r o m the solidification point of view a r e : solute d i s t r i b u t i o n r a t i o , eutectic t e m p e r a t u r e , and eutectic c o m p o s i t i o n of the a l l o y s ; these a r e given in Table I. The d i s t r i b u tion r a
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