Dendrite morphology of steady state unidirectionally solidified steel
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Table I, Compositions and Temperatures T L and -Is of the Investigated Steels
Steel
C, Pct
Mn, Pet
Sl, Pct
A B
059 1.48
1 10 1.14
003 0.03
P, Pct
S, Pet
AI, Pct
0 0 0 9 0005 0.04 0.010 0,002 0 20
TL, ~
1492 1423
TS, ~ 1411 1257
of the m i c r o s e g r e g a t i o n of m a n g a n e s e ) w e r e a s s u m e d to have b e e n d e c r e a s e d by the s a m e a m o u n t . T h e a p p a r a t u s used for u n i d i r e c t i o n a l s o l i d i f i c a t i o n i s shown in F i g . 1. The s a m p l e is contained i n a n a l u m i n a tube which is w i t h d r a w n at a c o n s t a n t r a t e R f r o m a high t e m p e r a t u r e m o l y b d e n u m wound tube f u r n a c e . The a l u m i n a tube (650 ram, 15 m m ID, 20 m m OD) i s closed at its top and attached to the w i t h d r a w i n g m e c h a n i s m below the f u r n a c e . A w a t e r cooled cooling d e v i c e is i n s e r t e d into the f u r n a c e tube at its b o t t o m . The f u r n a c e t e m p e r a t u r e i s c o n t r o l l e d by a t h e r m o couple located i n the f u r n a c e tube. The t e m p e r a t u r e of the s a m p l e is r e c o r d e d by a s e c o n d t h e r m o c o u p l e placed at the c e n t r a l axis of the s t e e l rod. At the b e g i n n i n g of each r u n the s p e c i m e n tube i s i n s e r t e d into the f u r n a c e at a c o n s t a n t r a t e of 120 m m / h u n t i l the u p p e r p a r t of the tube r e a c h e s the t e m p e r a t u r e m a x i m u m . S i m u l t a n e o u s l y , the s t e e l r o d m e l t s . A f t e r the t e m p e r a t u r e e q u i l i b r i u m is a t t a i n e d the s a m ple tube is withdrawn. T h r e e d i s t i n c t zones develop d u r i n g w i t h d r a w a l : the solidified zone, the h e t e r o g e n e ous (mushy) zone c o n s i s t i n g of solid and liquid phase, and the liquid zone, When steady s t a t e is e s t a b l i s h e d the i n t e r f a c e s between t h e s e zones as well as the t e m p e r a t u r e p r o f i l e in the s a m p l e a r e s t a t i o n a r y with r e s p e c t to the f u r n a c e . The length ( x L - x s ) of the h e t e r o g e n e o u s zone depends on the t e m p e r a t u r e s T L and T S , and the t e m p e r a t u r e field. F o r s i m p l i c i t y the l o c a t i o n x S of the s o l i d / m u s h y i n t e r f a c e is t a k e n to be a t the t h e r m o d y n a m i c s o l i d u s t e m p e r a t u r e T S . I n r e a l i t y , this i n t e r f a c e is at a t e m p e r a t u r e s o m e w h a t below T S due to m i c r o s e g r e g a t i o n of m a n g a n e s e . Cons e q u e n t l y the e x t e n s i o n of the m u s h y zone is s o m e w h a t l a r g e r than x L - x s . T h i s s i m p l i f i c a t i o n , however, has p r a c t i c a l l y no effect on the c a l c u l a t e d G v a l u e s (Eq. VOLUME 7A, JUNE 1976-811
control thermocou
0
0
0
o
0
~
furnace tube {olumJno) winding
O 0
hquld he ttherm~176176 erogeneou5
i
........ I . . . . _ L ~ "f~ l
I
I
sol/c
t r e a t m e n t . T
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