A mathematical model to predict the growth and elimination of inclusions in liquid steel stirred by natural convection
- PDF / 731,074 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 162 Views
THEr e m o v a l
of i n c l u s i o n s f r o m liquid s t e e l has b e e n a s u b j e c t of growing i n t e r e s t . In a r e c e n t p u b l i c a t i o n , ~ it was concluded that the size d i s t r i b u t i o n of i n c l u s i o n s in liquid s t e e l held in a s m a l l c r u c i b l e could not be explained by S t o k e s ' law. S a m p l e s taken at a fixed height at v a r i o u s t i m e i n t e r v a l s showed the p r e s e n c e of i n c l u s i o n s l a r g e r than p r e d i c t e d by S t o k e s ' law. It was s u g g e s t e d that these l a r g e i n c l u s i o n s f o r m e d by a p r o c e s s of c o l l i s i o n and c o a l e s c e n c e of s m a l l e r ones in the liquid s t e e l . The following hypot h e s i s was p o s t u l a t e d for the growth and r e m o v a l of i n c l u s i o n s in liquid s t e e l . Due to the s t i r r i n g of liquid m e t a l , the i n c l u s i o n s a r e e n t r a i n e d by the fluid. They no l o n g e r move v e r t i c a l l y in a c c o r d a n c e with Stokes' law, but a r e c a r r i e d along by the c u r r e n t s in the liquid m e t a l . The s t i r r i n g also c a u s e s a r a n d o m d i s t r i b u t i o n of i n c l u s i o n s throughout the v o l u m e of the m e l t . At any t i m e some of the i n c l u s i o n s p r e s e n t in the m e l t a r e b r o u g h t n e a r the s u r f a c e of the m e l t w h e r e they a r e a s s i m i l a t e d and t h e r e f o r e e s c a p e f r o m the m e l t . Of the total n u m b e r of i n c l u s i o n s b r o u g h t to the s u r f a c e , only a f r a c t i o n a r e a s s i m i l a t e d ; the r e s t a r e r e t u r n e d into the bulk of the m e t a l by the c o n v e c t i o n c u r r e n t s . In the bulk of the m e t a l , s o m e i n c l u s i o n s collide and c o a l e s c e to grow l a r g e r and a r e again b r o u g h t n e a r the s u r f a c e . T h u s the hypothesis p o s t u l a t e s that l a r g e i n c l u s i o n s can p e r s i s t in the m e l t due to two r e a s o n s . F i r s t , they m a y be fully or p a r t i a l l y e n t r a i n e d by the convection c u r r e n t s . Secondly, at the s u r f a c e of R. K. IYENGAR is Research Supervisor, Graham Research Laboratory, Jones and Laughlin Steel Corp., Pittsburgh, Pa. W. O. PHILBROOK is Professor of Metallurgy and MaterialsScience, Carnegie-Mellon University, Pittsburgh, Pa. Manuscript submitted May 21, 1971. METALLURGICALTRANSACTIONS
the m e l t the i n c l u s i o n may not be a s s i m i l a t e d b e c a u s e the c o a l e s c e n c e p r o c e s s r e q u i r e s r u p t u r e of the m e t a l l i c f i l m and m a y take longer than the r e s i d e n c e t i m e at the i n t e r f a c e . In o r d e r to c o m p r e h e n d the total p r o b l e m of e l i m i n a t i o n of i n c l u s i o n s , t h r e e a s p e c t s have to be u n d e r stood. The f i r s t is the motion of i n c l u s i o n s in t u r b u l e n t or l a m i n a r flow e s t a b l i s h e d u n d e r v a r i o u s c o n d i t i
Data Loading...
