Steady state segregation and heat flow in ESR
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I. INTRODUCTION
to d e t e r m i n e t e m p e r a t u r e p r o f i l e s , size, and shape of the liquid m e t a l pool and the " m u s h y " zone.
A L T H O U G H t h e r e a r e a n u m b e r of i m p o r t a n t f a c t o r s which d e t e r m i n e the a c c e p t a b i l i t y of an ESR ingot, in g e n e r a l , the m o s t i m p o r t a n t a r e ingot s t r u c t u r e and homogeneity which g e n e r a l l y a r e the l i m i t i n g f a c t o r s in d e t e r m i n i n g a m o n g other things m a x i m u m ingot c r o s s s e c t i o n a l a r e a and ingot m e l t r a t e . Homogeneity considerations are especially important for alloys which a r e s e g r e g a t i o n p r o n e such as s o m e n i c k e l - b a s e s u p e r a l l o y s , and a n u m b e r of tool and high alloyed s t e e l s . E v e n with c a r e f u l c o n t r o l of the remelt parameters, segregation sometimes occurs. T h i s r e s e a r c h outlined h e r e i n was a i m e d at d e v e l o p ing a model of the ESR p r o c e s s which would allow the p r e d i c t i o n of the c o r r e c t r e m e l t i n g p a r a m e t e r s for p r o d u c t i o n of ingots with the d e s i r e d s t r u c t u r e and f r e e - f r o m s e g r e g a t i o n . At the p r e s e n t t i m e , a n u m b e r of f u l l - s c a l e ESR p r o d u c t i o n r u n s a r e n o r m a l l y r e q u i r e d in o r d e r to d e t e r m i n e the c o r r e c t p r o c e s s i n g p a r a m e t e r s for each new alloy. F u r t h e r m o r e , while s e g r e g a t i o n is r e d u c e d , it g e n e r a l l y p e r s i s t s and can r e a c h u n a c c e p t a b l e l e v e l s with i n c r e a s i n g ingot s i z e . T h i s p a p e r s u m m a r i z e s r e s u l t s of the work c a r r i e d out in the following a r e a s : a) A s t e a d y - s t a t e a x i s y m m e t r i c m a t h e m a t i c a l m o d e l of heat flow and s o l i d i f i c a t i o n (segregation) for the e l e c t r o s l a g r e m e l t i n g p r o c e s s was developed, and b) T h i s s t e a d y - s t a t e m o d e l was e x p e r i m e n t a l l y v e r i f i e d on a l o w - t e m p e r a t u r e s i m u l a t e d l a b o r a t o r y ESR a p p a r a t u s and on 200 m m d i a m e t e r ESR ingots of a b i n a r y n i c k e l - b a s e alloy. D i r e c t t e m p e r a t u r e m e a s u r e m e n t s and pool m a p p i n g t e c h n i q u e s coupled with d e n d r i t e a r m s p a c i n g m e a s u r e m e n t s w e r e used S. D. RIDDER and F. C. REYES are Research Assistants, Department of Metallurgyand Mining Engineering, University of I1/inois, Urbana-Champaign,IL, S. CHAKRAVORTY,formerly Research Associate, Department of Metallurgy and Mining Engineering,University of Illinois, is now Professor, Department of Materials Science and Engineering,Pahlavi University, Shiraz, Iran. R. MEHRABIANis Associate Professor, Department of Metallurgy and MiningEngineering and Department of Mechanical and Industrial Engineering,University of Illinois. J. D. NAUMAN,formerly Engineering Ass
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